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| @c %**start of header |
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| @documentencoding UTF-8 |
| @ifinfo |
| @*Generated by Sphinx 1.3b2.@* |
| @end ifinfo |
| @settitle GNAT Reference Manual |
| @defindex ge |
| @paragraphindent 0 |
| @exampleindent 4 |
| @finalout |
| @dircategory GNU Ada Tools |
| @direntry |
| * gnat_rm: (gnat_rm.info). gnat_rm |
| @end direntry |
| |
| @definfoenclose strong,`,' |
| @definfoenclose emph,`,' |
| @c %**end of header |
| |
| @copying |
| @quotation |
| GNAT Reference Manual , March 24, 2015 |
| |
| AdaCore |
| |
| Copyright @copyright{} 2008-2015, Free Software Foundation |
| @end quotation |
| |
| @end copying |
| |
| @titlepage |
| @title GNAT Reference Manual |
| @insertcopying |
| @end titlepage |
| @contents |
| |
| @c %** start of user preamble |
| |
| @c %** end of user preamble |
| |
| @ifnottex |
| @node Top |
| @top GNAT Reference Manual |
| @insertcopying |
| @end ifnottex |
| |
| @c %**start of body |
| @anchor{gnat_rm doc}@anchor{0} |
| @emph{GNAT, The GNU Ada Development Environment} |
| |
| |
| @include gcc-common.texi |
| GCC version @value{version-GCC}@* |
| AdaCore |
| |
| Permission is granted to copy, distribute and/or modify this document |
| under the terms of the GNU Free Documentation License, Version 1.3 or |
| any later version published by the Free Software Foundation; with no |
| Invariant Sections, with the Front-Cover Texts being "GNAT Reference |
| Manual", and with no Back-Cover Texts. A copy of the license is |
| included in the section entitled @ref{1,,GNU Free Documentation License}. |
| |
| @menu |
| * About This Guide:: |
| * Implementation Defined Pragmas:: |
| * Implementation Defined Aspects:: |
| * Implementation Defined Attributes:: |
| * Standard and Implementation Defined Restrictions:: |
| * Implementation Advice:: |
| * Implementation Defined Characteristics:: |
| * Intrinsic Subprograms:: |
| * Representation Clauses and Pragmas:: |
| * Standard Library Routines:: |
| * The Implementation of Standard I/O:: |
| * The GNAT Library:: |
| * Interfacing to Other Languages:: |
| * Specialized Needs Annexes:: |
| * Implementation of Specific Ada Features:: |
| * Implementation of Ada 2012 Features:: |
| * Obsolescent Features:: |
| * Compatibility and Porting Guide:: |
| * GNU Free Documentation License:: |
| * Index:: |
| |
| @detailmenu |
| --- The Detailed Node Listing --- |
| |
| About This Guide |
| |
| * What This Reference Manual Contains:: |
| * Conventions:: |
| * Related Information:: |
| |
| Implementation Defined Pragmas |
| |
| * Pragma Abort_Defer:: |
| * Pragma Abstract_State:: |
| * Pragma Ada_83:: |
| * Pragma Ada_95:: |
| * Pragma Ada_05:: |
| * Pragma Ada_2005:: |
| * Pragma Ada_12:: |
| * Pragma Ada_2012:: |
| * Pragma Allow_Integer_Address:: |
| * Pragma Annotate:: |
| * Pragma Assert:: |
| * Pragma Assert_And_Cut:: |
| * Pragma Assertion_Policy:: |
| * Pragma Assume:: |
| * Pragma Assume_No_Invalid_Values:: |
| * Pragma Async_Readers:: |
| * Pragma Async_Writers:: |
| * Pragma Attribute_Definition:: |
| * Pragma C_Pass_By_Copy:: |
| * Pragma Check:: |
| * Pragma Check_Float_Overflow:: |
| * Pragma Check_Name:: |
| * Pragma Check_Policy:: |
| * Pragma CIL_Constructor:: |
| * Pragma Comment:: |
| * Pragma Common_Object:: |
| * Pragma Compile_Time_Error:: |
| * Pragma Compile_Time_Warning:: |
| * Pragma Compiler_Unit:: |
| * Pragma Compiler_Unit_Warning:: |
| * Pragma Complete_Representation:: |
| * Pragma Complex_Representation:: |
| * Pragma Component_Alignment:: |
| * Pragma Contract_Cases:: |
| * Pragma Convention_Identifier:: |
| * Pragma CPP_Class:: |
| * Pragma CPP_Constructor:: |
| * Pragma CPP_Virtual:: |
| * Pragma CPP_Vtable:: |
| * Pragma CPU:: |
| * Pragma Debug:: |
| * Pragma Debug_Policy:: |
| * Pragma Default_Scalar_Storage_Order:: |
| * Pragma Default_Storage_Pool:: |
| * Pragma Depends:: |
| * Pragma Detect_Blocking:: |
| * Pragma Disable_Atomic_Synchronization:: |
| * Pragma Dispatching_Domain:: |
| * Pragma Effective_Reads:: |
| * Pragma Effective_Writes:: |
| * Pragma Elaboration_Checks:: |
| * Pragma Eliminate:: |
| * Pragma Enable_Atomic_Synchronization:: |
| * Pragma Export_Function:: |
| * Pragma Export_Object:: |
| * Pragma Export_Procedure:: |
| * Pragma Export_Value:: |
| * Pragma Export_Valued_Procedure:: |
| * Pragma Extend_System:: |
| * Pragma Extensions_Allowed:: |
| * Pragma External:: |
| * Pragma External_Name_Casing:: |
| * Pragma Fast_Math:: |
| * Pragma Favor_Top_Level:: |
| * Pragma Finalize_Storage_Only:: |
| * Pragma Float_Representation:: |
| * Pragma Global:: |
| * Pragma Ident:: |
| * Pragma Ignore_Pragma:: |
| * Pragma Implementation_Defined:: |
| * Pragma Implemented:: |
| * Pragma Implicit_Packing:: |
| * Pragma Import_Function:: |
| * Pragma Import_Object:: |
| * Pragma Import_Procedure:: |
| * Pragma Import_Valued_Procedure:: |
| * Pragma Independent:: |
| * Pragma Independent_Components:: |
| * Pragma Initial_Condition:: |
| * Pragma Initialize_Scalars:: |
| * Pragma Initializes:: |
| * Pragma Inline_Always:: |
| * Pragma Inline_Generic:: |
| * Pragma Interface:: |
| * Pragma Interface_Name:: |
| * Pragma Interrupt_Handler:: |
| * Pragma Interrupt_State:: |
| * Pragma Invariant:: |
| * Pragma Java_Constructor:: |
| * Pragma Java_Interface:: |
| * Pragma Keep_Names:: |
| * Pragma License:: |
| * Pragma Link_With:: |
| * Pragma Linker_Alias:: |
| * Pragma Linker_Constructor:: |
| * Pragma Linker_Destructor:: |
| * Pragma Linker_Section:: |
| * Pragma Lock_Free:: |
| * Pragma Loop_Invariant:: |
| * Pragma Loop_Optimize:: |
| * Pragma Loop_Variant:: |
| * Pragma Machine_Attribute:: |
| * Pragma Main:: |
| * Pragma Main_Storage:: |
| * Pragma No_Body:: |
| * Pragma No_Elaboration_Code_All:: |
| * Pragma No_Inline:: |
| * Pragma No_Return:: |
| * Pragma No_Run_Time:: |
| * Pragma No_Strict_Aliasing:: |
| * Pragma No_Tagged_Streams:: |
| * Pragma Normalize_Scalars:: |
| * Pragma Obsolescent:: |
| * Pragma Optimize_Alignment:: |
| * Pragma Ordered:: |
| * Pragma Overflow_Mode:: |
| * Pragma Overriding_Renamings:: |
| * Pragma Partition_Elaboration_Policy:: |
| * Pragma Part_Of:: |
| * Pragma Passive:: |
| * Pragma Persistent_BSS:: |
| * Pragma Polling:: |
| * Pragma Post:: |
| * Pragma Postcondition:: |
| * Pragma Post_Class:: |
| * Pragma Pre:: |
| * Pragma Precondition:: |
| * Pragma Predicate:: |
| * Pragma Preelaborable_Initialization:: |
| * Pragma Prefix_Exception_Messages:: |
| * Pragma Pre_Class:: |
| * Pragma Priority_Specific_Dispatching:: |
| * Pragma Profile:: |
| * Pragma Profile_Warnings:: |
| * Pragma Propagate_Exceptions:: |
| * Pragma Provide_Shift_Operators:: |
| * Pragma Psect_Object:: |
| * Pragma Pure_Function:: |
| * Pragma Rational:: |
| * Pragma Ravenscar:: |
| * Pragma Refined_Depends:: |
| * Pragma Refined_Global:: |
| * Pragma Refined_Post:: |
| * Pragma Refined_State:: |
| * Pragma Relative_Deadline:: |
| * Pragma Remote_Access_Type:: |
| * Pragma Restricted_Run_Time:: |
| * Pragma Restriction_Warnings:: |
| * Pragma Reviewable:: |
| * Pragma Share_Generic:: |
| * Pragma Shared:: |
| * Pragma Short_Circuit_And_Or:: |
| * Pragma Short_Descriptors:: |
| * Pragma Simple_Storage_Pool_Type:: |
| * Pragma Source_File_Name:: |
| * Pragma Source_File_Name_Project:: |
| * Pragma Source_Reference:: |
| * Pragma SPARK_Mode:: |
| * Pragma Static_Elaboration_Desired:: |
| * Pragma Stream_Convert:: |
| * Pragma Style_Checks:: |
| * Pragma Subtitle:: |
| * Pragma Suppress:: |
| * Pragma Suppress_All:: |
| * Pragma Suppress_Debug_Info:: |
| * Pragma Suppress_Exception_Locations:: |
| * Pragma Suppress_Initialization:: |
| * Pragma Task_Name:: |
| * Pragma Task_Storage:: |
| * Pragma Test_Case:: |
| * Pragma Thread_Local_Storage:: |
| * Pragma Time_Slice:: |
| * Pragma Title:: |
| * Pragma Type_Invariant:: |
| * Pragma Type_Invariant_Class:: |
| * Pragma Unchecked_Union:: |
| * Pragma Unevaluated_Use_Of_Old:: |
| * Pragma Unimplemented_Unit:: |
| * Pragma Universal_Aliasing:: |
| * Pragma Universal_Data:: |
| * Pragma Unmodified:: |
| * Pragma Unreferenced:: |
| * Pragma Unreferenced_Objects:: |
| * Pragma Unreserve_All_Interrupts:: |
| * Pragma Unsuppress:: |
| * Pragma Use_VADS_Size:: |
| * Pragma Validity_Checks:: |
| * Pragma Volatile:: |
| * Pragma Warning_As_Error:: |
| * Pragma Warnings:: |
| * Pragma Weak_External:: |
| * Pragma Wide_Character_Encoding:: |
| |
| Implementation Defined Aspects |
| |
| * Aspect Abstract_State:: |
| * Annotate:: |
| * Aspect Async_Readers:: |
| * Aspect Async_Writers:: |
| * Aspect Contract_Cases:: |
| * Aspect Depends:: |
| * Aspect Dimension:: |
| * Aspect Dimension_System:: |
| * Aspect Effective_Reads:: |
| * Aspect Effective_Writes:: |
| * Aspect Favor_Top_Level:: |
| * Aspect Global:: |
| * Aspect Initial_Condition:: |
| * Aspect Initializes:: |
| * Aspect Inline_Always:: |
| * Aspect Invariant:: |
| * Aspect Invariant'Class:: |
| * Aspect Iterable:: |
| * Aspect Linker_Section:: |
| * Aspect Lock_Free:: |
| * Aspect No_Elaboration_Code_All:: |
| * Aspect No_Tagged_Streams:: |
| * Aspect Object_Size:: |
| * Aspect Obsolescent:: |
| * Aspect Part_Of:: |
| * Aspect Persistent_BSS:: |
| * Aspect Predicate:: |
| * Aspect Pure_Function:: |
| * Aspect Refined_Depends:: |
| * Aspect Refined_Global:: |
| * Aspect Refined_Post:: |
| * Aspect Refined_State:: |
| * Aspect Remote_Access_Type:: |
| * Aspect Scalar_Storage_Order:: |
| * Aspect Shared:: |
| * Aspect Simple_Storage_Pool:: |
| * Aspect Simple_Storage_Pool_Type:: |
| * Aspect SPARK_Mode:: |
| * Aspect Suppress_Debug_Info:: |
| * Aspect Suppress_Initialization:: |
| * Aspect Test_Case:: |
| * Aspect Thread_Local_Storage:: |
| * Aspect Universal_Aliasing:: |
| * Aspect Universal_Data:: |
| * Aspect Unmodified:: |
| * Aspect Unreferenced:: |
| * Aspect Unreferenced_Objects:: |
| * Aspect Value_Size:: |
| * Aspect Warnings:: |
| |
| Implementation Defined Attributes |
| |
| * Attribute Abort_Signal:: |
| * Attribute Address_Size:: |
| * Attribute Asm_Input:: |
| * Attribute Asm_Output:: |
| * Attribute Atomic_Always_Lock_Free:: |
| * Attribute Bit:: |
| * Attribute Bit_Position:: |
| * Attribute Code_Address:: |
| * Attribute Compiler_Version:: |
| * Attribute Constrained:: |
| * Attribute Default_Bit_Order:: |
| * Attribute Default_Scalar_Storage_Order:: |
| * Attribute Deref:: |
| * Attribute Descriptor_Size:: |
| * Attribute Elaborated:: |
| * Attribute Elab_Body:: |
| * Attribute Elab_Spec:: |
| * Attribute Elab_Subp_Body:: |
| * Attribute Emax:: |
| * Attribute Enabled:: |
| * Attribute Enum_Rep:: |
| * Attribute Enum_Val:: |
| * Attribute Epsilon:: |
| * Attribute Fast_Math:: |
| * Attribute Fixed_Value:: |
| * Attribute From_Any:: |
| * Attribute Has_Access_Values:: |
| * Attribute Has_Discriminants:: |
| * Attribute Img:: |
| * Attribute Integer_Value:: |
| * Attribute Invalid_Value:: |
| * Attribute Iterable:: |
| * Attribute Large:: |
| * Attribute Library_Level:: |
| * Attribute Lock_Free:: |
| * Attribute Loop_Entry:: |
| * Attribute Machine_Size:: |
| * Attribute Mantissa:: |
| * Attribute Maximum_Alignment:: |
| * Attribute Mechanism_Code:: |
| * Attribute Null_Parameter:: |
| * Attribute Object_Size:: |
| * Attribute Old:: |
| * Attribute Passed_By_Reference:: |
| * Attribute Pool_Address:: |
| * Attribute Range_Length:: |
| * Attribute Ref:: |
| * Attribute Restriction_Set:: |
| * Attribute Result:: |
| * Attribute Safe_Emax:: |
| * Attribute Safe_Large:: |
| * Attribute Safe_Small:: |
| * Attribute Scalar_Storage_Order:: |
| * Attribute Simple_Storage_Pool:: |
| * Attribute Small:: |
| * Attribute Storage_Unit:: |
| * Attribute Stub_Type:: |
| * Attribute System_Allocator_Alignment:: |
| * Attribute Target_Name:: |
| * Attribute To_Address:: |
| * Attribute To_Any:: |
| * Attribute Type_Class:: |
| * Attribute Type_Key:: |
| * Attribute TypeCode:: |
| * Attribute UET_Address:: |
| * Attribute Unconstrained_Array:: |
| * Attribute Universal_Literal_String:: |
| * Attribute Unrestricted_Access:: |
| * Attribute Update:: |
| * Attribute Valid_Scalars:: |
| * Attribute VADS_Size:: |
| * Attribute Value_Size:: |
| * Attribute Wchar_T_Size:: |
| * Attribute Word_Size:: |
| |
| Standard and Implementation Defined Restrictions |
| |
| * Partition-Wide Restrictions:: |
| * Program Unit Level Restrictions:: |
| |
| Partition-Wide Restrictions |
| |
| * Immediate_Reclamation:: |
| * Max_Asynchronous_Select_Nesting:: |
| * Max_Entry_Queue_Length:: |
| * Max_Protected_Entries:: |
| * Max_Select_Alternatives:: |
| * Max_Storage_At_Blocking:: |
| * Max_Task_Entries:: |
| * Max_Tasks:: |
| * No_Abort_Statements:: |
| * No_Access_Parameter_Allocators:: |
| * No_Access_Subprograms:: |
| * No_Allocators:: |
| * No_Anonymous_Allocators:: |
| * No_Calendar:: |
| * No_Coextensions:: |
| * No_Default_Initialization:: |
| * No_Delay:: |
| * No_Dependence:: |
| * No_Direct_Boolean_Operators:: |
| * No_Dispatch:: |
| * No_Dispatching_Calls:: |
| * No_Dynamic_Attachment:: |
| * No_Dynamic_Priorities:: |
| * No_Entry_Calls_In_Elaboration_Code:: |
| * No_Enumeration_Maps:: |
| * No_Exception_Handlers:: |
| * No_Exception_Propagation:: |
| * No_Exception_Registration:: |
| * No_Exceptions:: |
| * No_Finalization:: |
| * No_Fixed_Point:: |
| * No_Floating_Point:: |
| * No_Implicit_Conditionals:: |
| * No_Implicit_Dynamic_Code:: |
| * No_Implicit_Heap_Allocations:: |
| * No_Implicit_Loops:: |
| * No_Initialize_Scalars:: |
| * No_IO:: |
| * No_Local_Allocators:: |
| * No_Local_Protected_Objects:: |
| * No_Local_Timing_Events:: |
| * No_Long_Long_Integers:: |
| * No_Multiple_Elaboration:: |
| * No_Nested_Finalization:: |
| * No_Protected_Type_Allocators:: |
| * No_Protected_Types:: |
| * No_Recursion:: |
| * No_Reentrancy:: |
| * No_Relative_Delay:: |
| * No_Requeue_Statements:: |
| * No_Secondary_Stack:: |
| * No_Select_Statements:: |
| * No_Specific_Termination_Handlers:: |
| * No_Specification_of_Aspect:: |
| * No_Standard_Allocators_After_Elaboration:: |
| * No_Standard_Storage_Pools:: |
| * No_Stream_Optimizations:: |
| * No_Streams:: |
| * No_Task_Allocators:: |
| * No_Task_Attributes_Package:: |
| * No_Task_Hierarchy:: |
| * No_Task_Termination:: |
| * No_Tasking:: |
| * No_Terminate_Alternatives:: |
| * No_Unchecked_Access:: |
| * No_Use_Of_Entity:: |
| * Simple_Barriers:: |
| * Static_Priorities:: |
| * Static_Storage_Size:: |
| |
| Program Unit Level Restrictions |
| |
| * No_Elaboration_Code:: |
| * No_Entry_Queue:: |
| * No_Implementation_Aspect_Specifications:: |
| * No_Implementation_Attributes:: |
| * No_Implementation_Identifiers:: |
| * No_Implementation_Pragmas:: |
| * No_Implementation_Restrictions:: |
| * No_Implementation_Units:: |
| * No_Implicit_Aliasing:: |
| * No_Obsolescent_Features:: |
| * No_Wide_Characters:: |
| * SPARK_05:: |
| |
| Implementation Advice |
| |
| * RM 1.1.3(20); Error Detection: RM 1 1 3 20 Error Detection. |
| * RM 1.1.3(31); Child Units: RM 1 1 3 31 Child Units. |
| * RM 1.1.5(12); Bounded Errors: RM 1 1 5 12 Bounded Errors. |
| * RM 2.8(16); Pragmas: RM 2 8 16 Pragmas. |
| * RM 2.8(17-19); Pragmas: RM 2 8 17-19 Pragmas. |
| * RM 3.5.2(5); Alternative Character Sets: RM 3 5 2 5 Alternative Character Sets. |
| * RM 3.5.4(28); Integer Types: RM 3 5 4 28 Integer Types. |
| * RM 3.5.4(29); Integer Types: RM 3 5 4 29 Integer Types. |
| * RM 3.5.5(8); Enumeration Values: RM 3 5 5 8 Enumeration Values. |
| * RM 3.5.7(17); Float Types: RM 3 5 7 17 Float Types. |
| * RM 3.6.2(11); Multidimensional Arrays: RM 3 6 2 11 Multidimensional Arrays. |
| * RM 9.6(30-31); Duration'Small: RM 9 6 30-31 Duration'Small. |
| * RM 10.2.1(12); Consistent Representation: RM 10 2 1 12 Consistent Representation. |
| * RM 11.4.1(19); Exception Information: RM 11 4 1 19 Exception Information. |
| * RM 11.5(28); Suppression of Checks: RM 11 5 28 Suppression of Checks. |
| * RM 13.1 (21-24); Representation Clauses: RM 13 1 21-24 Representation Clauses. |
| * RM 13.2(6-8); Packed Types: RM 13 2 6-8 Packed Types. |
| * RM 13.3(14-19); Address Clauses: RM 13 3 14-19 Address Clauses. |
| * RM 13.3(29-35); Alignment Clauses: RM 13 3 29-35 Alignment Clauses. |
| * RM 13.3(42-43); Size Clauses: RM 13 3 42-43 Size Clauses. |
| * RM 13.3(50-56); Size Clauses: RM 13 3 50-56 Size Clauses. |
| * RM 13.3(71-73); Component Size Clauses: RM 13 3 71-73 Component Size Clauses. |
| * RM 13.4(9-10); Enumeration Representation Clauses: RM 13 4 9-10 Enumeration Representation Clauses. |
| * RM 13.5.1(17-22); Record Representation Clauses: RM 13 5 1 17-22 Record Representation Clauses. |
| * RM 13.5.2(5); Storage Place Attributes: RM 13 5 2 5 Storage Place Attributes. |
| * RM 13.5.3(7-8); Bit Ordering: RM 13 5 3 7-8 Bit Ordering. |
| * RM 13.7(37); Address as Private: RM 13 7 37 Address as Private. |
| * RM 13.7.1(16); Address Operations: RM 13 7 1 16 Address Operations. |
| * RM 13.9(14-17); Unchecked Conversion: RM 13 9 14-17 Unchecked Conversion. |
| * RM 13.11(23-25); Implicit Heap Usage: RM 13 11 23-25 Implicit Heap Usage. |
| * RM 13.11.2(17); Unchecked Deallocation: RM 13 11 2 17 Unchecked Deallocation. |
| * RM 13.13.2(17); Stream Oriented Attributes: RM 13 13 2 17 Stream Oriented Attributes. |
| * RM A.1(52); Names of Predefined Numeric Types: RM A 1 52 Names of Predefined Numeric Types. |
| * RM A.3.2(49); Ada.Characters.Handling: RM A 3 2 49 Ada Characters Handling. |
| * RM A.4.4(106); Bounded-Length String Handling: RM A 4 4 106 Bounded-Length String Handling. |
| * RM A.5.2(46-47); Random Number Generation: RM A 5 2 46-47 Random Number Generation. |
| * RM A.10.7(23); Get_Immediate: RM A 10 7 23 Get_Immediate. |
| * RM B.1(39-41); Pragma Export: RM B 1 39-41 Pragma Export. |
| * RM B.2(12-13); Package Interfaces: RM B 2 12-13 Package Interfaces. |
| * RM B.3(63-71); Interfacing with C: RM B 3 63-71 Interfacing with C. |
| * RM B.4(95-98); Interfacing with COBOL: RM B 4 95-98 Interfacing with COBOL. |
| * RM B.5(22-26); Interfacing with Fortran: RM B 5 22-26 Interfacing with Fortran. |
| * RM C.1(3-5); Access to Machine Operations: RM C 1 3-5 Access to Machine Operations. |
| * RM C.1(10-16); Access to Machine Operations: RM C 1 10-16 Access to Machine Operations. |
| * RM C.3(28); Interrupt Support: RM C 3 28 Interrupt Support. |
| * RM C.3.1(20-21); Protected Procedure Handlers: RM C 3 1 20-21 Protected Procedure Handlers. |
| * RM C.3.2(25); Package Interrupts: RM C 3 2 25 Package Interrupts. |
| * RM C.4(14); Pre-elaboration Requirements: RM C 4 14 Pre-elaboration Requirements. |
| * RM C.5(8); Pragma Discard_Names: RM C 5 8 Pragma Discard_Names. |
| * RM C.7.2(30); The Package Task_Attributes: RM C 7 2 30 The Package Task_Attributes. |
| * RM D.3(17); Locking Policies: RM D 3 17 Locking Policies. |
| * RM D.4(16); Entry Queuing Policies: RM D 4 16 Entry Queuing Policies. |
| * RM D.6(9-10); Preemptive Abort: RM D 6 9-10 Preemptive Abort. |
| * RM D.7(21); Tasking Restrictions: RM D 7 21 Tasking Restrictions. |
| * RM D.8(47-49); Monotonic Time: RM D 8 47-49 Monotonic Time. |
| * RM E.5(28-29); Partition Communication Subsystem: RM E 5 28-29 Partition Communication Subsystem. |
| * RM F(7); COBOL Support: RM F 7 COBOL Support. |
| * RM F.1(2); Decimal Radix Support: RM F 1 2 Decimal Radix Support. |
| * RM G; Numerics: RM G Numerics. |
| * RM G.1.1(56-58); Complex Types: RM G 1 1 56-58 Complex Types. |
| * RM G.1.2(49); Complex Elementary Functions: RM G 1 2 49 Complex Elementary Functions. |
| * RM G.2.4(19); Accuracy Requirements: RM G 2 4 19 Accuracy Requirements. |
| * RM G.2.6(15); Complex Arithmetic Accuracy: RM G 2 6 15 Complex Arithmetic Accuracy. |
| * RM H.6(15/2); Pragma Partition_Elaboration_Policy: RM H 6 15/2 Pragma Partition_Elaboration_Policy. |
| |
| Intrinsic Subprograms |
| |
| * Intrinsic Operators:: |
| * Compilation_Date:: |
| * Compilation_Time:: |
| * Enclosing_Entity:: |
| * Exception_Information:: |
| * Exception_Message:: |
| * Exception_Name:: |
| * File:: |
| * Line:: |
| * Shifts and Rotates:: |
| * Source_Location:: |
| |
| Representation Clauses and Pragmas |
| |
| * Alignment Clauses:: |
| * Size Clauses:: |
| * Storage_Size Clauses:: |
| * Size of Variant Record Objects:: |
| * Biased Representation:: |
| * Value_Size and Object_Size Clauses:: |
| * Component_Size Clauses:: |
| * Bit_Order Clauses:: |
| * Effect of Bit_Order on Byte Ordering:: |
| * Pragma Pack for Arrays:: |
| * Pragma Pack for Records:: |
| * Record Representation Clauses:: |
| * Handling of Records with Holes:: |
| * Enumeration Clauses:: |
| * Address Clauses:: |
| * Use of Address Clauses for Memory-Mapped I/O:: |
| * Effect of Convention on Representation:: |
| * Conventions and Anonymous Access Types:: |
| * Determining the Representations chosen by GNAT:: |
| |
| The Implementation of Standard I/O |
| |
| * Standard I/O Packages:: |
| * FORM Strings:: |
| * Direct_IO:: |
| * Sequential_IO:: |
| * Text_IO:: |
| * Wide_Text_IO:: |
| * Wide_Wide_Text_IO:: |
| * Stream_IO:: |
| * Text Translation:: |
| * Shared Files:: |
| * Filenames encoding:: |
| * File content encoding:: |
| * Open Modes:: |
| * Operations on C Streams:: |
| * Interfacing to C Streams:: |
| |
| Text_IO |
| |
| * Stream Pointer Positioning:: |
| * Reading and Writing Non-Regular Files:: |
| * Get_Immediate:: |
| * Treating Text_IO Files as Streams:: |
| * Text_IO Extensions:: |
| * Text_IO Facilities for Unbounded Strings:: |
| |
| Wide_Text_IO |
| |
| * Stream Pointer Positioning: Stream Pointer Positioning<2>. |
| * Reading and Writing Non-Regular Files: Reading and Writing Non-Regular Files<2>. |
| |
| Wide_Wide_Text_IO |
| |
| * Stream Pointer Positioning: Stream Pointer Positioning<3>. |
| * Reading and Writing Non-Regular Files: Reading and Writing Non-Regular Files<3>. |
| |
| The GNAT Library |
| |
| * Ada.Characters.Latin_9 (a-chlat9.ads): Ada Characters Latin_9 a-chlat9 ads. |
| * Ada.Characters.Wide_Latin_1 (a-cwila1.ads): Ada Characters Wide_Latin_1 a-cwila1 ads. |
| * Ada.Characters.Wide_Latin_9 (a-cwila1.ads): Ada Characters Wide_Latin_9 a-cwila1 ads. |
| * Ada.Characters.Wide_Wide_Latin_1 (a-chzla1.ads): Ada Characters Wide_Wide_Latin_1 a-chzla1 ads. |
| * Ada.Characters.Wide_Wide_Latin_9 (a-chzla9.ads): Ada Characters Wide_Wide_Latin_9 a-chzla9 ads. |
| * Ada.Containers.Formal_Doubly_Linked_Lists (a-cfdlli.ads): Ada Containers Formal_Doubly_Linked_Lists a-cfdlli ads. |
| * Ada.Containers.Formal_Hashed_Maps (a-cfhama.ads): Ada Containers Formal_Hashed_Maps a-cfhama ads. |
| * Ada.Containers.Formal_Hashed_Sets (a-cfhase.ads): Ada Containers Formal_Hashed_Sets a-cfhase ads. |
| * Ada.Containers.Formal_Ordered_Maps (a-cforma.ads): Ada Containers Formal_Ordered_Maps a-cforma ads. |
| * Ada.Containers.Formal_Ordered_Sets (a-cforse.ads): Ada Containers Formal_Ordered_Sets a-cforse ads. |
| * Ada.Containers.Formal_Vectors (a-cofove.ads): Ada Containers Formal_Vectors a-cofove ads. |
| * Ada.Containers.Formal_Indefinite_Vectors (a-cfinve.ads): Ada Containers Formal_Indefinite_Vectors a-cfinve ads. |
| * Ada.Containers.Bounded_Holders (a-coboho.ads): Ada Containers Bounded_Holders a-coboho ads. |
| * Ada.Command_Line.Environment (a-colien.ads): Ada Command_Line Environment a-colien ads. |
| * Ada.Command_Line.Remove (a-colire.ads): Ada Command_Line Remove a-colire ads. |
| * Ada.Command_Line.Response_File (a-clrefi.ads): Ada Command_Line Response_File a-clrefi ads. |
| * Ada.Direct_IO.C_Streams (a-diocst.ads): Ada Direct_IO C_Streams a-diocst ads. |
| * Ada.Exceptions.Is_Null_Occurrence (a-einuoc.ads): Ada Exceptions Is_Null_Occurrence a-einuoc ads. |
| * Ada.Exceptions.Last_Chance_Handler (a-elchha.ads): Ada Exceptions Last_Chance_Handler a-elchha ads. |
| * Ada.Exceptions.Traceback (a-exctra.ads): Ada Exceptions Traceback a-exctra ads. |
| * Ada.Sequential_IO.C_Streams (a-siocst.ads): Ada Sequential_IO C_Streams a-siocst ads. |
| * Ada.Streams.Stream_IO.C_Streams (a-ssicst.ads): Ada Streams Stream_IO C_Streams a-ssicst ads. |
| * Ada.Strings.Unbounded.Text_IO (a-suteio.ads): Ada Strings Unbounded Text_IO a-suteio ads. |
| * Ada.Strings.Wide_Unbounded.Wide_Text_IO (a-swuwti.ads): Ada Strings Wide_Unbounded Wide_Text_IO a-swuwti ads. |
| * Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO (a-szuzti.ads): Ada Strings Wide_Wide_Unbounded Wide_Wide_Text_IO a-szuzti ads. |
| * Ada.Text_IO.C_Streams (a-tiocst.ads): Ada Text_IO C_Streams a-tiocst ads. |
| * Ada.Text_IO.Reset_Standard_Files (a-tirsfi.ads): Ada Text_IO Reset_Standard_Files a-tirsfi ads. |
| * Ada.Wide_Characters.Unicode (a-wichun.ads): Ada Wide_Characters Unicode a-wichun ads. |
| * Ada.Wide_Text_IO.C_Streams (a-wtcstr.ads): Ada Wide_Text_IO C_Streams a-wtcstr ads. |
| * Ada.Wide_Text_IO.Reset_Standard_Files (a-wrstfi.ads): Ada Wide_Text_IO Reset_Standard_Files a-wrstfi ads. |
| * Ada.Wide_Wide_Characters.Unicode (a-zchuni.ads): Ada Wide_Wide_Characters Unicode a-zchuni ads. |
| * Ada.Wide_Wide_Text_IO.C_Streams (a-ztcstr.ads): Ada Wide_Wide_Text_IO C_Streams a-ztcstr ads. |
| * Ada.Wide_Wide_Text_IO.Reset_Standard_Files (a-zrstfi.ads): Ada Wide_Wide_Text_IO Reset_Standard_Files a-zrstfi ads. |
| * GNAT.Altivec (g-altive.ads): GNAT Altivec g-altive ads. |
| * GNAT.Altivec.Conversions (g-altcon.ads): GNAT Altivec Conversions g-altcon ads. |
| * GNAT.Altivec.Vector_Operations (g-alveop.ads): GNAT Altivec Vector_Operations g-alveop ads. |
| * GNAT.Altivec.Vector_Types (g-alvety.ads): GNAT Altivec Vector_Types g-alvety ads. |
| * GNAT.Altivec.Vector_Views (g-alvevi.ads): GNAT Altivec Vector_Views g-alvevi ads. |
| * GNAT.Array_Split (g-arrspl.ads): GNAT Array_Split g-arrspl ads. |
| * GNAT.AWK (g-awk.ads): GNAT AWK g-awk ads. |
| * GNAT.Bounded_Buffers (g-boubuf.ads): GNAT Bounded_Buffers g-boubuf ads. |
| * GNAT.Bounded_Mailboxes (g-boumai.ads): GNAT Bounded_Mailboxes g-boumai ads. |
| * GNAT.Bubble_Sort (g-bubsor.ads): GNAT Bubble_Sort g-bubsor ads. |
| * GNAT.Bubble_Sort_A (g-busora.ads): GNAT Bubble_Sort_A g-busora ads. |
| * GNAT.Bubble_Sort_G (g-busorg.ads): GNAT Bubble_Sort_G g-busorg ads. |
| * GNAT.Byte_Order_Mark (g-byorma.ads): GNAT Byte_Order_Mark g-byorma ads. |
| * GNAT.Byte_Swapping (g-bytswa.ads): GNAT Byte_Swapping g-bytswa ads. |
| * GNAT.Calendar (g-calend.ads): GNAT Calendar g-calend ads. |
| * GNAT.Calendar.Time_IO (g-catiio.ads): GNAT Calendar Time_IO g-catiio ads. |
| * GNAT.CRC32 (g-crc32.ads): GNAT CRC32 g-crc32 ads. |
| * GNAT.Case_Util (g-casuti.ads): GNAT Case_Util g-casuti ads. |
| * GNAT.CGI (g-cgi.ads): GNAT CGI g-cgi ads. |
| * GNAT.CGI.Cookie (g-cgicoo.ads): GNAT CGI Cookie g-cgicoo ads. |
| * GNAT.CGI.Debug (g-cgideb.ads): GNAT CGI Debug g-cgideb ads. |
| * GNAT.Command_Line (g-comlin.ads): GNAT Command_Line g-comlin ads. |
| * GNAT.Compiler_Version (g-comver.ads): GNAT Compiler_Version g-comver ads. |
| * GNAT.Ctrl_C (g-ctrl_c.ads): GNAT Ctrl_C g-ctrl_c ads. |
| * GNAT.Current_Exception (g-curexc.ads): GNAT Current_Exception g-curexc ads. |
| * GNAT.Debug_Pools (g-debpoo.ads): GNAT Debug_Pools g-debpoo ads. |
| * GNAT.Debug_Utilities (g-debuti.ads): GNAT Debug_Utilities g-debuti ads. |
| * GNAT.Decode_String (g-decstr.ads): GNAT Decode_String g-decstr ads. |
| * GNAT.Decode_UTF8_String (g-deutst.ads): GNAT Decode_UTF8_String g-deutst ads. |
| * GNAT.Directory_Operations (g-dirope.ads): GNAT Directory_Operations g-dirope ads. |
| * GNAT.Directory_Operations.Iteration (g-diopit.ads): GNAT Directory_Operations Iteration g-diopit ads. |
| * GNAT.Dynamic_HTables (g-dynhta.ads): GNAT Dynamic_HTables g-dynhta ads. |
| * GNAT.Dynamic_Tables (g-dyntab.ads): GNAT Dynamic_Tables g-dyntab ads. |
| * GNAT.Encode_String (g-encstr.ads): GNAT Encode_String g-encstr ads. |
| * GNAT.Encode_UTF8_String (g-enutst.ads): GNAT Encode_UTF8_String g-enutst ads. |
| * GNAT.Exception_Actions (g-excact.ads): GNAT Exception_Actions g-excact ads. |
| * GNAT.Exception_Traces (g-exctra.ads): GNAT Exception_Traces g-exctra ads. |
| * GNAT.Exceptions (g-expect.ads): GNAT Exceptions g-expect ads. |
| * GNAT.Expect (g-expect.ads): GNAT Expect g-expect ads. |
| * GNAT.Expect.TTY (g-exptty.ads): GNAT Expect TTY g-exptty ads. |
| * GNAT.Float_Control (g-flocon.ads): GNAT Float_Control g-flocon ads. |
| * GNAT.Formatted_String (g-forstr.ads): GNAT Formatted_String g-forstr ads. |
| * GNAT.Heap_Sort (g-heasor.ads): GNAT Heap_Sort g-heasor ads. |
| * GNAT.Heap_Sort_A (g-hesora.ads): GNAT Heap_Sort_A g-hesora ads. |
| * GNAT.Heap_Sort_G (g-hesorg.ads): GNAT Heap_Sort_G g-hesorg ads. |
| * GNAT.HTable (g-htable.ads): GNAT HTable g-htable ads. |
| * GNAT.IO (g-io.ads): GNAT IO g-io ads. |
| * GNAT.IO_Aux (g-io_aux.ads): GNAT IO_Aux g-io_aux ads. |
| * GNAT.Lock_Files (g-locfil.ads): GNAT Lock_Files g-locfil ads. |
| * GNAT.MBBS_Discrete_Random (g-mbdira.ads): GNAT MBBS_Discrete_Random g-mbdira ads. |
| * GNAT.MBBS_Float_Random (g-mbflra.ads): GNAT MBBS_Float_Random g-mbflra ads. |
| * GNAT.MD5 (g-md5.ads): GNAT MD5 g-md5 ads. |
| * GNAT.Memory_Dump (g-memdum.ads): GNAT Memory_Dump g-memdum ads. |
| * GNAT.Most_Recent_Exception (g-moreex.ads): GNAT Most_Recent_Exception g-moreex ads. |
| * GNAT.OS_Lib (g-os_lib.ads): GNAT OS_Lib g-os_lib ads. |
| * GNAT.Perfect_Hash_Generators (g-pehage.ads): GNAT Perfect_Hash_Generators g-pehage ads. |
| * GNAT.Random_Numbers (g-rannum.ads): GNAT Random_Numbers g-rannum ads. |
| * GNAT.Regexp (g-regexp.ads): GNAT Regexp g-regexp ads. |
| * GNAT.Registry (g-regist.ads): GNAT Registry g-regist ads. |
| * GNAT.Regpat (g-regpat.ads): GNAT Regpat g-regpat ads. |
| * GNAT.Rewrite_Data (g-rewdat.ads): GNAT Rewrite_Data g-rewdat ads. |
| * GNAT.Secondary_Stack_Info (g-sestin.ads): GNAT Secondary_Stack_Info g-sestin ads. |
| * GNAT.Semaphores (g-semaph.ads): GNAT Semaphores g-semaph ads. |
| * GNAT.Serial_Communications (g-sercom.ads): GNAT Serial_Communications g-sercom ads. |
| * GNAT.SHA1 (g-sha1.ads): GNAT SHA1 g-sha1 ads. |
| * GNAT.SHA224 (g-sha224.ads): GNAT SHA224 g-sha224 ads. |
| * GNAT.SHA256 (g-sha256.ads): GNAT SHA256 g-sha256 ads. |
| * GNAT.SHA384 (g-sha384.ads): GNAT SHA384 g-sha384 ads. |
| * GNAT.SHA512 (g-sha512.ads): GNAT SHA512 g-sha512 ads. |
| * GNAT.Signals (g-signal.ads): GNAT Signals g-signal ads. |
| * GNAT.Sockets (g-socket.ads): GNAT Sockets g-socket ads. |
| * GNAT.Source_Info (g-souinf.ads): GNAT Source_Info g-souinf ads. |
| * GNAT.Spelling_Checker (g-speche.ads): GNAT Spelling_Checker g-speche ads. |
| * GNAT.Spelling_Checker_Generic (g-spchge.ads): GNAT Spelling_Checker_Generic g-spchge ads. |
| * GNAT.Spitbol.Patterns (g-spipat.ads): GNAT Spitbol Patterns g-spipat ads. |
| * GNAT.Spitbol (g-spitbo.ads): GNAT Spitbol g-spitbo ads. |
| * GNAT.Spitbol.Table_Boolean (g-sptabo.ads): GNAT Spitbol Table_Boolean g-sptabo ads. |
| * GNAT.Spitbol.Table_Integer (g-sptain.ads): GNAT Spitbol Table_Integer g-sptain ads. |
| * GNAT.Spitbol.Table_VString (g-sptavs.ads): GNAT Spitbol Table_VString g-sptavs ads. |
| * GNAT.SSE (g-sse.ads): GNAT SSE g-sse ads. |
| * GNAT.SSE.Vector_Types (g-ssvety.ads): GNAT SSE Vector_Types g-ssvety ads. |
| * GNAT.Strings (g-string.ads): GNAT Strings g-string ads. |
| * GNAT.String_Split (g-strspl.ads): GNAT String_Split g-strspl ads. |
| * GNAT.Table (g-table.ads): GNAT Table g-table ads. |
| * GNAT.Task_Lock (g-tasloc.ads): GNAT Task_Lock g-tasloc ads. |
| * GNAT.Time_Stamp (g-timsta.ads): GNAT Time_Stamp g-timsta ads. |
| * GNAT.Threads (g-thread.ads): GNAT Threads g-thread ads. |
| * GNAT.Traceback (g-traceb.ads): GNAT Traceback g-traceb ads. |
| * GNAT.Traceback.Symbolic (g-trasym.ads): GNAT Traceback Symbolic g-trasym ads. |
| * GNAT.UTF_32 (g-table.ads): GNAT UTF_32 g-table ads. |
| * GNAT.Wide_Spelling_Checker (g-u3spch.ads): GNAT Wide_Spelling_Checker g-u3spch ads. |
| * GNAT.Wide_Spelling_Checker (g-wispch.ads): GNAT Wide_Spelling_Checker g-wispch ads. |
| * GNAT.Wide_String_Split (g-wistsp.ads): GNAT Wide_String_Split g-wistsp ads. |
| * GNAT.Wide_Wide_Spelling_Checker (g-zspche.ads): GNAT Wide_Wide_Spelling_Checker g-zspche ads. |
| * GNAT.Wide_Wide_String_Split (g-zistsp.ads): GNAT Wide_Wide_String_Split g-zistsp ads. |
| * Interfaces.C.Extensions (i-cexten.ads): Interfaces C Extensions i-cexten ads. |
| * Interfaces.C.Streams (i-cstrea.ads): Interfaces C Streams i-cstrea ads. |
| * Interfaces.Packed_Decimal (i-pacdec.ads): Interfaces Packed_Decimal i-pacdec ads. |
| * Interfaces.VxWorks (i-vxwork.ads): Interfaces VxWorks i-vxwork ads. |
| * Interfaces.VxWorks.IO (i-vxwoio.ads): Interfaces VxWorks IO i-vxwoio ads. |
| * System.Address_Image (s-addima.ads): System Address_Image s-addima ads. |
| * System.Assertions (s-assert.ads): System Assertions s-assert ads. |
| * System.Atomic_Counters (s-atocou.ads): System Atomic_Counters s-atocou ads. |
| * System.Memory (s-memory.ads): System Memory s-memory ads. |
| * System.Multiprocessors (s-multip.ads): System Multiprocessors s-multip ads. |
| * System.Multiprocessors.Dispatching_Domains (s-mudido.ads): System Multiprocessors Dispatching_Domains s-mudido ads. |
| * System.Partition_Interface (s-parint.ads): System Partition_Interface s-parint ads. |
| * System.Pool_Global (s-pooglo.ads): System Pool_Global s-pooglo ads. |
| * System.Pool_Local (s-pooloc.ads): System Pool_Local s-pooloc ads. |
| * System.Restrictions (s-restri.ads): System Restrictions s-restri ads. |
| * System.Rident (s-rident.ads): System Rident s-rident ads. |
| * System.Strings.Stream_Ops (s-ststop.ads): System Strings Stream_Ops s-ststop ads. |
| * System.Unsigned_Types (s-unstyp.ads): System Unsigned_Types s-unstyp ads. |
| * System.Wch_Cnv (s-wchcnv.ads): System Wch_Cnv s-wchcnv ads. |
| * System.Wch_Con (s-wchcon.ads): System Wch_Con s-wchcon ads. |
| |
| Interfacing to Other Languages |
| |
| * Interfacing to C:: |
| * Interfacing to C++:: |
| * Interfacing to COBOL:: |
| * Interfacing to Fortran:: |
| * Interfacing to non-GNAT Ada code:: |
| |
| Implementation of Specific Ada Features |
| |
| * Machine Code Insertions:: |
| * GNAT Implementation of Tasking:: |
| * GNAT Implementation of Shared Passive Packages:: |
| * Code Generation for Array Aggregates:: |
| * The Size of Discriminated Records with Default Discriminants:: |
| * Strict Conformance to the Ada Reference Manual:: |
| |
| GNAT Implementation of Tasking |
| |
| * Mapping Ada Tasks onto the Underlying Kernel Threads:: |
| * Ensuring Compliance with the Real-Time Annex:: |
| |
| Code Generation for Array Aggregates |
| |
| * Static constant aggregates with static bounds:: |
| * Constant aggregates with unconstrained nominal types:: |
| * Aggregates with static bounds:: |
| * Aggregates with non-static bounds:: |
| * Aggregates in assignment statements:: |
| |
| Obsolescent Features |
| |
| * pragma No_Run_Time:: |
| * pragma Ravenscar:: |
| * pragma Restricted_Run_Time:: |
| * pragma Task_Info:: |
| * package System.Task_Info (s-tasinf.ads): package System Task_Info s-tasinf ads. |
| |
| Compatibility and Porting Guide |
| |
| * Writing Portable Fixed-Point Declarations:: |
| * Compatibility with Ada 83:: |
| * Compatibility between Ada 95 and Ada 2005:: |
| * Implementation-dependent characteristics:: |
| * Compatibility with Other Ada Systems:: |
| * Representation Clauses:: |
| * Compatibility with HP Ada 83:: |
| |
| Compatibility with Ada 83 |
| |
| * Legal Ada 83 programs that are illegal in Ada 95:: |
| * More deterministic semantics:: |
| * Changed semantics:: |
| * Other language compatibility issues:: |
| |
| Implementation-dependent characteristics |
| |
| * Implementation-defined pragmas:: |
| * Implementation-defined attributes:: |
| * Libraries:: |
| * Elaboration order:: |
| * Target-specific aspects:: |
| |
| @end detailmenu |
| @end menu |
| |
| @node About This Guide,Implementation Defined Pragmas,Top,Top |
| @anchor{gnat_rm/about_this_guide about-this-guide}@anchor{2}@anchor{gnat_rm/about_this_guide doc}@anchor{3}@anchor{gnat_rm/about_this_guide gnat-reference-manual}@anchor{4}@anchor{gnat_rm/about_this_guide id1}@anchor{5} |
| @chapter About This Guide |
| |
| |
| |
| This manual contains useful information in writing programs using the |
| GNAT compiler. It includes information on implementation dependent |
| characteristics of GNAT, including all the information required by |
| Annex M of the Ada language standard. |
| |
| GNAT implements Ada 95, Ada 2005 and Ada 2012, and it may also be |
| invoked in Ada 83 compatibility mode. |
| By default, GNAT assumes Ada 2012, |
| but you can override with a compiler switch |
| to explicitly specify the language version. |
| (Please refer to the @emph{GNAT User's Guide} for details on these switches.) |
| Throughout this manual, references to 'Ada' without a year suffix |
| apply to all the Ada versions of the language. |
| |
| Ada is designed to be highly portable. |
| In general, a program will have the same effect even when compiled by |
| different compilers on different platforms. |
| However, since Ada is designed to be used in a |
| wide variety of applications, it also contains a number of system |
| dependent features to be used in interfacing to the external world. |
| .. index:: Implementation-dependent features |
| |
| @geindex Portability |
| |
| Note: Any program that makes use of implementation-dependent features |
| may be non-portable. You should follow good programming practice and |
| isolate and clearly document any sections of your program that make use |
| of these features in a non-portable manner. |
| |
| @menu |
| * What This Reference Manual Contains:: |
| * Conventions:: |
| * Related Information:: |
| |
| @end menu |
| |
| @node What This Reference Manual Contains,Conventions,,About This Guide |
| @anchor{gnat_rm/about_this_guide what-this-reference-manual-contains}@anchor{6} |
| @section What This Reference Manual Contains |
| |
| |
| This reference manual contains the following chapters: |
| |
| |
| @itemize * |
| |
| @item |
| @ref{7,,Implementation Defined Pragmas}, lists GNAT implementation-dependent |
| pragmas, which can be used to extend and enhance the functionality of the |
| compiler. |
| |
| @item |
| @ref{8,,Implementation Defined Attributes}, lists GNAT |
| implementation-dependent attributes, which can be used to extend and |
| enhance the functionality of the compiler. |
| |
| @item |
| @ref{9,,Standard and Implementation Defined Restrictions}, lists GNAT |
| implementation-dependent restrictions, which can be used to extend and |
| enhance the functionality of the compiler. |
| |
| @item |
| @ref{a,,Implementation Advice}, provides information on generally |
| desirable behavior which are not requirements that all compilers must |
| follow since it cannot be provided on all systems, or which may be |
| undesirable on some systems. |
| |
| @item |
| @ref{b,,Implementation Defined Characteristics}, provides a guide to |
| minimizing implementation dependent features. |
| |
| @item |
| @ref{c,,Intrinsic Subprograms}, describes the intrinsic subprograms |
| implemented by GNAT, and how they can be imported into user |
| application programs. |
| |
| @item |
| @ref{d,,Representation Clauses and Pragmas}, describes in detail the |
| way that GNAT represents data, and in particular the exact set |
| of representation clauses and pragmas that is accepted. |
| |
| @item |
| @ref{e,,Standard Library Routines}, provides a listing of packages and a |
| brief description of the functionality that is provided by Ada's |
| extensive set of standard library routines as implemented by GNAT. |
| |
| @item |
| @ref{f,,The Implementation of Standard I/O}, details how the GNAT |
| implementation of the input-output facilities. |
| |
| @item |
| @ref{10,,The GNAT Library}, is a catalog of packages that complement |
| the Ada predefined library. |
| |
| @item |
| @ref{11,,Interfacing to Other Languages}, describes how programs |
| written in Ada using GNAT can be interfaced to other programming |
| languages. |
| |
| @item |
| @ref{12,,Specialized Needs Annexes}, describes the GNAT implementation of all |
| of the specialized needs annexes. |
| |
| @item |
| @ref{13,,Implementation of Specific Ada Features}, discusses issues related |
| to GNAT's implementation of machine code insertions, tasking, and several |
| other features. |
| |
| @item |
| @ref{14,,Implementation of Ada 2012 Features}, describes the status of the |
| GNAT implementation of the Ada 2012 language standard. |
| |
| @item |
| @ref{15,,Obsolescent Features} documents implementation dependent features, |
| including pragmas and attributes, which are considered obsolescent, since |
| there are other preferred ways of achieving the same results. These |
| obsolescent forms are retained for backwards compatibility. |
| |
| @item |
| @ref{16,,Compatibility and Porting Guide} presents some guidelines for |
| developing portable Ada code, describes the compatibility issues that |
| may arise between GNAT and other Ada compilation systems (including those |
| for Ada 83), and shows how GNAT can expedite porting applications |
| developed in other Ada environments. |
| |
| @item |
| @ref{1,,GNU Free Documentation License} contains the license for this document. |
| @end itemize |
| |
| @geindex Ada 95 Language Reference Manual |
| |
| @geindex Ada 2005 Language Reference Manual |
| |
| This reference manual assumes a basic familiarity with the Ada 95 language, as |
| described in the |
| @cite{International Standard ANSI/ISO/IEC-8652:1995}. |
| It does not require knowledge of the new features introduced by Ada 2005 or |
| Ada 2012. |
| All three reference manuals are included in the GNAT documentation |
| package. |
| |
| @node Conventions,Related Information,What This Reference Manual Contains,About This Guide |
| @anchor{gnat_rm/about_this_guide conventions}@anchor{17} |
| @section Conventions |
| |
| |
| @geindex Conventions |
| @geindex typographical |
| |
| @geindex Typographical conventions |
| |
| Following are examples of the typographical and graphic conventions used |
| in this guide: |
| |
| |
| @itemize * |
| |
| @item |
| @cite{Functions}, @cite{utility program names}, @cite{standard names}, |
| and @cite{classes}. |
| |
| @item |
| @cite{Option flags} |
| |
| @item |
| @code{File names} |
| |
| @item |
| @cite{Variables} |
| |
| @item |
| @emph{Emphasis} |
| |
| @item |
| [optional information or parameters] |
| |
| @item |
| Examples are described by text |
| |
| @example |
| and then shown this way. |
| @end example |
| |
| @item |
| Commands that are entered by the user are shown as preceded by a prompt string |
| comprising the @code{$} character followed by a space. |
| @end itemize |
| |
| @node Related Information,,Conventions,About This Guide |
| @anchor{gnat_rm/about_this_guide related-information}@anchor{18} |
| @section Related Information |
| |
| |
| See the following documents for further information on GNAT: |
| |
| |
| @itemize * |
| |
| @item |
| @cite{GNAT User's Guide for Native Platforms}, |
| which provides information on how to use the |
| GNAT development environment. |
| |
| @item |
| @cite{Ada 95 Reference Manual}, the Ada 95 programming language standard. |
| |
| @item |
| @cite{Ada 95 Annotated Reference Manual}, which is an annotated version |
| of the Ada 95 standard. The annotations describe |
| detailed aspects of the design decision, and in particular contain useful |
| sections on Ada 83 compatibility. |
| |
| @item |
| @cite{Ada 2005 Reference Manual}, the Ada 2005 programming language standard. |
| |
| @item |
| @cite{Ada 2005 Annotated Reference Manual}, which is an annotated version |
| of the Ada 2005 standard. The annotations describe |
| detailed aspects of the design decision. |
| |
| @item |
| @cite{Ada 2012 Reference Manual}, the Ada 2012 programming language standard. |
| |
| @item |
| @cite{DEC Ada@comma{} Technical Overview and Comparison on DIGITAL Platforms}, |
| which contains specific information on compatibility between GNAT and |
| DEC Ada 83 systems. |
| |
| @item |
| @cite{DEC Ada@comma{} Language Reference Manual}, part number AA-PYZAB-TK, which |
| describes in detail the pragmas and attributes provided by the DEC Ada 83 |
| compiler system. |
| @end itemize |
| |
| @node Implementation Defined Pragmas,Implementation Defined Aspects,About This Guide,Top |
| @anchor{gnat_rm/implementation_defined_pragmas implementation-defined-pragmas}@anchor{7}@anchor{gnat_rm/implementation_defined_pragmas doc}@anchor{19}@anchor{gnat_rm/implementation_defined_pragmas id1}@anchor{1a} |
| @chapter Implementation Defined Pragmas |
| |
| |
| Ada defines a set of pragmas that can be used to supply additional |
| information to the compiler. These language defined pragmas are |
| implemented in GNAT and work as described in the Ada Reference Manual. |
| |
| In addition, Ada allows implementations to define additional pragmas |
| whose meaning is defined by the implementation. GNAT provides a number |
| of these implementation-defined pragmas, which can be used to extend |
| and enhance the functionality of the compiler. This section of the GNAT |
| Reference Manual describes these additional pragmas. |
| |
| Note that any program using these pragmas might not be portable to other |
| compilers (although GNAT implements this set of pragmas on all |
| platforms). Therefore if portability to other compilers is an important |
| consideration, the use of these pragmas should be minimized. |
| |
| @menu |
| * Pragma Abort_Defer:: |
| * Pragma Abstract_State:: |
| * Pragma Ada_83:: |
| * Pragma Ada_95:: |
| * Pragma Ada_05:: |
| * Pragma Ada_2005:: |
| * Pragma Ada_12:: |
| * Pragma Ada_2012:: |
| * Pragma Allow_Integer_Address:: |
| * Pragma Annotate:: |
| * Pragma Assert:: |
| * Pragma Assert_And_Cut:: |
| * Pragma Assertion_Policy:: |
| * Pragma Assume:: |
| * Pragma Assume_No_Invalid_Values:: |
| * Pragma Async_Readers:: |
| * Pragma Async_Writers:: |
| * Pragma Attribute_Definition:: |
| * Pragma C_Pass_By_Copy:: |
| * Pragma Check:: |
| * Pragma Check_Float_Overflow:: |
| * Pragma Check_Name:: |
| * Pragma Check_Policy:: |
| * Pragma CIL_Constructor:: |
| * Pragma Comment:: |
| * Pragma Common_Object:: |
| * Pragma Compile_Time_Error:: |
| * Pragma Compile_Time_Warning:: |
| * Pragma Compiler_Unit:: |
| * Pragma Compiler_Unit_Warning:: |
| * Pragma Complete_Representation:: |
| * Pragma Complex_Representation:: |
| * Pragma Component_Alignment:: |
| * Pragma Contract_Cases:: |
| * Pragma Convention_Identifier:: |
| * Pragma CPP_Class:: |
| * Pragma CPP_Constructor:: |
| * Pragma CPP_Virtual:: |
| * Pragma CPP_Vtable:: |
| * Pragma CPU:: |
| * Pragma Debug:: |
| * Pragma Debug_Policy:: |
| * Pragma Default_Scalar_Storage_Order:: |
| * Pragma Default_Storage_Pool:: |
| * Pragma Depends:: |
| * Pragma Detect_Blocking:: |
| * Pragma Disable_Atomic_Synchronization:: |
| * Pragma Dispatching_Domain:: |
| * Pragma Effective_Reads:: |
| * Pragma Effective_Writes:: |
| * Pragma Elaboration_Checks:: |
| * Pragma Eliminate:: |
| * Pragma Enable_Atomic_Synchronization:: |
| * Pragma Export_Function:: |
| * Pragma Export_Object:: |
| * Pragma Export_Procedure:: |
| * Pragma Export_Value:: |
| * Pragma Export_Valued_Procedure:: |
| * Pragma Extend_System:: |
| * Pragma Extensions_Allowed:: |
| * Pragma External:: |
| * Pragma External_Name_Casing:: |
| * Pragma Fast_Math:: |
| * Pragma Favor_Top_Level:: |
| * Pragma Finalize_Storage_Only:: |
| * Pragma Float_Representation:: |
| * Pragma Global:: |
| * Pragma Ident:: |
| * Pragma Ignore_Pragma:: |
| * Pragma Implementation_Defined:: |
| * Pragma Implemented:: |
| * Pragma Implicit_Packing:: |
| * Pragma Import_Function:: |
| * Pragma Import_Object:: |
| * Pragma Import_Procedure:: |
| * Pragma Import_Valued_Procedure:: |
| * Pragma Independent:: |
| * Pragma Independent_Components:: |
| * Pragma Initial_Condition:: |
| * Pragma Initialize_Scalars:: |
| * Pragma Initializes:: |
| * Pragma Inline_Always:: |
| * Pragma Inline_Generic:: |
| * Pragma Interface:: |
| * Pragma Interface_Name:: |
| * Pragma Interrupt_Handler:: |
| * Pragma Interrupt_State:: |
| * Pragma Invariant:: |
| * Pragma Java_Constructor:: |
| * Pragma Java_Interface:: |
| * Pragma Keep_Names:: |
| * Pragma License:: |
| * Pragma Link_With:: |
| * Pragma Linker_Alias:: |
| * Pragma Linker_Constructor:: |
| * Pragma Linker_Destructor:: |
| * Pragma Linker_Section:: |
| * Pragma Lock_Free:: |
| * Pragma Loop_Invariant:: |
| * Pragma Loop_Optimize:: |
| * Pragma Loop_Variant:: |
| * Pragma Machine_Attribute:: |
| * Pragma Main:: |
| * Pragma Main_Storage:: |
| * Pragma No_Body:: |
| * Pragma No_Elaboration_Code_All:: |
| * Pragma No_Inline:: |
| * Pragma No_Return:: |
| * Pragma No_Run_Time:: |
| * Pragma No_Strict_Aliasing:: |
| * Pragma No_Tagged_Streams:: |
| * Pragma Normalize_Scalars:: |
| * Pragma Obsolescent:: |
| * Pragma Optimize_Alignment:: |
| * Pragma Ordered:: |
| * Pragma Overflow_Mode:: |
| * Pragma Overriding_Renamings:: |
| * Pragma Partition_Elaboration_Policy:: |
| * Pragma Part_Of:: |
| * Pragma Passive:: |
| * Pragma Persistent_BSS:: |
| * Pragma Polling:: |
| * Pragma Post:: |
| * Pragma Postcondition:: |
| * Pragma Post_Class:: |
| * Pragma Pre:: |
| * Pragma Precondition:: |
| * Pragma Predicate:: |
| * Pragma Preelaborable_Initialization:: |
| * Pragma Prefix_Exception_Messages:: |
| * Pragma Pre_Class:: |
| * Pragma Priority_Specific_Dispatching:: |
| * Pragma Profile:: |
| * Pragma Profile_Warnings:: |
| * Pragma Propagate_Exceptions:: |
| * Pragma Provide_Shift_Operators:: |
| * Pragma Psect_Object:: |
| * Pragma Pure_Function:: |
| * Pragma Rational:: |
| * Pragma Ravenscar:: |
| * Pragma Refined_Depends:: |
| * Pragma Refined_Global:: |
| * Pragma Refined_Post:: |
| * Pragma Refined_State:: |
| * Pragma Relative_Deadline:: |
| * Pragma Remote_Access_Type:: |
| * Pragma Restricted_Run_Time:: |
| * Pragma Restriction_Warnings:: |
| * Pragma Reviewable:: |
| * Pragma Share_Generic:: |
| * Pragma Shared:: |
| * Pragma Short_Circuit_And_Or:: |
| * Pragma Short_Descriptors:: |
| * Pragma Simple_Storage_Pool_Type:: |
| * Pragma Source_File_Name:: |
| * Pragma Source_File_Name_Project:: |
| * Pragma Source_Reference:: |
| * Pragma SPARK_Mode:: |
| * Pragma Static_Elaboration_Desired:: |
| * Pragma Stream_Convert:: |
| * Pragma Style_Checks:: |
| * Pragma Subtitle:: |
| * Pragma Suppress:: |
| * Pragma Suppress_All:: |
| * Pragma Suppress_Debug_Info:: |
| * Pragma Suppress_Exception_Locations:: |
| * Pragma Suppress_Initialization:: |
| * Pragma Task_Name:: |
| * Pragma Task_Storage:: |
| * Pragma Test_Case:: |
| * Pragma Thread_Local_Storage:: |
| * Pragma Time_Slice:: |
| * Pragma Title:: |
| * Pragma Type_Invariant:: |
| * Pragma Type_Invariant_Class:: |
| * Pragma Unchecked_Union:: |
| * Pragma Unevaluated_Use_Of_Old:: |
| * Pragma Unimplemented_Unit:: |
| * Pragma Universal_Aliasing:: |
| * Pragma Universal_Data:: |
| * Pragma Unmodified:: |
| * Pragma Unreferenced:: |
| * Pragma Unreferenced_Objects:: |
| * Pragma Unreserve_All_Interrupts:: |
| * Pragma Unsuppress:: |
| * Pragma Use_VADS_Size:: |
| * Pragma Validity_Checks:: |
| * Pragma Volatile:: |
| * Pragma Warning_As_Error:: |
| * Pragma Warnings:: |
| * Pragma Weak_External:: |
| * Pragma Wide_Character_Encoding:: |
| |
| @end menu |
| |
| @node Pragma Abort_Defer,Pragma Abstract_State,,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-abort-defer}@anchor{1b} |
| @section Pragma Abort_Defer |
| |
| |
| @geindex Deferring aborts |
| |
| Syntax: |
| |
| @example |
| pragma Abort_Defer; |
| @end example |
| |
| This pragma must appear at the start of the statement sequence of a |
| handled sequence of statements (right after the @cite{begin}). It has |
| the effect of deferring aborts for the sequence of statements (but not |
| for the declarations or handlers, if any, associated with this statement |
| sequence). |
| |
| @node Pragma Abstract_State,Pragma Ada_83,Pragma Abort_Defer,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-abstract-state}@anchor{1c} |
| @section Pragma Abstract_State |
| |
| |
| For the description of this pragma, see SPARK 2014 Reference Manual, |
| section 7.1.4. |
| |
| @node Pragma Ada_83,Pragma Ada_95,Pragma Abstract_State,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-ada-83}@anchor{1d} |
| @section Pragma Ada_83 |
| |
| |
| Syntax: |
| |
| @example |
| pragma Ada_83; |
| @end example |
| |
| A configuration pragma that establishes Ada 83 mode for the unit to |
| which it applies, regardless of the mode set by the command line |
| switches. In Ada 83 mode, GNAT attempts to be as compatible with |
| the syntax and semantics of Ada 83, as defined in the original Ada |
| 83 Reference Manual as possible. In particular, the keywords added by Ada 95 |
| and Ada 2005 are not recognized, optional package bodies are allowed, |
| and generics may name types with unknown discriminants without using |
| the @cite{(<>)} notation. In addition, some but not all of the additional |
| restrictions of Ada 83 are enforced. |
| |
| Ada 83 mode is intended for two purposes. Firstly, it allows existing |
| Ada 83 code to be compiled and adapted to GNAT with less effort. |
| Secondly, it aids in keeping code backwards compatible with Ada 83. |
| However, there is no guarantee that code that is processed correctly |
| by GNAT in Ada 83 mode will in fact compile and execute with an Ada |
| 83 compiler, since GNAT does not enforce all the additional checks |
| required by Ada 83. |
| |
| @node Pragma Ada_95,Pragma Ada_05,Pragma Ada_83,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-ada-95}@anchor{1e} |
| @section Pragma Ada_95 |
| |
| |
| Syntax: |
| |
| @example |
| pragma Ada_95; |
| @end example |
| |
| A configuration pragma that establishes Ada 95 mode for the unit to which |
| it applies, regardless of the mode set by the command line switches. |
| This mode is set automatically for the @cite{Ada} and @cite{System} |
| packages and their children, so you need not specify it in these |
| contexts. This pragma is useful when writing a reusable component that |
| itself uses Ada 95 features, but which is intended to be usable from |
| either Ada 83 or Ada 95 programs. |
| |
| @node Pragma Ada_05,Pragma Ada_2005,Pragma Ada_95,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-ada-05}@anchor{1f} |
| @section Pragma Ada_05 |
| |
| |
| Syntax: |
| |
| @example |
| pragma Ada_05; |
| pragma Ada_05 (local_NAME); |
| @end example |
| |
| A configuration pragma that establishes Ada 2005 mode for the unit to which |
| it applies, regardless of the mode set by the command line switches. |
| This pragma is useful when writing a reusable component that |
| itself uses Ada 2005 features, but which is intended to be usable from |
| either Ada 83 or Ada 95 programs. |
| |
| The one argument form (which is not a configuration pragma) |
| is used for managing the transition from |
| Ada 95 to Ada 2005 in the run-time library. If an entity is marked |
| as Ada_2005 only, then referencing the entity in Ada_83 or Ada_95 |
| mode will generate a warning. In addition, in Ada_83 or Ada_95 |
| mode, a preference rule is established which does not choose |
| such an entity unless it is unambiguously specified. This avoids |
| extra subprograms marked this way from generating ambiguities in |
| otherwise legal pre-Ada_2005 programs. The one argument form is |
| intended for exclusive use in the GNAT run-time library. |
| |
| @node Pragma Ada_2005,Pragma Ada_12,Pragma Ada_05,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-ada-2005}@anchor{20} |
| @section Pragma Ada_2005 |
| |
| |
| Syntax: |
| |
| @example |
| pragma Ada_2005; |
| @end example |
| |
| This configuration pragma is a synonym for pragma Ada_05 and has the |
| same syntax and effect. |
| |
| @node Pragma Ada_12,Pragma Ada_2012,Pragma Ada_2005,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-ada-12}@anchor{21} |
| @section Pragma Ada_12 |
| |
| |
| Syntax: |
| |
| @example |
| pragma Ada_12; |
| pragma Ada_12 (local_NAME); |
| @end example |
| |
| A configuration pragma that establishes Ada 2012 mode for the unit to which |
| it applies, regardless of the mode set by the command line switches. |
| This mode is set automatically for the @cite{Ada} and @cite{System} |
| packages and their children, so you need not specify it in these |
| contexts. This pragma is useful when writing a reusable component that |
| itself uses Ada 2012 features, but which is intended to be usable from |
| Ada 83, Ada 95, or Ada 2005 programs. |
| |
| The one argument form, which is not a configuration pragma, |
| is used for managing the transition from Ada |
| 2005 to Ada 2012 in the run-time library. If an entity is marked |
| as Ada_201 only, then referencing the entity in any pre-Ada_2012 |
| mode will generate a warning. In addition, in any pre-Ada_2012 |
| mode, a preference rule is established which does not choose |
| such an entity unless it is unambiguously specified. This avoids |
| extra subprograms marked this way from generating ambiguities in |
| otherwise legal pre-Ada_2012 programs. The one argument form is |
| intended for exclusive use in the GNAT run-time library. |
| |
| @node Pragma Ada_2012,Pragma Allow_Integer_Address,Pragma Ada_12,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-ada-2012}@anchor{22} |
| @section Pragma Ada_2012 |
| |
| |
| Syntax: |
| |
| @example |
| pragma Ada_2012; |
| @end example |
| |
| This configuration pragma is a synonym for pragma Ada_12 and has the |
| same syntax and effect. |
| |
| @node Pragma Allow_Integer_Address,Pragma Annotate,Pragma Ada_2012,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-allow-integer-address}@anchor{23} |
| @section Pragma Allow_Integer_Address |
| |
| |
| Syntax: |
| |
| @example |
| pragma Allow_Integer_Address; |
| @end example |
| |
| In almost all versions of GNAT, @cite{System.Address} is a private |
| type in accordance with the implementation advice in the RM. This |
| means that integer values, |
| in particular integer literals, are not allowed as address values. |
| If the configuration pragma |
| @cite{Allow_Integer_Address} is given, then integer expressions may |
| be used anywhere a value of type @cite{System.Address} is required. |
| The effect is to introduce an implicit unchecked conversion from the |
| integer value to type @cite{System.Address}. The reverse case of using |
| an address where an integer type is required is handled analogously. |
| The following example compiles without errors: |
| |
| @example |
| pragma Allow_Integer_Address; |
| with System; use System; |
| package AddrAsInt is |
| X : Integer; |
| Y : Integer; |
| for X'Address use 16#1240#; |
| for Y use at 16#3230#; |
| m : Address := 16#4000#; |
| n : constant Address := 4000; |
| p : constant Address := Address (X + Y); |
| v : Integer := y'Address; |
| w : constant Integer := Integer (Y'Address); |
| type R is new integer; |
| RR : R := 1000; |
| Z : Integer; |
| for Z'Address use RR; |
| end AddrAsInt; |
| @end example |
| |
| Note that pragma @cite{Allow_Integer_Address} is ignored if @cite{System.Address} |
| is not a private type. In implementations of @cite{GNAT} where |
| System.Address is a visible integer type, |
| this pragma serves no purpose but is ignored |
| rather than rejected to allow common sets of sources to be used |
| in the two situations. |
| |
| @node Pragma Annotate,Pragma Assert,Pragma Allow_Integer_Address,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-annotate}@anchor{24} |
| @section Pragma Annotate |
| |
| |
| Syntax: |
| |
| @example |
| pragma Annotate (IDENTIFIER [, IDENTIFIER @{, ARG@}] [, entity => local_NAME]); |
| |
| ARG ::= NAME | EXPRESSION |
| @end example |
| |
| This pragma is used to annotate programs. @cite{identifier} identifies |
| the type of annotation. GNAT verifies that it is an identifier, but does |
| not otherwise analyze it. The second optional identifier is also left |
| unanalyzed, and by convention is used to control the action of the tool to |
| which the annotation is addressed. The remaining @cite{arg} arguments |
| can be either string literals or more generally expressions. |
| String literals are assumed to be either of type |
| @cite{Standard.String} or else @cite{Wide_String} or @cite{Wide_Wide_String} |
| depending on the character literals they contain. |
| All other kinds of arguments are analyzed as expressions, and must be |
| unambiguous. The last argument if present must have the identifier |
| @cite{Entity} and GNAT verifies that a local name is given. |
| |
| The analyzed pragma is retained in the tree, but not otherwise processed |
| by any part of the GNAT compiler, except to generate corresponding note |
| lines in the generated ALI file. For the format of these note lines, see |
| the compiler source file lib-writ.ads. This pragma is intended for use by |
| external tools, including ASIS. The use of pragma Annotate does not |
| affect the compilation process in any way. This pragma may be used as |
| a configuration pragma. |
| |
| @node Pragma Assert,Pragma Assert_And_Cut,Pragma Annotate,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-assert}@anchor{25} |
| @section Pragma Assert |
| |
| |
| Syntax: |
| |
| @example |
| pragma Assert ( |
| boolean_EXPRESSION |
| [, string_EXPRESSION]); |
| @end example |
| |
| The effect of this pragma depends on whether the corresponding command |
| line switch is set to activate assertions. The pragma expands into code |
| equivalent to the following: |
| |
| @example |
| if assertions-enabled then |
| if not boolean_EXPRESSION then |
| System.Assertions.Raise_Assert_Failure |
| (string_EXPRESSION); |
| end if; |
| end if; |
| @end example |
| |
| The string argument, if given, is the message that will be associated |
| with the exception occurrence if the exception is raised. If no second |
| argument is given, the default message is @cite{file}:@cite{nnn}, |
| where @cite{file} is the name of the source file containing the assert, |
| and @cite{nnn} is the line number of the assert. A pragma is not a |
| statement, so if a statement sequence contains nothing but a pragma |
| assert, then a null statement is required in addition, as in: |
| |
| @example |
| ... |
| if J > 3 then |
| pragma Assert (K > 3, "Bad value for K"); |
| null; |
| end if; |
| @end example |
| |
| Note that, as with the @cite{if} statement to which it is equivalent, the |
| type of the expression is either @cite{Standard.Boolean}, or any type derived |
| from this standard type. |
| |
| Assert checks can be either checked or ignored. By default they are ignored. |
| They will be checked if either the command line switch @emph{-gnata} is |
| used, or if an @cite{Assertion_Policy} or @cite{Check_Policy} pragma is used |
| to enable @cite{Assert_Checks}. |
| |
| If assertions are ignored, then there |
| is no run-time effect (and in particular, any side effects from the |
| expression will not occur at run time). (The expression is still |
| analyzed at compile time, and may cause types to be frozen if they are |
| mentioned here for the first time). |
| |
| If assertions are checked, then the given expression is tested, and if |
| it is @cite{False} then @cite{System.Assertions.Raise_Assert_Failure} is called |
| which results in the raising of @cite{Assert_Failure} with the given message. |
| |
| You should generally avoid side effects in the expression arguments of |
| this pragma, because these side effects will turn on and off with the |
| setting of the assertions mode, resulting in assertions that have an |
| effect on the program. However, the expressions are analyzed for |
| semantic correctness whether or not assertions are enabled, so turning |
| assertions on and off cannot affect the legality of a program. |
| |
| Note that the implementation defined policy @cite{DISABLE}, given in a |
| pragma @cite{Assertion_Policy}, can be used to suppress this semantic analysis. |
| |
| Note: this is a standard language-defined pragma in versions |
| of Ada from 2005 on. In GNAT, it is implemented in all versions |
| of Ada, and the DISABLE policy is an implementation-defined |
| addition. |
| |
| @node Pragma Assert_And_Cut,Pragma Assertion_Policy,Pragma Assert,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-assert-and-cut}@anchor{26} |
| @section Pragma Assert_And_Cut |
| |
| |
| Syntax: |
| |
| @example |
| pragma Assert_And_Cut ( |
| boolean_EXPRESSION |
| [, string_EXPRESSION]); |
| @end example |
| |
| The effect of this pragma is identical to that of pragma @cite{Assert}, |
| except that in an @cite{Assertion_Policy} pragma, the identifier |
| @cite{Assert_And_Cut} is used to control whether it is ignored or checked |
| (or disabled). |
| |
| The intention is that this be used within a subprogram when the |
| given test expresion sums up all the work done so far in the |
| subprogram, so that the rest of the subprogram can be verified |
| (informally or formally) using only the entry preconditions, |
| and the expression in this pragma. This allows dividing up |
| a subprogram into sections for the purposes of testing or |
| formal verification. The pragma also serves as useful |
| documentation. |
| |
| @node Pragma Assertion_Policy,Pragma Assume,Pragma Assert_And_Cut,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-assertion-policy}@anchor{27} |
| @section Pragma Assertion_Policy |
| |
| |
| Syntax: |
| |
| @example |
| pragma Assertion_Policy (CHECK | DISABLE | IGNORE); |
| |
| pragma Assertion_Policy ( |
| ASSERTION_KIND => POLICY_IDENTIFIER |
| @{, ASSERTION_KIND => POLICY_IDENTIFIER@}); |
| |
| ASSERTION_KIND ::= RM_ASSERTION_KIND | ID_ASSERTION_KIND |
| |
| RM_ASSERTION_KIND ::= Assert | |
| Static_Predicate | |
| Dynamic_Predicate | |
| Pre | |
| Pre'Class | |
| Post | |
| Post'Class | |
| Type_Invariant | |
| Type_Invariant'Class |
| |
| ID_ASSERTION_KIND ::= Assertions | |
| Assert_And_Cut | |
| Assume | |
| Contract_Cases | |
| Debug | |
| Invariant | |
| Invariant'Class | |
| Loop_Invariant | |
| Loop_Variant | |
| Postcondition | |
| Precondition | |
| Predicate | |
| Refined_Post | |
| Statement_Assertions |
| |
| POLICY_IDENTIFIER ::= Check | Disable | Ignore |
| @end example |
| |
| This is a standard Ada 2012 pragma that is available as an |
| implementation-defined pragma in earlier versions of Ada. |
| The assertion kinds @cite{RM_ASSERTION_KIND} are those defined in |
| the Ada standard. The assertion kinds @cite{ID_ASSERTION_KIND} |
| are implementation defined additions recognized by the GNAT compiler. |
| |
| The pragma applies in both cases to pragmas and aspects with matching |
| names, e.g. @cite{Pre} applies to the Pre aspect, and @cite{Precondition} |
| applies to both the @cite{Precondition} pragma |
| and the aspect @cite{Precondition}. Note that the identifiers for |
| pragmas Pre_Class and Post_Class are Pre'Class and Post'Class (not |
| Pre_Class and Post_Class), since these pragmas are intended to be |
| identical to the corresponding aspects). |
| |
| If the policy is @cite{CHECK}, then assertions are enabled, i.e. |
| the corresponding pragma or aspect is activated. |
| If the policy is @cite{IGNORE}, then assertions are ignored, i.e. |
| the corresponding pragma or aspect is deactivated. |
| This pragma overrides the effect of the @emph{-gnata} switch on the |
| command line. |
| |
| The implementation defined policy @cite{DISABLE} is like |
| @cite{IGNORE} except that it completely disables semantic |
| checking of the corresponding pragma or aspect. This is |
| useful when the pragma or aspect argument references subprograms |
| in a with'ed package which is replaced by a dummy package |
| for the final build. |
| |
| The implementation defined assertion kind @cite{Assertions} applies to all |
| assertion kinds. The form with no assertion kind given implies this |
| choice, so it applies to all assertion kinds (RM defined, and |
| implementation defined). |
| |
| The implementation defined assertion kind @cite{Statement_Assertions} |
| applies to @cite{Assert}, @cite{Assert_And_Cut}, |
| @cite{Assume}, @cite{Loop_Invariant}, and @cite{Loop_Variant}. |
| |
| @node Pragma Assume,Pragma Assume_No_Invalid_Values,Pragma Assertion_Policy,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-assume}@anchor{28} |
| @section Pragma Assume |
| |
| |
| Syntax: |
| |
| @example |
| pragma Assume ( |
| boolean_EXPRESSION |
| [, string_EXPRESSION]); |
| @end example |
| |
| The effect of this pragma is identical to that of pragma @cite{Assert}, |
| except that in an @cite{Assertion_Policy} pragma, the identifier |
| @cite{Assume} is used to control whether it is ignored or checked |
| (or disabled). |
| |
| The intention is that this be used for assumptions about the |
| external environment. So you cannot expect to verify formally |
| or informally that the condition is met, this must be |
| established by examining things outside the program itself. |
| For example, we may have code that depends on the size of |
| @cite{Long_Long_Integer} being at least 64. So we could write: |
| |
| @example |
| pragma Assume (Long_Long_Integer'Size >= 64); |
| @end example |
| |
| This assumption cannot be proved from the program itself, |
| but it acts as a useful run-time check that the assumption |
| is met, and documents the need to ensure that it is met by |
| reference to information outside the program. |
| |
| @node Pragma Assume_No_Invalid_Values,Pragma Async_Readers,Pragma Assume,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-assume-no-invalid-values}@anchor{29} |
| @section Pragma Assume_No_Invalid_Values |
| |
| |
| @geindex Invalid representations |
| |
| @geindex Invalid values |
| |
| Syntax: |
| |
| @example |
| pragma Assume_No_Invalid_Values (On | Off); |
| @end example |
| |
| This is a configuration pragma that controls the assumptions made by the |
| compiler about the occurrence of invalid representations (invalid values) |
| in the code. |
| |
| The default behavior (corresponding to an Off argument for this pragma), is |
| to assume that values may in general be invalid unless the compiler can |
| prove they are valid. Consider the following example: |
| |
| @example |
| V1 : Integer range 1 .. 10; |
| V2 : Integer range 11 .. 20; |
| ... |
| for J in V2 .. V1 loop |
| ... |
| end loop; |
| @end example |
| |
| if V1 and V2 have valid values, then the loop is known at compile |
| time not to execute since the lower bound must be greater than the |
| upper bound. However in default mode, no such assumption is made, |
| and the loop may execute. If @cite{Assume_No_Invalid_Values (On)} |
| is given, the compiler will assume that any occurrence of a variable |
| other than in an explicit @cite{'Valid} test always has a valid |
| value, and the loop above will be optimized away. |
| |
| The use of @cite{Assume_No_Invalid_Values (On)} is appropriate if |
| you know your code is free of uninitialized variables and other |
| possible sources of invalid representations, and may result in |
| more efficient code. A program that accesses an invalid representation |
| with this pragma in effect is erroneous, so no guarantees can be made |
| about its behavior. |
| |
| It is peculiar though permissible to use this pragma in conjunction |
| with validity checking (-gnatVa). In such cases, accessing invalid |
| values will generally give an exception, though formally the program |
| is erroneous so there are no guarantees that this will always be the |
| case, and it is recommended that these two options not be used together. |
| |
| @node Pragma Async_Readers,Pragma Async_Writers,Pragma Assume_No_Invalid_Values,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-async-readers}@anchor{2a} |
| @section Pragma Async_Readers |
| |
| |
| For the description of this pragma, see SPARK 2014 Reference Manual, |
| section 7.1.2. |
| |
| @node Pragma Async_Writers,Pragma Attribute_Definition,Pragma Async_Readers,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-async-writers}@anchor{2b} |
| @section Pragma Async_Writers |
| |
| |
| For the description of this pragma, see SPARK 2014 Reference Manual, |
| section 7.1.2. |
| |
| @node Pragma Attribute_Definition,Pragma C_Pass_By_Copy,Pragma Async_Writers,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-attribute-definition}@anchor{2c} |
| @section Pragma Attribute_Definition |
| |
| |
| Syntax: |
| |
| @example |
| pragma Attribute_Definition |
| ([Attribute =>] ATTRIBUTE_DESIGNATOR, |
| [Entity =>] LOCAL_NAME, |
| [Expression =>] EXPRESSION | NAME); |
| @end example |
| |
| If @cite{Attribute} is a known attribute name, this pragma is equivalent to |
| the attribute definition clause: |
| |
| @example |
| for Entity'Attribute use Expression; |
| @end example |
| |
| If @cite{Attribute} is not a recognized attribute name, the pragma is |
| ignored, and a warning is emitted. This allows source |
| code to be written that takes advantage of some new attribute, while remaining |
| compilable with earlier compilers. |
| |
| @node Pragma C_Pass_By_Copy,Pragma Check,Pragma Attribute_Definition,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-c-pass-by-copy}@anchor{2d} |
| @section Pragma C_Pass_By_Copy |
| |
| |
| @geindex Passing by copy |
| |
| Syntax: |
| |
| @example |
| pragma C_Pass_By_Copy |
| ([Max_Size =>] static_integer_EXPRESSION); |
| @end example |
| |
| Normally the default mechanism for passing C convention records to C |
| convention subprograms is to pass them by reference, as suggested by RM |
| B.3(69). Use the configuration pragma @cite{C_Pass_By_Copy} to change |
| this default, by requiring that record formal parameters be passed by |
| copy if all of the following conditions are met: |
| |
| |
| @itemize * |
| |
| @item |
| The size of the record type does not exceed the value specified for |
| @cite{Max_Size}. |
| |
| @item |
| The record type has @cite{Convention C}. |
| |
| @item |
| The formal parameter has this record type, and the subprogram has a |
| foreign (non-Ada) convention. |
| @end itemize |
| |
| If these conditions are met the argument is passed by copy; i.e., in a |
| manner consistent with what C expects if the corresponding formal in the |
| C prototype is a struct (rather than a pointer to a struct). |
| |
| You can also pass records by copy by specifying the convention |
| @cite{C_Pass_By_Copy} for the record type, or by using the extended |
| @cite{Import} and @cite{Export} pragmas, which allow specification of |
| passing mechanisms on a parameter by parameter basis. |
| |
| @node Pragma Check,Pragma Check_Float_Overflow,Pragma C_Pass_By_Copy,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-check}@anchor{2e} |
| @section Pragma Check |
| |
| |
| @geindex Assertions |
| |
| @geindex Named assertions |
| |
| Syntax: |
| |
| @example |
| pragma Check ( |
| [Name =>] CHECK_KIND, |
| [Check =>] Boolean_EXPRESSION |
| [, [Message =>] string_EXPRESSION] ); |
| |
| CHECK_KIND ::= IDENTIFIER | |
| Pre'Class | |
| Post'Class | |
| Type_Invariant'Class | |
| Invariant'Class |
| @end example |
| |
| This pragma is similar to the predefined pragma @cite{Assert} except that an |
| extra identifier argument is present. In conjunction with pragma |
| @cite{Check_Policy}, this can be used to define groups of assertions that can |
| be independently controlled. The identifier @cite{Assertion} is special, it |
| refers to the normal set of pragma @cite{Assert} statements. |
| |
| Checks introduced by this pragma are normally deactivated by default. They can |
| be activated either by the command line option @emph{-gnata}, which turns on |
| all checks, or individually controlled using pragma @cite{Check_Policy}. |
| |
| The identifiers @cite{Assertions} and @cite{Statement_Assertions} are not |
| permitted as check kinds, since this would cause confusion with the use |
| of these identifiers in @cite{Assertion_Policy} and @cite{Check_Policy} |
| pragmas, where they are used to refer to sets of assertions. |
| |
| @node Pragma Check_Float_Overflow,Pragma Check_Name,Pragma Check,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-check-float-overflow}@anchor{2f} |
| @section Pragma Check_Float_Overflow |
| |
| |
| @geindex Floating-point overflow |
| |
| Syntax: |
| |
| @example |
| pragma Check_Float_Overflow; |
| @end example |
| |
| In Ada, the predefined floating-point types (@cite{Short_Float}, |
| @cite{Float}, @cite{Long_Float}, @cite{Long_Long_Float}) are |
| defined to be @emph{unconstrained}. This means that even though each |
| has a well-defined base range, an operation that delivers a result |
| outside this base range is not required to raise an exception. |
| This implementation permission accommodates the notion |
| of infinities in IEEE floating-point, and corresponds to the |
| efficient execution mode on most machines. GNAT will not raise |
| overflow exceptions on these machines; instead it will generate |
| infinities and NaN's as defined in the IEEE standard. |
| |
| Generating infinities, although efficient, is not always desirable. |
| Often the preferable approach is to check for overflow, even at the |
| (perhaps considerable) expense of run-time performance. |
| This can be accomplished by defining your own constrained floating-point subtypes -- i.e., by supplying explicit |
| range constraints -- and indeed such a subtype |
| can have the same base range as its base type. For example: |
| |
| @example |
| subtype My_Float is Float range Float'Range; |
| @end example |
| |
| Here @cite{My_Float} has the same range as |
| @cite{Float} but is constrained, so operations on |
| @cite{My_Float} values will be checked for overflow |
| against this range. |
| |
| This style will achieve the desired goal, but |
| it is often more convenient to be able to simply use |
| the standard predefined floating-point types as long |
| as overflow checking could be guaranteed. |
| The @cite{Check_Float_Overflow} |
| configuration pragma achieves this effect. If a unit is compiled |
| subject to this configuration pragma, then all operations |
| on predefined floating-point types including operations on |
| base types of these floating-point types will be treated as |
| though those types were constrained, and overflow checks |
| will be generated. The @cite{Constraint_Error} |
| exception is raised if the result is out of range. |
| |
| This mode can also be set by use of the compiler |
| switch @emph{-gnateF}. |
| |
| @node Pragma Check_Name,Pragma Check_Policy,Pragma Check_Float_Overflow,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-check-name}@anchor{30} |
| @section Pragma Check_Name |
| |
| |
| @geindex Defining check names |
| |
| @geindex Check names |
| @geindex defining |
| |
| Syntax: |
| |
| @example |
| pragma Check_Name (check_name_IDENTIFIER); |
| @end example |
| |
| This is a configuration pragma that defines a new implementation |
| defined check name (unless IDENTIFIER matches one of the predefined |
| check names, in which case the pragma has no effect). Check names |
| are global to a partition, so if two or more configuration pragmas |
| are present in a partition mentioning the same name, only one new |
| check name is introduced. |
| |
| An implementation defined check name introduced with this pragma may |
| be used in only three contexts: @cite{pragma Suppress}, |
| @cite{pragma Unsuppress}, |
| and as the prefix of a @cite{Check_Name'Enabled} attribute reference. For |
| any of these three cases, the check name must be visible. A check |
| name is visible if it is in the configuration pragmas applying to |
| the current unit, or if it appears at the start of any unit that |
| is part of the dependency set of the current unit (e.g., units that |
| are mentioned in @cite{with} clauses). |
| |
| Check names introduced by this pragma are subject to control by compiler |
| switches (in particular -gnatp) in the usual manner. |
| |
| @node Pragma Check_Policy,Pragma CIL_Constructor,Pragma Check_Name,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-check-policy}@anchor{31} |
| @section Pragma Check_Policy |
| |
| |
| @geindex Controlling assertions |
| |
| @geindex Assertions |
| @geindex control |
| |
| @geindex Check pragma control |
| |
| @geindex Named assertions |
| |
| Syntax: |
| |
| @example |
| pragma Check_Policy |
| ([Name =>] CHECK_KIND, |
| [Policy =>] POLICY_IDENTIFIER); |
| |
| pragma Check_Policy ( |
| CHECK_KIND => POLICY_IDENTIFIER |
| @{, CHECK_KIND => POLICY_IDENTIFIER@}); |
| |
| ASSERTION_KIND ::= RM_ASSERTION_KIND | ID_ASSERTION_KIND |
| |
| CHECK_KIND ::= IDENTIFIER | |
| Pre'Class | |
| Post'Class | |
| Type_Invariant'Class | |
| Invariant'Class |
| |
| The identifiers Name and Policy are not allowed as CHECK_KIND values. This |
| avoids confusion between the two possible syntax forms for this pragma. |
| |
| POLICY_IDENTIFIER ::= ON | OFF | CHECK | DISABLE | IGNORE |
| @end example |
| |
| This pragma is used to set the checking policy for assertions (specified |
| by aspects or pragmas), the @cite{Debug} pragma, or additional checks |
| to be checked using the @cite{Check} pragma. It may appear either as |
| a configuration pragma, or within a declarative part of package. In the |
| latter case, it applies from the point where it appears to the end of |
| the declarative region (like pragma @cite{Suppress}). |
| |
| The @cite{Check_Policy} pragma is similar to the |
| predefined @cite{Assertion_Policy} pragma, |
| and if the check kind corresponds to one of the assertion kinds that |
| are allowed by @cite{Assertion_Policy}, then the effect is identical. |
| |
| If the first argument is Debug, then the policy applies to Debug pragmas, |
| disabling their effect if the policy is @cite{OFF}, @cite{DISABLE}, or |
| @cite{IGNORE}, and allowing them to execute with normal semantics if |
| the policy is @cite{ON} or @cite{CHECK}. In addition if the policy is |
| @cite{DISABLE}, then the procedure call in @cite{Debug} pragmas will |
| be totally ignored and not analyzed semantically. |
| |
| Finally the first argument may be some other identifier than the above |
| possibilities, in which case it controls a set of named assertions |
| that can be checked using pragma @cite{Check}. For example, if the pragma: |
| |
| @example |
| pragma Check_Policy (Critical_Error, OFF); |
| @end example |
| |
| is given, then subsequent @cite{Check} pragmas whose first argument is also |
| @cite{Critical_Error} will be disabled. |
| |
| The check policy is @cite{OFF} to turn off corresponding checks, and @cite{ON} |
| to turn on corresponding checks. The default for a set of checks for which no |
| @cite{Check_Policy} is given is @cite{OFF} unless the compiler switch |
| @emph{-gnata} is given, which turns on all checks by default. |
| |
| The check policy settings @cite{CHECK} and @cite{IGNORE} are recognized |
| as synonyms for @cite{ON} and @cite{OFF}. These synonyms are provided for |
| compatibility with the standard @cite{Assertion_Policy} pragma. The check |
| policy setting @cite{DISABLE} causes the second argument of a corresponding |
| @cite{Check} pragma to be completely ignored and not analyzed. |
| |
| @node Pragma CIL_Constructor,Pragma Comment,Pragma Check_Policy,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-cil-constructor}@anchor{32} |
| @section Pragma CIL_Constructor |
| |
| |
| Syntax: |
| |
| @example |
| pragma CIL_Constructor ([Entity =>] function_LOCAL_NAME); |
| @end example |
| |
| This pragma is used to assert that the specified Ada function should be |
| mapped to the .NET constructor for some Ada tagged record type. |
| |
| See section 4.1 of the |
| @cite{GNAT User's Guide: Supplement for the .NET Platform.} |
| for related information. |
| |
| @node Pragma Comment,Pragma Common_Object,Pragma CIL_Constructor,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-comment}@anchor{33} |
| @section Pragma Comment |
| |
| |
| Syntax: |
| |
| @example |
| pragma Comment (static_string_EXPRESSION); |
| @end example |
| |
| This is almost identical in effect to pragma @cite{Ident}. It allows the |
| placement of a comment into the object file and hence into the |
| executable file if the operating system permits such usage. The |
| difference is that @cite{Comment}, unlike @cite{Ident}, has |
| no limitations on placement of the pragma (it can be placed |
| anywhere in the main source unit), and if more than one pragma |
| is used, all comments are retained. |
| |
| @node Pragma Common_Object,Pragma Compile_Time_Error,Pragma Comment,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-common-object}@anchor{34} |
| @section Pragma Common_Object |
| |
| |
| Syntax: |
| |
| @example |
| pragma Common_Object ( |
| [Internal =>] LOCAL_NAME |
| [, [External =>] EXTERNAL_SYMBOL] |
| [, [Size =>] EXTERNAL_SYMBOL] ); |
| |
| EXTERNAL_SYMBOL ::= |
| IDENTIFIER |
| | static_string_EXPRESSION |
| @end example |
| |
| This pragma enables the shared use of variables stored in overlaid |
| linker areas corresponding to the use of @cite{COMMON} |
| in Fortran. The single |
| object @cite{LOCAL_NAME} is assigned to the area designated by |
| the @cite{External} argument. |
| You may define a record to correspond to a series |
| of fields. The @cite{Size} argument |
| is syntax checked in GNAT, but otherwise ignored. |
| |
| @cite{Common_Object} is not supported on all platforms. If no |
| support is available, then the code generator will issue a message |
| indicating that the necessary attribute for implementation of this |
| pragma is not available. |
| |
| @node Pragma Compile_Time_Error,Pragma Compile_Time_Warning,Pragma Common_Object,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-compile-time-error}@anchor{35} |
| @section Pragma Compile_Time_Error |
| |
| |
| Syntax: |
| |
| @example |
| pragma Compile_Time_Error |
| (boolean_EXPRESSION, static_string_EXPRESSION); |
| @end example |
| |
| This pragma can be used to generate additional compile time |
| error messages. It |
| is particularly useful in generics, where errors can be issued for |
| specific problematic instantiations. The first parameter is a boolean |
| expression. The pragma is effective only if the value of this expression |
| is known at compile time, and has the value True. The set of expressions |
| whose values are known at compile time includes all static boolean |
| expressions, and also other values which the compiler can determine |
| at compile time (e.g., the size of a record type set by an explicit |
| size representation clause, or the value of a variable which was |
| initialized to a constant and is known not to have been modified). |
| If these conditions are met, an error message is generated using |
| the value given as the second argument. This string value may contain |
| embedded ASCII.LF characters to break the message into multiple lines. |
| |
| @node Pragma Compile_Time_Warning,Pragma Compiler_Unit,Pragma Compile_Time_Error,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-compile-time-warning}@anchor{36} |
| @section Pragma Compile_Time_Warning |
| |
| |
| Syntax: |
| |
| @example |
| pragma Compile_Time_Warning |
| (boolean_EXPRESSION, static_string_EXPRESSION); |
| @end example |
| |
| Same as pragma Compile_Time_Error, except a warning is issued instead |
| of an error message. Note that if this pragma is used in a package that |
| is with'ed by a client, the client will get the warning even though it |
| is issued by a with'ed package (normally warnings in with'ed units are |
| suppressed, but this is a special exception to that rule). |
| |
| One typical use is within a generic where compile time known characteristics |
| of formal parameters are tested, and warnings given appropriately. Another use |
| with a first parameter of True is to warn a client about use of a package, |
| for example that it is not fully implemented. |
| |
| @node Pragma Compiler_Unit,Pragma Compiler_Unit_Warning,Pragma Compile_Time_Warning,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-compiler-unit}@anchor{37} |
| @section Pragma Compiler_Unit |
| |
| |
| Syntax: |
| |
| @example |
| pragma Compiler_Unit; |
| @end example |
| |
| This pragma is obsolete. It is equivalent to Compiler_Unit_Warning. It is |
| retained so that old versions of the GNAT run-time that use this pragma can |
| be compiled with newer versions of the compiler. |
| |
| @node Pragma Compiler_Unit_Warning,Pragma Complete_Representation,Pragma Compiler_Unit,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-compiler-unit-warning}@anchor{38} |
| @section Pragma Compiler_Unit_Warning |
| |
| |
| Syntax: |
| |
| @example |
| pragma Compiler_Unit_Warning; |
| @end example |
| |
| This pragma is intended only for internal use in the GNAT run-time library. |
| It indicates that the unit is used as part of the compiler build. The effect |
| is to generate warnings for the use of constructs (for example, conditional |
| expressions) that would cause trouble when bootstrapping using an older |
| version of GNAT. For the exact list of restrictions, see the compiler sources |
| and references to Check_Compiler_Unit. |
| |
| @node Pragma Complete_Representation,Pragma Complex_Representation,Pragma Compiler_Unit_Warning,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-complete-representation}@anchor{39} |
| @section Pragma Complete_Representation |
| |
| |
| Syntax: |
| |
| @example |
| pragma Complete_Representation; |
| @end example |
| |
| This pragma must appear immediately within a record representation |
| clause. Typical placements are before the first component clause |
| or after the last component clause. The effect is to give an error |
| message if any component is missing a component clause. This pragma |
| may be used to ensure that a record representation clause is |
| complete, and that this invariant is maintained if fields are |
| added to the record in the future. |
| |
| @node Pragma Complex_Representation,Pragma Component_Alignment,Pragma Complete_Representation,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-complex-representation}@anchor{3a} |
| @section Pragma Complex_Representation |
| |
| |
| Syntax: |
| |
| @example |
| pragma Complex_Representation |
| ([Entity =>] LOCAL_NAME); |
| @end example |
| |
| The @cite{Entity} argument must be the name of a record type which has |
| two fields of the same floating-point type. The effect of this pragma is |
| to force gcc to use the special internal complex representation form for |
| this record, which may be more efficient. Note that this may result in |
| the code for this type not conforming to standard ABI (application |
| binary interface) requirements for the handling of record types. For |
| example, in some environments, there is a requirement for passing |
| records by pointer, and the use of this pragma may result in passing |
| this type in floating-point registers. |
| |
| @node Pragma Component_Alignment,Pragma Contract_Cases,Pragma Complex_Representation,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-component-alignment}@anchor{3b} |
| @section Pragma Component_Alignment |
| |
| |
| @geindex Alignments of components |
| |
| @geindex Pragma Component_Alignment |
| |
| Syntax: |
| |
| @example |
| pragma Component_Alignment ( |
| [Form =>] ALIGNMENT_CHOICE |
| [, [Name =>] type_LOCAL_NAME]); |
| |
| ALIGNMENT_CHOICE ::= |
| Component_Size |
| | Component_Size_4 |
| | Storage_Unit |
| | Default |
| @end example |
| |
| Specifies the alignment of components in array or record types. |
| The meaning of the @cite{Form} argument is as follows: |
| |
| @quotation |
| |
| @geindex Component_Size (in pragma Component_Alignment) |
| @end quotation |
| |
| |
| @table @asis |
| |
| @item @emph{Component_Size} |
| |
| Aligns scalar components and subcomponents of the array or record type |
| on boundaries appropriate to their inherent size (naturally |
| aligned). For example, 1-byte components are aligned on byte boundaries, |
| 2-byte integer components are aligned on 2-byte boundaries, 4-byte |
| integer components are aligned on 4-byte boundaries and so on. These |
| alignment rules correspond to the normal rules for C compilers on all |
| machines except the VAX. |
| |
| @geindex Component_Size_4 (in pragma Component_Alignment) |
| |
| @item @emph{Component_Size_4} |
| |
| Naturally aligns components with a size of four or fewer |
| bytes. Components that are larger than 4 bytes are placed on the next |
| 4-byte boundary. |
| |
| @geindex Storage_Unit (in pragma Component_Alignment) |
| |
| @item @emph{Storage_Unit} |
| |
| Specifies that array or record components are byte aligned, i.e., |
| aligned on boundaries determined by the value of the constant |
| @cite{System.Storage_Unit}. |
| |
| @geindex Default (in pragma Component_Alignment) |
| |
| @item @emph{Default} |
| |
| Specifies that array or record components are aligned on default |
| boundaries, appropriate to the underlying hardware or operating system or |
| both. The @cite{Default} choice is the same as @cite{Component_Size} (natural |
| alignment). |
| @end table |
| |
| If the @cite{Name} parameter is present, @cite{type_LOCAL_NAME} must |
| refer to a local record or array type, and the specified alignment |
| choice applies to the specified type. The use of |
| @cite{Component_Alignment} together with a pragma @cite{Pack} causes the |
| @cite{Component_Alignment} pragma to be ignored. The use of |
| @cite{Component_Alignment} together with a record representation clause |
| is only effective for fields not specified by the representation clause. |
| |
| If the @cite{Name} parameter is absent, the pragma can be used as either |
| a configuration pragma, in which case it applies to one or more units in |
| accordance with the normal rules for configuration pragmas, or it can be |
| used within a declarative part, in which case it applies to types that |
| are declared within this declarative part, or within any nested scope |
| within this declarative part. In either case it specifies the alignment |
| to be applied to any record or array type which has otherwise standard |
| representation. |
| |
| If the alignment for a record or array type is not specified (using |
| pragma @cite{Pack}, pragma @cite{Component_Alignment}, or a record rep |
| clause), the GNAT uses the default alignment as described previously. |
| |
| @node Pragma Contract_Cases,Pragma Convention_Identifier,Pragma Component_Alignment,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-contract-cases}@anchor{3c} |
| @section Pragma Contract_Cases |
| |
| |
| @geindex Contract cases |
| |
| Syntax: |
| |
| @example |
| pragma Contract_Cases ( |
| Condition => Consequence |
| @{,Condition => Consequence@}); |
| @end example |
| |
| The @cite{Contract_Cases} pragma allows defining fine-grain specifications |
| that can complement or replace the contract given by a precondition and a |
| postcondition. Additionally, the @cite{Contract_Cases} pragma can be used |
| by testing and formal verification tools. The compiler checks its validity and, |
| depending on the assertion policy at the point of declaration of the pragma, |
| it may insert a check in the executable. For code generation, the contract |
| cases |
| |
| @example |
| pragma Contract_Cases ( |
| Cond1 => Pred1, |
| Cond2 => Pred2); |
| @end example |
| |
| are equivalent to |
| |
| @example |
| C1 : constant Boolean := Cond1; -- evaluated at subprogram entry |
| C2 : constant Boolean := Cond2; -- evaluated at subprogram entry |
| pragma Precondition ((C1 and not C2) or (C2 and not C1)); |
| pragma Postcondition (if C1 then Pred1); |
| pragma Postcondition (if C2 then Pred2); |
| @end example |
| |
| The precondition ensures that one and only one of the conditions is |
| satisfied on entry to the subprogram. |
| The postcondition ensures that for the condition that was True on entry, |
| the corrresponding consequence is True on exit. Other consequence expressions |
| are not evaluated. |
| |
| A precondition @cite{P} and postcondition @cite{Q} can also be |
| expressed as contract cases: |
| |
| @example |
| pragma Contract_Cases (P => Q); |
| @end example |
| |
| The placement and visibility rules for @cite{Contract_Cases} pragmas are |
| identical to those described for preconditions and postconditions. |
| |
| The compiler checks that boolean expressions given in conditions and |
| consequences are valid, where the rules for conditions are the same as |
| the rule for an expression in @cite{Precondition} and the rules for |
| consequences are the same as the rule for an expression in |
| @cite{Postcondition}. In particular, attributes @cite{'Old} and |
| @cite{'Result} can only be used within consequence expressions. |
| The condition for the last contract case may be @cite{others}, to denote |
| any case not captured by the previous cases. The |
| following is an example of use within a package spec: |
| |
| @example |
| package Math_Functions is |
| ... |
| function Sqrt (Arg : Float) return Float; |
| pragma Contract_Cases ((Arg in 0 .. 99) => Sqrt'Result < 10, |
| Arg >= 100 => Sqrt'Result >= 10, |
| others => Sqrt'Result = 0); |
| ... |
| end Math_Functions; |
| @end example |
| |
| The meaning of contract cases is that only one case should apply at each |
| call, as determined by the corresponding condition evaluating to True, |
| and that the consequence for this case should hold when the subprogram |
| returns. |
| |
| @node Pragma Convention_Identifier,Pragma CPP_Class,Pragma Contract_Cases,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-convention-identifier}@anchor{3d} |
| @section Pragma Convention_Identifier |
| |
| |
| @geindex Conventions |
| @geindex synonyms |
| |
| Syntax: |
| |
| @example |
| pragma Convention_Identifier ( |
| [Name =>] IDENTIFIER, |
| [Convention =>] convention_IDENTIFIER); |
| @end example |
| |
| This pragma provides a mechanism for supplying synonyms for existing |
| convention identifiers. The @cite{Name} identifier can subsequently |
| be used as a synonym for the given convention in other pragmas (including |
| for example pragma @cite{Import} or another @cite{Convention_Identifier} |
| pragma). As an example of the use of this, suppose you had legacy code |
| which used Fortran77 as the identifier for Fortran. Then the pragma: |
| |
| @example |
| pragma Convention_Identifier (Fortran77, Fortran); |
| @end example |
| |
| would allow the use of the convention identifier @cite{Fortran77} in |
| subsequent code, avoiding the need to modify the sources. As another |
| example, you could use this to parameterize convention requirements |
| according to systems. Suppose you needed to use @cite{Stdcall} on |
| windows systems, and @cite{C} on some other system, then you could |
| define a convention identifier @cite{Library} and use a single |
| @cite{Convention_Identifier} pragma to specify which convention |
| would be used system-wide. |
| |
| @node Pragma CPP_Class,Pragma CPP_Constructor,Pragma Convention_Identifier,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-cpp-class}@anchor{3e} |
| @section Pragma CPP_Class |
| |
| |
| @geindex Interfacing with C++ |
| |
| Syntax: |
| |
| @example |
| pragma CPP_Class ([Entity =>] LOCAL_NAME); |
| @end example |
| |
| The argument denotes an entity in the current declarative region that is |
| declared as a record type. It indicates that the type corresponds to an |
| externally declared C++ class type, and is to be laid out the same way |
| that C++ would lay out the type. If the C++ class has virtual primitives |
| then the record must be declared as a tagged record type. |
| |
| Types for which @cite{CPP_Class} is specified do not have assignment or |
| equality operators defined (such operations can be imported or declared |
| as subprograms as required). Initialization is allowed only by constructor |
| functions (see pragma @cite{CPP_Constructor}). Such types are implicitly |
| limited if not explicitly declared as limited or derived from a limited |
| type, and an error is issued in that case. |
| |
| See @ref{3f,,Interfacing to C++} for related information. |
| |
| Note: Pragma @cite{CPP_Class} is currently obsolete. It is supported |
| for backward compatibility but its functionality is available |
| using pragma @cite{Import} with @cite{Convention} = @cite{CPP}. |
| |
| @node Pragma CPP_Constructor,Pragma CPP_Virtual,Pragma CPP_Class,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-cpp-constructor}@anchor{40} |
| @section Pragma CPP_Constructor |
| |
| |
| @geindex Interfacing with C++ |
| |
| Syntax: |
| |
| @example |
| pragma CPP_Constructor ([Entity =>] LOCAL_NAME |
| [, [External_Name =>] static_string_EXPRESSION ] |
| [, [Link_Name =>] static_string_EXPRESSION ]); |
| @end example |
| |
| This pragma identifies an imported function (imported in the usual way |
| with pragma @cite{Import}) as corresponding to a C++ constructor. If |
| @cite{External_Name} and @cite{Link_Name} are not specified then the |
| @cite{Entity} argument is a name that must have been previously mentioned |
| in a pragma @cite{Import} with @cite{Convention} = @cite{CPP}. Such name |
| must be of one of the following forms: |
| |
| |
| @itemize * |
| |
| @item |
| @strong{function} @cite{Fname} @strong{return} T` |
| |
| @item |
| @strong{function} @cite{Fname} @strong{return} T'Class |
| |
| @item |
| @strong{function} @cite{Fname} (...) @strong{return} T` |
| |
| @item |
| @strong{function} @cite{Fname} (...) @strong{return} T'Class |
| @end itemize |
| |
| where @cite{T} is a limited record type imported from C++ with pragma |
| @cite{Import} and @cite{Convention} = @cite{CPP}. |
| |
| The first two forms import the default constructor, used when an object |
| of type @cite{T} is created on the Ada side with no explicit constructor. |
| The latter two forms cover all the non-default constructors of the type. |
| See the GNAT User's Guide for details. |
| |
| If no constructors are imported, it is impossible to create any objects |
| on the Ada side and the type is implicitly declared abstract. |
| |
| Pragma @cite{CPP_Constructor} is intended primarily for automatic generation |
| using an automatic binding generator tool (such as the @cite{-fdump-ada-spec} |
| GCC switch). |
| See @ref{3f,,Interfacing to C++} for more related information. |
| |
| Note: The use of functions returning class-wide types for constructors is |
| currently obsolete. They are supported for backward compatibility. The |
| use of functions returning the type T leave the Ada sources more clear |
| because the imported C++ constructors always return an object of type T; |
| that is, they never return an object whose type is a descendant of type T. |
| |
| @node Pragma CPP_Virtual,Pragma CPP_Vtable,Pragma CPP_Constructor,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-cpp-virtual}@anchor{41} |
| @section Pragma CPP_Virtual |
| |
| |
| @geindex Interfacing to C++ |
| |
| This pragma is now obsolete and, other than generating a warning if warnings |
| on obsolescent features are enabled, is completely ignored. |
| It is retained for compatibility |
| purposes. It used to be required to ensure compoatibility with C++, but |
| is no longer required for that purpose because GNAT generates |
| the same object layout as the G++ compiler by default. |
| |
| See @ref{3f,,Interfacing to C++} for related information. |
| |
| @node Pragma CPP_Vtable,Pragma CPU,Pragma CPP_Virtual,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-cpp-vtable}@anchor{42} |
| @section Pragma CPP_Vtable |
| |
| |
| @geindex Interfacing with C++ |
| |
| This pragma is now obsolete and, other than generating a warning if warnings |
| on obsolescent features are enabled, is completely ignored. |
| It used to be required to ensure compatibility with C++, but |
| is no longer required for that purpose because GNAT generates |
| the same object layout as the G++ compiler by default. |
| |
| See @ref{3f,,Interfacing to C++} for related information. |
| |
| @node Pragma CPU,Pragma Debug,Pragma CPP_Vtable,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-cpu}@anchor{43} |
| @section Pragma CPU |
| |
| |
| Syntax: |
| |
| @example |
| pragma CPU (EXPRESSION); |
| @end example |
| |
| This pragma is standard in Ada 2012, but is available in all earlier |
| versions of Ada as an implementation-defined pragma. |
| See Ada 2012 Reference Manual for details. |
| |
| @node Pragma Debug,Pragma Debug_Policy,Pragma CPU,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-debug}@anchor{44} |
| @section Pragma Debug |
| |
| |
| Syntax: |
| |
| @example |
| pragma Debug ([CONDITION, ]PROCEDURE_CALL_WITHOUT_SEMICOLON); |
| |
| PROCEDURE_CALL_WITHOUT_SEMICOLON ::= |
| PROCEDURE_NAME |
| | PROCEDURE_PREFIX ACTUAL_PARAMETER_PART |
| @end example |
| |
| The procedure call argument has the syntactic form of an expression, meeting |
| the syntactic requirements for pragmas. |
| |
| If debug pragmas are not enabled or if the condition is present and evaluates |
| to False, this pragma has no effect. If debug pragmas are enabled, the |
| semantics of the pragma is exactly equivalent to the procedure call statement |
| corresponding to the argument with a terminating semicolon. Pragmas are |
| permitted in sequences of declarations, so you can use pragma @cite{Debug} to |
| intersperse calls to debug procedures in the middle of declarations. Debug |
| pragmas can be enabled either by use of the command line switch @emph{-gnata} |
| or by use of the pragma @cite{Check_Policy} with a first argument of |
| @cite{Debug}. |
| |
| @node Pragma Debug_Policy,Pragma Default_Scalar_Storage_Order,Pragma Debug,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-debug-policy}@anchor{45} |
| @section Pragma Debug_Policy |
| |
| |
| Syntax: |
| |
| @example |
| pragma Debug_Policy (CHECK | DISABLE | IGNORE | ON | OFF); |
| @end example |
| |
| This pragma is equivalent to a corresponding @cite{Check_Policy} pragma |
| with a first argument of @cite{Debug}. It is retained for historical |
| compatibility reasons. |
| |
| @node Pragma Default_Scalar_Storage_Order,Pragma Default_Storage_Pool,Pragma Debug_Policy,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-default-scalar-storage-order}@anchor{46} |
| @section Pragma Default_Scalar_Storage_Order |
| |
| |
| @geindex Default_Scalar_Storage_Order |
| |
| @geindex Scalar_Storage_Order |
| |
| Syntax: |
| |
| @example |
| pragma Default_Scalar_Storage_Order (High_Order_First | Low_Order_First); |
| @end example |
| |
| Normally if no explicit @cite{Scalar_Storage_Order} is given for a record |
| type or array type, then the scalar storage order defaults to the ordinary |
| default for the target. But this default may be overridden using this pragma. |
| The pragma may appear as a configuration pragma, or locally within a package |
| spec or declarative part. In the latter case, it applies to all subsequent |
| types declared within that package spec or declarative part. |
| |
| The following example shows the use of this pragma: |
| |
| @example |
| pragma Default_Scalar_Storage_Order (High_Order_First); |
| with System; use System; |
| package DSSO1 is |
| type H1 is record |
| a : Integer; |
| end record; |
| |
| type L2 is record |
| a : Integer; |
| end record; |
| for L2'Scalar_Storage_Order use Low_Order_First; |
| |
| type L2a is new L2; |
| |
| package Inner is |
| type H3 is record |
| a : Integer; |
| end record; |
| |
| pragma Default_Scalar_Storage_Order (Low_Order_First); |
| |
| type L4 is record |
| a : Integer; |
| end record; |
| end Inner; |
| |
| type H4a is new Inner.L4; |
| |
| type H5 is record |
| a : Integer; |
| end record; |
| end DSSO1; |
| @end example |
| |
| In this example record types L.. have @cite{Low_Order_First} scalar |
| storage order, and record types H.. have @cite{High_Order_First}. |
| Note that in the case of @cite{H4a}, the order is not inherited |
| from the parent type. Only an explicitly set @cite{Scalar_Storage_Order} |
| gets inherited on type derivation. |
| |
| If this pragma is used as a configuration pragma which appears within a |
| configuration pragma file (as opposed to appearing explicitly at the start |
| of a single unit), then the binder will require that all units in a partition |
| be compiled in a similar manner, other than run-time units, which are not |
| affected by this pragma. Note that the use of this form is discouraged because |
| it may significantly degrade the run-time performance of the software, instead |
| the default scalar storage order ought to be changed only on a local basis. |
| |
| @node Pragma Default_Storage_Pool,Pragma Depends,Pragma Default_Scalar_Storage_Order,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-default-storage-pool}@anchor{47} |
| @section Pragma Default_Storage_Pool |
| |
| |
| @geindex Default_Storage_Pool |
| |
| Syntax: |
| |
| @example |
| pragma Default_Storage_Pool (storage_pool_NAME | null); |
| @end example |
| |
| This pragma is standard in Ada 2012, but is available in all earlier |
| versions of Ada as an implementation-defined pragma. |
| See Ada 2012 Reference Manual for details. |
| |
| @node Pragma Depends,Pragma Detect_Blocking,Pragma Default_Storage_Pool,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-depends}@anchor{48} |
| @section Pragma Depends |
| |
| |
| For the description of this pragma, see SPARK 2014 Reference Manual, |
| section 6.1.5. |
| |
| @node Pragma Detect_Blocking,Pragma Disable_Atomic_Synchronization,Pragma Depends,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-detect-blocking}@anchor{49} |
| @section Pragma Detect_Blocking |
| |
| |
| Syntax: |
| |
| @example |
| pragma Detect_Blocking; |
| @end example |
| |
| This is a standard pragma in Ada 2005, that is available in all earlier |
| versions of Ada as an implementation-defined pragma. |
| |
| This is a configuration pragma that forces the detection of potentially |
| blocking operations within a protected operation, and to raise Program_Error |
| if that happens. |
| |
| @node Pragma Disable_Atomic_Synchronization,Pragma Dispatching_Domain,Pragma Detect_Blocking,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-disable-atomic-synchronization}@anchor{4a} |
| @section Pragma Disable_Atomic_Synchronization |
| |
| |
| @geindex Atomic Synchronization |
| |
| Syntax: |
| |
| @example |
| pragma Disable_Atomic_Synchronization [(Entity)]; |
| @end example |
| |
| Ada requires that accesses (reads or writes) of an atomic variable be |
| regarded as synchronization points in the case of multiple tasks. |
| Particularly in the case of multi-processors this may require special |
| handling, e.g. the generation of memory barriers. This capability may |
| be turned off using this pragma in cases where it is known not to be |
| required. |
| |
| The placement and scope rules for this pragma are the same as those |
| for @cite{pragma Suppress}. In particular it can be used as a |
| configuration pragma, or in a declaration sequence where it applies |
| till the end of the scope. If an @cite{Entity} argument is present, |
| the action applies only to that entity. |
| |
| @node Pragma Dispatching_Domain,Pragma Effective_Reads,Pragma Disable_Atomic_Synchronization,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-dispatching-domain}@anchor{4b} |
| @section Pragma Dispatching_Domain |
| |
| |
| Syntax: |
| |
| @example |
| pragma Dispatching_Domain (EXPRESSION); |
| @end example |
| |
| This pragma is standard in Ada 2012, but is available in all earlier |
| versions of Ada as an implementation-defined pragma. |
| See Ada 2012 Reference Manual for details. |
| |
| @node Pragma Effective_Reads,Pragma Effective_Writes,Pragma Dispatching_Domain,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-effective-reads}@anchor{4c} |
| @section Pragma Effective_Reads |
| |
| |
| For the description of this pragma, see SPARK 2014 Reference Manual, |
| section 7.1.2. |
| |
| @node Pragma Effective_Writes,Pragma Elaboration_Checks,Pragma Effective_Reads,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-effective-writes}@anchor{4d} |
| @section Pragma Effective_Writes |
| |
| |
| For the description of this pragma, see SPARK 2014 Reference Manual, |
| section 7.1.2. |
| |
| @node Pragma Elaboration_Checks,Pragma Eliminate,Pragma Effective_Writes,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-elaboration-checks}@anchor{4e} |
| @section Pragma Elaboration_Checks |
| |
| |
| @geindex Elaboration control |
| |
| Syntax: |
| |
| @example |
| pragma Elaboration_Checks (Dynamic | Static); |
| @end example |
| |
| This is a configuration pragma that provides control over the |
| elaboration model used by the compilation affected by the |
| pragma. If the parameter is @cite{Dynamic}, |
| then the dynamic elaboration |
| model described in the Ada Reference Manual is used, as though |
| the @emph{-gnatE} switch had been specified on the command |
| line. If the parameter is @cite{Static}, then the default GNAT static |
| model is used. This configuration pragma overrides the setting |
| of the command line. For full details on the elaboration models |
| used by the GNAT compiler, see the chapter on elaboration order handling |
| in the @emph{GNAT User's Guide}. |
| |
| @node Pragma Eliminate,Pragma Enable_Atomic_Synchronization,Pragma Elaboration_Checks,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-eliminate}@anchor{4f} |
| @section Pragma Eliminate |
| |
| |
| @geindex Elimination of unused subprograms |
| |
| Syntax: |
| |
| @example |
| pragma Eliminate ([Entity =>] DEFINING_DESIGNATOR, |
| [Source_Location =>] STRING_LITERAL); |
| @end example |
| |
| The string literal given for the source location is a string which |
| specifies the line number of the occurrence of the entity, using |
| the syntax for SOURCE_TRACE given below: |
| |
| @example |
| SOURCE_TRACE ::= SOURCE_REFERENCE [LBRACKET SOURCE_TRACE RBRACKET] |
| |
| LBRACKET ::= [ |
| RBRACKET ::= ] |
| |
| SOURCE_REFERENCE ::= FILE_NAME : LINE_NUMBER |
| |
| LINE_NUMBER ::= DIGIT @{DIGIT@} |
| @end example |
| |
| Spaces around the colon in a @cite{Source_Reference} are optional. |
| |
| The @cite{DEFINING_DESIGNATOR} matches the defining designator used in an |
| explicit subprogram declaration, where the @cite{entity} name in this |
| designator appears on the source line specified by the source location. |
| |
| The source trace that is given as the @cite{Source_Location} shall obey the |
| following rules. The @cite{FILE_NAME} is the short name (with no directory |
| information) of an Ada source file, given using exactly the required syntax |
| for the underlying file system (e.g. case is important if the underlying |
| operating system is case sensitive). @cite{LINE_NUMBER} gives the line |
| number of the occurrence of the @cite{entity} |
| as a decimal literal without an exponent or point. If an @cite{entity} is not |
| declared in a generic instantiation (this includes generic subprogram |
| instances), the source trace includes only one source reference. If an entity |
| is declared inside a generic instantiation, its source trace (when parsing |
| from left to right) starts with the source location of the declaration of the |
| entity in the generic unit and ends with the source location of the |
| instantiation (it is given in square brackets). This approach is recursively |
| used in case of nested instantiations: the rightmost (nested most deeply in |
| square brackets) element of the source trace is the location of the outermost |
| instantiation, the next to left element is the location of the next (first |
| nested) instantiation in the code of the corresponding generic unit, and so |
| on, and the leftmost element (that is out of any square brackets) is the |
| location of the declaration of the entity to eliminate in a generic unit. |
| |
| Note that the @cite{Source_Location} argument specifies which of a set of |
| similarly named entities is being eliminated, dealing both with overloading, |
| and also appearance of the same entity name in different scopes. |
| |
| This pragma indicates that the given entity is not used in the program to be |
| compiled and built. The effect of the pragma is to allow the compiler to |
| eliminate the code or data associated with the named entity. Any reference to |
| an eliminated entity causes a compile-time or link-time error. |
| |
| The intention of pragma @cite{Eliminate} is to allow a program to be compiled |
| in a system-independent manner, with unused entities eliminated, without |
| needing to modify the source text. Normally the required set of |
| @cite{Eliminate} pragmas is constructed automatically using the gnatelim tool. |
| |
| Any source file change that removes, splits, or |
| adds lines may make the set of Eliminate pragmas invalid because their |
| @cite{Source_Location} argument values may get out of date. |
| |
| Pragma @cite{Eliminate} may be used where the referenced entity is a dispatching |
| operation. In this case all the subprograms to which the given operation can |
| dispatch are considered to be unused (are never called as a result of a direct |
| or a dispatching call). |
| |
| @node Pragma Enable_Atomic_Synchronization,Pragma Export_Function,Pragma Eliminate,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-enable-atomic-synchronization}@anchor{50} |
| @section Pragma Enable_Atomic_Synchronization |
| |
| |
| @geindex Atomic Synchronization |
| |
| Syntax: |
| |
| @example |
| pragma Enable_Atomic_Synchronization [(Entity)]; |
| @end example |
| |
| Ada requires that accesses (reads or writes) of an atomic variable be |
| regarded as synchronization points in the case of multiple tasks. |
| Particularly in the case of multi-processors this may require special |
| handling, e.g. the generation of memory barriers. This synchronization |
| is performed by default, but can be turned off using |
| @cite{pragma Disable_Atomic_Synchronization}. The |
| @cite{Enable_Atomic_Synchronization} pragma can be used to turn |
| it back on. |
| |
| The placement and scope rules for this pragma are the same as those |
| for @cite{pragma Unsuppress}. In particular it can be used as a |
| configuration pragma, or in a declaration sequence where it applies |
| till the end of the scope. If an @cite{Entity} argument is present, |
| the action applies only to that entity. |
| |
| @node Pragma Export_Function,Pragma Export_Object,Pragma Enable_Atomic_Synchronization,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-export-function}@anchor{51} |
| @section Pragma Export_Function |
| |
| |
| @geindex Argument passing mechanisms |
| |
| Syntax: |
| |
| @example |
| pragma Export_Function ( |
| [Internal =>] LOCAL_NAME |
| [, [External =>] EXTERNAL_SYMBOL] |
| [, [Parameter_Types =>] PARAMETER_TYPES] |
| [, [Result_Type =>] result_SUBTYPE_MARK] |
| [, [Mechanism =>] MECHANISM] |
| [, [Result_Mechanism =>] MECHANISM_NAME]); |
| |
| EXTERNAL_SYMBOL ::= |
| IDENTIFIER |
| | static_string_EXPRESSION |
| | "" |
| |
| PARAMETER_TYPES ::= |
| null |
| | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@} |
| |
| TYPE_DESIGNATOR ::= |
| subtype_NAME |
| | subtype_Name ' Access |
| |
| MECHANISM ::= |
| MECHANISM_NAME |
| | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@}) |
| |
| MECHANISM_ASSOCIATION ::= |
| [formal_parameter_NAME =>] MECHANISM_NAME |
| |
| MECHANISM_NAME ::= Value | Reference |
| @end example |
| |
| Use this pragma to make a function externally callable and optionally |
| provide information on mechanisms to be used for passing parameter and |
| result values. We recommend, for the purposes of improving portability, |
| this pragma always be used in conjunction with a separate pragma |
| @cite{Export}, which must precede the pragma @cite{Export_Function}. |
| GNAT does not require a separate pragma @cite{Export}, but if none is |
| present, @cite{Convention Ada} is assumed, which is usually |
| not what is wanted, so it is usually appropriate to use this |
| pragma in conjunction with a @cite{Export} or @cite{Convention} |
| pragma that specifies the desired foreign convention. |
| Pragma @cite{Export_Function} |
| (and @cite{Export}, if present) must appear in the same declarative |
| region as the function to which they apply. |
| |
| @cite{internal_name} must uniquely designate the function to which the |
| pragma applies. If more than one function name exists of this name in |
| the declarative part you must use the @cite{Parameter_Types} and |
| @cite{Result_Type} parameters is mandatory to achieve the required |
| unique designation. @cite{subtype_mark`s in these parameters must exactly match the subtypes in the corresponding function specification@comma{} using positional notation to match parameters with subtype marks. The form with an `'Access} attribute can be used to match an |
| anonymous access parameter. |
| |
| @geindex Suppressing external name |
| |
| Special treatment is given if the EXTERNAL is an explicit null |
| string or a static string expressions that evaluates to the null |
| string. In this case, no external name is generated. This form |
| still allows the specification of parameter mechanisms. |
| |
| @node Pragma Export_Object,Pragma Export_Procedure,Pragma Export_Function,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-export-object}@anchor{52} |
| @section Pragma Export_Object |
| |
| |
| Syntax: |
| |
| @example |
| pragma Export_Object |
| [Internal =>] LOCAL_NAME |
| [, [External =>] EXTERNAL_SYMBOL] |
| [, [Size =>] EXTERNAL_SYMBOL] |
| |
| EXTERNAL_SYMBOL ::= |
| IDENTIFIER |
| | static_string_EXPRESSION |
| @end example |
| |
| This pragma designates an object as exported, and apart from the |
| extended rules for external symbols, is identical in effect to the use of |
| the normal @cite{Export} pragma applied to an object. You may use a |
| separate Export pragma (and you probably should from the point of view |
| of portability), but it is not required. @cite{Size} is syntax checked, |
| but otherwise ignored by GNAT. |
| |
| @node Pragma Export_Procedure,Pragma Export_Value,Pragma Export_Object,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-export-procedure}@anchor{53} |
| @section Pragma Export_Procedure |
| |
| |
| Syntax: |
| |
| @example |
| pragma Export_Procedure ( |
| [Internal =>] LOCAL_NAME |
| [, [External =>] EXTERNAL_SYMBOL] |
| [, [Parameter_Types =>] PARAMETER_TYPES] |
| [, [Mechanism =>] MECHANISM]); |
| |
| EXTERNAL_SYMBOL ::= |
| IDENTIFIER |
| | static_string_EXPRESSION |
| | "" |
| |
| PARAMETER_TYPES ::= |
| null |
| | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@} |
| |
| TYPE_DESIGNATOR ::= |
| subtype_NAME |
| | subtype_Name ' Access |
| |
| MECHANISM ::= |
| MECHANISM_NAME |
| | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@}) |
| |
| MECHANISM_ASSOCIATION ::= |
| [formal_parameter_NAME =>] MECHANISM_NAME |
| |
| MECHANISM_NAME ::= Value | Reference |
| @end example |
| |
| This pragma is identical to @cite{Export_Function} except that it |
| applies to a procedure rather than a function and the parameters |
| @cite{Result_Type} and @cite{Result_Mechanism} are not permitted. |
| GNAT does not require a separate pragma @cite{Export}, but if none is |
| present, @cite{Convention Ada} is assumed, which is usually |
| not what is wanted, so it is usually appropriate to use this |
| pragma in conjunction with a @cite{Export} or @cite{Convention} |
| pragma that specifies the desired foreign convention. |
| |
| @geindex Suppressing external name |
| |
| Special treatment is given if the EXTERNAL is an explicit null |
| string or a static string expressions that evaluates to the null |
| string. In this case, no external name is generated. This form |
| still allows the specification of parameter mechanisms. |
| |
| @node Pragma Export_Value,Pragma Export_Valued_Procedure,Pragma Export_Procedure,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-export-value}@anchor{54} |
| @section Pragma Export_Value |
| |
| |
| Syntax: |
| |
| @example |
| pragma Export_Value ( |
| [Value =>] static_integer_EXPRESSION, |
| [Link_Name =>] static_string_EXPRESSION); |
| @end example |
| |
| This pragma serves to export a static integer value for external use. |
| The first argument specifies the value to be exported. The Link_Name |
| argument specifies the symbolic name to be associated with the integer |
| value. This pragma is useful for defining a named static value in Ada |
| that can be referenced in assembly language units to be linked with |
| the application. This pragma is currently supported only for the |
| AAMP target and is ignored for other targets. |
| |
| @node Pragma Export_Valued_Procedure,Pragma Extend_System,Pragma Export_Value,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-export-valued-procedure}@anchor{55} |
| @section Pragma Export_Valued_Procedure |
| |
| |
| Syntax: |
| |
| @example |
| pragma Export_Valued_Procedure ( |
| [Internal =>] LOCAL_NAME |
| [, [External =>] EXTERNAL_SYMBOL] |
| [, [Parameter_Types =>] PARAMETER_TYPES] |
| [, [Mechanism =>] MECHANISM]); |
| |
| EXTERNAL_SYMBOL ::= |
| IDENTIFIER |
| | static_string_EXPRESSION |
| | "" |
| |
| PARAMETER_TYPES ::= |
| null |
| | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@} |
| |
| TYPE_DESIGNATOR ::= |
| subtype_NAME |
| | subtype_Name ' Access |
| |
| MECHANISM ::= |
| MECHANISM_NAME |
| | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@}) |
| |
| MECHANISM_ASSOCIATION ::= |
| [formal_parameter_NAME =>] MECHANISM_NAME |
| |
| MECHANISM_NAME ::= Value | Reference |
| @end example |
| |
| This pragma is identical to @cite{Export_Procedure} except that the |
| first parameter of @cite{LOCAL_NAME}, which must be present, must be of |
| mode @cite{OUT}, and externally the subprogram is treated as a function |
| with this parameter as the result of the function. GNAT provides for |
| this capability to allow the use of @cite{OUT} and @cite{IN OUT} |
| parameters in interfacing to external functions (which are not permitted |
| in Ada functions). |
| GNAT does not require a separate pragma @cite{Export}, but if none is |
| present, @cite{Convention Ada} is assumed, which is almost certainly |
| not what is wanted since the whole point of this pragma is to interface |
| with foreign language functions, so it is usually appropriate to use this |
| pragma in conjunction with a @cite{Export} or @cite{Convention} |
| pragma that specifies the desired foreign convention. |
| |
| @geindex Suppressing external name |
| |
| Special treatment is given if the EXTERNAL is an explicit null |
| string or a static string expressions that evaluates to the null |
| string. In this case, no external name is generated. This form |
| still allows the specification of parameter mechanisms. |
| |
| @node Pragma Extend_System,Pragma Extensions_Allowed,Pragma Export_Valued_Procedure,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-extend-system}@anchor{56} |
| @section Pragma Extend_System |
| |
| |
| @geindex System |
| @geindex extending |
| |
| @geindex DEC Ada 83 |
| |
| Syntax: |
| |
| @example |
| pragma Extend_System ([Name =>] IDENTIFIER); |
| @end example |
| |
| This pragma is used to provide backwards compatibility with other |
| implementations that extend the facilities of package @cite{System}. In |
| GNAT, @cite{System} contains only the definitions that are present in |
| the Ada RM. However, other implementations, notably the DEC Ada 83 |
| implementation, provide many extensions to package @cite{System}. |
| |
| For each such implementation accommodated by this pragma, GNAT provides a |
| package @cite{Aux_`xxx`}, e.g., @cite{Aux_DEC} for the DEC Ada 83 |
| implementation, which provides the required additional definitions. You |
| can use this package in two ways. You can @cite{with} it in the normal |
| way and access entities either by selection or using a @cite{use} |
| clause. In this case no special processing is required. |
| |
| However, if existing code contains references such as |
| @cite{System.`xxx`} where @cite{xxx} is an entity in the extended |
| definitions provided in package @cite{System}, you may use this pragma |
| to extend visibility in @cite{System} in a non-standard way that |
| provides greater compatibility with the existing code. Pragma |
| @cite{Extend_System} is a configuration pragma whose single argument is |
| the name of the package containing the extended definition |
| (e.g., @cite{Aux_DEC} for the DEC Ada case). A unit compiled under |
| control of this pragma will be processed using special visibility |
| processing that looks in package @cite{System.Aux_`xxx`} where |
| @cite{Aux_`xxx`} is the pragma argument for any entity referenced in |
| package @cite{System}, but not found in package @cite{System}. |
| |
| You can use this pragma either to access a predefined @cite{System} |
| extension supplied with the compiler, for example @cite{Aux_DEC} or |
| you can construct your own extension unit following the above |
| definition. Note that such a package is a child of @cite{System} |
| and thus is considered part of the implementation. |
| To compile it you will have to use the @emph{-gnatg} switch |
| for compiling System units, as explained in the |
| GNAT User's Guide. |
| |
| @node Pragma Extensions_Allowed,Pragma External,Pragma Extend_System,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-extensions-allowed}@anchor{57} |
| @section Pragma Extensions_Allowed |
| |
| |
| @geindex Ada Extensions |
| |
| @geindex GNAT Extensions |
| |
| Syntax: |
| |
| @example |
| pragma Extensions_Allowed (On | Off); |
| @end example |
| |
| This configuration pragma enables or disables the implementation |
| extension mode (the use of Off as a parameter cancels the effect |
| of the @emph{-gnatX} command switch). |
| |
| In extension mode, the latest version of the Ada language is |
| implemented (currently Ada 2012), and in addition a small number |
| of GNAT specific extensions are recognized as follows: |
| |
| |
| @table @asis |
| |
| @item @emph{Constrained attribute for generic objects} |
| |
| The @cite{Constrained} attribute is permitted for objects of |
| generic types. The result indicates if the corresponding actual |
| is constrained. |
| @end table |
| |
| @node Pragma External,Pragma External_Name_Casing,Pragma Extensions_Allowed,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-external}@anchor{58} |
| @section Pragma External |
| |
| |
| Syntax: |
| |
| @example |
| pragma External ( |
| [ Convention =>] convention_IDENTIFIER, |
| [ Entity =>] LOCAL_NAME |
| [, [External_Name =>] static_string_EXPRESSION ] |
| [, [Link_Name =>] static_string_EXPRESSION ]); |
| @end example |
| |
| This pragma is identical in syntax and semantics to pragma |
| @cite{Export} as defined in the Ada Reference Manual. It is |
| provided for compatibility with some Ada 83 compilers that |
| used this pragma for exactly the same purposes as pragma |
| @cite{Export} before the latter was standardized. |
| |
| @node Pragma External_Name_Casing,Pragma Fast_Math,Pragma External,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-external-name-casing}@anchor{59} |
| @section Pragma External_Name_Casing |
| |
| |
| @geindex Dec Ada 83 casing compatibility |
| |
| @geindex External Names |
| @geindex casing |
| |
| @geindex Casing of External names |
| |
| Syntax: |
| |
| @example |
| pragma External_Name_Casing ( |
| Uppercase | Lowercase |
| [, Uppercase | Lowercase | As_Is]); |
| @end example |
| |
| This pragma provides control over the casing of external names associated |
| with Import and Export pragmas. There are two cases to consider: |
| |
| |
| @itemize * |
| |
| @item |
| Implicit external names |
| |
| Implicit external names are derived from identifiers. The most common case |
| arises when a standard Ada Import or Export pragma is used with only two |
| arguments, as in: |
| |
| @example |
| pragma Import (C, C_Routine); |
| @end example |
| |
| Since Ada is a case-insensitive language, the spelling of the identifier in |
| the Ada source program does not provide any information on the desired |
| casing of the external name, and so a convention is needed. In GNAT the |
| default treatment is that such names are converted to all lower case |
| letters. This corresponds to the normal C style in many environments. |
| The first argument of pragma @cite{External_Name_Casing} can be used to |
| control this treatment. If @cite{Uppercase} is specified, then the name |
| will be forced to all uppercase letters. If @cite{Lowercase} is specified, |
| then the normal default of all lower case letters will be used. |
| |
| This same implicit treatment is also used in the case of extended DEC Ada 83 |
| compatible Import and Export pragmas where an external name is explicitly |
| specified using an identifier rather than a string. |
| |
| @item |
| Explicit external names |
| |
| Explicit external names are given as string literals. The most common case |
| arises when a standard Ada Import or Export pragma is used with three |
| arguments, as in: |
| |
| @example |
| pragma Import (C, C_Routine, "C_routine"); |
| @end example |
| |
| In this case, the string literal normally provides the exact casing required |
| for the external name. The second argument of pragma |
| @cite{External_Name_Casing} may be used to modify this behavior. |
| If @cite{Uppercase} is specified, then the name |
| will be forced to all uppercase letters. If @cite{Lowercase} is specified, |
| then the name will be forced to all lowercase letters. A specification of |
| @cite{As_Is} provides the normal default behavior in which the casing is |
| taken from the string provided. |
| @end itemize |
| |
| This pragma may appear anywhere that a pragma is valid. In particular, it |
| can be used as a configuration pragma in the @code{gnat.adc} file, in which |
| case it applies to all subsequent compilations, or it can be used as a program |
| unit pragma, in which case it only applies to the current unit, or it can |
| be used more locally to control individual Import/Export pragmas. |
| |
| It was primarily intended for use with OpenVMS systems, where many |
| compilers convert all symbols to upper case by default. For interfacing to |
| such compilers (e.g., the DEC C compiler), it may be convenient to use |
| the pragma: |
| |
| @example |
| pragma External_Name_Casing (Uppercase, Uppercase); |
| @end example |
| |
| to enforce the upper casing of all external symbols. |
| |
| @node Pragma Fast_Math,Pragma Favor_Top_Level,Pragma External_Name_Casing,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-fast-math}@anchor{5a} |
| @section Pragma Fast_Math |
| |
| |
| Syntax: |
| |
| @example |
| pragma Fast_Math; |
| @end example |
| |
| This is a configuration pragma which activates a mode in which speed is |
| considered more important for floating-point operations than absolutely |
| accurate adherence to the requirements of the standard. Currently the |
| following operations are affected: |
| |
| |
| @table @asis |
| |
| @item @emph{Complex Multiplication} |
| |
| The normal simple formula for complex multiplication can result in intermediate |
| overflows for numbers near the end of the range. The Ada standard requires that |
| this situation be detected and corrected by scaling, but in Fast_Math mode such |
| cases will simply result in overflow. Note that to take advantage of this you |
| must instantiate your own version of @cite{Ada.Numerics.Generic_Complex_Types} |
| under control of the pragma, rather than use the preinstantiated versions. |
| @end table |
| |
| @node Pragma Favor_Top_Level,Pragma Finalize_Storage_Only,Pragma Fast_Math,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-favor-top-level}@anchor{5b} |
| @section Pragma Favor_Top_Level |
| |
| |
| Syntax: |
| |
| @example |
| pragma Favor_Top_Level (type_NAME); |
| @end example |
| |
| The named type must be an access-to-subprogram type. This pragma is an |
| efficiency hint to the compiler, regarding the use of 'Access or |
| 'Unrestricted_Access on nested (non-library-level) subprograms. The |
| pragma means that nested subprograms are not used with this type, or |
| are rare, so that the generated code should be efficient in the |
| top-level case. When this pragma is used, dynamically generated |
| trampolines may be used on some targets for nested subprograms. |
| See also the No_Implicit_Dynamic_Code restriction. |
| |
| @node Pragma Finalize_Storage_Only,Pragma Float_Representation,Pragma Favor_Top_Level,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-finalize-storage-only}@anchor{5c} |
| @section Pragma Finalize_Storage_Only |
| |
| |
| Syntax: |
| |
| @example |
| pragma Finalize_Storage_Only (first_subtype_LOCAL_NAME); |
| @end example |
| |
| This pragma allows the compiler not to emit a Finalize call for objects |
| defined at the library level. This is mostly useful for types where |
| finalization is only used to deal with storage reclamation since in most |
| environments it is not necessary to reclaim memory just before terminating |
| execution, hence the name. |
| |
| @node Pragma Float_Representation,Pragma Global,Pragma Finalize_Storage_Only,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-float-representation}@anchor{5d} |
| @section Pragma Float_Representation |
| |
| |
| Syntax: |
| |
| @example |
| pragma Float_Representation (FLOAT_REP[, float_type_LOCAL_NAME]); |
| |
| FLOAT_REP ::= VAX_Float | IEEE_Float |
| @end example |
| |
| In the one argument form, this pragma is a configuration pragma which |
| allows control over the internal representation chosen for the predefined |
| floating point types declared in the packages @cite{Standard} and |
| @cite{System}. This pragma is only provided for compatibility and has no effect. |
| |
| The two argument form specifies the representation to be used for |
| the specified floating-point type. The argument must |
| be @cite{IEEE_Float} to specify the use of IEEE format, as follows: |
| |
| |
| @itemize * |
| |
| @item |
| For a digits value of 6, 32-bit IEEE short format will be used. |
| |
| @item |
| For a digits value of 15, 64-bit IEEE long format will be used. |
| |
| @item |
| No other value of digits is permitted. |
| @end itemize |
| |
| @node Pragma Global,Pragma Ident,Pragma Float_Representation,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-global}@anchor{5e} |
| @section Pragma Global |
| |
| |
| For the description of this pragma, see SPARK 2014 Reference Manual, |
| section 6.1.4. |
| |
| @node Pragma Ident,Pragma Ignore_Pragma,Pragma Global,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-ident}@anchor{5f} |
| @section Pragma Ident |
| |
| |
| Syntax: |
| |
| @example |
| pragma Ident (static_string_EXPRESSION); |
| @end example |
| |
| This pragma is identical in effect to pragma @cite{Comment}. It is provided |
| for compatibility with other Ada compilers providing this pragma. |
| |
| @node Pragma Ignore_Pragma,Pragma Implementation_Defined,Pragma Ident,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-ignore-pragma}@anchor{60} |
| @section Pragma Ignore_Pragma |
| |
| |
| Syntax: |
| |
| @example |
| pragma Ignore_Pragma (pragma_IDENTIFIER); |
| @end example |
| |
| This is a configuration pragma |
| that takes a single argument that is a simple identifier. Any subsequent |
| use of a pragma whose pragma identifier matches this argument will be |
| silently ignored. This may be useful when legacy code or code intended |
| for compilation with some other compiler contains pragmas that match the |
| name, but not the exact implementation, of a @cite{GNAT} pragma. The use of this |
| pragma allows such pragmas to be ignored, which may be useful in @cite{CodePeer} |
| mode, or during porting of legacy code. |
| |
| @node Pragma Implementation_Defined,Pragma Implemented,Pragma Ignore_Pragma,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-implementation-defined}@anchor{61} |
| @section Pragma Implementation_Defined |
| |
| |
| Syntax: |
| |
| @example |
| pragma Implementation_Defined (local_NAME); |
| @end example |
| |
| This pragma marks a previously declared entioty as implementation-defined. |
| For an overloaded entity, applies to the most recent homonym. |
| |
| @example |
| pragma Implementation_Defined; |
| @end example |
| |
| The form with no arguments appears anywhere within a scope, most |
| typically a package spec, and indicates that all entities that are |
| defined within the package spec are Implementation_Defined. |
| |
| This pragma is used within the GNAT runtime library to identify |
| implementation-defined entities introduced in language-defined units, |
| for the purpose of implementing the No_Implementation_Identifiers |
| restriction. |
| |
| @node Pragma Implemented,Pragma Implicit_Packing,Pragma Implementation_Defined,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-implemented}@anchor{62} |
| @section Pragma Implemented |
| |
| |
| Syntax: |
| |
| @example |
| pragma Implemented (procedure_LOCAL_NAME, implementation_kind); |
| |
| implementation_kind ::= By_Entry | By_Protected_Procedure | By_Any |
| @end example |
| |
| This is an Ada 2012 representation pragma which applies to protected, task |
| and synchronized interface primitives. The use of pragma Implemented provides |
| a way to impose a static requirement on the overriding operation by adhering |
| to one of the three implementation kinds: entry, protected procedure or any of |
| the above. This pragma is available in all earlier versions of Ada as an |
| implementation-defined pragma. |
| |
| @example |
| type Synch_Iface is synchronized interface; |
| procedure Prim_Op (Obj : in out Iface) is abstract; |
| pragma Implemented (Prim_Op, By_Protected_Procedure); |
| |
| protected type Prot_1 is new Synch_Iface with |
| procedure Prim_Op; -- Legal |
| end Prot_1; |
| |
| protected type Prot_2 is new Synch_Iface with |
| entry Prim_Op; -- Illegal |
| end Prot_2; |
| |
| task type Task_Typ is new Synch_Iface with |
| entry Prim_Op; -- Illegal |
| end Task_Typ; |
| @end example |
| |
| When applied to the procedure_or_entry_NAME of a requeue statement, pragma |
| Implemented determines the runtime behavior of the requeue. Implementation kind |
| By_Entry guarantees that the action of requeueing will proceed from an entry to |
| another entry. Implementation kind By_Protected_Procedure transforms the |
| requeue into a dispatching call, thus eliminating the chance of blocking. Kind |
| By_Any shares the behavior of By_Entry and By_Protected_Procedure depending on |
| the target's overriding subprogram kind. |
| |
| @node Pragma Implicit_Packing,Pragma Import_Function,Pragma Implemented,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-implicit-packing}@anchor{63} |
| @section Pragma Implicit_Packing |
| |
| |
| @geindex Rational Profile |
| |
| Syntax: |
| |
| @example |
| pragma Implicit_Packing; |
| @end example |
| |
| This is a configuration pragma that requests implicit packing for packed |
| arrays for which a size clause is given but no explicit pragma Pack or |
| specification of Component_Size is present. It also applies to records |
| where no record representation clause is present. Consider this example: |
| |
| @example |
| type R is array (0 .. 7) of Boolean; |
| for R'Size use 8; |
| @end example |
| |
| In accordance with the recommendation in the RM (RM 13.3(53)), a Size clause |
| does not change the layout of a composite object. So the Size clause in the |
| above example is normally rejected, since the default layout of the array uses |
| 8-bit components, and thus the array requires a minimum of 64 bits. |
| |
| If this declaration is compiled in a region of code covered by an occurrence |
| of the configuration pragma Implicit_Packing, then the Size clause in this |
| and similar examples will cause implicit packing and thus be accepted. For |
| this implicit packing to occur, the type in question must be an array of small |
| components whose size is known at compile time, and the Size clause must |
| specify the exact size that corresponds to the number of elements in the array |
| multiplied by the size in bits of the component type (both single and |
| multi-dimensioned arrays can be controlled with this pragma). |
| |
| @geindex Array packing |
| |
| Similarly, the following example shows the use in the record case |
| |
| @example |
| type r is record |
| a, b, c, d, e, f, g, h : boolean; |
| chr : character; |
| end record; |
| for r'size use 16; |
| @end example |
| |
| Without a pragma Pack, each Boolean field requires 8 bits, so the |
| minimum size is 72 bits, but with a pragma Pack, 16 bits would be |
| sufficient. The use of pragma Implicit_Packing allows this record |
| declaration to compile without an explicit pragma Pack. |
| |
| @node Pragma Import_Function,Pragma Import_Object,Pragma Implicit_Packing,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-import-function}@anchor{64} |
| @section Pragma Import_Function |
| |
| |
| Syntax: |
| |
| @example |
| pragma Import_Function ( |
| [Internal =>] LOCAL_NAME, |
| [, [External =>] EXTERNAL_SYMBOL] |
| [, [Parameter_Types =>] PARAMETER_TYPES] |
| [, [Result_Type =>] SUBTYPE_MARK] |
| [, [Mechanism =>] MECHANISM] |
| [, [Result_Mechanism =>] MECHANISM_NAME]); |
| |
| EXTERNAL_SYMBOL ::= |
| IDENTIFIER |
| | static_string_EXPRESSION |
| |
| PARAMETER_TYPES ::= |
| null |
| | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@} |
| |
| TYPE_DESIGNATOR ::= |
| subtype_NAME |
| | subtype_Name ' Access |
| |
| MECHANISM ::= |
| MECHANISM_NAME |
| | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@}) |
| |
| MECHANISM_ASSOCIATION ::= |
| [formal_parameter_NAME =>] MECHANISM_NAME |
| |
| MECHANISM_NAME ::= |
| Value |
| | Reference |
| @end example |
| |
| This pragma is used in conjunction with a pragma @cite{Import} to |
| specify additional information for an imported function. The pragma |
| @cite{Import} (or equivalent pragma @cite{Interface}) must precede the |
| @cite{Import_Function} pragma and both must appear in the same |
| declarative part as the function specification. |
| |
| The @cite{Internal} argument must uniquely designate |
| the function to which the |
| pragma applies. If more than one function name exists of this name in |
| the declarative part you must use the @cite{Parameter_Types} and |
| @cite{Result_Type} parameters to achieve the required unique |
| designation. Subtype marks in these parameters must exactly match the |
| subtypes in the corresponding function specification, using positional |
| notation to match parameters with subtype marks. |
| The form with an @cite{'Access} attribute can be used to match an |
| anonymous access parameter. |
| |
| You may optionally use the @cite{Mechanism} and @cite{Result_Mechanism} |
| parameters to specify passing mechanisms for the |
| parameters and result. If you specify a single mechanism name, it |
| applies to all parameters. Otherwise you may specify a mechanism on a |
| parameter by parameter basis using either positional or named |
| notation. If the mechanism is not specified, the default mechanism |
| is used. |
| |
| @node Pragma Import_Object,Pragma Import_Procedure,Pragma Import_Function,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-import-object}@anchor{65} |
| @section Pragma Import_Object |
| |
| |
| Syntax: |
| |
| @example |
| pragma Import_Object |
| [Internal =>] LOCAL_NAME |
| [, [External =>] EXTERNAL_SYMBOL] |
| [, [Size =>] EXTERNAL_SYMBOL]); |
| |
| EXTERNAL_SYMBOL ::= |
| IDENTIFIER |
| | static_string_EXPRESSION |
| @end example |
| |
| This pragma designates an object as imported, and apart from the |
| extended rules for external symbols, is identical in effect to the use of |
| the normal @cite{Import} pragma applied to an object. Unlike the |
| subprogram case, you need not use a separate @cite{Import} pragma, |
| although you may do so (and probably should do so from a portability |
| point of view). @cite{size} is syntax checked, but otherwise ignored by |
| GNAT. |
| |
| @node Pragma Import_Procedure,Pragma Import_Valued_Procedure,Pragma Import_Object,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-import-procedure}@anchor{66} |
| @section Pragma Import_Procedure |
| |
| |
| Syntax: |
| |
| @example |
| pragma Import_Procedure ( |
| [Internal =>] LOCAL_NAME |
| [, [External =>] EXTERNAL_SYMBOL] |
| [, [Parameter_Types =>] PARAMETER_TYPES] |
| [, [Mechanism =>] MECHANISM]); |
| |
| EXTERNAL_SYMBOL ::= |
| IDENTIFIER |
| | static_string_EXPRESSION |
| |
| PARAMETER_TYPES ::= |
| null |
| | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@} |
| |
| TYPE_DESIGNATOR ::= |
| subtype_NAME |
| | subtype_Name ' Access |
| |
| MECHANISM ::= |
| MECHANISM_NAME |
| | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@}) |
| |
| MECHANISM_ASSOCIATION ::= |
| [formal_parameter_NAME =>] MECHANISM_NAME |
| |
| MECHANISM_NAME ::= Value | Reference |
| @end example |
| |
| This pragma is identical to @cite{Import_Function} except that it |
| applies to a procedure rather than a function and the parameters |
| @cite{Result_Type} and @cite{Result_Mechanism} are not permitted. |
| |
| @node Pragma Import_Valued_Procedure,Pragma Independent,Pragma Import_Procedure,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-import-valued-procedure}@anchor{67} |
| @section Pragma Import_Valued_Procedure |
| |
| |
| Syntax: |
| |
| @example |
| pragma Import_Valued_Procedure ( |
| [Internal =>] LOCAL_NAME |
| [, [External =>] EXTERNAL_SYMBOL] |
| [, [Parameter_Types =>] PARAMETER_TYPES] |
| [, [Mechanism =>] MECHANISM]); |
| |
| EXTERNAL_SYMBOL ::= |
| IDENTIFIER |
| | static_string_EXPRESSION |
| |
| PARAMETER_TYPES ::= |
| null |
| | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@} |
| |
| TYPE_DESIGNATOR ::= |
| subtype_NAME |
| | subtype_Name ' Access |
| |
| MECHANISM ::= |
| MECHANISM_NAME |
| | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@}) |
| |
| MECHANISM_ASSOCIATION ::= |
| [formal_parameter_NAME =>] MECHANISM_NAME |
| |
| MECHANISM_NAME ::= Value | Reference |
| @end example |
| |
| This pragma is identical to @cite{Import_Procedure} except that the |
| first parameter of @cite{LOCAL_NAME}, which must be present, must be of |
| mode @cite{OUT}, and externally the subprogram is treated as a function |
| with this parameter as the result of the function. The purpose of this |
| capability is to allow the use of @cite{OUT} and @cite{IN OUT} |
| parameters in interfacing to external functions (which are not permitted |
| in Ada functions). You may optionally use the @cite{Mechanism} |
| parameters to specify passing mechanisms for the parameters. |
| If you specify a single mechanism name, it applies to all parameters. |
| Otherwise you may specify a mechanism on a parameter by parameter |
| basis using either positional or named notation. If the mechanism is not |
| specified, the default mechanism is used. |
| |
| Note that it is important to use this pragma in conjunction with a separate |
| pragma Import that specifies the desired convention, since otherwise the |
| default convention is Ada, which is almost certainly not what is required. |
| |
| @node Pragma Independent,Pragma Independent_Components,Pragma Import_Valued_Procedure,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-independent}@anchor{68} |
| @section Pragma Independent |
| |
| |
| Syntax: |
| |
| @example |
| pragma Independent (Local_NAME); |
| @end example |
| |
| This pragma is standard in Ada 2012 mode (which also provides an aspect |
| of the same name). It is also available as an implementation-defined |
| pragma in all earlier versions. It specifies that the |
| designated object or all objects of the designated type must be |
| independently addressable. This means that separate tasks can safely |
| manipulate such objects. For example, if two components of a record are |
| independent, then two separate tasks may access these two components. |
| This may place |
| constraints on the representation of the object (for instance prohibiting |
| tight packing). |
| |
| @node Pragma Independent_Components,Pragma Initial_Condition,Pragma Independent,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-independent-components}@anchor{69} |
| @section Pragma Independent_Components |
| |
| |
| Syntax: |
| |
| @example |
| pragma Independent_Components (Local_NAME); |
| @end example |
| |
| This pragma is standard in Ada 2012 mode (which also provides an aspect |
| of the same name). It is also available as an implementation-defined |
| pragma in all earlier versions. It specifies that the components of the |
| designated object, or the components of each object of the designated |
| type, must be |
| independently addressable. This means that separate tasks can safely |
| manipulate separate components in the composite object. This may place |
| constraints on the representation of the object (for instance prohibiting |
| tight packing). |
| |
| @node Pragma Initial_Condition,Pragma Initialize_Scalars,Pragma Independent_Components,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-initial-condition}@anchor{6a} |
| @section Pragma Initial_Condition |
| |
| |
| For the description of this pragma, see SPARK 2014 Reference Manual, |
| section 7.1.6. |
| |
| @node Pragma Initialize_Scalars,Pragma Initializes,Pragma Initial_Condition,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-initialize-scalars}@anchor{6b} |
| @section Pragma Initialize_Scalars |
| |
| |
| @geindex debugging with Initialize_Scalars |
| |
| Syntax: |
| |
| @example |
| pragma Initialize_Scalars; |
| @end example |
| |
| This pragma is similar to @cite{Normalize_Scalars} conceptually but has |
| two important differences. First, there is no requirement for the pragma |
| to be used uniformly in all units of a partition, in particular, it is fine |
| to use this just for some or all of the application units of a partition, |
| without needing to recompile the run-time library. |
| |
| In the case where some units are compiled with the pragma, and some without, |
| then a declaration of a variable where the type is defined in package |
| Standard or is locally declared will always be subject to initialization, |
| as will any declaration of a scalar variable. For composite variables, |
| whether the variable is initialized may also depend on whether the package |
| in which the type of the variable is declared is compiled with the pragma. |
| |
| The other important difference is that you can control the value used |
| for initializing scalar objects. At bind time, you can select several |
| options for initialization. You can |
| initialize with invalid values (similar to Normalize_Scalars, though for |
| Initialize_Scalars it is not always possible to determine the invalid |
| values in complex cases like signed component fields with non-standard |
| sizes). You can also initialize with high or |
| low values, or with a specified bit pattern. See the GNAT |
| User's Guide for binder options for specifying these cases. |
| |
| This means that you can compile a program, and then without having to |
| recompile the program, you can run it with different values being used |
| for initializing otherwise uninitialized values, to test if your program |
| behavior depends on the choice. Of course the behavior should not change, |
| and if it does, then most likely you have an incorrect reference to an |
| uninitialized value. |
| |
| It is even possible to change the value at execution time eliminating even |
| the need to rebind with a different switch using an environment variable. |
| See the GNAT User's Guide for details. |
| |
| Note that pragma @cite{Initialize_Scalars} is particularly useful in |
| conjunction with the enhanced validity checking that is now provided |
| in GNAT, which checks for invalid values under more conditions. |
| Using this feature (see description of the @emph{-gnatV} flag in the |
| GNAT User's Guide) in conjunction with |
| pragma @cite{Initialize_Scalars} |
| provides a powerful new tool to assist in the detection of problems |
| caused by uninitialized variables. |
| |
| Note: the use of @cite{Initialize_Scalars} has a fairly extensive |
| effect on the generated code. This may cause your code to be |
| substantially larger. It may also cause an increase in the amount |
| of stack required, so it is probably a good idea to turn on stack |
| checking (see description of stack checking in the GNAT |
| User's Guide) when using this pragma. |
| |
| @node Pragma Initializes,Pragma Inline_Always,Pragma Initialize_Scalars,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-initializes}@anchor{6c} |
| @section Pragma Initializes |
| |
| |
| For the description of this pragma, see SPARK 2014 Reference Manual, |
| section 7.1.5. |
| |
| @node Pragma Inline_Always,Pragma Inline_Generic,Pragma Initializes,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-inline-always}@anchor{6d} |
| @section Pragma Inline_Always |
| |
| |
| Syntax: |
| |
| @example |
| pragma Inline_Always (NAME [, NAME]); |
| @end example |
| |
| Similar to pragma @cite{Inline} except that inlining is not subject to |
| the use of option @emph{-gnatn} or @emph{-gnatN} and the inlining |
| happens regardless of whether these options are used. |
| |
| @node Pragma Inline_Generic,Pragma Interface,Pragma Inline_Always,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-inline-generic}@anchor{6e} |
| @section Pragma Inline_Generic |
| |
| |
| Syntax: |
| |
| @example |
| pragma Inline_Generic (GNAME @{, GNAME@}); |
| |
| GNAME ::= generic_unit_NAME | generic_instance_NAME |
| @end example |
| |
| This pragma is provided for compatibility with Dec Ada 83. It has |
| no effect in @cite{GNAT} (which always inlines generics), other |
| than to check that the given names are all names of generic units or |
| generic instances. |
| |
| @node Pragma Interface,Pragma Interface_Name,Pragma Inline_Generic,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-interface}@anchor{6f} |
| @section Pragma Interface |
| |
| |
| Syntax: |
| |
| @example |
| pragma Interface ( |
| [Convention =>] convention_identifier, |
| [Entity =>] local_NAME |
| [, [External_Name =>] static_string_expression] |
| [, [Link_Name =>] static_string_expression]); |
| @end example |
| |
| This pragma is identical in syntax and semantics to |
| the standard Ada pragma @cite{Import}. It is provided for compatibility |
| with Ada 83. The definition is upwards compatible both with pragma |
| @cite{Interface} as defined in the Ada 83 Reference Manual, and also |
| with some extended implementations of this pragma in certain Ada 83 |
| implementations. The only difference between pragma @cite{Interface} |
| and pragma @cite{Import} is that there is special circuitry to allow |
| both pragmas to appear for the same subprogram entity (normally it |
| is illegal to have multiple @cite{Import} pragmas. This is useful in |
| maintaining Ada 83/Ada 95 compatibility and is compatible with other |
| Ada 83 compilers. |
| |
| @node Pragma Interface_Name,Pragma Interrupt_Handler,Pragma Interface,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-interface-name}@anchor{70} |
| @section Pragma Interface_Name |
| |
| |
| Syntax: |
| |
| @example |
| pragma Interface_Name ( |
| [Entity =>] LOCAL_NAME |
| [, [External_Name =>] static_string_EXPRESSION] |
| [, [Link_Name =>] static_string_EXPRESSION]); |
| @end example |
| |
| This pragma provides an alternative way of specifying the interface name |
| for an interfaced subprogram, and is provided for compatibility with Ada |
| 83 compilers that use the pragma for this purpose. You must provide at |
| least one of @cite{External_Name} or @cite{Link_Name}. |
| |
| @node Pragma Interrupt_Handler,Pragma Interrupt_State,Pragma Interface_Name,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-interrupt-handler}@anchor{71} |
| @section Pragma Interrupt_Handler |
| |
| |
| Syntax: |
| |
| @example |
| pragma Interrupt_Handler (procedure_LOCAL_NAME); |
| @end example |
| |
| This program unit pragma is supported for parameterless protected procedures |
| as described in Annex C of the Ada Reference Manual. On the AAMP target |
| the pragma can also be specified for nonprotected parameterless procedures |
| that are declared at the library level (which includes procedures |
| declared at the top level of a library package). In the case of AAMP, |
| when this pragma is applied to a nonprotected procedure, the instruction |
| @cite{IERET} is generated for returns from the procedure, enabling |
| maskable interrupts, in place of the normal return instruction. |
| |
| @node Pragma Interrupt_State,Pragma Invariant,Pragma Interrupt_Handler,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-interrupt-state}@anchor{72} |
| @section Pragma Interrupt_State |
| |
| |
| Syntax: |
| |
| @example |
| pragma Interrupt_State |
| ([Name =>] value, |
| [State =>] SYSTEM | RUNTIME | USER); |
| @end example |
| |
| Normally certain interrupts are reserved to the implementation. Any attempt |
| to attach an interrupt causes Program_Error to be raised, as described in |
| RM C.3.2(22). A typical example is the @cite{SIGINT} interrupt used in |
| many systems for an @code{Ctrl-C} interrupt. Normally this interrupt is |
| reserved to the implementation, so that @code{Ctrl-C} can be used to |
| interrupt execution. Additionally, signals such as @cite{SIGSEGV}, |
| @cite{SIGABRT}, @cite{SIGFPE} and @cite{SIGILL} are often mapped to specific |
| Ada exceptions, or used to implement run-time functions such as the |
| @cite{abort} statement and stack overflow checking. |
| |
| Pragma @cite{Interrupt_State} provides a general mechanism for overriding |
| such uses of interrupts. It subsumes the functionality of pragma |
| @cite{Unreserve_All_Interrupts}. Pragma @cite{Interrupt_State} is not |
| available on Windows or VMS. On all other platforms than VxWorks, |
| it applies to signals; on VxWorks, it applies to vectored hardware interrupts |
| and may be used to mark interrupts required by the board support package |
| as reserved. |
| |
| Interrupts can be in one of three states: |
| |
| |
| @itemize * |
| |
| @item |
| System |
| |
| The interrupt is reserved (no Ada handler can be installed), and the |
| Ada run-time may not install a handler. As a result you are guaranteed |
| standard system default action if this interrupt is raised. |
| |
| @item |
| Runtime |
| |
| The interrupt is reserved (no Ada handler can be installed). The run time |
| is allowed to install a handler for internal control purposes, but is |
| not required to do so. |
| |
| @item |
| User |
| |
| The interrupt is unreserved. The user may install a handler to provide |
| some other action. |
| @end itemize |
| |
| These states are the allowed values of the @cite{State} parameter of the |
| pragma. The @cite{Name} parameter is a value of the type |
| @cite{Ada.Interrupts.Interrupt_ID}. Typically, it is a name declared in |
| @cite{Ada.Interrupts.Names}. |
| |
| This is a configuration pragma, and the binder will check that there |
| are no inconsistencies between different units in a partition in how a |
| given interrupt is specified. It may appear anywhere a pragma is legal. |
| |
| The effect is to move the interrupt to the specified state. |
| |
| By declaring interrupts to be SYSTEM, you guarantee the standard system |
| action, such as a core dump. |
| |
| By declaring interrupts to be USER, you guarantee that you can install |
| a handler. |
| |
| Note that certain signals on many operating systems cannot be caught and |
| handled by applications. In such cases, the pragma is ignored. See the |
| operating system documentation, or the value of the array @cite{Reserved} |
| declared in the spec of package @cite{System.OS_Interface}. |
| |
| Overriding the default state of signals used by the Ada runtime may interfere |
| with an application's runtime behavior in the cases of the synchronous signals, |
| and in the case of the signal used to implement the @cite{abort} statement. |
| |
| @node Pragma Invariant,Pragma Java_Constructor,Pragma Interrupt_State,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-invariant}@anchor{73} |
| @section Pragma Invariant |
| |
| |
| Syntax: |
| |
| @example |
| pragma Invariant |
| ([Entity =>] private_type_LOCAL_NAME, |
| [Check =>] EXPRESSION |
| [,[Message =>] String_Expression]); |
| @end example |
| |
| This pragma provides exactly the same capabilities as the Type_Invariant aspect |
| defined in AI05-0146-1, and in the Ada 2012 Reference Manual. The |
| Type_Invariant aspect is fully implemented in Ada 2012 mode, but since it |
| requires the use of the aspect syntax, which is not available except in 2012 |
| mode, it is not possible to use the Type_Invariant aspect in earlier versions |
| of Ada. However the Invariant pragma may be used in any version of Ada. Also |
| note that the aspect Invariant is a synonym in GNAT for the aspect |
| Type_Invariant, but there is no pragma Type_Invariant. |
| |
| The pragma must appear within the visible part of the package specification, |
| after the type to which its Entity argument appears. As with the Invariant |
| aspect, the Check expression is not analyzed until the end of the visible |
| part of the package, so it may contain forward references. The Message |
| argument, if present, provides the exception message used if the invariant |
| is violated. If no Message parameter is provided, a default message that |
| identifies the line on which the pragma appears is used. |
| |
| It is permissible to have multiple Invariants for the same type entity, in |
| which case they are and'ed together. It is permissible to use this pragma |
| in Ada 2012 mode, but you cannot have both an invariant aspect and an |
| invariant pragma for the same entity. |
| |
| For further details on the use of this pragma, see the Ada 2012 documentation |
| of the Type_Invariant aspect. |
| |
| @node Pragma Java_Constructor,Pragma Java_Interface,Pragma Invariant,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-java-constructor}@anchor{74} |
| @section Pragma Java_Constructor |
| |
| |
| Syntax: |
| |
| @example |
| pragma Java_Constructor ([Entity =>] function_LOCAL_NAME); |
| @end example |
| |
| This pragma is used to assert that the specified Ada function should be |
| mapped to the Java constructor for some Ada tagged record type. |
| |
| See section 7.3.2 of the |
| @cite{GNAT User's Guide: Supplement for the JVM Platform.} |
| for related information. |
| |
| @node Pragma Java_Interface,Pragma Keep_Names,Pragma Java_Constructor,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-java-interface}@anchor{75} |
| @section Pragma Java_Interface |
| |
| |
| Syntax: |
| |
| @example |
| pragma Java_Interface ([Entity =>] abstract_tagged_type_LOCAL_NAME); |
| @end example |
| |
| This pragma is used to assert that the specified Ada abstract tagged type |
| is to be mapped to a Java interface name. |
| |
| See sections 7.1 and 7.2 of the |
| @cite{GNAT User's Guide: Supplement for the JVM Platform.} |
| for related information. |
| |
| @node Pragma Keep_Names,Pragma License,Pragma Java_Interface,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-keep-names}@anchor{76} |
| @section Pragma Keep_Names |
| |
| |
| Syntax: |
| |
| @example |
| pragma Keep_Names ([On =>] enumeration_first_subtype_LOCAL_NAME); |
| @end example |
| |
| The @cite{LOCAL_NAME} argument |
| must refer to an enumeration first subtype |
| in the current declarative part. The effect is to retain the enumeration |
| literal names for use by @cite{Image} and @cite{Value} even if a global |
| @cite{Discard_Names} pragma applies. This is useful when you want to |
| generally suppress enumeration literal names and for example you therefore |
| use a @cite{Discard_Names} pragma in the @code{gnat.adc} file, but you |
| want to retain the names for specific enumeration types. |
| |
| @node Pragma License,Pragma Link_With,Pragma Keep_Names,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-license}@anchor{77} |
| @section Pragma License |
| |
| |
| @geindex License checking |
| |
| Syntax: |
| |
| @example |
| pragma License (Unrestricted | GPL | Modified_GPL | Restricted); |
| @end example |
| |
| This pragma is provided to allow automated checking for appropriate license |
| conditions with respect to the standard and modified GPL. A pragma |
| @cite{License}, which is a configuration pragma that typically appears at |
| the start of a source file or in a separate @code{gnat.adc} file, specifies |
| the licensing conditions of a unit as follows: |
| |
| |
| @itemize * |
| |
| @item |
| Unrestricted |
| This is used for a unit that can be freely used with no license restrictions. |
| Examples of such units are public domain units, and units from the Ada |
| Reference Manual. |
| |
| @item |
| GPL |
| This is used for a unit that is licensed under the unmodified GPL, and which |
| therefore cannot be @cite{with}'ed by a restricted unit. |
| |
| @item |
| Modified_GPL |
| This is used for a unit licensed under the GNAT modified GPL that includes |
| a special exception paragraph that specifically permits the inclusion of |
| the unit in programs without requiring the entire program to be released |
| under the GPL. |
| |
| @item |
| Restricted |
| This is used for a unit that is restricted in that it is not permitted to |
| depend on units that are licensed under the GPL. Typical examples are |
| proprietary code that is to be released under more restrictive license |
| conditions. Note that restricted units are permitted to @cite{with} units |
| which are licensed under the modified GPL (this is the whole point of the |
| modified GPL). |
| @end itemize |
| |
| Normally a unit with no @cite{License} pragma is considered to have an |
| unknown license, and no checking is done. However, standard GNAT headers |
| are recognized, and license information is derived from them as follows. |
| |
| A GNAT license header starts with a line containing 78 hyphens. The following |
| comment text is searched for the appearance of any of the following strings. |
| |
| If the string 'GNU General Public License' is found, then the unit is assumed |
| to have GPL license, unless the string 'As a special exception' follows, in |
| which case the license is assumed to be modified GPL. |
| |
| If one of the strings |
| 'This specification is adapted from the Ada Semantic Interface' or |
| 'This specification is derived from the Ada Reference Manual' is found |
| then the unit is assumed to be unrestricted. |
| |
| These default actions means that a program with a restricted license pragma |
| will automatically get warnings if a GPL unit is inappropriately |
| @cite{with}'ed. For example, the program: |
| |
| @example |
| with Sem_Ch3; |
| with GNAT.Sockets; |
| procedure Secret_Stuff is |
| ... |
| end Secret_Stuff |
| @end example |
| |
| if compiled with pragma @cite{License} (@cite{Restricted}) in a |
| @code{gnat.adc} file will generate the warning: |
| |
| @example |
| 1. with Sem_Ch3; |
| | |
| >>> license of withed unit "Sem_Ch3" is incompatible |
| |
| 2. with GNAT.Sockets; |
| 3. procedure Secret_Stuff is |
| @end example |
| |
| Here we get a warning on @cite{Sem_Ch3} since it is part of the GNAT |
| compiler and is licensed under the |
| GPL, but no warning for @cite{GNAT.Sockets} which is part of the GNAT |
| run time, and is therefore licensed under the modified GPL. |
| |
| @node Pragma Link_With,Pragma Linker_Alias,Pragma License,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-link-with}@anchor{78} |
| @section Pragma Link_With |
| |
| |
| Syntax: |
| |
| @example |
| pragma Link_With (static_string_EXPRESSION @{,static_string_EXPRESSION@}); |
| @end example |
| |
| This pragma is provided for compatibility with certain Ada 83 compilers. |
| It has exactly the same effect as pragma @cite{Linker_Options} except |
| that spaces occurring within one of the string expressions are treated |
| as separators. For example, in the following case: |
| |
| @example |
| pragma Link_With ("-labc -ldef"); |
| @end example |
| |
| results in passing the strings @cite{-labc} and @cite{-ldef} as two |
| separate arguments to the linker. In addition pragma Link_With allows |
| multiple arguments, with the same effect as successive pragmas. |
| |
| @node Pragma Linker_Alias,Pragma Linker_Constructor,Pragma Link_With,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-linker-alias}@anchor{79} |
| @section Pragma Linker_Alias |
| |
| |
| Syntax: |
| |
| @example |
| pragma Linker_Alias ( |
| [Entity =>] LOCAL_NAME, |
| [Target =>] static_string_EXPRESSION); |
| @end example |
| |
| @cite{LOCAL_NAME} must refer to an object that is declared at the library |
| level. This pragma establishes the given entity as a linker alias for the |
| given target. It is equivalent to @cite{__attribute__((alias))} in GNU C |
| and causes @cite{LOCAL_NAME} to be emitted as an alias for the symbol |
| @cite{static_string_EXPRESSION} in the object file, that is to say no space |
| is reserved for @cite{LOCAL_NAME} by the assembler and it will be resolved |
| to the same address as @cite{static_string_EXPRESSION} by the linker. |
| |
| The actual linker name for the target must be used (e.g., the fully |
| encoded name with qualification in Ada, or the mangled name in C++), |
| or it must be declared using the C convention with @cite{pragma Import} |
| or @cite{pragma Export}. |
| |
| Not all target machines support this pragma. On some of them it is accepted |
| only if @cite{pragma Weak_External} has been applied to @cite{LOCAL_NAME}. |
| |
| @example |
| -- Example of the use of pragma Linker_Alias |
| |
| package p is |
| i : Integer := 1; |
| pragma Export (C, i); |
| |
| new_name_for_i : Integer; |
| pragma Linker_Alias (new_name_for_i, "i"); |
| end p; |
| @end example |
| |
| @node Pragma Linker_Constructor,Pragma Linker_Destructor,Pragma Linker_Alias,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-linker-constructor}@anchor{7a} |
| @section Pragma Linker_Constructor |
| |
| |
| Syntax: |
| |
| @example |
| pragma Linker_Constructor (procedure_LOCAL_NAME); |
| @end example |
| |
| @cite{procedure_LOCAL_NAME} must refer to a parameterless procedure that |
| is declared at the library level. A procedure to which this pragma is |
| applied will be treated as an initialization routine by the linker. |
| It is equivalent to @cite{__attribute__((constructor))} in GNU C and |
| causes @cite{procedure_LOCAL_NAME} to be invoked before the entry point |
| of the executable is called (or immediately after the shared library is |
| loaded if the procedure is linked in a shared library), in particular |
| before the Ada run-time environment is set up. |
| |
| Because of these specific contexts, the set of operations such a procedure |
| can perform is very limited and the type of objects it can manipulate is |
| essentially restricted to the elementary types. In particular, it must only |
| contain code to which pragma Restrictions (No_Elaboration_Code) applies. |
| |
| This pragma is used by GNAT to implement auto-initialization of shared Stand |
| Alone Libraries, which provides a related capability without the restrictions |
| listed above. Where possible, the use of Stand Alone Libraries is preferable |
| to the use of this pragma. |
| |
| @node Pragma Linker_Destructor,Pragma Linker_Section,Pragma Linker_Constructor,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-linker-destructor}@anchor{7b} |
| @section Pragma Linker_Destructor |
| |
| |
| Syntax: |
| |
| @example |
| pragma Linker_Destructor (procedure_LOCAL_NAME); |
| @end example |
| |
| @cite{procedure_LOCAL_NAME} must refer to a parameterless procedure that |
| is declared at the library level. A procedure to which this pragma is |
| applied will be treated as a finalization routine by the linker. |
| It is equivalent to @cite{__attribute__((destructor))} in GNU C and |
| causes @cite{procedure_LOCAL_NAME} to be invoked after the entry point |
| of the executable has exited (or immediately before the shared library |
| is unloaded if the procedure is linked in a shared library), in particular |
| after the Ada run-time environment is shut down. |
| |
| See @cite{pragma Linker_Constructor} for the set of restrictions that apply |
| because of these specific contexts. |
| |
| @node Pragma Linker_Section,Pragma Lock_Free,Pragma Linker_Destructor,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-linker-section}@anchor{7c} |
| @section Pragma Linker_Section |
| |
| |
| Syntax: |
| |
| @example |
| pragma Linker_Section ( |
| [Entity =>] LOCAL_NAME, |
| [Section =>] static_string_EXPRESSION); |
| @end example |
| |
| @cite{LOCAL_NAME} must refer to an object, type, or subprogram that is |
| declared at the library level. This pragma specifies the name of the |
| linker section for the given entity. It is equivalent to |
| @cite{__attribute__((section))} in GNU C and causes @cite{LOCAL_NAME} to |
| be placed in the @cite{static_string_EXPRESSION} section of the |
| executable (assuming the linker doesn't rename the section). |
| GNAT also provides an implementation defined aspect of the same name. |
| |
| In the case of specifying this aspect for a type, the effect is to |
| specify the corresponding for all library level objects of the type which |
| do not have an explicit linker section set. Note that this only applies to |
| whole objects, not to components of composite objects. |
| |
| In the case of a subprogram, the linker section applies to all previously |
| declared matching overloaded subprograms in the current declarative part |
| which do not already have a linker section assigned. The linker section |
| aspect is useful in this case for specifying different linker sections |
| for different elements of such an overloaded set. |
| |
| Note that an empty string specifies that no linker section is specified. |
| This is not quite the same as omitting the pragma or aspect, since it |
| can be used to specify that one element of an overloaded set of subprograms |
| has the default linker section, or that one object of a type for which a |
| linker section is specified should has the default linker section. |
| |
| The compiler normally places library-level entities in standard sections |
| depending on the class: procedures and functions generally go in the |
| @cite{.text} section, initialized variables in the @cite{.data} section |
| and uninitialized variables in the @cite{.bss} section. |
| |
| Other, special sections may exist on given target machines to map special |
| hardware, for example I/O ports or flash memory. This pragma is a means to |
| defer the final layout of the executable to the linker, thus fully working |
| at the symbolic level with the compiler. |
| |
| Some file formats do not support arbitrary sections so not all target |
| machines support this pragma. The use of this pragma may cause a program |
| execution to be erroneous if it is used to place an entity into an |
| inappropriate section (e.g., a modified variable into the @cite{.text} |
| section). See also @cite{pragma Persistent_BSS}. |
| |
| @example |
| -- Example of the use of pragma Linker_Section |
| |
| package IO_Card is |
| Port_A : Integer; |
| pragma Volatile (Port_A); |
| pragma Linker_Section (Port_A, ".bss.port_a"); |
| |
| Port_B : Integer; |
| pragma Volatile (Port_B); |
| pragma Linker_Section (Port_B, ".bss.port_b"); |
| |
| type Port_Type is new Integer with Linker_Section => ".bss"; |
| PA : Port_Type with Linker_Section => ".bss.PA"; |
| PB : Port_Type; -- ends up in linker section ".bss" |
| |
| procedure Q with Linker_Section => "Qsection"; |
| end IO_Card; |
| @end example |
| |
| @node Pragma Lock_Free,Pragma Loop_Invariant,Pragma Linker_Section,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-lock-free}@anchor{7d} |
| @section Pragma Lock_Free |
| |
| |
| Syntax: |
| This pragma may be specified for protected types or objects. It specifies that |
| the implementation of protected operations must be implemented without locks. |
| Compilation fails if the compiler cannot generate lock-free code for the |
| operations. |
| |
| @node Pragma Loop_Invariant,Pragma Loop_Optimize,Pragma Lock_Free,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-loop-invariant}@anchor{7e} |
| @section Pragma Loop_Invariant |
| |
| |
| Syntax: |
| |
| @example |
| pragma Loop_Invariant ( boolean_EXPRESSION ); |
| @end example |
| |
| The effect of this pragma is similar to that of pragma @cite{Assert}, |
| except that in an @cite{Assertion_Policy} pragma, the identifier |
| @cite{Loop_Invariant} is used to control whether it is ignored or checked |
| (or disabled). |
| |
| @cite{Loop_Invariant} can only appear as one of the items in the sequence |
| of statements of a loop body, or nested inside block statements that |
| appear in the sequence of statements of a loop body. |
| The intention is that it be used to |
| represent a "loop invariant" assertion, i.e. something that is true each |
| time through the loop, and which can be used to show that the loop is |
| achieving its purpose. |
| |
| Multiple @cite{Loop_Invariant} and @cite{Loop_Variant} pragmas that |
| apply to the same loop should be grouped in the same sequence of |
| statements. |
| |
| To aid in writing such invariants, the special attribute @cite{Loop_Entry} |
| may be used to refer to the value of an expression on entry to the loop. This |
| attribute can only be used within the expression of a @cite{Loop_Invariant} |
| pragma. For full details, see documentation of attribute @cite{Loop_Entry}. |
| |
| @node Pragma Loop_Optimize,Pragma Loop_Variant,Pragma Loop_Invariant,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-loop-optimize}@anchor{7f} |
| @section Pragma Loop_Optimize |
| |
| |
| Syntax: |
| |
| @example |
| pragma Loop_Optimize (OPTIMIZATION_HINT @{, OPTIMIZATION_HINT@}); |
| |
| OPTIMIZATION_HINT ::= Ivdep | No_Unroll | Unroll | No_Vector | Vector |
| @end example |
| |
| This pragma must appear immediately within a loop statement. It allows the |
| programmer to specify optimization hints for the enclosing loop. The hints |
| are not mutually exclusive and can be freely mixed, but not all combinations |
| will yield a sensible outcome. |
| |
| There are five supported optimization hints for a loop: |
| |
| |
| @itemize * |
| |
| @item |
| Ivdep |
| |
| The programmer asserts that there are no loop-carried dependencies |
| which would prevent consecutive iterations of the loop from being |
| executed simultaneously. |
| |
| @item |
| No_Unroll |
| |
| The loop must not be unrolled. This is a strong hint: the compiler will not |
| unroll a loop marked with this hint. |
| |
| @item |
| Unroll |
| |
| The loop should be unrolled. This is a weak hint: the compiler will try to |
| apply unrolling to this loop preferably to other optimizations, notably |
| vectorization, but there is no guarantee that the loop will be unrolled. |
| |
| @item |
| No_Vector |
| |
| The loop must not be vectorized. This is a strong hint: the compiler will not |
| vectorize a loop marked with this hint. |
| |
| @item |
| Vector |
| |
| The loop should be vectorized. This is a weak hint: the compiler will try to |
| apply vectorization to this loop preferably to other optimizations, notably |
| unrolling, but there is no guarantee that the loop will be vectorized. |
| @end itemize |
| |
| These hints do not remove the need to pass the appropriate switches to the |
| compiler in order to enable the relevant optimizations, that is to say |
| @emph{-funroll-loops} for unrolling and @emph{-ftree-vectorize} for |
| vectorization. |
| |
| @node Pragma Loop_Variant,Pragma Machine_Attribute,Pragma Loop_Optimize,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-loop-variant}@anchor{80} |
| @section Pragma Loop_Variant |
| |
| |
| Syntax: |
| |
| @example |
| pragma Loop_Variant ( LOOP_VARIANT_ITEM @{, LOOP_VARIANT_ITEM @} ); |
| LOOP_VARIANT_ITEM ::= CHANGE_DIRECTION => discrete_EXPRESSION |
| CHANGE_DIRECTION ::= Increases | Decreases |
| @end example |
| |
| @cite{Loop_Variant} can only appear as one of the items in the sequence |
| of statements of a loop body, or nested inside block statements that |
| appear in the sequence of statements of a loop body. |
| It allows the specification of quantities which must always |
| decrease or increase in successive iterations of the loop. In its simplest |
| form, just one expression is specified, whose value must increase or decrease |
| on each iteration of the loop. |
| |
| In a more complex form, multiple arguments can be given which are intepreted |
| in a nesting lexicographic manner. For example: |
| |
| @example |
| pragma Loop_Variant (Increases => X, Decreases => Y); |
| @end example |
| |
| specifies that each time through the loop either X increases, or X stays |
| the same and Y decreases. A @cite{Loop_Variant} pragma ensures that the |
| loop is making progress. It can be useful in helping to show informally |
| or prove formally that the loop always terminates. |
| |
| @cite{Loop_Variant} is an assertion whose effect can be controlled using |
| an @cite{Assertion_Policy} with a check name of @cite{Loop_Variant}. The |
| policy can be @cite{Check} to enable the loop variant check, @cite{Ignore} |
| to ignore the check (in which case the pragma has no effect on the program), |
| or @cite{Disable} in which case the pragma is not even checked for correct |
| syntax. |
| |
| Multiple @cite{Loop_Invariant} and @cite{Loop_Variant} pragmas that |
| apply to the same loop should be grouped in the same sequence of |
| statements. |
| |
| The @cite{Loop_Entry} attribute may be used within the expressions of the |
| @cite{Loop_Variant} pragma to refer to values on entry to the loop. |
| |
| @node Pragma Machine_Attribute,Pragma Main,Pragma Loop_Variant,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-machine-attribute}@anchor{81} |
| @section Pragma Machine_Attribute |
| |
| |
| Syntax: |
| |
| @example |
| pragma Machine_Attribute ( |
| [Entity =>] LOCAL_NAME, |
| [Attribute_Name =>] static_string_EXPRESSION |
| [, [Info =>] static_EXPRESSION] ); |
| @end example |
| |
| Machine-dependent attributes can be specified for types and/or |
| declarations. This pragma is semantically equivalent to |
| @cite{__attribute__((`attribute_name}))` (if @cite{info} is not |
| specified) or @cite{__attribute__((`attribute_name`(`info}))) |
| in GNU C, where @code{attribute_name} is recognized by the |
| compiler middle-end or the @cite{TARGET_ATTRIBUTE_TABLE} machine |
| specific macro. A string literal for the optional parameter @cite{info} |
| is transformed into an identifier, which may make this pragma unusable |
| for some attributes. |
| For further information see @cite{GNU Compiler Collection (GCC) Internals}. |
| |
| @node Pragma Main,Pragma Main_Storage,Pragma Machine_Attribute,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-main}@anchor{82} |
| @section Pragma Main |
| |
| |
| Syntax: |
| |
| @example |
| pragma Main |
| (MAIN_OPTION [, MAIN_OPTION]); |
| |
| MAIN_OPTION ::= |
| [Stack_Size =>] static_integer_EXPRESSION |
| | [Task_Stack_Size_Default =>] static_integer_EXPRESSION |
| | [Time_Slicing_Enabled =>] static_boolean_EXPRESSION |
| @end example |
| |
| This pragma is provided for compatibility with OpenVMS VAX Systems. It has |
| no effect in GNAT, other than being syntax checked. |
| |
| @node Pragma Main_Storage,Pragma No_Body,Pragma Main,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-main-storage}@anchor{83} |
| @section Pragma Main_Storage |
| |
| |
| Syntax: |
| |
| @example |
| pragma Main_Storage |
| (MAIN_STORAGE_OPTION [, MAIN_STORAGE_OPTION]); |
| |
| MAIN_STORAGE_OPTION ::= |
| [WORKING_STORAGE =>] static_SIMPLE_EXPRESSION |
| | [TOP_GUARD =>] static_SIMPLE_EXPRESSION |
| @end example |
| |
| This pragma is provided for compatibility with OpenVMS VAX Systems. It has |
| no effect in GNAT, other than being syntax checked. |
| |
| @node Pragma No_Body,Pragma No_Elaboration_Code_All,Pragma Main_Storage,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-no-body}@anchor{84} |
| @section Pragma No_Body |
| |
| |
| Syntax: |
| |
| @example |
| pragma No_Body; |
| @end example |
| |
| There are a number of cases in which a package spec does not require a body, |
| and in fact a body is not permitted. GNAT will not permit the spec to be |
| compiled if there is a body around. The pragma No_Body allows you to provide |
| a body file, even in a case where no body is allowed. The body file must |
| contain only comments and a single No_Body pragma. This is recognized by |
| the compiler as indicating that no body is logically present. |
| |
| This is particularly useful during maintenance when a package is modified in |
| such a way that a body needed before is no longer needed. The provision of a |
| dummy body with a No_Body pragma ensures that there is no interference from |
| earlier versions of the package body. |
| |
| @node Pragma No_Elaboration_Code_All,Pragma No_Inline,Pragma No_Body,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-no-elaboration-code-all}@anchor{85} |
| @section Pragma No_Elaboration_Code_All |
| |
| |
| Syntax: |
| |
| @example |
| pragma No_Elaboration_Code_All [(program_unit_NAME)]; |
| @end example |
| |
| This is a program unit pragma (there is also an equivalent aspect of the |
| same name) that establishes the restriction @cite{No_Elaboration_Code} for |
| the current unit and any extended main source units (body and subunits. |
| It also has has the effect of enforcing a transitive application of this |
| aspect, so that if any unit is implicitly or explicitly WITH'ed by the |
| current unit, it must also have the No_Elaboration_Code_All aspect set. |
| It may be applied to package or subprogram specs or their generic versions. |
| |
| @node Pragma No_Inline,Pragma No_Return,Pragma No_Elaboration_Code_All,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-no-inline}@anchor{86} |
| @section Pragma No_Inline |
| |
| |
| Syntax: |
| |
| @example |
| pragma No_Inline (NAME @{, NAME@}); |
| @end example |
| |
| This pragma suppresses inlining for the callable entity or the instances of |
| the generic subprogram designated by @cite{NAME}, including inlining that |
| results from the use of pragma @cite{Inline}. This pragma is always active, |
| in particular it is not subject to the use of option @emph{-gnatn} or |
| @emph{-gnatN}. It is illegal to specify both pragma @cite{No_Inline} and |
| pragma @cite{Inline_Always} for the same @cite{NAME}. |
| |
| @node Pragma No_Return,Pragma No_Run_Time,Pragma No_Inline,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-no-return}@anchor{87} |
| @section Pragma No_Return |
| |
| |
| Syntax: |
| |
| @example |
| pragma No_Return (procedure_LOCAL_NAME @{, procedure_LOCAL_NAME@}); |
| @end example |
| |
| Each @cite{procedure_LOCAL_NAME} argument must refer to one or more procedure |
| declarations in the current declarative part. A procedure to which this |
| pragma is applied may not contain any explicit @cite{return} statements. |
| In addition, if the procedure contains any implicit returns from falling |
| off the end of a statement sequence, then execution of that implicit |
| return will cause Program_Error to be raised. |
| |
| One use of this pragma is to identify procedures whose only purpose is to raise |
| an exception. Another use of this pragma is to suppress incorrect warnings |
| about missing returns in functions, where the last statement of a function |
| statement sequence is a call to such a procedure. |
| |
| Note that in Ada 2005 mode, this pragma is part of the language. It is |
| available in all earlier versions of Ada as an implementation-defined |
| pragma. |
| |
| @node Pragma No_Run_Time,Pragma No_Strict_Aliasing,Pragma No_Return,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-no-run-time}@anchor{88} |
| @section Pragma No_Run_Time |
| |
| |
| Syntax: |
| |
| @example |
| pragma No_Run_Time; |
| @end example |
| |
| This is an obsolete configuration pragma that historically was used to |
| set up a runtime library with no object code. It is now used only for |
| internal testing. The pragma has been superseded by the reconfigurable |
| runtime capability of @cite{GNAT}. |
| |
| @node Pragma No_Strict_Aliasing,Pragma No_Tagged_Streams,Pragma No_Run_Time,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-no-strict-aliasing}@anchor{89} |
| @section Pragma No_Strict_Aliasing |
| |
| |
| Syntax: |
| |
| @example |
| pragma No_Strict_Aliasing [([Entity =>] type_LOCAL_NAME)]; |
| @end example |
| |
| @cite{type_LOCAL_NAME} must refer to an access type |
| declaration in the current declarative part. The effect is to inhibit |
| strict aliasing optimization for the given type. The form with no |
| arguments is a configuration pragma which applies to all access types |
| declared in units to which the pragma applies. For a detailed |
| description of the strict aliasing optimization, and the situations |
| in which it must be suppressed, see the section on Optimization and Strict Aliasing |
| in the @cite{GNAT User's Guide}. |
| |
| This pragma currently has no effects on access to unconstrained array types. |
| |
| @node Pragma No_Tagged_Streams,Pragma Normalize_Scalars,Pragma No_Strict_Aliasing,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-no-tagged-streams}@anchor{8a} |
| @section Pragma No_Tagged_Streams |
| |
| |
| Syntax: |
| |
| @example |
| pragma No_Tagged_Streams; |
| pragma No_Tagged_Streams [([Entity =>] tagged_type_LOCAL_NAME)]; |
| @end example |
| |
| Normally when a tagged type is introduced using a full type declaration, |
| part of the processing includes generating stream access routines to be |
| used by stream attributes referencing the type (or one of its subtypes |
| or derived types). This can involve the generation of significant amounts |
| of code which is wasted space if stream routines are not needed for the |
| type in question. |
| |
| The @cite{No_Tagged_Streams} pragma causes the generation of these stream |
| routines to be skipped, and any attempt to use stream operations on |
| types subject to this pragma will be statically rejected as illegal. |
| |
| There are two forms of the pragma. The form with no arguments must appear |
| in a declarative sequence or in the declarations of a package spec. This |
| pragma affects all subsequent root tagged types declared in the declaration |
| sequence, and specifies that no stream routines be generated. The form with |
| an argument (for which there is also a corresponding aspect) specifies a |
| single root tagged type for which stream routines are not to be generated. |
| |
| Once the pragma has been given for a particular root tagged type, all subtypes |
| and derived types of this type inherit the pragma automatically, so the effect |
| applies to a complete hierarchy (this is necessary to deal with the class-wide |
| dispatching versions of the stream routines). |
| |
| @node Pragma Normalize_Scalars,Pragma Obsolescent,Pragma No_Tagged_Streams,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-normalize-scalars}@anchor{8b} |
| @section Pragma Normalize_Scalars |
| |
| |
| Syntax: |
| |
| @example |
| pragma Normalize_Scalars; |
| @end example |
| |
| This is a language defined pragma which is fully implemented in GNAT. The |
| effect is to cause all scalar objects that are not otherwise initialized |
| to be initialized. The initial values are implementation dependent and |
| are as follows: |
| |
| |
| @table @asis |
| |
| @item @emph{Standard.Character} |
| |
| Objects whose root type is Standard.Character are initialized to |
| Character'Last unless the subtype range excludes NUL (in which case |
| NUL is used). This choice will always generate an invalid value if |
| one exists. |
| |
| @item @emph{Standard.Wide_Character} |
| |
| Objects whose root type is Standard.Wide_Character are initialized to |
| Wide_Character'Last unless the subtype range excludes NUL (in which case |
| NUL is used). This choice will always generate an invalid value if |
| one exists. |
| |
| @item @emph{Standard.Wide_Wide_Character} |
| |
| Objects whose root type is Standard.Wide_Wide_Character are initialized to |
| the invalid value 16#FFFF_FFFF# unless the subtype range excludes NUL (in |
| which case NUL is used). This choice will always generate an invalid value if |
| one exists. |
| |
| @item @emph{Integer types} |
| |
| Objects of an integer type are treated differently depending on whether |
| negative values are present in the subtype. If no negative values are |
| present, then all one bits is used as the initial value except in the |
| special case where zero is excluded from the subtype, in which case |
| all zero bits are used. This choice will always generate an invalid |
| value if one exists. |
| |
| For subtypes with negative values present, the largest negative number |
| is used, except in the unusual case where this largest negative number |
| is in the subtype, and the largest positive number is not, in which case |
| the largest positive value is used. This choice will always generate |
| an invalid value if one exists. |
| |
| @item @emph{Floating-Point Types} |
| |
| Objects of all floating-point types are initialized to all 1-bits. For |
| standard IEEE format, this corresponds to a NaN (not a number) which is |
| indeed an invalid value. |
| |
| @item @emph{Fixed-Point Types} |
| |
| Objects of all fixed-point types are treated as described above for integers, |
| with the rules applying to the underlying integer value used to represent |
| the fixed-point value. |
| |
| @item @emph{Modular types} |
| |
| Objects of a modular type are initialized to all one bits, except in |
| the special case where zero is excluded from the subtype, in which |
| case all zero bits are used. This choice will always generate an |
| invalid value if one exists. |
| |
| @item @emph{Enumeration types} |
| |
| Objects of an enumeration type are initialized to all one-bits, i.e., to |
| the value @cite{2 ** typ'Size - 1} unless the subtype excludes the literal |
| whose Pos value is zero, in which case a code of zero is used. This choice |
| will always generate an invalid value if one exists. |
| @end table |
| |
| @node Pragma Obsolescent,Pragma Optimize_Alignment,Pragma Normalize_Scalars,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-obsolescent}@anchor{8c}@anchor{gnat_rm/implementation_defined_pragmas id2}@anchor{8d} |
| @section Pragma Obsolescent |
| |
| |
| Syntax: |
| |
| @example |
| pragma Obsolescent; |
| |
| pragma Obsolescent ( |
| [Message =>] static_string_EXPRESSION |
| [,[Version =>] Ada_05]]); |
| |
| pragma Obsolescent ( |
| [Entity =>] NAME |
| [,[Message =>] static_string_EXPRESSION |
| [,[Version =>] Ada_05]] ); |
| @end example |
| |
| This pragma can occur immediately following a declaration of an entity, |
| including the case of a record component. If no Entity argument is present, |
| then this declaration is the one to which the pragma applies. If an Entity |
| parameter is present, it must either match the name of the entity in this |
| declaration, or alternatively, the pragma can immediately follow an enumeration |
| type declaration, where the Entity argument names one of the enumeration |
| literals. |
| |
| This pragma is used to indicate that the named entity |
| is considered obsolescent and should not be used. Typically this is |
| used when an API must be modified by eventually removing or modifying |
| existing subprograms or other entities. The pragma can be used at an |
| intermediate stage when the entity is still present, but will be |
| removed later. |
| |
| The effect of this pragma is to output a warning message on a reference to |
| an entity thus marked that the subprogram is obsolescent if the appropriate |
| warning option in the compiler is activated. If the Message parameter is |
| present, then a second warning message is given containing this text. In |
| addition, a reference to the entity is considered to be a violation of pragma |
| Restrictions (No_Obsolescent_Features). |
| |
| This pragma can also be used as a program unit pragma for a package, |
| in which case the entity name is the name of the package, and the |
| pragma indicates that the entire package is considered |
| obsolescent. In this case a client @cite{with}'ing such a package |
| violates the restriction, and the @cite{with} statement is |
| flagged with warnings if the warning option is set. |
| |
| If the Version parameter is present (which must be exactly |
| the identifier Ada_05, no other argument is allowed), then the |
| indication of obsolescence applies only when compiling in Ada 2005 |
| mode. This is primarily intended for dealing with the situations |
| in the predefined library where subprograms or packages |
| have become defined as obsolescent in Ada 2005 |
| (e.g., in Ada.Characters.Handling), but may be used anywhere. |
| |
| The following examples show typical uses of this pragma: |
| |
| @example |
| package p is |
| pragma Obsolescent (p, Message => "use pp instead of p"); |
| end p; |
| |
| package q is |
| procedure q2; |
| pragma Obsolescent ("use q2new instead"); |
| |
| type R is new integer; |
| pragma Obsolescent |
| (Entity => R, |
| Message => "use RR in Ada 2005", |
| Version => Ada_05); |
| |
| type M is record |
| F1 : Integer; |
| F2 : Integer; |
| pragma Obsolescent; |
| F3 : Integer; |
| end record; |
| |
| type E is (a, bc, 'd', quack); |
| pragma Obsolescent (Entity => bc) |
| pragma Obsolescent (Entity => 'd') |
| |
| function "+" |
| (a, b : character) return character; |
| pragma Obsolescent (Entity => "+"); |
| end; |
| @end example |
| |
| Note that, as for all pragmas, if you use a pragma argument identifier, |
| then all subsequent parameters must also use a pragma argument identifier. |
| So if you specify "Entity =>" for the Entity argument, and a Message |
| argument is present, it must be preceded by "Message =>". |
| |
| @node Pragma Optimize_Alignment,Pragma Ordered,Pragma Obsolescent,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-optimize-alignment}@anchor{8e} |
| @section Pragma Optimize_Alignment |
| |
| |
| @geindex Alignment |
| @geindex default settings |
| |
| Syntax: |
| |
| @example |
| pragma Optimize_Alignment (TIME | SPACE | OFF); |
| @end example |
| |
| This is a configuration pragma which affects the choice of default alignments |
| for types and objects where no alignment is explicitly specified. There is a |
| time/space trade-off in the selection of these values. Large alignments result |
| in more efficient code, at the expense of larger data space, since sizes have |
| to be increased to match these alignments. Smaller alignments save space, but |
| the access code is slower. The normal choice of default alignments for types |
| and individual alignment promotions for objects (which is what you get if you |
| do not use this pragma, or if you use an argument of OFF), tries to balance |
| these two requirements. |
| |
| Specifying SPACE causes smaller default alignments to be chosen in two cases. |
| First any packed record is given an alignment of 1. Second, if a size is given |
| for the type, then the alignment is chosen to avoid increasing this size. For |
| example, consider: |
| |
| @example |
| type R is record |
| X : Integer; |
| Y : Character; |
| end record; |
| |
| for R'Size use 5*8; |
| @end example |
| |
| In the default mode, this type gets an alignment of 4, so that access to the |
| Integer field X are efficient. But this means that objects of the type end up |
| with a size of 8 bytes. This is a valid choice, since sizes of objects are |
| allowed to be bigger than the size of the type, but it can waste space if for |
| example fields of type R appear in an enclosing record. If the above type is |
| compiled in @cite{Optimize_Alignment (Space)} mode, the alignment is set to 1. |
| |
| However, there is one case in which SPACE is ignored. If a variable length |
| record (that is a discriminated record with a component which is an array |
| whose length depends on a discriminant), has a pragma Pack, then it is not |
| in general possible to set the alignment of such a record to one, so the |
| pragma is ignored in this case (with a warning). |
| |
| Specifying SPACE also disables alignment promotions for standalone objects, |
| which occur when the compiler increases the alignment of a specific object |
| without changing the alignment of its type. |
| |
| Specifying TIME causes larger default alignments to be chosen in the case of |
| small types with sizes that are not a power of 2. For example, consider: |
| |
| @example |
| type R is record |
| A : Character; |
| B : Character; |
| C : Boolean; |
| end record; |
| |
| pragma Pack (R); |
| for R'Size use 17; |
| @end example |
| |
| The default alignment for this record is normally 1, but if this type is |
| compiled in @cite{Optimize_Alignment (Time)} mode, then the alignment is set |
| to 4, which wastes space for objects of the type, since they are now 4 bytes |
| long, but results in more efficient access when the whole record is referenced. |
| |
| As noted above, this is a configuration pragma, and there is a requirement |
| that all units in a partition be compiled with a consistent setting of the |
| optimization setting. This would normally be achieved by use of a configuration |
| pragma file containing the appropriate setting. The exception to this rule is |
| that units with an explicit configuration pragma in the same file as the source |
| unit are excluded from the consistency check, as are all predefined units. The |
| latter are compiled by default in pragma Optimize_Alignment (Off) mode if no |
| pragma appears at the start of the file. |
| |
| @node Pragma Ordered,Pragma Overflow_Mode,Pragma Optimize_Alignment,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-ordered}@anchor{8f} |
| @section Pragma Ordered |
| |
| |
| Syntax: |
| |
| @example |
| pragma Ordered (enumeration_first_subtype_LOCAL_NAME); |
| @end example |
| |
| Most enumeration types are from a conceptual point of view unordered. |
| For example, consider: |
| |
| @example |
| type Color is (Red, Blue, Green, Yellow); |
| @end example |
| |
| By Ada semantics @cite{Blue > Red} and @cite{Green > Blue}, |
| but really these relations make no sense; the enumeration type merely |
| specifies a set of possible colors, and the order is unimportant. |
| |
| For unordered enumeration types, it is generally a good idea if |
| clients avoid comparisons (other than equality or inequality) and |
| explicit ranges. (A @emph{client} is a unit where the type is referenced, |
| other than the unit where the type is declared, its body, and its subunits.) |
| For example, if code buried in some client says: |
| |
| @example |
| if Current_Color < Yellow then ... |
| if Current_Color in Blue .. Green then ... |
| @end example |
| |
| then the client code is relying on the order, which is undesirable. |
| It makes the code hard to read and creates maintenance difficulties if |
| entries have to be added to the enumeration type. Instead, |
| the code in the client should list the possibilities, or an |
| appropriate subtype should be declared in the unit that declares |
| the original enumeration type. E.g., the following subtype could |
| be declared along with the type @cite{Color}: |
| |
| @example |
| subtype RBG is Color range Red .. Green; |
| @end example |
| |
| and then the client could write: |
| |
| @example |
| if Current_Color in RBG then ... |
| if Current_Color = Blue or Current_Color = Green then ... |
| @end example |
| |
| However, some enumeration types are legitimately ordered from a conceptual |
| point of view. For example, if you declare: |
| |
| @example |
| type Day is (Mon, Tue, Wed, Thu, Fri, Sat, Sun); |
| @end example |
| |
| then the ordering imposed by the language is reasonable, and |
| clients can depend on it, writing for example: |
| |
| @example |
| if D in Mon .. Fri then ... |
| if D < Wed then ... |
| @end example |
| |
| The pragma @emph{Ordered} is provided to mark enumeration types that |
| are conceptually ordered, alerting the reader that clients may depend |
| on the ordering. GNAT provides a pragma to mark enumerations as ordered |
| rather than one to mark them as unordered, since in our experience, |
| the great majority of enumeration types are conceptually unordered. |
| |
| The types @cite{Boolean}, @cite{Character}, @cite{Wide_Character}, |
| and @cite{Wide_Wide_Character} |
| are considered to be ordered types, so each is declared with a |
| pragma @cite{Ordered} in package @cite{Standard}. |
| |
| Normally pragma @cite{Ordered} serves only as documentation and a guide for |
| coding standards, but GNAT provides a warning switch @emph{-gnatw.u} that |
| requests warnings for inappropriate uses (comparisons and explicit |
| subranges) for unordered types. If this switch is used, then any |
| enumeration type not marked with pragma @cite{Ordered} will be considered |
| as unordered, and will generate warnings for inappropriate uses. |
| |
| Note that generic types are not considered ordered or unordered (since the |
| template can be instantiated for both cases), so we never generate warnings |
| for the case of generic enumerated types. |
| |
| For additional information please refer to the description of the |
| @emph{-gnatw.u} switch in the GNAT User's Guide. |
| |
| @node Pragma Overflow_Mode,Pragma Overriding_Renamings,Pragma Ordered,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-overflow-mode}@anchor{90} |
| @section Pragma Overflow_Mode |
| |
| |
| Syntax: |
| |
| @example |
| pragma Overflow_Mode |
| ( [General =>] MODE |
| [,[Assertions =>] MODE]); |
| |
| MODE ::= STRICT | MINIMIZED | ELIMINATED |
| @end example |
| |
| This pragma sets the current overflow mode to the given setting. For details |
| of the meaning of these modes, please refer to the |
| 'Overflow Check Handling in GNAT' appendix in the |
| GNAT User's Guide. If only the @cite{General} parameter is present, |
| the given mode applies to all expressions. If both parameters are present, |
| the @cite{General} mode applies to expressions outside assertions, and |
| the @cite{Eliminated} mode applies to expressions within assertions. |
| |
| The case of the @cite{MODE} parameter is ignored, |
| so @cite{MINIMIZED}, @cite{Minimized} and |
| @cite{minimized} all have the same effect. |
| |
| The @cite{Overflow_Mode} pragma has the same scoping and placement |
| rules as pragma @cite{Suppress}, so it can occur either as a |
| configuration pragma, specifying a default for the whole |
| program, or in a declarative scope, where it applies to the |
| remaining declarations and statements in that scope. |
| |
| The pragma @cite{Suppress (Overflow_Check)} suppresses |
| overflow checking, but does not affect the overflow mode. |
| |
| The pragma @cite{Unsuppress (Overflow_Check)} unsuppresses (enables) |
| overflow checking, but does not affect the overflow mode. |
| |
| @node Pragma Overriding_Renamings,Pragma Partition_Elaboration_Policy,Pragma Overflow_Mode,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-overriding-renamings}@anchor{91} |
| @section Pragma Overriding_Renamings |
| |
| |
| @geindex Rational profile |
| |
| @geindex Rational compatibility |
| |
| Syntax: |
| |
| @example |
| pragma Overriding_Renamings; |
| @end example |
| |
| This is a GNAT configuration pragma to simplify porting |
| legacy code accepted by the Rational |
| Ada compiler. In the presence of this pragma, a renaming declaration that |
| renames an inherited operation declared in the same scope is legal if selected |
| notation is used as in: |
| |
| @example |
| pragma Overriding_Renamings; |
| ... |
| package R is |
| function F (..); |
| ... |
| function F (..) renames R.F; |
| end R; |
| @end example |
| |
| even though |
| RM 8.3 (15) stipulates that an overridden operation is not visible within the |
| declaration of the overriding operation. |
| |
| @node Pragma Partition_Elaboration_Policy,Pragma Part_Of,Pragma Overriding_Renamings,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-partition-elaboration-policy}@anchor{92} |
| @section Pragma Partition_Elaboration_Policy |
| |
| |
| Syntax: |
| |
| @example |
| pragma Partition_Elaboration_Policy (POLICY_IDENTIFIER); |
| |
| POLICY_IDENTIFIER ::= Concurrent | Sequential |
| @end example |
| |
| This pragma is standard in Ada 2005, but is available in all earlier |
| versions of Ada as an implementation-defined pragma. |
| See Ada 2012 Reference Manual for details. |
| |
| @node Pragma Part_Of,Pragma Passive,Pragma Partition_Elaboration_Policy,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-part-of}@anchor{93} |
| @section Pragma Part_Of |
| |
| |
| For the description of this pragma, see SPARK 2014 Reference Manual, |
| section 7.2.6. |
| |
| @node Pragma Passive,Pragma Persistent_BSS,Pragma Part_Of,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-passive}@anchor{94} |
| @section Pragma Passive |
| |
| |
| Syntax: |
| |
| @example |
| pragma Passive [(Semaphore | No)]; |
| @end example |
| |
| Syntax checked, but otherwise ignored by GNAT. This is recognized for |
| compatibility with DEC Ada 83 implementations, where it is used within a |
| task definition to request that a task be made passive. If the argument |
| @cite{Semaphore} is present, or the argument is omitted, then DEC Ada 83 |
| treats the pragma as an assertion that the containing task is passive |
| and that optimization of context switch with this task is permitted and |
| desired. If the argument @cite{No} is present, the task must not be |
| optimized. GNAT does not attempt to optimize any tasks in this manner |
| (since protected objects are available in place of passive tasks). |
| |
| For more information on the subject of passive tasks, see the section |
| 'Passive Task Optimization' in the GNAT Users Guide. |
| |
| @node Pragma Persistent_BSS,Pragma Polling,Pragma Passive,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-persistent-bss}@anchor{95} |
| @section Pragma Persistent_BSS |
| |
| |
| Syntax: |
| |
| @example |
| pragma Persistent_BSS [(LOCAL_NAME)] |
| @end example |
| |
| This pragma allows selected objects to be placed in the @cite{.persistent_bss} |
| section. On some targets the linker and loader provide for special |
| treatment of this section, allowing a program to be reloaded without |
| affecting the contents of this data (hence the name persistent). |
| |
| There are two forms of usage. If an argument is given, it must be the |
| local name of a library level object, with no explicit initialization |
| and whose type is potentially persistent. If no argument is given, then |
| the pragma is a configuration pragma, and applies to all library level |
| objects with no explicit initialization of potentially persistent types. |
| |
| A potentially persistent type is a scalar type, or an untagged, |
| non-discriminated record, all of whose components have no explicit |
| initialization and are themselves of a potentially persistent type, |
| or an array, all of whose constraints are static, and whose component |
| type is potentially persistent. |
| |
| If this pragma is used on a target where this feature is not supported, |
| then the pragma will be ignored. See also @cite{pragma Linker_Section}. |
| |
| @node Pragma Polling,Pragma Post,Pragma Persistent_BSS,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-polling}@anchor{96} |
| @section Pragma Polling |
| |
| |
| Syntax: |
| |
| @example |
| pragma Polling (ON | OFF); |
| @end example |
| |
| This pragma controls the generation of polling code. This is normally off. |
| If @cite{pragma Polling (ON)} is used then periodic calls are generated to |
| the routine @cite{Ada.Exceptions.Poll}. This routine is a separate unit in the |
| runtime library, and can be found in file @code{a-excpol.adb}. |
| |
| Pragma @cite{Polling} can appear as a configuration pragma (for example it |
| can be placed in the @code{gnat.adc} file) to enable polling globally, or it |
| can be used in the statement or declaration sequence to control polling |
| more locally. |
| |
| A call to the polling routine is generated at the start of every loop and |
| at the start of every subprogram call. This guarantees that the @cite{Poll} |
| routine is called frequently, and places an upper bound (determined by |
| the complexity of the code) on the period between two @cite{Poll} calls. |
| |
| The primary purpose of the polling interface is to enable asynchronous |
| aborts on targets that cannot otherwise support it (for example Windows |
| NT), but it may be used for any other purpose requiring periodic polling. |
| The standard version is null, and can be replaced by a user program. This |
| will require re-compilation of the @cite{Ada.Exceptions} package that can |
| be found in files @code{a-except.ads} and @code{a-except.adb}. |
| |
| A standard alternative unit (in file @code{4wexcpol.adb} in the standard GNAT |
| distribution) is used to enable the asynchronous abort capability on |
| targets that do not normally support the capability. The version of |
| @cite{Poll} in this file makes a call to the appropriate runtime routine |
| to test for an abort condition. |
| |
| Note that polling can also be enabled by use of the @emph{-gnatP} switch. |
| See the section on switches for gcc in the @cite{GNAT User's Guide}. |
| |
| @node Pragma Post,Pragma Postcondition,Pragma Polling,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-post}@anchor{97} |
| @section Pragma Post |
| |
| |
| @geindex Post |
| |
| @geindex Checks |
| @geindex postconditions |
| |
| Syntax: |
| |
| @example |
| pragma Post (Boolean_Expression); |
| @end example |
| |
| The @cite{Post} pragma is intended to be an exact replacement for |
| the language-defined |
| @cite{Post} aspect, and shares its restrictions and semantics. |
| It must appear either immediately following the corresponding |
| subprogram declaration (only other pragmas may intervene), or |
| if there is no separate subprogram declaration, then it can |
| appear at the start of the declarations in a subprogram body |
| (preceded only by other pragmas). |
| |
| @node Pragma Postcondition,Pragma Post_Class,Pragma Post,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-postcondition}@anchor{98} |
| @section Pragma Postcondition |
| |
| |
| @geindex Postcondition |
| |
| @geindex Checks |
| @geindex postconditions |
| |
| Syntax: |
| |
| @example |
| pragma Postcondition ( |
| [Check =>] Boolean_Expression |
| [,[Message =>] String_Expression]); |
| @end example |
| |
| The @cite{Postcondition} pragma allows specification of automatic |
| postcondition checks for subprograms. These checks are similar to |
| assertions, but are automatically inserted just prior to the return |
| statements of the subprogram with which they are associated (including |
| implicit returns at the end of procedure bodies and associated |
| exception handlers). |
| |
| In addition, the boolean expression which is the condition which |
| must be true may contain references to function'Result in the case |
| of a function to refer to the returned value. |
| |
| @cite{Postcondition} pragmas may appear either immediately following the |
| (separate) declaration of a subprogram, or at the start of the |
| declarations of a subprogram body. Only other pragmas may intervene |
| (that is appear between the subprogram declaration and its |
| postconditions, or appear before the postcondition in the |
| declaration sequence in a subprogram body). In the case of a |
| postcondition appearing after a subprogram declaration, the |
| formal arguments of the subprogram are visible, and can be |
| referenced in the postcondition expressions. |
| |
| The postconditions are collected and automatically tested just |
| before any return (implicit or explicit) in the subprogram body. |
| A postcondition is only recognized if postconditions are active |
| at the time the pragma is encountered. The compiler switch @emph{gnata} |
| turns on all postconditions by default, and pragma @cite{Check_Policy} |
| with an identifier of @cite{Postcondition} can also be used to |
| control whether postconditions are active. |
| |
| The general approach is that postconditions are placed in the spec |
| if they represent functional aspects which make sense to the client. |
| For example we might have: |
| |
| @example |
| function Direction return Integer; |
| pragma Postcondition |
| (Direction'Result = +1 |
| or else |
| Direction'Result = -1); |
| @end example |
| |
| which serves to document that the result must be +1 or -1, and |
| will test that this is the case at run time if postcondition |
| checking is active. |
| |
| Postconditions within the subprogram body can be used to |
| check that some internal aspect of the implementation, |
| not visible to the client, is operating as expected. |
| For instance if a square root routine keeps an internal |
| counter of the number of times it is called, then we |
| might have the following postcondition: |
| |
| @example |
| Sqrt_Calls : Natural := 0; |
| |
| function Sqrt (Arg : Float) return Float is |
| pragma Postcondition |
| (Sqrt_Calls = Sqrt_Calls'Old + 1); |
| ... |
| end Sqrt |
| @end example |
| |
| As this example, shows, the use of the @cite{Old} attribute |
| is often useful in postconditions to refer to the state on |
| entry to the subprogram. |
| |
| Note that postconditions are only checked on normal returns |
| from the subprogram. If an abnormal return results from |
| raising an exception, then the postconditions are not checked. |
| |
| If a postcondition fails, then the exception |
| @cite{System.Assertions.Assert_Failure} is raised. If |
| a message argument was supplied, then the given string |
| will be used as the exception message. If no message |
| argument was supplied, then the default message has |
| the form "Postcondition failed at file_name:line". The |
| exception is raised in the context of the subprogram |
| body, so it is possible to catch postcondition failures |
| within the subprogram body itself. |
| |
| Within a package spec, normal visibility rules |
| in Ada would prevent forward references within a |
| postcondition pragma to functions defined later in |
| the same package. This would introduce undesirable |
| ordering constraints. To avoid this problem, all |
| postcondition pragmas are analyzed at the end of |
| the package spec, allowing forward references. |
| |
| The following example shows that this even allows |
| mutually recursive postconditions as in: |
| |
| @example |
| package Parity_Functions is |
| function Odd (X : Natural) return Boolean; |
| pragma Postcondition |
| (Odd'Result = |
| (x = 1 |
| or else |
| (x /= 0 and then Even (X - 1)))); |
| |
| function Even (X : Natural) return Boolean; |
| pragma Postcondition |
| (Even'Result = |
| (x = 0 |
| or else |
| (x /= 1 and then Odd (X - 1)))); |
| |
| end Parity_Functions; |
| @end example |
| |
| There are no restrictions on the complexity or form of |
| conditions used within @cite{Postcondition} pragmas. |
| The following example shows that it is even possible |
| to verify performance behavior. |
| |
| @example |
| package Sort is |
| |
| Performance : constant Float; |
| -- Performance constant set by implementation |
| -- to match target architecture behavior. |
| |
| procedure Treesort (Arg : String); |
| -- Sorts characters of argument using N*logN sort |
| pragma Postcondition |
| (Float (Clock - Clock'Old) <= |
| Float (Arg'Length) * |
| log (Float (Arg'Length)) * |
| Performance); |
| end Sort; |
| @end example |
| |
| Note: postcondition pragmas associated with subprograms that are |
| marked as Inline_Always, or those marked as Inline with front-end |
| inlining (-gnatN option set) are accepted and legality-checked |
| by the compiler, but are ignored at run-time even if postcondition |
| checking is enabled. |
| |
| Note that pragma @cite{Postcondition} differs from the language-defined |
| @cite{Post} aspect (and corresponding @cite{Post} pragma) in allowing |
| multiple occurrences, allowing occurences in the body even if there |
| is a separate spec, and allowing a second string parameter, and the |
| use of the pragma identifier @cite{Check}. Historically, pragma |
| @cite{Postcondition} was implemented prior to the development of |
| Ada 2012, and has been retained in its original form for |
| compatibility purposes. |
| |
| @node Pragma Post_Class,Pragma Pre,Pragma Postcondition,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-post-class}@anchor{99} |
| @section Pragma Post_Class |
| |
| |
| @geindex Post |
| |
| @geindex Checks |
| @geindex postconditions |
| |
| Syntax: |
| |
| @example |
| pragma Post_Class (Boolean_Expression); |
| @end example |
| |
| The @cite{Post_Class} pragma is intended to be an exact replacement for |
| the language-defined |
| @cite{Post'Class} aspect, and shares its restrictions and semantics. |
| It must appear either immediately following the corresponding |
| subprogram declaration (only other pragmas may intervene), or |
| if there is no separate subprogram declaration, then it can |
| appear at the start of the declarations in a subprogram body |
| (preceded only by other pragmas). |
| |
| Note: This pragma is called @cite{Post_Class} rather than |
| @cite{Post'Class} because the latter would not be strictly |
| conforming to the allowed syntax for pragmas. The motivation |
| for provinding pragmas equivalent to the aspects is to allow a program |
| to be written using the pragmas, and then compiled if necessary |
| using an Ada compiler that does not recognize the pragmas or |
| aspects, but is prepared to ignore the pragmas. The assertion |
| policy that controls this pragma is @cite{Post'Class}, not |
| @cite{Post_Class}. |
| |
| @node Pragma Pre,Pragma Precondition,Pragma Post_Class,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-pre}@anchor{9a} |
| @section Pragma Pre |
| |
| |
| @geindex Pre |
| |
| @geindex Checks |
| @geindex preconditions |
| |
| Syntax: |
| |
| @example |
| pragma Pre (Boolean_Expression); |
| @end example |
| |
| The @cite{Pre} pragma is intended to be an exact replacement for |
| the language-defined |
| @cite{Pre} aspect, and shares its restrictions and semantics. |
| It must appear either immediately following the corresponding |
| subprogram declaration (only other pragmas may intervene), or |
| if there is no separate subprogram declaration, then it can |
| appear at the start of the declarations in a subprogram body |
| (preceded only by other pragmas). |
| |
| @node Pragma Precondition,Pragma Predicate,Pragma Pre,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-precondition}@anchor{9b} |
| @section Pragma Precondition |
| |
| |
| @geindex Preconditions |
| |
| @geindex Checks |
| @geindex preconditions |
| |
| Syntax: |
| |
| @example |
| pragma Precondition ( |
| [Check =>] Boolean_Expression |
| [,[Message =>] String_Expression]); |
| @end example |
| |
| The @cite{Precondition} pragma is similar to @cite{Postcondition} |
| except that the corresponding checks take place immediately upon |
| entry to the subprogram, and if a precondition fails, the exception |
| is raised in the context of the caller, and the attribute 'Result |
| cannot be used within the precondition expression. |
| |
| Otherwise, the placement and visibility rules are identical to those |
| described for postconditions. The following is an example of use |
| within a package spec: |
| |
| @example |
| package Math_Functions is |
| ... |
| function Sqrt (Arg : Float) return Float; |
| pragma Precondition (Arg >= 0.0) |
| ... |
| end Math_Functions; |
| @end example |
| |
| @cite{Precondition} pragmas may appear either immediately following the |
| (separate) declaration of a subprogram, or at the start of the |
| declarations of a subprogram body. Only other pragmas may intervene |
| (that is appear between the subprogram declaration and its |
| postconditions, or appear before the postcondition in the |
| declaration sequence in a subprogram body). |
| |
| Note: precondition pragmas associated with subprograms that are |
| marked as Inline_Always, or those marked as Inline with front-end |
| inlining (-gnatN option set) are accepted and legality-checked |
| by the compiler, but are ignored at run-time even if precondition |
| checking is enabled. |
| |
| Note that pragma @cite{Precondition} differs from the language-defined |
| @cite{Pre} aspect (and corresponding @cite{Pre} pragma) in allowing |
| multiple occurrences, allowing occurences in the body even if there |
| is a separate spec, and allowing a second string parameter, and the |
| use of the pragma identifier @cite{Check}. Historically, pragma |
| @cite{Precondition} was implemented prior to the development of |
| Ada 2012, and has been retained in its original form for |
| compatibility purposes. |
| |
| @node Pragma Predicate,Pragma Preelaborable_Initialization,Pragma Precondition,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-predicate}@anchor{9c} |
| @section Pragma Predicate |
| |
| |
| Syntax: |
| |
| @example |
| pragma Predicate |
| ([Entity =>] type_LOCAL_NAME, |
| [Check =>] EXPRESSION); |
| @end example |
| |
| This pragma (available in all versions of Ada in GNAT) encompasses both |
| the @cite{Static_Predicate} and @cite{Dynamic_Predicate} aspects in |
| Ada 2012. A predicate is regarded as static if it has an allowed form |
| for @cite{Static_Predicate} and is otherwise treated as a |
| @cite{Dynamic_Predicate}. Otherwise, predicates specified by this |
| pragma behave exactly as described in the Ada 2012 reference manual. |
| For example, if we have |
| |
| @example |
| type R is range 1 .. 10; |
| subtype S is R; |
| pragma Predicate (Entity => S, Check => S not in 4 .. 6); |
| subtype Q is R |
| pragma Predicate (Entity => Q, Check => F(Q) or G(Q)); |
| @end example |
| |
| the effect is identical to the following Ada 2012 code: |
| |
| @example |
| type R is range 1 .. 10; |
| subtype S is R with |
| Static_Predicate => S not in 4 .. 6; |
| subtype Q is R with |
| Dynamic_Predicate => F(Q) or G(Q); |
| @end example |
| |
| Note that there is are no pragmas @cite{Dynamic_Predicate} |
| or @cite{Static_Predicate}. That is |
| because these pragmas would affect legality and semantics of |
| the program and thus do not have a neutral effect if ignored. |
| The motivation behind providing pragmas equivalent to |
| corresponding aspects is to allow a program to be written |
| using the pragmas, and then compiled with a compiler that |
| will ignore the pragmas. That doesn't work in the case of |
| static and dynamic predicates, since if the corresponding |
| pragmas are ignored, then the behavior of the program is |
| fundamentally changed (for example a membership test |
| @cite{A in B} would not take into account a predicate |
| defined for subtype B). When following this approach, the |
| use of predicates should be avoided. |
| |
| @node Pragma Preelaborable_Initialization,Pragma Prefix_Exception_Messages,Pragma Predicate,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-preelaborable-initialization}@anchor{9d} |
| @section Pragma Preelaborable_Initialization |
| |
| |
| Syntax: |
| |
| @example |
| pragma Preelaborable_Initialization (DIRECT_NAME); |
| @end example |
| |
| This pragma is standard in Ada 2005, but is available in all earlier |
| versions of Ada as an implementation-defined pragma. |
| See Ada 2012 Reference Manual for details. |
| |
| @node Pragma Prefix_Exception_Messages,Pragma Pre_Class,Pragma Preelaborable_Initialization,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-prefix-exception-messages}@anchor{9e} |
| @section Pragma Prefix_Exception_Messages |
| |
| |
| @geindex Prefix_Exception_Messages |
| |
| @geindex exception |
| |
| @geindex Exception_Message |
| |
| Syntax: |
| |
| @example |
| pragma Prefix_Exception_Messages; |
| @end example |
| |
| This is an implementation-defined configuration pragma that affects the |
| behavior of raise statements with a message given as a static string |
| constant (typically a string literal). In such cases, the string will |
| be automatically prefixed by the name of the enclosing entity (giving |
| the package and subprogram containing the raise statement). This helps |
| to identify where messages are coming from, and this mode is automatic |
| for the run-time library. |
| |
| The pragma has no effect if the message is computed with an expression other |
| than a static string constant, since the assumption in this case is that |
| the program computes exactly the string it wants. If you still want the |
| prefixing in this case, you can always call |
| @cite{GNAT.Source_Info.Enclosing_Entity} and prepend the string manually. |
| |
| @node Pragma Pre_Class,Pragma Priority_Specific_Dispatching,Pragma Prefix_Exception_Messages,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-pre-class}@anchor{9f} |
| @section Pragma Pre_Class |
| |
| |
| @geindex Pre_Class |
| |
| @geindex Checks |
| @geindex preconditions |
| |
| Syntax: |
| |
| @example |
| pragma Pre_Class (Boolean_Expression); |
| @end example |
| |
| The @cite{Pre_Class} pragma is intended to be an exact replacement for |
| the language-defined |
| @cite{Pre'Class} aspect, and shares its restrictions and semantics. |
| It must appear either immediately following the corresponding |
| subprogram declaration (only other pragmas may intervene), or |
| if there is no separate subprogram declaration, then it can |
| appear at the start of the declarations in a subprogram body |
| (preceded only by other pragmas). |
| |
| Note: This pragma is called @cite{Pre_Class} rather than |
| @cite{Pre'Class} because the latter would not be strictly |
| conforming to the allowed syntax for pragmas. The motivation |
| for providing pragmas equivalent to the aspects is to allow a program |
| to be written using the pragmas, and then compiled if necessary |
| using an Ada compiler that does not recognize the pragmas or |
| aspects, but is prepared to ignore the pragmas. The assertion |
| policy that controls this pragma is @cite{Pre'Class}, not |
| @cite{Pre_Class}. |
| |
| @node Pragma Priority_Specific_Dispatching,Pragma Profile,Pragma Pre_Class,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-priority-specific-dispatching}@anchor{a0} |
| @section Pragma Priority_Specific_Dispatching |
| |
| |
| Syntax: |
| |
| @example |
| pragma Priority_Specific_Dispatching ( |
| POLICY_IDENTIFIER, |
| first_priority_EXPRESSION, |
| last_priority_EXPRESSION) |
| |
| POLICY_IDENTIFIER ::= |
| EDF_Across_Priorities | |
| FIFO_Within_Priorities | |
| Non_Preemptive_Within_Priorities | |
| Round_Robin_Within_Priorities |
| @end example |
| |
| This pragma is standard in Ada 2005, but is available in all earlier |
| versions of Ada as an implementation-defined pragma. |
| See Ada 2012 Reference Manual for details. |
| |
| @node Pragma Profile,Pragma Profile_Warnings,Pragma Priority_Specific_Dispatching,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-profile}@anchor{a1} |
| @section Pragma Profile |
| |
| |
| Syntax: |
| |
| @example |
| pragma Profile (Ravenscar | Restricted | Rational); |
| @end example |
| |
| This pragma is standard in Ada 2005, but is available in all earlier |
| versions of Ada as an implementation-defined pragma. This is a |
| configuration pragma that establishes a set of configuration pragmas |
| that depend on the argument. @cite{Ravenscar} is standard in Ada 2005. |
| The other two possibilities (@cite{Restricted} or @cite{Rational}) |
| are implementation-defined. The set of configuration pragmas |
| is defined in the following sections. |
| |
| |
| @itemize * |
| |
| @item |
| Pragma Profile (Ravenscar) |
| |
| The @cite{Ravenscar} profile is standard in Ada 2005, |
| but is available in all earlier |
| versions of Ada as an implementation-defined pragma. This profile |
| establishes the following set of configuration pragmas: |
| |
| |
| @itemize * |
| |
| @item |
| @code{Task_Dispatching_Policy (FIFO_Within_Priorities)} |
| |
| [RM D.2.2] Tasks are dispatched following a preemptive |
| priority-ordered scheduling policy. |
| |
| @item |
| @code{Locking_Policy (Ceiling_Locking)} |
| |
| [RM D.3] While tasks and interrupts execute a protected action, they inherit |
| the ceiling priority of the corresponding protected object. |
| |
| @item |
| @code{Detect_Blocking} |
| |
| This pragma forces the detection of potentially blocking operations within a |
| protected operation, and to raise Program_Error if that happens. |
| @end itemize |
| |
| plus the following set of restrictions: |
| |
| |
| @itemize * |
| |
| @item |
| @code{Max_Entry_Queue_Length => 1} |
| |
| No task can be queued on a protected entry. |
| |
| @item |
| @code{Max_Protected_Entries => 1} |
| |
| @item |
| @code{Max_Task_Entries => 0} |
| |
| No rendezvous statements are allowed. |
| |
| @item |
| @code{No_Abort_Statements} |
| |
| @item |
| @code{No_Dynamic_Attachment} |
| |
| @item |
| @code{No_Dynamic_Priorities} |
| |
| @item |
| @code{No_Implicit_Heap_Allocations} |
| |
| @item |
| @code{No_Local_Protected_Objects} |
| |
| @item |
| @code{No_Local_Timing_Events} |
| |
| @item |
| @code{No_Protected_Type_Allocators} |
| |
| @item |
| @code{No_Relative_Delay} |
| |
| @item |
| @code{No_Requeue_Statements} |
| |
| @item |
| @code{No_Select_Statements} |
| |
| @item |
| @code{No_Specific_Termination_Handlers} |
| |
| @item |
| @code{No_Task_Allocators} |
| |
| @item |
| @code{No_Task_Hierarchy} |
| |
| @item |
| @code{No_Task_Termination} |
| |
| @item |
| @code{Simple_Barriers} |
| @end itemize |
| |
| The Ravenscar profile also includes the following restrictions that specify |
| that there are no semantic dependences on the corresponding predefined |
| packages: |
| |
| |
| @itemize * |
| |
| @item |
| @code{No_Dependence => Ada.Asynchronous_Task_Control} |
| |
| @item |
| @code{No_Dependence => Ada.Calendar} |
| |
| @item |
| @code{No_Dependence => Ada.Execution_Time.Group_Budget} |
| |
| @item |
| @code{No_Dependence => Ada.Execution_Time.Timers} |
| |
| @item |
| @code{No_Dependence => Ada.Task_Attributes} |
| |
| @item |
| @code{No_Dependence => System.Multiprocessors.Dispatching_Domains} |
| @end itemize |
| |
| This set of configuration pragmas and restrictions correspond to the |
| definition of the 'Ravenscar Profile' for limited tasking, devised and |
| published by the @cite{International Real-Time Ada Workshop@comma{} 1997}. |
| A description is also available at |
| @indicateurl{http://www-users.cs.york.ac.uk/~burns/ravenscar.ps}. |
| |
| The original definition of the profile was revised at subsequent IRTAW |
| meetings. It has been included in the ISO |
| @cite{Guide for the Use of the Ada Programming Language in High Integrity Systems}, |
| and was made part of the Ada 2005 standard. |
| The formal definition given by |
| the Ada Rapporteur Group (ARG) can be found in two Ada Issues (AI-249 and |
| AI-305) available at |
| @indicateurl{http://www.ada-auth.org/cgi-bin/cvsweb.cgi/ais/ai-00249.txt} and |
| @indicateurl{http://www.ada-auth.org/cgi-bin/cvsweb.cgi/ais/ai-00305.txt}. |
| |
| The above set is a superset of the restrictions provided by pragma |
| @code{Profile (Restricted)}, it includes six additional restrictions |
| (@code{Simple_Barriers}, @code{No_Select_Statements}, |
| @code{No_Calendar}, @code{No_Implicit_Heap_Allocations}, |
| @code{No_Relative_Delay} and @code{No_Task_Termination}). This means |
| that pragma @code{Profile (Ravenscar)}, like the pragma |
| @code{Profile (Restricted)}, |
| automatically causes the use of a simplified, |
| more efficient version of the tasking run-time library. |
| |
| @item |
| Pragma Profile (Restricted) |
| |
| This profile corresponds to the GNAT restricted run time. It |
| establishes the following set of restrictions: |
| |
| |
| @itemize * |
| |
| @item |
| @code{No_Abort_Statements} |
| |
| @item |
| @code{No_Entry_Queue} |
| |
| @item |
| @code{No_Task_Hierarchy} |
| |
| @item |
| @code{No_Task_Allocators} |
| |
| @item |
| @code{No_Dynamic_Priorities} |
| |
| @item |
| @code{No_Terminate_Alternatives} |
| |
| @item |
| @code{No_Dynamic_Attachment} |
| |
| @item |
| @code{No_Protected_Type_Allocators} |
| |
| @item |
| @code{No_Local_Protected_Objects} |
| |
| @item |
| @code{No_Requeue_Statements} |
| |
| @item |
| @code{No_Task_Attributes_Package} |
| |
| @item |
| @code{Max_Asynchronous_Select_Nesting = 0} |
| |
| @item |
| @code{Max_Task_Entries = 0} |
| |
| @item |
| @code{Max_Protected_Entries = 1} |
| |
| @item |
| @code{Max_Select_Alternatives = 0} |
| @end itemize |
| |
| This set of restrictions causes the automatic selection of a simplified |
| version of the run time that provides improved performance for the |
| limited set of tasking functionality permitted by this set of restrictions. |
| |
| @item |
| Pragma Profile (Rational) |
| |
| The Rational profile is intended to facilitate porting legacy code that |
| compiles with the Rational APEX compiler, even when the code includes non- |
| conforming Ada constructs. The profile enables the following three pragmas: |
| |
| |
| @itemize * |
| |
| @item |
| @code{pragma Implicit_Packing} |
| |
| @item |
| @code{pragma Overriding_Renamings} |
| |
| @item |
| @code{pragma Use_VADS_Size} |
| @end itemize |
| @end itemize |
| |
| @node Pragma Profile_Warnings,Pragma Propagate_Exceptions,Pragma Profile,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-profile-warnings}@anchor{a2} |
| @section Pragma Profile_Warnings |
| |
| |
| Syntax: |
| |
| @example |
| pragma Profile_Warnings (Ravenscar | Restricted | Rational); |
| @end example |
| |
| This is an implementation-defined pragma that is similar in |
| effect to @cite{pragma Profile} except that instead of |
| generating @cite{Restrictions} pragmas, it generates |
| @cite{Restriction_Warnings} pragmas. The result is that |
| violations of the profile generate warning messages instead |
| of error messages. |
| |
| @node Pragma Propagate_Exceptions,Pragma Provide_Shift_Operators,Pragma Profile_Warnings,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-propagate-exceptions}@anchor{a3} |
| @section Pragma Propagate_Exceptions |
| |
| |
| @geindex Interfacing to C++ |
| |
| Syntax: |
| |
| @example |
| pragma Propagate_Exceptions; |
| @end example |
| |
| This pragma is now obsolete and, other than generating a warning if warnings |
| on obsolescent features are enabled, is ignored. |
| It is retained for compatibility |
| purposes. It used to be used in connection with optimization of |
| a now-obsolete mechanism for implementation of exceptions. |
| |
| @node Pragma Provide_Shift_Operators,Pragma Psect_Object,Pragma Propagate_Exceptions,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-provide-shift-operators}@anchor{a4} |
| @section Pragma Provide_Shift_Operators |
| |
| |
| @geindex Shift operators |
| |
| Syntax: |
| |
| @example |
| pragma Provide_Shift_Operators (integer_first_subtype_LOCAL_NAME); |
| @end example |
| |
| This pragma can be applied to a first subtype local name that specifies |
| either an unsigned or signed type. It has the effect of providing the |
| five shift operators (Shift_Left, Shift_Right, Shift_Right_Arithmetic, |
| Rotate_Left and Rotate_Right) for the given type. It is similar to |
| including the function declarations for these five operators, together |
| with the pragma Import (Intrinsic, ...) statements. |
| |
| @node Pragma Psect_Object,Pragma Pure_Function,Pragma Provide_Shift_Operators,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-psect-object}@anchor{a5} |
| @section Pragma Psect_Object |
| |
| |
| Syntax: |
| |
| @example |
| pragma Psect_Object ( |
| [Internal =>] LOCAL_NAME, |
| [, [External =>] EXTERNAL_SYMBOL] |
| [, [Size =>] EXTERNAL_SYMBOL]); |
| |
| EXTERNAL_SYMBOL ::= |
| IDENTIFIER |
| | static_string_EXPRESSION |
| @end example |
| |
| This pragma is identical in effect to pragma @cite{Common_Object}. |
| |
| @node Pragma Pure_Function,Pragma Rational,Pragma Psect_Object,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-pure-function}@anchor{a6} |
| @section Pragma Pure_Function |
| |
| |
| Syntax: |
| |
| @example |
| pragma Pure_Function ([Entity =>] function_LOCAL_NAME); |
| @end example |
| |
| This pragma appears in the same declarative part as a function |
| declaration (or a set of function declarations if more than one |
| overloaded declaration exists, in which case the pragma applies |
| to all entities). It specifies that the function @cite{Entity} is |
| to be considered pure for the purposes of code generation. This means |
| that the compiler can assume that there are no side effects, and |
| in particular that two calls with identical arguments produce the |
| same result. It also means that the function can be used in an |
| address clause. |
| |
| Note that, quite deliberately, there are no static checks to try |
| to ensure that this promise is met, so @cite{Pure_Function} can be used |
| with functions that are conceptually pure, even if they do modify |
| global variables. For example, a square root function that is |
| instrumented to count the number of times it is called is still |
| conceptually pure, and can still be optimized, even though it |
| modifies a global variable (the count). Memo functions are another |
| example (where a table of previous calls is kept and consulted to |
| avoid re-computation). |
| |
| Note also that the normal rules excluding optimization of subprograms |
| in pure units (when parameter types are descended from System.Address, |
| or when the full view of a parameter type is limited), do not apply |
| for the Pure_Function case. If you explicitly specify Pure_Function, |
| the compiler may optimize away calls with identical arguments, and |
| if that results in unexpected behavior, the proper action is not to |
| use the pragma for subprograms that are not (conceptually) pure. |
| |
| Note: Most functions in a @cite{Pure} package are automatically pure, and |
| there is no need to use pragma @cite{Pure_Function} for such functions. One |
| exception is any function that has at least one formal of type |
| @cite{System.Address} or a type derived from it. Such functions are not |
| considered pure by default, since the compiler assumes that the |
| @cite{Address} parameter may be functioning as a pointer and that the |
| referenced data may change even if the address value does not. |
| Similarly, imported functions are not considered to be pure by default, |
| since there is no way of checking that they are in fact pure. The use |
| of pragma @cite{Pure_Function} for such a function will override these default |
| assumption, and cause the compiler to treat a designated subprogram as pure |
| in these cases. |
| |
| Note: If pragma @cite{Pure_Function} is applied to a renamed function, it |
| applies to the underlying renamed function. This can be used to |
| disambiguate cases of overloading where some but not all functions |
| in a set of overloaded functions are to be designated as pure. |
| |
| If pragma @cite{Pure_Function} is applied to a library level function, the |
| function is also considered pure from an optimization point of view, but the |
| unit is not a Pure unit in the categorization sense. So for example, a function |
| thus marked is free to @cite{with} non-pure units. |
| |
| @node Pragma Rational,Pragma Ravenscar,Pragma Pure_Function,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-rational}@anchor{a7} |
| @section Pragma Rational |
| |
| |
| Syntax: |
| |
| @example |
| pragma Rational; |
| @end example |
| |
| This pragma is considered obsolescent, but is retained for |
| compatibility purposes. It is equivalent to: |
| |
| @example |
| pragma Profile (Rational); |
| @end example |
| |
| @node Pragma Ravenscar,Pragma Refined_Depends,Pragma Rational,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-ravenscar}@anchor{a8} |
| @section Pragma Ravenscar |
| |
| |
| Syntax: |
| |
| @example |
| pragma Ravenscar; |
| @end example |
| |
| This pragma is considered obsolescent, but is retained for |
| compatibility purposes. It is equivalent to: |
| |
| @example |
| pragma Profile (Ravenscar); |
| @end example |
| |
| which is the preferred method of setting the @cite{Ravenscar} profile. |
| |
| @node Pragma Refined_Depends,Pragma Refined_Global,Pragma Ravenscar,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-refined-depends}@anchor{a9} |
| @section Pragma Refined_Depends |
| |
| |
| For the description of this pragma, see SPARK 2014 Reference Manual, |
| section 6.1.5. |
| |
| @node Pragma Refined_Global,Pragma Refined_Post,Pragma Refined_Depends,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-refined-global}@anchor{aa} |
| @section Pragma Refined_Global |
| |
| |
| For the description of this pragma, see SPARK 2014 Reference Manual, |
| section 6.1.4. |
| |
| @node Pragma Refined_Post,Pragma Refined_State,Pragma Refined_Global,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-refined-post}@anchor{ab} |
| @section Pragma Refined_Post |
| |
| |
| For the description of this pragma, see SPARK 2014 Reference Manual, |
| section 7.2.7. |
| |
| @node Pragma Refined_State,Pragma Relative_Deadline,Pragma Refined_Post,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-refined-state}@anchor{ac} |
| @section Pragma Refined_State |
| |
| |
| For the description of this pragma, see SPARK 2014 Reference Manual, |
| section 7.2.2. |
| |
| @node Pragma Relative_Deadline,Pragma Remote_Access_Type,Pragma Refined_State,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-relative-deadline}@anchor{ad} |
| @section Pragma Relative_Deadline |
| |
| |
| Syntax: |
| |
| @example |
| pragma Relative_Deadline (time_span_EXPRESSION); |
| @end example |
| |
| This pragma is standard in Ada 2005, but is available in all earlier |
| versions of Ada as an implementation-defined pragma. |
| See Ada 2012 Reference Manual for details. |
| |
| @node Pragma Remote_Access_Type,Pragma Restricted_Run_Time,Pragma Relative_Deadline,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-remote-access-type}@anchor{ae} |
| @section Pragma Remote_Access_Type |
| |
| |
| Syntax: |
| |
| @example |
| pragma Remote_Access_Type ([Entity =>] formal_access_type_LOCAL_NAME); |
| @end example |
| |
| This pragma appears in the formal part of a generic declaration. |
| It specifies an exception to the RM rule from E.2.2(17/2), which forbids |
| the use of a remote access to class-wide type as actual for a formal |
| access type. |
| |
| When this pragma applies to a formal access type @cite{Entity}, that |
| type is treated as a remote access to class-wide type in the generic. |
| It must be a formal general access type, and its designated type must |
| be the class-wide type of a formal tagged limited private type from the |
| same generic declaration. |
| |
| In the generic unit, the formal type is subject to all restrictions |
| pertaining to remote access to class-wide types. At instantiation, the |
| actual type must be a remote access to class-wide type. |
| |
| @node Pragma Restricted_Run_Time,Pragma Restriction_Warnings,Pragma Remote_Access_Type,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-restricted-run-time}@anchor{af} |
| @section Pragma Restricted_Run_Time |
| |
| |
| Syntax: |
| |
| @example |
| pragma Restricted_Run_Time; |
| @end example |
| |
| This pragma is considered obsolescent, but is retained for |
| compatibility purposes. It is equivalent to: |
| |
| @example |
| pragma Profile (Restricted); |
| @end example |
| |
| which is the preferred method of setting the restricted run time |
| profile. |
| |
| @node Pragma Restriction_Warnings,Pragma Reviewable,Pragma Restricted_Run_Time,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-restriction-warnings}@anchor{b0} |
| @section Pragma Restriction_Warnings |
| |
| |
| Syntax: |
| |
| @example |
| pragma Restriction_Warnings |
| (restriction_IDENTIFIER @{, restriction_IDENTIFIER@}); |
| @end example |
| |
| This pragma allows a series of restriction identifiers to be |
| specified (the list of allowed identifiers is the same as for |
| pragma @cite{Restrictions}). For each of these identifiers |
| the compiler checks for violations of the restriction, but |
| generates a warning message rather than an error message |
| if the restriction is violated. |
| |
| One use of this is in situations where you want to know |
| about violations of a restriction, but you want to ignore some of |
| these violations. Consider this example, where you want to set |
| Ada_95 mode and enable style checks, but you want to know about |
| any other use of implementation pragmas: |
| |
| @example |
| pragma Restriction_Warnings (No_Implementation_Pragmas); |
| pragma Warnings (Off, "violation of No_Implementation_Pragmas"); |
| pragma Ada_95; |
| pragma Style_Checks ("2bfhkM160"); |
| pragma Warnings (On, "violation of No_Implementation_Pragmas"); |
| @end example |
| |
| By including the above lines in a configuration pragmas file, |
| the Ada_95 and Style_Checks pragmas are accepted without |
| generating a warning, but any other use of implementation |
| defined pragmas will cause a warning to be generated. |
| |
| @node Pragma Reviewable,Pragma Share_Generic,Pragma Restriction_Warnings,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-reviewable}@anchor{b1} |
| @section Pragma Reviewable |
| |
| |
| Syntax: |
| |
| @example |
| pragma Reviewable; |
| @end example |
| |
| This pragma is an RM-defined standard pragma, but has no effect on the |
| program being compiled, or on the code generated for the program. |
| |
| To obtain the required output specified in RM H.3.1, the compiler must be |
| run with various special switches as follows: |
| |
| |
| @itemize * |
| |
| @item |
| @emph{Where compiler-generated run-time checks remain} |
| |
| The switch @emph{-gnatGL} |
| may be used to list the expanded code in pseudo-Ada form. |
| Runtime checks show up in the listing either as explicit |
| checks or operators marked with @{@} to indicate a check is present. |
| |
| @item |
| @emph{An identification of known exceptions at compile time} |
| |
| If the program is compiled with @emph{-gnatwa}, |
| the compiler warning messages will indicate all cases where the compiler |
| detects that an exception is certain to occur at run time. |
| |
| @item |
| @emph{Possible reads of uninitialized variables} |
| |
| The compiler warns of many such cases, but its output is incomplete. |
| @end itemize |
| |
| |
| A supplemental static analysis tool |
| may be used to obtain a comprehensive list of all |
| possible points at which uninitialized data may be read. |
| |
| |
| @itemize * |
| |
| @item |
| @emph{Where run-time support routines are implicitly invoked} |
| |
| In the output from @emph{-gnatGL}, |
| run-time calls are explicitly listed as calls to the relevant |
| run-time routine. |
| |
| @item |
| @emph{Object code listing} |
| |
| This may be obtained either by using the @emph{-S} switch, |
| or the objdump utility. |
| |
| @item |
| @emph{Constructs known to be erroneous at compile time} |
| |
| These are identified by warnings issued by the compiler (use @emph{-gnatwa}). |
| |
| @item |
| @emph{Stack usage information} |
| |
| Static stack usage data (maximum per-subprogram) can be obtained via the |
| @emph{-fstack-usage} switch to the compiler. |
| Dynamic stack usage data (per task) can be obtained via the @emph{-u} switch |
| to gnatbind |
| @end itemize |
| |
| |
| |
| @itemize * |
| |
| @item |
| @emph{Object code listing of entire partition} |
| |
| This can be obtained by compiling the partition with @emph{-S}, |
| or by applying objdump |
| to all the object files that are part of the partition. |
| |
| @item |
| @emph{A description of the run-time model} |
| |
| The full sources of the run-time are available, and the documentation of |
| these routines describes how these run-time routines interface to the |
| underlying operating system facilities. |
| |
| @item |
| @emph{Control and data-flow information} |
| @end itemize |
| |
| |
| A supplemental static analysis tool |
| may be used to obtain complete control and data-flow information, as well as |
| comprehensive messages identifying possible problems based on this |
| information. |
| |
| @node Pragma Share_Generic,Pragma Shared,Pragma Reviewable,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-share-generic}@anchor{b2} |
| @section Pragma Share_Generic |
| |
| |
| Syntax: |
| |
| @example |
| pragma Share_Generic (GNAME @{, GNAME@}); |
| |
| GNAME ::= generic_unit_NAME | generic_instance_NAME |
| @end example |
| |
| This pragma is provided for compatibility with Dec Ada 83. It has |
| no effect in @cite{GNAT} (which does not implement shared generics), other |
| than to check that the given names are all names of generic units or |
| generic instances. |
| |
| @node Pragma Shared,Pragma Short_Circuit_And_Or,Pragma Share_Generic,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-shared}@anchor{b3} |
| @section Pragma Shared |
| |
| |
| This pragma is provided for compatibility with Ada 83. The syntax and |
| semantics are identical to pragma Atomic. |
| |
| @node Pragma Short_Circuit_And_Or,Pragma Short_Descriptors,Pragma Shared,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-short-circuit-and-or}@anchor{b4} |
| @section Pragma Short_Circuit_And_Or |
| |
| |
| Syntax: |
| |
| @example |
| pragma Short_Circuit_And_Or; |
| @end example |
| |
| This configuration pragma causes any occurrence of the AND operator applied to |
| operands of type Standard.Boolean to be short-circuited (i.e. the AND operator |
| is treated as if it were AND THEN). Or is similarly treated as OR ELSE. This |
| may be useful in the context of certification protocols requiring the use of |
| short-circuited logical operators. If this configuration pragma occurs locally |
| within the file being compiled, it applies only to the file being compiled. |
| There is no requirement that all units in a partition use this option. |
| |
| @node Pragma Short_Descriptors,Pragma Simple_Storage_Pool_Type,Pragma Short_Circuit_And_Or,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-short-descriptors}@anchor{b5} |
| @section Pragma Short_Descriptors |
| |
| |
| Syntax: |
| |
| @example |
| pragma Short_Descriptors |
| @end example |
| |
| This pragma is provided for compatibility with other Ada implementations. It |
| is recognized but ignored by all current versions of GNAT. |
| |
| @node Pragma Simple_Storage_Pool_Type,Pragma Source_File_Name,Pragma Short_Descriptors,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-simple-storage-pool-type}@anchor{b6} |
| @section Pragma Simple_Storage_Pool_Type |
| |
| |
| @geindex Storage pool |
| @geindex simple |
| |
| @geindex Simple storage pool |
| |
| Syntax: |
| |
| @example |
| pragma Simple_Storage_Pool_Type (type_LOCAL_NAME); |
| @end example |
| |
| A type can be established as a 'simple storage pool type' by applying |
| the representation pragma @cite{Simple_Storage_Pool_Type} to the type. |
| A type named in the pragma must be a library-level immutably limited record |
| type or limited tagged type declared immediately within a package declaration. |
| The type can also be a limited private type whose full type is allowed as |
| a simple storage pool type. |
| |
| For a simple storage pool type @cite{SSP}, nonabstract primitive subprograms |
| @cite{Allocate}, @cite{Deallocate}, and @cite{Storage_Size} can be declared that |
| are subtype conformant with the following subprogram declarations: |
| |
| @example |
| procedure Allocate |
| (Pool : in out SSP; |
| Storage_Address : out System.Address; |
| Size_In_Storage_Elements : System.Storage_Elements.Storage_Count; |
| Alignment : System.Storage_Elements.Storage_Count); |
| |
| procedure Deallocate |
| (Pool : in out SSP; |
| Storage_Address : System.Address; |
| Size_In_Storage_Elements : System.Storage_Elements.Storage_Count; |
| Alignment : System.Storage_Elements.Storage_Count); |
| |
| function Storage_Size (Pool : SSP) |
| return System.Storage_Elements.Storage_Count; |
| @end example |
| |
| Procedure @cite{Allocate} must be declared, whereas @cite{Deallocate} and |
| @cite{Storage_Size} are optional. If @cite{Deallocate} is not declared, then |
| applying an unchecked deallocation has no effect other than to set its actual |
| parameter to null. If @cite{Storage_Size} is not declared, then the |
| @cite{Storage_Size} attribute applied to an access type associated with |
| a pool object of type SSP returns zero. Additional operations can be declared |
| for a simple storage pool type (such as for supporting a mark/release |
| storage-management discipline). |
| |
| An object of a simple storage pool type can be associated with an access |
| type by specifying the attribute |
| @ref{b7,,Simple_Storage_Pool}. For example: |
| |
| @example |
| My_Pool : My_Simple_Storage_Pool_Type; |
| |
| type Acc is access My_Data_Type; |
| |
| for Acc'Simple_Storage_Pool use My_Pool; |
| @end example |
| |
| See attribute @ref{b7,,Simple_Storage_Pool} |
| for further details. |
| |
| @node Pragma Source_File_Name,Pragma Source_File_Name_Project,Pragma Simple_Storage_Pool_Type,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-source-file-name}@anchor{b8}@anchor{gnat_rm/implementation_defined_pragmas id3}@anchor{b9} |
| @section Pragma Source_File_Name |
| |
| |
| Syntax: |
| |
| @example |
| pragma Source_File_Name ( |
| [Unit_Name =>] unit_NAME, |
| Spec_File_Name => STRING_LITERAL, |
| [Index => INTEGER_LITERAL]); |
| |
| pragma Source_File_Name ( |
| [Unit_Name =>] unit_NAME, |
| Body_File_Name => STRING_LITERAL, |
| [Index => INTEGER_LITERAL]); |
| @end example |
| |
| Use this to override the normal naming convention. It is a configuration |
| pragma, and so has the usual applicability of configuration pragmas |
| (i.e., it applies to either an entire partition, or to all units in a |
| compilation, or to a single unit, depending on how it is used. |
| @cite{unit_name} is mapped to @cite{file_name_literal}. The identifier for |
| the second argument is required, and indicates whether this is the file |
| name for the spec or for the body. |
| |
| The optional Index argument should be used when a file contains multiple |
| units, and when you do not want to use @cite{gnatchop} to separate then |
| into multiple files (which is the recommended procedure to limit the |
| number of recompilations that are needed when some sources change). |
| For instance, if the source file @code{source.ada} contains |
| |
| @example |
| package B is |
| ... |
| end B; |
| |
| with B; |
| procedure A is |
| begin |
| .. |
| end A; |
| @end example |
| |
| you could use the following configuration pragmas: |
| |
| @example |
| pragma Source_File_Name |
| (B, Spec_File_Name => "source.ada", Index => 1); |
| pragma Source_File_Name |
| (A, Body_File_Name => "source.ada", Index => 2); |
| @end example |
| |
| Note that the @cite{gnatname} utility can also be used to generate those |
| configuration pragmas. |
| |
| Another form of the @cite{Source_File_Name} pragma allows |
| the specification of patterns defining alternative file naming schemes |
| to apply to all files. |
| |
| @example |
| pragma Source_File_Name |
| ( [Spec_File_Name =>] STRING_LITERAL |
| [,[Casing =>] CASING_SPEC] |
| [,[Dot_Replacement =>] STRING_LITERAL]); |
| |
| pragma Source_File_Name |
| ( [Body_File_Name =>] STRING_LITERAL |
| [,[Casing =>] CASING_SPEC] |
| [,[Dot_Replacement =>] STRING_LITERAL]); |
| |
| pragma Source_File_Name |
| ( [Subunit_File_Name =>] STRING_LITERAL |
| [,[Casing =>] CASING_SPEC] |
| [,[Dot_Replacement =>] STRING_LITERAL]); |
| |
| CASING_SPEC ::= Lowercase | Uppercase | Mixedcase |
| @end example |
| |
| The first argument is a pattern that contains a single asterisk indicating |
| the point at which the unit name is to be inserted in the pattern string |
| to form the file name. The second argument is optional. If present it |
| specifies the casing of the unit name in the resulting file name string. |
| The default is lower case. Finally the third argument allows for systematic |
| replacement of any dots in the unit name by the specified string literal. |
| |
| Note that Source_File_Name pragmas should not be used if you are using |
| project files. The reason for this rule is that the project manager is not |
| aware of these pragmas, and so other tools that use the projet file would not |
| be aware of the intended naming conventions. If you are using project files, |
| file naming is controlled by Source_File_Name_Project pragmas, which are |
| usually supplied automatically by the project manager. A pragma |
| Source_File_Name cannot appear after a @ref{ba,,Pragma Source_File_Name_Project}. |
| |
| For more details on the use of the @cite{Source_File_Name} pragma, see the |
| sections on @cite{Using Other File Names} and @cite{Alternative File Naming Schemes' in the :title:`GNAT User's Guide}. |
| |
| @node Pragma Source_File_Name_Project,Pragma Source_Reference,Pragma Source_File_Name,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas id4}@anchor{bb}@anchor{gnat_rm/implementation_defined_pragmas pragma-source-file-name-project}@anchor{ba} |
| @section Pragma Source_File_Name_Project |
| |
| |
| This pragma has the same syntax and semantics as pragma Source_File_Name. |
| It is only allowed as a stand alone configuration pragma. |
| It cannot appear after a @ref{b8,,Pragma Source_File_Name}, and |
| most importantly, once pragma Source_File_Name_Project appears, |
| no further Source_File_Name pragmas are allowed. |
| |
| The intention is that Source_File_Name_Project pragmas are always |
| generated by the Project Manager in a manner consistent with the naming |
| specified in a project file, and when naming is controlled in this manner, |
| it is not permissible to attempt to modify this naming scheme using |
| Source_File_Name or Source_File_Name_Project pragmas (which would not be |
| known to the project manager). |
| |
| @node Pragma Source_Reference,Pragma SPARK_Mode,Pragma Source_File_Name_Project,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-source-reference}@anchor{bc} |
| @section Pragma Source_Reference |
| |
| |
| Syntax: |
| |
| @example |
| pragma Source_Reference (INTEGER_LITERAL, STRING_LITERAL); |
| @end example |
| |
| This pragma must appear as the first line of a source file. |
| @cite{integer_literal} is the logical line number of the line following |
| the pragma line (for use in error messages and debugging |
| information). @cite{string_literal} is a static string constant that |
| specifies the file name to be used in error messages and debugging |
| information. This is most notably used for the output of @cite{gnatchop} |
| with the @emph{-r} switch, to make sure that the original unchopped |
| source file is the one referred to. |
| |
| The second argument must be a string literal, it cannot be a static |
| string expression other than a string literal. This is because its value |
| is needed for error messages issued by all phases of the compiler. |
| |
| @node Pragma SPARK_Mode,Pragma Static_Elaboration_Desired,Pragma Source_Reference,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-spark-mode}@anchor{bd} |
| @section Pragma SPARK_Mode |
| |
| |
| Syntax: |
| |
| @example |
| pragma SPARK_Mode [(On | Off)] ; |
| @end example |
| |
| In general a program can have some parts that are in SPARK 2014 (and |
| follow all the rules in the SPARK Reference Manual), and some parts |
| that are full Ada 2012. |
| |
| The SPARK_Mode pragma is used to identify which parts are in SPARK |
| 2014 (by default programs are in full Ada). The SPARK_Mode pragma can |
| be used in the following places: |
| |
| |
| @itemize * |
| |
| @item |
| As a configuration pragma, in which case it sets the default mode for |
| all units compiled with this pragma. |
| |
| @item |
| Immediately following a library-level subprogram spec |
| |
| @item |
| Immediately within a library-level package body |
| |
| @item |
| Immediately following the @cite{private} keyword of a library-level |
| package spec |
| |
| @item |
| Immediately following the @cite{begin} keyword of a library-level |
| package body |
| |
| @item |
| Immediately within a library-level subprogram body |
| @end itemize |
| |
| Normally a subprogram or package spec/body inherits the current mode |
| that is active at the point it is declared. But this can be overridden |
| by pragma within the spec or body as above. |
| |
| The basic consistency rule is that you can't turn SPARK_Mode back |
| @cite{On}, once you have explicitly (with a pragma) turned if |
| @cite{Off}. So the following rules apply: |
| |
| If a subprogram spec has SPARK_Mode @cite{Off}, then the body must |
| also have SPARK_Mode @cite{Off}. |
| |
| For a package, we have four parts: |
| |
| |
| @itemize * |
| |
| @item |
| the package public declarations |
| |
| @item |
| the package private part |
| |
| @item |
| the body of the package |
| |
| @item |
| the elaboration code after @cite{begin} |
| @end itemize |
| |
| For a package, the rule is that if you explicitly turn SPARK_Mode |
| @cite{Off} for any part, then all the following parts must have |
| SPARK_Mode @cite{Off}. Note that this may require repeating a pragma |
| SPARK_Mode (@cite{Off}) in the body. For example, if we have a |
| configuration pragma SPARK_Mode (@cite{On}) that turns the mode on by |
| default everywhere, and one particular package spec has pragma |
| SPARK_Mode (@cite{Off}), then that pragma will need to be repeated in |
| the package body. |
| |
| @node Pragma Static_Elaboration_Desired,Pragma Stream_Convert,Pragma SPARK_Mode,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-static-elaboration-desired}@anchor{be} |
| @section Pragma Static_Elaboration_Desired |
| |
| |
| Syntax: |
| |
| @example |
| pragma Static_Elaboration_Desired; |
| @end example |
| |
| This pragma is used to indicate that the compiler should attempt to initialize |
| statically the objects declared in the library unit to which the pragma applies, |
| when these objects are initialized (explicitly or implicitly) by an aggregate. |
| In the absence of this pragma, aggregates in object declarations are expanded |
| into assignments and loops, even when the aggregate components are static |
| constants. When the aggregate is present the compiler builds a static expression |
| that requires no run-time code, so that the initialized object can be placed in |
| read-only data space. If the components are not static, or the aggregate has |
| more that 100 components, the compiler emits a warning that the pragma cannot |
| be obeyed. (See also the restriction No_Implicit_Loops, which supports static |
| construction of larger aggregates with static components that include an others |
| choice.) |
| |
| @node Pragma Stream_Convert,Pragma Style_Checks,Pragma Static_Elaboration_Desired,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-stream-convert}@anchor{bf} |
| @section Pragma Stream_Convert |
| |
| |
| Syntax: |
| |
| @example |
| pragma Stream_Convert ( |
| [Entity =>] type_LOCAL_NAME, |
| [Read =>] function_NAME, |
| [Write =>] function_NAME); |
| @end example |
| |
| This pragma provides an efficient way of providing user-defined stream |
| attributes. Not only is it simpler to use than specifying the attributes |
| directly, but more importantly, it allows the specification to be made in such |
| a way that the predefined unit Ada.Streams is not loaded unless it is actually |
| needed (i.e. unless the stream attributes are actually used); the use of |
| the Stream_Convert pragma adds no overhead at all, unless the stream |
| attributes are actually used on the designated type. |
| |
| The first argument specifies the type for which stream functions are |
| provided. The second parameter provides a function used to read values |
| of this type. It must name a function whose argument type may be any |
| subtype, and whose returned type must be the type given as the first |
| argument to the pragma. |
| |
| The meaning of the @cite{Read} parameter is that if a stream attribute directly |
| or indirectly specifies reading of the type given as the first parameter, |
| then a value of the type given as the argument to the Read function is |
| read from the stream, and then the Read function is used to convert this |
| to the required target type. |
| |
| Similarly the @cite{Write} parameter specifies how to treat write attributes |
| that directly or indirectly apply to the type given as the first parameter. |
| It must have an input parameter of the type specified by the first parameter, |
| and the return type must be the same as the input type of the Read function. |
| The effect is to first call the Write function to convert to the given stream |
| type, and then write the result type to the stream. |
| |
| The Read and Write functions must not be overloaded subprograms. If necessary |
| renamings can be supplied to meet this requirement. |
| The usage of this attribute is best illustrated by a simple example, taken |
| from the GNAT implementation of package Ada.Strings.Unbounded: |
| |
| @example |
| function To_Unbounded (S : String) return Unbounded_String |
| renames To_Unbounded_String; |
| |
| pragma Stream_Convert |
| (Unbounded_String, To_Unbounded, To_String); |
| @end example |
| |
| The specifications of the referenced functions, as given in the Ada |
| Reference Manual are: |
| |
| @example |
| function To_Unbounded_String (Source : String) |
| return Unbounded_String; |
| |
| function To_String (Source : Unbounded_String) |
| return String; |
| @end example |
| |
| The effect is that if the value of an unbounded string is written to a stream, |
| then the representation of the item in the stream is in the same format that |
| would be used for @cite{Standard.String'Output}, and this same representation |
| is expected when a value of this type is read from the stream. Note that the |
| value written always includes the bounds, even for Unbounded_String'Write, |
| since Unbounded_String is not an array type. |
| |
| Note that the @cite{Stream_Convert} pragma is not effective in the case of |
| a derived type of a non-limited tagged type. If such a type is specified then |
| the pragma is silently ignored, and the default implementation of the stream |
| attributes is used instead. |
| |
| @node Pragma Style_Checks,Pragma Subtitle,Pragma Stream_Convert,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-style-checks}@anchor{c0} |
| @section Pragma Style_Checks |
| |
| |
| Syntax: |
| |
| @example |
| pragma Style_Checks (string_LITERAL | ALL_CHECKS | |
| On | Off [, LOCAL_NAME]); |
| @end example |
| |
| This pragma is used in conjunction with compiler switches to control the |
| built in style checking provided by GNAT. The compiler switches, if set, |
| provide an initial setting for the switches, and this pragma may be used |
| to modify these settings, or the settings may be provided entirely by |
| the use of the pragma. This pragma can be used anywhere that a pragma |
| is legal, including use as a configuration pragma (including use in |
| the @code{gnat.adc} file). |
| |
| The form with a string literal specifies which style options are to be |
| activated. These are additive, so they apply in addition to any previously |
| set style check options. The codes for the options are the same as those |
| used in the @emph{-gnaty} switch to @emph{gcc} or @emph{gnatmake}. |
| For example the following two methods can be used to enable |
| layout checking: |
| |
| |
| @itemize * |
| |
| @item |
| @example |
| pragma Style_Checks ("l"); |
| @end example |
| |
| @item |
| @example |
| gcc -c -gnatyl ... |
| @end example |
| @end itemize |
| |
| The form ALL_CHECKS activates all standard checks (its use is equivalent |
| to the use of the @cite{gnaty} switch with no options. |
| See the @cite{GNAT User's Guide} for details.) |
| |
| Note: the behavior is slightly different in GNAT mode (@emph{-gnatg} used). |
| In this case, ALL_CHECKS implies the standard set of GNAT mode style check |
| options (i.e. equivalent to @emph{-gnatyg}). |
| |
| The forms with @cite{Off} and @cite{On} |
| can be used to temporarily disable style checks |
| as shown in the following example: |
| |
| @example |
| pragma Style_Checks ("k"); -- requires keywords in lower case |
| pragma Style_Checks (Off); -- turn off style checks |
| NULL; -- this will not generate an error message |
| pragma Style_Checks (On); -- turn style checks back on |
| NULL; -- this will generate an error message |
| @end example |
| |
| Finally the two argument form is allowed only if the first argument is |
| @cite{On} or @cite{Off}. The effect is to turn of semantic style checks |
| for the specified entity, as shown in the following example: |
| |
| @example |
| pragma Style_Checks ("r"); -- require consistency of identifier casing |
| Arg : Integer; |
| Rf1 : Integer := ARG; -- incorrect, wrong case |
| pragma Style_Checks (Off, Arg); |
| Rf2 : Integer := ARG; -- OK, no error |
| @end example |
| |
| @node Pragma Subtitle,Pragma Suppress,Pragma Style_Checks,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-subtitle}@anchor{c1} |
| @section Pragma Subtitle |
| |
| |
| Syntax: |
| |
| @example |
| pragma Subtitle ([Subtitle =>] STRING_LITERAL); |
| @end example |
| |
| This pragma is recognized for compatibility with other Ada compilers |
| but is ignored by GNAT. |
| |
| @node Pragma Suppress,Pragma Suppress_All,Pragma Subtitle,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-suppress}@anchor{c2} |
| @section Pragma Suppress |
| |
| |
| Syntax: |
| |
| @example |
| pragma Suppress (Identifier [, [On =>] Name]); |
| @end example |
| |
| This is a standard pragma, and supports all the check names required in |
| the RM. It is included here because GNAT recognizes some additional check |
| names that are implementation defined (as permitted by the RM): |
| |
| |
| @itemize * |
| |
| @item |
| @cite{Alignment_Check} can be used to suppress alignment checks |
| on addresses used in address clauses. Such checks can also be suppressed |
| by suppressing range checks, but the specific use of @cite{Alignment_Check} |
| allows suppression of alignment checks without suppressing other range checks. |
| Note that @cite{Alignment_Check} is suppressed by default on machines (such as |
| the x86) with non-strict alignment. |
| |
| @item |
| @cite{Atomic_Synchronization} can be used to suppress the special memory |
| synchronization instructions that are normally generated for access to |
| @cite{Atomic} variables to ensure correct synchronization between tasks |
| that use such variables for synchronization purposes. |
| |
| @item |
| @cite{Duplicated_Tag_Check} Can be used to suppress the check that is generated |
| for a duplicated tag value when a tagged type is declared. |
| |
| @item |
| @cite{Predicate_Check} can be used to control whether predicate checks are |
| active. It is applicable only to predicates for which the policy is |
| @cite{Check}. Unlike @cite{Assertion_Policy}, which determines if a given |
| predicate is ignored or checked for the whole program, the use of |
| @cite{Suppress} and @cite{Unsuppress} with this check name allows a given |
| predicate to be turned on and off at specific points in the program. |
| |
| @item |
| @cite{Validity_Check} can be used specifically to control validity checks. |
| If @cite{Suppress} is used to suppress validity checks, then no validity |
| checks are performed, including those specified by the appropriate compiler |
| switch or the @cite{Validity_Checks} pragma. |
| |
| @item |
| Additional check names previously introduced by use of the @cite{Check_Name} |
| pragma are also allowed. |
| @end itemize |
| |
| Note that pragma Suppress gives the compiler permission to omit |
| checks, but does not require the compiler to omit checks. The compiler |
| will generate checks if they are essentially free, even when they are |
| suppressed. In particular, if the compiler can prove that a certain |
| check will necessarily fail, it will generate code to do an |
| unconditional 'raise', even if checks are suppressed. The compiler |
| warns in this case. |
| |
| Of course, run-time checks are omitted whenever the compiler can prove |
| that they will not fail, whether or not checks are suppressed. |
| |
| @node Pragma Suppress_All,Pragma Suppress_Debug_Info,Pragma Suppress,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-suppress-all}@anchor{c3} |
| @section Pragma Suppress_All |
| |
| |
| Syntax: |
| |
| @example |
| pragma Suppress_All; |
| @end example |
| |
| This pragma can appear anywhere within a unit. |
| The effect is to apply @cite{Suppress (All_Checks)} to the unit |
| in which it appears. This pragma is implemented for compatibility with DEC |
| Ada 83 usage where it appears at the end of a unit, and for compatibility |
| with Rational Ada, where it appears as a program unit pragma. |
| The use of the standard Ada pragma @cite{Suppress (All_Checks)} |
| as a normal configuration pragma is the preferred usage in GNAT. |
| |
| @node Pragma Suppress_Debug_Info,Pragma Suppress_Exception_Locations,Pragma Suppress_All,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-suppress-debug-info}@anchor{c4} |
| @section Pragma Suppress_Debug_Info |
| |
| |
| Syntax: |
| |
| @example |
| pragma Suppress_Debug_Info ([Entity =>] LOCAL_NAME); |
| @end example |
| |
| This pragma can be used to suppress generation of debug information |
| for the specified entity. It is intended primarily for use in debugging |
| the debugger, and navigating around debugger problems. |
| |
| @node Pragma Suppress_Exception_Locations,Pragma Suppress_Initialization,Pragma Suppress_Debug_Info,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-suppress-exception-locations}@anchor{c5} |
| @section Pragma Suppress_Exception_Locations |
| |
| |
| Syntax: |
| |
| @example |
| pragma Suppress_Exception_Locations; |
| @end example |
| |
| In normal mode, a raise statement for an exception by default generates |
| an exception message giving the file name and line number for the location |
| of the raise. This is useful for debugging and logging purposes, but this |
| entails extra space for the strings for the messages. The configuration |
| pragma @cite{Suppress_Exception_Locations} can be used to suppress the |
| generation of these strings, with the result that space is saved, but the |
| exception message for such raises is null. This configuration pragma may |
| appear in a global configuration pragma file, or in a specific unit as |
| usual. It is not required that this pragma be used consistently within |
| a partition, so it is fine to have some units within a partition compiled |
| with this pragma and others compiled in normal mode without it. |
| |
| @node Pragma Suppress_Initialization,Pragma Task_Name,Pragma Suppress_Exception_Locations,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-suppress-initialization}@anchor{c6} |
| @section Pragma Suppress_Initialization |
| |
| |
| @geindex Suppressing initialization |
| |
| @geindex Initialization |
| @geindex suppression of |
| |
| Syntax: |
| |
| @example |
| pragma Suppress_Initialization ([Entity =>] variable_or_subtype_Name); |
| @end example |
| |
| Here variable_or_subtype_Name is the name introduced by a type declaration |
| or subtype declaration or the name of a variable introduced by an |
| object declaration. |
| |
| In the case of a type or subtype |
| this pragma suppresses any implicit or explicit initialization |
| for all variables of the given type or subtype, |
| including initialization resulting from the use of pragmas |
| Normalize_Scalars or Initialize_Scalars. |
| |
| This is considered a representation item, so it cannot be given after |
| the type is frozen. It applies to all subsequent object declarations, |
| and also any allocator that creates objects of the type. |
| |
| If the pragma is given for the first subtype, then it is considered |
| to apply to the base type and all its subtypes. If the pragma is given |
| for other than a first subtype, then it applies only to the given subtype. |
| The pragma may not be given after the type is frozen. |
| |
| Note that this includes eliminating initialization of discriminants |
| for discriminated types, and tags for tagged types. In these cases, |
| you will have to use some non-portable mechanism (e.g. address |
| overlays or unchecked conversion) to achieve required initialization |
| of these fields before accessing any object of the corresponding type. |
| |
| For the variable case, implicit initialization for the named variable |
| is suppressed, just as though its subtype had been given in a pragma |
| Suppress_Initialization, as described above. |
| |
| @node Pragma Task_Name,Pragma Task_Storage,Pragma Suppress_Initialization,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-task-name}@anchor{c7} |
| @section Pragma Task_Name |
| |
| |
| Syntax |
| |
| @example |
| pragma Task_Name (string_EXPRESSION); |
| @end example |
| |
| This pragma appears within a task definition (like pragma |
| @cite{Priority}) and applies to the task in which it appears. The |
| argument must be of type String, and provides a name to be used for |
| the task instance when the task is created. Note that this expression |
| is not required to be static, and in particular, it can contain |
| references to task discriminants. This facility can be used to |
| provide different names for different tasks as they are created, |
| as illustrated in the example below. |
| |
| The task name is recorded internally in the run-time structures |
| and is accessible to tools like the debugger. In addition the |
| routine @cite{Ada.Task_Identification.Image} will return this |
| string, with a unique task address appended. |
| |
| @example |
| -- Example of the use of pragma Task_Name |
| |
| with Ada.Task_Identification; |
| use Ada.Task_Identification; |
| with Text_IO; use Text_IO; |
| procedure t3 is |
| |
| type Astring is access String; |
| |
| task type Task_Typ (Name : access String) is |
| pragma Task_Name (Name.all); |
| end Task_Typ; |
| |
| task body Task_Typ is |
| Nam : constant String := Image (Current_Task); |
| begin |
| Put_Line ("-->" & Nam (1 .. 14) & "<--"); |
| end Task_Typ; |
| |
| type Ptr_Task is access Task_Typ; |
| Task_Var : Ptr_Task; |
| |
| begin |
| Task_Var := |
| new Task_Typ (new String'("This is task 1")); |
| Task_Var := |
| new Task_Typ (new String'("This is task 2")); |
| end; |
| @end example |
| |
| @node Pragma Task_Storage,Pragma Test_Case,Pragma Task_Name,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-task-storage}@anchor{c8} |
| @section Pragma Task_Storage |
| |
| |
| Syntax: |
| |
| @example |
| pragma Task_Storage ( |
| [Task_Type =>] LOCAL_NAME, |
| [Top_Guard =>] static_integer_EXPRESSION); |
| @end example |
| |
| This pragma specifies the length of the guard area for tasks. The guard |
| area is an additional storage area allocated to a task. A value of zero |
| means that either no guard area is created or a minimal guard area is |
| created, depending on the target. This pragma can appear anywhere a |
| @cite{Storage_Size} attribute definition clause is allowed for a task |
| type. |
| |
| @node Pragma Test_Case,Pragma Thread_Local_Storage,Pragma Task_Storage,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-test-case}@anchor{c9} |
| @section Pragma Test_Case |
| |
| |
| @geindex Test cases |
| |
| Syntax: |
| |
| @example |
| pragma Test_Case ( |
| [Name =>] static_string_Expression |
| ,[Mode =>] (Nominal | Robustness) |
| [, Requires => Boolean_Expression] |
| [, Ensures => Boolean_Expression]); |
| @end example |
| |
| The @cite{Test_Case} pragma allows defining fine-grain specifications |
| for use by testing tools. |
| The compiler checks the validity of the @cite{Test_Case} pragma, but its |
| presence does not lead to any modification of the code generated by the |
| compiler. |
| |
| @cite{Test_Case} pragmas may only appear immediately following the |
| (separate) declaration of a subprogram in a package declaration, inside |
| a package spec unit. Only other pragmas may intervene (that is appear |
| between the subprogram declaration and a test case). |
| |
| The compiler checks that boolean expressions given in @cite{Requires} and |
| @cite{Ensures} are valid, where the rules for @cite{Requires} are the |
| same as the rule for an expression in @cite{Precondition} and the rules |
| for @cite{Ensures} are the same as the rule for an expression in |
| @cite{Postcondition}. In particular, attributes @cite{'Old} and |
| @cite{'Result} can only be used within the @cite{Ensures} |
| expression. The following is an example of use within a package spec: |
| |
| @example |
| package Math_Functions is |
| ... |
| function Sqrt (Arg : Float) return Float; |
| pragma Test_Case (Name => "Test 1", |
| Mode => Nominal, |
| Requires => Arg < 10000, |
| Ensures => Sqrt'Result < 10); |
| ... |
| end Math_Functions; |
| @end example |
| |
| The meaning of a test case is that there is at least one context where |
| @cite{Requires} holds such that, if the associated subprogram is executed in |
| that context, then @cite{Ensures} holds when the subprogram returns. |
| Mode @cite{Nominal} indicates that the input context should also satisfy the |
| precondition of the subprogram, and the output context should also satisfy its |
| postcondition. Mode @cite{Robustness} indicates that the precondition and |
| postcondition of the subprogram should be ignored for this test case. |
| |
| @node Pragma Thread_Local_Storage,Pragma Time_Slice,Pragma Test_Case,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-thread-local-storage}@anchor{ca} |
| @section Pragma Thread_Local_Storage |
| |
| |
| @geindex Task specific storage |
| |
| @geindex TLS (Thread Local Storage) |
| |
| @geindex Task_Attributes |
| |
| Syntax: |
| |
| @example |
| pragma Thread_Local_Storage ([Entity =>] LOCAL_NAME); |
| @end example |
| |
| This pragma specifies that the specified entity, which must be |
| a variable declared in a library level package, is to be marked as |
| "Thread Local Storage" (@cite{TLS}). On systems supporting this (which |
| include Solaris, GNU/Linux and VxWorks 6), this causes each thread |
| (and hence each Ada task) to see a distinct copy of the variable. |
| |
| The variable may not have default initialization, and if there is |
| an explicit initialization, it must be either @cite{null} for an |
| access variable, or a static expression for a scalar variable. |
| This provides a low level mechanism similar to that provided by |
| the @cite{Ada.Task_Attributes} package, but much more efficient |
| and is also useful in writing interface code that will interact |
| with foreign threads. |
| |
| If this pragma is used on a system where @cite{TLS} is not supported, |
| then an error message will be generated and the program will be rejected. |
| |
| @node Pragma Time_Slice,Pragma Title,Pragma Thread_Local_Storage,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-time-slice}@anchor{cb} |
| @section Pragma Time_Slice |
| |
| |
| Syntax: |
| |
| @example |
| pragma Time_Slice (static_duration_EXPRESSION); |
| @end example |
| |
| For implementations of GNAT on operating systems where it is possible |
| to supply a time slice value, this pragma may be used for this purpose. |
| It is ignored if it is used in a system that does not allow this control, |
| or if it appears in other than the main program unit. |
| |
| @node Pragma Title,Pragma Type_Invariant,Pragma Time_Slice,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-title}@anchor{cc} |
| @section Pragma Title |
| |
| |
| Syntax: |
| |
| @example |
| pragma Title (TITLING_OPTION [, TITLING OPTION]); |
| |
| TITLING_OPTION ::= |
| [Title =>] STRING_LITERAL, |
| | [Subtitle =>] STRING_LITERAL |
| @end example |
| |
| Syntax checked but otherwise ignored by GNAT. This is a listing control |
| pragma used in DEC Ada 83 implementations to provide a title and/or |
| subtitle for the program listing. The program listing generated by GNAT |
| does not have titles or subtitles. |
| |
| Unlike other pragmas, the full flexibility of named notation is allowed |
| for this pragma, i.e., the parameters may be given in any order if named |
| notation is used, and named and positional notation can be mixed |
| following the normal rules for procedure calls in Ada. |
| |
| @node Pragma Type_Invariant,Pragma Type_Invariant_Class,Pragma Title,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-type-invariant}@anchor{cd} |
| @section Pragma Type_Invariant |
| |
| |
| Syntax: |
| |
| @example |
| pragma Type_Invariant |
| ([Entity =>] type_LOCAL_NAME, |
| [Check =>] EXPRESSION); |
| @end example |
| |
| The @cite{Type_Invariant} pragma is intended to be an exact |
| replacement for the language-defined @cite{Type_Invariant} |
| aspect, and shares its restrictions and semantics. It differs |
| from the language defined @cite{Invariant} pragma in that it |
| does not permit a string parameter, and it is |
| controlled by the assertion identifier @cite{Type_Invariant} |
| rather than @cite{Invariant}. |
| |
| @node Pragma Type_Invariant_Class,Pragma Unchecked_Union,Pragma Type_Invariant,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-type-invariant-class}@anchor{ce} |
| @section Pragma Type_Invariant_Class |
| |
| |
| Syntax: |
| |
| @example |
| pragma Type_Invariant_Class |
| ([Entity =>] type_LOCAL_NAME, |
| [Check =>] EXPRESSION); |
| @end example |
| |
| The @cite{Type_Invariant_Class} pragma is intended to be an exact |
| replacement for the language-defined @cite{Type_Invariant'Class} |
| aspect, and shares its restrictions and semantics. |
| |
| Note: This pragma is called @cite{Type_Invariant_Class} rather than |
| @cite{Type_Invariant'Class} because the latter would not be strictly |
| conforming to the allowed syntax for pragmas. The motivation |
| for providing pragmas equivalent to the aspects is to allow a program |
| to be written using the pragmas, and then compiled if necessary |
| using an Ada compiler that does not recognize the pragmas or |
| aspects, but is prepared to ignore the pragmas. The assertion |
| policy that controls this pragma is @cite{Type_Invariant'Class}, |
| not @cite{Type_Invariant_Class}. |
| |
| @node Pragma Unchecked_Union,Pragma Unevaluated_Use_Of_Old,Pragma Type_Invariant_Class,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-unchecked-union}@anchor{cf} |
| @section Pragma Unchecked_Union |
| |
| |
| @geindex Unions in C |
| |
| Syntax: |
| |
| @example |
| pragma Unchecked_Union (first_subtype_LOCAL_NAME); |
| @end example |
| |
| This pragma is used to specify a representation of a record type that is |
| equivalent to a C union. It was introduced as a GNAT implementation defined |
| pragma in the GNAT Ada 95 mode. Ada 2005 includes an extended version of this |
| pragma, making it language defined, and GNAT fully implements this extended |
| version in all language modes (Ada 83, Ada 95, and Ada 2005). For full |
| details, consult the Ada 2012 Reference Manual, section B.3.3. |
| |
| @node Pragma Unevaluated_Use_Of_Old,Pragma Unimplemented_Unit,Pragma Unchecked_Union,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-unevaluated-use-of-old}@anchor{d0} |
| @section Pragma Unevaluated_Use_Of_Old |
| |
| |
| @geindex Attribute Old |
| |
| @geindex Attribute Loop_Entry |
| |
| @geindex Unevaluated_Use_Of_Old |
| |
| Syntax: |
| |
| @example |
| pragma Unevaluated_Use_Of_Old (Error | Warn | Allow); |
| @end example |
| |
| This pragma controls the processing of attributes Old and Loop_Entry. |
| If either of these attributes is used in a potentially unevaluated |
| expression (e.g. the then or else parts of an if expression), then |
| normally this usage is considered illegal if the prefix of the attribute |
| is other than an entity name. The language requires this |
| behavior for Old, and GNAT copies the same rule for Loop_Entry. |
| |
| The reason for this rule is that otherwise, we can have a situation |
| where we save the Old value, and this results in an exception, even |
| though we might not evaluate the attribute. Consider this example: |
| |
| @example |
| package UnevalOld is |
| K : Character; |
| procedure U (A : String; C : Boolean) -- ERROR |
| with Post => (if C then A(1)'Old = K else True); |
| end; |
| @end example |
| |
| If procedure U is called with a string with a lower bound of 2, and |
| C false, then an exception would be raised trying to evaluate A(1) |
| on entry even though the value would not be actually used. |
| |
| Although the rule guarantees against this possibility, it is sometimes |
| too restrictive. For example if we know that the string has a lower |
| bound of 1, then we will never raise an exception. |
| The pragma @cite{Unevaluated_Use_Of_Old} can be |
| used to modify this behavior. If the argument is @cite{Error} then an |
| error is given (this is the default RM behavior). If the argument is |
| @cite{Warn} then the usage is allowed as legal but with a warning |
| that an exception might be raised. If the argument is @cite{Allow} |
| then the usage is allowed as legal without generating a warning. |
| |
| This pragma may appear as a configuration pragma, or in a declarative |
| part or package specification. In the latter case it applies to |
| uses up to the end of the corresponding statement sequence or |
| sequence of package declarations. |
| |
| @node Pragma Unimplemented_Unit,Pragma Universal_Aliasing,Pragma Unevaluated_Use_Of_Old,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-unimplemented-unit}@anchor{d1} |
| @section Pragma Unimplemented_Unit |
| |
| |
| Syntax: |
| |
| @example |
| pragma Unimplemented_Unit; |
| @end example |
| |
| If this pragma occurs in a unit that is processed by the compiler, GNAT |
| aborts with the message @code{xxx not implemented}, where |
| @cite{xxx} is the name of the current compilation unit. This pragma is |
| intended to allow the compiler to handle unimplemented library units in |
| a clean manner. |
| |
| The abort only happens if code is being generated. Thus you can use |
| specs of unimplemented packages in syntax or semantic checking mode. |
| |
| @node Pragma Universal_Aliasing,Pragma Universal_Data,Pragma Unimplemented_Unit,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-universal-aliasing}@anchor{d2} |
| @section Pragma Universal_Aliasing |
| |
| |
| Syntax: |
| |
| @example |
| pragma Universal_Aliasing [([Entity =>] type_LOCAL_NAME)]; |
| @end example |
| |
| @cite{type_LOCAL_NAME} must refer to a type declaration in the current |
| declarative part. The effect is to inhibit strict type-based aliasing |
| optimization for the given type. In other words, the effect is as though |
| access types designating this type were subject to pragma No_Strict_Aliasing. |
| For a detailed description of the strict aliasing optimization, and the |
| situations in which it must be suppressed, see the section on |
| @cite{Optimization and Strict Aliasing} in the @cite{GNAT User's Guide}. |
| |
| @node Pragma Universal_Data,Pragma Unmodified,Pragma Universal_Aliasing,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-universal-data}@anchor{d3} |
| @section Pragma Universal_Data |
| |
| |
| Syntax: |
| |
| @example |
| pragma Universal_Data [(library_unit_Name)]; |
| @end example |
| |
| This pragma is supported only for the AAMP target and is ignored for |
| other targets. The pragma specifies that all library-level objects |
| (Counter 0 data) associated with the library unit are to be accessed |
| and updated using universal addressing (24-bit addresses for AAMP5) |
| rather than the default of 16-bit Data Environment (DENV) addressing. |
| Use of this pragma will generally result in less efficient code for |
| references to global data associated with the library unit, but |
| allows such data to be located anywhere in memory. This pragma is |
| a library unit pragma, but can also be used as a configuration pragma |
| (including use in the @code{gnat.adc} file). The functionality |
| of this pragma is also available by applying the -univ switch on the |
| compilations of units where universal addressing of the data is desired. |
| |
| @node Pragma Unmodified,Pragma Unreferenced,Pragma Universal_Data,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-unmodified}@anchor{d4} |
| @section Pragma Unmodified |
| |
| |
| @geindex Warnings |
| @geindex unmodified |
| |
| Syntax: |
| |
| @example |
| pragma Unmodified (LOCAL_NAME @{, LOCAL_NAME@}); |
| @end example |
| |
| This pragma signals that the assignable entities (variables, |
| @cite{out} parameters, @cite{in out} parameters) whose names are listed are |
| deliberately not assigned in the current source unit. This |
| suppresses warnings about the |
| entities being referenced but not assigned, and in addition a warning will be |
| generated if one of these entities is in fact assigned in the |
| same unit as the pragma (or in the corresponding body, or one |
| of its subunits). |
| |
| This is particularly useful for clearly signaling that a particular |
| parameter is not modified, even though the spec suggests that it might |
| be. |
| |
| For the variable case, warnings are never given for unreferenced variables |
| whose name contains one of the substrings |
| @cite{DISCARD@comma{} DUMMY@comma{} IGNORE@comma{} JUNK@comma{} UNUSED} in any casing. Such names |
| are typically to be used in cases where such warnings are expected. |
| Thus it is never necessary to use @cite{pragma Unmodified} for such |
| variables, though it is harmless to do so. |
| |
| @node Pragma Unreferenced,Pragma Unreferenced_Objects,Pragma Unmodified,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-unreferenced}@anchor{d5} |
| @section Pragma Unreferenced |
| |
| |
| @geindex Warnings |
| @geindex unreferenced |
| |
| Syntax: |
| |
| @example |
| pragma Unreferenced (LOCAL_NAME @{, LOCAL_NAME@}); |
| pragma Unreferenced (library_unit_NAME @{, library_unit_NAME@}); |
| @end example |
| |
| This pragma signals that the entities whose names are listed are |
| deliberately not referenced in the current source unit after the |
| occurrence of the pragma. This |
| suppresses warnings about the |
| entities being unreferenced, and in addition a warning will be |
| generated if one of these entities is in fact subsequently referenced in the |
| same unit as the pragma (or in the corresponding body, or one |
| of its subunits). |
| |
| This is particularly useful for clearly signaling that a particular |
| parameter is not referenced in some particular subprogram implementation |
| and that this is deliberate. It can also be useful in the case of |
| objects declared only for their initialization or finalization side |
| effects. |
| |
| If @cite{LOCAL_NAME} identifies more than one matching homonym in the |
| current scope, then the entity most recently declared is the one to which |
| the pragma applies. Note that in the case of accept formals, the pragma |
| Unreferenced may appear immediately after the keyword @cite{do} which |
| allows the indication of whether or not accept formals are referenced |
| or not to be given individually for each accept statement. |
| |
| The left hand side of an assignment does not count as a reference for the |
| purpose of this pragma. Thus it is fine to assign to an entity for which |
| pragma Unreferenced is given. |
| |
| Note that if a warning is desired for all calls to a given subprogram, |
| regardless of whether they occur in the same unit as the subprogram |
| declaration, then this pragma should not be used (calls from another |
| unit would not be flagged); pragma Obsolescent can be used instead |
| for this purpose, see @ref{8c,,Pragma Obsolescent}. |
| |
| The second form of pragma @cite{Unreferenced} is used within a context |
| clause. In this case the arguments must be unit names of units previously |
| mentioned in @cite{with} clauses (similar to the usage of pragma |
| @cite{Elaborate_All}. The effect is to suppress warnings about unreferenced |
| units and unreferenced entities within these units. |
| |
| For the variable case, warnings are never given for unreferenced variables |
| whose name contains one of the substrings |
| @cite{DISCARD@comma{} DUMMY@comma{} IGNORE@comma{} JUNK@comma{} UNUSED} in any casing. Such names |
| are typically to be used in cases where such warnings are expected. |
| Thus it is never necessary to use @cite{pragma Unreferenced} for such |
| variables, though it is harmless to do so. |
| |
| @node Pragma Unreferenced_Objects,Pragma Unreserve_All_Interrupts,Pragma Unreferenced,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-unreferenced-objects}@anchor{d6} |
| @section Pragma Unreferenced_Objects |
| |
| |
| @geindex Warnings |
| @geindex unreferenced |
| |
| Syntax: |
| |
| @example |
| pragma Unreferenced_Objects (local_subtype_NAME @{, local_subtype_NAME@}); |
| @end example |
| |
| This pragma signals that for the types or subtypes whose names are |
| listed, objects which are declared with one of these types or subtypes may |
| not be referenced, and if no references appear, no warnings are given. |
| |
| This is particularly useful for objects which are declared solely for their |
| initialization and finalization effect. Such variables are sometimes referred |
| to as RAII variables (Resource Acquisition Is Initialization). Using this |
| pragma on the relevant type (most typically a limited controlled type), the |
| compiler will automatically suppress unwanted warnings about these variables |
| not being referenced. |
| |
| @node Pragma Unreserve_All_Interrupts,Pragma Unsuppress,Pragma Unreferenced_Objects,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-unreserve-all-interrupts}@anchor{d7} |
| @section Pragma Unreserve_All_Interrupts |
| |
| |
| Syntax: |
| |
| @example |
| pragma Unreserve_All_Interrupts; |
| @end example |
| |
| Normally certain interrupts are reserved to the implementation. Any attempt |
| to attach an interrupt causes Program_Error to be raised, as described in |
| RM C.3.2(22). A typical example is the @cite{SIGINT} interrupt used in |
| many systems for a @code{Ctrl-C} interrupt. Normally this interrupt is |
| reserved to the implementation, so that @code{Ctrl-C} can be used to |
| interrupt execution. |
| |
| If the pragma @cite{Unreserve_All_Interrupts} appears anywhere in any unit in |
| a program, then all such interrupts are unreserved. This allows the |
| program to handle these interrupts, but disables their standard |
| functions. For example, if this pragma is used, then pressing |
| @code{Ctrl-C} will not automatically interrupt execution. However, |
| a program can then handle the @cite{SIGINT} interrupt as it chooses. |
| |
| For a full list of the interrupts handled in a specific implementation, |
| see the source code for the spec of @cite{Ada.Interrupts.Names} in |
| file @code{a-intnam.ads}. This is a target dependent file that contains the |
| list of interrupts recognized for a given target. The documentation in |
| this file also specifies what interrupts are affected by the use of |
| the @cite{Unreserve_All_Interrupts} pragma. |
| |
| For a more general facility for controlling what interrupts can be |
| handled, see pragma @cite{Interrupt_State}, which subsumes the functionality |
| of the @cite{Unreserve_All_Interrupts} pragma. |
| |
| @node Pragma Unsuppress,Pragma Use_VADS_Size,Pragma Unreserve_All_Interrupts,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-unsuppress}@anchor{d8} |
| @section Pragma Unsuppress |
| |
| |
| Syntax: |
| |
| @example |
| pragma Unsuppress (IDENTIFIER [, [On =>] NAME]); |
| @end example |
| |
| This pragma undoes the effect of a previous pragma @cite{Suppress}. If |
| there is no corresponding pragma @cite{Suppress} in effect, it has no |
| effect. The range of the effect is the same as for pragma |
| @cite{Suppress}. The meaning of the arguments is identical to that used |
| in pragma @cite{Suppress}. |
| |
| One important application is to ensure that checks are on in cases where |
| code depends on the checks for its correct functioning, so that the code |
| will compile correctly even if the compiler switches are set to suppress |
| checks. For example, in a program that depends on external names of tagged |
| types and wants to ensure that the duplicated tag check occurs even if all |
| run-time checks are suppressed by a compiler switch, the following |
| configuration pragma will ensure this test is not suppressed: |
| |
| @example |
| pragma Unsuppress (Duplicated_Tag_Check); |
| @end example |
| |
| This pragma is standard in Ada 2005. It is available in all earlier versions |
| of Ada as an implementation-defined pragma. |
| |
| Note that in addition to the checks defined in the Ada RM, GNAT recogizes |
| a number of implementation-defined check names. See description of pragma |
| @cite{Suppress} for full details. |
| |
| @node Pragma Use_VADS_Size,Pragma Validity_Checks,Pragma Unsuppress,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-use-vads-size}@anchor{d9} |
| @section Pragma Use_VADS_Size |
| |
| |
| @geindex Size |
| @geindex VADS compatibility |
| |
| @geindex Rational profile |
| |
| Syntax: |
| |
| @example |
| pragma Use_VADS_Size; |
| @end example |
| |
| This is a configuration pragma. In a unit to which it applies, any use |
| of the 'Size attribute is automatically interpreted as a use of the |
| 'VADS_Size attribute. Note that this may result in incorrect semantic |
| processing of valid Ada 95 or Ada 2005 programs. This is intended to aid in |
| the handling of existing code which depends on the interpretation of Size |
| as implemented in the VADS compiler. See description of the VADS_Size |
| attribute for further details. |
| |
| @node Pragma Validity_Checks,Pragma Volatile,Pragma Use_VADS_Size,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-validity-checks}@anchor{da} |
| @section Pragma Validity_Checks |
| |
| |
| Syntax: |
| |
| @example |
| pragma Validity_Checks (string_LITERAL | ALL_CHECKS | On | Off); |
| @end example |
| |
| This pragma is used in conjunction with compiler switches to control the |
| built-in validity checking provided by GNAT. The compiler switches, if set |
| provide an initial setting for the switches, and this pragma may be used |
| to modify these settings, or the settings may be provided entirely by |
| the use of the pragma. This pragma can be used anywhere that a pragma |
| is legal, including use as a configuration pragma (including use in |
| the @code{gnat.adc} file). |
| |
| The form with a string literal specifies which validity options are to be |
| activated. The validity checks are first set to include only the default |
| reference manual settings, and then a string of letters in the string |
| specifies the exact set of options required. The form of this string |
| is exactly as described for the @emph{-gnatVx} compiler switch (see the |
| GNAT User's Guide for details). For example the following two |
| methods can be used to enable validity checking for mode @cite{in} and |
| @cite{in out} subprogram parameters: |
| |
| |
| @itemize * |
| |
| @item |
| @example |
| pragma Validity_Checks ("im"); |
| @end example |
| |
| @item |
| @example |
| $ gcc -c -gnatVim ... |
| @end example |
| @end itemize |
| |
| The form ALL_CHECKS activates all standard checks (its use is equivalent |
| to the use of the @cite{gnatva} switch. |
| |
| The forms with @cite{Off} and @cite{On} |
| can be used to temporarily disable validity checks |
| as shown in the following example: |
| |
| @example |
| pragma Validity_Checks ("c"); -- validity checks for copies |
| pragma Validity_Checks (Off); -- turn off validity checks |
| A := B; -- B will not be validity checked |
| pragma Validity_Checks (On); -- turn validity checks back on |
| A := C; -- C will be validity checked |
| @end example |
| |
| @node Pragma Volatile,Pragma Warning_As_Error,Pragma Validity_Checks,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-volatile}@anchor{db} |
| @section Pragma Volatile |
| |
| |
| Syntax: |
| |
| @example |
| pragma Volatile (LOCAL_NAME); |
| @end example |
| |
| This pragma is defined by the Ada Reference Manual, and the GNAT |
| implementation is fully conformant with this definition. The reason it |
| is mentioned in this section is that a pragma of the same name was supplied |
| in some Ada 83 compilers, including DEC Ada 83. The Ada 95 / Ada 2005 |
| implementation of pragma Volatile is upwards compatible with the |
| implementation in DEC Ada 83. |
| |
| @node Pragma Warning_As_Error,Pragma Warnings,Pragma Volatile,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-warning-as-error}@anchor{dc} |
| @section Pragma Warning_As_Error |
| |
| |
| Syntax: |
| |
| @example |
| pragma Warning_As_Error (static_string_EXPRESSION); |
| @end example |
| |
| This configuration pragma allows the programmer to specify a set |
| of warnings that will be treated as errors. Any warning which |
| matches the pattern given by the pragma argument will be treated |
| as an error. This gives much more precise control that -gnatwe |
| which treats all warnings as errors. |
| |
| The pattern may contain asterisks, which match zero or more characters in |
| the message. For example, you can use |
| @cite{pragma Warning_As_Error ("bits of*unused")} to treat the warning |
| message @cite{warning: 960 bits of "a" unused} as an error. No other regular |
| expression notations are permitted. All characters other than asterisk in |
| these three specific cases are treated as literal characters in the match. |
| The match is case insensitive, for example XYZ matches xyz. |
| |
| Note that the pattern matches if it occurs anywhere within the warning |
| message string (it is not necessary to put an asterisk at the start and |
| the end of the message, since this is implied). |
| |
| Another possibility for the static_string_EXPRESSION which works whether |
| or not error tags are enabled (@emph{-gnatw.d}) is to use the |
| @emph{-gnatw} tag string, enclosed in brackets, |
| as shown in the example below, to treat a class of warnings as errors. |
| |
| The above use of patterns to match the message applies only to warning |
| messages generated by the front end. This pragma can also be applied to |
| warnings provided by the back end and mentioned in @ref{dd,,Pragma Warnings}. |
| By using a single full @emph{-Wxxx} switch in the pragma, such warnings |
| can also be treated as errors. |
| |
| The pragma can appear either in a global configuration pragma file |
| (e.g. @code{gnat.adc}), or at the start of a file. Given a global |
| configuration pragma file containing: |
| |
| @example |
| pragma Warning_As_Error ("[-gnatwj]"); |
| @end example |
| |
| which will treat all obsolescent feature warnings as errors, the |
| following program compiles as shown (compile options here are |
| @emph{-gnatwa.d -gnatl -gnatj55}). |
| |
| @example |
| 1. pragma Warning_As_Error ("*never assigned*"); |
| 2. function Warnerr return String is |
| 3. X : Integer; |
| | |
| >>> error: variable "X" is never read and |
| never assigned [-gnatwv] [warning-as-error] |
| |
| 4. Y : Integer; |
| | |
| >>> warning: variable "Y" is assigned but |
| never read [-gnatwu] |
| |
| 5. begin |
| 6. Y := 0; |
| 7. return %ABC%; |
| | |
| >>> error: use of "%" is an obsolescent |
| feature (RM J.2(4)), use """ instead |
| [-gnatwj] [warning-as-error] |
| |
| 8. end; |
| |
| 8 lines: No errors, 3 warnings (2 treated as errors) |
| @end example |
| |
| Note that this pragma does not affect the set of warnings issued in |
| any way, it merely changes the effect of a matching warning if one |
| is produced as a result of other warnings options. As shown in this |
| example, if the pragma results in a warning being treated as an error, |
| the tag is changed from "warning:" to "error:" and the string |
| "[warning-as-error]" is appended to the end of the message. |
| |
| @node Pragma Warnings,Pragma Weak_External,Pragma Warning_As_Error,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas id5}@anchor{de}@anchor{gnat_rm/implementation_defined_pragmas pragma-warnings}@anchor{dd} |
| @section Pragma Warnings |
| |
| |
| Syntax: |
| |
| @example |
| pragma Warnings ([TOOL_NAME,] DETAILS [, REASON]); |
| |
| DETAILS ::= On | Off |
| DETAILS ::= On | Off, local_NAME |
| DETAILS ::= static_string_EXPRESSION |
| DETAILS ::= On | Off, static_string_EXPRESSION |
| |
| TOOL_NAME ::= GNAT | GNATProve |
| |
| REASON ::= Reason => STRING_LITERAL @{& STRING_LITERAL@} |
| @end example |
| |
| Note: in Ada 83 mode, a string literal may be used in place of a static string |
| expression (which does not exist in Ada 83). |
| |
| Note if the second argument of @cite{DETAILS} is a @cite{local_NAME} then the |
| second form is always understood. If the intention is to use |
| the fourth form, then you can write @cite{NAME & ""} to force the |
| intepretation as a @cite{static_string_EXPRESSION}. |
| |
| Note: if the first argument is a valid @cite{TOOL_NAME}, it will be interpreted |
| that way. The use of the @cite{TOOL_NAME} argument is relevant only to users |
| of SPARK and GNATprove, see last part of this section for details. |
| |
| Normally warnings are enabled, with the output being controlled by |
| the command line switch. Warnings (@cite{Off}) turns off generation of |
| warnings until a Warnings (@cite{On}) is encountered or the end of the |
| current unit. If generation of warnings is turned off using this |
| pragma, then some or all of the warning messages are suppressed, |
| regardless of the setting of the command line switches. |
| |
| The @cite{Reason} parameter may optionally appear as the last argument |
| in any of the forms of this pragma. It is intended purely for the |
| purposes of documenting the reason for the @cite{Warnings} pragma. |
| The compiler will check that the argument is a static string but |
| otherwise ignore this argument. Other tools may provide specialized |
| processing for this string. |
| |
| The form with a single argument (or two arguments if Reason present), |
| where the first argument is @cite{ON} or @cite{OFF} |
| may be used as a configuration pragma. |
| |
| If the @cite{LOCAL_NAME} parameter is present, warnings are suppressed for |
| the specified entity. This suppression is effective from the point where |
| it occurs till the end of the extended scope of the variable (similar to |
| the scope of @cite{Suppress}). This form cannot be used as a configuration |
| pragma. |
| |
| In the case where the first argument is other than @cite{ON} or |
| @cite{OFF}, |
| the third form with a single static_string_EXPRESSION argument (and possible |
| reason) provides more precise |
| control over which warnings are active. The string is a list of letters |
| specifying which warnings are to be activated and which deactivated. The |
| code for these letters is the same as the string used in the command |
| line switch controlling warnings. For a brief summary, use the gnatmake |
| command with no arguments, which will generate usage information containing |
| the list of warnings switches supported. For |
| full details see the section on @cite{Warning Message Control} in the |
| @cite{GNAT User's Guide}. |
| This form can also be used as a configuration pragma. |
| |
| The warnings controlled by the @emph{-gnatw} switch are generated by the |
| front end of the compiler. The GCC back end can provide additional warnings |
| and they are controlled by the @emph{-W} switch. Such warnings can be |
| identified by the appearance of a string of the form @cite{[-Wxxx]} in the |
| message which designates the @emph{-Wxxx} switch that controls the message. |
| The form with a single static_string_EXPRESSION argument also works for these |
| warnings, but the string must be a single full @emph{-Wxxx} switch in this |
| case. The above reference lists a few examples of these additional warnings. |
| |
| The specified warnings will be in effect until the end of the program |
| or another pragma Warnings is encountered. The effect of the pragma is |
| cumulative. Initially the set of warnings is the standard default set |
| as possibly modified by compiler switches. Then each pragma Warning |
| modifies this set of warnings as specified. This form of the pragma may |
| also be used as a configuration pragma. |
| |
| The fourth form, with an @cite{On|Off} parameter and a string, is used to |
| control individual messages, based on their text. The string argument |
| is a pattern that is used to match against the text of individual |
| warning messages (not including the initial "warning: " tag). |
| |
| The pattern may contain asterisks, which match zero or more characters in |
| the message. For example, you can use |
| @cite{pragma Warnings (Off@comma{} "bits of*unused")} to suppress the warning |
| message @cite{warning: 960 bits of "a" unused}. No other regular |
| expression notations are permitted. All characters other than asterisk in |
| these three specific cases are treated as literal characters in the match. |
| The match is case insensitive, for example XYZ matches xyz. |
| |
| Note that the pattern matches if it occurs anywhere within the warning |
| message string (it is not necessary to put an asterisk at the start and |
| the end of the message, since this is implied). |
| |
| The above use of patterns to match the message applies only to warning |
| messages generated by the front end. This form of the pragma with a string |
| argument can also be used to control warnings provided by the back end and |
| mentioned above. By using a single full @emph{-Wxxx} switch in the pragma, |
| such warnings can be turned on and off. |
| |
| There are two ways to use the pragma in this form. The OFF form can be used |
| as a configuration pragma. The effect is to suppress all warnings (if any) |
| that match the pattern string throughout the compilation (or match the |
| -W switch in the back end case). |
| |
| The second usage is to suppress a warning locally, and in this case, two |
| pragmas must appear in sequence: |
| |
| @example |
| pragma Warnings (Off, Pattern); |
| ... code where given warning is to be suppressed |
| pragma Warnings (On, Pattern); |
| @end example |
| |
| In this usage, the pattern string must match in the Off and On |
| pragmas, and (if @emph{-gnatw.w} is given) at least one matching |
| warning must be suppressed. |
| |
| Note: to write a string that will match any warning, use the string |
| @cite{"***"}. It will not work to use a single asterisk or two |
| asterisks since this looks like an operator name. This form with three |
| asterisks is similar in effect to specifying @cite{pragma Warnings (Off)} except (if @emph{-gnatw.w} is given) that a matching |
| @cite{pragma Warnings (On@comma{} "***")} will be required. This can be |
| helpful in avoiding forgetting to turn warnings back on. |
| |
| Note: the debug flag -gnatd.i (@cite{/NOWARNINGS_PRAGMAS} in VMS) can be |
| used to cause the compiler to entirely ignore all WARNINGS pragmas. This can |
| be useful in checking whether obsolete pragmas in existing programs are hiding |
| real problems. |
| |
| Note: pragma Warnings does not affect the processing of style messages. See |
| separate entry for pragma Style_Checks for control of style messages. |
| |
| Users of the formal verification tool GNATprove for the SPARK subset of Ada may |
| use the version of the pragma with a @cite{TOOL_NAME} parameter. |
| |
| If present, @cite{TOOL_NAME} is the name of a tool, currently either @cite{GNAT} for the |
| compiler or @cite{GNATprove} for the formal verification tool. A given tool only |
| takes into account pragma Warnings that do not specify a tool name, or that |
| specify the matching tool name. This makes it possible to disable warnings |
| selectively for each tool, and as a consequence to detect useless pragma |
| Warnings with switch @cite{-gnatw.w}. |
| |
| @node Pragma Weak_External,Pragma Wide_Character_Encoding,Pragma Warnings,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-weak-external}@anchor{df} |
| @section Pragma Weak_External |
| |
| |
| Syntax: |
| |
| @example |
| pragma Weak_External ([Entity =>] LOCAL_NAME); |
| @end example |
| |
| @cite{LOCAL_NAME} must refer to an object that is declared at the library |
| level. This pragma specifies that the given entity should be marked as a |
| weak symbol for the linker. It is equivalent to @cite{__attribute__((weak))} |
| in GNU C and causes @cite{LOCAL_NAME} to be emitted as a weak symbol instead |
| of a regular symbol, that is to say a symbol that does not have to be |
| resolved by the linker if used in conjunction with a pragma Import. |
| |
| When a weak symbol is not resolved by the linker, its address is set to |
| zero. This is useful in writing interfaces to external modules that may |
| or may not be linked in the final executable, for example depending on |
| configuration settings. |
| |
| If a program references at run time an entity to which this pragma has been |
| applied, and the corresponding symbol was not resolved at link time, then |
| the execution of the program is erroneous. It is not erroneous to take the |
| Address of such an entity, for example to guard potential references, |
| as shown in the example below. |
| |
| Some file formats do not support weak symbols so not all target machines |
| support this pragma. |
| |
| @example |
| -- Example of the use of pragma Weak_External |
| |
| package External_Module is |
| key : Integer; |
| pragma Import (C, key); |
| pragma Weak_External (key); |
| function Present return boolean; |
| end External_Module; |
| |
| with System; use System; |
| package body External_Module is |
| function Present return boolean is |
| begin |
| return key'Address /= System.Null_Address; |
| end Present; |
| end External_Module; |
| @end example |
| |
| @node Pragma Wide_Character_Encoding,,Pragma Weak_External,Implementation Defined Pragmas |
| @anchor{gnat_rm/implementation_defined_pragmas pragma-wide-character-encoding}@anchor{e0} |
| @section Pragma Wide_Character_Encoding |
| |
| |
| Syntax: |
| |
| @example |
| pragma Wide_Character_Encoding (IDENTIFIER | CHARACTER_LITERAL); |
| @end example |
| |
| This pragma specifies the wide character encoding to be used in program |
| source text appearing subsequently. It is a configuration pragma, but may |
| also be used at any point that a pragma is allowed, and it is permissible |
| to have more than one such pragma in a file, allowing multiple encodings |
| to appear within the same file. |
| |
| The argument can be an identifier or a character literal. In the identifier |
| case, it is one of @cite{HEX}, @cite{UPPER}, @cite{SHIFT_JIS}, |
| @cite{EUC}, @cite{UTF8}, or @cite{BRACKETS}. In the character literal |
| case it is correspondingly one of the characters @code{h}, @code{u}, |
| @code{s}, @code{e}, @code{8}, or @code{b}. |
| |
| Note that when the pragma is used within a file, it affects only the |
| encoding within that file, and does not affect withed units, specs, |
| or subunits. |
| |
| @node Implementation Defined Aspects,Implementation Defined Attributes,Implementation Defined Pragmas,Top |
| @anchor{gnat_rm/implementation_defined_aspects implementation-defined-aspects}@anchor{e1}@anchor{gnat_rm/implementation_defined_aspects doc}@anchor{e2}@anchor{gnat_rm/implementation_defined_aspects id1}@anchor{e3} |
| @chapter Implementation Defined Aspects |
| |
| |
| Ada defines (throughout the Ada 2012 reference manual, summarized |
| in Annex K) a set of aspects that can be specified for certain entities. |
| These language defined aspects are implemented in GNAT in Ada 2012 mode |
| and work as described in the Ada 2012 Reference Manual. |
| |
| In addition, Ada 2012 allows implementations to define additional aspects |
| whose meaning is defined by the implementation. GNAT provides |
| a number of these implementation-defined aspects which can be used |
| to extend and enhance the functionality of the compiler. This section of |
| the GNAT reference manual describes these additional aspects. |
| |
| Note that any program using these aspects may not be portable to |
| other compilers (although GNAT implements this set of aspects on all |
| platforms). Therefore if portability to other compilers is an important |
| consideration, you should minimize the use of these aspects. |
| |
| Note that for many of these aspects, the effect is essentially similar |
| to the use of a pragma or attribute specification with the same name |
| applied to the entity. For example, if we write: |
| |
| @example |
| type R is range 1 .. 100 |
| with Value_Size => 10; |
| @end example |
| |
| then the effect is the same as: |
| |
| @example |
| type R is range 1 .. 100; |
| for R'Value_Size use 10; |
| @end example |
| |
| and if we write: |
| |
| @example |
| type R is new Integer |
| with Shared => True; |
| @end example |
| |
| then the effect is the same as: |
| |
| @example |
| type R is new Integer; |
| pragma Shared (R); |
| @end example |
| |
| In the documentation below, such cases are simply marked |
| as being boolean aspects equivalent to the corresponding pragma |
| or attribute definition clause. |
| |
| @menu |
| * Aspect Abstract_State:: |
| * Annotate:: |
| * Aspect Async_Readers:: |
| * Aspect Async_Writers:: |
| * Aspect Contract_Cases:: |
| * Aspect Depends:: |
| * Aspect Dimension:: |
| * Aspect Dimension_System:: |
| * Aspect Effective_Reads:: |
| * Aspect Effective_Writes:: |
| * Aspect Favor_Top_Level:: |
| * Aspect Global:: |
| * Aspect Initial_Condition:: |
| * Aspect Initializes:: |
| * Aspect Inline_Always:: |
| * Aspect Invariant:: |
| * Aspect Invariant'Class:: |
| * Aspect Iterable:: |
| * Aspect Linker_Section:: |
| * Aspect Lock_Free:: |
| * Aspect No_Elaboration_Code_All:: |
| * Aspect No_Tagged_Streams:: |
| * Aspect Object_Size:: |
| * Aspect Obsolescent:: |
| * Aspect Part_Of:: |
| * Aspect Persistent_BSS:: |
| * Aspect Predicate:: |
| * Aspect Pure_Function:: |
| * Aspect Refined_Depends:: |
| * Aspect Refined_Global:: |
| * Aspect Refined_Post:: |
| * Aspect Refined_State:: |
| * Aspect Remote_Access_Type:: |
| * Aspect Scalar_Storage_Order:: |
| * Aspect Shared:: |
| * Aspect Simple_Storage_Pool:: |
| * Aspect Simple_Storage_Pool_Type:: |
| * Aspect SPARK_Mode:: |
| * Aspect Suppress_Debug_Info:: |
| * Aspect Suppress_Initialization:: |
| * Aspect Test_Case:: |
| * Aspect Thread_Local_Storage:: |
| * Aspect Universal_Aliasing:: |
| * Aspect Universal_Data:: |
| * Aspect Unmodified:: |
| * Aspect Unreferenced:: |
| * Aspect Unreferenced_Objects:: |
| * Aspect Value_Size:: |
| * Aspect Warnings:: |
| |
| @end menu |
| |
| @node Aspect Abstract_State,Annotate,,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-abstract-state}@anchor{e4} |
| @section Aspect Abstract_State |
| |
| |
| @geindex Abstract_State |
| |
| This aspect is equivalent to pragma @cite{Abstract_State}. |
| |
| @node Annotate,Aspect Async_Readers,Aspect Abstract_State,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects annotate}@anchor{e5} |
| @section Annotate |
| |
| |
| @geindex Annotate |
| |
| There are three forms of this aspect (where ID is an identifier, |
| and ARG is a general expression). |
| |
| |
| @table @asis |
| |
| @item @emph{Annotate => ID} |
| |
| Equivalent to @cite{pragma Annotate (ID@comma{} Entity => Name);} |
| |
| @item @emph{Annotate => (ID)} |
| |
| Equivalent to @cite{pragma Annotate (ID@comma{} Entity => Name);} |
| |
| @item @emph{Annotate => (ID ,ID @{, ARG@})} |
| |
| Equivalent to @cite{pragma Annotate (ID@comma{} ID @{@comma{} ARG@}@comma{} Entity => Name);} |
| @end table |
| |
| @node Aspect Async_Readers,Aspect Async_Writers,Annotate,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-async-readers}@anchor{e6} |
| @section Aspect Async_Readers |
| |
| |
| @geindex Async_Readers |
| |
| This boolean aspect is equivalent to pragma @cite{Async_Readers}. |
| |
| @node Aspect Async_Writers,Aspect Contract_Cases,Aspect Async_Readers,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-async-writers}@anchor{e7} |
| @section Aspect Async_Writers |
| |
| |
| @geindex Async_Writers |
| |
| This boolean aspect is equivalent to pragma @cite{Async_Writers}. |
| |
| @node Aspect Contract_Cases,Aspect Depends,Aspect Async_Writers,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-contract-cases}@anchor{e8} |
| @section Aspect Contract_Cases |
| |
| |
| @geindex Contract_Cases |
| |
| This aspect is equivalent to pragma @cite{Contract_Cases}, the sequence |
| of clauses being enclosed in parentheses so that syntactically it is an |
| aggregate. |
| |
| @node Aspect Depends,Aspect Dimension,Aspect Contract_Cases,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-depends}@anchor{e9} |
| @section Aspect Depends |
| |
| |
| @geindex Depends |
| |
| This aspect is equivalent to pragma @cite{Depends}. |
| |
| @node Aspect Dimension,Aspect Dimension_System,Aspect Depends,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-dimension}@anchor{ea} |
| @section Aspect Dimension |
| |
| |
| @geindex Dimension |
| |
| The @cite{Dimension} aspect is used to specify the dimensions of a given |
| subtype of a dimensioned numeric type. The aspect also specifies a symbol |
| used when doing formatted output of dimensioned quantities. The syntax is: |
| |
| @example |
| with Dimension => |
| ([Symbol =>] SYMBOL, DIMENSION_VALUE @{, DIMENSION_Value@}) |
| |
| SYMBOL ::= STRING_LITERAL | CHARACTER_LITERAL |
| |
| DIMENSION_VALUE ::= |
| RATIONAL |
| | others => RATIONAL |
| | DISCRETE_CHOICE_LIST => RATIONAL |
| |
| RATIONAL ::= [-] NUMERIC_LITERAL [/ NUMERIC_LITERAL] |
| @end example |
| |
| This aspect can only be applied to a subtype whose parent type has |
| a @cite{Dimension_Systen} aspect. The aspect must specify values for |
| all dimensions of the system. The rational values are the powers of the |
| corresponding dimensions that are used by the compiler to verify that |
| physical (numeric) computations are dimensionally consistent. For example, |
| the computation of a force must result in dimensions (L => 1, M => 1, T => -2). |
| For further examples of the usage |
| of this aspect, see package @cite{System.Dim.Mks}. |
| Note that when the dimensioned type is an integer type, then any |
| dimension value must be an integer literal. |
| |
| @node Aspect Dimension_System,Aspect Effective_Reads,Aspect Dimension,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-dimension-system}@anchor{eb} |
| @section Aspect Dimension_System |
| |
| |
| @geindex Dimension_System |
| |
| The @cite{Dimension_System} aspect is used to define a system of |
| dimensions that will be used in subsequent subtype declarations with |
| @cite{Dimension} aspects that reference this system. The syntax is: |
| |
| @example |
| with Dimension_System => (DIMENSION @{, DIMENSION@}); |
| |
| DIMENSION ::= ([Unit_Name =>] IDENTIFIER, |
| [Unit_Symbol =>] SYMBOL, |
| [Dim_Symbol =>] SYMBOL) |
| |
| SYMBOL ::= CHARACTER_LITERAL | STRING_LITERAL |
| @end example |
| |
| This aspect is applied to a type, which must be a numeric derived type |
| (typically a floating-point type), that |
| will represent values within the dimension system. Each @cite{DIMENSION} |
| corresponds to one particular dimension. A maximum of 7 dimensions may |
| be specified. @cite{Unit_Name} is the name of the dimension (for example |
| @cite{Meter}). @cite{Unit_Symbol} is the shorthand used for quantities |
| of this dimension (for example @cite{m} for @cite{Meter}). |
| @cite{Dim_Symbol} gives |
| the identification within the dimension system (typically this is a |
| single letter, e.g. @cite{L} standing for length for unit name @cite{Meter}). |
| The @cite{Unit_Symbol} is used in formatted output of dimensioned quantities. |
| The @cite{Dim_Symbol} is used in error messages when numeric operations have |
| inconsistent dimensions. |
| |
| GNAT provides the standard definition of the International MKS system in |
| the run-time package @cite{System.Dim.Mks}. You can easily define |
| similar packages for cgs units or British units, and define conversion factors |
| between values in different systems. The MKS system is characterized by the |
| following aspect: |
| |
| @example |
| type Mks_Type is new Long_Long_Float with |
| Dimension_System => ( |
| (Unit_Name => Meter, Unit_Symbol => 'm', Dim_Symbol => 'L'), |
| (Unit_Name => Kilogram, Unit_Symbol => "kg", Dim_Symbol => 'M'), |
| (Unit_Name => Second, Unit_Symbol => 's', Dim_Symbol => 'T'), |
| (Unit_Name => Ampere, Unit_Symbol => 'A', Dim_Symbol => 'I'), |
| (Unit_Name => Kelvin, Unit_Symbol => 'K', Dim_Symbol => '@@'), |
| (Unit_Name => Mole, Unit_Symbol => "mol", Dim_Symbol => 'N'), |
| (Unit_Name => Candela, Unit_Symbol => "cd", Dim_Symbol => 'J')); |
| @end example |
| |
| Note that in the above type definition, we use the @cite{at} symbol (@code{@@}) to |
| represent a theta character (avoiding the use of extended Latin-1 |
| characters in this context). |
| |
| See section 'Performing Dimensionality Analysis in GNAT' in the GNAT Users |
| Guide for detailed examples of use of the dimension system. |
| |
| @node Aspect Effective_Reads,Aspect Effective_Writes,Aspect Dimension_System,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-effective-reads}@anchor{ec} |
| @section Aspect Effective_Reads |
| |
| |
| @geindex Effective_Reads |
| |
| This aspect is equivalent to pragma @cite{Effective_Reads}. |
| |
| @node Aspect Effective_Writes,Aspect Favor_Top_Level,Aspect Effective_Reads,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-effective-writes}@anchor{ed} |
| @section Aspect Effective_Writes |
| |
| |
| @geindex Effective_Writes |
| |
| This aspect is equivalent to pragma @cite{Effective_Writes}. |
| |
| @node Aspect Favor_Top_Level,Aspect Global,Aspect Effective_Writes,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-favor-top-level}@anchor{ee} |
| @section Aspect Favor_Top_Level |
| |
| |
| @geindex Favor_Top_Level |
| |
| This boolean aspect is equivalent to pragma @cite{Favor_Top_Level}. |
| |
| @node Aspect Global,Aspect Initial_Condition,Aspect Favor_Top_Level,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-global}@anchor{ef} |
| @section Aspect Global |
| |
| |
| @geindex Global |
| |
| This aspect is equivalent to pragma @cite{Global}. |
| |
| @node Aspect Initial_Condition,Aspect Initializes,Aspect Global,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-initial-condition}@anchor{f0} |
| @section Aspect Initial_Condition |
| |
| |
| @geindex Initial_Condition |
| |
| This aspect is equivalent to pragma @cite{Initial_Condition}. |
| |
| @node Aspect Initializes,Aspect Inline_Always,Aspect Initial_Condition,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-initializes}@anchor{f1} |
| @section Aspect Initializes |
| |
| |
| @geindex Initializes |
| |
| This aspect is equivalent to pragma @cite{Initializes}. |
| |
| @node Aspect Inline_Always,Aspect Invariant,Aspect Initializes,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-inline-always}@anchor{f2} |
| @section Aspect Inline_Always |
| |
| |
| @geindex Inline_Always |
| |
| This boolean aspect is equivalent to pragma @cite{Inline_Always}. |
| |
| @node Aspect Invariant,Aspect Invariant'Class,Aspect Inline_Always,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-invariant}@anchor{f3} |
| @section Aspect Invariant |
| |
| |
| @geindex Invariant |
| |
| This aspect is equivalent to pragma @cite{Invariant}. It is a |
| synonym for the language defined aspect @cite{Type_Invariant} except |
| that it is separately controllable using pragma @cite{Assertion_Policy}. |
| |
| @node Aspect Invariant'Class,Aspect Iterable,Aspect Invariant,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-invariant-class}@anchor{f4} |
| @section Aspect Invariant'Class |
| |
| |
| @geindex Invariant'Class |
| |
| This aspect is equivalent to pragma @cite{Type_Invariant_Class}. It is a |
| synonym for the language defined aspect @cite{Type_Invariant'Class} except |
| that it is separately controllable using pragma @cite{Assertion_Policy}. |
| |
| @node Aspect Iterable,Aspect Linker_Section,Aspect Invariant'Class,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-iterable}@anchor{f5} |
| @section Aspect Iterable |
| |
| |
| @geindex Iterable |
| |
| This aspect provides a light-weight mechanism for loops and quantified |
| expressions over container types, without the overhead imposed by the tampering |
| checks of standard Ada 2012 iterators. The value of the aspect is an aggregate |
| with four named components: @cite{First}, @cite{Next}, @cite{Has_Element}, and @cite{Element} (the |
| last one being optional). When only 3 components are specified, only the |
| @cite{for .. in} form of iteration over cursors is available. When all 4 components |
| are specified, both this form and the @cite{for .. of} form of iteration over |
| elements are available. The following is a typical example of use: |
| |
| @example |
| type List is private with |
| Iterable => (First => First_Cursor, |
| Next => Advance, |
| Has_Element => Cursor_Has_Element, |
| [Element => Get_Element]); |
| @end example |
| |
| |
| @itemize * |
| |
| @item |
| The value denoted by @cite{First} must denote a primitive operation of the |
| container type that returns a @cite{Cursor}, which must a be a type declared in |
| the container package or visible from it. For example: |
| @end itemize |
| |
| @example |
| function First_Cursor (Cont : Container) return Cursor; |
| @end example |
| |
| |
| @itemize * |
| |
| @item |
| The value of @cite{Next} is a primitive operation of the container type that takes |
| both a container and a cursor and yields a cursor. For example: |
| @end itemize |
| |
| @example |
| function Advance (Cont : Container; Position : Cursor) return Cursor; |
| @end example |
| |
| |
| @itemize * |
| |
| @item |
| The value of @cite{Has_Element} is a primitive operation of the container type |
| that takes both a container and a cursor and yields a boolean. For example: |
| @end itemize |
| |
| @example |
| function Cursor_Has_Element (Cont : Container; Position : Cursor) return Boolean; |
| @end example |
| |
| |
| @itemize * |
| |
| @item |
| The value of @cite{Element} is a primitive operation of the container type that |
| takes both a container and a cursor and yields an @cite{Element_Type}, which must |
| be a type declared in the container package or visible from it. For example: |
| @end itemize |
| |
| @example |
| function Get_Element (Cont : Container; Position : Cursor) return Element_Type; |
| @end example |
| |
| This aspect is used in the GNAT-defined formal container packages. |
| |
| @node Aspect Linker_Section,Aspect Lock_Free,Aspect Iterable,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-linker-section}@anchor{f6} |
| @section Aspect Linker_Section |
| |
| |
| @geindex Linker_Section |
| |
| This aspect is equivalent to an @cite{Linker_Section} pragma. |
| |
| @node Aspect Lock_Free,Aspect No_Elaboration_Code_All,Aspect Linker_Section,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-lock-free}@anchor{f7} |
| @section Aspect Lock_Free |
| |
| |
| @geindex Lock_Free |
| |
| This boolean aspect is equivalent to pragma @cite{Lock_Free}. |
| |
| @node Aspect No_Elaboration_Code_All,Aspect No_Tagged_Streams,Aspect Lock_Free,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-no-elaboration-code-all}@anchor{f8} |
| @section Aspect No_Elaboration_Code_All |
| |
| |
| @geindex No_Elaboration_Code_All |
| |
| This aspect is equivalent to a @cite{pragma No_Elaboration_Code_All} |
| statement for a program unit. |
| |
| @node Aspect No_Tagged_Streams,Aspect Object_Size,Aspect No_Elaboration_Code_All,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-no-tagged-streams}@anchor{f9} |
| @section Aspect No_Tagged_Streams |
| |
| |
| @geindex No_Tagged_Streams |
| |
| This aspect is equivalent to a @cite{pragma No_Tagged_Streams} with an |
| argument specifying a root tagged type (thus this aspect can only be |
| applied to such a type). |
| |
| @node Aspect Object_Size,Aspect Obsolescent,Aspect No_Tagged_Streams,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-object-size}@anchor{fa} |
| @section Aspect Object_Size |
| |
| |
| @geindex Object_Size |
| |
| This aspect is equivalent to an @cite{Object_Size} attribute definition |
| clause. |
| |
| @node Aspect Obsolescent,Aspect Part_Of,Aspect Object_Size,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-obsolescent}@anchor{fb} |
| @section Aspect Obsolescent |
| |
| |
| @geindex Obsolsecent |
| |
| This aspect is equivalent to an @cite{Obsolescent} pragma. Note that the |
| evaluation of this aspect happens at the point of occurrence, it is not |
| delayed until the freeze point. |
| |
| @node Aspect Part_Of,Aspect Persistent_BSS,Aspect Obsolescent,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-part-of}@anchor{fc} |
| @section Aspect Part_Of |
| |
| |
| @geindex Part_Of |
| |
| This aspect is equivalent to pragma @cite{Part_Of}. |
| |
| @node Aspect Persistent_BSS,Aspect Predicate,Aspect Part_Of,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-persistent-bss}@anchor{fd} |
| @section Aspect Persistent_BSS |
| |
| |
| @geindex Persistent_BSS |
| |
| This boolean aspect is equivalent to pragma @cite{Persistent_BSS}. |
| |
| @node Aspect Predicate,Aspect Pure_Function,Aspect Persistent_BSS,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-predicate}@anchor{fe} |
| @section Aspect Predicate |
| |
| |
| @geindex Predicate |
| |
| This aspect is equivalent to pragma @cite{Predicate}. It is thus |
| similar to the language defined aspects @cite{Dynamic_Predicate} |
| and @cite{Static_Predicate} except that whether the resulting |
| predicate is static or dynamic is controlled by the form of the |
| expression. It is also separately controllable using pragma |
| @cite{Assertion_Policy}. |
| |
| @node Aspect Pure_Function,Aspect Refined_Depends,Aspect Predicate,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-pure-function}@anchor{ff} |
| @section Aspect Pure_Function |
| |
| |
| @geindex Pure_Function |
| |
| This boolean aspect is equivalent to pragma @cite{Pure_Function}. |
| |
| @node Aspect Refined_Depends,Aspect Refined_Global,Aspect Pure_Function,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-refined-depends}@anchor{100} |
| @section Aspect Refined_Depends |
| |
| |
| @geindex Refined_Depends |
| |
| This aspect is equivalent to pragma @cite{Refined_Depends}. |
| |
| @node Aspect Refined_Global,Aspect Refined_Post,Aspect Refined_Depends,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-refined-global}@anchor{101} |
| @section Aspect Refined_Global |
| |
| |
| @geindex Refined_Global |
| |
| This aspect is equivalent to pragma @cite{Refined_Global}. |
| |
| @node Aspect Refined_Post,Aspect Refined_State,Aspect Refined_Global,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-refined-post}@anchor{102} |
| @section Aspect Refined_Post |
| |
| |
| @geindex Refined_Post |
| |
| This aspect is equivalent to pragma @cite{Refined_Post}. |
| |
| @node Aspect Refined_State,Aspect Remote_Access_Type,Aspect Refined_Post,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-refined-state}@anchor{103} |
| @section Aspect Refined_State |
| |
| |
| @geindex Refined_State |
| |
| This aspect is equivalent to pragma @cite{Refined_State}. |
| |
| @node Aspect Remote_Access_Type,Aspect Scalar_Storage_Order,Aspect Refined_State,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-remote-access-type}@anchor{104} |
| @section Aspect Remote_Access_Type |
| |
| |
| @geindex Remote_Access_Type |
| |
| This aspect is equivalent to pragma @cite{Remote_Access_Type}. |
| |
| @node Aspect Scalar_Storage_Order,Aspect Shared,Aspect Remote_Access_Type,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-scalar-storage-order}@anchor{105} |
| @section Aspect Scalar_Storage_Order |
| |
| |
| @geindex Scalar_Storage_Order |
| |
| This aspect is equivalent to a @cite{Scalar_Storage_Order} |
| attribute definition clause. |
| |
| @node Aspect Shared,Aspect Simple_Storage_Pool,Aspect Scalar_Storage_Order,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-shared}@anchor{106} |
| @section Aspect Shared |
| |
| |
| @geindex Shared |
| |
| This boolean aspect is equivalent to pragma @cite{Shared}, |
| and is thus a synonym for aspect @cite{Atomic}. |
| |
| @node Aspect Simple_Storage_Pool,Aspect Simple_Storage_Pool_Type,Aspect Shared,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-simple-storage-pool}@anchor{107} |
| @section Aspect Simple_Storage_Pool |
| |
| |
| @geindex Simple_Storage_Pool |
| |
| This aspect is equivalent to a @cite{Simple_Storage_Pool} |
| attribute definition clause. |
| |
| @node Aspect Simple_Storage_Pool_Type,Aspect SPARK_Mode,Aspect Simple_Storage_Pool,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-simple-storage-pool-type}@anchor{108} |
| @section Aspect Simple_Storage_Pool_Type |
| |
| |
| @geindex Simple_Storage_Pool_Type |
| |
| This boolean aspect is equivalent to pragma @cite{Simple_Storage_Pool_Type}. |
| |
| @node Aspect SPARK_Mode,Aspect Suppress_Debug_Info,Aspect Simple_Storage_Pool_Type,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-spark-mode}@anchor{109} |
| @section Aspect SPARK_Mode |
| |
| |
| @geindex SPARK_Mode |
| |
| This aspect is equivalent to pragma @cite{SPARK_Mode} and |
| may be specified for either or both of the specification and body |
| of a subprogram or package. |
| |
| @node Aspect Suppress_Debug_Info,Aspect Suppress_Initialization,Aspect SPARK_Mode,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-suppress-debug-info}@anchor{10a} |
| @section Aspect Suppress_Debug_Info |
| |
| |
| @geindex Suppress_Debug_Info |
| |
| This boolean aspect is equivalent to pragma @cite{Suppress_Debug_Info}. |
| |
| @node Aspect Suppress_Initialization,Aspect Test_Case,Aspect Suppress_Debug_Info,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-suppress-initialization}@anchor{10b} |
| @section Aspect Suppress_Initialization |
| |
| |
| @geindex Suppress_Initialization |
| |
| This boolean aspect is equivalent to pragma @cite{Suppress_Initialization}. |
| |
| @node Aspect Test_Case,Aspect Thread_Local_Storage,Aspect Suppress_Initialization,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-test-case}@anchor{10c} |
| @section Aspect Test_Case |
| |
| |
| @geindex Test_Case |
| |
| This aspect is equivalent to pragma @cite{Test_Case}. |
| |
| @node Aspect Thread_Local_Storage,Aspect Universal_Aliasing,Aspect Test_Case,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-thread-local-storage}@anchor{10d} |
| @section Aspect Thread_Local_Storage |
| |
| |
| @geindex Thread_Local_Storage |
| |
| This boolean aspect is equivalent to pragma @cite{Thread_Local_Storage}. |
| |
| @node Aspect Universal_Aliasing,Aspect Universal_Data,Aspect Thread_Local_Storage,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-universal-aliasing}@anchor{10e} |
| @section Aspect Universal_Aliasing |
| |
| |
| @geindex Universal_Aliasing |
| |
| This boolean aspect is equivalent to pragma @cite{Universal_Aliasing}. |
| |
| @node Aspect Universal_Data,Aspect Unmodified,Aspect Universal_Aliasing,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-universal-data}@anchor{10f} |
| @section Aspect Universal_Data |
| |
| |
| @geindex Universal_Data |
| |
| This aspect is equivalent to pragma @cite{Universal_Data}. |
| |
| @node Aspect Unmodified,Aspect Unreferenced,Aspect Universal_Data,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-unmodified}@anchor{110} |
| @section Aspect Unmodified |
| |
| |
| @geindex Unmodified |
| |
| This boolean aspect is equivalent to pragma @cite{Unmodified}. |
| |
| @node Aspect Unreferenced,Aspect Unreferenced_Objects,Aspect Unmodified,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-unreferenced}@anchor{111} |
| @section Aspect Unreferenced |
| |
| |
| @geindex Unreferenced |
| |
| This boolean aspect is equivalent to pragma @cite{Unreferenced}. Note that |
| in the case of formal parameters, it is not permitted to have aspects for |
| a formal parameter, so in this case the pragma form must be used. |
| |
| @node Aspect Unreferenced_Objects,Aspect Value_Size,Aspect Unreferenced,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-unreferenced-objects}@anchor{112} |
| @section Aspect Unreferenced_Objects |
| |
| |
| @geindex Unreferenced_Objects |
| |
| This boolean aspect is equivalent to pragma @cite{Unreferenced_Objects}. |
| |
| @node Aspect Value_Size,Aspect Warnings,Aspect Unreferenced_Objects,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-value-size}@anchor{113} |
| @section Aspect Value_Size |
| |
| |
| @geindex Value_Size |
| |
| This aspect is equivalent to a @cite{Value_Size} |
| attribute definition clause. |
| |
| @node Aspect Warnings,,Aspect Value_Size,Implementation Defined Aspects |
| @anchor{gnat_rm/implementation_defined_aspects aspect-warnings}@anchor{114} |
| @section Aspect Warnings |
| |
| |
| @geindex Warnings |
| |
| This aspect is equivalent to the two argument form of pragma @cite{Warnings}, |
| where the first argument is @cite{ON} or @cite{OFF} and the second argument |
| is the entity. |
| |
| @node Implementation Defined Attributes,Standard and Implementation Defined Restrictions,Implementation Defined Aspects,Top |
| @anchor{gnat_rm/implementation_defined_attributes doc}@anchor{115}@anchor{gnat_rm/implementation_defined_attributes implementation-defined-attributes}@anchor{8}@anchor{gnat_rm/implementation_defined_attributes id1}@anchor{116} |
| @chapter Implementation Defined Attributes |
| |
| |
| Ada defines (throughout the Ada reference manual, |
| summarized in Annex K), |
| a set of attributes that provide useful additional functionality in all |
| areas of the language. These language defined attributes are implemented |
| in GNAT and work as described in the Ada Reference Manual. |
| |
| In addition, Ada allows implementations to define additional |
| attributes whose meaning is defined by the implementation. GNAT provides |
| a number of these implementation-dependent attributes which can be used |
| to extend and enhance the functionality of the compiler. This section of |
| the GNAT reference manual describes these additional attributes. It also |
| describes additional implementation-dependent features of standard |
| language-defined attributes. |
| |
| Note that any program using these attributes may not be portable to |
| other compilers (although GNAT implements this set of attributes on all |
| platforms). Therefore if portability to other compilers is an important |
| consideration, you should minimize the use of these attributes. |
| |
| @menu |
| * Attribute Abort_Signal:: |
| * Attribute Address_Size:: |
| * Attribute Asm_Input:: |
| * Attribute Asm_Output:: |
| * Attribute Atomic_Always_Lock_Free:: |
| * Attribute Bit:: |
| * Attribute Bit_Position:: |
| * Attribute Code_Address:: |
| * Attribute Compiler_Version:: |
| * Attribute Constrained:: |
| * Attribute Default_Bit_Order:: |
| * Attribute Default_Scalar_Storage_Order:: |
| * Attribute Deref:: |
| * Attribute Descriptor_Size:: |
| * Attribute Elaborated:: |
| * Attribute Elab_Body:: |
| * Attribute Elab_Spec:: |
| * Attribute Elab_Subp_Body:: |
| * Attribute Emax:: |
| * Attribute Enabled:: |
| * Attribute Enum_Rep:: |
| * Attribute Enum_Val:: |
| * Attribute Epsilon:: |
| * Attribute Fast_Math:: |
| * Attribute Fixed_Value:: |
| * Attribute From_Any:: |
| * Attribute Has_Access_Values:: |
| * Attribute Has_Discriminants:: |
| * Attribute Img:: |
| * Attribute Integer_Value:: |
| * Attribute Invalid_Value:: |
| * Attribute Iterable:: |
| * Attribute Large:: |
| * Attribute Library_Level:: |
| * Attribute Lock_Free:: |
| * Attribute Loop_Entry:: |
| * Attribute Machine_Size:: |
| * Attribute Mantissa:: |
| * Attribute Maximum_Alignment:: |
| * Attribute Mechanism_Code:: |
| * Attribute Null_Parameter:: |
| * Attribute Object_Size:: |
| * Attribute Old:: |
| * Attribute Passed_By_Reference:: |
| * Attribute Pool_Address:: |
| * Attribute Range_Length:: |
| * Attribute Ref:: |
| * Attribute Restriction_Set:: |
| * Attribute Result:: |
| * Attribute Safe_Emax:: |
| * Attribute Safe_Large:: |
| * Attribute Safe_Small:: |
| * Attribute Scalar_Storage_Order:: |
| * Attribute Simple_Storage_Pool:: |
| * Attribute Small:: |
| * Attribute Storage_Unit:: |
| * Attribute Stub_Type:: |
| * Attribute System_Allocator_Alignment:: |
| * Attribute Target_Name:: |
| * Attribute To_Address:: |
| * Attribute To_Any:: |
| * Attribute Type_Class:: |
| * Attribute Type_Key:: |
| * Attribute TypeCode:: |
| * Attribute UET_Address:: |
| * Attribute Unconstrained_Array:: |
| * Attribute Universal_Literal_String:: |
| * Attribute Unrestricted_Access:: |
| * Attribute Update:: |
| * Attribute Valid_Scalars:: |
| * Attribute VADS_Size:: |
| * Attribute Value_Size:: |
| * Attribute Wchar_T_Size:: |
| * Attribute Word_Size:: |
| |
| @end menu |
| |
| @node Attribute Abort_Signal,Attribute Address_Size,,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-abort-signal}@anchor{117} |
| @section Attribute Abort_Signal |
| |
| |
| @geindex Abort_Signal |
| |
| @cite{Standard'Abort_Signal} (@cite{Standard} is the only allowed |
| prefix) provides the entity for the special exception used to signal |
| task abort or asynchronous transfer of control. Normally this attribute |
| should only be used in the tasking runtime (it is highly peculiar, and |
| completely outside the normal semantics of Ada, for a user program to |
| intercept the abort exception). |
| |
| @node Attribute Address_Size,Attribute Asm_Input,Attribute Abort_Signal,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-address-size}@anchor{118} |
| @section Attribute Address_Size |
| |
| |
| @geindex Size of `Address` |
| |
| @geindex Address_Size |
| |
| @cite{Standard'Address_Size} (@cite{Standard} is the only allowed |
| prefix) is a static constant giving the number of bits in an |
| @cite{Address}. It is the same value as System.Address'Size, |
| but has the advantage of being static, while a direct |
| reference to System.Address'Size is non-static because Address |
| is a private type. |
| |
| @node Attribute Asm_Input,Attribute Asm_Output,Attribute Address_Size,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-asm-input}@anchor{119} |
| @section Attribute Asm_Input |
| |
| |
| @geindex Asm_Input |
| |
| The @cite{Asm_Input} attribute denotes a function that takes two |
| parameters. The first is a string, the second is an expression of the |
| type designated by the prefix. The first (string) argument is required |
| to be a static expression, and is the constraint for the parameter, |
| (e.g., what kind of register is required). The second argument is the |
| value to be used as the input argument. The possible values for the |
| constant are the same as those used in the RTL, and are dependent on |
| the configuration file used to built the GCC back end. |
| @ref{11a,,Machine Code Insertions} |
| |
| @node Attribute Asm_Output,Attribute Atomic_Always_Lock_Free,Attribute Asm_Input,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-asm-output}@anchor{11b} |
| @section Attribute Asm_Output |
| |
| |
| @geindex Asm_Output |
| |
| The @cite{Asm_Output} attribute denotes a function that takes two |
| parameters. The first is a string, the second is the name of a variable |
| of the type designated by the attribute prefix. The first (string) |
| argument is required to be a static expression and designates the |
| constraint for the parameter (e.g., what kind of register is |
| required). The second argument is the variable to be updated with the |
| result. The possible values for constraint are the same as those used in |
| the RTL, and are dependent on the configuration file used to build the |
| GCC back end. If there are no output operands, then this argument may |
| either be omitted, or explicitly given as @cite{No_Output_Operands}. |
| @ref{11a,,Machine Code Insertions} |
| |
| @node Attribute Atomic_Always_Lock_Free,Attribute Bit,Attribute Asm_Output,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-atomic-always-lock-free}@anchor{11c} |
| @section Attribute Atomic_Always_Lock_Free |
| |
| |
| @geindex Atomic_Always_Lock_Free |
| |
| The prefix of the @cite{Atomic_Always_Lock_Free} attribute is a type. |
| The result is a Boolean value which is True if the type has discriminants, |
| and False otherwise. The result indicate whether atomic operations are |
| supported by the target for the given type. |
| |
| @node Attribute Bit,Attribute Bit_Position,Attribute Atomic_Always_Lock_Free,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-bit}@anchor{11d} |
| @section Attribute Bit |
| |
| |
| @geindex Bit |
| |
| @code{obj'Bit}, where @cite{obj} is any object, yields the bit |
| offset within the storage unit (byte) that contains the first bit of |
| storage allocated for the object. The value of this attribute is of the |
| type @cite{Universal_Integer}, and is always a non-negative number not |
| exceeding the value of @cite{System.Storage_Unit}. |
| |
| For an object that is a variable or a constant allocated in a register, |
| the value is zero. (The use of this attribute does not force the |
| allocation of a variable to memory). |
| |
| For an object that is a formal parameter, this attribute applies |
| to either the matching actual parameter or to a copy of the |
| matching actual parameter. |
| |
| For an access object the value is zero. Note that |
| @code{obj.all'Bit} is subject to an @cite{Access_Check} for the |
| designated object. Similarly for a record component |
| @code{X.C'Bit} is subject to a discriminant check and |
| @code{X(I).Bit} and @code{X(I1..I2)'Bit} |
| are subject to index checks. |
| |
| This attribute is designed to be compatible with the DEC Ada 83 definition |
| and implementation of the @cite{Bit} attribute. |
| |
| @node Attribute Bit_Position,Attribute Code_Address,Attribute Bit,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-bit-position}@anchor{11e} |
| @section Attribute Bit_Position |
| |
| |
| @geindex Bit_Position |
| |
| @code{R.C'Bit_Position}, where @cite{R} is a record object and @cite{C} is one |
| of the fields of the record type, yields the bit |
| offset within the record contains the first bit of |
| storage allocated for the object. The value of this attribute is of the |
| type @cite{Universal_Integer}. The value depends only on the field |
| @cite{C} and is independent of the alignment of |
| the containing record @cite{R}. |
| |
| @node Attribute Code_Address,Attribute Compiler_Version,Attribute Bit_Position,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-code-address}@anchor{11f} |
| @section Attribute Code_Address |
| |
| |
| @geindex Code_Address |
| |
| @geindex Subprogram address |
| |
| @geindex Address of subprogram code |
| |
| The @cite{'Address} |
| attribute may be applied to subprograms in Ada 95 and Ada 2005, but the |
| intended effect seems to be to provide |
| an address value which can be used to call the subprogram by means of |
| an address clause as in the following example: |
| |
| @example |
| procedure K is ... |
| |
| procedure L; |
| for L'Address use K'Address; |
| pragma Import (Ada, L); |
| @end example |
| |
| A call to @cite{L} is then expected to result in a call to @cite{K}. |
| In Ada 83, where there were no access-to-subprogram values, this was |
| a common work-around for getting the effect of an indirect call. |
| GNAT implements the above use of @cite{Address} and the technique |
| illustrated by the example code works correctly. |
| |
| However, for some purposes, it is useful to have the address of the start |
| of the generated code for the subprogram. On some architectures, this is |
| not necessarily the same as the @cite{Address} value described above. |
| For example, the @cite{Address} value may reference a subprogram |
| descriptor rather than the subprogram itself. |
| |
| The @cite{'Code_Address} attribute, which can only be applied to |
| subprogram entities, always returns the address of the start of the |
| generated code of the specified subprogram, which may or may not be |
| the same value as is returned by the corresponding @cite{'Address} |
| attribute. |
| |
| @node Attribute Compiler_Version,Attribute Constrained,Attribute Code_Address,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-compiler-version}@anchor{120} |
| @section Attribute Compiler_Version |
| |
| |
| @geindex Compiler_Version |
| |
| @cite{Standard'Compiler_Version} (@cite{Standard} is the only allowed |
| prefix) yields a static string identifying the version of the compiler |
| being used to compile the unit containing the attribute reference. |
| |
| @node Attribute Constrained,Attribute Default_Bit_Order,Attribute Compiler_Version,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-constrained}@anchor{121} |
| @section Attribute Constrained |
| |
| |
| @geindex Constrained |
| |
| In addition to the usage of this attribute in the Ada RM, @cite{GNAT} |
| also permits the use of the @cite{'Constrained} attribute |
| in a generic template |
| for any type, including types without discriminants. The value of this |
| attribute in the generic instance when applied to a scalar type or a |
| record type without discriminants is always @cite{True}. This usage is |
| compatible with older Ada compilers, including notably DEC Ada. |
| |
| @node Attribute Default_Bit_Order,Attribute Default_Scalar_Storage_Order,Attribute Constrained,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-default-bit-order}@anchor{122} |
| @section Attribute Default_Bit_Order |
| |
| |
| @geindex Big endian |
| |
| @geindex Little endian |
| |
| @geindex Default_Bit_Order |
| |
| @cite{Standard'Default_Bit_Order} (@cite{Standard} is the only |
| permissible prefix), provides the value @cite{System.Default_Bit_Order} |
| as a @cite{Pos} value (0 for @cite{High_Order_First}, 1 for |
| @cite{Low_Order_First}). This is used to construct the definition of |
| @cite{Default_Bit_Order} in package @cite{System}. |
| |
| @node Attribute Default_Scalar_Storage_Order,Attribute Deref,Attribute Default_Bit_Order,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-default-scalar-storage-order}@anchor{123} |
| @section Attribute Default_Scalar_Storage_Order |
| |
| |
| @geindex Big endian |
| |
| @geindex Little endian |
| |
| @geindex Default_Scalar_Storage_Order |
| |
| @cite{Standard'Default_Scalar_Storage_Order} (@cite{Standard} is the only |
| permissible prefix), provides the current value of the default scalar storage |
| order (as specified using pragma @cite{Default_Scalar_Storage_Order}, or |
| equal to @cite{Default_Bit_Order} if unspecified) as a |
| @cite{System.Bit_Order} value. This is a static attribute. |
| |
| @node Attribute Deref,Attribute Descriptor_Size,Attribute Default_Scalar_Storage_Order,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-deref}@anchor{124} |
| @section Attribute Deref |
| |
| |
| @geindex Deref |
| |
| The attribute @cite{typ'Deref(expr)} where @cite{expr} is of type @cite{System.Address} yields |
| the variable of type @cite{typ} that is located at the given address. It is similar |
| to @cite{(totyp (expr).all)}, where @cite{totyp} is an unchecked conversion from address to |
| a named access-to-@cite{typ} type, except that it yields a variable, so it can be |
| used on the left side of an assignment. |
| |
| @node Attribute Descriptor_Size,Attribute Elaborated,Attribute Deref,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-descriptor-size}@anchor{125} |
| @section Attribute Descriptor_Size |
| |
| |
| @geindex Descriptor |
| |
| @geindex Dope vector |
| |
| @geindex Descriptor_Size |
| |
| Non-static attribute @cite{Descriptor_Size} returns the size in bits of the |
| descriptor allocated for a type. The result is non-zero only for unconstrained |
| array types and the returned value is of type universal integer. In GNAT, an |
| array descriptor contains bounds information and is located immediately before |
| the first element of the array. |
| |
| @example |
| type Unconstr_Array is array (Positive range <>) of Boolean; |
| Put_Line ("Descriptor size = " & Unconstr_Array'Descriptor_Size'Img); |
| @end example |
| |
| The attribute takes into account any additional padding due to type alignment. |
| In the example above, the descriptor contains two values of type |
| @cite{Positive} representing the low and high bound. Since @cite{Positive} has |
| a size of 31 bits and an alignment of 4, the descriptor size is @cite{2 * Positive'Size + 2} or 64 bits. |
| |
| @node Attribute Elaborated,Attribute Elab_Body,Attribute Descriptor_Size,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-elaborated}@anchor{126} |
| @section Attribute Elaborated |
| |
| |
| @geindex Elaborated |
| |
| The prefix of the @cite{'Elaborated} attribute must be a unit name. The |
| value is a Boolean which indicates whether or not the given unit has been |
| elaborated. This attribute is primarily intended for internal use by the |
| generated code for dynamic elaboration checking, but it can also be used |
| in user programs. The value will always be True once elaboration of all |
| units has been completed. An exception is for units which need no |
| elaboration, the value is always False for such units. |
| |
| @node Attribute Elab_Body,Attribute Elab_Spec,Attribute Elaborated,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-elab-body}@anchor{127} |
| @section Attribute Elab_Body |
| |
| |
| @geindex Elab_Body |
| |
| This attribute can only be applied to a program unit name. It returns |
| the entity for the corresponding elaboration procedure for elaborating |
| the body of the referenced unit. This is used in the main generated |
| elaboration procedure by the binder and is not normally used in any |
| other context. However, there may be specialized situations in which it |
| is useful to be able to call this elaboration procedure from Ada code, |
| e.g., if it is necessary to do selective re-elaboration to fix some |
| error. |
| |
| @node Attribute Elab_Spec,Attribute Elab_Subp_Body,Attribute Elab_Body,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-elab-spec}@anchor{128} |
| @section Attribute Elab_Spec |
| |
| |
| @geindex Elab_Spec |
| |
| This attribute can only be applied to a program unit name. It returns |
| the entity for the corresponding elaboration procedure for elaborating |
| the spec of the referenced unit. This is used in the main |
| generated elaboration procedure by the binder and is not normally used |
| in any other context. However, there may be specialized situations in |
| which it is useful to be able to call this elaboration procedure from |
| Ada code, e.g., if it is necessary to do selective re-elaboration to fix |
| some error. |
| |
| @node Attribute Elab_Subp_Body,Attribute Emax,Attribute Elab_Spec,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-elab-subp-body}@anchor{129} |
| @section Attribute Elab_Subp_Body |
| |
| |
| @geindex Elab_Subp_Body |
| |
| This attribute can only be applied to a library level subprogram |
| name and is only allowed in CodePeer mode. It returns the entity |
| for the corresponding elaboration procedure for elaborating the body |
| of the referenced subprogram unit. This is used in the main generated |
| elaboration procedure by the binder in CodePeer mode only and is unrecognized |
| otherwise. |
| |
| @node Attribute Emax,Attribute Enabled,Attribute Elab_Subp_Body,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-emax}@anchor{12a} |
| @section Attribute Emax |
| |
| |
| @geindex Ada 83 attributes |
| |
| @geindex Emax |
| |
| The @cite{Emax} attribute is provided for compatibility with Ada 83. See |
| the Ada 83 reference manual for an exact description of the semantics of |
| this attribute. |
| |
| @node Attribute Enabled,Attribute Enum_Rep,Attribute Emax,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-enabled}@anchor{12b} |
| @section Attribute Enabled |
| |
| |
| @geindex Enabled |
| |
| The @cite{Enabled} attribute allows an application program to check at compile |
| time to see if the designated check is currently enabled. The prefix is a |
| simple identifier, referencing any predefined check name (other than |
| @cite{All_Checks}) or a check name introduced by pragma Check_Name. If |
| no argument is given for the attribute, the check is for the general state |
| of the check, if an argument is given, then it is an entity name, and the |
| check indicates whether an @cite{Suppress} or @cite{Unsuppress} has been |
| given naming the entity (if not, then the argument is ignored). |
| |
| Note that instantiations inherit the check status at the point of the |
| instantiation, so a useful idiom is to have a library package that |
| introduces a check name with @cite{pragma Check_Name}, and then contains |
| generic packages or subprograms which use the @cite{Enabled} attribute |
| to see if the check is enabled. A user of this package can then issue |
| a @cite{pragma Suppress} or @cite{pragma Unsuppress} before instantiating |
| the package or subprogram, controlling whether the check will be present. |
| |
| @node Attribute Enum_Rep,Attribute Enum_Val,Attribute Enabled,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-enum-rep}@anchor{12c} |
| @section Attribute Enum_Rep |
| |
| |
| @geindex Representation of enums |
| |
| @geindex Enum_Rep |
| |
| For every enumeration subtype @cite{S}, @code{S'Enum_Rep} denotes a |
| function with the following spec: |
| |
| @example |
| function S'Enum_Rep (Arg : S'Base) return <Universal_Integer>; |
| @end example |
| |
| It is also allowable to apply @cite{Enum_Rep} directly to an object of an |
| enumeration type or to a non-overloaded enumeration |
| literal. In this case @code{S'Enum_Rep} is equivalent to |
| @code{typ'Enum_Rep(S)} where @cite{typ} is the type of the |
| enumeration literal or object. |
| |
| The function returns the representation value for the given enumeration |
| value. This will be equal to value of the @cite{Pos} attribute in the |
| absence of an enumeration representation clause. This is a static |
| attribute (i.e.,:the result is static if the argument is static). |
| |
| @code{S'Enum_Rep} can also be used with integer types and objects, |
| in which case it simply returns the integer value. The reason for this |
| is to allow it to be used for @cite{(<>)} discrete formal arguments in |
| a generic unit that can be instantiated with either enumeration types |
| or integer types. Note that if @cite{Enum_Rep} is used on a modular |
| type whose upper bound exceeds the upper bound of the largest signed |
| integer type, and the argument is a variable, so that the universal |
| integer calculation is done at run time, then the call to @cite{Enum_Rep} |
| may raise @cite{Constraint_Error}. |
| |
| @node Attribute Enum_Val,Attribute Epsilon,Attribute Enum_Rep,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-enum-val}@anchor{12d} |
| @section Attribute Enum_Val |
| |
| |
| @geindex Representation of enums |
| |
| @geindex Enum_Val |
| |
| For every enumeration subtype @cite{S}, @code{S'Enum_Val} denotes a |
| function with the following spec: |
| |
| @example |
| function S'Enum_Val (Arg : <Universal_Integer>) return S'Base; |
| @end example |
| |
| The function returns the enumeration value whose representation matches the |
| argument, or raises Constraint_Error if no enumeration literal of the type |
| has the matching value. |
| This will be equal to value of the @cite{Val} attribute in the |
| absence of an enumeration representation clause. This is a static |
| attribute (i.e., the result is static if the argument is static). |
| |
| @node Attribute Epsilon,Attribute Fast_Math,Attribute Enum_Val,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-epsilon}@anchor{12e} |
| @section Attribute Epsilon |
| |
| |
| @geindex Ada 83 attributes |
| |
| @geindex Epsilon |
| |
| The @cite{Epsilon} attribute is provided for compatibility with Ada 83. See |
| the Ada 83 reference manual for an exact description of the semantics of |
| this attribute. |
| |
| @node Attribute Fast_Math,Attribute Fixed_Value,Attribute Epsilon,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-fast-math}@anchor{12f} |
| @section Attribute Fast_Math |
| |
| |
| @geindex Fast_Math |
| |
| @cite{Standard'Fast_Math} (@cite{Standard} is the only allowed |
| prefix) yields a static Boolean value that is True if pragma |
| @cite{Fast_Math} is active, and False otherwise. |
| |
| @node Attribute Fixed_Value,Attribute From_Any,Attribute Fast_Math,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-fixed-value}@anchor{130} |
| @section Attribute Fixed_Value |
| |
| |
| @geindex Fixed_Value |
| |
| For every fixed-point type @cite{S}, @code{S'Fixed_Value} denotes a |
| function with the following specification: |
| |
| @example |
| function S'Fixed_Value (Arg : <Universal_Integer>) return S; |
| @end example |
| |
| The value returned is the fixed-point value @cite{V} such that: |
| |
| @example |
| V = Arg * S'Small |
| @end example |
| |
| The effect is thus similar to first converting the argument to the |
| integer type used to represent @cite{S}, and then doing an unchecked |
| conversion to the fixed-point type. The difference is |
| that there are full range checks, to ensure that the result is in range. |
| This attribute is primarily intended for use in implementation of the |
| input-output functions for fixed-point values. |
| |
| @node Attribute From_Any,Attribute Has_Access_Values,Attribute Fixed_Value,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-from-any}@anchor{131} |
| @section Attribute From_Any |
| |
| |
| @geindex From_Any |
| |
| This internal attribute is used for the generation of remote subprogram |
| stubs in the context of the Distributed Systems Annex. |
| |
| @node Attribute Has_Access_Values,Attribute Has_Discriminants,Attribute From_Any,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-has-access-values}@anchor{132} |
| @section Attribute Has_Access_Values |
| |
| |
| @geindex Access values |
| @geindex testing for |
| |
| @geindex Has_Access_Values |
| |
| The prefix of the @cite{Has_Access_Values} attribute is a type. The result |
| is a Boolean value which is True if the is an access type, or is a composite |
| type with a component (at any nesting depth) that is an access type, and is |
| False otherwise. |
| The intended use of this attribute is in conjunction with generic |
| definitions. If the attribute is applied to a generic private type, it |
| indicates whether or not the corresponding actual type has access values. |
| |
| @node Attribute Has_Discriminants,Attribute Img,Attribute Has_Access_Values,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-has-discriminants}@anchor{133} |
| @section Attribute Has_Discriminants |
| |
| |
| @geindex Discriminants |
| @geindex testing for |
| |
| @geindex Has_Discriminants |
| |
| The prefix of the @cite{Has_Discriminants} attribute is a type. The result |
| is a Boolean value which is True if the type has discriminants, and False |
| otherwise. The intended use of this attribute is in conjunction with generic |
| definitions. If the attribute is applied to a generic private type, it |
| indicates whether or not the corresponding actual type has discriminants. |
| |
| @node Attribute Img,Attribute Integer_Value,Attribute Has_Discriminants,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-img}@anchor{134} |
| @section Attribute Img |
| |
| |
| @geindex Img |
| |
| The @cite{Img} attribute differs from @cite{Image} in that it is applied |
| directly to an object, and yields the same result as |
| @cite{Image} for the subtype of the object. This is convenient for |
| debugging: |
| |
| @example |
| Put_Line ("X = " & X'Img); |
| @end example |
| |
| has the same meaning as the more verbose: |
| |
| @example |
| Put_Line ("X = " & T'Image (X)); |
| @end example |
| |
| where @cite{T} is the (sub)type of the object @cite{X}. |
| |
| Note that technically, in analogy to @cite{Image}, |
| @cite{X'Img} returns a parameterless function |
| that returns the appropriate string when called. This means that |
| @cite{X'Img} can be renamed as a function-returning-string, or used |
| in an instantiation as a function parameter. |
| |
| @node Attribute Integer_Value,Attribute Invalid_Value,Attribute Img,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-integer-value}@anchor{135} |
| @section Attribute Integer_Value |
| |
| |
| @geindex Integer_Value |
| |
| For every integer type @cite{S}, @code{S'Integer_Value} denotes a |
| function with the following spec: |
| |
| @example |
| function S'Integer_Value (Arg : <Universal_Fixed>) return S; |
| @end example |
| |
| The value returned is the integer value @cite{V}, such that: |
| |
| @example |
| Arg = V * T'Small |
| @end example |
| |
| where @cite{T} is the type of @cite{Arg}. |
| The effect is thus similar to first doing an unchecked conversion from |
| the fixed-point type to its corresponding implementation type, and then |
| converting the result to the target integer type. The difference is |
| that there are full range checks, to ensure that the result is in range. |
| This attribute is primarily intended for use in implementation of the |
| standard input-output functions for fixed-point values. |
| |
| @node Attribute Invalid_Value,Attribute Iterable,Attribute Integer_Value,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-invalid-value}@anchor{136} |
| @section Attribute Invalid_Value |
| |
| |
| @geindex Invalid_Value |
| |
| For every scalar type S, S'Invalid_Value returns an undefined value of the |
| type. If possible this value is an invalid representation for the type. The |
| value returned is identical to the value used to initialize an otherwise |
| uninitialized value of the type if pragma Initialize_Scalars is used, |
| including the ability to modify the value with the binder -Sxx flag and |
| relevant environment variables at run time. |
| |
| @node Attribute Iterable,Attribute Large,Attribute Invalid_Value,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-iterable}@anchor{137} |
| @section Attribute Iterable |
| |
| |
| @geindex Iterable |
| |
| Equivalent to Aspect Iterable. |
| |
| @node Attribute Large,Attribute Library_Level,Attribute Iterable,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-large}@anchor{138} |
| @section Attribute Large |
| |
| |
| @geindex Ada 83 attributes |
| |
| @geindex Large |
| |
| The @cite{Large} attribute is provided for compatibility with Ada 83. See |
| the Ada 83 reference manual for an exact description of the semantics of |
| this attribute. |
| |
| @node Attribute Library_Level,Attribute Lock_Free,Attribute Large,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-library-level}@anchor{139} |
| @section Attribute Library_Level |
| |
| |
| @geindex Library_Level |
| |
| @cite{P'Library_Level}, where P is an entity name, |
| returns a Boolean value which is True if the entity is declared |
| at the library level, and False otherwise. Note that within a |
| generic instantition, the name of the generic unit denotes the |
| instance, which means that this attribute can be used to test |
| if a generic is instantiated at the library level, as shown |
| in this example: |
| |
| @example |
| generic |
| ... |
| package Gen is |
| pragma Compile_Time_Error |
| (not Gen'Library_Level, |
| "Gen can only be instantiated at library level"); |
| ... |
| end Gen; |
| @end example |
| |
| @node Attribute Lock_Free,Attribute Loop_Entry,Attribute Library_Level,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-lock-free}@anchor{13a} |
| @section Attribute Lock_Free |
| |
| |
| @geindex Lock_Free |
| |
| @cite{P'Lock_Free}, where P is a protected object, returns True if a |
| pragma @cite{Lock_Free} applies to P. |
| |
| @node Attribute Loop_Entry,Attribute Machine_Size,Attribute Lock_Free,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-loop-entry}@anchor{13b} |
| @section Attribute Loop_Entry |
| |
| |
| @geindex Loop_Entry |
| |
| Syntax: |
| |
| @example |
| X'Loop_Entry [(loop_name)] |
| @end example |
| |
| The @cite{Loop_Entry} attribute is used to refer to the value that an |
| expression had upon entry to a given loop in much the same way that the |
| @cite{Old} attribute in a subprogram postcondition can be used to refer |
| to the value an expression had upon entry to the subprogram. The |
| relevant loop is either identified by the given loop name, or it is the |
| innermost enclosing loop when no loop name is given. |
| |
| A @cite{Loop_Entry} attribute can only occur within a |
| @cite{Loop_Variant} or @cite{Loop_Invariant} pragma. A common use of |
| @cite{Loop_Entry} is to compare the current value of objects with their |
| initial value at loop entry, in a @cite{Loop_Invariant} pragma. |
| |
| The effect of using @cite{X'Loop_Entry} is the same as declaring |
| a constant initialized with the initial value of @cite{X} at loop |
| entry. This copy is not performed if the loop is not entered, or if the |
| corresponding pragmas are ignored or disabled. |
| |
| @node Attribute Machine_Size,Attribute Mantissa,Attribute Loop_Entry,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-machine-size}@anchor{13c} |
| @section Attribute Machine_Size |
| |
| |
| @geindex Machine_Size |
| |
| This attribute is identical to the @cite{Object_Size} attribute. It is |
| provided for compatibility with the DEC Ada 83 attribute of this name. |
| |
| @node Attribute Mantissa,Attribute Maximum_Alignment,Attribute Machine_Size,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-mantissa}@anchor{13d} |
| @section Attribute Mantissa |
| |
| |
| @geindex Ada 83 attributes |
| |
| @geindex Mantissa |
| |
| The @cite{Mantissa} attribute is provided for compatibility with Ada 83. See |
| the Ada 83 reference manual for an exact description of the semantics of |
| this attribute. |
| |
| @node Attribute Maximum_Alignment,Attribute Mechanism_Code,Attribute Mantissa,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-maximum-alignment}@anchor{13e}@anchor{gnat_rm/implementation_defined_attributes id2}@anchor{13f} |
| @section Attribute Maximum_Alignment |
| |
| |
| @geindex Alignment |
| @geindex maximum |
| |
| @geindex Maximum_Alignment |
| |
| @cite{Standard'Maximum_Alignment} (@cite{Standard} is the only |
| permissible prefix) provides the maximum useful alignment value for the |
| target. This is a static value that can be used to specify the alignment |
| for an object, guaranteeing that it is properly aligned in all |
| cases. |
| |
| @node Attribute Mechanism_Code,Attribute Null_Parameter,Attribute Maximum_Alignment,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-mechanism-code}@anchor{140} |
| @section Attribute Mechanism_Code |
| |
| |
| @geindex Return values |
| @geindex passing mechanism |
| |
| @geindex Parameters |
| @geindex passing mechanism |
| |
| @geindex Mechanism_Code |
| |
| @code{function'Mechanism_Code} yields an integer code for the |
| mechanism used for the result of function, and |
| @code{subprogram'Mechanism_Code (n)} yields the mechanism |
| used for formal parameter number @cite{n} (a static integer value with 1 |
| meaning the first parameter) of @cite{subprogram}. The code returned is: |
| |
| |
| @table @asis |
| |
| @item @emph{1} |
| |
| by copy (value) |
| |
| @item @emph{2} |
| |
| by reference |
| @end table |
| |
| @node Attribute Null_Parameter,Attribute Object_Size,Attribute Mechanism_Code,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-null-parameter}@anchor{141} |
| @section Attribute Null_Parameter |
| |
| |
| @geindex Zero address |
| @geindex passing |
| |
| @geindex Null_Parameter |
| |
| A reference @code{T'Null_Parameter} denotes an imaginary object of |
| type or subtype @cite{T} allocated at machine address zero. The attribute |
| is allowed only as the default expression of a formal parameter, or as |
| an actual expression of a subprogram call. In either case, the |
| subprogram must be imported. |
| |
| The identity of the object is represented by the address zero in the |
| argument list, independent of the passing mechanism (explicit or |
| default). |
| |
| This capability is needed to specify that a zero address should be |
| passed for a record or other composite object passed by reference. |
| There is no way of indicating this without the @cite{Null_Parameter} |
| attribute. |
| |
| @node Attribute Object_Size,Attribute Old,Attribute Null_Parameter,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-object-size}@anchor{142} |
| @section Attribute Object_Size |
| |
| |
| @geindex Size |
| @geindex used for objects |
| |
| @geindex Object_Size |
| |
| The size of an object is not necessarily the same as the size of the type |
| of an object. This is because by default object sizes are increased to be |
| a multiple of the alignment of the object. For example, |
| @cite{Natural'Size} is |
| 31, but by default objects of type @cite{Natural} will have a size of 32 bits. |
| Similarly, a record containing an integer and a character: |
| |
| @example |
| type Rec is record |
| I : Integer; |
| C : Character; |
| end record; |
| @end example |
| |
| will have a size of 40 (that is @cite{Rec'Size} will be 40). The |
| alignment will be 4, because of the |
| integer field, and so the default size of record objects for this type |
| will be 64 (8 bytes). |
| |
| If the alignment of the above record is specified to be 1, then the |
| object size will be 40 (5 bytes). This is true by default, and also |
| an object size of 40 can be explicitly specified in this case. |
| |
| A consequence of this capability is that different object sizes can be |
| given to subtypes that would otherwise be considered in Ada to be |
| statically matching. But it makes no sense to consider such subtypes |
| as statically matching. Consequently, in @cite{GNAT} we add a rule |
| to the static matching rules that requires object sizes to match. |
| Consider this example: |
| |
| @example |
| 1. procedure BadAVConvert is |
| 2. type R is new Integer; |
| 3. subtype R1 is R range 1 .. 10; |
| 4. subtype R2 is R range 1 .. 10; |
| 5. for R1'Object_Size use 8; |
| 6. for R2'Object_Size use 16; |
| 7. type R1P is access all R1; |
| 8. type R2P is access all R2; |
| 9. R1PV : R1P := new R1'(4); |
| 10. R2PV : R2P; |
| 11. begin |
| 12. R2PV := R2P (R1PV); |
| | |
| >>> target designated subtype not compatible with |
| type "R1" defined at line 3 |
| |
| 13. end; |
| @end example |
| |
| In the absence of lines 5 and 6, |
| types @cite{R1} and @cite{R2} statically match and |
| hence the conversion on line 12 is legal. But since lines 5 and 6 |
| cause the object sizes to differ, @cite{GNAT} considers that types |
| @cite{R1} and @cite{R2} are not statically matching, and line 12 |
| generates the diagnostic shown above. |
| |
| Similar additional checks are performed in other contexts requiring |
| statically matching subtypes. |
| |
| @node Attribute Old,Attribute Passed_By_Reference,Attribute Object_Size,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-old}@anchor{143} |
| @section Attribute Old |
| |
| |
| @geindex Old |
| |
| In addition to the usage of @cite{Old} defined in the Ada 2012 RM (usage |
| within @cite{Post} aspect), GNAT also permits the use of this attribute |
| in implementation defined pragmas @cite{Postcondition}, |
| @cite{Contract_Cases} and @cite{Test_Case}. Also usages of |
| @cite{Old} which would be illegal according to the Ada 2012 RM |
| definition are allowed under control of |
| implementation defined pragma @cite{Unevaluated_Use_Of_Old}. |
| |
| @node Attribute Passed_By_Reference,Attribute Pool_Address,Attribute Old,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-passed-by-reference}@anchor{144} |
| @section Attribute Passed_By_Reference |
| |
| |
| @geindex Parameters |
| @geindex when passed by reference |
| |
| @geindex Passed_By_Reference |
| |
| @code{type'Passed_By_Reference} for any subtype @cite{type} returns |
| a value of type @cite{Boolean} value that is @cite{True} if the type is |
| normally passed by reference and @cite{False} if the type is normally |
| passed by copy in calls. For scalar types, the result is always @cite{False} |
| and is static. For non-scalar types, the result is non-static. |
| |
| @node Attribute Pool_Address,Attribute Range_Length,Attribute Passed_By_Reference,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-pool-address}@anchor{145} |
| @section Attribute Pool_Address |
| |
| |
| @geindex Parameters |
| @geindex when passed by reference |
| |
| @geindex Pool_Address |
| |
| @code{X'Pool_Address} for any object @cite{X} returns the address |
| of X within its storage pool. This is the same as |
| @code{X'Address}, except that for an unconstrained array whose |
| bounds are allocated just before the first component, |
| @code{X'Pool_Address} returns the address of those bounds, |
| whereas @code{X'Address} returns the address of the first |
| component. |
| |
| Here, we are interpreting 'storage pool' broadly to mean |
| @code{wherever the object is allocated}, which could be a |
| user-defined storage pool, |
| the global heap, on the stack, or in a static memory area. |
| For an object created by @cite{new}, @code{Ptr.all'Pool_Address} is |
| what is passed to @cite{Allocate} and returned from @cite{Deallocate}. |
| |
| @node Attribute Range_Length,Attribute Ref,Attribute Pool_Address,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-range-length}@anchor{146} |
| @section Attribute Range_Length |
| |
| |
| @geindex Range_Length |
| |
| @code{type'Range_Length} for any discrete type @cite{type} yields |
| the number of values represented by the subtype (zero for a null |
| range). The result is static for static subtypes. @cite{Range_Length} |
| applied to the index subtype of a one dimensional array always gives the |
| same result as @cite{Length} applied to the array itself. |
| |
| @node Attribute Ref,Attribute Restriction_Set,Attribute Range_Length,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-ref}@anchor{147} |
| @section Attribute Ref |
| |
| |
| @geindex Ref |
| |
| @node Attribute Restriction_Set,Attribute Result,Attribute Ref,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-restriction-set}@anchor{148} |
| @section Attribute Restriction_Set |
| |
| |
| @geindex Restriction_Set |
| |
| @geindex Restrictions |
| |
| This attribute allows compile time testing of restrictions that |
| are currently in effect. It is primarily intended for specializing |
| code in the run-time based on restrictions that are active (e.g. |
| don't need to save fpt registers if restriction No_Floating_Point |
| is known to be in effect), but can be used anywhere. |
| |
| There are two forms: |
| |
| @example |
| System'Restriction_Set (partition_boolean_restriction_NAME) |
| System'Restriction_Set (No_Dependence => library_unit_NAME); |
| @end example |
| |
| In the case of the first form, the only restriction names |
| allowed are parameterless restrictions that are checked |
| for consistency at bind time. For a complete list see the |
| subtype @cite{System.Rident.Partition_Boolean_Restrictions}. |
| |
| The result returned is True if the restriction is known to |
| be in effect, and False if the restriction is known not to |
| be in effect. An important guarantee is that the value of |
| a Restriction_Set attribute is known to be consistent throughout |
| all the code of a partition. |
| |
| This is trivially achieved if the entire partition is compiled |
| with a consistent set of restriction pragmas. However, the |
| compilation model does not require this. It is possible to |
| compile one set of units with one set of pragmas, and another |
| set of units with another set of pragmas. It is even possible |
| to compile a spec with one set of pragmas, and then WITH the |
| same spec with a different set of pragmas. Inconsistencies |
| in the actual use of the restriction are checked at bind time. |
| |
| In order to achieve the guarantee of consistency for the |
| Restriction_Set pragma, we consider that a use of the pragma |
| that yields False is equivalent to a violation of the |
| restriction. |
| |
| So for example if you write |
| |
| @example |
| if System'Restriction_Set (No_Floating_Point) then |
| ... |
| else |
| ... |
| end if; |
| @end example |
| |
| And the result is False, so that the else branch is executed, |
| you can assume that this restriction is not set for any unit |
| in the partition. This is checked by considering this use of |
| the restriction pragma to be a violation of the restriction |
| No_Floating_Point. This means that no other unit can attempt |
| to set this restriction (if some unit does attempt to set it, |
| the binder will refuse to bind the partition). |
| |
| Technical note: The restriction name and the unit name are |
| intepreted entirely syntactically, as in the corresponding |
| Restrictions pragma, they are not analyzed semantically, |
| so they do not have a type. |
| |
| @node Attribute Result,Attribute Safe_Emax,Attribute Restriction_Set,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-result}@anchor{149} |
| @section Attribute Result |
| |
| |
| @geindex Result |
| |
| @code{function'Result} can only be used with in a Postcondition pragma |
| for a function. The prefix must be the name of the corresponding function. This |
| is used to refer to the result of the function in the postcondition expression. |
| For a further discussion of the use of this attribute and examples of its use, |
| see the description of pragma Postcondition. |
| |
| @node Attribute Safe_Emax,Attribute Safe_Large,Attribute Result,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-safe-emax}@anchor{14a} |
| @section Attribute Safe_Emax |
| |
| |
| @geindex Ada 83 attributes |
| |
| @geindex Safe_Emax |
| |
| The @cite{Safe_Emax} attribute is provided for compatibility with Ada 83. See |
| the Ada 83 reference manual for an exact description of the semantics of |
| this attribute. |
| |
| @node Attribute Safe_Large,Attribute Safe_Small,Attribute Safe_Emax,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-safe-large}@anchor{14b} |
| @section Attribute Safe_Large |
| |
| |
| @geindex Ada 83 attributes |
| |
| @geindex Safe_Large |
| |
| The @cite{Safe_Large} attribute is provided for compatibility with Ada 83. See |
| the Ada 83 reference manual for an exact description of the semantics of |
| this attribute. |
| |
| @node Attribute Safe_Small,Attribute Scalar_Storage_Order,Attribute Safe_Large,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-safe-small}@anchor{14c} |
| @section Attribute Safe_Small |
| |
| |
| @geindex Ada 83 attributes |
| |
| @geindex Safe_Small |
| |
| The @cite{Safe_Small} attribute is provided for compatibility with Ada 83. See |
| the Ada 83 reference manual for an exact description of the semantics of |
| this attribute. |
| |
| @node Attribute Scalar_Storage_Order,Attribute Simple_Storage_Pool,Attribute Safe_Small,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-scalar-storage-order}@anchor{14d} |
| @section Attribute Scalar_Storage_Order |
| |
| |
| @geindex Endianness |
| |
| @geindex Scalar storage order |
| |
| @geindex Scalar_Storage_Order |
| |
| For every array or record type @cite{S}, the representation attribute |
| @cite{Scalar_Storage_Order} denotes the order in which storage elements |
| that make up scalar components are ordered within S. The value given must |
| be a static expression of type System.Bit_Order. The following is an example |
| of the use of this feature: |
| |
| @example |
| -- Component type definitions |
| |
| subtype Yr_Type is Natural range 0 .. 127; |
| subtype Mo_Type is Natural range 1 .. 12; |
| subtype Da_Type is Natural range 1 .. 31; |
| |
| -- Record declaration |
| |
| type Date is record |
| Years_Since_1980 : Yr_Type; |
| Month : Mo_Type; |
| Day_Of_Month : Da_Type; |
| end record; |
| |
| -- Record representation clause |
| |
| for Date use record |
| Years_Since_1980 at 0 range 0 .. 6; |
| Month at 0 range 7 .. 10; |
| Day_Of_Month at 0 range 11 .. 15; |
| end record; |
| |
| -- Attribute definition clauses |
| |
| for Date'Bit_Order use System.High_Order_First; |
| for Date'Scalar_Storage_Order use System.High_Order_First; |
| -- If Scalar_Storage_Order is specified, it must be consistent with |
| -- Bit_Order, so it's best to always define the latter explicitly if |
| -- the former is used. |
| @end example |
| |
| Other properties are as for standard representation attribute @cite{Bit_Order}, |
| as defined by Ada RM 13.5.3(4). The default is @cite{System.Default_Bit_Order}. |
| |
| For a record type @cite{T}, if @code{T'Scalar_Storage_Order} is |
| specified explicitly, it shall be equal to @code{T'Bit_Order}. Note: |
| this means that if a @cite{Scalar_Storage_Order} attribute definition |
| clause is not confirming, then the type's @cite{Bit_Order} shall be |
| specified explicitly and set to the same value. |
| |
| Derived types inherit an explicitly set scalar storage order from their parent |
| types. This may be overridden for the derived type by giving an explicit scalar |
| storage order for the derived type. For a record extension, the derived type |
| must have the same scalar storage order as the parent type. |
| |
| If a component of @cite{T} is of a record or array type, then that type must |
| also have a @cite{Scalar_Storage_Order} attribute definition clause. |
| |
| A component of a record or array type that is a packed array, or that |
| does not start on a byte boundary, must have the same scalar storage order |
| as the enclosing record or array type. |
| |
| No component of a type that has an explicit @cite{Scalar_Storage_Order} |
| attribute definition may be aliased. |
| |
| A confirming @cite{Scalar_Storage_Order} attribute definition clause (i.e. |
| with a value equal to @cite{System.Default_Bit_Order}) has no effect. |
| |
| If the opposite storage order is specified, then whenever the value of |
| a scalar component of an object of type @cite{S} is read, the storage |
| elements of the enclosing machine scalar are first reversed (before |
| retrieving the component value, possibly applying some shift and mask |
| operatings on the enclosing machine scalar), and the opposite operation |
| is done for writes. |
| |
| In that case, the restrictions set forth in 13.5.1(10.3/2) for scalar components |
| are relaxed. Instead, the following rules apply: |
| |
| |
| @itemize * |
| |
| @item |
| the underlying storage elements are those at positions |
| @cite{(position + first_bit / storage_element_size) .. (position + (last_bit + storage_element_size - 1) / storage_element_size)} |
| |
| @item |
| the sequence of underlying storage elements shall have |
| a size no greater than the largest machine scalar |
| |
| @item |
| the enclosing machine scalar is defined as the smallest machine |
| scalar starting at a position no greater than |
| @cite{position + first_bit / storage_element_size} and covering |
| storage elements at least up to @cite{position + (last_bit + storage_element_size - 1) / storage_element_size} |
| |
| @item |
| the position of the component is interpreted relative to that machine |
| scalar. |
| @end itemize |
| |
| If no scalar storage order is specified for a type (either directly, or by |
| inheritance in the case of a derived type), then the default is normally |
| the native ordering of the target, but this default can be overridden using |
| pragma @cite{Default_Scalar_Storage_Order}. |
| |
| Note that the scalar storage order only affects the in-memory data |
| representation. It has no effect on the representation used by stream |
| attributes. |
| |
| @node Attribute Simple_Storage_Pool,Attribute Small,Attribute Scalar_Storage_Order,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-simple-storage-pool}@anchor{b7}@anchor{gnat_rm/implementation_defined_attributes id3}@anchor{14e} |
| @section Attribute Simple_Storage_Pool |
| |
| |
| @geindex Storage pool |
| @geindex simple |
| |
| @geindex Simple storage pool |
| |
| @geindex Simple_Storage_Pool |
| |
| For every nonformal, nonderived access-to-object type @cite{Acc}, the |
| representation attribute @cite{Simple_Storage_Pool} may be specified |
| via an attribute_definition_clause (or by specifying the equivalent aspect): |
| |
| @example |
| My_Pool : My_Simple_Storage_Pool_Type; |
| |
| type Acc is access My_Data_Type; |
| |
| for Acc'Simple_Storage_Pool use My_Pool; |
| @end example |
| |
| The name given in an attribute_definition_clause for the |
| @cite{Simple_Storage_Pool} attribute shall denote a variable of |
| a 'simple storage pool type' (see pragma @cite{Simple_Storage_Pool_Type}). |
| |
| The use of this attribute is only allowed for a prefix denoting a type |
| for which it has been specified. The type of the attribute is the type |
| of the variable specified as the simple storage pool of the access type, |
| and the attribute denotes that variable. |
| |
| It is illegal to specify both @cite{Storage_Pool} and @cite{Simple_Storage_Pool} |
| for the same access type. |
| |
| If the @cite{Simple_Storage_Pool} attribute has been specified for an access |
| type, then applying the @cite{Storage_Pool} attribute to the type is flagged |
| with a warning and its evaluation raises the exception @cite{Program_Error}. |
| |
| If the Simple_Storage_Pool attribute has been specified for an access |
| type @cite{S}, then the evaluation of the attribute @code{S'Storage_Size} |
| returns the result of calling @code{Storage_Size (S'Simple_Storage_Pool)}, |
| which is intended to indicate the number of storage elements reserved for |
| the simple storage pool. If the Storage_Size function has not been defined |
| for the simple storage pool type, then this attribute returns zero. |
| |
| If an access type @cite{S} has a specified simple storage pool of type |
| @cite{SSP}, then the evaluation of an allocator for that access type calls |
| the primitive @cite{Allocate} procedure for type @cite{SSP}, passing |
| @code{S'Simple_Storage_Pool} as the pool parameter. The detailed |
| semantics of such allocators is the same as those defined for allocators |
| in section 13.11 of the @cite{Ada Reference Manual}, with the term |
| @cite{simple storage pool} substituted for @cite{storage pool}. |
| |
| If an access type @cite{S} has a specified simple storage pool of type |
| @cite{SSP}, then a call to an instance of the @cite{Ada.Unchecked_Deallocation} |
| for that access type invokes the primitive @cite{Deallocate} procedure |
| for type @cite{SSP}, passing @code{S'Simple_Storage_Pool} as the pool |
| parameter. The detailed semantics of such unchecked deallocations is the same |
| as defined in section 13.11.2 of the Ada Reference Manual, except that the |
| term 'simple storage pool' is substituted for 'storage pool'. |
| |
| @node Attribute Small,Attribute Storage_Unit,Attribute Simple_Storage_Pool,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-small}@anchor{14f} |
| @section Attribute Small |
| |
| |
| @geindex Ada 83 attributes |
| |
| @geindex Small |
| |
| The @cite{Small} attribute is defined in Ada 95 (and Ada 2005) only for |
| fixed-point types. |
| GNAT also allows this attribute to be applied to floating-point types |
| for compatibility with Ada 83. See |
| the Ada 83 reference manual for an exact description of the semantics of |
| this attribute when applied to floating-point types. |
| |
| @node Attribute Storage_Unit,Attribute Stub_Type,Attribute Small,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-storage-unit}@anchor{150} |
| @section Attribute Storage_Unit |
| |
| |
| @geindex Storage_Unit |
| |
| @cite{Standard'Storage_Unit} (@cite{Standard} is the only permissible |
| prefix) provides the same value as @cite{System.Storage_Unit}. |
| |
| @node Attribute Stub_Type,Attribute System_Allocator_Alignment,Attribute Storage_Unit,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-stub-type}@anchor{151} |
| @section Attribute Stub_Type |
| |
| |
| @geindex Stub_Type |
| |
| The GNAT implementation of remote access-to-classwide types is |
| organized as described in AARM section E.4 (20.t): a value of an RACW type |
| (designating a remote object) is represented as a normal access |
| value, pointing to a "stub" object which in turn contains the |
| necessary information to contact the designated remote object. A |
| call on any dispatching operation of such a stub object does the |
| remote call, if necessary, using the information in the stub object |
| to locate the target partition, etc. |
| |
| For a prefix @cite{T} that denotes a remote access-to-classwide type, |
| @cite{T'Stub_Type} denotes the type of the corresponding stub objects. |
| |
| By construction, the layout of @cite{T'Stub_Type} is identical to that of |
| type @cite{RACW_Stub_Type} declared in the internal implementation-defined |
| unit @cite{System.Partition_Interface}. Use of this attribute will create |
| an implicit dependency on this unit. |
| |
| @node Attribute System_Allocator_Alignment,Attribute Target_Name,Attribute Stub_Type,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-system-allocator-alignment}@anchor{152} |
| @section Attribute System_Allocator_Alignment |
| |
| |
| @geindex Alignment |
| @geindex allocator |
| |
| @geindex System_Allocator_Alignment |
| |
| @cite{Standard'System_Allocator_Alignment} (@cite{Standard} is the only |
| permissible prefix) provides the observable guaranted to be honored by |
| the system allocator (malloc). This is a static value that can be used |
| in user storage pools based on malloc either to reject allocation |
| with alignment too large or to enable a realignment circuitry if the |
| alignment request is larger than this value. |
| |
| @node Attribute Target_Name,Attribute To_Address,Attribute System_Allocator_Alignment,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-target-name}@anchor{153} |
| @section Attribute Target_Name |
| |
| |
| @geindex Target_Name |
| |
| @cite{Standard'Target_Name} (@cite{Standard} is the only permissible |
| prefix) provides a static string value that identifies the target |
| for the current compilation. For GCC implementations, this is the |
| standard gcc target name without the terminating slash (for |
| example, GNAT 5.0 on windows yields "i586-pc-mingw32msv"). |
| |
| @node Attribute To_Address,Attribute To_Any,Attribute Target_Name,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-to-address}@anchor{154} |
| @section Attribute To_Address |
| |
| |
| @geindex To_Address |
| |
| The @cite{System'To_Address} |
| (@cite{System} is the only permissible prefix) |
| denotes a function identical to |
| @cite{System.Storage_Elements.To_Address} except that |
| it is a static attribute. This means that if its argument is |
| a static expression, then the result of the attribute is a |
| static expression. This means that such an expression can be |
| used in contexts (e.g., preelaborable packages) which require a |
| static expression and where the function call could not be used |
| (since the function call is always non-static, even if its |
| argument is static). The argument must be in the range |
| -(2**(m-1) .. 2**m-1, where m is the memory size |
| (typically 32 or 64). Negative values are intepreted in a |
| modular manner (e.g., -1 means the same as 16#FFFF_FFFF# on |
| a 32 bits machine). |
| |
| @node Attribute To_Any,Attribute Type_Class,Attribute To_Address,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-to-any}@anchor{155} |
| @section Attribute To_Any |
| |
| |
| @geindex To_Any |
| |
| This internal attribute is used for the generation of remote subprogram |
| stubs in the context of the Distributed Systems Annex. |
| |
| @node Attribute Type_Class,Attribute Type_Key,Attribute To_Any,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-type-class}@anchor{156} |
| @section Attribute Type_Class |
| |
| |
| @geindex Type_Class |
| |
| @code{type'Type_Class} for any type or subtype @cite{type} yields |
| the value of the type class for the full type of @cite{type}. If |
| @cite{type} is a generic formal type, the value is the value for the |
| corresponding actual subtype. The value of this attribute is of type |
| @code{System.Aux_DEC.Type_Class}, which has the following definition: |
| |
| @example |
| type Type_Class is |
| (Type_Class_Enumeration, |
| Type_Class_Integer, |
| Type_Class_Fixed_Point, |
| Type_Class_Floating_Point, |
| Type_Class_Array, |
| Type_Class_Record, |
| Type_Class_Access, |
| Type_Class_Task, |
| Type_Class_Address); |
| @end example |
| |
| Protected types yield the value @cite{Type_Class_Task}, which thus |
| applies to all concurrent types. This attribute is designed to |
| be compatible with the DEC Ada 83 attribute of the same name. |
| |
| @node Attribute Type_Key,Attribute TypeCode,Attribute Type_Class,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-type-key}@anchor{157} |
| @section Attribute Type_Key |
| |
| |
| @geindex Type_Key |
| |
| The @cite{Type_Key} attribute is applicable to a type or subtype and |
| yields a value of type Standard.String containing encoded information |
| about the type or subtype. This provides improved compatibility with |
| other implementations that support this attribute. |
| |
| @node Attribute TypeCode,Attribute UET_Address,Attribute Type_Key,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-typecode}@anchor{158} |
| @section Attribute TypeCode |
| |
| |
| @geindex TypeCode |
| |
| This internal attribute is used for the generation of remote subprogram |
| stubs in the context of the Distributed Systems Annex. |
| |
| @node Attribute UET_Address,Attribute Unconstrained_Array,Attribute TypeCode,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-uet-address}@anchor{159} |
| @section Attribute UET_Address |
| |
| |
| @geindex UET_Address |
| |
| The @cite{UET_Address} attribute can only be used for a prefix which |
| denotes a library package. It yields the address of the unit exception |
| table when zero cost exception handling is used. This attribute is |
| intended only for use within the GNAT implementation. See the unit |
| @cite{Ada.Exceptions} in files @code{a-except.ads} and @code{a-except.adb} |
| for details on how this attribute is used in the implementation. |
| |
| @node Attribute Unconstrained_Array,Attribute Universal_Literal_String,Attribute UET_Address,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-unconstrained-array}@anchor{15a} |
| @section Attribute Unconstrained_Array |
| |
| |
| @geindex Unconstrained_Array |
| |
| The @cite{Unconstrained_Array} attribute can be used with a prefix that |
| denotes any type or subtype. It is a static attribute that yields |
| @cite{True} if the prefix designates an unconstrained array, |
| and @cite{False} otherwise. In a generic instance, the result is |
| still static, and yields the result of applying this test to the |
| generic actual. |
| |
| @node Attribute Universal_Literal_String,Attribute Unrestricted_Access,Attribute Unconstrained_Array,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-universal-literal-string}@anchor{15b} |
| @section Attribute Universal_Literal_String |
| |
| |
| @geindex Named numbers |
| @geindex representation of |
| |
| @geindex Universal_Literal_String |
| |
| The prefix of @cite{Universal_Literal_String} must be a named |
| number. The static result is the string consisting of the characters of |
| the number as defined in the original source. This allows the user |
| program to access the actual text of named numbers without intermediate |
| conversions and without the need to enclose the strings in quotes (which |
| would preclude their use as numbers). |
| |
| For example, the following program prints the first 50 digits of pi: |
| |
| @example |
| with Text_IO; use Text_IO; |
| with Ada.Numerics; |
| procedure Pi is |
| begin |
| Put (Ada.Numerics.Pi'Universal_Literal_String); |
| end; |
| @end example |
| |
| @node Attribute Unrestricted_Access,Attribute Update,Attribute Universal_Literal_String,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-unrestricted-access}@anchor{15c} |
| @section Attribute Unrestricted_Access |
| |
| |
| @geindex Access |
| @geindex unrestricted |
| |
| @geindex Unrestricted_Access |
| |
| The @cite{Unrestricted_Access} attribute is similar to @cite{Access} |
| except that all accessibility and aliased view checks are omitted. This |
| is a user-beware attribute. |
| |
| For objects, it is similar to @cite{Address}, for which it is a |
| desirable replacement where the value desired is an access type. |
| In other words, its effect is similar to first applying the |
| @cite{Address} attribute and then doing an unchecked conversion to a |
| desired access type. |
| |
| For subprograms, @cite{P'Unrestricted_Access} may be used where |
| @cite{P'Access} would be illegal, to construct a value of a |
| less-nested named access type that designates a more-nested |
| subprogram. This value may be used in indirect calls, so long as the |
| more-nested subprogram still exists; once the subprogram containing it |
| has returned, such calls are erroneous. For example: |
| |
| @example |
| package body P is |
| |
| type Less_Nested is not null access procedure; |
| Global : Less_Nested; |
| |
| procedure P1 is |
| begin |
| Global.all; |
| end P1; |
| |
| procedure P2 is |
| Local_Var : Integer; |
| |
| procedure More_Nested is |
| begin |
| ... Local_Var ... |
| end More_Nested; |
| begin |
| Global := More_Nested'Unrestricted_Access; |
| P1; |
| end P2; |
| |
| end P; |
| @end example |
| |
| When P1 is called from P2, the call via Global is OK, but if P1 were |
| called after P2 returns, it would be an erroneous use of a dangling |
| pointer. |
| |
| For objects, it is possible to use @cite{Unrestricted_Access} for any |
| type. However, if the result is of an access-to-unconstrained array |
| subtype, then the resulting pointer has the same scope as the context |
| of the attribute, and must not be returned to some enclosing scope. |
| For instance, if a function uses @cite{Unrestricted_Access} to create |
| an access-to-unconstrained-array and returns that value to the caller, |
| the result will involve dangling pointers. In addition, it is only |
| valid to create pointers to unconstrained arrays using this attribute |
| if the pointer has the normal default 'fat' representation where a |
| pointer has two components, one points to the array and one points to |
| the bounds. If a size clause is used to force 'thin' representation |
| for a pointer to unconstrained where there is only space for a single |
| pointer, then the resulting pointer is not usable. |
| |
| In the simple case where a direct use of Unrestricted_Access attempts |
| to make a thin pointer for a non-aliased object, the compiler will |
| reject the use as illegal, as shown in the following example: |
| |
| @example |
| with System; use System; |
| procedure SliceUA2 is |
| type A is access all String; |
| for A'Size use Standard'Address_Size; |
| |
| procedure P (Arg : A) is |
| begin |
| null; |
| end P; |
| |
| X : String := "hello world!"; |
| X2 : aliased String := "hello world!"; |
| |
| AV : A := X'Unrestricted_Access; -- ERROR |
| | |
| >>> illegal use of Unrestricted_Access attribute |
| >>> attempt to generate thin pointer to unaliased object |
| |
| begin |
| P (X'Unrestricted_Access); -- ERROR |
| | |
| >>> illegal use of Unrestricted_Access attribute |
| >>> attempt to generate thin pointer to unaliased object |
| |
| P (X(7 .. 12)'Unrestricted_Access); -- ERROR |
| | |
| >>> illegal use of Unrestricted_Access attribute |
| >>> attempt to generate thin pointer to unaliased object |
| |
| P (X2'Unrestricted_Access); -- OK |
| end; |
| @end example |
| |
| but other cases cannot be detected by the compiler, and are |
| considered to be erroneous. Consider the following example: |
| |
| @example |
| with System; use System; |
| with System; use System; |
| procedure SliceUA is |
| type AF is access all String; |
| |
| type A is access all String; |
| for A'Size use Standard'Address_Size; |
| |
| procedure P (Arg : A) is |
| begin |
| if Arg'Length /= 6 then |
| raise Program_Error; |
| end if; |
| end P; |
| |
| X : String := "hello world!"; |
| Y : AF := X (7 .. 12)'Unrestricted_Access; |
| |
| begin |
| P (A (Y)); |
| end; |
| @end example |
| |
| A normal unconstrained array value |
| or a constrained array object marked as aliased has the bounds in memory |
| just before the array, so a thin pointer can retrieve both the data and |
| the bounds. But in this case, the non-aliased object @cite{X} does not have the |
| bounds before the string. If the size clause for type @cite{A} |
| were not present, then the pointer |
| would be a fat pointer, where one component is a pointer to the bounds, |
| and all would be well. But with the size clause present, the conversion from |
| fat pointer to thin pointer in the call loses the bounds, and so this |
| is erroneous, and the program likely raises a @cite{Program_Error} exception. |
| |
| In general, it is advisable to completely |
| avoid mixing the use of thin pointers and the use of |
| @cite{Unrestricted_Access} where the designated type is an |
| unconstrained array. The use of thin pointers should be restricted to |
| cases of porting legacy code that implicitly assumes the size of pointers, |
| and such code should not in any case be using this attribute. |
| |
| Another erroneous situation arises if the attribute is |
| applied to a constant. The resulting pointer can be used to access the |
| constant, but the effect of trying to modify a constant in this manner |
| is not well-defined. Consider this example: |
| |
| @example |
| P : constant Integer := 4; |
| type R is access all Integer; |
| RV : R := P'Unrestricted_Access; |
| .. |
| RV.all := 3; |
| @end example |
| |
| Here we attempt to modify the constant P from 4 to 3, but the compiler may |
| or may not notice this attempt, and subsequent references to P may yield |
| either the value 3 or the value 4 or the assignment may blow up if the |
| compiler decides to put P in read-only memory. One particular case where |
| @cite{Unrestricted_Access} can be used in this way is to modify the |
| value of an @cite{IN} parameter: |
| |
| @example |
| procedure K (S : in String) is |
| type R is access all Character; |
| RV : R := S (3)'Unrestricted_Access; |
| begin |
| RV.all := 'a'; |
| end; |
| @end example |
| |
| In general this is a risky approach. It may appear to "work" but such uses of |
| @cite{Unrestricted_Access} are potentially non-portable, even from one version |
| of @cite{GNAT} to another, so are best avoided if possible. |
| |
| @node Attribute Update,Attribute Valid_Scalars,Attribute Unrestricted_Access,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-update}@anchor{15d} |
| @section Attribute Update |
| |
| |
| @geindex Update |
| |
| The @cite{Update} attribute creates a copy of an array or record value |
| with one or more modified components. The syntax is: |
| |
| @example |
| PREFIX'Update ( RECORD_COMPONENT_ASSOCIATION_LIST ) |
| PREFIX'Update ( ARRAY_COMPONENT_ASSOCIATION @{, ARRAY_COMPONENT_ASSOCIATION @} ) |
| PREFIX'Update ( MULTIDIMENSIONAL_ARRAY_COMPONENT_ASSOCIATION |
| @{, MULTIDIMENSIONAL_ARRAY_COMPONENT_ASSOCIATION @} ) |
| |
| MULTIDIMENSIONAL_ARRAY_COMPONENT_ASSOCIATION ::= INDEX_EXPRESSION_LIST_LIST => EXPRESSION |
| INDEX_EXPRESSION_LIST_LIST ::= INDEX_EXPRESSION_LIST @{| INDEX_EXPRESSION_LIST @} |
| INDEX_EXPRESSION_LIST ::= ( EXPRESSION @{, EXPRESSION @} ) |
| @end example |
| |
| where @cite{PREFIX} is the name of an array or record object, the |
| association list in parentheses does not contain an @cite{others} |
| choice and the box symbol @cite{<>} may not appear in any |
| expression. The effect is to yield a copy of the array or record value |
| which is unchanged apart from the components mentioned in the |
| association list, which are changed to the indicated value. The |
| original value of the array or record value is not affected. For |
| example: |
| |
| @example |
| type Arr is Array (1 .. 5) of Integer; |
| ... |
| Avar1 : Arr := (1,2,3,4,5); |
| Avar2 : Arr := Avar1'Update (2 => 10, 3 .. 4 => 20); |
| @end example |
| |
| yields a value for @cite{Avar2} of 1,10,20,20,5 with @cite{Avar1} |
| begin unmodified. Similarly: |
| |
| @example |
| type Rec is A, B, C : Integer; |
| ... |
| Rvar1 : Rec := (A => 1, B => 2, C => 3); |
| Rvar2 : Rec := Rvar1'Update (B => 20); |
| @end example |
| |
| yields a value for @cite{Rvar2} of (A => 1, B => 20, C => 3), |
| with @cite{Rvar1} being unmodifed. |
| Note that the value of the attribute reference is computed |
| completely before it is used. This means that if you write: |
| |
| @example |
| Avar1 := Avar1'Update (1 => 10, 2 => Function_Call); |
| @end example |
| |
| then the value of @cite{Avar1} is not modified if @cite{Function_Call} |
| raises an exception, unlike the effect of a series of direct assignments |
| to elements of @cite{Avar1}. In general this requires that |
| two extra complete copies of the object are required, which should be |
| kept in mind when considering efficiency. |
| |
| The @cite{Update} attribute cannot be applied to prefixes of a limited |
| type, and cannot reference discriminants in the case of a record type. |
| The accessibility level of an Update attribute result object is defined |
| as for an aggregate. |
| |
| In the record case, no component can be mentioned more than once. In |
| the array case, two overlapping ranges can appear in the association list, |
| in which case the modifications are processed left to right. |
| |
| Multi-dimensional arrays can be modified, as shown by this example: |
| |
| @example |
| A : array (1 .. 10, 1 .. 10) of Integer; |
| .. |
| A := A'Update ((1, 2) => 20, (3, 4) => 30); |
| @end example |
| |
| which changes element (1,2) to 20 and (3,4) to 30. |
| |
| @node Attribute Valid_Scalars,Attribute VADS_Size,Attribute Update,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-valid-scalars}@anchor{15e} |
| @section Attribute Valid_Scalars |
| |
| |
| @geindex Valid_Scalars |
| |
| The @cite{'Valid_Scalars} attribute is intended to make it easier to |
| check the validity of scalar subcomponents of composite objects. It |
| is defined for any prefix @cite{X} that denotes an object. |
| The value of this attribute is of the predefined type Boolean. |
| @cite{X'Valid_Scalars} yields True if and only if evaluation of |
| @cite{P'Valid} yields True for every scalar part P of X or if X has |
| no scalar parts. It is not specified in what order the scalar parts |
| are checked, nor whether any more are checked after any one of them |
| is determined to be invalid. If the prefix @cite{X} is of a class-wide |
| type @cite{T'Class} (where @cite{T} is the associated specific type), |
| or if the prefix @cite{X} is of a specific tagged type @cite{T}, then |
| only the scalar parts of components of @cite{T} are traversed; in other |
| words, components of extensions of @cite{T} are not traversed even if |
| @cite{T'Class (X)'Tag /= T'Tag} . The compiler will issue a warning if it can |
| be determined at compile time that the prefix of the attribute has no |
| scalar parts (e.g., if the prefix is of an access type, an interface type, |
| an undiscriminated task type, or an undiscriminated protected type). |
| |
| For scalar types, @cite{Valid_Scalars} is equivalent to @cite{Valid}. The use |
| of this attribute is not permitted for @cite{Unchecked_Union} types for which |
| in general it is not possible to determine the values of the discriminants. |
| |
| Note: @cite{Valid_Scalars} can generate a lot of code, especially in the case |
| of a large variant record. If the attribute is called in many places in the |
| same program applied to objects of the same type, it can reduce program size |
| to write a function with a single use of the attribute, and then call that |
| function from multiple places. |
| |
| @node Attribute VADS_Size,Attribute Value_Size,Attribute Valid_Scalars,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-vads-size}@anchor{15f} |
| @section Attribute VADS_Size |
| |
| |
| @geindex Size |
| @geindex VADS compatibility |
| |
| @geindex VADS_Size |
| |
| The @cite{'VADS_Size} attribute is intended to make it easier to port |
| legacy code which relies on the semantics of @cite{'Size} as implemented |
| by the VADS Ada 83 compiler. GNAT makes a best effort at duplicating the |
| same semantic interpretation. In particular, @cite{'VADS_Size} applied |
| to a predefined or other primitive type with no Size clause yields the |
| Object_Size (for example, @cite{Natural'Size} is 32 rather than 31 on |
| typical machines). In addition @cite{'VADS_Size} applied to an object |
| gives the result that would be obtained by applying the attribute to |
| the corresponding type. |
| |
| @node Attribute Value_Size,Attribute Wchar_T_Size,Attribute VADS_Size,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-value-size}@anchor{160} |
| @section Attribute Value_Size |
| |
| |
| @geindex Size |
| @geindex setting for not-first subtype |
| |
| @geindex Value_Size |
| |
| @code{type'Value_Size} is the number of bits required to represent |
| a value of the given subtype. It is the same as @code{type'Size}, |
| but, unlike @cite{Size}, may be set for non-first subtypes. |
| |
| @node Attribute Wchar_T_Size,Attribute Word_Size,Attribute Value_Size,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-wchar-t-size}@anchor{161} |
| @section Attribute Wchar_T_Size |
| |
| |
| @geindex Wchar_T_Size |
| |
| @cite{Standard'Wchar_T_Size} (@cite{Standard} is the only permissible |
| prefix) provides the size in bits of the C @cite{wchar_t} type |
| primarily for constructing the definition of this type in |
| package @cite{Interfaces.C}. The result is a static constant. |
| |
| @node Attribute Word_Size,,Attribute Wchar_T_Size,Implementation Defined Attributes |
| @anchor{gnat_rm/implementation_defined_attributes attribute-word-size}@anchor{162} |
| @section Attribute Word_Size |
| |
| |
| @geindex Word_Size |
| |
| @cite{Standard'Word_Size} (@cite{Standard} is the only permissible |
| prefix) provides the value @cite{System.Word_Size}. The result is |
| a static constant. |
| |
| @node Standard and Implementation Defined Restrictions,Implementation Advice,Implementation Defined Attributes,Top |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions standard-and-implementation-defined-restrictions}@anchor{9}@anchor{gnat_rm/standard_and_implementation_defined_restrictions doc}@anchor{163}@anchor{gnat_rm/standard_and_implementation_defined_restrictions id1}@anchor{164} |
| @chapter Standard and Implementation Defined Restrictions |
| |
| |
| All Ada Reference Manual-defined Restriction identifiers are implemented: |
| |
| |
| @itemize * |
| |
| @item |
| language-defined restrictions (see 13.12.1) |
| |
| @item |
| tasking restrictions (see D.7) |
| |
| @item |
| high integrity restrictions (see H.4) |
| @end itemize |
| |
| GNAT implements additional restriction identifiers. All restrictions, whether |
| language defined or GNAT-specific, are listed in the following. |
| |
| @menu |
| * Partition-Wide Restrictions:: |
| * Program Unit Level Restrictions:: |
| |
| @end menu |
| |
| @node Partition-Wide Restrictions,Program Unit Level Restrictions,,Standard and Implementation Defined Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions partition-wide-restrictions}@anchor{165}@anchor{gnat_rm/standard_and_implementation_defined_restrictions id2}@anchor{166} |
| @section Partition-Wide Restrictions |
| |
| |
| There are two separate lists of restriction identifiers. The first |
| set requires consistency throughout a partition (in other words, if the |
| restriction identifier is used for any compilation unit in the partition, |
| then all compilation units in the partition must obey the restriction). |
| |
| @menu |
| * Immediate_Reclamation:: |
| * Max_Asynchronous_Select_Nesting:: |
| * Max_Entry_Queue_Length:: |
| * Max_Protected_Entries:: |
| * Max_Select_Alternatives:: |
| * Max_Storage_At_Blocking:: |
| * Max_Task_Entries:: |
| * Max_Tasks:: |
| * No_Abort_Statements:: |
| * No_Access_Parameter_Allocators:: |
| * No_Access_Subprograms:: |
| * No_Allocators:: |
| * No_Anonymous_Allocators:: |
| * No_Calendar:: |
| * No_Coextensions:: |
| * No_Default_Initialization:: |
| * No_Delay:: |
| * No_Dependence:: |
| * No_Direct_Boolean_Operators:: |
| * No_Dispatch:: |
| * No_Dispatching_Calls:: |
| * No_Dynamic_Attachment:: |
| * No_Dynamic_Priorities:: |
| * No_Entry_Calls_In_Elaboration_Code:: |
| * No_Enumeration_Maps:: |
| * No_Exception_Handlers:: |
| * No_Exception_Propagation:: |
| * No_Exception_Registration:: |
| * No_Exceptions:: |
| * No_Finalization:: |
| * No_Fixed_Point:: |
| * No_Floating_Point:: |
| * No_Implicit_Conditionals:: |
| * No_Implicit_Dynamic_Code:: |
| * No_Implicit_Heap_Allocations:: |
| * No_Implicit_Loops:: |
| * No_Initialize_Scalars:: |
| * No_IO:: |
| * No_Local_Allocators:: |
| * No_Local_Protected_Objects:: |
| * No_Local_Timing_Events:: |
| * No_Long_Long_Integers:: |
| * No_Multiple_Elaboration:: |
| * No_Nested_Finalization:: |
| * No_Protected_Type_Allocators:: |
| * No_Protected_Types:: |
| * No_Recursion:: |
| * No_Reentrancy:: |
| * No_Relative_Delay:: |
| * No_Requeue_Statements:: |
| * No_Secondary_Stack:: |
| * No_Select_Statements:: |
| * No_Specific_Termination_Handlers:: |
| * No_Specification_of_Aspect:: |
| * No_Standard_Allocators_After_Elaboration:: |
| * No_Standard_Storage_Pools:: |
| * No_Stream_Optimizations:: |
| * No_Streams:: |
| * No_Task_Allocators:: |
| * No_Task_Attributes_Package:: |
| * No_Task_Hierarchy:: |
| * No_Task_Termination:: |
| * No_Tasking:: |
| * No_Terminate_Alternatives:: |
| * No_Unchecked_Access:: |
| * No_Use_Of_Entity:: |
| * Simple_Barriers:: |
| * Static_Priorities:: |
| * Static_Storage_Size:: |
| |
| @end menu |
| |
| @node Immediate_Reclamation,Max_Asynchronous_Select_Nesting,,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions immediate-reclamation}@anchor{167} |
| @subsection Immediate_Reclamation |
| |
| |
| @geindex Immediate_Reclamation |
| |
| [RM H.4] This restriction ensures that, except for storage occupied by |
| objects created by allocators and not deallocated via unchecked |
| deallocation, any storage reserved at run time for an object is |
| immediately reclaimed when the object no longer exists. |
| |
| @node Max_Asynchronous_Select_Nesting,Max_Entry_Queue_Length,Immediate_Reclamation,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions max-asynchronous-select-nesting}@anchor{168} |
| @subsection Max_Asynchronous_Select_Nesting |
| |
| |
| @geindex Max_Asynchronous_Select_Nesting |
| |
| [RM D.7] Specifies the maximum dynamic nesting level of asynchronous |
| selects. Violations of this restriction with a value of zero are |
| detected at compile time. Violations of this restriction with values |
| other than zero cause Storage_Error to be raised. |
| |
| @node Max_Entry_Queue_Length,Max_Protected_Entries,Max_Asynchronous_Select_Nesting,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions max-entry-queue-length}@anchor{169} |
| @subsection Max_Entry_Queue_Length |
| |
| |
| @geindex Max_Entry_Queue_Length |
| |
| [RM D.7] This restriction is a declaration that any protected entry compiled in |
| the scope of the restriction has at most the specified number of |
| tasks waiting on the entry at any one time, and so no queue is required. |
| Note that this restriction is checked at run time. Violation of this |
| restriction results in the raising of Program_Error exception at the point of |
| the call. |
| |
| @geindex Max_Entry_Queue_Depth |
| |
| The restriction @cite{Max_Entry_Queue_Depth} is recognized as a |
| synonym for @cite{Max_Entry_Queue_Length}. This is retained for historical |
| compatibility purposes (and a warning will be generated for its use if |
| warnings on obsolescent features are activated). |
| |
| @node Max_Protected_Entries,Max_Select_Alternatives,Max_Entry_Queue_Length,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions max-protected-entries}@anchor{16a} |
| @subsection Max_Protected_Entries |
| |
| |
| @geindex Max_Protected_Entries |
| |
| [RM D.7] Specifies the maximum number of entries per protected type. The |
| bounds of every entry family of a protected unit shall be static, or shall be |
| defined by a discriminant of a subtype whose corresponding bound is static. |
| |
| @node Max_Select_Alternatives,Max_Storage_At_Blocking,Max_Protected_Entries,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions max-select-alternatives}@anchor{16b} |
| @subsection Max_Select_Alternatives |
| |
| |
| @geindex Max_Select_Alternatives |
| |
| [RM D.7] Specifies the maximum number of alternatives in a selective accept. |
| |
| @node Max_Storage_At_Blocking,Max_Task_Entries,Max_Select_Alternatives,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions max-storage-at-blocking}@anchor{16c} |
| @subsection Max_Storage_At_Blocking |
| |
| |
| @geindex Max_Storage_At_Blocking |
| |
| [RM D.7] Specifies the maximum portion (in storage elements) of a task's |
| Storage_Size that can be retained by a blocked task. A violation of this |
| restriction causes Storage_Error to be raised. |
| |
| @node Max_Task_Entries,Max_Tasks,Max_Storage_At_Blocking,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions max-task-entries}@anchor{16d} |
| @subsection Max_Task_Entries |
| |
| |
| @geindex Max_Task_Entries |
| |
| [RM D.7] Specifies the maximum number of entries |
| per task. The bounds of every entry family |
| of a task unit shall be static, or shall be |
| defined by a discriminant of a subtype whose |
| corresponding bound is static. |
| |
| @node Max_Tasks,No_Abort_Statements,Max_Task_Entries,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions max-tasks}@anchor{16e} |
| @subsection Max_Tasks |
| |
| |
| @geindex Max_Tasks |
| |
| [RM D.7] Specifies the maximum number of task that may be created, not |
| counting the creation of the environment task. Violations of this |
| restriction with a value of zero are detected at compile |
| time. Violations of this restriction with values other than zero cause |
| Storage_Error to be raised. |
| |
| @node No_Abort_Statements,No_Access_Parameter_Allocators,Max_Tasks,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-abort-statements}@anchor{16f} |
| @subsection No_Abort_Statements |
| |
| |
| @geindex No_Abort_Statements |
| |
| [RM D.7] There are no abort_statements, and there are |
| no calls to Task_Identification.Abort_Task. |
| |
| @node No_Access_Parameter_Allocators,No_Access_Subprograms,No_Abort_Statements,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-access-parameter-allocators}@anchor{170} |
| @subsection No_Access_Parameter_Allocators |
| |
| |
| @geindex No_Access_Parameter_Allocators |
| |
| [RM H.4] This restriction ensures at compile time that there are no |
| occurrences of an allocator as the actual parameter to an access |
| parameter. |
| |
| @node No_Access_Subprograms,No_Allocators,No_Access_Parameter_Allocators,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-access-subprograms}@anchor{171} |
| @subsection No_Access_Subprograms |
| |
| |
| @geindex No_Access_Subprograms |
| |
| [RM H.4] This restriction ensures at compile time that there are no |
| declarations of access-to-subprogram types. |
| |
| @node No_Allocators,No_Anonymous_Allocators,No_Access_Subprograms,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-allocators}@anchor{172} |
| @subsection No_Allocators |
| |
| |
| @geindex No_Allocators |
| |
| [RM H.4] This restriction ensures at compile time that there are no |
| occurrences of an allocator. |
| |
| @node No_Anonymous_Allocators,No_Calendar,No_Allocators,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-anonymous-allocators}@anchor{173} |
| @subsection No_Anonymous_Allocators |
| |
| |
| @geindex No_Anonymous_Allocators |
| |
| [RM H.4] This restriction ensures at compile time that there are no |
| occurrences of an allocator of anonymous access type. |
| |
| @node No_Calendar,No_Coextensions,No_Anonymous_Allocators,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-calendar}@anchor{174} |
| @subsection No_Calendar |
| |
| |
| @geindex No_Calendar |
| |
| [GNAT] This restriction ensures at compile time that there is no implicit or |
| explicit dependence on the package @cite{Ada.Calendar}. |
| |
| @node No_Coextensions,No_Default_Initialization,No_Calendar,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-coextensions}@anchor{175} |
| @subsection No_Coextensions |
| |
| |
| @geindex No_Coextensions |
| |
| [RM H.4] This restriction ensures at compile time that there are no |
| coextensions. See 3.10.2. |
| |
| @node No_Default_Initialization,No_Delay,No_Coextensions,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-default-initialization}@anchor{176} |
| @subsection No_Default_Initialization |
| |
| |
| @geindex No_Default_Initialization |
| |
| [GNAT] This restriction prohibits any instance of default initialization |
| of variables. The binder implements a consistency rule which prevents |
| any unit compiled without the restriction from with'ing a unit with the |
| restriction (this allows the generation of initialization procedures to |
| be skipped, since you can be sure that no call is ever generated to an |
| initialization procedure in a unit with the restriction active). If used |
| in conjunction with Initialize_Scalars or Normalize_Scalars, the effect |
| is to prohibit all cases of variables declared without a specific |
| initializer (including the case of OUT scalar parameters). |
| |
| @node No_Delay,No_Dependence,No_Default_Initialization,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-delay}@anchor{177} |
| @subsection No_Delay |
| |
| |
| @geindex No_Delay |
| |
| [RM H.4] This restriction ensures at compile time that there are no |
| delay statements and no dependences on package Calendar. |
| |
| @node No_Dependence,No_Direct_Boolean_Operators,No_Delay,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-dependence}@anchor{178} |
| @subsection No_Dependence |
| |
| |
| @geindex No_Dependence |
| |
| [RM 13.12.1] This restriction checks at compile time that there are no |
| dependence on a library unit. |
| |
| @node No_Direct_Boolean_Operators,No_Dispatch,No_Dependence,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-direct-boolean-operators}@anchor{179} |
| @subsection No_Direct_Boolean_Operators |
| |
| |
| @geindex No_Direct_Boolean_Operators |
| |
| [GNAT] This restriction ensures that no logical operators (and/or/xor) |
| are used on operands of type Boolean (or any type derived from Boolean). |
| This is intended for use in safety critical programs where the certification |
| protocol requires the use of short-circuit (and then, or else) forms for all |
| composite boolean operations. |
| |
| @node No_Dispatch,No_Dispatching_Calls,No_Direct_Boolean_Operators,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-dispatch}@anchor{17a} |
| @subsection No_Dispatch |
| |
| |
| @geindex No_Dispatch |
| |
| [RM H.4] This restriction ensures at compile time that there are no |
| occurrences of @cite{T'Class}, for any (tagged) subtype @cite{T}. |
| |
| @node No_Dispatching_Calls,No_Dynamic_Attachment,No_Dispatch,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-dispatching-calls}@anchor{17b} |
| @subsection No_Dispatching_Calls |
| |
| |
| @geindex No_Dispatching_Calls |
| |
| [GNAT] This restriction ensures at compile time that the code generated by the |
| compiler involves no dispatching calls. The use of this restriction allows the |
| safe use of record extensions, classwide membership tests and other classwide |
| features not involving implicit dispatching. This restriction ensures that |
| the code contains no indirect calls through a dispatching mechanism. Note that |
| this includes internally-generated calls created by the compiler, for example |
| in the implementation of class-wide objects assignments. The |
| membership test is allowed in the presence of this restriction, because its |
| implementation requires no dispatching. |
| This restriction is comparable to the official Ada restriction |
| @cite{No_Dispatch} except that it is a bit less restrictive in that it allows |
| all classwide constructs that do not imply dispatching. |
| The following example indicates constructs that violate this restriction. |
| |
| @example |
| package Pkg is |
| type T is tagged record |
| Data : Natural; |
| end record; |
| procedure P (X : T); |
| |
| type DT is new T with record |
| More_Data : Natural; |
| end record; |
| procedure Q (X : DT); |
| end Pkg; |
| |
| with Pkg; use Pkg; |
| procedure Example is |
| procedure Test (O : T'Class) is |
| N : Natural := O'Size;-- Error: Dispatching call |
| C : T'Class := O; -- Error: implicit Dispatching Call |
| begin |
| if O in DT'Class then -- OK : Membership test |
| Q (DT (O)); -- OK : Type conversion plus direct call |
| else |
| P (O); -- Error: Dispatching call |
| end if; |
| end Test; |
| |
| Obj : DT; |
| begin |
| P (Obj); -- OK : Direct call |
| P (T (Obj)); -- OK : Type conversion plus direct call |
| P (T'Class (Obj)); -- Error: Dispatching call |
| |
| Test (Obj); -- OK : Type conversion |
| |
| if Obj in T'Class then -- OK : Membership test |
| null; |
| end if; |
| end Example; |
| @end example |
| |
| @node No_Dynamic_Attachment,No_Dynamic_Priorities,No_Dispatching_Calls,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-dynamic-attachment}@anchor{17c} |
| @subsection No_Dynamic_Attachment |
| |
| |
| @geindex No_Dynamic_Attachment |
| |
| [RM D.7] This restriction ensures that there is no call to any of the |
| operations defined in package Ada.Interrupts |
| (Is_Reserved, Is_Attached, Current_Handler, Attach_Handler, Exchange_Handler, |
| Detach_Handler, and Reference). |
| |
| @geindex No_Dynamic_Interrupts |
| |
| The restriction @cite{No_Dynamic_Interrupts} is recognized as a |
| synonym for @cite{No_Dynamic_Attachment}. This is retained for historical |
| compatibility purposes (and a warning will be generated for its use if |
| warnings on obsolescent features are activated). |
| |
| @node No_Dynamic_Priorities,No_Entry_Calls_In_Elaboration_Code,No_Dynamic_Attachment,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-dynamic-priorities}@anchor{17d} |
| @subsection No_Dynamic_Priorities |
| |
| |
| @geindex No_Dynamic_Priorities |
| |
| [RM D.7] There are no semantic dependencies on the package Dynamic_Priorities. |
| |
| @node No_Entry_Calls_In_Elaboration_Code,No_Enumeration_Maps,No_Dynamic_Priorities,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-entry-calls-in-elaboration-code}@anchor{17e} |
| @subsection No_Entry_Calls_In_Elaboration_Code |
| |
| |
| @geindex No_Entry_Calls_In_Elaboration_Code |
| |
| [GNAT] This restriction ensures at compile time that no task or protected entry |
| calls are made during elaboration code. As a result of the use of this |
| restriction, the compiler can assume that no code past an accept statement |
| in a task can be executed at elaboration time. |
| |
| @node No_Enumeration_Maps,No_Exception_Handlers,No_Entry_Calls_In_Elaboration_Code,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-enumeration-maps}@anchor{17f} |
| @subsection No_Enumeration_Maps |
| |
| |
| @geindex No_Enumeration_Maps |
| |
| [GNAT] This restriction ensures at compile time that no operations requiring |
| enumeration maps are used (that is Image and Value attributes applied |
| to enumeration types). |
| |
| @node No_Exception_Handlers,No_Exception_Propagation,No_Enumeration_Maps,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-exception-handlers}@anchor{180} |
| @subsection No_Exception_Handlers |
| |
| |
| @geindex No_Exception_Handlers |
| |
| [GNAT] This restriction ensures at compile time that there are no explicit |
| exception handlers. It also indicates that no exception propagation will |
| be provided. In this mode, exceptions may be raised but will result in |
| an immediate call to the last chance handler, a routine that the user |
| must define with the following profile: |
| |
| @example |
| procedure Last_Chance_Handler |
| (Source_Location : System.Address; Line : Integer); |
| pragma Export (C, Last_Chance_Handler, |
| "__gnat_last_chance_handler"); |
| @end example |
| |
| The parameter is a C null-terminated string representing a message to be |
| associated with the exception (typically the source location of the raise |
| statement generated by the compiler). The Line parameter when nonzero |
| represents the line number in the source program where the raise occurs. |
| |
| @node No_Exception_Propagation,No_Exception_Registration,No_Exception_Handlers,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-exception-propagation}@anchor{181} |
| @subsection No_Exception_Propagation |
| |
| |
| @geindex No_Exception_Propagation |
| |
| [GNAT] This restriction guarantees that exceptions are never propagated |
| to an outer subprogram scope. The only case in which an exception may |
| be raised is when the handler is statically in the same subprogram, so |
| that the effect of a raise is essentially like a goto statement. Any |
| other raise statement (implicit or explicit) will be considered |
| unhandled. Exception handlers are allowed, but may not contain an |
| exception occurrence identifier (exception choice). In addition, use of |
| the package GNAT.Current_Exception is not permitted, and reraise |
| statements (raise with no operand) are not permitted. |
| |
| @node No_Exception_Registration,No_Exceptions,No_Exception_Propagation,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-exception-registration}@anchor{182} |
| @subsection No_Exception_Registration |
| |
| |
| @geindex No_Exception_Registration |
| |
| [GNAT] This restriction ensures at compile time that no stream operations for |
| types Exception_Id or Exception_Occurrence are used. This also makes it |
| impossible to pass exceptions to or from a partition with this restriction |
| in a distributed environment. If this restriction is active, the generated |
| code is simplified by omitting the otherwise-required global registration |
| of exceptions when they are declared. |
| |
| @node No_Exceptions,No_Finalization,No_Exception_Registration,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-exceptions}@anchor{183} |
| @subsection No_Exceptions |
| |
| |
| @geindex No_Exceptions |
| |
| [RM H.4] This restriction ensures at compile time that there are no |
| raise statements and no exception handlers. |
| |
| @node No_Finalization,No_Fixed_Point,No_Exceptions,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-finalization}@anchor{184} |
| @subsection No_Finalization |
| |
| |
| @geindex No_Finalization |
| |
| [GNAT] This restriction disables the language features described in |
| chapter 7.6 of the Ada 2005 RM as well as all form of code generation |
| performed by the compiler to support these features. The following types |
| are no longer considered controlled when this restriction is in effect: |
| |
| |
| @itemize * |
| |
| @item |
| @cite{Ada.Finalization.Controlled} |
| |
| @item |
| @cite{Ada.Finalization.Limited_Controlled} |
| |
| @item |
| Derivations from @cite{Controlled} or @cite{Limited_Controlled} |
| |
| @item |
| Class-wide types |
| |
| @item |
| Protected types |
| |
| @item |
| Task types |
| |
| @item |
| Array and record types with controlled components |
| @end itemize |
| |
| The compiler no longer generates code to initialize, finalize or adjust an |
| object or a nested component, either declared on the stack or on the heap. The |
| deallocation of a controlled object no longer finalizes its contents. |
| |
| @node No_Fixed_Point,No_Floating_Point,No_Finalization,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-fixed-point}@anchor{185} |
| @subsection No_Fixed_Point |
| |
| |
| @geindex No_Fixed_Point |
| |
| [RM H.4] This restriction ensures at compile time that there are no |
| occurrences of fixed point types and operations. |
| |
| @node No_Floating_Point,No_Implicit_Conditionals,No_Fixed_Point,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-floating-point}@anchor{186} |
| @subsection No_Floating_Point |
| |
| |
| @geindex No_Floating_Point |
| |
| [RM H.4] This restriction ensures at compile time that there are no |
| occurrences of floating point types and operations. |
| |
| @node No_Implicit_Conditionals,No_Implicit_Dynamic_Code,No_Floating_Point,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-implicit-conditionals}@anchor{187} |
| @subsection No_Implicit_Conditionals |
| |
| |
| @geindex No_Implicit_Conditionals |
| |
| [GNAT] This restriction ensures that the generated code does not contain any |
| implicit conditionals, either by modifying the generated code where possible, |
| or by rejecting any construct that would otherwise generate an implicit |
| conditional. Note that this check does not include run time constraint |
| checks, which on some targets may generate implicit conditionals as |
| well. To control the latter, constraint checks can be suppressed in the |
| normal manner. Constructs generating implicit conditionals include comparisons |
| of composite objects and the Max/Min attributes. |
| |
| @node No_Implicit_Dynamic_Code,No_Implicit_Heap_Allocations,No_Implicit_Conditionals,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-implicit-dynamic-code}@anchor{188} |
| @subsection No_Implicit_Dynamic_Code |
| |
| |
| @geindex No_Implicit_Dynamic_Code |
| |
| @geindex trampoline |
| |
| [GNAT] This restriction prevents the compiler from building 'trampolines'. |
| This is a structure that is built on the stack and contains dynamic |
| code to be executed at run time. On some targets, a trampoline is |
| built for the following features: @cite{Access}, |
| @cite{Unrestricted_Access}, or @cite{Address} of a nested subprogram; |
| nested task bodies; primitive operations of nested tagged types. |
| Trampolines do not work on machines that prevent execution of stack |
| data. For example, on windows systems, enabling DEP (data execution |
| protection) will cause trampolines to raise an exception. |
| Trampolines are also quite slow at run time. |
| |
| On many targets, trampolines have been largely eliminated. Look at the |
| version of system.ads for your target --- if it has |
| Always_Compatible_Rep equal to False, then trampolines are largely |
| eliminated. In particular, a trampoline is built for the following |
| features: @cite{Address} of a nested subprogram; |
| @cite{Access} or @cite{Unrestricted_Access} of a nested subprogram, |
| but only if pragma Favor_Top_Level applies, or the access type has a |
| foreign-language convention; primitive operations of nested tagged |
| types. |
| |
| @node No_Implicit_Heap_Allocations,No_Implicit_Loops,No_Implicit_Dynamic_Code,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-implicit-heap-allocations}@anchor{189} |
| @subsection No_Implicit_Heap_Allocations |
| |
| |
| @geindex No_Implicit_Heap_Allocations |
| |
| [RM D.7] No constructs are allowed to cause implicit heap allocation. |
| |
| @node No_Implicit_Loops,No_Initialize_Scalars,No_Implicit_Heap_Allocations,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-implicit-loops}@anchor{18a} |
| @subsection No_Implicit_Loops |
| |
| |
| @geindex No_Implicit_Loops |
| |
| [GNAT] This restriction ensures that the generated code does not contain any |
| implicit @cite{for} loops, either by modifying |
| the generated code where possible, |
| or by rejecting any construct that would otherwise generate an implicit |
| @cite{for} loop. If this restriction is active, it is possible to build |
| large array aggregates with all static components without generating an |
| intermediate temporary, and without generating a loop to initialize individual |
| components. Otherwise, a loop is created for arrays larger than about 5000 |
| scalar components. |
| |
| @node No_Initialize_Scalars,No_IO,No_Implicit_Loops,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-initialize-scalars}@anchor{18b} |
| @subsection No_Initialize_Scalars |
| |
| |
| @geindex No_Initialize_Scalars |
| |
| [GNAT] This restriction ensures that no unit in the partition is compiled with |
| pragma Initialize_Scalars. This allows the generation of more efficient |
| code, and in particular eliminates dummy null initialization routines that |
| are otherwise generated for some record and array types. |
| |
| @node No_IO,No_Local_Allocators,No_Initialize_Scalars,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-io}@anchor{18c} |
| @subsection No_IO |
| |
| |
| @geindex No_IO |
| |
| [RM H.4] This restriction ensures at compile time that there are no |
| dependences on any of the library units Sequential_IO, Direct_IO, |
| Text_IO, Wide_Text_IO, Wide_Wide_Text_IO, or Stream_IO. |
| |
| @node No_Local_Allocators,No_Local_Protected_Objects,No_IO,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-local-allocators}@anchor{18d} |
| @subsection No_Local_Allocators |
| |
| |
| @geindex No_Local_Allocators |
| |
| [RM H.4] This restriction ensures at compile time that there are no |
| occurrences of an allocator in subprograms, generic subprograms, tasks, |
| and entry bodies. |
| |
| @node No_Local_Protected_Objects,No_Local_Timing_Events,No_Local_Allocators,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-local-protected-objects}@anchor{18e} |
| @subsection No_Local_Protected_Objects |
| |
| |
| @geindex No_Local_Protected_Objects |
| |
| [RM D.7] This restriction ensures at compile time that protected objects are |
| only declared at the library level. |
| |
| @node No_Local_Timing_Events,No_Long_Long_Integers,No_Local_Protected_Objects,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-local-timing-events}@anchor{18f} |
| @subsection No_Local_Timing_Events |
| |
| |
| @geindex No_Local_Timing_Events |
| |
| [RM D.7] All objects of type Ada.Timing_Events.Timing_Event are |
| declared at the library level. |
| |
| @node No_Long_Long_Integers,No_Multiple_Elaboration,No_Local_Timing_Events,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-long-long-integers}@anchor{190} |
| @subsection No_Long_Long_Integers |
| |
| |
| @geindex No_Long_Long_Integers |
| |
| [GNAT] This partition-wide restriction forbids any explicit reference to |
| type Standard.Long_Long_Integer, and also forbids declaring range types whose |
| implicit base type is Long_Long_Integer, and modular types whose size exceeds |
| Long_Integer'Size. |
| |
| @node No_Multiple_Elaboration,No_Nested_Finalization,No_Long_Long_Integers,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-multiple-elaboration}@anchor{191} |
| @subsection No_Multiple_Elaboration |
| |
| |
| @geindex No_Multiple_Elaboration |
| |
| [GNAT] Normally each package contains a 16-bit counter used to check for access |
| before elaboration, and to control multiple elaboration attempts. |
| This counter is eliminated for units compiled with the static model |
| of elaboration if restriction @cite{No_Elaboration_Code} |
| is active but because of |
| the need to check for multiple elaboration in the general case, these |
| counters cannot be eliminated if elaboration code may be present. The |
| restriction @cite{No_Multiple_Elaboration} |
| allows suppression of these counters |
| in static elaboration units even if they do have elaboration code. If this |
| restriction is used, then the situations in which multiple elaboration is |
| possible, including non-Ada main programs, and Stand Alone libraries, are not |
| permitted, and will be diagnosed by the binder. |
| |
| @node No_Nested_Finalization,No_Protected_Type_Allocators,No_Multiple_Elaboration,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-nested-finalization}@anchor{192} |
| @subsection No_Nested_Finalization |
| |
| |
| @geindex No_Nested_Finalization |
| |
| [RM D.7] All objects requiring finalization are declared at the library level. |
| |
| @node No_Protected_Type_Allocators,No_Protected_Types,No_Nested_Finalization,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-protected-type-allocators}@anchor{193} |
| @subsection No_Protected_Type_Allocators |
| |
| |
| @geindex No_Protected_Type_Allocators |
| |
| [RM D.7] This restriction ensures at compile time that there are no allocator |
| expressions that attempt to allocate protected objects. |
| |
| @node No_Protected_Types,No_Recursion,No_Protected_Type_Allocators,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-protected-types}@anchor{194} |
| @subsection No_Protected_Types |
| |
| |
| @geindex No_Protected_Types |
| |
| [RM H.4] This restriction ensures at compile time that there are no |
| declarations of protected types or protected objects. |
| |
| @node No_Recursion,No_Reentrancy,No_Protected_Types,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-recursion}@anchor{195} |
| @subsection No_Recursion |
| |
| |
| @geindex No_Recursion |
| |
| [RM H.4] A program execution is erroneous if a subprogram is invoked as |
| part of its execution. |
| |
| @node No_Reentrancy,No_Relative_Delay,No_Recursion,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-reentrancy}@anchor{196} |
| @subsection No_Reentrancy |
| |
| |
| @geindex No_Reentrancy |
| |
| [RM H.4] A program execution is erroneous if a subprogram is executed by |
| two tasks at the same time. |
| |
| @node No_Relative_Delay,No_Requeue_Statements,No_Reentrancy,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-relative-delay}@anchor{197} |
| @subsection No_Relative_Delay |
| |
| |
| @geindex No_Relative_Delay |
| |
| [RM D.7] This restriction ensures at compile time that there are no delay |
| relative statements and prevents expressions such as @cite{delay 1.23;} from |
| appearing in source code. |
| |
| @node No_Requeue_Statements,No_Secondary_Stack,No_Relative_Delay,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-requeue-statements}@anchor{198} |
| @subsection No_Requeue_Statements |
| |
| |
| @geindex No_Requeue_Statements |
| |
| [RM D.7] This restriction ensures at compile time that no requeue statements |
| are permitted and prevents keyword @cite{requeue} from being used in source |
| code. |
| |
| @geindex No_Requeue |
| |
| The restriction @cite{No_Requeue} is recognized as a |
| synonym for @cite{No_Requeue_Statements}. This is retained for historical |
| compatibility purposes (and a warning will be generated for its use if |
| warnings on oNobsolescent features are activated). |
| |
| @node No_Secondary_Stack,No_Select_Statements,No_Requeue_Statements,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-secondary-stack}@anchor{199} |
| @subsection No_Secondary_Stack |
| |
| |
| @geindex No_Secondary_Stack |
| |
| [GNAT] This restriction ensures at compile time that the generated code |
| does not contain any reference to the secondary stack. The secondary |
| stack is used to implement functions returning unconstrained objects |
| (arrays or records) on some targets. |
| |
| @node No_Select_Statements,No_Specific_Termination_Handlers,No_Secondary_Stack,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-select-statements}@anchor{19a} |
| @subsection No_Select_Statements |
| |
| |
| @geindex No_Select_Statements |
| |
| [RM D.7] This restriction ensures at compile time no select statements of any |
| kind are permitted, that is the keyword @cite{select} may not appear. |
| |
| @node No_Specific_Termination_Handlers,No_Specification_of_Aspect,No_Select_Statements,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-specific-termination-handlers}@anchor{19b} |
| @subsection No_Specific_Termination_Handlers |
| |
| |
| @geindex No_Specific_Termination_Handlers |
| |
| [RM D.7] There are no calls to Ada.Task_Termination.Set_Specific_Handler |
| or to Ada.Task_Termination.Specific_Handler. |
| |
| @node No_Specification_of_Aspect,No_Standard_Allocators_After_Elaboration,No_Specific_Termination_Handlers,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-specification-of-aspect}@anchor{19c} |
| @subsection No_Specification_of_Aspect |
| |
| |
| @geindex No_Specification_of_Aspect |
| |
| [RM 13.12.1] This restriction checks at compile time that no aspect |
| specification, attribute definition clause, or pragma is given for a |
| given aspect. |
| |
| @node No_Standard_Allocators_After_Elaboration,No_Standard_Storage_Pools,No_Specification_of_Aspect,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-standard-allocators-after-elaboration}@anchor{19d} |
| @subsection No_Standard_Allocators_After_Elaboration |
| |
| |
| @geindex No_Standard_Allocators_After_Elaboration |
| |
| [RM D.7] Specifies that an allocator using a standard storage pool |
| should never be evaluated at run time after the elaboration of the |
| library items of the partition has completed. Otherwise, Storage_Error |
| is raised. |
| |
| @node No_Standard_Storage_Pools,No_Stream_Optimizations,No_Standard_Allocators_After_Elaboration,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-standard-storage-pools}@anchor{19e} |
| @subsection No_Standard_Storage_Pools |
| |
| |
| @geindex No_Standard_Storage_Pools |
| |
| [GNAT] This restriction ensures at compile time that no access types |
| use the standard default storage pool. Any access type declared must |
| have an explicit Storage_Pool attribute defined specifying a |
| user-defined storage pool. |
| |
| @node No_Stream_Optimizations,No_Streams,No_Standard_Storage_Pools,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-stream-optimizations}@anchor{19f} |
| @subsection No_Stream_Optimizations |
| |
| |
| @geindex No_Stream_Optimizations |
| |
| [GNAT] This restriction affects the performance of stream operations on types |
| @cite{String}, @cite{Wide_String} and @cite{Wide_Wide_String}. By default, the |
| compiler uses block reads and writes when manipulating @cite{String} objects |
| due to their supperior performance. When this restriction is in effect, the |
| compiler performs all IO operations on a per-character basis. |
| |
| @node No_Streams,No_Task_Allocators,No_Stream_Optimizations,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-streams}@anchor{1a0} |
| @subsection No_Streams |
| |
| |
| @geindex No_Streams |
| |
| [GNAT] This restriction ensures at compile/bind time that there are no |
| stream objects created and no use of stream attributes. |
| This restriction does not forbid dependences on the package |
| @cite{Ada.Streams}. So it is permissible to with |
| @cite{Ada.Streams} (or another package that does so itself) |
| as long as no actual stream objects are created and no |
| stream attributes are used. |
| |
| Note that the use of restriction allows optimization of tagged types, |
| since they do not need to worry about dispatching stream operations. |
| To take maximum advantage of this space-saving optimization, any |
| unit declaring a tagged type should be compiled with the restriction, |
| though this is not required. |
| |
| @node No_Task_Allocators,No_Task_Attributes_Package,No_Streams,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-task-allocators}@anchor{1a1} |
| @subsection No_Task_Allocators |
| |
| |
| @geindex No_Task_Allocators |
| |
| [RM D.7] There are no allocators for task types |
| or types containing task subcomponents. |
| |
| @node No_Task_Attributes_Package,No_Task_Hierarchy,No_Task_Allocators,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-task-attributes-package}@anchor{1a2} |
| @subsection No_Task_Attributes_Package |
| |
| |
| @geindex No_Task_Attributes_Package |
| |
| [GNAT] This restriction ensures at compile time that there are no implicit or |
| explicit dependencies on the package @cite{Ada.Task_Attributes}. |
| |
| @geindex No_Task_Attributes |
| |
| The restriction @cite{No_Task_Attributes} is recognized as a synonym |
| for @cite{No_Task_Attributes_Package}. This is retained for historical |
| compatibility purposes (and a warning will be generated for its use if |
| warnings on obsolescent features are activated). |
| |
| @node No_Task_Hierarchy,No_Task_Termination,No_Task_Attributes_Package,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-task-hierarchy}@anchor{1a3} |
| @subsection No_Task_Hierarchy |
| |
| |
| @geindex No_Task_Hierarchy |
| |
| [RM D.7] All (non-environment) tasks depend |
| directly on the environment task of the partition. |
| |
| @node No_Task_Termination,No_Tasking,No_Task_Hierarchy,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-task-termination}@anchor{1a4} |
| @subsection No_Task_Termination |
| |
| |
| @geindex No_Task_Termination |
| |
| [RM D.7] Tasks that terminate are erroneous. |
| |
| @node No_Tasking,No_Terminate_Alternatives,No_Task_Termination,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-tasking}@anchor{1a5} |
| @subsection No_Tasking |
| |
| |
| @geindex No_Tasking |
| |
| [GNAT] This restriction prevents the declaration of tasks or task types |
| throughout the partition. It is similar in effect to the use of |
| @cite{Max_Tasks => 0} except that violations are caught at compile time |
| and cause an error message to be output either by the compiler or |
| binder. |
| |
| @node No_Terminate_Alternatives,No_Unchecked_Access,No_Tasking,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-terminate-alternatives}@anchor{1a6} |
| @subsection No_Terminate_Alternatives |
| |
| |
| @geindex No_Terminate_Alternatives |
| |
| [RM D.7] There are no selective accepts with terminate alternatives. |
| |
| @node No_Unchecked_Access,No_Use_Of_Entity,No_Terminate_Alternatives,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-unchecked-access}@anchor{1a7} |
| @subsection No_Unchecked_Access |
| |
| |
| @geindex No_Unchecked_Access |
| |
| [RM H.4] This restriction ensures at compile time that there are no |
| occurrences of the Unchecked_Access attribute. |
| |
| @node No_Use_Of_Entity,Simple_Barriers,No_Unchecked_Access,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-use-of-entity}@anchor{1a8} |
| @subsection No_Use_Of_Entity |
| |
| |
| @geindex No_Use_Of_Entity |
| |
| [GNAT] This restriction ensures at compile time that there are no references |
| to the entity given in the form |
| |
| @example |
| No_Use_Of_Entity => Name |
| @end example |
| |
| where @code{Name} is the fully qualified entity, for example |
| |
| @example |
| No_Use_Of_Entity => Ada.Text_IO.Put_Line |
| @end example |
| |
| @node Simple_Barriers,Static_Priorities,No_Use_Of_Entity,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions simple-barriers}@anchor{1a9} |
| @subsection Simple_Barriers |
| |
| |
| @geindex Simple_Barriers |
| |
| [RM D.7] This restriction ensures at compile time that barriers in entry |
| declarations for protected types are restricted to either static boolean |
| expressions or references to simple boolean variables defined in the private |
| part of the protected type. No other form of entry barriers is permitted. |
| |
| @geindex Boolean_Entry_Barriers |
| |
| The restriction @cite{Boolean_Entry_Barriers} is recognized as a |
| synonym for @cite{Simple_Barriers}. This is retained for historical |
| compatibility purposes (and a warning will be generated for its use if |
| warnings on obsolescent features are activated). |
| |
| @node Static_Priorities,Static_Storage_Size,Simple_Barriers,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions static-priorities}@anchor{1aa} |
| @subsection Static_Priorities |
| |
| |
| @geindex Static_Priorities |
| |
| [GNAT] This restriction ensures at compile time that all priority expressions |
| are static, and that there are no dependences on the package |
| @cite{Ada.Dynamic_Priorities}. |
| |
| @node Static_Storage_Size,,Static_Priorities,Partition-Wide Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions static-storage-size}@anchor{1ab} |
| @subsection Static_Storage_Size |
| |
| |
| @geindex Static_Storage_Size |
| |
| [GNAT] This restriction ensures at compile time that any expression appearing |
| in a Storage_Size pragma or attribute definition clause is static. |
| |
| @node Program Unit Level Restrictions,,Partition-Wide Restrictions,Standard and Implementation Defined Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions program-unit-level-restrictions}@anchor{1ac}@anchor{gnat_rm/standard_and_implementation_defined_restrictions id3}@anchor{1ad} |
| @section Program Unit Level Restrictions |
| |
| |
| The second set of restriction identifiers |
| does not require partition-wide consistency. |
| The restriction may be enforced for a single |
| compilation unit without any effect on any of the |
| other compilation units in the partition. |
| |
| @menu |
| * No_Elaboration_Code:: |
| * No_Entry_Queue:: |
| * No_Implementation_Aspect_Specifications:: |
| * No_Implementation_Attributes:: |
| * No_Implementation_Identifiers:: |
| * No_Implementation_Pragmas:: |
| * No_Implementation_Restrictions:: |
| * No_Implementation_Units:: |
| * No_Implicit_Aliasing:: |
| * No_Obsolescent_Features:: |
| * No_Wide_Characters:: |
| * SPARK_05:: |
| |
| @end menu |
| |
| @node No_Elaboration_Code,No_Entry_Queue,,Program Unit Level Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-elaboration-code}@anchor{1ae} |
| @subsection No_Elaboration_Code |
| |
| |
| @geindex No_Elaboration_Code |
| |
| [GNAT] This restriction ensures at compile time that no elaboration code is |
| generated. Note that this is not the same condition as is enforced |
| by pragma @cite{Preelaborate}. There are cases in which pragma |
| @cite{Preelaborate} still permits code to be generated (e.g., code |
| to initialize a large array to all zeroes), and there are cases of units |
| which do not meet the requirements for pragma @cite{Preelaborate}, |
| but for which no elaboration code is generated. Generally, it is |
| the case that preelaborable units will meet the restrictions, with |
| the exception of large aggregates initialized with an others_clause, |
| and exception declarations (which generate calls to a run-time |
| registry procedure). This restriction is enforced on |
| a unit by unit basis, it need not be obeyed consistently |
| throughout a partition. |
| |
| In the case of aggregates with others, if the aggregate has a dynamic |
| size, there is no way to eliminate the elaboration code (such dynamic |
| bounds would be incompatible with @cite{Preelaborate} in any case). If |
| the bounds are static, then use of this restriction actually modifies |
| the code choice of the compiler to avoid generating a loop, and instead |
| generate the aggregate statically if possible, no matter how many times |
| the data for the others clause must be repeatedly generated. |
| |
| It is not possible to precisely document |
| the constructs which are compatible with this restriction, since, |
| unlike most other restrictions, this is not a restriction on the |
| source code, but a restriction on the generated object code. For |
| example, if the source contains a declaration: |
| |
| @example |
| Val : constant Integer := X; |
| @end example |
| |
| where X is not a static constant, it may be possible, depending |
| on complex optimization circuitry, for the compiler to figure |
| out the value of X at compile time, in which case this initialization |
| can be done by the loader, and requires no initialization code. It |
| is not possible to document the precise conditions under which the |
| optimizer can figure this out. |
| |
| Note that this the implementation of this restriction requires full |
| code generation. If it is used in conjunction with "semantics only" |
| checking, then some cases of violations may be missed. |
| |
| @node No_Entry_Queue,No_Implementation_Aspect_Specifications,No_Elaboration_Code,Program Unit Level Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-entry-queue}@anchor{1af} |
| @subsection No_Entry_Queue |
| |
| |
| @geindex No_Entry_Queue |
| |
| [GNAT] This restriction is a declaration that any protected entry compiled in |
| the scope of the restriction has at most one task waiting on the entry |
| at any one time, and so no queue is required. This restriction is not |
| checked at compile time. A program execution is erroneous if an attempt |
| is made to queue a second task on such an entry. |
| |
| @node No_Implementation_Aspect_Specifications,No_Implementation_Attributes,No_Entry_Queue,Program Unit Level Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-implementation-aspect-specifications}@anchor{1b0} |
| @subsection No_Implementation_Aspect_Specifications |
| |
| |
| @geindex No_Implementation_Aspect_Specifications |
| |
| [RM 13.12.1] This restriction checks at compile time that no |
| GNAT-defined aspects are present. With this restriction, the only |
| aspects that can be used are those defined in the Ada Reference Manual. |
| |
| @node No_Implementation_Attributes,No_Implementation_Identifiers,No_Implementation_Aspect_Specifications,Program Unit Level Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-implementation-attributes}@anchor{1b1} |
| @subsection No_Implementation_Attributes |
| |
| |
| @geindex No_Implementation_Attributes |
| |
| [RM 13.12.1] This restriction checks at compile time that no |
| GNAT-defined attributes are present. With this restriction, the only |
| attributes that can be used are those defined in the Ada Reference |
| Manual. |
| |
| @node No_Implementation_Identifiers,No_Implementation_Pragmas,No_Implementation_Attributes,Program Unit Level Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-implementation-identifiers}@anchor{1b2} |
| @subsection No_Implementation_Identifiers |
| |
| |
| @geindex No_Implementation_Identifiers |
| |
| [RM 13.12.1] This restriction checks at compile time that no |
| implementation-defined identifiers (marked with pragma Implementation_Defined) |
| occur within language-defined packages. |
| |
| @node No_Implementation_Pragmas,No_Implementation_Restrictions,No_Implementation_Identifiers,Program Unit Level Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-implementation-pragmas}@anchor{1b3} |
| @subsection No_Implementation_Pragmas |
| |
| |
| @geindex No_Implementation_Pragmas |
| |
| [RM 13.12.1] This restriction checks at compile time that no |
| GNAT-defined pragmas are present. With this restriction, the only |
| pragmas that can be used are those defined in the Ada Reference Manual. |
| |
| @node No_Implementation_Restrictions,No_Implementation_Units,No_Implementation_Pragmas,Program Unit Level Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-implementation-restrictions}@anchor{1b4} |
| @subsection No_Implementation_Restrictions |
| |
| |
| @geindex No_Implementation_Restrictions |
| |
| [GNAT] This restriction checks at compile time that no GNAT-defined restriction |
| identifiers (other than @cite{No_Implementation_Restrictions} itself) |
| are present. With this restriction, the only other restriction identifiers |
| that can be used are those defined in the Ada Reference Manual. |
| |
| @node No_Implementation_Units,No_Implicit_Aliasing,No_Implementation_Restrictions,Program Unit Level Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-implementation-units}@anchor{1b5} |
| @subsection No_Implementation_Units |
| |
| |
| @geindex No_Implementation_Units |
| |
| [RM 13.12.1] This restriction checks at compile time that there is no |
| mention in the context clause of any implementation-defined descendants |
| of packages Ada, Interfaces, or System. |
| |
| @node No_Implicit_Aliasing,No_Obsolescent_Features,No_Implementation_Units,Program Unit Level Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-implicit-aliasing}@anchor{1b6} |
| @subsection No_Implicit_Aliasing |
| |
| |
| @geindex No_Implicit_Aliasing |
| |
| [GNAT] This restriction, which is not required to be partition-wide consistent, |
| requires an explicit aliased keyword for an object to which 'Access, |
| 'Unchecked_Access, or 'Address is applied, and forbids entirely the use of |
| the 'Unrestricted_Access attribute for objects. Note: the reason that |
| Unrestricted_Access is forbidden is that it would require the prefix |
| to be aliased, and in such cases, it can always be replaced by |
| the standard attribute Unchecked_Access which is preferable. |
| |
| @node No_Obsolescent_Features,No_Wide_Characters,No_Implicit_Aliasing,Program Unit Level Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-obsolescent-features}@anchor{1b7} |
| @subsection No_Obsolescent_Features |
| |
| |
| @geindex No_Obsolescent_Features |
| |
| [RM 13.12.1] This restriction checks at compile time that no obsolescent |
| features are used, as defined in Annex J of the Ada Reference Manual. |
| |
| @node No_Wide_Characters,SPARK_05,No_Obsolescent_Features,Program Unit Level Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions no-wide-characters}@anchor{1b8} |
| @subsection No_Wide_Characters |
| |
| |
| @geindex No_Wide_Characters |
| |
| [GNAT] This restriction ensures at compile time that no uses of the types |
| @cite{Wide_Character} or @cite{Wide_String} or corresponding wide |
| wide types |
| appear, and that no wide or wide wide string or character literals |
| appear in the program (that is literals representing characters not in |
| type @cite{Character}). |
| |
| @node SPARK_05,,No_Wide_Characters,Program Unit Level Restrictions |
| @anchor{gnat_rm/standard_and_implementation_defined_restrictions spark-05}@anchor{1b9} |
| @subsection SPARK_05 |
| |
| |
| @geindex SPARK_05 |
| |
| [GNAT] This restriction checks at compile time that some constructs |
| forbidden in SPARK 2005 are not present. Error messages related to |
| SPARK restriction have the form: |
| |
| @example |
| violation of restriction "SPARK_05" at <source-location> |
| <error message> |
| @end example |
| |
| @geindex SPARK |
| |
| The restriction @cite{SPARK} is recognized as a |
| synonym for @cite{SPARK_05}. This is retained for historical |
| compatibility purposes (and an unconditional warning will be generated |
| for its use, advising replacement by @cite{SPARK}). |
| |
| This is not a replacement for the semantic checks performed by the |
| SPARK Examiner tool, as the compiler currently only deals with code, |
| not SPARK 2005 annotations, and does not guarantee catching all |
| cases of constructs forbidden by SPARK 2005. |
| |
| Thus it may well be the case that code which passes the compiler with |
| the SPARK restriction is rejected by the SPARK Examiner, e.g. due to |
| the different visibility rules of the Examiner based on SPARK 2005 |
| @cite{inherit} annotations. |
| |
| This restriction can be useful in providing an initial filter for code |
| developed using SPARK 2005, or in examining legacy code to see how far |
| it is from meeting SPARK restrictions. |
| |
| The list below summarizes the checks that are performed when this |
| restriction is in force: |
| |
| |
| @itemize * |
| |
| @item |
| No block statements |
| |
| @item |
| No case statements with only an others clause |
| |
| @item |
| Exit statements in loops must respect the SPARK 2005 language restrictions |
| |
| @item |
| No goto statements |
| |
| @item |
| Return can only appear as last statement in function |
| |
| @item |
| Function must have return statement |
| |
| @item |
| Loop parameter specification must include subtype mark |
| |
| @item |
| Prefix of expanded name cannot be a loop statement |
| |
| @item |
| Abstract subprogram not allowed |
| |
| @item |
| User-defined operators not allowed |
| |
| @item |
| Access type parameters not allowed |
| |
| @item |
| Default expressions for parameters not allowed |
| |
| @item |
| Default expressions for record fields not allowed |
| |
| @item |
| No tasking constructs allowed |
| |
| @item |
| Label needed at end of subprograms and packages |
| |
| @item |
| No mixing of positional and named parameter association |
| |
| @item |
| No access types as result type |
| |
| @item |
| No unconstrained arrays as result types |
| |
| @item |
| No null procedures |
| |
| @item |
| Initial and later declarations must be in correct order (declaration can't come after body) |
| |
| @item |
| No attributes on private types if full declaration not visible |
| |
| @item |
| No package declaration within package specification |
| |
| @item |
| No controlled types |
| |
| @item |
| No discriminant types |
| |
| @item |
| No overloading |
| |
| @item |
| Selector name cannot be operator symbol (i.e. operator symbol cannot be prefixed) |
| |
| @item |
| Access attribute not allowed |
| |
| @item |
| Allocator not allowed |
| |
| @item |
| Result of catenation must be String |
| |
| @item |
| Operands of catenation must be string literal, static char or another catenation |
| |
| @item |
| No conditional expressions |
| |
| @item |
| No explicit dereference |
| |
| @item |
| Quantified expression not allowed |
| |
| @item |
| Slicing not allowed |
| |
| @item |
| No exception renaming |
| |
| @item |
| No generic renaming |
| |
| @item |
| No object renaming |
| |
| @item |
| No use clause |
| |
| @item |
| Aggregates must be qualified |
| |
| @item |
| Non-static choice in array aggregates not allowed |
| |
| @item |
| The only view conversions which are allowed as in-out parameters are conversions of a tagged type to an ancestor type |
| |
| @item |
| No mixing of positional and named association in aggregate, no multi choice |
| |
| @item |
| AND, OR and XOR for arrays only allowed when operands have same static bounds |
| |
| @item |
| Fixed point operands to * or / must be qualified or converted |
| |
| @item |
| Comparison operators not allowed for Booleans or arrays (except strings) |
| |
| @item |
| Equality not allowed for arrays with non-matching static bounds (except strings) |
| |
| @item |
| Conversion / qualification not allowed for arrays with non-matching static bounds |
| |
| @item |
| Subprogram declaration only allowed in package spec (unless followed by import) |
| |
| @item |
| Access types not allowed |
| |
| @item |
| Incomplete type declaration not allowed |
| |
| @item |
| Object and subtype declarations must respect SPARK restrictions |
| |
| @item |
| Digits or delta constraint not allowed |
| |
| @item |
| Decimal fixed point type not allowed |
| |
| @item |
| Aliasing of objects not allowed |
| |
| @item |
| Modular type modulus must be power of 2 |
| |
| @item |
| Base not allowed on subtype mark |
| |
| @item |
| Unary operators not allowed on modular types (except not) |
| |
| @item |
| Untagged record cannot be null |
| |
| @item |
| No class-wide operations |
| |
| @item |
| Initialization expressions must respect SPARK restrictions |
| |
| @item |
| Non-static ranges not allowed except in iteration schemes |
| |
| @item |
| String subtypes must have lower bound of 1 |
| |
| @item |
| Subtype of Boolean cannot have constraint |
| |
| @item |
| At most one tagged type or extension per package |
| |
| @item |
| Interface is not allowed |
| |
| @item |
| Character literal cannot be prefixed (selector name cannot be character literal) |
| |
| @item |
| Record aggregate cannot contain 'others' |
| |
| @item |
| Component association in record aggregate must contain a single choice |
| |
| @item |
| Ancestor part cannot be a type mark |
| |
| @item |
| Attributes 'Image, 'Width and 'Value not allowed |
| |
| @item |
| Functions may not update globals |
| |
| @item |
| Subprograms may not contain direct calls to themselves (prevents recursion within unit) |
| |
| @item |
| Call to subprogram not allowed in same unit before body has been seen (prevents recursion within unit) |
| @end itemize |
| |
| The following restrictions are enforced, but note that they are actually more |
| strict that the latest SPARK 2005 language definition: |
| |
| |
| @itemize * |
| |
| @item |
| No derived types other than tagged type extensions |
| |
| @item |
| Subtype of unconstrained array must have constraint |
| @end itemize |
| |
| This list summarises the main SPARK 2005 language rules that are not |
| currently checked by the SPARK_05 restriction: |
| |
| |
| @itemize * |
| |
| @item |
| SPARK annotations are treated as comments so are not checked at all |
| |
| @item |
| Based real literals not allowed |
| |
| @item |
| Objects cannot be initialized at declaration by calls to user-defined functions |
| |
| @item |
| Objects cannot be initialized at declaration by assignments from variables |
| |
| @item |
| Objects cannot be initialized at declaration by assignments from indexed/selected components |
| |
| @item |
| Ranges shall not be null |
| |
| @item |
| A fixed point delta expression must be a simple expression |
| |
| @item |
| Restrictions on where renaming declarations may be placed |
| |
| @item |
| Externals of mode 'out' cannot be referenced |
| |
| @item |
| Externals of mode 'in' cannot be updated |
| |
| @item |
| Loop with no iteration scheme or exits only allowed as last statement in main program or task |
| |
| @item |
| Subprogram cannot have parent unit name |
| |
| @item |
| SPARK 2005 inherited subprogram must be prefixed with overriding |
| |
| @item |
| External variables (or functions that reference them) may not be passed as actual parameters |
| |
| @item |
| Globals must be explicitly mentioned in contract |
| |
| @item |
| Deferred constants cannot be completed by pragma Import |
| |
| @item |
| Package initialization cannot read/write variables from other packages |
| |
| @item |
| Prefix not allowed for entities that are directly visible |
| |
| @item |
| Identifier declaration can't override inherited package name |
| |
| @item |
| Cannot use Standard or other predefined packages as identifiers |
| |
| @item |
| After renaming, cannot use the original name |
| |
| @item |
| Subprograms can only be renamed to remove package prefix |
| |
| @item |
| Pragma import must be immediately after entity it names |
| |
| @item |
| No mutual recursion between multiple units (this can be checked with gnatcheck) |
| @end itemize |
| |
| Note that if a unit is compiled in Ada 95 mode with the SPARK restriction, |
| violations will be reported for constructs forbidden in SPARK 95, |
| instead of SPARK 2005. |
| |
| @node Implementation Advice,Implementation Defined Characteristics,Standard and Implementation Defined Restrictions,Top |
| @anchor{gnat_rm/implementation_advice doc}@anchor{1ba}@anchor{gnat_rm/implementation_advice implementation-advice}@anchor{a}@anchor{gnat_rm/implementation_advice id1}@anchor{1bb} |
| @chapter Implementation Advice |
| |
| |
| The main text of the Ada Reference Manual describes the required |
| behavior of all Ada compilers, and the GNAT compiler conforms to |
| these requirements. |
| |
| In addition, there are sections throughout the Ada Reference Manual headed |
| by the phrase 'Implementation advice'. These sections are not normative, |
| i.e., they do not specify requirements that all compilers must |
| follow. Rather they provide advice on generally desirable behavior. |
| They are not requirements, because they describe behavior that cannot |
| be provided on all systems, or may be undesirable on some systems. |
| |
| As far as practical, GNAT follows the implementation advice in |
| the Ada Reference Manual. Each such RM section corresponds to a section |
| in this chapter whose title specifies the |
| RM section number and paragraph number and the subject of |
| the advice. The contents of each section consists of the RM text within |
| quotation marks, |
| followed by the GNAT interpretation of the advice. Most often, this simply says |
| 'followed', which means that GNAT follows the advice. However, in a |
| number of cases, GNAT deliberately deviates from this advice, in which |
| case the text describes what GNAT does and why. |
| |
| @geindex Error detection |
| |
| @menu |
| * RM 1.1.3(20); Error Detection: RM 1 1 3 20 Error Detection. |
| * RM 1.1.3(31); Child Units: RM 1 1 3 31 Child Units. |
| * RM 1.1.5(12); Bounded Errors: RM 1 1 5 12 Bounded Errors. |
| * RM 2.8(16); Pragmas: RM 2 8 16 Pragmas. |
| * RM 2.8(17-19); Pragmas: RM 2 8 17-19 Pragmas. |
| * RM 3.5.2(5); Alternative Character Sets: RM 3 5 2 5 Alternative Character Sets. |
| * RM 3.5.4(28); Integer Types: RM 3 5 4 28 Integer Types. |
| * RM 3.5.4(29); Integer Types: RM 3 5 4 29 Integer Types. |
| * RM 3.5.5(8); Enumeration Values: RM 3 5 5 8 Enumeration Values. |
| * RM 3.5.7(17); Float Types: RM 3 5 7 17 Float Types. |
| * RM 3.6.2(11); Multidimensional Arrays: RM 3 6 2 11 Multidimensional Arrays. |
| * RM 9.6(30-31); Duration'Small: RM 9 6 30-31 Duration'Small. |
| * RM 10.2.1(12); Consistent Representation: RM 10 2 1 12 Consistent Representation. |
| * RM 11.4.1(19); Exception Information: RM 11 4 1 19 Exception Information. |
| * RM 11.5(28); Suppression of Checks: RM 11 5 28 Suppression of Checks. |
| * RM 13.1 (21-24); Representation Clauses: RM 13 1 21-24 Representation Clauses. |
| * RM 13.2(6-8); Packed Types: RM 13 2 6-8 Packed Types. |
| * RM 13.3(14-19); Address Clauses: RM 13 3 14-19 Address Clauses. |
| * RM 13.3(29-35); Alignment Clauses: RM 13 3 29-35 Alignment Clauses. |
| * RM 13.3(42-43); Size Clauses: RM 13 3 42-43 Size Clauses. |
| * RM 13.3(50-56); Size Clauses: RM 13 3 50-56 Size Clauses. |
| * RM 13.3(71-73); Component Size Clauses: RM 13 3 71-73 Component Size Clauses. |
| * RM 13.4(9-10); Enumeration Representation Clauses: RM 13 4 9-10 Enumeration Representation Clauses. |
| * RM 13.5.1(17-22); Record Representation Clauses: RM 13 5 1 17-22 Record Representation Clauses. |
| * RM 13.5.2(5); Storage Place Attributes: RM 13 5 2 5 Storage Place Attributes. |
| * RM 13.5.3(7-8); Bit Ordering: RM 13 5 3 7-8 Bit Ordering. |
| * RM 13.7(37); Address as Private: RM 13 7 37 Address as Private. |
| * RM 13.7.1(16); Address Operations: RM 13 7 1 16 Address Operations. |
| * RM 13.9(14-17); Unchecked Conversion: RM 13 9 14-17 Unchecked Conversion. |
| * RM 13.11(23-25); Implicit Heap Usage: RM 13 11 23-25 Implicit Heap Usage. |
| * RM 13.11.2(17); Unchecked Deallocation: RM 13 11 2 17 Unchecked Deallocation. |
| * RM 13.13.2(17); Stream Oriented Attributes: RM 13 13 2 17 Stream Oriented Attributes. |
| * RM A.1(52); Names of Predefined Numeric Types: RM A 1 52 Names of Predefined Numeric Types. |
| * RM A.3.2(49); Ada.Characters.Handling: RM A 3 2 49 Ada Characters Handling. |
| * RM A.4.4(106); Bounded-Length String Handling: RM A 4 4 106 Bounded-Length String Handling. |
| * RM A.5.2(46-47); Random Number Generation: RM A 5 2 46-47 Random Number Generation. |
| * RM A.10.7(23); Get_Immediate: RM A 10 7 23 Get_Immediate. |
| * RM B.1(39-41); Pragma Export: RM B 1 39-41 Pragma Export. |
| * RM B.2(12-13); Package Interfaces: RM B 2 12-13 Package Interfaces. |
| * RM B.3(63-71); Interfacing with C: RM B 3 63-71 Interfacing with C. |
| * RM B.4(95-98); Interfacing with COBOL: RM B 4 95-98 Interfacing with COBOL. |
| * RM B.5(22-26); Interfacing with Fortran: RM B 5 22-26 Interfacing with Fortran. |
| * RM C.1(3-5); Access to Machine Operations: RM C 1 3-5 Access to Machine Operations. |
| * RM C.1(10-16); Access to Machine Operations: RM C 1 10-16 Access to Machine Operations. |
| * RM C.3(28); Interrupt Support: RM C 3 28 Interrupt Support. |
| * RM C.3.1(20-21); Protected Procedure Handlers: RM C 3 1 20-21 Protected Procedure Handlers. |
| * RM C.3.2(25); Package Interrupts: RM C 3 2 25 Package Interrupts. |
| * RM C.4(14); Pre-elaboration Requirements: RM C 4 14 Pre-elaboration Requirements. |
| * RM C.5(8); Pragma Discard_Names: RM C 5 8 Pragma Discard_Names. |
| * RM C.7.2(30); The Package Task_Attributes: RM C 7 2 30 The Package Task_Attributes. |
| * RM D.3(17); Locking Policies: RM D 3 17 Locking Policies. |
| * RM D.4(16); Entry Queuing Policies: RM D 4 16 Entry Queuing Policies. |
| * RM D.6(9-10); Preemptive Abort: RM D 6 9-10 Preemptive Abort. |
| * RM D.7(21); Tasking Restrictions: RM D 7 21 Tasking Restrictions. |
| * RM D.8(47-49); Monotonic Time: RM D 8 47-49 Monotonic Time. |
| * RM E.5(28-29); Partition Communication Subsystem: RM E 5 28-29 Partition Communication Subsystem. |
| * RM F(7); COBOL Support: RM F 7 COBOL Support. |
| * RM F.1(2); Decimal Radix Support: RM F 1 2 Decimal Radix Support. |
| * RM G; Numerics: RM G Numerics. |
| * RM G.1.1(56-58); Complex Types: RM G 1 1 56-58 Complex Types. |
| * RM G.1.2(49); Complex Elementary Functions: RM G 1 2 49 Complex Elementary Functions. |
| * RM G.2.4(19); Accuracy Requirements: RM G 2 4 19 Accuracy Requirements. |
| * RM G.2.6(15); Complex Arithmetic Accuracy: RM G 2 6 15 Complex Arithmetic Accuracy. |
| * RM H.6(15/2); Pragma Partition_Elaboration_Policy: RM H 6 15/2 Pragma Partition_Elaboration_Policy. |
| |
| @end menu |
| |
| @node RM 1 1 3 20 Error Detection,RM 1 1 3 31 Child Units,,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-1-1-3-20-error-detection}@anchor{1bc} |
| @section RM 1.1.3(20): Error Detection |
| |
| |
| @quotation |
| |
| "If an implementation detects the use of an unsupported Specialized Needs |
| Annex feature at run time, it should raise @cite{Program_Error} if |
| feasible." |
| @end quotation |
| |
| Not relevant. All specialized needs annex features are either supported, |
| or diagnosed at compile time. |
| |
| @geindex Child Units |
| |
| @node RM 1 1 3 31 Child Units,RM 1 1 5 12 Bounded Errors,RM 1 1 3 20 Error Detection,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-1-1-3-31-child-units}@anchor{1bd} |
| @section RM 1.1.3(31): Child Units |
| |
| |
| @quotation |
| |
| "If an implementation wishes to provide implementation-defined |
| extensions to the functionality of a language-defined library unit, it |
| should normally do so by adding children to the library unit." |
| @end quotation |
| |
| Followed. |
| |
| @geindex Bounded errors |
| |
| @node RM 1 1 5 12 Bounded Errors,RM 2 8 16 Pragmas,RM 1 1 3 31 Child Units,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-1-1-5-12-bounded-errors}@anchor{1be} |
| @section RM 1.1.5(12): Bounded Errors |
| |
| |
| @quotation |
| |
| "If an implementation detects a bounded error or erroneous |
| execution, it should raise @cite{Program_Error}." |
| @end quotation |
| |
| Followed in all cases in which the implementation detects a bounded |
| error or erroneous execution. Not all such situations are detected at |
| runtime. |
| |
| @geindex Pragmas |
| |
| @node RM 2 8 16 Pragmas,RM 2 8 17-19 Pragmas,RM 1 1 5 12 Bounded Errors,Implementation Advice |
| @anchor{gnat_rm/implementation_advice id2}@anchor{1bf}@anchor{gnat_rm/implementation_advice rm-2-8-16-pragmas}@anchor{1c0} |
| @section RM 2.8(16): Pragmas |
| |
| |
| @quotation |
| |
| "Normally, implementation-defined pragmas should have no semantic effect |
| for error-free programs; that is, if the implementation-defined pragmas |
| are removed from a working program, the program should still be legal, |
| and should still have the same semantics." |
| @end quotation |
| |
| The following implementation defined pragmas are exceptions to this |
| rule: |
| |
| |
| @multitable {xxxxxxxxxxxxxxxxxxxxxx} {xxxxxxxxxxxxxxxxxxxxx} |
| @headitem |
| |
| Pragma |
| |
| @tab |
| |
| Explanation |
| |
| @item |
| |
| @emph{Abort_Defer} |
| |
| @tab |
| |
| Affects semantics |
| |
| @item |
| |
| @emph{Ada_83} |
| |
| @tab |
| |
| Affects legality |
| |
| @item |
| |
| @emph{Assert} |
| |
| @tab |
| |
| Affects semantics |
| |
| @item |
| |
| @emph{CPP_Class} |
| |
| @tab |
| |
| Affects semantics |
| |
| @item |
| |
| @emph{CPP_Constructor} |
| |
| @tab |
| |
| Affects semantics |
| |
| @item |
| |
| @emph{Debug} |
| |
| @tab |
| |
| Affects semantics |
| |
| @item |
| |
| @emph{Interface_Name} |
| |
| @tab |
| |
| Affects semantics |
| |
| @item |
| |
| @emph{Machine_Attribute} |
| |
| @tab |
| |
| Affects semantics |
| |
| @item |
| |
| @emph{Unimplemented_Unit} |
| |
| @tab |
| |
| Affects legality |
| |
| @item |
| |
| @emph{Unchecked_Union} |
| |
| @tab |
| |
| Affects semantics |
| |
| @end multitable |
| |
| |
| In each of the above cases, it is essential to the purpose of the pragma |
| that this advice not be followed. For details see |
| @ref{7,,Implementation Defined Pragmas}. |
| |
| @node RM 2 8 17-19 Pragmas,RM 3 5 2 5 Alternative Character Sets,RM 2 8 16 Pragmas,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-2-8-17-19-pragmas}@anchor{1c1} |
| @section RM 2.8(17-19): Pragmas |
| |
| |
| @quotation |
| |
| "Normally, an implementation should not define pragmas that can |
| make an illegal program legal, except as follows: |
| |
| |
| @itemize * |
| |
| @item |
| A pragma used to complete a declaration, such as a pragma @cite{Import}; |
| |
| @item |
| A pragma used to configure the environment by adding, removing, or |
| replacing @cite{library_items}." |
| @end itemize |
| @end quotation |
| |
| See @ref{1c0,,RM 2.8(16); Pragmas}. |
| |
| @geindex Character Sets |
| |
| @geindex Alternative Character Sets |
| |
| @node RM 3 5 2 5 Alternative Character Sets,RM 3 5 4 28 Integer Types,RM 2 8 17-19 Pragmas,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-3-5-2-5-alternative-character-sets}@anchor{1c2} |
| @section RM 3.5.2(5): Alternative Character Sets |
| |
| |
| @quotation |
| |
| "If an implementation supports a mode with alternative interpretations |
| for @cite{Character} and @cite{Wide_Character}, the set of graphic |
| characters of @cite{Character} should nevertheless remain a proper |
| subset of the set of graphic characters of @cite{Wide_Character}. Any |
| character set 'localizations' should be reflected in the results of |
| the subprograms defined in the language-defined package |
| @cite{Characters.Handling} (see A.3) available in such a mode. In a mode with |
| an alternative interpretation of @cite{Character}, the implementation should |
| also support a corresponding change in what is a legal |
| @cite{identifier_letter}." |
| @end quotation |
| |
| Not all wide character modes follow this advice, in particular the JIS |
| and IEC modes reflect standard usage in Japan, and in these encoding, |
| the upper half of the Latin-1 set is not part of the wide-character |
| subset, since the most significant bit is used for wide character |
| encoding. However, this only applies to the external forms. Internally |
| there is no such restriction. |
| |
| @geindex Integer types |
| |
| @node RM 3 5 4 28 Integer Types,RM 3 5 4 29 Integer Types,RM 3 5 2 5 Alternative Character Sets,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-3-5-4-28-integer-types}@anchor{1c3} |
| @section RM 3.5.4(28): Integer Types |
| |
| |
| @quotation |
| |
| "An implementation should support @cite{Long_Integer} in addition to |
| @cite{Integer} if the target machine supports 32-bit (or longer) |
| arithmetic. No other named integer subtypes are recommended for package |
| @cite{Standard}. Instead, appropriate named integer subtypes should be |
| provided in the library package @cite{Interfaces} (see B.2)." |
| @end quotation |
| |
| @cite{Long_Integer} is supported. Other standard integer types are supported |
| so this advice is not fully followed. These types |
| are supported for convenient interface to C, and so that all hardware |
| types of the machine are easily available. |
| |
| @node RM 3 5 4 29 Integer Types,RM 3 5 5 8 Enumeration Values,RM 3 5 4 28 Integer Types,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-3-5-4-29-integer-types}@anchor{1c4} |
| @section RM 3.5.4(29): Integer Types |
| |
| |
| @quotation |
| |
| "An implementation for a two's complement machine should support |
| modular types with a binary modulus up to @code{System.Max_Int*2+2}. An |
| implementation should support a non-binary modules up to @cite{Integer'Last}." |
| @end quotation |
| |
| Followed. |
| |
| @geindex Enumeration values |
| |
| @node RM 3 5 5 8 Enumeration Values,RM 3 5 7 17 Float Types,RM 3 5 4 29 Integer Types,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-3-5-5-8-enumeration-values}@anchor{1c5} |
| @section RM 3.5.5(8): Enumeration Values |
| |
| |
| @quotation |
| |
| "For the evaluation of a call on @code{S'Pos} for an enumeration |
| subtype, if the value of the operand does not correspond to the internal |
| code for any enumeration literal of its type (perhaps due to an |
| un-initialized variable), then the implementation should raise |
| @cite{Program_Error}. This is particularly important for enumeration |
| types with noncontiguous internal codes specified by an |
| enumeration_representation_clause." |
| @end quotation |
| |
| Followed. |
| |
| @geindex Float types |
| |
| @node RM 3 5 7 17 Float Types,RM 3 6 2 11 Multidimensional Arrays,RM 3 5 5 8 Enumeration Values,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-3-5-7-17-float-types}@anchor{1c6} |
| @section RM 3.5.7(17): Float Types |
| |
| |
| @quotation |
| |
| "An implementation should support @cite{Long_Float} in addition to |
| @cite{Float} if the target machine supports 11 or more digits of |
| precision. No other named floating point subtypes are recommended for |
| package @cite{Standard}. Instead, appropriate named floating point subtypes |
| should be provided in the library package @cite{Interfaces} (see B.2)." |
| @end quotation |
| |
| @cite{Short_Float} and @cite{Long_Long_Float} are also provided. The |
| former provides improved compatibility with other implementations |
| supporting this type. The latter corresponds to the highest precision |
| floating-point type supported by the hardware. On most machines, this |
| will be the same as @cite{Long_Float}, but on some machines, it will |
| correspond to the IEEE extended form. The notable case is all ia32 |
| (x86) implementations, where @cite{Long_Long_Float} corresponds to |
| the 80-bit extended precision format supported in hardware on this |
| processor. Note that the 128-bit format on SPARC is not supported, |
| since this is a software rather than a hardware format. |
| |
| @geindex Multidimensional arrays |
| |
| @geindex Arrays |
| @geindex multidimensional |
| |
| @node RM 3 6 2 11 Multidimensional Arrays,RM 9 6 30-31 Duration'Small,RM 3 5 7 17 Float Types,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-3-6-2-11-multidimensional-arrays}@anchor{1c7} |
| @section RM 3.6.2(11): Multidimensional Arrays |
| |
| |
| @quotation |
| |
| "An implementation should normally represent multidimensional arrays in |
| row-major order, consistent with the notation used for multidimensional |
| array aggregates (see 4.3.3). However, if a pragma @cite{Convention} |
| (@cite{Fortran}, ...) applies to a multidimensional array type, then |
| column-major order should be used instead (see B.5, @cite{Interfacing with Fortran})." |
| @end quotation |
| |
| Followed. |
| |
| @geindex Duration'Small |
| |
| @node RM 9 6 30-31 Duration'Small,RM 10 2 1 12 Consistent Representation,RM 3 6 2 11 Multidimensional Arrays,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-9-6-30-31-duration-small}@anchor{1c8} |
| @section RM 9.6(30-31): Duration'Small |
| |
| |
| @quotation |
| |
| "Whenever possible in an implementation, the value of @cite{Duration'Small} |
| should be no greater than 100 microseconds." |
| @end quotation |
| |
| Followed. (@cite{Duration'Small} = 10**(-9)). |
| |
| @quotation |
| |
| "The time base for @cite{delay_relative_statements} should be monotonic; |
| it need not be the same time base as used for @cite{Calendar.Clock}." |
| @end quotation |
| |
| Followed. |
| |
| @node RM 10 2 1 12 Consistent Representation,RM 11 4 1 19 Exception Information,RM 9 6 30-31 Duration'Small,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-10-2-1-12-consistent-representation}@anchor{1c9} |
| @section RM 10.2.1(12): Consistent Representation |
| |
| |
| @quotation |
| |
| "In an implementation, a type declared in a pre-elaborated package should |
| have the same representation in every elaboration of a given version of |
| the package, whether the elaborations occur in distinct executions of |
| the same program, or in executions of distinct programs or partitions |
| that include the given version." |
| @end quotation |
| |
| Followed, except in the case of tagged types. Tagged types involve |
| implicit pointers to a local copy of a dispatch table, and these pointers |
| have representations which thus depend on a particular elaboration of the |
| package. It is not easy to see how it would be possible to follow this |
| advice without severely impacting efficiency of execution. |
| |
| @geindex Exception information |
| |
| @node RM 11 4 1 19 Exception Information,RM 11 5 28 Suppression of Checks,RM 10 2 1 12 Consistent Representation,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-11-4-1-19-exception-information}@anchor{1ca} |
| @section RM 11.4.1(19): Exception Information |
| |
| |
| @quotation |
| |
| "@cite{Exception_Message} by default and @cite{Exception_Information} |
| should produce information useful for |
| debugging. @cite{Exception_Message} should be short, about one |
| line. @cite{Exception_Information} can be long. @cite{Exception_Message} |
| should not include the |
| @cite{Exception_Name}. @cite{Exception_Information} should include both |
| the @cite{Exception_Name} and the @cite{Exception_Message}." |
| @end quotation |
| |
| Followed. For each exception that doesn't have a specified |
| @cite{Exception_Message}, the compiler generates one containing the location |
| of the raise statement. This location has the form 'file_name:line', where |
| file_name is the short file name (without path information) and line is the line |
| number in the file. Note that in the case of the Zero Cost Exception |
| mechanism, these messages become redundant with the Exception_Information that |
| contains a full backtrace of the calling sequence, so they are disabled. |
| To disable explicitly the generation of the source location message, use the |
| Pragma @cite{Discard_Names}. |
| |
| @geindex Suppression of checks |
| |
| @geindex Checks |
| @geindex suppression of |
| |
| @node RM 11 5 28 Suppression of Checks,RM 13 1 21-24 Representation Clauses,RM 11 4 1 19 Exception Information,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-11-5-28-suppression-of-checks}@anchor{1cb} |
| @section RM 11.5(28): Suppression of Checks |
| |
| |
| @quotation |
| |
| "The implementation should minimize the code executed for checks that |
| have been suppressed." |
| @end quotation |
| |
| Followed. |
| |
| @geindex Representation clauses |
| |
| @node RM 13 1 21-24 Representation Clauses,RM 13 2 6-8 Packed Types,RM 11 5 28 Suppression of Checks,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-13-1-21-24-representation-clauses}@anchor{1cc} |
| @section RM 13.1 (21-24): Representation Clauses |
| |
| |
| @quotation |
| |
| "The recommended level of support for all representation items is |
| qualified as follows: |
| |
| An implementation need not support representation items containing |
| non-static expressions, except that an implementation should support a |
| representation item for a given entity if each non-static expression in |
| the representation item is a name that statically denotes a constant |
| declared before the entity." |
| @end quotation |
| |
| Followed. In fact, GNAT goes beyond the recommended level of support |
| by allowing nonstatic expressions in some representation clauses even |
| without the need to declare constants initialized with the values of |
| such expressions. |
| For example: |
| |
| @example |
| X : Integer; |
| Y : Float; |
| for Y'Address use X'Address;>> |
| |
| |
| "An implementation need not support a specification for the `Size` |
| for a given composite subtype, nor the size or storage place for an |
| object (including a component) of a given composite subtype, unless the |
| constraints on the subtype and its composite subcomponents (if any) are |
| all static constraints." |
| @end example |
| |
| Followed. Size Clauses are not permitted on non-static components, as |
| described above. |
| |
| @quotation |
| |
| "An aliased component, or a component whose type is by-reference, should |
| always be allocated at an addressable location." |
| @end quotation |
| |
| Followed. |
| |
| @geindex Packed types |
| |
| @node RM 13 2 6-8 Packed Types,RM 13 3 14-19 Address Clauses,RM 13 1 21-24 Representation Clauses,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-13-2-6-8-packed-types}@anchor{1cd} |
| @section RM 13.2(6-8): Packed Types |
| |
| |
| @quotation |
| |
| "If a type is packed, then the implementation should try to minimize |
| storage allocated to objects of the type, possibly at the expense of |
| speed of accessing components, subject to reasonable complexity in |
| addressing calculations. |
| |
| The recommended level of support pragma @cite{Pack} is: |
| |
| For a packed record type, the components should be packed as tightly as |
| possible subject to the Sizes of the component subtypes, and subject to |
| any @cite{record_representation_clause} that applies to the type; the |
| implementation may, but need not, reorder components or cross aligned |
| word boundaries to improve the packing. A component whose @cite{Size} is |
| greater than the word size may be allocated an integral number of words." |
| @end quotation |
| |
| Followed. Tight packing of arrays is supported for all component sizes |
| up to 64-bits. If the array component size is 1 (that is to say, if |
| the component is a boolean type or an enumeration type with two values) |
| then values of the type are implicitly initialized to zero. This |
| happens both for objects of the packed type, and for objects that have a |
| subcomponent of the packed type. |
| |
| @quotation |
| |
| "An implementation should support Address clauses for imported |
| subprograms." |
| @end quotation |
| |
| Followed. |
| |
| @geindex Address clauses |
| |
| @node RM 13 3 14-19 Address Clauses,RM 13 3 29-35 Alignment Clauses,RM 13 2 6-8 Packed Types,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-13-3-14-19-address-clauses}@anchor{1ce} |
| @section RM 13.3(14-19): Address Clauses |
| |
| |
| @quotation |
| |
| "For an array @cite{X}, @code{X'Address} should point at the first |
| component of the array, and not at the array bounds." |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "The recommended level of support for the @cite{Address} attribute is: |
| |
| @code{X'Address} should produce a useful result if @cite{X} is an |
| object that is aliased or of a by-reference type, or is an entity whose |
| @cite{Address} has been specified." |
| @end quotation |
| |
| Followed. A valid address will be produced even if none of those |
| conditions have been met. If necessary, the object is forced into |
| memory to ensure the address is valid. |
| |
| @quotation |
| |
| "An implementation should support @cite{Address} clauses for imported |
| subprograms." |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "Objects (including subcomponents) that are aliased or of a by-reference |
| type should be allocated on storage element boundaries." |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "If the @cite{Address} of an object is specified, or it is imported or exported, |
| then the implementation should not perform optimizations based on |
| assumptions of no aliases." |
| @end quotation |
| |
| Followed. |
| |
| @geindex Alignment clauses |
| |
| @node RM 13 3 29-35 Alignment Clauses,RM 13 3 42-43 Size Clauses,RM 13 3 14-19 Address Clauses,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-13-3-29-35-alignment-clauses}@anchor{1cf} |
| @section RM 13.3(29-35): Alignment Clauses |
| |
| |
| @quotation |
| |
| "The recommended level of support for the @cite{Alignment} attribute for |
| subtypes is: |
| |
| An implementation should support specified Alignments that are factors |
| and multiples of the number of storage elements per word, subject to the |
| following:" |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "An implementation need not support specified Alignments for |
| combinations of Sizes and Alignments that cannot be easily |
| loaded and stored by available machine instructions." |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "An implementation need not support specified Alignments that are |
| greater than the maximum @cite{Alignment} the implementation ever returns by |
| default." |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "The recommended level of support for the @cite{Alignment} attribute for |
| objects is: |
| |
| Same as above, for subtypes, but in addition:" |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "For stand-alone library-level objects of statically constrained |
| subtypes, the implementation should support all alignments |
| supported by the target linker. For example, page alignment is likely to |
| be supported for such objects, but not for subtypes." |
| @end quotation |
| |
| Followed. |
| |
| @geindex Size clauses |
| |
| @node RM 13 3 42-43 Size Clauses,RM 13 3 50-56 Size Clauses,RM 13 3 29-35 Alignment Clauses,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-13-3-42-43-size-clauses}@anchor{1d0} |
| @section RM 13.3(42-43): Size Clauses |
| |
| |
| @quotation |
| |
| "The recommended level of support for the @cite{Size} attribute of |
| objects is: |
| |
| A @cite{Size} clause should be supported for an object if the specified |
| @cite{Size} is at least as large as its subtype's @cite{Size}, and |
| corresponds to a size in storage elements that is a multiple of the |
| object's @cite{Alignment} (if the @cite{Alignment} is nonzero)." |
| @end quotation |
| |
| Followed. |
| |
| @node RM 13 3 50-56 Size Clauses,RM 13 3 71-73 Component Size Clauses,RM 13 3 42-43 Size Clauses,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-13-3-50-56-size-clauses}@anchor{1d1} |
| @section RM 13.3(50-56): Size Clauses |
| |
| |
| @quotation |
| |
| "If the @cite{Size} of a subtype is specified, and allows for efficient |
| independent addressability (see 9.10) on the target architecture, then |
| the @cite{Size} of the following objects of the subtype should equal the |
| @cite{Size} of the subtype: |
| |
| Aliased objects (including components)." |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "@cite{Size} clause on a composite subtype should not affect the |
| internal layout of components." |
| @end quotation |
| |
| Followed. But note that this can be overridden by use of the implementation |
| pragma Implicit_Packing in the case of packed arrays. |
| |
| @quotation |
| |
| "The recommended level of support for the @cite{Size} attribute of subtypes is: |
| |
| The @cite{Size} (if not specified) of a static discrete or fixed point |
| subtype should be the number of bits needed to represent each value |
| belonging to the subtype using an unbiased representation, leaving space |
| for a sign bit only if the subtype contains negative values. If such a |
| subtype is a first subtype, then an implementation should support a |
| specified @cite{Size} for it that reflects this representation." |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "For a subtype implemented with levels of indirection, the @cite{Size} |
| should include the size of the pointers, but not the size of what they |
| point at." |
| @end quotation |
| |
| Followed. |
| |
| @geindex Component_Size clauses |
| |
| @node RM 13 3 71-73 Component Size Clauses,RM 13 4 9-10 Enumeration Representation Clauses,RM 13 3 50-56 Size Clauses,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-13-3-71-73-component-size-clauses}@anchor{1d2} |
| @section RM 13.3(71-73): Component Size Clauses |
| |
| |
| @quotation |
| |
| "The recommended level of support for the @cite{Component_Size} |
| attribute is: |
| |
| An implementation need not support specified @cite{Component_Sizes} that are |
| less than the @cite{Size} of the component subtype." |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "An implementation should support specified Component_Sizes that |
| are factors and multiples of the word size. For such |
| Component_Sizes, the array should contain no gaps between |
| components. For other Component_Sizes (if supported), the array |
| should contain no gaps between components when packing is also |
| specified; the implementation should forbid this combination in cases |
| where it cannot support a no-gaps representation." |
| @end quotation |
| |
| Followed. |
| |
| @geindex Enumeration representation clauses |
| |
| @geindex Representation clauses |
| @geindex enumeration |
| |
| @node RM 13 4 9-10 Enumeration Representation Clauses,RM 13 5 1 17-22 Record Representation Clauses,RM 13 3 71-73 Component Size Clauses,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-13-4-9-10-enumeration-representation-clauses}@anchor{1d3} |
| @section RM 13.4(9-10): Enumeration Representation Clauses |
| |
| |
| @quotation |
| |
| "The recommended level of support for enumeration representation clauses |
| is: |
| |
| An implementation need not support enumeration representation clauses |
| for boolean types, but should at minimum support the internal codes in |
| the range @cite{System.Min_Int .. System.Max_Int}." |
| @end quotation |
| |
| Followed. |
| |
| @geindex Record representation clauses |
| |
| @geindex Representation clauses |
| @geindex records |
| |
| @node RM 13 5 1 17-22 Record Representation Clauses,RM 13 5 2 5 Storage Place Attributes,RM 13 4 9-10 Enumeration Representation Clauses,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-13-5-1-17-22-record-representation-clauses}@anchor{1d4} |
| @section RM 13.5.1(17-22): Record Representation Clauses |
| |
| |
| @quotation |
| |
| "The recommended level of support for |
| @cite{record_representation_clauses} is: |
| |
| An implementation should support storage places that can be extracted |
| with a load, mask, shift sequence of machine code, and set with a load, |
| shift, mask, store sequence, given the available machine instructions |
| and run-time model." |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "A storage place should be supported if its size is equal to the |
| @cite{Size} of the component subtype, and it starts and ends on a |
| boundary that obeys the @cite{Alignment} of the component subtype." |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "If the default bit ordering applies to the declaration of a given type, |
| then for a component whose subtype's @cite{Size} is less than the word |
| size, any storage place that does not cross an aligned word boundary |
| should be supported." |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "An implementation may reserve a storage place for the tag field of a |
| tagged type, and disallow other components from overlapping that place." |
| @end quotation |
| |
| Followed. The storage place for the tag field is the beginning of the tagged |
| record, and its size is Address'Size. GNAT will reject an explicit component |
| clause for the tag field. |
| |
| @quotation |
| |
| "An implementation need not support a @cite{component_clause} for a |
| component of an extension part if the storage place is not after the |
| storage places of all components of the parent type, whether or not |
| those storage places had been specified." |
| @end quotation |
| |
| Followed. The above advice on record representation clauses is followed, |
| and all mentioned features are implemented. |
| |
| @geindex Storage place attributes |
| |
| @node RM 13 5 2 5 Storage Place Attributes,RM 13 5 3 7-8 Bit Ordering,RM 13 5 1 17-22 Record Representation Clauses,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-13-5-2-5-storage-place-attributes}@anchor{1d5} |
| @section RM 13.5.2(5): Storage Place Attributes |
| |
| |
| @quotation |
| |
| "If a component is represented using some form of pointer (such as an |
| offset) to the actual data of the component, and this data is contiguous |
| with the rest of the object, then the storage place attributes should |
| reflect the place of the actual data, not the pointer. If a component is |
| allocated discontinuously from the rest of the object, then a warning |
| should be generated upon reference to one of its storage place |
| attributes." |
| @end quotation |
| |
| Followed. There are no such components in GNAT. |
| |
| @geindex Bit ordering |
| |
| @node RM 13 5 3 7-8 Bit Ordering,RM 13 7 37 Address as Private,RM 13 5 2 5 Storage Place Attributes,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-13-5-3-7-8-bit-ordering}@anchor{1d6} |
| @section RM 13.5.3(7-8): Bit Ordering |
| |
| |
| @quotation |
| |
| "The recommended level of support for the non-default bit ordering is: |
| |
| If @cite{Word_Size} = @cite{Storage_Unit}, then the implementation |
| should support the non-default bit ordering in addition to the default |
| bit ordering." |
| @end quotation |
| |
| Followed. Word size does not equal storage size in this implementation. |
| Thus non-default bit ordering is not supported. |
| |
| @geindex Address |
| @geindex as private type |
| |
| @node RM 13 7 37 Address as Private,RM 13 7 1 16 Address Operations,RM 13 5 3 7-8 Bit Ordering,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-13-7-37-address-as-private}@anchor{1d7} |
| @section RM 13.7(37): Address as Private |
| |
| |
| @quotation |
| |
| "@cite{Address} should be of a private type." |
| @end quotation |
| |
| Followed. |
| |
| @geindex Operations |
| @geindex on `Address` |
| |
| @geindex Address |
| @geindex operations of |
| |
| @node RM 13 7 1 16 Address Operations,RM 13 9 14-17 Unchecked Conversion,RM 13 7 37 Address as Private,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-13-7-1-16-address-operations}@anchor{1d8} |
| @section RM 13.7.1(16): Address Operations |
| |
| |
| @quotation |
| |
| "Operations in @cite{System} and its children should reflect the target |
| environment semantics as closely as is reasonable. For example, on most |
| machines, it makes sense for address arithmetic to 'wrap around'. |
| Operations that do not make sense should raise @cite{Program_Error}." |
| @end quotation |
| |
| Followed. Address arithmetic is modular arithmetic that wraps around. No |
| operation raises @cite{Program_Error}, since all operations make sense. |
| |
| @geindex Unchecked conversion |
| |
| @node RM 13 9 14-17 Unchecked Conversion,RM 13 11 23-25 Implicit Heap Usage,RM 13 7 1 16 Address Operations,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-13-9-14-17-unchecked-conversion}@anchor{1d9} |
| @section RM 13.9(14-17): Unchecked Conversion |
| |
| |
| @quotation |
| |
| "The @cite{Size} of an array object should not include its bounds; hence, |
| the bounds should not be part of the converted data." |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "The implementation should not generate unnecessary run-time checks to |
| ensure that the representation of @cite{S} is a representation of the |
| target type. It should take advantage of the permission to return by |
| reference when possible. Restrictions on unchecked conversions should be |
| avoided unless required by the target environment." |
| @end quotation |
| |
| Followed. There are no restrictions on unchecked conversion. A warning is |
| generated if the source and target types do not have the same size since |
| the semantics in this case may be target dependent. |
| |
| @quotation |
| |
| "The recommended level of support for unchecked conversions is: |
| |
| Unchecked conversions should be supported and should be reversible in |
| the cases where this clause defines the result. To enable meaningful use |
| of unchecked conversion, a contiguous representation should be used for |
| elementary subtypes, for statically constrained array subtypes whose |
| component subtype is one of the subtypes described in this paragraph, |
| and for record subtypes without discriminants whose component subtypes |
| are described in this paragraph." |
| @end quotation |
| |
| Followed. |
| |
| @geindex Heap usage |
| @geindex implicit |
| |
| @node RM 13 11 23-25 Implicit Heap Usage,RM 13 11 2 17 Unchecked Deallocation,RM 13 9 14-17 Unchecked Conversion,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-13-11-23-25-implicit-heap-usage}@anchor{1da} |
| @section RM 13.11(23-25): Implicit Heap Usage |
| |
| |
| @quotation |
| |
| "An implementation should document any cases in which it dynamically |
| allocates heap storage for a purpose other than the evaluation of an |
| allocator." |
| @end quotation |
| |
| Followed, the only other points at which heap storage is dynamically |
| allocated are as follows: |
| |
| |
| @itemize * |
| |
| @item |
| At initial elaboration time, to allocate dynamically sized global |
| objects. |
| |
| @item |
| To allocate space for a task when a task is created. |
| |
| @item |
| To extend the secondary stack dynamically when needed. The secondary |
| stack is used for returning variable length results. |
| @end itemize |
| |
| |
| @quotation |
| |
| "A default (implementation-provided) storage pool for an |
| access-to-constant type should not have overhead to support deallocation of |
| individual objects." |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "A storage pool for an anonymous access type should be created at the |
| point of an allocator for the type, and be reclaimed when the designated |
| object becomes inaccessible." |
| @end quotation |
| |
| Followed. |
| |
| @geindex Unchecked deallocation |
| |
| @node RM 13 11 2 17 Unchecked Deallocation,RM 13 13 2 17 Stream Oriented Attributes,RM 13 11 23-25 Implicit Heap Usage,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-13-11-2-17-unchecked-deallocation}@anchor{1db} |
| @section RM 13.11.2(17): Unchecked Deallocation |
| |
| |
| @quotation |
| |
| "For a standard storage pool, @cite{Free} should actually reclaim the |
| storage." |
| @end quotation |
| |
| Followed. |
| |
| @geindex Stream oriented attributes |
| |
| @node RM 13 13 2 17 Stream Oriented Attributes,RM A 1 52 Names of Predefined Numeric Types,RM 13 11 2 17 Unchecked Deallocation,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-13-13-2-17-stream-oriented-attributes}@anchor{1dc} |
| @section RM 13.13.2(17): Stream Oriented Attributes |
| |
| |
| @quotation |
| |
| "If a stream element is the same size as a storage element, then the |
| normal in-memory representation should be used by @cite{Read} and |
| @cite{Write} for scalar objects. Otherwise, @cite{Read} and @cite{Write} |
| should use the smallest number of stream elements needed to represent |
| all values in the base range of the scalar type." |
| @end quotation |
| |
| Followed. By default, GNAT uses the interpretation suggested by AI-195, |
| which specifies using the size of the first subtype. |
| However, such an implementation is based on direct binary |
| representations and is therefore target- and endianness-dependent. |
| To address this issue, GNAT also supplies an alternate implementation |
| of the stream attributes @cite{Read} and @cite{Write}, |
| which uses the target-independent XDR standard representation |
| for scalar types. |
| |
| @geindex XDR representation |
| |
| @geindex Read attribute |
| |
| @geindex Write attribute |
| |
| @geindex Stream oriented attributes |
| |
| The XDR implementation is provided as an alternative body of the |
| @cite{System.Stream_Attributes} package, in the file |
| @code{s-stratt-xdr.adb} in the GNAT library. |
| There is no @code{s-stratt-xdr.ads} file. |
| In order to install the XDR implementation, do the following: |
| |
| |
| @itemize * |
| |
| @item |
| Replace the default implementation of the |
| @cite{System.Stream_Attributes} package with the XDR implementation. |
| For example on a Unix platform issue the commands: |
| |
| @example |
| $ mv s-stratt.adb s-stratt-default.adb |
| $ mv s-stratt-xdr.adb s-stratt.adb |
| @end example |
| |
| @item |
| Rebuild the GNAT run-time library as documented in |
| the @cite{GNAT and Libraries} section of the @cite{GNAT User's Guide}. |
| @end itemize |
| |
| @node RM A 1 52 Names of Predefined Numeric Types,RM A 3 2 49 Ada Characters Handling,RM 13 13 2 17 Stream Oriented Attributes,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-a-1-52-names-of-predefined-numeric-types}@anchor{1dd} |
| @section RM A.1(52): Names of Predefined Numeric Types |
| |
| |
| @quotation |
| |
| "If an implementation provides additional named predefined integer types, |
| then the names should end with @code{Integer} as in |
| @code{Long_Integer}. If an implementation provides additional named |
| predefined floating point types, then the names should end with |
| @code{Float} as in @code{Long_Float}." |
| @end quotation |
| |
| Followed. |
| |
| @geindex Ada.Characters.Handling |
| |
| @node RM A 3 2 49 Ada Characters Handling,RM A 4 4 106 Bounded-Length String Handling,RM A 1 52 Names of Predefined Numeric Types,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-a-3-2-49-ada-characters-handling}@anchor{1de} |
| @section RM A.3.2(49): @cite{Ada.Characters.Handling} |
| |
| |
| @quotation |
| |
| "If an implementation provides a localized definition of @cite{Character} |
| or @cite{Wide_Character}, then the effects of the subprograms in |
| @cite{Characters.Handling} should reflect the localizations. |
| See also 3.5.2." |
| @end quotation |
| |
| Followed. GNAT provides no such localized definitions. |
| |
| @geindex Bounded-length strings |
| |
| @node RM A 4 4 106 Bounded-Length String Handling,RM A 5 2 46-47 Random Number Generation,RM A 3 2 49 Ada Characters Handling,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-a-4-4-106-bounded-length-string-handling}@anchor{1df} |
| @section RM A.4.4(106): Bounded-Length String Handling |
| |
| |
| @quotation |
| |
| "Bounded string objects should not be implemented by implicit pointers |
| and dynamic allocation." |
| @end quotation |
| |
| Followed. No implicit pointers or dynamic allocation are used. |
| |
| @geindex Random number generation |
| |
| @node RM A 5 2 46-47 Random Number Generation,RM A 10 7 23 Get_Immediate,RM A 4 4 106 Bounded-Length String Handling,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-a-5-2-46-47-random-number-generation}@anchor{1e0} |
| @section RM A.5.2(46-47): Random Number Generation |
| |
| |
| @quotation |
| |
| "Any storage associated with an object of type @cite{Generator} should be |
| reclaimed on exit from the scope of the object." |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "If the generator period is sufficiently long in relation to the number |
| of distinct initiator values, then each possible value of |
| @cite{Initiator} passed to @cite{Reset} should initiate a sequence of |
| random numbers that does not, in a practical sense, overlap the sequence |
| initiated by any other value. If this is not possible, then the mapping |
| between initiator values and generator states should be a rapidly |
| varying function of the initiator value." |
| @end quotation |
| |
| Followed. The generator period is sufficiently long for the first |
| condition here to hold true. |
| |
| @geindex Get_Immediate |
| |
| @node RM A 10 7 23 Get_Immediate,RM B 1 39-41 Pragma Export,RM A 5 2 46-47 Random Number Generation,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-a-10-7-23-get-immediate}@anchor{1e1} |
| @section RM A.10.7(23): @cite{Get_Immediate} |
| |
| |
| @quotation |
| |
| "The @cite{Get_Immediate} procedures should be implemented with |
| unbuffered input. For a device such as a keyboard, input should be |
| available if a key has already been typed, whereas for a disk |
| file, input should always be available except at end of file. For a file |
| associated with a keyboard-like device, any line-editing features of the |
| underlying operating system should be disabled during the execution of |
| @cite{Get_Immediate}." |
| @end quotation |
| |
| Followed on all targets except VxWorks. For VxWorks, there is no way to |
| provide this functionality that does not result in the input buffer being |
| flushed before the @cite{Get_Immediate} call. A special unit |
| @cite{Interfaces.Vxworks.IO} is provided that contains routines to enable |
| this functionality. |
| |
| @geindex Export |
| |
| @node RM B 1 39-41 Pragma Export,RM B 2 12-13 Package Interfaces,RM A 10 7 23 Get_Immediate,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-b-1-39-41-pragma-export}@anchor{1e2} |
| @section RM B.1(39-41): Pragma @cite{Export} |
| |
| |
| @quotation |
| |
| "If an implementation supports pragma @cite{Export} to a given language, |
| then it should also allow the main subprogram to be written in that |
| language. It should support some mechanism for invoking the elaboration |
| of the Ada library units included in the system, and for invoking the |
| finalization of the environment task. On typical systems, the |
| recommended mechanism is to provide two subprograms whose link names are |
| @cite{adainit} and @cite{adafinal}. @cite{adainit} should contain the |
| elaboration code for library units. @cite{adafinal} should contain the |
| finalization code. These subprograms should have no effect the second |
| and subsequent time they are called." |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "Automatic elaboration of pre-elaborated packages should be |
| provided when pragma @cite{Export} is supported." |
| @end quotation |
| |
| Followed when the main program is in Ada. If the main program is in a |
| foreign language, then |
| @cite{adainit} must be called to elaborate pre-elaborated |
| packages. |
| |
| @quotation |
| |
| "For each supported convention @cite{L} other than @cite{Intrinsic}, an |
| implementation should support @cite{Import} and @cite{Export} pragmas |
| for objects of @cite{L}-compatible types and for subprograms, and pragma |
| @cite{Convention} for @cite{L}-eligible types and for subprograms, |
| presuming the other language has corresponding features. Pragma |
| @cite{Convention} need not be supported for scalar types." |
| @end quotation |
| |
| Followed. |
| |
| @geindex Package Interfaces |
| |
| @geindex Interfaces |
| |
| @node RM B 2 12-13 Package Interfaces,RM B 3 63-71 Interfacing with C,RM B 1 39-41 Pragma Export,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-b-2-12-13-package-interfaces}@anchor{1e3} |
| @section RM B.2(12-13): Package @cite{Interfaces} |
| |
| |
| @quotation |
| |
| "For each implementation-defined convention identifier, there should be a |
| child package of package Interfaces with the corresponding name. This |
| package should contain any declarations that would be useful for |
| interfacing to the language (implementation) represented by the |
| convention. Any declarations useful for interfacing to any language on |
| the given hardware architecture should be provided directly in |
| @cite{Interfaces}." |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "An implementation supporting an interface to C, COBOL, or Fortran should |
| provide the corresponding package or packages described in the following |
| clauses." |
| @end quotation |
| |
| Followed. GNAT provides all the packages described in this section. |
| |
| @geindex C |
| @geindex interfacing with |
| |
| @node RM B 3 63-71 Interfacing with C,RM B 4 95-98 Interfacing with COBOL,RM B 2 12-13 Package Interfaces,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-b-3-63-71-interfacing-with-c}@anchor{1e4} |
| @section RM B.3(63-71): Interfacing with C |
| |
| |
| @quotation |
| |
| "An implementation should support the following interface correspondences |
| between Ada and C." |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "An Ada procedure corresponds to a void-returning C function." |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "An Ada function corresponds to a non-void C function." |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "An Ada @cite{in} scalar parameter is passed as a scalar argument to a C |
| function." |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "An Ada @cite{in} parameter of an access-to-object type with designated |
| type @cite{T} is passed as a @code{t*} argument to a C function, |
| where @code{t} is the C type corresponding to the Ada type @cite{T}." |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "An Ada access @cite{T} parameter, or an Ada @cite{out} or @cite{in out} |
| parameter of an elementary type @cite{T}, is passed as a @code{t*} |
| argument to a C function, where @code{t} is the C type corresponding to |
| the Ada type @cite{T}. In the case of an elementary @cite{out} or |
| @cite{in out} parameter, a pointer to a temporary copy is used to |
| preserve by-copy semantics." |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "An Ada parameter of a record type @cite{T}, of any mode, is passed as a |
| @code{t*} argument to a C function, where @code{t} is the C |
| structure corresponding to the Ada type @cite{T}." |
| @end quotation |
| |
| Followed. This convention may be overridden by the use of the C_Pass_By_Copy |
| pragma, or Convention, or by explicitly specifying the mechanism for a given |
| call using an extended import or export pragma. |
| |
| @quotation |
| |
| "An Ada parameter of an array type with component type @cite{T}, of any |
| mode, is passed as a @code{t*} argument to a C function, where |
| @code{t} is the C type corresponding to the Ada type @cite{T}." |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "An Ada parameter of an access-to-subprogram type is passed as a pointer |
| to a C function whose prototype corresponds to the designated |
| subprogram's specification." |
| @end quotation |
| |
| Followed. |
| |
| @geindex COBOL |
| @geindex interfacing with |
| |
| @node RM B 4 95-98 Interfacing with COBOL,RM B 5 22-26 Interfacing with Fortran,RM B 3 63-71 Interfacing with C,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-b-4-95-98-interfacing-with-cobol}@anchor{1e5} |
| @section RM B.4(95-98): Interfacing with COBOL |
| |
| |
| @quotation |
| |
| "An Ada implementation should support the following interface |
| correspondences between Ada and COBOL." |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "An Ada access @cite{T} parameter is passed as a @code{BY REFERENCE} data item of |
| the COBOL type corresponding to @cite{T}." |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "An Ada in scalar parameter is passed as a @code{BY CONTENT} data item of |
| the corresponding COBOL type." |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "Any other Ada parameter is passed as a @code{BY REFERENCE} data item of the |
| COBOL type corresponding to the Ada parameter type; for scalars, a local |
| copy is used if necessary to ensure by-copy semantics." |
| @end quotation |
| |
| Followed. |
| |
| @geindex Fortran |
| @geindex interfacing with |
| |
| @node RM B 5 22-26 Interfacing with Fortran,RM C 1 3-5 Access to Machine Operations,RM B 4 95-98 Interfacing with COBOL,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-b-5-22-26-interfacing-with-fortran}@anchor{1e6} |
| @section RM B.5(22-26): Interfacing with Fortran |
| |
| |
| @quotation |
| |
| "An Ada implementation should support the following interface |
| correspondences between Ada and Fortran:" |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "An Ada procedure corresponds to a Fortran subroutine." |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "An Ada function corresponds to a Fortran function." |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "An Ada parameter of an elementary, array, or record type @cite{T} is |
| passed as a @cite{T} argument to a Fortran procedure, where @cite{T} is |
| the Fortran type corresponding to the Ada type @cite{T}, and where the |
| INTENT attribute of the corresponding dummy argument matches the Ada |
| formal parameter mode; the Fortran implementation's parameter passing |
| conventions are used. For elementary types, a local copy is used if |
| necessary to ensure by-copy semantics." |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "An Ada parameter of an access-to-subprogram type is passed as a |
| reference to a Fortran procedure whose interface corresponds to the |
| designated subprogram's specification." |
| @end quotation |
| |
| Followed. |
| |
| @geindex Machine operations |
| |
| @node RM C 1 3-5 Access to Machine Operations,RM C 1 10-16 Access to Machine Operations,RM B 5 22-26 Interfacing with Fortran,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-c-1-3-5-access-to-machine-operations}@anchor{1e7} |
| @section RM C.1(3-5): Access to Machine Operations |
| |
| |
| @quotation |
| |
| "The machine code or intrinsic support should allow access to all |
| operations normally available to assembly language programmers for the |
| target environment, including privileged instructions, if any." |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "The interfacing pragmas (see Annex B) should support interface to |
| assembler; the default assembler should be associated with the |
| convention identifier @cite{Assembler}." |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "If an entity is exported to assembly language, then the implementation |
| should allocate it at an addressable location, and should ensure that it |
| is retained by the linking process, even if not otherwise referenced |
| from the Ada code. The implementation should assume that any call to a |
| machine code or assembler subprogram is allowed to read or update every |
| object that is specified as exported." |
| @end quotation |
| |
| Followed. |
| |
| @node RM C 1 10-16 Access to Machine Operations,RM C 3 28 Interrupt Support,RM C 1 3-5 Access to Machine Operations,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-c-1-10-16-access-to-machine-operations}@anchor{1e8} |
| @section RM C.1(10-16): Access to Machine Operations |
| |
| |
| @quotation |
| |
| "The implementation should ensure that little or no overhead is |
| associated with calling intrinsic and machine-code subprograms." |
| @end quotation |
| |
| Followed for both intrinsics and machine-code subprograms. |
| |
| @quotation |
| |
| "It is recommended that intrinsic subprograms be provided for convenient |
| access to any machine operations that provide special capabilities or |
| efficiency and that are not otherwise available through the language |
| constructs." |
| @end quotation |
| |
| Followed. A full set of machine operation intrinsic subprograms is provided. |
| |
| @quotation |
| |
| "Atomic read-modify-write operations---e.g., test and set, compare and |
| swap, decrement and test, enqueue/dequeue." |
| @end quotation |
| |
| Followed on any target supporting such operations. |
| |
| @quotation |
| |
| "Standard numeric functions---e.g.:, sin, log." |
| @end quotation |
| |
| Followed on any target supporting such operations. |
| |
| @quotation |
| |
| "String manipulation operations---e.g.:, translate and test." |
| @end quotation |
| |
| Followed on any target supporting such operations. |
| |
| @quotation |
| |
| "Vector operations---e.g.:, compare vector against thresholds." |
| @end quotation |
| |
| Followed on any target supporting such operations. |
| |
| @quotation |
| |
| "Direct operations on I/O ports." |
| @end quotation |
| |
| Followed on any target supporting such operations. |
| |
| @geindex Interrupt support |
| |
| @node RM C 3 28 Interrupt Support,RM C 3 1 20-21 Protected Procedure Handlers,RM C 1 10-16 Access to Machine Operations,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-c-3-28-interrupt-support}@anchor{1e9} |
| @section RM C.3(28): Interrupt Support |
| |
| |
| @quotation |
| |
| "If the @cite{Ceiling_Locking} policy is not in effect, the |
| implementation should provide means for the application to specify which |
| interrupts are to be blocked during protected actions, if the underlying |
| system allows for a finer-grain control of interrupt blocking." |
| @end quotation |
| |
| Followed. The underlying system does not allow for finer-grain control |
| of interrupt blocking. |
| |
| @geindex Protected procedure handlers |
| |
| @node RM C 3 1 20-21 Protected Procedure Handlers,RM C 3 2 25 Package Interrupts,RM C 3 28 Interrupt Support,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-c-3-1-20-21-protected-procedure-handlers}@anchor{1ea} |
| @section RM C.3.1(20-21): Protected Procedure Handlers |
| |
| |
| @quotation |
| |
| "Whenever possible, the implementation should allow interrupt handlers to |
| be called directly by the hardware." |
| @end quotation |
| |
| Followed on any target where the underlying operating system permits |
| such direct calls. |
| |
| @quotation |
| |
| "Whenever practical, violations of any |
| implementation-defined restrictions should be detected before run time." |
| @end quotation |
| |
| Followed. Compile time warnings are given when possible. |
| |
| @geindex Package `Interrupts` |
| |
| @geindex Interrupts |
| |
| @node RM C 3 2 25 Package Interrupts,RM C 4 14 Pre-elaboration Requirements,RM C 3 1 20-21 Protected Procedure Handlers,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-c-3-2-25-package-interrupts}@anchor{1eb} |
| @section RM C.3.2(25): Package @cite{Interrupts} |
| |
| |
| @quotation |
| |
| "If implementation-defined forms of interrupt handler procedures are |
| supported, such as protected procedures with parameters, then for each |
| such form of a handler, a type analogous to @cite{Parameterless_Handler} |
| should be specified in a child package of @cite{Interrupts}, with the |
| same operations as in the predefined package Interrupts." |
| @end quotation |
| |
| Followed. |
| |
| @geindex Pre-elaboration requirements |
| |
| @node RM C 4 14 Pre-elaboration Requirements,RM C 5 8 Pragma Discard_Names,RM C 3 2 25 Package Interrupts,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-c-4-14-pre-elaboration-requirements}@anchor{1ec} |
| @section RM C.4(14): Pre-elaboration Requirements |
| |
| |
| @quotation |
| |
| "It is recommended that pre-elaborated packages be implemented in such a |
| way that there should be little or no code executed at run time for the |
| elaboration of entities not already covered by the Implementation |
| Requirements." |
| @end quotation |
| |
| Followed. Executable code is generated in some cases, e.g., loops |
| to initialize large arrays. |
| |
| @node RM C 5 8 Pragma Discard_Names,RM C 7 2 30 The Package Task_Attributes,RM C 4 14 Pre-elaboration Requirements,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-c-5-8-pragma-discard-names}@anchor{1ed} |
| @section RM C.5(8): Pragma @cite{Discard_Names} |
| |
| |
| @quotation |
| |
| "If the pragma applies to an entity, then the implementation should |
| reduce the amount of storage used for storing names associated with that |
| entity." |
| @end quotation |
| |
| Followed. |
| |
| @geindex Package Task_Attributes |
| |
| @geindex Task_Attributes |
| |
| @node RM C 7 2 30 The Package Task_Attributes,RM D 3 17 Locking Policies,RM C 5 8 Pragma Discard_Names,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-c-7-2-30-the-package-task-attributes}@anchor{1ee} |
| @section RM C.7.2(30): The Package Task_Attributes |
| |
| |
| @quotation |
| |
| "Some implementations are targeted to domains in which memory use at run |
| time must be completely deterministic. For such implementations, it is |
| recommended that the storage for task attributes will be pre-allocated |
| statically and not from the heap. This can be accomplished by either |
| placing restrictions on the number and the size of the task's |
| attributes, or by using the pre-allocated storage for the first @cite{N} |
| attribute objects, and the heap for the others. In the latter case, |
| @cite{N} should be documented." |
| @end quotation |
| |
| Not followed. This implementation is not targeted to such a domain. |
| |
| @geindex Locking Policies |
| |
| @node RM D 3 17 Locking Policies,RM D 4 16 Entry Queuing Policies,RM C 7 2 30 The Package Task_Attributes,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-d-3-17-locking-policies}@anchor{1ef} |
| @section RM D.3(17): Locking Policies |
| |
| |
| @quotation |
| |
| "The implementation should use names that end with @code{_Locking} for |
| locking policies defined by the implementation." |
| @end quotation |
| |
| Followed. Two implementation-defined locking policies are defined, |
| whose names (@cite{Inheritance_Locking} and |
| @cite{Concurrent_Readers_Locking}) follow this suggestion. |
| |
| @geindex Entry queuing policies |
| |
| @node RM D 4 16 Entry Queuing Policies,RM D 6 9-10 Preemptive Abort,RM D 3 17 Locking Policies,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-d-4-16-entry-queuing-policies}@anchor{1f0} |
| @section RM D.4(16): Entry Queuing Policies |
| |
| |
| @quotation |
| |
| "Names that end with @code{_Queuing} should be used |
| for all implementation-defined queuing policies." |
| @end quotation |
| |
| Followed. No such implementation-defined queuing policies exist. |
| |
| @geindex Preemptive abort |
| |
| @node RM D 6 9-10 Preemptive Abort,RM D 7 21 Tasking Restrictions,RM D 4 16 Entry Queuing Policies,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-d-6-9-10-preemptive-abort}@anchor{1f1} |
| @section RM D.6(9-10): Preemptive Abort |
| |
| |
| @quotation |
| |
| "Even though the @cite{abort_statement} is included in the list of |
| potentially blocking operations (see 9.5.1), it is recommended that this |
| statement be implemented in a way that never requires the task executing |
| the @cite{abort_statement} to block." |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "On a multi-processor, the delay associated with aborting a task on |
| another processor should be bounded; the implementation should use |
| periodic polling, if necessary, to achieve this." |
| @end quotation |
| |
| Followed. |
| |
| @geindex Tasking restrictions |
| |
| @node RM D 7 21 Tasking Restrictions,RM D 8 47-49 Monotonic Time,RM D 6 9-10 Preemptive Abort,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-d-7-21-tasking-restrictions}@anchor{1f2} |
| @section RM D.7(21): Tasking Restrictions |
| |
| |
| @quotation |
| |
| "When feasible, the implementation should take advantage of the specified |
| restrictions to produce a more efficient implementation." |
| @end quotation |
| |
| GNAT currently takes advantage of these restrictions by providing an optimized |
| run time when the Ravenscar profile and the GNAT restricted run time set |
| of restrictions are specified. See pragma @cite{Profile (Ravenscar)} and |
| pragma @cite{Profile (Restricted)} for more details. |
| |
| @geindex Time |
| @geindex monotonic |
| |
| @node RM D 8 47-49 Monotonic Time,RM E 5 28-29 Partition Communication Subsystem,RM D 7 21 Tasking Restrictions,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-d-8-47-49-monotonic-time}@anchor{1f3} |
| @section RM D.8(47-49): Monotonic Time |
| |
| |
| @quotation |
| |
| "When appropriate, implementations should provide configuration |
| mechanisms to change the value of @cite{Tick}." |
| @end quotation |
| |
| Such configuration mechanisms are not appropriate to this implementation |
| and are thus not supported. |
| |
| @quotation |
| |
| "It is recommended that @cite{Calendar.Clock} and @cite{Real_Time.Clock} |
| be implemented as transformations of the same time base." |
| @end quotation |
| |
| Followed. |
| |
| @quotation |
| |
| "It is recommended that the best time base which exists in |
| the underlying system be available to the application through |
| @cite{Clock}. @cite{Best} may mean highest accuracy or largest range." |
| @end quotation |
| |
| Followed. |
| |
| @geindex Partition communication subsystem |
| |
| @geindex PCS |
| |
| @node RM E 5 28-29 Partition Communication Subsystem,RM F 7 COBOL Support,RM D 8 47-49 Monotonic Time,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-e-5-28-29-partition-communication-subsystem}@anchor{1f4} |
| @section RM E.5(28-29): Partition Communication Subsystem |
| |
| |
| @quotation |
| |
| "Whenever possible, the PCS on the called partition should allow for |
| multiple tasks to call the RPC-receiver with different messages and |
| should allow them to block until the corresponding subprogram body |
| returns." |
| @end quotation |
| |
| Followed by GLADE, a separately supplied PCS that can be used with |
| GNAT. |
| |
| @quotation |
| |
| "The @cite{Write} operation on a stream of type @cite{Params_Stream_Type} |
| should raise @cite{Storage_Error} if it runs out of space trying to |
| write the @cite{Item} into the stream." |
| @end quotation |
| |
| Followed by GLADE, a separately supplied PCS that can be used with |
| GNAT. |
| |
| @geindex COBOL support |
| |
| @node RM F 7 COBOL Support,RM F 1 2 Decimal Radix Support,RM E 5 28-29 Partition Communication Subsystem,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-f-7-cobol-support}@anchor{1f5} |
| @section RM F(7): COBOL Support |
| |
| |
| @quotation |
| |
| "If COBOL (respectively, C) is widely supported in the target |
| environment, implementations supporting the Information Systems Annex |
| should provide the child package @cite{Interfaces.COBOL} (respectively, |
| @cite{Interfaces.C}) specified in Annex B and should support a |
| @cite{convention_identifier} of COBOL (respectively, C) in the interfacing |
| pragmas (see Annex B), thus allowing Ada programs to interface with |
| programs written in that language." |
| @end quotation |
| |
| Followed. |
| |
| @geindex Decimal radix support |
| |
| @node RM F 1 2 Decimal Radix Support,RM G Numerics,RM F 7 COBOL Support,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-f-1-2-decimal-radix-support}@anchor{1f6} |
| @section RM F.1(2): Decimal Radix Support |
| |
| |
| @quotation |
| |
| "Packed decimal should be used as the internal representation for objects |
| of subtype @cite{S} when @cite{S}'Machine_Radix = 10." |
| @end quotation |
| |
| Not followed. GNAT ignores @cite{S}'Machine_Radix and always uses binary |
| representations. |
| |
| @geindex Numerics |
| |
| @node RM G Numerics,RM G 1 1 56-58 Complex Types,RM F 1 2 Decimal Radix Support,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-g-numerics}@anchor{1f7} |
| @section RM G: Numerics |
| |
| |
| @quotation |
| |
| "If Fortran (respectively, C) is widely supported in the target |
| environment, implementations supporting the Numerics Annex |
| should provide the child package @cite{Interfaces.Fortran} (respectively, |
| @cite{Interfaces.C}) specified in Annex B and should support a |
| @cite{convention_identifier} of Fortran (respectively, C) in the interfacing |
| pragmas (see Annex B), thus allowing Ada programs to interface with |
| programs written in that language." |
| @end quotation |
| |
| Followed. |
| |
| @geindex Complex types |
| |
| @node RM G 1 1 56-58 Complex Types,RM G 1 2 49 Complex Elementary Functions,RM G Numerics,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-g-1-1-56-58-complex-types}@anchor{1f8} |
| @section RM G.1.1(56-58): Complex Types |
| |
| |
| @quotation |
| |
| "Because the usual mathematical meaning of multiplication of a complex |
| operand and a real operand is that of the scaling of both components of |
| the former by the latter, an implementation should not perform this |
| operation by first promoting the real operand to complex type and then |
| performing a full complex multiplication. In systems that, in the |
| future, support an Ada binding to IEC 559:1989, the latter technique |
| will not generate the required result when one of the components of the |
| complex operand is infinite. (Explicit multiplication of the infinite |
| component by the zero component obtained during promotion yields a NaN |
| that propagates into the final result.) Analogous advice applies in the |
| case of multiplication of a complex operand and a pure-imaginary |
| operand, and in the case of division of a complex operand by a real or |
| pure-imaginary operand." |
| @end quotation |
| |
| Not followed. |
| |
| @quotation |
| |
| "Similarly, because the usual mathematical meaning of addition of a |
| complex operand and a real operand is that the imaginary operand remains |
| unchanged, an implementation should not perform this operation by first |
| promoting the real operand to complex type and then performing a full |
| complex addition. In implementations in which the @cite{Signed_Zeros} |
| attribute of the component type is @cite{True} (and which therefore |
| conform to IEC 559:1989 in regard to the handling of the sign of zero in |
| predefined arithmetic operations), the latter technique will not |
| generate the required result when the imaginary component of the complex |
| operand is a negatively signed zero. (Explicit addition of the negative |
| zero to the zero obtained during promotion yields a positive zero.) |
| Analogous advice applies in the case of addition of a complex operand |
| and a pure-imaginary operand, and in the case of subtraction of a |
| complex operand and a real or pure-imaginary operand." |
| @end quotation |
| |
| Not followed. |
| |
| @quotation |
| |
| "Implementations in which @cite{Real'Signed_Zeros} is @cite{True} should |
| attempt to provide a rational treatment of the signs of zero results and |
| result components. As one example, the result of the @cite{Argument} |
| function should have the sign of the imaginary component of the |
| parameter @cite{X} when the point represented by that parameter lies on |
| the positive real axis; as another, the sign of the imaginary component |
| of the @cite{Compose_From_Polar} function should be the same as |
| (respectively, the opposite of) that of the @cite{Argument} parameter when that |
| parameter has a value of zero and the @cite{Modulus} parameter has a |
| nonnegative (respectively, negative) value." |
| @end quotation |
| |
| Followed. |
| |
| @geindex Complex elementary functions |
| |
| @node RM G 1 2 49 Complex Elementary Functions,RM G 2 4 19 Accuracy Requirements,RM G 1 1 56-58 Complex Types,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-g-1-2-49-complex-elementary-functions}@anchor{1f9} |
| @section RM G.1.2(49): Complex Elementary Functions |
| |
| |
| @quotation |
| |
| "Implementations in which @cite{Complex_Types.Real'Signed_Zeros} is |
| @cite{True} should attempt to provide a rational treatment of the signs |
| of zero results and result components. For example, many of the complex |
| elementary functions have components that are odd functions of one of |
| the parameter components; in these cases, the result component should |
| have the sign of the parameter component at the origin. Other complex |
| elementary functions have zero components whose sign is opposite that of |
| a parameter component at the origin, or is always positive or always |
| negative." |
| @end quotation |
| |
| Followed. |
| |
| @geindex Accuracy requirements |
| |
| @node RM G 2 4 19 Accuracy Requirements,RM G 2 6 15 Complex Arithmetic Accuracy,RM G 1 2 49 Complex Elementary Functions,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-g-2-4-19-accuracy-requirements}@anchor{1fa} |
| @section RM G.2.4(19): Accuracy Requirements |
| |
| |
| @quotation |
| |
| "The versions of the forward trigonometric functions without a |
| @cite{Cycle} parameter should not be implemented by calling the |
| corresponding version with a @cite{Cycle} parameter of |
| @cite{2.0*Numerics.Pi}, since this will not provide the required |
| accuracy in some portions of the domain. For the same reason, the |
| version of @cite{Log} without a @cite{Base} parameter should not be |
| implemented by calling the corresponding version with a @cite{Base} |
| parameter of @cite{Numerics.e}." |
| @end quotation |
| |
| Followed. |
| |
| @geindex Complex arithmetic accuracy |
| |
| @geindex Accuracy |
| @geindex complex arithmetic |
| |
| @node RM G 2 6 15 Complex Arithmetic Accuracy,RM H 6 15/2 Pragma Partition_Elaboration_Policy,RM G 2 4 19 Accuracy Requirements,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-g-2-6-15-complex-arithmetic-accuracy}@anchor{1fb} |
| @section RM G.2.6(15): Complex Arithmetic Accuracy |
| |
| |
| @quotation |
| |
| "The version of the @cite{Compose_From_Polar} function without a |
| @cite{Cycle} parameter should not be implemented by calling the |
| corresponding version with a @cite{Cycle} parameter of |
| @cite{2.0*Numerics.Pi}, since this will not provide the required |
| accuracy in some portions of the domain." |
| @end quotation |
| |
| Followed. |
| |
| @geindex Sequential elaboration policy |
| |
| @node RM H 6 15/2 Pragma Partition_Elaboration_Policy,,RM G 2 6 15 Complex Arithmetic Accuracy,Implementation Advice |
| @anchor{gnat_rm/implementation_advice rm-h-6-15-2-pragma-partition-elaboration-policy}@anchor{1fc} |
| @section RM H.6(15/2): Pragma Partition_Elaboration_Policy |
| |
| |
| @quotation |
| |
| "If the partition elaboration policy is @cite{Sequential} and the |
| Environment task becomes permanently blocked during elaboration then the |
| partition is deadlocked and it is recommended that the partition be |
| immediately terminated." |
| @end quotation |
| |
| Not followed. |
| |
| @node Implementation Defined Characteristics,Intrinsic Subprograms,Implementation Advice,Top |
| @anchor{gnat_rm/implementation_defined_characteristics implementation-defined-characteristics}@anchor{b}@anchor{gnat_rm/implementation_defined_characteristics doc}@anchor{1fd}@anchor{gnat_rm/implementation_defined_characteristics id1}@anchor{1fe} |
| @chapter Implementation Defined Characteristics |
| |
| |
| In addition to the implementation dependent pragmas and attributes, and the |
| implementation advice, there are a number of other Ada features that are |
| potentially implementation dependent and are designated as |
| implementation-defined. These are mentioned throughout the Ada Reference |
| Manual, and are summarized in Annex M. |
| |
| A requirement for conforming Ada compilers is that they provide |
| documentation describing how the implementation deals with each of these |
| issues. In this chapter you will find each point in Annex M listed, |
| followed by a description of how GNAT |
| handles the implementation dependence. |
| |
| You can use this chapter as a guide to minimizing implementation |
| dependent features in your programs if portability to other compilers |
| and other operating systems is an important consideration. The numbers |
| in each entry below correspond to the paragraph numbers in the Ada |
| Reference Manual. |
| |
| |
| @itemize * |
| |
| @item |
| "Whether or not each recommendation given in Implementation |
| Advice is followed. See 1.1.2(37)." |
| @end itemize |
| |
| See @ref{a,,Implementation Advice}. |
| |
| |
| @itemize * |
| |
| @item |
| "Capacity limitations of the implementation. See 1.1.3(3)." |
| @end itemize |
| |
| The complexity of programs that can be processed is limited only by the |
| total amount of available virtual memory, and disk space for the |
| generated object files. |
| |
| |
| @itemize * |
| |
| @item |
| "Variations from the standard that are impractical to avoid |
| given the implementation's execution environment. See 1.1.3(6)." |
| @end itemize |
| |
| There are no variations from the standard. |
| |
| |
| @itemize * |
| |
| @item |
| "Which code_statements cause external |
| interactions. See 1.1.3(10)." |
| @end itemize |
| |
| Any @cite{code_statement} can potentially cause external interactions. |
| |
| |
| @itemize * |
| |
| @item |
| "The coded representation for the text of an Ada |
| program. See 2.1(4)." |
| @end itemize |
| |
| See separate section on source representation. |
| |
| |
| @itemize * |
| |
| @item |
| "The control functions allowed in comments. See 2.1(14)." |
| @end itemize |
| |
| See separate section on source representation. |
| |
| |
| @itemize * |
| |
| @item |
| "The representation for an end of line. See 2.2(2)." |
| @end itemize |
| |
| See separate section on source representation. |
| |
| |
| @itemize * |
| |
| @item |
| "Maximum supported line length and lexical element |
| length. See 2.2(15)." |
| @end itemize |
| |
| The maximum line length is 255 characters and the maximum length of |
| a lexical element is also 255 characters. This is the default setting |
| if not overridden by the use of compiler switch @emph{-gnaty} (which |
| sets the maximum to 79) or @emph{-gnatyMnn} which allows the maximum |
| line length to be specified to be any value up to 32767. The maximum |
| length of a lexical element is the same as the maximum line length. |
| |
| |
| @itemize * |
| |
| @item |
| "Implementation defined pragmas. See 2.8(14)." |
| @end itemize |
| |
| See @ref{7,,Implementation Defined Pragmas}. |
| |
| |
| @itemize * |
| |
| @item |
| "Effect of pragma @cite{Optimize}. See 2.8(27)." |
| @end itemize |
| |
| Pragma @cite{Optimize}, if given with a @cite{Time} or @cite{Space} |
| parameter, checks that the optimization flag is set, and aborts if it is |
| not. |
| |
| |
| @itemize * |
| |
| @item |
| "The sequence of characters of the value returned by |
| @code{S'Image} when some of the graphic characters of |
| @code{S'Wide_Image} are not defined in @cite{Character}. See |
| 3.5(37)." |
| @end itemize |
| |
| The sequence of characters is as defined by the wide character encoding |
| method used for the source. See section on source representation for |
| further details. |
| |
| |
| @itemize * |
| |
| @item |
| "The predefined integer types declared in |
| @cite{Standard}. See 3.5.4(25)." |
| @end itemize |
| |
| |
| @multitable {xxxxxxxxxxxxxxxxxxxxxxxx} {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx} |
| @headitem |
| |
| Type |
| |
| @tab |
| |
| Representation |
| |
| @item |
| |
| @emph{Short_Short_Integer} |
| |
| @tab |
| |
| 8 bit signed |
| |
| @item |
| |
| @emph{Short_Integer} |
| |
| @tab |
| |
| (Short) 16 bit signed |
| |
| @item |
| |
| @emph{Integer} |
| |
| @tab |
| |
| 32 bit signed |
| |
| @item |
| |
| @emph{Long_Integer} |
| |
| @tab |
| |
| 64 bit signed (on most 64 bit targets, |
| depending on the C definition of long). |
| 32 bit signed (all other targets) |
| |
| @item |
| |
| @emph{Long_Long_Integer} |
| |
| @tab |
| |
| 64 bit signed |
| |
| @end multitable |
| |
| |
| |
| @itemize * |
| |
| @item |
| "Any nonstandard integer types and the operators defined |
| for them. See 3.5.4(26)." |
| @end itemize |
| |
| There are no nonstandard integer types. |
| |
| |
| @itemize * |
| |
| @item |
| "Any nonstandard real types and the operators defined for |
| them. See 3.5.6(8)." |
| @end itemize |
| |
| There are no nonstandard real types. |
| |
| |
| @itemize * |
| |
| @item |
| "What combinations of requested decimal precision and range |
| are supported for floating point types. See 3.5.7(7)." |
| @end itemize |
| |
| The precision and range is as defined by the IEEE standard. |
| |
| |
| @itemize * |
| |
| @item |
| "The predefined floating point types declared in |
| @cite{Standard}. See 3.5.7(16)." |
| @end itemize |
| |
| |
| @multitable {xxxxxxxxxxxxxxxxxxxxxxxx} {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx} |
| @headitem |
| |
| Type |
| |
| @tab |
| |
| Representation |
| |
| @item |
| |
| @emph{Short_Float} |
| |
| @tab |
| |
| 32 bit IEEE short |
| |
| @item |
| |
| @emph{Float} |
| |
| @tab |
| |
| (Short) 32 bit IEEE short |
| |
| @item |
| |
| @emph{Long_Float} |
| |
| @tab |
| |
| 64 bit IEEE long |
| |
| @item |
| |
| @emph{Long_Long_Float} |
| |
| @tab |
| |
| 64 bit IEEE long (80 bit IEEE long on x86 processors) |
| |
| @end multitable |
| |
| |
| |
| @itemize * |
| |
| @item |
| "The small of an ordinary fixed point type. See 3.5.9(8)." |
| @end itemize |
| |
| @cite{Fine_Delta} is 2**(-63) |
| |
| |
| @itemize * |
| |
| @item |
| "What combinations of small, range, and digits are |
| supported for fixed point types. See 3.5.9(10)." |
| @end itemize |
| |
| Any combinations are permitted that do not result in a small less than |
| @cite{Fine_Delta} and do not result in a mantissa larger than 63 bits. |
| If the mantissa is larger than 53 bits on machines where Long_Long_Float |
| is 64 bits (true of all architectures except ia32), then the output from |
| Text_IO is accurate to only 53 bits, rather than the full mantissa. This |
| is because floating-point conversions are used to convert fixed point. |
| |
| |
| @itemize * |
| |
| @item |
| "The result of @cite{Tags.Expanded_Name} for types declared |
| within an unnamed @cite{block_statement}. See 3.9(10)." |
| @end itemize |
| |
| Block numbers of the form @cite{B`nnn`}, where @cite{nnn} is a |
| decimal integer are allocated. |
| |
| |
| @itemize * |
| |
| @item |
| "Implementation-defined attributes. See 4.1.4(12)." |
| @end itemize |
| |
| See @ref{8,,Implementation Defined Attributes}. |
| |
| |
| @itemize * |
| |
| @item |
| "Any implementation-defined time types. See 9.6(6)." |
| @end itemize |
| |
| There are no implementation-defined time types. |
| |
| |
| @itemize * |
| |
| @item |
| "The time base associated with relative delays." |
| @end itemize |
| |
| See 9.6(20). The time base used is that provided by the C library |
| function @cite{gettimeofday}. |
| |
| |
| @itemize * |
| |
| @item |
| "The time base of the type @cite{Calendar.Time}. See |
| 9.6(23)." |
| @end itemize |
| |
| The time base used is that provided by the C library function |
| @cite{gettimeofday}. |
| |
| |
| @itemize * |
| |
| @item |
| "The time zone used for package @cite{Calendar} |
| operations. See 9.6(24)." |
| @end itemize |
| |
| The time zone used by package @cite{Calendar} is the current system time zone |
| setting for local time, as accessed by the C library function |
| @cite{localtime}. |
| |
| |
| @itemize * |
| |
| @item |
| "Any limit on @cite{delay_until_statements} of |
| @cite{select_statements}. See 9.6(29)." |
| @end itemize |
| |
| There are no such limits. |
| |
| |
| @itemize * |
| |
| @item |
| "Whether or not two non-overlapping parts of a composite |
| object are independently addressable, in the case where packing, record |
| layout, or @cite{Component_Size} is specified for the object. See |
| 9.10(1)." |
| @end itemize |
| |
| Separate components are independently addressable if they do not share |
| overlapping storage units. |
| |
| |
| @itemize * |
| |
| @item |
| "The representation for a compilation. See 10.1(2)." |
| @end itemize |
| |
| A compilation is represented by a sequence of files presented to the |
| compiler in a single invocation of the @emph{gcc} command. |
| |
| |
| @itemize * |
| |
| @item |
| "Any restrictions on compilations that contain multiple |
| compilation_units. See 10.1(4)." |
| @end itemize |
| |
| No single file can contain more than one compilation unit, but any |
| sequence of files can be presented to the compiler as a single |
| compilation. |
| |
| |
| @itemize * |
| |
| @item |
| "The mechanisms for creating an environment and for adding |
| and replacing compilation units. See 10.1.4(3)." |
| @end itemize |
| |
| See separate section on compilation model. |
| |
| |
| @itemize * |
| |
| @item |
| "The manner of explicitly assigning library units to a |
| partition. See 10.2(2)." |
| @end itemize |
| |
| If a unit contains an Ada main program, then the Ada units for the partition |
| are determined by recursive application of the rules in the Ada Reference |
| Manual section 10.2(2-6). In other words, the Ada units will be those that |
| are needed by the main program, and then this definition of need is applied |
| recursively to those units, and the partition contains the transitive |
| closure determined by this relationship. In short, all the necessary units |
| are included, with no need to explicitly specify the list. If additional |
| units are required, e.g., by foreign language units, then all units must be |
| mentioned in the context clause of one of the needed Ada units. |
| |
| If the partition contains no main program, or if the main program is in |
| a language other than Ada, then GNAT |
| provides the binder options @emph{-z} and @emph{-n} respectively, and in |
| this case a list of units can be explicitly supplied to the binder for |
| inclusion in the partition (all units needed by these units will also |
| be included automatically). For full details on the use of these |
| options, refer to the @cite{GNAT Make Program gnatmake} in the |
| @cite{GNAT User's Guide}. |
| |
| |
| @itemize * |
| |
| @item |
| "The implementation-defined means, if any, of specifying |
| which compilation units are needed by a given compilation unit. See |
| 10.2(2)." |
| @end itemize |
| |
| The units needed by a given compilation unit are as defined in |
| the Ada Reference Manual section 10.2(2-6). There are no |
| implementation-defined pragmas or other implementation-defined |
| means for specifying needed units. |
| |
| |
| @itemize * |
| |
| @item |
| "The manner of designating the main subprogram of a |
| partition. See 10.2(7)." |
| @end itemize |
| |
| The main program is designated by providing the name of the |
| corresponding @code{ALI} file as the input parameter to the binder. |
| |
| |
| @itemize * |
| |
| @item |
| "The order of elaboration of @cite{library_items}. See |
| 10.2(18)." |
| @end itemize |
| |
| The first constraint on ordering is that it meets the requirements of |
| Chapter 10 of the Ada Reference Manual. This still leaves some |
| implementation dependent choices, which are resolved by first |
| elaborating bodies as early as possible (i.e., in preference to specs |
| where there is a choice), and second by evaluating the immediate with |
| clauses of a unit to determine the probably best choice, and |
| third by elaborating in alphabetical order of unit names |
| where a choice still remains. |
| |
| |
| @itemize * |
| |
| @item |
| "Parameter passing and function return for the main |
| subprogram. See 10.2(21)." |
| @end itemize |
| |
| The main program has no parameters. It may be a procedure, or a function |
| returning an integer type. In the latter case, the returned integer |
| value is the return code of the program (overriding any value that |
| may have been set by a call to @cite{Ada.Command_Line.Set_Exit_Status}). |
| |
| |
| @itemize * |
| |
| @item |
| "The mechanisms for building and running partitions. See |
| 10.2(24)." |
| @end itemize |
| |
| GNAT itself supports programs with only a single partition. The GNATDIST |
| tool provided with the GLADE package (which also includes an implementation |
| of the PCS) provides a completely flexible method for building and running |
| programs consisting of multiple partitions. See the separate GLADE manual |
| for details. |
| |
| |
| @itemize * |
| |
| @item |
| "The details of program execution, including program |
| termination. See 10.2(25)." |
| @end itemize |
| |
| See separate section on compilation model. |
| |
| |
| @itemize * |
| |
| @item |
| "The semantics of any non-active partitions supported by the |
| implementation. See 10.2(28)." |
| @end itemize |
| |
| Passive partitions are supported on targets where shared memory is |
| provided by the operating system. See the GLADE reference manual for |
| further details. |
| |
| |
| @itemize * |
| |
| @item |
| "The information returned by @cite{Exception_Message}. See |
| 11.4.1(10)." |
| @end itemize |
| |
| Exception message returns the null string unless a specific message has |
| been passed by the program. |
| |
| |
| @itemize * |
| |
| @item |
| "The result of @cite{Exceptions.Exception_Name} for types |
| declared within an unnamed @cite{block_statement}. See 11.4.1(12)." |
| @end itemize |
| |
| Blocks have implementation defined names of the form @cite{B`nnn`} |
| where @cite{nnn} is an integer. |
| |
| |
| @itemize * |
| |
| @item |
| "The information returned by |
| @cite{Exception_Information}. See 11.4.1(13)." |
| @end itemize |
| |
| @cite{Exception_Information} returns a string in the following format: |
| |
| @example |
| *Exception_Name:* nnnnn |
| *Message:* mmmmm |
| *PID:* ppp |
| *Load address:* 0xhhhh |
| *Call stack traceback locations:* |
| 0xhhhh 0xhhhh 0xhhhh ... 0xhhh |
| @end example |
| |
| where |
| |
| @quotation |
| |
| |
| @itemize * |
| |
| @item |
| @cite{nnnn} is the fully qualified name of the exception in all upper |
| case letters. This line is always present. |
| |
| @item |
| @cite{mmmm} is the message (this line present only if message is non-null) |
| |
| @item |
| @cite{ppp} is the Process Id value as a decimal integer (this line is |
| present only if the Process Id is nonzero). Currently we are |
| not making use of this field. |
| |
| @item |
| The Load address line, the Call stack traceback locations line and the |
| following values are present only if at least one traceback location was |
| recorded. The Load address indicates the address at which the main executable |
| was loaded; this line may not be present if operating system hasn't relocated |
| the main executable. The values are given in C style format, with lower case |
| letters for a-f, and only as many digits present as are necessary. |
| The line terminator sequence at the end of each line, including |
| the last line is a single @cite{LF} character (@cite{16#0A#}). |
| @end itemize |
| @end quotation |
| |
| |
| @itemize * |
| |
| @item |
| "Implementation-defined check names. See 11.5(27)." |
| @end itemize |
| |
| The implementation defined check name Alignment_Check controls checking of |
| address clause values for proper alignment (that is, the address supplied |
| must be consistent with the alignment of the type). |
| |
| The implementation defined check name Predicate_Check controls whether |
| predicate checks are generated. |
| |
| The implementation defined check name Validity_Check controls whether |
| validity checks are generated. |
| |
| In addition, a user program can add implementation-defined check names |
| by means of the pragma Check_Name. |
| |
| |
| @itemize * |
| |
| @item |
| "The interpretation of each aspect of representation. See |
| 13.1(20)." |
| @end itemize |
| |
| See separate section on data representations. |
| |
| |
| @itemize * |
| |
| @item |
| "Any restrictions placed upon representation items. See |
| 13.1(20)." |
| @end itemize |
| |
| See separate section on data representations. |
| |
| |
| @itemize * |
| |
| @item |
| "The meaning of @cite{Size} for indefinite subtypes. See |
| 13.3(48)." |
| @end itemize |
| |
| Size for an indefinite subtype is the maximum possible size, except that |
| for the case of a subprogram parameter, the size of the parameter object |
| is the actual size. |
| |
| |
| @itemize * |
| |
| @item |
| "The default external representation for a type tag. See |
| 13.3(75)." |
| @end itemize |
| |
| The default external representation for a type tag is the fully expanded |
| name of the type in upper case letters. |
| |
| |
| @itemize * |
| |
| @item |
| "What determines whether a compilation unit is the same in |
| two different partitions. See 13.3(76)." |
| @end itemize |
| |
| A compilation unit is the same in two different partitions if and only |
| if it derives from the same source file. |
| |
| |
| @itemize * |
| |
| @item |
| "Implementation-defined components. See 13.5.1(15)." |
| @end itemize |
| |
| The only implementation defined component is the tag for a tagged type, |
| which contains a pointer to the dispatching table. |
| |
| |
| @itemize * |
| |
| @item |
| "If @cite{Word_Size} = @cite{Storage_Unit}, the default bit |
| ordering. See 13.5.3(5)." |
| @end itemize |
| |
| @cite{Word_Size} (32) is not the same as @cite{Storage_Unit} (8) for this |
| implementation, so no non-default bit ordering is supported. The default |
| bit ordering corresponds to the natural endianness of the target architecture. |
| |
| |
| @itemize * |
| |
| @item |
| "The contents of the visible part of package @cite{System} |
| and its language-defined children. See 13.7(2)." |
| @end itemize |
| |
| See the definition of these packages in files @code{system.ads} and |
| @code{s-stoele.ads}. Note that two declarations are added to package |
| System. |
| |
| @example |
| Max_Priority : constant Positive := Priority'Last; |
| Max_Interrupt_Priority : constant Positive := Interrupt_Priority'Last; |
| @end example |
| |
| |
| @itemize * |
| |
| @item |
| "The contents of the visible part of package |
| @cite{System.Machine_Code}, and the meaning of |
| @cite{code_statements}. See 13.8(7)." |
| @end itemize |
| |
| See the definition and documentation in file @code{s-maccod.ads}. |
| |
| |
| @itemize * |
| |
| @item |
| "The effect of unchecked conversion. See 13.9(11)." |
| @end itemize |
| |
| Unchecked conversion between types of the same size |
| results in an uninterpreted transmission of the bits from one type |
| to the other. If the types are of unequal sizes, then in the case of |
| discrete types, a shorter source is first zero or sign extended as |
| necessary, and a shorter target is simply truncated on the left. |
| For all non-discrete types, the source is first copied if necessary |
| to ensure that the alignment requirements of the target are met, then |
| a pointer is constructed to the source value, and the result is obtained |
| by dereferencing this pointer after converting it to be a pointer to the |
| target type. Unchecked conversions where the target subtype is an |
| unconstrained array are not permitted. If the target alignment is |
| greater than the source alignment, then a copy of the result is |
| made with appropriate alignment |
| |
| |
| @itemize * |
| |
| @item |
| "The semantics of operations on invalid representations. |
| See 13.9.2(10-11)." |
| @end itemize |
| |
| For assignments and other operations where the use of invalid values cannot |
| result in erroneous behavior, the compiler ignores the possibility of invalid |
| values. An exception is raised at the point where an invalid value would |
| result in erroneous behavior. For example executing: |
| |
| @example |
| procedure invalidvals is |
| X : Integer := -1; |
| Y : Natural range 1 .. 10; |
| for Y'Address use X'Address; |
| Z : Natural range 1 .. 10; |
| A : array (Natural range 1 .. 10) of Integer; |
| begin |
| Z := Y; -- no exception |
| A (Z) := 3; -- exception raised; |
| end; |
| @end example |
| |
| As indicated, an exception is raised on the array assignment, but not |
| on the simple assignment of the invalid negative value from Y to Z. |
| |
| |
| @itemize * |
| |
| @item |
| "The manner of choosing a storage pool for an access type |
| when @cite{Storage_Pool} is not specified for the type. See 13.11(17)." |
| @end itemize |
| |
| There are 3 different standard pools used by the compiler when |
| @cite{Storage_Pool} is not specified depending whether the type is local |
| to a subprogram or defined at the library level and whether |
| @cite{Storage_Size`is specified or not. See documentation in the runtime library units `System.Pool_Global}, @cite{System.Pool_Size} and |
| @cite{System.Pool_Local} in files @code{s-poosiz.ads}, |
| @code{s-pooglo.ads} and @code{s-pooloc.ads} for full details on the |
| default pools used. |
| |
| |
| @itemize * |
| |
| @item |
| "Whether or not the implementation provides user-accessible |
| names for the standard pool type(s). See 13.11(17)." |
| @end itemize |
| |
| See documentation in the sources of the run time mentioned in the previous |
| paragraph. All these pools are accessible by means of @cite{with}'ing |
| these units. |
| |
| |
| @itemize * |
| |
| @item |
| "The meaning of @cite{Storage_Size}. See 13.11(18)." |
| @end itemize |
| |
| @cite{Storage_Size} is measured in storage units, and refers to the |
| total space available for an access type collection, or to the primary |
| stack space for a task. |
| |
| |
| @itemize * |
| |
| @item |
| "Implementation-defined aspects of storage pools. See |
| 13.11(22)." |
| @end itemize |
| |
| See documentation in the sources of the run time mentioned in the |
| paragraph about standard storage pools above |
| for details on GNAT-defined aspects of storage pools. |
| |
| |
| @itemize * |
| |
| @item |
| "The set of restrictions allowed in a pragma |
| @cite{Restrictions}. See 13.12(7)." |
| @end itemize |
| |
| See @ref{9,,Standard and Implementation Defined Restrictions}. |
| |
| |
| @itemize * |
| |
| @item |
| "The consequences of violating limitations on |
| @cite{Restrictions} pragmas. See 13.12(9)." |
| @end itemize |
| |
| Restrictions that can be checked at compile time result in illegalities |
| if violated. Currently there are no other consequences of violating |
| restrictions. |
| |
| |
| @itemize * |
| |
| @item |
| "The representation used by the @cite{Read} and |
| @cite{Write} attributes of elementary types in terms of stream |
| elements. See 13.13.2(9)." |
| @end itemize |
| |
| The representation is the in-memory representation of the base type of |
| the type, using the number of bits corresponding to the |
| @code{type'Size} value, and the natural ordering of the machine. |
| |
| |
| @itemize * |
| |
| @item |
| "The names and characteristics of the numeric subtypes |
| declared in the visible part of package @cite{Standard}. See A.1(3)." |
| @end itemize |
| |
| See items describing the integer and floating-point types supported. |
| |
| |
| @itemize * |
| |
| @item |
| "The string returned by @cite{Character_Set_Version}. |
| See A.3.5(3)." |
| @end itemize |
| |
| @cite{Ada.Wide_Characters.Handling.Character_Set_Version} returns |
| the string "Unicode 4.0", referring to version 4.0 of the |
| Unicode specification. |
| |
| |
| @itemize * |
| |
| @item |
| "The accuracy actually achieved by the elementary |
| functions. See A.5.1(1)." |
| @end itemize |
| |
| The elementary functions correspond to the functions available in the C |
| library. Only fast math mode is implemented. |
| |
| |
| @itemize * |
| |
| @item |
| "The sign of a zero result from some of the operators or |
| functions in @cite{Numerics.Generic_Elementary_Functions}, when |
| @cite{Float_Type'Signed_Zeros} is @cite{True}. See A.5.1(46)." |
| @end itemize |
| |
| The sign of zeroes follows the requirements of the IEEE 754 standard on |
| floating-point. |
| |
| |
| @itemize * |
| |
| @item |
| "The value of |
| @cite{Numerics.Float_Random.Max_Image_Width}. See A.5.2(27)." |
| @end itemize |
| |
| Maximum image width is 6864, see library file @code{s-rannum.ads}. |
| |
| |
| @itemize * |
| |
| @item |
| "The value of |
| @cite{Numerics.Discrete_Random.Max_Image_Width}. See A.5.2(27)." |
| @end itemize |
| |
| Maximum image width is 6864, see library file @code{s-rannum.ads}. |
| |
| |
| @itemize * |
| |
| @item |
| "The algorithms for random number generation. See |
| A.5.2(32)." |
| @end itemize |
| |
| The algorithm is the Mersenne Twister, as documented in the source file |
| @code{s-rannum.adb}. This version of the algorithm has a period of |
| 2**19937-1. |
| |
| |
| @itemize * |
| |
| @item |
| "The string representation of a random number generator's |
| state. See A.5.2(38)." |
| @end itemize |
| |
| The value returned by the Image function is the concatenation of |
| the fixed-width decimal representations of the 624 32-bit integers |
| of the state vector. |
| |
| |
| @itemize * |
| |
| @item |
| "The minimum time interval between calls to the |
| time-dependent Reset procedure that are guaranteed to initiate different |
| random number sequences. See A.5.2(45)." |
| @end itemize |
| |
| The minimum period between reset calls to guarantee distinct series of |
| random numbers is one microsecond. |
| |
| |
| @itemize * |
| |
| @item |
| "The values of the @cite{Model_Mantissa}, |
| @cite{Model_Emin}, @cite{Model_Epsilon}, @cite{Model}, |
| @cite{Safe_First}, and @cite{Safe_Last} attributes, if the Numerics |
| Annex is not supported. See A.5.3(72)." |
| @end itemize |
| |
| Run the compiler with @emph{-gnatS} to produce a listing of package |
| @cite{Standard}, has the values of all numeric attributes. |
| |
| |
| @itemize * |
| |
| @item |
| "Any implementation-defined characteristics of the |
| input-output packages. See A.7(14)." |
| @end itemize |
| |
| There are no special implementation defined characteristics for these |
| packages. |
| |
| |
| @itemize * |
| |
| @item |
| "The value of @cite{Buffer_Size} in @cite{Storage_IO}. See |
| A.9(10)." |
| @end itemize |
| |
| All type representations are contiguous, and the @cite{Buffer_Size} is |
| the value of @code{type'Size} rounded up to the next storage unit |
| boundary. |
| |
| |
| @itemize * |
| |
| @item |
| "External files for standard input, standard output, and |
| standard error See A.10(5)." |
| @end itemize |
| |
| These files are mapped onto the files provided by the C streams |
| libraries. See source file @code{i-cstrea.ads} for further details. |
| |
| |
| @itemize * |
| |
| @item |
| "The accuracy of the value produced by @cite{Put}. See |
| A.10.9(36)." |
| @end itemize |
| |
| If more digits are requested in the output than are represented by the |
| precision of the value, zeroes are output in the corresponding least |
| significant digit positions. |
| |
| |
| @itemize * |
| |
| @item |
| "The meaning of @cite{Argument_Count}, @cite{Argument}, and |
| @cite{Command_Name}. See A.15(1)." |
| @end itemize |
| |
| These are mapped onto the @cite{argv} and @cite{argc} parameters of the |
| main program in the natural manner. |
| |
| |
| @itemize * |
| |
| @item |
| "The interpretation of the @cite{Form} parameter in procedure |
| @cite{Create_Directory}. See A.16(56)." |
| @end itemize |
| |
| The @cite{Form} parameter is not used. |
| |
| |
| @itemize * |
| |
| @item |
| "The interpretation of the @cite{Form} parameter in procedure |
| @cite{Create_Path}. See A.16(60)." |
| @end itemize |
| |
| The @cite{Form} parameter is not used. |
| |
| |
| @itemize * |
| |
| @item |
| "The interpretation of the @cite{Form} parameter in procedure |
| @cite{Copy_File}. See A.16(68)." |
| @end itemize |
| |
| The @cite{Form} parameter is case-insensitive. |
| Two fields are recognized in the @cite{Form} parameter: |
| |
| @example |
| *preserve=<value>* |
| *mode=<value>* |
| @end example |
| |
| <value> starts immediately after the character '=' and ends with the |
| character immediately preceding the next comma (',') or with the last |
| character of the parameter. |
| |
| The only possible values for preserve= are: |
| |
| |
| @multitable {xxxxxxxxxxxxxxxxxxxx} {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx} |
| @headitem |
| |
| Value |
| |
| @tab |
| |
| Meaning |
| |
| @item |
| |
| @emph{no_attributes} |
| |
| @tab |
| |
| Do not try to preserve any file attributes. This is the |
| default if no preserve= is found in Form. |
| |
| @item |
| |
| @emph{all_attributes} |
| |
| @tab |
| |
| Try to preserve all file attributes (timestamps, access rights). |
| |
| @item |
| |
| @emph{timestamps} |
| |
| @tab |
| |
| Preserve the timestamp of the copied file, but not the other |
| file attributes. |
| |
| @end multitable |
| |
| |
| The only possible values for mode= are: |
| |
| |
| @multitable {xxxxxxxxxxxxxxxx} {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx} |
| @headitem |
| |
| Value |
| |
| @tab |
| |
| Meaning |
| |
| @item |
| |
| @emph{copy} |
| |
| @tab |
| |
| Only do the copy if the destination file does not already exist. |
| If it already exists, Copy_File fails. |
| |
| @item |
| |
| @emph{overwrite} |
| |
| @tab |
| |
| Copy the file in all cases. Overwrite an already existing destination file. |
| |
| @item |
| |
| @emph{append} |
| |
| @tab |
| |
| Append the original file to the destination file. If the destination file |
| does not exist, the destination file is a copy of the source file. |
| When mode=append, the field preserve=, if it exists, is not taken into account. |
| |
| @end multitable |
| |
| |
| If the Form parameter includes one or both of the fields and the value or |
| values are incorrect, Copy_file fails with Use_Error. |
| |
| Examples of correct Forms: |
| |
| @example |
| Form => "preserve=no_attributes,mode=overwrite" (the default) |
| Form => "mode=append" |
| Form => "mode=copy, preserve=all_attributes" |
| @end example |
| |
| Examples of incorrect Forms: |
| |
| @example |
| Form => "preserve=junk" |
| Form => "mode=internal, preserve=timestamps" |
| @end example |
| |
| |
| @itemize * |
| |
| @item |
| "The interpretation of the @cite{Pattern} parameter, when not the null string, |
| in the @cite{Start_Search} and @cite{Search} procedures. |
| See A.16(104) and A.16(112)." |
| @end itemize |
| |
| When the @cite{Pattern} parameter is not the null string, it is interpreted |
| according to the syntax of regular expressions as defined in the |
| @cite{GNAT.Regexp} package. |
| |
| See @ref{1ff,,GNAT.Regexp (g-regexp.ads)}. |
| |
| |
| @itemize * |
| |
| @item |
| "Implementation-defined convention names. See B.1(11)." |
| @end itemize |
| |
| The following convention names are supported |
| |
| |
| @multitable {xxxxxxxxxxxxxxxxxxxxxxxxx} {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx} |
| @headitem |
| |
| Convention Name |
| |
| @tab |
| |
| Interpretation |
| |
| @item |
| |
| @emph{Ada} |
| |
| @tab |
| |
| Ada |
| |
| @item |
| |
| @emph{Ada_Pass_By_Copy} |
| |
| @tab |
| |
| Allowed for any types except by-reference types such as limited |
| records. Compatible with convention Ada, but causes any parameters |
| with this convention to be passed by copy. |
| |
| @item |
| |
| @emph{Ada_Pass_By_Reference} |
| |
| @tab |
| |
| Allowed for any types except by-copy types such as scalars. |
| Compatible with convention Ada, but causes any parameters |
| with this convention to be passed by reference. |
| |
| @item |
| |
| @emph{Assembler} |
| |
| @tab |
| |
| Assembly language |
| |
| @item |
| |
| @emph{Asm} |
| |
| @tab |
| |
| Synonym for Assembler |
| |
| @item |
| |
| @emph{Assembly} |
| |
| @tab |
| |
| Synonym for Assembler |
| |
| @item |
| |
| @emph{C} |
| |
| @tab |
| |
| C |
| |
| @item |
| |
| @emph{C_Pass_By_Copy} |
| |
| @tab |
| |
| Allowed only for record types, like C, but also notes that record |
| is to be passed by copy rather than reference. |
| |
| @item |
| |
| @emph{COBOL} |
| |
| @tab |
| |
| COBOL |
| |
| @item |
| |
| @emph{C_Plus_Plus (or CPP)} |
| |
| @tab |
| |
| C++ |
| |
| @item |
| |
| @emph{Default} |
| |
| @tab |
| |
| Treated the same as C |
| |
| @item |
| |
| @emph{External} |
| |
| @tab |
| |
| Treated the same as C |
| |
| @item |
| |
| @emph{Fortran} |
| |
| @tab |
| |
| Fortran |
| |
| @item |
| |
| @emph{Intrinsic} |
| |
| @tab |
| |
| For support of pragma @cite{Import} with convention Intrinsic, see |
| separate section on Intrinsic Subprograms. |
| |
| @item |
| |
| @emph{Stdcall} |
| |
| @tab |
| |
| Stdcall (used for Windows implementations only). This convention correspond |
| to the WINAPI (previously called Pascal convention) C/C++ convention under |
| Windows. A routine with this convention cleans the stack before |
| exit. This pragma cannot be applied to a dispatching call. |
| |
| @item |
| |
| @emph{DLL} |
| |
| @tab |
| |
| Synonym for Stdcall |
| |
| @item |
| |
| @emph{Win32} |
| |
| @tab |
| |
| Synonym for Stdcall |
| |
| @item |
| |
| @emph{Stubbed} |
| |
| @tab |
| |
| Stubbed is a special convention used to indicate that the body of the |
| subprogram will be entirely ignored. Any call to the subprogram |
| is converted into a raise of the @cite{Program_Error} exception. If a |
| pragma @cite{Import} specifies convention @cite{stubbed} then no body need |
| be present at all. This convention is useful during development for the |
| inclusion of subprograms whose body has not yet been written. |
| In addition, all otherwise unrecognized convention names are also |
| treated as being synonymous with convention C. In all implementations |
| except for VMS, use of such other names results in a warning. In VMS |
| implementations, these names are accepted silently. |
| |
| @end multitable |
| |
| |
| |
| @itemize * |
| |
| @item |
| "The meaning of link names. See B.1(36)." |
| @end itemize |
| |
| Link names are the actual names used by the linker. |
| |
| |
| @itemize * |
| |
| @item |
| "The manner of choosing link names when neither the link |
| name nor the address of an imported or exported entity is specified. See |
| B.1(36)." |
| @end itemize |
| |
| The default linker name is that which would be assigned by the relevant |
| external language, interpreting the Ada name as being in all lower case |
| letters. |
| |
| |
| @itemize * |
| |
| @item |
| "The effect of pragma @cite{Linker_Options}. See B.1(37)." |
| @end itemize |
| |
| The string passed to @cite{Linker_Options} is presented uninterpreted as |
| an argument to the link command, unless it contains ASCII.NUL characters. |
| NUL characters if they appear act as argument separators, so for example |
| |
| @example |
| pragma Linker_Options ("-labc" & ASCII.NUL & "-ldef"); |
| @end example |
| |
| causes two separate arguments @cite{-labc} and @cite{-ldef} to be passed to the |
| linker. The order of linker options is preserved for a given unit. The final |
| list of options passed to the linker is in reverse order of the elaboration |
| order. For example, linker options for a body always appear before the options |
| from the corresponding package spec. |
| |
| |
| @itemize * |
| |
| @item |
| "The contents of the visible part of package |
| @cite{Interfaces} and its language-defined descendants. See B.2(1)." |
| @end itemize |
| |
| See files with prefix @code{i-} in the distributed library. |
| |
| |
| @itemize * |
| |
| @item |
| "Implementation-defined children of package |
| @cite{Interfaces}. The contents of the visible part of package |
| @cite{Interfaces}. See B.2(11)." |
| @end itemize |
| |
| See files with prefix @code{i-} in the distributed library. |
| |
| |
| @itemize * |
| |
| @item |
| "The types @cite{Floating}, @cite{Long_Floating}, |
| @cite{Binary}, @cite{Long_Binary}, @cite{Decimal_ Element}, and |
| @cite{COBOL_Character}; and the initialization of the variables |
| @cite{Ada_To_COBOL} and @cite{COBOL_To_Ada}, in |
| @cite{Interfaces.COBOL}. See B.4(50)." |
| @end itemize |
| |
| |
| @multitable {xxxxxxxxxxxxxxxxxxxxxxx} {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx} |
| @headitem |
| |
| COBOL |
| |
| @tab |
| |
| Ada |
| |
| @item |
| |
| @emph{Floating} |
| |
| @tab |
| |
| Float |
| |
| @item |
| |
| @emph{Long_Floating} |
| |
| @tab |
| |
| (Floating) Long_Float |
| |
| @item |
| |
| @emph{Binary} |
| |
| @tab |
| |
| Integer |
| |
| @item |
| |
| @emph{Long_Binary} |
| |
| @tab |
| |
| Long_Long_Integer |
| |
| @item |
| |
| @emph{Decimal_Element} |
| |
| @tab |
| |
| Character |
| |
| @item |
| |
| @emph{COBOL_Character} |
| |
| @tab |
| |
| Character |
| |
| @end multitable |
| |
| |
| For initialization, see the file @code{i-cobol.ads} in the distributed library. |
| |
| |
| @itemize * |
| |
| @item |
| "Support for access to machine instructions. See C.1(1)." |
| @end itemize |
| |
| See documentation in file @code{s-maccod.ads} in the distributed library. |
| |
| |
| @itemize * |
| |
| @item |
| "Implementation-defined aspects of access to machine |
| operations. See C.1(9)." |
| @end itemize |
| |
| See documentation in file @code{s-maccod.ads} in the distributed library. |
| |
| |
| @itemize * |
| |
| @item |
| "Implementation-defined aspects of interrupts. See C.3(2)." |
| @end itemize |
| |
| Interrupts are mapped to signals or conditions as appropriate. See |
| definition of unit |
| @cite{Ada.Interrupt_Names} in source file @code{a-intnam.ads} for details |
| on the interrupts supported on a particular target. |
| |
| |
| @itemize * |
| |
| @item |
| "Implementation-defined aspects of pre-elaboration. See |
| C.4(13)." |
| @end itemize |
| |
| GNAT does not permit a partition to be restarted without reloading, |
| except under control of the debugger. |
| |
| |
| @itemize * |
| |
| @item |
| "The semantics of pragma @cite{Discard_Names}. See C.5(7)." |
| @end itemize |
| |
| Pragma @cite{Discard_Names} causes names of enumeration literals to |
| be suppressed. In the presence of this pragma, the Image attribute |
| provides the image of the Pos of the literal, and Value accepts |
| Pos values. |
| |
| |
| @itemize * |
| |
| @item |
| "The result of the @cite{Task_Identification.Image} |
| attribute. See C.7.1(7)." |
| @end itemize |
| |
| The result of this attribute is a string that identifies |
| the object or component that denotes a given task. If a variable @cite{Var} |
| has a task type, the image for this task will have the form @cite{Var_`XXXXXXXX`}, |
| where the suffix |
| is the hexadecimal representation of the virtual address of the corresponding |
| task control block. If the variable is an array of tasks, the image of each |
| task will have the form of an indexed component indicating the position of a |
| given task in the array, e.g., @cite{Group(5)_`XXXXXXX`}. If the task is a |
| component of a record, the image of the task will have the form of a selected |
| component. These rules are fully recursive, so that the image of a task that |
| is a subcomponent of a composite object corresponds to the expression that |
| designates this task. |
| |
| If a task is created by an allocator, its image depends on the context. If the |
| allocator is part of an object declaration, the rules described above are used |
| to construct its image, and this image is not affected by subsequent |
| assignments. If the allocator appears within an expression, the image |
| includes only the name of the task type. |
| |
| If the configuration pragma Discard_Names is present, or if the restriction |
| No_Implicit_Heap_Allocation is in effect, the image reduces to |
| the numeric suffix, that is to say the hexadecimal representation of the |
| virtual address of the control block of the task. |
| |
| |
| @itemize * |
| |
| @item |
| "The value of @cite{Current_Task} when in a protected entry |
| or interrupt handler. See C.7.1(17)." |
| @end itemize |
| |
| Protected entries or interrupt handlers can be executed by any |
| convenient thread, so the value of @cite{Current_Task} is undefined. |
| |
| |
| @itemize * |
| |
| @item |
| "The effect of calling @cite{Current_Task} from an entry |
| body or interrupt handler. See C.7.1(19)." |
| @end itemize |
| |
| The effect of calling @cite{Current_Task} from an entry body or |
| interrupt handler is to return the identification of the task currently |
| executing the code. |
| |
| |
| @itemize * |
| |
| @item |
| "Implementation-defined aspects of |
| @cite{Task_Attributes}. See C.7.2(19)." |
| @end itemize |
| |
| There are no implementation-defined aspects of @cite{Task_Attributes}. |
| |
| |
| @itemize * |
| |
| @item |
| "Values of all @cite{Metrics}. See D(2)." |
| @end itemize |
| |
| The metrics information for GNAT depends on the performance of the |
| underlying operating system. The sources of the run-time for tasking |
| implementation, together with the output from @emph{-gnatG} can be |
| used to determine the exact sequence of operating systems calls made |
| to implement various tasking constructs. Together with appropriate |
| information on the performance of the underlying operating system, |
| on the exact target in use, this information can be used to determine |
| the required metrics. |
| |
| |
| @itemize * |
| |
| @item |
| "The declarations of @cite{Any_Priority} and |
| @cite{Priority}. See D.1(11)." |
| @end itemize |
| |
| See declarations in file @code{system.ads}. |
| |
| |
| @itemize * |
| |
| @item |
| "Implementation-defined execution resources. See D.1(15)." |
| @end itemize |
| |
| There are no implementation-defined execution resources. |
| |
| |
| @itemize * |
| |
| @item |
| "Whether, on a multiprocessor, a task that is waiting for |
| access to a protected object keeps its processor busy. See D.2.1(3)." |
| @end itemize |
| |
| On a multi-processor, a task that is waiting for access to a protected |
| object does not keep its processor busy. |
| |
| |
| @itemize * |
| |
| @item |
| "The affect of implementation defined execution resources |
| on task dispatching. See D.2.1(9)." |
| @end itemize |
| |
| Tasks map to threads in the threads package used by GNAT. Where possible |
| and appropriate, these threads correspond to native threads of the |
| underlying operating system. |
| |
| |
| @itemize * |
| |
| @item |
| "Implementation-defined @cite{policy_identifiers} allowed |
| in a pragma @cite{Task_Dispatching_Policy}. See D.2.2(3)." |
| @end itemize |
| |
| There are no implementation-defined policy-identifiers allowed in this |
| pragma. |
| |
| |
| @itemize * |
| |
| @item |
| "Implementation-defined aspects of priority inversion. See |
| D.2.2(16)." |
| @end itemize |
| |
| Execution of a task cannot be preempted by the implementation processing |
| of delay expirations for lower priority tasks. |
| |
| |
| @itemize * |
| |
| @item |
| "Implementation-defined task dispatching. See D.2.2(18)." |
| @end itemize |
| |
| The policy is the same as that of the underlying threads implementation. |
| |
| |
| @itemize * |
| |
| @item |
| "Implementation-defined @cite{policy_identifiers} allowed |
| in a pragma @cite{Locking_Policy}. See D.3(4)." |
| @end itemize |
| |
| The two implementation defined policies permitted in GNAT are |
| @cite{Inheritance_Locking} and @cite{Conccurent_Readers_Locking}. On |
| targets that support the @cite{Inheritance_Locking} policy, locking is |
| implemented by inheritance, i.e., the task owning the lock operates |
| at a priority equal to the highest priority of any task currently |
| requesting the lock. On targets that support the |
| @cite{Conccurent_Readers_Locking} policy, locking is implemented with a |
| read/write lock allowing multiple propected object functions to enter |
| concurrently. |
| |
| |
| @itemize * |
| |
| @item |
| "Default ceiling priorities. See D.3(10)." |
| @end itemize |
| |
| The ceiling priority of protected objects of the type |
| @cite{System.Interrupt_Priority'Last} as described in the Ada |
| Reference Manual D.3(10), |
| |
| |
| @itemize * |
| |
| @item |
| "The ceiling of any protected object used internally by |
| the implementation. See D.3(16)." |
| @end itemize |
| |
| The ceiling priority of internal protected objects is |
| @cite{System.Priority'Last}. |
| |
| |
| @itemize * |
| |
| @item |
| "Implementation-defined queuing policies. See D.4(1)." |
| @end itemize |
| |
| There are no implementation-defined queuing policies. |
| |
| |
| @itemize * |
| |
| @item |
| "On a multiprocessor, any conditions that cause the |
| completion of an aborted construct to be delayed later than what is |
| specified for a single processor. See D.6(3)." |
| @end itemize |
| |
| The semantics for abort on a multi-processor is the same as on a single |
| processor, there are no further delays. |
| |
| |
| @itemize * |
| |
| @item |
| "Any operations that implicitly require heap storage |
| allocation. See D.7(8)." |
| @end itemize |
| |
| The only operation that implicitly requires heap storage allocation is |
| task creation. |
| |
| |
| @itemize * |
| |
| @item |
| "What happens when a task terminates in the presence of |
| pragma @cite{No_Task_Termination}. See D.7(15)." |
| @end itemize |
| |
| Execution is erroneous in that case. |
| |
| |
| @itemize * |
| |
| @item |
| "Implementation-defined aspects of pragma |
| @cite{Restrictions}. See D.7(20)." |
| @end itemize |
| |
| There are no such implementation-defined aspects. |
| |
| |
| @itemize * |
| |
| @item |
| "Implementation-defined aspects of package |
| @cite{Real_Time}. See D.8(17)." |
| @end itemize |
| |
| There are no implementation defined aspects of package @cite{Real_Time}. |
| |
| |
| @itemize * |
| |
| @item |
| "Implementation-defined aspects of |
| @cite{delay_statements}. See D.9(8)." |
| @end itemize |
| |
| Any difference greater than one microsecond will cause the task to be |
| delayed (see D.9(7)). |
| |
| |
| @itemize * |
| |
| @item |
| "The upper bound on the duration of interrupt blocking |
| caused by the implementation. See D.12(5)." |
| @end itemize |
| |
| The upper bound is determined by the underlying operating system. In |
| no cases is it more than 10 milliseconds. |
| |
| |
| @itemize * |
| |
| @item |
| "The means for creating and executing distributed |
| programs. See E(5)." |
| @end itemize |
| |
| The GLADE package provides a utility GNATDIST for creating and executing |
| distributed programs. See the GLADE reference manual for further details. |
| |
| |
| @itemize * |
| |
| @item |
| "Any events that can result in a partition becoming |
| inaccessible. See E.1(7)." |
| @end itemize |
| |
| See the GLADE reference manual for full details on such events. |
| |
| |
| @itemize * |
| |
| @item |
| "The scheduling policies, treatment of priorities, and |
| management of shared resources between partitions in certain cases. See |
| E.1(11)." |
| @end itemize |
| |
| See the GLADE reference manual for full details on these aspects of |
| multi-partition execution. |
| |
| |
| @itemize * |
| |
| @item |
| "Events that cause the version of a compilation unit to |
| change. See E.3(5)." |
| @end itemize |
| |
| Editing the source file of a compilation unit, or the source files of |
| any units on which it is dependent in a significant way cause the version |
| to change. No other actions cause the version number to change. All changes |
| are significant except those which affect only layout, capitalization or |
| comments. |
| |
| |
| @itemize * |
| |
| @item |
| "Whether the execution of the remote subprogram is |
| immediately aborted as a result of cancellation. See E.4(13)." |
| @end itemize |
| |
| See the GLADE reference manual for details on the effect of abort in |
| a distributed application. |
| |
| |
| @itemize * |
| |
| @item |
| "Implementation-defined aspects of the PCS. See E.5(25)." |
| @end itemize |
| |
| See the GLADE reference manual for a full description of all implementation |
| defined aspects of the PCS. |
| |
| |
| @itemize * |
| |
| @item |
| "Implementation-defined interfaces in the PCS. See |
| E.5(26)." |
| @end itemize |
| |
| See the GLADE reference manual for a full description of all |
| implementation defined interfaces. |
| |
| |
| @itemize * |
| |
| @item |
| "The values of named numbers in the package |
| @cite{Decimal}. See F.2(7)." |
| @end itemize |
| |
| |
| @multitable {xxxxxxxxxxxxxxxxxxxxxx} {xxxxxxxxxxxx} |
| @headitem |
| |
| Named Number |
| |
| @tab |
| |
| Value |
| |
| @item |
| |
| @emph{Max_Scale} |
| |
| @tab |
| |
| +18 |
| |
| @item |
| |
| @emph{Min_Scale} |
| |
| @tab |
| |
| -18 |
| |
| @item |
| |
| @emph{Min_Delta} |
| |
| @tab |
| |
| 1.0E-18 |
| |
| @item |
| |
| @emph{Max_Delta} |
| |
| @tab |
| |
| 1.0E+18 |
| |
| @item |
| |
| @emph{Max_Decimal_Digits} |
| |
| @tab |
| |
| 18 |
| |
| @end multitable |
| |
| |
| |
| @itemize * |
| |
| @item |
| "The value of @cite{Max_Picture_Length} in the package |
| @cite{Text_IO.Editing}. See F.3.3(16)." |
| @end itemize |
| |
| 64 |
| |
| |
| @itemize * |
| |
| @item |
| "The value of @cite{Max_Picture_Length} in the package |
| @cite{Wide_Text_IO.Editing}. See F.3.4(5)." |
| @end itemize |
| |
| 64 |
| |
| |
| @itemize * |
| |
| @item |
| "The accuracy actually achieved by the complex elementary |
| functions and by other complex arithmetic operations. See G.1(1)." |
| @end itemize |
| |
| Standard library functions are used for the complex arithmetic |
| operations. Only fast math mode is currently supported. |
| |
| |
| @itemize * |
| |
| @item |
| "The sign of a zero result (or a component thereof) from |
| any operator or function in @cite{Numerics.Generic_Complex_Types}, when |
| @cite{Real'Signed_Zeros} is True. See G.1.1(53)." |
| @end itemize |
| |
| The signs of zero values are as recommended by the relevant |
| implementation advice. |
| |
| |
| @itemize * |
| |
| @item |
| "The sign of a zero result (or a component thereof) from |
| any operator or function in |
| @cite{Numerics.Generic_Complex_Elementary_Functions}, when |
| @cite{Real'Signed_Zeros} is @cite{True}. See G.1.2(45)." |
| @end itemize |
| |
| The signs of zero values are as recommended by the relevant |
| implementation advice. |
| |
| |
| @itemize * |
| |
| @item |
| "Whether the strict mode or the relaxed mode is the |
| default. See G.2(2)." |
| @end itemize |
| |
| The strict mode is the default. There is no separate relaxed mode. GNAT |
| provides a highly efficient implementation of strict mode. |
| |
| |
| @itemize * |
| |
| @item |
| "The result interval in certain cases of fixed-to-float |
| conversion. See G.2.1(10)." |
| @end itemize |
| |
| For cases where the result interval is implementation dependent, the |
| accuracy is that provided by performing all operations in 64-bit IEEE |
| floating-point format. |
| |
| |
| @itemize * |
| |
| @item |
| "The result of a floating point arithmetic operation in |
| overflow situations, when the @cite{Machine_Overflows} attribute of the |
| result type is @cite{False}. See G.2.1(13)." |
| @end itemize |
| |
| Infinite and NaN values are produced as dictated by the IEEE |
| floating-point standard. |
| Note that on machines that are not fully compliant with the IEEE |
| floating-point standard, such as Alpha, the @emph{-mieee} compiler flag |
| must be used for achieving IEEE conforming behavior (although at the cost |
| of a significant performance penalty), so infinite and NaN values are |
| properly generated. |
| |
| |
| @itemize * |
| |
| @item |
| "The result interval for division (or exponentiation by a |
| negative exponent), when the floating point hardware implements division |
| as multiplication by a reciprocal. See G.2.1(16)." |
| @end itemize |
| |
| Not relevant, division is IEEE exact. |
| |
| |
| @itemize * |
| |
| @item |
| "The definition of close result set, which determines the |
| accuracy of certain fixed point multiplications and divisions. See |
| G.2.3(5)." |
| @end itemize |
| |
| Operations in the close result set are performed using IEEE long format |
| floating-point arithmetic. The input operands are converted to |
| floating-point, the operation is done in floating-point, and the result |
| is converted to the target type. |
| |
| |
| @itemize * |
| |
| @item |
| "Conditions on a @cite{universal_real} operand of a fixed |
| point multiplication or division for which the result shall be in the |
| perfect result set. See G.2.3(22)." |
| @end itemize |
| |
| The result is only defined to be in the perfect result set if the result |
| can be computed by a single scaling operation involving a scale factor |
| representable in 64-bits. |
| |
| |
| @itemize * |
| |
| @item |
| "The result of a fixed point arithmetic operation in |
| overflow situations, when the @cite{Machine_Overflows} attribute of the |
| result type is @cite{False}. See G.2.3(27)." |
| @end itemize |
| |
| Not relevant, @cite{Machine_Overflows} is @cite{True} for fixed-point |
| types. |
| |
| |
| @itemize * |
| |
| @item |
| "The result of an elementary function reference in |
| overflow situations, when the @cite{Machine_Overflows} attribute of the |
| result type is @cite{False}. See G.2.4(4)." |
| @end itemize |
| |
| IEEE infinite and Nan values are produced as appropriate. |
| |
| |
| @itemize * |
| |
| @item |
| "The value of the angle threshold, within which certain |
| elementary functions, complex arithmetic operations, and complex |
| elementary functions yield results conforming to a maximum relative |
| error bound. See G.2.4(10)." |
| @end itemize |
| |
| Information on this subject is not yet available. |
| |
| |
| @itemize * |
| |
| @item |
| "The accuracy of certain elementary functions for |
| parameters beyond the angle threshold. See G.2.4(10)." |
| @end itemize |
| |
| Information on this subject is not yet available. |
| |
| |
| @itemize * |
| |
| @item |
| "The result of a complex arithmetic operation or complex |
| elementary function reference in overflow situations, when the |
| @cite{Machine_Overflows} attribute of the corresponding real type is |
| @cite{False}. See G.2.6(5)." |
| @end itemize |
| |
| IEEE infinite and Nan values are produced as appropriate. |
| |
| |
| @itemize * |
| |
| @item |
| "The accuracy of certain complex arithmetic operations and |
| certain complex elementary functions for parameters (or components |
| thereof) beyond the angle threshold. See G.2.6(8)." |
| @end itemize |
| |
| Information on those subjects is not yet available. |
| |
| |
| @itemize * |
| |
| @item |
| "Information regarding bounded errors and erroneous |
| execution. See H.2(1)." |
| @end itemize |
| |
| Information on this subject is not yet available. |
| |
| |
| @itemize * |
| |
| @item |
| "Implementation-defined aspects of pragma |
| @cite{Inspection_Point}. See H.3.2(8)." |
| @end itemize |
| |
| Pragma @cite{Inspection_Point} ensures that the variable is live and can |
| be examined by the debugger at the inspection point. |
| |
| |
| @itemize * |
| |
| @item |
| "Implementation-defined aspects of pragma |
| @cite{Restrictions}. See H.4(25)." |
| @end itemize |
| |
| There are no implementation-defined aspects of pragma @cite{Restrictions}. The |
| use of pragma @cite{Restrictions [No_Exceptions]} has no effect on the |
| generated code. Checks must suppressed by use of pragma @cite{Suppress}. |
| |
| |
| @itemize * |
| |
| @item |
| "Any restrictions on pragma @cite{Restrictions}. See |
| H.4(27)." |
| @end itemize |
| |
| There are no restrictions on pragma @cite{Restrictions}. |
| |
| @node Intrinsic Subprograms,Representation Clauses and Pragmas,Implementation Defined Characteristics,Top |
| @anchor{gnat_rm/intrinsic_subprograms doc}@anchor{200}@anchor{gnat_rm/intrinsic_subprograms intrinsic-subprograms}@anchor{c}@anchor{gnat_rm/intrinsic_subprograms id1}@anchor{201} |
| @chapter Intrinsic Subprograms |
| |
| |
| @geindex Intrinsic Subprograms |
| |
| GNAT allows a user application program to write the declaration: |
| |
| @example |
| pragma Import (Intrinsic, name); |
| @end example |
| |
| providing that the name corresponds to one of the implemented intrinsic |
| subprograms in GNAT, and that the parameter profile of the referenced |
| subprogram meets the requirements. This chapter describes the set of |
| implemented intrinsic subprograms, and the requirements on parameter profiles. |
| Note that no body is supplied; as with other uses of pragma Import, the |
| body is supplied elsewhere (in this case by the compiler itself). Note |
| that any use of this feature is potentially non-portable, since the |
| Ada standard does not require Ada compilers to implement this feature. |
| |
| @menu |
| * Intrinsic Operators:: |
| * Compilation_Date:: |
| * Compilation_Time:: |
| * Enclosing_Entity:: |
| * Exception_Information:: |
| * Exception_Message:: |
| * Exception_Name:: |
| * File:: |
| * Line:: |
| * Shifts and Rotates:: |
| * Source_Location:: |
| |
| @end menu |
| |
| @node Intrinsic Operators,Compilation_Date,,Intrinsic Subprograms |
| @anchor{gnat_rm/intrinsic_subprograms id2}@anchor{202}@anchor{gnat_rm/intrinsic_subprograms intrinsic-operators}@anchor{203} |
| @section Intrinsic Operators |
| |
| |
| @geindex Intrinsic operator |
| |
| All the predefined numeric operators in package Standard |
| in @cite{pragma Import (Intrinsic@comma{}..)} |
| declarations. In the binary operator case, the operands must have the same |
| size. The operand or operands must also be appropriate for |
| the operator. For example, for addition, the operands must |
| both be floating-point or both be fixed-point, and the |
| right operand for @cite{"**"} must have a root type of |
| @cite{Standard.Integer'Base}. |
| You can use an intrinsic operator declaration as in the following example: |
| |
| @example |
| type Int1 is new Integer; |
| type Int2 is new Integer; |
| |
| function "+" (X1 : Int1; X2 : Int2) return Int1; |
| function "+" (X1 : Int1; X2 : Int2) return Int2; |
| pragma Import (Intrinsic, "+"); |
| @end example |
| |
| This declaration would permit 'mixed mode' arithmetic on items |
| of the differing types @cite{Int1} and @cite{Int2}. |
| It is also possible to specify such operators for private types, if the |
| full views are appropriate arithmetic types. |
| |
| @node Compilation_Date,Compilation_Time,Intrinsic Operators,Intrinsic Subprograms |
| @anchor{gnat_rm/intrinsic_subprograms compilation-date}@anchor{204}@anchor{gnat_rm/intrinsic_subprograms id3}@anchor{205} |
| @section Compilation_Date |
| |
| |
| @geindex Compilation_Date |
| |
| This intrinsic subprogram is used in the implementation of the |
| library package @cite{GNAT.Source_Info}. The only useful use of the |
| intrinsic import in this case is the one in this unit, so an |
| application program should simply call the function |
| @cite{GNAT.Source_Info.Compilation_Date} to obtain the date of |
| the current compilation (in local time format MMM DD YYYY). |
| |
| @node Compilation_Time,Enclosing_Entity,Compilation_Date,Intrinsic Subprograms |
| @anchor{gnat_rm/intrinsic_subprograms compilation-time}@anchor{206}@anchor{gnat_rm/intrinsic_subprograms id4}@anchor{207} |
| @section Compilation_Time |
| |
| |
| @geindex Compilation_Time |
| |
| This intrinsic subprogram is used in the implementation of the |
| library package @cite{GNAT.Source_Info}. The only useful use of the |
| intrinsic import in this case is the one in this unit, so an |
| application program should simply call the function |
| @cite{GNAT.Source_Info.Compilation_Time} to obtain the time of |
| the current compilation (in local time format HH:MM:SS). |
| |
| @node Enclosing_Entity,Exception_Information,Compilation_Time,Intrinsic Subprograms |
| @anchor{gnat_rm/intrinsic_subprograms id5}@anchor{208}@anchor{gnat_rm/intrinsic_subprograms enclosing-entity}@anchor{209} |
| @section Enclosing_Entity |
| |
| |
| @geindex Enclosing_Entity |
| |
| This intrinsic subprogram is used in the implementation of the |
| library package @cite{GNAT.Source_Info}. The only useful use of the |
| intrinsic import in this case is the one in this unit, so an |
| application program should simply call the function |
| @cite{GNAT.Source_Info.Enclosing_Entity} to obtain the name of |
| the current subprogram, package, task, entry, or protected subprogram. |
| |
| @node Exception_Information,Exception_Message,Enclosing_Entity,Intrinsic Subprograms |
| @anchor{gnat_rm/intrinsic_subprograms id6}@anchor{20a}@anchor{gnat_rm/intrinsic_subprograms exception-information}@anchor{20b} |
| @section Exception_Information |
| |
| |
| @geindex Exception_Information' |
| |
| This intrinsic subprogram is used in the implementation of the |
| library package @cite{GNAT.Current_Exception}. The only useful |
| use of the intrinsic import in this case is the one in this unit, |
| so an application program should simply call the function |
| @cite{GNAT.Current_Exception.Exception_Information} to obtain |
| the exception information associated with the current exception. |
| |
| @node Exception_Message,Exception_Name,Exception_Information,Intrinsic Subprograms |
| @anchor{gnat_rm/intrinsic_subprograms exception-message}@anchor{20c}@anchor{gnat_rm/intrinsic_subprograms id7}@anchor{20d} |
| @section Exception_Message |
| |
| |
| @geindex Exception_Message |
| |
| This intrinsic subprogram is used in the implementation of the |
| library package @cite{GNAT.Current_Exception}. The only useful |
| use of the intrinsic import in this case is the one in this unit, |
| so an application program should simply call the function |
| @cite{GNAT.Current_Exception.Exception_Message} to obtain |
| the message associated with the current exception. |
| |
| @node Exception_Name,File,Exception_Message,Intrinsic Subprograms |
| @anchor{gnat_rm/intrinsic_subprograms exception-name}@anchor{20e}@anchor{gnat_rm/intrinsic_subprograms id8}@anchor{20f} |
| @section Exception_Name |
| |
| |
| @geindex Exception_Name |
| |
| This intrinsic subprogram is used in the implementation of the |
| library package @cite{GNAT.Current_Exception}. The only useful |
| use of the intrinsic import in this case is the one in this unit, |
| so an application program should simply call the function |
| @cite{GNAT.Current_Exception.Exception_Name} to obtain |
| the name of the current exception. |
| |
| @node File,Line,Exception_Name,Intrinsic Subprograms |
| @anchor{gnat_rm/intrinsic_subprograms file}@anchor{210}@anchor{gnat_rm/intrinsic_subprograms id9}@anchor{211} |
| @section File |
| |
| |
| @geindex File |
| |
| This intrinsic subprogram is used in the implementation of the |
| library package @cite{GNAT.Source_Info}. The only useful use of the |
| intrinsic import in this case is the one in this unit, so an |
| application program should simply call the function |
| @cite{GNAT.Source_Info.File} to obtain the name of the current |
| file. |
| |
| @node Line,Shifts and Rotates,File,Intrinsic Subprograms |
| @anchor{gnat_rm/intrinsic_subprograms id10}@anchor{212}@anchor{gnat_rm/intrinsic_subprograms line}@anchor{213} |
| @section Line |
| |
| |
| @geindex Line |
| |
| This intrinsic subprogram is used in the implementation of the |
| library package @cite{GNAT.Source_Info}. The only useful use of the |
| intrinsic import in this case is the one in this unit, so an |
| application program should simply call the function |
| @cite{GNAT.Source_Info.Line} to obtain the number of the current |
| source line. |
| |
| @node Shifts and Rotates,Source_Location,Line,Intrinsic Subprograms |
| @anchor{gnat_rm/intrinsic_subprograms id11}@anchor{214}@anchor{gnat_rm/intrinsic_subprograms shifts-and-rotates}@anchor{215} |
| @section Shifts and Rotates |
| |
| |
| @geindex Shift_Left |
| |
| @geindex Shift_Right |
| |
| @geindex Shift_Right_Arithmetic |
| |
| @geindex Rotate_Left |
| |
| @geindex Rotate_Right |
| |
| In standard Ada, the shift and rotate functions are available only |
| for the predefined modular types in package @cite{Interfaces}. However, in |
| GNAT it is possible to define these functions for any integer |
| type (signed or modular), as in this example: |
| |
| @example |
| function Shift_Left |
| (Value : T; |
| Amount : Natural) return T; |
| @end example |
| |
| The function name must be one of |
| Shift_Left, Shift_Right, Shift_Right_Arithmetic, Rotate_Left, or |
| Rotate_Right. T must be an integer type. T'Size must be |
| 8, 16, 32 or 64 bits; if T is modular, the modulus |
| must be 2**8, 2**16, 2**32 or 2**64. |
| The result type must be the same as the type of @cite{Value}. |
| The shift amount must be Natural. |
| The formal parameter names can be anything. |
| |
| A more convenient way of providing these shift operators is to use |
| the Provide_Shift_Operators pragma, which provides the function declarations |
| and corresponding pragma Import's for all five shift functions. |
| |
| @node Source_Location,,Shifts and Rotates,Intrinsic Subprograms |
| @anchor{gnat_rm/intrinsic_subprograms source-location}@anchor{216}@anchor{gnat_rm/intrinsic_subprograms id12}@anchor{217} |
| @section Source_Location |
| |
| |
| @geindex Source_Location |
| |
| This intrinsic subprogram is used in the implementation of the |
| library routine @cite{GNAT.Source_Info}. The only useful use of the |
| intrinsic import in this case is the one in this unit, so an |
| application program should simply call the function |
| @cite{GNAT.Source_Info.Source_Location} to obtain the current |
| source file location. |
| |
| @node Representation Clauses and Pragmas,Standard Library Routines,Intrinsic Subprograms,Top |
| @anchor{gnat_rm/representation_clauses_and_pragmas representation-clauses-and-pragmas}@anchor{d}@anchor{gnat_rm/representation_clauses_and_pragmas doc}@anchor{218}@anchor{gnat_rm/representation_clauses_and_pragmas id1}@anchor{219} |
| @chapter Representation Clauses and Pragmas |
| |
| |
| @geindex Representation Clauses |
| |
| @geindex Representation Clause |
| |
| @geindex Representation Pragma |
| |
| @geindex Pragma |
| @geindex representation |
| |
| This section describes the representation clauses accepted by GNAT, and |
| their effect on the representation of corresponding data objects. |
| |
| GNAT fully implements Annex C (Systems Programming). This means that all |
| the implementation advice sections in chapter 13 are fully implemented. |
| However, these sections only require a minimal level of support for |
| representation clauses. GNAT provides much more extensive capabilities, |
| and this section describes the additional capabilities provided. |
| |
| @menu |
| * Alignment Clauses:: |
| * Size Clauses:: |
| * Storage_Size Clauses:: |
| * Size of Variant Record Objects:: |
| * Biased Representation:: |
| * Value_Size and Object_Size Clauses:: |
| * Component_Size Clauses:: |
| * Bit_Order Clauses:: |
| * Effect of Bit_Order on Byte Ordering:: |
| * Pragma Pack for Arrays:: |
| * Pragma Pack for Records:: |
| * Record Representation Clauses:: |
| * Handling of Records with Holes:: |
| * Enumeration Clauses:: |
| * Address Clauses:: |
| * Use of Address Clauses for Memory-Mapped I/O:: |
| * Effect of Convention on Representation:: |
| * Conventions and Anonymous Access Types:: |
| * Determining the Representations chosen by GNAT:: |
| |
| @end menu |
| |
| @node Alignment Clauses,Size Clauses,,Representation Clauses and Pragmas |
| @anchor{gnat_rm/representation_clauses_and_pragmas id2}@anchor{21a}@anchor{gnat_rm/representation_clauses_and_pragmas alignment-clauses}@anchor{21b} |
| @section Alignment Clauses |
| |
| |
| @geindex Alignment Clause |
| |
| GNAT requires that all alignment clauses specify a power of 2, and all |
| default alignments are always a power of 2. The default alignment |
| values are as follows: |
| |
| |
| @itemize * |
| |
| @item |
| @emph{Primitive Types}. |
| |
| For primitive types, the alignment is the minimum of the actual size of |
| objects of the type divided by @cite{Storage_Unit}, |
| and the maximum alignment supported by the target. |
| (This maximum alignment is given by the GNAT-specific attribute |
| @cite{Standard'Maximum_Alignment}; see @ref{13e,,Attribute Maximum_Alignment}.) |
| |
| @geindex Maximum_Alignment attribute |
| |
| For example, for type @cite{Long_Float}, the object size is 8 bytes, and the |
| default alignment will be 8 on any target that supports alignments |
| this large, but on some targets, the maximum alignment may be smaller |
| than 8, in which case objects of type @cite{Long_Float} will be maximally |
| aligned. |
| |
| @item |
| @emph{Arrays}. |
| |
| For arrays, the alignment is equal to the alignment of the component type |
| for the normal case where no packing or component size is given. If the |
| array is packed, and the packing is effective (see separate section on |
| packed arrays), then the alignment will be one for long packed arrays, |
| or arrays whose length is not known at compile time. For short packed |
| arrays, which are handled internally as modular types, the alignment |
| will be as described for primitive types, e.g., a packed array of length |
| 31 bits will have an object size of four bytes, and an alignment of 4. |
| |
| @item |
| @emph{Records}. |
| |
| For the normal non-packed case, the alignment of a record is equal to |
| the maximum alignment of any of its components. For tagged records, this |
| includes the implicit access type used for the tag. If a pragma @cite{Pack} |
| is used and all components are packable (see separate section on pragma |
| @cite{Pack}), then the resulting alignment is 1, unless the layout of the |
| record makes it profitable to increase it. |
| |
| A special case is when: |
| |
| |
| @itemize * |
| |
| @item |
| the size of the record is given explicitly, or a |
| full record representation clause is given, and |
| |
| @item |
| the size of the record is 2, 4, or 8 bytes. |
| @end itemize |
| |
| In this case, an alignment is chosen to match the |
| size of the record. For example, if we have: |
| |
| @example |
| type Small is record |
| A, B : Character; |
| end record; |
| for Small'Size use 16; |
| @end example |
| |
| then the default alignment of the record type @cite{Small} is 2, not 1. This |
| leads to more efficient code when the record is treated as a unit, and also |
| allows the type to specified as @cite{Atomic} on architectures requiring |
| strict alignment. |
| @end itemize |
| |
| An alignment clause may specify a larger alignment than the default value |
| up to some maximum value dependent on the target (obtainable by using the |
| attribute reference @cite{Standard'Maximum_Alignment}). It may also specify |
| a smaller alignment than the default value for enumeration, integer and |
| fixed point types, as well as for record types, for example |
| |
| @example |
| type V is record |
| A : Integer; |
| end record; |
| |
| for V'alignment use 1; |
| @end example |
| |
| @geindex Alignment |
| @geindex default |
| |
| The default alignment for the type @cite{V} is 4, as a result of the |
| Integer field in the record, but it is permissible, as shown, to |
| override the default alignment of the record with a smaller value. |
| |
| @geindex Alignment |
| @geindex subtypes |
| |
| Note that according to the Ada standard, an alignment clause applies only |
| to the first named subtype. If additional subtypes are declared, then the |
| compiler is allowed to choose any alignment it likes, and there is no way |
| to control this choice. Consider: |
| |
| @example |
| type R is range 1 .. 10_000; |
| for R'Alignment use 1; |
| subtype RS is R range 1 .. 1000; |
| @end example |
| |
| The alignment clause specifies an alignment of 1 for the first named subtype |
| @cite{R} but this does not necessarily apply to @cite{RS}. When writing |
| portable Ada code, you should avoid writing code that explicitly or |
| implicitly relies on the alignment of such subtypes. |
| |
| For the GNAT compiler, if an explicit alignment clause is given, this |
| value is also used for any subsequent subtypes. So for GNAT, in the |
| above example, you can count on the alignment of @cite{RS} being 1. But this |
| assumption is non-portable, and other compilers may choose different |
| alignments for the subtype @cite{RS}. |
| |
| @node Size Clauses,Storage_Size Clauses,Alignment Clauses,Representation Clauses and Pragmas |
| @anchor{gnat_rm/representation_clauses_and_pragmas id3}@anchor{21c}@anchor{gnat_rm/representation_clauses_and_pragmas size-clauses}@anchor{21d} |
| @section Size Clauses |
| |
| |
| @geindex Size Clause |
| |
| The default size for a type @cite{T} is obtainable through the |
| language-defined attribute @cite{T'Size} and also through the |
| equivalent GNAT-defined attribute @cite{T'Value_Size}. |
| For objects of type @cite{T}, GNAT will generally increase the type size |
| so that the object size (obtainable through the GNAT-defined attribute |
| @cite{T'Object_Size}) |
| is a multiple of @cite{T'Alignment * Storage_Unit}. |
| |
| For example: |
| |
| @example |
| type Smallint is range 1 .. 6; |
| |
| type Rec is record |
| Y1 : integer; |
| Y2 : boolean; |
| end record; |
| @end example |
| |
| In this example, @cite{Smallint'Size} = @cite{Smallint'Value_Size} = 3, |
| as specified by the RM rules, |
| but objects of this type will have a size of 8 |
| (@cite{Smallint'Object_Size} = 8), |
| since objects by default occupy an integral number |
| of storage units. On some targets, notably older |
| versions of the Digital Alpha, the size of stand |
| alone objects of this type may be 32, reflecting |
| the inability of the hardware to do byte load/stores. |
| |
| Similarly, the size of type @cite{Rec} is 40 bits |
| (@cite{Rec'Size} = @cite{Rec'Value_Size} = 40), but |
| the alignment is 4, so objects of this type will have |
| their size increased to 64 bits so that it is a multiple |
| of the alignment (in bits). This decision is |
| in accordance with the specific Implementation Advice in RM 13.3(43): |
| |
| @quotation |
| |
| "A @cite{Size} clause should be supported for an object if the specified |
| @cite{Size} is at least as large as its subtype's @cite{Size}, and corresponds |
| to a size in storage elements that is a multiple of the object's |
| @cite{Alignment} (if the @cite{Alignment} is nonzero)." |
| @end quotation |
| |
| An explicit size clause may be used to override the default size by |
| increasing it. For example, if we have: |
| |
| @example |
| type My_Boolean is new Boolean; |
| for My_Boolean'Size use 32; |
| @end example |
| |
| then values of this type will always be 32 bits long. In the case of |
| discrete types, the size can be increased up to 64 bits, with the effect |
| that the entire specified field is used to hold the value, sign- or |
| zero-extended as appropriate. If more than 64 bits is specified, then |
| padding space is allocated after the value, and a warning is issued that |
| there are unused bits. |
| |
| Similarly the size of records and arrays may be increased, and the effect |
| is to add padding bits after the value. This also causes a warning message |
| to be generated. |
| |
| The largest Size value permitted in GNAT is 2**31-1. Since this is a |
| Size in bits, this corresponds to an object of size 256 megabytes (minus |
| one). This limitation is true on all targets. The reason for this |
| limitation is that it improves the quality of the code in many cases |
| if it is known that a Size value can be accommodated in an object of |
| type Integer. |
| |
| @node Storage_Size Clauses,Size of Variant Record Objects,Size Clauses,Representation Clauses and Pragmas |
| @anchor{gnat_rm/representation_clauses_and_pragmas storage-size-clauses}@anchor{21e}@anchor{gnat_rm/representation_clauses_and_pragmas id4}@anchor{21f} |
| @section Storage_Size Clauses |
| |
| |
| @geindex Storage_Size Clause |
| |
| For tasks, the @cite{Storage_Size} clause specifies the amount of space |
| to be allocated for the task stack. This cannot be extended, and if the |
| stack is exhausted, then @cite{Storage_Error} will be raised (if stack |
| checking is enabled). Use a @cite{Storage_Size} attribute definition clause, |
| or a @cite{Storage_Size} pragma in the task definition to set the |
| appropriate required size. A useful technique is to include in every |
| task definition a pragma of the form: |
| |
| @example |
| pragma Storage_Size (Default_Stack_Size); |
| @end example |
| |
| Then @cite{Default_Stack_Size} can be defined in a global package, and |
| modified as required. Any tasks requiring stack sizes different from the |
| default can have an appropriate alternative reference in the pragma. |
| |
| You can also use the @emph{-d} binder switch to modify the default stack |
| size. |
| |
| For access types, the @cite{Storage_Size} clause specifies the maximum |
| space available for allocation of objects of the type. If this space is |
| exceeded then @cite{Storage_Error} will be raised by an allocation attempt. |
| In the case where the access type is declared local to a subprogram, the |
| use of a @cite{Storage_Size} clause triggers automatic use of a special |
| predefined storage pool (@cite{System.Pool_Size}) that ensures that all |
| space for the pool is automatically reclaimed on exit from the scope in |
| which the type is declared. |
| |
| A special case recognized by the compiler is the specification of a |
| @cite{Storage_Size} of zero for an access type. This means that no |
| items can be allocated from the pool, and this is recognized at compile |
| time, and all the overhead normally associated with maintaining a fixed |
| size storage pool is eliminated. Consider the following example: |
| |
| @example |
| procedure p is |
| type R is array (Natural) of Character; |
| type P is access all R; |
| for P'Storage_Size use 0; |
| -- Above access type intended only for interfacing purposes |
| |
| y : P; |
| |
| procedure g (m : P); |
| pragma Import (C, g); |
| |
| -- ... |
| |
| begin |
| -- ... |
| y := new R; |
| end; |
| @end example |
| |
| As indicated in this example, these dummy storage pools are often useful in |
| connection with interfacing where no object will ever be allocated. If you |
| compile the above example, you get the warning: |
| |
| @example |
| p.adb:16:09: warning: allocation from empty storage pool |
| p.adb:16:09: warning: Storage_Error will be raised at run time |
| @end example |
| |
| Of course in practice, there will not be any explicit allocators in the |
| case of such an access declaration. |
| |
| @node Size of Variant Record Objects,Biased Representation,Storage_Size Clauses,Representation Clauses and Pragmas |
| @anchor{gnat_rm/representation_clauses_and_pragmas id5}@anchor{220}@anchor{gnat_rm/representation_clauses_and_pragmas size-of-variant-record-objects}@anchor{221} |
| @section Size of Variant Record Objects |
| |
| |
| @geindex Size |
| @geindex variant record objects |
| |
| @geindex Variant record objects |
| @geindex size |
| |
| In the case of variant record objects, there is a question whether Size gives |
| information about a particular variant, or the maximum size required |
| for any variant. Consider the following program |
| |
| @example |
| with Text_IO; use Text_IO; |
| procedure q is |
| type R1 (A : Boolean := False) is record |
| case A is |
| when True => X : Character; |
| when False => null; |
| end case; |
| end record; |
| |
| V1 : R1 (False); |
| V2 : R1; |
| |
| begin |
| Put_Line (Integer'Image (V1'Size)); |
| Put_Line (Integer'Image (V2'Size)); |
| end q; |
| @end example |
| |
| Here we are dealing with a variant record, where the True variant |
| requires 16 bits, and the False variant requires 8 bits. |
| In the above example, both V1 and V2 contain the False variant, |
| which is only 8 bits long. However, the result of running the |
| program is: |
| |
| @example |
| 8 |
| 16 |
| @end example |
| |
| The reason for the difference here is that the discriminant value of |
| V1 is fixed, and will always be False. It is not possible to assign |
| a True variant value to V1, therefore 8 bits is sufficient. On the |
| other hand, in the case of V2, the initial discriminant value is |
| False (from the default), but it is possible to assign a True |
| variant value to V2, therefore 16 bits must be allocated for V2 |
| in the general case, even fewer bits may be needed at any particular |
| point during the program execution. |
| |
| As can be seen from the output of this program, the @cite{'Size} |
| attribute applied to such an object in GNAT gives the actual allocated |
| size of the variable, which is the largest size of any of the variants. |
| The Ada Reference Manual is not completely clear on what choice should |
| be made here, but the GNAT behavior seems most consistent with the |
| language in the RM. |
| |
| In some cases, it may be desirable to obtain the size of the current |
| variant, rather than the size of the largest variant. This can be |
| achieved in GNAT by making use of the fact that in the case of a |
| subprogram parameter, GNAT does indeed return the size of the current |
| variant (because a subprogram has no way of knowing how much space |
| is actually allocated for the actual). |
| |
| Consider the following modified version of the above program: |
| |
| @example |
| with Text_IO; use Text_IO; |
| procedure q is |
| type R1 (A : Boolean := False) is record |
| case A is |
| when True => X : Character; |
| when False => null; |
| end case; |
| end record; |
| |
| V2 : R1; |
| |
| function Size (V : R1) return Integer is |
| begin |
| return V'Size; |
| end Size; |
| |
| begin |
| Put_Line (Integer'Image (V2'Size)); |
| Put_Line (Integer'IMage (Size (V2))); |
| V2 := (True, 'x'); |
| Put_Line (Integer'Image (V2'Size)); |
| Put_Line (Integer'IMage (Size (V2))); |
| end q; |
| @end example |
| |
| The output from this program is |
| |
| @example |
| 16 |
| 8 |
| 16 |
| 16 |
| @end example |
| |
| Here we see that while the @cite{'Size} attribute always returns |
| the maximum size, regardless of the current variant value, the |
| @cite{Size} function does indeed return the size of the current |
| variant value. |
| |
| @node Biased Representation,Value_Size and Object_Size Clauses,Size of Variant Record Objects,Representation Clauses and Pragmas |
| @anchor{gnat_rm/representation_clauses_and_pragmas id6}@anchor{222}@anchor{gnat_rm/representation_clauses_and_pragmas biased-representation}@anchor{223} |
| @section Biased Representation |
| |
| |
| @geindex Size for biased representation |
| |
| @geindex Biased representation |
| |
| In the case of scalars with a range starting at other than zero, it is |
| possible in some cases to specify a size smaller than the default minimum |
| value, and in such cases, GNAT uses an unsigned biased representation, |
| in which zero is used to represent the lower bound, and successive values |
| represent successive values of the type. |
| |
| For example, suppose we have the declaration: |
| |
| @example |
| type Small is range -7 .. -4; |
| for Small'Size use 2; |
| @end example |
| |
| Although the default size of type @cite{Small} is 4, the @cite{Size} |
| clause is accepted by GNAT and results in the following representation |
| scheme: |
| |
| @example |
| -7 is represented as 2#00# |
| -6 is represented as 2#01# |
| -5 is represented as 2#10# |
| -4 is represented as 2#11# |
| @end example |
| |
| Biased representation is only used if the specified @cite{Size} clause |
| cannot be accepted in any other manner. These reduced sizes that force |
| biased representation can be used for all discrete types except for |
| enumeration types for which a representation clause is given. |
| |
| @node Value_Size and Object_Size Clauses,Component_Size Clauses,Biased Representation,Representation Clauses and Pragmas |
| @anchor{gnat_rm/representation_clauses_and_pragmas id7}@anchor{224}@anchor{gnat_rm/representation_clauses_and_pragmas value-size-and-object-size-clauses}@anchor{225} |
| @section Value_Size and Object_Size Clauses |
| |
| |
| @geindex Value_Size |
| |
| @geindex Object_Size |
| |
| @geindex Size |
| @geindex of objects |
| |
| In Ada 95 and Ada 2005, @cite{T'Size} for a type @cite{T} is the minimum |
| number of bits required to hold values of type @cite{T}. |
| Although this interpretation was allowed in Ada 83, it was not required, |
| and this requirement in practice can cause some significant difficulties. |
| For example, in most Ada 83 compilers, @cite{Natural'Size} was 32. |
| However, in Ada 95 and Ada 2005, |
| @cite{Natural'Size} is |
| typically 31. This means that code may change in behavior when moving |
| from Ada 83 to Ada 95 or Ada 2005. For example, consider: |
| |
| @example |
| type Rec is record; |
| A : Natural; |
| B : Natural; |
| end record; |
| |
| for Rec use record |
| at 0 range 0 .. Natural'Size - 1; |
| at 0 range Natural'Size .. 2 * Natural'Size - 1; |
| end record; |
| @end example |
| |
| In the above code, since the typical size of @cite{Natural} objects |
| is 32 bits and @cite{Natural'Size} is 31, the above code can cause |
| unexpected inefficient packing in Ada 95 and Ada 2005, and in general |
| there are cases where the fact that the object size can exceed the |
| size of the type causes surprises. |
| |
| To help get around this problem GNAT provides two implementation |
| defined attributes, @cite{Value_Size} and @cite{Object_Size}. When |
| applied to a type, these attributes yield the size of the type |
| (corresponding to the RM defined size attribute), and the size of |
| objects of the type respectively. |
| |
| The @cite{Object_Size} is used for determining the default size of |
| objects and components. This size value can be referred to using the |
| @cite{Object_Size} attribute. The phrase 'is used' here means that it is |
| the basis of the determination of the size. The backend is free to |
| pad this up if necessary for efficiency, e.g., an 8-bit stand-alone |
| character might be stored in 32 bits on a machine with no efficient |
| byte access instructions such as the Alpha. |
| |
| The default rules for the value of @cite{Object_Size} for |
| discrete types are as follows: |
| |
| |
| @itemize * |
| |
| @item |
| The @cite{Object_Size} for base subtypes reflect the natural hardware |
| size in bits (run the compiler with @emph{-gnatS} to find those values |
| for numeric types). Enumeration types and fixed-point base subtypes have |
| 8, 16, 32 or 64 bits for this size, depending on the range of values |
| to be stored. |
| |
| @item |
| The @cite{Object_Size} of a subtype is the same as the |
| @cite{Object_Size} of |
| the type from which it is obtained. |
| |
| @item |
| The @cite{Object_Size} of a derived base type is copied from the parent |
| base type, and the @cite{Object_Size} of a derived first subtype is copied |
| from the parent first subtype. |
| @end itemize |
| |
| The @cite{Value_Size} attribute |
| is the (minimum) number of bits required to store a value |
| of the type. |
| This value is used to determine how tightly to pack |
| records or arrays with components of this type, and also affects |
| the semantics of unchecked conversion (unchecked conversions where |
| the @cite{Value_Size} values differ generate a warning, and are potentially |
| target dependent). |
| |
| The default rules for the value of @cite{Value_Size} are as follows: |
| |
| |
| @itemize * |
| |
| @item |
| The @cite{Value_Size} for a base subtype is the minimum number of bits |
| required to store all values of the type (including the sign bit |
| only if negative values are possible). |
| |
| @item |
| If a subtype statically matches the first subtype of a given type, then it has |
| by default the same @cite{Value_Size} as the first subtype. This is a |
| consequence of RM 13.1(14): "if two subtypes statically match, |
| then their subtype-specific aspects are the same".) |
| |
| @item |
| All other subtypes have a @cite{Value_Size} corresponding to the minimum |
| number of bits required to store all values of the subtype. For |
| dynamic bounds, it is assumed that the value can range down or up |
| to the corresponding bound of the ancestor |
| @end itemize |
| |
| The RM defined attribute @cite{Size} corresponds to the |
| @cite{Value_Size} attribute. |
| |
| The @cite{Size} attribute may be defined for a first-named subtype. This sets |
| the @cite{Value_Size} of |
| the first-named subtype to the given value, and the |
| @cite{Object_Size} of this first-named subtype to the given value padded up |
| to an appropriate boundary. It is a consequence of the default rules |
| above that this @cite{Object_Size} will apply to all further subtypes. On the |
| other hand, @cite{Value_Size} is affected only for the first subtype, any |
| dynamic subtypes obtained from it directly, and any statically matching |
| subtypes. The @cite{Value_Size} of any other static subtypes is not affected. |
| |
| @cite{Value_Size} and |
| @cite{Object_Size} may be explicitly set for any subtype using |
| an attribute definition clause. Note that the use of these attributes |
| can cause the RM 13.1(14) rule to be violated. If two access types |
| reference aliased objects whose subtypes have differing @cite{Object_Size} |
| values as a result of explicit attribute definition clauses, then it |
| is illegal to convert from one access subtype to the other. For a more |
| complete description of this additional legality rule, see the |
| description of the @cite{Object_Size} attribute. |
| |
| At the implementation level, Esize stores the Object_Size and the |
| RM_Size field stores the @cite{Value_Size} (and hence the value of the |
| @cite{Size} attribute, |
| which, as noted above, is equivalent to @cite{Value_Size}). |
| |
| To get a feel for the difference, consider the following examples (note |
| that in each case the base is @cite{Short_Short_Integer} with a size of 8): |
| |
| |
| @multitable {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx} {xxxxxxxxxxxxxxx} {xxxxxxxxxxxxxxx} |
| @headitem |
| |
| Type or subtype declaration |
| |
| @tab |
| |
| Object_Size |
| |
| @tab |
| |
| Value_Size |
| |
| @item |
| |
| @code{type x1 is range 0 .. 5;} |
| |
| @tab |
| |
| 8 |
| |
| @tab |
| |
| 3 |
| |
| @item |
| |
| @code{type x2 is range 0 .. 5;} |
| @code{for x2'size use 12;} |
| |
| @tab |
| |
| 16 |
| |
| @tab |
| |
| 12 |
| |
| @item |
| |
| @code{subtype x3 is x2 range 0 .. 3;} |
| |
| @tab |
| |
| 16 |
| |
| @tab |
| |
| 2 |
| |
| @item |
| |
| @code{subtype x4 is x2'base range 0 .. 10;} |
| |
| @tab |
| |
| 8 |
| |
| @tab |
| |
| 4 |
| |
| @item |
| |
| @code{subtype x5 is x2 range 0 .. dynamic;} |
| |
| @tab |
| |
| 16 |
| |
| @tab |
| |
| 3* |
| |
| @item |
| |
| @code{subtype x6 is x2'base range 0 .. dynamic;} |
| |
| @tab |
| |
| 8 |
| |
| @tab |
| |
| 3* |
| |
| @end multitable |
| |
| |
| Note: the entries marked '3*' are not actually specified by the Ada |
| Reference Manual, but it seems in the spirit of the RM rules to allocate |
| the minimum number of bits (here 3, given the range for @cite{x2}) |
| known to be large enough to hold the given range of values. |
| |
| So far, so good, but GNAT has to obey the RM rules, so the question is |
| under what conditions must the RM @cite{Size} be used. |
| The following is a list |
| of the occasions on which the RM @cite{Size} must be used: |
| |
| |
| @itemize * |
| |
| @item |
| Component size for packed arrays or records |
| |
| @item |
| Value of the attribute @cite{Size} for a type |
| |
| @item |
| Warning about sizes not matching for unchecked conversion |
| @end itemize |
| |
| For record types, the @cite{Object_Size} is always a multiple of the |
| alignment of the type (this is true for all types). In some cases the |
| @cite{Value_Size} can be smaller. Consider: |
| |
| @example |
| type R is record |
| X : Integer; |
| Y : Character; |
| end record; |
| @end example |
| |
| On a typical 32-bit architecture, the X component will be four bytes, and |
| require four-byte alignment, and the Y component will be one byte. In this |
| case @cite{R'Value_Size} will be 40 (bits) since this is the minimum size |
| required to store a value of this type, and for example, it is permissible |
| to have a component of type R in an outer array whose component size is |
| specified to be 48 bits. However, @cite{R'Object_Size} will be 64 (bits), |
| since it must be rounded up so that this value is a multiple of the |
| alignment (4 bytes = 32 bits). |
| |
| For all other types, the @cite{Object_Size} |
| and Value_Size are the same (and equivalent to the RM attribute @cite{Size}). |
| Only @cite{Size} may be specified for such types. |
| |
| Note that @cite{Value_Size} can be used to force biased representation |
| for a particular subtype. Consider this example: |
| |
| @example |
| type R is (A, B, C, D, E, F); |
| subtype RAB is R range A .. B; |
| subtype REF is R range E .. F; |
| @end example |
| |
| By default, @cite{RAB} |
| has a size of 1 (sufficient to accommodate the representation |
| of @cite{A} and @cite{B}, 0 and 1), and @cite{REF} |
| has a size of 3 (sufficient to accommodate the representation |
| of @cite{E} and @cite{F}, 4 and 5). But if we add the |
| following @cite{Value_Size} attribute definition clause: |
| |
| @example |
| for REF'Value_Size use 1; |
| @end example |
| |
| then biased representation is forced for @cite{REF}, |
| and 0 will represent @cite{E} and 1 will represent @cite{F}. |
| A warning is issued when a @cite{Value_Size} attribute |
| definition clause forces biased representation. This |
| warning can be turned off using @cite{-gnatw.B}. |
| |
| @node Component_Size Clauses,Bit_Order Clauses,Value_Size and Object_Size Clauses,Representation Clauses and Pragmas |
| @anchor{gnat_rm/representation_clauses_and_pragmas id8}@anchor{226}@anchor{gnat_rm/representation_clauses_and_pragmas component-size-clauses}@anchor{227} |
| @section Component_Size Clauses |
| |
| |
| @geindex Component_Size Clause |
| |
| Normally, the value specified in a component size clause must be consistent |
| with the subtype of the array component with regard to size and alignment. |
| In other words, the value specified must be at least equal to the size |
| of this subtype, and must be a multiple of the alignment value. |
| |
| In addition, component size clauses are allowed which cause the array |
| to be packed, by specifying a smaller value. A first case is for |
| component size values in the range 1 through 63. The value specified |
| must not be smaller than the Size of the subtype. GNAT will accurately |
| honor all packing requests in this range. For example, if we have: |
| |
| @example |
| type r is array (1 .. 8) of Natural; |
| for r'Component_Size use 31; |
| @end example |
| |
| then the resulting array has a length of 31 bytes (248 bits = 8 * 31). |
| Of course access to the components of such an array is considerably |
| less efficient than if the natural component size of 32 is used. |
| A second case is when the subtype of the component is a record type |
| padded because of its default alignment. For example, if we have: |
| |
| @example |
| type r is record |
| i : Integer; |
| j : Integer; |
| b : Boolean; |
| end record; |
| |
| type a is array (1 .. 8) of r; |
| for a'Component_Size use 72; |
| @end example |
| |
| then the resulting array has a length of 72 bytes, instead of 96 bytes |
| if the alignment of the record (4) was obeyed. |
| |
| Note that there is no point in giving both a component size clause |
| and a pragma Pack for the same array type. if such duplicate |
| clauses are given, the pragma Pack will be ignored. |
| |
| @node Bit_Order Clauses,Effect of Bit_Order on Byte Ordering,Component_Size Clauses,Representation Clauses and Pragmas |
| @anchor{gnat_rm/representation_clauses_and_pragmas bit-order-clauses}@anchor{228}@anchor{gnat_rm/representation_clauses_and_pragmas id9}@anchor{229} |
| @section Bit_Order Clauses |
| |
| |
| @geindex Bit_Order Clause |
| |
| @geindex bit ordering |
| |
| @geindex ordering |
| @geindex of bits |
| |
| For record subtypes, GNAT permits the specification of the @cite{Bit_Order} |
| attribute. The specification may either correspond to the default bit |
| order for the target, in which case the specification has no effect and |
| places no additional restrictions, or it may be for the non-standard |
| setting (that is the opposite of the default). |
| |
| In the case where the non-standard value is specified, the effect is |
| to renumber bits within each byte, but the ordering of bytes is not |
| affected. There are certain |
| restrictions placed on component clauses as follows: |
| |
| |
| @itemize * |
| |
| @item |
| Components fitting within a single storage unit. |
| |
| These are unrestricted, and the effect is merely to renumber bits. For |
| example if we are on a little-endian machine with @cite{Low_Order_First} |
| being the default, then the following two declarations have exactly |
| the same effect: |
| |
| @example |
| type R1 is record |
| A : Boolean; |
| B : Integer range 1 .. 120; |
| end record; |
| |
| for R1 use record |
| A at 0 range 0 .. 0; |
| B at 0 range 1 .. 7; |
| end record; |
| |
| type R2 is record |
| A : Boolean; |
| B : Integer range 1 .. 120; |
| end record; |
| |
| for R2'Bit_Order use High_Order_First; |
| |
| for R2 use record |
| A at 0 range 7 .. 7; |
| B at 0 range 0 .. 6; |
| end record; |
| @end example |
| |
| The useful application here is to write the second declaration with the |
| @cite{Bit_Order} attribute definition clause, and know that it will be treated |
| the same, regardless of whether the target is little-endian or big-endian. |
| |
| @item |
| Components occupying an integral number of bytes. |
| |
| These are components that exactly fit in two or more bytes. Such component |
| declarations are allowed, but have no effect, since it is important to realize |
| that the @cite{Bit_Order} specification does not affect the ordering of bytes. |
| In particular, the following attempt at getting an endian-independent integer |
| does not work: |
| |
| @example |
| type R2 is record |
| A : Integer; |
| end record; |
| |
| for R2'Bit_Order use High_Order_First; |
| |
| for R2 use record |
| A at 0 range 0 .. 31; |
| end record; |
| @end example |
| |
| This declaration will result in a little-endian integer on a |
| little-endian machine, and a big-endian integer on a big-endian machine. |
| If byte flipping is required for interoperability between big- and |
| little-endian machines, this must be explicitly programmed. This capability |
| is not provided by @cite{Bit_Order}. |
| |
| @item |
| Components that are positioned across byte boundaries |
| |
| but do not occupy an integral number of bytes. Given that bytes are not |
| reordered, such fields would occupy a non-contiguous sequence of bits |
| in memory, requiring non-trivial code to reassemble. They are for this |
| reason not permitted, and any component clause specifying such a layout |
| will be flagged as illegal by GNAT. |
| @end itemize |
| |
| Since the misconception that Bit_Order automatically deals with all |
| endian-related incompatibilities is a common one, the specification of |
| a component field that is an integral number of bytes will always |
| generate a warning. This warning may be suppressed using @cite{pragma Warnings (Off)} |
| if desired. The following section contains additional |
| details regarding the issue of byte ordering. |
| |
| @node Effect of Bit_Order on Byte Ordering,Pragma Pack for Arrays,Bit_Order Clauses,Representation Clauses and Pragmas |
| @anchor{gnat_rm/representation_clauses_and_pragmas id10}@anchor{22a}@anchor{gnat_rm/representation_clauses_and_pragmas effect-of-bit-order-on-byte-ordering}@anchor{22b} |
| @section Effect of Bit_Order on Byte Ordering |
| |
| |
| @geindex byte ordering |
| |
| @geindex ordering |
| @geindex of bytes |
| |
| In this section we will review the effect of the @cite{Bit_Order} attribute |
| definition clause on byte ordering. Briefly, it has no effect at all, but |
| a detailed example will be helpful. Before giving this |
| example, let us review the precise |
| definition of the effect of defining @cite{Bit_Order}. The effect of a |
| non-standard bit order is described in section 15.5.3 of the Ada |
| Reference Manual: |
| |
| @quotation |
| |
| "2 A bit ordering is a method of interpreting the meaning of |
| the storage place attributes." |
| @end quotation |
| |
| To understand the precise definition of storage place attributes in |
| this context, we visit section 13.5.1 of the manual: |
| |
| @quotation |
| |
| "13 A record_representation_clause (without the mod_clause) |
| specifies the layout. The storage place attributes (see 13.5.2) |
| are taken from the values of the position, first_bit, and last_bit |
| expressions after normalizing those values so that first_bit is |
| less than Storage_Unit." |
| @end quotation |
| |
| The critical point here is that storage places are taken from |
| the values after normalization, not before. So the @cite{Bit_Order} |
| interpretation applies to normalized values. The interpretation |
| is described in the later part of the 15.5.3 paragraph: |
| |
| @quotation |
| |
| "2 A bit ordering is a method of interpreting the meaning of |
| the storage place attributes. High_Order_First (known in the |
| vernacular as 'big endian') means that the first bit of a |
| storage element (bit 0) is the most significant bit (interpreting |
| the sequence of bits that represent a component as an unsigned |
| integer value). Low_Order_First (known in the vernacular as |
| 'little endian') means the opposite: the first bit is the |
| least significant." |
| @end quotation |
| |
| Note that the numbering is with respect to the bits of a storage |
| unit. In other words, the specification affects only the numbering |
| of bits within a single storage unit. |
| |
| We can make the effect clearer by giving an example. |
| |
| Suppose that we have an external device which presents two bytes, the first |
| byte presented, which is the first (low addressed byte) of the two byte |
| record is called Master, and the second byte is called Slave. |
| |
| The left most (most significant bit is called Control for each byte, and |
| the remaining 7 bits are called V1, V2, ... V7, where V7 is the rightmost |
| (least significant) bit. |
| |
| On a big-endian machine, we can write the following representation clause |
| |
| @example |
| type Data is record |
| Master_Control : Bit; |
| Master_V1 : Bit; |
| Master_V2 : Bit; |
| Master_V3 : Bit; |
| Master_V4 : Bit; |
| Master_V5 : Bit; |
| Master_V6 : Bit; |
| Master_V7 : Bit; |
| Slave_Control : Bit; |
| Slave_V1 : Bit; |
| Slave_V2 : Bit; |
| Slave_V3 : Bit; |
| Slave_V4 : Bit; |
| Slave_V5 : Bit; |
| Slave_V6 : Bit; |
| Slave_V7 : Bit; |
| end record; |
| |
| for Data use record |
| Master_Control at 0 range 0 .. 0; |
| Master_V1 at 0 range 1 .. 1; |
| Master_V2 at 0 range 2 .. 2; |
| Master_V3 at 0 range 3 .. 3; |
| Master_V4 at 0 range 4 .. 4; |
| Master_V5 at 0 range 5 .. 5; |
| Master_V6 at 0 range 6 .. 6; |
| Master_V7 at 0 range 7 .. 7; |
| Slave_Control at 1 range 0 .. 0; |
| Slave_V1 at 1 range 1 .. 1; |
| Slave_V2 at 1 range 2 .. 2; |
| Slave_V3 at 1 range 3 .. 3; |
| Slave_V4 at 1 range 4 .. 4; |
| Slave_V5 at 1 range 5 .. 5; |
| Slave_V6 at 1 range 6 .. 6; |
| Slave_V7 at 1 range 7 .. 7; |
| end record; |
| @end example |
| |
| Now if we move this to a little endian machine, then the bit ordering within |
| the byte is backwards, so we have to rewrite the record rep clause as: |
| |
| @example |
| for Data use record |
| Master_Control at 0 range 7 .. 7; |
| Master_V1 at 0 range 6 .. 6; |
| Master_V2 at 0 range 5 .. 5; |
| Master_V3 at 0 range 4 .. 4; |
| Master_V4 at 0 range 3 .. 3; |
| Master_V5 at 0 range 2 .. 2; |
| Master_V6 at 0 range 1 .. 1; |
| Master_V7 at 0 range 0 .. 0; |
| Slave_Control at 1 range 7 .. 7; |
| Slave_V1 at 1 range 6 .. 6; |
| Slave_V2 at 1 range 5 .. 5; |
| Slave_V3 at 1 range 4 .. 4; |
| Slave_V4 at 1 range 3 .. 3; |
| Slave_V5 at 1 range 2 .. 2; |
| Slave_V6 at 1 range 1 .. 1; |
| Slave_V7 at 1 range 0 .. 0; |
| end record; |
| @end example |
| |
| It is a nuisance to have to rewrite the clause, especially if |
| the code has to be maintained on both machines. However, |
| this is a case that we can handle with the |
| @cite{Bit_Order} attribute if it is implemented. |
| Note that the implementation is not required on byte addressed |
| machines, but it is indeed implemented in GNAT. |
| This means that we can simply use the |
| first record clause, together with the declaration |
| |
| @example |
| for Data'Bit_Order use High_Order_First; |
| @end example |
| |
| and the effect is what is desired, namely the layout is exactly the same, |
| independent of whether the code is compiled on a big-endian or little-endian |
| machine. |
| |
| The important point to understand is that byte ordering is not affected. |
| A @cite{Bit_Order} attribute definition never affects which byte a field |
| ends up in, only where it ends up in that byte. |
| To make this clear, let us rewrite the record rep clause of the previous |
| example as: |
| |
| @example |
| for Data'Bit_Order use High_Order_First; |
| for Data use record |
| Master_Control at 0 range 0 .. 0; |
| Master_V1 at 0 range 1 .. 1; |
| Master_V2 at 0 range 2 .. 2; |
| Master_V3 at 0 range 3 .. 3; |
| Master_V4 at 0 range 4 .. 4; |
| Master_V5 at 0 range 5 .. 5; |
| Master_V6 at 0 range 6 .. 6; |
| Master_V7 at 0 range 7 .. 7; |
| Slave_Control at 0 range 8 .. 8; |
| Slave_V1 at 0 range 9 .. 9; |
| Slave_V2 at 0 range 10 .. 10; |
| Slave_V3 at 0 range 11 .. 11; |
| Slave_V4 at 0 range 12 .. 12; |
| Slave_V5 at 0 range 13 .. 13; |
| Slave_V6 at 0 range 14 .. 14; |
| Slave_V7 at 0 range 15 .. 15; |
| end record; |
| @end example |
| |
| This is exactly equivalent to saying (a repeat of the first example): |
| |
| @example |
| for Data'Bit_Order use High_Order_First; |
| for Data use record |
| Master_Control at 0 range 0 .. 0; |
| Master_V1 at 0 range 1 .. 1; |
| Master_V2 at 0 range 2 .. 2; |
| Master_V3 at 0 range 3 .. 3; |
| Master_V4 at 0 range 4 .. 4; |
| Master_V5 at 0 range 5 .. 5; |
| Master_V6 at 0 range 6 .. 6; |
| Master_V7 at 0 range 7 .. 7; |
| Slave_Control at 1 range 0 .. 0; |
| Slave_V1 at 1 range 1 .. 1; |
| Slave_V2 at 1 range 2 .. 2; |
| Slave_V3 at 1 range 3 .. 3; |
| Slave_V4 at 1 range 4 .. 4; |
| Slave_V5 at 1 range 5 .. 5; |
| Slave_V6 at 1 range 6 .. 6; |
| Slave_V7 at 1 range 7 .. 7; |
| end record; |
| @end example |
| |
| Why are they equivalent? Well take a specific field, the @cite{Slave_V2} |
| field. The storage place attributes are obtained by normalizing the |
| values given so that the @cite{First_Bit} value is less than 8. After |
| normalizing the values (0,10,10) we get (1,2,2) which is exactly what |
| we specified in the other case. |
| |
| Now one might expect that the @cite{Bit_Order} attribute might affect |
| bit numbering within the entire record component (two bytes in this |
| case, thus affecting which byte fields end up in), but that is not |
| the way this feature is defined, it only affects numbering of bits, |
| not which byte they end up in. |
| |
| Consequently it never makes sense to specify a starting bit number |
| greater than 7 (for a byte addressable field) if an attribute |
| definition for @cite{Bit_Order} has been given, and indeed it |
| may be actively confusing to specify such a value, so the compiler |
| generates a warning for such usage. |
| |
| If you do need to control byte ordering then appropriate conditional |
| values must be used. If in our example, the slave byte came first on |
| some machines we might write: |
| |
| @example |
| Master_Byte_First constant Boolean := ...; |
| |
| Master_Byte : constant Natural := |
| 1 - Boolean'Pos (Master_Byte_First); |
| Slave_Byte : constant Natural := |
| Boolean'Pos (Master_Byte_First); |
| |
| for Data'Bit_Order use High_Order_First; |
| for Data use record |
| Master_Control at Master_Byte range 0 .. 0; |
| Master_V1 at Master_Byte range 1 .. 1; |
| Master_V2 at Master_Byte range 2 .. 2; |
| Master_V3 at Master_Byte range 3 .. 3; |
| Master_V4 at Master_Byte range 4 .. 4; |
| Master_V5 at Master_Byte range 5 .. 5; |
| Master_V6 at Master_Byte range 6 .. 6; |
| Master_V7 at Master_Byte range 7 .. 7; |
| Slave_Control at Slave_Byte range 0 .. 0; |
| Slave_V1 at Slave_Byte range 1 .. 1; |
| Slave_V2 at Slave_Byte range 2 .. 2; |
| Slave_V3 at Slave_Byte range 3 .. 3; |
| Slave_V4 at Slave_Byte range 4 .. 4; |
| Slave_V5 at Slave_Byte range 5 .. 5; |
| Slave_V6 at Slave_Byte range 6 .. 6; |
| Slave_V7 at Slave_Byte range 7 .. 7; |
| end record; |
| @end example |
| |
| Now to switch between machines, all that is necessary is |
| to set the boolean constant @cite{Master_Byte_First} in |
| an appropriate manner. |
| |
| @node Pragma Pack for Arrays,Pragma Pack for Records,Effect of Bit_Order on Byte Ordering,Representation Clauses and Pragmas |
| @anchor{gnat_rm/representation_clauses_and_pragmas pragma-pack-for-arrays}@anchor{22c}@anchor{gnat_rm/representation_clauses_and_pragmas id11}@anchor{22d} |
| @section Pragma Pack for Arrays |
| |
| |
| @geindex Pragma Pack (for arrays) |
| |
| Pragma @cite{Pack} applied to an array has no effect unless the component type |
| is packable. For a component type to be packable, it must be one of the |
| following cases: |
| |
| |
| @itemize * |
| |
| @item |
| Any scalar type |
| |
| @item |
| Any type whose size is specified with a size clause |
| |
| @item |
| Any packed array type with a static size |
| |
| @item |
| Any record type padded because of its default alignment |
| @end itemize |
| |
| For all these cases, if the component subtype size is in the range |
| 1 through 63, then the effect of the pragma @cite{Pack} is exactly as though a |
| component size were specified giving the component subtype size. |
| For example if we have: |
| |
| @example |
| type r is range 0 .. 17; |
| |
| type ar is array (1 .. 8) of r; |
| pragma Pack (ar); |
| @end example |
| |
| Then the component size of @cite{ar} will be set to 5 (i.e., to @cite{r'size}, |
| and the size of the array @cite{ar} will be exactly 40 bits. |
| |
| Note that in some cases this rather fierce approach to packing can produce |
| unexpected effects. For example, in Ada 95 and Ada 2005, |
| subtype @cite{Natural} typically has a size of 31, meaning that if you |
| pack an array of @cite{Natural}, you get 31-bit |
| close packing, which saves a few bits, but results in far less efficient |
| access. Since many other Ada compilers will ignore such a packing request, |
| GNAT will generate a warning on some uses of pragma @cite{Pack} that it guesses |
| might not be what is intended. You can easily remove this warning by |
| using an explicit @cite{Component_Size} setting instead, which never generates |
| a warning, since the intention of the programmer is clear in this case. |
| |
| GNAT treats packed arrays in one of two ways. If the size of the array is |
| known at compile time and is less than 64 bits, then internally the array |
| is represented as a single modular type, of exactly the appropriate number |
| of bits. If the length is greater than 63 bits, or is not known at compile |
| time, then the packed array is represented as an array of bytes, and the |
| length is always a multiple of 8 bits. |
| |
| Note that to represent a packed array as a modular type, the alignment must |
| be suitable for the modular type involved. For example, on typical machines |
| a 32-bit packed array will be represented by a 32-bit modular integer with |
| an alignment of four bytes. If you explicitly override the default alignment |
| with an alignment clause that is too small, the modular representation |
| cannot be used. For example, consider the following set of declarations: |
| |
| @example |
| type R is range 1 .. 3; |
| type S is array (1 .. 31) of R; |
| for S'Component_Size use 2; |
| for S'Size use 62; |
| for S'Alignment use 1; |
| @end example |
| |
| If the alignment clause were not present, then a 62-bit modular |
| representation would be chosen (typically with an alignment of 4 or 8 |
| bytes depending on the target). But the default alignment is overridden |
| with the explicit alignment clause. This means that the modular |
| representation cannot be used, and instead the array of bytes |
| representation must be used, meaning that the length must be a multiple |
| of 8. Thus the above set of declarations will result in a diagnostic |
| rejecting the size clause and noting that the minimum size allowed is 64. |
| |
| @geindex Pragma Pack (for type Natural) |
| |
| @geindex Pragma Pack warning |
| |
| One special case that is worth noting occurs when the base type of the |
| component size is 8/16/32 and the subtype is one bit less. Notably this |
| occurs with subtype @cite{Natural}. Consider: |
| |
| @example |
| type Arr is array (1 .. 32) of Natural; |
| pragma Pack (Arr); |
| @end example |
| |
| In all commonly used Ada 83 compilers, this pragma Pack would be ignored, |
| since typically @cite{Natural'Size} is 32 in Ada 83, and in any case most |
| Ada 83 compilers did not attempt 31 bit packing. |
| |
| In Ada 95 and Ada 2005, @cite{Natural'Size} is required to be 31. Furthermore, |
| GNAT really does pack 31-bit subtype to 31 bits. This may result in a |
| substantial unintended performance penalty when porting legacy Ada 83 code. |
| To help prevent this, GNAT generates a warning in such cases. If you really |
| want 31 bit packing in a case like this, you can set the component size |
| explicitly: |
| |
| @example |
| type Arr is array (1 .. 32) of Natural; |
| for Arr'Component_Size use 31; |
| @end example |
| |
| Here 31-bit packing is achieved as required, and no warning is generated, |
| since in this case the programmer intention is clear. |
| |
| @node Pragma Pack for Records,Record Representation Clauses,Pragma Pack for Arrays,Representation Clauses and Pragmas |
| @anchor{gnat_rm/representation_clauses_and_pragmas pragma-pack-for-records}@anchor{22e}@anchor{gnat_rm/representation_clauses_and_pragmas id12}@anchor{22f} |
| @section Pragma Pack for Records |
| |
| |
| @geindex Pragma Pack (for records) |
| |
| Pragma @cite{Pack} applied to a record will pack the components to reduce |
| wasted space from alignment gaps and by reducing the amount of space |
| taken by components. We distinguish between @emph{packable} components and |
| @emph{non-packable} components. |
| Components of the following types are considered packable: |
| |
| |
| @itemize * |
| |
| @item |
| Components of a primitive type are packable unless they are aliased |
| or of an atomic type. |
| |
| @item |
| Small packed arrays, whose size does not exceed 64 bits, and where the |
| size is statically known at compile time, are represented internally |
| as modular integers, and so they are also packable. |
| @end itemize |
| |
| All packable components occupy the exact number of bits corresponding to |
| their @cite{Size} value, and are packed with no padding bits, i.e., they |
| can start on an arbitrary bit boundary. |
| |
| All other types are non-packable, they occupy an integral number of |
| storage units, and |
| are placed at a boundary corresponding to their alignment requirements. |
| |
| For example, consider the record |
| |
| @example |
| type Rb1 is array (1 .. 13) of Boolean; |
| pragma Pack (Rb1); |
| |
| type Rb2 is array (1 .. 65) of Boolean; |
| pragma Pack (Rb2); |
| |
| type AF is new Float with Atomic; |
| |
| type X2 is record |
| L1 : Boolean; |
| L2 : Duration; |
| L3 : AF; |
| L4 : Boolean; |
| L5 : Rb1; |
| L6 : Rb2; |
| end record; |
| pragma Pack (X2); |
| @end example |
| |
| The representation for the record X2 is as follows: |
| |
| @example |
| for X2'Size use 224; |
| for X2 use record |
| L1 at 0 range 0 .. 0; |
| L2 at 0 range 1 .. 64; |
| L3 at 12 range 0 .. 31; |
| L4 at 16 range 0 .. 0; |
| L5 at 16 range 1 .. 13; |
| L6 at 18 range 0 .. 71; |
| end record; |
| @end example |
| |
| Studying this example, we see that the packable fields @cite{L1} |
| and @cite{L2} are |
| of length equal to their sizes, and placed at specific bit boundaries (and |
| not byte boundaries) to |
| eliminate padding. But @cite{L3} is of a non-packable float type (because |
| it is aliased), so it is on the next appropriate alignment boundary. |
| |
| The next two fields are fully packable, so @cite{L4} and @cite{L5} are |
| minimally packed with no gaps. However, type @cite{Rb2} is a packed |
| array that is longer than 64 bits, so it is itself non-packable. Thus |
| the @cite{L6} field is aligned to the next byte boundary, and takes an |
| integral number of bytes, i.e., 72 bits. |
| |
| @node Record Representation Clauses,Handling of Records with Holes,Pragma Pack for Records,Representation Clauses and Pragmas |
| @anchor{gnat_rm/representation_clauses_and_pragmas id13}@anchor{230}@anchor{gnat_rm/representation_clauses_and_pragmas record-representation-clauses}@anchor{231} |
| @section Record Representation Clauses |
| |
| |
| @geindex Record Representation Clause |
| |
| Record representation clauses may be given for all record types, including |
| types obtained by record extension. Component clauses are allowed for any |
| static component. The restrictions on component clauses depend on the type |
| of the component. |
| |
| @geindex Component Clause |
| |
| For all components of an elementary type, the only restriction on component |
| clauses is that the size must be at least the 'Size value of the type |
| (actually the Value_Size). There are no restrictions due to alignment, |
| and such components may freely cross storage boundaries. |
| |
| Packed arrays with a size up to and including 64 bits are represented |
| internally using a modular type with the appropriate number of bits, and |
| thus the same lack of restriction applies. For example, if you declare: |
| |
| @example |
| type R is array (1 .. 49) of Boolean; |
| pragma Pack (R); |
| for R'Size use 49; |
| @end example |
| |
| then a component clause for a component of type R may start on any |
| specified bit boundary, and may specify a value of 49 bits or greater. |
| |
| For packed bit arrays that are longer than 64 bits, there are two |
| cases. If the component size is a power of 2 (1,2,4,8,16,32 bits), |
| including the important case of single bits or boolean values, then |
| there are no limitations on placement of such components, and they |
| may start and end at arbitrary bit boundaries. |
| |
| If the component size is not a power of 2 (e.g., 3 or 5), then |
| an array of this type longer than 64 bits must always be placed on |
| on a storage unit (byte) boundary and occupy an integral number |
| of storage units (bytes). Any component clause that does not |
| meet this requirement will be rejected. |
| |
| Any aliased component, or component of an aliased type, must |
| have its normal alignment and size. A component clause that |
| does not meet this requirement will be rejected. |
| |
| The tag field of a tagged type always occupies an address sized field at |
| the start of the record. No component clause may attempt to overlay this |
| tag. When a tagged type appears as a component, the tag field must have |
| proper alignment |
| |
| In the case of a record extension T1, of a type T, no component clause applied |
| to the type T1 can specify a storage location that would overlap the first |
| T'Size bytes of the record. |
| |
| For all other component types, including non-bit-packed arrays, |
| the component can be placed at an arbitrary bit boundary, |
| so for example, the following is permitted: |
| |
| @example |
| type R is array (1 .. 10) of Boolean; |
| for R'Size use 80; |
| |
| type Q is record |
| G, H : Boolean; |
| L, M : R; |
| end record; |
| |
| for Q use record |
| G at 0 range 0 .. 0; |
| H at 0 range 1 .. 1; |
| L at 0 range 2 .. 81; |
| R at 0 range 82 .. 161; |
| end record; |
| @end example |
| |
| Note: the above rules apply to recent releases of GNAT 5. |
| In GNAT 3, there are more severe restrictions on larger components. |
| For non-primitive types, including packed arrays with a size greater than |
| 64 bits, component clauses must respect the alignment requirement of the |
| type, in particular, always starting on a byte boundary, and the length |
| must be a multiple of the storage unit. |
| |
| @node Handling of Records with Holes,Enumeration Clauses,Record Representation Clauses,Representation Clauses and Pragmas |
| @anchor{gnat_rm/representation_clauses_and_pragmas handling-of-records-with-holes}@anchor{232}@anchor{gnat_rm/representation_clauses_and_pragmas id14}@anchor{233} |
| @section Handling of Records with Holes |
| |
| |
| @geindex Handling of Records with Holes |
| |
| As a result of alignment considerations, records may contain "holes" |
| or gaps |
| which do not correspond to the data bits of any of the components. |
| Record representation clauses can also result in holes in records. |
| |
| GNAT does not attempt to clear these holes, so in record objects, |
| they should be considered to hold undefined rubbish. The generated |
| equality routine just tests components so does not access these |
| undefined bits, and assignment and copy operations may or may not |
| preserve the contents of these holes (for assignments, the holes |
| in the target will in practice contain either the bits that are |
| present in the holes in the source, or the bits that were present |
| in the target before the assignment). |
| |
| If it is necessary to ensure that holes in records have all zero |
| bits, then record objects for which this initialization is desired |
| should be explicitly set to all zero values using Unchecked_Conversion |
| or address overlays. For example |
| |
| @example |
| type HRec is record |
| C : Character; |
| I : Integer; |
| end record; |
| @end example |
| |
| On typical machines, integers need to be aligned on a four-byte |
| boundary, resulting in three bytes of undefined rubbish following |
| the 8-bit field for C. To ensure that the hole in a variable of |
| type HRec is set to all zero bits, |
| you could for example do: |
| |
| @example |
| type Base is record |
| Dummy1, Dummy2 : Integer := 0; |
| end record; |
| |
| BaseVar : Base; |
| RealVar : Hrec; |
| for RealVar'Address use BaseVar'Address; |
| @end example |
| |
| Now the 8-bytes of the value of RealVar start out containing all zero |
| bits. A safer approach is to just define dummy fields, avoiding the |
| holes, as in: |
| |
| @example |
| type HRec is record |
| C : Character; |
| Dummy1 : Short_Short_Integer := 0; |
| Dummy2 : Short_Short_Integer := 0; |
| Dummy3 : Short_Short_Integer := 0; |
| I : Integer; |
| end record; |
| @end example |
| |
| And to make absolutely sure that the intent of this is followed, you |
| can use representation clauses: |
| |
| @example |
| for Hrec use record |
| C at 0 range 0 .. 7; |
| Dummy1 at 1 range 0 .. 7; |
| Dummy2 at 2 range 0 .. 7; |
| Dummy3 at 3 range 0 .. 7; |
| I at 4 range 0 .. 31; |
| end record; |
| for Hrec'Size use 64; |
| @end example |
| |
| @node Enumeration Clauses,Address Clauses,Handling of Records with Holes,Representation Clauses and Pragmas |
| @anchor{gnat_rm/representation_clauses_and_pragmas enumeration-clauses}@anchor{234}@anchor{gnat_rm/representation_clauses_and_pragmas id15}@anchor{235} |
| @section Enumeration Clauses |
| |
| |
| The only restriction on enumeration clauses is that the range of values |
| must be representable. For the signed case, if one or more of the |
| representation values are negative, all values must be in the range: |
| |
| @example |
| System.Min_Int .. System.Max_Int |
| @end example |
| |
| For the unsigned case, where all values are nonnegative, the values must |
| be in the range: |
| |
| @example |
| 0 .. System.Max_Binary_Modulus; |
| @end example |
| |
| A @emph{confirming} representation clause is one in which the values range |
| from 0 in sequence, i.e., a clause that confirms the default representation |
| for an enumeration type. |
| Such a confirming representation |
| is permitted by these rules, and is specially recognized by the compiler so |
| that no extra overhead results from the use of such a clause. |
| |
| If an array has an index type which is an enumeration type to which an |
| enumeration clause has been applied, then the array is stored in a compact |
| manner. Consider the declarations: |
| |
| @example |
| type r is (A, B, C); |
| for r use (A => 1, B => 5, C => 10); |
| type t is array (r) of Character; |
| @end example |
| |
| The array type t corresponds to a vector with exactly three elements and |
| has a default size equal to @cite{3*Character'Size}. This ensures efficient |
| use of space, but means that accesses to elements of the array will incur |
| the overhead of converting representation values to the corresponding |
| positional values, (i.e., the value delivered by the @cite{Pos} attribute). |
| |
| @node Address Clauses,Use of Address Clauses for Memory-Mapped I/O,Enumeration Clauses,Representation Clauses and Pragmas |
| @anchor{gnat_rm/representation_clauses_and_pragmas id16}@anchor{236}@anchor{gnat_rm/representation_clauses_and_pragmas address-clauses}@anchor{237} |
| @section Address Clauses |
| |
| |
| @geindex Address Clause |
| |
| The reference manual allows a general restriction on representation clauses, |
| as found in RM 13.1(22): |
| |
| @quotation |
| |
| "An implementation need not support representation |
| items containing nonstatic expressions, except that |
| an implementation should support a representation item |
| for a given entity if each nonstatic expression in the |
| representation item is a name that statically denotes |
| a constant declared before the entity." |
| @end quotation |
| |
| In practice this is applicable only to address clauses, since this is the |
| only case in which a non-static expression is permitted by the syntax. As |
| the AARM notes in sections 13.1 (22.a-22.h): |
| |
| @quotation |
| |
| 22.a Reason: This is to avoid the following sort of thing: |
| |
| 22.b X : Integer := F(...); |
| Y : Address := G(...); |
| for X'Address use Y; |
| |
| 22.c In the above, we have to evaluate the |
| initialization expression for X before we |
| know where to put the result. This seems |
| like an unreasonable implementation burden. |
| |
| 22.d The above code should instead be written |
| like this: |
| |
| 22.e Y : constant Address := G(...); |
| X : Integer := F(...); |
| for X'Address use Y; |
| |
| 22.f This allows the expression 'Y' to be safely |
| evaluated before X is created. |
| |
| 22.g The constant could be a formal parameter of mode in. |
| |
| 22.h An implementation can support other nonstatic |
| expressions if it wants to. Expressions of type |
| Address are hardly ever static, but their value |
| might be known at compile time anyway in many |
| cases. |
| @end quotation |
| |
| GNAT does indeed permit many additional cases of non-static expressions. In |
| particular, if the type involved is elementary there are no restrictions |
| (since in this case, holding a temporary copy of the initialization value, |
| if one is present, is inexpensive). In addition, if there is no implicit or |
| explicit initialization, then there are no restrictions. GNAT will reject |
| only the case where all three of these conditions hold: |
| |
| |
| @itemize * |
| |
| @item |
| The type of the item is non-elementary (e.g., a record or array). |
| |
| @item |
| There is explicit or implicit initialization required for the object. |
| Note that access values are always implicitly initialized. |
| |
| @item |
| The address value is non-static. Here GNAT is more permissive than the |
| RM, and allows the address value to be the address of a previously declared |
| stand-alone variable, as long as it does not itself have an address clause. |
| |
| @example |
| Anchor : Some_Initialized_Type; |
| Overlay : Some_Initialized_Type; |
| for Overlay'Address use Anchor'Address; |
| @end example |
| |
| However, the prefix of the address clause cannot be an array component, or |
| a component of a discriminated record. |
| @end itemize |
| |
| As noted above in section 22.h, address values are typically non-static. In |
| particular the To_Address function, even if applied to a literal value, is |
| a non-static function call. To avoid this minor annoyance, GNAT provides |
| the implementation defined attribute 'To_Address. The following two |
| expressions have identical values: |
| |
| @geindex Attribute |
| |
| @geindex To_Address |
| |
| @example |
| To_Address (16#1234_0000#) |
| System'To_Address (16#1234_0000#); |
| @end example |
| |
| except that the second form is considered to be a static expression, and |
| thus when used as an address clause value is always permitted. |
| |
| Additionally, GNAT treats as static an address clause that is an |
| unchecked_conversion of a static integer value. This simplifies the porting |
| of legacy code, and provides a portable equivalent to the GNAT attribute |
| @cite{To_Address}. |
| |
| Another issue with address clauses is the interaction with alignment |
| requirements. When an address clause is given for an object, the address |
| value must be consistent with the alignment of the object (which is usually |
| the same as the alignment of the type of the object). If an address clause |
| is given that specifies an inappropriately aligned address value, then the |
| program execution is erroneous. |
| |
| Since this source of erroneous behavior can have unfortunate effects on |
| machines with strict alignment requirements, GNAT |
| checks (at compile time if possible, generating a warning, or at execution |
| time with a run-time check) that the alignment is appropriate. If the |
| run-time check fails, then @cite{Program_Error} is raised. This run-time |
| check is suppressed if range checks are suppressed, or if the special GNAT |
| check Alignment_Check is suppressed, or if |
| @cite{pragma Restrictions (No_Elaboration_Code)} is in effect. It is also |
| suppressed by default on non-strict alignment machines (such as the x86). |
| |
| Finally, GNAT does not permit overlaying of objects of controlled types or |
| composite types containing a controlled component. In most cases, the compiler |
| can detect an attempt at such overlays and will generate a warning at compile |
| time and a Program_Error exception at run time. |
| |
| @geindex Export |
| |
| An address clause cannot be given for an exported object. More |
| understandably the real restriction is that objects with an address |
| clause cannot be exported. This is because such variables are not |
| defined by the Ada program, so there is no external object to export. |
| |
| @geindex Import |
| |
| It is permissible to give an address clause and a pragma Import for the |
| same object. In this case, the variable is not really defined by the |
| Ada program, so there is no external symbol to be linked. The link name |
| and the external name are ignored in this case. The reason that we allow this |
| combination is that it provides a useful idiom to avoid unwanted |
| initializations on objects with address clauses. |
| |
| When an address clause is given for an object that has implicit or |
| explicit initialization, then by default initialization takes place. This |
| means that the effect of the object declaration is to overwrite the |
| memory at the specified address. This is almost always not what the |
| programmer wants, so GNAT will output a warning: |
| |
| @example |
| with System; |
| package G is |
| type R is record |
| M : Integer := 0; |
| end record; |
| |
| Ext : R; |
| for Ext'Address use System'To_Address (16#1234_1234#); |
| | |
| >>> warning: implicit initialization of "Ext" may |
| modify overlaid storage |
| >>> warning: use pragma Import for "Ext" to suppress |
| initialization (RM B(24)) |
| |
| end G; |
| @end example |
| |
| As indicated by the warning message, the solution is to use a (dummy) pragma |
| Import to suppress this initialization. The pragma tell the compiler that the |
| object is declared and initialized elsewhere. The following package compiles |
| without warnings (and the initialization is suppressed): |
| |
| @example |
| with System; |
| package G is |
| type R is record |
| M : Integer := 0; |
| end record; |
| |
| Ext : R; |
| for Ext'Address use System'To_Address (16#1234_1234#); |
| pragma Import (Ada, Ext); |
| end G; |
| @end example |
| |
| A final issue with address clauses involves their use for overlaying |
| variables, as in the following example: |
| |
| @geindex Overlaying of objects |
| |
| @example |
| A : Integer; |
| B : Integer; |
| for B'Address use A'Address; |
| @end example |
| |
| or alternatively, using the form recommended by the RM: |
| |
| @example |
| A : Integer; |
| Addr : constant Address := A'Address; |
| B : Integer; |
| for B'Address use Addr; |
| @end example |
| |
| In both of these cases, @cite{A} |
| and @cite{B} become aliased to one another via the |
| address clause. This use of address clauses to overlay |
| variables, achieving an effect similar to unchecked |
| conversion was erroneous in Ada 83, but in Ada 95 and Ada 2005 |
| the effect is implementation defined. Furthermore, the |
| Ada RM specifically recommends that in a situation |
| like this, @cite{B} should be subject to the following |
| implementation advice (RM 13.3(19)): |
| |
| @quotation |
| |
| "19 If the Address of an object is specified, or it is imported |
| or exported, then the implementation should not perform |
| optimizations based on assumptions of no aliases." |
| @end quotation |
| |
| GNAT follows this recommendation, and goes further by also applying |
| this recommendation to the overlaid variable (@cite{A} |
| in the above example) in this case. This means that the overlay |
| works "as expected", in that a modification to one of the variables |
| will affect the value of the other. |
| |
| Note that when address clause overlays are used in this way, there is an |
| issue of unintentional initialization, as shown by this example: |
| |
| @example |
| package Overwrite_Record is |
| type R is record |
| A : Character := 'C'; |
| B : Character := 'A'; |
| end record; |
| X : Short_Integer := 3; |
| Y : R; |
| for Y'Address use X'Address; |
| | |
| >>> warning: default initialization of "Y" may |
| modify "X", use pragma Import for "Y" to |
| suppress initialization (RM B.1(24)) |
| |
| end Overwrite_Record; |
| @end example |
| |
| Here the default initialization of @cite{Y} will clobber the value |
| of @cite{X}, which justifies the warning. The warning notes that |
| this effect can be eliminated by adding a @cite{pragma Import} |
| which suppresses the initialization: |
| |
| @example |
| package Overwrite_Record is |
| type R is record |
| A : Character := 'C'; |
| B : Character := 'A'; |
| end record; |
| X : Short_Integer := 3; |
| Y : R; |
| for Y'Address use X'Address; |
| pragma Import (Ada, Y); |
| end Overwrite_Record; |
| @end example |
| |
| Note that the use of @cite{pragma Initialize_Scalars} may cause variables to |
| be initialized when they would not otherwise have been in the absence |
| of the use of this pragma. This may cause an overlay to have this |
| unintended clobbering effect. The compiler avoids this for scalar |
| types, but not for composite objects (where in general the effect |
| of @cite{Initialize_Scalars} is part of the initialization routine |
| for the composite object: |
| |
| @example |
| pragma Initialize_Scalars; |
| with Ada.Text_IO; use Ada.Text_IO; |
| procedure Overwrite_Array is |
| type Arr is array (1 .. 5) of Integer; |
| X : Arr := (others => 1); |
| A : Arr; |
| for A'Address use X'Address; |
| | |
| >>> warning: default initialization of "A" may |
| modify "X", use pragma Import for "A" to |
| suppress initialization (RM B.1(24)) |
| |
| begin |
| if X /= Arr'(others => 1) then |
| Put_Line ("X was clobbered"); |
| else |
| Put_Line ("X was not clobbered"); |
| end if; |
| end Overwrite_Array; |
| @end example |
| |
| The above program generates the warning as shown, and at execution |
| time, prints @cite{X was clobbered}. If the @cite{pragma Import} is |
| added as suggested: |
| |
| @example |
| pragma Initialize_Scalars; |
| with Ada.Text_IO; use Ada.Text_IO; |
| procedure Overwrite_Array is |
| type Arr is array (1 .. 5) of Integer; |
| X : Arr := (others => 1); |
| A : Arr; |
| for A'Address use X'Address; |
| pragma Import (Ada, A); |
| begin |
| if X /= Arr'(others => 1) then |
| Put_Line ("X was clobbered"); |
| else |
| Put_Line ("X was not clobbered"); |
| end if; |
| end Overwrite_Array; |
| @end example |
| |
| then the program compiles without the warning and when run will generate |
| the output @cite{X was not clobbered}. |
| |
| @node Use of Address Clauses for Memory-Mapped I/O,Effect of Convention on Representation,Address Clauses,Representation Clauses and Pragmas |
| @anchor{gnat_rm/representation_clauses_and_pragmas id17}@anchor{238}@anchor{gnat_rm/representation_clauses_and_pragmas use-of-address-clauses-for-memory-mapped-i-o}@anchor{239} |
| @section Use of Address Clauses for Memory-Mapped I/O |
| |
| |
| @geindex Memory-mapped I/O |
| |
| A common pattern is to use an address clause to map an atomic variable to |
| a location in memory that corresponds to a memory-mapped I/O operation or |
| operations, for example: |
| |
| @example |
| type Mem_Word is record |
| A,B,C,D : Byte; |
| end record; |
| pragma Atomic (Mem_Word); |
| for Mem_Word_Size use 32; |
| |
| Mem : Mem_Word; |
| for Mem'Address use some-address; |
| ... |
| Temp := Mem; |
| Temp.A := 32; |
| Mem := Temp; |
| @end example |
| |
| For a full access (reference or modification) of the variable (Mem) in |
| this case, as in the above examples, GNAT guarantees that the entire atomic |
| word will be accessed. It is not clear whether the RM requires this. For |
| example in the above, can the compiler reference only the Mem.A field as |
| an optimization? Whatever the answer to this question is, GNAT makes the |
| guarantee that for such a reference, the entire word is read or written. |
| |
| A problem arises with a component access such as: |
| |
| @example |
| Mem.A := 32; |
| @end example |
| |
| Note that the component A is not declared as atomic. This means that it is |
| not clear what this assignment means. It could correspond to full word read |
| and write as given in the first example, or on architectures that supported |
| such an operation it might be a single byte store instruction. The RM does |
| not have anything to say in this situation, and GNAT does not make any |
| guarantee. The code generated may vary from target to target. GNAT will issue |
| a warning in such a case: |
| |
| @example |
| Mem.A := 32; |
| | |
| >>> warning: access to non-atomic component of atomic array, |
| may cause unexpected accesses to atomic object |
| @end example |
| |
| It is best to be explicit in this situation, by either declaring the |
| components to be atomic if you want the byte store, or explicitly writing |
| the full word access sequence if that is what the hardware requires. |
| |
| @node Effect of Convention on Representation,Conventions and Anonymous Access Types,Use of Address Clauses for Memory-Mapped I/O,Representation Clauses and Pragmas |
| @anchor{gnat_rm/representation_clauses_and_pragmas id18}@anchor{23a}@anchor{gnat_rm/representation_clauses_and_pragmas effect-of-convention-on-representation}@anchor{23b} |
| @section Effect of Convention on Representation |
| |
| |
| @geindex Convention |
| @geindex effect on representation |
| |
| Normally the specification of a foreign language convention for a type or |
| an object has no effect on the chosen representation. In particular, the |
| representation chosen for data in GNAT generally meets the standard system |
| conventions, and for example records are laid out in a manner that is |
| consistent with C. This means that specifying convention C (for example) |
| has no effect. |
| |
| There are four exceptions to this general rule: |
| |
| |
| @itemize * |
| |
| @item |
| @emph{Convention Fortran and array subtypes}. |
| |
| If pragma Convention Fortran is specified for an array subtype, then in |
| accordance with the implementation advice in section 3.6.2(11) of the |
| Ada Reference Manual, the array will be stored in a Fortran-compatible |
| column-major manner, instead of the normal default row-major order. |
| |
| @item |
| @emph{Convention C and enumeration types} |
| |
| GNAT normally stores enumeration types in 8, 16, or 32 bits as required |
| to accommodate all values of the type. For example, for the enumeration |
| type declared by: |
| |
| @example |
| type Color is (Red, Green, Blue); |
| @end example |
| |
| 8 bits is sufficient to store all values of the type, so by default, objects |
| of type @cite{Color} will be represented using 8 bits. However, normal C |
| convention is to use 32 bits for all enum values in C, since enum values |
| are essentially of type int. If pragma @cite{Convention C} is specified for an |
| Ada enumeration type, then the size is modified as necessary (usually to |
| 32 bits) to be consistent with the C convention for enum values. |
| |
| Note that this treatment applies only to types. If Convention C is given for |
| an enumeration object, where the enumeration type is not Convention C, then |
| Object_Size bits are allocated. For example, for a normal enumeration type, |
| with less than 256 elements, only 8 bits will be allocated for the object. |
| Since this may be a surprise in terms of what C expects, GNAT will issue a |
| warning in this situation. The warning can be suppressed by giving an explicit |
| size clause specifying the desired size. |
| |
| @item |
| @emph{Convention C/Fortran and Boolean types} |
| |
| In C, the usual convention for boolean values, that is values used for |
| conditions, is that zero represents false, and nonzero values represent |
| true. In Ada, the normal convention is that two specific values, typically |
| 0/1, are used to represent false/true respectively. |
| |
| Fortran has a similar convention for @cite{LOGICAL} values (any nonzero |
| value represents true). |
| |
| To accommodate the Fortran and C conventions, if a pragma Convention specifies |
| C or Fortran convention for a derived Boolean, as in the following example: |
| |
| @example |
| type C_Switch is new Boolean; |
| pragma Convention (C, C_Switch); |
| @end example |
| |
| then the GNAT generated code will treat any nonzero value as true. For truth |
| values generated by GNAT, the conventional value 1 will be used for True, but |
| when one of these values is read, any nonzero value is treated as True. |
| @end itemize |
| |
| @node Conventions and Anonymous Access Types,Determining the Representations chosen by GNAT,Effect of Convention on Representation,Representation Clauses and Pragmas |
| @anchor{gnat_rm/representation_clauses_and_pragmas conventions-and-anonymous-access-types}@anchor{23c}@anchor{gnat_rm/representation_clauses_and_pragmas id19}@anchor{23d} |
| @section Conventions and Anonymous Access Types |
| |
| |
| @geindex Anonymous access types |
| |
| @geindex Convention for anonymous access types |
| |
| The RM is not entirely clear on convention handling in a number of cases, |
| and in particular, it is not clear on the convention to be given to |
| anonymous access types in general, and in particular what is to be |
| done for the case of anonymous access-to-subprogram. |
| |
| In GNAT, we decide that if an explicit Convention is applied |
| to an object or component, and its type is such an anonymous type, |
| then the convention will apply to this anonymous type as well. This |
| seems to make sense since it is anomolous in any case to have a |
| different convention for an object and its type, and there is clearly |
| no way to explicitly specify a convention for an anonymous type, since |
| it doesn't have a name to specify! |
| |
| Furthermore, we decide that if a convention is applied to a record type, |
| then this convention is inherited by any of its components that are of an |
| anonymous access type which do not have an explicitly specified convention. |
| |
| The following program shows these conventions in action: |
| |
| @example |
| package ConvComp is |
| type Foo is range 1 .. 10; |
| type T1 is record |
| A : access function (X : Foo) return Integer; |
| B : Integer; |
| end record; |
| pragma Convention (C, T1); |
| |
| type T2 is record |
| A : access function (X : Foo) return Integer; |
| pragma Convention (C, A); |
| B : Integer; |
| end record; |
| pragma Convention (COBOL, T2); |
| |
| type T3 is record |
| A : access function (X : Foo) return Integer; |
| pragma Convention (COBOL, A); |
| B : Integer; |
| end record; |
| pragma Convention (C, T3); |
| |
| type T4 is record |
| A : access function (X : Foo) return Integer; |
| B : Integer; |
| end record; |
| pragma Convention (COBOL, T4); |
| |
| function F (X : Foo) return Integer; |
| pragma Convention (C, F); |
| |
| function F (X : Foo) return Integer is (13); |
| |
| TV1 : T1 := (F'Access, 12); -- OK |
| TV2 : T2 := (F'Access, 13); -- OK |
| |
| TV3 : T3 := (F'Access, 13); -- ERROR |
| | |
| >>> subprogram "F" has wrong convention |
| >>> does not match access to subprogram declared at line 17 |
| 38. TV4 : T4 := (F'Access, 13); -- ERROR |
| | |
| >>> subprogram "F" has wrong convention |
| >>> does not match access to subprogram declared at line 24 |
| 39. end ConvComp; |
| @end example |
| |
| @node Determining the Representations chosen by GNAT,,Conventions and Anonymous Access Types,Representation Clauses and Pragmas |
| @anchor{gnat_rm/representation_clauses_and_pragmas id20}@anchor{23e}@anchor{gnat_rm/representation_clauses_and_pragmas determining-the-representations-chosen-by-gnat}@anchor{23f} |
| @section Determining the Representations chosen by GNAT |
| |
| |
| @geindex Representation |
| @geindex determination of |
| |
| @geindex -gnatR (gcc) |
| |
| Although the descriptions in this section are intended to be complete, it is |
| often easier to simply experiment to see what GNAT accepts and what the |
| effect is on the layout of types and objects. |
| |
| As required by the Ada RM, if a representation clause is not accepted, then |
| it must be rejected as illegal by the compiler. However, when a |
| representation clause or pragma is accepted, there can still be questions |
| of what the compiler actually does. For example, if a partial record |
| representation clause specifies the location of some components and not |
| others, then where are the non-specified components placed? Or if pragma |
| @cite{Pack} is used on a record, then exactly where are the resulting |
| fields placed? The section on pragma @cite{Pack} in this chapter can be |
| used to answer the second question, but it is often easier to just see |
| what the compiler does. |
| |
| For this purpose, GNAT provides the option @emph{-gnatR}. If you compile |
| with this option, then the compiler will output information on the actual |
| representations chosen, in a format similar to source representation |
| clauses. For example, if we compile the package: |
| |
| @example |
| package q is |
| type r (x : boolean) is tagged record |
| case x is |
| when True => S : String (1 .. 100); |
| when False => null; |
| end case; |
| end record; |
| |
| type r2 is new r (false) with record |
| y2 : integer; |
| end record; |
| |
| for r2 use record |
| y2 at 16 range 0 .. 31; |
| end record; |
| |
| type x is record |
| y : character; |
| end record; |
| |
| type x1 is array (1 .. 10) of x; |
| for x1'component_size use 11; |
| |
| type ia is access integer; |
| |
| type Rb1 is array (1 .. 13) of Boolean; |
| pragma Pack (rb1); |
| |
| type Rb2 is array (1 .. 65) of Boolean; |
| pragma Pack (rb2); |
| |
| type x2 is record |
| l1 : Boolean; |
| l2 : Duration; |
| l3 : Float; |
| l4 : Boolean; |
| l5 : Rb1; |
| l6 : Rb2; |
| end record; |
| pragma Pack (x2); |
| end q; |
| @end example |
| |
| using the switch @emph{-gnatR} we obtain the following output: |
| |
| @example |
| Representation information for unit q |
| ------------------------------------- |
| |
| for r'Size use ??; |
| for r'Alignment use 4; |
| for r use record |
| x at 4 range 0 .. 7; |
| _tag at 0 range 0 .. 31; |
| s at 5 range 0 .. 799; |
| end record; |
| |
| for r2'Size use 160; |
| for r2'Alignment use 4; |
| for r2 use record |
| x at 4 range 0 .. 7; |
| _tag at 0 range 0 .. 31; |
| _parent at 0 range 0 .. 63; |
| y2 at 16 range 0 .. 31; |
| end record; |
| |
| for x'Size use 8; |
| for x'Alignment use 1; |
| for x use record |
| y at 0 range 0 .. 7; |
| end record; |
| |
| for x1'Size use 112; |
| for x1'Alignment use 1; |
| for x1'Component_Size use 11; |
| |
| for rb1'Size use 13; |
| for rb1'Alignment use 2; |
| for rb1'Component_Size use 1; |
| |
| for rb2'Size use 72; |
| for rb2'Alignment use 1; |
| for rb2'Component_Size use 1; |
| |
| for x2'Size use 224; |
| for x2'Alignment use 4; |
| for x2 use record |
| l1 at 0 range 0 .. 0; |
| l2 at 0 range 1 .. 64; |
| l3 at 12 range 0 .. 31; |
| l4 at 16 range 0 .. 0; |
| l5 at 16 range 1 .. 13; |
| l6 at 18 range 0 .. 71; |
| end record; |
| @end example |
| |
| The Size values are actually the Object_Size, i.e., the default size that |
| will be allocated for objects of the type. |
| The @code{??} size for type r indicates that we have a variant record, and the |
| actual size of objects will depend on the discriminant value. |
| |
| The Alignment values show the actual alignment chosen by the compiler |
| for each record or array type. |
| |
| The record representation clause for type r shows where all fields |
| are placed, including the compiler generated tag field (whose location |
| cannot be controlled by the programmer). |
| |
| The record representation clause for the type extension r2 shows all the |
| fields present, including the parent field, which is a copy of the fields |
| of the parent type of r2, i.e., r1. |
| |
| The component size and size clauses for types rb1 and rb2 show |
| the exact effect of pragma @cite{Pack} on these arrays, and the record |
| representation clause for type x2 shows how pragma @cite{Pack} affects |
| this record type. |
| |
| In some cases, it may be useful to cut and paste the representation clauses |
| generated by the compiler into the original source to fix and guarantee |
| the actual representation to be used. |
| |
| @node Standard Library Routines,The Implementation of Standard I/O,Representation Clauses and Pragmas,Top |
| @anchor{gnat_rm/standard_library_routines standard-library-routines}@anchor{e}@anchor{gnat_rm/standard_library_routines doc}@anchor{240}@anchor{gnat_rm/standard_library_routines id1}@anchor{241} |
| @chapter Standard Library Routines |
| |
| |
| The Ada Reference Manual contains in Annex A a full description of an |
| extensive set of standard library routines that can be used in any Ada |
| program, and which must be provided by all Ada compilers. They are |
| analogous to the standard C library used by C programs. |
| |
| GNAT implements all of the facilities described in annex A, and for most |
| purposes the description in the Ada Reference Manual, or appropriate Ada |
| text book, will be sufficient for making use of these facilities. |
| |
| In the case of the input-output facilities, |
| @ref{f,,The Implementation of Standard I/O}, |
| gives details on exactly how GNAT interfaces to the |
| file system. For the remaining packages, the Ada Reference Manual |
| should be sufficient. The following is a list of the packages included, |
| together with a brief description of the functionality that is provided. |
| |
| For completeness, references are included to other predefined library |
| routines defined in other sections of the Ada Reference Manual (these are |
| cross-indexed from Annex A). For further details see the relevant |
| package declarations in the run-time library. In particular, a few units |
| are not implemented, as marked by the presence of pragma Unimplemented_Unit, |
| and in this case the package declaration contains comments explaining why |
| the unit is not implemented. |
| |
| |
| @table @asis |
| |
| @item @code{Ada} @emph{(A.2)} |
| |
| This is a parent package for all the standard library packages. It is |
| usually included implicitly in your program, and itself contains no |
| useful data or routines. |
| |
| @item @code{Ada.Assertions} @emph{(11.4.2)} |
| |
| @cite{Assertions} provides the @cite{Assert} subprograms, and also |
| the declaration of the @cite{Assertion_Error} exception. |
| |
| @item @code{Ada.Asynchronous_Task_Control} @emph{(D.11)} |
| |
| @cite{Asynchronous_Task_Control} provides low level facilities for task |
| synchronization. It is typically not implemented. See package spec for details. |
| |
| @item @code{Ada.Calendar} @emph{(9.6)} |
| |
| @cite{Calendar} provides time of day access, and routines for |
| manipulating times and durations. |
| |
| @item @code{Ada.Calendar.Arithmetic} @emph{(9.6.1)} |
| |
| This package provides additional arithmetic |
| operations for @cite{Calendar}. |
| |
| @item @code{Ada.Calendar.Formatting} @emph{(9.6.1)} |
| |
| This package provides formatting operations for @cite{Calendar}. |
| |
| @item @code{Ada.Calendar.Time_Zones} @emph{(9.6.1)} |
| |
| This package provides additional @cite{Calendar} facilities |
| for handling time zones. |
| |
| @item @code{Ada.Characters} @emph{(A.3.1)} |
| |
| This is a dummy parent package that contains no useful entities |
| |
| @item @code{Ada.Characters.Conversions} @emph{(A.3.2)} |
| |
| This package provides character conversion functions. |
| |
| @item @code{Ada.Characters.Handling} @emph{(A.3.2)} |
| |
| This package provides some basic character handling capabilities, |
| including classification functions for classes of characters (e.g., test |
| for letters, or digits). |
| |
| @item @code{Ada.Characters.Latin_1} @emph{(A.3.3)} |
| |
| This package includes a complete set of definitions of the characters |
| that appear in type CHARACTER. It is useful for writing programs that |
| will run in international environments. For example, if you want an |
| upper case E with an acute accent in a string, it is often better to use |
| the definition of @cite{UC_E_Acute} in this package. Then your program |
| will print in an understandable manner even if your environment does not |
| support these extended characters. |
| |
| @item @code{Ada.Command_Line} @emph{(A.15)} |
| |
| This package provides access to the command line parameters and the name |
| of the current program (analogous to the use of @cite{argc} and @cite{argv} |
| in C), and also allows the exit status for the program to be set in a |
| system-independent manner. |
| |
| @item @code{Ada.Complex_Text_IO} @emph{(G.1.3)} |
| |
| This package provides text input and output of complex numbers. |
| |
| @item @code{Ada.Containers} @emph{(A.18.1)} |
| |
| A top level package providing a few basic definitions used by all the |
| following specific child packages that provide specific kinds of |
| containers. |
| @end table |
| |
| @code{Ada.Containers.Bounded_Priority_Queues} @emph{(A.18.31)} |
| |
| @code{Ada.Containers.Bounded_Synchronized_Queues} @emph{(A.18.29)} |
| |
| @code{Ada.Containers.Doubly_Linked_Lists} @emph{(A.18.3)} |
| |
| @code{Ada.Containers.Generic_Array_Sort} @emph{(A.18.26)} |
| |
| @code{Ada.Containers.Generic_Constrained_Array_Sort} @emph{(A.18.26)} |
| |
| @code{Ada.Containers.Generic_Sort} @emph{(A.18.26)} |
| |
| @code{Ada.Containers.Hashed_Maps} @emph{(A.18.5)} |
| |
| @code{Ada.Containers.Hashed_Sets} @emph{(A.18.8)} |
| |
| @code{Ada.Containers.Indefinite_Doubly_Linked_Lists} @emph{(A.18.12)} |
| |
| @code{Ada.Containers.Indefinite_Hashed_Maps} @emph{(A.18.13)} |
| |
| @code{Ada.Containers.Indefinite_Hashed_Sets} @emph{(A.18.15)} |
| |
| @code{Ada.Containers.Indefinite_Holders} @emph{(A.18.18)} |
| |
| @code{Ada.Containers.Indefinite_Multiway_Trees} @emph{(A.18.17)} |
| |
| @code{Ada.Containers.Indefinite_Ordered_Maps} @emph{(A.18.14)} |
| |
| @code{Ada.Containers.Indefinite_Ordered_Sets} @emph{(A.18.16)} |
| |
| @code{Ada.Containers.Indefinite_Vectors} @emph{(A.18.11)} |
| |
| @code{Ada.Containers.Multiway_Trees} @emph{(A.18.10)} |
| |
| @code{Ada.Containers.Ordered_Maps} @emph{(A.18.6)} |
| |
| @code{Ada.Containers.Ordered_Sets} @emph{(A.18.9)} |
| |
| @code{Ada.Containers.Synchronized_Queue_Interfaces} @emph{(A.18.27)} |
| |
| @code{Ada.Containers.Unbounded_Priority_Queues} @emph{(A.18.30)} |
| |
| @code{Ada.Containers.Unbounded_Synchronized_Queues} @emph{(A.18.28)} |
| |
| @code{Ada.Containers.Vectors} @emph{(A.18.2)} |
| |
| |
| @table @asis |
| |
| @item @code{Ada.Directories} @emph{(A.16)} |
| |
| This package provides operations on directories. |
| |
| @item @code{Ada.Directories.Hierarchical_File_Names} @emph{(A.16.1)} |
| |
| This package provides additional directory operations handling |
| hiearchical file names. |
| |
| @item @code{Ada.Directories.Information} @emph{(A.16)} |
| |
| This is an implementation defined package for additional directory |
| operations, which is not implemented in GNAT. |
| |
| @item @code{Ada.Decimal} @emph{(F.2)} |
| |
| This package provides constants describing the range of decimal numbers |
| implemented, and also a decimal divide routine (analogous to the COBOL |
| verb DIVIDE ... GIVING ... REMAINDER ...) |
| |
| @item @code{Ada.Direct_IO} @emph{(A.8.4)} |
| |
| This package provides input-output using a model of a set of records of |
| fixed-length, containing an arbitrary definite Ada type, indexed by an |
| integer record number. |
| |
| @item @code{Ada.Dispatching} @emph{(D.2.1)} |
| |
| A parent package containing definitions for task dispatching operations. |
| |
| @item @code{Ada.Dispatching.EDF} @emph{(D.2.6)} |
| |
| Not implemented in GNAT. |
| |
| @item @code{Ada.Dispatching.Non_Preemptive} @emph{(D.2.4)} |
| |
| Not implemented in GNAT. |
| |
| @item @code{Ada.Dispatching.Round_Robin} @emph{(D.2.5)} |
| |
| Not implemented in GNAT. |
| |
| @item @code{Ada.Dynamic_Priorities} @emph{(D.5)} |
| |
| This package allows the priorities of a task to be adjusted dynamically |
| as the task is running. |
| |
| @item @code{Ada.Environment_Variables} @emph{(A.17)} |
| |
| This package provides facilities for accessing environment variables. |
| |
| @item @code{Ada.Exceptions} @emph{(11.4.1)} |
| |
| This package provides additional information on exceptions, and also |
| contains facilities for treating exceptions as data objects, and raising |
| exceptions with associated messages. |
| |
| @item @code{Ada.Execution_Time} @emph{(D.14)} |
| |
| Not implemented in GNAT. |
| |
| @item @code{Ada.Execution_Time.Group_Budgets} @emph{(D.14.2)} |
| |
| Not implemented in GNAT. |
| |
| @item @code{Ada.Execution_Time.Timers} @emph{(D.14.1)'} |
| |
| Not implemented in GNAT. |
| |
| @item @code{Ada.Finalization} @emph{(7.6)} |
| |
| This package contains the declarations and subprograms to support the |
| use of controlled types, providing for automatic initialization and |
| finalization (analogous to the constructors and destructors of C++). |
| |
| @item @code{Ada.Float_Text_IO} @emph{(A.10.9)} |
| |
| A library level instantiation of Text_IO.Float_IO for type Float. |
| |
| @item @code{Ada.Float_Wide_Text_IO} @emph{(A.10.9)} |
| |
| A library level instantiation of Wide_Text_IO.Float_IO for type Float. |
| |
| @item @code{Ada.Float_Wide_Wide_Text_IO} @emph{(A.10.9)} |
| |
| A library level instantiation of Wide_Wide_Text_IO.Float_IO for type Float. |
| |
| @item @code{Ada.Integer_Text_IO} @emph{(A.10.9)} |
| |
| A library level instantiation of Text_IO.Integer_IO for type Integer. |
| |
| @item @code{Ada.Integer_Wide_Text_IO} @emph{(A.10.9)} |
| |
| A library level instantiation of Wide_Text_IO.Integer_IO for type Integer. |
| |
| @item @code{Ada.Integer_Wide_Wide_Text_IO} @emph{(A.10.9)} |
| |
| A library level instantiation of Wide_Wide_Text_IO.Integer_IO for type Integer. |
| |
| @item @code{Ada.Interrupts} @emph{(C.3.2)} |
| |
| This package provides facilities for interfacing to interrupts, which |
| includes the set of signals or conditions that can be raised and |
| recognized as interrupts. |
| |
| @item @code{Ada.Interrupts.Names} @emph{(C.3.2)} |
| |
| This package provides the set of interrupt names (actually signal |
| or condition names) that can be handled by GNAT. |
| |
| @item @code{Ada.IO_Exceptions} @emph{(A.13)} |
| |
| This package defines the set of exceptions that can be raised by use of |
| the standard IO packages. |
| |
| @item @code{Ada.Iterator_Interfaces} @emph{(5.5.1)} |
| |
| This package provides a generic interface to generalized iterators. |
| |
| @item @code{Ada.Locales} @emph{(A.19)} |
| |
| This package provides declarations providing information (Language |
| and Country) about the current locale. |
| |
| @item @code{Ada.Numerics} |
| |
| This package contains some standard constants and exceptions used |
| throughout the numerics packages. Note that the constants pi and e are |
| defined here, and it is better to use these definitions than rolling |
| your own. |
| |
| @item @code{Ada.Numerics.Complex_Arrays} @emph{(G.3.2)} |
| |
| Provides operations on arrays of complex numbers. |
| |
| @item @code{Ada.Numerics.Complex_Elementary_Functions} |
| |
| Provides the implementation of standard elementary functions (such as |
| log and trigonometric functions) operating on complex numbers using the |
| standard @cite{Float} and the @cite{Complex} and @cite{Imaginary} types |
| created by the package @cite{Numerics.Complex_Types}. |
| |
| @item @code{Ada.Numerics.Complex_Types} |
| |
| This is a predefined instantiation of |
| @cite{Numerics.Generic_Complex_Types} using @cite{Standard.Float} to |
| build the type @cite{Complex} and @cite{Imaginary}. |
| |
| @item @code{Ada.Numerics.Discrete_Random} |
| |
| This generic package provides a random number generator suitable for generating |
| uniformly distributed values of a specified discrete subtype. |
| |
| @item @code{Ada.Numerics.Float_Random} |
| |
| This package provides a random number generator suitable for generating |
| uniformly distributed floating point values in the unit interval. |
| |
| @item @code{Ada.Numerics.Generic_Complex_Elementary_Functions} |
| |
| This is a generic version of the package that provides the |
| implementation of standard elementary functions (such as log and |
| trigonometric functions) for an arbitrary complex type. |
| |
| The following predefined instantiations of this package are provided: |
| |
| |
| @itemize * |
| |
| @item |
| @code{Short_Float} |
| |
| @cite{Ada.Numerics.Short_Complex_Elementary_Functions} |
| |
| @item |
| @code{Float} |
| |
| @cite{Ada.Numerics.Complex_Elementary_Functions} |
| |
| @item |
| @code{Long_Float} |
| |
| @cite{Ada.Numerics.Long_Complex_Elementary_Functions} |
| @end itemize |
| |
| @item @code{Ada.Numerics.Generic_Complex_Types} |
| |
| This is a generic package that allows the creation of complex types, |
| with associated complex arithmetic operations. |
| |
| The following predefined instantiations of this package exist |
| |
| |
| @itemize * |
| |
| @item |
| @code{Short_Float} |
| |
| @cite{Ada.Numerics.Short_Complex_Complex_Types} |
| |
| @item |
| @code{Float} |
| |
| @cite{Ada.Numerics.Complex_Complex_Types} |
| |
| @item |
| @code{Long_Float} |
| |
| @cite{Ada.Numerics.Long_Complex_Complex_Types} |
| @end itemize |
| |
| @item @code{Ada.Numerics.Generic_Elementary_Functions} |
| |
| This is a generic package that provides the implementation of standard |
| elementary functions (such as log an trigonometric functions) for an |
| arbitrary float type. |
| |
| The following predefined instantiations of this package exist |
| |
| |
| @itemize * |
| |
| @item |
| @code{Short_Float} |
| |
| @cite{Ada.Numerics.Short_Elementary_Functions} |
| |
| @item |
| @code{Float} |
| |
| @cite{Ada.Numerics.Elementary_Functions} |
| |
| @item |
| @code{Long_Float} |
| |
| @cite{Ada.Numerics.Long_Elementary_Functions} |
| @end itemize |
| |
| @item @code{Ada.Numerics.Generic_Real_Arrays} @emph{(G.3.1)} |
| |
| Generic operations on arrays of reals |
| |
| @item @code{Ada.Numerics.Real_Arrays} @emph{(G.3.1)} |
| |
| Preinstantiation of Ada.Numerics.Generic_Real_Arrays (Float). |
| |
| @item @code{Ada.Real_Time} @emph{(D.8)} |
| |
| This package provides facilities similar to those of @cite{Calendar}, but |
| operating with a finer clock suitable for real time control. Note that |
| annex D requires that there be no backward clock jumps, and GNAT generally |
| guarantees this behavior, but of course if the external clock on which |
| the GNAT runtime depends is deliberately reset by some external event, |
| then such a backward jump may occur. |
| |
| @item @code{Ada.Real_Time.Timing_Events} @emph{(D.15)} |
| |
| Not implemented in GNAT. |
| |
| @item @code{Ada.Sequential_IO} @emph{(A.8.1)} |
| |
| This package provides input-output facilities for sequential files, |
| which can contain a sequence of values of a single type, which can be |
| any Ada type, including indefinite (unconstrained) types. |
| |
| @item @code{Ada.Storage_IO} @emph{(A.9)} |
| |
| This package provides a facility for mapping arbitrary Ada types to and |
| from a storage buffer. It is primarily intended for the creation of new |
| IO packages. |
| |
| @item @code{Ada.Streams} @emph{(13.13.1)} |
| |
| This is a generic package that provides the basic support for the |
| concept of streams as used by the stream attributes (@cite{Input}, |
| @cite{Output}, @cite{Read} and @cite{Write}). |
| |
| @item @code{Ada.Streams.Stream_IO} @emph{(A.12.1)} |
| |
| This package is a specialization of the type @cite{Streams} defined in |
| package @cite{Streams} together with a set of operations providing |
| Stream_IO capability. The Stream_IO model permits both random and |
| sequential access to a file which can contain an arbitrary set of values |
| of one or more Ada types. |
| |
| @item @code{Ada.Strings} @emph{(A.4.1)} |
| |
| This package provides some basic constants used by the string handling |
| packages. |
| |
| @item @code{Ada.Strings.Bounded} @emph{(A.4.4)} |
| |
| This package provides facilities for handling variable length |
| strings. The bounded model requires a maximum length. It is thus |
| somewhat more limited than the unbounded model, but avoids the use of |
| dynamic allocation or finalization. |
| |
| @item @code{Ada.Strings.Bounded.Equal_Case_Insensitive} @emph{(A.4.10)} |
| |
| Provides case-insensitive comparisons of bounded strings |
| |
| @item @code{Ada.Strings.Bounded.Hash} @emph{(A.4.9)} |
| |
| This package provides a generic hash function for bounded strings |
| |
| @item @code{Ada.Strings.Bounded.Hash_Case_Insensitive} @emph{(A.4.9)} |
| |
| This package provides a generic hash function for bounded strings that |
| converts the string to be hashed to lower case. |
| |
| @item @code{Ada.Strings.Bounded.Less_Case_Insensitive} @emph{(A.4.10)} |
| |
| This package provides a comparison function for bounded strings that works |
| in a case insensitive manner by converting to lower case before the comparison. |
| |
| @item @code{Ada.Strings.Fixed} @emph{(A.4.3)} |
| |
| This package provides facilities for handling fixed length strings. |
| |
| @item @code{Ada.Strings.Fixed.Equal_Case_Insensitive} @emph{(A.4.10)} |
| |
| This package provides an equality function for fixed strings that compares |
| the strings after converting both to lower case. |
| |
| @item @code{Ada.Strings.Fixed.Hash_Case_Insensitive} @emph{(A.4.9)} |
| |
| This package provides a case insensitive hash function for fixed strings that |
| converts the string to lower case before computing the hash. |
| |
| @item @code{Ada.Strings.Fixed.Less_Case_Insensitive} @emph{(A.4.10)} |
| |
| This package provides a comparison function for fixed strings that works |
| in a case insensitive manner by converting to lower case before the comparison. |
| |
| @item @code{Ada.Strings.Hash} @emph{(A.4.9)} |
| |
| This package provides a hash function for strings. |
| |
| @item @code{Ada.Strings.Hash_Case_Insensitive} @emph{(A.4.9)} |
| |
| This package provides a hash function for strings that is case insensitive. |
| The string is converted to lower case before computing the hash. |
| |
| @item @code{Ada.Strings.Less_Case_Insensitive} @emph{(A.4.10)} |
| |
| This package provides a comparison function for\strings that works |
| in a case insensitive manner by converting to lower case before the comparison. |
| |
| @item @code{Ada.Strings.Maps} @emph{(A.4.2)} |
| |
| This package provides facilities for handling character mappings and |
| arbitrarily defined subsets of characters. For instance it is useful in |
| defining specialized translation tables. |
| |
| @item @code{Ada.Strings.Maps.Constants} @emph{(A.4.6)} |
| |
| This package provides a standard set of predefined mappings and |
| predefined character sets. For example, the standard upper to lower case |
| conversion table is found in this package. Note that upper to lower case |
| conversion is non-trivial if you want to take the entire set of |
| characters, including extended characters like E with an acute accent, |
| into account. You should use the mappings in this package (rather than |
| adding 32 yourself) to do case mappings. |
| |
| @item @code{Ada.Strings.Unbounded} @emph{(A.4.5)} |
| |
| This package provides facilities for handling variable length |
| strings. The unbounded model allows arbitrary length strings, but |
| requires the use of dynamic allocation and finalization. |
| |
| @item @code{Ada.Strings.Unbounded.Equal_Case_Insensitive} @emph{(A.4.10)} |
| |
| Provides case-insensitive comparisons of unbounded strings |
| |
| @item @code{Ada.Strings.Unbounded.Hash} @emph{(A.4.9)} |
| |
| This package provides a generic hash function for unbounded strings |
| |
| @item @code{Ada.Strings.Unbounded.Hash_Case_Insensitive} @emph{(A.4.9)} |
| |
| This package provides a generic hash function for unbounded strings that |
| converts the string to be hashed to lower case. |
| |
| @item @code{Ada.Strings.Unbounded.Less_Case_Insensitive} @emph{(A.4.10)} |
| |
| This package provides a comparison function for unbounded strings that works |
| in a case insensitive manner by converting to lower case before the comparison. |
| |
| @item @code{Ada.Strings.UTF_Encoding} @emph{(A.4.11)} |
| |
| This package provides basic definitions for dealing with UTF-encoded strings. |
| |
| @item @code{Ada.Strings.UTF_Encoding.Conversions} @emph{(A.4.11)} |
| |
| This package provides conversion functions for UTF-encoded strings. |
| @end table |
| |
| @code{Ada.Strings.UTF_Encoding.Strings} @emph{(A.4.11)} |
| |
| @code{Ada.Strings.UTF_Encoding.Wide_Strings} @emph{(A.4.11)} |
| |
| |
| @table @asis |
| |
| @item @code{Ada.Strings.UTF_Encoding.Wide_Wide_Strings} @emph{(A.4.11)} |
| |
| These packages provide facilities for handling UTF encodings for |
| Strings, Wide_Strings and Wide_Wide_Strings. |
| @end table |
| |
| @code{Ada.Strings.Wide_Bounded} @emph{(A.4.7)} |
| |
| @code{Ada.Strings.Wide_Fixed} @emph{(A.4.7)} |
| |
| @code{Ada.Strings.Wide_Maps} @emph{(A.4.7)} |
| |
| |
| @table @asis |
| |
| @item @code{Ada.Strings.Wide_Unbounded} @emph{(A.4.7)} |
| |
| These packages provide analogous capabilities to the corresponding |
| packages without @code{Wide_} in the name, but operate with the types |
| @cite{Wide_String} and @cite{Wide_Character} instead of @cite{String} |
| and @cite{Character}. Versions of all the child packages are available. |
| @end table |
| |
| @code{Ada.Strings.Wide_Wide_Bounded} @emph{(A.4.7)} |
| |
| @code{Ada.Strings.Wide_Wide_Fixed} @emph{(A.4.7)} |
| |
| @code{Ada.Strings.Wide_Wide_Maps} @emph{(A.4.7)} |
| |
| |
| @table @asis |
| |
| @item @code{Ada.Strings.Wide_Wide_Unbounded} @emph{(A.4.7)} |
| |
| These packages provide analogous capabilities to the corresponding |
| packages without @code{Wide_} in the name, but operate with the types |
| @cite{Wide_Wide_String} and @cite{Wide_Wide_Character} instead |
| of @cite{String} and @cite{Character}. |
| |
| @item @code{Ada.Synchronous_Barriers} @emph{(D.10.1)} |
| |
| This package provides facilities for synchronizing tasks at a low level |
| with barriers. |
| |
| @item @code{Ada.Synchronous_Task_Control} @emph{(D.10)} |
| |
| This package provides some standard facilities for controlling task |
| communication in a synchronous manner. |
| |
| @item @code{Ada.Synchronous_Task_Control.EDF} @emph{(D.10)} |
| |
| Not implemented in GNAT. |
| |
| @item @code{Ada.Tags} |
| |
| This package contains definitions for manipulation of the tags of tagged |
| values. |
| |
| @item @code{Ada.Tags.Generic_Dispatching_Constructor} @emph{(3.9)} |
| |
| This package provides a way of constructing tagged class-wide values given |
| only the tag value. |
| |
| @item @code{Ada.Task_Attributes} @emph{(C.7.2)} |
| |
| This package provides the capability of associating arbitrary |
| task-specific data with separate tasks. |
| |
| @item @code{Ada.Task_Identifification} @emph{(C.7.1)} |
| |
| This package provides capabilities for task identification. |
| |
| @item @code{Ada.Task_Termination} @emph{(C.7.3)} |
| |
| This package provides control over task termination. |
| |
| @item @code{Ada.Text_IO} |
| |
| This package provides basic text input-output capabilities for |
| character, string and numeric data. The subpackages of this |
| package are listed next. Note that although these are defined |
| as subpackages in the RM, they are actually transparently |
| implemented as child packages in GNAT, meaning that they |
| are only loaded if needed. |
| |
| @item @code{Ada.Text_IO.Decimal_IO} |
| |
| Provides input-output facilities for decimal fixed-point types |
| |
| @item @code{Ada.Text_IO.Enumeration_IO} |
| |
| Provides input-output facilities for enumeration types. |
| |
| @item @code{Ada.Text_IO.Fixed_IO} |
| |
| Provides input-output facilities for ordinary fixed-point types. |
| |
| @item @code{Ada.Text_IO.Float_IO} |
| |
| Provides input-output facilities for float types. The following |
| predefined instantiations of this generic package are available: |
| |
| |
| @itemize * |
| |
| @item |
| @code{Short_Float} |
| |
| @cite{Short_Float_Text_IO} |
| |
| @item |
| @code{Float} |
| |
| @cite{Float_Text_IO} |
| |
| @item |
| @code{Long_Float} |
| |
| @cite{Long_Float_Text_IO} |
| @end itemize |
| |
| @item @code{Ada.Text_IO.Integer_IO} |
| |
| Provides input-output facilities for integer types. The following |
| predefined instantiations of this generic package are available: |
| |
| |
| @itemize * |
| |
| @item |
| @code{Short_Short_Integer} |
| |
| @cite{Ada.Short_Short_Integer_Text_IO} |
| |
| @item |
| @code{Short_Integer} |
| |
| @cite{Ada.Short_Integer_Text_IO} |
| |
| @item |
| @code{Integer} |
| |
| @cite{Ada.Integer_Text_IO} |
| |
| @item |
| @code{Long_Integer} |
| |
| @cite{Ada.Long_Integer_Text_IO} |
| |
| @item |
| @code{Long_Long_Integer} |
| |
| @cite{Ada.Long_Long_Integer_Text_IO} |
| @end itemize |
| |
| @item @code{Ada.Text_IO.Modular_IO} |
| |
| Provides input-output facilities for modular (unsigned) types. |
| |
| @item @code{Ada.Text_IO.Bounded_IO (A.10.11)} |
| |
| Provides input-output facilities for bounded strings. |
| |
| @item @code{Ada.Text_IO.Complex_IO (G.1.3)} |
| |
| This package provides basic text input-output capabilities for complex |
| data. |
| |
| @item @code{Ada.Text_IO.Editing (F.3.3)} |
| |
| This package contains routines for edited output, analogous to the use |
| of pictures in COBOL. The picture formats used by this package are a |
| close copy of the facility in COBOL. |
| |
| @item @code{Ada.Text_IO.Text_Streams (A.12.2)} |
| |
| This package provides a facility that allows Text_IO files to be treated |
| as streams, so that the stream attributes can be used for writing |
| arbitrary data, including binary data, to Text_IO files. |
| |
| @item @code{Ada.Text_IO.Unbounded_IO (A.10.12)} |
| |
| This package provides input-output facilities for unbounded strings. |
| |
| @item @code{Ada.Unchecked_Conversion (13.9)} |
| |
| This generic package allows arbitrary conversion from one type to |
| another of the same size, providing for breaking the type safety in |
| special circumstances. |
| |
| If the types have the same Size (more accurately the same Value_Size), |
| then the effect is simply to transfer the bits from the source to the |
| target type without any modification. This usage is well defined, and |
| for simple types whose representation is typically the same across |
| all implementations, gives a portable method of performing such |
| conversions. |
| |
| If the types do not have the same size, then the result is implementation |
| defined, and thus may be non-portable. The following describes how GNAT |
| handles such unchecked conversion cases. |
| |
| If the types are of different sizes, and are both discrete types, then |
| the effect is of a normal type conversion without any constraint checking. |
| In particular if the result type has a larger size, the result will be |
| zero or sign extended. If the result type has a smaller size, the result |
| will be truncated by ignoring high order bits. |
| |
| If the types are of different sizes, and are not both discrete types, |
| then the conversion works as though pointers were created to the source |
| and target, and the pointer value is converted. The effect is that bits |
| are copied from successive low order storage units and bits of the source |
| up to the length of the target type. |
| |
| A warning is issued if the lengths differ, since the effect in this |
| case is implementation dependent, and the above behavior may not match |
| that of some other compiler. |
| |
| A pointer to one type may be converted to a pointer to another type using |
| unchecked conversion. The only case in which the effect is undefined is |
| when one or both pointers are pointers to unconstrained array types. In |
| this case, the bounds information may get incorrectly transferred, and in |
| particular, GNAT uses double size pointers for such types, and it is |
| meaningless to convert between such pointer types. GNAT will issue a |
| warning if the alignment of the target designated type is more strict |
| than the alignment of the source designated type (since the result may |
| be unaligned in this case). |
| |
| A pointer other than a pointer to an unconstrained array type may be |
| converted to and from System.Address. Such usage is common in Ada 83 |
| programs, but note that Ada.Address_To_Access_Conversions is the |
| preferred method of performing such conversions in Ada 95 and Ada 2005. |
| Neither |
| unchecked conversion nor Ada.Address_To_Access_Conversions should be |
| used in conjunction with pointers to unconstrained objects, since |
| the bounds information cannot be handled correctly in this case. |
| |
| @item @code{Ada.Unchecked_Deallocation} @emph{(13.11.2)} |
| |
| This generic package allows explicit freeing of storage previously |
| allocated by use of an allocator. |
| |
| @item @code{Ada.Wide_Text_IO} @emph{(A.11)} |
| |
| This package is similar to @cite{Ada.Text_IO}, except that the external |
| file supports wide character representations, and the internal types are |
| @cite{Wide_Character} and @cite{Wide_String} instead of @cite{Character} |
| and @cite{String}. The corresponding set of nested packages and child |
| packages are defined. |
| |
| @item @code{Ada.Wide_Wide_Text_IO} @emph{(A.11)} |
| |
| This package is similar to @cite{Ada.Text_IO}, except that the external |
| file supports wide character representations, and the internal types are |
| @cite{Wide_Character} and @cite{Wide_String} instead of @cite{Character} |
| and @cite{String}. The corresponding set of nested packages and child |
| packages are defined. |
| @end table |
| |
| For packages in Interfaces and System, all the RM defined packages are |
| available in GNAT, see the Ada 2012 RM for full details. |
| |
| @node The Implementation of Standard I/O,The GNAT Library,Standard Library Routines,Top |
| @anchor{gnat_rm/the_implementation_of_standard_i_o the-implementation-of-standard-i-o}@anchor{f}@anchor{gnat_rm/the_implementation_of_standard_i_o doc}@anchor{242}@anchor{gnat_rm/the_implementation_of_standard_i_o id1}@anchor{243} |
| @chapter The Implementation of Standard I/O |
| |
| |
| GNAT implements all the required input-output facilities described in |
| A.6 through A.14. These sections of the Ada Reference Manual describe the |
| required behavior of these packages from the Ada point of view, and if |
| you are writing a portable Ada program that does not need to know the |
| exact manner in which Ada maps to the outside world when it comes to |
| reading or writing external files, then you do not need to read this |
| chapter. As long as your files are all regular files (not pipes or |
| devices), and as long as you write and read the files only from Ada, the |
| description in the Ada Reference Manual is sufficient. |
| |
| However, if you want to do input-output to pipes or other devices, such |
| as the keyboard or screen, or if the files you are dealing with are |
| either generated by some other language, or to be read by some other |
| language, then you need to know more about the details of how the GNAT |
| implementation of these input-output facilities behaves. |
| |
| In this chapter we give a detailed description of exactly how GNAT |
| interfaces to the file system. As always, the sources of the system are |
| available to you for answering questions at an even more detailed level, |
| but for most purposes the information in this chapter will suffice. |
| |
| Another reason that you may need to know more about how input-output is |
| implemented arises when you have a program written in mixed languages |
| where, for example, files are shared between the C and Ada sections of |
| the same program. GNAT provides some additional facilities, in the form |
| of additional child library packages, that facilitate this sharing, and |
| these additional facilities are also described in this chapter. |
| |
| @menu |
| * Standard I/O Packages:: |
| * FORM Strings:: |
| * Direct_IO:: |
| * Sequential_IO:: |
| * Text_IO:: |
| * Wide_Text_IO:: |
| * Wide_Wide_Text_IO:: |
| * Stream_IO:: |
| * Text Translation:: |
| * Shared Files:: |
| * Filenames encoding:: |
| * File content encoding:: |
| * Open Modes:: |
| * Operations on C Streams:: |
| * Interfacing to C Streams:: |
| |
| @end menu |
| |
| @node Standard I/O Packages,FORM Strings,,The Implementation of Standard I/O |
| @anchor{gnat_rm/the_implementation_of_standard_i_o standard-i-o-packages}@anchor{244}@anchor{gnat_rm/the_implementation_of_standard_i_o id2}@anchor{245} |
| @section Standard I/O Packages |
| |
| |
| The Standard I/O packages described in Annex A for |
| |
| |
| @itemize * |
| |
| @item |
| Ada.Text_IO |
| |
| @item |
| Ada.Text_IO.Complex_IO |
| |
| @item |
| Ada.Text_IO.Text_Streams |
| |
| @item |
| Ada.Wide_Text_IO |
| |
| @item |
| Ada.Wide_Text_IO.Complex_IO |
| |
| @item |
| Ada.Wide_Text_IO.Text_Streams |
| |
| @item |
| Ada.Wide_Wide_Text_IO |
| |
| @item |
| Ada.Wide_Wide_Text_IO.Complex_IO |
| |
| @item |
| Ada.Wide_Wide_Text_IO.Text_Streams |
| |
| @item |
| Ada.Stream_IO |
| |
| @item |
| Ada.Sequential_IO |
| |
| @item |
| Ada.Direct_IO |
| @end itemize |
| |
| are implemented using the C |
| library streams facility; where |
| |
| |
| @itemize * |
| |
| @item |
| All files are opened using @cite{fopen}. |
| |
| @item |
| All input/output operations use @cite{fread}/@cite{fwrite}. |
| @end itemize |
| |
| There is no internal buffering of any kind at the Ada library level. The only |
| buffering is that provided at the system level in the implementation of the |
| library routines that support streams. This facilitates shared use of these |
| streams by mixed language programs. Note though that system level buffering is |
| explicitly enabled at elaboration of the standard I/O packages and that can |
| have an impact on mixed language programs, in particular those using I/O before |
| calling the Ada elaboration routine (e.g., adainit). It is recommended to call |
| the Ada elaboration routine before performing any I/O or when impractical, |
| flush the common I/O streams and in particular Standard_Output before |
| elaborating the Ada code. |
| |
| @node FORM Strings,Direct_IO,Standard I/O Packages,The Implementation of Standard I/O |
| @anchor{gnat_rm/the_implementation_of_standard_i_o form-strings}@anchor{246}@anchor{gnat_rm/the_implementation_of_standard_i_o id3}@anchor{247} |
| @section FORM Strings |
| |
| |
| The format of a FORM string in GNAT is: |
| |
| @example |
| "keyword=value,keyword=value,...,keyword=value" |
| @end example |
| |
| where letters may be in upper or lower case, and there are no spaces |
| between values. The order of the entries is not important. Currently |
| the following keywords defined. |
| |
| @example |
| TEXT_TRANSLATION=[YES|NO|TEXT|BINARY|U8TEXT|WTEXT|U16TEXT] |
| SHARED=[YES|NO] |
| WCEM=[n|h|u|s|e|8|b] |
| ENCODING=[UTF8|8BITS] |
| @end example |
| |
| The use of these parameters is described later in this section. If an |
| unrecognized keyword appears in a form string, it is silently ignored |
| and not considered invalid. |
| |
| @node Direct_IO,Sequential_IO,FORM Strings,The Implementation of Standard I/O |
| @anchor{gnat_rm/the_implementation_of_standard_i_o direct-io}@anchor{248}@anchor{gnat_rm/the_implementation_of_standard_i_o id4}@anchor{249} |
| @section Direct_IO |
| |
| |
| Direct_IO can only be instantiated for definite types. This is a |
| restriction of the Ada language, which means that the records are fixed |
| length (the length being determined by @code{type'Size}, rounded |
| up to the next storage unit boundary if necessary). |
| |
| The records of a Direct_IO file are simply written to the file in index |
| sequence, with the first record starting at offset zero, and subsequent |
| records following. There is no control information of any kind. For |
| example, if 32-bit integers are being written, each record takes |
| 4-bytes, so the record at index @cite{K} starts at offset |
| (@cite{K}-1)*4. |
| |
| There is no limit on the size of Direct_IO files, they are expanded as |
| necessary to accommodate whatever records are written to the file. |
| |
| @node Sequential_IO,Text_IO,Direct_IO,The Implementation of Standard I/O |
| @anchor{gnat_rm/the_implementation_of_standard_i_o sequential-io}@anchor{24a}@anchor{gnat_rm/the_implementation_of_standard_i_o id5}@anchor{24b} |
| @section Sequential_IO |
| |
| |
| Sequential_IO may be instantiated with either a definite (constrained) |
| or indefinite (unconstrained) type. |
| |
| For the definite type case, the elements written to the file are simply |
| the memory images of the data values with no control information of any |
| kind. The resulting file should be read using the same type, no validity |
| checking is performed on input. |
| |
| For the indefinite type case, the elements written consist of two |
| parts. First is the size of the data item, written as the memory image |
| of a @cite{Interfaces.C.size_t} value, followed by the memory image of |
| the data value. The resulting file can only be read using the same |
| (unconstrained) type. Normal assignment checks are performed on these |
| read operations, and if these checks fail, @cite{Data_Error} is |
| raised. In particular, in the array case, the lengths must match, and in |
| the variant record case, if the variable for a particular read operation |
| is constrained, the discriminants must match. |
| |
| Note that it is not possible to use Sequential_IO to write variable |
| length array items, and then read the data back into different length |
| arrays. For example, the following will raise @cite{Data_Error}: |
| |
| @example |
| package IO is new Sequential_IO (String); |
| F : IO.File_Type; |
| S : String (1..4); |
| ... |
| IO.Create (F) |
| IO.Write (F, "hello!") |
| IO.Reset (F, Mode=>In_File); |
| IO.Read (F, S); |
| Put_Line (S); |
| @end example |
| |
| On some Ada implementations, this will print @cite{hell}, but the program is |
| clearly incorrect, since there is only one element in the file, and that |
| element is the string @cite{hello!}. |
| |
| In Ada 95 and Ada 2005, this kind of behavior can be legitimately achieved |
| using Stream_IO, and this is the preferred mechanism. In particular, the |
| above program fragment rewritten to use Stream_IO will work correctly. |
| |
| @node Text_IO,Wide_Text_IO,Sequential_IO,The Implementation of Standard I/O |
| @anchor{gnat_rm/the_implementation_of_standard_i_o id6}@anchor{24c}@anchor{gnat_rm/the_implementation_of_standard_i_o text-io}@anchor{24d} |
| @section Text_IO |
| |
| |
| Text_IO files consist of a stream of characters containing the following |
| special control characters: |
| |
| @example |
| LF (line feed, 16#0A#) Line Mark |
| FF (form feed, 16#0C#) Page Mark |
| @end example |
| |
| A canonical Text_IO file is defined as one in which the following |
| conditions are met: |
| |
| |
| @itemize * |
| |
| @item |
| The character @cite{LF} is used only as a line mark, i.e., to mark the end |
| of the line. |
| |
| @item |
| The character @cite{FF} is used only as a page mark, i.e., to mark the |
| end of a page and consequently can appear only immediately following a |
| @cite{LF} (line mark) character. |
| |
| @item |
| The file ends with either @cite{LF} (line mark) or @cite{LF}-@cite{FF} |
| (line mark, page mark). In the former case, the page mark is implicitly |
| assumed to be present. |
| @end itemize |
| |
| A file written using Text_IO will be in canonical form provided that no |
| explicit @cite{LF} or @cite{FF} characters are written using @cite{Put} |
| or @cite{Put_Line}. There will be no @cite{FF} character at the end of |
| the file unless an explicit @cite{New_Page} operation was performed |
| before closing the file. |
| |
| A canonical Text_IO file that is a regular file (i.e., not a device or a |
| pipe) can be read using any of the routines in Text_IO. The |
| semantics in this case will be exactly as defined in the Ada Reference |
| Manual, and all the routines in Text_IO are fully implemented. |
| |
| A text file that does not meet the requirements for a canonical Text_IO |
| file has one of the following: |
| |
| |
| @itemize * |
| |
| @item |
| The file contains @cite{FF} characters not immediately following a |
| @cite{LF} character. |
| |
| @item |
| The file contains @cite{LF} or @cite{FF} characters written by |
| @cite{Put} or @cite{Put_Line}, which are not logically considered to be |
| line marks or page marks. |
| |
| @item |
| The file ends in a character other than @cite{LF} or @cite{FF}, |
| i.e., there is no explicit line mark or page mark at the end of the file. |
| @end itemize |
| |
| Text_IO can be used to read such non-standard text files but subprograms |
| to do with line or page numbers do not have defined meanings. In |
| particular, a @cite{FF} character that does not follow a @cite{LF} |
| character may or may not be treated as a page mark from the point of |
| view of page and line numbering. Every @cite{LF} character is considered |
| to end a line, and there is an implied @cite{LF} character at the end of |
| the file. |
| |
| @menu |
| * Stream Pointer Positioning:: |
| * Reading and Writing Non-Regular Files:: |
| * Get_Immediate:: |
| * Treating Text_IO Files as Streams:: |
| * Text_IO Extensions:: |
| * Text_IO Facilities for Unbounded Strings:: |
| |
| @end menu |
| |
| @node Stream Pointer Positioning,Reading and Writing Non-Regular Files,,Text_IO |
| @anchor{gnat_rm/the_implementation_of_standard_i_o id7}@anchor{24e}@anchor{gnat_rm/the_implementation_of_standard_i_o stream-pointer-positioning}@anchor{24f} |
| @subsection Stream Pointer Positioning |
| |
| |
| @cite{Ada.Text_IO} has a definition of current position for a file that |
| is being read. No internal buffering occurs in Text_IO, and usually the |
| physical position in the stream used to implement the file corresponds |
| to this logical position defined by Text_IO. There are two exceptions: |
| |
| |
| @itemize * |
| |
| @item |
| After a call to @cite{End_Of_Page} that returns @cite{True}, the stream |
| is positioned past the @cite{LF} (line mark) that precedes the page |
| mark. Text_IO maintains an internal flag so that subsequent read |
| operations properly handle the logical position which is unchanged by |
| the @cite{End_Of_Page} call. |
| |
| @item |
| After a call to @cite{End_Of_File} that returns @cite{True}, if the |
| Text_IO file was positioned before the line mark at the end of file |
| before the call, then the logical position is unchanged, but the stream |
| is physically positioned right at the end of file (past the line mark, |
| and past a possible page mark following the line mark. Again Text_IO |
| maintains internal flags so that subsequent read operations properly |
| handle the logical position. |
| @end itemize |
| |
| These discrepancies have no effect on the observable behavior of |
| Text_IO, but if a single Ada stream is shared between a C program and |
| Ada program, or shared (using @code{shared=yes} in the form string) |
| between two Ada files, then the difference may be observable in some |
| situations. |
| |
| @node Reading and Writing Non-Regular Files,Get_Immediate,Stream Pointer Positioning,Text_IO |
| @anchor{gnat_rm/the_implementation_of_standard_i_o reading-and-writing-non-regular-files}@anchor{250}@anchor{gnat_rm/the_implementation_of_standard_i_o id8}@anchor{251} |
| @subsection Reading and Writing Non-Regular Files |
| |
| |
| A non-regular file is a device (such as a keyboard), or a pipe. Text_IO |
| can be used for reading and writing. Writing is not affected and the |
| sequence of characters output is identical to the normal file case, but |
| for reading, the behavior of Text_IO is modified to avoid undesirable |
| look-ahead as follows: |
| |
| An input file that is not a regular file is considered to have no page |
| marks. Any @cite{Ascii.FF} characters (the character normally used for a |
| page mark) appearing in the file are considered to be data |
| characters. In particular: |
| |
| |
| @itemize * |
| |
| @item |
| @cite{Get_Line} and @cite{Skip_Line} do not test for a page mark |
| following a line mark. If a page mark appears, it will be treated as a |
| data character. |
| |
| @item |
| This avoids the need to wait for an extra character to be typed or |
| entered from the pipe to complete one of these operations. |
| |
| @item |
| @cite{End_Of_Page} always returns @cite{False} |
| |
| @item |
| @cite{End_Of_File} will return @cite{False} if there is a page mark at |
| the end of the file. |
| @end itemize |
| |
| Output to non-regular files is the same as for regular files. Page marks |
| may be written to non-regular files using @cite{New_Page}, but as noted |
| above they will not be treated as page marks on input if the output is |
| piped to another Ada program. |
| |
| Another important discrepancy when reading non-regular files is that the end |
| of file indication is not 'sticky'. If an end of file is entered, e.g., by |
| pressing the @code{EOT} key, |
| then end of file |
| is signaled once (i.e., the test @cite{End_Of_File} |
| will yield @cite{True}, or a read will |
| raise @cite{End_Error}), but then reading can resume |
| to read data past that end of |
| file indication, until another end of file indication is entered. |
| |
| @node Get_Immediate,Treating Text_IO Files as Streams,Reading and Writing Non-Regular Files,Text_IO |
| @anchor{gnat_rm/the_implementation_of_standard_i_o get-immediate}@anchor{252}@anchor{gnat_rm/the_implementation_of_standard_i_o id9}@anchor{253} |
| @subsection Get_Immediate |
| |
| |
| @geindex Get_Immediate |
| |
| Get_Immediate returns the next character (including control characters) |
| from the input file. In particular, Get_Immediate will return LF or FF |
| characters used as line marks or page marks. Such operations leave the |
| file positioned past the control character, and it is thus not treated |
| as having its normal function. This means that page, line and column |
| counts after this kind of Get_Immediate call are set as though the mark |
| did not occur. In the case where a Get_Immediate leaves the file |
| positioned between the line mark and page mark (which is not normally |
| possible), it is undefined whether the FF character will be treated as a |
| page mark. |
| |
| @node Treating Text_IO Files as Streams,Text_IO Extensions,Get_Immediate,Text_IO |
| @anchor{gnat_rm/the_implementation_of_standard_i_o id10}@anchor{254}@anchor{gnat_rm/the_implementation_of_standard_i_o treating-text-io-files-as-streams}@anchor{255} |
| @subsection Treating Text_IO Files as Streams |
| |
| |
| @geindex Stream files |
| |
| The package @cite{Text_IO.Streams} allows a Text_IO file to be treated |
| as a stream. Data written to a Text_IO file in this stream mode is |
| binary data. If this binary data contains bytes 16#0A# (@cite{LF}) or |
| 16#0C# (@cite{FF}), the resulting file may have non-standard |
| format. Similarly if read operations are used to read from a Text_IO |
| file treated as a stream, then @cite{LF} and @cite{FF} characters may be |
| skipped and the effect is similar to that described above for |
| @cite{Get_Immediate}. |
| |
| @node Text_IO Extensions,Text_IO Facilities for Unbounded Strings,Treating Text_IO Files as Streams,Text_IO |
| @anchor{gnat_rm/the_implementation_of_standard_i_o id11}@anchor{256}@anchor{gnat_rm/the_implementation_of_standard_i_o text-io-extensions}@anchor{257} |
| @subsection Text_IO Extensions |
| |
| |
| @geindex Text_IO extensions |
| |
| A package GNAT.IO_Aux in the GNAT library provides some useful extensions |
| to the standard @cite{Text_IO} package: |
| |
| |
| @itemize * |
| |
| @item |
| function File_Exists (Name : String) return Boolean; |
| Determines if a file of the given name exists. |
| |
| @item |
| function Get_Line return String; |
| Reads a string from the standard input file. The value returned is exactly |
| the length of the line that was read. |
| |
| @item |
| function Get_Line (File : Ada.Text_IO.File_Type) return String; |
| Similar, except that the parameter File specifies the file from which |
| the string is to be read. |
| @end itemize |
| |
| @node Text_IO Facilities for Unbounded Strings,,Text_IO Extensions,Text_IO |
| @anchor{gnat_rm/the_implementation_of_standard_i_o text-io-facilities-for-unbounded-strings}@anchor{258}@anchor{gnat_rm/the_implementation_of_standard_i_o id12}@anchor{259} |
| @subsection Text_IO Facilities for Unbounded Strings |
| |
| |
| @geindex Text_IO for unbounded strings |
| |
| @geindex Unbounded_String |
| @geindex Text_IO operations |
| |
| The package @cite{Ada.Strings.Unbounded.Text_IO} |
| in library files @cite{a-suteio.ads/adb} contains some GNAT-specific |
| subprograms useful for Text_IO operations on unbounded strings: |
| |
| |
| @itemize * |
| |
| @item |
| function Get_Line (File : File_Type) return Unbounded_String; |
| Reads a line from the specified file |
| and returns the result as an unbounded string. |
| |
| @item |
| procedure Put (File : File_Type; U : Unbounded_String); |
| Writes the value of the given unbounded string to the specified file |
| Similar to the effect of |
| @cite{Put (To_String (U))} except that an extra copy is avoided. |
| |
| @item |
| procedure Put_Line (File : File_Type; U : Unbounded_String); |
| Writes the value of the given unbounded string to the specified file, |
| followed by a @cite{New_Line}. |
| Similar to the effect of @cite{Put_Line (To_String (U))} except |
| that an extra copy is avoided. |
| @end itemize |
| |
| In the above procedures, @cite{File} is of type @cite{Ada.Text_IO.File_Type} |
| and is optional. If the parameter is omitted, then the standard input or |
| output file is referenced as appropriate. |
| |
| The package @cite{Ada.Strings.Wide_Unbounded.Wide_Text_IO} in library |
| files @code{a-swuwti.ads} and @code{a-swuwti.adb} provides similar extended |
| @cite{Wide_Text_IO} functionality for unbounded wide strings. |
| |
| The package @cite{Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO} in library |
| files @code{a-szuzti.ads} and @code{a-szuzti.adb} provides similar extended |
| @cite{Wide_Wide_Text_IO} functionality for unbounded wide wide strings. |
| |
| @node Wide_Text_IO,Wide_Wide_Text_IO,Text_IO,The Implementation of Standard I/O |
| @anchor{gnat_rm/the_implementation_of_standard_i_o wide-text-io}@anchor{25a}@anchor{gnat_rm/the_implementation_of_standard_i_o id13}@anchor{25b} |
| @section Wide_Text_IO |
| |
| |
| @cite{Wide_Text_IO} is similar in most respects to Text_IO, except that |
| both input and output files may contain special sequences that represent |
| wide character values. The encoding scheme for a given file may be |
| specified using a FORM parameter: |
| |
| @example |
| WCEM=`x` |
| @end example |
| |
| as part of the FORM string (WCEM = wide character encoding method), |
| where @cite{x} is one of the following characters |
| |
| |
| @multitable {xxxxxxxxxxxx} {xxxxxxxxxxxxxxxxxxxxxx} |
| @headitem |
| |
| Character |
| |
| @tab |
| |
| Encoding |
| |
| @item |
| |
| @emph{h} |
| |
| @tab |
| |
| Hex ESC encoding |
| |
| @item |
| |
| @emph{u} |
| |
| @tab |
| |
| Upper half encoding |
| |
| @item |
| |
| @emph{s} |
| |
| @tab |
| |
| Shift-JIS encoding |
| |
| @item |
| |
| @emph{e} |
| |
| @tab |
| |
| EUC Encoding |
| |
| @item |
| |
| @emph{8} |
| |
| @tab |
| |
| UTF-8 encoding |
| |
| @item |
| |
| @emph{b} |
| |
| @tab |
| |
| Brackets encoding |
| |
| @end multitable |
| |
| |
| The encoding methods match those that |
| can be used in a source |
| program, but there is no requirement that the encoding method used for |
| the source program be the same as the encoding method used for files, |
| and different files may use different encoding methods. |
| |
| The default encoding method for the standard files, and for opened files |
| for which no WCEM parameter is given in the FORM string matches the |
| wide character encoding specified for the main program (the default |
| being brackets encoding if no coding method was specified with -gnatW). |
| |
| |
| @table @asis |
| |
| @item @emph{Hex Coding} |
| |
| In this encoding, a wide character is represented by a five character |
| sequence: |
| @end table |
| |
| @example |
| ESC a b c d |
| @end example |
| |
| |
| @quotation |
| |
| where @cite{a}, @cite{b}, @cite{c}, @cite{d} are the four hexadecimal |
| characters (using upper case letters) of the wide character code. For |
| example, ESC A345 is used to represent the wide character with code |
| 16#A345#. This scheme is compatible with use of the full |
| @cite{Wide_Character} set. |
| @end quotation |
| |
| |
| @table @asis |
| |
| @item @emph{Upper Half Coding} |
| |
| The wide character with encoding 16#abcd#, where the upper bit is on |
| (i.e., a is in the range 8-F) is represented as two bytes 16#ab# and |
| 16#cd#. The second byte may never be a format control character, but is |
| not required to be in the upper half. This method can be also used for |
| shift-JIS or EUC where the internal coding matches the external coding. |
| |
| @item @emph{Shift JIS Coding} |
| |
| A wide character is represented by a two character sequence 16#ab# and |
| 16#cd#, with the restrictions described for upper half encoding as |
| described above. The internal character code is the corresponding JIS |
| character according to the standard algorithm for Shift-JIS |
| conversion. Only characters defined in the JIS code set table can be |
| used with this encoding method. |
| |
| @item @emph{EUC Coding} |
| |
| A wide character is represented by a two character sequence 16#ab# and |
| 16#cd#, with both characters being in the upper half. The internal |
| character code is the corresponding JIS character according to the EUC |
| encoding algorithm. Only characters defined in the JIS code set table |
| can be used with this encoding method. |
| |
| @item @emph{UTF-8 Coding} |
| |
| A wide character is represented using |
| UCS Transformation Format 8 (UTF-8) as defined in Annex R of ISO |
| 10646-1/Am.2. Depending on the character value, the representation |
| is a one, two, or three byte sequence: |
| @end table |
| |
| @example |
| 16#0000#-16#007f#: 2#0xxxxxxx# |
| 16#0080#-16#07ff#: 2#110xxxxx# 2#10xxxxxx# |
| 16#0800#-16#ffff#: 2#1110xxxx# 2#10xxxxxx# 2#10xxxxxx# |
| @end example |
| |
| |
| @quotation |
| |
| where the @cite{xxx} bits correspond to the left-padded bits of the |
| 16-bit character value. Note that all lower half ASCII characters |
| are represented as ASCII bytes and all upper half characters and |
| other wide characters are represented as sequences of upper-half |
| (The full UTF-8 scheme allows for encoding 31-bit characters as |
| 6-byte sequences, but in this implementation, all UTF-8 sequences |
| of four or more bytes length will raise a Constraint_Error, as |
| will all invalid UTF-8 sequences.) |
| @end quotation |
| |
| |
| @table @asis |
| |
| @item @emph{Brackets Coding} |
| |
| In this encoding, a wide character is represented by the following eight |
| character sequence: |
| @end table |
| |
| @example |
| [ " a b c d " ] |
| @end example |
| |
| |
| @quotation |
| |
| where @cite{a}, @cite{b}, @cite{c}, @cite{d} are the four hexadecimal |
| characters (using uppercase letters) of the wide character code. For |
| example, @cite{["A345"]} is used to represent the wide character with code |
| @cite{16#A345#}. |
| This scheme is compatible with use of the full Wide_Character set. |
| On input, brackets coding can also be used for upper half characters, |
| e.g., @cite{["C1"]} for lower case a. However, on output, brackets notation |
| is only used for wide characters with a code greater than @cite{16#FF#}. |
| |
| Note that brackets coding is not normally used in the context of |
| Wide_Text_IO or Wide_Wide_Text_IO, since it is really just designed as |
| a portable way of encoding source files. In the context of Wide_Text_IO |
| or Wide_Wide_Text_IO, it can only be used if the file does not contain |
| any instance of the left bracket character other than to encode wide |
| character values using the brackets encoding method. In practice it is |
| expected that some standard wide character encoding method such |
| as UTF-8 will be used for text input output. |
| |
| If brackets notation is used, then any occurrence of a left bracket |
| in the input file which is not the start of a valid wide character |
| sequence will cause Constraint_Error to be raised. It is possible to |
| encode a left bracket as ["5B"] and Wide_Text_IO and Wide_Wide_Text_IO |
| input will interpret this as a left bracket. |
| |
| However, when a left bracket is output, it will be output as a left bracket |
| and not as ["5B"]. We make this decision because for normal use of |
| Wide_Text_IO for outputting messages, it is unpleasant to clobber left |
| brackets. For example, if we write: |
| |
| @example |
| Put_Line ("Start of output [first run]"); |
| @end example |
| |
| we really do not want to have the left bracket in this message clobbered so |
| that the output reads: |
| @end quotation |
| |
| @example |
| Start of output ["5B"]first run] |
| @end example |
| |
| |
| @quotation |
| |
| In practice brackets encoding is reasonably useful for normal Put_Line use |
| since we won't get confused between left brackets and wide character |
| sequences in the output. But for input, or when files are written out |
| and read back in, it really makes better sense to use one of the standard |
| encoding methods such as UTF-8. |
| @end quotation |
| |
| For the coding schemes other than UTF-8, Hex, or Brackets encoding, |
| not all wide character |
| values can be represented. An attempt to output a character that cannot |
| be represented using the encoding scheme for the file causes |
| Constraint_Error to be raised. An invalid wide character sequence on |
| input also causes Constraint_Error to be raised. |
| |
| @menu |
| * Stream Pointer Positioning: Stream Pointer Positioning<2>. |
| * Reading and Writing Non-Regular Files: Reading and Writing Non-Regular Files<2>. |
| |
| @end menu |
| |
| @node Stream Pointer Positioning<2>,Reading and Writing Non-Regular Files<2>,,Wide_Text_IO |
| @anchor{gnat_rm/the_implementation_of_standard_i_o stream-pointer-positioning-1}@anchor{25c}@anchor{gnat_rm/the_implementation_of_standard_i_o id14}@anchor{25d} |
| @subsection Stream Pointer Positioning |
| |
| |
| @cite{Ada.Wide_Text_IO} is similar to @cite{Ada.Text_IO} in its handling |
| of stream pointer positioning (@ref{24d,,Text_IO}). There is one additional |
| case: |
| |
| If @cite{Ada.Wide_Text_IO.Look_Ahead} reads a character outside the |
| normal lower ASCII set (i.e., a character in the range: |
| |
| @example |
| Wide_Character'Val (16#0080#) .. Wide_Character'Val (16#FFFF#) |
| @end example |
| |
| then although the logical position of the file pointer is unchanged by |
| the @cite{Look_Ahead} call, the stream is physically positioned past the |
| wide character sequence. Again this is to avoid the need for buffering |
| or backup, and all @cite{Wide_Text_IO} routines check the internal |
| indication that this situation has occurred so that this is not visible |
| to a normal program using @cite{Wide_Text_IO}. However, this discrepancy |
| can be observed if the wide text file shares a stream with another file. |
| |
| @node Reading and Writing Non-Regular Files<2>,,Stream Pointer Positioning<2>,Wide_Text_IO |
| @anchor{gnat_rm/the_implementation_of_standard_i_o reading-and-writing-non-regular-files-1}@anchor{25e}@anchor{gnat_rm/the_implementation_of_standard_i_o id15}@anchor{25f} |
| @subsection Reading and Writing Non-Regular Files |
| |
| |
| As in the case of Text_IO, when a non-regular file is read, it is |
| assumed that the file contains no page marks (any form characters are |
| treated as data characters), and @cite{End_Of_Page} always returns |
| @cite{False}. Similarly, the end of file indication is not sticky, so |
| it is possible to read beyond an end of file. |
| |
| @node Wide_Wide_Text_IO,Stream_IO,Wide_Text_IO,The Implementation of Standard I/O |
| @anchor{gnat_rm/the_implementation_of_standard_i_o id16}@anchor{260}@anchor{gnat_rm/the_implementation_of_standard_i_o wide-wide-text-io}@anchor{261} |
| @section Wide_Wide_Text_IO |
| |
| |
| @cite{Wide_Wide_Text_IO} is similar in most respects to Text_IO, except that |
| both input and output files may contain special sequences that represent |
| wide wide character values. The encoding scheme for a given file may be |
| specified using a FORM parameter: |
| |
| @example |
| WCEM=`x` |
| @end example |
| |
| as part of the FORM string (WCEM = wide character encoding method), |
| where @cite{x} is one of the following characters |
| |
| |
| @multitable {xxxxxxxxxxxx} {xxxxxxxxxxxxxxxxxxxxxx} |
| @headitem |
| |
| Character |
| |
| @tab |
| |
| Encoding |
| |
| @item |
| |
| @emph{h} |
| |
| @tab |
| |
| Hex ESC encoding |
| |
| @item |
| |
| @emph{u} |
| |
| @tab |
| |
| Upper half encoding |
| |
| @item |
| |
| @emph{s} |
| |
| @tab |
| |
| Shift-JIS encoding |
| |
| @item |
| |
| @emph{e} |
| |
| @tab |
| |
| EUC Encoding |
| |
| @item |
| |
| @emph{8} |
| |
| @tab |
| |
| UTF-8 encoding |
| |
| @item |
| |
| @emph{b} |
| |
| @tab |
| |
| Brackets encoding |
| |
| @end multitable |
| |
| |
| The encoding methods match those that |
| can be used in a source |
| program, but there is no requirement that the encoding method used for |
| the source program be the same as the encoding method used for files, |
| and different files may use different encoding methods. |
| |
| The default encoding method for the standard files, and for opened files |
| for which no WCEM parameter is given in the FORM string matches the |
| wide character encoding specified for the main program (the default |
| being brackets encoding if no coding method was specified with -gnatW). |
| |
| |
| @table @asis |
| |
| @item @emph{UTF-8 Coding} |
| |
| A wide character is represented using |
| UCS Transformation Format 8 (UTF-8) as defined in Annex R of ISO |
| 10646-1/Am.2. Depending on the character value, the representation |
| is a one, two, three, or four byte sequence: |
| @end table |
| |
| @example |
| 16#000000#-16#00007f#: 2#0xxxxxxx# |
| 16#000080#-16#0007ff#: 2#110xxxxx# 2#10xxxxxx# |
| 16#000800#-16#00ffff#: 2#1110xxxx# 2#10xxxxxx# 2#10xxxxxx# |
| 16#010000#-16#10ffff#: 2#11110xxx# 2#10xxxxxx# 2#10xxxxxx# 2#10xxxxxx# |
| @end example |
| |
| |
| @quotation |
| |
| where the @cite{xxx} bits correspond to the left-padded bits of the |
| 21-bit character value. Note that all lower half ASCII characters |
| are represented as ASCII bytes and all upper half characters and |
| other wide characters are represented as sequences of upper-half |
| characters. |
| @end quotation |
| |
| |
| @table @asis |
| |
| @item @emph{Brackets Coding} |
| |
| In this encoding, a wide wide character is represented by the following eight |
| character sequence if is in wide character range |
| @end table |
| |
| @example |
| [ " a b c d " ] |
| @end example |
| |
| |
| @quotation |
| |
| and by the following ten character sequence if not |
| @end quotation |
| |
| @example |
| [ " a b c d e f " ] |
| @end example |
| |
| |
| @quotation |
| |
| where @cite{a}, @cite{b}, @cite{c}, @cite{d}, @cite{e}, and @cite{f} |
| are the four or six hexadecimal |
| characters (using uppercase letters) of the wide wide character code. For |
| example, @cite{["01A345"]} is used to represent the wide wide character |
| with code @cite{16#01A345#}. |
| |
| This scheme is compatible with use of the full Wide_Wide_Character set. |
| On input, brackets coding can also be used for upper half characters, |
| e.g., @cite{["C1"]} for lower case a. However, on output, brackets notation |
| is only used for wide characters with a code greater than @cite{16#FF#}. |
| @end quotation |
| |
| If is also possible to use the other Wide_Character encoding methods, |
| such as Shift-JIS, but the other schemes cannot support the full range |
| of wide wide characters. |
| An attempt to output a character that cannot |
| be represented using the encoding scheme for the file causes |
| Constraint_Error to be raised. An invalid wide character sequence on |
| input also causes Constraint_Error to be raised. |
| |
| @menu |
| * Stream Pointer Positioning: Stream Pointer Positioning<3>. |
| * Reading and Writing Non-Regular Files: Reading and Writing Non-Regular Files<3>. |
| |
| @end menu |
| |
| @node Stream Pointer Positioning<3>,Reading and Writing Non-Regular Files<3>,,Wide_Wide_Text_IO |
| @anchor{gnat_rm/the_implementation_of_standard_i_o stream-pointer-positioning-2}@anchor{262}@anchor{gnat_rm/the_implementation_of_standard_i_o id17}@anchor{263} |
| @subsection Stream Pointer Positioning |
| |
| |
| @cite{Ada.Wide_Wide_Text_IO} is similar to @cite{Ada.Text_IO} in its handling |
| of stream pointer positioning (@ref{24d,,Text_IO}). There is one additional |
| case: |
| |
| If @cite{Ada.Wide_Wide_Text_IO.Look_Ahead} reads a character outside the |
| normal lower ASCII set (i.e., a character in the range: |
| |
| @example |
| Wide_Wide_Character'Val (16#0080#) .. Wide_Wide_Character'Val (16#10FFFF#) |
| @end example |
| |
| then although the logical position of the file pointer is unchanged by |
| the @cite{Look_Ahead} call, the stream is physically positioned past the |
| wide character sequence. Again this is to avoid the need for buffering |
| or backup, and all @cite{Wide_Wide_Text_IO} routines check the internal |
| indication that this situation has occurred so that this is not visible |
| to a normal program using @cite{Wide_Wide_Text_IO}. However, this discrepancy |
| can be observed if the wide text file shares a stream with another file. |
| |
| @node Reading and Writing Non-Regular Files<3>,,Stream Pointer Positioning<3>,Wide_Wide_Text_IO |
| @anchor{gnat_rm/the_implementation_of_standard_i_o id18}@anchor{264}@anchor{gnat_rm/the_implementation_of_standard_i_o reading-and-writing-non-regular-files-2}@anchor{265} |
| @subsection Reading and Writing Non-Regular Files |
| |
| |
| As in the case of Text_IO, when a non-regular file is read, it is |
| assumed that the file contains no page marks (any form characters are |
| treated as data characters), and @cite{End_Of_Page} always returns |
| @cite{False}. Similarly, the end of file indication is not sticky, so |
| it is possible to read beyond an end of file. |
| |
| @node Stream_IO,Text Translation,Wide_Wide_Text_IO,The Implementation of Standard I/O |
| @anchor{gnat_rm/the_implementation_of_standard_i_o id19}@anchor{266}@anchor{gnat_rm/the_implementation_of_standard_i_o stream-io}@anchor{267} |
| @section Stream_IO |
| |
| |
| A stream file is a sequence of bytes, where individual elements are |
| written to the file as described in the Ada Reference Manual. The type |
| @cite{Stream_Element} is simply a byte. There are two ways to read or |
| write a stream file. |
| |
| |
| @itemize * |
| |
| @item |
| The operations @cite{Read} and @cite{Write} directly read or write a |
| sequence of stream elements with no control information. |
| |
| @item |
| The stream attributes applied to a stream file transfer data in the |
| manner described for stream attributes. |
| @end itemize |
| |
| @node Text Translation,Shared Files,Stream_IO,The Implementation of Standard I/O |
| @anchor{gnat_rm/the_implementation_of_standard_i_o id20}@anchor{268}@anchor{gnat_rm/the_implementation_of_standard_i_o text-translation}@anchor{269} |
| @section Text Translation |
| |
| |
| @code{Text_Translation=xxx} may be used as the Form parameter |
| passed to Text_IO.Create and Text_IO.Open. @code{Text_Translation=xxx} |
| has no effect on Unix systems. Possible values are: |
| |
| |
| @itemize * |
| |
| @item |
| @code{Yes} or @code{Text} is the default, which means to |
| translate LF to/from CR/LF on Windows systems. |
| |
| @code{No} disables this translation; i.e. it |
| uses binary mode. For output files, @code{Text_Translation=No} |
| may be used to create Unix-style files on |
| Windows. |
| |
| @item |
| @code{wtext} translation enabled in Unicode mode. |
| (corresponds to _O_WTEXT). |
| |
| @item |
| @code{u8text} translation enabled in Unicode UTF-8 mode. |
| (corresponds to O_U8TEXT). |
| |
| @item |
| @code{u16text} translation enabled in Unicode UTF-16 |
| mode. (corresponds to_O_U16TEXT). |
| @end itemize |
| |
| @node Shared Files,Filenames encoding,Text Translation,The Implementation of Standard I/O |
| @anchor{gnat_rm/the_implementation_of_standard_i_o id21}@anchor{26a}@anchor{gnat_rm/the_implementation_of_standard_i_o shared-files}@anchor{26b} |
| @section Shared Files |
| |
| |
| Section A.14 of the Ada Reference Manual allows implementations to |
| provide a wide variety of behavior if an attempt is made to access the |
| same external file with two or more internal files. |
| |
| To provide a full range of functionality, while at the same time |
| minimizing the problems of portability caused by this implementation |
| dependence, GNAT handles file sharing as follows: |
| |
| |
| @itemize * |
| |
| @item |
| In the absence of a @code{shared=xxx} form parameter, an attempt |
| to open two or more files with the same full name is considered an error |
| and is not supported. The exception @cite{Use_Error} will be |
| raised. Note that a file that is not explicitly closed by the program |
| remains open until the program terminates. |
| |
| @item |
| If the form parameter @code{shared=no} appears in the form string, the |
| file can be opened or created with its own separate stream identifier, |
| regardless of whether other files sharing the same external file are |
| opened. The exact effect depends on how the C stream routines handle |
| multiple accesses to the same external files using separate streams. |
| |
| @item |
| If the form parameter @code{shared=yes} appears in the form string for |
| each of two or more files opened using the same full name, the same |
| stream is shared between these files, and the semantics are as described |
| in Ada Reference Manual, Section A.14. |
| @end itemize |
| |
| When a program that opens multiple files with the same name is ported |
| from another Ada compiler to GNAT, the effect will be that |
| @cite{Use_Error} is raised. |
| |
| The documentation of the original compiler and the documentation of the |
| program should then be examined to determine if file sharing was |
| expected, and @code{shared=xxx} parameters added to @cite{Open} |
| and @cite{Create} calls as required. |
| |
| When a program is ported from GNAT to some other Ada compiler, no |
| special attention is required unless the @code{shared=xxx} form |
| parameter is used in the program. In this case, you must examine the |
| documentation of the new compiler to see if it supports the required |
| file sharing semantics, and form strings modified appropriately. Of |
| course it may be the case that the program cannot be ported if the |
| target compiler does not support the required functionality. The best |
| approach in writing portable code is to avoid file sharing (and hence |
| the use of the @code{shared=xxx} parameter in the form string) |
| completely. |
| |
| One common use of file sharing in Ada 83 is the use of instantiations of |
| Sequential_IO on the same file with different types, to achieve |
| heterogeneous input-output. Although this approach will work in GNAT if |
| @code{shared=yes} is specified, it is preferable in Ada to use Stream_IO |
| for this purpose (using the stream attributes) |
| |
| @node Filenames encoding,File content encoding,Shared Files,The Implementation of Standard I/O |
| @anchor{gnat_rm/the_implementation_of_standard_i_o filenames-encoding}@anchor{26c}@anchor{gnat_rm/the_implementation_of_standard_i_o id22}@anchor{26d} |
| @section Filenames encoding |
| |
| |
| An encoding form parameter can be used to specify the filename |
| encoding @code{encoding=xxx}. |
| |
| |
| @itemize * |
| |
| @item |
| If the form parameter @code{encoding=utf8} appears in the form string, the |
| filename must be encoded in UTF-8. |
| |
| @item |
| If the form parameter @code{encoding=8bits} appears in the form |
| string, the filename must be a standard 8bits string. |
| @end itemize |
| |
| In the absence of a @code{encoding=xxx} form parameter, the |
| encoding is controlled by the @code{GNAT_CODE_PAGE} environment |
| variable. And if not set @code{utf8} is assumed. |
| |
| |
| @table @asis |
| |
| @item @emph{CP_ACP} |
| |
| The current system Windows ANSI code page. |
| |
| @item @emph{CP_UTF8} |
| |
| UTF-8 encoding |
| @end table |
| |
| This encoding form parameter is only supported on the Windows |
| platform. On the other Operating Systems the run-time is supporting |
| UTF-8 natively. |
| |
| @node File content encoding,Open Modes,Filenames encoding,The Implementation of Standard I/O |
| @anchor{gnat_rm/the_implementation_of_standard_i_o file-content-encoding}@anchor{26e}@anchor{gnat_rm/the_implementation_of_standard_i_o id23}@anchor{26f} |
| @section File content encoding |
| |
| |
| For text files it is possible to specify the encoding to use. This is |
| controlled by the by the @code{GNAT_CCS_ENCODING} environment |
| variable. And if not set @code{TEXT} is assumed. |
| |
| The possible values are those supported on Windows: |
| |
| |
| @table @asis |
| |
| @item @emph{TEXT} |
| |
| Translated text mode |
| |
| @item @emph{WTEXT} |
| |
| Translated unicode encoding |
| |
| @item @emph{U16TEXT} |
| |
| Unicode 16-bit encoding |
| |
| @item @emph{U8TEXT} |
| |
| Unicode 8-bit encoding |
| @end table |
| |
| This encoding is only supported on the Windows platform. |
| |
| @node Open Modes,Operations on C Streams,File content encoding,The Implementation of Standard I/O |
| @anchor{gnat_rm/the_implementation_of_standard_i_o open-modes}@anchor{270}@anchor{gnat_rm/the_implementation_of_standard_i_o id24}@anchor{271} |
| @section Open Modes |
| |
| |
| @cite{Open} and @cite{Create} calls result in a call to @cite{fopen} |
| using the mode shown in the following table: |
| |
| |
| @multitable {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx} {xxxxxxxxxxxxxxxxx} {xxxxxxxxxxxxxxxxxxxx} |
| @headitem |
| |
| @cite{Open} and @cite{Create} Call Modes |
| |
| @tab |
| |
| @tab |
| |
| @item |
| |
| @tab |
| |
| @strong{OPEN} |
| |
| @tab |
| |
| @strong{CREATE} |
| |
| @item |
| |
| Append_File |
| |
| @tab |
| |
| "r+" |
| |
| @tab |
| |
| "w+" |
| |
| @item |
| |
| In_File |
| |
| @tab |
| |
| "r" |
| |
| @tab |
| |
| "w+" |
| |
| @item |
| |
| Out_File (Direct_IO) |
| |
| @tab |
| |
| "r+" |
| |
| @tab |
| |
| "w" |
| |
| @item |
| |
| Out_File (all other cases) |
| |
| @tab |
| |
| "w" |
| |
| @tab |
| |
| "w" |
| |
| @item |
| |
| Inout_File |
| |
| @tab |
| |
| "r+" |
| |
| @tab |
| |
| "w+" |
| |
| @end multitable |
| |
| |
| If text file translation is required, then either @code{b} or @code{t} |
| is added to the mode, depending on the setting of Text. Text file |
| translation refers to the mapping of CR/LF sequences in an external file |
| to LF characters internally. This mapping only occurs in DOS and |
| DOS-like systems, and is not relevant to other systems. |
| |
| A special case occurs with Stream_IO. As shown in the above table, the |
| file is initially opened in @code{r} or @code{w} mode for the |
| @cite{In_File} and @cite{Out_File} cases. If a @cite{Set_Mode} operation |
| subsequently requires switching from reading to writing or vice-versa, |
| then the file is reopened in @code{r+} mode to permit the required operation. |
| |
| @node Operations on C Streams,Interfacing to C Streams,Open Modes,The Implementation of Standard I/O |
| @anchor{gnat_rm/the_implementation_of_standard_i_o operations-on-c-streams}@anchor{272}@anchor{gnat_rm/the_implementation_of_standard_i_o id25}@anchor{273} |
| @section Operations on C Streams |
| |
| |
| The package @cite{Interfaces.C_Streams} provides an Ada program with direct |
| access to the C library functions for operations on C streams: |
| |
| @example |
| package Interfaces.C_Streams is |
| -- Note: the reason we do not use the types that are in |
| -- Interfaces.C is that we want to avoid dragging in the |
| -- code in this unit if possible. |
| subtype chars is System.Address; |
| -- Pointer to null-terminated array of characters |
| subtype FILEs is System.Address; |
| -- Corresponds to the C type FILE* |
| subtype voids is System.Address; |
| -- Corresponds to the C type void* |
| subtype int is Integer; |
| subtype long is Long_Integer; |
| -- Note: the above types are subtypes deliberately, and it |
| -- is part of this spec that the above correspondences are |
| -- guaranteed. This means that it is legitimate to, for |
| -- example, use Integer instead of int. We provide these |
| -- synonyms for clarity, but in some cases it may be |
| -- convenient to use the underlying types (for example to |
| -- avoid an unnecessary dependency of a spec on the spec |
| -- of this unit). |
| type size_t is mod 2 ** Standard'Address_Size; |
| NULL_Stream : constant FILEs; |
| -- Value returned (NULL in C) to indicate an |
| -- fdopen/fopen/tmpfile error |
| ---------------------------------- |
| -- Constants Defined in stdio.h -- |
| ---------------------------------- |
| EOF : constant int; |
| -- Used by a number of routines to indicate error or |
| -- end of file |
| IOFBF : constant int; |
| IOLBF : constant int; |
| IONBF : constant int; |
| -- Used to indicate buffering mode for setvbuf call |
| SEEK_CUR : constant int; |
| SEEK_END : constant int; |
| SEEK_SET : constant int; |
| -- Used to indicate origin for fseek call |
| function stdin return FILEs; |
| function stdout return FILEs; |
| function stderr return FILEs; |
| -- Streams associated with standard files |
| -------------------------- |
| -- Standard C functions -- |
| -------------------------- |
| -- The functions selected below are ones that are |
| -- available in UNIX (but not necessarily in ANSI C). |
| -- These are very thin interfaces |
| -- which copy exactly the C headers. For more |
| -- documentation on these functions, see the Microsoft C |
| -- "Run-Time Library Reference" (Microsoft Press, 1990, |
| -- ISBN 1-55615-225-6), which includes useful information |
| -- on system compatibility. |
| procedure clearerr (stream : FILEs); |
| function fclose (stream : FILEs) return int; |
| function fdopen (handle : int; mode : chars) return FILEs; |
| function feof (stream : FILEs) return int; |
| function ferror (stream : FILEs) return int; |
| function fflush (stream : FILEs) return int; |
| function fgetc (stream : FILEs) return int; |
| function fgets (strng : chars; n : int; stream : FILEs) |
| return chars; |
| function fileno (stream : FILEs) return int; |
| function fopen (filename : chars; Mode : chars) |
| return FILEs; |
| -- Note: to maintain target independence, use |
| -- text_translation_required, a boolean variable defined in |
| -- a-sysdep.c to deal with the target dependent text |
| -- translation requirement. If this variable is set, |
| -- then b/t should be appended to the standard mode |
| -- argument to set the text translation mode off or on |
| -- as required. |
| function fputc (C : int; stream : FILEs) return int; |
| function fputs (Strng : chars; Stream : FILEs) return int; |
| function fread |
| (buffer : voids; |
| size : size_t; |
| count : size_t; |
| stream : FILEs) |
| return size_t; |
| function freopen |
| (filename : chars; |
| mode : chars; |
| stream : FILEs) |
| return FILEs; |
| function fseek |
| (stream : FILEs; |
| offset : long; |
| origin : int) |
| return int; |
| function ftell (stream : FILEs) return long; |
| function fwrite |
| (buffer : voids; |
| size : size_t; |
| count : size_t; |
| stream : FILEs) |
| return size_t; |
| function isatty (handle : int) return int; |
| procedure mktemp (template : chars); |
| -- The return value (which is just a pointer to template) |
| -- is discarded |
| procedure rewind (stream : FILEs); |
| function rmtmp return int; |
| function setvbuf |
| (stream : FILEs; |
| buffer : chars; |
| mode : int; |
| size : size_t) |
| return int; |
| |
| function tmpfile return FILEs; |
| function ungetc (c : int; stream : FILEs) return int; |
| function unlink (filename : chars) return int; |
| --------------------- |
| -- Extra functions -- |
| --------------------- |
| -- These functions supply slightly thicker bindings than |
| -- those above. They are derived from functions in the |
| -- C Run-Time Library, but may do a bit more work than |
| -- just directly calling one of the Library functions. |
| function is_regular_file (handle : int) return int; |
| -- Tests if given handle is for a regular file (result 1) |
| -- or for a non-regular file (pipe or device, result 0). |
| --------------------------------- |
| -- Control of Text/Binary Mode -- |
| --------------------------------- |
| -- If text_translation_required is true, then the following |
| -- functions may be used to dynamically switch a file from |
| -- binary to text mode or vice versa. These functions have |
| -- no effect if text_translation_required is false (i.e., in |
| -- normal UNIX mode). Use fileno to get a stream handle. |
| procedure set_binary_mode (handle : int); |
| procedure set_text_mode (handle : int); |
| ---------------------------- |
| -- Full Path Name support -- |
| ---------------------------- |
| procedure full_name (nam : chars; buffer : chars); |
| -- Given a NUL terminated string representing a file |
| -- name, returns in buffer a NUL terminated string |
| -- representing the full path name for the file name. |
| -- On systems where it is relevant the drive is also |
| -- part of the full path name. It is the responsibility |
| -- of the caller to pass an actual parameter for buffer |
