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\input texinfo @c -*-texinfo-*-
@c %**start of header
@c oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo
@c o
@c GNAT DOCUMENTATION o
@c o
@c G N A T _ RM o
@c o
@c Copyright (C) 1995-2003 Free Software Foundation o
@c o
@c o
@c GNAT is maintained by Ada Core Technologies Inc (http://www.gnat.com). o
@c o
@c oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo
@setfilename gnat_rm.info
@settitle GNAT Reference Manual
@setchapternewpage odd
@syncodeindex fn cp
@include gcc-common.texi
@dircategory GNU Ada tools
@direntry
* GNAT Reference Manual: (gnat_rm). Reference Manual for GNU Ada tools.
@end direntry
@copying
Copyright @copyright{} 1995-2004, Free Software Foundation
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.2
or any later version published by the Free Software Foundation;
with the Invariant Sections being ``GNU Free Documentation License'',
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 ``GNU Free Documentation License''.
@end copying
@titlepage
@title GNAT Reference Manual
@subtitle GNAT, The GNU Ada 95 Compiler
@subtitle GCC version @value{version-GCC}
@author Ada Core Technologies, Inc.
@page
@vskip 0pt plus 1filll
@insertcopying
@end titlepage
@ifnottex
@node Top, About This Guide, (dir), (dir)
@top GNAT Reference Manual
@noindent
GNAT Reference Manual
@noindent
GNAT, The GNU Ada 95 Compiler@*
Version @value{gnat_version}@*
Document revision level $Revision: 1.381 $@*
Date: $Date: 2004/01/05 19:49:12 $
@noindent
Ada Core Technologies, Inc.
@noindent
Copyright @copyright{} 1995-2003, Free Software Foundation
@noindent
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1
or any later version published by the Free Software Foundation;
with the Invariant Sections being ``GNU Free Documentation License'', 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 ``GNU
Free Documentation License''.
@menu
* About This Guide::
* Implementation Defined Pragmas::
* Implementation Defined Attributes::
* 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::
* Project File Reference::
* GNU Free Documentation License::
* Index::
--- The Detailed Node Listing ---
About This Guide
* What This Reference Manual Contains::
* Related Information::
Implementation Defined Pragmas
* Pragma Abort_Defer::
* Pragma Ada_83::
* Pragma Ada_95::
* Pragma Annotate::
* Pragma Assert::
* Pragma Ast_Entry::
* Pragma C_Pass_By_Copy::
* Pragma Comment::
* Pragma Common_Object::
* Pragma Compile_Time_Warning::
* Pragma Complex_Representation::
* Pragma Component_Alignment::
* Pragma Convention_Identifier::
* Pragma CPP_Class::
* Pragma CPP_Constructor::
* Pragma CPP_Virtual::
* Pragma CPP_Vtable::
* Pragma Debug::
* Pragma Elaboration_Checks::
* Pragma Eliminate::
* Pragma Export_Exception::
* Pragma Export_Function::
* Pragma Export_Object::
* Pragma Export_Procedure::
* Pragma Export_Value::
* Pragma Export_Valued_Procedure::
* Pragma Extend_System::
* Pragma External::
* Pragma External_Name_Casing::
* Pragma Finalize_Storage_Only::
* Pragma Float_Representation::
* Pragma Ident::
* Pragma Import_Exception::
* Pragma Import_Function::
* Pragma Import_Object::
* Pragma Import_Procedure::
* Pragma Import_Valued_Procedure::
* Pragma Initialize_Scalars::
* Pragma Inline_Always::
* Pragma Inline_Generic::
* Pragma Interface::
* Pragma Interface_Name::
* Pragma Interrupt_Handler::
* Pragma Interrupt_State::
* Pragma Keep_Names::
* Pragma License::
* Pragma Link_With::
* Pragma Linker_Alias::
* Pragma Linker_Section::
* Pragma Long_Float::
* Pragma Machine_Attribute::
* Pragma Main_Storage::
* Pragma No_Return::
* Pragma Normalize_Scalars::
* Pragma Obsolescent::
* Pragma Passive::
* Pragma Polling::
* Pragma Propagate_Exceptions::
* Pragma Psect_Object::
* Pragma Pure_Function::
* Pragma Ravenscar::
* Pragma Restricted_Run_Time::
* Pragma Restriction_Warnings::
* Pragma Source_File_Name::
* Pragma Source_File_Name_Project::
* Pragma Source_Reference::
* Pragma Stream_Convert::
* Pragma Style_Checks::
* Pragma Subtitle::
* Pragma Suppress_All::
* Pragma Suppress_Exception_Locations::
* Pragma Suppress_Initialization::
* Pragma Task_Info::
* Pragma Task_Name::
* Pragma Task_Storage::
* Pragma Thread_Body::
* Pragma Time_Slice::
* Pragma Title::
* Pragma Unchecked_Union::
* Pragma Unimplemented_Unit::
* Pragma Universal_Data::
* Pragma Unreferenced::
* Pragma Unreserve_All_Interrupts::
* Pragma Unsuppress::
* Pragma Use_VADS_Size::
* Pragma Validity_Checks::
* Pragma Volatile::
* Pragma Warnings::
* Pragma Weak_External::
Implementation Defined Attributes
* Abort_Signal::
* Address_Size::
* Asm_Input::
* Asm_Output::
* AST_Entry::
* Bit::
* Bit_Position::
* Code_Address::
* Default_Bit_Order::
* Elaborated::
* Elab_Body::
* Elab_Spec::
* Emax::
* Enum_Rep::
* Epsilon::
* Fixed_Value::
* Has_Discriminants::
* Img::
* Integer_Value::
* Large::
* Machine_Size::
* Mantissa::
* Max_Interrupt_Priority::
* Max_Priority::
* Maximum_Alignment::
* Mechanism_Code::
* Null_Parameter::
* Object_Size::
* Passed_By_Reference::
* Range_Length::
* Safe_Emax::
* Safe_Large::
* Small::
* Storage_Unit::
* Target_Name::
* Tick::
* To_Address::
* Type_Class::
* UET_Address::
* Unconstrained_Array::
* Universal_Literal_String::
* Unrestricted_Access::
* VADS_Size::
* Value_Size::
* Wchar_T_Size::
* Word_Size::
The Implementation of Standard I/O
* Standard I/O Packages::
* FORM Strings::
* Direct_IO::
* Sequential_IO::
* Text_IO::
* Wide_Text_IO::
* Stream_IO::
* Shared Files::
* Open Modes::
* Operations on C Streams::
* Interfacing to C Streams::
The GNAT Library
* Ada.Characters.Latin_9 (a-chlat9.ads)::
* Ada.Characters.Wide_Latin_1 (a-cwila1.ads)::
* Ada.Characters.Wide_Latin_9 (a-cwila9.ads)::
* Ada.Command_Line.Remove (a-colire.ads)::
* Ada.Command_Line.Environment (a-colien.ads)::
* Ada.Direct_IO.C_Streams (a-diocst.ads)::
* Ada.Exceptions.Is_Null_Occurrence (a-einuoc.ads)::
* Ada.Exceptions.Traceback (a-exctra.ads)::
* Ada.Sequential_IO.C_Streams (a-siocst.ads)::
* Ada.Streams.Stream_IO.C_Streams (a-ssicst.ads)::
* Ada.Strings.Unbounded.Text_IO (a-suteio.ads)::
* Ada.Strings.Wide_Unbounded.Wide_Text_IO (a-swuwti.ads)::
* Ada.Text_IO.C_Streams (a-tiocst.ads)::
* Ada.Wide_Text_IO.C_Streams (a-wtcstr.ads)::
* GNAT.Array_Split (g-arrspl.ads)::
* GNAT.AWK (g-awk.ads)::
* GNAT.Bounded_Buffers (g-boubuf.ads)::
* GNAT.Bounded_Mailboxes (g-boumai.ads)::
* GNAT.Bubble_Sort (g-bubsor.ads)::
* GNAT.Bubble_Sort_A (g-busora.ads)::
* GNAT.Bubble_Sort_G (g-busorg.ads)::
* GNAT.Calendar (g-calend.ads)::
* GNAT.Calendar.Time_IO (g-catiio.ads)::
* GNAT.Case_Util (g-casuti.ads)::
* GNAT.CGI (g-cgi.ads)::
* GNAT.CGI.Cookie (g-cgicoo.ads)::
* GNAT.CGI.Debug (g-cgideb.ads)::
* GNAT.Command_Line (g-comlin.ads)::
* GNAT.Compiler_Version (g-comver.ads)::
* GNAT.Ctrl_C (g-ctrl_c.ads)::
* GNAT.CRC32 (g-crc32.ads)::
* GNAT.Current_Exception (g-curexc.ads)::
* GNAT.Debug_Pools (g-debpoo.ads)::
* GNAT.Debug_Utilities (g-debuti.ads)::
* GNAT.Directory_Operations (g-dirope.ads)::
* GNAT.Dynamic_HTables (g-dynhta.ads)::
* GNAT.Dynamic_Tables (g-dyntab.ads)::
* GNAT.Exception_Actions (g-excact.ads)::
* GNAT.Exception_Traces (g-exctra.ads)::
* GNAT.Exceptions (g-except.ads)::
* GNAT.Expect (g-expect.ads)::
* GNAT.Float_Control (g-flocon.ads)::
* GNAT.Heap_Sort (g-heasor.ads)::
* GNAT.Heap_Sort_A (g-hesora.ads)::
* GNAT.Heap_Sort_G (g-hesorg.ads)::
* GNAT.HTable (g-htable.ads)::
* GNAT.IO (g-io.ads)::
* GNAT.IO_Aux (g-io_aux.ads)::
* GNAT.Lock_Files (g-locfil.ads)::
* GNAT.MD5 (g-md5.ads)::
* GNAT.Memory_Dump (g-memdum.ads)::
* GNAT.Most_Recent_Exception (g-moreex.ads)::
* GNAT.OS_Lib (g-os_lib.ads)::
* GNAT.Perfect_Hash.Generators (g-pehage.ads)::
* GNAT.Regexp (g-regexp.ads)::
* GNAT.Registry (g-regist.ads)::
* GNAT.Regpat (g-regpat.ads)::
* GNAT.Secondary_Stack_Info (g-sestin.ads)::
* GNAT.Semaphores (g-semaph.ads)::
* GNAT.Signals (g-signal.ads)::
* GNAT.Sockets (g-socket.ads)::
* GNAT.Source_Info (g-souinf.ads)::
* GNAT.Spell_Checker (g-speche.ads)::
* GNAT.Spitbol.Patterns (g-spipat.ads)::
* GNAT.Spitbol (g-spitbo.ads)::
* GNAT.Spitbol.Table_Boolean (g-sptabo.ads)::
* GNAT.Spitbol.Table_Integer (g-sptain.ads)::
* GNAT.Spitbol.Table_VString (g-sptavs.ads)::
* GNAT.Strings (g-string.ads)::
* GNAT.String_Split (g-strspl.ads)::
* GNAT.Table (g-table.ads)::
* GNAT.Task_Lock (g-tasloc.ads)::
* GNAT.Threads (g-thread.ads)::
* GNAT.Traceback (g-traceb.ads)::
* GNAT.Traceback.Symbolic (g-trasym.ads)::
* GNAT.Wide_String_Split (g-wistsp.ads)::
* Interfaces.C.Extensions (i-cexten.ads)::
* Interfaces.C.Streams (i-cstrea.ads)::
* Interfaces.CPP (i-cpp.ads)::
* Interfaces.Os2lib (i-os2lib.ads)::
* Interfaces.Os2lib.Errors (i-os2err.ads)::
* Interfaces.Os2lib.Synchronization (i-os2syn.ads)::
* Interfaces.Os2lib.Threads (i-os2thr.ads)::
* Interfaces.Packed_Decimal (i-pacdec.ads)::
* Interfaces.VxWorks (i-vxwork.ads)::
* Interfaces.VxWorks.IO (i-vxwoio.ads)::
* System.Address_Image (s-addima.ads)::
* System.Assertions (s-assert.ads)::
* System.Memory (s-memory.ads)::
* System.Partition_Interface (s-parint.ads)::
* System.Task_Info (s-tasinf.ads)::
* System.Wch_Cnv (s-wchcnv.ads)::
* System.Wch_Con (s-wchcon.ads)::
Text_IO
* Text_IO Stream Pointer Positioning::
* Text_IO 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
* Wide_Text_IO Stream Pointer Positioning::
* Wide_Text_IO Reading and Writing Non-Regular Files::
Interfacing to Other Languages
* Interfacing to C::
* Interfacing to C++::
* Interfacing to COBOL::
* Interfacing to Fortran::
* Interfacing to non-GNAT Ada code::
Specialized Needs Annexes
Implementation of Specific Ada Features
* Machine Code Insertions::
* GNAT Implementation of Tasking::
* GNAT Implementation of Shared Passive Packages::
* Code Generation for Array Aggregates::
Project File Reference
GNU Free Documentation License
Index
@end menu
@end ifnottex
@node About This Guide
@unnumbered About This Guide
@noindent
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 standard.
Ada 95 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 95 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.
@cindex Implementation-dependent features
@cindex 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
@unnumberedsec What This Reference Manual Contains
@noindent
This reference manual contains the following chapters:
@itemize @bullet
@item
@ref{Implementation Defined Pragmas}, lists GNAT implementation-dependent
pragmas, which can be used to extend and enhance the functionality of the
compiler.
@item
@ref{Implementation Defined Attributes}, lists GNAT
implementation-dependent attributes which can be used to extend and
enhance the functionality of the compiler.
@item
@ref{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{Implementation Defined Characteristics}, provides a guide to
minimizing implementation dependent features.
@item
@ref{Intrinsic Subprograms}, describes the intrinsic subprograms
implemented by GNAT, and how they can be imported into user
application programs.
@item
@ref{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{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{The Implementation of Standard I/O}, details how the GNAT
implementation of the input-output facilities.
@item
@ref{The GNAT Library}, is a catalog of packages that complement
the Ada predefined library.
@item
@ref{Interfacing to Other Languages}, describes how programs
written in Ada using GNAT can be interfaced to other programming
languages.
@ref{Specialized Needs Annexes}, describes the GNAT implementation of all
of the specialized needs annexes.
@item
@ref{Implementation of Specific Ada Features}, discusses issues related
to GNAT's implementation of machine code insertions, tasking, and several
other features.
@item
@ref{Project File Reference}, presents the syntax and semantics
of project files.
@end itemize
@cindex Ada 95 ISO/ANSI Standard
@noindent
This reference manual assumes that you are familiar with Ada 95
language, as described in the International Standard
ANSI/ISO/IEC-8652:1995, Jan 1995.
@node Conventions
@unnumberedsec Conventions
@cindex Conventions, typographical
@cindex Typographical conventions
@noindent
Following are examples of the typographical and graphic conventions used
in this guide:
@itemize @bullet
@item
@code{Functions}, @code{utility program names}, @code{standard names},
and @code{classes}.
@item
@code{Option flags}
@item
@file{File Names}, @samp{button names}, and @samp{field names}.
@item
@code{Variables}.
@item
@emph{Emphasis}.
@item
[optional information or parameters]
@item
Examples are described by text
@smallexample
and then shown this way.
@end smallexample
@end itemize
@noindent
Commands that are entered by the user are preceded in this manual by the
characters @samp{$ } (dollar sign followed by space). If your system uses this
sequence as a prompt, then the commands will appear exactly as you see them
in the manual. If your system uses some other prompt, then the command will
appear with the @samp{$} replaced by whatever prompt character you are using.
@node Related Information
@unnumberedsec Related Information
@noindent
See the following documents for further information on GNAT:
@itemize @bullet
@item
@cite{GNAT User's Guide}, which provides information on how to use
the GNAT compiler system.
@item
@cite{Ada 95 Reference Manual}, which contains all reference
material for the Ada 95 programming language.
@item
@cite{Ada 95 Annotated Reference Manual}, which is an annotated version
of the standard reference manual cited above. The annotations describe
detailed aspects of the design decision, and in particular contain useful
sections on Ada 83 compatibility.
@item
@cite{DEC Ada, Technical Overview and Comparison on DIGITAL Platforms},
which contains specific information on compatibility between GNAT and
DEC Ada 83 systems.
@item
@cite{DEC Ada, 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
@chapter Implementation Defined Pragmas
@noindent
Ada 95 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 95 Reference
Manual.
In addition, Ada 95 allows implementations to define additional pragmas
whose meaning is defined by the implementation. GNAT provides a number
of these implementation-dependent 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 may 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 Ada_83::
* Pragma Ada_95::
* Pragma Annotate::
* Pragma Assert::
* Pragma Ast_Entry::
* Pragma C_Pass_By_Copy::
* Pragma Comment::
* Pragma Common_Object::
* Pragma Compile_Time_Warning::
* Pragma Complex_Representation::
* Pragma Component_Alignment::
* Pragma Convention_Identifier::
* Pragma CPP_Class::
* Pragma CPP_Constructor::
* Pragma CPP_Virtual::
* Pragma CPP_Vtable::
* Pragma Debug::
* Pragma Elaboration_Checks::
* Pragma Eliminate::
* Pragma Export_Exception::
* Pragma Export_Function::
* Pragma Export_Object::
* Pragma Export_Procedure::
* Pragma Export_Value::
* Pragma Export_Valued_Procedure::
* Pragma Extend_System::
* Pragma External::
* Pragma External_Name_Casing::
* Pragma Finalize_Storage_Only::
* Pragma Float_Representation::
* Pragma Ident::
* Pragma Import_Exception::
* Pragma Import_Function::
* Pragma Import_Object::
* Pragma Import_Procedure::
* Pragma Import_Valued_Procedure::
* Pragma Initialize_Scalars::
* Pragma Inline_Always::
* Pragma Inline_Generic::
* Pragma Interface::
* Pragma Interface_Name::
* Pragma Interrupt_Handler::
* Pragma Interrupt_State::
* Pragma Keep_Names::
* Pragma License::
* Pragma Link_With::
* Pragma Linker_Alias::
* Pragma Linker_Section::
* Pragma Long_Float::
* Pragma Machine_Attribute::
* Pragma Main_Storage::
* Pragma No_Return::
* Pragma Normalize_Scalars::
* Pragma Obsolescent::
* Pragma Passive::
* Pragma Polling::
* Pragma Propagate_Exceptions::
* Pragma Psect_Object::
* Pragma Pure_Function::
* Pragma Ravenscar::
* Pragma Restricted_Run_Time::
* Pragma Restriction_Warnings::
* Pragma Source_File_Name::
* Pragma Source_File_Name_Project::
* Pragma Source_Reference::
* Pragma Stream_Convert::
* Pragma Style_Checks::
* Pragma Subtitle::
* Pragma Suppress_All::
* Pragma Suppress_Exception_Locations::
* Pragma Suppress_Initialization::
* Pragma Task_Info::
* Pragma Task_Name::
* Pragma Task_Storage::
* Pragma Thread_Body::
* Pragma Time_Slice::
* Pragma Title::
* Pragma Unchecked_Union::
* Pragma Unimplemented_Unit::
* Pragma Universal_Data::
* Pragma Unreferenced::
* Pragma Unreserve_All_Interrupts::
* Pragma Unsuppress::
* Pragma Use_VADS_Size::
* Pragma Validity_Checks::
* Pragma Volatile::
* Pragma Warnings::
* Pragma Weak_External::
@end menu
@node Pragma Abort_Defer
@unnumberedsec Pragma Abort_Defer
@findex Abort_Defer
@cindex Deferring aborts
@noindent
Syntax:
@smallexample
pragma Abort_Defer;
@end smallexample
@noindent
This pragma must appear at the start of the statement sequence of a
handled sequence of statements (right after the @code{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 Ada_83
@unnumberedsec Pragma Ada_83
@findex Ada_83
@noindent
Syntax:
@smallexample @c ada
pragma Ada_83;
@end smallexample
@noindent
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 new Ada 95
keywords are not recognized, optional package bodies are allowed,
and generics may name types with unknown discriminants without using
the @code{(<>)} 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
legacy 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
@unnumberedsec Pragma Ada_95
@findex Ada_95
@noindent
Syntax:
@smallexample @c ada
pragma Ada_95;
@end smallexample
@noindent
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 @code{Ada} and @code{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 Annotate
@unnumberedsec Pragma Annotate
@findex Annotate
@noindent
Syntax:
@smallexample @c ada
pragma Annotate (IDENTIFIER @{, ARG@});
ARG ::= NAME | EXPRESSION
@end smallexample
@noindent
This pragma is used to annotate programs. @var{identifier} identifies
the type of annotation. GNAT verifies this is an identifier, but does
not otherwise analyze it. The @var{arg} argument
can be either a string literal or an
expression. String literals are assumed to be of type
@code{Standard.String}. Names of entities are simply analyzed as entity
names. All other expressions are analyzed as expressions, and must be
unambiguous.
The analyzed pragma is retained in the tree, but not otherwise processed
by any part of the GNAT compiler. This pragma is intended for use by
external tools, including ASIS@.
@node Pragma Assert
@unnumberedsec Pragma Assert
@findex Assert
@noindent
Syntax:
@smallexample @c ada
pragma Assert (
boolean_EXPRESSION
[, static_string_EXPRESSION]);
@end smallexample
@noindent
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:
@smallexample @c ada
if assertions-enabled then
if not boolean_EXPRESSION then
System.Assertions.Raise_Assert_Failure
(string_EXPRESSION);
end if;
end if;
@end smallexample
@noindent
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 @samp{@var{file}:@var{nnn}},
where @var{file} is the name of the source file containing the assert,
and @var{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:
@smallexample @c ada
@dots{}
if J > 3 then
pragma Assert (K > 3, "Bad value for K");
null;
end if;
@end smallexample
@noindent
Note that, as with the @code{if} statement to which it is equivalent, the
type of the expression is either @code{Standard.Boolean}, or any type derived
from this standard type.
If assertions are disabled (switch @code{-gnata} not used), then there
is no effect (and in particular, any side effects from the expression
are suppressed). More precisely it is not quite true that the pragma
has no effect, since the expression is analyzed, and may cause types
to be frozen if they are mentioned here for the first time.
If assertions are enabled, then the given expression is tested, and if
it is @code{False} then @code{System.Assertions.Raise_Assert_Failure} is called
which results in the raising of @code{Assert_Failure} with the given message.
If the boolean expression has side effects, 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. You should generally
avoid side effects in the expression arguments of this pragma. 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.
@node Pragma Ast_Entry
@unnumberedsec Pragma Ast_Entry
@cindex OpenVMS
@findex Ast_Entry
@noindent
Syntax:
@smallexample @c ada
pragma AST_Entry (entry_IDENTIFIER);
@end smallexample
@noindent
This pragma is implemented only in the OpenVMS implementation of GNAT@. The
argument is the simple name of a single entry; at most one @code{AST_Entry}
pragma is allowed for any given entry. This pragma must be used in
conjunction with the @code{AST_Entry} attribute, and is only allowed after
the entry declaration and in the same task type specification or single task
as the entry to which it applies. This pragma specifies that the given entry
may be used to handle an OpenVMS asynchronous system trap (@code{AST})
resulting from an OpenVMS system service call. The pragma does not affect
normal use of the entry. For further details on this pragma, see the
DEC Ada Language Reference Manual, section 9.12a.
@node Pragma C_Pass_By_Copy
@unnumberedsec Pragma C_Pass_By_Copy
@cindex Passing by copy
@findex C_Pass_By_Copy
@noindent
Syntax:
@smallexample @c ada
pragma C_Pass_By_Copy
([Max_Size =>] static_integer_EXPRESSION);
@end smallexample
@noindent
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 @code{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 @bullet
@item
The size of the record type does not exceed@*@var{static_integer_expression}.
@item
The record type has @code{Convention C}.
@item
The formal parameter has this record type, and the subprogram has a
foreign (non-Ada) convention.
@end itemize
@noindent
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
@code{C_Pass_By_Copy} for the record type, or by using the extended
@code{Import} and @code{Export} pragmas, which allow specification of
passing mechanisms on a parameter by parameter basis.
@node Pragma Comment
@unnumberedsec Pragma Comment
@findex Comment
@noindent
Syntax:
@smallexample @c ada
pragma Comment (static_string_EXPRESSION);
@end smallexample
@noindent
This is almost identical in effect to pragma @code{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 @code{Comment}, unlike @code{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
@unnumberedsec Pragma Common_Object
@findex Common_Object
@noindent
Syntax:
@smallexample @c ada
pragma Common_Object (
[Internal =>] LOCAL_NAME,
[, [External =>] EXTERNAL_SYMBOL]
[, [Size =>] EXTERNAL_SYMBOL] );
EXTERNAL_SYMBOL ::=
IDENTIFIER
| static_string_EXPRESSION
@end smallexample
@noindent
This pragma enables the shared use of variables stored in overlaid
linker areas corresponding to the use of @code{COMMON}
in Fortran. The single
object @var{local_name} is assigned to the area designated by
the @var{External} argument.
You may define a record to correspond to a series
of fields. The @var{size} argument
is syntax checked in GNAT, but otherwise ignored.
@code{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_Warning
@unnumberedsec Pragma Compile_Time_Warning
@findex Compile_Time_Warning
@noindent
Syntax:
@smallexample @c ada
pragma Compile_Time_Warning
(boolean_EXPRESSION, static_string_EXPRESSION);
@end smallexample
@noindent
This pragma can be used to generate additional compile time warnings. It
is particularly useful in generics, where warnings 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, a warning 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 Complex_Representation
@unnumberedsec Pragma Complex_Representation
@findex Complex_Representation
@noindent
Syntax:
@smallexample @c ada
pragma Complex_Representation
([Entity =>] LOCAL_NAME);
@end smallexample
@noindent
The @var{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
@unnumberedsec Pragma Component_Alignment
@cindex Alignments of components
@findex Component_Alignment
@noindent
Syntax:
@smallexample @c ada
pragma Component_Alignment (
[Form =>] ALIGNMENT_CHOICE
[, [Name =>] type_LOCAL_NAME]);
ALIGNMENT_CHOICE ::=
Component_Size
| Component_Size_4
| Storage_Unit
| Default
@end smallexample
@noindent
Specifies the alignment of components in array or record types.
The meaning of the @var{Form} argument is as follows:
@table @code
@findex Component_Size
@item 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@.
@findex Component_Size_4
@item 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.
@findex Storage_Unit
@item Storage_Unit
Specifies that array or record components are byte aligned, i.e.@:
aligned on boundaries determined by the value of the constant
@code{System.Storage_Unit}.
@cindex OpenVMS
@item Default
Specifies that array or record components are aligned on default
boundaries, appropriate to the underlying hardware or operating system or
both. For OpenVMS VAX systems, the @code{Default} choice is the same as
the @code{Storage_Unit} choice (byte alignment). For all other systems,
the @code{Default} choice is the same as @code{Component_Size} (natural
alignment).
@end table
@noindent
If the @code{Name} parameter is present, @var{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
@code{Component_Alignment} together with a pragma @code{Pack} causes the
@code{Component_Alignment} pragma to be ignored. The use of
@code{Component_Alignment} together with a record representation clause
is only effective for fields not specified by the representation clause.
If the @code{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 @code{Pack}, pragma @code{Component_Alignment}, or a record rep
clause), the GNAT uses the default alignment as described previously.
@node Pragma Convention_Identifier
@unnumberedsec Pragma Convention_Identifier
@findex Convention_Identifier
@cindex Conventions, synonyms
@noindent
Syntax:
@smallexample @c ada
pragma Convention_Identifier (
[Name =>] IDENTIFIER,
[Convention =>] convention_IDENTIFIER);
@end smallexample
@noindent
This pragma provides a mechanism for supplying synonyms for existing
convention identifiers. The @code{Name} identifier can subsequently
be used as a synonym for the given convention in other pragmas (including
for example pragma @code{Import} or another @code{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:
@smallexample @c ada
pragma Convention_Indentifier (Fortran77, Fortran);
@end smallexample
@noindent
would allow the use of the convention identifier @code{Fortran77} in
subsequent code, avoiding the need to modify the sources. As another
example, you could use this to parametrize convention requirements
according to systems. Suppose you needed to use @code{Stdcall} on
windows systems, and @code{C} on some other system, then you could
define a convention identifier @code{Library} and use a single
@code{Convention_Identifier} pragma to specify which convention
would be used system-wide.
@node Pragma CPP_Class
@unnumberedsec Pragma CPP_Class
@findex CPP_Class
@cindex Interfacing with C++
@noindent
Syntax:
@smallexample @c ada
pragma CPP_Class ([Entity =>] LOCAL_NAME);
@end smallexample
@noindent
The argument denotes an entity in the current declarative region
that is declared as a tagged or untagged 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 (and only if) the type is tagged, at least one component in the
record must be of type @code{Interfaces.CPP.Vtable_Ptr}, corresponding
to the C++ Vtable (or Vtables in the case of multiple inheritance) used
for dispatching.
Types for which @code{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 @code{CPP_Constructor}).
Pragma @code{CPP_Class} is intended primarily for automatic generation
using an automatic binding generator tool.
See @ref{Interfacing to C++} for related information.
@node Pragma CPP_Constructor
@unnumberedsec Pragma CPP_Constructor
@cindex Interfacing with C++
@findex CPP_Constructor
@noindent
Syntax:
@smallexample @c ada
pragma CPP_Constructor ([Entity =>] LOCAL_NAME);
@end smallexample
@noindent
This pragma identifies an imported function (imported in the usual way
with pragma @code{Import}) as corresponding to a C++
constructor. The argument is a name that must have been
previously mentioned in a pragma @code{Import}
with @code{Convention} = @code{CPP}, and must be of one of the following
forms:
@itemize @bullet
@item
@code{function @var{Fname} return @var{T}'Class}
@item
@code{function @var{Fname} (@dots{}) return @var{T}'Class}
@end itemize
@noindent
where @var{T} is a tagged type to which the pragma @code{CPP_Class} applies.
The first form is the default constructor, used when an object of type
@var{T} is created on the Ada side with no explicit constructor. Other
constructors (including the copy constructor, which is simply a special
case of the second form in which the one and only argument is of type
@var{T}), can only appear in two contexts:
@itemize @bullet
@item
On the right side of an initialization of an object of type @var{T}.
@item
In an extension aggregate for an object of a type derived from @var{T}.
@end itemize
@noindent
Although the constructor is described as a function that returns a value
on the Ada side, it is typically a procedure with an extra implicit
argument (the object being initialized) at the implementation
level. GNAT issues the appropriate call, whatever it is, to get the
object properly initialized.
In the case of derived objects, you may use one of two possible forms
for declaring and creating an object:
@itemize @bullet
@item @code{New_Object : Derived_T}
@item @code{New_Object : Derived_T := (@var{constructor-call with} @dots{})}
@end itemize
@noindent
In the first case the default constructor is called and extension fields
if any are initialized according to the default initialization
expressions in the Ada declaration. In the second case, the given
constructor is called and the extension aggregate indicates the explicit
values of the extension fields.
If no constructors are imported, it is impossible to create any objects
on the Ada side. If no default constructor is imported, only the
initialization forms using an explicit call to a constructor are
permitted.
Pragma @code{CPP_Constructor} is intended primarily for automatic generation
using an automatic binding generator tool.
See @ref{Interfacing to C++} for more related information.
@node Pragma CPP_Virtual
@unnumberedsec Pragma CPP_Virtual
@cindex Interfacing to C++
@findex CPP_Virtual
@noindent
Syntax:
@smallexample @c ada
pragma CPP_Virtual
[Entity =>] ENTITY,
[, [Vtable_Ptr =>] vtable_ENTITY,]
[, [Position =>] static_integer_EXPRESSION]);
@end smallexample
@noindent
This pragma serves the same function as pragma @code{Import} in that
case of a virtual function imported from C++. The @var{Entity} argument
must be a
primitive subprogram of a tagged type to which pragma @code{CPP_Class}
applies. The @var{Vtable_Ptr} argument specifies
the Vtable_Ptr component which contains the
entry for this virtual function. The @var{Position} argument
is the sequential number
counting virtual functions for this Vtable starting at 1.
The @code{Vtable_Ptr} and @code{Position} arguments may be omitted if
there is one Vtable_Ptr present (single inheritance case) and all
virtual functions are imported. In that case the compiler can deduce both
these values.
No @code{External_Name} or @code{Link_Name} arguments are required for a
virtual function, since it is always accessed indirectly via the
appropriate Vtable entry.
Pragma @code{CPP_Virtual} is intended primarily for automatic generation
using an automatic binding generator tool.
See @ref{Interfacing to C++} for related information.
@node Pragma CPP_Vtable
@unnumberedsec Pragma CPP_Vtable
@cindex Interfacing with C++
@findex CPP_Vtable
@noindent
Syntax:
@smallexample @c ada
pragma CPP_Vtable (
[Entity =>] ENTITY,
[Vtable_Ptr =>] vtable_ENTITY,
[Entry_Count =>] static_integer_EXPRESSION);
@end smallexample
@noindent
Given a record to which the pragma @code{CPP_Class} applies,
this pragma can be specified for each component of type
@code{CPP.Interfaces.Vtable_Ptr}.
@var{Entity} is the tagged type, @var{Vtable_Ptr}
is the record field of type @code{Vtable_Ptr}, and @var{Entry_Count} is
the number of virtual functions on the C++ side. Not all of these
functions need to be imported on the Ada side.
You may omit the @code{CPP_Vtable} pragma if there is only one
@code{Vtable_Ptr} component in the record and all virtual functions are
imported on the Ada side (the default value for the entry count in this
case is simply the total number of virtual functions).
Pragma @code{CPP_Vtable} is intended primarily for automatic generation
using an automatic binding generator tool.
See @ref{Interfacing to C++} for related information.
@node Pragma Debug
@unnumberedsec Pragma Debug
@findex Debug
@noindent
Syntax:
@smallexample @c ada
pragma Debug (PROCEDURE_CALL_WITHOUT_SEMICOLON);
PROCEDURE_CALL_WITHOUT_SEMICOLON ::=
PROCEDURE_NAME
| PROCEDURE_PREFIX ACTUAL_PARAMETER_PART
@end smallexample
@noindent
The argument has the syntactic form of an expression, meeting the
syntactic requirements for pragmas.
If assertions are not enabled on the command line, this pragma has no
effect. If asserts 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 @code{Debug} to intersperse calls to
debug procedures in the middle of declarations.
@node Pragma Elaboration_Checks
@unnumberedsec Pragma Elaboration_Checks
@cindex Elaboration control
@findex Elaboration_Checks
@noindent
Syntax:
@smallexample @c ada
pragma Elaboration_Checks (RM | Static);
@end smallexample
@noindent
This is a configuration pragma that provides control over the
elaboration model used by the compilation affected by the
pragma. If the parameter is RM, then the dynamic elaboration
model described in the Ada Reference Manual is used, as though
the @code{-gnatE} switch had been specified on the command
line. If the parameter is 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 section ``Elaboration Order
Handling in GNAT'' in the @cite{GNAT User's Guide}.
@node Pragma Eliminate
@unnumberedsec Pragma Eliminate
@cindex Elimination of unused subprograms
@findex Eliminate
@noindent
Syntax:
@smallexample @c ada
pragma Eliminate (
[Unit_Name =>] IDENTIFIER |
SELECTED_COMPONENT);
pragma Eliminate (
[Unit_Name =>] IDENTIFIER |
SELECTED_COMPONENT,
[Entity =>] IDENTIFIER |
SELECTED_COMPONENT |
STRING_LITERAL
[,[Parameter_Types =>] PARAMETER_TYPES]
[,[Result_Type =>] result_SUBTYPE_NAME]
[,[Homonym_Number =>] INTEGER_LITERAL]);
PARAMETER_TYPES ::= (SUBTYPE_NAME @{, SUBTYPE_NAME@})
SUBTYPE_NAME ::= STRING_LITERAL
@end smallexample
@noindent
This pragma indicates that the given entity is not used outside the
compilation unit it is defined in. The entity may be either a subprogram
or a variable.
If the entity to be eliminated is a library level subprogram, then
the first form of pragma @code{Eliminate} is used with only a single argument.
In this form, the @code{Unit_Name} argument specifies the name of the
library level unit to be eliminated.
In all other cases, both @code{Unit_Name} and @code{Entity} arguments
are required. If item is an entity of a library package, then the first
argument specifies the unit name, and the second argument specifies
the particular entity. If the second argument is in string form, it must
correspond to the internal manner in which GNAT stores entity names (see
compilation unit Namet in the compiler sources for details).
The remaining parameters are optionally used to distinguish
between overloaded subprograms. There are two ways of doing this.
Use @code{Parameter_Types} and @code{Result_Type} to specify the
profile of the subprogram to be eliminated in a manner similar to that
used for
the extended @code{Import} and @code{Export} pragmas, except that the
subtype names are always given as string literals, again corresponding
to the internal manner in which GNAT stores entity names.
Alternatively, the @code{Homonym_Number} parameter is used to specify
which overloaded alternative is to be eliminated. A value of 1 indicates
the first subprogram (in lexical order), 2 indicates the second etc.
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 outside the compilation unit it is defined in,
causes a compile time or link time error.
The parameters of this pragma may be given in any order, as long as
the usual rules for use of named parameters and position parameters
are used.
The intention of pragma @code{Eliminate} is to allow a program to be compiled
in a system independent manner, with unused entities eliminated, without
the requirement of modifying the source text. Normally the required set
of @code{Eliminate} pragmas is constructed automatically using the gnatelim
tool. Elimination of unused entities local to a compilation unit is
automatic, without requiring the use of pragma @code{Eliminate}.
Note that the reason this pragma takes string literals where names might
be expected is that a pragma @code{Eliminate} can appear in a context where the
relevant names are not visible.
@node Pragma Export_Exception
@unnumberedsec Pragma Export_Exception
@cindex OpenVMS
@findex Export_Exception
@noindent
Syntax:
@smallexample @c ada
pragma Export_Exception (
[Internal =>] LOCAL_NAME,
[, [External =>] EXTERNAL_SYMBOL,]
[, [Form =>] Ada | VMS]
[, [Code =>] static_integer_EXPRESSION]);
EXTERNAL_SYMBOL ::=
IDENTIFIER
| static_string_EXPRESSION
@end smallexample
@noindent
This pragma is implemented only in the OpenVMS implementation of GNAT@. It
causes the specified exception to be propagated outside of the Ada program,
so that it can be handled by programs written in other OpenVMS languages.
This pragma establishes an external name for an Ada exception and makes the
name available to the OpenVMS Linker as a global symbol. For further details
on this pragma, see the
DEC Ada Language Reference Manual, section 13.9a3.2.
@node Pragma Export_Function
@unnumberedsec Pragma Export_Function
@cindex Argument passing mechanisms
@findex Export_Function
@noindent
Syntax:
@smallexample @c ada
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 smallexample
@noindent
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
@code{Export}, which must precede the pragma @code{Export_Function}.
GNAT does not require a separate pragma @code{Export}, but if none is
present, @code{Convention Ada} is assumed, which is usually
not what is wanted, so it is usually appropriate to use this
pragma in conjunction with a @code{Export} or @code{Convention}
pragma that specifies the desired foreign convention.
Pragma @code{Export_Function}
(and @code{Export}, if present) must appear in the same declarative
region as the function to which they apply.
@var{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 @code{Parameter_Types} and
@code{Result_Type} parameters is mandatory to achieve the required
unique designation. @var{subtype_ mark}s 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 @code{'Access} attribute can be used to match an
anonymous access parameter.
@cindex OpenVMS
@cindex Passing by descriptor
Note that passing by descriptor is not supported, even on the OpenVMS
ports of GNAT@.
@cindex 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
@unnumberedsec Pragma Export_Object
@findex Export_Object
@noindent
Syntax:
@smallexample @c ada
pragma Export_Object
[Internal =>] LOCAL_NAME,
[, [External =>] EXTERNAL_SYMBOL]
[, [Size =>] EXTERNAL_SYMBOL]
EXTERNAL_SYMBOL ::=
IDENTIFIER
| static_string_EXPRESSION
@end smallexample
@noindent
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 @code{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. @var{Size} is syntax checked,
but otherwise ignored by GNAT@.
@node Pragma Export_Procedure
@unnumberedsec Pragma Export_Procedure
@findex Export_Procedure
@noindent
Syntax:
@smallexample @c ada
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 smallexample
@noindent
This pragma is identical to @code{Export_Function} except that it
applies to a procedure rather than a function and the parameters
@code{Result_Type} and @code{Result_Mechanism} are not permitted.
GNAT does not require a separate pragma @code{Export}, but if none is
present, @code{Convention Ada} is assumed, which is usually
not what is wanted, so it is usually appropriate to use this
pragma in conjunction with a @code{Export} or @code{Convention}
pragma that specifies the desired foreign convention.
@cindex OpenVMS
@cindex Passing by descriptor
Note that passing by descriptor is not supported, even on the OpenVMS
ports of GNAT@.
@cindex 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
@unnumberedsec Pragma Export_Value
@findex Export_Value
@noindent
Syntax:
@smallexample @c ada
pragma Export_Value (
[Value =>] static_integer_EXPRESSION,
[Link_Name =>] static_string_EXPRESSION);
@end smallexample
@noindent
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
@unnumberedsec Pragma Export_Valued_Procedure
@findex Export_Valued_Procedure
@noindent
Syntax:
@smallexample @c ada
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 smallexample
@noindent
This pragma is identical to @code{Export_Procedure} except that the
first parameter of @var{local_name}, which must be present, must be of
mode @code{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 @code{OUT} and @code{IN OUT}
parameters in interfacing to external functions (which are not permitted
in Ada functions).
GNAT does not require a separate pragma @code{Export}, but if none is
present, @code{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 @code{Export} or @code{Convention}
pragma that specifies the desired foreign convention.
@cindex OpenVMS
@cindex Passing by descriptor
Note that passing by descriptor is not supported, even on the OpenVMS
ports of GNAT@.
@cindex 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
@unnumberedsec Pragma Extend_System
@cindex @code{system}, extending
@cindex Dec Ada 83
@findex Extend_System
@noindent
Syntax:
@smallexample @c ada
pragma Extend_System ([Name =>] IDENTIFIER);
@end smallexample
@noindent
This pragma is used to provide backwards compatibility with other
implementations that extend the facilities of package @code{System}. In
GNAT, @code{System} contains only the definitions that are present in
the Ada 95 RM@. However, other implementations, notably the DEC Ada 83
implementation, provide many extensions to package @code{System}.
For each such implementation accommodated by this pragma, GNAT provides a
package @code{Aux_@var{xxx}}, e.g.@: @code{Aux_DEC} for the DEC Ada 83
implementation, which provides the required additional definitions. You
can use this package in two ways. You can @code{with} it in the normal
way and access entities either by selection or using a @code{use}
clause. In this case no special processing is required.
However, if existing code contains references such as
@code{System.@var{xxx}} where @var{xxx} is an entity in the extended
definitions provided in package @code{System}, you may use this pragma
to extend visibility in @code{System} in a non-standard way that
provides greater compatibility with the existing code. Pragma
@code{Extend_System} is a configuration pragma whose single argument is
the name of the package containing the extended definition
(e.g.@: @code{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 @code{System.Aux_@var{xxx}} where
@code{Aux_@var{xxx}} is the pragma argument for any entity referenced in
package @code{System}, but not found in package @code{System}.
You can use this pragma either to access a predefined @code{System}
extension supplied with the compiler, for example @code{Aux_DEC} or
you can construct your own extension unit following the above
definition. Note that such a package is a child of @code{System}
and thus is considered part of the implementation. To compile
it you will have to use the appropriate switch for compiling
system units. See the GNAT User's Guide for details.
@node Pragma External
@unnumberedsec Pragma External
@findex External
@noindent
Syntax:
@smallexample @c ada
pragma External (
[ Convention =>] convention_IDENTIFIER,
[ Entity =>] local_NAME
[, [External_Name =>] static_string_EXPRESSION ]
[, [Link_Name =>] static_string_EXPRESSION ]);
@end smallexample
@noindent
This pragma is identical in syntax and semantics to pragma
@code{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
@code{Export} before the latter was standardized.
@node Pragma External_Name_Casing
@unnumberedsec Pragma External_Name_Casing
@cindex Dec Ada 83 casing compatibility
@cindex External Names, casing
@cindex Casing of External names
@findex External_Name_Casing
@noindent
Syntax:
@smallexample @c ada
pragma External_Name_Casing (
Uppercase | Lowercase
[, Uppercase | Lowercase | As_Is]);
@end smallexample
@noindent
This pragma provides control over the casing of external names associated
with Import and Export pragmas. There are two cases to consider:
@table @asis
@item Implicit external names
Implicit external names are derived from identifiers. The most common case
arises when a standard Ada 95 Import or Export pragma is used with only two
arguments, as in:
@smallexample @c ada
pragma Import (C, C_Routine);
@end smallexample
@noindent
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 @code{External_Name_Casing} can be used to
control this treatment. If @code{Uppercase} is specified, then the name
will be forced to all uppercase letters. If @code{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 95 Import or Export pragma is used with three
arguments, as in:
@smallexample @c ada
pragma Import (C, C_Routine, "C_routine");
@end smallexample
@noindent
In this case, the string literal normally provides the exact casing required
for the external name. The second argument of pragma
@code{External_Name_Casing} may be used to modify this behavior.
If @code{Uppercase} is specified, then the name
will be forced to all uppercase letters. If @code{Lowercase} is specified,
then the name will be forced to all lowercase letters. A specification of
@code{As_Is} provides the normal default behavior in which the casing is
taken from the string provided.
@end table
@noindent
This pragma may appear anywhere that a pragma is valid. In particular, it
can be used as a configuration pragma in the @file{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 is 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:
@smallexample @c ada
pragma External_Name_Casing (Uppercase, Uppercase);
@end smallexample
@noindent
to enforce the upper casing of all external symbols.
@node Pragma Finalize_Storage_Only
@unnumberedsec Pragma Finalize_Storage_Only
@findex Finalize_Storage_Only
@noindent
Syntax:
@smallexample @c ada
pragma Finalize_Storage_Only (first_subtype_LOCAL_NAME);
@end smallexample
@noindent
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
@unnumberedsec Pragma Float_Representation
@cindex OpenVMS
@findex Float_Representation
@noindent
Syntax:
@smallexample @c ada
pragma Float_Representation (FLOAT_REP);
FLOAT_REP ::= VAX_Float | IEEE_Float
@end smallexample
@noindent
This pragma
allows control over the internal representation chosen for the predefined
floating point types declared in the packages @code{Standard} and
@code{System}. On all systems other than OpenVMS, the argument must
be @code{IEEE_Float} and the pragma has no effect. On OpenVMS, the
argument may be @code{VAX_Float} to specify the use of the VAX float
format for the floating-point types in Standard. This requires that
the standard runtime libraries be recompiled. See the
description of the @code{GNAT LIBRARY} command in the OpenVMS version
of the GNAT Users Guide for details on the use of this command.
@node Pragma Ident
@unnumberedsec Pragma Ident
@findex Ident
@noindent
Syntax:
@smallexample @c ada
pragma Ident (static_string_EXPRESSION);
@end smallexample
@noindent
This pragma provides a string identification in the generated object file,
if the system supports the concept of this kind of identification string.
This pragma is allowed only in the outermost declarative part or
declarative items of a compilation unit. If more than one @code{Ident}
pragma is given, only the last one processed is effective.
@cindex OpenVMS
On OpenVMS systems, the effect of the pragma is identical to the effect of
the DEC Ada 83 pragma of the same name. Note that in DEC Ada 83, the
maximum allowed length is 31 characters, so if it is important to
maintain compatibility with this compiler, you should obey this length
limit.
@node Pragma Import_Exception
@unnumberedsec Pragma Import_Exception
@cindex OpenVMS
@findex Import_Exception
@noindent
Syntax:
@smallexample @c ada
pragma Import_Exception (
[Internal =>] LOCAL_NAME,
[, [External =>] EXTERNAL_SYMBOL,]
[, [Form =>] Ada | VMS]
[, [Code =>] static_integer_EXPRESSION]);
EXTERNAL_SYMBOL ::=
IDENTIFIER
| static_string_EXPRESSION
@end smallexample
@noindent
This pragma is implemented only in the OpenVMS implementation of GNAT@.
It allows OpenVMS conditions (for example, from OpenVMS system services or
other OpenVMS languages) to be propagated to Ada programs as Ada exceptions.
The pragma specifies that the exception associated with an exception
declaration in an Ada program be defined externally (in non-Ada code).
For further details on this pragma, see the
DEC Ada Language Reference Manual, section 13.9a.3.1.
@node Pragma Import_Function
@unnumberedsec Pragma Import_Function
@findex Import_Function
@noindent
Syntax:
@smallexample @c ada
pragma Import_Function (
[Internal =>] LOCAL_NAME,
[, [External =>] EXTERNAL_SYMBOL]
[, [Parameter_Types =>] PARAMETER_TYPES]
[, [Result_Type =>] SUBTYPE_MARK]
[, [Mechanism =>] MECHANISM]
[, [Result_Mechanism =>] MECHANISM_NAME]
[, [First_Optional_Parameter =>] IDENTIFIER]);
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
| Descriptor [([Class =>] CLASS_NAME)]
CLASS_NAME ::= ubs | ubsb | uba | s | sb | a | nca
@end smallexample
@noindent
This pragma is used in conjunction with a pragma @code{Import} to
specify additional information for an imported function. The pragma
@code{Import} (or equivalent pragma @code{Interface}) must precede the
@code{Import_Function} pragma and both must appear in the same
declarative part as the function specification.
The @var{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 @code{Parameter_Types} and
@var{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 @code{'Access} attribute can be used to match an
anonymous access parameter.
You may optionally use the @var{Mechanism} and @var{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.
@cindex OpenVMS
@cindex Passing by descriptor
Passing by descriptor is supported only on the OpenVMS ports of GNAT@.
@code{First_Optional_Parameter} applies only to OpenVMS ports of GNAT@.
It specifies that the designated parameter and all following parameters
are optional, meaning that they are not passed at the generated code
level (this is distinct from the notion of optional parameters in Ada
where the parameters are passed anyway with the designated optional
parameters). All optional parameters must be of mode @code{IN} and have
default parameter values that are either known at compile time
expressions, or uses of the @code{'Null_Parameter} attribute.
@node Pragma Import_Object
@unnumberedsec Pragma Import_Object
@findex Import_Object
@noindent
Syntax:
@smallexample @c ada
pragma Import_Object
[Internal =>] LOCAL_NAME,
[, [External =>] EXTERNAL_SYMBOL],
[, [Size =>] EXTERNAL_SYMBOL]);
EXTERNAL_SYMBOL ::=
IDENTIFIER
| static_string_EXPRESSION
@end smallexample
@noindent
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 @code{Import} pragma applied to an object. Unlike the
subprogram case, you need not use a separate @code{Import} pragma,
although you may do so (and probably should do so from a portability
point of view). @var{size} is syntax checked, but otherwise ignored by
GNAT@.
@node Pragma Import_Procedure
@unnumberedsec Pragma Import_Procedure
@findex Import_Procedure
@noindent
Syntax:
@smallexample @c ada
pragma Import_Procedure (
[Internal =>] LOCAL_NAME,
[, [External =>] EXTERNAL_SYMBOL]
[, [Parameter_Types =>] PARAMETER_TYPES]
[, [Mechanism =>] MECHANISM]
[, [First_Optional_Parameter =>] IDENTIFIER]);
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
| Descriptor [([Class =>] CLASS_NAME)]
CLASS_NAME ::= ubs | ubsb | uba | s | sb | a | nca
@end smallexample
@noindent
This pragma is identical to @code{Import_Function} except that it
applies to a procedure rather than a function and the parameters
@code{Result_Type} and @code{Result_Mechanism} are not permitted.
@node Pragma Import_Valued_Procedure
@unnumberedsec Pragma Import_Valued_Procedure
@findex Import_Valued_Procedure
@noindent
Syntax:
@smallexample @c ada
pragma Import_Valued_Procedure (
[Internal =>] LOCAL_NAME,
[, [External =>] EXTERNAL_SYMBOL]
[, [Parameter_Types =>] PARAMETER_TYPES]
[, [Mechanism =>] MECHANISM]
[, [First_Optional_Parameter =>] IDENTIFIER]);
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
| Descriptor [([Class =>] CLASS_NAME)]
CLASS_NAME ::= ubs | ubsb | uba | s | sb | a | nca
@end smallexample
@noindent
This pragma is identical to @code{Import_Procedure} except that the
first parameter of @var{local_name}, which must be present, must be of
mode @code{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 @code{OUT} and @code{IN OUT}
parameters in interfacing to external functions (which are not permitted
in Ada functions). You may optionally use the @code{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 Initialize_Scalars
@unnumberedsec Pragma Initialize_Scalars
@findex Initialize_Scalars
@cindex debugging with Initialize_Scalars
@noindent
Syntax:
@smallexample @c ada
pragma Initialize_Scalars;
@end smallexample
@noindent
This pragma is similar to @code{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 there is control over the value used
for initializing scalar objects. At bind time, you can select whether to
initialize with invalid values (like Normalize_Scalars), or with high or
low values, or with a specified bit pattern. See the users 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 erroneous reference to an
uninitialized value.
Note that pragma @code{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 @code{-gnatV} flag in the
users guide) in conjunction with pragma @code{Initialize_Scalars}
provides a powerful new tool to assist in the detection of problems
caused by uninitialized variables.
@node Pragma Inline_Always
@unnumberedsec Pragma Inline_Always
@findex Inline_Always
@noindent
Syntax:
@smallexample @c ada
pragma Inline_Always (NAME [, NAME]);
@end smallexample
@noindent
Similar to pragma @code{Inline} except that inlining is not subject to
the use of option @code{-gnatn} and the inlining happens regardless of
whether this option is used.
@node Pragma Inline_Generic
@unnumberedsec Pragma Inline_Generic
@findex Inline_Generic
@noindent
Syntax:
@smallexample @c ada
pragma Inline_Generic (generic_package_NAME);
@end smallexample
@noindent
This is implemented for compatibility with DEC Ada 83 and is recognized,
but otherwise ignored, by GNAT@. All generic instantiations are inlined
by default when using GNAT@.
@node Pragma Interface
@unnumberedsec Pragma Interface
@findex Interface
@noindent
Syntax:
@smallexample @c ada
pragma Interface (
[Convention =>] convention_identifier,
[Entity =>] local_name
[, [External_Name =>] static_string_expression],
[, [Link_Name =>] static_string_expression]);
@end smallexample
@noindent
This pragma is identical in syntax and semantics to
the standard Ada 95 pragma @code{Import}. It is provided for compatibility
with Ada 83. The definition is upwards compatible both with pragma
@code{Interface} as defined in the Ada 83 Reference Manual, and also
with some extended implementations of this pragma in certain Ada 83
implementations.
@node Pragma Interface_Name
@unnumberedsec Pragma Interface_Name
@findex Interface_Name
@noindent
Syntax:
@smallexample @c ada
pragma Interface_Name (
[Entity =>] LOCAL_NAME
[, [External_Name =>] static_string_EXPRESSION]
[, [Link_Name =>] static_string_EXPRESSION]);
@end smallexample
@noindent
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 @var{External_Name} or @var{Link_Name}.
@node Pragma Interrupt_Handler
@unnumberedsec Pragma Interrupt_Handler
@findex Interrupt_Handler
@noindent
Syntax:
@smallexample @c ada
pragma Interrupt_Handler (procedure_LOCAL_NAME);
@end smallexample
@noindent
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
@code{IERET} is generated for returns from the procedure, enabling
maskable interrupts, in place of the normal return instruction.
@node Pragma Interrupt_State
@unnumberedsec Pragma Interrupt_State
@findex Interrupt_State
@noindent
Syntax:
@smallexample @c ada
pragma Interrupt_State (Name => value, State => SYSTEM | RUNTIME | USER);
@end smallexample
@noindent
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 @code{SIGINT} interrupt used in
many systems for an @kbd{Ctrl-C} interrupt. Normally this interrupt is
reserved to the implementation, so that @kbd{Ctrl-C} can be used to
interrupt execution. Additionally, signals such as @code{SIGSEGV},
@code{SIGABRT}, @code{SIGFPE} and @code{SIGILL} are often mapped to specific
Ada exceptions, or used to implement run-time functions such as the
@code{abort} statement and stack overflow checking.
Pragma @code{Interrupt_State} provides a general mechanism for overriding
such uses of interrupts. It subsumes the functionality of pragma
@code{Unreserve_All_Interrupts}. Pragma @code{Interrupt_State} is not
available on OS/2, 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 @bullet
@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
@noindent
These states are the allowed values of the @code{State} parameter of the
pragma. The @code{Name} parameter is a value of the type
@code{Ada.Interrupts.Interrupt_ID}. Typically, it is a name declared in
@code{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 @code{Reserved}
declared in the specification of package @code{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 @code{abort} statement.
@node Pragma Keep_Names
@unnumberedsec Pragma Keep_Names
@findex Keep_Names
@noindent
Syntax:
@smallexample @c ada
pragma Keep_Names ([On =>] enumeration_first_subtype_LOCAL_NAME);
@end smallexample
@noindent
The @var{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 @code{Image} and @code{Value} even if a global
@code{Discard_Names} pragma applies. This is useful when you want to
generally suppress enumeration literal names and for example you therefore
use a @code{Discard_Names} pragma in the @file{gnat.adc} file, but you
want to retain the names for specific enumeration types.
@node Pragma License
@unnumberedsec Pragma License
@findex License
@cindex License checking
@noindent
Syntax:
@smallexample @c ada
pragma License (Unrestricted | GPL | Modified_GPL | Restricted);
@end smallexample
@noindent
This pragma is provided to allow automated checking for appropriate license
conditions with respect to the standard and modified GPL@. A pragma
@code{License}, which is a configuration pragma that typically appears at
the start of a source file or in a separate @file{gnat.adc} file, specifies
the licensing conditions of a unit as follows:
@itemize @bullet
@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 @code{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@. This is the license used for the GNAT run-time which ensures
that the run-time can be used freely in any program without GPL concerns.
@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 @code{with} units
which are licensed under the modified GPL (this is the whole point of the
modified GPL).
@end itemize
@noindent
Normally a unit with no @code{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.
@itemize @bullet
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.
@end itemize
@noindent
These default actions means that a program with a restricted license pragma
will automatically get warnings if a GPL unit is inappropriately
@code{with}'ed. For example, the program:
@smallexample @c ada
with Sem_Ch3;
with GNAT.Sockets;
procedure Secret_Stuff is
@dots{}
end Secret_Stuff
@end smallexample
@noindent
if compiled with pragma @code{License} (@code{Restricted}) in a
@file{gnat.adc} file will generate the warning:
@smallexample
1. with Sem_Ch3;
|
>>> license of withed unit "Sem_Ch3" is incompatible
2. with GNAT.Sockets;
3. procedure Secret_Stuff is
@end smallexample
@noindent
Here we get a warning on @code{Sem_Ch3} since it is part of the GNAT
compiler and is licensed under the
GPL, but no warning for @code{GNAT.Sockets} which is part of the GNAT
run time, and is therefore licensed under the modified GPL@.
@node Pragma Link_With
@unnumberedsec Pragma Link_With
@findex Link_With
@noindent
Syntax:
@smallexample @c ada
pragma Link_With (static_string_EXPRESSION @{,static_string_EXPRESSION@});
@end smallexample
@noindent
This pragma is provided for compatibility with certain Ada 83 compilers.
It has exactly the same effect as pragma @code{Linker_Options} except
that spaces occurring within one of the string expressions are treated
as separators. For example, in the following case:
@smallexample @c ada
pragma Link_With ("-labc -ldef");
@end smallexample
@noindent
results in passing the strings @code{-labc} and @code{-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
@unnumberedsec Pragma Linker_Alias
@findex Linker_Alias
@noindent
Syntax:
@smallexample @c ada
pragma Linker_Alias (
[Entity =>] LOCAL_NAME
[Alias =>] static_string_EXPRESSION);
@end smallexample
@noindent
This pragma establishes a linker alias for the given named entity. For
further details on the exact effect, consult the GCC manual.
@node Pragma Linker_Section
@unnumberedsec Pragma Linker_Section
@findex Linker_Section
@noindent
Syntax:
@smallexample @c ada
pragma Linker_Section (
[Entity =>] LOCAL_NAME
[Section =>] static_string_EXPRESSION);
@end smallexample
@noindent
This pragma specifies the name of the linker section for the given entity.
For further details on the exact effect, consult the GCC manual.
@node Pragma Long_Float
@unnumberedsec Pragma Long_Float
@cindex OpenVMS
@findex Long_Float
@noindent
Syntax:
@smallexample @c ada
pragma Long_Float (FLOAT_FORMAT);
FLOAT_FORMAT ::= D_Float | G_Float
@end smallexample
@noindent
This pragma is implemented only in the OpenVMS implementation of GNAT@.
It allows control over the internal representation chosen for the predefined
type @code{Long_Float} and for floating point type representations with
@code{digits} specified in the range 7 through 15.
For further details on this pragma, see the
@cite{DEC Ada Language Reference Manual}, section 3.5.7b. Note that to use
this pragma, the standard runtime libraries must be recompiled. See the
description of the @code{GNAT LIBRARY} command in the OpenVMS version
of the GNAT User's Guide for details on the use of this command.
@node Pragma Machine_Attribute
@unnumberedsec Pragma Machine_Attribute
@findex Machine_Attribute
@noindent
Syntax:
@smallexample @c ada
pragma Machine_Attribute (
[Attribute_Name =>] string_EXPRESSION,
[Entity =>] LOCAL_NAME);
@end smallexample
@noindent
Machine dependent attributes can be specified for types and/or
declarations. Currently only subprogram entities are supported. This
pragma is semantically equivalent to
@code{__attribute__((@var{string_expression}))} in GNU C,
where @code{@var{string_expression}} is
recognized by the GNU C macros @code{VALID_MACHINE_TYPE_ATTRIBUTE} and
@code{VALID_MACHINE_DECL_ATTRIBUTE} which are defined in the
configuration header file @file{tm.h} for each machine. See the GCC
manual for further information.
@node Pragma Main_Storage
@unnumberedsec Pragma Main_Storage
@cindex OpenVMS
@findex Main_Storage
@noindent
Syntax:
@smallexample @c ada
pragma Main_Storage
(MAIN_STORAGE_OPTION [, MAIN_STORAGE_OPTION]);
MAIN_STORAGE_OPTION ::=
[WORKING_STORAGE =>] static_SIMPLE_EXPRESSION
| [TOP_GUARD =>] static_SIMPLE_EXPRESSION
@end smallexample
@noindent
This pragma is provided for compatibility with OpenVMS VAX Systems. It has
no effect in GNAT, other than being syntax checked. Note that the pragma
also has no effect in DEC Ada 83 for OpenVMS Alpha Systems.
@node Pragma No_Return
@unnumberedsec Pragma No_Return
@findex No_Return
@noindent
Syntax:
@smallexample @c ada
pragma No_Return (procedure_LOCAL_NAME);
@end smallexample
@noindent
@var{procedure_local_NAME} 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 @code{return} statements,
and also may not contain any implicit return statements from falling off
the end of a statement sequence. 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.
@node Pragma Normalize_Scalars
@unnumberedsec Pragma Normalize_Scalars
@findex Normalize_Scalars
@noindent
Syntax:
@smallexample @c ada
pragma Normalize_Scalars;
@end smallexample
@noindent
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 @code
@item Standard.Character
@noindent
Objects whose root type is Standard.Character are initialized to
Character'Last. This will be out of range of the subtype only if
the subtype range excludes this value.
@item Standard.Wide_Character
@noindent
Objects whose root type is Standard.Wide_Character are initialized to
Wide_Character'Last. This will be out of range of the subtype only if
the subtype range excludes this value.
@item Integer types
@noindent
Objects of an integer type are initialized to base_type'First, where
base_type is the base type of the object type. This will be out of range
of the subtype only if the subtype range excludes this value. For example,
if you declare the subtype:
@smallexample @c ada
subtype Ityp is integer range 1 .. 10;
@end smallexample
@noindent
then objects of type x will be initialized to Integer'First, a negative
number that is certainly outside the range of subtype @code{Ityp}.
@item Real types
Objects of all real types (fixed and floating) are initialized to
base_type'First, where base_Type is the base type of the object type.
This will be out of range of the subtype only if the subtype range
excludes this value.
@item Modular types
Objects of a modular type are initialized to typ'Last. This will be out
of range of the subtype only if the subtype excludes this value.
@item Enumeration types
Objects of an enumeration type are initialized to all one-bits, i.e.@: to
the value @code{2 ** typ'Size - 1}. This will be out of range of the
enumeration subtype in all cases except where the subtype contains
exactly 2**8, 2**16, or 2**32 elements.
@end table
@node Pragma Obsolescent
@unnumberedsec Pragma Obsolescent
@findex Obsolescent
@noindent
Syntax:
@smallexample @c ada
pragma Obsolescent [(static_string_EXPRESSION)];
@end smallexample
@noindent
This pragma must occur immediately following a subprogram
declaration. It indicates that the associated function or procedure
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. The pragma can be used at an intermediate stage
when the subprogram is still present, but will be removed later.
The effect of this pragma is to output a warning message that the
subprogram is obsolescent if the appropriate warning option in the
compiler is activated. If a parameter is present, then a second
warning message is given containing this text.
@node Pragma Passive
@unnumberedsec Pragma Passive
@findex Passive
@noindent
Syntax:
@smallexample @c ada
pragma Passive ([Semaphore | No]);
@end smallexample
@noindent
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
@code{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 @code{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).
@node Pragma Polling
@unnumberedsec Pragma Polling
@findex Polling
@noindent
Syntax:
@smallexample @c ada
pragma Polling (ON | OFF);
@end smallexample
@noindent
This pragma controls the generation of polling code. This is normally off.
If @code{pragma Polling (ON)} is used then periodic calls are generated to
the routine @code{Ada.Exceptions.Poll}. This routine is a separate unit in the
runtime library, and can be found in file @file{a-excpol.adb}.
Pragma @code{Polling} can appear as a configuration pragma (for example it
can be placed in the @file{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 @code{Poll}
routine is called frequently, and places an upper bound (determined by
the complexity of the code) on the period between two @code{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 @code{Ada.Exceptions} package that can
be found in files @file{a-except.ads} and @file{a-except.adb}.
A standard alternative unit (in file @file{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
@code{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 @code{-gnatP} switch. See
the @cite{GNAT User's Guide} for details.
@node Pragma Propagate_Exceptions
@unnumberedsec Pragma Propagate_Exceptions
@findex Propagate_Exceptions
@cindex Zero Cost Exceptions
@noindent
Syntax:
@smallexample @c ada
pragma Propagate_Exceptions (subprogram_LOCAL_NAME);
@end smallexample
@noindent
This pragma indicates that the given entity, which is the name of an
imported foreign-language subprogram may receive an Ada exception,
and that the exception should be propagated. It is relevant only if
zero cost exception handling is in use, and is thus never needed if
the alternative @code{longjmp} / @code{setjmp} implementation of
exceptions is used (although it is harmless to use it in such cases).
The implementation of fast exceptions always properly propagates
exceptions through Ada code, as described in the Ada Reference Manual.
However, this manual is silent about the propagation of exceptions
through foreign code. For example, consider the
situation where @code{P1} calls
@code{P2}, and @code{P2} calls @code{P3}, where
@code{P1} and @code{P3} are in Ada, but @code{P2} is in C@.
@code{P3} raises an Ada exception. The question is whether or not
it will be propagated through @code{P2} and can be handled in
@code{P1}.
For the @code{longjmp} / @code{setjmp} implementation of exceptions,
the answer is always yes. For some targets on which zero cost exception
handling is implemented, the answer is also always yes. However, there
are some targets, notably in the current version all x86 architecture
targets, in which the answer is that such propagation does not
happen automatically. If such propagation is required on these
targets, it is mandatory to use @code{Propagate_Exceptions} to
name all foreign language routines through which Ada exceptions
may be propagated.
@node Pragma Psect_Object
@unnumberedsec Pragma Psect_Object
@findex Psect_Object
@noindent
Syntax:
@smallexample @c ada
pragma Psect_Object (
[Internal =>] LOCAL_NAME,
[, [External =>] EXTERNAL_SYMBOL]
[, [Size =>] EXTERNAL_SYMBOL]);
EXTERNAL_SYMBOL ::=
IDENTIFIER
| static_string_EXPRESSION
@end smallexample
@noindent
This pragma is identical in effect to pragma @code{Common_Object}.
@node Pragma Pure_Function
@unnumberedsec Pragma Pure_Function
@findex Pure_Function
@noindent
Syntax:
@smallexample @c ada
pragma Pure_Function ([Entity =>] function_LOCAL_NAME);
@end smallexample
@noindent
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 @code{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 @code{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).
@findex Pure
Note: Most functions in a @code{Pure} package are automatically pure, and
there is no need to use pragma @code{Pure_Function} for such functions. One
exception is any function that has at least one formal of type
@code{System.Address} or a type derived from it. Such functions are not
considered pure by default, since the compiler assumes that the
@code{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 consdered to be pure by default,
since there is no way of checking that they are in fact pure. The use
of pragma @code{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 @code{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.
@node Pragma Ravenscar
@unnumberedsec Pragma Ravenscar
@findex Ravenscar
@noindent
Syntax:
@smallexample @c ada
pragma Ravenscar;
@end smallexample
@noindent
A configuration pragma that establishes the following set of restrictions:
@table @code
@item No_Abort_Statements
[RM D.7] There are no abort_statements, and there are
no calls to Task_Identification.Abort_Task.
@item No_Select_Statements
There are no select_statements.
@item No_Task_Hierarchy
[RM D.7] All (non-environment) tasks depend
directly on the environment task of the partition.
@item No_Task_Allocators
[RM D.7] There are no allocators for task types
or types containing task subcomponents.
@item No_Dynamic_Priorities
[RM D.7] There are no semantic dependencies on the package Dynamic_Priorities.
@item No_Terminate_Alternatives
[RM D.7] There are no selective_accepts with terminate_alternatives
@item No_Dynamic_Interrupts
There are no semantic dependencies on Ada.Interrupts.
@item No_Implicit_Heap_Allocations
[RM D.7] No constructs are allowed to cause implicit heap allocation
@item No_Protected_Type_Allocators
There are no allocators for protected types or
types containing protected subcomponents.
@item No_Local_Protected_Objects
Protected objects and access types that designate
such objects shall be declared only at library level.
@item No_Requeue
Requeue statements are not allowed.
@item No_Calendar
There are no semantic dependencies on the package Ada.Calendar.
@item No_Relative_Delay
There are no delay_relative_statements.
@item No_Task_Attributes
There are no semantic dependencies on the Ada.Task_Attributes package and
there are no references to the attributes Callable and Terminated [RM 9.9].
@item Boolean_Entry_Barriers
Entry barrier condition expressions shall be boolean
objects which are declared in the protected type
which contains the entry.
@item Max_Asynchronous_Select_Nesting = 0
[RM D.7] Specifies the maximum dynamic nesting level of asynchronous_selects.
A value of zero prevents the use of any asynchronous_select.
@item Max_Task_Entries = 0
[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. A value of zero
indicates that no rendezvous are possible. For
the Ravenscar pragma, the value of Max_Task_Entries is always
0 (zero).
@item Max_Protected_Entries = 1
[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. For the Ravenscar pragma the value of
Max_Protected_Entries is always 1.
@item Max_Select_Alternatives = 0
[RM D.7] Specifies the maximum number of alternatives in a selective_accept.
For the Ravenscar pragma the value is always 0.
@item No_Task_Termination
Tasks which terminate are erroneous.
@item No_Entry_Queue
No task can be queued on a protected entry. Note that this restrictions is
checked at run time. The violation of this restriction generates a
Program_Error exception.
@end table
@noindent
This set of restrictions corresponds to the definition of the ``Ravenscar
Profile'' for limited tasking, devised and published by the
@cite{International Real-Time Ada Workshop}, 1997,
and whose most recent description is available at
@url{ftp://ftp.openravenscar.org/openravenscar/ravenscar00.pdf}.
The above set is a superset of the restrictions provided by pragma
@code{Restricted_Run_Time}, it includes five additional restrictions
(@code{Boolean_Entry_Barriers}, @code{No_Select_Statements},
@code{No_Calendar},
@code{No_Relative_Delay} and @code{No_Task_Termination}). This means
that pragma @code{Ravenscar}, like the pragma @code{Restricted_Run_Time},
automatically causes the use of a simplified, more efficient version
of the tasking run-time system.
@node Pragma Restricted_Run_Time
@unnumberedsec Pragma Restricted_Run_Time
@findex Restricted_Run_Time
@noindent
Syntax:
@smallexample @c ada
pragma Restricted_Run_Time;
@end smallexample
@noindent
A configuration pragma that establishes the following set of restrictions:
@itemize @bullet
@item No_Abort_Statements
@item No_Entry_Queue
@item No_Task_Hierarchy
@item No_Task_Allocators
@item No_Dynamic_Priorities
@item No_Terminate_Alternatives
@item No_Dynamic_Interrupts
@item No_Protected_Type_Allocators
@item No_Local_Protected_Objects
@item No_Requeue
@item No_Task_Attributes
@item Max_Asynchronous_Select_Nesting = 0
@item Max_Task_Entries = 0
@item Max_Protected_Entries = 1
@item Max_Select_Alternatives = 0
@end itemize
@noindent
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.
@node Pragma Restriction_Warnings
@unnumberedsec Pragma Restriction_Warnings
@findex Restriction_Warnings
@noindent
Syntax:
@smallexample @c ada
pragma Restriction_Warnings
(restriction_IDENTIFIER @{, restriction_IDENTIFIER@});
@end smallexample
@noindent
This pragma allows a series of restriction identifiers to be
specified (the list of allowed identifiers is the same as for
pragma @code{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.
@node Pragma Source_File_Name
@unnumberedsec Pragma Source_File_Name
@findex Source_File_Name
@noindent
Syntax:
@smallexample @c ada
pragma Source_File_Name (
[Unit_Name =>] unit_NAME,
Spec_File_Name => STRING_LITERAL);
pragma Source_File_Name (
[Unit_Name =>] unit_NAME,
Body_File_Name => STRING_LITERAL);
@end smallexample
@noindent
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.
@var{unit_name} is mapped to @var{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.
Another form of the @code{Source_File_Name} pragma allows
the specification of patterns defining alternative file naming schemes
to apply to all files.
@smallexample @c ada
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 smallexample
@noindent
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.
A pragma Source_File_Name cannot appear after a
@ref{Pragma Source_File_Name_Project}.
For more details on the use of the @code{Source_File_Name} pragma,
see the sections ``Using Other File Names'' and
``Alternative File Naming Schemes'' in the @cite{GNAT User's Guide}.
@node Pragma Source_File_Name_Project
@unnumberedsec Pragma Source_File_Name_Project
@findex Source_File_Name_Project
@noindent
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{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 pragmas (which would not be known to the project manager).
@node Pragma Source_Reference
@unnumberedsec Pragma Source_Reference
@findex Source_Reference
@noindent
Syntax:
@smallexample @c ada
pragma Source_Reference (INTEGER_LITERAL, STRING_LITERAL);
@end smallexample
@noindent
This pragma must appear as the first line of a source file.
@var{integer_literal} is the logical line number of the line following
the pragma line (for use in error messages and debugging
information). @var{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 @code{gnatchop}
with the @code{-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 Stream_Convert
@unnumberedsec Pragma Stream_Convert
@findex Stream_Convert
@noindent
Syntax:
@smallexample @c ada
pragma Stream_Convert (
[Entity =>] type_LOCAL_NAME,
[Read =>] function_NAME,
[Write =>] function NAME);
@end smallexample
@noindent
This pragma provides an efficient way of providing stream functions for
types defined in packages. Not only is it simpler to use than declaring
the necessary functions with attribute representation clauses, but more
significantly, it allows the declaration to made in such a way that the
stream packages are not loaded unless they are needed. 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 @var{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 @var{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:
@smallexample @c ada
function To_Unbounded (S : String)
return Unbounded_String
renames To_Unbounded_String;
pragma Stream_Convert
(Unbounded_String, To_Unbounded, To_String);
@end smallexample
@noindent
The specifications of the referenced functions, as given in the Ada 95
Reference Manual are:
@smallexample @c ada
function To_Unbounded_String (Source : String)
return Unbounded_String;
function To_String (Source : Unbounded_String)
return String;
@end smallexample
@noindent
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 used for @code{Standard.String}, and this same representation is
expected when a value of this type is read from the stream.
@node Pragma Style_Checks
@unnumberedsec Pragma Style_Checks
@findex Style_Checks
@noindent
Syntax:
@smallexample @c ada
pragma Style_Checks (string_LITERAL | ALL_CHECKS |
On | Off [, LOCAL_NAME]);
@end smallexample
@noindent
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 @file{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 @code{-gnaty} switch to @code{gcc} or @code{gnatmake}.
For example the following two methods can be used to enable
layout checking:
@itemize @bullet
@item
@smallexample @c ada
pragma Style_Checks ("l");
@end smallexample
@item
@smallexample
gcc -c -gnatyl @dots{}
@end smallexample
@end itemize
@noindent
The form ALL_CHECKS activates all standard checks (its use is equivalent
to the use of the @code{gnaty} switch with no options. See GNAT User's
Guide for details.
The forms with @code{Off} and @code{On}
can be used to temporarily disable style checks
as shown in the following example:
@smallexample @c ada
@iftex
@leftskip=0cm
@end iftex
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 smallexample
@noindent
Finally the two argument form is allowed only if the first argument is
@code{On} or @code{Off}. The effect is to turn of semantic style checks
for the specified entity, as shown in the following example:
@smallexample @c ada
@iftex
@leftskip=0cm
@end iftex
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 smallexample
@node Pragma Subtitle
@unnumberedsec Pragma Subtitle
@findex Subtitle
@noindent
Syntax:
@smallexample @c ada
pragma Subtitle ([Subtitle =>] STRING_LITERAL);
@end smallexample
@noindent
This pragma is recognized for compatibility with other Ada compilers
but is ignored by GNAT@.
@node Pragma Suppress_All
@unnumberedsec Pragma Suppress_All
@findex Suppress_All
@noindent
Syntax:
@smallexample @c ada
pragma Suppress_All;
@end smallexample
@noindent
This pragma can only appear immediately following a compilation
unit. The effect is to apply @code{Suppress (All_Checks)} to the unit
which it follows. This pragma is implemented for compatibility with DEC
Ada 83 usage. The use of pragma @code{Suppress (All_Checks)} as a normal
configuration pragma is the preferred usage in GNAT@.
@node Pragma Suppress_Exception_Locations
@unnumberedsec Pragma Suppress_Exception_Locations
@findex Suppress_Exception_Locations
@noindent
Syntax:
@smallexample @c ada
pragma Suppress_Exception_Locations;
@end smallexample
@noindent
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 @code{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
@unnumberedsec Pragma Suppress_Initialization
@findex Suppress_Initialization
@cindex Suppressing initialization
@cindex Initialization, suppression of
@noindent
Syntax:
@smallexample @c ada
pragma Suppress_Initialization ([Entity =>] type_Name);
@end smallexample
@noindent
This pragma suppresses any implicit or explicit initialization
associated with the given type name for all variables of this type.
@node Pragma Task_Info
@unnumberedsec Pragma Task_Info
@findex Task_Info
@noindent
Syntax
@smallexample @c ada
pragma Task_Info (EXPRESSION);
@end smallexample
@noindent
This pragma appears within a task definition (like pragma
@code{Priority}) and applies to the task in which it appears. The
argument must be of type @code{System.Task_Info.Task_Info_Type}.
The @code{Task_Info} pragma provides system dependent control over
aspects of tasking implementation, for example, the ability to map
tasks to specific processors. For details on the facilities available
for the version of GNAT that you are using, see the documentation
in the specification of package System.Task_Info in the runtime
library.
@node Pragma Task_Name
@unnumberedsec Pragma Task_Name
@findex Task_Name
@noindent
Syntax
@smallexample @c ada
pragma Task_Name (string_EXPRESSION);
@end smallexample
@noindent
This pragma appears within a task definition (like pragma
@code{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 @code{Ada.Task_Identification.Image} will return this
string, with a unique task address appended.
@smallexample @c ada
-- 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 smallexample
@node Pragma Task_Storage
@unnumberedsec Pragma Task_Storage
@findex Task_Storage
Syntax:
@smallexample @c ada
pragma Task_Storage (
[Task_Type =>] LOCAL_NAME,
[Top_Guard =>] static_integer_EXPRESSION);
@end smallexample
@noindent
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
@code{Storage_Size} attribute definition clause is allowed for a task
type.
@node Pragma Thread_Body
@unnumberedsec Pragma Thread_Body
@findex Thread_Body
Syntax:
@smallexample @c ada
pragma Thread_Body (
[Entity =>] LOCAL_NAME,
[[Secondary_Stack_Size =>] static_integer_EXPRESSION)];
@end smallexample
@noindent
This pragma specifies that the subprogram whose name is given as the
@code{Entity} argument is a thread body, which will be activated
by being called via its Address from foreign code. The purpose is
to allow execution and registration of the foreign thread within the
Ada run-time system.
See the library unit @code{System.Threads} for details on the expansion of
a thread body subprogram, including the calls made to subprograms
within System.Threads to register the task. This unit also lists the
targets and runtime systems for which this pragma is supported.
A thread body subprogram may not be called directly from Ada code, and
it is not permitted to apply the Access (or Unrestricted_Access) attributes
to such a subprogram. The only legitimate way of calling such a subprogram
is to pass its Address to foreign code and then make the call from the
foreign code.
A thread body subprogram may have any parameters, and it may be a function
returning a result. The convention of the thread body subprogram may be
set in the usual manner using @code{pragma Convention}.
The secondary stack size parameter, if given, is used to set the size
of secondary stack for the thread. The secondary stack is allocated as
a local variable of the expanded thread body subprogram, and thus is
allocated out of the main thread stack size. If no secondary stack
size parameter is present, the default size (from the declaration in
@code{System.Secondary_Stack} is used.
@node Pragma Time_Slice
@unnumberedsec Pragma Time_Slice
@findex Time_Slice
@noindent
Syntax:
@smallexample @c ada
pragma Time_Slice (static_duration_EXPRESSION);
@end smallexample
@noindent
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.
@cindex OpenVMS
Note that the effect of this pragma is identical to the effect of the
DEC Ada 83 pragma of the same name when operating under OpenVMS systems.
@node Pragma Title
@unnumberedsec Pragma Title
@findex Title
@noindent
Syntax:
@smallexample @c ada
pragma Title (TITLING_OPTION [, TITLING OPTION]);
TITLING_OPTION ::=
[Title =>] STRING_LITERAL,
| [Subtitle =>] STRING_LITERAL
@end smallexample
@noindent
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 Unchecked_Union
@unnumberedsec Pragma Unchecked_Union
@cindex Unions in C
@findex Unchecked_Union
@noindent
Syntax:
@smallexample @c ada
pragma Unchecked_Union (first_subtype_LOCAL_NAME);
@end smallexample
@noindent
This pragma is used to declare that the specified type should be represented
in a manner
equivalent to a C union type, and is intended only for use in
interfacing with C code that uses union types. In Ada terms, the named
type must obey the following rules:
@itemize @bullet
@item
It is a non-tagged non-limited record type.
@item
It has a single discrete discriminant with a default value.
@item
The component list consists of a single variant part.
@item
Each variant has a component list with a single component.
@item
No nested variants are allowed.
@item
No component has an explicit default value.
@item
No component has a non-static constraint.
@end itemize
@noindent
In addition, given a type that meets the above requirements, the
following restrictions apply to its use throughout the program:
@itemize @bullet
@item
The discriminant name can be mentioned only in an aggregate.
@item
No subtypes may be created of this type.
@item
The type may not be constrained by giving a discriminant value.
@item
The type cannot be passed as the actual for a generic formal with a
discriminant.
@end itemize
@noindent
Equality and inequality operations on @code{unchecked_unions} are not
available, since there is no discriminant to compare and the compiler
does not even know how many bits to compare. It is implementation
dependent whether this is detected at compile time as an illegality or
whether it is undetected and considered to be an erroneous construct. In
GNAT, a direct comparison is illegal, but GNAT does not attempt to catch
the composite case (where two composites are compared that contain an
unchecked union component), so such comparisons are simply considered
erroneous.
The layout of the resulting type corresponds exactly to a C union, where
each branch of the union corresponds to a single variant in the Ada
record. The semantics of the Ada program is not changed in any way by
the pragma, i.e.@: provided the above restrictions are followed, and no
erroneous incorrect references to fields or erroneous comparisons occur,
the semantics is exactly as described by the Ada reference manual.
Pragma @code{Suppress (Discriminant_Check)} applies implicitly to the
type and the default convention is C.
@node Pragma Unimplemented_Unit
@unnumberedsec Pragma Unimplemented_Unit
@findex Unimplemented_Unit
@noindent
Syntax:
@smallexample @c ada
pragma Unimplemented_Unit;
@end smallexample
@noindent
If this pragma occurs in a unit that is processed by the compiler, GNAT
aborts with the message @samp{@var{xxx} not implemented}, where
@var{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_Data
@unnumberedsec Pragma Universal_Data
@findex Universal_Data
@noindent
Syntax:
@smallexample @c ada
pragma Universal_Data [(library_unit_Name)];
@end smallexample
@noindent
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 @file{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 Unreferenced
@unnumberedsec Pragma Unreferenced
@findex Unreferenced
@cindex Warnings, unreferenced
@noindent
Syntax:
@smallexample @c ada
pragma Unreferenced (local_Name @{, local_Name@});
@end smallexample
@noindent
This pragma signals that the entities whose names are listed are
deliberately not referenced. This suppresses warnings about the
entities being unreferenced, and in addition a warning will be
generated if one of these entities is in fact referenced.
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 @code{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.
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.
@node Pragma Unreserve_All_Interrupts
@unnumberedsec Pragma Unreserve_All_Interrupts
@findex Unreserve_All_Interrupts
@noindent
Syntax:
@smallexample @c ada
pragma Unreserve_All_Interrupts;
@end smallexample
@noindent
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 @code{SIGINT} interrupt used in
many systems for a @kbd{Ctrl-C} interrupt. Normally this interrupt is
reserved to the implementation, so that @kbd{Ctrl-C} can be used to
interrupt execution.
If the pragma @code{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
@kbd{Ctrl-C} will not automatically interrupt execution. However,
a program can then handle the @code{SIGINT} interrupt as it chooses.
For a full list of the interrupts handled in a specific implementation,
see the source code for the specification of @code{Ada.Interrupts.Names} in
file @file{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 @code{Unreserve_All_Interrupts} pragma.
For a more general facility for controlling what interrupts can be
handled, see pragma @code{Interrupt_State}, which subsumes the functionality
of the @code{Unreserve_All_Interrupts} pragma.
@node Pragma Unsuppress
@unnumberedsec Pragma Unsuppress
@findex Unsuppress
@noindent
Syntax:
@smallexample @c ada
pragma Unsuppress (IDENTIFIER [, [On =>] NAME]);
@end smallexample
@noindent
This pragma undoes the effect of a previous pragma @code{Suppress}. If
there is no corresponding pragma @code{Suppress} in effect, it has no
effect. The range of the effect is the same as for pragma
@code{Suppress}. The meaning of the arguments is identical to that used
in pragma @code{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.
@node Pragma Use_VADS_Size
@unnumberedsec Pragma Use_VADS_Size
@cindex @code{Size}, VADS compatibility
@findex Use_VADS_Size
@noindent
Syntax:
@smallexample @c ada
pragma Use_VADS_Size;
@end smallexample
@noindent
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 programs. This is intended to aid in the
handling of legacy 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
@unnumberedsec Pragma Validity_Checks
@findex Validity_Checks
@noindent
Syntax:
@smallexample @c ada
pragma Validity_Checks (string_LITERAL | ALL_CHECKS | On | Off);
@end smallexample
@noindent
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 @file{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 @code{-gnatVx} compiler switch (see the
GNAT users guide for details). For example the following two methods
can be used to enable validity checking for mode @code{in} and
@code{in out} subprogram parameters:
@itemize @bullet
@item
@smallexample @c ada
pragma Validity_Checks ("im");
@end smallexample
@item
@smallexample
gcc -c -gnatVim @dots{}
@end smallexample
@end itemize
@noindent
The form ALL_CHECKS activates all standard checks (its use is equivalent
to the use of the @code{gnatva} switch.
The forms with @code{Off} and @code{On}
can be used to temporarily disable validity checks
as shown in the following example:
@smallexample @c ada
@iftex
@leftskip=0cm
@end iftex
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 smallexample
@node Pragma Volatile
@unnumberedsec Pragma Volatile
@findex Volatile
@noindent
Syntax:
@smallexample @c ada
pragma Volatile (local_NAME);
@end smallexample
@noindent
This pragma is defined by the Ada 95 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 implementation
of pragma Volatile is upwards compatible with the implementation in
Dec Ada 83.
@node Pragma Warnings
@unnumberedsec Pragma Warnings
@findex Warnings
@noindent
Syntax:
@smallexample @c ada
pragma Warnings (On | Off [, LOCAL_NAME]);
@end smallexample
@noindent
Normally warnings are enabled, with the output being controlled by
the command line switch. Warnings (@code{Off}) turns off generation of
warnings until a Warnings (@code{On}) is encountered or the end of the
current unit. If generation of warnings is turned off using this
pragma, then no warning messages are output, regardless of the
setting of the command line switches.
The form with a single argument is a configuration pragma.
If the @var{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 @code{Suppress}).
@node Pragma Weak_External
@unnumberedsec Pragma Weak_External
@findex Weak_External
@noindent
Syntax:
@smallexample @c ada
pragma Weak_External ([Entity =>] LOCAL_NAME);
@end smallexample
@noindent
This pragma specifies that the given entity should be marked as a weak
external (one that does not have to be resolved) for the linker. For
further details, consult the GCC manual.
@node Implementation Defined Attributes
@chapter Implementation Defined Attributes
Ada 95 defines (throughout the Ada 95 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 95 Reference Manual.
In addition, Ada 95 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.
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
* Abort_Signal::
* Address_Size::
* Asm_Input::
* Asm_Output::
* AST_Entry::
* Bit::
* Bit_Position::
* Code_Address::
* Default_Bit_Order::
* Elaborated::
* Elab_Body::
* Elab_Spec::
* Emax::
* Enum_Rep::
* Epsilon::
* Fixed_Value::
* Has_Discriminants::
* Img::
* Integer_Value::
* Large::
* Machine_Size::
* Mantissa::
* Max_Interrupt_Priority::
* Max_Priority::
* Maximum_Alignment::
* Mechanism_Code::
* Null_Parameter::
* Object_Size::
* Passed_By_Reference::
* Range_Length::
* Safe_Emax::
* Safe_Large::
* Small::
* Storage_Unit::
* Target_Name::
* Tick::
* To_Address::
* Type_Class::
* UET_Address::
* Unconstrained_Array::
* Universal_Literal_String::
* Unrestricted_Access::
* VADS_Size::
* Value_Size::
* Wchar_T_Size::
* Word_Size::
@end menu
@node Abort_Signal
@unnumberedsec Abort_Signal
@findex Abort_Signal
@noindent
@code{Standard'Abort_Signal} (@code{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 Address_Size
@unnumberedsec Address_Size
@cindex Size of @code{Address}
@findex Address_Size
@noindent
@code{Standard'Address_Size} (@code{Standard} is the only allowed
prefix) is a static constant giving the number of bits in an
@code{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 Asm_Input
@unnumberedsec Asm_Input
@findex Asm_Input
@noindent
The @code{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{Machine Code Insertions}
@node Asm_Output
@unnumberedsec Asm_Output
@findex Asm_Output
@noindent
The @code{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 @code{No_Output_Operands}.
@ref{Machine Code Insertions}
@node AST_Entry
@unnumberedsec AST_Entry
@cindex OpenVMS
@findex AST_Entry
@noindent
This attribute is implemented only in OpenVMS versions of GNAT@. Applied to
the name of an entry, it yields a value of the predefined type AST_Handler
(declared in the predefined package System, as extended by the use of
pragma @code{Extend_System (Aux_DEC)}). This value enables the given entry to
be called when an AST occurs. For further details, refer to the @cite{DEC Ada
Language Reference Manual}, section 9.12a.
@node Bit
@unnumberedsec Bit
@findex Bit
@code{@var{obj}'Bit}, where @var{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 @code{Universal_Integer}, and is always a non-negative number not
exceeding the value of @code{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{@var{obj}.all'Bit} is subject to an @code{Access_Check} for the
designated object. Similarly for a record component
@code{@var{X}.@var{C}'Bit} is subject to a discriminant check and
@code{@var{X}(@var{I}).Bit} and @code{@var{X}(@var{I1}..@var{I2})'Bit}
are subject to index checks.
This attribute is designed to be compatible with the DEC Ada 83 definition
and implementation of the @code{Bit} attribute.
@node Bit_Position
@unnumberedsec Bit_Position
@findex Bit_Position
@noindent
@code{@var{R.C}'Bit}, where @var{R} is a record object and 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 @code{Universal_Integer}. The value depends only on the field
@var{C} and is independent of the alignment of
the containing record @var{R}.
@node Code_Address
@unnumberedsec Code_Address
@findex Code_Address
@cindex Subprogram address
@cindex Address of subprogram code
@noindent
The @code{'Address}
attribute may be applied to subprograms in Ada 95, but the
intended effect from the Ada 95 reference manual 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:
@smallexample @c ada
procedure K is @dots{}
procedure L;
for L'Address use K'Address;
pragma Import (Ada, L);
@end smallexample
@noindent
A call to @code{L} is then expected to result in a call to @code{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 @code{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 @code{Address} value described above.
For example, the @code{Address} value may reference a subprogram
descriptor rather than the subprogram itself.
The @code{'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 @code{'Address}
attribute.
@node Default_Bit_Order
@unnumberedsec Default_Bit_Order
@cindex Big endian
@cindex Little endian
@findex Default_Bit_Order
@noindent
@code{Standard'Default_Bit_Order} (@code{Standard} is the only
permissible prefix), provides the value @code{System.Default_Bit_Order}
as a @code{Pos} value (0 for @code{High_Order_First}, 1 for
@code{Low_Order_First}). This is used to construct the definition of
@code{Default_Bit_Order} in package @code{System}.
@node Elaborated
@unnumberedsec Elaborated
@findex Elaborated
@noindent
The prefix of the @code{'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.
@node Elab_Body
@unnumberedsec Elab_Body
@findex Elab_Body
@noindent
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 Elab_Spec
@unnumberedsec Elab_Spec
@findex Elab_Spec
@noindent
This attribute can only be applied to a program unit name. It returns
the entity for the corresponding elaboration procedure for elaborating
the specification 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 Emax
@unnumberedsec Emax
@cindex Ada 83 attributes
@findex Emax
@noindent
The @code{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 Enum_Rep
@unnumberedsec Enum_Rep
@cindex Representation of enums
@findex Enum_Rep
@noindent
For every enumeration subtype @var{S}, @code{@var{S}'Enum_Rep} denotes a
function with the following spec:
@smallexample @c ada
function @var{S}'Enum_Rep (Arg : @var{S}'Base)
return @i{Universal_Integer};
@end smallexample
@noindent
It is also allowable to apply @code{Enum_Rep} directly to an object of an
enumeration type or to a non-overloaded enumeration
literal. In this case @code{@var{S}'Enum_Rep} is equivalent to
@code{@var{typ}'Enum_Rep(@var{S})} where @var{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 @code{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{@var{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 @code{(<>)} discrete formal arguments in
a generic unit that can be instantiated with either enumeration types
or integer types. Note that if @code{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 @code{Enum_Rep}
may raise @code{Constraint_Error}.
@node Epsilon
@unnumberedsec Epsilon
@cindex Ada 83 attributes
@findex Epsilon
@noindent
The @code{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 Fixed_Value
@unnumberedsec Fixed_Value
@findex Fixed_Value
@noindent
For every fixed-point type @var{S}, @code{@var{S}'Fixed_Value} denotes a
function with the following specification:
@smallexample @c ada
function @var{S}'Fixed_Value (Arg : @i{Universal_Integer})
return @var{S};
@end smallexample
@noindent
The value returned is the fixed-point value @var{V} such that
@smallexample @c ada
@var{V} = Arg * @var{S}'Small
@end smallexample
@noindent
The effect is thus similar to first converting the argument to the
integer type used to represent @var{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 Has_Discriminants
@unnumberedsec Has_Discriminants
@cindex Discriminants, testing for
@findex Has_Discriminants
@noindent
The prefix of the @code{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 Img
@unnumberedsec Img
@findex Img
@noindent
The @code{Img} attribute differs from @code{Image} in that it may be
applied to objects as well as types, in which case it gives the
@code{Image} for the subtype of the object. This is convenient for
debugging:
@smallexample @c ada
Put_Line ("X = " & X'Img);
@end smallexample
@noindent
has the same meaning as the more verbose:
@smallexample @c ada
Put_Line ("X = " & @var{T}'Image (X));
@end smallexample
@noindent
where @var{T} is the (sub)type of the object @code{X}.
@node Integer_Value
@unnumberedsec Integer_Value
@findex Integer_Value
@noindent
For every integer type @var{S}, @code{@var{S}'Integer_Value} denotes a
function with the following spec:
@smallexample @c ada
function @var{S}'Integer_Value (Arg : @i{Universal_Fixed})
return @var{S};
@end smallexample
@noindent
The value returned is the integer value @var{V}, such that
@smallexample @c ada
Arg = @var{V} * @var{T}'Small
@end smallexample
@noindent
where @var{T} is the type of @code{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 Large
@unnumberedsec Large
@cindex Ada 83 attributes