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@c Copyright (C) 1988-2017 Free Software Foundation, Inc.
@c This is part of the GCC manual.
@c For copying conditions, see the file gcc.texi.
@ignore
@c man begin INCLUDE
@include gcc-vers.texi
@c man end
@c man begin COPYRIGHT
Copyright @copyright{} 1988-2017 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being ``GNU General Public License'' and ``Funding
Free Software'', the Front-Cover texts being (a) (see below), and with
the Back-Cover Texts being (b) (see below). A copy of the license is
included in the gfdl(7) man page.
(a) The FSF's Front-Cover Text is:
A GNU Manual
(b) The FSF's Back-Cover Text is:
You have freedom to copy and modify this GNU Manual, like GNU
software. Copies published by the Free Software Foundation raise
funds for GNU development.
@c man end
@c Set file name and title for the man page.
@setfilename gcc
@settitle GNU project C and C++ compiler
@c man begin SYNOPSIS
gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}]
[@option{-g}] [@option{-pg}] [@option{-O}@var{level}]
[@option{-W}@var{warn}@dots{}] [@option{-Wpedantic}]
[@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}]
[@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}]
[@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}]
[@option{-o} @var{outfile}] [@@@var{file}] @var{infile}@dots{}
Only the most useful options are listed here; see below for the
remainder. @command{g++} accepts mostly the same options as @command{gcc}.
@c man end
@c man begin SEEALSO
gpl(7), gfdl(7), fsf-funding(7),
cpp(1), gcov(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1)
and the Info entries for @file{gcc}, @file{cpp}, @file{as},
@file{ld}, @file{binutils} and @file{gdb}.
@c man end
@c man begin BUGS
For instructions on reporting bugs, see
@w{@value{BUGURL}}.
@c man end
@c man begin AUTHOR
See the Info entry for @command{gcc}, or
@w{@uref{http://gcc.gnu.org/onlinedocs/gcc/Contributors.html}},
for contributors to GCC@.
@c man end
@end ignore
@node Invoking GCC
@chapter GCC Command Options
@cindex GCC command options
@cindex command options
@cindex options, GCC command
@c man begin DESCRIPTION
When you invoke GCC, it normally does preprocessing, compilation,
assembly and linking. The ``overall options'' allow you to stop this
process at an intermediate stage. For example, the @option{-c} option
says not to run the linker. Then the output consists of object files
output by the assembler.
@xref{Overall Options,,Options Controlling the Kind of Output}.
Other options are passed on to one or more stages of processing. Some options
control the preprocessor and others the compiler itself. Yet other
options control the assembler and linker; most of these are not
documented here, since you rarely need to use any of them.
@cindex C compilation options
Most of the command-line options that you can use with GCC are useful
for C programs; when an option is only useful with another language
(usually C++), the explanation says so explicitly. If the description
for a particular option does not mention a source language, you can use
that option with all supported languages.
@cindex cross compiling
@cindex specifying machine version
@cindex specifying compiler version and target machine
@cindex compiler version, specifying
@cindex target machine, specifying
The usual way to run GCC is to run the executable called @command{gcc}, or
@command{@var{machine}-gcc} when cross-compiling, or
@command{@var{machine}-gcc-@var{version}} to run a specific version of GCC.
When you compile C++ programs, you should invoke GCC as @command{g++}
instead. @xref{Invoking G++,,Compiling C++ Programs},
for information about the differences in behavior between @command{gcc}
and @code{g++} when compiling C++ programs.
@cindex grouping options
@cindex options, grouping
The @command{gcc} program accepts options and file names as operands. Many
options have multi-letter names; therefore multiple single-letter options
may @emph{not} be grouped: @option{-dv} is very different from @w{@samp{-d
-v}}.
@cindex order of options
@cindex options, order
You can mix options and other arguments. For the most part, the order
you use doesn't matter. Order does matter when you use several
options of the same kind; for example, if you specify @option{-L} more
than once, the directories are searched in the order specified. Also,
the placement of the @option{-l} option is significant.
Many options have long names starting with @samp{-f} or with
@samp{-W}---for example,
@option{-fmove-loop-invariants}, @option{-Wformat} and so on. Most of
these have both positive and negative forms; the negative form of
@option{-ffoo} is @option{-fno-foo}. This manual documents
only one of these two forms, whichever one is not the default.
@c man end
@xref{Option Index}, for an index to GCC's options.
@menu
* Option Summary:: Brief list of all options, without explanations.
* Overall Options:: Controlling the kind of output:
an executable, object files, assembler files,
or preprocessed source.
* Invoking G++:: Compiling C++ programs.
* C Dialect Options:: Controlling the variant of C language compiled.
* C++ Dialect Options:: Variations on C++.
* Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
and Objective-C++.
* Diagnostic Message Formatting Options:: Controlling how diagnostics should
be formatted.
* Warning Options:: How picky should the compiler be?
* Debugging Options:: Producing debuggable code.
* Optimize Options:: How much optimization?
* Instrumentation Options:: Enabling profiling and extra run-time error checking.
* Preprocessor Options:: Controlling header files and macro definitions.
Also, getting dependency information for Make.
* Assembler Options:: Passing options to the assembler.
* Link Options:: Specifying libraries and so on.
* Directory Options:: Where to find header files and libraries.
Where to find the compiler executable files.
* Code Gen Options:: Specifying conventions for function calls, data layout
and register usage.
* Developer Options:: Printing GCC configuration info, statistics, and
debugging dumps.
* Submodel Options:: Target-specific options, such as compiling for a
specific processor variant.
* Spec Files:: How to pass switches to sub-processes.
* Environment Variables:: Env vars that affect GCC.
* Precompiled Headers:: Compiling a header once, and using it many times.
@end menu
@c man begin OPTIONS
@node Option Summary
@section Option Summary
Here is a summary of all the options, grouped by type. Explanations are
in the following sections.
@table @emph
@item Overall Options
@xref{Overall Options,,Options Controlling the Kind of Output}.
@gccoptlist{-c -S -E -o @var{file} -x @var{language} @gol
-v -### --help@r{[}=@var{class}@r{[},@dots{}@r{]]} --target-help --version @gol
-pass-exit-codes -pipe -specs=@var{file} -wrapper @gol
@@@var{file} -fplugin=@var{file} -fplugin-arg-@var{name}=@var{arg} @gol
-fdump-ada-spec@r{[}-slim@r{]} -fada-spec-parent=@var{unit} -fdump-go-spec=@var{file}}
@item C Language Options
@xref{C Dialect Options,,Options Controlling C Dialect}.
@gccoptlist{-ansi -std=@var{standard} -fgnu89-inline @gol
-fpermitted-flt-eval-methods=@var{standard} @gol
-aux-info @var{filename} -fallow-parameterless-variadic-functions @gol
-fno-asm -fno-builtin -fno-builtin-@var{function} -fgimple@gol
-fhosted -ffreestanding -fopenacc -fopenmp -fopenmp-simd @gol
-fms-extensions -fplan9-extensions -fsso-struct=@var{endianness} @gol
-fallow-single-precision -fcond-mismatch -flax-vector-conversions @gol
-fsigned-bitfields -fsigned-char @gol
-funsigned-bitfields -funsigned-char}
@item C++ Language Options
@xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
@gccoptlist{-fabi-version=@var{n} -fno-access-control @gol
-faligned-new=@var{n} -fargs-in-order=@var{n} -fcheck-new @gol
-fconstexpr-depth=@var{n} -fconstexpr-loop-limit=@var{n} @gol
-ffriend-injection @gol
-fno-elide-constructors @gol
-fno-enforce-eh-specs @gol
-ffor-scope -fno-for-scope -fno-gnu-keywords @gol
-fno-implicit-templates @gol
-fno-implicit-inline-templates @gol
-fno-implement-inlines -fms-extensions @gol
-fnew-inheriting-ctors @gol
-fnew-ttp-matching @gol
-fno-nonansi-builtins -fnothrow-opt -fno-operator-names @gol
-fno-optional-diags -fpermissive @gol
-fno-pretty-templates @gol
-frepo -fno-rtti -fsized-deallocation @gol
-ftemplate-backtrace-limit=@var{n} @gol
-ftemplate-depth=@var{n} @gol
-fno-threadsafe-statics -fuse-cxa-atexit @gol
-fno-weak -nostdinc++ @gol
-fvisibility-inlines-hidden @gol
-fvisibility-ms-compat @gol
-fext-numeric-literals @gol
-Wabi=@var{n} -Wabi-tag -Wconversion-null -Wctor-dtor-privacy @gol
-Wdelete-non-virtual-dtor -Wliteral-suffix -Wmultiple-inheritance @gol
-Wnamespaces -Wnarrowing @gol
-Wnoexcept -Wnoexcept-type -Wnon-virtual-dtor -Wreorder -Wregister @gol
-Weffc++ -Wstrict-null-sentinel -Wtemplates @gol
-Wno-non-template-friend -Wold-style-cast @gol
-Woverloaded-virtual -Wno-pmf-conversions @gol
-Wsign-promo -Wvirtual-inheritance}
@item Objective-C and Objective-C++ Language Options
@xref{Objective-C and Objective-C++ Dialect Options,,Options Controlling
Objective-C and Objective-C++ Dialects}.
@gccoptlist{-fconstant-string-class=@var{class-name} @gol
-fgnu-runtime -fnext-runtime @gol
-fno-nil-receivers @gol
-fobjc-abi-version=@var{n} @gol
-fobjc-call-cxx-cdtors @gol
-fobjc-direct-dispatch @gol
-fobjc-exceptions @gol
-fobjc-gc @gol
-fobjc-nilcheck @gol
-fobjc-std=objc1 @gol
-fno-local-ivars @gol
-fivar-visibility=@r{[}public@r{|}protected@r{|}private@r{|}package@r{]} @gol
-freplace-objc-classes @gol
-fzero-link @gol
-gen-decls @gol
-Wassign-intercept @gol
-Wno-protocol -Wselector @gol
-Wstrict-selector-match @gol
-Wundeclared-selector}
@item Diagnostic Message Formatting Options
@xref{Diagnostic Message Formatting Options,,Options to Control Diagnostic Messages Formatting}.
@gccoptlist{-fmessage-length=@var{n} @gol
-fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]} @gol
-fdiagnostics-color=@r{[}auto@r{|}never@r{|}always@r{]} @gol
-fno-diagnostics-show-option -fno-diagnostics-show-caret @gol
-fdiagnostics-parseable-fixits -fdiagnostics-generate-patch @gol
-fno-show-column}
@item Warning Options
@xref{Warning Options,,Options to Request or Suppress Warnings}.
@gccoptlist{-fsyntax-only -fmax-errors=@var{n} -Wpedantic @gol
-pedantic-errors @gol
-w -Wextra -Wall -Waddress -Waggregate-return -Waligned-new @gol
-Walloc-zero -Walloc-size-larger-than=@var{n}
-Walloca -Walloca-larger-than=@var{n} @gol
-Wno-aggressive-loop-optimizations -Warray-bounds -Warray-bounds=@var{n} @gol
-Wno-attributes -Wbool-compare -Wbool-operation @gol
-Wno-builtin-declaration-mismatch @gol
-Wno-builtin-macro-redefined -Wc90-c99-compat -Wc99-c11-compat @gol
-Wc++-compat -Wc++11-compat -Wc++14-compat -Wcast-align -Wcast-qual @gol
-Wchar-subscripts -Wchkp -Wclobbered -Wcomment @gol
-Wconditionally-supported @gol
-Wconversion -Wcoverage-mismatch -Wno-cpp -Wdangling-else -Wdate-time @gol
-Wdelete-incomplete @gol
-Wno-deprecated -Wno-deprecated-declarations -Wno-designated-init @gol
-Wdisabled-optimization @gol
-Wno-discarded-qualifiers -Wno-discarded-array-qualifiers @gol
-Wno-div-by-zero -Wdouble-promotion @gol
-Wduplicated-branches -Wduplicated-cond @gol
-Wempty-body -Wenum-compare -Wno-endif-labels -Wexpansion-to-defined @gol
-Werror -Werror=* -Wfatal-errors -Wfloat-equal -Wformat -Wformat=2 @gol
-Wno-format-contains-nul -Wno-format-extra-args @gol
-Wformat-nonliteral -Wformat-overflow=@var{n} @gol
-Wformat-security -Wformat-signedness -Wformat-truncation=@var{n} @gol
-Wformat-y2k -Wframe-address @gol
-Wframe-larger-than=@var{len} -Wno-free-nonheap-object -Wjump-misses-init @gol
-Wignored-qualifiers -Wignored-attributes -Wincompatible-pointer-types @gol
-Wimplicit -Wimplicit-fallthrough -Wimplicit-fallthrough=@var{n} @gol
-Wimplicit-function-declaration -Wimplicit-int @gol
-Winit-self -Winline -Wno-int-conversion -Wint-in-bool-context @gol
-Wno-int-to-pointer-cast -Winvalid-memory-model -Wno-invalid-offsetof @gol
-Winvalid-pch -Wlarger-than=@var{len} @gol
-Wlogical-op -Wlogical-not-parentheses -Wlong-long @gol
-Wmain -Wmaybe-uninitialized -Wmemset-elt-size -Wmemset-transposed-args @gol
-Wmisleading-indentation -Wmissing-braces @gol
-Wmissing-field-initializers -Wmissing-include-dirs @gol
-Wno-multichar -Wnonnull -Wnonnull-compare @gol
-Wnormalized=@r{[}none@r{|}id@r{|}nfc@r{|}nfkc@r{]} @gol
-Wnull-dereference -Wodr -Wno-overflow -Wopenmp-simd @gol
-Woverride-init-side-effects -Woverlength-strings @gol
-Wpacked -Wpacked-bitfield-compat -Wpadded @gol
-Wparentheses -Wno-pedantic-ms-format @gol
-Wplacement-new -Wplacement-new=@var{n} @gol
-Wpointer-arith -Wpointer-compare -Wno-pointer-to-int-cast @gol
-Wno-pragmas -Wredundant-decls -Wrestrict -Wno-return-local-addr @gol
-Wreturn-type -Wsequence-point -Wshadow -Wno-shadow-ivar @gol
-Wshadow=global, -Wshadow=local, -Wshadow=compatible-local @gol
-Wshift-overflow -Wshift-overflow=@var{n} @gol
-Wshift-count-negative -Wshift-count-overflow -Wshift-negative-value @gol
-Wsign-compare -Wsign-conversion -Wfloat-conversion @gol
-Wno-scalar-storage-order @gol
-Wsizeof-pointer-memaccess -Wsizeof-array-argument @gol
-Wstack-protector -Wstack-usage=@var{len} -Wstrict-aliasing @gol
-Wstrict-aliasing=n -Wstrict-overflow -Wstrict-overflow=@var{n} @gol
-Wstringop-overflow=@var{n} @gol
-Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{|}format@r{]} @gol
-Wsuggest-final-types @gol -Wsuggest-final-methods -Wsuggest-override @gol
-Wmissing-format-attribute -Wsubobject-linkage @gol
-Wswitch -Wswitch-bool -Wswitch-default -Wswitch-enum @gol
-Wswitch-unreachable -Wsync-nand @gol
-Wsystem-headers -Wtautological-compare -Wtrampolines -Wtrigraphs @gol
-Wtype-limits -Wundef @gol
-Wuninitialized -Wunknown-pragmas -Wunsafe-loop-optimizations @gol
-Wunsuffixed-float-constants -Wunused -Wunused-function @gol
-Wunused-label -Wunused-local-typedefs -Wunused-macros @gol
-Wunused-parameter -Wno-unused-result @gol
-Wunused-value -Wunused-variable @gol
-Wunused-const-variable -Wunused-const-variable=@var{n} @gol
-Wunused-but-set-parameter -Wunused-but-set-variable @gol
-Wuseless-cast -Wvariadic-macros -Wvector-operation-performance @gol
-Wvla -Wvla-larger-than=@var{n} -Wvolatile-register-var -Wwrite-strings @gol
-Wzero-as-null-pointer-constant -Whsa}
@item C and Objective-C-only Warning Options
@gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol
-Wmissing-parameter-type -Wmissing-prototypes -Wnested-externs @gol
-Wold-style-declaration -Wold-style-definition @gol
-Wstrict-prototypes -Wtraditional -Wtraditional-conversion @gol
-Wdeclaration-after-statement -Wpointer-sign}
@item Debugging Options
@xref{Debugging Options,,Options for Debugging Your Program}.
@gccoptlist{-g -g@var{level} -gcoff -gdwarf -gdwarf-@var{version} @gol
-ggdb -grecord-gcc-switches -gno-record-gcc-switches @gol
-gstabs -gstabs+ -gstrict-dwarf -gno-strict-dwarf @gol
-gcolumn-info -gno-column-info @gol
-gvms -gxcoff -gxcoff+ -gz@r{[}=@var{type}@r{]} @gol
-fdebug-prefix-map=@var{old}=@var{new} -fdebug-types-section @gol
-feliminate-dwarf2-dups -fno-eliminate-unused-debug-types @gol
-femit-struct-debug-baseonly -femit-struct-debug-reduced @gol
-femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]} @gol
-feliminate-unused-debug-symbols -femit-class-debug-always @gol
-fno-merge-debug-strings -fno-dwarf2-cfi-asm @gol
-fvar-tracking -fvar-tracking-assignments}
@item Optimization Options
@xref{Optimize Options,,Options that Control Optimization}.
@gccoptlist{-faggressive-loop-optimizations -falign-functions[=@var{n}] @gol
-falign-jumps[=@var{n}] @gol
-falign-labels[=@var{n}] -falign-loops[=@var{n}] @gol
-fassociative-math -fauto-profile -fauto-profile[=@var{path}] @gol
-fauto-inc-dec -fbranch-probabilities @gol
-fbranch-target-load-optimize -fbranch-target-load-optimize2 @gol
-fbtr-bb-exclusive -fcaller-saves @gol
-fcombine-stack-adjustments -fconserve-stack @gol
-fcompare-elim -fcprop-registers -fcrossjumping @gol
-fcse-follow-jumps -fcse-skip-blocks -fcx-fortran-rules @gol
-fcx-limited-range @gol
-fdata-sections -fdce -fdelayed-branch @gol
-fdelete-null-pointer-checks -fdevirtualize -fdevirtualize-speculatively @gol
-fdevirtualize-at-ltrans -fdse @gol
-fearly-inlining -fipa-sra -fexpensive-optimizations -ffat-lto-objects @gol
-ffast-math -ffinite-math-only -ffloat-store -fexcess-precision=@var{style} @gol
-fforward-propagate -ffp-contract=@var{style} -ffunction-sections @gol
-fgcse -fgcse-after-reload -fgcse-las -fgcse-lm -fgraphite-identity @gol
-fgcse-sm -fhoist-adjacent-loads -fif-conversion @gol
-fif-conversion2 -findirect-inlining @gol
-finline-functions -finline-functions-called-once -finline-limit=@var{n} @gol
-finline-small-functions -fipa-cp -fipa-cp-clone @gol
-fipa-bit-cp -fipa-vrp @gol
-fipa-pta -fipa-profile -fipa-pure-const -fipa-reference -fipa-icf @gol
-fira-algorithm=@var{algorithm} @gol
-fira-region=@var{region} -fira-hoist-pressure @gol
-fira-loop-pressure -fno-ira-share-save-slots @gol
-fno-ira-share-spill-slots @gol
-fisolate-erroneous-paths-dereference -fisolate-erroneous-paths-attribute @gol
-fivopts -fkeep-inline-functions -fkeep-static-functions @gol
-fkeep-static-consts -flimit-function-alignment -flive-range-shrinkage @gol
-floop-block -floop-interchange -floop-strip-mine @gol
-floop-unroll-and-jam -floop-nest-optimize @gol
-floop-parallelize-all -flra-remat -flto -flto-compression-level @gol
-flto-partition=@var{alg} -fmerge-all-constants @gol
-fmerge-constants -fmodulo-sched -fmodulo-sched-allow-regmoves @gol
-fmove-loop-invariants -fno-branch-count-reg @gol
-fno-defer-pop -fno-fp-int-builtin-inexact -fno-function-cse @gol
-fno-guess-branch-probability -fno-inline -fno-math-errno -fno-peephole @gol
-fno-peephole2 -fno-printf-return-value -fno-sched-interblock @gol
-fno-sched-spec -fno-signed-zeros @gol
-fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss @gol
-fomit-frame-pointer -foptimize-sibling-calls @gol
-fpartial-inlining -fpeel-loops -fpredictive-commoning @gol
-fprefetch-loop-arrays @gol
-fprofile-correction @gol
-fprofile-use -fprofile-use=@var{path} -fprofile-values @gol
-fprofile-reorder-functions @gol
-freciprocal-math -free -frename-registers -freorder-blocks @gol
-freorder-blocks-algorithm=@var{algorithm} @gol
-freorder-blocks-and-partition -freorder-functions @gol
-frerun-cse-after-loop -freschedule-modulo-scheduled-loops @gol
-frounding-math -fsched2-use-superblocks -fsched-pressure @gol
-fsched-spec-load -fsched-spec-load-dangerous @gol
-fsched-stalled-insns-dep[=@var{n}] -fsched-stalled-insns[=@var{n}] @gol
-fsched-group-heuristic -fsched-critical-path-heuristic @gol
-fsched-spec-insn-heuristic -fsched-rank-heuristic @gol
-fsched-last-insn-heuristic -fsched-dep-count-heuristic @gol
-fschedule-fusion @gol
-fschedule-insns -fschedule-insns2 -fsection-anchors @gol
-fselective-scheduling -fselective-scheduling2 @gol
-fsel-sched-pipelining -fsel-sched-pipelining-outer-loops @gol
-fsemantic-interposition -fshrink-wrap -fshrink-wrap-separate @gol
-fsignaling-nans @gol
-fsingle-precision-constant -fsplit-ivs-in-unroller -fsplit-loops@gol
-fsplit-paths @gol
-fsplit-wide-types -fssa-backprop -fssa-phiopt @gol
-fstdarg-opt -fstore-merging -fstrict-aliasing @gol
-fstrict-overflow -fthread-jumps -ftracer -ftree-bit-ccp @gol
-ftree-builtin-call-dce -ftree-ccp -ftree-ch @gol
-ftree-coalesce-vars -ftree-copy-prop -ftree-dce -ftree-dominator-opts @gol
-ftree-dse -ftree-forwprop -ftree-fre -fcode-hoisting @gol
-ftree-loop-if-convert -ftree-loop-im @gol
-ftree-phiprop -ftree-loop-distribution -ftree-loop-distribute-patterns @gol
-ftree-loop-ivcanon -ftree-loop-linear -ftree-loop-optimize @gol
-ftree-loop-vectorize @gol
-ftree-parallelize-loops=@var{n} -ftree-pre -ftree-partial-pre -ftree-pta @gol
-ftree-reassoc -ftree-sink -ftree-slsr -ftree-sra @gol
-ftree-switch-conversion -ftree-tail-merge @gol
-ftree-ter -ftree-vectorize -ftree-vrp -funconstrained-commons @gol
-funit-at-a-time -funroll-all-loops -funroll-loops @gol
-funsafe-math-optimizations -funswitch-loops @gol
-fipa-ra -fvariable-expansion-in-unroller -fvect-cost-model -fvpt @gol
-fweb -fwhole-program -fwpa -fuse-linker-plugin @gol
--param @var{name}=@var{value}
-O -O0 -O1 -O2 -O3 -Os -Ofast -Og}
@item Program Instrumentation Options
@xref{Instrumentation Options,,Program Instrumentation Options}.
@gccoptlist{-p -pg -fprofile-arcs --coverage -ftest-coverage @gol
-fprofile-dir=@var{path} -fprofile-generate -fprofile-generate=@var{path} @gol
-fsanitize=@var{style} -fsanitize-recover -fsanitize-recover=@var{style} @gol
-fasan-shadow-offset=@var{number} -fsanitize-sections=@var{s1},@var{s2},... @gol
-fsanitize-undefined-trap-on-error -fbounds-check @gol
-fcheck-pointer-bounds -fchkp-check-incomplete-type @gol
-fchkp-first-field-has-own-bounds -fchkp-narrow-bounds @gol
-fchkp-narrow-to-innermost-array -fchkp-optimize @gol
-fchkp-use-fast-string-functions -fchkp-use-nochk-string-functions @gol
-fchkp-use-static-bounds -fchkp-use-static-const-bounds @gol
-fchkp-treat-zero-dynamic-size-as-infinite -fchkp-check-read @gol
-fchkp-check-read -fchkp-check-write -fchkp-store-bounds @gol
-fchkp-instrument-calls -fchkp-instrument-marked-only @gol
-fchkp-use-wrappers -fchkp-flexible-struct-trailing-arrays@gol
-fstack-protector -fstack-protector-all -fstack-protector-strong @gol
-fstack-protector-explicit -fstack-check @gol
-fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
-fno-stack-limit -fsplit-stack @gol
-fvtable-verify=@r{[}std@r{|}preinit@r{|}none@r{]} @gol
-fvtv-counts -fvtv-debug @gol
-finstrument-functions @gol
-finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{} @gol
-finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{}}
@item Preprocessor Options
@xref{Preprocessor Options,,Options Controlling the Preprocessor}.
@gccoptlist{-A@var{question}=@var{answer} @gol
-A-@var{question}@r{[}=@var{answer}@r{]} @gol
-C -CC -D@var{macro}@r{[}=@var{defn}@r{]} @gol
-dD -dI -dM -dN -dU @gol
-fdebug-cpp -fdirectives-only -fdollars-in-identifiers @gol
-fexec-charset=@var{charset} -fextended-identifiers @gol
-finput-charset=@var{charset} -fno-canonical-system-headers @gol
-fpch-deps -fpch-preprocess -fpreprocessed @gol
-ftabstop=@var{width} -ftrack-macro-expansion @gol
-fwide-exec-charset=@var{charset} -fworking-directory @gol
-H -imacros @var{file} -include @var{file} @gol
-M -MD -MF -MG -MM -MMD -MP -MQ -MT @gol
-no-integrated-cpp -P -pthread -remap @gol
-traditional -traditional-cpp -trigraphs @gol
-U@var{macro} -undef @gol
-Wp,@var{option} -Xpreprocessor @var{option}}
@item Assembler Options
@xref{Assembler Options,,Passing Options to the Assembler}.
@gccoptlist{-Wa,@var{option} -Xassembler @var{option}}
@item Linker Options
@xref{Link Options,,Options for Linking}.
@gccoptlist{@var{object-file-name} -fuse-ld=@var{linker} -l@var{library} @gol
-nostartfiles -nodefaultlibs -nostdlib -pie -pthread -rdynamic @gol
-s -static -static-libgcc -static-libstdc++ @gol
-static-libasan -static-libtsan -static-liblsan -static-libubsan @gol
-static-libmpx -static-libmpxwrappers @gol
-shared -shared-libgcc -symbolic @gol
-T @var{script} -Wl,@var{option} -Xlinker @var{option} @gol
-u @var{symbol} -z @var{keyword}}
@item Directory Options
@xref{Directory Options,,Options for Directory Search}.
@gccoptlist{-B@var{prefix} -I@var{dir} -I- @gol
-idirafter @var{dir} @gol
-imacros @var{file} -imultilib @var{dir} @gol
-iplugindir=@var{dir} -iprefix @var{file} @gol
-iquote @var{dir} -isysroot @var{dir} -isystem @var{dir} @gol
-iwithprefix @var{dir} -iwithprefixbefore @var{dir} @gol
-L@var{dir} -no-canonical-prefixes --no-sysroot-suffix @gol
-nostdinc -nostdinc++ --sysroot=@var{dir}}
@item Code Generation Options
@xref{Code Gen Options,,Options for Code Generation Conventions}.
@gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
-ffixed-@var{reg} -fexceptions @gol
-fnon-call-exceptions -fdelete-dead-exceptions -funwind-tables @gol
-fasynchronous-unwind-tables @gol
-fno-gnu-unique @gol
-finhibit-size-directive -fno-common -fno-ident @gol
-fpcc-struct-return -fpic -fPIC -fpie -fPIE -fno-plt @gol
-fno-jump-tables @gol
-frecord-gcc-switches @gol
-freg-struct-return -fshort-enums -fshort-wchar @gol
-fverbose-asm -fpack-struct[=@var{n}] @gol
-fleading-underscore -ftls-model=@var{model} @gol
-fstack-reuse=@var{reuse_level} @gol
-ftrampolines -ftrapv -fwrapv @gol
-fvisibility=@r{[}default@r{|}internal@r{|}hidden@r{|}protected@r{]} @gol
-fstrict-volatile-bitfields -fsync-libcalls}
@item Developer Options
@xref{Developer Options,,GCC Developer Options}.
@gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
-dumpfullversion -fchecking -fchecking=@var{n} -fdbg-cnt-list @gol
-fdbg-cnt=@var{counter-value-list} @gol
-fdisable-ipa-@var{pass_name} @gol
-fdisable-rtl-@var{pass_name} @gol
-fdisable-rtl-@var{pass-name}=@var{range-list} @gol
-fdisable-tree-@var{pass_name} @gol
-fdisable-tree-@var{pass-name}=@var{range-list} @gol
-fdump-noaddr -fdump-unnumbered -fdump-unnumbered-links @gol
-fdump-translation-unit@r{[}-@var{n}@r{]} @gol
-fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
-fdump-ipa-all -fdump-ipa-cgraph -fdump-ipa-inline @gol
-fdump-passes @gol
-fdump-rtl-@var{pass} -fdump-rtl-@var{pass}=@var{filename} @gol
-fdump-statistics @gol
-fdump-final-insns@r{[}=@var{file}@r{]}
-fdump-tree-all @gol
-fdump-tree-@var{switch} @gol
-fdump-tree-@var{switch}-@var{options} @gol
-fdump-tree-@var{switch}-@var{options}=@var{filename} @gol
-fcompare-debug@r{[}=@var{opts}@r{]} -fcompare-debug-second @gol
-fenable-@var{kind}-@var{pass} @gol
-fenable-@var{kind}-@var{pass}=@var{range-list} @gol
-fira-verbose=@var{n} @gol
-flto-report -flto-report-wpa -fmem-report-wpa @gol
-fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report @gol
-fopt-info -fopt-info-@var{options}@r{[}=@var{file}@r{]} @gol
-fprofile-report @gol
-frandom-seed=@var{string} -fsched-verbose=@var{n} @gol
-fsel-sched-verbose -fsel-sched-dump-cfg -fsel-sched-pipelining-verbose @gol
-fstats -fstack-usage -ftime-report -ftime-report-details @gol
-fvar-tracking-assignments-toggle -gtoggle @gol
-print-file-name=@var{library} -print-libgcc-file-name @gol
-print-multi-directory -print-multi-lib -print-multi-os-directory @gol
-print-prog-name=@var{program} -print-search-dirs -Q @gol
-print-sysroot -print-sysroot-headers-suffix @gol
-save-temps -save-temps=cwd -save-temps=obj -time@r{[}=@var{file}@r{]}}
@item Machine-Dependent Options
@xref{Submodel Options,,Machine-Dependent Options}.
@c This list is ordered alphanumerically by subsection name.
@c Try and put the significant identifier (CPU or system) first,
@c so users have a clue at guessing where the ones they want will be.
@emph{AArch64 Options}
@gccoptlist{-mabi=@var{name} -mbig-endian -mlittle-endian @gol
-mgeneral-regs-only @gol
-mcmodel=tiny -mcmodel=small -mcmodel=large @gol
-mstrict-align @gol
-momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol
-mtls-dialect=desc -mtls-dialect=traditional @gol
-mtls-size=@var{size} @gol
-mfix-cortex-a53-835769 -mno-fix-cortex-a53-835769 @gol
-mfix-cortex-a53-843419 -mno-fix-cortex-a53-843419 @gol
-mlow-precision-recip-sqrt -mno-low-precision-recip-sqrt@gol
-mlow-precision-sqrt -mno-low-precision-sqrt@gol
-mlow-precision-div -mno-low-precision-div @gol
-march=@var{name} -mcpu=@var{name} -mtune=@var{name}}
@emph{Adapteva Epiphany Options}
@gccoptlist{-mhalf-reg-file -mprefer-short-insn-regs @gol
-mbranch-cost=@var{num} -mcmove -mnops=@var{num} -msoft-cmpsf @gol
-msplit-lohi -mpost-inc -mpost-modify -mstack-offset=@var{num} @gol
-mround-nearest -mlong-calls -mshort-calls -msmall16 @gol
-mfp-mode=@var{mode} -mvect-double -max-vect-align=@var{num} @gol
-msplit-vecmove-early -m1reg-@var{reg}}
@emph{ARC Options}
@gccoptlist{-mbarrel-shifter @gol
-mcpu=@var{cpu} -mA6 -mARC600 -mA7 -mARC700 @gol
-mdpfp -mdpfp-compact -mdpfp-fast -mno-dpfp-lrsr @gol
-mea -mno-mpy -mmul32x16 -mmul64 -matomic @gol
-mnorm -mspfp -mspfp-compact -mspfp-fast -msimd -msoft-float -mswap @gol
-mcrc -mdsp-packa -mdvbf -mlock -mmac-d16 -mmac-24 -mrtsc -mswape @gol
-mtelephony -mxy -misize -mannotate-align -marclinux -marclinux_prof @gol
-mlong-calls -mmedium-calls -msdata @gol
-mvolatile-cache -mtp-regno=@var{regno} @gol
-malign-call -mauto-modify-reg -mbbit-peephole -mno-brcc @gol
-mcase-vector-pcrel -mcompact-casesi -mno-cond-exec -mearly-cbranchsi @gol
-mexpand-adddi -mindexed-loads -mlra -mlra-priority-none @gol
-mlra-priority-compact mlra-priority-noncompact -mno-millicode @gol
-mmixed-code -mq-class -mRcq -mRcw -msize-level=@var{level} @gol
-mtune=@var{cpu} -mmultcost=@var{num} @gol
-munalign-prob-threshold=@var{probability} -mmpy-option=@var{multo} @gol
-mdiv-rem -mcode-density -mll64 -mfpu=@var{fpu}}
@emph{ARM Options}
@gccoptlist{-mapcs-frame -mno-apcs-frame @gol
-mabi=@var{name} @gol
-mapcs-stack-check -mno-apcs-stack-check @gol
-mapcs-reentrant -mno-apcs-reentrant @gol
-msched-prolog -mno-sched-prolog @gol
-mlittle-endian -mbig-endian @gol
-mfloat-abi=@var{name} @gol
-mfp16-format=@var{name}
-mthumb-interwork -mno-thumb-interwork @gol
-mcpu=@var{name} -march=@var{name} -mfpu=@var{name} @gol
-mtune=@var{name} -mprint-tune-info @gol
-mstructure-size-boundary=@var{n} @gol
-mabort-on-noreturn @gol
-mlong-calls -mno-long-calls @gol
-msingle-pic-base -mno-single-pic-base @gol
-mpic-register=@var{reg} @gol
-mnop-fun-dllimport @gol
-mpoke-function-name @gol
-mthumb -marm @gol
-mtpcs-frame -mtpcs-leaf-frame @gol
-mcaller-super-interworking -mcallee-super-interworking @gol
-mtp=@var{name} -mtls-dialect=@var{dialect} @gol
-mword-relocations @gol
-mfix-cortex-m3-ldrd @gol
-munaligned-access @gol
-mneon-for-64bits @gol
-mslow-flash-data @gol
-masm-syntax-unified @gol
-mrestrict-it @gol
-mpure-code @gol
-mcmse}
@emph{AVR Options}
@gccoptlist{-mmcu=@var{mcu} -mabsdata -maccumulate-args @gol
-mbranch-cost=@var{cost} @gol
-mcall-prologues -mint8 -mn_flash=@var{size} -mno-interrupts @gol
-mrelax -mrmw -mstrict-X -mtiny-stack -mfract-convert-truncate @gol
-nodevicelib @gol
-Waddr-space-convert -Wmisspelled-isr}
@emph{Blackfin Options}
@gccoptlist{-mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]} @gol
-msim -momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol
-mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly @gol
-mlow-64k -mno-low64k -mstack-check-l1 -mid-shared-library @gol
-mno-id-shared-library -mshared-library-id=@var{n} @gol
-mleaf-id-shared-library -mno-leaf-id-shared-library @gol
-msep-data -mno-sep-data -mlong-calls -mno-long-calls @gol
-mfast-fp -minline-plt -mmulticore -mcorea -mcoreb -msdram @gol
-micplb}
@emph{C6X Options}
@gccoptlist{-mbig-endian -mlittle-endian -march=@var{cpu} @gol
-msim -msdata=@var{sdata-type}}
@emph{CRIS Options}
@gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
-mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol
-metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol
-mstack-align -mdata-align -mconst-align @gol
-m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol
-melf -maout -melinux -mlinux -sim -sim2 @gol
-mmul-bug-workaround -mno-mul-bug-workaround}
@emph{CR16 Options}
@gccoptlist{-mmac @gol
-mcr16cplus -mcr16c @gol
-msim -mint32 -mbit-ops
-mdata-model=@var{model}}
@emph{Darwin Options}
@gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol
-arch_only -bind_at_load -bundle -bundle_loader @gol
-client_name -compatibility_version -current_version @gol
-dead_strip @gol
-dependency-file -dylib_file -dylinker_install_name @gol
-dynamic -dynamiclib -exported_symbols_list @gol
-filelist -flat_namespace -force_cpusubtype_ALL @gol
-force_flat_namespace -headerpad_max_install_names @gol
-iframework @gol
-image_base -init -install_name -keep_private_externs @gol
-multi_module -multiply_defined -multiply_defined_unused @gol
-noall_load -no_dead_strip_inits_and_terms @gol
-nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol
-pagezero_size -prebind -prebind_all_twolevel_modules @gol
-private_bundle -read_only_relocs -sectalign @gol
-sectobjectsymbols -whyload -seg1addr @gol
-sectcreate -sectobjectsymbols -sectorder @gol
-segaddr -segs_read_only_addr -segs_read_write_addr @gol
-seg_addr_table -seg_addr_table_filename -seglinkedit @gol
-segprot -segs_read_only_addr -segs_read_write_addr @gol
-single_module -static -sub_library -sub_umbrella @gol
-twolevel_namespace -umbrella -undefined @gol
-unexported_symbols_list -weak_reference_mismatches @gol
-whatsloaded -F -gused -gfull -mmacosx-version-min=@var{version} @gol
-mkernel -mone-byte-bool}
@emph{DEC Alpha Options}
@gccoptlist{-mno-fp-regs -msoft-float @gol
-mieee -mieee-with-inexact -mieee-conformant @gol
-mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
-mtrap-precision=@var{mode} -mbuild-constants @gol
-mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol
-mbwx -mmax -mfix -mcix @gol
-mfloat-vax -mfloat-ieee @gol
-mexplicit-relocs -msmall-data -mlarge-data @gol
-msmall-text -mlarge-text @gol
-mmemory-latency=@var{time}}
@emph{FR30 Options}
@gccoptlist{-msmall-model -mno-lsim}
@emph{FT32 Options}
@gccoptlist{-msim -mlra -mnodiv}
@emph{FRV Options}
@gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol
-mhard-float -msoft-float @gol
-malloc-cc -mfixed-cc -mdword -mno-dword @gol
-mdouble -mno-double @gol
-mmedia -mno-media -mmuladd -mno-muladd @gol
-mfdpic -minline-plt -mgprel-ro -multilib-library-pic @gol
-mlinked-fp -mlong-calls -malign-labels @gol
-mlibrary-pic -macc-4 -macc-8 @gol
-mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol
-moptimize-membar -mno-optimize-membar @gol
-mscc -mno-scc -mcond-exec -mno-cond-exec @gol
-mvliw-branch -mno-vliw-branch @gol
-mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol
-mno-nested-cond-exec -mtomcat-stats @gol
-mTLS -mtls @gol
-mcpu=@var{cpu}}
@emph{GNU/Linux Options}
@gccoptlist{-mglibc -muclibc -mmusl -mbionic -mandroid @gol
-tno-android-cc -tno-android-ld}
@emph{H8/300 Options}
@gccoptlist{-mrelax -mh -ms -mn -mexr -mno-exr -mint32 -malign-300}
@emph{HPPA Options}
@gccoptlist{-march=@var{architecture-type} @gol
-mcaller-copies -mdisable-fpregs -mdisable-indexing @gol
-mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol
-mfixed-range=@var{register-range} @gol
-mjump-in-delay -mlinker-opt -mlong-calls @gol
-mlong-load-store -mno-disable-fpregs @gol
-mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
-mno-jump-in-delay -mno-long-load-store @gol
-mno-portable-runtime -mno-soft-float @gol
-mno-space-regs -msoft-float -mpa-risc-1-0 @gol
-mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
-mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol
-munix=@var{unix-std} -nolibdld -static -threads}
@emph{IA-64 Options}
@gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
-mvolatile-asm-stop -mregister-names -msdata -mno-sdata @gol
-mconstant-gp -mauto-pic -mfused-madd @gol
-minline-float-divide-min-latency @gol
-minline-float-divide-max-throughput @gol
-mno-inline-float-divide @gol
-minline-int-divide-min-latency @gol
-minline-int-divide-max-throughput @gol
-mno-inline-int-divide @gol
-minline-sqrt-min-latency -minline-sqrt-max-throughput @gol
-mno-inline-sqrt @gol
-mdwarf2-asm -mearly-stop-bits @gol
-mfixed-range=@var{register-range} -mtls-size=@var{tls-size} @gol
-mtune=@var{cpu-type} -milp32 -mlp64 @gol
-msched-br-data-spec -msched-ar-data-spec -msched-control-spec @gol
-msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec @gol
-msched-spec-ldc -msched-spec-control-ldc @gol
-msched-prefer-non-data-spec-insns -msched-prefer-non-control-spec-insns @gol
-msched-stop-bits-after-every-cycle -msched-count-spec-in-critical-path @gol
-msel-sched-dont-check-control-spec -msched-fp-mem-deps-zero-cost @gol
-msched-max-memory-insns-hard-limit -msched-max-memory-insns=@var{max-insns}}
@emph{LM32 Options}
@gccoptlist{-mbarrel-shift-enabled -mdivide-enabled -mmultiply-enabled @gol
-msign-extend-enabled -muser-enabled}
@emph{M32R/D Options}
@gccoptlist{-m32r2 -m32rx -m32r @gol
-mdebug @gol
-malign-loops -mno-align-loops @gol
-missue-rate=@var{number} @gol
-mbranch-cost=@var{number} @gol
-mmodel=@var{code-size-model-type} @gol
-msdata=@var{sdata-type} @gol
-mno-flush-func -mflush-func=@var{name} @gol
-mno-flush-trap -mflush-trap=@var{number} @gol
-G @var{num}}
@emph{M32C Options}
@gccoptlist{-mcpu=@var{cpu} -msim -memregs=@var{number}}
@emph{M680x0 Options}
@gccoptlist{-march=@var{arch} -mcpu=@var{cpu} -mtune=@var{tune} @gol
-m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
-m68060 -mcpu32 -m5200 -m5206e -m528x -m5307 -m5407 @gol
-mcfv4e -mbitfield -mno-bitfield -mc68000 -mc68020 @gol
-mnobitfield -mrtd -mno-rtd -mdiv -mno-div -mshort @gol
-mno-short -mhard-float -m68881 -msoft-float -mpcrel @gol
-malign-int -mstrict-align -msep-data -mno-sep-data @gol
-mshared-library-id=n -mid-shared-library -mno-id-shared-library @gol
-mxgot -mno-xgot -mlong-jump-table-offsets}
@emph{MCore Options}
@gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
-mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
-m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
-mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
-mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
@emph{MeP Options}
@gccoptlist{-mabsdiff -mall-opts -maverage -mbased=@var{n} -mbitops @gol
-mc=@var{n} -mclip -mconfig=@var{name} -mcop -mcop32 -mcop64 -mivc2 @gol
-mdc -mdiv -meb -mel -mio-volatile -ml -mleadz -mm -mminmax @gol
-mmult -mno-opts -mrepeat -ms -msatur -msdram -msim -msimnovec -mtf @gol
-mtiny=@var{n}}
@emph{MicroBlaze Options}
@gccoptlist{-msoft-float -mhard-float -msmall-divides -mcpu=@var{cpu} @gol
-mmemcpy -mxl-soft-mul -mxl-soft-div -mxl-barrel-shift @gol
-mxl-pattern-compare -mxl-stack-check -mxl-gp-opt -mno-clearbss @gol
-mxl-multiply-high -mxl-float-convert -mxl-float-sqrt @gol
-mbig-endian -mlittle-endian -mxl-reorder -mxl-mode-@var{app-model}}
@emph{MIPS Options}
@gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol
-mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips32r3 -mips32r5 @gol
-mips32r6 -mips64 -mips64r2 -mips64r3 -mips64r5 -mips64r6 @gol
-mips16 -mno-mips16 -mflip-mips16 @gol
-minterlink-compressed -mno-interlink-compressed @gol
-minterlink-mips16 -mno-interlink-mips16 @gol
-mabi=@var{abi} -mabicalls -mno-abicalls @gol
-mshared -mno-shared -mplt -mno-plt -mxgot -mno-xgot @gol
-mgp32 -mgp64 -mfp32 -mfpxx -mfp64 -mhard-float -msoft-float @gol
-mno-float -msingle-float -mdouble-float @gol
-modd-spreg -mno-odd-spreg @gol
-mabs=@var{mode} -mnan=@var{encoding} @gol
-mdsp -mno-dsp -mdspr2 -mno-dspr2 @gol
-mmcu -mmno-mcu @gol
-meva -mno-eva @gol
-mvirt -mno-virt @gol
-mxpa -mno-xpa @gol
-mmicromips -mno-micromips @gol
-mmsa -mno-msa @gol
-mfpu=@var{fpu-type} @gol
-msmartmips -mno-smartmips @gol
-mpaired-single -mno-paired-single -mdmx -mno-mdmx @gol
-mips3d -mno-mips3d -mmt -mno-mt -mllsc -mno-llsc @gol
-mlong64 -mlong32 -msym32 -mno-sym32 @gol
-G@var{num} -mlocal-sdata -mno-local-sdata @gol
-mextern-sdata -mno-extern-sdata -mgpopt -mno-gopt @gol
-membedded-data -mno-embedded-data @gol
-muninit-const-in-rodata -mno-uninit-const-in-rodata @gol
-mcode-readable=@var{setting} @gol
-msplit-addresses -mno-split-addresses @gol
-mexplicit-relocs -mno-explicit-relocs @gol
-mcheck-zero-division -mno-check-zero-division @gol
-mdivide-traps -mdivide-breaks @gol
-mload-store-pairs -mno-load-store-pairs @gol
-mmemcpy -mno-memcpy -mlong-calls -mno-long-calls @gol
-mmad -mno-mad -mimadd -mno-imadd -mfused-madd -mno-fused-madd -nocpp @gol
-mfix-24k -mno-fix-24k @gol
-mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 @gol
-mfix-r10000 -mno-fix-r10000 -mfix-rm7000 -mno-fix-rm7000 @gol
-mfix-vr4120 -mno-fix-vr4120 @gol
-mfix-vr4130 -mno-fix-vr4130 -mfix-sb1 -mno-fix-sb1 @gol
-mflush-func=@var{func} -mno-flush-func @gol
-mbranch-cost=@var{num} -mbranch-likely -mno-branch-likely @gol
-mcompact-branches=@var{policy} @gol
-mfp-exceptions -mno-fp-exceptions @gol
-mvr4130-align -mno-vr4130-align -msynci -mno-synci @gol
-mlxc1-sxc1 -mno-lxc1-sxc1 -mmadd4 -mno-madd4 @gol
-mrelax-pic-calls -mno-relax-pic-calls -mmcount-ra-address @gol
-mframe-header-opt -mno-frame-header-opt}
@emph{MMIX Options}
@gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
-mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
-melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol
-mno-base-addresses -msingle-exit -mno-single-exit}
@emph{MN10300 Options}
@gccoptlist{-mmult-bug -mno-mult-bug @gol
-mno-am33 -mam33 -mam33-2 -mam34 @gol
-mtune=@var{cpu-type} @gol
-mreturn-pointer-on-d0 @gol
-mno-crt0 -mrelax -mliw -msetlb}
@emph{Moxie Options}
@gccoptlist{-meb -mel -mmul.x -mno-crt0}
@emph{MSP430 Options}
@gccoptlist{-msim -masm-hex -mmcu= -mcpu= -mlarge -msmall -mrelax @gol
-mwarn-mcu @gol
-mcode-region= -mdata-region= @gol
-msilicon-errata= -msilicon-errata-warn= @gol
-mhwmult= -minrt}
@emph{NDS32 Options}
@gccoptlist{-mbig-endian -mlittle-endian @gol
-mreduced-regs -mfull-regs @gol
-mcmov -mno-cmov @gol
-mperf-ext -mno-perf-ext @gol
-mv3push -mno-v3push @gol
-m16bit -mno-16bit @gol
-misr-vector-size=@var{num} @gol
-mcache-block-size=@var{num} @gol
-march=@var{arch} @gol
-mcmodel=@var{code-model} @gol
-mctor-dtor -mrelax}
@emph{Nios II Options}
@gccoptlist{-G @var{num} -mgpopt=@var{option} -mgpopt -mno-gpopt @gol
-mel -meb @gol
-mno-bypass-cache -mbypass-cache @gol
-mno-cache-volatile -mcache-volatile @gol
-mno-fast-sw-div -mfast-sw-div @gol
-mhw-mul -mno-hw-mul -mhw-mulx -mno-hw-mulx -mno-hw-div -mhw-div @gol
-mcustom-@var{insn}=@var{N} -mno-custom-@var{insn} @gol
-mcustom-fpu-cfg=@var{name} @gol
-mhal -msmallc -msys-crt0=@var{name} -msys-lib=@var{name} @gol
-march=@var{arch} -mbmx -mno-bmx -mcdx -mno-cdx}
@emph{Nvidia PTX Options}
@gccoptlist{-m32 -m64 -mmainkernel -moptimize}
@emph{PDP-11 Options}
@gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol
-mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol
-mint16 -mno-int32 -mfloat32 -mno-float64 @gol
-mfloat64 -mno-float32 -mabshi -mno-abshi @gol
-mbranch-expensive -mbranch-cheap @gol
-munix-asm -mdec-asm}
@emph{picoChip Options}
@gccoptlist{-mae=@var{ae_type} -mvliw-lookahead=@var{N} @gol
-msymbol-as-address -mno-inefficient-warnings}
@emph{PowerPC Options}
See RS/6000 and PowerPC Options.
@emph{RISC-V Options}
@gccoptlist{-mbranch-cost=@var{N-instruction} @gol
-mplt -mno-plt @gol
-mabi=@var{ABI-string} @gol
-mfdiv -mno-fdiv @gol
-mdiv -mno-div @gol
-march=@var{ISA-string} @gol
-mtune=@var{processor-string} @gol
-msmall-data-limit=@var{N-bytes} @gol
-msave-restore -mno-save-restore @gol
-mstrict-align -mno-strict-align @gol
-mcmodel=medlow -mcmodel=medany @gol
-mexplicit-relocs -mno-explicit-relocs @gol}
@emph{RL78 Options}
@gccoptlist{-msim -mmul=none -mmul=g13 -mmul=g14 -mallregs @gol
-mcpu=g10 -mcpu=g13 -mcpu=g14 -mg10 -mg13 -mg14 @gol
-m64bit-doubles -m32bit-doubles -msave-mduc-in-interrupts}
@emph{RS/6000 and PowerPC Options}
@gccoptlist{-mcpu=@var{cpu-type} @gol
-mtune=@var{cpu-type} @gol
-mcmodel=@var{code-model} @gol
-mpowerpc64 @gol
-maltivec -mno-altivec @gol
-mpowerpc-gpopt -mno-powerpc-gpopt @gol
-mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
-mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mpopcntd -mno-popcntd @gol
-mfprnd -mno-fprnd @gol
-mcmpb -mno-cmpb -mmfpgpr -mno-mfpgpr -mhard-dfp -mno-hard-dfp @gol
-mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
-m64 -m32 -mxl-compat -mno-xl-compat -mpe @gol
-malign-power -malign-natural @gol
-msoft-float -mhard-float -mmultiple -mno-multiple @gol
-msingle-float -mdouble-float -msimple-fpu @gol
-mstring -mno-string -mupdate -mno-update @gol
-mavoid-indexed-addresses -mno-avoid-indexed-addresses @gol
-mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
-mstrict-align -mno-strict-align -mrelocatable @gol
-mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
-mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
-mdynamic-no-pic -maltivec -mswdiv -msingle-pic-base @gol
-mprioritize-restricted-insns=@var{priority} @gol
-msched-costly-dep=@var{dependence_type} @gol
-minsert-sched-nops=@var{scheme} @gol
-mcall-sysv -mcall-netbsd @gol
-maix-struct-return -msvr4-struct-return @gol
-mabi=@var{abi-type} -msecure-plt -mbss-plt @gol
-mblock-move-inline-limit=@var{num} @gol
-misel -mno-isel @gol
-misel=yes -misel=no @gol
-mspe -mno-spe @gol
-mspe=yes -mspe=no @gol
-mpaired @gol
-mgen-cell-microcode -mwarn-cell-microcode @gol
-mvrsave -mno-vrsave @gol
-mmulhw -mno-mulhw @gol
-mdlmzb -mno-dlmzb @gol
-mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double @gol
-mprototype -mno-prototype @gol
-msim -mmvme -mads -myellowknife -memb -msdata @gol
-msdata=@var{opt} -mreadonly-in-sdata -mvxworks -G @var{num} @gol
-mrecip -mrecip=@var{opt} -mno-recip -mrecip-precision @gol
-mno-recip-precision @gol
-mveclibabi=@var{type} -mfriz -mno-friz @gol
-mpointers-to-nested-functions -mno-pointers-to-nested-functions @gol
-msave-toc-indirect -mno-save-toc-indirect @gol
-mpower8-fusion -mno-mpower8-fusion -mpower8-vector -mno-power8-vector @gol
-mcrypto -mno-crypto -mhtm -mno-htm -mdirect-move -mno-direct-move @gol
-mquad-memory -mno-quad-memory @gol
-mquad-memory-atomic -mno-quad-memory-atomic @gol
-mcompat-align-parm -mno-compat-align-parm @gol
-mupper-regs-df -mno-upper-regs-df -mupper-regs-sf -mno-upper-regs-sf @gol
-mupper-regs-di -mno-upper-regs-di @gol
-mupper-regs -mno-upper-regs @gol
-mfloat128 -mno-float128 -mfloat128-hardware -mno-float128-hardware @gol
-mgnu-attribute -mno-gnu-attribute @gol
-mstack-protector-guard=@var{guard} -mstack-protector-guard-reg=@var{reg} @gol
-mstack-protector-guard-offset=@var{offset} @gol
-mlra -mno-lra}
@emph{RX Options}
@gccoptlist{-m64bit-doubles -m32bit-doubles -fpu -nofpu@gol
-mcpu=@gol
-mbig-endian-data -mlittle-endian-data @gol
-msmall-data @gol
-msim -mno-sim@gol
-mas100-syntax -mno-as100-syntax@gol
-mrelax@gol
-mmax-constant-size=@gol
-mint-register=@gol
-mpid@gol
-mallow-string-insns -mno-allow-string-insns@gol
-mjsr@gol
-mno-warn-multiple-fast-interrupts@gol
-msave-acc-in-interrupts}
@emph{S/390 and zSeries Options}
@gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
-mhard-float -msoft-float -mhard-dfp -mno-hard-dfp @gol
-mlong-double-64 -mlong-double-128 @gol
-mbackchain -mno-backchain -mpacked-stack -mno-packed-stack @gol
-msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
-m64 -m31 -mdebug -mno-debug -mesa -mzarch @gol
-mhtm -mvx -mzvector @gol
-mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd @gol
-mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard @gol
-mhotpatch=@var{halfwords},@var{halfwords}}
@emph{Score Options}
@gccoptlist{-meb -mel @gol
-mnhwloop @gol
-muls @gol
-mmac @gol
-mscore5 -mscore5u -mscore7 -mscore7d}
@emph{SH Options}
@gccoptlist{-m1 -m2 -m2e @gol
-m2a-nofpu -m2a-single-only -m2a-single -m2a @gol
-m3 -m3e @gol
-m4-nofpu -m4-single-only -m4-single -m4 @gol
-m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol
-mb -ml -mdalign -mrelax @gol
-mbigtable -mfmovd -mrenesas -mno-renesas -mnomacsave @gol
-mieee -mno-ieee -mbitops -misize -minline-ic_invalidate -mpadstruct @gol
-mprefergot -musermode -multcost=@var{number} -mdiv=@var{strategy} @gol
-mdivsi3_libfunc=@var{name} -mfixed-range=@var{register-range} @gol
-maccumulate-outgoing-args @gol
-matomic-model=@var{atomic-model} @gol
-mbranch-cost=@var{num} -mzdcbranch -mno-zdcbranch @gol
-mcbranch-force-delay-slot @gol
-mfused-madd -mno-fused-madd -mfsca -mno-fsca -mfsrra -mno-fsrra @gol
-mpretend-cmove -mtas}
@emph{Solaris 2 Options}
@gccoptlist{-mclear-hwcap -mno-clear-hwcap -mimpure-text -mno-impure-text @gol
-pthreads}
@emph{SPARC Options}
@gccoptlist{-mcpu=@var{cpu-type} @gol
-mtune=@var{cpu-type} @gol
-mcmodel=@var{code-model} @gol
-mmemory-model=@var{mem-model} @gol
-m32 -m64 -mapp-regs -mno-app-regs @gol
-mfaster-structs -mno-faster-structs -mflat -mno-flat @gol
-mfpu -mno-fpu -mhard-float -msoft-float @gol
-mhard-quad-float -msoft-quad-float @gol
-mstack-bias -mno-stack-bias @gol
-mstd-struct-return -mno-std-struct-return @gol
-munaligned-doubles -mno-unaligned-doubles @gol
-muser-mode -mno-user-mode @gol
-mv8plus -mno-v8plus -mvis -mno-vis @gol
-mvis2 -mno-vis2 -mvis3 -mno-vis3 @gol
-mvis4 -mno-vis4 -mvis4b -mno-vis4b @gol
-mcbcond -mno-cbcond -mfmaf -mno-fmaf -mfsmuld -mno-fsmuld @gol
-mpopc -mno-popc -msubxc -mno-subxc @gol
-mfix-at697f -mfix-ut699 -mfix-ut700 -mfix-gr712rc @gol
-mlra -mno-lra}
@emph{SPU Options}
@gccoptlist{-mwarn-reloc -merror-reloc @gol
-msafe-dma -munsafe-dma @gol
-mbranch-hints @gol
-msmall-mem -mlarge-mem -mstdmain @gol
-mfixed-range=@var{register-range} @gol
-mea32 -mea64 @gol
-maddress-space-conversion -mno-address-space-conversion @gol
-mcache-size=@var{cache-size} @gol
-matomic-updates -mno-atomic-updates}
@emph{System V Options}
@gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
@emph{TILE-Gx Options}
@gccoptlist{-mcpu=CPU -m32 -m64 -mbig-endian -mlittle-endian @gol
-mcmodel=@var{code-model}}
@emph{TILEPro Options}
@gccoptlist{-mcpu=@var{cpu} -m32}
@emph{V850 Options}
@gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol
-mprolog-function -mno-prolog-function -mspace @gol
-mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
-mapp-regs -mno-app-regs @gol
-mdisable-callt -mno-disable-callt @gol
-mv850e2v3 -mv850e2 -mv850e1 -mv850es @gol
-mv850e -mv850 -mv850e3v5 @gol
-mloop @gol
-mrelax @gol
-mlong-jumps @gol
-msoft-float @gol
-mhard-float @gol
-mgcc-abi @gol
-mrh850-abi @gol
-mbig-switch}
@emph{VAX Options}
@gccoptlist{-mg -mgnu -munix}
@emph{Visium Options}
@gccoptlist{-mdebug -msim -mfpu -mno-fpu -mhard-float -msoft-float @gol
-mcpu=@var{cpu-type} -mtune=@var{cpu-type} -msv-mode -muser-mode}
@emph{VMS Options}
@gccoptlist{-mvms-return-codes -mdebug-main=@var{prefix} -mmalloc64 @gol
-mpointer-size=@var{size}}
@emph{VxWorks Options}
@gccoptlist{-mrtp -non-static -Bstatic -Bdynamic @gol
-Xbind-lazy -Xbind-now}
@emph{x86 Options}
@gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
-mtune-ctrl=@var{feature-list} -mdump-tune-features -mno-default @gol
-mfpmath=@var{unit} @gol
-masm=@var{dialect} -mno-fancy-math-387 @gol
-mno-fp-ret-in-387 -m80387 -mhard-float -msoft-float @gol
-mno-wide-multiply -mrtd -malign-double @gol
-mpreferred-stack-boundary=@var{num} @gol
-mincoming-stack-boundary=@var{num} @gol
-mcld -mcx16 -msahf -mmovbe -mcrc32 @gol
-mrecip -mrecip=@var{opt} @gol
-mvzeroupper -mprefer-avx128 @gol
-mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 -mavx @gol
-mavx2 -mavx512f -mavx512pf -mavx512er -mavx512cd -mavx512vl @gol
-mavx512bw -mavx512dq -mavx512ifma -mavx512vbmi -msha -maes @gol
-mpclmul -mfsgsbase -mrdrnd -mf16c -mfma @gol
-mprefetchwt1 -mclflushopt -mxsavec -mxsaves @gol
-msse4a -m3dnow -m3dnowa -mpopcnt -mabm -mbmi -mtbm -mfma4 -mxop @gol
-mlzcnt -mbmi2 -mfxsr -mxsave -mxsaveopt -mrtm -mlwp -mmpx @gol
-mmwaitx -mclzero -mpku -mthreads @gol
-mms-bitfields -mno-align-stringops -minline-all-stringops @gol
-minline-stringops-dynamically -mstringop-strategy=@var{alg} @gol
-mmemcpy-strategy=@var{strategy} -mmemset-strategy=@var{strategy} @gol
-mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
-m96bit-long-double -mlong-double-64 -mlong-double-80 -mlong-double-128 @gol
-mregparm=@var{num} -msseregparm @gol
-mveclibabi=@var{type} -mvect8-ret-in-mem @gol
-mpc32 -mpc64 -mpc80 -mstackrealign @gol
-momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs @gol
-mcmodel=@var{code-model} -mabi=@var{name} -maddress-mode=@var{mode} @gol
-m32 -m64 -mx32 -m16 -miamcu -mlarge-data-threshold=@var{num} @gol
-msse2avx -mfentry -mrecord-mcount -mnop-mcount -m8bit-idiv @gol
-mavx256-split-unaligned-load -mavx256-split-unaligned-store @gol
-malign-data=@var{type} -mstack-protector-guard=@var{guard} @gol
-mmitigate-rop -mgeneral-regs-only @gol
-mindirect-branch=@var{choice} -mfunction-return=@var{choice} @gol
-mindirect-branch-register}
@emph{x86 Windows Options}
@gccoptlist{-mconsole -mcygwin -mno-cygwin -mdll @gol
-mnop-fun-dllimport -mthread @gol
-municode -mwin32 -mwindows -fno-set-stack-executable}
@emph{Xstormy16 Options}
@gccoptlist{-msim}
@emph{Xtensa Options}
@gccoptlist{-mconst16 -mno-const16 @gol
-mfused-madd -mno-fused-madd @gol
-mforce-no-pic @gol
-mserialize-volatile -mno-serialize-volatile @gol
-mtext-section-literals -mno-text-section-literals @gol
-mauto-litpools -mno-auto-litpools @gol
-mtarget-align -mno-target-align @gol
-mlongcalls -mno-longcalls}
@emph{zSeries Options}
See S/390 and zSeries Options.
@end table
@node Overall Options
@section Options Controlling the Kind of Output
Compilation can involve up to four stages: preprocessing, compilation
proper, assembly and linking, always in that order. GCC is capable of
preprocessing and compiling several files either into several
assembler input files, or into one assembler input file; then each
assembler input file produces an object file, and linking combines all
the object files (those newly compiled, and those specified as input)
into an executable file.
@cindex file name suffix
For any given input file, the file name suffix determines what kind of
compilation is done:
@table @gcctabopt
@item @var{file}.c
C source code that must be preprocessed.
@item @var{file}.i
C source code that should not be preprocessed.
@item @var{file}.ii
C++ source code that should not be preprocessed.
@item @var{file}.m
Objective-C source code. Note that you must link with the @file{libobjc}
library to make an Objective-C program work.
@item @var{file}.mi
Objective-C source code that should not be preprocessed.
@item @var{file}.mm
@itemx @var{file}.M
Objective-C++ source code. Note that you must link with the @file{libobjc}
library to make an Objective-C++ program work. Note that @samp{.M} refers
to a literal capital M@.
@item @var{file}.mii
Objective-C++ source code that should not be preprocessed.
@item @var{file}.h
C, C++, Objective-C or Objective-C++ header file to be turned into a
precompiled header (default), or C, C++ header file to be turned into an
Ada spec (via the @option{-fdump-ada-spec} switch).
@item @var{file}.cc
@itemx @var{file}.cp
@itemx @var{file}.cxx
@itemx @var{file}.cpp
@itemx @var{file}.CPP
@itemx @var{file}.c++
@itemx @var{file}.C
C++ source code that must be preprocessed. Note that in @samp{.cxx},
the last two letters must both be literally @samp{x}. Likewise,
@samp{.C} refers to a literal capital C@.
@item @var{file}.mm
@itemx @var{file}.M
Objective-C++ source code that must be preprocessed.
@item @var{file}.mii
Objective-C++ source code that should not be preprocessed.
@item @var{file}.hh
@itemx @var{file}.H
@itemx @var{file}.hp
@itemx @var{file}.hxx
@itemx @var{file}.hpp
@itemx @var{file}.HPP
@itemx @var{file}.h++
@itemx @var{file}.tcc
C++ header file to be turned into a precompiled header or Ada spec.
@item @var{file}.f
@itemx @var{file}.for
@itemx @var{file}.ftn
Fixed form Fortran source code that should not be preprocessed.
@item @var{file}.F
@itemx @var{file}.FOR
@itemx @var{file}.fpp
@itemx @var{file}.FPP
@itemx @var{file}.FTN
Fixed form Fortran source code that must be preprocessed (with the traditional
preprocessor).
@item @var{file}.f90
@itemx @var{file}.f95
@itemx @var{file}.f03
@itemx @var{file}.f08
Free form Fortran source code that should not be preprocessed.
@item @var{file}.F90
@itemx @var{file}.F95
@itemx @var{file}.F03
@itemx @var{file}.F08
Free form Fortran source code that must be preprocessed (with the
traditional preprocessor).
@item @var{file}.go
Go source code.
@item @var{file}.brig
BRIG files (binary representation of HSAIL).
@item @var{file}.ads
Ada source code file that contains a library unit declaration (a
declaration of a package, subprogram, or generic, or a generic
instantiation), or a library unit renaming declaration (a package,
generic, or subprogram renaming declaration). Such files are also
called @dfn{specs}.
@item @var{file}.adb
Ada source code file containing a library unit body (a subprogram or
package body). Such files are also called @dfn{bodies}.
@c GCC also knows about some suffixes for languages not yet included:
@c Pascal:
@c @var{file}.p
@c @var{file}.pas
@c Ratfor:
@c @var{file}.r
@item @var{file}.s
Assembler code.
@item @var{file}.S
@itemx @var{file}.sx
Assembler code that must be preprocessed.
@item @var{other}
An object file to be fed straight into linking.
Any file name with no recognized suffix is treated this way.
@end table
@opindex x
You can specify the input language explicitly with the @option{-x} option:
@table @gcctabopt
@item -x @var{language}
Specify explicitly the @var{language} for the following input files
(rather than letting the compiler choose a default based on the file
name suffix). This option applies to all following input files until
the next @option{-x} option. Possible values for @var{language} are:
@smallexample
c c-header cpp-output
c++ c++-header c++-cpp-output
objective-c objective-c-header objective-c-cpp-output
objective-c++ objective-c++-header objective-c++-cpp-output
assembler assembler-with-cpp
ada
f77 f77-cpp-input f95 f95-cpp-input
go
brig
@end smallexample
@item -x none
Turn off any specification of a language, so that subsequent files are
handled according to their file name suffixes (as they are if @option{-x}
has not been used at all).
@end table
If you only want some of the stages of compilation, you can use
@option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
one of the options @option{-c}, @option{-S}, or @option{-E} to say where
@command{gcc} is to stop. Note that some combinations (for example,
@samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
@table @gcctabopt
@item -c
@opindex c
Compile or assemble the source files, but do not link. The linking
stage simply is not done. The ultimate output is in the form of an
object file for each source file.
By default, the object file name for a source file is made by replacing
the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
Unrecognized input files, not requiring compilation or assembly, are
ignored.
@item -S
@opindex S
Stop after the stage of compilation proper; do not assemble. The output
is in the form of an assembler code file for each non-assembler input
file specified.
By default, the assembler file name for a source file is made by
replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
Input files that don't require compilation are ignored.
@item -E
@opindex E
Stop after the preprocessing stage; do not run the compiler proper. The
output is in the form of preprocessed source code, which is sent to the
standard output.
Input files that don't require preprocessing are ignored.
@cindex output file option
@item -o @var{file}
@opindex o
Place output in file @var{file}. This applies to whatever
sort of output is being produced, whether it be an executable file,
an object file, an assembler file or preprocessed C code.
If @option{-o} is not specified, the default is to put an executable
file in @file{a.out}, the object file for
@file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its
assembler file in @file{@var{source}.s}, a precompiled header file in
@file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on
standard output.
@item -v
@opindex v
Print (on standard error output) the commands executed to run the stages
of compilation. Also print the version number of the compiler driver
program and of the preprocessor and the compiler proper.
@item -###
@opindex ###
Like @option{-v} except the commands are not executed and arguments
are quoted unless they contain only alphanumeric characters or @code{./-_}.
This is useful for shell scripts to capture the driver-generated command lines.
@item --help
@opindex help
Print (on the standard output) a description of the command-line options
understood by @command{gcc}. If the @option{-v} option is also specified
then @option{--help} is also passed on to the various processes
invoked by @command{gcc}, so that they can display the command-line options
they accept. If the @option{-Wextra} option has also been specified
(prior to the @option{--help} option), then command-line options that
have no documentation associated with them are also displayed.
@item --target-help
@opindex target-help
Print (on the standard output) a description of target-specific command-line
options for each tool. For some targets extra target-specific
information may also be printed.
@item --help=@{@var{class}@r{|[}^@r{]}@var{qualifier}@}@r{[},@dots{}@r{]}
Print (on the standard output) a description of the command-line
options understood by the compiler that fit into all specified classes
and qualifiers. These are the supported classes:
@table @asis
@item @samp{optimizers}
Display all of the optimization options supported by the
compiler.
@item @samp{warnings}
Display all of the options controlling warning messages
produced by the compiler.
@item @samp{target}
Display target-specific options. Unlike the
@option{--target-help} option however, target-specific options of the
linker and assembler are not displayed. This is because those
tools do not currently support the extended @option{--help=} syntax.
@item @samp{params}
Display the values recognized by the @option{--param}
option.
@item @var{language}
Display the options supported for @var{language}, where
@var{language} is the name of one of the languages supported in this
version of GCC@.
@item @samp{common}
Display the options that are common to all languages.
@end table
These are the supported qualifiers:
@table @asis
@item @samp{undocumented}
Display only those options that are undocumented.
@item @samp{joined}
Display options taking an argument that appears after an equal
sign in the same continuous piece of text, such as:
@samp{--help=target}.
@item @samp{separate}
Display options taking an argument that appears as a separate word
following the original option, such as: @samp{-o output-file}.
@end table
Thus for example to display all the undocumented target-specific
switches supported by the compiler, use:
@smallexample
--help=target,undocumented
@end smallexample
The sense of a qualifier can be inverted by prefixing it with the
@samp{^} character, so for example to display all binary warning
options (i.e., ones that are either on or off and that do not take an
argument) that have a description, use:
@smallexample
--help=warnings,^joined,^undocumented
@end smallexample
The argument to @option{--help=} should not consist solely of inverted
qualifiers.
Combining several classes is possible, although this usually
restricts the output so much that there is nothing to display. One
case where it does work, however, is when one of the classes is
@var{target}. For example, to display all the target-specific
optimization options, use:
@smallexample
--help=target,optimizers
@end smallexample
The @option{--help=} option can be repeated on the command line. Each
successive use displays its requested class of options, skipping
those that have already been displayed.
If the @option{-Q} option appears on the command line before the
@option{--help=} option, then the descriptive text displayed by
@option{--help=} is changed. Instead of describing the displayed
options, an indication is given as to whether the option is enabled,
disabled or set to a specific value (assuming that the compiler
knows this at the point where the @option{--help=} option is used).
Here is a truncated example from the ARM port of @command{gcc}:
@smallexample
% gcc -Q -mabi=2 --help=target -c
The following options are target specific:
-mabi= 2
-mabort-on-noreturn [disabled]
-mapcs [disabled]
@end smallexample
The output is sensitive to the effects of previous command-line
options, so for example it is possible to find out which optimizations
are enabled at @option{-O2} by using:
@smallexample
-Q -O2 --help=optimizers
@end smallexample
Alternatively you can discover which binary optimizations are enabled
by @option{-O3} by using:
@smallexample
gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts
gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts
diff /tmp/O2-opts /tmp/O3-opts | grep enabled
@end smallexample
@item --version
@opindex version
Display the version number and copyrights of the invoked GCC@.
@item -pass-exit-codes
@opindex pass-exit-codes
Normally the @command{gcc} program exits with the code of 1 if any
phase of the compiler returns a non-success return code. If you specify
@option{-pass-exit-codes}, the @command{gcc} program instead returns with
the numerically highest error produced by any phase returning an error
indication. The C, C++, and Fortran front ends return 4 if an internal
compiler error is encountered.
@item -pipe
@opindex pipe
Use pipes rather than temporary files for communication between the
various stages of compilation. This fails to work on some systems where
the assembler is unable to read from a pipe; but the GNU assembler has
no trouble.
@item -specs=@var{file}
@opindex specs
Process @var{file} after the compiler reads in the standard @file{specs}
file, in order to override the defaults which the @command{gcc} driver
program uses when determining what switches to pass to @command{cc1},
@command{cc1plus}, @command{as}, @command{ld}, etc. More than one
@option{-specs=@var{file}} can be specified on the command line, and they
are processed in order, from left to right. @xref{Spec Files}, for
information about the format of the @var{file}.
@item -wrapper
@opindex wrapper
Invoke all subcommands under a wrapper program. The name of the
wrapper program and its parameters are passed as a comma separated
list.
@smallexample
gcc -c t.c -wrapper gdb,--args
@end smallexample
@noindent
This invokes all subprograms of @command{gcc} under
@samp{gdb --args}, thus the invocation of @command{cc1} is
@samp{gdb --args cc1 @dots{}}.
@item -fplugin=@var{name}.so
@opindex fplugin
Load the plugin code in file @var{name}.so, assumed to be a
shared object to be dlopen'd by the compiler. The base name of
the shared object file is used to identify the plugin for the
purposes of argument parsing (See
@option{-fplugin-arg-@var{name}-@var{key}=@var{value}} below).
Each plugin should define the callback functions specified in the
Plugins API.
@item -fplugin-arg-@var{name}-@var{key}=@var{value}
@opindex fplugin-arg
Define an argument called @var{key} with a value of @var{value}
for the plugin called @var{name}.
@item -fdump-ada-spec@r{[}-slim@r{]}
@opindex fdump-ada-spec
For C and C++ source and include files, generate corresponding Ada specs.
@xref{Generating Ada Bindings for C and C++ headers,,, gnat_ugn,
GNAT User's Guide}, which provides detailed documentation on this feature.
@item -fada-spec-parent=@var{unit}
@opindex fada-spec-parent
In conjunction with @option{-fdump-ada-spec@r{[}-slim@r{]}} above, generate
Ada specs as child units of parent @var{unit}.
@item -fdump-go-spec=@var{file}
@opindex fdump-go-spec
For input files in any language, generate corresponding Go
declarations in @var{file}. This generates Go @code{const},
@code{type}, @code{var}, and @code{func} declarations which may be a
useful way to start writing a Go interface to code written in some
other language.
@include @value{srcdir}/../libiberty/at-file.texi
@end table
@node Invoking G++
@section Compiling C++ Programs
@cindex suffixes for C++ source
@cindex C++ source file suffixes
C++ source files conventionally use one of the suffixes @samp{.C},
@samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
@samp{.cxx}; C++ header files often use @samp{.hh}, @samp{.hpp},
@samp{.H}, or (for shared template code) @samp{.tcc}; and
preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
files with these names and compiles them as C++ programs even if you
call the compiler the same way as for compiling C programs (usually
with the name @command{gcc}).
@findex g++
@findex c++
However, the use of @command{gcc} does not add the C++ library.
@command{g++} is a program that calls GCC and automatically specifies linking
against the C++ library. It treats @samp{.c},
@samp{.h} and @samp{.i} files as C++ source files instead of C source
files unless @option{-x} is used. This program is also useful when
precompiling a C header file with a @samp{.h} extension for use in C++
compilations. On many systems, @command{g++} is also installed with
the name @command{c++}.
@cindex invoking @command{g++}
When you compile C++ programs, you may specify many of the same
command-line options that you use for compiling programs in any
language; or command-line options meaningful for C and related
languages; or options that are meaningful only for C++ programs.
@xref{C Dialect Options,,Options Controlling C Dialect}, for
explanations of options for languages related to C@.
@xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
explanations of options that are meaningful only for C++ programs.
@node C Dialect Options
@section Options Controlling C Dialect
@cindex dialect options
@cindex language dialect options
@cindex options, dialect
The following options control the dialect of C (or languages derived
from C, such as C++, Objective-C and Objective-C++) that the compiler
accepts:
@table @gcctabopt
@cindex ANSI support
@cindex ISO support
@item -ansi
@opindex ansi
In C mode, this is equivalent to @option{-std=c90}. In C++ mode, it is
equivalent to @option{-std=c++98}.
This turns off certain features of GCC that are incompatible with ISO
C90 (when compiling C code), or of standard C++ (when compiling C++ code),
such as the @code{asm} and @code{typeof} keywords, and
predefined macros such as @code{unix} and @code{vax} that identify the
type of system you are using. It also enables the undesirable and
rarely used ISO trigraph feature. For the C compiler,
it disables recognition of C++ style @samp{//} comments as well as
the @code{inline} keyword.
The alternate keywords @code{__asm__}, @code{__extension__},
@code{__inline__} and @code{__typeof__} continue to work despite
@option{-ansi}. You would not want to use them in an ISO C program, of
course, but it is useful to put them in header files that might be included
in compilations done with @option{-ansi}. Alternate predefined macros
such as @code{__unix__} and @code{__vax__} are also available, with or
without @option{-ansi}.
The @option{-ansi} option does not cause non-ISO programs to be
rejected gratuitously. For that, @option{-Wpedantic} is required in
addition to @option{-ansi}. @xref{Warning Options}.
The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
option is used. Some header files may notice this macro and refrain
from declaring certain functions or defining certain macros that the
ISO standard doesn't call for; this is to avoid interfering with any
programs that might use these names for other things.
Functions that are normally built in but do not have semantics
defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
functions when @option{-ansi} is used. @xref{Other Builtins,,Other
built-in functions provided by GCC}, for details of the functions
affected.
@item -std=
@opindex std
Determine the language standard. @xref{Standards,,Language Standards
Supported by GCC}, for details of these standard versions. This option
is currently only supported when compiling C or C++.
The compiler can accept several base standards, such as @samp{c90} or
@samp{c++98}, and GNU dialects of those standards, such as
@samp{gnu90} or @samp{gnu++98}. When a base standard is specified, the
compiler accepts all programs following that standard plus those
using GNU extensions that do not contradict it. For example,
@option{-std=c90} turns off certain features of GCC that are
incompatible with ISO C90, such as the @code{asm} and @code{typeof}
keywords, but not other GNU extensions that do not have a meaning in
ISO C90, such as omitting the middle term of a @code{?:}
expression. On the other hand, when a GNU dialect of a standard is
specified, all features supported by the compiler are enabled, even when
those features change the meaning of the base standard. As a result, some
strict-conforming programs may be rejected. The particular standard
is used by @option{-Wpedantic} to identify which features are GNU
extensions given that version of the standard. For example
@option{-std=gnu90 -Wpedantic} warns about C++ style @samp{//}
comments, while @option{-std=gnu99 -Wpedantic} does not.
A value for this option must be provided; possible values are
@table @samp
@item c90
@itemx c89
@itemx iso9899:1990
Support all ISO C90 programs (certain GNU extensions that conflict
with ISO C90 are disabled). Same as @option{-ansi} for C code.
@item iso9899:199409
ISO C90 as modified in amendment 1.
@item c99
@itemx c9x
@itemx iso9899:1999
@itemx iso9899:199x
ISO C99. This standard is substantially completely supported, modulo
bugs and floating-point issues
(mainly but not entirely relating to optional C99 features from
Annexes F and G). See
@w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
names @samp{c9x} and @samp{iso9899:199x} are deprecated.
@item c11
@itemx c1x
@itemx iso9899:2011
ISO C11, the 2011 revision of the ISO C standard. This standard is
substantially completely supported, modulo bugs, floating-point issues
(mainly but not entirely relating to optional C11 features from
Annexes F and G) and the optional Annexes K (Bounds-checking
interfaces) and L (Analyzability). The name @samp{c1x} is deprecated.
@item gnu90
@itemx gnu89
GNU dialect of ISO C90 (including some C99 features).
@item gnu99
@itemx gnu9x
GNU dialect of ISO C99. The name @samp{gnu9x} is deprecated.
@item gnu11
@itemx gnu1x
GNU dialect of ISO C11. This is the default for C code.
The name @samp{gnu1x} is deprecated.
@item c++98
@itemx c++03
The 1998 ISO C++ standard plus the 2003 technical corrigendum and some
additional defect reports. Same as @option{-ansi} for C++ code.
@item gnu++98
@itemx gnu++03
GNU dialect of @option{-std=c++98}.
@item c++11
@itemx c++0x
The 2011 ISO C++ standard plus amendments.
The name @samp{c++0x} is deprecated.
@item gnu++11
@itemx gnu++0x
GNU dialect of @option{-std=c++11}.
The name @samp{gnu++0x} is deprecated.
@item c++14
@itemx c++1y
The 2014 ISO C++ standard plus amendments.
The name @samp{c++1y} is deprecated.
@item gnu++14
@itemx gnu++1y
GNU dialect of @option{-std=c++14}.
This is the default for C++ code.
The name @samp{gnu++1y} is deprecated.
@item c++1z
The next revision of the ISO C++ standard, tentatively planned for
2017. Support is highly experimental, and will almost certainly
change in incompatible ways in future releases.
@item gnu++1z
GNU dialect of @option{-std=c++1z}. Support is highly experimental,
and will almost certainly change in incompatible ways in future
releases.
@end table
@item -fgnu89-inline
@opindex fgnu89-inline
The option @option{-fgnu89-inline} tells GCC to use the traditional
GNU semantics for @code{inline} functions when in C99 mode.
@xref{Inline,,An Inline Function is As Fast As a Macro}.
Using this option is roughly equivalent to adding the
@code{gnu_inline} function attribute to all inline functions
(@pxref{Function Attributes}).
The option @option{-fno-gnu89-inline} explicitly tells GCC to use the
C99 semantics for @code{inline} when in C99 or gnu99 mode (i.e., it
specifies the default behavior).
This option is not supported in @option{-std=c90} or
@option{-std=gnu90} mode.
The preprocessor macros @code{__GNUC_GNU_INLINE__} and
@code{__GNUC_STDC_INLINE__} may be used to check which semantics are
in effect for @code{inline} functions. @xref{Common Predefined
Macros,,,cpp,The C Preprocessor}.
@item -fpermitted-flt-eval-methods=@var{style}
@opindex fpermitted-flt-eval-methods
@opindex fpermitted-flt-eval-methods=c11
@opindex fpermitted-flt-eval-methods=ts-18661-3
ISO/IEC TS 18661-3 defines new permissible values for
@code{FLT_EVAL_METHOD} that indicate that operations and constants with
a semantic type that is an interchange or extended format should be
evaluated to the precision and range of that type. These new values are
a superset of those permitted under C99/C11, which does not specify the
meaning of other positive values of @code{FLT_EVAL_METHOD}. As such, code
conforming to C11 may not have been written expecting the possibility of
the new values.
@option{-fpermitted-flt-eval-methods} specifies whether the compiler
should allow only the values of @code{FLT_EVAL_METHOD} specified in C99/C11,
or the extended set of values specified in ISO/IEC TS 18661-3.
@var{style} is either @code{c11} or @code{ts-18661-3} as appropriate.
The default when in a standards compliant mode (@option{-std=c11} or similar)
is @option{-fpermitted-flt-eval-methods=c11}. The default when in a GNU
dialect (@option{-std=gnu11} or similar) is
@option{-fpermitted-flt-eval-methods=ts-18661-3}.
@item -aux-info @var{filename}
@opindex aux-info
Output to the given filename prototyped declarations for all functions
declared and/or defined in a translation unit, including those in header
files. This option is silently ignored in any language other than C@.
Besides declarations, the file indicates, in comments, the origin of
each declaration (source file and line), whether the declaration was
implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
@samp{O} for old, respectively, in the first character after the line
number and the colon), and whether it came from a declaration or a
definition (@samp{C} or @samp{F}, respectively, in the following
character). In the case of function definitions, a K&R-style list of
arguments followed by their declarations is also provided, inside
comments, after the declaration.
@item -fallow-parameterless-variadic-functions
@opindex fallow-parameterless-variadic-functions
Accept variadic functions without named parameters.
Although it is possible to define such a function, this is not very
useful as it is not possible to read the arguments. This is only
supported for C as this construct is allowed by C++.
@item -fno-asm
@opindex fno-asm
Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
keyword, so that code can use these words as identifiers. You can use
the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
instead. @option{-ansi} implies @option{-fno-asm}.
In C++, this switch only affects the @code{typeof} keyword, since
@code{asm} and @code{inline} are standard keywords. You may want to
use the @option{-fno-gnu-keywords} flag instead, which has the same
effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
switch only affects the @code{asm} and @code{typeof} keywords, since
@code{inline} is a standard keyword in ISO C99.
@item -fno-builtin
@itemx -fno-builtin-@var{function}
@opindex fno-builtin
@cindex built-in functions
Don't recognize built-in functions that do not begin with
@samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
functions provided by GCC}, for details of the functions affected,
including those which are not built-in functions when @option{-ansi} or
@option{-std} options for strict ISO C conformance are used because they
do not have an ISO standard meaning.
GCC normally generates special code to handle certain built-in functions
more efficiently; for instance, calls to @code{alloca} may become single
instructions which adjust the stack directly, and calls to @code{memcpy}
may become inline copy loops. The resulting code is often both smaller
and faster, but since the function calls no longer appear as such, you
cannot set a breakpoint on those calls, nor can you change the behavior
of the functions by linking with a different library. In addition,
when a function is recognized as a built-in function, GCC may use
information about that function to warn about problems with calls to
that function, or to generate more efficient code, even if the
resulting code still contains calls to that function. For example,
warnings are given with @option{-Wformat} for bad calls to
@code{printf} when @code{printf} is built in and @code{strlen} is
known not to modify global memory.
With the @option{-fno-builtin-@var{function}} option
only the built-in function @var{function} is
disabled. @var{function} must not begin with @samp{__builtin_}. If a
function is named that is not built-in in this version of GCC, this
option is ignored. There is no corresponding
@option{-fbuiltin-@var{function}} option; if you wish to enable
built-in functions selectively when using @option{-fno-builtin} or
@option{-ffreestanding}, you may define macros such as:
@smallexample
#define abs(n) __builtin_abs ((n))
#define strcpy(d, s) __builtin_strcpy ((d), (s))
@end smallexample
@item -fgimple
@opindex fgimple
Enable parsing of function definitions marked with @code{__GIMPLE}.
This is an experimental feature that allows unit testing of GIMPLE
passes.
@item -fhosted
@opindex fhosted
@cindex hosted environment
Assert that compilation targets a hosted environment. This implies
@option{-fbuiltin}. A hosted environment is one in which the
entire standard library is available, and in which @code{main} has a return
type of @code{int}. Examples are nearly everything except a kernel.
This is equivalent to @option{-fno-freestanding}.
@item -ffreestanding
@opindex ffreestanding
@cindex hosted environment
Assert that compilation targets a freestanding environment. This
implies @option{-fno-builtin}. A freestanding environment
is one in which the standard library may not exist, and program startup may
not necessarily be at @code{main}. The most obvious example is an OS kernel.
This is equivalent to @option{-fno-hosted}.
@xref{Standards,,Language Standards Supported by GCC}, for details of
freestanding and hosted environments.
@item -fopenacc
@opindex fopenacc
@cindex OpenACC accelerator programming
Enable handling of OpenACC directives @code{#pragma acc} in C/C++ and
@code{!$acc} in Fortran. When @option{-fopenacc} is specified, the
compiler generates accelerated code according to the OpenACC Application
Programming Interface v2.0 @w{@uref{http://www.openacc.org/}}. This option
implies @option{-pthread}, and thus is only supported on targets that
have support for @option{-pthread}.
@item -fopenacc-dim=@var{geom}
@opindex fopenacc-dim
@cindex OpenACC accelerator programming
Specify default compute dimensions for parallel offload regions that do
not explicitly specify. The @var{geom} value is a triple of
':'-separated sizes, in order 'gang', 'worker' and, 'vector'. A size
can be omitted, to use a target-specific default value.
@item -fopenmp
@opindex fopenmp
@cindex OpenMP parallel
Enable handling of OpenMP directives @code{#pragma omp} in C/C++ and
@code{!$omp} in Fortran. When @option{-fopenmp} is specified, the
compiler generates parallel code according to the OpenMP Application
Program Interface v4.5 @w{@uref{http://www.openmp.org/}}. This option
implies @option{-pthread}, and thus is only supported on targets that
have support for @option{-pthread}. @option{-fopenmp} implies
@option{-fopenmp-simd}.
@item -fopenmp-simd
@opindex fopenmp-simd
@cindex OpenMP SIMD
@cindex SIMD
Enable handling of OpenMP's SIMD directives with @code{#pragma omp}
in C/C++ and @code{!$omp} in Fortran. Other OpenMP directives
are ignored.
@item -fcilkplus
@opindex fcilkplus
@cindex Enable Cilk Plus
Enable the usage of Cilk Plus language extension features for C/C++.
When the option @option{-fcilkplus} is specified, enable the usage of
the Cilk Plus Language extension features for C/C++. The present
implementation follows ABI version 1.2. This is an experimental
feature that is only partially complete, and whose interface may
change in future versions of GCC as the official specification
changes. Currently, all features but @code{_Cilk_for} have been
implemented.
@item -fgnu-tm
@opindex fgnu-tm
When the option @option{-fgnu-tm} is specified, the compiler
generates code for the Linux variant of Intel's current Transactional
Memory ABI specification document (Revision 1.1, May 6 2009). This is
an experimental feature whose interface may change in future versions
of GCC, as the official specification changes. Please note that not
all architectures are supported for this feature.
For more information on GCC's support for transactional memory,
@xref{Enabling libitm,,The GNU Transactional Memory Library,libitm,GNU
Transactional Memory Library}.
Note that the transactional memory feature is not supported with
non-call exceptions (@option{-fnon-call-exceptions}).
@item -fms-extensions
@opindex fms-extensions
Accept some non-standard constructs used in Microsoft header files.
In C++ code, this allows member names in structures to be similar
to previous types declarations.
@smallexample
typedef int UOW;
struct ABC @{
UOW UOW;
@};
@end smallexample
Some cases of unnamed fields in structures and unions are only
accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union
fields within structs/unions}, for details.
Note that this option is off for all targets but x86
targets using ms-abi.
@item -fplan9-extensions
@opindex fplan9-extensions
Accept some non-standard constructs used in Plan 9 code.
This enables @option{-fms-extensions}, permits passing pointers to
structures with anonymous fields to functions that expect pointers to
elements of the type of the field, and permits referring to anonymous
fields declared using a typedef. @xref{Unnamed Fields,,Unnamed
struct/union fields within structs/unions}, for details. This is only
supported for C, not C++.
@item -fcond-mismatch
@opindex fcond-mismatch
Allow conditional expressions with mismatched types in the second and
third arguments. The value of such an expression is void. This option
is not supported for C++.
@item -flax-vector-conversions
@opindex flax-vector-conversions
Allow implicit conversions between vectors with differing numbers of
elements and/or incompatible element types. This option should not be
used for new code.
@item -funsigned-char
@opindex funsigned-char
Let the type @code{char} be unsigned, like @code{unsigned char}.
Each kind of machine has a default for what @code{char} should
be. It is either like @code{unsigned char} by default or like
@code{signed char} by default.
Ideally, a portable program should always use @code{signed char} or
@code{unsigned char} when it depends on the signedness of an object.
But many programs have been written to use plain @code{char} and
expect it to be signed, or expect it to be unsigned, depending on the
machines they were written for. This option, and its inverse, let you
make such a program work with the opposite default.
The type @code{char} is always a distinct type from each of
@code{signed char} or @code{unsigned char}, even though its behavior
is always just like one of those two.
@item -fsigned-char
@opindex fsigned-char
Let the type @code{char} be signed, like @code{signed char}.
Note that this is equivalent to @option{-fno-unsigned-char}, which is
the negative form of @option{-funsigned-char}. Likewise, the option
@option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
@item -fsigned-bitfields
@itemx -funsigned-bitfields
@itemx -fno-signed-bitfields
@itemx -fno-unsigned-bitfields
@opindex fsigned-bitfields
@opindex funsigned-bitfields
@opindex fno-signed-bitfields
@opindex fno-unsigned-bitfields
These options control whether a bit-field is signed or unsigned, when the
declaration does not use either @code{signed} or @code{unsigned}. By
default, such a bit-field is signed, because this is consistent: the
basic integer types such as @code{int} are signed types.
@item -fsso-struct=@var{endianness}
@opindex fsso-struct
Set the default scalar storage order of structures and unions to the
specified endianness. The accepted values are @samp{big-endian},
@samp{little-endian} and @samp{native} for the native endianness of
the target (the default). This option is not supported for C++.
@strong{Warning:} the @option{-fsso-struct} switch causes GCC to generate
code that is not binary compatible with code generated without it if the
specified endianness is not the native endianness of the target.
@end table
@node C++ Dialect Options
@section Options Controlling C++ Dialect
@cindex compiler options, C++
@cindex C++ options, command-line
@cindex options, C++
This section describes the command-line options that are only meaningful
for C++ programs. You can also use most of the GNU compiler options
regardless of what language your program is in. For example, you
might compile a file @file{firstClass.C} like this:
@smallexample
g++ -g -fstrict-enums -O -c firstClass.C
@end smallexample
@noindent
In this example, only @option{-fstrict-enums} is an option meant
only for C++ programs; you can use the other options with any
language supported by GCC@.
Some options for compiling C programs, such as @option{-std}, are also
relevant for C++ programs.
@xref{C Dialect Options,,Options Controlling C Dialect}.
Here is a list of options that are @emph{only} for compiling C++ programs:
@table @gcctabopt
@item -fabi-version=@var{n}
@opindex fabi-version
Use version @var{n} of the C++ ABI@. The default is version 0.
Version 0 refers to the version conforming most closely to
the C++ ABI specification. Therefore, the ABI obtained using version 0
will change in different versions of G++ as ABI bugs are fixed.
Version 1 is the version of the C++ ABI that first appeared in G++ 3.2.
Version 2 is the version of the C++ ABI that first appeared in G++
3.4, and was the default through G++ 4.9.
Version 3 corrects an error in mangling a constant address as a
template argument.
Version 4, which first appeared in G++ 4.5, implements a standard
mangling for vector types.
Version 5, which first appeared in G++ 4.6, corrects the mangling of
attribute const/volatile on function pointer types, decltype of a
plain decl, and use of a function parameter in the declaration of
another parameter.
Version 6, which first appeared in G++ 4.7, corrects the promotion
behavior of C++11 scoped enums and the mangling of template argument
packs, const/static_cast, prefix ++ and --, and a class scope function
used as a template argument.
Version 7, which first appeared in G++ 4.8, that treats nullptr_t as a
builtin type and corrects the mangling of lambdas in default argument
scope.
Version 8, which first appeared in G++ 4.9, corrects the substitution
behavior of function types with function-cv-qualifiers.
Version 9, which first appeared in G++ 5.2, corrects the alignment of
@code{nullptr_t}.
Version 10, which first appeared in G++ 6.1, adds mangling of
attributes that affect type identity, such as ia32 calling convention
attributes (e.g. @samp{stdcall}).
Version 11, which first appeared in G++ 7, corrects the mangling of
sizeof... expressions and operator names. For multiple entities with
the same name within a function, that are declared in different scopes,
the mangling now changes starting with the twelfth occurrence. It also
implies @option{-fnew-inheriting-ctors}.
See also @option{-Wabi}.
@item -fabi-compat-version=@var{n}
@opindex fabi-compat-version
On targets that support strong aliases, G++
works around mangling changes by creating an alias with the correct
mangled name when defining a symbol with an incorrect mangled name.
This switch specifies which ABI version to use for the alias.
With @option{-fabi-version=0} (the default), this defaults to 8 (GCC 5
compatibility). If another ABI version is explicitly selected, this
defaults to 0. For compatibility with GCC versions 3.2 through 4.9,
use @option{-fabi-compat-version=2}.
If this option is not provided but @option{-Wabi=@var{n}} is, that
version is used for compatibility aliases. If this option is provided
along with @option{-Wabi} (without the version), the version from this
option is used for the warning.
@item -fno-access-control
@opindex fno-access-control
Turn off all access checking. This switch is mainly useful for working
around bugs in the access control code.
@item -faligned-new
@opindex faligned-new
Enable support for C++17 @code{new} of types that require more
alignment than @code{void* ::operator new(std::size_t)} provides. A
numeric argument such as @code{-faligned-new=32} can be used to
specify how much alignment (in bytes) is provided by that function,
but few users will need to override the default of
@code{alignof(std::max_align_t)}.
@item -fcheck-new
@opindex fcheck-new
Check that the pointer returned by @code{operator new} is non-null
before attempting to modify the storage allocated. This check is
normally unnecessary because the C++ standard specifies that
@code{operator new} only returns @code{0} if it is declared
@code{throw()}, in which case the compiler always checks the
return value even without this option. In all other cases, when
@code{operator new} has a non-empty exception specification, memory
exhaustion is signalled by throwing @code{std::bad_alloc}. See also
@samp{new (nothrow)}.
@item -fconcepts
@opindex fconcepts
Enable support for the C++ Extensions for Concepts Technical
Specification, ISO 19217 (2015), which allows code like
@smallexample
template <class T> concept bool Addable = requires (T t) @{ t + t; @};
template <Addable T> T add (T a, T b) @{ return a + b; @}
@end smallexample
@item -fconstexpr-depth=@var{n}
@opindex fconstexpr-depth
Set the maximum nested evaluation depth for C++11 constexpr functions
to @var{n}. A limit is needed to detect endless recursion during
constant expression evaluation. The minimum specified by the standard
is 512.
@item -fconstexpr-loop-limit=@var{n}
@opindex fconstexpr-loop-limit
Set the maximum number of iterations for a loop in C++14 constexpr functions
to @var{n}. A limit is needed to detect infinite loops during
constant expression evaluation. The default is 262144 (1<<18).
@item -fdeduce-init-list
@opindex fdeduce-init-list
Enable deduction of a template type parameter as
@code{std::initializer_list} from a brace-enclosed initializer list, i.e.@:
@smallexample
template <class T> auto forward(T t) -> decltype (realfn (t))
@{
return realfn (t);
@}
void f()
@{
forward(@{1,2@}); // call forward<std::initializer_list<int>>
@}
@end smallexample
This deduction was implemented as a possible extension to the
originally proposed semantics for the C++11 standard, but was not part
of the final standard, so it is disabled by default. This option is
deprecated, and may be removed in a future version of G++.
@item -ffriend-injection
@opindex ffriend-injection
Inject friend functions into the enclosing namespace, so that they are
visible outside the scope of the class in which they are declared.
Friend functions were documented to work this way in the old Annotated
C++ Reference Manual.
However, in ISO C++ a friend function that is not declared
in an enclosing scope can only be found using argument dependent
lookup. GCC defaults to the standard behavior.
This option is for compatibility, and may be removed in a future
release of G++.
@item -fno-elide-constructors
@opindex fno-elide-constructors
The C++ standard allows an implementation to omit creating a temporary
that is only used to initialize another object of the same type.
Specifying this option disables that optimization, and forces G++ to
call the copy constructor in all cases. This option also causes G++
to call trivial member functions which otherwise would be expanded inline.
In C++17, the compiler is required to omit these temporaries, but this
option still affects trivial member functions.
@item -fno-enforce-eh-specs
@opindex fno-enforce-eh-specs
Don't generate code to check for violation of exception specifications
at run time. This option violates the C++ standard, but may be useful
for reducing code size in production builds, much like defining
@code{NDEBUG}. This does not give user code permission to throw
exceptions in violation of the exception specifications; the compiler
still optimizes based on the specifications, so throwing an
unexpected exception results in undefined behavior at run time.
@item -fextern-tls-init
@itemx -fno-extern-tls-init
@opindex fextern-tls-init
@opindex fno-extern-tls-init
The C++11 and OpenMP standards allow @code{thread_local} and
@code{threadprivate} variables to have dynamic (runtime)
initialization. To support this, any use of such a variable goes
through a wrapper function that performs any necessary initialization.
When the use and definition of the variable are in the same
translation unit, this overhead can be optimized away, but when the
use is in a different translation unit there is significant overhead
even if the variable doesn't actually need dynamic initialization. If
the programmer can be sure that no use of the variable in a
non-defining TU needs to trigger dynamic initialization (either
because the variable is statically initialized, or a use of the
variable in the defining TU will be executed before any uses in
another TU), they can avoid this overhead with the
@option{-fno-extern-tls-init} option.
On targets that support symbol aliases, the default is
@option{-fextern-tls-init}. On targets that do not support symbol
aliases, the default is @option{-fno-extern-tls-init}.
@item -ffor-scope
@itemx -fno-for-scope
@opindex ffor-scope
@opindex fno-for-scope
If @option{-ffor-scope} is specified, the scope of variables declared in
a @i{for-init-statement} is limited to the @code{for} loop itself,
as specified by the C++ standard.
If @option{-fno-for-scope} is specified, the scope of variables declared in
a @i{for-init-statement} extends to the end of the enclosing scope,
as was the case in old versions of G++, and other (traditional)
implementations of C++.
If neither flag is given, the default is to follow the standard,
but to allow and give a warning for old-style code that would
otherwise be invalid, or have different behavior.
@item -fno-gnu-keywords
@opindex fno-gnu-keywords
Do not recognize @code{typeof} as a keyword, so that code can use this
word as an identifier. You can use the keyword @code{__typeof__} instead.
This option is implied by the strict ISO C++ dialects: @option{-ansi},
@option{-std=c++98}, @option{-std=c++11}, etc.
@item -fno-implicit-templates
@opindex fno-implicit-templates
Never emit code for non-inline templates that are instantiated
implicitly (i.e.@: by use); only emit code for explicit instantiations.
@xref{Template Instantiation}, for more information.
@item -fno-implicit-inline-templates
@opindex fno-implicit-inline-templates
Don't emit code for implicit instantiations of inline templates, either.
The default is to handle inlines differently so that compiles with and
without optimization need the same set of explicit instantiations.
@item -fno-implement-inlines
@opindex fno-implement-inlines
To save space, do not emit out-of-line copies of inline functions
controlled by @code{#pragma implementation}. This causes linker
errors if these functions are not inlined everywhere they are called.
@item -fms-extensions
@opindex fms-extensions
Disable Wpedantic warnings about constructs used in MFC, such as implicit
int and getting a pointer to member function via non-standard syntax.
@item -fnew-inheriting-ctors
@opindex fnew-inheriting-ctors
Enable the P0136 adjustment to the semantics of C++11 constructor
inheritance. This is part of C++17 but also considered to be a Defect
Report against C++11 and C++14. This flag is enabled by default
unless @option{-fabi-version=10} or lower is specified.
@item -fnew-ttp-matching
@opindex fnew-ttp-matching
Enable the P0522 resolution to Core issue 150, template template
parameters and default arguments: this allows a template with default
template arguments as an argument for a template template parameter
with fewer template parameters. This flag is enabled by default for
@option{-std=c++1z}.
@item -fno-nonansi-builtins
@opindex fno-nonansi-builtins
Disable built-in declarations of functions that are not mandated by
ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
@code{index}, @code{bzero}, @code{conjf}, and other related functions.
@item -fnothrow-opt
@opindex fnothrow-opt
Treat a @code{throw()} exception specification as if it were a
@code{noexcept} specification to reduce or eliminate the text size
overhead relative to a function with no exception specification. If
the function has local variables of types with non-trivial
destructors, the exception specification actually makes the
function smaller because the EH cleanups for those variables can be
optimized away. The semantic effect is that an exception thrown out of
a function with such an exception specification results in a call
to @code{terminate} rather than @code{unexpected}.
@item -fno-operator-names
@opindex fno-operator-names
Do not treat the operator name keywords @code{and}, @code{bitand},
@code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
synonyms as keywords.
@item -fno-optional-diags
@opindex fno-optional-diags
Disable diagnostics that the standard says a compiler does not need to
issue. Currently, the only such diagnostic issued by G++ is the one for
a name having multiple meanings within a class.
@item -fpermissive
@opindex fpermissive
Downgrade some diagnostics about nonconformant code from errors to
warnings. Thus, using @option{-fpermissive} allows some
nonconforming code to compile.
@item -fno-pretty-templates
@opindex fno-pretty-templates
When an error message refers to a specialization of a function
template, the compiler normally prints the signature of the
template followed by the template arguments and any typedefs or
typenames in the signature (e.g. @code{void f(T) [with T = int]}
rather than @code{void f(int)}) so that it's clear which template is
involved. When an error message refers to a specialization of a class
template, the compiler omits any template arguments that match
the default template arguments for that template. If either of these
behaviors make it harder to understand the error message rather than
easier, you can use @option{-fno-pretty-templates} to disable them.
@item -frepo
@opindex frepo
Enable automatic template instantiation at link time. This option also
implies @option{-fno-implicit-templates}. @xref{Template
Instantiation}, for more information.
@item -fno-rtti
@opindex fno-rtti
Disable generation of information about every class with virtual
functions for use by the C++ run-time type identification features
(@code{dynamic_cast} and @code{typeid}). If you don't use those parts
of the language, you can save some space by using this flag. Note that
exception handling uses the same information, but G++ generates it as
needed. The @code{dynamic_cast} operator can still be used for casts that
do not require run-time type information, i.e.@: casts to @code{void *} or to
unambiguous base classes.
@item -fsized-deallocation
@opindex fsized-deallocation
Enable the built-in global declarations
@smallexample
void operator delete (void *, std::size_t) noexcept;
void operator delete[] (void *, std::size_t) noexcept;
@end smallexample
as introduced in C++14. This is useful for user-defined replacement
deallocation functions that, for example, use the size of the object
to make deallocation faster. Enabled by default under
@option{-std=c++14} and above. The flag @option{-Wsized-deallocation}
warns about places that might want to add a definition.
@item -fstrict-enums
@opindex fstrict-enums
Allow the compiler to optimize using the assumption that a value of
enumerated type can only be one of the values of the enumeration (as
defined in the C++ standard; basically, a value that can be
represented in the minimum number of bits needed to represent all the
enumerators). This assumption may not be valid if the program uses a
cast to convert an arbitrary integer value to the enumerated type.
@item -fstrong-eval-order
@opindex fstrong-eval-order
Evaluate member access, array subscripting, and shift expressions in
left-to-right order, and evaluate assignment in right-to-left order,
as adopted for C++17. Enabled by default with @option{-std=c++1z}.
@option{-fstrong-eval-order=some} enables just the ordering of member
access and shift expressions, and is the default without
@option{-std=c++1z}.
@item -ftemplate-backtrace-limit=@var{n}
@opindex ftemplate-backtrace-limit
Set the maximum number of template instantiation notes for a single
warning or error to @var{n}. The default value is 10.
@item -ftemplate-depth=@var{n}
@opindex ftemplate-depth
Set the maximum instantiation depth for template classes to @var{n}.
A limit on the template instantiation depth is needed to detect
endless recursions during template class instantiation. ANSI/ISO C++
conforming programs must not rely on a maximum depth greater than 17
(changed to 1024 in C++11). The default value is 900, as the compiler
can run out of stack space before hitting 1024 in some situations.
@item -fno-threadsafe-statics
@opindex fno-threadsafe-statics
Do not emit the extra code to use the routines specified in the C++
ABI for thread-safe initialization of local statics. You can use this
option to reduce code size slightly in code that doesn't need to be
thread-safe.
@item -fuse-cxa-atexit
@opindex fuse-cxa-atexit
Register destructors for objects with static storage duration with the
@code{__cxa_atexit} function rather than the @code{atexit} function.
This option is required for fully standards-compliant handling of static
destructors, but only works if your C library supports
@code{__cxa_atexit}.
@item -fno-use-cxa-get-exception-ptr
@opindex fno-use-cxa-get-exception-ptr
Don't use the @code{__cxa_get_exception_ptr} runtime routine. This
causes @code{std::uncaught_exception} to be incorrect, but is necessary
if the runtime routine is not available.
@item -fvisibility-inlines-hidden
@opindex fvisibility-inlines-hidden
This switch declares that the user does not attempt to compare
pointers to inline functions or methods where the addresses of the two functions
are taken in different shared objects.
The effect of this is that GCC may, effectively, mark inline methods with
@code{__attribute__ ((visibility ("hidden")))} so that they do not
appear in the export table of a DSO and do not require a PLT indirection
when used within the DSO@. Enabling this option can have a dramatic effect
on load and link times of a DSO as it massively reduces the size of the
dynamic export table when the library makes heavy use of templates.
The behavior of this switch is not quite the same as marking the
methods as hidden directly, because it does not affect static variables
local to the function or cause the compiler to deduce that
the function is defined in only one shared object.
You may mark a method as having a visibility explicitly to negate the
effect of the switch for that method. For example, if you do want to
compare pointers to a particular inline method, you might mark it as
having default visibility. Marking the enclosing class with explicit
visibility has no effect.
Explicitly instantiated inline methods are unaffected by this option
as their linkage might otherwise cross a shared library boundary.
@xref{Template Instantiation}.
@item -fvisibility-ms-compat
@opindex fvisibility-ms-compat
This flag attempts to use visibility settings to make GCC's C++
linkage model compatible with that of Microsoft Visual Studio.
The flag makes these changes to GCC's linkage model:
@enumerate
@item
It sets the default visibility to @code{hidden}, like
@option{-fvisibility=hidden}.
@item
Types, but not their members, are not hidden by default.
@item
The One Definition Rule is relaxed for types without explicit
visibility specifications that are defined in more than one
shared object: those declarations are permitted if they are
permitted when this option is not used.
@end enumerate
In new code it is better to use @option{-fvisibility=hidden} and
export those classes that are intended to be externally visible.
Unfortunately it is possible for code to rely, perhaps accidentally,
on the Visual Studio behavior.
Among the consequences of these changes are that static data members
of the same type with the same name but defined in different shared
objects are different, so changing one does not change the other;
and that pointers to function members defined in different shared
objects may not compare equal. When this flag is given, it is a
violation of the ODR to define types with the same name differently.
@item -fno-weak
@opindex fno-weak
Do not use weak symbol support, even if it is provided by the linker.
By default, G++ uses weak symbols if they are available. This
option exists only for testing, and should not be used by end-users;
it results in inferior code and has no benefits. This option may
be removed in a future release of G++.
@item -nostdinc++
@opindex nostdinc++
Do not search for header files in the standard directories specific to
C++, but do still search the other standard directories. (This option
is used when building the C++ library.)
@end table
In addition, these optimization, warning, and code generation options
have meanings only for C++ programs:
@table @gcctabopt
@item -Wabi @r{(C, Objective-C, C++ and Objective-C++ only)}
@opindex Wabi
@opindex Wno-abi
Warn when G++ it generates code that is probably not compatible with
the vendor-neutral C++ ABI@. Since G++ now defaults to updating the
ABI with each major release, normally @option{-Wabi} will warn only if
there is a check added later in a release series for an ABI issue
discovered since the initial release. @option{-Wabi} will warn about
more things if an older ABI version is selected (with
@option{-fabi-version=@var{n}}).
@option{-Wabi} can also be used with an explicit version number to
warn about compatibility with a particular @option{-fabi-version}
level, e.g. @option{-Wabi=2} to warn about changes relative to
@option{-fabi-version=2}.
If an explicit version number is provided and
@option{-fabi-compat-version} is not specified, the version number
from this option is used for compatibility aliases. If no explicit
version number is provided with this option, but
@option{-fabi-compat-version} is specified, that version number is
used for ABI warnings.
Although an effort has been made to warn about
all such cases, there are probably some cases that are not warned about,
even though G++ is generating incompatible code. There may also be
cases where warnings are emitted even though the code that is generated
is compatible.
You should rewrite your code to avoid these warnings if you are
concerned about the fact that code generated by G++ may not be binary
compatible with code generated by other compilers.
Known incompatibilities in @option{-fabi-version=2} (which was the
default from GCC 3.4 to 4.9) include:
@itemize @bullet
@item
A template with a non-type template parameter of reference type was
mangled incorrectly:
@smallexample
extern int N;
template <int &> struct S @{@};
void n (S<N>) @{2@}
@end smallexample
This was fixed in @option{-fabi-version=3}.
@item
SIMD vector types declared using @code{__attribute ((vector_size))} were
mangled in a non-standard way that does not allow for overloading of
functions taking vectors of different sizes.
The mangling was changed in @option{-fabi-version=4}.
@item
@code{__attribute ((const))} and @code{noreturn} were mangled as type
qualifiers, and @code{decltype} of a plain declaration was folded away.
These mangling issues were fixed in @option{-fabi-version=5}.
@item
Scoped enumerators passed as arguments to a variadic function are
promoted like unscoped enumerators, causing @code{va_arg} to complain.
On most targets this does not actually affect the parameter passing
ABI, as there is no way to pass an argument smaller than @code{int}.
Also, the ABI changed the mangling of template argument packs,
@code{const_cast}, @code{static_cast}, prefix increment/decrement, and
a class scope function used as a template argument.
These issues were corrected in @option{-fabi-version=6}.
@item
Lambdas in default argument scope were mangled incorrectly, and the
ABI changed the mangling of @code{nullptr_t}.
These issues were corrected in @option{-fabi-version=7}.
@item
When mangling a function type with function-cv-qualifiers, the
un-qualified function type was incorrectly treated as a substitution
candidate.
This was fixed in @option{-fabi-version=8}, the default for GCC 5.1.
@item
@code{decltype(nullptr)} incorrectly had an alignment of 1, leading to
unaligned accesses. Note that this did not affect the ABI of a
function with a @code{nullptr_t} parameter, as parameters have a
minimum alignment.
This was fixed in @option{-fabi-version=9}, the default for GCC 5.2.
@item
Target-specific attributes that affect the identity of a type, such as
ia32 calling conventions on a function type (stdcall, regparm, etc.),
did not affect the mangled name, leading to name collisions when
function pointers were used as template arguments.
This was fixed in @option{-fabi-version=10}, the default for GCC 6.1.
@end itemize
It also warns about psABI-related changes. The known psABI changes at this
point include:
@itemize @bullet
@item
For SysV/x86-64, unions with @code{long double} members are
passed in memory as specified in psABI. For example:
@smallexample
union U @{
long double ld;
int i;
@};
@end smallexample
@noindent
@code{union U} is always passed in memory.
@end itemize
@item -Wabi-tag @r{(C++ and Objective-C++ only)}
@opindex Wabi-tag
@opindex -Wabi-tag
Warn when a type with an ABI tag is used in a context that does not
have that ABI tag. See @ref{C++ Attributes} for more information
about ABI tags.
@item -Wctor-dtor-privacy @r{(C++ and Objective-C++ only)}
@opindex Wctor-dtor-privacy
@opindex Wno-ctor-dtor-privacy
Warn when a class seems unusable because all the constructors or
destructors in that class are private, and it has neither friends nor
public static member functions. Also warn if there are no non-private
methods, and there's at least one private member function that isn't
a constructor or destructor.
@item -Wdelete-non-virtual-dtor @r{(C++ and Objective-C++ only)}
@opindex Wdelete-non-virtual-dtor
@opindex Wno-delete-non-virtual-dtor
Warn when @code{delete} is used to destroy an instance of a class that
has virtual functions and non-virtual destructor. It is unsafe to delete
an instance of a derived class through a pointer to a base class if the
base class does not have a virtual destructor. This warning is enabled
by @option{-Wall}.
@item -Wliteral-suffix @r{(C++ and Objective-C++ only)}
@opindex Wliteral-suffix
@opindex Wno-literal-suffix
Warn when a string or character literal is followed by a ud-suffix which does
not begin with an underscore. As a conforming extension, GCC treats such
suffixes as separate preprocessing tokens in order to maintain backwards
compatibility with code that uses formatting macros from @code{<inttypes.h>}.
For example:
@smallexample
#define __STDC_FORMAT_MACROS
#include <inttypes.h>
#include <stdio.h>
int main() @{
int64_t i64 = 123;
printf("My int64: %" PRId64"\n", i64);
@}
@end smallexample
In this case, @code{PRId64} is treated as a separate preprocessing token.
Additionally, warn when a user-defined literal operator is declared with
a literal suffix identifier that doesn't begin with an underscore. Literal
suffix identifiers that don't begin with an underscore are reserved for
future standardization.
This warning is enabled by default.
@item -Wlto-type-mismatch
@opindex Wlto-type-mismatch
@opindex Wno-lto-type-mismatch
During the link-time optimization warn about type mismatches in
global declarations from different compilation units.
Requires @option{-flto} to be enabled. Enabled by default.
@item -Wno-narrowing @r{(C++ and Objective-C++ only)}
@opindex Wnarrowing
@opindex Wno-narrowing
For C++11 and later standards, narrowing conversions are diagnosed by default,
as required by the standard. A narrowing conversion from a constant produces
an error, and a narrowing conversion from a non-constant produces a warning,
but @option{-Wno-narrowing} suppresses the diagnostic.
Note that this does not affect the meaning of well-formed code;
narrowing conversions are still considered ill-formed in SFINAE contexts.
With @option{-Wnarrowing} in C++98, warn when a narrowing
conversion prohibited by C++11 occurs within
@samp{@{ @}}, e.g.
@smallexample
int i = @{ 2.2 @}; // error: narrowing from double to int
@end smallexample
This flag is included in @option{-Wall} and @option{-Wc++11-compat}.
@item -Wnoexcept @r{(C++ and Objective-C++ only)}
@opindex Wnoexcept
@opindex Wno-noexcept
Warn when a noexcept-expression evaluates to false because of a call
to a function that does not have a non-throwing exception
specification (i.e. @code{throw()} or @code{noexcept}) but is known by
the compiler to never throw an exception.
@item -Wnoexcept-type @r{(C++ and Objective-C++ only)}
@opindex Wnoexcept-type
@opindex Wno-noexcept-type
Warn if the C++1z feature making @code{noexcept} part of a function
type changes the mangled name of a symbol relative to C++14. Enabled
by @option{-Wabi} and @option{-Wc++1z-compat}.
@smallexample
template <class T> void f(T t) @{ t(); @};
void g() noexcept;
void h() @{ f(g); @} // in C++14 calls f<void(*)()>, in C++1z calls f<void(*)()noexcept>
@end smallexample
@item -Wnon-virtual-dtor @r{(C++ and Objective-C++ only)}
@opindex Wnon-virtual-dtor
@opindex Wno-non-virtual-dtor
Warn when a class has virtual functions and an accessible non-virtual
destructor itself or in an accessible polymorphic base class, in which
case it is possible but unsafe to delete an instance of a derived
class through a pointer to the class itself or base class. This
warning is automatically enabled if @option{-Weffc++} is specified.
@item -Wregister @r{(C++ and Objective-C++ only)}
@opindex Wregister
@opindex Wno-register
Warn on uses of the @code{register} storage class specifier, except
when it is part of the GNU @ref{Explicit Register Variables} extension.
The use of the @code{register} keyword as storage class specifier has
been deprecated in C++11 and removed in C++17.
Enabled by default with @option{-std=c++1z}.
@item -Wreorder @r{(C++ and Objective-C++ only)}
@opindex Wreorder
@opindex Wno-reorder
@cindex reordering, warning
@cindex warning for reordering of member initializers
Warn when the order of member initializers given in the code does not
match the order in which they must be executed. For instance:
@smallexample
struct A @{
int i;
int j;
A(): j (0), i (1) @{ @}
@};
@end smallexample
@noindent
The compiler rearranges the member initializers for @code{i}
and @code{j} to match the declaration order of the members, emitting
a warning to that effect. This warning is enabled by @option{-Wall}.
@item -fext-numeric-literals @r{(C++ and Objective-C++ only)}
@opindex fext-numeric-literals
@opindex fno-ext-numeric-literals
Accept imaginary, fixed-point, or machine-defined
literal number suffixes as GNU extensions.
When this option is turned off these suffixes are treated
as C++11 user-defined literal numeric suffixes.
This is on by default for all pre-C++11 dialects and all GNU dialects:
@option{-std=c++98}, @option{-std=gnu++98}, @option{-std=gnu++11},
@option{-std=gnu++14}.
This option is off by default
for ISO C++11 onwards (@option{-std=c++11}, ...).
@end table
The following @option{-W@dots{}} options are not affected by @option{-Wall}.
@table @gcctabopt
@item -Weffc++ @r{(C++ and Objective-C++ only)}
@opindex Weffc++
@opindex Wno-effc++
Warn about violations of the following style guidelines from Scott Meyers'
@cite{Effective C++} series of books:
@itemize @bullet
@item
Define a copy constructor and an assignment operator for classes
with dynamically-allocated memory.
@item
Prefer initialization to assignment in constructors.
@item
Have @code{operator=} return a reference to @code{*this}.
@item
Don't try to return a reference when you must return an object.
@item
Distinguish between prefix and postfix forms of increment and
decrement operators.
@item
Never overload @code{&&}, @code{||}, or @code{,}.
@end itemize
This option also enables @option{-Wnon-virtual-dtor}, which is also
one of the effective C++ recommendations. However, the check is
extended to warn about the lack of virtual destructor in accessible
non-polymorphic bases classes too.
When selecting this option, be aware that the standard library
headers do not obey all of these guidelines; use @samp{grep -v}
to filter out those warnings.
@item -Wstrict-null-sentinel @r{(C++ and Objective-C++ only)}
@opindex Wstrict-null-sentinel
@opindex Wno-strict-null-sentinel
Warn about the use of an uncasted @code{NULL} as sentinel. When
compiling only with GCC this is a valid sentinel, as @code{NULL} is defined
to @code{__null}. Although it is a null pointer constant rather than a
null pointer, it is guaranteed to be of the same size as a pointer.
But this use is not portable across different compilers.
@item -Wno-non-template-friend @r{(C++ and Objective-C++ only)}
@opindex Wno-non-template-friend
@opindex Wnon-template-friend
Disable warnings when non-template friend functions are declared
within a template. In very old versions of GCC that predate implementation
of the ISO standard, declarations such as
@samp{friend int foo(int)}, where the name of the friend is an unqualified-id,
could be interpreted as a particular specialization of a template
function; the warning exists to diagnose compatibility problems,
and is enabled by default.
@item -Wold-style-cast @r{(C++ and Objective-C++ only)}
@opindex Wold-style-cast
@opindex Wno-old-style-cast
Warn if an old-style (C-style) cast to a non-void type is used within
a C++ program. The new-style casts (@code{dynamic_cast},
@code{static_cast}, @code{reinterpret_cast}, and @code{const_cast}) are
less vulnerable to unintended effects and much easier to search for.
@item -Woverloaded-virtual @r{(C++ and Objective-C++ only)}
@opindex Woverloaded-virtual
@opindex Wno-overloaded-virtual
@cindex overloaded virtual function, warning
@cindex warning for overloaded virtual function
Warn when a function declaration hides virtual functions from a
base class. For example, in:
@smallexample
struct A @{
virtual void f();
@};
struct B: public A @{
void f(int);
@};
@end smallexample
the @code{A} class version of @code{f} is hidden in @code{B}, and code
like:
@smallexample
B* b;
b->f();
@end smallexample
@noindent
fails to compile.
@item -Wno-pmf-conversions @r{(C++ and Objective-C++ only)}
@opindex Wno-pmf-conversions
@opindex Wpmf-conversions
Disable the diagnostic for converting a bound pointer to member function
to a plain pointer.
@item -Wsign-promo @r{(C++ and Objective-C++ only)}
@opindex Wsign-promo
@opindex Wno-sign-promo
Warn when overload resolution chooses a promotion from unsigned or
enumerated type to a signed type, over a conversion to an unsigned type of
the same size. Previous versions of G++ tried to preserve
unsignedness, but the standard mandates the current behavior.
@item -Wtemplates @r{(C++ and Objective-C++ only)}
@opindex Wtemplates
Warn when a primary template declaration is encountered. Some coding
rules disallow templates, and this may be used to enforce that rule.
The warning is inactive inside a system header file, such as the STL, so
one can still use the STL. One may also instantiate or specialize
templates.
@item -Wmultiple-inheritance @r{(C++ and Objective-C++ only)}
@opindex Wmultiple-inheritance
Warn when a class is defined with multiple direct base classes. Some
coding rules disallow multiple inheritance, and this may be used to
enforce that rule. The warning is inactive inside a system header file,
such as the STL, so one can still use the STL. One may also define
classes that indirectly use multiple inheritance.
@item -Wvirtual-inheritance
@opindex Wvirtual-inheritance
Warn when a class is defined with a virtual direct base class. Some
coding rules disallow multiple inheritance, and this may be used to
enforce that rule. The warning is inactive inside a system header file,
such as the STL, so one can still use the STL. One may also define
classes that indirectly use virtual inheritance.
@item -Wnamespaces
@opindex Wnamespaces
Warn when a namespace definition is opened. Some coding rules disallow
namespaces, and this may be used to enforce that rule. The warning is
inactive inside a system header file, such as the STL, so one can still
use the STL. One may also use using directives and qualified names.
@item -Wno-terminate @r{(C++ and Objective-C++ only)}
@opindex Wterminate
@opindex Wno-terminate
Disable the warning about a throw-expression that will immediately
result in a call to @code{terminate}.
@end table
@node Objective-C and Objective-C++ Dialect Options
@section Options Controlling Objective-C and Objective-C++ Dialects
@cindex compiler options, Objective-C and Objective-C++
@cindex Objective-C and Objective-C++ options, command-line
@cindex options, Objective-C and Objective-C++
(NOTE: This manual does not describe the Objective-C and Objective-C++
languages themselves. @xref{Standards,,Language Standards
Supported by GCC}, for references.)
This section describes the command-line options that are only meaningful
for Objective-C and Objective-C++ programs. You can also use most of
the language-independent GNU compiler options.
For example, you might compile a file @file{some_class.m} like this:
@smallexample
gcc -g -fgnu-runtime -O -c some_class.m
@end smallexample
@noindent
In this example, @option{-fgnu-runtime} is an option meant only for
Objective-C and Objective-C++ programs; you can use the other options with
any language supported by GCC@.
Note that since Objective-C is an extension of the C language, Objective-C
compilations may also use options specific to the C front-end (e.g.,
@option{-Wtraditional}). Similarly, Objective-C++ compilations may use
C++-specific options (e.g., @option{-Wabi}).
Here is a list of options that are @emph{only} for compiling Objective-C
and Objective-C++ programs:
@table @gcctabopt
@item -fconstant-string-class=@var{class-name}
@opindex fconstant-string-class
Use @var{class-name} as the name of the class to instantiate for each
literal string specified with the syntax @code{@@"@dots{}"}. The default
class name is @code{NXConstantString} if the GNU runtime is being used, and
@code{NSConstantString} if the NeXT runtime is being used (see below). The
@option{-fconstant-cfstrings} option, if also present, overrides the
@option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals
to be laid out as constant CoreFoundation strings.
@item -fgnu-runtime
@opindex fgnu-runtime
Generate object code compatible with the standard GNU Objective-C
runtime. This is the default for most types of systems.
@item -fnext-runtime
@opindex fnext-runtime
Generate output compatible with the NeXT runtime. This is the default
for NeXT-based systems, including Darwin and Mac OS X@. The macro
@code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
used.
@item -fno-nil-receivers
@opindex fno-nil-receivers
Assume that all Objective-C message dispatches (@code{[receiver
message:arg]}) in this translation unit ensure that the receiver is
not @code{nil}. This allows for more efficient entry points in the
runtime to be used. This option is only available in conjunction with
the NeXT runtime and ABI version 0 or 1.
@item -fobjc-abi-version=@var{n}
@opindex fobjc-abi-version
Use version @var{n} of the Objective-C ABI for the selected runtime.
This option is currently supported only for the NeXT runtime. In that
case, Version 0 is the traditional (32-bit) ABI without support for
properties and other Objective-C 2.0 additions. Version 1 is the
traditional (32-bit) ABI with support for properties and other
Objective-C 2.0 additions. Version 2 is the modern (64-bit) ABI. If
nothing is specified, the default is Version 0 on 32-bit target
machines, and Version 2 on 64-bit target machines.
@item -fobjc-call-cxx-cdtors
@opindex fobjc-call-cxx-cdtors
For each Objective-C class, check if any of its instance variables is a
C++ object with a non-trivial default constructor. If so, synthesize a
special @code{- (id) .cxx_construct} instance method which runs
non-trivial default constructors on any such instance variables, in order,
and then return @code{self}. Similarly, check if any instance variable
is a C++ object with a non-trivial destructor, and if so, synthesize a
special @code{- (void) .cxx_destruct} method which runs
all such default destructors, in reverse order.
The @code{- (id) .cxx_construct} and @code{- (void) .cxx_destruct}
methods thusly generated only operate on instance variables
declared in the current Objective-C class, and not those inherited
from superclasses. It is the responsibility of the Objective-C
runtime to invoke all such methods in an object's inheritance
hierarchy. The @code{- (id) .cxx_construct} methods are invoked
by the runtime immediately after a new object instance is allocated;
the @code{- (void) .cxx_destruct} methods are invoked immediately
before the runtime deallocates an object instance.
As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has
support for invoking the @code{- (id) .cxx_construct} and
@code{- (void) .cxx_destruct} methods.
@item -fobjc-direct-dispatch
@opindex fobjc-direct-dispatch
Allow fast jumps to the message dispatcher. On Darwin this is
accomplished via the comm page.
@item -fobjc-exceptions
@opindex fobjc-exceptions
Enable syntactic support for structured exception handling in
Objective-C, similar to what is offered by C++. This option
is required to use the Objective-C keywords @code{@@try},
@code{@@throw}, @code{@@catch}, @code{@@finally} and
@code{@@synchronized}. This option is available with both the GNU
runtime and the NeXT runtime (but not available in conjunction with
the NeXT runtime on Mac OS X 10.2 and earlier).
@item -fobjc-gc
@opindex fobjc-gc
Enable garbage collection (GC) in Objective-C and Objective-C++
programs. This option is only available with the NeXT runtime; the
GNU runtime has a different garbage collection implementation that
does not require special compiler flags.
@item -fobjc-nilcheck
@opindex fobjc-nilcheck
For the NeXT runtime with version 2 of the ABI, check for a nil
receiver in method invocations before doing the actual method call.
This is the default and can be disabled using
@option{-fno-objc-nilcheck}. Class methods and super calls are never
checked for nil in this way no matter what this flag is set to.
Currently this flag does nothing when the GNU runtime, or an older
version of the NeXT runtime ABI, is used.
@item -fobjc-std=objc1
@opindex fobjc-std
Conform to the language syntax of Objective-C 1.0, the language
recognized by GCC 4.0. This only affects the Objective-C additions to
the C/C++ language; it does not affect conformance to C/C++ standards,
which is controlled by the separate C/C++ dialect option flags. When
this option is used with the Objective-C or Objective-C++ compiler,
any Objective-C syntax that is not recognized by GCC 4.0 is rejected.
This is useful if you need to make sure that your Objective-C code can
be compiled with older versions of GCC@.
@item -freplace-objc-classes
@opindex freplace-objc-classes
Emit a special marker instructing @command{ld(1)} not to statically link in
the resulting object file, and allow @command{dyld(1)} to load it in at
run time instead. This is used in conjunction with the Fix-and-Continue
debugging mode, where the object file in question may be recompiled and
dynamically reloaded in the course of program execution, without the need
to restart the program itself. Currently, Fix-and-Continue functionality
is only available in conjunction with the NeXT runtime on Mac OS X 10.3
and later.
@item -fzero-link
@opindex fzero-link
When compiling for the NeXT runtime, the compiler ordinarily replaces calls
to @code{objc_getClass("@dots{}")} (when the name of the class is known at
compile time) with static class references that get initialized at load time,
which improves run-time performance. Specifying the @option{-fzero-link} flag
suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")}
to be retained. This is useful in Zero-Link debugging mode, since it allows
for individual class implementations to be modified during program execution.
The GNU runtime currently always retains calls to @code{objc_get_class("@dots{}")}
regardless of command-line options.
@item -fno-local-ivars
@opindex fno-local-ivars
@opindex flocal-ivars
By default instance variables in Objective-C can be accessed as if
they were local variables from within the methods of the class they're
declared in. This can lead to shadowing between instance variables
and other variables declared either locally inside a class method or
globally with the same name. Specifying the @option{-fno-local-ivars}
flag disables this behavior thus avoiding variable shadowing issues.
@item -fivar-visibility=@r{[}public@r{|}protected@r{|}private@r{|}package@r{]}
@opindex fivar-visibility
Set the default instance variable visibility to the specified option
so that instance variables declared outside the scope of any access
modifier directives default to the specified visibility.
@item -gen-decls
@opindex gen-decls
Dump interface declarations for all classes seen in the source file to a
file named @file{@var{sourcename}.decl}.
@item -Wassign-intercept @r{(Objective-C and Objective-C++ only)}
@opindex Wassign-intercept
@opindex Wno-assign-intercept
Warn whenever an Objective-C assignment is being intercepted by the
garbage collector.
@item -Wno-protocol @r{(Objective-C and Objective-C++ only)}
@opindex Wno-protocol
@opindex Wprotocol
If a class is declared to implement a protocol, a warning is issued for
every method in the protocol that is not implemented by the class. The
default behavior is to issue a warning for every method not explicitly
implemented in the class, even if a method implementation is inherited
from the superclass. If you use the @option{-Wno-protocol} option, then
methods inherited from the superclass are considered to be implemented,
and no warning is issued for them.
@item -Wselector @r{(Objective-C and Objective-C++ only)}
@opindex Wselector
@opindex Wno-selector
Warn if multiple methods of different types for the same selector are
found during compilation. The check is performed on the list of methods
in the final stage of compilation. Additionally, a check is performed
for each selector appearing in a @code{@@selector(@dots{})}
expression, and a corresponding method for that selector has been found
during compilation. Because these checks scan the method table only at
the end of compilation, these warnings are not produced if the final
stage of compilation is not reached, for example because an error is
found during compilation, or because the @option{-fsyntax-only} option is
being used.
@item -Wstrict-selector-match @r{(Objective-C and Objective-C++ only)}
@opindex Wstrict-selector-match
@opindex Wno-strict-selector-match
Warn if multiple methods with differing argument and/or return types are
found for a given selector when attempting to send a message using this
selector to a receiver of type @code{id} or @code{Class}. When this flag
is off (which is the default behavior), the compiler omits such warnings
if any differences found are confined to types that share the same size
and alignment.
@item -Wundeclared-selector @r{(Objective-C and Objective-C++ only)}
@opindex Wundeclared-selector
@opindex Wno-undeclared-selector
Warn if a @code{@@selector(@dots{})} expression referring to an
undeclared selector is found. A selector is considered undeclared if no
method with that name has been declared before the
@code{@@selector(@dots{})} expression, either explicitly in an
@code{@@interface} or @code{@@protocol} declaration, or implicitly in
an @code{@@implementation} section. This option always performs its
checks as soon as a @code{@@selector(@dots{})} expression is found,
while @option{-Wselector} only performs its checks in the final stage of
compilation. This also enforces the coding style convention
that methods and selectors must be declared before being used.
@item -print-objc-runtime-info
@opindex print-objc-runtime-info
Generate C header describing the largest structure that is passed by
value, if any.
@end table
@node Diagnostic Message Formatting Options
@section Options to Control Diagnostic Messages Formatting
@cindex options to control diagnostics formatting
@cindex diagnostic messages
@cindex message formatting
Traditionally, diagnostic messages have been formatted irrespective of
the output device's aspect (e.g.@: its width, @dots{}). You can use the
options described below
to control the formatting algorithm for diagnostic messages,
e.g.@: how many characters per line, how often source location
information should be reported. Note that some language front ends may not
honor these options.
@table @gcctabopt
@item -fmessage-length=@var{n}
@opindex fmessage-length
Try to format error messages so that they fit on lines of about
@var{n} characters. If @var{n} is zero, then no line-wrapping is
done; each error message appears on a single line. This is the
default for all front ends.
@item -fdiagnostics-show-location=once
@opindex fdiagnostics-show-location
Only meaningful in line-wrapping mode. Instructs the diagnostic messages
reporter to emit source location information @emph{once}; that is, in
case the message is too long to fit on a single physical line and has to
be wrapped, the source location won't be emitted (as prefix) again,
over and over, in subsequent continuation lines. This is the default
behavior.
@item -fdiagnostics-show-location=every-line
Only meaningful in line-wrapping mode. Instructs the diagnostic
messages reporter to emit the same source location information (as
prefix) for physical lines that result from the process of breaking
a message which is too long to fit on a single line.
@item -fdiagnostics-color[=@var{WHEN}]
@itemx -fno-diagnostics-color
@opindex fdiagnostics-color
@cindex highlight, color
@vindex GCC_COLORS @r{environment variable}
Use color in diagnostics. @var{WHEN} is @samp{never}, @samp{always},
or @samp{auto}. The default depends on how the compiler has been configured,
it can be any of the above @var{WHEN} options or also @samp{never}
if @env{GCC_COLORS} environment variable isn't present in the environment,
and @samp{auto} otherwise.
@samp{auto} means to use color only when the standard error is a terminal.
The forms @option{-fdiagnostics-color} and @option{-fno-diagnostics-color} are
aliases for @option{-fdiagnostics-color=always} and
@option{-fdiagnostics-color=never}, respectively.
The colors are defined by the environment variable @env{GCC_COLORS}.
Its value is a colon-separated list of capabilities and Select Graphic
Rendition (SGR) substrings. SGR commands are interpreted by the
terminal or terminal emulator. (See the section in the documentation
of your text terminal for permitted values and their meanings as
character attributes.) These substring values are integers in decimal
representation and can be concatenated with semicolons.
Common values to concatenate include
@samp{1} for bold,
@samp{4} for underline,
@samp{5} for blink,
@samp{7} for inverse,
@samp{39} for default foreground color,
@samp{30} to @samp{37} for foreground colors,
@samp{90} to @samp{97} for 16-color mode foreground colors,
@samp{38;5;0} to @samp{38;5;255}
for 88-color and 256-color modes foreground colors,
@samp{49} for default background color,
@samp{40} to @samp{47} for background colors,
@samp{100} to @samp{107} for 16-color mode background colors,
and @samp{48;5;0} to @samp{48;5;255}
for 88-color and 256-color modes background colors.
The default @env{GCC_COLORS} is
@smallexample
error=01;31:warning=01;35:note=01;36:range1=32:range2=34:locus=01:\
quote=01:fixit-insert=32:fixit-delete=31:\
diff-filename=01:diff-hunk=32:diff-delete=31:diff-insert=32
@end smallexample
@noindent
where @samp{01;31} is bold red, @samp{01;35} is bold magenta,
@samp{01;36} is bold cyan, @samp{32} is green, @samp{34} is blue,
@samp{01} is bold, and @samp{31} is red.
Setting @env{GCC_COLORS} to the empty string disables colors.
Supported capabilities are as follows.
@table @code
@item error=
@vindex error GCC_COLORS @r{capability}
SGR substring for error: markers.
@item warning=
@vindex warning GCC_COLORS @r{capability}
SGR substring for warning: markers.
@item note=
@vindex note GCC_COLORS @r{capability}
SGR substring for note: markers.
@item range1=
@vindex range1 GCC_COLORS @r{capability}
SGR substring for first additional range.
@item range2=
@vindex range2 GCC_COLORS @r{capability}
SGR substring for second additional range.
@item locus=
@vindex locus GCC_COLORS @r{capability}
SGR substring for location information, @samp{file:line} or
@samp{file:line:column} etc.
@item quote=
@vindex quote GCC_COLORS @r{capability}
SGR substring for information printed within quotes.
@item fixit-insert=
@vindex fixit-insert GCC_COLORS @r{capability}
SGR substring for fix-it hints suggesting text to
be inserted or replaced.
@item fixit-delete=
@vindex fixit-delete GCC_COLORS @r{capability}
SGR substring for fix-it hints suggesting text to
be deleted.
@item diff-filename=
@vindex diff-filename GCC_COLORS @r{capability}
SGR substring for filename headers within generated patches.
@item diff-hunk=
@vindex diff-hunk GCC_COLORS @r{capability}
SGR substring for the starts of hunks within generated patches.
@item diff-delete=
@vindex diff-delete GCC_COLORS @r{capability}
SGR substring for deleted lines within generated patches.
@item diff-insert=
@vindex diff-insert GCC_COLORS @r{capability}
SGR substring for inserted lines within generated patches.
@end table
@item -fno-diagnostics-show-option
@opindex fno-diagnostics-show-option
@opindex fdiagnostics-show-option
By default, each diagnostic emitted includes text indicating the
command-line option that directly controls the diagnostic (if such an
option is known to the diagnostic machinery). Specifying the
@option{-fno-diagnostics-show-option} flag suppresses that behavior.
@item -fno-diagnostics-show-caret
@opindex fno-diagnostics-show-caret
@opindex fdiagnostics-show-caret
By default, each diagnostic emitted includes the original source line
and a caret @samp{^} indicating the column. This option suppresses this
information. The source line is truncated to @var{n} characters, if
the @option{-fmessage-length=n} option is given. When the output is done
to the terminal, the width is limited to the width given by the
@env{COLUMNS} environment variable or, if not set, to the terminal width.
@item -fdiagnostics-parseable-fixits
@opindex fdiagnostics-parseable-fixits
Emit fix-it hints in a machine-parseable format, suitable for consumption
by IDEs. For each fix-it, a line will be printed after the relevant
diagnostic, starting with the string ``fix-it:''. For example:
@smallexample
fix-it:"test.c":@{45:3-45:21@}:"gtk_widget_show_all"
@end smallexample
The location is expressed as a half-open range, expressed as a count of
bytes, starting at byte 1 for the initial column. In the above example,
bytes 3 through 20 of line 45 of ``test.c'' are to be replaced with the
given string:
@smallexample
00000000011111111112222222222
12345678901234567890123456789
gtk_widget_showall (dlg);
^^^^^^^^^^^^^^^^^^
gtk_widget_show_all
@end smallexample
The filename and replacement string escape backslash as ``\\", tab as ``\t'',
newline as ``\n'', double quotes as ``\"'', non-printable characters as octal
(e.g. vertical tab as ``\013'').
An empty replacement string indicates that the given range is to be removed.
An empty range (e.g. ``45:3-45:3'') indicates that the string is to
be inserted at the given position.
@item -fdiagnostics-generate-patch
@opindex fdiagnostics-generate-patch
Print fix-it hints to stderr in unified diff format, after any diagnostics
are printed. For example:
@smallexample
--- test.c
+++ test.c
@@ -42,5 +42,5 @@
void show_cb(GtkDialog *dlg)
@{
- gtk_widget_showall(dlg);
+ gtk_widget_show_all(dlg);
@}
@end smallexample
The diff may or may not be colorized, following the same rules
as for diagnostics (see @option{-fdiagnostics-color}).
@item -fno-show-column
@opindex fno-show-column
Do not print column numbers in diagnostics. This may be necessary if
diagnostics are being scanned by a program that does not understand the
column numbers, such as @command{dejagnu}.
@end table
@node Warning Options
@section Options to Request or Suppress Warnings
@cindex options to control warnings
@cindex warning messages
@cindex messages, warning
@cindex suppressing warnings
Warnings are diagnostic messages that report constructions that
are not inherently erroneous but that are risky or suggest there
may have been an error.
The following language-independent options do not enable specific
warnings but control the kinds of diagnostics produced by GCC@.
@table @gcctabopt
@cindex syntax checking
@item -fsyntax-only
@opindex fsyntax-only
Check the code for syntax errors, but don't do anything beyond that.
@item -fmax-errors=@var{n}
@opindex fmax-errors
Limits the maximum number of error messages to @var{n}, at which point
GCC bails out rather than attempting to continue processing the source
code. If @var{n} is 0 (the default), there is no limit on the number
of error messages produced. If @option{-Wfatal-errors} is also
specified, then @option{-Wfatal-errors} takes precedence over this
option.
@item -w
@opindex w
Inhibit all warning messages.
@item -Werror
@opindex Werror
@opindex Wno-error
Make all warnings into errors.
@item -Werror=
@opindex Werror=
@opindex Wno-error=
Make the specified warning into an error. The specifier for a warning
is appended; for example @option{-Werror=switch} turns the warnings
controlled by @option{-Wswitch} into errors. This switch takes a
negative form, to be used to negate @option{-Werror} for specific
warnings; for example @option{-Wno-error=switch} makes
@option{-Wswitch} warnings not be errors, even when @option{-Werror}
is in effect.
The warning message for each controllable warning includes the
option that controls the warning. That option can then be used with
@option{-Werror=} and @option{-Wno-error=} as described above.
(Printing of the option in the warning message can be disabled using the
@option{-fno-diagnostics-show-option} flag.)
Note that specifying @option{-Werror=}@var{foo} automatically implies
@option{-W}@var{foo}. However, @option{-Wno-error=}@var{foo} does not
imply anything.
@item -Wfatal-errors
@opindex Wfatal-errors
@opindex Wno-fatal-errors
This option causes the compiler to abort compilation on the first error
occurred rather than trying to keep going and printing further error
messages.
@end table
You can request many specific warnings with options beginning with
@samp{-W}, for example @option{-Wimplicit} to request warnings on
implicit declarations. Each of these specific warning options also
has a negative form beginning @samp{-Wno-} to turn off warnings; for
example, @option{-Wno-implicit}. This manual lists only one of the
two forms, whichever is not the default. For further
language-specific options also refer to @ref{C++ Dialect Options} and
@ref{Objective-C and Objective-C++ Dialect Options}.
Some options, such as @option{-Wall} and @option{-Wextra}, turn on other
options, such as @option{-Wunused}, which may turn on further options,
such as @option{-Wunused-value}. The combined effect of positive and
negative forms is that more specific options have priority over less
specific ones, independently of their position in the command-line. For
options of the same specificity, the last one takes effect. Options
enabled or disabled via pragmas (@pxref{Diagnostic Pragmas}) take effect
as if they appeared at the end of the command-line.
When an unrecognized warning option is requested (e.g.,
@option{-Wunknown-warning}), GCC emits a diagnostic stating
that the option is not recognized. However, if the @option{-Wno-} form
is used, the behavior is slightly different: no diagnostic is
produced for @option{-Wno-unknown-warning} unless other diagnostics
are being produced. This allows the use of new @option{-Wno-} options
with old compilers, but if something goes wrong, the compiler
warns that an unrecognized option is present.
@table @gcctabopt
@item -Wpedantic
@itemx -pedantic
@opindex pedantic
@opindex Wpedantic
Issue all the warnings demanded by strict ISO C and ISO C++;
reject all programs that use forbidden extensions, and some other
programs that do not follow ISO C and ISO C++. For ISO C, follows the
version of the ISO C standard specified by any @option{-std} option used.
Valid ISO C and ISO C++ programs should compile properly with or without
this option (though a rare few require @option{-ansi} or a
@option{-std} option specifying the required version of ISO C)@. However,
without this option, certain GNU extensions and traditional C and C++
features are supported as well. With this option, they are rejected.
@option{-Wpedantic} does not cause warning messages for use of the
alternate keywords whose names begin and end with @samp{__}. Pedantic
warnings are also disabled in the expression that follows
@code{__extension__}. However, only system header files should use
these escape routes; application programs should avoid them.
@xref{Alternate Keywords}.
Some users try to use @option{-Wpedantic} to check programs for strict ISO
C conformance. They soon find that it does not do quite what they want:
it finds some non-ISO practices, but not all---only those for which
ISO C @emph{requires} a diagnostic, and some others for which
diagnostics have been added.
A feature to report any failure to conform to ISO C might be useful in
some instances, but would require considerable additional work and would
be quite different from @option{-Wpedantic}. We don't have plans to
support such a feature in the near future.
Where the standard specified with @option{-std} represents a GNU
extended dialect of C, such as @samp{gnu90} or @samp{gnu99}, there is a
corresponding @dfn{base standard}, the version of ISO C on which the GNU
extended dialect is based. Warnings from @option{-Wpedantic} are given
where they are required by the base standard. (It does not make sense
for such warnings to be given only for features not in the specified GNU
C dialect, since by definition the GNU dialects of C include all
features the compiler supports with the given option, and there would be
nothing to warn about.)
@item -pedantic-errors
@opindex pedantic-errors
Give an error whenever the @dfn{base standard} (see @option{-Wpedantic})
requires a diagnostic, in some cases where there is undefined behavior
at compile-time and in some other cases that do not prevent compilation
of programs that are valid according to the standard. This is not
equivalent to @option{-Werror=pedantic}, since there are errors enabled
by this option and not enabled by the latter and vice versa.
@item -Wall
@opindex Wall
@opindex Wno-all
This enables all the warnings about constructions that some users
consider questionable, and that are easy to avoid (or modify to
prevent the warning), even in conjunction with macros. This also
enables some language-specific warnings described in @ref{C++ Dialect
Options} and @ref{Objective-C and Objective-C++ Dialect Options}.
@option{-Wall} turns on the following warning flags:
@gccoptlist{-Waddress @gol
-Warray-bounds=1 @r{(only with} @option{-O2}@r{)} @gol
-Wbool-compare @gol
-Wbool-operation @gol
-Wc++11-compat -Wc++14-compat @gol
-Wchar-subscripts @gol
-Wcomment @gol
-Wduplicate-decl-specifier @r{(C and Objective-C only)} @gol
-Wenum-compare @r{(in C/ObjC; this is on by default in C++)} @gol
-Wformat @gol
-Wint-in-bool-context @gol
-Wimplicit @r{(C and Objective-C only)} @gol
-Wimplicit-int @r{(C and Objective-C only)} @gol
-Wimplicit-function-declaration @r{(C and Objective-C only)} @gol
-Winit-self @r{(only for C++)} @gol
-Wlogical-not-parentheses @gol
-Wmain @r{(only for C/ObjC and unless} @option{-ffreestanding}@r{)} @gol
-Wmaybe-uninitialized @gol
-Wmemset-elt-size @gol
-Wmemset-transposed-args @gol
-Wmisleading-indentation @r{(only for C/C++)} @gol
-Wmissing-braces @r{(only for C/ObjC)} @gol
-Wnarrowing @r{(only for C++)} @gol
-Wnonnull @gol
-Wnonnull-compare @gol
-Wopenmp-simd @gol
-Wparentheses @gol
-Wpointer-sign @gol
-Wreorder @gol
-Wreturn-type @gol
-Wsequence-point @gol
-Wsign-compare @r{(only in C++)} @gol
-Wsizeof-pointer-memaccess @gol
-Wstrict-aliasing @gol
-Wstrict-overflow=1 @gol
-Wswitch @gol
-Wtautological-compare @gol
-Wtrigraphs @gol
-Wuninitialized @gol
-Wunknown-pragmas @gol
-Wunused-function @gol
-Wunused-label @gol
-Wunused-value @gol
-Wunused-variable @gol
-Wvolatile-register-var @gol
}
Note that some warning flags are not implied by @option{-Wall}. Some of
them warn about constructions that users generally do not consider
questionable, but which occasionally you might wish to check for;
others warn about constructions that are necessary or hard to avoid in
some cases, and there is no simple way to modify the code to suppress
the warning. Some of them are enabled by @option{-Wextra} but many of
them must be enabled individually.
@item -Wextra
@opindex W
@opindex Wextra
@opindex Wno-extra
This enables some extra warning flags that are not enabled by
@option{-Wall}. (This option used to be called @option{-W}. The older
name is still supported, but the newer name is more descriptive.)
@gccoptlist{-Wclobbered @gol
-Wempty-body @gol
-Wignored-qualifiers @gol
-Wimplicit-fallthrough=3 @gol
-Wmissing-field-initializers @gol
-Wmissing-parameter-type @r{(C only)} @gol
-Wold-style-declaration @r{(C only)} @gol
-Woverride-init @gol
-Wsign-compare @r{(C only)} @gol
-Wtype-limits @gol
-Wuninitialized @gol
-Wshift-negative-value @r{(in C++03 and in C99 and newer)} @gol
-Wunused-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol
-Wunused-but-set-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol
}
The option @option{-Wextra} also prints warning messages for the
following cases:
@itemize @bullet
@item
A pointer is compared against integer zero with @code{<}, @code{<=},
@code{>}, or @code{>=}.
@item
(C++ only) An enumerator and a non-enumerator both appear in a
conditional expression.
@item
(C++ only) Ambiguous virtual bases.
@item
(C++ only) Subscripting an array that has been declared @code{register}.
@item
(C++ only) Taking the address of a variable that has been declared
@code{register}.
@item
(C++ only) A base class is not initialized in the copy constructor
of a derived class.
@end itemize
@item -Wchar-subscripts
@opindex Wchar-subscripts
@opindex Wno-char-subscripts
Warn if an array subscript has type @code{char}. This is a common cause
of error, as programmers often forget that this type is signed on some
machines.
This warning is enabled by @option{-Wall}.
@item -Wchkp
@opindex Wchkp
Warn about an invalid memory access that is found by Pointer Bounds Checker
(@option{-fcheck-pointer-bounds}).
@item -Wno-coverage-mismatch
@opindex Wno-coverage-mismatch
Warn if feedback profiles do not match when using the
@option{-fprofile-use} option.
If a source file is changed between compiling with @option{-fprofile-gen} and
with @option{-fprofile-use}, the files with the profile feedback can fail
to match the source file and GCC cannot use the profile feedback
information. By default, this warning is enabled and is treated as an
error. @option{-Wno-coverage-mismatch} can be used to disable the
warning or @option{-Wno-error=coverage-mismatch} can be used to
disable the error. Disabling the error for this warning can result in
poorly optimized code and is useful only in the
case of very minor changes such as bug fixes to an existing code-base.
Completely disabling the warning is not recommended.
@item -Wno-cpp
@r{(C, Objective-C, C++, Objective-C++ and Fortran only)}
Suppress warning messages emitted by @code{#warning} directives.
@item -Wdouble-promotion @r{(C, C++, Objective-C and Objective-C++ only)}
@opindex Wdouble-promotion
@opindex Wno-double-promotion
Give a warning when a value of type @code{float} is implicitly
promoted to @code{double}. CPUs with a 32-bit ``single-precision''
floating-point unit implement @code{float} in hardware, but emulate
@code{double} in software. On such a machine, doing computations
using @code{double} values is much more expensive because of the
overhead required for software emulation.
It is easy to accidentally do computations with @code{double} because
floating-point literals are implicitly of type @code{double}. For
example, in:
@smallexample
@group
float area(float radius)
@{
return 3.14159 * radius * radius;
@}
@end group
@end smallexample
the compiler performs the entire computation with @code{double}
because the floating-point literal is a @code{double}.
@item -Wduplicate-decl-specifier @r{(C and Objective-C only)}
@opindex Wduplicate-decl-specifier
@opindex Wno-duplicate-decl-specifier
Warn if a declaration has duplicate @code{const}, @code{volatile},
@code{restrict} or @code{_Atomic} specifier. This warning is enabled by
@option{-Wall}.
@item -Wformat
@itemx -Wformat=@var{n}
@opindex Wformat
@opindex Wno-format
@opindex ffreestanding
@opindex fno-builtin
@opindex Wformat=
Check calls to @code{printf} and @code{scanf}, etc., to make sure that
the arguments supplied have types appropriate to the format string
specified, and that the conversions specified in the format string make
sense. This includes standard functions, and others specified by format
attributes (@pxref{Function Attributes}), in the @code{printf},
@code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
not in the C standard) families (or other target-specific families).
Which functions are checked without format attributes having been
specified depends on the standard version selected, and such checks of
functions without the attribute specified are disabled by
@option{-ffreestanding} or @option{-fno-builtin}.
The formats are checked against the format features supported by GNU
libc version 2.2. These include all ISO C90 and C99 features, as well
as features from the Single Unix Specification and some BSD and GNU
extensions. Other library implementations may not support all these
features; GCC does not support warning about features that go beyond a
particular library's limitations. However, if @option{-Wpedantic} is used
with @option{-Wformat}, warnings are given about format features not
in the selected standard version (but not for @code{strfmon} formats,
since those are not in any version of the C standard). @xref{C Dialect
Options,,Options Controlling C Dialect}.
@table @gcctabopt
@item -Wformat=1
@itemx -Wformat
@opindex Wformat
@opindex Wformat=1
Option @option{-Wformat} is equivalent to @option{-Wformat=1}, and
@option{-Wno-format} is equivalent to @option{-Wformat=0}. Since
@option{-Wformat} also checks for null format arguments for several
functions, @option{-Wformat} also implies @option{-Wnonnull}. Some
aspects of this level of format checking can be disabled by the
options: @option{-Wno-format-contains-nul},
@option{-Wno-format-extra-args}, and @option{-Wno-format-zero-length}.
@option{-Wformat} is enabled by @option{-Wall}.
@item -Wno-format-contains-nul
@opindex Wno-format-contains-nul
@opindex Wformat-contains-nul
If @option{-Wformat} is specified, do not warn about format strings that
contain NUL bytes.
@item -Wno-format-extra-args
@opindex Wno-format-extra-args
@opindex Wformat-extra-args
If @option{-Wformat} is specified, do not warn about excess arguments to a
@code{printf} or @code{scanf} format function. The C standard specifies
that such arguments are ignored.
Where the unused arguments lie between used arguments that are
specified with @samp{$} operand number specifications, normally
warnings are still given, since the implementation could not know what
type to pass to @code{va_arg} to skip the unused arguments. However,
in the case of @code{scanf} formats, this option suppresses the
warning if the unused arguments are all pointers, since the Single
Unix Specification says that such unused arguments are allowed.
@item -Wformat-overflow
@itemx -Wformat-overflow=@var{level}
@opindex Wformat-overflow
@opindex Wno-format-overflow
Warn about calls to formatted input/output functions such as @code{sprintf}
and @code{vsprintf} that might overflow the destination buffer. When the
exact number of bytes written by a format directive cannot be determined
at compile-time it is estimated based on heuristics that depend on the
@var{level} argument and on optimization. While enabling optimization
will in most cases improve the accuracy of the warning, it may also
result in false positives.
@table @gcctabopt
@item -Wformat-overflow
@item -Wformat-overflow=1
@opindex Wformat-overflow
@opindex Wno-format-overflow
Level @var{1} of @option{-Wformat-overflow} enabled by @option{-Wformat}
employs a conservative approach that warns only about calls that most
likely overflow the buffer. At this level, numeric arguments to format
directives with unknown values are assumed to have the value of one, and
strings of unknown length to be empty. Numeric arguments that are known
to be bounded to a subrange of their type, or string arguments whose output
is bounded either by their directive's precision or by a finite set of
string literals, are assumed to take on the value within the range that
results in the most bytes on output. For example, the call to @code{sprintf}
below is diagnosed because even with both @var{a} and @var{b} equal to zero,
the terminating NUL character (@code{'\0'}) appended by the function
to the destination buffer will be written past its end. Increasing
the size of the buffer by a single byte is sufficient to avoid the
warning, though it may not be sufficient to avoid the overflow.
@smallexample
void f (int a, int b)
@{
char buf [12];
sprintf (buf, "a = %i, b = %i\n", a, b);
@}
@end smallexample
@item -Wformat-overflow=2
Level @var{2} warns also about calls that might overflow the destination
buffer given an argument of sufficient length or magnitude. At level
@var{2}, unknown numeric arguments are assumed to have the minimum
representable value for signed types with a precision greater than 1, and
the maximum representable value otherwise. Unknown string arguments whose
length cannot be assumed to be bounded either by the directive's precision,
or by a finite set of string literals they may evaluate to, or the character
array they may point to, are assumed to be 1 character long.
At level @var{2}, the call in the example above is again diagnosed, but
this time because with @var{a} equal to a 32-bit @code{INT_MIN} the first
@code{%i} directive will write some of its digits beyond the end of
the destination buffer. To make the call safe regardless of the values
of the two variables, the size of the destination buffer must be increased
to at least 34 bytes. GCC includes the minimum size of the buffer in
an informational note following the warning.
An alternative to increasing the size of the destination buffer is to
constrain the range of formatted values. The maximum length of string
arguments can be bounded by specifying the precision in the format
directive. When numeric arguments of format directives can be assumed
to be bounded by less than the precision of their type, choosing
an appropriate length modifier to the format specifier will reduce
the required buffer size. For example, if @var{a} and @var{b} in the
example above can be assumed to be within the precision of
the @code{short int} type then using either the @code{%hi} format
directive or casting the argument to @code{short} reduces the maximum
required size of the buffer to 24 bytes.
@smallexample
void f (int a, int b)
@{
char buf [23];
sprintf (buf, "a = %hi, b = %i\n", a, (short)b);
@}
@end smallexample
@end table
@item -Wno-format-zero-length
@opindex Wno-format-zero-length
@opindex Wformat-zero-length
If @option{-Wformat} is specified, do not warn about zero-length formats.
The C standard specifies that zero-length formats are allowed.
@item -Wformat=2
@opindex Wformat=2
Enable @option{-Wformat} plus additional format checks. Currently
equivalent to @option{-Wformat -Wformat-nonliteral -Wformat-security
-Wformat-y2k}.
@item -Wformat-nonliteral
@opindex Wformat-nonliteral
@opindex Wno-format-nonliteral
If @option{-Wformat} is specified, also warn if the format string is not a
string literal and so cannot be checked, unless the format function
takes its format arguments as a @code{va_list}.
@item -Wformat-security
@opindex Wformat-security
@opindex Wno-format-security
If @option{-Wformat} is specified, also warn about uses of format
functions that represent possible security problems. At present, this
warns about calls to @code{printf} and @code{scanf} functions where the
format string is not a string literal and there are no format arguments,
as in @code{printf (foo);}. This may be a security hole if the format
string came from untrusted input and contains @samp{%n}. (This is
currently a subset of what @option{-Wformat-nonliteral} warns about, but
in future warnings may be added to @option{-Wformat-security} that are not
included in @option{-Wformat-nonliteral}.)
@item -Wformat-signedness
@opindex Wformat-signedness
@opindex Wno-format-signedness
If @option{-Wformat} is specified, also warn if the format string
requires an unsigned argument and the argument is signed and vice versa.
@item -Wformat-truncation
@itemx -Wformat-truncation=@var{level}
@opindex Wformat-truncation
@opindex Wno-format-truncation
Warn about calls to formatted input/output functions such as @code{snprintf}
and @code{vsnprintf} that might result in output truncation. When the exact
number of bytes written by a format directive cannot be determined at
compile-time it is estimated based on heuristics that depend on
the @var{level} argument and on optimization. While enabling optimization
will in most cases improve the accuracy of the warning, it may also result
in false positives. Except as noted otherwise, the option uses the same
logic @option{-Wformat-overflow}.
@table @gcctabopt
@item -Wformat-truncation
@item -Wformat-truncation=1
@opindex Wformat-truncation
@opindex Wno-format-overflow
Level @var{1} of @option{-Wformat-truncation} enabled by @option{-Wformat}
employs a conservative approach that warns only about calls to bounded
functions whose return value is unused and that will most likely result
in output truncation.
@item -Wformat-truncation=2
Level @var{2} warns also about calls to bounded functions whose return
value is used and that might result in truncation given an argument of
sufficient length or magnitude.
@end table
@item -Wformat-y2k
@opindex Wformat-y2k
@opindex Wno-format-y2k
If @option{-Wformat} is specified, also warn about @code{strftime}
formats that may yield only a two-digit year.
@end table
@item -Wnonnull
@opindex Wnonnull
@opindex Wno-nonnull
Warn about passing a null pointer for arguments marked as
requiring a non-null value by the @code{nonnull} function attribute.
@option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
can be disabled with the @option{-Wno-nonnull} option.
@item -Wnonnull-compare
@opindex Wnonnull-compare
@opindex Wno-nonnull-compare
Warn when comparing an argument marked with the @code{nonnull}
function attribute against null inside the function.
@option{-Wnonnull-compare} is included in @option{-Wall}. It
can be disabled with the @option{-Wno-nonnull-compare} option.
@item -Wnull-dereference
@opindex Wnull-dereference
@opindex Wno-null-dereference
Warn if the compiler detects paths that trigger erroneous or
undefined behavior due to dereferencing a null pointer. This option
is only active when @option{-fdelete-null-pointer-checks} is active,
which is enabled by optimizations in most targets. The precision of
the warnings depends on the optimization options used.
@item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)}
@opindex Winit-self
@opindex Wno-init-self
Warn about uninitialized variables that are initialized with themselves.
Note this option can only be used with the @option{-Wuninitialized} option.
For example, GCC warns about @code{i} being uninitialized in the
following snippet only when @option{-Winit-self} has been specified:
@smallexample
@group
int f()
@{
int i = i;
return i;
@}