blob: 9ce33606a69d778f305c50f84844d48957824266 [file] [log] [blame]
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Always turn off hyphenation; it makes .\" way too many mistakes in technical documents. .if n .ad l .nh .SH "NAME" gcc \- GNU project C and C++ compiler .SH "SYNOPSIS" .IX Header "SYNOPSIS" gcc [\fB\-c\fR|\fB\-S\fR|\fB\-E\fR] [\fB\-std=\fR\fIstandard\fR] [\fB\-g\fR] [\fB\-pg\fR] [\fB\-O\fR\fIlevel\fR] [\fB\-W\fR\fIwarn\fR...] [\fB\-Wpedantic\fR] [\fB\-I\fR\fIdir\fR...] [\fB\-L\fR\fIdir\fR...] [\fB\-D\fR\fImacro\fR[=\fIdefn\fR]...] [\fB\-U\fR\fImacro\fR] [\fB\-f\fR\fIoption\fR...] [\fB\-m\fR\fImachine-option\fR...] [\fB\-o\fR \fIoutfile\fR] [@\fIfile\fR] \fIinfile\fR... .PP Only the most useful options are listed here; see below for the remainder. \fBg++\fR accepts mostly the same options as \fBgcc\fR. .SH "DESCRIPTION" .IX Header "DESCRIPTION" When you invoke \s-1GCC,\s0 it normally does preprocessing, compilation, assembly and linking. The \*(L"overall options\*(R" allow you to stop this process at an intermediate stage. For example, the \fB\-c\fR option says not to run the linker. Then the output consists of object files output by the assembler. .PP Other options are passed on to one stage 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. .PP Most of the command-line options that you can use with \s-1GCC\s0 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. .PP The \fBgcc\fR program accepts options and file names as operands. Many options have multi-letter names; therefore multiple single-letter options may \fInot\fR be grouped: \fB\-dv\fR is very different from \fB\-d\ \-v\fR. .PP 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 \fB\-L\fR more than once, the directories are searched in the order specified. Also, the placement of the \fB\-l\fR option is significant. .PP Many options have long names starting with \fB\-f\fR or with \&\fB\-W\fR\-\-\-for example, \&\fB\-fmove\-loop\-invariants\fR, \fB\-Wformat\fR and so on. Most of these have both positive and negative forms; the negative form of \&\fB\-ffoo\fR is \fB\-fno\-foo\fR. This manual documents only one of these two forms, whichever one is not the default. .SH "OPTIONS" .IX Header "OPTIONS" .SS "Option Summary" .IX Subsection "Option Summary" Here is a summary of all the options, grouped by type. Explanations are in the following sections. .IP "\fIOverall Options\fR" 4 .IX Item "Overall Options" \&\fB\-c \-S \-E \-o\fR \fIfile\fR \fB\-no\-canonical\-prefixes \&\-pipe \-pass\-exit\-codes \&\-x\fR \fIlanguage\fR \fB\-v \-### \-\-help\fR[\fB=\fR\fIclass\fR[\fB,...\fR]] \fB\-\-target\-help \&\-\-version \-wrapper @\fR\fIfile\fR \fB\-fplugin=\fR\fIfile\fR \fB\-fplugin\-arg\-\fR\fIname\fR\fB=\fR\fIarg\fR \&\fB\-fdump\-ada\-spec\fR[\fB\-slim\fR] \fB\-fada\-spec\-parent=\fR\fIunit\fR \fB\-fdump\-go\-spec=\fR\fIfile\fR .IP "\fIC Language Options\fR" 4 .IX Item "C Language Options" \&\fB\-ansi \-std=\fR\fIstandard\fR \fB\-fgnu89\-inline \&\-aux\-info\fR \fIfilename\fR \fB\-fallow\-parameterless\-variadic\-functions \&\-fno\-asm \-fno\-builtin \-fno\-builtin\-\fR\fIfunction\fR \&\fB\-fhosted \-ffreestanding \-fopenacc \-fopenmp \-fopenmp\-simd \&\-fms\-extensions \-fplan9\-extensions \-trigraphs \-traditional \-traditional\-cpp \&\-fallow\-single\-precision \-fcond\-mismatch \-flax\-vector\-conversions \&\-fsigned\-bitfields \-fsigned\-char \&\-funsigned\-bitfields \-funsigned\-char\fR .IP "\fI\*(C+ Language Options\fR" 4 .IX Item " Language Options" \&\fB\-fabi\-version=\fR\fIn\fR \fB\-fno\-access\-control \-fcheck\-new \&\-fconstexpr\-depth=\fR\fIn\fR \fB\-ffriend\-injection \&\-fno\-elide\-constructors \&\-fno\-enforce\-eh\-specs \&\-ffor\-scope \-fno\-for\-scope \-fno\-gnu\-keywords \&\-fno\-implicit\-templates \&\-fno\-implicit\-inline\-templates \&\-fno\-implement\-inlines \-fms\-extensions \&\-fno\-nonansi\-builtins \-fnothrow\-opt \-fno\-operator\-names \&\-fno\-optional\-diags \-fpermissive \&\-fno\-pretty\-templates \&\-frepo \-fno\-rtti \-fsized\-deallocation \&\-fstats \-ftemplate\-backtrace\-limit=\fR\fIn\fR \&\fB\-ftemplate\-depth=\fR\fIn\fR \&\fB\-fno\-threadsafe\-statics \-fuse\-cxa\-atexit \&\-fno\-weak \-nostdinc++ \&\-fvisibility\-inlines\-hidden \&\-fvtable\-verify=\fR[\fBstd\fR|\fBpreinit\fR|\fBnone\fR] \&\fB\-fvtv\-counts \-fvtv\-debug \&\-fvisibility\-ms\-compat \&\-fext\-numeric\-literals \&\-Wabi=\fR\fIn\fR \fB\-Wabi\-tag \-Wconversion\-null \-Wctor\-dtor\-privacy \&\-Wdelete\-non\-virtual\-dtor \-Wliteral\-suffix \-Wnarrowing \&\-Wnoexcept \-Wnon\-virtual\-dtor \-Wreorder \&\-Weffc++ \-Wstrict\-null\-sentinel \&\-Wno\-non\-template\-friend \-Wold\-style\-cast \&\-Woverloaded\-virtual \-Wno\-pmf\-conversions \&\-Wsign\-promo\fR .IP "\fIObjective-C and Objective\-\*(C+ Language Options\fR" 4 .IX Item "Objective-C and Objective- Language Options" \&\fB\-fconstant\-string\-class=\fR\fIclass-name\fR \&\fB\-fgnu\-runtime \-fnext\-runtime \&\-fno\-nil\-receivers \&\-fobjc\-abi\-version=\fR\fIn\fR \&\fB\-fobjc\-call\-cxx\-cdtors \&\-fobjc\-direct\-dispatch \&\-fobjc\-exceptions \&\-fobjc\-gc \&\-fobjc\-nilcheck \&\-fobjc\-std=objc1 \&\-fno\-local\-ivars \&\-fivar\-visibility=\fR[\fBpublic\fR|\fBprotected\fR|\fBprivate\fR|\fBpackage\fR] \&\fB\-freplace\-objc\-classes \&\-fzero\-link \&\-gen\-decls \&\-Wassign\-intercept \&\-Wno\-protocol \-Wselector \&\-Wstrict\-selector\-match \&\-Wundeclared\-selector\fR .IP "\fILanguage Independent Options\fR" 4 .IX Item "Language Independent Options" \&\fB\-fmessage\-length=\fR\fIn\fR \&\fB\-fdiagnostics\-show\-location=\fR[\fBonce\fR|\fBevery-line\fR] \&\fB\-fdiagnostics\-color=\fR[\fBauto\fR|\fBnever\fR|\fBalways\fR] \&\fB\-fno\-diagnostics\-show\-option \-fno\-diagnostics\-show\-caret\fR .IP "\fIWarning Options\fR" 4 .IX Item "Warning Options" \&\fB\-fsyntax\-only \-fmax\-errors=\fR\fIn\fR \fB\-Wpedantic \&\-pedantic\-errors \&\-w \-Wextra \-Wall \-Waddress \-Waggregate\-return \&\-Waggressive\-loop\-optimizations \-Warray\-bounds \-Warray\-bounds=\fR\fIn\fR \&\fB\-Wbool\-compare \&\-Wno\-attributes \-Wno\-builtin\-macro\-redefined \&\-Wc90\-c99\-compat \-Wc99\-c11\-compat \&\-Wc++\-compat \-Wc++11\-compat \-Wc++14\-compat \-Wcast\-align \-Wcast\-qual \&\-Wchar\-subscripts \-Wclobbered \-Wcomment \-Wconditionally\-supported \&\-Wconversion \-Wcoverage\-mismatch \-Wdate\-time \-Wdelete\-incomplete \-Wno\-cpp \&\-Wno\-deprecated \-Wno\-deprecated\-declarations \-Wno\-designated\-init \&\-Wdisabled\-optimization \&\-Wno\-discarded\-qualifiers \-Wno\-discarded\-array\-qualifiers \&\-Wno\-div\-by\-zero \-Wdouble\-promotion \-Wempty\-body \-Wenum\-compare \&\-Wno\-endif\-labels \-Werror \-Werror=* \&\-Wfatal\-errors \-Wfloat\-equal \-Wformat \-Wformat=2 \&\-Wno\-format\-contains\-nul \-Wno\-format\-extra\-args \-Wformat\-nonliteral \&\-Wformat\-security \-Wformat\-signedness \-Wformat\-y2k \&\-Wframe\-larger\-than=\fR\fIlen\fR \fB\-Wno\-free\-nonheap\-object \-Wjump\-misses\-init \&\-Wignored\-qualifiers \-Wincompatible\-pointer\-types \&\-Wimplicit \-Wimplicit\-function\-declaration \-Wimplicit\-int \&\-Winit\-self \-Winline \-Wno\-int\-conversion \&\-Wno\-int\-to\-pointer\-cast \-Wno\-invalid\-offsetof \&\-Winvalid\-pch \-Wlarger\-than=\fR\fIlen\fR \fB\-Wunsafe\-loop\-optimizations \&\-Wlogical\-op \-Wlogical\-not\-parentheses \-Wlong\-long \&\-Wmain \-Wmaybe\-uninitialized \-Wmemset\-transposed\-args \-Wmissing\-braces \&\-Wmissing\-field\-initializers \-Wmissing\-include\-dirs \&\-Wno\-multichar \-Wnonnull \-Wnormalized=\fR[\fBnone\fR|\fBid\fR|\fBnfc\fR|\fBnfkc\fR] \fB\-Wodr \-Wno\-overflow \-Wopenmp\-simd \&\-Woverlength\-strings \-Wpacked \-Wpacked\-bitfield\-compat \-Wpadded \&\-Wparentheses \-Wpedantic\-ms\-format \-Wno\-pedantic\-ms\-format \&\-Wpointer\-arith \-Wno\-pointer\-to\-int\-cast \&\-Wredundant\-decls \-Wno\-return\-local\-addr \&\-Wreturn\-type \-Wsequence\-point \-Wshadow \-Wno\-shadow\-ivar \&\-Wshift\-count\-negative \-Wshift\-count\-overflow \&\-Wsign\-compare \-Wsign\-conversion \-Wfloat\-conversion \&\-Wsizeof\-pointer\-memaccess \-Wsizeof\-array\-argument \&\-Wstack\-protector \-Wstack\-usage=\fR\fIlen\fR \fB\-Wstrict\-aliasing \&\-Wstrict\-aliasing=n \-Wstrict\-overflow \-Wstrict\-overflow=\fR\fIn\fR \&\fB\-Wsuggest\-attribute=\fR[\fBpure\fR|\fBconst\fR|\fBnoreturn\fR|\fBformat\fR] \&\fB\-Wsuggest\-final\-types \-Wsuggest\-final\-methods \-Wsuggest\-override \&\-Wmissing\-format\-attribute \&\-Wswitch \-Wswitch\-default \-Wswitch\-enum \-Wswitch\-bool \-Wsync\-nand \&\-Wsystem\-headers \-Wtrampolines \-Wtrigraphs \-Wtype\-limits \-Wundef \&\-Wuninitialized \-Wunknown\-pragmas \-Wno\-pragmas \&\-Wunsuffixed\-float\-constants \-Wunused \-Wunused\-function \&\-Wunused\-label \-Wunused\-local\-typedefs \-Wunused\-parameter \&\-Wno\-unused\-result \-Wunused\-value \-Wunused\-variable \&\-Wunused\-but\-set\-parameter \-Wunused\-but\-set\-variable \&\-Wuseless\-cast \-Wvariadic\-macros \-Wvector\-operation\-performance \&\-Wvla \-Wvolatile\-register\-var \-Wwrite\-strings \&\-Wzero\-as\-null\-pointer\-constant\fR .IP "\fIC and Objective-C-only Warning Options\fR" 4 .IX Item "C and Objective-C-only Warning Options" \&\fB\-Wbad\-function\-cast \-Wmissing\-declarations \&\-Wmissing\-parameter\-type \-Wmissing\-prototypes \-Wnested\-externs \&\-Wold\-style\-declaration \-Wold\-style\-definition \&\-Wstrict\-prototypes \-Wtraditional \-Wtraditional\-conversion \&\-Wdeclaration\-after\-statement \-Wpointer\-sign\fR .IP "\fIDebugging Options\fR" 4 .IX Item "Debugging Options" \&\fB\-d\fR\fIletters\fR \fB\-dumpspecs \-dumpmachine \-dumpversion \&\-fsanitize=\fR\fIstyle\fR \fB\-fsanitize\-recover \-fsanitize\-recover=\fR\fIstyle\fR \&\fB\-fasan\-shadow\-offset=\fR\fInumber\fR \fB\-fsanitize\-undefined\-trap\-on\-error \&\-fcheck\-pointer\-bounds \-fchkp\-check\-incomplete\-type \&\-fchkp\-first\-field\-has\-own\-bounds \-fchkp\-narrow\-bounds \&\-fchkp\-narrow\-to\-innermost\-array \-fchkp\-optimize \&\-fchkp\-use\-fast\-string\-functions \-fchkp\-use\-nochk\-string\-functions \&\-fchkp\-use\-static\-bounds \-fchkp\-use\-static\-const\-bounds \&\-fchkp\-treat\-zero\-dynamic\-size\-as\-infinite \-fchkp\-check\-read \&\-fchkp\-check\-read \-fchkp\-check\-write \-fchkp\-store\-bounds \&\-fchkp\-instrument\-calls \-fchkp\-instrument\-marked\-only \&\-fchkp\-use\-wrappers \&\-fdbg\-cnt\-list \-fdbg\-cnt=\fR\fIcounter-value-list\fR \&\fB\-fdisable\-ipa\-\fR\fIpass_name\fR \&\fB\-fdisable\-rtl\-\fR\fIpass_name\fR \&\fB\-fdisable\-rtl\-\fR\fIpass-name\fR\fB=\fR\fIrange-list\fR \&\fB\-fdisable\-tree\-\fR\fIpass_name\fR \&\fB\-fdisable\-tree\-\fR\fIpass-name\fR\fB=\fR\fIrange-list\fR \&\fB\-fdump\-noaddr \-fdump\-unnumbered \-fdump\-unnumbered\-links \&\-fdump\-translation\-unit\fR[\fB\-\fR\fIn\fR] \&\fB\-fdump\-class\-hierarchy\fR[\fB\-\fR\fIn\fR] \&\fB\-fdump\-ipa\-all \-fdump\-ipa\-cgraph \-fdump\-ipa\-inline \&\-fdump\-passes \&\-fdump\-statistics \&\-fdump\-tree\-all \&\-fdump\-tree\-original\fR[\fB\-\fR\fIn\fR] \&\fB\-fdump\-tree\-optimized\fR[\fB\-\fR\fIn\fR] \&\fB\-fdump\-tree\-cfg \-fdump\-tree\-alias \&\-fdump\-tree\-ch \&\-fdump\-tree\-ssa\fR[\fB\-\fR\fIn\fR] \fB\-fdump\-tree\-pre\fR[\fB\-\fR\fIn\fR] \&\fB\-fdump\-tree\-ccp\fR[\fB\-\fR\fIn\fR] \fB\-fdump\-tree\-dce\fR[\fB\-\fR\fIn\fR] \&\fB\-fdump\-tree\-gimple\fR[\fB\-raw\fR] \&\fB\-fdump\-tree\-dom\fR[\fB\-\fR\fIn\fR] \&\fB\-fdump\-tree\-dse\fR[\fB\-\fR\fIn\fR] \&\fB\-fdump\-tree\-phiprop\fR[\fB\-\fR\fIn\fR] \&\fB\-fdump\-tree\-phiopt\fR[\fB\-\fR\fIn\fR] \&\fB\-fdump\-tree\-forwprop\fR[\fB\-\fR\fIn\fR] \&\fB\-fdump\-tree\-copyrename\fR[\fB\-\fR\fIn\fR] \&\fB\-fdump\-tree\-nrv \-fdump\-tree\-vect \&\-fdump\-tree\-sink \&\-fdump\-tree\-sra\fR[\fB\-\fR\fIn\fR] \&\fB\-fdump\-tree\-forwprop\fR[\fB\-\fR\fIn\fR] \&\fB\-fdump\-tree\-fre\fR[\fB\-\fR\fIn\fR] \&\fB\-fdump\-tree\-vtable\-verify \&\-fdump\-tree\-vrp\fR[\fB\-\fR\fIn\fR] \&\fB\-fdump\-tree\-storeccp\fR[\fB\-\fR\fIn\fR] \&\fB\-fdump\-final\-insns=\fR\fIfile\fR \&\fB\-fcompare\-debug\fR[\fB=\fR\fIopts\fR] \fB\-fcompare\-debug\-second \&\-feliminate\-dwarf2\-dups \-fno\-eliminate\-unused\-debug\-types \&\-feliminate\-unused\-debug\-symbols \-femit\-class\-debug\-always \&\-fenable\-\fR\fIkind\fR\fB\-\fR\fIpass\fR \&\fB\-fenable\-\fR\fIkind\fR\fB\-\fR\fIpass\fR\fB=\fR\fIrange-list\fR \&\fB\-fdebug\-types\-section \-fmem\-report\-wpa \&\-fmem\-report \-fpre\-ipa\-mem\-report \-fpost\-ipa\-mem\-report \-fprofile\-arcs \&\-fopt\-info \&\-fopt\-info\-\fR\fIoptions\fR[\fB=\fR\fIfile\fR] \&\fB\-frandom\-seed=\fR\fInumber\fR \fB\-fsched\-verbose=\fR\fIn\fR \&\fB\-fsel\-sched\-verbose \-fsel\-sched\-dump\-cfg \-fsel\-sched\-pipelining\-verbose \&\-fstack\-usage \-ftest\-coverage \-ftime\-report \-fvar\-tracking \&\-fvar\-tracking\-assignments \-fvar\-tracking\-assignments\-toggle \&\-g \-g\fR\fIlevel\fR \fB\-gtoggle \-gcoff \-gdwarf\-\fR\fIversion\fR \&\fB\-ggdb \-grecord\-gcc\-switches \-gno\-record\-gcc\-switches \&\-gstabs \-gstabs+ \-gstrict\-dwarf \-gno\-strict\-dwarf \&\-gvms \-gxcoff \-gxcoff+ \-gz\fR[\fB=\fR\fItype\fR] \&\fB\-fno\-merge\-debug\-strings \-fno\-dwarf2\-cfi\-asm \&\-fdebug\-prefix\-map=\fR\fIold\fR\fB=\fR\fInew\fR \&\fB\-femit\-struct\-debug\-baseonly \-femit\-struct\-debug\-reduced \&\-femit\-struct\-debug\-detailed\fR[\fB=\fR\fIspec-list\fR] \&\fB\-p \-pg \-print\-file\-name=\fR\fIlibrary\fR \fB\-print\-libgcc\-file\-name \&\-print\-multi\-directory \-print\-multi\-lib \-print\-multi\-os\-directory \&\-print\-prog\-name=\fR\fIprogram\fR \fB\-print\-search\-dirs \-Q \&\-print\-sysroot \-print\-sysroot\-headers\-suffix \&\-save\-temps \-save\-temps=cwd \-save\-temps=obj \-time\fR[\fB=\fR\fIfile\fR] .IP "\fIOptimization Options\fR" 4 .IX Item "Optimization Options" \&\fB\-faggressive\-loop\-optimizations \-falign\-functions[=\fR\fIn\fR\fB] \&\-falign\-jumps[=\fR\fIn\fR\fB] \&\-falign\-labels[=\fR\fIn\fR\fB] \-falign\-loops[=\fR\fIn\fR\fB] \&\-fassociative\-math \-fauto\-profile \-fauto\-profile[=\fR\fIpath\fR\fB] \&\-fauto\-inc\-dec \-fbranch\-probabilities \&\-fbranch\-target\-load\-optimize \-fbranch\-target\-load\-optimize2 \&\-fbtr\-bb\-exclusive \-fcaller\-saves \&\-fcheck\-data\-deps \-fcombine\-stack\-adjustments \-fconserve\-stack \&\-fcompare\-elim \-fcprop\-registers \-fcrossjumping \&\-fcse\-follow\-jumps \-fcse\-skip\-blocks \-fcx\-fortran\-rules \&\-fcx\-limited\-range \&\-fdata\-sections \-fdce \-fdelayed\-branch \&\-fdelete\-null\-pointer\-checks \-fdevirtualize \-fdevirtualize\-speculatively \&\-fdevirtualize\-at\-ltrans \-fdse \&\-fearly\-inlining \-fipa\-sra \-fexpensive\-optimizations \-ffat\-lto\-objects \&\-ffast\-math \-ffinite\-math\-only \-ffloat\-store \-fexcess\-precision=\fR\fIstyle\fR \&\fB\-fforward\-propagate \-ffp\-contract=\fR\fIstyle\fR \fB\-ffunction\-sections \&\-fgcse \-fgcse\-after\-reload \-fgcse\-las \-fgcse\-lm \-fgraphite\-identity \&\-fgcse\-sm \-fhoist\-adjacent\-loads \-fif\-conversion \&\-fif\-conversion2 \-findirect\-inlining \&\-finline\-functions \-finline\-functions\-called\-once \-finline\-limit=\fR\fIn\fR \&\fB\-finline\-small\-functions \-fipa\-cp \-fipa\-cp\-clone \-fipa\-cp\-alignment \&\-fipa\-pta \-fipa\-profile \-fipa\-pure\-const \-fipa\-reference \-fipa\-icf \&\-fira\-algorithm=\fR\fIalgorithm\fR \&\fB\-fira\-region=\fR\fIregion\fR \fB\-fira\-hoist\-pressure \&\-fira\-loop\-pressure \-fno\-ira\-share\-save\-slots \&\-fno\-ira\-share\-spill\-slots \-fira\-verbose=\fR\fIn\fR \&\fB\-fisolate\-erroneous\-paths\-dereference \-fisolate\-erroneous\-paths\-attribute \&\-fivopts \-fkeep\-inline\-functions \-fkeep\-static\-consts \&\-flive\-range\-shrinkage \&\-floop\-block \-floop\-interchange \-floop\-strip\-mine \&\-floop\-unroll\-and\-jam \-floop\-nest\-optimize \&\-floop\-parallelize\-all \-flra\-remat \-flto \-flto\-compression\-level \&\-flto\-partition=\fR\fIalg\fR \fB\-flto\-report \-flto\-report\-wpa \-fmerge\-all\-constants \&\-fmerge\-constants \-fmodulo\-sched \-fmodulo\-sched\-allow\-regmoves \&\-fmove\-loop\-invariants \-fno\-branch\-count\-reg \&\-fno\-defer\-pop \-fno\-function\-cse \-fno\-guess\-branch\-probability \&\-fno\-inline \-fno\-math\-errno \-fno\-peephole \-fno\-peephole2 \&\-fno\-sched\-interblock \-fno\-sched\-spec \-fno\-signed\-zeros \&\-fno\-toplevel\-reorder \-fno\-trapping\-math \-fno\-zero\-initialized\-in\-bss \&\-fomit\-frame\-pointer \-foptimize\-sibling\-calls \&\-fpartial\-inlining \-fpeel\-loops \-fpredictive\-commoning \&\-fprefetch\-loop\-arrays \-fprofile\-report \&\-fprofile\-correction \-fprofile\-dir=\fR\fIpath\fR \fB\-fprofile\-generate \&\-fprofile\-generate=\fR\fIpath\fR \&\fB\-fprofile\-use \-fprofile\-use=\fR\fIpath\fR \fB\-fprofile\-values \&\-fprofile\-reorder\-functions \&\-freciprocal\-math \-free \-frename\-registers \-freorder\-blocks \&\-freorder\-blocks\-and\-partition \-freorder\-functions \&\-frerun\-cse\-after\-loop \-freschedule\-modulo\-scheduled\-loops \&\-frounding\-math \-fsched2\-use\-superblocks \-fsched\-pressure \&\-fsched\-spec\-load \-fsched\-spec\-load\-dangerous \&\-fsched\-stalled\-insns\-dep[=\fR\fIn\fR\fB] \-fsched\-stalled\-insns[=\fR\fIn\fR\fB] \&\-fsched\-group\-heuristic \-fsched\-critical\-path\-heuristic \&\-fsched\-spec\-insn\-heuristic \-fsched\-rank\-heuristic \&\-fsched\-last\-insn\-heuristic \-fsched\-dep\-count\-heuristic \&\-fschedule\-fusion \&\-fschedule\-insns \-fschedule\-insns2 \-fsection\-anchors \&\-fselective\-scheduling \-fselective\-scheduling2 \&\-fsel\-sched\-pipelining \-fsel\-sched\-pipelining\-outer\-loops \&\-fsemantic\-interposition \&\-fshrink\-wrap \-fsignaling\-nans \-fsingle\-precision\-constant \&\-fsplit\-ivs\-in\-unroller \-fsplit\-wide\-types \-fssa\-phiopt \&\-fstack\-protector \-fstack\-protector\-all \-fstack\-protector\-strong \&\-fstack\-protector\-explicit \-fstdarg\-opt \-fstrict\-aliasing \&\-fstrict\-overflow \-fthread\-jumps \-ftracer \-ftree\-bit\-ccp \&\-ftree\-builtin\-call\-dce \-ftree\-ccp \-ftree\-ch \&\-ftree\-coalesce\-inline\-vars \-ftree\-coalesce\-vars \-ftree\-copy\-prop \&\-ftree\-copyrename \-ftree\-dce \-ftree\-dominator\-opts \-ftree\-dse \&\-ftree\-forwprop \-ftree\-fre \-ftree\-loop\-if\-convert \&\-ftree\-loop\-if\-convert\-stores \-ftree\-loop\-im \&\-ftree\-phiprop \-ftree\-loop\-distribution \-ftree\-loop\-distribute\-patterns \&\-ftree\-loop\-ivcanon \-ftree\-loop\-linear \-ftree\-loop\-optimize \&\-ftree\-loop\-vectorize \&\-ftree\-parallelize\-loops=\fR\fIn\fR \fB\-ftree\-pre \-ftree\-partial\-pre \-ftree\-pta \&\-ftree\-reassoc \-ftree\-sink \-ftree\-slsr \-ftree\-sra \&\-ftree\-switch\-conversion \-ftree\-tail\-merge \-ftree\-ter \&\-ftree\-vectorize \-ftree\-vrp \&\-funit\-at\-a\-time \-funroll\-all\-loops \-funroll\-loops \&\-funsafe\-loop\-optimizations \-funsafe\-math\-optimizations \-funswitch\-loops \&\-fipa\-ra \-fvariable\-expansion\-in\-unroller \-fvect\-cost\-model \-fvpt \&\-fweb \-fwhole\-program \-fwpa \-fuse\-linker\-plugin \&\-\-param\fR \fIname\fR\fB=\fR\fIvalue\fR \&\fB\-O \-O0 \-O1 \-O2 \-O3 \-Os \-Ofast \-Og\fR .IP "\fIPreprocessor Options\fR" 4 .IX Item "Preprocessor Options" \&\fB\-A\fR\fIquestion\fR\fB=\fR\fIanswer\fR \&\fB\-A\-\fR\fIquestion\fR[\fB=\fR\fIanswer\fR] \&\fB\-C \-dD \-dI \-dM \-dN \&\-D\fR\fImacro\fR[\fB=\fR\fIdefn\fR] \fB\-E \-H \&\-idirafter\fR \fIdir\fR \&\fB\-include\fR \fIfile\fR \fB\-imacros\fR \fIfile\fR \&\fB\-iprefix\fR \fIfile\fR \fB\-iwithprefix\fR \fIdir\fR \&\fB\-iwithprefixbefore\fR \fIdir\fR \fB\-isystem\fR \fIdir\fR \&\fB\-imultilib\fR \fIdir\fR \fB\-isysroot\fR \fIdir\fR \&\fB\-M \-MM \-MF \-MG \-MP \-MQ \-MT \-nostdinc \&\-P \-fdebug\-cpp \-ftrack\-macro\-expansion \-fworking\-directory \&\-remap \-trigraphs \-undef \-U\fR\fImacro\fR \&\fB\-Wp,\fR\fIoption\fR \fB\-Xpreprocessor\fR \fIoption\fR \fB\-no\-integrated\-cpp\fR .IP "\fIAssembler Option\fR" 4 .IX Item "Assembler Option" \&\fB\-Wa,\fR\fIoption\fR \fB\-Xassembler\fR \fIoption\fR .IP "\fILinker Options\fR" 4 .IX Item "Linker Options" \&\fIobject-file-name\fR \fB\-fuse\-ld=\fR\fIlinker\fR \fB\-l\fR\fIlibrary\fR \&\fB\-nostartfiles \-nodefaultlibs \-nostdlib \-pie \-rdynamic \&\-s \-static \-static\-libgcc \-static\-libstdc++ \&\-static\-libasan \-static\-libtsan \-static\-liblsan \-static\-libubsan \&\-static\-libmpx \-static\-libmpxwrappers \&\-shared \-shared\-libgcc \-symbolic \&\-T\fR \fIscript\fR \fB\-Wl,\fR\fIoption\fR \fB\-Xlinker\fR \fIoption\fR \&\fB\-u\fR \fIsymbol\fR \fB\-z\fR \fIkeyword\fR .IP "\fIDirectory Options\fR" 4 .IX Item "Directory Options" \&\fB\-B\fR\fIprefix\fR \fB\-I\fR\fIdir\fR \fB\-iplugindir=\fR\fIdir\fR \&\fB\-iquote\fR\fIdir\fR \fB\-L\fR\fIdir\fR \fB\-specs=\fR\fIfile\fR \fB\-I\- \&\-\-sysroot=\fR\fIdir\fR \fB\-\-no\-sysroot\-suffix\fR .IP "\fIMachine Dependent Options\fR" 4 .IX Item "Machine Dependent Options" \&\fIAArch64 Options\fR \&\fB\-mabi=\fR\fIname\fR \fB\-mbig\-endian \-mlittle\-endian \&\-mgeneral\-regs\-only \&\-mcmodel=tiny \-mcmodel=small \-mcmodel=large \&\-mstrict\-align \&\-momit\-leaf\-frame\-pointer \-mno\-omit\-leaf\-frame\-pointer \&\-mtls\-dialect=desc \-mtls\-dialect=traditional \&\-mfix\-cortex\-a53\-835769 \-mno\-fix\-cortex\-a53\-835769 \&\-mfix\-cortex\-a53\-843419 \-mno\-fix\-cortex\-a53\-843419 \&\-march=\fR\fIname\fR \fB\-mcpu=\fR\fIname\fR \fB\-mtune=\fR\fIname\fR .Sp \&\fIAdapteva Epiphany Options\fR \&\fB\-mhalf\-reg\-file \-mprefer\-short\-insn\-regs \&\-mbranch\-cost=\fR\fInum\fR \fB\-mcmove \-mnops=\fR\fInum\fR \fB\-msoft\-cmpsf \&\-msplit\-lohi \-mpost\-inc \-mpost\-modify \-mstack\-offset=\fR\fInum\fR \&\fB\-mround\-nearest \-mlong\-calls \-mshort\-calls \-msmall16 \&\-mfp\-mode=\fR\fImode\fR \fB\-mvect\-double \-max\-vect\-align=\fR\fInum\fR \&\fB\-msplit\-vecmove\-early \-m1reg\-\fR\fIreg\fR .Sp \&\fI\s-1ARC\s0 Options\fR \&\fB\-mbarrel\-shifter \&\-mcpu=\fR\fIcpu\fR \fB\-mA6 \-mARC600 \-mA7 \-mARC700 \&\-mdpfp \-mdpfp\-compact \-mdpfp\-fast \-mno\-dpfp\-lrsr \&\-mea \-mno\-mpy \-mmul32x16 \-mmul64 \&\-mnorm \-mspfp \-mspfp\-compact \-mspfp\-fast \-msimd \-msoft\-float \-mswap \&\-mcrc \-mdsp\-packa \-mdvbf \-mlock \-mmac\-d16 \-mmac\-24 \-mrtsc \-mswape \&\-mtelephony \-mxy \-misize \-mannotate\-align \-marclinux \-marclinux_prof \&\-mepilogue\-cfi \-mlong\-calls \-mmedium\-calls \-msdata \&\-mucb\-mcount \-mvolatile\-cache \&\-malign\-call \-mauto\-modify\-reg \-mbbit\-peephole \-mno\-brcc \&\-mcase\-vector\-pcrel \-mcompact\-casesi \-mno\-cond\-exec \-mearly\-cbranchsi \&\-mexpand\-adddi \-mindexed\-loads \-mlra \-mlra\-priority\-none \&\-mlra\-priority\-compact mlra-priority-noncompact \-mno\-millicode \&\-mmixed\-code \-mq\-class \-mRcq \-mRcw \-msize\-level=\fR\fIlevel\fR \&\fB\-mtune=\fR\fIcpu\fR \fB\-mmultcost=\fR\fInum\fR \fB\-munalign\-prob\-threshold=\fR\fIprobability\fR .Sp \&\fI\s-1ARM\s0 Options\fR \&\fB\-mapcs\-frame \-mno\-apcs\-frame \&\-mabi=\fR\fIname\fR \&\fB\-mapcs\-stack\-check \-mno\-apcs\-stack\-check \&\-mapcs\-float \-mno\-apcs\-float \&\-mapcs\-reentrant \-mno\-apcs\-reentrant \&\-msched\-prolog \-mno\-sched\-prolog \&\-mlittle\-endian \-mbig\-endian \&\-mfloat\-abi=\fR\fIname\fR \&\fB\-mfp16\-format=\fR\fIname\fR \&\fB\-mthumb\-interwork \-mno\-thumb\-interwork \&\-mcpu=\fR\fIname\fR \fB\-march=\fR\fIname\fR \fB\-mfpu=\fR\fIname\fR \&\fB\-mtune=\fR\fIname\fR \fB\-mprint\-tune\-info \&\-mstructure\-size\-boundary=\fR\fIn\fR \&\fB\-mabort\-on\-noreturn \&\-mlong\-calls \-mno\-long\-calls \&\-msingle\-pic\-base \-mno\-single\-pic\-base \&\-mpic\-register=\fR\fIreg\fR \&\fB\-mnop\-fun\-dllimport \&\-mpoke\-function\-name \&\-mthumb \-marm \&\-mtpcs\-frame \-mtpcs\-leaf\-frame \&\-mcaller\-super\-interworking \-mcallee\-super\-interworking \&\-mtp=\fR\fIname\fR \fB\-mtls\-dialect=\fR\fIdialect\fR \&\fB\-mword\-relocations \&\-mfix\-cortex\-m3\-ldrd \&\-munaligned\-access \&\-mneon\-for\-64bits \&\-mslow\-flash\-data \&\-masm\-syntax\-unified \&\-mrestrict\-it\fR .Sp \&\fI\s-1AVR\s0 Options\fR \&\fB\-mmcu=\fR\fImcu\fR \fB\-maccumulate\-args \-mbranch\-cost=\fR\fIcost\fR \&\fB\-mcall\-prologues \-mint8 \-mn_flash=\fR\fIsize\fR \fB\-mno\-interrupts \&\-mrelax \-mrmw \-mstrict\-X \-mtiny\-stack \-nodevicelib \-Waddr\-space\-convert\fR .Sp \&\fIBlackfin Options\fR \&\fB\-mcpu=\fR\fIcpu\fR[\fB\-\fR\fIsirevision\fR] \&\fB\-msim \-momit\-leaf\-frame\-pointer \-mno\-omit\-leaf\-frame\-pointer \&\-mspecld\-anomaly \-mno\-specld\-anomaly \-mcsync\-anomaly \-mno\-csync\-anomaly \&\-mlow\-64k \-mno\-low64k \-mstack\-check\-l1 \-mid\-shared\-library \&\-mno\-id\-shared\-library \-mshared\-library\-id=\fR\fIn\fR \&\fB\-mleaf\-id\-shared\-library \-mno\-leaf\-id\-shared\-library \&\-msep\-data \-mno\-sep\-data \-mlong\-calls \-mno\-long\-calls \&\-mfast\-fp \-minline\-plt \-mmulticore \-mcorea \-mcoreb \-msdram \&\-micplb\fR .Sp \&\fIC6X Options\fR \&\fB\-mbig\-endian \-mlittle\-endian \-march=\fR\fIcpu\fR \&\fB\-msim \-msdata=\fR\fIsdata-type\fR .Sp \&\fI\s-1CRIS\s0 Options\fR \&\fB\-mcpu=\fR\fIcpu\fR \fB\-march=\fR\fIcpu\fR \fB\-mtune=\fR\fIcpu\fR \&\fB\-mmax\-stack\-frame=\fR\fIn\fR \fB\-melinux\-stacksize=\fR\fIn\fR \&\fB\-metrax4 \-metrax100 \-mpdebug \-mcc\-init \-mno\-side\-effects \&\-mstack\-align \-mdata\-align \-mconst\-align \&\-m32\-bit \-m16\-bit \-m8\-bit \-mno\-prologue\-epilogue \-mno\-gotplt \&\-melf \-maout \-melinux \-mlinux \-sim \-sim2 \&\-mmul\-bug\-workaround \-mno\-mul\-bug\-workaround\fR .Sp \&\fI\s-1CR16\s0 Options\fR \&\fB\-mmac \&\-mcr16cplus \-mcr16c \&\-msim \-mint32 \-mbit\-ops \&\-mdata\-model=\fR\fImodel\fR .Sp \&\fIDarwin Options\fR \&\fB\-all_load \-allowable_client \-arch \-arch_errors_fatal \&\-arch_only \-bind_at_load \-bundle \-bundle_loader \&\-client_name \-compatibility_version \-current_version \&\-dead_strip \&\-dependency\-file \-dylib_file \-dylinker_install_name \&\-dynamic \-dynamiclib \-exported_symbols_list \&\-filelist \-flat_namespace \-force_cpusubtype_ALL \&\-force_flat_namespace \-headerpad_max_install_names \&\-iframework \&\-image_base \-init \-install_name \-keep_private_externs \&\-multi_module \-multiply_defined \-multiply_defined_unused \&\-noall_load \-no_dead_strip_inits_and_terms \&\-nofixprebinding \-nomultidefs \-noprebind \-noseglinkedit \&\-pagezero_size \-prebind \-prebind_all_twolevel_modules \&\-private_bundle \-read_only_relocs \-sectalign \&\-sectobjectsymbols \-whyload \-seg1addr \&\-sectcreate \-sectobjectsymbols \-sectorder \&\-segaddr \-segs_read_only_addr \-segs_read_write_addr \&\-seg_addr_table \-seg_addr_table_filename \-seglinkedit \&\-segprot \-segs_read_only_addr \-segs_read_write_addr \&\-single_module \-static \-sub_library \-sub_umbrella \&\-twolevel_namespace \-umbrella \-undefined \&\-unexported_symbols_list \-weak_reference_mismatches \&\-whatsloaded \-F \-gused \-gfull \-mmacosx\-version\-min=\fR\fIversion\fR \&\fB\-mkernel \-mone\-byte\-bool\fR .Sp \&\fI\s-1DEC\s0 Alpha Options\fR \&\fB\-mno\-fp\-regs \-msoft\-float \&\-mieee \-mieee\-with\-inexact \-mieee\-conformant \&\-mfp\-trap\-mode=\fR\fImode\fR \fB\-mfp\-rounding\-mode=\fR\fImode\fR \&\fB\-mtrap\-precision=\fR\fImode\fR \fB\-mbuild\-constants \&\-mcpu=\fR\fIcpu-type\fR \fB\-mtune=\fR\fIcpu-type\fR \&\fB\-mbwx \-mmax \-mfix \-mcix \&\-mfloat\-vax \-mfloat\-ieee \&\-mexplicit\-relocs \-msmall\-data \-mlarge\-data \&\-msmall\-text \-mlarge\-text \&\-mmemory\-latency=\fR\fItime\fR .Sp \&\fI\s-1FR30\s0 Options\fR \&\fB\-msmall\-model \-mno\-lsim\fR .Sp \&\fI\s-1FRV\s0 Options\fR \&\fB\-mgpr\-32 \-mgpr\-64 \-mfpr\-32 \-mfpr\-64 \&\-mhard\-float \-msoft\-float \&\-malloc\-cc \-mfixed\-cc \-mdword \-mno\-dword \&\-mdouble \-mno\-double \&\-mmedia \-mno\-media \-mmuladd \-mno\-muladd \&\-mfdpic \-minline\-plt \-mgprel\-ro \-multilib\-library\-pic \&\-mlinked\-fp \-mlong\-calls \-malign\-labels \&\-mlibrary\-pic \-macc\-4 \-macc\-8 \&\-mpack \-mno\-pack \-mno\-eflags \-mcond\-move \-mno\-cond\-move \&\-moptimize\-membar \-mno\-optimize\-membar \&\-mscc \-mno\-scc \-mcond\-exec \-mno\-cond\-exec \&\-mvliw\-branch \-mno\-vliw\-branch \&\-mmulti\-cond\-exec \-mno\-multi\-cond\-exec \-mnested\-cond\-exec \&\-mno\-nested\-cond\-exec \-mtomcat\-stats \&\-mTLS \-mtls \&\-mcpu=\fR\fIcpu\fR .Sp \&\fIGNU/Linux Options\fR \&\fB\-mglibc \-muclibc \-mmusl \-mbionic \-mandroid \&\-tno\-android\-cc \-tno\-android\-ld\fR .Sp \&\fIH8/300 Options\fR \&\fB\-mrelax \-mh \-ms \-mn \-mexr \-mno\-exr \-mint32 \-malign\-300\fR .Sp \&\fI\s-1HPPA\s0 Options\fR \&\fB\-march=\fR\fIarchitecture-type\fR \&\fB\-mdisable\-fpregs \-mdisable\-indexing \&\-mfast\-indirect\-calls \-mgas \-mgnu\-ld \-mhp\-ld \&\-mfixed\-range=\fR\fIregister-range\fR \&\fB\-mjump\-in\-delay \-mlinker\-opt \-mlong\-calls \&\-mlong\-load\-store \-mno\-disable\-fpregs \&\-mno\-disable\-indexing \-mno\-fast\-indirect\-calls \-mno\-gas \&\-mno\-jump\-in\-delay \-mno\-long\-load\-store \&\-mno\-portable\-runtime \-mno\-soft\-float \&\-mno\-space\-regs \-msoft\-float \-mpa\-risc\-1\-0 \&\-mpa\-risc\-1\-1 \-mpa\-risc\-2\-0 \-mportable\-runtime \&\-mschedule=\fR\fIcpu-type\fR \fB\-mspace\-regs \-msio \-mwsio \&\-munix=\fR\fIunix-std\fR \fB\-nolibdld \-static \-threads\fR .Sp \&\fI\s-1IA\-64\s0 Options\fR \&\fB\-mbig\-endian \-mlittle\-endian \-mgnu\-as \-mgnu\-ld \-mno\-pic \&\-mvolatile\-asm\-stop \-mregister\-names \-msdata \-mno\-sdata \&\-mconstant\-gp \-mauto\-pic \-mfused\-madd \&\-minline\-float\-divide\-min\-latency \&\-minline\-float\-divide\-max\-throughput \&\-mno\-inline\-float\-divide \&\-minline\-int\-divide\-min\-latency \&\-minline\-int\-divide\-max\-throughput \&\-mno\-inline\-int\-divide \&\-minline\-sqrt\-min\-latency \-minline\-sqrt\-max\-throughput \&\-mno\-inline\-sqrt \&\-mdwarf2\-asm \-mearly\-stop\-bits \&\-mfixed\-range=\fR\fIregister-range\fR \fB\-mtls\-size=\fR\fItls-size\fR \&\fB\-mtune=\fR\fIcpu-type\fR \fB\-milp32 \-mlp64 \&\-msched\-br\-data\-spec \-msched\-ar\-data\-spec \-msched\-control\-spec \&\-msched\-br\-in\-data\-spec \-msched\-ar\-in\-data\-spec \-msched\-in\-control\-spec \&\-msched\-spec\-ldc \-msched\-spec\-control\-ldc \&\-msched\-prefer\-non\-data\-spec\-insns \-msched\-prefer\-non\-control\-spec\-insns \&\-msched\-stop\-bits\-after\-every\-cycle \-msched\-count\-spec\-in\-critical\-path \&\-msel\-sched\-dont\-check\-control\-spec \-msched\-fp\-mem\-deps\-zero\-cost \&\-msched\-max\-memory\-insns\-hard\-limit \-msched\-max\-memory\-insns=\fR\fImax-insns\fR .Sp \&\fI\s-1LM32\s0 Options\fR \&\fB\-mbarrel\-shift\-enabled \-mdivide\-enabled \-mmultiply\-enabled \&\-msign\-extend\-enabled \-muser\-enabled\fR .Sp \&\fIM32R/D Options\fR \&\fB\-m32r2 \-m32rx \-m32r \&\-mdebug \&\-malign\-loops \-mno\-align\-loops \&\-missue\-rate=\fR\fInumber\fR \&\fB\-mbranch\-cost=\fR\fInumber\fR \&\fB\-mmodel=\fR\fIcode-size-model-type\fR \&\fB\-msdata=\fR\fIsdata-type\fR \&\fB\-mno\-flush\-func \-mflush\-func=\fR\fIname\fR \&\fB\-mno\-flush\-trap \-mflush\-trap=\fR\fInumber\fR \&\fB\-G\fR \fInum\fR .Sp \&\fIM32C Options\fR \&\fB\-mcpu=\fR\fIcpu\fR \fB\-msim \-memregs=\fR\fInumber\fR .Sp \&\fIM680x0 Options\fR \&\fB\-march=\fR\fIarch\fR \fB\-mcpu=\fR\fIcpu\fR \fB\-mtune=\fR\fItune\fR \&\fB\-m68000 \-m68020 \-m68020\-40 \-m68020\-60 \-m68030 \-m68040 \&\-m68060 \-mcpu32 \-m5200 \-m5206e \-m528x \-m5307 \-m5407 \&\-mcfv4e \-mbitfield \-mno\-bitfield \-mc68000 \-mc68020 \&\-mnobitfield \-mrtd \-mno\-rtd \-mdiv \-mno\-div \-mshort \&\-mno\-short \-mhard\-float \-m68881 \-msoft\-float \-mpcrel \&\-malign\-int \-mstrict\-align \-msep\-data \-mno\-sep\-data \&\-mshared\-library\-id=n \-mid\-shared\-library \-mno\-id\-shared\-library \&\-mxgot \-mno\-xgot\fR .Sp \&\fIMCore Options\fR \&\fB\-mhardlit \-mno\-hardlit \-mdiv \-mno\-div \-mrelax\-immediates \&\-mno\-relax\-immediates \-mwide\-bitfields \-mno\-wide\-bitfields \&\-m4byte\-functions \-mno\-4byte\-functions \-mcallgraph\-data \&\-mno\-callgraph\-data \-mslow\-bytes \-mno\-slow\-bytes \-mno\-lsim \&\-mlittle\-endian \-mbig\-endian \-m210 \-m340 \-mstack\-increment\fR .Sp \&\fIMeP Options\fR \&\fB\-mabsdiff \-mall\-opts \-maverage \-mbased=\fR\fIn\fR \fB\-mbitops \&\-mc=\fR\fIn\fR \fB\-mclip \-mconfig=\fR\fIname\fR \fB\-mcop \-mcop32 \-mcop64 \-mivc2 \&\-mdc \-mdiv \-meb \-mel \-mio\-volatile \-ml \-mleadz \-mm \-mminmax \&\-mmult \-mno\-opts \-mrepeat \-ms \-msatur \-msdram \-msim \-msimnovec \-mtf \&\-mtiny=\fR\fIn\fR .Sp \&\fIMicroBlaze Options\fR \&\fB\-msoft\-float \-mhard\-float \-msmall\-divides \-mcpu=\fR\fIcpu\fR \&\fB\-mmemcpy \-mxl\-soft\-mul \-mxl\-soft\-div \-mxl\-barrel\-shift \&\-mxl\-pattern\-compare \-mxl\-stack\-check \-mxl\-gp\-opt \-mno\-clearbss \&\-mxl\-multiply\-high \-mxl\-float\-convert \-mxl\-float\-sqrt \&\-mbig\-endian \-mlittle\-endian \-mxl\-reorder \-mxl\-mode\-\fR\fIapp-model\fR .Sp \&\fI\s-1MIPS\s0 Options\fR \&\fB\-EL \-EB \-march=\fR\fIarch\fR \fB\-mtune=\fR\fIarch\fR \&\fB\-mips1 \-mips2 \-mips3 \-mips4 \-mips32 \-mips32r2 \-mips32r3 \-mips32r5 \&\-mips32r6 \-mips64 \-mips64r2 \-mips64r3 \-mips64r5 \-mips64r6 \&\-mips16 \-mno\-mips16 \-mflip\-mips16 \&\-minterlink\-compressed \-mno\-interlink\-compressed \&\-minterlink\-mips16 \-mno\-interlink\-mips16 \&\-mabi=\fR\fIabi\fR \fB\-mabicalls \-mno\-abicalls \&\-mshared \-mno\-shared \-mplt \-mno\-plt \-mxgot \-mno\-xgot \&\-mgp32 \-mgp64 \-mfp32 \-mfpxx \-mfp64 \-mhard\-float \-msoft\-float \&\-mno\-float \-msingle\-float \-mdouble\-float \&\-modd\-spreg \-mno\-odd\-spreg \&\-mabs=\fR\fImode\fR \fB\-mnan=\fR\fIencoding\fR \&\fB\-mdsp \-mno\-dsp \-mdspr2 \-mno\-dspr2 \&\-mmcu \-mmno\-mcu \&\-meva \-mno\-eva \&\-mvirt \-mno\-virt \&\-mxpa \-mno\-xpa \&\-mmicromips \-mno\-micromips \&\-mfpu=\fR\fIfpu-type\fR \&\fB\-msmartmips \-mno\-smartmips \&\-mpaired\-single \-mno\-paired\-single \-mdmx \-mno\-mdmx \&\-mips3d \-mno\-mips3d \-mmt \-mno\-mt \-mllsc \-mno\-llsc \&\-mlong64 \-mlong32 \-msym32 \-mno\-sym32 \&\-G\fR\fInum\fR \fB\-mlocal\-sdata \-mno\-local\-sdata \&\-mextern\-sdata \-mno\-extern\-sdata \-mgpopt \-mno\-gopt \&\-membedded\-data \-mno\-embedded\-data \&\-muninit\-const\-in\-rodata \-mno\-uninit\-const\-in\-rodata \&\-mcode\-readable=\fR\fIsetting\fR \&\fB\-msplit\-addresses \-mno\-split\-addresses \&\-mexplicit\-relocs \-mno\-explicit\-relocs \&\-mcheck\-zero\-division \-mno\-check\-zero\-division \&\-mdivide\-traps \-mdivide\-breaks \&\-mmemcpy \-mno\-memcpy \-mlong\-calls \-mno\-long\-calls \&\-mmad \-mno\-mad \-mimadd \-mno\-imadd \-mfused\-madd \-mno\-fused\-madd \-nocpp \&\-mfix\-24k \-mno\-fix\-24k \&\-mfix\-r4000 \-mno\-fix\-r4000 \-mfix\-r4400 \-mno\-fix\-r4400 \&\-mfix\-r10000 \-mno\-fix\-r10000 \-mfix\-rm7000 \-mno\-fix\-rm7000 \&\-mfix\-vr4120 \-mno\-fix\-vr4120 \&\-mfix\-vr4130 \-mno\-fix\-vr4130 \-mfix\-sb1 \-mno\-fix\-sb1 \&\-mflush\-func=\fR\fIfunc\fR \fB\-mno\-flush\-func \&\-mbranch\-cost=\fR\fInum\fR \fB\-mbranch\-likely \-mno\-branch\-likely \&\-mfp\-exceptions \-mno\-fp\-exceptions \&\-mvr4130\-align \-mno\-vr4130\-align \-msynci \-mno\-synci \&\-mrelax\-pic\-calls \-mno\-relax\-pic\-calls \-mmcount\-ra\-address\fR .Sp \&\fI\s-1MMIX\s0 Options\fR \&\fB\-mlibfuncs \-mno\-libfuncs \-mepsilon \-mno\-epsilon \-mabi=gnu \&\-mabi=mmixware \-mzero\-extend \-mknuthdiv \-mtoplevel\-symbols \&\-melf \-mbranch\-predict \-mno\-branch\-predict \-mbase\-addresses \&\-mno\-base\-addresses \-msingle\-exit \-mno\-single\-exit\fR .Sp \&\fI\s-1MN10300\s0 Options\fR \&\fB\-mmult\-bug \-mno\-mult\-bug \&\-mno\-am33 \-mam33 \-mam33\-2 \-mam34 \&\-mtune=\fR\fIcpu-type\fR \&\fB\-mreturn\-pointer\-on\-d0 \&\-mno\-crt0 \-mrelax \-mliw \-msetlb\fR .Sp \&\fIMoxie Options\fR \&\fB\-meb \-mel \-mmul.x \-mno\-crt0\fR .Sp \&\fI\s-1MSP430\s0 Options\fR \&\fB\-msim \-masm\-hex \-mmcu= \-mcpu= \-mlarge \-msmall \-mrelax \&\-mhwmult= \-minrt\fR .Sp \&\fI\s-1NDS32\s0 Options\fR \&\fB\-mbig\-endian \-mlittle\-endian \&\-mreduced\-regs \-mfull\-regs \&\-mcmov \-mno\-cmov \&\-mperf\-ext \-mno\-perf\-ext \&\-mv3push \-mno\-v3push \&\-m16bit \-mno\-16bit \&\-misr\-vector\-size=\fR\fInum\fR \&\fB\-mcache\-block\-size=\fR\fInum\fR \&\fB\-march=\fR\fIarch\fR \&\fB\-mcmodel=\fR\fIcode-model\fR \&\fB\-mctor\-dtor \-mrelax\fR .Sp \&\fINios \s-1II\s0 Options\fR \&\fB\-G\fR \fInum\fR \fB\-mgpopt=\fR\fIoption\fR \fB\-mgpopt \-mno\-gpopt \&\-mel \-meb \&\-mno\-bypass\-cache \-mbypass\-cache \&\-mno\-cache\-volatile \-mcache\-volatile \&\-mno\-fast\-sw\-div \-mfast\-sw\-div \&\-mhw\-mul \-mno\-hw\-mul \-mhw\-mulx \-mno\-hw\-mulx \-mno\-hw\-div \-mhw\-div \&\-mcustom\-\fR\fIinsn\fR\fB=\fR\fIN\fR \fB\-mno\-custom\-\fR\fIinsn\fR \&\fB\-mcustom\-fpu\-cfg=\fR\fIname\fR \&\fB\-mhal \-msmallc \-msys\-crt0=\fR\fIname\fR \fB\-msys\-lib=\fR\fIname\fR .Sp \&\fINvidia \s-1PTX\s0 Options\fR \&\fB\-m32 \-m64 \-mmainkernel\fR .Sp \&\fI\s-1PDP\-11\s0 Options\fR \&\fB\-mfpu \-msoft\-float \-mac0 \-mno\-ac0 \-m40 \-m45 \-m10 \&\-mbcopy \-mbcopy\-builtin \-mint32 \-mno\-int16 \&\-mint16 \-mno\-int32 \-mfloat32 \-mno\-float64 \&\-mfloat64 \-mno\-float32 \-mabshi \-mno\-abshi \&\-mbranch\-expensive \-mbranch\-cheap \&\-munix\-asm \-mdec\-asm\fR .Sp \&\fIpicoChip Options\fR \&\fB\-mae=\fR\fIae_type\fR \fB\-mvliw\-lookahead=\fR\fIN\fR \&\fB\-msymbol\-as\-address \-mno\-inefficient\-warnings\fR .Sp \&\fIPowerPC Options\fR See \s-1RS/6000\s0 and PowerPC Options. .Sp \&\fI\s-1RL78\s0 Options\fR \&\fB\-msim \-mmul=none \-mmul=g13 \-mmul=rl78 \&\-m64bit\-doubles \-m32bit\-doubles\fR .Sp \&\fI\s-1RS/6000\s0 and PowerPC Options\fR \&\fB\-mcpu=\fR\fIcpu-type\fR \&\fB\-mtune=\fR\fIcpu-type\fR \&\fB\-mcmodel=\fR\fIcode-model\fR \&\fB\-mpowerpc64 \&\-maltivec \-mno\-altivec \&\-mpowerpc\-gpopt \-mno\-powerpc\-gpopt \&\-mpowerpc\-gfxopt \-mno\-powerpc\-gfxopt \&\-mmfcrf \-mno\-mfcrf \-mpopcntb \-mno\-popcntb \-mpopcntd \-mno\-popcntd \&\-mfprnd \-mno\-fprnd \&\-mcmpb \-mno\-cmpb \-mmfpgpr \-mno\-mfpgpr \-mhard\-dfp \-mno\-hard\-dfp \&\-mfull\-toc \-mminimal\-toc \-mno\-fp\-in\-toc \-mno\-sum\-in\-toc \&\-m64 \-m32 \-mxl\-compat \-mno\-xl\-compat \-mpe \&\-malign\-power \-malign\-natural \&\-msoft\-float \-mhard\-float \-mmultiple \-mno\-multiple \&\-msingle\-float \-mdouble\-float \-msimple\-fpu \&\-mstring \-mno\-string \-mupdate \-mno\-update \&\-mavoid\-indexed\-addresses \-mno\-avoid\-indexed\-addresses \&\-mfused\-madd \-mno\-fused\-madd \-mbit\-align \-mno\-bit\-align \&\-mstrict\-align \-mno\-strict\-align \-mrelocatable \&\-mno\-relocatable \-mrelocatable\-lib \-mno\-relocatable\-lib \&\-mtoc \-mno\-toc \-mlittle \-mlittle\-endian \-mbig \-mbig\-endian \&\-mdynamic\-no\-pic \-maltivec \-mswdiv \-msingle\-pic\-base \&\-mprioritize\-restricted\-insns=\fR\fIpriority\fR \&\fB\-msched\-costly\-dep=\fR\fIdependence_type\fR \&\fB\-minsert\-sched\-nops=\fR\fIscheme\fR \&\fB\-mcall\-sysv \-mcall\-netbsd \&\-maix\-struct\-return \-msvr4\-struct\-return \&\-mabi=\fR\fIabi-type\fR \fB\-msecure\-plt \-mbss\-plt \&\-mblock\-move\-inline\-limit=\fR\fInum\fR \&\fB\-misel \-mno\-isel \&\-misel=yes \-misel=no \&\-mspe \-mno\-spe \&\-mspe=yes \-mspe=no \&\-mpaired \&\-mgen\-cell\-microcode \-mwarn\-cell\-microcode \&\-mvrsave \-mno\-vrsave \&\-mmulhw \-mno\-mulhw \&\-mdlmzb \-mno\-dlmzb \&\-mfloat\-gprs=yes \-mfloat\-gprs=no \-mfloat\-gprs=single \-mfloat\-gprs=double \&\-mprototype \-mno\-prototype \&\-msim \-mmvme \-mads \-myellowknife \-memb \-msdata \&\-msdata=\fR\fIopt\fR \fB\-mvxworks \-G\fR \fInum\fR \fB\-pthread \&\-mrecip \-mrecip=\fR\fIopt\fR \fB\-mno\-recip \-mrecip\-precision \&\-mno\-recip\-precision \&\-mveclibabi=\fR\fItype\fR \fB\-mfriz \-mno\-friz \&\-mpointers\-to\-nested\-functions \-mno\-pointers\-to\-nested\-functions \&\-msave\-toc\-indirect \-mno\-save\-toc\-indirect \&\-mpower8\-fusion \-mno\-mpower8\-fusion \-mpower8\-vector \-mno\-power8\-vector \&\-mcrypto \-mno\-crypto \-mdirect\-move \-mno\-direct\-move \&\-mquad\-memory \-mno\-quad\-memory \&\-mquad\-memory\-atomic \-mno\-quad\-memory\-atomic \&\-mcompat\-align\-parm \-mno\-compat\-align\-parm \&\-mupper\-regs\-df \-mno\-upper\-regs\-df \-mupper\-regs\-sf \-mno\-upper\-regs\-sf \&\-mupper\-regs \-mno\-upper\-regs\fR .Sp \&\fI\s-1RX\s0 Options\fR \&\fB\-m64bit\-doubles \-m32bit\-doubles \-fpu \-nofpu \&\-mcpu= \&\-mbig\-endian\-data \-mlittle\-endian\-data \&\-msmall\-data \&\-msim \-mno\-sim \&\-mas100\-syntax \-mno\-as100\-syntax \&\-mrelax \&\-mmax\-constant\-size= \&\-mint\-register= \&\-mpid \&\-mno\-warn\-multiple\-fast\-interrupts \&\-msave\-acc\-in\-interrupts\fR .Sp \&\fIS/390 and zSeries Options\fR \&\fB\-mtune=\fR\fIcpu-type\fR \fB\-march=\fR\fIcpu-type\fR \&\fB\-mhard\-float \-msoft\-float \-mhard\-dfp \-mno\-hard\-dfp \&\-mlong\-double\-64 \-mlong\-double\-128 \&\-mbackchain \-mno\-backchain \-mpacked\-stack \-mno\-packed\-stack \&\-msmall\-exec \-mno\-small\-exec \-mmvcle \-mno\-mvcle \&\-m64 \-m31 \-mdebug \-mno\-debug \-mesa \-mzarch \&\-mtpf\-trace \-mno\-tpf\-trace \-mfused\-madd \-mno\-fused\-madd \&\-mwarn\-framesize \-mwarn\-dynamicstack \-mstack\-size \-mstack\-guard \&\-mhotpatch=\fR\fIhalfwords\fR\fB,\fR\fIhalfwords\fR .Sp \&\fIScore Options\fR \&\fB\-meb \-mel \&\-mnhwloop \&\-muls \&\-mmac \&\-mscore5 \-mscore5u \-mscore7 \-mscore7d\fR .Sp \&\fI\s-1SH\s0 Options\fR \&\fB\-m1 \-m2 \-m2e \&\-m2a\-nofpu \-m2a\-single\-only \-m2a\-single \-m2a \&\-m3 \-m3e \&\-m4\-nofpu \-m4\-single\-only \-m4\-single \-m4 \&\-m4a\-nofpu \-m4a\-single\-only \-m4a\-single \-m4a \-m4al \&\-m5\-64media \-m5\-64media\-nofpu \&\-m5\-32media \-m5\-32media\-nofpu \&\-m5\-compact \-m5\-compact\-nofpu \&\-mb \-ml \-mdalign \-mrelax \&\-mbigtable \-mfmovd \-mhitachi \-mrenesas \-mno\-renesas \-mnomacsave \&\-mieee \-mno\-ieee \-mbitops \-misize \-minline\-ic_invalidate \-mpadstruct \&\-mspace \-mprefergot \-musermode \-multcost=\fR\fInumber\fR \fB\-mdiv=\fR\fIstrategy\fR \&\fB\-mdivsi3_libfunc=\fR\fIname\fR \fB\-mfixed\-range=\fR\fIregister-range\fR \&\fB\-mindexed\-addressing \-mgettrcost=\fR\fInumber\fR \fB\-mpt\-fixed \&\-maccumulate\-outgoing\-args \-minvalid\-symbols \&\-matomic\-model=\fR\fIatomic-model\fR \&\fB\-mbranch\-cost=\fR\fInum\fR \fB\-mzdcbranch \-mno\-zdcbranch \&\-mcbranch\-force\-delay\-slot \&\-mfused\-madd \-mno\-fused\-madd \-mfsca \-mno\-fsca \-mfsrra \-mno\-fsrra \&\-mpretend\-cmove \-mtas\fR .Sp \&\fISolaris 2 Options\fR \&\fB\-mclear\-hwcap \-mno\-clear\-hwcap \-mimpure\-text \-mno\-impure\-text \&\-pthreads \-pthread\fR .Sp \&\fI\s-1SPARC\s0 Options\fR \&\fB\-mcpu=\fR\fIcpu-type\fR \&\fB\-mtune=\fR\fIcpu-type\fR \&\fB\-mcmodel=\fR\fIcode-model\fR \&\fB\-mmemory\-model=\fR\fImem-model\fR \&\fB\-m32 \-m64 \-mapp\-regs \-mno\-app\-regs \&\-mfaster\-structs \-mno\-faster\-structs \-mflat \-mno\-flat \&\-mfpu \-mno\-fpu \-mhard\-float \-msoft\-float \&\-mhard\-quad\-float \-msoft\-quad\-float \&\-mstack\-bias \-mno\-stack\-bias \&\-munaligned\-doubles \-mno\-unaligned\-doubles \&\-muser\-mode \-mno\-user\-mode \&\-mv8plus \-mno\-v8plus \-mvis \-mno\-vis \&\-mvis2 \-mno\-vis2 \-mvis3 \-mno\-vis3 \&\-mcbcond \-mno\-cbcond \&\-mfmaf \-mno\-fmaf \-mpopc \-mno\-popc \&\-mfix\-at697f \-mfix\-ut699\fR .Sp \&\fI\s-1SPU\s0 Options\fR \&\fB\-mwarn\-reloc \-merror\-reloc \&\-msafe\-dma \-munsafe\-dma \&\-mbranch\-hints \&\-msmall\-mem \-mlarge\-mem \-mstdmain \&\-mfixed\-range=\fR\fIregister-range\fR \&\fB\-mea32 \-mea64 \&\-maddress\-space\-conversion \-mno\-address\-space\-conversion \&\-mcache\-size=\fR\fIcache-size\fR \&\fB\-matomic\-updates \-mno\-atomic\-updates\fR .Sp \&\fISystem V Options\fR \&\fB\-Qy \-Qn \-YP,\fR\fIpaths\fR \fB\-Ym,\fR\fIdir\fR .Sp \&\fITILE-Gx Options\fR \&\fB\-mcpu=CPU \-m32 \-m64 \-mbig\-endian \-mlittle\-endian \&\-mcmodel=\fR\fIcode-model\fR .Sp \&\fITILEPro Options\fR \&\fB\-mcpu=\fR\fIcpu\fR \fB\-m32\fR .Sp \&\fIV850 Options\fR \&\fB\-mlong\-calls \-mno\-long\-calls \-mep \-mno\-ep \&\-mprolog\-function \-mno\-prolog\-function \-mspace \&\-mtda=\fR\fIn\fR \fB\-msda=\fR\fIn\fR \fB\-mzda=\fR\fIn\fR \&\fB\-mapp\-regs \-mno\-app\-regs \&\-mdisable\-callt \-mno\-disable\-callt \&\-mv850e2v3 \-mv850e2 \-mv850e1 \-mv850es \&\-mv850e \-mv850 \-mv850e3v5 \&\-mloop \&\-mrelax \&\-mlong\-jumps \&\-msoft\-float \&\-mhard\-float \&\-mgcc\-abi \&\-mrh850\-abi \&\-mbig\-switch\fR .Sp \&\fI\s-1VAX\s0 Options\fR \&\fB\-mg \-mgnu \-munix\fR .Sp \&\fIVisium Options\fR \&\fB\-mdebug \-msim \-mfpu \-mno\-fpu \-mhard\-float \-msoft\-float \&\-mcpu=\fR\fIcpu-type\fR \fB\-mtune=\fR\fIcpu-type\fR \fB\-msv\-mode \-muser\-mode\fR .Sp \&\fI\s-1VMS\s0 Options\fR \&\fB\-mvms\-return\-codes \-mdebug\-main=\fR\fIprefix\fR \fB\-mmalloc64 \&\-mpointer\-size=\fR\fIsize\fR .Sp \&\fIVxWorks Options\fR \&\fB\-mrtp \-non\-static \-Bstatic \-Bdynamic \&\-Xbind\-lazy \-Xbind\-now\fR .Sp \&\fIx86 Options\fR \&\fB\-mtune=\fR\fIcpu-type\fR \fB\-march=\fR\fIcpu-type\fR \&\fB\-mtune\-ctrl=\fR\fIfeature-list\fR \fB\-mdump\-tune\-features \-mno\-default \&\-mfpmath=\fR\fIunit\fR \&\fB\-masm=\fR\fIdialect\fR \fB\-mno\-fancy\-math\-387 \&\-mno\-fp\-ret\-in\-387 \-msoft\-float \&\-mno\-wide\-multiply \-mrtd \-malign\-double \&\-mpreferred\-stack\-boundary=\fR\fInum\fR \&\fB\-mincoming\-stack\-boundary=\fR\fInum\fR \&\fB\-mcld \-mcx16 \-msahf \-mmovbe \-mcrc32 \&\-mrecip \-mrecip=\fR\fIopt\fR \&\fB\-mvzeroupper \-mprefer\-avx128 \&\-mmmx \-msse \-msse2 \-msse3 \-mssse3 \-msse4.1 \-msse4.2 \-msse4 \-mavx \&\-mavx2 \-mavx512f \-mavx512pf \-mavx512er \-mavx512cd \-msha \&\-maes \-mpclmul \-mfsgsbase \-mrdrnd \-mf16c \-mfma \-mprefetchwt1 \&\-mclflushopt \-mxsavec \-mxsaves \&\-msse4a \-m3dnow \-mpopcnt \-mabm \-mbmi \-mtbm \-mfma4 \-mxop \-mlzcnt \&\-mbmi2 \-mfxsr \-mxsave \-mxsaveopt \-mrtm \-mlwp \-mmpx \-mmwaitx \-mthreads \&\-mno\-align\-stringops \-minline\-all\-stringops \&\-minline\-stringops\-dynamically \-mstringop\-strategy=\fR\fIalg\fR \&\fB\-mmemcpy\-strategy=\fR\fIstrategy\fR \fB\-mmemset\-strategy=\fR\fIstrategy\fR \&\fB\-mpush\-args \-maccumulate\-outgoing\-args \-m128bit\-long\-double \&\-m96bit\-long\-double \-mlong\-double\-64 \-mlong\-double\-80 \-mlong\-double\-128 \&\-mregparm=\fR\fInum\fR \fB\-msseregparm \&\-mveclibabi=\fR\fItype\fR \fB\-mvect8\-ret\-in\-mem \&\-mpc32 \-mpc64 \-mpc80 \-mstackrealign \&\-momit\-leaf\-frame\-pointer \-mno\-red\-zone \-mno\-tls\-direct\-seg\-refs \&\-mcmodel=\fR\fIcode-model\fR \fB\-mabi=\fR\fIname\fR \fB\-maddress\-mode=\fR\fImode\fR \&\fB\-m32 \-m64 \-mx32 \-m16 \-mlarge\-data\-threshold=\fR\fInum\fR \&\fB\-msse2avx \-mfentry \-mrecord\-mcount \-mnop\-mcount \-m8bit\-idiv \&\-mavx256\-split\-unaligned\-load \-mavx256\-split\-unaligned\-store \&\-malign\-data=\fR\fItype\fR \fB\-mstack\-protector\-guard=\fR\fIguard\fR .Sp \&\fIx86 Windows Options\fR \&\fB\-mconsole \-mcygwin \-mno\-cygwin \-mdll \&\-mnop\-fun\-dllimport \-mthread \&\-municode \-mwin32 \-mwindows \-fno\-set\-stack\-executable\fR .Sp \&\fIXstormy16 Options\fR \&\fB\-msim\fR .Sp \&\fIXtensa Options\fR \&\fB\-mconst16 \-mno\-const16 \&\-mfused\-madd \-mno\-fused\-madd \&\-mforce\-no\-pic \&\-mserialize\-volatile \-mno\-serialize\-volatile \&\-mtext\-section\-literals \-mno\-text\-section\-literals \&\-mtarget\-align \-mno\-target\-align \&\-mlongcalls \-mno\-longcalls\fR .Sp \&\fIzSeries Options\fR See S/390 and zSeries Options. .IP "\fICode Generation Options\fR" 4 .IX Item "Code Generation Options" \&\fB\-fcall\-saved\-\fR\fIreg\fR \fB\-fcall\-used\-\fR\fIreg\fR \&\fB\-ffixed\-\fR\fIreg\fR \fB\-fexceptions \&\-fnon\-call\-exceptions \-fdelete\-dead\-exceptions \-funwind\-tables \&\-fasynchronous\-unwind\-tables \&\-fno\-gnu\-unique \&\-finhibit\-size\-directive \-finstrument\-functions \&\-finstrument\-functions\-exclude\-function\-list=\fR\fIsym\fR\fB,\fR\fIsym\fR\fB,... \&\-finstrument\-functions\-exclude\-file\-list=\fR\fIfile\fR\fB,\fR\fIfile\fR\fB,... \&\-fno\-common \-fno\-ident \&\-fpcc\-struct\-return \-fpic \-fPIC \-fpie \-fPIE \&\-fno\-jump\-tables \&\-frecord\-gcc\-switches \&\-freg\-struct\-return \-fshort\-enums \&\-fshort\-double \-fshort\-wchar \&\-fverbose\-asm \-fpack\-struct[=\fR\fIn\fR\fB] \-fstack\-check \&\-fstack\-limit\-register=\fR\fIreg\fR \fB\-fstack\-limit\-symbol=\fR\fIsym\fR \&\fB\-fno\-stack\-limit \-fsplit\-stack \&\-fleading\-underscore \-ftls\-model=\fR\fImodel\fR \&\fB\-fstack\-reuse=\fR\fIreuse_level\fR \&\fB\-ftrapv \-fwrapv \-fbounds\-check \&\-fvisibility=\fR[\fBdefault\fR|\fBinternal\fR|\fBhidden\fR|\fBprotected\fR] \&\fB\-fstrict\-volatile\-bitfields \-fsync\-libcalls\fR .SS "Options Controlling the Kind of Output" .IX Subsection "Options Controlling the Kind of Output" Compilation can involve up to four stages: preprocessing, compilation proper, assembly and linking, always in that order. \s-1GCC\s0 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. .PP For any given input file, the file name suffix determines what kind of compilation is done: .IP "\fIfile\fR\fB.c\fR" 4 .IX Item "file.c" C source code that must be preprocessed. .IP "\fIfile\fR\fB.i\fR" 4 .IX Item "file.i" C source code that should not be preprocessed. .IP "\fIfile\fR\fB.ii\fR" 4 .IX Item "file.ii" \&\*(C+ source code that should not be preprocessed. .IP "\fIfile\fR\fB.m\fR" 4 .IX Item "file.m" Objective-C source code. Note that you must link with the \fIlibobjc\fR library to make an Objective-C program work. .IP "\fIfile\fR\fB.mi\fR" 4 .IX Item "file.mi" Objective-C source code that should not be preprocessed. .IP "\fIfile\fR\fB.mm\fR" 4 .IX Item "file.mm" .PD 0 .IP "\fIfile\fR\fB.M\fR" 4 .IX Item "file.M" .PD Objective\-\*(C+ source code. Note that you must link with the \fIlibobjc\fR library to make an Objective\-\*(C+ program work. Note that \fB.M\fR refers to a literal capital M. .IP "\fIfile\fR\fB.mii\fR" 4 .IX Item "file.mii" Objective\-\*(C+ source code that should not be preprocessed. .IP "\fIfile\fR\fB.h\fR" 4 .IX Item "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 \fB\-fdump\-ada\-spec\fR switch). .IP "\fIfile\fR\fB.cc\fR" 4 .IX Item "file.cc" .PD 0 .IP "\fIfile\fR\fB.cp\fR" 4 .IX Item "file.cp" .IP "\fIfile\fR\fB.cxx\fR" 4 .IX Item "file.cxx" .IP "\fIfile\fR\fB.cpp\fR" 4 .IX Item "file.cpp" .IP "\fIfile\fR\fB.CPP\fR" 4 .IX Item "file.CPP" .IP "\fIfile\fR\fB.c++\fR" 4 .IX Item "file.c++" .IP "\fIfile\fR\fB.C\fR" 4 .IX Item "file.C" .PD \&\*(C+ source code that must be preprocessed. Note that in \fB.cxx\fR, the last two letters must both be literally \fBx\fR. Likewise, \&\fB.C\fR refers to a literal capital C. .IP "\fIfile\fR\fB.mm\fR" 4 .IX Item "file.mm" .PD 0 .IP "\fIfile\fR\fB.M\fR" 4 .IX Item "file.M" .PD Objective\-\*(C+ source code that must be preprocessed. .IP "\fIfile\fR\fB.mii\fR" 4 .IX Item "file.mii" Objective\-\*(C+ source code that should not be preprocessed. .IP "\fIfile\fR\fB.hh\fR" 4 .IX Item "file.hh" .PD 0 .IP "\fIfile\fR\fB.H\fR" 4 .IX Item "file.H" .IP "\fIfile\fR\fB.hp\fR" 4 .IX Item "file.hp" .IP "\fIfile\fR\fB.hxx\fR" 4 .IX Item "file.hxx" .IP "\fIfile\fR\fB.hpp\fR" 4 .IX Item "file.hpp" .IP "\fIfile\fR\fB.HPP\fR" 4 .IX Item "file.HPP" .IP "\fIfile\fR\fB.h++\fR" 4 .IX Item "file.h++" .IP "\fIfile\fR\fB.tcc\fR" 4 .IX Item "file.tcc" .PD \&\*(C+ header file to be turned into a precompiled header or Ada spec. .IP "\fIfile\fR\fB.f\fR" 4 .IX Item "file.f" .PD 0 .IP "\fIfile\fR\fB.for\fR" 4 .IX Item "file.for" .IP "\fIfile\fR\fB.ftn\fR" 4 .IX Item "file.ftn" .PD Fixed form Fortran source code that should not be preprocessed. .IP "\fIfile\fR\fB.F\fR" 4 .IX Item "file.F" .PD 0 .IP "\fIfile\fR\fB.FOR\fR" 4 .IX Item "file.FOR" .IP "\fIfile\fR\fB.fpp\fR" 4 .IX Item "file.fpp" .IP "\fIfile\fR\fB.FPP\fR" 4 .IX Item "file.FPP" .IP "\fIfile\fR\fB.FTN\fR" 4 .IX Item "file.FTN" .PD Fixed form Fortran source code that must be preprocessed (with the traditional preprocessor). .IP "\fIfile\fR\fB.f90\fR" 4 .IX Item "file.f90" .PD 0 .IP "\fIfile\fR\fB.f95\fR" 4 .IX Item "file.f95" .IP "\fIfile\fR\fB.f03\fR" 4 .IX Item "file.f03" .IP "\fIfile\fR\fB.f08\fR" 4 .IX Item "file.f08" .PD Free form Fortran source code that should not be preprocessed. .IP "\fIfile\fR\fB.F90\fR" 4 .IX Item "file.F90" .PD 0 .IP "\fIfile\fR\fB.F95\fR" 4 .IX Item "file.F95" .IP "\fIfile\fR\fB.F03\fR" 4 .IX Item "file.F03" .IP "\fIfile\fR\fB.F08\fR" 4 .IX Item "file.F08" .PD Free form Fortran source code that must be preprocessed (with the traditional preprocessor). .IP "\fIfile\fR\fB.go\fR" 4 .IX Item "file.go" Go source code. .IP "\fIfile\fR\fB.ads\fR" 4 .IX Item "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 \fIspecs\fR. .IP "\fIfile\fR\fB.adb\fR" 4 .IX Item "file.adb" Ada source code file containing a library unit body (a subprogram or package body). Such files are also called \fIbodies\fR. .IP "\fIfile\fR\fB.s\fR" 4 .IX Item "file.s" Assembler code. .IP "\fIfile\fR\fB.S\fR" 4 .IX Item "file.S" .PD 0 .IP "\fIfile\fR\fB.sx\fR" 4 .IX Item "file.sx" .PD Assembler code that must be preprocessed. .IP "\fIother\fR" 4 .IX Item "other" An object file to be fed straight into linking. Any file name with no recognized suffix is treated this way. .PP You can specify the input language explicitly with the \fB\-x\fR option: .IP "\fB\-x\fR \fIlanguage\fR" 4 .IX Item "-x language" Specify explicitly the \fIlanguage\fR 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 \fB\-x\fR option. Possible values for \fIlanguage\fR are: .Sp .Vb 9 \& 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 \& java .Ve .IP "\fB\-x none\fR" 4 .IX 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 \fB\-x\fR has not been used at all). .IP "\fB\-pass\-exit\-codes\fR" 4 .IX Item "-pass-exit-codes" Normally the \fBgcc\fR program exits with the code of 1 if any phase of the compiler returns a non-success return code. If you specify \&\fB\-pass\-exit\-codes\fR, the \fBgcc\fR 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. .PP If you only want some of the stages of compilation, you can use \&\fB\-x\fR (or filename suffixes) to tell \fBgcc\fR where to start, and one of the options \fB\-c\fR, \fB\-S\fR, or \fB\-E\fR to say where \&\fBgcc\fR is to stop. Note that some combinations (for example, \&\fB\-x cpp-output \-E\fR) instruct \fBgcc\fR to do nothing at all. .IP "\fB\-c\fR" 4 .IX Item "-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. .Sp By default, the object file name for a source file is made by replacing the suffix \fB.c\fR, \fB.i\fR, \fB.s\fR, etc., with \fB.o\fR. .Sp Unrecognized input files, not requiring compilation or assembly, are ignored. .IP "\fB\-S\fR" 4 .IX Item "-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. .Sp By default, the assembler file name for a source file is made by replacing the suffix \fB.c\fR, \fB.i\fR, etc., with \fB.s\fR. .Sp Input files that don't require compilation are ignored. .IP "\fB\-E\fR" 4 .IX Item "-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. .Sp Input files that don't require preprocessing are ignored. .IP "\fB\-o\fR \fIfile\fR" 4 .IX Item "-o file" Place output in file \fIfile\fR. 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. .Sp If \fB\-o\fR is not specified, the default is to put an executable file in \fIa.out\fR, the object file for \&\fI\fIsource\fI.\fIsuffix\fI\fR in \fI\fIsource\fI.o\fR, its assembler file in \fI\fIsource\fI.s\fR, a precompiled header file in \&\fI\fIsource\fI.\fIsuffix\fI.gch\fR, and all preprocessed C source on standard output. .IP "\fB\-v\fR" 4 .IX Item "-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. .IP "\fB\-###\fR" 4 .IX Item "-###" Like \fB\-v\fR except the commands are not executed and arguments are quoted unless they contain only alphanumeric characters or \f(CW\*(C`./\-_\*(C'\fR. This is useful for shell scripts to capture the driver-generated command lines. .IP "\fB\-pipe\fR" 4 .IX Item "-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 \s-1GNU\s0 assembler has no trouble. .IP "\fB\-\-help\fR" 4 .IX Item "--help" Print (on the standard output) a description of the command-line options understood by \fBgcc\fR. If the \fB\-v\fR option is also specified then \fB\-\-help\fR is also passed on to the various processes invoked by \fBgcc\fR, so that they can display the command-line options they accept. If the \fB\-Wextra\fR option has also been specified (prior to the \fB\-\-help\fR option), then command-line options that have no documentation associated with them are also displayed. .IP "\fB\-\-target\-help\fR" 4 .IX Item "--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. .IP "\fB\-\-help={\fR\fIclass\fR|[\fB^\fR]\fIqualifier\fR\fB}\fR[\fB,...\fR]" 4 .IX Item "--help={class|[^]qualifier}[,...]" 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: .RS 4 .IP "\fBoptimizers\fR" 4 .IX Item "optimizers" Display all of the optimization options supported by the compiler. .IP "\fBwarnings\fR" 4 .IX Item "warnings" Display all of the options controlling warning messages produced by the compiler. .IP "\fBtarget\fR" 4 .IX Item "target" Display target-specific options. Unlike the \&\fB\-\-target\-help\fR option however, target-specific options of the linker and assembler are not displayed. This is because those tools do not currently support the extended \fB\-\-help=\fR syntax. .IP "\fBparams\fR" 4 .IX Item "params" Display the values recognized by the \fB\-\-param\fR option. .IP "\fIlanguage\fR" 4 .IX Item "language" Display the options supported for \fIlanguage\fR, where \&\fIlanguage\fR is the name of one of the languages supported in this version of \s-1GCC.\s0 .IP "\fBcommon\fR" 4 .IX Item "common" Display the options that are common to all languages. .RE .RS 4 .Sp These are the supported qualifiers: .IP "\fBundocumented\fR" 4 .IX Item "undocumented" Display only those options that are undocumented. .IP "\fBjoined\fR" 4 .IX Item "joined" Display options taking an argument that appears after an equal sign in the same continuous piece of text, such as: \&\fB\-\-help=target\fR. .IP "\fBseparate\fR" 4 .IX Item "separate" Display options taking an argument that appears as a separate word following the original option, such as: \fB\-o output-file\fR. .RE .RS 4 .Sp Thus for example to display all the undocumented target-specific switches supported by the compiler, use: .Sp .Vb 1 \& \-\-help=target,undocumented .Ve .Sp The sense of a qualifier can be inverted by prefixing it with the \&\fB^\fR 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: .Sp .Vb 1 \& \-\-help=warnings,^joined,^undocumented .Ve .Sp The argument to \fB\-\-help=\fR should not consist solely of inverted qualifiers. .Sp 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 \&\fItarget\fR. For example, to display all the target-specific optimization options, use: .Sp .Vb 1 \& \-\-help=target,optimizers .Ve .Sp The \fB\-\-help=\fR option can be repeated on the command line. Each successive use displays its requested class of options, skipping those that have already been displayed. .Sp If the \fB\-Q\fR option appears on the command line before the \&\fB\-\-help=\fR option, then the descriptive text displayed by \&\fB\-\-help=\fR 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 \fB\-\-help=\fR option is used). .Sp Here is a truncated example from the \s-1ARM\s0 port of \fBgcc\fR: .Sp .Vb 5 \& % gcc \-Q \-mabi=2 \-\-help=target \-c \& The following options are target specific: \& \-mabi= 2 \& \-mabort\-on\-noreturn [disabled] \& \-mapcs [disabled] .Ve .Sp 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 \fB\-O2\fR by using: .Sp .Vb 1 \& \-Q \-O2 \-\-help=optimizers .Ve .Sp Alternatively you can discover which binary optimizations are enabled by \fB\-O3\fR by using: .Sp .Vb 3 \& 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 .Ve .RE .IP "\fB\-no\-canonical\-prefixes\fR" 4 .IX Item "-no-canonical-prefixes" Do not expand any symbolic links, resolve references to \fB/../\fR or \fB/./\fR, or make the path absolute when generating a relative prefix. .IP "\fB\-\-version\fR" 4 .IX Item "--version" Display the version number and copyrights of the invoked \s-1GCC.\s0 .IP "\fB\-wrapper\fR" 4 .IX Item "-wrapper" Invoke all subcommands under a wrapper program. The name of the wrapper program and its parameters are passed as a comma separated list. .Sp .Vb 1 \& gcc \-c t.c \-wrapper gdb,\-\-args .Ve .Sp This invokes all subprograms of \fBgcc\fR under \&\fBgdb \-\-args\fR, thus the invocation of \fBcc1\fR is \&\fBgdb \-\-args cc1 ...\fR. .IP "\fB\-fplugin=\fR\fIname\fR\fB.so\fR" 4 .IX Item "-fplugin=name.so" Load the plugin code in file \fIname\fR.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 \&\fB\-fplugin\-arg\-\fR\fIname\fR\fB\-\fR\fIkey\fR\fB=\fR\fIvalue\fR below). Each plugin should define the callback functions specified in the Plugins \s-1API.\s0 .IP "\fB\-fplugin\-arg\-\fR\fIname\fR\fB\-\fR\fIkey\fR\fB=\fR\fIvalue\fR" 4 .IX Item "-fplugin-arg-name-key=value" Define an argument called \fIkey\fR with a value of \fIvalue\fR for the plugin called \fIname\fR. .IP "\fB\-fdump\-ada\-spec\fR[\fB\-slim\fR]" 4 .IX Item "-fdump-ada-spec[-slim]" For C and \*(C+ source and include files, generate corresponding Ada specs. .IP "\fB\-fada\-spec\-parent=\fR\fIunit\fR" 4 .IX Item "-fada-spec-parent=unit" In conjunction with \fB\-fdump\-ada\-spec\fR[\fB\-slim\fR] above, generate Ada specs as child units of parent \fIunit\fR. .IP "\fB\-fdump\-go\-spec=\fR\fIfile\fR" 4 .IX Item "-fdump-go-spec=file" For input files in any language, generate corresponding Go declarations in \fIfile\fR. This generates Go \f(CW\*(C`const\*(C'\fR, \&\f(CW\*(C`type\*(C'\fR, \f(CW\*(C`var\*(C'\fR, and \f(CW\*(C`func\*(C'\fR declarations which may be a useful way to start writing a Go interface to code written in some other language. .IP "\fB@\fR\fIfile\fR" 4 .IX Item "@file" Read command-line options from \fIfile\fR. The options read are inserted in place of the original @\fIfile\fR option. If \fIfile\fR does not exist, or cannot be read, then the option will be treated literally, and not removed. .Sp Options in \fIfile\fR are separated by whitespace. A whitespace character may be included in an option by surrounding the entire option in either single or double quotes. Any character (including a backslash) may be included by prefixing the character to be included with a backslash. The \fIfile\fR may itself contain additional @\fIfile\fR options; any such options will be processed recursively. .SS "Compiling \*(C+ Programs" .IX Subsection "Compiling Programs" \&\*(C+ source files conventionally use one of the suffixes \fB.C\fR, \&\fB.cc\fR, \fB.cpp\fR, \fB.CPP\fR, \fB.c++\fR, \fB.cp\fR, or \&\fB.cxx\fR; \*(C+ header files often use \fB.hh\fR, \fB.hpp\fR, \&\fB.H\fR, or (for shared template code) \fB.tcc\fR; and preprocessed \*(C+ files use the suffix \fB.ii\fR. \s-1GCC\s0 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 \fBgcc\fR). .PP However, the use of \fBgcc\fR does not add the \*(C+ library. \&\fBg++\fR is a program that calls \s-1GCC\s0 and automatically specifies linking against the \*(C+ library. It treats \fB.c\fR, \&\fB.h\fR and \fB.i\fR files as \*(C+ source files instead of C source files unless \fB\-x\fR is used. This program is also useful when precompiling a C header file with a \fB.h\fR extension for use in \*(C+ compilations. On many systems, \fBg++\fR is also installed with the name \fBc++\fR. .PP 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. .SS "Options Controlling C Dialect" .IX Subsection "Options Controlling C 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: .IP "\fB\-ansi\fR" 4 .IX Item "-ansi" In C mode, this is equivalent to \fB\-std=c90\fR. In \*(C+ mode, it is equivalent to \fB\-std=c++98\fR. .Sp This turns off certain features of \s-1GCC\s0 that are incompatible with \s-1ISO C90 \s0(when compiling C code), or of standard \*(C+ (when compiling \*(C+ code), such as the \f(CW\*(C`asm\*(C'\fR and \f(CW\*(C`typeof\*(C'\fR keywords, and predefined macros such as \f(CW\*(C`unix\*(C'\fR and \f(CW\*(C`vax\*(C'\fR that identify the type of system you are using. It also enables the undesirable and rarely used \s-1ISO\s0 trigraph feature. For the C compiler, it disables recognition of \*(C+ style \fB//\fR comments as well as the \f(CW\*(C`inline\*(C'\fR keyword. .Sp The alternate keywords \f(CW\*(C`_\|_asm_\|_\*(C'\fR, \f(CW\*(C`_\|_extension_\|_\*(C'\fR, \&\f(CW\*(C`_\|_inline_\|_\*(C'\fR and \f(CW\*(C`_\|_typeof_\|_\*(C'\fR continue to work despite \&\fB\-ansi\fR. You would not want to use them in an \s-1ISO C\s0 program, of course, but it is useful to put them in header files that might be included in compilations done with \fB\-ansi\fR. Alternate predefined macros such as \f(CW\*(C`_\|_unix_\|_\*(C'\fR and \f(CW\*(C`_\|_vax_\|_\*(C'\fR are also available, with or without \fB\-ansi\fR. .Sp The \fB\-ansi\fR option does not cause non-ISO programs to be rejected gratuitously. For that, \fB\-Wpedantic\fR is required in addition to \fB\-ansi\fR. .Sp The macro \f(CW\*(C`_\|_STRICT_ANSI_\|_\*(C'\fR is predefined when the \fB\-ansi\fR option is used. Some header files may notice this macro and refrain from declaring certain functions or defining certain macros that the \&\s-1ISO\s0 standard doesn't call for; this is to avoid interfering with any programs that might use these names for other things. .Sp Functions that are normally built in but do not have semantics defined by \s-1ISO C \s0(such as \f(CW\*(C`alloca\*(C'\fR and \f(CW\*(C`ffs\*(C'\fR) are not built-in functions when \fB\-ansi\fR is used. .IP "\fB\-std=\fR" 4 .IX Item "-std=" Determine the language standard. This option is currently only supported when compiling C or \*(C+. .Sp The compiler can accept several base standards, such as \fBc90\fR or \&\fBc++98\fR, and \s-1GNU\s0 dialects of those standards, such as \&\fBgnu90\fR or \fBgnu++98\fR. When a base standard is specified, the compiler accepts all programs following that standard plus those using \s-1GNU\s0 extensions that do not contradict it. For example, \&\fB\-std=c90\fR turns off certain features of \s-1GCC\s0 that are incompatible with \s-1ISO C90,\s0 such as the \f(CW\*(C`asm\*(C'\fR and \f(CW\*(C`typeof\*(C'\fR keywords, but not other \s-1GNU\s0 extensions that do not have a meaning in \&\s-1ISO C90,\s0 such as omitting the middle term of a \f(CW\*(C`?:\*(C'\fR expression. On the other hand, when a \s-1GNU\s0 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 \fB\-Wpedantic\fR to identify which features are \s-1GNU\s0 extensions given that version of the standard. For example \&\fB\-std=gnu90 \-Wpedantic\fR warns about \*(C+ style \fB//\fR comments, while \fB\-std=gnu99 \-Wpedantic\fR does not. .Sp A value for this option must be provided; possible values are .RS 4 .IP "\fBc90\fR" 4 .IX Item "c90" .PD 0 .IP "\fBc89\fR" 4 .IX Item "c89" .IP "\fBiso9899:1990\fR" 4 .IX Item "iso9899:1990" .PD Support all \s-1ISO C90\s0 programs (certain \s-1GNU\s0 extensions that conflict with \s-1ISO C90\s0 are disabled). Same as \fB\-ansi\fR for C code. .IP "\fBiso9899:199409\fR" 4 .IX Item "iso9899:199409" \&\s-1ISO C90\s0 as modified in amendment 1. .IP "\fBc99\fR" 4 .IX Item "c99" .PD 0 .IP "\fBc9x\fR" 4 .IX Item "c9x" .IP "\fBiso9899:1999\fR" 4 .IX Item "iso9899:1999" .IP "\fBiso9899:199x\fR" 4 .IX Item "iso9899:199x" .PD \&\s-1ISO C99. \s0 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 <\fBhttp://gcc.gnu.org/c99status.html\fR> for more information. The names \fBc9x\fR and \fBiso9899:199x\fR are deprecated. .IP "\fBc11\fR" 4 .IX Item "c11" .PD 0 .IP "\fBc1x\fR" 4 .IX Item "c1x" .IP "\fBiso9899:2011\fR" 4 .IX Item "iso9899:2011" .PD \&\s-1ISO C11,\s0 the 2011 revision of the \s-1ISO C\s0 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 \fBc1x\fR is deprecated. .IP "\fBgnu90\fR" 4 .IX Item "gnu90" .PD 0 .IP "\fBgnu89\fR" 4 .IX Item "gnu89" .PD \&\s-1GNU\s0 dialect of \s-1ISO C90 \s0(including some C99 features). .IP "\fBgnu99\fR" 4 .IX Item "gnu99" .PD 0 .IP "\fBgnu9x\fR" 4 .IX Item "gnu9x" .PD \&\s-1GNU\s0 dialect of \s-1ISO C99. \s0 The name \fBgnu9x\fR is deprecated. .IP "\fBgnu11\fR" 4 .IX Item "gnu11" .PD 0 .IP "\fBgnu1x\fR" 4 .IX Item "gnu1x" .PD \&\s-1GNU\s0 dialect of \s-1ISO C11. \s0 This is the default for C code. The name \fBgnu1x\fR is deprecated. .IP "\fBc++98\fR" 4 .IX Item "c++98" .PD 0 .IP "\fBc++03\fR" 4 .IX Item "c++03" .PD The 1998 \s-1ISO \*(C+\s0 standard plus the 2003 technical corrigendum and some additional defect reports. Same as \fB\-ansi\fR for \*(C+ code. .IP "\fBgnu++98\fR" 4 .IX Item "gnu++98" .PD 0 .IP "\fBgnu++03\fR" 4 .IX Item "gnu++03" .PD \&\s-1GNU\s0 dialect of \fB\-std=c++98\fR. This is the default for \&\*(C+ code. .IP "\fBc++11\fR" 4 .IX Item "c++11" .PD 0 .IP "\fBc++0x\fR" 4 .IX Item "c++0x" .PD The 2011 \s-1ISO \*(C+\s0 standard plus amendments. The name \fBc++0x\fR is deprecated. .IP "\fBgnu++11\fR" 4 .IX Item "gnu++11" .PD 0 .IP "\fBgnu++0x\fR" 4 .IX Item "gnu++0x" .PD \&\s-1GNU\s0 dialect of \fB\-std=c++11\fR. The name \fBgnu++0x\fR is deprecated. .IP "\fBc++14\fR" 4 .IX Item "c++14" .PD 0 .IP "\fBc++1y\fR" 4 .IX Item "c++1y" .PD The 2014 \s-1ISO \*(C+\s0 standard plus amendments. The name \fBc++1y\fR is deprecated. .IP "\fBgnu++14\fR" 4 .IX Item "gnu++14" .PD 0 .IP "\fBgnu++1y\fR" 4 .IX Item "gnu++1y" .PD \&\s-1GNU\s0 dialect of \fB\-std=c++14\fR. The name \fBgnu++1y\fR is deprecated. .IP "\fBc++1z\fR" 4 .IX Item "c++1z" The next revision of the \s-1ISO \*(C+\s0 standard, tentatively planned for 2017. Support is highly experimental, and will almost certainly change in incompatible ways in future releases. .IP "\fBgnu++1z\fR" 4 .IX Item "gnu++1z" \&\s-1GNU\s0 dialect of \fB\-std=c++1z\fR. Support is highly experimental, and will almost certainly change in incompatible ways in future releases. .RE .RS 4 .RE .IP "\fB\-fgnu89\-inline\fR" 4 .IX Item "-fgnu89-inline" The option \fB\-fgnu89\-inline\fR tells \s-1GCC\s0 to use the traditional \&\s-1GNU\s0 semantics for \f(CW\*(C`inline\*(C'\fR functions when in C99 mode. .Sp Using this option is roughly equivalent to adding the \&\f(CW\*(C`gnu_inline\*(C'\fR function attribute to all inline functions. .Sp The option \fB\-fno\-gnu89\-inline\fR explicitly tells \s-1GCC\s0 to use the C99 semantics for \f(CW\*(C`inline\*(C'\fR when in C99 or gnu99 mode (i.e., it specifies the default behavior). This option is not supported in \fB\-std=c90\fR or \&\fB\-std=gnu90\fR mode. .Sp The preprocessor macros \f(CW\*(C`_\|_GNUC_GNU_INLINE_\|_\*(C'\fR and \&\f(CW\*(C`_\|_GNUC_STDC_INLINE_\|_\*(C'\fR may be used to check which semantics are in effect for \f(CW\*(C`inline\*(C'\fR functions. .IP "\fB\-aux\-info\fR \fIfilename\fR" 4 .IX Item "-aux-info filename" 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. .Sp Besides declarations, the file indicates, in comments, the origin of each declaration (source file and line), whether the declaration was implicit, prototyped or unprototyped (\fBI\fR, \fBN\fR for new or \&\fBO\fR for old, respectively, in the first character after the line number and the colon), and whether it came from a declaration or a definition (\fBC\fR or \fBF\fR, 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. .IP "\fB\-fallow\-parameterless\-variadic\-functions\fR" 4 .IX Item "-fallow-parameterless-variadic-functions" Accept variadic functions without named parameters. .Sp 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+. .IP "\fB\-fno\-asm\fR" 4 .IX Item "-fno-asm" Do not recognize \f(CW\*(C`asm\*(C'\fR, \f(CW\*(C`inline\*(C'\fR or \f(CW\*(C`typeof\*(C'\fR as a keyword, so that code can use these words as identifiers. You can use the keywords \f(CW\*(C`_\|_asm_\|_\*(C'\fR, \f(CW\*(C`_\|_inline_\|_\*(C'\fR and \f(CW\*(C`_\|_typeof_\|_\*(C'\fR instead. \fB\-ansi\fR implies \fB\-fno\-asm\fR. .Sp In \*(C+, this switch only affects the \f(CW\*(C`typeof\*(C'\fR keyword, since \&\f(CW\*(C`asm\*(C'\fR and \f(CW\*(C`inline\*(C'\fR are standard keywords. You may want to use the \fB\-fno\-gnu\-keywords\fR flag instead, which has the same effect. In C99 mode (\fB\-std=c99\fR or \fB\-std=gnu99\fR), this switch only affects the \f(CW\*(C`asm\*(C'\fR and \f(CW\*(C`typeof\*(C'\fR keywords, since \&\f(CW\*(C`inline\*(C'\fR is a standard keyword in \s-1ISO C99.\s0 .IP "\fB\-fno\-builtin\fR" 4 .IX Item "-fno-builtin" .PD 0 .IP "\fB\-fno\-builtin\-\fR\fIfunction\fR" 4 .IX Item "-fno-builtin-function" .PD Don't recognize built-in functions that do not begin with \&\fB_\|_builtin_\fR as prefix. .Sp \&\s-1GCC\s0 normally generates special code to handle certain built-in functions more efficiently; for instance, calls to \f(CW\*(C`alloca\*(C'\fR may become single instructions which adjust the stack directly, and calls to \f(CW\*(C`memcpy\*(C'\fR 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, \s-1GCC\s0 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 \fB\-Wformat\fR for bad calls to \&\f(CW\*(C`printf\*(C'\fR when \f(CW\*(C`printf\*(C'\fR is built in and \f(CW\*(C`strlen\*(C'\fR is known not to modify global memory. .Sp With the \fB\-fno\-builtin\-\fR\fIfunction\fR option only the built-in function \fIfunction\fR is disabled. \fIfunction\fR must not begin with \fB_\|_builtin_\fR. If a function is named that is not built-in in this version of \s-1GCC,\s0 this option is ignored. There is no corresponding \&\fB\-fbuiltin\-\fR\fIfunction\fR option; if you wish to enable built-in functions selectively when using \fB\-fno\-builtin\fR or \&\fB\-ffreestanding\fR, you may define macros such as: .Sp .Vb 2 \& #define abs(n) _\|_builtin_abs ((n)) \& #define strcpy(d, s) _\|_builtin_strcpy ((d), (s)) .Ve .IP "\fB\-fhosted\fR" 4 .IX Item "-fhosted" Assert that compilation targets a hosted environment. This implies \&\fB\-fbuiltin\fR. A hosted environment is one in which the entire standard library is available, and in which \f(CW\*(C`main\*(C'\fR has a return type of \f(CW\*(C`int\*(C'\fR. Examples are nearly everything except a kernel. This is equivalent to \fB\-fno\-freestanding\fR. .IP "\fB\-ffreestanding\fR" 4 .IX Item "-ffreestanding" Assert that compilation targets a freestanding environment. This implies \fB\-fno\-builtin\fR. A freestanding environment is one in which the standard library may not exist, and program startup may not necessarily be at \f(CW\*(C`main\*(C'\fR. The most obvious example is an \s-1OS\s0 kernel. This is equivalent to \fB\-fno\-hosted\fR. .IP "\fB\-fopenacc\fR" 4 .IX Item "-fopenacc" Enable handling of OpenACC directives \f(CW\*(C`#pragma acc\*(C'\fR in C/\*(C+ and \&\f(CW\*(C`!\$acc\*(C'\fR in Fortran. When \fB\-fopenacc\fR is specified, the compiler generates accelerated code according to the OpenACC Application Programming Interface v2.0 <\fBhttp://www.openacc.org/\fR>. This option implies \fB\-pthread\fR, and thus is only supported on targets that have support for \fB\-pthread\fR. .Sp Note that this is an experimental feature, incomplete, and subject to change in future versions of \s-1GCC. \s0 See <\fBhttps://gcc.gnu.org/wiki/OpenACC\fR> for more information. .IP "\fB\-fopenmp\fR" 4 .IX Item "-fopenmp" Enable handling of OpenMP directives \f(CW\*(C`#pragma omp\*(C'\fR in C/\*(C+ and \&\f(CW\*(C`!\$omp\*(C'\fR in Fortran. When \fB\-fopenmp\fR is specified, the compiler generates parallel code according to the OpenMP Application Program Interface v4.0 <\fBhttp://www.openmp.org/\fR>. This option implies \fB\-pthread\fR, and thus is only supported on targets that have support for \fB\-pthread\fR. \fB\-fopenmp\fR implies \&\fB\-fopenmp\-simd\fR. .IP "\fB\-fopenmp\-simd\fR" 4 .IX Item "-fopenmp-simd" Enable handling of OpenMP's \s-1SIMD\s0 directives with \f(CW\*(C`#pragma omp\*(C'\fR in C/\*(C+ and \f(CW\*(C`!\$omp\*(C'\fR in Fortran. Other OpenMP directives are ignored. .IP "\fB\-fcilkplus\fR" 4 .IX Item "-fcilkplus" Enable the usage of Cilk Plus language extension features for C/\*(C+. When the option \fB\-fcilkplus\fR is specified, enable the usage of the Cilk Plus Language extension features for C/\*(C+. The present implementation follows \s-1ABI\s0 version 1.2. This is an experimental feature that is only partially complete, and whose interface may change in future versions of \s-1GCC\s0 as the official specification changes. Currently, all features but \f(CW\*(C`_Cilk_for\*(C'\fR have been implemented. .IP "\fB\-fgnu\-tm\fR" 4 .IX Item "-fgnu-tm" When the option \fB\-fgnu\-tm\fR is specified, the compiler generates code for the Linux variant of Intel's current Transactional Memory \s-1ABI\s0 specification document (Revision 1.1, May 6 2009). This is an experimental feature whose interface may change in future versions of \s-1GCC,\s0 as the official specification changes. Please note that not all architectures are supported for this feature. .Sp For more information on \s-1GCC\s0's support for transactional memory, .Sp Note that the transactional memory feature is not supported with non-call exceptions (\fB\-fnon\-call\-exceptions\fR). .IP "\fB\-fms\-extensions\fR" 4 .IX Item "-fms-extensions" Accept some non-standard constructs used in Microsoft header files. .Sp In \*(C+ code, this allows member names in structures to be similar to previous types declarations. .Sp .Vb 4 \& typedef int UOW; \& struct ABC { \& UOW UOW; \& }; .Ve .Sp Some cases of unnamed fields in structures and unions are only accepted with this option. .Sp Note that this option is off for all targets but x86 targets using ms-abi. .IP "\fB\-fplan9\-extensions\fR" 4 .IX Item "-fplan9-extensions" Accept some non-standard constructs used in Plan 9 code. .Sp This enables \fB\-fms\-extensions\fR, 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. This is only supported for C, not \*(C+. .IP "\fB\-trigraphs\fR" 4 .IX Item "-trigraphs" Support \s-1ISO C\s0 trigraphs. The \fB\-ansi\fR option (and \fB\-std\fR options for strict \s-1ISO C\s0 conformance) implies \fB\-trigraphs\fR. .IP "\fB\-traditional\fR" 4 .IX Item "-traditional" .PD 0 .IP "\fB\-traditional\-cpp\fR" 4 .IX Item "-traditional-cpp" .PD Formerly, these options caused \s-1GCC\s0 to attempt to emulate a pre-standard C compiler. They are now only supported with the \fB\-E\fR switch. The preprocessor continues to support a pre-standard mode. See the \s-1GNU CPP\s0 manual for details. .IP "\fB\-fcond\-mismatch\fR" 4 .IX Item "-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+. .IP "\fB\-flax\-vector\-conversions\fR" 4 .IX Item "-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. .IP "\fB\-funsigned\-char\fR" 4 .IX Item "-funsigned-char" Let the type \f(CW\*(C`char\*(C'\fR be unsigned, like \f(CW\*(C`unsigned char\*(C'\fR. .Sp Each kind of machine has a default for what \f(CW\*(C`char\*(C'\fR should be. It is either like \f(CW\*(C`unsigned char\*(C'\fR by default or like \&\f(CW\*(C`signed char\*(C'\fR by default. .Sp Ideally, a portable program should always use \f(CW\*(C`signed char\*(C'\fR or \&\f(CW\*(C`unsigned char\*(C'\fR when it depends on the signedness of an object. But many programs have been written to use plain \f(CW\*(C`char\*(C'\fR 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. .Sp The type \f(CW\*(C`char\*(C'\fR is always a distinct type from each of \&\f(CW\*(C`signed char\*(C'\fR or \f(CW\*(C`unsigned char\*(C'\fR, even though its behavior is always just like one of those two. .IP "\fB\-fsigned\-char\fR" 4 .IX Item "-fsigned-char" Let the type \f(CW\*(C`char\*(C'\fR be signed, like \f(CW\*(C`signed char\*(C'\fR. .Sp Note that this is equivalent to \fB\-fno\-unsigned\-char\fR, which is the negative form of \fB\-funsigned\-char\fR. Likewise, the option \&\fB\-fno\-signed\-char\fR is equivalent to \fB\-funsigned\-char\fR. .IP "\fB\-fsigned\-bitfields\fR" 4 .IX Item "-fsigned-bitfields" .PD 0 .IP "\fB\-funsigned\-bitfields\fR" 4 .IX Item "-funsigned-bitfields" .IP "\fB\-fno\-signed\-bitfields\fR" 4 .IX Item "-fno-signed-bitfields" .IP "\fB\-fno\-unsigned\-bitfields\fR" 4 .IX Item "-fno-unsigned-bitfields" .PD These options control whether a bit-field is signed or unsigned, when the declaration does not use either \f(CW\*(C`signed\*(C'\fR or \f(CW\*(C`unsigned\*(C'\fR. By default, such a bit-field is signed, because this is consistent: the basic integer types such as \f(CW\*(C`int\*(C'\fR are signed types. .SS "Options Controlling \*(C+ Dialect" .IX Subsection "Options Controlling Dialect" This section describes the command-line options that are only meaningful for \*(C+ programs. You can also use most of the \s-1GNU\s0 compiler options regardless of what language your program is in. For example, you might compile a file \fIfirstClass.C\fR like this: .PP .Vb 1 \& g++ \-g \-frepo \-O \-c firstClass.C .Ve .PP In this example, only \fB\-frepo\fR is an option meant only for \*(C+ programs; you can use the other options with any language supported by \s-1GCC.\s0 .PP Here is a list of options that are \fIonly\fR for compiling \*(C+ programs: .IP "\fB\-fabi\-version=\fR\fIn\fR" 4 .IX Item "-fabi-version=n" Use version \fIn\fR of the \*(C+ \s-1ABI. \s0 The default is version 0. .Sp Version 0 refers to the version conforming most closely to the \*(C+ \s-1ABI\s0 specification. Therefore, the \s-1ABI\s0 obtained using version 0 will change in different versions of G++ as \s-1ABI\s0 bugs are fixed. .Sp Version 1 is the version of the \*(C+ \s-1ABI\s0 that first appeared in G++ 3.2. .Sp Version 2 is the version of the \*(C+ \s-1ABI\s0 that first appeared in G++ 3.4, and was the default through G++ 4.9. .Sp Version 3 corrects an error in mangling a constant address as a template argument. .Sp Version 4, which first appeared in G++ 4.5, implements a standard mangling for vector types. .Sp 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. .Sp 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. .Sp 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. .Sp Version 8, which first appeared in G++ 4.9, corrects the substitution behavior of function types with function-cv-qualifiers. .Sp See also \fB\-Wabi\fR. .IP "\fB\-fabi\-compat\-version=\fR\fIn\fR" 4 .IX Item "-fabi-compat-version=n" 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 \s-1ABI\s0 version to use for the alias. .Sp With \fB\-fabi\-version=0\fR (the default), this defaults to 2. If another \s-1ABI\s0 version is explicitly selected, this defaults to 0. .Sp The compatibility version is also set by \fB\-Wabi=\fR\fIn\fR. .IP "\fB\-fno\-access\-control\fR" 4 .IX Item "-fno-access-control" Turn off all access checking. This switch is mainly useful for working around bugs in the access control code. .IP "\fB\-fcheck\-new\fR" 4 .IX Item "-fcheck-new" Check that the pointer returned by \f(CW\*(C`operator new\*(C'\fR is non-null before attempting to modify the storage allocated. This check is normally unnecessary because the \*(C+ standard specifies that \&\f(CW\*(C`operator new\*(C'\fR only returns \f(CW0\fR if it is declared \&\f(CW\*(C`throw()\*(C'\fR, in which case the compiler always checks the return value even without this option. In all other cases, when \&\f(CW\*(C`operator new\*(C'\fR has a non-empty exception specification, memory exhaustion is signalled by throwing \f(CW\*(C`std::bad_alloc\*(C'\fR. See also \&\fBnew (nothrow)\fR. .IP "\fB\-fconstexpr\-depth=\fR\fIn\fR" 4 .IX Item "-fconstexpr-depth=n" Set the maximum nested evaluation depth for \*(C+11 constexpr functions to \fIn\fR. A limit is needed to detect endless recursion during constant expression evaluation. The minimum specified by the standard is 512. .IP "\fB\-fdeduce\-init\-list\fR" 4 .IX Item "-fdeduce-init-list" Enable deduction of a template type parameter as \&\f(CW\*(C`std::initializer_list\*(C'\fR from a brace-enclosed initializer list, i.e. .Sp .Vb 4 \& template auto forward(T t) \-> decltype (realfn (t)) \& { \& return realfn (t); \& } \& \& void f() \& { \& forward({1,2}); // call forward> \& } .Ve .Sp 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++. .IP "\fB\-ffriend\-injection\fR" 4 .IX Item "-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 \s-1ISO \*(C+\s0 a friend function that is not declared in an enclosing scope can only be found using argument dependent lookup. \s-1GCC\s0 defaults to the standard behavior. .Sp This option is for compatibility, and may be removed in a future release of G++. .IP "\fB\-fno\-elide\-constructors\fR" 4 .IX Item "-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. .IP "\fB\-fno\-enforce\-eh\-specs\fR" 4 .IX Item "-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 \&\f(CW\*(C`NDEBUG\*(C'\fR. 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. .IP "\fB\-fextern\-tls\-init\fR" 4 .IX Item "-fextern-tls-init" .PD 0 .IP "\fB\-fno\-extern\-tls\-init\fR" 4 .IX Item "-fno-extern-tls-init" .PD The \*(C+11 and OpenMP standards allow \f(CW\*(C`thread_local\*(C'\fR and \&\f(CW\*(C`threadprivate\*(C'\fR 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 \s-1TU\s0 needs to trigger dynamic initialization (either because the variable is statically initialized, or a use of the variable in the defining \s-1TU\s0 will be executed before any uses in another \s-1TU\s0), they can avoid this overhead with the \&\fB\-fno\-extern\-tls\-init\fR option. .Sp On targets that support symbol aliases, the default is \&\fB\-fextern\-tls\-init\fR. On targets that do not support symbol aliases, the default is \fB\-fno\-extern\-tls\-init\fR. .IP "\fB\-ffor\-scope\fR" 4 .IX Item "-ffor-scope" .PD 0 .IP "\fB\-fno\-for\-scope\fR" 4 .IX Item "-fno-for-scope" .PD If \fB\-ffor\-scope\fR is specified, the scope of variables declared in a \fIfor-init-statement\fR is limited to the \f(CW\*(C`for\*(C'\fR loop itself, as specified by the \*(C+ standard. If \fB\-fno\-for\-scope\fR is specified, the scope of variables declared in a \fIfor-init-statement\fR extends to the end of the enclosing scope, as was the case in old versions of G++, and other (traditional) implementations of \*(C+. .Sp 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. .IP "\fB\-fno\-gnu\-keywords\fR" 4 .IX Item "-fno-gnu-keywords" Do not recognize \f(CW\*(C`typeof\*(C'\fR as a keyword, so that code can use this word as an identifier. You can use the keyword \f(CW\*(C`_\|_typeof_\|_\*(C'\fR instead. \&\fB\-ansi\fR implies \fB\-fno\-gnu\-keywords\fR. .IP "\fB\-fno\-implicit\-templates\fR" 4 .IX Item "-fno-implicit-templates" Never emit code for non-inline templates that are instantiated implicitly (i.e. by use); only emit code for explicit instantiations. .IP "\fB\-fno\-implicit\-inline\-templates\fR" 4 .IX Item "-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. .IP "\fB\-fno\-implement\-inlines\fR" 4 .IX Item "-fno-implement-inlines" To save space, do not emit out-of-line copies of inline functions controlled by \f(CW\*(C`#pragma implementation\*(C'\fR. This causes linker errors if these functions are not inlined everywhere they are called. .IP "\fB\-fms\-extensions\fR" 4 .IX Item "-fms-extensions" Disable Wpedantic warnings about constructs used in \s-1MFC,\s0 such as implicit int and getting a pointer to member function via non-standard syntax. .IP "\fB\-fno\-nonansi\-builtins\fR" 4 .IX Item "-fno-nonansi-builtins" Disable built-in declarations of functions that are not mandated by \&\s-1ANSI/ISO C. \s0 These include \f(CW\*(C`ffs\*(C'\fR, \f(CW\*(C`alloca\*(C'\fR, \f(CW\*(C`_exit\*(C'\fR, \&\f(CW\*(C`index\*(C'\fR, \f(CW\*(C`bzero\*(C'\fR, \f(CW\*(C`conjf\*(C'\fR, and other related functions. .IP "\fB\-fnothrow\-opt\fR" 4 .IX Item "-fnothrow-opt" Treat a \f(CW\*(C`throw()\*(C'\fR exception specification as if it were a \&\f(CW\*(C`noexcept\*(C'\fR 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 \s-1EH\s0 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 \f(CW\*(C`terminate\*(C'\fR rather than \f(CW\*(C`unexpected\*(C'\fR. .IP "\fB\-fno\-operator\-names\fR" 4 .IX Item "-fno-operator-names" Do not treat the operator name keywords \f(CW\*(C`and\*(C'\fR, \f(CW\*(C`bitand\*(C'\fR, \&\f(CW\*(C`bitor\*(C'\fR, \f(CW\*(C`compl\*(C'\fR, \f(CW\*(C`not\*(C'\fR, \f(CW\*(C`or\*(C'\fR and \f(CW\*(C`xor\*(C'\fR as synonyms as keywords. .IP "\fB\-fno\-optional\-diags\fR" 4 .IX Item "-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. .IP "\fB\-fpermissive\fR" 4 .IX Item "-fpermissive" Downgrade some diagnostics about nonconformant code from errors to warnings. Thus, using \fB\-fpermissive\fR allows some nonconforming code to compile. .IP "\fB\-fno\-pretty\-templates\fR" 4 .IX Item "-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. \f(CW\*(C`void f(T) [with T = int]\*(C'\fR rather than \f(CW\*(C`void f(int)\*(C'\fR) 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 \fB\-fno\-pretty\-templates\fR to disable them. .IP "\fB\-frepo\fR" 4 .IX Item "-frepo" Enable automatic template instantiation at link time. This option also implies \fB\-fno\-implicit\-templates\fR. .IP "\fB\-fno\-rtti\fR" 4 .IX Item "-fno-rtti" Disable generation of information about every class with virtual functions for use by the \*(C+ run-time type identification features (\f(CW\*(C`dynamic_cast\*(C'\fR and \f(CW\*(C`typeid\*(C'\fR). 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 \f(CW\*(C`dynamic_cast\*(C'\fR operator can still be used for casts that do not require run-time type information, i.e. casts to \f(CW\*(C`void *\*(C'\fR or to unambiguous base classes. .IP "\fB\-fsized\-deallocation\fR" 4 .IX Item "-fsized-deallocation" Enable the built-in global declarations .Sp .Vb 2 \& void operator delete (void *, std::size_t) noexcept; \& void operator delete[] (void *, std::size_t) noexcept; .Ve .Sp 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 \&\fB\-std=c++14\fR and above. The flag \fB\-Wsized\-deallocation\fR warns about places that might want to add a definition. .IP "\fB\-fstats\fR" 4 .IX Item "-fstats" Emit statistics about front-end processing at the end of the compilation. This information is generally only useful to the G++ development team. .IP "\fB\-fstrict\-enums\fR" 4 .IX Item "-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. .IP "\fB\-ftemplate\-backtrace\-limit=\fR\fIn\fR" 4 .IX Item "-ftemplate-backtrace-limit=n" Set the maximum number of template instantiation notes for a single warning or error to \fIn\fR. The default value is 10. .IP "\fB\-ftemplate\-depth=\fR\fIn\fR" 4 .IX Item "-ftemplate-depth=n" Set the maximum instantiation depth for template classes to \fIn\fR. A limit on the template instantiation depth is needed to detect endless recursions during template class instantiation. \s-1ANSI/ISO \*(C+\s0 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. .IP "\fB\-fno\-threadsafe\-statics\fR" 4 .IX Item "-fno-threadsafe-statics" Do not emit the extra code to use the routines specified in the \*(C+ \&\s-1ABI\s0 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. .IP "\fB\-fuse\-cxa\-atexit\fR" 4 .IX Item "-fuse-cxa-atexit" Register destructors for objects with static storage duration with the \&\f(CW\*(C`_\|_cxa_atexit\*(C'\fR function rather than the \f(CW\*(C`atexit\*(C'\fR function. This option is required for fully standards-compliant handling of static destructors, but only works if your C library supports \&\f(CW\*(C`_\|_cxa_atexit\*(C'\fR. .IP "\fB\-fno\-use\-cxa\-get\-exception\-ptr\fR" 4 .IX Item "-fno-use-cxa-get-exception-ptr" Don't use the \f(CW\*(C`_\|_cxa_get_exception_ptr\*(C'\fR runtime routine. This causes \f(CW\*(C`std::uncaught_exception\*(C'\fR to be incorrect, but is necessary if the runtime routine is not available. .IP "\fB\-fvisibility\-inlines\-hidden\fR" 4 .IX Item "-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. .Sp The effect of this is that \s-1GCC\s0 may, effectively, mark inline methods with \&\f(CW\*(C`_\|_attribute_\|_ ((visibility ("hidden")))\*(C'\fR so that they do not appear in the export table of a \s-1DSO\s0 and do not require a \s-1PLT\s0 indirection when used within the \s-1DSO. \s0 Enabling this option can have a dramatic effect on load and link times of a \s-1DSO\s0 as it massively reduces the size of the dynamic export table when the library makes heavy use of templates. .Sp 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. .Sp 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. .Sp Explicitly instantiated inline methods are unaffected by this option as their linkage might otherwise cross a shared library boundary. .IP "\fB\-fvisibility\-ms\-compat\fR" 4 .IX Item "-fvisibility-ms-compat" This flag attempts to use visibility settings to make \s-1GCC\s0's \*(C+ linkage model compatible with that of Microsoft Visual Studio. .Sp The flag makes these changes to \s-1GCC\s0's linkage model: .RS 4 .IP "1." 4 .IX Item "1." It sets the default visibility to \f(CW\*(C`hidden\*(C'\fR, like \&\fB\-fvisibility=hidden\fR. .IP "2." 4 .IX Item "2." Types, but not their members, are not hidden by default. .IP "3." 4 .IX Item "3." 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. .RE .RS 4 .Sp In new code it is better to use \fB\-fvisibility=hidden\fR 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. .Sp 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 \s-1ODR\s0 to define types with the same name differently. .RE .IP "\fB\-fvtable\-verify=\fR[\fBstd\fR|\fBpreinit\fR|\fBnone\fR]" 4 .IX Item "-fvtable-verify=[std|preinit|none]" Turn on (or off, if using \fB\-fvtable\-verify=none\fR) the security feature that verifies at run time, for every virtual call, that the vtable pointer through which the call is made is valid for the type of the object, and has not been corrupted or overwritten. If an invalid vtable pointer is detected at run time, an error is reported and execution of the program is immediately halted. .Sp This option causes run-time data structures to be built at program startup, which are used for verifying the vtable pointers. The options \fBstd\fR and \fBpreinit\fR control the timing of when these data structures are built. In both cases the data structures are built before execution reaches \f(CW\*(C`main\*(C'\fR. Using \&\fB\-fvtable\-verify=std\fR causes the data structures to be built after shared libraries have been loaded and initialized. \&\fB\-fvtable\-verify=preinit\fR causes them to be built before shared libraries have been loaded and initialized. .Sp If this option appears multiple times in the command line with different values specified, \fBnone\fR takes highest priority over both \fBstd\fR and \&\fBpreinit\fR; \fBpreinit\fR takes priority over \fBstd\fR. .IP "\fB\-fvtv\-debug\fR" 4 .IX Item "-fvtv-debug" When used in conjunction with \fB\-fvtable\-verify=std\fR or \&\fB\-fvtable\-verify=preinit\fR, causes debug versions of the runtime functions for the vtable verification feature to be called. This flag also causes the compiler to log information about which vtable pointers it finds for each class. This information is written to a file named \fIvtv_set_ptr_data.log\fR in the directory named by the environment variable \fB\s-1VTV_LOGS_DIR\s0\fR if that is defined or the current working directory otherwise. .Sp Note: This feature \fIappends\fR data to the log file. If you want a fresh log file, be sure to delete any existing one. .IP "\fB\-fvtv\-counts\fR" 4 .IX Item "-fvtv-counts" This is a debugging flag. When used in conjunction with \&\fB\-fvtable\-verify=std\fR or \fB\-fvtable\-verify=preinit\fR, this causes the compiler to keep track of the total number of virtual calls it encounters and the number of verifications it inserts. It also counts the number of calls to certain run-time library functions that it inserts and logs this information for each compilation unit. The compiler writes this information to a file named \&\fIvtv_count_data.log\fR in the directory named by the environment variable \fB\s-1VTV_LOGS_DIR\s0\fR if that is defined or the current working directory otherwise. It also counts the size of the vtable pointer sets for each class, and writes this information to \fIvtv_class_set_sizes.log\fR in the same directory. .Sp Note: This feature \fIappends\fR data to the log files. To get fresh log files, be sure to delete any existing ones. .IP "\fB\-fno\-weak\fR" 4 .IX Item "-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++. .IP "\fB\-nostdinc++\fR" 4 .IX Item "-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.) .PP In addition, these optimization, warning, and code generation options have meanings only for \*(C+ programs: .IP "\fB\-Wabi\fR (C, Objective-C, \*(C+ and Objective\-\*(C+ only)" 4 .IX Item "-Wabi (C, Objective-C, and Objective- only)" When an explicit \fB\-fabi\-version=\fR\fIn\fR option is used, causes G++ to warn when it generates code that is probably not compatible with the vendor-neutral \*(C+ \s-1ABI. \s0 Since G++ now defaults to \&\fB\-fabi\-version=0\fR, \fB\-Wabi\fR has no effect unless either an older \s-1ABI\s0 version is selected (with \fB\-fabi\-version=\fR\fIn\fR) or an older compatibility version is selected (with \&\fB\-Wabi=\fR\fIn\fR or \fB\-fabi\-compat\-version=\fR\fIn\fR). .Sp 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. .Sp 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. .Sp \&\fB\-Wabi\fR can also be used with an explicit version number to warn about compatibility with a particular \fB\-fabi\-version\fR level, e.g. \fB\-Wabi=2\fR to warn about changes relative to \&\fB\-fabi\-version=2\fR. Specifying a version number also sets \&\fB\-fabi\-compat\-version=\fR\fIn\fR. .Sp The known incompatibilities in \fB\-fabi\-version=2\fR (which was the default from \s-1GCC 3.4\s0 to 4.9) include: .RS 4 .IP "*" 4 A template with a non-type template parameter of reference type was mangled incorrectly: .Sp .Vb 3 \& extern int N; \& template struct S {}; \& void n (S) {2} .Ve .Sp This was fixed in \fB\-fabi\-version=3\fR. .IP "*" 4 \&\s-1SIMD\s0 vector types declared using \f(CW\*(C`_\|_attribute ((vector_size))\*(C'\fR were mangled in a non-standard way that does not allow for overloading of functions taking vectors of different sizes. .Sp The mangling was changed in \fB\-fabi\-version=4\fR. .IP "*" 4 \&\f(CW\*(C`_\|_attribute ((const))\*(C'\fR and \f(CW\*(C`noreturn\*(C'\fR were mangled as type qualifiers, and \f(CW\*(C`decltype\*(C'\fR of a plain declaration was folded away. .Sp These mangling issues were fixed in \fB\-fabi\-version=5\fR. .IP "*" 4 Scoped enumerators passed as arguments to a variadic function are promoted like unscoped enumerators, causing \f(CW\*(C`va_arg\*(C'\fR to complain. On most targets this does not actually affect the parameter passing \&\s-1ABI,\s0 as there is no way to pass an argument smaller than \f(CW\*(C`int\*(C'\fR. .Sp Also, the \s-1ABI\s0 changed the mangling of template argument packs, \&\f(CW\*(C`const_cast\*(C'\fR, \f(CW\*(C`static_cast\*(C'\fR, prefix increment/decrement, and a class scope function used as a template argument. .Sp These issues were corrected in \fB\-fabi\-version=6\fR. .IP "*" 4 Lambdas in default argument scope were mangled incorrectly, and the \&\s-1ABI\s0 changed the mangling of \f(CW\*(C`nullptr_t\*(C'\fR. .Sp These issues were corrected in \fB\-fabi\-version=7\fR. .IP "*" 4 When mangling a function type with function-cv-qualifiers, the un-qualified function type was incorrectly treated as a substitution candidate. .Sp This was fixed in \fB\-fabi\-version=8\fR. .RE .RS 4 .Sp It also warns about psABI-related changes. The known psABI changes at this point include: .IP "*" 4 For SysV/x86\-64, unions with \f(CW\*(C`long double\*(C'\fR members are passed in memory as specified in psABI. For example: .Sp .Vb 4 \& union U { \& long double ld; \& int i; \& }; .Ve .Sp \&\f(CW\*(C`union U\*(C'\fR is always passed in memory. .RE .RS 4 .RE .IP "\fB\-Wabi\-tag\fR (\*(C+ and Objective\-\*(C+ only)" 4 .IX Item "-Wabi-tag ( and Objective- only)" Warn when a type with an \s-1ABI\s0 tag is used in a context that does not have that \s-1ABI\s0 tag. See \fB\*(C+ Attributes\fR for more information about \s-1ABI\s0 tags. .IP "\fB\-Wctor\-dtor\-privacy\fR (\*(C+ and Objective\-\*(C+ only)" 4 .IX Item "-Wctor-dtor-privacy ( and Objective- only)" 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. .IP "\fB\-Wdelete\-non\-virtual\-dtor\fR (\*(C+ and Objective\-\*(C+ only)" 4 .IX Item "-Wdelete-non-virtual-dtor ( and Objective- only)" Warn when \f(CW\*(C`delete\*(C'\fR 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 \fB\-Wall\fR. .IP "\fB\-Wliteral\-suffix\fR (\*(C+ and Objective\-\*(C+ only)" 4 .IX Item "-Wliteral-suffix ( and Objective- only)" Warn when a string or character literal is followed by a ud-suffix which does not begin with an underscore. As a conforming extension, \s-1GCC\s0 treats such suffixes as separate preprocessing tokens in order to maintain backwards compatibility with code that uses formatting macros from \f(CW\*(C`\*(C'\fR. For example: .Sp .Vb 3 \& #define _\|_STDC_FORMAT_MACROS \& #include \& #include \& \& int main() { \& int64_t i64 = 123; \& printf("My int64: %"PRId64"\en", i64); \& } .Ve .Sp In this case, \f(CW\*(C`PRId64\*(C'\fR is treated as a separate preprocessing token. .Sp This warning is enabled by default. .IP "\fB\-Wnarrowing\fR (\*(C+ and Objective\-\*(C+ only)" 4 .IX Item "-Wnarrowing ( and Objective- only)" Warn when a narrowing conversion prohibited by \*(C+11 occurs within \&\fB{ }\fR, e.g. .Sp .Vb 1 \& int i = { 2.2 }; // error: narrowing from double to int .Ve .Sp This flag is included in \fB\-Wall\fR and \fB\-Wc++11\-compat\fR. .Sp With \fB\-std=c++11\fR, \fB\-Wno\-narrowing\fR suppresses the diagnostic required by the standard. Note that this does not affect the meaning of well-formed code; narrowing conversions are still considered ill-formed in \s-1SFINAE\s0 context. .IP "\fB\-Wnoexcept\fR (\*(C+ and Objective\-\*(C+ only)" 4 .IX Item "-Wnoexcept ( and Objective- only)" 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. \f(CW\*(C`throw()\*(C'\fR or \f(CW\*(C`noexcept\*(C'\fR) but is known by the compiler to never throw an exception. .IP "\fB\-Wnon\-virtual\-dtor\fR (\*(C+ and Objective\-\*(C+ only)" 4 .IX Item "-Wnon-virtual-dtor ( and Objective- only)" 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 \fB\-Weffc++\fR is specified. .IP "\fB\-Wreorder\fR (\*(C+ and Objective\-\*(C+ only)" 4 .IX Item "-Wreorder ( and Objective- only)" Warn when the order of member initializers given in the code does not match the order in which they must be executed. For instance: .Sp .Vb 5 \& struct A { \& int i; \& int j; \& A(): j (0), i (1) { } \& }; .Ve .Sp The compiler rearranges the member initializers for \f(CW\*(C`i\*(C'\fR and \f(CW\*(C`j\*(C'\fR to match the declaration order of the members, emitting a warning to that effect. This warning is enabled by \fB\-Wall\fR. .IP "\fB\-fext\-numeric\-literals\fR (\*(C+ and Objective\-\*(C+ only)" 4 .IX Item "-fext-numeric-literals ( and Objective- only)" Accept imaginary, fixed-point, or machine-defined literal number suffixes as \s-1GNU\s0 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 \s-1GNU\s0 dialects: \&\fB\-std=c++98\fR, \fB\-std=gnu++98\fR, \fB\-std=gnu++11\fR, \&\fB\-std=gnu++14\fR. This option is off by default for \s-1ISO \*(C+11\s0 onwards (\fB\-std=c++11\fR, ...). .PP The following \fB\-W...\fR options are not affected by \fB\-Wall\fR. .IP "\fB\-Weffc++\fR (\*(C+ and Objective\-\*(C+ only)" 4 .IX Item "-Weffc++ ( and Objective- only)" Warn about violations of the following style guidelines from Scott Meyers' \&\fIEffective \*(C+\fR series of books: .RS 4 .IP "*" 4 Define a copy constructor and an assignment operator for classes with dynamically-allocated memory. .IP "*" 4 Prefer initialization to assignment in constructors. .IP "*" 4 Have \f(CW\*(C`operator=\*(C'\fR return a reference to \f(CW*this\fR. .IP "*" 4 Don't try to return a reference when you must return an object. .IP "*" 4 Distinguish between prefix and postfix forms of increment and decrement operators. .IP "*" 4 Never overload \f(CW\*(C`&&\*(C'\fR, \f(CW\*(C`||\*(C'\fR, or \f(CW\*(C`,\*(C'\fR. .RE .RS 4 .Sp This option also enables \fB\-Wnon\-virtual\-dtor\fR, 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. .Sp When selecting this option, be aware that the standard library headers do not obey all of these guidelines; use \fBgrep \-v\fR to filter out those warnings. .RE .IP "\fB\-Wstrict\-null\-sentinel\fR (\*(C+ and Objective\-\*(C+ only)" 4 .IX Item "-Wstrict-null-sentinel ( and Objective- only)" Warn about the use of an uncasted \f(CW\*(C`NULL\*(C'\fR as sentinel. When compiling only with \s-1GCC\s0 this is a valid sentinel, as \f(CW\*(C`NULL\*(C'\fR is defined to \f(CW\*(C`_\|_null\*(C'\fR. 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. .IP "\fB\-Wno\-non\-template\-friend\fR (\*(C+ and Objective\-\*(C+ only)" 4 .IX Item "-Wno-non-template-friend ( and Objective- only)" Disable warnings when non-templatized friend functions are declared within a template. Since the advent of explicit template specification support in G++, if the name of the friend is an unqualified-id (i.e., \&\fBfriend foo(int)\fR), the \*(C+ language specification demands that the friend declare or define an ordinary, nontemplate function. (Section 14.5.3). Before G++ implemented explicit specification, unqualified-ids could be interpreted as a particular specialization of a templatized function. Because this non-conforming behavior is no longer the default behavior for G++, \fB\-Wnon\-template\-friend\fR allows the compiler to check existing code for potential trouble spots and is on by default. This new compiler behavior can be turned off with \&\fB\-Wno\-non\-template\-friend\fR, which keeps the conformant compiler code but disables the helpful warning. .IP "\fB\-Wold\-style\-cast\fR (\*(C+ and Objective\-\*(C+ only)" 4 .IX Item "-Wold-style-cast ( and Objective- only)" Warn if an old-style (C\-style) cast to a non-void type is used within a \*(C+ program. The new-style casts (\f(CW\*(C`dynamic_cast\*(C'\fR, \&\f(CW\*(C`static_cast\*(C'\fR, \f(CW\*(C`reinterpret_cast\*(C'\fR, and \f(CW\*(C`const_cast\*(C'\fR) are less vulnerable to unintended effects and much easier to search for. .IP "\fB\-Woverloaded\-virtual\fR (\*(C+ and Objective\-\*(C+ only)" 4 .IX Item "-Woverloaded-virtual ( and Objective- only)" Warn when a function declaration hides virtual functions from a base class. For example, in: .Sp .Vb 3 \& struct A { \& virtual void f(); \& }; \& \& struct B: public A { \& void f(int); \& }; .Ve .Sp the \f(CW\*(C`A\*(C'\fR class version of \f(CW\*(C`f\*(C'\fR is hidden in \f(CW\*(C`B\*(C'\fR, and code like: .Sp .Vb 2 \& B* b; \& b\->f(); .Ve .Sp fails to compile. .IP "\fB\-Wno\-pmf\-conversions\fR (\*(C+ and Objective\-\*(C+ only)" 4 .IX Item "-Wno-pmf-conversions ( and Objective- only)" Disable the diagnostic for converting a bound pointer to member function to a plain pointer. .IP "\fB\-Wsign\-promo\fR (\*(C+ and Objective\-\*(C+ only)" 4 .IX Item "-Wsign-promo ( and Objective- only)" 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. .SS "Options Controlling Objective-C and Objective\-\*(C+ Dialects" .IX Subsection "Options Controlling Objective-C and Objective- Dialects" (\s-1NOTE:\s0 This manual does not describe the Objective-C and Objective\-\*(C+ languages themselves. .PP 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 \s-1GNU\s0 compiler options. For example, you might compile a file \fIsome_class.m\fR like this: .PP .Vb 1 \& gcc \-g \-fgnu\-runtime \-O \-c some_class.m .Ve .PP In this example, \fB\-fgnu\-runtime\fR is an option meant only for Objective-C and Objective\-\*(C+ programs; you can use the other options with any language supported by \s-1GCC.\s0 .PP 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., \&\fB\-Wtraditional\fR). Similarly, Objective\-\*(C+ compilations may use \&\*(C+\-specific options (e.g., \fB\-Wabi\fR). .PP Here is a list of options that are \fIonly\fR for compiling Objective-C and Objective\-\*(C+ programs: .IP "\fB\-fconstant\-string\-class=\fR\fIclass-name\fR" 4 .IX Item "-fconstant-string-class=class-name" Use \fIclass-name\fR as the name of the class to instantiate for each literal string specified with the syntax \f(CW\*(C`@"..."\*(C'\fR. The default class name is \f(CW\*(C`NXConstantString\*(C'\fR if the \s-1GNU\s0 runtime is being used, and \&\f(CW\*(C`NSConstantString\*(C'\fR if the NeXT runtime is being used (see below). The \&\fB\-fconstant\-cfstrings\fR option, if also present, overrides the \&\fB\-fconstant\-string\-class\fR setting and cause \f(CW\*(C`@"..."\*(C'\fR literals to be laid out as constant CoreFoundation strings. .IP "\fB\-fgnu\-runtime\fR" 4 .IX Item "-fgnu-runtime" Generate object code compatible with the standard \s-1GNU\s0 Objective-C runtime. This is the default for most types of systems. .IP "\fB\-fnext\-runtime\fR" 4 .IX Item "-fnext-runtime" Generate output compatible with the NeXT runtime. This is the default for NeXT-based systems, including Darwin and Mac \s-1OS X. \s0 The macro \&\f(CW\*(C`_\|_NEXT_RUNTIME_\|_\*(C'\fR is predefined if (and only if) this option is used. .IP "\fB\-fno\-nil\-receivers\fR" 4 .IX Item "-fno-nil-receivers" Assume that all Objective-C message dispatches (\f(CW\*(C`[receiver message:arg]\*(C'\fR) in this translation unit ensure that the receiver is not \f(CW\*(C`nil\*(C'\fR. 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 \s-1ABI\s0 version 0 or 1. .IP "\fB\-fobjc\-abi\-version=\fR\fIn\fR" 4 .IX Item "-fobjc-abi-version=n" Use version \fIn\fR of the Objective-C \s-1ABI\s0 for the selected runtime. This option is currently supported only for the NeXT runtime. In that case, Version 0 is the traditional (32\-bit) \s-1ABI\s0 without support for properties and other Objective-C 2.0 additions. Version 1 is the traditional (32\-bit) \s-1ABI\s0 with support for properties and other Objective-C 2.0 additions. Version 2 is the modern (64\-bit) \s-1ABI. \s0 If nothing is specified, the default is Version 0 on 32\-bit target machines, and Version 2 on 64\-bit target machines. .IP "\fB\-fobjc\-call\-cxx\-cdtors\fR" 4 .IX Item "-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 \f(CW\*(C`\- (id) .cxx_construct\*(C'\fR instance method which runs non-trivial default constructors on any such instance variables, in order, and then return \f(CW\*(C`self\*(C'\fR. Similarly, check if any instance variable is a \*(C+ object with a non-trivial destructor, and if so, synthesize a special \f(CW\*(C`\- (void) .cxx_destruct\*(C'\fR method which runs all such default destructors, in reverse order. .Sp The \f(CW\*(C`\- (id) .cxx_construct\*(C'\fR and \f(CW\*(C`\- (void) .cxx_destruct\*(C'\fR 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 \f(CW\*(C`\- (id) .cxx_construct\*(C'\fR methods are invoked by the runtime immediately after a new object instance is allocated; the \f(CW\*(C`\- (void) .cxx_destruct\*(C'\fR methods are invoked immediately before the runtime deallocates an object instance. .Sp As of this writing, only the NeXT runtime on Mac \s-1OS X 10.4\s0 and later has support for invoking the \f(CW\*(C`\- (id) .cxx_construct\*(C'\fR and \&\f(CW\*(C`\- (void) .cxx_destruct\*(C'\fR methods. .IP "\fB\-fobjc\-direct\-dispatch\fR" 4 .IX Item "-fobjc-direct-dispatch" Allow fast jumps to the message dispatcher. On Darwin this is accomplished via the comm page. .IP "\fB\-fobjc\-exceptions\fR" 4 .IX Item "-fobjc-exceptions" Enable syntactic support for structured exception handling in Objective-C, similar to what is offered by \*(C+ and Java. This option is required to use the Objective-C keywords \f(CW@try\fR, \&\f(CW@throw\fR, \f(CW@catch\fR, \f(CW@finally\fR and \&\f(CW@synchronized\fR. This option is available with both the \s-1GNU\s0 runtime and the NeXT runtime (but not available in conjunction with the NeXT runtime on Mac \s-1OS X 10.2\s0 and earlier). .IP "\fB\-fobjc\-gc\fR" 4 .IX Item "-fobjc-gc" Enable garbage collection (\s-1GC\s0) in Objective-C and Objective\-\*(C+ programs. This option is only available with the NeXT runtime; the \&\s-1GNU\s0 runtime has a different garbage collection implementation that does not require special compiler flags. .IP "\fB\-fobjc\-nilcheck\fR" 4 .IX Item "-fobjc-nilcheck" For the NeXT runtime with version 2 of the \s-1ABI,\s0 check for a nil receiver in method invocations before doing the actual method call. This is the default and can be disabled using \&\fB\-fno\-objc\-nilcheck\fR. 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 \s-1GNU\s0 runtime, or an older version of the NeXT runtime \s-1ABI,\s0 is used. .IP "\fB\-fobjc\-std=objc1\fR" 4 .IX Item "-fobjc-std=objc1" Conform to the language syntax of Objective-C 1.0, the language recognized by \s-1GCC 4.0. \s0 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 \s-1GCC 4.0\s0 is rejected. This is useful if you need to make sure that your Objective-C code can be compiled with older versions of \s-1GCC.\s0 .IP "\fB\-freplace\-objc\-classes\fR" 4 .IX Item "-freplace-objc-classes" Emit a special marker instructing \fB\f(BIld\fB\|(1)\fR not to statically link in the resulting object file, and allow \fB\f(BIdyld\fB\|(1)\fR 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 \s-1OS X 10.3\s0 and later. .IP "\fB\-fzero\-link\fR" 4 .IX Item "-fzero-link" When compiling for the NeXT runtime, the compiler ordinarily replaces calls to \f(CW\*(C`objc_getClass("...")\*(C'\fR (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 \fB\-fzero\-link\fR flag suppresses this behavior and causes calls to \f(CW\*(C`objc_getClass("...")\*(C'\fR 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 \s-1GNU\s0 runtime currently always retains calls to \f(CW\*(C`objc_get_class("...")\*(C'\fR regardless of command-line options. .IP "\fB\-fno\-local\-ivars\fR" 4 .IX Item "-fno-local-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 \fB\-fno\-local\-ivars\fR flag disables this behavior thus avoiding variable shadowing issues. .IP "\fB\-fivar\-visibility=\fR[\fBpublic\fR|\fBprotected\fR|\fBprivate\fR|\fBpackage\fR]" 4 .IX Item "-fivar-visibility=[public|protected|private|package]" 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. .IP "\fB\-gen\-decls\fR" 4 .IX Item "-gen-decls" Dump interface declarations for all classes seen in the source file to a file named \fI\fIsourcename\fI.decl\fR. .IP "\fB\-Wassign\-intercept\fR (Objective-C and Objective\-\*(C+ only)" 4 .IX Item "-Wassign-intercept (Objective-C and Objective- only)" Warn whenever an Objective-C assignment is being intercepted by the garbage collector. .IP "\fB\-Wno\-protocol\fR (Objective-C and Objective\-\*(C+ only)" 4 .IX Item "-Wno-protocol (Objective-C and Objective- only)" 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 \fB\-Wno\-protocol\fR option, then methods inherited from the superclass are considered to be implemented, and no warning is issued for them. .IP "\fB\-Wselector\fR (Objective-C and Objective\-\*(C+ only)" 4 .IX Item "-Wselector (Objective-C and Objective- only)" 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 \f(CW\*(C`@selector(...)\*(C'\fR 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 \fB\-fsyntax\-only\fR option is being used. .IP "\fB\-Wstrict\-selector\-match\fR (Objective-C and Objective\-\*(C+ only)" 4 .IX Item "-Wstrict-selector-match (Objective-C and Objective- only)" 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 \f(CW\*(C`id\*(C'\fR or \f(CW\*(C`Class\*(C'\fR. 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. .IP "\fB\-Wundeclared\-selector\fR (Objective-C and Objective\-\*(C+ only)" 4 .IX Item "-Wundeclared-selector (Objective-C and Objective- only)" Warn if a \f(CW\*(C`@selector(...)\*(C'\fR expression referring to an undeclared selector is found. A selector is considered undeclared if no method with that name has been declared before the \&\f(CW\*(C`@selector(...)\*(C'\fR expression, either explicitly in an \&\f(CW@interface\fR or \f(CW@protocol\fR declaration, or implicitly in an \f(CW@implementation\fR section. This option always performs its checks as soon as a \f(CW\*(C`@selector(...)\*(C'\fR expression is found, while \fB\-Wselector\fR 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. .IP "\fB\-print\-objc\-runtime\-info\fR" 4 .IX Item "-print-objc-runtime-info" Generate C header describing the largest structure that is passed by value, if any. .SS "Options to Control Diagnostic Messages Formatting" .IX Subsection "Options to Control Diagnostic Messages Formatting" Traditionally, diagnostic messages have been formatted irrespective of the output device's aspect (e.g. its width, ...). 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. .IP "\fB\-fmessage\-length=\fR\fIn\fR" 4 .IX Item "-fmessage-length=n" Try to format error messages so that they fit on lines of about \&\fIn\fR characters. If \fIn\fR is zero, then no line-wrapping is done; each error message appears on a single line. This is the default for all front ends. .IP "\fB\-fdiagnostics\-show\-location=once\fR" 4 .IX Item "-fdiagnostics-show-location=once" Only meaningful in line-wrapping mode. Instructs the diagnostic messages reporter to emit source location information \fIonce\fR; 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. .IP "\fB\-fdiagnostics\-show\-location=every\-line\fR" 4 .IX 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. .IP "\fB\-fdiagnostics\-color[=\fR\fI\s-1WHEN\s0\fR\fB]\fR" 4 .IX Item "-fdiagnostics-color[=WHEN]" .PD 0 .IP "\fB\-fno\-diagnostics\-color\fR" 4 .IX Item "-fno-diagnostics-color" .PD Use color in diagnostics. \fI\s-1WHEN\s0\fR is \fBnever\fR, \fBalways\fR, or \fBauto\fR. The default depends on how the compiler has been configured, it can be any of the above \fI\s-1WHEN\s0\fR options or also \fBnever\fR if \fB\s-1GCC_COLORS\s0\fR environment variable isn't present in the environment, and \fBauto\fR otherwise. \&\fBauto\fR means to use color only when the standard error is a terminal. The forms \fB\-fdiagnostics\-color\fR and \fB\-fno\-diagnostics\-color\fR are aliases for \fB\-fdiagnostics\-color=always\fR and \&\fB\-fdiagnostics\-color=never\fR, respectively. .Sp The colors are defined by the environment variable \fB\s-1GCC_COLORS\s0\fR. Its value is a colon-separated list of capabilities and Select Graphic Rendition (\s-1SGR\s0) substrings. \s-1SGR\s0 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 \&\fB1\fR for bold, \&\fB4\fR for underline, \&\fB5\fR for blink, \&\fB7\fR for inverse, \&\fB39\fR for default foreground color, \&\fB30\fR to \fB37\fR for foreground colors, \&\fB90\fR to \fB97\fR for 16\-color mode foreground colors, \&\fB38;5;0\fR to \fB38;5;255\fR for 88\-color and 256\-color modes foreground colors, \&\fB49\fR for default background color, \&\fB40\fR to \fB47\fR for background colors, \&\fB100\fR to \fB107\fR for 16\-color mode background colors, and \fB48;5;0\fR to \fB48;5;255\fR for 88\-color and 256\-color modes background colors. .Sp The default \fB\s-1GCC_COLORS\s0\fR is .Sp .Vb 1 \& error=01;31:warning=01;35:note=01;36:caret=01;32:locus=01:quote=01 .Ve .Sp where \fB01;31\fR is bold red, \fB01;35\fR is bold magenta, \&\fB01;36\fR is bold cyan, \fB01;32\fR is bold green and \&\fB01\fR is bold. Setting \fB\s-1GCC_COLORS\s0\fR to the empty string disables colors. Supported capabilities are as follows. .RS 4 .ie n .IP """error=""" 4 .el .IP "\f(CWerror=\fR" 4 .IX Item "error=" \&\s-1SGR\s0 substring for error: markers. .ie n .IP """warning=""" 4 .el .IP "\f(CWwarning=\fR" 4 .IX Item "warning=" \&\s-1SGR\s0 substring for warning: markers. .ie n .IP """note=""" 4 .el .IP "\f(CWnote=\fR" 4 .IX Item "note=" \&\s-1SGR\s0 substring for note: markers. .ie n .IP """caret=""" 4 .el .IP "\f(CWcaret=\fR" 4 .IX Item "caret=" \&\s-1SGR\s0 substring for caret line. .ie n .IP """locus=""" 4 .el .IP "\f(CWlocus=\fR" 4 .IX Item "locus=" \&\s-1SGR\s0 substring for location information, \fBfile:line\fR or \&\fBfile:line:column\fR etc. .ie n .IP """quote=""" 4 .el .IP "\f(CWquote=\fR" 4 .IX Item "quote=" \&\s-1SGR\s0 substring for information printed within quotes. .RE .RS 4 .RE .IP "\fB\-fno\-diagnostics\-show\-option\fR" 4 .IX Item "-fno-diagnostics-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 \&\fB\-fno\-diagnostics\-show\-option\fR flag suppresses that behavior. .IP "\fB\-fno\-diagnostics\-show\-caret\fR" 4 .IX Item "-fno-diagnostics-show-caret" By default, each diagnostic emitted includes the original source line and a caret '^' indicating the column. This option suppresses this information. The source line is truncated to \fIn\fR characters, if the \fB\-fmessage\-length=n\fR option is given. When the output is done to the terminal, the width is limited to the width given by the \&\fB\s-1COLUMNS\s0\fR environment variable or, if not set, to the terminal width. .SS "Options to Request or Suppress Warnings" .IX Subsection "Options to Request or Suppress 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. .PP The following language-independent options do not enable specific warnings but control the kinds of diagnostics produced by \s-1GCC.\s0 .IP "\fB\-fsyntax\-only\fR" 4 .IX Item "-fsyntax-only" Check the code for syntax errors, but don't do anything beyond that. .IP "\fB\-fmax\-errors=\fR\fIn\fR" 4 .IX Item "-fmax-errors=n" Limits the maximum number of error messages to \fIn\fR, at which point \&\s-1GCC\s0 bails out rather than attempting to continue processing the source code. If \fIn\fR is 0 (the default), there is no limit on the number of error messages produced. If \fB\-Wfatal\-errors\fR is also specified, then \fB\-Wfatal\-errors\fR takes precedence over this option. .IP "\fB\-w\fR" 4 .IX Item "-w" Inhibit all warning messages. .IP "\fB\-Werror\fR" 4 .IX Item "-Werror" Make all warnings into errors. .IP "\fB\-Werror=\fR" 4 .IX Item "-Werror=" Make the specified warning into an error. The specifier for a warning is appended; for example \fB\-Werror=switch\fR turns the warnings controlled by \fB\-Wswitch\fR into errors. This switch takes a negative form, to be used to negate \fB\-Werror\fR for specific warnings; for example \fB\-Wno\-error=switch\fR makes \&\fB\-Wswitch\fR warnings not be errors, even when \fB\-Werror\fR is in effect. .Sp The warning message for each controllable warning includes the option that controls the warning. That option can then be used with \&\fB\-Werror=\fR and \fB\-Wno\-error=\fR as described above. (Printing of the option in the warning message can be disabled using the \&\fB\-fno\-diagnostics\-show\-option\fR flag.) .Sp Note that specifying \fB\-Werror=\fR\fIfoo\fR automatically implies \&\fB\-W\fR\fIfoo\fR. However, \fB\-Wno\-error=\fR\fIfoo\fR does not imply anything. .IP "\fB\-Wfatal\-errors\fR" 4 .IX Item "-Wfatal-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. .PP You can request many specific warnings with options beginning with \&\fB\-W\fR, for example \fB\-Wimplicit\fR to request warnings on implicit declarations. Each of these specific warning options also has a negative form beginning \fB\-Wno\-\fR to turn off warnings; for example, \fB\-Wno\-implicit\fR. This manual lists only one of the two forms, whichever is not the default. For further language-specific options also refer to \fB\*(C+ Dialect Options\fR and \&\fBObjective-C and Objective\-\*(C+ Dialect Options\fR. .PP Some options, such as \fB\-Wall\fR and \fB\-Wextra\fR, turn on other options, such as \fB\-Wunused\fR, which may turn on further options, such as \fB\-Wunused\-value\fR. 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 take effect as if they appeared at the end of the command-line. .PP When an unrecognized warning option is requested (e.g., \&\fB\-Wunknown\-warning\fR), \s-1GCC\s0 emits a diagnostic stating that the option is not recognized. However, if the \fB\-Wno\-\fR form is used, the behavior is slightly different: no diagnostic is produced for \fB\-Wno\-unknown\-warning\fR unless other diagnostics are being produced. This allows the use of new \fB\-Wno\-\fR options with old compilers, but if something goes wrong, the compiler warns that an unrecognized option is present. .IP "\fB\-Wpedantic\fR" 4 .IX Item "-Wpedantic" .PD 0 .IP "\fB\-pedantic\fR" 4 .IX Item "-pedantic" .PD Issue all the warnings demanded by strict \s-1ISO C\s0 and \s-1ISO \*(C+\s0; reject all programs that use forbidden extensions, and some other programs that do not follow \s-1ISO C\s0 and \s-1ISO \*(C+. \s0 For \s-1ISO C,\s0 follows the version of the \s-1ISO C\s0 standard specified by any \fB\-std\fR option used. .Sp Valid \s-1ISO C\s0 and \s-1ISO \*(C+\s0 programs should compile properly with or without this option (though a rare few require \fB\-ansi\fR or a \&\fB\-std\fR option specifying the required version of \s-1ISO C\s0). However, without this option, certain \s-1GNU\s0 extensions and traditional C and \*(C+ features are supported as well. With this option, they are rejected. .Sp \&\fB\-Wpedantic\fR does not cause warning messages for use of the alternate keywords whose names begin and end with \fB_\|_\fR. Pedantic warnings are also disabled in the expression that follows \&\f(CW\*(C`_\|_extension_\|_\*(C'\fR. However, only system header files should use these escape routes; application programs should avoid them. .Sp Some users try to use \fB\-Wpedantic\fR to check programs for strict \s-1ISO C\s0 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 \&\s-1ISO C \s0\fIrequires\fR a diagnostic, and some others for which diagnostics have been added. .Sp A feature to report any failure to conform to \s-1ISO C\s0 might be useful in some instances, but would require considerable additional work and would be quite different from \fB\-Wpedantic\fR. We don't have plans to support such a feature in the near future. .Sp Where the standard specified with \fB\-std\fR represents a \s-1GNU\s0 extended dialect of C, such as \fBgnu90\fR or \fBgnu99\fR, there is a corresponding \fIbase standard\fR, the version of \s-1ISO C\s0 on which the \s-1GNU\s0 extended dialect is based. Warnings from \fB\-Wpedantic\fR 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 \s-1GNU C\s0 dialect, since by definition the \s-1GNU\s0 dialects of C include all features the compiler supports with the given option, and there would be nothing to warn about.) .IP "\fB\-pedantic\-errors\fR" 4 .IX Item "-pedantic-errors" Give an error whenever the \fIbase standard\fR (see \fB\-Wpedantic\fR) 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 \fB\-Werror=pedantic\fR, since there are errors enabled by this option and not enabled by the latter and vice versa. .IP "\fB\-Wall\fR" 4 .IX Item "-Wall" 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 \fB\*(C+ Dialect Options\fR and \fBObjective-C and Objective\-\*(C+ Dialect Options\fR. .Sp \&\fB\-Wall\fR turns on the following warning flags: .Sp \&\fB\-Waddress \&\-Warray\-bounds=1\fR (only with\fB \fR\fB\-O2\fR) \&\fB\-Wc++11\-compat \-Wc++14\-compat \&\-Wchar\-subscripts \&\-Wenum\-compare\fR (in C/ObjC; this is on by default in \*(C+) \&\fB\-Wimplicit\-int\fR (C and Objective-C only) \&\fB\-Wimplicit\-function\-declaration\fR (C and Objective-C only) \&\fB\-Wcomment \&\-Wformat \&\-Wmain\fR (only for C/ObjC and unless\fB \fR\fB\-ffreestanding\fR) \&\fB\-Wmaybe\-uninitialized \&\-Wmissing\-braces\fR (only for C/ObjC) \&\fB\-Wnonnull \&\-Wopenmp\-simd \&\-Wparentheses \&\-Wpointer\-sign \&\-Wreorder \&\-Wreturn\-type \&\-Wsequence\-point \&\-Wsign\-compare\fR (only in \*(C+) \&\fB\-Wstrict\-aliasing \&\-Wstrict\-overflow=1 \&\-Wswitch \&\-Wtrigraphs \&\-Wuninitialized \&\-Wunknown\-pragmas \&\-Wunused\-function \&\-Wunused\-label \&\-Wunused\-value \&\-Wunused\-variable \&\-Wvolatile\-register\-var\fR .Sp Note that some warning flags are not implied by \fB\-Wall\fR. 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 \fB\-Wextra\fR but many of them must be enabled individually. .IP "\fB\-Wextra\fR" 4 .IX Item "-Wextra" This enables some extra warning flags that are not enabled by \&\fB\-Wall\fR. (This option used to be called \fB\-W\fR. The older name is still supported, but the newer name is more descriptive.) .Sp \&\fB\-Wclobbered \&\-Wempty\-body \&\-Wignored\-qualifiers \&\-Wmissing\-field\-initializers \&\-Wmissing\-parameter\-type\fR (C only) \&\fB\-Wold\-style\-declaration\fR (C only) \&\fB\-Woverride\-init \&\-Wsign\-compare \&\-Wtype\-limits \&\-Wuninitialized \&\-Wunused\-parameter\fR (only with\fB \fR\fB\-Wunused\fR\fB \fRor\fB \fR\fB\-Wall\fR) \&\fB\-Wunused\-but\-set\-parameter\fR (only with\fB \fR\fB\-Wunused\fR\fB \fRor\fB \fR\fB\-Wall\fR) \fB \fR .Sp The option \fB\-Wextra\fR also prints warning messages for the following cases: .RS 4 .IP "*" 4 A pointer is compared against integer zero with \f(CW\*(C`<\*(C'\fR, \f(CW\*(C`<=\*(C'\fR, \&\f(CW\*(C`>\*(C'\fR, or \f(CW\*(C`>=\*(C'\fR. .IP "*" 4 (\*(C+ only) An enumerator and a non-enumerator both appear in a conditional expression. .IP "*" 4 (\*(C+ only) Ambiguous virtual bases. .IP "*" 4 (\*(C+ only) Subscripting an array that has been declared \f(CW\*(C`register\*(C'\fR. .IP "*" 4 (\*(C+ only) Taking the address of a variable that has been declared \&\f(CW\*(C`register\*(C'\fR. .IP "*" 4 (\*(C+ only) A base class is not initialized in a derived class's copy constructor. .RE .RS 4 .RE .IP "\fB\-Wchar\-subscripts\fR" 4 .IX Item "-Wchar-subscripts" Warn if an array subscript has type \f(CW\*(C`char\*(C'\fR. This is a common cause of error, as programmers often forget that this type is signed on some machines. This warning is enabled by \fB\-Wall\fR. .IP "\fB\-Wcomment\fR" 4 .IX Item "-Wcomment" Warn whenever a comment-start sequence \fB/*\fR appears in a \fB/*\fR comment, or whenever a Backslash-Newline appears in a \fB//\fR comment. This warning is enabled by \fB\-Wall\fR. .IP "\fB\-Wno\-coverage\-mismatch\fR" 4 .IX Item "-Wno-coverage-mismatch" Warn if feedback profiles do not match when using the \&\fB\-fprofile\-use\fR option. If a source file is changed between compiling with \fB\-fprofile\-gen\fR and with \fB\-fprofile\-use\fR, the files with the profile feedback can fail to match the source file and \s-1GCC\s0 cannot use the profile feedback information. By default, this warning is enabled and is treated as an error. \fB\-Wno\-coverage\-mismatch\fR can be used to disable the warning or \fB\-Wno\-error=coverage\-mismatch\fR 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. .IP "\fB\-Wno\-cpp\fR" 4 .IX Item "-Wno-cpp" (C, Objective-C, \*(C+, Objective\-\*(C+ and Fortran only) .Sp Suppress warning messages emitted by \f(CW\*(C`#warning\*(C'\fR directives. .IP "\fB\-Wdouble\-promotion\fR (C, \*(C+, Objective-C and Objective\-\*(C+ only)" 4 .IX Item "-Wdouble-promotion (C, , Objective-C and Objective- only)" Give a warning when a value of type \f(CW\*(C`float\*(C'\fR is implicitly promoted to \f(CW\*(C`double\*(C'\fR. CPUs with a 32\-bit \*(L"single-precision\*(R" floating-point unit implement \f(CW\*(C`float\*(C'\fR in hardware, but emulate \&\f(CW\*(C`double\*(C'\fR in software. On such a machine, doing computations using \f(CW\*(C`double\*(C'\fR values is much more expensive because of the overhead required for software emulation. .Sp It is easy to accidentally do computations with \f(CW\*(C`double\*(C'\fR because floating-point literals are implicitly of type \f(CW\*(C`double\*(C'\fR. For example, in: .Sp .Vb 4 \& float area(float radius) \& { \& return 3.14159 * radius * radius; \& } .Ve .Sp the compiler performs the entire computation with \f(CW\*(C`double\*(C'\fR because the floating-point literal is a \f(CW\*(C`double\*(C'\fR. .IP "\fB\-Wformat\fR" 4 .IX Item "-Wformat" .PD 0 .IP "\fB\-Wformat=\fR\fIn\fR" 4 .IX Item "-Wformat=n" .PD Check calls to \f(CW\*(C`printf\*(C'\fR and \f(CW\*(C`scanf\*(C'\fR, 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, in the \f(CW\*(C`printf\*(C'\fR, \&\f(CW\*(C`scanf\*(C'\fR, \f(CW\*(C`strftime\*(C'\fR and \f(CW\*(C`strfmon\*(C'\fR (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 \&\fB\-ffreestanding\fR or \fB\-fno\-builtin\fR. .Sp The formats are checked against the format features supported by \s-1GNU\s0 libc version 2.2. These include all \s-1ISO C90\s0 and C99 features, as well as features from the Single Unix Specification and some \s-1BSD\s0 and \s-1GNU\s0 extensions. Other library implementations may not support all these features; \s-1GCC\s0 does not support warning about features that go beyond a particular library's limitations. However, if \fB\-Wpedantic\fR is used with \fB\-Wformat\fR, warnings are given about format features not in the selected standard version (but not for \f(CW\*(C`strfmon\*(C'\fR formats, since those are not in any version of the C standard). .RS 4 .IP "\fB\-Wformat=1\fR" 4 .IX Item "-Wformat=1" .PD 0 .IP "\fB\-Wformat\fR" 4 .IX Item "-Wformat" .PD Option \fB\-Wformat\fR is equivalent to \fB\-Wformat=1\fR, and \&\fB\-Wno\-format\fR is equivalent to \fB\-Wformat=0\fR. Since \&\fB\-Wformat\fR also checks for null format arguments for several functions, \fB\-Wformat\fR also implies \fB\-Wnonnull\fR. Some aspects of this level of format checking can be disabled by the options: \fB\-Wno\-format\-contains\-nul\fR, \&\fB\-Wno\-format\-extra\-args\fR, and \fB\-Wno\-format\-zero\-length\fR. \&\fB\-Wformat\fR is enabled by \fB\-Wall\fR. .IP "\fB\-Wno\-format\-contains\-nul\fR" 4 .IX Item "-Wno-format-contains-nul" If \fB\-Wformat\fR is specified, do not warn about format strings that contain \s-1NUL\s0 bytes. .IP "\fB\-Wno\-format\-extra\-args\fR" 4 .IX Item "-Wno-format-extra-args" If \fB\-Wformat\fR is specified, do not warn about excess arguments to a \&\f(CW\*(C`printf\*(C'\fR or \f(CW\*(C`scanf\*(C'\fR format function. The C standard specifies that such arguments are ignored. .Sp Where the unused arguments lie between used arguments that are specified with \fB\$\fR operand number specifications, normally warnings are still given, since the implementation could not know what type to pass to \f(CW\*(C`va_arg\*(C'\fR to skip the unused arguments. However, in the case of \f(CW\*(C`scanf\*(C'\fR 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. .IP "\fB\-Wno\-format\-zero\-length\fR" 4 .IX Item "-Wno-format-zero-length" If \fB\-Wformat\fR is specified, do not warn about zero-length formats. The C standard specifies that zero-length formats are allowed. .IP "\fB\-Wformat=2\fR" 4 .IX Item "-Wformat=2" Enable \fB\-Wformat\fR plus additional format checks. Currently equivalent to \fB\-Wformat \-Wformat\-nonliteral \-Wformat\-security \&\-Wformat\-y2k\fR. .IP "\fB\-Wformat\-nonliteral\fR" 4 .IX Item "-Wformat-nonliteral" If \fB\-Wformat\fR 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 \f(CW\*(C`va_list\*(C'\fR. .IP "\fB\-Wformat\-security\fR" 4 .IX Item "-Wformat-security" If \fB\-Wformat\fR is specified, also warn about uses of format functions that represent possible security problems. At present, this warns about calls to \f(CW\*(C`printf\*(C'\fR and \f(CW\*(C`scanf\*(C'\fR functions where the format string is not a string literal and there are no format arguments, as in \f(CW\*(C`printf (foo);\*(C'\fR. This may be a security hole if the format string came from untrusted input and contains \fB\f(CB%n\fB\fR. (This is currently a subset of what \fB\-Wformat\-nonliteral\fR warns about, but in future warnings may be added to \fB\-Wformat\-security\fR that are not included in \fB\-Wformat\-nonliteral\fR.) .IP "\fB\-Wformat\-signedness\fR" 4 .IX Item "-Wformat-signedness" If \fB\-Wformat\fR is specified, also warn if the format string requires an unsigned argument and the argument is signed and vice versa. .IP "\fB\-Wformat\-y2k\fR" 4 .IX Item "-Wformat-y2k" If \fB\-Wformat\fR is specified, also warn about \f(CW\*(C`strftime\*(C'\fR formats that may yield only a two-digit year. .RE .RS 4 .RE .IP "\fB\-Wnonnull\fR" 4 .IX Item "-Wnonnull" Warn about passing a null pointer for arguments marked as requiring a non-null value by the \f(CW\*(C`nonnull\*(C'\fR function attribute. .Sp \&\fB\-Wnonnull\fR is included in \fB\-Wall\fR and \fB\-Wformat\fR. It can be disabled with the \fB\-Wno\-nonnull\fR option. .IP "\fB\-Winit\-self\fR (C, \*(C+, Objective-C and Objective\-\*(C+ only)" 4 .IX Item "-Winit-self (C, , Objective-C and Objective- only)" Warn about uninitialized variables that are initialized with themselves. Note this option can only be used with the \fB\-Wuninitialized\fR option. .Sp For example, \s-1GCC\s0 warns about \f(CW\*(C`i\*(C'\fR being uninitialized in the following snippet only when \fB\-Winit\-self\fR has been specified: .Sp .Vb 5 \& int f() \& { \& int i = i; \& return i; \& } .Ve .Sp This warning is enabled by \fB\-Wall\fR in \*(C+. .IP "\fB\-Wimplicit\-int\fR (C and Objective-C only)" 4 .IX Item "-Wimplicit-int (C and Objective-C only)" Warn when a declaration does not specify a type. This warning is enabled by \fB\-Wall\fR. .IP "\fB\-Wimplicit\-function\-declaration\fR (C and Objective-C only)" 4 .IX Item "-Wimplicit-function-declaration (C and Objective-C only)" Give a warning whenever a function is used before being declared. In C99 mode (\fB\-std=c99\fR or \fB\-std=gnu99\fR), this warning is enabled by default and it is made into an error by \&\fB\-pedantic\-errors\fR. This warning is also enabled by \&\fB\-Wall\fR. .IP "\fB\-Wimplicit\fR (C and Objective-C only)" 4 .IX Item "-Wimplicit (C and Objective-C only)" Same as \fB\-Wimplicit\-int\fR and \fB\-Wimplicit\-function\-declaration\fR. This warning is enabled by \fB\-Wall\fR. .IP "\fB\-Wignored\-qualifiers\fR (C and \*(C+ only)" 4 .IX Item "-Wignored-qualifiers (C and only)" Warn if the return type of a function has a type qualifier such as \f(CW\*(C`const\*(C'\fR. For \s-1ISO C\s0 such a type qualifier has no effect, since the value returned by a function is not an lvalue. For \*(C+, the warning is only emitted for scalar types or \f(CW\*(C`void\*(C'\fR. \&\s-1ISO C\s0 prohibits qualified \f(CW\*(C`void\*(C'\fR return types on function definitions, so such return types always receive a warning even without this option. .Sp This warning is also enabled by \fB\-Wextra\fR. .IP "\fB\-Wmain\fR" 4 .IX Item "-Wmain" Warn if the type of \f(CW\*(C`main\*(C'\fR is suspicious. \f(CW\*(C`main\*(C'\fR should be a function with external linkage, returning int, taking either zero arguments, two, or three arguments of appropriate types. This warning is enabled by default in \*(C+ and is enabled by either \fB\-Wall\fR or \fB\-Wpedantic\fR. .IP "\fB\-Wmissing\-braces\fR" 4 .IX Item "-Wmissing-braces" Warn if an aggregate or union initializer is not fully bracketed. In the following example, the initializer for \f(CW\*(C`a\*(C'\fR is not fully bracketed, but that for \f(CW\*(C`b\*(C'\fR is fully bracketed. This warning is enabled by \fB\-Wall\fR in C. .Sp .Vb 2 \& int a[2][2] = { 0, 1, 2, 3 }; \& int b[2][2] = { { 0, 1 }, { 2, 3 } }; .Ve .Sp This warning is enabled by \fB\-Wall\fR. .IP "\fB\-Wmissing\-include\-dirs\fR (C, \*(C+, Objective-C and Objective\-\*(C+ only)" 4 .IX Item "-Wmissing-include-dirs (C, , Objective-C and Objective- only)" Warn if a user-supplied include directory does not exist. .IP "\fB\-Wparentheses\fR" 4 .IX Item "-Wparentheses" Warn if parentheses are omitted in certain contexts, such as when there is an assignment in a context where a truth value is expected, or when operators are nested whose precedence people often get confused about. .Sp Also warn if a comparison like \f(CW\*(C`x<=y<=z\*(C'\fR appears; this is equivalent to \f(CW\*(C`(x<=y ? 1 : 0) <= z\*(C'\fR, which is a different interpretation from that of ordinary mathematical notation. .Sp Also warn about constructions where there may be confusion to which \&\f(CW\*(C`if\*(C'\fR statement an \f(CW\*(C`else\*(C'\fR branch belongs. Here is an example of such a case: .Sp .Vb 7 \& { \& if (a) \& if (b) \& foo (); \& else \& bar (); \& } .Ve .Sp In C/\*(C+, every \f(CW\*(C`else\*(C'\fR branch belongs to the innermost possible \&\f(CW\*(C`if\*(C'\fR statement, which in this example is \f(CW\*(C`if (b)\*(C'\fR. This is often not what the programmer expected, as illustrated in the above example by indentation the programmer chose. When there is the potential for this confusion, \s-1GCC\s0 issues a warning when this flag is specified. To eliminate the warning, add explicit braces around the innermost \f(CW\*(C`if\*(C'\fR statement so there is no way the \f(CW\*(C`else\*(C'\fR can belong to the enclosing \f(CW\*(C`if\*(C'\fR. The resulting code looks like this: .Sp .Vb 9 \& { \& if (a) \& { \& if (b) \& foo (); \& else \& bar (); \& } \& } .Ve .Sp Also warn for dangerous uses of the \s-1GNU\s0 extension to \&\f(CW\*(C`?:\*(C'\fR with omitted middle operand. When the condition in the \f(CW\*(C`?\*(C'\fR: operator is a boolean expression, the omitted value is always 1. Often programmers expect it to be a value computed inside the conditional expression instead. .Sp This warning is enabled by \fB\-Wall\fR. .IP "\fB\-Wsequence\-point\fR" 4 .IX Item "-Wsequence-point" Warn about code that may have undefined semantics because of violations of sequence point rules in the C and \*(C+ standards. .Sp The C and \*(C+ standards define the order in which expressions in a C/\*(C+ program are evaluated in terms of \fIsequence points\fR, which represent a partial ordering between the execution of parts of the program: those executed before the sequence point, and those executed after it. These occur after the evaluation of a full expression (one which is not part of a larger expression), after the evaluation of the first operand of a \&\f(CW\*(C`&&\*(C'\fR, \f(CW\*(C`||\*(C'\fR, \f(CW\*(C`? :\*(C'\fR or \f(CW\*(C`,\*(C'\fR (comma) operator, before a function is called (but after the evaluation of its arguments and the expression denoting the called function), and in certain other places. Other than as expressed by the sequence point rules, the order of evaluation of subexpressions of an expression is not specified. All these rules describe only a partial order rather than a total order, since, for example, if two functions are called within one expression with no sequence point between them, the order in which the functions are called is not specified. However, the standards committee have ruled that function calls do not overlap. .Sp It is not specified when between sequence points modifications to the values of objects take effect. Programs whose behavior depends on this have undefined behavior; the C and \*(C+ standards specify that \*(L"Between the previous and next sequence point an object shall have its stored value modified at most once by the evaluation of an expression. Furthermore, the prior value shall be read only to determine the value to be stored.\*(R". If a program breaks these rules, the results on any particular implementation are entirely unpredictable. .Sp Examples of code with undefined behavior are \f(CW\*(C`a = a++;\*(C'\fR, \f(CW\*(C`a[n] = b[n++]\*(C'\fR and \f(CW\*(C`a[i++] = i;\*(C'\fR. Some more complicated cases are not diagnosed by this option, and it may give an occasional false positive result, but in general it has been found fairly effective at detecting this sort of problem in programs. .Sp The standard is worded confusingly, therefore there is some debate over the precise meaning of the sequence point rules in subtle cases. Links to discussions of the problem, including proposed formal definitions, may be found on the \s-1GCC\s0 readings page, at <\fBhttp://gcc.gnu.org/readings.html\fR>. .Sp This warning is enabled by \fB\-Wall\fR for C and \*(C+. .IP "\fB\-Wno\-return\-local\-addr\fR" 4 .IX Item "-Wno-return-local-addr" Do not warn about returning a pointer (or in \*(C+, a reference) to a variable that goes out of scope after the function returns. .IP "\fB\-Wreturn\-type\fR" 4 .IX Item "-Wreturn-type" Warn whenever a function is defined with a return type that defaults to \f(CW\*(C`int\*(C'\fR. Also warn about any \f(CW\*(C`return\*(C'\fR statement with no return value in a function whose return type is not \f(CW\*(C`void\*(C'\fR (falling off the end of the function body is considered returning without a value), and about a \f(CW\*(C`return\*(C'\fR statement with an expression in a function whose return type is \f(CW\*(C`void\*(C'\fR. .Sp For \*(C+, a function without return type always produces a diagnostic message, even when \fB\-Wno\-return\-type\fR is specified. The only exceptions are \f(CW\*(C`main\*(C'\fR and functions defined in system headers. .Sp This warning is enabled by \fB\-Wall\fR. .IP "\fB\-Wshift\-count\-negative\fR" 4 .IX Item "-Wshift-count-negative" Warn if shift count is negative. This warning is enabled by default. .IP "\fB\-Wshift\-count\-overflow\fR" 4 .IX Item "-Wshift-count-overflow" Warn if shift count >= width of type. This warning is enabled by default. .IP "\fB\-Wswitch\fR" 4 .IX Item "-Wswitch" Warn whenever a \f(CW\*(C`switch\*(C'\fR statement has an index of enumerated type and lacks a \f(CW\*(C`case\*(C'\fR for one or more of the named codes of that enumeration. (The presence of a \f(CW\*(C`default\*(C'\fR label prevents this warning.) \f(CW\*(C`case\*(C'\fR labels outside the enumeration range also provoke warnings when this option is used (even if there is a \&\f(CW\*(C`default\*(C'\fR label). This warning is enabled by \fB\-Wall\fR. .IP "\fB\-Wswitch\-default\fR" 4 .IX Item "-Wswitch-default" Warn whenever a \f(CW\*(C`switch\*(C'\fR statement does not have a \f(CW\*(C`default\*(C'\fR case. .IP "\fB\-Wswitch\-enum\fR" 4 .IX Item "-Wswitch-enum" Warn whenever a \f(CW\*(C`switch\*(C'\fR statement has an index of enumerated type and lacks a \f(CW\*(C`case\*(C'\fR for one or more of the named codes of that enumeration. \f(CW\*(C`case\*(C'\fR labels outside the enumeration range also provoke warnings when this option is used. The only difference between \fB\-Wswitch\fR and this option is that this option gives a warning about an omitted enumeration code even if there is a \&\f(CW\*(C`default\*(C'\fR label. .IP "\fB\-Wswitch\-bool\fR" 4 .IX Item "-Wswitch-bool" Warn whenever a \f(CW\*(C`switch\*(C'\fR statement has an index of boolean type. It is possible to suppress this warning by casting the controlling expression to a type other than \f(CW\*(C`bool\*(C'\fR. For example: .Sp .Vb 4 \& switch ((int) (a == 4)) \& { \& ... \& } .Ve .Sp This warning is enabled by default for C and \*(C+ programs. .IP "\fB\-Wsync\-nand\fR (C and \*(C+ only)" 4 .IX Item "-Wsync-nand (C and only)" Warn when \f(CW\*(C`_\|_sync_fetch_and_nand\*(C'\fR and \f(CW\*(C`_\|_sync_nand_and_fetch\*(C'\fR built-in functions are used. These functions changed semantics in \s-1GCC 4.4.\s0 .IP "\fB\-Wtrigraphs\fR" 4 .IX Item "-Wtrigraphs" Warn if any trigraphs are encountered that might change the meaning of the program (trigraphs within comments are not warned about). This warning is enabled by \fB\-Wall\fR. .IP "\fB\-Wunused\-but\-set\-parameter\fR" 4 .IX Item "-Wunused-but-set-parameter" Warn whenever a function parameter is assigned to, but otherwise unused (aside from its declaration). .Sp To suppress this warning use the \f(CW\*(C`unused\*(C'\fR attribute. .Sp This warning is also enabled by \fB\-Wunused\fR together with \&\fB\-Wextra\fR. .IP "\fB\-Wunused\-but\-set\-variable\fR" 4 .IX Item "-Wunused-but-set-variable" Warn whenever a local variable is assigned to, but otherwise unused (aside from its declaration). This warning is enabled by \fB\-Wall\fR. .Sp To suppress this warning use the \f(CW\*(C`unused\*(C'\fR attribute. .Sp This warning is also enabled by \fB\-Wunused\fR, which is enabled by \fB\-Wall\fR. .IP "\fB\-Wunused\-function\fR" 4 .IX Item "-Wunused-function" Warn whenever a static function is declared but not defined or a non-inline static function is unused. This warning is enabled by \fB\-Wall\fR. .IP "\fB\-Wunused\-label\fR" 4 .IX Item "-Wunused-label" Warn whenever a label is declared but not used. This warning is enabled by \fB\-Wall\fR. .Sp To suppress this warning use the \f(CW\*(C`unused\*(C'\fR attribute. .IP "\fB\-Wunused\-local\-typedefs\fR (C, Objective-C, \*(C+ and Objective\-\*(C+ only)" 4 .IX Item "-Wunused-local-typedefs (C, Objective-C, and Objective- only)" Warn when a typedef locally defined in a function is not used. This warning is enabled by \fB\-Wall\fR. .IP "\fB\-Wunused\-parameter\fR" 4 .IX Item "-Wunused-parameter" Warn whenever a function parameter is unused aside from its declaration. .Sp To suppress this warning use the \f(CW\*(C`unused\*(C'\fR attribute. .IP "\fB\-Wno\-unused\-result\fR" 4 .IX Item "-Wno-unused-result" Do not warn if a caller of a function marked with attribute \&\f(CW\*(C`warn_unused_result\*(C'\fR does not use its return value. The default is \fB\-Wunused\-result\fR. .IP "\fB\-Wunused\-variable\fR" 4 .IX Item "-Wunused-variable" Warn whenever a local variable or non-constant static variable is unused aside from its declaration. This warning is enabled by \fB\-Wall\fR. .Sp To suppress this warning use the \f(CW\*(C`unused\*(C'\fR attribute. .IP "\fB\-Wunused\-value\fR" 4 .IX Item "-Wunused-value" Warn whenever a statement computes a result that is explicitly not used. To suppress this warning cast the unused expression to \&\f(CW\*(C`void\*(C'\fR. This includes an expression-statement or the left-hand side of a comma expression that contains no side effects. For example, an expression such as \f(CW\*(C`x[i,j]\*(C'\fR causes a warning, while \&\f(CW\*(C`x[(void)i,j]\*(C'\fR does not. .Sp This warning is enabled by \fB\-Wall\fR. .IP "\fB\-Wunused\fR" 4 .IX Item "-Wunused" All the above \fB\-Wunused\fR options combined. .Sp In order to get a warning about an unused function parameter, you must either specify \fB\-Wextra \-Wunused\fR (note that \fB\-Wall\fR implies \&\fB\-Wunused\fR), or separately specify \fB\-Wunused\-parameter\fR. .IP "\fB\-Wuninitialized\fR" 4 .IX Item "-Wuninitialized" Warn if an automatic variable is used without first being initialized or if a variable may be clobbered by a \f(CW\*(C`setjmp\*(C'\fR call. In \*(C+, warn if a non-static reference or non-static \f(CW\*(C`const\*(C'\fR member appears in a class without constructors. .Sp If you want to warn about code that uses the uninitialized value of the variable in its own initializer, use the \fB\-Winit\-self\fR option. .Sp These warnings occur for individual uninitialized or clobbered elements of structure, union or array variables as well as for variables that are uninitialized or clobbered as a whole. They do not occur for variables or elements declared \f(CW\*(C`volatile\*(C'\fR. Because these warnings depend on optimization, the exact variables or elements for which there are warnings depends on the precise optimization options and version of \s-1GCC\s0 used. .Sp Note that there may be no warning about a variable that is used only to compute a value that itself is never used, because such computations may be deleted by data flow analysis before the warnings are printed. .IP "\fB\-Wmaybe\-uninitialized\fR" 4 .IX Item "-Wmaybe-uninitialized" For an automatic variable, if there exists a path from the function entry to a use of the variable that is initialized, but there exist some other paths for which the variable is not initialized, the compiler emits a warning if it cannot prove the uninitialized paths are not executed at run time. These warnings are made optional because \s-1GCC\s0 is not smart enough to see all the reasons why the code might be correct in spite of appearing to have an error. Here is one example of how this can happen: .Sp .Vb 12 \& { \& int x; \& switch (y) \& { \& case 1: x = 1; \& break; \& case 2: x = 4; \& break; \& case 3: x = 5; \& } \& foo (x); \& } .Ve .Sp If the value of \f(CW\*(C`y\*(C'\fR is always 1, 2 or 3, then \f(CW\*(C`x\*(C'\fR is always initialized, but \s-1GCC\s0 doesn't know this. To suppress the warning, you need to provide a default case with \fIassert\fR\|(0) or similar code. .Sp This option also warns when a non-volatile automatic variable might be changed by a call to \f(CW\*(C`longjmp\*(C'\fR. These warnings as well are possible only in optimizing compilation. .Sp The compiler sees only the calls to \f(CW\*(C`setjmp\*(C'\fR. It cannot know where \f(CW\*(C`longjmp\*(C'\fR will be called; in fact, a signal handler could call it at any point in the code. As a result, you may get a warning even when there is in fact no problem because \f(CW\*(C`longjmp\*(C'\fR cannot in fact be called at the place that would cause a problem. .Sp Some spurious warnings can be avoided if you declare all the functions you use that never return as \f(CW\*(C`noreturn\*(C'\fR. .Sp This warning is enabled by \fB\-Wall\fR or \fB\-Wextra\fR. .IP "\fB\-Wunknown\-pragmas\fR" 4 .IX Item "-Wunknown-pragmas" Warn when a \f(CW\*(C`#pragma\*(C'\fR directive is encountered that is not understood by \&\s-1GCC. \s0 If this command-line option is used, warnings are even issued for unknown pragmas in system header files. This is not the case if the warnings are only enabled by the \fB\-Wall\fR command-line option. .IP "\fB\-Wno\-pragmas\fR" 4 .IX Item "-Wno-pragmas" Do not warn about misuses of pragmas, such as incorrect parameters, invalid syntax, or conflicts between pragmas. See also \&\fB\-Wunknown\-pragmas\fR. .IP "\fB\-Wstrict\-aliasing\fR" 4 .IX Item "-Wstrict-aliasing" This option is only active when \fB\-fstrict\-aliasing\fR is active. It warns about code that might break the strict aliasing rules that the compiler is using for optimization. The warning does not catch all cases, but does attempt to catch the more common pitfalls. It is included in \fB\-Wall\fR. It is equivalent to \fB\-Wstrict\-aliasing=3\fR .IP "\fB\-Wstrict\-aliasing=n\fR" 4 .IX Item "-Wstrict-aliasing=n" This option is only active when \fB\-fstrict\-aliasing\fR is active. It warns about code that might break the strict aliasing rules that the compiler is using for optimization. Higher levels correspond to higher accuracy (fewer false positives). Higher levels also correspond to more effort, similar to the way \fB\-O\fR works. \&\fB\-Wstrict\-aliasing\fR is equivalent to \fB\-Wstrict\-aliasing=3\fR. .Sp Level 1: Most aggressive, quick, least accurate. Possibly useful when higher levels do not warn but \fB\-fstrict\-aliasing\fR still breaks the code, as it has very few false negatives. However, it has many false positives. Warns for all pointer conversions between possibly incompatible types, even if never dereferenced. Runs in the front end only. .Sp Level 2: Aggressive, quick, not too precise. May still have many false positives (not as many as level 1 though), and few false negatives (but possibly more than level 1). Unlike level 1, it only warns when an address is taken. Warns about incomplete types. Runs in the front end only. .Sp Level 3 (default for \fB\-Wstrict\-aliasing\fR): Should have very few false positives and few false negatives. Slightly slower than levels 1 or 2 when optimization is enabled. Takes care of the common pun+dereference pattern in the front end: \&\f(CW\*(C`*(int*)&some_float\*(C'\fR. If optimization is enabled, it also runs in the back end, where it deals with multiple statement cases using flow-sensitive points-to information. Only warns when the converted pointer is dereferenced. Does not warn about incomplete types. .IP "\fB\-Wstrict\-overflow\fR" 4 .IX Item "-Wstrict-overflow" .PD 0 .IP "\fB\-Wstrict\-overflow=\fR\fIn\fR" 4 .IX Item "-Wstrict-overflow=n" .PD This option is only active when \fB\-fstrict\-overflow\fR is active. It warns about cases where the compiler optimizes based on the assumption that signed overflow does not occur. Note that it does not warn about all cases where the code might overflow: it only warns about cases where the compiler implements some optimization. Thus this warning depends on the optimization level. .Sp An optimization that assumes that signed overflow does not occur is perfectly safe if the values of the variables involved are such that overflow never does, in fact, occur. Therefore this warning can easily give a false positive: a warning about code that is not actually a problem. To help focus on important issues, several warning levels are defined. No warnings are issued for the use of undefined signed overflow when estimating how many iterations a loop requires, in particular when determining whether a loop will be executed at all. .RS 4 .IP "\fB\-Wstrict\-overflow=1\fR" 4 .IX Item "-Wstrict-overflow=1" Warn about cases that are both questionable and easy to avoid. For example, with \fB\-fstrict\-overflow\fR, the compiler simplifies \&\f(CW\*(C`x + 1 > x\*(C'\fR to \f(CW1\fR. This level of \&\fB\-Wstrict\-overflow\fR is enabled by \fB\-Wall\fR; higher levels are not, and must be explicitly requested. .IP "\fB\-Wstrict\-overflow=2\fR" 4 .IX Item "-Wstrict-overflow=2" Also warn about other cases where a comparison is simplified to a constant. For example: \f(CW\*(C`abs (x) >= 0\*(C'\fR. This can only be simplified when \fB\-fstrict\-overflow\fR is in effect, because \&\f(CW\*(C`abs (INT_MIN)\*(C'\fR overflows to \f(CW\*(C`INT_MIN\*(C'\fR, which is less than zero. \fB\-Wstrict\-overflow\fR (with no level) is the same as \&\fB\-Wstrict\-overflow=2\fR. .IP "\fB\-Wstrict\-overflow=3\fR" 4 .IX Item "-Wstrict-overflow=3" Also warn about other cases where a comparison is simplified. For example: \f(CW\*(C`x + 1 > 1\*(C'\fR is simplified to \f(CW\*(C`x > 0\*(C'\fR. .IP "\fB\-Wstrict\-overflow=4\fR" 4 .IX Item "-Wstrict-overflow=4" Also warn about other simplifications not covered by the above cases. For example: \f(CW\*(C`(x * 10) / 5\*(C'\fR is simplified to \f(CW\*(C`x * 2\*(C'\fR. .IP "\fB\-Wstrict\-overflow=5\fR" 4 .IX Item "-Wstrict-overflow=5" Also warn about cases where the compiler reduces the magnitude of a constant involved in a comparison. For example: \f(CW\*(C`x + 2 > y\*(C'\fR is simplified to \f(CW\*(C`x + 1 >= y\*(C'\fR. This is reported only at the highest warning level because this simplification applies to many comparisons, so this warning level gives a very large number of false positives. .RE .RS 4 .RE .IP "\fB\-Wsuggest\-attribute=\fR[\fBpure\fR|\fBconst\fR|\fBnoreturn\fR|\fBformat\fR]" 4 .IX Item "-Wsuggest-attribute=[pure|const|noreturn|format]" Warn for cases where adding an attribute may be beneficial. The attributes currently supported are listed below. .RS 4 .IP "\fB\-Wsuggest\-attribute=pure\fR" 4 .IX Item "-Wsuggest-attribute=pure" .PD 0 .IP "\fB\-Wsuggest\-attribute=const\fR" 4 .IX Item "-Wsuggest-attribute=const" .IP "\fB\-Wsuggest\-attribute=noreturn\fR" 4 .IX Item "-Wsuggest-attribute=noreturn" .PD Warn about functions that might be candidates for attributes \&\f(CW\*(C`pure\*(C'\fR, \f(CW\*(C`const\*(C'\fR or \f(CW\*(C`noreturn\*(C'\fR. The compiler only warns for functions visible in other compilation units or (in the case of \f(CW\*(C`pure\*(C'\fR and