@c Copyright (C) 1988-2025 Free Software Foundation, Inc. @c This is part of the GCC manual. @c For copying conditions, see the file gcc.texi. @ignore @c man begin INCLUDE @include gcc-vers.texi @c man end @c man begin COPYRIGHT Copyright @copyright{} 1988-2025 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with the Invariant Sections being ``GNU General Public License'' and ``Funding Free Software'', the Front-Cover texts being (a) (see below), and with the Back-Cover Texts being (b) (see below). A copy of the license is included in the gfdl(7) man page. (a) The FSF's Front-Cover Text is: A GNU Manual (b) The FSF's Back-Cover Text is: You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development. @c man end @c Set file name and title for the man page. @setfilename gcc @settitle GNU project C and C++ compiler @c man begin SYNOPSIS gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}] [@option{-g}] [@option{-pg}] [@option{-O}@var{level}] [@option{-W}@var{warn}@dots{}] [@option{-Wpedantic}] [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}] [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}] [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}] [@option{-o} @var{outfile}] [@@@var{file}] @var{infile}@dots{} Only the most useful options are listed here; see below for the remainder. @command{g++} accepts mostly the same options as @command{gcc}. @c man end @c man begin SEEALSO gpl(7), gfdl(7), fsf-funding(7), cpp(1), gcov(1), as(1), ld(1), gdb(1) and the Info entries for @file{gcc}, @file{cpp}, @file{as}, @file{ld}, @file{binutils} and @file{gdb}. @c man end @c man begin BUGS For instructions on reporting bugs, see @w{@value{BUGURL}}. @c man end @c man begin AUTHOR See the Info entry for @command{gcc}, or @w{@uref{https://gcc.gnu.org/onlinedocs/gcc/Contributors.html}}, for contributors to GCC@. @c man end @end ignore @node Invoking GCC @chapter GCC Command Options @cindex GCC command options @cindex command options @cindex options, GCC command @c man begin DESCRIPTION When you invoke GCC, it normally does preprocessing, compilation, assembly and linking. The ``overall options'' allow you to stop this process at an intermediate stage. For example, the @option{-c} option says not to run the linker. Then the output consists of object files output by the assembler. @xref{Overall Options,,Options Controlling the Kind of Output}. Other options are passed on to one or more stages of processing. Some options control the preprocessor and others the compiler itself. Yet other options control the assembler and linker; most of these are not documented here, since you rarely need to use any of them. @cindex C compilation options Most of the command-line options that you can use with GCC are useful for C programs; when an option is only useful with another language (usually C++), the explanation says so explicitly. If the description for a particular option does not mention a source language, you can use that option with all supported languages. @cindex cross compiling @cindex specifying machine version @cindex specifying compiler version and target machine @cindex compiler version, specifying @cindex target machine, specifying The usual way to run GCC is to run the executable called @command{gcc}, or @command{@var{machine}-gcc} when cross-compiling, or @command{@var{machine}-gcc-@var{version}} to run a specific version of GCC. When you compile C++ programs, you should invoke GCC as @command{g++} instead. @xref{Invoking G++,,Compiling C++ Programs}, for information about the differences in behavior between @command{gcc} and @command{g++} when compiling C++ programs. @cindex grouping options @cindex options, grouping The @command{gcc} program accepts options and file names as operands. Many options have multi-letter names; therefore multiple single-letter options may @emph{not} be grouped: @option{-dv} is very different from @w{@samp{-d -v}}. @cindex order of options @cindex options, order You can mix options and other arguments. For the most part, the order you use doesn't matter. Order does matter when you use several options of the same kind; for example, if you specify @option{-L} more than once, the directories are searched in the order specified. Also, the placement of the @option{-l} option is significant. Many options have long names starting with @samp{-f} or with @samp{-W}---for example, @option{-fmove-loop-invariants}, @option{-Wformat} and so on. Most of these have both positive and negative forms; the negative form of @option{-ffoo} is @option{-fno-foo}. This manual documents only one of these two forms, whichever one is not the default. Some options take one or more arguments typically separated either by a space or by the equals sign (@samp{=}) from the option name. Unless documented otherwise, an argument can be either numeric or a string. Numeric arguments must typically be small unsigned decimal or hexadecimal integers. Hexadecimal arguments must begin with the @samp{0x} prefix. Arguments to options that specify a size threshold of some sort may be arbitrarily large decimal or hexadecimal integers followed by a byte size suffix designating a multiple of bytes such as @code{kB} and @code{KiB} for kilobyte and kibibyte, respectively, @code{MB} and @code{MiB} for megabyte and mebibyte, @code{GB} and @code{GiB} for gigabyte and gigibyte, and so on. Such arguments are designated by @var{byte-size} in the following text. Refer to the NIST, IEC, and other relevant national and international standards for the full listing and explanation of the binary and decimal byte size prefixes. @c man end @xref{Option Index}, for an index to GCC's options. @menu * Option Summary:: Brief list of all options, without explanations. * Overall Options:: Controlling the kind of output: an executable, object files, assembler files, or preprocessed source. * Invoking G++:: Compiling C++ programs. * C Dialect Options:: Controlling the variant of C language compiled. * C++ Dialect Options:: Variations on C++. * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C and Objective-C++. * OpenMP and OpenACC Options:: Controlling multiprocessing and offloading. * Diagnostic Message Formatting Options:: Controlling how diagnostics should be formatted. * Warning Options:: How picky should the compiler be? * Static Analyzer Options:: More expensive warnings. * Debugging Options:: Producing debuggable code. * Optimize Options:: How much optimization? * Instrumentation Options:: Enabling profiling and extra run-time error checking. * Preprocessor Options:: Controlling header files and macro definitions. Also, getting dependency information for Make. * Assembler Options:: Passing options to the assembler. * Link Options:: Specifying libraries and so on. * Directory Options:: Where to find header files and libraries. Where to find the compiler executable files. * Code Gen Options:: Specifying conventions for function calls, data layout and register usage. * Developer Options:: Printing GCC configuration info, statistics, and debugging dumps. * Submodel Options:: Target-specific options, such as compiling for a specific processor variant. * Spec Files:: How to pass switches to sub-processes. * Environment Variables:: Env vars that affect GCC. * Precompiled Headers:: Compiling a header once, and using it many times. * C++ Modules:: Experimental C++20 module system. @end menu @c man begin OPTIONS @node Option Summary @section Option Summary Here is a summary of all the options, grouped by type. Explanations are in the following sections. @table @emph @item Overall Options @xref{Overall Options,,Options Controlling the Kind of Output}. @gccoptlist{-c -S -E -o @var{file} -dumpbase @var{dumpbase} -dumpbase-ext @var{auxdropsuf} -dumpdir @var{dumppfx} -x @var{language} -v -### --help@r{[}=@var{class}@r{[},@dots{}@r{]]} --target-help --version -pass-exit-codes -pipe -specs=@var{file} -wrapper @@@var{file} -ffile-prefix-map=@var{old}=@var{new} -fcanon-prefix-map -fplugin=@var{file} -fplugin-arg-@var{name}=@var{arg} -fdump-ada-spec@r{[}-slim@r{]} -fada-spec-parent=@var{unit} -fdump-go-spec=@var{file}} @item C Language Options @xref{C Dialect Options,,Options Controlling C Dialect}. @gccoptlist{-ansi -std=@var{standard} -aux-info @var{filename} -fno-asm -fno-builtin -fno-builtin-@var{function} -fcond-mismatch -ffreestanding -fgimple -fgnu-tm -fgnu89-inline -fhosted -flax-vector-conversions -fms-extensions -fpermitted-flt-eval-methods=@var{standard} -fplan9-extensions -fsigned-bitfields -funsigned-bitfields -fsigned-char -funsigned-char -fstrict-flex-arrays[=@var{n}] -fsso-struct=@var{endianness}} @item C++ Language Options @xref{C++ Dialect Options,,Options Controlling C++ Dialect}. @gccoptlist{-fabi-version=@var{n} -fno-access-control -faligned-new=@var{n} -fno-assume-sane-operators-new-delete -fchar8_t -fcheck-new -fconcepts -fconstexpr-depth=@var{n} -fconstexpr-cache-depth=@var{n} -fconstexpr-loop-limit=@var{n} -fconstexpr-ops-limit=@var{n} -fno-elide-constructors -fno-enforce-eh-specs -fno-gnu-keywords -fno-immediate-escalation -fno-implicit-templates -fno-implicit-inline-templates -fno-implement-inlines -fmodule-header@r{[}=@var{kind}@r{]} -fmodule-only -fmodules -fmodule-implicit-inline -fno-module-lazy -fmodule-mapper=@var{specification} -fmodule-version-ignore -fms-extensions -fnew-inheriting-ctors -fnew-ttp-matching -fno-nonansi-builtins -fnothrow-opt -fno-operator-names -fno-optional-diags -fno-pretty-templates -frange-for-ext-temps -fno-rtti -fsized-deallocation -fstrong-eval-order@r{[}=@var{kind}@r{]} -ftemplate-backtrace-limit=@var{n} -ftemplate-depth=@var{n} -fno-threadsafe-statics -fuse-cxa-atexit -fno-weak -nostdinc++ -fvisibility-inlines-hidden -fvisibility-ms-compat -fext-numeric-literals -flang-info-include-translate@r{[}=@var{header}@r{]} -flang-info-include-translate-not -flang-info-module-cmi@r{[}=@var{module}@r{]} -stdlib=@var{libstdc++,libc++} -Wabi-tag -Wcatch-value -Wcatch-value=@var{n} -Wno-class-conversion -Wclass-memaccess -Wcomma-subscript -Wconditionally-supported -Wno-conversion-null -Wctad-maybe-unsupported -Wctor-dtor-privacy -Wdangling-reference -Wno-defaulted-function-deleted -Wno-delete-incomplete -Wdelete-non-virtual-dtor -Wno-deprecated-array-compare -Wdeprecated-copy -Wdeprecated-copy-dtor -Wno-deprecated-enum-enum-conversion -Wno-deprecated-enum-float-conversion -Weffc++ -Wno-elaborated-enum-base -Wno-exceptions -Wextra-semi -Wno-global-module -Wno-inaccessible-base -Wno-inherited-variadic-ctor -Wno-init-list-lifetime -Winvalid-constexpr -Winvalid-imported-macros -Wno-invalid-offsetof -Wno-literal-suffix -Wmismatched-new-delete -Wmismatched-tags -Wmultiple-inheritance -Wnamespaces -Wnarrowing -Wnoexcept -Wnoexcept-type -Wnon-virtual-dtor -Wpessimizing-move -Wno-placement-new -Wplacement-new=@var{n} -Wrange-loop-construct -Wredundant-move -Wredundant-tags -Wreorder -Wregister -Wno-sfinae-incomplete -Wstrict-null-sentinel -Wno-subobject-linkage -Wtemplates -Wno-non-c-typedef-for-linkage -Wno-non-template-friend -Wold-style-cast -Woverloaded-virtual -Wno-pmf-conversions -Wself-move -Wsign-promo -Wsized-deallocation -Wsuggest-final-methods -Wsuggest-final-types -Wsuggest-override -Wno-template-body -Wno-template-id-cdtor -Wtemplate-names-tu-local -Wno-terminate -Wno-vexing-parse -Wvirtual-inheritance -Wno-virtual-move-assign -Wvolatile} @item Objective-C and Objective-C++ Language Options @xref{Objective-C and Objective-C++ Dialect Options,,Options Controlling Objective-C and Objective-C++ Dialects}. @gccoptlist{-fconstant-string-class=@var{class-name} -fgnu-runtime -fnext-runtime -fno-nil-receivers -fobjc-abi-version=@var{n} -fobjc-call-cxx-cdtors -fobjc-direct-dispatch -fobjc-exceptions -fobjc-gc -fobjc-nilcheck -fobjc-std=objc1 -fno-local-ivars -fivar-visibility=@r{[}public@r{|}protected@r{|}private@r{|}package@r{]} -freplace-objc-classes -fzero-link -gen-decls -Wassign-intercept -Wno-property-assign-default -Wno-protocol -Wobjc-root-class -Wselector -Wstrict-selector-match -Wundeclared-selector} @item OpenMP and OpenACC Options @xref{OpenMP and OpenACC Options,,Options Controlling OpenMP and OpenACC}. @gccoptlist{-foffload=@var{arg} -foffload-options=@var{arg} -fopenacc -fopenacc-dim=@var{geom} -fopenmp -fopenmp-simd -fopenmp-target-simd-clone@r{[}=@var{device-type}@r{]}} @item Diagnostic Message Formatting Options @xref{Diagnostic Message Formatting Options,,Options to Control Diagnostic Messages Formatting}. @gccoptlist{-fmessage-length=@var{n} -fdiagnostics-plain-output -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]} -fdiagnostics-color=@r{[}auto@r{|}never@r{|}always@r{]} -fdiagnostics-urls=@r{[}auto@r{|}never@r{|}always@r{]} -fdiagnostics-format=@r{[}text@r{|}sarif-stderr@r{|}sarif-file@r{]} -fdiagnostics-add-output=@var{DIAGNOSTICS-OUTPUT-SPEC} -fdiagnostics-set-output=@var{DIAGNOSTICS-OUTPUT-SPEC} -fno-diagnostics-json-formatting -fno-diagnostics-show-option -fno-diagnostics-show-caret -fno-diagnostics-show-event-links -fno-diagnostics-show-labels -fno-diagnostics-show-line-numbers -fno-diagnostics-show-cwe -fno-diagnostics-show-rules -fno-diagnostics-show-highlight-colors -fno-diagnostics-show-nesting -fno-diagnostics-show-nesting-locations -fdiagnostics-show-nesting-levels -fdiagnostics-minimum-margin-width=@var{width} -fdiagnostics-parseable-fixits -fdiagnostics-generate-patch -fdiagnostics-show-template-tree -fno-elide-type -fdiagnostics-path-format=@r{[}none@r{|}separate-events@r{|}inline-events@r{]} -fdiagnostics-show-path-depths -fno-show-column -fdiagnostics-column-unit=@r{[}display@r{|}byte@r{]} -fdiagnostics-column-origin=@var{origin} -fdiagnostics-escape-format=@r{[}unicode@r{|}bytes@r{]} -fdiagnostics-text-art-charset=@r{[}none@r{|}ascii@r{|}unicode@r{|}emoji@r{]} -fdiagnostics-show-context@r{[}=@var{depth}@r{]}} @item Warning Options @xref{Warning Options,,Options to Request or Suppress Warnings}. @gccoptlist{-fsyntax-only -fmax-errors=@var{n} -Wpedantic -pedantic-errors -fpermissive -w -Wextra -Wall -Wabi=@var{n} -Waddress -Wno-address-of-packed-member -Waggregate-return -Walloc-size -Walloc-size-larger-than=@var{byte-size} -Walloc-zero -Walloca -Walloca-larger-than=@var{byte-size} -Wauto-profile -Wno-aggressive-loop-optimizations -Warith-conversion -Warray-bounds -Warray-bounds=@var{n} -Warray-compare -Warray-parameter -Warray-parameter=@var{n} -Wno-attributes -Wattribute-alias=@var{n} -Wno-attribute-alias -Wno-attribute-warning -Wbidi-chars=@r{[}none@r{|}unpaired@r{|}any@r{|}ucn@r{]} -Wbool-compare -Wbool-operation -Wno-builtin-declaration-mismatch -Wno-builtin-macro-redefined -Wc90-c99-compat -Wc99-c11-compat -Wc11-c23-compat -Wc23-c2y-compat -Wc++-compat -Wc++11-compat -Wc++14-compat -Wc++17-compat -Wc++20-compat -Wc++26-compat -Wno-c++11-extensions -Wno-c++14-extensions -Wno-c++17-extensions -Wno-c++20-extensions -Wno-c++23-extensions -Wcalloc-transposed-args -Wcast-align -Wcast-align=strict -Wcast-function-type -Wcast-qual -Wchar-subscripts -Wclobbered -Wcomment -Wcompare-distinct-pointer-types -Wno-complain-wrong-lang -Wconversion -Wno-coverage-mismatch -Wno-cpp -Wdangling-else -Wdangling-pointer -Wdangling-pointer=@var{n} -Wdate-time -Wno-deprecated -Wno-deprecated-declarations -Wno-designated-init -Wdisabled-optimization -Wno-discarded-array-qualifiers -Wno-discarded-qualifiers -Wno-div-by-zero -Wdouble-promotion -Wduplicated-branches -Wduplicated-cond -Wempty-body -Wno-endif-labels -Wenum-compare -Wenum-conversion -Wenum-int-mismatch -Werror -Werror=* -Wexpansion-to-defined -Wfatal-errors -Wflex-array-member-not-at-end -Wfloat-conversion -Wfloat-equal -Wformat -Wformat=2 -Wno-format-contains-nul -Wno-format-extra-args -Wformat-nonliteral -Wformat-overflow=@var{n} -Wformat-security -Wformat-signedness -Wformat-truncation=@var{n} -Wformat-y2k -Wframe-address -Wframe-larger-than=@var{byte-size} -Wno-free-nonheap-object -Wheader-guard -Wno-if-not-aligned -Wno-ignored-attributes -Wignored-qualifiers -Wno-incompatible-pointer-types -Whardened -Wimplicit -Wimplicit-fallthrough -Wimplicit-fallthrough=@var{n} -Wno-implicit-function-declaration -Wno-implicit-int -Winfinite-recursion -Winit-self -Winline -Wno-int-conversion -Wint-in-bool-context -Wno-int-to-pointer-cast -Wno-invalid-memory-model -Winvalid-pch -Winvalid-utf8 -Wno-unicode -Wjump-misses-init -Wkeyword-macro -Wlarger-than=@var{byte-size} -Wleading-whitespace=@var{kind} -Wlogical-not-parentheses -Wlogical-op -Wlong-long -Wno-lto-type-mismatch -Wmain -Wmaybe-uninitialized -Wmemset-elt-size -Wmemset-transposed-args -Wmisleading-indentation -Wmissing-attributes -Wmissing-braces -Wmissing-field-initializers -Wmissing-format-attribute -Wmissing-include-dirs -Wmissing-noreturn -Wmusttail-local-addr -Wmaybe-musttail-local-addr -Wno-missing-profile -Wno-multichar -Wmultistatement-macros -Wnonnull -Wnonnull-compare -Wnormalized=@r{[}none@r{|}id@r{|}nfc@r{|}nfkc@r{]} -Wnull-dereference -Wno-odr -Wopenacc-parallelism -Wopenmp -Wopenmp-simd -Wno-overflow -Woverlength-strings -Wno-override-init-side-effects -Wpacked -Wno-packed-bitfield-compat -Wpacked-not-aligned -Wpadded -Wparentheses -Wno-pedantic-ms-format -Wpointer-arith -Wno-pointer-compare -Wno-pointer-to-int-cast -Wno-pragmas -Wno-pragma-once-outside-header -Wno-prio-ctor-dtor -Wno-psabi -Wredundant-decls -Wrestrict -Wno-return-local-addr -Wreturn-type -Wno-scalar-storage-order -Wsequence-point -Wshadow -Wshadow=global -Wshadow=local -Wshadow=compatible-local -Wno-shadow-ivar -Wno-shift-count-negative -Wno-shift-count-overflow -Wshift-negative-value -Wno-shift-overflow -Wshift-overflow=@var{n} -Wsign-compare -Wsign-conversion -Wno-sizeof-array-argument -Wsizeof-array-div -Wsizeof-pointer-div -Wsizeof-pointer-memaccess -Wstack-protector -Wstack-usage=@var{byte-size} -Wstrict-aliasing -Wstrict-aliasing=n -Wstrict-overflow -Wstrict-overflow=@var{n} -Wstring-compare -Wno-stringop-overflow -Wno-stringop-overread -Wno-stringop-truncation -Wstrict-flex-arrays -Wsuggest-attribute=@var{attribute-name} -Wswitch -Wno-switch-bool -Wswitch-default -Wswitch-enum -Wno-switch-outside-range -Wno-switch-unreachable -Wsync-nand -Wsystem-headers -Wtautological-compare -Wtrailing-whitespace -Wtrailing-whitespace=@var{kind} -Wtrampolines -Wtrigraphs -Wtrivial-auto-var-init -Wno-tsan -Wtype-limits -Wundef -Wuninitialized -Wunknown-pragmas -Wunsuffixed-float-constants -Wunterminated-string-initialization -Wunused -Wunused-but-set-parameter -Wunused-but-set-parameter=@var{n} -Wunused-but-set-variable -Wunused-but-set-variable=@var{n} -Wunused-const-variable -Wunused-const-variable=@var{n} -Wunused-function -Wunused-label -Wunused-local-typedefs -Wunused-macros -Wunused-parameter -Wno-unused-result -Wunused-value -Wunused-variable -Wuse-after-free -Wuse-after-free=@var{n} -Wuseless-cast -Wno-varargs -Wvariadic-macros -Wvector-operation-performance -Wvla -Wvla-larger-than=@var{byte-size} -Wno-vla-larger-than -Wvolatile-register-var -Wwrite-strings -Wno-xor-used-as-pow -Wzero-as-null-pointer-constant -Wzero-length-bounds} @item Static Analyzer Options @gccoptlist{ -fanalyzer -fanalyzer-call-summaries -fanalyzer-checker=@var{name} -fno-analyzer-feasibility -fanalyzer-fine-grained -fanalyzer-show-events-in-system-headers -fno-analyzer-state-merge -fno-analyzer-state-purge -fno-analyzer-suppress-followups -fanalyzer-transitivity -fno-analyzer-undo-inlining -fanalyzer-verbose-edges -fanalyzer-verbose-state-changes -fanalyzer-verbosity=@var{level} -fdump-analyzer -fdump-analyzer-callgraph -fdump-analyzer-exploded-graph -fdump-analyzer-exploded-nodes -fdump-analyzer-exploded-nodes-2 -fdump-analyzer-exploded-nodes-3 -fdump-analyzer-exploded-paths -fdump-analyzer-feasibility -fdump-analyzer-infinite-loop -fdump-analyzer-json -fdump-analyzer-state-purge -fdump-analyzer-stderr -fdump-analyzer-supergraph -fdump-analyzer-untracked -Wno-analyzer-double-fclose -Wno-analyzer-double-free -Wno-analyzer-exposure-through-output-file -Wno-analyzer-exposure-through-uninit-copy -Wno-analyzer-fd-access-mode-mismatch -Wno-analyzer-fd-double-close -Wno-analyzer-fd-leak -Wno-analyzer-fd-phase-mismatch -Wno-analyzer-fd-type-mismatch -Wno-analyzer-fd-use-after-close -Wno-analyzer-fd-use-without-check -Wno-analyzer-file-leak -Wno-analyzer-free-of-non-heap -Wno-analyzer-imprecise-fp-arithmetic -Wno-analyzer-infinite-loop -Wno-analyzer-infinite-recursion -Wno-analyzer-jump-through-null -Wno-analyzer-malloc-leak -Wno-analyzer-mismatching-deallocation -Wno-analyzer-null-argument -Wno-analyzer-null-dereference -Wno-analyzer-out-of-bounds -Wno-analyzer-overlapping-buffers -Wno-analyzer-possible-null-argument -Wno-analyzer-possible-null-dereference -Wno-analyzer-putenv-of-auto-var -Wno-analyzer-shift-count-negative -Wno-analyzer-shift-count-overflow -Wno-analyzer-stale-setjmp-buffer -Wno-analyzer-tainted-allocation-size -Wno-analyzer-tainted-assertion -Wno-analyzer-tainted-array-index -Wno-analyzer-tainted-divisor -Wno-analyzer-tainted-offset -Wno-analyzer-tainted-size -Wno-analyzer-throw-of-unexpected-type -Wanalyzer-symbol-too-complex -Wanalyzer-too-complex -Wno-analyzer-undefined-behavior-ptrdiff -Wno-analyzer-undefined-behavior-strtok -Wno-analyzer-unsafe-call-within-signal-handler -Wno-analyzer-use-after-free -Wno-analyzer-use-of-pointer-in-stale-stack-frame -Wno-analyzer-use-of-uninitialized-value -Wno-analyzer-va-arg-type-mismatch -Wno-analyzer-va-list-exhausted -Wno-analyzer-va-list-leak -Wno-analyzer-va-list-use-after-va-end -Wno-analyzer-write-to-const -Wno-analyzer-write-to-string-literal } @item C and Objective-C-only Warning Options @gccoptlist{-Wbad-function-cast -Wdeprecated-non-prototype -Wfree-labels -Wmissing-declarations -Wmissing-parameter-name -Wmissing-parameter-type -Wdeclaration-missing-parameter-type -Wmissing-prototypes -Wmissing-variable-declarations -Wnested-externs -Wold-style-declaration -Wold-style-definition -Wstrict-prototypes -Wtraditional -Wtraditional-conversion -Wdeclaration-after-statement -Wpointer-sign} @item Debugging Options @xref{Debugging Options,,Options for Debugging Your Program}. @gccoptlist{-g -g@var{level} -gdwarf -gdwarf-@var{version} -gbtf -gctf -gctf@var{level} -gprune-btf -gno-prune-btf -ggdb -grecord-gcc-switches -gno-record-gcc-switches -gstrict-dwarf -gno-strict-dwarf -gas-loc-support -gno-as-loc-support -gas-locview-support -gno-as-locview-support -gcodeview -gcolumn-info -gno-column-info -gdwarf32 -gdwarf64 -gstatement-frontiers -gno-statement-frontiers -gvariable-location-views -gno-variable-location-views -ginternal-reset-location-views -gno-internal-reset-location-views -ginline-points -gno-inline-points -gvms -gz@r{[}=@var{type}@r{]} -gsplit-dwarf -gdescribe-dies -gno-describe-dies -fdebug-prefix-map=@var{old}=@var{new} -fdebug-types-section -fno-eliminate-unused-debug-types -femit-struct-debug-baseonly -femit-struct-debug-reduced -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]} -fno-eliminate-unused-debug-symbols -femit-class-debug-always -fno-merge-debug-strings -fno-dwarf2-cfi-asm -fvar-tracking -fvar-tracking-assignments} @item Optimization Options @xref{Optimize Options,,Options that Control Optimization}. @gccoptlist{-faggressive-loop-optimizations -falign-functions[=@var{n}[:@var{m}:[@var{n2}[:@var{m2}]]]] -falign-jumps[=@var{n}[:@var{m}:[@var{n2}[:@var{m2}]]]] -falign-labels[=@var{n}[:@var{m}:[@var{n2}[:@var{m2}]]]] -falign-loops[=@var{n}[:@var{m}:[@var{n2}[:@var{m2}]]]] -fmin-function-alignment=[@var{n}] -fno-allocation-dce -fallow-store-data-races -fassociative-math -fauto-profile -fauto-profile[=@var{path}] -fauto-profile-inlining -fauto-inc-dec -fbranch-probabilities -fcaller-saves -fcombine-stack-adjustments -fconserve-stack -ffold-mem-offsets -fcompare-elim -fcprop-registers -fcrossjumping -fcse-follow-jumps -fcse-skip-blocks -fcx-fortran-rules -fcx-limited-range -fcx-method -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=@var{style} -ffinite-loops -fforward-propagate -ffp-contract=@var{style} -ffunction-sections -fgcse -fgcse-after-reload -fgcse-las -fgcse-lm -fgraphite-identity -fgcse-sm -fhoist-adjacent-loads -fif-conversion -fif-conversion2 -findirect-inlining -finline-stringops[=@var{fn}] -finline-functions -finline-functions-called-once -finline-limit=@var{n} -finline-small-functions -fipa-modref -fipa-cp -fipa-cp-clone -fipa-bit-cp -fipa-vrp -fipa-pta -fipa-profile -fipa-pure-const -fipa-reference -fipa-reference-addressable -fipa-reorder-for-locality -fipa-stack-alignment -fipa-icf -fira-algorithm=@var{algorithm} -flate-combine-instructions -flifetime-dse -flive-patching=@var{level} -fira-region=@var{region} -fira-hoist-pressure -fira-loop-pressure -fno-ira-share-save-slots -fno-ira-share-spill-slots -fisolate-erroneous-paths-dereference -fisolate-erroneous-paths-attribute -fivopts -fkeep-inline-functions -fkeep-static-functions -fkeep-static-consts -flimit-function-alignment -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=@var{alg} -flto-incremental=@var{path} -flto-incremental-cache-size=@var{n} -fmalloc-dce -fmerge-all-constants -fmerge-constants -fmodulo-sched -fmodulo-sched-allow-regmoves -fmove-loop-invariants -fmove-loop-stores -fno-branch-count-reg -fno-defer-pop -fno-fp-int-builtin-inexact -fno-function-cse -fno-guess-branch-probability -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 -fno-printf-return-value -fno-sched-interblock -fno-sched-spec -fno-signed-zeros -fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss -fomit-frame-pointer -foptimize-crc -foptimize-sibling-calls -fpartial-inlining -fpeel-loops -fpredictive-commoning -fprefetch-loop-arrays -fprofile-correction -fprofile-use -fprofile-use=@var{path} -fprofile-partial-training -fprofile-values -fprofile-reorder-functions -freciprocal-math -free -frename-registers -freorder-blocks -freorder-blocks-algorithm=@var{algorithm} -freorder-blocks-and-partition -freorder-functions -frerun-cse-after-loop -freschedule-modulo-scheduled-loops -frounding-math -fsave-optimization-record -fsched2-use-superblocks -fsched-pressure -fsched-spec-load -fsched-spec-load-dangerous -fsched-stalled-insns-dep[=@var{n}] -fsched-stalled-insns[=@var{n}] -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 -fshrink-wrap-separate -fsignaling-nans -fsingle-precision-constant -fsplit-ivs-in-unroller -fsplit-loops -fsplit-paths -fsplit-wide-types -fsplit-wide-types-early -fssa-backprop -fssa-phiopt -fstdarg-opt -fstore-merging -fstrict-aliasing -fipa-strict-aliasing -fthread-jumps -ftracer -ftree-bit-ccp -ftree-builtin-call-dce -ftree-ccp -ftree-ch -ftree-coalesce-vars -ftree-copy-prop -ftree-cselim -ftree-dce -ftree-dominator-opts -ftree-dse -ftree-forwprop -ftree-fre -fcode-hoisting -ftree-loop-if-convert -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=@var{n} -ftree-pre -ftree-partial-pre -ftree-pta -ftree-reassoc -ftree-scev-cprop -ftree-sink -ftree-slsr -ftree-sra -ftree-switch-conversion -ftree-tail-merge -ftree-ter -ftree-vectorize -ftree-vrp -ftrivial-auto-var-init -funconstrained-commons -funit-at-a-time -funroll-all-loops -funroll-loops -funsafe-math-optimizations -funswitch-loops -fipa-ra -fvariable-expansion-in-unroller -fvect-cost-model -fvpt -fweb -fwhole-program -fwpa -fuse-linker-plugin -fzero-call-used-regs --param @var{name}=@var{value} -O -O0 -O1 -O2 -O3 -Os -Ofast -Og -Oz} @item Program Instrumentation Options @xref{Instrumentation Options,,Program Instrumentation Options}. @gccoptlist{-p -pg -fprofile-arcs --coverage -ftest-coverage -fcondition-coverage -fpath-coverage -fprofile-abs-path -fprofile-dir=@var{path} -fprofile-generate -fprofile-generate=@var{path} -fprofile-info-section -fprofile-info-section=@var{name} -fprofile-note=@var{path} -fprofile-prefix-path=@var{path} -fprofile-update=@var{method} -fprofile-filter-files=@var{regex} -fprofile-exclude-files=@var{regex} -fprofile-reproducible=@r{[}multithreaded@r{|}parallel-runs@r{|}serial@r{]} -fsanitize=@var{style} -fsanitize-recover -fsanitize-recover=@var{style} -fsanitize-trap -fsanitize-trap=@var{style} -fasan-shadow-offset=@var{number} -fsanitize-sections=@var{s1},@var{s2},... -fsanitize-undefined-trap-on-error -fbounds-check -fcf-protection -fcf-protection=@r{[}full@r{|}branch@r{|}return@r{|}none@r{|}check@r{]} -fharden-compares -fharden-conditional-branches -fhardened -fharden-control-flow-redundancy -fhardcfr-skip-leaf -fhardcfr-check-exceptions -fhardcfr-check-returning-calls -fhardcfr-check-noreturn-calls=@r{[}always@r{|}no-xthrow@r{|}nothrow@r{|}never@r{]} -fstack-protector -fstack-protector-all -fstack-protector-strong -fstack-protector-explicit -fstack-check -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} -fno-stack-limit -fsplit-stack -fstrub=disable -fstrub=strict -fstrub=relaxed -fstrub=all -fstrub=at-calls -fstrub=internal -fvtable-verify=@r{[}std@r{|}preinit@r{|}none@r{]} -fvtv-counts -fvtv-debug -finstrument-functions -finstrument-functions-once -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{} -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{} -fprofile-prefix-map=@var{old}=@var{new} -fpatchable-function-entry=@var{N}@r{[},@var{M}@r{]}} @item Preprocessor Options @xref{Preprocessor Options,,Options Controlling the Preprocessor}. @gccoptlist{-A@var{question}=@var{answer} -A-@var{question}@r{[}=@var{answer}@r{]} -C -CC -D@var{macro}@r{[}=@var{defn}@r{]} -dD -dI -dM -dN -dU -fdebug-cpp -fdirectives-only -fdollars-in-identifiers -fexec-charset=@var{charset} -fextended-identifiers -finput-charset=@var{charset} -fmacro-prefix-map=@var{old}=@var{new} -fmax-include-depth=@var{depth} -fno-canonical-system-headers -fpch-deps -fpch-preprocess -fpreprocessed -ftabstop=@var{width} -ftrack-macro-expansion -fwide-exec-charset=@var{charset} -fworking-directory -H -imacros @var{file} -include @var{file} -M -MD -MF -MG -MM -MMD -MP -MQ -MT -Mno-modules -no-integrated-cpp -P -pthread -remap -traditional -traditional-cpp -trigraphs -U@var{macro} -undef -Wp,@var{option} -Xpreprocessor @var{option}} @item Assembler Options @xref{Assembler Options,,Passing Options to the Assembler}. @gccoptlist{-Wa,@var{option} -Xassembler @var{option}} @item Linker Options @xref{Link Options,,Options for Linking}. @gccoptlist{@var{object-file-name} -fuse-ld=@var{linker} -l@var{library} -nostartfiles -nodefaultlibs -nolibc -nostdlib -nostdlib++ -e @var{entry} --entry=@var{entry} -pie -pthread -r -rdynamic -s -static -static-pie -static-libgcc -static-libstdc++ -static-libasan -static-libtsan -static-liblsan -static-libubsan -shared -shared-libgcc -symbolic -T @var{script} -Wl,@var{option} -Xlinker @var{option} -u @var{symbol} -z @var{keyword}} @item Directory Options @xref{Directory Options,,Options for Directory Search}. @gccoptlist{-B@var{prefix} -I@var{dir} -I- -idirafter @var{dir} -imacros @var{file} -imultilib @var{dir} -iplugindir=@var{dir} -iprefix @var{file} -iquote @var{dir} -isysroot @var{dir} -isystem @var{dir} -iwithprefix @var{dir} -iwithprefixbefore @var{dir} --embed-dir=@var{dir} -L@var{dir} -no-canonical-prefixes --no-sysroot-suffix -nostdinc -nostdinc++ --sysroot=@var{dir}} @item Code Generation Options @xref{Code Gen Options,,Options for Code Generation Conventions}. @gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} -ffixed-@var{reg} -fexceptions -fnon-call-exceptions -fdelete-dead-exceptions -funwind-tables -fasynchronous-unwind-tables -fno-gnu-unique -finhibit-size-directive -fcommon -fno-ident -fpcc-struct-return -fpic -fPIC -fpie -fPIE -fno-plt -fno-jump-tables -fno-bit-tests -frecord-gcc-switches -freg-struct-return -fshort-enums -fshort-wchar -fverbose-asm -fpack-struct[=@var{n}] -fleading-underscore -ftls-model=@var{model} -fstack-reuse=@var{reuse_level} -ftrampolines -ftrampoline-impl=@r{[}stack@r{|}heap@r{]} -ftrapv -fwrapv -fvisibility=@r{[}default@r{|}internal@r{|}hidden@r{|}protected@r{]} -fstrict-volatile-bitfields -fsync-libcalls -fzero-init-padding-bits=@var{value}} @item Developer Options @xref{Developer Options,,GCC Developer Options}. @gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion -dumpfullversion -fcallgraph-info@r{[}=su,da@r{]} -fchecking -fchecking=@var{n} -fdbg-cnt-list -fdbg-cnt=@var{counter-value-list} -fdisable-ipa-@var{pass_name} -fdisable-rtl-@var{pass_name} -fdisable-rtl-@var{pass-name}=@var{range-list} -fdisable-tree-@var{pass_name} -fdisable-tree-@var{pass-name}=@var{range-list} -fdump-debug -fdump-earlydebug -fdump-noaddr -fdump-unnumbered -fdump-unnumbered-links -fdump-final-insns@r{[}=@var{file}@r{]} -fdump-ipa-all -fdump-ipa-cgraph -fdump-ipa-inline -fdump-lang-all -fdump-lang-@var{switch} -fdump-lang-@var{switch}-@var{options} -fdump-lang-@var{switch}-@var{options}=@var{filename} -fdump-passes -fdump-rtl-@var{pass} -fdump-rtl-@var{pass}=@var{filename} -fdump-statistics -fdump-tree-all -fdump-tree-@var{switch} -fdump-tree-@var{switch}-@var{options} -fdump-tree-@var{switch}-@var{options}=@var{filename} -fcompare-debug@r{[}=@var{opts}@r{]} -fcompare-debug-second -fenable-@var{kind}-@var{pass} -fenable-@var{kind}-@var{pass}=@var{range-list} -fira-verbose=@var{n} -flto-report -flto-report-wpa -fmem-report-wpa -fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report -fopt-info -fopt-info-@var{options}@r{[}=@var{file}@r{]} -fmultiflags -fprofile-report -frandom-seed=@var{string} -fsched-verbose=@var{n} -fsel-sched-verbose -fsel-sched-dump-cfg -fsel-sched-pipelining-verbose -fstats -fstack-usage -ftime-report -ftime-report-details -fvar-tracking-assignments-toggle -gtoggle -print-file-name=@var{library} -print-libgcc-file-name -print-multi-directory -print-multi-lib -print-multi-os-directory -print-prog-name=@var{program} -print-search-dirs -Q -print-sysroot -print-sysroot-headers-suffix -save-temps -save-temps=cwd -save-temps=obj -time@r{[}=@var{file}@r{]}} @item Machine-Dependent Options @xref{Submodel Options,,Machine-Dependent Options}. @c This list is ordered alphanumerically by subsection name. @c Try and put the significant identifier (CPU or system) first, @c so users have a clue at guessing where the ones they want will be. @emph{AArch64 Options} (@ref{AArch64 Options}) @gccoptlist{-mabi=@var{name} -mbig-endian -mlittle-endian -mgeneral-regs-only -mcmodel=tiny -mcmodel=small -mcmodel=large -mstrict-align -mno-strict-align -momit-leaf-frame-pointer -mtls-dialect=desc -mtls-dialect=traditional -mtls-size=@var{size} -mfix-cortex-a53-835769 -mfix-cortex-a53-843419 -mlow-precision-recip-sqrt -mlow-precision-sqrt -mlow-precision-div -mpc-relative-literal-loads -msign-return-address=@var{scope} -mbranch-protection=@var{none}|@var{standard}|@var{pac-ret}[+@var{leaf} +@var{b-key}]|@var{bti}|@var{gcs} -mharden-sls=@var{opts} -march=@var{name} -mcpu=@var{name} -mtune=@var{name} -moverride=@var{string} -mverbose-cost-dump -mstack-protector-guard=@var{guard} -mstack-protector-guard-reg=@var{sysreg} -mstack-protector-guard-offset=@var{offset} -mtrack-speculation -moutline-atomics -mearly-ldp-fusion -mlate-ldp-fusion -Wexperimental-fmv-target} @emph{Adapteva Epiphany Options} (@ref{Adapteva Epiphany Options}) @gccoptlist{-mhalf-reg-file -mprefer-short-insn-regs -mbranch-cost=@var{num} -mcmove -mnops=@var{num} -msoft-cmpsf -msplit-lohi -mpost-inc -mpost-modify -mstack-offset=@var{num} -mround-nearest -mlong-calls -mshort-calls -msmall16 -mfp-mode=@var{mode} -mvect-double -max-vect-align=@var{num} -msplit-vecmove-early -m1reg-@var{reg}} @emph{AMD GCN Options} (@ref{AMD GCN Options}) @gccoptlist{-march=@var{gpu} -mtune=@var{gpu} -mstack-size=@var{bytes}} @emph{ARC Options} (@ref{ARC Options}) @gccoptlist{-mbarrel-shifter -mjli-always -mcpu=@var{cpu} -mA6 -mARC600 -mA7 -mARC700 -mdpfp -mdpfp-compact -mdpfp-fast -mno-dpfp-lrsr -mea -mno-mpy -mmul32x16 -mmul64 -matomic -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 -mlong-calls -mmedium-calls -msdata -mirq-ctrl-saved -mrgf-banked-regs -mlpc-width=@var{width} -G @var{num} -mvolatile-cache -mtp-regno=@var{regno} -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 -mmillicode -mmixed-code -mq-class -mRcq -mRcw -msize-level=@var{level} -mtune=@var{cpu} -mmultcost=@var{num} -mcode-density-frame -munalign-prob-threshold=@var{probability} -mmpy-option=@var{multo} -mdiv-rem -mcode-density -mll64 -mfpu=@var{fpu} -mrf16 -mbranch-index} @emph{ARM Options} (@ref{ARM Options}) @gccoptlist{-mapcs-frame -mno-apcs-frame -mabi=@var{name} -mapcs-stack-check -mno-apcs-stack-check -mapcs-reentrant -mno-apcs-reentrant -mgeneral-regs-only -msched-prolog -mno-sched-prolog -mlittle-endian -mbig-endian -mbe8 -mbe32 -mfloat-abi=@var{name} -mfp16-format=@var{name} -mthumb-interwork -mno-thumb-interwork -mcpu=@var{name} -march=@var{name} -mfpu=@var{name} -mtune=@var{name} -mprint-tune-info -mstructure-size-boundary=@var{n} -mabort-on-noreturn -mlong-calls -mno-long-calls -msingle-pic-base -mno-single-pic-base -mpic-register=@var{reg} -mnop-fun-dllimport -mpoke-function-name -mthumb -marm -mflip-thumb -mtpcs-frame -mtpcs-leaf-frame -mcaller-super-interworking -mcallee-super-interworking -mtp=@var{name} -mtls-dialect=@var{dialect} -mword-relocations -mfix-cortex-m3-ldrd -mfix-cortex-a57-aes-1742098 -mfix-cortex-a72-aes-1655431 -munaligned-access -mneon-for-64bits -mslow-flash-data -masm-syntax-unified -mrestrict-it -mverbose-cost-dump -mpure-code -mcmse -mfix-cmse-cve-2021-35465 -mstack-protector-guard=@var{guard} -mstack-protector-guard-offset=@var{offset} -mfdpic -mbranch-protection=@var{none}|@var{standard}|@var{pac-ret}[+@var{leaf}] [+@var{bti}]|@var{bti}[+@var{pac-ret}[+@var{leaf}]]} @emph{AVR Options} (@ref{AVR Options}) @gccoptlist{-mmcu=@var{mcu} -mabsdata -maccumulate-args -mcvt -mbranch-cost=@var{cost} -mfuse-add=@var{level} -mfuse-move=@var{level} -mfuse-move2 -mcall-prologues -mgas-isr-prologues -mint8 -mflmap -mdouble=@var{bits} -mlong-double=@var{bits} -mno-call-main -mn_flash=@var{size} -mfract-convert-truncate -mno-interrupts -mmain-is-OS_task -mrelax -mrmw -mstrict-X -mtiny-stack -mrodata-in-ram -msplit-bit-shift -msplit-ldst -mshort-calls -mskip-bug -muse-nonzero-bits -nodevicelib -nodevicespecs -Waddr-space-convert -Wmisspelled-isr} @emph{Blackfin Options} (@ref{Blackfin Options}) @gccoptlist{-mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]} -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=@var{n} -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} @emph{C6X Options} (@ref{C6X Options}) @gccoptlist{-mbig-endian -mlittle-endian -march=@var{cpu} -msim -msdata=@var{sdata-type}} @emph{CRIS Options} (@ref{CRIS Options}) @gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} -mmax-stack-frame=@var{n} -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects -mstack-align -mdata-align -mconst-align -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -melf -maout -sim -sim2 -mmul-bug-workaround -mno-mul-bug-workaround} @emph{C-SKY Options} (@ref{C-SKY Options}) @gccoptlist{-march=@var{arch} -mcpu=@var{cpu} -mbig-endian -EB -mlittle-endian -EL -mhard-float -msoft-float -mfpu=@var{fpu} -mdouble-float -mfdivdu -mfloat-abi=@var{name} -melrw -mistack -mmp -mcp -mcache -msecurity -mtrust -mdsp -medsp -mvdsp -mdiv -msmart -mhigh-registers -manchor -mpushpop -mmultiple-stld -mconstpool -mstack-size -mccrt -mbranch-cost=@var{n} -mcse-cc -msched-prolog -msim} @emph{Cygwin and MinGW Options} (@ref{Cygwin and MinGW Options}) @gccoptlist{-mconsole -mcrtdll=@var{library} -mdll -mnop-fun-dllimport -mthread -municode -mwin32 -mwindows -fno-set-stack-executable} @emph{Darwin Options} (@ref{Darwin Options}) @gccoptlist{-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 -nodefaultrpaths -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=@var{version} -mkernel -mone-byte-bool} @emph{DEC Alpha Options} (@ref{DEC Alpha Options}) @gccoptlist{-mno-fp-regs -msoft-float -mieee -mieee-with-inexact -mieee-conformant -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} -mtrap-precision=@var{mode} -mbuild-constants -mcpu=@var{cpu-type} -mtune=@var{cpu-type} -mbwx -mmax -mfix -mcix -msafe-bwa -msafe-partial -mfloat-vax -mfloat-ieee -mexplicit-relocs -msmall-data -mlarge-data -msmall-text -mlarge-text -mmemory-latency=@var{time}} @emph{eBPF Options} (@ref{eBPF Options}) @gccoptlist{-mbig-endian -mlittle-endian -mframe-limit=@var{bytes} -mxbpf -mco-re -mno-co-re -mjmpext -mjmp32 -malu32 -mv3-atomics -mbswap -msdiv -msmov -mcpu=@var{version} -masm=@var{dialect} -minline-memops-threshold=@var{bytes}} @emph{FR30 Options} (@ref{FR30 Options}) @gccoptlist{-msmall-model -mno-lsim} @emph{FT32 Options} (@ref{FT32 Options}) @gccoptlist{-msim -mlra -mnodiv -mft32b -mcompress -mnopm} @emph{FRV Options} (@ref{FRV Options}) @gccoptlist{-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=@var{cpu}} @emph{GNU/Linux Options} (@ref{GNU/Linux Options}) @gccoptlist{-mglibc -muclibc -mmusl -mbionic -mandroid -tno-android-cc -tno-android-ld} @emph{H8/300 Options} (@ref{H8/300 Options}) @gccoptlist{-mrelax -mh -ms -mn -mexr -mno-exr -mint32 -malign-300} @emph{HPPA Options} (@ref{HPPA Options}) @gccoptlist{-march=@var{architecture-type} -matomic-libcalls -mbig-switch -mcaller-copies -mdisable-fpregs -mdisable-indexing -mordered -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld -mfixed-range=@var{register-range} -mcoherent-ldcw -mjump-in-delay -mlinker-opt -mlong-calls -mlong-load-store -mno-atomic-libcalls -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=@var{cpu-type} -mspace-regs -msoft-mult -msio -mwsio -munix=@var{unix-std} -nolibdld -static -threads} @emph{IA-64 Options} (@ref{IA-64 Options}) @gccoptlist{-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=@var{register-range} -mtls-size=@var{tls-size} -mtune=@var{cpu-type} -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=@var{max-insns}} @emph{LM32 Options} (@ref{LM32 Options}) @gccoptlist{-mbarrel-shift-enabled -mdivide-enabled -mmultiply-enabled -msign-extend-enabled -muser-enabled} @emph{LoongArch Options} (@ref{LoongArch Options}) @gccoptlist{-march=@var{arch-type} -mtune=@var{tune-type} -mabi=@var{base-abi-type} -mfpu=@var{fpu-type} -msimd=@var{simd-type} -msoft-float -msingle-float -mdouble-float -mlsx -mno-lsx -mlasx -mno-lasx -mbranch-cost=@var{n} -maddr-reg-reg-cost=@var{n} -mcheck-zero-division -mno-check-zero-division -mcond-move-int -mno-cond-move-int -mcond-move-float -mno-cond-move-float -memcpy -mno-memcpy -mstrict-align -mno-strict-align -G @var{num} -mmax-inline-memcpy-size=@var{n} -mexplicit-relocs=@var{style} -mexplicit-relocs -mno-explicit-relocs -mdirect-extern-access -mno-direct-extern-access -mcmodel=@var{code-model} -mrelax -mpass-mrelax-to-as -mrecip -mrecip=@var{opt} -mfrecipe -mno-frecipe -mdiv32 -mno-div32 -mlam-bh -mno-lam-bh -mlamcas -mno-lamcas -mld-seq-sa -mno-ld-seq-sa -mscq -mno-scq -mtls-dialect=@var{opt} -mannotate-tablejump -mno-annotate-tablejump} @emph{M32C Options} (@ref{M32C Options}) @gccoptlist{-mcpu=@var{cpu} -msim -memregs=@var{number}} @emph{M32R/D Options} (@ref{M32R/D Options}) @gccoptlist{-m32r2 -m32rx -m32r -mdebug -malign-loops -mno-align-loops -missue-rate=@var{number} -mbranch-cost=@var{number} -mmodel=@var{code-size-model-type} -msdata=@var{sdata-type} -mno-flush-func -mflush-func=@var{name} -mno-flush-trap -mflush-trap=@var{number} -G @var{num}} @emph{M680x0 Options} (@ref{M680x0 Options}) @gccoptlist{-march=@var{arch} -mcpu=@var{cpu} -mtune=@var{tune} -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 -mlong-jump-table-offsets} @emph{MCore Options} (@ref{MCore Options}) @gccoptlist{-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} @emph{MicroBlaze Options} (@ref{MicroBlaze Options}) @gccoptlist{-msoft-float -mhard-float -msmall-divides -mcpu=@var{cpu} -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-@var{app-model} -mpic-data-is-text-relative} @emph{MIPS Options} (@ref{MIPS Options}) @gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} -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=@var{abi} -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=@var{mode} -mnan=@var{encoding} -mdsp -mno-dsp -mdspr2 -mno-dspr2 -mmcu -mmno-mcu -meva -mno-eva -mvirt -mno-virt -mxpa -mno-xpa -mcrc -mno-crc -mginv -mno-ginv -mmicromips -mno-micromips -mmsa -mno-msa -mloongson-mmi -mno-loongson-mmi -mloongson-ext -mno-loongson-ext -mloongson-ext2 -mno-loongson-ext2 -mfpu=@var{fpu-type} -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@var{num} -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=@var{setting} -msplit-addresses -mno-split-addresses -mexplicit-relocs -mno-explicit-relocs -mexplicit-relocs=@var{release} -mcheck-zero-division -mno-check-zero-division -mdivide-traps -mdivide-breaks -mload-store-pairs -mno-load-store-pairs -mstrict-align -mno-strict-align -mno-unaligned-access -munaligned-access -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-r5900 -mno-fix-r5900 -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=@var{func} -mno-flush-func -mbranch-cost=@var{num} -mbranch-likely -mno-branch-likely -mcompact-branches=@var{policy} -mfp-exceptions -mno-fp-exceptions -mvr4130-align -mno-vr4130-align -msynci -mno-synci -mlxc1-sxc1 -mno-lxc1-sxc1 -mmadd4 -mno-madd4 -mrelax-pic-calls -mno-relax-pic-calls -mmcount-ra-address -mframe-header-opt -mno-frame-header-opt} @emph{MMIX Options} (@ref{MMIX Options}) @gccoptlist{-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} @emph{MN10300 Options} (@ref{MN10300 Options}) @gccoptlist{-mmult-bug -mno-mult-bug -mno-am33 -mam33 -mam33-2 -mam34 -mtune=@var{cpu-type} -mreturn-pointer-on-d0 -mno-crt0 -mrelax -mliw -msetlb} @emph{Moxie Options} (@ref{Moxie Options}) @gccoptlist{-meb -mel -mmul.x -mno-crt0} @emph{MSP430 Options} (@ref{MSP430 Options}) @gccoptlist{-msim -masm-hex -mmcu= -mcpu= -mlarge -msmall -mrelax -mwarn-mcu -mcode-region= -mdata-region= -msilicon-errata= -msilicon-errata-warn= -mhwmult= -minrt -mtiny-printf -mmax-inline-shift=} @emph{NDS32 Options} (@ref{NDS32 Options}) @gccoptlist{-mbig-endian -mlittle-endian -mreduced-regs -mfull-regs -mcmov -mno-cmov -mext-perf -mno-ext-perf -mext-perf2 -mno-ext-perf2 -mext-string -mno-ext-string -mv3push -mno-v3push -m16bit -mno-16bit -misr-vector-size=@var{num} -mcache-block-size=@var{num} -march=@var{arch} -mcmodel=@var{code-model} -mctor-dtor -mrelax} @emph{Nvidia PTX Options} (@ref{Nvidia PTX Options}) @gccoptlist{-m64 -mmainkernel -moptimize} @emph{OpenRISC Options} (@ref{OpenRISC Options}) @gccoptlist{-mboard=@var{name} -mnewlib -mhard-mul -mhard-div -msoft-mul -msoft-div -msoft-float -mhard-float -mdouble-float -munordered-float -mcmov -mror -mrori -msext -msfimm -mshftimm -mcmodel=@var{code-model}} @emph{PDP-11 Options} (@ref{PDP-11 Options}) @gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 -mint32 -mno-int16 -mint16 -mno-int32 -msplit -munix-asm -mdec-asm -mgnu-asm -mlra} @emph{PowerPC Options} See RS/6000 and PowerPC Options. @emph{PRU Options} (@ref{PRU Options}) @gccoptlist{-mmcu=@var{mcu} -minrt -mno-relax -mloop -mmul -mfillzero -mabi=@var{variant}} @emph{RISC-V Options} (@ref{RISC-V Options}) @gccoptlist{-mbranch-cost=@var{N-instruction} -mplt -mno-plt -mabi=@var{ABI-string} -mfdiv -mno-fdiv -mfence-tso -mno-fence-tso -mdiv -mno-div -misa-spec=@var{ISA-spec-string} -march=@var{ISA-string|Profiles|Profiles_ISA-string|CPU/processor string} -mtune=@var{processor-string} -mpreferred-stack-boundary=@var{num} -msmall-data-limit=@var{N-bytes} -msave-restore -mno-save-restore -mshorten-memrefs -mno-shorten-memrefs -mstrict-align -mno-strict-align -mcmodel=medlow -mcmodel=medany -mcmodel=large -mexplicit-relocs -mno-explicit-relocs -mrelax -mno-relax -mriscv-attribute -mno-riscv-attribute -malign-data=@var{type} -mbig-endian -mlittle-endian -mstack-protector-guard=@var{guard} -mstack-protector-guard-reg=@var{reg} -mstack-protector-guard-offset=@var{offset} -mcsr-check -mno-csr-check -mmovcc -mno-movcc -minline-atomics -mno-inline-atomics -minline-strlen -mno-inline-strlen -minline-strcmp -mno-inline-strcmp -minline-strncmp -mno-inline-strncmp -mtls-dialect=desc -mtls-dialect=trad} @emph{RL78 Options} (@ref{RL78 Options}) @gccoptlist{-msim -mmul=none -mmul=g13 -mmul=g14 -mallregs -mcpu=g10 -mcpu=g13 -mcpu=g14 -mg10 -mg13 -mg14 -m64bit-doubles -m32bit-doubles -msave-mduc-in-interrupts} @emph{RS/6000 and PowerPC Options} (@ref{RS/6000 and PowerPC Options}) @gccoptlist{-mcpu=@var{cpu-type} -mtune=@var{cpu-type} -mcmodel=@var{code-model} -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 -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 -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 -mswdiv -msingle-pic-base -mprioritize-restricted-insns=@var{priority} -msched-costly-dep=@var{dependence_type} -minsert-sched-nops=@var{scheme} -mcall-aixdesc -mcall-eabi -mcall-freebsd -mcall-linux -mcall-netbsd -mcall-openbsd -mcall-sysv -mcall-sysv-eabi -mcall-sysv-noeabi -mtraceback=@var{traceback_type} -maix-struct-return -msvr4-struct-return -mabi=@var{abi-type} -msecure-plt -mbss-plt -msplit-patch-nops -mlongcall -mno-longcall -mpltseq -mno-pltseq -mblock-move-inline-limit=@var{num} -mblock-compare-inline-limit=@var{num} -mblock-compare-inline-loop-limit=@var{num} -mno-block-ops-unaligned-vsx -mstring-compare-inline-limit=@var{num} -misel -mno-isel -mvrsave -mno-vrsave -mmulhw -mno-mulhw -mdlmzb -mno-dlmzb -mprototype -mno-prototype -msim -mmvme -mads -myellowknife -memb -msdata -msdata=@var{opt} -mreadonly-in-sdata -mvxworks -G @var{num} -mrecip -mrecip=@var{opt} -mno-recip -mrecip-precision -mno-recip-precision -mveclibabi=@var{type} -mfriz -mno-friz -mpointers-to-nested-functions -mno-pointers-to-nested-functions -msave-toc-indirect -mno-save-toc-indirect -mpower8-fusion -mno-mpower8-fusion -mcrypto -mno-crypto -mhtm -mno-htm -mquad-memory -mno-quad-memory -mquad-memory-atomic -mno-quad-memory-atomic -mcompat-align-parm -mno-compat-align-parm -mfloat128 -mno-float128 -mfloat128-hardware -mno-float128-hardware -mgnu-attribute -mno-gnu-attribute -mstack-protector-guard=@var{guard} -mstack-protector-guard-reg=@var{reg} -mstack-protector-guard-offset=@var{offset} -mprefixed -mno-prefixed -mpcrel -mno-pcrel -mmma -mno-mmma -mrop-protect -mno-rop-protect -mprivileged -mno-privileged} @emph{RX Options} (@ref{RX Options}) @gccoptlist{-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 -mallow-string-insns -mno-allow-string-insns -mjsr -mno-warn-multiple-fast-interrupts -msave-acc-in-interrupts} @emph{S/390 and zSeries Options} (@ref{S/390 and zSeries Options}) @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} -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 -mhtm -mvx -mzvector -mtpf-trace -mno-tpf-trace -mtpf-trace-skip -mno-tpf-trace-skip -mfused-madd -mno-fused-madd -mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard -mhotpatch=@var{halfwords},@var{halfwords}} @emph{SH Options} (@ref{SH Options}) @gccoptlist{-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 -mb -ml -mdalign -mrelax -mbigtable -mfmovd -mrenesas -mno-renesas -mnomacsave -mieee -mno-ieee -mbitops -misize -minline-ic_invalidate -mpadstruct -mprefergot -musermode -multcost=@var{number} -mdiv=@var{strategy} -mdivsi3_libfunc=@var{name} -mfixed-range=@var{register-range} -maccumulate-outgoing-args -matomic-model=@var{atomic-model} -mbranch-cost=@var{num} -mzdcbranch -mno-zdcbranch -mcbranch-force-delay-slot -mfused-madd -mno-fused-madd -mfsca -mno-fsca -mfsrra -mno-fsrra -mpretend-cmove -mtas} @emph{Solaris 2 Options} (@ref{Solaris 2 Options}) @gccoptlist{-mclear-hwcap -mno-clear-hwcap -mimpure-text -mno-impure-text -pthreads} @emph{SPARC Options} (@ref{SPARC Options}) @gccoptlist{-mcpu=@var{cpu-type} -mtune=@var{cpu-type} -mcmodel=@var{code-model} -mmemory-model=@var{mem-model} -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 -mstd-struct-return -mno-std-struct-return -munaligned-doubles -mno-unaligned-doubles -muser-mode -mno-user-mode -mv8plus -mno-v8plus -mvis -mno-vis -mvis2 -mno-vis2 -mvis3 -mno-vis3 -mvis3b -mno-vis3b -mvis4 -mno-vis4 -mvis4b -mno-vis4b -mcbcond -mno-cbcond -mfmaf -mno-fmaf -mfsmuld -mno-fsmuld -mpopc -mno-popc -msubxc -mno-subxc -mfix-at697f -mfix-ut699 -mfix-ut700 -mfix-gr712rc} @emph{System V Options} (@ref{System V Options}) @gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}} @emph{V850 Options} (@ref{V850 Options}) @gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep -mprolog-function -mno-prolog-function -mspace -mtda=@var{n} -msda=@var{n} -mzda=@var{n} -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} @emph{VAX Options} (@ref{VAX Options}) @gccoptlist{-munix -mgnu -md -md-float -mg -mg-float -mlra} @emph{Visium Options} (@ref{Visium Options}) @gccoptlist{-mdebug -msim -mfpu -mno-fpu -mhard-float -msoft-float -mcpu=@var{cpu-type} -mtune=@var{cpu-type} -msv-mode -muser-mode} @emph{VMS Options} (@ref{VMS Options}) @gccoptlist{-mvms-return-codes -mdebug-main=@var{prefix} -mmalloc64 -mpointer-size=@var{size}} @emph{VxWorks Options} (@ref{VxWorks Options}) @gccoptlist{-mrtp -msmp -non-static -Bstatic -Bdynamic -Xbind-lazy -Xbind-now} @emph{x86 Options} (@ref{x86 Options}) @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} -mtune-ctrl=@var{feature-list} -mdump-tune-features -mno-default -mfpmath=@var{unit} -masm=@var{dialect} -mno-fancy-math-387 -mno-fp-ret-in-387 -m80387 -mhard-float -msoft-float -mno-wide-multiply -mrtd -malign-double -mpreferred-stack-boundary=@var{num} -mincoming-stack-boundary=@var{num} -mcld -mcx16 -msahf -mmovbe -mcrc32 -mmwait -mrecip -mrecip=@var{opt} -mvzeroupper -mprefer-avx128 -mprefer-vector-width=@var{opt} -mpartial-vector-fp-math -mmove-max=@var{bits} -mstore-max=@var{bits} -mnoreturn-no-callee-saved-registers -mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 -mavx -mavx2 -mavx512f -mavx512cd -mavx512vl -mavx512bw -mavx512dq -mavx512ifma -mavx512vbmi -msha -maes -mpclmul -mfsgsbase -mrdrnd -mf16c -mfma -mpconfig -mwbnoinvd -mptwrite -mclflushopt -mclwb -mxsavec -mxsaves -msse4a -m3dnow -m3dnowa -mpopcnt -mabm -mbmi -mtbm -mfma4 -mxop -madx -mlzcnt -mbmi2 -mfxsr -mxsave -mxsaveopt -mrtm -mhle -mlwp -mmwaitx -mclzero -mpku -mthreads -mgfni -mvaes -mwaitpkg -mshstk -mmanual-endbr -mcet-switch -mforce-indirect-call -mavx512vbmi2 -mavx512bf16 -menqcmd -mvpclmulqdq -mavx512bitalg -mmovdiri -mmovdir64b -mavx512vpopcntdq -mavx512vnni -mprfchw -mrdpid -mrdseed -msgx -mavx512vp2intersect -mserialize -mtsxldtrk -mamx-tile -mamx-int8 -mamx-bf16 -muintr -mhreset -mavxvnni -mamx-fp8 -mavx512fp16 -mavxifma -mavxvnniint8 -mavxneconvert -mcmpccxadd -mamx-fp16 -mprefetchi -mraoint -mamx-complex -mavxvnniint16 -msm3 -msha512 -msm4 -mapxf -musermsr -mavx10.1 -mavx10.2 -mamx-avx512 -mamx-tf32 -mamx-transpose -mmovrs -mamx-movrs -mcldemote -mms-bitfields -mno-align-stringops -minline-all-stringops -minline-stringops-dynamically -mstringop-strategy=@var{alg} -mkl -mwidekl -mmemcpy-strategy=@var{strategy} -mmemset-strategy=@var{strategy} -mpush-args -maccumulate-outgoing-args -m128bit-long-double -m96bit-long-double -mlong-double-64 -mlong-double-80 -mlong-double-128 -mregparm=@var{num} -msseregparm -mveclibabi=@var{type} -mvect8-ret-in-mem -mpc32 -mpc64 -mpc80 -mdaz-ftz -mstackrealign -momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs -mcmodel=@var{code-model} -mabi=@var{name} -maddress-mode=@var{mode} -m32 -m64 -mx32 -m16 -miamcu -mlarge-data-threshold=@var{num} -msse2avx -mfentry -mrecord-mcount -mnop-mcount -m8bit-idiv -minstrument-return=@var{type} -mfentry-name=@var{name} -mfentry-section=@var{name} -mavx256-split-unaligned-load -mavx256-split-unaligned-store -malign-data=@var{type} -mstack-protector-guard=@var{guard} -mstack-protector-guard-reg=@var{reg} -mstack-protector-guard-offset=@var{offset} -mstack-protector-guard-symbol=@var{symbol} -mgeneral-regs-only -mcall-ms2sysv-xlogues -mrelax-cmpxchg-loop -mindirect-branch=@var{choice} -mfunction-return=@var{choice} -mindirect-branch-register -mharden-sls=@var{choice} -mindirect-branch-cs-prefix -mneeded -mno-direct-extern-access -munroll-only-small-loops -mlam=@var{choice}} @emph{x86 Windows Options} See Cygwin and MinGW Options. @emph{Xstormy16 Options} (@ref{Xstormy16 Options}) @gccoptlist{-msim} @emph{Xtensa Options} (@ref{Xtensa Options}) @gccoptlist{-mconst16 -mno-const16 -mfused-madd -mno-fused-madd -mforce-no-pic -mserialize-volatile -mno-serialize-volatile -mtext-section-literals -mno-text-section-literals -mauto-litpools -mno-auto-litpools -mtarget-align -mno-target-align -mlongcalls -mno-longcalls -mabi=@var{abi-type} -mextra-l32r-costs=@var{cycles} -mstrict-align -mno-strict-align} @emph{zSeries Options} See S/390 and zSeries Options. @end table @node Overall Options @section Options Controlling the Kind of Output Compilation can involve up to four stages: preprocessing, compilation proper, assembly and linking, always in that order. GCC is capable of preprocessing and compiling several files either into several assembler input files, or into one assembler input file; then each assembler input file produces an object file, and linking combines all the object files (those newly compiled, and those specified as input) into an executable file. @cindex file name suffix For any given input file, the file name suffix determines what kind of compilation is done: @table @gcctabopt @item @var{file}.c C source code that must be preprocessed. @item @var{file}.i C source code that should not be preprocessed. @item @var{file}.ii C++ source code that should not be preprocessed. @item @var{file}.m Objective-C source code. Note that you must link with the @file{libobjc} library to make an Objective-C program work. @item @var{file}.mi Objective-C source code that should not be preprocessed. @item @var{file}.mm @itemx @var{file}.M Objective-C++ source code. Note that you must link with the @file{libobjc} library to make an Objective-C++ program work. Note that @samp{.M} refers to a literal capital M@. @item @var{file}.mii Objective-C++ source code that should not be preprocessed. @item @var{file}.h C, C++, Objective-C or Objective-C++ header file to be turned into a precompiled header (default), or C, C++ header file to be turned into an Ada spec (via the @option{-fdump-ada-spec} switch). @item @var{file}.cc @itemx @var{file}.cp @itemx @var{file}.cxx @itemx @var{file}.cpp @itemx @var{file}.CPP @itemx @var{file}.c++ @itemx @var{file}.C C++ source code that must be preprocessed. Note that in @samp{.cxx}, the last two letters must both be literally @samp{x}. Likewise, @samp{.C} refers to a literal capital C@. @item @var{file}.mm @itemx @var{file}.M Objective-C++ source code that must be preprocessed. @item @var{file}.mii Objective-C++ source code that should not be preprocessed. @item @var{file}.hh @itemx @var{file}.H @itemx @var{file}.hp @itemx @var{file}.hxx @itemx @var{file}.hpp @itemx @var{file}.HPP @itemx @var{file}.h++ @itemx @var{file}.tcc C++ header file to be turned into a precompiled header or Ada spec. @item @var{file}.f @itemx @var{file}.for @itemx @var{file}.ftn @itemx @var{file}.fi Fixed form Fortran source code that should not be preprocessed. @item @var{file}.F @itemx @var{file}.FOR @itemx @var{file}.fpp @itemx @var{file}.FPP @itemx @var{file}.FTN Fixed form Fortran source code that must be preprocessed (with the traditional preprocessor). @item @var{file}.f90 @itemx @var{file}.f95 @itemx @var{file}.f03 @itemx @var{file}.f08 @itemx @var{file}.fii Free form Fortran source code that should not be preprocessed. @item @var{file}.F90 @itemx @var{file}.F95 @itemx @var{file}.F03 @itemx @var{file}.F08 Free form Fortran source code that must be preprocessed (with the traditional preprocessor). @item @var{file}.cob @item @var{file}.COB @item @var{file}.cbl @item @var{file}.CBL COBOL source code. @item @var{file}.go Go source code. @item @var{file}.d D source code. @item @var{file}.di D interface file. @item @var{file}.dd D documentation code (Ddoc). @item @var{file}.ads Ada source code file that contains a library unit declaration (a declaration of a package, subprogram, or generic, or a generic instantiation), or a library unit renaming declaration (a package, generic, or subprogram renaming declaration). Such files are also called @dfn{specs}. @item @var{file}.adb Ada source code file containing a library unit body (a subprogram or package body). Such files are also called @dfn{bodies}. @c GCC also knows about some suffixes for languages not yet included: @c Ratfor: @c @var{file}.r @item @var{file}.s Assembler code. @item @var{file}.S @itemx @var{file}.sx Assembler code that must be preprocessed. @item @var{other} An object file to be fed straight into linking. Any file name with no recognized suffix is treated this way. @end table @opindex x You can specify the input language explicitly with the @option{-x} option: @table @gcctabopt @item -x @var{language} Specify explicitly the @var{language} for the following input files (rather than letting the compiler choose a default based on the file name suffix). This option applies to all following input files until the next @option{-x} option. Possible values for @var{language} are: @smallexample c c-header cpp-output c++ c++-header c++-system-header c++-user-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 cobol d f77 f77-cpp-input f95 f95-cpp-input go @end smallexample Note that @option{-x} does not imply a particular language standard. For example @option{-x f77} may also require @option{-std=legacy} for some older source codes. @item -x none Turn off any specification of a language, so that subsequent files are handled according to their file name suffixes (as if @option{-x} has not been used at all). @end table If you only want some of the stages of compilation, you can use @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and one of the options @option{-c}, @option{-S}, or @option{-E} to say where @command{gcc} is to stop. Note that some combinations (for example, @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all. @table @gcctabopt @opindex c @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. By default, the object file name for a source file is made by replacing the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}. Unrecognized input files, not requiring compilation or assembly, are ignored. @opindex S @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. By default, the assembler file name for a source file is made by replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}. Input files that don't require compilation are ignored. @opindex E @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. Input files that don't require preprocessing are ignored. @cindex output file option @opindex o @item -o @var{file} Place the primary output in file @var{file}. This applies to whatever sort of output is being produced, whether it be an executable file, an object file, an assembler file or preprocessed C code. If @option{-o} is not specified, the default is to put an executable file in @file{a.out}, the object file for @file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its assembler file in @file{@var{source}.s}, a precompiled header file in @file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on standard output. Though @option{-o} names only the primary output, it also affects the naming of auxiliary and dump outputs. See the examples below. Unless overridden, both auxiliary outputs and dump outputs are placed in the same directory as the primary output. In auxiliary outputs, the suffix of the input file is replaced with that of the auxiliary output file type; in dump outputs, the suffix of the dump file is appended to the input file suffix. In compilation commands, the base name of both auxiliary and dump outputs is that of the primary output; in compile and link commands, the primary output name, minus the executable suffix, is combined with the input file name. If both share the same base name, disregarding the suffix, the result of the combination is that base name, otherwise, they are concatenated, separated by a dash. @smallexample gcc -c foo.c ... @end smallexample will use @file{foo.o} as the primary output, and place aux outputs and dumps next to it, e.g., aux file @file{foo.dwo} for @option{-gsplit-dwarf}, and dump file @file{foo.c.???r.final} for @option{-fdump-rtl-final}. If a non-linker output file is explicitly specified, aux and dump files by default take the same base name: @smallexample gcc -c foo.c -o dir/foobar.o ... @end smallexample will name aux outputs @file{dir/foobar.*} and dump outputs @file{dir/foobar.c.*}. A linker output will instead prefix aux and dump outputs: @smallexample gcc foo.c bar.c -o dir/foobar ... @end smallexample will generally name aux outputs @file{dir/foobar-foo.*} and @file{dir/foobar-bar.*}, and dump outputs @file{dir/foobar-foo.c.*} and @file{dir/foobar-bar.c.*}. The one exception to the above is when the executable shares the base name with the single input: @smallexample gcc foo.c -o dir/foo ... @end smallexample in which case aux outputs are named @file{dir/foo.*} and dump outputs named @file{dir/foo.c.*}. The location and the names of auxiliary and dump outputs can be adjusted by the options @option{-dumpbase}, @option{-dumpbase-ext}, @option{-dumpdir}, @option{-save-temps=cwd}, and @option{-save-temps=obj}. @opindex dumpbase @item -dumpbase @var{dumpbase} This option sets the base name for auxiliary and dump output files. It does not affect the name of the primary output file. Intermediate outputs, when preserved, are not regarded as primary outputs, but as auxiliary outputs: @smallexample gcc -save-temps -S foo.c @end smallexample saves the (no longer) temporary preprocessed file in @file{foo.i}, and then compiles to the (implied) output file @file{foo.s}, whereas: @smallexample gcc -save-temps -dumpbase save-foo -c foo.c @end smallexample preprocesses to in @file{save-foo.i}, compiles to @file{save-foo.s} (now an intermediate, thus auxiliary output), and then assembles to the (implied) output file @file{foo.o}. Absent this option, dump and aux files take their names from the input file, or from the (non-linker) output file, if one is explicitly specified: dump output files (e.g. those requested by @option{-fdump-*} options) with the input name suffix, and aux output files (those requested by other non-dump options, e.g. @code{-save-temps}, @code{-gsplit-dwarf}, @code{-fcallgraph-info}) without it. Similar suffix differentiation of dump and aux outputs can be attained for explicitly-given @option{-dumpbase basename.suf} by also specifying @option{-dumpbase-ext .suf}. If @var{dumpbase} is explicitly specified with any directory component, any @var{dumppfx} specification (e.g. @option{-dumpdir} or @option{-save-temps=*}) is ignored, and instead of appending to it, @var{dumpbase} fully overrides it: @smallexample gcc foo.c -c -o dir/foo.o -dumpbase alt/foo \ -dumpdir pfx- -save-temps=cwd ... @end smallexample creates auxiliary and dump outputs named @file{alt/foo.*}, disregarding @file{dir/} in @option{-o}, the @file{./} prefix implied by @option{-save-temps=cwd}, and @file{pfx-} in @option{-dumpdir}. When @option{-dumpbase} is specified in a command that compiles multiple inputs, or that compiles and then links, it may be combined with @var{dumppfx}, as specified under @option{-dumpdir}. Then, each input file is compiled using the combined @var{dumppfx}, and default values for @var{dumpbase} and @var{auxdropsuf} are computed for each input file: @smallexample gcc foo.c bar.c -c -dumpbase main ... @end smallexample creates @file{foo.o} and @file{bar.o} as primary outputs, and avoids overwriting the auxiliary and dump outputs by using the @var{dumpbase} as a prefix, creating auxiliary and dump outputs named @file{main-foo.*} and @file{main-bar.*}. An empty string specified as @var{dumpbase} avoids the influence of the output basename in the naming of auxiliary and dump outputs during compilation, computing default values : @smallexample gcc -c foo.c -o dir/foobar.o -dumpbase '' ... @end smallexample will name aux outputs @file{dir/foo.*} and dump outputs @file{dir/foo.c.*}. Note how their basenames are taken from the input name, but the directory still defaults to that of the output. The empty-string dumpbase does not prevent the use of the output basename for outputs during linking: @smallexample gcc foo.c bar.c -o dir/foobar -dumpbase '' -flto ... @end smallexample The compilation of the source files will name auxiliary outputs @file{dir/foo.*} and @file{dir/bar.*}, and dump outputs @file{dir/foo.c.*} and @file{dir/bar.c.*}. LTO recompilation during linking will use @file{dir/foobar.} as the prefix for dumps and auxiliary files. @opindex dumpbase-ext @item -dumpbase-ext @var{auxdropsuf} When forming the name of an auxiliary (but not a dump) output file, drop trailing @var{auxdropsuf} from @var{dumpbase} before appending any suffixes. If not specified, this option defaults to the suffix of a default @var{dumpbase}, i.e., the suffix of the input file when @option{-dumpbase} is not present in the command line, or @var{dumpbase} is combined with @var{dumppfx}. @smallexample gcc foo.c -c -o dir/foo.o -dumpbase x-foo.c -dumpbase-ext .c ... @end smallexample creates @file{dir/foo.o} as the main output, and generates auxiliary outputs in @file{dir/x-foo.*}, taking the location of the primary output, and dropping the @file{.c} suffix from the @var{dumpbase}. Dump outputs retain the suffix: @file{dir/x-foo.c.*}. This option is disregarded if it does not match the suffix of a specified @var{dumpbase}, except as an alternative to the executable suffix when appending the linker output base name to @var{dumppfx}, as specified below: @smallexample gcc foo.c bar.c -o main.out -dumpbase-ext .out ... @end smallexample creates @file{main.out} as the primary output, and avoids overwriting the auxiliary and dump outputs by using the executable name minus @var{auxdropsuf} as a prefix, creating auxiliary outputs named @file{main-foo.*} and @file{main-bar.*} and dump outputs named @file{main-foo.c.*} and @file{main-bar.c.*}. @opindex dumpdir @item -dumpdir @var{dumppfx} When forming the name of an auxiliary or dump output file, use @var{dumppfx} as a prefix: @smallexample gcc -dumpdir pfx- -c foo.c ... @end smallexample creates @file{foo.o} as the primary output, and auxiliary outputs named @file{pfx-foo.*}, combining the given @var{dumppfx} with the default @var{dumpbase} derived from the default primary output, derived in turn from the input name. Dump outputs also take the input name suffix: @file{pfx-foo.c.*}. If @var{dumppfx} is to be used as a directory name, it must end with a directory separator: @smallexample gcc -dumpdir dir/ -c foo.c -o obj/bar.o ... @end smallexample creates @file{obj/bar.o} as the primary output, and auxiliary outputs named @file{dir/bar.*}, combining the given @var{dumppfx} with the default @var{dumpbase} derived from the primary output name. Dump outputs also take the input name suffix: @file{dir/bar.c.*}. It defaults to the location of the output file, unless the output file is a special file like @code{/dev/null}. Options @option{-save-temps=cwd} and @option{-save-temps=obj} override this default, just like an explicit @option{-dumpdir} option. In case multiple such options are given, the last one prevails: @smallexample gcc -dumpdir pfx- -c foo.c -save-temps=obj ... @end smallexample outputs @file{foo.o}, with auxiliary outputs named @file{foo.*} because @option{-save-temps=*} overrides the @var{dumppfx} given by the earlier @option{-dumpdir} option. It does not matter that @option{=obj} is the default for @option{-save-temps}, nor that the output directory is implicitly the current directory. Dump outputs are named @file{foo.c.*}. When compiling from multiple input files, if @option{-dumpbase} is specified, @var{dumpbase}, minus a @var{auxdropsuf} suffix, and a dash are appended to (or override, if containing any directory components) an explicit or defaulted @var{dumppfx}, so that each of the multiple compilations gets differently-named aux and dump outputs. @smallexample gcc foo.c bar.c -c -dumpdir dir/pfx- -dumpbase main ... @end smallexample outputs auxiliary dumps to @file{dir/pfx-main-foo.*} and @file{dir/pfx-main-bar.*}, appending @var{dumpbase}- to @var{dumppfx}. Dump outputs retain the input file suffix: @file{dir/pfx-main-foo.c.*} and @file{dir/pfx-main-bar.c.*}, respectively. Contrast with the single-input compilation: @smallexample gcc foo.c -c -dumpdir dir/pfx- -dumpbase main ... @end smallexample that, applying @option{-dumpbase} to a single source, does not compute and append a separate @var{dumpbase} per input file. Its auxiliary and dump outputs go in @file{dir/pfx-main.*}. When compiling and then linking from multiple input files, a defaulted or explicitly specified @var{dumppfx} also undergoes the @var{dumpbase}- transformation above (e.g. the compilation of @file{foo.c} and @file{bar.c} above, but without @option{-c}). If neither @option{-dumpdir} nor @option{-dumpbase} are given, the linker output base name, minus @var{auxdropsuf}, if specified, or the executable suffix otherwise, plus a dash is appended to the default @var{dumppfx} instead. Note, however, that unlike earlier cases of linking: @smallexample gcc foo.c bar.c -dumpdir dir/pfx- -o main ... @end smallexample does not append the output name @file{main} to @var{dumppfx}, because @option{-dumpdir} is explicitly specified. The goal is that the explicitly-specified @var{dumppfx} may contain the specified output name as part of the prefix, if desired; only an explicitly-specified @option{-dumpbase} would be combined with it, in order to avoid simply discarding a meaningful option. When compiling and then linking from a single input file, the linker output base name will only be appended to the default @var{dumppfx} as above if it does not share the base name with the single input file name. This has been covered in single-input linking cases above, but not with an explicit @option{-dumpdir} that inhibits the combination, even if overridden by @option{-save-temps=*}: @smallexample gcc foo.c -dumpdir alt/pfx- -o dir/main.exe -save-temps=cwd ... @end smallexample Auxiliary outputs are named @file{foo.*}, and dump outputs @file{foo.c.*}, in the current working directory as ultimately requested by @option{-save-temps=cwd}. Summing it all up for an intuitive though slightly imprecise data flow: the primary output name is broken into a directory part and a basename part; @var{dumppfx} is set to the former, unless overridden by @option{-dumpdir} or @option{-save-temps=*}, and @var{dumpbase} is set to the latter, unless overriden by @option{-dumpbase}. If there are multiple inputs or linking, this @var{dumpbase} may be combined with @var{dumppfx} and taken from each input file. Auxiliary output names for each input are formed by combining @var{dumppfx}, @var{dumpbase} minus suffix, and the auxiliary output suffix; dump output names are only different in that the suffix from @var{dumpbase} is retained. When it comes to auxiliary and dump outputs created during LTO recompilation, a combination of @var{dumppfx} and @var{dumpbase}, as given or as derived from the linker output name but not from inputs, even in cases in which this combination would not otherwise be used as such, is passed down with a trailing period replacing the compiler-added dash, if any, as a @option{-dumpdir} option to @command{lto-wrapper}; being involved in linking, this program does not normally get any @option{-dumpbase} and @option{-dumpbase-ext}, and it ignores them. When running sub-compilers, @command{lto-wrapper} appends LTO stage names to the received @var{dumppfx}, ensures it contains a directory component so that it overrides any @option{-dumpdir}, and passes that as @option{-dumpbase} to sub-compilers. @opindex v @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. @opindex ### @item -### Like @option{-v} except the commands are not executed and arguments are quoted unless they contain only alphanumeric characters or @code{./-_}. This is useful for shell scripts to capture the driver-generated command lines. @opindex help @item --help Print (on the standard output) a description of the command-line options understood by @command{gcc}. If the @option{-v} option is also specified then @option{--help} is also passed on to the various processes invoked by @command{gcc}, so that they can display the command-line options they accept. If the @option{-Wextra} option has also been specified (prior to the @option{--help} option), then command-line options that have no documentation associated with them are also displayed. @opindex target-help @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. @item --help=@{@var{class}@r{|[}^@r{]}@var{qualifier}@}@r{[},@dots{}@r{]} Print (on the standard output) a description of the command-line options understood by the compiler that fit into all specified classes and qualifiers. These are the supported classes: @table @asis @item @samp{optimizers} Display all of the optimization options supported by the compiler. @item @samp{warnings} Display all of the options controlling warning messages produced by the compiler. @item @samp{target} Display target-specific options. Unlike the @option{--target-help} option however, target-specific options of the linker and assembler are not displayed. This is because those tools do not currently support the extended @option{--help=} syntax. @item @samp{params} Display the values recognized by the @option{--param} option. @item @var{language} Display the options supported for @var{language}, where @var{language} is the name of one of the languages supported in this version of GCC@. If an option is supported by all languages, one needs to select @samp{common} class. @item @samp{common} Display the options that are common to all languages. @end table These are the supported qualifiers: @table @asis @item @samp{undocumented} Display only those options that are undocumented. @item @samp{joined} Display options taking an argument that appears after an equal sign in the same continuous piece of text, such as: @samp{--help=target}. @item @samp{separate} Display options taking an argument that appears as a separate word following the original option, such as: @samp{-o output-file}. @end table Thus for example to display all the undocumented target-specific switches supported by the compiler, use: @smallexample --help=target,undocumented @end smallexample The sense of a qualifier can be inverted by prefixing it with the @samp{^} character, so for example to display all binary warning options (i.e., ones that are either on or off and that do not take an argument) that have a description, use: @smallexample --help=warnings,^joined,^undocumented @end smallexample The argument to @option{--help=} should not consist solely of inverted qualifiers. Combining several classes is possible, although this usually restricts the output so much that there is nothing to display. One case where it does work, however, is when one of the classes is @var{target}. For example, to display all the target-specific optimization options, use: @smallexample --help=target,optimizers @end smallexample The @option{--help=} option can be repeated on the command line. Each successive use displays its requested class of options, skipping those that have already been displayed. If @option{--help} is also specified anywhere on the command line then this takes precedence over any @option{--help=} option. @opindex Q If the @option{-Q} option appears on the command line before the @option{--help=} option, then the descriptive text displayed by @option{--help=} is changed. Instead of describing the displayed options, an indication is given as to whether the option is enabled, disabled or set to a specific value (assuming that the compiler knows this at the point where the @option{--help=} option is used). Here is a truncated example from the ARM port of @command{gcc}: @smallexample % gcc -Q -mabi=2 --help=target -c The following options are target specific: -mabi= 2 -mabort-on-noreturn [disabled] -mapcs [disabled] @end smallexample The output is sensitive to the effects of previous command-line options, so for example it is possible to find out which optimizations are enabled at @option{-O2} by using: @smallexample -Q -O2 --help=optimizers @end smallexample Alternatively you can discover which binary optimizations are enabled by @option{-O3} by using: @smallexample gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts diff /tmp/O2-opts /tmp/O3-opts | grep enabled @end smallexample @opindex version @item --version Display the version number and copyrights of the invoked GCC@. @opindex pass-exit-codes @item -pass-exit-codes Normally the @command{gcc} program exits with the code of 1 if any phase of the compiler returns a non-success return code. If you specify @option{-pass-exit-codes}, the @command{gcc} program instead returns with the numerically highest error produced by any phase returning an error indication. The C, C++, and Fortran front ends return 4 if an internal compiler error is encountered. @opindex pipe @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 GNU assembler has no trouble. @opindex specs @item -specs=@var{file} Process @var{file} after the compiler reads in the standard @file{specs} file, in order to override the defaults which the @command{gcc} driver program uses when determining what switches to pass to @command{cc1}, @command{cc1plus}, @command{as}, @command{ld}, etc. More than one @option{-specs=@var{file}} can be specified on the command line, and they are processed in order, from left to right. @xref{Spec Files}, for information about the format of the @var{file}. @opindex wrapper @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. @smallexample gcc -c t.c -wrapper gdb,--args @end smallexample @noindent This invokes all subprograms of @command{gcc} under @samp{gdb --args}, thus the invocation of @command{cc1} is @samp{gdb --args cc1 @dots{}}. @opindex ffile-prefix-map @item -ffile-prefix-map=@var{old}=@var{new} When compiling files residing in directory @file{@var{old}}, record any references to them in the result of the compilation as if the files resided in directory @file{@var{new}} instead. Specifying this option is equivalent to specifying all the individual @option{-f*-prefix-map} options. This can be used to make reproducible builds that are location independent. Directories referenced by directives are not affected by these options. See also @option{-fmacro-prefix-map}, @option{-fdebug-prefix-map}, @option{-fprofile-prefix-map} and @option{-fcanon-prefix-map}. @opindex fcanon-prefix-map @item -fcanon-prefix-map For the @option{-f*-prefix-map} options normally comparison of @file{@var{old}} prefix against the filename that would be normally referenced in the result of the compilation is done using textual comparison of the prefixes, or ignoring character case for case insensitive filesystems and considering slashes and backslashes as equal on DOS based filesystems. The @option{-fcanon-prefix-map} causes such comparisons to be done on canonicalized paths of @file{@var{old}} and the referenced filename. @opindex fplugin @item -fplugin=@var{name}.so Load the plugin code in file @var{name}.so, assumed to be a shared object to be dlopen'd by the compiler. The base name of the shared object file is used to identify the plugin for the purposes of argument parsing (See @option{-fplugin-arg-@var{name}-@var{key}=@var{value}} below). Each plugin should define the callback functions specified in the Plugins API. @opindex fplugin-arg @item -fplugin-arg-@var{name}-@var{key}=@var{value} Define an argument called @var{key} with a value of @var{value} for the plugin called @var{name}. @opindex fdump-ada-spec @item -fdump-ada-spec@r{[}-slim@r{]} For C and C++ source and include files, generate corresponding Ada specs. @xref{Generating Ada Bindings for C and C++ headers,,, gnat_ugn, GNAT User's Guide}, which provides detailed documentation on this feature. @opindex fada-spec-parent @item -fada-spec-parent=@var{unit} In conjunction with @option{-fdump-ada-spec@r{[}-slim@r{]}} above, generate Ada specs as child units of parent @var{unit}. @opindex fdump-go-spec @item -fdump-go-spec=@var{file} For input files in any language, generate corresponding Go declarations in @var{file}. This generates Go @code{const}, @code{type}, @code{var}, and @code{func} declarations which may be a useful way to start writing a Go interface to code written in some other language. @include @value{srcdir}/../libiberty/at-file.texi @end table @node Invoking G++ @section Compiling C++ Programs @cindex suffixes for C++ source @cindex C++ source file suffixes C++ source files conventionally use one of the suffixes @samp{.C}, @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or @samp{.cxx}; C++ header files often use @samp{.hh}, @samp{.hpp}, @samp{.H}, or (for shared template code) @samp{.tcc}; preprocessed C++ files use the suffix @samp{.ii}; and C++20 module interface units sometimes use @samp{.ixx}, @samp{.cppm}, @samp{.cxxm}, @samp{.c++m}, or @samp{.ccm}. GCC recognizes files with these names and compiles them as C++ programs even if you call the compiler the same way as for compiling C programs (usually with the name @command{gcc}). @findex g++ @findex c++ However, the use of @command{gcc} does not add the C++ library. @command{g++} is a program that calls GCC and automatically specifies linking against the C++ library. It treats @samp{.c}, @samp{.h} and @samp{.i} files as C++ source files instead of C source files unless @option{-x} is used. This program is also useful when precompiling a C header file with a @samp{.h} extension for use in C++ compilations. On many systems, @command{g++} is also installed with the name @command{c++}. @cindex invoking @command{g++} When you compile C++ programs, you may specify many of the same command-line options that you use for compiling programs in any language; or command-line options meaningful for C and related languages; or options that are meaningful only for C++ programs. @xref{C Dialect Options,,Options Controlling C Dialect}, for explanations of options for languages related to C@. @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for explanations of options that are meaningful only for C++ programs. @node C Dialect Options @section Options Controlling C Dialect @cindex dialect options @cindex language dialect options @cindex options, dialect The following options control the dialect of C (or languages derived from C, such as C++, Objective-C and Objective-C++) that the compiler accepts: @table @gcctabopt @cindex ANSI support @cindex ISO support @opindex ansi @item -ansi In C mode, this is equivalent to @option{-std=c90}. In C++ mode, it is equivalent to @option{-std=c++98}. @opindex std @item -std= Determine the language standard. @xref{Standards,,Language Standards Supported by GCC}, for details of these standard versions. This option is currently only supported when compiling C or C++. The compiler can accept several base standards, such as @samp{c90} or @samp{c++98}, and GNU dialects of those standards, such as @samp{gnu90} or @samp{gnu++98}. When a base standard is specified, the compiler accepts all programs following that standard plus those using GNU extensions that do not contradict it. For example, @option{-std=c90} turns off certain features of GCC that are incompatible with ISO C90, such as the @code{asm} and @code{typeof} keywords, but not other GNU extensions that do not have a meaning in ISO C90, such as omitting the middle term of a @code{?:} expression. On the other hand, when a GNU dialect of a standard is specified, all features supported by the compiler are enabled, even when those features change the meaning of the base standard. As a result, some strict-conforming programs may be rejected. The particular standard is used by @option{-Wpedantic} to identify which features are GNU extensions given that version of the standard. For example @option{-std=gnu90 -Wpedantic} warns about C++ style @samp{//} comments, while @option{-std=gnu99 -Wpedantic} does not. A value for this option must be provided; possible values are @table @samp @item c90 @itemx c89 @itemx iso9899:1990 Support all ISO C90 programs (certain GNU extensions that conflict with ISO C90 are disabled). Same as @option{-ansi} for C code. @item iso9899:199409 ISO C90 as modified in amendment 1. @item c99 @itemx c9x @itemx iso9899:1999 @itemx iso9899:199x ISO C99. This standard is substantially completely supported, modulo bugs and floating-point issues (mainly but not entirely relating to optional C99 features from Annexes F and G). See @w{@uref{https://gcc.gnu.org/projects/c-status.html}} for more information. The names @samp{c9x} and @samp{iso9899:199x} are deprecated. @item c11 @itemx c1x @itemx iso9899:2011 ISO C11, the 2011 revision of the ISO C standard. This standard is substantially completely supported, modulo bugs, floating-point issues (mainly but not entirely relating to optional C11 features from Annexes F and G) and the optional Annexes K (Bounds-checking interfaces) and L (Analyzability). The name @samp{c1x} is deprecated. @item c17 @itemx c18 @itemx iso9899:2017 @itemx iso9899:2018 ISO C17, the 2017 revision of the ISO C standard (published in 2018). This standard is same as C11 except for corrections of defects (all of which are also applied with @option{-std=c11}) and a new value of @code{__STDC_VERSION__}, and so is supported to the same extent as C11. @item c23 @itemx c2x @itemx iso9899:2024 ISO C23, the 2023 revision of the ISO C standard (published in 2024). The name @samp{c2x} is deprecated. @item c2y The next version of the ISO C standard, still under development. The support for this version is experimental and incomplete. @item gnu90 @itemx gnu89 GNU dialect of ISO C90 (including some C99 features). @item gnu99 @itemx gnu9x GNU dialect of ISO C99. The name @samp{gnu9x} is deprecated. @item gnu11 @itemx gnu1x GNU dialect of ISO C11. The name @samp{gnu1x} is deprecated. @item gnu17 @itemx gnu18 GNU dialect of ISO C17. @item gnu23 @itemx gnu2x GNU dialect of ISO C23. This is the default for C code. The name @samp{gnu2x} is deprecated. @item gnu2y The next version of the ISO C standard, still under development, plus GNU extensions. The support for this version is experimental and incomplete. The name @samp{gnu2x} is deprecated. @item c++98 @itemx c++03 The 1998 ISO C++ standard plus the 2003 technical corrigendum and some additional defect reports. Same as @option{-ansi} for C++ code. @item gnu++98 @itemx gnu++03 GNU dialect of @option{-std=c++98}. @item c++11 @itemx c++0x The 2011 ISO C++ standard plus amendments. The name @samp{c++0x} is deprecated. @item gnu++11 @itemx gnu++0x GNU dialect of @option{-std=c++11}. The name @samp{gnu++0x} is deprecated. @item c++14 @itemx c++1y The 2014 ISO C++ standard plus amendments. The name @samp{c++1y} is deprecated. @item gnu++14 @itemx gnu++1y GNU dialect of @option{-std=c++14}. The name @samp{gnu++1y} is deprecated. @item c++17 @itemx c++1z The 2017 ISO C++ standard plus amendments. The name @samp{c++1z} is deprecated. @item gnu++17 @itemx gnu++1z GNU dialect of @option{-std=c++17}. This is the default for C++ code. The name @samp{gnu++1z} is deprecated. @item c++20 @itemx c++2a The 2020 ISO C++ standard plus amendments. Support is experimental, and could change in incompatible ways in future releases. The name @samp{c++2a} is deprecated. @item gnu++20 @itemx gnu++2a GNU dialect of @option{-std=c++20}. Support is experimental, and could change in incompatible ways in future releases. The name @samp{gnu++2a} is deprecated. @item c++23 @itemx c++2b The 2023 ISO C++ standard plus amendments (published in 2024). Support is experimental, and could change in incompatible ways in future releases. The name @samp{c++2b} is deprecated. @item gnu++23 @itemx gnu++2b GNU dialect of @option{-std=c++23}. Support is experimental, and could change in incompatible ways in future releases. The name @samp{gnu++2b} is deprecated. @item c++2c @itemx c++26 The next revision of the ISO C++ standard, planned for 2026. Support is highly experimental, and will almost certainly change in incompatible ways in future releases. @item gnu++2c @itemx gnu++26 GNU dialect of @option{-std=c++2c}. Support is highly experimental, and will almost certainly change in incompatible ways in future releases. @end table @opindex aux-info @item -aux-info @var{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@. Besides declarations, the file indicates, in comments, the origin of each declaration (source file and line), whether the declaration was implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or @samp{O} for old, respectively, in the first character after the line number and the colon), and whether it came from a declaration or a definition (@samp{C} or @samp{F}, respectively, in the following character). In the case of function definitions, a K&R-style list of arguments followed by their declarations is also provided, inside comments, after the declaration. @opindex fno-asm @opindex fasm @item -fno-asm Do not recognize @code{asm}, @code{inline} or @code{typeof} as a keyword, so that code can use these words as identifiers. You can use the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__} instead. In C, @option{-ansi} implies @option{-fno-asm}. In C++, @code{inline} is a standard keyword and is not affected by this switch. You may want to use the @option{-fno-gnu-keywords} flag instead, which disables @code{typeof} but not @code{asm} and @code{inline}. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this switch only affects the @code{asm} and @code{typeof} keywords, since @code{inline} is a standard keyword in ISO C99. In C23 mode (@option{-std=c23} or @option{-std=gnu23}), this switch only affects the @code{asm} keyword, since @code{typeof} is a standard keyword in ISO C23. @opindex fno-builtin @opindex fbuiltin @cindex built-in functions @item -fno-builtin @itemx -fno-builtin-@var{function} Don't recognize built-in functions that do not begin with @samp{__builtin_} as prefix. @xref{Library Builtins}, for details of the functions affected, including those which are not built-in functions when @option{-ansi} or @option{-std} options for strict ISO C conformance are used because they do not have an ISO standard meaning. GCC normally generates special code to handle certain built-in functions more efficiently; for instance, calls to @code{alloca} may become single instructions which adjust the stack directly, and calls to @code{memcpy} may become inline copy loops. The resulting code is often both smaller and faster, but since the function calls no longer appear as such, you cannot set a breakpoint on those calls, nor can you change the behavior of the functions by linking with a different library. In addition, when a function is recognized as a built-in function, GCC may use information about that function to warn about problems with calls to that function, or to generate more efficient code, even if the resulting code still contains calls to that function. For example, warnings are given with @option{-Wformat} for bad calls to @code{printf} when @code{printf} is built in and @code{strlen} is known not to modify global memory. With the @option{-fno-builtin-@var{function}} option only the built-in function @var{function} is disabled. @var{function} must not begin with @samp{__builtin_}. If a function is named that is not built-in in this version of GCC, this option is ignored. There is no corresponding @option{-fbuiltin-@var{function}} option; if you wish to enable built-in functions selectively when using @option{-fno-builtin} or @option{-ffreestanding}, you may define macros such as: @smallexample #define abs(n) __builtin_abs ((n)) #define strcpy(d, s) __builtin_strcpy ((d), (s)) @end smallexample @opindex fcond-mismatch @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++. @opindex ffreestanding @cindex hosted environment @item -ffreestanding Assert that compilation targets a freestanding environment. This implies @option{-fno-builtin}. A freestanding environment is one in which the standard library may not exist, and program startup may not necessarily be at @code{main}. The most obvious example is an OS kernel. This is equivalent to @option{-fno-hosted}. @xref{Standards,,Language Standards Supported by GCC}, for details of freestanding and hosted environments. @opindex fgimple @item -fgimple Enable parsing of function definitions marked with @code{__GIMPLE}. This is an experimental feature that allows unit testing of GIMPLE passes. @opindex fgnu-tm @item -fgnu-tm When the option @option{-fgnu-tm} is specified, the compiler generates code for the Linux variant of Intel's current Transactional Memory ABI specification document (Revision 1.1, May 6 2009). This is an experimental feature whose interface may change in future versions of GCC, as the official specification changes. Please note that not all architectures are supported for this feature. For more information on GCC's support for transactional memory, @xref{Enabling libitm,,The GNU Transactional Memory Library,libitm,GNU Transactional Memory Library}. Note that the transactional memory feature is not supported with non-call exceptions (@option{-fnon-call-exceptions}). @opindex fgnu89-inline @item -fgnu89-inline The option @option{-fgnu89-inline} tells GCC to use the traditional GNU semantics for @code{inline} functions when in C99 mode. @xref{Inline,,An Inline Function is As Fast As a Macro}. Using this option is roughly equivalent to adding the @code{gnu_inline} function attribute to all inline functions (@pxref{Function Attributes}). The option @option{-fno-gnu89-inline} explicitly tells GCC to use the C99 semantics for @code{inline} when in C99 or gnu99 mode (i.e., it specifies the default behavior). This option is not supported in @option{-std=c90} or @option{-std=gnu90} mode. The preprocessor macros @code{__GNUC_GNU_INLINE__} and @code{__GNUC_STDC_INLINE__} may be used to check which semantics are in effect for @code{inline} functions. @xref{Common Predefined Macros,,,cpp,The C Preprocessor}. @opindex fhosted @cindex hosted environment @item -fhosted Assert that compilation targets a hosted environment. This implies @option{-fbuiltin}. A hosted environment is one in which the entire standard library is available, and in which @code{main} has a return type of @code{int}. Examples are nearly everything except a kernel. This is equivalent to @option{-fno-freestanding}. @opindex flax-vector-conversions @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. @opindex fms-extensions @item -fms-extensions Accept some non-standard constructs used in Microsoft header files. In C++ code, this allows member names in structures to be similar to previous types declarations. @smallexample typedef int UOW; struct ABC @{ UOW UOW; @}; @end smallexample Some cases of unnamed fields in structures and unions are only accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union fields within structs/unions}, for details. Note that this option is off for all targets except for x86 targets using ms-abi. @opindex fpermitted-flt-eval-methods @opindex fpermitted-flt-eval-methods=c11 @opindex fpermitted-flt-eval-methods=ts-18661-3 @item -fpermitted-flt-eval-methods=@var{style} ISO/IEC TS 18661-3 defines new permissible values for @code{FLT_EVAL_METHOD} that indicate that operations and constants with a semantic type that is an interchange or extended format should be evaluated to the precision and range of that type. These new values are a superset of those permitted under C99/C11, which does not specify the meaning of other positive values of @code{FLT_EVAL_METHOD}. As such, code conforming to C11 may not have been written expecting the possibility of the new values. @option{-fpermitted-flt-eval-methods} specifies whether the compiler should allow only the values of @code{FLT_EVAL_METHOD} specified in C99/C11, or the extended set of values specified in ISO/IEC TS 18661-3. @var{style} is either @code{c11} or @code{ts-18661-3} as appropriate. The default when in a standards compliant mode (@option{-std=c11} or similar) is @option{-fpermitted-flt-eval-methods=c11}. The default when in a GNU dialect (@option{-std=gnu11} or similar) is @option{-fpermitted-flt-eval-methods=ts-18661-3}. @opindex fdeps- The @samp{-fdeps-*} options are used to extract structured dependency information for a source. This involves determining what resources provided by other source files will be required to compile the source as well as what resources are provided by the source. This information can be used to add required dependencies between compilation rules of dependent sources based on their contents rather than requiring such information be reflected within the build tools as well. @opindex fdeps-file @item -fdeps-file=@var{file} Where to write structured dependency information. @opindex fdeps-format @item -fdeps-format=@var{format} The format to use for structured dependency information. @samp{p1689r5} is the only supported format right now. Note that when this argument is specified, the output of @samp{-MF} is stripped of some information (namely C++ modules) so that it does not use extended makefile syntax not understood by most tools. @opindex fdeps-target @item -fdeps-target=@var{file} Analogous to @option{-MT} but for structured dependency information. This indicates the target which will ultimately need any required resources and provide any resources extracted from the source that may be required by other sources. @opindex fplan9-extensions @item -fplan9-extensions Accept some non-standard constructs used in Plan 9 code. This enables @option{-fms-extensions}, permits passing pointers to structures with anonymous fields to functions that expect pointers to elements of the type of the field, and permits referring to anonymous fields declared using a typedef. @xref{Unnamed Fields,,Unnamed struct/union fields within structs/unions}, for details. This is only supported for C, not C++. @opindex fsigned-bitfields @opindex funsigned-bitfields @opindex fno-signed-bitfields @opindex fno-unsigned-bitfields @item -fsigned-bitfields @itemx -funsigned-bitfields @itemx -fno-signed-bitfields @itemx -fno-unsigned-bitfields These options control whether a bit-field is signed or unsigned, when the declaration does not use either @code{signed} or @code{unsigned}. By default, such a bit-field is signed, because this is consistent: the basic integer types such as @code{int} are signed types. @opindex fsigned-char @item -fsigned-char Let the type @code{char} be signed, like @code{signed char}. Note that this is equivalent to @option{-fno-unsigned-char}, which is the negative form of @option{-funsigned-char}. Likewise, the option @option{-fno-signed-char} is equivalent to @option{-funsigned-char}. @opindex funsigned-char @item -funsigned-char Let the type @code{char} be unsigned, like @code{unsigned char}. Each kind of machine has a default for what @code{char} should be. It is either like @code{unsigned char} by default or like @code{signed char} by default. Ideally, a portable program should always use @code{signed char} or @code{unsigned char} when it depends on the signedness of an object. But many programs have been written to use plain @code{char} and expect it to be signed, or expect it to be unsigned, depending on the machines they were written for. This option, and its inverse, let you make such a program work with the opposite default. The type @code{char} is always a distinct type from each of @code{signed char} or @code{unsigned char}, even though its behavior is always just like one of those two. @opindex fstrict-flex-arrays @opindex fno-strict-flex-arrays @opindex fstrict-flex-arrays=@var{level} @item -fstrict-flex-arrays @r{(C and C++ only)} @itemx -fstrict-flex-arrays=@var{level} @r{(C and C++ only)} Control when to treat the trailing array of a structure as a flexible array member for the purpose of accessing the elements of such an array. The value of @var{level} controls the level of strictness. @option{-fstrict-flex-arrays} is equivalent to @option{-fstrict-flex-arrays=3}, which is the strictest; a trailing array is treated as a flexible array member only when it is declared as a flexible array member per C99 standard onwards. The negative form @option{-fno-strict-flex-arrays} is equivalent to @option{-fstrict-flex-arrays=0}, which is the least strict. In this case all trailing arrays of structures are treated as flexible array members. There are two more levels in between 0 and 3, which are provided to support older code that uses the GCC zero-length array extension (@samp{[0]}) or one-element array as flexible array members (@samp{[1]}). When @var{level} is 1, the trailing array is treated as a flexible array member when it is declared as either @samp{[]}, @samp{[0]}, or @samp{[1]}. When @var{level} is 2, the trailing array is treated as a flexible array member when it is declared as either @samp{[]}, or @samp{[0]}. You can control this behavior for a specific trailing array field of a structure by using the variable attribute @code{strict_flex_array} attribute (@pxref{Variable Attributes}). The @option{-fstrict_flex_arrays} option interacts with the @option{-Wstrict-flex-arrays} option. @xref{Warning Options}, for more information. @opindex fsso-struct @item -fsso-struct=@var{endianness} Set the default scalar storage order of structures and unions to the specified endianness. The accepted values are @samp{big-endian}, @samp{little-endian} and @samp{native} for the native endianness of the target (the default). This option is not supported for C++. @strong{Warning:} the @option{-fsso-struct} switch causes GCC to generate code that is not binary compatible with code generated without it if the specified endianness is not the native endianness of the target. @end table @node C++ Dialect Options @section Options Controlling C++ Dialect @cindex compiler options, C++ @cindex C++ options, command-line @cindex options, C++ This section describes the command-line options that are only meaningful for C++ programs. You can also use most of the GNU compiler options regardless of what language your program is in. For example, you might compile a file @file{firstClass.C} like this: @smallexample g++ -g -fstrict-enums -O -c firstClass.C @end smallexample @noindent In this example, only @option{-fstrict-enums} is an option meant only for C++ programs; you can use the other options with any language supported by GCC@. Some options for compiling C programs, such as @option{-std}, are also relevant for C++ programs. @xref{C Dialect Options,,Options Controlling C Dialect}. Here is a list of options that are @emph{only} for compiling C++ programs: @table @gcctabopt @opindex fabi-version @item -fabi-version=@var{n} Use version @var{n} of the C++ ABI@. The default is version 0. Version 0 refers to the version conforming most closely to the C++ ABI specification. Therefore, the ABI obtained using version 0 will change in different versions of G++ as ABI bugs are fixed. Version 1 is the version of the C++ ABI that first appeared in G++ 3.2. Version 2 is the version of the C++ ABI that first appeared in G++ 3.4, and was the default through G++ 4.9. Version 3 corrects an error in mangling a constant address as a template argument. Version 4, which first appeared in G++ 4.5, implements a standard mangling for vector types. Version 5, which first appeared in G++ 4.6, corrects the mangling of attribute const/volatile on function pointer types, decltype of a plain decl, and use of a function parameter in the declaration of another parameter. Version 6, which first appeared in G++ 4.7, corrects the promotion behavior of C++11 scoped enums and the mangling of template argument packs, const/static_cast, prefix ++ and --, and a class scope function used as a template argument. Version 7, which first appeared in G++ 4.8, that treats nullptr_t as a builtin type and corrects the mangling of lambdas in default argument scope. Version 8, which first appeared in G++ 4.9, corrects the substitution behavior of function types with function-cv-qualifiers. Version 9, which first appeared in G++ 5.2, corrects the alignment of @code{nullptr_t}. Version 10, which first appeared in G++ 6.1, adds mangling of attributes that affect type identity, such as ia32 calling convention attributes (e.g.@: @samp{stdcall}). Version 11, which first appeared in G++ 7, corrects the mangling of sizeof... expressions and operator names. For multiple entities with the same name within a function, that are declared in different scopes, the mangling now changes starting with the twelfth occurrence. It also implies @option{-fnew-inheriting-ctors}. Version 12, which first appeared in G++ 8, corrects the calling conventions for empty classes on the x86_64 target and for classes with only deleted copy/move constructors. It accidentally changes the calling convention for classes with a deleted copy constructor and a trivial move constructor. Version 13, which first appeared in G++ 8.2, fixes the accidental change in version 12. Version 14, which first appeared in G++ 10, corrects the mangling of the nullptr expression. Version 15, which first appeared in G++ 10.3, corrects G++ 10 ABI tag regression. Version 16, which first appeared in G++ 11, changes the mangling of @code{__alignof__} to be distinct from that of @code{alignof}, and dependent operator names. Version 17, which first appeared in G++ 12, fixes layout of classes that inherit from aggregate classes with default member initializers in C++14 and up. Version 18, which first appeared in G++ 13, fixes manglings of lambdas that have additional context. Version 19, which first appeared in G++ 14, fixes manglings of structured bindings to include ABI tags, handling of cv-qualified [[no_unique_address]] members, and adds mangling of C++20 constraints on function templates. Version 20, which first appeared in G++ 15, fixes manglings of lambdas in static data member initializers. Version 21, which first appeared in G++ 16, fixes unnecessary captures in noexcept lambdas (c++/119764), layout of a base class with all explicitly defaulted constructors (c++/120012), and mangling of class and array objects with implicitly zero-initialized non-trailing subobjects (c++/121231). See also @option{-Wabi}. @opindex fabi-compat-version @item -fabi-compat-version=@var{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 ABI version to use for the alias. With @option{-fabi-version=0} (the default), this defaults to 13 (GCC 8.2 compatibility). If another ABI version is explicitly selected, this defaults to 0. For compatibility with GCC versions 3.2 through 4.9, use @option{-fabi-compat-version=2}. If this option is not provided but @option{-Wabi=@var{n}} is, that version is used for compatibility aliases. If this option is provided along with @option{-Wabi} (without the version), the version from this option is used for the warning. @opindex fno-access-control @opindex faccess-control @item -fno-access-control Turn off all access checking. This switch is mainly useful for working around bugs in the access control code. @opindex faligned-new @item -faligned-new Enable support for C++17 @code{new} of types that require more alignment than @code{void* ::operator new(std::size_t)} provides. A numeric argument such as @code{-faligned-new=32} can be used to specify how much alignment (in bytes) is provided by that function, but few users will need to override the default of @code{alignof(std::max_align_t)}. This flag is enabled by default for @option{-std=c++17}. @opindex fno-assume-sane-operators-new-delete @opindex fassume-sane-operators-new-delete @item -fno-assume-sane-operators-new The C++ standard allows replacing the global @code{new}, @code{new[]}, @code{delete} and @code{delete[]} operators, though a lot of C++ programs don't replace them and just use the implementation provided version. Furthermore, the C++ standard allows omitting those calls if they are made from new or delete expressions (and by extension the same is assumed if @code{__builtin_operator_new} or @code{__builtin_operator_delete} functions are used). This option allows control over some optimizations around calls to those operators. With @code{-fassume-sane-operators-new-delete} option GCC may assume that calls to the replaceable global operators from new or delete expressions or from @code{__builtin_operator_new} or @code{__builtin_operator_delete} calls don't read or modify any global variables or variables whose address could escape to the operators (global state; except for @code{errno} for the @code{new} and @code{new[]} operators). This allows most optimizations across those calls and is something that the implementation provided operators satisfy unless @code{malloc} implementation details are observable in the code or unless @code{malloc} hooks are used, but might not be satisfied if a program replaces those operators. This behavior is enabled by default. With @code{-fno-assume-sane-operators-new-delete} option GCC must assume all these calls (whether from new or delete expressions or called directly) may read and write global state unless proven otherwise (e.g.@: when GCC compiles their implementation). Use this option if those operators are or may be replaced and code needs to expect such behavior. @opindex fchar8_t @opindex fno-char8_t @item -fchar8_t @itemx -fno-char8_t Enable support for @code{char8_t} as adopted for C++20. This includes the addition of a new @code{char8_t} fundamental type, changes to the types of UTF-8 string and character literals, new signatures for user-defined literals, associated standard library updates, and new @code{__cpp_char8_t} and @code{__cpp_lib_char8_t} feature test macros. This option enables functions to be overloaded for ordinary and UTF-8 strings: @smallexample int f(const char *); // #1 int f(const char8_t *); // #2 int v1 = f("text"); // Calls #1 int v2 = f(u8"text"); // Calls #2 @end smallexample @noindent and introduces new signatures for user-defined literals: @smallexample int operator""_udl1(char8_t); int v3 = u8'x'_udl1; int operator""_udl2(const char8_t*, std::size_t); int v4 = u8"text"_udl2; template int operator""_udl3(); int v5 = u8"text"_udl3; @end smallexample @noindent The change to the types of UTF-8 string and character literals introduces incompatibilities with ISO C++11 and later standards. For example, the following code is well-formed under ISO C++11, but is ill-formed when @option{-fchar8_t} is specified. @smallexample const char *cp = u8"xx";// error: invalid conversion from // `const char8_t*' to `const char*' int f(const char*); auto v = f(u8"xx"); // error: invalid conversion from // `const char8_t*' to `const char*' std::string s@{u8"xx"@}; // error: no matching function for call to // `std::basic_string::basic_string()' using namespace std::literals; s = u8"xx"s; // error: conversion from // `basic_string' to non-scalar // type `basic_string' requested @end smallexample @opindex fcheck-new @item -fcheck-new Check that the pointer returned by @code{operator new} is non-null before attempting to modify the storage allocated. This check is normally unnecessary because the C++ standard specifies that @code{operator new} only returns @code{0} if it is declared @code{throw()}, in which case the compiler always checks the return value even without this option. In all other cases, when @code{operator new} has a non-empty exception specification, memory exhaustion is signalled by throwing @code{std::bad_alloc}. See also @samp{new (nothrow)}. @opindex fconcepts @item -fconcepts Enable support for the C++ Concepts feature for constraining template arguments. With @option{-std=c++20} and above, Concepts are part of the language standard, so @option{-fconcepts} defaults to on. Some constructs that were allowed by the earlier C++ Extensions for Concepts Technical Specification, ISO 19217 (2015), but didn't make it into the standard, could additionally be enabled by @option{-fconcepts-ts}. The option @option{-fconcepts-ts} was deprecated in GCC 14 and removed in GCC 15; users are expected to convert their code to C++20 concepts. @opindex fconstexpr-depth @item -fconstexpr-depth=@var{n} Set the maximum nested evaluation depth for C++11 constexpr functions to @var{n}. A limit is needed to detect endless recursion during constant expression evaluation. The minimum specified by the standard is 512. @opindex fconstexpr-cache-depth @item -fconstexpr-cache-depth=@var{n} Set the maximum level of nested evaluation depth for C++11 constexpr functions that will be cached to @var{n}. This is a heuristic that trades off compilation speed (when the cache avoids repeated calculations) against memory consumption (when the cache grows very large from highly recursive evaluations). The default is 8. Very few users are likely to want to adjust it, but if your code does heavy constexpr calculations you might want to experiment to find which value works best for you. @opindex fconstexpr-fp-except @item -fconstexpr-fp-except Annex F of the C standard specifies that IEC559 floating point exceptions encountered at compile time should not stop compilation. C++ compilers have historically not followed this guidance, instead treating floating point division by zero as non-constant even though it has a well defined value. This flag tells the compiler to give Annex F priority over other rules saying that a particular operation is undefined. @smallexample constexpr float inf = 1./0.; // OK with -fconstexpr-fp-except @end smallexample @opindex fconstexpr-loop-limit @item -fconstexpr-loop-limit=@var{n} Set the maximum number of iterations for a loop in C++14 constexpr functions to @var{n}. A limit is needed to detect infinite loops during constant expression evaluation. The default is 262144 (1<<18). @opindex fconstexpr-ops-limit @item -fconstexpr-ops-limit=@var{n} Set the maximum number of operations during a single constexpr evaluation. Even when number of iterations of a single loop is limited with the above limit, if there are several nested loops and each of them has many iterations but still smaller than the above limit, or if in a body of some loop or even outside of a loop too many expressions need to be evaluated, the resulting constexpr evaluation might take too long. The default is 33554432 (1<<25). @opindex fcontracts @item -fcontracts Enable experimental support for the C++ Contracts feature, as briefly added to and then removed from the C++20 working paper (N4820). The implementation also includes proposed enhancements from papers P1290, P1332, and P1429. This functionality is intended mostly for those interested in experimentation towards refining the feature to get it into shape for a future C++ standard. On violation of a checked contract, the violation handler is called. Users can replace the violation handler by defining @smallexample void handle_contract_violation (const std::experimental::contract_violation&); @end smallexample There are different sets of additional flags that can be used together to specify which contracts will be checked and how, for N4820 contracts, P1332 contracts, or P1429 contracts; these sets cannot be used together. @table @gcctabopt @opindex fcontract-mode @item -fcontract-mode=[on|off] Control whether any contracts have any semantics at all. Defaults to on. @opindex fcontract-assumption-mode @item -fcontract-assumption-mode=[on|off] [N4820] Control whether contracts with level @samp{axiom} should have the assume semantic. Defaults to on. @opindex fcontract-build-level @item -fcontract-build-level=[off|default|audit] [N4820] Specify which level of contracts to generate checks for. Defaults to @samp{default}. @opindex fcontract-continuation-mode @item -fcontract-continuation-mode=[on|off] [N4820] Control whether to allow the program to continue executing after a contract violation. That is, do checked contracts have the @samp{maybe} semantic described below rather than the @samp{never} semantic. Defaults to off. @opindex fcontract-role @item -fcontract-role=:,, [P1332] Specify the concrete semantics for each contract level of a particular contract role. @item -fcontract-semantic=[default|audit|axiom]: [P1429] Specify the concrete semantic for a particular contract level. @opindex fcontract-strict-declarations @item -fcontract-strict-declarations=[on|off] Control whether to reject adding contracts to a function after its first declaration. Defaults to off. @end table The possible concrete semantics for that can be specified with @samp{-fcontract-role} or @samp{-fcontract-semantic} are: @table @code @item ignore This contract has no effect. @item assume This contract is treated like C++23 @code{[[assume]]}. @item check_never_continue @itemx never @itemx abort This contract is checked. If it fails, the violation handler is called. If the handler returns, @code{std::terminate} is called. @item check_maybe_continue @itemx maybe This contract is checked. If it fails, the violation handler is called. If the handler returns, execution continues normally. @end table @opindex fcoroutines @item -fcoroutines Enable support for the C++ coroutines extension (experimental). @opindex fdiagnostics-all-candidates @item -fdiagnostics-all-candidates Permit the C++ front end to note all candidates during overload resolution failure, including when a deleted function is selected. @item -fdump-lang- @itemx -fdump-lang-@var{switch} @itemx -fdump-lang-@var{switch}-@var{options} @itemx -fdump-lang-@var{switch}-@var{options}=@var{filename} Control the dumping of C++-specific information. The @var{options} and @var{filename} portions behave as described in the @option{-fdump-tree} option. The following @var{switch} values are accepted: @table @samp @item all Enable all of the below. @opindex fdump-lang-class @item class Dump class hierarchy information. Virtual table information is emitted unless '@option{slim}' is specified. @opindex fdump-lang-module @item module Dump module information. Options @option{lineno} (locations), @option{graph} (reachability), @option{blocks} (clusters), @option{uid} (serialization), @option{alias} (mergeable), @option{asmname} (Elrond), @option{eh} (mapper) & @option{vops} (macros) may provide additional information. @opindex fdump-lang-raw @item raw Dump the raw internal tree data. @opindex fdump-lang-tinst @item tinst Dump the sequence of template instantiations, indented to show the depth of recursion. The @option{lineno} option adds the source location where the instantiation was triggered, and the @option{details} option also dumps pre-instantiation substitutions such as those performed during template argument deduction. Lines in the .tinst dump start with @samp{I} for an instantiation, @samp{S} for another substitution, and @samp{R[IS]} for the reopened context of a deferred instantiation. @end table @opindex fno-elide-constructors @opindex felide-constructors @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. This option also causes G++ to call trivial member functions which otherwise would be expanded inline. In C++17, the compiler is required to omit these temporaries, but this option still affects trivial member functions. @opindex fno-enforce-eh-specs @opindex fenforce-eh-specs @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 @code{NDEBUG}. This does not give user code permission to throw exceptions in violation of the exception specifications; the compiler still optimizes based on the specifications, so throwing an unexpected exception results in undefined behavior at run time. @opindex fextern-tls-init @opindex fno-extern-tls-init @item -fextern-tls-init @itemx -fno-extern-tls-init The C++11 and OpenMP standards allow @code{thread_local} and @code{threadprivate} variables to have dynamic (runtime) initialization. To support this, any use of such a variable goes through a wrapper function that performs any necessary initialization. When the use and definition of the variable are in the same translation unit, this overhead can be optimized away, but when the use is in a different translation unit there is significant overhead even if the variable doesn't actually need dynamic initialization. If the programmer can be sure that no use of the variable in a non-defining TU needs to trigger dynamic initialization (either because the variable is statically initialized, or a use of the variable in the defining TU will be executed before any uses in another TU), they can avoid this overhead with the @option{-fno-extern-tls-init} option. On targets that support symbol aliases, the default is @option{-fextern-tls-init}. On targets that do not support symbol aliases, the default is @option{-fno-extern-tls-init}. @opindex ffold-simple-inlines @opindex fno-fold-simple-inlines @item -ffold-simple-inlines @itemx -fno-fold-simple-inlines Permit the C++ frontend to fold calls to @code{std::move}, @code{std::forward}, @code{std::addressof}, @code{std::to_underlying} and @code{std::as_const}. In contrast to inlining, this means no debug information will be generated for such calls. Since these functions are rarely interesting to debug, this flag is enabled by default unless @option{-fno-inline} is active. @opindex fno-gnu-keywords @opindex fgnu-keywords @item -fno-gnu-keywords Do not recognize @code{typeof} as a keyword, so that code can use this word as an identifier. You can use the keyword @code{__typeof__} instead. This option is implied by the strict ISO C++ dialects: @option{-ansi}, @option{-std=c++98}, @option{-std=c++11}, etc. @opindex fno-immediate-escalation @opindex fimmediate-escalation @item -fno-immediate-escalation Do not enable immediate function escalation whereby certain functions can be promoted to consteval, as specified in P2564R3. For example: @example consteval int id(int i) @{ return i; @} constexpr int f(auto t) @{ return t + id(t); // id causes f to be promoted to consteval @} void g(int i) @{ f (3); @} @end example compiles in C++20: @code{f} is an immediate-escalating function (due to the @code{auto} it is a function template and is declared @code{constexpr}) and @code{id(t)} is an immediate-escalating expression, so @code{f} is promoted to @code{consteval}. Consequently, the call to @code{id(t)} is in an immediate context, so doesn't have to produce a constant (that is the mechanism allowing consteval function composition). However, with @option{-fno-immediate-escalation}, @code{f} is not promoted to @code{consteval}, and since the call to consteval function @code{id(t)} is not a constant expression, the compiler rejects the code. This option is turned on by default; it is only effective in C++20 mode or later. @opindex fimplicit-constexpr @item -fimplicit-constexpr Make inline functions implicitly constexpr, if they satisfy the requirements for a constexpr function. This option can be used in C++14 mode or later. This can result in initialization changing from dynamic to static and other optimizations. @opindex fno-implicit-templates @opindex fimplicit-templates @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. If you use this option, you must take care to structure your code to include all the necessary explicit instantiations to avoid getting undefined symbols at link time. @xref{Template Instantiation}, for more information. @opindex fno-implicit-inline-templates @opindex fimplicit-inline-templates @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. @opindex fno-implement-inlines @opindex fimplement-inlines @item -fno-implement-inlines To save space, do not emit out-of-line copies of inline functions controlled by @code{#pragma implementation}. This causes linker errors if these functions are not inlined everywhere they are called. @opindex fmodules @opindex fno-modules @item -fmodules @itemx -fno-modules Enable support for C++20 modules (@pxref{C++ Modules}). The @option{-fno-modules} is usually not needed, as that is the default. Even though this is a C++20 feature, it is not currently implicitly enabled by selecting that standard version. @opindex fmodule-header @item -fmodule-header @itemx -fmodule-header=user @itemx -fmodule-header=system Compile a header file to create an importable header unit. @opindex fmodule-implicit-inline @item -fmodule-implicit-inline Member functions defined in their class definitions are not implicitly inline for modular code. This is different to traditional C++ behavior, for good reasons. However, it may result in a difficulty during code porting. This option makes such function definitions implicitly inline. It does however generate an ABI incompatibility, so you must use it everywhere or nowhere. (Such definitions outside of a named module remain implicitly inline, regardless.) @opindex fno-module-lazy @opindex fmodule-lazy @item -fno-module-lazy Disable lazy module importing and module mapper creation. @vindex CXX_MODULE_MAPPER @r{environment variable} @opindex fmodule-mapper @item -fmodule-mapper=@r{[}@var{hostname}@r{]}:@var{port}@r{[}?@var{ident}@r{]} @itemx -fmodule-mapper=|@var{program}@r{[}?@var{ident}@r{]} @var{args...} @itemx -fmodule-mapper==@var{socket}@r{[}?@var{ident}@r{]} @itemx -fmodule-mapper=<>@r{[}@var{inout}@r{]}@r{[}?@var{ident}@r{]} @itemx -fmodule-mapper=<@var{in}>@var{out}@r{[}?@var{ident}@r{]} @itemx -fmodule-mapper=@var{file}@r{[}?@var{ident}@r{]} An oracle to query for module name to filename mappings. If unspecified the @env{CXX_MODULE_MAPPER} environment variable is used, and if that is unset, an in-process default is provided. @opindex fmodule-only @item -fmodule-only Only emit the Compiled Module Interface, inhibiting any object file. @opindex fms-extensions @item -fms-extensions Disable Wpedantic warnings about constructs used in MFC, such as implicit int and getting a pointer to member function via non-standard syntax. @opindex fnew-inheriting-ctors @item -fnew-inheriting-ctors Enable the P0136 adjustment to the semantics of C++11 constructor inheritance. This is part of C++17 but also considered to be a Defect Report against C++11 and C++14. This flag is enabled by default unless @option{-fabi-version=10} or lower is specified. @opindex fnew-ttp-matching @item -fnew-ttp-matching Enable the P0522 resolution to Core issue 150, template template parameters and default arguments: this allows a template with default template arguments as an argument for a template template parameter with fewer template parameters. This flag is enabled by default for @option{-std=c++17}. @opindex fno-nonansi-builtins @opindex fnonansi-builtins @item -fno-nonansi-builtins Disable built-in declarations of functions that are not mandated by ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit}, @code{index}, @code{bzero}, @code{conjf}, and other related functions. @opindex fnothrow-opt @item -fnothrow-opt Treat a @code{throw()} exception specification as if it were a @code{noexcept} specification to reduce or eliminate the text size overhead relative to a function with no exception specification. If the function has local variables of types with non-trivial destructors, the exception specification actually makes the function smaller because the EH cleanups for those variables can be optimized away. The semantic effect is that an exception thrown out of a function with such an exception specification results in a call to @code{terminate} rather than @code{unexpected}. @opindex fno-operator-names @opindex foperator-names @item -fno-operator-names Do not treat the operator name keywords @code{and}, @code{bitand}, @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as synonyms as keywords. @opindex fno-optional-diags @opindex foptional-diags @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. @opindex fno-pretty-templates @opindex fpretty-templates @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.@: @code{void f(T) [with T = int]} rather than @code{void f(int)}) so that it's clear which template is involved. When an error message refers to a specialization of a class template, the compiler omits any template arguments that match the default template arguments for that template. If either of these behaviors make it harder to understand the error message rather than easier, you can use @option{-fno-pretty-templates} to disable them. @opindex frange-for-ext-temps @item -frange-for-ext-temps Enable lifetime extension of C++ range based for temporaries. With @option{-std=c++23} and above this is part of the language standard, so lifetime of the temporaries is extended until the end of the loop by default. This option allows enabling that behavior also in earlier versions of the standard. @opindex fno-rtti @opindex frtti @item -fno-rtti Disable generation of information about every class with virtual functions for use by the C++ run-time type identification features (@code{dynamic_cast} and @code{typeid}). If you don't use those parts of the language, you can save some space by using this flag. Note that exception handling uses the same information, but G++ generates it as needed. The @code{dynamic_cast} operator can still be used for casts that do not require run-time type information, i.e.@: casts to @code{void *} or to unambiguous base classes. Mixing code compiled with @option{-frtti} with that compiled with @option{-fno-rtti} may not work. For example, programs may fail to link if a class compiled with @option{-fno-rtti} is used as a base for a class compiled with @option{-frtti}. @opindex fsized-deallocation @item -fsized-deallocation Enable the built-in global declarations @smallexample void operator delete (void *, std::size_t) noexcept; void operator delete[] (void *, std::size_t) noexcept; @end smallexample as introduced in C++14. This is useful for user-defined replacement deallocation functions that, for example, use the size of the object to make deallocation faster. Enabled by default under @option{-std=c++14} and above. The flag @option{-Wsized-deallocation} warns about places that might want to add a definition. @opindex fstrict-enums @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. This option has no effect for an enumeration type with a fixed underlying type. @opindex fstrong-eval-order @item -fstrong-eval-order @itemx -fstrong-eval-order=@var{kind} Evaluate member access, array subscripting, and shift expressions in left-to-right order, and evaluate assignment in right-to-left order, as adopted for C++17. @option{-fstrong-eval-order} is equivalent to @option{-fstrong-eval-order=all}, and is enabled by default with @option{-std=c++17} or later. @option{-fstrong-eval-order=some} enables just the ordering of member access and shift expressions, and is the default for C++ dialects prior to C++17. @option{-fstrong-eval-order=none} is equivalent to @option{-fno-strong-eval-order}. @opindex ftemplate-backtrace-limit @item -ftemplate-backtrace-limit=@var{n} Set the maximum number of template instantiation notes for a single warning or error to @var{n}. The default value is 10. @opindex ftemplate-depth @item -ftemplate-depth=@var{n} Set the maximum instantiation depth for template classes to @var{n}. A limit on the template instantiation depth is needed to detect endless recursions during template class instantiation. ANSI/ISO C++ conforming programs must not rely on a maximum depth greater than 17 (changed to 1024 in C++11). The default value is 900, as the compiler can run out of stack space before hitting 1024 in some situations. @opindex fno-threadsafe-statics @opindex fthreadsafe-statics @item -fno-threadsafe-statics Do not emit the extra code to use the routines specified in the C++ ABI for thread-safe initialization of local statics. You can use this option to reduce code size slightly in code that doesn't need to be thread-safe. @opindex fuse-cxa-atexit @item -fuse-cxa-atexit Register destructors for objects with static storage duration with the @code{__cxa_atexit} function rather than the @code{atexit} function. This option is required for fully standards-compliant handling of static destructors, but only works if your C library supports @code{__cxa_atexit}. @opindex fno-use-cxa-get-exception-ptr @opindex fuse-cxa-get-exception-ptr @item -fno-use-cxa-get-exception-ptr Don't use the @code{__cxa_get_exception_ptr} runtime routine. This causes @code{std::uncaught_exception} to be incorrect, but is necessary if the runtime routine is not available. @opindex fvisibility-inlines-hidden @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. The effect of this is that GCC may, effectively, mark inline methods with @code{__attribute__ ((visibility ("hidden")))} so that they do not appear in the export table of a DSO and do not require a PLT indirection when used within the DSO@. Enabling this option can have a dramatic effect on load and link times of a DSO as it massively reduces the size of the dynamic export table when the library makes heavy use of templates. The behavior of this switch is not quite the same as marking the methods as hidden directly, because it does not affect static variables local to the function or cause the compiler to deduce that the function is defined in only one shared object. You may mark a method as having a visibility explicitly to negate the effect of the switch for that method. For example, if you do want to compare pointers to a particular inline method, you might mark it as having default visibility. Marking the enclosing class with explicit visibility has no effect. Explicitly instantiated inline methods are unaffected by this option as their linkage might otherwise cross a shared library boundary. @xref{Template Instantiation}. @opindex fvisibility-ms-compat @item -fvisibility-ms-compat This flag attempts to use visibility settings to make GCC's C++ linkage model compatible with that of Microsoft Visual Studio. The flag makes these changes to GCC's linkage model: @enumerate @item It sets the default visibility to @code{hidden}, like @option{-fvisibility=hidden}. @item Types, but not their members, are not hidden by default. @item The One Definition Rule is relaxed for types without explicit visibility specifications that are defined in more than one shared object: those declarations are permitted if they are permitted when this option is not used. @end enumerate In new code it is better to use @option{-fvisibility=hidden} and export those classes that are intended to be externally visible. Unfortunately it is possible for code to rely, perhaps accidentally, on the Visual Studio behavior. Among the consequences of these changes are that static data members of the same type with the same name but defined in different shared objects are different, so changing one does not change the other; and that pointers to function members defined in different shared objects may not compare equal. When this flag is given, it is a violation of the ODR to define types with the same name differently. @opindex fno-weak @opindex fweak @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++. @opindex fext-numeric-literals @opindex fno-ext-numeric-literals @item -fext-numeric-literals @r{(C++ and Objective-C++ only)} Accept imaginary, fixed-point, or machine-defined literal number suffixes as GNU extensions. When this option is turned off these suffixes are treated as C++11 user-defined literal numeric suffixes. This is on by default for all pre-C++11 dialects and all GNU dialects: @option{-std=c++98}, @option{-std=gnu++98}, @option{-std=gnu++11}, @option{-std=gnu++14}. This option is off by default for ISO C++11 onwards (@option{-std=c++11}, ...). @opindex nostdinc++ @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.) @opindex flang-info-include-translate @opindex flang-info-include-translate-not @item -flang-info-include-translate @itemx -flang-info-include-translate-not @itemx -flang-info-include-translate=@var{header} Inform of include translation events. The first will note accepted include translations, the second will note declined include translations. The @var{header} form will inform of include translations relating to that specific header. If @var{header} is of the form @code{"user"} or @code{} it will be resolved to a specific user or system header using the include path. @opindex flang-info-module-cmi @item -flang-info-module-cmi @itemx -flang-info-module-cmi=@var{module} Inform of Compiled Module Interface pathnames. The first will note all read CMI pathnames. The @var{module} form will not reading a specific module's CMI. @var{module} may be a named module or a header-unit (the latter indicated by either being a pathname containing directory separators or enclosed in @code{<>} or @code{""}). @opindex stdlib @item -stdlib=@var{libstdc++,libc++} When G++ is configured to support this option, it allows specification of alternate C++ runtime libraries. Two options are available: @var{libstdc++} (the default, native C++ runtime for G++) and @var{libc++} which is the C++ runtime installed on some operating systems (e.g. Darwin versions from Darwin11 onwards). The option switches G++ to use the headers from the specified library and to emit @code{-lstdc++} or @code{-lc++} respectively, when a C++ runtime is required for linking. @end table In addition, these warning options have meanings only for C++ programs: @table @gcctabopt @opindex Wabi-tag @item -Wabi-tag @r{(C++ and Objective-C++ only)} Warn when a type with an ABI tag is used in a context that does not have that ABI tag. See @ref{C++ Attributes} for more information about ABI tags. @opindex Wabbreviated-auto-in-template-arg @opindex Wno-abbreviated-auto-in-template-arg @item -Wno-abbreviated-auto-in-template-arg Disable the error for an @code{auto} placeholder type used within a template argument list to declare a C++20 abbreviated function template, e.g. @smallexample void f(S); @end smallexample This feature was proposed in the Concepts TS, but was not adopted into C++20; in the standard, a placeholder in a parameter declaration must appear as a decl-specifier. The error can also be reduced to a warning by @option{-fpermissive} or @option{-Wno-error=abbreviated-auto-in-template-arg}. @opindex Wcomma-subscript @opindex Wno-comma-subscript @item -Wcomma-subscript @r{(C++ and Objective-C++ only)} Warn about uses of a comma expression within a subscripting expression. This usage was deprecated in C++20 and is going to be removed in C++23. However, a comma expression wrapped in @code{( )} is not deprecated. Example: @smallexample @group void f(int *a, int b, int c) @{ a[b,c]; // deprecated in C++20, invalid in C++23 a[(b,c)]; // OK @} @end group @end smallexample In C++23 it is valid to have comma separated expressions in a subscript when an overloaded subscript operator is found and supports the right number and types of arguments. G++ will accept the formerly valid syntax for code that is not valid in C++23 but used to be valid but deprecated in C++20 with a pedantic warning that can be disabled with @option{-Wno-comma-subscript}. Enabled by default with @option{-std=c++20} unless @option{-Wno-deprecated}, and after @option{-std=c++23} regardless of @option{-Wno-deprecated}. Before @option{-std=c++20}, enabled with explicit @option{-Wdeprecated}. This warning is upgraded to an error by @option{-pedantic-errors} in C++23 mode or later. @opindex Wctad-maybe-unsupported @opindex Wno-ctad-maybe-unsupported @item -Wctad-maybe-unsupported @r{(C++ and Objective-C++ only)} Warn when performing class template argument deduction (CTAD) on a type with no explicitly written deduction guides. This warning will point out cases where CTAD succeeded only because the compiler synthesized the implicit deduction guides, which might not be what the programmer intended. Certain style guides allow CTAD only on types that specifically "opt-in"; i.e., on types that are designed to support CTAD. This warning can be suppressed with the following pattern: @smallexample struct allow_ctad_t; // any name works template struct S @{ S(T) @{ @} @}; // Guide with incomplete parameter type will never be considered. S(allow_ctad_t) -> S; @end smallexample @opindex Wctor-dtor-privacy @opindex Wno-ctor-dtor-privacy @item -Wctor-dtor-privacy @r{(C++ and Objective-C++ 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. @opindex Wdangling-reference @opindex Wno-dangling-reference @item -Wdangling-reference @r{(C++ and Objective-C++ only)} Warn when a reference is bound to a temporary whose lifetime has ended. For example: @smallexample int n = 1; const int& r = std::max(n - 1, n + 1); // r is dangling @end smallexample In the example above, two temporaries are created, one for each argument, and a reference to one of the temporaries is returned. However, both temporaries are destroyed at the end of the full expression, so the reference @code{r} is dangling. This warning also detects dangling references in member initializer lists: @smallexample const int& f(const int& i) @{ return i; @} struct S @{ const int &r; // r is dangling S() : r(f(10)) @{ @} @}; @end smallexample Member functions are checked as well, but only their object argument: @smallexample struct S @{ const S& self () @{ return *this; @} @}; const S& s = S().self(); // s is dangling @end smallexample Certain functions are safe in this respect, for example @code{std::use_facet}: they take and return a reference, but they don't return one of its arguments, which can fool the warning. Such functions can be excluded from the warning by wrapping them in a @code{#pragma}: @smallexample #pragma GCC diagnostic push #pragma GCC diagnostic ignored "-Wdangling-reference" const T& foo (const T&) @{ @dots{} @} #pragma GCC diagnostic pop @end smallexample The @code{#pragma} can also surround the class; in that case, the warning will be disabled for all the member functions. @option{-Wdangling-reference} also warns about code like @smallexample auto p = std::minmax(1, 2); @end smallexample where @code{std::minmax} returns @code{std::pair}, and both references dangle after the end of the full expression that contains the call to @code{std::minmax}. The warning does not warn for @code{std::span}-like classes. We consider classes of the form: @smallexample template struct Span @{ T* data_; std::size len_; @}; @end smallexample as @code{std::span}-like; that is, the class is a non-union class that has a pointer data member and a trivial destructor. The warning can be disabled by using the @code{gnu::no_dangling} attribute (@pxref{C++ Attributes}). This warning is enabled by @option{-Wextra}. @opindex Wdelete-non-virtual-dtor @opindex Wno-delete-non-virtual-dtor @item -Wdelete-non-virtual-dtor @r{(C++ and Objective-C++ only)} Warn when @code{delete} is used to destroy an instance of a class that has virtual functions and non-virtual destructor. It is unsafe to delete an instance of a derived class through a pointer to a base class if the base class does not have a virtual destructor. This warning is enabled by @option{-Wall}. @opindex Wdeprecated-copy @opindex Wno-deprecated-copy @item -Wdeprecated-copy @r{(C++ and Objective-C++ only)} Warn that the implicit declaration of a copy constructor or copy assignment operator is deprecated if the class has a user-provided copy constructor or copy assignment operator, in C++11 and up. This warning is enabled by @option{-Wextra}. With @option{-Wdeprecated-copy-dtor}, also deprecate if the class has a user-provided destructor. @opindex Wdeprecated-enum-enum-conversion @opindex Wno-deprecated-enum-enum-conversion @item -Wno-deprecated-enum-enum-conversion @r{(C++ and Objective-C++ only)} Disable the warning about the case when the usual arithmetic conversions are applied on operands where one is of enumeration type and the other is of a different enumeration type. This conversion was deprecated in C++20. For example: @smallexample enum E1 @{ e @}; enum E2 @{ f @}; int k = f - e; @end smallexample @option{-Wdeprecated-enum-enum-conversion} is enabled by default with @option{-std=c++20}. In pre-C++20 dialects, this warning can be enabled by @option{-Wenum-conversion} or @option{-Wdeprecated}. @opindex Wdeprecated-enum-float-conversion @opindex Wno-deprecated-enum-float-conversion @item -Wno-deprecated-enum-float-conversion @r{(C++ and Objective-C++ only)} Disable the warning about the case when the usual arithmetic conversions are applied on operands where one is of enumeration type and the other is of a floating-point type. This conversion was deprecated in C++20. For example: @smallexample enum E1 @{ e @}; enum E2 @{ f @}; bool b = e <= 3.7; @end smallexample @option{-Wdeprecated-enum-float-conversion} is enabled by default with @option{-std=c++20}. In pre-C++20 dialects, this warning can be enabled by @option{-Wenum-conversion} or @option{-Wdeprecated}. @opindex Wdeprecated-literal-operator @opindex Wno-deprecated-literal-operator @item -Wdeprecated-literal-operator @r{(C++ and Objective-C++ only)} Warn that the declaration of a user-defined literal operator with a space before the suffix is deprecated. This warning is enabled by default in C++23, or with explicit @option{-Wdeprecated}. @smallexample string operator "" _i18n(const char*, std::size_t); // deprecated string operator ""_i18n(const char*, std::size_t); // preferred @end smallexample @opindex Wdeprecated-variadic-comma-omission @opindex Wno-deprecated-variadic-comma-omission @item -Wdeprecated-variadic-comma-omission @r{(C++ and Objective-C++ only)} Warn that omitting a comma before the varargs @code{...} at the end of a function parameter list is deprecated. This warning is enabled by default in C++26, or with explicit @option{-Wdeprecated}. @smallexample void f1(int...); // deprecated void f1(int, ...); // preferred template void f2(T...); // ok template void f3(T......); // deprecated @end smallexample @opindex Welaborated-enum-base @opindex Wno-elaborated-enum-base @item -Wno-elaborated-enum-base For C++11 and above, warn if an (invalid) additional enum-base is used in an elaborated-type-specifier. That is, if an enum with given underlying type and no enumerator list is used in a declaration other than just a standalone declaration of the enum. Enabled by default. This warning is upgraded to an error with -pedantic-errors. @opindex Winit-list-lifetime @opindex Wno-init-list-lifetime @item -Wno-init-list-lifetime @r{(C++ and Objective-C++ only)} Do not warn about uses of @code{std::initializer_list} that are likely to result in dangling pointers. Since the underlying array for an @code{initializer_list} is handled like a normal C++ temporary object, it is easy to inadvertently keep a pointer to the array past the end of the array's lifetime. For example: @itemize @bullet @item If a function returns a temporary @code{initializer_list}, or a local @code{initializer_list} variable, the array's lifetime ends at the end of the return statement, so the value returned has a dangling pointer. @item If a new-expression creates an @code{initializer_list}, the array only lives until the end of the enclosing full-expression, so the @code{initializer_list} in the heap has a dangling pointer. @item When an @code{initializer_list} variable is assigned from a brace-enclosed initializer list, the temporary array created for the right side of the assignment only lives until the end of the full-expression, so at the next statement the @code{initializer_list} variable has a dangling pointer. @smallexample // li's initial underlying array lives as long as li std::initializer_list li = @{ 1,2,3 @}; // assignment changes li to point to a temporary array li = @{ 4, 5 @}; // now the temporary is gone and li has a dangling pointer int i = li.begin()[0] // undefined behavior @end smallexample @item When a list constructor stores the @code{begin} pointer from the @code{initializer_list} argument, this doesn't extend the lifetime of the array, so if a class variable is constructed from a temporary @code{initializer_list}, the pointer is left dangling by the end of the variable declaration statement. @end itemize @opindex Winvalid-constexpr @opindex Wno-invalid-constexpr @item -Winvalid-constexpr Warn when a function never produces a constant expression. In C++20 and earlier, for every @code{constexpr} function and function template, there must be at least one set of function arguments in at least one instantiation such that an invocation of the function or constructor could be an evaluated subexpression of a core constant expression. C++23 removed this restriction, so it's possible to have a function or a function template marked @code{constexpr} for which no invocation satisfies the requirements of a core constant expression. This warning is enabled as a pedantic warning by default in C++20 and earlier. In C++23, @option{-Winvalid-constexpr} can be turned on, in which case it will be an ordinary warning. For example: @smallexample void f (int& i); constexpr void g (int& i) @{ // Warns by default in C++20, in C++23 only with -Winvalid-constexpr. f(i); @} @end smallexample @opindex Winvalid-imported-macros @opindex Wno-invalid-imported-macros @item -Winvalid-imported-macros Verify all imported macro definitions are valid at the end of compilation. This is not enabled by default, as it requires additional processing to determine. It may be useful when preparing sets of header-units to ensure consistent macros. @opindex Wliteral-suffix @opindex Wno-literal-suffix @item -Wno-literal-suffix @r{(C++ and Objective-C++ only)} Do not warn when a string or character literal is followed by a ud-suffix which does not begin with an underscore. As a conforming extension, GCC treats such suffixes as separate preprocessing tokens in order to maintain backwards compatibility with code that uses formatting macros from @code{}. For example: @smallexample #define __STDC_FORMAT_MACROS #include #include int main() @{ int64_t i64 = 123; printf("My int64: %" PRId64"\n", i64); @} @end smallexample In this case, @code{PRId64} is treated as a separate preprocessing token. This option also controls warnings when a user-defined literal operator is declared with a literal suffix identifier that doesn't begin with an underscore. Literal suffix identifiers that don't begin with an underscore are reserved for future standardization. These warnings are enabled by default. @opindex Wnarrowing @opindex Wno-narrowing @item -Wno-narrowing @r{(C++ and Objective-C++ only)} For C++11 and later standards, narrowing conversions are diagnosed by default, as required by the standard. A narrowing conversion from a constant produces an error, and a narrowing conversion from a non-constant produces a warning, but @option{-Wno-narrowing} suppresses the diagnostic. Note that this does not affect the meaning of well-formed code; narrowing conversions are still considered ill-formed in SFINAE contexts. With @option{-Wnarrowing} in C++98, warn when a narrowing conversion prohibited by C++11 occurs within @samp{@{ @}}, e.g. @smallexample int i = @{ 2.2 @}; // error: narrowing from double to int @end smallexample This flag is included in @option{-Wall} and @option{-Wc++11-compat}. @opindex Wnoexcept @opindex Wno-noexcept @item -Wnoexcept @r{(C++ and Objective-C++ 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. @code{throw()} or @code{noexcept}) but is known by the compiler to never throw an exception. @opindex Wnoexcept-type @opindex Wno-noexcept-type @item -Wnoexcept-type @r{(C++ and Objective-C++ only)} Warn if the C++17 feature making @code{noexcept} part of a function type changes the mangled name of a symbol relative to C++14. Enabled by @option{-Wabi} and @option{-Wc++17-compat}. As an example: @smallexample template void f(T t) @{ t(); @}; void g() noexcept; void h() @{ f(g); @} @end smallexample @noindent In C++14, @code{f} calls @code{f}, but in C++17 it calls @code{f}. @opindex Wclass-memaccess @opindex Wno-class-memaccess @item -Wclass-memaccess @r{(C++ and Objective-C++ only)} Warn when the destination of a call to a raw memory function such as @code{memset} or @code{memcpy} is an object of class type, and when writing into such an object might bypass the class non-trivial or deleted constructor or copy assignment, violate const-correctness or encapsulation, or corrupt virtual table pointers. Modifying the representation of such objects may violate invariants maintained by member functions of the class. For example, the call to @code{memset} below is undefined because it modifies a non-trivial class object and is, therefore, diagnosed. The safe way to either initialize or clear the storage of objects of such types is by using the appropriate constructor or assignment operator, if one is available. @smallexample std::string str = "abc"; memset (&str, 0, sizeof str); @end smallexample The @option{-Wclass-memaccess} option is enabled by @option{-Wall}. Explicitly casting the pointer to the class object to @code{void *} or to a type that can be safely accessed by the raw memory function suppresses the warning. @opindex Wnon-virtual-dtor @opindex Wno-non-virtual-dtor @item -Wnon-virtual-dtor @r{(C++ and Objective-C++ 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 @option{-Weffc++} is specified. The @option{-Wdelete-non-virtual-dtor} option (enabled by @option{-Wall}) should be preferred because it warns about the unsafe cases without false positives. @opindex Wregister @opindex Wno-register @item -Wregister @r{(C++ and Objective-C++ only)} Warn on uses of the @code{register} storage class specifier, except when it is part of the GNU @ref{Explicit Register Variables} extension. The use of the @code{register} keyword as storage class specifier has been deprecated in C++11 and removed in C++17. Enabled by default with @option{-std=c++17}. @opindex Wreorder @opindex Wno-reorder @cindex reordering, warning @cindex warning for reordering of member initializers @item -Wreorder @r{(C++ and Objective-C++ 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: @smallexample struct A @{ int i; int j; A(): j (0), i (1) @{ @} @}; @end smallexample @noindent The compiler rearranges the member initializers for @code{i} and @code{j} to match the declaration order of the members, emitting a warning to that effect. This warning is enabled by @option{-Wall}. @opindex Wpessimizing-move @opindex Wno-pessimizing-move @item -Wno-pessimizing-move @r{(C++ and Objective-C++ only)} This warning warns when a call to @code{std::move} prevents copy elision. A typical scenario when copy elision can occur is when returning in a function with a class return type, when the expression being returned is the name of a non-volatile automatic object, and is not a function parameter, and has the same type as the function return type. @smallexample struct T @{ @dots{} @}; T fn() @{ T t; @dots{} return std::move (t); @} @end smallexample But in this example, the @code{std::move} call prevents copy elision. This warning is enabled by @option{-Wall}. @opindex Wredundant-move @opindex Wno-redundant-move @item -Wno-redundant-move @r{(C++ and Objective-C++ only)} This warning warns about redundant calls to @code{std::move}; that is, when a move operation would have been performed even without the @code{std::move} call. This happens because the compiler is forced to treat the object as if it were an rvalue in certain situations such as returning a local variable, where copy elision isn't applicable. Consider: @smallexample struct T @{ @dots{} @}; T fn(T t) @{ @dots{} return std::move (t); @} @end smallexample Here, the @code{std::move} call is redundant. Because G++ implements Core Issue 1579, another example is: @smallexample struct T @{ // convertible to U @dots{} @}; struct U @{ @dots{} @}; U fn() @{ T t; @dots{} return std::move (t); @} @end smallexample In this example, copy elision isn't applicable because the type of the expression being returned and the function return type differ, yet G++ treats the return value as if it were designated by an rvalue. This warning is enabled by @option{-Wextra}. @opindex Wrange-loop-construct @opindex Wno-range-loop-construct @item -Wrange-loop-construct @r{(C++ and Objective-C++ only)} This warning warns when a C++ range-based for-loop is creating an unnecessary copy. This can happen when the range declaration is not a reference, but probably should be. For example: @smallexample struct S @{ char arr[128]; @}; void fn () @{ S arr[5]; for (const auto x : arr) @{ @dots{} @} @} @end smallexample It does not warn when the type being copied is a trivially-copyable type whose size is less than 64 bytes. This warning also warns when a loop variable in a range-based for-loop is initialized with a value of a different type resulting in a copy. For example: @smallexample void fn() @{ int arr[10]; for (const double &x : arr) @{ @dots{} @} @} @end smallexample In the example above, in every iteration of the loop a temporary value of type @code{double} is created and destroyed, to which the reference @code{const double &} is bound. This warning is enabled by @option{-Wall}. @opindex Wredundant-tags @opindex Wno-redundant-tags @item -Wredundant-tags @r{(C++ and Objective-C++ only)} Warn about redundant class-key and enum-key in references to class types and enumerated types in contexts where the key can be eliminated without causing an ambiguity. For example: @smallexample struct foo; struct foo *p; // warn that keyword struct can be eliminated @end smallexample @noindent On the other hand, in this example there is no warning: @smallexample struct foo; void foo (); // "hides" struct foo void bar (struct foo&); // no warning, keyword struct is necessary @end smallexample @opindex Wsubobject-linkage @opindex Wno-subobject-linkage @item -Wno-subobject-linkage @r{(C++ and Objective-C++ only)} Do not warn if a class type has a base or a field whose type uses the anonymous namespace or depends on a type with no linkage. If a type A depends on a type B with no or internal linkage, defining it in multiple translation units would be an ODR violation because the meaning of B is different in each translation unit. If A only appears in a single translation unit, the best way to silence the warning is to give it internal linkage by putting it in an anonymous namespace as well. The compiler doesn't give this warning for types defined in the main .C file, as those are unlikely to have multiple definitions. @option{-Wsubobject-linkage} is enabled by default. @opindex Weffc++ @opindex Wno-effc++ @item -Weffc++ @r{(C++ and Objective-C++ only)} Warn about violations of the following style guidelines from Scott Meyers' @cite{Effective C++} series of books: @itemize @bullet @item Define a copy constructor and an assignment operator for classes with dynamically-allocated memory. @item Prefer initialization to assignment in constructors. @item Have @code{operator=} return a reference to @code{*this}. @item Don't try to return a reference when you must return an object. @item Distinguish between prefix and postfix forms of increment and decrement operators. @item Never overload @code{&&}, @code{||}, or @code{,}. @end itemize This option also enables @option{-Wnon-virtual-dtor}, which is also one of the effective C++ recommendations. However, the check is extended to warn about the lack of virtual destructor in accessible non-polymorphic bases classes too. When selecting this option, be aware that the standard library headers do not obey all of these guidelines; use @samp{grep -v} to filter out those warnings. @opindex Wexceptions @opindex Wno-exceptions @item -Wno-exceptions @r{(C++ and Objective-C++ only)} Disable the warning about the case when an exception handler is shadowed by another handler, which can point out a wrong ordering of exception handlers. @opindex Wsfinae-incomplete @opindex Wno-sfinae-incomplete Warn about a class that is found to be incomplete, or a function with auto return type that has not yet been deduced, in a context where that causes substitution failure rather than an error, and then the class or function is defined later in the translation unit. This is problematic because template instantiations or concept checks could have different results if they first occur either before or after the definition. This warning is enabled by default. @option{-Wsfinae-incomplete=2} adds a warning at the point of substitution failure, to make it easier to track down problems flagged by the default mode. @opindex Wstrict-null-sentinel @opindex Wno-strict-null-sentinel @item -Wstrict-null-sentinel @r{(C++ and Objective-C++ only)} Warn about the use of an uncasted @code{NULL} as sentinel. When compiling only with GCC this is a valid sentinel, as @code{NULL} is defined to @code{__null}. Although it is a null pointer constant rather than a null pointer, it is guaranteed to be of the same size as a pointer. But this use is not portable across different compilers. @opindex Wno-non-c-typedef-for-linkage @opindex Wnon-c-typedef-for-linkage @item -Wno-non-c-typedef-for-linkage @r{(C++ and Objective-C++ only)} Disable pedwarn for unnamed classes with a typedef name for linkage purposes containing C++ specific members, base classes, default member initializers or lambda expressions, including those on nested member classes. @smallexample typedef struct @{ int a; // non-static data members are ok struct T @{ int b; @}; // member classes too enum E @{ E1, E2, E3 @}; // member enumerations as well int c = 42; // default member initializers are not ok struct U : A @{ int c; @}; // classes with base classes are not ok typedef int V; // typedef is not ok using W = int; // using declaration is not ok decltype([]()@{@}) x; // lambda expressions not ok @} S; @end smallexample In all these cases, the tag name S should be added after the struct keyword. @opindex Wno-non-template-friend @opindex Wnon-template-friend @item -Wno-non-template-friend @r{(C++ and Objective-C++ only)} Disable warnings when non-template friend functions are declared within a template. In very old versions of GCC that predate implementation of the ISO standard, declarations such as @samp{friend int foo(int)}, where the name of the friend is an unqualified-id, could be interpreted as a particular specialization of a template function; the warning exists to diagnose compatibility problems, and is enabled by default. @opindex Wold-style-cast @opindex Wno-old-style-cast @item -Wold-style-cast @r{(C++ and Objective-C++ only)} Warn if an old-style (C-style) cast to a non-void type is used within a C++ program. The new-style casts (@code{dynamic_cast}, @code{static_cast}, @code{reinterpret_cast}, and @code{const_cast}) are less vulnerable to unintended effects and much easier to search for. @opindex Woverloaded-virtual @opindex Wno-overloaded-virtual @cindex overloaded virtual function, warning @cindex warning for overloaded virtual function @item -Woverloaded-virtual @r{(C++ and Objective-C++ only)} @itemx -Woverloaded-virtual=@var{n} Warn when a function declaration hides virtual functions from a base class. For example, in: @smallexample struct A @{ virtual void f(); @}; struct B: public A @{ void f(int); // does not override @}; @end smallexample the @code{A} class version of @code{f} is hidden in @code{B}, and code like: @smallexample B* b; b->f(); @end smallexample @noindent fails to compile. In cases where the different signatures are not an accident, the simplest solution is to add a using-declaration to the derived class to un-hide the base function, e.g. add @code{using A::f;} to @code{B}. The optional level suffix controls the behavior when all the declarations in the derived class override virtual functions in the base class, even if not all of the base functions are overridden: @smallexample struct C @{ virtual void f(); virtual void f(int); @}; struct D: public C @{ void f(int); // does override @} @end smallexample This pattern is less likely to be a mistake; if D is only used virtually, the user might have decided that the base class semantics for some of the overloads are fine. At level 1, this case does not warn; at level 2, it does. @option{-Woverloaded-virtual} by itself selects level 2. Level 1 is included in @option{-Wall}. @opindex Wno-pmf-conversions @opindex Wpmf-conversions @item -Wno-pmf-conversions @r{(C++ and Objective-C++ only)} Disable the diagnostic for converting a bound pointer to member function to a plain pointer. @opindex Wsign-promo @opindex Wno-sign-promo @item -Wsign-promo @r{(C++ and Objective-C++ 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. @opindex Wtemplates @opindex Wno-templates @item -Wtemplates @r{(C++ and Objective-C++ only)} Warn when a primary template declaration is encountered. Some coding rules disallow templates, and this may be used to enforce that rule. The warning is inactive inside a system header file, such as the STL, so one can still use the STL. One may also instantiate or specialize templates. @opindex Wmismatched-new-delete @opindex Wno-mismatched-new-delete @item -Wmismatched-new-delete @r{(C++ and Objective-C++ only)} Warn for mismatches between calls to @code{operator new} or @code{operator delete} and the corresponding call to the allocation or deallocation function. This includes invocations of C++ @code{operator delete} with pointers returned from either mismatched forms of @code{operator new}, or from other functions that allocate objects for which the @code{operator delete} isn't a suitable deallocator, as well as calls to other deallocation functions with pointers returned from @code{operator new} for which the deallocation function isn't suitable. For example, the @code{delete} expression in the function below is diagnosed because it doesn't match the array form of the @code{new} expression the pointer argument was returned from. Similarly, the call to @code{free} is also diagnosed. @smallexample void f () @{ int *a = new int[n]; delete a; // warning: mismatch in array forms of expressions char *p = new char[n]; free (p); // warning: mismatch between new and free @} @end smallexample The related option @option{-Wmismatched-dealloc} diagnoses mismatches involving allocation and deallocation functions other than @code{operator new} and @code{operator delete}. @option{-Wmismatched-new-delete} is included in @option{-Wall}. @opindex Wmismatched-tags @opindex Wno-mismatched-tags @item -Wmismatched-tags @r{(C++ and Objective-C++ only)} Warn for declarations of structs, classes, and class templates and their specializations with a class-key that does not match either the definition or the first declaration if no definition is provided. For example, the declaration of @code{struct Object} in the argument list of @code{draw} triggers the warning. To avoid it, either remove the redundant class-key @code{struct} or replace it with @code{class} to match its definition. @smallexample class Object @{ public: virtual ~Object () = 0; @}; void draw (struct Object*); @end smallexample It is not wrong to declare a class with the class-key @code{struct} as the example above shows. The @option{-Wmismatched-tags} option is intended to help achieve a consistent style of class declarations. In code that is intended to be portable to Windows-based compilers the warning helps prevent unresolved references due to the difference in the mangling of symbols declared with different class-keys. The option can be used either on its own or in conjunction with @option{-Wredundant-tags}. @opindex Wmultiple-inheritance @opindex Wno-multiple-inheritance @item -Wmultiple-inheritance @r{(C++ and Objective-C++ only)} Warn when a class is defined with multiple direct base classes. Some coding rules disallow multiple inheritance, and this may be used to enforce that rule. The warning is inactive inside a system header file, such as the STL, so one can still use the STL. One may also define classes that indirectly use multiple inheritance. @opindex Wvirtual-inheritance @opindex Wno-virtual-inheritance @item -Wvirtual-inheritance Warn when a class is defined with a virtual direct base class. Some coding rules disallow multiple inheritance, and this may be used to enforce that rule. The warning is inactive inside a system header file, such as the STL, so one can still use the STL. One may also define classes that indirectly use virtual inheritance. @opindex Wvirtual-move-assign @opindex Wno-virtual-move-assign @item -Wno-virtual-move-assign Suppress warnings about inheriting from a virtual base with a non-trivial C++11 move assignment operator. This is dangerous because if the virtual base is reachable along more than one path, it is moved multiple times, which can mean both objects end up in the moved-from state. If the move assignment operator is written to avoid moving from a moved-from object, this warning can be disabled. @opindex Wnamespaces @opindex Wno-namespaces @item -Wnamespaces Warn when a namespace definition is opened. Some coding rules disallow namespaces, and this may be used to enforce that rule. The warning is inactive inside a system header file, such as the STL, so one can still use the STL. One may also use using directives and qualified names. @opindex Wtemplate-body @opindex Wno-template-body @item -Wno-template-body @r{(C++ and Objective-C++ only)} Disable diagnosing errors when parsing a template, and instead issue an error only upon instantiation of the template. This flag can also be used to downgrade such errors into warnings with @option{Wno-error=} or @option{-fpermissive}. @opindex Wtemplate-id-cdtor @opindex Wno-template-id-cdtor @item -Wno-template-id-cdtor @r{(C++ and Objective-C++ only)} Disable the warning about the use of simple-template-id as the declarator-id of a constructor or destructor, which became invalid in C++20 via DR 2237. For example: @smallexample template struct S @{ S(); // should be S(); ~S(); // should be ~S(); @}; @end smallexample @option{-Wtemplate-id-cdtor} is enabled by default with @option{-std=c++20}; it is also enabled by @option{-Wc++20-compat}. @opindex Wtemplate-names-tu-local @opindex Wno-template-names-tu-local @item -Wtemplate-names-tu-local Warn when a template body hides an exposure of a translation-unit-local entity. In most cases, referring to a translation-unit-local entity (such as an internal linkage declaration) within an entity that is emitted into a module's CMI is an error. However, within the initializer of a variable, or in the body of a non-inline function, this is not an exposure and no error is emitted. This can cause variable or function templates to accidentally become unusable if they reference such an entity, because other translation units that import the template will never be able to instantiate it. This warning attempts to detect cases where this might occur. The presence of an explicit instantiation silences the warning. This flag is enabled by @option{-Wextra}. @opindex Wterminate @opindex Wno-terminate @item -Wno-terminate @r{(C++ and Objective-C++ only)} Disable the warning about a throw-expression that will immediately result in a call to @code{terminate}. @opindex Wvexing-parse @opindex Wno-vexing-parse @item -Wno-vexing-parse @r{(C++ and Objective-C++ only)} Warn about the most vexing parse syntactic ambiguity. This warns about the cases when a declaration looks like a variable definition, but the C++ language requires it to be interpreted as a function declaration. For instance: @smallexample void f(double a) @{ int i(); // extern int i (void); int n(int(a)); // extern int n (int); @} @end smallexample Another example: @smallexample struct S @{ S(int); @}; void f(double a) @{ S x(int(a)); // extern struct S x (int); S y(int()); // extern struct S y (int (*) (void)); S z(); // extern struct S z (void); @} @end smallexample The warning will suggest options how to deal with such an ambiguity; e.g., it can suggest removing the parentheses or using braces instead. This warning is enabled by default. @opindex Wno-class-conversion @opindex Wclass-conversion @item -Wno-class-conversion @r{(C++ and Objective-C++ only)} Do not warn when a conversion function converts an object to the same type, to a base class of that type, or to void; such a conversion function will never be called. @opindex Wvolatile @opindex Wno-volatile @item -Wvolatile @r{(C++ and Objective-C++ only)} Warn about deprecated uses of the @code{volatile} qualifier. This includes postfix and prefix @code{++} and @code{--} expressions of @code{volatile}-qualified types, using simple assignments where the left operand is a @code{volatile}-qualified non-class type for their value, compound assignments where the left operand is a @code{volatile}-qualified non-class type, @code{volatile}-qualified function return type, @code{volatile}-qualified parameter type, and structured bindings of a @code{volatile}-qualified type. This usage was deprecated in C++20. Enabled by default with @option{-std=c++20}. Before @option{-std=c++20}, enabled with explicit @option{-Wdeprecated}. @opindex Waligned-new @opindex Wno-aligned-new @item -Waligned-new Warn about a new-expression of a type that requires greater alignment than the @code{alignof(std::max_align_t)} but uses an allocation function without an explicit alignment parameter. This option is enabled by @option{-Wall}. Normally this only warns about global allocation functions, but @option{-Waligned-new=all} also warns about class member allocation functions. @opindex Wplacement-new @opindex Wno-placement-new @item -Wno-placement-new @itemx -Wplacement-new=@var{n} Warn about placement new expressions with undefined behavior, such as constructing an object in a buffer that is smaller than the type of the object. For example, the placement new expression below is diagnosed because it attempts to construct an array of 64 integers in a buffer only 64 bytes large. @smallexample char buf [64]; new (buf) int[64]; @end smallexample This warning is enabled by default. @table @gcctabopt @item -Wplacement-new=1 This is the default warning level of @option{-Wplacement-new}. At this level the warning is not issued for some strictly undefined constructs that GCC allows as extensions for compatibility with legacy code. For example, the following @code{new} expression is not diagnosed at this level even though it has undefined behavior according to the C++ standard because it writes past the end of the one-element array. @smallexample struct S @{ int n, a[1]; @}; S *s = (S *)malloc (sizeof *s + 31 * sizeof s->a[0]); new (s->a)int [32](); @end smallexample @item -Wplacement-new=2 At this level, in addition to diagnosing all the same constructs as at level 1, a diagnostic is also issued for placement new expressions that construct an object in the last member of structure whose type is an array of a single element and whose size is less than the size of the object being constructed. While the previous example would be diagnosed, the following construct makes use of the flexible member array extension to avoid the warning at level 2. @smallexample struct S @{ int n, a[]; @}; S *s = (S *)malloc (sizeof *s + 32 * sizeof s->a[0]); new (s->a)int [32](); @end smallexample @end table @opindex Wcatch-value @opindex Wno-catch-value @item -Wcatch-value @itemx -Wcatch-value=@var{n} @r{(C++ and Objective-C++ only)} Warn about catch handlers that do not catch via reference. With @option{-Wcatch-value=1} (or @option{-Wcatch-value} for short) warn about polymorphic class types that are caught by value. With @option{-Wcatch-value=2} warn about all class types that are caught by value. With @option{-Wcatch-value=3} warn about all types that are not caught by reference. @option{-Wcatch-value} is enabled by @option{-Wall}. @opindex Wconditionally-supported @opindex Wno-conditionally-supported @item -Wconditionally-supported @r{(C++ and Objective-C++ only)} Warn for conditionally-supported (C++11 [intro.defs]) constructs. @opindex Wdefaulted-function-deleted @opindex Wno-defaulted-function-deleted @item -Wno-defaulted-function-deleted @r{(C++ and Objective-C++ only)} Warn when an explicitly defaulted function is deleted by the compiler. That can occur when the function's declared type does not match the type of the function that would have been implicitly declared. This warning is enabled by default. @opindex Wdelete-incomplete @opindex Wno-delete-incomplete @item -Wno-delete-incomplete @r{(C++ and Objective-C++ only)} Do not warn when deleting a pointer to incomplete type, which may cause undefined behavior at runtime. This warning is enabled by default. @opindex Wextra-semi @opindex Wno-extra-semi @item -Wextra-semi @r{(C++, Objective-C++ only)} Warn about redundant semicolons. There are various contexts in which an extra semicolon can occur. One is a semicolon after in-class function definitions, which is valid in all C++ dialects (and is never a pedwarn): @smallexample struct S @{ void foo () @{@}; @}; @end smallexample Another is an extra semicolon at namespace scope, which has been allowed since C++11 (therefore is a pedwarn in C++98): @smallexample struct S @{ @}; ; @end smallexample And yet another is an extra semicolon in class definitions, which has been allowed since C++11 (therefore is a pedwarn in C++98): @smallexample struct S @{ int a; ; @}; @end smallexample @opindex Wno-global-module @opindex Wglobal-module @item -Wno-global-module @r{(C++ and Objective-C++ only)} Disable the diagnostic for when the global module fragment of a module unit does not consist only of preprocessor directives. @opindex Winaccessible-base @opindex Wno-inaccessible-base @item -Wno-inaccessible-base @r{(C++, Objective-C++ only)} This option controls warnings when a base class is inaccessible in a class derived from it due to ambiguity. The warning is enabled by default. Note that the warning for ambiguous virtual bases is enabled by the @option{-Wextra} option. @smallexample @group struct A @{ int a; @}; struct B : A @{ @}; struct C : B, A @{ @}; @end group @end smallexample @opindex Winherited-variadic-ctor @opindex Wno-inherited-variadic-ctor @item -Wno-inherited-variadic-ctor Suppress warnings about use of C++11 inheriting constructors when the base class inherited from has a C variadic constructor; the warning is on by default because the ellipsis is not inherited. @opindex Wno-invalid-offsetof @opindex Winvalid-offsetof @item -Wno-invalid-offsetof @r{(C++ and Objective-C++ only)} Suppress warnings from applying the @code{offsetof} macro to a non-POD type. According to the 2014 ISO C++ standard, applying @code{offsetof} to a non-standard-layout type is undefined. In existing C++ implementations, however, @code{offsetof} typically gives meaningful results. This flag is for users who are aware that they are writing nonportable code and who have deliberately chosen to ignore the warning about it. The restrictions on @code{offsetof} may be relaxed in a future version of the C++ standard. @opindex Wsized-deallocation @opindex Wno-sized-deallocation @item -Wsized-deallocation @r{(C++ and Objective-C++ only)} Warn about a definition of an unsized deallocation function @smallexample void operator delete (void *) noexcept; void operator delete[] (void *) noexcept; @end smallexample without a definition of the corresponding sized deallocation function @smallexample void operator delete (void *, std::size_t) noexcept; void operator delete[] (void *, std::size_t) noexcept; @end smallexample or vice versa. Enabled by @option{-Wextra} along with @option{-fsized-deallocation}. @opindex Wno-suggest-final-types @opindex Wsuggest-final-types @item -Wsuggest-final-types Warn about types with virtual methods where code quality would be improved if the type were declared with the C++11 @code{final} specifier, or, if possible, declared in an anonymous namespace. This allows GCC to more aggressively devirtualize the polymorphic calls. This warning is more effective with link-time optimization, where the information about the class hierarchy graph is more complete. @opindex Wno-suggest-final-methods @opindex Wsuggest-final-methods @item -Wsuggest-final-methods Warn about virtual methods where code quality would be improved if the method were declared with the C++11 @code{final} specifier, or, if possible, its type were declared in an anonymous namespace or with the @code{final} specifier. This warning is more effective with link-time optimization, where the information about the class hierarchy graph is more complete. It is recommended to first consider suggestions of @option{-Wsuggest-final-types} and then rebuild with new annotations. @opindex Wsuggest-override @opindex Wno-suggest-override @item -Wsuggest-override Warn about overriding virtual functions that are not marked with the @code{override} keyword. @opindex Wconversion-null @opindex Wno-conversion-null @item -Wno-conversion-null @r{(C++ and Objective-C++ only)} Do not warn for conversions between @code{NULL} and non-pointer types. @option{-Wconversion-null} is enabled by default. @end table @node Objective-C and Objective-C++ Dialect Options @section Options Controlling Objective-C and Objective-C++ Dialects @cindex compiler options, Objective-C and Objective-C++ @cindex Objective-C and Objective-C++ options, command-line @cindex options, Objective-C and Objective-C++ (NOTE: This manual does not describe the Objective-C and Objective-C++ languages themselves. @xref{Standards,,Language Standards Supported by GCC}, for references.) This section describes the command-line options that are only meaningful for Objective-C and Objective-C++ programs. You can also use most of the language-independent GNU compiler options. For example, you might compile a file @file{some_class.m} like this: @smallexample gcc -g -fgnu-runtime -O -c some_class.m @end smallexample @noindent In this example, @option{-fgnu-runtime} is an option meant only for Objective-C and Objective-C++ programs; you can use the other options with any language supported by GCC@. Note that since Objective-C is an extension of the C language, Objective-C compilations may also use options specific to the C front-end (e.g., @option{-Wtraditional}). Similarly, Objective-C++ compilations may use C++-specific options (e.g., @option{-Wabi}). Here is a list of options that are @emph{only} for compiling Objective-C and Objective-C++ programs: @table @gcctabopt @opindex fconstant-string-class @item -fconstant-string-class=@var{class-name} Use @var{class-name} as the name of the class to instantiate for each literal string specified with the syntax @code{@@"@dots{}"}. The default class name is @code{NXConstantString} if the GNU runtime is being used, and @code{NSConstantString} if the NeXT runtime is being used (see below). On Darwin / macOS platforms, the @option{-fconstant-cfstrings} option, if also present, overrides the @option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals to be laid out as constant CoreFoundation strings. Note that @option{-fconstant-cfstrings} is an alias for the target-specific @option{-mconstant-cfstrings} equivalent. @opindex fgnu-runtime @item -fgnu-runtime Generate object code compatible with the standard GNU Objective-C runtime. This is the default for most types of systems. @opindex fnext-runtime @item -fnext-runtime Generate output compatible with the NeXT runtime. This is the default for NeXT-based systems, including Darwin / macOS. The macro @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is used. @opindex fno-nil-receivers @opindex fnil-receivers @item -fno-nil-receivers Assume that all Objective-C message dispatches (@code{[receiver message:arg]}) in this translation unit ensure that the receiver is not @code{nil}. This allows for more efficient entry points in the runtime to be used. This option is only available in conjunction with the NeXT runtime and ABI version 0 or 1. @opindex fobjc-abi-version @item -fobjc-abi-version=@var{n} Use version @var{n} of the Objective-C ABI for the selected runtime. This option is currently supported only for the NeXT runtime. In that case, Version 0 is the traditional (32-bit) ABI without support for properties and other Objective-C 2.0 additions. Version 1 is the traditional (32-bit) ABI with support for properties and other Objective-C 2.0 additions. Version 2 is the modern (64-bit) ABI. If nothing is specified, the default is Version 0 on 32-bit target machines, and Version 2 on 64-bit target machines. @opindex fobjc-call-cxx-cdtors @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 @code{- (id) .cxx_construct} instance method which runs non-trivial default constructors on any such instance variables, in order, and then return @code{self}. Similarly, check if any instance variable is a C++ object with a non-trivial destructor, and if so, synthesize a special @code{- (void) .cxx_destruct} method which runs all such default destructors, in reverse order. The @code{- (id) .cxx_construct} and @code{- (void) .cxx_destruct} methods thusly generated only operate on instance variables declared in the current Objective-C class, and not those inherited from superclasses. It is the responsibility of the Objective-C runtime to invoke all such methods in an object's inheritance hierarchy. The @code{- (id) .cxx_construct} methods are invoked by the runtime immediately after a new object instance is allocated; the @code{- (void) .cxx_destruct} methods are invoked immediately before the runtime deallocates an object instance. As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has support for invoking the @code{- (id) .cxx_construct} and @code{- (void) .cxx_destruct} methods. @opindex fobjc-direct-dispatch @item -fobjc-direct-dispatch Allow fast jumps to the message dispatcher. On Darwin this is accomplished via the comm page. @opindex fobjc-exceptions @item -fobjc-exceptions Enable syntactic support for structured exception handling in Objective-C, similar to what is offered by C++. This option is required to use the Objective-C keywords @code{@@try}, @code{@@throw}, @code{@@catch}, @code{@@finally} and @code{@@synchronized}. This option is available with both the GNU runtime and the NeXT runtime (but not available in conjunction with the NeXT runtime on Mac OS X 10.2 and earlier). @opindex fobjc-gc @item -fobjc-gc Enable garbage collection (GC) in Objective-C and Objective-C++ programs. This option is only available with the NeXT runtime; the GNU runtime has a different garbage collection implementation that does not require special compiler flags. @opindex fobjc-nilcheck @item -fobjc-nilcheck For the NeXT runtime with version 2 of the ABI, check for a nil receiver in method invocations before doing the actual method call. This is the default and can be disabled using @option{-fno-objc-nilcheck}. Class methods and super calls are never checked for nil in this way no matter what this flag is set to. Currently this flag does nothing when the GNU runtime, or an older version of the NeXT runtime ABI, is used. @opindex fobjc-std @item -fobjc-std=objc1 Conform to the language syntax of Objective-C 1.0, the language recognized by GCC 4.0. This only affects the Objective-C additions to the C/C++ language; it does not affect conformance to C/C++ standards, which is controlled by the separate C/C++ dialect option flags. When this option is used with the Objective-C or Objective-C++ compiler, any Objective-C syntax that is not recognized by GCC 4.0 is rejected. This is useful if you need to make sure that your Objective-C code can be compiled with older versions of GCC@. @opindex freplace-objc-classes @item -freplace-objc-classes Emit a special marker instructing @command{ld(1)} not to statically link in the resulting object file, and allow @command{dyld(1)} to load it in at run time instead. This is used in conjunction with the Fix-and-Continue debugging mode, where the object file in question may be recompiled and dynamically reloaded in the course of program execution, without the need to restart the program itself. Currently, Fix-and-Continue functionality is only available in conjunction with the NeXT runtime on Mac OS X 10.3 and later. @opindex fzero-link @item -fzero-link When compiling for the NeXT runtime, the compiler ordinarily replaces calls to @code{objc_getClass("@dots{}")} (when the name of the class is known at compile time) with static class references that get initialized at load time, which improves run-time performance. Specifying the @option{-fzero-link} flag suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")} to be retained. This is useful in Zero-Link debugging mode, since it allows for individual class implementations to be modified during program execution. The GNU runtime currently always retains calls to @code{objc_get_class("@dots{}")} regardless of command-line options. @opindex fno-local-ivars @opindex flocal-ivars @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 @option{-fno-local-ivars} flag disables this behavior thus avoiding variable shadowing issues. @opindex fivar-visibility @item -fivar-visibility=@r{[}public@r{|}protected@r{|}private@r{|}package@r{]} 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. @opindex gen-decls @item -gen-decls Dump interface declarations for all classes seen in the source file to a file named @file{@var{sourcename}.decl}. @opindex Wassign-intercept @opindex Wno-assign-intercept @item -Wassign-intercept @r{(Objective-C and Objective-C++ only)} Warn whenever an Objective-C assignment is being intercepted by the garbage collector. @opindex Wproperty-assign-default @opindex Wno-property-assign-default @item -Wno-property-assign-default @r{(Objective-C and Objective-C++ only)} Do not warn if a property for an Objective-C object has no assign semantics specified. @opindex Wno-protocol @opindex Wprotocol @item -Wno-protocol @r{(Objective-C and Objective-C++ 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 @option{-Wno-protocol} option, then methods inherited from the superclass are considered to be implemented, and no warning is issued for them. @opindex Wobjc-root-class @item -Wobjc-root-class @r{(Objective-C and Objective-C++ only)} Warn if a class interface lacks a superclass. Most classes will inherit from @code{NSObject} (or @code{Object}) for example. When declaring classes intended to be root classes, the warning can be suppressed by marking their interfaces with @code{__attribute__((objc_root_class))}. @opindex Wselector @opindex Wno-selector @item -Wselector @r{(Objective-C and Objective-C++ 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 @code{@@selector(@dots{})} expression, and a corresponding method for that selector has been found during compilation. Because these checks scan the method table only at the end of compilation, these warnings are not produced if the final stage of compilation is not reached, for example because an error is found during compilation, or because the @option{-fsyntax-only} option is being used. @opindex Wstrict-selector-match @opindex Wno-strict-selector-match @item -Wstrict-selector-match @r{(Objective-C and Objective-C++ 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 @code{id} or @code{Class}. When this flag is off (which is the default behavior), the compiler omits such warnings if any differences found are confined to types that share the same size and alignment. @opindex Wundeclared-selector @opindex Wno-undeclared-selector @item -Wundeclared-selector @r{(Objective-C and Objective-C++ only)} Warn if a @code{@@selector(@dots{})} expression referring to an undeclared selector is found. A selector is considered undeclared if no method with that name has been declared before the @code{@@selector(@dots{})} expression, either explicitly in an @code{@@interface} or @code{@@protocol} declaration, or implicitly in an @code{@@implementation} section. This option always performs its checks as soon as a @code{@@selector(@dots{})} expression is found, while @option{-Wselector} only performs its checks in the final stage of compilation. This also enforces the coding style convention that methods and selectors must be declared before being used. @opindex print-objc-runtime-info @item -print-objc-runtime-info Generate C header describing the largest structure that is passed by value, if any. @end table @node OpenMP and OpenACC Options @section Options Controlling OpenMP and OpenACC @cindex OpenMP options @cindex OpenACC options GCC supports OpenMP extensions to the C, C++, and Fortran languages with the @option{-fopenmp} option. Similarly, OpenACC extensions are supported in all three languages with @option{-fopenacc}. @xref{OpenMP} and @ref{OpenACC} for an overview of these extensions. @table @gcctabopt @opindex foffload @cindex Offloading targets @cindex OpenACC offloading targets @cindex OpenMP offloading targets @item -foffload=disable @itemx -foffload=default @itemx -foffload=@var{target-list} Specify for which OpenMP and OpenACC offload targets code should be generated. The default behavior, equivalent to @option{-foffload=default}, is to generate code for all supported offload targets. The @option{-foffload=disable} form generates code only for the host fallback, while @option{-foffload=@var{target-list}} generates code only for the specified comma-separated list of offload targets. Offload targets are specified in GCC's internal target-triplet format. You can run the compiler with @option{-v} to show the list of configured offload targets under @code{OFFLOAD_TARGET_NAMES}. @opindex foffload-options @cindex Offloading options @cindex OpenACC offloading options @cindex OpenMP offloading options @item -foffload-options=@var{options} @itemx -foffload-options=@var{target-triplet-list}=@var{options} With @option{-foffload-options=@var{options}}, GCC passes the specified @var{options} to the compilers for all enabled offloading targets. You can specify options that apply only to a specific target or targets by using the @option{-foffload-options=@var{target-list}=@var{options}} form. The @var{target-list} is a comma-separated list in the same format as for the @option{-foffload=} option. Typical command lines are @smallexample -foffload-options='-fno-math-errno -ffinite-math-only' \ -foffload-options=nvptx-none=-latomic -foffload-options=amdgcn-amdhsa=-march=gfx906 @end smallexample @opindex fopenacc @cindex OpenACC accelerator programming @item -fopenacc Enable handling of OpenACC directives @samp{#pragma acc} in C/C++ and @samp{!$acc} in free-form Fortran and @samp{!$acc}, @samp{c$acc} and @samp{*$acc} in fixed-form Fortran. This option implies @option{-pthread}, and thus is only supported on targets that have support for @option{-pthread}. @opindex fopenacc-dim @item -fopenacc-dim=@var{geom} Specify default compute dimensions for parallel offload regions that do not explicitly specify them. The @var{geom} value is a triple of @samp{:}-separated sizes, in order @var{gang}, @var{worker}, and @var{vector}. A size can be omitted, to use a target-specific default value. @opindex fopenmp @cindex OpenMP parallel @item -fopenmp Enable handling of OpenMP directives @samp{#pragma omp}, @samp{[[omp::directive(...)]]}, @samp{[[omp::decl(...)]]}, and @samp{[[omp::sequence(...)]]} in C/C++. In Fortran, it enables @samp{!$omp} and the conditional compilation sentinel @samp{!$}. In fixed source form Fortran, the sentinels can also start with @samp{c} or @samp{*}. This option implies @option{-pthread}, and thus is only supported on targets that have support for @option{-pthread}. @option{-fopenmp} implies @option{-fopenmp-simd}. @opindex fopenmp-simd @cindex OpenMP SIMD @cindex SIMD @item -fopenmp-simd Enable handling of OpenMP's @code{simd}, @code{declare simd}, @code{declare reduction}, @code{assume}, @code{ordered}, @code{scan} and @code{loop} directive, and of combined or composite directives with @code{simd} as constituent with @code{#pragma omp}, @code{[[omp::directive(...)]]}, @code{[[omp::sequence(...)]]} and @code{[[omp::decl(...)]]} in C/C++ and @code{!$omp} in Fortran. It additionally enables the conditional compilation sentinel @samp{!$} in Fortran. In fixed source form Fortran, the sentinels can also start with @samp{c} or @samp{*}. Other OpenMP directives are ignored. Unless @option{-fopenmp} is additionally specified, the @code{loop} region binds to the current task region, independent of the specified @code{bind} clause. @opindex fopenmp-target-simd-clone @cindex OpenMP target SIMD clone @item -fopenmp-target-simd-clone @item -fopenmp-target-simd-clone=@var{device-type} In addition to generating SIMD clones for functions marked with the @code{declare simd} directive, GCC also generates clones for functions marked with the OpenMP @code{declare target} directive that are suitable for vectorization when this option is in effect. The @var{device-type} may be one of @code{none}, @code{host}, @code{nohost}, and @code{any}, which correspond to keywords for the @code{device_type} clause of the @code{declare target} directive; clones are generated for the intersection of devices specified. @option{-fopenmp-target-simd-clone} is equivalent to @option{-fopenmp-target-simd-clone=any} and @option{-fno-openmp-target-simd-clone} is equivalent to @option{-fopenmp-target-simd-clone=none}. At @option{-O2} and higher (but not @option{-Os} or @option{-Og}) this optimization defaults to @option{-fopenmp-target-simd-clone=nohost}; otherwise it is disabled by default. @end table @node Diagnostic Message Formatting Options @section Options to Control Diagnostic Messages Formatting @cindex options to control diagnostics formatting @cindex diagnostic messages @cindex message formatting Traditionally, diagnostic messages have been formatted irrespective of the output device's aspect (e.g.@: its width, @dots{}). You can use the options described below to control the formatting algorithm for diagnostic messages, e.g.@: how many characters per line, how often source location information should be reported. Note that some language front ends may not honor these options. @table @gcctabopt @opindex fmessage-length @item -fmessage-length=@var{n} Try to format error messages so that they fit on lines of about @var{n} characters. If @var{n} is zero, then no line-wrapping is done; each error message appears on a single line. This is the default for all front ends. Note - this option also affects the display of the @samp{#error} and @samp{#warning} pre-processor directives, and the @samp{deprecated} function/type/variable attribute. It does not however affect the @samp{pragma GCC warning} and @samp{pragma GCC error} pragmas. @item -fdiagnostics-plain-output This option requests that diagnostic output look as plain as possible, which may be useful when running @command{dejagnu} or other utilities that need to parse diagnostics output and prefer that it remain more stable over time. @option{-fdiagnostics-plain-output} is currently equivalent to the following options: @gccoptlist{-fno-diagnostics-show-caret -fno-diagnostics-show-line-numbers -fdiagnostics-color=never -fdiagnostics-urls=never -fdiagnostics-path-format=separate-events -fdiagnostics-text-art-charset=none -fno-diagnostics-show-event-links -fno-diagnostics-show-nesting} In the future, if GCC changes the default appearance of its diagnostics, the corresponding option to disable the new behavior will be added to this list. @opindex fdiagnostics-show-location @item -fdiagnostics-show-location=once Only meaningful in line-wrapping mode. Instructs the diagnostic messages reporter to emit source location information @emph{once}; that is, in case the message is too long to fit on a single physical line and has to be wrapped, the source location won't be emitted (as prefix) again, over and over, in subsequent continuation lines. This is the default behavior. @item -fdiagnostics-show-location=every-line Only meaningful in line-wrapping mode. Instructs the diagnostic messages reporter to emit the same source location information (as prefix) for physical lines that result from the process of breaking a message which is too long to fit on a single line. @opindex fdiagnostics-color @cindex highlight, color @vindex GCC_COLORS @r{environment variable} @item -fdiagnostics-color[=@var{WHEN}] @itemx -fno-diagnostics-color Use color in diagnostics. @var{WHEN} is @samp{never}, @samp{always}, or @samp{auto}. The default depends on how the compiler has been configured, it can be any of the above @var{WHEN} options or also @samp{never} if @env{GCC_COLORS} environment variable isn't present in the environment, and @samp{auto} otherwise. @samp{auto} makes GCC use color only when the standard error is a terminal, and when not executing in an emacs shell. The forms @option{-fdiagnostics-color} and @option{-fno-diagnostics-color} are aliases for @option{-fdiagnostics-color=always} and @option{-fdiagnostics-color=never}, respectively. The colors are defined by the environment variable @env{GCC_COLORS}. Its value is a colon-separated list of capabilities and Select Graphic Rendition (SGR) substrings. SGR commands are interpreted by the terminal or terminal emulator. (See the section in the documentation of your text terminal for permitted values and their meanings as character attributes.) These substring values are integers in decimal representation and can be concatenated with semicolons. Common values to concatenate include @samp{1} for bold, @samp{4} for underline, @samp{5} for blink, @samp{7} for inverse, @samp{39} for default foreground color, @samp{30} to @samp{37} for foreground colors, @samp{90} to @samp{97} for 16-color mode foreground colors, @samp{38;5;0} to @samp{38;5;255} for 88-color and 256-color modes foreground colors, @samp{49} for default background color, @samp{40} to @samp{47} for background colors, @samp{100} to @samp{107} for 16-color mode background colors, and @samp{48;5;0} to @samp{48;5;255} for 88-color and 256-color modes background colors. The default @env{GCC_COLORS} is @smallexample error=01;31:warning=01;35:note=01;36:range1=32:range2=34:locus=01:\ quote=01:path=01;36:fixit-insert=32:fixit-delete=31:\ diff-filename=01:diff-hunk=32:diff-delete=31:diff-insert=32:\ type-diff=01;32:fnname=01;32:targs=35:valid=01;31:invalid=01;32\ highlight-a=01;32:highlight-b=01;34 @end smallexample @noindent where @samp{01;31} is bold red, @samp{01;35} is bold magenta, @samp{01;36} is bold cyan, @samp{32} is green, @samp{34} is blue, @samp{01} is bold, and @samp{31} is red. Setting @env{GCC_COLORS} to the empty string disables colors. Supported capabilities are as follows. @table @code @vindex error GCC_COLORS @r{capability} @item error= SGR substring for error: markers. @vindex warning GCC_COLORS @r{capability} @item warning= SGR substring for warning: markers. @vindex note GCC_COLORS @r{capability} @item note= SGR substring for note: markers. @vindex path GCC_COLORS @r{capability} @item path= SGR substring for colorizing paths of control-flow events as printed via @option{-fdiagnostics-path-format=}, such as the identifiers of individual events and lines indicating interprocedural calls and returns. @vindex range1 GCC_COLORS @r{capability} @item range1= SGR substring for first additional range. @vindex range2 GCC_COLORS @r{capability} @item range2= SGR substring for second additional range. @vindex locus GCC_COLORS @r{capability} @item locus= SGR substring for location information, @samp{file:line} or @samp{file:line:column} etc. @vindex quote GCC_COLORS @r{capability} @item quote= SGR substring for information printed within quotes. @vindex fnname GCC_COLORS @r{capability} @item fnname= SGR substring for names of C++ functions. @vindex targs GCC_COLORS @r{capability} @item targs= SGR substring for C++ function template parameter bindings. @vindex fixit-insert GCC_COLORS @r{capability} @item fixit-insert= SGR substring for fix-it hints suggesting text to be inserted or replaced. @vindex fixit-delete GCC_COLORS @r{capability} @item fixit-delete= SGR substring for fix-it hints suggesting text to be deleted. @vindex diff-filename GCC_COLORS @r{capability} @item diff-filename= SGR substring for filename headers within generated patches. @vindex diff-hunk GCC_COLORS @r{capability} @item diff-hunk= SGR substring for the starts of hunks within generated patches. @vindex diff-delete GCC_COLORS @r{capability} @item diff-delete= SGR substring for deleted lines within generated patches. @vindex diff-insert GCC_COLORS @r{capability} @item diff-insert= SGR substring for inserted lines within generated patches. @vindex type-diff GCC_COLORS @r{capability} @item type-diff= SGR substring for highlighting mismatching types within template arguments in the C++ frontend. @vindex valid GCC_COLORS @r{capability} @item valid= SGR substring for highlighting valid elements within text art diagrams. @vindex invalid GCC_COLORS @r{capability} @item invalid= SGR substring for highlighting invalid elements within text art diagrams. @vindex highlight-a GCC_COLORS @r{capability} @vindex highlight-b GCC_COLORS @r{capability} @item highlight-a= @item highlight-b= SGR substrings for contrasting two different things within diagnostics, such as a pair of mismatching types. See @option{-fdiagnostics-show-highlight-colors}. @end table @opindex fdiagnostics-urls @cindex urls @vindex GCC_URLS @r{environment variable} @vindex TERM_URLS @r{environment variable} @item -fdiagnostics-urls[=@var{WHEN}] Use escape sequences to embed URLs in diagnostics. For example, when @option{-fdiagnostics-show-option} emits text showing the command-line option controlling a diagnostic, embed a URL for documentation of that option. @var{WHEN} is @samp{never}, @samp{always}, or @samp{auto}. @samp{auto} makes GCC use URL escape sequences only when the standard error is a terminal, and when not executing in an emacs shell or any graphical terminal which is known to be incompatible with this feature, see below. The default depends on how the compiler has been configured. It can be any of the above @var{WHEN} options. GCC can also be configured (via the @option{--with-diagnostics-urls=auto-if-env} configure-time option) so that the default is affected by environment variables. Under such a configuration, GCC defaults to using @samp{auto} if either @env{GCC_URLS} or @env{TERM_URLS} environment variables are present and non-empty in the environment of the compiler, or @samp{never} if neither are. However, even with @option{-fdiagnostics-urls=always} the behavior is dependent on those environment variables: If @env{GCC_URLS} is set to empty or @samp{no}, do not embed URLs in diagnostics. If set to @samp{st}, URLs use ST escape sequences. If set to @samp{bel}, the default, URLs use BEL escape sequences. Any other non-empty value enables the feature. If @env{GCC_URLS} is not set, use @env{TERM_URLS} as a fallback. Note: ST is an ANSI escape sequence, string terminator @samp{ESC \}, BEL is an ASCII character, CTRL-G that usually sounds like a beep. At this time GCC tries to detect also a few terminals that are known to not implement the URL feature, and have bugs or at least had bugs in some versions that are still in use, where the URL escapes are likely to misbehave, i.e. print garbage on the screen. That list is currently xfce4-terminal, certain known to be buggy gnome-terminal versions, the linux console, and mingw. This check can be skipped with the @option{-fdiagnostics-urls=always}. @opindex fno-diagnostics-show-option @opindex fdiagnostics-show-option @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 @option{-fno-diagnostics-show-option} flag suppresses that behavior. @opindex fno-diagnostics-show-caret @opindex fdiagnostics-show-caret @item -fno-diagnostics-show-caret By default, each diagnostic emitted includes the original source line and a caret @samp{^} indicating the column. This option suppresses this information. The source line is truncated to @var{n} characters, if the @option{-fmessage-length=n} option is given. When the output is done to the terminal, the width is limited to the width given by the @env{COLUMNS} environment variable or, if not set, to the terminal width. @opindex fno-diagnostics-show-labels @opindex fdiagnostics-show-labels @item -fno-diagnostics-show-labels By default, when printing source code (via @option{-fdiagnostics-show-caret}), diagnostics can label ranges of source code with pertinent information, such as the types of expressions: @smallexample printf ("foo %s bar", long_i + long_j); ~^ ~~~~~~~~~~~~~~~ | | char * long int @end smallexample This option suppresses the printing of these labels (in the example above, the vertical bars and the ``char *'' and ``long int'' text). @opindex fno-diagnostics-show-event-links @opindex fdiagnostics-show-event-links @item -fno-diagnostics-show-event-links By default, when printing execution paths (via @option{-fdiagnostics-path-format=inline-events}), GCC will print lines connecting related events, such as the line connecting events 1 and 2 in: @smallexample 3 | if (p) | ^ | | | (1) following `false' branch (when `p' is NULL)... ->-+ | | | | |+------------------------------------------------------------+ 4 || return 0; 5 || return *p; || ~ || | |+-------->(2) ...to here | (3) dereference of NULL `p' @end smallexample This option suppresses the printing of such connector lines. @opindex fno-diagnostics-show-cwe @opindex fdiagnostics-show-cwe @item -fno-diagnostics-show-cwe Diagnostic messages can optionally have an associated @uref{https://cwe.mitre.org/index.html, CWE} identifier. GCC itself only provides such metadata for some of the @option{-fanalyzer} diagnostics. GCC plugins may also provide diagnostics with such metadata. By default, if this information is present, it will be printed with the diagnostic. This option suppresses the printing of this metadata. @opindex fno-diagnostics-show-rules @opindex fdiagnostics-show-rules @item -fno-diagnostics-show-rules Diagnostic messages can optionally have rules associated with them, such as from a coding standard, or a specification. GCC itself does not do this for any of its diagnostics, but plugins may do so. By default, if this information is present, it will be printed with the diagnostic. This option suppresses the printing of this metadata. @opindex fno-diagnostics-show-highlight-colors @opindex fdiagnostics-show-highlight-colors @item -fno-diagnostics-show-highlight-colors GCC can use color for emphasis and contrast when printing diagnostic messages and quoting the user's source. For example, in @smallexample demo.c: In function `test_bad_format_string_args': ../../src/demo.c:25:18: warning: format `%i' expects argument of type `int', but argument 2 has type `const char *' [-Wformat=] 25 | printf("hello %i", msg); | ~^ ~~~ | | | | int const char * | %s @end smallexample @itemize @bullet @item the @code{%i} and @code{int} in the message and the @code{int} in the quoted source are colored using @code{highlight-a} (bold green by default), and @item the @code{const char *} in the message and in the quoted source are both colored using @code{highlight-b} (bold blue by default). @end itemize The intent is to draw the reader's eyes to the relationships between the various aspects of the diagnostic message and the source, using color to group related elements and distinguish between mismatching ones. This additional colorization is enabled by default if color printing is enabled (as per @option{-fdiagnostics-color=}), but it can be separately disabled via @option{-fno-diagnostics-show-highlight-colors}. @opindex fno-diagnostics-show-line-numbers @opindex fdiagnostics-show-line-numbers @item -fno-diagnostics-show-line-numbers By default, when printing source code (via @option{-fdiagnostics-show-caret}), a left margin is printed, showing line numbers. This option suppresses this left margin. @opindex fdiagnostics-minimum-margin-width @item -fdiagnostics-minimum-margin-width=@var{width} This option controls the minimum width of the left margin printed by @option{-fdiagnostics-show-line-numbers}. It defaults to 6. @opindex fdiagnostics-show-context @item -fdiagnostics-show-context[=@var{depth}] @itemx -fno-diagnostics-show-context With this option, the compiler might print the interesting control flow chain that guards the basic block of the statement which has the warning. @var{depth} is the maximum depth of the control flow chain. Currently, The list of the impacted warning options includes: @option{-Warray-bounds}, @option{-Wstringop-overflow}, @option{-Wstringop-overread}, @option{-Wstringop-truncation}. and @option{-Wrestrict}. More warning options might be added to this list in future releases. The forms @option{-fdiagnostics-show-context} and @option{-fno-diagnostics-show-context} are aliases for @option{-fdiagnostics-show-context=1} and @option{-fdiagnostics-show-context=0}, respectively. @opindex fdiagnostics-parseable-fixits @item -fdiagnostics-parseable-fixits Emit fix-it hints in a machine-parseable format, suitable for consumption by IDEs. For each fix-it, a line will be printed after the relevant diagnostic, starting with the string ``fix-it:''. For example: @smallexample fix-it:"test.c":@{45:3-45:21@}:"gtk_widget_show_all" @end smallexample The location is expressed as a half-open range, expressed as a count of bytes, starting at byte 1 for the initial column. In the above example, bytes 3 through 20 of line 45 of ``test.c'' are to be replaced with the given string: @smallexample 00000000011111111112222222222 12345678901234567890123456789 gtk_widget_showall (dlg); ^^^^^^^^^^^^^^^^^^ gtk_widget_show_all @end smallexample The filename and replacement string escape backslash as ``\\", tab as ``\t'', newline as ``\n'', double quotes as ``\"'', non-printable characters as octal (e.g. vertical tab as ``\013''). An empty replacement string indicates that the given range is to be removed. An empty range (e.g. ``45:3-45:3'') indicates that the string is to be inserted at the given position. @opindex fdiagnostics-generate-patch @item -fdiagnostics-generate-patch Print fix-it hints to stderr in unified diff format, after any diagnostics are printed. For example: @smallexample --- test.c +++ test.c @@ -42,5 +42,5 @@ void show_cb(GtkDialog *dlg) @{ - gtk_widget_showall(dlg); + gtk_widget_show_all(dlg); @} @end smallexample The diff may or may not be colorized, following the same rules as for diagnostics (see @option{-fdiagnostics-color}). @opindex fdiagnostics-show-template-tree @item -fdiagnostics-show-template-tree In the C++ frontend, when printing diagnostics showing mismatching template types, such as: @smallexample could not convert 'std::map >()' from 'map<[...],vector>' to 'map<[...],vector> @end smallexample the @option{-fdiagnostics-show-template-tree} flag enables printing a tree-like structure showing the common and differing parts of the types, such as: @smallexample map< [...], vector< [double != float]>> @end smallexample The parts that differ are highlighted with color (``double'' and ``float'' in this case). @opindex fno-elide-type @opindex felide-type @item -fno-elide-type By default when the C++ frontend prints diagnostics showing mismatching template types, common parts of the types are printed as ``[...]'' to simplify the error message. For example: @smallexample could not convert 'std::map >()' from 'map<[...],vector>' to 'map<[...],vector> @end smallexample Specifying the @option{-fno-elide-type} flag suppresses that behavior. This flag also affects the output of the @option{-fdiagnostics-show-template-tree} flag. @opindex fdiagnostics-path-format @item -fdiagnostics-path-format=@var{KIND} Specify how to print paths of control-flow events for diagnostics that have such a path associated with them. @var{KIND} is @samp{none}, @samp{separate-events}, or @samp{inline-events}, the default. @samp{none} means to not print diagnostic paths. @samp{separate-events} means to print a separate ``note'' diagnostic for each event within the diagnostic. For example: @smallexample test.c:29:5: error: passing NULL as argument 1 to 'PyList_Append' which requires a non-NULL parameter test.c:25:10: note: (1) when 'PyList_New' fails, returning NULL test.c:27:3: note: (2) when 'i < count' test.c:29:5: note: (3) when calling 'PyList_Append', passing NULL from (1) as argument 1 @end smallexample @samp{inline-events} means to print the events ``inline'' within the source code. This view attempts to consolidate the events into runs of sufficiently-close events, printing them as labelled ranges within the source. For example, the same events as above might be printed as: @smallexample 'test': events 1-3 25 | list = PyList_New(0); | ^~~~~~~~~~~~~ | | | (1) when 'PyList_New' fails, returning NULL 26 | 27 | for (i = 0; i < count; i++) @{ | ~~~ | | | (2) when 'i < count' 28 | item = PyLong_FromLong(random()); 29 | PyList_Append(list, item); | ~~~~~~~~~~~~~~~~~~~~~~~~~ | | | (3) when calling 'PyList_Append', passing NULL from (1) as argument 1 @end smallexample Interprocedural control flow is shown by grouping the events by stack frame, and using indentation to show how stack frames are nested, pushed, and popped. For example: @smallexample 'test': events 1-2 | | 133 | @{ | | ^ | | | | | (1) entering 'test' | 134 | boxed_int *obj = make_boxed_int (i); | | ~~~~~~~~~~~~~~~~~~ | | | | | (2) calling 'make_boxed_int' | +--> 'make_boxed_int': events 3-4 | | 120 | @{ | | ^ | | | | | (3) entering 'make_boxed_int' | 121 | boxed_int *result = (boxed_int *)wrapped_malloc (sizeof (boxed_int)); | | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | | | | | (4) calling 'wrapped_malloc' | +--> 'wrapped_malloc': events 5-6 | | 7 | @{ | | ^ | | | | | (5) entering 'wrapped_malloc' | 8 | return malloc (size); | | ~~~~~~~~~~~~~ | | | | | (6) calling 'malloc' | <-------------+ | 'test': event 7 | | 138 | free_boxed_int (obj); | | ^~~~~~~~~~~~~~~~~~~~ | | | | | (7) calling 'free_boxed_int' | (etc) @end smallexample @opindex fdiagnostics-show-path-depths @item -fdiagnostics-show-path-depths This option provides additional information when printing control-flow paths associated with a diagnostic. If this is option is provided then the stack depth will be printed for each run of events within @option{-fdiagnostics-path-format=inline-events}. If provided with @option{-fdiagnostics-path-format=separate-events}, then the stack depth and function declaration will be appended when printing each event. This is intended for use by GCC developers and plugin developers when debugging diagnostics that report interprocedural control flow. @opindex fno-show-column @opindex fshow-column @item -fno-show-column Do not print column numbers in diagnostics. This may be necessary if diagnostics are being scanned by a program that does not understand the column numbers, such as @command{dejagnu}. @opindex fdiagnostics-column-unit @item -fdiagnostics-column-unit=@var{UNIT} Select the units for the column number. This affects traditional diagnostics (in the absence of @option{-fno-show-column}). The default @var{UNIT}, @samp{display}, considers the number of display columns occupied by each character. This may be larger than the number of bytes required to encode the character, in the case of tab characters, or it may be smaller, in the case of multibyte characters. For example, the character ``GREEK SMALL LETTER PI (U+03C0)'' occupies one display column, and its UTF-8 encoding requires two bytes; the character ``SLIGHTLY SMILING FACE (U+1F642)'' occupies two display columns, and its UTF-8 encoding requires four bytes. Setting @var{UNIT} to @samp{byte} changes the column number to the raw byte count in all cases, as was traditionally output by GCC prior to version 11.1.0. @opindex fdiagnostics-column-origin @item -fdiagnostics-column-origin=@var{ORIGIN} Select the origin for column numbers, i.e. the column number assigned to the first column. The default value of 1 corresponds to traditional GCC behavior and to the GNU style guide. Some utilities may perform better with an origin of 0; any non-negative value may be specified. @opindex fdiagnostics-escape-format @item -fdiagnostics-escape-format=@var{FORMAT} When GCC prints pertinent source lines for a diagnostic it normally attempts to print the source bytes directly. However, some diagnostics relate to encoding issues in the source file, such as malformed UTF-8, or issues with Unicode normalization. These diagnostics are flagged so that GCC will escape bytes that are not printable ASCII when printing their pertinent source lines. This option controls how such bytes should be escaped. The default @var{FORMAT}, @samp{unicode} displays Unicode characters that are not printable ASCII in the form @samp{}, and bytes that do not correspond to a Unicode character validly-encoded in UTF-8-encoded will be displayed as hexadecimal in the form @samp{}. For example, a source line containing the string @samp{before} followed by the Unicode character U+03C0 (``GREEK SMALL LETTER PI'', with UTF-8 encoding 0xCF 0x80) followed by the byte 0xBF (a stray UTF-8 trailing byte), followed by the string @samp{after} will be printed for such a diagnostic as: @smallexample beforeafter @end smallexample Setting @var{FORMAT} to @samp{bytes} will display all non-printable-ASCII bytes in the form @samp{}, thus showing the underlying encoding of non-ASCII Unicode characters. For the example above, the following will be printed: @smallexample before<80>after @end smallexample @opindex fdiagnostics-text-art-charset @item -fdiagnostics-text-art-charset=@var{CHARSET} Some diagnostics can contain ``text art'' diagrams: visualizations created from text, intended to be viewed in a monospaced font. This option selects which characters should be used for printing such diagrams, if any. @var{CHARSET} is @samp{none}, @samp{ascii}, @samp{unicode}, or @samp{emoji}. The @samp{none} value suppresses the printing of such diagrams. The @samp{ascii} value will ensure that such diagrams are pure ASCII (``ASCII art''). The @samp{unicode} value will allow for conservative use of unicode drawing characters (such as box-drawing characters). The @samp{emoji} value further adds the possibility of emoji in the output (such as emitting U+26A0 WARNING SIGN followed by U+FE0F VARIATION SELECTOR-16 to select the emoji variant of the character). The default is @samp{emoji}, except when the environment variable @env{LANG} is set to @samp{C}, in which case the default is @samp{ascii}. @opindex fno-diagnostics-show-nesting @opindex fdiagnostics-show-nesting @item -fno-diagnostics-show-nesting Some GCC diagnostics have an internal tree-like structure of nested sub-diagnostics, such as for problems when instantiating C++ templates. By default GCC uses indentation and bullet points in its text output to show the nesting structure of these diagnostics, moves location information to separate lines to make the structure clearer, and eliminates redundant repeated information. Selecting @option{-fno-diagnostics-show-nesting} suppresses this indentation, reformatting, and elision, restoring an older `look'' for the diagnostics. @opindex fno-diagnostics-show-nesting-locations @opindex fdiagnostics-show-nesting-locations @item -fno-diagnostics-show-nesting-locations When @option{fdiagnostics-show-nesting} is enabled, file names and line- and column- numbers are displayed on separate lines from the messages. This location information can be disabled altogether with @option{-fno-diagnostics-show-nesting-locations}. This option exists for use by GCC developers, for writing DejaGnu test cases. @opindex fdiagnostics-show-nesting-levels @opindex fno-diagnostics-show-nesting-levels @item -fdiagnostics-show-nesting-levels When @option{fdiagnostics-show-nesting} is enabled, use @option{fdiagnostics-show-nesting-levels} to also display numbers showing the depth of the nesting. This option exists for use by GCC developers for debugging nested diagnostics, but may be of use to plugin authors. @opindex fdiagnostics-format @item -fdiagnostics-format=@var{FORMAT} Select a different format for printing diagnostics. @var{FORMAT} is @samp{text}, @samp{sarif-stderr} or @samp{sarif-file}. Using this option replaces any additional ``output sinks'' added by @option{-fdiagnostics-add-output=}, or that set by @option{-fdiagnostics-set-output=}. The default is @samp{text}. The @samp{sarif-stderr} and @samp{sarif-file} formats both emit diagnostics in SARIF Version 2.1.0 format, either to stderr, or to a file named @file{@var{source}.sarif}, respectively. @opindex fdiagnostics-add-output @item -fdiagnostics-add-output=@var{DIAGNOSTICS-OUTPUT-SPEC} Add an additional ``output sink'' for emitting diagnostics. @var{DIAGNOSTICS-OUTPUT-SPEC} should specify a scheme, optionally followed by @code{:} and one or more @var{KEY}=@var{VALUE} pairs, in this form: @smallexample @var{SCHEME} @var{SCHEME}:@var{KEY}=@var{VALUE} @var{SCHEME}:@var{KEY}=@var{VALUE},@var{KEY2}=@var{VALUE2} @end smallexample etc. Schemes, keys, or values with a name prefixed ``experimental'' may change or be removed without notice. @var{SCHEME} can be @table @gcctabopt @item text Emit diagnostics to stderr using GCC's classic text output format. Supported keys are: @table @gcctabopt @item color=@r{[}yes@r{|}no@r{]} Override colorization settings from @option{-fdiagnostics-color} for this text output. @item show-nesting=@r{[}yes@r{|}no@r{]} Enable a mode that emphasizes hierarchical relationships within diagnostics messages, as per @option{-fdiagnostics-show-nesting}. Defaults to @code{yes}. @item show-nesting-locations=@r{[}yes@r{|}no@r{]} If @code{show-nesting=yes}, then by default locations are shown; set this key to @code{no} to disable printing such locations. This exists for use by GCC developers, for writing DejaGnu test cases. @item show-nesting-levels=@r{[}yes@r{|}no@r{]} This is a debugging option for use with @code{show-nesting=yes}. Set this key to @code{yes} to print explicit nesting levels in the output. This exists for use by GCC developers. @end table @item sarif Emit diagnostics to a file in SARIF format. Supported keys are: @table @gcctabopt @item file=@var{FILENAME} Specify the filename to write the SARIF output to, potentially with a leading absolute or relative path. If not specified, it defaults to @file{@var{source}.sarif}. @item serialization=@r{[}json@r{]} Specify the serialization format to use when writing out the SARIF. Currently this can only be @code{json}, but is present as an extension point for experimenting with other serializations. @item version=@r{[}2.1@r{|}2.2-prerelease@r{]} Specify the version of SARIF to use for the output. If not specified, defaults to 2.1. @code{2.2-prerelease} uses an unofficial draft of the future SARIF 2.2 specification and should only be used for experimentation in this release. @end table There is also this key intended for use by GCC developers, rather than end-users, and subject to change or removal without notice: @table @gcctabopt @item state-graphs=@r{[}yes@r{|}no@r{]} This is a debugging feature and defaults to @code{no}. If @code{state-graphs=yes}, then attempt to capture detailed state information from @option{-fanalyzer} in the generated SARIF. @end table @item experimental-html Emit diagnostics to a file in HTML format. This scheme is experimental, and may go away in future GCC releases. The keys and details of the output are also subject to change. Supported keys are: @table @gcctabopt @item css=@r{[}yes@r{|}no@r{]} Add an embedded