This is doc/gcc.info, produced by makeinfo version 4.11 from /gcc-4.3/gcc-4.3.1/gcc-4.3.1/gcc/doc/gcc.texi. Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007 2008 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 1.2 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 section entitled "GNU Free Documentation License". (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. INFO-DIR-SECTION Software development START-INFO-DIR-ENTRY * gcc: (gcc). The GNU Compiler Collection. * g++: (gcc). The GNU C++ compiler. END-INFO-DIR-ENTRY This file documents the use of the GNU compilers. Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007 2008 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 1.2 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 section entitled "GNU Free Documentation License". (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.  File: gcc.info, Node: Top, Next: G++ and GCC, Up: (DIR) Introduction ************ This manual documents how to use the GNU compilers, as well as their features and incompatibilities, and how to report bugs. It corresponds to the compilers (GCC) version 4.3.1. The internals of the GNU compilers, including how to port them to new targets and some information about how to write front ends for new languages, are documented in a separate manual. *Note Introduction: (gccint)Top. * Menu: * G++ and GCC:: You can compile C or C++ programs. * Standards:: Language standards supported by GCC. * Invoking GCC:: Command options supported by `gcc'. * C Implementation:: How GCC implements the ISO C specification. * C Extensions:: GNU extensions to the C language family. * C++ Extensions:: GNU extensions to the C++ language. * Objective-C:: GNU Objective-C runtime features. * Compatibility:: Binary Compatibility * Gcov:: `gcov'---a test coverage program. * Trouble:: If you have trouble using GCC. * Bugs:: How, why and where to report bugs. * Service:: How to find suppliers of support for GCC. * Contributing:: How to contribute to testing and developing GCC. * Funding:: How to help assure funding for free software. * GNU Project:: The GNU Project and GNU/Linux. * Copying:: GNU General Public License says how you can copy and share GCC. * GNU Free Documentation License:: How you can copy and share this manual. * Contributors:: People who have contributed to GCC. * Option Index:: Index to command line options. * Keyword Index:: Index of concepts and symbol names.  File: gcc.info, Node: G++ and GCC, Next: Standards, Prev: Top, Up: Top 1 Programming Languages Supported by GCC **************************************** GCC stands for "GNU Compiler Collection". GCC is an integrated distribution of compilers for several major programming languages. These languages currently include C, C++, Objective-C, Objective-C++, Java, Fortran, and Ada. The abbreviation "GCC" has multiple meanings in common use. The current official meaning is "GNU Compiler Collection", which refers generically to the complete suite of tools. The name historically stood for "GNU C Compiler", and this usage is still common when the emphasis is on compiling C programs. Finally, the name is also used when speaking of the "language-independent" component of GCC: code shared among the compilers for all supported languages. The language-independent component of GCC includes the majority of the optimizers, as well as the "back ends" that generate machine code for various processors. The part of a compiler that is specific to a particular language is called the "front end". In addition to the front ends that are integrated components of GCC, there are several other front ends that are maintained separately. These support languages such as Pascal, Mercury, and COBOL. To use these, they must be built together with GCC proper. Most of the compilers for languages other than C have their own names. The C++ compiler is G++, the Ada compiler is GNAT, and so on. When we talk about compiling one of those languages, we might refer to that compiler by its own name, or as GCC. Either is correct. Historically, compilers for many languages, including C++ and Fortran, have been implemented as "preprocessors" which emit another high level language such as C. None of the compilers included in GCC are implemented this way; they all generate machine code directly. This sort of preprocessor should not be confused with the "C preprocessor", which is an integral feature of the C, C++, Objective-C and Objective-C++ languages.  File: gcc.info, Node: Standards, Next: Invoking GCC, Prev: G++ and GCC, Up: Top 2 Language Standards Supported by GCC ************************************* For each language compiled by GCC for which there is a standard, GCC attempts to follow one or more versions of that standard, possibly with some exceptions, and possibly with some extensions. 2.1 C language ============== GCC supports three versions of the C standard, although support for the most recent version is not yet complete. The original ANSI C standard (X3.159-1989) was ratified in 1989 and published in 1990. This standard was ratified as an ISO standard (ISO/IEC 9899:1990) later in 1990. There were no technical differences between these publications, although the sections of the ANSI standard were renumbered and became clauses in the ISO standard. This standard, in both its forms, is commonly known as "C89", or occasionally as "C90", from the dates of ratification. The ANSI standard, but not the ISO standard, also came with a Rationale document. To select this standard in GCC, use one of the options `-ansi', `-std=c89' or `-std=iso9899:1990'; to obtain all the diagnostics required by the standard, you should also specify `-pedantic' (or `-pedantic-errors' if you want them to be errors rather than warnings). *Note Options Controlling C Dialect: C Dialect Options. Errors in the 1990 ISO C standard were corrected in two Technical Corrigenda published in 1994 and 1996. GCC does not support the uncorrected version. An amendment to the 1990 standard was published in 1995. This amendment added digraphs and `__STDC_VERSION__' to the language, but otherwise concerned the library. This amendment is commonly known as "AMD1"; the amended standard is sometimes known as "C94" or "C95". To select this standard in GCC, use the option `-std=iso9899:199409' (with, as for other standard versions, `-pedantic' to receive all required diagnostics). A new edition of the ISO C standard was published in 1999 as ISO/IEC 9899:1999, and is commonly known as "C99". GCC has incomplete support for this standard version; see `http://gcc.gnu.org/gcc-4.3/c99status.html' for details. To select this standard, use `-std=c99' or `-std=iso9899:1999'. (While in development, drafts of this standard version were referred to as "C9X".) Errors in the 1999 ISO C standard were corrected in three Technical Corrigenda published in 2001, 2004 and 2007. GCC does not support the uncorrected version. By default, GCC provides some extensions to the C language that on rare occasions conflict with the C standard. *Note Extensions to the C Language Family: C Extensions. Use of the `-std' options listed above will disable these extensions where they conflict with the C standard version selected. You may also select an extended version of the C language explicitly with `-std=gnu89' (for C89 with GNU extensions) or `-std=gnu99' (for C99 with GNU extensions). The default, if no C language dialect options are given, is `-std=gnu89'; this will change to `-std=gnu99' in some future release when the C99 support is complete. Some features that are part of the C99 standard are accepted as extensions in C89 mode. The ISO C standard defines (in clause 4) two classes of conforming implementation. A "conforming hosted implementation" supports the whole standard including all the library facilities; a "conforming freestanding implementation" is only required to provide certain library facilities: those in `', `', `', and `'; since AMD1, also those in `'; and in C99, also those in `' and `'. In addition, complex types, added in C99, are not required for freestanding implementations. The standard also defines two environments for programs, a "freestanding environment", required of all implementations and which may not have library facilities beyond those required of freestanding implementations, where the handling of program startup and termination are implementation-defined, and a "hosted environment", which is not required, in which all the library facilities are provided and startup is through a function `int main (void)' or `int main (int, char *[])'. An OS kernel would be a freestanding environment; a program using the facilities of an operating system would normally be in a hosted implementation. GCC aims towards being usable as a conforming freestanding implementation, or as the compiler for a conforming hosted implementation. By default, it will act as the compiler for a hosted implementation, defining `__STDC_HOSTED__' as `1' and presuming that when the names of ISO C functions are used, they have the semantics defined in the standard. To make it act as a conforming freestanding implementation for a freestanding environment, use the option `-ffreestanding'; it will then define `__STDC_HOSTED__' to `0' and not make assumptions about the meanings of function names from the standard library, with exceptions noted below. To build an OS kernel, you may well still need to make your own arrangements for linking and startup. *Note Options Controlling C Dialect: C Dialect Options. GCC does not provide the library facilities required only of hosted implementations, nor yet all the facilities required by C99 of freestanding implementations; to use the facilities of a hosted environment, you will need to find them elsewhere (for example, in the GNU C library). *Note Standard Libraries: Standard Libraries. Most of the compiler support routines used by GCC are present in `libgcc', but there are a few exceptions. GCC requires the freestanding environment provide `memcpy', `memmove', `memset' and `memcmp'. Finally, if `__builtin_trap' is used, and the target does not implement the `trap' pattern, then GCC will emit a call to `abort'. For references to Technical Corrigenda, Rationale documents and information concerning the history of C that is available online, see `http://gcc.gnu.org/readings.html' 2.2 C++ language ================ GCC supports the ISO C++ standard (1998) and contains experimental support for the upcoming ISO C++ standard (200x). The original ISO C++ standard was published as the ISO standard (ISO/IEC 14882:1998) and amended by a Technical Corrigenda published in 2003 (ISO/IEC 14882:2003). These standards are referred to as C++98 and C++03, respectively. GCC implements the majority of C++98 (`export' is a notable exception) and most of the changes in C++03. To select this standard in GCC, use one of the options `-ansi' or `-std=c++98'; to obtain all the diagnostics required by the standard, you should also specify `-pedantic' (or `-pedantic-errors' if you want them to be errors rather than warnings). The ISO C++ committee is working on a new ISO C++ standard, dubbed C++0x, that is intended to be published by 2009. C++0x contains several changes to the C++ language, some of which have been implemented in an experimental C++0x mode in GCC. The C++0x mode in GCC tracks the draft working paper for the C++0x standard; the latest working paper is available on the ISO C++ committee's web site at `http://www.open-std.org/jtc1/sc22/wg21/'. For information regarding the C++0x features available in the experimental C++0x mode, see `http://gcc.gnu.org/gcc-4.3/cxx0x_status.html'. To select this standard in GCC, use the option `-std=c++0x'; to obtain all the diagnostics required by the standard, you should also specify `-pedantic' (or `-pedantic-errors' if you want them to be errors rather than warnings). By default, GCC provides some extensions to the C++ language; *Note Options Controlling C++ Dialect: C++ Dialect Options. Use of the `-std' option listed above will disable these extensions. You may also select an extended version of the C++ language explicitly with `-std=gnu++98' (for C++98 with GNU extensions) or `-std=gnu++0x' (for C++0x with GNU extensions). The default, if no C++ language dialect options are given, is `-std=gnu++98'. 2.3 Objective-C and Objective-C++ languages =========================================== There is no formal written standard for Objective-C or Objective-C++. The most authoritative manual is "Object-Oriented Programming and the Objective-C Language", available at a number of web sites: * `http://developer.apple.com/documentation/Cocoa/Conceptual/ObjectiveC/' is a recent (and periodically updated) version; * `http://www.toodarkpark.org/computers/objc/' is an older example; * `http://www.gnustep.org' and `http://gcc.gnu.org/readings.html' have additional useful information. 2.4 Treelang language ===================== There is no standard for treelang, which is a sample language front end for GCC. Its only purpose is as a sample for people wishing to write a new language for GCC. The language is documented in `gcc/treelang/treelang.texi' which can be turned into info or HTML format. *Note GNAT Reference Manual: (gnat_rm)Top, for information on standard conformance and compatibility of the Ada compiler. *Note Standards: (gfortran)Standards, for details of standards supported by GNU Fortran. *Note Compatibility with the Java Platform: (gcj)Compatibility, for details of compatibility between `gcj' and the Java Platform.  File: gcc.info, Node: Invoking GCC, Next: C Implementation, Prev: Standards, Up: Top 3 GCC Command Options ********************* 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 `-c' option says not to run the linker. Then the output consists of object files output by the assembler. Other options are passed on to one stage of processing. Some options control the preprocessor and others the compiler itself. Yet other options control the assembler and linker; most of these are not documented here, since you rarely need to use any of them. 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. *Note Compiling C++ Programs: Invoking G++, for a summary of special options for compiling C++ programs. The `gcc' program accepts options and file names as operands. Many options have multi-letter names; therefore multiple single-letter options may _not_ be grouped: `-dr' is very different from `-d -r'. 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 `-L' more than once, the directories are searched in the order specified. Also, the placement of the `-l' option is significant. Many options have long names starting with `-f' or with `-W'--for example, `-fmove-loop-invariants', `-Wformat' and so on. Most of these have both positive and negative forms; the negative form of `-ffoo' would be `-fno-foo'. This manual documents only one of these two forms, whichever one is not the default. *Note 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++. * Language Independent Options:: Controlling how diagnostics should be formatted. * Warning Options:: How picky should the compiler be? * Debugging Options:: Symbol tables, measurements, and debugging dumps. * Optimize Options:: How much optimization? * 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. * Spec Files:: How to pass switches to sub-processes. * Target Options:: Running a cross-compiler, or an old version of GCC. * Submodel Options:: Specifying minor hardware or convention variations, such as 68010 vs 68020. * Code Gen Options:: Specifying conventions for function calls, data layout and register usage. * Environment Variables:: Env vars that affect GCC. * Precompiled Headers:: Compiling a header once, and using it many times. * Running Protoize:: Automatically adding or removing function prototypes.  File: gcc.info, Node: Option Summary, Next: Overall Options, Up: Invoking GCC 3.1 Option Summary ================== Here is a summary of all the options, grouped by type. Explanations are in the following sections. _Overall Options_ *Note Options Controlling the Kind of Output: Overall Options. -c -S -E -o FILE -combine -pipe -pass-exit-codes -x LANGUAGE -v -### --help[=CLASS] --target-help --version @FILE _C Language Options_ *Note Options Controlling C Dialect: C Dialect Options. -ansi -std=STANDARD -fgnu89-inline -aux-info FILENAME -fno-asm -fno-builtin -fno-builtin-FUNCTION -fhosted -ffreestanding -fopenmp -fms-extensions -trigraphs -no-integrated-cpp -traditional -traditional-cpp -fallow-single-precision -fcond-mismatch -flax-vector-conversions -fsigned-bitfields -fsigned-char -funsigned-bitfields -funsigned-char _C++ Language Options_ *Note Options Controlling C++ Dialect: C++ Dialect Options. -fabi-version=N -fno-access-control -fcheck-new -fconserve-space -ffriend-injection -fno-elide-constructors -fno-enforce-eh-specs -ffor-scope -fno-for-scope -fno-gnu-keywords -fno-implicit-templates -fno-implicit-inline-templates -fno-implement-inlines -fms-extensions -fno-nonansi-builtins -fno-operator-names -fno-optional-diags -fpermissive -frepo -fno-rtti -fstats -ftemplate-depth-N -fno-threadsafe-statics -fuse-cxa-atexit -fno-weak -nostdinc++ -fno-default-inline -fvisibility-inlines-hidden -fvisibility-ms-compat -Wabi -Wctor-dtor-privacy -Wnon-virtual-dtor -Wreorder -Weffc++ -Wno-deprecated -Wstrict-null-sentinel -Wno-non-template-friend -Wold-style-cast -Woverloaded-virtual -Wno-pmf-conversions -Wsign-promo _Objective-C and Objective-C++ Language Options_ *Note Options Controlling Objective-C and Objective-C++ Dialects: Objective-C and Objective-C++ Dialect Options. -fconstant-string-class=CLASS-NAME -fgnu-runtime -fnext-runtime -fno-nil-receivers -fobjc-call-cxx-cdtors -fobjc-direct-dispatch -fobjc-exceptions -fobjc-gc -freplace-objc-classes -fzero-link -gen-decls -Wassign-intercept -Wno-protocol -Wselector -Wstrict-selector-match -Wundeclared-selector _Language Independent Options_ *Note Options to Control Diagnostic Messages Formatting: Language Independent Options. -fmessage-length=N -fdiagnostics-show-location=[once|every-line] -fdiagnostics-show-option _Warning Options_ *Note Options to Request or Suppress Warnings: Warning Options. -fsyntax-only -pedantic -pedantic-errors -w -Wextra -Wall -Waddress -Waggregate-return -Warray-bounds -Wno-attributes -Wc++-compat -Wc++0x-compat -Wcast-align -Wcast-qual -Wchar-subscripts -Wclobbered -Wcomment -Wconversion -Wcoverage-mismatch -Wno-deprecated-declarations -Wdisabled-optimization -Wno-div-by-zero -Wempty-body -Wno-endif-labels -Werror -Werror=* -Wfatal-errors -Wfloat-equal -Wformat -Wformat=2 -Wno-format-extra-args -Wformat-nonliteral -Wformat-security -Wformat-y2k -Wignored-qualifiers -Wimplicit -Wimplicit-function-declaration -Wimplicit-int -Wimport -Wno-import -Winit-self -Winline -Wno-int-to-pointer-cast -Wno-invalid-offsetof -Winvalid-pch -Wlarger-than-LEN -Wunsafe-loop-optimizations -Wlogical-op -Wlong-long -Wmain -Wmissing-braces -Wmissing-field-initializers -Wmissing-format-attribute -Wmissing-include-dirs -Wmissing-noreturn -Wno-multichar -Wnonnull -Wno-overflow -Woverlength-strings -Wpacked -Wpadded -Wparentheses -Wpointer-arith -Wno-pointer-to-int-cast -Wredundant-decls -Wreturn-type -Wsequence-point -Wshadow -Wsign-compare -Wsign-conversion -Wstack-protector -Wstrict-aliasing -Wstrict-aliasing=n -Wstrict-overflow -Wstrict-overflow=N -Wswitch -Wswitch-default -Wswitch-enum -Wsystem-headers -Wtrigraphs -Wtype-limits -Wundef -Wuninitialized -Wunknown-pragmas -Wno-pragmas -Wunreachable-code -Wunused -Wunused-function -Wunused-label -Wunused-parameter -Wunused-value -Wunused-variable -Wvariadic-macros -Wvla -Wvolatile-register-var -Wwrite-strings _C and Objective-C-only Warning Options_ -Wbad-function-cast -Wmissing-declarations -Wmissing-parameter-type -Wmissing-prototypes -Wnested-externs -Wold-style-declaration -Wold-style-definition -Wstrict-prototypes -Wtraditional -Wtraditional-conversion -Wdeclaration-after-statement -Wpointer-sign _Debugging Options_ *Note Options for Debugging Your Program or GCC: Debugging Options. -dLETTERS -dumpspecs -dumpmachine -dumpversion -fdbg-cnt-list -fdbg-cnt=COUNTER-VALUE-LIST -fdump-noaddr -fdump-unnumbered -fdump-translation-unit[-N] -fdump-class-hierarchy[-N] -fdump-ipa-all -fdump-ipa-cgraph -fdump-ipa-inline -fdump-tree-all -fdump-tree-original[-N] -fdump-tree-optimized[-N] -fdump-tree-cfg -fdump-tree-vcg -fdump-tree-alias -fdump-tree-ch -fdump-tree-ssa[-N] -fdump-tree-pre[-N] -fdump-tree-ccp[-N] -fdump-tree-dce[-N] -fdump-tree-gimple[-raw] -fdump-tree-mudflap[-N] -fdump-tree-dom[-N] -fdump-tree-dse[-N] -fdump-tree-phiopt[-N] -fdump-tree-forwprop[-N] -fdump-tree-copyrename[-N] -fdump-tree-nrv -fdump-tree-vect -fdump-tree-sink -fdump-tree-sra[-N] -fdump-tree-salias -fdump-tree-fre[-N] -fdump-tree-vrp[-N] -ftree-vectorizer-verbose=N -fdump-tree-storeccp[-N] -feliminate-dwarf2-dups -feliminate-unused-debug-types -feliminate-unused-debug-symbols -femit-class-debug-always -fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report -fprofile-arcs -frandom-seed=STRING -fsched-verbose=N -ftest-coverage -ftime-report -fvar-tracking -g -gLEVEL -gcoff -gdwarf-2 -ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ -fno-merge-debug-strings -fdebug-prefix-map=OLD=NEW -femit-struct-debug-baseonly -femit-struct-debug-reduced -femit-struct-debug-detailed[=SPEC-LIST] -p -pg -print-file-name=LIBRARY -print-libgcc-file-name -print-multi-directory -print-multi-lib -print-prog-name=PROGRAM -print-search-dirs -Q -print-sysroot-headers-suffix -save-temps -time _Optimization Options_ *Note Options that Control Optimization: Optimize Options. -falign-functions[=N] -falign-jumps[=N] -falign-labels[=N] -falign-loops[=N] -fassociative-math -fauto-inc-dec -fbranch-probabilities -fbranch-target-load-optimize -fbranch-target-load-optimize2 -fbtr-bb-exclusive -fcaller-saves -fcheck-data-deps -fcprop-registers -fcrossjumping -fcse-follow-jumps -fcse-skip-blocks -fcx-limited-range -fdata-sections -fdce -fdce -fdelayed-branch -fdelete-null-pointer-checks -fdse -fdse -fearly-inlining -fexpensive-optimizations -ffast-math -ffinite-math-only -ffloat-store -fforward-propagate -ffunction-sections -fgcse -fgcse-after-reload -fgcse-las -fgcse-lm -fgcse-sm -fif-conversion -fif-conversion2 -finline-functions -finline-functions-called-once -finline-limit=N -finline-small-functions -fipa-cp -fipa-marix-reorg -fipa-pta -fipa-pure-const -fipa-reference -fipa-struct-reorg -fipa-type-escape -fivopts -fkeep-inline-functions -fkeep-static-consts -fmerge-all-constants -fmerge-constants -fmodulo-sched -fmodulo-sched-allow-regmoves -fmove-loop-invariants -fmudflap -fmudflapir -fmudflapth -fno-branch-count-reg -fno-default-inline -fno-defer-pop -fno-function-cse -fno-guess-branch-probability -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 -fno-sched-interblock -fno-sched-spec -fno-signed-zeros -fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss -fomit-frame-pointer -foptimize-register-move -foptimize-sibling-calls -fpeel-loops -fpredictive-commoning -fprefetch-loop-arrays -fprofile-generate -fprofile-use -fprofile-values -freciprocal-math -fregmove -frename-registers -freorder-blocks -freorder-blocks-and-partition -freorder-functions -frerun-cse-after-loop -freschedule-modulo-scheduled-loops -frounding-math -frtl-abstract-sequences -fsched2-use-superblocks -fsched2-use-traces -fsched-spec-load -fsched-spec-load-dangerous -fsched-stalled-insns-dep[=N] -fsched-stalled-insns[=N] -fschedule-insns -fschedule-insns2 -fsection-anchors -fsee -fsignaling-nans -fsingle-precision-constant -fsplit-ivs-in-unroller -fsplit-wide-types -fstack-protector -fstack-protector-all -fstrict-aliasing -fstrict-overflow -fthread-jumps -ftracer -ftree-ccp -ftree-ch -ftree-copy-prop -ftree-copyrename -ftree-dce -ftree-dominator-opts -ftree-dse -ftree-fre -ftree-loop-im -ftree-loop-ivcanon -ftree-loop-linear -ftree-loop-optimize -ftree-parallelize-loops=N -ftree-pre -ftree-reassoc -ftree-salias -ftree-sink -ftree-sra -ftree-store-ccp -ftree-ter -ftree-vect-loop-version -ftree-vectorize -ftree-vrp -funit-at-a-time -funroll-all-loops -funroll-loops -funsafe-loop-optimizations -funsafe-math-optimizations -funswitch-loops -fvariable-expansion-in-unroller -fvect-cost-model -fvpt -fweb -fwhole-program --param NAME=VALUE -O -O0 -O1 -O2 -O3 -Os _Preprocessor Options_ *Note Options Controlling the Preprocessor: Preprocessor Options. -AQUESTION=ANSWER -A-QUESTION[=ANSWER] -C -dD -dI -dM -dN -DMACRO[=DEFN] -E -H -idirafter DIR -include FILE -imacros FILE -iprefix FILE -iwithprefix DIR -iwithprefixbefore DIR -isystem DIR -imultilib DIR -isysroot DIR -M -MM -MF -MG -MP -MQ -MT -nostdinc -P -fworking-directory -remap -trigraphs -undef -UMACRO -Wp,OPTION -Xpreprocessor OPTION _Assembler Option_ *Note Passing Options to the Assembler: Assembler Options. -Wa,OPTION -Xassembler OPTION _Linker Options_ *Note Options for Linking: Link Options. OBJECT-FILE-NAME -lLIBRARY -nostartfiles -nodefaultlibs -nostdlib -pie -rdynamic -s -static -static-libgcc -shared -shared-libgcc -symbolic -Wl,OPTION -Xlinker OPTION -u SYMBOL _Directory Options_ *Note Options for Directory Search: Directory Options. -BPREFIX -IDIR -iquoteDIR -LDIR -specs=FILE -I- --sysroot=DIR _Target Options_ *Note Target Options::. -V VERSION -b MACHINE _Machine Dependent Options_ *Note Hardware Models and Configurations: Submodel Options. _ARC Options_ -EB -EL -mmangle-cpu -mcpu=CPU -mtext=TEXT-SECTION -mdata=DATA-SECTION -mrodata=READONLY-DATA-SECTION _ARM Options_ -mapcs-frame -mno-apcs-frame -mabi=NAME -mapcs-stack-check -mno-apcs-stack-check -mapcs-float -mno-apcs-float -mapcs-reentrant -mno-apcs-reentrant -msched-prolog -mno-sched-prolog -mlittle-endian -mbig-endian -mwords-little-endian -mfloat-abi=NAME -msoft-float -mhard-float -mfpe -mthumb-interwork -mno-thumb-interwork -mcpu=NAME -march=NAME -mfpu=NAME -mstructure-size-boundary=N -mabort-on-noreturn -mlong-calls -mno-long-calls -msingle-pic-base -mno-single-pic-base -mpic-register=REG -mnop-fun-dllimport -mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns -mpoke-function-name -mthumb -marm -mtpcs-frame -mtpcs-leaf-frame -mcaller-super-interworking -mcallee-super-interworking -mtp=NAME _AVR Options_ -mmcu=MCU -msize -minit-stack=N -mno-interrupts -mcall-prologues -mno-tablejump -mtiny-stack -mint8 _Blackfin Options_ -mcpu=CPU[-SIREVISION] -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=N -mleaf-id-shared-library -mno-leaf-id-shared-library -msep-data -mno-sep-data -mlong-calls -mno-long-calls -mfast-fp -minline-plt _CRIS Options_ -mcpu=CPU -march=CPU -mtune=CPU -mmax-stack-frame=N -melinux-stacksize=N -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects -mstack-align -mdata-align -mconst-align -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt -melf -maout -melinux -mlinux -sim -sim2 -mmul-bug-workaround -mno-mul-bug-workaround _CRX Options_ -mmac -mpush-args _Darwin Options_ -all_load -allowable_client -arch -arch_errors_fatal -arch_only -bind_at_load -bundle -bundle_loader -client_name -compatibility_version -current_version -dead_strip -dependency-file -dylib_file -dylinker_install_name -dynamic -dynamiclib -exported_symbols_list -filelist -flat_namespace -force_cpusubtype_ALL -force_flat_namespace -headerpad_max_install_names -iframework -image_base -init -install_name -keep_private_externs -multi_module -multiply_defined -multiply_defined_unused -noall_load -no_dead_strip_inits_and_terms -nofixprebinding -nomultidefs -noprebind -noseglinkedit -pagezero_size -prebind -prebind_all_twolevel_modules -private_bundle -read_only_relocs -sectalign -sectobjectsymbols -whyload -seg1addr -sectcreate -sectobjectsymbols -sectorder -segaddr -segs_read_only_addr -segs_read_write_addr -seg_addr_table -seg_addr_table_filename -seglinkedit -segprot -segs_read_only_addr -segs_read_write_addr -single_module -static -sub_library -sub_umbrella -twolevel_namespace -umbrella -undefined -unexported_symbols_list -weak_reference_mismatches -whatsloaded -F -gused -gfull -mmacosx-version-min=VERSION -mkernel -mone-byte-bool _DEC Alpha Options_ -mno-fp-regs -msoft-float -malpha-as -mgas -mieee -mieee-with-inexact -mieee-conformant -mfp-trap-mode=MODE -mfp-rounding-mode=MODE -mtrap-precision=MODE -mbuild-constants -mcpu=CPU-TYPE -mtune=CPU-TYPE -mbwx -mmax -mfix -mcix -mfloat-vax -mfloat-ieee -mexplicit-relocs -msmall-data -mlarge-data -msmall-text -mlarge-text -mmemory-latency=TIME _DEC Alpha/VMS Options_ -mvms-return-codes _FRV Options_ -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=CPU _GNU/Linux Options_ -muclibc _H8/300 Options_ -mrelax -mh -ms -mn -mint32 -malign-300 _HPPA Options_ -march=ARCHITECTURE-TYPE -mbig-switch -mdisable-fpregs -mdisable-indexing -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld -mfixed-range=REGISTER-RANGE -mjump-in-delay -mlinker-opt -mlong-calls -mlong-load-store -mno-big-switch -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=CPU-TYPE -mspace-regs -msio -mwsio -munix=UNIX-STD -nolibdld -static -threads _i386 and x86-64 Options_ -mtune=CPU-TYPE -march=CPU-TYPE -mfpmath=UNIT -masm=DIALECT -mno-fancy-math-387 -mno-fp-ret-in-387 -msoft-float -mno-wide-multiply -mrtd -malign-double -mpreferred-stack-boundary=NUM -mcld -mcx16 -msahf -mrecip -mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 -msse4a -m3dnow -mpopcnt -mabm -msse5 -mthreads -mno-align-stringops -minline-all-stringops -mpush-args -maccumulate-outgoing-args -m128bit-long-double -m96bit-long-double -mregparm=NUM -msseregparm -mveclibabi=TYPE -mpc32 -mpc64 -mpc80 -mstackrealign -momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs -mcmodel=CODE-MODEL -m32 -m64 -mlarge-data-threshold=NUM -mfused-madd -mno-fused-madd _IA-64 Options_ -mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic -mvolatile-asm-stop -mregister-names -mno-sdata -mconstant-gp -mauto-pic -minline-float-divide-min-latency -minline-float-divide-max-throughput -minline-int-divide-min-latency -minline-int-divide-max-throughput -minline-sqrt-min-latency -minline-sqrt-max-throughput -mno-dwarf2-asm -mearly-stop-bits -mfixed-range=REGISTER-RANGE -mtls-size=TLS-SIZE -mtune=CPU-TYPE -mt -pthread -milp32 -mlp64 -mno-sched-br-data-spec -msched-ar-data-spec -mno-sched-control-spec -msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec -msched-ldc -mno-sched-control-ldc -mno-sched-spec-verbose -mno-sched-prefer-non-data-spec-insns -mno-sched-prefer-non-control-spec-insns -mno-sched-count-spec-in-critical-path _M32R/D Options_ -m32r2 -m32rx -m32r -mdebug -malign-loops -mno-align-loops -missue-rate=NUMBER -mbranch-cost=NUMBER -mmodel=CODE-SIZE-MODEL-TYPE -msdata=SDATA-TYPE -mno-flush-func -mflush-func=NAME -mno-flush-trap -mflush-trap=NUMBER -G NUM _M32C Options_ -mcpu=CPU -msim -memregs=NUMBER _M680x0 Options_ -march=ARCH -mcpu=CPU -mtune=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 _M68hc1x Options_ -m6811 -m6812 -m68hc11 -m68hc12 -m68hcs12 -mauto-incdec -minmax -mlong-calls -mshort -msoft-reg-count=COUNT _MCore Options_ -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 _MIPS Options_ -EL -EB -march=ARCH -mtune=ARCH -mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips64 -mips16 -mno-mips16 -mflip-mips16 -minterlink-mips16 -mno-interlink-mips16 -mabi=ABI -mabicalls -mno-abicalls -mshared -mno-shared -mxgot -mno-xgot -mgp32 -mgp64 -mfp32 -mfp64 -mhard-float -msoft-float -msingle-float -mdouble-float -mdsp -mno-dsp -mdspr2 -mno-dspr2 -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 -GNUM -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=SETTING -msplit-addresses -mno-split-addresses -mexplicit-relocs -mno-explicit-relocs -mcheck-zero-division -mno-check-zero-division -mdivide-traps -mdivide-breaks -mmemcpy -mno-memcpy -mlong-calls -mno-long-calls -mmad -mno-mad -mfused-madd -mno-fused-madd -nocpp -mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 -mfix-vr4120 -mno-fix-vr4120 -mfix-vr4130 -mno-fix-vr4130 -mfix-sb1 -mno-fix-sb1 -mflush-func=FUNC -mno-flush-func -mbranch-cost=NUM -mbranch-likely -mno-branch-likely -mfp-exceptions -mno-fp-exceptions -mvr4130-align -mno-vr4130-align _MMIX Options_ -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 _MN10300 Options_ -mmult-bug -mno-mult-bug -mam33 -mno-am33 -mam33-2 -mno-am33-2 -mreturn-pointer-on-d0 -mno-crt0 -mrelax _MT Options_ -mno-crt0 -mbacc -msim -march=CPU-TYPE _PDP-11 Options_ -mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 -mbcopy -mbcopy-builtin -mint32 -mno-int16 -mint16 -mno-int32 -mfloat32 -mno-float64 -mfloat64 -mno-float32 -mabshi -mno-abshi -mbranch-expensive -mbranch-cheap -msplit -mno-split -munix-asm -mdec-asm _PowerPC Options_ See RS/6000 and PowerPC Options. _RS/6000 and PowerPC Options_ -mcpu=CPU-TYPE -mtune=CPU-TYPE -mpower -mno-power -mpower2 -mno-power2 -mpowerpc -mpowerpc64 -mno-powerpc -maltivec -mno-altivec -mpowerpc-gpopt -mno-powerpc-gpopt -mpowerpc-gfxopt -mno-powerpc-gfxopt -mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mfprnd -mno-fprnd -mcmpb -mno-cmpb -mmfpgpr -mno-mfpgpr -mhard-dfp -mno-hard-dfp -mnew-mnemonics -mold-mnemonics -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 -mstring -mno-string -mupdate -mno-update -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align -mstrict-align -mno-strict-align -mrelocatable -mno-relocatable -mrelocatable-lib -mno-relocatable-lib -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian -mdynamic-no-pic -maltivec -mswdiv -mprioritize-restricted-insns=PRIORITY -msched-costly-dep=DEPENDENCE_TYPE -minsert-sched-nops=SCHEME -mcall-sysv -mcall-netbsd -maix-struct-return -msvr4-struct-return -mabi=ABI-TYPE -msecure-plt -mbss-plt -misel -mno-isel -misel=yes -misel=no -mspe -mno-spe -mspe=yes -mspe=no -mpaired -mvrsave -mno-vrsave -mmulhw -mno-mulhw -mdlmzb -mno-dlmzb -mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double -mprototype -mno-prototype -msim -mmvme -mads -myellowknife -memb -msdata -msdata=OPT -mvxworks -mwindiss -G NUM -pthread _S/390 and zSeries Options_ -mtune=CPU-TYPE -march=CPU-TYPE -mhard-float -msoft-float -mlong-double-64 -mlong-double-128 -mbackchain -mno-backchain -mpacked-stack -mno-packed-stack -msmall-exec -mno-small-exec -mmvcle -mno-mvcle -m64 -m31 -mdebug -mno-debug -mesa -mzarch -mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd -mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard _Score Options_ -meb -mel -mnhwloop -muls -mmac -mscore5 -mscore5u -mscore7 -mscore7d _SH Options_ -m1 -m2 -m2e -m3 -m3e -m4-nofpu -m4-single-only -m4-single -m4 -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al -m5-64media -m5-64media-nofpu -m5-32media -m5-32media-nofpu -m5-compact -m5-compact-nofpu -mb -ml -mdalign -mrelax -mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave -mieee -misize -minline-ic_invalidate -mpadstruct -mspace -mprefergot -musermode -multcost=NUMBER -mdiv=STRATEGY -mdivsi3_libfunc=NAME -madjust-unroll -mindexed-addressing -mgettrcost=NUMBER -mpt-fixed -minvalid-symbols _SPARC Options_ -mcpu=CPU-TYPE -mtune=CPU-TYPE -mcmodel=CODE-MODEL -m32 -m64 -mapp-regs -mno-app-regs -mfaster-structs -mno-faster-structs -mfpu -mno-fpu -mhard-float -msoft-float -mhard-quad-float -msoft-quad-float -mimpure-text -mno-impure-text -mlittle-endian -mstack-bias -mno-stack-bias -munaligned-doubles -mno-unaligned-doubles -mv8plus -mno-v8plus -mvis -mno-vis -threads -pthreads -pthread _SPU Options_ -mwarn-reloc -merror-reloc -msafe-dma -munsafe-dma -mbranch-hints -msmall-mem -mlarge-mem -mstdmain -mfixed-range=REGISTER-RANGE _System V Options_ -Qy -Qn -YP,PATHS -Ym,DIR _V850 Options_ -mlong-calls -mno-long-calls -mep -mno-ep -mprolog-function -mno-prolog-function -mspace -mtda=N -msda=N -mzda=N -mapp-regs -mno-app-regs -mdisable-callt -mno-disable-callt -mv850e1 -mv850e -mv850 -mbig-switch _VAX Options_ -mg -mgnu -munix _VxWorks Options_ -mrtp -non-static -Bstatic -Bdynamic -Xbind-lazy -Xbind-now _x86-64 Options_ See i386 and x86-64 Options. _Xstormy16 Options_ -msim _Xtensa Options_ -mconst16 -mno-const16 -mfused-madd -mno-fused-madd -mtext-section-literals -mno-text-section-literals -mtarget-align -mno-target-align -mlongcalls -mno-longcalls _zSeries Options_ See S/390 and zSeries Options. _Code Generation Options_ *Note Options for Code Generation Conventions: Code Gen Options. -fcall-saved-REG -fcall-used-REG -ffixed-REG -fexceptions -fnon-call-exceptions -funwind-tables -fasynchronous-unwind-tables -finhibit-size-directive -finstrument-functions -finstrument-functions-exclude-function-list=SYM,SYM,... -finstrument-functions-exclude-file-list=FILE,FILE,... -fno-common -fno-ident -fpcc-struct-return -fpic -fPIC -fpie -fPIE -fno-jump-tables -frecord-gcc-switches -freg-struct-return -fshort-enums -fshort-double -fshort-wchar -fverbose-asm -fpack-struct[=N] -fstack-check -fstack-limit-register=REG -fstack-limit-symbol=SYM -fno-stack-limit -fargument-alias -fargument-noalias -fargument-noalias-global -fargument-noalias-anything -fleading-underscore -ftls-model=MODEL -ftrapv -fwrapv -fbounds-check -fvisibility * Menu: * Overall Options:: Controlling the kind of output: an executable, object files, assembler files, or preprocessed source. * 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++. * Language Independent Options:: Controlling how diagnostics should be formatted. * Warning Options:: How picky should the compiler be? * Debugging Options:: Symbol tables, measurements, and debugging dumps. * Optimize Options:: How much optimization? * 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. * Spec Files:: How to pass switches to sub-processes. * Target Options:: Running a cross-compiler, or an old version of GCC.  File: gcc.info, Node: Overall Options, Next: Invoking G++, Prev: Option Summary, Up: Invoking GCC 3.2 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. For any given input file, the file name suffix determines what kind of compilation is done: `FILE.c' C source code which must be preprocessed. `FILE.i' C source code which should not be preprocessed. `FILE.ii' C++ source code which should not be preprocessed. `FILE.m' Objective-C source code. Note that you must link with the `libobjc' library to make an Objective-C program work. `FILE.mi' Objective-C source code which should not be preprocessed. `FILE.mm' `FILE.M' Objective-C++ source code. Note that you must link with the `libobjc' library to make an Objective-C++ program work. Note that `.M' refers to a literal capital M. `FILE.mii' Objective-C++ source code which should not be preprocessed. `FILE.h' C, C++, Objective-C or Objective-C++ header file to be turned into a precompiled header. `FILE.cc' `FILE.cp' `FILE.cxx' `FILE.cpp' `FILE.CPP' `FILE.c++' `FILE.C' C++ source code which must be preprocessed. Note that in `.cxx', the last two letters must both be literally `x'. Likewise, `.C' refers to a literal capital C. `FILE.mm' `FILE.M' Objective-C++ source code which must be preprocessed. `FILE.mii' Objective-C++ source code which should not be preprocessed. `FILE.hh' `FILE.H' `FILE.hp' `FILE.hxx' `FILE.hpp' `FILE.HPP' `FILE.h++' `FILE.tcc' C++ header file to be turned into a precompiled header. `FILE.f' `FILE.for' `FILE.FOR' Fixed form Fortran source code which should not be preprocessed. `FILE.F' `FILE.fpp' `FILE.FPP' Fixed form Fortran source code which must be preprocessed (with the traditional preprocessor). `FILE.f90' `FILE.f95' Free form Fortran source code which should not be preprocessed. `FILE.F90' `FILE.F95' Free form Fortran source code which must be preprocessed (with the traditional preprocessor). `FILE.ads' Ada source code file which 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 "specs". `FILE.adb' Ada source code file containing a library unit body (a subprogram or package body). Such files are also called "bodies". `FILE.s' Assembler code. `FILE.S' `FILE.sx' Assembler code which must be preprocessed. `OTHER' An object file to be fed straight into linking. Any file name with no recognized suffix is treated this way. You can specify the input language explicitly with the `-x' option: `-x LANGUAGE' Specify explicitly the 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 `-x' option. Possible values for LANGUAGE are: c c-header c-cpp-output c++ c++-header c++-cpp-output objective-c objective-c-header objective-c-cpp-output objective-c++ objective-c++-header objective-c++-cpp-output assembler assembler-with-cpp ada f95 f95-cpp-input java treelang `-x none' Turn off any specification of a language, so that subsequent files are handled according to their file name suffixes (as they are if `-x' has not been used at all). `-pass-exit-codes' Normally the `gcc' program will exit with the code of 1 if any phase of the compiler returns a non-success return code. If you specify `-pass-exit-codes', the `gcc' program will instead return with numerically highest error produced by any phase that returned an error indication. The C, C++, and Fortran frontends return 4, if an internal compiler error is encountered. If you only want some of the stages of compilation, you can use `-x' (or filename suffixes) to tell `gcc' where to start, and one of the options `-c', `-S', or `-E' to say where `gcc' is to stop. Note that some combinations (for example, `-x cpp-output -E') instruct `gcc' to do nothing at all. `-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 `.c', `.i', `.s', etc., with `.o'. Unrecognized input files, not requiring compilation or assembly, are ignored. `-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 `.c', `.i', etc., with `.s'. Input files that don't require compilation are ignored. `-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 which don't require preprocessing are ignored. `-o FILE' Place output in file FILE. This applies regardless 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 `-o' is not specified, the default is to put an executable file in `a.out', the object file for `SOURCE.SUFFIX' in `SOURCE.o', its assembler file in `SOURCE.s', a precompiled header file in `SOURCE.SUFFIX.gch', and all preprocessed C source on standard output. `-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. `-###' Like `-v' except the commands are not executed and all command arguments are quoted. This is useful for shell scripts to capture the driver-generated command lines. `-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. `-combine' If you are compiling multiple source files, this option tells the driver to pass all the source files to the compiler at once (for those languages for which the compiler can handle this). This will allow intermodule analysis (IMA) to be performed by the compiler. Currently the only language for which this is supported is C. If you pass source files for multiple languages to the driver, using this option, the driver will invoke the compiler(s) that support IMA once each, passing each compiler all the source files appropriate for it. For those languages that do not support IMA this option will be ignored, and the compiler will be invoked once for each source file in that language. If you use this option in conjunction with `-save-temps', the compiler will generate multiple pre-processed files (one for each source file), but only one (combined) `.o' or `.s' file. `--help' Print (on the standard output) a description of the command line options understood by `gcc'. If the `-v' option is also specified then `--help' will also be passed on to the various processes invoked by `gcc', so that they can display the command line options they accept. If the `-Wextra' option has also been specified (prior to the `--help' option), then command line options which have no documentation associated with them will also be displayed. `--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. `--help=CLASS[,QUALIFIER]' Print (on the standard output) a description of the command line options understood by the compiler that fit into a specific class. The class can be one of `optimizers', `warnings', `target', `params', or LANGUAGE: `optimizers' This will display all of the optimization options supported by the compiler. `warnings' This will display all of the options controlling warning messages produced by the compiler. `target' This will display target-specific options. Unlike the `--target-help' option however, target-specific options of the linker and assembler will not be displayed. This is because those tools do not currently support the extended `--help=' syntax. `params' This will display the values recognized by the `--param' option. LANGUAGE This will display the options supported for LANGUAGE, where LANGUAGE is the name of one of the languages supported in this version of GCC. `common' This will display the options that are common to all languages. It is possible to further refine the output of the `--help=' option by adding a comma separated list of qualifiers after the class. These can be any from the following list: `undocumented' Display only those options which are undocumented. `joined' Display options which take an argument that appears after an equal sign in the same continuous piece of text, such as: `--help=target'. `separate' Display options which take an argument that appears as a separate word following the original option, such as: `-o output-file'. Thus for example to display all the undocumented target-specific switches supported by the compiler the following can be used: --help=target,undocumented The sense of a qualifier can be inverted by prefixing it with the ^ 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), which have a description the following can be used: --help=warnings,^joined,^undocumented A class can also be used as a qualifier, although this usually restricts the output by so much that there is nothing to display. One case where it does work however is when one of the classes is TARGET. So for example to display all the target-specific optimization options the following can be used: --help=target,optimizers The `--help=' option can be repeated on the command line. Each successive use will display its requested class of options, skipping those that have already been displayed. If the `-Q' option appears on the command line before the `--help=' option, then the descriptive text displayed by `--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 `--help=' option is used). Here is a truncated example from the ARM port of `gcc': % gcc -Q -mabi=2 --help=target -c The following options are target specific: -mabi= 2 -mabort-on-noreturn [disabled] -mapcs [disabled] 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 `-O2' by using: -O2 --help=optimizers Alternatively you can discover which binary optimizations are enabled by `-O3' by using: 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 `--version' Display the version number and copyrights of the invoked GCC. `@FILE' Read command-line options from FILE. The options read are inserted in place of the original @FILE option. If FILE does not exist, or cannot be read, then the option will be treated literally, and not removed. Options in FILE are separated by whitespace. A whitespace character may be included in an option by surrounding the entire option in either single or double quotes. Any character (including a backslash) may be included by prefixing the character to be included with a backslash. The FILE may itself contain additional @FILE options; any such options will be processed recursively.  File: gcc.info, Node: Invoking G++, Next: C Dialect Options, Prev: Overall Options, Up: Invoking GCC 3.3 Compiling C++ Programs ========================== C++ source files conventionally use one of the suffixes `.C', `.cc', `.cpp', `.CPP', `.c++', `.cp', or `.cxx'; C++ header files often use `.hh', `.hpp', `.H', or (for shared template code) `.tcc'; and preprocessed C++ files use the suffix `.ii'. GCC recognizes files with these names and compiles them as C++ programs even if you call the compiler the same way as for compiling C programs (usually with the name `gcc'). However, the use of `gcc' does not add the C++ library. `g++' is a program that calls GCC and treats `.c', `.h' and `.i' files as C++ source files instead of C source files unless `-x' is used, and automatically specifies linking against the C++ library. This program is also useful when precompiling a C header file with a `.h' extension for use in C++ compilations. On many systems, `g++' is also installed with the name `c++'. 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. *Note Options Controlling C Dialect: C Dialect Options, for explanations of options for languages related to C. *Note Options Controlling C++ Dialect: C++ Dialect Options, for explanations of options that are meaningful only for C++ programs.  File: gcc.info, Node: C Dialect Options, Next: C++ Dialect Options, Prev: Invoking G++, Up: Invoking GCC 3.4 Options Controlling C Dialect ================================= The following options control the dialect of C (or languages derived from C, such as C++, Objective-C and Objective-C++) that the compiler accepts: `-ansi' In C mode, this is equivalent to `-std=c89'. In C++ mode, it is equivalent to `-std=c++98'. This turns off certain features of GCC that are incompatible with ISO C90 (when compiling C code), or of standard C++ (when compiling C++ code), such as the `asm' and `typeof' keywords, and predefined macros such as `unix' and `vax' that identify the type of system you are using. It also enables the undesirable and rarely used ISO trigraph feature. For the C compiler, it disables recognition of C++ style `//' comments as well as the `inline' keyword. The alternate keywords `__asm__', `__extension__', `__inline__' and `__typeof__' continue to work despite `-ansi'. You would not want to use them in an ISO C program, of course, but it is useful to put them in header files that might be included in compilations done with `-ansi'. Alternate predefined macros such as `__unix__' and `__vax__' are also available, with or without `-ansi'. The `-ansi' option does not cause non-ISO programs to be rejected gratuitously. For that, `-pedantic' is required in addition to `-ansi'. *Note Warning Options::. The macro `__STRICT_ANSI__' is predefined when the `-ansi' option is used. Some header files may notice this macro and refrain from declaring certain functions or defining certain macros that the ISO standard doesn't call for; this is to avoid interfering with any programs that might use these names for other things. Functions that would normally be built in but do not have semantics defined by ISO C (such as `alloca' and `ffs') are not built-in functions when `-ansi' is used. *Note Other built-in functions provided by GCC: Other Builtins, for details of the functions affected. `-std=' Determine the language standard. *Note Language Standards Supported by GCC: Standards, 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 `c89' or `c++98', and GNU dialects of those standards, such as `gnu89' or `gnu++98'. By specifing a base standard, the compiler will accept all programs following that standard and those using GNU extensions that do not contradict it. For example, `-std=c89' turns off certain features of GCC that are incompatible with ISO C90, such as the `asm' and `typeof' keywords, but not other GNU extensions that do not have a meaning in ISO C90, such as omitting the middle term of a `?:' expression. On the other hand, by specifing a GNU dialect of a standard, all features the compiler support are enabled, even when those features change the meaning of the base standard and some strict-conforming programs may be rejected. The particular standard is used by `-pedantic' to identify which features are GNU extensions given that version of the standard. For example `-std=gnu89 -pedantic' would warn about C++ style `//' comments, while `-std=gnu99 -pedantic' would not. A value for this option must be provided; possible values are `c89' `iso9899:1990' Support all ISO C90 programs (certain GNU extensions that conflict with ISO C90 are disabled). Same as `-ansi' for C code. `iso9899:199409' ISO C90 as modified in amendment 1. `c99' `c9x' `iso9899:1999' `iso9899:199x' ISO C99. Note that this standard is not yet fully supported; see `http://gcc.gnu.org/gcc-4.3/c99status.html' for more information. The names `c9x' and `iso9899:199x' are deprecated. `gnu89' GNU dialect of ISO C90 (including some C99 features). This is the default for C code. `gnu99' `gnu9x' GNU dialect of ISO C99. When ISO C99 is fully implemented in GCC, this will become the default. The name `gnu9x' is deprecated. `c++98' The 1998 ISO C++ standard plus amendments. Same as `-ansi' for C++ code. `gnu++98' GNU dialect of `-std=c++98'. This is the default for C++ code. `c++0x' The working draft of the upcoming ISO C++0x standard. This option enables experimental features that are likely to be included in C++0x. The working draft is constantly changing, and any feature that is enabled by this flag may be removed from future versions of GCC if it is not part of the C++0x standard. `gnu++0x' GNU dialect of `-std=c++0x'. This option enables experimental features that may be removed in future versions of GCC. `-fgnu89-inline' The option `-fgnu89-inline' tells GCC to use the traditional GNU semantics for `inline' functions when in C99 mode. *Note An Inline Function is As Fast As a Macro: Inline. This option is accepted and ignored by GCC versions 4.1.3 up to but not including 4.3. In GCC versions 4.3 and later it changes the behavior of GCC in C99 mode. Using this option is roughly equivalent to adding the `gnu_inline' function attribute to all inline functions (*note Function Attributes::). The option `-fno-gnu89-inline' explicitly tells GCC to use the C99 semantics for `inline' when in C99 or gnu99 mode (i.e., it specifies the default behavior). This option was first supported in GCC 4.3. This option is not supported in C89 or gnu89 mode. The preprocessor macros `__GNUC_GNU_INLINE__' and `__GNUC_STDC_INLINE__' may be used to check which semantics are in effect for `inline' functions. *Note Common Predefined Macros: (cpp)Common Predefined Macros. `-aux-info FILENAME' Output to the given filename prototyped declarations for all functions declared and/or defined in a translation unit, including those in header files. This option is silently ignored in any language other than C. Besides declarations, the file indicates, in comments, the origin of each declaration (source file and line), whether the declaration was implicit, prototyped or unprototyped (`I', `N' for new or `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 (`C' or `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. `-fno-asm' Do not recognize `asm', `inline' or `typeof' as a keyword, so that code can use these words as identifiers. You can use the keywords `__asm__', `__inline__' and `__typeof__' instead. `-ansi' implies `-fno-asm'. In C++, this switch only affects the `typeof' keyword, since `asm' and `inline' are standard keywords. You may want to use the `-fno-gnu-keywords' flag instead, which has the same effect. In C99 mode (`-std=c99' or `-std=gnu99'), this switch only affects the `asm' and `typeof' keywords, since `inline' is a standard keyword in ISO C99. `-fno-builtin' `-fno-builtin-FUNCTION' Don't recognize built-in functions that do not begin with `__builtin_' as prefix. *Note Other built-in functions provided by GCC: Other Builtins, for details of the functions affected, including those which are not built-in functions when `-ansi' or `-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 `alloca' may become single instructions that adjust the stack directly, and calls to `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 `-Wformat' for bad calls to `printf', when `printf' is built in, and `strlen' is known not to modify global memory. With the `-fno-builtin-FUNCTION' option only the built-in function FUNCTION is disabled. FUNCTION must not begin with `__builtin_'. If a function is named this is not built-in in this version of GCC, this option is ignored. There is no corresponding `-fbuiltin-FUNCTION' option; if you wish to enable built-in functions selectively when using `-fno-builtin' or `-ffreestanding', you may define macros such as: #define abs(n) __builtin_abs ((n)) #define strcpy(d, s) __builtin_strcpy ((d), (s)) `-fhosted' Assert that compilation takes place in a hosted environment. This implies `-fbuiltin'. A hosted environment is one in which the entire standard library is available, and in which `main' has a return type of `int'. Examples are nearly everything except a kernel. This is equivalent to `-fno-freestanding'. `-ffreestanding' Assert that compilation takes place in a freestanding environment. This implies `-fno-builtin'. A freestanding environment is one in which the standard library may not exist, and program startup may not necessarily be at `main'. The most obvious example is an OS kernel. This is equivalent to `-fno-hosted'. *Note Language Standards Supported by GCC: Standards, for details of freestanding and hosted environments. `-fopenmp' Enable handling of OpenMP directives `#pragma omp' in C/C++ and `!$omp' in Fortran. When `-fopenmp' is specified, the compiler generates parallel code according to the OpenMP Application Program Interface v2.5 `http://www.openmp.org/'. This option implies `-pthread', and thus is only supported on targets that have support for `-pthread'. `-fms-extensions' Accept some non-standard constructs used in Microsoft header files. Some cases of unnamed fields in structures and unions are only accepted with this option. *Note Unnamed struct/union fields within structs/unions: Unnamed Fields, for details. `-trigraphs' Support ISO C trigraphs. The `-ansi' option (and `-std' options for strict ISO C conformance) implies `-trigraphs'. `-no-integrated-cpp' Performs a compilation in two passes: preprocessing and compiling. This option allows a user supplied "cc1", "cc1plus", or "cc1obj" via the `-B' option. The user supplied compilation step can then add in an additional preprocessing step after normal preprocessing but before compiling. The default is to use the integrated cpp (internal cpp) The semantics of this option will change if "cc1", "cc1plus", and "cc1obj" are merged. `-traditional' `-traditional-cpp' Formerly, these options caused GCC to attempt to emulate a pre-standard C compiler. They are now only supported with the `-E' switch. The preprocessor continues to support a pre-standard mode. See the GNU CPP manual for details. `-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++. `-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. `-funsigned-char' Let the type `char' be unsigned, like `unsigned char'. Each kind of machine has a default for what `char' should be. It is either like `unsigned char' by default or like `signed char' by default. Ideally, a portable program should always use `signed char' or `unsigned char' when it depends on the signedness of an object. But many programs have been written to use plain `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 `char' is always a distinct type from each of `signed char' or `unsigned char', even though its behavior is always just like one of those two. `-fsigned-char' Let the type `char' be signed, like `signed char'. Note that this is equivalent to `-fno-unsigned-char', which is the negative form of `-funsigned-char'. Likewise, the option `-fno-signed-char' is equivalent to `-funsigned-char'. `-fsigned-bitfields' `-funsigned-bitfields' `-fno-signed-bitfields' `-fno-unsigned-bitfields' These options control whether a bit-field is signed or unsigned, when the declaration does not use either `signed' or `unsigned'. By default, such a bit-field is signed, because this is consistent: the basic integer types such as `int' are signed types.  File: gcc.info, Node: C++ Dialect Options, Next: Objective-C and Objective-C++ Dialect Options, Prev: C Dialect Options, Up: Invoking GCC 3.5 Options Controlling C++ Dialect =================================== This section describes the command-line options that are only meaningful for C++ programs; but 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 `firstClass.C' like this: g++ -g -frepo -O -c firstClass.C In this example, only `-frepo' is an option meant only for C++ programs; you can use the other options with any language supported by GCC. Here is a list of options that are _only_ for compiling C++ programs: `-fabi-version=N' Use version N of the C++ ABI. Version 2 is the version of the C++ ABI that first appeared in G++ 3.4. Version 1 is the version of the C++ ABI that first appeared in G++ 3.2. Version 0 will always be the version that conforms most closely to the C++ ABI specification. Therefore, the ABI obtained using version 0 will change as ABI bugs are fixed. The default is version 2. `-fno-access-control' Turn off all access checking. This switch is mainly useful for working around bugs in the access control code. `-fcheck-new' Check that the pointer returned by `operator new' is non-null before attempting to modify the storage allocated. This check is normally unnecessary because the C++ standard specifies that `operator new' will only return `0' if it is declared `throw()', in which case the compiler will always check the return value even without this option. In all other cases, when `operator new' has a non-empty exception specification, memory exhaustion is signalled by throwing `std::bad_alloc'. See also `new (nothrow)'. `-fconserve-space' Put uninitialized or runtime-initialized global variables into the common segment, as C does. This saves space in the executable at the cost of not diagnosing duplicate definitions. If you compile with this flag and your program mysteriously crashes after `main()' has completed, you may have an object that is being destroyed twice because two definitions were merged. This option is no longer useful on most targets, now that support has been added for putting variables into BSS without making them common. `-ffriend-injection' Inject friend functions into the enclosing namespace, so that they are visible outside the scope of the class in which they are declared. Friend functions were documented to work this way in the old Annotated C++ Reference Manual, and versions of G++ before 4.1 always worked that way. However, in ISO C++ a friend function which is not declared in an enclosing scope can only be found using argument dependent lookup. This option causes friends to be injected as they were in earlier releases. This option is for compatibility, and may be removed in a future release of G++. `-fno-elide-constructors' The C++ standard allows an implementation to omit creating a temporary which 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. `-fno-enforce-eh-specs' Don't generate code to check for violation of exception specifications at runtime. This option violates the C++ standard, but may be useful for reducing code size in production builds, much like defining `NDEBUG'. This does not give user code permission to throw exceptions in violation of the exception specifications; the compiler will still optimize based on the specifications, so throwing an unexpected exception will result in undefined behavior. `-ffor-scope' `-fno-for-scope' If `-ffor-scope' is specified, the scope of variables declared in a for-init-statement is limited to the `for' loop itself, as specified by the C++ standard. If `-fno-for-scope' is specified, the scope of variables declared in a for-init-statement extends to the end of the enclosing scope, as was the case in old versions of G++, and other (traditional) implementations of C++. The default if neither flag is given to follow the standard, but to allow and give a warning for old-style code that would otherwise be invalid, or have different behavior. `-fno-gnu-keywords' Do not recognize `typeof' as a keyword, so that code can use this word as an identifier. You can use the keyword `__typeof__' instead. `-ansi' implies `-fno-gnu-keywords'. `-fno-implicit-templates' Never emit code for non-inline templates which are instantiated implicitly (i.e. by use); only emit code for explicit instantiations. *Note Template Instantiation::, for more information. `-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 will need the same set of explicit instantiations. `-fno-implement-inlines' To save space, do not emit out-of-line copies of inline functions controlled by `#pragma implementation'. This will cause linker errors if these functions are not inlined everywhere they are called. `-fms-extensions' Disable pedantic warnings about constructs used in MFC, such as implicit int and getting a pointer to member function via non-standard syntax. `-fno-nonansi-builtins' Disable built-in declarations of functions that are not mandated by ANSI/ISO C. These include `ffs', `alloca', `_exit', `index', `bzero', `conjf', and other related functions. `-fno-operator-names' Do not treat the operator name keywords `and', `bitand', `bitor', `compl', `not', `or' and `xor' as synonyms as keywords. `-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. `-fpermissive' Downgrade some diagnostics about nonconformant code from errors to warnings. Thus, using `-fpermissive' will allow some nonconforming code to compile. `-frepo' Enable automatic template instantiation at link time. This option also implies `-fno-implicit-templates'. *Note Template Instantiation::, for more information. `-fno-rtti' Disable generation of information about every class with virtual functions for use by the C++ runtime type identification features (`dynamic_cast' and `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 it will generate it as needed. The `dynamic_cast' operator can still be used for casts that do not require runtime type information, i.e. casts to `void *' or to unambiguous base classes. `-fstats' Emit statistics about front-end processing at the end of the compilation. This information is generally only useful to the G++ development team. `-ftemplate-depth-N' Set the maximum instantiation depth for template classes to 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. `-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. `-fuse-cxa-atexit' Register destructors for objects with static storage duration with the `__cxa_atexit' function rather than the `atexit' function. This option is required for fully standards-compliant handling of static destructors, but will only work if your C library supports `__cxa_atexit'. `-fno-use-cxa-get-exception-ptr' Don't use the `__cxa_get_exception_ptr' runtime routine. This will cause `std::uncaught_exception' to be incorrect, but is necessary if the runtime routine is not available. `-fvisibility-inlines-hidden' This switch declares that the user does not attempt to compare pointers to inline methods where the addresses of the two functions were taken in different shared objects. The effect of this is that GCC may, effectively, mark inline methods with `__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 will have no effect. Explicitly instantiated inline methods are unaffected by this option as their linkage might otherwise cross a shared library boundary. *Note Template Instantiation::. `-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: 1. It sets the default visibility to `hidden', like `-fvisibility=hidden'. 2. Types, but not their members, are not hidden by default. 3. The One Definition Rule is relaxed for types without explicit visibility specifications which are defined in more than one different shared object: those declarations are permitted if they would have been permitted when this option was not used. In new code it is better to use `-fvisibility=hidden' and export those classes which 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 will be different, so changing one will 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. `-fno-weak' Do not use weak symbol support, even if it is provided by the linker. By default, G++ will use weak symbols if they are available. This option exists only for testing, and should not be used by end-users; it will result in inferior code and has no benefits. This option may be removed in a future release of G++. `-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.) In addition, these optimization, warning, and code generation options have meanings only for C++ programs: `-fno-default-inline' Do not assume `inline' for functions defined inside a class scope. *Note Options That Control Optimization: Optimize Options. Note that these functions will have linkage like inline functions; they just won't be inlined by default. `-Wabi (C++ and Objective-C++ only)' Warn when G++ generates code that is probably not compatible with the vendor-neutral C++ ABI. Although an effort has been made to warn about all such cases, there are probably some cases that are not warned about, even though G++ is generating incompatible code. There may also be cases where warnings are emitted even though the code that is generated will be compatible. You should rewrite your code to avoid these warnings if you are concerned about the fact that code generated by G++ may not be binary compatible with code generated by other compilers. The known incompatibilities at this point include: * Incorrect handling of tail-padding for bit-fields. G++ may attempt to pack data into the same byte as a base class. For example: struct A { virtual void f(); int f1 : 1; }; struct B : public A { int f2 : 1; }; In this case, G++ will place `B::f2' into the same byte as`A::f1'; other compilers will not. You can avoid this problem by explicitly padding `A' so that its size is a multiple of the byte size on your platform; that will cause G++ and other compilers to layout `B' identically. * Incorrect handling of tail-padding for virtual bases. G++ does not use tail padding when laying out virtual bases. For example: struct A { virtual void f(); char c1; }; struct B { B(); char c2; }; struct C : public A, public virtual B {}; In this case, G++ will not place `B' into the tail-padding for `A'; other compilers will. You can avoid this problem by explicitly padding `A' so that its size is a multiple of its alignment (ignoring virtual base classes); that will cause G++ and other compilers to layout `C' identically. * Incorrect handling of bit-fields with declared widths greater than that of their underlying types, when the bit-fields appear in a union. For example: union U { int i : 4096; }; Assuming that an `int' does not have 4096 bits, G++ will make the union too small by the number of bits in an `int'. * Empty classes can be placed at incorrect offsets. For example: struct A {}; struct B { A a; virtual void f (); }; struct C : public B, public A {}; G++ will place the `A' base class of `C' at a nonzero offset; it should be placed at offset zero. G++ mistakenly believes that the `A' data member of `B' is already at offset zero. * Names of template functions whose types involve `typename' or template template parameters can be mangled incorrectly. template void f(typename Q::X) {} template