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This is Info file gcc.info, produced by Makeinfo version 1.68 from the input file ./gcc.texi. INFO-DIR-SECTION Programming START-INFO-DIR-ENTRY * gcc: (gcc). The GNU Compiler Collection. END-INFO-DIR-ENTRY This file documents the use and the internals of the GNU compiler. Published by the Free Software Foundation 59 Temple Place - Suite 330 Boston, MA 02111-1307 USA Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the sections entitled "GNU General Public License" and "Funding for Free Software" are included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that the sections entitled "GNU General Public License" and "Funding for Free Software", and this permission notice, may be included in translations approved by the Free Software Foundation instead of in the original English. File: gcc.info, Node: Top, Next: G++ and GCC, Up: (DIR) Introduction ************ This manual documents how to run, install and port the GNU compiler, as well as its new features and incompatibilities, and how to report bugs. It corresponds to GCC version 2.95. * Menu: * G++ and GCC:: You can compile C or C++ programs. * Invoking GCC:: Command options supported by `gcc'. * Installation:: How to configure, compile and install GCC. * C Extensions:: GNU extensions to the C language family. * C++ Extensions:: GNU extensions to the C++ language. * Gcov:: gcov: a GCC test coverage program. * Trouble:: If you have trouble installing 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. * VMS:: Using GCC on VMS. * Portability:: Goals of GCC's portability features. * Interface:: Function-call interface of GCC output. * Passes:: Order of passes, what they do, and what each file is for. * RTL:: The intermediate representation that most passes work on. * Machine Desc:: How to write machine description instruction patterns. * Target Macros:: How to write the machine description C macros. * Config:: Writing the `xm-MACHINE.h' file. * Fragments:: Writing the `t-TARGET' and `x-HOST' files. * Funding:: How to help assure funding for free software. * GNU/Linux:: Linux and the GNU Project * Copying:: GNU General Public License says how you can copy and share GCC. * Contributors:: People who have contributed to GCC. * Index:: Index of concepts and symbol names. File: gcc.info, Node: G++ and GCC, Next: Invoking GCC, Prev: Top, Up: Top Compile C, C++, Objective C, or Fortran *************************************** The C, C++, and Objective C, and Fortran versions of the compiler are integrated; this is why we use the name "GNU Compiler Collection". GCC can compile programs written in C, C++, Objective C, or Fortran. The Fortran compiler is described in a separate manual. "GCC" is a common shorthand term for the GNU Compiler Collection. This is both the most general name for the compiler, and the name used when the emphasis is on compiling C programs (as the abbreviation formerly stood for "GNU C Compiler"). When referring to C++ compilation, it is usual to call the compiler "G++". Since there is only one compiler, it is also accurate to call it "GCC" no matter what the language context; however, the term "G++" is more useful when the emphasis is on compiling C++ programs. We use the name "GCC" to refer to the compilation system as a whole, and more specifically to the language-independent part of the compiler. For example, we refer to the optimization options as affecting the behavior of "GCC" or sometimes just "the compiler". Front ends for other languages, such as Ada 9X, Fortran, Modula-3, and Pascal, are under development. These front-ends, like that for C++, are built in subdirectories of GCC and link to it. The result is an integrated compiler that can compile programs written in C, C++, Objective C, or any of the languages for which you have installed front ends. In this manual, we only discuss the options for the C, Objective-C, and C++ compilers and those of the GCC core. Consult the documentation of the other front ends for the options to use when compiling programs written in other languages. G++ is a *compiler*, not merely a preprocessor. G++ builds object code directly from your C++ program source. There is no intermediate C version of the program. (By contrast, for example, some other implementations use a program that generates a C program from your C++ source.) Avoiding an intermediate C representation of the program means that you get better object code, and better debugging information. The GNU debugger, GDB, works with this information in the object code to give you comprehensive C++ source-level editing capabilities (*note C and C++: (gdb.info)C.). File: gcc.info, Node: Invoking GCC, Next: Installation, Prev: G++ and GCC, Up: Top 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 multiletter 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. Many options have long names starting with `-f' or with `-W'--for example, `-fforce-mem', `-fstrength-reduce', `-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. * 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++. * 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. * 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. * Running Protoize:: Automatically adding or removing function prototypes. File: gcc.info, Node: Option Summary, Next: Overall Options, Up: Invoking GCC 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 -pipe -v --help -x LANGUAGE *C Language Options* *Note Options Controlling C Dialect: C Dialect Options. -ansi -fstd -fallow-single-precision -fcond-mismatch -fno-asm -fno-builtin -ffreestanding -fhosted -fsigned-bitfields -fsigned-char -funsigned-bitfields -funsigned-char -fwritable-strings -traditional -traditional-cpp -trigraphs *C++ Language Options* *Note Options Controlling C++ Dialect: C++ Dialect Options. -fno-access-control -fcheck-new -fconserve-space -fdollars-in-identifiers -fno-elide-constructors -fexternal-templates -ffor-scope -fno-for-scope -fno-gnu-keywords -fguiding-decls -fhandle-signatures -fhonor-std -fhuge-objects -fno-implicit-templates -finit-priority -fno-implement-inlines -fname-mangling-version-N -fno-default-inline -foperator-names -fno-optional-diags -fpermissive -frepo -fstrict-prototype -fsquangle -ftemplate-depth-N -fthis-is-variable -fvtable-thunks -nostdinc++ -Wctor-dtor-privacy -Wno-deprecated -Weffc++ -Wno-non-template-friend -Wnon-virtual-dtor -Wold-style-cast -Woverloaded-virtual -Wno-pmf-conversions -Wreorder -Wsign-promo -Wsynth *Warning Options* *Note Options to Request or Suppress Warnings: Warning Options. -fsyntax-only -pedantic -pedantic-errors -w -W -Wall -Waggregate-return -Wbad-function-cast -Wcast-align -Wcast-qual -Wchar-subscripts -Wcomment -Wconversion -Werror -Wformat -Wid-clash-LEN -Wimplicit -Wimplicit-int -Wimplicit-function-declaration -Wimport -Werror-implicit-function-declaration -Winline -Wlarger-than-LEN -Wlong-long -Wmain -Wmissing-declarations -Wmissing-noreturn -Wmissing-prototypes -Wmultichar -Wnested-externs -Wno-import -Wparentheses -Wpointer-arith -Wredundant-decls -Wreturn-type -Wshadow -Wsign-compare -Wstrict-prototypes -Wswitch -Wtraditional -Wtrigraphs -Wundef -Wuninitialized -Wunused -Wwrite-strings -Wunknown-pragmas *Debugging Options* *Note Options for Debugging Your Program or GCC: Debugging Options. -a -ax -dLETTERS -fdump-unnumbered -fpretend-float -fprofile-arcs -ftest-coverage -g -gLEVEL -gcoff -gdwarf -gdwarf-1 -gdwarf-1+ -gdwarf-2 -ggdb -gstabs -gstabs+ -gxcoff -gxcoff+ -p -pg -print-file-name=LIBRARY -print-libgcc-file-name -print-prog-name=PROGRAM -print-search-dirs -save-temps *Optimization Options* *Note Options that Control Optimization: Optimize Options. -fbranch-probabilities -foptimize-register-moves -fcaller-saves -fcse-follow-jumps -fcse-skip-blocks -fdelayed-branch -fexpensive-optimizations -ffast-math -ffloat-store -fforce-addr -fforce-mem -fdata-sections -ffunction-sections -fgcse -finline-functions -finline-limit-N -fkeep-inline-functions -fno-default-inline -fno-defer-pop -fno-function-cse -fno-inline -fno-peephole -fomit-frame-pointer -fregmove -frerun-cse-after-loop -frerun-loop-opt -fschedule-insns -fschedule-insns2 -fstrength-reduce -fthread-jumps -funroll-all-loops -funroll-loops -fmove-all-movables -freduce-all-givs -fstrict-aliasing -O -O0 -O1 -O2 -O3 -Os *Preprocessor Options* *Note Options Controlling the Preprocessor: Preprocessor Options. -AQUESTION(ANSWER) -C -dD -dM -dN -DMACRO[=DEFN] -E -H -idirafter DIR -include FILE -imacros FILE -iprefix FILE -iwithprefix DIR -iwithprefixbefore DIR -isystem DIR -isystem-c++ DIR -M -MD -MM -MMD -MG -nostdinc -P -trigraphs -undef -UMACRO -Wp,OPTION *Assembler Option* *Note Passing Options to the Assembler: Assembler Options. -Wa,OPTION *Linker Options* *Note Options for Linking: Link Options. OBJECT-FILE-NAME -lLIBRARY -nostartfiles -nodefaultlibs -nostdlib -s -static -shared -symbolic -Wl,OPTION -Xlinker OPTION -u SYMBOL *Directory Options* *Note Options for Directory Search: Directory Options. -BPREFIX -IDIR -I- -LDIR -specs=FILE *Target Options* *Note Target Options::. -b MACHINE -V VERSION *Machine Dependent Options* *Note Hardware Models and Configurations: Submodel Options. *M680x0 Options* -m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 -m68060 -mcpu32 -m5200 -m68881 -mbitfield -mc68000 -mc68020 -mfpa -mnobitfield -mrtd -mshort -msoft-float -malign-int *VAX Options* -mg -mgnu -munix *SPARC Options* -mcpu=CPU TYPE -mtune=CPU TYPE -mcmodel=CODE MODEL -malign-jumps=NUM -malign-loops=NUM -malign-functions=NUM -m32 -m64 -mapp-regs -mbroken-saverestore -mcypress -mepilogue -mflat -mfpu -mhard-float -mhard-quad-float -mimpure-text -mlive-g0 -mno-app-regs -mno-epilogue -mno-flat -mno-fpu -mno-impure-text -mno-stack-bias -mno-unaligned-doubles -msoft-float -msoft-quad-float -msparclite -mstack-bias -msupersparc -munaligned-doubles -mv8 *Convex Options* -mc1 -mc2 -mc32 -mc34 -mc38 -margcount -mnoargcount -mlong32 -mlong64 -mvolatile-cache -mvolatile-nocache *AMD29K Options* -m29000 -m29050 -mbw -mnbw -mdw -mndw -mlarge -mnormal -msmall -mkernel-registers -mno-reuse-arg-regs -mno-stack-check -mno-storem-bug -mreuse-arg-regs -msoft-float -mstack-check -mstorem-bug -muser-registers *ARM Options* -mapcs-frame -mno-apcs-frame -mapcs-26 -mapcs-32 -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 -mshort-load-bytes -mno-short-load-bytes -mshort-load-words -mno-short-load-words -msoft-float -mhard-float -mfpe -mthumb-interwork -mno-thumb-interwork -mcpu= -march= -mfpe= -mstructure-size-boundary= -mbsd -mxopen -mno-symrename -mabort-on-noreturn -mno-sched-prolog *Thumb Options* -mtpcs-frame -mno-tpcs-frame -mtpcs-leaf-frame -mno-tpcs-leaf-frame -mlittle-endian -mbig-endian -mthumb-interwork -mno-thumb-interwork -mstructure-size-boundary= *MN10200 Options* -mrelax *MN10300 Options* -mmult-bug -mno-mult-bug -mrelax *M32R/D Options* -mcode-model=MODEL TYPE -msdata=SDATA TYPE -G NUM *M88K Options* -m88000 -m88100 -m88110 -mbig-pic -mcheck-zero-division -mhandle-large-shift -midentify-revision -mno-check-zero-division -mno-ocs-debug-info -mno-ocs-frame-position -mno-optimize-arg-area -mno-serialize-volatile -mno-underscores -mocs-debug-info -mocs-frame-position -moptimize-arg-area -mserialize-volatile -mshort-data-NUM -msvr3 -msvr4 -mtrap-large-shift -muse-div-instruction -mversion-03.00 -mwarn-passed-structs *RS/6000 and PowerPC Options* -mcpu=CPU TYPE -mtune=CPU TYPE -mpower -mno-power -mpower2 -mno-power2 -mpowerpc -mno-powerpc -mpowerpc-gpopt -mno-powerpc-gpopt -mpowerpc-gfxopt -mno-powerpc-gfxopt -mnew-mnemonics -mno-new-mnemonics -mfull-toc -mminimal-toc -mno-fop-in-toc -mno-sum-in-toc -maix64 -maix32 -mxl-call -mno-xl-call -mthreads -mpe -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 -mcall-aix -mcall-sysv -mprototype -mno-prototype -msim -mmvme -mads -myellowknife -memb -msdata -msdata=OPT -G NUM *RT Options* -mcall-lib-mul -mfp-arg-in-fpregs -mfp-arg-in-gregs -mfull-fp-blocks -mhc-struct-return -min-line-mul -mminimum-fp-blocks -mnohc-struct-return *MIPS Options* -mabicalls -mcpu=CPU TYPE -membedded-data -membedded-pic -mfp32 -mfp64 -mgas -mgp32 -mgp64 -mgpopt -mhalf-pic -mhard-float -mint64 -mips1 -mips2 -mips3 -mips4 -mlong64 -mlong32 -mlong-calls -mmemcpy -mmips-as -mmips-tfile -mno-abicalls -mno-embedded-data -mno-embedded-pic -mno-gpopt -mno-long-calls -mno-memcpy -mno-mips-tfile -mno-rnames -mno-stats -mrnames -msoft-float -m4650 -msingle-float -mmad -mstats -EL -EB -G NUM -nocpp -mabi=32 -mabi=n32 -mabi=64 -mabi=eabi *i386 Options* -mcpu=CPU TYPE -march=CPU TYPE -mieee-fp -mno-fancy-math-387 -mno-fp-ret-in-387 -msoft-float -msvr3-shlib -mno-wide-multiply -mrtd -malign-double -mreg-alloc=LIST -mregparm=NUM -malign-jumps=NUM -malign-loops=NUM -malign-functions=NUM -mpreferred-stack-boundary=NUM *HPPA Options* -march=ARCHITECTURE TYPE -mbig-switch -mdisable-fpregs -mdisable-indexing -mfast-indirect-calls -mgas -mjump-in-delay -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 -mno-space-regs -msoft-float -mpa-risc-1-0 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime -mschedule=CPU TYPE -mspace -mspace-regs *Intel 960 Options* -mCPU TYPE -masm-compat -mclean-linkage -mcode-align -mcomplex-addr -mleaf-procedures -mic-compat -mic2.0-compat -mic3.0-compat -mintel-asm -mno-clean-linkage -mno-code-align -mno-complex-addr -mno-leaf-procedures -mno-old-align -mno-strict-align -mno-tail-call -mnumerics -mold-align -msoft-float -mstrict-align -mtail-call *DEC Alpha Options* -mfp-regs -mno-fp-regs -mno-soft-float -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 -mbwx -mno-bwx -mcix -mno-cix -mmax -mno-max -mmemory-latency=TIME *Clipper Options* -mc300 -mc400 *H8/300 Options* -mrelax -mh -ms -mint32 -malign-300 *SH Options* -m1 -m2 -m3 -m3e -mb -ml -mdalign -mrelax *System V Options* -Qy -Qn -YP,PATHS -Ym,DIR *ARC Options* -EB -EL -mmangle-cpu -mcpu=CPU -mtext=TEXT SECTION -mdata=DATA SECTION -mrodata=READONLY DATA SECTION *TMS320C3x/C4x Options* -mcpu=CPU -mbig -msmall -mregparm -mmemparm -mfast-fix -mmpyi -mbk -mti -mdp-isr-reload -mrpts=COUNT -mrptb -mdb -mloop-unsigned -mparallel-insns -mparallel-mpy -mpreserve-float *V850 Options* -mlong-calls -mno-long-calls -mep -mno-ep -mprolog-function -mno-prolog-function -mspace -mtda=N -msda=N -mzda=N -mv850 -mbig-switch *NS32K Options* -m32032 -m32332 -m32532 -m32081 -m32381 -mmult-add -mnomult-add -msoft-float -mrtd -mnortd -mregparam -mnoregparam -msb -mnosb -mbitfield -mnobitfield -mhimem -mnohimem *Code Generation Options* *Note Options for Code Generation Conventions: Code Gen Options. -fcall-saved-REG -fcall-used-REG -fexceptions -ffixed-REG -finhibit-size-directive -fcheck-memory-usage -fprefix-function-name -fno-common -fno-ident -fno-gnu-linker -fpcc-struct-return -fpic -fPIC -freg-struct-return -fshared-data -fshort-enums -fshort-double -fvolatile -fvolatile-global -fvolatile-static -fverbose-asm -fpack-struct -fstack-check -fargument-alias -fargument-noalias -fargument-noalias-global -fleading-underscore * 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++. * 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. * 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 Options Controlling the Kind of Output ====================================== Compilation can involve up to four stages: preprocessing, compilation proper, assembly and linking, always in that order. The first three stages apply to an individual source file, and end by producing an object file; 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 library `libobjc.a' to make an Objective-C program work. `FILE.h' C header file (not to be compiled or linked). `FILE.cc' `FILE.cxx' `FILE.cpp' `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.s' Assembler code. `FILE.S' 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 objective-c c++ c-header cpp-output c++-cpp-output assembler assembler-with-cpp `-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). 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. Since only one output file can be specified, it does not make sense to use `-o' when compiling more than one input file, unless you are producing an executable file as output. 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', 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. `-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. `--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 `-W' option is also specified then command line options which have no documentation associated with them will also be displayed. File: gcc.info, Node: Invoking G++, Next: C Dialect Options, Prev: Overall Options, Up: Invoking GCC Compiling C++ Programs ====================== C++ source files conventionally use one of the suffixes `.C', `.cc', `.cpp', `.c++', `.cp', or `.cxx'; 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, C++ programs often require class libraries as well as a compiler that understands the C++ language--and under some circumstances, you might want to compile programs from standard input, or otherwise without a suffix that flags them as C++ programs. `g++' is a program that calls GCC with the default language set to C++, and automatically specifies linking against the C++ library. On many systems, the script `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 Options Controlling C Dialect ============================= The following options control the dialect of C (or languages derived from C, such as C++ and Objective C) that the compiler accepts: `-ansi' In C mode, support all ANSI standard C programs. In C++ mode, remove GNU extensions that conflict with ANSI C++. This turns off certain features of GCC that are incompatible with ANSI C (when compiling C code), or of ANSI 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 ANSI trigraph feature. For the C compiler, it disables recognition of C++ style `//' comments as well as the `inline' keyword. For the C++ compiler, `-foperator-names' is enabled as well. The alternate keywords `__asm__', `__extension__', `__inline__' and `__typeof__' continue to work despite `-ansi'. You would not want to use them in an ANSI 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-ANSI 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 ANSI standard doesn't call for; this is to avoid interfering with any programs that might use these names for other things. The functions `alloca', `abort', `exit', and `_exit' are not builtin functions when `-ansi' is used. `-fstd=' Determine the language standard. A value for this option must be provided; possible values are - iso9899:1990 Same as -ansi - iso9899:199409 ISO C as modified in amend. 1 - iso9899:199x ISO C 9x - c89 same as -std=iso9899:1990 - c9x same as -std=iso9899:199x - gnu89 default, iso9899:1990 + gnu extensions - gnu9x iso9899:199x + gnu extensions Even when this option is not specified, you can still use some of the features of newer standards in so far as they do not conflict with previous C standards. For example, you may use `__restrict__' even when -fstd=c9x is not specified. `-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, as it also disables the other, C++-specific, extension keywords such as `headof'. `-fno-builtin' Don't recognize builtin functions that do not begin with `__builtin_' as prefix. Currently, the functions affected include `abort', `abs', `alloca', `cos', `exit', `fabs', `ffs', `labs', `memcmp', `memcpy', `sin', `sqrt', `strcmp', `strcpy', and `strlen'. GCC normally generates special code to handle certain builtin 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. The `-ansi' option prevents `alloca' and `ffs' from being builtin functions, since these functions do not have an ANSI standard meaning. `-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'. `-trigraphs' Support ANSI C trigraphs. You don't want to know about this brain-damage. The `-ansi' option implies `-trigraphs'. `-traditional' Attempt to support some aspects of traditional C compilers. Specifically: * All `extern' declarations take effect globally even if they are written inside of a function definition. This includes implicit declarations of functions. * The newer keywords `typeof', `inline', `signed', `const' and `volatile' are not recognized. (You can still use the alternative keywords such as `__typeof__', `__inline__', and so on.) * Comparisons between pointers and integers are always allowed. * Integer types `unsigned short' and `unsigned char' promote to `unsigned int'. * Out-of-range floating point literals are not an error. * Certain constructs which ANSI regards as a single invalid preprocessing number, such as `0xe-0xd', are treated as expressions instead. * String "constants" are not necessarily constant; they are stored in writable space, and identical looking constants are allocated separately. (This is the same as the effect of `-fwritable-strings'.) * All automatic variables not declared `register' are preserved by `longjmp'. Ordinarily, GNU C follows ANSI C: automatic variables not declared `volatile' may be clobbered. * The character escape sequences `\x' and `\a' evaluate as the literal characters `x' and `a' respectively. Without `-traditional', `\x' is a prefix for the hexadecimal representation of a character, and `\a' produces a bell. You may wish to use `-fno-builtin' as well as `-traditional' if your program uses names that are normally GNU C builtin functions for other purposes of its own. You cannot use `-traditional' if you include any header files that rely on ANSI C features. Some vendors are starting to ship systems with ANSI C header files and you cannot use `-traditional' on such systems to compile files that include any system headers. The `-traditional' option also enables `-traditional-cpp', which is described next. `-traditional-cpp' Attempt to support some aspects of traditional C preprocessors. Specifically: * Comments convert to nothing at all, rather than to a space. This allows traditional token concatenation. * In a preprocessing directive, the `#' symbol must appear as the first character of a line. * Macro arguments are recognized within string constants in a macro definition (and their values are stringified, though without additional quote marks, when they appear in such a context). The preprocessor always considers a string constant to end at a newline. * The predefined macro `__STDC__' is not defined when you use `-traditional', but `__GNUC__' is (since the GNU extensions which `__GNUC__' indicates are not affected by `-traditional'). If you need to write header files that work differently depending on whether `-traditional' is in use, by testing both of these predefined macros you can distinguish four situations: GNU C, traditional GNU C, other ANSI C compilers, and other old C compilers. The predefined macro `__STDC_VERSION__' is also not defined when you use `-traditional'. *Note Standard Predefined Macros: (cpp.info)Standard Predefined, for more discussion of these and other predefined macros. * The preprocessor considers a string constant to end at a newline (unless the newline is escaped with `\'). (Without `-traditional', string constants can contain the newline character as typed.) `-fcond-mismatch' Allow conditional expressions with mismatched types in the second and third arguments. The value of such an expression is void. `-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'. You may wish to use `-fno-builtin' as well as `-traditional' if your program uses names that are normally GNU C builtin functions for other purposes of its own. You cannot use `-traditional' if you include any header files that rely on ANSI C features. Some vendors are starting to ship systems with ANSI C header files and you cannot use `-traditional' on such systems to compile files that include any system headers. `-fsigned-bitfields' `-funsigned-bitfields' `-fno-signed-bitfields' `-fno-unsigned-bitfields' These options control whether a bitfield is signed or unsigned, when the declaration does not use either `signed' or `unsigned'. By default, such a bitfield is signed, because this is consistent: the basic integer types such as `int' are signed types. However, when `-traditional' is used, bitfields are all unsigned no matter what. `-fwritable-strings' Store string constants in the writable data segment and don't uniquize them. This is for compatibility with old programs which assume they can write into string constants. The option `-traditional' also has this effect. Writing into string constants is a very bad idea; "constants" should be constant. `-fallow-single-precision' Do not promote single precision math operations to double precision, even when compiling with `-traditional'. Traditional K&R C promotes all floating point operations to double precision, regardless of the sizes of the operands. On the architecture for which you are compiling, single precision may be faster than double precision. If you must use `-traditional', but want to use single precision operations when the operands are single precision, use this option. This option has no effect when compiling with ANSI or GNU C conventions (the default).