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Initial commit of GCC 2.8.1
2020-09-21 03:06:00 +02:00
This is Info file gcc.info, produced by Makeinfo version 1.67 from the
input file gcc.texi.
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
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," "Funding for
Free Software," and "Protect Your Freedom--Fight `Look And Feel'" 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," "Funding for Free Software," and "Protect Your Freedom--Fight
`Look And Feel'", 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 GNU CC version 2.8.1.
* 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 GNU CC.
* C Extensions:: GNU extensions to the C language family.
* C++ Extensions:: GNU extensions to the C++ language.
* Gcov:: gcov: a GNU CC test coverage program.
* Trouble:: If you have trouble installing GNU CC.
* Bugs:: How, why and where to report bugs.
* Service:: How to find suppliers of support for GNU CC.
* Contributing:: How to contribute to testing and developing GNU CC.
* VMS:: Using GNU CC on VMS.
* Portability:: Goals of GNU CC's portability features.
* Interface:: Function-call interface of GNU CC 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.
* Look and Feel:: Protect your freedom--fight "look and feel".
* Copying:: GNU General Public License says
how you can copy and share GNU CC.
* Contributors:: People who have contributed to GNU CC.
* Index:: Index of concepts and symbol names.

File: gcc.info, Node: G++ and GCC, Next: Invoking GCC, Prev: Top, Up: Top
Compile C, C++, or Objective C
******************************
The C, C++, and Objective C versions of the compiler are integrated;
the GNU C compiler can compile programs written in C, C++, or Objective
C.
"GCC" is a common shorthand term for the GNU C compiler. This is
both the most general name for the compiler, and the name used when the
emphasis is on compiling C programs.
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 "GNU CC" 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 "GNU CC" 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 GNU CC 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 GNU CC 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
GNU CC Command Options
**********************
When you invoke GNU CC, 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 GNU CC 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 GNU CC.
* 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 GNU CC.
* 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 -x LANGUAGE
*C Language Options*
*Note Options Controlling C Dialect: C Dialect Options.
-ansi -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.
-fall-virtual -fdollars-in-identifiers -felide-constructors
-fenum-int-equiv -fexternal-templates -ffor-scope -fno-for-scope
-fhandle-signatures -fmemoize-lookups -fname-mangling-version-N
-fno-default-inline -fno-gnu-keywords -fnonnull-objects -fguiding-decls
-foperator-names -fstrict-prototype -fthis-is-variable
-ftemplate-depth-N -nostdinc++ -traditional +eN
*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-subscript -Wcomment
-Wconversion -Werror -Wformat
-Wid-clash-LEN -Wimplicit -Wimplicit-int
-Wimplicit-function-declarations -Wimport -Winline
-Wlarger-than-LEN -Wmain -Wmissing-declarations
-Wmissing-prototypes -Wnested-externs
-Wno-import -Wold-style-cast -Woverloaded-virtual -Wparentheses
-Wpointer-arith -Wredundant-decls -Wreorder -Wreturn-type -Wshadow
-Wsign-compare -Wstrict-prototypes -Wswitch -Wsynth
-Wtemplate-debugging -Wtraditional -Wtrigraphs
-Wundef -Wuninitialized -Wunused -Wwrite-strings
*Debugging Options*
*Note Options for Debugging Your Program or GCC: Debugging Options.
-a -ax -dLETTERS -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
-fcaller-saves -fcse-follow-jumps -fcse-skip-blocks
-fdelayed-branch -fexpensive-optimizations
-ffast-math -ffloat-store -fforce-addr -fforce-mem
-ffunction-sections -finline-functions
-fkeep-inline-functions -fno-default-inline
-fno-defer-pop -fno-function-cse
-fno-inline -fno-peephole -fomit-frame-pointer
-frerun-cse-after-loop -fschedule-insns
-fschedule-insns2 -fstrength-reduce -fthread-jumps
-funroll-all-loops -funroll-loops
-O -O0 -O1 -O2 -O3
*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
-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 -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 -mapcs-26 -mapcs-32
-mlittle-endian -mbig-endian -mwords-little-endian
-mshort-load-bytes -mno-short-load-bytes
-msoft-float -mhard-float
-mbsd -mxopen -mno-symrename
*MN10300 Options*
-mmult-bug
-mno-mult-bug
*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
-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 -mtraceback -mno-traceback
-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 -mlong64 -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
*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
*HPPA Options*
-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 -mportable-runtime
-mschedule=LIST -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
*Clipper Options*
-mc300 -mc400
*H8/300 Options*
-mrelax -mh -ms -mint32 -malign-300
*SH Options*
-m1 -m2 -m3 -m3e -mb -ml -mrelax
*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
-mv850 -mbig-switch
*Code Generation Options*
*Note Options for Code Generation Conventions: Code Gen Options.
-fcall-saved-REG -fcall-used-REG
-ffixed-REG -finhibit-size-directive
-fcheck-memory-usage -fprefix-function-name
-fno-common -fno-ident -fno-gnu-linker
-fpcc-struct-return -freg-struct-return
-fshared-data -fpic -fPIC -fexceptions
-fshort-enums -fshort-double -fvolatile -fvolatile-global
-fverbose-asm -fpack-struct -fstack-check +e0 +e1
* 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 GNU CC.

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.

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', or `.cxx'; preprocessed C++ files use the suffix `.ii'. GNU CC
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 GNU CC with the default language set to C++,
and automatically specifies linking against the C++ library. (1) 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.
---------- Footnotes ----------
(1) Prior to release 2 of the compiler, there was a separate `g++'
compiler. That version was based on GNU CC, but not integrated with
it. Versions of `g++' with a `1.XX' version number--for example, `g++'
version 1.37 or 1.42--are much less reliable than the versions
integrated with GCC 2. Moreover, combining G++ `1.XX' with a version 2
GCC will simply not work.

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'
Support all ANSI standard C programs.
This turns off certain features of GNU C that are incompatible
with ANSI C, such as the `asm', `inline' 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, and it disables recognition of
C++ style `//' comments.
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.
`-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 two
leading underscores. 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.
* In C++ programs, assignment to `this' is permitted with
`-traditional'. (The option `-fthis-is-variable' also has
this effect.)
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 the `-traditional-cpp'
option, 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).

File: gcc.info, Node: C++ Dialect Options, Next: Warning Options, Prev: C Dialect Options, Up: Invoking GCC
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 -felide-constructors -O -c firstClass.C
In this example, only `-felide-constructors' is an option meant only
for C++ programs; you can use the other options with any language
supported by GNU CC.
Here is a list of options that are *only* for compiling C++ programs:
`-fno-access-control'
Turn off all access checking. This switch is mainly useful for
working around bugs in the access control code.
`-fall-virtual'
Treat all possible member functions as virtual, implicitly. All
member functions (except for constructor functions and `new' or
`delete' member operators) are treated as virtual functions of the
class where they appear.
This does not mean that all calls to these member functions will
be made through the internal table of virtual functions. Under
some circumstances, the compiler can determine that a call to a
given virtual function can be made directly; in these cases the
calls are direct in any case.
`-fcheck-new'
Check that the pointer returned by `operator new' is non-null
before attempting to modify the storage allocated. The current
Working Paper requires that `operator new' never return a null
pointer, so this check is normally unnecessary.
`-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.
`-fdollars-in-identifiers'
Accept `$' in identifiers. You can also explicitly prohibit use of
`$' with the option `-fno-dollars-in-identifiers'. (GNU C allows
`$' by default on most target systems, but there are a few
exceptions.) Traditional C allowed the character `$' to form part
of identifiers. However, ANSI C and C++ forbid `$' in identifiers.
`-fenum-int-equiv'
Anachronistically permit implicit conversion of `int' to
enumeration types. Current C++ allows conversion of `enum' to
`int', but not the other way around.
`-fexternal-templates'
Cause template instantiations to obey `#pragma interface' and
`implementation'; template instances are emitted or not according
to the location of the template definition. *Note Template
Instantiation::, for more information.
This option is deprecated.
`-falt-external-templates'
Similar to -fexternal-templates, but template instances are
emitted or not according to the place where they are first
instantiated. *Note Template Instantiation::, for more
information.
This option is deprecated.
`-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 draft 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 gcc, 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 `classof', `headof', `signature', `sigof' or
`typeof' as a keyword, so that code can use these words as
identifiers. You can use the keywords `__classof__',
`__headof__', `__signature__', `__sigof__', and `__typeof__'
instead. `-ansi' implies `-fno-gnu-keywords'.
`-fguiding-decls'
Treat a function declaration with the same type as a potential
function template instantiation as though it declares that
instantiation, not a normal function. If a definition is given
for the function later in the translation unit (or another
translation unit if the target supports weak symbols), that
definition will be used; otherwise the template will be
instantiated. This behavior reflects the C++ language prior to
September 1996, when guiding declarations were removed.
This option implies `-fname-mangling-version-0', and will not work
with other name mangling versions.
`-fno-implicit-templates'
Never emit code for templates which are instantiated implicitly
(i.e. by use); only emit code for explicit instantiations. *Note
Template Instantiation::, for more information.
`-fhandle-signatures'
Recognize the `signature' and `sigof' keywords for specifying
abstract types. The default (`-fno-handle-signatures') is not to
recognize them. *Note Type Abstraction using Signatures: C++
Signatures.
`-fhuge-objects'
Support virtual function calls for objects that exceed the size
representable by a `short int'. Users should not use this flag by
default; if you need to use it, the compiler will tell you so. If
you compile any of your code with this flag, you must compile
*all* of your code with this flag (including the C++ library, if
you use it).
This flag is not useful when compiling with -fvtable-thunks.
`-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.
`-fmemoize-lookups'
`-fsave-memoized'
Use heuristics to compile faster. These heuristics are not
enabled by default, since they are only effective for certain
input files. Other input files compile more slowly.
The first time the compiler must build a call to a member function
(or reference to a data member), it must (1) determine whether the
class implements member functions of that name; (2) resolve which
member function to call (which involves figuring out what sorts of
type conversions need to be made); and (3) check the visibility of
the member function to the caller. All of this adds up to slower
compilation. Normally, the second time a call is made to that
member function (or reference to that data member), it must go
through the same lengthy process again. This means that code like
this:
cout << "This " << p << " has " << n << " legs.\n";
makes six passes through all three steps. By using a software
cache, a "hit" significantly reduces this cost. Unfortunately,
using the cache introduces another layer of mechanisms which must
be implemented, and so incurs its own overhead.
`-fmemoize-lookups' enables the software cache.
Because access privileges (visibility) to members and member
functions may differ from one function context to the next, G++
may need to flush the cache. With the `-fmemoize-lookups' flag,
the cache is flushed after every function that is compiled. The
`-fsave-memoized' flag enables the same software cache, but when
the compiler determines that the context of the last function
compiled would yield the same access privileges of the next
function to compile, it preserves the cache. This is most helpful
when defining many member functions for the same class: with the
exception of member functions which are friends of other classes,
each member function has exactly the same access privileges as
every other, and the cache need not be flushed.
The code that implements these flags has rotted; you should
probably avoid using them.
`-fstrict-prototype'
Within an `extern "C"' linkage specification, treat a function
declaration with no arguments, such as `int foo ();', as declaring
the function to take no arguments. Normally, such a declaration
means that the function `foo' can take any combination of
arguments, as in C. `-pedantic' implies `-fstrict-prototype'
unless overridden with `-fno-strict-prototype'.
This flag no longer affects declarations with C++ linkage.
`-fname-mangling-version-N'
Control the way in which names are mangled. Version 0 is
compatible with versions of g++ before 2.8. Version 1 is the
default. Version 1 will allow correct mangling of function
templates. For example, version 0 mangling does not mangle
foo<int, double> and foo<int, char> given this declaration:
template <class T, class U> void foo(T t);
`-fno-nonnull-objects'
Don't assume that a reference is initialized to refer to a valid
object. Although the current C++ Working Paper prohibits null
references, some old code may rely on them, and you can use
`-fno-nonnull-objects' to turn on checking.
At the moment, the compiler only does this checking for
conversions to virtual base classes.
`-foperator-names'
Recognize the operator name keywords `and', `bitand', `bitor',
`compl', `not', `or' and `xor' as synonyms for the symbols they
refer to. `-ansi' implies `-foperator-names'.
`-fthis-is-variable'
Permit assignment to `this'. The incorporation of user-defined
free store management into C++ has made assignment to `this' an
anachronism. Therefore, by default it is invalid to assign to
`this' within a class member function; that is, GNU C++ treats
`this' in a member function of class `X' as a non-lvalue of type
`X *'. However, for backwards compatibility, you can make it
valid with `-fthis-is-variable'.
`-fvtable-thunks'
Use `thunks' to implement the virtual function dispatch table
(`vtable'). The traditional (cfront-style) approach to
implementing vtables was to store a pointer to the function and two
offsets for adjusting the `this' pointer at the call site. Newer
implementations store a single pointer to a `thunk' function which
does any necessary adjustment and then calls the target function.
This option also enables a heuristic for controlling emission of
vtables; if a class has any non-inline virtual functions, the
vtable will be emitted in the translation unit containing the
first one of those.
`-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.
`-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.)
`-traditional'
For C++ programs (in addition to the effects that apply to both C
and C++), this has the same effect as `-fthis-is-variable'. *Note
Options Controlling C Dialect: C Dialect Options.
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.
`-Wold-style-cast'
`-Woverloaded-virtual'
`-Wtemplate-debugging'
Warnings that apply only to C++ programs. *Note Options to
Request or Suppress Warnings: Warning Options.
`-Weffc++'
Warn about violation of some style rules from Effective C++ by
Scott Myers.
`+eN'
Control how virtual function definitions are used, in a fashion
compatible with `cfront' 1.x. *Note Options for Code Generation
Conventions: Code Gen Options.
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