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GCC
Section: GNU Tools (1)
Updated: 1998/08/29
Index Return to Main Contents
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NAME
gcc, g++ - GNU project C and C++ Compiler (egcs-1.1.2)
SYNOPSIS
gcc [ option | filename ]...
g++ [ option | filename ]...
WARNING
The information in this man page is an extract from the full documentation of the GNU C compiler, and is limited to the meaning of the options.
This man page is not kept up to date except when volunteers want to maintain it. If you find a discrepancy between the man page and the software, please check the Info file, which is the authoritative documentation.
If we find that the things in this man page that are out of date cause significant confusion or complaints, we will stop distributing the man page. The alternative, updating the man page when we update the Info file, is impossible because the rest of the work of maintaining GNU CC leaves us no time for that. The GNU project regards man pages as obsolete and should not let them take time away from other things.
For complete and current documentation, refer to the Info file `gcc' or the manual Using and Porting GNU CC (for version 2.0). Both are made from the Texinfo source file gcc.texinfo.
DEs criptION
The C and C++ compilers are integrated. Both process input files through one or more of four stages: preprocessing, compilation, assembly, and linking. Source filename suffixes identify the source language, but which name you use for the compiler governs default assumptions:
gcc
assumes preprocessed (.i) files are C and assumes C style linking.
g++
assumes preprocessed (.i) files are C++ and assumes C++ style linking.
Suffixes of source file names indicate the language and kind of processing to be done:
.c C source; preprocess, compile, assemble
.C C++ source; preprocess, compile, assemble
.cc C++ source; preprocess, compile, assemble
.cxx C++ source; preprocess, compile, assemble
.m Objective-C source; preprocess, compile, assemble
.i preprocessed C; compile, assemble
.ii preprocessed C++; compile, assemble
.s Assembler source; assemble
.S Assembler source; preprocess, assemble
.h Preprocessor file; not usually named on command line
Files with other suffixes are passed to the linker. Common cases include:
.o Object file
.a Archive file
Linking is always the last stage unless you use one of the -c, -S, or -E options to avoid it (or unless compilation errors stop the whole process). For the link stage, all .o files corresponding to source files, -l libraries, unrecognized filenames (including named .o object files and .a archives) are passed to the linker in command-line order.
OPTIONS
Options must be separate: `-dr' is quite different from `-d -r '.
Most `-f' and `-W' options have two contrary forms: -fname and -fno-name (or -Wname and -Wno-name). Only the non-default forms are shown here.
Here is a summary of all the options, grouped by type. Explanations are in the following sections.
Overall Options
-c -S -E -o file -pipe -v -x language
Language Options
-ansi -fall-virtual -fcond-mismatch -fdollars-in-identifiers -fenum-int-equiv -fexternal-templates -fno-asm -fno-builtin -fhosted -fno-hosted -ffreestanding -fno-freestanding -fno-strict-prototype -fsigned-bitfields -fsigned-char -fthis-is-variable -funsigned-bitfields -funsigned-char -fwritable-strings -traditional -traditional-cpp -trigraphs
Warning Options
-fsyntax-only -pedantic -pedantic-errors -w -W -Wall -Waggregate-return -Wcast-align -Wcast-qual -Wchar-subs cript -Wcomment -Wconversion -Wenum-clash -Werror -Wformat -Wid-clash-len -Wimplicit -Wimplicit-int -Wimplicit-function-declaration -Winline -Wlong-long -Wmain -Wmissing-prototypes -Wmissing-declarations -Wnested-externs -Wno-import -Wparentheses -Wpointer-arith -Wredundant-decls -Wreturn-type -Wshadow -Wstrict-prototypes -Wswitch -Wtemplate-debugging -Wtraditional -Wtrigraphs -Wuninitialized -Wunused -Wwrite-strings
Debugging Options
-a -dletters -fpretend-float -g -glevel -gcoff -gxcoff -gxcoff+ -gdwarf -gdwarf+ -gstabs -gstabs+ -ggdb -p -pg -save-temps -print-file-name=library -print-libgcc-file-name -print-prog-name=program
Optimization Options
-fcaller-saves -fcse-follow-jumps -fcse-skip-blocks -fdelayed-branch -felide-constructors -fexpensive-optimizations -ffast-math -ffloat-store -fforce-addr -fforce-mem -finline-functions -fkeep-inline-functions -fmemoize-lookups -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 -O2 -O3
Preprocessor Options
-Aassertion -C -dD -dM -dN -Dmacro[=defn] -E -H -idirafter dir -include file -imacros file -iprefix
file -iwithprefix dir -M -MD -MM -MMD -nostdinc -P -Umacro -undef
Assembler Option
-Wa,option
Linker Options
-llibrary -nostartfiles -nostdlib -static -shared -symbolic -Xlinker option -Wl,option -u symbol
Directory Options
-Bprefix -Idir -I- -Ldir
Target Options
-b machine -V version
Configuration Dependent Options
M680x0 Options
-m68000 -m68020 -m68020-40 -m68030 -m68040 -m68881 -mbitfield -mc68000 -mc68020 -mfpa -mnobitfield -mrtd -mshort -msoft-float
VAX Options
-mg -mgnu -munix
SPARC Options
-mepilogue -mfpu -mhard-float -mno-fpu -mno-epilogue -msoft-float -msparclite -mv8 -msupersparc -mcypress
Convex Options
-margcount -mc1 -mc2 -mnoargcount
AMD29K Options
-m29000 -m29050 -mbw -mdw -mkernel-registers -mlarge -mnbw -mnodw -msmall -mstack-check -muser-registers
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
RS6000 Options
-mfp-in-toc -mno-fop-in-toc
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
-mcpu=cpu type -mips2 -mips3 -mint64 -mlong64 -mlonglong128 -mmips-as -mgas -mrnames -mno-rnames -mgpopt -mno-gpopt -mstats -mno-stats -mmemcpy -mno-memcpy -mno-mips-tfile -mmips-tfile -msoft-float -mhard-float -mabicalls -mno-abicalls -mhalf-pic -mno-half-pic -G num -nocpp
i386 Options
-m486 -mno-486 -msoft-float -mno-fp-ret-in-387
HPPA Options
-mpa-risc-1-0 -mpa-risc-1-1 -mkernel -mshared-libs -mno-shared-libs -mlong-calls -mdisable-fpregs -mdisable-indexing -mtrailing-colon
i960 Options
-mcpu-type -mnumerics -msoft-float -mleaf-procedures -mno-leaf-procedures -mtail-call -mno-tail-call -mcomplex-addr -mno-complex-addr -mcode-align -mno-code-align -mic-compat -mic2.0-compat -mic3.0-compat -masm-compat -mintel-asm -mstrict-align -mno-strict-align -mold-align -mno-old-align
DEC Alpha Options
-mfp-regs -mno-fp-regs -mno-soft-float -msoft-float
System V Options
-G -Qy -Qn -YP,paths -Ym,dir
Code Generation Options
-fcall-saved-reg -fcall-used-reg -ffixed-reg -finhibit-size-directive -fnonnull-objects -fno-common -fno-ident -fno-gnu-linker -fpcc-struct-return -fpic -fPIC -freg-struct-return -fshared-data -fshort-enums -fshort-double -fvolatile -fvolatile-global -fverbose-asm
OVERALL OPTIONS
-x language
Specify explicitly the language for the following input files (rather than choosing a default based on the file name suffix) . This option applies to all following input files until the next `-x' option. Possible values of language are `c', `objective-c', `c-header', `c++', `cpp-output', `assembler', and `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 want only some of the four stages (preprocess, compile, assemble, link), 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 compiler output is an object file corresponding to each source file.
By default, GCC makes the object file name for a source file by replacing the suffix `.c', `.i', `.s', etc., with `.o'. Use -o to select another name.
GCC ignores any unrecognized input files (those that do not require compilation or assembly) with the -c option.
-S
Stop after the stage of compilation proper; do not assemble. The output is an assembler code file for each non-assembler input file specified.
By default, GCC makes the assembler file name for a source file by replacing the suffix `.c', `.i', etc., with `.s'. Use -o to select another name.
GCC ignores any input files that don't require compilation.
-E
Stop after the preprocessing stage; do not run the compiler proper. The output is preprocessed source code, which is sent to the standard output.
GCC ignores input files which don't require preprocessing.
-o file
Place output in file file. This applies regardless to whatever sort of output GCC is producing, 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 you do not specify `-o', 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 cannot read from a pipe; but the GNU assembler has no trouble.
LANGUAGE OPTIONS
The following options control the dialect of 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 disallows `$' as part of identifiers.
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'.
The preprocessor predefines a macro __STRICT_ANSI__ when you use the `-ansi' option. 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.
-fno-asm
Do not recognize asm, inline or typeof as a keyword. These words may then be used as identifiers. You can use __asm__, __inline__ and __typeof__ instead. `-ansi' implies `-fno-asm'.
-fno-builtin
Don't recognize built-in functions that do not begin with two leading underscores. Currently, the functions affected include _exit, abort, abs, alloca, cos, exit, fabs, labs, memcmp, memcpy, sin, sqrt, strcmp, strcpy, and strlen.
The `-ansi' option prevents alloca and _exit from being builtin functions.
-fhosted
Compile for a hosted environment; this implies the `-fbuiltin' option, and implies that suspicious declarations of main should be warned about.
-ffreestanding
Compile for a freestanding environment; this implies the `-fno-builtin' option, and implies that main has no special requirements.
-fno-strict-prototype
Treat a function declaration with no arguments, such as `int foo ();', as C would treat it---as saying nothing about the number of arguments or their types (C++ only). Normally, such a declaration in C++ means that the function foo takes no arguments.
-trigraphs
Support ANSI C trigraphs. The `-ansi' option implies `-trigraphs'.
-traditional
Attempt to support some aspects of traditional C compilers. For details, see the GNU C Manual; the duplicate list here has been deleted so that we won't get complaints when it is out of date.
But one note about C++ programs only (not C). `-traditional' has one additional effect for C++: assignment to this is permitted. This is the same as the effect of `-fthis-is-variable'.
-traditional-cpp
Attempt to support some aspects of traditional C preprocessors. This includes the items that specifically mention the preprocessor above, but none of the other effects of `-traditional'.
-fdollars-in-identifiers
Permit the use of `$' in identifiers (C++ only). You can also use `-fno-dollars-in-identifiers' to explicitly prohibit use of `$'. (GNU C++ allows `$' by default on some target systems but not others.)
-fenum-int-equiv
Permit implicit conversion of int to enumeration types (C++ only). Normally GNU C++ allows conversion of enum to int, but not the other way around.
-fexternal-templates
Produce smaller code for template declarations, by generating only a single copy of each template function where it is defined (C++ only). To use this option successfully, you must also mark all files that use templates with either `#pragma implementation' (the definition) or `#pragma interface' (declarations).
When your code is compiled with `-fexternal-templates', all template instantiations are external. You must arrange for all necessary instantiations to appear in the implementation file; you can do this with a typedef that references each instantiation needed. Conversely, when you compile using the default option `-fno-external-templates', all template instantiations are explicitly internal.
-fall-virtual
Treat all possible member functions as virtual, implicitly. All member functions (except for constructor functions and ne
w 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.
-fcond-mismatch
Allow conditional expressions with mismatched types in the second and third arguments. The value of such an expression is void.
-fthis-is-variable
Permit assignment to this (C++ only). 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. However, for backwards compatibility, you can make it valid with `-fthis-is-variable'.
-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 and 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, `-fno-signed-char' is equivalent to `-funsigned-char'.
-fsigned-bitfields
-funsigned-bitfields
-fno-signed-bitfields
-fno-unsigned-bitfields
These options control whether a bitfield is signed or unsigned, when declared with no explicit `signed' or `unsigned' qualifier. By default, such a bitfield is signed, because this is consistent: the basic integer types such as int are signed types.
However, when you specify `-traditional', 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. `-traditional' also has this effect.
Writing into string constants is a very bad idea; ``constants'' should be constant.
PREPROCESSOR OPTIONS
These options control the C preprocessor, which is run on each C source file before actual compilation.
If you use the `-E' option, GCC does nothing except preprocessing. Some of these options make sense only together with `-E' because they cause the preprocessor output to be unsuitable for actual compilation.
-include file
Process file as input before processing the regular input file. In effect, the contents of file are compiled first. Any `-D' and `-U' options on the command line are always processed before `-include file', regardless of the order in which they are written. All the `-include' and `-imacros' options are processed in the order in which they are written.
-imacros file
Process file as input, discarding the resulting output, before processing the regular input file. Because the output generated from file is discarded, the only effect of `-imacros file' is to make the macros defined in file available for use in the main input. The preprocessor evaluates any `-D' and `-U' options on the command line before processing `-imacrosfile', regardless of the order in which they are written. All the `-include' and `-imacros' options are processed in the order in which they are written.
-idirafter dir
Add the directory dir to the second include path. The directories on the second include path are searched when a header file is not found in any of the directories in the main include path (the one that `-I' adds to).
-iprefix prefix
Specify prefix as the prefix for subsequent `-iwithprefix' options.
-iwithprefix dir
Add a directory to the second include path. The directory's name is made by concatenating prefix and dir, where prefix was specified previously with `-iprefix'.
-nostdinc
Do not search the standard system directories for header files. Only the directories you have specified with `-I' options (and the current directory, if appropriate) are searched.
By using both `-nostdinc' and `-I-', you can limit the include-file search file to only those directories you specify explicitly.
-nostdinc++
Do not search for header files in the C++-specific standard directories, but do still search the other standard directories. (This option is used when building `libg++'.)
-undef
Do not predefine any nonstandard macros. (Including architecture flags).
-E
Run only the C preprocessor. Pr
eprocess all the C source files specified and output the results to standard output or to the specified output file.
-C
Tell the preprocessor not to discard comments. Used with the `-E' option.
-P
Tell the preprocessor not to generate `#line' commands. Used with the `-E' option.
-M [ -MG ]
Tell the preprocessor to output a rule suitable for make describing the dependencies of each object file. For each source file, the preprocessor outputs one make-rule whose target is the object file name for that source file and whose dependencies are all the files `#include'd in it. This rule may be a single line or may be continued with `'-newline if it is long. The list of rules is printed on standard output instead of the preprocessed C program.
`-M' implies `-E'.
`-MG' says to treat missing header files as generated files and assume they live in the same directory as the source file. It must be specified in addition to `-M'.
-MM [ -MG ]
Like `-M' but the output mentions only the user header files included with `#include file"'. System header files included with `#include <file>' are omitted.
-MD
Like `-M' but the dependency information is written to files with names made by replacing `.o' with `.d' at the end of the output file names. This is in addition to compiling the file as specified---`-MD' does not inhibit ordinary compilation the way `-M' does.
The Mach utility `md' can be used to merge the `.d' files into a single dependency file suitable for using with the `make' command.
-MMD
Like `-MD' except mention only user header files, not system header files.
-H
Print the name of each header file used, in addition to other normal activities.
-Aquestion(answer)
Assert the answer answer for question, in case it is tested with a preprocessor conditional such as `#if #question(answer)'. `-A-' disables the standard assertions that normally describe the target machine.
-Aquestion
(answer) Assert the answer answer for question, in case it is tested with a preprocessor conditional such as `#if #question(answer)'. `-A-' disables the standard assertions that normally describe the target machine.
-Dmacro
Define macro macro with the string `1' as its definition.
-Dmacro=defn
Define macro macro as defn. All instances of `-D' on the command line are processed before any `-U' options.
-Umacro
Undefine macro macro. `-U' options are evaluated after all `-D' options, but before any `-include' and `-imacros' options.
-dM
Tell the preprocessor to output only a list of the macro definitions that are in effect at the end of preprocessing. Used with the `-E' option.
-dD
Tell the preprocessor to pass all macro definitions into the output, in their proper sequence in the rest of the output.
-dN
Like `-dD' except that the macro arguments and contents are omitted. Only `#define name' is included in the output.
ASSEMBLER OPTION
-Wa,option
Pass option as an option to the assembler. If option contains commas, it is split into multiple options at the commas.
LINKER OPTIONS
These options come into play when the compiler links object files into an executable output file. They are meaningless if the compiler is not doing a link step.
object-file-name
A file name that does not end in a special recognized suffix is considered to name an object file or library. (Object files are distinguished from libraries by the linker according to the file contents.) If GCC does a link step, these object files are used as input to the linker.
-llibrary
Use the library named library when linking.
The linker searches a standard list of directories for the library, which is actually a file named `liblibrary.a'. The linker then uses this file as if it had been specified precisely by name.
The directories searched include several standard system directories plus any that you specify with `-L'.
Normally the files found this way are library files---archive files whose members are object files. The linker handles an archive file by scanning through it for members which define symbols that have so far been referenced but not defined. However, if the linker finds an ordinary object file rather than a library, the object file is linked in the usual fashion. The only difference between using an `-l' option and specifying a file name is that `-l' surrounds library with `lib' and `.a' and searches several directories.
-lobjc
You need this special case of the -l option in order to link an Objective C program.
-nostartfiles
Do not use the standard system startup files when linking. The standard libraries are used normally.
-nostdlib
Don't use the standard system libraries and startup files when linking. Only the files you specify will be passed to the linker.
-static
On systems that support dynamic linking, this prevents linking with the shared libraries. On other systems, this option has no effect.
-shared
Produce a shared object which can then be linked with
other objects to form an executable. Only a few systems support this option.
-symbolic
Bind references to global symbols when building a shared object. Warn about any unresolved references (unless overridden by the link editor option `-Xlinker -z -Xlinker defs'). Only a few systems support this option.
-Xlinker option
Pass option as an option to the linker. You can use this to supply system-specific linker options which GNU CC does not know how to recognize.
If you want to pass an option that takes an argument, you must use `-Xlinker' twice, once for the option and once for the argument. For example, to pass `-assert definitions', you must write `-Xlinker -assert -Xlinker definitions'. It does not work to write `-Xlinker "-assert definitions"', because this passes the entire string as a single argument, which is not what the linker expects.
-Wl,option
Pass option as an option to the linker. If option contains commas, it is split into multiple options at the commas.
-u symbol
Pretend the symbol symbol is undefined, to force linking of library modules to define it. You can use `-u' multiple times with different symbols to force loading of additional library modules.
DIRECTORY OPTIONS
These options specify directories to search for header files, for libraries and for parts of the compiler:
-Idir
Append directory dir to the list of directories searched for include files.
-I-
Any directories you specify with `-I' options before the `-I-' option are searched only for the case of `#include "file"'; they are not searched for `#include <file>'.
If additional directories are specified with `-I' options after the `-I-', these directories are searched for all `#include' directives. (Ordinarily all `-I' directories are used this way.)
In addition, the `-I-' option inhibits the use of the current directory (where the current input file came from) as the first search directory for `#include "file"'. There is no way to override this effect of `-I-'. With `-I.' you can specify searching the directory which was current when the compiler was invoked. That is not exactly the same as what the preprocessor does by default, but it is often satisfactory.
`-I-' does not inhibit the use of the standard system directories for header files. Thus, `-I-' and `-nostdinc' are independent.
-Ldir
Add directory dir to the list of directories to be searched for `-l'.
-Bprefix
This option specifies where to find the executables, libraries and data files of the compiler itself.
The compiler driver program runs one or more of the subprograms `cpp', `cc1' (or, for C++, `cc1plus'), `as' and `ld'. It tries prefix as a prefix for each program it tries to run, both with and without `machine/version/'.
For each subprogram to be run, the compiler driver first tries the `-B' prefix, if any. If that name is not found, or if `-B' was not specified, the driver tries two standard prefixes, which are `/usr/lib/gcc/' and `/usr/local/lib/gcc-lib/'. If neither of those results in a file name that is found, the compiler driver searches for the unmodified program name, using the directories specified in your `PATH' environment variable.
The run-time support file `libgcc.a' is also searched for using the `-B' prefix, if needed. If it is not found there, the two standard prefixes above are tried, and that is all. The file is left out of the link if it is not found by those means. Most of the time, on most machines, `libgcc.a' is not actually necessary.
You can get a similar result from the environment variable GCC_EXEC_PREFIX; if it is defined, its value is used as a prefix in the same way. If both the `-B' option and the GCC_EXEC_PREFIX variable are present, the `-B' option is used first and the environment variable value second.
WARNING OPTIONS
Warnings are diagnostic messages that report constructions which are not inherently erroneous but which are risky or suggest there may have been an error.
These options control the amount and kinds of warnings produced by GNU CC:
-fsyntax-only
Check the code for syntax errors, but don't emit any output.
-w
Inhibit all warning messages.
-Wno-import
Inhibit warning messages about the use of #import.
-pedantic
Issue all the warnings demanded by strict ANSI standard C; reject all programs that use forbidden extensions.
Valid ANSI standard C programs should compile properly with or without this option (though a rare few will require `-ansi'). However, without this option, certain GNU extensions and traditional C features are supported as well. With this option, they are rejected. There is no reason to use this option; it exists only to satisfy pedants.
`-pedantic' does not cause warning messages for use of the alternate keywords whose names begin and end with `__'. Pedantic warnings are also disabled in the expression that follows __extension__. However, only system header files should use these escape routes; application progra
ms should avoid them.
-pedantic-errors
Like `-pedantic', except that errors are produced rather than warnings.
-W
Print extra warning messages for these events:
*
A nonvolatile automatic variable might be changed by a call to longjmp. These warnings are possible only in optimizing compilation.
The compiler sees only the calls to setjmp. It cannot know where longjmp will be called; in fact, a signal handler could call it at any point in the code. As a result, you may get a warning even when there is in fact no problem because longjmp cannot in fact be called at the place which would cause a problem.
*
A function can return either with or without a value. (Falling off the end of the function body is considered returning without a value.) For example, this function would evoke such a warning:
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