CPP(1)                                GNU                               CPP(1)



NAME
       cpp - The C Preprocessor

SYNOPSIS
       cpp [-Dmacro[=defn]...] [-Umacro]
           [-Idir...] [-iquotedir...]
           [-Wwarn...]
           [-M|-MM] [-MG] [-MF filename]
           [-MP] [-MQ target...]
           [-MT target...]
           [-P] [-fno-working-directory]
           [-x language] [-std=standard]
           infile outfile

       Only the most useful options are listed here; see below for the remain-
       der.

DESCRIPTION
       The C preprocessor, often known as cpp, is a macro processor that is
       used automatically by the C compiler to transform your program before
       compilation.  It is called a macro processor because it allows you to
       define macros, which are brief abbreviations for longer constructs.

       The C preprocessor is intended to be used only with C, C++, and Objec-
       tive-C source code.  In the past, it has been abused as a general text
       processor.  It will choke on input which does not obey C's lexical
       rules.  For example, apostrophes will be interpreted as the beginning
       of character constants, and cause errors.  Also, you cannot rely on it
       preserving characteristics of the input which are not significant to
       C-family languages.  If a Makefile is preprocessed, all the hard tabs
       will be removed, and the Makefile will not work.

       Having said that, you can often get away with using cpp on things which
       are not C.  Other Algol-ish programming languages are often safe (Pas-
       cal, Ada, etc.) So is assembly, with caution.  -traditional-cpp mode
       preserves more white space, and is otherwise more permissive.  Many of
       the problems can be avoided by writing C or C++ style comments instead
       of native language comments, and keeping macros simple.

       Wherever possible, you should use a preprocessor geared to the language
       you are writing in.  Modern versions of the GNU assembler have macro
       facilities.  Most high level programming languages have their own con-
       ditional compilation and inclusion mechanism.  If all else fails, try a
       true general text processor, such as GNU M4.

       C preprocessors vary in some details.  This manual discusses the GNU C
       preprocessor, which provides a small superset of the features of ISO
       Standard C.  In its default mode, the GNU C preprocessor does not do a
       few things required by the standard.  These are features which are
       rarely, if ever, used, and may cause surprising changes to the meaning
       of a program which does not expect them.  To get strict ISO Standard C,
       you should use the -std=c89 or -std=c99 options, depending on which
       version of the standard you want.  To get all the mandatory diagnos-
       tics, you must also use -pedantic.

       This manual describes the behavior of the ISO preprocessor.  To mini-
       mize gratuitous differences, where the ISO preprocessor's behavior does
       not conflict with traditional semantics, the traditional preprocessor
       should behave the same way.  The various differences that do exist are
       detailed in the section Traditional Mode.

       For clarity, unless noted otherwise, references to CPP in this manual
       refer to GNU CPP.

OPTIONS
       The C preprocessor expects two file names as arguments, infile and out-
       file.  The preprocessor reads infile together with any other files it
       specifies with #include.  All the output generated by the combined
       input files is written in outfile.

       Either infile or outfile may be -, which as infile means to read from
       standard input and as outfile means to write to standard output.  Also,
       if either file is omitted, it means the same as if - had been specified
       for that file.

       Unless otherwise noted, or the option ends in =, all options which take
       an argument may have that argument appear either immediately after the
       option, or with a space between option and argument: -Ifoo and -I foo
       have the same effect.

       Many options have multi-letter names; therefore multiple single-letter
       options may not be grouped: -dM is very different from -d -M.

       -D name
           Predefine name as a macro, with definition 1.

       -D name=definition
           The contents of definition are tokenized and processed as if they
           appeared during translation phase three in a #define directive.  In
           particular, the definition will be truncated by embedded newline
           characters.

           If you are invoking the preprocessor from a shell or shell-like
           program you may need to use the shell's quoting syntax to protect
           characters such as spaces that have a meaning in the shell syntax.

           If you wish to define a function-like macro on the command line,
           write its argument list with surrounding parentheses before the
           equals sign (if any).  Parentheses are meaningful to most shells,
           so you will need to quote the option.  With sh and csh,
           -D'name(args...)=definition' works.

           -D and -U options are processed in the order they are given on the
           command line.  All -imacros file and -include file options are pro-
           cessed after all -D and -U options.

       -U name
           Cancel any previous definition of name, either built in or provided
           with a -D option.

       -undef
           Do not predefine any system-specific or GCC-specific macros.  The
           standard predefined macros remain defined.

       -I dir
           Add the directory dir to the list of directories to be searched for
           header files.

           Directories named by -I are searched before the standard system
           include directories.  If the directory dir is a standard system
           include directory, the option is ignored to ensure that the default
           search order for system directories and the special treatment of
           system headers are not defeated .

       -o file
           Write output to file.  This is the same as specifying file as the
           second non-option argument to cpp.  gcc has a different interpreta-
           tion of a second non-option argument, so you must use -o to specify
           the output file.

       -Wall
           Turns on all optional warnings which are desirable for normal code.
           At present this is -Wcomment, -Wtrigraphs, -Wmultichar and a warn-
           ing about integer promotion causing a change of sign in "#if"
           expressions.  Note that many of the preprocessor's warnings are on
           by default and have no options to control them.

       -Wcomment
       -Wcomments
           Warn whenever a comment-start sequence /* appears in a /* comment,
           or whenever a backslash-newline appears in a // comment.  (Both
           forms have the same effect.)

       -Wtrigraphs
           @anchor{Wtrigraphs} Most trigraphs in comments cannot affect the
           meaning of the program.  However, a trigraph that would form an
           escaped newline (??/ at the end of a line) can, by changing where
           the comment begins or ends.  Therefore, only trigraphs that would
           form escaped newlines produce warnings inside a comment.

           This option is implied by -Wall.  If -Wall is not given, this
           option is still enabled unless trigraphs are enabled.  To get tri-
           graph conversion without warnings, but get the other -Wall warn-
           ings, use -trigraphs -Wall -Wno-trigraphs.

       -Wtraditional
           Warn about certain constructs that behave differently in tradi-
           tional and ISO C.  Also warn about ISO C constructs that have no
           traditional C equivalent, and problematic constructs which should
           be avoided.

       -Wimport
           Warn the first time #import is used.

       -Wundef
           Warn whenever an identifier which is not a macro is encountered in
           an #if directive, outside of defined.  Such identifiers are
           replaced with zero.

       -Wunused-macros
           Warn about macros defined in the main file that are unused.  A
           macro is used if it is expanded or tested for existence at least
           once.  The preprocessor will also warn if the macro has not been
           used at the time it is redefined or undefined.

           Built-in macros, macros defined on the command line, and macros
           defined in include files are not warned about.

           Note: If a macro is actually used, but only used in skipped condi-
           tional blocks, then CPP will report it as unused.  To avoid the
           warning in such a case, you might improve the scope of the macro's
           definition by, for example, moving it into the first skipped block.
           Alternatively, you could provide a dummy use with something like:

                   #if defined the_macro_causing_the_warning
                   #endif

       -Wendif-labels
           Warn whenever an #else or an #endif are followed by text.  This
           usually happens in code of the form

                   #if FOO
                   ...
                   #else FOO
                   ...
                   #endif FOO

           The second and third "FOO" should be in comments, but often are not
           in older programs.  This warning is on by default.

       -Werror
           Make all warnings into hard errors.  Source code which triggers
           warnings will be rejected.

       -Wsystem-headers
           Issue warnings for code in system headers.  These are normally
           unhelpful in finding bugs in your own code, therefore suppressed.
           If you are responsible for the system library, you may want to see
           them.

       -w  Suppress all warnings, including those which GNU CPP issues by
           default.

       -pedantic
           Issue all the mandatory diagnostics listed in the C standard.  Some
           of them are left out by default, since they trigger frequently on
           harmless code.

       -pedantic-errors
           Issue all the mandatory diagnostics, and make all mandatory diag-
           nostics into errors.  This includes mandatory diagnostics that GCC
           issues without -pedantic but treats as warnings.

       -M  Instead of outputting the result of preprocessing, output a rule
           suitable for make describing the dependencies of the main source
           file.  The preprocessor outputs one make rule containing the object
           file name for that source file, a colon, and the names of all the
           included files, including those coming from -include or -imacros
           command line options.

           Unless specified explicitly (with -MT or -MQ), the object file name
           consists of the basename of the source file with any suffix
           replaced with object file suffix.  If there are many included files
           then the rule is split into several lines using \-newline.  The
           rule has no commands.

           This option does not suppress the preprocessor's debug output, such
           as -dM.  To avoid mixing such debug output with the dependency
           rules you should explicitly specify the dependency output file with
           -MF, or use an environment variable like DEPENDENCIES_OUTPUT.
           Debug output will still be sent to the regular output stream as
           normal.

           Passing -M to the driver implies -E, and suppresses warnings with
           an implicit -w.

       -MM Like -M but do not mention header files that are found in system
           header directories, nor header files that are included, directly or
           indirectly, from such a header.

           This implies that the choice of angle brackets or double quotes in
           an #include directive does not in itself determine whether that
           header will appear in -MM dependency output.  This is a slight
           change in semantics from GCC versions 3.0 and earlier.

           @anchor{dashMF}

       -MF file
           When used with -M or -MM, specifies a file to write the dependen-
           cies to.  If no -MF switch is given the preprocessor sends the
           rules to the same place it would have sent preprocessed output.

           When used with the driver options -MD or -MMD, -MF overrides the
           default dependency output file.

       -MG In conjunction with an option such as -M requesting dependency gen-
           eration, -MG assumes missing header files are generated files and
           adds them to the dependency list without raising an error.  The
           dependency filename is taken directly from the "#include" directive
           without prepending any path.  -MG also suppresses preprocessed out-
           put, as a missing header file renders this useless.

           This feature is used in automatic updating of makefiles.

       -MP This option instructs CPP to add a phony target for each dependency
           other than the main file, causing each to depend on nothing.  These
           dummy rules work around errors make gives if you remove header
           files without updating the Makefile to match.

           This is typical output:

                   test.o: test.c test.h

                   test.h:

       -MT target
           Change the target of the rule emitted by dependency generation.  By
           default CPP takes the name of the main input file, including any
           path, deletes any file suffix such as .c, and appends the plat-
           form's usual object suffix.  The result is the target.

           An -MT option will set the target to be exactly the string you
           specify.  If you want multiple targets, you can specify them as a
           single argument to -MT, or use multiple -MT options.

           For example, -MT '$(objpfx)foo.o' might give

                   $(objpfx)foo.o: foo.c

       -MQ target
           Same as -MT, but it quotes any characters which are special to
           Make.  -MQ '$(objpfx)foo.o' gives

                   $$(objpfx)foo.o: foo.c

           The default target is automatically quoted, as if it were given
           with -MQ.

       -MD -MD is equivalent to -M -MF file, except that -E is not implied.
           The driver determines file based on whether an -o option is given.
           If it is, the driver uses its argument but with a suffix of .d,
           otherwise it take the basename of the input file and applies a .d
           suffix.

           If -MD is used in conjunction with -E, any -o switch is understood
           to specify the dependency output file (but @pxref{dashMF,,-MF}),
           but if used without -E, each -o is understood to specify a target
           object file.

           Since -E is not implied, -MD can be used to generate a dependency
           output file as a side-effect of the compilation process.

       -MMD
           Like -MD except mention only user header files, not system header
           files.

       -x c
       -x c++
       -x objective-c
       -x assembler-with-cpp
           Specify the source language: C, C++, Objective-C, or assembly.
           This has nothing to do with standards conformance or extensions; it
           merely selects which base syntax to expect.  If you give none of
           these options, cpp will deduce the language from the extension of
           the source file: .c, .cc, .m, or .S.  Some other common extensions
           for C++ and assembly are also recognized.  If cpp does not recog-
           nize the extension, it will treat the file as C; this is the most
           generic mode.

           Note: Previous versions of cpp accepted a -lang option which
           selected both the language and the standards conformance level.
           This option has been removed, because it conflicts with the -l
           option.

       -std=standard
       -ansi
           Specify the standard to which the code should conform.  Currently
           CPP knows about C and C++ standards; others may be added in the
           future.

           standard may be one of:

           "iso9899:1990"
           "c89"
               The ISO C standard from 1990.  c89 is the customary shorthand
               for this version of the standard.

               The -ansi option is equivalent to -std=c89.

           "iso9899:199409"
               The 1990 C standard, as amended in 1994.

           "iso9899:1999"
           "c99"
           "iso9899:199x"
           "c9x"
               The revised ISO C standard, published in December 1999.  Before
               publication, this was known as C9X.

           "gnu89"
               The 1990 C standard plus GNU extensions.  This is the default.

           "gnu99"
           "gnu9x"
               The 1999 C standard plus GNU extensions.

           "c++98"
               The 1998 ISO C++ standard plus amendments.

           "gnu++98"
               The same as -std=c++98 plus GNU extensions.  This is the
               default for C++ code.

       -I- Split the include path.  Any directories specified with -I options
           before -I- are searched only for headers requested with
           "#include "file""; they are not searched for "#include <file>".  If
           additional directories are specified with -I options after the -I-,
           those directories are searched for all #include directives.

           In addition, -I- inhibits the use of the directory of the current
           file directory as the first search directory for "#include "file"".

           This option has been deprecated.

       -nostdinc
           Do not search the standard system directories for header files.
           Only the directories you have specified with -I options (and the
           directory of the current file, if appropriate) are searched.

       -nostdinc++
           Do not search for header files in the C++-specific standard direc-
           tories, but do still search the other standard directories.  (This
           option is used when building the C++ library.)

       -include file
           Process file as if "#include "file"" appeared as the first line of
           the primary source file.  However, the first directory searched for
           file is the preprocessor's working directory instead of the direc-
           tory containing the main source file.  If not found there, it is
           searched for in the remainder of the "#include "..."" search chain
           as normal.

           If multiple -include options are given, the files are included in
           the order they appear on the command line.

       -imacros file
           Exactly like -include, except that any output produced by scanning
           file is thrown away.  Macros it defines remain defined.  This
           allows you to acquire all the macros from a header without also
           processing its declarations.

           All files specified by -imacros are processed before all files
           specified by -include.

       -idirafter dir
           Search dir for header files, but do it after all directories speci-
           fied with -I and the standard system directories have been
           exhausted.  dir is treated as a system include directory.

       -iprefix prefix
           Specify prefix as the prefix for subsequent -iwithprefix options.
           If the prefix represents a directory, you should include the final
           /.

       -iwithprefix dir
       -iwithprefixbefore dir
           Append dir to the prefix specified previously with -iprefix, and
           add the resulting directory to the include search path.  -iwithpre-
           fixbefore puts it in the same place -I would; -iwithprefix puts it
           where -idirafter would.

       -isysroot dir
           This option is like the --sysroot option, but applies only to
           header files.  See the --sysroot option for more information.

       -isystem dir
           Search dir for header files, after all directories specified by -I
           but before the standard system directories.  Mark it as a system
           directory, so that it gets the same special treatment as is applied
           to the standard system directories.

       -iquote dir
           Search dir only for header files requested with "#include "file"";
           they are not searched for "#include <file>", before all directories
           specified by -I and before the standard system directories.

       -fdollars-in-identifiers
           @anchor{fdollars-in-identifiers} Accept $ in identifiers.

       -fextended-identifiers
           Accept universal character names in identifiers.  This option is
           experimental; in a future version of GCC, it will be enabled by
           default for C99 and C++.

       -fpreprocessed
           Indicate to the preprocessor that the input file has already been
           preprocessed.  This suppresses things like macro expansion, tri-
           graph conversion, escaped newline splicing, and processing of most
           directives.  The preprocessor still recognizes and removes com-
           ments, so that you can pass a file preprocessed with -C to the com-
           piler without problems.  In this mode the integrated preprocessor
           is little more than a tokenizer for the front ends.

           -fpreprocessed is implicit if the input file has one of the exten-
           sions .i, .ii or .mi.  These are the extensions that GCC uses for
           preprocessed files created by -save-temps.

       -ftabstop=width
           Set the distance between tab stops.  This helps the preprocessor
           report correct column numbers in warnings or errors, even if tabs
           appear on the line.  If the value is less than 1 or greater than
           100, the option is ignored.  The default is 8.

       -fexec-charset=charset
           Set the execution character set, used for string and character con-
           stants.  The default is UTF-8.  charset can be any encoding sup-
           ported by the system's "iconv" library routine.

       -fwide-exec-charset=charset
           Set the wide execution character set, used for wide string and
           character constants.  The default is UTF-32 or UTF-16, whichever
           corresponds to the width of "wchar_t".  As with -fexec-charset,
           charset can be any encoding supported by the system's "iconv"
           library routine; however, you will have problems with encodings
           that do not fit exactly in "wchar_t".

       -finput-charset=charset
           Set the input character set, used for translation from the charac-
           ter set of the input file to the source character set used by GCC.
           If the locale does not specify, or GCC cannot get this information
           from the locale, the default is UTF-8.  This can be overridden by
           either the locale or this command line option.  Currently the com-
           mand line option takes precedence if there's a conflict.  charset
           can be any encoding supported by the system's "iconv" library rou-
           tine.

       -fworking-directory
           Enable generation of linemarkers in the preprocessor output that
           will let the compiler know the current working directory at the
           time of preprocessing.  When this option is enabled, the preproces-
           sor will emit, after the initial linemarker, a second linemarker
           with the current working directory followed by two slashes.  GCC
           will use this directory, when it's present in the preprocessed
           input, as the directory emitted as the current working directory in
           some debugging information formats.  This option is implicitly
           enabled if debugging information is enabled, but this can be inhib-
           ited with the negated form -fno-working-directory.  If the -P flag
           is present in the command line, this option has no effect, since no
           "#line" directives are emitted whatsoever.

       -fno-show-column
           Do not print column numbers in diagnostics.  This may be necessary
           if diagnostics are being scanned by a program that does not under-
           stand the column numbers, such as dejagnu.

       -A predicate=answer
           Make an assertion with the predicate predicate and answer answer.
           This form is preferred to the older form -A predicate(answer),
           which is still supported, because it does not use shell special
           characters.

       -A -predicate=answer
           Cancel an assertion with the predicate predicate and answer answer.

       -dCHARS
           CHARS is a sequence of one or more of the following characters, and
           must not be preceded by a space.  Other characters are interpreted
           by the compiler proper, or reserved for future versions of GCC, and
           so are silently ignored.  If you specify characters whose behavior
           conflicts, the result is undefined.

           M   Instead of the normal output, generate a list of #define direc-
               tives for all the macros defined during the execution of the
               preprocessor, including predefined macros.  This gives you a
               way of finding out what is predefined in your version of the
               preprocessor.  Assuming you have no file foo.h, the command

                       touch foo.h; cpp -dM foo.h

               will show all the predefined macros.

           D   Like M except in two respects: it does not include the prede-
               fined macros, and it outputs both the #define directives and
               the result of preprocessing.  Both kinds of output go to the
               standard output file.

           N   Like D, but emit only the macro names, not their expansions.

           I   Output #include directives in addition to the result of prepro-
               cessing.

       -P  Inhibit generation of linemarkers in the output from the preproces-
           sor.  This might be useful when running the preprocessor on some-
           thing that is not C code, and will be sent to a program which might
           be confused by the linemarkers.

       -C  Do not discard comments.  All comments are passed through to the
           output file, except for comments in processed directives, which are
           deleted along with the directive.

           You should be prepared for side effects when using -C; it causes
           the preprocessor to treat comments as tokens in their own right.
           For example, comments appearing at the start of what would be a
           directive line have the effect of turning that line into an ordi-
           nary source line, since the first token on the line is no longer a
           #.

       -CC Do not discard comments, including during macro expansion.  This is
           like -C, except that comments contained within macros are also
           passed through to the output file where the macro is expanded.

           In addition to the side-effects of the -C option, the -CC option
           causes all C++-style comments inside a macro to be converted to
           C-style comments.  This is to prevent later use of that macro from
           inadvertently commenting out the remainder of the source line.

           The -CC option is generally used to support lint comments.

       -traditional-cpp
           Try to imitate the behavior of old-fashioned C preprocessors, as
           opposed to ISO C preprocessors.

       -trigraphs
           Process trigraph sequences.

       -remap
           Enable special code to work around file systems which only permit
           very short file names, such as MS-DOS.

       --help
       --target-help
           Print text describing all the command line options instead of pre-
           processing anything.

       -v  Verbose mode.  Print out GNU CPP's version number at the beginning
           of execution, and report the final form of the include path.

       -H  Print the name of each header file used, in addition to other nor-
           mal activities.  Each name is indented to show how deep in the
           #include stack it is.  Precompiled header files are also printed,
           even if they are found to be invalid; an invalid precompiled header
           file is printed with ...x and a valid one with ...! .

       -version
       --version
           Print out GNU CPP's version number.  With one dash, proceed to pre-
           process as normal.  With two dashes, exit immediately.

ENVIRONMENT
       This section describes the environment variables that affect how CPP
       operates.  You can use them to specify directories or prefixes to use
       when searching for include files, or to control dependency output.

       Note that you can also specify places to search using options such as
       -I, and control dependency output with options like -M.  These take
       precedence over environment variables, which in turn take precedence
       over the configuration of GCC.

       CPATH
       C_INCLUDE_PATH
       CPLUS_INCLUDE_PATH
       OBJC_INCLUDE_PATH
           Each variable's value is a list of directories separated by a spe-
           cial character, much like PATH, in which to look for header files.
           The special character, "PATH_SEPARATOR", is target-dependent and
           determined at GCC build time.  For Microsoft Windows-based targets
           it is a semicolon, and for almost all other targets it is a colon.

           CPATH specifies a list of directories to be searched as if speci-
           fied with -I, but after any paths given with -I options on the com-
           mand line.  This environment variable is used regardless of which
           language is being preprocessed.

           The remaining environment variables apply only when preprocessing
           the particular language indicated.  Each specifies a list of direc-
           tories to be searched as if specified with -isystem, but after any
           paths given with -isystem options on the command line.

           In all these variables, an empty element instructs the compiler to
           search its current working directory.  Empty elements can appear at
           the beginning or end of a path.  For instance, if the value of
           CPATH is ":/special/include", that has the same effect as
           -I. -I/special/include.

       DEPENDENCIES_OUTPUT
           If this variable is set, its value specifies how to output depen-
           dencies for Make based on the non-system header files processed by
           the compiler.  System header files are ignored in the dependency
           output.

           The value of DEPENDENCIES_OUTPUT can be just a file name, in which
           case the Make rules are written to that file, guessing the target
           name from the source file name.  Or the value can have the form
           file target, in which case the rules are written to file file using
           target as the target name.

           In other words, this environment variable is equivalent to combin-
           ing the options -MM and -MF, with an optional -MT switch too.

       SUNPRO_DEPENDENCIES
           This variable is the same as DEPENDENCIES_OUTPUT (see above),
           except that system header files are not ignored, so it implies -M
           rather than -MM.  However, the dependence on the main input file is
           omitted.

SEE ALSO
       gpl(7), gfdl(7), fsf-funding(7), gcc(1), as(1), ld(1), and the Info
       entries for cpp, gcc, and binutils.

COPYRIGHT
       Copyright (c) 1987, 1989, 1991, 1992, 1993, 1994, 1995, 1996, 1997,
       1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005 Free Software Founda-
       tion, Inc.

       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.1 or
       any later version published by the Free Software Foundation.  A copy of
       the license is included in the man page gfdl(7).  This manual contains
       no Invariant Sections.  The Front-Cover Texts are (a) (see below), and
       the Back-Cover Texts are (b) (see below).

       (a) The FSF's Front-Cover Text is:

            A GNU Manual

       (b) The FSF's Back-Cover Text is:

            You have freedom to copy and modify this GNU Manual, like GNU
            software.  Copies published by the Free Software Foundation raise
            funds for GNU development.



gcc-4.1.1                         2006-05-06                            CPP(1)
