cpp

CPP(1)                                 GNU                                CPP(1)



NAME
       cpp - The C Preprocessor

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

       Only the most useful options are listed here; see below for the
       remainder.

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
       Objective-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 (Pascal,
       Ada, etc.) So is assembly, with caution.  -traditional 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
       conditional 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 diagnostics, you must
       also use -pedantic.

OPTIONS
       The C preprocessor expects two file names as arguments, infile and
       outfile.  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
           Predefine name as a macro, with definition definition.  There are no
           restrictions on the contents of definition, but 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
           processed 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 macros.  The common 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.

           It is dangerous to specify a standard system include directory in an
           -I option.  This defeats the special treatment of system headers .
           It can also defeat the repairs to buggy system headers which GCC
           makes when it is installed.

       -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
           interpretation 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 and -Wtrigraphs.  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
           Warn if any trigraphs are encountered.  This option used to take
           effect only if -trigraphs was also specified, but now works
           independently.  Warnings are not given for trigraphs within comments,
           as they do not affect the meaning of the program.

       -Wtraditional
           Warn about certain constructs that behave differently in traditional
           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.

       -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
           diagnostics 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.

       -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.

       -MF file
           @anchor{-MF} When used with -M or -MM, specifies a file to write the
           dependencies 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 When used with -M or -MM, -MG says to treat missing header files as
           generated files and assume they live in the same directory as the
           source file.  It suppresses preprocessed output, as a missing header
           file is ordinarily an error.

           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 platform'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{-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 recognize 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
           only knows about the standards for C; other language standards will
           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.

       -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"".

       -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
           directories, 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 directory
           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
           specified 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.
           -iwithprefixbefore puts it in the same place -I would; -iwithprefix
           puts it where -idirafter would.

           Use of these options is discouraged.

       -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.

       -fpreprocessed
           Indicate to the preprocessor that the input file has already been
           preprocessed.  This suppresses things like macro expansion, trigraph
           conversion, escaped newline splicing, and processing of most
           directives.  The preprocessor still recognizes and removes comments,
           so that you can pass a file preprocessed with -C to the compiler
           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
           extensions .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.

       -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 understand
           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.

       -A- Cancel all predefined assertions and all assertions preceding it on
           the command line.  Also, undefine all predefined macros and all
           macros preceding it on the command line.  (This is a historical wart
           and may change in the future.)

       -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
               directives 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 predefined
               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
               preprocessing.

       -P  Inhibit generation of linemarkers in the output from the
           preprocessor.  This might be useful when running the preprocessor on
           something 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 ordinary source
           line, since the first token on the line is no longer a #.

       -gcc
           Define the macros __GNUC__, __GNUC_MINOR__ and __GNUC_PATCHLEVEL__.
           These are defined automatically when you use gcc -E; you can turn
           them off in that case with -no-gcc.

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

       -trigraphs
           Process trigraph sequences.

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

       -$  Forbid the use of $ in identifiers.  The C standard allows
           implementations to define extra characters that can appear in
           identifiers.  By default GNU CPP permits $, a common extension.

       -h
       --help
       --target-help
           Print text describing all the command line options instead of
           preprocessing 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 normal
           activities.  Each name is indented to show how deep in the #include
           stack it is.

       -version
       --version
           Print out GNU CPP's version number.  With one dash, proceed to
           preprocess 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 special
           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 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 specified
           with -I, but after any paths given with -I options on the command
           line.  The 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 directories
           to be searched as if specified with -isystem, but after any paths
           given with -isystem options on the command line.

           See also @ref{Search Path}.

       DEPENDENCIES_OUTPUT
           @anchor{DEPENDENCIES_OUTPUT} If this variable is set, its value
           specifies how to output dependencies 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 combining
           the options -MM and -MF, with an optional -MT switch too.

       SUNPRO_DEPENDENCIES
           This variable is the same as the environment variable
           DEPENDENCIES_OUTPUT, 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 Free Software Foundation, Inc.

       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.1 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.




3rd Berkeley Distribution           gcc-3.2.1                             CPP(1)