CPP linux command manual

CPP(1)                                   GNU                               CPP(1)

       cpp - The C Preprocessor

       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

       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
       (Pascal, 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 lan-
       guage 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 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 prepro-
       cessor should behave the same way.  The various differences that do
       exist are detailed in the section @ref{Traditional Mode}.

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

       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 pro-
           vided with a -D option.

           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 treat-
           ment 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 interpre-
           tation of a second non-option argument, so you must use -o to
           specify the output file.

           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.

           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.)

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

           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.

           Warn the first time #import is used.

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

           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 some-
           thing like:

                   #if defined the_macro_causing_the_warning

           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.

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

           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

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

           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.

           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 depen-
           dency rules you should explicitly specify the dependency output
           file with -MF, or use an environment variable like DEPENDEN-
           CIES_OUTPUT.  Debug output will still be sent to the regular out-
           put 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.

       -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

           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
           generation, -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 pre-
           processed output, 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 depen-
           dency 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


       -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

           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

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

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

       -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 exten-
           sions 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

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

           standard may be one of:

               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.

               The 1990 C standard, as amended in 1994.

               The revised ISO C standard, published in December 1999.
               Before publication, this was known as C9X.

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

               The 1999 C standard plus GNU extensions.

               The 1998 ISO C++ standard plus amendments.

               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 ".
           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"".

           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.

           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
           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 spec-
           ified 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.  -iwith-
           prefixbefore 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.

           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
           compiler without problems.  In this mode the integrated preproces-
           sor 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.

           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.

           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

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

           CHARS is a sequence of one or more of the following characters,
           and must not be preceded by a space.  Other characters are inter-
           preted 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 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 pre-

       -P  Inhibit generation of linemarkers in the output from the prepro-
           cessor.  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 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.

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

           Process trigraph sequences.

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

           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.

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

       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.

           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 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
           command 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
           directories 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.

           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

           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.

           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.

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

       Copyright (c) 1987, 1989, 1991, 1992, 1993, 1994, 1995, 1996, 1997,
       1998, 1999, 2000, 2001, 2002, 2003, 2004 Free Software Foundation,

       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 con-
       tains 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-3.3.3                         2004-04-13                           CPP(1)