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 remain-


       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 mode pre-
       serves 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.


       The C preprocessor expects two file names as arguments, infile and out-
       file.  The preprocessor reads infile together with any other files it
       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 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.

           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 interpreta-
           tion 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
           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.

           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 dependency
           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 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


       -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.


           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 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

           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:

               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.

           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 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.

           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 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 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.)

           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-

       -P  Inhibit generation of linemarkers in the output from the preproces-
           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

           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.

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

           Process trigraph sequences.

           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 imple-
           mentations to define extra characters that can appear in identi-
           fiers.  By default GNU CPP permits $, a common extension.

           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 pre-
           process 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.

           mand 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 direc-
           tories 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}.

           @anchor{DEPENDENCIES_OUTPUT} If this variable is set, its value
           specifies how to output dependencies for Make based on the non-sys-
           tem 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.

           This variable is the same as the environment variable DEPENDEN-
           CIES_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.


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


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       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.