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CPP(1)                                               GNU                                              CPP(1)

       cpp - The C Preprocessor

       cpp [-Dmacro[=defn]...] [-Umacro]
           [-Idir...] [-iquotedir...]
           [-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 remainder.

       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-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 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.

       This manual describes the behavior of the ISO preprocessor.  To minimize 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.

       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
           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

           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'

           -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.

           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 interpretation 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, -Wtrigraphs, -Wmultichar and a warning 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.

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

           @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 trigraph conversion without warnings, but get the other -Wall
           warnings, use -trigraphs -Wall -Wno-trigraphs.

           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.

           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 conditional 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

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

                   #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 them.

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

           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 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, 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
           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.

           Like -MF. (APPLE ONLY)

       -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 preprocessed 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 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
           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 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.

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

       -x c
       -x c++
       -x objective-c
       -x objective-c++
       -x assembler-with-cpp
           Specify the source language: C, C++, Objective-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, .mm, 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

           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:

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

               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 <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.

           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 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.

       -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

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

           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.

           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.

           Set the execution character set, used for string and character constants.  The default is UTF-8.
           charset can be any encoding supported by the system's "iconv" library routine.

           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".

           Set the input character set, used for translation from the character 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 command line option takes precedence if there's a
           conflict.  charset can be any encoding supported by the system's "iconv" library routine.

           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
           preprocessor 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 inhibited 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.

           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

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

           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 #.

       -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

           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.  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 ...! .

           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

       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 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 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 specified 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 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

           In other words, this environment variable is equivalent to combining 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

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

       Copyright (c) 1987, 1989, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002,
       2003, 2004, 2005 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.

gcc-4.0.1                                        2007-09-23                                           CPP(1)

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