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Linux 2.6 - man page for cpp-4.6 (linux section 1)

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

       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=c90, -std=c99 or -std=c1x 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 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.

	   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 .  If dir begins with "=", then the "=" will be
	   replaced by the sysroot prefix; see --sysroot and -isysroot.

       -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 appears in a // comment.  (Both forms have the same effect.)

	   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 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 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

	   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

       -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
	   name of the source file with any suffix replaced with object file suffix and with any
	   leading directory parts removed.  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

	   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

       -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.

       -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, deletes any directory components and 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 takes the name of the input file,
	   removes any directory components and suffix, 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 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.

	   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.  c90 is the customary shorthand for this version of
	       the standard.

	       The -ansi option is equivalent to -std=c90.

	       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 next version of the ISO C standard, still under development.

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

	       The 1999 C standard plus GNU extensions.

	       The next version of the ISO C standard, still under development, plus GNU

	       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++

       -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

	   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.  If dir begins with "=", then the "=" will be replaced by the sysroot
	   prefix; see --sysroot and -isysroot.

       -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.

       -isysroot dir
	   This option is like the --sysroot option, but applies only to header files (except for
	   Darwin targets, where it applies to both header files and libraries).  See the
	   --sysroot option for more information.

       -imultilib dir
	   Use dir as a subdirectory of the directory containing target-specific C++ headers.

       -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.

	   If dir begins with "=", then the "=" will be replaced by the sysroot prefix; see
	   --sysroot and -isysroot.

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

	   If dir begins with "=", then the "=" will be replaced by the sysroot prefix; see
	   --sysroot and -isysroot.

	   When preprocessing, handle directives, but do not expand macros.

	   The option's behavior depends on the -E and -fpreprocessed options.

	   With -E, preprocessing is limited to the handling of directives such as "#define",
	   "#ifdef", and "#error".  Other preprocessor operations, such as macro expansion and
	   trigraph conversion are not performed.  In addition, the -dD option is implicitly

	   With -fpreprocessed, predefinition of command line and most builtin macros is
	   disabled.  Macros such as "__LINE__", which are contextually dependent, are handled
	   normally.  This enables compilation of files previously preprocessed with "-E

	   With both -E and -fpreprocessed, the rules for -fpreprocessed take precedence.  This
	   enables full preprocessing of files previously preprocessed with "-E

	   Accept $ in identifiers.

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

	   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

	   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

       -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.

	   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.

	       If you use -dM without the -E option, -dM is interpreted as a synonym for

	   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.

	   U   Like D except that only macros that are expanded, or whose definedness is tested
	       in preprocessor directives, are output; the output is delayed until the use or
	       test of the macro; and #undef directives are also output for macros tested but
	       undefined at the time.

       -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

	   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 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 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 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

	   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 name.

	   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 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, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Free Software Foundation,

       Permission is granted to copy, distribute and/or modify this document under the terms of
       the GNU Free Documentation License, Version 1.3 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-4.6.1				    2011-09-03					   CPP(1)

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