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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 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 proces-
       sor because it allows you to define macros, which are brief abbreviations for longer con-

       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 preserv-
       ing 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

       Having said that, you can often get away with using cpp on things which are not C.  Other
       Algol-ish programming languages are often safe (Pascal, Ada, etc.) So is assembly, with
       caution.  -traditional mode preserves more white space, and is otherwise more permissive.
       Many of the problems can be avoided by writing C or C++ style comments instead of native
       language comments, and keeping macros simple.

       Wherever possible, you should use a preprocessor geared to the language you are writing
       in.  Modern versions of the GNU assembler have macro facilities.  Most high level program-
       ming 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 pro-
       gram 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.

       The C preprocessor expects two file names as arguments, infile and outfile.  The pre-
       processor 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 charac-
	   ters 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 macros.  The common predefined macros remain

       -I dir
	   Add the directory dir to the list of directories to be searched for header files.

	   Directories named by -I are searched before the standard system include directories.

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

       -o file
	   Write output to file.  This is the same as specifying file as the second non-option
	   argument to cpp.  gcc has a different interpretation of a second non-option argument,
	   so you must use -o to specify the output file.

	   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 back-
	   slash-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 -tri-
	   graphs was also specified, but now works independently.  Warnings are not given for
	   trigraphs within comments, as they do not affect the meaning of the program.

	   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.

	   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
	   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 \-new-
	   line.  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_OUT-
	   PUT.  Debug output will still be sent to the regular output stream as normal.

	   Passing -M to the driver implies -E.

       -MM Like -M but do not mention header files that are found in system header directories,
	   nor header files that are included, directly or indirectly, from such a header.

	   This implies that the choice of angle brackets or double quotes in an #include direc-
	   tive does not in itself determine whether that header will appear in -MM dependency
	   output.  This is a slight change in semantics from GCC versions 3.0 and earlier.

       -MF file
	   @anchor{-MF} When used with -M or -MM, specifies a file to write the dependencies to.
	   If no -MF switch is given the preprocessor sends the rules to the same place it would
	   have sent preprocessed output.

	   When used with the driver options -MD or -MMD, -MF overrides the default dependency
	   output file.

       -MG When used with -M or -MM, -MG says to treat missing header files as generated files
	   and assume they live in the same directory as the source file.  It suppresses prepro-
	   cessed 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 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 deter-
	   mines file based on whether an -o option is given.  If it is, the driver uses its
	   argument but with a suffix of .d, otherwise it take the basename of the input file and
	   applies a .d suffix.

	   If -MD is used in conjunction with -E, any -o switch is understood to specify the
	   dependency output file (but @pxref{-MF}), but if used without -E, each -o is under-
	   stood 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 lan-
	   guage 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 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.

	       The 1999 C standard plus GNU extensions.

       -I- Split the include path.  Any directories specified with -I options before -I- are
	   searched only for headers requested with "#include "file""; they are not searched for
	   "#include <file>".  If additional directories are specified with -I options after the
	   -I-, those directories are searched for all #include directives.

	   In addition, -I- inhibits the use of the directory of the current file directory as
	   the first search directory for "#include "file"".

	   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 appro-
	   priate) 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

       -iprefix prefix
	   Specify prefix as the prefix for subsequent -iwithprefix options.  If the prefix rep-
	   resents a directory, you should include the final /.

       -iwithprefix dir
       -iwithprefixbefore dir
	   Append dir to the prefix specified previously with -iprefix, and add the resulting
	   directory to the include search path.  -iwithprefixbefore puts it in the same place -I
	   would; -iwithprefix puts it where -idirafter would.

	   Use of these options is discouraged.

       -isystem dir
	   Search dir for header files, after all directories specified by -I but before the
	   standard system directories.  Mark it as a system directory, so that it gets the same
	   special treatment as is applied to the standard system directories.

	   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 com-
	   ments, so that you can pass a file preprocessed with -C to the compiler without prob-
	   lems.  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.

	   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 pre-
	   ferred to the older form -A predicate(answer), which is still supported, because it
	   does not use shell special characters.

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

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

	   CHARS is a sequence of one or more of the following characters, and must not be pre-
	   ceded 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 #.

	   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 C.

	   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 implementations to define
	   extra characters that can appear in identifiers.  By default GNU CPP permits $, a com-
	   mon extension.

	   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.

	   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_SEPARA-
	   TOR", is target-dependent and determined at GCC build time.	For Windows-based targets
	   it is a semicolon, and for almost all other targets it is a colon.

	   CPATH specifies a list of directories to be searched as if specified with -I, but
	   after any paths given with -I options on the command line.  The environment variable
	   is used regardless of which language is being preprocessed.

	   The remaining environment variables apply only when preprocessing the particular lan-
	   guage indicated.  Each specifies a list of directories to be searched as if specified
	   with -isystem, but after any paths given with -isystem options on the command line.

	   See also @ref{Search Path}.

	   @anchor{DEPENDENCIES_OUTPUT} If this variable is set, its value specifies how to out-
	   put dependencies for Make based on the non-system header files processed by the com-
	   piler.  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 the environment variable DEPENDENCIES_OUTPUT, except that
	   system header files are not ignored, so it implies -M rather than -MM.  However, the
	   dependence on the main input file is omitted.

       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
       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-3.2.2				    2003-02-25					   CPP(1)
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