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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 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-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 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.

       This manual describes the behavior of the ISO preprocessor.  To mini-
       mize gratuitous differences, where the ISO preprocessor's behavior does
       not conflict with traditional semantics, the traditional preprocessor
       should behave the same way.  The various differences that do exist are
       detailed in the section @ref{Traditional Mode}.

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


       The C preprocessor expects two file names as arguments, infile and out-
       file.  The preprocessor reads infile together with any other files it
       specifies with #include.	 All the output generated by the combined
       input files is written in outfile.

       Either infile or outfile may be -, which as infile means to read from
       standard input and as outfile means to write to standard output.	 Also,
       if either file is omitted, it means the same as if - had been specified
       for that file.

       Unless otherwise noted, or the option ends in =, all options which take
       an argument may have that argument appear either immediately after the
       option, or with a space between option and argument: -Ifoo and -I foo
       have the same effect.

       Many options have multi-letter names; therefore multiple single-letter
       options may not be grouped: -dM is very different from -d -M.

       -D name
	   Predefine name as a macro, with definition 1.

       -D name=definition
	   Predefine name as a macro, with definition definition.  There are
	   no restrictions on the contents of definition, but if you are
	   invoking the preprocessor from a shell or shell-like program you
	   may need to use the shell's quoting syntax to protect characters
	   such as spaces that have a meaning in the shell syntax.

	   If you wish to define a function-like macro on the command line,
	   write its argument list with surrounding parentheses before the
	   equals sign (if any).  Parentheses are meaningful to most shells,
	   so you will need to quote the option.  With sh and csh,
	   -D'name(args...)=definition' works.

	   -D and -U options are processed in the order they are given on the
	   command line.  All -imacros file and -include file options are 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.	 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 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
	   to control them.

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

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

	   Warn about certain constructs that behave differently in tradi-
	   tional and ISO C.  Also warn about ISO C constructs that have no
	   traditional C equivalent, and problematic constructs which should
	   be avoided.

	   Warn the first time #import is used.

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

	   Warn about macros defined in the main file that are unused.	A
	   macro is used if it is expanded or tested for existence at least
	   once.  The preprocessor will also warn if the macro has not been
	   used at the time it is redefined or undefined.

	   Built-in macros, macros defined on the command line, and macros
	   defined in include files are not warned about.

	   Note: If a macro is actually used, but only used in skipped condi-
	   tional blocks, then CPP will report it as unused.  To avoid the
	   warning in such a case, you might improve the scope of the macro's
	   definition by, for example, moving it into the first skipped block.
	   Alternatively, you could provide a dummy use with 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 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
	   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 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.

	   Like -MF. (APPLE ONLY)

       -MG In conjunction with an option such as -M requesting dependency gen-
	   eration, -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 out-
	   put, 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 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.

       -MD -MD is equivalent to -M -MF file, except that -E is not implied.
	   The driver determines file based on whether an -o option is given.
	   If it is, the driver uses its argument but with a suffix of .d,
	   otherwise it take the basename of the input file and applies a .d

	   If -MD is used in conjunction with -E, any -o switch is understood
	   to specify the dependency output file (but @pxref{-MF}), but if
	   used without -E, each -o is understood to specify a target object

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

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

       -x c
       -x c++
       -x objective-c
       -x 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

	   standard may be one of:

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

	       The -ansi option is equivalent to -std=c89.

	       The 1990 C standard, as amended in 1994.

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

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

	       The 1999 C standard plus GNU extensions.

	       The 1998 ISO C++ standard plus amendments.

	       The same as -std=c++98 plus GNU extensions.  This is the
	       default for C++ code.

       -I- Split the include path.  Any directories specified with -I options
	   before -I- are searched only for headers requested with
	   "#include "file""; they are not searched for "#include <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 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.

	   Indicate to the preprocessor that the input file has already been
	   preprocessed.  This suppresses things like macro expansion, tri-
	   graph conversion, escaped newline splicing, and processing of most
	   directives.	The preprocessor still recognizes and removes com-
	   ments, so that you can pass a file preprocessed with -C to the com-
	   piler 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 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-
	   sor.	 This might be useful when running the preprocessor on some-
	   thing that is not C code, and will be sent to a program which might
	   be confused by the linemarkers.

       -C  Do not discard comments.  All comments are passed through to the
	   output file, except for comments in processed directives, which are
	   deleted along with the directive.

	   You should be prepared for side effects when using -C; it causes
	   the preprocessor to treat comments as tokens in their own right.
	   For example, comments appearing at the start of what would be a
	   directive line have the effect of turning that line into an ordi-
	   nary source line, since the first token on the line is no longer a

       -CC Do not discard comments, including during macro expansion.  This is
	   like -C, except that comments contained within macros are also
	   passed through to the output file where the macro is expanded.

	   In addition to the side-effects of the -C option, the -CC option
	   causes all C++-style comments inside a macro to be converted to
	   C-style comments.  This is to prevent later use of that macro from
	   inadvertently commenting out the remainder of the source line.

	   The -CC option is generally used to support lint comments.

	   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 preprocessors, as
	   opposed to ISO C preprocessors.

	   Process trigraph sequences.

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

	   Print text describing all the command line options instead of pre-
	   processing anything.

       -v  Verbose mode.  Print out GNU CPP's version number at the beginning
	   of execution, and report the final form of the include path.

       -H  Print the name of each header file used, in addition to other nor-
	   mal activities.  Each name is indented to show how deep in the
	   #include stack it is.  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 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.

	   Each variable's value is a list of directories separated by a spe-
	   cial character, much like PATH, in which to look for header files.
	   The special character, "PATH_SEPARATOR", is target-dependent and
	   determined at GCC build time.  For Windows-based targets it is a
	   semicolon, and for almost all other targets it is a colon.

	   CPATH specifies a list of directories to be searched as if speci-
	   fied with -I, but after any paths given with -I options on the com-
	   mand 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 direc-
	   tories to be searched as if specified with -isystem, but after any
	   paths given with -isystem options on the command line.

	   In all these variables, an empty element instructs the compiler to
	   search its current working directory.  Empty elements can appear at
	   the beginning or end of a path.  For instance, if the value of
	   CPATH is ":/special/include", that has the same effect as
	   -I. -I/special/include.

	   If this variable is set, its value specifies how to output depen-
	   dencies for Make based on the non-system header files processed by
	   the compiler.  System header files are ignored in the dependency

	   The value of DEPENDENCIES_OUTPUT can be just a file name, in which
	   case the Make rules are written to that file, guessing the target
	   name from the source file name.  Or the value can have the form
	   file target, in which case the rules are written to file file using
	   target as the target name.

	   In other words, this environment variable is equivalent to combin-
	   ing the options -MM and -MF, with an optional -MT switch too.

	   This variable is the same as DEPENDENCIES_OUTPUT (see above),
	   except that system header files are not ignored, so it implies -M
	   rather than -MM.  However, the dependence on the main input file is


       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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       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-3.3				  2003-09-12				CPP(1)

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