ecpp

CPP(1)                                GNU                               CPP(1)



NAME
       cpp - The C Preprocessor

SYNOPSIS
       cpp [-P] [-C] [-gcc] [-traditional]
           [-undef] [-trigraphs] [-pedantic]
           [-Wwarn...] [-Idir...]
           [-Dmacro[=defn]...] [-Umacro]
           [-Apredicate(answer)]
           [-M-MM-MD-MMD [-MG]]
           [-x language] [-std=standard]
           infile outfile

       Only the most useful options are listed here; see below for the
       remainder.

DESCRIPTION
       The C preprocessor is a macro processor that is used automatically by
       the C compiler to transform your program before actual 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 only for macro processing of C, C++ and
       Objective C source files.  For macro processing of other files, you are
       strongly encouraged to use alternatives like M4, which will likely give
       you better results and avoid many problems.  For example, normally the
       C preprocessor does not preserve arbitrary whitespace verbatim, but
       instead replaces each sequence with a single space.

       For use on C-like source files, the C preprocessor provides four
       separate facilities that you can use as you see fit:

       ·   Inclusion of header files.  These are files of declarations that
           can be substituted into your program.

       ·   Macro expansion.  You can define macros, which are abbreviations
           for arbitrary fragments of C code, and then the C preprocessor will
           replace the macros with their definitions throughout the program.

       ·   Conditional compilation.  Using special preprocessing directives,
           you can include or exclude parts of the program according to
           various conditions.

       ·   Line control.  If you use a program to combine or rearrange source
           files into an intermediate file which is then compiled, you can use
           line control to inform the compiler of where each source line
           originally came from.

       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.

OPTIONS
       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.

       Here is a table of command options accepted by the C preprocessor.
       These options can also be given when compiling a C program; they are
       passed along automatically to the preprocessor when it is invoked by
       the compiler.

       -P  Inhibit generation of #-lines with line-number information 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 #-lines.

       -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.  Comments appearing in the
           expansion list of a macro will be preserved, and appear in place
           wherever the macro is invoked.

           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, macro redefinitions that were trivial when comments
           were replaced by a single space might become significant when
           comments are retained.  Also, 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 #.

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

           ·   Traditional macro expansion pays no attention to single-quote
               or double-quote characters; macro argument symbols are replaced
               by the argument values even when they appear within apparent
               string or character constants.

           ·   Traditionally, it is permissible for a macro expansion to end
               in the middle of a string or character constant.  The constant
               continues into the text surrounding the macro call.

           ·   However, traditionally the end of the line terminates a string
               or character constant, with no error.

           ·   In traditional C, a comment is equivalent to no text at all.
               (In ISO C, a comment counts as whitespace.)

           ·   Traditional C does not have the concept of a ``preprocessing
               number''.  It considers 1.0e+4 to be three tokens: 1.0e, +, and
               4.

           ·   A macro is not suppressed within its own definition, in
               traditional C.  Thus, any macro that is used recursively
               inevitably causes an error.

           ·   The character # has no special meaning within a macro
               definition in traditional C.

           ·   In traditional C, the text at the end of a macro expansion can
               run together with the text after the macro call, to produce a
               single token.  (This is impossible in ISO C.)

           ·   None of the GNU extensions to the preprocessor are available in
               -traditional mode.

           Use the -traditional option when preprocessing Fortran code, so
           that single-quotes and double-quotes within Fortran comment lines
           (which are generally not recognized as such by the preprocessor) do
           not cause diagnostics about unterminated character or string
           constants.

           However, this option does not prevent diagnostics about
           unterminated comments when a C-style comment appears to start, but
           not end, within Fortran-style commentary.

           So, the following Fortran comment lines are accepted with
           -traditional:

                   C This isn't an unterminated character constant
                   C Neither is "20000000000, an octal constant
                   C in some dialects of Fortran

           However, this type of comment line will likely produce a
           diagnostic, or at least unexpected output from the preprocessor,
           due to the unterminated comment:

                   C Some Fortran compilers accept /* as starting
                   C an inline comment.

           Note that g77 automatically supplies the -traditional option when
           it invokes the preprocessor.  However, a future version of g77
           might use a different, more-Fortran-aware preprocessor in place of
           cpp.

       -trigraphs
           Process ISO standard trigraph sequences.  These are three-character
           sequences, all starting with ??, that are defined by ISO C to stand
           for single characters.  For example, ??/ stands for \, so '??/n' is
           a character constant for a newline.  By default, GCC ignores
           trigraphs, but in standard-conforming modes it converts them.  See
           the -std option.

           The nine trigraph sequences are
           ??(   ->   [
           ??)   ->   ]
           ??<   ->   @{
           ??>   ->   @}
           ??=   ->   #
           ??/   ->   \
           ??'   ->   ^
           ??!   ->   
           ??-   ->   ~

           Trigraph support is not popular, so many compilers do not implement
           it properly.  Portable code should not rely on trigraphs being
           either converted or ignored.

       -pedantic
           Issue warnings required by the ISO C standard in certain cases such
           as when text other than a comment follows #else or #endif.

       -pedantic-errors
           Like -pedantic, except that errors are produced rather than
           warnings.

       -Wcomment

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

       -Wtrigraphs
           Warn if any trigraphs are encountered.  This option used to take
           effect only if -trigraphs was also specified, but now works
           independently.

       -Wwhite-space
           Warn about possible white space confusion, e.g. white space between
           a backslash and a newline.

       -Wall
           Requests -Wcomment, -Wtrigraphs, and -Wwhite-space (but not
           -Wtraditional or -Wundef).

       -Wtraditional
           Warn about certain constructs that behave differently in
           traditional and ISO C.

       -Wundef
           Warn if an undefined identifier is evaluated in an #if directive.

       -I directory
           Add the directory directory to the head of the list of directories
           to be searched for header files This can be used to override a
           system header file, substituting your own version, since these
           directories are searched before the system header file directories.
           If you use more than one -I option, the directories are scanned in
           left-to-right order; the standard system directories come after.

       -I- Any directories specified with -I options before the -I- option are
           searched only for the case of #include "file"; they are not
           searched for #include <file>.

           If additional directories are specified with -I options after the
           -I-, these directories are searched for all #include directives.

           In addition, the -I- option inhibits the use of the current
           directory as the first search directory for #include "file".
           Therefore, the current directory is searched only if it is
           requested explicitly with -I..  Specifying both -I- and -I.  allows
           you to control precisely which directories are searched before the
           current one and which are searched after.

       -nostdinc
           Do not search the standard system directories for header files.
           Only the directories you have specified with -I options (and the
           current directory, if appropriate) are searched.

       -nostdinc++
           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.)

       -remap
           When searching for a header file in a directory, remap file names
           if a file named header.gcc exists in that directory.  This can be
           used to work around limitations of file systems with file name
           restrictions.  The header.gcc file should contain a series of lines
           with two tokens on each line: the first token is the name to map,
           and the second token is the actual name to use.

       -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 use
           more than one -D for the same name, the rightmost definition takes
           effect.

       -U name
           Do not predefine name.  If both -U and -D are specified for one
           name, whichever one appears later on the command line wins.

       -undef
           Do not predefine any nonstandard macros.

       -gcc
           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.

       -A predicate(answer)
           Make an assertion with the predicate predicate and answer answer.

       -A -predicate(answer)
           Disable an assertion with the predicate predicate and answer
           answer.  Specifying no predicate, by -A- or -A -, disables all
           predefined assertions and all assertions preceding it on the
           command line; and also undefines all predefined macros and all
           macros preceding it on the command line.

       -dM Instead of outputting the result of preprocessing, output 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 the values of any predefined macros.

       -dD Like -dM 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.

       -dN Like -dD, but emit only the macro names, not their expansions.

       -dI Output #include directives in addition to the result of
           preprocessing.

       -M [-MG]
           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.  If there are many included files then the rule is
           split into several lines using \-newline.

           -MG says to treat missing header files as generated files and
           assume they live in the same directory as the source file.  It must
           be specified in addition to -M.

           This feature is used in automatic updating of makefiles.

       -MM [-MG]
           Like -M but mention only the files included with #include "file".
           System header files included with #include <file> are omitted.

       -MD file
           Like -M but the dependency information is written to file.  This is
           in addition to compiling the file as specified --- -MD does not
           inhibit ordinary compilation the way -M does.

           When invoking gcc, do not specify the file argument.  gcc will
           create file names made by replacing ".c" with ".d" at the end of
           the input file names.

           In Mach, you can use the utility md to merge multiple dependency
           files into a single dependency file suitable for using with the
           make command.

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

       -H  Print the name of each header file used, in addition to other
           normal activities.

       -imacros file
           Process file as input, discarding the resulting output, before
           processing the regular input file.  Because the output generated
           from file is discarded, the only effect of -imacros file is to make
           the macros defined in file available for use in the main input.

       -include file
           Process file as input, and include all the resulting output, before
           processing the regular input file.

       -idirafter dir
           Add the directory dir to the second include path.  The directories
           on the second include path are searched when a header file is not
           found in any of the directories in the main include path (the one
           that -I adds to).

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

       -iwithprefix dir
           Add a directory to the second include path.  The directory's name
           is made by concatenating prefix and dir, where prefix was specified
           previously with -iprefix.

       -isystem dir
           Add a directory to the beginning of the second include path,
           marking it as a system directory, so that it gets the same special
           treatment as is applied to the standard system directories.

       -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.

       -std=standard

       -ansi
           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:

           iso9899:1990
           c89
               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.

           iso9899:199409
               The 1990 C standard, as amended in 1994.

           iso9899:1999
           c99
           iso9899:199x
           c9x
               The revised ISO C standard, published in December 1999.  Before
               publication, this was known as C9X.

           gnu89
               The 1990 C standard plus GNU extensions.  This is the default.

           gnu99
           gnu9x
               The 1999 C standard plus GNU extensions.

       -ftabstop=NUMBER
           Set the distance between tabstops.  This helps the preprocessor
           report correct column numbers in warnings or errors, even if tabs
           appear on the line.  Values less than 1 or greater than 100 are
           ignored.  The default is 8.

       -$  Forbid the use of $ in identifiers.  The C standard allows
           implementations to define extra characters that can appear in
           identifiers.  By default the GNU C preprocessor permits $, a common
           extension.

SEE ALSO
       gcc(1), as(1), ld(1), and the Info entries for cpp, gcc, and binutils.

COPYRIGHT
       Copyright  1987, 1989, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
       1999, 2000 Free Software Foundation, Inc.

       Permission is granted to make and distribute verbatim copies of this
       manual provided the copyright notice and this permission notice are
       preserved on all copies.

       Permission is granted to copy and distribute modified versions of this
       manual under the conditions for verbatim copying, provided also that
       the entire resulting derived work is distributed under the terms of a
       permission notice identical to this one.

       Permission is granted to copy and distribute translations of this
       manual into another language, under the above conditions for modified
       versions.



3rd Berkeley Distribution           gcc-3.0                             CPP(1)