MirBSD manpage: mcpp(1)

CPP(1)                         GNU                         CPP(1)


     mcpp - The GNU C Preprocessor


     cpp [-Dmacro[=defn]...] [-Umacro]
         [-Idir...] [-Wwarn...]
         [-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.

     MirBSD no longer ships a separate cpp binary; /usr/bin/mcpp
     is GNU cpp as below whereas /usr/libexec/cpp is Reiser CCCP.


     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 pro-
     cessor because it allows you to define macros, which are
     brief abbreviations for longer constructs.

     The C preprocessor is intended to be used only with C, C++,
     and Objective-C source code.  In the past, it has been
     abused as a general text processor.  It will choke on input
     which does not obey C's lexical rules.  For example, apos-
     trophes 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 signi-
     ficant to C-family languages.  If a Makefile is prepro-
     cessed, 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 prob-
     lems can be avoided by writing C or C++ style comments
     instead of native language comments, and keeping macros sim-

     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.

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CPP(1)                         GNU                         CPP(1)

     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 Stan-
     dard C, you should use the -std=c89 or -std=c99 options,
     depending on which version of the standard you want.  To get
     all the mandatory diagnostics, you must also use -pedantic.

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

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


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

     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 dif-
     ferent from -d -M.

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

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

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         If you are invoking the preprocessor from a shell or
         shell-like program you may need to use the shell's quot-
         ing 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 com-
         mand 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

     -U name
         Cancel any previous definition of name, either built in
         or provided with a -D option.

         Do not predefine any system-specific or GCC-specific
         macros.  The standard predefined macros remain defined.

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

         Directories named by -I are searched before the standard
         system include directories.  If the directory dir is a
         standard system include directory, the option is ignored
         to ensure that the default search order for system
         directories and the special treatment of system headers
         are not defeated .

     -o file
         Write output to file.  This is the same as specifying
         file as the second non-option argument to cpp.  gcc has
         a different interpretation of a second non-option argu-
         ment, 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 caus-
         ing 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.


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         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.)

         @anchor{Wtrigraphs} Most trigraphs in comments cannot
         affect the meaning of the program. However, a trigraph
         that would form an escaped newline (??/ at the end of a
         line) can, by changing where the comment begins or ends.
         Therefore, only trigraphs that would form escaped new-
         lines 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

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

         Warn the first time #import is used.

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

         Warn about macros defined in the main file that are
         unused.  A macro is used if it is expanded or tested for
         existence at least once. The preprocessor will also warn
         if the macro has not been used at the time it is rede-
         fined 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. Alter-
         natively, you could provide a dummy use with something

                 #if defined the_macro_causing_the_warning

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CPP(1)                         GNU                         CPP(1)

         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

         Make all warnings into hard errors.  Source code which
         triggers warnings will be rejected.

         Act like -Wno-error if the GCC_NO_WERROR environment
         variable is set to anything other than 0 or empty.

         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 manda-
         tory diagnostics into errors.  This includes mandatory
         diagnostics that GCC issues without -pedantic but treats
         as warnings.

     -M  Instead of outputting the result of preprocessing, out-
         put 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

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CPP(1)                         GNU                         CPP(1)

         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 com-

         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 environ-
         ment variable like DEPENDENCIES_OUTPUT.  Debug output
         will still be sent to the regular output stream as nor-

         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 depen-
         dency output.  This is a slight change in semantics from
         GCC versions 3.0 and earlier.


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

         When used with the driver options -MD or -MMD, -MF over-
         rides 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.

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CPP(1)                         GNU                         CPP(1)

         This is typical output:

                 test.o: test.c test.h


     -MT target
         Change the target of the rule emitted by dependency gen-
         eration.  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 suf-
         fix.  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 spe-
         cial 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 argu-
         ment 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{dashMF,,-MF}), 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 compila-
         tion process.

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

     -x c
     -x c++

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CPP(1)                         GNU                         CPP(1)

     -x objective-c
     -x assembler-with-cpp
         Specify the source language: C, C++, Objective-C, or
         assembly.  This has nothing to do with standards confor-
         mance 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 con-
         formance 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.  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.

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CPP(1)                         GNU                         CPP(1)

             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 direc-
         tories 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 stan-
         dard 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 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 mac-
         ros from a header without also processing its declara-

         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 direc-
         tories specified with -I and the standard system

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CPP(1)                         GNU                         CPP(1)

         directories have been exhausted.  dir is treated as a
         system include directory.

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

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

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

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

         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 prepro-
         cessor 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 prepro-
         cessor is little more than a tokenizer for the front

         -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

         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

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CPP(1)                         GNU                         CPP(1)

         character constants.  The default is UTF-8.  charset can
         be any encoding supported by the system's "iconv"
         library routine.

         Set the wide execution character set, used for wide
         string and character constants.  The default is UTF-32
         or UTF-16, whichever corresponds to the width of
         "wchar_t".  As with -ftarget-charset, charset can be any
         encoding supported by the system's "iconv" library rou-
         tine; 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 char-
         acter 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 com-
         mand 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 work-
         ing 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.

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CPP(1)                         GNU                         CPP(1)

     -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 con-
         flicts, 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 prede-
             fined macros.  This gives you a way of finding out
             what is predefined in your version of the preproces-
             sor. 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

         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

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

         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

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CPP(1)                         GNU                         CPP(1)

     -CC Do not discard comments, including during macro expan-
         sion.  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 com-

         Try to imitate the behavior of old-fashioned C prepro-
         cessors, as opposed to ISO C preprocessors.

         Process trigraph sequences.

         Enable special code to work around filesystems 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


     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.

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CPP(1)                         GNU                         CPP(1)

     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 configura-
     tion 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 prepro-

         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 out-
         put 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 tar-
         get as the target name.

         In other words, this environment variable is equivalent
         to combining the options -MM and -MF, with an optional

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CPP(1)                         GNU                         CPP(1)

         -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 depen-
         dence on the main input file is omitted.


     gpl(7), gfdl(7), fsf-funding(7), mgcc(1), as(1), ld(1), and
     the Info entries for cpp, gcc, and binutils: cpp(GNU),
     gcc(GNU), binutils(GNU), cppinternals(GNU).


     Copyright (c) 1987, 1989, 1991, 1992, 1993, 1994, 1995,
     1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
     Free Software Foundation, Inc.
     Copyright (c) 2021 Thorsten Glaser, assigned to the FSF.

     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-3.4.6                  2022-12-23                          15

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