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CPP(1)                               GNU                              CPP(1)

NAME         top

       cpp - The C Preprocessor

SYNOPSIS         top

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

DESCRIPTION         top

       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
       Objective-C source code.  In the past, it has been abused as a
       general text processor.  It will choke on input which does not obey
       C's lexical rules.  For example, apostrophes will be interpreted as
       the beginning of character constants, and cause errors.  Also, you
       cannot rely on it preserving characteristics of the input which are
       not significant to C-family languages.  If a Makefile is
       preprocessed, all the hard tabs will be removed, and the Makefile
       will not work.

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

       Wherever possible, you should use a preprocessor geared to the
       language you are writing in.  Modern versions of the GNU assembler
       have macro facilities.  Most high level programming languages have
       their own conditional compilation and inclusion mechanism.  If all
       else fails, try a true general text processor, such as GNU M4.

       C preprocessors vary in some details.  This manual discusses the GNU
       C preprocessor, which provides a small superset of the features of
       ISO Standard C.  In its default mode, the GNU C preprocessor does not
       do a few things required by the standard.  These are features which
       are rarely, if ever, used, and may cause surprising changes to the
       meaning of a program which does not expect them.  To get strict ISO
       Standard C, you should use the -std=c90, -std=c99 or -std=c11
       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.

OPTIONS         top

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

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

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

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

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

       -D name=definition
           The contents of definition are tokenized and processed as if they
           appeared during translation phase three in a #define directive.
           In particular, the definition will be truncated by embedded
           newline characters.

           If you are invoking the preprocessor from a shell or shell-like
           program you may need to use the shell's quoting syntax to protect
           characters such as spaces that have a meaning in the shell
           syntax.

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

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

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

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

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

           Directories named by -I are searched before the standard system
           include directories.  If the directory dir is a standard system
           include directory, the option is ignored to ensure that the
           default search order for system directories and the special
           treatment of system headers are not defeated .  If dir begins
           with "=", then the "=" will be replaced by the sysroot prefix;
           see --sysroot and -isysroot.

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

       -Wall
           Turns on all optional warnings which are desirable for normal
           code.  At present this is -Wcomment, -Wtrigraphs, -Wmultichar and
           a warning about integer promotion causing a change of sign in
           "#if" expressions.  Note that many of the preprocessor's warnings
           are on by default and have no options to control them.

       -Wcomment
       -Wcomments
           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.)

       -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 newlines produce warnings inside a comment.

           This option is implied by -Wall.  If -Wall is not given, this
           option is still enabled unless trigraphs are enabled.  To get
           trigraph conversion without warnings, but get the other -Wall
           warnings, use -trigraphs -Wall -Wno-trigraphs.

       -Wtraditional
           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.

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

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

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

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

                   #if defined the_macro_causing_the_warning
                   #endif

       -Wendif-labels
           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.

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

       -Wsystem-headers
           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.

       -pedantic
           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.

       -pedantic-errors
           Issue all the mandatory diagnostics, and make all mandatory
           diagnostics 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 name of the source file with any suffix
           replaced with object file suffix and with any leading directory
           parts removed.  If there are many included files then the rule is
           split into several lines using \-newline.  The rule has no
           commands.

           This option does not suppress the preprocessor's debug output,
           such as -dM.  To avoid mixing such debug output with the
           dependency rules you should explicitly specify the dependency
           output file with -MF, or use an environment variable like
           DEPENDENCIES_OUTPUT.  Debug output will still be sent to the
           regular output stream as normal.

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

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

       -MG In conjunction with an option such as -M requesting dependency
           generation, -MG assumes missing header files are generated files
           and adds them to the dependency list without raising an error.
           The dependency filename is taken directly from the "#include"
           directive without prepending any path.  -MG also suppresses
           preprocessed output, as a missing header file renders this
           useless.

           This feature is used in automatic updating of makefiles.

       -MP This option instructs CPP to add a phony target for each
           dependency other than the main file, causing each to depend on
           nothing.  These dummy rules work around errors make gives if you
           remove header files without updating the Makefile to match.

           This is typical output:

                   test.o: test.c test.h

                   test.h:

       -MT target
           Change the target of the rule emitted by dependency generation.
           By default CPP takes the name of the main input file, deletes any
           directory components and any file suffix such as .c, and appends
           the platform's usual object suffix.  The result is the target.

           An -MT option will set the target to be exactly the string you
           specify.  If you want multiple targets, you can specify them as a
           single argument to -MT, or use multiple -MT options.

           For example, -MT '$(objpfx)foo.o' might give

                   $(objpfx)foo.o: foo.c

       -MQ target
           Same as -MT, but it quotes any characters which are special to
           Make.  -MQ '$(objpfx)foo.o' gives

                   $$(objpfx)foo.o: foo.c

           The default target is automatically quoted, as if it were given
           with -MQ.

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

           If -MD is used in conjunction with -E, any -o switch is
           understood to specify the dependency output file, but if used
           without -E, each -o is understood to specify a target object
           file.

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

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

       -x c
       -x c++
       -x objective-c
       -x assembler-with-cpp
           Specify the source language: C, C++, Objective-C, or assembly.
           This has nothing to do with standards conformance or extensions;
           it merely selects which base syntax to expect.  If you give none
           of these options, cpp will deduce the language from the extension
           of the source file: .c, .cc, .m, or .S.  Some other common
           extensions for C++ and assembly are also recognized.  If cpp does
           not recognize the extension, it will treat the file as C; this is
           the most generic mode.

           Note: Previous versions of cpp accepted a -lang option which
           selected both the language and the standards conformance level.
           This option has been removed, because it conflicts with the -l
           option.

       -std=standard
       -ansi
           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:

           "c90"
           "c89"
           "iso9899:1990"
               The ISO C standard from 1990.  c90 is the customary shorthand
               for this version of the standard.

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

           "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.

           "iso9899:2011"
           "c11"
           "c1x"
               The revised ISO C standard, published in December 2011.
               Before publication, this was known as C1X.

           "gnu90"
           "gnu89"
               The 1990 C standard plus GNU extensions.  This is the
               default.

           "gnu99"
           "gnu9x"
               The 1999 C standard plus GNU extensions.

           "gnu11"
           "gnu1x"
               The 2011 C standard plus GNU extensions.

           "c++98"
               The 1998 ISO C++ standard plus amendments.

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

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

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

           This option has been deprecated.

       -nostdinc
           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.

       -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.)

       -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 macros from a header without
           also processing its declarations.

           All files specified by -imacros are processed before all files
           specified by -include.

       -idirafter dir
           Search dir for header files, but do it after all directories
           specified with -I and the standard system directories have been
           exhausted.  dir is treated as a system include directory.  If dir
           begins with "=", then the "=" will be replaced by the sysroot
           prefix; see --sysroot and -isysroot.

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

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

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

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

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

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

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

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

       -fdirectives-only
           When preprocessing, handle directives, but do not expand macros.

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

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

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

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

       -fdollars-in-identifiers
           Accept $ in identifiers.

       -fextended-identifiers
           Accept universal character names in identifiers.  This option is
           enabled by default for C99 (and later C standard versions) and
           C++.

       -fno-canonical-system-headers
           When preprocessing, do not shorten system header paths with
           canonicalization.

       -fpreprocessed
           Indicate to the preprocessor that the input file has already been
           preprocessed.  This suppresses things like macro expansion,
           trigraph conversion, escaped newline splicing, and processing of
           most directives.  The preprocessor still recognizes and removes
           comments, so that you can pass a file preprocessed with -C to the
           compiler without problems.  In this mode the integrated
           preprocessor is little more than a tokenizer for the front ends.

           -fpreprocessed is implicit if the input file has one of the
           extensions .i, .ii or .mi.  These are the extensions that GCC
           uses for preprocessed files created by -save-temps.

       -ftabstop=width
           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.

       -fdebug-cpp
           This option is only useful for debugging GCC.  When used with -E,
           dumps debugging information about location maps.  Every token in
           the output is preceded by the dump of the map its location
           belongs to.  The dump of the map holding the location of a token
           would be:

                   {"P":F</file/path>;"F":F</includer/path>;"L":<line_num>;"C":<col_num>;"S":<system_header_p>;"M":<map_address>;"E":<macro_expansion_p>,"loc":<location>}

           When used without -E, this option has no effect.

       -ftrack-macro-expansion[=level]
           Track locations of tokens across macro expansions. This allows
           the compiler to emit diagnostic about the current macro expansion
           stack when a compilation error occurs in a macro expansion. Using
           this option makes the preprocessor and the compiler consume more
           memory. The level parameter can be used to choose the level of
           precision of token location tracking thus decreasing the memory
           consumption if necessary. Value 0 of level de-activates this
           option just as if no -ftrack-macro-expansion was present on the
           command line. Value 1 tracks tokens locations in a degraded mode
           for the sake of minimal memory overhead. In this mode all tokens
           resulting from the expansion of an argument of a function-like
           macro have the same location. Value 2 tracks tokens locations
           completely. This value is the most memory hungry.  When this
           option is given no argument, the default parameter value is 2.

           Note that "-ftrack-macro-expansion=2" is activated by default.

       -fexec-charset=charset
           Set the execution character set, used for string and character
           constants.  The default is UTF-8.  charset can be any encoding
           supported by the system's "iconv" library routine.

       -fwide-exec-charset=charset
           Set the wide execution character set, used for wide string and
           character constants.  The default is UTF-32 or UTF-16, whichever
           corresponds to the width of "wchar_t".  As with -fexec-charset,
           charset can be any encoding supported by the system's "iconv"
           library routine; however, you will have problems with encodings
           that do not fit exactly in "wchar_t".

       -finput-charset=charset
           Set the input character set, used for translation from the
           character set of the input file to the source character set used
           by GCC.  If the locale does not specify, or GCC cannot get this
           information from the locale, the default is UTF-8.  This can be
           overridden by either the locale or this command-line option.
           Currently the command-line option takes precedence if there's a
           conflict.  charset can be any encoding supported by the system's
           "iconv" library routine.

       -fworking-directory
           Enable generation of linemarkers in the preprocessor output that
           will let the compiler know the current working directory at the
           time of preprocessing.  When this option is enabled, the
           preprocessor will emit, after the initial linemarker, a second
           linemarker with the current working directory followed by two
           slashes.  GCC will use this directory, when it's present in the
           preprocessed input, as the directory emitted as the current
           working directory in some debugging information formats.  This
           option is implicitly enabled if debugging information is enabled,
           but this can be inhibited with the negated form
           -fno-working-directory.  If the -P flag is present in the command
           line, this option has no effect, since no "#line" directives are
           emitted whatsoever.

       -fno-show-column
           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 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
           characters.

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

       -dCHARS
           CHARS is a sequence of one or more of the following characters,
           and must not be preceded by a space.  Other characters are
           interpreted by the compiler proper, or reserved for future
           versions of GCC, and so are silently ignored.  If you specify
           characters whose behavior conflicts, the result is undefined.

           M   Instead of the normal output, generate a list of #define
               directives for all the macros defined during the execution of
               the preprocessor, including predefined macros.  This gives
               you a way of finding out what is predefined in your version
               of the preprocessor.  Assuming you have no file foo.h, the
               command

                       touch foo.h; cpp -dM foo.h

               will show all the predefined macros.

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

           D   Like M except in two respects: it does not include the
               predefined macros, and it outputs both the #define directives
               and the result of preprocessing.  Both kinds of output go to
               the standard output file.

           N   Like D, but emit only the macro names, not their expansions.

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

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

       -P  Inhibit generation of linemarkers in the output from the
           preprocessor.  This might be useful when running the preprocessor
           on something that is not C code, and will be sent to a program
           which might be confused by the linemarkers.

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

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

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

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

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

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

       -trigraphs
           Process trigraph sequences.

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

       --help
       --target-help
           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 ...! .

       -version
       --version
           Print out GNU CPP's version number.  With one dash, proceed to
           preprocess as normal.  With two dashes, exit immediately.

ENVIRONMENT         top

       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.

       CPATH
       C_INCLUDE_PATH
       CPLUS_INCLUDE_PATH
       OBJC_INCLUDE_PATH
           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 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.  This environment variable is used regardless
           of which language is being preprocessed.

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

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

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

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

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

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

SEE ALSO         top

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

COPYRIGHT         top

       Copyright (c) 1987-2016 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 1.3 or
       any later version published by the Free Software Foundation.  A copy
       of the license is included in the man page gfdl(7).  This manual
       contains no Invariant Sections.  The Front-Cover Texts are (a) (see
       below), and the Back-Cover Texts are (b) (see below).

       (a) The FSF's Front-Cover Text is:

            A GNU Manual

       (b) The FSF's Back-Cover Text is:

            You have freedom to copy and modify this GNU Manual, like GNU
            software.  Copies published by the Free Software Foundation raise
            funds for GNU development.

COLOPHON         top

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       If you have a bug report for this manual page, see 
       ⟨http://gcc.gnu.org/bugs/⟩.  This page was obtained from the tarball
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gcc-6.1.0                        2016-04-27                           CPP(1)