cpp [-Dmacro[=defn]...] [-Umacro]
 [-Idir...] [-iquotedir...]
 [-iremapsrc:dst]
 [-Wwarn...]
 [-M|-MM] [-MG] [-MF filename]
 [-MP] [-MQ target...]
 [-MT target...]
 infile [[-o] outfile]
Only the most useful options are given above; see below for a more
    complete list of preprocessor-specific options. In addition, cpp
    accepts most gcc driver options, which are not listed here. Refer to
    the GCC documentation for details.
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 (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, -std=c11 or -std=c17
    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 cpp command 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. If either file is omitted, it means the same as
    if - had been specified for that file. You can also use the -o
    outfile option to specify the output 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 is 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
        should 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.
- -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. 
- -undef
- Do not predefine any system-specific or GCC-specific macros. The standard
      predefined macros remain defined.
- -pthread
- Define additional macros required for using the POSIX threads library. You
      should use this option consistently for both compilation and linking. This
      option is supported on GNU/Linux targets, most other Unix derivatives, and
      also on x86 Cygwin and MinGW targets.
- -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 is still 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 appears in -MM dependency output. 
- -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 send preprocessed output.
    When used with the driver options -MD or -MMD,
        -MF overrides the default dependency output file. If file is -, then the dependencies are written
        to stdout. 
- -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 sets 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.
- -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. 
- -cxx-isystem dir
- Search dir for C++ 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.
- -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". 
- -iremap src:dst
- Replace the prefix src in __FILE__ with dst at expansion
      time. This option can be specified more than once. Processing stops at the
      first match.
- -fdollars-in-identifiers
- Accept $ in identifiers.
- -fextended-identifiers
- Accept universal character names and extended characters 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.
- -fmax-include-depth=depth
- Set the maximum depth of the nested #include. The default is 200.
- -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.
- -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. 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. 
- -fmacro-prefix-map=old=new
- When preprocessing files residing in directory old,
      expand the "__FILE__" and
      "__BASE_FILE__" macros as if the files
      resided in directory new instead. This can be used to
      change an absolute path to a relative path by using . for
      new which can result in more reproducible builds that are location
      independent. This option also affects
      "__builtin_FILE()" during compilation.
      See also -ffile-prefix-map.
- -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 one of UTF-32BE, UTF-32LE, UTF-16BE, or
      UTF-16LE, whichever corresponds to the width of
      "wchar_t" and the big-endian or
      little-endian byte order being used for code generation. 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 let the
      compiler know the current working directory at the time of preprocessing.
      When this option is enabled, the preprocessor emits, after the initial
      linemarker, a second linemarker with the current working directory
      followed by two slashes. GCC uses 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.
- -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.
- -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. 
- -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.
- -traditional
- -traditional-cpp
- Try to imitate the behavior of pre-standard C preprocessors, as opposed to
      ISO C preprocessors.
    Note that GCC does not otherwise attempt to emulate a
        pre-standard C compiler, and these options are only supported with the
        -E switch, or when invoking CPP explicitly. 
- -trigraphs
- Support ISO C trigraphs. 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 and -ansi
      options. 
- -remap
- Enable special code to work around file systems which only permit very
      short file names, such as MS-DOS.
- -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 ...! .
- -dletters
- Says to make debugging dumps during compilation as specified by
      letters. The flags documented here are those relevant to the
      preprocessor. Other letters are interpreted by the compiler proper,
      or reserved for future versions of GCC, and so are silently ignored. If
      you specify letters whose behavior conflicts, the result is
      undefined.
  - -dM
- 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
    shows all the 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.
- -dU
- Like -dD 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.
 
  - -fdebug-cpp
- This option is only useful for debugging GCC. When used from CPP or with
      -E, it dumps debugging information about location maps. Every token
      in the output is preceded by the dump of the map its location belongs to.
    When used from GCC without -E, this option has no
        effect. 
- -I dir
- -iquote dir
- -isystem dir
- -idirafter dir
- Add the directory dir to the list of directories to be searched for
      header files during preprocessing.
    If dir begins with = or
        $SYSROOT, then the = or
        $SYSROOT is replaced by the sysroot prefix; see
        --sysroot and -isysroot. Directories specified with -iquote apply only to the
        quote form of the directive,
        "#include "file"".
        Directories specified with -I, -isystem, or
        -idirafter apply to lookup for both the
        "#include "file""
        and
        "#include <file>"
        directives. You can specify any number or combination of these options on
        the command line to search for header files in several directories. The
        lookup order is as follows: 
  - 1.
- For the quote form of the include directive, the directory of the current
      file is searched first.
- 2.
- For the quote form of the include directive, the directories specified by
      -iquote options are searched in left-to-right order, as they appear
      on the command line.
- 3.
- Directories specified with -I options are scanned in left-to-right
      order.
- 4.
- Directories specified with -isystem options are scanned in
      left-to-right order.
- 5.
- Standard system directories are scanned.
- 6.
- Directories specified with -idirafter options are scanned in
      left-to-right order.
 
You can use -I to override a system header file,
    substituting your own version, since these directories are searched before
    the standard system header file directories. However, you should not use
    this option to add directories that contain vendor-supplied system header
    files; use -isystem for that.
The -isystem and -idirafter options also mark the
    directory as a system directory, so that it gets the same special treatment
    that is applied to the standard system directories.
If a standard system include directory, or a directory specified
    with -isystem, is also specified with -I, the -I option
    is ignored. The directory is still searched but as a system directory at its
    normal position in the system include chain. This is to ensure that GCC's
    procedure to fix buggy system headers and the ordering for the
    "#include_next" directive are not
    inadvertently changed. If you really need to change the search order for
    system directories, use the -nostdinc and/or -isystem
  options.
 
  - -I-
- Split the include path. This option has been deprecated. Please use
      -iquote instead for -I directories before the -I- and
      remove the -I- option.
    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"".
        There is no way to override this effect of -I-. 
- -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.
- -nostdinc
- Do not search the standard system directories for header files. Only the
      directories explicitly specified with -I, -iquote,
      -isystem, and/or -idirafter 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.)
- -Wcomment
- -Wcomments
- Warn whenever a comment-start sequence /* appears in a /*
      comment, or whenever a backslash-newline appears in a // comment.
      This warning is enabled by -Wall.
- -Wtrigraphs
- Warn if any trigraphs are encountered that might change the meaning of the
      program. Trigraphs within comments are not warned about, except those that
      would form escaped newlines.
    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. 
- -Wundef
- Warn if an undefined identifier is evaluated in an
      "#if" directive. Such identifiers are
      replaced with zero.
- -Wexpansion-to-defined
- Warn whenever defined is encountered in the expansion of a macro
      (including the case where the macro is expanded by an #if
      directive). Such usage is not portable. This warning is also enabled by
      -Wpedantic and -Wextra.
- -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 also warns 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 the preprocessor reports 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
    
- -Wno-endif-labels
- Do not warn whenever an "#else" or an
      "#endif" are followed by text. This
      sometimes happens in older programs with code of the form
    
 
        #if FOO
        ...
        #else FOO
        ...
        #endif FOO
    The second and third "FOO"
        should be in comments. This warning is on by default. 
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.
- CPP_RESTRICTED
- If this variable is defined, cpp will skip any include file which is not a
      regular file, and will continue searching for the requested name (this is
      always done if the found file is a directory).
- SOURCE_DATE_EPOCH
- If this variable is set, its value specifies a UNIX timestamp to be used
      in replacement of the current date and time in the
      "__DATE__" and
      "__TIME__" macros, so that the embedded
      timestamps become reproducible.
    The value of SOURCE_DATE_EPOCH must be a UNIX
        timestamp, defined as the number of seconds (excluding leap seconds)
        since 01 Jan 1970 00:00:00 represented in ASCII; identical to the output
        of @command{date +%s} on GNU/Linux and other
        systems that support the %s extension in the
        "date" command. The value should be a known timestamp such as the last
        modification time of the source or package and it should be set by the
        build process. 
gpl(7), gfdl(7), fsf-funding(7), gcc(1), and the
  Info entries for cpp and gcc.
Copyright (c) 1987-2020 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
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