1CPP(1) GNU CPP(1)
2
6 cpp - The C Preprocessor
7
9 cpp [-Dmacro[=defn]...] [-Umacro]
10 [-Idir...] [-iquotedir...]
11 [-M|-MM] [-MG] [-MF filename]
12 [-MP] [-MQ target...]
13 [-MT target...]
14 infile [[-o] outfile]
15 Only the most useful options are given above; see below for a more
17 complete list of preprocessor-specific options. In addition, cpp
18 accepts most gcc driver options, which are not listed here. Refer to
19 the GCC documentation for details.
20
22 The C preprocessor, often known as cpp, is a macro processor that is
23 used automatically by the C compiler to transform your program before
24 compilation. It is called a macro processor because it allows you to
25 define macros, which are brief abbreviations for longer constructs.
26 The C preprocessor is intended to be used only with C, C++, and
28 Objective-C source code. In the past, it has been abused as a general
29 text processor. It will choke on input which does not obey C's lexical
30 rules. For example, apostrophes will be interpreted as the beginning
31 of character constants, and cause errors. Also, you cannot rely on it
32 preserving characteristics of the input which are not significant to
33 C-family languages. If a Makefile is preprocessed, all the hard tabs
34 will be removed, and the Makefile will not work.
35 Having said that, you can often get away with using cpp on things which
37 are not C. Other Algol-ish programming languages are often safe (Ada,
38 etc.) So is assembly, with caution. -traditional-cpp mode preserves
39 more white space, and is otherwise more permissive. Many of the
40 problems can be avoided by writing C or C++ style comments instead of
41 native language comments, and keeping macros simple.
42 Wherever possible, you should use a preprocessor geared to the language
44 you are writing in. Modern versions of the GNU assembler have macro
45 facilities. Most high level programming languages have their own
46 conditional compilation and inclusion mechanism. If all else fails,
47 try a true general text processor, such as GNU M4.
48 C preprocessors vary in some details. This manual discusses the GNU C
50 preprocessor, which provides a small superset of the features of ISO
51 Standard C. In its default mode, the GNU C preprocessor does not do a
52 few things required by the standard. These are features which are
53 rarely, if ever, used, and may cause surprising changes to the meaning
54 of a program which does not expect them. To get strict ISO Standard C,
55 you should use the -std=c90, -std=c99, -std=c11 or -std=c17 options,
56 depending on which version of the standard you want. To get all the
57 mandatory diagnostics, you must also use -pedantic.
58 This manual describes the behavior of the ISO preprocessor. To
60 minimize gratuitous differences, where the ISO preprocessor's behavior
61 does not conflict with traditional semantics, the traditional
62 preprocessor should behave the same way. The various differences that
63 do exist are detailed in the section Traditional Mode.
64 For clarity, unless noted otherwise, references to CPP in this manual
66 refer to GNU CPP.
67
69 The cpp command expects two file names as arguments, infile and
70 outfile. The preprocessor reads infile together with any other files
71 it specifies with #include. All the output generated by the combined
72 input files is written in outfile.
73 Either infile or outfile may be -, which as infile means to read from
75 standard input and as outfile means to write to standard output. If
76 either file is omitted, it means the same as if - had been specified
77 for that file. You can also use the -o outfile option to specify the
78 output file.
79 Unless otherwise noted, or the option ends in =, all options which take
81 an argument may have that argument appear either immediately after the
82 option, or with a space between option and argument: -Ifoo and -I foo
83 have the same effect.
84 Many options have multi-letter names; therefore multiple single-letter
86 options may not be grouped: -dM is very different from -d -M.
87 -D name
89 Predefine name as a macro, with definition 1.
90 -D name=definition
92 The contents of definition are tokenized and processed as if they
93 appeared during translation phase three in a #define directive. In
94 particular, the definition is truncated by embedded newline
95 characters.
96 If you are invoking the preprocessor from a shell or shell-like
98 program you may need to use the shell's quoting syntax to protect
99 characters such as spaces that have a meaning in the shell syntax.
100 If you wish to define a function-like macro on the command line,
102 write its argument list with surrounding parentheses before the
103 equals sign (if any). Parentheses are meaningful to most shells,
104 so you should quote the option. With sh and csh,
105 -D'name(args...)=definition' works.
106 -D and -U options are processed in the order they are given on the
108 command line. All -imacros file and -include file options are
109 processed after all -D and -U options.
110 -U name
112 Cancel any previous definition of name, either built in or provided
113 with a -D option.
114 -include file
116 Process file as if "#include "file"" appeared as the first line of
117 the primary source file. However, the first directory searched for
118 file is the preprocessor's working directory instead of the
119 directory containing the main source file. If not found there, it
120 is searched for in the remainder of the "#include "..."" search
121 chain as normal.
122 If multiple -include options are given, the files are included in
124 the order they appear on the command line.
125 -imacros file
127 Exactly like -include, except that any output produced by scanning
128 file is thrown away. Macros it defines remain defined. This
129 allows you to acquire all the macros from a header without also
130 processing its declarations.
131 All files specified by -imacros are processed before all files
133 specified by -include.
134 -undef
136 Do not predefine any system-specific or GCC-specific macros. The
137 standard predefined macros remain defined.
138 -pthread
140 Define additional macros required for using the POSIX threads
141 library. You should use this option consistently for both
142 compilation and linking. This option is supported on GNU/Linux
143 targets, most other Unix derivatives, and also on x86 Cygwin and
144 MinGW targets.
145 -M Instead of outputting the result of preprocessing, output a rule
147 suitable for make describing the dependencies of the main source
148 file. The preprocessor outputs one make rule containing the object
149 file name for that source file, a colon, and the names of all the
150 included files, including those coming from -include or -imacros
151 command-line options.
152 Unless specified explicitly (with -MT or -MQ), the object file name
154 consists of the name of the source file with any suffix replaced
155 with object file suffix and with any leading directory parts
156 removed. If there are many included files then the rule is split
157 into several lines using \-newline. The rule has no commands.
158 This option does not suppress the preprocessor's debug output, such
160 as -dM. To avoid mixing such debug output with the dependency
161 rules you should explicitly specify the dependency output file with
162 -MF, or use an environment variable like DEPENDENCIES_OUTPUT.
163 Debug output is still sent to the regular output stream as normal.
164 Passing -M to the driver implies -E, and suppresses warnings with
166 an implicit -w.
167 -MM Like -M but do not mention header files that are found in system
169 header directories, nor header files that are included, directly or
170 indirectly, from such a header.
171 This implies that the choice of angle brackets or double quotes in
173 an #include directive does not in itself determine whether that
174 header appears in -MM dependency output.
175 -MF file
177 When used with -M or -MM, specifies a file to write the
178 dependencies to. If no -MF switch is given the preprocessor sends
179 the rules to the same place it would send preprocessed output.
180 When used with the driver options -MD or -MMD, -MF overrides the
182 default dependency output file.
183 If file is -, then the dependencies are written to stdout.
185 -MG In conjunction with an option such as -M requesting dependency
187 generation, -MG assumes missing header files are generated files
188 and adds them to the dependency list without raising an error. The
189 dependency filename is taken directly from the "#include" directive
190 without prepending any path. -MG also suppresses preprocessed
191 output, as a missing header file renders this useless.
192 This feature is used in automatic updating of makefiles.
194 -MP This option instructs CPP to add a phony target for each dependency
196 other than the main file, causing each to depend on nothing. These
197 dummy rules work around errors make gives if you remove header
198 files without updating the Makefile to match.
199 This is typical output:
201 test.o: test.c test.h
203 test.h:
205 -MT target
207 Change the target of the rule emitted by dependency generation. By
208 default CPP takes the name of the main input file, deletes any
209 directory components and any file suffix such as .c, and appends
210 the platform's usual object suffix. The result is the target.
211 An -MT option sets the target to be exactly the string you specify.
213 If you want multiple targets, you can specify them as a single
214 argument to -MT, or use multiple -MT options.
215 For example, -MT '$(objpfx)foo.o' might give
217 $(objpfx)foo.o: foo.c
219 -MQ target
221 Same as -MT, but it quotes any characters which are special to
222 Make. -MQ '$(objpfx)foo.o' gives
223 $$(objpfx)foo.o: foo.c
225 The default target is automatically quoted, as if it were given
227 with -MQ.
228 -MD -MD is equivalent to -M -MF file, except that -E is not implied.
230 The driver determines file based on whether an -o option is given.
231 If it is, the driver uses its argument but with a suffix of .d,
232 otherwise it takes the name of the input file, removes any
233 directory components and suffix, and applies a .d suffix.
234 If -MD is used in conjunction with -E, any -o switch is understood
236 to specify the dependency output file, but if used without -E, each
237 -o is understood to specify a target object file.
238 Since -E is not implied, -MD can be used to generate a dependency
240 output file as a side effect of the compilation process.
241 -MMD
243 Like -MD except mention only user header files, not system header
244 files.
245 -fpreprocessed
247 Indicate to the preprocessor that the input file has already been
248 preprocessed. This suppresses things like macro expansion,
249 trigraph conversion, escaped newline splicing, and processing of
250 most directives. The preprocessor still recognizes and removes
251 comments, so that you can pass a file preprocessed with -C to the
252 compiler without problems. In this mode the integrated
253 preprocessor is little more than a tokenizer for the front ends.
254 -fpreprocessed is implicit if the input file has one of the
256 extensions .i, .ii or .mi. These are the extensions that GCC uses
257 for preprocessed files created by -save-temps.
258 -fdirectives-only
260 When preprocessing, handle directives, but do not expand macros.
261 The option's behavior depends on the -E and -fpreprocessed options.
263 With -E, preprocessing is limited to the handling of directives
265 such as "#define", "#ifdef", and "#error". Other preprocessor
266 operations, such as macro expansion and trigraph conversion are not
267 performed. In addition, the -dD option is implicitly enabled.
268 With -fpreprocessed, predefinition of command line and most builtin
270 macros is disabled. Macros such as "__LINE__", which are
271 contextually dependent, are handled normally. This enables
272 compilation of files previously preprocessed with "-E
273 -fdirectives-only".
274 With both -E and -fpreprocessed, the rules for -fpreprocessed take
276 precedence. This enables full preprocessing of files previously
277 preprocessed with "-E -fdirectives-only".
278 -fdollars-in-identifiers
280 Accept $ in identifiers.
281 -fextended-identifiers
283 Accept universal character names and extended characters in
284 identifiers. This option is enabled by default for C99 (and later
285 C standard versions) and C++.
286 -fno-canonical-system-headers
288 When preprocessing, do not shorten system header paths with
289 canonicalization.
290 -fmax-include-depth=depth
292 Set the maximum depth of the nested #include. The default is 200.
293 -ftabstop=width
295 Set the distance between tab stops. This helps the preprocessor
296 report correct column numbers in warnings or errors, even if tabs
297 appear on the line. If the value is less than 1 or greater than
298 100, the option is ignored. The default is 8.
299 -ftrack-macro-expansion[=level]
301 Track locations of tokens across macro expansions. This allows the
302 compiler to emit diagnostic about the current macro expansion stack
303 when a compilation error occurs in a macro expansion. Using this
304 option makes the preprocessor and the compiler consume more memory.
305 The level parameter can be used to choose the level of precision of
306 token location tracking thus decreasing the memory consumption if
307 necessary. Value 0 of level de-activates this option. Value 1
308 tracks tokens locations in a degraded mode for the sake of minimal
309 memory overhead. In this mode all tokens resulting from the
310 expansion of an argument of a function-like macro have the same
311 location. Value 2 tracks tokens locations completely. This value is
312 the most memory hungry. When this option is given no argument, the
313 default parameter value is 2.
314 Note that "-ftrack-macro-expansion=2" is activated by default.
316 -fmacro-prefix-map=old=new
318 When preprocessing files residing in directory old, expand the
319 "__FILE__" and "__BASE_FILE__" macros as if the files resided in
320 directory new instead. This can be used to change an absolute path
321 to a relative path by using . for new which can result in more
322 reproducible builds that are location independent. This option
323 also affects "__builtin_FILE()" during compilation. See also
324 -ffile-prefix-map.
325 -fexec-charset=charset
327 Set the execution character set, used for string and character
328 constants. The default is UTF-8. charset can be any encoding
329 supported by the system's "iconv" library routine.
330 -fwide-exec-charset=charset
332 Set the wide execution character set, used for wide string and
333 character constants. The default is UTF-32 or UTF-16, whichever
334 corresponds to the width of "wchar_t". As with -fexec-charset,
335 charset can be any encoding supported by the system's "iconv"
336 library routine; however, you will have problems with encodings
337 that do not fit exactly in "wchar_t".
338 -finput-charset=charset
340 Set the input character set, used for translation from the
341 character set of the input file to the source character set used by
342 GCC. If the locale does not specify, or GCC cannot get this
343 information from the locale, the default is UTF-8. This can be
344 overridden by either the locale or this command-line option.
345 Currently the command-line option takes precedence if there's a
346 conflict. charset can be any encoding supported by the system's
347 "iconv" library routine.
348 -fworking-directory
350 Enable generation of linemarkers in the preprocessor output that
351 let the compiler know the current working directory at the time of
352 preprocessing. When this option is enabled, the preprocessor
353 emits, after the initial linemarker, a second linemarker with the
354 current working directory followed by two slashes. GCC uses this
355 directory, when it's present in the preprocessed input, as the
356 directory emitted as the current working directory in some
357 debugging information formats. This option is implicitly enabled
358 if debugging information is enabled, but this can be inhibited with
359 the negated form -fno-working-directory. If the -P flag is present
360 in the command line, this option has no effect, since no "#line"
361 directives are emitted whatsoever.
362 -A predicate=answer
364 Make an assertion with the predicate predicate and answer answer.
365 This form is preferred to the older form -A predicate(answer),
366 which is still supported, because it does not use shell special
367 characters.
368 -A -predicate=answer
370 Cancel an assertion with the predicate predicate and answer answer.
371 -C Do not discard comments. All comments are passed through to the
373 output file, except for comments in processed directives, which are
374 deleted along with the directive.
375 You should be prepared for side effects when using -C; it causes
377 the preprocessor to treat comments as tokens in their own right.
378 For example, comments appearing at the start of what would be a
379 directive line have the effect of turning that line into an
380 ordinary source line, since the first token on the line is no
381 longer a #.
382 -CC Do not discard comments, including during macro expansion. This is
384 like -C, except that comments contained within macros are also
385 passed through to the output file where the macro is expanded.
386 In addition to the side effects of the -C option, the -CC option
388 causes all C++-style comments inside a macro to be converted to
389 C-style comments. This is to prevent later use of that macro from
390 inadvertently commenting out the remainder of the source line.
391 The -CC option is generally used to support lint comments.
393 -P Inhibit generation of linemarkers in the output from the
395 preprocessor. This might be useful when running the preprocessor
396 on something that is not C code, and will be sent to a program
397 which might be confused by the linemarkers.
398 -traditional
400 -traditional-cpp
401 Try to imitate the behavior of pre-standard C preprocessors, as
402 opposed to ISO C preprocessors.
403 Note that GCC does not otherwise attempt to emulate a pre-standard
405 C compiler, and these options are only supported with the -E
406 switch, or when invoking CPP explicitly.
407 -trigraphs
409 Support ISO C trigraphs. These are three-character sequences, all
410 starting with ??, that are defined by ISO C to stand for single
411 characters. For example, ??/ stands for \, so '??/n' is a
412 character constant for a newline.
413 By default, GCC ignores trigraphs, but in standard-conforming modes
415 it converts them. See the -std and -ansi options.
416 -remap
418 Enable special code to work around file systems which only permit
419 very short file names, such as MS-DOS.
420 -H Print the name of each header file used, in addition to other
422 normal activities. Each name is indented to show how deep in the
423 #include stack it is. Precompiled header files are also printed,
424 even if they are found to be invalid; an invalid precompiled header
425 file is printed with ...x and a valid one with ...! .
426 -dletters
428 Says to make debugging dumps during compilation as specified by
429 letters. The flags documented here are those relevant to the
430 preprocessor. Other letters are interpreted by the compiler
431 proper, or reserved for future versions of GCC, and so are silently
432 ignored. If you specify letters whose behavior conflicts, the
433 result is undefined.
434 -dM Instead of the normal output, generate a list of #define
436 directives for all the macros defined during the execution of
437 the preprocessor, including predefined macros. This gives you
438 a way of finding out what is predefined in your version of the
439 preprocessor. Assuming you have no file foo.h, the command
440 touch foo.h; cpp -dM foo.h
442 shows all the predefined macros.
444 -dD Like -dM except in two respects: it does not include the
446 predefined macros, and it outputs both the #define directives
447 and the result of preprocessing. Both kinds of output go to
448 the standard output file.
449 -dN Like -dD, but emit only the macro names, not their expansions.
451 -dI Output #include directives in addition to the result of
453 preprocessing.
454 -dU Like -dD except that only macros that are expanded, or whose
456 definedness is tested in preprocessor directives, are output;
457 the output is delayed until the use or test of the macro; and
458 #undef directives are also output for macros tested but
459 undefined at the time.
460 -fdebug-cpp
462 This option is only useful for debugging GCC. When used from CPP
463 or with -E, it dumps debugging information about location maps.
464 Every token in the output is preceded by the dump of the map its
465 location belongs to.
466 When used from GCC without -E, this option has no effect.
468 -I dir
470 -iquote dir
471 -isystem dir
472 -idirafter dir
473 Add the directory dir to the list of directories to be searched for
474 header files during preprocessing.
475 If dir begins with = or $SYSROOT, then the = or $SYSROOT is
477 replaced by the sysroot prefix; see --sysroot and -isysroot.
478 Directories specified with -iquote apply only to the quote form of
480 the directive, "#include "file"". Directories specified with -I,
481 -isystem, or -idirafter apply to lookup for both the
482 "#include "file"" and "#include <file>" directives.
483 You can specify any number or combination of these options on the
485 command line to search for header files in several directories.
486 The lookup order is as follows:
487 1. For the quote form of the include directive, the directory of
489 the current file is searched first.
490 2. For the quote form of the include directive, the directories
492 specified by -iquote options are searched in left-to-right
493 order, as they appear on the command line.
494 3. Directories specified with -I options are scanned in left-to-
496 right order.
497 4. Directories specified with -isystem options are scanned in
499 left-to-right order.
500 5. Standard system directories are scanned.
502 6. Directories specified with -idirafter options are scanned in
504 left-to-right order.
505 You can use -I to override a system header file, substituting your
507 own version, since these directories are searched before the
508 standard system header file directories. However, you should not
509 use this option to add directories that contain vendor-supplied
510 system header files; use -isystem for that.
511 The -isystem and -idirafter options also mark the directory as a
513 system directory, so that it gets the same special treatment that
514 is applied to the standard system directories.
515 If a standard system include directory, or a directory specified
517 with -isystem, is also specified with -I, the -I option is ignored.
518 The directory is still searched but as a system directory at its
519 normal position in the system include chain. This is to ensure
520 that GCC's procedure to fix buggy system headers and the ordering
521 for the "#include_next" directive are not inadvertently changed.
522 If you really need to change the search order for system
523 directories, use the -nostdinc and/or -isystem options.
524 -I- Split the include path. This option has been deprecated. Please
526 use -iquote instead for -I directories before the -I- and remove
527 the -I- option.
528 Any directories specified with -I options before -I- are searched
530 only for headers requested with "#include "file""; they are not
531 searched for "#include <file>". If additional directories are
532 specified with -I options after the -I-, those directories are
533 searched for all #include directives.
534 In addition, -I- inhibits the use of the directory of the current
536 file directory as the first search directory for "#include "file"".
537 There is no way to override this effect of -I-.
538 -iprefix prefix
540 Specify prefix as the prefix for subsequent -iwithprefix options.
541 If the prefix represents a directory, you should include the final
542 /.
543 -iwithprefix dir
545 -iwithprefixbefore dir
546 Append dir to the prefix specified previously with -iprefix, and
547 add the resulting directory to the include search path.
548 -iwithprefixbefore puts it in the same place -I would; -iwithprefix
549 puts it where -idirafter would.
550 -isysroot dir
552 This option is like the --sysroot option, but applies only to
553 header files (except for Darwin targets, where it applies to both
554 header files and libraries). See the --sysroot option for more
555 information.
556 -imultilib dir
558 Use dir as a subdirectory of the directory containing target-
559 specific C++ headers.
560 -nostdinc
562 Do not search the standard system directories for header files.
563 Only the directories explicitly specified with -I, -iquote,
564 -isystem, and/or -idirafter options (and the directory of the
565 current file, if appropriate) are searched.
566 -nostdinc++
568 Do not search for header files in the C++-specific standard
569 directories, but do still search the other standard directories.
570 (This option is used when building the C++ library.)
571 -Wcomment
573 -Wcomments
574 Warn whenever a comment-start sequence /* appears in a /* comment,
575 or whenever a backslash-newline appears in a // comment. This
576 warning is enabled by -Wall.
577 -Wtrigraphs
579 Warn if any trigraphs are encountered that might change the meaning
580 of the program. Trigraphs within comments are not warned about,
581 except those that would form escaped newlines.
582 This option is implied by -Wall. If -Wall is not given, this
584 option is still enabled unless trigraphs are enabled. To get
585 trigraph conversion without warnings, but get the other -Wall
586 warnings, use -trigraphs -Wall -Wno-trigraphs.
587 -Wundef
589 Warn if an undefined identifier is evaluated in an "#if" directive.
590 Such identifiers are replaced with zero.
591 -Wexpansion-to-defined
593 Warn whenever defined is encountered in the expansion of a macro
594 (including the case where the macro is expanded by an #if
595 directive). Such usage is not portable. This warning is also
596 enabled by -Wpedantic and -Wextra.
597 -Wunused-macros
599 Warn about macros defined in the main file that are unused. A
600 macro is used if it is expanded or tested for existence at least
601 once. The preprocessor also warns if the macro has not been used
602 at the time it is redefined or undefined.
603 Built-in macros, macros defined on the command line, and macros
605 defined in include files are not warned about.
606 Note: If a macro is actually used, but only used in skipped
608 conditional blocks, then the preprocessor reports it as unused. To
609 avoid the warning in such a case, you might improve the scope of
610 the macro's definition by, for example, moving it into the first
611 skipped block. Alternatively, you could provide a dummy use with
612 something like:
613 #if defined the_macro_causing_the_warning
615 #endif
616 -Wno-endif-labels
618 Do not warn whenever an "#else" or an "#endif" are followed by
619 text. This sometimes happens in older programs with code of the
620 form
621 #if FOO
623 ...
624 #else FOO
625 ...
626 #endif FOO
627 The second and third "FOO" should be in comments. This warning is
629 on by default.
630
632 This section describes the environment variables that affect how CPP
633 operates. You can use them to specify directories or prefixes to use
634 when searching for include files, or to control dependency output.
635 Note that you can also specify places to search using options such as
637 -I, and control dependency output with options like -M. These take
638 precedence over environment variables, which in turn take precedence
639 over the configuration of GCC.
640 CPATH
642 C_INCLUDE_PATH
643 CPLUS_INCLUDE_PATH
644 OBJC_INCLUDE_PATH
645 Each variable's value is a list of directories separated by a
646 special character, much like PATH, in which to look for header
647 files. The special character, "PATH_SEPARATOR", is target-
648 dependent and determined at GCC build time. For Microsoft Windows-
649 based targets it is a semicolon, and for almost all other targets
650 it is a colon.
651 CPATH specifies a list of directories to be searched as if
653 specified with -I, but after any paths given with -I options on the
654 command line. This environment variable is used regardless of
655 which language is being preprocessed.
656 The remaining environment variables apply only when preprocessing
658 the particular language indicated. Each specifies a list of
659 directories to be searched as if specified with -isystem, but after
660 any paths given with -isystem options on the command line.
661 In all these variables, an empty element instructs the compiler to
663 search its current working directory. Empty elements can appear at
664 the beginning or end of a path. For instance, if the value of
665 CPATH is ":/special/include", that has the same effect as
666 -I. -I/special/include.
667 DEPENDENCIES_OUTPUT
669 If this variable is set, its value specifies how to output
670 dependencies for Make based on the non-system header files
671 processed by the compiler. System header files are ignored in the
672 dependency output.
673 The value of DEPENDENCIES_OUTPUT can be just a file name, in which
675 case the Make rules are written to that file, guessing the target
676 name from the source file name. Or the value can have the form
677 file target, in which case the rules are written to file file using
678 target as the target name.
679 In other words, this environment variable is equivalent to
681 combining the options -MM and -MF, with an optional -MT switch too.
682 SUNPRO_DEPENDENCIES
684 This variable is the same as DEPENDENCIES_OUTPUT (see above),
685 except that system header files are not ignored, so it implies -M
686 rather than -MM. However, the dependence on the main input file is
687 omitted.
688 SOURCE_DATE_EPOCH
690 If this variable is set, its value specifies a UNIX timestamp to be
691 used in replacement of the current date and time in the "__DATE__"
692 and "__TIME__" macros, so that the embedded timestamps become
693 reproducible.
694 The value of SOURCE_DATE_EPOCH must be a UNIX timestamp, defined as
696 the number of seconds (excluding leap seconds) since 01 Jan 1970
697 00:00:00 represented in ASCII; identical to the output of
698 @command{date +%s} on GNU/Linux and other systems that support the
699 %s extension in the "date" command.
700 The value should be a known timestamp such as the last modification
702 time of the source or package and it should be set by the build
703 process.
704
706 gpl(7), gfdl(7), fsf-funding(7), gcc(1), and the Info entries for cpp
707 and gcc.
708
710 Copyright (c) 1987-2020 Free Software Foundation, Inc.
711 Permission is granted to copy, distribute and/or modify this document
713 under the terms of the GNU Free Documentation License, Version 1.3 or
714 any later version published by the Free Software Foundation. A copy of
715 the license is included in the man page gfdl(7). This manual contains
716 no Invariant Sections. The Front-Cover Texts are (a) (see below), and
717 the Back-Cover Texts are (b) (see below).
718 (a) The FSF's Front-Cover Text is:
720 A GNU Manual
722 (b) The FSF's Back-Cover Text is:
724 You have freedom to copy and modify this GNU Manual, like GNU
726 software. Copies published by the Free Software Foundation raise
727 funds for GNU development.
728gcc-10.3.1 2021-04-22 CPP(1)