1CPP(1) GNU CPP(1)
2
3
4
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
16 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
27 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
36 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
38 (Pascal, Ada, etc.) So is assembly, with caution. -traditional-cpp
39 mode preserves more white space, and is otherwise more permissive.
40 Many of the problems can be avoided by writing C or C++ style comments
41 instead of native language comments, and keeping macros simple.
42
43 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
49 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 or -std=c11 options, depending on
56 which version of the standard you want. To get all the mandatory
57 diagnostics, you must also use -pedantic.
58
59 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
65 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
74 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
80 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
85 Many options have multi-letter names; therefore multiple single-letter
86 options may not be grouped: -dM is very different from -d -M.
87
88 -D name
89 Predefine name as a macro, with definition 1.
90
91 -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
97 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
101 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
107 -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
111 -U name
112 Cancel any previous definition of name, either built in or provided
113 with a -D option.
114
115 -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
123 If multiple -include options are given, the files are included in
124 the order they appear on the command line.
125
126 -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
132 All files specified by -imacros are processed before all files
133 specified by -include.
134
135 -undef
136 Do not predefine any system-specific or GCC-specific macros. The
137 standard predefined macros remain defined.
138
139 -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
146 -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
153 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
159 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
165 Passing -M to the driver implies -E, and suppresses warnings with
166 an implicit -w.
167
168 -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
172 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
176 -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
181 When used with the driver options -MD or -MMD, -MF overrides the
182 default dependency output file.
183
184 -MG In conjunction with an option such as -M requesting dependency
185 generation, -MG assumes missing header files are generated files
186 and adds them to the dependency list without raising an error. The
187 dependency filename is taken directly from the "#include" directive
188 without prepending any path. -MG also suppresses preprocessed
189 output, as a missing header file renders this useless.
190
191 This feature is used in automatic updating of makefiles.
192
193 -MP This option instructs CPP to add a phony target for each dependency
194 other than the main file, causing each to depend on nothing. These
195 dummy rules work around errors make gives if you remove header
196 files without updating the Makefile to match.
197
198 This is typical output:
199
200 test.o: test.c test.h
201
202 test.h:
203
204 -MT target
205 Change the target of the rule emitted by dependency generation. By
206 default CPP takes the name of the main input file, deletes any
207 directory components and any file suffix such as .c, and appends
208 the platform's usual object suffix. The result is the target.
209
210 An -MT option sets the target to be exactly the string you specify.
211 If you want multiple targets, you can specify them as a single
212 argument to -MT, or use multiple -MT options.
213
214 For example, -MT '$(objpfx)foo.o' might give
215
216 $(objpfx)foo.o: foo.c
217
218 -MQ target
219 Same as -MT, but it quotes any characters which are special to
220 Make. -MQ '$(objpfx)foo.o' gives
221
222 $$(objpfx)foo.o: foo.c
223
224 The default target is automatically quoted, as if it were given
225 with -MQ.
226
227 -MD -MD is equivalent to -M -MF file, except that -E is not implied.
228 The driver determines file based on whether an -o option is given.
229 If it is, the driver uses its argument but with a suffix of .d,
230 otherwise it takes the name of the input file, removes any
231 directory components and suffix, and applies a .d suffix.
232
233 If -MD is used in conjunction with -E, any -o switch is understood
234 to specify the dependency output file, but if used without -E, each
235 -o is understood to specify a target object file.
236
237 Since -E is not implied, -MD can be used to generate a dependency
238 output file as a side-effect of the compilation process.
239
240 -MMD
241 Like -MD except mention only user header files, not system header
242 files.
243
244 -fpreprocessed
245 Indicate to the preprocessor that the input file has already been
246 preprocessed. This suppresses things like macro expansion,
247 trigraph conversion, escaped newline splicing, and processing of
248 most directives. The preprocessor still recognizes and removes
249 comments, so that you can pass a file preprocessed with -C to the
250 compiler without problems. In this mode the integrated
251 preprocessor is little more than a tokenizer for the front ends.
252
253 -fpreprocessed is implicit if the input file has one of the
254 extensions .i, .ii or .mi. These are the extensions that GCC uses
255 for preprocessed files created by -save-temps.
256
257 -fdirectives-only
258 When preprocessing, handle directives, but do not expand macros.
259
260 The option's behavior depends on the -E and -fpreprocessed options.
261
262 With -E, preprocessing is limited to the handling of directives
263 such as "#define", "#ifdef", and "#error". Other preprocessor
264 operations, such as macro expansion and trigraph conversion are not
265 performed. In addition, the -dD option is implicitly enabled.
266
267 With -fpreprocessed, predefinition of command line and most builtin
268 macros is disabled. Macros such as "__LINE__", which are
269 contextually dependent, are handled normally. This enables
270 compilation of files previously preprocessed with "-E
271 -fdirectives-only".
272
273 With both -E and -fpreprocessed, the rules for -fpreprocessed take
274 precedence. This enables full preprocessing of files previously
275 preprocessed with "-E -fdirectives-only".
276
277 -fdollars-in-identifiers
278 Accept $ in identifiers.
279
280 -fextended-identifiers
281 Accept universal character names in identifiers. This option is
282 enabled by default for C99 (and later C standard versions) and C++.
283
284 -fno-canonical-system-headers
285 When preprocessing, do not shorten system header paths with
286 canonicalization.
287
288 -ftabstop=width
289 Set the distance between tab stops. This helps the preprocessor
290 report correct column numbers in warnings or errors, even if tabs
291 appear on the line. If the value is less than 1 or greater than
292 100, the option is ignored. The default is 8.
293
294 -ftrack-macro-expansion[=level]
295 Track locations of tokens across macro expansions. This allows the
296 compiler to emit diagnostic about the current macro expansion stack
297 when a compilation error occurs in a macro expansion. Using this
298 option makes the preprocessor and the compiler consume more memory.
299 The level parameter can be used to choose the level of precision of
300 token location tracking thus decreasing the memory consumption if
301 necessary. Value 0 of level de-activates this option. Value 1
302 tracks tokens locations in a degraded mode for the sake of minimal
303 memory overhead. In this mode all tokens resulting from the
304 expansion of an argument of a function-like macro have the same
305 location. Value 2 tracks tokens locations completely. This value is
306 the most memory hungry. When this option is given no argument, the
307 default parameter value is 2.
308
309 Note that "-ftrack-macro-expansion=2" is activated by default.
310
311 -fexec-charset=charset
312 Set the execution character set, used for string and character
313 constants. The default is UTF-8. charset can be any encoding
314 supported by the system's "iconv" library routine.
315
316 -fwide-exec-charset=charset
317 Set the wide execution character set, used for wide string and
318 character constants. The default is UTF-32 or UTF-16, whichever
319 corresponds to the width of "wchar_t". As with -fexec-charset,
320 charset can be any encoding supported by the system's "iconv"
321 library routine; however, you will have problems with encodings
322 that do not fit exactly in "wchar_t".
323
324 -finput-charset=charset
325 Set the input character set, used for translation from the
326 character set of the input file to the source character set used by
327 GCC. If the locale does not specify, or GCC cannot get this
328 information from the locale, the default is UTF-8. This can be
329 overridden by either the locale or this command-line option.
330 Currently the command-line option takes precedence if there's a
331 conflict. charset can be any encoding supported by the system's
332 "iconv" library routine.
333
334 -fworking-directory
335 Enable generation of linemarkers in the preprocessor output that
336 let the compiler know the current working directory at the time of
337 preprocessing. When this option is enabled, the preprocessor
338 emits, after the initial linemarker, a second linemarker with the
339 current working directory followed by two slashes. GCC uses this
340 directory, when it's present in the preprocessed input, as the
341 directory emitted as the current working directory in some
342 debugging information formats. This option is implicitly enabled
343 if debugging information is enabled, but this can be inhibited with
344 the negated form -fno-working-directory. If the -P flag is present
345 in the command line, this option has no effect, since no "#line"
346 directives are emitted whatsoever.
347
348 -A predicate=answer
349 Make an assertion with the predicate predicate and answer answer.
350 This form is preferred to the older form -A predicate(answer),
351 which is still supported, because it does not use shell special
352 characters.
353
354 -A -predicate=answer
355 Cancel an assertion with the predicate predicate and answer answer.
356
357 -C Do not discard comments. All comments are passed through to the
358 output file, except for comments in processed directives, which are
359 deleted along with the directive.
360
361 You should be prepared for side effects when using -C; it causes
362 the preprocessor to treat comments as tokens in their own right.
363 For example, comments appearing at the start of what would be a
364 directive line have the effect of turning that line into an
365 ordinary source line, since the first token on the line is no
366 longer a #.
367
368 -CC Do not discard comments, including during macro expansion. This is
369 like -C, except that comments contained within macros are also
370 passed through to the output file where the macro is expanded.
371
372 In addition to the side-effects of the -C option, the -CC option
373 causes all C++-style comments inside a macro to be converted to
374 C-style comments. This is to prevent later use of that macro from
375 inadvertently commenting out the remainder of the source line.
376
377 The -CC option is generally used to support lint comments.
378
379 -P Inhibit generation of linemarkers in the output from the
380 preprocessor. This might be useful when running the preprocessor
381 on something that is not C code, and will be sent to a program
382 which might be confused by the linemarkers.
383
384 -traditional
385 -traditional-cpp
386 Try to imitate the behavior of pre-standard C preprocessors, as
387 opposed to ISO C preprocessors.
388
389 Note that GCC does not otherwise attempt to emulate a pre-standard
390 C compiler, and these options are only supported with the -E
391 switch, or when invoking CPP explicitly.
392
393 -trigraphs
394 Support ISO C trigraphs. These are three-character sequences, all
395 starting with ??, that are defined by ISO C to stand for single
396 characters. For example, ??/ stands for \, so '??/n' is a
397 character constant for a newline.
398
399 By default, GCC ignores trigraphs, but in standard-conforming modes
400 it converts them. See the -std and -ansi options.
401
402 -remap
403 Enable special code to work around file systems which only permit
404 very short file names, such as MS-DOS.
405
406 -H Print the name of each header file used, in addition to other
407 normal activities. Each name is indented to show how deep in the
408 #include stack it is. Precompiled header files are also printed,
409 even if they are found to be invalid; an invalid precompiled header
410 file is printed with ...x and a valid one with ...! .
411
412 -dletters
413 Says to make debugging dumps during compilation as specified by
414 letters. The flags documented here are those relevant to the
415 preprocessor. Other letters are interpreted by the compiler
416 proper, or reserved for future versions of GCC, and so are silently
417 ignored. If you specify letters whose behavior conflicts, the
418 result is undefined.
419
420 -dM Instead of the normal output, generate a list of #define
421 directives for all the macros defined during the execution of
422 the preprocessor, including predefined macros. This gives you
423 a way of finding out what is predefined in your version of the
424 preprocessor. Assuming you have no file foo.h, the command
425
426 touch foo.h; cpp -dM foo.h
427
428 shows all the predefined macros.
429
430 -dD Like -dM except in two respects: it does not include the
431 predefined macros, and it outputs both the #define directives
432 and the result of preprocessing. Both kinds of output go to
433 the standard output file.
434
435 -dN Like -dD, but emit only the macro names, not their expansions.
436
437 -dI Output #include directives in addition to the result of
438 preprocessing.
439
440 -dU Like -dD except that only macros that are expanded, or whose
441 definedness is tested in preprocessor directives, are output;
442 the output is delayed until the use or test of the macro; and
443 #undef directives are also output for macros tested but
444 undefined at the time.
445
446 -fdebug-cpp
447 This option is only useful for debugging GCC. When used from CPP
448 or with -E, it dumps debugging information about location maps.
449 Every token in the output is preceded by the dump of the map its
450 location belongs to.
451
452 When used from GCC without -E, this option has no effect.
453
454 -I dir
455 -iquote dir
456 -isystem dir
457 -idirafter dir
458 Add the directory dir to the list of directories to be searched for
459 header files during preprocessing.
460
461 If dir begins with =, then the = is replaced by the sysroot prefix;
462 see --sysroot and -isysroot.
463
464 Directories specified with -iquote apply only to the quote form of
465 the directive, "#include "file"". Directories specified with -I,
466 -isystem, or -idirafter apply to lookup for both the
467 "#include "file"" and "#include <file>" directives.
468
469 You can specify any number or combination of these options on the
470 command line to search for header files in several directories.
471 The lookup order is as follows:
472
473 1. For the quote form of the include directive, the directory of
474 the current file is searched first.
475
476 2. For the quote form of the include directive, the directories
477 specified by -iquote options are searched in left-to-right
478 order, as they appear on the command line.
479
480 3. Directories specified with -I options are scanned in left-to-
481 right order.
482
483 4. Directories specified with -isystem options are scanned in
484 left-to-right order.
485
486 5. Standard system directories are scanned.
487
488 6. Directories specified with -idirafter options are scanned in
489 left-to-right order.
490
491 You can use -I to override a system header file, substituting your
492 own version, since these directories are searched before the
493 standard system header file directories. However, you should not
494 use this option to add directories that contain vendor-supplied
495 system header files; use -isystem for that.
496
497 The -isystem and -idirafter options also mark the directory as a
498 system directory, so that it gets the same special treatment that
499 is applied to the standard system directories.
500
501 If a standard system include directory, or a directory specified
502 with -isystem, is also specified with -I, the -I option is ignored.
503 The directory is still searched but as a system directory at its
504 normal position in the system include chain. This is to ensure
505 that GCC's procedure to fix buggy system headers and the ordering
506 for the "#include_next" directive are not inadvertently changed.
507 If you really need to change the search order for system
508 directories, use the -nostdinc and/or -isystem options.
509
510 -I- Split the include path. This option has been deprecated. Please
511 use -iquote instead for -I directories before the -I- and remove
512 the -I- option.
513
514 Any directories specified with -I options before -I- are searched
515 only for headers requested with "#include "file""; they are not
516 searched for "#include <file>". If additional directories are
517 specified with -I options after the -I-, those directories are
518 searched for all #include directives.
519
520 In addition, -I- inhibits the use of the directory of the current
521 file directory as the first search directory for "#include "file"".
522 There is no way to override this effect of -I-.
523
524 -iprefix prefix
525 Specify prefix as the prefix for subsequent -iwithprefix options.
526 If the prefix represents a directory, you should include the final
527 /.
528
529 -iwithprefix dir
530 -iwithprefixbefore dir
531 Append dir to the prefix specified previously with -iprefix, and
532 add the resulting directory to the include search path.
533 -iwithprefixbefore puts it in the same place -I would; -iwithprefix
534 puts it where -idirafter would.
535
536 -isysroot dir
537 This option is like the --sysroot option, but applies only to
538 header files (except for Darwin targets, where it applies to both
539 header files and libraries). See the --sysroot option for more
540 information.
541
542 -imultilib dir
543 Use dir as a subdirectory of the directory containing target-
544 specific C++ headers.
545
546 -nostdinc
547 Do not search the standard system directories for header files.
548 Only the directories explicitly specified with -I, -iquote,
549 -isystem, and/or -idirafter options (and the directory of the
550 current file, if appropriate) are searched.
551
552 -nostdinc++
553 Do not search for header files in the C++-specific standard
554 directories, but do still search the other standard directories.
555 (This option is used when building the C++ library.)
556
557 -Wcomment
558 -Wcomments
559 Warn whenever a comment-start sequence /* appears in a /* comment,
560 or whenever a backslash-newline appears in a // comment. This
561 warning is enabled by -Wall.
562
563 -Wtrigraphs
564 Warn if any trigraphs are encountered that might change the meaning
565 of the program. Trigraphs within comments are not warned about,
566 except those that would form escaped newlines.
567
568 This option is implied by -Wall. If -Wall is not given, this
569 option is still enabled unless trigraphs are enabled. To get
570 trigraph conversion without warnings, but get the other -Wall
571 warnings, use -trigraphs -Wall -Wno-trigraphs.
572
573 -Wundef
574 Warn if an undefined identifier is evaluated in an "#if" directive.
575 Such identifiers are replaced with zero.
576
577 -Wexpansion-to-defined
578 Warn whenever defined is encountered in the expansion of a macro
579 (including the case where the macro is expanded by an #if
580 directive). Such usage is not portable. This warning is also
581 enabled by -Wpedantic and -Wextra.
582
583 -Wunused-macros
584 Warn about macros defined in the main file that are unused. A
585 macro is used if it is expanded or tested for existence at least
586 once. The preprocessor also warns if the macro has not been used
587 at the time it is redefined or undefined.
588
589 Built-in macros, macros defined on the command line, and macros
590 defined in include files are not warned about.
591
592 Note: If a macro is actually used, but only used in skipped
593 conditional blocks, then the preprocessor reports it as unused. To
594 avoid the warning in such a case, you might improve the scope of
595 the macro's definition by, for example, moving it into the first
596 skipped block. Alternatively, you could provide a dummy use with
597 something like:
598
599 #if defined the_macro_causing_the_warning
600 #endif
601
602 -Wno-endif-labels
603 Do not warn whenever an "#else" or an "#endif" are followed by
604 text. This sometimes happens in older programs with code of the
605 form
606
607 #if FOO
608 ...
609 #else FOO
610 ...
611 #endif FOO
612
613 The second and third "FOO" should be in comments. This warning is
614 on by default.
615
617 This section describes the environment variables that affect how CPP
618 operates. You can use them to specify directories or prefixes to use
619 when searching for include files, or to control dependency output.
620
621 Note that you can also specify places to search using options such as
622 -I, and control dependency output with options like -M. These take
623 precedence over environment variables, which in turn take precedence
624 over the configuration of GCC.
625
626 CPATH
627 C_INCLUDE_PATH
628 CPLUS_INCLUDE_PATH
629 OBJC_INCLUDE_PATH
630 Each variable's value is a list of directories separated by a
631 special character, much like PATH, in which to look for header
632 files. The special character, "PATH_SEPARATOR", is target-
633 dependent and determined at GCC build time. For Microsoft Windows-
634 based targets it is a semicolon, and for almost all other targets
635 it is a colon.
636
637 CPATH specifies a list of directories to be searched as if
638 specified with -I, but after any paths given with -I options on the
639 command line. This environment variable is used regardless of
640 which language is being preprocessed.
641
642 The remaining environment variables apply only when preprocessing
643 the particular language indicated. Each specifies a list of
644 directories to be searched as if specified with -isystem, but after
645 any paths given with -isystem options on the command line.
646
647 In all these variables, an empty element instructs the compiler to
648 search its current working directory. Empty elements can appear at
649 the beginning or end of a path. For instance, if the value of
650 CPATH is ":/special/include", that has the same effect as
651 -I. -I/special/include.
652
653 DEPENDENCIES_OUTPUT
654 If this variable is set, its value specifies how to output
655 dependencies for Make based on the non-system header files
656 processed by the compiler. System header files are ignored in the
657 dependency output.
658
659 The value of DEPENDENCIES_OUTPUT can be just a file name, in which
660 case the Make rules are written to that file, guessing the target
661 name from the source file name. Or the value can have the form
662 file target, in which case the rules are written to file file using
663 target as the target name.
664
665 In other words, this environment variable is equivalent to
666 combining the options -MM and -MF, with an optional -MT switch too.
667
668 SUNPRO_DEPENDENCIES
669 This variable is the same as DEPENDENCIES_OUTPUT (see above),
670 except that system header files are not ignored, so it implies -M
671 rather than -MM. However, the dependence on the main input file is
672 omitted.
673
674 SOURCE_DATE_EPOCH
675 If this variable is set, its value specifies a UNIX timestamp to be
676 used in replacement of the current date and time in the "__DATE__"
677 and "__TIME__" macros, so that the embedded timestamps become
678 reproducible.
679
680 The value of SOURCE_DATE_EPOCH must be a UNIX timestamp, defined as
681 the number of seconds (excluding leap seconds) since 01 Jan 1970
682 00:00:00 represented in ASCII; identical to the output of
683 @command{date +%s} on GNU/Linux and other systems that support the
684 %s extension in the "date" command.
685
686 The value should be a known timestamp such as the last modification
687 time of the source or package and it should be set by the build
688 process.
689
691 gpl(7), gfdl(7), fsf-funding(7), gcc(1), and the Info entries for cpp
692 and gcc.
693
695 Copyright (c) 1987-2017 Free Software Foundation, Inc.
696
697 Permission is granted to copy, distribute and/or modify this document
698 under the terms of the GNU Free Documentation License, Version 1.3 or
699 any later version published by the Free Software Foundation. A copy of
700 the license is included in the man page gfdl(7). This manual contains
701 no Invariant Sections. The Front-Cover Texts are (a) (see below), and
702 the Back-Cover Texts are (b) (see below).
703
704 (a) The FSF's Front-Cover Text is:
705
706 A GNU Manual
707
708 (b) The FSF's Back-Cover Text is:
709
710 You have freedom to copy and modify this GNU Manual, like GNU
711 software. Copies published by the Free Software Foundation raise
712 funds for GNU development.
713
714
715
716gcc-7.4.0 2018-12-06 CPP(1)