1CPP(1)                                GNU                               CPP(1)
2
3
4

NAME

6       cpp - The C Preprocessor
7

SYNOPSIS

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

DESCRIPTION

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 (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
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, -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
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

OPTIONS

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           If file is -, then the dependencies are written to stdout.
185
186       -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
193           This feature is used in automatic updating of makefiles.
194
195       -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
200           This is typical output:
201
202                   test.o: test.c test.h
203
204                   test.h:
205
206       -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
212           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
216           For example, -MT '$(objpfx)foo.o' might give
217
218                   $(objpfx)foo.o: foo.c
219
220       -MQ target
221           Same as -MT, but it quotes any characters which are special to
222           Make.  -MQ '$(objpfx)foo.o' gives
223
224                   $$(objpfx)foo.o: foo.c
225
226           The default target is automatically quoted, as if it were given
227           with -MQ.
228
229       -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
235           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
239           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
242       -MMD
243           Like -MD except mention only user header files, not system header
244           files.
245
246       -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
255           -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
259       -fdirectives-only
260           When preprocessing, handle directives, but do not expand macros.
261
262           The option's behavior depends on the -E and -fpreprocessed options.
263
264           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
269           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
275           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
279       -fdollars-in-identifiers
280           Accept $ in identifiers.
281
282       -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
287       -fno-canonical-system-headers
288           When preprocessing, do not shorten system header paths with
289           canonicalization.
290
291       -fmax-include-depth=depth
292           Set the maximum depth of the nested #include. The default is 200.
293
294       -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
300       -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
315           Note that "-ftrack-macro-expansion=2" is activated by default.
316
317       -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
326       -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
331       -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
339       -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
349       -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
363       -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
369       -A -predicate=answer
370           Cancel an assertion with the predicate predicate and answer answer.
371
372       -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
376           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
383       -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
387           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
392           The -CC option is generally used to support lint comments.
393
394       -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
399       -traditional
400       -traditional-cpp
401           Try to imitate the behavior of pre-standard C preprocessors, as
402           opposed to ISO C preprocessors.
403
404           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
408       -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
414           By default, GCC ignores trigraphs, but in standard-conforming modes
415           it converts them.  See the -std and -ansi options.
416
417       -remap
418           Enable special code to work around file systems which only permit
419           very short file names, such as MS-DOS.
420
421       -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
427       -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
435           -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
441                       touch foo.h; cpp -dM foo.h
442
443               shows all the predefined macros.
444
445           -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
450           -dN Like -dD, but emit only the macro names, not their expansions.
451
452           -dI Output #include directives in addition to the result of
453               preprocessing.
454
455           -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
461       -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
467           When used from GCC without -E, this option has no effect.
468
469       -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
476           If dir begins with = or $SYSROOT, then the = or $SYSROOT is
477           replaced by the sysroot prefix; see --sysroot and -isysroot.
478
479           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
484           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
488           1.  For the quote form of the include directive, the directory of
489               the current file is searched first.
490
491           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
495           3.  Directories specified with -I options are scanned in left-to-
496               right order.
497
498           4.  Directories specified with -isystem options are scanned in
499               left-to-right order.
500
501           5.  Standard system directories are scanned.
502
503           6.  Directories specified with -idirafter options are scanned in
504               left-to-right order.
505
506           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
512           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
516           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
525       -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
529           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
535           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
539       -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
544       -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
551       -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
557       -imultilib dir
558           Use dir as a subdirectory of the directory containing target-
559           specific C++ headers.
560
561       -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
567       -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
572       -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
578       -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
583           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
588       -Wundef
589           Warn if an undefined identifier is evaluated in an "#if" directive.
590           Such identifiers are replaced with zero.
591
592       -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
598       -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
604           Built-in macros, macros defined on the command line, and macros
605           defined in include files are not warned about.
606
607           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
614                   #if defined the_macro_causing_the_warning
615                   #endif
616
617       -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
622                   #if FOO
623                   ...
624                   #else FOO
625                   ...
626                   #endif FOO
627
628           The second and third "FOO" should be in comments.  This warning is
629           on by default.
630

ENVIRONMENT

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
636       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
641       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
652           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
657           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
662           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
668       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
674           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
680           In other words, this environment variable is equivalent to
681           combining the options -MM and -MF, with an optional -MT switch too.
682
683       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
689       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
695           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
701           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

SEE ALSO

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
712       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
719       (a) The FSF's Front-Cover Text is:
720
721            A GNU Manual
722
723       (b) The FSF's Back-Cover Text is:
724
725            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.
728
729
730
731gcc-10                            2020-08-26                            CPP(1)
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