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       -Mno-modules
196           Disable dependency generation for compiled module interfaces.
197
198       -MP This option instructs CPP to add a phony target for each dependency
199           other than the main file, causing each to depend on nothing.  These
200           dummy rules work around errors make gives if you remove header
201           files without updating the Makefile to match.
202
203           This is typical output:
204
205                   test.o: test.c test.h
206
207                   test.h:
208
209       -MT target
210           Change the target of the rule emitted by dependency generation.  By
211           default CPP takes the name of the main input file, deletes any
212           directory components and any file suffix such as .c, and appends
213           the platform's usual object suffix.  The result is the target.
214
215           An -MT option sets the target to be exactly the string you specify.
216           If you want multiple targets, you can specify them as a single
217           argument to -MT, or use multiple -MT options.
218
219           For example, -MT '$(objpfx)foo.o' might give
220
221                   $(objpfx)foo.o: foo.c
222
223       -MQ target
224           Same as -MT, but it quotes any characters which are special to
225           Make.  -MQ '$(objpfx)foo.o' gives
226
227                   $$(objpfx)foo.o: foo.c
228
229           The default target is automatically quoted, as if it were given
230           with -MQ.
231
232       -MD -MD is equivalent to -M -MF file, except that -E is not implied.
233           The driver determines file based on whether an -o option is given.
234           If it is, the driver uses its argument but with a suffix of .d,
235           otherwise it takes the name of the input file, removes any
236           directory components and suffix, and applies a .d suffix.
237
238           If -MD is used in conjunction with -E, any -o switch is understood
239           to specify the dependency output file, but if used without -E, each
240           -o is understood to specify a target object file.
241
242           Since -E is not implied, -MD can be used to generate a dependency
243           output file as a side effect of the compilation process.
244
245       -MMD
246           Like -MD except mention only user header files, not system header
247           files.
248
249       -fpreprocessed
250           Indicate to the preprocessor that the input file has already been
251           preprocessed.  This suppresses things like macro expansion,
252           trigraph conversion, escaped newline splicing, and processing of
253           most directives.  The preprocessor still recognizes and removes
254           comments, so that you can pass a file preprocessed with -C to the
255           compiler without problems.  In this mode the integrated
256           preprocessor is little more than a tokenizer for the front ends.
257
258           -fpreprocessed is implicit if the input file has one of the
259           extensions .i, .ii or .mi.  These are the extensions that GCC uses
260           for preprocessed files created by -save-temps.
261
262       -fdirectives-only
263           When preprocessing, handle directives, but do not expand macros.
264
265           The option's behavior depends on the -E and -fpreprocessed options.
266
267           With -E, preprocessing is limited to the handling of directives
268           such as "#define", "#ifdef", and "#error".  Other preprocessor
269           operations, such as macro expansion and trigraph conversion are not
270           performed.  In addition, the -dD option is implicitly enabled.
271
272           With -fpreprocessed, predefinition of command line and most builtin
273           macros is disabled.  Macros such as "__LINE__", which are
274           contextually dependent, are handled normally.  This enables
275           compilation of files previously preprocessed with "-E
276           -fdirectives-only".
277
278           With both -E and -fpreprocessed, the rules for -fpreprocessed take
279           precedence.  This enables full preprocessing of files previously
280           preprocessed with "-E -fdirectives-only".
281
282       -fdollars-in-identifiers
283           Accept $ in identifiers.
284
285       -fextended-identifiers
286           Accept universal character names and extended characters in
287           identifiers.  This option is enabled by default for C99 (and later
288           C standard versions) and C++.
289
290       -fno-canonical-system-headers
291           When preprocessing, do not shorten system header paths with
292           canonicalization.
293
294       -fmax-include-depth=depth
295           Set the maximum depth of the nested #include. The default is 200.
296
297       -ftabstop=width
298           Set the distance between tab stops.  This helps the preprocessor
299           report correct column numbers in warnings or errors, even if tabs
300           appear on the line.  If the value is less than 1 or greater than
301           100, the option is ignored.  The default is 8.
302
303       -ftrack-macro-expansion[=level]
304           Track locations of tokens across macro expansions. This allows the
305           compiler to emit diagnostic about the current macro expansion stack
306           when a compilation error occurs in a macro expansion. Using this
307           option makes the preprocessor and the compiler consume more memory.
308           The level parameter can be used to choose the level of precision of
309           token location tracking thus decreasing the memory consumption if
310           necessary. Value 0 of level de-activates this option. Value 1
311           tracks tokens locations in a degraded mode for the sake of minimal
312           memory overhead. In this mode all tokens resulting from the
313           expansion of an argument of a function-like macro have the same
314           location. Value 2 tracks tokens locations completely. This value is
315           the most memory hungry.  When this option is given no argument, the
316           default parameter value is 2.
317
318           Note that "-ftrack-macro-expansion=2" is activated by default.
319
320       -fmacro-prefix-map=old=new
321           When preprocessing files residing in directory old, expand the
322           "__FILE__" and "__BASE_FILE__" macros as if the files resided in
323           directory new instead.  This can be used to change an absolute path
324           to a relative path by using . for new which can result in more
325           reproducible builds that are location independent.  This option
326           also affects "__builtin_FILE()" during compilation.  See also
327           -ffile-prefix-map.
328
329       -fexec-charset=charset
330           Set the execution character set, used for string and character
331           constants.  The default is UTF-8.  charset can be any encoding
332           supported by the system's "iconv" library routine.
333
334       -fwide-exec-charset=charset
335           Set the wide execution character set, used for wide string and
336           character constants.  The default is UTF-32 or UTF-16, whichever
337           corresponds to the width of "wchar_t".  As with -fexec-charset,
338           charset can be any encoding supported by the system's "iconv"
339           library routine; however, you will have problems with encodings
340           that do not fit exactly in "wchar_t".
341
342       -finput-charset=charset
343           Set the input character set, used for translation from the
344           character set of the input file to the source character set used by
345           GCC.  If the locale does not specify, or GCC cannot get this
346           information from the locale, the default is UTF-8.  This can be
347           overridden by either the locale or this command-line option.
348           Currently the command-line option takes precedence if there's a
349           conflict.  charset can be any encoding supported by the system's
350           "iconv" library routine.
351
352       -fworking-directory
353           Enable generation of linemarkers in the preprocessor output that
354           let the compiler know the current working directory at the time of
355           preprocessing.  When this option is enabled, the preprocessor
356           emits, after the initial linemarker, a second linemarker with the
357           current working directory followed by two slashes.  GCC uses this
358           directory, when it's present in the preprocessed input, as the
359           directory emitted as the current working directory in some
360           debugging information formats.  This option is implicitly enabled
361           if debugging information is enabled, but this can be inhibited with
362           the negated form -fno-working-directory.  If the -P flag is present
363           in the command line, this option has no effect, since no "#line"
364           directives are emitted whatsoever.
365
366       -A predicate=answer
367           Make an assertion with the predicate predicate and answer answer.
368           This form is preferred to the older form -A predicate(answer),
369           which is still supported, because it does not use shell special
370           characters.
371
372       -A -predicate=answer
373           Cancel an assertion with the predicate predicate and answer answer.
374
375       -C  Do not discard comments.  All comments are passed through to the
376           output file, except for comments in processed directives, which are
377           deleted along with the directive.
378
379           You should be prepared for side effects when using -C; it causes
380           the preprocessor to treat comments as tokens in their own right.
381           For example, comments appearing at the start of what would be a
382           directive line have the effect of turning that line into an
383           ordinary source line, since the first token on the line is no
384           longer a #.
385
386       -CC Do not discard comments, including during macro expansion.  This is
387           like -C, except that comments contained within macros are also
388           passed through to the output file where the macro is expanded.
389
390           In addition to the side effects of the -C option, the -CC option
391           causes all C++-style comments inside a macro to be converted to
392           C-style comments.  This is to prevent later use of that macro from
393           inadvertently commenting out the remainder of the source line.
394
395           The -CC option is generally used to support lint comments.
396
397       -P  Inhibit generation of linemarkers in the output from the
398           preprocessor.  This might be useful when running the preprocessor
399           on something that is not C code, and will be sent to a program
400           which might be confused by the linemarkers.
401
402       -traditional
403       -traditional-cpp
404           Try to imitate the behavior of pre-standard C preprocessors, as
405           opposed to ISO C preprocessors.
406
407           Note that GCC does not otherwise attempt to emulate a pre-standard
408           C compiler, and these options are only supported with the -E
409           switch, or when invoking CPP explicitly.
410
411       -trigraphs
412           Support ISO C trigraphs.  These are three-character sequences, all
413           starting with ??, that are defined by ISO C to stand for single
414           characters.  For example, ??/ stands for \, so '??/n' is a
415           character constant for a newline.
416
417           By default, GCC ignores trigraphs, but in standard-conforming modes
418           it converts them.  See the -std and -ansi options.
419
420       -remap
421           Enable special code to work around file systems which only permit
422           very short file names, such as MS-DOS.
423
424       -H  Print the name of each header file used, in addition to other
425           normal activities.  Each name is indented to show how deep in the
426           #include stack it is.  Precompiled header files are also printed,
427           even if they are found to be invalid; an invalid precompiled header
428           file is printed with ...x and a valid one with ...! .
429
430       -dletters
431           Says to make debugging dumps during compilation as specified by
432           letters.  The flags documented here are those relevant to the
433           preprocessor.  Other letters are interpreted by the compiler
434           proper, or reserved for future versions of GCC, and so are silently
435           ignored.  If you specify letters whose behavior conflicts, the
436           result is undefined.
437
438           -dM Instead of the normal output, generate a list of #define
439               directives for all the macros defined during the execution of
440               the preprocessor, including predefined macros.  This gives you
441               a way of finding out what is predefined in your version of the
442               preprocessor.  Assuming you have no file foo.h, the command
443
444                       touch foo.h; cpp -dM foo.h
445
446               shows all the predefined macros.
447
448           -dD Like -dM except in two respects: it does not include the
449               predefined macros, and it outputs both the #define directives
450               and the result of preprocessing.  Both kinds of output go to
451               the standard output file.
452
453           -dN Like -dD, but emit only the macro names, not their expansions.
454
455           -dI Output #include directives in addition to the result of
456               preprocessing.
457
458           -dU Like -dD except that only macros that are expanded, or whose
459               definedness is tested in preprocessor directives, are output;
460               the output is delayed until the use or test of the macro; and
461               #undef directives are also output for macros tested but
462               undefined at the time.
463
464       -fdebug-cpp
465           This option is only useful for debugging GCC.  When used from CPP
466           or with -E, it dumps debugging information about location maps.
467           Every token in the output is preceded by the dump of the map its
468           location belongs to.
469
470           When used from GCC without -E, this option has no effect.
471
472       -I dir
473       -iquote dir
474       -isystem dir
475       -idirafter dir
476           Add the directory dir to the list of directories to be searched for
477           header files during preprocessing.
478
479           If dir begins with = or $SYSROOT, then the = or $SYSROOT is
480           replaced by the sysroot prefix; see --sysroot and -isysroot.
481
482           Directories specified with -iquote apply only to the quote form of
483           the directive, "#include "file"".  Directories specified with -I,
484           -isystem, or -idirafter apply to lookup for both the
485           "#include "file"" and "#include <file>" directives.
486
487           You can specify any number or combination of these options on the
488           command line to search for header files in several directories.
489           The lookup order is as follows:
490
491           1.  For the quote form of the include directive, the directory of
492               the current file is searched first.
493
494           2.  For the quote form of the include directive, the directories
495               specified by -iquote options are searched in left-to-right
496               order, as they appear on the command line.
497
498           3.  Directories specified with -I options are scanned in left-to-
499               right order.
500
501           4.  Directories specified with -isystem options are scanned in
502               left-to-right order.
503
504           5.  Standard system directories are scanned.
505
506           6.  Directories specified with -idirafter options are scanned in
507               left-to-right order.
508
509           You can use -I to override a system header file, substituting your
510           own version, since these directories are searched before the
511           standard system header file directories.  However, you should not
512           use this option to add directories that contain vendor-supplied
513           system header files; use -isystem for that.
514
515           The -isystem and -idirafter options also mark the directory as a
516           system directory, so that it gets the same special treatment that
517           is applied to the standard system directories.
518
519           If a standard system include directory, or a directory specified
520           with -isystem, is also specified with -I, the -I option is ignored.
521           The directory is still searched but as a system directory at its
522           normal position in the system include chain.  This is to ensure
523           that GCC's procedure to fix buggy system headers and the ordering
524           for the "#include_next" directive are not inadvertently changed.
525           If you really need to change the search order for system
526           directories, use the -nostdinc and/or -isystem options.
527
528       -I- Split the include path.  This option has been deprecated.  Please
529           use -iquote instead for -I directories before the -I- and remove
530           the -I- option.
531
532           Any directories specified with -I options before -I- are searched
533           only for headers requested with "#include "file""; they are not
534           searched for "#include <file>".  If additional directories are
535           specified with -I options after the -I-, those directories are
536           searched for all #include directives.
537
538           In addition, -I- inhibits the use of the directory of the current
539           file directory as the first search directory for "#include "file"".
540           There is no way to override this effect of -I-.
541
542       -iprefix prefix
543           Specify prefix as the prefix for subsequent -iwithprefix options.
544           If the prefix represents a directory, you should include the final
545           /.
546
547       -iwithprefix dir
548       -iwithprefixbefore dir
549           Append dir to the prefix specified previously with -iprefix, and
550           add the resulting directory to the include search path.
551           -iwithprefixbefore puts it in the same place -I would; -iwithprefix
552           puts it where -idirafter would.
553
554       -isysroot dir
555           This option is like the --sysroot option, but applies only to
556           header files (except for Darwin targets, where it applies to both
557           header files and libraries).  See the --sysroot option for more
558           information.
559
560       -imultilib dir
561           Use dir as a subdirectory of the directory containing target-
562           specific C++ headers.
563
564       -nostdinc
565           Do not search the standard system directories for header files.
566           Only the directories explicitly specified with -I, -iquote,
567           -isystem, and/or -idirafter options (and the directory of the
568           current file, if appropriate) are searched.
569
570       -nostdinc++
571           Do not search for header files in the C++-specific standard
572           directories, but do still search the other standard directories.
573           (This option is used when building the C++ library.)
574
575       -Wcomment
576       -Wcomments
577           Warn whenever a comment-start sequence /* appears in a /* comment,
578           or whenever a backslash-newline appears in a // comment.  This
579           warning is enabled by -Wall.
580
581       -Wtrigraphs
582           Warn if any trigraphs are encountered that might change the meaning
583           of the program.  Trigraphs within comments are not warned about,
584           except those that would form escaped newlines.
585
586           This option is implied by -Wall.  If -Wall is not given, this
587           option is still enabled unless trigraphs are enabled.  To get
588           trigraph conversion without warnings, but get the other -Wall
589           warnings, use -trigraphs -Wall -Wno-trigraphs.
590
591       -Wundef
592           Warn if an undefined identifier is evaluated in an "#if" directive.
593           Such identifiers are replaced with zero.
594
595       -Wexpansion-to-defined
596           Warn whenever defined is encountered in the expansion of a macro
597           (including the case where the macro is expanded by an #if
598           directive).  Such usage is not portable.  This warning is also
599           enabled by -Wpedantic and -Wextra.
600
601       -Wunused-macros
602           Warn about macros defined in the main file that are unused.  A
603           macro is used if it is expanded or tested for existence at least
604           once.  The preprocessor also warns if the macro has not been used
605           at the time it is redefined or undefined.
606
607           Built-in macros, macros defined on the command line, and macros
608           defined in include files are not warned about.
609
610           Note: If a macro is actually used, but only used in skipped
611           conditional blocks, then the preprocessor reports it as unused.  To
612           avoid the warning in such a case, you might improve the scope of
613           the macro's definition by, for example, moving it into the first
614           skipped block.  Alternatively, you could provide a dummy use with
615           something like:
616
617                   #if defined the_macro_causing_the_warning
618                   #endif
619
620       -Wno-endif-labels
621           Do not warn whenever an "#else" or an "#endif" are followed by
622           text.  This sometimes happens in older programs with code of the
623           form
624
625                   #if FOO
626                   ...
627                   #else FOO
628                   ...
629                   #endif FOO
630
631           The second and third "FOO" should be in comments.  This warning is
632           on by default.
633

ENVIRONMENT

635       This section describes the environment variables that affect how CPP
636       operates.  You can use them to specify directories or prefixes to use
637       when searching for include files, or to control dependency output.
638
639       Note that you can also specify places to search using options such as
640       -I, and control dependency output with options like -M.  These take
641       precedence over environment variables, which in turn take precedence
642       over the configuration of GCC.
643
644       CPATH
645       C_INCLUDE_PATH
646       CPLUS_INCLUDE_PATH
647       OBJC_INCLUDE_PATH
648           Each variable's value is a list of directories separated by a
649           special character, much like PATH, in which to look for header
650           files.  The special character, "PATH_SEPARATOR", is target-
651           dependent and determined at GCC build time.  For Microsoft Windows-
652           based targets it is a semicolon, and for almost all other targets
653           it is a colon.
654
655           CPATH specifies a list of directories to be searched as if
656           specified with -I, but after any paths given with -I options on the
657           command line.  This environment variable is used regardless of
658           which language is being preprocessed.
659
660           The remaining environment variables apply only when preprocessing
661           the particular language indicated.  Each specifies a list of
662           directories to be searched as if specified with -isystem, but after
663           any paths given with -isystem options on the command line.
664
665           In all these variables, an empty element instructs the compiler to
666           search its current working directory.  Empty elements can appear at
667           the beginning or end of a path.  For instance, if the value of
668           CPATH is ":/special/include", that has the same effect as
669           -I. -I/special/include.
670
671       DEPENDENCIES_OUTPUT
672           If this variable is set, its value specifies how to output
673           dependencies for Make based on the non-system header files
674           processed by the compiler.  System header files are ignored in the
675           dependency output.
676
677           The value of DEPENDENCIES_OUTPUT can be just a file name, in which
678           case the Make rules are written to that file, guessing the target
679           name from the source file name.  Or the value can have the form
680           file target, in which case the rules are written to file file using
681           target as the target name.
682
683           In other words, this environment variable is equivalent to
684           combining the options -MM and -MF, with an optional -MT switch too.
685
686       SUNPRO_DEPENDENCIES
687           This variable is the same as DEPENDENCIES_OUTPUT (see above),
688           except that system header files are not ignored, so it implies -M
689           rather than -MM.  However, the dependence on the main input file is
690           omitted.
691
692       SOURCE_DATE_EPOCH
693           If this variable is set, its value specifies a UNIX timestamp to be
694           used in replacement of the current date and time in the "__DATE__"
695           and "__TIME__" macros, so that the embedded timestamps become
696           reproducible.
697
698           The value of SOURCE_DATE_EPOCH must be a UNIX timestamp, defined as
699           the number of seconds (excluding leap seconds) since 01 Jan 1970
700           00:00:00 represented in ASCII; identical to the output of "date
701           +%s" on GNU/Linux and other systems that support the %s extension
702           in the "date" command.
703
704           The value should be a known timestamp such as the last modification
705           time of the source or package and it should be set by the build
706           process.
707

SEE ALSO

709       gpl(7), gfdl(7), fsf-funding(7), gcc(1), and the Info entries for cpp
710       and gcc.
711
713       Copyright (c) 1987-2022 Free Software Foundation, Inc.
714
715       Permission is granted to copy, distribute and/or modify this document
716       under the terms of the GNU Free Documentation License, Version 1.3 or
717       any later version published by the Free Software Foundation.  A copy of
718       the license is included in the man page gfdl(7).  This manual contains
719       no Invariant Sections.  The Front-Cover Texts are (a) (see below), and
720       the Back-Cover Texts are (b) (see below).
721
722       (a) The FSF's Front-Cover Text is:
723
724            A GNU Manual
725
726       (b) The FSF's Back-Cover Text is:
727
728            You have freedom to copy and modify this GNU Manual, like GNU
729            software.  Copies published by the Free Software Foundation raise
730            funds for GNU development.
731
732
733
734gcc-12.1.0                        2022-05-06                            CPP(1)
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