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1This is Info file cpp.info, produced by Makeinfo-1.55 from the input
2file cpp.texi.
3
4   This file documents the GNU C Preprocessor.
5
6   Copyright 1987, 1989, 1991, 1992, 1993, 1994, 1995 Free Software
7Foundation, Inc.
8
9   Permission is granted to make and distribute verbatim copies of this
10manual provided the copyright notice and this permission notice are
11preserved on all copies.
12
13   Permission is granted to copy and distribute modified versions of
14this manual under the conditions for verbatim copying, provided also
15that the entire resulting derived work is distributed under the terms
16of a permission notice identical to this one.
17
18   Permission is granted to copy and distribute translations of this
19manual into another language, under the above conditions for modified
20versions.
21
22
23File: cpp.info,  Node: Invocation,  Next: Concept Index,  Prev: Output,  Up: Top
24
25Invoking the C Preprocessor
26===========================
27
28   Most often when you use the C preprocessor you will not have to
29invoke it explicitly: the C compiler will do so automatically.
30However, the preprocessor is sometimes useful on its own.
31
32   The C preprocessor expects two file names as arguments, INFILE and
33OUTFILE.  The preprocessor reads INFILE together with any other files
34it specifies with `#include'.  All the output generated by the combined
35input files is written in OUTFILE.
36
37   Either INFILE or OUTFILE may be `-', which as INFILE means to read
38from standard input and as OUTFILE means to write to standard output.
39Also, if OUTFILE or both file names are omitted, the standard output
40and standard input are used for the omitted file names.
41
42   Here is a table of command options accepted by the C preprocessor.
43These options can also be given when compiling a C program; they are
44passed along automatically to the preprocessor when it is invoked by the
45compiler.
46
47`-P'
48     Inhibit generation of `#'-lines with line-number information in
49     the output from the preprocessor (*note Output::.).  This might be
50     useful when running the preprocessor on something that is not C
51     code and will be sent to a program which might be confused by the
52     `#'-lines.
53
54`-C'
55     Do not discard comments: pass them through to the output file.
56     Comments appearing in arguments of a macro call will be copied to
57     the output before the expansion of the macro call.
58
59`-traditional'
60     Try to imitate the behavior of old-fashioned C, as opposed to ANSI
61     C.
62
63        * Traditional macro expansion pays no attention to singlequote
64          or doublequote characters; macro argument symbols are
65          replaced by the argument values even when they appear within
66          apparent string or character constants.
67
68        * Traditionally, it is permissible for a macro expansion to end
69          in the middle of a string or character constant.  The
70          constant continues into the text surrounding the macro call.
71
72        * However, traditionally the end of the line terminates a
73          string or character constant, with no error.
74
75        * In traditional C, a comment is equivalent to no text at all.
76          (In ANSI C, a comment counts as whitespace.)
77
78        * Traditional C does not have the concept of a "preprocessing
79          number".  It considers `1.0e+4' to be three tokens: `1.0e',
80          `+', and `4'.
81
82        * A macro is not suppressed within its own definition, in
83          traditional C.  Thus, any macro that is used recursively
84          inevitably causes an error.
85
86        * The character `#' has no special meaning within a macro
87          definition in traditional C.
88
89        * In traditional C, the text at the end of a macro expansion
90          can run together with the text after the macro call, to
91          produce a single token.  (This is impossible in ANSI C.)
92
93        * Traditionally, `\' inside a macro argument suppresses the
94          syntactic significance of the following character.
95
96`-trigraphs'
97     Process ANSI standard trigraph sequences.  These are
98     three-character sequences, all starting with `??', that are
99     defined by ANSI C to stand for single characters.  For example,
100     `??/' stands for `\', so `'??/n'' is a character constant for a
101     newline.  Strictly speaking, the GNU C preprocessor does not
102     support all programs in ANSI Standard C unless `-trigraphs' is
103     used, but if you ever notice the difference it will be with relief.
104
105     You don't want to know any more about trigraphs.
106
107`-pedantic'
108     Issue warnings required by the ANSI C standard in certain cases
109     such as when text other than a comment follows `#else' or `#endif'.
110
111`-pedantic-errors'
112     Like `-pedantic', except that errors are produced rather than
113     warnings.
114
115`-Wtrigraphs'
116     Warn if any trigraphs are encountered (assuming they are enabled).
117
118`-Wcomment'
119     Warn whenever a comment-start sequence `/*' appears in a comment.
120
121`-Wall'
122     Requests both `-Wtrigraphs' and `-Wcomment' (but not
123     `-Wtraditional').
124
125`-Wtraditional'
126     Warn about certain constructs that behave differently in
127     traditional and ANSI C.
128
129`-I DIRECTORY'
130     Add the directory DIRECTORY to the head of the list of directories
131     to be searched for header files (*note Include Syntax::.).  This
132     can be used to override a system header file, substituting your
133     own version, since these directories are searched before the system
134     header file directories.  If you use more than one `-I' option,
135     the directories are scanned in left-to-right order; the standard
136     system directories come after.
137
138`-I-'
139     Any directories specified with `-I' options before the `-I-'
140     option are searched only for the case of `#include "FILE"'; they
141     are not searched for `#include <FILE>'.
142
143     If additional directories are specified with `-I' options after
144     the `-I-', these directories are searched for all `#include'
145     directives.
146
147     In addition, the `-I-' option inhibits the use of the current
148     directory as the first search directory for `#include "FILE"'.
149     Therefore, the current directory is searched only if it is
150     requested explicitly with `-I.'.  Specifying both `-I-' and `-I.'
151     allows you to control precisely which directories are searched
152     before the current one and which are searched after.
153
154`-nostdinc'
155     Do not search the standard system directories for header files.
156     Only the directories you have specified with `-I' options (and the
157     current directory, if appropriate) are searched.
158
159`-nostdinc++'
160     Do not search for header files in the C++-specific standard
161     directories, but do still search the other standard directories.
162     (This option is used when building libg++.)
163
164`-D NAME'
165     Predefine NAME as a macro, with definition `1'.
166
167`-D NAME=DEFINITION'
168     Predefine NAME as a macro, with definition DEFINITION.  There are
169     no restrictions on the contents of DEFINITION, but if you are
170     invoking the preprocessor from a shell or shell-like program you
171     may need to use the shell's quoting syntax to protect characters
172     such as spaces that have a meaning in the shell syntax.  If you
173     use more than one `-D' for the same NAME, the rightmost definition
174     takes effect.
175
176`-U NAME'
177     Do not predefine NAME.  If both `-U' and `-D' are specified for
178     one name, the `-U' beats the `-D' and the name is not predefined.
179
180`-undef'
181     Do not predefine any nonstandard macros.
182
183`-A PREDICATE(ANSWER)'
184     Make an assertion with the predicate PREDICATE and answer ANSWER.
185     *Note Assertions::.
186
187     You can use `-A-' to disable all predefined assertions; it also
188     undefines all predefined macros that identify the type of target
189     system.
190
191`-dM'
192     Instead of outputting the result of preprocessing, output a list of
193     `#define' directives for all the macros defined during the
194     execution of the preprocessor, including predefined macros.  This
195     gives you a way of finding out what is predefined in your version
196     of the preprocessor; assuming you have no file `foo.h', the command
197
198          touch foo.h; cpp -dM foo.h
199
200     will show the values of any predefined macros.
201
202`-dD'
203     Like `-dM' except in two respects: it does *not* include the
204     predefined macros, and it outputs *both* the `#define' directives
205     and the result of preprocessing.  Both kinds of output go to the
206     standard output file.
207
208`-M [-MG]'
209     Instead of outputting the result of preprocessing, output a rule
210     suitable for `make' describing the dependencies of the main source
211     file.  The preprocessor outputs one `make' rule containing the
212     object file name for that source file, a colon, and the names of
213     all the included files.  If there are many included files then the
214     rule is split into several lines using `\'-newline.
215
216     `-MG' says to treat missing header files as generated files and
217     assume they live in the same directory as the source file.  It
218     must be specified in addition to `-M'.
219
220     This feature is used in automatic updating of makefiles.
221
222`-MM [-MG]'
223     Like `-M' but mention only the files included with `#include
224     "FILE"'.  System header files included with `#include <FILE>' are
225     omitted.
226
227`-MD FILE'
228     Like `-M' but the dependency information is written to FILE.  This
229     is in addition to compiling the file as specified--`-MD' does not
230     inhibit ordinary compilation the way `-M' does.
231
232     When invoking gcc, do not specify the FILE argument.  Gcc will
233     create file names made by replacing ".c" with ".d" at the end of
234     the input file names.
235
236     In Mach, you can use the utility `md' to merge multiple dependency
237     files into a single dependency file suitable for using with the
238     `make' command.
239
240`-MMD FILE'
241     Like `-MD' except mention only user header files, not system
242     header files.
243
244`-H'
245     Print the name of each header file used, in addition to other
246     normal activities.
247
248`-imacros FILE'
249     Process FILE as input, discarding the resulting output, before
250     processing the regular input file.  Because the output generated
251     from FILE is discarded, the only effect of `-imacros FILE' is to
252     make the macros defined in FILE available for use in the main
253     input.
254
255`-include FILE'
256     Process FILE as input, and include all the resulting output,
257     before processing the regular input file.
258
259`-idirafter DIR'
260     Add the directory DIR to the second include path.  The directories
261     on the second include path are searched when a header file is not
262     found in any of the directories in the main include path (the one
263     that `-I' adds to).
264
265`-iprefix PREFIX'
266     Specify PREFIX as the prefix for subsequent `-iwithprefix' options.
267
268`-iwithprefix DIR'
269     Add a directory to the second include path.  The directory's name
270     is made by concatenating PREFIX and DIR, where PREFIX was
271     specified previously with `-iprefix'.
272
273`-isystem DIR'
274     Add a directory to the beginning of the second include path,
275     marking it as a system directory, so that it gets the same special
276     treatment as is applied to the standard system directories.
277
278`-lang-c'
279`-lang-c89'
280`-lang-c++'
281`-lang-objc'
282`-lang-objc++'
283     Specify the source language.  `-lang-c' is the default; it allows
284     recognition of C++ comments (comments that begin with `//' and end
285     at end of line), since this is a common feature and it will most
286     likely be in the next C standard.  `-lang-c89' disables
287     recognition of C++ comments.  `-lang-c++' handles C++ comment
288     syntax and includes extra default include directories for C++.
289     `-lang-objc' enables the Objective C `#import' directive.
290     `-lang-objc++' enables both C++ and Objective C extensions.
291
292     These options are generated by the compiler driver `gcc', but not
293     passed from the `gcc' command line unless you use the driver's
294     `-Wp' option.
295
296`-lint'
297     Look for commands to the program checker `lint' embedded in
298     comments, and emit them preceded by `#pragma lint'.  For example,
299     the comment `/* NOTREACHED */' becomes `#pragma lint NOTREACHED'.
300
301     This option is available only when you call `cpp' directly; `gcc'
302     will not pass it from its command line.
303
304`-$'
305     Forbid the use of `$' in identifiers.  This is required for ANSI
306     conformance.  `gcc' automatically supplies this option to the
307     preprocessor if you specify `-ansi', but `gcc' doesn't recognize
308     the `-$' option itself--to use it without the other effects of
309     `-ansi', you must call the preprocessor directly.
310
311
312File: cpp.info,  Node: Concept Index,  Next: Index,  Prev: Invocation,  Up: Top
313
314Concept Index
315*************
316
317* Menu:
318
319* ##:                                   Concatenation.
320* arguments in macro definitions:       Argument Macros.
321* assertions:                           Assertions.
322* assertions, undoing:                  Assertions.
323* blank macro arguments:                Argument Macros.
324* cascaded macros:                      Cascaded Macros.
325* commenting out code:                  Deleted Code.
326* computed #include:                    Include Syntax.
327* concatenation:                        Concatenation.
328* conditionals:                         Conditionals.
329* directives:                           Directives.
330* expansion of arguments:               Argument Prescan.
331* function-like macro:                  Argument Macros.
332* header file:                          Header Files.
333* including just once:                  Once-Only.
334* inheritance:                          Inheritance.
335* invocation of the preprocessor:       Invocation.
336* line control:                         Combining Sources.
337* macro argument expansion:             Argument Prescan.
338* macro body uses macro:                Cascaded Macros.
339* macros with argument:                 Argument Macros.
340* manifest constant:                    Simple Macros.
341* newlines in macro arguments:          Newlines in Args.
342* null directive:                       Other Directives.
343* options:                              Invocation.
344* output format:                        Output.
345* overriding a header file:             Inheritance.
346* parentheses in macro bodies:          Macro Parentheses.
347* pitfalls of macros:                   Macro Pitfalls.
348* predefined macros:                    Predefined.
349* predicates:                           Assertions.
350* preprocessing directives:             Directives.
351* prescan of macro arguments:           Argument Prescan.
352* problems with macros:                 Macro Pitfalls.
353* redefining macros:                    Redefining.
354* repeated inclusion:                   Once-Only.
355* retracting assertions:                Assertions.
356* second include path:                  Invocation.
357* self-reference:                       Self-Reference.
358* semicolons (after macro calls):       Swallow Semicolon.
359* side effects (in macro arguments):    Side Effects.
360* simple macro:                         Simple Macros.
361* space as macro argument:              Argument Macros.
362* standard predefined macros:           Standard Predefined.
363* stringification:                      Stringification.
364* testing predicates:                   Assertions.
365* unassert:                             Assertions.
366* undefining macros:                    Undefining.
367* unsafe macros:                        Side Effects.
368
369
370File: cpp.info,  Node: Index,  Prev: Concept Index,  Up: Top
371
372Index of Directives, Macros and Options
373***************************************
374
375* Menu:
376
377* #assert:                              Assertions.
378* #cpu:                                 Assertions.
379* #define:                              Argument Macros.
380* #elif:                                #elif Directive.
381* #else:                                #else Directive.
382* #error:                               #error Directive.
383* #ident:                               Other Directives.
384* #if:                                  Conditional Syntax.
385* #ifdef:                               Conditionals-Macros.
386* #ifndef:                              Conditionals-Macros.
387* #import:                              Once-Only.
388* #include:                             Include Syntax.
389* #include_next:                        Inheritance.
390* #line:                                Combining Sources.
391* #machine:                             Assertions.
392* #pragma:                              Other Directives.
393* #pragma once:                         Once-Only.
394* #system:                              Assertions.
395* #unassert:                            Assertions.
396* #warning:                             #error Directive.
397* -$:                                   Invocation.
398* -A:                                   Invocation.
399* -C:                                   Invocation.
400* -D:                                   Invocation.
401* -dD:                                  Invocation.
402* -dM:                                  Invocation.
403* -H:                                   Invocation.
404* -I:                                   Invocation.
405* -idirafter:                           Invocation.
406* -imacros:                             Invocation.
407* -include:                             Invocation.
408* -iprefix:                             Invocation.
409* -isystem:                             Invocation.
410* -iwithprefix:                         Invocation.
411* -lang-c:                              Invocation.
412* -lang-c++:                            Invocation.
413* -lang-c89:                            Invocation.
414* -lang-objc:                           Invocation.
415* -lang-objc++:                         Invocation.
416* -M:                                   Invocation.
417* -MD:                                  Invocation.
418* -MM:                                  Invocation.
419* -MMD:                                 Invocation.
420* -nostdinc:                            Invocation.
421* -nostdinc++:                          Invocation.
422* -P:                                   Invocation.
423* -pedantic:                            Invocation.
424* -pedantic-errors:                     Invocation.
425* -traditional:                         Invocation.
426* -trigraphs:                           Invocation.
427* -U:                                   Invocation.
428* -undef:                               Invocation.
429* -Wall:                                Invocation.
430* -Wcomment:                            Invocation.
431* -Wtraditional:                        Invocation.
432* -Wtrigraphs:                          Invocation.
433* BSD:                                  Nonstandard Predefined.
434* defined:                              Conditionals-Macros.
435* M68020:                               Nonstandard Predefined.
436* m68k:                                 Nonstandard Predefined.
437* mc68000:                              Nonstandard Predefined.
438* ns32000:                              Nonstandard Predefined.
439* pyr:                                  Nonstandard Predefined.
440* sequent:                              Nonstandard Predefined.
441* sun:                                  Nonstandard Predefined.
442* system header files:                  Header Uses.
443* unix:                                 Nonstandard Predefined.
444* vax:                                  Nonstandard Predefined.
445* _AM29000:                             Nonstandard Predefined.
446* _AM29K:                               Nonstandard Predefined.
447* __BASE_FILE__:                        Standard Predefined.
448* __CHAR_UNSIGNED__:                    Standard Predefined.
449* __cplusplus:                          Standard Predefined.
450* __DATE__:                             Standard Predefined.
451* __FILE__:                             Standard Predefined.
452* __GNUC_MINOR__:                       Standard Predefined.
453* __GNUC__:                             Standard Predefined.
454* __GNUG__:                             Standard Predefined.
455* __INCLUDE_LEVEL_:                     Standard Predefined.
456* __LINE__:                             Standard Predefined.
457* __OPTIMIZE__:                         Standard Predefined.
458* __REGISTER_PREFIX__:                  Standard Predefined.
459* __STDC_VERSION__:                     Standard Predefined.
460* __STDC__:                             Standard Predefined.
461* __STRICT_ANSI__:                      Standard Predefined.
462* __TIME__:                             Standard Predefined.
463* __USER_LABEL_PREFIX__:                Standard Predefined.
464* __VERSION__:                          Standard Predefined.
465
466
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