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1	This is Info file cpp.info, produced by Makeinfo version 1.67 from the
2	input file cpp.texi.
3
4	This file documents the GNU C Preprocessor.
5
6	Copyright 1987, 1989, 1991, 1992, 1993, 1994, 1995 Free Software
7	Foundation, Inc.
8
9	Permission is granted to make and distribute verbatim copies of this
10	manual provided the copyright notice and this permission notice are
11	preserved on all copies.
12
13	Permission is granted to copy and distribute modified versions of
14	this manual under the conditions for verbatim copying, provided also
15	that the entire resulting derived work is distributed under the terms
16	of a permission notice identical to this one.
17
18	Permission is granted to copy and distribute translations of this
19	manual into another language, under the above conditions for modified
20	versions.
21
22
23	File: cpp.info, Node: Invocation, Next: Concept Index, Prev: Output, Up: Top
24
25	Invoking the C Preprocessor
26	===========================
27
28	Most often when you use the C preprocessor you will not have to
29	invoke it explicitly: the C compiler will do so automatically.
30	However, the preprocessor is sometimes useful on its own.
31
32	The C preprocessor expects two file names as arguments, INFILE and
33	OUTFILE. The preprocessor reads INFILE together with any other files
34	it specifies with `#include'. All the output generated by the combined
35	input files is written in OUTFILE.
36
37	Either INFILE or OUTFILE may be `-', which as INFILE means to read
38	from standard input and as OUTFILE means to write to standard output.
39	Also, if OUTFILE or both file names are omitted, the standard output
40	and standard input are used for the omitted file names.
41
42	Here is a table of command options accepted by the C preprocessor.
43	These options can also be given when compiling a C program; they are
44	passed along automatically to the preprocessor when it is invoked by the
45	compiler.
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 `/'
120	comment, or whenever a Backslash-Newline appears in a `//' comment.
121
122	`-Wall'
123	Requests both `-Wtrigraphs' and `-Wcomment' (but not
124	`-Wtraditional' or `-Wundef').
125
126	`-Wtraditional'
127	Warn about certain constructs that behave differently in
128	traditional and ANSI C.
129
130	`-Wundef'
131	Warn if an undefined identifier is evaluated in an `#if' directive.
132
133	`-I DIRECTORY'
134	Add the directory DIRECTORY to the head of the list of directories
135	to be searched for header files (*note Include Syntax::.). This
136	can be used to override a system header file, substituting your
137	own version, since these directories are searched before the system
138	header file directories. If you use more than one `-I' option,
139	the directories are scanned in left-to-right order; the standard
140	system directories come after.
141
142	`-I-'
143	Any directories specified with `-I' options before the `-I-'
144	option are searched only for the case of `#include "FILE"'; they
145	are not searched for `#include <FILE>'.
146
147	If additional directories are specified with `-I' options after
148	the `-I-', these directories are searched for all `#include'
149	directives.
150
151	In addition, the `-I-' option inhibits the use of the current
152	directory as the first search directory for `#include "FILE"'.
153	Therefore, the current directory is searched only if it is
154	requested explicitly with `-I.'. Specifying both `-I-' and `-I.'
155	allows you to control precisely which directories are searched
156	before the current one and which are searched after.
157
158	`-nostdinc'
159	Do not search the standard system directories for header files.
160	Only the directories you have specified with `-I' options (and the
161	current directory, if appropriate) are searched.
162
163	`-nostdinc++'
164	Do not search for header files in the C++-specific standard
165	directories, but do still search the other standard directories.
166	(This option is used when building the C++ library.)
167
168	`-remap'
169	When searching for a header file in a directory, remap file names
170	if a file named `header.gcc' exists in that directory. This can
171	be used to work around limitations of file systems with file name
172	restrictions. The `header.gcc' file should contain a series of
173	lines with two tokens on each line: the first token is the name to
174	map, and the second token is the actual name to use.
175
176	`-D NAME'
177	Predefine NAME as a macro, with definition `1'.
178
179	`-D NAME=DEFINITION'
180	Predefine NAME as a macro, with definition DEFINITION. There are
181	no restrictions on the contents of DEFINITION, but if you are
182	invoking the preprocessor from a shell or shell-like program you
183	may need to use the shell's quoting syntax to protect characters
184	such as spaces that have a meaning in the shell syntax. If you
185	use more than one `-D' for the same NAME, the rightmost definition
186	takes effect.
187
188	`-U NAME'
189	Do not predefine NAME. If both `-U' and `-D' are specified for
190	one name, the `-U' beats the `-D' and the name is not predefined.
191
192	`-undef'
193	Do not predefine any nonstandard macros.
194
195	`-A PREDICATE(ANSWER)'
196	Make an assertion with the predicate PREDICATE and answer ANSWER.
197	*Note Assertions::.
198
199	You can use `-A-' to disable all predefined assertions; it also
200	undefines all predefined macros that identify the type of target
201	system.
202
203	`-dM'
204	Instead of outputting the result of preprocessing, output a list of
205	`#define' directives for all the macros defined during the
206	execution of the preprocessor, including predefined macros. This
207	gives you a way of finding out what is predefined in your version
208	of the preprocessor; assuming you have no file `foo.h', the command
209
210	touch foo.h; cpp -dM foo.h
211
212	will show the values of any predefined macros.
213
214	`-dD'
215	Like `-dM' except in two respects: it does not include the
216	predefined macros, and it outputs both the `#define' directives
217	and the result of preprocessing. Both kinds of output go to the
218	standard output file.
219
220	`-dI'
221	Output `#include' directives in addition to the result of
222	preprocessing.
223
224	`-M [-MG]'
225	Instead of outputting the result of preprocessing, output a rule
226	suitable for `make' describing the dependencies of the main source
227	file. The preprocessor outputs one `make' rule containing the
228	object file name for that source file, a colon, and the names of
229	all the included files. If there are many included files then the
230	rule is split into several lines using `\'-newline.
231
232	`-MG' says to treat missing header files as generated files and
233	assume they live in the same directory as the source file. It
234	must be specified in addition to `-M'.
235
236	This feature is used in automatic updating of makefiles.
237
238	`-MM [-MG]'
239	Like `-M' but mention only the files included with `#include
240	"FILE"'. System header files included with `#include <FILE>' are
241	omitted.
242
243	`-MD FILE'
244	Like `-M' but the dependency information is written to FILE. This
245	is in addition to compiling the file as specified--`-MD' does not
246	inhibit ordinary compilation the way `-M' does.
247
248	When invoking gcc, do not specify the FILE argument. Gcc will
249	create file names made by replacing ".c" with ".d" at the end of
250	the input file names.
251
252	In Mach, you can use the utility `md' to merge multiple dependency
253	files into a single dependency file suitable for using with the
254	`make' command.
255
256	`-MMD FILE'
257	Like `-MD' except mention only user header files, not system
258	header files.
259
260	`-H'
261	Print the name of each header file used, in addition to other
262	normal activities.
263
264	`-imacros FILE'
265	Process FILE as input, discarding the resulting output, before
266	processing the regular input file. Because the output generated
267	from FILE is discarded, the only effect of `-imacros FILE' is to
268	make the macros defined in FILE available for use in the main
269	input.
270
271	`-include FILE'
272	Process FILE as input, and include all the resulting output,
273	before processing the regular input file.
274
275	`-idirafter DIR'
276	Add the directory DIR to the second include path. The directories
277	on the second include path are searched when a header file is not
278	found in any of the directories in the main include path (the one
279	that `-I' adds to).
280
281	`-iprefix PREFIX'
282	Specify PREFIX as the prefix for subsequent `-iwithprefix' options.
283
284	`-iwithprefix DIR'
285	Add a directory to the second include path. The directory's name
286	is made by concatenating PREFIX and DIR, where PREFIX was
287	specified previously with `-iprefix'.
288
289	`-isystem DIR'
290	Add a directory to the beginning of the second include path,
291	marking it as a system directory, so that it gets the same special
292	treatment as is applied to the standard system directories.
293
294	`-lang-c'
295	`-lang-c89'
296	`-lang-c++'
297	`-lang-objc'
298	`-lang-objc++'
299	Specify the source language. `-lang-c' is the default; it allows
300	recognition of C++ comments (comments that begin with `//' and end
301	at end of line) and hexadecimal floating-point constants, since
302	these features will most likely appear in the next C standard.
303	`-lang-c89' disables recognition of C++ comments and hexadecimal
304	floating-point constants. `-lang-c++' handles C++ comment syntax
305	and includes extra default include directories for C++.
306	`-lang-objc' enables the Objective C `#import' directive.
307	`-lang-objc++' enables both C++ and Objective C extensions.
308
309	These options are generated by the compiler driver `gcc', but not
310	passed from the `gcc' command line unless you use the driver's
311	`-Wp' option.
312
313	`-lint'
314	Look for commands to the program checker `lint' embedded in
315	comments, and emit them preceded by `#pragma lint'. For example,
316	the comment `/* NOTREACHED */' becomes `#pragma lint NOTREACHED'.
317
318	This option is available only when you call `cpp' directly; `gcc'
319	will not pass it from its command line.
320
321	`-$'
322	Forbid the use of `$' in identifiers. This was formerly required
323	for strict conformance to the C Standard before the standard was
324	corrected.
325
326	This option is available only when you call `cpp' directly; `gcc'
327	will not pass it from its command line.
328
329
330	File: cpp.info, Node: Concept Index, Next: Index, Prev: Invocation, Up: Top
331
332	Concept Index
333	*************
334
335	* Menu:
336
337	* ##: Concatenation.
338	* arguments in macro definitions: Argument Macros.
339	* assertions: Assertions.
340	* assertions, undoing: Assertions.
341	* blank macro arguments: Argument Macros.
342	* cascaded macros: Cascaded Macros.
343	* commenting out code: Deleted Code.
344	* computed #include: Include Syntax.
345	* concatenation: Concatenation.
346	* conditionals: Conditionals.
347	* directives: Directives.
348	* expansion of arguments: Argument Prescan.
349	* function-like macro: Argument Macros.
350	* header file: Header Files.
351	* including just once: Once-Only.
352	* inheritance: Inheritance.
353	* invocation of the preprocessor: Invocation.
354	* line control: Combining Sources.
355	* macro argument expansion: Argument Prescan.
356	* macro body uses macro: Cascaded Macros.
357	* macros with argument: Argument Macros.
358	* manifest constant: Simple Macros.
359	* newlines in macro arguments: Newlines in Args.
360	* null directive: Other Directives.
361	* options: Invocation.
362	* output format: Output.
363	* overriding a header file: Inheritance.
364	* parentheses in macro bodies: Macro Parentheses.
365	* pitfalls of macros: Macro Pitfalls.
366	* predefined macros: Predefined.
367	* predicates: Assertions.
368	* preprocessing directives: Directives.
369	* prescan of macro arguments: Argument Prescan.
370	* problems with macros: Macro Pitfalls.
371	* redefining macros: Redefining.
372	* repeated inclusion: Once-Only.
373	* retracting assertions: Assertions.
374	* second include path: Invocation.
375	* self-reference: Self-Reference.
376	* semicolons (after macro calls): Swallow Semicolon.
377	* side effects (in macro arguments): Side Effects.
378	* simple macro: Simple Macros.
379	* space as macro argument: Argument Macros.
380	* standard predefined macros: Standard Predefined.
381	* stringification: Stringification.
382	* testing predicates: Assertions.
383	* unassert: Assertions.
384	* undefining macros: Undefining.
385	* unsafe macros: Side Effects.
386
387
388	File: cpp.info, Node: Index, Prev: Concept Index, Up: Top
389
390	Index of Directives, Macros and Options
391	***************************************
392
393	* Menu:
394
395	* #assert: Assertions.
396	* #cpu: Assertions.
397	* #define: Argument Macros.
398	* #elif: #elif Directive.
399	* #else: #else Directive.
400	* #error: #error Directive.
401	* #ident: Other Directives.
402	* #if: Conditional Syntax.
403	* #ifdef: Conditionals-Macros.
404	* #ifndef: Conditionals-Macros.
405	* #import: Once-Only.
406	* #include: Include Syntax.
407	* #include_next: Inheritance.
408	* #line: Combining Sources.
409	* #machine: Assertions.
410	* #pragma: Other Directives.
411	* #pragma once: Once-Only.
412	* #system: Assertions.
413	* #unassert: Assertions.
414	* #warning: #error Directive.
415	* -$: Invocation.
416	* -A: Invocation.
417	* -C: Invocation.
418	* -D: Invocation.
419	* -dD: Invocation.
420	* -dI: Invocation.
421	* -dM: Invocation.
422	* -H: Invocation.
423	* -I: Invocation.
424	* -idirafter: Invocation.
425	* -imacros: Invocation.
426	* -include: Invocation.
427	* -iprefix: Invocation.
428	* -isystem: Invocation.
429	* -iwithprefix: Invocation.
430	* -lang-c: Invocation.
431	* -lang-c++: Invocation.
432	* -lang-c89: Invocation.
433	* -lang-objc: Invocation.
434	* -lang-objc++: Invocation.
435	* -M: Invocation.
436	* -MD: Invocation.
437	* -MM: Invocation.
438	* -MMD: Invocation.
439	* -nostdinc: Invocation.
440	* -nostdinc++: Invocation.
441	* -P: Invocation.
442	* -pedantic: Invocation.
443	* -pedantic-errors: Invocation.
444	* -remap: Invocation.
445	* -traditional: Invocation.
446	* -trigraphs: Invocation.
447	* -U: Invocation.
448	* -undef: Invocation.
449	* -Wall: Invocation.
450	* -Wcomment: Invocation.
451	* -Wtraditional: Invocation.
452	* -Wtrigraphs: Invocation.
453	* -Wundef: Invocation.
454	* __BASE_FILE__: Standard Predefined.
455	* __CHAR_UNSIGNED__: Standard Predefined.
456	* __cplusplus: Standard Predefined.
457	* __DATE__: Standard Predefined.
458	* __FILE__: Standard Predefined.
459	* __GNUC__: Standard Predefined.
460	* __GNUC_MINOR__: Standard Predefined.
461	* __GNUG__: Standard Predefined.
462	* __INCLUDE_LEVEL_: Standard Predefined.
463	* __LINE__: Standard Predefined.
464	* __OPTIMIZE__: Standard Predefined.
465	* __REGISTER_PREFIX__: Standard Predefined.
466	* __STDC__: Standard Predefined.
467	* __STDC_VERSION__: Standard Predefined.
468	* __STRICT_ANSI__: Standard Predefined.
469	* __TIME__: Standard Predefined.
470	* __USER_LABEL_PREFIX__: Standard Predefined.
471	* __VERSION__: Standard Predefined.
472	* _AM29000: Nonstandard Predefined.
473	* _AM29K: Nonstandard Predefined.
474	* BSD: Nonstandard Predefined.
475	* defined: Conditionals-Macros.
476	* M68020: Nonstandard Predefined.
477	* m68k: Nonstandard Predefined.
478	* mc68000: Nonstandard Predefined.
479	* ns32000: Nonstandard Predefined.
480	* pyr: Nonstandard Predefined.
481	* sequent: Nonstandard Predefined.
482	* sun: Nonstandard Predefined.
483	* system header files: Header Uses.
484	* unix: Nonstandard Predefined.
485	* vax: Nonstandard Predefined.
486
487

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