/[pcre]/code/trunk/doc/pcreapi.3
ViewVC logotype

Contents of /code/trunk/doc/pcreapi.3

Parent Directory Parent Directory | Revision Log Revision Log


Revision 71 - (show annotations) (download)
Sat Feb 24 21:40:24 2007 UTC (7 years, 4 months ago) by nigel
File size: 44892 byte(s)
Load pcre-4.4 into code/trunk.

1 .TH PCRE 3
2 .SH NAME
3 PCRE - Perl-compatible regular expressions
4 .SH SYNOPSIS OF PCRE API
5 .rs
6 .sp
7 .B #include <pcre.h>
8 .PP
9 .SM
10 .br
11 .B pcre *pcre_compile(const char *\fIpattern\fR, int \fIoptions\fR,
12 .ti +5n
13 .B const char **\fIerrptr\fR, int *\fIerroffset\fR,
14 .ti +5n
15 .B const unsigned char *\fItableptr\fR);
16 .PP
17 .br
18 .B pcre_extra *pcre_study(const pcre *\fIcode\fR, int \fIoptions\fR,
19 .ti +5n
20 .B const char **\fIerrptr\fR);
21 .PP
22 .br
23 .B int pcre_exec(const pcre *\fIcode\fR, "const pcre_extra *\fIextra\fR,"
24 .ti +5n
25 .B "const char *\fIsubject\fR," int \fIlength\fR, int \fIstartoffset\fR,
26 .ti +5n
27 .B int \fIoptions\fR, int *\fIovector\fR, int \fIovecsize\fR);
28 .PP
29 .br
30 .B int pcre_copy_named_substring(const pcre *\fIcode\fR,
31 .ti +5n
32 .B const char *\fIsubject\fR, int *\fIovector\fR,
33 .ti +5n
34 .B int \fIstringcount\fR, const char *\fIstringname\fR,
35 .ti +5n
36 .B char *\fIbuffer\fR, int \fIbuffersize\fR);
37 .PP
38 .br
39 .B int pcre_copy_substring(const char *\fIsubject\fR, int *\fIovector\fR,
40 .ti +5n
41 .B int \fIstringcount\fR, int \fIstringnumber\fR, char *\fIbuffer\fR,
42 .ti +5n
43 .B int \fIbuffersize\fR);
44 .PP
45 .br
46 .B int pcre_get_named_substring(const pcre *\fIcode\fR,
47 .ti +5n
48 .B const char *\fIsubject\fR, int *\fIovector\fR,
49 .ti +5n
50 .B int \fIstringcount\fR, const char *\fIstringname\fR,
51 .ti +5n
52 .B const char **\fIstringptr\fR);
53 .PP
54 .br
55 .B int pcre_get_stringnumber(const pcre *\fIcode\fR,
56 .ti +5n
57 .B const char *\fIname\fR);
58 .PP
59 .br
60 .B int pcre_get_substring(const char *\fIsubject\fR, int *\fIovector\fR,
61 .ti +5n
62 .B int \fIstringcount\fR, int \fIstringnumber\fR,
63 .ti +5n
64 .B const char **\fIstringptr\fR);
65 .PP
66 .br
67 .B int pcre_get_substring_list(const char *\fIsubject\fR,
68 .ti +5n
69 .B int *\fIovector\fR, int \fIstringcount\fR, "const char ***\fIlistptr\fR);"
70 .PP
71 .br
72 .B void pcre_free_substring(const char *\fIstringptr\fR);
73 .PP
74 .br
75 .B void pcre_free_substring_list(const char **\fIstringptr\fR);
76 .PP
77 .br
78 .B const unsigned char *pcre_maketables(void);
79 .PP
80 .br
81 .B int pcre_fullinfo(const pcre *\fIcode\fR, "const pcre_extra *\fIextra\fR,"
82 .ti +5n
83 .B int \fIwhat\fR, void *\fIwhere\fR);
84 .PP
85 .br
86 .B int pcre_info(const pcre *\fIcode\fR, int *\fIoptptr\fR, int
87 .B *\fIfirstcharptr\fR);
88 .PP
89 .br
90 .B int pcre_config(int \fIwhat\fR, void *\fIwhere\fR);
91 .PP
92 .br
93 .B char *pcre_version(void);
94 .PP
95 .br
96 .B void *(*pcre_malloc)(size_t);
97 .PP
98 .br
99 .B void (*pcre_free)(void *);
100 .PP
101 .br
102 .B int (*pcre_callout)(pcre_callout_block *);
103
104 .SH PCRE API
105 .rs
106 .sp
107 PCRE has its own native API, which is described in this document. There is also
108 a set of wrapper functions that correspond to the POSIX regular expression API.
109 These are described in the \fBpcreposix\fR documentation.
110
111 The native API function prototypes are defined in the header file \fBpcre.h\fR,
112 and on Unix systems the library itself is called \fBlibpcre.a\fR, so can be
113 accessed by adding \fB-lpcre\fR to the command for linking an application which
114 calls it. The header file defines the macros PCRE_MAJOR and PCRE_MINOR to
115 contain the major and minor release numbers for the library. Applications can
116 use these to include support for different releases.
117
118 The functions \fBpcre_compile()\fR, \fBpcre_study()\fR, and \fBpcre_exec()\fR
119 are used for compiling and matching regular expressions. A sample program that
120 demonstrates the simplest way of using them is given in the file
121 \fIpcredemo.c\fR. The \fBpcresample\fR documentation describes how to run it.
122
123 There are convenience functions for extracting captured substrings from a
124 matched subject string. They are:
125
126 \fBpcre_copy_substring()\fR
127 \fBpcre_copy_named_substring()\fR
128 \fBpcre_get_substring()\fR
129 \fBpcre_get_named_substring()\fR
130 \fBpcre_get_substring_list()\fR
131
132 \fBpcre_free_substring()\fR and \fBpcre_free_substring_list()\fR are also
133 provided, to free the memory used for extracted strings.
134
135 The function \fBpcre_maketables()\fR is used (optionally) to build a set of
136 character tables in the current locale for passing to \fBpcre_compile()\fR.
137
138 The function \fBpcre_fullinfo()\fR is used to find out information about a
139 compiled pattern; \fBpcre_info()\fR is an obsolete version which returns only
140 some of the available information, but is retained for backwards compatibility.
141 The function \fBpcre_version()\fR returns a pointer to a string containing the
142 version of PCRE and its date of release.
143
144 The global variables \fBpcre_malloc\fR and \fBpcre_free\fR initially contain
145 the entry points of the standard \fBmalloc()\fR and \fBfree()\fR functions
146 respectively. PCRE calls the memory management functions via these variables,
147 so a calling program can replace them if it wishes to intercept the calls. This
148 should be done before calling any PCRE functions.
149
150 The global variable \fBpcre_callout\fR initially contains NULL. It can be set
151 by the caller to a "callout" function, which PCRE will then call at specified
152 points during a matching operation. Details are given in the \fBpcrecallout\fR
153 documentation.
154
155 .SH MULTITHREADING
156 .rs
157 .sp
158 The PCRE functions can be used in multi-threading applications, with the
159 proviso that the memory management functions pointed to by \fBpcre_malloc\fR
160 and \fBpcre_free\fR, and the callout function pointed to by \fBpcre_callout\fR,
161 are shared by all threads.
162
163 The compiled form of a regular expression is not altered during matching, so
164 the same compiled pattern can safely be used by several threads at once.
165
166 .SH CHECKING BUILD-TIME OPTIONS
167 .rs
168 .sp
169 .B int pcre_config(int \fIwhat\fR, void *\fIwhere\fR);
170 .PP
171 The function \fBpcre_config()\fR makes it possible for a PCRE client to
172 discover which optional features have been compiled into the PCRE library. The
173 .\" HREF
174 \fBpcrebuild\fR
175 .\"
176 documentation has more details about these optional features.
177
178 The first argument for \fBpcre_config()\fR is an integer, specifying which
179 information is required; the second argument is a pointer to a variable into
180 which the information is placed. The following information is available:
181
182 PCRE_CONFIG_UTF8
183
184 The output is an integer that is set to one if UTF-8 support is available;
185 otherwise it is set to zero.
186
187 PCRE_CONFIG_NEWLINE
188
189 The output is an integer that is set to the value of the code that is used for
190 the newline character. It is either linefeed (10) or carriage return (13), and
191 should normally be the standard character for your operating system.
192
193 PCRE_CONFIG_LINK_SIZE
194
195 The output is an integer that contains the number of bytes used for internal
196 linkage in compiled regular expressions. The value is 2, 3, or 4. Larger values
197 allow larger regular expressions to be compiled, at the expense of slower
198 matching. The default value of 2 is sufficient for all but the most massive
199 patterns, since it allows the compiled pattern to be up to 64K in size.
200
201 PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
202
203 The output is an integer that contains the threshold above which the POSIX
204 interface uses \fBmalloc()\fR for output vectors. Further details are given in
205 the \fBpcreposix\fR documentation.
206
207 PCRE_CONFIG_MATCH_LIMIT
208
209 The output is an integer that gives the default limit for the number of
210 internal matching function calls in a \fBpcre_exec()\fR execution. Further
211 details are given with \fBpcre_exec()\fR below.
212
213 .SH COMPILING A PATTERN
214 .rs
215 .sp
216 .B pcre *pcre_compile(const char *\fIpattern\fR, int \fIoptions\fR,
217 .ti +5n
218 .B const char **\fIerrptr\fR, int *\fIerroffset\fR,
219 .ti +5n
220 .B const unsigned char *\fItableptr\fR);
221 .PP
222
223 The function \fBpcre_compile()\fR is called to compile a pattern into an
224 internal form. The pattern is a C string terminated by a binary zero, and
225 is passed in the argument \fIpattern\fR. A pointer to a single block of memory
226 that is obtained via \fBpcre_malloc\fR is returned. This contains the compiled
227 code and related data. The \fBpcre\fR type is defined for the returned block;
228 this is a typedef for a structure whose contents are not externally defined. It
229 is up to the caller to free the memory when it is no longer required.
230
231 Although the compiled code of a PCRE regex is relocatable, that is, it does not
232 depend on memory location, the complete \fBpcre\fR data block is not
233 fully relocatable, because it contains a copy of the \fItableptr\fR argument,
234 which is an address (see below).
235
236 The \fIoptions\fR argument contains independent bits that affect the
237 compilation. It should be zero if no options are required. Some of the options,
238 in particular, those that are compatible with Perl, can also be set and unset
239 from within the pattern (see the detailed description of regular expressions
240 in the \fBpcrepattern\fR documentation). For these options, the contents of the
241 \fIoptions\fR argument specifies their initial settings at the start of
242 compilation and execution. The PCRE_ANCHORED option can be set at the time of
243 matching as well as at compile time.
244
245 If \fIerrptr\fR is NULL, \fBpcre_compile()\fR returns NULL immediately.
246 Otherwise, if compilation of a pattern fails, \fBpcre_compile()\fR returns
247 NULL, and sets the variable pointed to by \fIerrptr\fR to point to a textual
248 error message. The offset from the start of the pattern to the character where
249 the error was discovered is placed in the variable pointed to by
250 \fIerroffset\fR, which must not be NULL. If it is, an immediate error is given.
251
252 If the final argument, \fItableptr\fR, is NULL, PCRE uses a default set of
253 character tables which are built when it is compiled, using the default C
254 locale. Otherwise, \fItableptr\fR must be the result of a call to
255 \fBpcre_maketables()\fR. See the section on locale support below.
256
257 This code fragment shows a typical straightforward call to \fBpcre_compile()\fR:
258
259 pcre *re;
260 const char *error;
261 int erroffset;
262 re = pcre_compile(
263 "^A.*Z", /* the pattern */
264 0, /* default options */
265 &error, /* for error message */
266 &erroffset, /* for error offset */
267 NULL); /* use default character tables */
268
269 The following option bits are defined:
270
271 PCRE_ANCHORED
272
273 If this bit is set, the pattern is forced to be "anchored", that is, it is
274 constrained to match only at the first matching point in the string which is
275 being searched (the "subject string"). This effect can also be achieved by
276 appropriate constructs in the pattern itself, which is the only way to do it in
277 Perl.
278
279 PCRE_CASELESS
280
281 If this bit is set, letters in the pattern match both upper and lower case
282 letters. It is equivalent to Perl's /i option, and it can be changed within a
283 pattern by a (?i) option setting.
284
285 PCRE_DOLLAR_ENDONLY
286
287 If this bit is set, a dollar metacharacter in the pattern matches only at the
288 end of the subject string. Without this option, a dollar also matches
289 immediately before the final character if it is a newline (but not before any
290 other newlines). The PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is
291 set. There is no equivalent to this option in Perl, and no way to set it within
292 a pattern.
293
294 PCRE_DOTALL
295
296 If this bit is set, a dot metacharater in the pattern matches all characters,
297 including newlines. Without it, newlines are excluded. This option is
298 equivalent to Perl's /s option, and it can be changed within a pattern by a
299 (?s) option setting. A negative class such as [^a] always matches a newline
300 character, independent of the setting of this option.
301
302 PCRE_EXTENDED
303
304 If this bit is set, whitespace data characters in the pattern are totally
305 ignored except when escaped or inside a character class. Whitespace does not
306 include the VT character (code 11). In addition, characters between an
307 unescaped # outside a character class and the next newline character,
308 inclusive, are also ignored. This is equivalent to Perl's /x option, and it can
309 be changed within a pattern by a (?x) option setting.
310
311 This option makes it possible to include comments inside complicated patterns.
312 Note, however, that this applies only to data characters. Whitespace characters
313 may never appear within special character sequences in a pattern, for example
314 within the sequence (?( which introduces a conditional subpattern.
315
316 PCRE_EXTRA
317
318 This option was invented in order to turn on additional functionality of PCRE
319 that is incompatible with Perl, but it is currently of very little use. When
320 set, any backslash in a pattern that is followed by a letter that has no
321 special meaning causes an error, thus reserving these combinations for future
322 expansion. By default, as in Perl, a backslash followed by a letter with no
323 special meaning is treated as a literal. There are at present no other features
324 controlled by this option. It can also be set by a (?X) option setting within a
325 pattern.
326
327 PCRE_MULTILINE
328
329 By default, PCRE treats the subject string as consisting of a single "line" of
330 characters (even if it actually contains several newlines). The "start of line"
331 metacharacter (^) matches only at the start of the string, while the "end of
332 line" metacharacter ($) matches only at the end of the string, or before a
333 terminating newline (unless PCRE_DOLLAR_ENDONLY is set). This is the same as
334 Perl.
335
336 When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs
337 match immediately following or immediately before any newline in the subject
338 string, respectively, as well as at the very start and end. This is equivalent
339 to Perl's /m option, and it can be changed within a pattern by a (?m) option
340 setting. If there are no "\\n" characters in a subject string, or no
341 occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no effect.
342
343 PCRE_NO_AUTO_CAPTURE
344
345 If this option is set, it disables the use of numbered capturing parentheses in
346 the pattern. Any opening parenthesis that is not followed by ? behaves as if it
347 were followed by ?: but named parentheses can still be used for capturing (and
348 they acquire numbers in the usual way). There is no equivalent of this option
349 in Perl.
350
351 PCRE_UNGREEDY
352
353 This option inverts the "greediness" of the quantifiers so that they are not
354 greedy by default, but become greedy if followed by "?". It is not compatible
355 with Perl. It can also be set by a (?U) option setting within the pattern.
356
357 PCRE_UTF8
358
359 This option causes PCRE to regard both the pattern and the subject as strings
360 of UTF-8 characters instead of single-byte character strings. However, it is
361 available only if PCRE has been built to include UTF-8 support. If not, the use
362 of this option provokes an error. Details of how this option changes the
363 behaviour of PCRE are given in the
364 .\" HTML <a href="pcre.html#utf8support">
365 .\" </a>
366 section on UTF-8 support
367 .\"
368 in the main
369 .\" HREF
370 \fBpcre\fR
371 .\"
372 page.
373
374 PCRE_NO_UTF8_CHECK
375
376 When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
377 automatically checked. If an invalid UTF-8 sequence of bytes is found,
378 \fBpcre_compile()\fR returns an error. If you already know that your pattern is
379 valid, and you want to skip this check for performance reasons, you can set the
380 PCRE_NO_UTF8_CHECK option. When it is set, the effect of passing an invalid
381 UTF-8 string as a pattern is undefined. It may cause your program to crash.
382 Note that there is a similar option for suppressing the checking of subject
383 strings passed to \fBpcre_exec()\fR.
384
385
386 .SH STUDYING A PATTERN
387 .rs
388 .sp
389 .B pcre_extra *pcre_study(const pcre *\fIcode\fR, int \fIoptions\fR,
390 .ti +5n
391 .B const char **\fIerrptr\fR);
392 .PP
393 When a pattern is going to be used several times, it is worth spending more
394 time analyzing it in order to speed up the time taken for matching. The
395 function \fBpcre_study()\fR takes a pointer to a compiled pattern as its first
396 argument. If studing the pattern produces additional information that will help
397 speed up matching, \fBpcre_study()\fR returns a pointer to a \fBpcre_extra\fR
398 block, in which the \fIstudy_data\fR field points to the results of the study.
399
400 The returned value from a \fBpcre_study()\fR can be passed directly to
401 \fBpcre_exec()\fR. However, the \fBpcre_extra\fR block also contains other
402 fields that can be set by the caller before the block is passed; these are
403 described below. If studying the pattern does not produce any additional
404 information, \fBpcre_study()\fR returns NULL. In that circumstance, if the
405 calling program wants to pass some of the other fields to \fBpcre_exec()\fR, it
406 must set up its own \fBpcre_extra\fR block.
407
408 The second argument contains option bits. At present, no options are defined
409 for \fBpcre_study()\fR, and this argument should always be zero.
410
411 The third argument for \fBpcre_study()\fR is a pointer for an error message. If
412 studying succeeds (even if no data is returned), the variable it points to is
413 set to NULL. Otherwise it points to a textual error message. You should
414 therefore test the error pointer for NULL after calling \fBpcre_study()\fR, to
415 be sure that it has run successfully.
416
417 This is a typical call to \fBpcre_study\fR():
418
419 pcre_extra *pe;
420 pe = pcre_study(
421 re, /* result of pcre_compile() */
422 0, /* no options exist */
423 &error); /* set to NULL or points to a message */
424
425 At present, studying a pattern is useful only for non-anchored patterns that do
426 not have a single fixed starting character. A bitmap of possible starting
427 characters is created.
428
429 .\" HTML <a name="localesupport"></a>
430 .SH LOCALE SUPPORT
431 .rs
432 .sp
433 PCRE handles caseless matching, and determines whether characters are letters,
434 digits, or whatever, by reference to a set of tables. When running in UTF-8
435 mode, this applies only to characters with codes less than 256. The library
436 contains a default set of tables that is created in the default C locale when
437 PCRE is compiled. This is used when the final argument of \fBpcre_compile()\fR
438 is NULL, and is sufficient for many applications.
439
440 An alternative set of tables can, however, be supplied. Such tables are built
441 by calling the \fBpcre_maketables()\fR function, which has no arguments, in the
442 relevant locale. The result can then be passed to \fBpcre_compile()\fR as often
443 as necessary. For example, to build and use tables that are appropriate for the
444 French locale (where accented characters with codes greater than 128 are
445 treated as letters), the following code could be used:
446
447 setlocale(LC_CTYPE, "fr");
448 tables = pcre_maketables();
449 re = pcre_compile(..., tables);
450
451 The tables are built in memory that is obtained via \fBpcre_malloc\fR. The
452 pointer that is passed to \fBpcre_compile\fR is saved with the compiled
453 pattern, and the same tables are used via this pointer by \fBpcre_study()\fR
454 and \fBpcre_exec()\fR. Thus, for any single pattern, compilation, studying and
455 matching all happen in the same locale, but different patterns can be compiled
456 in different locales. It is the caller's responsibility to ensure that the
457 memory containing the tables remains available for as long as it is needed.
458
459 .SH INFORMATION ABOUT A PATTERN
460 .rs
461 .sp
462 .B int pcre_fullinfo(const pcre *\fIcode\fR, "const pcre_extra *\fIextra\fR,"
463 .ti +5n
464 .B int \fIwhat\fR, void *\fIwhere\fR);
465 .PP
466 The \fBpcre_fullinfo()\fR function returns information about a compiled
467 pattern. It replaces the obsolete \fBpcre_info()\fR function, which is
468 nevertheless retained for backwards compability (and is documented below).
469
470 The first argument for \fBpcre_fullinfo()\fR is a pointer to the compiled
471 pattern. The second argument is the result of \fBpcre_study()\fR, or NULL if
472 the pattern was not studied. The third argument specifies which piece of
473 information is required, and the fourth argument is a pointer to a variable
474 to receive the data. The yield of the function is zero for success, or one of
475 the following negative numbers:
476
477 PCRE_ERROR_NULL the argument \fIcode\fR was NULL
478 the argument \fIwhere\fR was NULL
479 PCRE_ERROR_BADMAGIC the "magic number" was not found
480 PCRE_ERROR_BADOPTION the value of \fIwhat\fR was invalid
481
482 Here is a typical call of \fBpcre_fullinfo()\fR, to obtain the length of the
483 compiled pattern:
484
485 int rc;
486 unsigned long int length;
487 rc = pcre_fullinfo(
488 re, /* result of pcre_compile() */
489 pe, /* result of pcre_study(), or NULL */
490 PCRE_INFO_SIZE, /* what is required */
491 &length); /* where to put the data */
492
493 The possible values for the third argument are defined in \fBpcre.h\fR, and are
494 as follows:
495
496 PCRE_INFO_BACKREFMAX
497
498 Return the number of the highest back reference in the pattern. The fourth
499 argument should point to an \fBint\fR variable. Zero is returned if there are
500 no back references.
501
502 PCRE_INFO_CAPTURECOUNT
503
504 Return the number of capturing subpatterns in the pattern. The fourth argument
505 should point to an \fbint\fR variable.
506
507 PCRE_INFO_FIRSTBYTE
508
509 Return information about the first byte of any matched string, for a
510 non-anchored pattern. (This option used to be called PCRE_INFO_FIRSTCHAR; the
511 old name is still recognized for backwards compatibility.)
512
513 If there is a fixed first byte, e.g. from a pattern such as (cat|cow|coyote),
514 it is returned in the integer pointed to by \fIwhere\fR. Otherwise, if either
515
516 (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
517 starts with "^", or
518
519 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
520 (if it were set, the pattern would be anchored),
521
522 -1 is returned, indicating that the pattern matches only at the start of a
523 subject string or after any newline within the string. Otherwise -2 is
524 returned. For anchored patterns, -2 is returned.
525
526 PCRE_INFO_FIRSTTABLE
527
528 If the pattern was studied, and this resulted in the construction of a 256-bit
529 table indicating a fixed set of bytes for the first byte in any matching
530 string, a pointer to the table is returned. Otherwise NULL is returned. The
531 fourth argument should point to an \fBunsigned char *\fR variable.
532
533 PCRE_INFO_LASTLITERAL
534
535 Return the value of the rightmost literal byte that must exist in any matched
536 string, other than at its start, if such a byte has been recorded. The fourth
537 argument should point to an \fBint\fR variable. If there is no such byte, -1 is
538 returned. For anchored patterns, a last literal byte is recorded only if it
539 follows something of variable length. For example, for the pattern
540 /^a\\d+z\\d+/ the returned value is "z", but for /^a\\dz\\d/ the returned value
541 is -1.
542
543 PCRE_INFO_NAMECOUNT
544 PCRE_INFO_NAMEENTRYSIZE
545 PCRE_INFO_NAMETABLE
546
547 PCRE supports the use of named as well as numbered capturing parentheses. The
548 names are just an additional way of identifying the parentheses, which still
549 acquire a number. A caller that wants to extract data from a named subpattern
550 must convert the name to a number in order to access the correct pointers in
551 the output vector (described with \fBpcre_exec()\fR below). In order to do
552 this, it must first use these three values to obtain the name-to-number mapping
553 table for the pattern.
554
555 The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives
556 the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each
557 entry; both of these return an \fBint\fR value. The entry size depends on the
558 length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first
559 entry of the table (a pointer to \fBchar\fR). The first two bytes of each entry
560 are the number of the capturing parenthesis, most significant byte first. The
561 rest of the entry is the corresponding name, zero terminated. The names are in
562 alphabetical order. For example, consider the following pattern (assume
563 PCRE_EXTENDED is set, so white space - including newlines - is ignored):
564
565 (?P<date> (?P<year>(\\d\\d)?\\d\\d) -
566 (?P<month>\\d\\d) - (?P<day>\\d\\d) )
567
568 There are four named subpatterns, so the table has four entries, and each entry
569 in the table is eight bytes long. The table is as follows, with non-printing
570 bytes shows in hex, and undefined bytes shown as ??:
571
572 00 01 d a t e 00 ??
573 00 05 d a y 00 ?? ??
574 00 04 m o n t h 00
575 00 02 y e a r 00 ??
576
577 When writing code to extract data from named subpatterns, remember that the
578 length of each entry may be different for each compiled pattern.
579
580 PCRE_INFO_OPTIONS
581
582 Return a copy of the options with which the pattern was compiled. The fourth
583 argument should point to an \fBunsigned long int\fR variable. These option bits
584 are those specified in the call to \fBpcre_compile()\fR, modified by any
585 top-level option settings within the pattern itself.
586
587 A pattern is automatically anchored by PCRE if all of its top-level
588 alternatives begin with one of the following:
589
590 ^ unless PCRE_MULTILINE is set
591 \\A always
592 \\G always
593 .* if PCRE_DOTALL is set and there are no back
594 references to the subpattern in which .* appears
595
596 For such patterns, the PCRE_ANCHORED bit is set in the options returned by
597 \fBpcre_fullinfo()\fR.
598
599 PCRE_INFO_SIZE
600
601 Return the size of the compiled pattern, that is, the value that was passed as
602 the argument to \fBpcre_malloc()\fR when PCRE was getting memory in which to
603 place the compiled data. The fourth argument should point to a \fBsize_t\fR
604 variable.
605
606 PCRE_INFO_STUDYSIZE
607
608 Returns the size of the data block pointed to by the \fIstudy_data\fR field in
609 a \fBpcre_extra\fR block. That is, it is the value that was passed to
610 \fBpcre_malloc()\fR when PCRE was getting memory into which to place the data
611 created by \fBpcre_study()\fR. The fourth argument should point to a
612 \fBsize_t\fR variable.
613
614 .SH OBSOLETE INFO FUNCTION
615 .rs
616 .sp
617 .B int pcre_info(const pcre *\fIcode\fR, int *\fIoptptr\fR, int
618 .B *\fIfirstcharptr\fR);
619 .PP
620 The \fBpcre_info()\fR function is now obsolete because its interface is too
621 restrictive to return all the available data about a compiled pattern. New
622 programs should use \fBpcre_fullinfo()\fR instead. The yield of
623 \fBpcre_info()\fR is the number of capturing subpatterns, or one of the
624 following negative numbers:
625
626 PCRE_ERROR_NULL the argument \fIcode\fR was NULL
627 PCRE_ERROR_BADMAGIC the "magic number" was not found
628
629 If the \fIoptptr\fR argument is not NULL, a copy of the options with which the
630 pattern was compiled is placed in the integer it points to (see
631 PCRE_INFO_OPTIONS above).
632
633 If the pattern is not anchored and the \fIfirstcharptr\fR argument is not NULL,
634 it is used to pass back information about the first character of any matched
635 string (see PCRE_INFO_FIRSTBYTE above).
636
637 .SH MATCHING A PATTERN
638 .rs
639 .sp
640 .B int pcre_exec(const pcre *\fIcode\fR, "const pcre_extra *\fIextra\fR,"
641 .ti +5n
642 .B "const char *\fIsubject\fR," int \fIlength\fR, int \fIstartoffset\fR,
643 .ti +5n
644 .B int \fIoptions\fR, int *\fIovector\fR, int \fIovecsize\fR);
645 .PP
646 The function \fBpcre_exec()\fR is called to match a subject string against a
647 pre-compiled pattern, which is passed in the \fIcode\fR argument. If the
648 pattern has been studied, the result of the study should be passed in the
649 \fIextra\fR argument.
650
651 Here is an example of a simple call to \fBpcre_exec()\fR:
652
653 int rc;
654 int ovector[30];
655 rc = pcre_exec(
656 re, /* result of pcre_compile() */
657 NULL, /* we didn't study the pattern */
658 "some string", /* the subject string */
659 11, /* the length of the subject string */
660 0, /* start at offset 0 in the subject */
661 0, /* default options */
662 ovector, /* vector for substring information */
663 30); /* number of elements in the vector */
664
665 If the \fIextra\fR argument is not NULL, it must point to a \fBpcre_extra\fR
666 data block. The \fBpcre_study()\fR function returns such a block (when it
667 doesn't return NULL), but you can also create one for yourself, and pass
668 additional information in it. The fields in the block are as follows:
669
670 unsigned long int \fIflags\fR;
671 void *\fIstudy_data\fR;
672 unsigned long int \fImatch_limit\fR;
673 void *\fIcallout_data\fR;
674
675 The \fIflags\fR field is a bitmap that specifies which of the other fields
676 are set. The flag bits are:
677
678 PCRE_EXTRA_STUDY_DATA
679 PCRE_EXTRA_MATCH_LIMIT
680 PCRE_EXTRA_CALLOUT_DATA
681
682 Other flag bits should be set to zero. The \fIstudy_data\fR field is set in the
683 \fBpcre_extra\fR block that is returned by \fBpcre_study()\fR, together with
684 the appropriate flag bit. You should not set this yourself, but you can add to
685 the block by setting the other fields.
686
687 The \fImatch_limit\fR field provides a means of preventing PCRE from using up a
688 vast amount of resources when running patterns that are not going to match,
689 but which have a very large number of possibilities in their search trees. The
690 classic example is the use of nested unlimited repeats. Internally, PCRE uses a
691 function called \fBmatch()\fR which it calls repeatedly (sometimes
692 recursively). The limit is imposed on the number of times this function is
693 called during a match, which has the effect of limiting the amount of recursion
694 and backtracking that can take place. For patterns that are not anchored, the
695 count starts from zero for each position in the subject string.
696
697 The default limit for the library can be set when PCRE is built; the default
698 default is 10 million, which handles all but the most extreme cases. You can
699 reduce the default by suppling \fBpcre_exec()\fR with a \fRpcre_extra\fR block
700 in which \fImatch_limit\fR is set to a smaller value, and
701 PCRE_EXTRA_MATCH_LIMIT is set in the \fIflags\fR field. If the limit is
702 exceeded, \fBpcre_exec()\fR returns PCRE_ERROR_MATCHLIMIT.
703
704 The \fIpcre_callout\fR field is used in conjunction with the "callout" feature,
705 which is described in the \fBpcrecallout\fR documentation.
706
707 The PCRE_ANCHORED option can be passed in the \fIoptions\fR argument, whose
708 unused bits must be zero. This limits \fBpcre_exec()\fR to matching at the
709 first matching position. However, if a pattern was compiled with PCRE_ANCHORED,
710 or turned out to be anchored by virtue of its contents, it cannot be made
711 unachored at matching time.
712
713 When PCRE_UTF8 was set at compile time, the validity of the subject as a UTF-8
714 string is automatically checked. If an invalid UTF-8 sequence of bytes is
715 found, \fBpcre_exec()\fR returns the error PCRE_ERROR_BADUTF8. If you already
716 know that your subject is valid, and you want to skip this check for
717 performance reasons, you can set the PCRE_NO_UTF8_CHECK option when calling
718 \fBpcre_exec()\fR. When this option is set, the effect of passing an invalid
719 UTF-8 string as a subject is undefined. It may cause your program to crash.
720
721 There are also three further options that can be set only at matching time:
722
723 PCRE_NOTBOL
724
725 The first character of the string is not the beginning of a line, so the
726 circumflex metacharacter should not match before it. Setting this without
727 PCRE_MULTILINE (at compile time) causes circumflex never to match.
728
729 PCRE_NOTEOL
730
731 The end of the string is not the end of a line, so the dollar metacharacter
732 should not match it nor (except in multiline mode) a newline immediately before
733 it. Setting this without PCRE_MULTILINE (at compile time) causes dollar never
734 to match.
735
736 PCRE_NOTEMPTY
737
738 An empty string is not considered to be a valid match if this option is set. If
739 there are alternatives in the pattern, they are tried. If all the alternatives
740 match the empty string, the entire match fails. For example, if the pattern
741
742 a?b?
743
744 is applied to a string not beginning with "a" or "b", it matches the empty
745 string at the start of the subject. With PCRE_NOTEMPTY set, this match is not
746 valid, so PCRE searches further into the string for occurrences of "a" or "b".
747
748 Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a special case
749 of a pattern match of the empty string within its \fBsplit()\fR function, and
750 when using the /g modifier. It is possible to emulate Perl's behaviour after
751 matching a null string by first trying the match again at the same offset with
752 PCRE_NOTEMPTY set, and then if that fails by advancing the starting offset (see
753 below) and trying an ordinary match again.
754
755 The subject string is passed to \fBpcre_exec()\fR as a pointer in
756 \fIsubject\fR, a length in \fIlength\fR, and a starting offset in
757 \fIstartoffset\fR. Unlike the pattern string, the subject may contain binary
758 zero bytes. When the starting offset is zero, the search for a match starts at
759 the beginning of the subject, and this is by far the most common case.
760
761 If the pattern was compiled with the PCRE_UTF8 option, the subject must be a
762 sequence of bytes that is a valid UTF-8 string. If an invalid UTF-8 string is
763 passed, PCRE's behaviour is not defined.
764
765 A non-zero starting offset is useful when searching for another match in the
766 same subject by calling \fBpcre_exec()\fR again after a previous success.
767 Setting \fIstartoffset\fR differs from just passing over a shortened string and
768 setting PCRE_NOTBOL in the case of a pattern that begins with any kind of
769 lookbehind. For example, consider the pattern
770
771 \\Biss\\B
772
773 which finds occurrences of "iss" in the middle of words. (\\B matches only if
774 the current position in the subject is not a word boundary.) When applied to
775 the string "Mississipi" the first call to \fBpcre_exec()\fR finds the first
776 occurrence. If \fBpcre_exec()\fR is called again with just the remainder of the
777 subject, namely "issipi", it does not match, because \\B is always false at the
778 start of the subject, which is deemed to be a word boundary. However, if
779 \fBpcre_exec()\fR is passed the entire string again, but with \fIstartoffset\fR
780 set to 4, it finds the second occurrence of "iss" because it is able to look
781 behind the starting point to discover that it is preceded by a letter.
782
783 If a non-zero starting offset is passed when the pattern is anchored, one
784 attempt to match at the given offset is tried. This can only succeed if the
785 pattern does not require the match to be at the start of the subject.
786
787 In general, a pattern matches a certain portion of the subject, and in
788 addition, further substrings from the subject may be picked out by parts of the
789 pattern. Following the usage in Jeffrey Friedl's book, this is called
790 "capturing" in what follows, and the phrase "capturing subpattern" is used for
791 a fragment of a pattern that picks out a substring. PCRE supports several other
792 kinds of parenthesized subpattern that do not cause substrings to be captured.
793
794 Captured substrings are returned to the caller via a vector of integer offsets
795 whose address is passed in \fIovector\fR. The number of elements in the vector
796 is passed in \fIovecsize\fR. The first two-thirds of the vector is used to pass
797 back captured substrings, each substring using a pair of integers. The
798 remaining third of the vector is used as workspace by \fBpcre_exec()\fR while
799 matching capturing subpatterns, and is not available for passing back
800 information. The length passed in \fIovecsize\fR should always be a multiple of
801 three. If it is not, it is rounded down.
802
803 When a match has been successful, information about captured substrings is
804 returned in pairs of integers, starting at the beginning of \fIovector\fR, and
805 continuing up to two-thirds of its length at the most. The first element of a
806 pair is set to the offset of the first character in a substring, and the second
807 is set to the offset of the first character after the end of a substring. The
808 first pair, \fIovector[0]\fR and \fIovector[1]\fR, identify the portion of the
809 subject string matched by the entire pattern. The next pair is used for the
810 first capturing subpattern, and so on. The value returned by \fBpcre_exec()\fR
811 is the number of pairs that have been set. If there are no capturing
812 subpatterns, the return value from a successful match is 1, indicating that
813 just the first pair of offsets has been set.
814
815 Some convenience functions are provided for extracting the captured substrings
816 as separate strings. These are described in the following section.
817
818 It is possible for an capturing subpattern number \fIn+1\fR to match some
819 part of the subject when subpattern \fIn\fR has not been used at all. For
820 example, if the string "abc" is matched against the pattern (a|(z))(bc)
821 subpatterns 1 and 3 are matched, but 2 is not. When this happens, both offset
822 values corresponding to the unused subpattern are set to -1.
823
824 If a capturing subpattern is matched repeatedly, it is the last portion of the
825 string that it matched that gets returned.
826
827 If the vector is too small to hold all the captured substrings, it is used as
828 far as possible (up to two-thirds of its length), and the function returns a
829 value of zero. In particular, if the substring offsets are not of interest,
830 \fBpcre_exec()\fR may be called with \fIovector\fR passed as NULL and
831 \fIovecsize\fR as zero. However, if the pattern contains back references and
832 the \fIovector\fR isn't big enough to remember the related substrings, PCRE has
833 to get additional memory for use during matching. Thus it is usually advisable
834 to supply an \fIovector\fR.
835
836 Note that \fBpcre_info()\fR can be used to find out how many capturing
837 subpatterns there are in a compiled pattern. The smallest size for
838 \fIovector\fR that will allow for \fIn\fR captured substrings, in addition to
839 the offsets of the substring matched by the whole pattern, is (\fIn\fR+1)*3.
840
841 If \fBpcre_exec()\fR fails, it returns a negative number. The following are
842 defined in the header file:
843
844 PCRE_ERROR_NOMATCH (-1)
845
846 The subject string did not match the pattern.
847
848 PCRE_ERROR_NULL (-2)
849
850 Either \fIcode\fR or \fIsubject\fR was passed as NULL, or \fIovector\fR was
851 NULL and \fIovecsize\fR was not zero.
852
853 PCRE_ERROR_BADOPTION (-3)
854
855 An unrecognized bit was set in the \fIoptions\fR argument.
856
857 PCRE_ERROR_BADMAGIC (-4)
858
859 PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch
860 the case when it is passed a junk pointer. This is the error it gives when the
861 magic number isn't present.
862
863 PCRE_ERROR_UNKNOWN_NODE (-5)
864
865 While running the pattern match, an unknown item was encountered in the
866 compiled pattern. This error could be caused by a bug in PCRE or by overwriting
867 of the compiled pattern.
868
869 PCRE_ERROR_NOMEMORY (-6)
870
871 If a pattern contains back references, but the \fIovector\fR that is passed to
872 \fBpcre_exec()\fR is not big enough to remember the referenced substrings, PCRE
873 gets a block of memory at the start of matching to use for this purpose. If the
874 call via \fBpcre_malloc()\fR fails, this error is given. The memory is freed at
875 the end of matching.
876
877 PCRE_ERROR_NOSUBSTRING (-7)
878
879 This error is used by the \fBpcre_copy_substring()\fR,
880 \fBpcre_get_substring()\fR, and \fBpcre_get_substring_list()\fR functions (see
881 below). It is never returned by \fBpcre_exec()\fR.
882
883 PCRE_ERROR_MATCHLIMIT (-8)
884
885 The recursion and backtracking limit, as specified by the \fImatch_limit\fR
886 field in a \fBpcre_extra\fR structure (or defaulted) was reached. See the
887 description above.
888
889 PCRE_ERROR_CALLOUT (-9)
890
891 This error is never generated by \fBpcre_exec()\fR itself. It is provided for
892 use by callout functions that want to yield a distinctive error code. See the
893 \fBpcrecallout\fR documentation for details.
894
895 PCRE_ERROR_BADUTF8 (-10)
896
897 A string that contains an invalid UTF-8 byte sequence was passed as a subject.
898
899 .SH EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
900 .rs
901 .sp
902 .B int pcre_copy_substring(const char *\fIsubject\fR, int *\fIovector\fR,
903 .ti +5n
904 .B int \fIstringcount\fR, int \fIstringnumber\fR, char *\fIbuffer\fR,
905 .ti +5n
906 .B int \fIbuffersize\fR);
907 .PP
908 .br
909 .B int pcre_get_substring(const char *\fIsubject\fR, int *\fIovector\fR,
910 .ti +5n
911 .B int \fIstringcount\fR, int \fIstringnumber\fR,
912 .ti +5n
913 .B const char **\fIstringptr\fR);
914 .PP
915 .br
916 .B int pcre_get_substring_list(const char *\fIsubject\fR,
917 .ti +5n
918 .B int *\fIovector\fR, int \fIstringcount\fR, "const char ***\fIlistptr\fR);"
919 .PP
920 Captured substrings can be accessed directly by using the offsets returned by
921 \fBpcre_exec()\fR in \fIovector\fR. For convenience, the functions
922 \fBpcre_copy_substring()\fR, \fBpcre_get_substring()\fR, and
923 \fBpcre_get_substring_list()\fR are provided for extracting captured substrings
924 as new, separate, zero-terminated strings. These functions identify substrings
925 by number. The next section describes functions for extracting named
926 substrings. A substring that contains a binary zero is correctly extracted and
927 has a further zero added on the end, but the result is not, of course,
928 a C string.
929
930 The first three arguments are the same for all three of these functions:
931 \fIsubject\fR is the subject string which has just been successfully matched,
932 \fIovector\fR is a pointer to the vector of integer offsets that was passed to
933 \fBpcre_exec()\fR, and \fIstringcount\fR is the number of substrings that were
934 captured by the match, including the substring that matched the entire regular
935 expression. This is the value returned by \fBpcre_exec\fR if it is greater than
936 zero. If \fBpcre_exec()\fR returned zero, indicating that it ran out of space
937 in \fIovector\fR, the value passed as \fIstringcount\fR should be the size of
938 the vector divided by three.
939
940 The functions \fBpcre_copy_substring()\fR and \fBpcre_get_substring()\fR
941 extract a single substring, whose number is given as \fIstringnumber\fR. A
942 value of zero extracts the substring that matched the entire pattern, while
943 higher values extract the captured substrings. For \fBpcre_copy_substring()\fR,
944 the string is placed in \fIbuffer\fR, whose length is given by
945 \fIbuffersize\fR, while for \fBpcre_get_substring()\fR a new block of memory is
946 obtained via \fBpcre_malloc\fR, and its address is returned via
947 \fIstringptr\fR. The yield of the function is the length of the string, not
948 including the terminating zero, or one of
949
950 PCRE_ERROR_NOMEMORY (-6)
951
952 The buffer was too small for \fBpcre_copy_substring()\fR, or the attempt to get
953 memory failed for \fBpcre_get_substring()\fR.
954
955 PCRE_ERROR_NOSUBSTRING (-7)
956
957 There is no substring whose number is \fIstringnumber\fR.
958
959 The \fBpcre_get_substring_list()\fR function extracts all available substrings
960 and builds a list of pointers to them. All this is done in a single block of
961 memory which is obtained via \fBpcre_malloc\fR. The address of the memory block
962 is returned via \fIlistptr\fR, which is also the start of the list of string
963 pointers. The end of the list is marked by a NULL pointer. The yield of the
964 function is zero if all went well, or
965
966 PCRE_ERROR_NOMEMORY (-6)
967
968 if the attempt to get the memory block failed.
969
970 When any of these functions encounter a substring that is unset, which can
971 happen when capturing subpattern number \fIn+1\fR matches some part of the
972 subject, but subpattern \fIn\fR has not been used at all, they return an empty
973 string. This can be distinguished from a genuine zero-length substring by
974 inspecting the appropriate offset in \fIovector\fR, which is negative for unset
975 substrings.
976
977 The two convenience functions \fBpcre_free_substring()\fR and
978 \fBpcre_free_substring_list()\fR can be used to free the memory returned by
979 a previous call of \fBpcre_get_substring()\fR or
980 \fBpcre_get_substring_list()\fR, respectively. They do nothing more than call
981 the function pointed to by \fBpcre_free\fR, which of course could be called
982 directly from a C program. However, PCRE is used in some situations where it is
983 linked via a special interface to another programming language which cannot use
984 \fBpcre_free\fR directly; it is for these cases that the functions are
985 provided.
986
987 .SH EXTRACTING CAPTURED SUBSTRINGS BY NAME
988 .rs
989 .sp
990 .B int pcre_copy_named_substring(const pcre *\fIcode\fR,
991 .ti +5n
992 .B const char *\fIsubject\fR, int *\fIovector\fR,
993 .ti +5n
994 .B int \fIstringcount\fR, const char *\fIstringname\fR,
995 .ti +5n
996 .B char *\fIbuffer\fR, int \fIbuffersize\fR);
997 .PP
998 .br
999 .B int pcre_get_stringnumber(const pcre *\fIcode\fR,
1000 .ti +5n
1001 .B const char *\fIname\fR);
1002 .PP
1003 .br
1004 .B int pcre_get_named_substring(const pcre *\fIcode\fR,
1005 .ti +5n
1006 .B const char *\fIsubject\fR, int *\fIovector\fR,
1007 .ti +5n
1008 .B int \fIstringcount\fR, const char *\fIstringname\fR,
1009 .ti +5n
1010 .B const char **\fIstringptr\fR);
1011 .PP
1012 To extract a substring by name, you first have to find associated number. This
1013 can be done by calling \fBpcre_get_stringnumber()\fR. The first argument is the
1014 compiled pattern, and the second is the name. For example, for this pattern
1015
1016 ab(?<xxx>\\d+)...
1017
1018 the number of the subpattern called "xxx" is 1. Given the number, you can then
1019 extract the substring directly, or use one of the functions described in the
1020 previous section. For convenience, there are also two functions that do the
1021 whole job.
1022
1023 Most of the arguments of \fIpcre_copy_named_substring()\fR and
1024 \fIpcre_get_named_substring()\fR are the same as those for the functions that
1025 extract by number, and so are not re-described here. There are just two
1026 differences.
1027
1028 First, instead of a substring number, a substring name is given. Second, there
1029 is an extra argument, given at the start, which is a pointer to the compiled
1030 pattern. This is needed in order to gain access to the name-to-number
1031 translation table.
1032
1033 These functions call \fBpcre_get_stringnumber()\fR, and if it succeeds, they
1034 then call \fIpcre_copy_substring()\fR or \fIpcre_get_substring()\fR, as
1035 appropriate.
1036
1037 .in 0
1038 Last updated: 20 August 2003
1039 .br
1040 Copyright (c) 1997-2003 University of Cambridge.

webmaster@exim.org
ViewVC Help
Powered by ViewVC 1.1.12