ViewVC logotype

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

Parent Directory Parent Directory | Revision Log Revision Log

Revision 73 - (show annotations)
Sat Feb 24 21:40:30 2007 UTC (14 years, 2 months ago) by nigel
File MIME type: text/html
File size: 51200 byte(s)
Error occurred while calculating annotation data.
Load pcre-4.5 into code/trunk.
1 <html>
2 <head>
3 <title>pcreapi specification</title>
4 </head>
5 <body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
6 This HTML document has been generated automatically from the original man page.
7 If there is any nonsense in it, please consult the man page, in case the
8 conversion went wrong.<br>
9 <ul>
10 <li><a name="TOC1" href="#SEC1">SYNOPSIS OF PCRE API</a>
11 <li><a name="TOC2" href="#SEC2">PCRE API</a>
12 <li><a name="TOC3" href="#SEC3">MULTITHREADING</a>
13 <li><a name="TOC4" href="#SEC4">CHECKING BUILD-TIME OPTIONS</a>
14 <li><a name="TOC5" href="#SEC5">COMPILING A PATTERN</a>
15 <li><a name="TOC6" href="#SEC6">STUDYING A PATTERN</a>
16 <li><a name="TOC7" href="#SEC7">LOCALE SUPPORT</a>
17 <li><a name="TOC8" href="#SEC8">INFORMATION ABOUT A PATTERN</a>
18 <li><a name="TOC9" href="#SEC9">OBSOLETE INFO FUNCTION</a>
19 <li><a name="TOC10" href="#SEC10">MATCHING A PATTERN</a>
22 </ul>
23 <br><a name="SEC1" href="#TOC1">SYNOPSIS OF PCRE API</a><br>
24 <P>
25 <b>#include &#60;pcre.h&#62;</b>
26 </P>
27 <P>
28 <b>pcre *pcre_compile(const char *<i>pattern</i>, int <i>options</i>,</b>
29 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
30 <b>const unsigned char *<i>tableptr</i>);</b>
31 </P>
32 <P>
33 <b>pcre_extra *pcre_study(const pcre *<i>code</i>, int <i>options</i>,</b>
34 <b>const char **<i>errptr</i>);</b>
35 </P>
36 <P>
37 <b>int pcre_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
38 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
39 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>);</b>
40 </P>
41 <P>
42 <b>int pcre_copy_named_substring(const pcre *<i>code</i>,</b>
43 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
44 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
45 <b>char *<i>buffer</i>, int <i>buffersize</i>);</b>
46 </P>
47 <P>
48 <b>int pcre_copy_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
49 <b>int <i>stringcount</i>, int <i>stringnumber</i>, char *<i>buffer</i>,</b>
50 <b>int <i>buffersize</i>);</b>
51 </P>
52 <P>
53 <b>int pcre_get_named_substring(const pcre *<i>code</i>,</b>
54 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
55 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
56 <b>const char **<i>stringptr</i>);</b>
57 </P>
58 <P>
59 <b>int pcre_get_stringnumber(const pcre *<i>code</i>,</b>
60 <b>const char *<i>name</i>);</b>
61 </P>
62 <P>
63 <b>int pcre_get_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
64 <b>int <i>stringcount</i>, int <i>stringnumber</i>,</b>
65 <b>const char **<i>stringptr</i>);</b>
66 </P>
67 <P>
68 <b>int pcre_get_substring_list(const char *<i>subject</i>,</b>
69 <b>int *<i>ovector</i>, int <i>stringcount</i>, const char ***<i>listptr</i>);</b>
70 </P>
71 <P>
72 <b>void pcre_free_substring(const char *<i>stringptr</i>);</b>
73 </P>
74 <P>
75 <b>void pcre_free_substring_list(const char **<i>stringptr</i>);</b>
76 </P>
77 <P>
78 <b>const unsigned char *pcre_maketables(void);</b>
79 </P>
80 <P>
81 <b>int pcre_fullinfo(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
82 <b>int <i>what</i>, void *<i>where</i>);</b>
83 </P>
84 <P>
85 <b>int pcre_info(const pcre *<i>code</i>, int *<i>optptr</i>, int</b>
86 <b>*<i>firstcharptr</i>);</b>
87 </P>
88 <P>
89 <b>int pcre_config(int <i>what</i>, void *<i>where</i>);</b>
90 </P>
91 <P>
92 <b>char *pcre_version(void);</b>
93 </P>
94 <P>
95 <b>void *(*pcre_malloc)(size_t);</b>
96 </P>
97 <P>
98 <b>void (*pcre_free)(void *);</b>
99 </P>
100 <P>
101 <b>void *(*pcre_stack_malloc)(size_t);</b>
102 </P>
103 <P>
104 <b>void (*pcre_stack_free)(void *);</b>
105 </P>
106 <P>
107 <b>int (*pcre_callout)(pcre_callout_block *);</b>
108 </P>
109 <br><a name="SEC2" href="#TOC1">PCRE API</a><br>
110 <P>
111 PCRE has its own native API, which is described in this document. There is also
112 a set of wrapper functions that correspond to the POSIX regular expression API.
113 These are described in the <b>pcreposix</b> documentation.
114 </P>
115 <P>
116 The native API function prototypes are defined in the header file <b>pcre.h</b>,
117 and on Unix systems the library itself is called <b>libpcre.a</b>, so can be
118 accessed by adding <b>-lpcre</b> to the command for linking an application which
119 calls it. The header file defines the macros PCRE_MAJOR and PCRE_MINOR to
120 contain the major and minor release numbers for the library. Applications can
121 use these to include support for different releases.
122 </P>
123 <P>
124 The functions <b>pcre_compile()</b>, <b>pcre_study()</b>, and <b>pcre_exec()</b>
125 are used for compiling and matching regular expressions. A sample program that
126 demonstrates the simplest way of using them is given in the file
127 <i>pcredemo.c</i>. The <b>pcresample</b> documentation describes how to run it.
128 </P>
129 <P>
130 There are convenience functions for extracting captured substrings from a
131 matched subject string. They are:
132 </P>
133 <P>
134 <pre>
135 <b>pcre_copy_substring()</b>
136 <b>pcre_copy_named_substring()</b>
137 <b>pcre_get_substring()</b>
138 <b>pcre_get_named_substring()</b>
139 <b>pcre_get_substring_list()</b>
140 </PRE>
141 </P>
142 <P>
143 <b>pcre_free_substring()</b> and <b>pcre_free_substring_list()</b> are also
144 provided, to free the memory used for extracted strings.
145 </P>
146 <P>
147 The function <b>pcre_maketables()</b> is used (optionally) to build a set of
148 character tables in the current locale for passing to <b>pcre_compile()</b>.
149 </P>
150 <P>
151 The function <b>pcre_fullinfo()</b> is used to find out information about a
152 compiled pattern; <b>pcre_info()</b> is an obsolete version which returns only
153 some of the available information, but is retained for backwards compatibility.
154 The function <b>pcre_version()</b> returns a pointer to a string containing the
155 version of PCRE and its date of release.
156 </P>
157 <P>
158 The global variables <b>pcre_malloc</b> and <b>pcre_free</b> initially contain
159 the entry points of the standard <b>malloc()</b> and <b>free()</b> functions
160 respectively. PCRE calls the memory management functions via these variables,
161 so a calling program can replace them if it wishes to intercept the calls. This
162 should be done before calling any PCRE functions.
163 </P>
164 <P>
165 The global variables <b>pcre_stack_malloc</b> and <b>pcre_stack_free</b> are also
166 indirections to memory management functions. These special functions are used
167 only when PCRE is compiled to use the heap for remembering data, instead of
168 recursive function calls. This is a non-standard way of building PCRE, for use
169 in environments that have limited stacks. Because of the greater use of memory
170 management, it runs more slowly. Separate functions are provided so that
171 special-purpose external code can be used for this case. When used, these
172 functions are always called in a stack-like manner (last obtained, first
173 freed), and always for memory blocks of the same size.
174 </P>
175 <P>
176 The global variable <b>pcre_callout</b> initially contains NULL. It can be set
177 by the caller to a "callout" function, which PCRE will then call at specified
178 points during a matching operation. Details are given in the <b>pcrecallout</b>
179 documentation.
180 </P>
181 <br><a name="SEC3" href="#TOC1">MULTITHREADING</a><br>
182 <P>
183 The PCRE functions can be used in multi-threading applications, with the
184 proviso that the memory management functions pointed to by <b>pcre_malloc</b>,
185 <b>pcre_free</b>, <b>pcre_stack_malloc</b>, and <b>pcre_stack_free</b>, and the
186 callout function pointed to by <b>pcre_callout</b>, are shared by all threads.
187 </P>
188 <P>
189 The compiled form of a regular expression is not altered during matching, so
190 the same compiled pattern can safely be used by several threads at once.
191 </P>
192 <br><a name="SEC4" href="#TOC1">CHECKING BUILD-TIME OPTIONS</a><br>
193 <P>
194 <b>int pcre_config(int <i>what</i>, void *<i>where</i>);</b>
195 </P>
196 <P>
197 The function <b>pcre_config()</b> makes it possible for a PCRE client to
198 discover which optional features have been compiled into the PCRE library. The
199 <a href="pcrebuild.html"><b>pcrebuild</b></a>
200 documentation has more details about these optional features.
201 </P>
202 <P>
203 The first argument for <b>pcre_config()</b> is an integer, specifying which
204 information is required; the second argument is a pointer to a variable into
205 which the information is placed. The following information is available:
206 </P>
207 <P>
208 <pre>
210 </PRE>
211 </P>
212 <P>
213 The output is an integer that is set to one if UTF-8 support is available;
214 otherwise it is set to zero.
215 </P>
216 <P>
217 <pre>
219 </PRE>
220 </P>
221 <P>
222 The output is an integer that is set to the value of the code that is used for
223 the newline character. It is either linefeed (10) or carriage return (13), and
224 should normally be the standard character for your operating system.
225 </P>
226 <P>
227 <pre>
229 </PRE>
230 </P>
231 <P>
232 The output is an integer that contains the number of bytes used for internal
233 linkage in compiled regular expressions. The value is 2, 3, or 4. Larger values
234 allow larger regular expressions to be compiled, at the expense of slower
235 matching. The default value of 2 is sufficient for all but the most massive
236 patterns, since it allows the compiled pattern to be up to 64K in size.
237 </P>
238 <P>
239 <pre>
241 </PRE>
242 </P>
243 <P>
244 The output is an integer that contains the threshold above which the POSIX
245 interface uses <b>malloc()</b> for output vectors. Further details are given in
246 the <b>pcreposix</b> documentation.
247 </P>
248 <P>
249 <pre>
251 </PRE>
252 </P>
253 <P>
254 The output is an integer that gives the default limit for the number of
255 internal matching function calls in a <b>pcre_exec()</b> execution. Further
256 details are given with <b>pcre_exec()</b> below.
257 </P>
258 <P>
259 <pre>
261 </PRE>
262 </P>
263 <P>
264 The output is an integer that is set to one if internal recursion is
265 implemented by recursive function calls that use the stack to remember their
266 state. This is the usual way that PCRE is compiled. The output is zero if PCRE
267 was compiled to use blocks of data on the heap instead of recursive function
268 calls. In this case, <b>pcre_stack_malloc</b> and <b>pcre_stack_free</b> are
269 called to manage memory blocks on the heap, thus avoiding the use of the stack.
270 </P>
271 <br><a name="SEC5" href="#TOC1">COMPILING A PATTERN</a><br>
272 <P>
273 <b>pcre *pcre_compile(const char *<i>pattern</i>, int <i>options</i>,</b>
274 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
275 <b>const unsigned char *<i>tableptr</i>);</b>
276 </P>
277 <P>
278 The function <b>pcre_compile()</b> is called to compile a pattern into an
279 internal form. The pattern is a C string terminated by a binary zero, and
280 is passed in the argument <i>pattern</i>. A pointer to a single block of memory
281 that is obtained via <b>pcre_malloc</b> is returned. This contains the compiled
282 code and related data. The <b>pcre</b> type is defined for the returned block;
283 this is a typedef for a structure whose contents are not externally defined. It
284 is up to the caller to free the memory when it is no longer required.
285 </P>
286 <P>
287 Although the compiled code of a PCRE regex is relocatable, that is, it does not
288 depend on memory location, the complete <b>pcre</b> data block is not
289 fully relocatable, because it contains a copy of the <i>tableptr</i> argument,
290 which is an address (see below).
291 </P>
292 <P>
293 The <i>options</i> argument contains independent bits that affect the
294 compilation. It should be zero if no options are required. Some of the options,
295 in particular, those that are compatible with Perl, can also be set and unset
296 from within the pattern (see the detailed description of regular expressions
297 in the <b>pcrepattern</b> documentation). For these options, the contents of the
298 <i>options</i> argument specifies their initial settings at the start of
299 compilation and execution. The PCRE_ANCHORED option can be set at the time of
300 matching as well as at compile time.
301 </P>
302 <P>
303 If <i>errptr</i> is NULL, <b>pcre_compile()</b> returns NULL immediately.
304 Otherwise, if compilation of a pattern fails, <b>pcre_compile()</b> returns
305 NULL, and sets the variable pointed to by <i>errptr</i> to point to a textual
306 error message. The offset from the start of the pattern to the character where
307 the error was discovered is placed in the variable pointed to by
308 <i>erroffset</i>, which must not be NULL. If it is, an immediate error is given.
309 </P>
310 <P>
311 If the final argument, <i>tableptr</i>, is NULL, PCRE uses a default set of
312 character tables which are built when it is compiled, using the default C
313 locale. Otherwise, <i>tableptr</i> must be the result of a call to
314 <b>pcre_maketables()</b>. See the section on locale support below.
315 </P>
316 <P>
317 This code fragment shows a typical straightforward call to <b>pcre_compile()</b>:
318 </P>
319 <P>
320 <pre>
321 pcre *re;
322 const char *error;
323 int erroffset;
324 re = pcre_compile(
325 "^A.*Z", /* the pattern */
326 0, /* default options */
327 &error, /* for error message */
328 &erroffset, /* for error offset */
329 NULL); /* use default character tables */
330 </PRE>
331 </P>
332 <P>
333 The following option bits are defined:
334 </P>
335 <P>
336 <pre>
338 </PRE>
339 </P>
340 <P>
341 If this bit is set, the pattern is forced to be "anchored", that is, it is
342 constrained to match only at the first matching point in the string which is
343 being searched (the "subject string"). This effect can also be achieved by
344 appropriate constructs in the pattern itself, which is the only way to do it in
345 Perl.
346 </P>
347 <P>
348 <pre>
350 </PRE>
351 </P>
352 <P>
353 If this bit is set, letters in the pattern match both upper and lower case
354 letters. It is equivalent to Perl's /i option, and it can be changed within a
355 pattern by a (?i) option setting.
356 </P>
357 <P>
358 <pre>
360 </PRE>
361 </P>
362 <P>
363 If this bit is set, a dollar metacharacter in the pattern matches only at the
364 end of the subject string. Without this option, a dollar also matches
365 immediately before the final character if it is a newline (but not before any
366 other newlines). The PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is
367 set. There is no equivalent to this option in Perl, and no way to set it within
368 a pattern.
369 </P>
370 <P>
371 <pre>
373 </PRE>
374 </P>
375 <P>
376 If this bit is set, a dot metacharater in the pattern matches all characters,
377 including newlines. Without it, newlines are excluded. This option is
378 equivalent to Perl's /s option, and it can be changed within a pattern by a
379 (?s) option setting. A negative class such as [^a] always matches a newline
380 character, independent of the setting of this option.
381 </P>
382 <P>
383 <pre>
385 </PRE>
386 </P>
387 <P>
388 If this bit is set, whitespace data characters in the pattern are totally
389 ignored except when escaped or inside a character class. Whitespace does not
390 include the VT character (code 11). In addition, characters between an
391 unescaped # outside a character class and the next newline character,
392 inclusive, are also ignored. This is equivalent to Perl's /x option, and it can
393 be changed within a pattern by a (?x) option setting.
394 </P>
395 <P>
396 This option makes it possible to include comments inside complicated patterns.
397 Note, however, that this applies only to data characters. Whitespace characters
398 may never appear within special character sequences in a pattern, for example
399 within the sequence (?( which introduces a conditional subpattern.
400 </P>
401 <P>
402 <pre>
404 </PRE>
405 </P>
406 <P>
407 This option was invented in order to turn on additional functionality of PCRE
408 that is incompatible with Perl, but it is currently of very little use. When
409 set, any backslash in a pattern that is followed by a letter that has no
410 special meaning causes an error, thus reserving these combinations for future
411 expansion. By default, as in Perl, a backslash followed by a letter with no
412 special meaning is treated as a literal. There are at present no other features
413 controlled by this option. It can also be set by a (?X) option setting within a
414 pattern.
415 </P>
416 <P>
417 <pre>
419 </PRE>
420 </P>
421 <P>
422 By default, PCRE treats the subject string as consisting of a single "line" of
423 characters (even if it actually contains several newlines). The "start of line"
424 metacharacter (^) matches only at the start of the string, while the "end of
425 line" metacharacter ($) matches only at the end of the string, or before a
426 terminating newline (unless PCRE_DOLLAR_ENDONLY is set). This is the same as
427 Perl.
428 </P>
429 <P>
430 When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs
431 match immediately following or immediately before any newline in the subject
432 string, respectively, as well as at the very start and end. This is equivalent
433 to Perl's /m option, and it can be changed within a pattern by a (?m) option
434 setting. If there are no "\n" characters in a subject string, or no
435 occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no effect.
436 </P>
437 <P>
438 <pre>
440 </PRE>
441 </P>
442 <P>
443 If this option is set, it disables the use of numbered capturing parentheses in
444 the pattern. Any opening parenthesis that is not followed by ? behaves as if it
445 were followed by ?: but named parentheses can still be used for capturing (and
446 they acquire numbers in the usual way). There is no equivalent of this option
447 in Perl.
448 </P>
449 <P>
450 <pre>
452 </PRE>
453 </P>
454 <P>
455 This option inverts the "greediness" of the quantifiers so that they are not
456 greedy by default, but become greedy if followed by "?". It is not compatible
457 with Perl. It can also be set by a (?U) option setting within the pattern.
458 </P>
459 <P>
460 <pre>
462 </PRE>
463 </P>
464 <P>
465 This option causes PCRE to regard both the pattern and the subject as strings
466 of UTF-8 characters instead of single-byte character strings. However, it is
467 available only if PCRE has been built to include UTF-8 support. If not, the use
468 of this option provokes an error. Details of how this option changes the
469 behaviour of PCRE are given in the
470 <a href="pcre.html#utf8support">section on UTF-8 support</a>
471 in the main
472 <a href="pcre.html"><b>pcre</b></a>
473 page.
474 </P>
475 <P>
476 <pre>
478 </PRE>
479 </P>
480 <P>
481 When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
482 automatically checked. If an invalid UTF-8 sequence of bytes is found,
483 <b>pcre_compile()</b> returns an error. If you already know that your pattern is
484 valid, and you want to skip this check for performance reasons, you can set the
485 PCRE_NO_UTF8_CHECK option. When it is set, the effect of passing an invalid
486 UTF-8 string as a pattern is undefined. It may cause your program to crash.
487 Note that there is a similar option for suppressing the checking of subject
488 strings passed to <b>pcre_exec()</b>.
489 </P>
490 <br><a name="SEC6" href="#TOC1">STUDYING A PATTERN</a><br>
491 <P>
492 <b>pcre_extra *pcre_study(const pcre *<i>code</i>, int <i>options</i>,</b>
493 <b>const char **<i>errptr</i>);</b>
494 </P>
495 <P>
496 When a pattern is going to be used several times, it is worth spending more
497 time analyzing it in order to speed up the time taken for matching. The
498 function <b>pcre_study()</b> takes a pointer to a compiled pattern as its first
499 argument. If studing the pattern produces additional information that will help
500 speed up matching, <b>pcre_study()</b> returns a pointer to a <b>pcre_extra</b>
501 block, in which the <i>study_data</i> field points to the results of the study.
502 </P>
503 <P>
504 The returned value from a <b>pcre_study()</b> can be passed directly to
505 <b>pcre_exec()</b>. However, the <b>pcre_extra</b> block also contains other
506 fields that can be set by the caller before the block is passed; these are
507 described below. If studying the pattern does not produce any additional
508 information, <b>pcre_study()</b> returns NULL. In that circumstance, if the
509 calling program wants to pass some of the other fields to <b>pcre_exec()</b>, it
510 must set up its own <b>pcre_extra</b> block.
511 </P>
512 <P>
513 The second argument contains option bits. At present, no options are defined
514 for <b>pcre_study()</b>, and this argument should always be zero.
515 </P>
516 <P>
517 The third argument for <b>pcre_study()</b> is a pointer for an error message. If
518 studying succeeds (even if no data is returned), the variable it points to is
519 set to NULL. Otherwise it points to a textual error message. You should
520 therefore test the error pointer for NULL after calling <b>pcre_study()</b>, to
521 be sure that it has run successfully.
522 </P>
523 <P>
524 This is a typical call to <b>pcre_study</b>():
525 </P>
526 <P>
527 <pre>
528 pcre_extra *pe;
529 pe = pcre_study(
530 re, /* result of pcre_compile() */
531 0, /* no options exist */
532 &error); /* set to NULL or points to a message */
533 </PRE>
534 </P>
535 <P>
536 At present, studying a pattern is useful only for non-anchored patterns that do
537 not have a single fixed starting character. A bitmap of possible starting
538 characters is created.
539 </P>
540 <a name="localesupport"></a><br><a name="SEC7" href="#TOC1">LOCALE SUPPORT</a><br>
541 <P>
542 PCRE handles caseless matching, and determines whether characters are letters,
543 digits, or whatever, by reference to a set of tables. When running in UTF-8
544 mode, this applies only to characters with codes less than 256. The library
545 contains a default set of tables that is created in the default C locale when
546 PCRE is compiled. This is used when the final argument of <b>pcre_compile()</b>
547 is NULL, and is sufficient for many applications.
548 </P>
549 <P>
550 An alternative set of tables can, however, be supplied. Such tables are built
551 by calling the <b>pcre_maketables()</b> function, which has no arguments, in the
552 relevant locale. The result can then be passed to <b>pcre_compile()</b> as often
553 as necessary. For example, to build and use tables that are appropriate for the
554 French locale (where accented characters with codes greater than 128 are
555 treated as letters), the following code could be used:
556 </P>
557 <P>
558 <pre>
559 setlocale(LC_CTYPE, "fr");
560 tables = pcre_maketables();
561 re = pcre_compile(..., tables);
562 </PRE>
563 </P>
564 <P>
565 The tables are built in memory that is obtained via <b>pcre_malloc</b>. The
566 pointer that is passed to <b>pcre_compile</b> is saved with the compiled
567 pattern, and the same tables are used via this pointer by <b>pcre_study()</b>
568 and <b>pcre_exec()</b>. Thus, for any single pattern, compilation, studying and
569 matching all happen in the same locale, but different patterns can be compiled
570 in different locales. It is the caller's responsibility to ensure that the
571 memory containing the tables remains available for as long as it is needed.
572 </P>
573 <br><a name="SEC8" href="#TOC1">INFORMATION ABOUT A PATTERN</a><br>
574 <P>
575 <b>int pcre_fullinfo(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
576 <b>int <i>what</i>, void *<i>where</i>);</b>
577 </P>
578 <P>
579 The <b>pcre_fullinfo()</b> function returns information about a compiled
580 pattern. It replaces the obsolete <b>pcre_info()</b> function, which is
581 nevertheless retained for backwards compability (and is documented below).
582 </P>
583 <P>
584 The first argument for <b>pcre_fullinfo()</b> is a pointer to the compiled
585 pattern. The second argument is the result of <b>pcre_study()</b>, or NULL if
586 the pattern was not studied. The third argument specifies which piece of
587 information is required, and the fourth argument is a pointer to a variable
588 to receive the data. The yield of the function is zero for success, or one of
589 the following negative numbers:
590 </P>
591 <P>
592 <pre>
593 PCRE_ERROR_NULL the argument <i>code</i> was NULL
594 the argument <i>where</i> was NULL
595 PCRE_ERROR_BADMAGIC the "magic number" was not found
596 PCRE_ERROR_BADOPTION the value of <i>what</i> was invalid
597 </PRE>
598 </P>
599 <P>
600 Here is a typical call of <b>pcre_fullinfo()</b>, to obtain the length of the
601 compiled pattern:
602 </P>
603 <P>
604 <pre>
605 int rc;
606 unsigned long int length;
607 rc = pcre_fullinfo(
608 re, /* result of pcre_compile() */
609 pe, /* result of pcre_study(), or NULL */
610 PCRE_INFO_SIZE, /* what is required */
611 &length); /* where to put the data */
612 </PRE>
613 </P>
614 <P>
615 The possible values for the third argument are defined in <b>pcre.h</b>, and are
616 as follows:
617 </P>
618 <P>
619 <pre>
621 </PRE>
622 </P>
623 <P>
624 Return the number of the highest back reference in the pattern. The fourth
625 argument should point to an <b>int</b> variable. Zero is returned if there are
626 no back references.
627 </P>
628 <P>
629 <pre>
631 </PRE>
632 </P>
633 <P>
634 Return the number of capturing subpatterns in the pattern. The fourth argument
635 should point to an \fbint\fR variable.
636 </P>
637 <P>
638 <pre>
640 </PRE>
641 </P>
642 <P>
643 Return information about the first byte of any matched string, for a
644 non-anchored pattern. (This option used to be called PCRE_INFO_FIRSTCHAR; the
645 old name is still recognized for backwards compatibility.)
646 </P>
647 <P>
648 If there is a fixed first byte, e.g. from a pattern such as (cat|cow|coyote),
649 it is returned in the integer pointed to by <i>where</i>. Otherwise, if either
650 </P>
651 <P>
652 (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
653 starts with "^", or
654 </P>
655 <P>
656 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
657 (if it were set, the pattern would be anchored),
658 </P>
659 <P>
660 -1 is returned, indicating that the pattern matches only at the start of a
661 subject string or after any newline within the string. Otherwise -2 is
662 returned. For anchored patterns, -2 is returned.
663 </P>
664 <P>
665 <pre>
667 </PRE>
668 </P>
669 <P>
670 If the pattern was studied, and this resulted in the construction of a 256-bit
671 table indicating a fixed set of bytes for the first byte in any matching
672 string, a pointer to the table is returned. Otherwise NULL is returned. The
673 fourth argument should point to an <b>unsigned char *</b> variable.
674 </P>
675 <P>
676 <pre>
678 </PRE>
679 </P>
680 <P>
681 Return the value of the rightmost literal byte that must exist in any matched
682 string, other than at its start, if such a byte has been recorded. The fourth
683 argument should point to an <b>int</b> variable. If there is no such byte, -1 is
684 returned. For anchored patterns, a last literal byte is recorded only if it
685 follows something of variable length. For example, for the pattern
686 /^a\d+z\d+/ the returned value is "z", but for /^a\dz\d/ the returned value
687 is -1.
688 </P>
689 <P>
690 <pre>
694 </PRE>
695 </P>
696 <P>
697 PCRE supports the use of named as well as numbered capturing parentheses. The
698 names are just an additional way of identifying the parentheses, which still
699 acquire a number. A caller that wants to extract data from a named subpattern
700 must convert the name to a number in order to access the correct pointers in
701 the output vector (described with <b>pcre_exec()</b> below). In order to do
702 this, it must first use these three values to obtain the name-to-number mapping
703 table for the pattern.
704 </P>
705 <P>
706 The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives
707 the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each
708 entry; both of these return an <b>int</b> value. The entry size depends on the
709 length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first
710 entry of the table (a pointer to <b>char</b>). The first two bytes of each entry
711 are the number of the capturing parenthesis, most significant byte first. The
712 rest of the entry is the corresponding name, zero terminated. The names are in
713 alphabetical order. For example, consider the following pattern (assume
714 PCRE_EXTENDED is set, so white space - including newlines - is ignored):
715 </P>
716 <P>
717 <pre>
718 (?P&#60;date&#62; (?P&#60;year&#62;(\d\d)?\d\d) -
719 (?P&#60;month&#62;\d\d) - (?P&#60;day&#62;\d\d) )
720 </PRE>
721 </P>
722 <P>
723 There are four named subpatterns, so the table has four entries, and each entry
724 in the table is eight bytes long. The table is as follows, with non-printing
725 bytes shows in hex, and undefined bytes shown as ??:
726 </P>
727 <P>
728 <pre>
729 00 01 d a t e 00 ??
730 00 05 d a y 00 ?? ??
731 00 04 m o n t h 00
732 00 02 y e a r 00 ??
733 </PRE>
734 </P>
735 <P>
736 When writing code to extract data from named subpatterns, remember that the
737 length of each entry may be different for each compiled pattern.
738 </P>
739 <P>
740 <pre>
742 </PRE>
743 </P>
744 <P>
745 Return a copy of the options with which the pattern was compiled. The fourth
746 argument should point to an <b>unsigned long int</b> variable. These option bits
747 are those specified in the call to <b>pcre_compile()</b>, modified by any
748 top-level option settings within the pattern itself.
749 </P>
750 <P>
751 A pattern is automatically anchored by PCRE if all of its top-level
752 alternatives begin with one of the following:
753 </P>
754 <P>
755 <pre>
756 ^ unless PCRE_MULTILINE is set
757 \A always
758 \G always
759 .* if PCRE_DOTALL is set and there are no back
760 references to the subpattern in which .* appears
761 </PRE>
762 </P>
763 <P>
764 For such patterns, the PCRE_ANCHORED bit is set in the options returned by
765 <b>pcre_fullinfo()</b>.
766 </P>
767 <P>
768 <pre>
770 </PRE>
771 </P>
772 <P>
773 Return the size of the compiled pattern, that is, the value that was passed as
774 the argument to <b>pcre_malloc()</b> when PCRE was getting memory in which to
775 place the compiled data. The fourth argument should point to a <b>size_t</b>
776 variable.
777 </P>
778 <P>
779 <pre>
781 </PRE>
782 </P>
783 <P>
784 Returns the size of the data block pointed to by the <i>study_data</i> field in
785 a <b>pcre_extra</b> block. That is, it is the value that was passed to
786 <b>pcre_malloc()</b> when PCRE was getting memory into which to place the data
787 created by <b>pcre_study()</b>. The fourth argument should point to a
788 <b>size_t</b> variable.
789 </P>
790 <br><a name="SEC9" href="#TOC1">OBSOLETE INFO FUNCTION</a><br>
791 <P>
792 <b>int pcre_info(const pcre *<i>code</i>, int *<i>optptr</i>, int</b>
793 <b>*<i>firstcharptr</i>);</b>
794 </P>
795 <P>
796 The <b>pcre_info()</b> function is now obsolete because its interface is too
797 restrictive to return all the available data about a compiled pattern. New
798 programs should use <b>pcre_fullinfo()</b> instead. The yield of
799 <b>pcre_info()</b> is the number of capturing subpatterns, or one of the
800 following negative numbers:
801 </P>
802 <P>
803 <pre>
804 PCRE_ERROR_NULL the argument <i>code</i> was NULL
805 PCRE_ERROR_BADMAGIC the "magic number" was not found
806 </PRE>
807 </P>
808 <P>
809 If the <i>optptr</i> argument is not NULL, a copy of the options with which the
810 pattern was compiled is placed in the integer it points to (see
812 </P>
813 <P>
814 If the pattern is not anchored and the <i>firstcharptr</i> argument is not NULL,
815 it is used to pass back information about the first character of any matched
816 string (see PCRE_INFO_FIRSTBYTE above).
817 </P>
818 <br><a name="SEC10" href="#TOC1">MATCHING A PATTERN</a><br>
819 <P>
820 <b>int pcre_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
821 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
822 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>);</b>
823 </P>
824 <P>
825 The function <b>pcre_exec()</b> is called to match a subject string against a
826 pre-compiled pattern, which is passed in the <i>code</i> argument. If the
827 pattern has been studied, the result of the study should be passed in the
828 <i>extra</i> argument.
829 </P>
830 <P>
831 Here is an example of a simple call to <b>pcre_exec()</b>:
832 </P>
833 <P>
834 <pre>
835 int rc;
836 int ovector[30];
837 rc = pcre_exec(
838 re, /* result of pcre_compile() */
839 NULL, /* we didn't study the pattern */
840 "some string", /* the subject string */
841 11, /* the length of the subject string */
842 0, /* start at offset 0 in the subject */
843 0, /* default options */
844 ovector, /* vector for substring information */
845 30); /* number of elements in the vector */
846 </PRE>
847 </P>
848 <P>
849 If the <i>extra</i> argument is not NULL, it must point to a <b>pcre_extra</b>
850 data block. The <b>pcre_study()</b> function returns such a block (when it
851 doesn't return NULL), but you can also create one for yourself, and pass
852 additional information in it. The fields in the block are as follows:
853 </P>
854 <P>
855 <pre>
856 unsigned long int <i>flags</i>;
857 void *<i>study_data</i>;
858 unsigned long int <i>match_limit</i>;
859 void *<i>callout_data</i>;
860 </PRE>
861 </P>
862 <P>
863 The <i>flags</i> field is a bitmap that specifies which of the other fields
864 are set. The flag bits are:
865 </P>
866 <P>
867 <pre>
871 </PRE>
872 </P>
873 <P>
874 Other flag bits should be set to zero. The <i>study_data</i> field is set in the
875 <b>pcre_extra</b> block that is returned by <b>pcre_study()</b>, together with
876 the appropriate flag bit. You should not set this yourself, but you can add to
877 the block by setting the other fields.
878 </P>
879 <P>
880 The <i>match_limit</i> field provides a means of preventing PCRE from using up a
881 vast amount of resources when running patterns that are not going to match,
882 but which have a very large number of possibilities in their search trees. The
883 classic example is the use of nested unlimited repeats. Internally, PCRE uses a
884 function called <b>match()</b> which it calls repeatedly (sometimes
885 recursively). The limit is imposed on the number of times this function is
886 called during a match, which has the effect of limiting the amount of recursion
887 and backtracking that can take place. For patterns that are not anchored, the
888 count starts from zero for each position in the subject string.
889 </P>
890 <P>
891 The default limit for the library can be set when PCRE is built; the default
892 default is 10 million, which handles all but the most extreme cases. You can
893 reduce the default by suppling <b>pcre_exec()</b> with a \fRpcre_extra\fR block
894 in which <i>match_limit</i> is set to a smaller value, and
895 PCRE_EXTRA_MATCH_LIMIT is set in the <i>flags</i> field. If the limit is
896 exceeded, <b>pcre_exec()</b> returns PCRE_ERROR_MATCHLIMIT.
897 </P>
898 <P>
899 The <i>pcre_callout</i> field is used in conjunction with the "callout" feature,
900 which is described in the <b>pcrecallout</b> documentation.
901 </P>
902 <P>
903 The PCRE_ANCHORED option can be passed in the <i>options</i> argument, whose
904 unused bits must be zero. This limits <b>pcre_exec()</b> to matching at the
905 first matching position. However, if a pattern was compiled with PCRE_ANCHORED,
906 or turned out to be anchored by virtue of its contents, it cannot be made
907 unachored at matching time.
908 </P>
909 <P>
910 When PCRE_UTF8 was set at compile time, the validity of the subject as a UTF-8
911 string is automatically checked, and the value of <i>startoffset</i> is also
912 checked to ensure that it points to the start of a UTF-8 character. If an
913 invalid UTF-8 sequence of bytes is found, <b>pcre_exec()</b> returns the error
914 PCRE_ERROR_BADUTF8. If <i>startoffset</i> contains an invalid value,
915 PCRE_ERROR_BADUTF8_OFFSET is returned.
916 </P>
917 <P>
918 If you already know that your subject is valid, and you want to skip these
919 checks for performance reasons, you can set the PCRE_NO_UTF8_CHECK option when
920 calling <b>pcre_exec()</b>. You might want to do this for the second and
921 subsequent calls to <b>pcre_exec()</b> if you are making repeated calls to find
922 all the matches in a single subject string. However, you should be sure that
923 the value of <i>startoffset</i> points to the start of a UTF-8 character. When
924 PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid UTF-8 string as a
925 subject, or a value of <i>startoffset</i> that does not point to the start of a
926 UTF-8 character, is undefined. Your program may crash.
927 </P>
928 <P>
929 There are also three further options that can be set only at matching time:
930 </P>
931 <P>
932 <pre>
934 </PRE>
935 </P>
936 <P>
937 The first character of the string is not the beginning of a line, so the
938 circumflex metacharacter should not match before it. Setting this without
939 PCRE_MULTILINE (at compile time) causes circumflex never to match.
940 </P>
941 <P>
942 <pre>
944 </PRE>
945 </P>
946 <P>
947 The end of the string is not the end of a line, so the dollar metacharacter
948 should not match it nor (except in multiline mode) a newline immediately before
949 it. Setting this without PCRE_MULTILINE (at compile time) causes dollar never
950 to match.
951 </P>
952 <P>
953 <pre>
955 </PRE>
956 </P>
957 <P>
958 An empty string is not considered to be a valid match if this option is set. If
959 there are alternatives in the pattern, they are tried. If all the alternatives
960 match the empty string, the entire match fails. For example, if the pattern
961 </P>
962 <P>
963 <pre>
964 a?b?
965 </PRE>
966 </P>
967 <P>
968 is applied to a string not beginning with "a" or "b", it matches the empty
969 string at the start of the subject. With PCRE_NOTEMPTY set, this match is not
970 valid, so PCRE searches further into the string for occurrences of "a" or "b".
971 </P>
972 <P>
973 Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a special case
974 of a pattern match of the empty string within its <b>split()</b> function, and
975 when using the /g modifier. It is possible to emulate Perl's behaviour after
976 matching a null string by first trying the match again at the same offset with
977 PCRE_NOTEMPTY set, and then if that fails by advancing the starting offset (see
978 below) and trying an ordinary match again.
979 </P>
980 <P>
981 The subject string is passed to <b>pcre_exec()</b> as a pointer in
982 <i>subject</i>, a length in <i>length</i>, and a starting byte offset in
983 <i>startoffset</i>. Unlike the pattern string, the subject may contain binary
984 zero bytes. When the starting offset is zero, the search for a match starts at
985 the beginning of the subject, and this is by far the most common case.
986 </P>
987 <P>
988 If the pattern was compiled with the PCRE_UTF8 option, the subject must be a
989 sequence of bytes that is a valid UTF-8 string, and the starting offset must
990 point to the beginning of a UTF-8 character. If an invalid UTF-8 string or
991 offset is passed, an error (either PCRE_ERROR_BADUTF8 or
992 PCRE_ERROR_BADUTF8_OFFSET) is returned, unless the option PCRE_NO_UTF8_CHECK is
993 set, in which case PCRE's behaviour is not defined.
994 </P>
995 <P>
996 A non-zero starting offset is useful when searching for another match in the
997 same subject by calling <b>pcre_exec()</b> again after a previous success.
998 Setting <i>startoffset</i> differs from just passing over a shortened string and
999 setting PCRE_NOTBOL in the case of a pattern that begins with any kind of
1000 lookbehind. For example, consider the pattern
1001 </P>
1002 <P>
1003 <pre>
1004 \Biss\B
1005 </PRE>
1006 </P>
1007 <P>
1008 which finds occurrences of "iss" in the middle of words. (\B matches only if
1009 the current position in the subject is not a word boundary.) When applied to
1010 the string "Mississipi" the first call to <b>pcre_exec()</b> finds the first
1011 occurrence. If <b>pcre_exec()</b> is called again with just the remainder of the
1012 subject, namely "issipi", it does not match, because \B is always false at the
1013 start of the subject, which is deemed to be a word boundary. However, if
1014 <b>pcre_exec()</b> is passed the entire string again, but with <i>startoffset</i>
1015 set to 4, it finds the second occurrence of "iss" because it is able to look
1016 behind the starting point to discover that it is preceded by a letter.
1017 </P>
1018 <P>
1019 If a non-zero starting offset is passed when the pattern is anchored, one
1020 attempt to match at the given offset is tried. This can only succeed if the
1021 pattern does not require the match to be at the start of the subject.
1022 </P>
1023 <P>
1024 In general, a pattern matches a certain portion of the subject, and in
1025 addition, further substrings from the subject may be picked out by parts of the
1026 pattern. Following the usage in Jeffrey Friedl's book, this is called
1027 "capturing" in what follows, and the phrase "capturing subpattern" is used for
1028 a fragment of a pattern that picks out a substring. PCRE supports several other
1029 kinds of parenthesized subpattern that do not cause substrings to be captured.
1030 </P>
1031 <P>
1032 Captured substrings are returned to the caller via a vector of integer offsets
1033 whose address is passed in <i>ovector</i>. The number of elements in the vector
1034 is passed in <i>ovecsize</i>. The first two-thirds of the vector is used to pass
1035 back captured substrings, each substring using a pair of integers. The
1036 remaining third of the vector is used as workspace by <b>pcre_exec()</b> while
1037 matching capturing subpatterns, and is not available for passing back
1038 information. The length passed in <i>ovecsize</i> should always be a multiple of
1039 three. If it is not, it is rounded down.
1040 </P>
1041 <P>
1042 When a match has been successful, information about captured substrings is
1043 returned in pairs of integers, starting at the beginning of <i>ovector</i>, and
1044 continuing up to two-thirds of its length at the most. The first element of a
1045 pair is set to the offset of the first character in a substring, and the second
1046 is set to the offset of the first character after the end of a substring. The
1047 first pair, <i>ovector[0]</i> and <i>ovector[1]</i>, identify the portion of the
1048 subject string matched by the entire pattern. The next pair is used for the
1049 first capturing subpattern, and so on. The value returned by <b>pcre_exec()</b>
1050 is the number of pairs that have been set. If there are no capturing
1051 subpatterns, the return value from a successful match is 1, indicating that
1052 just the first pair of offsets has been set.
1053 </P>
1054 <P>
1055 Some convenience functions are provided for extracting the captured substrings
1056 as separate strings. These are described in the following section.
1057 </P>
1058 <P>
1059 It is possible for an capturing subpattern number <i>n+1</i> to match some
1060 part of the subject when subpattern <i>n</i> has not been used at all. For
1061 example, if the string "abc" is matched against the pattern (a|(z))(bc)
1062 subpatterns 1 and 3 are matched, but 2 is not. When this happens, both offset
1063 values corresponding to the unused subpattern are set to -1.
1064 </P>
1065 <P>
1066 If a capturing subpattern is matched repeatedly, it is the last portion of the
1067 string that it matched that gets returned.
1068 </P>
1069 <P>
1070 If the vector is too small to hold all the captured substrings, it is used as
1071 far as possible (up to two-thirds of its length), and the function returns a
1072 value of zero. In particular, if the substring offsets are not of interest,
1073 <b>pcre_exec()</b> may be called with <i>ovector</i> passed as NULL and
1074 <i>ovecsize</i> as zero. However, if the pattern contains back references and
1075 the <i>ovector</i> isn't big enough to remember the related substrings, PCRE has
1076 to get additional memory for use during matching. Thus it is usually advisable
1077 to supply an <i>ovector</i>.
1078 </P>
1079 <P>
1080 Note that <b>pcre_info()</b> can be used to find out how many capturing
1081 subpatterns there are in a compiled pattern. The smallest size for
1082 <i>ovector</i> that will allow for <i>n</i> captured substrings, in addition to
1083 the offsets of the substring matched by the whole pattern, is (<i>n</i>+1)*3.
1084 </P>
1085 <P>
1086 If <b>pcre_exec()</b> fails, it returns a negative number. The following are
1087 defined in the header file:
1088 </P>
1089 <P>
1090 <pre>
1092 </PRE>
1093 </P>
1094 <P>
1095 The subject string did not match the pattern.
1096 </P>
1097 <P>
1098 <pre>
1100 </PRE>
1101 </P>
1102 <P>
1103 Either <i>code</i> or <i>subject</i> was passed as NULL, or <i>ovector</i> was
1104 NULL and <i>ovecsize</i> was not zero.
1105 </P>
1106 <P>
1107 <pre>
1109 </PRE>
1110 </P>
1111 <P>
1112 An unrecognized bit was set in the <i>options</i> argument.
1113 </P>
1114 <P>
1115 <pre>
1117 </PRE>
1118 </P>
1119 <P>
1120 PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch
1121 the case when it is passed a junk pointer. This is the error it gives when the
1122 magic number isn't present.
1123 </P>
1124 <P>
1125 <pre>
1127 </PRE>
1128 </P>
1129 <P>
1130 While running the pattern match, an unknown item was encountered in the
1131 compiled pattern. This error could be caused by a bug in PCRE or by overwriting
1132 of the compiled pattern.
1133 </P>
1134 <P>
1135 <pre>
1137 </PRE>
1138 </P>
1139 <P>
1140 If a pattern contains back references, but the <i>ovector</i> that is passed to
1141 <b>pcre_exec()</b> is not big enough to remember the referenced substrings, PCRE
1142 gets a block of memory at the start of matching to use for this purpose. If the
1143 call via <b>pcre_malloc()</b> fails, this error is given. The memory is freed at
1144 the end of matching.
1145 </P>
1146 <P>
1147 <pre>
1149 </PRE>
1150 </P>
1151 <P>
1152 This error is used by the <b>pcre_copy_substring()</b>,
1153 <b>pcre_get_substring()</b>, and <b>pcre_get_substring_list()</b> functions (see
1154 below). It is never returned by <b>pcre_exec()</b>.
1155 </P>
1156 <P>
1157 <pre>
1159 </PRE>
1160 </P>
1161 <P>
1162 The recursion and backtracking limit, as specified by the <i>match_limit</i>
1163 field in a <b>pcre_extra</b> structure (or defaulted) was reached. See the
1164 description above.
1165 </P>
1166 <P>
1167 <pre>
1169 </PRE>
1170 </P>
1171 <P>
1172 This error is never generated by <b>pcre_exec()</b> itself. It is provided for
1173 use by callout functions that want to yield a distinctive error code. See the
1174 <b>pcrecallout</b> documentation for details.
1175 </P>
1176 <P>
1177 <pre>
1179 </PRE>
1180 </P>
1181 <P>
1182 A string that contains an invalid UTF-8 byte sequence was passed as a subject.
1183 </P>
1184 <P>
1185 <pre>
1187 </PRE>
1188 </P>
1189 <P>
1190 The UTF-8 byte sequence that was passed as a subject was valid, but the value
1191 of <i>startoffset</i> did not point to the beginning of a UTF-8 character.
1192 </P>
1193 <br><a name="SEC11" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NUMBER</a><br>
1194 <P>
1195 <b>int pcre_copy_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1196 <b>int <i>stringcount</i>, int <i>stringnumber</i>, char *<i>buffer</i>,</b>
1197 <b>int <i>buffersize</i>);</b>
1198 </P>
1199 <P>
1200 <b>int pcre_get_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1201 <b>int <i>stringcount</i>, int <i>stringnumber</i>,</b>
1202 <b>const char **<i>stringptr</i>);</b>
1203 </P>
1204 <P>
1205 <b>int pcre_get_substring_list(const char *<i>subject</i>,</b>
1206 <b>int *<i>ovector</i>, int <i>stringcount</i>, const char ***<i>listptr</i>);</b>
1207 </P>
1208 <P>
1209 Captured substrings can be accessed directly by using the offsets returned by
1210 <b>pcre_exec()</b> in <i>ovector</i>. For convenience, the functions
1211 <b>pcre_copy_substring()</b>, <b>pcre_get_substring()</b>, and
1212 <b>pcre_get_substring_list()</b> are provided for extracting captured substrings
1213 as new, separate, zero-terminated strings. These functions identify substrings
1214 by number. The next section describes functions for extracting named
1215 substrings. A substring that contains a binary zero is correctly extracted and
1216 has a further zero added on the end, but the result is not, of course,
1217 a C string.
1218 </P>
1219 <P>
1220 The first three arguments are the same for all three of these functions:
1221 <i>subject</i> is the subject string which has just been successfully matched,
1222 <i>ovector</i> is a pointer to the vector of integer offsets that was passed to
1223 <b>pcre_exec()</b>, and <i>stringcount</i> is the number of substrings that were
1224 captured by the match, including the substring that matched the entire regular
1225 expression. This is the value returned by <b>pcre_exec</b> if it is greater than
1226 zero. If <b>pcre_exec()</b> returned zero, indicating that it ran out of space
1227 in <i>ovector</i>, the value passed as <i>stringcount</i> should be the size of
1228 the vector divided by three.
1229 </P>
1230 <P>
1231 The functions <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>
1232 extract a single substring, whose number is given as <i>stringnumber</i>. A
1233 value of zero extracts the substring that matched the entire pattern, while
1234 higher values extract the captured substrings. For <b>pcre_copy_substring()</b>,
1235 the string is placed in <i>buffer</i>, whose length is given by
1236 <i>buffersize</i>, while for <b>pcre_get_substring()</b> a new block of memory is
1237 obtained via <b>pcre_malloc</b>, and its address is returned via
1238 <i>stringptr</i>. The yield of the function is the length of the string, not
1239 including the terminating zero, or one of
1240 </P>
1241 <P>
1242 <pre>
1244 </PRE>
1245 </P>
1246 <P>
1247 The buffer was too small for <b>pcre_copy_substring()</b>, or the attempt to get
1248 memory failed for <b>pcre_get_substring()</b>.
1249 </P>
1250 <P>
1251 <pre>
1253 </PRE>
1254 </P>
1255 <P>
1256 There is no substring whose number is <i>stringnumber</i>.
1257 </P>
1258 <P>
1259 The <b>pcre_get_substring_list()</b> function extracts all available substrings
1260 and builds a list of pointers to them. All this is done in a single block of
1261 memory which is obtained via <b>pcre_malloc</b>. The address of the memory block
1262 is returned via <i>listptr</i>, which is also the start of the list of string
1263 pointers. The end of the list is marked by a NULL pointer. The yield of the
1264 function is zero if all went well, or
1265 </P>
1266 <P>
1267 <pre>
1269 </PRE>
1270 </P>
1271 <P>
1272 if the attempt to get the memory block failed.
1273 </P>
1274 <P>
1275 When any of these functions encounter a substring that is unset, which can
1276 happen when capturing subpattern number <i>n+1</i> matches some part of the
1277 subject, but subpattern <i>n</i> has not been used at all, they return an empty
1278 string. This can be distinguished from a genuine zero-length substring by
1279 inspecting the appropriate offset in <i>ovector</i>, which is negative for unset
1280 substrings.
1281 </P>
1282 <P>
1283 The two convenience functions <b>pcre_free_substring()</b> and
1284 <b>pcre_free_substring_list()</b> can be used to free the memory returned by
1285 a previous call of <b>pcre_get_substring()</b> or
1286 <b>pcre_get_substring_list()</b>, respectively. They do nothing more than call
1287 the function pointed to by <b>pcre_free</b>, which of course could be called
1288 directly from a C program. However, PCRE is used in some situations where it is
1289 linked via a special interface to another programming language which cannot use
1290 <b>pcre_free</b> directly; it is for these cases that the functions are
1291 provided.
1292 </P>
1293 <br><a name="SEC12" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NAME</a><br>
1294 <P>
1295 <b>int pcre_copy_named_substring(const pcre *<i>code</i>,</b>
1296 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
1297 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
1298 <b>char *<i>buffer</i>, int <i>buffersize</i>);</b>
1299 </P>
1300 <P>
1301 <b>int pcre_get_stringnumber(const pcre *<i>code</i>,</b>
1302 <b>const char *<i>name</i>);</b>
1303 </P>
1304 <P>
1305 <b>int pcre_get_named_substring(const pcre *<i>code</i>,</b>
1306 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
1307 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
1308 <b>const char **<i>stringptr</i>);</b>
1309 </P>
1310 <P>
1311 To extract a substring by name, you first have to find associated number. This
1312 can be done by calling <b>pcre_get_stringnumber()</b>. The first argument is the
1313 compiled pattern, and the second is the name. For example, for this pattern
1314 </P>
1315 <P>
1316 <pre>
1317 ab(?&#60;xxx&#62;\d+)...
1318 </PRE>
1319 </P>
1320 <P>
1321 the number of the subpattern called "xxx" is 1. Given the number, you can then
1322 extract the substring directly, or use one of the functions described in the
1323 previous section. For convenience, there are also two functions that do the
1324 whole job.
1325 </P>
1326 <P>
1327 Most of the arguments of <i>pcre_copy_named_substring()</i> and
1328 <i>pcre_get_named_substring()</i> are the same as those for the functions that
1329 extract by number, and so are not re-described here. There are just two
1330 differences.
1331 </P>
1332 <P>
1333 First, instead of a substring number, a substring name is given. Second, there
1334 is an extra argument, given at the start, which is a pointer to the compiled
1335 pattern. This is needed in order to gain access to the name-to-number
1336 translation table.
1337 </P>
1338 <P>
1339 These functions call <b>pcre_get_stringnumber()</b>, and if it succeeds, they
1340 then call <i>pcre_copy_substring()</i> or <i>pcre_get_substring()</i>, as
1341 appropriate.
1342 </P>
1343 <P>
1344 Last updated: 09 December 2003
1345 <br>
1346 Copyright &copy; 1997-2003 University of Cambridge.

  ViewVC Help
Powered by ViewVC 1.1.5