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

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

Parent Directory Parent Directory | Revision Log Revision Log


Revision 75 - (show annotations) (download) (as text)
Sat Feb 24 21:40:37 2007 UTC (7 years, 4 months ago) by nigel
File MIME type: text/html
File size: 57335 byte(s)
Load pcre-5.0 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 <h1>pcreapi man page</h1>
7 <p>
8 Return to the <a href="index.html">PCRE index page</a>.
9 </p>
10 <p>
11 This page is part of the PCRE HTML documentation. It was generated automatically
12 from the original man page. If there is any nonsense in it, please consult the
13 man page, in case the conversion went wrong.
14 <br>
15 <ul>
16 <li><a name="TOC1" href="#SEC1">PCRE NATIVE API</a>
17 <li><a name="TOC2" href="#SEC2">PCRE API OVERVIEW</a>
18 <li><a name="TOC3" href="#SEC3">MULTITHREADING</a>
19 <li><a name="TOC4" href="#SEC4">SAVING PRECOMPILED PATTERNS FOR LATER USE</a>
20 <li><a name="TOC5" href="#SEC5">CHECKING BUILD-TIME OPTIONS</a>
21 <li><a name="TOC6" href="#SEC6">COMPILING A PATTERN</a>
22 <li><a name="TOC7" href="#SEC7">STUDYING A PATTERN</a>
23 <li><a name="TOC8" href="#SEC8">LOCALE SUPPORT</a>
24 <li><a name="TOC9" href="#SEC9">INFORMATION ABOUT A PATTERN</a>
25 <li><a name="TOC10" href="#SEC10">OBSOLETE INFO FUNCTION</a>
26 <li><a name="TOC11" href="#SEC11">MATCHING A PATTERN</a>
27 <li><a name="TOC12" href="#SEC12">EXTRACTING CAPTURED SUBSTRINGS BY NUMBER</a>
28 <li><a name="TOC13" href="#SEC13">EXTRACTING CAPTURED SUBSTRINGS BY NAME</a>
29 </ul>
30 <br><a name="SEC1" href="#TOC1">PCRE NATIVE API</a><br>
31 <P>
32 <b>#include &#60;pcre.h&#62;</b>
33 </P>
34 <P>
35 <b>pcre *pcre_compile(const char *<i>pattern</i>, int <i>options</i>,</b>
36 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
37 <b>const unsigned char *<i>tableptr</i>);</b>
38 </P>
39 <P>
40 <b>pcre_extra *pcre_study(const pcre *<i>code</i>, int <i>options</i>,</b>
41 <b>const char **<i>errptr</i>);</b>
42 </P>
43 <P>
44 <b>int pcre_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
45 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
46 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>);</b>
47 </P>
48 <P>
49 <b>int pcre_copy_named_substring(const pcre *<i>code</i>,</b>
50 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
51 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
52 <b>char *<i>buffer</i>, int <i>buffersize</i>);</b>
53 </P>
54 <P>
55 <b>int pcre_copy_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
56 <b>int <i>stringcount</i>, int <i>stringnumber</i>, char *<i>buffer</i>,</b>
57 <b>int <i>buffersize</i>);</b>
58 </P>
59 <P>
60 <b>int pcre_get_named_substring(const pcre *<i>code</i>,</b>
61 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
62 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
63 <b>const char **<i>stringptr</i>);</b>
64 </P>
65 <P>
66 <b>int pcre_get_stringnumber(const pcre *<i>code</i>,</b>
67 <b>const char *<i>name</i>);</b>
68 </P>
69 <P>
70 <b>int pcre_get_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
71 <b>int <i>stringcount</i>, int <i>stringnumber</i>,</b>
72 <b>const char **<i>stringptr</i>);</b>
73 </P>
74 <P>
75 <b>int pcre_get_substring_list(const char *<i>subject</i>,</b>
76 <b>int *<i>ovector</i>, int <i>stringcount</i>, const char ***<i>listptr</i>);</b>
77 </P>
78 <P>
79 <b>void pcre_free_substring(const char *<i>stringptr</i>);</b>
80 </P>
81 <P>
82 <b>void pcre_free_substring_list(const char **<i>stringptr</i>);</b>
83 </P>
84 <P>
85 <b>const unsigned char *pcre_maketables(void);</b>
86 </P>
87 <P>
88 <b>int pcre_fullinfo(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
89 <b>int <i>what</i>, void *<i>where</i>);</b>
90 </P>
91 <P>
92 <b>int pcre_info(const pcre *<i>code</i>, int *<i>optptr</i>, int</b>
93 <b>*<i>firstcharptr</i>);</b>
94 </P>
95 <P>
96 <b>int pcre_config(int <i>what</i>, void *<i>where</i>);</b>
97 </P>
98 <P>
99 <b>char *pcre_version(void);</b>
100 </P>
101 <P>
102 <b>void *(*pcre_malloc)(size_t);</b>
103 </P>
104 <P>
105 <b>void (*pcre_free)(void *);</b>
106 </P>
107 <P>
108 <b>void *(*pcre_stack_malloc)(size_t);</b>
109 </P>
110 <P>
111 <b>void (*pcre_stack_free)(void *);</b>
112 </P>
113 <P>
114 <b>int (*pcre_callout)(pcre_callout_block *);</b>
115 </P>
116 <br><a name="SEC2" href="#TOC1">PCRE API OVERVIEW</a><br>
117 <P>
118 PCRE has its own native API, which is described in this document. There is also
119 a set of wrapper functions that correspond to the POSIX regular expression API.
120 These are described in the
121 <a href="pcreposix.html"><b>pcreposix</b></a>
122 documentation.
123 </P>
124 <P>
125 The native API function prototypes are defined in the header file <b>pcre.h</b>,
126 and on Unix systems the library itself is called <b>libpcre</b>. It can
127 normally be accessed by adding <b>-lpcre</b> to the command for linking an
128 application that uses PCRE. The header file defines the macros PCRE_MAJOR and
129 PCRE_MINOR to contain the major and minor release numbers for the library.
130 Applications can use these to include support for different releases of PCRE.
131 </P>
132 <P>
133 The functions <b>pcre_compile()</b>, <b>pcre_study()</b>, and <b>pcre_exec()</b>
134 are used for compiling and matching regular expressions. A sample program that
135 demonstrates the simplest way of using them is provided in the file called
136 <i>pcredemo.c</i> in the source distribution. The
137 <a href="pcresample.html"><b>pcresample</b></a>
138 documentation describes how to run it.
139 </P>
140 <P>
141 In addition to the main compiling and matching functions, there are convenience
142 functions for extracting captured substrings from a matched subject string.
143 They are:
144 <pre>
145 <b>pcre_copy_substring()</b>
146 <b>pcre_copy_named_substring()</b>
147 <b>pcre_get_substring()</b>
148 <b>pcre_get_named_substring()</b>
149 <b>pcre_get_substring_list()</b>
150 <b>pcre_get_stringnumber()</b>
151 </pre>
152 <b>pcre_free_substring()</b> and <b>pcre_free_substring_list()</b> are also
153 provided, to free the memory used for extracted strings.
154 </P>
155 <P>
156 The function <b>pcre_maketables()</b> is used to build a set of character tables
157 in the current locale for passing to <b>pcre_compile()</b> or <b>pcre_exec()</b>.
158 This is an optional facility that is provided for specialist use. Most
159 commonly, no special tables are passed, in which case internal tables that are
160 generated when PCRE is built are used.
161 </P>
162 <P>
163 The function <b>pcre_fullinfo()</b> is used to find out information about a
164 compiled pattern; <b>pcre_info()</b> is an obsolete version that returns only
165 some of the available information, but is retained for backwards compatibility.
166 The function <b>pcre_version()</b> returns a pointer to a string containing the
167 version of PCRE and its date of release.
168 </P>
169 <P>
170 The global variables <b>pcre_malloc</b> and <b>pcre_free</b> initially contain
171 the entry points of the standard <b>malloc()</b> and <b>free()</b> functions,
172 respectively. PCRE calls the memory management functions via these variables,
173 so a calling program can replace them if it wishes to intercept the calls. This
174 should be done before calling any PCRE functions.
175 </P>
176 <P>
177 The global variables <b>pcre_stack_malloc</b> and <b>pcre_stack_free</b> are also
178 indirections to memory management functions. These special functions are used
179 only when PCRE is compiled to use the heap for remembering data, instead of
180 recursive function calls. This is a non-standard way of building PCRE, for use
181 in environments that have limited stacks. Because of the greater use of memory
182 management, it runs more slowly. Separate functions are provided so that
183 special-purpose external code can be used for this case. When used, these
184 functions are always called in a stack-like manner (last obtained, first
185 freed), and always for memory blocks of the same size.
186 </P>
187 <P>
188 The global variable <b>pcre_callout</b> initially contains NULL. It can be set
189 by the caller to a "callout" function, which PCRE will then call at specified
190 points during a matching operation. Details are given in the
191 <a href="pcrecallout.html"><b>pcrecallout</b></a>
192 documentation.
193 </P>
194 <br><a name="SEC3" href="#TOC1">MULTITHREADING</a><br>
195 <P>
196 The PCRE functions can be used in multi-threading applications, with the
197 proviso that the memory management functions pointed to by <b>pcre_malloc</b>,
198 <b>pcre_free</b>, <b>pcre_stack_malloc</b>, and <b>pcre_stack_free</b>, and the
199 callout function pointed to by <b>pcre_callout</b>, are shared by all threads.
200 </P>
201 <P>
202 The compiled form of a regular expression is not altered during matching, so
203 the same compiled pattern can safely be used by several threads at once.
204 </P>
205 <br><a name="SEC4" href="#TOC1">SAVING PRECOMPILED PATTERNS FOR LATER USE</a><br>
206 <P>
207 The compiled form of a regular expression can be saved and re-used at a later
208 time, possibly by a different program, and even on a host other than the one on
209 which it was compiled. Details are given in the
210 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
211 documentation.
212 </P>
213 <br><a name="SEC5" href="#TOC1">CHECKING BUILD-TIME OPTIONS</a><br>
214 <P>
215 <b>int pcre_config(int <i>what</i>, void *<i>where</i>);</b>
216 </P>
217 <P>
218 The function <b>pcre_config()</b> makes it possible for a PCRE client to
219 discover which optional features have been compiled into the PCRE library. The
220 <a href="pcrebuild.html"><b>pcrebuild</b></a>
221 documentation has more details about these optional features.
222 </P>
223 <P>
224 The first argument for <b>pcre_config()</b> is an integer, specifying which
225 information is required; the second argument is a pointer to a variable into
226 which the information is placed. The following information is available:
227 <pre>
228 PCRE_CONFIG_UTF8
229 </pre>
230 The output is an integer that is set to one if UTF-8 support is available;
231 otherwise it is set to zero.
232 <pre>
233 PCRE_CONFIG_UNICODE_PROPERTIES
234 </pre>
235 The output is an integer that is set to one if support for Unicode character
236 properties is available; otherwise it is set to zero.
237 <pre>
238 PCRE_CONFIG_NEWLINE
239 </pre>
240 The output is an integer that is set to the value of the code that is used for
241 the newline character. It is either linefeed (10) or carriage return (13), and
242 should normally be the standard character for your operating system.
243 <pre>
244 PCRE_CONFIG_LINK_SIZE
245 </pre>
246 The output is an integer that contains the number of bytes used for internal
247 linkage in compiled regular expressions. The value is 2, 3, or 4. Larger values
248 allow larger regular expressions to be compiled, at the expense of slower
249 matching. The default value of 2 is sufficient for all but the most massive
250 patterns, since it allows the compiled pattern to be up to 64K in size.
251 <pre>
252 PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
253 </pre>
254 The output is an integer that contains the threshold above which the POSIX
255 interface uses <b>malloc()</b> for output vectors. Further details are given in
256 the
257 <a href="pcreposix.html"><b>pcreposix</b></a>
258 documentation.
259 <pre>
260 PCRE_CONFIG_MATCH_LIMIT
261 </pre>
262 The output is an integer that gives the default limit for the number of
263 internal matching function calls in a <b>pcre_exec()</b> execution. Further
264 details are given with <b>pcre_exec()</b> below.
265 <pre>
266 PCRE_CONFIG_STACKRECURSE
267 </pre>
268 The output is an integer that is set to one if internal recursion is
269 implemented by recursive function calls that use the stack to remember their
270 state. This is the usual way that PCRE is compiled. The output is zero if PCRE
271 was compiled to use blocks of data on the heap instead of recursive function
272 calls. In this case, <b>pcre_stack_malloc</b> and <b>pcre_stack_free</b> are
273 called to manage memory blocks on the heap, thus avoiding the use of the stack.
274 </P>
275 <br><a name="SEC6" href="#TOC1">COMPILING A PATTERN</a><br>
276 <P>
277 <b>pcre *pcre_compile(const char *<i>pattern</i>, int <i>options</i>,</b>
278 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
279 <b>const unsigned char *<i>tableptr</i>);</b>
280 </P>
281 <P>
282 The function <b>pcre_compile()</b> is called to compile a pattern into an
283 internal form. The pattern is a C string terminated by a binary zero, and
284 is passed in the <i>pattern</i> argument. A pointer to a single block of memory
285 that is obtained via <b>pcre_malloc</b> is returned. This contains the compiled
286 code and related data. The <b>pcre</b> type is defined for the returned block;
287 this is a typedef for a structure whose contents are not externally defined. It
288 is up to the caller to free the memory when it is no longer required.
289 </P>
290 <P>
291 Although the compiled code of a PCRE regex is relocatable, that is, it does not
292 depend on memory location, the complete <b>pcre</b> data block is not
293 fully relocatable, because it may contain a copy of the <i>tableptr</i>
294 argument, which is an address (see below).
295 </P>
296 <P>
297 The <i>options</i> argument contains independent bits that affect the
298 compilation. It should be zero if no options are required. The available
299 options are described below. Some of them, in particular, those that are
300 compatible with Perl, can also be set and unset from within the pattern (see
301 the detailed description in the
302 <a href="pcrepattern.html"><b>pcrepattern</b></a>
303 documentation). For these options, the contents of the <i>options</i> argument
304 specifies their initial settings at the start of compilation and execution. The
305 PCRE_ANCHORED option can be set at the time of matching as well as at compile
306 time.
307 </P>
308 <P>
309 If <i>errptr</i> is NULL, <b>pcre_compile()</b> returns NULL immediately.
310 Otherwise, if compilation of a pattern fails, <b>pcre_compile()</b> returns
311 NULL, and sets the variable pointed to by <i>errptr</i> to point to a textual
312 error message. The offset from the start of the pattern to the character where
313 the error was discovered is placed in the variable pointed to by
314 <i>erroffset</i>, which must not be NULL. If it is, an immediate error is given.
315 </P>
316 <P>
317 If the final argument, <i>tableptr</i>, is NULL, PCRE uses a default set of
318 character tables that are built when PCRE is compiled, using the default C
319 locale. Otherwise, <i>tableptr</i> must be an address that is the result of a
320 call to <b>pcre_maketables()</b>. This value is stored with the compiled
321 pattern, and used again by <b>pcre_exec()</b>, unless another table pointer is
322 passed to it. For more discussion, see the section on locale support below.
323 </P>
324 <P>
325 This code fragment shows a typical straightforward call to <b>pcre_compile()</b>:
326 <pre>
327 pcre *re;
328 const char *error;
329 int erroffset;
330 re = pcre_compile(
331 "^A.*Z", /* the pattern */
332 0, /* default options */
333 &error, /* for error message */
334 &erroffset, /* for error offset */
335 NULL); /* use default character tables */
336 </pre>
337 The following names for option bits are defined in the <b>pcre.h</b> header
338 file:
339 <pre>
340 PCRE_ANCHORED
341 </pre>
342 If this bit is set, the pattern is forced to be "anchored", that is, it is
343 constrained to match only at the first matching point in the string that is
344 being searched (the "subject string"). This effect can also be achieved by
345 appropriate constructs in the pattern itself, which is the only way to do it in
346 Perl.
347 <pre>
348 PCRE_AUTO_CALLOUT
349 </pre>
350 If this bit is set, <b>pcre_compile()</b> automatically inserts callout items,
351 all with number 255, before each pattern item. For discussion of the callout
352 facility, see the
353 <a href="pcrecallout.html"><b>pcrecallout</b></a>
354 documentation.
355 <pre>
356 PCRE_CASELESS
357 </pre>
358 If this bit is set, letters in the pattern match both upper and lower case
359 letters. It is equivalent to Perl's /i option, and it can be changed within a
360 pattern by a (?i) option setting. When running in UTF-8 mode, case support for
361 high-valued characters is available only when PCRE is built with Unicode
362 character property support.
363 <pre>
364 PCRE_DOLLAR_ENDONLY
365 </pre>
366 If this bit is set, a dollar metacharacter in the pattern matches only at the
367 end of the subject string. Without this option, a dollar also matches
368 immediately before the final character if it is a newline (but not before any
369 other newlines). The PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is
370 set. There is no equivalent to this option in Perl, and no way to set it within
371 a pattern.
372 <pre>
373 PCRE_DOTALL
374 </pre>
375 If this bit is set, a dot metacharater in the pattern matches all characters,
376 including newlines. Without it, newlines are excluded. This option is
377 equivalent to Perl's /s option, and it can be changed within a pattern by a
378 (?s) option setting. A negative class such as [^a] always matches a newline
379 character, independent of the setting of this option.
380 <pre>
381 PCRE_EXTENDED
382 </pre>
383 If this bit is set, whitespace data characters in the pattern are totally
384 ignored except when escaped or inside a character class. Whitespace does not
385 include the VT character (code 11). In addition, characters between an
386 unescaped # outside a character class and the next newline character,
387 inclusive, are also ignored. This is equivalent to Perl's /x option, and it can
388 be changed within a pattern by a (?x) option setting.
389 </P>
390 <P>
391 This option makes it possible to include comments inside complicated patterns.
392 Note, however, that this applies only to data characters. Whitespace characters
393 may never appear within special character sequences in a pattern, for example
394 within the sequence (?( which introduces a conditional subpattern.
395 <pre>
396 PCRE_EXTRA
397 </pre>
398 This option was invented in order to turn on additional functionality of PCRE
399 that is incompatible with Perl, but it is currently of very little use. When
400 set, any backslash in a pattern that is followed by a letter that has no
401 special meaning causes an error, thus reserving these combinations for future
402 expansion. By default, as in Perl, a backslash followed by a letter with no
403 special meaning is treated as a literal. There are at present no other features
404 controlled by this option. It can also be set by a (?X) option setting within a
405 pattern.
406 <pre>
407 PCRE_MULTILINE
408 </pre>
409 By default, PCRE treats the subject string as consisting of a single line of
410 characters (even if it actually contains newlines). The "start of line"
411 metacharacter (^) matches only at the start of the string, while the "end of
412 line" metacharacter ($) matches only at the end of the string, or before a
413 terminating newline (unless PCRE_DOLLAR_ENDONLY is set). This is the same as
414 Perl.
415 </P>
416 <P>
417 When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs
418 match immediately following or immediately before any newline in the subject
419 string, respectively, as well as at the very start and end. This is equivalent
420 to Perl's /m option, and it can be changed within a pattern by a (?m) option
421 setting. If there are no "\n" characters in a subject string, or no
422 occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no effect.
423 <pre>
424 PCRE_NO_AUTO_CAPTURE
425 </pre>
426 If this option is set, it disables the use of numbered capturing parentheses in
427 the pattern. Any opening parenthesis that is not followed by ? behaves as if it
428 were followed by ?: but named parentheses can still be used for capturing (and
429 they acquire numbers in the usual way). There is no equivalent of this option
430 in Perl.
431 <pre>
432 PCRE_UNGREEDY
433 </pre>
434 This option inverts the "greediness" of the quantifiers so that they are not
435 greedy by default, but become greedy if followed by "?". It is not compatible
436 with Perl. It can also be set by a (?U) option setting within the pattern.
437 <pre>
438 PCRE_UTF8
439 </pre>
440 This option causes PCRE to regard both the pattern and the subject as strings
441 of UTF-8 characters instead of single-byte character strings. However, it is
442 available only when PCRE is built to include UTF-8 support. If not, the use
443 of this option provokes an error. Details of how this option changes the
444 behaviour of PCRE are given in the
445 <a href="pcre.html#utf8support">section on UTF-8 support</a>
446 in the main
447 <a href="pcre.html"><b>pcre</b></a>
448 page.
449 <pre>
450 PCRE_NO_UTF8_CHECK
451 </pre>
452 When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
453 automatically checked. If an invalid UTF-8 sequence of bytes is found,
454 <b>pcre_compile()</b> returns an error. If you already know that your pattern is
455 valid, and you want to skip this check for performance reasons, you can set the
456 PCRE_NO_UTF8_CHECK option. When it is set, the effect of passing an invalid
457 UTF-8 string as a pattern is undefined. It may cause your program to crash.
458 Note that this option can also be passed to <b>pcre_exec()</b>, to suppress the
459 UTF-8 validity checking of subject strings.
460 </P>
461 <br><a name="SEC7" href="#TOC1">STUDYING A PATTERN</a><br>
462 <P>
463 <b>pcre_extra *pcre_study(const pcre *<i>code</i>, int <i>options</i>,</b>
464 <b>const char **<i>errptr</i>);</b>
465 </P>
466 <P>
467 If a compiled pattern is going to be used several times, it is worth spending
468 more time analyzing it in order to speed up the time taken for matching. The
469 function <b>pcre_study()</b> takes a pointer to a compiled pattern as its first
470 argument. If studying the pattern produces additional information that will
471 help speed up matching, <b>pcre_study()</b> returns a pointer to a
472 <b>pcre_extra</b> block, in which the <i>study_data</i> field points to the
473 results of the study.
474 </P>
475 <P>
476 The returned value from <b>pcre_study()</b> can be passed directly to
477 <b>pcre_exec()</b>. However, a <b>pcre_extra</b> block also contains other
478 fields that can be set by the caller before the block is passed; these are
479 described
480 <a href="#extradata">below</a>
481 in the section on matching a pattern.
482 </P>
483 <P>
484 If studying the pattern does not produce any additional information,
485 <b>pcre_study()</b> returns NULL. In that circumstance, if the calling program
486 wants to pass any of the other fields to <b>pcre_exec()</b>, it must set up its
487 own <b>pcre_extra</b> block.
488 </P>
489 <P>
490 The second argument of <b>pcre_study()</b> contains option bits. At present, no
491 options are defined, and this argument should always be zero.
492 </P>
493 <P>
494 The third argument for <b>pcre_study()</b> is a pointer for an error message. If
495 studying succeeds (even if no data is returned), the variable it points to is
496 set to NULL. Otherwise it points to a textual error message. You should
497 therefore test the error pointer for NULL after calling <b>pcre_study()</b>, to
498 be sure that it has run successfully.
499 </P>
500 <P>
501 This is a typical call to <b>pcre_study</b>():
502 <pre>
503 pcre_extra *pe;
504 pe = pcre_study(
505 re, /* result of pcre_compile() */
506 0, /* no options exist */
507 &error); /* set to NULL or points to a message */
508 </pre>
509 At present, studying a pattern is useful only for non-anchored patterns that do
510 not have a single fixed starting character. A bitmap of possible starting
511 bytes is created.
512 <a name="localesupport"></a></P>
513 <br><a name="SEC8" href="#TOC1">LOCALE SUPPORT</a><br>
514 <P>
515 PCRE handles caseless matching, and determines whether characters are letters,
516 digits, or whatever, by reference to a set of tables, indexed by character
517 value. (When running in UTF-8 mode, this applies only to characters with codes
518 less than 128. Higher-valued codes never match escapes such as \w or \d, but
519 can be tested with \p if PCRE is built with Unicode character property
520 support.)
521 </P>
522 <P>
523 An internal set of tables is created in the default C locale when PCRE is
524 built. This is used when the final argument of <b>pcre_compile()</b> is NULL,
525 and is sufficient for many applications. An alternative set of tables can,
526 however, be supplied. These may be created in a different locale from the
527 default. As more and more applications change to using Unicode, the need for
528 this locale support is expected to die away.
529 </P>
530 <P>
531 External tables are built by calling the <b>pcre_maketables()</b> function,
532 which has no arguments, in the relevant locale. The result can then be passed
533 to <b>pcre_compile()</b> or <b>pcre_exec()</b> as often as necessary. For
534 example, to build and use tables that are appropriate for the French locale
535 (where accented characters with values greater than 128 are treated as letters),
536 the following code could be used:
537 <pre>
538 setlocale(LC_CTYPE, "fr_FR");
539 tables = pcre_maketables();
540 re = pcre_compile(..., tables);
541 </pre>
542 When <b>pcre_maketables()</b> runs, the tables are built in memory that is
543 obtained via <b>pcre_malloc</b>. It is the caller's responsibility to ensure
544 that the memory containing the tables remains available for as long as it is
545 needed.
546 </P>
547 <P>
548 The pointer that is passed to <b>pcre_compile()</b> is saved with the compiled
549 pattern, and the same tables are used via this pointer by <b>pcre_study()</b>
550 and normally also by <b>pcre_exec()</b>. Thus, by default, for any single
551 pattern, compilation, studying and matching all happen in the same locale, but
552 different patterns can be compiled in different locales.
553 </P>
554 <P>
555 It is possible to pass a table pointer or NULL (indicating the use of the
556 internal tables) to <b>pcre_exec()</b>. Although not intended for this purpose,
557 this facility could be used to match a pattern in a different locale from the
558 one in which it was compiled. Passing table pointers at run time is discussed
559 below in the section on matching a pattern.
560 </P>
561 <br><a name="SEC9" href="#TOC1">INFORMATION ABOUT A PATTERN</a><br>
562 <P>
563 <b>int pcre_fullinfo(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
564 <b>int <i>what</i>, void *<i>where</i>);</b>
565 </P>
566 <P>
567 The <b>pcre_fullinfo()</b> function returns information about a compiled
568 pattern. It replaces the obsolete <b>pcre_info()</b> function, which is
569 nevertheless retained for backwards compability (and is documented below).
570 </P>
571 <P>
572 The first argument for <b>pcre_fullinfo()</b> is a pointer to the compiled
573 pattern. The second argument is the result of <b>pcre_study()</b>, or NULL if
574 the pattern was not studied. The third argument specifies which piece of
575 information is required, and the fourth argument is a pointer to a variable
576 to receive the data. The yield of the function is zero for success, or one of
577 the following negative numbers:
578 <pre>
579 PCRE_ERROR_NULL the argument <i>code</i> was NULL
580 the argument <i>where</i> was NULL
581 PCRE_ERROR_BADMAGIC the "magic number" was not found
582 PCRE_ERROR_BADOPTION the value of <i>what</i> was invalid
583 </pre>
584 The "magic number" is placed at the start of each compiled pattern as an simple
585 check against passing an arbitrary memory pointer. Here is a typical call of
586 <b>pcre_fullinfo()</b>, to obtain the length of the compiled pattern:
587 <pre>
588 int rc;
589 unsigned long int length;
590 rc = pcre_fullinfo(
591 re, /* result of pcre_compile() */
592 pe, /* result of pcre_study(), or NULL */
593 PCRE_INFO_SIZE, /* what is required */
594 &length); /* where to put the data */
595 </pre>
596 The possible values for the third argument are defined in <b>pcre.h</b>, and are
597 as follows:
598 <pre>
599 PCRE_INFO_BACKREFMAX
600 </pre>
601 Return the number of the highest back reference in the pattern. The fourth
602 argument should point to an <b>int</b> variable. Zero is returned if there are
603 no back references.
604 <pre>
605 PCRE_INFO_CAPTURECOUNT
606 </pre>
607 Return the number of capturing subpatterns in the pattern. The fourth argument
608 should point to an <b>int</b> variable.
609 <pre>
610 PCRE_INFO_DEFAULTTABLES
611 </pre>
612 Return a pointer to the internal default character tables within PCRE. The
613 fourth argument should point to an <b>unsigned char *</b> variable. This
614 information call is provided for internal use by the <b>pcre_study()</b>
615 function. External callers can cause PCRE to use its internal tables by passing
616 a NULL table pointer.
617 <pre>
618 PCRE_INFO_FIRSTBYTE
619 </pre>
620 Return information about the first byte of any matched string, for a
621 non-anchored pattern. (This option used to be called PCRE_INFO_FIRSTCHAR; the
622 old name is still recognized for backwards compatibility.)
623 </P>
624 <P>
625 If there is a fixed first byte, for example, from a pattern such as
626 (cat|cow|coyote), it is returned in the integer pointed to by <i>where</i>.
627 Otherwise, if either
628 <br>
629 <br>
630 (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
631 starts with "^", or
632 <br>
633 <br>
634 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
635 (if it were set, the pattern would be anchored),
636 <br>
637 <br>
638 -1 is returned, indicating that the pattern matches only at the start of a
639 subject string or after any newline within the string. Otherwise -2 is
640 returned. For anchored patterns, -2 is returned.
641 <pre>
642 PCRE_INFO_FIRSTTABLE
643 </pre>
644 If the pattern was studied, and this resulted in the construction of a 256-bit
645 table indicating a fixed set of bytes for the first byte in any matching
646 string, a pointer to the table is returned. Otherwise NULL is returned. The
647 fourth argument should point to an <b>unsigned char *</b> variable.
648 <pre>
649 PCRE_INFO_LASTLITERAL
650 </pre>
651 Return the value of the rightmost literal byte that must exist in any matched
652 string, other than at its start, if such a byte has been recorded. The fourth
653 argument should point to an <b>int</b> variable. If there is no such byte, -1 is
654 returned. For anchored patterns, a last literal byte is recorded only if it
655 follows something of variable length. For example, for the pattern
656 /^a\d+z\d+/ the returned value is "z", but for /^a\dz\d/ the returned value
657 is -1.
658 <pre>
659 PCRE_INFO_NAMECOUNT
660 PCRE_INFO_NAMEENTRYSIZE
661 PCRE_INFO_NAMETABLE
662 </pre>
663 PCRE supports the use of named as well as numbered capturing parentheses. The
664 names are just an additional way of identifying the parentheses, which still
665 acquire numbers. A convenience function called <b>pcre_get_named_substring()</b>
666 is provided for extracting an individual captured substring by name. It is also
667 possible to extract the data directly, by first converting the name to a number
668 in order to access the correct pointers in the output vector (described with
669 <b>pcre_exec()</b> below). To do the conversion, you need to use the
670 name-to-number map, which is described by these three values.
671 </P>
672 <P>
673 The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives
674 the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each
675 entry; both of these return an <b>int</b> value. The entry size depends on the
676 length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first
677 entry of the table (a pointer to <b>char</b>). The first two bytes of each entry
678 are the number of the capturing parenthesis, most significant byte first. The
679 rest of the entry is the corresponding name, zero terminated. The names are in
680 alphabetical order. For example, consider the following pattern (assume
681 PCRE_EXTENDED is set, so white space - including newlines - is ignored):
682 <pre>
683 (?P&#60;date&#62; (?P&#60;year&#62;(\d\d)?\d\d) - (?P&#60;month&#62;\d\d) - (?P&#60;day&#62;\d\d) )
684 </pre>
685 There are four named subpatterns, so the table has four entries, and each entry
686 in the table is eight bytes long. The table is as follows, with non-printing
687 bytes shows in hexadecimal, and undefined bytes shown as ??:
688 <pre>
689 00 01 d a t e 00 ??
690 00 05 d a y 00 ?? ??
691 00 04 m o n t h 00
692 00 02 y e a r 00 ??
693 </pre>
694 When writing code to extract data from named subpatterns using the
695 name-to-number map, remember that the length of each entry is likely to be
696 different for each compiled pattern.
697 <pre>
698 PCRE_INFO_OPTIONS
699 </pre>
700 Return a copy of the options with which the pattern was compiled. The fourth
701 argument should point to an <b>unsigned long int</b> variable. These option bits
702 are those specified in the call to <b>pcre_compile()</b>, modified by any
703 top-level option settings within the pattern itself.
704 </P>
705 <P>
706 A pattern is automatically anchored by PCRE if all of its top-level
707 alternatives begin with one of the following:
708 <pre>
709 ^ unless PCRE_MULTILINE is set
710 \A always
711 \G always
712 .* if PCRE_DOTALL is set and there are no back references to the subpattern in which .* appears
713 </pre>
714 For such patterns, the PCRE_ANCHORED bit is set in the options returned by
715 <b>pcre_fullinfo()</b>.
716 <pre>
717 PCRE_INFO_SIZE
718 </pre>
719 Return the size of the compiled pattern, that is, the value that was passed as
720 the argument to <b>pcre_malloc()</b> when PCRE was getting memory in which to
721 place the compiled data. The fourth argument should point to a <b>size_t</b>
722 variable.
723 <pre>
724 PCRE_INFO_STUDYSIZE
725 </pre>
726 Return the size of the data block pointed to by the <i>study_data</i> field in
727 a <b>pcre_extra</b> block. That is, it is the value that was passed to
728 <b>pcre_malloc()</b> when PCRE was getting memory into which to place the data
729 created by <b>pcre_study()</b>. The fourth argument should point to a
730 <b>size_t</b> variable.
731 </P>
732 <br><a name="SEC10" href="#TOC1">OBSOLETE INFO FUNCTION</a><br>
733 <P>
734 <b>int pcre_info(const pcre *<i>code</i>, int *<i>optptr</i>, int</b>
735 <b>*<i>firstcharptr</i>);</b>
736 </P>
737 <P>
738 The <b>pcre_info()</b> function is now obsolete because its interface is too
739 restrictive to return all the available data about a compiled pattern. New
740 programs should use <b>pcre_fullinfo()</b> instead. The yield of
741 <b>pcre_info()</b> is the number of capturing subpatterns, or one of the
742 following negative numbers:
743 <pre>
744 PCRE_ERROR_NULL the argument <i>code</i> was NULL
745 PCRE_ERROR_BADMAGIC the "magic number" was not found
746 </pre>
747 If the <i>optptr</i> argument is not NULL, a copy of the options with which the
748 pattern was compiled is placed in the integer it points to (see
749 PCRE_INFO_OPTIONS above).
750 </P>
751 <P>
752 If the pattern is not anchored and the <i>firstcharptr</i> argument is not NULL,
753 it is used to pass back information about the first character of any matched
754 string (see PCRE_INFO_FIRSTBYTE above).
755 </P>
756 <br><a name="SEC11" href="#TOC1">MATCHING A PATTERN</a><br>
757 <P>
758 <b>int pcre_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
759 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
760 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>);</b>
761 </P>
762 <P>
763 The function <b>pcre_exec()</b> is called to match a subject string against a
764 compiled pattern, which is passed in the <i>code</i> argument. If the
765 pattern has been studied, the result of the study should be passed in the
766 <i>extra</i> argument.
767 </P>
768 <P>
769 In most applications, the pattern will have been compiled (and optionally
770 studied) in the same process that calls <b>pcre_exec()</b>. However, it is
771 possible to save compiled patterns and study data, and then use them later
772 in different processes, possibly even on different hosts. For a discussion
773 about this, see the
774 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
775 documentation.
776 </P>
777 <P>
778 Here is an example of a simple call to <b>pcre_exec()</b>:
779 <pre>
780 int rc;
781 int ovector[30];
782 rc = pcre_exec(
783 re, /* result of pcre_compile() */
784 NULL, /* we didn't study the pattern */
785 "some string", /* the subject string */
786 11, /* the length of the subject string */
787 0, /* start at offset 0 in the subject */
788 0, /* default options */
789 ovector, /* vector of integers for substring information */
790 30); /* number of elements in the vector (NOT size in bytes) */
791 <a name="extradata"></a></PRE>
792 </P>
793 <br><b>
794 Extra data for <b>pcre_exec()</b>
795 </b><br>
796 <P>
797 If the <i>extra</i> argument is not NULL, it must point to a <b>pcre_extra</b>
798 data block. The <b>pcre_study()</b> function returns such a block (when it
799 doesn't return NULL), but you can also create one for yourself, and pass
800 additional information in it. The fields in a <b>pcre_extra</b> block are as
801 follows:
802 <pre>
803 unsigned long int <i>flags</i>;
804 void *<i>study_data</i>;
805 unsigned long int <i>match_limit</i>;
806 void *<i>callout_data</i>;
807 const unsigned char *<i>tables</i>;
808 </pre>
809 The <i>flags</i> field is a bitmap that specifies which of the other fields
810 are set. The flag bits are:
811 <pre>
812 PCRE_EXTRA_STUDY_DATA
813 PCRE_EXTRA_MATCH_LIMIT
814 PCRE_EXTRA_CALLOUT_DATA
815 PCRE_EXTRA_TABLES
816 </pre>
817 Other flag bits should be set to zero. The <i>study_data</i> field is set in the
818 <b>pcre_extra</b> block that is returned by <b>pcre_study()</b>, together with
819 the appropriate flag bit. You should not set this yourself, but you may add to
820 the block by setting the other fields and their corresponding flag bits.
821 </P>
822 <P>
823 The <i>match_limit</i> field provides a means of preventing PCRE from using up a
824 vast amount of resources when running patterns that are not going to match,
825 but which have a very large number of possibilities in their search trees. The
826 classic example is the use of nested unlimited repeats.
827 </P>
828 <P>
829 Internally, PCRE uses a function called <b>match()</b> which it calls repeatedly
830 (sometimes recursively). The limit is imposed on the number of times this
831 function is called during a match, which has the effect of limiting the amount
832 of recursion and backtracking that can take place. For patterns that are not
833 anchored, the count starts from zero for each position in the subject string.
834 </P>
835 <P>
836 The default limit for the library can be set when PCRE is built; the default
837 default is 10 million, which handles all but the most extreme cases. You can
838 reduce the default by suppling <b>pcre_exec()</b> with a <b>pcre_extra</b> block
839 in which <i>match_limit</i> is set to a smaller value, and
840 PCRE_EXTRA_MATCH_LIMIT is set in the <i>flags</i> field. If the limit is
841 exceeded, <b>pcre_exec()</b> returns PCRE_ERROR_MATCHLIMIT.
842 </P>
843 <P>
844 The <i>pcre_callout</i> field is used in conjunction with the "callout" feature,
845 which is described in the
846 <a href="pcrecallout.html"><b>pcrecallout</b></a>
847 documentation.
848 </P>
849 <P>
850 The <i>tables</i> field is used to pass a character tables pointer to
851 <b>pcre_exec()</b>; this overrides the value that is stored with the compiled
852 pattern. A non-NULL value is stored with the compiled pattern only if custom
853 tables were supplied to <b>pcre_compile()</b> via its <i>tableptr</i> argument.
854 If NULL is passed to <b>pcre_exec()</b> using this mechanism, it forces PCRE's
855 internal tables to be used. This facility is helpful when re-using patterns
856 that have been saved after compiling with an external set of tables, because
857 the external tables might be at a different address when <b>pcre_exec()</b> is
858 called. See the
859 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
860 documentation for a discussion of saving compiled patterns for later use.
861 </P>
862 <br><b>
863 Option bits for <b>pcre_exec()</b>
864 </b><br>
865 <P>
866 The unused bits of the <i>options</i> argument for <b>pcre_exec()</b> must be
867 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NOTBOL,
868 PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK and PCRE_PARTIAL.
869 <pre>
870 PCRE_ANCHORED
871 </pre>
872 The PCRE_ANCHORED option limits <b>pcre_exec()</b> to matching at the first
873 matching position. If a pattern was compiled with PCRE_ANCHORED, or turned out
874 to be anchored by virtue of its contents, it cannot be made unachored at
875 matching time.
876 <pre>
877 PCRE_NOTBOL
878 </pre>
879 This option specifies that first character of the subject string is not the
880 beginning of a line, so the circumflex metacharacter should not match before
881 it. Setting this without PCRE_MULTILINE (at compile time) causes circumflex
882 never to match. This option affects only the behaviour of the circumflex
883 metacharacter. It does not affect \A.
884 <pre>
885 PCRE_NOTEOL
886 </pre>
887 This option specifies that the end of the subject string is not the end of a
888 line, so the dollar metacharacter should not match it nor (except in multiline
889 mode) a newline immediately before it. Setting this without PCRE_MULTILINE (at
890 compile time) causes dollar never to match. This option affects only the
891 behaviour of the dollar metacharacter. It does not affect \Z or \z.
892 <pre>
893 PCRE_NOTEMPTY
894 </pre>
895 An empty string is not considered to be a valid match if this option is set. If
896 there are alternatives in the pattern, they are tried. If all the alternatives
897 match the empty string, the entire match fails. For example, if the pattern
898 <pre>
899 a?b?
900 </pre>
901 is applied to a string not beginning with "a" or "b", it matches the empty
902 string at the start of the subject. With PCRE_NOTEMPTY set, this match is not
903 valid, so PCRE searches further into the string for occurrences of "a" or "b".
904 </P>
905 <P>
906 Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a special case
907 of a pattern match of the empty string within its <b>split()</b> function, and
908 when using the /g modifier. It is possible to emulate Perl's behaviour after
909 matching a null string by first trying the match again at the same offset with
910 PCRE_NOTEMPTY and PCRE_ANCHORED, and then if that fails by advancing the
911 starting offset (see below) and trying an ordinary match again. There is some
912 code that demonstrates how to do this in the <i>pcredemo.c</i> sample program.
913 <pre>
914 PCRE_NO_UTF8_CHECK
915 </pre>
916 When PCRE_UTF8 is set at compile time, the validity of the subject as a UTF-8
917 string is automatically checked when <b>pcre_exec()</b> is subsequently called.
918 The value of <i>startoffset</i> is also checked to ensure that it points to the
919 start of a UTF-8 character. If an invalid UTF-8 sequence of bytes is found,
920 <b>pcre_exec()</b> returns the error PCRE_ERROR_BADUTF8. If <i>startoffset</i>
921 contains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
922 </P>
923 <P>
924 If you already know that your subject is valid, and you want to skip these
925 checks for performance reasons, you can set the PCRE_NO_UTF8_CHECK option when
926 calling <b>pcre_exec()</b>. You might want to do this for the second and
927 subsequent calls to <b>pcre_exec()</b> if you are making repeated calls to find
928 all the matches in a single subject string. However, you should be sure that
929 the value of <i>startoffset</i> points to the start of a UTF-8 character. When
930 PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid UTF-8 string as a
931 subject, or a value of <i>startoffset</i> that does not point to the start of a
932 UTF-8 character, is undefined. Your program may crash.
933 <pre>
934 PCRE_PARTIAL
935 </pre>
936 This option turns on the partial matching feature. If the subject string fails
937 to match the pattern, but at some point during the matching process the end of
938 the subject was reached (that is, the subject partially matches the pattern and
939 the failure to match occurred only because there were not enough subject
940 characters), <b>pcre_exec()</b> returns PCRE_ERROR_PARTIAL instead of
941 PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is used, there are restrictions on what
942 may appear in the pattern. These are discussed in the
943 <a href="pcrepartial.html"><b>pcrepartial</b></a>
944 documentation.
945 </P>
946 <br><b>
947 The string to be matched by <b>pcre_exec()</b>
948 </b><br>
949 <P>
950 The subject string is passed to <b>pcre_exec()</b> as a pointer in
951 <i>subject</i>, a length in <i>length</i>, and a starting byte offset in
952 <i>startoffset</i>. In UTF-8 mode, the byte offset must point to the start of a
953 UTF-8 character. Unlike the pattern string, the subject may contain binary zero
954 bytes. When the starting offset is zero, the search for a match starts at the
955 beginning of the subject, and this is by far the most common case.
956 </P>
957 <P>
958 A non-zero starting offset is useful when searching for another match in the
959 same subject by calling <b>pcre_exec()</b> again after a previous success.
960 Setting <i>startoffset</i> differs from just passing over a shortened string and
961 setting PCRE_NOTBOL in the case of a pattern that begins with any kind of
962 lookbehind. For example, consider the pattern
963 <pre>
964 \Biss\B
965 </pre>
966 which finds occurrences of "iss" in the middle of words. (\B matches only if
967 the current position in the subject is not a word boundary.) When applied to
968 the string "Mississipi" the first call to <b>pcre_exec()</b> finds the first
969 occurrence. If <b>pcre_exec()</b> is called again with just the remainder of the
970 subject, namely "issipi", it does not match, because \B is always false at the
971 start of the subject, which is deemed to be a word boundary. However, if
972 <b>pcre_exec()</b> is passed the entire string again, but with <i>startoffset</i>
973 set to 4, it finds the second occurrence of "iss" because it is able to look
974 behind the starting point to discover that it is preceded by a letter.
975 </P>
976 <P>
977 If a non-zero starting offset is passed when the pattern is anchored, one
978 attempt to match at the given offset is made. This can only succeed if the
979 pattern does not require the match to be at the start of the subject.
980 </P>
981 <br><b>
982 How <b>pcre_exec()</b> returns captured substrings
983 </b><br>
984 <P>
985 In general, a pattern matches a certain portion of the subject, and in
986 addition, further substrings from the subject may be picked out by parts of the
987 pattern. Following the usage in Jeffrey Friedl's book, this is called
988 "capturing" in what follows, and the phrase "capturing subpattern" is used for
989 a fragment of a pattern that picks out a substring. PCRE supports several other
990 kinds of parenthesized subpattern that do not cause substrings to be captured.
991 </P>
992 <P>
993 Captured substrings are returned to the caller via a vector of integer offsets
994 whose address is passed in <i>ovector</i>. The number of elements in the vector
995 is passed in <i>ovecsize</i>, which must be a non-negative number. <b>Note</b>:
996 this argument is NOT the size of <i>ovector</i> in bytes.
997 </P>
998 <P>
999 The first two-thirds of the vector is used to pass back captured substrings,
1000 each substring using a pair of integers. The remaining third of the vector is
1001 used as workspace by <b>pcre_exec()</b> while matching capturing subpatterns,
1002 and is not available for passing back information. The length passed in
1003 <i>ovecsize</i> should always be a multiple of three. If it is not, it is
1004 rounded down.
1005 </P>
1006 <P>
1007 When a match is successful, information about captured substrings is returned
1008 in pairs of integers, starting at the beginning of <i>ovector</i>, and
1009 continuing up to two-thirds of its length at the most. The first element of a
1010 pair is set to the offset of the first character in a substring, and the second
1011 is set to the offset of the first character after the end of a substring. The
1012 first pair, <i>ovector[0]</i> and <i>ovector[1]</i>, identify the portion of the
1013 subject string matched by the entire pattern. The next pair is used for the
1014 first capturing subpattern, and so on. The value returned by <b>pcre_exec()</b>
1015 is the number of pairs that have been set. If there are no capturing
1016 subpatterns, the return value from a successful match is 1, indicating that
1017 just the first pair of offsets has been set.
1018 </P>
1019 <P>
1020 Some convenience functions are provided for extracting the captured substrings
1021 as separate strings. These are described in the following section.
1022 </P>
1023 <P>
1024 It is possible for an capturing subpattern number <i>n+1</i> to match some
1025 part of the subject when subpattern <i>n</i> has not been used at all. For
1026 example, if the string "abc" is matched against the pattern (a|(z))(bc)
1027 subpatterns 1 and 3 are matched, but 2 is not. When this happens, both offset
1028 values corresponding to the unused subpattern are set to -1.
1029 </P>
1030 <P>
1031 If a capturing subpattern is matched repeatedly, it is the last portion of the
1032 string that it matched that is returned.
1033 </P>
1034 <P>
1035 If the vector is too small to hold all the captured substring offsets, it is
1036 used as far as possible (up to two-thirds of its length), and the function
1037 returns a value of zero. In particular, if the substring offsets are not of
1038 interest, <b>pcre_exec()</b> may be called with <i>ovector</i> passed as NULL and
1039 <i>ovecsize</i> as zero. However, if the pattern contains back references and
1040 the <i>ovector</i> is not big enough to remember the related substrings, PCRE
1041 has to get additional memory for use during matching. Thus it is usually
1042 advisable to supply an <i>ovector</i>.
1043 </P>
1044 <P>
1045 Note that <b>pcre_info()</b> can be used to find out how many capturing
1046 subpatterns there are in a compiled pattern. The smallest size for
1047 <i>ovector</i> that will allow for <i>n</i> captured substrings, in addition to
1048 the offsets of the substring matched by the whole pattern, is (<i>n</i>+1)*3.
1049 </P>
1050 <br><b>
1051 Return values from <b>pcre_exec()</b>
1052 </b><br>
1053 <P>
1054 If <b>pcre_exec()</b> fails, it returns a negative number. The following are
1055 defined in the header file:
1056 <pre>
1057 PCRE_ERROR_NOMATCH (-1)
1058 </pre>
1059 The subject string did not match the pattern.
1060 <pre>
1061 PCRE_ERROR_NULL (-2)
1062 </pre>
1063 Either <i>code</i> or <i>subject</i> was passed as NULL, or <i>ovector</i> was
1064 NULL and <i>ovecsize</i> was not zero.
1065 <pre>
1066 PCRE_ERROR_BADOPTION (-3)
1067 </pre>
1068 An unrecognized bit was set in the <i>options</i> argument.
1069 <pre>
1070 PCRE_ERROR_BADMAGIC (-4)
1071 </pre>
1072 PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch
1073 the case when it is passed a junk pointer and to detect when a pattern that was
1074 compiled in an environment of one endianness is run in an environment with the
1075 other endianness. This is the error that PCRE gives when the magic number is
1076 not present.
1077 <pre>
1078 PCRE_ERROR_UNKNOWN_NODE (-5)
1079 </pre>
1080 While running the pattern match, an unknown item was encountered in the
1081 compiled pattern. This error could be caused by a bug in PCRE or by overwriting
1082 of the compiled pattern.
1083 <pre>
1084 PCRE_ERROR_NOMEMORY (-6)
1085 </pre>
1086 If a pattern contains back references, but the <i>ovector</i> that is passed to
1087 <b>pcre_exec()</b> is not big enough to remember the referenced substrings, PCRE
1088 gets a block of memory at the start of matching to use for this purpose. If the
1089 call via <b>pcre_malloc()</b> fails, this error is given. The memory is
1090 automatically freed at the end of matching.
1091 <pre>
1092 PCRE_ERROR_NOSUBSTRING (-7)
1093 </pre>
1094 This error is used by the <b>pcre_copy_substring()</b>,
1095 <b>pcre_get_substring()</b>, and <b>pcre_get_substring_list()</b> functions (see
1096 below). It is never returned by <b>pcre_exec()</b>.
1097 <pre>
1098 PCRE_ERROR_MATCHLIMIT (-8)
1099 </pre>
1100 The recursion and backtracking limit, as specified by the <i>match_limit</i>
1101 field in a <b>pcre_extra</b> structure (or defaulted) was reached. See the
1102 description above.
1103 <pre>
1104 PCRE_ERROR_CALLOUT (-9)
1105 </pre>
1106 This error is never generated by <b>pcre_exec()</b> itself. It is provided for
1107 use by callout functions that want to yield a distinctive error code. See the
1108 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1109 documentation for details.
1110 <pre>
1111 PCRE_ERROR_BADUTF8 (-10)
1112 </pre>
1113 A string that contains an invalid UTF-8 byte sequence was passed as a subject.
1114 <pre>
1115 PCRE_ERROR_BADUTF8_OFFSET (-11)
1116 </pre>
1117 The UTF-8 byte sequence that was passed as a subject was valid, but the value
1118 of <i>startoffset</i> did not point to the beginning of a UTF-8 character.
1119 <pre>
1120 PCRE_ERROR_PARTIAL (-12)
1121 </pre>
1122 The subject string did not match, but it did match partially. See the
1123 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1124 documentation for details of partial matching.
1125 <pre>
1126 PCRE_ERROR_BAD_PARTIAL (-13)
1127 </pre>
1128 The PCRE_PARTIAL option was used with a compiled pattern containing items that
1129 are not supported for partial matching. See the
1130 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1131 documentation for details of partial matching.
1132 <pre>
1133 PCRE_ERROR_INTERNAL (-14)
1134 </pre>
1135 An unexpected internal error has occurred. This error could be caused by a bug
1136 in PCRE or by overwriting of the compiled pattern.
1137 <pre>
1138 PCRE_ERROR_BADCOUNT (-15)
1139 </pre>
1140 This error is given if the value of the <i>ovecsize</i> argument is negative.
1141 </P>
1142 <br><a name="SEC12" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NUMBER</a><br>
1143 <P>
1144 <b>int pcre_copy_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1145 <b>int <i>stringcount</i>, int <i>stringnumber</i>, char *<i>buffer</i>,</b>
1146 <b>int <i>buffersize</i>);</b>
1147 </P>
1148 <P>
1149 <b>int pcre_get_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1150 <b>int <i>stringcount</i>, int <i>stringnumber</i>,</b>
1151 <b>const char **<i>stringptr</i>);</b>
1152 </P>
1153 <P>
1154 <b>int pcre_get_substring_list(const char *<i>subject</i>,</b>
1155 <b>int *<i>ovector</i>, int <i>stringcount</i>, const char ***<i>listptr</i>);</b>
1156 </P>
1157 <P>
1158 Captured substrings can be accessed directly by using the offsets returned by
1159 <b>pcre_exec()</b> in <i>ovector</i>. For convenience, the functions
1160 <b>pcre_copy_substring()</b>, <b>pcre_get_substring()</b>, and
1161 <b>pcre_get_substring_list()</b> are provided for extracting captured substrings
1162 as new, separate, zero-terminated strings. These functions identify substrings
1163 by number. The next section describes functions for extracting named
1164 substrings. A substring that contains a binary zero is correctly extracted and
1165 has a further zero added on the end, but the result is not, of course,
1166 a C string.
1167 </P>
1168 <P>
1169 The first three arguments are the same for all three of these functions:
1170 <i>subject</i> is the subject string that has just been successfully matched,
1171 <i>ovector</i> is a pointer to the vector of integer offsets that was passed to
1172 <b>pcre_exec()</b>, and <i>stringcount</i> is the number of substrings that were
1173 captured by the match, including the substring that matched the entire regular
1174 expression. This is the value returned by <b>pcre_exec()</b> if it is greater
1175 than zero. If <b>pcre_exec()</b> returned zero, indicating that it ran out of
1176 space in <i>ovector</i>, the value passed as <i>stringcount</i> should be the
1177 number of elements in the vector divided by three.
1178 </P>
1179 <P>
1180 The functions <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>
1181 extract a single substring, whose number is given as <i>stringnumber</i>. A
1182 value of zero extracts the substring that matched the entire pattern, whereas
1183 higher values extract the captured substrings. For <b>pcre_copy_substring()</b>,
1184 the string is placed in <i>buffer</i>, whose length is given by
1185 <i>buffersize</i>, while for <b>pcre_get_substring()</b> a new block of memory is
1186 obtained via <b>pcre_malloc</b>, and its address is returned via
1187 <i>stringptr</i>. The yield of the function is the length of the string, not
1188 including the terminating zero, or one of
1189 <pre>
1190 PCRE_ERROR_NOMEMORY (-6)
1191 </pre>
1192 The buffer was too small for <b>pcre_copy_substring()</b>, or the attempt to get
1193 memory failed for <b>pcre_get_substring()</b>.
1194 <pre>
1195 PCRE_ERROR_NOSUBSTRING (-7)
1196 </pre>
1197 There is no substring whose number is <i>stringnumber</i>.
1198 </P>
1199 <P>
1200 The <b>pcre_get_substring_list()</b> function extracts all available substrings
1201 and builds a list of pointers to them. All this is done in a single block of
1202 memory that is obtained via <b>pcre_malloc</b>. The address of the memory block
1203 is returned via <i>listptr</i>, which is also the start of the list of string
1204 pointers. The end of the list is marked by a NULL pointer. The yield of the
1205 function is zero if all went well, or
1206 <pre>
1207 PCRE_ERROR_NOMEMORY (-6)
1208 </pre>
1209 if the attempt to get the memory block failed.
1210 </P>
1211 <P>
1212 When any of these functions encounter a substring that is unset, which can
1213 happen when capturing subpattern number <i>n+1</i> matches some part of the
1214 subject, but subpattern <i>n</i> has not been used at all, they return an empty
1215 string. This can be distinguished from a genuine zero-length substring by
1216 inspecting the appropriate offset in <i>ovector</i>, which is negative for unset
1217 substrings.
1218 </P>
1219 <P>
1220 The two convenience functions <b>pcre_free_substring()</b> and
1221 <b>pcre_free_substring_list()</b> can be used to free the memory returned by
1222 a previous call of <b>pcre_get_substring()</b> or
1223 <b>pcre_get_substring_list()</b>, respectively. They do nothing more than call
1224 the function pointed to by <b>pcre_free</b>, which of course could be called
1225 directly from a C program. However, PCRE is used in some situations where it is
1226 linked via a special interface to another programming language which cannot use
1227 <b>pcre_free</b> directly; it is for these cases that the functions are
1228 provided.
1229 </P>
1230 <br><a name="SEC13" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NAME</a><br>
1231 <P>
1232 <b>int pcre_get_stringnumber(const pcre *<i>code</i>,</b>
1233 <b>const char *<i>name</i>);</b>
1234 </P>
1235 <P>
1236 <b>int pcre_copy_named_substring(const pcre *<i>code</i>,</b>
1237 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
1238 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
1239 <b>char *<i>buffer</i>, int <i>buffersize</i>);</b>
1240 </P>
1241 <P>
1242 <b>int pcre_get_named_substring(const pcre *<i>code</i>,</b>
1243 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
1244 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
1245 <b>const char **<i>stringptr</i>);</b>
1246 </P>
1247 <P>
1248 To extract a substring by name, you first have to find associated number.
1249 For example, for this pattern
1250 <pre>
1251 (a+)b(?&#60;xxx&#62;\d+)...
1252 </pre>
1253 the number of the subpattern called "xxx" is 2. You can find the number from
1254 the name by calling <b>pcre_get_stringnumber()</b>. The first argument is the
1255 compiled pattern, and the second is the name. The yield of the function is the
1256 subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no subpattern of
1257 that name.
1258 </P>
1259 <P>
1260 Given the number, you can extract the substring directly, or use one of the
1261 functions described in the previous section. For convenience, there are also
1262 two functions that do the whole job.
1263 </P>
1264 <P>
1265 Most of the arguments of <i>pcre_copy_named_substring()</i> and
1266 <i>pcre_get_named_substring()</i> are the same as those for the similarly named
1267 functions that extract by number. As these are described in the previous
1268 section, they are not re-described here. There are just two differences:
1269 </P>
1270 <P>
1271 First, instead of a substring number, a substring name is given. Second, there
1272 is an extra argument, given at the start, which is a pointer to the compiled
1273 pattern. This is needed in order to gain access to the name-to-number
1274 translation table.
1275 </P>
1276 <P>
1277 These functions call <b>pcre_get_stringnumber()</b>, and if it succeeds, they
1278 then call <i>pcre_copy_substring()</i> or <i>pcre_get_substring()</i>, as
1279 appropriate.
1280 </P>
1281 <P>
1282 Last updated: 09 September 2004
1283 <br>
1284 Copyright &copy; 1997-2004 University of Cambridge.
1285 <p>
1286 Return to the <a href="index.html">PCRE index page</a>.
1287 </p>

webmaster@exim.org
ViewVC Help
Powered by ViewVC 1.1.12