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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">NEWLINES</a>
19 <li><a name="TOC4" href="#SEC4">MULTITHREADING</a>
21 <li><a name="TOC6" href="#SEC6">CHECKING BUILD-TIME OPTIONS</a>
22 <li><a name="TOC7" href="#SEC7">COMPILING A PATTERN</a>
23 <li><a name="TOC8" href="#SEC8">COMPILATION ERROR CODES</a>
24 <li><a name="TOC9" href="#SEC9">STUDYING A PATTERN</a>
25 <li><a name="TOC10" href="#SEC10">LOCALE SUPPORT</a>
26 <li><a name="TOC11" href="#SEC11">INFORMATION ABOUT A PATTERN</a>
27 <li><a name="TOC12" href="#SEC12">OBSOLETE INFO FUNCTION</a>
28 <li><a name="TOC13" href="#SEC13">REFERENCE COUNTS</a>
32 <li><a name="TOC17" href="#SEC17">DUPLICATE SUBPATTERN NAMES</a>
33 <li><a name="TOC18" href="#SEC18">FINDING ALL POSSIBLE MATCHES</a>
35 <li><a name="TOC20" href="#SEC20">SEE ALSO</a>
36 <li><a name="TOC21" href="#SEC21">AUTHOR</a>
37 <li><a name="TOC22" href="#SEC22">REVISION</a>
38 </ul>
39 <br><a name="SEC1" href="#TOC1">PCRE NATIVE API</a><br>
40 <P>
41 <b>#include &#60;pcre.h&#62;</b>
42 </P>
43 <P>
44 <b>pcre *pcre_compile(const char *<i>pattern</i>, int <i>options</i>,</b>
45 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
46 <b>const unsigned char *<i>tableptr</i>);</b>
47 </P>
48 <P>
49 <b>pcre *pcre_compile2(const char *<i>pattern</i>, int <i>options</i>,</b>
50 <b>int *<i>errorcodeptr</i>,</b>
51 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
52 <b>const unsigned char *<i>tableptr</i>);</b>
53 </P>
54 <P>
55 <b>pcre_extra *pcre_study(const pcre *<i>code</i>, int <i>options</i>,</b>
56 <b>const char **<i>errptr</i>);</b>
57 </P>
58 <P>
59 <b>int pcre_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
60 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
61 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>);</b>
62 </P>
63 <P>
64 <b>int pcre_dfa_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
65 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
66 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>,</b>
67 <b>int *<i>workspace</i>, int <i>wscount</i>);</b>
68 </P>
69 <P>
70 <b>int pcre_copy_named_substring(const pcre *<i>code</i>,</b>
71 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
72 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
73 <b>char *<i>buffer</i>, int <i>buffersize</i>);</b>
74 </P>
75 <P>
76 <b>int pcre_copy_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
77 <b>int <i>stringcount</i>, int <i>stringnumber</i>, char *<i>buffer</i>,</b>
78 <b>int <i>buffersize</i>);</b>
79 </P>
80 <P>
81 <b>int pcre_get_named_substring(const pcre *<i>code</i>,</b>
82 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
83 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
84 <b>const char **<i>stringptr</i>);</b>
85 </P>
86 <P>
87 <b>int pcre_get_stringnumber(const pcre *<i>code</i>,</b>
88 <b>const char *<i>name</i>);</b>
89 </P>
90 <P>
91 <b>int pcre_get_stringtable_entries(const pcre *<i>code</i>,</b>
92 <b>const char *<i>name</i>, char **<i>first</i>, char **<i>last</i>);</b>
93 </P>
94 <P>
95 <b>int pcre_get_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
96 <b>int <i>stringcount</i>, int <i>stringnumber</i>,</b>
97 <b>const char **<i>stringptr</i>);</b>
98 </P>
99 <P>
100 <b>int pcre_get_substring_list(const char *<i>subject</i>,</b>
101 <b>int *<i>ovector</i>, int <i>stringcount</i>, const char ***<i>listptr</i>);</b>
102 </P>
103 <P>
104 <b>void pcre_free_substring(const char *<i>stringptr</i>);</b>
105 </P>
106 <P>
107 <b>void pcre_free_substring_list(const char **<i>stringptr</i>);</b>
108 </P>
109 <P>
110 <b>const unsigned char *pcre_maketables(void);</b>
111 </P>
112 <P>
113 <b>int pcre_fullinfo(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
114 <b>int <i>what</i>, void *<i>where</i>);</b>
115 </P>
116 <P>
117 <b>int pcre_info(const pcre *<i>code</i>, int *<i>optptr</i>, int</b>
118 <b>*<i>firstcharptr</i>);</b>
119 </P>
120 <P>
121 <b>int pcre_refcount(pcre *<i>code</i>, int <i>adjust</i>);</b>
122 </P>
123 <P>
124 <b>int pcre_config(int <i>what</i>, void *<i>where</i>);</b>
125 </P>
126 <P>
127 <b>char *pcre_version(void);</b>
128 </P>
129 <P>
130 <b>void *(*pcre_malloc)(size_t);</b>
131 </P>
132 <P>
133 <b>void (*pcre_free)(void *);</b>
134 </P>
135 <P>
136 <b>void *(*pcre_stack_malloc)(size_t);</b>
137 </P>
138 <P>
139 <b>void (*pcre_stack_free)(void *);</b>
140 </P>
141 <P>
142 <b>int (*pcre_callout)(pcre_callout_block *);</b>
143 </P>
144 <br><a name="SEC2" href="#TOC1">PCRE API OVERVIEW</a><br>
145 <P>
146 PCRE has its own native API, which is described in this document. There are
147 also some wrapper functions that correspond to the POSIX regular expression
148 API. These are described in the
149 <a href="pcreposix.html"><b>pcreposix</b></a>
150 documentation. Both of these APIs define a set of C function calls. A C++
151 wrapper is distributed with PCRE. It is documented in the
152 <a href="pcrecpp.html"><b>pcrecpp</b></a>
153 page.
154 </P>
155 <P>
156 The native API C function prototypes are defined in the header file
157 <b>pcre.h</b>, and on Unix systems the library itself is called <b>libpcre</b>.
158 It can normally be accessed by adding <b>-lpcre</b> to the command for linking
159 an application that uses PCRE. The header file defines the macros PCRE_MAJOR
160 and PCRE_MINOR to contain the major and minor release numbers for the library.
161 Applications can use these to include support for different releases of PCRE.
162 </P>
163 <P>
164 In a Windows environment, if you want to statically link an application program
165 against a non-dll <b>pcre.a</b> file, you must define PCRE_STATIC before
166 including <b>pcre.h</b> or <b>pcrecpp.h</b>, because otherwise the
167 <b>pcre_malloc()</b> and <b>pcre_free()</b> exported functions will be declared
168 <b>__declspec(dllimport)</b>, with unwanted results.
169 </P>
170 <P>
171 The functions <b>pcre_compile()</b>, <b>pcre_compile2()</b>, <b>pcre_study()</b>,
172 and <b>pcre_exec()</b> are used for compiling and matching regular expressions
173 in a Perl-compatible manner. A sample program that demonstrates the simplest
174 way of using them is provided in the file called <i>pcredemo.c</i> in the PCRE
175 source distribution. A listing of this program is given in the
176 <a href="pcredemo.html"><b>pcredemo</b></a>
177 documentation, and the
178 <a href="pcresample.html"><b>pcresample</b></a>
179 documentation describes how to compile and run it.
180 </P>
181 <P>
182 A second matching function, <b>pcre_dfa_exec()</b>, which is not
183 Perl-compatible, is also provided. This uses a different algorithm for the
184 matching. The alternative algorithm finds all possible matches (at a given
185 point in the subject), and scans the subject just once (unless there are
186 lookbehind assertions). However, this algorithm does not return captured
187 substrings. A description of the two matching algorithms and their advantages
188 and disadvantages is given in the
189 <a href="pcrematching.html"><b>pcrematching</b></a>
190 documentation.
191 </P>
192 <P>
193 In addition to the main compiling and matching functions, there are convenience
194 functions for extracting captured substrings from a subject string that is
195 matched by <b>pcre_exec()</b>. They are:
196 <pre>
197 <b>pcre_copy_substring()</b>
198 <b>pcre_copy_named_substring()</b>
199 <b>pcre_get_substring()</b>
200 <b>pcre_get_named_substring()</b>
201 <b>pcre_get_substring_list()</b>
202 <b>pcre_get_stringnumber()</b>
203 <b>pcre_get_stringtable_entries()</b>
204 </pre>
205 <b>pcre_free_substring()</b> and <b>pcre_free_substring_list()</b> are also
206 provided, to free the memory used for extracted strings.
207 </P>
208 <P>
209 The function <b>pcre_maketables()</b> is used to build a set of character tables
210 in the current locale for passing to <b>pcre_compile()</b>, <b>pcre_exec()</b>,
211 or <b>pcre_dfa_exec()</b>. This is an optional facility that is provided for
212 specialist use. Most commonly, no special tables are passed, in which case
213 internal tables that are generated when PCRE is built are used.
214 </P>
215 <P>
216 The function <b>pcre_fullinfo()</b> is used to find out information about a
217 compiled pattern; <b>pcre_info()</b> is an obsolete version that returns only
218 some of the available information, but is retained for backwards compatibility.
219 The function <b>pcre_version()</b> returns a pointer to a string containing the
220 version of PCRE and its date of release.
221 </P>
222 <P>
223 The function <b>pcre_refcount()</b> maintains a reference count in a data block
224 containing a compiled pattern. This is provided for the benefit of
225 object-oriented applications.
226 </P>
227 <P>
228 The global variables <b>pcre_malloc</b> and <b>pcre_free</b> initially contain
229 the entry points of the standard <b>malloc()</b> and <b>free()</b> functions,
230 respectively. PCRE calls the memory management functions via these variables,
231 so a calling program can replace them if it wishes to intercept the calls. This
232 should be done before calling any PCRE functions.
233 </P>
234 <P>
235 The global variables <b>pcre_stack_malloc</b> and <b>pcre_stack_free</b> are also
236 indirections to memory management functions. These special functions are used
237 only when PCRE is compiled to use the heap for remembering data, instead of
238 recursive function calls, when running the <b>pcre_exec()</b> function. See the
239 <a href="pcrebuild.html"><b>pcrebuild</b></a>
240 documentation for details of how to do this. It is a non-standard way of
241 building PCRE, for use in environments that have limited stacks. Because of the
242 greater use of memory management, it runs more slowly. Separate functions are
243 provided so that special-purpose external code can be used for this case. When
244 used, these functions are always called in a stack-like manner (last obtained,
245 first freed), and always for memory blocks of the same size. There is a
246 discussion about PCRE's stack usage in the
247 <a href="pcrestack.html"><b>pcrestack</b></a>
248 documentation.
249 </P>
250 <P>
251 The global variable <b>pcre_callout</b> initially contains NULL. It can be set
252 by the caller to a "callout" function, which PCRE will then call at specified
253 points during a matching operation. Details are given in the
254 <a href="pcrecallout.html"><b>pcrecallout</b></a>
255 documentation.
256 <a name="newlines"></a></P>
257 <br><a name="SEC3" href="#TOC1">NEWLINES</a><br>
258 <P>
259 PCRE supports five different conventions for indicating line breaks in
260 strings: a single CR (carriage return) character, a single LF (linefeed)
261 character, the two-character sequence CRLF, any of the three preceding, or any
262 Unicode newline sequence. The Unicode newline sequences are the three just
263 mentioned, plus the single characters VT (vertical tab, U+000B), FF (formfeed,
264 U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS
265 (paragraph separator, U+2029).
266 </P>
267 <P>
268 Each of the first three conventions is used by at least one operating system as
269 its standard newline sequence. When PCRE is built, a default can be specified.
270 The default default is LF, which is the Unix standard. When PCRE is run, the
271 default can be overridden, either when a pattern is compiled, or when it is
272 matched.
273 </P>
274 <P>
275 At compile time, the newline convention can be specified by the <i>options</i>
276 argument of <b>pcre_compile()</b>, or it can be specified by special text at the
277 start of the pattern itself; this overrides any other settings. See the
278 <a href="pcrepattern.html"><b>pcrepattern</b></a>
279 page for details of the special character sequences.
280 </P>
281 <P>
282 In the PCRE documentation the word "newline" is used to mean "the character or
283 pair of characters that indicate a line break". The choice of newline
284 convention affects the handling of the dot, circumflex, and dollar
285 metacharacters, the handling of #-comments in /x mode, and, when CRLF is a
286 recognized line ending sequence, the match position advancement for a
287 non-anchored pattern. There is more detail about this in the
288 <a href="#execoptions">section on <b>pcre_exec()</b> options</a>
289 below.
290 </P>
291 <P>
292 The choice of newline convention does not affect the interpretation of
293 the \n or \r escape sequences, nor does it affect what \R matches, which is
294 controlled in a similar way, but by separate options.
295 </P>
296 <br><a name="SEC4" href="#TOC1">MULTITHREADING</a><br>
297 <P>
298 The PCRE functions can be used in multi-threading applications, with the
299 proviso that the memory management functions pointed to by <b>pcre_malloc</b>,
300 <b>pcre_free</b>, <b>pcre_stack_malloc</b>, and <b>pcre_stack_free</b>, and the
301 callout function pointed to by <b>pcre_callout</b>, are shared by all threads.
302 </P>
303 <P>
304 The compiled form of a regular expression is not altered during matching, so
305 the same compiled pattern can safely be used by several threads at once.
306 </P>
307 <br><a name="SEC5" href="#TOC1">SAVING PRECOMPILED PATTERNS FOR LATER USE</a><br>
308 <P>
309 The compiled form of a regular expression can be saved and re-used at a later
310 time, possibly by a different program, and even on a host other than the one on
311 which it was compiled. Details are given in the
312 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
313 documentation. However, compiling a regular expression with one version of PCRE
314 for use with a different version is not guaranteed to work and may cause
315 crashes.
316 </P>
317 <br><a name="SEC6" href="#TOC1">CHECKING BUILD-TIME OPTIONS</a><br>
318 <P>
319 <b>int pcre_config(int <i>what</i>, void *<i>where</i>);</b>
320 </P>
321 <P>
322 The function <b>pcre_config()</b> makes it possible for a PCRE client to
323 discover which optional features have been compiled into the PCRE library. The
324 <a href="pcrebuild.html"><b>pcrebuild</b></a>
325 documentation has more details about these optional features.
326 </P>
327 <P>
328 The first argument for <b>pcre_config()</b> is an integer, specifying which
329 information is required; the second argument is a pointer to a variable into
330 which the information is placed. The following information is available:
331 <pre>
333 </pre>
334 The output is an integer that is set to one if UTF-8 support is available;
335 otherwise it is set to zero.
336 <pre>
338 </pre>
339 The output is an integer that is set to one if support for Unicode character
340 properties is available; otherwise it is set to zero.
341 <pre>
343 </pre>
344 The output is an integer whose value specifies the default character sequence
345 that is recognized as meaning "newline". The four values that are supported
346 are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF, and -1 for ANY.
347 Though they are derived from ASCII, the same values are returned in EBCDIC
348 environments. The default should normally correspond to the standard sequence
349 for your operating system.
350 <pre>
352 </pre>
353 The output is an integer whose value indicates what character sequences the \R
354 escape sequence matches by default. A value of 0 means that \R matches any
355 Unicode line ending sequence; a value of 1 means that \R matches only CR, LF,
356 or CRLF. The default can be overridden when a pattern is compiled or matched.
357 <pre>
359 </pre>
360 The output is an integer that contains the number of bytes used for internal
361 linkage in compiled regular expressions. The value is 2, 3, or 4. Larger values
362 allow larger regular expressions to be compiled, at the expense of slower
363 matching. The default value of 2 is sufficient for all but the most massive
364 patterns, since it allows the compiled pattern to be up to 64K in size.
365 <pre>
367 </pre>
368 The output is an integer that contains the threshold above which the POSIX
369 interface uses <b>malloc()</b> for output vectors. Further details are given in
370 the
371 <a href="pcreposix.html"><b>pcreposix</b></a>
372 documentation.
373 <pre>
375 </pre>
376 The output is a long integer that gives the default limit for the number of
377 internal matching function calls in a <b>pcre_exec()</b> execution. Further
378 details are given with <b>pcre_exec()</b> below.
379 <pre>
381 </pre>
382 The output is a long integer that gives the default limit for the depth of
383 recursion when calling the internal matching function in a <b>pcre_exec()</b>
384 execution. Further details are given with <b>pcre_exec()</b> below.
385 <pre>
387 </pre>
388 The output is an integer that is set to one if internal recursion when running
389 <b>pcre_exec()</b> is implemented by recursive function calls that use the stack
390 to remember their state. This is the usual way that PCRE is compiled. The
391 output is zero if PCRE was compiled to use blocks of data on the heap instead
392 of recursive function calls. In this case, <b>pcre_stack_malloc</b> and
393 <b>pcre_stack_free</b> are called to manage memory blocks on the heap, thus
394 avoiding the use of the stack.
395 </P>
396 <br><a name="SEC7" href="#TOC1">COMPILING A PATTERN</a><br>
397 <P>
398 <b>pcre *pcre_compile(const char *<i>pattern</i>, int <i>options</i>,</b>
399 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
400 <b>const unsigned char *<i>tableptr</i>);</b>
401 <b>pcre *pcre_compile2(const char *<i>pattern</i>, int <i>options</i>,</b>
402 <b>int *<i>errorcodeptr</i>,</b>
403 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
404 <b>const unsigned char *<i>tableptr</i>);</b>
405 </P>
406 <P>
407 Either of the functions <b>pcre_compile()</b> or <b>pcre_compile2()</b> can be
408 called to compile a pattern into an internal form. The only difference between
409 the two interfaces is that <b>pcre_compile2()</b> has an additional argument,
410 <i>errorcodeptr</i>, via which a numerical error code can be returned. To avoid
411 too much repetition, we refer just to <b>pcre_compile()</b> below, but the
412 information applies equally to <b>pcre_compile2()</b>.
413 </P>
414 <P>
415 The pattern is a C string terminated by a binary zero, and is passed in the
416 <i>pattern</i> argument. A pointer to a single block of memory that is obtained
417 via <b>pcre_malloc</b> is returned. This contains the compiled code and related
418 data. The <b>pcre</b> type is defined for the returned block; this is a typedef
419 for a structure whose contents are not externally defined. It is up to the
420 caller to free the memory (via <b>pcre_free</b>) when it is no longer required.
421 </P>
422 <P>
423 Although the compiled code of a PCRE regex is relocatable, that is, it does not
424 depend on memory location, the complete <b>pcre</b> data block is not
425 fully relocatable, because it may contain a copy of the <i>tableptr</i>
426 argument, which is an address (see below).
427 </P>
428 <P>
429 The <i>options</i> argument contains various bit settings that affect the
430 compilation. It should be zero if no options are required. The available
431 options are described below. Some of them (in particular, those that are
432 compatible with Perl, but some others as well) can also be set and unset from
433 within the pattern (see the detailed description in the
434 <a href="pcrepattern.html"><b>pcrepattern</b></a>
435 documentation). For those options that can be different in different parts of
436 the pattern, the contents of the <i>options</i> argument specifies their
437 settings at the start of compilation and execution. The PCRE_ANCHORED,
438 PCRE_BSR_<i>xxx</i>, and PCRE_NEWLINE_<i>xxx</i> options can be set at the time
439 of matching as well as at compile time.
440 </P>
441 <P>
442 If <i>errptr</i> is NULL, <b>pcre_compile()</b> returns NULL immediately.
443 Otherwise, if compilation of a pattern fails, <b>pcre_compile()</b> returns
444 NULL, and sets the variable pointed to by <i>errptr</i> to point to a textual
445 error message. This is a static string that is part of the library. You must
446 not try to free it. The byte offset from the start of the pattern to the
447 character that was being processed when the error was discovered is placed in
448 the variable pointed to by <i>erroffset</i>, which must not be NULL. If it is,
449 an immediate error is given. Some errors are not detected until checks are
450 carried out when the whole pattern has been scanned; in this case the offset is
451 set to the end of the pattern.
452 </P>
453 <P>
454 If <b>pcre_compile2()</b> is used instead of <b>pcre_compile()</b>, and the
455 <i>errorcodeptr</i> argument is not NULL, a non-zero error code number is
456 returned via this argument in the event of an error. This is in addition to the
457 textual error message. Error codes and messages are listed below.
458 </P>
459 <P>
460 If the final argument, <i>tableptr</i>, is NULL, PCRE uses a default set of
461 character tables that are built when PCRE is compiled, using the default C
462 locale. Otherwise, <i>tableptr</i> must be an address that is the result of a
463 call to <b>pcre_maketables()</b>. This value is stored with the compiled
464 pattern, and used again by <b>pcre_exec()</b>, unless another table pointer is
465 passed to it. For more discussion, see the section on locale support below.
466 </P>
467 <P>
468 This code fragment shows a typical straightforward call to <b>pcre_compile()</b>:
469 <pre>
470 pcre *re;
471 const char *error;
472 int erroffset;
473 re = pcre_compile(
474 "^A.*Z", /* the pattern */
475 0, /* default options */
476 &error, /* for error message */
477 &erroffset, /* for error offset */
478 NULL); /* use default character tables */
479 </pre>
480 The following names for option bits are defined in the <b>pcre.h</b> header
481 file:
482 <pre>
484 </pre>
485 If this bit is set, the pattern is forced to be "anchored", that is, it is
486 constrained to match only at the first matching point in the string that is
487 being searched (the "subject string"). This effect can also be achieved by
488 appropriate constructs in the pattern itself, which is the only way to do it in
489 Perl.
490 <pre>
492 </pre>
493 If this bit is set, <b>pcre_compile()</b> automatically inserts callout items,
494 all with number 255, before each pattern item. For discussion of the callout
495 facility, see the
496 <a href="pcrecallout.html"><b>pcrecallout</b></a>
497 documentation.
498 <pre>
501 </pre>
502 These options (which are mutually exclusive) control what the \R escape
503 sequence matches. The choice is either to match only CR, LF, or CRLF, or to
504 match any Unicode newline sequence. The default is specified when PCRE is
505 built. It can be overridden from within the pattern, or by setting an option
506 when a compiled pattern is matched.
507 <pre>
509 </pre>
510 If this bit is set, letters in the pattern match both upper and lower case
511 letters. It is equivalent to Perl's /i option, and it can be changed within a
512 pattern by a (?i) option setting. In UTF-8 mode, PCRE always understands the
513 concept of case for characters whose values are less than 128, so caseless
514 matching is always possible. For characters with higher values, the concept of
515 case is supported if PCRE is compiled with Unicode property support, but not
516 otherwise. If you want to use caseless matching for characters 128 and above,
517 you must ensure that PCRE is compiled with Unicode property support as well as
518 with UTF-8 support.
519 <pre>
521 </pre>
522 If this bit is set, a dollar metacharacter in the pattern matches only at the
523 end of the subject string. Without this option, a dollar also matches
524 immediately before a newline at the end of the string (but not before any other
525 newlines). The PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is set.
526 There is no equivalent to this option in Perl, and no way to set it within a
527 pattern.
528 <pre>
530 </pre>
531 If this bit is set, a dot metacharater in the pattern matches all characters,
532 including those that indicate newline. Without it, a dot does not match when
533 the current position is at a newline. This option is equivalent to Perl's /s
534 option, and it can be changed within a pattern by a (?s) option setting. A
535 negative class such as [^a] always matches newline characters, independent of
536 the setting of this option.
537 <pre>
539 </pre>
540 If this bit is set, names used to identify capturing subpatterns need not be
541 unique. This can be helpful for certain types of pattern when it is known that
542 only one instance of the named subpattern can ever be matched. There are more
543 details of named subpatterns below; see also the
544 <a href="pcrepattern.html"><b>pcrepattern</b></a>
545 documentation.
546 <pre>
548 </pre>
549 If this bit is set, whitespace data characters in the pattern are totally
550 ignored except when escaped or inside a character class. Whitespace does not
551 include the VT character (code 11). In addition, characters between an
552 unescaped # outside a character class and the next newline, inclusive, are also
553 ignored. This is equivalent to Perl's /x option, and it can be changed within a
554 pattern by a (?x) option setting.
555 </P>
556 <P>
557 This option makes it possible to include comments inside complicated patterns.
558 Note, however, that this applies only to data characters. Whitespace characters
559 may never appear within special character sequences in a pattern, for example
560 within the sequence (?( which introduces a conditional subpattern.
561 <pre>
563 </pre>
564 This option was invented in order to turn on additional functionality of PCRE
565 that is incompatible with Perl, but it is currently of very little use. When
566 set, any backslash in a pattern that is followed by a letter that has no
567 special meaning causes an error, thus reserving these combinations for future
568 expansion. By default, as in Perl, a backslash followed by a letter with no
569 special meaning is treated as a literal. (Perl can, however, be persuaded to
570 give an error for this, by running it with the -w option.) There are at present
571 no other features controlled by this option. It can also be set by a (?X)
572 option setting within a pattern.
573 <pre>
575 </pre>
576 If this option is set, an unanchored pattern is required to match before or at
577 the first newline in the subject string, though the matched text may continue
578 over the newline.
579 <pre>
581 </pre>
582 If this option is set, PCRE's behaviour is changed in some ways so that it is
583 compatible with JavaScript rather than Perl. The changes are as follows:
584 </P>
585 <P>
586 (1) A lone closing square bracket in a pattern causes a compile-time error,
587 because this is illegal in JavaScript (by default it is treated as a data
588 character). Thus, the pattern AB]CD becomes illegal when this option is set.
589 </P>
590 <P>
591 (2) At run time, a back reference to an unset subpattern group matches an empty
592 string (by default this causes the current matching alternative to fail). A
593 pattern such as (\1)(a) succeeds when this option is set (assuming it can find
594 an "a" in the subject), whereas it fails by default, for Perl compatibility.
595 <pre>
597 </pre>
598 By default, PCRE treats the subject string as consisting of a single line of
599 characters (even if it actually contains newlines). The "start of line"
600 metacharacter (^) matches only at the start of the string, while the "end of
601 line" metacharacter ($) matches only at the end of the string, or before a
602 terminating newline (unless PCRE_DOLLAR_ENDONLY is set). This is the same as
603 Perl.
604 </P>
605 <P>
606 When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs
607 match immediately following or immediately before internal newlines in the
608 subject string, respectively, as well as at the very start and end. This is
609 equivalent to Perl's /m option, and it can be changed within a pattern by a
610 (?m) option setting. If there are no newlines in a subject string, or no
611 occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no effect.
612 <pre>
618 </pre>
619 These options override the default newline definition that was chosen when PCRE
620 was built. Setting the first or the second specifies that a newline is
621 indicated by a single character (CR or LF, respectively). Setting
622 PCRE_NEWLINE_CRLF specifies that a newline is indicated by the two-character
623 CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies that any of the three
624 preceding sequences should be recognized. Setting PCRE_NEWLINE_ANY specifies
625 that any Unicode newline sequence should be recognized. The Unicode newline
626 sequences are the three just mentioned, plus the single characters VT (vertical
627 tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS (line
628 separator, U+2028), and PS (paragraph separator, U+2029). The last two are
629 recognized only in UTF-8 mode.
630 </P>
631 <P>
632 The newline setting in the options word uses three bits that are treated
633 as a number, giving eight possibilities. Currently only six are used (default
634 plus the five values above). This means that if you set more than one newline
635 option, the combination may or may not be sensible. For example,
637 other combinations may yield unused numbers and cause an error.
638 </P>
639 <P>
640 The only time that a line break is specially recognized when compiling a
641 pattern is if PCRE_EXTENDED is set, and an unescaped # outside a character
642 class is encountered. This indicates a comment that lasts until after the next
643 line break sequence. In other circumstances, line break sequences are treated
644 as literal data, except that in PCRE_EXTENDED mode, both CR and LF are treated
645 as whitespace characters and are therefore ignored.
646 </P>
647 <P>
648 The newline option that is set at compile time becomes the default that is used
649 for <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b>, but it can be overridden.
650 <pre>
652 </pre>
653 If this option is set, it disables the use of numbered capturing parentheses in
654 the pattern. Any opening parenthesis that is not followed by ? behaves as if it
655 were followed by ?: but named parentheses can still be used for capturing (and
656 they acquire numbers in the usual way). There is no equivalent of this option
657 in Perl.
658 <pre>
660 </pre>
661 This option changes the way PCRE processes \b, \d, \s, \w, and some of the
662 POSIX character classes. By default, only ASCII characters are recognized, but
663 if PCRE_UCP is set, Unicode properties are used instead to classify characters.
664 More details are given in the section on
665 <a href="pcre.html#genericchartypes">generic character types</a>
666 in the
667 <a href="pcrepattern.html"><b>pcrepattern</b></a>
668 page. If you set PCRE_UCP, matching one of the items it affects takes much
669 longer. The option is available only if PCRE has been compiled with Unicode
670 property support.
671 <pre>
673 </pre>
674 This option inverts the "greediness" of the quantifiers so that they are not
675 greedy by default, but become greedy if followed by "?". It is not compatible
676 with Perl. It can also be set by a (?U) option setting within the pattern.
677 <pre>
679 </pre>
680 This option causes PCRE to regard both the pattern and the subject as strings
681 of UTF-8 characters instead of single-byte character strings. However, it is
682 available only when PCRE is built to include UTF-8 support. If not, the use
683 of this option provokes an error. Details of how this option changes the
684 behaviour of PCRE are given in the
685 <a href="pcre.html#utf8support">section on UTF-8 support</a>
686 in the main
687 <a href="pcre.html"><b>pcre</b></a>
688 page.
689 <pre>
691 </pre>
692 When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
693 automatically checked. There is a discussion about the
694 <a href="pcre.html#utf8strings">validity of UTF-8 strings</a>
695 in the main
696 <a href="pcre.html"><b>pcre</b></a>
697 page. If an invalid UTF-8 sequence of bytes is found, <b>pcre_compile()</b>
698 returns an error. If you already know that your pattern is valid, and you want
699 to skip this check for performance reasons, you can set the PCRE_NO_UTF8_CHECK
700 option. When it is set, the effect of passing an invalid UTF-8 string as a
701 pattern is undefined. It may cause your program to crash. Note that this option
702 can also be passed to <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b>, to suppress
703 the UTF-8 validity checking of subject strings.
704 </P>
705 <br><a name="SEC8" href="#TOC1">COMPILATION ERROR CODES</a><br>
706 <P>
707 The following table lists the error codes than may be returned by
708 <b>pcre_compile2()</b>, along with the error messages that may be returned by
709 both compiling functions. As PCRE has developed, some error codes have fallen
710 out of use. To avoid confusion, they have not been re-used.
711 <pre>
712 0 no error
713 1 \ at end of pattern
714 2 \c at end of pattern
715 3 unrecognized character follows \
716 4 numbers out of order in {} quantifier
717 5 number too big in {} quantifier
718 6 missing terminating ] for character class
719 7 invalid escape sequence in character class
720 8 range out of order in character class
721 9 nothing to repeat
722 10 [this code is not in use]
723 11 internal error: unexpected repeat
724 12 unrecognized character after (? or (?-
725 13 POSIX named classes are supported only within a class
726 14 missing )
727 15 reference to non-existent subpattern
728 16 erroffset passed as NULL
729 17 unknown option bit(s) set
730 18 missing ) after comment
731 19 [this code is not in use]
732 20 regular expression is too large
733 21 failed to get memory
734 22 unmatched parentheses
735 23 internal error: code overflow
736 24 unrecognized character after (?&#60;
737 25 lookbehind assertion is not fixed length
738 26 malformed number or name after (?(
739 27 conditional group contains more than two branches
740 28 assertion expected after (?(
741 29 (?R or (?[+-]digits must be followed by )
742 30 unknown POSIX class name
743 31 POSIX collating elements are not supported
744 32 this version of PCRE is not compiled with PCRE_UTF8 support
745 33 [this code is not in use]
746 34 character value in \x{...} sequence is too large
747 35 invalid condition (?(0)
748 36 \C not allowed in lookbehind assertion
749 37 PCRE does not support \L, \l, \N, \U, or \u
750 38 number after (?C is &#62; 255
751 39 closing ) for (?C expected
752 40 recursive call could loop indefinitely
753 41 unrecognized character after (?P
754 42 syntax error in subpattern name (missing terminator)
755 43 two named subpatterns have the same name
756 44 invalid UTF-8 string
757 45 support for \P, \p, and \X has not been compiled
758 46 malformed \P or \p sequence
759 47 unknown property name after \P or \p
760 48 subpattern name is too long (maximum 32 characters)
761 49 too many named subpatterns (maximum 10000)
762 50 [this code is not in use]
763 51 octal value is greater than \377 (not in UTF-8 mode)
764 52 internal error: overran compiling workspace
765 53 internal error: previously-checked referenced subpattern
766 not found
767 54 DEFINE group contains more than one branch
768 55 repeating a DEFINE group is not allowed
769 56 inconsistent NEWLINE options
770 57 \g is not followed by a braced, angle-bracketed, or quoted
771 name/number or by a plain number
772 58 a numbered reference must not be zero
773 59 an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT)
774 60 (*VERB) not recognized
775 61 number is too big
776 62 subpattern name expected
777 63 digit expected after (?+
778 64 ] is an invalid data character in JavaScript compatibility mode
779 65 different names for subpatterns of the same number are
780 not allowed
781 66 (*MARK) must have an argument
782 67 this version of PCRE is not compiled with PCRE_UCP support
783 </pre>
784 The numbers 32 and 10000 in errors 48 and 49 are defaults; different values may
785 be used if the limits were changed when PCRE was built.
786 </P>
787 <br><a name="SEC9" href="#TOC1">STUDYING A PATTERN</a><br>
788 <P>
789 <b>pcre_extra *pcre_study(const pcre *<i>code</i>, int <i>options</i></b>
790 <b>const char **<i>errptr</i>);</b>
791 </P>
792 <P>
793 If a compiled pattern is going to be used several times, it is worth spending
794 more time analyzing it in order to speed up the time taken for matching. The
795 function <b>pcre_study()</b> takes a pointer to a compiled pattern as its first
796 argument. If studying the pattern produces additional information that will
797 help speed up matching, <b>pcre_study()</b> returns a pointer to a
798 <b>pcre_extra</b> block, in which the <i>study_data</i> field points to the
799 results of the study.
800 </P>
801 <P>
802 The returned value from <b>pcre_study()</b> can be passed directly to
803 <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b>. However, a <b>pcre_extra</b> block
804 also contains other fields that can be set by the caller before the block is
805 passed; these are described
806 <a href="#extradata">below</a>
807 in the section on matching a pattern.
808 </P>
809 <P>
810 If studying the pattern does not produce any useful information,
811 <b>pcre_study()</b> returns NULL. In that circumstance, if the calling program
812 wants to pass any of the other fields to <b>pcre_exec()</b> or
813 <b>pcre_dfa_exec()</b>, it must set up its own <b>pcre_extra</b> block.
814 </P>
815 <P>
816 The second argument of <b>pcre_study()</b> contains option bits. At present, no
817 options are defined, and this argument should always be zero.
818 </P>
819 <P>
820 The third argument for <b>pcre_study()</b> is a pointer for an error message. If
821 studying succeeds (even if no data is returned), the variable it points to is
822 set to NULL. Otherwise it is set to point to a textual error message. This is a
823 static string that is part of the library. You must not try to free it. You
824 should test the error pointer for NULL after calling <b>pcre_study()</b>, to be
825 sure that it has run successfully.
826 </P>
827 <P>
828 This is a typical call to <b>pcre_study</b>():
829 <pre>
830 pcre_extra *pe;
831 pe = pcre_study(
832 re, /* result of pcre_compile() */
833 0, /* no options exist */
834 &error); /* set to NULL or points to a message */
835 </pre>
836 Studying a pattern does two things: first, a lower bound for the length of
837 subject string that is needed to match the pattern is computed. This does not
838 mean that there are any strings of that length that match, but it does
839 guarantee that no shorter strings match. The value is used by
840 <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b> to avoid wasting time by trying to
841 match strings that are shorter than the lower bound. You can find out the value
842 in a calling program via the <b>pcre_fullinfo()</b> function.
843 </P>
844 <P>
845 Studying a pattern is also useful for non-anchored patterns that do not have a
846 single fixed starting character. A bitmap of possible starting bytes is
847 created. This speeds up finding a position in the subject at which to start
848 matching.
849 </P>
850 <P>
851 The two optimizations just described can be disabled by setting the
852 PCRE_NO_START_OPTIMIZE option when calling <b>pcre_exec()</b> or
853 <b>pcre_dfa_exec()</b>. You might want to do this if your pattern contains
854 callouts, or make use of (*MARK), and you make use of these in cases where
855 matching fails. See the discussion of PCRE_NO_START_OPTIMIZE
856 <a href="#execoptions">below.</a>
857 <a name="localesupport"></a></P>
858 <br><a name="SEC10" href="#TOC1">LOCALE SUPPORT</a><br>
859 <P>
860 PCRE handles caseless matching, and determines whether characters are letters,
861 digits, or whatever, by reference to a set of tables, indexed by character
862 value. When running in UTF-8 mode, this applies only to characters with codes
863 less than 128. By default, higher-valued codes never match escapes such as \w
864 or \d, but they can be tested with \p if PCRE is built with Unicode character
865 property support. Alternatively, the PCRE_UCP option can be set at compile
866 time; this causes \w and friends to use Unicode property support instead of
867 built-in tables. The use of locales with Unicode is discouraged. If you are
868 handling characters with codes greater than 128, you should either use UTF-8
869 and Unicode, or use locales, but not try to mix the two.
870 </P>
871 <P>
872 PCRE contains an internal set of tables that are used when the final argument
873 of <b>pcre_compile()</b> is NULL. These are sufficient for many applications.
874 Normally, the internal tables recognize only ASCII characters. However, when
875 PCRE is built, it is possible to cause the internal tables to be rebuilt in the
876 default "C" locale of the local system, which may cause them to be different.
877 </P>
878 <P>
879 The internal tables can always be overridden by tables supplied by the
880 application that calls PCRE. These may be created in a different locale from
881 the default. As more and more applications change to using Unicode, the need
882 for this locale support is expected to die away.
883 </P>
884 <P>
885 External tables are built by calling the <b>pcre_maketables()</b> function,
886 which has no arguments, in the relevant locale. The result can then be passed
887 to <b>pcre_compile()</b> or <b>pcre_exec()</b> as often as necessary. For
888 example, to build and use tables that are appropriate for the French locale
889 (where accented characters with values greater than 128 are treated as letters),
890 the following code could be used:
891 <pre>
892 setlocale(LC_CTYPE, "fr_FR");
893 tables = pcre_maketables();
894 re = pcre_compile(..., tables);
895 </pre>
896 The locale name "fr_FR" is used on Linux and other Unix-like systems; if you
897 are using Windows, the name for the French locale is "french".
898 </P>
899 <P>
900 When <b>pcre_maketables()</b> runs, the tables are built in memory that is
901 obtained via <b>pcre_malloc</b>. It is the caller's responsibility to ensure
902 that the memory containing the tables remains available for as long as it is
903 needed.
904 </P>
905 <P>
906 The pointer that is passed to <b>pcre_compile()</b> is saved with the compiled
907 pattern, and the same tables are used via this pointer by <b>pcre_study()</b>
908 and normally also by <b>pcre_exec()</b>. Thus, by default, for any single
909 pattern, compilation, studying and matching all happen in the same locale, but
910 different patterns can be compiled in different locales.
911 </P>
912 <P>
913 It is possible to pass a table pointer or NULL (indicating the use of the
914 internal tables) to <b>pcre_exec()</b>. Although not intended for this purpose,
915 this facility could be used to match a pattern in a different locale from the
916 one in which it was compiled. Passing table pointers at run time is discussed
917 below in the section on matching a pattern.
918 </P>
919 <br><a name="SEC11" href="#TOC1">INFORMATION ABOUT A PATTERN</a><br>
920 <P>
921 <b>int pcre_fullinfo(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
922 <b>int <i>what</i>, void *<i>where</i>);</b>
923 </P>
924 <P>
925 The <b>pcre_fullinfo()</b> function returns information about a compiled
926 pattern. It replaces the obsolete <b>pcre_info()</b> function, which is
927 nevertheless retained for backwards compability (and is documented below).
928 </P>
929 <P>
930 The first argument for <b>pcre_fullinfo()</b> is a pointer to the compiled
931 pattern. The second argument is the result of <b>pcre_study()</b>, or NULL if
932 the pattern was not studied. The third argument specifies which piece of
933 information is required, and the fourth argument is a pointer to a variable
934 to receive the data. The yield of the function is zero for success, or one of
935 the following negative numbers:
936 <pre>
937 PCRE_ERROR_NULL the argument <i>code</i> was NULL
938 the argument <i>where</i> was NULL
939 PCRE_ERROR_BADMAGIC the "magic number" was not found
940 PCRE_ERROR_BADOPTION the value of <i>what</i> was invalid
941 </pre>
942 The "magic number" is placed at the start of each compiled pattern as an simple
943 check against passing an arbitrary memory pointer. Here is a typical call of
944 <b>pcre_fullinfo()</b>, to obtain the length of the compiled pattern:
945 <pre>
946 int rc;
947 size_t length;
948 rc = pcre_fullinfo(
949 re, /* result of pcre_compile() */
950 pe, /* result of pcre_study(), or NULL */
951 PCRE_INFO_SIZE, /* what is required */
952 &length); /* where to put the data */
953 </pre>
954 The possible values for the third argument are defined in <b>pcre.h</b>, and are
955 as follows:
956 <pre>
958 </pre>
959 Return the number of the highest back reference in the pattern. The fourth
960 argument should point to an <b>int</b> variable. Zero is returned if there are
961 no back references.
962 <pre>
964 </pre>
965 Return the number of capturing subpatterns in the pattern. The fourth argument
966 should point to an <b>int</b> variable.
967 <pre>
969 </pre>
970 Return a pointer to the internal default character tables within PCRE. The
971 fourth argument should point to an <b>unsigned char *</b> variable. This
972 information call is provided for internal use by the <b>pcre_study()</b>
973 function. External callers can cause PCRE to use its internal tables by passing
974 a NULL table pointer.
975 <pre>
977 </pre>
978 Return information about the first byte of any matched string, for a
979 non-anchored pattern. The fourth argument should point to an <b>int</b>
980 variable. (This option used to be called PCRE_INFO_FIRSTCHAR; the old name is
981 still recognized for backwards compatibility.)
982 </P>
983 <P>
984 If there is a fixed first byte, for example, from a pattern such as
985 (cat|cow|coyote), its value is returned. Otherwise, if either
986 <br>
987 <br>
988 (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
989 starts with "^", or
990 <br>
991 <br>
992 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
993 (if it were set, the pattern would be anchored),
994 <br>
995 <br>
996 -1 is returned, indicating that the pattern matches only at the start of a
997 subject string or after any newline within the string. Otherwise -2 is
998 returned. For anchored patterns, -2 is returned.
999 <pre>
1001 </pre>
1002 If the pattern was studied, and this resulted in the construction of a 256-bit
1003 table indicating a fixed set of bytes for the first byte in any matching
1004 string, a pointer to the table is returned. Otherwise NULL is returned. The
1005 fourth argument should point to an <b>unsigned char *</b> variable.
1006 <pre>
1008 </pre>
1009 Return 1 if the pattern contains any explicit matches for CR or LF characters,
1010 otherwise 0. The fourth argument should point to an <b>int</b> variable. An
1011 explicit match is either a literal CR or LF character, or \r or \n.
1012 <pre>
1014 </pre>
1015 Return 1 if the (?J) or (?-J) option setting is used in the pattern, otherwise
1016 0. The fourth argument should point to an <b>int</b> variable. (?J) and
1017 (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
1018 <pre>
1020 </pre>
1021 Return the value of the rightmost literal byte that must exist in any matched
1022 string, other than at its start, if such a byte has been recorded. The fourth
1023 argument should point to an <b>int</b> variable. If there is no such byte, -1 is
1024 returned. For anchored patterns, a last literal byte is recorded only if it
1025 follows something of variable length. For example, for the pattern
1026 /^a\d+z\d+/ the returned value is "z", but for /^a\dz\d/ the returned value
1027 is -1.
1028 <pre>
1030 </pre>
1031 If the pattern was studied and a minimum length for matching subject strings
1032 was computed, its value is returned. Otherwise the returned value is -1. The
1033 value is a number of characters, not bytes (this may be relevant in UTF-8
1034 mode). The fourth argument should point to an <b>int</b> variable. A
1035 non-negative value is a lower bound to the length of any matching string. There
1036 may not be any strings of that length that do actually match, but every string
1037 that does match is at least that long.
1038 <pre>
1042 </pre>
1043 PCRE supports the use of named as well as numbered capturing parentheses. The
1044 names are just an additional way of identifying the parentheses, which still
1045 acquire numbers. Several convenience functions such as
1046 <b>pcre_get_named_substring()</b> are provided for extracting captured
1047 substrings by name. It is also possible to extract the data directly, by first
1048 converting the name to a number in order to access the correct pointers in the
1049 output vector (described with <b>pcre_exec()</b> below). To do the conversion,
1050 you need to use the name-to-number map, which is described by these three
1051 values.
1052 </P>
1053 <P>
1054 The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives
1055 the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each
1056 entry; both of these return an <b>int</b> value. The entry size depends on the
1057 length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first
1058 entry of the table (a pointer to <b>char</b>). The first two bytes of each entry
1059 are the number of the capturing parenthesis, most significant byte first. The
1060 rest of the entry is the corresponding name, zero terminated.
1061 </P>
1062 <P>
1063 The names are in alphabetical order. Duplicate names may appear if (?| is used
1064 to create multiple groups with the same number, as described in the
1065 <a href="pcrepattern.html#dupsubpatternnumber">section on duplicate subpattern numbers</a>
1066 in the
1067 <a href="pcrepattern.html"><b>pcrepattern</b></a>
1068 page. Duplicate names for subpatterns with different numbers are permitted only
1069 if PCRE_DUPNAMES is set. In all cases of duplicate names, they appear in the
1070 table in the order in which they were found in the pattern. In the absence of
1071 (?| this is the order of increasing number; when (?| is used this is not
1072 necessarily the case because later subpatterns may have lower numbers.
1073 </P>
1074 <P>
1075 As a simple example of the name/number table, consider the following pattern
1076 (assume PCRE_EXTENDED is set, so white space - including newlines - is
1077 ignored):
1078 <pre>
1079 (?&#60;date&#62; (?&#60;year&#62;(\d\d)?\d\d) - (?&#60;month&#62;\d\d) - (?&#60;day&#62;\d\d) )
1080 </pre>
1081 There are four named subpatterns, so the table has four entries, and each entry
1082 in the table is eight bytes long. The table is as follows, with non-printing
1083 bytes shows in hexadecimal, and undefined bytes shown as ??:
1084 <pre>
1085 00 01 d a t e 00 ??
1086 00 05 d a y 00 ?? ??
1087 00 04 m o n t h 00
1088 00 02 y e a r 00 ??
1089 </pre>
1090 When writing code to extract data from named subpatterns using the
1091 name-to-number map, remember that the length of the entries is likely to be
1092 different for each compiled pattern.
1093 <pre>
1095 </pre>
1096 Return 1 if the pattern can be used for partial matching with
1097 <b>pcre_exec()</b>, otherwise 0. The fourth argument should point to an
1098 <b>int</b> variable. From release 8.00, this always returns 1, because the
1099 restrictions that previously applied to partial matching have been lifted. The
1100 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1101 documentation gives details of partial matching.
1102 <pre>
1104 </pre>
1105 Return a copy of the options with which the pattern was compiled. The fourth
1106 argument should point to an <b>unsigned long int</b> variable. These option bits
1107 are those specified in the call to <b>pcre_compile()</b>, modified by any
1108 top-level option settings at the start of the pattern itself. In other words,
1109 they are the options that will be in force when matching starts. For example,
1110 if the pattern /(?im)abc(?-i)d/ is compiled with the PCRE_EXTENDED option, the
1112 </P>
1113 <P>
1114 A pattern is automatically anchored by PCRE if all of its top-level
1115 alternatives begin with one of the following:
1116 <pre>
1117 ^ unless PCRE_MULTILINE is set
1118 \A always
1119 \G always
1120 .* if PCRE_DOTALL is set and there are no back references to the subpattern in which .* appears
1121 </pre>
1122 For such patterns, the PCRE_ANCHORED bit is set in the options returned by
1123 <b>pcre_fullinfo()</b>.
1124 <pre>
1126 </pre>
1127 Return the size of the compiled pattern, that is, the value that was passed as
1128 the argument to <b>pcre_malloc()</b> when PCRE was getting memory in which to
1129 place the compiled data. The fourth argument should point to a <b>size_t</b>
1130 variable.
1131 <pre>
1133 </pre>
1134 Return the size of the data block pointed to by the <i>study_data</i> field in
1135 a <b>pcre_extra</b> block. That is, it is the value that was passed to
1136 <b>pcre_malloc()</b> when PCRE was getting memory into which to place the data
1137 created by <b>pcre_study()</b>. If <b>pcre_extra</b> is NULL, or there is no
1138 study data, zero is returned. The fourth argument should point to a
1139 <b>size_t</b> variable.
1140 </P>
1141 <br><a name="SEC12" href="#TOC1">OBSOLETE INFO FUNCTION</a><br>
1142 <P>
1143 <b>int pcre_info(const pcre *<i>code</i>, int *<i>optptr</i>, int</b>
1144 <b>*<i>firstcharptr</i>);</b>
1145 </P>
1146 <P>
1147 The <b>pcre_info()</b> function is now obsolete because its interface is too
1148 restrictive to return all the available data about a compiled pattern. New
1149 programs should use <b>pcre_fullinfo()</b> instead. The yield of
1150 <b>pcre_info()</b> is the number of capturing subpatterns, or one of the
1151 following negative numbers:
1152 <pre>
1153 PCRE_ERROR_NULL the argument <i>code</i> was NULL
1154 PCRE_ERROR_BADMAGIC the "magic number" was not found
1155 </pre>
1156 If the <i>optptr</i> argument is not NULL, a copy of the options with which the
1157 pattern was compiled is placed in the integer it points to (see
1158 PCRE_INFO_OPTIONS above).
1159 </P>
1160 <P>
1161 If the pattern is not anchored and the <i>firstcharptr</i> argument is not NULL,
1162 it is used to pass back information about the first character of any matched
1163 string (see PCRE_INFO_FIRSTBYTE above).
1164 </P>
1165 <br><a name="SEC13" href="#TOC1">REFERENCE COUNTS</a><br>
1166 <P>
1167 <b>int pcre_refcount(pcre *<i>code</i>, int <i>adjust</i>);</b>
1168 </P>
1169 <P>
1170 The <b>pcre_refcount()</b> function is used to maintain a reference count in the
1171 data block that contains a compiled pattern. It is provided for the benefit of
1172 applications that operate in an object-oriented manner, where different parts
1173 of the application may be using the same compiled pattern, but you want to free
1174 the block when they are all done.
1175 </P>
1176 <P>
1177 When a pattern is compiled, the reference count field is initialized to zero.
1178 It is changed only by calling this function, whose action is to add the
1179 <i>adjust</i> value (which may be positive or negative) to it. The yield of the
1180 function is the new value. However, the value of the count is constrained to
1181 lie between 0 and 65535, inclusive. If the new value is outside these limits,
1182 it is forced to the appropriate limit value.
1183 </P>
1184 <P>
1185 Except when it is zero, the reference count is not correctly preserved if a
1186 pattern is compiled on one host and then transferred to a host whose byte-order
1187 is different. (This seems a highly unlikely scenario.)
1188 </P>
1189 <br><a name="SEC14" href="#TOC1">MATCHING A PATTERN: THE TRADITIONAL FUNCTION</a><br>
1190 <P>
1191 <b>int pcre_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
1192 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
1193 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>);</b>
1194 </P>
1195 <P>
1196 The function <b>pcre_exec()</b> is called to match a subject string against a
1197 compiled pattern, which is passed in the <i>code</i> argument. If the
1198 pattern was studied, the result of the study should be passed in the
1199 <i>extra</i> argument. This function is the main matching facility of the
1200 library, and it operates in a Perl-like manner. For specialist use there is
1201 also an alternative matching function, which is described
1202 <a href="#dfamatch">below</a>
1203 in the section about the <b>pcre_dfa_exec()</b> function.
1204 </P>
1205 <P>
1206 In most applications, the pattern will have been compiled (and optionally
1207 studied) in the same process that calls <b>pcre_exec()</b>. However, it is
1208 possible to save compiled patterns and study data, and then use them later
1209 in different processes, possibly even on different hosts. For a discussion
1210 about this, see the
1211 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
1212 documentation.
1213 </P>
1214 <P>
1215 Here is an example of a simple call to <b>pcre_exec()</b>:
1216 <pre>
1217 int rc;
1218 int ovector[30];
1219 rc = pcre_exec(
1220 re, /* result of pcre_compile() */
1221 NULL, /* we didn't study the pattern */
1222 "some string", /* the subject string */
1223 11, /* the length of the subject string */
1224 0, /* start at offset 0 in the subject */
1225 0, /* default options */
1226 ovector, /* vector of integers for substring information */
1227 30); /* number of elements (NOT size in bytes) */
1228 <a name="extradata"></a></PRE>
1229 </P>
1230 <br><b>
1231 Extra data for <b>pcre_exec()</b>
1232 </b><br>
1233 <P>
1234 If the <i>extra</i> argument is not NULL, it must point to a <b>pcre_extra</b>
1235 data block. The <b>pcre_study()</b> function returns such a block (when it
1236 doesn't return NULL), but you can also create one for yourself, and pass
1237 additional information in it. The <b>pcre_extra</b> block contains the following
1238 fields (not necessarily in this order):
1239 <pre>
1240 unsigned long int <i>flags</i>;
1241 void *<i>study_data</i>;
1242 unsigned long int <i>match_limit</i>;
1243 unsigned long int <i>match_limit_recursion</i>;
1244 void *<i>callout_data</i>;
1245 const unsigned char *<i>tables</i>;
1246 unsigned char **<i>mark</i>;
1247 </pre>
1248 The <i>flags</i> field is a bitmap that specifies which of the other fields
1249 are set. The flag bits are:
1250 <pre>
1257 </pre>
1258 Other flag bits should be set to zero. The <i>study_data</i> field is set in the
1259 <b>pcre_extra</b> block that is returned by <b>pcre_study()</b>, together with
1260 the appropriate flag bit. You should not set this yourself, but you may add to
1261 the block by setting the other fields and their corresponding flag bits.
1262 </P>
1263 <P>
1264 The <i>match_limit</i> field provides a means of preventing PCRE from using up a
1265 vast amount of resources when running patterns that are not going to match,
1266 but which have a very large number of possibilities in their search trees. The
1267 classic example is a pattern that uses nested unlimited repeats.
1268 </P>
1269 <P>
1270 Internally, PCRE uses a function called <b>match()</b> which it calls repeatedly
1271 (sometimes recursively). The limit set by <i>match_limit</i> is imposed on the
1272 number of times this function is called during a match, which has the effect of
1273 limiting the amount of backtracking that can take place. For patterns that are
1274 not anchored, the count restarts from zero for each position in the subject
1275 string.
1276 </P>
1277 <P>
1278 The default value for the limit can be set when PCRE is built; the default
1279 default is 10 million, which handles all but the most extreme cases. You can
1280 override the default by suppling <b>pcre_exec()</b> with a <b>pcre_extra</b>
1281 block in which <i>match_limit</i> is set, and PCRE_EXTRA_MATCH_LIMIT is set in
1282 the <i>flags</i> field. If the limit is exceeded, <b>pcre_exec()</b> returns
1284 </P>
1285 <P>
1286 The <i>match_limit_recursion</i> field is similar to <i>match_limit</i>, but
1287 instead of limiting the total number of times that <b>match()</b> is called, it
1288 limits the depth of recursion. The recursion depth is a smaller number than the
1289 total number of calls, because not all calls to <b>match()</b> are recursive.
1290 This limit is of use only if it is set smaller than <i>match_limit</i>.
1291 </P>
1292 <P>
1293 Limiting the recursion depth limits the amount of stack that can be used, or,
1294 when PCRE has been compiled to use memory on the heap instead of the stack, the
1295 amount of heap memory that can be used.
1296 </P>
1297 <P>
1298 The default value for <i>match_limit_recursion</i> can be set when PCRE is
1299 built; the default default is the same value as the default for
1300 <i>match_limit</i>. You can override the default by suppling <b>pcre_exec()</b>
1301 with a <b>pcre_extra</b> block in which <i>match_limit_recursion</i> is set, and
1302 PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the <i>flags</i> field. If the limit
1303 is exceeded, <b>pcre_exec()</b> returns PCRE_ERROR_RECURSIONLIMIT.
1304 </P>
1305 <P>
1306 The <i>callout_data</i> field is used in conjunction with the "callout" feature,
1307 and is described in the
1308 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1309 documentation.
1310 </P>
1311 <P>
1312 The <i>tables</i> field is used to pass a character tables pointer to
1313 <b>pcre_exec()</b>; this overrides the value that is stored with the compiled
1314 pattern. A non-NULL value is stored with the compiled pattern only if custom
1315 tables were supplied to <b>pcre_compile()</b> via its <i>tableptr</i> argument.
1316 If NULL is passed to <b>pcre_exec()</b> using this mechanism, it forces PCRE's
1317 internal tables to be used. This facility is helpful when re-using patterns
1318 that have been saved after compiling with an external set of tables, because
1319 the external tables might be at a different address when <b>pcre_exec()</b> is
1320 called. See the
1321 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
1322 documentation for a discussion of saving compiled patterns for later use.
1323 </P>
1324 <P>
1325 If PCRE_EXTRA_MARK is set in the <i>flags</i> field, the <i>mark</i> field must
1326 be set to point to a <b>char *</b> variable. If the pattern contains any
1327 backtracking control verbs such as (*MARK:NAME), and the execution ends up with
1328 a name to pass back, a pointer to the name string (zero terminated) is placed
1329 in the variable pointed to by the <i>mark</i> field. The names are within the
1330 compiled pattern; if you wish to retain such a name you must copy it before
1331 freeing the memory of a compiled pattern. If there is no name to pass back, the
1332 variable pointed to by the <i>mark</i> field set to NULL. For details of the
1333 backtracking control verbs, see the section entitled
1334 <a href="pcrepattern#backtrackcontrol">"Backtracking control"</a>
1335 in the
1336 <a href="pcrepattern.html"><b>pcrepattern</b></a>
1337 documentation.
1338 <a name="execoptions"></a></P>
1339 <br><b>
1340 Option bits for <b>pcre_exec()</b>
1341 </b><br>
1342 <P>
1343 The unused bits of the <i>options</i> argument for <b>pcre_exec()</b> must be
1344 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_<i>xxx</i>,
1348 <pre>
1350 </pre>
1351 The PCRE_ANCHORED option limits <b>pcre_exec()</b> to matching at the first
1352 matching position. If a pattern was compiled with PCRE_ANCHORED, or turned out
1353 to be anchored by virtue of its contents, it cannot be made unachored at
1354 matching time.
1355 <pre>
1358 </pre>
1359 These options (which are mutually exclusive) control what the \R escape
1360 sequence matches. The choice is either to match only CR, LF, or CRLF, or to
1361 match any Unicode newline sequence. These options override the choice that was
1362 made or defaulted when the pattern was compiled.
1363 <pre>
1369 </pre>
1370 These options override the newline definition that was chosen or defaulted when
1371 the pattern was compiled. For details, see the description of
1372 <b>pcre_compile()</b> above. During matching, the newline choice affects the
1373 behaviour of the dot, circumflex, and dollar metacharacters. It may also alter
1374 the way the match position is advanced after a match failure for an unanchored
1375 pattern.
1376 </P>
1377 <P>
1379 match attempt for an unanchored pattern fails when the current position is at a
1380 CRLF sequence, and the pattern contains no explicit matches for CR or LF
1381 characters, the match position is advanced by two characters instead of one, in
1382 other words, to after the CRLF.
1383 </P>
1384 <P>
1385 The above rule is a compromise that makes the most common cases work as
1386 expected. For example, if the pattern is .+A (and the PCRE_DOTALL option is not
1387 set), it does not match the string "\r\nA" because, after failing at the
1388 start, it skips both the CR and the LF before retrying. However, the pattern
1389 [\r\n]A does match that string, because it contains an explicit CR or LF
1390 reference, and so advances only by one character after the first failure.
1391 </P>
1392 <P>
1393 An explicit match for CR of LF is either a literal appearance of one of those
1394 characters, or one of the \r or \n escape sequences. Implicit matches such as
1395 [^X] do not count, nor does \s (which includes CR and LF in the characters
1396 that it matches).
1397 </P>
1398 <P>
1399 Notwithstanding the above, anomalous effects may still occur when CRLF is a
1400 valid newline sequence and explicit \r or \n escapes appear in the pattern.
1401 <pre>
1403 </pre>
1404 This option specifies that first character of the subject string is not the
1405 beginning of a line, so the circumflex metacharacter should not match before
1406 it. Setting this without PCRE_MULTILINE (at compile time) causes circumflex
1407 never to match. This option affects only the behaviour of the circumflex
1408 metacharacter. It does not affect \A.
1409 <pre>
1411 </pre>
1412 This option specifies that the end of the subject string is not the end of a
1413 line, so the dollar metacharacter should not match it nor (except in multiline
1414 mode) a newline immediately before it. Setting this without PCRE_MULTILINE (at
1415 compile time) causes dollar never to match. This option affects only the
1416 behaviour of the dollar metacharacter. It does not affect \Z or \z.
1417 <pre>
1419 </pre>
1420 An empty string is not considered to be a valid match if this option is set. If
1421 there are alternatives in the pattern, they are tried. If all the alternatives
1422 match the empty string, the entire match fails. For example, if the pattern
1423 <pre>
1424 a?b?
1425 </pre>
1426 is applied to a string not beginning with "a" or "b", it matches an empty
1427 string at the start of the subject. With PCRE_NOTEMPTY set, this match is not
1428 valid, so PCRE searches further into the string for occurrences of "a" or "b".
1429 <pre>
1431 </pre>
1432 This is like PCRE_NOTEMPTY, except that an empty string match that is not at
1433 the start of the subject is permitted. If the pattern is anchored, such a match
1434 can occur only if the pattern contains \K.
1435 </P>
1436 <P>
1437 Perl has no direct equivalent of PCRE_NOTEMPTY or PCRE_NOTEMPTY_ATSTART, but it
1438 does make a special case of a pattern match of the empty string within its
1439 <b>split()</b> function, and when using the /g modifier. It is possible to
1440 emulate Perl's behaviour after matching a null string by first trying the match
1441 again at the same offset with PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED, and then
1442 if that fails, by advancing the starting offset (see below) and trying an
1443 ordinary match again. There is some code that demonstrates how to do this in
1444 the
1445 <a href="pcredemo.html"><b>pcredemo</b></a>
1446 sample program.
1447 <pre>
1449 </pre>
1450 There are a number of optimizations that <b>pcre_exec()</b> uses at the start of
1451 a match, in order to speed up the process. For example, if it is known that an
1452 unanchored match must start with a specific character, it searches the subject
1453 for that character, and fails immediately if it cannot find it, without
1454 actually running the main matching function. This means that a special item
1455 such as (*COMMIT) at the start of a pattern is not considered until after a
1456 suitable starting point for the match has been found. When callouts or (*MARK)
1457 items are in use, these "start-up" optimizations can cause them to be skipped
1458 if the pattern is never actually used. The start-up optimizations are in effect
1459 a pre-scan of the subject that takes place before the pattern is run.
1460 </P>
1461 <P>
1462 The PCRE_NO_START_OPTIMIZE option disables the start-up optimizations, possibly
1463 causing performance to suffer, but ensuring that in cases where the result is
1464 "no match", the callouts do occur, and that items such as (*COMMIT) and (*MARK)
1465 are considered at every possible starting position in the subject string.
1466 Setting PCRE_NO_START_OPTIMIZE can change the outcome of a matching operation.
1467 Consider the pattern
1468 <pre>
1470 </pre>
1471 When this is compiled, PCRE records the fact that a match must start with the
1472 character "A". Suppose the subject string is "DEFABC". The start-up
1473 optimization scans along the subject, finds "A" and runs the first match
1474 attempt from there. The (*COMMIT) item means that the pattern must match the
1475 current starting position, which in this case, it does. However, if the same
1476 match is run with PCRE_NO_START_OPTIMIZE set, the initial scan along the
1477 subject string does not happen. The first match attempt is run starting from
1478 "D" and when this fails, (*COMMIT) prevents any further matches being tried, so
1479 the overall result is "no match". If the pattern is studied, more start-up
1480 optimizations may be used. For example, a minimum length for the subject may be
1481 recorded. Consider the pattern
1482 <pre>
1483 (*MARK:A)(X|Y)
1484 </pre>
1485 The minimum length for a match is one character. If the subject is "ABC", there
1486 will be attempts to match "ABC", "BC", "C", and then finally an empty string.
1487 If the pattern is studied, the final attempt does not take place, because PCRE
1488 knows that the subject is too short, and so the (*MARK) is never encountered.
1489 In this case, studying the pattern does not affect the overall match result,
1490 which is still "no match", but it does affect the auxiliary information that is
1491 returned.
1492 <pre>
1494 </pre>
1495 When PCRE_UTF8 is set at compile time, the validity of the subject as a UTF-8
1496 string is automatically checked when <b>pcre_exec()</b> is subsequently called.
1497 The value of <i>startoffset</i> is also checked to ensure that it points to the
1498 start of a UTF-8 character. There is a discussion about the validity of UTF-8
1499 strings in the
1500 <a href="pcre.html#utf8strings">section on UTF-8 support</a>
1501 in the main
1502 <a href="pcre.html"><b>pcre</b></a>
1503 page. If an invalid UTF-8 sequence of bytes is found, <b>pcre_exec()</b> returns
1504 the error PCRE_ERROR_BADUTF8. If <i>startoffset</i> contains an invalid value,
1505 PCRE_ERROR_BADUTF8_OFFSET is returned.
1506 </P>
1507 <P>
1508 If you already know that your subject is valid, and you want to skip these
1509 checks for performance reasons, you can set the PCRE_NO_UTF8_CHECK option when
1510 calling <b>pcre_exec()</b>. You might want to do this for the second and
1511 subsequent calls to <b>pcre_exec()</b> if you are making repeated calls to find
1512 all the matches in a single subject string. However, you should be sure that
1513 the value of <i>startoffset</i> points to the start of a UTF-8 character. When
1514 PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid UTF-8 string as a
1515 subject, or a value of <i>startoffset</i> that does not point to the start of a
1516 UTF-8 character, is undefined. Your program may crash.
1517 <pre>
1520 </pre>
1521 These options turn on the partial matching feature. For backwards
1522 compatibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial match
1523 occurs if the end of the subject string is reached successfully, but there are
1524 not enough subject characters to complete the match. If this happens when
1525 PCRE_PARTIAL_HARD is set, <b>pcre_exec()</b> immediately returns
1526 PCRE_ERROR_PARTIAL. Otherwise, if PCRE_PARTIAL_SOFT is set, matching continues
1527 by testing any other alternatives. Only if they all fail is PCRE_ERROR_PARTIAL
1528 returned (instead of PCRE_ERROR_NOMATCH). The portion of the string that
1529 was inspected when the partial match was found is set as the first matching
1530 string. There is a more detailed discussion in the
1531 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1532 documentation.
1533 </P>
1534 <br><b>
1535 The string to be matched by <b>pcre_exec()</b>
1536 </b><br>
1537 <P>
1538 The subject string is passed to <b>pcre_exec()</b> as a pointer in
1539 <i>subject</i>, a length (in bytes) in <i>length</i>, and a starting byte offset
1540 in <i>startoffset</i>. In UTF-8 mode, the byte offset must point to the start of
1541 a UTF-8 character. Unlike the pattern string, the subject may contain binary
1542 zero bytes. When the starting offset is zero, the search for a match starts at
1543 the beginning of the subject, and this is by far the most common case.
1544 </P>
1545 <P>
1546 A non-zero starting offset is useful when searching for another match in the
1547 same subject by calling <b>pcre_exec()</b> again after a previous success.
1548 Setting <i>startoffset</i> differs from just passing over a shortened string and
1549 setting PCRE_NOTBOL in the case of a pattern that begins with any kind of
1550 lookbehind. For example, consider the pattern
1551 <pre>
1552 \Biss\B
1553 </pre>
1554 which finds occurrences of "iss" in the middle of words. (\B matches only if
1555 the current position in the subject is not a word boundary.) When applied to
1556 the string "Mississipi" the first call to <b>pcre_exec()</b> finds the first
1557 occurrence. If <b>pcre_exec()</b> is called again with just the remainder of the
1558 subject, namely "issipi", it does not match, because \B is always false at the
1559 start of the subject, which is deemed to be a word boundary. However, if
1560 <b>pcre_exec()</b> is passed the entire string again, but with <i>startoffset</i>
1561 set to 4, it finds the second occurrence of "iss" because it is able to look
1562 behind the starting point to discover that it is preceded by a letter.
1563 </P>
1564 <P>
1565 If a non-zero starting offset is passed when the pattern is anchored, one
1566 attempt to match at the given offset is made. This can only succeed if the
1567 pattern does not require the match to be at the start of the subject.
1568 </P>
1569 <br><b>
1570 How <b>pcre_exec()</b> returns captured substrings
1571 </b><br>
1572 <P>
1573 In general, a pattern matches a certain portion of the subject, and in
1574 addition, further substrings from the subject may be picked out by parts of the
1575 pattern. Following the usage in Jeffrey Friedl's book, this is called
1576 "capturing" in what follows, and the phrase "capturing subpattern" is used for
1577 a fragment of a pattern that picks out a substring. PCRE supports several other
1578 kinds of parenthesized subpattern that do not cause substrings to be captured.
1579 </P>
1580 <P>
1581 Captured substrings are returned to the caller via a vector of integers whose
1582 address is passed in <i>ovector</i>. The number of elements in the vector is
1583 passed in <i>ovecsize</i>, which must be a non-negative number. <b>Note</b>: this
1584 argument is NOT the size of <i>ovector</i> in bytes.
1585 </P>
1586 <P>
1587 The first two-thirds of the vector is used to pass back captured substrings,
1588 each substring using a pair of integers. The remaining third of the vector is
1589 used as workspace by <b>pcre_exec()</b> while matching capturing subpatterns,
1590 and is not available for passing back information. The number passed in
1591 <i>ovecsize</i> should always be a multiple of three. If it is not, it is
1592 rounded down.
1593 </P>
1594 <P>
1595 When a match is successful, information about captured substrings is returned
1596 in pairs of integers, starting at the beginning of <i>ovector</i>, and
1597 continuing up to two-thirds of its length at the most. The first element of
1598 each pair is set to the byte offset of the first character in a substring, and
1599 the second is set to the byte offset of the first character after the end of a
1600 substring. <b>Note</b>: these values are always byte offsets, even in UTF-8
1601 mode. They are not character counts.
1602 </P>
1603 <P>
1604 The first pair of integers, <i>ovector[0]</i> and <i>ovector[1]</i>, identify the
1605 portion of the subject string matched by the entire pattern. The next pair is
1606 used for the first capturing subpattern, and so on. The value returned by
1607 <b>pcre_exec()</b> is one more than the highest numbered pair that has been set.
1608 For example, if two substrings have been captured, the returned value is 3. If
1609 there are no capturing subpatterns, the return value from a successful match is
1610 1, indicating that just the first pair of offsets has been set.
1611 </P>
1612 <P>
1613 If a capturing subpattern is matched repeatedly, it is the last portion of the
1614 string that it matched that is returned.
1615 </P>
1616 <P>
1617 If the vector is too small to hold all the captured substring offsets, it is
1618 used as far as possible (up to two-thirds of its length), and the function
1619 returns a value of zero. If the substring offsets are not of interest,
1620 <b>pcre_exec()</b> may be called with <i>ovector</i> passed as NULL and
1621 <i>ovecsize</i> as zero. However, if the pattern contains back references and
1622 the <i>ovector</i> is not big enough to remember the related substrings, PCRE
1623 has to get additional memory for use during matching. Thus it is usually
1624 advisable to supply an <i>ovector</i>.
1625 </P>
1626 <P>
1627 The <b>pcre_fullinfo()</b> function can be used to find out how many capturing
1628 subpatterns there are in a compiled pattern. The smallest size for
1629 <i>ovector</i> that will allow for <i>n</i> captured substrings, in addition to
1630 the offsets of the substring matched by the whole pattern, is (<i>n</i>+1)*3.
1631 </P>
1632 <P>
1633 It is possible for capturing subpattern number <i>n+1</i> to match some part of
1634 the subject when subpattern <i>n</i> has not been used at all. For example, if
1635 the string "abc" is matched against the pattern (a|(z))(bc) the return from the
1636 function is 4, and subpatterns 1 and 3 are matched, but 2 is not. When this
1637 happens, both values in the offset pairs corresponding to unused subpatterns
1638 are set to -1.
1639 </P>
1640 <P>
1641 Offset values that correspond to unused subpatterns at the end of the
1642 expression are also set to -1. For example, if the string "abc" is matched
1643 against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not matched. The
1644 return from the function is 2, because the highest used capturing subpattern
1645 number is 1. However, you can refer to the offsets for the second and third
1646 capturing subpatterns if you wish (assuming the vector is large enough, of
1647 course).
1648 </P>
1649 <P>
1650 Some convenience functions are provided for extracting the captured substrings
1651 as separate strings. These are described below.
1652 <a name="errorlist"></a></P>
1653 <br><b>
1654 Error return values from <b>pcre_exec()</b>
1655 </b><br>
1656 <P>
1657 If <b>pcre_exec()</b> fails, it returns a negative number. The following are
1658 defined in the header file:
1659 <pre>
1661 </pre>
1662 The subject string did not match the pattern.
1663 <pre>
1665 </pre>
1666 Either <i>code</i> or <i>subject</i> was passed as NULL, or <i>ovector</i> was
1667 NULL and <i>ovecsize</i> was not zero.
1668 <pre>
1670 </pre>
1671 An unrecognized bit was set in the <i>options</i> argument.
1672 <pre>
1674 </pre>
1675 PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch
1676 the case when it is passed a junk pointer and to detect when a pattern that was
1677 compiled in an environment of one endianness is run in an environment with the
1678 other endianness. This is the error that PCRE gives when the magic number is
1679 not present.
1680 <pre>
1682 </pre>
1683 While running the pattern match, an unknown item was encountered in the
1684 compiled pattern. This error could be caused by a bug in PCRE or by overwriting
1685 of the compiled pattern.
1686 <pre>
1688 </pre>
1689 If a pattern contains back references, but the <i>ovector</i> that is passed to
1690 <b>pcre_exec()</b> is not big enough to remember the referenced substrings, PCRE
1691 gets a block of memory at the start of matching to use for this purpose. If the
1692 call via <b>pcre_malloc()</b> fails, this error is given. The memory is
1693 automatically freed at the end of matching.
1694 </P>
1695 <P>
1696 This error is also given if <b>pcre_stack_malloc()</b> fails in
1697 <b>pcre_exec()</b>. This can happen only when PCRE has been compiled with
1698 <b>--disable-stack-for-recursion</b>.
1699 <pre>
1701 </pre>
1702 This error is used by the <b>pcre_copy_substring()</b>,
1703 <b>pcre_get_substring()</b>, and <b>pcre_get_substring_list()</b> functions (see
1704 below). It is never returned by <b>pcre_exec()</b>.
1705 <pre>
1707 </pre>
1708 The backtracking limit, as specified by the <i>match_limit</i> field in a
1709 <b>pcre_extra</b> structure (or defaulted) was reached. See the description
1710 above.
1711 <pre>
1713 </pre>
1714 This error is never generated by <b>pcre_exec()</b> itself. It is provided for
1715 use by callout functions that want to yield a distinctive error code. See the
1716 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1717 documentation for details.
1718 <pre>
1720 </pre>
1721 A string that contains an invalid UTF-8 byte sequence was passed as a subject.
1722 <pre>
1724 </pre>
1725 The UTF-8 byte sequence that was passed as a subject was valid, but the value
1726 of <i>startoffset</i> did not point to the beginning of a UTF-8 character.
1727 <pre>
1729 </pre>
1730 The subject string did not match, but it did match partially. See the
1731 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1732 documentation for details of partial matching.
1733 <pre>
1735 </pre>
1736 This code is no longer in use. It was formerly returned when the PCRE_PARTIAL
1737 option was used with a compiled pattern containing items that were not
1738 supported for partial matching. From release 8.00 onwards, there are no
1739 restrictions on partial matching.
1740 <pre>
1742 </pre>
1743 An unexpected internal error has occurred. This error could be caused by a bug
1744 in PCRE or by overwriting of the compiled pattern.
1745 <pre>
1747 </pre>
1748 This error is given if the value of the <i>ovecsize</i> argument is negative.
1749 <pre>
1751 </pre>
1752 The internal recursion limit, as specified by the <i>match_limit_recursion</i>
1753 field in a <b>pcre_extra</b> structure (or defaulted) was reached. See the
1754 description above.
1755 <pre>
1757 </pre>
1758 An invalid combination of PCRE_NEWLINE_<i>xxx</i> options was given.
1759 </P>
1760 <P>
1761 Error numbers -16 to -20 and -22 are not used by <b>pcre_exec()</b>.
1762 </P>
1763 <br><a name="SEC15" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NUMBER</a><br>
1764 <P>
1765 <b>int pcre_copy_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1766 <b>int <i>stringcount</i>, int <i>stringnumber</i>, char *<i>buffer</i>,</b>
1767 <b>int <i>buffersize</i>);</b>
1768 </P>
1769 <P>
1770 <b>int pcre_get_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1771 <b>int <i>stringcount</i>, int <i>stringnumber</i>,</b>
1772 <b>const char **<i>stringptr</i>);</b>
1773 </P>
1774 <P>
1775 <b>int pcre_get_substring_list(const char *<i>subject</i>,</b>
1776 <b>int *<i>ovector</i>, int <i>stringcount</i>, const char ***<i>listptr</i>);</b>
1777 </P>
1778 <P>
1779 Captured substrings can be accessed directly by using the offsets returned by
1780 <b>pcre_exec()</b> in <i>ovector</i>. For convenience, the functions
1781 <b>pcre_copy_substring()</b>, <b>pcre_get_substring()</b>, and
1782 <b>pcre_get_substring_list()</b> are provided for extracting captured substrings
1783 as new, separate, zero-terminated strings. These functions identify substrings
1784 by number. The next section describes functions for extracting named
1785 substrings.
1786 </P>
1787 <P>
1788 A substring that contains a binary zero is correctly extracted and has a
1789 further zero added on the end, but the result is not, of course, a C string.
1790 However, you can process such a string by referring to the length that is
1791 returned by <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>.
1792 Unfortunately, the interface to <b>pcre_get_substring_list()</b> is not adequate
1793 for handling strings containing binary zeros, because the end of the final
1794 string is not independently indicated.
1795 </P>
1796 <P>
1797 The first three arguments are the same for all three of these functions:
1798 <i>subject</i> is the subject string that has just been successfully matched,
1799 <i>ovector</i> is a pointer to the vector of integer offsets that was passed to
1800 <b>pcre_exec()</b>, and <i>stringcount</i> is the number of substrings that were
1801 captured by the match, including the substring that matched the entire regular
1802 expression. This is the value returned by <b>pcre_exec()</b> if it is greater
1803 than zero. If <b>pcre_exec()</b> returned zero, indicating that it ran out of
1804 space in <i>ovector</i>, the value passed as <i>stringcount</i> should be the
1805 number of elements in the vector divided by three.
1806 </P>
1807 <P>
1808 The functions <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>
1809 extract a single substring, whose number is given as <i>stringnumber</i>. A
1810 value of zero extracts the substring that matched the entire pattern, whereas
1811 higher values extract the captured substrings. For <b>pcre_copy_substring()</b>,
1812 the string is placed in <i>buffer</i>, whose length is given by
1813 <i>buffersize</i>, while for <b>pcre_get_substring()</b> a new block of memory is
1814 obtained via <b>pcre_malloc</b>, and its address is returned via
1815 <i>stringptr</i>. The yield of the function is the length of the string, not
1816 including the terminating zero, or one of these error codes:
1817 <pre>
1819 </pre>
1820 The buffer was too small for <b>pcre_copy_substring()</b>, or the attempt to get
1821 memory failed for <b>pcre_get_substring()</b>.
1822 <pre>
1824 </pre>
1825 There is no substring whose number is <i>stringnumber</i>.
1826 </P>
1827 <P>
1828 The <b>pcre_get_substring_list()</b> function extracts all available substrings
1829 and builds a list of pointers to them. All this is done in a single block of
1830 memory that is obtained via <b>pcre_malloc</b>. The address of the memory block
1831 is returned via <i>listptr</i>, which is also the start of the list of string
1832 pointers. The end of the list is marked by a NULL pointer. The yield of the
1833 function is zero if all went well, or the error code
1834 <pre>
1836 </pre>
1837 if the attempt to get the memory block failed.
1838 </P>
1839 <P>
1840 When any of these functions encounter a substring that is unset, which can
1841 happen when capturing subpattern number <i>n+1</i> matches some part of the
1842 subject, but subpattern <i>n</i> has not been used at all, they return an empty
1843 string. This can be distinguished from a genuine zero-length substring by
1844 inspecting the appropriate offset in <i>ovector</i>, which is negative for unset
1845 substrings.
1846 </P>
1847 <P>
1848 The two convenience functions <b>pcre_free_substring()</b> and
1849 <b>pcre_free_substring_list()</b> can be used to free the memory returned by
1850 a previous call of <b>pcre_get_substring()</b> or
1851 <b>pcre_get_substring_list()</b>, respectively. They do nothing more than call
1852 the function pointed to by <b>pcre_free</b>, which of course could be called
1853 directly from a C program. However, PCRE is used in some situations where it is
1854 linked via a special interface to another programming language that cannot use
1855 <b>pcre_free</b> directly; it is for these cases that the functions are
1856 provided.
1857 </P>
1858 <br><a name="SEC16" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NAME</a><br>
1859 <P>
1860 <b>int pcre_get_stringnumber(const pcre *<i>code</i>,</b>
1861 <b>const char *<i>name</i>);</b>
1862 </P>
1863 <P>
1864 <b>int pcre_copy_named_substring(const pcre *<i>code</i>,</b>
1865 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
1866 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
1867 <b>char *<i>buffer</i>, int <i>buffersize</i>);</b>
1868 </P>
1869 <P>
1870 <b>int pcre_get_named_substring(const pcre *<i>code</i>,</b>
1871 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
1872 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
1873 <b>const char **<i>stringptr</i>);</b>
1874 </P>
1875 <P>
1876 To extract a substring by name, you first have to find associated number.
1877 For example, for this pattern
1878 <pre>
1879 (a+)b(?&#60;xxx&#62;\d+)...
1880 </pre>
1881 the number of the subpattern called "xxx" is 2. If the name is known to be
1882 unique (PCRE_DUPNAMES was not set), you can find the number from the name by
1883 calling <b>pcre_get_stringnumber()</b>. The first argument is the compiled
1884 pattern, and the second is the name. The yield of the function is the
1885 subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no subpattern of
1886 that name.
1887 </P>
1888 <P>
1889 Given the number, you can extract the substring directly, or use one of the
1890 functions described in the previous section. For convenience, there are also
1891 two functions that do the whole job.
1892 </P>
1893 <P>
1894 Most of the arguments of <b>pcre_copy_named_substring()</b> and
1895 <b>pcre_get_named_substring()</b> are the same as those for the similarly named
1896 functions that extract by number. As these are described in the previous
1897 section, they are not re-described here. There are just two differences:
1898 </P>
1899 <P>
1900 First, instead of a substring number, a substring name is given. Second, there
1901 is an extra argument, given at the start, which is a pointer to the compiled
1902 pattern. This is needed in order to gain access to the name-to-number
1903 translation table.
1904 </P>
1905 <P>
1906 These functions call <b>pcre_get_stringnumber()</b>, and if it succeeds, they
1907 then call <b>pcre_copy_substring()</b> or <b>pcre_get_substring()</b>, as
1908 appropriate. <b>NOTE:</b> If PCRE_DUPNAMES is set and there are duplicate names,
1909 the behaviour may not be what you want (see the next section).
1910 </P>
1911 <P>
1912 <b>Warning:</b> If the pattern uses the (?| feature to set up multiple
1913 subpatterns with the same number, as described in the
1914 <a href="pcrepattern.html#dupsubpatternnumber">section on duplicate subpattern numbers</a>
1915 in the
1916 <a href="pcrepattern.html"><b>pcrepattern</b></a>
1917 page, you cannot use names to distinguish the different subpatterns, because
1918 names are not included in the compiled code. The matching process uses only
1919 numbers. For this reason, the use of different names for subpatterns of the
1920 same number causes an error at compile time.
1921 </P>
1922 <br><a name="SEC17" href="#TOC1">DUPLICATE SUBPATTERN NAMES</a><br>
1923 <P>
1924 <b>int pcre_get_stringtable_entries(const pcre *<i>code</i>,</b>
1925 <b>const char *<i>name</i>, char **<i>first</i>, char **<i>last</i>);</b>
1926 </P>
1927 <P>
1928 When a pattern is compiled with the PCRE_DUPNAMES option, names for subpatterns
1929 are not required to be unique. (Duplicate names are always allowed for
1930 subpatterns with the same number, created by using the (?| feature. Indeed, if
1931 such subpatterns are named, they are required to use the same names.)
1932 </P>
1933 <P>
1934 Normally, patterns with duplicate names are such that in any one match, only
1935 one of the named subpatterns participates. An example is shown in the
1936 <a href="pcrepattern.html"><b>pcrepattern</b></a>
1937 documentation.
1938 </P>
1939 <P>
1940 When duplicates are present, <b>pcre_copy_named_substring()</b> and
1941 <b>pcre_get_named_substring()</b> return the first substring corresponding to
1942 the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING (-7) is
1943 returned; no data is returned. The <b>pcre_get_stringnumber()</b> function
1944 returns one of the numbers that are associated with the name, but it is not
1945 defined which it is.
1946 </P>
1947 <P>
1948 If you want to get full details of all captured substrings for a given name,
1949 you must use the <b>pcre_get_stringtable_entries()</b> function. The first
1950 argument is the compiled pattern, and the second is the name. The third and
1951 fourth are pointers to variables which are updated by the function. After it
1952 has run, they point to the first and last entries in the name-to-number table
1953 for the given name. The function itself returns the length of each entry, or
1954 PCRE_ERROR_NOSUBSTRING (-7) if there are none. The format of the table is
1955 described above in the section entitled <i>Information about a pattern</i>.
1956 Given all the relevant entries for the name, you can extract each of their
1957 numbers, and hence the captured data, if any.
1958 </P>
1959 <br><a name="SEC18" href="#TOC1">FINDING ALL POSSIBLE MATCHES</a><br>
1960 <P>
1961 The traditional matching function uses a similar algorithm to Perl, which stops
1962 when it finds the first match, starting at a given point in the subject. If you
1963 want to find all possible matches, or the longest possible match, consider
1964 using the alternative matching function (see below) instead. If you cannot use
1965 the alternative function, but still need to find all possible matches, you
1966 can kludge it up by making use of the callout facility, which is described in
1967 the
1968 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1969 documentation.
1970 </P>
1971 <P>
1972 What you have to do is to insert a callout right at the end of the pattern.
1973 When your callout function is called, extract and save the current matched
1974 substring. Then return 1, which forces <b>pcre_exec()</b> to backtrack and try
1975 other alternatives. Ultimately, when it runs out of matches, <b>pcre_exec()</b>
1976 will yield PCRE_ERROR_NOMATCH.
1977 <a name="dfamatch"></a></P>
1978 <br><a name="SEC19" href="#TOC1">MATCHING A PATTERN: THE ALTERNATIVE FUNCTION</a><br>
1979 <P>
1980 <b>int pcre_dfa_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
1981 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
1982 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>,</b>
1983 <b>int *<i>workspace</i>, int <i>wscount</i>);</b>
1984 </P>
1985 <P>
1986 The function <b>pcre_dfa_exec()</b> is called to match a subject string against
1987 a compiled pattern, using a matching algorithm that scans the subject string
1988 just once, and does not backtrack. This has different characteristics to the
1989 normal algorithm, and is not compatible with Perl. Some of the features of PCRE
1990 patterns are not supported. Nevertheless, there are times when this kind of
1991 matching can be useful. For a discussion of the two matching algorithms, and a
1992 list of features that <b>pcre_dfa_exec()</b> does not support, see the
1993 <a href="pcrematching.html"><b>pcrematching</b></a>
1994 documentation.
1995 </P>
1996 <P>
1997 The arguments for the <b>pcre_dfa_exec()</b> function are the same as for
1998 <b>pcre_exec()</b>, plus two extras. The <i>ovector</i> argument is used in a
1999 different way, and this is described below. The other common arguments are used
2000 in the same way as for <b>pcre_exec()</b>, so their description is not repeated
2001 here.
2002 </P>
2003 <P>
2004 The two additional arguments provide workspace for the function. The workspace
2005 vector should contain at least 20 elements. It is used for keeping track of
2006 multiple paths through the pattern tree. More workspace will be needed for
2007 patterns and subjects where there are a lot of potential matches.
2008 </P>
2009 <P>
2010 Here is an example of a simple call to <b>pcre_dfa_exec()</b>:
2011 <pre>
2012 int rc;
2013 int ovector[10];
2014 int wspace[20];
2015 rc = pcre_dfa_exec(
2016 re, /* result of pcre_compile() */
2017 NULL, /* we didn't study the pattern */
2018 "some string", /* the subject string */
2019 11, /* the length of the subject string */
2020 0, /* start at offset 0 in the subject */
2021 0, /* default options */
2022 ovector, /* vector of integers for substring information */
2023 10, /* number of elements (NOT size in bytes) */
2024 wspace, /* working space vector */
2025 20); /* number of elements (NOT size in bytes) */
2026 </PRE>
2027 </P>
2028 <br><b>
2029 Option bits for <b>pcre_dfa_exec()</b>
2030 </b><br>
2031 <P>
2032 The unused bits of the <i>options</i> argument for <b>pcre_dfa_exec()</b> must be
2033 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_<i>xxx</i>,
2037 All but the last four of these are exactly the same as for <b>pcre_exec()</b>,
2038 so their description is not repeated here.
2039 <pre>
2042 </pre>
2043 These have the same general effect as they do for <b>pcre_exec()</b>, but the
2044 details are slightly different. When PCRE_PARTIAL_HARD is set for
2045 <b>pcre_dfa_exec()</b>, it returns PCRE_ERROR_PARTIAL if the end of the subject
2046 is reached and there is still at least one matching possibility that requires
2047 additional characters. This happens even if some complete matches have also
2048 been found. When PCRE_PARTIAL_SOFT is set, the return code PCRE_ERROR_NOMATCH
2049 is converted into PCRE_ERROR_PARTIAL if the end of the subject is reached,
2050 there have been no complete matches, but there is still at least one matching
2051 possibility. The portion of the string that was inspected when the longest
2052 partial match was found is set as the first matching string in both cases.
2053 <pre>
2055 </pre>
2056 Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to stop as
2057 soon as it has found one match. Because of the way the alternative algorithm
2058 works, this is necessarily the shortest possible match at the first possible
2059 matching point in the subject string.
2060 <pre>
2062 </pre>
2063 When <b>pcre_dfa_exec()</b> returns a partial match, it is possible to call it
2064 again, with additional subject characters, and have it continue with the same
2065 match. The PCRE_DFA_RESTART option requests this action; when it is set, the
2066 <i>workspace</i> and <i>wscount</i> options must reference the same vector as
2067 before because data about the match so far is left in them after a partial
2068 match. There is more discussion of this facility in the
2069 <a href="pcrepartial.html"><b>pcrepartial</b></a>
2070 documentation.
2071 </P>
2072 <br><b>
2073 Successful returns from <b>pcre_dfa_exec()</b>
2074 </b><br>
2075 <P>
2076 When <b>pcre_dfa_exec()</b> succeeds, it may have matched more than one
2077 substring in the subject. Note, however, that all the matches from one run of
2078 the function start at the same point in the subject. The shorter matches are
2079 all initial substrings of the longer matches. For example, if the pattern
2080 <pre>
2081 &#60;.*&#62;
2082 </pre>
2083 is matched against the string
2084 <pre>
2085 This is &#60;something&#62; &#60;something else&#62; &#60;something further&#62; no more
2086 </pre>
2087 the three matched strings are
2088 <pre>
2089 &#60;something&#62;
2090 &#60;something&#62; &#60;something else&#62;
2091 &#60;something&#62; &#60;something else&#62; &#60;something further&#62;
2092 </pre>
2093 On success, the yield of the function is a number greater than zero, which is
2094 the number of matched substrings. The substrings themselves are returned in
2095 <i>ovector</i>. Each string uses two elements; the first is the offset to the
2096 start, and the second is the offset to the end. In fact, all the strings have
2097 the same start offset. (Space could have been saved by giving this only once,
2098 but it was decided to retain some compatibility with the way <b>pcre_exec()</b>
2099 returns data, even though the meaning of the strings is different.)
2100 </P>
2101 <P>
2102 The strings are returned in reverse order of length; that is, the longest
2103 matching string is given first. If there were too many matches to fit into
2104 <i>ovector</i>, the yield of the function is zero, and the vector is filled with
2105 the longest matches.
2106 </P>
2107 <br><b>
2108 Error returns from <b>pcre_dfa_exec()</b>
2109 </b><br>
2110 <P>
2111 The <b>pcre_dfa_exec()</b> function returns a negative number when it fails.
2112 Many of the errors are the same as for <b>pcre_exec()</b>, and these are
2113 described
2114 <a href="#errorlist">above.</a>
2115 There are in addition the following errors that are specific to
2116 <b>pcre_dfa_exec()</b>:
2117 <pre>
2119 </pre>
2120 This return is given if <b>pcre_dfa_exec()</b> encounters an item in the pattern
2121 that it does not support, for instance, the use of \C or a back reference.
2122 <pre>
2124 </pre>
2125 This return is given if <b>pcre_dfa_exec()</b> encounters a condition item that
2126 uses a back reference for the condition, or a test for recursion in a specific
2127 group. These are not supported.
2128 <pre>
2130 </pre>
2131 This return is given if <b>pcre_dfa_exec()</b> is called with an <i>extra</i>
2132 block that contains a setting of the <i>match_limit</i> field. This is not
2133 supported (it is meaningless).
2134 <pre>
2136 </pre>
2137 This return is given if <b>pcre_dfa_exec()</b> runs out of space in the
2138 <i>workspace</i> vector.
2139 <pre>
2141 </pre>
2142 When a recursive subpattern is processed, the matching function calls itself
2143 recursively, using private vectors for <i>ovector</i> and <i>workspace</i>. This
2144 error is given if the output vector is not large enough. This should be
2145 extremely rare, as a vector of size 1000 is used.
2146 </P>
2147 <br><a name="SEC20" href="#TOC1">SEE ALSO</a><br>
2148 <P>
2149 <b>pcrebuild</b>(3), <b>pcrecallout</b>(3), <b>pcrecpp(3)</b>(3),
2150 <b>pcrematching</b>(3), <b>pcrepartial</b>(3), <b>pcreposix</b>(3),
2151 <b>pcreprecompile</b>(3), <b>pcresample</b>(3), <b>pcrestack</b>(3).
2152 </P>
2153 <br><a name="SEC21" href="#TOC1">AUTHOR</a><br>
2154 <P>
2155 Philip Hazel
2156 <br>
2157 University Computing Service
2158 <br>
2159 Cambridge CB2 3QH, England.
2160 <br>
2161 </P>
2162 <br><a name="SEC22" href="#TOC1">REVISION</a><br>
2163 <P>
2164 Last updated: 21 June 2010
2165 <br>
2166 Copyright &copy; 1997-2010 University of Cambridge.
2167 <br>
2168 <p>
2169 Return to the <a href="index.html">PCRE index page</a>.
2170 </p>


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