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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>
20 <li><a name="TOC5" href="#SEC5">SAVING PRECOMPILED PATTERNS FOR LATER USE</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>
29 <li><a name="TOC14" href="#SEC14">MATCHING A PATTERN: THE TRADITIONAL FUNCTION</a>
30 <li><a name="TOC15" href="#SEC15">EXTRACTING CAPTURED SUBSTRINGS BY NUMBER</a>
31 <li><a name="TOC16" href="#SEC16">EXTRACTING CAPTURED SUBSTRINGS BY NAME</a>
32 <li><a name="TOC17" href="#SEC17">DUPLICATE SUBPATTERN NAMES</a>
33 <li><a name="TOC18" href="#SEC18">FINDING ALL POSSIBLE MATCHES</a>
34 <li><a name="TOC19" href="#SEC19">MATCHING A PATTERN: THE ALTERNATIVE FUNCTION</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 The functions <b>pcre_compile()</b>, <b>pcre_compile2()</b>, <b>pcre_study()</b>,
165 and <b>pcre_exec()</b> are used for compiling and matching regular expressions
166 in a Perl-compatible manner. A sample program that demonstrates the simplest
167 way of using them is provided in the file called <i>pcredemo.c</i> in the PCRE
168 source distribution. A listing of this program is given in the
169 <a href="pcredemo.html"><b>pcredemo</b></a>
170 documentation, and the
171 <a href="pcresample.html"><b>pcresample</b></a>
172 documentation describes how to compile and run it.
173 </P>
174 <P>
175 A second matching function, <b>pcre_dfa_exec()</b>, which is not
176 Perl-compatible, is also provided. This uses a different algorithm for the
177 matching. The alternative algorithm finds all possible matches (at a given
178 point in the subject), and scans the subject just once (unless there are
179 lookbehind assertions). However, this algorithm does not return captured
180 substrings. A description of the two matching algorithms and their advantages
181 and disadvantages is given in the
182 <a href="pcrematching.html"><b>pcrematching</b></a>
183 documentation.
184 </P>
185 <P>
186 In addition to the main compiling and matching functions, there are convenience
187 functions for extracting captured substrings from a subject string that is
188 matched by <b>pcre_exec()</b>. They are:
189 <pre>
190 <b>pcre_copy_substring()</b>
191 <b>pcre_copy_named_substring()</b>
192 <b>pcre_get_substring()</b>
193 <b>pcre_get_named_substring()</b>
194 <b>pcre_get_substring_list()</b>
195 <b>pcre_get_stringnumber()</b>
196 <b>pcre_get_stringtable_entries()</b>
197 </pre>
198 <b>pcre_free_substring()</b> and <b>pcre_free_substring_list()</b> are also
199 provided, to free the memory used for extracted strings.
200 </P>
201 <P>
202 The function <b>pcre_maketables()</b> is used to build a set of character tables
203 in the current locale for passing to <b>pcre_compile()</b>, <b>pcre_exec()</b>,
204 or <b>pcre_dfa_exec()</b>. This is an optional facility that is provided for
205 specialist use. Most commonly, no special tables are passed, in which case
206 internal tables that are generated when PCRE is built are used.
207 </P>
208 <P>
209 The function <b>pcre_fullinfo()</b> is used to find out information about a
210 compiled pattern; <b>pcre_info()</b> is an obsolete version that returns only
211 some of the available information, but is retained for backwards compatibility.
212 The function <b>pcre_version()</b> returns a pointer to a string containing the
213 version of PCRE and its date of release.
214 </P>
215 <P>
216 The function <b>pcre_refcount()</b> maintains a reference count in a data block
217 containing a compiled pattern. This is provided for the benefit of
218 object-oriented applications.
219 </P>
220 <P>
221 The global variables <b>pcre_malloc</b> and <b>pcre_free</b> initially contain
222 the entry points of the standard <b>malloc()</b> and <b>free()</b> functions,
223 respectively. PCRE calls the memory management functions via these variables,
224 so a calling program can replace them if it wishes to intercept the calls. This
225 should be done before calling any PCRE functions.
226 </P>
227 <P>
228 The global variables <b>pcre_stack_malloc</b> and <b>pcre_stack_free</b> are also
229 indirections to memory management functions. These special functions are used
230 only when PCRE is compiled to use the heap for remembering data, instead of
231 recursive function calls, when running the <b>pcre_exec()</b> function. See the
232 <a href="pcrebuild.html"><b>pcrebuild</b></a>
233 documentation for details of how to do this. It is a non-standard way of
234 building PCRE, for use in environments that have limited stacks. Because of the
235 greater use of memory management, it runs more slowly. Separate functions are
236 provided so that special-purpose external code can be used for this case. When
237 used, these functions are always called in a stack-like manner (last obtained,
238 first freed), and always for memory blocks of the same size. There is a
239 discussion about PCRE's stack usage in the
240 <a href="pcrestack.html"><b>pcrestack</b></a>
241 documentation.
242 </P>
243 <P>
244 The global variable <b>pcre_callout</b> initially contains NULL. It can be set
245 by the caller to a "callout" function, which PCRE will then call at specified
246 points during a matching operation. Details are given in the
247 <a href="pcrecallout.html"><b>pcrecallout</b></a>
248 documentation.
249 <a name="newlines"></a></P>
250 <br><a name="SEC3" href="#TOC1">NEWLINES</a><br>
251 <P>
252 PCRE supports five different conventions for indicating line breaks in
253 strings: a single CR (carriage return) character, a single LF (linefeed)
254 character, the two-character sequence CRLF, any of the three preceding, or any
255 Unicode newline sequence. The Unicode newline sequences are the three just
256 mentioned, plus the single characters VT (vertical tab, U+000B), FF (formfeed,
257 U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS
258 (paragraph separator, U+2029).
259 </P>
260 <P>
261 Each of the first three conventions is used by at least one operating system as
262 its standard newline sequence. When PCRE is built, a default can be specified.
263 The default default is LF, which is the Unix standard. When PCRE is run, the
264 default can be overridden, either when a pattern is compiled, or when it is
265 matched.
266 </P>
267 <P>
268 At compile time, the newline convention can be specified by the <i>options</i>
269 argument of <b>pcre_compile()</b>, or it can be specified by special text at the
270 start of the pattern itself; this overrides any other settings. See the
271 <a href="pcrepattern.html"><b>pcrepattern</b></a>
272 page for details of the special character sequences.
273 </P>
274 <P>
275 In the PCRE documentation the word "newline" is used to mean "the character or
276 pair of characters that indicate a line break". The choice of newline
277 convention affects the handling of the dot, circumflex, and dollar
278 metacharacters, the handling of #-comments in /x mode, and, when CRLF is a
279 recognized line ending sequence, the match position advancement for a
280 non-anchored pattern. There is more detail about this in the
281 <a href="#execoptions">section on <b>pcre_exec()</b> options</a>
282 below.
283 </P>
284 <P>
285 The choice of newline convention does not affect the interpretation of
286 the \n or \r escape sequences, nor does it affect what \R matches, which is
287 controlled in a similar way, but by separate options.
288 </P>
289 <br><a name="SEC4" href="#TOC1">MULTITHREADING</a><br>
290 <P>
291 The PCRE functions can be used in multi-threading applications, with the
292 proviso that the memory management functions pointed to by <b>pcre_malloc</b>,
293 <b>pcre_free</b>, <b>pcre_stack_malloc</b>, and <b>pcre_stack_free</b>, and the
294 callout function pointed to by <b>pcre_callout</b>, are shared by all threads.
295 </P>
296 <P>
297 The compiled form of a regular expression is not altered during matching, so
298 the same compiled pattern can safely be used by several threads at once.
299 </P>
300 <br><a name="SEC5" href="#TOC1">SAVING PRECOMPILED PATTERNS FOR LATER USE</a><br>
301 <P>
302 The compiled form of a regular expression can be saved and re-used at a later
303 time, possibly by a different program, and even on a host other than the one on
304 which it was compiled. Details are given in the
305 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
306 documentation. However, compiling a regular expression with one version of PCRE
307 for use with a different version is not guaranteed to work and may cause
308 crashes.
309 </P>
310 <br><a name="SEC6" href="#TOC1">CHECKING BUILD-TIME OPTIONS</a><br>
311 <P>
312 <b>int pcre_config(int <i>what</i>, void *<i>where</i>);</b>
313 </P>
314 <P>
315 The function <b>pcre_config()</b> makes it possible for a PCRE client to
316 discover which optional features have been compiled into the PCRE library. The
317 <a href="pcrebuild.html"><b>pcrebuild</b></a>
318 documentation has more details about these optional features.
319 </P>
320 <P>
321 The first argument for <b>pcre_config()</b> is an integer, specifying which
322 information is required; the second argument is a pointer to a variable into
323 which the information is placed. The following information is available:
324 <pre>
325 PCRE_CONFIG_UTF8
326 </pre>
327 The output is an integer that is set to one if UTF-8 support is available;
328 otherwise it is set to zero.
329 <pre>
330 PCRE_CONFIG_UNICODE_PROPERTIES
331 </pre>
332 The output is an integer that is set to one if support for Unicode character
333 properties is available; otherwise it is set to zero.
334 <pre>
335 PCRE_CONFIG_NEWLINE
336 </pre>
337 The output is an integer whose value specifies the default character sequence
338 that is recognized as meaning "newline". The four values that are supported
339 are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF, and -1 for ANY.
340 Though they are derived from ASCII, the same values are returned in EBCDIC
341 environments. The default should normally correspond to the standard sequence
342 for your operating system.
343 <pre>
344 PCRE_CONFIG_BSR
345 </pre>
346 The output is an integer whose value indicates what character sequences the \R
347 escape sequence matches by default. A value of 0 means that \R matches any
348 Unicode line ending sequence; a value of 1 means that \R matches only CR, LF,
349 or CRLF. The default can be overridden when a pattern is compiled or matched.
350 <pre>
351 PCRE_CONFIG_LINK_SIZE
352 </pre>
353 The output is an integer that contains the number of bytes used for internal
354 linkage in compiled regular expressions. The value is 2, 3, or 4. Larger values
355 allow larger regular expressions to be compiled, at the expense of slower
356 matching. The default value of 2 is sufficient for all but the most massive
357 patterns, since it allows the compiled pattern to be up to 64K in size.
358 <pre>
359 PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
360 </pre>
361 The output is an integer that contains the threshold above which the POSIX
362 interface uses <b>malloc()</b> for output vectors. Further details are given in
363 the
364 <a href="pcreposix.html"><b>pcreposix</b></a>
365 documentation.
366 <pre>
367 PCRE_CONFIG_MATCH_LIMIT
368 </pre>
369 The output is a long integer that gives the default limit for the number of
370 internal matching function calls in a <b>pcre_exec()</b> execution. Further
371 details are given with <b>pcre_exec()</b> below.
372 <pre>
373 PCRE_CONFIG_MATCH_LIMIT_RECURSION
374 </pre>
375 The output is a long integer that gives the default limit for the depth of
376 recursion when calling the internal matching function in a <b>pcre_exec()</b>
377 execution. Further details are given with <b>pcre_exec()</b> below.
378 <pre>
379 PCRE_CONFIG_STACKRECURSE
380 </pre>
381 The output is an integer that is set to one if internal recursion when running
382 <b>pcre_exec()</b> is implemented by recursive function calls that use the stack
383 to remember their state. This is the usual way that PCRE is compiled. The
384 output is zero if PCRE was compiled to use blocks of data on the heap instead
385 of recursive function calls. In this case, <b>pcre_stack_malloc</b> and
386 <b>pcre_stack_free</b> are called to manage memory blocks on the heap, thus
387 avoiding the use of the stack.
388 </P>
389 <br><a name="SEC7" href="#TOC1">COMPILING A PATTERN</a><br>
390 <P>
391 <b>pcre *pcre_compile(const char *<i>pattern</i>, int <i>options</i>,</b>
392 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
393 <b>const unsigned char *<i>tableptr</i>);</b>
394 <b>pcre *pcre_compile2(const char *<i>pattern</i>, int <i>options</i>,</b>
395 <b>int *<i>errorcodeptr</i>,</b>
396 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
397 <b>const unsigned char *<i>tableptr</i>);</b>
398 </P>
399 <P>
400 Either of the functions <b>pcre_compile()</b> or <b>pcre_compile2()</b> can be
401 called to compile a pattern into an internal form. The only difference between
402 the two interfaces is that <b>pcre_compile2()</b> has an additional argument,
403 <i>errorcodeptr</i>, via which a numerical error code can be returned. To avoid
404 too much repetition, we refer just to <b>pcre_compile()</b> below, but the
405 information applies equally to <b>pcre_compile2()</b>.
406 </P>
407 <P>
408 The pattern is a C string terminated by a binary zero, and is passed in the
409 <i>pattern</i> argument. A pointer to a single block of memory that is obtained
410 via <b>pcre_malloc</b> is returned. This contains the compiled code and related
411 data. The <b>pcre</b> type is defined for the returned block; this is a typedef
412 for a structure whose contents are not externally defined. It is up to the
413 caller to free the memory (via <b>pcre_free</b>) when it is no longer required.
414 </P>
415 <P>
416 Although the compiled code of a PCRE regex is relocatable, that is, it does not
417 depend on memory location, the complete <b>pcre</b> data block is not
418 fully relocatable, because it may contain a copy of the <i>tableptr</i>
419 argument, which is an address (see below).
420 </P>
421 <P>
422 The <i>options</i> argument contains various bit settings that affect the
423 compilation. It should be zero if no options are required. The available
424 options are described below. Some of them (in particular, those that are
425 compatible with Perl, but some others as well) can also be set and unset from
426 within the pattern (see the detailed description in the
427 <a href="pcrepattern.html"><b>pcrepattern</b></a>
428 documentation). For those options that can be different in different parts of
429 the pattern, the contents of the <i>options</i> argument specifies their
430 settings at the start of compilation and execution. The PCRE_ANCHORED,
431 PCRE_BSR_<i>xxx</i>, and PCRE_NEWLINE_<i>xxx</i> options can be set at the time
432 of matching as well as at compile time.
433 </P>
434 <P>
435 If <i>errptr</i> is NULL, <b>pcre_compile()</b> returns NULL immediately.
436 Otherwise, if compilation of a pattern fails, <b>pcre_compile()</b> returns
437 NULL, and sets the variable pointed to by <i>errptr</i> to point to a textual
438 error message. This is a static string that is part of the library. You must
439 not try to free it. The byte offset from the start of the pattern to the
440 character that was being processed when the error was discovered is placed in
441 the variable pointed to by <i>erroffset</i>, which must not be NULL. If it is,
442 an immediate error is given. Some errors are not detected until checks are
443 carried out when the whole pattern has been scanned; in this case the offset is
444 set to the end of the pattern.
445 </P>
446 <P>
447 If <b>pcre_compile2()</b> is used instead of <b>pcre_compile()</b>, and the
448 <i>errorcodeptr</i> argument is not NULL, a non-zero error code number is
449 returned via this argument in the event of an error. This is in addition to the
450 textual error message. Error codes and messages are listed below.
451 </P>
452 <P>
453 If the final argument, <i>tableptr</i>, is NULL, PCRE uses a default set of
454 character tables that are built when PCRE is compiled, using the default C
455 locale. Otherwise, <i>tableptr</i> must be an address that is the result of a
456 call to <b>pcre_maketables()</b>. This value is stored with the compiled
457 pattern, and used again by <b>pcre_exec()</b>, unless another table pointer is
458 passed to it. For more discussion, see the section on locale support below.
459 </P>
460 <P>
461 This code fragment shows a typical straightforward call to <b>pcre_compile()</b>:
462 <pre>
463 pcre *re;
464 const char *error;
465 int erroffset;
466 re = pcre_compile(
467 "^A.*Z", /* the pattern */
468 0, /* default options */
469 &error, /* for error message */
470 &erroffset, /* for error offset */
471 NULL); /* use default character tables */
472 </pre>
473 The following names for option bits are defined in the <b>pcre.h</b> header
474 file:
475 <pre>
476 PCRE_ANCHORED
477 </pre>
478 If this bit is set, the pattern is forced to be "anchored", that is, it is
479 constrained to match only at the first matching point in the string that is
480 being searched (the "subject string"). This effect can also be achieved by
481 appropriate constructs in the pattern itself, which is the only way to do it in
482 Perl.
483 <pre>
484 PCRE_AUTO_CALLOUT
485 </pre>
486 If this bit is set, <b>pcre_compile()</b> automatically inserts callout items,
487 all with number 255, before each pattern item. For discussion of the callout
488 facility, see the
489 <a href="pcrecallout.html"><b>pcrecallout</b></a>
490 documentation.
491 <pre>
492 PCRE_BSR_ANYCRLF
493 PCRE_BSR_UNICODE
494 </pre>
495 These options (which are mutually exclusive) control what the \R escape
496 sequence matches. The choice is either to match only CR, LF, or CRLF, or to
497 match any Unicode newline sequence. The default is specified when PCRE is
498 built. It can be overridden from within the pattern, or by setting an option
499 when a compiled pattern is matched.
500 <pre>
501 PCRE_CASELESS
502 </pre>
503 If this bit is set, letters in the pattern match both upper and lower case
504 letters. It is equivalent to Perl's /i option, and it can be changed within a
505 pattern by a (?i) option setting. In UTF-8 mode, PCRE always understands the
506 concept of case for characters whose values are less than 128, so caseless
507 matching is always possible. For characters with higher values, the concept of
508 case is supported if PCRE is compiled with Unicode property support, but not
509 otherwise. If you want to use caseless matching for characters 128 and above,
510 you must ensure that PCRE is compiled with Unicode property support as well as
511 with UTF-8 support.
512 <pre>
513 PCRE_DOLLAR_ENDONLY
514 </pre>
515 If this bit is set, a dollar metacharacter in the pattern matches only at the
516 end of the subject string. Without this option, a dollar also matches
517 immediately before a newline at the end of the string (but not before any other
518 newlines). The PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is set.
519 There is no equivalent to this option in Perl, and no way to set it within a
520 pattern.
521 <pre>
522 PCRE_DOTALL
523 </pre>
524 If this bit is set, a dot metacharater in the pattern matches all characters,
525 including those that indicate newline. Without it, a dot does not match when
526 the current position is at a newline. This option is equivalent to Perl's /s
527 option, and it can be changed within a pattern by a (?s) option setting. A
528 negative class such as [^a] always matches newline characters, independent of
529 the setting of this option.
530 <pre>
531 PCRE_DUPNAMES
532 </pre>
533 If this bit is set, names used to identify capturing subpatterns need not be
534 unique. This can be helpful for certain types of pattern when it is known that
535 only one instance of the named subpattern can ever be matched. There are more
536 details of named subpatterns below; see also the
537 <a href="pcrepattern.html"><b>pcrepattern</b></a>
538 documentation.
539 <pre>
540 PCRE_EXTENDED
541 </pre>
542 If this bit is set, whitespace data characters in the pattern are totally
543 ignored except when escaped or inside a character class. Whitespace does not
544 include the VT character (code 11). In addition, characters between an
545 unescaped # outside a character class and the next newline, inclusive, are also
546 ignored. This is equivalent to Perl's /x option, and it can be changed within a
547 pattern by a (?x) option setting.
548 </P>
549 <P>
550 This option makes it possible to include comments inside complicated patterns.
551 Note, however, that this applies only to data characters. Whitespace characters
552 may never appear within special character sequences in a pattern, for example
553 within the sequence (?( which introduces a conditional subpattern.
554 <pre>
555 PCRE_EXTRA
556 </pre>
557 This option was invented in order to turn on additional functionality of PCRE
558 that is incompatible with Perl, but it is currently of very little use. When
559 set, any backslash in a pattern that is followed by a letter that has no
560 special meaning causes an error, thus reserving these combinations for future
561 expansion. By default, as in Perl, a backslash followed by a letter with no
562 special meaning is treated as a literal. (Perl can, however, be persuaded to
563 give a warning for this.) There are at present no other features controlled by
564 this option. It can also be set by a (?X) option setting within a pattern.
565 <pre>
566 PCRE_FIRSTLINE
567 </pre>
568 If this option is set, an unanchored pattern is required to match before or at
569 the first newline in the subject string, though the matched text may continue
570 over the newline.
571 <pre>
572 PCRE_JAVASCRIPT_COMPAT
573 </pre>
574 If this option is set, PCRE's behaviour is changed in some ways so that it is
575 compatible with JavaScript rather than Perl. The changes are as follows:
576 </P>
577 <P>
578 (1) A lone closing square bracket in a pattern causes a compile-time error,
579 because this is illegal in JavaScript (by default it is treated as a data
580 character). Thus, the pattern AB]CD becomes illegal when this option is set.
581 </P>
582 <P>
583 (2) At run time, a back reference to an unset subpattern group matches an empty
584 string (by default this causes the current matching alternative to fail). A
585 pattern such as (\1)(a) succeeds when this option is set (assuming it can find
586 an "a" in the subject), whereas it fails by default, for Perl compatibility.
587 <pre>
588 PCRE_MULTILINE
589 </pre>
590 By default, PCRE treats the subject string as consisting of a single line of
591 characters (even if it actually contains newlines). The "start of line"
592 metacharacter (^) matches only at the start of the string, while the "end of
593 line" metacharacter ($) matches only at the end of the string, or before a
594 terminating newline (unless PCRE_DOLLAR_ENDONLY is set). This is the same as
595 Perl.
596 </P>
597 <P>
598 When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs
599 match immediately following or immediately before internal newlines in the
600 subject string, respectively, as well as at the very start and end. This is
601 equivalent to Perl's /m option, and it can be changed within a pattern by a
602 (?m) option setting. If there are no newlines in a subject string, or no
603 occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no effect.
604 <pre>
605 PCRE_NEWLINE_CR
606 PCRE_NEWLINE_LF
607 PCRE_NEWLINE_CRLF
608 PCRE_NEWLINE_ANYCRLF
609 PCRE_NEWLINE_ANY
610 </pre>
611 These options override the default newline definition that was chosen when PCRE
612 was built. Setting the first or the second specifies that a newline is
613 indicated by a single character (CR or LF, respectively). Setting
614 PCRE_NEWLINE_CRLF specifies that a newline is indicated by the two-character
615 CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies that any of the three
616 preceding sequences should be recognized. Setting PCRE_NEWLINE_ANY specifies
617 that any Unicode newline sequence should be recognized. The Unicode newline
618 sequences are the three just mentioned, plus the single characters VT (vertical
619 tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS (line
620 separator, U+2028), and PS (paragraph separator, U+2029). The last two are
621 recognized only in UTF-8 mode.
622 </P>
623 <P>
624 The newline setting in the options word uses three bits that are treated
625 as a number, giving eight possibilities. Currently only six are used (default
626 plus the five values above). This means that if you set more than one newline
627 option, the combination may or may not be sensible. For example,
628 PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to PCRE_NEWLINE_CRLF, but
629 other combinations may yield unused numbers and cause an error.
630 </P>
631 <P>
632 The only time that a line break is specially recognized when compiling a
633 pattern is if PCRE_EXTENDED is set, and an unescaped # outside a character
634 class is encountered. This indicates a comment that lasts until after the next
635 line break sequence. In other circumstances, line break sequences are treated
636 as literal data, except that in PCRE_EXTENDED mode, both CR and LF are treated
637 as whitespace characters and are therefore ignored.
638 </P>
639 <P>
640 The newline option that is set at compile time becomes the default that is used
641 for <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b>, but it can be overridden.
642 <pre>
643 PCRE_NO_AUTO_CAPTURE
644 </pre>
645 If this option is set, it disables the use of numbered capturing parentheses in
646 the pattern. Any opening parenthesis that is not followed by ? behaves as if it
647 were followed by ?: but named parentheses can still be used for capturing (and
648 they acquire numbers in the usual way). There is no equivalent of this option
649 in Perl.
650 <pre>
651 PCRE_UNGREEDY
652 </pre>
653 This option inverts the "greediness" of the quantifiers so that they are not
654 greedy by default, but become greedy if followed by "?". It is not compatible
655 with Perl. It can also be set by a (?U) option setting within the pattern.
656 <pre>
657 PCRE_UTF8
658 </pre>
659 This option causes PCRE to regard both the pattern and the subject as strings
660 of UTF-8 characters instead of single-byte character strings. However, it is
661 available only when PCRE is built to include UTF-8 support. If not, the use
662 of this option provokes an error. Details of how this option changes the
663 behaviour of PCRE are given in the
664 <a href="pcre.html#utf8support">section on UTF-8 support</a>
665 in the main
666 <a href="pcre.html"><b>pcre</b></a>
667 page.
668 <pre>
669 PCRE_NO_UTF8_CHECK
670 </pre>
671 When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
672 automatically checked. There is a discussion about the
673 <a href="pcre.html#utf8strings">validity of UTF-8 strings</a>
674 in the main
675 <a href="pcre.html"><b>pcre</b></a>
676 page. If an invalid UTF-8 sequence of bytes is found, <b>pcre_compile()</b>
677 returns an error. If you already know that your pattern is valid, and you want
678 to skip this check for performance reasons, you can set the PCRE_NO_UTF8_CHECK
679 option. When it is set, the effect of passing an invalid UTF-8 string as a
680 pattern is undefined. It may cause your program to crash. Note that this option
681 can also be passed to <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b>, to suppress
682 the UTF-8 validity checking of subject strings.
683 </P>
684 <br><a name="SEC8" href="#TOC1">COMPILATION ERROR CODES</a><br>
685 <P>
686 The following table lists the error codes than may be returned by
687 <b>pcre_compile2()</b>, along with the error messages that may be returned by
688 both compiling functions. As PCRE has developed, some error codes have fallen
689 out of use. To avoid confusion, they have not been re-used.
690 <pre>
691 0 no error
692 1 \ at end of pattern
693 2 \c at end of pattern
694 3 unrecognized character follows \
695 4 numbers out of order in {} quantifier
696 5 number too big in {} quantifier
697 6 missing terminating ] for character class
698 7 invalid escape sequence in character class
699 8 range out of order in character class
700 9 nothing to repeat
701 10 [this code is not in use]
702 11 internal error: unexpected repeat
703 12 unrecognized character after (? or (?-
704 13 POSIX named classes are supported only within a class
705 14 missing )
706 15 reference to non-existent subpattern
707 16 erroffset passed as NULL
708 17 unknown option bit(s) set
709 18 missing ) after comment
710 19 [this code is not in use]
711 20 regular expression is too large
712 21 failed to get memory
713 22 unmatched parentheses
714 23 internal error: code overflow
715 24 unrecognized character after (?&#60;
716 25 lookbehind assertion is not fixed length
717 26 malformed number or name after (?(
718 27 conditional group contains more than two branches
719 28 assertion expected after (?(
720 29 (?R or (?[+-]digits must be followed by )
721 30 unknown POSIX class name
722 31 POSIX collating elements are not supported
723 32 this version of PCRE is not compiled with PCRE_UTF8 support
724 33 [this code is not in use]
725 34 character value in \x{...} sequence is too large
726 35 invalid condition (?(0)
727 36 \C not allowed in lookbehind assertion
728 37 PCRE does not support \L, \l, \N, \U, or \u
729 38 number after (?C is &#62; 255
730 39 closing ) for (?C expected
731 40 recursive call could loop indefinitely
732 41 unrecognized character after (?P
733 42 syntax error in subpattern name (missing terminator)
734 43 two named subpatterns have the same name
735 44 invalid UTF-8 string
736 45 support for \P, \p, and \X has not been compiled
737 46 malformed \P or \p sequence
738 47 unknown property name after \P or \p
739 48 subpattern name is too long (maximum 32 characters)
740 49 too many named subpatterns (maximum 10000)
741 50 [this code is not in use]
742 51 octal value is greater than \377 (not in UTF-8 mode)
743 52 internal error: overran compiling workspace
744 53 internal error: previously-checked referenced subpattern not found
745 54 DEFINE group contains more than one branch
746 55 repeating a DEFINE group is not allowed
747 56 inconsistent NEWLINE options
748 57 \g is not followed by a braced, angle-bracketed, or quoted
749 name/number or by a plain number
750 58 a numbered reference must not be zero
751 59 (*VERB) with an argument is not supported
752 60 (*VERB) not recognized
753 61 number is too big
754 62 subpattern name expected
755 63 digit expected after (?+
756 64 ] is an invalid data character in JavaScript compatibility mode
757 </pre>
758 The numbers 32 and 10000 in errors 48 and 49 are defaults; different values may
759 be used if the limits were changed when PCRE was built.
760 </P>
761 <br><a name="SEC9" href="#TOC1">STUDYING A PATTERN</a><br>
762 <P>
763 <b>pcre_extra *pcre_study(const pcre *<i>code</i>, int <i>options</i></b>
764 <b>const char **<i>errptr</i>);</b>
765 </P>
766 <P>
767 If a compiled pattern is going to be used several times, it is worth spending
768 more time analyzing it in order to speed up the time taken for matching. The
769 function <b>pcre_study()</b> takes a pointer to a compiled pattern as its first
770 argument. If studying the pattern produces additional information that will
771 help speed up matching, <b>pcre_study()</b> returns a pointer to a
772 <b>pcre_extra</b> block, in which the <i>study_data</i> field points to the
773 results of the study.
774 </P>
775 <P>
776 The returned value from <b>pcre_study()</b> can be passed directly to
777 <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b>. However, a <b>pcre_extra</b> block
778 also contains other fields that can be set by the caller before the block is
779 passed; these are described
780 <a href="#extradata">below</a>
781 in the section on matching a pattern.
782 </P>
783 <P>
784 If studying the pattern does not produce any useful information,
785 <b>pcre_study()</b> returns NULL. In that circumstance, if the calling program
786 wants to pass any of the other fields to <b>pcre_exec()</b> or
787 <b>pcre_dfa_exec()</b>, it must set up its own <b>pcre_extra</b> block.
788 </P>
789 <P>
790 The second argument of <b>pcre_study()</b> contains option bits. At present, no
791 options are defined, and this argument should always be zero.
792 </P>
793 <P>
794 The third argument for <b>pcre_study()</b> is a pointer for an error message. If
795 studying succeeds (even if no data is returned), the variable it points to is
796 set to NULL. Otherwise it is set to point to a textual error message. This is a
797 static string that is part of the library. You must not try to free it. You
798 should test the error pointer for NULL after calling <b>pcre_study()</b>, to be
799 sure that it has run successfully.
800 </P>
801 <P>
802 This is a typical call to <b>pcre_study</b>():
803 <pre>
804 pcre_extra *pe;
805 pe = pcre_study(
806 re, /* result of pcre_compile() */
807 0, /* no options exist */
808 &error); /* set to NULL or points to a message */
809 </pre>
810 Studying a pattern does two things: first, a lower bound for the length of
811 subject string that is needed to match the pattern is computed. This does not
812 mean that there are any strings of that length that match, but it does
813 guarantee that no shorter strings match. The value is used by
814 <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b> to avoid wasting time by trying to
815 match strings that are shorter than the lower bound. You can find out the value
816 in a calling program via the <b>pcre_fullinfo()</b> function.
817 </P>
818 <P>
819 Studying a pattern is also useful for non-anchored patterns that do not have a
820 single fixed starting character. A bitmap of possible starting bytes is
821 created. This speeds up finding a position in the subject at which to start
822 matching.
823 <a name="localesupport"></a></P>
824 <br><a name="SEC10" href="#TOC1">LOCALE SUPPORT</a><br>
825 <P>
826 PCRE handles caseless matching, and determines whether characters are letters,
827 digits, or whatever, by reference to a set of tables, indexed by character
828 value. When running in UTF-8 mode, this applies only to characters with codes
829 less than 128. Higher-valued codes never match escapes such as \w or \d, but
830 can be tested with \p if PCRE is built with Unicode character property
831 support. The use of locales with Unicode is discouraged. If you are handling
832 characters with codes greater than 128, you should either use UTF-8 and
833 Unicode, or use locales, but not try to mix the two.
834 </P>
835 <P>
836 PCRE contains an internal set of tables that are used when the final argument
837 of <b>pcre_compile()</b> is NULL. These are sufficient for many applications.
838 Normally, the internal tables recognize only ASCII characters. However, when
839 PCRE is built, it is possible to cause the internal tables to be rebuilt in the
840 default "C" locale of the local system, which may cause them to be different.
841 </P>
842 <P>
843 The internal tables can always be overridden by tables supplied by the
844 application that calls PCRE. These may be created in a different locale from
845 the default. As more and more applications change to using Unicode, the need
846 for this locale support is expected to die away.
847 </P>
848 <P>
849 External tables are built by calling the <b>pcre_maketables()</b> function,
850 which has no arguments, in the relevant locale. The result can then be passed
851 to <b>pcre_compile()</b> or <b>pcre_exec()</b> as often as necessary. For
852 example, to build and use tables that are appropriate for the French locale
853 (where accented characters with values greater than 128 are treated as letters),
854 the following code could be used:
855 <pre>
856 setlocale(LC_CTYPE, "fr_FR");
857 tables = pcre_maketables();
858 re = pcre_compile(..., tables);
859 </pre>
860 The locale name "fr_FR" is used on Linux and other Unix-like systems; if you
861 are using Windows, the name for the French locale is "french".
862 </P>
863 <P>
864 When <b>pcre_maketables()</b> runs, the tables are built in memory that is
865 obtained via <b>pcre_malloc</b>. It is the caller's responsibility to ensure
866 that the memory containing the tables remains available for as long as it is
867 needed.
868 </P>
869 <P>
870 The pointer that is passed to <b>pcre_compile()</b> is saved with the compiled
871 pattern, and the same tables are used via this pointer by <b>pcre_study()</b>
872 and normally also by <b>pcre_exec()</b>. Thus, by default, for any single
873 pattern, compilation, studying and matching all happen in the same locale, but
874 different patterns can be compiled in different locales.
875 </P>
876 <P>
877 It is possible to pass a table pointer or NULL (indicating the use of the
878 internal tables) to <b>pcre_exec()</b>. Although not intended for this purpose,
879 this facility could be used to match a pattern in a different locale from the
880 one in which it was compiled. Passing table pointers at run time is discussed
881 below in the section on matching a pattern.
882 </P>
883 <br><a name="SEC11" href="#TOC1">INFORMATION ABOUT A PATTERN</a><br>
884 <P>
885 <b>int pcre_fullinfo(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
886 <b>int <i>what</i>, void *<i>where</i>);</b>
887 </P>
888 <P>
889 The <b>pcre_fullinfo()</b> function returns information about a compiled
890 pattern. It replaces the obsolete <b>pcre_info()</b> function, which is
891 nevertheless retained for backwards compability (and is documented below).
892 </P>
893 <P>
894 The first argument for <b>pcre_fullinfo()</b> is a pointer to the compiled
895 pattern. The second argument is the result of <b>pcre_study()</b>, or NULL if
896 the pattern was not studied. The third argument specifies which piece of
897 information is required, and the fourth argument is a pointer to a variable
898 to receive the data. The yield of the function is zero for success, or one of
899 the following negative numbers:
900 <pre>
901 PCRE_ERROR_NULL the argument <i>code</i> was NULL
902 the argument <i>where</i> was NULL
903 PCRE_ERROR_BADMAGIC the "magic number" was not found
904 PCRE_ERROR_BADOPTION the value of <i>what</i> was invalid
905 </pre>
906 The "magic number" is placed at the start of each compiled pattern as an simple
907 check against passing an arbitrary memory pointer. Here is a typical call of
908 <b>pcre_fullinfo()</b>, to obtain the length of the compiled pattern:
909 <pre>
910 int rc;
911 size_t length;
912 rc = pcre_fullinfo(
913 re, /* result of pcre_compile() */
914 pe, /* result of pcre_study(), or NULL */
915 PCRE_INFO_SIZE, /* what is required */
916 &length); /* where to put the data */
917 </pre>
918 The possible values for the third argument are defined in <b>pcre.h</b>, and are
919 as follows:
920 <pre>
921 PCRE_INFO_BACKREFMAX
922 </pre>
923 Return the number of the highest back reference in the pattern. The fourth
924 argument should point to an <b>int</b> variable. Zero is returned if there are
925 no back references.
926 <pre>
927 PCRE_INFO_CAPTURECOUNT
928 </pre>
929 Return the number of capturing subpatterns in the pattern. The fourth argument
930 should point to an <b>int</b> variable.
931 <pre>
932 PCRE_INFO_DEFAULT_TABLES
933 </pre>
934 Return a pointer to the internal default character tables within PCRE. The
935 fourth argument should point to an <b>unsigned char *</b> variable. This
936 information call is provided for internal use by the <b>pcre_study()</b>
937 function. External callers can cause PCRE to use its internal tables by passing
938 a NULL table pointer.
939 <pre>
940 PCRE_INFO_FIRSTBYTE
941 </pre>
942 Return information about the first byte of any matched string, for a
943 non-anchored pattern. The fourth argument should point to an <b>int</b>
944 variable. (This option used to be called PCRE_INFO_FIRSTCHAR; the old name is
945 still recognized for backwards compatibility.)
946 </P>
947 <P>
948 If there is a fixed first byte, for example, from a pattern such as
949 (cat|cow|coyote), its value is returned. Otherwise, if either
950 <br>
951 <br>
952 (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
953 starts with "^", or
954 <br>
955 <br>
956 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
957 (if it were set, the pattern would be anchored),
958 <br>
959 <br>
960 -1 is returned, indicating that the pattern matches only at the start of a
961 subject string or after any newline within the string. Otherwise -2 is
962 returned. For anchored patterns, -2 is returned.
963 <pre>
964 PCRE_INFO_FIRSTTABLE
965 </pre>
966 If the pattern was studied, and this resulted in the construction of a 256-bit
967 table indicating a fixed set of bytes for the first byte in any matching
968 string, a pointer to the table is returned. Otherwise NULL is returned. The
969 fourth argument should point to an <b>unsigned char *</b> variable.
970 <pre>
971 PCRE_INFO_HASCRORLF
972 </pre>
973 Return 1 if the pattern contains any explicit matches for CR or LF characters,
974 otherwise 0. The fourth argument should point to an <b>int</b> variable. An
975 explicit match is either a literal CR or LF character, or \r or \n.
976 <pre>
977 PCRE_INFO_JCHANGED
978 </pre>
979 Return 1 if the (?J) or (?-J) option setting is used in the pattern, otherwise
980 0. The fourth argument should point to an <b>int</b> variable. (?J) and
981 (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
982 <pre>
983 PCRE_INFO_LASTLITERAL
984 </pre>
985 Return the value of the rightmost literal byte that must exist in any matched
986 string, other than at its start, if such a byte has been recorded. The fourth
987 argument should point to an <b>int</b> variable. If there is no such byte, -1 is
988 returned. For anchored patterns, a last literal byte is recorded only if it
989 follows something of variable length. For example, for the pattern
990 /^a\d+z\d+/ the returned value is "z", but for /^a\dz\d/ the returned value
991 is -1.
992 <pre>
993 PCRE_INFO_MINLENGTH
994 </pre>
995 If the pattern was studied and a minimum length for matching subject strings
996 was computed, its value is returned. Otherwise the returned value is -1. The
997 value is a number of characters, not bytes (this may be relevant in UTF-8
998 mode). The fourth argument should point to an <b>int</b> variable. A
999 non-negative value is a lower bound to the length of any matching string. There
1000 may not be any strings of that length that do actually match, but every string
1001 that does match is at least that long.
1002 <pre>
1003 PCRE_INFO_NAMECOUNT
1004 PCRE_INFO_NAMEENTRYSIZE
1005 PCRE_INFO_NAMETABLE
1006 </pre>
1007 PCRE supports the use of named as well as numbered capturing parentheses. The
1008 names are just an additional way of identifying the parentheses, which still
1009 acquire numbers. Several convenience functions such as
1010 <b>pcre_get_named_substring()</b> are provided for extracting captured
1011 substrings by name. It is also possible to extract the data directly, by first
1012 converting the name to a number in order to access the correct pointers in the
1013 output vector (described with <b>pcre_exec()</b> below). To do the conversion,
1014 you need to use the name-to-number map, which is described by these three
1015 values.
1016 </P>
1017 <P>
1018 The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives
1019 the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each
1020 entry; both of these return an <b>int</b> value. The entry size depends on the
1021 length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first
1022 entry of the table (a pointer to <b>char</b>). The first two bytes of each entry
1023 are the number of the capturing parenthesis, most significant byte first. The
1024 rest of the entry is the corresponding name, zero terminated.
1025 </P>
1026 <P>
1027 The names are in alphabetical order. Duplicate names may appear if (?| is used
1028 to create multiple groups with the same number, as described in the
1029 <a href="pcrepattern.html#dupsubpatternnumber">section on duplicate subpattern numbers</a>
1030 in the
1031 <a href="pcrepattern.html"><b>pcrepattern</b></a>
1032 page. Duplicate names for subpatterns with different numbers are permitted only
1033 if PCRE_DUPNAMES is set. In all cases of duplicate names, they appear in the
1034 table in the order in which they were found in the pattern. In the absence of
1035 (?| this is the order of increasing number; when (?| is used this is not
1036 necessarily the case because later subpatterns may have lower numbers.
1037 </P>
1038 <P>
1039 As a simple example of the name/number table, consider the following pattern
1040 (assume PCRE_EXTENDED is set, so white space - including newlines - is
1041 ignored):
1042 <pre>
1043 (?&#60;date&#62; (?&#60;year&#62;(\d\d)?\d\d) - (?&#60;month&#62;\d\d) - (?&#60;day&#62;\d\d) )
1044 </pre>
1045 There are four named subpatterns, so the table has four entries, and each entry
1046 in the table is eight bytes long. The table is as follows, with non-printing
1047 bytes shows in hexadecimal, and undefined bytes shown as ??:
1048 <pre>
1049 00 01 d a t e 00 ??
1050 00 05 d a y 00 ?? ??
1051 00 04 m o n t h 00
1052 00 02 y e a r 00 ??
1053 </pre>
1054 When writing code to extract data from named subpatterns using the
1055 name-to-number map, remember that the length of the entries is likely to be
1056 different for each compiled pattern.
1057 <pre>
1058 PCRE_INFO_OKPARTIAL
1059 </pre>
1060 Return 1 if the pattern can be used for partial matching with
1061 <b>pcre_exec()</b>, otherwise 0. The fourth argument should point to an
1062 <b>int</b> variable. From release 8.00, this always returns 1, because the
1063 restrictions that previously applied to partial matching have been lifted. The
1064 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1065 documentation gives details of partial matching.
1066 <pre>
1067 PCRE_INFO_OPTIONS
1068 </pre>
1069 Return a copy of the options with which the pattern was compiled. The fourth
1070 argument should point to an <b>unsigned long int</b> variable. These option bits
1071 are those specified in the call to <b>pcre_compile()</b>, modified by any
1072 top-level option settings at the start of the pattern itself. In other words,
1073 they are the options that will be in force when matching starts. For example,
1074 if the pattern /(?im)abc(?-i)d/ is compiled with the PCRE_EXTENDED option, the
1075 result is PCRE_CASELESS, PCRE_MULTILINE, and PCRE_EXTENDED.
1076 </P>
1077 <P>
1078 A pattern is automatically anchored by PCRE if all of its top-level
1079 alternatives begin with one of the following:
1080 <pre>
1081 ^ unless PCRE_MULTILINE is set
1082 \A always
1083 \G always
1084 .* if PCRE_DOTALL is set and there are no back references to the subpattern in which .* appears
1085 </pre>
1086 For such patterns, the PCRE_ANCHORED bit is set in the options returned by
1087 <b>pcre_fullinfo()</b>.
1088 <pre>
1089 PCRE_INFO_SIZE
1090 </pre>
1091 Return the size of the compiled pattern, that is, the value that was passed as
1092 the argument to <b>pcre_malloc()</b> when PCRE was getting memory in which to
1093 place the compiled data. The fourth argument should point to a <b>size_t</b>
1094 variable.
1095 <pre>
1096 PCRE_INFO_STUDYSIZE
1097 </pre>
1098 Return the size of the data block pointed to by the <i>study_data</i> field in
1099 a <b>pcre_extra</b> block. That is, it is the value that was passed to
1100 <b>pcre_malloc()</b> when PCRE was getting memory into which to place the data
1101 created by <b>pcre_study()</b>. If <b>pcre_extra</b> is NULL, or there is no
1102 study data, zero is returned. The fourth argument should point to a
1103 <b>size_t</b> variable.
1104 </P>
1105 <br><a name="SEC12" href="#TOC1">OBSOLETE INFO FUNCTION</a><br>
1106 <P>
1107 <b>int pcre_info(const pcre *<i>code</i>, int *<i>optptr</i>, int</b>
1108 <b>*<i>firstcharptr</i>);</b>
1109 </P>
1110 <P>
1111 The <b>pcre_info()</b> function is now obsolete because its interface is too
1112 restrictive to return all the available data about a compiled pattern. New
1113 programs should use <b>pcre_fullinfo()</b> instead. The yield of
1114 <b>pcre_info()</b> is the number of capturing subpatterns, or one of the
1115 following negative numbers:
1116 <pre>
1117 PCRE_ERROR_NULL the argument <i>code</i> was NULL
1118 PCRE_ERROR_BADMAGIC the "magic number" was not found
1119 </pre>
1120 If the <i>optptr</i> argument is not NULL, a copy of the options with which the
1121 pattern was compiled is placed in the integer it points to (see
1122 PCRE_INFO_OPTIONS above).
1123 </P>
1124 <P>
1125 If the pattern is not anchored and the <i>firstcharptr</i> argument is not NULL,
1126 it is used to pass back information about the first character of any matched
1127 string (see PCRE_INFO_FIRSTBYTE above).
1128 </P>
1129 <br><a name="SEC13" href="#TOC1">REFERENCE COUNTS</a><br>
1130 <P>
1131 <b>int pcre_refcount(pcre *<i>code</i>, int <i>adjust</i>);</b>
1132 </P>
1133 <P>
1134 The <b>pcre_refcount()</b> function is used to maintain a reference count in the
1135 data block that contains a compiled pattern. It is provided for the benefit of
1136 applications that operate in an object-oriented manner, where different parts
1137 of the application may be using the same compiled pattern, but you want to free
1138 the block when they are all done.
1139 </P>
1140 <P>
1141 When a pattern is compiled, the reference count field is initialized to zero.
1142 It is changed only by calling this function, whose action is to add the
1143 <i>adjust</i> value (which may be positive or negative) to it. The yield of the
1144 function is the new value. However, the value of the count is constrained to
1145 lie between 0 and 65535, inclusive. If the new value is outside these limits,
1146 it is forced to the appropriate limit value.
1147 </P>
1148 <P>
1149 Except when it is zero, the reference count is not correctly preserved if a
1150 pattern is compiled on one host and then transferred to a host whose byte-order
1151 is different. (This seems a highly unlikely scenario.)
1152 </P>
1153 <br><a name="SEC14" href="#TOC1">MATCHING A PATTERN: THE TRADITIONAL FUNCTION</a><br>
1154 <P>
1155 <b>int pcre_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
1156 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
1157 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>);</b>
1158 </P>
1159 <P>
1160 The function <b>pcre_exec()</b> is called to match a subject string against a
1161 compiled pattern, which is passed in the <i>code</i> argument. If the
1162 pattern was studied, the result of the study should be passed in the
1163 <i>extra</i> argument. This function is the main matching facility of the
1164 library, and it operates in a Perl-like manner. For specialist use there is
1165 also an alternative matching function, which is described
1166 <a href="#dfamatch">below</a>
1167 in the section about the <b>pcre_dfa_exec()</b> function.
1168 </P>
1169 <P>
1170 In most applications, the pattern will have been compiled (and optionally
1171 studied) in the same process that calls <b>pcre_exec()</b>. However, it is
1172 possible to save compiled patterns and study data, and then use them later
1173 in different processes, possibly even on different hosts. For a discussion
1174 about this, see the
1175 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
1176 documentation.
1177 </P>
1178 <P>
1179 Here is an example of a simple call to <b>pcre_exec()</b>:
1180 <pre>
1181 int rc;
1182 int ovector[30];
1183 rc = pcre_exec(
1184 re, /* result of pcre_compile() */
1185 NULL, /* we didn't study the pattern */
1186 "some string", /* the subject string */
1187 11, /* the length of the subject string */
1188 0, /* start at offset 0 in the subject */
1189 0, /* default options */
1190 ovector, /* vector of integers for substring information */
1191 30); /* number of elements (NOT size in bytes) */
1192 <a name="extradata"></a></PRE>
1193 </P>
1194 <br><b>
1195 Extra data for <b>pcre_exec()</b>
1196 </b><br>
1197 <P>
1198 If the <i>extra</i> argument is not NULL, it must point to a <b>pcre_extra</b>
1199 data block. The <b>pcre_study()</b> function returns such a block (when it
1200 doesn't return NULL), but you can also create one for yourself, and pass
1201 additional information in it. The <b>pcre_extra</b> block contains the following
1202 fields (not necessarily in this order):
1203 <pre>
1204 unsigned long int <i>flags</i>;
1205 void *<i>study_data</i>;
1206 unsigned long int <i>match_limit</i>;
1207 unsigned long int <i>match_limit_recursion</i>;
1208 void *<i>callout_data</i>;
1209 const unsigned char *<i>tables</i>;
1210 </pre>
1211 The <i>flags</i> field is a bitmap that specifies which of the other fields
1212 are set. The flag bits are:
1213 <pre>
1214 PCRE_EXTRA_STUDY_DATA
1215 PCRE_EXTRA_MATCH_LIMIT
1216 PCRE_EXTRA_MATCH_LIMIT_RECURSION
1217 PCRE_EXTRA_CALLOUT_DATA
1218 PCRE_EXTRA_TABLES
1219 </pre>
1220 Other flag bits should be set to zero. The <i>study_data</i> field is set in the
1221 <b>pcre_extra</b> block that is returned by <b>pcre_study()</b>, together with
1222 the appropriate flag bit. You should not set this yourself, but you may add to
1223 the block by setting the other fields and their corresponding flag bits.
1224 </P>
1225 <P>
1226 The <i>match_limit</i> field provides a means of preventing PCRE from using up a
1227 vast amount of resources when running patterns that are not going to match,
1228 but which have a very large number of possibilities in their search trees. The
1229 classic example is a pattern that uses nested unlimited repeats.
1230 </P>
1231 <P>
1232 Internally, PCRE uses a function called <b>match()</b> which it calls repeatedly
1233 (sometimes recursively). The limit set by <i>match_limit</i> is imposed on the
1234 number of times this function is called during a match, which has the effect of
1235 limiting the amount of backtracking that can take place. For patterns that are
1236 not anchored, the count restarts from zero for each position in the subject
1237 string.
1238 </P>
1239 <P>
1240 The default value for the limit can be set when PCRE is built; the default
1241 default is 10 million, which handles all but the most extreme cases. You can
1242 override the default by suppling <b>pcre_exec()</b> with a <b>pcre_extra</b>
1243 block in which <i>match_limit</i> is set, and PCRE_EXTRA_MATCH_LIMIT is set in
1244 the <i>flags</i> field. If the limit is exceeded, <b>pcre_exec()</b> returns
1245 PCRE_ERROR_MATCHLIMIT.
1246 </P>
1247 <P>
1248 The <i>match_limit_recursion</i> field is similar to <i>match_limit</i>, but
1249 instead of limiting the total number of times that <b>match()</b> is called, it
1250 limits the depth of recursion. The recursion depth is a smaller number than the
1251 total number of calls, because not all calls to <b>match()</b> are recursive.
1252 This limit is of use only if it is set smaller than <i>match_limit</i>.
1253 </P>
1254 <P>
1255 Limiting the recursion depth limits the amount of stack that can be used, or,
1256 when PCRE has been compiled to use memory on the heap instead of the stack, the
1257 amount of heap memory that can be used.
1258 </P>
1259 <P>
1260 The default value for <i>match_limit_recursion</i> can be set when PCRE is
1261 built; the default default is the same value as the default for
1262 <i>match_limit</i>. You can override the default by suppling <b>pcre_exec()</b>
1263 with a <b>pcre_extra</b> block in which <i>match_limit_recursion</i> is set, and
1264 PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the <i>flags</i> field. If the limit
1265 is exceeded, <b>pcre_exec()</b> returns PCRE_ERROR_RECURSIONLIMIT.
1266 </P>
1267 <P>
1268 The <i>callout_data</i> field is used in conjunction with the "callout" feature,
1269 and is described in the
1270 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1271 documentation.
1272 </P>
1273 <P>
1274 The <i>tables</i> field is used to pass a character tables pointer to
1275 <b>pcre_exec()</b>; this overrides the value that is stored with the compiled
1276 pattern. A non-NULL value is stored with the compiled pattern only if custom
1277 tables were supplied to <b>pcre_compile()</b> via its <i>tableptr</i> argument.
1278 If NULL is passed to <b>pcre_exec()</b> using this mechanism, it forces PCRE's
1279 internal tables to be used. This facility is helpful when re-using patterns
1280 that have been saved after compiling with an external set of tables, because
1281 the external tables might be at a different address when <b>pcre_exec()</b> is
1282 called. See the
1283 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
1284 documentation for a discussion of saving compiled patterns for later use.
1285 <a name="execoptions"></a></P>
1286 <br><b>
1287 Option bits for <b>pcre_exec()</b>
1288 </b><br>
1289 <P>
1290 The unused bits of the <i>options</i> argument for <b>pcre_exec()</b> must be
1291 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_<i>xxx</i>,
1292 PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
1293 PCRE_NO_START_OPTIMIZE, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_SOFT, and
1294 PCRE_PARTIAL_HARD.
1295 <pre>
1296 PCRE_ANCHORED
1297 </pre>
1298 The PCRE_ANCHORED option limits <b>pcre_exec()</b> to matching at the first
1299 matching position. If a pattern was compiled with PCRE_ANCHORED, or turned out
1300 to be anchored by virtue of its contents, it cannot be made unachored at
1301 matching time.
1302 <pre>
1303 PCRE_BSR_ANYCRLF
1304 PCRE_BSR_UNICODE
1305 </pre>
1306 These options (which are mutually exclusive) control what the \R escape
1307 sequence matches. The choice is either to match only CR, LF, or CRLF, or to
1308 match any Unicode newline sequence. These options override the choice that was
1309 made or defaulted when the pattern was compiled.
1310 <pre>
1311 PCRE_NEWLINE_CR
1312 PCRE_NEWLINE_LF
1313 PCRE_NEWLINE_CRLF
1314 PCRE_NEWLINE_ANYCRLF
1315 PCRE_NEWLINE_ANY
1316 </pre>
1317 These options override the newline definition that was chosen or defaulted when
1318 the pattern was compiled. For details, see the description of
1319 <b>pcre_compile()</b> above. During matching, the newline choice affects the
1320 behaviour of the dot, circumflex, and dollar metacharacters. It may also alter
1321 the way the match position is advanced after a match failure for an unanchored
1322 pattern.
1323 </P>
1324 <P>
1325 When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY is set, and a
1326 match attempt for an unanchored pattern fails when the current position is at a
1327 CRLF sequence, and the pattern contains no explicit matches for CR or LF
1328 characters, the match position is advanced by two characters instead of one, in
1329 other words, to after the CRLF.
1330 </P>
1331 <P>
1332 The above rule is a compromise that makes the most common cases work as
1333 expected. For example, if the pattern is .+A (and the PCRE_DOTALL option is not
1334 set), it does not match the string "\r\nA" because, after failing at the
1335 start, it skips both the CR and the LF before retrying. However, the pattern
1336 [\r\n]A does match that string, because it contains an explicit CR or LF
1337 reference, and so advances only by one character after the first failure.
1338 </P>
1339 <P>
1340 An explicit match for CR of LF is either a literal appearance of one of those
1341 characters, or one of the \r or \n escape sequences. Implicit matches such as
1342 [^X] do not count, nor does \s (which includes CR and LF in the characters
1343 that it matches).
1344 </P>
1345 <P>
1346 Notwithstanding the above, anomalous effects may still occur when CRLF is a
1347 valid newline sequence and explicit \r or \n escapes appear in the pattern.
1348 <pre>
1349 PCRE_NOTBOL
1350 </pre>
1351 This option specifies that first character of the subject string is not the
1352 beginning of a line, so the circumflex metacharacter should not match before
1353 it. Setting this without PCRE_MULTILINE (at compile time) causes circumflex
1354 never to match. This option affects only the behaviour of the circumflex
1355 metacharacter. It does not affect \A.
1356 <pre>
1357 PCRE_NOTEOL
1358 </pre>
1359 This option specifies that the end of the subject string is not the end of a
1360 line, so the dollar metacharacter should not match it nor (except in multiline
1361 mode) a newline immediately before it. Setting this without PCRE_MULTILINE (at
1362 compile time) causes dollar never to match. This option affects only the
1363 behaviour of the dollar metacharacter. It does not affect \Z or \z.
1364 <pre>
1365 PCRE_NOTEMPTY
1366 </pre>
1367 An empty string is not considered to be a valid match if this option is set. If
1368 there are alternatives in the pattern, they are tried. If all the alternatives
1369 match the empty string, the entire match fails. For example, if the pattern
1370 <pre>
1371 a?b?
1372 </pre>
1373 is applied to a string not beginning with "a" or "b", it matches an empty
1374 string at the start of the subject. With PCRE_NOTEMPTY set, this match is not
1375 valid, so PCRE searches further into the string for occurrences of "a" or "b".
1376 <pre>
1377 PCRE_NOTEMPTY_ATSTART
1378 </pre>
1379 This is like PCRE_NOTEMPTY, except that an empty string match that is not at
1380 the start of the subject is permitted. If the pattern is anchored, such a match
1381 can occur only if the pattern contains \K.
1382 </P>
1383 <P>
1384 Perl has no direct equivalent of PCRE_NOTEMPTY or PCRE_NOTEMPTY_ATSTART, but it
1385 does make a special case of a pattern match of the empty string within its
1386 <b>split()</b> function, and when using the /g modifier. It is possible to
1387 emulate Perl's behaviour after matching a null string by first trying the match
1388 again at the same offset with PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED, and then
1389 if that fails, by advancing the starting offset (see below) and trying an
1390 ordinary match again. There is some code that demonstrates how to do this in
1391 the
1392 <a href="pcredemo.html"><b>pcredemo</b></a>
1393 sample program.
1394 <pre>
1395 PCRE_NO_START_OPTIMIZE
1396 </pre>
1397 There are a number of optimizations that <b>pcre_exec()</b> uses at the start of
1398 a match, in order to speed up the process. For example, if it is known that a
1399 match must start with a specific character, it searches the subject for that
1400 character, and fails immediately if it cannot find it, without actually running
1401 the main matching function. When callouts are in use, these optimizations can
1402 cause them to be skipped. This option disables the "start-up" optimizations,
1403 causing performance to suffer, but ensuring that the callouts do occur.
1404 <pre>
1405 PCRE_NO_UTF8_CHECK
1406 </pre>
1407 When PCRE_UTF8 is set at compile time, the validity of the subject as a UTF-8
1408 string is automatically checked when <b>pcre_exec()</b> is subsequently called.
1409 The value of <i>startoffset</i> is also checked to ensure that it points to the
1410 start of a UTF-8 character. There is a discussion about the validity of UTF-8
1411 strings in the
1412 <a href="pcre.html#utf8strings">section on UTF-8 support</a>
1413 in the main
1414 <a href="pcre.html"><b>pcre</b></a>
1415 page. If an invalid UTF-8 sequence of bytes is found, <b>pcre_exec()</b> returns
1416 the error PCRE_ERROR_BADUTF8. If <i>startoffset</i> contains an invalid value,
1417 PCRE_ERROR_BADUTF8_OFFSET is returned.
1418 </P>
1419 <P>
1420 If you already know that your subject is valid, and you want to skip these
1421 checks for performance reasons, you can set the PCRE_NO_UTF8_CHECK option when
1422 calling <b>pcre_exec()</b>. You might want to do this for the second and
1423 subsequent calls to <b>pcre_exec()</b> if you are making repeated calls to find
1424 all the matches in a single subject string. However, you should be sure that
1425 the value of <i>startoffset</i> points to the start of a UTF-8 character. When
1426 PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid UTF-8 string as a
1427 subject, or a value of <i>startoffset</i> that does not point to the start of a
1428 UTF-8 character, is undefined. Your program may crash.
1429 <pre>
1430 PCRE_PARTIAL_HARD
1431 PCRE_PARTIAL_SOFT
1432 </pre>
1433 These options turn on the partial matching feature. For backwards
1434 compatibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial match
1435 occurs if the end of the subject string is reached successfully, but there are
1436 not enough subject characters to complete the match. If this happens when
1437 PCRE_PARTIAL_HARD is set, <b>pcre_exec()</b> immediately returns
1438 PCRE_ERROR_PARTIAL. Otherwise, if PCRE_PARTIAL_SOFT is set, matching continues
1439 by testing any other alternatives. Only if they all fail is PCRE_ERROR_PARTIAL
1440 returned (instead of PCRE_ERROR_NOMATCH). The portion of the string that
1441 was inspected when the partial match was found is set as the first matching
1442 string. There is a more detailed discussion in the
1443 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1444 documentation.
1445 </P>
1446 <br><b>
1447 The string to be matched by <b>pcre_exec()</b>
1448 </b><br>
1449 <P>
1450 The subject string is passed to <b>pcre_exec()</b> as a pointer in
1451 <i>subject</i>, a length (in bytes) in <i>length</i>, and a starting byte offset
1452 in <i>startoffset</i>. In UTF-8 mode, the byte offset must point to the start of
1453 a UTF-8 character. Unlike the pattern string, the subject may contain binary
1454 zero bytes. When the starting offset is zero, the search for a match starts at
1455 the beginning of the subject, and this is by far the most common case.
1456 </P>
1457 <P>
1458 A non-zero starting offset is useful when searching for another match in the
1459 same subject by calling <b>pcre_exec()</b> again after a previous success.
1460 Setting <i>startoffset</i> differs from just passing over a shortened string and
1461 setting PCRE_NOTBOL in the case of a pattern that begins with any kind of
1462 lookbehind. For example, consider the pattern
1463 <pre>
1464 \Biss\B
1465 </pre>
1466 which finds occurrences of "iss" in the middle of words. (\B matches only if
1467 the current position in the subject is not a word boundary.) When applied to
1468 the string "Mississipi" the first call to <b>pcre_exec()</b> finds the first
1469 occurrence. If <b>pcre_exec()</b> is called again with just the remainder of the
1470 subject, namely "issipi", it does not match, because \B is always false at the
1471 start of the subject, which is deemed to be a word boundary. However, if
1472 <b>pcre_exec()</b> is passed the entire string again, but with <i>startoffset</i>
1473 set to 4, it finds the second occurrence of "iss" because it is able to look
1474 behind the starting point to discover that it is preceded by a letter.
1475 </P>
1476 <P>
1477 If a non-zero starting offset is passed when the pattern is anchored, one
1478 attempt to match at the given offset is made. This can only succeed if the
1479 pattern does not require the match to be at the start of the subject.
1480 </P>
1481 <br><b>
1482 How <b>pcre_exec()</b> returns captured substrings
1483 </b><br>
1484 <P>
1485 In general, a pattern matches a certain portion of the subject, and in
1486 addition, further substrings from the subject may be picked out by parts of the
1487 pattern. Following the usage in Jeffrey Friedl's book, this is called
1488 "capturing" in what follows, and the phrase "capturing subpattern" is used for
1489 a fragment of a pattern that picks out a substring. PCRE supports several other
1490 kinds of parenthesized subpattern that do not cause substrings to be captured.
1491 </P>
1492 <P>
1493 Captured substrings are returned to the caller via a vector of integers whose
1494 address is passed in <i>ovector</i>. The number of elements in the vector is
1495 passed in <i>ovecsize</i>, which must be a non-negative number. <b>Note</b>: this
1496 argument is NOT the size of <i>ovector</i> in bytes.
1497 </P>
1498 <P>
1499 The first two-thirds of the vector is used to pass back captured substrings,
1500 each substring using a pair of integers. The remaining third of the vector is
1501 used as workspace by <b>pcre_exec()</b> while matching capturing subpatterns,
1502 and is not available for passing back information. The number passed in
1503 <i>ovecsize</i> should always be a multiple of three. If it is not, it is
1504 rounded down.
1505 </P>
1506 <P>
1507 When a match is successful, information about captured substrings is returned
1508 in pairs of integers, starting at the beginning of <i>ovector</i>, and
1509 continuing up to two-thirds of its length at the most. The first element of
1510 each pair is set to the byte offset of the first character in a substring, and
1511 the second is set to the byte offset of the first character after the end of a
1512 substring. <b>Note</b>: these values are always byte offsets, even in UTF-8
1513 mode. They are not character counts.
1514 </P>
1515 <P>
1516 The first pair of integers, <i>ovector[0]</i> and <i>ovector[1]</i>, identify the
1517 portion of the subject string matched by the entire pattern. The next pair is
1518 used for the first capturing subpattern, and so on. The value returned by
1519 <b>pcre_exec()</b> is one more than the highest numbered pair that has been set.
1520 For example, if two substrings have been captured, the returned value is 3. If
1521 there are no capturing subpatterns, the return value from a successful match is
1522 1, indicating that just the first pair of offsets has been set.
1523 </P>
1524 <P>
1525 If a capturing subpattern is matched repeatedly, it is the last portion of the
1526 string that it matched that is returned.
1527 </P>
1528 <P>
1529 If the vector is too small to hold all the captured substring offsets, it is
1530 used as far as possible (up to two-thirds of its length), and the function
1531 returns a value of zero. If the substring offsets are not of interest,
1532 <b>pcre_exec()</b> may be called with <i>ovector</i> passed as NULL and
1533 <i>ovecsize</i> as zero. However, if the pattern contains back references and
1534 the <i>ovector</i> is not big enough to remember the related substrings, PCRE
1535 has to get additional memory for use during matching. Thus it is usually
1536 advisable to supply an <i>ovector</i>.
1537 </P>
1538 <P>
1539 The <b>pcre_fullinfo()</b> function can be used to find out how many capturing
1540 subpatterns there are in a compiled pattern. The smallest size for
1541 <i>ovector</i> that will allow for <i>n</i> captured substrings, in addition to
1542 the offsets of the substring matched by the whole pattern, is (<i>n</i>+1)*3.
1543 </P>
1544 <P>
1545 It is possible for capturing subpattern number <i>n+1</i> to match some part of
1546 the subject when subpattern <i>n</i> has not been used at all. For example, if
1547 the string "abc" is matched against the pattern (a|(z))(bc) the return from the
1548 function is 4, and subpatterns 1 and 3 are matched, but 2 is not. When this
1549 happens, both values in the offset pairs corresponding to unused subpatterns
1550 are set to -1.
1551 </P>
1552 <P>
1553 Offset values that correspond to unused subpatterns at the end of the
1554 expression are also set to -1. For example, if the string "abc" is matched
1555 against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not matched. The
1556 return from the function is 2, because the highest used capturing subpattern
1557 number is 1. However, you can refer to the offsets for the second and third
1558 capturing subpatterns if you wish (assuming the vector is large enough, of
1559 course).
1560 </P>
1561 <P>
1562 Some convenience functions are provided for extracting the captured substrings
1563 as separate strings. These are described below.
1564 <a name="errorlist"></a></P>
1565 <br><b>
1566 Error return values from <b>pcre_exec()</b>
1567 </b><br>
1568 <P>
1569 If <b>pcre_exec()</b> fails, it returns a negative number. The following are
1570 defined in the header file:
1571 <pre>
1572 PCRE_ERROR_NOMATCH (-1)
1573 </pre>
1574 The subject string did not match the pattern.
1575 <pre>
1576 PCRE_ERROR_NULL (-2)
1577 </pre>
1578 Either <i>code</i> or <i>subject</i> was passed as NULL, or <i>ovector</i> was
1579 NULL and <i>ovecsize</i> was not zero.
1580 <pre>
1581 PCRE_ERROR_BADOPTION (-3)
1582 </pre>
1583 An unrecognized bit was set in the <i>options</i> argument.
1584 <pre>
1585 PCRE_ERROR_BADMAGIC (-4)
1586 </pre>
1587 PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch
1588 the case when it is passed a junk pointer and to detect when a pattern that was
1589 compiled in an environment of one endianness is run in an environment with the
1590 other endianness. This is the error that PCRE gives when the magic number is
1591 not present.
1592 <pre>
1593 PCRE_ERROR_UNKNOWN_OPCODE (-5)
1594 </pre>
1595 While running the pattern match, an unknown item was encountered in the
1596 compiled pattern. This error could be caused by a bug in PCRE or by overwriting
1597 of the compiled pattern.
1598 <pre>
1599 PCRE_ERROR_NOMEMORY (-6)
1600 </pre>
1601 If a pattern contains back references, but the <i>ovector</i> that is passed to
1602 <b>pcre_exec()</b> is not big enough to remember the referenced substrings, PCRE
1603 gets a block of memory at the start of matching to use for this purpose. If the
1604 call via <b>pcre_malloc()</b> fails, this error is given. The memory is
1605 automatically freed at the end of matching.
1606 <pre>
1607 PCRE_ERROR_NOSUBSTRING (-7)
1608 </pre>
1609 This error is used by the <b>pcre_copy_substring()</b>,
1610 <b>pcre_get_substring()</b>, and <b>pcre_get_substring_list()</b> functions (see
1611 below). It is never returned by <b>pcre_exec()</b>.
1612 <pre>
1613 PCRE_ERROR_MATCHLIMIT (-8)
1614 </pre>
1615 The backtracking limit, as specified by the <i>match_limit</i> field in a
1616 <b>pcre_extra</b> structure (or defaulted) was reached. See the description
1617 above.
1618 <pre>
1619 PCRE_ERROR_CALLOUT (-9)
1620 </pre>
1621 This error is never generated by <b>pcre_exec()</b> itself. It is provided for
1622 use by callout functions that want to yield a distinctive error code. See the
1623 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1624 documentation for details.
1625 <pre>
1626 PCRE_ERROR_BADUTF8 (-10)
1627 </pre>
1628 A string that contains an invalid UTF-8 byte sequence was passed as a subject.
1629 <pre>
1630 PCRE_ERROR_BADUTF8_OFFSET (-11)
1631 </pre>
1632 The UTF-8 byte sequence that was passed as a subject was valid, but the value
1633 of <i>startoffset</i> did not point to the beginning of a UTF-8 character.
1634 <pre>
1635 PCRE_ERROR_PARTIAL (-12)
1636 </pre>
1637 The subject string did not match, but it did match partially. See the
1638 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1639 documentation for details of partial matching.
1640 <pre>
1641 PCRE_ERROR_BADPARTIAL (-13)
1642 </pre>
1643 This code is no longer in use. It was formerly returned when the PCRE_PARTIAL
1644 option was used with a compiled pattern containing items that were not
1645 supported for partial matching. From release 8.00 onwards, there are no
1646 restrictions on partial matching.
1647 <pre>
1648 PCRE_ERROR_INTERNAL (-14)
1649 </pre>
1650 An unexpected internal error has occurred. This error could be caused by a bug
1651 in PCRE or by overwriting of the compiled pattern.
1652 <pre>
1653 PCRE_ERROR_BADCOUNT (-15)
1654 </pre>
1655 This error is given if the value of the <i>ovecsize</i> argument is negative.
1656 <pre>
1657 PCRE_ERROR_RECURSIONLIMIT (-21)
1658 </pre>
1659 The internal recursion limit, as specified by the <i>match_limit_recursion</i>
1660 field in a <b>pcre_extra</b> structure (or defaulted) was reached. See the
1661 description above.
1662 <pre>
1663 PCRE_ERROR_BADNEWLINE (-23)
1664 </pre>
1665 An invalid combination of PCRE_NEWLINE_<i>xxx</i> options was given.
1666 </P>
1667 <P>
1668 Error numbers -16 to -20 and -22 are not used by <b>pcre_exec()</b>.
1669 </P>
1670 <br><a name="SEC15" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NUMBER</a><br>
1671 <P>
1672 <b>int pcre_copy_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1673 <b>int <i>stringcount</i>, int <i>stringnumber</i>, char *<i>buffer</i>,</b>
1674 <b>int <i>buffersize</i>);</b>
1675 </P>
1676 <P>
1677 <b>int pcre_get_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1678 <b>int <i>stringcount</i>, int <i>stringnumber</i>,</b>
1679 <b>const char **<i>stringptr</i>);</b>
1680 </P>
1681 <P>
1682 <b>int pcre_get_substring_list(const char *<i>subject</i>,</b>
1683 <b>int *<i>ovector</i>, int <i>stringcount</i>, const char ***<i>listptr</i>);</b>
1684 </P>
1685 <P>
1686 Captured substrings can be accessed directly by using the offsets returned by
1687 <b>pcre_exec()</b> in <i>ovector</i>. For convenience, the functions
1688 <b>pcre_copy_substring()</b>, <b>pcre_get_substring()</b>, and
1689 <b>pcre_get_substring_list()</b> are provided for extracting captured substrings
1690 as new, separate, zero-terminated strings. These functions identify substrings
1691 by number. The next section describes functions for extracting named
1692 substrings.
1693 </P>
1694 <P>
1695 A substring that contains a binary zero is correctly extracted and has a
1696 further zero added on the end, but the result is not, of course, a C string.
1697 However, you can process such a string by referring to the length that is
1698 returned by <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>.
1699 Unfortunately, the interface to <b>pcre_get_substring_list()</b> is not adequate
1700 for handling strings containing binary zeros, because the end of the final
1701 string is not independently indicated.
1702 </P>
1703 <P>
1704 The first three arguments are the same for all three of these functions:
1705 <i>subject</i> is the subject string that has just been successfully matched,
1706 <i>ovector</i> is a pointer to the vector of integer offsets that was passed to
1707 <b>pcre_exec()</b>, and <i>stringcount</i> is the number of substrings that were
1708 captured by the match, including the substring that matched the entire regular
1709 expression. This is the value returned by <b>pcre_exec()</b> if it is greater
1710 than zero. If <b>pcre_exec()</b> returned zero, indicating that it ran out of
1711 space in <i>ovector</i>, the value passed as <i>stringcount</i> should be the
1712 number of elements in the vector divided by three.
1713 </P>
1714 <P>
1715 The functions <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>
1716 extract a single substring, whose number is given as <i>stringnumber</i>. A
1717 value of zero extracts the substring that matched the entire pattern, whereas
1718 higher values extract the captured substrings. For <b>pcre_copy_substring()</b>,
1719 the string is placed in <i>buffer</i>, whose length is given by
1720 <i>buffersize</i>, while for <b>pcre_get_substring()</b> a new block of memory is
1721 obtained via <b>pcre_malloc</b>, and its address is returned via
1722 <i>stringptr</i>. The yield of the function is the length of the string, not
1723 including the terminating zero, or one of these error codes:
1724 <pre>
1725 PCRE_ERROR_NOMEMORY (-6)
1726 </pre>
1727 The buffer was too small for <b>pcre_copy_substring()</b>, or the attempt to get
1728 memory failed for <b>pcre_get_substring()</b>.
1729 <pre>
1730 PCRE_ERROR_NOSUBSTRING (-7)
1731 </pre>
1732 There is no substring whose number is <i>stringnumber</i>.
1733 </P>
1734 <P>
1735 The <b>pcre_get_substring_list()</b> function extracts all available substrings
1736 and builds a list of pointers to them. All this is done in a single block of
1737 memory that is obtained via <b>pcre_malloc</b>. The address of the memory block
1738 is returned via <i>listptr</i>, which is also the start of the list of string
1739 pointers. The end of the list is marked by a NULL pointer. The yield of the
1740 function is zero if all went well, or the error code
1741 <pre>
1742 PCRE_ERROR_NOMEMORY (-6)
1743 </pre>
1744 if the attempt to get the memory block failed.
1745 </P>
1746 <P>
1747 When any of these functions encounter a substring that is unset, which can
1748 happen when capturing subpattern number <i>n+1</i> matches some part of the
1749 subject, but subpattern <i>n</i> has not been used at all, they return an empty
1750 string. This can be distinguished from a genuine zero-length substring by
1751 inspecting the appropriate offset in <i>ovector</i>, which is negative for unset
1752 substrings.
1753 </P>
1754 <P>
1755 The two convenience functions <b>pcre_free_substring()</b> and
1756 <b>pcre_free_substring_list()</b> can be used to free the memory returned by
1757 a previous call of <b>pcre_get_substring()</b> or
1758 <b>pcre_get_substring_list()</b>, respectively. They do nothing more than call
1759 the function pointed to by <b>pcre_free</b>, which of course could be called
1760 directly from a C program. However, PCRE is used in some situations where it is
1761 linked via a special interface to another programming language that cannot use
1762 <b>pcre_free</b> directly; it is for these cases that the functions are
1763 provided.
1764 </P>
1765 <br><a name="SEC16" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NAME</a><br>
1766 <P>
1767 <b>int pcre_get_stringnumber(const pcre *<i>code</i>,</b>
1768 <b>const char *<i>name</i>);</b>
1769 </P>
1770 <P>
1771 <b>int pcre_copy_named_substring(const pcre *<i>code</i>,</b>
1772 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
1773 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
1774 <b>char *<i>buffer</i>, int <i>buffersize</i>);</b>
1775 </P>
1776 <P>
1777 <b>int pcre_get_named_substring(const pcre *<i>code</i>,</b>
1778 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
1779 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
1780 <b>const char **<i>stringptr</i>);</b>
1781 </P>
1782 <P>
1783 To extract a substring by name, you first have to find associated number.
1784 For example, for this pattern
1785 <pre>
1786 (a+)b(?&#60;xxx&#62;\d+)...
1787 </pre>
1788 the number of the subpattern called "xxx" is 2. If the name is known to be
1789 unique (PCRE_DUPNAMES was not set), you can find the number from the name by
1790 calling <b>pcre_get_stringnumber()</b>. The first argument is the compiled
1791 pattern, and the second is the name. The yield of the function is the
1792 subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no subpattern of
1793 that name.
1794 </P>
1795 <P>
1796 Given the number, you can extract the substring directly, or use one of the
1797 functions described in the previous section. For convenience, there are also
1798 two functions that do the whole job.
1799 </P>
1800 <P>
1801 Most of the arguments of <b>pcre_copy_named_substring()</b> and
1802 <b>pcre_get_named_substring()</b> are the same as those for the similarly named
1803 functions that extract by number. As these are described in the previous
1804 section, they are not re-described here. There are just two differences:
1805 </P>
1806 <P>
1807 First, instead of a substring number, a substring name is given. Second, there
1808 is an extra argument, given at the start, which is a pointer to the compiled
1809 pattern. This is needed in order to gain access to the name-to-number
1810 translation table.
1811 </P>
1812 <P>
1813 These functions call <b>pcre_get_stringnumber()</b>, and if it succeeds, they
1814 then call <b>pcre_copy_substring()</b> or <b>pcre_get_substring()</b>, as
1815 appropriate. <b>NOTE:</b> If PCRE_DUPNAMES is set and there are duplicate names,
1816 the behaviour may not be what you want (see the next section).
1817 </P>
1818 <P>
1819 <b>Warning:</b> If the pattern uses the (?| feature to set up multiple
1820 subpatterns with the same number, as described in the
1821 <a href="pcrepattern.html#dupsubpatternnumber">section on duplicate subpattern numbers</a>
1822 in the
1823 <a href="pcrepattern.html"><b>pcrepattern</b></a>
1824 page, you cannot use names to distinguish the different subpatterns, because
1825 names are not included in the compiled code. The matching process uses only
1826 numbers. For this reason, the use of different names for subpatterns of the
1827 same number causes an error at compile time.
1828 </P>
1829 <br><a name="SEC17" href="#TOC1">DUPLICATE SUBPATTERN NAMES</a><br>
1830 <P>
1831 <b>int pcre_get_stringtable_entries(const pcre *<i>code</i>,</b>
1832 <b>const char *<i>name</i>, char **<i>first</i>, char **<i>last</i>);</b>
1833 </P>
1834 <P>
1835 When a pattern is compiled with the PCRE_DUPNAMES option, names for subpatterns
1836 are not required to be unique. (Duplicate names are always allowed for
1837 subpatterns with the same number, created by using the (?| feature. Indeed, if
1838 such subpatterns are named, they are required to use the same names.)
1839 </P>
1840 <P>
1841 Normally, patterns with duplicate names are such that in any one match, only
1842 one of the named subpatterns participates. An example is shown in the
1843 <a href="pcrepattern.html"><b>pcrepattern</b></a>
1844 documentation.
1845 </P>
1846 <P>
1847 When duplicates are present, <b>pcre_copy_named_substring()</b> and
1848 <b>pcre_get_named_substring()</b> return the first substring corresponding to
1849 the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING (-7) is
1850 returned; no data is returned. The <b>pcre_get_stringnumber()</b> function
1851 returns one of the numbers that are associated with the name, but it is not
1852 defined which it is.
1853 </P>
1854 <P>
1855 If you want to get full details of all captured substrings for a given name,
1856 you must use the <b>pcre_get_stringtable_entries()</b> function. The first
1857 argument is the compiled pattern, and the second is the name. The third and
1858 fourth are pointers to variables which are updated by the function. After it
1859 has run, they point to the first and last entries in the name-to-number table
1860 for the given name. The function itself returns the length of each entry, or
1861 PCRE_ERROR_NOSUBSTRING (-7) if there are none. The format of the table is
1862 described above in the section entitled <i>Information about a pattern</i>.
1863 Given all the relevant entries for the name, you can extract each of their
1864 numbers, and hence the captured data, if any.
1865 </P>
1866 <br><a name="SEC18" href="#TOC1">FINDING ALL POSSIBLE MATCHES</a><br>
1867 <P>
1868 The traditional matching function uses a similar algorithm to Perl, which stops
1869 when it finds the first match, starting at a given point in the subject. If you
1870 want to find all possible matches, or the longest possible match, consider
1871 using the alternative matching function (see below) instead. If you cannot use
1872 the alternative function, but still need to find all possible matches, you
1873 can kludge it up by making use of the callout facility, which is described in
1874 the
1875 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1876 documentation.
1877 </P>
1878 <P>
1879 What you have to do is to insert a callout right at the end of the pattern.
1880 When your callout function is called, extract and save the current matched
1881 substring. Then return 1, which forces <b>pcre_exec()</b> to backtrack and try
1882 other alternatives. Ultimately, when it runs out of matches, <b>pcre_exec()</b>
1883 will yield PCRE_ERROR_NOMATCH.
1884 <a name="dfamatch"></a></P>
1885 <br><a name="SEC19" href="#TOC1">MATCHING A PATTERN: THE ALTERNATIVE FUNCTION</a><br>
1886 <P>
1887 <b>int pcre_dfa_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
1888 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
1889 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>,</b>
1890 <b>int *<i>workspace</i>, int <i>wscount</i>);</b>
1891 </P>
1892 <P>
1893 The function <b>pcre_dfa_exec()</b> is called to match a subject string against
1894 a compiled pattern, using a matching algorithm that scans the subject string
1895 just once, and does not backtrack. This has different characteristics to the
1896 normal algorithm, and is not compatible with Perl. Some of the features of PCRE
1897 patterns are not supported. Nevertheless, there are times when this kind of
1898 matching can be useful. For a discussion of the two matching algorithms, and a
1899 list of features that <b>pcre_dfa_exec()</b> does not support, see the
1900 <a href="pcrematching.html"><b>pcrematching</b></a>
1901 documentation.
1902 </P>
1903 <P>
1904 The arguments for the <b>pcre_dfa_exec()</b> function are the same as for
1905 <b>pcre_exec()</b>, plus two extras. The <i>ovector</i> argument is used in a
1906 different way, and this is described below. The other common arguments are used
1907 in the same way as for <b>pcre_exec()</b>, so their description is not repeated
1908 here.
1909 </P>
1910 <P>
1911 The two additional arguments provide workspace for the function. The workspace
1912 vector should contain at least 20 elements. It is used for keeping track of
1913 multiple paths through the pattern tree. More workspace will be needed for
1914 patterns and subjects where there are a lot of potential matches.
1915 </P>
1916 <P>
1917 Here is an example of a simple call to <b>pcre_dfa_exec()</b>:
1918 <pre>
1919 int rc;
1920 int ovector[10];
1921 int wspace[20];
1922 rc = pcre_dfa_exec(
1923 re, /* result of pcre_compile() */
1924 NULL, /* we didn't study the pattern */
1925 "some string", /* the subject string */
1926 11, /* the length of the subject string */
1927 0, /* start at offset 0 in the subject */
1928 0, /* default options */
1929 ovector, /* vector of integers for substring information */
1930 10, /* number of elements (NOT size in bytes) */
1931 wspace, /* working space vector */
1932 20); /* number of elements (NOT size in bytes) */
1933 </PRE>
1934 </P>
1935 <br><b>
1936 Option bits for <b>pcre_dfa_exec()</b>
1937 </b><br>
1938 <P>
1939 The unused bits of the <i>options</i> argument for <b>pcre_dfa_exec()</b> must be
1940 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_<i>xxx</i>,
1941 PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
1942 PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_HARD, PCRE_PARTIAL_SOFT, PCRE_DFA_SHORTEST,
1943 and PCRE_DFA_RESTART. All but the last four of these are exactly the same as
1944 for <b>pcre_exec()</b>, so their description is not repeated here.
1945 <pre>
1946 PCRE_PARTIAL_HARD
1947 PCRE_PARTIAL_SOFT
1948 </pre>
1949 These have the same general effect as they do for <b>pcre_exec()</b>, but the
1950 details are slightly different. When PCRE_PARTIAL_HARD is set for
1951 <b>pcre_dfa_exec()</b>, it returns PCRE_ERROR_PARTIAL if the end of the subject
1952 is reached and there is still at least one matching possibility that requires
1953 additional characters. This happens even if some complete matches have also
1954 been found. When PCRE_PARTIAL_SOFT is set, the return code PCRE_ERROR_NOMATCH
1955 is converted into PCRE_ERROR_PARTIAL if the end of the subject is reached,
1956 there have been no complete matches, but there is still at least one matching
1957 possibility. The portion of the string that was inspected when the longest
1958 partial match was found is set as the first matching string in both cases.
1959 <pre>
1960 PCRE_DFA_SHORTEST
1961 </pre>
1962 Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to stop as
1963 soon as it has found one match. Because of the way the alternative algorithm
1964 works, this is necessarily the shortest possible match at the first possible
1965 matching point in the subject string.
1966 <pre>
1967 PCRE_DFA_RESTART
1968 </pre>
1969 When <b>pcre_dfa_exec()</b> returns a partial match, it is possible to call it
1970 again, with additional subject characters, and have it continue with the same
1971 match. The PCRE_DFA_RESTART option requests this action; when it is set, the
1972 <i>workspace</i> and <i>wscount</i> options must reference the same vector as
1973 before because data about the match so far is left in them after a partial
1974 match. There is more discussion of this facility in the
1975 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1976 documentation.
1977 </P>
1978 <br><b>
1979 Successful returns from <b>pcre_dfa_exec()</b>
1980 </b><br>
1981 <P>
1982 When <b>pcre_dfa_exec()</b> succeeds, it may have matched more than one
1983 substring in the subject. Note, however, that all the matches from one run of
1984 the function start at the same point in the subject. The shorter matches are
1985 all initial substrings of the longer matches. For example, if the pattern
1986 <pre>
1987 &#60;.*&#62;
1988 </pre>
1989 is matched against the string
1990 <pre>
1991 This is &#60;something&#62; &#60;something else&#62; &#60;something further&#62; no more
1992 </pre>
1993 the three matched strings are
1994 <pre>
1995 &#60;something&#62;
1996 &#60;something&#62; &#60;something else&#62;
1997 &#60;something&#62; &#60;something else&#62; &#60;something further&#62;
1998 </pre>
1999 On success, the yield of the function is a number greater than zero, which is
2000 the number of matched substrings. The substrings themselves are returned in
2001 <i>ovector</i>. Each string uses two elements; the first is the offset to the
2002 start, and the second is the offset to the end. In fact, all the strings have
2003 the same start offset. (Space could have been saved by giving this only once,
2004 but it was decided to retain some compatibility with the way <b>pcre_exec()</b>
2005 returns data, even though the meaning of the strings is different.)
2006 </P>
2007 <P>
2008 The strings are returned in reverse order of length; that is, the longest
2009 matching string is given first. If there were too many matches to fit into
2010 <i>ovector</i>, the yield of the function is zero, and the vector is filled with
2011 the longest matches.
2012 </P>
2013 <br><b>
2014 Error returns from <b>pcre_dfa_exec()</b>
2015 </b><br>
2016 <P>
2017 The <b>pcre_dfa_exec()</b> function returns a negative number when it fails.
2018 Many of the errors are the same as for <b>pcre_exec()</b>, and these are
2019 described
2020 <a href="#errorlist">above.</a>
2021 There are in addition the following errors that are specific to
2022 <b>pcre_dfa_exec()</b>:
2023 <pre>
2024 PCRE_ERROR_DFA_UITEM (-16)
2025 </pre>
2026 This return is given if <b>pcre_dfa_exec()</b> encounters an item in the pattern
2027 that it does not support, for instance, the use of \C or a back reference.
2028 <pre>
2029 PCRE_ERROR_DFA_UCOND (-17)
2030 </pre>
2031 This return is given if <b>pcre_dfa_exec()</b> encounters a condition item that
2032 uses a back reference for the condition, or a test for recursion in a specific
2033 group. These are not supported.
2034 <pre>
2035 PCRE_ERROR_DFA_UMLIMIT (-18)
2036 </pre>
2037 This return is given if <b>pcre_dfa_exec()</b> is called with an <i>extra</i>
2038 block that contains a setting of the <i>match_limit</i> field. This is not
2039 supported (it is meaningless).
2040 <pre>
2041 PCRE_ERROR_DFA_WSSIZE (-19)
2042 </pre>
2043 This return is given if <b>pcre_dfa_exec()</b> runs out of space in the
2044 <i>workspace</i> vector.
2045 <pre>
2046 PCRE_ERROR_DFA_RECURSE (-20)
2047 </pre>
2048 When a recursive subpattern is processed, the matching function calls itself
2049 recursively, using private vectors for <i>ovector</i> and <i>workspace</i>. This
2050 error is given if the output vector is not large enough. This should be
2051 extremely rare, as a vector of size 1000 is used.
2052 </P>
2053 <br><a name="SEC20" href="#TOC1">SEE ALSO</a><br>
2054 <P>
2055 <b>pcrebuild</b>(3), <b>pcrecallout</b>(3), <b>pcrecpp(3)</b>(3),
2056 <b>pcrematching</b>(3), <b>pcrepartial</b>(3), <b>pcreposix</b>(3),
2057 <b>pcreprecompile</b>(3), <b>pcresample</b>(3), <b>pcrestack</b>(3).
2058 </P>
2059 <br><a name="SEC21" href="#TOC1">AUTHOR</a><br>
2060 <P>
2061 Philip Hazel
2062 <br>
2063 University Computing Service
2064 <br>
2065 Cambridge CB2 3QH, England.
2066 <br>
2067 </P>
2068 <br><a name="SEC22" href="#TOC1">REVISION</a><br>
2069 <P>
2070 Last updated: 03 October 2009
2071 <br>
2072 Copyright &copy; 1997-2009 University of Cambridge.
2073 <br>
2074 <p>
2075 Return to the <a href="index.html">PCRE index page</a>.
2076 </p>

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