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

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