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1 <html>
2 <head>
3 <title>pcreapi specification</title>
4 </head>
5 <body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
6 <h1>pcreapi man page</h1>
7 <p>
8 Return to the <a href="index.html">PCRE index page</a>.
9 </p>
10 <p>
11 This page is part of the PCRE HTML documentation. It was generated automatically
12 from the original man page. If there is any nonsense in it, please consult the
13 man page, in case the conversion went wrong.
14 <br>
15 <ul>
16 <li><a name="TOC1" href="#SEC1">PCRE NATIVE API</a>
17 <li><a name="TOC2" href="#SEC2">PCRE API OVERVIEW</a>
18 <li><a name="TOC3" href="#SEC3">NEWLINES</a>
19 <li><a name="TOC4" href="#SEC4">MULTITHREADING</a>
21 <li><a name="TOC6" href="#SEC6">CHECKING BUILD-TIME OPTIONS</a>
22 <li><a name="TOC7" href="#SEC7">COMPILING A PATTERN</a>
23 <li><a name="TOC8" href="#SEC8">COMPILATION ERROR CODES</a>
24 <li><a name="TOC9" href="#SEC9">STUDYING A PATTERN</a>
25 <li><a name="TOC10" href="#SEC10">LOCALE SUPPORT</a>
26 <li><a name="TOC11" href="#SEC11">INFORMATION ABOUT A PATTERN</a>
27 <li><a name="TOC12" href="#SEC12">OBSOLETE INFO FUNCTION</a>
28 <li><a name="TOC13" href="#SEC13">REFERENCE COUNTS</a>
32 <li><a name="TOC17" href="#SEC17">DUPLICATE SUBPATTERN NAMES</a>
33 <li><a name="TOC18" href="#SEC18">FINDING ALL POSSIBLE MATCHES</a>
35 <li><a name="TOC20" href="#SEC20">SEE ALSO</a>
36 <li><a name="TOC21" href="#SEC21">AUTHOR</a>
37 <li><a name="TOC22" href="#SEC22">REVISION</a>
38 </ul>
39 <br><a name="SEC1" href="#TOC1">PCRE NATIVE API</a><br>
40 <P>
41 <b>#include &#60;pcre.h&#62;</b>
42 </P>
43 <P>
44 <b>pcre *pcre_compile(const char *<i>pattern</i>, int <i>options</i>,</b>
45 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
46 <b>const unsigned char *<i>tableptr</i>);</b>
47 </P>
48 <P>
49 <b>pcre *pcre_compile2(const char *<i>pattern</i>, int <i>options</i>,</b>
50 <b>int *<i>errorcodeptr</i>,</b>
51 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
52 <b>const unsigned char *<i>tableptr</i>);</b>
53 </P>
54 <P>
55 <b>pcre_extra *pcre_study(const pcre *<i>code</i>, int <i>options</i>,</b>
56 <b>const char **<i>errptr</i>);</b>
57 </P>
58 <P>
59 <b>int pcre_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
60 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
61 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>);</b>
62 </P>
63 <P>
64 <b>int pcre_dfa_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
65 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
66 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>,</b>
67 <b>int *<i>workspace</i>, int <i>wscount</i>);</b>
68 </P>
69 <P>
70 <b>int pcre_copy_named_substring(const pcre *<i>code</i>,</b>
71 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
72 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
73 <b>char *<i>buffer</i>, int <i>buffersize</i>);</b>
74 </P>
75 <P>
76 <b>int pcre_copy_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
77 <b>int <i>stringcount</i>, int <i>stringnumber</i>, char *<i>buffer</i>,</b>
78 <b>int <i>buffersize</i>);</b>
79 </P>
80 <P>
81 <b>int pcre_get_named_substring(const pcre *<i>code</i>,</b>
82 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
83 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
84 <b>const char **<i>stringptr</i>);</b>
85 </P>
86 <P>
87 <b>int pcre_get_stringnumber(const pcre *<i>code</i>,</b>
88 <b>const char *<i>name</i>);</b>
89 </P>
90 <P>
91 <b>int pcre_get_stringtable_entries(const pcre *<i>code</i>,</b>
92 <b>const char *<i>name</i>, char **<i>first</i>, char **<i>last</i>);</b>
93 </P>
94 <P>
95 <b>int pcre_get_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
96 <b>int <i>stringcount</i>, int <i>stringnumber</i>,</b>
97 <b>const char **<i>stringptr</i>);</b>
98 </P>
99 <P>
100 <b>int pcre_get_substring_list(const char *<i>subject</i>,</b>
101 <b>int *<i>ovector</i>, int <i>stringcount</i>, const char ***<i>listptr</i>);</b>
102 </P>
103 <P>
104 <b>void pcre_free_substring(const char *<i>stringptr</i>);</b>
105 </P>
106 <P>
107 <b>void pcre_free_substring_list(const char **<i>stringptr</i>);</b>
108 </P>
109 <P>
110 <b>const unsigned char *pcre_maketables(void);</b>
111 </P>
112 <P>
113 <b>int pcre_fullinfo(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
114 <b>int <i>what</i>, void *<i>where</i>);</b>
115 </P>
116 <P>
117 <b>int pcre_info(const pcre *<i>code</i>, int *<i>optptr</i>, int</b>
118 <b>*<i>firstcharptr</i>);</b>
119 </P>
120 <P>
121 <b>int pcre_refcount(pcre *<i>code</i>, int <i>adjust</i>);</b>
122 </P>
123 <P>
124 <b>int pcre_config(int <i>what</i>, void *<i>where</i>);</b>
125 </P>
126 <P>
127 <b>char *pcre_version(void);</b>
128 </P>
129 <P>
130 <b>void *(*pcre_malloc)(size_t);</b>
131 </P>
132 <P>
133 <b>void (*pcre_free)(void *);</b>
134 </P>
135 <P>
136 <b>void *(*pcre_stack_malloc)(size_t);</b>
137 </P>
138 <P>
139 <b>void (*pcre_stack_free)(void *);</b>
140 </P>
141 <P>
142 <b>int (*pcre_callout)(pcre_callout_block *);</b>
143 </P>
144 <br><a name="SEC2" href="#TOC1">PCRE API OVERVIEW</a><br>
145 <P>
146 PCRE has its own native API, which is described in this document. There are
147 also some wrapper functions that correspond to the POSIX regular expression
148 API. These are described in the
149 <a href="pcreposix.html"><b>pcreposix</b></a>
150 documentation. Both of these APIs define a set of C function calls. A C++
151 wrapper is distributed with PCRE. It is documented in the
152 <a href="pcrecpp.html"><b>pcrecpp</b></a>
153 page.
154 </P>
155 <P>
156 The native API C function prototypes are defined in the header file
157 <b>pcre.h</b>, and on Unix systems the library itself is called <b>libpcre</b>.
158 It can normally be accessed by adding <b>-lpcre</b> to the command for linking
159 an application that uses PCRE. The header file defines the macros PCRE_MAJOR
160 and PCRE_MINOR to contain the major and minor release numbers for the library.
161 Applications can use these to include support for different releases of PCRE.
162 </P>
163 <P>
164 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 compile and 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 <a name="newlines"></a></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 At compile time, the newline convention can be specified by the <i>options</i>
266 argument of <b>pcre_compile()</b>, or it can be specified by special text at the
267 start of the pattern itself; this overrides any other settings. See the
268 <a href="pcrepattern.html"><b>pcrepattern</b></a>
269 page for details of the special character sequences.
270 </P>
271 <P>
272 In the PCRE documentation the word "newline" is used to mean "the character or
273 pair of characters that indicate a line break". The choice of newline
274 convention affects the handling of the dot, circumflex, and dollar
275 metacharacters, the handling of #-comments in /x mode, and, when CRLF is a
276 recognized line ending sequence, the match position advancement for a
277 non-anchored pattern. There is more detail about this in the
278 <a href="#execoptions">section on <b>pcre_exec()</b> options</a>
279 below.
280 </P>
281 <P>
282 The choice of newline convention does not affect the interpretation of
283 the \n or \r escape sequences, nor does it affect what \R matches, which is
284 controlled in a similar way, but by separate options.
285 </P>
286 <br><a name="SEC4" href="#TOC1">MULTITHREADING</a><br>
287 <P>
288 The PCRE functions can be used in multi-threading applications, with the
289 proviso that the memory management functions pointed to by <b>pcre_malloc</b>,
290 <b>pcre_free</b>, <b>pcre_stack_malloc</b>, and <b>pcre_stack_free</b>, and the
291 callout function pointed to by <b>pcre_callout</b>, are shared by all threads.
292 </P>
293 <P>
294 The compiled form of a regular expression is not altered during matching, so
295 the same compiled pattern can safely be used by several threads at once.
296 </P>
297 <br><a name="SEC5" href="#TOC1">SAVING PRECOMPILED PATTERNS FOR LATER USE</a><br>
298 <P>
299 The compiled form of a regular expression can be saved and re-used at a later
300 time, possibly by a different program, and even on a host other than the one on
301 which it was compiled. Details are given in the
302 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
303 documentation. However, compiling a regular expression with one version of PCRE
304 for use with a different version is not guaranteed to work and may cause
305 crashes.
306 </P>
307 <br><a name="SEC6" href="#TOC1">CHECKING BUILD-TIME OPTIONS</a><br>
308 <P>
309 <b>int pcre_config(int <i>what</i>, void *<i>where</i>);</b>
310 </P>
311 <P>
312 The function <b>pcre_config()</b> makes it possible for a PCRE client to
313 discover which optional features have been compiled into the PCRE library. The
314 <a href="pcrebuild.html"><b>pcrebuild</b></a>
315 documentation has more details about these optional features.
316 </P>
317 <P>
318 The first argument for <b>pcre_config()</b> is an integer, specifying which
319 information is required; the second argument is a pointer to a variable into
320 which the information is placed. The following information is available:
321 <pre>
323 </pre>
324 The output is an integer that is set to one if UTF-8 support is available;
325 otherwise it is set to zero.
326 <pre>
328 </pre>
329 The output is an integer that is set to one if support for Unicode character
330 properties is available; otherwise it is set to zero.
331 <pre>
333 </pre>
334 The output is an integer whose value specifies the default character sequence
335 that is recognized as meaning "newline". The four values that are supported
336 are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF, and -1 for ANY.
337 Though they are derived from ASCII, the same values are returned in EBCDIC
338 environments. The default should normally correspond to the standard sequence
339 for your operating system.
340 <pre>
342 </pre>
343 The output is an integer whose value indicates what character sequences the \R
344 escape sequence matches by default. A value of 0 means that \R matches any
345 Unicode line ending sequence; a value of 1 means that \R matches only CR, LF,
346 or CRLF. The default can be overridden when a pattern is compiled or matched.
347 <pre>
349 </pre>
350 The output is an integer that contains the number of bytes used for internal
351 linkage in compiled regular expressions. The value is 2, 3, or 4. Larger values
352 allow larger regular expressions to be compiled, at the expense of slower
353 matching. The default value of 2 is sufficient for all but the most massive
354 patterns, since it allows the compiled pattern to be up to 64K in size.
355 <pre>
357 </pre>
358 The output is an integer that contains the threshold above which the POSIX
359 interface uses <b>malloc()</b> for output vectors. Further details are given in
360 the
361 <a href="pcreposix.html"><b>pcreposix</b></a>
362 documentation.
363 <pre>
365 </pre>
366 The output is a long integer that gives the default limit for the number of
367 internal matching function calls in a <b>pcre_exec()</b> execution. Further
368 details are given with <b>pcre_exec()</b> below.
369 <pre>
371 </pre>
372 The output is a long integer that gives the default limit for the depth of
373 recursion when calling the internal matching function in a <b>pcre_exec()</b>
374 execution. Further details are given with <b>pcre_exec()</b> below.
375 <pre>
377 </pre>
378 The output is an integer that is set to one if internal recursion when running
379 <b>pcre_exec()</b> is implemented by recursive function calls that use the stack
380 to remember their state. This is the usual way that PCRE is compiled. The
381 output is zero if PCRE was compiled to use blocks of data on the heap instead
382 of recursive function calls. In this case, <b>pcre_stack_malloc</b> and
383 <b>pcre_stack_free</b> are called to manage memory blocks on the heap, thus
384 avoiding the use of the stack.
385 </P>
386 <br><a name="SEC7" href="#TOC1">COMPILING A PATTERN</a><br>
387 <P>
388 <b>pcre *pcre_compile(const char *<i>pattern</i>, int <i>options</i>,</b>
389 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
390 <b>const unsigned char *<i>tableptr</i>);</b>
391 <b>pcre *pcre_compile2(const char *<i>pattern</i>, int <i>options</i>,</b>
392 <b>int *<i>errorcodeptr</i>,</b>
393 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
394 <b>const unsigned char *<i>tableptr</i>);</b>
395 </P>
396 <P>
397 Either of the functions <b>pcre_compile()</b> or <b>pcre_compile2()</b> can be
398 called to compile a pattern into an internal form. The only difference between
399 the two interfaces is that <b>pcre_compile2()</b> has an additional argument,
400 <i>errorcodeptr</i>, via which a numerical error code can be returned.
401 </P>
402 <P>
403 The pattern is a C string terminated by a binary zero, and is passed in the
404 <i>pattern</i> argument. A pointer to a single block of memory that is obtained
405 via <b>pcre_malloc</b> is returned. This contains the compiled code and related
406 data. The <b>pcre</b> type is defined for the returned block; this is a typedef
407 for a structure whose contents are not externally defined. It is up to the
408 caller to free the memory (via <b>pcre_free</b>) when it is no longer required.
409 </P>
410 <P>
411 Although the compiled code of a PCRE regex is relocatable, that is, it does not
412 depend on memory location, the complete <b>pcre</b> data block is not
413 fully relocatable, because it may contain a copy of the <i>tableptr</i>
414 argument, which is an address (see below).
415 </P>
416 <P>
417 The <i>options</i> argument contains various bit settings that affect the
418 compilation. It should be zero if no options are required. The available
419 options are described below. Some of them (in particular, those that are
420 compatible with Perl, but also some others) can also be set and unset from
421 within the pattern (see the detailed description in the
422 <a href="pcrepattern.html"><b>pcrepattern</b></a>
423 documentation). For those options that can be different in different parts of
424 the pattern, the contents of the <i>options</i> argument specifies their initial
425 settings at the start of compilation and execution. The PCRE_ANCHORED and
426 PCRE_NEWLINE_<i>xxx</i> options can be set at the time of matching as well as at
427 compile time.
428 </P>
429 <P>
430 If <i>errptr</i> is NULL, <b>pcre_compile()</b> returns NULL immediately.
431 Otherwise, if compilation of a pattern fails, <b>pcre_compile()</b> returns
432 NULL, and sets the variable pointed to by <i>errptr</i> to point to a textual
433 error message. This is a static string that is part of the library. You must
434 not try to free it. The offset from the start of the pattern to the character
435 where the error was discovered is placed in the variable pointed to by
436 <i>erroffset</i>, which must not be NULL. If it is, an immediate error is given.
437 </P>
438 <P>
439 If <b>pcre_compile2()</b> is used instead of <b>pcre_compile()</b>, and the
440 <i>errorcodeptr</i> argument is not NULL, a non-zero error code number is
441 returned via this argument in the event of an error. This is in addition to the
442 textual error message. Error codes and messages are listed below.
443 </P>
444 <P>
445 If the final argument, <i>tableptr</i>, is NULL, PCRE uses a default set of
446 character tables that are built when PCRE is compiled, using the default C
447 locale. Otherwise, <i>tableptr</i> must be an address that is the result of a
448 call to <b>pcre_maketables()</b>. This value is stored with the compiled
449 pattern, and used again by <b>pcre_exec()</b>, unless another table pointer is
450 passed to it. For more discussion, see the section on locale support below.
451 </P>
452 <P>
453 This code fragment shows a typical straightforward call to <b>pcre_compile()</b>:
454 <pre>
455 pcre *re;
456 const char *error;
457 int erroffset;
458 re = pcre_compile(
459 "^A.*Z", /* the pattern */
460 0, /* default options */
461 &error, /* for error message */
462 &erroffset, /* for error offset */
463 NULL); /* use default character tables */
464 </pre>
465 The following names for option bits are defined in the <b>pcre.h</b> header
466 file:
467 <pre>
469 </pre>
470 If this bit is set, the pattern is forced to be "anchored", that is, it is
471 constrained to match only at the first matching point in the string that is
472 being searched (the "subject string"). This effect can also be achieved by
473 appropriate constructs in the pattern itself, which is the only way to do it in
474 Perl.
475 <pre>
477 </pre>
478 If this bit is set, <b>pcre_compile()</b> automatically inserts callout items,
479 all with number 255, before each pattern item. For discussion of the callout
480 facility, see the
481 <a href="pcrecallout.html"><b>pcrecallout</b></a>
482 documentation.
483 <pre>
486 </pre>
487 These options (which are mutually exclusive) control what the \R escape
488 sequence matches. The choice is either to match only CR, LF, or CRLF, or to
489 match any Unicode newline sequence. The default is specified when PCRE is
490 built. It can be overridden from within the pattern, or by setting an option
491 when a compiled pattern is matched.
492 <pre>
494 </pre>
495 If this bit is set, letters in the pattern match both upper and lower case
496 letters. It is equivalent to Perl's /i option, and it can be changed within a
497 pattern by a (?i) option setting. In UTF-8 mode, PCRE always understands the
498 concept of case for characters whose values are less than 128, so caseless
499 matching is always possible. For characters with higher values, the concept of
500 case is supported if PCRE is compiled with Unicode property support, but not
501 otherwise. If you want to use caseless matching for characters 128 and above,
502 you must ensure that PCRE is compiled with Unicode property support as well as
503 with UTF-8 support.
504 <pre>
506 </pre>
507 If this bit is set, a dollar metacharacter in the pattern matches only at the
508 end of the subject string. Without this option, a dollar also matches
509 immediately before a newline at the end of the string (but not before any other
510 newlines). The PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is set.
511 There is no equivalent to this option in Perl, and no way to set it within a
512 pattern.
513 <pre>
515 </pre>
516 If this bit is set, a dot metacharater in the pattern matches all characters,
517 including those that indicate newline. Without it, a dot does not match when
518 the current position is at a newline. This option is equivalent to Perl's /s
519 option, and it can be changed within a pattern by a (?s) option setting. A
520 negative class such as [^a] always matches newline characters, independent of
521 the setting of this option.
522 <pre>
524 </pre>
525 If this bit is set, names used to identify capturing subpatterns need not be
526 unique. This can be helpful for certain types of pattern when it is known that
527 only one instance of the named subpattern can ever be matched. There are more
528 details of named subpatterns below; see also the
529 <a href="pcrepattern.html"><b>pcrepattern</b></a>
530 documentation.
531 <pre>
533 </pre>
534 If this bit is set, whitespace data characters in the pattern are totally
535 ignored except when escaped or inside a character class. Whitespace does not
536 include the VT character (code 11). In addition, characters between an
537 unescaped # outside a character class and the next newline, inclusive, are also
538 ignored. This is equivalent to Perl's /x option, and it can be changed within a
539 pattern by a (?x) option setting.
540 </P>
541 <P>
542 This option makes it possible to include comments inside complicated patterns.
543 Note, however, that this applies only to data characters. Whitespace characters
544 may never appear within special character sequences in a pattern, for example
545 within the sequence (?( which introduces a conditional subpattern.
546 <pre>
548 </pre>
549 This option was invented in order to turn on additional functionality of PCRE
550 that is incompatible with Perl, but it is currently of very little use. When
551 set, any backslash in a pattern that is followed by a letter that has no
552 special meaning causes an error, thus reserving these combinations for future
553 expansion. By default, as in Perl, a backslash followed by a letter with no
554 special meaning is treated as a literal. (Perl can, however, be persuaded to
555 give a warning for this.) There are at present no other features controlled by
556 this option. It can also be set by a (?X) option setting within a pattern.
557 <pre>
559 </pre>
560 If this option is set, an unanchored pattern is required to match before or at
561 the first newline in the subject string, though the matched text may continue
562 over the newline.
563 <pre>
565 </pre>
566 If this option is set, PCRE's behaviour is changed in some ways so that it is
567 compatible with JavaScript rather than Perl. The changes are as follows:
568 </P>
569 <P>
570 (1) A lone closing square bracket in a pattern causes a compile-time error,
571 because this is illegal in JavaScript (by default it is treated as a data
572 character). Thus, the pattern AB]CD becomes illegal when this option is set.
573 </P>
574 <P>
575 (2) At run time, a back reference to an unset subpattern group matches an empty
576 string (by default this causes the current matching alternative to fail). A
577 pattern such as (\1)(a) succeeds when this option is set (assuming it can find
578 an "a" in the subject), whereas it fails by default, for Perl compatibility.
579 <pre>
581 </pre>
582 By default, PCRE treats the subject string as consisting of a single line of
583 characters (even if it actually contains newlines). The "start of line"
584 metacharacter (^) matches only at the start of the string, while the "end of
585 line" metacharacter ($) matches only at the end of the string, or before a
586 terminating newline (unless PCRE_DOLLAR_ENDONLY is set). This is the same as
587 Perl.
588 </P>
589 <P>
590 When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs
591 match immediately following or immediately before internal newlines in the
592 subject string, respectively, as well as at the very start and end. This is
593 equivalent to Perl's /m option, and it can be changed within a pattern by a
594 (?m) option setting. If there are no newlines in a subject string, or no
595 occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no effect.
596 <pre>
602 </pre>
603 These options override the default newline definition that was chosen when PCRE
604 was built. Setting the first or the second specifies that a newline is
605 indicated by a single character (CR or LF, respectively). Setting
606 PCRE_NEWLINE_CRLF specifies that a newline is indicated by the two-character
607 CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies that any of the three
608 preceding sequences should be recognized. Setting PCRE_NEWLINE_ANY specifies
609 that any Unicode newline sequence should be recognized. The Unicode newline
610 sequences are the three just mentioned, plus the single characters VT (vertical
611 tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS (line
612 separator, U+2028), and PS (paragraph separator, U+2029). The last two are
613 recognized only in UTF-8 mode.
614 </P>
615 <P>
616 The newline setting in the options word uses three bits that are treated
617 as a number, giving eight possibilities. Currently only six are used (default
618 plus the five values above). This means that if you set more than one newline
619 option, the combination may or may not be sensible. For example,
621 other combinations may yield unused numbers and cause an error.
622 </P>
623 <P>
624 The only time that a line break is specially recognized when compiling a
625 pattern is if PCRE_EXTENDED is set, and an unescaped # outside a character
626 class is encountered. This indicates a comment that lasts until after the next
627 line break sequence. In other circumstances, line break sequences are treated
628 as literal data, except that in PCRE_EXTENDED mode, both CR and LF are treated
629 as whitespace characters and are therefore ignored.
630 </P>
631 <P>
632 The newline option that is set at compile time becomes the default that is used
633 for <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b>, but it can be overridden.
634 <pre>
636 </pre>
637 If this option is set, it disables the use of numbered capturing parentheses in
638 the pattern. Any opening parenthesis that is not followed by ? behaves as if it
639 were followed by ?: but named parentheses can still be used for capturing (and
640 they acquire numbers in the usual way). There is no equivalent of this option
641 in Perl.
642 <pre>
644 </pre>
645 This option inverts the "greediness" of the quantifiers so that they are not
646 greedy by default, but become greedy if followed by "?". It is not compatible
647 with Perl. It can also be set by a (?U) option setting within the pattern.
648 <pre>
650 </pre>
651 This option causes PCRE to regard both the pattern and the subject as strings
652 of UTF-8 characters instead of single-byte character strings. However, it is
653 available only when PCRE is built to include UTF-8 support. If not, the use
654 of this option provokes an error. Details of how this option changes the
655 behaviour of PCRE are given in the
656 <a href="pcre.html#utf8support">section on UTF-8 support</a>
657 in the main
658 <a href="pcre.html"><b>pcre</b></a>
659 page.
660 <pre>
662 </pre>
663 When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
664 automatically checked. There is a discussion about the
665 <a href="pcre.html#utf8strings">validity of UTF-8 strings</a>
666 in the main
667 <a href="pcre.html"><b>pcre</b></a>
668 page. If an invalid UTF-8 sequence of bytes is found, <b>pcre_compile()</b>
669 returns an error. If you already know that your pattern is valid, and you want
670 to skip this check for performance reasons, you can set the PCRE_NO_UTF8_CHECK
671 option. When it is set, the effect of passing an invalid UTF-8 string as a
672 pattern is undefined. It may cause your program to crash. Note that this option
673 can also be passed to <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b>, to suppress
674 the UTF-8 validity checking of subject strings.
675 </P>
676 <br><a name="SEC8" href="#TOC1">COMPILATION ERROR CODES</a><br>
677 <P>
678 The following table lists the error codes than may be returned by
679 <b>pcre_compile2()</b>, along with the error messages that may be returned by
680 both compiling functions. As PCRE has developed, some error codes have fallen
681 out of use. To avoid confusion, they have not been re-used.
682 <pre>
683 0 no error
684 1 \ at end of pattern
685 2 \c at end of pattern
686 3 unrecognized character follows \
687 4 numbers out of order in {} quantifier
688 5 number too big in {} quantifier
689 6 missing terminating ] for character class
690 7 invalid escape sequence in character class
691 8 range out of order in character class
692 9 nothing to repeat
693 10 [this code is not in use]
694 11 internal error: unexpected repeat
695 12 unrecognized character after (? or (?-
696 13 POSIX named classes are supported only within a class
697 14 missing )
698 15 reference to non-existent subpattern
699 16 erroffset passed as NULL
700 17 unknown option bit(s) set
701 18 missing ) after comment
702 19 [this code is not in use]
703 20 regular expression is too large
704 21 failed to get memory
705 22 unmatched parentheses
706 23 internal error: code overflow
707 24 unrecognized character after (?&#60;
708 25 lookbehind assertion is not fixed length
709 26 malformed number or name after (?(
710 27 conditional group contains more than two branches
711 28 assertion expected after (?(
712 29 (?R or (?[+-]digits must be followed by )
713 30 unknown POSIX class name
714 31 POSIX collating elements are not supported
715 32 this version of PCRE is not compiled with PCRE_UTF8 support
716 33 [this code is not in use]
717 34 character value in \x{...} sequence is too large
718 35 invalid condition (?(0)
719 36 \C not allowed in lookbehind assertion
720 37 PCRE does not support \L, \l, \N, \U, or \u
721 38 number after (?C is &#62; 255
722 39 closing ) for (?C expected
723 40 recursive call could loop indefinitely
724 41 unrecognized character after (?P
725 42 syntax error in subpattern name (missing terminator)
726 43 two named subpatterns have the same name
727 44 invalid UTF-8 string
728 45 support for \P, \p, and \X has not been compiled
729 46 malformed \P or \p sequence
730 47 unknown property name after \P or \p
731 48 subpattern name is too long (maximum 32 characters)
732 49 too many named subpatterns (maximum 10000)
733 50 [this code is not in use]
734 51 octal value is greater than \377 (not in UTF-8 mode)
735 52 internal error: overran compiling workspace
736 53 internal error: previously-checked referenced subpattern not found
737 54 DEFINE group contains more than one branch
738 55 repeating a DEFINE group is not allowed
739 56 inconsistent NEWLINE options
740 57 \g is not followed by a braced, angle-bracketed, or quoted
741 name/number or by a plain number
742 58 a numbered reference must not be zero
743 59 (*VERB) with an argument is not supported
744 60 (*VERB) not recognized
745 61 number is too big
746 62 subpattern name expected
747 63 digit expected after (?+
748 64 ] is an invalid data character in JavaScript compatibility mode
749 </pre>
750 The numbers 32 and 10000 in errors 48 and 49 are defaults; different values may
751 be used if the limits were changed when PCRE was built.
752 </P>
753 <br><a name="SEC9" href="#TOC1">STUDYING A PATTERN</a><br>
754 <P>
755 <b>pcre_extra *pcre_study(const pcre *<i>code</i>, int <i>options</i></b>
756 <b>const char **<i>errptr</i>);</b>
757 </P>
758 <P>
759 If a compiled pattern is going to be used several times, it is worth spending
760 more time analyzing it in order to speed up the time taken for matching. The
761 function <b>pcre_study()</b> takes a pointer to a compiled pattern as its first
762 argument. If studying the pattern produces additional information that will
763 help speed up matching, <b>pcre_study()</b> returns a pointer to a
764 <b>pcre_extra</b> block, in which the <i>study_data</i> field points to the
765 results of the study.
766 </P>
767 <P>
768 The returned value from <b>pcre_study()</b> can be passed directly to
769 <b>pcre_exec()</b>. However, a <b>pcre_extra</b> block also contains other
770 fields that can be set by the caller before the block is passed; these are
771 described
772 <a href="#extradata">below</a>
773 in the section on matching a pattern.
774 </P>
775 <P>
776 If studying the pattern does not produce any additional information
777 <b>pcre_study()</b> returns NULL. In that circumstance, if the calling program
778 wants to pass any of the other fields to <b>pcre_exec()</b>, it must set up its
779 own <b>pcre_extra</b> block.
780 </P>
781 <P>
782 The second argument of <b>pcre_study()</b> contains option bits. At present, no
783 options are defined, and this argument should always be zero.
784 </P>
785 <P>
786 The third argument for <b>pcre_study()</b> is a pointer for an error message. If
787 studying succeeds (even if no data is returned), the variable it points to is
788 set to NULL. Otherwise it is set to point to a textual error message. This is a
789 static string that is part of the library. You must not try to free it. You
790 should test the error pointer for NULL after calling <b>pcre_study()</b>, to be
791 sure that it has run successfully.
792 </P>
793 <P>
794 This is a typical call to <b>pcre_study</b>():
795 <pre>
796 pcre_extra *pe;
797 pe = pcre_study(
798 re, /* result of pcre_compile() */
799 0, /* no options exist */
800 &error); /* set to NULL or points to a message */
801 </pre>
802 At present, studying a pattern is useful only for non-anchored patterns that do
803 not have a single fixed starting character. A bitmap of possible starting
804 bytes is created.
805 <a name="localesupport"></a></P>
806 <br><a name="SEC10" href="#TOC1">LOCALE SUPPORT</a><br>
807 <P>
808 PCRE handles caseless matching, and determines whether characters are letters,
809 digits, or whatever, by reference to a set of tables, indexed by character
810 value. When running in UTF-8 mode, this applies only to characters with codes
811 less than 128. Higher-valued codes never match escapes such as \w or \d, but
812 can be tested with \p if PCRE is built with Unicode character property
813 support. The use of locales with Unicode is discouraged. If you are handling
814 characters with codes greater than 128, you should either use UTF-8 and
815 Unicode, or use locales, but not try to mix the two.
816 </P>
817 <P>
818 PCRE contains an internal set of tables that are used when the final argument
819 of <b>pcre_compile()</b> is NULL. These are sufficient for many applications.
820 Normally, the internal tables recognize only ASCII characters. However, when
821 PCRE is built, it is possible to cause the internal tables to be rebuilt in the
822 default "C" locale of the local system, which may cause them to be different.
823 </P>
824 <P>
825 The internal tables can always be overridden by tables supplied by the
826 application that calls PCRE. These may be created in a different locale from
827 the default. As more and more applications change to using Unicode, the need
828 for this locale support is expected to die away.
829 </P>
830 <P>
831 External tables are built by calling the <b>pcre_maketables()</b> function,
832 which has no arguments, in the relevant locale. The result can then be passed
833 to <b>pcre_compile()</b> or <b>pcre_exec()</b> as often as necessary. For
834 example, to build and use tables that are appropriate for the French locale
835 (where accented characters with values greater than 128 are treated as letters),
836 the following code could be used:
837 <pre>
838 setlocale(LC_CTYPE, "fr_FR");
839 tables = pcre_maketables();
840 re = pcre_compile(..., tables);
841 </pre>
842 The locale name "fr_FR" is used on Linux and other Unix-like systems; if you
843 are using Windows, the name for the French locale is "french".
844 </P>
845 <P>
846 When <b>pcre_maketables()</b> runs, the tables are built in memory that is
847 obtained via <b>pcre_malloc</b>. It is the caller's responsibility to ensure
848 that the memory containing the tables remains available for as long as it is
849 needed.
850 </P>
851 <P>
852 The pointer that is passed to <b>pcre_compile()</b> is saved with the compiled
853 pattern, and the same tables are used via this pointer by <b>pcre_study()</b>
854 and normally also by <b>pcre_exec()</b>. Thus, by default, for any single
855 pattern, compilation, studying and matching all happen in the same locale, but
856 different patterns can be compiled in different locales.
857 </P>
858 <P>
859 It is possible to pass a table pointer or NULL (indicating the use of the
860 internal tables) to <b>pcre_exec()</b>. Although not intended for this purpose,
861 this facility could be used to match a pattern in a different locale from the
862 one in which it was compiled. Passing table pointers at run time is discussed
863 below in the section on matching a pattern.
864 </P>
865 <br><a name="SEC11" href="#TOC1">INFORMATION ABOUT A PATTERN</a><br>
866 <P>
867 <b>int pcre_fullinfo(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
868 <b>int <i>what</i>, void *<i>where</i>);</b>
869 </P>
870 <P>
871 The <b>pcre_fullinfo()</b> function returns information about a compiled
872 pattern. It replaces the obsolete <b>pcre_info()</b> function, which is
873 nevertheless retained for backwards compability (and is documented below).
874 </P>
875 <P>
876 The first argument for <b>pcre_fullinfo()</b> is a pointer to the compiled
877 pattern. The second argument is the result of <b>pcre_study()</b>, or NULL if
878 the pattern was not studied. The third argument specifies which piece of
879 information is required, and the fourth argument is a pointer to a variable
880 to receive the data. The yield of the function is zero for success, or one of
881 the following negative numbers:
882 <pre>
883 PCRE_ERROR_NULL the argument <i>code</i> was NULL
884 the argument <i>where</i> was NULL
885 PCRE_ERROR_BADMAGIC the "magic number" was not found
886 PCRE_ERROR_BADOPTION the value of <i>what</i> was invalid
887 </pre>
888 The "magic number" is placed at the start of each compiled pattern as an simple
889 check against passing an arbitrary memory pointer. Here is a typical call of
890 <b>pcre_fullinfo()</b>, to obtain the length of the compiled pattern:
891 <pre>
892 int rc;
893 size_t length;
894 rc = pcre_fullinfo(
895 re, /* result of pcre_compile() */
896 pe, /* result of pcre_study(), or NULL */
897 PCRE_INFO_SIZE, /* what is required */
898 &length); /* where to put the data */
899 </pre>
900 The possible values for the third argument are defined in <b>pcre.h</b>, and are
901 as follows:
902 <pre>
904 </pre>
905 Return the number of the highest back reference in the pattern. The fourth
906 argument should point to an <b>int</b> variable. Zero is returned if there are
907 no back references.
908 <pre>
910 </pre>
911 Return the number of capturing subpatterns in the pattern. The fourth argument
912 should point to an <b>int</b> variable.
913 <pre>
915 </pre>
916 Return a pointer to the internal default character tables within PCRE. The
917 fourth argument should point to an <b>unsigned char *</b> variable. This
918 information call is provided for internal use by the <b>pcre_study()</b>
919 function. External callers can cause PCRE to use its internal tables by passing
920 a NULL table pointer.
921 <pre>
923 </pre>
924 Return information about the first byte of any matched string, for a
925 non-anchored pattern. The fourth argument should point to an <b>int</b>
926 variable. (This option used to be called PCRE_INFO_FIRSTCHAR; the old name is
927 still recognized for backwards compatibility.)
928 </P>
929 <P>
930 If there is a fixed first byte, for example, from a pattern such as
931 (cat|cow|coyote), its value is returned. Otherwise, if either
932 <br>
933 <br>
934 (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
935 starts with "^", or
936 <br>
937 <br>
938 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
939 (if it were set, the pattern would be anchored),
940 <br>
941 <br>
942 -1 is returned, indicating that the pattern matches only at the start of a
943 subject string or after any newline within the string. Otherwise -2 is
944 returned. For anchored patterns, -2 is returned.
945 <pre>
947 </pre>
948 If the pattern was studied, and this resulted in the construction of a 256-bit
949 table indicating a fixed set of bytes for the first byte in any matching
950 string, a pointer to the table is returned. Otherwise NULL is returned. The
951 fourth argument should point to an <b>unsigned char *</b> variable.
952 <pre>
954 </pre>
955 Return 1 if the pattern contains any explicit matches for CR or LF characters,
956 otherwise 0. The fourth argument should point to an <b>int</b> variable. An
957 explicit match is either a literal CR or LF character, or \r or \n.
958 <pre>
960 </pre>
961 Return 1 if the (?J) or (?-J) option setting is used in the pattern, otherwise
962 0. The fourth argument should point to an <b>int</b> variable. (?J) and
963 (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
964 <pre>
966 </pre>
967 Return the value of the rightmost literal byte that must exist in any matched
968 string, other than at its start, if such a byte has been recorded. The fourth
969 argument should point to an <b>int</b> variable. If there is no such byte, -1 is
970 returned. For anchored patterns, a last literal byte is recorded only if it
971 follows something of variable length. For example, for the pattern
972 /^a\d+z\d+/ the returned value is "z", but for /^a\dz\d/ the returned value
973 is -1.
974 <pre>
978 </pre>
979 PCRE supports the use of named as well as numbered capturing parentheses. The
980 names are just an additional way of identifying the parentheses, which still
981 acquire numbers. Several convenience functions such as
982 <b>pcre_get_named_substring()</b> are provided for extracting captured
983 substrings by name. It is also possible to extract the data directly, by first
984 converting the name to a number in order to access the correct pointers in the
985 output vector (described with <b>pcre_exec()</b> below). To do the conversion,
986 you need to use the name-to-number map, which is described by these three
987 values.
988 </P>
989 <P>
990 The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives
991 the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each
992 entry; both of these return an <b>int</b> value. The entry size depends on the
993 length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first
994 entry of the table (a pointer to <b>char</b>). The first two bytes of each entry
995 are the number of the capturing parenthesis, most significant byte first. The
996 rest of the entry is the corresponding name, zero terminated. The names are in
997 alphabetical order. When PCRE_DUPNAMES is set, duplicate names are in order of
998 their parentheses numbers. For example, consider the following pattern (assume
999 PCRE_EXTENDED is set, so white space - including newlines - is ignored):
1000 <pre>
1001 (?&#60;date&#62; (?&#60;year&#62;(\d\d)?\d\d) - (?&#60;month&#62;\d\d) - (?&#60;day&#62;\d\d) )
1002 </pre>
1003 There are four named subpatterns, so the table has four entries, and each entry
1004 in the table is eight bytes long. The table is as follows, with non-printing
1005 bytes shows in hexadecimal, and undefined bytes shown as ??:
1006 <pre>
1007 00 01 d a t e 00 ??
1008 00 05 d a y 00 ?? ??
1009 00 04 m o n t h 00
1010 00 02 y e a r 00 ??
1011 </pre>
1012 When writing code to extract data from named subpatterns using the
1013 name-to-number map, remember that the length of the entries is likely to be
1014 different for each compiled pattern.
1015 <pre>
1017 </pre>
1018 Return 1 if the pattern can be used for partial matching, otherwise 0. The
1019 fourth argument should point to an <b>int</b> variable. The
1020 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1021 documentation lists the restrictions that apply to patterns when partial
1022 matching is used.
1023 <pre>
1025 </pre>
1026 Return a copy of the options with which the pattern was compiled. The fourth
1027 argument should point to an <b>unsigned long int</b> variable. These option bits
1028 are those specified in the call to <b>pcre_compile()</b>, modified by any
1029 top-level option settings at the start of the pattern itself. In other words,
1030 they are the options that will be in force when matching starts. For example,
1031 if the pattern /(?im)abc(?-i)d/ is compiled with the PCRE_EXTENDED option, the
1033 </P>
1034 <P>
1035 A pattern is automatically anchored by PCRE if all of its top-level
1036 alternatives begin with one of the following:
1037 <pre>
1038 ^ unless PCRE_MULTILINE is set
1039 \A always
1040 \G always
1041 .* if PCRE_DOTALL is set and there are no back references to the subpattern in which .* appears
1042 </pre>
1043 For such patterns, the PCRE_ANCHORED bit is set in the options returned by
1044 <b>pcre_fullinfo()</b>.
1045 <pre>
1047 </pre>
1048 Return the size of the compiled pattern, that is, the value that was passed as
1049 the argument to <b>pcre_malloc()</b> when PCRE was getting memory in which to
1050 place the compiled data. The fourth argument should point to a <b>size_t</b>
1051 variable.
1052 <pre>
1054 </pre>
1055 Return the size of the data block pointed to by the <i>study_data</i> field in
1056 a <b>pcre_extra</b> block. That is, it is the value that was passed to
1057 <b>pcre_malloc()</b> when PCRE was getting memory into which to place the data
1058 created by <b>pcre_study()</b>. The fourth argument should point to a
1059 <b>size_t</b> variable.
1060 </P>
1061 <br><a name="SEC12" href="#TOC1">OBSOLETE INFO FUNCTION</a><br>
1062 <P>
1063 <b>int pcre_info(const pcre *<i>code</i>, int *<i>optptr</i>, int</b>
1064 <b>*<i>firstcharptr</i>);</b>
1065 </P>
1066 <P>
1067 The <b>pcre_info()</b> function is now obsolete because its interface is too
1068 restrictive to return all the available data about a compiled pattern. New
1069 programs should use <b>pcre_fullinfo()</b> instead. The yield of
1070 <b>pcre_info()</b> is the number of capturing subpatterns, or one of the
1071 following negative numbers:
1072 <pre>
1073 PCRE_ERROR_NULL the argument <i>code</i> was NULL
1074 PCRE_ERROR_BADMAGIC the "magic number" was not found
1075 </pre>
1076 If the <i>optptr</i> argument is not NULL, a copy of the options with which the
1077 pattern was compiled is placed in the integer it points to (see
1078 PCRE_INFO_OPTIONS above).
1079 </P>
1080 <P>
1081 If the pattern is not anchored and the <i>firstcharptr</i> argument is not NULL,
1082 it is used to pass back information about the first character of any matched
1083 string (see PCRE_INFO_FIRSTBYTE above).
1084 </P>
1085 <br><a name="SEC13" href="#TOC1">REFERENCE COUNTS</a><br>
1086 <P>
1087 <b>int pcre_refcount(pcre *<i>code</i>, int <i>adjust</i>);</b>
1088 </P>
1089 <P>
1090 The <b>pcre_refcount()</b> function is used to maintain a reference count in the
1091 data block that contains a compiled pattern. It is provided for the benefit of
1092 applications that operate in an object-oriented manner, where different parts
1093 of the application may be using the same compiled pattern, but you want to free
1094 the block when they are all done.
1095 </P>
1096 <P>
1097 When a pattern is compiled, the reference count field is initialized to zero.
1098 It is changed only by calling this function, whose action is to add the
1099 <i>adjust</i> value (which may be positive or negative) to it. The yield of the
1100 function is the new value. However, the value of the count is constrained to
1101 lie between 0 and 65535, inclusive. If the new value is outside these limits,
1102 it is forced to the appropriate limit value.
1103 </P>
1104 <P>
1105 Except when it is zero, the reference count is not correctly preserved if a
1106 pattern is compiled on one host and then transferred to a host whose byte-order
1107 is different. (This seems a highly unlikely scenario.)
1108 </P>
1109 <br><a name="SEC14" href="#TOC1">MATCHING A PATTERN: THE TRADITIONAL FUNCTION</a><br>
1110 <P>
1111 <b>int pcre_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
1112 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
1113 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>);</b>
1114 </P>
1115 <P>
1116 The function <b>pcre_exec()</b> is called to match a subject string against a
1117 compiled pattern, which is passed in the <i>code</i> argument. If the
1118 pattern has been studied, the result of the study should be passed in the
1119 <i>extra</i> argument. This function is the main matching facility of the
1120 library, and it operates in a Perl-like manner. For specialist use there is
1121 also an alternative matching function, which is described
1122 <a href="#dfamatch">below</a>
1123 in the section about the <b>pcre_dfa_exec()</b> function.
1124 </P>
1125 <P>
1126 In most applications, the pattern will have been compiled (and optionally
1127 studied) in the same process that calls <b>pcre_exec()</b>. However, it is
1128 possible to save compiled patterns and study data, and then use them later
1129 in different processes, possibly even on different hosts. For a discussion
1130 about this, see the
1131 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
1132 documentation.
1133 </P>
1134 <P>
1135 Here is an example of a simple call to <b>pcre_exec()</b>:
1136 <pre>
1137 int rc;
1138 int ovector[30];
1139 rc = pcre_exec(
1140 re, /* result of pcre_compile() */
1141 NULL, /* we didn't study the pattern */
1142 "some string", /* the subject string */
1143 11, /* the length of the subject string */
1144 0, /* start at offset 0 in the subject */
1145 0, /* default options */
1146 ovector, /* vector of integers for substring information */
1147 30); /* number of elements (NOT size in bytes) */
1148 <a name="extradata"></a></PRE>
1149 </P>
1150 <br><b>
1151 Extra data for <b>pcre_exec()</b>
1152 </b><br>
1153 <P>
1154 If the <i>extra</i> argument is not NULL, it must point to a <b>pcre_extra</b>
1155 data block. The <b>pcre_study()</b> function returns such a block (when it
1156 doesn't return NULL), but you can also create one for yourself, and pass
1157 additional information in it. The <b>pcre_extra</b> block contains the following
1158 fields (not necessarily in this order):
1159 <pre>
1160 unsigned long int <i>flags</i>;
1161 void *<i>study_data</i>;
1162 unsigned long int <i>match_limit</i>;
1163 unsigned long int <i>match_limit_recursion</i>;
1164 void *<i>callout_data</i>;
1165 const unsigned char *<i>tables</i>;
1166 </pre>
1167 The <i>flags</i> field is a bitmap that specifies which of the other fields
1168 are set. The flag bits are:
1169 <pre>
1175 </pre>
1176 Other flag bits should be set to zero. The <i>study_data</i> field is set in the
1177 <b>pcre_extra</b> block that is returned by <b>pcre_study()</b>, together with
1178 the appropriate flag bit. You should not set this yourself, but you may add to
1179 the block by setting the other fields and their corresponding flag bits.
1180 </P>
1181 <P>
1182 The <i>match_limit</i> field provides a means of preventing PCRE from using up a
1183 vast amount of resources when running patterns that are not going to match,
1184 but which have a very large number of possibilities in their search trees. The
1185 classic example is the use of nested unlimited repeats.
1186 </P>
1187 <P>
1188 Internally, PCRE uses a function called <b>match()</b> which it calls repeatedly
1189 (sometimes recursively). The limit set by <i>match_limit</i> is imposed on the
1190 number of times this function is called during a match, which has the effect of
1191 limiting the amount of backtracking that can take place. For patterns that are
1192 not anchored, the count restarts from zero for each position in the subject
1193 string.
1194 </P>
1195 <P>
1196 The default value for the limit can be set when PCRE is built; the default
1197 default is 10 million, which handles all but the most extreme cases. You can
1198 override the default by suppling <b>pcre_exec()</b> with a <b>pcre_extra</b>
1199 block in which <i>match_limit</i> is set, and PCRE_EXTRA_MATCH_LIMIT is set in
1200 the <i>flags</i> field. If the limit is exceeded, <b>pcre_exec()</b> returns
1202 </P>
1203 <P>
1204 The <i>match_limit_recursion</i> field is similar to <i>match_limit</i>, but
1205 instead of limiting the total number of times that <b>match()</b> is called, it
1206 limits the depth of recursion. The recursion depth is a smaller number than the
1207 total number of calls, because not all calls to <b>match()</b> are recursive.
1208 This limit is of use only if it is set smaller than <i>match_limit</i>.
1209 </P>
1210 <P>
1211 Limiting the recursion depth limits the amount of stack that can be used, or,
1212 when PCRE has been compiled to use memory on the heap instead of the stack, the
1213 amount of heap memory that can be used.
1214 </P>
1215 <P>
1216 The default value for <i>match_limit_recursion</i> can be set when PCRE is
1217 built; the default default is the same value as the default for
1218 <i>match_limit</i>. You can override the default by suppling <b>pcre_exec()</b>
1219 with a <b>pcre_extra</b> block in which <i>match_limit_recursion</i> is set, and
1220 PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the <i>flags</i> field. If the limit
1221 is exceeded, <b>pcre_exec()</b> returns PCRE_ERROR_RECURSIONLIMIT.
1222 </P>
1223 <P>
1224 The <i>pcre_callout</i> field is used in conjunction with the "callout" feature,
1225 which is described in the
1226 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1227 documentation.
1228 </P>
1229 <P>
1230 The <i>tables</i> field is used to pass a character tables pointer to
1231 <b>pcre_exec()</b>; this overrides the value that is stored with the compiled
1232 pattern. A non-NULL value is stored with the compiled pattern only if custom
1233 tables were supplied to <b>pcre_compile()</b> via its <i>tableptr</i> argument.
1234 If NULL is passed to <b>pcre_exec()</b> using this mechanism, it forces PCRE's
1235 internal tables to be used. This facility is helpful when re-using patterns
1236 that have been saved after compiling with an external set of tables, because
1237 the external tables might be at a different address when <b>pcre_exec()</b> is
1238 called. See the
1239 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
1240 documentation for a discussion of saving compiled patterns for later use.
1241 <a name="execoptions"></a></P>
1242 <br><b>
1243 Option bits for <b>pcre_exec()</b>
1244 </b><br>
1245 <P>
1246 The unused bits of the <i>options</i> argument for <b>pcre_exec()</b> must be
1247 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_<i>xxx</i>,
1250 <pre>
1252 </pre>
1253 The PCRE_ANCHORED option limits <b>pcre_exec()</b> to matching at the first
1254 matching position. If a pattern was compiled with PCRE_ANCHORED, or turned out
1255 to be anchored by virtue of its contents, it cannot be made unachored at
1256 matching time.
1257 <pre>
1260 </pre>
1261 These options (which are mutually exclusive) control what the \R escape
1262 sequence matches. The choice is either to match only CR, LF, or CRLF, or to
1263 match any Unicode newline sequence. These options override the choice that was
1264 made or defaulted when the pattern was compiled.
1265 <pre>
1271 </pre>
1272 These options override the newline definition that was chosen or defaulted when
1273 the pattern was compiled. For details, see the description of
1274 <b>pcre_compile()</b> above. During matching, the newline choice affects the
1275 behaviour of the dot, circumflex, and dollar metacharacters. It may also alter
1276 the way the match position is advanced after a match failure for an unanchored
1277 pattern.
1278 </P>
1279 <P>
1281 match attempt for an unanchored pattern fails when the current position is at a
1282 CRLF sequence, and the pattern contains no explicit matches for CR or LF
1283 characters, the match position is advanced by two characters instead of one, in
1284 other words, to after the CRLF.
1285 </P>
1286 <P>
1287 The above rule is a compromise that makes the most common cases work as
1288 expected. For example, if the pattern is .+A (and the PCRE_DOTALL option is not
1289 set), it does not match the string "\r\nA" because, after failing at the
1290 start, it skips both the CR and the LF before retrying. However, the pattern
1291 [\r\n]A does match that string, because it contains an explicit CR or LF
1292 reference, and so advances only by one character after the first failure.
1293 </P>
1294 <P>
1295 An explicit match for CR of LF is either a literal appearance of one of those
1296 characters, or one of the \r or \n escape sequences. Implicit matches such as
1297 [^X] do not count, nor does \s (which includes CR and LF in the characters
1298 that it matches).
1299 </P>
1300 <P>
1301 Notwithstanding the above, anomalous effects may still occur when CRLF is a
1302 valid newline sequence and explicit \r or \n escapes appear in the pattern.
1303 <pre>
1305 </pre>
1306 This option specifies that first character of the subject string is not the
1307 beginning of a line, so the circumflex metacharacter should not match before
1308 it. Setting this without PCRE_MULTILINE (at compile time) causes circumflex
1309 never to match. This option affects only the behaviour of the circumflex
1310 metacharacter. It does not affect \A.
1311 <pre>
1313 </pre>
1314 This option specifies that the end of the subject string is not the end of a
1315 line, so the dollar metacharacter should not match it nor (except in multiline
1316 mode) a newline immediately before it. Setting this without PCRE_MULTILINE (at
1317 compile time) causes dollar never to match. This option affects only the
1318 behaviour of the dollar metacharacter. It does not affect \Z or \z.
1319 <pre>
1321 </pre>
1322 An empty string is not considered to be a valid match if this option is set. If
1323 there are alternatives in the pattern, they are tried. If all the alternatives
1324 match the empty string, the entire match fails. For example, if the pattern
1325 <pre>
1326 a?b?
1327 </pre>
1328 is applied to a string not beginning with "a" or "b", it matches the empty
1329 string at the start of the subject. With PCRE_NOTEMPTY set, this match is not
1330 valid, so PCRE searches further into the string for occurrences of "a" or "b".
1331 </P>
1332 <P>
1333 Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a special case
1334 of a pattern match of the empty string within its <b>split()</b> function, and
1335 when using the /g modifier. It is possible to emulate Perl's behaviour after
1336 matching a null string by first trying the match again at the same offset with
1337 PCRE_NOTEMPTY and PCRE_ANCHORED, and then if that fails by advancing the
1338 starting offset (see below) and trying an ordinary match again. There is some
1339 code that demonstrates how to do this in the <i>pcredemo.c</i> sample program.
1340 <pre>
1342 </pre>
1343 There are a number of optimizations that <b>pcre_exec()</b> uses at the start of
1344 a match, in order to speed up the process. For example, if it is known that a
1345 match must start with a specific character, it searches the subject for that
1346 character, and fails immediately if it cannot find it, without actually running
1347 the main matching function. When callouts are in use, these optimizations can
1348 cause them to be skipped. This option disables the "start-up" optimizations,
1349 causing performance to suffer, but ensuring that the callouts do occur.
1350 <pre>
1352 </pre>
1353 When PCRE_UTF8 is set at compile time, the validity of the subject as a UTF-8
1354 string is automatically checked when <b>pcre_exec()</b> is subsequently called.
1355 The value of <i>startoffset</i> is also checked to ensure that it points to the
1356 start of a UTF-8 character. There is a discussion about the validity of UTF-8
1357 strings in the
1358 <a href="pcre.html#utf8strings">section on UTF-8 support</a>
1359 in the main
1360 <a href="pcre.html"><b>pcre</b></a>
1361 page. If an invalid UTF-8 sequence of bytes is found, <b>pcre_exec()</b> returns
1362 the error PCRE_ERROR_BADUTF8. If <i>startoffset</i> contains an invalid value,
1363 PCRE_ERROR_BADUTF8_OFFSET is returned.
1364 </P>
1365 <P>
1366 If you already know that your subject is valid, and you want to skip these
1367 checks for performance reasons, you can set the PCRE_NO_UTF8_CHECK option when
1368 calling <b>pcre_exec()</b>. You might want to do this for the second and
1369 subsequent calls to <b>pcre_exec()</b> if you are making repeated calls to find
1370 all the matches in a single subject string. However, you should be sure that
1371 the value of <i>startoffset</i> points to the start of a UTF-8 character. When
1372 PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid UTF-8 string as a
1373 subject, or a value of <i>startoffset</i> that does not point to the start of a
1374 UTF-8 character, is undefined. Your program may crash.
1375 <pre>
1377 </pre>
1378 This option turns on the partial matching feature. If the subject string fails
1379 to match the pattern, but at some point during the matching process the end of
1380 the subject was reached (that is, the subject partially matches the pattern and
1381 the failure to match occurred only because there were not enough subject
1382 characters), <b>pcre_exec()</b> returns PCRE_ERROR_PARTIAL instead of
1383 PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is used, there are restrictions on what
1384 may appear in the pattern. These are discussed in the
1385 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1386 documentation.
1387 </P>
1388 <br><b>
1389 The string to be matched by <b>pcre_exec()</b>
1390 </b><br>
1391 <P>
1392 The subject string is passed to <b>pcre_exec()</b> as a pointer in
1393 <i>subject</i>, a length (in bytes) in <i>length</i>, and a starting byte offset
1394 in <i>startoffset</i>. In UTF-8 mode, the byte offset must point to the start of
1395 a UTF-8 character. Unlike the pattern string, the subject may contain binary
1396 zero bytes. When the starting offset is zero, the search for a match starts at
1397 the beginning of the subject, and this is by far the most common case.
1398 </P>
1399 <P>
1400 A non-zero starting offset is useful when searching for another match in the
1401 same subject by calling <b>pcre_exec()</b> again after a previous success.
1402 Setting <i>startoffset</i> differs from just passing over a shortened string and
1403 setting PCRE_NOTBOL in the case of a pattern that begins with any kind of
1404 lookbehind. For example, consider the pattern
1405 <pre>
1406 \Biss\B
1407 </pre>
1408 which finds occurrences of "iss" in the middle of words. (\B matches only if
1409 the current position in the subject is not a word boundary.) When applied to
1410 the string "Mississipi" the first call to <b>pcre_exec()</b> finds the first
1411 occurrence. If <b>pcre_exec()</b> is called again with just the remainder of the
1412 subject, namely "issipi", it does not match, because \B is always false at the
1413 start of the subject, which is deemed to be a word boundary. However, if
1414 <b>pcre_exec()</b> is passed the entire string again, but with <i>startoffset</i>
1415 set to 4, it finds the second occurrence of "iss" because it is able to look
1416 behind the starting point to discover that it is preceded by a letter.
1417 </P>
1418 <P>
1419 If a non-zero starting offset is passed when the pattern is anchored, one
1420 attempt to match at the given offset is made. This can only succeed if the
1421 pattern does not require the match to be at the start of the subject.
1422 </P>
1423 <br><b>
1424 How <b>pcre_exec()</b> returns captured substrings
1425 </b><br>
1426 <P>
1427 In general, a pattern matches a certain portion of the subject, and in
1428 addition, further substrings from the subject may be picked out by parts of the
1429 pattern. Following the usage in Jeffrey Friedl's book, this is called
1430 "capturing" in what follows, and the phrase "capturing subpattern" is used for
1431 a fragment of a pattern that picks out a substring. PCRE supports several other
1432 kinds of parenthesized subpattern that do not cause substrings to be captured.
1433 </P>
1434 <P>
1435 Captured substrings are returned to the caller via a vector of integers whose
1436 address is passed in <i>ovector</i>. The number of elements in the vector is
1437 passed in <i>ovecsize</i>, which must be a non-negative number. <b>Note</b>: this
1438 argument is NOT the size of <i>ovector</i> in bytes.
1439 </P>
1440 <P>
1441 The first two-thirds of the vector is used to pass back captured substrings,
1442 each substring using a pair of integers. The remaining third of the vector is
1443 used as workspace by <b>pcre_exec()</b> while matching capturing subpatterns,
1444 and is not available for passing back information. The number passed in
1445 <i>ovecsize</i> should always be a multiple of three. If it is not, it is
1446 rounded down.
1447 </P>
1448 <P>
1449 When a match is successful, information about captured substrings is returned
1450 in pairs of integers, starting at the beginning of <i>ovector</i>, and
1451 continuing up to two-thirds of its length at the most. The first element of
1452 each pair is set to the byte offset of the first character in a substring, and
1453 the second is set to the byte offset of the first character after the end of a
1454 substring. <b>Note</b>: these values are always byte offsets, even in UTF-8
1455 mode. They are not character counts.
1456 </P>
1457 <P>
1458 The first pair of integers, <i>ovector[0]</i> and <i>ovector[1]</i>, identify the
1459 portion of the subject string matched by the entire pattern. The next pair is
1460 used for the first capturing subpattern, and so on. The value returned by
1461 <b>pcre_exec()</b> is one more than the highest numbered pair that has been set.
1462 For example, if two substrings have been captured, the returned value is 3. If
1463 there are no capturing subpatterns, the return value from a successful match is
1464 1, indicating that just the first pair of offsets has been set.
1465 </P>
1466 <P>
1467 If a capturing subpattern is matched repeatedly, it is the last portion of the
1468 string that it matched that is returned.
1469 </P>
1470 <P>
1471 If the vector is too small to hold all the captured substring offsets, it is
1472 used as far as possible (up to two-thirds of its length), and the function
1473 returns a value of zero. If the substring offsets are not of interest,
1474 <b>pcre_exec()</b> may be called with <i>ovector</i> passed as NULL and
1475 <i>ovecsize</i> as zero. However, if the pattern contains back references and
1476 the <i>ovector</i> is not big enough to remember the related substrings, PCRE
1477 has to get additional memory for use during matching. Thus it is usually
1478 advisable to supply an <i>ovector</i>.
1479 </P>
1480 <P>
1481 The <b>pcre_info()</b> function can be used to find out how many capturing
1482 subpatterns there are in a compiled pattern. The smallest size for
1483 <i>ovector</i> that will allow for <i>n</i> captured substrings, in addition to
1484 the offsets of the substring matched by the whole pattern, is (<i>n</i>+1)*3.
1485 </P>
1486 <P>
1487 It is possible for capturing subpattern number <i>n+1</i> to match some part of
1488 the subject when subpattern <i>n</i> has not been used at all. For example, if
1489 the string "abc" is matched against the pattern (a|(z))(bc) the return from the
1490 function is 4, and subpatterns 1 and 3 are matched, but 2 is not. When this
1491 happens, both values in the offset pairs corresponding to unused subpatterns
1492 are set to -1.
1493 </P>
1494 <P>
1495 Offset values that correspond to unused subpatterns at the end of the
1496 expression are also set to -1. For example, if the string "abc" is matched
1497 against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not matched. The
1498 return from the function is 2, because the highest used capturing subpattern
1499 number is 1. However, you can refer to the offsets for the second and third
1500 capturing subpatterns if you wish (assuming the vector is large enough, of
1501 course).
1502 </P>
1503 <P>
1504 Some convenience functions are provided for extracting the captured substrings
1505 as separate strings. These are described below.
1506 <a name="errorlist"></a></P>
1507 <br><b>
1508 Error return values from <b>pcre_exec()</b>
1509 </b><br>
1510 <P>
1511 If <b>pcre_exec()</b> fails, it returns a negative number. The following are
1512 defined in the header file:
1513 <pre>
1515 </pre>
1516 The subject string did not match the pattern.
1517 <pre>
1519 </pre>
1520 Either <i>code</i> or <i>subject</i> was passed as NULL, or <i>ovector</i> was
1521 NULL and <i>ovecsize</i> was not zero.
1522 <pre>
1524 </pre>
1525 An unrecognized bit was set in the <i>options</i> argument.
1526 <pre>
1528 </pre>
1529 PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch
1530 the case when it is passed a junk pointer and to detect when a pattern that was
1531 compiled in an environment of one endianness is run in an environment with the
1532 other endianness. This is the error that PCRE gives when the magic number is
1533 not present.
1534 <pre>
1536 </pre>
1537 While running the pattern match, an unknown item was encountered in the
1538 compiled pattern. This error could be caused by a bug in PCRE or by overwriting
1539 of the compiled pattern.
1540 <pre>
1542 </pre>
1543 If a pattern contains back references, but the <i>ovector</i> that is passed to
1544 <b>pcre_exec()</b> is not big enough to remember the referenced substrings, PCRE
1545 gets a block of memory at the start of matching to use for this purpose. If the
1546 call via <b>pcre_malloc()</b> fails, this error is given. The memory is
1547 automatically freed at the end of matching.
1548 <pre>
1550 </pre>
1551 This error is used by the <b>pcre_copy_substring()</b>,
1552 <b>pcre_get_substring()</b>, and <b>pcre_get_substring_list()</b> functions (see
1553 below). It is never returned by <b>pcre_exec()</b>.
1554 <pre>
1556 </pre>
1557 The backtracking limit, as specified by the <i>match_limit</i> field in a
1558 <b>pcre_extra</b> structure (or defaulted) was reached. See the description
1559 above.
1560 <pre>
1562 </pre>
1563 This error is never generated by <b>pcre_exec()</b> itself. It is provided for
1564 use by callout functions that want to yield a distinctive error code. See the
1565 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1566 documentation for details.
1567 <pre>
1569 </pre>
1570 A string that contains an invalid UTF-8 byte sequence was passed as a subject.
1571 <pre>
1573 </pre>
1574 The UTF-8 byte sequence that was passed as a subject was valid, but the value
1575 of <i>startoffset</i> did not point to the beginning of a UTF-8 character.
1576 <pre>
1578 </pre>
1579 The subject string did not match, but it did match partially. See the
1580 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1581 documentation for details of partial matching.
1582 <pre>
1584 </pre>
1585 The PCRE_PARTIAL option was used with a compiled pattern containing items that
1586 are not supported for partial matching. See the
1587 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1588 documentation for details of partial matching.
1589 <pre>
1591 </pre>
1592 An unexpected internal error has occurred. This error could be caused by a bug
1593 in PCRE or by overwriting of the compiled pattern.
1594 <pre>
1596 </pre>
1597 This error is given if the value of the <i>ovecsize</i> argument is negative.
1598 <pre>
1600 </pre>
1601 The internal recursion limit, as specified by the <i>match_limit_recursion</i>
1602 field in a <b>pcre_extra</b> structure (or defaulted) was reached. See the
1603 description above.
1604 <pre>
1606 </pre>
1607 An invalid combination of PCRE_NEWLINE_<i>xxx</i> options was given.
1608 </P>
1609 <P>
1610 Error numbers -16 to -20 and -22 are not used by <b>pcre_exec()</b>.
1611 </P>
1612 <br><a name="SEC15" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NUMBER</a><br>
1613 <P>
1614 <b>int pcre_copy_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1615 <b>int <i>stringcount</i>, int <i>stringnumber</i>, char *<i>buffer</i>,</b>
1616 <b>int <i>buffersize</i>);</b>
1617 </P>
1618 <P>
1619 <b>int pcre_get_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1620 <b>int <i>stringcount</i>, int <i>stringnumber</i>,</b>
1621 <b>const char **<i>stringptr</i>);</b>
1622 </P>
1623 <P>
1624 <b>int pcre_get_substring_list(const char *<i>subject</i>,</b>
1625 <b>int *<i>ovector</i>, int <i>stringcount</i>, const char ***<i>listptr</i>);</b>
1626 </P>
1627 <P>
1628 Captured substrings can be accessed directly by using the offsets returned by
1629 <b>pcre_exec()</b> in <i>ovector</i>. For convenience, the functions
1630 <b>pcre_copy_substring()</b>, <b>pcre_get_substring()</b>, and
1631 <b>pcre_get_substring_list()</b> are provided for extracting captured substrings
1632 as new, separate, zero-terminated strings. These functions identify substrings
1633 by number. The next section describes functions for extracting named
1634 substrings.
1635 </P>
1636 <P>
1637 A substring that contains a binary zero is correctly extracted and has a
1638 further zero added on the end, but the result is not, of course, a C string.
1639 However, you can process such a string by referring to the length that is
1640 returned by <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>.
1641 Unfortunately, the interface to <b>pcre_get_substring_list()</b> is not adequate
1642 for handling strings containing binary zeros, because the end of the final
1643 string is not independently indicated.
1644 </P>
1645 <P>
1646 The first three arguments are the same for all three of these functions:
1647 <i>subject</i> is the subject string that has just been successfully matched,
1648 <i>ovector</i> is a pointer to the vector of integer offsets that was passed to
1649 <b>pcre_exec()</b>, and <i>stringcount</i> is the number of substrings that were
1650 captured by the match, including the substring that matched the entire regular
1651 expression. This is the value returned by <b>pcre_exec()</b> if it is greater
1652 than zero. If <b>pcre_exec()</b> returned zero, indicating that it ran out of
1653 space in <i>ovector</i>, the value passed as <i>stringcount</i> should be the
1654 number of elements in the vector divided by three.
1655 </P>
1656 <P>
1657 The functions <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>
1658 extract a single substring, whose number is given as <i>stringnumber</i>. A
1659 value of zero extracts the substring that matched the entire pattern, whereas
1660 higher values extract the captured substrings. For <b>pcre_copy_substring()</b>,
1661 the string is placed in <i>buffer</i>, whose length is given by
1662 <i>buffersize</i>, while for <b>pcre_get_substring()</b> a new block of memory is
1663 obtained via <b>pcre_malloc</b>, and its address is returned via
1664 <i>stringptr</i>. The yield of the function is the length of the string, not
1665 including the terminating zero, or one of these error codes:
1666 <pre>
1668 </pre>
1669 The buffer was too small for <b>pcre_copy_substring()</b>, or the attempt to get
1670 memory failed for <b>pcre_get_substring()</b>.
1671 <pre>
1673 </pre>
1674 There is no substring whose number is <i>stringnumber</i>.
1675 </P>
1676 <P>
1677 The <b>pcre_get_substring_list()</b> function extracts all available substrings
1678 and builds a list of pointers to them. All this is done in a single block of
1679 memory that is obtained via <b>pcre_malloc</b>. The address of the memory block
1680 is returned via <i>listptr</i>, which is also the start of the list of string
1681 pointers. The end of the list is marked by a NULL pointer. The yield of the
1682 function is zero if all went well, or the error code
1683 <pre>
1685 </pre>
1686 if the attempt to get the memory block failed.
1687 </P>
1688 <P>
1689 When any of these functions encounter a substring that is unset, which can
1690 happen when capturing subpattern number <i>n+1</i> matches some part of the
1691 subject, but subpattern <i>n</i> has not been used at all, they return an empty
1692 string. This can be distinguished from a genuine zero-length substring by
1693 inspecting the appropriate offset in <i>ovector</i>, which is negative for unset
1694 substrings.
1695 </P>
1696 <P>
1697 The two convenience functions <b>pcre_free_substring()</b> and
1698 <b>pcre_free_substring_list()</b> can be used to free the memory returned by
1699 a previous call of <b>pcre_get_substring()</b> or
1700 <b>pcre_get_substring_list()</b>, respectively. They do nothing more than call
1701 the function pointed to by <b>pcre_free</b>, which of course could be called
1702 directly from a C program. However, PCRE is used in some situations where it is
1703 linked via a special interface to another programming language that cannot use
1704 <b>pcre_free</b> directly; it is for these cases that the functions are
1705 provided.
1706 </P>
1707 <br><a name="SEC16" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NAME</a><br>
1708 <P>
1709 <b>int pcre_get_stringnumber(const pcre *<i>code</i>,</b>
1710 <b>const char *<i>name</i>);</b>
1711 </P>
1712 <P>
1713 <b>int pcre_copy_named_substring(const pcre *<i>code</i>,</b>
1714 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
1715 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
1716 <b>char *<i>buffer</i>, int <i>buffersize</i>);</b>
1717 </P>
1718 <P>
1719 <b>int pcre_get_named_substring(const pcre *<i>code</i>,</b>
1720 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
1721 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
1722 <b>const char **<i>stringptr</i>);</b>
1723 </P>
1724 <P>
1725 To extract a substring by name, you first have to find associated number.
1726 For example, for this pattern
1727 <pre>
1728 (a+)b(?&#60;xxx&#62;\d+)...
1729 </pre>
1730 the number of the subpattern called "xxx" is 2. If the name is known to be
1731 unique (PCRE_DUPNAMES was not set), you can find the number from the name by
1732 calling <b>pcre_get_stringnumber()</b>. The first argument is the compiled
1733 pattern, and the second is the name. The yield of the function is the
1734 subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no subpattern of
1735 that name.
1736 </P>
1737 <P>
1738 Given the number, you can extract the substring directly, or use one of the
1739 functions described in the previous section. For convenience, there are also
1740 two functions that do the whole job.
1741 </P>
1742 <P>
1743 Most of the arguments of <b>pcre_copy_named_substring()</b> and
1744 <b>pcre_get_named_substring()</b> are the same as those for the similarly named
1745 functions that extract by number. As these are described in the previous
1746 section, they are not re-described here. There are just two differences:
1747 </P>
1748 <P>
1749 First, instead of a substring number, a substring name is given. Second, there
1750 is an extra argument, given at the start, which is a pointer to the compiled
1751 pattern. This is needed in order to gain access to the name-to-number
1752 translation table.
1753 </P>
1754 <P>
1755 These functions call <b>pcre_get_stringnumber()</b>, and if it succeeds, they
1756 then call <b>pcre_copy_substring()</b> or <b>pcre_get_substring()</b>, as
1757 appropriate. <b>NOTE:</b> If PCRE_DUPNAMES is set and there are duplicate names,
1758 the behaviour may not be what you want (see the next section).
1759 </P>
1760 <P>
1761 <b>Warning:</b> If the pattern uses the "(?|" feature to set up multiple
1762 subpatterns with the same number, you cannot use names to distinguish them,
1763 because names are not included in the compiled code. The matching process uses
1764 only numbers.
1765 </P>
1766 <br><a name="SEC17" href="#TOC1">DUPLICATE SUBPATTERN NAMES</a><br>
1767 <P>
1768 <b>int pcre_get_stringtable_entries(const pcre *<i>code</i>,</b>
1769 <b>const char *<i>name</i>, char **<i>first</i>, char **<i>last</i>);</b>
1770 </P>
1771 <P>
1772 When a pattern is compiled with the PCRE_DUPNAMES option, names for subpatterns
1773 are not required to be unique. Normally, patterns with duplicate names are such
1774 that in any one match, only one of the named subpatterns participates. An
1775 example is shown in the
1776 <a href="pcrepattern.html"><b>pcrepattern</b></a>
1777 documentation.
1778 </P>
1779 <P>
1780 When duplicates are present, <b>pcre_copy_named_substring()</b> and
1781 <b>pcre_get_named_substring()</b> return the first substring corresponding to
1782 the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING (-7) is
1783 returned; no data is returned. The <b>pcre_get_stringnumber()</b> function
1784 returns one of the numbers that are associated with the name, but it is not
1785 defined which it is.
1786 </P>
1787 <P>
1788 If you want to get full details of all captured substrings for a given name,
1789 you must use the <b>pcre_get_stringtable_entries()</b> function. The first
1790 argument is the compiled pattern, and the second is the name. The third and
1791 fourth are pointers to variables which are updated by the function. After it
1792 has run, they point to the first and last entries in the name-to-number table
1793 for the given name. The function itself returns the length of each entry, or
1794 PCRE_ERROR_NOSUBSTRING (-7) if there are none. The format of the table is
1795 described above in the section entitled <i>Information about a pattern</i>.
1796 Given all the relevant entries for the name, you can extract each of their
1797 numbers, and hence the captured data, if any.
1798 </P>
1799 <br><a name="SEC18" href="#TOC1">FINDING ALL POSSIBLE MATCHES</a><br>
1800 <P>
1801 The traditional matching function uses a similar algorithm to Perl, which stops
1802 when it finds the first match, starting at a given point in the subject. If you
1803 want to find all possible matches, or the longest possible match, consider
1804 using the alternative matching function (see below) instead. If you cannot use
1805 the alternative function, but still need to find all possible matches, you
1806 can kludge it up by making use of the callout facility, which is described in
1807 the
1808 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1809 documentation.
1810 </P>
1811 <P>
1812 What you have to do is to insert a callout right at the end of the pattern.
1813 When your callout function is called, extract and save the current matched
1814 substring. Then return 1, which forces <b>pcre_exec()</b> to backtrack and try
1815 other alternatives. Ultimately, when it runs out of matches, <b>pcre_exec()</b>
1816 will yield PCRE_ERROR_NOMATCH.
1817 <a name="dfamatch"></a></P>
1818 <br><a name="SEC19" href="#TOC1">MATCHING A PATTERN: THE ALTERNATIVE FUNCTION</a><br>
1819 <P>
1820 <b>int pcre_dfa_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
1821 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
1822 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>,</b>
1823 <b>int *<i>workspace</i>, int <i>wscount</i>);</b>
1824 </P>
1825 <P>
1826 The function <b>pcre_dfa_exec()</b> is called to match a subject string against
1827 a compiled pattern, using a matching algorithm that scans the subject string
1828 just once, and does not backtrack. This has different characteristics to the
1829 normal algorithm, and is not compatible with Perl. Some of the features of PCRE
1830 patterns are not supported. Nevertheless, there are times when this kind of
1831 matching can be useful. For a discussion of the two matching algorithms, see
1832 the
1833 <a href="pcrematching.html"><b>pcrematching</b></a>
1834 documentation.
1835 </P>
1836 <P>
1837 The arguments for the <b>pcre_dfa_exec()</b> function are the same as for
1838 <b>pcre_exec()</b>, plus two extras. The <i>ovector</i> argument is used in a
1839 different way, and this is described below. The other common arguments are used
1840 in the same way as for <b>pcre_exec()</b>, so their description is not repeated
1841 here.
1842 </P>
1843 <P>
1844 The two additional arguments provide workspace for the function. The workspace
1845 vector should contain at least 20 elements. It is used for keeping track of
1846 multiple paths through the pattern tree. More workspace will be needed for
1847 patterns and subjects where there are a lot of potential matches.
1848 </P>
1849 <P>
1850 Here is an example of a simple call to <b>pcre_dfa_exec()</b>:
1851 <pre>
1852 int rc;
1853 int ovector[10];
1854 int wspace[20];
1855 rc = pcre_dfa_exec(
1856 re, /* result of pcre_compile() */
1857 NULL, /* we didn't study the pattern */
1858 "some string", /* the subject string */
1859 11, /* the length of the subject string */
1860 0, /* start at offset 0 in the subject */
1861 0, /* default options */
1862 ovector, /* vector of integers for substring information */
1863 10, /* number of elements (NOT size in bytes) */
1864 wspace, /* working space vector */
1865 20); /* number of elements (NOT size in bytes) */
1866 </PRE>
1867 </P>
1868 <br><b>
1869 Option bits for <b>pcre_dfa_exec()</b>
1870 </b><br>
1871 <P>
1872 The unused bits of the <i>options</i> argument for <b>pcre_dfa_exec()</b> must be
1873 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_<i>xxx</i>,
1875 PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last three of these are
1876 the same as for <b>pcre_exec()</b>, so their description is not repeated here.
1877 <pre>
1879 </pre>
1880 This has the same general effect as it does for <b>pcre_exec()</b>, but the
1881 details are slightly different. When PCRE_PARTIAL is set for
1882 <b>pcre_dfa_exec()</b>, the return code PCRE_ERROR_NOMATCH is converted into
1883 PCRE_ERROR_PARTIAL if the end of the subject is reached, there have been no
1884 complete matches, but there is still at least one matching possibility. The
1885 portion of the string that provided the partial match is set as the first
1886 matching string.
1887 <pre>
1889 </pre>
1890 Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to stop as
1891 soon as it has found one match. Because of the way the alternative algorithm
1892 works, this is necessarily the shortest possible match at the first possible
1893 matching point in the subject string.
1894 <pre>
1896 </pre>
1897 When <b>pcre_dfa_exec()</b> is called with the PCRE_PARTIAL option, and returns
1898 a partial match, it is possible to call it again, with additional subject
1899 characters, and have it continue with the same match. The PCRE_DFA_RESTART
1900 option requests this action; when it is set, the <i>workspace</i> and
1901 <i>wscount</i> options must reference the same vector as before because data
1902 about the match so far is left in them after a partial match. There is more
1903 discussion of this facility in the
1904 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1905 documentation.
1906 </P>
1907 <br><b>
1908 Successful returns from <b>pcre_dfa_exec()</b>
1909 </b><br>
1910 <P>
1911 When <b>pcre_dfa_exec()</b> succeeds, it may have matched more than one
1912 substring in the subject. Note, however, that all the matches from one run of
1913 the function start at the same point in the subject. The shorter matches are
1914 all initial substrings of the longer matches. For example, if the pattern
1915 <pre>
1916 &#60;.*&#62;
1917 </pre>
1918 is matched against the string
1919 <pre>
1920 This is &#60;something&#62; &#60;something else&#62; &#60;something further&#62; no more
1921 </pre>
1922 the three matched strings are
1923 <pre>
1924 &#60;something&#62;
1925 &#60;something&#62; &#60;something else&#62;
1926 &#60;something&#62; &#60;something else&#62; &#60;something further&#62;
1927 </pre>
1928 On success, the yield of the function is a number greater than zero, which is
1929 the number of matched substrings. The substrings themselves are returned in
1930 <i>ovector</i>. Each string uses two elements; the first is the offset to the
1931 start, and the second is the offset to the end. In fact, all the strings have
1932 the same start offset. (Space could have been saved by giving this only once,
1933 but it was decided to retain some compatibility with the way <b>pcre_exec()</b>
1934 returns data, even though the meaning of the strings is different.)
1935 </P>
1936 <P>
1937 The strings are returned in reverse order of length; that is, the longest
1938 matching string is given first. If there were too many matches to fit into
1939 <i>ovector</i>, the yield of the function is zero, and the vector is filled with
1940 the longest matches.
1941 </P>
1942 <br><b>
1943 Error returns from <b>pcre_dfa_exec()</b>
1944 </b><br>
1945 <P>
1946 The <b>pcre_dfa_exec()</b> function returns a negative number when it fails.
1947 Many of the errors are the same as for <b>pcre_exec()</b>, and these are
1948 described
1949 <a href="#errorlist">above.</a>
1950 There are in addition the following errors that are specific to
1951 <b>pcre_dfa_exec()</b>:
1952 <pre>
1954 </pre>
1955 This return is given if <b>pcre_dfa_exec()</b> encounters an item in the pattern
1956 that it does not support, for instance, the use of \C or a back reference.
1957 <pre>
1959 </pre>
1960 This return is given if <b>pcre_dfa_exec()</b> encounters a condition item that
1961 uses a back reference for the condition, or a test for recursion in a specific
1962 group. These are not supported.
1963 <pre>
1965 </pre>
1966 This return is given if <b>pcre_dfa_exec()</b> is called with an <i>extra</i>
1967 block that contains a setting of the <i>match_limit</i> field. This is not
1968 supported (it is meaningless).
1969 <pre>
1971 </pre>
1972 This return is given if <b>pcre_dfa_exec()</b> runs out of space in the
1973 <i>workspace</i> vector.
1974 <pre>
1976 </pre>
1977 When a recursive subpattern is processed, the matching function calls itself
1978 recursively, using private vectors for <i>ovector</i> and <i>workspace</i>. This
1979 error is given if the output vector is not large enough. This should be
1980 extremely rare, as a vector of size 1000 is used.
1981 </P>
1982 <br><a name="SEC20" href="#TOC1">SEE ALSO</a><br>
1983 <P>
1984 <b>pcrebuild</b>(3), <b>pcrecallout</b>(3), <b>pcrecpp(3)</b>(3),
1985 <b>pcrematching</b>(3), <b>pcrepartial</b>(3), <b>pcreposix</b>(3),
1986 <b>pcreprecompile</b>(3), <b>pcresample</b>(3), <b>pcrestack</b>(3).
1987 </P>
1988 <br><a name="SEC21" href="#TOC1">AUTHOR</a><br>
1989 <P>
1990 Philip Hazel
1991 <br>
1992 University Computing Service
1993 <br>
1994 Cambridge CB2 3QH, England.
1995 <br>
1996 </P>
1997 <br><a name="SEC22" href="#TOC1">REVISION</a><br>
1998 <P>
1999 Last updated: 11 April 2009
2000 <br>
2001 Copyright &copy; 1997-2009 University of Cambridge.
2002 <br>
2003 <p>
2004 Return to the <a href="index.html">PCRE index page</a>.
2005 </p>


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