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


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