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1 <html>
2 <head>
3 <title>pcreapi specification</title>
4 </head>
5 <body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
6 <h1>pcreapi man page</h1>
7 <p>
8 Return to the <a href="index.html">PCRE index page</a>.
9 </p>
10 <p>
11 This page is part of the PCRE HTML documentation. It was generated automatically
12 from the original man page. If there is any nonsense in it, please consult the
13 man page, in case the conversion went wrong.
14 <br>
15 <ul>
16 <li><a name="TOC1" href="#SEC1">PCRE NATIVE API</a>
17 <li><a name="TOC2" href="#SEC2">PCRE API OVERVIEW</a>
18 <li><a name="TOC3" href="#SEC3">NEWLINES</a>
19 <li><a name="TOC4" href="#SEC4">MULTITHREADING</a>
21 <li><a name="TOC6" href="#SEC6">CHECKING BUILD-TIME OPTIONS</a>
22 <li><a name="TOC7" href="#SEC7">COMPILING A PATTERN</a>
23 <li><a name="TOC8" href="#SEC8">COMPILATION ERROR CODES</a>
24 <li><a name="TOC9" href="#SEC9">STUDYING A PATTERN</a>
25 <li><a name="TOC10" href="#SEC10">LOCALE SUPPORT</a>
26 <li><a name="TOC11" href="#SEC11">INFORMATION ABOUT A PATTERN</a>
27 <li><a name="TOC12" href="#SEC12">OBSOLETE INFO FUNCTION</a>
28 <li><a name="TOC13" href="#SEC13">REFERENCE COUNTS</a>
32 <li><a name="TOC17" href="#SEC17">DUPLICATE SUBPATTERN NAMES</a>
33 <li><a name="TOC18" href="#SEC18">FINDING ALL POSSIBLE MATCHES</a>
35 <li><a name="TOC20" href="#SEC20">SEE ALSO</a>
36 <li><a name="TOC21" href="#SEC21">AUTHOR</a>
37 <li><a name="TOC22" href="#SEC22">REVISION</a>
38 </ul>
39 <br><a name="SEC1" href="#TOC1">PCRE NATIVE API</a><br>
40 <P>
41 <b>#include &#60;pcre.h&#62;</b>
42 </P>
43 <P>
44 <b>pcre *pcre_compile(const char *<i>pattern</i>, int <i>options</i>,</b>
45 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
46 <b>const unsigned char *<i>tableptr</i>);</b>
47 </P>
48 <P>
49 <b>pcre *pcre_compile2(const char *<i>pattern</i>, int <i>options</i>,</b>
50 <b>int *<i>errorcodeptr</i>,</b>
51 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
52 <b>const unsigned char *<i>tableptr</i>);</b>
53 </P>
54 <P>
55 <b>pcre_extra *pcre_study(const pcre *<i>code</i>, int <i>options</i>,</b>
56 <b>const char **<i>errptr</i>);</b>
57 </P>
58 <P>
59 <b>int pcre_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
60 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
61 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>);</b>
62 </P>
63 <P>
64 <b>int pcre_dfa_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
65 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
66 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>,</b>
67 <b>int *<i>workspace</i>, int <i>wscount</i>);</b>
68 </P>
69 <P>
70 <b>int pcre_copy_named_substring(const pcre *<i>code</i>,</b>
71 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
72 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
73 <b>char *<i>buffer</i>, int <i>buffersize</i>);</b>
74 </P>
75 <P>
76 <b>int pcre_copy_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
77 <b>int <i>stringcount</i>, int <i>stringnumber</i>, char *<i>buffer</i>,</b>
78 <b>int <i>buffersize</i>);</b>
79 </P>
80 <P>
81 <b>int pcre_get_named_substring(const pcre *<i>code</i>,</b>
82 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
83 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
84 <b>const char **<i>stringptr</i>);</b>
85 </P>
86 <P>
87 <b>int pcre_get_stringnumber(const pcre *<i>code</i>,</b>
88 <b>const char *<i>name</i>);</b>
89 </P>
90 <P>
91 <b>int pcre_get_stringtable_entries(const pcre *<i>code</i>,</b>
92 <b>const char *<i>name</i>, char **<i>first</i>, char **<i>last</i>);</b>
93 </P>
94 <P>
95 <b>int pcre_get_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
96 <b>int <i>stringcount</i>, int <i>stringnumber</i>,</b>
97 <b>const char **<i>stringptr</i>);</b>
98 </P>
99 <P>
100 <b>int pcre_get_substring_list(const char *<i>subject</i>,</b>
101 <b>int *<i>ovector</i>, int <i>stringcount</i>, const char ***<i>listptr</i>);</b>
102 </P>
103 <P>
104 <b>void pcre_free_substring(const char *<i>stringptr</i>);</b>
105 </P>
106 <P>
107 <b>void pcre_free_substring_list(const char **<i>stringptr</i>);</b>
108 </P>
109 <P>
110 <b>const unsigned char *pcre_maketables(void);</b>
111 </P>
112 <P>
113 <b>int pcre_fullinfo(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
114 <b>int <i>what</i>, void *<i>where</i>);</b>
115 </P>
116 <P>
117 <b>int pcre_info(const pcre *<i>code</i>, int *<i>optptr</i>, int</b>
118 <b>*<i>firstcharptr</i>);</b>
119 </P>
120 <P>
121 <b>int pcre_refcount(pcre *<i>code</i>, int <i>adjust</i>);</b>
122 </P>
123 <P>
124 <b>int pcre_config(int <i>what</i>, void *<i>where</i>);</b>
125 </P>
126 <P>
127 <b>char *pcre_version(void);</b>
128 </P>
129 <P>
130 <b>void *(*pcre_malloc)(size_t);</b>
131 </P>
132 <P>
133 <b>void (*pcre_free)(void *);</b>
134 </P>
135 <P>
136 <b>void *(*pcre_stack_malloc)(size_t);</b>
137 </P>
138 <P>
139 <b>void (*pcre_stack_free)(void *);</b>
140 </P>
141 <P>
142 <b>int (*pcre_callout)(pcre_callout_block *);</b>
143 </P>
144 <br><a name="SEC2" href="#TOC1">PCRE API OVERVIEW</a><br>
145 <P>
146 PCRE has its own native API, which is described in this document. There are
147 also some wrapper functions that correspond to the POSIX regular expression
148 API. These are described in the
149 <a href="pcreposix.html"><b>pcreposix</b></a>
150 documentation. Both of these APIs define a set of C function calls. A C++
151 wrapper is distributed with PCRE. It is documented in the
152 <a href="pcrecpp.html"><b>pcrecpp</b></a>
153 page.
154 </P>
155 <P>
156 The native API C function prototypes are defined in the header file
157 <b>pcre.h</b>, and on Unix systems the library itself is called <b>libpcre</b>.
158 It can normally be accessed by adding <b>-lpcre</b> to the command for linking
159 an application that uses PCRE. The header file defines the macros PCRE_MAJOR
160 and PCRE_MINOR to contain the major and minor release numbers for the library.
161 Applications can use these to include support for different releases of PCRE.
162 </P>
163 <P>
164 The functions <b>pcre_compile()</b>, <b>pcre_compile2()</b>, <b>pcre_study()</b>,
165 and <b>pcre_exec()</b> are used for compiling and matching regular expressions
166 in a Perl-compatible manner. A sample program that demonstrates the simplest
167 way of using them is provided in the file called <i>pcredemo.c</i> in the source
168 distribution. The
169 <a href="pcresample.html"><b>pcresample</b></a>
170 documentation describes how to compile and run it.
171 </P>
172 <P>
173 A second matching function, <b>pcre_dfa_exec()</b>, which is not
174 Perl-compatible, is also provided. This uses a different algorithm for the
175 matching. The alternative algorithm finds all possible matches (at a given
176 point in the subject), and scans the subject just once. However, this algorithm
177 does not return captured substrings. A description of the two matching
178 algorithms and their advantages and disadvantages is given in the
179 <a href="pcrematching.html"><b>pcrematching</b></a>
180 documentation.
181 </P>
182 <P>
183 In addition to the main compiling and matching functions, there are convenience
184 functions for extracting captured substrings from a subject string that is
185 matched by <b>pcre_exec()</b>. They are:
186 <pre>
187 <b>pcre_copy_substring()</b>
188 <b>pcre_copy_named_substring()</b>
189 <b>pcre_get_substring()</b>
190 <b>pcre_get_named_substring()</b>
191 <b>pcre_get_substring_list()</b>
192 <b>pcre_get_stringnumber()</b>
193 <b>pcre_get_stringtable_entries()</b>
194 </pre>
195 <b>pcre_free_substring()</b> and <b>pcre_free_substring_list()</b> are also
196 provided, to free the memory used for extracted strings.
197 </P>
198 <P>
199 The function <b>pcre_maketables()</b> is used to build a set of character tables
200 in the current locale for passing to <b>pcre_compile()</b>, <b>pcre_exec()</b>,
201 or <b>pcre_dfa_exec()</b>. This is an optional facility that is provided for
202 specialist use. Most commonly, no special tables are passed, in which case
203 internal tables that are generated when PCRE is built are used.
204 </P>
205 <P>
206 The function <b>pcre_fullinfo()</b> is used to find out information about a
207 compiled pattern; <b>pcre_info()</b> is an obsolete version that returns only
208 some of the available information, but is retained for backwards compatibility.
209 The function <b>pcre_version()</b> returns a pointer to a string containing the
210 version of PCRE and its date of release.
211 </P>
212 <P>
213 The function <b>pcre_refcount()</b> maintains a reference count in a data block
214 containing a compiled pattern. This is provided for the benefit of
215 object-oriented applications.
216 </P>
217 <P>
218 The global variables <b>pcre_malloc</b> and <b>pcre_free</b> initially contain
219 the entry points of the standard <b>malloc()</b> and <b>free()</b> functions,
220 respectively. PCRE calls the memory management functions via these variables,
221 so a calling program can replace them if it wishes to intercept the calls. This
222 should be done before calling any PCRE functions.
223 </P>
224 <P>
225 The global variables <b>pcre_stack_malloc</b> and <b>pcre_stack_free</b> are also
226 indirections to memory management functions. These special functions are used
227 only when PCRE is compiled to use the heap for remembering data, instead of
228 recursive function calls, when running the <b>pcre_exec()</b> function. See the
229 <a href="pcrebuild.html"><b>pcrebuild</b></a>
230 documentation for details of how to do this. It is a non-standard way of
231 building PCRE, for use in environments that have limited stacks. Because of the
232 greater use of memory management, it runs more slowly. Separate functions are
233 provided so that special-purpose external code can be used for this case. When
234 used, these functions are always called in a stack-like manner (last obtained,
235 first freed), and always for memory blocks of the same size. There is a
236 discussion about PCRE's stack usage in the
237 <a href="pcrestack.html"><b>pcrestack</b></a>
238 documentation.
239 </P>
240 <P>
241 The global variable <b>pcre_callout</b> initially contains NULL. It can be set
242 by the caller to a "callout" function, which PCRE will then call at specified
243 points during a matching operation. Details are given in the
244 <a href="pcrecallout.html"><b>pcrecallout</b></a>
245 documentation.
246 <a name="newlines"></a></P>
247 <br><a name="SEC3" href="#TOC1">NEWLINES</a><br>
248 <P>
249 PCRE supports five different conventions for indicating line breaks in
250 strings: a single CR (carriage return) character, a single LF (linefeed)
251 character, the two-character sequence CRLF, any of the three preceding, or any
252 Unicode newline sequence. The Unicode newline sequences are the three just
253 mentioned, plus the single characters VT (vertical tab, U+000B), FF (formfeed,
254 U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS
255 (paragraph separator, U+2029).
256 </P>
257 <P>
258 Each of the first three conventions is used by at least one operating system as
259 its standard newline sequence. When PCRE is built, a default can be specified.
260 The default default is LF, which is the Unix standard. When PCRE is run, the
261 default can be overridden, either when a pattern is compiled, or when it is
262 matched.
263 </P>
264 <P>
265 At compile time, the newline convention can be specified by the <i>options</i>
266 argument of <b>pcre_compile()</b>, or it can be specified by special text at the
267 start of the pattern itself; this overrides any other settings. See the
268 <a href="pcrepattern.html"><b>pcrepattern</b></a>
269 page for details of the special character sequences.
270 </P>
271 <P>
272 In the PCRE documentation the word "newline" is used to mean "the character or
273 pair of characters that indicate a line break". The choice of newline
274 convention affects the handling of the dot, circumflex, and dollar
275 metacharacters, the handling of #-comments in /x mode, and, when CRLF is a
276 recognized line ending sequence, the match position advancement for a
277 non-anchored pattern. There is more detail about this in the
278 <a href="#execoptions">section on <b>pcre_exec()</b> options</a>
279 below.
280 </P>
281 <P>
282 The choice of newline convention does not affect the interpretation of
283 the \n or \r escape sequences, nor does it affect what \R matches, which is
284 controlled in a similar way, but by separate options.
285 </P>
286 <br><a name="SEC4" href="#TOC1">MULTITHREADING</a><br>
287 <P>
288 The PCRE functions can be used in multi-threading applications, with the
289 proviso that the memory management functions pointed to by <b>pcre_malloc</b>,
290 <b>pcre_free</b>, <b>pcre_stack_malloc</b>, and <b>pcre_stack_free</b>, and the
291 callout function pointed to by <b>pcre_callout</b>, are shared by all threads.
292 </P>
293 <P>
294 The compiled form of a regular expression is not altered during matching, so
295 the same compiled pattern can safely be used by several threads at once.
296 </P>
297 <br><a name="SEC5" href="#TOC1">SAVING PRECOMPILED PATTERNS FOR LATER USE</a><br>
298 <P>
299 The compiled form of a regular expression can be saved and re-used at a later
300 time, possibly by a different program, and even on a host other than the one on
301 which it was compiled. Details are given in the
302 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
303 documentation. However, compiling a regular expression with one version of PCRE
304 for use with a different version is not guaranteed to work and may cause
305 crashes.
306 </P>
307 <br><a name="SEC6" href="#TOC1">CHECKING BUILD-TIME OPTIONS</a><br>
308 <P>
309 <b>int pcre_config(int <i>what</i>, void *<i>where</i>);</b>
310 </P>
311 <P>
312 The function <b>pcre_config()</b> makes it possible for a PCRE client to
313 discover which optional features have been compiled into the PCRE library. The
314 <a href="pcrebuild.html"><b>pcrebuild</b></a>
315 documentation has more details about these optional features.
316 </P>
317 <P>
318 The first argument for <b>pcre_config()</b> is an integer, specifying which
319 information is required; the second argument is a pointer to a variable into
320 which the information is placed. The following information is available:
321 <pre>
323 </pre>
324 The output is an integer that is set to one if UTF-8 support is available;
325 otherwise it is set to zero.
326 <pre>
328 </pre>
329 The output is an integer that is set to one if support for Unicode character
330 properties is available; otherwise it is set to zero.
331 <pre>
333 </pre>
334 The output is an integer whose value specifies the default character sequence
335 that is recognized as meaning "newline". The four values that are supported
336 are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF, and -1 for ANY.
337 Though they are derived from ASCII, the same values are returned in EBCDIC
338 environments. The default should normally correspond to the standard sequence
339 for your operating system.
340 <pre>
342 </pre>
343 The output is an integer whose value indicates what character sequences the \R
344 escape sequence matches by default. A value of 0 means that \R matches any
345 Unicode line ending sequence; a value of 1 means that \R matches only CR, LF,
346 or CRLF. The default can be overridden when a pattern is compiled or matched.
347 <pre>
349 </pre>
350 The output is an integer that contains the number of bytes used for internal
351 linkage in compiled regular expressions. The value is 2, 3, or 4. Larger values
352 allow larger regular expressions to be compiled, at the expense of slower
353 matching. The default value of 2 is sufficient for all but the most massive
354 patterns, since it allows the compiled pattern to be up to 64K in size.
355 <pre>
357 </pre>
358 The output is an integer that contains the threshold above which the POSIX
359 interface uses <b>malloc()</b> for output vectors. Further details are given in
360 the
361 <a href="pcreposix.html"><b>pcreposix</b></a>
362 documentation.
363 <pre>
365 </pre>
366 The output is a long integer that gives the default limit for the number of
367 internal matching function calls in a <b>pcre_exec()</b> execution. Further
368 details are given with <b>pcre_exec()</b> below.
369 <pre>
371 </pre>
372 The output is a long integer that gives the default limit for the depth of
373 recursion when calling the internal matching function in a <b>pcre_exec()</b>
374 execution. Further details are given with <b>pcre_exec()</b> below.
375 <pre>
377 </pre>
378 The output is an integer that is set to one if internal recursion when running
379 <b>pcre_exec()</b> is implemented by recursive function calls that use the stack
380 to remember their state. This is the usual way that PCRE is compiled. The
381 output is zero if PCRE was compiled to use blocks of data on the heap instead
382 of recursive function calls. In this case, <b>pcre_stack_malloc</b> and
383 <b>pcre_stack_free</b> are called to manage memory blocks on the heap, thus
384 avoiding the use of the stack.
385 </P>
386 <br><a name="SEC7" href="#TOC1">COMPILING A PATTERN</a><br>
387 <P>
388 <b>pcre *pcre_compile(const char *<i>pattern</i>, int <i>options</i>,</b>
389 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
390 <b>const unsigned char *<i>tableptr</i>);</b>
391 <b>pcre *pcre_compile2(const char *<i>pattern</i>, int <i>options</i>,</b>
392 <b>int *<i>errorcodeptr</i>,</b>
393 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
394 <b>const unsigned char *<i>tableptr</i>);</b>
395 </P>
396 <P>
397 Either of the functions <b>pcre_compile()</b> or <b>pcre_compile2()</b> can be
398 called to compile a pattern into an internal form. The only difference between
399 the two interfaces is that <b>pcre_compile2()</b> has an additional argument,
400 <i>errorcodeptr</i>, via which a numerical error code can be returned.
401 </P>
402 <P>
403 The pattern is a C string terminated by a binary zero, and is passed in the
404 <i>pattern</i> argument. A pointer to a single block of memory that is obtained
405 via <b>pcre_malloc</b> is returned. This contains the compiled code and related
406 data. The <b>pcre</b> type is defined for the returned block; this is a typedef
407 for a structure whose contents are not externally defined. It is up to the
408 caller to free the memory (via <b>pcre_free</b>) when it is no longer required.
409 </P>
410 <P>
411 Although the compiled code of a PCRE regex is relocatable, that is, it does not
412 depend on memory location, the complete <b>pcre</b> data block is not
413 fully relocatable, because it may contain a copy of the <i>tableptr</i>
414 argument, which is an address (see below).
415 </P>
416 <P>
417 The <i>options</i> argument contains various bit settings that affect the
418 compilation. It should be zero if no options are required. The available
419 options are described below. Some of them, in particular, those that are
420 compatible with Perl, can also be set and unset from within the pattern (see
421 the detailed description in the
422 <a href="pcrepattern.html"><b>pcrepattern</b></a>
423 documentation). For these options, the contents of the <i>options</i> argument
424 specifies their initial settings at the start of compilation and execution. The
425 PCRE_ANCHORED and PCRE_NEWLINE_<i>xxx</i> options can be set at the time of
426 matching as well as at compile time.
427 </P>
428 <P>
429 If <i>errptr</i> is NULL, <b>pcre_compile()</b> returns NULL immediately.
430 Otherwise, if compilation of a pattern fails, <b>pcre_compile()</b> returns
431 NULL, and sets the variable pointed to by <i>errptr</i> to point to a textual
432 error message. This is a static string that is part of the library. You must
433 not try to free it. The offset from the start of the pattern to the character
434 where the error was discovered is placed in the variable pointed to by
435 <i>erroffset</i>, which must not be NULL. If it is, an immediate error is given.
436 </P>
437 <P>
438 If <b>pcre_compile2()</b> is used instead of <b>pcre_compile()</b>, and the
439 <i>errorcodeptr</i> argument is not NULL, a non-zero error code number is
440 returned via this argument in the event of an error. This is in addition to the
441 textual error message. Error codes and messages are listed below.
442 </P>
443 <P>
444 If the final argument, <i>tableptr</i>, is NULL, PCRE uses a default set of
445 character tables that are built when PCRE is compiled, using the default C
446 locale. Otherwise, <i>tableptr</i> must be an address that is the result of a
447 call to <b>pcre_maketables()</b>. This value is stored with the compiled
448 pattern, and used again by <b>pcre_exec()</b>, unless another table pointer is
449 passed to it. For more discussion, see the section on locale support below.
450 </P>
451 <P>
452 This code fragment shows a typical straightforward call to <b>pcre_compile()</b>:
453 <pre>
454 pcre *re;
455 const char *error;
456 int erroffset;
457 re = pcre_compile(
458 "^A.*Z", /* the pattern */
459 0, /* default options */
460 &error, /* for error message */
461 &erroffset, /* for error offset */
462 NULL); /* use default character tables */
463 </pre>
464 The following names for option bits are defined in the <b>pcre.h</b> header
465 file:
466 <pre>
468 </pre>
469 If this bit is set, the pattern is forced to be "anchored", that is, it is
470 constrained to match only at the first matching point in the string that is
471 being searched (the "subject string"). This effect can also be achieved by
472 appropriate constructs in the pattern itself, which is the only way to do it in
473 Perl.
474 <pre>
476 </pre>
477 If this bit is set, <b>pcre_compile()</b> automatically inserts callout items,
478 all with number 255, before each pattern item. For discussion of the callout
479 facility, see the
480 <a href="pcrecallout.html"><b>pcrecallout</b></a>
481 documentation.
482 <pre>
485 </pre>
486 These options (which are mutually exclusive) control what the \R escape
487 sequence matches. The choice is either to match only CR, LF, or CRLF, or to
488 match any Unicode newline sequence. The default is specified when PCRE is
489 built. It can be overridden from within the pattern, or by setting an option
490 when a compiled pattern is matched.
491 <pre>
493 </pre>
494 If this bit is set, letters in the pattern match both upper and lower case
495 letters. It is equivalent to Perl's /i option, and it can be changed within a
496 pattern by a (?i) option setting. In UTF-8 mode, PCRE always understands the
497 concept of case for characters whose values are less than 128, so caseless
498 matching is always possible. For characters with higher values, the concept of
499 case is supported if PCRE is compiled with Unicode property support, but not
500 otherwise. If you want to use caseless matching for characters 128 and above,
501 you must ensure that PCRE is compiled with Unicode property support as well as
502 with UTF-8 support.
503 <pre>
505 </pre>
506 If this bit is set, a dollar metacharacter in the pattern matches only at the
507 end of the subject string. Without this option, a dollar also matches
508 immediately before a newline at the end of the string (but not before any other
509 newlines). The PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is set.
510 There is no equivalent to this option in Perl, and no way to set it within a
511 pattern.
512 <pre>
514 </pre>
515 If this bit is set, a dot metacharater in the pattern matches all characters,
516 including those that indicate newline. Without it, a dot does not match when
517 the current position is at a newline. This option is equivalent to Perl's /s
518 option, and it can be changed within a pattern by a (?s) option setting. A
519 negative class such as [^a] always matches newline characters, independent of
520 the setting of this option.
521 <pre>
523 </pre>
524 If this bit is set, names used to identify capturing subpatterns need not be
525 unique. This can be helpful for certain types of pattern when it is known that
526 only one instance of the named subpattern can ever be matched. There are more
527 details of named subpatterns below; see also the
528 <a href="pcrepattern.html"><b>pcrepattern</b></a>
529 documentation.
530 <pre>
532 </pre>
533 If this bit is set, whitespace data characters in the pattern are totally
534 ignored except when escaped or inside a character class. Whitespace does not
535 include the VT character (code 11). In addition, characters between an
536 unescaped # outside a character class and the next newline, inclusive, are also
537 ignored. This is equivalent to Perl's /x option, and it can be changed within a
538 pattern by a (?x) option setting.
539 </P>
540 <P>
541 This option makes it possible to include comments inside complicated patterns.
542 Note, however, that this applies only to data characters. Whitespace characters
543 may never appear within special character sequences in a pattern, for example
544 within the sequence (?( which introduces a conditional subpattern.
545 <pre>
547 </pre>
548 This option was invented in order to turn on additional functionality of PCRE
549 that is incompatible with Perl, but it is currently of very little use. When
550 set, any backslash in a pattern that is followed by a letter that has no
551 special meaning causes an error, thus reserving these combinations for future
552 expansion. By default, as in Perl, a backslash followed by a letter with no
553 special meaning is treated as a literal. (Perl can, however, be persuaded to
554 give a warning for this.) There are at present no other features controlled by
555 this option. It can also be set by a (?X) option setting within a pattern.
556 <pre>
558 </pre>
559 If this option is set, an unanchored pattern is required to match before or at
560 the first newline in the subject string, though the matched text may continue
561 over the newline.
562 <pre>
564 </pre>
565 If this option is set, PCRE's behaviour is changed in some ways so that it is
566 compatible with JavaScript rather than Perl. The changes are as follows:
567 </P>
568 <P>
569 (1) A lone closing square bracket in a pattern causes a compile-time error,
570 because this is illegal in JavaScript (by default it is treated as a data
571 character). Thus, the pattern AB]CD becomes illegal when this option is set.
572 </P>
573 <P>
574 (2) At run time, a back reference to an unset subpattern group matches an empty
575 string (by default this causes the current matching alternative to fail). A
576 pattern such as (\1)(a) succeeds when this option is set (assuming it can find
577 an "a" in the subject), whereas it fails by default, for Perl compatibility.
578 <pre>
580 </pre>
581 By default, PCRE treats the subject string as consisting of a single line of
582 characters (even if it actually contains newlines). The "start of line"
583 metacharacter (^) matches only at the start of the string, while the "end of
584 line" metacharacter ($) matches only at the end of the string, or before a
585 terminating newline (unless PCRE_DOLLAR_ENDONLY is set). This is the same as
586 Perl.
587 </P>
588 <P>
589 When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs
590 match immediately following or immediately before internal newlines in the
591 subject string, respectively, as well as at the very start and end. This is
592 equivalent to Perl's /m option, and it can be changed within a pattern by a
593 (?m) option setting. If there are no newlines in a subject string, or no
594 occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no effect.
595 <pre>
601 </pre>
602 These options override the default newline definition that was chosen when PCRE
603 was built. Setting the first or the second specifies that a newline is
604 indicated by a single character (CR or LF, respectively). Setting
605 PCRE_NEWLINE_CRLF specifies that a newline is indicated by the two-character
606 CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies that any of the three
607 preceding sequences should be recognized. Setting PCRE_NEWLINE_ANY specifies
608 that any Unicode newline sequence should be recognized. The Unicode newline
609 sequences are the three just mentioned, plus the single characters VT (vertical
610 tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS (line
611 separator, U+2028), and PS (paragraph separator, U+2029). The last two are
612 recognized only in UTF-8 mode.
613 </P>
614 <P>
615 The newline setting in the options word uses three bits that are treated
616 as a number, giving eight possibilities. Currently only six are used (default
617 plus the five values above). This means that if you set more than one newline
618 option, the combination may or may not be sensible. For example,
620 other combinations may yield unused numbers and cause an error.
621 </P>
622 <P>
623 The only time that a line break is specially recognized when compiling a
624 pattern is if PCRE_EXTENDED is set, and an unescaped # outside a character
625 class is encountered. This indicates a comment that lasts until after the next
626 line break sequence. In other circumstances, line break sequences are treated
627 as literal data, except that in PCRE_EXTENDED mode, both CR and LF are treated
628 as whitespace characters and are therefore ignored.
629 </P>
630 <P>
631 The newline option that is set at compile time becomes the default that is used
632 for <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b>, but it can be overridden.
633 <pre>
635 </pre>
636 If this option is set, it disables the use of numbered capturing parentheses in
637 the pattern. Any opening parenthesis that is not followed by ? behaves as if it
638 were followed by ?: but named parentheses can still be used for capturing (and
639 they acquire numbers in the usual way). There is no equivalent of this option
640 in Perl.
641 <pre>
643 </pre>
644 This option inverts the "greediness" of the quantifiers so that they are not
645 greedy by default, but become greedy if followed by "?". It is not compatible
646 with Perl. It can also be set by a (?U) option setting within the pattern.
647 <pre>
649 </pre>
650 This option causes PCRE to regard both the pattern and the subject as strings
651 of UTF-8 characters instead of single-byte character strings. However, it is
652 available only when PCRE is built to include UTF-8 support. If not, the use
653 of this option provokes an error. Details of how this option changes the
654 behaviour of PCRE are given in the
655 <a href="pcre.html#utf8support">section on UTF-8 support</a>
656 in the main
657 <a href="pcre.html"><b>pcre</b></a>
658 page.
659 <pre>
661 </pre>
662 When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
663 automatically checked. There is a discussion about the
664 <a href="pcre.html#utf8strings">validity of UTF-8 strings</a>
665 in the main
666 <a href="pcre.html"><b>pcre</b></a>
667 page. If an invalid UTF-8 sequence of bytes is found, <b>pcre_compile()</b>
668 returns an error. If you already know that your pattern is valid, and you want
669 to skip this check for performance reasons, you can set the PCRE_NO_UTF8_CHECK
670 option. When it is set, the effect of passing an invalid UTF-8 string as a
671 pattern is undefined. It may cause your program to crash. Note that this option
672 can also be passed to <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b>, to suppress
673 the UTF-8 validity checking of subject strings.
674 </P>
675 <br><a name="SEC8" href="#TOC1">COMPILATION ERROR CODES</a><br>
676 <P>
677 The following table lists the error codes than may be returned by
678 <b>pcre_compile2()</b>, along with the error messages that may be returned by
679 both compiling functions. As PCRE has developed, some error codes have fallen
680 out of use. To avoid confusion, they have not been re-used.
681 <pre>
682 0 no error
683 1 \ at end of pattern
684 2 \c at end of pattern
685 3 unrecognized character follows \
686 4 numbers out of order in {} quantifier
687 5 number too big in {} quantifier
688 6 missing terminating ] for character class
689 7 invalid escape sequence in character class
690 8 range out of order in character class
691 9 nothing to repeat
692 10 [this code is not in use]
693 11 internal error: unexpected repeat
694 12 unrecognized character after (? or (?-
695 13 POSIX named classes are supported only within a class
696 14 missing )
697 15 reference to non-existent subpattern
698 16 erroffset passed as NULL
699 17 unknown option bit(s) set
700 18 missing ) after comment
701 19 [this code is not in use]
702 20 regular expression is too large
703 21 failed to get memory
704 22 unmatched parentheses
705 23 internal error: code overflow
706 24 unrecognized character after (?&#60;
707 25 lookbehind assertion is not fixed length
708 26 malformed number or name after (?(
709 27 conditional group contains more than two branches
710 28 assertion expected after (?(
711 29 (?R or (?[+-]digits must be followed by )
712 30 unknown POSIX class name
713 31 POSIX collating elements are not supported
714 32 this version of PCRE is not compiled with PCRE_UTF8 support
715 33 [this code is not in use]
716 34 character value in \x{...} sequence is too large
717 35 invalid condition (?(0)
718 36 \C not allowed in lookbehind assertion
719 37 PCRE does not support \L, \l, \N, \U, or \u
720 38 number after (?C is &#62; 255
721 39 closing ) for (?C expected
722 40 recursive call could loop indefinitely
723 41 unrecognized character after (?P
724 42 syntax error in subpattern name (missing terminator)
725 43 two named subpatterns have the same name
726 44 invalid UTF-8 string
727 45 support for \P, \p, and \X has not been compiled
728 46 malformed \P or \p sequence
729 47 unknown property name after \P or \p
730 48 subpattern name is too long (maximum 32 characters)
731 49 too many named subpatterns (maximum 10000)
732 50 [this code is not in use]
733 51 octal value is greater than \377 (not in UTF-8 mode)
734 52 internal error: overran compiling workspace
735 53 internal error: previously-checked referenced subpattern not found
736 54 DEFINE group contains more than one branch
737 55 repeating a DEFINE group is not allowed
738 56 inconsistent NEWLINE options
739 57 \g is not followed by a braced, angle-bracketed, or quoted
740 name/number or by a plain number
741 58 a numbered reference must not be zero
742 59 (*VERB) with an argument is not supported
743 60 (*VERB) not recognized
744 61 number is too big
745 62 subpattern name expected
746 63 digit expected after (?+
747 64 ] is an invalid data character in JavaScript compatibility mode
748 </pre>
749 The numbers 32 and 10000 in errors 48 and 49 are defaults; different values may
750 be used if the limits were changed when PCRE was built.
751 </P>
752 <br><a name="SEC9" href="#TOC1">STUDYING A PATTERN</a><br>
753 <P>
754 <b>pcre_extra *pcre_study(const pcre *<i>code</i>, int <i>options</i></b>
755 <b>const char **<i>errptr</i>);</b>
756 </P>
757 <P>
758 If a compiled pattern is going to be used several times, it is worth spending
759 more time analyzing it in order to speed up the time taken for matching. The
760 function <b>pcre_study()</b> takes a pointer to a compiled pattern as its first
761 argument. If studying the pattern produces additional information that will
762 help speed up matching, <b>pcre_study()</b> returns a pointer to a
763 <b>pcre_extra</b> block, in which the <i>study_data</i> field points to the
764 results of the study.
765 </P>
766 <P>
767 The returned value from <b>pcre_study()</b> can be passed directly to
768 <b>pcre_exec()</b>. However, a <b>pcre_extra</b> block also contains other
769 fields that can be set by the caller before the block is passed; these are
770 described
771 <a href="#extradata">below</a>
772 in the section on matching a pattern.
773 </P>
774 <P>
775 If studying the pattern does not produce any additional information
776 <b>pcre_study()</b> returns NULL. In that circumstance, if the calling program
777 wants to pass any of the other fields to <b>pcre_exec()</b>, it must set up its
778 own <b>pcre_extra</b> block.
779 </P>
780 <P>
781 The second argument of <b>pcre_study()</b> contains option bits. At present, no
782 options are defined, and this argument should always be zero.
783 </P>
784 <P>
785 The third argument for <b>pcre_study()</b> is a pointer for an error message. If
786 studying succeeds (even if no data is returned), the variable it points to is
787 set to NULL. Otherwise it is set to point to a textual error message. This is a
788 static string that is part of the library. You must not try to free it. You
789 should test the error pointer for NULL after calling <b>pcre_study()</b>, to be
790 sure that it has run successfully.
791 </P>
792 <P>
793 This is a typical call to <b>pcre_study</b>():
794 <pre>
795 pcre_extra *pe;
796 pe = pcre_study(
797 re, /* result of pcre_compile() */
798 0, /* no options exist */
799 &error); /* set to NULL or points to a message */
800 </pre>
801 At present, studying a pattern is useful only for non-anchored patterns that do
802 not have a single fixed starting character. A bitmap of possible starting
803 bytes is created.
804 <a name="localesupport"></a></P>
805 <br><a name="SEC10" href="#TOC1">LOCALE SUPPORT</a><br>
806 <P>
807 PCRE handles caseless matching, and determines whether characters are letters,
808 digits, or whatever, by reference to a set of tables, indexed by character
809 value. When running in UTF-8 mode, this applies only to characters with codes
810 less than 128. Higher-valued codes never match escapes such as \w or \d, but
811 can be tested with \p if PCRE is built with Unicode character property
812 support. The use of locales with Unicode is discouraged. If you are handling
813 characters with codes greater than 128, you should either use UTF-8 and
814 Unicode, or use locales, but not try to mix the two.
815 </P>
816 <P>
817 PCRE contains an internal set of tables that are used when the final argument
818 of <b>pcre_compile()</b> is NULL. These are sufficient for many applications.
819 Normally, the internal tables recognize only ASCII characters. However, when
820 PCRE is built, it is possible to cause the internal tables to be rebuilt in the
821 default "C" locale of the local system, which may cause them to be different.
822 </P>
823 <P>
824 The internal tables can always be overridden by tables supplied by the
825 application that calls PCRE. These may be created in a different locale from
826 the default. As more and more applications change to using Unicode, the need
827 for this locale support is expected to die away.
828 </P>
829 <P>
830 External tables are built by calling the <b>pcre_maketables()</b> function,
831 which has no arguments, in the relevant locale. The result can then be passed
832 to <b>pcre_compile()</b> or <b>pcre_exec()</b> as often as necessary. For
833 example, to build and use tables that are appropriate for the French locale
834 (where accented characters with values greater than 128 are treated as letters),
835 the following code could be used:
836 <pre>
837 setlocale(LC_CTYPE, "fr_FR");
838 tables = pcre_maketables();
839 re = pcre_compile(..., tables);
840 </pre>
841 The locale name "fr_FR" is used on Linux and other Unix-like systems; if you
842 are using Windows, the name for the French locale is "french".
843 </P>
844 <P>
845 When <b>pcre_maketables()</b> runs, the tables are built in memory that is
846 obtained via <b>pcre_malloc</b>. It is the caller's responsibility to ensure
847 that the memory containing the tables remains available for as long as it is
848 needed.
849 </P>
850 <P>
851 The pointer that is passed to <b>pcre_compile()</b> is saved with the compiled
852 pattern, and the same tables are used via this pointer by <b>pcre_study()</b>
853 and normally also by <b>pcre_exec()</b>. Thus, by default, for any single
854 pattern, compilation, studying and matching all happen in the same locale, but
855 different patterns can be compiled in different locales.
856 </P>
857 <P>
858 It is possible to pass a table pointer or NULL (indicating the use of the
859 internal tables) to <b>pcre_exec()</b>. Although not intended for this purpose,
860 this facility could be used to match a pattern in a different locale from the
861 one in which it was compiled. Passing table pointers at run time is discussed
862 below in the section on matching a pattern.
863 </P>
864 <br><a name="SEC11" href="#TOC1">INFORMATION ABOUT A PATTERN</a><br>
865 <P>
866 <b>int pcre_fullinfo(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
867 <b>int <i>what</i>, void *<i>where</i>);</b>
868 </P>
869 <P>
870 The <b>pcre_fullinfo()</b> function returns information about a compiled
871 pattern. It replaces the obsolete <b>pcre_info()</b> function, which is
872 nevertheless retained for backwards compability (and is documented below).
873 </P>
874 <P>
875 The first argument for <b>pcre_fullinfo()</b> is a pointer to the compiled
876 pattern. The second argument is the result of <b>pcre_study()</b>, or NULL if
877 the pattern was not studied. The third argument specifies which piece of
878 information is required, and the fourth argument is a pointer to a variable
879 to receive the data. The yield of the function is zero for success, or one of
880 the following negative numbers:
881 <pre>
882 PCRE_ERROR_NULL the argument <i>code</i> was NULL
883 the argument <i>where</i> was NULL
884 PCRE_ERROR_BADMAGIC the "magic number" was not found
885 PCRE_ERROR_BADOPTION the value of <i>what</i> was invalid
886 </pre>
887 The "magic number" is placed at the start of each compiled pattern as an simple
888 check against passing an arbitrary memory pointer. Here is a typical call of
889 <b>pcre_fullinfo()</b>, to obtain the length of the compiled pattern:
890 <pre>
891 int rc;
892 size_t length;
893 rc = pcre_fullinfo(
894 re, /* result of pcre_compile() */
895 pe, /* result of pcre_study(), or NULL */
896 PCRE_INFO_SIZE, /* what is required */
897 &length); /* where to put the data */
898 </pre>
899 The possible values for the third argument are defined in <b>pcre.h</b>, and are
900 as follows:
901 <pre>
903 </pre>
904 Return the number of the highest back reference in the pattern. The fourth
905 argument should point to an <b>int</b> variable. Zero is returned if there are
906 no back references.
907 <pre>
909 </pre>
910 Return the number of capturing subpatterns in the pattern. The fourth argument
911 should point to an <b>int</b> variable.
912 <pre>
914 </pre>
915 Return a pointer to the internal default character tables within PCRE. The
916 fourth argument should point to an <b>unsigned char *</b> variable. This
917 information call is provided for internal use by the <b>pcre_study()</b>
918 function. External callers can cause PCRE to use its internal tables by passing
919 a NULL table pointer.
920 <pre>
922 </pre>
923 Return information about the first byte of any matched string, for a
924 non-anchored pattern. The fourth argument should point to an <b>int</b>
925 variable. (This option used to be called PCRE_INFO_FIRSTCHAR; the old name is
926 still recognized for backwards compatibility.)
927 </P>
928 <P>
929 If there is a fixed first byte, for example, from a pattern such as
930 (cat|cow|coyote), its value is returned. Otherwise, if either
931 <br>
932 <br>
933 (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
934 starts with "^", or
935 <br>
936 <br>
937 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
938 (if it were set, the pattern would be anchored),
939 <br>
940 <br>
941 -1 is returned, indicating that the pattern matches only at the start of a
942 subject string or after any newline within the string. Otherwise -2 is
943 returned. For anchored patterns, -2 is returned.
944 <pre>
946 </pre>
947 If the pattern was studied, and this resulted in the construction of a 256-bit
948 table indicating a fixed set of bytes for the first byte in any matching
949 string, a pointer to the table is returned. Otherwise NULL is returned. The
950 fourth argument should point to an <b>unsigned char *</b> variable.
951 <pre>
953 </pre>
954 Return 1 if the pattern contains any explicit matches for CR or LF characters,
955 otherwise 0. The fourth argument should point to an <b>int</b> variable. An
956 explicit match is either a literal CR or LF character, or \r or \n.
957 <pre>
959 </pre>
960 Return 1 if the (?J) or (?-J) option setting is used in the pattern, otherwise
961 0. The fourth argument should point to an <b>int</b> variable. (?J) and
962 (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
963 <pre>
965 </pre>
966 Return the value of the rightmost literal byte that must exist in any matched
967 string, other than at its start, if such a byte has been recorded. The fourth
968 argument should point to an <b>int</b> variable. If there is no such byte, -1 is
969 returned. For anchored patterns, a last literal byte is recorded only if it
970 follows something of variable length. For example, for the pattern
971 /^a\d+z\d+/ the returned value is "z", but for /^a\dz\d/ the returned value
972 is -1.
973 <pre>
977 </pre>
978 PCRE supports the use of named as well as numbered capturing parentheses. The
979 names are just an additional way of identifying the parentheses, which still
980 acquire numbers. Several convenience functions such as
981 <b>pcre_get_named_substring()</b> are provided for extracting captured
982 substrings by name. It is also possible to extract the data directly, by first
983 converting the name to a number in order to access the correct pointers in the
984 output vector (described with <b>pcre_exec()</b> below). To do the conversion,
985 you need to use the name-to-number map, which is described by these three
986 values.
987 </P>
988 <P>
989 The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives
990 the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each
991 entry; both of these return an <b>int</b> value. The entry size depends on the
992 length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first
993 entry of the table (a pointer to <b>char</b>). The first two bytes of each entry
994 are the number of the capturing parenthesis, most significant byte first. The
995 rest of the entry is the corresponding name, zero terminated. The names are in
996 alphabetical order. When PCRE_DUPNAMES is set, duplicate names are in order of
997 their parentheses numbers. For example, consider the following pattern (assume
998 PCRE_EXTENDED is set, so white space - including newlines - is ignored):
999 <pre>
1000 (?&#60;date&#62; (?&#60;year&#62;(\d\d)?\d\d) - (?&#60;month&#62;\d\d) - (?&#60;day&#62;\d\d) )
1001 </pre>
1002 There are four named subpatterns, so the table has four entries, and each entry
1003 in the table is eight bytes long. The table is as follows, with non-printing
1004 bytes shows in hexadecimal, and undefined bytes shown as ??:
1005 <pre>
1006 00 01 d a t e 00 ??
1007 00 05 d a y 00 ?? ??
1008 00 04 m o n t h 00
1009 00 02 y e a r 00 ??
1010 </pre>
1011 When writing code to extract data from named subpatterns using the
1012 name-to-number map, remember that the length of the entries is likely to be
1013 different for each compiled pattern.
1014 <pre>
1016 </pre>
1017 Return 1 if the pattern can be used for partial matching, otherwise 0. The
1018 fourth argument should point to an <b>int</b> variable. The
1019 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1020 documentation lists the restrictions that apply to patterns when partial
1021 matching is used.
1022 <pre>
1024 </pre>
1025 Return a copy of the options with which the pattern was compiled. The fourth
1026 argument should point to an <b>unsigned long int</b> variable. These option bits
1027 are those specified in the call to <b>pcre_compile()</b>, modified by any
1028 top-level option settings at the start of the pattern itself. In other words,
1029 they are the options that will be in force when matching starts. For example,
1030 if the pattern /(?im)abc(?-i)d/ is compiled with the PCRE_EXTENDED option, the
1032 </P>
1033 <P>
1034 A pattern is automatically anchored by PCRE if all of its top-level
1035 alternatives begin with one of the following:
1036 <pre>
1037 ^ unless PCRE_MULTILINE is set
1038 \A always
1039 \G always
1040 .* if PCRE_DOTALL is set and there are no back references to the subpattern in which .* appears
1041 </pre>
1042 For such patterns, the PCRE_ANCHORED bit is set in the options returned by
1043 <b>pcre_fullinfo()</b>.
1044 <pre>
1046 </pre>
1047 Return the size of the compiled pattern, that is, the value that was passed as
1048 the argument to <b>pcre_malloc()</b> when PCRE was getting memory in which to
1049 place the compiled data. The fourth argument should point to a <b>size_t</b>
1050 variable.
1051 <pre>
1053 </pre>
1054 Return the size of the data block pointed to by the <i>study_data</i> field in
1055 a <b>pcre_extra</b> block. That is, it is the value that was passed to
1056 <b>pcre_malloc()</b> when PCRE was getting memory into which to place the data
1057 created by <b>pcre_study()</b>. The fourth argument should point to a
1058 <b>size_t</b> variable.
1059 </P>
1060 <br><a name="SEC12" href="#TOC1">OBSOLETE INFO FUNCTION</a><br>
1061 <P>
1062 <b>int pcre_info(const pcre *<i>code</i>, int *<i>optptr</i>, int</b>
1063 <b>*<i>firstcharptr</i>);</b>
1064 </P>
1065 <P>
1066 The <b>pcre_info()</b> function is now obsolete because its interface is too
1067 restrictive to return all the available data about a compiled pattern. New
1068 programs should use <b>pcre_fullinfo()</b> instead. The yield of
1069 <b>pcre_info()</b> is the number of capturing subpatterns, or one of the
1070 following negative numbers:
1071 <pre>
1072 PCRE_ERROR_NULL the argument <i>code</i> was NULL
1073 PCRE_ERROR_BADMAGIC the "magic number" was not found
1074 </pre>
1075 If the <i>optptr</i> argument is not NULL, a copy of the options with which the
1076 pattern was compiled is placed in the integer it points to (see
1077 PCRE_INFO_OPTIONS above).
1078 </P>
1079 <P>
1080 If the pattern is not anchored and the <i>firstcharptr</i> argument is not NULL,
1081 it is used to pass back information about the first character of any matched
1082 string (see PCRE_INFO_FIRSTBYTE above).
1083 </P>
1084 <br><a name="SEC13" href="#TOC1">REFERENCE COUNTS</a><br>
1085 <P>
1086 <b>int pcre_refcount(pcre *<i>code</i>, int <i>adjust</i>);</b>
1087 </P>
1088 <P>
1089 The <b>pcre_refcount()</b> function is used to maintain a reference count in the
1090 data block that contains a compiled pattern. It is provided for the benefit of
1091 applications that operate in an object-oriented manner, where different parts
1092 of the application may be using the same compiled pattern, but you want to free
1093 the block when they are all done.
1094 </P>
1095 <P>
1096 When a pattern is compiled, the reference count field is initialized to zero.
1097 It is changed only by calling this function, whose action is to add the
1098 <i>adjust</i> value (which may be positive or negative) to it. The yield of the
1099 function is the new value. However, the value of the count is constrained to
1100 lie between 0 and 65535, inclusive. If the new value is outside these limits,
1101 it is forced to the appropriate limit value.
1102 </P>
1103 <P>
1104 Except when it is zero, the reference count is not correctly preserved if a
1105 pattern is compiled on one host and then transferred to a host whose byte-order
1106 is different. (This seems a highly unlikely scenario.)
1107 </P>
1108 <br><a name="SEC14" href="#TOC1">MATCHING A PATTERN: THE TRADITIONAL FUNCTION</a><br>
1109 <P>
1110 <b>int pcre_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
1111 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
1112 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>);</b>
1113 </P>
1114 <P>
1115 The function <b>pcre_exec()</b> is called to match a subject string against a
1116 compiled pattern, which is passed in the <i>code</i> argument. If the
1117 pattern has been studied, the result of the study should be passed in the
1118 <i>extra</i> argument. This function is the main matching facility of the
1119 library, and it operates in a Perl-like manner. For specialist use there is
1120 also an alternative matching function, which is described
1121 <a href="#dfamatch">below</a>
1122 in the section about the <b>pcre_dfa_exec()</b> function.
1123 </P>
1124 <P>
1125 In most applications, the pattern will have been compiled (and optionally
1126 studied) in the same process that calls <b>pcre_exec()</b>. However, it is
1127 possible to save compiled patterns and study data, and then use them later
1128 in different processes, possibly even on different hosts. For a discussion
1129 about this, see the
1130 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
1131 documentation.
1132 </P>
1133 <P>
1134 Here is an example of a simple call to <b>pcre_exec()</b>:
1135 <pre>
1136 int rc;
1137 int ovector[30];
1138 rc = pcre_exec(
1139 re, /* result of pcre_compile() */
1140 NULL, /* we didn't study the pattern */
1141 "some string", /* the subject string */
1142 11, /* the length of the subject string */
1143 0, /* start at offset 0 in the subject */
1144 0, /* default options */
1145 ovector, /* vector of integers for substring information */
1146 30); /* number of elements (NOT size in bytes) */
1147 <a name="extradata"></a></PRE>
1148 </P>
1149 <br><b>
1150 Extra data for <b>pcre_exec()</b>
1151 </b><br>
1152 <P>
1153 If the <i>extra</i> argument is not NULL, it must point to a <b>pcre_extra</b>
1154 data block. The <b>pcre_study()</b> function returns such a block (when it
1155 doesn't return NULL), but you can also create one for yourself, and pass
1156 additional information in it. The <b>pcre_extra</b> block contains the following
1157 fields (not necessarily in this order):
1158 <pre>
1159 unsigned long int <i>flags</i>;
1160 void *<i>study_data</i>;
1161 unsigned long int <i>match_limit</i>;
1162 unsigned long int <i>match_limit_recursion</i>;
1163 void *<i>callout_data</i>;
1164 const unsigned char *<i>tables</i>;
1165 </pre>
1166 The <i>flags</i> field is a bitmap that specifies which of the other fields
1167 are set. The flag bits are:
1168 <pre>
1174 </pre>
1175 Other flag bits should be set to zero. The <i>study_data</i> field is set in the
1176 <b>pcre_extra</b> block that is returned by <b>pcre_study()</b>, together with
1177 the appropriate flag bit. You should not set this yourself, but you may add to
1178 the block by setting the other fields and their corresponding flag bits.
1179 </P>
1180 <P>
1181 The <i>match_limit</i> field provides a means of preventing PCRE from using up a
1182 vast amount of resources when running patterns that are not going to match,
1183 but which have a very large number of possibilities in their search trees. The
1184 classic example is the use of nested unlimited repeats.
1185 </P>
1186 <P>
1187 Internally, PCRE uses a function called <b>match()</b> which it calls repeatedly
1188 (sometimes recursively). The limit set by <i>match_limit</i> is imposed on the
1189 number of times this function is called during a match, which has the effect of
1190 limiting the amount of backtracking that can take place. For patterns that are
1191 not anchored, the count restarts from zero for each position in the subject
1192 string.
1193 </P>
1194 <P>
1195 The default value for the limit can be set when PCRE is built; the default
1196 default is 10 million, which handles all but the most extreme cases. You can
1197 override the default by suppling <b>pcre_exec()</b> with a <b>pcre_extra</b>
1198 block in which <i>match_limit</i> is set, and PCRE_EXTRA_MATCH_LIMIT is set in
1199 the <i>flags</i> field. If the limit is exceeded, <b>pcre_exec()</b> returns
1201 </P>
1202 <P>
1203 The <i>match_limit_recursion</i> field is similar to <i>match_limit</i>, but
1204 instead of limiting the total number of times that <b>match()</b> is called, it
1205 limits the depth of recursion. The recursion depth is a smaller number than the
1206 total number of calls, because not all calls to <b>match()</b> are recursive.
1207 This limit is of use only if it is set smaller than <i>match_limit</i>.
1208 </P>
1209 <P>
1210 Limiting the recursion depth limits the amount of stack that can be used, or,
1211 when PCRE has been compiled to use memory on the heap instead of the stack, the
1212 amount of heap memory that can be used.
1213 </P>
1214 <P>
1215 The default value for <i>match_limit_recursion</i> can be set when PCRE is
1216 built; the default default is the same value as the default for
1217 <i>match_limit</i>. You can override the default by suppling <b>pcre_exec()</b>
1218 with a <b>pcre_extra</b> block in which <i>match_limit_recursion</i> is set, and
1219 PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the <i>flags</i> field. If the limit
1220 is exceeded, <b>pcre_exec()</b> returns PCRE_ERROR_RECURSIONLIMIT.
1221 </P>
1222 <P>
1223 The <i>pcre_callout</i> field is used in conjunction with the "callout" feature,
1224 which is described in the
1225 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1226 documentation.
1227 </P>
1228 <P>
1229 The <i>tables</i> field is used to pass a character tables pointer to
1230 <b>pcre_exec()</b>; this overrides the value that is stored with the compiled
1231 pattern. A non-NULL value is stored with the compiled pattern only if custom
1232 tables were supplied to <b>pcre_compile()</b> via its <i>tableptr</i> argument.
1233 If NULL is passed to <b>pcre_exec()</b> using this mechanism, it forces PCRE's
1234 internal tables to be used. This facility is helpful when re-using patterns
1235 that have been saved after compiling with an external set of tables, because
1236 the external tables might be at a different address when <b>pcre_exec()</b> is
1237 called. See the
1238 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
1239 documentation for a discussion of saving compiled patterns for later use.
1240 <a name="execoptions"></a></P>
1241 <br><b>
1242 Option bits for <b>pcre_exec()</b>
1243 </b><br>
1244 <P>
1245 The unused bits of the <i>options</i> argument for <b>pcre_exec()</b> must be
1246 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_<i>xxx</i>,
1249 <pre>
1251 </pre>
1252 The PCRE_ANCHORED option limits <b>pcre_exec()</b> to matching at the first
1253 matching position. If a pattern was compiled with PCRE_ANCHORED, or turned out
1254 to be anchored by virtue of its contents, it cannot be made unachored at
1255 matching time.
1256 <pre>
1259 </pre>
1260 These options (which are mutually exclusive) control what the \R escape
1261 sequence matches. The choice is either to match only CR, LF, or CRLF, or to
1262 match any Unicode newline sequence. These options override the choice that was
1263 made or defaulted when the pattern was compiled.
1264 <pre>
1270 </pre>
1271 These options override the newline definition that was chosen or defaulted when
1272 the pattern was compiled. For details, see the description of
1273 <b>pcre_compile()</b> above. During matching, the newline choice affects the
1274 behaviour of the dot, circumflex, and dollar metacharacters. It may also alter
1275 the way the match position is advanced after a match failure for an unanchored
1276 pattern.
1277 </P>
1278 <P>
1280 match attempt for an unanchored pattern fails when the current position is at a
1281 CRLF sequence, and the pattern contains no explicit matches for CR or LF
1282 characters, the match position is advanced by two characters instead of one, in
1283 other words, to after the CRLF.
1284 </P>
1285 <P>
1286 The above rule is a compromise that makes the most common cases work as
1287 expected. For example, if the pattern is .+A (and the PCRE_DOTALL option is not
1288 set), it does not match the string "\r\nA" because, after failing at the
1289 start, it skips both the CR and the LF before retrying. However, the pattern
1290 [\r\n]A does match that string, because it contains an explicit CR or LF
1291 reference, and so advances only by one character after the first failure.
1292 </P>
1293 <P>
1294 An explicit match for CR of LF is either a literal appearance of one of those
1295 characters, or one of the \r or \n escape sequences. Implicit matches such as
1296 [^X] do not count, nor does \s (which includes CR and LF in the characters
1297 that it matches).
1298 </P>
1299 <P>
1300 Notwithstanding the above, anomalous effects may still occur when CRLF is a
1301 valid newline sequence and explicit \r or \n escapes appear in the pattern.
1302 <pre>
1304 </pre>
1305 This option specifies that first character of the subject string is not the
1306 beginning of a line, so the circumflex metacharacter should not match before
1307 it. Setting this without PCRE_MULTILINE (at compile time) causes circumflex
1308 never to match. This option affects only the behaviour of the circumflex
1309 metacharacter. It does not affect \A.
1310 <pre>
1312 </pre>
1313 This option specifies that the end of the subject string is not the end of a
1314 line, so the dollar metacharacter should not match it nor (except in multiline
1315 mode) a newline immediately before it. Setting this without PCRE_MULTILINE (at
1316 compile time) causes dollar never to match. This option affects only the
1317 behaviour of the dollar metacharacter. It does not affect \Z or \z.
1318 <pre>
1320 </pre>
1321 An empty string is not considered to be a valid match if this option is set. If
1322 there are alternatives in the pattern, they are tried. If all the alternatives
1323 match the empty string, the entire match fails. For example, if the pattern
1324 <pre>
1325 a?b?
1326 </pre>
1327 is applied to a string not beginning with "a" or "b", it matches the empty
1328 string at the start of the subject. With PCRE_NOTEMPTY set, this match is not
1329 valid, so PCRE searches further into the string for occurrences of "a" or "b".
1330 </P>
1331 <P>
1332 Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a special case
1333 of a pattern match of the empty string within its <b>split()</b> function, and
1334 when using the /g modifier. It is possible to emulate Perl's behaviour after
1335 matching a null string by first trying the match again at the same offset with
1336 PCRE_NOTEMPTY and PCRE_ANCHORED, and then if that fails by advancing the
1337 starting offset (see below) and trying an ordinary match again. There is some
1338 code that demonstrates how to do this in the <i>pcredemo.c</i> sample program.
1339 <pre>
1341 </pre>
1342 There are a number of optimizations that <b>pcre_exec()</b> uses at the start of
1343 a match, in order to speed up the process. For example, if it is known that a
1344 match must start with a specific character, it searches the subject for that
1345 character, and fails immediately if it cannot find it, without actually running
1346 the main matching function. When callouts are in use, these optimizations can
1347 cause them to be skipped. This option disables the "start-up" optimizations,
1348 causing performance to suffer, but ensuring that the callouts do occur.
1349 <pre>
1351 </pre>
1352 When PCRE_UTF8 is set at compile time, the validity of the subject as a UTF-8
1353 string is automatically checked when <b>pcre_exec()</b> is subsequently called.
1354 The value of <i>startoffset</i> is also checked to ensure that it points to the
1355 start of a UTF-8 character. There is a discussion about the validity of UTF-8
1356 strings in the
1357 <a href="pcre.html#utf8strings">section on UTF-8 support</a>
1358 in the main
1359 <a href="pcre.html"><b>pcre</b></a>
1360 page. If an invalid UTF-8 sequence of bytes is found, <b>pcre_exec()</b> returns
1361 the error PCRE_ERROR_BADUTF8. If <i>startoffset</i> contains an invalid value,
1362 PCRE_ERROR_BADUTF8_OFFSET is returned.
1363 </P>
1364 <P>
1365 If you already know that your subject is valid, and you want to skip these
1366 checks for performance reasons, you can set the PCRE_NO_UTF8_CHECK option when
1367 calling <b>pcre_exec()</b>. You might want to do this for the second and
1368 subsequent calls to <b>pcre_exec()</b> if you are making repeated calls to find
1369 all the matches in a single subject string. However, you should be sure that
1370 the value of <i>startoffset</i> points to the start of a UTF-8 character. When
1371 PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid UTF-8 string as a
1372 subject, or a value of <i>startoffset</i> that does not point to the start of a
1373 UTF-8 character, is undefined. Your program may crash.
1374 <pre>
1376 </pre>
1377 This option turns on the partial matching feature. If the subject string fails
1378 to match the pattern, but at some point during the matching process the end of
1379 the subject was reached (that is, the subject partially matches the pattern and
1380 the failure to match occurred only because there were not enough subject
1381 characters), <b>pcre_exec()</b> returns PCRE_ERROR_PARTIAL instead of
1382 PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is used, there are restrictions on what
1383 may appear in the pattern. These are discussed in the
1384 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1385 documentation.
1386 </P>
1387 <br><b>
1388 The string to be matched by <b>pcre_exec()</b>
1389 </b><br>
1390 <P>
1391 The subject string is passed to <b>pcre_exec()</b> as a pointer in
1392 <i>subject</i>, a length (in bytes) in <i>length</i>, and a starting byte offset
1393 in <i>startoffset</i>. In UTF-8 mode, the byte offset must point to the start of
1394 a UTF-8 character. Unlike the pattern string, the subject may contain binary
1395 zero bytes. When the starting offset is zero, the search for a match starts at
1396 the beginning of the subject, and this is by far the most common case.
1397 </P>
1398 <P>
1399 A non-zero starting offset is useful when searching for another match in the
1400 same subject by calling <b>pcre_exec()</b> again after a previous success.
1401 Setting <i>startoffset</i> differs from just passing over a shortened string and
1402 setting PCRE_NOTBOL in the case of a pattern that begins with any kind of
1403 lookbehind. For example, consider the pattern
1404 <pre>
1405 \Biss\B
1406 </pre>
1407 which finds occurrences of "iss" in the middle of words. (\B matches only if
1408 the current position in the subject is not a word boundary.) When applied to
1409 the string "Mississipi" the first call to <b>pcre_exec()</b> finds the first
1410 occurrence. If <b>pcre_exec()</b> is called again with just the remainder of the
1411 subject, namely "issipi", it does not match, because \B is always false at the
1412 start of the subject, which is deemed to be a word boundary. However, if
1413 <b>pcre_exec()</b> is passed the entire string again, but with <i>startoffset</i>
1414 set to 4, it finds the second occurrence of "iss" because it is able to look
1415 behind the starting point to discover that it is preceded by a letter.
1416 </P>
1417 <P>
1418 If a non-zero starting offset is passed when the pattern is anchored, one
1419 attempt to match at the given offset is made. This can only succeed if the
1420 pattern does not require the match to be at the start of the subject.
1421 </P>
1422 <br><b>
1423 How <b>pcre_exec()</b> returns captured substrings
1424 </b><br>
1425 <P>
1426 In general, a pattern matches a certain portion of the subject, and in
1427 addition, further substrings from the subject may be picked out by parts of the
1428 pattern. Following the usage in Jeffrey Friedl's book, this is called
1429 "capturing" in what follows, and the phrase "capturing subpattern" is used for
1430 a fragment of a pattern that picks out a substring. PCRE supports several other
1431 kinds of parenthesized subpattern that do not cause substrings to be captured.
1432 </P>
1433 <P>
1434 Captured substrings are returned to the caller via a vector of integers whose
1435 address is passed in <i>ovector</i>. The number of elements in the vector is
1436 passed in <i>ovecsize</i>, which must be a non-negative number. <b>Note</b>: this
1437 argument is NOT the size of <i>ovector</i> in bytes.
1438 </P>
1439 <P>
1440 The first two-thirds of the vector is used to pass back captured substrings,
1441 each substring using a pair of integers. The remaining third of the vector is
1442 used as workspace by <b>pcre_exec()</b> while matching capturing subpatterns,
1443 and is not available for passing back information. The number passed in
1444 <i>ovecsize</i> should always be a multiple of three. If it is not, it is
1445 rounded down.
1446 </P>
1447 <P>
1448 When a match is successful, information about captured substrings is returned
1449 in pairs of integers, starting at the beginning of <i>ovector</i>, and
1450 continuing up to two-thirds of its length at the most. The first element of
1451 each pair is set to the byte offset of the first character in a substring, and
1452 the second is set to the byte offset of the first character after the end of a
1453 substring. <b>Note</b>: these values are always byte offsets, even in UTF-8
1454 mode. They are not character counts.
1455 </P>
1456 <P>
1457 The first pair of integers, <i>ovector[0]</i> and <i>ovector[1]</i>, identify the
1458 portion of the subject string matched by the entire pattern. The next pair is
1459 used for the first capturing subpattern, and so on. The value returned by
1460 <b>pcre_exec()</b> is one more than the highest numbered pair that has been set.
1461 For example, if two substrings have been captured, the returned value is 3. If
1462 there are no capturing subpatterns, the return value from a successful match is
1463 1, indicating that just the first pair of offsets has been set.
1464 </P>
1465 <P>
1466 If a capturing subpattern is matched repeatedly, it is the last portion of the
1467 string that it matched that is returned.
1468 </P>
1469 <P>
1470 If the vector is too small to hold all the captured substring offsets, it is
1471 used as far as possible (up to two-thirds of its length), and the function
1472 returns a value of zero. If the substring offsets are not of interest,
1473 <b>pcre_exec()</b> may be called with <i>ovector</i> passed as NULL and
1474 <i>ovecsize</i> as zero. However, if the pattern contains back references and
1475 the <i>ovector</i> is not big enough to remember the related substrings, PCRE
1476 has to get additional memory for use during matching. Thus it is usually
1477 advisable to supply an <i>ovector</i>.
1478 </P>
1479 <P>
1480 The <b>pcre_info()</b> function can be used to find out how many capturing
1481 subpatterns there are in a compiled pattern. The smallest size for
1482 <i>ovector</i> that will allow for <i>n</i> captured substrings, in addition to
1483 the offsets of the substring matched by the whole pattern, is (<i>n</i>+1)*3.
1484 </P>
1485 <P>
1486 It is possible for capturing subpattern number <i>n+1</i> to match some part of
1487 the subject when subpattern <i>n</i> has not been used at all. For example, if
1488 the string "abc" is matched against the pattern (a|(z))(bc) the return from the
1489 function is 4, and subpatterns 1 and 3 are matched, but 2 is not. When this
1490 happens, both values in the offset pairs corresponding to unused subpatterns
1491 are set to -1.
1492 </P>
1493 <P>
1494 Offset values that correspond to unused subpatterns at the end of the
1495 expression are also set to -1. For example, if the string "abc" is matched
1496 against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not matched. The
1497 return from the function is 2, because the highest used capturing subpattern
1498 number is 1. However, you can refer to the offsets for the second and third
1499 capturing subpatterns if you wish (assuming the vector is large enough, of
1500 course).
1501 </P>
1502 <P>
1503 Some convenience functions are provided for extracting the captured substrings
1504 as separate strings. These are described below.
1505 <a name="errorlist"></a></P>
1506 <br><b>
1507 Error return values from <b>pcre_exec()</b>
1508 </b><br>
1509 <P>
1510 If <b>pcre_exec()</b> fails, it returns a negative number. The following are
1511 defined in the header file:
1512 <pre>
1514 </pre>
1515 The subject string did not match the pattern.
1516 <pre>
1518 </pre>
1519 Either <i>code</i> or <i>subject</i> was passed as NULL, or <i>ovector</i> was
1520 NULL and <i>ovecsize</i> was not zero.
1521 <pre>
1523 </pre>
1524 An unrecognized bit was set in the <i>options</i> argument.
1525 <pre>
1527 </pre>
1528 PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch
1529 the case when it is passed a junk pointer and to detect when a pattern that was
1530 compiled in an environment of one endianness is run in an environment with the
1531 other endianness. This is the error that PCRE gives when the magic number is
1532 not present.
1533 <pre>
1535 </pre>
1536 While running the pattern match, an unknown item was encountered in the
1537 compiled pattern. This error could be caused by a bug in PCRE or by overwriting
1538 of the compiled pattern.
1539 <pre>
1541 </pre>
1542 If a pattern contains back references, but the <i>ovector</i> that is passed to
1543 <b>pcre_exec()</b> is not big enough to remember the referenced substrings, PCRE
1544 gets a block of memory at the start of matching to use for this purpose. If the
1545 call via <b>pcre_malloc()</b> fails, this error is given. The memory is
1546 automatically freed at the end of matching.
1547 <pre>
1549 </pre>
1550 This error is used by the <b>pcre_copy_substring()</b>,
1551 <b>pcre_get_substring()</b>, and <b>pcre_get_substring_list()</b> functions (see
1552 below). It is never returned by <b>pcre_exec()</b>.
1553 <pre>
1555 </pre>
1556 The backtracking limit, as specified by the <i>match_limit</i> field in a
1557 <b>pcre_extra</b> structure (or defaulted) was reached. See the description
1558 above.
1559 <pre>
1561 </pre>
1562 This error is never generated by <b>pcre_exec()</b> itself. It is provided for
1563 use by callout functions that want to yield a distinctive error code. See the
1564 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1565 documentation for details.
1566 <pre>
1568 </pre>
1569 A string that contains an invalid UTF-8 byte sequence was passed as a subject.
1570 <pre>
1572 </pre>
1573 The UTF-8 byte sequence that was passed as a subject was valid, but the value
1574 of <i>startoffset</i> did not point to the beginning of a UTF-8 character.
1575 <pre>
1577 </pre>
1578 The subject string did not match, but it did match partially. See the
1579 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1580 documentation for details of partial matching.
1581 <pre>
1583 </pre>
1584 The PCRE_PARTIAL option was used with a compiled pattern containing items that
1585 are not supported for partial matching. See the
1586 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1587 documentation for details of partial matching.
1588 <pre>
1590 </pre>
1591 An unexpected internal error has occurred. This error could be caused by a bug
1592 in PCRE or by overwriting of the compiled pattern.
1593 <pre>
1595 </pre>
1596 This error is given if the value of the <i>ovecsize</i> argument is negative.
1597 <pre>
1599 </pre>
1600 The internal recursion limit, as specified by the <i>match_limit_recursion</i>
1601 field in a <b>pcre_extra</b> structure (or defaulted) was reached. See the
1602 description above.
1603 <pre>
1605 </pre>
1606 An invalid combination of PCRE_NEWLINE_<i>xxx</i> options was given.
1607 </P>
1608 <P>
1609 Error numbers -16 to -20 and -22 are not used by <b>pcre_exec()</b>.
1610 </P>
1611 <br><a name="SEC15" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NUMBER</a><br>
1612 <P>
1613 <b>int pcre_copy_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1614 <b>int <i>stringcount</i>, int <i>stringnumber</i>, char *<i>buffer</i>,</b>
1615 <b>int <i>buffersize</i>);</b>
1616 </P>
1617 <P>
1618 <b>int pcre_get_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1619 <b>int <i>stringcount</i>, int <i>stringnumber</i>,</b>
1620 <b>const char **<i>stringptr</i>);</b>
1621 </P>
1622 <P>
1623 <b>int pcre_get_substring_list(const char *<i>subject</i>,</b>
1624 <b>int *<i>ovector</i>, int <i>stringcount</i>, const char ***<i>listptr</i>);</b>
1625 </P>
1626 <P>
1627 Captured substrings can be accessed directly by using the offsets returned by
1628 <b>pcre_exec()</b> in <i>ovector</i>. For convenience, the functions
1629 <b>pcre_copy_substring()</b>, <b>pcre_get_substring()</b>, and
1630 <b>pcre_get_substring_list()</b> are provided for extracting captured substrings
1631 as new, separate, zero-terminated strings. These functions identify substrings
1632 by number. The next section describes functions for extracting named
1633 substrings.
1634 </P>
1635 <P>
1636 A substring that contains a binary zero is correctly extracted and has a
1637 further zero added on the end, but the result is not, of course, a C string.
1638 However, you can process such a string by referring to the length that is
1639 returned by <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>.
1640 Unfortunately, the interface to <b>pcre_get_substring_list()</b> is not adequate
1641 for handling strings containing binary zeros, because the end of the final
1642 string is not independently indicated.
1643 </P>
1644 <P>
1645 The first three arguments are the same for all three of these functions:
1646 <i>subject</i> is the subject string that has just been successfully matched,
1647 <i>ovector</i> is a pointer to the vector of integer offsets that was passed to
1648 <b>pcre_exec()</b>, and <i>stringcount</i> is the number of substrings that were
1649 captured by the match, including the substring that matched the entire regular
1650 expression. This is the value returned by <b>pcre_exec()</b> if it is greater
1651 than zero. If <b>pcre_exec()</b> returned zero, indicating that it ran out of
1652 space in <i>ovector</i>, the value passed as <i>stringcount</i> should be the
1653 number of elements in the vector divided by three.
1654 </P>
1655 <P>
1656 The functions <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>
1657 extract a single substring, whose number is given as <i>stringnumber</i>. A
1658 value of zero extracts the substring that matched the entire pattern, whereas
1659 higher values extract the captured substrings. For <b>pcre_copy_substring()</b>,
1660 the string is placed in <i>buffer</i>, whose length is given by
1661 <i>buffersize</i>, while for <b>pcre_get_substring()</b> a new block of memory is
1662 obtained via <b>pcre_malloc</b>, and its address is returned via
1663 <i>stringptr</i>. The yield of the function is the length of the string, not
1664 including the terminating zero, or one of these error codes:
1665 <pre>
1667 </pre>
1668 The buffer was too small for <b>pcre_copy_substring()</b>, or the attempt to get
1669 memory failed for <b>pcre_get_substring()</b>.
1670 <pre>
1672 </pre>
1673 There is no substring whose number is <i>stringnumber</i>.
1674 </P>
1675 <P>
1676 The <b>pcre_get_substring_list()</b> function extracts all available substrings
1677 and builds a list of pointers to them. All this is done in a single block of
1678 memory that is obtained via <b>pcre_malloc</b>. The address of the memory block
1679 is returned via <i>listptr</i>, which is also the start of the list of string
1680 pointers. The end of the list is marked by a NULL pointer. The yield of the
1681 function is zero if all went well, or the error code
1682 <pre>
1684 </pre>
1685 if the attempt to get the memory block failed.
1686 </P>
1687 <P>
1688 When any of these functions encounter a substring that is unset, which can
1689 happen when capturing subpattern number <i>n+1</i> matches some part of the
1690 subject, but subpattern <i>n</i> has not been used at all, they return an empty
1691 string. This can be distinguished from a genuine zero-length substring by
1692 inspecting the appropriate offset in <i>ovector</i>, which is negative for unset
1693 substrings.
1694 </P>
1695 <P>
1696 The two convenience functions <b>pcre_free_substring()</b> and
1697 <b>pcre_free_substring_list()</b> can be used to free the memory returned by
1698 a previous call of <b>pcre_get_substring()</b> or
1699 <b>pcre_get_substring_list()</b>, respectively. They do nothing more than call
1700 the function pointed to by <b>pcre_free</b>, which of course could be called
1701 directly from a C program. However, PCRE is used in some situations where it is
1702 linked via a special interface to another programming language that cannot use
1703 <b>pcre_free</b> directly; it is for these cases that the functions are
1704 provided.
1705 </P>
1706 <br><a name="SEC16" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NAME</a><br>
1707 <P>
1708 <b>int pcre_get_stringnumber(const pcre *<i>code</i>,</b>
1709 <b>const char *<i>name</i>);</b>
1710 </P>
1711 <P>
1712 <b>int pcre_copy_named_substring(const pcre *<i>code</i>,</b>
1713 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
1714 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
1715 <b>char *<i>buffer</i>, int <i>buffersize</i>);</b>
1716 </P>
1717 <P>
1718 <b>int pcre_get_named_substring(const pcre *<i>code</i>,</b>
1719 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
1720 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
1721 <b>const char **<i>stringptr</i>);</b>
1722 </P>
1723 <P>
1724 To extract a substring by name, you first have to find associated number.
1725 For example, for this pattern
1726 <pre>
1727 (a+)b(?&#60;xxx&#62;\d+)...
1728 </pre>
1729 the number of the subpattern called "xxx" is 2. If the name is known to be
1730 unique (PCRE_DUPNAMES was not set), you can find the number from the name by
1731 calling <b>pcre_get_stringnumber()</b>. The first argument is the compiled
1732 pattern, and the second is the name. The yield of the function is the
1733 subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no subpattern of
1734 that name.
1735 </P>
1736 <P>
1737 Given the number, you can extract the substring directly, or use one of the
1738 functions described in the previous section. For convenience, there are also
1739 two functions that do the whole job.
1740 </P>
1741 <P>
1742 Most of the arguments of <b>pcre_copy_named_substring()</b> and
1743 <b>pcre_get_named_substring()</b> are the same as those for the similarly named
1744 functions that extract by number. As these are described in the previous
1745 section, they are not re-described here. There are just two differences:
1746 </P>
1747 <P>
1748 First, instead of a substring number, a substring name is given. Second, there
1749 is an extra argument, given at the start, which is a pointer to the compiled
1750 pattern. This is needed in order to gain access to the name-to-number
1751 translation table.
1752 </P>
1753 <P>
1754 These functions call <b>pcre_get_stringnumber()</b>, and if it succeeds, they
1755 then call <b>pcre_copy_substring()</b> or <b>pcre_get_substring()</b>, as
1756 appropriate. <b>NOTE:</b> If PCRE_DUPNAMES is set and there are duplicate names,
1757 the behaviour may not be what you want (see the next section).
1758 </P>
1759 <P>
1760 <b>Warning:</b> If the pattern uses the "(?|" feature to set up multiple
1761 subpatterns with the same number, you cannot use names to distinguish them,
1762 because names are not included in the compiled code. The matching process uses
1763 only numbers.
1764 </P>
1765 <br><a name="SEC17" href="#TOC1">DUPLICATE SUBPATTERN NAMES</a><br>
1766 <P>
1767 <b>int pcre_get_stringtable_entries(const pcre *<i>code</i>,</b>
1768 <b>const char *<i>name</i>, char **<i>first</i>, char **<i>last</i>);</b>
1769 </P>
1770 <P>
1771 When a pattern is compiled with the PCRE_DUPNAMES option, names for subpatterns
1772 are not required to be unique. Normally, patterns with duplicate names are such
1773 that in any one match, only one of the named subpatterns participates. An
1774 example is shown in the
1775 <a href="pcrepattern.html"><b>pcrepattern</b></a>
1776 documentation.
1777 </P>
1778 <P>
1779 When duplicates are present, <b>pcre_copy_named_substring()</b> and
1780 <b>pcre_get_named_substring()</b> return the first substring corresponding to
1781 the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING (-7) is
1782 returned; no data is returned. The <b>pcre_get_stringnumber()</b> function
1783 returns one of the numbers that are associated with the name, but it is not
1784 defined which it is.
1785 </P>
1786 <P>
1787 If you want to get full details of all captured substrings for a given name,
1788 you must use the <b>pcre_get_stringtable_entries()</b> function. The first
1789 argument is the compiled pattern, and the second is the name. The third and
1790 fourth are pointers to variables which are updated by the function. After it
1791 has run, they point to the first and last entries in the name-to-number table
1792 for the given name. The function itself returns the length of each entry, or
1793 PCRE_ERROR_NOSUBSTRING (-7) if there are none. The format of the table is
1794 described above in the section entitled <i>Information about a pattern</i>.
1795 Given all the relevant entries for the name, you can extract each of their
1796 numbers, and hence the captured data, if any.
1797 </P>
1798 <br><a name="SEC18" href="#TOC1">FINDING ALL POSSIBLE MATCHES</a><br>
1799 <P>
1800 The traditional matching function uses a similar algorithm to Perl, which stops
1801 when it finds the first match, starting at a given point in the subject. If you
1802 want to find all possible matches, or the longest possible match, consider
1803 using the alternative matching function (see below) instead. If you cannot use
1804 the alternative function, but still need to find all possible matches, you
1805 can kludge it up by making use of the callout facility, which is described in
1806 the
1807 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1808 documentation.
1809 </P>
1810 <P>
1811 What you have to do is to insert a callout right at the end of the pattern.
1812 When your callout function is called, extract and save the current matched
1813 substring. Then return 1, which forces <b>pcre_exec()</b> to backtrack and try
1814 other alternatives. Ultimately, when it runs out of matches, <b>pcre_exec()</b>
1815 will yield PCRE_ERROR_NOMATCH.
1816 <a name="dfamatch"></a></P>
1817 <br><a name="SEC19" href="#TOC1">MATCHING A PATTERN: THE ALTERNATIVE FUNCTION</a><br>
1818 <P>
1819 <b>int pcre_dfa_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
1820 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
1821 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>,</b>
1822 <b>int *<i>workspace</i>, int <i>wscount</i>);</b>
1823 </P>
1824 <P>
1825 The function <b>pcre_dfa_exec()</b> is called to match a subject string against
1826 a compiled pattern, using a matching algorithm that scans the subject string
1827 just once, and does not backtrack. This has different characteristics to the
1828 normal algorithm, and is not compatible with Perl. Some of the features of PCRE
1829 patterns are not supported. Nevertheless, there are times when this kind of
1830 matching can be useful. For a discussion of the two matching algorithms, see
1831 the
1832 <a href="pcrematching.html"><b>pcrematching</b></a>
1833 documentation.
1834 </P>
1835 <P>
1836 The arguments for the <b>pcre_dfa_exec()</b> function are the same as for
1837 <b>pcre_exec()</b>, plus two extras. The <i>ovector</i> argument is used in a
1838 different way, and this is described below. The other common arguments are used
1839 in the same way as for <b>pcre_exec()</b>, so their description is not repeated
1840 here.
1841 </P>
1842 <P>
1843 The two additional arguments provide workspace for the function. The workspace
1844 vector should contain at least 20 elements. It is used for keeping track of
1845 multiple paths through the pattern tree. More workspace will be needed for
1846 patterns and subjects where there are a lot of potential matches.
1847 </P>
1848 <P>
1849 Here is an example of a simple call to <b>pcre_dfa_exec()</b>:
1850 <pre>
1851 int rc;
1852 int ovector[10];
1853 int wspace[20];
1854 rc = pcre_dfa_exec(
1855 re, /* result of pcre_compile() */
1856 NULL, /* we didn't study the pattern */
1857 "some string", /* the subject string */
1858 11, /* the length of the subject string */
1859 0, /* start at offset 0 in the subject */
1860 0, /* default options */
1861 ovector, /* vector of integers for substring information */
1862 10, /* number of elements (NOT size in bytes) */
1863 wspace, /* working space vector */
1864 20); /* number of elements (NOT size in bytes) */
1865 </PRE>
1866 </P>
1867 <br><b>
1868 Option bits for <b>pcre_dfa_exec()</b>
1869 </b><br>
1870 <P>
1871 The unused bits of the <i>options</i> argument for <b>pcre_dfa_exec()</b> must be
1872 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_<i>xxx</i>,
1874 PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last three of these are
1875 the same as for <b>pcre_exec()</b>, so their description is not repeated here.
1876 <pre>
1878 </pre>
1879 This has the same general effect as it does for <b>pcre_exec()</b>, but the
1880 details are slightly different. When PCRE_PARTIAL is set for
1881 <b>pcre_dfa_exec()</b>, the return code PCRE_ERROR_NOMATCH is converted into
1882 PCRE_ERROR_PARTIAL if the end of the subject is reached, there have been no
1883 complete matches, but there is still at least one matching possibility. The
1884 portion of the string that provided the partial match is set as the first
1885 matching string.
1886 <pre>
1888 </pre>
1889 Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to stop as
1890 soon as it has found one match. Because of the way the alternative algorithm
1891 works, this is necessarily the shortest possible match at the first possible
1892 matching point in the subject string.
1893 <pre>
1895 </pre>
1896 When <b>pcre_dfa_exec()</b> is called with the PCRE_PARTIAL option, and returns
1897 a partial match, it is possible to call it again, with additional subject
1898 characters, and have it continue with the same match. The PCRE_DFA_RESTART
1899 option requests this action; when it is set, the <i>workspace</i> and
1900 <i>wscount</i> options must reference the same vector as before because data
1901 about the match so far is left in them after a partial match. There is more
1902 discussion of this facility in the
1903 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1904 documentation.
1905 </P>
1906 <br><b>
1907 Successful returns from <b>pcre_dfa_exec()</b>
1908 </b><br>
1909 <P>
1910 When <b>pcre_dfa_exec()</b> succeeds, it may have matched more than one
1911 substring in the subject. Note, however, that all the matches from one run of
1912 the function start at the same point in the subject. The shorter matches are
1913 all initial substrings of the longer matches. For example, if the pattern
1914 <pre>
1915 &#60;.*&#62;
1916 </pre>
1917 is matched against the string
1918 <pre>
1919 This is &#60;something&#62; &#60;something else&#62; &#60;something further&#62; no more
1920 </pre>
1921 the three matched strings are
1922 <pre>
1923 &#60;something&#62;
1924 &#60;something&#62; &#60;something else&#62;
1925 &#60;something&#62; &#60;something else&#62; &#60;something further&#62;
1926 </pre>
1927 On success, the yield of the function is a number greater than zero, which is
1928 the number of matched substrings. The substrings themselves are returned in
1929 <i>ovector</i>. Each string uses two elements; the first is the offset to the
1930 start, and the second is the offset to the end. In fact, all the strings have
1931 the same start offset. (Space could have been saved by giving this only once,
1932 but it was decided to retain some compatibility with the way <b>pcre_exec()</b>
1933 returns data, even though the meaning of the strings is different.)
1934 </P>
1935 <P>
1936 The strings are returned in reverse order of length; that is, the longest
1937 matching string is given first. If there were too many matches to fit into
1938 <i>ovector</i>, the yield of the function is zero, and the vector is filled with
1939 the longest matches.
1940 </P>
1941 <br><b>
1942 Error returns from <b>pcre_dfa_exec()</b>
1943 </b><br>
1944 <P>
1945 The <b>pcre_dfa_exec()</b> function returns a negative number when it fails.
1946 Many of the errors are the same as for <b>pcre_exec()</b>, and these are
1947 described
1948 <a href="#errorlist">above.</a>
1949 There are in addition the following errors that are specific to
1950 <b>pcre_dfa_exec()</b>:
1951 <pre>
1953 </pre>
1954 This return is given if <b>pcre_dfa_exec()</b> encounters an item in the pattern
1955 that it does not support, for instance, the use of \C or a back reference.
1956 <pre>
1958 </pre>
1959 This return is given if <b>pcre_dfa_exec()</b> encounters a condition item that
1960 uses a back reference for the condition, or a test for recursion in a specific
1961 group. These are not supported.
1962 <pre>
1964 </pre>
1965 This return is given if <b>pcre_dfa_exec()</b> is called with an <i>extra</i>
1966 block that contains a setting of the <i>match_limit</i> field. This is not
1967 supported (it is meaningless).
1968 <pre>
1970 </pre>
1971 This return is given if <b>pcre_dfa_exec()</b> runs out of space in the
1972 <i>workspace</i> vector.
1973 <pre>
1975 </pre>
1976 When a recursive subpattern is processed, the matching function calls itself
1977 recursively, using private vectors for <i>ovector</i> and <i>workspace</i>. This
1978 error is given if the output vector is not large enough. This should be
1979 extremely rare, as a vector of size 1000 is used.
1980 </P>
1981 <br><a name="SEC20" href="#TOC1">SEE ALSO</a><br>
1982 <P>
1983 <b>pcrebuild</b>(3), <b>pcrecallout</b>(3), <b>pcrecpp(3)</b>(3),
1984 <b>pcrematching</b>(3), <b>pcrepartial</b>(3), <b>pcreposix</b>(3),
1985 <b>pcreprecompile</b>(3), <b>pcresample</b>(3), <b>pcrestack</b>(3).
1986 </P>
1987 <br><a name="SEC21" href="#TOC1">AUTHOR</a><br>
1988 <P>
1989 Philip Hazel
1990 <br>
1991 University Computing Service
1992 <br>
1993 Cambridge CB2 3QH, England.
1994 <br>
1995 </P>
1996 <br><a name="SEC22" href="#TOC1">REVISION</a><br>
1997 <P>
1998 Last updated: 17 March 2009
1999 <br>
2000 Copyright &copy; 1997-2009 University of Cambridge.
2001 <br>
2002 <p>
2003 Return to the <a href="index.html">PCRE index page</a>.
2004 </p>


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