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


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