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1 <html>
2 <head>
3 <title>pcreapi specification</title>
4 </head>
5 <body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
6 <h1>pcreapi man page</h1>
7 <p>
8 Return to the <a href="index.html">PCRE index page</a>.
9 </p>
10 <p>
11 This page is part of the PCRE HTML documentation. It was generated automatically
12 from the original man page. If there is any nonsense in it, please consult the
13 man page, in case the conversion went wrong.
14 <br>
15 <ul>
16 <li><a name="TOC1" href="#SEC1">PCRE NATIVE API</a>
17 <li><a name="TOC2" href="#SEC2">PCRE API OVERVIEW</a>
18 <li><a name="TOC3" href="#SEC3">NEWLINES</a>
19 <li><a name="TOC4" href="#SEC4">MULTITHREADING</a>
20 <li><a name="TOC5" href="#SEC5">SAVING PRECOMPILED PATTERNS FOR LATER USE</a>
21 <li><a name="TOC6" href="#SEC6">CHECKING BUILD-TIME OPTIONS</a>
22 <li><a name="TOC7" href="#SEC7">COMPILING A PATTERN</a>
23 <li><a name="TOC8" href="#SEC8">COMPILATION ERROR CODES</a>
24 <li><a name="TOC9" href="#SEC9">STUDYING A PATTERN</a>
25 <li><a name="TOC10" href="#SEC10">LOCALE SUPPORT</a>
26 <li><a name="TOC11" href="#SEC11">INFORMATION ABOUT A PATTERN</a>
27 <li><a name="TOC12" href="#SEC12">OBSOLETE INFO FUNCTION</a>
28 <li><a name="TOC13" href="#SEC13">REFERENCE COUNTS</a>
29 <li><a name="TOC14" href="#SEC14">MATCHING A PATTERN: THE TRADITIONAL FUNCTION</a>
30 <li><a name="TOC15" href="#SEC15">EXTRACTING CAPTURED SUBSTRINGS BY NUMBER</a>
31 <li><a name="TOC16" href="#SEC16">EXTRACTING CAPTURED SUBSTRINGS BY NAME</a>
32 <li><a name="TOC17" href="#SEC17">DUPLICATE SUBPATTERN NAMES</a>
33 <li><a name="TOC18" href="#SEC18">FINDING ALL POSSIBLE MATCHES</a>
34 <li><a name="TOC19" href="#SEC19">MATCHING A PATTERN: THE ALTERNATIVE FUNCTION</a>
35 <li><a name="TOC20" href="#SEC20">SEE ALSO</a>
36 <li><a name="TOC21" href="#SEC21">AUTHOR</a>
37 <li><a name="TOC22" href="#SEC22">REVISION</a>
38 </ul>
39 <br><a name="SEC1" href="#TOC1">PCRE NATIVE API</a><br>
40 <P>
41 <b>#include &#60;pcre.h&#62;</b>
42 </P>
43 <P>
44 <b>pcre *pcre_compile(const char *<i>pattern</i>, int <i>options</i>,</b>
45 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
46 <b>const unsigned char *<i>tableptr</i>);</b>
47 </P>
48 <P>
49 <b>pcre *pcre_compile2(const char *<i>pattern</i>, int <i>options</i>,</b>
50 <b>int *<i>errorcodeptr</i>,</b>
51 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
52 <b>const unsigned char *<i>tableptr</i>);</b>
53 </P>
54 <P>
55 <b>pcre_extra *pcre_study(const pcre *<i>code</i>, int <i>options</i>,</b>
56 <b>const char **<i>errptr</i>);</b>
57 </P>
58 <P>
59 <b>int pcre_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
60 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
61 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>);</b>
62 </P>
63 <P>
64 <b>int pcre_dfa_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
65 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
66 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>,</b>
67 <b>int *<i>workspace</i>, int <i>wscount</i>);</b>
68 </P>
69 <P>
70 <b>int pcre_copy_named_substring(const pcre *<i>code</i>,</b>
71 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
72 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
73 <b>char *<i>buffer</i>, int <i>buffersize</i>);</b>
74 </P>
75 <P>
76 <b>int pcre_copy_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
77 <b>int <i>stringcount</i>, int <i>stringnumber</i>, char *<i>buffer</i>,</b>
78 <b>int <i>buffersize</i>);</b>
79 </P>
80 <P>
81 <b>int pcre_get_named_substring(const pcre *<i>code</i>,</b>
82 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
83 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
84 <b>const char **<i>stringptr</i>);</b>
85 </P>
86 <P>
87 <b>int pcre_get_stringnumber(const pcre *<i>code</i>,</b>
88 <b>const char *<i>name</i>);</b>
89 </P>
90 <P>
91 <b>int pcre_get_stringtable_entries(const pcre *<i>code</i>,</b>
92 <b>const char *<i>name</i>, char **<i>first</i>, char **<i>last</i>);</b>
93 </P>
94 <P>
95 <b>int pcre_get_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
96 <b>int <i>stringcount</i>, int <i>stringnumber</i>,</b>
97 <b>const char **<i>stringptr</i>);</b>
98 </P>
99 <P>
100 <b>int pcre_get_substring_list(const char *<i>subject</i>,</b>
101 <b>int *<i>ovector</i>, int <i>stringcount</i>, const char ***<i>listptr</i>);</b>
102 </P>
103 <P>
104 <b>void pcre_free_substring(const char *<i>stringptr</i>);</b>
105 </P>
106 <P>
107 <b>void pcre_free_substring_list(const char **<i>stringptr</i>);</b>
108 </P>
109 <P>
110 <b>const unsigned char *pcre_maketables(void);</b>
111 </P>
112 <P>
113 <b>int pcre_fullinfo(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
114 <b>int <i>what</i>, void *<i>where</i>);</b>
115 </P>
116 <P>
117 <b>int pcre_info(const pcre *<i>code</i>, int *<i>optptr</i>, int</b>
118 <b>*<i>firstcharptr</i>);</b>
119 </P>
120 <P>
121 <b>int pcre_refcount(pcre *<i>code</i>, int <i>adjust</i>);</b>
122 </P>
123 <P>
124 <b>int pcre_config(int <i>what</i>, void *<i>where</i>);</b>
125 </P>
126 <P>
127 <b>char *pcre_version(void);</b>
128 </P>
129 <P>
130 <b>void *(*pcre_malloc)(size_t);</b>
131 </P>
132 <P>
133 <b>void (*pcre_free)(void *);</b>
134 </P>
135 <P>
136 <b>void *(*pcre_stack_malloc)(size_t);</b>
137 </P>
138 <P>
139 <b>void (*pcre_stack_free)(void *);</b>
140 </P>
141 <P>
142 <b>int (*pcre_callout)(pcre_callout_block *);</b>
143 </P>
144 <br><a name="SEC2" href="#TOC1">PCRE API OVERVIEW</a><br>
145 <P>
146 PCRE has its own native API, which is described in this document. There are
147 also some wrapper functions that correspond to the POSIX regular expression
148 API. These are described in the
149 <a href="pcreposix.html"><b>pcreposix</b></a>
150 documentation. Both of these APIs define a set of C function calls. A C++
151 wrapper is distributed with PCRE. It is documented in the
152 <a href="pcrecpp.html"><b>pcrecpp</b></a>
153 page.
154 </P>
155 <P>
156 The native API C function prototypes are defined in the header file
157 <b>pcre.h</b>, and on Unix systems the library itself is called <b>libpcre</b>.
158 It can normally be accessed by adding <b>-lpcre</b> to the command for linking
159 an application that uses PCRE. The header file defines the macros PCRE_MAJOR
160 and PCRE_MINOR to contain the major and minor release numbers for the library.
161 Applications can use these to include support for different releases of PCRE.
162 </P>
163 <P>
164 The functions <b>pcre_compile()</b>, <b>pcre_compile2()</b>, <b>pcre_study()</b>,
165 and <b>pcre_exec()</b> are used for compiling and matching regular expressions
166 in a Perl-compatible manner. A sample program that demonstrates the simplest
167 way of using them is provided in the file called <i>pcredemo.c</i> in the source
168 distribution. The
169 <a href="pcresample.html"><b>pcresample</b></a>
170 documentation describes how to run it.
171 </P>
172 <P>
173 A second matching function, <b>pcre_dfa_exec()</b>, which is not
174 Perl-compatible, is also provided. This uses a different algorithm for the
175 matching. The alternative algorithm finds all possible matches (at a given
176 point in the subject), and scans the subject just once. However, this algorithm
177 does not return captured substrings. A description of the two matching
178 algorithms and their advantages and disadvantages is given in the
179 <a href="pcrematching.html"><b>pcrematching</b></a>
180 documentation.
181 </P>
182 <P>
183 In addition to the main compiling and matching functions, there are convenience
184 functions for extracting captured substrings from a subject string that is
185 matched by <b>pcre_exec()</b>. They are:
186 <pre>
187 <b>pcre_copy_substring()</b>
188 <b>pcre_copy_named_substring()</b>
189 <b>pcre_get_substring()</b>
190 <b>pcre_get_named_substring()</b>
191 <b>pcre_get_substring_list()</b>
192 <b>pcre_get_stringnumber()</b>
193 <b>pcre_get_stringtable_entries()</b>
194 </pre>
195 <b>pcre_free_substring()</b> and <b>pcre_free_substring_list()</b> are also
196 provided, to free the memory used for extracted strings.
197 </P>
198 <P>
199 The function <b>pcre_maketables()</b> is used to build a set of character tables
200 in the current locale for passing to <b>pcre_compile()</b>, <b>pcre_exec()</b>,
201 or <b>pcre_dfa_exec()</b>. This is an optional facility that is provided for
202 specialist use. Most commonly, no special tables are passed, in which case
203 internal tables that are generated when PCRE is built are used.
204 </P>
205 <P>
206 The function <b>pcre_fullinfo()</b> is used to find out information about a
207 compiled pattern; <b>pcre_info()</b> is an obsolete version that returns only
208 some of the available information, but is retained for backwards compatibility.
209 The function <b>pcre_version()</b> returns a pointer to a string containing the
210 version of PCRE and its date of release.
211 </P>
212 <P>
213 The function <b>pcre_refcount()</b> maintains a reference count in a data block
214 containing a compiled pattern. This is provided for the benefit of
215 object-oriented applications.
216 </P>
217 <P>
218 The global variables <b>pcre_malloc</b> and <b>pcre_free</b> initially contain
219 the entry points of the standard <b>malloc()</b> and <b>free()</b> functions,
220 respectively. PCRE calls the memory management functions via these variables,
221 so a calling program can replace them if it wishes to intercept the calls. This
222 should be done before calling any PCRE functions.
223 </P>
224 <P>
225 The global variables <b>pcre_stack_malloc</b> and <b>pcre_stack_free</b> are also
226 indirections to memory management functions. These special functions are used
227 only when PCRE is compiled to use the heap for remembering data, instead of
228 recursive function calls, when running the <b>pcre_exec()</b> function. See the
229 <a href="pcrebuild.html"><b>pcrebuild</b></a>
230 documentation for details of how to do this. It is a non-standard way of
231 building PCRE, for use in environments that have limited stacks. Because of the
232 greater use of memory management, it runs more slowly. Separate functions are
233 provided so that special-purpose external code can be used for this case. When
234 used, these functions are always called in a stack-like manner (last obtained,
235 first freed), and always for memory blocks of the same size. There is a
236 discussion about PCRE's stack usage in the
237 <a href="pcrestack.html"><b>pcrestack</b></a>
238 documentation.
239 </P>
240 <P>
241 The global variable <b>pcre_callout</b> initially contains NULL. It can be set
242 by the caller to a "callout" function, which PCRE will then call at specified
243 points during a matching operation. Details are given in the
244 <a href="pcrecallout.html"><b>pcrecallout</b></a>
245 documentation.
246 </P>
247 <br><a name="SEC3" href="#TOC1">NEWLINES</a><br>
248 <P>
249 PCRE supports five different conventions for indicating line breaks in
250 strings: a single CR (carriage return) character, a single LF (linefeed)
251 character, the two-character sequence CRLF, any of the three preceding, or any
252 Unicode newline sequence. The Unicode newline sequences are the three just
253 mentioned, plus the single characters VT (vertical tab, U+000B), FF (formfeed,
254 U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS
255 (paragraph separator, U+2029).
256 </P>
257 <P>
258 Each of the first three conventions is used by at least one operating system as
259 its standard newline sequence. When PCRE is built, a default can be specified.
260 The default default is LF, which is the Unix standard. When PCRE is run, the
261 default can be overridden, either when a pattern is compiled, or when it is
262 matched.
263 </P>
264 <P>
265 In the PCRE documentation the word "newline" is used to mean "the character or
266 pair of characters that indicate a line break". The choice of newline
267 convention affects the handling of the dot, circumflex, and dollar
268 metacharacters, the handling of #-comments in /x mode, and, when CRLF is a
269 recognized line ending sequence, the match position advancement for a
270 non-anchored pattern. The choice of newline convention does not affect the
271 interpretation of the \n or \r escape sequences.
272 </P>
273 <br><a name="SEC4" href="#TOC1">MULTITHREADING</a><br>
274 <P>
275 The PCRE functions can be used in multi-threading applications, with the
276 proviso that the memory management functions pointed to by <b>pcre_malloc</b>,
277 <b>pcre_free</b>, <b>pcre_stack_malloc</b>, and <b>pcre_stack_free</b>, and the
278 callout function pointed to by <b>pcre_callout</b>, are shared by all threads.
279 </P>
280 <P>
281 The compiled form of a regular expression is not altered during matching, so
282 the same compiled pattern can safely be used by several threads at once.
283 </P>
284 <br><a name="SEC5" href="#TOC1">SAVING PRECOMPILED PATTERNS FOR LATER USE</a><br>
285 <P>
286 The compiled form of a regular expression can be saved and re-used at a later
287 time, possibly by a different program, and even on a host other than the one on
288 which it was compiled. Details are given in the
289 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
290 documentation.
291 </P>
292 <br><a name="SEC6" href="#TOC1">CHECKING BUILD-TIME OPTIONS</a><br>
293 <P>
294 <b>int pcre_config(int <i>what</i>, void *<i>where</i>);</b>
295 </P>
296 <P>
297 The function <b>pcre_config()</b> makes it possible for a PCRE client to
298 discover which optional features have been compiled into the PCRE library. The
299 <a href="pcrebuild.html"><b>pcrebuild</b></a>
300 documentation has more details about these optional features.
301 </P>
302 <P>
303 The first argument for <b>pcre_config()</b> is an integer, specifying which
304 information is required; the second argument is a pointer to a variable into
305 which the information is placed. The following information is available:
306 <pre>
307 PCRE_CONFIG_UTF8
308 </pre>
309 The output is an integer that is set to one if UTF-8 support is available;
310 otherwise it is set to zero.
311 <pre>
312 PCRE_CONFIG_UNICODE_PROPERTIES
313 </pre>
314 The output is an integer that is set to one if support for Unicode character
315 properties is available; otherwise it is set to zero.
316 <pre>
317 PCRE_CONFIG_NEWLINE
318 </pre>
319 The output is an integer whose value specifies the default character sequence
320 that is recognized as meaning "newline". The four values that are supported
321 are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF, and -1 for ANY. The
322 default should normally be the standard sequence for your operating system.
323 <pre>
324 PCRE_CONFIG_LINK_SIZE
325 </pre>
326 The output is an integer that contains the number of bytes used for internal
327 linkage in compiled regular expressions. The value is 2, 3, or 4. Larger values
328 allow larger regular expressions to be compiled, at the expense of slower
329 matching. The default value of 2 is sufficient for all but the most massive
330 patterns, since it allows the compiled pattern to be up to 64K in size.
331 <pre>
332 PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
333 </pre>
334 The output is an integer that contains the threshold above which the POSIX
335 interface uses <b>malloc()</b> for output vectors. Further details are given in
336 the
337 <a href="pcreposix.html"><b>pcreposix</b></a>
338 documentation.
339 <pre>
340 PCRE_CONFIG_MATCH_LIMIT
341 </pre>
342 The output is an integer that gives the default limit for the number of
343 internal matching function calls in a <b>pcre_exec()</b> execution. Further
344 details are given with <b>pcre_exec()</b> below.
345 <pre>
346 PCRE_CONFIG_MATCH_LIMIT_RECURSION
347 </pre>
348 The output is an integer that gives the default limit for the depth of
349 recursion when calling the internal matching function in a <b>pcre_exec()</b>
350 execution. Further details are given with <b>pcre_exec()</b> below.
351 <pre>
352 PCRE_CONFIG_STACKRECURSE
353 </pre>
354 The output is an integer that is set to one if internal recursion when running
355 <b>pcre_exec()</b> is implemented by recursive function calls that use the stack
356 to remember their state. This is the usual way that PCRE is compiled. The
357 output is zero if PCRE was compiled to use blocks of data on the heap instead
358 of recursive function calls. In this case, <b>pcre_stack_malloc</b> and
359 <b>pcre_stack_free</b> are called to manage memory blocks on the heap, thus
360 avoiding the use of the stack.
361 </P>
362 <br><a name="SEC7" href="#TOC1">COMPILING A PATTERN</a><br>
363 <P>
364 <b>pcre *pcre_compile(const char *<i>pattern</i>, int <i>options</i>,</b>
365 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
366 <b>const unsigned char *<i>tableptr</i>);</b>
367 <b>pcre *pcre_compile2(const char *<i>pattern</i>, int <i>options</i>,</b>
368 <b>int *<i>errorcodeptr</i>,</b>
369 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
370 <b>const unsigned char *<i>tableptr</i>);</b>
371 </P>
372 <P>
373 Either of the functions <b>pcre_compile()</b> or <b>pcre_compile2()</b> can be
374 called to compile a pattern into an internal form. The only difference between
375 the two interfaces is that <b>pcre_compile2()</b> has an additional argument,
376 <i>errorcodeptr</i>, via which a numerical error code can be returned.
377 </P>
378 <P>
379 The pattern is a C string terminated by a binary zero, and is passed in the
380 <i>pattern</i> argument. A pointer to a single block of memory that is obtained
381 via <b>pcre_malloc</b> is returned. This contains the compiled code and related
382 data. The <b>pcre</b> type is defined for the returned block; this is a typedef
383 for a structure whose contents are not externally defined. It is up to the
384 caller to free the memory (via <b>pcre_free</b>) when it is no longer required.
385 </P>
386 <P>
387 Although the compiled code of a PCRE regex is relocatable, that is, it does not
388 depend on memory location, the complete <b>pcre</b> data block is not
389 fully relocatable, because it may contain a copy of the <i>tableptr</i>
390 argument, which is an address (see below).
391 </P>
392 <P>
393 The <i>options</i> argument contains various bit settings that affect the
394 compilation. It should be zero if no options are required. The available
395 options are described below. Some of them, in particular, those that are
396 compatible with Perl, can also be set and unset from within the pattern (see
397 the detailed description in the
398 <a href="pcrepattern.html"><b>pcrepattern</b></a>
399 documentation). For these options, the contents of the <i>options</i> argument
400 specifies their initial settings at the start of compilation and execution. The
401 PCRE_ANCHORED and PCRE_NEWLINE_<i>xxx</i> options can be set at the time of
402 matching as well as at compile time.
403 </P>
404 <P>
405 If <i>errptr</i> is NULL, <b>pcre_compile()</b> returns NULL immediately.
406 Otherwise, if compilation of a pattern fails, <b>pcre_compile()</b> returns
407 NULL, and sets the variable pointed to by <i>errptr</i> to point to a textual
408 error message. This is a static string that is part of the library. You must
409 not try to free it. The offset from the start of the pattern to the character
410 where the error was discovered is placed in the variable pointed to by
411 <i>erroffset</i>, which must not be NULL. If it is, an immediate error is given.
412 </P>
413 <P>
414 If <b>pcre_compile2()</b> is used instead of <b>pcre_compile()</b>, and the
415 <i>errorcodeptr</i> argument is not NULL, a non-zero error code number is
416 returned via this argument in the event of an error. This is in addition to the
417 textual error message. Error codes and messages are listed below.
418 </P>
419 <P>
420 If the final argument, <i>tableptr</i>, is NULL, PCRE uses a default set of
421 character tables that are built when PCRE is compiled, using the default C
422 locale. Otherwise, <i>tableptr</i> must be an address that is the result of a
423 call to <b>pcre_maketables()</b>. This value is stored with the compiled
424 pattern, and used again by <b>pcre_exec()</b>, unless another table pointer is
425 passed to it. For more discussion, see the section on locale support below.
426 </P>
427 <P>
428 This code fragment shows a typical straightforward call to <b>pcre_compile()</b>:
429 <pre>
430 pcre *re;
431 const char *error;
432 int erroffset;
433 re = pcre_compile(
434 "^A.*Z", /* the pattern */
435 0, /* default options */
436 &error, /* for error message */
437 &erroffset, /* for error offset */
438 NULL); /* use default character tables */
439 </pre>
440 The following names for option bits are defined in the <b>pcre.h</b> header
441 file:
442 <pre>
443 PCRE_ANCHORED
444 </pre>
445 If this bit is set, the pattern is forced to be "anchored", that is, it is
446 constrained to match only at the first matching point in the string that is
447 being searched (the "subject string"). This effect can also be achieved by
448 appropriate constructs in the pattern itself, which is the only way to do it in
449 Perl.
450 <pre>
451 PCRE_AUTO_CALLOUT
452 </pre>
453 If this bit is set, <b>pcre_compile()</b> automatically inserts callout items,
454 all with number 255, before each pattern item. For discussion of the callout
455 facility, see the
456 <a href="pcrecallout.html"><b>pcrecallout</b></a>
457 documentation.
458 <pre>
459 PCRE_CASELESS
460 </pre>
461 If this bit is set, letters in the pattern match both upper and lower case
462 letters. It is equivalent to Perl's /i option, and it can be changed within a
463 pattern by a (?i) option setting. In UTF-8 mode, PCRE always understands the
464 concept of case for characters whose values are less than 128, so caseless
465 matching is always possible. For characters with higher values, the concept of
466 case is supported if PCRE is compiled with Unicode property support, but not
467 otherwise. If you want to use caseless matching for characters 128 and above,
468 you must ensure that PCRE is compiled with Unicode property support as well as
469 with UTF-8 support.
470 <pre>
471 PCRE_DOLLAR_ENDONLY
472 </pre>
473 If this bit is set, a dollar metacharacter in the pattern matches only at the
474 end of the subject string. Without this option, a dollar also matches
475 immediately before a newline at the end of the string (but not before any other
476 newlines). The PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is set.
477 There is no equivalent to this option in Perl, and no way to set it within a
478 pattern.
479 <pre>
480 PCRE_DOTALL
481 </pre>
482 If this bit is set, a dot metacharater in the pattern matches all characters,
483 including those that indicate newline. Without it, a dot does not match when
484 the current position is at a newline. This option is equivalent to Perl's /s
485 option, and it can be changed within a pattern by a (?s) option setting. A
486 negative class such as [^a] always matches newline characters, independent of
487 the setting of this option.
488 <pre>
489 PCRE_DUPNAMES
490 </pre>
491 If this bit is set, names used to identify capturing subpatterns need not be
492 unique. This can be helpful for certain types of pattern when it is known that
493 only one instance of the named subpattern can ever be matched. There are more
494 details of named subpatterns below; see also the
495 <a href="pcrepattern.html"><b>pcrepattern</b></a>
496 documentation.
497 <pre>
498 PCRE_EXTENDED
499 </pre>
500 If this bit is set, whitespace data characters in the pattern are totally
501 ignored except when escaped or inside a character class. Whitespace does not
502 include the VT character (code 11). In addition, characters between an
503 unescaped # outside a character class and the next newline, inclusive, are also
504 ignored. This is equivalent to Perl's /x option, and it can be changed within a
505 pattern by a (?x) option setting.
506 </P>
507 <P>
508 This option makes it possible to include comments inside complicated patterns.
509 Note, however, that this applies only to data characters. Whitespace characters
510 may never appear within special character sequences in a pattern, for example
511 within the sequence (?( which introduces a conditional subpattern.
512 <pre>
513 PCRE_EXTRA
514 </pre>
515 This option was invented in order to turn on additional functionality of PCRE
516 that is incompatible with Perl, but it is currently of very little use. When
517 set, any backslash in a pattern that is followed by a letter that has no
518 special meaning causes an error, thus reserving these combinations for future
519 expansion. By default, as in Perl, a backslash followed by a letter with no
520 special meaning is treated as a literal. (Perl can, however, be persuaded to
521 give a warning for this.) There are at present no other features controlled by
522 this option. It can also be set by a (?X) option setting within a pattern.
523 <pre>
524 PCRE_FIRSTLINE
525 </pre>
526 If this option is set, an unanchored pattern is required to match before or at
527 the first newline in the subject string, though the matched text may continue
528 over the newline.
529 <pre>
530 PCRE_MULTILINE
531 </pre>
532 By default, PCRE treats the subject string as consisting of a single line of
533 characters (even if it actually contains newlines). The "start of line"
534 metacharacter (^) matches only at the start of the string, while the "end of
535 line" metacharacter ($) matches only at the end of the string, or before a
536 terminating newline (unless PCRE_DOLLAR_ENDONLY is set). This is the same as
537 Perl.
538 </P>
539 <P>
540 When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs
541 match immediately following or immediately before internal newlines in the
542 subject string, respectively, as well as at the very start and end. This is
543 equivalent to Perl's /m option, and it can be changed within a pattern by a
544 (?m) option setting. If there are no newlines in a subject string, or no
545 occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no effect.
546 <pre>
547 PCRE_NEWLINE_CR
548 PCRE_NEWLINE_LF
549 PCRE_NEWLINE_CRLF
550 PCRE_NEWLINE_ANYCRLF
551 PCRE_NEWLINE_ANY
552 </pre>
553 These options override the default newline definition that was chosen when PCRE
554 was built. Setting the first or the second specifies that a newline is
555 indicated by a single character (CR or LF, respectively). Setting
556 PCRE_NEWLINE_CRLF specifies that a newline is indicated by the two-character
557 CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies that any of the three
558 preceding sequences should be recognized. Setting PCRE_NEWLINE_ANY specifies
559 that any Unicode newline sequence should be recognized. The Unicode newline
560 sequences are the three just mentioned, plus the single characters VT (vertical
561 tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS (line
562 separator, U+2028), and PS (paragraph separator, U+2029). The last two are
563 recognized only in UTF-8 mode.
564 </P>
565 <P>
566 The newline setting in the options word uses three bits that are treated
567 as a number, giving eight possibilities. Currently only six are used (default
568 plus the five values above). This means that if you set more than one newline
569 option, the combination may or may not be sensible. For example,
570 PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to PCRE_NEWLINE_CRLF, but
571 other combinations may yield unused numbers and cause an error.
572 </P>
573 <P>
574 The only time that a line break is specially recognized when compiling a
575 pattern is if PCRE_EXTENDED is set, and an unescaped # outside a character
576 class is encountered. This indicates a comment that lasts until after the next
577 line break sequence. In other circumstances, line break sequences are treated
578 as literal data, except that in PCRE_EXTENDED mode, both CR and LF are treated
579 as whitespace characters and are therefore ignored.
580 </P>
581 <P>
582 The newline option that is set at compile time becomes the default that is used
583 for <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b>, but it can be overridden.
584 <pre>
585 PCRE_NO_AUTO_CAPTURE
586 </pre>
587 If this option is set, it disables the use of numbered capturing parentheses in
588 the pattern. Any opening parenthesis that is not followed by ? behaves as if it
589 were followed by ?: but named parentheses can still be used for capturing (and
590 they acquire numbers in the usual way). There is no equivalent of this option
591 in Perl.
592 <pre>
593 PCRE_UNGREEDY
594 </pre>
595 This option inverts the "greediness" of the quantifiers so that they are not
596 greedy by default, but become greedy if followed by "?". It is not compatible
597 with Perl. It can also be set by a (?U) option setting within the pattern.
598 <pre>
599 PCRE_UTF8
600 </pre>
601 This option causes PCRE to regard both the pattern and the subject as strings
602 of UTF-8 characters instead of single-byte character strings. However, it is
603 available only when PCRE is built to include UTF-8 support. If not, the use
604 of this option provokes an error. Details of how this option changes the
605 behaviour of PCRE are given in the
606 <a href="pcre.html#utf8support">section on UTF-8 support</a>
607 in the main
608 <a href="pcre.html"><b>pcre</b></a>
609 page.
610 <pre>
611 PCRE_NO_UTF8_CHECK
612 </pre>
613 When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
614 automatically checked. If an invalid UTF-8 sequence of bytes is found,
615 <b>pcre_compile()</b> returns an error. If you already know that your pattern is
616 valid, and you want to skip this check for performance reasons, you can set the
617 PCRE_NO_UTF8_CHECK option. When it is set, the effect of passing an invalid
618 UTF-8 string as a pattern is undefined. It may cause your program to crash.
619 Note that this option can also be passed to <b>pcre_exec()</b> and
620 <b>pcre_dfa_exec()</b>, to suppress the UTF-8 validity checking of subject
621 strings.
622 </P>
623 <br><a name="SEC8" href="#TOC1">COMPILATION ERROR CODES</a><br>
624 <P>
625 The following table lists the error codes than may be returned by
626 <b>pcre_compile2()</b>, along with the error messages that may be returned by
627 both compiling functions. As PCRE has developed, some error codes have fallen
628 out of use. To avoid confusion, they have not been re-used.
629 <pre>
630 0 no error
631 1 \ at end of pattern
632 2 \c at end of pattern
633 3 unrecognized character follows \
634 4 numbers out of order in {} quantifier
635 5 number too big in {} quantifier
636 6 missing terminating ] for character class
637 7 invalid escape sequence in character class
638 8 range out of order in character class
639 9 nothing to repeat
640 10 [this code is not in use]
641 11 internal error: unexpected repeat
642 12 unrecognized character after (?
643 13 POSIX named classes are supported only within a class
644 14 missing )
645 15 reference to non-existent subpattern
646 16 erroffset passed as NULL
647 17 unknown option bit(s) set
648 18 missing ) after comment
649 19 [this code is not in use]
650 20 regular expression too large
651 21 failed to get memory
652 22 unmatched parentheses
653 23 internal error: code overflow
654 24 unrecognized character after (?&#60;
655 25 lookbehind assertion is not fixed length
656 26 malformed number or name after (?(
657 27 conditional group contains more than two branches
658 28 assertion expected after (?(
659 29 (?R or (?digits must be followed by )
660 30 unknown POSIX class name
661 31 POSIX collating elements are not supported
662 32 this version of PCRE is not compiled with PCRE_UTF8 support
663 33 [this code is not in use]
664 34 character value in \x{...} sequence is too large
665 35 invalid condition (?(0)
666 36 \C not allowed in lookbehind assertion
667 37 PCRE does not support \L, \l, \N, \U, or \u
668 38 number after (?C is &#62; 255
669 39 closing ) for (?C expected
670 40 recursive call could loop indefinitely
671 41 unrecognized character after (?P
672 42 syntax error in subpattern name (missing terminator)
673 43 two named subpatterns have the same name
674 44 invalid UTF-8 string
675 45 support for \P, \p, and \X has not been compiled
676 46 malformed \P or \p sequence
677 47 unknown property name after \P or \p
678 48 subpattern name is too long (maximum 32 characters)
679 49 too many named subpatterns (maximum 10,000)
680 50 repeated subpattern is too long
681 51 octal value is greater than \377 (not in UTF-8 mode)
682 52 internal error: overran compiling workspace
683 53 internal error: previously-checked referenced subpattern not found
684 54 DEFINE group contains more than one branch
685 55 repeating a DEFINE group is not allowed
686 56 inconsistent NEWLINE options"
687 </PRE>
688 </P>
689 <br><a name="SEC9" href="#TOC1">STUDYING A PATTERN</a><br>
690 <P>
691 <b>pcre_extra *pcre_study(const pcre *<i>code</i>, int <i>options</i></b>
692 <b>const char **<i>errptr</i>);</b>
693 </P>
694 <P>
695 If a compiled pattern is going to be used several times, it is worth spending
696 more time analyzing it in order to speed up the time taken for matching. The
697 function <b>pcre_study()</b> takes a pointer to a compiled pattern as its first
698 argument. If studying the pattern produces additional information that will
699 help speed up matching, <b>pcre_study()</b> returns a pointer to a
700 <b>pcre_extra</b> block, in which the <i>study_data</i> field points to the
701 results of the study.
702 </P>
703 <P>
704 The returned value from <b>pcre_study()</b> can be passed directly to
705 <b>pcre_exec()</b>. However, a <b>pcre_extra</b> block also contains other
706 fields that can be set by the caller before the block is passed; these are
707 described
708 <a href="#extradata">below</a>
709 in the section on matching a pattern.
710 </P>
711 <P>
712 If studying the pattern does not produce any additional information
713 <b>pcre_study()</b> returns NULL. In that circumstance, if the calling program
714 wants to pass any of the other fields to <b>pcre_exec()</b>, it must set up its
715 own <b>pcre_extra</b> block.
716 </P>
717 <P>
718 The second argument of <b>pcre_study()</b> contains option bits. At present, no
719 options are defined, and this argument should always be zero.
720 </P>
721 <P>
722 The third argument for <b>pcre_study()</b> is a pointer for an error message. If
723 studying succeeds (even if no data is returned), the variable it points to is
724 set to NULL. Otherwise it is set to point to a textual error message. This is a
725 static string that is part of the library. You must not try to free it. You
726 should test the error pointer for NULL after calling <b>pcre_study()</b>, to be
727 sure that it has run successfully.
728 </P>
729 <P>
730 This is a typical call to <b>pcre_study</b>():
731 <pre>
732 pcre_extra *pe;
733 pe = pcre_study(
734 re, /* result of pcre_compile() */
735 0, /* no options exist */
736 &error); /* set to NULL or points to a message */
737 </pre>
738 At present, studying a pattern is useful only for non-anchored patterns that do
739 not have a single fixed starting character. A bitmap of possible starting
740 bytes is created.
741 <a name="localesupport"></a></P>
742 <br><a name="SEC10" href="#TOC1">LOCALE SUPPORT</a><br>
743 <P>
744 PCRE handles caseless matching, and determines whether characters are letters,
745 digits, or whatever, by reference to a set of tables, indexed by character
746 value. When running in UTF-8 mode, this applies only to characters with codes
747 less than 128. Higher-valued codes never match escapes such as \w or \d, but
748 can be tested with \p if PCRE is built with Unicode character property
749 support. The use of locales with Unicode is discouraged. If you are handling
750 characters with codes greater than 128, you should either use UTF-8 and
751 Unicode, or use locales, but not try to mix the two.
752 </P>
753 <P>
754 PCRE contains an internal set of tables that are used when the final argument
755 of <b>pcre_compile()</b> is NULL. These are sufficient for many applications.
756 Normally, the internal tables recognize only ASCII characters. However, when
757 PCRE is built, it is possible to cause the internal tables to be rebuilt in the
758 default "C" locale of the local system, which may cause them to be different.
759 </P>
760 <P>
761 The internal tables can always be overridden by tables supplied by the
762 application that calls PCRE. These may be created in a different locale from
763 the default. As more and more applications change to using Unicode, the need
764 for this locale support is expected to die away.
765 </P>
766 <P>
767 External tables are built by calling the <b>pcre_maketables()</b> function,
768 which has no arguments, in the relevant locale. The result can then be passed
769 to <b>pcre_compile()</b> or <b>pcre_exec()</b> as often as necessary. For
770 example, to build and use tables that are appropriate for the French locale
771 (where accented characters with values greater than 128 are treated as letters),
772 the following code could be used:
773 <pre>
774 setlocale(LC_CTYPE, "fr_FR");
775 tables = pcre_maketables();
776 re = pcre_compile(..., tables);
777 </pre>
778 The locale name "fr_FR" is used on Linux and other Unix-like systems; if you
779 are using Windows, the name for the French locale is "french".
780 </P>
781 <P>
782 When <b>pcre_maketables()</b> runs, the tables are built in memory that is
783 obtained via <b>pcre_malloc</b>. It is the caller's responsibility to ensure
784 that the memory containing the tables remains available for as long as it is
785 needed.
786 </P>
787 <P>
788 The pointer that is passed to <b>pcre_compile()</b> is saved with the compiled
789 pattern, and the same tables are used via this pointer by <b>pcre_study()</b>
790 and normally also by <b>pcre_exec()</b>. Thus, by default, for any single
791 pattern, compilation, studying and matching all happen in the same locale, but
792 different patterns can be compiled in different locales.
793 </P>
794 <P>
795 It is possible to pass a table pointer or NULL (indicating the use of the
796 internal tables) to <b>pcre_exec()</b>. Although not intended for this purpose,
797 this facility could be used to match a pattern in a different locale from the
798 one in which it was compiled. Passing table pointers at run time is discussed
799 below in the section on matching a pattern.
800 </P>
801 <br><a name="SEC11" href="#TOC1">INFORMATION ABOUT A PATTERN</a><br>
802 <P>
803 <b>int pcre_fullinfo(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
804 <b>int <i>what</i>, void *<i>where</i>);</b>
805 </P>
806 <P>
807 The <b>pcre_fullinfo()</b> function returns information about a compiled
808 pattern. It replaces the obsolete <b>pcre_info()</b> function, which is
809 nevertheless retained for backwards compability (and is documented below).
810 </P>
811 <P>
812 The first argument for <b>pcre_fullinfo()</b> is a pointer to the compiled
813 pattern. The second argument is the result of <b>pcre_study()</b>, or NULL if
814 the pattern was not studied. The third argument specifies which piece of
815 information is required, and the fourth argument is a pointer to a variable
816 to receive the data. The yield of the function is zero for success, or one of
817 the following negative numbers:
818 <pre>
819 PCRE_ERROR_NULL the argument <i>code</i> was NULL
820 the argument <i>where</i> was NULL
821 PCRE_ERROR_BADMAGIC the "magic number" was not found
822 PCRE_ERROR_BADOPTION the value of <i>what</i> was invalid
823 </pre>
824 The "magic number" is placed at the start of each compiled pattern as an simple
825 check against passing an arbitrary memory pointer. Here is a typical call of
826 <b>pcre_fullinfo()</b>, to obtain the length of the compiled pattern:
827 <pre>
828 int rc;
829 size_t length;
830 rc = pcre_fullinfo(
831 re, /* result of pcre_compile() */
832 pe, /* result of pcre_study(), or NULL */
833 PCRE_INFO_SIZE, /* what is required */
834 &length); /* where to put the data */
835 </pre>
836 The possible values for the third argument are defined in <b>pcre.h</b>, and are
837 as follows:
838 <pre>
839 PCRE_INFO_BACKREFMAX
840 </pre>
841 Return the number of the highest back reference in the pattern. The fourth
842 argument should point to an <b>int</b> variable. Zero is returned if there are
843 no back references.
844 <pre>
845 PCRE_INFO_CAPTURECOUNT
846 </pre>
847 Return the number of capturing subpatterns in the pattern. The fourth argument
848 should point to an <b>int</b> variable.
849 <pre>
850 PCRE_INFO_DEFAULT_TABLES
851 </pre>
852 Return a pointer to the internal default character tables within PCRE. The
853 fourth argument should point to an <b>unsigned char *</b> variable. This
854 information call is provided for internal use by the <b>pcre_study()</b>
855 function. External callers can cause PCRE to use its internal tables by passing
856 a NULL table pointer.
857 <pre>
858 PCRE_INFO_FIRSTBYTE
859 </pre>
860 Return information about the first byte of any matched string, for a
861 non-anchored pattern. The fourth argument should point to an <b>int</b>
862 variable. (This option used to be called PCRE_INFO_FIRSTCHAR; the old name is
863 still recognized for backwards compatibility.)
864 </P>
865 <P>
866 If there is a fixed first byte, for example, from a pattern such as
867 (cat|cow|coyote), its value is returned. Otherwise, if either
868 <br>
869 <br>
870 (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
871 starts with "^", or
872 <br>
873 <br>
874 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
875 (if it were set, the pattern would be anchored),
876 <br>
877 <br>
878 -1 is returned, indicating that the pattern matches only at the start of a
879 subject string or after any newline within the string. Otherwise -2 is
880 returned. For anchored patterns, -2 is returned.
881 <pre>
882 PCRE_INFO_FIRSTTABLE
883 </pre>
884 If the pattern was studied, and this resulted in the construction of a 256-bit
885 table indicating a fixed set of bytes for the first byte in any matching
886 string, a pointer to the table is returned. Otherwise NULL is returned. The
887 fourth argument should point to an <b>unsigned char *</b> variable.
888 <pre>
889 PCRE_INFO_LASTLITERAL
890 </pre>
891 Return the value of the rightmost literal byte that must exist in any matched
892 string, other than at its start, if such a byte has been recorded. The fourth
893 argument should point to an <b>int</b> variable. If there is no such byte, -1 is
894 returned. For anchored patterns, a last literal byte is recorded only if it
895 follows something of variable length. For example, for the pattern
896 /^a\d+z\d+/ the returned value is "z", but for /^a\dz\d/ the returned value
897 is -1.
898 <pre>
899 PCRE_INFO_NAMECOUNT
900 PCRE_INFO_NAMEENTRYSIZE
901 PCRE_INFO_NAMETABLE
902 </pre>
903 PCRE supports the use of named as well as numbered capturing parentheses. The
904 names are just an additional way of identifying the parentheses, which still
905 acquire numbers. Several convenience functions such as
906 <b>pcre_get_named_substring()</b> are provided for extracting captured
907 substrings by name. It is also possible to extract the data directly, by first
908 converting the name to a number in order to access the correct pointers in the
909 output vector (described with <b>pcre_exec()</b> below). To do the conversion,
910 you need to use the name-to-number map, which is described by these three
911 values.
912 </P>
913 <P>
914 The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives
915 the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each
916 entry; both of these return an <b>int</b> value. The entry size depends on the
917 length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first
918 entry of the table (a pointer to <b>char</b>). The first two bytes of each entry
919 are the number of the capturing parenthesis, most significant byte first. The
920 rest of the entry is the corresponding name, zero terminated. The names are in
921 alphabetical order. When PCRE_DUPNAMES is set, duplicate names are in order of
922 their parentheses numbers. For example, consider the following pattern (assume
923 PCRE_EXTENDED is set, so white space - including newlines - is ignored):
924 <pre>
925 (?&#60;date&#62; (?&#60;year&#62;(\d\d)?\d\d) - (?&#60;month&#62;\d\d) - (?&#60;day&#62;\d\d) )
926 </pre>
927 There are four named subpatterns, so the table has four entries, and each entry
928 in the table is eight bytes long. The table is as follows, with non-printing
929 bytes shows in hexadecimal, and undefined bytes shown as ??:
930 <pre>
931 00 01 d a t e 00 ??
932 00 05 d a y 00 ?? ??
933 00 04 m o n t h 00
934 00 02 y e a r 00 ??
935 </pre>
936 When writing code to extract data from named subpatterns using the
937 name-to-number map, remember that the length of the entries is likely to be
938 different for each compiled pattern.
939 <pre>
940 PCRE_INFO_OPTIONS
941 </pre>
942 Return a copy of the options with which the pattern was compiled. The fourth
943 argument should point to an <b>unsigned long int</b> variable. These option bits
944 are those specified in the call to <b>pcre_compile()</b>, modified by any
945 top-level option settings within the pattern itself.
946 </P>
947 <P>
948 A pattern is automatically anchored by PCRE if all of its top-level
949 alternatives begin with one of the following:
950 <pre>
951 ^ unless PCRE_MULTILINE is set
952 \A always
953 \G always
954 .* if PCRE_DOTALL is set and there are no back references to the subpattern in which .* appears
955 </pre>
956 For such patterns, the PCRE_ANCHORED bit is set in the options returned by
957 <b>pcre_fullinfo()</b>.
958 <pre>
959 PCRE_INFO_SIZE
960 </pre>
961 Return the size of the compiled pattern, that is, the value that was passed as
962 the argument to <b>pcre_malloc()</b> when PCRE was getting memory in which to
963 place the compiled data. The fourth argument should point to a <b>size_t</b>
964 variable.
965 <pre>
966 PCRE_INFO_STUDYSIZE
967 </pre>
968 Return the size of the data block pointed to by the <i>study_data</i> field in
969 a <b>pcre_extra</b> block. That is, it is the value that was passed to
970 <b>pcre_malloc()</b> when PCRE was getting memory into which to place the data
971 created by <b>pcre_study()</b>. The fourth argument should point to a
972 <b>size_t</b> variable.
973 </P>
974 <br><a name="SEC12" href="#TOC1">OBSOLETE INFO FUNCTION</a><br>
975 <P>
976 <b>int pcre_info(const pcre *<i>code</i>, int *<i>optptr</i>, int</b>
977 <b>*<i>firstcharptr</i>);</b>
978 </P>
979 <P>
980 The <b>pcre_info()</b> function is now obsolete because its interface is too
981 restrictive to return all the available data about a compiled pattern. New
982 programs should use <b>pcre_fullinfo()</b> instead. The yield of
983 <b>pcre_info()</b> is the number of capturing subpatterns, or one of the
984 following negative numbers:
985 <pre>
986 PCRE_ERROR_NULL the argument <i>code</i> was NULL
987 PCRE_ERROR_BADMAGIC the "magic number" was not found
988 </pre>
989 If the <i>optptr</i> argument is not NULL, a copy of the options with which the
990 pattern was compiled is placed in the integer it points to (see
991 PCRE_INFO_OPTIONS above).
992 </P>
993 <P>
994 If the pattern is not anchored and the <i>firstcharptr</i> argument is not NULL,
995 it is used to pass back information about the first character of any matched
996 string (see PCRE_INFO_FIRSTBYTE above).
997 </P>
998 <br><a name="SEC13" href="#TOC1">REFERENCE COUNTS</a><br>
999 <P>
1000 <b>int pcre_refcount(pcre *<i>code</i>, int <i>adjust</i>);</b>
1001 </P>
1002 <P>
1003 The <b>pcre_refcount()</b> function is used to maintain a reference count in the
1004 data block that contains a compiled pattern. It is provided for the benefit of
1005 applications that operate in an object-oriented manner, where different parts
1006 of the application may be using the same compiled pattern, but you want to free
1007 the block when they are all done.
1008 </P>
1009 <P>
1010 When a pattern is compiled, the reference count field is initialized to zero.
1011 It is changed only by calling this function, whose action is to add the
1012 <i>adjust</i> value (which may be positive or negative) to it. The yield of the
1013 function is the new value. However, the value of the count is constrained to
1014 lie between 0 and 65535, inclusive. If the new value is outside these limits,
1015 it is forced to the appropriate limit value.
1016 </P>
1017 <P>
1018 Except when it is zero, the reference count is not correctly preserved if a
1019 pattern is compiled on one host and then transferred to a host whose byte-order
1020 is different. (This seems a highly unlikely scenario.)
1021 </P>
1022 <br><a name="SEC14" href="#TOC1">MATCHING A PATTERN: THE TRADITIONAL FUNCTION</a><br>
1023 <P>
1024 <b>int pcre_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
1025 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
1026 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>);</b>
1027 </P>
1028 <P>
1029 The function <b>pcre_exec()</b> is called to match a subject string against a
1030 compiled pattern, which is passed in the <i>code</i> argument. If the
1031 pattern has been studied, the result of the study should be passed in the
1032 <i>extra</i> argument. This function is the main matching facility of the
1033 library, and it operates in a Perl-like manner. For specialist use there is
1034 also an alternative matching function, which is described
1035 <a href="#dfamatch">below</a>
1036 in the section about the <b>pcre_dfa_exec()</b> function.
1037 </P>
1038 <P>
1039 In most applications, the pattern will have been compiled (and optionally
1040 studied) in the same process that calls <b>pcre_exec()</b>. However, it is
1041 possible to save compiled patterns and study data, and then use them later
1042 in different processes, possibly even on different hosts. For a discussion
1043 about this, see the
1044 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
1045 documentation.
1046 </P>
1047 <P>
1048 Here is an example of a simple call to <b>pcre_exec()</b>:
1049 <pre>
1050 int rc;
1051 int ovector[30];
1052 rc = pcre_exec(
1053 re, /* result of pcre_compile() */
1054 NULL, /* we didn't study the pattern */
1055 "some string", /* the subject string */
1056 11, /* the length of the subject string */
1057 0, /* start at offset 0 in the subject */
1058 0, /* default options */
1059 ovector, /* vector of integers for substring information */
1060 30); /* number of elements (NOT size in bytes) */
1061 <a name="extradata"></a></PRE>
1062 </P>
1063 <br><b>
1064 Extra data for <b>pcre_exec()</b>
1065 </b><br>
1066 <P>
1067 If the <i>extra</i> argument is not NULL, it must point to a <b>pcre_extra</b>
1068 data block. The <b>pcre_study()</b> function returns such a block (when it
1069 doesn't return NULL), but you can also create one for yourself, and pass
1070 additional information in it. The <b>pcre_extra</b> block contains the following
1071 fields (not necessarily in this order):
1072 <pre>
1073 unsigned long int <i>flags</i>;
1074 void *<i>study_data</i>;
1075 unsigned long int <i>match_limit</i>;
1076 unsigned long int <i>match_limit_recursion</i>;
1077 void *<i>callout_data</i>;
1078 const unsigned char *<i>tables</i>;
1079 </pre>
1080 The <i>flags</i> field is a bitmap that specifies which of the other fields
1081 are set. The flag bits are:
1082 <pre>
1083 PCRE_EXTRA_STUDY_DATA
1084 PCRE_EXTRA_MATCH_LIMIT
1085 PCRE_EXTRA_MATCH_LIMIT_RECURSION
1086 PCRE_EXTRA_CALLOUT_DATA
1087 PCRE_EXTRA_TABLES
1088 </pre>
1089 Other flag bits should be set to zero. The <i>study_data</i> field is set in the
1090 <b>pcre_extra</b> block that is returned by <b>pcre_study()</b>, together with
1091 the appropriate flag bit. You should not set this yourself, but you may add to
1092 the block by setting the other fields and their corresponding flag bits.
1093 </P>
1094 <P>
1095 The <i>match_limit</i> field provides a means of preventing PCRE from using up a
1096 vast amount of resources when running patterns that are not going to match,
1097 but which have a very large number of possibilities in their search trees. The
1098 classic example is the use of nested unlimited repeats.
1099 </P>
1100 <P>
1101 Internally, PCRE uses a function called <b>match()</b> which it calls repeatedly
1102 (sometimes recursively). The limit set by <i>match_limit</i> is imposed on the
1103 number of times this function is called during a match, which has the effect of
1104 limiting the amount of backtracking that can take place. For patterns that are
1105 not anchored, the count restarts from zero for each position in the subject
1106 string.
1107 </P>
1108 <P>
1109 The default value for the limit can be set when PCRE is built; the default
1110 default is 10 million, which handles all but the most extreme cases. You can
1111 override the default by suppling <b>pcre_exec()</b> with a <b>pcre_extra</b>
1112 block in which <i>match_limit</i> is set, and PCRE_EXTRA_MATCH_LIMIT is set in
1113 the <i>flags</i> field. If the limit is exceeded, <b>pcre_exec()</b> returns
1114 PCRE_ERROR_MATCHLIMIT.
1115 </P>
1116 <P>
1117 The <i>match_limit_recursion</i> field is similar to <i>match_limit</i>, but
1118 instead of limiting the total number of times that <b>match()</b> is called, it
1119 limits the depth of recursion. The recursion depth is a smaller number than the
1120 total number of calls, because not all calls to <b>match()</b> are recursive.
1121 This limit is of use only if it is set smaller than <i>match_limit</i>.
1122 </P>
1123 <P>
1124 Limiting the recursion depth limits the amount of stack that can be used, or,
1125 when PCRE has been compiled to use memory on the heap instead of the stack, the
1126 amount of heap memory that can be used.
1127 </P>
1128 <P>
1129 The default value for <i>match_limit_recursion</i> can be set when PCRE is
1130 built; the default default is the same value as the default for
1131 <i>match_limit</i>. You can override the default by suppling <b>pcre_exec()</b>
1132 with a <b>pcre_extra</b> block in which <i>match_limit_recursion</i> is set, and
1133 PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the <i>flags</i> field. If the limit
1134 is exceeded, <b>pcre_exec()</b> returns PCRE_ERROR_RECURSIONLIMIT.
1135 </P>
1136 <P>
1137 The <i>pcre_callout</i> field is used in conjunction with the "callout" feature,
1138 which is described in the
1139 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1140 documentation.
1141 </P>
1142 <P>
1143 The <i>tables</i> field is used to pass a character tables pointer to
1144 <b>pcre_exec()</b>; this overrides the value that is stored with the compiled
1145 pattern. A non-NULL value is stored with the compiled pattern only if custom
1146 tables were supplied to <b>pcre_compile()</b> via its <i>tableptr</i> argument.
1147 If NULL is passed to <b>pcre_exec()</b> using this mechanism, it forces PCRE's
1148 internal tables to be used. This facility is helpful when re-using patterns
1149 that have been saved after compiling with an external set of tables, because
1150 the external tables might be at a different address when <b>pcre_exec()</b> is
1151 called. See the
1152 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
1153 documentation for a discussion of saving compiled patterns for later use.
1154 </P>
1155 <br><b>
1156 Option bits for <b>pcre_exec()</b>
1157 </b><br>
1158 <P>
1159 The unused bits of the <i>options</i> argument for <b>pcre_exec()</b> must be
1160 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_<i>xxx</i>,
1161 PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK and PCRE_PARTIAL.
1162 <pre>
1163 PCRE_ANCHORED
1164 </pre>
1165 The PCRE_ANCHORED option limits <b>pcre_exec()</b> to matching at the first
1166 matching position. If a pattern was compiled with PCRE_ANCHORED, or turned out
1167 to be anchored by virtue of its contents, it cannot be made unachored at
1168 matching time.
1169 <pre>
1170 PCRE_NEWLINE_CR
1171 PCRE_NEWLINE_LF
1172 PCRE_NEWLINE_CRLF
1173 PCRE_NEWLINE_ANYCRLF
1174 PCRE_NEWLINE_ANY
1175 </pre>
1176 These options override the newline definition that was chosen or defaulted when
1177 the pattern was compiled. For details, see the description of
1178 <b>pcre_compile()</b> above. During matching, the newline choice affects the
1179 behaviour of the dot, circumflex, and dollar metacharacters. It may also alter
1180 the way the match position is advanced after a match failure for an unanchored
1181 pattern. When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY is
1182 set, and a match attempt fails when the current position is at a CRLF sequence,
1183 the match position is advanced by two characters instead of one, in other
1184 words, to after the CRLF.
1185 <pre>
1186 PCRE_NOTBOL
1187 </pre>
1188 This option specifies that first character of the subject string is not the
1189 beginning of a line, so the circumflex metacharacter should not match before
1190 it. Setting this without PCRE_MULTILINE (at compile time) causes circumflex
1191 never to match. This option affects only the behaviour of the circumflex
1192 metacharacter. It does not affect \A.
1193 <pre>
1194 PCRE_NOTEOL
1195 </pre>
1196 This option specifies that the end of the subject string is not the end of a
1197 line, so the dollar metacharacter should not match it nor (except in multiline
1198 mode) a newline immediately before it. Setting this without PCRE_MULTILINE (at
1199 compile time) causes dollar never to match. This option affects only the
1200 behaviour of the dollar metacharacter. It does not affect \Z or \z.
1201 <pre>
1202 PCRE_NOTEMPTY
1203 </pre>
1204 An empty string is not considered to be a valid match if this option is set. If
1205 there are alternatives in the pattern, they are tried. If all the alternatives
1206 match the empty string, the entire match fails. For example, if the pattern
1207 <pre>
1208 a?b?
1209 </pre>
1210 is applied to a string not beginning with "a" or "b", it matches the empty
1211 string at the start of the subject. With PCRE_NOTEMPTY set, this match is not
1212 valid, so PCRE searches further into the string for occurrences of "a" or "b".
1213 </P>
1214 <P>
1215 Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a special case
1216 of a pattern match of the empty string within its <b>split()</b> function, and
1217 when using the /g modifier. It is possible to emulate Perl's behaviour after
1218 matching a null string by first trying the match again at the same offset with
1219 PCRE_NOTEMPTY and PCRE_ANCHORED, and then if that fails by advancing the
1220 starting offset (see below) and trying an ordinary match again. There is some
1221 code that demonstrates how to do this in the <i>pcredemo.c</i> sample program.
1222 <pre>
1223 PCRE_NO_UTF8_CHECK
1224 </pre>
1225 When PCRE_UTF8 is set at compile time, the validity of the subject as a UTF-8
1226 string is automatically checked when <b>pcre_exec()</b> is subsequently called.
1227 The value of <i>startoffset</i> is also checked to ensure that it points to the
1228 start of a UTF-8 character. If an invalid UTF-8 sequence of bytes is found,
1229 <b>pcre_exec()</b> returns the error PCRE_ERROR_BADUTF8. If <i>startoffset</i>
1230 contains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
1231 </P>
1232 <P>
1233 If you already know that your subject is valid, and you want to skip these
1234 checks for performance reasons, you can set the PCRE_NO_UTF8_CHECK option when
1235 calling <b>pcre_exec()</b>. You might want to do this for the second and
1236 subsequent calls to <b>pcre_exec()</b> if you are making repeated calls to find
1237 all the matches in a single subject string. However, you should be sure that
1238 the value of <i>startoffset</i> points to the start of a UTF-8 character. When
1239 PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid UTF-8 string as a
1240 subject, or a value of <i>startoffset</i> that does not point to the start of a
1241 UTF-8 character, is undefined. Your program may crash.
1242 <pre>
1243 PCRE_PARTIAL
1244 </pre>
1245 This option turns on the partial matching feature. If the subject string fails
1246 to match the pattern, but at some point during the matching process the end of
1247 the subject was reached (that is, the subject partially matches the pattern and
1248 the failure to match occurred only because there were not enough subject
1249 characters), <b>pcre_exec()</b> returns PCRE_ERROR_PARTIAL instead of
1250 PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is used, there are restrictions on what
1251 may appear in the pattern. These are discussed in the
1252 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1253 documentation.
1254 </P>
1255 <br><b>
1256 The string to be matched by <b>pcre_exec()</b>
1257 </b><br>
1258 <P>
1259 The subject string is passed to <b>pcre_exec()</b> as a pointer in
1260 <i>subject</i>, a length in <i>length</i>, and a starting byte offset in
1261 <i>startoffset</i>. In UTF-8 mode, the byte offset must point to the start of a
1262 UTF-8 character. Unlike the pattern string, the subject may contain binary zero
1263 bytes. When the starting offset is zero, the search for a match starts at the
1264 beginning of the subject, and this is by far the most common case.
1265 </P>
1266 <P>
1267 A non-zero starting offset is useful when searching for another match in the
1268 same subject by calling <b>pcre_exec()</b> again after a previous success.
1269 Setting <i>startoffset</i> differs from just passing over a shortened string and
1270 setting PCRE_NOTBOL in the case of a pattern that begins with any kind of
1271 lookbehind. For example, consider the pattern
1272 <pre>
1273 \Biss\B
1274 </pre>
1275 which finds occurrences of "iss" in the middle of words. (\B matches only if
1276 the current position in the subject is not a word boundary.) When applied to
1277 the string "Mississipi" the first call to <b>pcre_exec()</b> finds the first
1278 occurrence. If <b>pcre_exec()</b> is called again with just the remainder of the
1279 subject, namely "issipi", it does not match, because \B is always false at the
1280 start of the subject, which is deemed to be a word boundary. However, if
1281 <b>pcre_exec()</b> is passed the entire string again, but with <i>startoffset</i>
1282 set to 4, it finds the second occurrence of "iss" because it is able to look
1283 behind the starting point to discover that it is preceded by a letter.
1284 </P>
1285 <P>
1286 If a non-zero starting offset is passed when the pattern is anchored, one
1287 attempt to match at the given offset is made. This can only succeed if the
1288 pattern does not require the match to be at the start of the subject.
1289 </P>
1290 <br><b>
1291 How <b>pcre_exec()</b> returns captured substrings
1292 </b><br>
1293 <P>
1294 In general, a pattern matches a certain portion of the subject, and in
1295 addition, further substrings from the subject may be picked out by parts of the
1296 pattern. Following the usage in Jeffrey Friedl's book, this is called
1297 "capturing" in what follows, and the phrase "capturing subpattern" is used for
1298 a fragment of a pattern that picks out a substring. PCRE supports several other
1299 kinds of parenthesized subpattern that do not cause substrings to be captured.
1300 </P>
1301 <P>
1302 Captured substrings are returned to the caller via a vector of integer offsets
1303 whose address is passed in <i>ovector</i>. The number of elements in the vector
1304 is passed in <i>ovecsize</i>, which must be a non-negative number. <b>Note</b>:
1305 this argument is NOT the size of <i>ovector</i> in bytes.
1306 </P>
1307 <P>
1308 The first two-thirds of the vector is used to pass back captured substrings,
1309 each substring using a pair of integers. The remaining third of the vector is
1310 used as workspace by <b>pcre_exec()</b> while matching capturing subpatterns,
1311 and is not available for passing back information. The length passed in
1312 <i>ovecsize</i> should always be a multiple of three. If it is not, it is
1313 rounded down.
1314 </P>
1315 <P>
1316 When a match is successful, information about captured substrings is returned
1317 in pairs of integers, starting at the beginning of <i>ovector</i>, and
1318 continuing up to two-thirds of its length at the most. The first element of a
1319 pair is set to the offset of the first character in a substring, and the second
1320 is set to the offset of the first character after the end of a substring. The
1321 first pair, <i>ovector[0]</i> and <i>ovector[1]</i>, identify the portion of the
1322 subject string matched by the entire pattern. The next pair is used for the
1323 first capturing subpattern, and so on. The value returned by <b>pcre_exec()</b>
1324 is one more than the highest numbered pair that has been set. For example, if
1325 two substrings have been captured, the returned value is 3. If there are no
1326 capturing subpatterns, the return value from a successful match is 1,
1327 indicating that just the first pair of offsets has been set.
1328 </P>
1329 <P>
1330 If a capturing subpattern is matched repeatedly, it is the last portion of the
1331 string that it matched that is returned.
1332 </P>
1333 <P>
1334 If the vector is too small to hold all the captured substring offsets, it is
1335 used as far as possible (up to two-thirds of its length), and the function
1336 returns a value of zero. In particular, if the substring offsets are not of
1337 interest, <b>pcre_exec()</b> may be called with <i>ovector</i> passed as NULL and
1338 <i>ovecsize</i> as zero. However, if the pattern contains back references and
1339 the <i>ovector</i> is not big enough to remember the related substrings, PCRE
1340 has to get additional memory for use during matching. Thus it is usually
1341 advisable to supply an <i>ovector</i>.
1342 </P>
1343 <P>
1344 The <b>pcre_info()</b> function can be used to find out how many capturing
1345 subpatterns there are in a compiled pattern. The smallest size for
1346 <i>ovector</i> that will allow for <i>n</i> captured substrings, in addition to
1347 the offsets of the substring matched by the whole pattern, is (<i>n</i>+1)*3.
1348 </P>
1349 <P>
1350 It is possible for capturing subpattern number <i>n+1</i> to match some part of
1351 the subject when subpattern <i>n</i> has not been used at all. For example, if
1352 the string "abc" is matched against the pattern (a|(z))(bc) the return from the
1353 function is 4, and subpatterns 1 and 3 are matched, but 2 is not. When this
1354 happens, both values in the offset pairs corresponding to unused subpatterns
1355 are set to -1.
1356 </P>
1357 <P>
1358 Offset values that correspond to unused subpatterns at the end of the
1359 expression are also set to -1. For example, if the string "abc" is matched
1360 against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not matched. The
1361 return from the function is 2, because the highest used capturing subpattern
1362 number is 1. However, you can refer to the offsets for the second and third
1363 capturing subpatterns if you wish (assuming the vector is large enough, of
1364 course).
1365 </P>
1366 <P>
1367 Some convenience functions are provided for extracting the captured substrings
1368 as separate strings. These are described below.
1369 <a name="errorlist"></a></P>
1370 <br><b>
1371 Error return values from <b>pcre_exec()</b>
1372 </b><br>
1373 <P>
1374 If <b>pcre_exec()</b> fails, it returns a negative number. The following are
1375 defined in the header file:
1376 <pre>
1377 PCRE_ERROR_NOMATCH (-1)
1378 </pre>
1379 The subject string did not match the pattern.
1380 <pre>
1381 PCRE_ERROR_NULL (-2)
1382 </pre>
1383 Either <i>code</i> or <i>subject</i> was passed as NULL, or <i>ovector</i> was
1384 NULL and <i>ovecsize</i> was not zero.
1385 <pre>
1386 PCRE_ERROR_BADOPTION (-3)
1387 </pre>
1388 An unrecognized bit was set in the <i>options</i> argument.
1389 <pre>
1390 PCRE_ERROR_BADMAGIC (-4)
1391 </pre>
1392 PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch
1393 the case when it is passed a junk pointer and to detect when a pattern that was
1394 compiled in an environment of one endianness is run in an environment with the
1395 other endianness. This is the error that PCRE gives when the magic number is
1396 not present.
1397 <pre>
1398 PCRE_ERROR_UNKNOWN_OPCODE (-5)
1399 </pre>
1400 While running the pattern match, an unknown item was encountered in the
1401 compiled pattern. This error could be caused by a bug in PCRE or by overwriting
1402 of the compiled pattern.
1403 <pre>
1404 PCRE_ERROR_NOMEMORY (-6)
1405 </pre>
1406 If a pattern contains back references, but the <i>ovector</i> that is passed to
1407 <b>pcre_exec()</b> is not big enough to remember the referenced substrings, PCRE
1408 gets a block of memory at the start of matching to use for this purpose. If the
1409 call via <b>pcre_malloc()</b> fails, this error is given. The memory is
1410 automatically freed at the end of matching.
1411 <pre>
1412 PCRE_ERROR_NOSUBSTRING (-7)
1413 </pre>
1414 This error is used by the <b>pcre_copy_substring()</b>,
1415 <b>pcre_get_substring()</b>, and <b>pcre_get_substring_list()</b> functions (see
1416 below). It is never returned by <b>pcre_exec()</b>.
1417 <pre>
1418 PCRE_ERROR_MATCHLIMIT (-8)
1419 </pre>
1420 The backtracking limit, as specified by the <i>match_limit</i> field in a
1421 <b>pcre_extra</b> structure (or defaulted) was reached. See the description
1422 above.
1423 <pre>
1424 PCRE_ERROR_CALLOUT (-9)
1425 </pre>
1426 This error is never generated by <b>pcre_exec()</b> itself. It is provided for
1427 use by callout functions that want to yield a distinctive error code. See the
1428 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1429 documentation for details.
1430 <pre>
1431 PCRE_ERROR_BADUTF8 (-10)
1432 </pre>
1433 A string that contains an invalid UTF-8 byte sequence was passed as a subject.
1434 <pre>
1435 PCRE_ERROR_BADUTF8_OFFSET (-11)
1436 </pre>
1437 The UTF-8 byte sequence that was passed as a subject was valid, but the value
1438 of <i>startoffset</i> did not point to the beginning of a UTF-8 character.
1439 <pre>
1440 PCRE_ERROR_PARTIAL (-12)
1441 </pre>
1442 The subject string did not match, but it did match partially. See the
1443 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1444 documentation for details of partial matching.
1445 <pre>
1446 PCRE_ERROR_BADPARTIAL (-13)
1447 </pre>
1448 The PCRE_PARTIAL option was used with a compiled pattern containing items that
1449 are not supported for partial matching. See the
1450 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1451 documentation for details of partial matching.
1452 <pre>
1453 PCRE_ERROR_INTERNAL (-14)
1454 </pre>
1455 An unexpected internal error has occurred. This error could be caused by a bug
1456 in PCRE or by overwriting of the compiled pattern.
1457 <pre>
1458 PCRE_ERROR_BADCOUNT (-15)
1459 </pre>
1460 This error is given if the value of the <i>ovecsize</i> argument is negative.
1461 <pre>
1462 PCRE_ERROR_RECURSIONLIMIT (-21)
1463 </pre>
1464 The internal recursion limit, as specified by the <i>match_limit_recursion</i>
1465 field in a <b>pcre_extra</b> structure (or defaulted) was reached. See the
1466 description above.
1467 <pre>
1468 PCRE_ERROR_NULLWSLIMIT (-22)
1469 </pre>
1470 When a group that can match an empty substring is repeated with an unbounded
1471 upper limit, the subject position at the start of the group must be remembered,
1472 so that a test for an empty string can be made when the end of the group is
1473 reached. Some workspace is required for this; if it runs out, this error is
1474 given.
1475 <pre>
1476 PCRE_ERROR_BADNEWLINE (-23)
1477 </pre>
1478 An invalid combination of PCRE_NEWLINE_<i>xxx</i> options was given.
1479 </P>
1480 <P>
1481 Error numbers -16 to -20 are not used by <b>pcre_exec()</b>.
1482 </P>
1483 <br><a name="SEC15" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NUMBER</a><br>
1484 <P>
1485 <b>int pcre_copy_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1486 <b>int <i>stringcount</i>, int <i>stringnumber</i>, char *<i>buffer</i>,</b>
1487 <b>int <i>buffersize</i>);</b>
1488 </P>
1489 <P>
1490 <b>int pcre_get_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1491 <b>int <i>stringcount</i>, int <i>stringnumber</i>,</b>
1492 <b>const char **<i>stringptr</i>);</b>
1493 </P>
1494 <P>
1495 <b>int pcre_get_substring_list(const char *<i>subject</i>,</b>
1496 <b>int *<i>ovector</i>, int <i>stringcount</i>, const char ***<i>listptr</i>);</b>
1497 </P>
1498 <P>
1499 Captured substrings can be accessed directly by using the offsets returned by
1500 <b>pcre_exec()</b> in <i>ovector</i>. For convenience, the functions
1501 <b>pcre_copy_substring()</b>, <b>pcre_get_substring()</b>, and
1502 <b>pcre_get_substring_list()</b> are provided for extracting captured substrings
1503 as new, separate, zero-terminated strings. These functions identify substrings
1504 by number. The next section describes functions for extracting named
1505 substrings.
1506 </P>
1507 <P>
1508 A substring that contains a binary zero is correctly extracted and has a
1509 further zero added on the end, but the result is not, of course, a C string.
1510 However, you can process such a string by referring to the length that is
1511 returned by <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>.
1512 Unfortunately, the interface to <b>pcre_get_substring_list()</b> is not adequate
1513 for handling strings containing binary zeros, because the end of the final
1514 string is not independently indicated.
1515 </P>
1516 <P>
1517 The first three arguments are the same for all three of these functions:
1518 <i>subject</i> is the subject string that has just been successfully matched,
1519 <i>ovector</i> is a pointer to the vector of integer offsets that was passed to
1520 <b>pcre_exec()</b>, and <i>stringcount</i> is the number of substrings that were
1521 captured by the match, including the substring that matched the entire regular
1522 expression. This is the value returned by <b>pcre_exec()</b> if it is greater
1523 than zero. If <b>pcre_exec()</b> returned zero, indicating that it ran out of
1524 space in <i>ovector</i>, the value passed as <i>stringcount</i> should be the
1525 number of elements in the vector divided by three.
1526 </P>
1527 <P>
1528 The functions <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>
1529 extract a single substring, whose number is given as <i>stringnumber</i>. A
1530 value of zero extracts the substring that matched the entire pattern, whereas
1531 higher values extract the captured substrings. For <b>pcre_copy_substring()</b>,
1532 the string is placed in <i>buffer</i>, whose length is given by
1533 <i>buffersize</i>, while for <b>pcre_get_substring()</b> a new block of memory is
1534 obtained via <b>pcre_malloc</b>, and its address is returned via
1535 <i>stringptr</i>. The yield of the function is the length of the string, not
1536 including the terminating zero, or one of these error codes:
1537 <pre>
1538 PCRE_ERROR_NOMEMORY (-6)
1539 </pre>
1540 The buffer was too small for <b>pcre_copy_substring()</b>, or the attempt to get
1541 memory failed for <b>pcre_get_substring()</b>.
1542 <pre>
1543 PCRE_ERROR_NOSUBSTRING (-7)
1544 </pre>
1545 There is no substring whose number is <i>stringnumber</i>.
1546 </P>
1547 <P>
1548 The <b>pcre_get_substring_list()</b> function extracts all available substrings
1549 and builds a list of pointers to them. All this is done in a single block of
1550 memory that is obtained via <b>pcre_malloc</b>. The address of the memory block
1551 is returned via <i>listptr</i>, which is also the start of the list of string
1552 pointers. The end of the list is marked by a NULL pointer. The yield of the
1553 function is zero if all went well, or the error code
1554 <pre>
1555 PCRE_ERROR_NOMEMORY (-6)
1556 </pre>
1557 if the attempt to get the memory block failed.
1558 </P>
1559 <P>
1560 When any of these functions encounter a substring that is unset, which can
1561 happen when capturing subpattern number <i>n+1</i> matches some part of the
1562 subject, but subpattern <i>n</i> has not been used at all, they return an empty
1563 string. This can be distinguished from a genuine zero-length substring by
1564 inspecting the appropriate offset in <i>ovector</i>, which is negative for unset
1565 substrings.
1566 </P>
1567 <P>
1568 The two convenience functions <b>pcre_free_substring()</b> and
1569 <b>pcre_free_substring_list()</b> can be used to free the memory returned by
1570 a previous call of <b>pcre_get_substring()</b> or
1571 <b>pcre_get_substring_list()</b>, respectively. They do nothing more than call
1572 the function pointed to by <b>pcre_free</b>, which of course could be called
1573 directly from a C program. However, PCRE is used in some situations where it is
1574 linked via a special interface to another programming language that cannot use
1575 <b>pcre_free</b> directly; it is for these cases that the functions are
1576 provided.
1577 </P>
1578 <br><a name="SEC16" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NAME</a><br>
1579 <P>
1580 <b>int pcre_get_stringnumber(const pcre *<i>code</i>,</b>
1581 <b>const char *<i>name</i>);</b>
1582 </P>
1583 <P>
1584 <b>int pcre_copy_named_substring(const pcre *<i>code</i>,</b>
1585 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
1586 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
1587 <b>char *<i>buffer</i>, int <i>buffersize</i>);</b>
1588 </P>
1589 <P>
1590 <b>int pcre_get_named_substring(const pcre *<i>code</i>,</b>
1591 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
1592 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
1593 <b>const char **<i>stringptr</i>);</b>
1594 </P>
1595 <P>
1596 To extract a substring by name, you first have to find associated number.
1597 For example, for this pattern
1598 <pre>
1599 (a+)b(?&#60;xxx&#62;\d+)...
1600 </pre>
1601 the number of the subpattern called "xxx" is 2. If the name is known to be
1602 unique (PCRE_DUPNAMES was not set), you can find the number from the name by
1603 calling <b>pcre_get_stringnumber()</b>. The first argument is the compiled
1604 pattern, and the second is the name. The yield of the function is the
1605 subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no subpattern of
1606 that name.
1607 </P>
1608 <P>
1609 Given the number, you can extract the substring directly, or use one of the
1610 functions described in the previous section. For convenience, there are also
1611 two functions that do the whole job.
1612 </P>
1613 <P>
1614 Most of the arguments of <b>pcre_copy_named_substring()</b> and
1615 <b>pcre_get_named_substring()</b> are the same as those for the similarly named
1616 functions that extract by number. As these are described in the previous
1617 section, they are not re-described here. There are just two differences:
1618 </P>
1619 <P>
1620 First, instead of a substring number, a substring name is given. Second, there
1621 is an extra argument, given at the start, which is a pointer to the compiled
1622 pattern. This is needed in order to gain access to the name-to-number
1623 translation table.
1624 </P>
1625 <P>
1626 These functions call <b>pcre_get_stringnumber()</b>, and if it succeeds, they
1627 then call <b>pcre_copy_substring()</b> or <b>pcre_get_substring()</b>, as
1628 appropriate. <b>NOTE:</b> If PCRE_DUPNAMES is set and there are duplicate names,
1629 the behaviour may not be what you want (see the next section).
1630 </P>
1631 <br><a name="SEC17" href="#TOC1">DUPLICATE SUBPATTERN NAMES</a><br>
1632 <P>
1633 <b>int pcre_get_stringtable_entries(const pcre *<i>code</i>,</b>
1634 <b>const char *<i>name</i>, char **<i>first</i>, char **<i>last</i>);</b>
1635 </P>
1636 <P>
1637 When a pattern is compiled with the PCRE_DUPNAMES option, names for subpatterns
1638 are not required to be unique. Normally, patterns with duplicate names are such
1639 that in any one match, only one of the named subpatterns participates. An
1640 example is shown in the
1641 <a href="pcrepattern.html"><b>pcrepattern</b></a>
1642 documentation. When duplicates are present, <b>pcre_copy_named_substring()</b>
1643 and <b>pcre_get_named_substring()</b> return the first substring corresponding
1644 to the given name that is set. If none are set, an empty string is returned.
1645 The <b>pcre_get_stringnumber()</b> function returns one of the numbers that are
1646 associated with the name, but it is not defined which it is.
1647 <br>
1648 <br>
1649 If you want to get full details of all captured substrings for a given name,
1650 you must use the <b>pcre_get_stringtable_entries()</b> function. The first
1651 argument is the compiled pattern, and the second is the name. The third and
1652 fourth are pointers to variables which are updated by the function. After it
1653 has run, they point to the first and last entries in the name-to-number table
1654 for the given name. The function itself returns the length of each entry, or
1655 PCRE_ERROR_NOSUBSTRING (-7) if there are none. The format of the table is
1656 described above in the section entitled <i>Information about a pattern</i>.
1657 Given all the relevant entries for the name, you can extract each of their
1658 numbers, and hence the captured data, if any.
1659 </P>
1660 <br><a name="SEC18" href="#TOC1">FINDING ALL POSSIBLE MATCHES</a><br>
1661 <P>
1662 The traditional matching function uses a similar algorithm to Perl, which stops
1663 when it finds the first match, starting at a given point in the subject. If you
1664 want to find all possible matches, or the longest possible match, consider
1665 using the alternative matching function (see below) instead. If you cannot use
1666 the alternative function, but still need to find all possible matches, you
1667 can kludge it up by making use of the callout facility, which is described in
1668 the
1669 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1670 documentation.
1671 </P>
1672 <P>
1673 What you have to do is to insert a callout right at the end of the pattern.
1674 When your callout function is called, extract and save the current matched
1675 substring. Then return 1, which forces <b>pcre_exec()</b> to backtrack and try
1676 other alternatives. Ultimately, when it runs out of matches, <b>pcre_exec()</b>
1677 will yield PCRE_ERROR_NOMATCH.
1678 <a name="dfamatch"></a></P>
1679 <br><a name="SEC19" href="#TOC1">MATCHING A PATTERN: THE ALTERNATIVE FUNCTION</a><br>
1680 <P>
1681 <b>int pcre_dfa_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
1682 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
1683 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>,</b>
1684 <b>int *<i>workspace</i>, int <i>wscount</i>);</b>
1685 </P>
1686 <P>
1687 The function <b>pcre_dfa_exec()</b> is called to match a subject string against
1688 a compiled pattern, using a matching algorithm that scans the subject string
1689 just once, and does not backtrack. This has different characteristics to the
1690 normal algorithm, and is not compatible with Perl. Some of the features of PCRE
1691 patterns are not supported. Nevertheless, there are times when this kind of
1692 matching can be useful. For a discussion of the two matching algorithms, see
1693 the
1694 <a href="pcrematching.html"><b>pcrematching</b></a>
1695 documentation.
1696 </P>
1697 <P>
1698 The arguments for the <b>pcre_dfa_exec()</b> function are the same as for
1699 <b>pcre_exec()</b>, plus two extras. The <i>ovector</i> argument is used in a
1700 different way, and this is described below. The other common arguments are used
1701 in the same way as for <b>pcre_exec()</b>, so their description is not repeated
1702 here.
1703 </P>
1704 <P>
1705 The two additional arguments provide workspace for the function. The workspace
1706 vector should contain at least 20 elements. It is used for keeping track of
1707 multiple paths through the pattern tree. More workspace will be needed for
1708 patterns and subjects where there are a lot of potential matches.
1709 </P>
1710 <P>
1711 Here is an example of a simple call to <b>pcre_dfa_exec()</b>:
1712 <pre>
1713 int rc;
1714 int ovector[10];
1715 int wspace[20];
1716 rc = pcre_dfa_exec(
1717 re, /* result of pcre_compile() */
1718 NULL, /* we didn't study the pattern */
1719 "some string", /* the subject string */
1720 11, /* the length of the subject string */
1721 0, /* start at offset 0 in the subject */
1722 0, /* default options */
1723 ovector, /* vector of integers for substring information */
1724 10, /* number of elements (NOT size in bytes) */
1725 wspace, /* working space vector */
1726 20); /* number of elements (NOT size in bytes) */
1727 </PRE>
1728 </P>
1729 <br><b>
1730 Option bits for <b>pcre_dfa_exec()</b>
1731 </b><br>
1732 <P>
1733 The unused bits of the <i>options</i> argument for <b>pcre_dfa_exec()</b> must be
1734 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_<i>xxx</i>,
1735 PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL,
1736 PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last three of these are
1737 the same as for <b>pcre_exec()</b>, so their description is not repeated here.
1738 <pre>
1739 PCRE_PARTIAL
1740 </pre>
1741 This has the same general effect as it does for <b>pcre_exec()</b>, but the
1742 details are slightly different. When PCRE_PARTIAL is set for
1743 <b>pcre_dfa_exec()</b>, the return code PCRE_ERROR_NOMATCH is converted into
1744 PCRE_ERROR_PARTIAL if the end of the subject is reached, there have been no
1745 complete matches, but there is still at least one matching possibility. The
1746 portion of the string that provided the partial match is set as the first
1747 matching string.
1748 <pre>
1749 PCRE_DFA_SHORTEST
1750 </pre>
1751 Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to stop as
1752 soon as it has found one match. Because of the way the alternative algorithm
1753 works, this is necessarily the shortest possible match at the first possible
1754 matching point in the subject string.
1755 <pre>
1756 PCRE_DFA_RESTART
1757 </pre>
1758 When <b>pcre_dfa_exec()</b> is called with the PCRE_PARTIAL option, and returns
1759 a partial match, it is possible to call it again, with additional subject
1760 characters, and have it continue with the same match. The PCRE_DFA_RESTART
1761 option requests this action; when it is set, the <i>workspace</i> and
1762 <i>wscount</i> options must reference the same vector as before because data
1763 about the match so far is left in them after a partial match. There is more
1764 discussion of this facility in the
1765 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1766 documentation.
1767 </P>
1768 <br><b>
1769 Successful returns from <b>pcre_dfa_exec()</b>
1770 </b><br>
1771 <P>
1772 When <b>pcre_dfa_exec()</b> succeeds, it may have matched more than one
1773 substring in the subject. Note, however, that all the matches from one run of
1774 the function start at the same point in the subject. The shorter matches are
1775 all initial substrings of the longer matches. For example, if the pattern
1776 <pre>
1777 &#60;.*&#62;
1778 </pre>
1779 is matched against the string
1780 <pre>
1781 This is &#60;something&#62; &#60;something else&#62; &#60;something further&#62; no more
1782 </pre>
1783 the three matched strings are
1784 <pre>
1785 &#60;something&#62;
1786 &#60;something&#62; &#60;something else&#62;
1787 &#60;something&#62; &#60;something else&#62; &#60;something further&#62;
1788 </pre>
1789 On success, the yield of the function is a number greater than zero, which is
1790 the number of matched substrings. The substrings themselves are returned in
1791 <i>ovector</i>. Each string uses two elements; the first is the offset to the
1792 start, and the second is the offset to the end. In fact, all the strings have
1793 the same start offset. (Space could have been saved by giving this only once,
1794 but it was decided to retain some compatibility with the way <b>pcre_exec()</b>
1795 returns data, even though the meaning of the strings is different.)
1796 </P>
1797 <P>
1798 The strings are returned in reverse order of length; that is, the longest
1799 matching string is given first. If there were too many matches to fit into
1800 <i>ovector</i>, the yield of the function is zero, and the vector is filled with
1801 the longest matches.
1802 </P>
1803 <br><b>
1804 Error returns from <b>pcre_dfa_exec()</b>
1805 </b><br>
1806 <P>
1807 The <b>pcre_dfa_exec()</b> function returns a negative number when it fails.
1808 Many of the errors are the same as for <b>pcre_exec()</b>, and these are
1809 described
1810 <a href="#errorlist">above.</a>
1811 There are in addition the following errors that are specific to
1812 <b>pcre_dfa_exec()</b>:
1813 <pre>
1814 PCRE_ERROR_DFA_UITEM (-16)
1815 </pre>
1816 This return is given if <b>pcre_dfa_exec()</b> encounters an item in the pattern
1817 that it does not support, for instance, the use of \C or a back reference.
1818 <pre>
1819 PCRE_ERROR_DFA_UCOND (-17)
1820 </pre>
1821 This return is given if <b>pcre_dfa_exec()</b> encounters a condition item that
1822 uses a back reference for the condition, or a test for recursion in a specific
1823 group. These are not supported.
1824 <pre>
1825 PCRE_ERROR_DFA_UMLIMIT (-18)
1826 </pre>
1827 This return is given if <b>pcre_dfa_exec()</b> is called with an <i>extra</i>
1828 block that contains a setting of the <i>match_limit</i> field. This is not
1829 supported (it is meaningless).
1830 <pre>
1831 PCRE_ERROR_DFA_WSSIZE (-19)
1832 </pre>
1833 This return is given if <b>pcre_dfa_exec()</b> runs out of space in the
1834 <i>workspace</i> vector.
1835 <pre>
1836 PCRE_ERROR_DFA_RECURSE (-20)
1837 </pre>
1838 When a recursive subpattern is processed, the matching function calls itself
1839 recursively, using private vectors for <i>ovector</i> and <i>workspace</i>. This
1840 error is given if the output vector is not large enough. This should be
1841 extremely rare, as a vector of size 1000 is used.
1842 </P>
1843 <br><a name="SEC20" href="#TOC1">SEE ALSO</a><br>
1844 <P>
1845 <b>pcrebuild</b>(3), <b>pcrecallout</b>(3), <b>pcrecpp(3)</b>(3),
1846 <b>pcrematching</b>(3), <b>pcrepartial</b>(3), <b>pcreposix</b>(3),
1847 <b>pcreprecompile</b>(3), <b>pcresample</b>(3), <b>pcrestack</b>(3).
1848 </P>
1849 <br><a name="SEC21" href="#TOC1">AUTHOR</a><br>
1850 <P>
1851 Philip Hazel
1852 <br>
1853 University Computing Service
1854 <br>
1855 Cambridge CB2 3QH, England.
1856 <br>
1857 </P>
1858 <br><a name="SEC22" href="#TOC1">REVISION</a><br>
1859 <P>
1860 Last updated: 16 April 2007
1861 <br>
1862 Copyright &copy; 1997-2007 University of Cambridge.
1863 <br>
1864 <p>
1865 Return to the <a href="index.html">PCRE index page</a>.
1866 </p>

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