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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 four 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, or any Unicode newline sequence.
252 The Unicode newline sequences are the three just mentioned, plus the single
253 characters VT (vertical tab, U+000B), FF (formfeed, U+000C), NEL (next line,
254 U+0085), LS (line separator, U+2028), and PS (paragraph separator, U+2029).
255 </P>
256 <P>
257 Each of the first three conventions is used by at least one operating system as
258 its standard newline sequence. When PCRE is built, a default can be specified.
259 The default default is LF, which is the Unix standard. When PCRE is run, the
260 default can be overridden, either when a pattern is compiled, or when it is
261 matched.
262 </P>
263 <P>
264 In the PCRE documentation the word "newline" is used to mean "the character or
265 pair of characters that indicate a line break". The choice of newline
266 convention affects the handling of the dot, circumflex, and dollar
267 metacharacters, the handling of #-comments in /x mode, and, when CRLF is a
268 recognized line ending sequence, the match position advancement for a
269 non-anchored pattern. The choice of newline convention does not affect the
270 interpretation of the \n or \r escape sequences.
271 </P>
272 <br><a name="SEC4" href="#TOC1">MULTITHREADING</a><br>
273 <P>
274 The PCRE functions can be used in multi-threading applications, with the
275 proviso that the memory management functions pointed to by <b>pcre_malloc</b>,
276 <b>pcre_free</b>, <b>pcre_stack_malloc</b>, and <b>pcre_stack_free</b>, and the
277 callout function pointed to by <b>pcre_callout</b>, are shared by all threads.
278 </P>
279 <P>
280 The compiled form of a regular expression is not altered during matching, so
281 the same compiled pattern can safely be used by several threads at once.
282 </P>
283 <br><a name="SEC5" href="#TOC1">SAVING PRECOMPILED PATTERNS FOR LATER USE</a><br>
284 <P>
285 The compiled form of a regular expression can be saved and re-used at a later
286 time, possibly by a different program, and even on a host other than the one on
287 which it was compiled. Details are given in the
288 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
289 documentation.
290 </P>
291 <br><a name="SEC6" href="#TOC1">CHECKING BUILD-TIME OPTIONS</a><br>
292 <P>
293 <b>int pcre_config(int <i>what</i>, void *<i>where</i>);</b>
294 </P>
295 <P>
296 The function <b>pcre_config()</b> makes it possible for a PCRE client to
297 discover which optional features have been compiled into the PCRE library. The
298 <a href="pcrebuild.html"><b>pcrebuild</b></a>
299 documentation has more details about these optional features.
300 </P>
301 <P>
302 The first argument for <b>pcre_config()</b> is an integer, specifying which
303 information is required; the second argument is a pointer to a variable into
304 which the information is placed. The following information is available:
305 <pre>
306 PCRE_CONFIG_UTF8
307 </pre>
308 The output is an integer that is set to one if UTF-8 support is available;
309 otherwise it is set to zero.
310 <pre>
311 PCRE_CONFIG_UNICODE_PROPERTIES
312 </pre>
313 The output is an integer that is set to one if support for Unicode character
314 properties is available; otherwise it is set to zero.
315 <pre>
316 PCRE_CONFIG_NEWLINE
317 </pre>
318 The output is an integer whose value specifies the default character sequence
319 that is recognized as meaning "newline". The four values that are supported
320 are: 10 for LF, 13 for CR, 3338 for CRLF, and -1 for ANY. The default should
321 normally be the standard sequence for your operating system.
322 <pre>
323 PCRE_CONFIG_LINK_SIZE
324 </pre>
325 The output is an integer that contains the number of bytes used for internal
326 linkage in compiled regular expressions. The value is 2, 3, or 4. Larger values
327 allow larger regular expressions to be compiled, at the expense of slower
328 matching. The default value of 2 is sufficient for all but the most massive
329 patterns, since it allows the compiled pattern to be up to 64K in size.
330 <pre>
331 PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
332 </pre>
333 The output is an integer that contains the threshold above which the POSIX
334 interface uses <b>malloc()</b> for output vectors. Further details are given in
335 the
336 <a href="pcreposix.html"><b>pcreposix</b></a>
337 documentation.
338 <pre>
339 PCRE_CONFIG_MATCH_LIMIT
340 </pre>
341 The output is an integer that gives the default limit for the number of
342 internal matching function calls in a <b>pcre_exec()</b> execution. Further
343 details are given with <b>pcre_exec()</b> below.
344 <pre>
345 PCRE_CONFIG_MATCH_LIMIT_RECURSION
346 </pre>
347 The output is an integer that gives the default limit for the depth of
348 recursion when calling the internal matching function in a <b>pcre_exec()</b>
349 execution. Further details are given with <b>pcre_exec()</b> below.
350 <pre>
351 PCRE_CONFIG_STACKRECURSE
352 </pre>
353 The output is an integer that is set to one if internal recursion when running
354 <b>pcre_exec()</b> is implemented by recursive function calls that use the stack
355 to remember their state. This is the usual way that PCRE is compiled. The
356 output is zero if PCRE was compiled to use blocks of data on the heap instead
357 of recursive function calls. In this case, <b>pcre_stack_malloc</b> and
358 <b>pcre_stack_free</b> are called to manage memory blocks on the heap, thus
359 avoiding the use of the stack.
360 </P>
361 <br><a name="SEC7" href="#TOC1">COMPILING A PATTERN</a><br>
362 <P>
363 <b>pcre *pcre_compile(const char *<i>pattern</i>, int <i>options</i>,</b>
364 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
365 <b>const unsigned char *<i>tableptr</i>);</b>
366 <b>pcre *pcre_compile2(const char *<i>pattern</i>, int <i>options</i>,</b>
367 <b>int *<i>errorcodeptr</i>,</b>
368 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
369 <b>const unsigned char *<i>tableptr</i>);</b>
370 </P>
371 <P>
372 Either of the functions <b>pcre_compile()</b> or <b>pcre_compile2()</b> can be
373 called to compile a pattern into an internal form. The only difference between
374 the two interfaces is that <b>pcre_compile2()</b> has an additional argument,
375 <i>errorcodeptr</i>, via which a numerical error code can be returned.
376 </P>
377 <P>
378 The pattern is a C string terminated by a binary zero, and is passed in the
379 <i>pattern</i> argument. A pointer to a single block of memory that is obtained
380 via <b>pcre_malloc</b> is returned. This contains the compiled code and related
381 data. The <b>pcre</b> type is defined for the returned block; this is a typedef
382 for a structure whose contents are not externally defined. It is up to the
383 caller to free the memory (via <b>pcre_free</b>) when it is no longer required.
384 </P>
385 <P>
386 Although the compiled code of a PCRE regex is relocatable, that is, it does not
387 depend on memory location, the complete <b>pcre</b> data block is not
388 fully relocatable, because it may contain a copy of the <i>tableptr</i>
389 argument, which is an address (see below).
390 </P>
391 <P>
392 The <i>options</i> argument contains various bit settings that affect the
393 compilation. It should be zero if no options are required. The available
394 options are described below. Some of them, in particular, those that are
395 compatible with Perl, can also be set and unset from within the pattern (see
396 the detailed description in the
397 <a href="pcrepattern.html"><b>pcrepattern</b></a>
398 documentation). For these options, the contents of the <i>options</i> argument
399 specifies their initial settings at the start of compilation and execution. The
400 PCRE_ANCHORED and PCRE_NEWLINE_<i>xxx</i> options can be set at the time of
401 matching as well as at compile time.
402 </P>
403 <P>
404 If <i>errptr</i> is NULL, <b>pcre_compile()</b> returns NULL immediately.
405 Otherwise, if compilation of a pattern fails, <b>pcre_compile()</b> returns
406 NULL, and sets the variable pointed to by <i>errptr</i> to point to a textual
407 error message. This is a static string that is part of the library. You must
408 not try to free it. The offset from the start of the pattern to the character
409 where the error was discovered is placed in the variable pointed to by
410 <i>erroffset</i>, which must not be NULL. If it is, an immediate error is given.
411 </P>
412 <P>
413 If <b>pcre_compile2()</b> is used instead of <b>pcre_compile()</b>, and the
414 <i>errorcodeptr</i> argument is not NULL, a non-zero error code number is
415 returned via this argument in the event of an error. This is in addition to the
416 textual error message. Error codes and messages are listed below.
417 </P>
418 <P>
419 If the final argument, <i>tableptr</i>, is NULL, PCRE uses a default set of
420 character tables that are built when PCRE is compiled, using the default C
421 locale. Otherwise, <i>tableptr</i> must be an address that is the result of a
422 call to <b>pcre_maketables()</b>. This value is stored with the compiled
423 pattern, and used again by <b>pcre_exec()</b>, unless another table pointer is
424 passed to it. For more discussion, see the section on locale support below.
425 </P>
426 <P>
427 This code fragment shows a typical straightforward call to <b>pcre_compile()</b>:
428 <pre>
429 pcre *re;
430 const char *error;
431 int erroffset;
432 re = pcre_compile(
433 "^A.*Z", /* the pattern */
434 0, /* default options */
435 &error, /* for error message */
436 &erroffset, /* for error offset */
437 NULL); /* use default character tables */
438 </pre>
439 The following names for option bits are defined in the <b>pcre.h</b> header
440 file:
441 <pre>
442 PCRE_ANCHORED
443 </pre>
444 If this bit is set, the pattern is forced to be "anchored", that is, it is
445 constrained to match only at the first matching point in the string that is
446 being searched (the "subject string"). This effect can also be achieved by
447 appropriate constructs in the pattern itself, which is the only way to do it in
448 Perl.
449 <pre>
450 PCRE_AUTO_CALLOUT
451 </pre>
452 If this bit is set, <b>pcre_compile()</b> automatically inserts callout items,
453 all with number 255, before each pattern item. For discussion of the callout
454 facility, see the
455 <a href="pcrecallout.html"><b>pcrecallout</b></a>
456 documentation.
457 <pre>
458 PCRE_CASELESS
459 </pre>
460 If this bit is set, letters in the pattern match both upper and lower case
461 letters. It is equivalent to Perl's /i option, and it can be changed within a
462 pattern by a (?i) option setting. In UTF-8 mode, PCRE always understands the
463 concept of case for characters whose values are less than 128, so caseless
464 matching is always possible. For characters with higher values, the concept of
465 case is supported if PCRE is compiled with Unicode property support, but not
466 otherwise. If you want to use caseless matching for characters 128 and above,
467 you must ensure that PCRE is compiled with Unicode property support as well as
468 with UTF-8 support.
469 <pre>
470 PCRE_DOLLAR_ENDONLY
471 </pre>
472 If this bit is set, a dollar metacharacter in the pattern matches only at the
473 end of the subject string. Without this option, a dollar also matches
474 immediately before a newline at the end of the string (but not before any other
475 newlines). The PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is set.
476 There is no equivalent to this option in Perl, and no way to set it within a
477 pattern.
478 <pre>
479 PCRE_DOTALL
480 </pre>
481 If this bit is set, a dot metacharater in the pattern matches all characters,
482 including those that indicate newline. Without it, a dot does not match when
483 the current position is at a newline. This option is equivalent to Perl's /s
484 option, and it can be changed within a pattern by a (?s) option setting. A
485 negative class such as [^a] always matches newline characters, independent of
486 the setting of this option.
487 <pre>
488 PCRE_DUPNAMES
489 </pre>
490 If this bit is set, names used to identify capturing subpatterns need not be
491 unique. This can be helpful for certain types of pattern when it is known that
492 only one instance of the named subpattern can ever be matched. There are more
493 details of named subpatterns below; see also the
494 <a href="pcrepattern.html"><b>pcrepattern</b></a>
495 documentation.
496 <pre>
497 PCRE_EXTENDED
498 </pre>
499 If this bit is set, whitespace data characters in the pattern are totally
500 ignored except when escaped or inside a character class. Whitespace does not
501 include the VT character (code 11). In addition, characters between an
502 unescaped # outside a character class and the next newline, inclusive, are also
503 ignored. This is equivalent to Perl's /x option, and it can be changed within a
504 pattern by a (?x) option setting.
505 </P>
506 <P>
507 This option makes it possible to include comments inside complicated patterns.
508 Note, however, that this applies only to data characters. Whitespace characters
509 may never appear within special character sequences in a pattern, for example
510 within the sequence (?( which introduces a conditional subpattern.
511 <pre>
512 PCRE_EXTRA
513 </pre>
514 This option was invented in order to turn on additional functionality of PCRE
515 that is incompatible with Perl, but it is currently of very little use. When
516 set, any backslash in a pattern that is followed by a letter that has no
517 special meaning causes an error, thus reserving these combinations for future
518 expansion. By default, as in Perl, a backslash followed by a letter with no
519 special meaning is treated as a literal. (Perl can, however, be persuaded to
520 give a warning for this.) There are at present no other features controlled by
521 this option. It can also be set by a (?X) option setting within a pattern.
522 <pre>
523 PCRE_FIRSTLINE
524 </pre>
525 If this option is set, an unanchored pattern is required to match before or at
526 the first newline in the subject string, though the matched text may continue
527 over the newline.
528 <pre>
529 PCRE_MULTILINE
530 </pre>
531 By default, PCRE treats the subject string as consisting of a single line of
532 characters (even if it actually contains newlines). The "start of line"
533 metacharacter (^) matches only at the start of the string, while the "end of
534 line" metacharacter ($) matches only at the end of the string, or before a
535 terminating newline (unless PCRE_DOLLAR_ENDONLY is set). This is the same as
536 Perl.
537 </P>
538 <P>
539 When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs
540 match immediately following or immediately before internal newlines in the
541 subject string, respectively, as well as at the very start and end. This is
542 equivalent to Perl's /m option, and it can be changed within a pattern by a
543 (?m) option setting. If there are no newlines in a subject string, or no
544 occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no effect.
545 <pre>
546 PCRE_NEWLINE_CR
547 PCRE_NEWLINE_LF
548 PCRE_NEWLINE_CRLF
549 PCRE_NEWLINE_ANY
550 </pre>
551 These options override the default newline definition that was chosen when PCRE
552 was built. Setting the first or the second specifies that a newline is
553 indicated by a single character (CR or LF, respectively). Setting
554 PCRE_NEWLINE_CRLF specifies that a newline is indicated by the two-character
555 CRLF sequence. Setting PCRE_NEWLINE_ANY specifies that any Unicode newline
556 sequence should be recognized. The Unicode newline sequences are the three just
557 mentioned, plus the single characters VT (vertical tab, U+000B), FF (formfeed,
558 U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS
559 (paragraph separator, U+2029). The last two are recognized only in UTF-8 mode.
560 </P>
561 <P>
562 The newline setting in the options word uses three bits that are treated
563 as a number, giving eight possibilities. Currently only five are used (default
564 plus the four values above). This means that if you set more than one newline
565 option, the combination may or may not be sensible. For example,
566 PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to PCRE_NEWLINE_CRLF, but
567 other combinations yield unused numbers and cause an error.
568 </P>
569 <P>
570 The only time that a line break is specially recognized when compiling a
571 pattern is if PCRE_EXTENDED is set, and an unescaped # outside a character
572 class is encountered. This indicates a comment that lasts until after the next
573 line break sequence. In other circumstances, line break sequences are treated
574 as literal data, except that in PCRE_EXTENDED mode, both CR and LF are treated
575 as whitespace characters and are therefore ignored.
576 </P>
577 <P>
578 The newline option that is set at compile time becomes the default that is used
579 for <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b>, but it can be overridden.
580 <pre>
581 PCRE_NO_AUTO_CAPTURE
582 </pre>
583 If this option is set, it disables the use of numbered capturing parentheses in
584 the pattern. Any opening parenthesis that is not followed by ? behaves as if it
585 were followed by ?: but named parentheses can still be used for capturing (and
586 they acquire numbers in the usual way). There is no equivalent of this option
587 in Perl.
588 <pre>
589 PCRE_UNGREEDY
590 </pre>
591 This option inverts the "greediness" of the quantifiers so that they are not
592 greedy by default, but become greedy if followed by "?". It is not compatible
593 with Perl. It can also be set by a (?U) option setting within the pattern.
594 <pre>
595 PCRE_UTF8
596 </pre>
597 This option causes PCRE to regard both the pattern and the subject as strings
598 of UTF-8 characters instead of single-byte character strings. However, it is
599 available only when PCRE is built to include UTF-8 support. If not, the use
600 of this option provokes an error. Details of how this option changes the
601 behaviour of PCRE are given in the
602 <a href="pcre.html#utf8support">section on UTF-8 support</a>
603 in the main
604 <a href="pcre.html"><b>pcre</b></a>
605 page.
606 <pre>
607 PCRE_NO_UTF8_CHECK
608 </pre>
609 When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
610 automatically checked. If an invalid UTF-8 sequence of bytes is found,
611 <b>pcre_compile()</b> returns an error. If you already know that your pattern is
612 valid, and you want to skip this check for performance reasons, you can set the
613 PCRE_NO_UTF8_CHECK option. When it is set, the effect of passing an invalid
614 UTF-8 string as a pattern is undefined. It may cause your program to crash.
615 Note that this option can also be passed to <b>pcre_exec()</b> and
616 <b>pcre_dfa_exec()</b>, to suppress the UTF-8 validity checking of subject
617 strings.
618 </P>
619 <br><a name="SEC8" href="#TOC1">COMPILATION ERROR CODES</a><br>
620 <P>
621 The following table lists the error codes than may be returned by
622 <b>pcre_compile2()</b>, along with the error messages that may be returned by
623 both compiling functions. As PCRE has developed, some error codes have fallen
624 out of use. To avoid confusion, they have not been re-used.
625 <pre>
626 0 no error
627 1 \ at end of pattern
628 2 \c at end of pattern
629 3 unrecognized character follows \
630 4 numbers out of order in {} quantifier
631 5 number too big in {} quantifier
632 6 missing terminating ] for character class
633 7 invalid escape sequence in character class
634 8 range out of order in character class
635 9 nothing to repeat
636 10 [this code is not in use]
637 11 internal error: unexpected repeat
638 12 unrecognized character after (?
639 13 POSIX named classes are supported only within a class
640 14 missing )
641 15 reference to non-existent subpattern
642 16 erroffset passed as NULL
643 17 unknown option bit(s) set
644 18 missing ) after comment
645 19 [this code is not in use]
646 20 regular expression too large
647 21 failed to get memory
648 22 unmatched parentheses
649 23 internal error: code overflow
650 24 unrecognized character after (?&#60;
651 25 lookbehind assertion is not fixed length
652 26 malformed number or name after (?(
653 27 conditional group contains more than two branches
654 28 assertion expected after (?(
655 29 (?R or (?digits must be followed by )
656 30 unknown POSIX class name
657 31 POSIX collating elements are not supported
658 32 this version of PCRE is not compiled with PCRE_UTF8 support
659 33 [this code is not in use]
660 34 character value in \x{...} sequence is too large
661 35 invalid condition (?(0)
662 36 \C not allowed in lookbehind assertion
663 37 PCRE does not support \L, \l, \N, \U, or \u
664 38 number after (?C is &#62; 255
665 39 closing ) for (?C expected
666 40 recursive call could loop indefinitely
667 41 unrecognized character after (?P
668 42 syntax error in subpattern name (missing terminator)
669 43 two named subpatterns have the same name
670 44 invalid UTF-8 string
671 45 support for \P, \p, and \X has not been compiled
672 46 malformed \P or \p sequence
673 47 unknown property name after \P or \p
674 48 subpattern name is too long (maximum 32 characters)
675 49 too many named subpatterns (maximum 10,000)
676 50 repeated subpattern is too long
677 51 octal value is greater than \377 (not in UTF-8 mode)
678 52 internal error: overran compiling workspace
679 53 internal error: previously-checked referenced subpattern not found
680 54 DEFINE group contains more than one branch
681 55 repeating a DEFINE group is not allowed
682 56 inconsistent NEWLINE options"
683 </PRE>
684 </P>
685 <br><a name="SEC9" href="#TOC1">STUDYING A PATTERN</a><br>
686 <P>
687 <b>pcre_extra *pcre_study(const pcre *<i>code</i>, int <i>options</i></b>
688 <b>const char **<i>errptr</i>);</b>
689 </P>
690 <P>
691 If a compiled pattern is going to be used several times, it is worth spending
692 more time analyzing it in order to speed up the time taken for matching. The
693 function <b>pcre_study()</b> takes a pointer to a compiled pattern as its first
694 argument. If studying the pattern produces additional information that will
695 help speed up matching, <b>pcre_study()</b> returns a pointer to a
696 <b>pcre_extra</b> block, in which the <i>study_data</i> field points to the
697 results of the study.
698 </P>
699 <P>
700 The returned value from <b>pcre_study()</b> can be passed directly to
701 <b>pcre_exec()</b>. However, a <b>pcre_extra</b> block also contains other
702 fields that can be set by the caller before the block is passed; these are
703 described
704 <a href="#extradata">below</a>
705 in the section on matching a pattern.
706 </P>
707 <P>
708 If studying the pattern does not produce any additional information
709 <b>pcre_study()</b> returns NULL. In that circumstance, if the calling program
710 wants to pass any of the other fields to <b>pcre_exec()</b>, it must set up its
711 own <b>pcre_extra</b> block.
712 </P>
713 <P>
714 The second argument of <b>pcre_study()</b> contains option bits. At present, no
715 options are defined, and this argument should always be zero.
716 </P>
717 <P>
718 The third argument for <b>pcre_study()</b> is a pointer for an error message. If
719 studying succeeds (even if no data is returned), the variable it points to is
720 set to NULL. Otherwise it is set to point to a textual error message. This is a
721 static string that is part of the library. You must not try to free it. You
722 should test the error pointer for NULL after calling <b>pcre_study()</b>, to be
723 sure that it has run successfully.
724 </P>
725 <P>
726 This is a typical call to <b>pcre_study</b>():
727 <pre>
728 pcre_extra *pe;
729 pe = pcre_study(
730 re, /* result of pcre_compile() */
731 0, /* no options exist */
732 &error); /* set to NULL or points to a message */
733 </pre>
734 At present, studying a pattern is useful only for non-anchored patterns that do
735 not have a single fixed starting character. A bitmap of possible starting
736 bytes is created.
737 <a name="localesupport"></a></P>
738 <br><a name="SEC10" href="#TOC1">LOCALE SUPPORT</a><br>
739 <P>
740 PCRE handles caseless matching, and determines whether characters are letters,
741 digits, or whatever, by reference to a set of tables, indexed by character
742 value. When running in UTF-8 mode, this applies only to characters with codes
743 less than 128. Higher-valued codes never match escapes such as \w or \d, but
744 can be tested with \p if PCRE is built with Unicode character property
745 support. The use of locales with Unicode is discouraged. If you are handling
746 characters with codes greater than 128, you should either use UTF-8 and
747 Unicode, or use locales, but not try to mix the two.
748 </P>
749 <P>
750 PCRE contains an internal set of tables that are used when the final argument
751 of <b>pcre_compile()</b> is NULL. These are sufficient for many applications.
752 Normally, the internal tables recognize only ASCII characters. However, when
753 PCRE is built, it is possible to cause the internal tables to be rebuilt in the
754 default "C" locale of the local system, which may cause them to be different.
755 </P>
756 <P>
757 The internal tables can always be overridden by tables supplied by the
758 application that calls PCRE. These may be created in a different locale from
759 the default. As more and more applications change to using Unicode, the need
760 for this locale support is expected to die away.
761 </P>
762 <P>
763 External tables are built by calling the <b>pcre_maketables()</b> function,
764 which has no arguments, in the relevant locale. The result can then be passed
765 to <b>pcre_compile()</b> or <b>pcre_exec()</b> as often as necessary. For
766 example, to build and use tables that are appropriate for the French locale
767 (where accented characters with values greater than 128 are treated as letters),
768 the following code could be used:
769 <pre>
770 setlocale(LC_CTYPE, "fr_FR");
771 tables = pcre_maketables();
772 re = pcre_compile(..., tables);
773 </pre>
774 The locale name "fr_FR" is used on Linux and other Unix-like systems; if you
775 are using Windows, the name for the French locale is "french".
776 </P>
777 <P>
778 When <b>pcre_maketables()</b> runs, the tables are built in memory that is
779 obtained via <b>pcre_malloc</b>. It is the caller's responsibility to ensure
780 that the memory containing the tables remains available for as long as it is
781 needed.
782 </P>
783 <P>
784 The pointer that is passed to <b>pcre_compile()</b> is saved with the compiled
785 pattern, and the same tables are used via this pointer by <b>pcre_study()</b>
786 and normally also by <b>pcre_exec()</b>. Thus, by default, for any single
787 pattern, compilation, studying and matching all happen in the same locale, but
788 different patterns can be compiled in different locales.
789 </P>
790 <P>
791 It is possible to pass a table pointer or NULL (indicating the use of the
792 internal tables) to <b>pcre_exec()</b>. Although not intended for this purpose,
793 this facility could be used to match a pattern in a different locale from the
794 one in which it was compiled. Passing table pointers at run time is discussed
795 below in the section on matching a pattern.
796 </P>
797 <br><a name="SEC11" href="#TOC1">INFORMATION ABOUT A PATTERN</a><br>
798 <P>
799 <b>int pcre_fullinfo(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
800 <b>int <i>what</i>, void *<i>where</i>);</b>
801 </P>
802 <P>
803 The <b>pcre_fullinfo()</b> function returns information about a compiled
804 pattern. It replaces the obsolete <b>pcre_info()</b> function, which is
805 nevertheless retained for backwards compability (and is documented below).
806 </P>
807 <P>
808 The first argument for <b>pcre_fullinfo()</b> is a pointer to the compiled
809 pattern. The second argument is the result of <b>pcre_study()</b>, or NULL if
810 the pattern was not studied. The third argument specifies which piece of
811 information is required, and the fourth argument is a pointer to a variable
812 to receive the data. The yield of the function is zero for success, or one of
813 the following negative numbers:
814 <pre>
815 PCRE_ERROR_NULL the argument <i>code</i> was NULL
816 the argument <i>where</i> was NULL
817 PCRE_ERROR_BADMAGIC the "magic number" was not found
818 PCRE_ERROR_BADOPTION the value of <i>what</i> was invalid
819 </pre>
820 The "magic number" is placed at the start of each compiled pattern as an simple
821 check against passing an arbitrary memory pointer. Here is a typical call of
822 <b>pcre_fullinfo()</b>, to obtain the length of the compiled pattern:
823 <pre>
824 int rc;
825 size_t length;
826 rc = pcre_fullinfo(
827 re, /* result of pcre_compile() */
828 pe, /* result of pcre_study(), or NULL */
829 PCRE_INFO_SIZE, /* what is required */
830 &length); /* where to put the data */
831 </pre>
832 The possible values for the third argument are defined in <b>pcre.h</b>, and are
833 as follows:
834 <pre>
835 PCRE_INFO_BACKREFMAX
836 </pre>
837 Return the number of the highest back reference in the pattern. The fourth
838 argument should point to an <b>int</b> variable. Zero is returned if there are
839 no back references.
840 <pre>
841 PCRE_INFO_CAPTURECOUNT
842 </pre>
843 Return the number of capturing subpatterns in the pattern. The fourth argument
844 should point to an <b>int</b> variable.
845 <pre>
846 PCRE_INFO_DEFAULT_TABLES
847 </pre>
848 Return a pointer to the internal default character tables within PCRE. The
849 fourth argument should point to an <b>unsigned char *</b> variable. This
850 information call is provided for internal use by the <b>pcre_study()</b>
851 function. External callers can cause PCRE to use its internal tables by passing
852 a NULL table pointer.
853 <pre>
854 PCRE_INFO_FIRSTBYTE
855 </pre>
856 Return information about the first byte of any matched string, for a
857 non-anchored pattern. The fourth argument should point to an <b>int</b>
858 variable. (This option used to be called PCRE_INFO_FIRSTCHAR; the old name is
859 still recognized for backwards compatibility.)
860 </P>
861 <P>
862 If there is a fixed first byte, for example, from a pattern such as
863 (cat|cow|coyote), its value is returned. Otherwise, if either
864 <br>
865 <br>
866 (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
867 starts with "^", or
868 <br>
869 <br>
870 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
871 (if it were set, the pattern would be anchored),
872 <br>
873 <br>
874 -1 is returned, indicating that the pattern matches only at the start of a
875 subject string or after any newline within the string. Otherwise -2 is
876 returned. For anchored patterns, -2 is returned.
877 <pre>
878 PCRE_INFO_FIRSTTABLE
879 </pre>
880 If the pattern was studied, and this resulted in the construction of a 256-bit
881 table indicating a fixed set of bytes for the first byte in any matching
882 string, a pointer to the table is returned. Otherwise NULL is returned. The
883 fourth argument should point to an <b>unsigned char *</b> variable.
884 <pre>
885 PCRE_INFO_LASTLITERAL
886 </pre>
887 Return the value of the rightmost literal byte that must exist in any matched
888 string, other than at its start, if such a byte has been recorded. The fourth
889 argument should point to an <b>int</b> variable. If there is no such byte, -1 is
890 returned. For anchored patterns, a last literal byte is recorded only if it
891 follows something of variable length. For example, for the pattern
892 /^a\d+z\d+/ the returned value is "z", but for /^a\dz\d/ the returned value
893 is -1.
894 <pre>
895 PCRE_INFO_NAMECOUNT
896 PCRE_INFO_NAMEENTRYSIZE
897 PCRE_INFO_NAMETABLE
898 </pre>
899 PCRE supports the use of named as well as numbered capturing parentheses. The
900 names are just an additional way of identifying the parentheses, which still
901 acquire numbers. Several convenience functions such as
902 <b>pcre_get_named_substring()</b> are provided for extracting captured
903 substrings by name. It is also possible to extract the data directly, by first
904 converting the name to a number in order to access the correct pointers in the
905 output vector (described with <b>pcre_exec()</b> below). To do the conversion,
906 you need to use the name-to-number map, which is described by these three
907 values.
908 </P>
909 <P>
910 The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives
911 the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each
912 entry; both of these return an <b>int</b> value. The entry size depends on the
913 length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first
914 entry of the table (a pointer to <b>char</b>). The first two bytes of each entry
915 are the number of the capturing parenthesis, most significant byte first. The
916 rest of the entry is the corresponding name, zero terminated. The names are in
917 alphabetical order. When PCRE_DUPNAMES is set, duplicate names are in order of
918 their parentheses numbers. For example, consider the following pattern (assume
919 PCRE_EXTENDED is set, so white space - including newlines - is ignored):
920 <pre>
921 (?&#60;date&#62; (?&#60;year&#62;(\d\d)?\d\d) - (?&#60;month&#62;\d\d) - (?&#60;day&#62;\d\d) )
922 </pre>
923 There are four named subpatterns, so the table has four entries, and each entry
924 in the table is eight bytes long. The table is as follows, with non-printing
925 bytes shows in hexadecimal, and undefined bytes shown as ??:
926 <pre>
927 00 01 d a t e 00 ??
928 00 05 d a y 00 ?? ??
929 00 04 m o n t h 00
930 00 02 y e a r 00 ??
931 </pre>
932 When writing code to extract data from named subpatterns using the
933 name-to-number map, remember that the length of the entries is likely to be
934 different for each compiled pattern.
935 <pre>
936 PCRE_INFO_OPTIONS
937 </pre>
938 Return a copy of the options with which the pattern was compiled. The fourth
939 argument should point to an <b>unsigned long int</b> variable. These option bits
940 are those specified in the call to <b>pcre_compile()</b>, modified by any
941 top-level option settings within the pattern itself.
942 </P>
943 <P>
944 A pattern is automatically anchored by PCRE if all of its top-level
945 alternatives begin with one of the following:
946 <pre>
947 ^ unless PCRE_MULTILINE is set
948 \A always
949 \G always
950 .* if PCRE_DOTALL is set and there are no back references to the subpattern in which .* appears
951 </pre>
952 For such patterns, the PCRE_ANCHORED bit is set in the options returned by
953 <b>pcre_fullinfo()</b>.
954 <pre>
955 PCRE_INFO_SIZE
956 </pre>
957 Return the size of the compiled pattern, that is, the value that was passed as
958 the argument to <b>pcre_malloc()</b> when PCRE was getting memory in which to
959 place the compiled data. The fourth argument should point to a <b>size_t</b>
960 variable.
961 <pre>
962 PCRE_INFO_STUDYSIZE
963 </pre>
964 Return the size of the data block pointed to by the <i>study_data</i> field in
965 a <b>pcre_extra</b> block. That is, it is the value that was passed to
966 <b>pcre_malloc()</b> when PCRE was getting memory into which to place the data
967 created by <b>pcre_study()</b>. The fourth argument should point to a
968 <b>size_t</b> variable.
969 </P>
970 <br><a name="SEC12" href="#TOC1">OBSOLETE INFO FUNCTION</a><br>
971 <P>
972 <b>int pcre_info(const pcre *<i>code</i>, int *<i>optptr</i>, int</b>
973 <b>*<i>firstcharptr</i>);</b>
974 </P>
975 <P>
976 The <b>pcre_info()</b> function is now obsolete because its interface is too
977 restrictive to return all the available data about a compiled pattern. New
978 programs should use <b>pcre_fullinfo()</b> instead. The yield of
979 <b>pcre_info()</b> is the number of capturing subpatterns, or one of the
980 following negative numbers:
981 <pre>
982 PCRE_ERROR_NULL the argument <i>code</i> was NULL
983 PCRE_ERROR_BADMAGIC the "magic number" was not found
984 </pre>
985 If the <i>optptr</i> argument is not NULL, a copy of the options with which the
986 pattern was compiled is placed in the integer it points to (see
987 PCRE_INFO_OPTIONS above).
988 </P>
989 <P>
990 If the pattern is not anchored and the <i>firstcharptr</i> argument is not NULL,
991 it is used to pass back information about the first character of any matched
992 string (see PCRE_INFO_FIRSTBYTE above).
993 </P>
994 <br><a name="SEC13" href="#TOC1">REFERENCE COUNTS</a><br>
995 <P>
996 <b>int pcre_refcount(pcre *<i>code</i>, int <i>adjust</i>);</b>
997 </P>
998 <P>
999 The <b>pcre_refcount()</b> function is used to maintain a reference count in the
1000 data block that contains a compiled pattern. It is provided for the benefit of
1001 applications that operate in an object-oriented manner, where different parts
1002 of the application may be using the same compiled pattern, but you want to free
1003 the block when they are all done.
1004 </P>
1005 <P>
1006 When a pattern is compiled, the reference count field is initialized to zero.
1007 It is changed only by calling this function, whose action is to add the
1008 <i>adjust</i> value (which may be positive or negative) to it. The yield of the
1009 function is the new value. However, the value of the count is constrained to
1010 lie between 0 and 65535, inclusive. If the new value is outside these limits,
1011 it is forced to the appropriate limit value.
1012 </P>
1013 <P>
1014 Except when it is zero, the reference count is not correctly preserved if a
1015 pattern is compiled on one host and then transferred to a host whose byte-order
1016 is different. (This seems a highly unlikely scenario.)
1017 </P>
1018 <br><a name="SEC14" href="#TOC1">MATCHING A PATTERN: THE TRADITIONAL FUNCTION</a><br>
1019 <P>
1020 <b>int pcre_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
1021 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
1022 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>);</b>
1023 </P>
1024 <P>
1025 The function <b>pcre_exec()</b> is called to match a subject string against a
1026 compiled pattern, which is passed in the <i>code</i> argument. If the
1027 pattern has been studied, the result of the study should be passed in the
1028 <i>extra</i> argument. This function is the main matching facility of the
1029 library, and it operates in a Perl-like manner. For specialist use there is
1030 also an alternative matching function, which is described
1031 <a href="#dfamatch">below</a>
1032 in the section about the <b>pcre_dfa_exec()</b> function.
1033 </P>
1034 <P>
1035 In most applications, the pattern will have been compiled (and optionally
1036 studied) in the same process that calls <b>pcre_exec()</b>. However, it is
1037 possible to save compiled patterns and study data, and then use them later
1038 in different processes, possibly even on different hosts. For a discussion
1039 about this, see the
1040 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
1041 documentation.
1042 </P>
1043 <P>
1044 Here is an example of a simple call to <b>pcre_exec()</b>:
1045 <pre>
1046 int rc;
1047 int ovector[30];
1048 rc = pcre_exec(
1049 re, /* result of pcre_compile() */
1050 NULL, /* we didn't study the pattern */
1051 "some string", /* the subject string */
1052 11, /* the length of the subject string */
1053 0, /* start at offset 0 in the subject */
1054 0, /* default options */
1055 ovector, /* vector of integers for substring information */
1056 30); /* number of elements (NOT size in bytes) */
1057 <a name="extradata"></a></PRE>
1058 </P>
1059 <br><b>
1060 Extra data for <b>pcre_exec()</b>
1061 </b><br>
1062 <P>
1063 If the <i>extra</i> argument is not NULL, it must point to a <b>pcre_extra</b>
1064 data block. The <b>pcre_study()</b> function returns such a block (when it
1065 doesn't return NULL), but you can also create one for yourself, and pass
1066 additional information in it. The <b>pcre_extra</b> block contains the following
1067 fields (not necessarily in this order):
1068 <pre>
1069 unsigned long int <i>flags</i>;
1070 void *<i>study_data</i>;
1071 unsigned long int <i>match_limit</i>;
1072 unsigned long int <i>match_limit_recursion</i>;
1073 void *<i>callout_data</i>;
1074 const unsigned char *<i>tables</i>;
1075 </pre>
1076 The <i>flags</i> field is a bitmap that specifies which of the other fields
1077 are set. The flag bits are:
1078 <pre>
1079 PCRE_EXTRA_STUDY_DATA
1080 PCRE_EXTRA_MATCH_LIMIT
1081 PCRE_EXTRA_MATCH_LIMIT_RECURSION
1082 PCRE_EXTRA_CALLOUT_DATA
1083 PCRE_EXTRA_TABLES
1084 </pre>
1085 Other flag bits should be set to zero. The <i>study_data</i> field is set in the
1086 <b>pcre_extra</b> block that is returned by <b>pcre_study()</b>, together with
1087 the appropriate flag bit. You should not set this yourself, but you may add to
1088 the block by setting the other fields and their corresponding flag bits.
1089 </P>
1090 <P>
1091 The <i>match_limit</i> field provides a means of preventing PCRE from using up a
1092 vast amount of resources when running patterns that are not going to match,
1093 but which have a very large number of possibilities in their search trees. The
1094 classic example is the use of nested unlimited repeats.
1095 </P>
1096 <P>
1097 Internally, PCRE uses a function called <b>match()</b> which it calls repeatedly
1098 (sometimes recursively). The limit set by <i>match_limit</i> is imposed on the
1099 number of times this function is called during a match, which has the effect of
1100 limiting the amount of backtracking that can take place. For patterns that are
1101 not anchored, the count restarts from zero for each position in the subject
1102 string.
1103 </P>
1104 <P>
1105 The default value for the limit can be set when PCRE is built; the default
1106 default is 10 million, which handles all but the most extreme cases. You can
1107 override the default by suppling <b>pcre_exec()</b> with a <b>pcre_extra</b>
1108 block in which <i>match_limit</i> is set, and PCRE_EXTRA_MATCH_LIMIT is set in
1109 the <i>flags</i> field. If the limit is exceeded, <b>pcre_exec()</b> returns
1110 PCRE_ERROR_MATCHLIMIT.
1111 </P>
1112 <P>
1113 The <i>match_limit_recursion</i> field is similar to <i>match_limit</i>, but
1114 instead of limiting the total number of times that <b>match()</b> is called, it
1115 limits the depth of recursion. The recursion depth is a smaller number than the
1116 total number of calls, because not all calls to <b>match()</b> are recursive.
1117 This limit is of use only if it is set smaller than <i>match_limit</i>.
1118 </P>
1119 <P>
1120 Limiting the recursion depth limits the amount of stack that can be used, or,
1121 when PCRE has been compiled to use memory on the heap instead of the stack, the
1122 amount of heap memory that can be used.
1123 </P>
1124 <P>
1125 The default value for <i>match_limit_recursion</i> can be set when PCRE is
1126 built; the default default is the same value as the default for
1127 <i>match_limit</i>. You can override the default by suppling <b>pcre_exec()</b>
1128 with a <b>pcre_extra</b> block in which <i>match_limit_recursion</i> is set, and
1129 PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the <i>flags</i> field. If the limit
1130 is exceeded, <b>pcre_exec()</b> returns PCRE_ERROR_RECURSIONLIMIT.
1131 </P>
1132 <P>
1133 The <i>pcre_callout</i> field is used in conjunction with the "callout" feature,
1134 which is described in the
1135 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1136 documentation.
1137 </P>
1138 <P>
1139 The <i>tables</i> field is used to pass a character tables pointer to
1140 <b>pcre_exec()</b>; this overrides the value that is stored with the compiled
1141 pattern. A non-NULL value is stored with the compiled pattern only if custom
1142 tables were supplied to <b>pcre_compile()</b> via its <i>tableptr</i> argument.
1143 If NULL is passed to <b>pcre_exec()</b> using this mechanism, it forces PCRE's
1144 internal tables to be used. This facility is helpful when re-using patterns
1145 that have been saved after compiling with an external set of tables, because
1146 the external tables might be at a different address when <b>pcre_exec()</b> is
1147 called. See the
1148 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
1149 documentation for a discussion of saving compiled patterns for later use.
1150 </P>
1151 <br><b>
1152 Option bits for <b>pcre_exec()</b>
1153 </b><br>
1154 <P>
1155 The unused bits of the <i>options</i> argument for <b>pcre_exec()</b> must be
1156 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_<i>xxx</i>,
1157 PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK and PCRE_PARTIAL.
1158 <pre>
1159 PCRE_ANCHORED
1160 </pre>
1161 The PCRE_ANCHORED option limits <b>pcre_exec()</b> to matching at the first
1162 matching position. If a pattern was compiled with PCRE_ANCHORED, or turned out
1163 to be anchored by virtue of its contents, it cannot be made unachored at
1164 matching time.
1165 <pre>
1166 PCRE_NEWLINE_CR
1167 PCRE_NEWLINE_LF
1168 PCRE_NEWLINE_CRLF
1169 PCRE_NEWLINE_ANY
1170 </pre>
1171 These options override the newline definition that was chosen or defaulted when
1172 the pattern was compiled. For details, see the description of
1173 <b>pcre_compile()</b> above. During matching, the newline choice affects the
1174 behaviour of the dot, circumflex, and dollar metacharacters. It may also alter
1175 the way the match position is advanced after a match failure for an unanchored
1176 pattern. When PCRE_NEWLINE_CRLF or PCRE_NEWLINE_ANY is set, and a match attempt
1177 fails when the current position is at a CRLF sequence, the match position is
1178 advanced by two characters instead of one, in other words, to after the CRLF.
1179 <pre>
1180 PCRE_NOTBOL
1181 </pre>
1182 This option specifies that first character of the subject string is not the
1183 beginning of a line, so the circumflex metacharacter should not match before
1184 it. Setting this without PCRE_MULTILINE (at compile time) causes circumflex
1185 never to match. This option affects only the behaviour of the circumflex
1186 metacharacter. It does not affect \A.
1187 <pre>
1188 PCRE_NOTEOL
1189 </pre>
1190 This option specifies that the end of the subject string is not the end of a
1191 line, so the dollar metacharacter should not match it nor (except in multiline
1192 mode) a newline immediately before it. Setting this without PCRE_MULTILINE (at
1193 compile time) causes dollar never to match. This option affects only the
1194 behaviour of the dollar metacharacter. It does not affect \Z or \z.
1195 <pre>
1196 PCRE_NOTEMPTY
1197 </pre>
1198 An empty string is not considered to be a valid match if this option is set. If
1199 there are alternatives in the pattern, they are tried. If all the alternatives
1200 match the empty string, the entire match fails. For example, if the pattern
1201 <pre>
1202 a?b?
1203 </pre>
1204 is applied to a string not beginning with "a" or "b", it matches the empty
1205 string at the start of the subject. With PCRE_NOTEMPTY set, this match is not
1206 valid, so PCRE searches further into the string for occurrences of "a" or "b".
1207 </P>
1208 <P>
1209 Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a special case
1210 of a pattern match of the empty string within its <b>split()</b> function, and
1211 when using the /g modifier. It is possible to emulate Perl's behaviour after
1212 matching a null string by first trying the match again at the same offset with
1213 PCRE_NOTEMPTY and PCRE_ANCHORED, and then if that fails by advancing the
1214 starting offset (see below) and trying an ordinary match again. There is some
1215 code that demonstrates how to do this in the <i>pcredemo.c</i> sample program.
1216 <pre>
1217 PCRE_NO_UTF8_CHECK
1218 </pre>
1219 When PCRE_UTF8 is set at compile time, the validity of the subject as a UTF-8
1220 string is automatically checked when <b>pcre_exec()</b> is subsequently called.
1221 The value of <i>startoffset</i> is also checked to ensure that it points to the
1222 start of a UTF-8 character. If an invalid UTF-8 sequence of bytes is found,
1223 <b>pcre_exec()</b> returns the error PCRE_ERROR_BADUTF8. If <i>startoffset</i>
1224 contains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
1225 </P>
1226 <P>
1227 If you already know that your subject is valid, and you want to skip these
1228 checks for performance reasons, you can set the PCRE_NO_UTF8_CHECK option when
1229 calling <b>pcre_exec()</b>. You might want to do this for the second and
1230 subsequent calls to <b>pcre_exec()</b> if you are making repeated calls to find
1231 all the matches in a single subject string. However, you should be sure that
1232 the value of <i>startoffset</i> points to the start of a UTF-8 character. When
1233 PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid UTF-8 string as a
1234 subject, or a value of <i>startoffset</i> that does not point to the start of a
1235 UTF-8 character, is undefined. Your program may crash.
1236 <pre>
1237 PCRE_PARTIAL
1238 </pre>
1239 This option turns on the partial matching feature. If the subject string fails
1240 to match the pattern, but at some point during the matching process the end of
1241 the subject was reached (that is, the subject partially matches the pattern and
1242 the failure to match occurred only because there were not enough subject
1243 characters), <b>pcre_exec()</b> returns PCRE_ERROR_PARTIAL instead of
1244 PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is used, there are restrictions on what
1245 may appear in the pattern. These are discussed in the
1246 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1247 documentation.
1248 </P>
1249 <br><b>
1250 The string to be matched by <b>pcre_exec()</b>
1251 </b><br>
1252 <P>
1253 The subject string is passed to <b>pcre_exec()</b> as a pointer in
1254 <i>subject</i>, a length in <i>length</i>, and a starting byte offset in
1255 <i>startoffset</i>. In UTF-8 mode, the byte offset must point to the start of a
1256 UTF-8 character. Unlike the pattern string, the subject may contain binary zero
1257 bytes. When the starting offset is zero, the search for a match starts at the
1258 beginning of the subject, and this is by far the most common case.
1259 </P>
1260 <P>
1261 A non-zero starting offset is useful when searching for another match in the
1262 same subject by calling <b>pcre_exec()</b> again after a previous success.
1263 Setting <i>startoffset</i> differs from just passing over a shortened string and
1264 setting PCRE_NOTBOL in the case of a pattern that begins with any kind of
1265 lookbehind. For example, consider the pattern
1266 <pre>
1267 \Biss\B
1268 </pre>
1269 which finds occurrences of "iss" in the middle of words. (\B matches only if
1270 the current position in the subject is not a word boundary.) When applied to
1271 the string "Mississipi" the first call to <b>pcre_exec()</b> finds the first
1272 occurrence. If <b>pcre_exec()</b> is called again with just the remainder of the
1273 subject, namely "issipi", it does not match, because \B is always false at the
1274 start of the subject, which is deemed to be a word boundary. However, if
1275 <b>pcre_exec()</b> is passed the entire string again, but with <i>startoffset</i>
1276 set to 4, it finds the second occurrence of "iss" because it is able to look
1277 behind the starting point to discover that it is preceded by a letter.
1278 </P>
1279 <P>
1280 If a non-zero starting offset is passed when the pattern is anchored, one
1281 attempt to match at the given offset is made. This can only succeed if the
1282 pattern does not require the match to be at the start of the subject.
1283 </P>
1284 <br><b>
1285 How <b>pcre_exec()</b> returns captured substrings
1286 </b><br>
1287 <P>
1288 In general, a pattern matches a certain portion of the subject, and in
1289 addition, further substrings from the subject may be picked out by parts of the
1290 pattern. Following the usage in Jeffrey Friedl's book, this is called
1291 "capturing" in what follows, and the phrase "capturing subpattern" is used for
1292 a fragment of a pattern that picks out a substring. PCRE supports several other
1293 kinds of parenthesized subpattern that do not cause substrings to be captured.
1294 </P>
1295 <P>
1296 Captured substrings are returned to the caller via a vector of integer offsets
1297 whose address is passed in <i>ovector</i>. The number of elements in the vector
1298 is passed in <i>ovecsize</i>, which must be a non-negative number. <b>Note</b>:
1299 this argument is NOT the size of <i>ovector</i> in bytes.
1300 </P>
1301 <P>
1302 The first two-thirds of the vector is used to pass back captured substrings,
1303 each substring using a pair of integers. The remaining third of the vector is
1304 used as workspace by <b>pcre_exec()</b> while matching capturing subpatterns,
1305 and is not available for passing back information. The length passed in
1306 <i>ovecsize</i> should always be a multiple of three. If it is not, it is
1307 rounded down.
1308 </P>
1309 <P>
1310 When a match is successful, information about captured substrings is returned
1311 in pairs of integers, starting at the beginning of <i>ovector</i>, and
1312 continuing up to two-thirds of its length at the most. The first element of a
1313 pair is set to the offset of the first character in a substring, and the second
1314 is set to the offset of the first character after the end of a substring. The
1315 first pair, <i>ovector[0]</i> and <i>ovector[1]</i>, identify the portion of the
1316 subject string matched by the entire pattern. The next pair is used for the
1317 first capturing subpattern, and so on. The value returned by <b>pcre_exec()</b>
1318 is one more than the highest numbered pair that has been set. For example, if
1319 two substrings have been captured, the returned value is 3. If there are no
1320 capturing subpatterns, the return value from a successful match is 1,
1321 indicating that just the first pair of offsets has been set.
1322 </P>
1323 <P>
1324 If a capturing subpattern is matched repeatedly, it is the last portion of the
1325 string that it matched that is returned.
1326 </P>
1327 <P>
1328 If the vector is too small to hold all the captured substring offsets, it is
1329 used as far as possible (up to two-thirds of its length), and the function
1330 returns a value of zero. In particular, if the substring offsets are not of
1331 interest, <b>pcre_exec()</b> may be called with <i>ovector</i> passed as NULL and
1332 <i>ovecsize</i> as zero. However, if the pattern contains back references and
1333 the <i>ovector</i> is not big enough to remember the related substrings, PCRE
1334 has to get additional memory for use during matching. Thus it is usually
1335 advisable to supply an <i>ovector</i>.
1336 </P>
1337 <P>
1338 The <b>pcre_info()</b> function can be used to find out how many capturing
1339 subpatterns there are in a compiled pattern. The smallest size for
1340 <i>ovector</i> that will allow for <i>n</i> captured substrings, in addition to
1341 the offsets of the substring matched by the whole pattern, is (<i>n</i>+1)*3.
1342 </P>
1343 <P>
1344 It is possible for capturing subpattern number <i>n+1</i> to match some part of
1345 the subject when subpattern <i>n</i> has not been used at all. For example, if
1346 the string "abc" is matched against the pattern (a|(z))(bc) the return from the
1347 function is 4, and subpatterns 1 and 3 are matched, but 2 is not. When this
1348 happens, both values in the offset pairs corresponding to unused subpatterns
1349 are set to -1.
1350 </P>
1351 <P>
1352 Offset values that correspond to unused subpatterns at the end of the
1353 expression are also set to -1. For example, if the string "abc" is matched
1354 against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not matched. The
1355 return from the function is 2, because the highest used capturing subpattern
1356 number is 1. However, you can refer to the offsets for the second and third
1357 capturing subpatterns if you wish (assuming the vector is large enough, of
1358 course).
1359 </P>
1360 <P>
1361 Some convenience functions are provided for extracting the captured substrings
1362 as separate strings. These are described below.
1363 <a name="errorlist"></a></P>
1364 <br><b>
1365 Error return values from <b>pcre_exec()</b>
1366 </b><br>
1367 <P>
1368 If <b>pcre_exec()</b> fails, it returns a negative number. The following are
1369 defined in the header file:
1370 <pre>
1371 PCRE_ERROR_NOMATCH (-1)
1372 </pre>
1373 The subject string did not match the pattern.
1374 <pre>
1375 PCRE_ERROR_NULL (-2)
1376 </pre>
1377 Either <i>code</i> or <i>subject</i> was passed as NULL, or <i>ovector</i> was
1378 NULL and <i>ovecsize</i> was not zero.
1379 <pre>
1380 PCRE_ERROR_BADOPTION (-3)
1381 </pre>
1382 An unrecognized bit was set in the <i>options</i> argument.
1383 <pre>
1384 PCRE_ERROR_BADMAGIC (-4)
1385 </pre>
1386 PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch
1387 the case when it is passed a junk pointer and to detect when a pattern that was
1388 compiled in an environment of one endianness is run in an environment with the
1389 other endianness. This is the error that PCRE gives when the magic number is
1390 not present.
1391 <pre>
1392 PCRE_ERROR_UNKNOWN_OPCODE (-5)
1393 </pre>
1394 While running the pattern match, an unknown item was encountered in the
1395 compiled pattern. This error could be caused by a bug in PCRE or by overwriting
1396 of the compiled pattern.
1397 <pre>
1398 PCRE_ERROR_NOMEMORY (-6)
1399 </pre>
1400 If a pattern contains back references, but the <i>ovector</i> that is passed to
1401 <b>pcre_exec()</b> is not big enough to remember the referenced substrings, PCRE
1402 gets a block of memory at the start of matching to use for this purpose. If the
1403 call via <b>pcre_malloc()</b> fails, this error is given. The memory is
1404 automatically freed at the end of matching.
1405 <pre>
1406 PCRE_ERROR_NOSUBSTRING (-7)
1407 </pre>
1408 This error is used by the <b>pcre_copy_substring()</b>,
1409 <b>pcre_get_substring()</b>, and <b>pcre_get_substring_list()</b> functions (see
1410 below). It is never returned by <b>pcre_exec()</b>.
1411 <pre>
1412 PCRE_ERROR_MATCHLIMIT (-8)
1413 </pre>
1414 The backtracking limit, as specified by the <i>match_limit</i> field in a
1415 <b>pcre_extra</b> structure (or defaulted) was reached. See the description
1416 above.
1417 <pre>
1418 PCRE_ERROR_CALLOUT (-9)
1419 </pre>
1420 This error is never generated by <b>pcre_exec()</b> itself. It is provided for
1421 use by callout functions that want to yield a distinctive error code. See the
1422 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1423 documentation for details.
1424 <pre>
1425 PCRE_ERROR_BADUTF8 (-10)
1426 </pre>
1427 A string that contains an invalid UTF-8 byte sequence was passed as a subject.
1428 <pre>
1429 PCRE_ERROR_BADUTF8_OFFSET (-11)
1430 </pre>
1431 The UTF-8 byte sequence that was passed as a subject was valid, but the value
1432 of <i>startoffset</i> did not point to the beginning of a UTF-8 character.
1433 <pre>
1434 PCRE_ERROR_PARTIAL (-12)
1435 </pre>
1436 The subject string did not match, but it did match partially. See the
1437 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1438 documentation for details of partial matching.
1439 <pre>
1440 PCRE_ERROR_BADPARTIAL (-13)
1441 </pre>
1442 The PCRE_PARTIAL option was used with a compiled pattern containing items that
1443 are not supported for partial matching. See the
1444 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1445 documentation for details of partial matching.
1446 <pre>
1447 PCRE_ERROR_INTERNAL (-14)
1448 </pre>
1449 An unexpected internal error has occurred. This error could be caused by a bug
1450 in PCRE or by overwriting of the compiled pattern.
1451 <pre>
1452 PCRE_ERROR_BADCOUNT (-15)
1453 </pre>
1454 This error is given if the value of the <i>ovecsize</i> argument is negative.
1455 <pre>
1456 PCRE_ERROR_RECURSIONLIMIT (-21)
1457 </pre>
1458 The internal recursion limit, as specified by the <i>match_limit_recursion</i>
1459 field in a <b>pcre_extra</b> structure (or defaulted) was reached. See the
1460 description above.
1461 <pre>
1462 PCRE_ERROR_NULLWSLIMIT (-22)
1463 </pre>
1464 When a group that can match an empty substring is repeated with an unbounded
1465 upper limit, the subject position at the start of the group must be remembered,
1466 so that a test for an empty string can be made when the end of the group is
1467 reached. Some workspace is required for this; if it runs out, this error is
1468 given.
1469 <pre>
1470 PCRE_ERROR_BADNEWLINE (-23)
1471 </pre>
1472 An invalid combination of PCRE_NEWLINE_<i>xxx</i> options was given.
1473 </P>
1474 <P>
1475 Error numbers -16 to -20 are not used by <b>pcre_exec()</b>.
1476 </P>
1477 <br><a name="SEC15" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NUMBER</a><br>
1478 <P>
1479 <b>int pcre_copy_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1480 <b>int <i>stringcount</i>, int <i>stringnumber</i>, char *<i>buffer</i>,</b>
1481 <b>int <i>buffersize</i>);</b>
1482 </P>
1483 <P>
1484 <b>int pcre_get_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1485 <b>int <i>stringcount</i>, int <i>stringnumber</i>,</b>
1486 <b>const char **<i>stringptr</i>);</b>
1487 </P>
1488 <P>
1489 <b>int pcre_get_substring_list(const char *<i>subject</i>,</b>
1490 <b>int *<i>ovector</i>, int <i>stringcount</i>, const char ***<i>listptr</i>);</b>
1491 </P>
1492 <P>
1493 Captured substrings can be accessed directly by using the offsets returned by
1494 <b>pcre_exec()</b> in <i>ovector</i>. For convenience, the functions
1495 <b>pcre_copy_substring()</b>, <b>pcre_get_substring()</b>, and
1496 <b>pcre_get_substring_list()</b> are provided for extracting captured substrings
1497 as new, separate, zero-terminated strings. These functions identify substrings
1498 by number. The next section describes functions for extracting named
1499 substrings.
1500 </P>
1501 <P>
1502 A substring that contains a binary zero is correctly extracted and has a
1503 further zero added on the end, but the result is not, of course, a C string.
1504 However, you can process such a string by referring to the length that is
1505 returned by <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>.
1506 Unfortunately, the interface to <b>pcre_get_substring_list()</b> is not adequate
1507 for handling strings containing binary zeros, because the end of the final
1508 string is not independently indicated.
1509 </P>
1510 <P>
1511 The first three arguments are the same for all three of these functions:
1512 <i>subject</i> is the subject string that has just been successfully matched,
1513 <i>ovector</i> is a pointer to the vector of integer offsets that was passed to
1514 <b>pcre_exec()</b>, and <i>stringcount</i> is the number of substrings that were
1515 captured by the match, including the substring that matched the entire regular
1516 expression. This is the value returned by <b>pcre_exec()</b> if it is greater
1517 than zero. If <b>pcre_exec()</b> returned zero, indicating that it ran out of
1518 space in <i>ovector</i>, the value passed as <i>stringcount</i> should be the
1519 number of elements in the vector divided by three.
1520 </P>
1521 <P>
1522 The functions <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>
1523 extract a single substring, whose number is given as <i>stringnumber</i>. A
1524 value of zero extracts the substring that matched the entire pattern, whereas
1525 higher values extract the captured substrings. For <b>pcre_copy_substring()</b>,
1526 the string is placed in <i>buffer</i>, whose length is given by
1527 <i>buffersize</i>, while for <b>pcre_get_substring()</b> a new block of memory is
1528 obtained via <b>pcre_malloc</b>, and its address is returned via
1529 <i>stringptr</i>. The yield of the function is the length of the string, not
1530 including the terminating zero, or one of these error codes:
1531 <pre>
1532 PCRE_ERROR_NOMEMORY (-6)
1533 </pre>
1534 The buffer was too small for <b>pcre_copy_substring()</b>, or the attempt to get
1535 memory failed for <b>pcre_get_substring()</b>.
1536 <pre>
1537 PCRE_ERROR_NOSUBSTRING (-7)
1538 </pre>
1539 There is no substring whose number is <i>stringnumber</i>.
1540 </P>
1541 <P>
1542 The <b>pcre_get_substring_list()</b> function extracts all available substrings
1543 and builds a list of pointers to them. All this is done in a single block of
1544 memory that is obtained via <b>pcre_malloc</b>. The address of the memory block
1545 is returned via <i>listptr</i>, which is also the start of the list of string
1546 pointers. The end of the list is marked by a NULL pointer. The yield of the
1547 function is zero if all went well, or the error code
1548 <pre>
1549 PCRE_ERROR_NOMEMORY (-6)
1550 </pre>
1551 if the attempt to get the memory block failed.
1552 </P>
1553 <P>
1554 When any of these functions encounter a substring that is unset, which can
1555 happen when capturing subpattern number <i>n+1</i> matches some part of the
1556 subject, but subpattern <i>n</i> has not been used at all, they return an empty
1557 string. This can be distinguished from a genuine zero-length substring by
1558 inspecting the appropriate offset in <i>ovector</i>, which is negative for unset
1559 substrings.
1560 </P>
1561 <P>
1562 The two convenience functions <b>pcre_free_substring()</b> and
1563 <b>pcre_free_substring_list()</b> can be used to free the memory returned by
1564 a previous call of <b>pcre_get_substring()</b> or
1565 <b>pcre_get_substring_list()</b>, respectively. They do nothing more than call
1566 the function pointed to by <b>pcre_free</b>, which of course could be called
1567 directly from a C program. However, PCRE is used in some situations where it is
1568 linked via a special interface to another programming language that cannot use
1569 <b>pcre_free</b> directly; it is for these cases that the functions are
1570 provided.
1571 </P>
1572 <br><a name="SEC16" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NAME</a><br>
1573 <P>
1574 <b>int pcre_get_stringnumber(const pcre *<i>code</i>,</b>
1575 <b>const char *<i>name</i>);</b>
1576 </P>
1577 <P>
1578 <b>int pcre_copy_named_substring(const pcre *<i>code</i>,</b>
1579 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
1580 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
1581 <b>char *<i>buffer</i>, int <i>buffersize</i>);</b>
1582 </P>
1583 <P>
1584 <b>int pcre_get_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>const char **<i>stringptr</i>);</b>
1588 </P>
1589 <P>
1590 To extract a substring by name, you first have to find associated number.
1591 For example, for this pattern
1592 <pre>
1593 (a+)b(?&#60;xxx&#62;\d+)...
1594 </pre>
1595 the number of the subpattern called "xxx" is 2. If the name is known to be
1596 unique (PCRE_DUPNAMES was not set), you can find the number from the name by
1597 calling <b>pcre_get_stringnumber()</b>. The first argument is the compiled
1598 pattern, and the second is the name. The yield of the function is the
1599 subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no subpattern of
1600 that name.
1601 </P>
1602 <P>
1603 Given the number, you can extract the substring directly, or use one of the
1604 functions described in the previous section. For convenience, there are also
1605 two functions that do the whole job.
1606 </P>
1607 <P>
1608 Most of the arguments of <b>pcre_copy_named_substring()</b> and
1609 <b>pcre_get_named_substring()</b> are the same as those for the similarly named
1610 functions that extract by number. As these are described in the previous
1611 section, they are not re-described here. There are just two differences:
1612 </P>
1613 <P>
1614 First, instead of a substring number, a substring name is given. Second, there
1615 is an extra argument, given at the start, which is a pointer to the compiled
1616 pattern. This is needed in order to gain access to the name-to-number
1617 translation table.
1618 </P>
1619 <P>
1620 These functions call <b>pcre_get_stringnumber()</b>, and if it succeeds, they
1621 then call <b>pcre_copy_substring()</b> or <b>pcre_get_substring()</b>, as
1622 appropriate. <b>NOTE:</b> If PCRE_DUPNAMES is set and there are duplicate names,
1623 the behaviour may not be what you want (see the next section).
1624 </P>
1625 <br><a name="SEC17" href="#TOC1">DUPLICATE SUBPATTERN NAMES</a><br>
1626 <P>
1627 <b>int pcre_get_stringtable_entries(const pcre *<i>code</i>,</b>
1628 <b>const char *<i>name</i>, char **<i>first</i>, char **<i>last</i>);</b>
1629 </P>
1630 <P>
1631 When a pattern is compiled with the PCRE_DUPNAMES option, names for subpatterns
1632 are not required to be unique. Normally, patterns with duplicate names are such
1633 that in any one match, only one of the named subpatterns participates. An
1634 example is shown in the
1635 <a href="pcrepattern.html"><b>pcrepattern</b></a>
1636 documentation. When duplicates are present, <b>pcre_copy_named_substring()</b>
1637 and <b>pcre_get_named_substring()</b> return the first substring corresponding
1638 to the given name that is set. If none are set, an empty string is returned.
1639 The <b>pcre_get_stringnumber()</b> function returns one of the numbers that are
1640 associated with the name, but it is not defined which it is.
1641 <br>
1642 <br>
1643 If you want to get full details of all captured substrings for a given name,
1644 you must use the <b>pcre_get_stringtable_entries()</b> function. The first
1645 argument is the compiled pattern, and the second is the name. The third and
1646 fourth are pointers to variables which are updated by the function. After it
1647 has run, they point to the first and last entries in the name-to-number table
1648 for the given name. The function itself returns the length of each entry, or
1649 PCRE_ERROR_NOSUBSTRING (-7) if there are none. The format of the table is
1650 described above in the section entitled <i>Information about a pattern</i>.
1651 Given all the relevant entries for the name, you can extract each of their
1652 numbers, and hence the captured data, if any.
1653 </P>
1654 <br><a name="SEC18" href="#TOC1">FINDING ALL POSSIBLE MATCHES</a><br>
1655 <P>
1656 The traditional matching function uses a similar algorithm to Perl, which stops
1657 when it finds the first match, starting at a given point in the subject. If you
1658 want to find all possible matches, or the longest possible match, consider
1659 using the alternative matching function (see below) instead. If you cannot use
1660 the alternative function, but still need to find all possible matches, you
1661 can kludge it up by making use of the callout facility, which is described in
1662 the
1663 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1664 documentation.
1665 </P>
1666 <P>
1667 What you have to do is to insert a callout right at the end of the pattern.
1668 When your callout function is called, extract and save the current matched
1669 substring. Then return 1, which forces <b>pcre_exec()</b> to backtrack and try
1670 other alternatives. Ultimately, when it runs out of matches, <b>pcre_exec()</b>
1671 will yield PCRE_ERROR_NOMATCH.
1672 <a name="dfamatch"></a></P>
1673 <br><a name="SEC19" href="#TOC1">MATCHING A PATTERN: THE ALTERNATIVE FUNCTION</a><br>
1674 <P>
1675 <b>int pcre_dfa_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
1676 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
1677 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>,</b>
1678 <b>int *<i>workspace</i>, int <i>wscount</i>);</b>
1679 </P>
1680 <P>
1681 The function <b>pcre_dfa_exec()</b> is called to match a subject string against
1682 a compiled pattern, using a matching algorithm that scans the subject string
1683 just once, and does not backtrack. This has different characteristics to the
1684 normal algorithm, and is not compatible with Perl. Some of the features of PCRE
1685 patterns are not supported. Nevertheless, there are times when this kind of
1686 matching can be useful. For a discussion of the two matching algorithms, see
1687 the
1688 <a href="pcrematching.html"><b>pcrematching</b></a>
1689 documentation.
1690 </P>
1691 <P>
1692 The arguments for the <b>pcre_dfa_exec()</b> function are the same as for
1693 <b>pcre_exec()</b>, plus two extras. The <i>ovector</i> argument is used in a
1694 different way, and this is described below. The other common arguments are used
1695 in the same way as for <b>pcre_exec()</b>, so their description is not repeated
1696 here.
1697 </P>
1698 <P>
1699 The two additional arguments provide workspace for the function. The workspace
1700 vector should contain at least 20 elements. It is used for keeping track of
1701 multiple paths through the pattern tree. More workspace will be needed for
1702 patterns and subjects where there are a lot of potential matches.
1703 </P>
1704 <P>
1705 Here is an example of a simple call to <b>pcre_dfa_exec()</b>:
1706 <pre>
1707 int rc;
1708 int ovector[10];
1709 int wspace[20];
1710 rc = pcre_dfa_exec(
1711 re, /* result of pcre_compile() */
1712 NULL, /* we didn't study the pattern */
1713 "some string", /* the subject string */
1714 11, /* the length of the subject string */
1715 0, /* start at offset 0 in the subject */
1716 0, /* default options */
1717 ovector, /* vector of integers for substring information */
1718 10, /* number of elements (NOT size in bytes) */
1719 wspace, /* working space vector */
1720 20); /* number of elements (NOT size in bytes) */
1721 </PRE>
1722 </P>
1723 <br><b>
1724 Option bits for <b>pcre_dfa_exec()</b>
1725 </b><br>
1726 <P>
1727 The unused bits of the <i>options</i> argument for <b>pcre_dfa_exec()</b> must be
1728 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_<i>xxx</i>,
1729 PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL,
1730 PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last three of these are
1731 the same as for <b>pcre_exec()</b>, so their description is not repeated here.
1732 <pre>
1733 PCRE_PARTIAL
1734 </pre>
1735 This has the same general effect as it does for <b>pcre_exec()</b>, but the
1736 details are slightly different. When PCRE_PARTIAL is set for
1737 <b>pcre_dfa_exec()</b>, the return code PCRE_ERROR_NOMATCH is converted into
1738 PCRE_ERROR_PARTIAL if the end of the subject is reached, there have been no
1739 complete matches, but there is still at least one matching possibility. The
1740 portion of the string that provided the partial match is set as the first
1741 matching string.
1742 <pre>
1743 PCRE_DFA_SHORTEST
1744 </pre>
1745 Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to stop as
1746 soon as it has found one match. Because of the way the alternative algorithm
1747 works, this is necessarily the shortest possible match at the first possible
1748 matching point in the subject string.
1749 <pre>
1750 PCRE_DFA_RESTART
1751 </pre>
1752 When <b>pcre_dfa_exec()</b> is called with the PCRE_PARTIAL option, and returns
1753 a partial match, it is possible to call it again, with additional subject
1754 characters, and have it continue with the same match. The PCRE_DFA_RESTART
1755 option requests this action; when it is set, the <i>workspace</i> and
1756 <i>wscount</i> options must reference the same vector as before because data
1757 about the match so far is left in them after a partial match. There is more
1758 discussion of this facility in the
1759 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1760 documentation.
1761 </P>
1762 <br><b>
1763 Successful returns from <b>pcre_dfa_exec()</b>
1764 </b><br>
1765 <P>
1766 When <b>pcre_dfa_exec()</b> succeeds, it may have matched more than one
1767 substring in the subject. Note, however, that all the matches from one run of
1768 the function start at the same point in the subject. The shorter matches are
1769 all initial substrings of the longer matches. For example, if the pattern
1770 <pre>
1771 &#60;.*&#62;
1772 </pre>
1773 is matched against the string
1774 <pre>
1775 This is &#60;something&#62; &#60;something else&#62; &#60;something further&#62; no more
1776 </pre>
1777 the three matched strings are
1778 <pre>
1779 &#60;something&#62;
1780 &#60;something&#62; &#60;something else&#62;
1781 &#60;something&#62; &#60;something else&#62; &#60;something further&#62;
1782 </pre>
1783 On success, the yield of the function is a number greater than zero, which is
1784 the number of matched substrings. The substrings themselves are returned in
1785 <i>ovector</i>. Each string uses two elements; the first is the offset to the
1786 start, and the second is the offset to the end. In fact, all the strings have
1787 the same start offset. (Space could have been saved by giving this only once,
1788 but it was decided to retain some compatibility with the way <b>pcre_exec()</b>
1789 returns data, even though the meaning of the strings is different.)
1790 </P>
1791 <P>
1792 The strings are returned in reverse order of length; that is, the longest
1793 matching string is given first. If there were too many matches to fit into
1794 <i>ovector</i>, the yield of the function is zero, and the vector is filled with
1795 the longest matches.
1796 </P>
1797 <br><b>
1798 Error returns from <b>pcre_dfa_exec()</b>
1799 </b><br>
1800 <P>
1801 The <b>pcre_dfa_exec()</b> function returns a negative number when it fails.
1802 Many of the errors are the same as for <b>pcre_exec()</b>, and these are
1803 described
1804 <a href="#errorlist">above.</a>
1805 There are in addition the following errors that are specific to
1806 <b>pcre_dfa_exec()</b>:
1807 <pre>
1808 PCRE_ERROR_DFA_UITEM (-16)
1809 </pre>
1810 This return is given if <b>pcre_dfa_exec()</b> encounters an item in the pattern
1811 that it does not support, for instance, the use of \C or a back reference.
1812 <pre>
1813 PCRE_ERROR_DFA_UCOND (-17)
1814 </pre>
1815 This return is given if <b>pcre_dfa_exec()</b> encounters a condition item that
1816 uses a back reference for the condition, or a test for recursion in a specific
1817 group. These are not supported.
1818 <pre>
1819 PCRE_ERROR_DFA_UMLIMIT (-18)
1820 </pre>
1821 This return is given if <b>pcre_dfa_exec()</b> is called with an <i>extra</i>
1822 block that contains a setting of the <i>match_limit</i> field. This is not
1823 supported (it is meaningless).
1824 <pre>
1825 PCRE_ERROR_DFA_WSSIZE (-19)
1826 </pre>
1827 This return is given if <b>pcre_dfa_exec()</b> runs out of space in the
1828 <i>workspace</i> vector.
1829 <pre>
1830 PCRE_ERROR_DFA_RECURSE (-20)
1831 </pre>
1832 When a recursive subpattern is processed, the matching function calls itself
1833 recursively, using private vectors for <i>ovector</i> and <i>workspace</i>. This
1834 error is given if the output vector is not large enough. This should be
1835 extremely rare, as a vector of size 1000 is used.
1836 </P>
1837 <br><a name="SEC20" href="#TOC1">SEE ALSO</a><br>
1838 <P>
1839 <b>pcrebuild</b>(3), <b>pcrecallout</b>(3), <b>pcrecpp(3)</b>(3),
1840 <b>pcrematching</b>(3), <b>pcrepartial</b>(3), <b>pcreposix</b>(3),
1841 <b>pcreprecompile</b>(3), <b>pcresample</b>(3), <b>pcrestack</b>(3).
1842 </P>
1843 <br><a name="SEC21" href="#TOC1">AUTHOR</a><br>
1844 <P>
1845 Philip Hazel
1846 <br>
1847 University Computing Service
1848 <br>
1849 Cambridge CB2 3QH, England.
1850 <br>
1851 </P>
1852 <br><a name="SEC22" href="#TOC1">REVISION</a><br>
1853 <P>
1854 Last updated: 06 March 2007
1855 <br>
1856 Copyright &copy; 1997-2007 University of Cambridge.
1857 <br>
1858 <p>
1859 Return to the <a href="index.html">PCRE index page</a>.
1860 </p>

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