/[pcre]/code/trunk/doc/html/pcreapi.html
ViewVC logotype

Contents of /code/trunk/doc/html/pcreapi.html

Parent Directory Parent Directory | Revision Log Revision Log


Revision 155 - (show annotations) (download) (as text)
Tue Apr 24 13:36:11 2007 UTC (7 years, 4 months ago) by ph10
File MIME type: text/html
File size: 84634 byte(s)
Tidies and final updates for 7.1.

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. However, compiling a regular expression with one version of PCRE
291 for use with a different version is not guaranteed to work and may cause
292 crashes.
293 </P>
294 <br><a name="SEC6" href="#TOC1">CHECKING BUILD-TIME OPTIONS</a><br>
295 <P>
296 <b>int pcre_config(int <i>what</i>, void *<i>where</i>);</b>
297 </P>
298 <P>
299 The function <b>pcre_config()</b> makes it possible for a PCRE client to
300 discover which optional features have been compiled into the PCRE library. The
301 <a href="pcrebuild.html"><b>pcrebuild</b></a>
302 documentation has more details about these optional features.
303 </P>
304 <P>
305 The first argument for <b>pcre_config()</b> is an integer, specifying which
306 information is required; the second argument is a pointer to a variable into
307 which the information is placed. The following information is available:
308 <pre>
309 PCRE_CONFIG_UTF8
310 </pre>
311 The output is an integer that is set to one if UTF-8 support is available;
312 otherwise it is set to zero.
313 <pre>
314 PCRE_CONFIG_UNICODE_PROPERTIES
315 </pre>
316 The output is an integer that is set to one if support for Unicode character
317 properties is available; otherwise it is set to zero.
318 <pre>
319 PCRE_CONFIG_NEWLINE
320 </pre>
321 The output is an integer whose value specifies the default character sequence
322 that is recognized as meaning "newline". The four values that are supported
323 are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF, and -1 for ANY. The
324 default should normally be the standard sequence for your operating system.
325 <pre>
326 PCRE_CONFIG_LINK_SIZE
327 </pre>
328 The output is an integer that contains the number of bytes used for internal
329 linkage in compiled regular expressions. The value is 2, 3, or 4. Larger values
330 allow larger regular expressions to be compiled, at the expense of slower
331 matching. The default value of 2 is sufficient for all but the most massive
332 patterns, since it allows the compiled pattern to be up to 64K in size.
333 <pre>
334 PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
335 </pre>
336 The output is an integer that contains the threshold above which the POSIX
337 interface uses <b>malloc()</b> for output vectors. Further details are given in
338 the
339 <a href="pcreposix.html"><b>pcreposix</b></a>
340 documentation.
341 <pre>
342 PCRE_CONFIG_MATCH_LIMIT
343 </pre>
344 The output is an integer that gives the default limit for the number of
345 internal matching function calls in a <b>pcre_exec()</b> execution. Further
346 details are given with <b>pcre_exec()</b> below.
347 <pre>
348 PCRE_CONFIG_MATCH_LIMIT_RECURSION
349 </pre>
350 The output is an integer that gives the default limit for the depth of
351 recursion when calling the internal matching function in a <b>pcre_exec()</b>
352 execution. Further details are given with <b>pcre_exec()</b> below.
353 <pre>
354 PCRE_CONFIG_STACKRECURSE
355 </pre>
356 The output is an integer that is set to one if internal recursion when running
357 <b>pcre_exec()</b> is implemented by recursive function calls that use the stack
358 to remember their state. This is the usual way that PCRE is compiled. The
359 output is zero if PCRE was compiled to use blocks of data on the heap instead
360 of recursive function calls. In this case, <b>pcre_stack_malloc</b> and
361 <b>pcre_stack_free</b> are called to manage memory blocks on the heap, thus
362 avoiding the use of the stack.
363 </P>
364 <br><a name="SEC7" href="#TOC1">COMPILING A PATTERN</a><br>
365 <P>
366 <b>pcre *pcre_compile(const char *<i>pattern</i>, int <i>options</i>,</b>
367 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
368 <b>const unsigned char *<i>tableptr</i>);</b>
369 <b>pcre *pcre_compile2(const char *<i>pattern</i>, int <i>options</i>,</b>
370 <b>int *<i>errorcodeptr</i>,</b>
371 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
372 <b>const unsigned char *<i>tableptr</i>);</b>
373 </P>
374 <P>
375 Either of the functions <b>pcre_compile()</b> or <b>pcre_compile2()</b> can be
376 called to compile a pattern into an internal form. The only difference between
377 the two interfaces is that <b>pcre_compile2()</b> has an additional argument,
378 <i>errorcodeptr</i>, via which a numerical error code can be returned.
379 </P>
380 <P>
381 The pattern is a C string terminated by a binary zero, and is passed in the
382 <i>pattern</i> argument. A pointer to a single block of memory that is obtained
383 via <b>pcre_malloc</b> is returned. This contains the compiled code and related
384 data. The <b>pcre</b> type is defined for the returned block; this is a typedef
385 for a structure whose contents are not externally defined. It is up to the
386 caller to free the memory (via <b>pcre_free</b>) when it is no longer required.
387 </P>
388 <P>
389 Although the compiled code of a PCRE regex is relocatable, that is, it does not
390 depend on memory location, the complete <b>pcre</b> data block is not
391 fully relocatable, because it may contain a copy of the <i>tableptr</i>
392 argument, which is an address (see below).
393 </P>
394 <P>
395 The <i>options</i> argument contains various bit settings that affect the
396 compilation. It should be zero if no options are required. The available
397 options are described below. Some of them, in particular, those that are
398 compatible with Perl, can also be set and unset from within the pattern (see
399 the detailed description in the
400 <a href="pcrepattern.html"><b>pcrepattern</b></a>
401 documentation). For these options, the contents of the <i>options</i> argument
402 specifies their initial settings at the start of compilation and execution. The
403 PCRE_ANCHORED and PCRE_NEWLINE_<i>xxx</i> options can be set at the time of
404 matching as well as at compile time.
405 </P>
406 <P>
407 If <i>errptr</i> is NULL, <b>pcre_compile()</b> returns NULL immediately.
408 Otherwise, if compilation of a pattern fails, <b>pcre_compile()</b> returns
409 NULL, and sets the variable pointed to by <i>errptr</i> to point to a textual
410 error message. This is a static string that is part of the library. You must
411 not try to free it. The offset from the start of the pattern to the character
412 where the error was discovered is placed in the variable pointed to by
413 <i>erroffset</i>, which must not be NULL. If it is, an immediate error is given.
414 </P>
415 <P>
416 If <b>pcre_compile2()</b> is used instead of <b>pcre_compile()</b>, and the
417 <i>errorcodeptr</i> argument is not NULL, a non-zero error code number is
418 returned via this argument in the event of an error. This is in addition to the
419 textual error message. Error codes and messages are listed below.
420 </P>
421 <P>
422 If the final argument, <i>tableptr</i>, is NULL, PCRE uses a default set of
423 character tables that are built when PCRE is compiled, using the default C
424 locale. Otherwise, <i>tableptr</i> must be an address that is the result of a
425 call to <b>pcre_maketables()</b>. This value is stored with the compiled
426 pattern, and used again by <b>pcre_exec()</b>, unless another table pointer is
427 passed to it. For more discussion, see the section on locale support below.
428 </P>
429 <P>
430 This code fragment shows a typical straightforward call to <b>pcre_compile()</b>:
431 <pre>
432 pcre *re;
433 const char *error;
434 int erroffset;
435 re = pcre_compile(
436 "^A.*Z", /* the pattern */
437 0, /* default options */
438 &error, /* for error message */
439 &erroffset, /* for error offset */
440 NULL); /* use default character tables */
441 </pre>
442 The following names for option bits are defined in the <b>pcre.h</b> header
443 file:
444 <pre>
445 PCRE_ANCHORED
446 </pre>
447 If this bit is set, the pattern is forced to be "anchored", that is, it is
448 constrained to match only at the first matching point in the string that is
449 being searched (the "subject string"). This effect can also be achieved by
450 appropriate constructs in the pattern itself, which is the only way to do it in
451 Perl.
452 <pre>
453 PCRE_AUTO_CALLOUT
454 </pre>
455 If this bit is set, <b>pcre_compile()</b> automatically inserts callout items,
456 all with number 255, before each pattern item. For discussion of the callout
457 facility, see the
458 <a href="pcrecallout.html"><b>pcrecallout</b></a>
459 documentation.
460 <pre>
461 PCRE_CASELESS
462 </pre>
463 If this bit is set, letters in the pattern match both upper and lower case
464 letters. It is equivalent to Perl's /i option, and it can be changed within a
465 pattern by a (?i) option setting. In UTF-8 mode, PCRE always understands the
466 concept of case for characters whose values are less than 128, so caseless
467 matching is always possible. For characters with higher values, the concept of
468 case is supported if PCRE is compiled with Unicode property support, but not
469 otherwise. If you want to use caseless matching for characters 128 and above,
470 you must ensure that PCRE is compiled with Unicode property support as well as
471 with UTF-8 support.
472 <pre>
473 PCRE_DOLLAR_ENDONLY
474 </pre>
475 If this bit is set, a dollar metacharacter in the pattern matches only at the
476 end of the subject string. Without this option, a dollar also matches
477 immediately before a newline at the end of the string (but not before any other
478 newlines). The PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is set.
479 There is no equivalent to this option in Perl, and no way to set it within a
480 pattern.
481 <pre>
482 PCRE_DOTALL
483 </pre>
484 If this bit is set, a dot metacharater in the pattern matches all characters,
485 including those that indicate newline. Without it, a dot does not match when
486 the current position is at a newline. This option is equivalent to Perl's /s
487 option, and it can be changed within a pattern by a (?s) option setting. A
488 negative class such as [^a] always matches newline characters, independent of
489 the setting of this option.
490 <pre>
491 PCRE_DUPNAMES
492 </pre>
493 If this bit is set, names used to identify capturing subpatterns need not be
494 unique. This can be helpful for certain types of pattern when it is known that
495 only one instance of the named subpattern can ever be matched. There are more
496 details of named subpatterns below; see also the
497 <a href="pcrepattern.html"><b>pcrepattern</b></a>
498 documentation.
499 <pre>
500 PCRE_EXTENDED
501 </pre>
502 If this bit is set, whitespace data characters in the pattern are totally
503 ignored except when escaped or inside a character class. Whitespace does not
504 include the VT character (code 11). In addition, characters between an
505 unescaped # outside a character class and the next newline, inclusive, are also
506 ignored. This is equivalent to Perl's /x option, and it can be changed within a
507 pattern by a (?x) option setting.
508 </P>
509 <P>
510 This option makes it possible to include comments inside complicated patterns.
511 Note, however, that this applies only to data characters. Whitespace characters
512 may never appear within special character sequences in a pattern, for example
513 within the sequence (?( which introduces a conditional subpattern.
514 <pre>
515 PCRE_EXTRA
516 </pre>
517 This option was invented in order to turn on additional functionality of PCRE
518 that is incompatible with Perl, but it is currently of very little use. When
519 set, any backslash in a pattern that is followed by a letter that has no
520 special meaning causes an error, thus reserving these combinations for future
521 expansion. By default, as in Perl, a backslash followed by a letter with no
522 special meaning is treated as a literal. (Perl can, however, be persuaded to
523 give a warning for this.) There are at present no other features controlled by
524 this option. It can also be set by a (?X) option setting within a pattern.
525 <pre>
526 PCRE_FIRSTLINE
527 </pre>
528 If this option is set, an unanchored pattern is required to match before or at
529 the first newline in the subject string, though the matched text may continue
530 over the newline.
531 <pre>
532 PCRE_MULTILINE
533 </pre>
534 By default, PCRE treats the subject string as consisting of a single line of
535 characters (even if it actually contains newlines). The "start of line"
536 metacharacter (^) matches only at the start of the string, while the "end of
537 line" metacharacter ($) matches only at the end of the string, or before a
538 terminating newline (unless PCRE_DOLLAR_ENDONLY is set). This is the same as
539 Perl.
540 </P>
541 <P>
542 When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs
543 match immediately following or immediately before internal newlines in the
544 subject string, respectively, as well as at the very start and end. This is
545 equivalent to Perl's /m option, and it can be changed within a pattern by a
546 (?m) option setting. If there are no newlines in a subject string, or no
547 occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no effect.
548 <pre>
549 PCRE_NEWLINE_CR
550 PCRE_NEWLINE_LF
551 PCRE_NEWLINE_CRLF
552 PCRE_NEWLINE_ANYCRLF
553 PCRE_NEWLINE_ANY
554 </pre>
555 These options override the default newline definition that was chosen when PCRE
556 was built. Setting the first or the second specifies that a newline is
557 indicated by a single character (CR or LF, respectively). Setting
558 PCRE_NEWLINE_CRLF specifies that a newline is indicated by the two-character
559 CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies that any of the three
560 preceding sequences should be recognized. Setting PCRE_NEWLINE_ANY specifies
561 that any Unicode newline sequence should be recognized. The Unicode newline
562 sequences are the three just mentioned, plus the single characters VT (vertical
563 tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS (line
564 separator, U+2028), and PS (paragraph separator, U+2029). The last two are
565 recognized only in UTF-8 mode.
566 </P>
567 <P>
568 The newline setting in the options word uses three bits that are treated
569 as a number, giving eight possibilities. Currently only six are used (default
570 plus the five values above). This means that if you set more than one newline
571 option, the combination may or may not be sensible. For example,
572 PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to PCRE_NEWLINE_CRLF, but
573 other combinations may yield unused numbers and cause an error.
574 </P>
575 <P>
576 The only time that a line break is specially recognized when compiling a
577 pattern is if PCRE_EXTENDED is set, and an unescaped # outside a character
578 class is encountered. This indicates a comment that lasts until after the next
579 line break sequence. In other circumstances, line break sequences are treated
580 as literal data, except that in PCRE_EXTENDED mode, both CR and LF are treated
581 as whitespace characters and are therefore ignored.
582 </P>
583 <P>
584 The newline option that is set at compile time becomes the default that is used
585 for <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b>, but it can be overridden.
586 <pre>
587 PCRE_NO_AUTO_CAPTURE
588 </pre>
589 If this option is set, it disables the use of numbered capturing parentheses in
590 the pattern. Any opening parenthesis that is not followed by ? behaves as if it
591 were followed by ?: but named parentheses can still be used for capturing (and
592 they acquire numbers in the usual way). There is no equivalent of this option
593 in Perl.
594 <pre>
595 PCRE_UNGREEDY
596 </pre>
597 This option inverts the "greediness" of the quantifiers so that they are not
598 greedy by default, but become greedy if followed by "?". It is not compatible
599 with Perl. It can also be set by a (?U) option setting within the pattern.
600 <pre>
601 PCRE_UTF8
602 </pre>
603 This option causes PCRE to regard both the pattern and the subject as strings
604 of UTF-8 characters instead of single-byte character strings. However, it is
605 available only when PCRE is built to include UTF-8 support. If not, the use
606 of this option provokes an error. Details of how this option changes the
607 behaviour of PCRE are given in the
608 <a href="pcre.html#utf8support">section on UTF-8 support</a>
609 in the main
610 <a href="pcre.html"><b>pcre</b></a>
611 page.
612 <pre>
613 PCRE_NO_UTF8_CHECK
614 </pre>
615 When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
616 automatically checked. If an invalid UTF-8 sequence of bytes is found,
617 <b>pcre_compile()</b> returns an error. If you already know that your pattern is
618 valid, and you want to skip this check for performance reasons, you can set the
619 PCRE_NO_UTF8_CHECK option. When it is set, the effect of passing an invalid
620 UTF-8 string as a pattern is undefined. It may cause your program to crash.
621 Note that this option can also be passed to <b>pcre_exec()</b> and
622 <b>pcre_dfa_exec()</b>, to suppress the UTF-8 validity checking of subject
623 strings.
624 </P>
625 <br><a name="SEC8" href="#TOC1">COMPILATION ERROR CODES</a><br>
626 <P>
627 The following table lists the error codes than may be returned by
628 <b>pcre_compile2()</b>, along with the error messages that may be returned by
629 both compiling functions. As PCRE has developed, some error codes have fallen
630 out of use. To avoid confusion, they have not been re-used.
631 <pre>
632 0 no error
633 1 \ at end of pattern
634 2 \c at end of pattern
635 3 unrecognized character follows \
636 4 numbers out of order in {} quantifier
637 5 number too big in {} quantifier
638 6 missing terminating ] for character class
639 7 invalid escape sequence in character class
640 8 range out of order in character class
641 9 nothing to repeat
642 10 [this code is not in use]
643 11 internal error: unexpected repeat
644 12 unrecognized character after (?
645 13 POSIX named classes are supported only within a class
646 14 missing )
647 15 reference to non-existent subpattern
648 16 erroffset passed as NULL
649 17 unknown option bit(s) set
650 18 missing ) after comment
651 19 [this code is not in use]
652 20 regular expression too large
653 21 failed to get memory
654 22 unmatched parentheses
655 23 internal error: code overflow
656 24 unrecognized character after (?&#60;
657 25 lookbehind assertion is not fixed length
658 26 malformed number or name after (?(
659 27 conditional group contains more than two branches
660 28 assertion expected after (?(
661 29 (?R or (?digits must be followed by )
662 30 unknown POSIX class name
663 31 POSIX collating elements are not supported
664 32 this version of PCRE is not compiled with PCRE_UTF8 support
665 33 [this code is not in use]
666 34 character value in \x{...} sequence is too large
667 35 invalid condition (?(0)
668 36 \C not allowed in lookbehind assertion
669 37 PCRE does not support \L, \l, \N, \U, or \u
670 38 number after (?C is &#62; 255
671 39 closing ) for (?C expected
672 40 recursive call could loop indefinitely
673 41 unrecognized character after (?P
674 42 syntax error in subpattern name (missing terminator)
675 43 two named subpatterns have the same name
676 44 invalid UTF-8 string
677 45 support for \P, \p, and \X has not been compiled
678 46 malformed \P or \p sequence
679 47 unknown property name after \P or \p
680 48 subpattern name is too long (maximum 32 characters)
681 49 too many named subpatterns (maximum 10,000)
682 50 repeated subpattern is too long
683 51 octal value is greater than \377 (not in UTF-8 mode)
684 52 internal error: overran compiling workspace
685 53 internal error: previously-checked referenced subpattern not found
686 54 DEFINE group contains more than one branch
687 55 repeating a DEFINE group is not allowed
688 56 inconsistent NEWLINE options"
689 </PRE>
690 </P>
691 <br><a name="SEC9" href="#TOC1">STUDYING A PATTERN</a><br>
692 <P>
693 <b>pcre_extra *pcre_study(const pcre *<i>code</i>, int <i>options</i></b>
694 <b>const char **<i>errptr</i>);</b>
695 </P>
696 <P>
697 If a compiled pattern is going to be used several times, it is worth spending
698 more time analyzing it in order to speed up the time taken for matching. The
699 function <b>pcre_study()</b> takes a pointer to a compiled pattern as its first
700 argument. If studying the pattern produces additional information that will
701 help speed up matching, <b>pcre_study()</b> returns a pointer to a
702 <b>pcre_extra</b> block, in which the <i>study_data</i> field points to the
703 results of the study.
704 </P>
705 <P>
706 The returned value from <b>pcre_study()</b> can be passed directly to
707 <b>pcre_exec()</b>. However, a <b>pcre_extra</b> block also contains other
708 fields that can be set by the caller before the block is passed; these are
709 described
710 <a href="#extradata">below</a>
711 in the section on matching a pattern.
712 </P>
713 <P>
714 If studying the pattern does not produce any additional information
715 <b>pcre_study()</b> returns NULL. In that circumstance, if the calling program
716 wants to pass any of the other fields to <b>pcre_exec()</b>, it must set up its
717 own <b>pcre_extra</b> block.
718 </P>
719 <P>
720 The second argument of <b>pcre_study()</b> contains option bits. At present, no
721 options are defined, and this argument should always be zero.
722 </P>
723 <P>
724 The third argument for <b>pcre_study()</b> is a pointer for an error message. If
725 studying succeeds (even if no data is returned), the variable it points to is
726 set to NULL. Otherwise it is set to point to a textual error message. This is a
727 static string that is part of the library. You must not try to free it. You
728 should test the error pointer for NULL after calling <b>pcre_study()</b>, to be
729 sure that it has run successfully.
730 </P>
731 <P>
732 This is a typical call to <b>pcre_study</b>():
733 <pre>
734 pcre_extra *pe;
735 pe = pcre_study(
736 re, /* result of pcre_compile() */
737 0, /* no options exist */
738 &error); /* set to NULL or points to a message */
739 </pre>
740 At present, studying a pattern is useful only for non-anchored patterns that do
741 not have a single fixed starting character. A bitmap of possible starting
742 bytes is created.
743 <a name="localesupport"></a></P>
744 <br><a name="SEC10" href="#TOC1">LOCALE SUPPORT</a><br>
745 <P>
746 PCRE handles caseless matching, and determines whether characters are letters,
747 digits, or whatever, by reference to a set of tables, indexed by character
748 value. When running in UTF-8 mode, this applies only to characters with codes
749 less than 128. Higher-valued codes never match escapes such as \w or \d, but
750 can be tested with \p if PCRE is built with Unicode character property
751 support. The use of locales with Unicode is discouraged. If you are handling
752 characters with codes greater than 128, you should either use UTF-8 and
753 Unicode, or use locales, but not try to mix the two.
754 </P>
755 <P>
756 PCRE contains an internal set of tables that are used when the final argument
757 of <b>pcre_compile()</b> is NULL. These are sufficient for many applications.
758 Normally, the internal tables recognize only ASCII characters. However, when
759 PCRE is built, it is possible to cause the internal tables to be rebuilt in the
760 default "C" locale of the local system, which may cause them to be different.
761 </P>
762 <P>
763 The internal tables can always be overridden by tables supplied by the
764 application that calls PCRE. These may be created in a different locale from
765 the default. As more and more applications change to using Unicode, the need
766 for this locale support is expected to die away.
767 </P>
768 <P>
769 External tables are built by calling the <b>pcre_maketables()</b> function,
770 which has no arguments, in the relevant locale. The result can then be passed
771 to <b>pcre_compile()</b> or <b>pcre_exec()</b> as often as necessary. For
772 example, to build and use tables that are appropriate for the French locale
773 (where accented characters with values greater than 128 are treated as letters),
774 the following code could be used:
775 <pre>
776 setlocale(LC_CTYPE, "fr_FR");
777 tables = pcre_maketables();
778 re = pcre_compile(..., tables);
779 </pre>
780 The locale name "fr_FR" is used on Linux and other Unix-like systems; if you
781 are using Windows, the name for the French locale is "french".
782 </P>
783 <P>
784 When <b>pcre_maketables()</b> runs, the tables are built in memory that is
785 obtained via <b>pcre_malloc</b>. It is the caller's responsibility to ensure
786 that the memory containing the tables remains available for as long as it is
787 needed.
788 </P>
789 <P>
790 The pointer that is passed to <b>pcre_compile()</b> is saved with the compiled
791 pattern, and the same tables are used via this pointer by <b>pcre_study()</b>
792 and normally also by <b>pcre_exec()</b>. Thus, by default, for any single
793 pattern, compilation, studying and matching all happen in the same locale, but
794 different patterns can be compiled in different locales.
795 </P>
796 <P>
797 It is possible to pass a table pointer or NULL (indicating the use of the
798 internal tables) to <b>pcre_exec()</b>. Although not intended for this purpose,
799 this facility could be used to match a pattern in a different locale from the
800 one in which it was compiled. Passing table pointers at run time is discussed
801 below in the section on matching a pattern.
802 </P>
803 <br><a name="SEC11" href="#TOC1">INFORMATION ABOUT A PATTERN</a><br>
804 <P>
805 <b>int pcre_fullinfo(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
806 <b>int <i>what</i>, void *<i>where</i>);</b>
807 </P>
808 <P>
809 The <b>pcre_fullinfo()</b> function returns information about a compiled
810 pattern. It replaces the obsolete <b>pcre_info()</b> function, which is
811 nevertheless retained for backwards compability (and is documented below).
812 </P>
813 <P>
814 The first argument for <b>pcre_fullinfo()</b> is a pointer to the compiled
815 pattern. The second argument is the result of <b>pcre_study()</b>, or NULL if
816 the pattern was not studied. The third argument specifies which piece of
817 information is required, and the fourth argument is a pointer to a variable
818 to receive the data. The yield of the function is zero for success, or one of
819 the following negative numbers:
820 <pre>
821 PCRE_ERROR_NULL the argument <i>code</i> was NULL
822 the argument <i>where</i> was NULL
823 PCRE_ERROR_BADMAGIC the "magic number" was not found
824 PCRE_ERROR_BADOPTION the value of <i>what</i> was invalid
825 </pre>
826 The "magic number" is placed at the start of each compiled pattern as an simple
827 check against passing an arbitrary memory pointer. Here is a typical call of
828 <b>pcre_fullinfo()</b>, to obtain the length of the compiled pattern:
829 <pre>
830 int rc;
831 size_t length;
832 rc = pcre_fullinfo(
833 re, /* result of pcre_compile() */
834 pe, /* result of pcre_study(), or NULL */
835 PCRE_INFO_SIZE, /* what is required */
836 &length); /* where to put the data */
837 </pre>
838 The possible values for the third argument are defined in <b>pcre.h</b>, and are
839 as follows:
840 <pre>
841 PCRE_INFO_BACKREFMAX
842 </pre>
843 Return the number of the highest back reference in the pattern. The fourth
844 argument should point to an <b>int</b> variable. Zero is returned if there are
845 no back references.
846 <pre>
847 PCRE_INFO_CAPTURECOUNT
848 </pre>
849 Return the number of capturing subpatterns in the pattern. The fourth argument
850 should point to an <b>int</b> variable.
851 <pre>
852 PCRE_INFO_DEFAULT_TABLES
853 </pre>
854 Return a pointer to the internal default character tables within PCRE. The
855 fourth argument should point to an <b>unsigned char *</b> variable. This
856 information call is provided for internal use by the <b>pcre_study()</b>
857 function. External callers can cause PCRE to use its internal tables by passing
858 a NULL table pointer.
859 <pre>
860 PCRE_INFO_FIRSTBYTE
861 </pre>
862 Return information about the first byte of any matched string, for a
863 non-anchored pattern. The fourth argument should point to an <b>int</b>
864 variable. (This option used to be called PCRE_INFO_FIRSTCHAR; the old name is
865 still recognized for backwards compatibility.)
866 </P>
867 <P>
868 If there is a fixed first byte, for example, from a pattern such as
869 (cat|cow|coyote), its value is returned. Otherwise, if either
870 <br>
871 <br>
872 (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
873 starts with "^", or
874 <br>
875 <br>
876 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
877 (if it were set, the pattern would be anchored),
878 <br>
879 <br>
880 -1 is returned, indicating that the pattern matches only at the start of a
881 subject string or after any newline within the string. Otherwise -2 is
882 returned. For anchored patterns, -2 is returned.
883 <pre>
884 PCRE_INFO_FIRSTTABLE
885 </pre>
886 If the pattern was studied, and this resulted in the construction of a 256-bit
887 table indicating a fixed set of bytes for the first byte in any matching
888 string, a pointer to the table is returned. Otherwise NULL is returned. The
889 fourth argument should point to an <b>unsigned char *</b> variable.
890 <pre>
891 PCRE_INFO_LASTLITERAL
892 </pre>
893 Return the value of the rightmost literal byte that must exist in any matched
894 string, other than at its start, if such a byte has been recorded. The fourth
895 argument should point to an <b>int</b> variable. If there is no such byte, -1 is
896 returned. For anchored patterns, a last literal byte is recorded only if it
897 follows something of variable length. For example, for the pattern
898 /^a\d+z\d+/ the returned value is "z", but for /^a\dz\d/ the returned value
899 is -1.
900 <pre>
901 PCRE_INFO_NAMECOUNT
902 PCRE_INFO_NAMEENTRYSIZE
903 PCRE_INFO_NAMETABLE
904 </pre>
905 PCRE supports the use of named as well as numbered capturing parentheses. The
906 names are just an additional way of identifying the parentheses, which still
907 acquire numbers. Several convenience functions such as
908 <b>pcre_get_named_substring()</b> are provided for extracting captured
909 substrings by name. It is also possible to extract the data directly, by first
910 converting the name to a number in order to access the correct pointers in the
911 output vector (described with <b>pcre_exec()</b> below). To do the conversion,
912 you need to use the name-to-number map, which is described by these three
913 values.
914 </P>
915 <P>
916 The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives
917 the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each
918 entry; both of these return an <b>int</b> value. The entry size depends on the
919 length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first
920 entry of the table (a pointer to <b>char</b>). The first two bytes of each entry
921 are the number of the capturing parenthesis, most significant byte first. The
922 rest of the entry is the corresponding name, zero terminated. The names are in
923 alphabetical order. When PCRE_DUPNAMES is set, duplicate names are in order of
924 their parentheses numbers. For example, consider the following pattern (assume
925 PCRE_EXTENDED is set, so white space - including newlines - is ignored):
926 <pre>
927 (?&#60;date&#62; (?&#60;year&#62;(\d\d)?\d\d) - (?&#60;month&#62;\d\d) - (?&#60;day&#62;\d\d) )
928 </pre>
929 There are four named subpatterns, so the table has four entries, and each entry
930 in the table is eight bytes long. The table is as follows, with non-printing
931 bytes shows in hexadecimal, and undefined bytes shown as ??:
932 <pre>
933 00 01 d a t e 00 ??
934 00 05 d a y 00 ?? ??
935 00 04 m o n t h 00
936 00 02 y e a r 00 ??
937 </pre>
938 When writing code to extract data from named subpatterns using the
939 name-to-number map, remember that the length of the entries is likely to be
940 different for each compiled pattern.
941 <pre>
942 PCRE_INFO_OPTIONS
943 </pre>
944 Return a copy of the options with which the pattern was compiled. The fourth
945 argument should point to an <b>unsigned long int</b> variable. These option bits
946 are those specified in the call to <b>pcre_compile()</b>, modified by any
947 top-level option settings within the pattern itself.
948 </P>
949 <P>
950 A pattern is automatically anchored by PCRE if all of its top-level
951 alternatives begin with one of the following:
952 <pre>
953 ^ unless PCRE_MULTILINE is set
954 \A always
955 \G always
956 .* if PCRE_DOTALL is set and there are no back references to the subpattern in which .* appears
957 </pre>
958 For such patterns, the PCRE_ANCHORED bit is set in the options returned by
959 <b>pcre_fullinfo()</b>.
960 <pre>
961 PCRE_INFO_SIZE
962 </pre>
963 Return the size of the compiled pattern, that is, the value that was passed as
964 the argument to <b>pcre_malloc()</b> when PCRE was getting memory in which to
965 place the compiled data. The fourth argument should point to a <b>size_t</b>
966 variable.
967 <pre>
968 PCRE_INFO_STUDYSIZE
969 </pre>
970 Return the size of the data block pointed to by the <i>study_data</i> field in
971 a <b>pcre_extra</b> block. That is, it is the value that was passed to
972 <b>pcre_malloc()</b> when PCRE was getting memory into which to place the data
973 created by <b>pcre_study()</b>. The fourth argument should point to a
974 <b>size_t</b> variable.
975 </P>
976 <br><a name="SEC12" href="#TOC1">OBSOLETE INFO FUNCTION</a><br>
977 <P>
978 <b>int pcre_info(const pcre *<i>code</i>, int *<i>optptr</i>, int</b>
979 <b>*<i>firstcharptr</i>);</b>
980 </P>
981 <P>
982 The <b>pcre_info()</b> function is now obsolete because its interface is too
983 restrictive to return all the available data about a compiled pattern. New
984 programs should use <b>pcre_fullinfo()</b> instead. The yield of
985 <b>pcre_info()</b> is the number of capturing subpatterns, or one of the
986 following negative numbers:
987 <pre>
988 PCRE_ERROR_NULL the argument <i>code</i> was NULL
989 PCRE_ERROR_BADMAGIC the "magic number" was not found
990 </pre>
991 If the <i>optptr</i> argument is not NULL, a copy of the options with which the
992 pattern was compiled is placed in the integer it points to (see
993 PCRE_INFO_OPTIONS above).
994 </P>
995 <P>
996 If the pattern is not anchored and the <i>firstcharptr</i> argument is not NULL,
997 it is used to pass back information about the first character of any matched
998 string (see PCRE_INFO_FIRSTBYTE above).
999 </P>
1000 <br><a name="SEC13" href="#TOC1">REFERENCE COUNTS</a><br>
1001 <P>
1002 <b>int pcre_refcount(pcre *<i>code</i>, int <i>adjust</i>);</b>
1003 </P>
1004 <P>
1005 The <b>pcre_refcount()</b> function is used to maintain a reference count in the
1006 data block that contains a compiled pattern. It is provided for the benefit of
1007 applications that operate in an object-oriented manner, where different parts
1008 of the application may be using the same compiled pattern, but you want to free
1009 the block when they are all done.
1010 </P>
1011 <P>
1012 When a pattern is compiled, the reference count field is initialized to zero.
1013 It is changed only by calling this function, whose action is to add the
1014 <i>adjust</i> value (which may be positive or negative) to it. The yield of the
1015 function is the new value. However, the value of the count is constrained to
1016 lie between 0 and 65535, inclusive. If the new value is outside these limits,
1017 it is forced to the appropriate limit value.
1018 </P>
1019 <P>
1020 Except when it is zero, the reference count is not correctly preserved if a
1021 pattern is compiled on one host and then transferred to a host whose byte-order
1022 is different. (This seems a highly unlikely scenario.)
1023 </P>
1024 <br><a name="SEC14" href="#TOC1">MATCHING A PATTERN: THE TRADITIONAL FUNCTION</a><br>
1025 <P>
1026 <b>int pcre_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
1027 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
1028 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>);</b>
1029 </P>
1030 <P>
1031 The function <b>pcre_exec()</b> is called to match a subject string against a
1032 compiled pattern, which is passed in the <i>code</i> argument. If the
1033 pattern has been studied, the result of the study should be passed in the
1034 <i>extra</i> argument. This function is the main matching facility of the
1035 library, and it operates in a Perl-like manner. For specialist use there is
1036 also an alternative matching function, which is described
1037 <a href="#dfamatch">below</a>
1038 in the section about the <b>pcre_dfa_exec()</b> function.
1039 </P>
1040 <P>
1041 In most applications, the pattern will have been compiled (and optionally
1042 studied) in the same process that calls <b>pcre_exec()</b>. However, it is
1043 possible to save compiled patterns and study data, and then use them later
1044 in different processes, possibly even on different hosts. For a discussion
1045 about this, see the
1046 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
1047 documentation.
1048 </P>
1049 <P>
1050 Here is an example of a simple call to <b>pcre_exec()</b>:
1051 <pre>
1052 int rc;
1053 int ovector[30];
1054 rc = pcre_exec(
1055 re, /* result of pcre_compile() */
1056 NULL, /* we didn't study the pattern */
1057 "some string", /* the subject string */
1058 11, /* the length of the subject string */
1059 0, /* start at offset 0 in the subject */
1060 0, /* default options */
1061 ovector, /* vector of integers for substring information */
1062 30); /* number of elements (NOT size in bytes) */
1063 <a name="extradata"></a></PRE>
1064 </P>
1065 <br><b>
1066 Extra data for <b>pcre_exec()</b>
1067 </b><br>
1068 <P>
1069 If the <i>extra</i> argument is not NULL, it must point to a <b>pcre_extra</b>
1070 data block. The <b>pcre_study()</b> function returns such a block (when it
1071 doesn't return NULL), but you can also create one for yourself, and pass
1072 additional information in it. The <b>pcre_extra</b> block contains the following
1073 fields (not necessarily in this order):
1074 <pre>
1075 unsigned long int <i>flags</i>;
1076 void *<i>study_data</i>;
1077 unsigned long int <i>match_limit</i>;
1078 unsigned long int <i>match_limit_recursion</i>;
1079 void *<i>callout_data</i>;
1080 const unsigned char *<i>tables</i>;
1081 </pre>
1082 The <i>flags</i> field is a bitmap that specifies which of the other fields
1083 are set. The flag bits are:
1084 <pre>
1085 PCRE_EXTRA_STUDY_DATA
1086 PCRE_EXTRA_MATCH_LIMIT
1087 PCRE_EXTRA_MATCH_LIMIT_RECURSION
1088 PCRE_EXTRA_CALLOUT_DATA
1089 PCRE_EXTRA_TABLES
1090 </pre>
1091 Other flag bits should be set to zero. The <i>study_data</i> field is set in the
1092 <b>pcre_extra</b> block that is returned by <b>pcre_study()</b>, together with
1093 the appropriate flag bit. You should not set this yourself, but you may add to
1094 the block by setting the other fields and their corresponding flag bits.
1095 </P>
1096 <P>
1097 The <i>match_limit</i> field provides a means of preventing PCRE from using up a
1098 vast amount of resources when running patterns that are not going to match,
1099 but which have a very large number of possibilities in their search trees. The
1100 classic example is the use of nested unlimited repeats.
1101 </P>
1102 <P>
1103 Internally, PCRE uses a function called <b>match()</b> which it calls repeatedly
1104 (sometimes recursively). The limit set by <i>match_limit</i> is imposed on the
1105 number of times this function is called during a match, which has the effect of
1106 limiting the amount of backtracking that can take place. For patterns that are
1107 not anchored, the count restarts from zero for each position in the subject
1108 string.
1109 </P>
1110 <P>
1111 The default value for the limit can be set when PCRE is built; the default
1112 default is 10 million, which handles all but the most extreme cases. You can
1113 override the default by suppling <b>pcre_exec()</b> with a <b>pcre_extra</b>
1114 block in which <i>match_limit</i> is set, and PCRE_EXTRA_MATCH_LIMIT is set in
1115 the <i>flags</i> field. If the limit is exceeded, <b>pcre_exec()</b> returns
1116 PCRE_ERROR_MATCHLIMIT.
1117 </P>
1118 <P>
1119 The <i>match_limit_recursion</i> field is similar to <i>match_limit</i>, but
1120 instead of limiting the total number of times that <b>match()</b> is called, it
1121 limits the depth of recursion. The recursion depth is a smaller number than the
1122 total number of calls, because not all calls to <b>match()</b> are recursive.
1123 This limit is of use only if it is set smaller than <i>match_limit</i>.
1124 </P>
1125 <P>
1126 Limiting the recursion depth limits the amount of stack that can be used, or,
1127 when PCRE has been compiled to use memory on the heap instead of the stack, the
1128 amount of heap memory that can be used.
1129 </P>
1130 <P>
1131 The default value for <i>match_limit_recursion</i> can be set when PCRE is
1132 built; the default default is the same value as the default for
1133 <i>match_limit</i>. You can override the default by suppling <b>pcre_exec()</b>
1134 with a <b>pcre_extra</b> block in which <i>match_limit_recursion</i> is set, and
1135 PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the <i>flags</i> field. If the limit
1136 is exceeded, <b>pcre_exec()</b> returns PCRE_ERROR_RECURSIONLIMIT.
1137 </P>
1138 <P>
1139 The <i>pcre_callout</i> field is used in conjunction with the "callout" feature,
1140 which is described in the
1141 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1142 documentation.
1143 </P>
1144 <P>
1145 The <i>tables</i> field is used to pass a character tables pointer to
1146 <b>pcre_exec()</b>; this overrides the value that is stored with the compiled
1147 pattern. A non-NULL value is stored with the compiled pattern only if custom
1148 tables were supplied to <b>pcre_compile()</b> via its <i>tableptr</i> argument.
1149 If NULL is passed to <b>pcre_exec()</b> using this mechanism, it forces PCRE's
1150 internal tables to be used. This facility is helpful when re-using patterns
1151 that have been saved after compiling with an external set of tables, because
1152 the external tables might be at a different address when <b>pcre_exec()</b> is
1153 called. See the
1154 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
1155 documentation for a discussion of saving compiled patterns for later use.
1156 </P>
1157 <br><b>
1158 Option bits for <b>pcre_exec()</b>
1159 </b><br>
1160 <P>
1161 The unused bits of the <i>options</i> argument for <b>pcre_exec()</b> must be
1162 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_<i>xxx</i>,
1163 PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK and PCRE_PARTIAL.
1164 <pre>
1165 PCRE_ANCHORED
1166 </pre>
1167 The PCRE_ANCHORED option limits <b>pcre_exec()</b> to matching at the first
1168 matching position. If a pattern was compiled with PCRE_ANCHORED, or turned out
1169 to be anchored by virtue of its contents, it cannot be made unachored at
1170 matching time.
1171 <pre>
1172 PCRE_NEWLINE_CR
1173 PCRE_NEWLINE_LF
1174 PCRE_NEWLINE_CRLF
1175 PCRE_NEWLINE_ANYCRLF
1176 PCRE_NEWLINE_ANY
1177 </pre>
1178 These options override the newline definition that was chosen or defaulted when
1179 the pattern was compiled. For details, see the description of
1180 <b>pcre_compile()</b> above. During matching, the newline choice affects the
1181 behaviour of the dot, circumflex, and dollar metacharacters. It may also alter
1182 the way the match position is advanced after a match failure for an unanchored
1183 pattern. When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY is
1184 set, and a match attempt fails when the current position is at a CRLF sequence,
1185 the match position is advanced by two characters instead of one, in other
1186 words, to after the CRLF.
1187 <pre>
1188 PCRE_NOTBOL
1189 </pre>
1190 This option specifies that first character of the subject string is not the
1191 beginning of a line, so the circumflex metacharacter should not match before
1192 it. Setting this without PCRE_MULTILINE (at compile time) causes circumflex
1193 never to match. This option affects only the behaviour of the circumflex
1194 metacharacter. It does not affect \A.
1195 <pre>
1196 PCRE_NOTEOL
1197 </pre>
1198 This option specifies that the end of the subject string is not the end of a
1199 line, so the dollar metacharacter should not match it nor (except in multiline
1200 mode) a newline immediately before it. Setting this without PCRE_MULTILINE (at
1201 compile time) causes dollar never to match. This option affects only the
1202 behaviour of the dollar metacharacter. It does not affect \Z or \z.
1203 <pre>
1204 PCRE_NOTEMPTY
1205 </pre>
1206 An empty string is not considered to be a valid match if this option is set. If
1207 there are alternatives in the pattern, they are tried. If all the alternatives
1208 match the empty string, the entire match fails. For example, if the pattern
1209 <pre>
1210 a?b?
1211 </pre>
1212 is applied to a string not beginning with "a" or "b", it matches the empty
1213 string at the start of the subject. With PCRE_NOTEMPTY set, this match is not
1214 valid, so PCRE searches further into the string for occurrences of "a" or "b".
1215 </P>
1216 <P>
1217 Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a special case
1218 of a pattern match of the empty string within its <b>split()</b> function, and
1219 when using the /g modifier. It is possible to emulate Perl's behaviour after
1220 matching a null string by first trying the match again at the same offset with
1221 PCRE_NOTEMPTY and PCRE_ANCHORED, and then if that fails by advancing the
1222 starting offset (see below) and trying an ordinary match again. There is some
1223 code that demonstrates how to do this in the <i>pcredemo.c</i> sample program.
1224 <pre>
1225 PCRE_NO_UTF8_CHECK
1226 </pre>
1227 When PCRE_UTF8 is set at compile time, the validity of the subject as a UTF-8
1228 string is automatically checked when <b>pcre_exec()</b> is subsequently called.
1229 The value of <i>startoffset</i> is also checked to ensure that it points to the
1230 start of a UTF-8 character. If an invalid UTF-8 sequence of bytes is found,
1231 <b>pcre_exec()</b> returns the error PCRE_ERROR_BADUTF8. If <i>startoffset</i>
1232 contains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
1233 </P>
1234 <P>
1235 If you already know that your subject is valid, and you want to skip these
1236 checks for performance reasons, you can set the PCRE_NO_UTF8_CHECK option when
1237 calling <b>pcre_exec()</b>. You might want to do this for the second and
1238 subsequent calls to <b>pcre_exec()</b> if you are making repeated calls to find
1239 all the matches in a single subject string. However, you should be sure that
1240 the value of <i>startoffset</i> points to the start of a UTF-8 character. When
1241 PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid UTF-8 string as a
1242 subject, or a value of <i>startoffset</i> that does not point to the start of a
1243 UTF-8 character, is undefined. Your program may crash.
1244 <pre>
1245 PCRE_PARTIAL
1246 </pre>
1247 This option turns on the partial matching feature. If the subject string fails
1248 to match the pattern, but at some point during the matching process the end of
1249 the subject was reached (that is, the subject partially matches the pattern and
1250 the failure to match occurred only because there were not enough subject
1251 characters), <b>pcre_exec()</b> returns PCRE_ERROR_PARTIAL instead of
1252 PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is used, there are restrictions on what
1253 may appear in the pattern. These are discussed in the
1254 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1255 documentation.
1256 </P>
1257 <br><b>
1258 The string to be matched by <b>pcre_exec()</b>
1259 </b><br>
1260 <P>
1261 The subject string is passed to <b>pcre_exec()</b> as a pointer in
1262 <i>subject</i>, a length in <i>length</i>, and a starting byte offset in
1263 <i>startoffset</i>. In UTF-8 mode, the byte offset must point to the start of a
1264 UTF-8 character. Unlike the pattern string, the subject may contain binary zero
1265 bytes. When the starting offset is zero, the search for a match starts at the
1266 beginning of the subject, and this is by far the most common case.
1267 </P>
1268 <P>
1269 A non-zero starting offset is useful when searching for another match in the
1270 same subject by calling <b>pcre_exec()</b> again after a previous success.
1271 Setting <i>startoffset</i> differs from just passing over a shortened string and
1272 setting PCRE_NOTBOL in the case of a pattern that begins with any kind of
1273 lookbehind. For example, consider the pattern
1274 <pre>
1275 \Biss\B
1276 </pre>
1277 which finds occurrences of "iss" in the middle of words. (\B matches only if
1278 the current position in the subject is not a word boundary.) When applied to
1279 the string "Mississipi" the first call to <b>pcre_exec()</b> finds the first
1280 occurrence. If <b>pcre_exec()</b> is called again with just the remainder of the
1281 subject, namely "issipi", it does not match, because \B is always false at the
1282 start of the subject, which is deemed to be a word boundary. However, if
1283 <b>pcre_exec()</b> is passed the entire string again, but with <i>startoffset</i>
1284 set to 4, it finds the second occurrence of "iss" because it is able to look
1285 behind the starting point to discover that it is preceded by a letter.
1286 </P>
1287 <P>
1288 If a non-zero starting offset is passed when the pattern is anchored, one
1289 attempt to match at the given offset is made. This can only succeed if the
1290 pattern does not require the match to be at the start of the subject.
1291 </P>
1292 <br><b>
1293 How <b>pcre_exec()</b> returns captured substrings
1294 </b><br>
1295 <P>
1296 In general, a pattern matches a certain portion of the subject, and in
1297 addition, further substrings from the subject may be picked out by parts of the
1298 pattern. Following the usage in Jeffrey Friedl's book, this is called
1299 "capturing" in what follows, and the phrase "capturing subpattern" is used for
1300 a fragment of a pattern that picks out a substring. PCRE supports several other
1301 kinds of parenthesized subpattern that do not cause substrings to be captured.
1302 </P>
1303 <P>
1304 Captured substrings are returned to the caller via a vector of integer offsets
1305 whose address is passed in <i>ovector</i>. The number of elements in the vector
1306 is passed in <i>ovecsize</i>, which must be a non-negative number. <b>Note</b>:
1307 this argument is NOT the size of <i>ovector</i> in bytes.
1308 </P>
1309 <P>
1310 The first two-thirds of the vector is used to pass back captured substrings,
1311 each substring using a pair of integers. The remaining third of the vector is
1312 used as workspace by <b>pcre_exec()</b> while matching capturing subpatterns,
1313 and is not available for passing back information. The length passed in
1314 <i>ovecsize</i> should always be a multiple of three. If it is not, it is
1315 rounded down.
1316 </P>
1317 <P>
1318 When a match is successful, information about captured substrings is returned
1319 in pairs of integers, starting at the beginning of <i>ovector</i>, and
1320 continuing up to two-thirds of its length at the most. The first element of a
1321 pair is set to the offset of the first character in a substring, and the second
1322 is set to the offset of the first character after the end of a substring. The
1323 first pair, <i>ovector[0]</i> and <i>ovector[1]</i>, identify the portion of the
1324 subject string matched by the entire pattern. The next pair is used for the
1325 first capturing subpattern, and so on. The value returned by <b>pcre_exec()</b>
1326 is one more than the highest numbered pair that has been set. For example, if
1327 two substrings have been captured, the returned value is 3. If there are no
1328 capturing subpatterns, the return value from a successful match is 1,
1329 indicating that just the first pair of offsets has been set.
1330 </P>
1331 <P>
1332 If a capturing subpattern is matched repeatedly, it is the last portion of the
1333 string that it matched that is returned.
1334 </P>
1335 <P>
1336 If the vector is too small to hold all the captured substring offsets, it is
1337 used as far as possible (up to two-thirds of its length), and the function
1338 returns a value of zero. In particular, if the substring offsets are not of
1339 interest, <b>pcre_exec()</b> may be called with <i>ovector</i> passed as NULL and
1340 <i>ovecsize</i> as zero. However, if the pattern contains back references and
1341 the <i>ovector</i> is not big enough to remember the related substrings, PCRE
1342 has to get additional memory for use during matching. Thus it is usually
1343 advisable to supply an <i>ovector</i>.
1344 </P>
1345 <P>
1346 The <b>pcre_info()</b> function can be used to find out how many capturing
1347 subpatterns there are in a compiled pattern. The smallest size for
1348 <i>ovector</i> that will allow for <i>n</i> captured substrings, in addition to
1349 the offsets of the substring matched by the whole pattern, is (<i>n</i>+1)*3.
1350 </P>
1351 <P>
1352 It is possible for capturing subpattern number <i>n+1</i> to match some part of
1353 the subject when subpattern <i>n</i> has not been used at all. For example, if
1354 the string "abc" is matched against the pattern (a|(z))(bc) the return from the
1355 function is 4, and subpatterns 1 and 3 are matched, but 2 is not. When this
1356 happens, both values in the offset pairs corresponding to unused subpatterns
1357 are set to -1.
1358 </P>
1359 <P>
1360 Offset values that correspond to unused subpatterns at the end of the
1361 expression are also set to -1. For example, if the string "abc" is matched
1362 against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not matched. The
1363 return from the function is 2, because the highest used capturing subpattern
1364 number is 1. However, you can refer to the offsets for the second and third
1365 capturing subpatterns if you wish (assuming the vector is large enough, of
1366 course).
1367 </P>
1368 <P>
1369 Some convenience functions are provided for extracting the captured substrings
1370 as separate strings. These are described below.
1371 <a name="errorlist"></a></P>
1372 <br><b>
1373 Error return values from <b>pcre_exec()</b>
1374 </b><br>
1375 <P>
1376 If <b>pcre_exec()</b> fails, it returns a negative number. The following are
1377 defined in the header file:
1378 <pre>
1379 PCRE_ERROR_NOMATCH (-1)
1380 </pre>
1381 The subject string did not match the pattern.
1382 <pre>
1383 PCRE_ERROR_NULL (-2)
1384 </pre>
1385 Either <i>code</i> or <i>subject</i> was passed as NULL, or <i>ovector</i> was
1386 NULL and <i>ovecsize</i> was not zero.
1387 <pre>
1388 PCRE_ERROR_BADOPTION (-3)
1389 </pre>
1390 An unrecognized bit was set in the <i>options</i> argument.
1391 <pre>
1392 PCRE_ERROR_BADMAGIC (-4)
1393 </pre>
1394 PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch
1395 the case when it is passed a junk pointer and to detect when a pattern that was
1396 compiled in an environment of one endianness is run in an environment with the
1397 other endianness. This is the error that PCRE gives when the magic number is
1398 not present.
1399 <pre>
1400 PCRE_ERROR_UNKNOWN_OPCODE (-5)
1401 </pre>
1402 While running the pattern match, an unknown item was encountered in the
1403 compiled pattern. This error could be caused by a bug in PCRE or by overwriting
1404 of the compiled pattern.
1405 <pre>
1406 PCRE_ERROR_NOMEMORY (-6)
1407 </pre>
1408 If a pattern contains back references, but the <i>ovector</i> that is passed to
1409 <b>pcre_exec()</b> is not big enough to remember the referenced substrings, PCRE
1410 gets a block of memory at the start of matching to use for this purpose. If the
1411 call via <b>pcre_malloc()</b> fails, this error is given. The memory is
1412 automatically freed at the end of matching.
1413 <pre>
1414 PCRE_ERROR_NOSUBSTRING (-7)
1415 </pre>
1416 This error is used by the <b>pcre_copy_substring()</b>,
1417 <b>pcre_get_substring()</b>, and <b>pcre_get_substring_list()</b> functions (see
1418 below). It is never returned by <b>pcre_exec()</b>.
1419 <pre>
1420 PCRE_ERROR_MATCHLIMIT (-8)
1421 </pre>
1422 The backtracking limit, as specified by the <i>match_limit</i> field in a
1423 <b>pcre_extra</b> structure (or defaulted) was reached. See the description
1424 above.
1425 <pre>
1426 PCRE_ERROR_CALLOUT (-9)
1427 </pre>
1428 This error is never generated by <b>pcre_exec()</b> itself. It is provided for
1429 use by callout functions that want to yield a distinctive error code. See the
1430 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1431 documentation for details.
1432 <pre>
1433 PCRE_ERROR_BADUTF8 (-10)
1434 </pre>
1435 A string that contains an invalid UTF-8 byte sequence was passed as a subject.
1436 <pre>
1437 PCRE_ERROR_BADUTF8_OFFSET (-11)
1438 </pre>
1439 The UTF-8 byte sequence that was passed as a subject was valid, but the value
1440 of <i>startoffset</i> did not point to the beginning of a UTF-8 character.
1441 <pre>
1442 PCRE_ERROR_PARTIAL (-12)
1443 </pre>
1444 The subject string did not match, but it did match partially. See the
1445 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1446 documentation for details of partial matching.
1447 <pre>
1448 PCRE_ERROR_BADPARTIAL (-13)
1449 </pre>
1450 The PCRE_PARTIAL option was used with a compiled pattern containing items that
1451 are not supported for partial matching. See the
1452 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1453 documentation for details of partial matching.
1454 <pre>
1455 PCRE_ERROR_INTERNAL (-14)
1456 </pre>
1457 An unexpected internal error has occurred. This error could be caused by a bug
1458 in PCRE or by overwriting of the compiled pattern.
1459 <pre>
1460 PCRE_ERROR_BADCOUNT (-15)
1461 </pre>
1462 This error is given if the value of the <i>ovecsize</i> argument is negative.
1463 <pre>
1464 PCRE_ERROR_RECURSIONLIMIT (-21)
1465 </pre>
1466 The internal recursion limit, as specified by the <i>match_limit_recursion</i>
1467 field in a <b>pcre_extra</b> structure (or defaulted) was reached. See the
1468 description above.
1469 <pre>
1470 PCRE_ERROR_NULLWSLIMIT (-22)
1471 </pre>
1472 When a group that can match an empty substring is repeated with an unbounded
1473 upper limit, the subject position at the start of the group must be remembered,
1474 so that a test for an empty string can be made when the end of the group is
1475 reached. Some workspace is required for this; if it runs out, this error is
1476 given.
1477 <pre>
1478 PCRE_ERROR_BADNEWLINE (-23)
1479 </pre>
1480 An invalid combination of PCRE_NEWLINE_<i>xxx</i> options was given.
1481 </P>
1482 <P>
1483 Error numbers -16 to -20 are not used by <b>pcre_exec()</b>.
1484 </P>
1485 <br><a name="SEC15" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NUMBER</a><br>
1486 <P>
1487 <b>int pcre_copy_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1488 <b>int <i>stringcount</i>, int <i>stringnumber</i>, char *<i>buffer</i>,</b>
1489 <b>int <i>buffersize</i>);</b>
1490 </P>
1491 <P>
1492 <b>int pcre_get_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1493 <b>int <i>stringcount</i>, int <i>stringnumber</i>,</b>
1494 <b>const char **<i>stringptr</i>);</b>
1495 </P>
1496 <P>
1497 <b>int pcre_get_substring_list(const char *<i>subject</i>,</b>
1498 <b>int *<i>ovector</i>, int <i>stringcount</i>, const char ***<i>listptr</i>);</b>
1499 </P>
1500 <P>
1501 Captured substrings can be accessed directly by using the offsets returned by
1502 <b>pcre_exec()</b> in <i>ovector</i>. For convenience, the functions
1503 <b>pcre_copy_substring()</b>, <b>pcre_get_substring()</b>, and
1504 <b>pcre_get_substring_list()</b> are provided for extracting captured substrings
1505 as new, separate, zero-terminated strings. These functions identify substrings
1506 by number. The next section describes functions for extracting named
1507 substrings.
1508 </P>
1509 <P>
1510 A substring that contains a binary zero is correctly extracted and has a
1511 further zero added on the end, but the result is not, of course, a C string.
1512 However, you can process such a string by referring to the length that is
1513 returned by <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>.
1514 Unfortunately, the interface to <b>pcre_get_substring_list()</b> is not adequate
1515 for handling strings containing binary zeros, because the end of the final
1516 string is not independently indicated.
1517 </P>
1518 <P>
1519 The first three arguments are the same for all three of these functions:
1520 <i>subject</i> is the subject string that has just been successfully matched,
1521 <i>ovector</i> is a pointer to the vector of integer offsets that was passed to
1522 <b>pcre_exec()</b>, and <i>stringcount</i> is the number of substrings that were
1523 captured by the match, including the substring that matched the entire regular
1524 expression. This is the value returned by <b>pcre_exec()</b> if it is greater
1525 than zero. If <b>pcre_exec()</b> returned zero, indicating that it ran out of
1526 space in <i>ovector</i>, the value passed as <i>stringcount</i> should be the
1527 number of elements in the vector divided by three.
1528 </P>
1529 <P>
1530 The functions <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>
1531 extract a single substring, whose number is given as <i>stringnumber</i>. A
1532 value of zero extracts the substring that matched the entire pattern, whereas
1533 higher values extract the captured substrings. For <b>pcre_copy_substring()</b>,
1534 the string is placed in <i>buffer</i>, whose length is given by
1535 <i>buffersize</i>, while for <b>pcre_get_substring()</b> a new block of memory is
1536 obtained via <b>pcre_malloc</b>, and its address is returned via
1537 <i>stringptr</i>. The yield of the function is the length of the string, not
1538 including the terminating zero, or one of these error codes:
1539 <pre>
1540 PCRE_ERROR_NOMEMORY (-6)
1541 </pre>
1542 The buffer was too small for <b>pcre_copy_substring()</b>, or the attempt to get
1543 memory failed for <b>pcre_get_substring()</b>.
1544 <pre>
1545 PCRE_ERROR_NOSUBSTRING (-7)
1546 </pre>
1547 There is no substring whose number is <i>stringnumber</i>.
1548 </P>
1549 <P>
1550 The <b>pcre_get_substring_list()</b> function extracts all available substrings
1551 and builds a list of pointers to them. All this is done in a single block of
1552 memory that is obtained via <b>pcre_malloc</b>. The address of the memory block
1553 is returned via <i>listptr</i>, which is also the start of the list of string
1554 pointers. The end of the list is marked by a NULL pointer. The yield of the
1555 function is zero if all went well, or the error code
1556 <pre>
1557 PCRE_ERROR_NOMEMORY (-6)
1558 </pre>
1559 if the attempt to get the memory block failed.
1560 </P>
1561 <P>
1562 When any of these functions encounter a substring that is unset, which can
1563 happen when capturing subpattern number <i>n+1</i> matches some part of the
1564 subject, but subpattern <i>n</i> has not been used at all, they return an empty
1565 string. This can be distinguished from a genuine zero-length substring by
1566 inspecting the appropriate offset in <i>ovector</i>, which is negative for unset
1567 substrings.
1568 </P>
1569 <P>
1570 The two convenience functions <b>pcre_free_substring()</b> and
1571 <b>pcre_free_substring_list()</b> can be used to free the memory returned by
1572 a previous call of <b>pcre_get_substring()</b> or
1573 <b>pcre_get_substring_list()</b>, respectively. They do nothing more than call
1574 the function pointed to by <b>pcre_free</b>, which of course could be called
1575 directly from a C program. However, PCRE is used in some situations where it is
1576 linked via a special interface to another programming language that cannot use
1577 <b>pcre_free</b> directly; it is for these cases that the functions are
1578 provided.
1579 </P>
1580 <br><a name="SEC16" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NAME</a><br>
1581 <P>
1582 <b>int pcre_get_stringnumber(const pcre *<i>code</i>,</b>
1583 <b>const char *<i>name</i>);</b>
1584 </P>
1585 <P>
1586 <b>int pcre_copy_named_substring(const pcre *<i>code</i>,</b>
1587 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
1588 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
1589 <b>char *<i>buffer</i>, int <i>buffersize</i>);</b>
1590 </P>
1591 <P>
1592 <b>int pcre_get_named_substring(const pcre *<i>code</i>,</b>
1593 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
1594 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
1595 <b>const char **<i>stringptr</i>);</b>
1596 </P>
1597 <P>
1598 To extract a substring by name, you first have to find associated number.
1599 For example, for this pattern
1600 <pre>
1601 (a+)b(?&#60;xxx&#62;\d+)...
1602 </pre>
1603 the number of the subpattern called "xxx" is 2. If the name is known to be
1604 unique (PCRE_DUPNAMES was not set), you can find the number from the name by
1605 calling <b>pcre_get_stringnumber()</b>. The first argument is the compiled
1606 pattern, and the second is the name. The yield of the function is the
1607 subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no subpattern of
1608 that name.
1609 </P>
1610 <P>
1611 Given the number, you can extract the substring directly, or use one of the
1612 functions described in the previous section. For convenience, there are also
1613 two functions that do the whole job.
1614 </P>
1615 <P>
1616 Most of the arguments of <b>pcre_copy_named_substring()</b> and
1617 <b>pcre_get_named_substring()</b> are the same as those for the similarly named
1618 functions that extract by number. As these are described in the previous
1619 section, they are not re-described here. There are just two differences:
1620 </P>
1621 <P>
1622 First, instead of a substring number, a substring name is given. Second, there
1623 is an extra argument, given at the start, which is a pointer to the compiled
1624 pattern. This is needed in order to gain access to the name-to-number
1625 translation table.
1626 </P>
1627 <P>
1628 These functions call <b>pcre_get_stringnumber()</b>, and if it succeeds, they
1629 then call <b>pcre_copy_substring()</b> or <b>pcre_get_substring()</b>, as
1630 appropriate. <b>NOTE:</b> If PCRE_DUPNAMES is set and there are duplicate names,
1631 the behaviour may not be what you want (see the next section).
1632 </P>
1633 <br><a name="SEC17" href="#TOC1">DUPLICATE SUBPATTERN NAMES</a><br>
1634 <P>
1635 <b>int pcre_get_stringtable_entries(const pcre *<i>code</i>,</b>
1636 <b>const char *<i>name</i>, char **<i>first</i>, char **<i>last</i>);</b>
1637 </P>
1638 <P>
1639 When a pattern is compiled with the PCRE_DUPNAMES option, names for subpatterns
1640 are not required to be unique. Normally, patterns with duplicate names are such
1641 that in any one match, only one of the named subpatterns participates. An
1642 example is shown in the
1643 <a href="pcrepattern.html"><b>pcrepattern</b></a>
1644 documentation. When duplicates are present, <b>pcre_copy_named_substring()</b>
1645 and <b>pcre_get_named_substring()</b> return the first substring corresponding
1646 to the given name that is set. If none are set, an empty string is returned.
1647 The <b>pcre_get_stringnumber()</b> function returns one of the numbers that are
1648 associated with the name, but it is not defined which it is.
1649 <br>
1650 <br>
1651 If you want to get full details of all captured substrings for a given name,
1652 you must use the <b>pcre_get_stringtable_entries()</b> function. The first
1653 argument is the compiled pattern, and the second is the name. The third and
1654 fourth are pointers to variables which are updated by the function. After it
1655 has run, they point to the first and last entries in the name-to-number table
1656 for the given name. The function itself returns the length of each entry, or
1657 PCRE_ERROR_NOSUBSTRING (-7) if there are none. The format of the table is
1658 described above in the section entitled <i>Information about a pattern</i>.
1659 Given all the relevant entries for the name, you can extract each of their
1660 numbers, and hence the captured data, if any.
1661 </P>
1662 <br><a name="SEC18" href="#TOC1">FINDING ALL POSSIBLE MATCHES</a><br>
1663 <P>
1664 The traditional matching function uses a similar algorithm to Perl, which stops
1665 when it finds the first match, starting at a given point in the subject. If you
1666 want to find all possible matches, or the longest possible match, consider
1667 using the alternative matching function (see below) instead. If you cannot use
1668 the alternative function, but still need to find all possible matches, you
1669 can kludge it up by making use of the callout facility, which is described in
1670 the
1671 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1672 documentation.
1673 </P>
1674 <P>
1675 What you have to do is to insert a callout right at the end of the pattern.
1676 When your callout function is called, extract and save the current matched
1677 substring. Then return 1, which forces <b>pcre_exec()</b> to backtrack and try
1678 other alternatives. Ultimately, when it runs out of matches, <b>pcre_exec()</b>
1679 will yield PCRE_ERROR_NOMATCH.
1680 <a name="dfamatch"></a></P>
1681 <br><a name="SEC19" href="#TOC1">MATCHING A PATTERN: THE ALTERNATIVE FUNCTION</a><br>
1682 <P>
1683 <b>int pcre_dfa_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
1684 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
1685 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>,</b>
1686 <b>int *<i>workspace</i>, int <i>wscount</i>);</b>
1687 </P>
1688 <P>
1689 The function <b>pcre_dfa_exec()</b> is called to match a subject string against
1690 a compiled pattern, using a matching algorithm that scans the subject string
1691 just once, and does not backtrack. This has different characteristics to the
1692 normal algorithm, and is not compatible with Perl. Some of the features of PCRE
1693 patterns are not supported. Nevertheless, there are times when this kind of
1694 matching can be useful. For a discussion of the two matching algorithms, see
1695 the
1696 <a href="pcrematching.html"><b>pcrematching</b></a>
1697 documentation.
1698 </P>
1699 <P>
1700 The arguments for the <b>pcre_dfa_exec()</b> function are the same as for
1701 <b>pcre_exec()</b>, plus two extras. The <i>ovector</i> argument is used in a
1702 different way, and this is described below. The other common arguments are used
1703 in the same way as for <b>pcre_exec()</b>, so their description is not repeated
1704 here.
1705 </P>
1706 <P>
1707 The two additional arguments provide workspace for the function. The workspace
1708 vector should contain at least 20 elements. It is used for keeping track of
1709 multiple paths through the pattern tree. More workspace will be needed for
1710 patterns and subjects where there are a lot of potential matches.
1711 </P>
1712 <P>
1713 Here is an example of a simple call to <b>pcre_dfa_exec()</b>:
1714 <pre>
1715 int rc;
1716 int ovector[10];
1717 int wspace[20];
1718 rc = pcre_dfa_exec(
1719 re, /* result of pcre_compile() */
1720 NULL, /* we didn't study the pattern */
1721 "some string", /* the subject string */
1722 11, /* the length of the subject string */
1723 0, /* start at offset 0 in the subject */
1724 0, /* default options */
1725 ovector, /* vector of integers for substring information */
1726 10, /* number of elements (NOT size in bytes) */
1727 wspace, /* working space vector */
1728 20); /* number of elements (NOT size in bytes) */
1729 </PRE>
1730 </P>
1731 <br><b>
1732 Option bits for <b>pcre_dfa_exec()</b>
1733 </b><br>
1734 <P>
1735 The unused bits of the <i>options</i> argument for <b>pcre_dfa_exec()</b> must be
1736 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_<i>xxx</i>,
1737 PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL,
1738 PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last three of these are
1739 the same as for <b>pcre_exec()</b>, so their description is not repeated here.
1740 <pre>
1741 PCRE_PARTIAL
1742 </pre>
1743 This has the same general effect as it does for <b>pcre_exec()</b>, but the
1744 details are slightly different. When PCRE_PARTIAL is set for
1745 <b>pcre_dfa_exec()</b>, the return code PCRE_ERROR_NOMATCH is converted into
1746 PCRE_ERROR_PARTIAL if the end of the subject is reached, there have been no
1747 complete matches, but there is still at least one matching possibility. The
1748 portion of the string that provided the partial match is set as the first
1749 matching string.
1750 <pre>
1751 PCRE_DFA_SHORTEST
1752 </pre>
1753 Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to stop as
1754 soon as it has found one match. Because of the way the alternative algorithm
1755 works, this is necessarily the shortest possible match at the first possible
1756 matching point in the subject string.
1757 <pre>
1758 PCRE_DFA_RESTART
1759 </pre>
1760 When <b>pcre_dfa_exec()</b> is called with the PCRE_PARTIAL option, and returns
1761 a partial match, it is possible to call it again, with additional subject
1762 characters, and have it continue with the same match. The PCRE_DFA_RESTART
1763 option requests this action; when it is set, the <i>workspace</i> and
1764 <i>wscount</i> options must reference the same vector as before because data
1765 about the match so far is left in them after a partial match. There is more
1766 discussion of this facility in the
1767 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1768 documentation.
1769 </P>
1770 <br><b>
1771 Successful returns from <b>pcre_dfa_exec()</b>
1772 </b><br>
1773 <P>
1774 When <b>pcre_dfa_exec()</b> succeeds, it may have matched more than one
1775 substring in the subject. Note, however, that all the matches from one run of
1776 the function start at the same point in the subject. The shorter matches are
1777 all initial substrings of the longer matches. For example, if the pattern
1778 <pre>
1779 &#60;.*&#62;
1780 </pre>
1781 is matched against the string
1782 <pre>
1783 This is &#60;something&#62; &#60;something else&#62; &#60;something further&#62; no more
1784 </pre>
1785 the three matched strings are
1786 <pre>
1787 &#60;something&#62;
1788 &#60;something&#62; &#60;something else&#62;
1789 &#60;something&#62; &#60;something else&#62; &#60;something further&#62;
1790 </pre>
1791 On success, the yield of the function is a number greater than zero, which is
1792 the number of matched substrings. The substrings themselves are returned in
1793 <i>ovector</i>. Each string uses two elements; the first is the offset to the
1794 start, and the second is the offset to the end. In fact, all the strings have
1795 the same start offset. (Space could have been saved by giving this only once,
1796 but it was decided to retain some compatibility with the way <b>pcre_exec()</b>
1797 returns data, even though the meaning of the strings is different.)
1798 </P>
1799 <P>
1800 The strings are returned in reverse order of length; that is, the longest
1801 matching string is given first. If there were too many matches to fit into
1802 <i>ovector</i>, the yield of the function is zero, and the vector is filled with
1803 the longest matches.
1804 </P>
1805 <br><b>
1806 Error returns from <b>pcre_dfa_exec()</b>
1807 </b><br>
1808 <P>
1809 The <b>pcre_dfa_exec()</b> function returns a negative number when it fails.
1810 Many of the errors are the same as for <b>pcre_exec()</b>, and these are
1811 described
1812 <a href="#errorlist">above.</a>
1813 There are in addition the following errors that are specific to
1814 <b>pcre_dfa_exec()</b>:
1815 <pre>
1816 PCRE_ERROR_DFA_UITEM (-16)
1817 </pre>
1818 This return is given if <b>pcre_dfa_exec()</b> encounters an item in the pattern
1819 that it does not support, for instance, the use of \C or a back reference.
1820 <pre>
1821 PCRE_ERROR_DFA_UCOND (-17)
1822 </pre>
1823 This return is given if <b>pcre_dfa_exec()</b> encounters a condition item that
1824 uses a back reference for the condition, or a test for recursion in a specific
1825 group. These are not supported.
1826 <pre>
1827 PCRE_ERROR_DFA_UMLIMIT (-18)
1828 </pre>
1829 This return is given if <b>pcre_dfa_exec()</b> is called with an <i>extra</i>
1830 block that contains a setting of the <i>match_limit</i> field. This is not
1831 supported (it is meaningless).
1832 <pre>
1833 PCRE_ERROR_DFA_WSSIZE (-19)
1834 </pre>
1835 This return is given if <b>pcre_dfa_exec()</b> runs out of space in the
1836 <i>workspace</i> vector.
1837 <pre>
1838 PCRE_ERROR_DFA_RECURSE (-20)
1839 </pre>
1840 When a recursive subpattern is processed, the matching function calls itself
1841 recursively, using private vectors for <i>ovector</i> and <i>workspace</i>. This
1842 error is given if the output vector is not large enough. This should be
1843 extremely rare, as a vector of size 1000 is used.
1844 </P>
1845 <br><a name="SEC20" href="#TOC1">SEE ALSO</a><br>
1846 <P>
1847 <b>pcrebuild</b>(3), <b>pcrecallout</b>(3), <b>pcrecpp(3)</b>(3),
1848 <b>pcrematching</b>(3), <b>pcrepartial</b>(3), <b>pcreposix</b>(3),
1849 <b>pcreprecompile</b>(3), <b>pcresample</b>(3), <b>pcrestack</b>(3).
1850 </P>
1851 <br><a name="SEC21" href="#TOC1">AUTHOR</a><br>
1852 <P>
1853 Philip Hazel
1854 <br>
1855 University Computing Service
1856 <br>
1857 Cambridge CB2 3QH, England.
1858 <br>
1859 </P>
1860 <br><a name="SEC22" href="#TOC1">REVISION</a><br>
1861 <P>
1862 Last updated: 24 April 2007
1863 <br>
1864 Copyright &copy; 1997-2007 University of Cambridge.
1865 <br>
1866 <p>
1867 Return to the <a href="index.html">PCRE index page</a>.
1868 </p>

Properties

Name Value
svn:eol-style native
svn:keywords "Author Date Id Revision Url"

webmaster@exim.org
ViewVC Help
Powered by ViewVC 1.1.12