ViewVC logotype

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

Parent Directory Parent Directory | Revision Log Revision Log

Revision 572 - (show annotations)
Wed Nov 17 17:55:57 2010 UTC (9 years, 2 months ago) by ph10
File MIME type: text/html
File size: 103189 byte(s)
Documentation updates and tidies.
1 <html>
2 <head>
3 <title>pcreapi specification</title>
4 </head>
5 <body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
6 <h1>pcreapi man page</h1>
7 <p>
8 Return to the <a href="index.html">PCRE index page</a>.
9 </p>
10 <p>
11 This page is part of the PCRE HTML documentation. It was generated automatically
12 from the original man page. If there is any nonsense in it, please consult the
13 man page, in case the conversion went wrong.
14 <br>
15 <ul>
16 <li><a name="TOC1" href="#SEC1">PCRE NATIVE API</a>
17 <li><a name="TOC2" href="#SEC2">PCRE API OVERVIEW</a>
18 <li><a name="TOC3" href="#SEC3">NEWLINES</a>
19 <li><a name="TOC4" href="#SEC4">MULTITHREADING</a>
21 <li><a name="TOC6" href="#SEC6">CHECKING BUILD-TIME OPTIONS</a>
22 <li><a name="TOC7" href="#SEC7">COMPILING A PATTERN</a>
23 <li><a name="TOC8" href="#SEC8">COMPILATION ERROR CODES</a>
24 <li><a name="TOC9" href="#SEC9">STUDYING A PATTERN</a>
25 <li><a name="TOC10" href="#SEC10">LOCALE SUPPORT</a>
26 <li><a name="TOC11" href="#SEC11">INFORMATION ABOUT A PATTERN</a>
27 <li><a name="TOC12" href="#SEC12">OBSOLETE INFO FUNCTION</a>
28 <li><a name="TOC13" href="#SEC13">REFERENCE COUNTS</a>
32 <li><a name="TOC17" href="#SEC17">DUPLICATE SUBPATTERN NAMES</a>
33 <li><a name="TOC18" href="#SEC18">FINDING ALL POSSIBLE MATCHES</a>
35 <li><a name="TOC20" href="#SEC20">SEE ALSO</a>
36 <li><a name="TOC21" href="#SEC21">AUTHOR</a>
37 <li><a name="TOC22" href="#SEC22">REVISION</a>
38 </ul>
39 <br><a name="SEC1" href="#TOC1">PCRE NATIVE API</a><br>
40 <P>
41 <b>#include &#60;pcre.h&#62;</b>
42 </P>
43 <P>
44 <b>pcre *pcre_compile(const char *<i>pattern</i>, int <i>options</i>,</b>
45 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
46 <b>const unsigned char *<i>tableptr</i>);</b>
47 </P>
48 <P>
49 <b>pcre *pcre_compile2(const char *<i>pattern</i>, int <i>options</i>,</b>
50 <b>int *<i>errorcodeptr</i>,</b>
51 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
52 <b>const unsigned char *<i>tableptr</i>);</b>
53 </P>
54 <P>
55 <b>pcre_extra *pcre_study(const pcre *<i>code</i>, int <i>options</i>,</b>
56 <b>const char **<i>errptr</i>);</b>
57 </P>
58 <P>
59 <b>int pcre_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
60 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
61 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>);</b>
62 </P>
63 <P>
64 <b>int pcre_dfa_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
65 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
66 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>,</b>
67 <b>int *<i>workspace</i>, int <i>wscount</i>);</b>
68 </P>
69 <P>
70 <b>int pcre_copy_named_substring(const pcre *<i>code</i>,</b>
71 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
72 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
73 <b>char *<i>buffer</i>, int <i>buffersize</i>);</b>
74 </P>
75 <P>
76 <b>int pcre_copy_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
77 <b>int <i>stringcount</i>, int <i>stringnumber</i>, char *<i>buffer</i>,</b>
78 <b>int <i>buffersize</i>);</b>
79 </P>
80 <P>
81 <b>int pcre_get_named_substring(const pcre *<i>code</i>,</b>
82 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
83 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
84 <b>const char **<i>stringptr</i>);</b>
85 </P>
86 <P>
87 <b>int pcre_get_stringnumber(const pcre *<i>code</i>,</b>
88 <b>const char *<i>name</i>);</b>
89 </P>
90 <P>
91 <b>int pcre_get_stringtable_entries(const pcre *<i>code</i>,</b>
92 <b>const char *<i>name</i>, char **<i>first</i>, char **<i>last</i>);</b>
93 </P>
94 <P>
95 <b>int pcre_get_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
96 <b>int <i>stringcount</i>, int <i>stringnumber</i>,</b>
97 <b>const char **<i>stringptr</i>);</b>
98 </P>
99 <P>
100 <b>int pcre_get_substring_list(const char *<i>subject</i>,</b>
101 <b>int *<i>ovector</i>, int <i>stringcount</i>, const char ***<i>listptr</i>);</b>
102 </P>
103 <P>
104 <b>void pcre_free_substring(const char *<i>stringptr</i>);</b>
105 </P>
106 <P>
107 <b>void pcre_free_substring_list(const char **<i>stringptr</i>);</b>
108 </P>
109 <P>
110 <b>const unsigned char *pcre_maketables(void);</b>
111 </P>
112 <P>
113 <b>int pcre_fullinfo(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
114 <b>int <i>what</i>, void *<i>where</i>);</b>
115 </P>
116 <P>
117 <b>int pcre_info(const pcre *<i>code</i>, int *<i>optptr</i>, int</b>
118 <b>*<i>firstcharptr</i>);</b>
119 </P>
120 <P>
121 <b>int pcre_refcount(pcre *<i>code</i>, int <i>adjust</i>);</b>
122 </P>
123 <P>
124 <b>int pcre_config(int <i>what</i>, void *<i>where</i>);</b>
125 </P>
126 <P>
127 <b>char *pcre_version(void);</b>
128 </P>
129 <P>
130 <b>void *(*pcre_malloc)(size_t);</b>
131 </P>
132 <P>
133 <b>void (*pcre_free)(void *);</b>
134 </P>
135 <P>
136 <b>void *(*pcre_stack_malloc)(size_t);</b>
137 </P>
138 <P>
139 <b>void (*pcre_stack_free)(void *);</b>
140 </P>
141 <P>
142 <b>int (*pcre_callout)(pcre_callout_block *);</b>
143 </P>
144 <br><a name="SEC2" href="#TOC1">PCRE API OVERVIEW</a><br>
145 <P>
146 PCRE has its own native API, which is described in this document. There are
147 also some wrapper functions that correspond to the POSIX regular expression
148 API. These are described in the
149 <a href="pcreposix.html"><b>pcreposix</b></a>
150 documentation. Both of these APIs define a set of C function calls. A C++
151 wrapper is distributed with PCRE. It is documented in the
152 <a href="pcrecpp.html"><b>pcrecpp</b></a>
153 page.
154 </P>
155 <P>
156 The native API C function prototypes are defined in the header file
157 <b>pcre.h</b>, and on Unix systems the library itself is called <b>libpcre</b>.
158 It can normally be accessed by adding <b>-lpcre</b> to the command for linking
159 an application that uses PCRE. The header file defines the macros PCRE_MAJOR
160 and PCRE_MINOR to contain the major and minor release numbers for the library.
161 Applications can use these to include support for different releases of PCRE.
162 </P>
163 <P>
164 In a Windows environment, if you want to statically link an application program
165 against a non-dll <b>pcre.a</b> file, you must define PCRE_STATIC before
166 including <b>pcre.h</b> or <b>pcrecpp.h</b>, because otherwise the
167 <b>pcre_malloc()</b> and <b>pcre_free()</b> exported functions will be declared
168 <b>__declspec(dllimport)</b>, with unwanted results.
169 </P>
170 <P>
171 The functions <b>pcre_compile()</b>, <b>pcre_compile2()</b>, <b>pcre_study()</b>,
172 and <b>pcre_exec()</b> are used for compiling and matching regular expressions
173 in a Perl-compatible manner. A sample program that demonstrates the simplest
174 way of using them is provided in the file called <i>pcredemo.c</i> in the PCRE
175 source distribution. A listing of this program is given in the
176 <a href="pcredemo.html"><b>pcredemo</b></a>
177 documentation, and the
178 <a href="pcresample.html"><b>pcresample</b></a>
179 documentation describes how to compile and run it.
180 </P>
181 <P>
182 A second matching function, <b>pcre_dfa_exec()</b>, which is not
183 Perl-compatible, is also provided. This uses a different algorithm for the
184 matching. The alternative algorithm finds all possible matches (at a given
185 point in the subject), and scans the subject just once (unless there are
186 lookbehind assertions). However, this algorithm does not return captured
187 substrings. A description of the two matching algorithms and their advantages
188 and disadvantages is given in the
189 <a href="pcrematching.html"><b>pcrematching</b></a>
190 documentation.
191 </P>
192 <P>
193 In addition to the main compiling and matching functions, there are convenience
194 functions for extracting captured substrings from a subject string that is
195 matched by <b>pcre_exec()</b>. They are:
196 <pre>
197 <b>pcre_copy_substring()</b>
198 <b>pcre_copy_named_substring()</b>
199 <b>pcre_get_substring()</b>
200 <b>pcre_get_named_substring()</b>
201 <b>pcre_get_substring_list()</b>
202 <b>pcre_get_stringnumber()</b>
203 <b>pcre_get_stringtable_entries()</b>
204 </pre>
205 <b>pcre_free_substring()</b> and <b>pcre_free_substring_list()</b> are also
206 provided, to free the memory used for extracted strings.
207 </P>
208 <P>
209 The function <b>pcre_maketables()</b> is used to build a set of character tables
210 in the current locale for passing to <b>pcre_compile()</b>, <b>pcre_exec()</b>,
211 or <b>pcre_dfa_exec()</b>. This is an optional facility that is provided for
212 specialist use. Most commonly, no special tables are passed, in which case
213 internal tables that are generated when PCRE is built are used.
214 </P>
215 <P>
216 The function <b>pcre_fullinfo()</b> is used to find out information about a
217 compiled pattern; <b>pcre_info()</b> is an obsolete version that returns only
218 some of the available information, but is retained for backwards compatibility.
219 The function <b>pcre_version()</b> returns a pointer to a string containing the
220 version of PCRE and its date of release.
221 </P>
222 <P>
223 The function <b>pcre_refcount()</b> maintains a reference count in a data block
224 containing a compiled pattern. This is provided for the benefit of
225 object-oriented applications.
226 </P>
227 <P>
228 The global variables <b>pcre_malloc</b> and <b>pcre_free</b> initially contain
229 the entry points of the standard <b>malloc()</b> and <b>free()</b> functions,
230 respectively. PCRE calls the memory management functions via these variables,
231 so a calling program can replace them if it wishes to intercept the calls. This
232 should be done before calling any PCRE functions.
233 </P>
234 <P>
235 The global variables <b>pcre_stack_malloc</b> and <b>pcre_stack_free</b> are also
236 indirections to memory management functions. These special functions are used
237 only when PCRE is compiled to use the heap for remembering data, instead of
238 recursive function calls, when running the <b>pcre_exec()</b> function. See the
239 <a href="pcrebuild.html"><b>pcrebuild</b></a>
240 documentation for details of how to do this. It is a non-standard way of
241 building PCRE, for use in environments that have limited stacks. Because of the
242 greater use of memory management, it runs more slowly. Separate functions are
243 provided so that special-purpose external code can be used for this case. When
244 used, these functions are always called in a stack-like manner (last obtained,
245 first freed), and always for memory blocks of the same size. There is a
246 discussion about PCRE's stack usage in the
247 <a href="pcrestack.html"><b>pcrestack</b></a>
248 documentation.
249 </P>
250 <P>
251 The global variable <b>pcre_callout</b> initially contains NULL. It can be set
252 by the caller to a "callout" function, which PCRE will then call at specified
253 points during a matching operation. Details are given in the
254 <a href="pcrecallout.html"><b>pcrecallout</b></a>
255 documentation.
256 <a name="newlines"></a></P>
257 <br><a name="SEC3" href="#TOC1">NEWLINES</a><br>
258 <P>
259 PCRE supports five different conventions for indicating line breaks in
260 strings: a single CR (carriage return) character, a single LF (linefeed)
261 character, the two-character sequence CRLF, any of the three preceding, or any
262 Unicode newline sequence. The Unicode newline sequences are the three just
263 mentioned, plus the single characters VT (vertical tab, U+000B), FF (formfeed,
264 U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS
265 (paragraph separator, U+2029).
266 </P>
267 <P>
268 Each of the first three conventions is used by at least one operating system as
269 its standard newline sequence. When PCRE is built, a default can be specified.
270 The default default is LF, which is the Unix standard. When PCRE is run, the
271 default can be overridden, either when a pattern is compiled, or when it is
272 matched.
273 </P>
274 <P>
275 At compile time, the newline convention can be specified by the <i>options</i>
276 argument of <b>pcre_compile()</b>, or it can be specified by special text at the
277 start of the pattern itself; this overrides any other settings. See the
278 <a href="pcrepattern.html"><b>pcrepattern</b></a>
279 page for details of the special character sequences.
280 </P>
281 <P>
282 In the PCRE documentation the word "newline" is used to mean "the character or
283 pair of characters that indicate a line break". The choice of newline
284 convention affects the handling of the dot, circumflex, and dollar
285 metacharacters, the handling of #-comments in /x mode, and, when CRLF is a
286 recognized line ending sequence, the match position advancement for a
287 non-anchored pattern. There is more detail about this in the
288 <a href="#execoptions">section on <b>pcre_exec()</b> options</a>
289 below.
290 </P>
291 <P>
292 The choice of newline convention does not affect the interpretation of
293 the \n or \r escape sequences, nor does it affect what \R matches, which is
294 controlled in a similar way, but by separate options.
295 </P>
296 <br><a name="SEC4" href="#TOC1">MULTITHREADING</a><br>
297 <P>
298 The PCRE functions can be used in multi-threading applications, with the
299 proviso that the memory management functions pointed to by <b>pcre_malloc</b>,
300 <b>pcre_free</b>, <b>pcre_stack_malloc</b>, and <b>pcre_stack_free</b>, and the
301 callout function pointed to by <b>pcre_callout</b>, are shared by all threads.
302 </P>
303 <P>
304 The compiled form of a regular expression is not altered during matching, so
305 the same compiled pattern can safely be used by several threads at once.
306 </P>
307 <br><a name="SEC5" href="#TOC1">SAVING PRECOMPILED PATTERNS FOR LATER USE</a><br>
308 <P>
309 The compiled form of a regular expression can be saved and re-used at a later
310 time, possibly by a different program, and even on a host other than the one on
311 which it was compiled. Details are given in the
312 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
313 documentation. However, compiling a regular expression with one version of PCRE
314 for use with a different version is not guaranteed to work and may cause
315 crashes.
316 </P>
317 <br><a name="SEC6" href="#TOC1">CHECKING BUILD-TIME OPTIONS</a><br>
318 <P>
319 <b>int pcre_config(int <i>what</i>, void *<i>where</i>);</b>
320 </P>
321 <P>
322 The function <b>pcre_config()</b> makes it possible for a PCRE client to
323 discover which optional features have been compiled into the PCRE library. The
324 <a href="pcrebuild.html"><b>pcrebuild</b></a>
325 documentation has more details about these optional features.
326 </P>
327 <P>
328 The first argument for <b>pcre_config()</b> is an integer, specifying which
329 information is required; the second argument is a pointer to a variable into
330 which the information is placed. The following information is available:
331 <pre>
333 </pre>
334 The output is an integer that is set to one if UTF-8 support is available;
335 otherwise it is set to zero.
336 <pre>
338 </pre>
339 The output is an integer that is set to one if support for Unicode character
340 properties is available; otherwise it is set to zero.
341 <pre>
343 </pre>
344 The output is an integer whose value specifies the default character sequence
345 that is recognized as meaning "newline". The four values that are supported
346 are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF, and -1 for ANY.
347 Though they are derived from ASCII, the same values are returned in EBCDIC
348 environments. The default should normally correspond to the standard sequence
349 for your operating system.
350 <pre>
352 </pre>
353 The output is an integer whose value indicates what character sequences the \R
354 escape sequence matches by default. A value of 0 means that \R matches any
355 Unicode line ending sequence; a value of 1 means that \R matches only CR, LF,
356 or CRLF. The default can be overridden when a pattern is compiled or matched.
357 <pre>
359 </pre>
360 The output is an integer that contains the number of bytes used for internal
361 linkage in compiled regular expressions. The value is 2, 3, or 4. Larger values
362 allow larger regular expressions to be compiled, at the expense of slower
363 matching. The default value of 2 is sufficient for all but the most massive
364 patterns, since it allows the compiled pattern to be up to 64K in size.
365 <pre>
367 </pre>
368 The output is an integer that contains the threshold above which the POSIX
369 interface uses <b>malloc()</b> for output vectors. Further details are given in
370 the
371 <a href="pcreposix.html"><b>pcreposix</b></a>
372 documentation.
373 <pre>
375 </pre>
376 The output is a long integer that gives the default limit for the number of
377 internal matching function calls in a <b>pcre_exec()</b> execution. Further
378 details are given with <b>pcre_exec()</b> below.
379 <pre>
381 </pre>
382 The output is a long integer that gives the default limit for the depth of
383 recursion when calling the internal matching function in a <b>pcre_exec()</b>
384 execution. Further details are given with <b>pcre_exec()</b> below.
385 <pre>
387 </pre>
388 The output is an integer that is set to one if internal recursion when running
389 <b>pcre_exec()</b> is implemented by recursive function calls that use the stack
390 to remember their state. This is the usual way that PCRE is compiled. The
391 output is zero if PCRE was compiled to use blocks of data on the heap instead
392 of recursive function calls. In this case, <b>pcre_stack_malloc</b> and
393 <b>pcre_stack_free</b> are called to manage memory blocks on the heap, thus
394 avoiding the use of the stack.
395 </P>
396 <br><a name="SEC7" href="#TOC1">COMPILING A PATTERN</a><br>
397 <P>
398 <b>pcre *pcre_compile(const char *<i>pattern</i>, int <i>options</i>,</b>
399 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
400 <b>const unsigned char *<i>tableptr</i>);</b>
401 <b>pcre *pcre_compile2(const char *<i>pattern</i>, int <i>options</i>,</b>
402 <b>int *<i>errorcodeptr</i>,</b>
403 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
404 <b>const unsigned char *<i>tableptr</i>);</b>
405 </P>
406 <P>
407 Either of the functions <b>pcre_compile()</b> or <b>pcre_compile2()</b> can be
408 called to compile a pattern into an internal form. The only difference between
409 the two interfaces is that <b>pcre_compile2()</b> has an additional argument,
410 <i>errorcodeptr</i>, via which a numerical error code can be returned. To avoid
411 too much repetition, we refer just to <b>pcre_compile()</b> below, but the
412 information applies equally to <b>pcre_compile2()</b>.
413 </P>
414 <P>
415 The pattern is a C string terminated by a binary zero, and is passed in the
416 <i>pattern</i> argument. A pointer to a single block of memory that is obtained
417 via <b>pcre_malloc</b> is returned. This contains the compiled code and related
418 data. The <b>pcre</b> type is defined for the returned block; this is a typedef
419 for a structure whose contents are not externally defined. It is up to the
420 caller to free the memory (via <b>pcre_free</b>) when it is no longer required.
421 </P>
422 <P>
423 Although the compiled code of a PCRE regex is relocatable, that is, it does not
424 depend on memory location, the complete <b>pcre</b> data block is not
425 fully relocatable, because it may contain a copy of the <i>tableptr</i>
426 argument, which is an address (see below).
427 </P>
428 <P>
429 The <i>options</i> argument contains various bit settings that affect the
430 compilation. It should be zero if no options are required. The available
431 options are described below. Some of them (in particular, those that are
432 compatible with Perl, but some others as well) can also be set and unset from
433 within the pattern (see the detailed description in the
434 <a href="pcrepattern.html"><b>pcrepattern</b></a>
435 documentation). For those options that can be different in different parts of
436 the pattern, the contents of the <i>options</i> argument specifies their
437 settings at the start of compilation and execution. The PCRE_ANCHORED,
438 PCRE_BSR_<i>xxx</i>, and PCRE_NEWLINE_<i>xxx</i> options can be set at the time
439 of matching as well as at compile time.
440 </P>
441 <P>
442 If <i>errptr</i> is NULL, <b>pcre_compile()</b> returns NULL immediately.
443 Otherwise, if compilation of a pattern fails, <b>pcre_compile()</b> returns
444 NULL, and sets the variable pointed to by <i>errptr</i> to point to a textual
445 error message. This is a static string that is part of the library. You must
446 not try to free it. The offset from the start of the pattern to the byte that
447 was being processed when the error was discovered is placed in the variable
448 pointed to by <i>erroffset</i>, which must not be NULL. If it is, an immediate
449 error is given. Some errors are not detected until checks are carried out when
450 the whole pattern has been scanned; in this case the offset is set to the end
451 of the pattern.
452 </P>
453 <P>
454 Note that the offset is in bytes, not characters, even in UTF-8 mode. It may
455 point into the middle of a UTF-8 character (for example, when
456 PCRE_ERROR_BADUTF8 is returned for an invalid UTF-8 string).
457 </P>
458 <P>
459 If <b>pcre_compile2()</b> is used instead of <b>pcre_compile()</b>, and the
460 <i>errorcodeptr</i> argument is not NULL, a non-zero error code number is
461 returned via this argument in the event of an error. This is in addition to the
462 textual error message. Error codes and messages are listed below.
463 </P>
464 <P>
465 If the final argument, <i>tableptr</i>, is NULL, PCRE uses a default set of
466 character tables that are built when PCRE is compiled, using the default C
467 locale. Otherwise, <i>tableptr</i> must be an address that is the result of a
468 call to <b>pcre_maketables()</b>. This value is stored with the compiled
469 pattern, and used again by <b>pcre_exec()</b>, unless another table pointer is
470 passed to it. For more discussion, see the section on locale support below.
471 </P>
472 <P>
473 This code fragment shows a typical straightforward call to <b>pcre_compile()</b>:
474 <pre>
475 pcre *re;
476 const char *error;
477 int erroffset;
478 re = pcre_compile(
479 "^A.*Z", /* the pattern */
480 0, /* default options */
481 &error, /* for error message */
482 &erroffset, /* for error offset */
483 NULL); /* use default character tables */
484 </pre>
485 The following names for option bits are defined in the <b>pcre.h</b> header
486 file:
487 <pre>
489 </pre>
490 If this bit is set, the pattern is forced to be "anchored", that is, it is
491 constrained to match only at the first matching point in the string that is
492 being searched (the "subject string"). This effect can also be achieved by
493 appropriate constructs in the pattern itself, which is the only way to do it in
494 Perl.
495 <pre>
497 </pre>
498 If this bit is set, <b>pcre_compile()</b> automatically inserts callout items,
499 all with number 255, before each pattern item. For discussion of the callout
500 facility, see the
501 <a href="pcrecallout.html"><b>pcrecallout</b></a>
502 documentation.
503 <pre>
506 </pre>
507 These options (which are mutually exclusive) control what the \R escape
508 sequence matches. The choice is either to match only CR, LF, or CRLF, or to
509 match any Unicode newline sequence. The default is specified when PCRE is
510 built. It can be overridden from within the pattern, or by setting an option
511 when a compiled pattern is matched.
512 <pre>
514 </pre>
515 If this bit is set, letters in the pattern match both upper and lower case
516 letters. It is equivalent to Perl's /i option, and it can be changed within a
517 pattern by a (?i) option setting. In UTF-8 mode, PCRE always understands the
518 concept of case for characters whose values are less than 128, so caseless
519 matching is always possible. For characters with higher values, the concept of
520 case is supported if PCRE is compiled with Unicode property support, but not
521 otherwise. If you want to use caseless matching for characters 128 and above,
522 you must ensure that PCRE is compiled with Unicode property support as well as
523 with UTF-8 support.
524 <pre>
526 </pre>
527 If this bit is set, a dollar metacharacter in the pattern matches only at the
528 end of the subject string. Without this option, a dollar also matches
529 immediately before a newline at the end of the string (but not before any other
530 newlines). The PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is set.
531 There is no equivalent to this option in Perl, and no way to set it within a
532 pattern.
533 <pre>
535 </pre>
536 If this bit is set, a dot metacharacter in the pattern matches a character of
537 any value, including one that indicates a newline. However, it only ever
538 matches one character, even if newlines are coded as CRLF. Without this option,
539 a dot does not match when the current position is at a newline. This option is
540 equivalent to Perl's /s option, and it can be changed within a pattern by a
541 (?s) option setting. A negative class such as [^a] always matches newline
542 characters, independent of the setting of this option.
543 <pre>
545 </pre>
546 If this bit is set, names used to identify capturing subpatterns need not be
547 unique. This can be helpful for certain types of pattern when it is known that
548 only one instance of the named subpattern can ever be matched. There are more
549 details of named subpatterns below; see also the
550 <a href="pcrepattern.html"><b>pcrepattern</b></a>
551 documentation.
552 <pre>
554 </pre>
555 If this bit is set, whitespace data characters in the pattern are totally
556 ignored except when escaped or inside a character class. Whitespace does not
557 include the VT character (code 11). In addition, characters between an
558 unescaped # outside a character class and the next newline, inclusive, are also
559 ignored. This is equivalent to Perl's /x option, and it can be changed within a
560 pattern by a (?x) option setting.
561 </P>
562 <P>
563 Which characters are interpreted as newlines
564 is controlled by the options passed to <b>pcre_compile()</b> or by a special
565 sequence at the start of the pattern, as described in the section entitled
566 <a href="pcrepattern.html#newlines">"Newline conventions"</a>
567 in the <b>pcrepattern</b> documentation. Note that the end of this type of
568 comment is a literal newline sequence in the pattern; escape sequences that
569 happen to represent a newline do not count.
570 </P>
571 <P>
572 This option makes it possible to include comments inside complicated patterns.
573 Note, however, that this applies only to data characters. Whitespace characters
574 may never appear within special character sequences in a pattern, for example
575 within the sequence (?( that introduces a conditional subpattern.
576 <pre>
578 </pre>
579 This option was invented in order to turn on additional functionality of PCRE
580 that is incompatible with Perl, but it is currently of very little use. When
581 set, any backslash in a pattern that is followed by a letter that has no
582 special meaning causes an error, thus reserving these combinations for future
583 expansion. By default, as in Perl, a backslash followed by a letter with no
584 special meaning is treated as a literal. (Perl can, however, be persuaded to
585 give an error for this, by running it with the -w option.) There are at present
586 no other features controlled by this option. It can also be set by a (?X)
587 option setting within a pattern.
588 <pre>
590 </pre>
591 If this option is set, an unanchored pattern is required to match before or at
592 the first newline in the subject string, though the matched text may continue
593 over the newline.
594 <pre>
596 </pre>
597 If this option is set, PCRE's behaviour is changed in some ways so that it is
598 compatible with JavaScript rather than Perl. The changes are as follows:
599 </P>
600 <P>
601 (1) A lone closing square bracket in a pattern causes a compile-time error,
602 because this is illegal in JavaScript (by default it is treated as a data
603 character). Thus, the pattern AB]CD becomes illegal when this option is set.
604 </P>
605 <P>
606 (2) At run time, a back reference to an unset subpattern group matches an empty
607 string (by default this causes the current matching alternative to fail). A
608 pattern such as (\1)(a) succeeds when this option is set (assuming it can find
609 an "a" in the subject), whereas it fails by default, for Perl compatibility.
610 <pre>
612 </pre>
613 By default, PCRE treats the subject string as consisting of a single line of
614 characters (even if it actually contains newlines). The "start of line"
615 metacharacter (^) matches only at the start of the string, while the "end of
616 line" metacharacter ($) matches only at the end of the string, or before a
617 terminating newline (unless PCRE_DOLLAR_ENDONLY is set). This is the same as
618 Perl.
619 </P>
620 <P>
621 When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs
622 match immediately following or immediately before internal newlines in the
623 subject string, respectively, as well as at the very start and end. This is
624 equivalent to Perl's /m option, and it can be changed within a pattern by a
625 (?m) option setting. If there are no newlines in a subject string, or no
626 occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no effect.
627 <pre>
633 </pre>
634 These options override the default newline definition that was chosen when PCRE
635 was built. Setting the first or the second specifies that a newline is
636 indicated by a single character (CR or LF, respectively). Setting
637 PCRE_NEWLINE_CRLF specifies that a newline is indicated by the two-character
638 CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies that any of the three
639 preceding sequences should be recognized. Setting PCRE_NEWLINE_ANY specifies
640 that any Unicode newline sequence should be recognized. The Unicode newline
641 sequences are the three just mentioned, plus the single characters VT (vertical
642 tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS (line
643 separator, U+2028), and PS (paragraph separator, U+2029). The last two are
644 recognized only in UTF-8 mode.
645 </P>
646 <P>
647 The newline setting in the options word uses three bits that are treated
648 as a number, giving eight possibilities. Currently only six are used (default
649 plus the five values above). This means that if you set more than one newline
650 option, the combination may or may not be sensible. For example,
652 other combinations may yield unused numbers and cause an error.
653 </P>
654 <P>
655 The only time that a line break in a pattern is specially recognized when
656 compiling is when PCRE_EXTENDED is set. CR and LF are whitespace characters,
657 and so are ignored in this mode. Also, an unescaped # outside a character class
658 indicates a comment that lasts until after the next line break sequence. In
659 other circumstances, line break sequences in patterns are treated as literal
660 data.
661 </P>
662 <P>
663 The newline option that is set at compile time becomes the default that is used
664 for <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b>, but it can be overridden.
665 <pre>
667 </pre>
668 If this option is set, it disables the use of numbered capturing parentheses in
669 the pattern. Any opening parenthesis that is not followed by ? behaves as if it
670 were followed by ?: but named parentheses can still be used for capturing (and
671 they acquire numbers in the usual way). There is no equivalent of this option
672 in Perl.
673 <pre>
675 </pre>
676 This option changes the way PCRE processes \B, \b, \D, \d, \S, \s, \W,
677 \w, and some of the POSIX character classes. By default, only ASCII characters
678 are recognized, but if PCRE_UCP is set, Unicode properties are used instead to
679 classify characters. More details are given in the section on
680 <a href="pcre.html#genericchartypes">generic character types</a>
681 in the
682 <a href="pcrepattern.html"><b>pcrepattern</b></a>
683 page. If you set PCRE_UCP, matching one of the items it affects takes much
684 longer. The option is available only if PCRE has been compiled with Unicode
685 property support.
686 <pre>
688 </pre>
689 This option inverts the "greediness" of the quantifiers so that they are not
690 greedy by default, but become greedy if followed by "?". It is not compatible
691 with Perl. It can also be set by a (?U) option setting within the pattern.
692 <pre>
694 </pre>
695 This option causes PCRE to regard both the pattern and the subject as strings
696 of UTF-8 characters instead of single-byte character strings. However, it is
697 available only when PCRE is built to include UTF-8 support. If not, the use
698 of this option provokes an error. Details of how this option changes the
699 behaviour of PCRE are given in the
700 <a href="pcre.html#utf8support">section on UTF-8 support</a>
701 in the main
702 <a href="pcre.html"><b>pcre</b></a>
703 page.
704 <pre>
706 </pre>
707 When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
708 automatically checked. There is a discussion about the
709 <a href="pcre.html#utf8strings">validity of UTF-8 strings</a>
710 in the main
711 <a href="pcre.html"><b>pcre</b></a>
712 page. If an invalid UTF-8 sequence of bytes is found, <b>pcre_compile()</b>
713 returns an error. If you already know that your pattern is valid, and you want
714 to skip this check for performance reasons, you can set the PCRE_NO_UTF8_CHECK
715 option. When it is set, the effect of passing an invalid UTF-8 string as a
716 pattern is undefined. It may cause your program to crash. Note that this option
717 can also be passed to <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b>, to suppress
718 the UTF-8 validity checking of subject strings.
719 </P>
720 <br><a name="SEC8" href="#TOC1">COMPILATION ERROR CODES</a><br>
721 <P>
722 The following table lists the error codes than may be returned by
723 <b>pcre_compile2()</b>, along with the error messages that may be returned by
724 both compiling functions. As PCRE has developed, some error codes have fallen
725 out of use. To avoid confusion, they have not been re-used.
726 <pre>
727 0 no error
728 1 \ at end of pattern
729 2 \c at end of pattern
730 3 unrecognized character follows \
731 4 numbers out of order in {} quantifier
732 5 number too big in {} quantifier
733 6 missing terminating ] for character class
734 7 invalid escape sequence in character class
735 8 range out of order in character class
736 9 nothing to repeat
737 10 [this code is not in use]
738 11 internal error: unexpected repeat
739 12 unrecognized character after (? or (?-
740 13 POSIX named classes are supported only within a class
741 14 missing )
742 15 reference to non-existent subpattern
743 16 erroffset passed as NULL
744 17 unknown option bit(s) set
745 18 missing ) after comment
746 19 [this code is not in use]
747 20 regular expression is too large
748 21 failed to get memory
749 22 unmatched parentheses
750 23 internal error: code overflow
751 24 unrecognized character after (?&#60;
752 25 lookbehind assertion is not fixed length
753 26 malformed number or name after (?(
754 27 conditional group contains more than two branches
755 28 assertion expected after (?(
756 29 (?R or (?[+-]digits must be followed by )
757 30 unknown POSIX class name
758 31 POSIX collating elements are not supported
759 32 this version of PCRE is not compiled with PCRE_UTF8 support
760 33 [this code is not in use]
761 34 character value in \x{...} sequence is too large
762 35 invalid condition (?(0)
763 36 \C not allowed in lookbehind assertion
764 37 PCRE does not support \L, \l, \N, \U, or \u
765 38 number after (?C is &#62; 255
766 39 closing ) for (?C expected
767 40 recursive call could loop indefinitely
768 41 unrecognized character after (?P
769 42 syntax error in subpattern name (missing terminator)
770 43 two named subpatterns have the same name
771 44 invalid UTF-8 string
772 45 support for \P, \p, and \X has not been compiled
773 46 malformed \P or \p sequence
774 47 unknown property name after \P or \p
775 48 subpattern name is too long (maximum 32 characters)
776 49 too many named subpatterns (maximum 10000)
777 50 [this code is not in use]
778 51 octal value is greater than \377 (not in UTF-8 mode)
779 52 internal error: overran compiling workspace
780 53 internal error: previously-checked referenced subpattern
781 not found
782 54 DEFINE group contains more than one branch
783 55 repeating a DEFINE group is not allowed
784 56 inconsistent NEWLINE options
785 57 \g is not followed by a braced, angle-bracketed, or quoted
786 name/number or by a plain number
787 58 a numbered reference must not be zero
788 59 an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT)
789 60 (*VERB) not recognized
790 61 number is too big
791 62 subpattern name expected
792 63 digit expected after (?+
793 64 ] is an invalid data character in JavaScript compatibility mode
794 65 different names for subpatterns of the same number are
795 not allowed
796 66 (*MARK) must have an argument
797 67 this version of PCRE is not compiled with PCRE_UCP support
798 </pre>
799 The numbers 32 and 10000 in errors 48 and 49 are defaults; different values may
800 be used if the limits were changed when PCRE was built.
801 </P>
802 <br><a name="SEC9" href="#TOC1">STUDYING A PATTERN</a><br>
803 <P>
804 <b>pcre_extra *pcre_study(const pcre *<i>code</i>, int <i>options</i></b>
805 <b>const char **<i>errptr</i>);</b>
806 </P>
807 <P>
808 If a compiled pattern is going to be used several times, it is worth spending
809 more time analyzing it in order to speed up the time taken for matching. The
810 function <b>pcre_study()</b> takes a pointer to a compiled pattern as its first
811 argument. If studying the pattern produces additional information that will
812 help speed up matching, <b>pcre_study()</b> returns a pointer to a
813 <b>pcre_extra</b> block, in which the <i>study_data</i> field points to the
814 results of the study.
815 </P>
816 <P>
817 The returned value from <b>pcre_study()</b> can be passed directly to
818 <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b>. However, a <b>pcre_extra</b> block
819 also contains other fields that can be set by the caller before the block is
820 passed; these are described
821 <a href="#extradata">below</a>
822 in the section on matching a pattern.
823 </P>
824 <P>
825 If studying the pattern does not produce any useful information,
826 <b>pcre_study()</b> returns NULL. In that circumstance, if the calling program
827 wants to pass any of the other fields to <b>pcre_exec()</b> or
828 <b>pcre_dfa_exec()</b>, it must set up its own <b>pcre_extra</b> block.
829 </P>
830 <P>
831 The second argument of <b>pcre_study()</b> contains option bits. At present, no
832 options are defined, and this argument should always be zero.
833 </P>
834 <P>
835 The third argument for <b>pcre_study()</b> is a pointer for an error message. If
836 studying succeeds (even if no data is returned), the variable it points to is
837 set to NULL. Otherwise it is set to point to a textual error message. This is a
838 static string that is part of the library. You must not try to free it. You
839 should test the error pointer for NULL after calling <b>pcre_study()</b>, to be
840 sure that it has run successfully.
841 </P>
842 <P>
843 This is a typical call to <b>pcre_study</b>():
844 <pre>
845 pcre_extra *pe;
846 pe = pcre_study(
847 re, /* result of pcre_compile() */
848 0, /* no options exist */
849 &error); /* set to NULL or points to a message */
850 </pre>
851 Studying a pattern does two things: first, a lower bound for the length of
852 subject string that is needed to match the pattern is computed. This does not
853 mean that there are any strings of that length that match, but it does
854 guarantee that no shorter strings match. The value is used by
855 <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b> to avoid wasting time by trying to
856 match strings that are shorter than the lower bound. You can find out the value
857 in a calling program via the <b>pcre_fullinfo()</b> function.
858 </P>
859 <P>
860 Studying a pattern is also useful for non-anchored patterns that do not have a
861 single fixed starting character. A bitmap of possible starting bytes is
862 created. This speeds up finding a position in the subject at which to start
863 matching.
864 </P>
865 <P>
866 The two optimizations just described can be disabled by setting the
867 PCRE_NO_START_OPTIMIZE option when calling <b>pcre_exec()</b> or
868 <b>pcre_dfa_exec()</b>. You might want to do this if your pattern contains
869 callouts or (*MARK), and you want to make use of these facilities in cases
870 where matching fails. See the discussion of PCRE_NO_START_OPTIMIZE
871 <a href="#execoptions">below.</a>
872 <a name="localesupport"></a></P>
873 <br><a name="SEC10" href="#TOC1">LOCALE SUPPORT</a><br>
874 <P>
875 PCRE handles caseless matching, and determines whether characters are letters,
876 digits, or whatever, by reference to a set of tables, indexed by character
877 value. When running in UTF-8 mode, this applies only to characters with codes
878 less than 128. By default, higher-valued codes never match escapes such as \w
879 or \d, but they can be tested with \p if PCRE is built with Unicode character
880 property support. Alternatively, the PCRE_UCP option can be set at compile
881 time; this causes \w and friends to use Unicode property support instead of
882 built-in tables. The use of locales with Unicode is discouraged. If you are
883 handling characters with codes greater than 128, you should either use UTF-8
884 and Unicode, or use locales, but not try to mix the two.
885 </P>
886 <P>
887 PCRE contains an internal set of tables that are used when the final argument
888 of <b>pcre_compile()</b> is NULL. These are sufficient for many applications.
889 Normally, the internal tables recognize only ASCII characters. However, when
890 PCRE is built, it is possible to cause the internal tables to be rebuilt in the
891 default "C" locale of the local system, which may cause them to be different.
892 </P>
893 <P>
894 The internal tables can always be overridden by tables supplied by the
895 application that calls PCRE. These may be created in a different locale from
896 the default. As more and more applications change to using Unicode, the need
897 for this locale support is expected to die away.
898 </P>
899 <P>
900 External tables are built by calling the <b>pcre_maketables()</b> function,
901 which has no arguments, in the relevant locale. The result can then be passed
902 to <b>pcre_compile()</b> or <b>pcre_exec()</b> as often as necessary. For
903 example, to build and use tables that are appropriate for the French locale
904 (where accented characters with values greater than 128 are treated as letters),
905 the following code could be used:
906 <pre>
907 setlocale(LC_CTYPE, "fr_FR");
908 tables = pcre_maketables();
909 re = pcre_compile(..., tables);
910 </pre>
911 The locale name "fr_FR" is used on Linux and other Unix-like systems; if you
912 are using Windows, the name for the French locale is "french".
913 </P>
914 <P>
915 When <b>pcre_maketables()</b> runs, the tables are built in memory that is
916 obtained via <b>pcre_malloc</b>. It is the caller's responsibility to ensure
917 that the memory containing the tables remains available for as long as it is
918 needed.
919 </P>
920 <P>
921 The pointer that is passed to <b>pcre_compile()</b> is saved with the compiled
922 pattern, and the same tables are used via this pointer by <b>pcre_study()</b>
923 and normally also by <b>pcre_exec()</b>. Thus, by default, for any single
924 pattern, compilation, studying and matching all happen in the same locale, but
925 different patterns can be compiled in different locales.
926 </P>
927 <P>
928 It is possible to pass a table pointer or NULL (indicating the use of the
929 internal tables) to <b>pcre_exec()</b>. Although not intended for this purpose,
930 this facility could be used to match a pattern in a different locale from the
931 one in which it was compiled. Passing table pointers at run time is discussed
932 below in the section on matching a pattern.
933 </P>
934 <br><a name="SEC11" href="#TOC1">INFORMATION ABOUT A PATTERN</a><br>
935 <P>
936 <b>int pcre_fullinfo(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
937 <b>int <i>what</i>, void *<i>where</i>);</b>
938 </P>
939 <P>
940 The <b>pcre_fullinfo()</b> function returns information about a compiled
941 pattern. It replaces the obsolete <b>pcre_info()</b> function, which is
942 nevertheless retained for backwards compability (and is documented below).
943 </P>
944 <P>
945 The first argument for <b>pcre_fullinfo()</b> is a pointer to the compiled
946 pattern. The second argument is the result of <b>pcre_study()</b>, or NULL if
947 the pattern was not studied. The third argument specifies which piece of
948 information is required, and the fourth argument is a pointer to a variable
949 to receive the data. The yield of the function is zero for success, or one of
950 the following negative numbers:
951 <pre>
952 PCRE_ERROR_NULL the argument <i>code</i> was NULL
953 the argument <i>where</i> was NULL
954 PCRE_ERROR_BADMAGIC the "magic number" was not found
955 PCRE_ERROR_BADOPTION the value of <i>what</i> was invalid
956 </pre>
957 The "magic number" is placed at the start of each compiled pattern as an simple
958 check against passing an arbitrary memory pointer. Here is a typical call of
959 <b>pcre_fullinfo()</b>, to obtain the length of the compiled pattern:
960 <pre>
961 int rc;
962 size_t length;
963 rc = pcre_fullinfo(
964 re, /* result of pcre_compile() */
965 pe, /* result of pcre_study(), or NULL */
966 PCRE_INFO_SIZE, /* what is required */
967 &length); /* where to put the data */
968 </pre>
969 The possible values for the third argument are defined in <b>pcre.h</b>, and are
970 as follows:
971 <pre>
973 </pre>
974 Return the number of the highest back reference in the pattern. The fourth
975 argument should point to an <b>int</b> variable. Zero is returned if there are
976 no back references.
977 <pre>
979 </pre>
980 Return the number of capturing subpatterns in the pattern. The fourth argument
981 should point to an <b>int</b> variable.
982 <pre>
984 </pre>
985 Return a pointer to the internal default character tables within PCRE. The
986 fourth argument should point to an <b>unsigned char *</b> variable. This
987 information call is provided for internal use by the <b>pcre_study()</b>
988 function. External callers can cause PCRE to use its internal tables by passing
989 a NULL table pointer.
990 <pre>
992 </pre>
993 Return information about the first byte of any matched string, for a
994 non-anchored pattern. The fourth argument should point to an <b>int</b>
995 variable. (This option used to be called PCRE_INFO_FIRSTCHAR; the old name is
996 still recognized for backwards compatibility.)
997 </P>
998 <P>
999 If there is a fixed first byte, for example, from a pattern such as
1000 (cat|cow|coyote), its value is returned. Otherwise, if either
1001 <br>
1002 <br>
1003 (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
1004 starts with "^", or
1005 <br>
1006 <br>
1007 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
1008 (if it were set, the pattern would be anchored),
1009 <br>
1010 <br>
1011 -1 is returned, indicating that the pattern matches only at the start of a
1012 subject string or after any newline within the string. Otherwise -2 is
1013 returned. For anchored patterns, -2 is returned.
1014 <pre>
1016 </pre>
1017 If the pattern was studied, and this resulted in the construction of a 256-bit
1018 table indicating a fixed set of bytes for the first byte in any matching
1019 string, a pointer to the table is returned. Otherwise NULL is returned. The
1020 fourth argument should point to an <b>unsigned char *</b> variable.
1021 <pre>
1023 </pre>
1024 Return 1 if the pattern contains any explicit matches for CR or LF characters,
1025 otherwise 0. The fourth argument should point to an <b>int</b> variable. An
1026 explicit match is either a literal CR or LF character, or \r or \n.
1027 <pre>
1029 </pre>
1030 Return 1 if the (?J) or (?-J) option setting is used in the pattern, otherwise
1031 0. The fourth argument should point to an <b>int</b> variable. (?J) and
1032 (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
1033 <pre>
1035 </pre>
1036 Return the value of the rightmost literal byte that must exist in any matched
1037 string, other than at its start, if such a byte has been recorded. The fourth
1038 argument should point to an <b>int</b> variable. If there is no such byte, -1 is
1039 returned. For anchored patterns, a last literal byte is recorded only if it
1040 follows something of variable length. For example, for the pattern
1041 /^a\d+z\d+/ the returned value is "z", but for /^a\dz\d/ the returned value
1042 is -1.
1043 <pre>
1045 </pre>
1046 If the pattern was studied and a minimum length for matching subject strings
1047 was computed, its value is returned. Otherwise the returned value is -1. The
1048 value is a number of characters, not bytes (this may be relevant in UTF-8
1049 mode). The fourth argument should point to an <b>int</b> variable. A
1050 non-negative value is a lower bound to the length of any matching string. There
1051 may not be any strings of that length that do actually match, but every string
1052 that does match is at least that long.
1053 <pre>
1057 </pre>
1058 PCRE supports the use of named as well as numbered capturing parentheses. The
1059 names are just an additional way of identifying the parentheses, which still
1060 acquire numbers. Several convenience functions such as
1061 <b>pcre_get_named_substring()</b> are provided for extracting captured
1062 substrings by name. It is also possible to extract the data directly, by first
1063 converting the name to a number in order to access the correct pointers in the
1064 output vector (described with <b>pcre_exec()</b> below). To do the conversion,
1065 you need to use the name-to-number map, which is described by these three
1066 values.
1067 </P>
1068 <P>
1069 The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives
1070 the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each
1071 entry; both of these return an <b>int</b> value. The entry size depends on the
1072 length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first
1073 entry of the table (a pointer to <b>char</b>). The first two bytes of each entry
1074 are the number of the capturing parenthesis, most significant byte first. The
1075 rest of the entry is the corresponding name, zero terminated.
1076 </P>
1077 <P>
1078 The names are in alphabetical order. Duplicate names may appear if (?| is used
1079 to create multiple groups with the same number, as described in the
1080 <a href="pcrepattern.html#dupsubpatternnumber">section on duplicate subpattern numbers</a>
1081 in the
1082 <a href="pcrepattern.html"><b>pcrepattern</b></a>
1083 page. Duplicate names for subpatterns with different numbers are permitted only
1084 if PCRE_DUPNAMES is set. In all cases of duplicate names, they appear in the
1085 table in the order in which they were found in the pattern. In the absence of
1086 (?| this is the order of increasing number; when (?| is used this is not
1087 necessarily the case because later subpatterns may have lower numbers.
1088 </P>
1089 <P>
1090 As a simple example of the name/number table, consider the following pattern
1091 (assume PCRE_EXTENDED is set, so white space - including newlines - is
1092 ignored):
1093 <pre>
1094 (?&#60;date&#62; (?&#60;year&#62;(\d\d)?\d\d) - (?&#60;month&#62;\d\d) - (?&#60;day&#62;\d\d) )
1095 </pre>
1096 There are four named subpatterns, so the table has four entries, and each entry
1097 in the table is eight bytes long. The table is as follows, with non-printing
1098 bytes shows in hexadecimal, and undefined bytes shown as ??:
1099 <pre>
1100 00 01 d a t e 00 ??
1101 00 05 d a y 00 ?? ??
1102 00 04 m o n t h 00
1103 00 02 y e a r 00 ??
1104 </pre>
1105 When writing code to extract data from named subpatterns using the
1106 name-to-number map, remember that the length of the entries is likely to be
1107 different for each compiled pattern.
1108 <pre>
1110 </pre>
1111 Return 1 if the pattern can be used for partial matching with
1112 <b>pcre_exec()</b>, otherwise 0. The fourth argument should point to an
1113 <b>int</b> variable. From release 8.00, this always returns 1, because the
1114 restrictions that previously applied to partial matching have been lifted. The
1115 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1116 documentation gives details of partial matching.
1117 <pre>
1119 </pre>
1120 Return a copy of the options with which the pattern was compiled. The fourth
1121 argument should point to an <b>unsigned long int</b> variable. These option bits
1122 are those specified in the call to <b>pcre_compile()</b>, modified by any
1123 top-level option settings at the start of the pattern itself. In other words,
1124 they are the options that will be in force when matching starts. For example,
1125 if the pattern /(?im)abc(?-i)d/ is compiled with the PCRE_EXTENDED option, the
1127 </P>
1128 <P>
1129 A pattern is automatically anchored by PCRE if all of its top-level
1130 alternatives begin with one of the following:
1131 <pre>
1132 ^ unless PCRE_MULTILINE is set
1133 \A always
1134 \G always
1135 .* if PCRE_DOTALL is set and there are no back references to the subpattern in which .* appears
1136 </pre>
1137 For such patterns, the PCRE_ANCHORED bit is set in the options returned by
1138 <b>pcre_fullinfo()</b>.
1139 <pre>
1141 </pre>
1142 Return the size of the compiled pattern, that is, the value that was passed as
1143 the argument to <b>pcre_malloc()</b> when PCRE was getting memory in which to
1144 place the compiled data. The fourth argument should point to a <b>size_t</b>
1145 variable.
1146 <pre>
1148 </pre>
1149 Return the size of the data block pointed to by the <i>study_data</i> field in
1150 a <b>pcre_extra</b> block. That is, it is the value that was passed to
1151 <b>pcre_malloc()</b> when PCRE was getting memory into which to place the data
1152 created by <b>pcre_study()</b>. If <b>pcre_extra</b> is NULL, or there is no
1153 study data, zero is returned. The fourth argument should point to a
1154 <b>size_t</b> variable.
1155 </P>
1156 <br><a name="SEC12" href="#TOC1">OBSOLETE INFO FUNCTION</a><br>
1157 <P>
1158 <b>int pcre_info(const pcre *<i>code</i>, int *<i>optptr</i>, int</b>
1159 <b>*<i>firstcharptr</i>);</b>
1160 </P>
1161 <P>
1162 The <b>pcre_info()</b> function is now obsolete because its interface is too
1163 restrictive to return all the available data about a compiled pattern. New
1164 programs should use <b>pcre_fullinfo()</b> instead. The yield of
1165 <b>pcre_info()</b> is the number of capturing subpatterns, or one of the
1166 following negative numbers:
1167 <pre>
1168 PCRE_ERROR_NULL the argument <i>code</i> was NULL
1169 PCRE_ERROR_BADMAGIC the "magic number" was not found
1170 </pre>
1171 If the <i>optptr</i> argument is not NULL, a copy of the options with which the
1172 pattern was compiled is placed in the integer it points to (see
1173 PCRE_INFO_OPTIONS above).
1174 </P>
1175 <P>
1176 If the pattern is not anchored and the <i>firstcharptr</i> argument is not NULL,
1177 it is used to pass back information about the first character of any matched
1178 string (see PCRE_INFO_FIRSTBYTE above).
1179 </P>
1180 <br><a name="SEC13" href="#TOC1">REFERENCE COUNTS</a><br>
1181 <P>
1182 <b>int pcre_refcount(pcre *<i>code</i>, int <i>adjust</i>);</b>
1183 </P>
1184 <P>
1185 The <b>pcre_refcount()</b> function is used to maintain a reference count in the
1186 data block that contains a compiled pattern. It is provided for the benefit of
1187 applications that operate in an object-oriented manner, where different parts
1188 of the application may be using the same compiled pattern, but you want to free
1189 the block when they are all done.
1190 </P>
1191 <P>
1192 When a pattern is compiled, the reference count field is initialized to zero.
1193 It is changed only by calling this function, whose action is to add the
1194 <i>adjust</i> value (which may be positive or negative) to it. The yield of the
1195 function is the new value. However, the value of the count is constrained to
1196 lie between 0 and 65535, inclusive. If the new value is outside these limits,
1197 it is forced to the appropriate limit value.
1198 </P>
1199 <P>
1200 Except when it is zero, the reference count is not correctly preserved if a
1201 pattern is compiled on one host and then transferred to a host whose byte-order
1202 is different. (This seems a highly unlikely scenario.)
1203 </P>
1204 <br><a name="SEC14" href="#TOC1">MATCHING A PATTERN: THE TRADITIONAL FUNCTION</a><br>
1205 <P>
1206 <b>int pcre_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
1207 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
1208 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>);</b>
1209 </P>
1210 <P>
1211 The function <b>pcre_exec()</b> is called to match a subject string against a
1212 compiled pattern, which is passed in the <i>code</i> argument. If the
1213 pattern was studied, the result of the study should be passed in the
1214 <i>extra</i> argument. This function is the main matching facility of the
1215 library, and it operates in a Perl-like manner. For specialist use there is
1216 also an alternative matching function, which is described
1217 <a href="#dfamatch">below</a>
1218 in the section about the <b>pcre_dfa_exec()</b> function.
1219 </P>
1220 <P>
1221 In most applications, the pattern will have been compiled (and optionally
1222 studied) in the same process that calls <b>pcre_exec()</b>. However, it is
1223 possible to save compiled patterns and study data, and then use them later
1224 in different processes, possibly even on different hosts. For a discussion
1225 about this, see the
1226 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
1227 documentation.
1228 </P>
1229 <P>
1230 Here is an example of a simple call to <b>pcre_exec()</b>:
1231 <pre>
1232 int rc;
1233 int ovector[30];
1234 rc = pcre_exec(
1235 re, /* result of pcre_compile() */
1236 NULL, /* we didn't study the pattern */
1237 "some string", /* the subject string */
1238 11, /* the length of the subject string */
1239 0, /* start at offset 0 in the subject */
1240 0, /* default options */
1241 ovector, /* vector of integers for substring information */
1242 30); /* number of elements (NOT size in bytes) */
1243 <a name="extradata"></a></PRE>
1244 </P>
1245 <br><b>
1246 Extra data for <b>pcre_exec()</b>
1247 </b><br>
1248 <P>
1249 If the <i>extra</i> argument is not NULL, it must point to a <b>pcre_extra</b>
1250 data block. The <b>pcre_study()</b> function returns such a block (when it
1251 doesn't return NULL), but you can also create one for yourself, and pass
1252 additional information in it. The <b>pcre_extra</b> block contains the following
1253 fields (not necessarily in this order):
1254 <pre>
1255 unsigned long int <i>flags</i>;
1256 void *<i>study_data</i>;
1257 unsigned long int <i>match_limit</i>;
1258 unsigned long int <i>match_limit_recursion</i>;
1259 void *<i>callout_data</i>;
1260 const unsigned char *<i>tables</i>;
1261 unsigned char **<i>mark</i>;
1262 </pre>
1263 The <i>flags</i> field is a bitmap that specifies which of the other fields
1264 are set. The flag bits are:
1265 <pre>
1272 </pre>
1273 Other flag bits should be set to zero. The <i>study_data</i> field is set in the
1274 <b>pcre_extra</b> block that is returned by <b>pcre_study()</b>, together with
1275 the appropriate flag bit. You should not set this yourself, but you may add to
1276 the block by setting the other fields and their corresponding flag bits.
1277 </P>
1278 <P>
1279 The <i>match_limit</i> field provides a means of preventing PCRE from using up a
1280 vast amount of resources when running patterns that are not going to match,
1281 but which have a very large number of possibilities in their search trees. The
1282 classic example is a pattern that uses nested unlimited repeats.
1283 </P>
1284 <P>
1285 Internally, PCRE uses a function called <b>match()</b> which it calls repeatedly
1286 (sometimes recursively). The limit set by <i>match_limit</i> is imposed on the
1287 number of times this function is called during a match, which has the effect of
1288 limiting the amount of backtracking that can take place. For patterns that are
1289 not anchored, the count restarts from zero for each position in the subject
1290 string.
1291 </P>
1292 <P>
1293 The default value for the limit can be set when PCRE is built; the default
1294 default is 10 million, which handles all but the most extreme cases. You can
1295 override the default by suppling <b>pcre_exec()</b> with a <b>pcre_extra</b>
1296 block in which <i>match_limit</i> is set, and PCRE_EXTRA_MATCH_LIMIT is set in
1297 the <i>flags</i> field. If the limit is exceeded, <b>pcre_exec()</b> returns
1299 </P>
1300 <P>
1301 The <i>match_limit_recursion</i> field is similar to <i>match_limit</i>, but
1302 instead of limiting the total number of times that <b>match()</b> is called, it
1303 limits the depth of recursion. The recursion depth is a smaller number than the
1304 total number of calls, because not all calls to <b>match()</b> are recursive.
1305 This limit is of use only if it is set smaller than <i>match_limit</i>.
1306 </P>
1307 <P>
1308 Limiting the recursion depth limits the amount of stack that can be used, or,
1309 when PCRE has been compiled to use memory on the heap instead of the stack, the
1310 amount of heap memory that can be used.
1311 </P>
1312 <P>
1313 The default value for <i>match_limit_recursion</i> can be set when PCRE is
1314 built; the default default is the same value as the default for
1315 <i>match_limit</i>. You can override the default by suppling <b>pcre_exec()</b>
1316 with a <b>pcre_extra</b> block in which <i>match_limit_recursion</i> is set, and
1317 PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the <i>flags</i> field. If the limit
1318 is exceeded, <b>pcre_exec()</b> returns PCRE_ERROR_RECURSIONLIMIT.
1319 </P>
1320 <P>
1321 The <i>callout_data</i> field is used in conjunction with the "callout" feature,
1322 and is described in the
1323 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1324 documentation.
1325 </P>
1326 <P>
1327 The <i>tables</i> field is used to pass a character tables pointer to
1328 <b>pcre_exec()</b>; this overrides the value that is stored with the compiled
1329 pattern. A non-NULL value is stored with the compiled pattern only if custom
1330 tables were supplied to <b>pcre_compile()</b> via its <i>tableptr</i> argument.
1331 If NULL is passed to <b>pcre_exec()</b> using this mechanism, it forces PCRE's
1332 internal tables to be used. This facility is helpful when re-using patterns
1333 that have been saved after compiling with an external set of tables, because
1334 the external tables might be at a different address when <b>pcre_exec()</b> is
1335 called. See the
1336 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
1337 documentation for a discussion of saving compiled patterns for later use.
1338 </P>
1339 <P>
1340 If PCRE_EXTRA_MARK is set in the <i>flags</i> field, the <i>mark</i> field must
1341 be set to point to a <b>char *</b> variable. If the pattern contains any
1342 backtracking control verbs such as (*MARK:NAME), and the execution ends up with
1343 a name to pass back, a pointer to the name string (zero terminated) is placed
1344 in the variable pointed to by the <i>mark</i> field. The names are within the
1345 compiled pattern; if you wish to retain such a name you must copy it before
1346 freeing the memory of a compiled pattern. If there is no name to pass back, the
1347 variable pointed to by the <i>mark</i> field set to NULL. For details of the
1348 backtracking control verbs, see the section entitled
1349 <a href="pcrepattern#backtrackcontrol">"Backtracking control"</a>
1350 in the
1351 <a href="pcrepattern.html"><b>pcrepattern</b></a>
1352 documentation.
1353 <a name="execoptions"></a></P>
1354 <br><b>
1355 Option bits for <b>pcre_exec()</b>
1356 </b><br>
1357 <P>
1358 The unused bits of the <i>options</i> argument for <b>pcre_exec()</b> must be
1359 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_<i>xxx</i>,
1363 <pre>
1365 </pre>
1366 The PCRE_ANCHORED option limits <b>pcre_exec()</b> to matching at the first
1367 matching position. If a pattern was compiled with PCRE_ANCHORED, or turned out
1368 to be anchored by virtue of its contents, it cannot be made unachored at
1369 matching time.
1370 <pre>
1373 </pre>
1374 These options (which are mutually exclusive) control what the \R escape
1375 sequence matches. The choice is either to match only CR, LF, or CRLF, or to
1376 match any Unicode newline sequence. These options override the choice that was
1377 made or defaulted when the pattern was compiled.
1378 <pre>
1384 </pre>
1385 These options override the newline definition that was chosen or defaulted when
1386 the pattern was compiled. For details, see the description of
1387 <b>pcre_compile()</b> above. During matching, the newline choice affects the
1388 behaviour of the dot, circumflex, and dollar metacharacters. It may also alter
1389 the way the match position is advanced after a match failure for an unanchored
1390 pattern.
1391 </P>
1392 <P>
1394 match attempt for an unanchored pattern fails when the current position is at a
1395 CRLF sequence, and the pattern contains no explicit matches for CR or LF
1396 characters, the match position is advanced by two characters instead of one, in
1397 other words, to after the CRLF.
1398 </P>
1399 <P>
1400 The above rule is a compromise that makes the most common cases work as
1401 expected. For example, if the pattern is .+A (and the PCRE_DOTALL option is not
1402 set), it does not match the string "\r\nA" because, after failing at the
1403 start, it skips both the CR and the LF before retrying. However, the pattern
1404 [\r\n]A does match that string, because it contains an explicit CR or LF
1405 reference, and so advances only by one character after the first failure.
1406 </P>
1407 <P>
1408 An explicit match for CR of LF is either a literal appearance of one of those
1409 characters, or one of the \r or \n escape sequences. Implicit matches such as
1410 [^X] do not count, nor does \s (which includes CR and LF in the characters
1411 that it matches).
1412 </P>
1413 <P>
1414 Notwithstanding the above, anomalous effects may still occur when CRLF is a
1415 valid newline sequence and explicit \r or \n escapes appear in the pattern.
1416 <pre>
1418 </pre>
1419 This option specifies that first character of the subject string is not the
1420 beginning of a line, so the circumflex metacharacter should not match before
1421 it. Setting this without PCRE_MULTILINE (at compile time) causes circumflex
1422 never to match. This option affects only the behaviour of the circumflex
1423 metacharacter. It does not affect \A.
1424 <pre>
1426 </pre>
1427 This option specifies that the end of the subject string is not the end of a
1428 line, so the dollar metacharacter should not match it nor (except in multiline
1429 mode) a newline immediately before it. Setting this without PCRE_MULTILINE (at
1430 compile time) causes dollar never to match. This option affects only the
1431 behaviour of the dollar metacharacter. It does not affect \Z or \z.
1432 <pre>
1434 </pre>
1435 An empty string is not considered to be a valid match if this option is set. If
1436 there are alternatives in the pattern, they are tried. If all the alternatives
1437 match the empty string, the entire match fails. For example, if the pattern
1438 <pre>
1439 a?b?
1440 </pre>
1441 is applied to a string not beginning with "a" or "b", it matches an empty
1442 string at the start of the subject. With PCRE_NOTEMPTY set, this match is not
1443 valid, so PCRE searches further into the string for occurrences of "a" or "b".
1444 <pre>
1446 </pre>
1447 This is like PCRE_NOTEMPTY, except that an empty string match that is not at
1448 the start of the subject is permitted. If the pattern is anchored, such a match
1449 can occur only if the pattern contains \K.
1450 </P>
1451 <P>
1452 Perl has no direct equivalent of PCRE_NOTEMPTY or PCRE_NOTEMPTY_ATSTART, but it
1453 does make a special case of a pattern match of the empty string within its
1454 <b>split()</b> function, and when using the /g modifier. It is possible to
1455 emulate Perl's behaviour after matching a null string by first trying the match
1456 again at the same offset with PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED, and then
1457 if that fails, by advancing the starting offset (see below) and trying an
1458 ordinary match again. There is some code that demonstrates how to do this in
1459 the
1460 <a href="pcredemo.html"><b>pcredemo</b></a>
1461 sample program. In the most general case, you have to check to see if the
1462 newline convention recognizes CRLF as a newline, and if so, and the current
1463 character is CR followed by LF, advance the starting offset by two characters
1464 instead of one.
1465 <pre>
1467 </pre>
1468 There are a number of optimizations that <b>pcre_exec()</b> uses at the start of
1469 a match, in order to speed up the process. For example, if it is known that an
1470 unanchored match must start with a specific character, it searches the subject
1471 for that character, and fails immediately if it cannot find it, without
1472 actually running the main matching function. This means that a special item
1473 such as (*COMMIT) at the start of a pattern is not considered until after a
1474 suitable starting point for the match has been found. When callouts or (*MARK)
1475 items are in use, these "start-up" optimizations can cause them to be skipped
1476 if the pattern is never actually used. The start-up optimizations are in effect
1477 a pre-scan of the subject that takes place before the pattern is run.
1478 </P>
1479 <P>
1480 The PCRE_NO_START_OPTIMIZE option disables the start-up optimizations, possibly
1481 causing performance to suffer, but ensuring that in cases where the result is
1482 "no match", the callouts do occur, and that items such as (*COMMIT) and (*MARK)
1483 are considered at every possible starting position in the subject string.
1484 Setting PCRE_NO_START_OPTIMIZE can change the outcome of a matching operation.
1485 Consider the pattern
1486 <pre>
1488 </pre>
1489 When this is compiled, PCRE records the fact that a match must start with the
1490 character "A". Suppose the subject string is "DEFABC". The start-up
1491 optimization scans along the subject, finds "A" and runs the first match
1492 attempt from there. The (*COMMIT) item means that the pattern must match the
1493 current starting position, which in this case, it does. However, if the same
1494 match is run with PCRE_NO_START_OPTIMIZE set, the initial scan along the
1495 subject string does not happen. The first match attempt is run starting from
1496 "D" and when this fails, (*COMMIT) prevents any further matches being tried, so
1497 the overall result is "no match". If the pattern is studied, more start-up
1498 optimizations may be used. For example, a minimum length for the subject may be
1499 recorded. Consider the pattern
1500 <pre>
1501 (*MARK:A)(X|Y)
1502 </pre>
1503 The minimum length for a match is one character. If the subject is "ABC", there
1504 will be attempts to match "ABC", "BC", "C", and then finally an empty string.
1505 If the pattern is studied, the final attempt does not take place, because PCRE
1506 knows that the subject is too short, and so the (*MARK) is never encountered.
1507 In this case, studying the pattern does not affect the overall match result,
1508 which is still "no match", but it does affect the auxiliary information that is
1509 returned.
1510 <pre>
1512 </pre>
1513 When PCRE_UTF8 is set at compile time, the validity of the subject as a UTF-8
1514 string is automatically checked when <b>pcre_exec()</b> is subsequently called.
1515 The value of <i>startoffset</i> is also checked to ensure that it points to the
1516 start of a UTF-8 character. There is a discussion about the validity of UTF-8
1517 strings in the
1518 <a href="pcre.html#utf8strings">section on UTF-8 support</a>
1519 in the main
1520 <a href="pcre.html"><b>pcre</b></a>
1521 page. If an invalid UTF-8 sequence of bytes is found, <b>pcre_exec()</b> returns
1522 the error PCRE_ERROR_BADUTF8 or, if PCRE_PARTIAL_HARD is set and the problem is
1523 a truncated UTF-8 character at the end of the subject, PCRE_ERROR_SHORTUTF8. If
1524 <i>startoffset</i> contains a value that does not point to the start of a UTF-8
1525 character (or to the end of the subject), PCRE_ERROR_BADUTF8_OFFSET is
1526 returned.
1527 </P>
1528 <P>
1529 If you already know that your subject is valid, and you want to skip these
1530 checks for performance reasons, you can set the PCRE_NO_UTF8_CHECK option when
1531 calling <b>pcre_exec()</b>. You might want to do this for the second and
1532 subsequent calls to <b>pcre_exec()</b> if you are making repeated calls to find
1533 all the matches in a single subject string. However, you should be sure that
1534 the value of <i>startoffset</i> points to the start of a UTF-8 character (or the
1535 end of the subject). When PCRE_NO_UTF8_CHECK is set, the effect of passing an
1536 invalid UTF-8 string as a subject or an invalid value of <i>startoffset</i> is
1537 undefined. Your program may crash.
1538 <pre>
1541 </pre>
1542 These options turn on the partial matching feature. For backwards
1543 compatibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial match
1544 occurs if the end of the subject string is reached successfully, but there are
1545 not enough subject characters to complete the match. If this happens when
1546 PCRE_PARTIAL_SOFT (but not PCRE_PARTIAL_HARD) is set, matching continues by
1547 testing any remaining alternatives. Only if no complete match can be found is
1548 PCRE_ERROR_PARTIAL returned instead of PCRE_ERROR_NOMATCH. In other words,
1549 PCRE_PARTIAL_SOFT says that the caller is prepared to handle a partial match,
1550 but only if no complete match can be found.
1551 </P>
1552 <P>
1553 If PCRE_PARTIAL_HARD is set, it overrides PCRE_PARTIAL_SOFT. In this case, if a
1554 partial match is found, <b>pcre_exec()</b> immediately returns
1555 PCRE_ERROR_PARTIAL, without considering any other alternatives. In other words,
1556 when PCRE_PARTIAL_HARD is set, a partial match is considered to be more
1557 important that an alternative complete match.
1558 </P>
1559 <P>
1560 In both cases, the portion of the string that was inspected when the partial
1561 match was found is set as the first matching string. There is a more detailed
1562 discussion of partial and multi-segment matching, with examples, in the
1563 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1564 documentation.
1565 </P>
1566 <br><b>
1567 The string to be matched by <b>pcre_exec()</b>
1568 </b><br>
1569 <P>
1570 The subject string is passed to <b>pcre_exec()</b> as a pointer in
1571 <i>subject</i>, a length (in bytes) in <i>length</i>, and a starting byte offset
1572 in <i>startoffset</i>. If this is negative or greater than the length of the
1573 subject, <b>pcre_exec()</b> returns PCRE_ERROR_BADOFFSET. When the starting
1574 offset is zero, the search for a match starts at the beginning of the subject,
1575 and this is by far the most common case. In UTF-8 mode, the byte offset must
1576 point to the start of a UTF-8 character (or the end of the subject). Unlike the
1577 pattern string, the subject may contain binary zero bytes.
1578 </P>
1579 <P>
1580 A non-zero starting offset is useful when searching for another match in the
1581 same subject by calling <b>pcre_exec()</b> again after a previous success.
1582 Setting <i>startoffset</i> differs from just passing over a shortened string and
1583 setting PCRE_NOTBOL in the case of a pattern that begins with any kind of
1584 lookbehind. For example, consider the pattern
1585 <pre>
1586 \Biss\B
1587 </pre>
1588 which finds occurrences of "iss" in the middle of words. (\B matches only if
1589 the current position in the subject is not a word boundary.) When applied to
1590 the string "Mississipi" the first call to <b>pcre_exec()</b> finds the first
1591 occurrence. If <b>pcre_exec()</b> is called again with just the remainder of the
1592 subject, namely "issipi", it does not match, because \B is always false at the
1593 start of the subject, which is deemed to be a word boundary. However, if
1594 <b>pcre_exec()</b> is passed the entire string again, but with <i>startoffset</i>
1595 set to 4, it finds the second occurrence of "iss" because it is able to look
1596 behind the starting point to discover that it is preceded by a letter.
1597 </P>
1598 <P>
1599 Finding all the matches in a subject is tricky when the pattern can match an
1600 empty string. It is possible to emulate Perl's /g behaviour by first trying the
1601 match again at the same offset, with the PCRE_NOTEMPTY_ATSTART and
1602 PCRE_ANCHORED options, and then if that fails, advancing the starting offset
1603 and trying an ordinary match again. There is some code that demonstrates how to
1604 do this in the
1605 <a href="pcredemo.html"><b>pcredemo</b></a>
1606 sample program. In the most general case, you have to check to see if the
1607 newline convention recognizes CRLF as a newline, and if so, and the current
1608 character is CR followed by LF, advance the starting offset by two characters
1609 instead of one.
1610 </P>
1611 <P>
1612 If a non-zero starting offset is passed when the pattern is anchored, one
1613 attempt to match at the given offset is made. This can only succeed if the
1614 pattern does not require the match to be at the start of the subject.
1615 </P>
1616 <br><b>
1617 How <b>pcre_exec()</b> returns captured substrings
1618 </b><br>
1619 <P>
1620 In general, a pattern matches a certain portion of the subject, and in
1621 addition, further substrings from the subject may be picked out by parts of the
1622 pattern. Following the usage in Jeffrey Friedl's book, this is called
1623 "capturing" in what follows, and the phrase "capturing subpattern" is used for
1624 a fragment of a pattern that picks out a substring. PCRE supports several other
1625 kinds of parenthesized subpattern that do not cause substrings to be captured.
1626 </P>
1627 <P>
1628 Captured substrings are returned to the caller via a vector of integers whose
1629 address is passed in <i>ovector</i>. The number of elements in the vector is
1630 passed in <i>ovecsize</i>, which must be a non-negative number. <b>Note</b>: this
1631 argument is NOT the size of <i>ovector</i> in bytes.
1632 </P>
1633 <P>
1634 The first two-thirds of the vector is used to pass back captured substrings,
1635 each substring using a pair of integers. The remaining third of the vector is
1636 used as workspace by <b>pcre_exec()</b> while matching capturing subpatterns,
1637 and is not available for passing back information. The number passed in
1638 <i>ovecsize</i> should always be a multiple of three. If it is not, it is
1639 rounded down.
1640 </P>
1641 <P>
1642 When a match is successful, information about captured substrings is returned
1643 in pairs of integers, starting at the beginning of <i>ovector</i>, and
1644 continuing up to two-thirds of its length at the most. The first element of
1645 each pair is set to the byte offset of the first character in a substring, and
1646 the second is set to the byte offset of the first character after the end of a
1647 substring. <b>Note</b>: these values are always byte offsets, even in UTF-8
1648 mode. They are not character counts.
1649 </P>
1650 <P>
1651 The first pair of integers, <i>ovector[0]</i> and <i>ovector[1]</i>, identify the
1652 portion of the subject string matched by the entire pattern. The next pair is
1653 used for the first capturing subpattern, and so on. The value returned by
1654 <b>pcre_exec()</b> is one more than the highest numbered pair that has been set.
1655 For example, if two substrings have been captured, the returned value is 3. If
1656 there are no capturing subpatterns, the return value from a successful match is
1657 1, indicating that just the first pair of offsets has been set.
1658 </P>
1659 <P>
1660 If a capturing subpattern is matched repeatedly, it is the last portion of the
1661 string that it matched that is returned.
1662 </P>
1663 <P>
1664 If the vector is too small to hold all the captured substring offsets, it is
1665 used as far as possible (up to two-thirds of its length), and the function
1666 returns a value of zero. If the substring offsets are not of interest,
1667 <b>pcre_exec()</b> may be called with <i>ovector</i> passed as NULL and
1668 <i>ovecsize</i> as zero. However, if the pattern contains back references and
1669 the <i>ovector</i> is not big enough to remember the related substrings, PCRE
1670 has to get additional memory for use during matching. Thus it is usually
1671 advisable to supply an <i>ovector</i>.
1672 </P>
1673 <P>
1674 The <b>pcre_fullinfo()</b> function can be used to find out how many capturing
1675 subpatterns there are in a compiled pattern. The smallest size for
1676 <i>ovector</i> that will allow for <i>n</i> captured substrings, in addition to
1677 the offsets of the substring matched by the whole pattern, is (<i>n</i>+1)*3.
1678 </P>
1679 <P>
1680 It is possible for capturing subpattern number <i>n+1</i> to match some part of
1681 the subject when subpattern <i>n</i> has not been used at all. For example, if
1682 the string "abc" is matched against the pattern (a|(z))(bc) the return from the
1683 function is 4, and subpatterns 1 and 3 are matched, but 2 is not. When this
1684 happens, both values in the offset pairs corresponding to unused subpatterns
1685 are set to -1.
1686 </P>
1687 <P>
1688 Offset values that correspond to unused subpatterns at the end of the
1689 expression are also set to -1. For example, if the string "abc" is matched
1690 against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not matched. The
1691 return from the function is 2, because the highest used capturing subpattern
1692 number is 1, and the offsets for for the second and third capturing subpatterns
1693 (assuming the vector is large enough, of course) are set to -1.
1694 </P>
1695 <P>
1696 <b>Note</b>: Elements of <i>ovector</i> that do not correspond to capturing
1697 parentheses in the pattern are never changed. That is, if a pattern contains
1698 <i>n</i> capturing parentheses, no more than <i>ovector[0]</i> to
1699 <i>ovector[2n+1]</i> are set by <b>pcre_exec()</b>. The other elements retain
1700 whatever values they previously had.
1701 </P>
1702 <P>
1703 Some convenience functions are provided for extracting the captured substrings
1704 as separate strings. These are described below.
1705 <a name="errorlist"></a></P>
1706 <br><b>
1707 Error return values from <b>pcre_exec()</b>
1708 </b><br>
1709 <P>
1710 If <b>pcre_exec()</b> fails, it returns a negative number. The following are
1711 defined in the header file:
1712 <pre>
1714 </pre>
1715 The subject string did not match the pattern.
1716 <pre>
1718 </pre>
1719 Either <i>code</i> or <i>subject</i> was passed as NULL, or <i>ovector</i> was
1720 NULL and <i>ovecsize</i> was not zero.
1721 <pre>
1723 </pre>
1724 An unrecognized bit was set in the <i>options</i> argument.
1725 <pre>
1727 </pre>
1728 PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch
1729 the case when it is passed a junk pointer and to detect when a pattern that was
1730 compiled in an environment of one endianness is run in an environment with the
1731 other endianness. This is the error that PCRE gives when the magic number is
1732 not present.
1733 <pre>
1735 </pre>
1736 While running the pattern match, an unknown item was encountered in the
1737 compiled pattern. This error could be caused by a bug in PCRE or by overwriting
1738 of the compiled pattern.
1739 <pre>
1741 </pre>
1742 If a pattern contains back references, but the <i>ovector</i> that is passed to
1743 <b>pcre_exec()</b> is not big enough to remember the referenced substrings, PCRE
1744 gets a block of memory at the start of matching to use for this purpose. If the
1745 call via <b>pcre_malloc()</b> fails, this error is given. The memory is
1746 automatically freed at the end of matching.
1747 </P>
1748 <P>
1749 This error is also given if <b>pcre_stack_malloc()</b> fails in
1750 <b>pcre_exec()</b>. This can happen only when PCRE has been compiled with
1751 <b>--disable-stack-for-recursion</b>.
1752 <pre>
1754 </pre>
1755 This error is used by the <b>pcre_copy_substring()</b>,
1756 <b>pcre_get_substring()</b>, and <b>pcre_get_substring_list()</b> functions (see
1757 below). It is never returned by <b>pcre_exec()</b>.
1758 <pre>
1760 </pre>
1761 The backtracking limit, as specified by the <i>match_limit</i> field in a
1762 <b>pcre_extra</b> structure (or defaulted) was reached. See the description
1763 above.
1764 <pre>
1766 </pre>
1767 This error is never generated by <b>pcre_exec()</b> itself. It is provided for
1768 use by callout functions that want to yield a distinctive error code. See the
1769 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1770 documentation for details.
1771 <pre>
1773 </pre>
1774 A string that contains an invalid UTF-8 byte sequence was passed as a subject.
1775 However, if PCRE_PARTIAL_HARD is set and the problem is a truncated UTF-8
1776 character at the end of the subject, PCRE_ERROR_SHORTUTF8 is used instead.
1777 <pre>
1779 </pre>
1780 The UTF-8 byte sequence that was passed as a subject was valid, but the value
1781 of <i>startoffset</i> did not point to the beginning of a UTF-8 character or the
1782 end of the subject.
1783 <pre>
1785 </pre>
1786 The subject string did not match, but it did match partially. See the
1787 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1788 documentation for details of partial matching.
1789 <pre>
1791 </pre>
1792 This code is no longer in use. It was formerly returned when the PCRE_PARTIAL
1793 option was used with a compiled pattern containing items that were not
1794 supported for partial matching. From release 8.00 onwards, there are no
1795 restrictions on partial matching.
1796 <pre>
1798 </pre>
1799 An unexpected internal error has occurred. This error could be caused by a bug
1800 in PCRE or by overwriting of the compiled pattern.
1801 <pre>
1803 </pre>
1804 This error is given if the value of the <i>ovecsize</i> argument is negative.
1805 <pre>
1807 </pre>
1808 The internal recursion limit, as specified by the <i>match_limit_recursion</i>
1809 field in a <b>pcre_extra</b> structure (or defaulted) was reached. See the
1810 description above.
1811 <pre>
1813 </pre>
1814 An invalid combination of PCRE_NEWLINE_<i>xxx</i> options was given.
1815 <pre>
1817 </pre>
1818 The value of <i>startoffset</i> was negative or greater than the length of the
1819 subject, that is, the value in <i>length</i>.
1820 <pre>
1822 </pre>
1823 The subject string ended with an incomplete (truncated) UTF-8 character, and
1824 the PCRE_PARTIAL_HARD option was set. Without this option, PCRE_ERROR_BADUTF8
1825 is returned in this situation.
1826 </P>
1827 <P>
1828 Error numbers -16 to -20 and -22 are not used by <b>pcre_exec()</b>.
1829 </P>
1830 <br><a name="SEC15" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NUMBER</a><br>
1831 <P>
1832 <b>int pcre_copy_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1833 <b>int <i>stringcount</i>, int <i>stringnumber</i>, char *<i>buffer</i>,</b>
1834 <b>int <i>buffersize</i>);</b>
1835 </P>
1836 <P>
1837 <b>int pcre_get_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1838 <b>int <i>stringcount</i>, int <i>stringnumber</i>,</b>
1839 <b>const char **<i>stringptr</i>);</b>
1840 </P>
1841 <P>
1842 <b>int pcre_get_substring_list(const char *<i>subject</i>,</b>
1843 <b>int *<i>ovector</i>, int <i>stringcount</i>, const char ***<i>listptr</i>);</b>
1844 </P>
1845 <P>
1846 Captured substrings can be accessed directly by using the offsets returned by
1847 <b>pcre_exec()</b> in <i>ovector</i>. For convenience, the functions
1848 <b>pcre_copy_substring()</b>, <b>pcre_get_substring()</b>, and
1849 <b>pcre_get_substring_list()</b> are provided for extracting captured substrings
1850 as new, separate, zero-terminated strings. These functions identify substrings
1851 by number. The next section describes functions for extracting named
1852 substrings.
1853 </P>
1854 <P>
1855 A substring that contains a binary zero is correctly extracted and has a
1856 further zero added on the end, but the result is not, of course, a C string.
1857 However, you can process such a string by referring to the length that is
1858 returned by <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>.
1859 Unfortunately, the interface to <b>pcre_get_substring_list()</b> is not adequate
1860 for handling strings containing binary zeros, because the end of the final
1861 string is not independently indicated.
1862 </P>
1863 <P>
1864 The first three arguments are the same for all three of these functions:
1865 <i>subject</i> is the subject string that has just been successfully matched,
1866 <i>ovector</i> is a pointer to the vector of integer offsets that was passed to
1867 <b>pcre_exec()</b>, and <i>stringcount</i> is the number of substrings that were
1868 captured by the match, including the substring that matched the entire regular
1869 expression. This is the value returned by <b>pcre_exec()</b> if it is greater
1870 than zero. If <b>pcre_exec()</b> returned zero, indicating that it ran out of
1871 space in <i>ovector</i>, the value passed as <i>stringcount</i> should be the
1872 number of elements in the vector divided by three.
1873 </P>
1874 <P>
1875 The functions <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>
1876 extract a single substring, whose number is given as <i>stringnumber</i>. A
1877 value of zero extracts the substring that matched the entire pattern, whereas
1878 higher values extract the captured substrings. For <b>pcre_copy_substring()</b>,
1879 the string is placed in <i>buffer</i>, whose length is given by
1880 <i>buffersize</i>, while for <b>pcre_get_substring()</b> a new block of memory is
1881 obtained via <b>pcre_malloc</b>, and its address is returned via
1882 <i>stringptr</i>. The yield of the function is the length of the string, not
1883 including the terminating zero, or one of these error codes:
1884 <pre>
1886 </pre>
1887 The buffer was too small for <b>pcre_copy_substring()</b>, or the attempt to get
1888 memory failed for <b>pcre_get_substring()</b>.
1889 <pre>
1891 </pre>
1892 There is no substring whose number is <i>stringnumber</i>.
1893 </P>
1894 <P>
1895 The <b>pcre_get_substring_list()</b> function extracts all available substrings
1896 and builds a list of pointers to them. All this is done in a single block of
1897 memory that is obtained via <b>pcre_malloc</b>. The address of the memory block
1898 is returned via <i>listptr</i>, which is also the start of the list of string
1899 pointers. The end of the list is marked by a NULL pointer. The yield of the
1900 function is zero if all went well, or the error code
1901 <pre>
1903 </pre>
1904 if the attempt to get the memory block failed.
1905 </P>
1906 <P>
1907 When any of these functions encounter a substring that is unset, which can
1908 happen when capturing subpattern number <i>n+1</i> matches some part of the
1909 subject, but subpattern <i>n</i> has not been used at all, they return an empty
1910 string. This can be distinguished from a genuine zero-length substring by
1911 inspecting the appropriate offset in <i>ovector</i>, which is negative for unset
1912 substrings.
1913 </P>
1914 <P>
1915 The two convenience functions <b>pcre_free_substring()</b> and
1916 <b>pcre_free_substring_list()</b> can be used to free the memory returned by
1917 a previous call of <b>pcre_get_substring()</b> or
1918 <b>pcre_get_substring_list()</b>, respectively. They do nothing more than call
1919 the function pointed to by <b>pcre_free</b>, which of course could be called
1920 directly from a C program. However, PCRE is used in some situations where it is
1921 linked via a special interface to another programming language that cannot use
1922 <b>pcre_free</b> directly; it is for these cases that the functions are
1923 provided.
1924 </P>
1925 <br><a name="SEC16" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NAME</a><br>
1926 <P>
1927 <b>int pcre_get_stringnumber(const pcre *<i>code</i>,</b>
1928 <b>const char *<i>name</i>);</b>
1929 </P>
1930 <P>
1931 <b>int pcre_copy_named_substring(const pcre *<i>code</i>,</b>
1932 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
1933 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
1934 <b>char *<i>buffer</i>, int <i>buffersize</i>);</b>
1935 </P>
1936 <P>
1937 <b>int pcre_get_named_substring(const pcre *<i>code</i>,</b>
1938 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
1939 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
1940 <b>const char **<i>stringptr</i>);</b>
1941 </P>
1942 <P>
1943 To extract a substring by name, you first have to find associated number.
1944 For example, for this pattern
1945 <pre>
1946 (a+)b(?&#60;xxx&#62;\d+)...
1947 </pre>
1948 the number of the subpattern called "xxx" is 2. If the name is known to be
1949 unique (PCRE_DUPNAMES was not set), you can find the number from the name by
1950 calling <b>pcre_get_stringnumber()</b>. The first argument is the compiled
1951 pattern, and the second is the name. The yield of the function is the
1952 subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no subpattern of
1953 that name.
1954 </P>
1955 <P>
1956 Given the number, you can extract the substring directly, or use one of the
1957 functions described in the previous section. For convenience, there are also
1958 two functions that do the whole job.
1959 </P>
1960 <P>
1961 Most of the arguments of <b>pcre_copy_named_substring()</b> and
1962 <b>pcre_get_named_substring()</b> are the same as those for the similarly named
1963 functions that extract by number. As these are described in the previous
1964 section, they are not re-described here. There are just two differences:
1965 </P>
1966 <P>
1967 First, instead of a substring number, a substring name is given. Second, there
1968 is an extra argument, given at the start, which is a pointer to the compiled
1969 pattern. This is needed in order to gain access to the name-to-number
1970 translation table.
1971 </P>
1972 <P>
1973 These functions call <b>pcre_get_stringnumber()</b>, and if it succeeds, they
1974 then call <b>pcre_copy_substring()</b> or <b>pcre_get_substring()</b>, as
1975 appropriate. <b>NOTE:</b> If PCRE_DUPNAMES is set and there are duplicate names,
1976 the behaviour may not be what you want (see the next section).
1977 </P>
1978 <P>
1979 <b>Warning:</b> If the pattern uses the (?| feature to set up multiple
1980 subpatterns with the same number, as described in the
1981 <a href="pcrepattern.html#dupsubpatternnumber">section on duplicate subpattern numbers</a>
1982 in the
1983 <a href="pcrepattern.html"><b>pcrepattern</b></a>
1984 page, you cannot use names to distinguish the different subpatterns, because
1985 names are not included in the compiled code. The matching process uses only
1986 numbers. For this reason, the use of different names for subpatterns of the
1987 same number causes an error at compile time.
1988 </P>
1989 <br><a name="SEC17" href="#TOC1">DUPLICATE SUBPATTERN NAMES</a><br>
1990 <P>
1991 <b>int pcre_get_stringtable_entries(const pcre *<i>code</i>,</b>
1992 <b>const char *<i>name</i>, char **<i>first</i>, char **<i>last</i>);</b>
1993 </P>
1994 <P>
1995 When a pattern is compiled with the PCRE_DUPNAMES option, names for subpatterns
1996 are not required to be unique. (Duplicate names are always allowed for
1997 subpatterns with the same number, created by using the (?| feature. Indeed, if
1998 such subpatterns are named, they are required to use the same names.)
1999 </P>
2000 <P>
2001 Normally, patterns with duplicate names are such that in any one match, only
2002 one of the named subpatterns participates. An example is shown in the
2003 <a href="pcrepattern.html"><b>pcrepattern</b></a>
2004 documentation.
2005 </P>
2006 <P>
2007 When duplicates are present, <b>pcre_copy_named_substring()</b> and
2008 <b>pcre_get_named_substring()</b> return the first substring corresponding to
2009 the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING (-7) is
2010 returned; no data is returned. The <b>pcre_get_stringnumber()</b> function
2011 returns one of the numbers that are associated with the name, but it is not
2012 defined which it is.
2013 </P>
2014 <P>
2015 If you want to get full details of all captured substrings for a given name,
2016 you must use the <b>pcre_get_stringtable_entries()</b> function. The first
2017 argument is the compiled pattern, and the second is the name. The third and
2018 fourth are pointers to variables which are updated by the function. After it
2019 has run, they point to the first and last entries in the name-to-number table
2020 for the given name. The function itself returns the length of each entry, or
2021 PCRE_ERROR_NOSUBSTRING (-7) if there are none. The format of the table is
2022 described above in the section entitled <i>Information about a pattern</i>.
2023 Given all the relevant entries for the name, you can extract each of their
2024 numbers, and hence the captured data, if any.
2025 </P>
2026 <br><a name="SEC18" href="#TOC1">FINDING ALL POSSIBLE MATCHES</a><br>
2027 <P>
2028 The traditional matching function uses a similar algorithm to Perl, which stops
2029 when it finds the first match, starting at a given point in the subject. If you
2030 want to find all possible matches, or the longest possible match, consider
2031 using the alternative matching function (see below) instead. If you cannot use
2032 the alternative function, but still need to find all possible matches, you
2033 can kludge it up by making use of the callout facility, which is described in
2034 the
2035 <a href="pcrecallout.html"><b>pcrecallout</b></a>
2036 documentation.
2037 </P>
2038 <P>
2039 What you have to do is to insert a callout right at the end of the pattern.
2040 When your callout function is called, extract and save the current matched
2041 substring. Then return 1, which forces <b>pcre_exec()</b> to backtrack and try
2042 other alternatives. Ultimately, when it runs out of matches, <b>pcre_exec()</b>
2043 will yield PCRE_ERROR_NOMATCH.
2044 <a name="dfamatch"></a></P>
2045 <br><a name="SEC19" href="#TOC1">MATCHING A PATTERN: THE ALTERNATIVE FUNCTION</a><br>
2046 <P>
2047 <b>int pcre_dfa_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
2048 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
2049 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>,</b>
2050 <b>int *<i>workspace</i>, int <i>wscount</i>);</b>
2051 </P>
2052 <P>
2053 The function <b>pcre_dfa_exec()</b> is called to match a subject string against
2054 a compiled pattern, using a matching algorithm that scans the subject string
2055 just once, and does not backtrack. This has different characteristics to the
2056 normal algorithm, and is not compatible with Perl. Some of the features of PCRE
2057 patterns are not supported. Nevertheless, there are times when this kind of
2058 matching can be useful. For a discussion of the two matching algorithms, and a
2059 list of features that <b>pcre_dfa_exec()</b> does not support, see the
2060 <a href="pcrematching.html"><b>pcrematching</b></a>
2061 documentation.
2062 </P>
2063 <P>
2064 The arguments for the <b>pcre_dfa_exec()</b> function are the same as for
2065 <b>pcre_exec()</b>, plus two extras. The <i>ovector</i> argument is used in a
2066 different way, and this is described below. The other common arguments are used
2067 in the same way as for <b>pcre_exec()</b>, so their description is not repeated
2068 here.
2069 </P>
2070 <P>
2071 The two additional arguments provide workspace for the function. The workspace
2072 vector should contain at least 20 elements. It is used for keeping track of
2073 multiple paths through the pattern tree. More workspace will be needed for
2074 patterns and subjects where there are a lot of potential matches.
2075 </P>
2076 <P>
2077 Here is an example of a simple call to <b>pcre_dfa_exec()</b>:
2078 <pre>
2079 int rc;
2080 int ovector[10];
2081 int wspace[20];
2082 rc = pcre_dfa_exec(
2083 re, /* result of pcre_compile() */
2084 NULL, /* we didn't study the pattern */
2085 "some string", /* the subject string */
2086 11, /* the length of the subject string */
2087 0, /* start at offset 0 in the subject */
2088 0, /* default options */
2089 ovector, /* vector of integers for substring information */
2090 10, /* number of elements (NOT size in bytes) */
2091 wspace, /* working space vector */
2092 20); /* number of elements (NOT size in bytes) */
2093 </PRE>
2094 </P>
2095 <br><b>
2096 Option bits for <b>pcre_dfa_exec()</b>
2097 </b><br>
2098 <P>
2099 The unused bits of the <i>options</i> argument for <b>pcre_dfa_exec()</b> must be
2100 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_<i>xxx</i>,
2104 All but the last four of these are exactly the same as for <b>pcre_exec()</b>,
2105 so their description is not repeated here.
2106 <pre>
2109 </pre>
2110 These have the same general effect as they do for <b>pcre_exec()</b>, but the
2111 details are slightly different. When PCRE_PARTIAL_HARD is set for
2112 <b>pcre_dfa_exec()</b>, it returns PCRE_ERROR_PARTIAL if the end of the subject
2113 is reached and there is still at least one matching possibility that requires
2114 additional characters. This happens even if some complete matches have also
2115 been found. When PCRE_PARTIAL_SOFT is set, the return code PCRE_ERROR_NOMATCH
2116 is converted into PCRE_ERROR_PARTIAL if the end of the subject is reached,
2117 there have been no complete matches, but there is still at least one matching
2118 possibility. The portion of the string that was inspected when the longest
2119 partial match was found is set as the first matching string in both cases.
2120 There is a more detailed discussion of partial and multi-segment matching, with
2121 examples, in the
2122 <a href="pcrepartial.html"><b>pcrepartial</b></a>
2123 documentation.
2124 <pre>
2126 </pre>
2127 Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to stop as
2128 soon as it has found one match. Because of the way the alternative algorithm
2129 works, this is necessarily the shortest possible match at the first possible
2130 matching point in the subject string.
2131 <pre>
2133 </pre>
2134 When <b>pcre_dfa_exec()</b> returns a partial match, it is possible to call it
2135 again, with additional subject characters, and have it continue with the same
2136 match. The PCRE_DFA_RESTART option requests this action; when it is set, the
2137 <i>workspace</i> and <i>wscount</i> options must reference the same vector as
2138 before because data about the match so far is left in them after a partial
2139 match. There is more discussion of this facility in the
2140 <a href="pcrepartial.html"><b>pcrepartial</b></a>
2141 documentation.
2142 </P>
2143 <br><b>
2144 Successful returns from <b>pcre_dfa_exec()</b>
2145 </b><br>
2146 <P>
2147 When <b>pcre_dfa_exec()</b> succeeds, it may have matched more than one
2148 substring in the subject. Note, however, that all the matches from one run of
2149 the function start at the same point in the subject. The shorter matches are
2150 all initial substrings of the longer matches. For example, if the pattern
2151 <pre>
2152 &#60;.*&#62;
2153 </pre>
2154 is matched against the string
2155 <pre>
2156 This is &#60;something&#62; &#60;something else&#62; &#60;something further&#62; no more
2157 </pre>
2158 the three matched strings are
2159 <pre>
2160 &#60;something&#62;
2161 &#60;something&#62; &#60;something else&#62;
2162 &#60;something&#62; &#60;something else&#62; &#60;something further&#62;
2163 </pre>
2164 On success, the yield of the function is a number greater than zero, which is
2165 the number of matched substrings. The substrings themselves are returned in
2166 <i>ovector</i>. Each string uses two elements; the first is the offset to the
2167 start, and the second is the offset to the end. In fact, all the strings have
2168 the same start offset. (Space could have been saved by giving this only once,
2169 but it was decided to retain some compatibility with the way <b>pcre_exec()</b>
2170 returns data, even though the meaning of the strings is different.)
2171 </P>
2172 <P>
2173 The strings are returned in reverse order of length; that is, the longest
2174 matching string is given first. If there were too many matches to fit into
2175 <i>ovector</i>, the yield of the function is zero, and the vector is filled with
2176 the longest matches.
2177 </P>
2178 <br><b>
2179 Error returns from <b>pcre_dfa_exec()</b>
2180 </b><br>
2181 <P>
2182 The <b>pcre_dfa_exec()</b> function returns a negative number when it fails.
2183 Many of the errors are the same as for <b>pcre_exec()</b>, and these are
2184 described
2185 <a href="#errorlist">above.</a>
2186 There are in addition the following errors that are specific to
2187 <b>pcre_dfa_exec()</b>:
2188 <pre>
2190 </pre>
2191 This return is given if <b>pcre_dfa_exec()</b> encounters an item in the pattern
2192 that it does not support, for instance, the use of \C or a back reference.
2193 <pre>
2195 </pre>
2196 This return is given if <b>pcre_dfa_exec()</b> encounters a condition item that
2197 uses a back reference for the condition, or a test for recursion in a specific
2198 group. These are not supported.
2199 <pre>
2201 </pre>
2202 This return is given if <b>pcre_dfa_exec()</b> is called with an <i>extra</i>
2203 block that contains a setting of the <i>match_limit</i> field. This is not
2204 supported (it is meaningless).
2205 <pre>
2207 </pre>
2208 This return is given if <b>pcre_dfa_exec()</b> runs out of space in the
2209 <i>workspace</i> vector.
2210 <pre>
2212 </pre>
2213 When a recursive subpattern is processed, the matching function calls itself
2214 recursively, using private vectors for <i>ovector</i> and <i>workspace</i>. This
2215 error is given if the output vector is not large enough. This should be
2216 extremely rare, as a vector of size 1000 is used.
2217 </P>
2218 <br><a name="SEC20" href="#TOC1">SEE ALSO</a><br>
2219 <P>
2220 <b>pcrebuild</b>(3), <b>pcrecallout</b>(3), <b>pcrecpp(3)</b>(3),
2221 <b>pcrematching</b>(3), <b>pcrepartial</b>(3), <b>pcreposix</b>(3),
2222 <b>pcreprecompile</b>(3), <b>pcresample</b>(3), <b>pcrestack</b>(3).
2223 </P>
2224 <br><a name="SEC21" href="#TOC1">AUTHOR</a><br>
2225 <P>
2226 Philip Hazel
2227 <br>
2228 University Computing Service
2229 <br>
2230 Cambridge CB2 3QH, England.
2231 <br>
2232 </P>
2233 <br><a name="SEC22" href="#TOC1">REVISION</a><br>
2234 <P>
2235 Last updated: 13 November 2010
2236 <br>
2237 Copyright &copy; 1997-2010 University of Cambridge.
2238 <br>
2239 <p>
2240 Return to the <a href="index.html">PCRE index page</a>.
2241 </p>


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

  ViewVC Help
Powered by ViewVC 1.1.5