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1 <html>
2 <head>
3 <title>pcreapi specification</title>
4 </head>
5 <body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
6 <h1>pcreapi man page</h1>
7 <p>
8 Return to the <a href="index.html">PCRE index page</a>.
9 </p>
10 <p>
11 This page is part of the PCRE HTML documentation. It was generated automatically
12 from the original man page. If there is any nonsense in it, please consult the
13 man page, in case the conversion went wrong.
14 <br>
15 <ul>
16 <li><a name="TOC1" href="#SEC1">PCRE NATIVE API</a>
17 <li><a name="TOC2" href="#SEC2">PCRE API OVERVIEW</a>
18 <li><a name="TOC3" href="#SEC3">NEWLINES</a>
19 <li><a name="TOC4" href="#SEC4">MULTITHREADING</a>
21 <li><a name="TOC6" href="#SEC6">CHECKING BUILD-TIME OPTIONS</a>
22 <li><a name="TOC7" href="#SEC7">COMPILING A PATTERN</a>
23 <li><a name="TOC8" href="#SEC8">COMPILATION ERROR CODES</a>
24 <li><a name="TOC9" href="#SEC9">STUDYING A PATTERN</a>
25 <li><a name="TOC10" href="#SEC10">LOCALE SUPPORT</a>
26 <li><a name="TOC11" href="#SEC11">INFORMATION ABOUT A PATTERN</a>
27 <li><a name="TOC12" href="#SEC12">OBSOLETE INFO FUNCTION</a>
28 <li><a name="TOC13" href="#SEC13">REFERENCE COUNTS</a>
32 <li><a name="TOC17" href="#SEC17">DUPLICATE SUBPATTERN NAMES</a>
33 <li><a name="TOC18" href="#SEC18">FINDING ALL POSSIBLE MATCHES</a>
35 <li><a name="TOC20" href="#SEC20">SEE ALSO</a>
36 <li><a name="TOC21" href="#SEC21">AUTHOR</a>
37 <li><a name="TOC22" href="#SEC22">REVISION</a>
38 </ul>
39 <br><a name="SEC1" href="#TOC1">PCRE NATIVE API</a><br>
40 <P>
41 <b>#include &#60;pcre.h&#62;</b>
42 </P>
43 <P>
44 <b>pcre *pcre_compile(const char *<i>pattern</i>, int <i>options</i>,</b>
45 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
46 <b>const unsigned char *<i>tableptr</i>);</b>
47 </P>
48 <P>
49 <b>pcre *pcre_compile2(const char *<i>pattern</i>, int <i>options</i>,</b>
50 <b>int *<i>errorcodeptr</i>,</b>
51 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
52 <b>const unsigned char *<i>tableptr</i>);</b>
53 </P>
54 <P>
55 <b>pcre_extra *pcre_study(const pcre *<i>code</i>, int <i>options</i>,</b>
56 <b>const char **<i>errptr</i>);</b>
57 </P>
58 <P>
59 <b>int pcre_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
60 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
61 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>);</b>
62 </P>
63 <P>
64 <b>int pcre_dfa_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
65 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
66 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>,</b>
67 <b>int *<i>workspace</i>, int <i>wscount</i>);</b>
68 </P>
69 <P>
70 <b>int pcre_copy_named_substring(const pcre *<i>code</i>,</b>
71 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
72 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
73 <b>char *<i>buffer</i>, int <i>buffersize</i>);</b>
74 </P>
75 <P>
76 <b>int pcre_copy_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
77 <b>int <i>stringcount</i>, int <i>stringnumber</i>, char *<i>buffer</i>,</b>
78 <b>int <i>buffersize</i>);</b>
79 </P>
80 <P>
81 <b>int pcre_get_named_substring(const pcre *<i>code</i>,</b>
82 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
83 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
84 <b>const char **<i>stringptr</i>);</b>
85 </P>
86 <P>
87 <b>int pcre_get_stringnumber(const pcre *<i>code</i>,</b>
88 <b>const char *<i>name</i>);</b>
89 </P>
90 <P>
91 <b>int pcre_get_stringtable_entries(const pcre *<i>code</i>,</b>
92 <b>const char *<i>name</i>, char **<i>first</i>, char **<i>last</i>);</b>
93 </P>
94 <P>
95 <b>int pcre_get_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
96 <b>int <i>stringcount</i>, int <i>stringnumber</i>,</b>
97 <b>const char **<i>stringptr</i>);</b>
98 </P>
99 <P>
100 <b>int pcre_get_substring_list(const char *<i>subject</i>,</b>
101 <b>int *<i>ovector</i>, int <i>stringcount</i>, const char ***<i>listptr</i>);</b>
102 </P>
103 <P>
104 <b>void pcre_free_substring(const char *<i>stringptr</i>);</b>
105 </P>
106 <P>
107 <b>void pcre_free_substring_list(const char **<i>stringptr</i>);</b>
108 </P>
109 <P>
110 <b>const unsigned char *pcre_maketables(void);</b>
111 </P>
112 <P>
113 <b>int pcre_fullinfo(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
114 <b>int <i>what</i>, void *<i>where</i>);</b>
115 </P>
116 <P>
117 <b>int pcre_info(const pcre *<i>code</i>, int *<i>optptr</i>, int</b>
118 <b>*<i>firstcharptr</i>);</b>
119 </P>
120 <P>
121 <b>int pcre_refcount(pcre *<i>code</i>, int <i>adjust</i>);</b>
122 </P>
123 <P>
124 <b>int pcre_config(int <i>what</i>, void *<i>where</i>);</b>
125 </P>
126 <P>
127 <b>char *pcre_version(void);</b>
128 </P>
129 <P>
130 <b>void *(*pcre_malloc)(size_t);</b>
131 </P>
132 <P>
133 <b>void (*pcre_free)(void *);</b>
134 </P>
135 <P>
136 <b>void *(*pcre_stack_malloc)(size_t);</b>
137 </P>
138 <P>
139 <b>void (*pcre_stack_free)(void *);</b>
140 </P>
141 <P>
142 <b>int (*pcre_callout)(pcre_callout_block *);</b>
143 </P>
144 <br><a name="SEC2" href="#TOC1">PCRE API OVERVIEW</a><br>
145 <P>
146 PCRE has its own native API, which is described in this document. There are
147 also some wrapper functions that correspond to the POSIX regular expression
148 API. These are described in the
149 <a href="pcreposix.html"><b>pcreposix</b></a>
150 documentation. Both of these APIs define a set of C function calls. A C++
151 wrapper is distributed with PCRE. It is documented in the
152 <a href="pcrecpp.html"><b>pcrecpp</b></a>
153 page.
154 </P>
155 <P>
156 The native API C function prototypes are defined in the header file
157 <b>pcre.h</b>, and on Unix systems the library itself is called <b>libpcre</b>.
158 It can normally be accessed by adding <b>-lpcre</b> to the command for linking
159 an application that uses PCRE. The header file defines the macros PCRE_MAJOR
160 and PCRE_MINOR to contain the major and minor release numbers for the library.
161 Applications can use these to include support for different releases of PCRE.
162 </P>
163 <P>
164 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>, PCRE_NEWLINE_<i>xxx</i>, PCRE_NO_UTF8_CHECK, and
439 PCRE_NO_START_OPT options can be set at the time of matching as well as at
440 compile time.
441 </P>
442 <P>
443 If <i>errptr</i> is NULL, <b>pcre_compile()</b> returns NULL immediately.
444 Otherwise, if compilation of a pattern fails, <b>pcre_compile()</b> returns
445 NULL, and sets the variable pointed to by <i>errptr</i> to point to a textual
446 error message. This is a static string that is part of the library. You must
447 not try to free it. The offset from the start of the pattern to the byte that
448 was being processed when the error was discovered is placed in the variable
449 pointed to by <i>erroffset</i>, which must not be NULL. If it is, an immediate
450 error is given. Some errors are not detected until checks are carried out when
451 the whole pattern has been scanned; in this case the offset is set to the end
452 of the pattern.
453 </P>
454 <P>
455 Note that the offset is in bytes, not characters, even in UTF-8 mode. It may
456 point into the middle of a UTF-8 character (for example, when
457 PCRE_ERROR_BADUTF8 is returned for an invalid UTF-8 string).
458 </P>
459 <P>
460 If <b>pcre_compile2()</b> is used instead of <b>pcre_compile()</b>, and the
461 <i>errorcodeptr</i> argument is not NULL, a non-zero error code number is
462 returned via this argument in the event of an error. This is in addition to the
463 textual error message. Error codes and messages are listed below.
464 </P>
465 <P>
466 If the final argument, <i>tableptr</i>, is NULL, PCRE uses a default set of
467 character tables that are built when PCRE is compiled, using the default C
468 locale. Otherwise, <i>tableptr</i> must be an address that is the result of a
469 call to <b>pcre_maketables()</b>. This value is stored with the compiled
470 pattern, and used again by <b>pcre_exec()</b>, unless another table pointer is
471 passed to it. For more discussion, see the section on locale support below.
472 </P>
473 <P>
474 This code fragment shows a typical straightforward call to <b>pcre_compile()</b>:
475 <pre>
476 pcre *re;
477 const char *error;
478 int erroffset;
479 re = pcre_compile(
480 "^A.*Z", /* the pattern */
481 0, /* default options */
482 &error, /* for error message */
483 &erroffset, /* for error offset */
484 NULL); /* use default character tables */
485 </pre>
486 The following names for option bits are defined in the <b>pcre.h</b> header
487 file:
488 <pre>
490 </pre>
491 If this bit is set, the pattern is forced to be "anchored", that is, it is
492 constrained to match only at the first matching point in the string that is
493 being searched (the "subject string"). This effect can also be achieved by
494 appropriate constructs in the pattern itself, which is the only way to do it in
495 Perl.
496 <pre>
498 </pre>
499 If this bit is set, <b>pcre_compile()</b> automatically inserts callout items,
500 all with number 255, before each pattern item. For discussion of the callout
501 facility, see the
502 <a href="pcrecallout.html"><b>pcrecallout</b></a>
503 documentation.
504 <pre>
507 </pre>
508 These options (which are mutually exclusive) control what the \R escape
509 sequence matches. The choice is either to match only CR, LF, or CRLF, or to
510 match any Unicode newline sequence. The default is specified when PCRE is
511 built. It can be overridden from within the pattern, or by setting an option
512 when a compiled pattern is matched.
513 <pre>
515 </pre>
516 If this bit is set, letters in the pattern match both upper and lower case
517 letters. It is equivalent to Perl's /i option, and it can be changed within a
518 pattern by a (?i) option setting. In UTF-8 mode, PCRE always understands the
519 concept of case for characters whose values are less than 128, so caseless
520 matching is always possible. For characters with higher values, the concept of
521 case is supported if PCRE is compiled with Unicode property support, but not
522 otherwise. If you want to use caseless matching for characters 128 and above,
523 you must ensure that PCRE is compiled with Unicode property support as well as
524 with UTF-8 support.
525 <pre>
527 </pre>
528 If this bit is set, a dollar metacharacter in the pattern matches only at the
529 end of the subject string. Without this option, a dollar also matches
530 immediately before a newline at the end of the string (but not before any other
531 newlines). The PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is set.
532 There is no equivalent to this option in Perl, and no way to set it within a
533 pattern.
534 <pre>
536 </pre>
537 If this bit is set, a dot metacharacter in the pattern matches a character of
538 any value, including one that indicates a newline. However, it only ever
539 matches one character, even if newlines are coded as CRLF. Without this option,
540 a dot does not match when the current position is at a newline. This option is
541 equivalent to Perl's /s option, and it can be changed within a pattern by a
542 (?s) option setting. A negative class such as [^a] always matches newline
543 characters, independent of the setting of this option.
544 <pre>
546 </pre>
547 If this bit is set, names used to identify capturing subpatterns need not be
548 unique. This can be helpful for certain types of pattern when it is known that
549 only one instance of the named subpattern can ever be matched. There are more
550 details of named subpatterns below; see also the
551 <a href="pcrepattern.html"><b>pcrepattern</b></a>
552 documentation.
553 <pre>
555 </pre>
556 If this bit is set, whitespace data characters in the pattern are totally
557 ignored except when escaped or inside a character class. Whitespace does not
558 include the VT character (code 11). In addition, characters between an
559 unescaped # outside a character class and the next newline, inclusive, are also
560 ignored. This is equivalent to Perl's /x option, and it can be changed within a
561 pattern by a (?x) option setting.
562 </P>
563 <P>
564 Which characters are interpreted as newlines
565 is controlled by the options passed to <b>pcre_compile()</b> or by a special
566 sequence at the start of the pattern, as described in the section entitled
567 <a href="pcrepattern.html#newlines">"Newline conventions"</a>
568 in the <b>pcrepattern</b> documentation. Note that the end of this type of
569 comment is a literal newline sequence in the pattern; escape sequences that
570 happen to represent a newline do not count.
571 </P>
572 <P>
573 This option makes it possible to include comments inside complicated patterns.
574 Note, however, that this applies only to data characters. Whitespace characters
575 may never appear within special character sequences in a pattern, for example
576 within the sequence (?( that introduces a conditional subpattern.
577 <pre>
579 </pre>
580 This option was invented in order to turn on additional functionality of PCRE
581 that is incompatible with Perl, but it is currently of very little use. When
582 set, any backslash in a pattern that is followed by a letter that has no
583 special meaning causes an error, thus reserving these combinations for future
584 expansion. By default, as in Perl, a backslash followed by a letter with no
585 special meaning is treated as a literal. (Perl can, however, be persuaded to
586 give an error for this, by running it with the -w option.) There are at present
587 no other features controlled by this option. It can also be set by a (?X)
588 option setting within a pattern.
589 <pre>
591 </pre>
592 If this option is set, an unanchored pattern is required to match before or at
593 the first newline in the subject string, though the matched text may continue
594 over the newline.
595 <pre>
597 </pre>
598 If this option is set, PCRE's behaviour is changed in some ways so that it is
599 compatible with JavaScript rather than Perl. The changes are as follows:
600 </P>
601 <P>
602 (1) A lone closing square bracket in a pattern causes a compile-time error,
603 because this is illegal in JavaScript (by default it is treated as a data
604 character). Thus, the pattern AB]CD becomes illegal when this option is set.
605 </P>
606 <P>
607 (2) At run time, a back reference to an unset subpattern group matches an empty
608 string (by default this causes the current matching alternative to fail). A
609 pattern such as (\1)(a) succeeds when this option is set (assuming it can find
610 an "a" in the subject), whereas it fails by default, for Perl compatibility.
611 <pre>
613 </pre>
614 By default, PCRE treats the subject string as consisting of a single line of
615 characters (even if it actually contains newlines). The "start of line"
616 metacharacter (^) matches only at the start of the string, while the "end of
617 line" metacharacter ($) matches only at the end of the string, or before a
618 terminating newline (unless PCRE_DOLLAR_ENDONLY is set). This is the same as
619 Perl.
620 </P>
621 <P>
622 When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs
623 match immediately following or immediately before internal newlines in the
624 subject string, respectively, as well as at the very start and end. This is
625 equivalent to Perl's /m option, and it can be changed within a pattern by a
626 (?m) option setting. If there are no newlines in a subject string, or no
627 occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no effect.
628 <pre>
634 </pre>
635 These options override the default newline definition that was chosen when PCRE
636 was built. Setting the first or the second specifies that a newline is
637 indicated by a single character (CR or LF, respectively). Setting
638 PCRE_NEWLINE_CRLF specifies that a newline is indicated by the two-character
639 CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies that any of the three
640 preceding sequences should be recognized. Setting PCRE_NEWLINE_ANY specifies
641 that any Unicode newline sequence should be recognized. The Unicode newline
642 sequences are the three just mentioned, plus the single characters VT (vertical
643 tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS (line
644 separator, U+2028), and PS (paragraph separator, U+2029). The last two are
645 recognized only in UTF-8 mode.
646 </P>
647 <P>
648 The newline setting in the options word uses three bits that are treated
649 as a number, giving eight possibilities. Currently only six are used (default
650 plus the five values above). This means that if you set more than one newline
651 option, the combination may or may not be sensible. For example,
653 other combinations may yield unused numbers and cause an error.
654 </P>
655 <P>
656 The only time that a line break in a pattern is specially recognized when
657 compiling is when PCRE_EXTENDED is set. CR and LF are whitespace characters,
658 and so are ignored in this mode. Also, an unescaped # outside a character class
659 indicates a comment that lasts until after the next line break sequence. In
660 other circumstances, line break sequences in patterns are treated as literal
661 data.
662 </P>
663 <P>
664 The newline option that is set at compile time becomes the default that is used
665 for <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b>, but it can be overridden.
666 <pre>
668 </pre>
669 If this option is set, it disables the use of numbered capturing parentheses in
670 the pattern. Any opening parenthesis that is not followed by ? behaves as if it
671 were followed by ?: but named parentheses can still be used for capturing (and
672 they acquire numbers in the usual way). There is no equivalent of this option
673 in Perl.
674 <pre>
676 </pre>
677 This is an option that acts at matching time; that is, it is really an option
678 for <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b>. If it is set at compile time,
679 it is remembered with the compiled pattern and assumed at matching time. For
680 details see the discussion of PCRE_NO_START_OPTIMIZE
681 <a href="#execoptions">below.</a>
682 <pre>
684 </pre>
685 This option changes the way PCRE processes \B, \b, \D, \d, \S, \s, \W,
686 \w, and some of the POSIX character classes. By default, only ASCII characters
687 are recognized, but if PCRE_UCP is set, Unicode properties are used instead to
688 classify characters. More details are given in the section on
689 <a href="pcre.html#genericchartypes">generic character types</a>
690 in the
691 <a href="pcrepattern.html"><b>pcrepattern</b></a>
692 page. If you set PCRE_UCP, matching one of the items it affects takes much
693 longer. The option is available only if PCRE has been compiled with Unicode
694 property support.
695 <pre>
697 </pre>
698 This option inverts the "greediness" of the quantifiers so that they are not
699 greedy by default, but become greedy if followed by "?". It is not compatible
700 with Perl. It can also be set by a (?U) option setting within the pattern.
701 <pre>
703 </pre>
704 This option causes PCRE to regard both the pattern and the subject as strings
705 of UTF-8 characters instead of single-byte character strings. However, it is
706 available only when PCRE is built to include UTF-8 support. If not, the use
707 of this option provokes an error. Details of how this option changes the
708 behaviour of PCRE are given in the
709 <a href="pcre.html#utf8support">section on UTF-8 support</a>
710 in the main
711 <a href="pcre.html"><b>pcre</b></a>
712 page.
713 <pre>
715 </pre>
716 When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
717 automatically checked. There is a discussion about the
718 <a href="pcre.html#utf8strings">validity of UTF-8 strings</a>
719 in the main
720 <a href="pcre.html"><b>pcre</b></a>
721 page. If an invalid UTF-8 sequence of bytes is found, <b>pcre_compile()</b>
722 returns an error. If you already know that your pattern is valid, and you want
723 to skip this check for performance reasons, you can set the PCRE_NO_UTF8_CHECK
724 option. When it is set, the effect of passing an invalid UTF-8 string as a
725 pattern is undefined. It may cause your program to crash. Note that this option
726 can also be passed to <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b>, to suppress
727 the UTF-8 validity checking of subject strings.
728 </P>
729 <br><a name="SEC8" href="#TOC1">COMPILATION ERROR CODES</a><br>
730 <P>
731 The following table lists the error codes than may be returned by
732 <b>pcre_compile2()</b>, along with the error messages that may be returned by
733 both compiling functions. As PCRE has developed, some error codes have fallen
734 out of use. To avoid confusion, they have not been re-used.
735 <pre>
736 0 no error
737 1 \ at end of pattern
738 2 \c at end of pattern
739 3 unrecognized character follows \
740 4 numbers out of order in {} quantifier
741 5 number too big in {} quantifier
742 6 missing terminating ] for character class
743 7 invalid escape sequence in character class
744 8 range out of order in character class
745 9 nothing to repeat
746 10 [this code is not in use]
747 11 internal error: unexpected repeat
748 12 unrecognized character after (? or (?-
749 13 POSIX named classes are supported only within a class
750 14 missing )
751 15 reference to non-existent subpattern
752 16 erroffset passed as NULL
753 17 unknown option bit(s) set
754 18 missing ) after comment
755 19 [this code is not in use]
756 20 regular expression is too large
757 21 failed to get memory
758 22 unmatched parentheses
759 23 internal error: code overflow
760 24 unrecognized character after (?&#60;
761 25 lookbehind assertion is not fixed length
762 26 malformed number or name after (?(
763 27 conditional group contains more than two branches
764 28 assertion expected after (?(
765 29 (?R or (?[+-]digits must be followed by )
766 30 unknown POSIX class name
767 31 POSIX collating elements are not supported
768 32 this version of PCRE is not compiled with PCRE_UTF8 support
769 33 [this code is not in use]
770 34 character value in \x{...} sequence is too large
771 35 invalid condition (?(0)
772 36 \C not allowed in lookbehind assertion
773 37 PCRE does not support \L, \l, \N, \U, or \u
774 38 number after (?C is &#62; 255
775 39 closing ) for (?C expected
776 40 recursive call could loop indefinitely
777 41 unrecognized character after (?P
778 42 syntax error in subpattern name (missing terminator)
779 43 two named subpatterns have the same name
780 44 invalid UTF-8 string
781 45 support for \P, \p, and \X has not been compiled
782 46 malformed \P or \p sequence
783 47 unknown property name after \P or \p
784 48 subpattern name is too long (maximum 32 characters)
785 49 too many named subpatterns (maximum 10000)
786 50 [this code is not in use]
787 51 octal value is greater than \377 (not in UTF-8 mode)
788 52 internal error: overran compiling workspace
789 53 internal error: previously-checked referenced subpattern
790 not found
791 54 DEFINE group contains more than one branch
792 55 repeating a DEFINE group is not allowed
793 56 inconsistent NEWLINE options
794 57 \g is not followed by a braced, angle-bracketed, or quoted
795 name/number or by a plain number
796 58 a numbered reference must not be zero
797 59 an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT)
798 60 (*VERB) not recognized
799 61 number is too big
800 62 subpattern name expected
801 63 digit expected after (?+
802 64 ] is an invalid data character in JavaScript compatibility mode
803 65 different names for subpatterns of the same number are
804 not allowed
805 66 (*MARK) must have an argument
806 67 this version of PCRE is not compiled with PCRE_UCP support
807 </pre>
808 The numbers 32 and 10000 in errors 48 and 49 are defaults; different values may
809 be used if the limits were changed when PCRE was built.
810 </P>
811 <br><a name="SEC9" href="#TOC1">STUDYING A PATTERN</a><br>
812 <P>
813 <b>pcre_extra *pcre_study(const pcre *<i>code</i>, int <i>options</i></b>
814 <b>const char **<i>errptr</i>);</b>
815 </P>
816 <P>
817 If a compiled pattern is going to be used several times, it is worth spending
818 more time analyzing it in order to speed up the time taken for matching. The
819 function <b>pcre_study()</b> takes a pointer to a compiled pattern as its first
820 argument. If studying the pattern produces additional information that will
821 help speed up matching, <b>pcre_study()</b> returns a pointer to a
822 <b>pcre_extra</b> block, in which the <i>study_data</i> field points to the
823 results of the study.
824 </P>
825 <P>
826 The returned value from <b>pcre_study()</b> can be passed directly to
827 <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b>. However, a <b>pcre_extra</b> block
828 also contains other fields that can be set by the caller before the block is
829 passed; these are described
830 <a href="#extradata">below</a>
831 in the section on matching a pattern.
832 </P>
833 <P>
834 If studying the pattern does not produce any useful information,
835 <b>pcre_study()</b> returns NULL. In that circumstance, if the calling program
836 wants to pass any of the other fields to <b>pcre_exec()</b> or
837 <b>pcre_dfa_exec()</b>, it must set up its own <b>pcre_extra</b> block.
838 </P>
839 <P>
840 The second argument of <b>pcre_study()</b> contains option bits. At present, no
841 options are defined, and this argument should always be zero.
842 </P>
843 <P>
844 The third argument for <b>pcre_study()</b> is a pointer for an error message. If
845 studying succeeds (even if no data is returned), the variable it points to is
846 set to NULL. Otherwise it is set to point to a textual error message. This is a
847 static string that is part of the library. You must not try to free it. You
848 should test the error pointer for NULL after calling <b>pcre_study()</b>, to be
849 sure that it has run successfully.
850 </P>
851 <P>
852 This is a typical call to <b>pcre_study</b>():
853 <pre>
854 pcre_extra *pe;
855 pe = pcre_study(
856 re, /* result of pcre_compile() */
857 0, /* no options exist */
858 &error); /* set to NULL or points to a message */
859 </pre>
860 Studying a pattern does two things: first, a lower bound for the length of
861 subject string that is needed to match the pattern is computed. This does not
862 mean that there are any strings of that length that match, but it does
863 guarantee that no shorter strings match. The value is used by
864 <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b> to avoid wasting time by trying to
865 match strings that are shorter than the lower bound. You can find out the value
866 in a calling program via the <b>pcre_fullinfo()</b> function.
867 </P>
868 <P>
869 Studying a pattern is also useful for non-anchored patterns that do not have a
870 single fixed starting character. A bitmap of possible starting bytes is
871 created. This speeds up finding a position in the subject at which to start
872 matching.
873 </P>
874 <P>
875 The two optimizations just described can be disabled by setting the
876 PCRE_NO_START_OPTIMIZE option when calling <b>pcre_exec()</b> or
877 <b>pcre_dfa_exec()</b>. You might want to do this if your pattern contains
878 callouts or (*MARK), and you want to make use of these facilities in cases
879 where matching fails. See the discussion of PCRE_NO_START_OPTIMIZE
880 <a href="#execoptions">below.</a>
881 <a name="localesupport"></a></P>
882 <br><a name="SEC10" href="#TOC1">LOCALE SUPPORT</a><br>
883 <P>
884 PCRE handles caseless matching, and determines whether characters are letters,
885 digits, or whatever, by reference to a set of tables, indexed by character
886 value. When running in UTF-8 mode, this applies only to characters with codes
887 less than 128. By default, higher-valued codes never match escapes such as \w
888 or \d, but they can be tested with \p if PCRE is built with Unicode character
889 property support. Alternatively, the PCRE_UCP option can be set at compile
890 time; this causes \w and friends to use Unicode property support instead of
891 built-in tables. The use of locales with Unicode is discouraged. If you are
892 handling characters with codes greater than 128, you should either use UTF-8
893 and Unicode, or use locales, but not try to mix the two.
894 </P>
895 <P>
896 PCRE contains an internal set of tables that are used when the final argument
897 of <b>pcre_compile()</b> is NULL. These are sufficient for many applications.
898 Normally, the internal tables recognize only ASCII characters. However, when
899 PCRE is built, it is possible to cause the internal tables to be rebuilt in the
900 default "C" locale of the local system, which may cause them to be different.
901 </P>
902 <P>
903 The internal tables can always be overridden by tables supplied by the
904 application that calls PCRE. These may be created in a different locale from
905 the default. As more and more applications change to using Unicode, the need
906 for this locale support is expected to die away.
907 </P>
908 <P>
909 External tables are built by calling the <b>pcre_maketables()</b> function,
910 which has no arguments, in the relevant locale. The result can then be passed
911 to <b>pcre_compile()</b> or <b>pcre_exec()</b> as often as necessary. For
912 example, to build and use tables that are appropriate for the French locale
913 (where accented characters with values greater than 128 are treated as letters),
914 the following code could be used:
915 <pre>
916 setlocale(LC_CTYPE, "fr_FR");
917 tables = pcre_maketables();
918 re = pcre_compile(..., tables);
919 </pre>
920 The locale name "fr_FR" is used on Linux and other Unix-like systems; if you
921 are using Windows, the name for the French locale is "french".
922 </P>
923 <P>
924 When <b>pcre_maketables()</b> runs, the tables are built in memory that is
925 obtained via <b>pcre_malloc</b>. It is the caller's responsibility to ensure
926 that the memory containing the tables remains available for as long as it is
927 needed.
928 </P>
929 <P>
930 The pointer that is passed to <b>pcre_compile()</b> is saved with the compiled
931 pattern, and the same tables are used via this pointer by <b>pcre_study()</b>
932 and normally also by <b>pcre_exec()</b>. Thus, by default, for any single
933 pattern, compilation, studying and matching all happen in the same locale, but
934 different patterns can be compiled in different locales.
935 </P>
936 <P>
937 It is possible to pass a table pointer or NULL (indicating the use of the
938 internal tables) to <b>pcre_exec()</b>. Although not intended for this purpose,
939 this facility could be used to match a pattern in a different locale from the
940 one in which it was compiled. Passing table pointers at run time is discussed
941 below in the section on matching a pattern.
942 </P>
943 <br><a name="SEC11" href="#TOC1">INFORMATION ABOUT A PATTERN</a><br>
944 <P>
945 <b>int pcre_fullinfo(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
946 <b>int <i>what</i>, void *<i>where</i>);</b>
947 </P>
948 <P>
949 The <b>pcre_fullinfo()</b> function returns information about a compiled
950 pattern. It replaces the obsolete <b>pcre_info()</b> function, which is
951 nevertheless retained for backwards compability (and is documented below).
952 </P>
953 <P>
954 The first argument for <b>pcre_fullinfo()</b> is a pointer to the compiled
955 pattern. The second argument is the result of <b>pcre_study()</b>, or NULL if
956 the pattern was not studied. The third argument specifies which piece of
957 information is required, and the fourth argument is a pointer to a variable
958 to receive the data. The yield of the function is zero for success, or one of
959 the following negative numbers:
960 <pre>
961 PCRE_ERROR_NULL the argument <i>code</i> was NULL
962 the argument <i>where</i> was NULL
963 PCRE_ERROR_BADMAGIC the "magic number" was not found
964 PCRE_ERROR_BADOPTION the value of <i>what</i> was invalid
965 </pre>
966 The "magic number" is placed at the start of each compiled pattern as an simple
967 check against passing an arbitrary memory pointer. Here is a typical call of
968 <b>pcre_fullinfo()</b>, to obtain the length of the compiled pattern:
969 <pre>
970 int rc;
971 size_t length;
972 rc = pcre_fullinfo(
973 re, /* result of pcre_compile() */
974 pe, /* result of pcre_study(), or NULL */
975 PCRE_INFO_SIZE, /* what is required */
976 &length); /* where to put the data */
977 </pre>
978 The possible values for the third argument are defined in <b>pcre.h</b>, and are
979 as follows:
980 <pre>
982 </pre>
983 Return the number of the highest back reference in the pattern. The fourth
984 argument should point to an <b>int</b> variable. Zero is returned if there are
985 no back references.
986 <pre>
988 </pre>
989 Return the number of capturing subpatterns in the pattern. The fourth argument
990 should point to an <b>int</b> variable.
991 <pre>
993 </pre>
994 Return a pointer to the internal default character tables within PCRE. The
995 fourth argument should point to an <b>unsigned char *</b> variable. This
996 information call is provided for internal use by the <b>pcre_study()</b>
997 function. External callers can cause PCRE to use its internal tables by passing
998 a NULL table pointer.
999 <pre>
1001 </pre>
1002 Return information about the first byte of any matched string, for a
1003 non-anchored pattern. The fourth argument should point to an <b>int</b>
1004 variable. (This option used to be called PCRE_INFO_FIRSTCHAR; the old name is
1005 still recognized for backwards compatibility.)
1006 </P>
1007 <P>
1008 If there is a fixed first byte, for example, from a pattern such as
1009 (cat|cow|coyote), its value is returned. Otherwise, if either
1010 <br>
1011 <br>
1012 (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
1013 starts with "^", or
1014 <br>
1015 <br>
1016 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
1017 (if it were set, the pattern would be anchored),
1018 <br>
1019 <br>
1020 -1 is returned, indicating that the pattern matches only at the start of a
1021 subject string or after any newline within the string. Otherwise -2 is
1022 returned. For anchored patterns, -2 is returned.
1023 <pre>
1025 </pre>
1026 If the pattern was studied, and this resulted in the construction of a 256-bit
1027 table indicating a fixed set of bytes for the first byte in any matching
1028 string, a pointer to the table is returned. Otherwise NULL is returned. The
1029 fourth argument should point to an <b>unsigned char *</b> variable.
1030 <pre>
1032 </pre>
1033 Return 1 if the pattern contains any explicit matches for CR or LF characters,
1034 otherwise 0. The fourth argument should point to an <b>int</b> variable. An
1035 explicit match is either a literal CR or LF character, or \r or \n.
1036 <pre>
1038 </pre>
1039 Return 1 if the (?J) or (?-J) option setting is used in the pattern, otherwise
1040 0. The fourth argument should point to an <b>int</b> variable. (?J) and
1041 (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
1042 <pre>
1044 </pre>
1045 Return the value of the rightmost literal byte that must exist in any matched
1046 string, other than at its start, if such a byte has been recorded. The fourth
1047 argument should point to an <b>int</b> variable. If there is no such byte, -1 is
1048 returned. For anchored patterns, a last literal byte is recorded only if it
1049 follows something of variable length. For example, for the pattern
1050 /^a\d+z\d+/ the returned value is "z", but for /^a\dz\d/ the returned value
1051 is -1.
1052 <pre>
1054 </pre>
1055 If the pattern was studied and a minimum length for matching subject strings
1056 was computed, its value is returned. Otherwise the returned value is -1. The
1057 value is a number of characters, not bytes (this may be relevant in UTF-8
1058 mode). The fourth argument should point to an <b>int</b> variable. A
1059 non-negative value is a lower bound to the length of any matching string. There
1060 may not be any strings of that length that do actually match, but every string
1061 that does match is at least that long.
1062 <pre>
1066 </pre>
1067 PCRE supports the use of named as well as numbered capturing parentheses. The
1068 names are just an additional way of identifying the parentheses, which still
1069 acquire numbers. Several convenience functions such as
1070 <b>pcre_get_named_substring()</b> are provided for extracting captured
1071 substrings by name. It is also possible to extract the data directly, by first
1072 converting the name to a number in order to access the correct pointers in the
1073 output vector (described with <b>pcre_exec()</b> below). To do the conversion,
1074 you need to use the name-to-number map, which is described by these three
1075 values.
1076 </P>
1077 <P>
1078 The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives
1079 the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each
1080 entry; both of these return an <b>int</b> value. The entry size depends on the
1081 length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first
1082 entry of the table (a pointer to <b>char</b>). The first two bytes of each entry
1083 are the number of the capturing parenthesis, most significant byte first. The
1084 rest of the entry is the corresponding name, zero terminated.
1085 </P>
1086 <P>
1087 The names are in alphabetical order. Duplicate names may appear if (?| is used
1088 to create multiple groups with the same number, as described in the
1089 <a href="pcrepattern.html#dupsubpatternnumber">section on duplicate subpattern numbers</a>
1090 in the
1091 <a href="pcrepattern.html"><b>pcrepattern</b></a>
1092 page. Duplicate names for subpatterns with different numbers are permitted only
1093 if PCRE_DUPNAMES is set. In all cases of duplicate names, they appear in the
1094 table in the order in which they were found in the pattern. In the absence of
1095 (?| this is the order of increasing number; when (?| is used this is not
1096 necessarily the case because later subpatterns may have lower numbers.
1097 </P>
1098 <P>
1099 As a simple example of the name/number table, consider the following pattern
1100 (assume PCRE_EXTENDED is set, so white space - including newlines - is
1101 ignored):
1102 <pre>
1103 (?&#60;date&#62; (?&#60;year&#62;(\d\d)?\d\d) - (?&#60;month&#62;\d\d) - (?&#60;day&#62;\d\d) )
1104 </pre>
1105 There are four named subpatterns, so the table has four entries, and each entry
1106 in the table is eight bytes long. The table is as follows, with non-printing
1107 bytes shows in hexadecimal, and undefined bytes shown as ??:
1108 <pre>
1109 00 01 d a t e 00 ??
1110 00 05 d a y 00 ?? ??
1111 00 04 m o n t h 00
1112 00 02 y e a r 00 ??
1113 </pre>
1114 When writing code to extract data from named subpatterns using the
1115 name-to-number map, remember that the length of the entries is likely to be
1116 different for each compiled pattern.
1117 <pre>
1119 </pre>
1120 Return 1 if the pattern can be used for partial matching with
1121 <b>pcre_exec()</b>, otherwise 0. The fourth argument should point to an
1122 <b>int</b> variable. From release 8.00, this always returns 1, because the
1123 restrictions that previously applied to partial matching have been lifted. The
1124 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1125 documentation gives details of partial matching.
1126 <pre>
1128 </pre>
1129 Return a copy of the options with which the pattern was compiled. The fourth
1130 argument should point to an <b>unsigned long int</b> variable. These option bits
1131 are those specified in the call to <b>pcre_compile()</b>, modified by any
1132 top-level option settings at the start of the pattern itself. In other words,
1133 they are the options that will be in force when matching starts. For example,
1134 if the pattern /(?im)abc(?-i)d/ is compiled with the PCRE_EXTENDED option, the
1136 </P>
1137 <P>
1138 A pattern is automatically anchored by PCRE if all of its top-level
1139 alternatives begin with one of the following:
1140 <pre>
1141 ^ unless PCRE_MULTILINE is set
1142 \A always
1143 \G always
1144 .* if PCRE_DOTALL is set and there are no back references to the subpattern in which .* appears
1145 </pre>
1146 For such patterns, the PCRE_ANCHORED bit is set in the options returned by
1147 <b>pcre_fullinfo()</b>.
1148 <pre>
1150 </pre>
1151 Return the size of the compiled pattern, that is, the value that was passed as
1152 the argument to <b>pcre_malloc()</b> when PCRE was getting memory in which to
1153 place the compiled data. The fourth argument should point to a <b>size_t</b>
1154 variable.
1155 <pre>
1157 </pre>
1158 Return the size of the data block pointed to by the <i>study_data</i> field in
1159 a <b>pcre_extra</b> block. That is, it is the value that was passed to
1160 <b>pcre_malloc()</b> when PCRE was getting memory into which to place the data
1161 created by <b>pcre_study()</b>. If <b>pcre_extra</b> is NULL, or there is no
1162 study data, zero is returned. The fourth argument should point to a
1163 <b>size_t</b> variable.
1164 </P>
1165 <br><a name="SEC12" href="#TOC1">OBSOLETE INFO FUNCTION</a><br>
1166 <P>
1167 <b>int pcre_info(const pcre *<i>code</i>, int *<i>optptr</i>, int</b>
1168 <b>*<i>firstcharptr</i>);</b>
1169 </P>
1170 <P>
1171 The <b>pcre_info()</b> function is now obsolete because its interface is too
1172 restrictive to return all the available data about a compiled pattern. New
1173 programs should use <b>pcre_fullinfo()</b> instead. The yield of
1174 <b>pcre_info()</b> is the number of capturing subpatterns, or one of the
1175 following negative numbers:
1176 <pre>
1177 PCRE_ERROR_NULL the argument <i>code</i> was NULL
1178 PCRE_ERROR_BADMAGIC the "magic number" was not found
1179 </pre>
1180 If the <i>optptr</i> argument is not NULL, a copy of the options with which the
1181 pattern was compiled is placed in the integer it points to (see
1182 PCRE_INFO_OPTIONS above).
1183 </P>
1184 <P>
1185 If the pattern is not anchored and the <i>firstcharptr</i> argument is not NULL,
1186 it is used to pass back information about the first character of any matched
1187 string (see PCRE_INFO_FIRSTBYTE above).
1188 </P>
1189 <br><a name="SEC13" href="#TOC1">REFERENCE COUNTS</a><br>
1190 <P>
1191 <b>int pcre_refcount(pcre *<i>code</i>, int <i>adjust</i>);</b>
1192 </P>
1193 <P>
1194 The <b>pcre_refcount()</b> function is used to maintain a reference count in the
1195 data block that contains a compiled pattern. It is provided for the benefit of
1196 applications that operate in an object-oriented manner, where different parts
1197 of the application may be using the same compiled pattern, but you want to free
1198 the block when they are all done.
1199 </P>
1200 <P>
1201 When a pattern is compiled, the reference count field is initialized to zero.
1202 It is changed only by calling this function, whose action is to add the
1203 <i>adjust</i> value (which may be positive or negative) to it. The yield of the
1204 function is the new value. However, the value of the count is constrained to
1205 lie between 0 and 65535, inclusive. If the new value is outside these limits,
1206 it is forced to the appropriate limit value.
1207 </P>
1208 <P>
1209 Except when it is zero, the reference count is not correctly preserved if a
1210 pattern is compiled on one host and then transferred to a host whose byte-order
1211 is different. (This seems a highly unlikely scenario.)
1212 </P>
1213 <br><a name="SEC14" href="#TOC1">MATCHING A PATTERN: THE TRADITIONAL FUNCTION</a><br>
1214 <P>
1215 <b>int pcre_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
1216 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
1217 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>);</b>
1218 </P>
1219 <P>
1220 The function <b>pcre_exec()</b> is called to match a subject string against a
1221 compiled pattern, which is passed in the <i>code</i> argument. If the
1222 pattern was studied, the result of the study should be passed in the
1223 <i>extra</i> argument. This function is the main matching facility of the
1224 library, and it operates in a Perl-like manner. For specialist use there is
1225 also an alternative matching function, which is described
1226 <a href="#dfamatch">below</a>
1227 in the section about the <b>pcre_dfa_exec()</b> function.
1228 </P>
1229 <P>
1230 In most applications, the pattern will have been compiled (and optionally
1231 studied) in the same process that calls <b>pcre_exec()</b>. However, it is
1232 possible to save compiled patterns and study data, and then use them later
1233 in different processes, possibly even on different hosts. For a discussion
1234 about this, see the
1235 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
1236 documentation.
1237 </P>
1238 <P>
1239 Here is an example of a simple call to <b>pcre_exec()</b>:
1240 <pre>
1241 int rc;
1242 int ovector[30];
1243 rc = pcre_exec(
1244 re, /* result of pcre_compile() */
1245 NULL, /* we didn't study the pattern */
1246 "some string", /* the subject string */
1247 11, /* the length of the subject string */
1248 0, /* start at offset 0 in the subject */
1249 0, /* default options */
1250 ovector, /* vector of integers for substring information */
1251 30); /* number of elements (NOT size in bytes) */
1252 <a name="extradata"></a></PRE>
1253 </P>
1254 <br><b>
1255 Extra data for <b>pcre_exec()</b>
1256 </b><br>
1257 <P>
1258 If the <i>extra</i> argument is not NULL, it must point to a <b>pcre_extra</b>
1259 data block. The <b>pcre_study()</b> function returns such a block (when it
1260 doesn't return NULL), but you can also create one for yourself, and pass
1261 additional information in it. The <b>pcre_extra</b> block contains the following
1262 fields (not necessarily in this order):
1263 <pre>
1264 unsigned long int <i>flags</i>;
1265 void *<i>study_data</i>;
1266 unsigned long int <i>match_limit</i>;
1267 unsigned long int <i>match_limit_recursion</i>;
1268 void *<i>callout_data</i>;
1269 const unsigned char *<i>tables</i>;
1270 unsigned char **<i>mark</i>;
1271 </pre>
1272 The <i>flags</i> field is a bitmap that specifies which of the other fields
1273 are set. The flag bits are:
1274 <pre>
1281 </pre>
1282 Other flag bits should be set to zero. The <i>study_data</i> field is set in the
1283 <b>pcre_extra</b> block that is returned by <b>pcre_study()</b>, together with
1284 the appropriate flag bit. You should not set this yourself, but you may add to
1285 the block by setting the other fields and their corresponding flag bits.
1286 </P>
1287 <P>
1288 The <i>match_limit</i> field provides a means of preventing PCRE from using up a
1289 vast amount of resources when running patterns that are not going to match,
1290 but which have a very large number of possibilities in their search trees. The
1291 classic example is a pattern that uses nested unlimited repeats.
1292 </P>
1293 <P>
1294 Internally, PCRE uses a function called <b>match()</b> which it calls repeatedly
1295 (sometimes recursively). The limit set by <i>match_limit</i> is imposed on the
1296 number of times this function is called during a match, which has the effect of
1297 limiting the amount of backtracking that can take place. For patterns that are
1298 not anchored, the count restarts from zero for each position in the subject
1299 string.
1300 </P>
1301 <P>
1302 The default value for the limit can be set when PCRE is built; the default
1303 default is 10 million, which handles all but the most extreme cases. You can
1304 override the default by suppling <b>pcre_exec()</b> with a <b>pcre_extra</b>
1305 block in which <i>match_limit</i> is set, and PCRE_EXTRA_MATCH_LIMIT is set in
1306 the <i>flags</i> field. If the limit is exceeded, <b>pcre_exec()</b> returns
1308 </P>
1309 <P>
1310 The <i>match_limit_recursion</i> field is similar to <i>match_limit</i>, but
1311 instead of limiting the total number of times that <b>match()</b> is called, it
1312 limits the depth of recursion. The recursion depth is a smaller number than the
1313 total number of calls, because not all calls to <b>match()</b> are recursive.
1314 This limit is of use only if it is set smaller than <i>match_limit</i>.
1315 </P>
1316 <P>
1317 Limiting the recursion depth limits the amount of stack that can be used, or,
1318 when PCRE has been compiled to use memory on the heap instead of the stack, the
1319 amount of heap memory that can be used.
1320 </P>
1321 <P>
1322 The default value for <i>match_limit_recursion</i> can be set when PCRE is
1323 built; the default default is the same value as the default for
1324 <i>match_limit</i>. You can override the default by suppling <b>pcre_exec()</b>
1325 with a <b>pcre_extra</b> block in which <i>match_limit_recursion</i> is set, and
1326 PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the <i>flags</i> field. If the limit
1327 is exceeded, <b>pcre_exec()</b> returns PCRE_ERROR_RECURSIONLIMIT.
1328 </P>
1329 <P>
1330 The <i>callout_data</i> field is used in conjunction with the "callout" feature,
1331 and is described in the
1332 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1333 documentation.
1334 </P>
1335 <P>
1336 The <i>tables</i> field is used to pass a character tables pointer to
1337 <b>pcre_exec()</b>; this overrides the value that is stored with the compiled
1338 pattern. A non-NULL value is stored with the compiled pattern only if custom
1339 tables were supplied to <b>pcre_compile()</b> via its <i>tableptr</i> argument.
1340 If NULL is passed to <b>pcre_exec()</b> using this mechanism, it forces PCRE's
1341 internal tables to be used. This facility is helpful when re-using patterns
1342 that have been saved after compiling with an external set of tables, because
1343 the external tables might be at a different address when <b>pcre_exec()</b> is
1344 called. See the
1345 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
1346 documentation for a discussion of saving compiled patterns for later use.
1347 </P>
1348 <P>
1349 If PCRE_EXTRA_MARK is set in the <i>flags</i> field, the <i>mark</i> field must
1350 be set to point to a <b>char *</b> variable. If the pattern contains any
1351 backtracking control verbs such as (*MARK:NAME), and the execution ends up with
1352 a name to pass back, a pointer to the name string (zero terminated) is placed
1353 in the variable pointed to by the <i>mark</i> field. The names are within the
1354 compiled pattern; if you wish to retain such a name you must copy it before
1355 freeing the memory of a compiled pattern. If there is no name to pass back, the
1356 variable pointed to by the <i>mark</i> field set to NULL. For details of the
1357 backtracking control verbs, see the section entitled
1358 <a href="pcrepattern#backtrackcontrol">"Backtracking control"</a>
1359 in the
1360 <a href="pcrepattern.html"><b>pcrepattern</b></a>
1361 documentation.
1362 <a name="execoptions"></a></P>
1363 <br><b>
1364 Option bits for <b>pcre_exec()</b>
1365 </b><br>
1366 <P>
1367 The unused bits of the <i>options</i> argument for <b>pcre_exec()</b> must be
1368 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_<i>xxx</i>,
1372 <pre>
1374 </pre>
1375 The PCRE_ANCHORED option limits <b>pcre_exec()</b> to matching at the first
1376 matching position. If a pattern was compiled with PCRE_ANCHORED, or turned out
1377 to be anchored by virtue of its contents, it cannot be made unachored at
1378 matching time.
1379 <pre>
1382 </pre>
1383 These options (which are mutually exclusive) control what the \R escape
1384 sequence matches. The choice is either to match only CR, LF, or CRLF, or to
1385 match any Unicode newline sequence. These options override the choice that was
1386 made or defaulted when the pattern was compiled.
1387 <pre>
1393 </pre>
1394 These options override the newline definition that was chosen or defaulted when
1395 the pattern was compiled. For details, see the description of
1396 <b>pcre_compile()</b> above. During matching, the newline choice affects the
1397 behaviour of the dot, circumflex, and dollar metacharacters. It may also alter
1398 the way the match position is advanced after a match failure for an unanchored
1399 pattern.
1400 </P>
1401 <P>
1403 match attempt for an unanchored pattern fails when the current position is at a
1404 CRLF sequence, and the pattern contains no explicit matches for CR or LF
1405 characters, the match position is advanced by two characters instead of one, in
1406 other words, to after the CRLF.
1407 </P>
1408 <P>
1409 The above rule is a compromise that makes the most common cases work as
1410 expected. For example, if the pattern is .+A (and the PCRE_DOTALL option is not
1411 set), it does not match the string "\r\nA" because, after failing at the
1412 start, it skips both the CR and the LF before retrying. However, the pattern
1413 [\r\n]A does match that string, because it contains an explicit CR or LF
1414 reference, and so advances only by one character after the first failure.
1415 </P>
1416 <P>
1417 An explicit match for CR of LF is either a literal appearance of one of those
1418 characters, or one of the \r or \n escape sequences. Implicit matches such as
1419 [^X] do not count, nor does \s (which includes CR and LF in the characters
1420 that it matches).
1421 </P>
1422 <P>
1423 Notwithstanding the above, anomalous effects may still occur when CRLF is a
1424 valid newline sequence and explicit \r or \n escapes appear in the pattern.
1425 <pre>
1427 </pre>
1428 This option specifies that first character of the subject string is not the
1429 beginning of a line, so the circumflex metacharacter should not match before
1430 it. Setting this without PCRE_MULTILINE (at compile time) causes circumflex
1431 never to match. This option affects only the behaviour of the circumflex
1432 metacharacter. It does not affect \A.
1433 <pre>
1435 </pre>
1436 This option specifies that the end of the subject string is not the end of a
1437 line, so the dollar metacharacter should not match it nor (except in multiline
1438 mode) a newline immediately before it. Setting this without PCRE_MULTILINE (at
1439 compile time) causes dollar never to match. This option affects only the
1440 behaviour of the dollar metacharacter. It does not affect \Z or \z.
1441 <pre>
1443 </pre>
1444 An empty string is not considered to be a valid match if this option is set. If
1445 there are alternatives in the pattern, they are tried. If all the alternatives
1446 match the empty string, the entire match fails. For example, if the pattern
1447 <pre>
1448 a?b?
1449 </pre>
1450 is applied to a string not beginning with "a" or "b", it matches an empty
1451 string at the start of the subject. With PCRE_NOTEMPTY set, this match is not
1452 valid, so PCRE searches further into the string for occurrences of "a" or "b".
1453 <pre>
1455 </pre>
1456 This is like PCRE_NOTEMPTY, except that an empty string match that is not at
1457 the start of the subject is permitted. If the pattern is anchored, such a match
1458 can occur only if the pattern contains \K.
1459 </P>
1460 <P>
1461 Perl has no direct equivalent of PCRE_NOTEMPTY or PCRE_NOTEMPTY_ATSTART, but it
1462 does make a special case of a pattern match of the empty string within its
1463 <b>split()</b> function, and when using the /g modifier. It is possible to
1464 emulate Perl's behaviour after matching a null string by first trying the match
1465 again at the same offset with PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED, and then
1466 if that fails, by advancing the starting offset (see below) and trying an
1467 ordinary match again. There is some code that demonstrates how to do this in
1468 the
1469 <a href="pcredemo.html"><b>pcredemo</b></a>
1470 sample program. In the most general case, you have to check to see if the
1471 newline convention recognizes CRLF as a newline, and if so, and the current
1472 character is CR followed by LF, advance the starting offset by two characters
1473 instead of one.
1474 <pre>
1476 </pre>
1477 There are a number of optimizations that <b>pcre_exec()</b> uses at the start of
1478 a match, in order to speed up the process. For example, if it is known that an
1479 unanchored match must start with a specific character, it searches the subject
1480 for that character, and fails immediately if it cannot find it, without
1481 actually running the main matching function. This means that a special item
1482 such as (*COMMIT) at the start of a pattern is not considered until after a
1483 suitable starting point for the match has been found. When callouts or (*MARK)
1484 items are in use, these "start-up" optimizations can cause them to be skipped
1485 if the pattern is never actually used. The start-up optimizations are in effect
1486 a pre-scan of the subject that takes place before the pattern is run.
1487 </P>
1488 <P>
1489 The PCRE_NO_START_OPTIMIZE option disables the start-up optimizations, possibly
1490 causing performance to suffer, but ensuring that in cases where the result is
1491 "no match", the callouts do occur, and that items such as (*COMMIT) and (*MARK)
1492 are considered at every possible starting position in the subject string. If
1493 PCRE_NO_START_OPTIMIZE is set at compile time, it cannot be unset at matching
1494 time.
1495 </P>
1496 <P>
1497 Setting PCRE_NO_START_OPTIMIZE can change the outcome of a matching operation.
1498 Consider the pattern
1499 <pre>
1501 </pre>
1502 When this is compiled, PCRE records the fact that a match must start with the
1503 character "A". Suppose the subject string is "DEFABC". The start-up
1504 optimization scans along the subject, finds "A" and runs the first match
1505 attempt from there. The (*COMMIT) item means that the pattern must match the
1506 current starting position, which in this case, it does. However, if the same
1507 match is run with PCRE_NO_START_OPTIMIZE set, the initial scan along the
1508 subject string does not happen. The first match attempt is run starting from
1509 "D" and when this fails, (*COMMIT) prevents any further matches being tried, so
1510 the overall result is "no match". If the pattern is studied, more start-up
1511 optimizations may be used. For example, a minimum length for the subject may be
1512 recorded. Consider the pattern
1513 <pre>
1514 (*MARK:A)(X|Y)
1515 </pre>
1516 The minimum length for a match is one character. If the subject is "ABC", there
1517 will be attempts to match "ABC", "BC", "C", and then finally an empty string.
1518 If the pattern is studied, the final attempt does not take place, because PCRE
1519 knows that the subject is too short, and so the (*MARK) is never encountered.
1520 In this case, studying the pattern does not affect the overall match result,
1521 which is still "no match", but it does affect the auxiliary information that is
1522 returned.
1523 <pre>
1525 </pre>
1526 When PCRE_UTF8 is set at compile time, the validity of the subject as a UTF-8
1527 string is automatically checked when <b>pcre_exec()</b> is subsequently called.
1528 The value of <i>startoffset</i> is also checked to ensure that it points to the
1529 start of a UTF-8 character. There is a discussion about the validity of UTF-8
1530 strings in the
1531 <a href="pcre.html#utf8strings">section on UTF-8 support</a>
1532 in the main
1533 <a href="pcre.html"><b>pcre</b></a>
1534 page. If an invalid UTF-8 sequence of bytes is found, <b>pcre_exec()</b> returns
1535 the error PCRE_ERROR_BADUTF8 or, if PCRE_PARTIAL_HARD is set and the problem is
1536 a truncated UTF-8 character at the end of the subject, PCRE_ERROR_SHORTUTF8. If
1537 <i>startoffset</i> contains a value that does not point to the start of a UTF-8
1538 character (or to the end of the subject), PCRE_ERROR_BADUTF8_OFFSET is
1539 returned.
1540 </P>
1541 <P>
1542 If you already know that your subject is valid, and you want to skip these
1543 checks for performance reasons, you can set the PCRE_NO_UTF8_CHECK option when
1544 calling <b>pcre_exec()</b>. You might want to do this for the second and
1545 subsequent calls to <b>pcre_exec()</b> if you are making repeated calls to find
1546 all the matches in a single subject string. However, you should be sure that
1547 the value of <i>startoffset</i> points to the start of a UTF-8 character (or the
1548 end of the subject). When PCRE_NO_UTF8_CHECK is set, the effect of passing an
1549 invalid UTF-8 string as a subject or an invalid value of <i>startoffset</i> is
1550 undefined. Your program may crash.
1551 <pre>
1554 </pre>
1555 These options turn on the partial matching feature. For backwards
1556 compatibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial match
1557 occurs if the end of the subject string is reached successfully, but there are
1558 not enough subject characters to complete the match. If this happens when
1559 PCRE_PARTIAL_SOFT (but not PCRE_PARTIAL_HARD) is set, matching continues by
1560 testing any remaining alternatives. Only if no complete match can be found is
1561 PCRE_ERROR_PARTIAL returned instead of PCRE_ERROR_NOMATCH. In other words,
1562 PCRE_PARTIAL_SOFT says that the caller is prepared to handle a partial match,
1563 but only if no complete match can be found.
1564 </P>
1565 <P>
1566 If PCRE_PARTIAL_HARD is set, it overrides PCRE_PARTIAL_SOFT. In this case, if a
1567 partial match is found, <b>pcre_exec()</b> immediately returns
1568 PCRE_ERROR_PARTIAL, without considering any other alternatives. In other words,
1569 when PCRE_PARTIAL_HARD is set, a partial match is considered to be more
1570 important that an alternative complete match.
1571 </P>
1572 <P>
1573 In both cases, the portion of the string that was inspected when the partial
1574 match was found is set as the first matching string. There is a more detailed
1575 discussion of partial and multi-segment matching, with examples, in the
1576 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1577 documentation.
1578 </P>
1579 <br><b>
1580 The string to be matched by <b>pcre_exec()</b>
1581 </b><br>
1582 <P>
1583 The subject string is passed to <b>pcre_exec()</b> as a pointer in
1584 <i>subject</i>, a length (in bytes) in <i>length</i>, and a starting byte offset
1585 in <i>startoffset</i>. If this is negative or greater than the length of the
1586 subject, <b>pcre_exec()</b> returns PCRE_ERROR_BADOFFSET. When the starting
1587 offset is zero, the search for a match starts at the beginning of the subject,
1588 and this is by far the most common case. In UTF-8 mode, the byte offset must
1589 point to the start of a UTF-8 character (or the end of the subject). Unlike the
1590 pattern string, the subject may contain binary zero bytes.
1591 </P>
1592 <P>
1593 A non-zero starting offset is useful when searching for another match in the
1594 same subject by calling <b>pcre_exec()</b> again after a previous success.
1595 Setting <i>startoffset</i> differs from just passing over a shortened string and
1596 setting PCRE_NOTBOL in the case of a pattern that begins with any kind of
1597 lookbehind. For example, consider the pattern
1598 <pre>
1599 \Biss\B
1600 </pre>
1601 which finds occurrences of "iss" in the middle of words. (\B matches only if
1602 the current position in the subject is not a word boundary.) When applied to
1603 the string "Mississipi" the first call to <b>pcre_exec()</b> finds the first
1604 occurrence. If <b>pcre_exec()</b> is called again with just the remainder of the
1605 subject, namely "issipi", it does not match, because \B is always false at the
1606 start of the subject, which is deemed to be a word boundary. However, if
1607 <b>pcre_exec()</b> is passed the entire string again, but with <i>startoffset</i>
1608 set to 4, it finds the second occurrence of "iss" because it is able to look
1609 behind the starting point to discover that it is preceded by a letter.
1610 </P>
1611 <P>
1612 Finding all the matches in a subject is tricky when the pattern can match an
1613 empty string. It is possible to emulate Perl's /g behaviour by first trying the
1614 match again at the same offset, with the PCRE_NOTEMPTY_ATSTART and
1615 PCRE_ANCHORED options, and then if that fails, advancing the starting offset
1616 and trying an ordinary match again. There is some code that demonstrates how to
1617 do this in the
1618 <a href="pcredemo.html"><b>pcredemo</b></a>
1619 sample program. In the most general case, you have to check to see if the
1620 newline convention recognizes CRLF as a newline, and if so, and the current
1621 character is CR followed by LF, advance the starting offset by two characters
1622 instead of one.
1623 </P>
1624 <P>
1625 If a non-zero starting offset is passed when the pattern is anchored, one
1626 attempt to match at the given offset is made. This can only succeed if the
1627 pattern does not require the match to be at the start of the subject.
1628 </P>
1629 <br><b>
1630 How <b>pcre_exec()</b> returns captured substrings
1631 </b><br>
1632 <P>
1633 In general, a pattern matches a certain portion of the subject, and in
1634 addition, further substrings from the subject may be picked out by parts of the
1635 pattern. Following the usage in Jeffrey Friedl's book, this is called
1636 "capturing" in what follows, and the phrase "capturing subpattern" is used for
1637 a fragment of a pattern that picks out a substring. PCRE supports several other
1638 kinds of parenthesized subpattern that do not cause substrings to be captured.
1639 </P>
1640 <P>
1641 Captured substrings are returned to the caller via a vector of integers whose
1642 address is passed in <i>ovector</i>. The number of elements in the vector is
1643 passed in <i>ovecsize</i>, which must be a non-negative number. <b>Note</b>: this
1644 argument is NOT the size of <i>ovector</i> in bytes.
1645 </P>
1646 <P>
1647 The first two-thirds of the vector is used to pass back captured substrings,
1648 each substring using a pair of integers. The remaining third of the vector is
1649 used as workspace by <b>pcre_exec()</b> while matching capturing subpatterns,
1650 and is not available for passing back information. The number passed in
1651 <i>ovecsize</i> should always be a multiple of three. If it is not, it is
1652 rounded down.
1653 </P>
1654 <P>
1655 When a match is successful, information about captured substrings is returned
1656 in pairs of integers, starting at the beginning of <i>ovector</i>, and
1657 continuing up to two-thirds of its length at the most. The first element of
1658 each pair is set to the byte offset of the first character in a substring, and
1659 the second is set to the byte offset of the first character after the end of a
1660 substring. <b>Note</b>: these values are always byte offsets, even in UTF-8
1661 mode. They are not character counts.
1662 </P>
1663 <P>
1664 The first pair of integers, <i>ovector[0]</i> and <i>ovector[1]</i>, identify the
1665 portion of the subject string matched by the entire pattern. The next pair is
1666 used for the first capturing subpattern, and so on. The value returned by
1667 <b>pcre_exec()</b> is one more than the highest numbered pair that has been set.
1668 For example, if two substrings have been captured, the returned value is 3. If
1669 there are no capturing subpatterns, the return value from a successful match is
1670 1, indicating that just the first pair of offsets has been set.
1671 </P>
1672 <P>
1673 If a capturing subpattern is matched repeatedly, it is the last portion of the
1674 string that it matched that is returned.
1675 </P>
1676 <P>
1677 If the vector is too small to hold all the captured substring offsets, it is
1678 used as far as possible (up to two-thirds of its length), and the function
1679 returns a value of zero. If the substring offsets are not of interest,
1680 <b>pcre_exec()</b> may be called with <i>ovector</i> passed as NULL and
1681 <i>ovecsize</i> as zero. However, if the pattern contains back references and
1682 the <i>ovector</i> is not big enough to remember the related substrings, PCRE
1683 has to get additional memory for use during matching. Thus it is usually
1684 advisable to supply an <i>ovector</i>.
1685 </P>
1686 <P>
1687 The <b>pcre_fullinfo()</b> function can be used to find out how many capturing
1688 subpatterns there are in a compiled pattern. The smallest size for
1689 <i>ovector</i> that will allow for <i>n</i> captured substrings, in addition to
1690 the offsets of the substring matched by the whole pattern, is (<i>n</i>+1)*3.
1691 </P>
1692 <P>
1693 It is possible for capturing subpattern number <i>n+1</i> to match some part of
1694 the subject when subpattern <i>n</i> has not been used at all. For example, if
1695 the string "abc" is matched against the pattern (a|(z))(bc) the return from the
1696 function is 4, and subpatterns 1 and 3 are matched, but 2 is not. When this
1697 happens, both values in the offset pairs corresponding to unused subpatterns
1698 are set to -1.
1699 </P>
1700 <P>
1701 Offset values that correspond to unused subpatterns at the end of the
1702 expression are also set to -1. For example, if the string "abc" is matched
1703 against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not matched. The
1704 return from the function is 2, because the highest used capturing subpattern
1705 number is 1, and the offsets for for the second and third capturing subpatterns
1706 (assuming the vector is large enough, of course) are set to -1.
1707 </P>
1708 <P>
1709 <b>Note</b>: Elements of <i>ovector</i> that do not correspond to capturing
1710 parentheses in the pattern are never changed. That is, if a pattern contains
1711 <i>n</i> capturing parentheses, no more than <i>ovector[0]</i> to
1712 <i>ovector[2n+1]</i> are set by <b>pcre_exec()</b>. The other elements retain
1713 whatever values they previously had.
1714 </P>
1715 <P>
1716 Some convenience functions are provided for extracting the captured substrings
1717 as separate strings. These are described below.
1718 <a name="errorlist"></a></P>
1719 <br><b>
1720 Error return values from <b>pcre_exec()</b>
1721 </b><br>
1722 <P>
1723 If <b>pcre_exec()</b> fails, it returns a negative number. The following are
1724 defined in the header file:
1725 <pre>
1727 </pre>
1728 The subject string did not match the pattern.
1729 <pre>
1731 </pre>
1732 Either <i>code</i> or <i>subject</i> was passed as NULL, or <i>ovector</i> was
1733 NULL and <i>ovecsize</i> was not zero.
1734 <pre>
1736 </pre>
1737 An unrecognized bit was set in the <i>options</i> argument.
1738 <pre>
1740 </pre>
1741 PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch
1742 the case when it is passed a junk pointer and to detect when a pattern that was
1743 compiled in an environment of one endianness is run in an environment with the
1744 other endianness. This is the error that PCRE gives when the magic number is
1745 not present.
1746 <pre>
1748 </pre>
1749 While running the pattern match, an unknown item was encountered in the
1750 compiled pattern. This error could be caused by a bug in PCRE or by overwriting
1751 of the compiled pattern.
1752 <pre>
1754 </pre>
1755 If a pattern contains back references, but the <i>ovector</i> that is passed to
1756 <b>pcre_exec()</b> is not big enough to remember the referenced substrings, PCRE
1757 gets a block of memory at the start of matching to use for this purpose. If the
1758 call via <b>pcre_malloc()</b> fails, this error is given. The memory is
1759 automatically freed at the end of matching.
1760 </P>
1761 <P>
1762 This error is also given if <b>pcre_stack_malloc()</b> fails in
1763 <b>pcre_exec()</b>. This can happen only when PCRE has been compiled with
1764 <b>--disable-stack-for-recursion</b>.
1765 <pre>
1767 </pre>
1768 This error is used by the <b>pcre_copy_substring()</b>,
1769 <b>pcre_get_substring()</b>, and <b>pcre_get_substring_list()</b> functions (see
1770 below). It is never returned by <b>pcre_exec()</b>.
1771 <pre>
1773 </pre>
1774 The backtracking limit, as specified by the <i>match_limit</i> field in a
1775 <b>pcre_extra</b> structure (or defaulted) was reached. See the description
1776 above.
1777 <pre>
1779 </pre>
1780 This error is never generated by <b>pcre_exec()</b> itself. It is provided for
1781 use by callout functions that want to yield a distinctive error code. See the
1782 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1783 documentation for details.
1784 <pre>
1786 </pre>
1787 A string that contains an invalid UTF-8 byte sequence was passed as a subject.
1788 However, if PCRE_PARTIAL_HARD is set and the problem is a truncated UTF-8
1789 character at the end of the subject, PCRE_ERROR_SHORTUTF8 is used instead.
1790 <pre>
1792 </pre>
1793 The UTF-8 byte sequence that was passed as a subject was valid, but the value
1794 of <i>startoffset</i> did not point to the beginning of a UTF-8 character or the
1795 end of the subject.
1796 <pre>
1798 </pre>
1799 The subject string did not match, but it did match partially. See the
1800 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1801 documentation for details of partial matching.
1802 <pre>
1804 </pre>
1805 This code is no longer in use. It was formerly returned when the PCRE_PARTIAL
1806 option was used with a compiled pattern containing items that were not
1807 supported for partial matching. From release 8.00 onwards, there are no
1808 restrictions on partial matching.
1809 <pre>
1811 </pre>
1812 An unexpected internal error has occurred. This error could be caused by a bug
1813 in PCRE or by overwriting of the compiled pattern.
1814 <pre>
1816 </pre>
1817 This error is given if the value of the <i>ovecsize</i> argument is negative.
1818 <pre>
1820 </pre>
1821 The internal recursion limit, as specified by the <i>match_limit_recursion</i>
1822 field in a <b>pcre_extra</b> structure (or defaulted) was reached. See the
1823 description above.
1824 <pre>
1826 </pre>
1827 An invalid combination of PCRE_NEWLINE_<i>xxx</i> options was given.
1828 <pre>
1830 </pre>
1831 The value of <i>startoffset</i> was negative or greater than the length of the
1832 subject, that is, the value in <i>length</i>.
1833 <pre>
1835 </pre>
1836 The subject string ended with an incomplete (truncated) UTF-8 character, and
1837 the PCRE_PARTIAL_HARD option was set. Without this option, PCRE_ERROR_BADUTF8
1838 is returned in this situation.
1839 </P>
1840 <P>
1841 Error numbers -16 to -20 and -22 are not used by <b>pcre_exec()</b>.
1842 </P>
1843 <br><a name="SEC15" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NUMBER</a><br>
1844 <P>
1845 <b>int pcre_copy_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1846 <b>int <i>stringcount</i>, int <i>stringnumber</i>, char *<i>buffer</i>,</b>
1847 <b>int <i>buffersize</i>);</b>
1848 </P>
1849 <P>
1850 <b>int pcre_get_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1851 <b>int <i>stringcount</i>, int <i>stringnumber</i>,</b>
1852 <b>const char **<i>stringptr</i>);</b>
1853 </P>
1854 <P>
1855 <b>int pcre_get_substring_list(const char *<i>subject</i>,</b>
1856 <b>int *<i>ovector</i>, int <i>stringcount</i>, const char ***<i>listptr</i>);</b>
1857 </P>
1858 <P>
1859 Captured substrings can be accessed directly by using the offsets returned by
1860 <b>pcre_exec()</b> in <i>ovector</i>. For convenience, the functions
1861 <b>pcre_copy_substring()</b>, <b>pcre_get_substring()</b>, and
1862 <b>pcre_get_substring_list()</b> are provided for extracting captured substrings
1863 as new, separate, zero-terminated strings. These functions identify substrings
1864 by number. The next section describes functions for extracting named
1865 substrings.
1866 </P>
1867 <P>
1868 A substring that contains a binary zero is correctly extracted and has a
1869 further zero added on the end, but the result is not, of course, a C string.
1870 However, you can process such a string by referring to the length that is
1871 returned by <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>.
1872 Unfortunately, the interface to <b>pcre_get_substring_list()</b> is not adequate
1873 for handling strings containing binary zeros, because the end of the final
1874 string is not independently indicated.
1875 </P>
1876 <P>
1877 The first three arguments are the same for all three of these functions:
1878 <i>subject</i> is the subject string that has just been successfully matched,
1879 <i>ovector</i> is a pointer to the vector of integer offsets that was passed to
1880 <b>pcre_exec()</b>, and <i>stringcount</i> is the number of substrings that were
1881 captured by the match, including the substring that matched the entire regular
1882 expression. This is the value returned by <b>pcre_exec()</b> if it is greater
1883 than zero. If <b>pcre_exec()</b> returned zero, indicating that it ran out of
1884 space in <i>ovector</i>, the value passed as <i>stringcount</i> should be the
1885 number of elements in the vector divided by three.
1886 </P>
1887 <P>
1888 The functions <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>
1889 extract a single substring, whose number is given as <i>stringnumber</i>. A
1890 value of zero extracts the substring that matched the entire pattern, whereas
1891 higher values extract the captured substrings. For <b>pcre_copy_substring()</b>,
1892 the string is placed in <i>buffer</i>, whose length is given by
1893 <i>buffersize</i>, while for <b>pcre_get_substring()</b> a new block of memory is
1894 obtained via <b>pcre_malloc</b>, and its address is returned via
1895 <i>stringptr</i>. The yield of the function is the length of the string, not
1896 including the terminating zero, or one of these error codes:
1897 <pre>
1899 </pre>
1900 The buffer was too small for <b>pcre_copy_substring()</b>, or the attempt to get
1901 memory failed for <b>pcre_get_substring()</b>.
1902 <pre>
1904 </pre>
1905 There is no substring whose number is <i>stringnumber</i>.
1906 </P>
1907 <P>
1908 The <b>pcre_get_substring_list()</b> function extracts all available substrings
1909 and builds a list of pointers to them. All this is done in a single block of
1910 memory that is obtained via <b>pcre_malloc</b>. The address of the memory block
1911 is returned via <i>listptr</i>, which is also the start of the list of string
1912 pointers. The end of the list is marked by a NULL pointer. The yield of the
1913 function is zero if all went well, or the error code
1914 <pre>
1916 </pre>
1917 if the attempt to get the memory block failed.
1918 </P>
1919 <P>
1920 When any of these functions encounter a substring that is unset, which can
1921 happen when capturing subpattern number <i>n+1</i> matches some part of the
1922 subject, but subpattern <i>n</i> has not been used at all, they return an empty
1923 string. This can be distinguished from a genuine zero-length substring by
1924 inspecting the appropriate offset in <i>ovector</i>, which is negative for unset
1925 substrings.
1926 </P>
1927 <P>
1928 The two convenience functions <b>pcre_free_substring()</b> and
1929 <b>pcre_free_substring_list()</b> can be used to free the memory returned by
1930 a previous call of <b>pcre_get_substring()</b> or
1931 <b>pcre_get_substring_list()</b>, respectively. They do nothing more than call
1932 the function pointed to by <b>pcre_free</b>, which of course could be called
1933 directly from a C program. However, PCRE is used in some situations where it is
1934 linked via a special interface to another programming language that cannot use
1935 <b>pcre_free</b> directly; it is for these cases that the functions are
1936 provided.
1937 </P>
1938 <br><a name="SEC16" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NAME</a><br>
1939 <P>
1940 <b>int pcre_get_stringnumber(const pcre *<i>code</i>,</b>
1941 <b>const char *<i>name</i>);</b>
1942 </P>
1943 <P>
1944 <b>int pcre_copy_named_substring(const pcre *<i>code</i>,</b>
1945 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
1946 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
1947 <b>char *<i>buffer</i>, int <i>buffersize</i>);</b>
1948 </P>
1949 <P>
1950 <b>int pcre_get_named_substring(const pcre *<i>code</i>,</b>
1951 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
1952 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
1953 <b>const char **<i>stringptr</i>);</b>
1954 </P>
1955 <P>
1956 To extract a substring by name, you first have to find associated number.
1957 For example, for this pattern
1958 <pre>
1959 (a+)b(?&#60;xxx&#62;\d+)...
1960 </pre>
1961 the number of the subpattern called "xxx" is 2. If the name is known to be
1962 unique (PCRE_DUPNAMES was not set), you can find the number from the name by
1963 calling <b>pcre_get_stringnumber()</b>. The first argument is the compiled
1964 pattern, and the second is the name. The yield of the function is the
1965 subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no subpattern of
1966 that name.
1967 </P>
1968 <P>
1969 Given the number, you can extract the substring directly, or use one of the
1970 functions described in the previous section. For convenience, there are also
1971 two functions that do the whole job.
1972 </P>
1973 <P>
1974 Most of the arguments of <b>pcre_copy_named_substring()</b> and
1975 <b>pcre_get_named_substring()</b> are the same as those for the similarly named
1976 functions that extract by number. As these are described in the previous
1977 section, they are not re-described here. There are just two differences:
1978 </P>
1979 <P>
1980 First, instead of a substring number, a substring name is given. Second, there
1981 is an extra argument, given at the start, which is a pointer to the compiled
1982 pattern. This is needed in order to gain access to the name-to-number
1983 translation table.
1984 </P>
1985 <P>
1986 These functions call <b>pcre_get_stringnumber()</b>, and if it succeeds, they
1987 then call <b>pcre_copy_substring()</b> or <b>pcre_get_substring()</b>, as
1988 appropriate. <b>NOTE:</b> If PCRE_DUPNAMES is set and there are duplicate names,
1989 the behaviour may not be what you want (see the next section).
1990 </P>
1991 <P>
1992 <b>Warning:</b> If the pattern uses the (?| feature to set up multiple
1993 subpatterns with the same number, as described in the
1994 <a href="pcrepattern.html#dupsubpatternnumber">section on duplicate subpattern numbers</a>
1995 in the
1996 <a href="pcrepattern.html"><b>pcrepattern</b></a>
1997 page, you cannot use names to distinguish the different subpatterns, because
1998 names are not included in the compiled code. The matching process uses only
1999 numbers. For this reason, the use of different names for subpatterns of the
2000 same number causes an error at compile time.
2001 </P>
2002 <br><a name="SEC17" href="#TOC1">DUPLICATE SUBPATTERN NAMES</a><br>
2003 <P>
2004 <b>int pcre_get_stringtable_entries(const pcre *<i>code</i>,</b>
2005 <b>const char *<i>name</i>, char **<i>first</i>, char **<i>last</i>);</b>
2006 </P>
2007 <P>
2008 When a pattern is compiled with the PCRE_DUPNAMES option, names for subpatterns
2009 are not required to be unique. (Duplicate names are always allowed for
2010 subpatterns with the same number, created by using the (?| feature. Indeed, if
2011 such subpatterns are named, they are required to use the same names.)
2012 </P>
2013 <P>
2014 Normally, patterns with duplicate names are such that in any one match, only
2015 one of the named subpatterns participates. An example is shown in the
2016 <a href="pcrepattern.html"><b>pcrepattern</b></a>
2017 documentation.
2018 </P>
2019 <P>
2020 When duplicates are present, <b>pcre_copy_named_substring()</b> and
2021 <b>pcre_get_named_substring()</b> return the first substring corresponding to
2022 the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING (-7) is
2023 returned; no data is returned. The <b>pcre_get_stringnumber()</b> function
2024 returns one of the numbers that are associated with the name, but it is not
2025 defined which it is.
2026 </P>
2027 <P>
2028 If you want to get full details of all captured substrings for a given name,
2029 you must use the <b>pcre_get_stringtable_entries()</b> function. The first
2030 argument is the compiled pattern, and the second is the name. The third and
2031 fourth are pointers to variables which are updated by the function. After it
2032 has run, they point to the first and last entries in the name-to-number table
2033 for the given name. The function itself returns the length of each entry, or
2034 PCRE_ERROR_NOSUBSTRING (-7) if there are none. The format of the table is
2035 described above in the section entitled <i>Information about a pattern</i>.
2036 Given all the relevant entries for the name, you can extract each of their
2037 numbers, and hence the captured data, if any.
2038 </P>
2039 <br><a name="SEC18" href="#TOC1">FINDING ALL POSSIBLE MATCHES</a><br>
2040 <P>
2041 The traditional matching function uses a similar algorithm to Perl, which stops
2042 when it finds the first match, starting at a given point in the subject. If you
2043 want to find all possible matches, or the longest possible match, consider
2044 using the alternative matching function (see below) instead. If you cannot use
2045 the alternative function, but still need to find all possible matches, you
2046 can kludge it up by making use of the callout facility, which is described in
2047 the
2048 <a href="pcrecallout.html"><b>pcrecallout</b></a>
2049 documentation.
2050 </P>
2051 <P>
2052 What you have to do is to insert a callout right at the end of the pattern.
2053 When your callout function is called, extract and save the current matched
2054 substring. Then return 1, which forces <b>pcre_exec()</b> to backtrack and try
2055 other alternatives. Ultimately, when it runs out of matches, <b>pcre_exec()</b>
2056 will yield PCRE_ERROR_NOMATCH.
2057 <a name="dfamatch"></a></P>
2058 <br><a name="SEC19" href="#TOC1">MATCHING A PATTERN: THE ALTERNATIVE FUNCTION</a><br>
2059 <P>
2060 <b>int pcre_dfa_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
2061 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
2062 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>,</b>
2063 <b>int *<i>workspace</i>, int <i>wscount</i>);</b>
2064 </P>
2065 <P>
2066 The function <b>pcre_dfa_exec()</b> is called to match a subject string against
2067 a compiled pattern, using a matching algorithm that scans the subject string
2068 just once, and does not backtrack. This has different characteristics to the
2069 normal algorithm, and is not compatible with Perl. Some of the features of PCRE
2070 patterns are not supported. Nevertheless, there are times when this kind of
2071 matching can be useful. For a discussion of the two matching algorithms, and a
2072 list of features that <b>pcre_dfa_exec()</b> does not support, see the
2073 <a href="pcrematching.html"><b>pcrematching</b></a>
2074 documentation.
2075 </P>
2076 <P>
2077 The arguments for the <b>pcre_dfa_exec()</b> function are the same as for
2078 <b>pcre_exec()</b>, plus two extras. The <i>ovector</i> argument is used in a
2079 different way, and this is described below. The other common arguments are used
2080 in the same way as for <b>pcre_exec()</b>, so their description is not repeated
2081 here.
2082 </P>
2083 <P>
2084 The two additional arguments provide workspace for the function. The workspace
2085 vector should contain at least 20 elements. It is used for keeping track of
2086 multiple paths through the pattern tree. More workspace will be needed for
2087 patterns and subjects where there are a lot of potential matches.
2088 </P>
2089 <P>
2090 Here is an example of a simple call to <b>pcre_dfa_exec()</b>:
2091 <pre>
2092 int rc;
2093 int ovector[10];
2094 int wspace[20];
2095 rc = pcre_dfa_exec(
2096 re, /* result of pcre_compile() */
2097 NULL, /* we didn't study the pattern */
2098 "some string", /* the subject string */
2099 11, /* the length of the subject string */
2100 0, /* start at offset 0 in the subject */
2101 0, /* default options */
2102 ovector, /* vector of integers for substring information */
2103 10, /* number of elements (NOT size in bytes) */
2104 wspace, /* working space vector */
2105 20); /* number of elements (NOT size in bytes) */
2106 </PRE>
2107 </P>
2108 <br><b>
2109 Option bits for <b>pcre_dfa_exec()</b>
2110 </b><br>
2111 <P>
2112 The unused bits of the <i>options</i> argument for <b>pcre_dfa_exec()</b> must be
2113 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_<i>xxx</i>,
2117 All but the last four of these are exactly the same as for <b>pcre_exec()</b>,
2118 so their description is not repeated here.
2119 <pre>
2122 </pre>
2123 These have the same general effect as they do for <b>pcre_exec()</b>, but the
2124 details are slightly different. When PCRE_PARTIAL_HARD is set for
2125 <b>pcre_dfa_exec()</b>, it returns PCRE_ERROR_PARTIAL if the end of the subject
2126 is reached and there is still at least one matching possibility that requires
2127 additional characters. This happens even if some complete matches have also
2128 been found. When PCRE_PARTIAL_SOFT is set, the return code PCRE_ERROR_NOMATCH
2129 is converted into PCRE_ERROR_PARTIAL if the end of the subject is reached,
2130 there have been no complete matches, but there is still at least one matching
2131 possibility. The portion of the string that was inspected when the longest
2132 partial match was found is set as the first matching string in both cases.
2133 There is a more detailed discussion of partial and multi-segment matching, with
2134 examples, in the
2135 <a href="pcrepartial.html"><b>pcrepartial</b></a>
2136 documentation.
2137 <pre>
2139 </pre>
2140 Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to stop as
2141 soon as it has found one match. Because of the way the alternative algorithm
2142 works, this is necessarily the shortest possible match at the first possible
2143 matching point in the subject string.
2144 <pre>
2146 </pre>
2147 When <b>pcre_dfa_exec()</b> returns a partial match, it is possible to call it
2148 again, with additional subject characters, and have it continue with the same
2149 match. The PCRE_DFA_RESTART option requests this action; when it is set, the
2150 <i>workspace</i> and <i>wscount</i> options must reference the same vector as
2151 before because data about the match so far is left in them after a partial
2152 match. There is more discussion of this facility in the
2153 <a href="pcrepartial.html"><b>pcrepartial</b></a>
2154 documentation.
2155 </P>
2156 <br><b>
2157 Successful returns from <b>pcre_dfa_exec()</b>
2158 </b><br>
2159 <P>
2160 When <b>pcre_dfa_exec()</b> succeeds, it may have matched more than one
2161 substring in the subject. Note, however, that all the matches from one run of
2162 the function start at the same point in the subject. The shorter matches are
2163 all initial substrings of the longer matches. For example, if the pattern
2164 <pre>
2165 &#60;.*&#62;
2166 </pre>
2167 is matched against the string
2168 <pre>
2169 This is &#60;something&#62; &#60;something else&#62; &#60;something further&#62; no more
2170 </pre>
2171 the three matched strings are
2172 <pre>
2173 &#60;something&#62;
2174 &#60;something&#62; &#60;something else&#62;
2175 &#60;something&#62; &#60;something else&#62; &#60;something further&#62;
2176 </pre>
2177 On success, the yield of the function is a number greater than zero, which is
2178 the number of matched substrings. The substrings themselves are returned in
2179 <i>ovector</i>. Each string uses two elements; the first is the offset to the
2180 start, and the second is the offset to the end. In fact, all the strings have
2181 the same start offset. (Space could have been saved by giving this only once,
2182 but it was decided to retain some compatibility with the way <b>pcre_exec()</b>
2183 returns data, even though the meaning of the strings is different.)
2184 </P>
2185 <P>
2186 The strings are returned in reverse order of length; that is, the longest
2187 matching string is given first. If there were too many matches to fit into
2188 <i>ovector</i>, the yield of the function is zero, and the vector is filled with
2189 the longest matches.
2190 </P>
2191 <br><b>
2192 Error returns from <b>pcre_dfa_exec()</b>
2193 </b><br>
2194 <P>
2195 The <b>pcre_dfa_exec()</b> function returns a negative number when it fails.
2196 Many of the errors are the same as for <b>pcre_exec()</b>, and these are
2197 described
2198 <a href="#errorlist">above.</a>
2199 There are in addition the following errors that are specific to
2200 <b>pcre_dfa_exec()</b>:
2201 <pre>
2203 </pre>
2204 This return is given if <b>pcre_dfa_exec()</b> encounters an item in the pattern
2205 that it does not support, for instance, the use of \C or a back reference.
2206 <pre>
2208 </pre>
2209 This return is given if <b>pcre_dfa_exec()</b> encounters a condition item that
2210 uses a back reference for the condition, or a test for recursion in a specific
2211 group. These are not supported.
2212 <pre>
2214 </pre>
2215 This return is given if <b>pcre_dfa_exec()</b> is called with an <i>extra</i>
2216 block that contains a setting of the <i>match_limit</i> field. This is not
2217 supported (it is meaningless).
2218 <pre>
2220 </pre>
2221 This return is given if <b>pcre_dfa_exec()</b> runs out of space in the
2222 <i>workspace</i> vector.
2223 <pre>
2225 </pre>
2226 When a recursive subpattern is processed, the matching function calls itself
2227 recursively, using private vectors for <i>ovector</i> and <i>workspace</i>. This
2228 error is given if the output vector is not large enough. This should be
2229 extremely rare, as a vector of size 1000 is used.
2230 </P>
2231 <br><a name="SEC20" href="#TOC1">SEE ALSO</a><br>
2232 <P>
2233 <b>pcrebuild</b>(3), <b>pcrecallout</b>(3), <b>pcrecpp(3)</b>(3),
2234 <b>pcrematching</b>(3), <b>pcrepartial</b>(3), <b>pcreposix</b>(3),
2235 <b>pcreprecompile</b>(3), <b>pcresample</b>(3), <b>pcrestack</b>(3).
2236 </P>
2237 <br><a name="SEC21" href="#TOC1">AUTHOR</a><br>
2238 <P>
2239 Philip Hazel
2240 <br>
2241 University Computing Service
2242 <br>
2243 Cambridge CB2 3QH, England.
2244 <br>
2245 </P>
2246 <br><a name="SEC22" href="#TOC1">REVISION</a><br>
2247 <P>
2248 Last updated: 21 November 2010
2249 <br>
2250 Copyright &copy; 1997-2010 University of Cambridge.
2251 <br>
2252 <p>
2253 Return to the <a href="index.html">PCRE index page</a>.
2254 </p>


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