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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 The functions <b>pcre_compile()</b>, <b>pcre_compile2()</b>, <b>pcre_study()</b>,
165 and <b>pcre_exec()</b> are used for compiling and matching regular expressions
166 in a Perl-compatible manner. A sample program that demonstrates the simplest
167 way of using them is provided in the file called <i>pcredemo.c</i> in the source
168 distribution. The
169 <a href="pcresample.html"><b>pcresample</b></a>
170 documentation describes how to run it.
171 </P>
172 <P>
173 A second matching function, <b>pcre_dfa_exec()</b>, which is not
174 Perl-compatible, is also provided. This uses a different algorithm for the
175 matching. The alternative algorithm finds all possible matches (at a given
176 point in the subject), and scans the subject just once. However, this algorithm
177 does not return captured substrings. A description of the two matching
178 algorithms and their advantages and disadvantages is given in the
179 <a href="pcrematching.html"><b>pcrematching</b></a>
180 documentation.
181 </P>
182 <P>
183 In addition to the main compiling and matching functions, there are convenience
184 functions for extracting captured substrings from a subject string that is
185 matched by <b>pcre_exec()</b>. They are:
186 <pre>
187 <b>pcre_copy_substring()</b>
188 <b>pcre_copy_named_substring()</b>
189 <b>pcre_get_substring()</b>
190 <b>pcre_get_named_substring()</b>
191 <b>pcre_get_substring_list()</b>
192 <b>pcre_get_stringnumber()</b>
193 <b>pcre_get_stringtable_entries()</b>
194 </pre>
195 <b>pcre_free_substring()</b> and <b>pcre_free_substring_list()</b> are also
196 provided, to free the memory used for extracted strings.
197 </P>
198 <P>
199 The function <b>pcre_maketables()</b> is used to build a set of character tables
200 in the current locale for passing to <b>pcre_compile()</b>, <b>pcre_exec()</b>,
201 or <b>pcre_dfa_exec()</b>. This is an optional facility that is provided for
202 specialist use. Most commonly, no special tables are passed, in which case
203 internal tables that are generated when PCRE is built are used.
204 </P>
205 <P>
206 The function <b>pcre_fullinfo()</b> is used to find out information about a
207 compiled pattern; <b>pcre_info()</b> is an obsolete version that returns only
208 some of the available information, but is retained for backwards compatibility.
209 The function <b>pcre_version()</b> returns a pointer to a string containing the
210 version of PCRE and its date of release.
211 </P>
212 <P>
213 The function <b>pcre_refcount()</b> maintains a reference count in a data block
214 containing a compiled pattern. This is provided for the benefit of
215 object-oriented applications.
216 </P>
217 <P>
218 The global variables <b>pcre_malloc</b> and <b>pcre_free</b> initially contain
219 the entry points of the standard <b>malloc()</b> and <b>free()</b> functions,
220 respectively. PCRE calls the memory management functions via these variables,
221 so a calling program can replace them if it wishes to intercept the calls. This
222 should be done before calling any PCRE functions.
223 </P>
224 <P>
225 The global variables <b>pcre_stack_malloc</b> and <b>pcre_stack_free</b> are also
226 indirections to memory management functions. These special functions are used
227 only when PCRE is compiled to use the heap for remembering data, instead of
228 recursive function calls, when running the <b>pcre_exec()</b> function. See the
229 <a href="pcrebuild.html"><b>pcrebuild</b></a>
230 documentation for details of how to do this. It is a non-standard way of
231 building PCRE, for use in environments that have limited stacks. Because of the
232 greater use of memory management, it runs more slowly. Separate functions are
233 provided so that special-purpose external code can be used for this case. When
234 used, these functions are always called in a stack-like manner (last obtained,
235 first freed), and always for memory blocks of the same size. There is a
236 discussion about PCRE's stack usage in the
237 <a href="pcrestack.html"><b>pcrestack</b></a>
238 documentation.
239 </P>
240 <P>
241 The global variable <b>pcre_callout</b> initially contains NULL. It can be set
242 by the caller to a "callout" function, which PCRE will then call at specified
243 points during a matching operation. Details are given in the
244 <a href="pcrecallout.html"><b>pcrecallout</b></a>
245 documentation.
246 <a name="newlines"></a></P>
247 <br><a name="SEC3" href="#TOC1">NEWLINES</a><br>
248 <P>
249 PCRE supports five different conventions for indicating line breaks in
250 strings: a single CR (carriage return) character, a single LF (linefeed)
251 character, the two-character sequence CRLF, any of the three preceding, or any
252 Unicode newline sequence. The Unicode newline sequences are the three just
253 mentioned, plus the single characters VT (vertical tab, U+000B), FF (formfeed,
254 U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS
255 (paragraph separator, U+2029).
256 </P>
257 <P>
258 Each of the first three conventions is used by at least one operating system as
259 its standard newline sequence. When PCRE is built, a default can be specified.
260 The default default is LF, which is the Unix standard. When PCRE is run, the
261 default can be overridden, either when a pattern is compiled, or when it is
262 matched.
263 </P>
264 <P>
265 At compile time, the newline convention can be specified by the <i>options</i>
266 argument of <b>pcre_compile()</b>, or it can be specified by special text at the
267 start of the pattern itself; this overrides any other settings. See the
268 <a href="pcrepattern.html"><b>pcrepattern</b></a>
269 page for details of the special character sequences.
270 </P>
271 <P>
272 In the PCRE documentation the word "newline" is used to mean "the character or
273 pair of characters that indicate a line break". The choice of newline
274 convention affects the handling of the dot, circumflex, and dollar
275 metacharacters, the handling of #-comments in /x mode, and, when CRLF is a
276 recognized line ending sequence, the match position advancement for a
277 non-anchored pattern. There is more detail about this in the
278 <a href="#execoptions">section on <b>pcre_exec()</b> options</a>
279 below.
280 </P>
281 <P>
282 The choice of newline convention does not affect the interpretation of
283 the \n or \r escape sequences, nor does it affect what \R matches, which is
284 controlled in a similar way, but by separate options.
285 </P>
286 <br><a name="SEC4" href="#TOC1">MULTITHREADING</a><br>
287 <P>
288 The PCRE functions can be used in multi-threading applications, with the
289 proviso that the memory management functions pointed to by <b>pcre_malloc</b>,
290 <b>pcre_free</b>, <b>pcre_stack_malloc</b>, and <b>pcre_stack_free</b>, and the
291 callout function pointed to by <b>pcre_callout</b>, are shared by all threads.
292 </P>
293 <P>
294 The compiled form of a regular expression is not altered during matching, so
295 the same compiled pattern can safely be used by several threads at once.
296 </P>
297 <br><a name="SEC5" href="#TOC1">SAVING PRECOMPILED PATTERNS FOR LATER USE</a><br>
298 <P>
299 The compiled form of a regular expression can be saved and re-used at a later
300 time, possibly by a different program, and even on a host other than the one on
301 which it was compiled. Details are given in the
302 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
303 documentation. However, compiling a regular expression with one version of PCRE
304 for use with a different version is not guaranteed to work and may cause
305 crashes.
306 </P>
307 <br><a name="SEC6" href="#TOC1">CHECKING BUILD-TIME OPTIONS</a><br>
308 <P>
309 <b>int pcre_config(int <i>what</i>, void *<i>where</i>);</b>
310 </P>
311 <P>
312 The function <b>pcre_config()</b> makes it possible for a PCRE client to
313 discover which optional features have been compiled into the PCRE library. The
314 <a href="pcrebuild.html"><b>pcrebuild</b></a>
315 documentation has more details about these optional features.
316 </P>
317 <P>
318 The first argument for <b>pcre_config()</b> is an integer, specifying which
319 information is required; the second argument is a pointer to a variable into
320 which the information is placed. The following information is available:
321 <pre>
323 </pre>
324 The output is an integer that is set to one if UTF-8 support is available;
325 otherwise it is set to zero.
326 <pre>
328 </pre>
329 The output is an integer that is set to one if support for Unicode character
330 properties is available; otherwise it is set to zero.
331 <pre>
333 </pre>
334 The output is an integer whose value specifies the default character sequence
335 that is recognized as meaning "newline". The four values that are supported
336 are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF, and -1 for ANY. The
337 default should normally be the standard sequence for your operating system.
338 <pre>
340 </pre>
341 The output is an integer whose value indicates what character sequences the \R
342 escape sequence matches by default. A value of 0 means that \R matches any
343 Unicode line ending sequence; a value of 1 means that \R matches only CR, LF,
344 or CRLF. The default can be overridden when a pattern is compiled or matched.
345 <pre>
347 </pre>
348 The output is an integer that contains the number of bytes used for internal
349 linkage in compiled regular expressions. The value is 2, 3, or 4. Larger values
350 allow larger regular expressions to be compiled, at the expense of slower
351 matching. The default value of 2 is sufficient for all but the most massive
352 patterns, since it allows the compiled pattern to be up to 64K in size.
353 <pre>
355 </pre>
356 The output is an integer that contains the threshold above which the POSIX
357 interface uses <b>malloc()</b> for output vectors. Further details are given in
358 the
359 <a href="pcreposix.html"><b>pcreposix</b></a>
360 documentation.
361 <pre>
363 </pre>
364 The output is an integer that gives the default limit for the number of
365 internal matching function calls in a <b>pcre_exec()</b> execution. Further
366 details are given with <b>pcre_exec()</b> below.
367 <pre>
369 </pre>
370 The output is an integer that gives the default limit for the depth of
371 recursion when calling the internal matching function in a <b>pcre_exec()</b>
372 execution. Further details are given with <b>pcre_exec()</b> below.
373 <pre>
375 </pre>
376 The output is an integer that is set to one if internal recursion when running
377 <b>pcre_exec()</b> is implemented by recursive function calls that use the stack
378 to remember their state. This is the usual way that PCRE is compiled. The
379 output is zero if PCRE was compiled to use blocks of data on the heap instead
380 of recursive function calls. In this case, <b>pcre_stack_malloc</b> and
381 <b>pcre_stack_free</b> are called to manage memory blocks on the heap, thus
382 avoiding the use of the stack.
383 </P>
384 <br><a name="SEC7" href="#TOC1">COMPILING A PATTERN</a><br>
385 <P>
386 <b>pcre *pcre_compile(const char *<i>pattern</i>, int <i>options</i>,</b>
387 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
388 <b>const unsigned char *<i>tableptr</i>);</b>
389 <b>pcre *pcre_compile2(const char *<i>pattern</i>, int <i>options</i>,</b>
390 <b>int *<i>errorcodeptr</i>,</b>
391 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
392 <b>const unsigned char *<i>tableptr</i>);</b>
393 </P>
394 <P>
395 Either of the functions <b>pcre_compile()</b> or <b>pcre_compile2()</b> can be
396 called to compile a pattern into an internal form. The only difference between
397 the two interfaces is that <b>pcre_compile2()</b> has an additional argument,
398 <i>errorcodeptr</i>, via which a numerical error code can be returned.
399 </P>
400 <P>
401 The pattern is a C string terminated by a binary zero, and is passed in the
402 <i>pattern</i> argument. A pointer to a single block of memory that is obtained
403 via <b>pcre_malloc</b> is returned. This contains the compiled code and related
404 data. The <b>pcre</b> type is defined for the returned block; this is a typedef
405 for a structure whose contents are not externally defined. It is up to the
406 caller to free the memory (via <b>pcre_free</b>) when it is no longer required.
407 </P>
408 <P>
409 Although the compiled code of a PCRE regex is relocatable, that is, it does not
410 depend on memory location, the complete <b>pcre</b> data block is not
411 fully relocatable, because it may contain a copy of the <i>tableptr</i>
412 argument, which is an address (see below).
413 </P>
414 <P>
415 The <i>options</i> argument contains various bit settings that affect the
416 compilation. It should be zero if no options are required. The available
417 options are described below. Some of them, in particular, those that are
418 compatible with Perl, can also be set and unset from within the pattern (see
419 the detailed description in the
420 <a href="pcrepattern.html"><b>pcrepattern</b></a>
421 documentation). For these options, the contents of the <i>options</i> argument
422 specifies their initial settings at the start of compilation and execution. The
423 PCRE_ANCHORED and PCRE_NEWLINE_<i>xxx</i> options can be set at the time of
424 matching as well as at compile time.
425 </P>
426 <P>
427 If <i>errptr</i> is NULL, <b>pcre_compile()</b> returns NULL immediately.
428 Otherwise, if compilation of a pattern fails, <b>pcre_compile()</b> returns
429 NULL, and sets the variable pointed to by <i>errptr</i> to point to a textual
430 error message. This is a static string that is part of the library. You must
431 not try to free it. The offset from the start of the pattern to the character
432 where the error was discovered is placed in the variable pointed to by
433 <i>erroffset</i>, which must not be NULL. If it is, an immediate error is given.
434 </P>
435 <P>
436 If <b>pcre_compile2()</b> is used instead of <b>pcre_compile()</b>, and the
437 <i>errorcodeptr</i> argument is not NULL, a non-zero error code number is
438 returned via this argument in the event of an error. This is in addition to the
439 textual error message. Error codes and messages are listed below.
440 </P>
441 <P>
442 If the final argument, <i>tableptr</i>, is NULL, PCRE uses a default set of
443 character tables that are built when PCRE is compiled, using the default C
444 locale. Otherwise, <i>tableptr</i> must be an address that is the result of a
445 call to <b>pcre_maketables()</b>. This value is stored with the compiled
446 pattern, and used again by <b>pcre_exec()</b>, unless another table pointer is
447 passed to it. For more discussion, see the section on locale support below.
448 </P>
449 <P>
450 This code fragment shows a typical straightforward call to <b>pcre_compile()</b>:
451 <pre>
452 pcre *re;
453 const char *error;
454 int erroffset;
455 re = pcre_compile(
456 "^A.*Z", /* the pattern */
457 0, /* default options */
458 &error, /* for error message */
459 &erroffset, /* for error offset */
460 NULL); /* use default character tables */
461 </pre>
462 The following names for option bits are defined in the <b>pcre.h</b> header
463 file:
464 <pre>
466 </pre>
467 If this bit is set, the pattern is forced to be "anchored", that is, it is
468 constrained to match only at the first matching point in the string that is
469 being searched (the "subject string"). This effect can also be achieved by
470 appropriate constructs in the pattern itself, which is the only way to do it in
471 Perl.
472 <pre>
474 </pre>
475 If this bit is set, <b>pcre_compile()</b> automatically inserts callout items,
476 all with number 255, before each pattern item. For discussion of the callout
477 facility, see the
478 <a href="pcrecallout.html"><b>pcrecallout</b></a>
479 documentation.
480 <pre>
483 </pre>
484 These options (which are mutually exclusive) control what the \R escape
485 sequence matches. The choice is either to match only CR, LF, or CRLF, or to
486 match any Unicode newline sequence. The default is specified when PCRE is
487 built. It can be overridden from within the pattern, or by setting an option
488 when a compiled pattern is matched.
489 <pre>
491 </pre>
492 If this bit is set, letters in the pattern match both upper and lower case
493 letters. It is equivalent to Perl's /i option, and it can be changed within a
494 pattern by a (?i) option setting. In UTF-8 mode, PCRE always understands the
495 concept of case for characters whose values are less than 128, so caseless
496 matching is always possible. For characters with higher values, the concept of
497 case is supported if PCRE is compiled with Unicode property support, but not
498 otherwise. If you want to use caseless matching for characters 128 and above,
499 you must ensure that PCRE is compiled with Unicode property support as well as
500 with UTF-8 support.
501 <pre>
503 </pre>
504 If this bit is set, a dollar metacharacter in the pattern matches only at the
505 end of the subject string. Without this option, a dollar also matches
506 immediately before a newline at the end of the string (but not before any other
507 newlines). The PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is set.
508 There is no equivalent to this option in Perl, and no way to set it within a
509 pattern.
510 <pre>
512 </pre>
513 If this bit is set, a dot metacharater in the pattern matches all characters,
514 including those that indicate newline. Without it, a dot does not match when
515 the current position is at a newline. This option is equivalent to Perl's /s
516 option, and it can be changed within a pattern by a (?s) option setting. A
517 negative class such as [^a] always matches newline characters, independent of
518 the setting of this option.
519 <pre>
521 </pre>
522 If this bit is set, names used to identify capturing subpatterns need not be
523 unique. This can be helpful for certain types of pattern when it is known that
524 only one instance of the named subpattern can ever be matched. There are more
525 details of named subpatterns below; see also the
526 <a href="pcrepattern.html"><b>pcrepattern</b></a>
527 documentation.
528 <pre>
530 </pre>
531 If this bit is set, whitespace data characters in the pattern are totally
532 ignored except when escaped or inside a character class. Whitespace does not
533 include the VT character (code 11). In addition, characters between an
534 unescaped # outside a character class and the next newline, inclusive, are also
535 ignored. This is equivalent to Perl's /x option, and it can be changed within a
536 pattern by a (?x) option setting.
537 </P>
538 <P>
539 This option makes it possible to include comments inside complicated patterns.
540 Note, however, that this applies only to data characters. Whitespace characters
541 may never appear within special character sequences in a pattern, for example
542 within the sequence (?( which introduces a conditional subpattern.
543 <pre>
545 </pre>
546 This option was invented in order to turn on additional functionality of PCRE
547 that is incompatible with Perl, but it is currently of very little use. When
548 set, any backslash in a pattern that is followed by a letter that has no
549 special meaning causes an error, thus reserving these combinations for future
550 expansion. By default, as in Perl, a backslash followed by a letter with no
551 special meaning is treated as a literal. (Perl can, however, be persuaded to
552 give a warning for this.) There are at present no other features controlled by
553 this option. It can also be set by a (?X) option setting within a pattern.
554 <pre>
556 </pre>
557 If this option is set, an unanchored pattern is required to match before or at
558 the first newline in the subject string, though the matched text may continue
559 over the newline.
560 <pre>
562 </pre>
563 By default, PCRE treats the subject string as consisting of a single line of
564 characters (even if it actually contains newlines). The "start of line"
565 metacharacter (^) matches only at the start of the string, while the "end of
566 line" metacharacter ($) matches only at the end of the string, or before a
567 terminating newline (unless PCRE_DOLLAR_ENDONLY is set). This is the same as
568 Perl.
569 </P>
570 <P>
571 When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs
572 match immediately following or immediately before internal newlines in the
573 subject string, respectively, as well as at the very start and end. This is
574 equivalent to Perl's /m option, and it can be changed within a pattern by a
575 (?m) option setting. If there are no newlines in a subject string, or no
576 occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no effect.
577 <pre>
583 </pre>
584 These options override the default newline definition that was chosen when PCRE
585 was built. Setting the first or the second specifies that a newline is
586 indicated by a single character (CR or LF, respectively). Setting
587 PCRE_NEWLINE_CRLF specifies that a newline is indicated by the two-character
588 CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies that any of the three
589 preceding sequences should be recognized. Setting PCRE_NEWLINE_ANY specifies
590 that any Unicode newline sequence should be recognized. The Unicode newline
591 sequences are the three just mentioned, plus the single characters VT (vertical
592 tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS (line
593 separator, U+2028), and PS (paragraph separator, U+2029). The last two are
594 recognized only in UTF-8 mode.
595 </P>
596 <P>
597 The newline setting in the options word uses three bits that are treated
598 as a number, giving eight possibilities. Currently only six are used (default
599 plus the five values above). This means that if you set more than one newline
600 option, the combination may or may not be sensible. For example,
602 other combinations may yield unused numbers and cause an error.
603 </P>
604 <P>
605 The only time that a line break is specially recognized when compiling a
606 pattern is if PCRE_EXTENDED is set, and an unescaped # outside a character
607 class is encountered. This indicates a comment that lasts until after the next
608 line break sequence. In other circumstances, line break sequences are treated
609 as literal data, except that in PCRE_EXTENDED mode, both CR and LF are treated
610 as whitespace characters and are therefore ignored.
611 </P>
612 <P>
613 The newline option that is set at compile time becomes the default that is used
614 for <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b>, but it can be overridden.
615 <pre>
617 </pre>
618 If this option is set, it disables the use of numbered capturing parentheses in
619 the pattern. Any opening parenthesis that is not followed by ? behaves as if it
620 were followed by ?: but named parentheses can still be used for capturing (and
621 they acquire numbers in the usual way). There is no equivalent of this option
622 in Perl.
623 <pre>
625 </pre>
626 This option inverts the "greediness" of the quantifiers so that they are not
627 greedy by default, but become greedy if followed by "?". It is not compatible
628 with Perl. It can also be set by a (?U) option setting within the pattern.
629 <pre>
631 </pre>
632 This option causes PCRE to regard both the pattern and the subject as strings
633 of UTF-8 characters instead of single-byte character strings. However, it is
634 available only when PCRE is built to include UTF-8 support. If not, the use
635 of this option provokes an error. Details of how this option changes the
636 behaviour of PCRE are given in the
637 <a href="pcre.html#utf8support">section on UTF-8 support</a>
638 in the main
639 <a href="pcre.html"><b>pcre</b></a>
640 page.
641 <pre>
643 </pre>
644 When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
645 automatically checked. There is a discussion about the
646 <a href="pcre.html#utf8strings">validity of UTF-8 strings</a>
647 in the main
648 <a href="pcre.html"><b>pcre</b></a>
649 page. If an invalid UTF-8 sequence of bytes is found, <b>pcre_compile()</b>
650 returns an error. If you already know that your pattern is valid, and you want
651 to skip this check for performance reasons, you can set the PCRE_NO_UTF8_CHECK
652 option. When it is set, the effect of passing an invalid UTF-8 string as a
653 pattern is undefined. It may cause your program to crash. Note that this option
654 can also be passed to <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b>, to suppress
655 the UTF-8 validity checking of subject strings.
656 </P>
657 <br><a name="SEC8" href="#TOC1">COMPILATION ERROR CODES</a><br>
658 <P>
659 The following table lists the error codes than may be returned by
660 <b>pcre_compile2()</b>, along with the error messages that may be returned by
661 both compiling functions. As PCRE has developed, some error codes have fallen
662 out of use. To avoid confusion, they have not been re-used.
663 <pre>
664 0 no error
665 1 \ at end of pattern
666 2 \c at end of pattern
667 3 unrecognized character follows \
668 4 numbers out of order in {} quantifier
669 5 number too big in {} quantifier
670 6 missing terminating ] for character class
671 7 invalid escape sequence in character class
672 8 range out of order in character class
673 9 nothing to repeat
674 10 [this code is not in use]
675 11 internal error: unexpected repeat
676 12 unrecognized character after (?
677 13 POSIX named classes are supported only within a class
678 14 missing )
679 15 reference to non-existent subpattern
680 16 erroffset passed as NULL
681 17 unknown option bit(s) set
682 18 missing ) after comment
683 19 [this code is not in use]
684 20 regular expression too large
685 21 failed to get memory
686 22 unmatched parentheses
687 23 internal error: code overflow
688 24 unrecognized character after (?&#60;
689 25 lookbehind assertion is not fixed length
690 26 malformed number or name after (?(
691 27 conditional group contains more than two branches
692 28 assertion expected after (?(
693 29 (?R or (?[+-]digits must be followed by )
694 30 unknown POSIX class name
695 31 POSIX collating elements are not supported
696 32 this version of PCRE is not compiled with PCRE_UTF8 support
697 33 [this code is not in use]
698 34 character value in \x{...} sequence is too large
699 35 invalid condition (?(0)
700 36 \C not allowed in lookbehind assertion
701 37 PCRE does not support \L, \l, \N, \U, or \u
702 38 number after (?C is &#62; 255
703 39 closing ) for (?C expected
704 40 recursive call could loop indefinitely
705 41 unrecognized character after (?P
706 42 syntax error in subpattern name (missing terminator)
707 43 two named subpatterns have the same name
708 44 invalid UTF-8 string
709 45 support for \P, \p, and \X has not been compiled
710 46 malformed \P or \p sequence
711 47 unknown property name after \P or \p
712 48 subpattern name is too long (maximum 32 characters)
713 49 too many named subpatterns (maximum 10,000)
714 50 [this code is not in use]
715 51 octal value is greater than \377 (not in UTF-8 mode)
716 52 internal error: overran compiling workspace
717 53 internal error: previously-checked referenced subpattern not found
718 54 DEFINE group contains more than one branch
719 55 repeating a DEFINE group is not allowed
720 56 inconsistent NEWLINE options
721 57 \g is not followed by a braced name or an optionally braced
722 non-zero number
723 58 (?+ or (?- or (?(+ or (?(- must be followed by a non-zero number
724 </PRE>
725 </P>
726 <br><a name="SEC9" href="#TOC1">STUDYING A PATTERN</a><br>
727 <P>
728 <b>pcre_extra *pcre_study(const pcre *<i>code</i>, int <i>options</i></b>
729 <b>const char **<i>errptr</i>);</b>
730 </P>
731 <P>
732 If a compiled pattern is going to be used several times, it is worth spending
733 more time analyzing it in order to speed up the time taken for matching. The
734 function <b>pcre_study()</b> takes a pointer to a compiled pattern as its first
735 argument. If studying the pattern produces additional information that will
736 help speed up matching, <b>pcre_study()</b> returns a pointer to a
737 <b>pcre_extra</b> block, in which the <i>study_data</i> field points to the
738 results of the study.
739 </P>
740 <P>
741 The returned value from <b>pcre_study()</b> can be passed directly to
742 <b>pcre_exec()</b>. However, a <b>pcre_extra</b> block also contains other
743 fields that can be set by the caller before the block is passed; these are
744 described
745 <a href="#extradata">below</a>
746 in the section on matching a pattern.
747 </P>
748 <P>
749 If studying the pattern does not produce any additional information
750 <b>pcre_study()</b> returns NULL. In that circumstance, if the calling program
751 wants to pass any of the other fields to <b>pcre_exec()</b>, it must set up its
752 own <b>pcre_extra</b> block.
753 </P>
754 <P>
755 The second argument of <b>pcre_study()</b> contains option bits. At present, no
756 options are defined, and this argument should always be zero.
757 </P>
758 <P>
759 The third argument for <b>pcre_study()</b> is a pointer for an error message. If
760 studying succeeds (even if no data is returned), the variable it points to is
761 set to NULL. Otherwise it is set to point to a textual error message. This is a
762 static string that is part of the library. You must not try to free it. You
763 should test the error pointer for NULL after calling <b>pcre_study()</b>, to be
764 sure that it has run successfully.
765 </P>
766 <P>
767 This is a typical call to <b>pcre_study</b>():
768 <pre>
769 pcre_extra *pe;
770 pe = pcre_study(
771 re, /* result of pcre_compile() */
772 0, /* no options exist */
773 &error); /* set to NULL or points to a message */
774 </pre>
775 At present, studying a pattern is useful only for non-anchored patterns that do
776 not have a single fixed starting character. A bitmap of possible starting
777 bytes is created.
778 <a name="localesupport"></a></P>
779 <br><a name="SEC10" href="#TOC1">LOCALE SUPPORT</a><br>
780 <P>
781 PCRE handles caseless matching, and determines whether characters are letters,
782 digits, or whatever, by reference to a set of tables, indexed by character
783 value. When running in UTF-8 mode, this applies only to characters with codes
784 less than 128. Higher-valued codes never match escapes such as \w or \d, but
785 can be tested with \p if PCRE is built with Unicode character property
786 support. The use of locales with Unicode is discouraged. If you are handling
787 characters with codes greater than 128, you should either use UTF-8 and
788 Unicode, or use locales, but not try to mix the two.
789 </P>
790 <P>
791 PCRE contains an internal set of tables that are used when the final argument
792 of <b>pcre_compile()</b> is NULL. These are sufficient for many applications.
793 Normally, the internal tables recognize only ASCII characters. However, when
794 PCRE is built, it is possible to cause the internal tables to be rebuilt in the
795 default "C" locale of the local system, which may cause them to be different.
796 </P>
797 <P>
798 The internal tables can always be overridden by tables supplied by the
799 application that calls PCRE. These may be created in a different locale from
800 the default. As more and more applications change to using Unicode, the need
801 for this locale support is expected to die away.
802 </P>
803 <P>
804 External tables are built by calling the <b>pcre_maketables()</b> function,
805 which has no arguments, in the relevant locale. The result can then be passed
806 to <b>pcre_compile()</b> or <b>pcre_exec()</b> as often as necessary. For
807 example, to build and use tables that are appropriate for the French locale
808 (where accented characters with values greater than 128 are treated as letters),
809 the following code could be used:
810 <pre>
811 setlocale(LC_CTYPE, "fr_FR");
812 tables = pcre_maketables();
813 re = pcre_compile(..., tables);
814 </pre>
815 The locale name "fr_FR" is used on Linux and other Unix-like systems; if you
816 are using Windows, the name for the French locale is "french".
817 </P>
818 <P>
819 When <b>pcre_maketables()</b> runs, the tables are built in memory that is
820 obtained via <b>pcre_malloc</b>. It is the caller's responsibility to ensure
821 that the memory containing the tables remains available for as long as it is
822 needed.
823 </P>
824 <P>
825 The pointer that is passed to <b>pcre_compile()</b> is saved with the compiled
826 pattern, and the same tables are used via this pointer by <b>pcre_study()</b>
827 and normally also by <b>pcre_exec()</b>. Thus, by default, for any single
828 pattern, compilation, studying and matching all happen in the same locale, but
829 different patterns can be compiled in different locales.
830 </P>
831 <P>
832 It is possible to pass a table pointer or NULL (indicating the use of the
833 internal tables) to <b>pcre_exec()</b>. Although not intended for this purpose,
834 this facility could be used to match a pattern in a different locale from the
835 one in which it was compiled. Passing table pointers at run time is discussed
836 below in the section on matching a pattern.
837 </P>
838 <br><a name="SEC11" href="#TOC1">INFORMATION ABOUT A PATTERN</a><br>
839 <P>
840 <b>int pcre_fullinfo(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
841 <b>int <i>what</i>, void *<i>where</i>);</b>
842 </P>
843 <P>
844 The <b>pcre_fullinfo()</b> function returns information about a compiled
845 pattern. It replaces the obsolete <b>pcre_info()</b> function, which is
846 nevertheless retained for backwards compability (and is documented below).
847 </P>
848 <P>
849 The first argument for <b>pcre_fullinfo()</b> is a pointer to the compiled
850 pattern. The second argument is the result of <b>pcre_study()</b>, or NULL if
851 the pattern was not studied. The third argument specifies which piece of
852 information is required, and the fourth argument is a pointer to a variable
853 to receive the data. The yield of the function is zero for success, or one of
854 the following negative numbers:
855 <pre>
856 PCRE_ERROR_NULL the argument <i>code</i> was NULL
857 the argument <i>where</i> was NULL
858 PCRE_ERROR_BADMAGIC the "magic number" was not found
859 PCRE_ERROR_BADOPTION the value of <i>what</i> was invalid
860 </pre>
861 The "magic number" is placed at the start of each compiled pattern as an simple
862 check against passing an arbitrary memory pointer. Here is a typical call of
863 <b>pcre_fullinfo()</b>, to obtain the length of the compiled pattern:
864 <pre>
865 int rc;
866 size_t length;
867 rc = pcre_fullinfo(
868 re, /* result of pcre_compile() */
869 pe, /* result of pcre_study(), or NULL */
870 PCRE_INFO_SIZE, /* what is required */
871 &length); /* where to put the data */
872 </pre>
873 The possible values for the third argument are defined in <b>pcre.h</b>, and are
874 as follows:
875 <pre>
877 </pre>
878 Return the number of the highest back reference in the pattern. The fourth
879 argument should point to an <b>int</b> variable. Zero is returned if there are
880 no back references.
881 <pre>
883 </pre>
884 Return the number of capturing subpatterns in the pattern. The fourth argument
885 should point to an <b>int</b> variable.
886 <pre>
888 </pre>
889 Return a pointer to the internal default character tables within PCRE. The
890 fourth argument should point to an <b>unsigned char *</b> variable. This
891 information call is provided for internal use by the <b>pcre_study()</b>
892 function. External callers can cause PCRE to use its internal tables by passing
893 a NULL table pointer.
894 <pre>
896 </pre>
897 Return information about the first byte of any matched string, for a
898 non-anchored pattern. The fourth argument should point to an <b>int</b>
899 variable. (This option used to be called PCRE_INFO_FIRSTCHAR; the old name is
900 still recognized for backwards compatibility.)
901 </P>
902 <P>
903 If there is a fixed first byte, for example, from a pattern such as
904 (cat|cow|coyote), its value is returned. Otherwise, if either
905 <br>
906 <br>
907 (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
908 starts with "^", or
909 <br>
910 <br>
911 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
912 (if it were set, the pattern would be anchored),
913 <br>
914 <br>
915 -1 is returned, indicating that the pattern matches only at the start of a
916 subject string or after any newline within the string. Otherwise -2 is
917 returned. For anchored patterns, -2 is returned.
918 <pre>
920 </pre>
921 If the pattern was studied, and this resulted in the construction of a 256-bit
922 table indicating a fixed set of bytes for the first byte in any matching
923 string, a pointer to the table is returned. Otherwise NULL is returned. The
924 fourth argument should point to an <b>unsigned char *</b> variable.
925 <pre>
927 </pre>
928 Return 1 if the pattern contains any explicit matches for CR or LF characters,
929 otherwise 0. The fourth argument should point to an <b>int</b> variable. An
930 explicit match is either a literal CR or LF character, or \r or \n.
931 <pre>
933 </pre>
934 Return 1 if the (?J) option setting is used in the pattern, otherwise 0. The
935 fourth argument should point to an <b>int</b> variable. The (?J) internal option
936 setting changes the local PCRE_DUPNAMES option.
937 <pre>
939 </pre>
940 Return the value of the rightmost literal byte that must exist in any matched
941 string, other than at its start, if such a byte has been recorded. The fourth
942 argument should point to an <b>int</b> variable. If there is no such byte, -1 is
943 returned. For anchored patterns, a last literal byte is recorded only if it
944 follows something of variable length. For example, for the pattern
945 /^a\d+z\d+/ the returned value is "z", but for /^a\dz\d/ the returned value
946 is -1.
947 <pre>
951 </pre>
952 PCRE supports the use of named as well as numbered capturing parentheses. The
953 names are just an additional way of identifying the parentheses, which still
954 acquire numbers. Several convenience functions such as
955 <b>pcre_get_named_substring()</b> are provided for extracting captured
956 substrings by name. It is also possible to extract the data directly, by first
957 converting the name to a number in order to access the correct pointers in the
958 output vector (described with <b>pcre_exec()</b> below). To do the conversion,
959 you need to use the name-to-number map, which is described by these three
960 values.
961 </P>
962 <P>
963 The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives
964 the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each
965 entry; both of these return an <b>int</b> value. The entry size depends on the
966 length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first
967 entry of the table (a pointer to <b>char</b>). The first two bytes of each entry
968 are the number of the capturing parenthesis, most significant byte first. The
969 rest of the entry is the corresponding name, zero terminated. The names are in
970 alphabetical order. When PCRE_DUPNAMES is set, duplicate names are in order of
971 their parentheses numbers. For example, consider the following pattern (assume
972 PCRE_EXTENDED is set, so white space - including newlines - is ignored):
973 <pre>
974 (?&#60;date&#62; (?&#60;year&#62;(\d\d)?\d\d) - (?&#60;month&#62;\d\d) - (?&#60;day&#62;\d\d) )
975 </pre>
976 There are four named subpatterns, so the table has four entries, and each entry
977 in the table is eight bytes long. The table is as follows, with non-printing
978 bytes shows in hexadecimal, and undefined bytes shown as ??:
979 <pre>
980 00 01 d a t e 00 ??
981 00 05 d a y 00 ?? ??
982 00 04 m o n t h 00
983 00 02 y e a r 00 ??
984 </pre>
985 When writing code to extract data from named subpatterns using the
986 name-to-number map, remember that the length of the entries is likely to be
987 different for each compiled pattern.
988 <pre>
990 </pre>
991 Return 1 if the pattern can be used for partial matching, otherwise 0. The
992 fourth argument should point to an <b>int</b> variable. The
993 <a href="pcrepartial.html"><b>pcrepartial</b></a>
994 documentation lists the restrictions that apply to patterns when partial
995 matching is used.
996 <pre>
998 </pre>
999 Return a copy of the options with which the pattern was compiled. The fourth
1000 argument should point to an <b>unsigned long int</b> variable. These option bits
1001 are those specified in the call to <b>pcre_compile()</b>, modified by any
1002 top-level option settings at the start of the pattern itself. In other words,
1003 they are the options that will be in force when matching starts. For example,
1004 if the pattern /(?im)abc(?-i)d/ is compiled with the PCRE_EXTENDED option, the
1006 </P>
1007 <P>
1008 A pattern is automatically anchored by PCRE if all of its top-level
1009 alternatives begin with one of the following:
1010 <pre>
1011 ^ unless PCRE_MULTILINE is set
1012 \A always
1013 \G always
1014 .* if PCRE_DOTALL is set and there are no back references to the subpattern in which .* appears
1015 </pre>
1016 For such patterns, the PCRE_ANCHORED bit is set in the options returned by
1017 <b>pcre_fullinfo()</b>.
1018 <pre>
1020 </pre>
1021 Return the size of the compiled pattern, that is, the value that was passed as
1022 the argument to <b>pcre_malloc()</b> when PCRE was getting memory in which to
1023 place the compiled data. The fourth argument should point to a <b>size_t</b>
1024 variable.
1025 <pre>
1027 </pre>
1028 Return the size of the data block pointed to by the <i>study_data</i> field in
1029 a <b>pcre_extra</b> block. That is, it is the value that was passed to
1030 <b>pcre_malloc()</b> when PCRE was getting memory into which to place the data
1031 created by <b>pcre_study()</b>. The fourth argument should point to a
1032 <b>size_t</b> variable.
1033 </P>
1034 <br><a name="SEC12" href="#TOC1">OBSOLETE INFO FUNCTION</a><br>
1035 <P>
1036 <b>int pcre_info(const pcre *<i>code</i>, int *<i>optptr</i>, int</b>
1037 <b>*<i>firstcharptr</i>);</b>
1038 </P>
1039 <P>
1040 The <b>pcre_info()</b> function is now obsolete because its interface is too
1041 restrictive to return all the available data about a compiled pattern. New
1042 programs should use <b>pcre_fullinfo()</b> instead. The yield of
1043 <b>pcre_info()</b> is the number of capturing subpatterns, or one of the
1044 following negative numbers:
1045 <pre>
1046 PCRE_ERROR_NULL the argument <i>code</i> was NULL
1047 PCRE_ERROR_BADMAGIC the "magic number" was not found
1048 </pre>
1049 If the <i>optptr</i> argument is not NULL, a copy of the options with which the
1050 pattern was compiled is placed in the integer it points to (see
1051 PCRE_INFO_OPTIONS above).
1052 </P>
1053 <P>
1054 If the pattern is not anchored and the <i>firstcharptr</i> argument is not NULL,
1055 it is used to pass back information about the first character of any matched
1056 string (see PCRE_INFO_FIRSTBYTE above).
1057 </P>
1058 <br><a name="SEC13" href="#TOC1">REFERENCE COUNTS</a><br>
1059 <P>
1060 <b>int pcre_refcount(pcre *<i>code</i>, int <i>adjust</i>);</b>
1061 </P>
1062 <P>
1063 The <b>pcre_refcount()</b> function is used to maintain a reference count in the
1064 data block that contains a compiled pattern. It is provided for the benefit of
1065 applications that operate in an object-oriented manner, where different parts
1066 of the application may be using the same compiled pattern, but you want to free
1067 the block when they are all done.
1068 </P>
1069 <P>
1070 When a pattern is compiled, the reference count field is initialized to zero.
1071 It is changed only by calling this function, whose action is to add the
1072 <i>adjust</i> value (which may be positive or negative) to it. The yield of the
1073 function is the new value. However, the value of the count is constrained to
1074 lie between 0 and 65535, inclusive. If the new value is outside these limits,
1075 it is forced to the appropriate limit value.
1076 </P>
1077 <P>
1078 Except when it is zero, the reference count is not correctly preserved if a
1079 pattern is compiled on one host and then transferred to a host whose byte-order
1080 is different. (This seems a highly unlikely scenario.)
1081 </P>
1082 <br><a name="SEC14" href="#TOC1">MATCHING A PATTERN: THE TRADITIONAL FUNCTION</a><br>
1083 <P>
1084 <b>int pcre_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
1085 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
1086 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>);</b>
1087 </P>
1088 <P>
1089 The function <b>pcre_exec()</b> is called to match a subject string against a
1090 compiled pattern, which is passed in the <i>code</i> argument. If the
1091 pattern has been studied, the result of the study should be passed in the
1092 <i>extra</i> argument. This function is the main matching facility of the
1093 library, and it operates in a Perl-like manner. For specialist use there is
1094 also an alternative matching function, which is described
1095 <a href="#dfamatch">below</a>
1096 in the section about the <b>pcre_dfa_exec()</b> function.
1097 </P>
1098 <P>
1099 In most applications, the pattern will have been compiled (and optionally
1100 studied) in the same process that calls <b>pcre_exec()</b>. However, it is
1101 possible to save compiled patterns and study data, and then use them later
1102 in different processes, possibly even on different hosts. For a discussion
1103 about this, see the
1104 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
1105 documentation.
1106 </P>
1107 <P>
1108 Here is an example of a simple call to <b>pcre_exec()</b>:
1109 <pre>
1110 int rc;
1111 int ovector[30];
1112 rc = pcre_exec(
1113 re, /* result of pcre_compile() */
1114 NULL, /* we didn't study the pattern */
1115 "some string", /* the subject string */
1116 11, /* the length of the subject string */
1117 0, /* start at offset 0 in the subject */
1118 0, /* default options */
1119 ovector, /* vector of integers for substring information */
1120 30); /* number of elements (NOT size in bytes) */
1121 <a name="extradata"></a></PRE>
1122 </P>
1123 <br><b>
1124 Extra data for <b>pcre_exec()</b>
1125 </b><br>
1126 <P>
1127 If the <i>extra</i> argument is not NULL, it must point to a <b>pcre_extra</b>
1128 data block. The <b>pcre_study()</b> function returns such a block (when it
1129 doesn't return NULL), but you can also create one for yourself, and pass
1130 additional information in it. The <b>pcre_extra</b> block contains the following
1131 fields (not necessarily in this order):
1132 <pre>
1133 unsigned long int <i>flags</i>;
1134 void *<i>study_data</i>;
1135 unsigned long int <i>match_limit</i>;
1136 unsigned long int <i>match_limit_recursion</i>;
1137 void *<i>callout_data</i>;
1138 const unsigned char *<i>tables</i>;
1139 </pre>
1140 The <i>flags</i> field is a bitmap that specifies which of the other fields
1141 are set. The flag bits are:
1142 <pre>
1148 </pre>
1149 Other flag bits should be set to zero. The <i>study_data</i> field is set in the
1150 <b>pcre_extra</b> block that is returned by <b>pcre_study()</b>, together with
1151 the appropriate flag bit. You should not set this yourself, but you may add to
1152 the block by setting the other fields and their corresponding flag bits.
1153 </P>
1154 <P>
1155 The <i>match_limit</i> field provides a means of preventing PCRE from using up a
1156 vast amount of resources when running patterns that are not going to match,
1157 but which have a very large number of possibilities in their search trees. The
1158 classic example is the use of nested unlimited repeats.
1159 </P>
1160 <P>
1161 Internally, PCRE uses a function called <b>match()</b> which it calls repeatedly
1162 (sometimes recursively). The limit set by <i>match_limit</i> is imposed on the
1163 number of times this function is called during a match, which has the effect of
1164 limiting the amount of backtracking that can take place. For patterns that are
1165 not anchored, the count restarts from zero for each position in the subject
1166 string.
1167 </P>
1168 <P>
1169 The default value for the limit can be set when PCRE is built; the default
1170 default is 10 million, which handles all but the most extreme cases. You can
1171 override the default by suppling <b>pcre_exec()</b> with a <b>pcre_extra</b>
1172 block in which <i>match_limit</i> is set, and PCRE_EXTRA_MATCH_LIMIT is set in
1173 the <i>flags</i> field. If the limit is exceeded, <b>pcre_exec()</b> returns
1175 </P>
1176 <P>
1177 The <i>match_limit_recursion</i> field is similar to <i>match_limit</i>, but
1178 instead of limiting the total number of times that <b>match()</b> is called, it
1179 limits the depth of recursion. The recursion depth is a smaller number than the
1180 total number of calls, because not all calls to <b>match()</b> are recursive.
1181 This limit is of use only if it is set smaller than <i>match_limit</i>.
1182 </P>
1183 <P>
1184 Limiting the recursion depth limits the amount of stack that can be used, or,
1185 when PCRE has been compiled to use memory on the heap instead of the stack, the
1186 amount of heap memory that can be used.
1187 </P>
1188 <P>
1189 The default value for <i>match_limit_recursion</i> can be set when PCRE is
1190 built; the default default is the same value as the default for
1191 <i>match_limit</i>. You can override the default by suppling <b>pcre_exec()</b>
1192 with a <b>pcre_extra</b> block in which <i>match_limit_recursion</i> is set, and
1193 PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the <i>flags</i> field. If the limit
1194 is exceeded, <b>pcre_exec()</b> returns PCRE_ERROR_RECURSIONLIMIT.
1195 </P>
1196 <P>
1197 The <i>pcre_callout</i> field is used in conjunction with the "callout" feature,
1198 which is described in the
1199 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1200 documentation.
1201 </P>
1202 <P>
1203 The <i>tables</i> field is used to pass a character tables pointer to
1204 <b>pcre_exec()</b>; this overrides the value that is stored with the compiled
1205 pattern. A non-NULL value is stored with the compiled pattern only if custom
1206 tables were supplied to <b>pcre_compile()</b> via its <i>tableptr</i> argument.
1207 If NULL is passed to <b>pcre_exec()</b> using this mechanism, it forces PCRE's
1208 internal tables to be used. This facility is helpful when re-using patterns
1209 that have been saved after compiling with an external set of tables, because
1210 the external tables might be at a different address when <b>pcre_exec()</b> is
1211 called. See the
1212 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
1213 documentation for a discussion of saving compiled patterns for later use.
1214 <a name="execoptions"></a></P>
1215 <br><b>
1216 Option bits for <b>pcre_exec()</b>
1217 </b><br>
1218 <P>
1219 The unused bits of the <i>options</i> argument for <b>pcre_exec()</b> must be
1220 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_<i>xxx</i>,
1222 <pre>
1224 </pre>
1225 The PCRE_ANCHORED option limits <b>pcre_exec()</b> to matching at the first
1226 matching position. If a pattern was compiled with PCRE_ANCHORED, or turned out
1227 to be anchored by virtue of its contents, it cannot be made unachored at
1228 matching time.
1229 <pre>
1232 </pre>
1233 These options (which are mutually exclusive) control what the \R escape
1234 sequence matches. The choice is either to match only CR, LF, or CRLF, or to
1235 match any Unicode newline sequence. These options override the choice that was
1236 made or defaulted when the pattern was compiled.
1237 <pre>
1243 </pre>
1244 These options override the newline definition that was chosen or defaulted when
1245 the pattern was compiled. For details, see the description of
1246 <b>pcre_compile()</b> above. During matching, the newline choice affects the
1247 behaviour of the dot, circumflex, and dollar metacharacters. It may also alter
1248 the way the match position is advanced after a match failure for an unanchored
1249 pattern.
1250 </P>
1251 <P>
1253 match attempt for an unanchored pattern fails when the current position is at a
1254 CRLF sequence, and the pattern contains no explicit matches for CR or LF
1255 characters, the match position is advanced by two characters instead of one, in
1256 other words, to after the CRLF.
1257 </P>
1258 <P>
1259 The above rule is a compromise that makes the most common cases work as
1260 expected. For example, if the pattern is .+A (and the PCRE_DOTALL option is not
1261 set), it does not match the string "\r\nA" because, after failing at the
1262 start, it skips both the CR and the LF before retrying. However, the pattern
1263 [\r\n]A does match that string, because it contains an explicit CR or LF
1264 reference, and so advances only by one character after the first failure.
1265 </P>
1266 <P>
1267 An explicit match for CR of LF is either a literal appearance of one of those
1268 characters, or one of the \r or \n escape sequences. Implicit matches such as
1269 [^X] do not count, nor does \s (which includes CR and LF in the characters
1270 that it matches).
1271 </P>
1272 <P>
1273 Notwithstanding the above, anomalous effects may still occur when CRLF is a
1274 valid newline sequence and explicit \r or \n escapes appear in the pattern.
1275 <pre>
1277 </pre>
1278 This option specifies that first character of the subject string is not the
1279 beginning of a line, so the circumflex metacharacter should not match before
1280 it. Setting this without PCRE_MULTILINE (at compile time) causes circumflex
1281 never to match. This option affects only the behaviour of the circumflex
1282 metacharacter. It does not affect \A.
1283 <pre>
1285 </pre>
1286 This option specifies that the end of the subject string is not the end of a
1287 line, so the dollar metacharacter should not match it nor (except in multiline
1288 mode) a newline immediately before it. Setting this without PCRE_MULTILINE (at
1289 compile time) causes dollar never to match. This option affects only the
1290 behaviour of the dollar metacharacter. It does not affect \Z or \z.
1291 <pre>
1293 </pre>
1294 An empty string is not considered to be a valid match if this option is set. If
1295 there are alternatives in the pattern, they are tried. If all the alternatives
1296 match the empty string, the entire match fails. For example, if the pattern
1297 <pre>
1298 a?b?
1299 </pre>
1300 is applied to a string not beginning with "a" or "b", it matches the empty
1301 string at the start of the subject. With PCRE_NOTEMPTY set, this match is not
1302 valid, so PCRE searches further into the string for occurrences of "a" or "b".
1303 </P>
1304 <P>
1305 Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a special case
1306 of a pattern match of the empty string within its <b>split()</b> function, and
1307 when using the /g modifier. It is possible to emulate Perl's behaviour after
1308 matching a null string by first trying the match again at the same offset with
1309 PCRE_NOTEMPTY and PCRE_ANCHORED, and then if that fails by advancing the
1310 starting offset (see below) and trying an ordinary match again. There is some
1311 code that demonstrates how to do this in the <i>pcredemo.c</i> sample program.
1312 <pre>
1314 </pre>
1315 When PCRE_UTF8 is set at compile time, the validity of the subject as a UTF-8
1316 string is automatically checked when <b>pcre_exec()</b> is subsequently called.
1317 The value of <i>startoffset</i> is also checked to ensure that it points to the
1318 start of a UTF-8 character. There is a discussion about the validity of UTF-8
1319 strings in the
1320 <a href="pcre.html#utf8strings">section on UTF-8 support</a>
1321 in the main
1322 <a href="pcre.html"><b>pcre</b></a>
1323 page. If an invalid UTF-8 sequence of bytes is found, <b>pcre_exec()</b> returns
1324 the error PCRE_ERROR_BADUTF8. If <i>startoffset</i> contains an invalid value,
1325 PCRE_ERROR_BADUTF8_OFFSET is returned.
1326 </P>
1327 <P>
1328 If you already know that your subject is valid, and you want to skip these
1329 checks for performance reasons, you can set the PCRE_NO_UTF8_CHECK option when
1330 calling <b>pcre_exec()</b>. You might want to do this for the second and
1331 subsequent calls to <b>pcre_exec()</b> if you are making repeated calls to find
1332 all the matches in a single subject string. However, you should be sure that
1333 the value of <i>startoffset</i> points to the start of a UTF-8 character. When
1334 PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid UTF-8 string as a
1335 subject, or a value of <i>startoffset</i> that does not point to the start of a
1336 UTF-8 character, is undefined. Your program may crash.
1337 <pre>
1339 </pre>
1340 This option turns on the partial matching feature. If the subject string fails
1341 to match the pattern, but at some point during the matching process the end of
1342 the subject was reached (that is, the subject partially matches the pattern and
1343 the failure to match occurred only because there were not enough subject
1344 characters), <b>pcre_exec()</b> returns PCRE_ERROR_PARTIAL instead of
1345 PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is used, there are restrictions on what
1346 may appear in the pattern. These are discussed in the
1347 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1348 documentation.
1349 </P>
1350 <br><b>
1351 The string to be matched by <b>pcre_exec()</b>
1352 </b><br>
1353 <P>
1354 The subject string is passed to <b>pcre_exec()</b> as a pointer in
1355 <i>subject</i>, a length in <i>length</i>, and a starting byte offset in
1356 <i>startoffset</i>. In UTF-8 mode, the byte offset must point to the start of a
1357 UTF-8 character. Unlike the pattern string, the subject may contain binary zero
1358 bytes. When the starting offset is zero, the search for a match starts at the
1359 beginning of the subject, and this is by far the most common case.
1360 </P>
1361 <P>
1362 A non-zero starting offset is useful when searching for another match in the
1363 same subject by calling <b>pcre_exec()</b> again after a previous success.
1364 Setting <i>startoffset</i> differs from just passing over a shortened string and
1365 setting PCRE_NOTBOL in the case of a pattern that begins with any kind of
1366 lookbehind. For example, consider the pattern
1367 <pre>
1368 \Biss\B
1369 </pre>
1370 which finds occurrences of "iss" in the middle of words. (\B matches only if
1371 the current position in the subject is not a word boundary.) When applied to
1372 the string "Mississipi" the first call to <b>pcre_exec()</b> finds the first
1373 occurrence. If <b>pcre_exec()</b> is called again with just the remainder of the
1374 subject, namely "issipi", it does not match, because \B is always false at the
1375 start of the subject, which is deemed to be a word boundary. However, if
1376 <b>pcre_exec()</b> is passed the entire string again, but with <i>startoffset</i>
1377 set to 4, it finds the second occurrence of "iss" because it is able to look
1378 behind the starting point to discover that it is preceded by a letter.
1379 </P>
1380 <P>
1381 If a non-zero starting offset is passed when the pattern is anchored, one
1382 attempt to match at the given offset is made. This can only succeed if the
1383 pattern does not require the match to be at the start of the subject.
1384 </P>
1385 <br><b>
1386 How <b>pcre_exec()</b> returns captured substrings
1387 </b><br>
1388 <P>
1389 In general, a pattern matches a certain portion of the subject, and in
1390 addition, further substrings from the subject may be picked out by parts of the
1391 pattern. Following the usage in Jeffrey Friedl's book, this is called
1392 "capturing" in what follows, and the phrase "capturing subpattern" is used for
1393 a fragment of a pattern that picks out a substring. PCRE supports several other
1394 kinds of parenthesized subpattern that do not cause substrings to be captured.
1395 </P>
1396 <P>
1397 Captured substrings are returned to the caller via a vector of integer offsets
1398 whose address is passed in <i>ovector</i>. The number of elements in the vector
1399 is passed in <i>ovecsize</i>, which must be a non-negative number. <b>Note</b>:
1400 this argument is NOT the size of <i>ovector</i> in bytes.
1401 </P>
1402 <P>
1403 The first two-thirds of the vector is used to pass back captured substrings,
1404 each substring using a pair of integers. The remaining third of the vector is
1405 used as workspace by <b>pcre_exec()</b> while matching capturing subpatterns,
1406 and is not available for passing back information. The length passed in
1407 <i>ovecsize</i> should always be a multiple of three. If it is not, it is
1408 rounded down.
1409 </P>
1410 <P>
1411 When a match is successful, information about captured substrings is returned
1412 in pairs of integers, starting at the beginning of <i>ovector</i>, and
1413 continuing up to two-thirds of its length at the most. The first element of a
1414 pair is set to the offset of the first character in a substring, and the second
1415 is set to the offset of the first character after the end of a substring. The
1416 first pair, <i>ovector[0]</i> and <i>ovector[1]</i>, identify the portion of the
1417 subject string matched by the entire pattern. The next pair is used for the
1418 first capturing subpattern, and so on. The value returned by <b>pcre_exec()</b>
1419 is one more than the highest numbered pair that has been set. For example, if
1420 two substrings have been captured, the returned value is 3. If there are no
1421 capturing subpatterns, the return value from a successful match is 1,
1422 indicating that just the first pair of offsets has been set.
1423 </P>
1424 <P>
1425 If a capturing subpattern is matched repeatedly, it is the last portion of the
1426 string that it matched that is returned.
1427 </P>
1428 <P>
1429 If the vector is too small to hold all the captured substring offsets, it is
1430 used as far as possible (up to two-thirds of its length), and the function
1431 returns a value of zero. In particular, if the substring offsets are not of
1432 interest, <b>pcre_exec()</b> may be called with <i>ovector</i> passed as NULL and
1433 <i>ovecsize</i> as zero. However, if the pattern contains back references and
1434 the <i>ovector</i> is not big enough to remember the related substrings, PCRE
1435 has to get additional memory for use during matching. Thus it is usually
1436 advisable to supply an <i>ovector</i>.
1437 </P>
1438 <P>
1439 The <b>pcre_info()</b> function can be used to find out how many capturing
1440 subpatterns there are in a compiled pattern. The smallest size for
1441 <i>ovector</i> that will allow for <i>n</i> captured substrings, in addition to
1442 the offsets of the substring matched by the whole pattern, is (<i>n</i>+1)*3.
1443 </P>
1444 <P>
1445 It is possible for capturing subpattern number <i>n+1</i> to match some part of
1446 the subject when subpattern <i>n</i> has not been used at all. For example, if
1447 the string "abc" is matched against the pattern (a|(z))(bc) the return from the
1448 function is 4, and subpatterns 1 and 3 are matched, but 2 is not. When this
1449 happens, both values in the offset pairs corresponding to unused subpatterns
1450 are set to -1.
1451 </P>
1452 <P>
1453 Offset values that correspond to unused subpatterns at the end of the
1454 expression are also set to -1. For example, if the string "abc" is matched
1455 against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not matched. The
1456 return from the function is 2, because the highest used capturing subpattern
1457 number is 1. However, you can refer to the offsets for the second and third
1458 capturing subpatterns if you wish (assuming the vector is large enough, of
1459 course).
1460 </P>
1461 <P>
1462 Some convenience functions are provided for extracting the captured substrings
1463 as separate strings. These are described below.
1464 <a name="errorlist"></a></P>
1465 <br><b>
1466 Error return values from <b>pcre_exec()</b>
1467 </b><br>
1468 <P>
1469 If <b>pcre_exec()</b> fails, it returns a negative number. The following are
1470 defined in the header file:
1471 <pre>
1473 </pre>
1474 The subject string did not match the pattern.
1475 <pre>
1477 </pre>
1478 Either <i>code</i> or <i>subject</i> was passed as NULL, or <i>ovector</i> was
1479 NULL and <i>ovecsize</i> was not zero.
1480 <pre>
1482 </pre>
1483 An unrecognized bit was set in the <i>options</i> argument.
1484 <pre>
1486 </pre>
1487 PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch
1488 the case when it is passed a junk pointer and to detect when a pattern that was
1489 compiled in an environment of one endianness is run in an environment with the
1490 other endianness. This is the error that PCRE gives when the magic number is
1491 not present.
1492 <pre>
1494 </pre>
1495 While running the pattern match, an unknown item was encountered in the
1496 compiled pattern. This error could be caused by a bug in PCRE or by overwriting
1497 of the compiled pattern.
1498 <pre>
1500 </pre>
1501 If a pattern contains back references, but the <i>ovector</i> that is passed to
1502 <b>pcre_exec()</b> is not big enough to remember the referenced substrings, PCRE
1503 gets a block of memory at the start of matching to use for this purpose. If the
1504 call via <b>pcre_malloc()</b> fails, this error is given. The memory is
1505 automatically freed at the end of matching.
1506 <pre>
1508 </pre>
1509 This error is used by the <b>pcre_copy_substring()</b>,
1510 <b>pcre_get_substring()</b>, and <b>pcre_get_substring_list()</b> functions (see
1511 below). It is never returned by <b>pcre_exec()</b>.
1512 <pre>
1514 </pre>
1515 The backtracking limit, as specified by the <i>match_limit</i> field in a
1516 <b>pcre_extra</b> structure (or defaulted) was reached. See the description
1517 above.
1518 <pre>
1520 </pre>
1521 This error is never generated by <b>pcre_exec()</b> itself. It is provided for
1522 use by callout functions that want to yield a distinctive error code. See the
1523 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1524 documentation for details.
1525 <pre>
1527 </pre>
1528 A string that contains an invalid UTF-8 byte sequence was passed as a subject.
1529 <pre>
1531 </pre>
1532 The UTF-8 byte sequence that was passed as a subject was valid, but the value
1533 of <i>startoffset</i> did not point to the beginning of a UTF-8 character.
1534 <pre>
1536 </pre>
1537 The subject string did not match, but it did match partially. See the
1538 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1539 documentation for details of partial matching.
1540 <pre>
1542 </pre>
1543 The PCRE_PARTIAL option was used with a compiled pattern containing items that
1544 are not supported for partial matching. See the
1545 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1546 documentation for details of partial matching.
1547 <pre>
1549 </pre>
1550 An unexpected internal error has occurred. This error could be caused by a bug
1551 in PCRE or by overwriting of the compiled pattern.
1552 <pre>
1554 </pre>
1555 This error is given if the value of the <i>ovecsize</i> argument is negative.
1556 <pre>
1558 </pre>
1559 The internal recursion limit, as specified by the <i>match_limit_recursion</i>
1560 field in a <b>pcre_extra</b> structure (or defaulted) was reached. See the
1561 description above.
1562 <pre>
1564 </pre>
1565 An invalid combination of PCRE_NEWLINE_<i>xxx</i> options was given.
1566 </P>
1567 <P>
1568 Error numbers -16 to -20 and -22 are not used by <b>pcre_exec()</b>.
1569 </P>
1570 <br><a name="SEC15" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NUMBER</a><br>
1571 <P>
1572 <b>int pcre_copy_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1573 <b>int <i>stringcount</i>, int <i>stringnumber</i>, char *<i>buffer</i>,</b>
1574 <b>int <i>buffersize</i>);</b>
1575 </P>
1576 <P>
1577 <b>int pcre_get_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1578 <b>int <i>stringcount</i>, int <i>stringnumber</i>,</b>
1579 <b>const char **<i>stringptr</i>);</b>
1580 </P>
1581 <P>
1582 <b>int pcre_get_substring_list(const char *<i>subject</i>,</b>
1583 <b>int *<i>ovector</i>, int <i>stringcount</i>, const char ***<i>listptr</i>);</b>
1584 </P>
1585 <P>
1586 Captured substrings can be accessed directly by using the offsets returned by
1587 <b>pcre_exec()</b> in <i>ovector</i>. For convenience, the functions
1588 <b>pcre_copy_substring()</b>, <b>pcre_get_substring()</b>, and
1589 <b>pcre_get_substring_list()</b> are provided for extracting captured substrings
1590 as new, separate, zero-terminated strings. These functions identify substrings
1591 by number. The next section describes functions for extracting named
1592 substrings.
1593 </P>
1594 <P>
1595 A substring that contains a binary zero is correctly extracted and has a
1596 further zero added on the end, but the result is not, of course, a C string.
1597 However, you can process such a string by referring to the length that is
1598 returned by <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>.
1599 Unfortunately, the interface to <b>pcre_get_substring_list()</b> is not adequate
1600 for handling strings containing binary zeros, because the end of the final
1601 string is not independently indicated.
1602 </P>
1603 <P>
1604 The first three arguments are the same for all three of these functions:
1605 <i>subject</i> is the subject string that has just been successfully matched,
1606 <i>ovector</i> is a pointer to the vector of integer offsets that was passed to
1607 <b>pcre_exec()</b>, and <i>stringcount</i> is the number of substrings that were
1608 captured by the match, including the substring that matched the entire regular
1609 expression. This is the value returned by <b>pcre_exec()</b> if it is greater
1610 than zero. If <b>pcre_exec()</b> returned zero, indicating that it ran out of
1611 space in <i>ovector</i>, the value passed as <i>stringcount</i> should be the
1612 number of elements in the vector divided by three.
1613 </P>
1614 <P>
1615 The functions <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>
1616 extract a single substring, whose number is given as <i>stringnumber</i>. A
1617 value of zero extracts the substring that matched the entire pattern, whereas
1618 higher values extract the captured substrings. For <b>pcre_copy_substring()</b>,
1619 the string is placed in <i>buffer</i>, whose length is given by
1620 <i>buffersize</i>, while for <b>pcre_get_substring()</b> a new block of memory is
1621 obtained via <b>pcre_malloc</b>, and its address is returned via
1622 <i>stringptr</i>. The yield of the function is the length of the string, not
1623 including the terminating zero, or one of these error codes:
1624 <pre>
1626 </pre>
1627 The buffer was too small for <b>pcre_copy_substring()</b>, or the attempt to get
1628 memory failed for <b>pcre_get_substring()</b>.
1629 <pre>
1631 </pre>
1632 There is no substring whose number is <i>stringnumber</i>.
1633 </P>
1634 <P>
1635 The <b>pcre_get_substring_list()</b> function extracts all available substrings
1636 and builds a list of pointers to them. All this is done in a single block of
1637 memory that is obtained via <b>pcre_malloc</b>. The address of the memory block
1638 is returned via <i>listptr</i>, which is also the start of the list of string
1639 pointers. The end of the list is marked by a NULL pointer. The yield of the
1640 function is zero if all went well, or the error code
1641 <pre>
1643 </pre>
1644 if the attempt to get the memory block failed.
1645 </P>
1646 <P>
1647 When any of these functions encounter a substring that is unset, which can
1648 happen when capturing subpattern number <i>n+1</i> matches some part of the
1649 subject, but subpattern <i>n</i> has not been used at all, they return an empty
1650 string. This can be distinguished from a genuine zero-length substring by
1651 inspecting the appropriate offset in <i>ovector</i>, which is negative for unset
1652 substrings.
1653 </P>
1654 <P>
1655 The two convenience functions <b>pcre_free_substring()</b> and
1656 <b>pcre_free_substring_list()</b> can be used to free the memory returned by
1657 a previous call of <b>pcre_get_substring()</b> or
1658 <b>pcre_get_substring_list()</b>, respectively. They do nothing more than call
1659 the function pointed to by <b>pcre_free</b>, which of course could be called
1660 directly from a C program. However, PCRE is used in some situations where it is
1661 linked via a special interface to another programming language that cannot use
1662 <b>pcre_free</b> directly; it is for these cases that the functions are
1663 provided.
1664 </P>
1665 <br><a name="SEC16" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NAME</a><br>
1666 <P>
1667 <b>int pcre_get_stringnumber(const pcre *<i>code</i>,</b>
1668 <b>const char *<i>name</i>);</b>
1669 </P>
1670 <P>
1671 <b>int pcre_copy_named_substring(const pcre *<i>code</i>,</b>
1672 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
1673 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
1674 <b>char *<i>buffer</i>, int <i>buffersize</i>);</b>
1675 </P>
1676 <P>
1677 <b>int pcre_get_named_substring(const pcre *<i>code</i>,</b>
1678 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
1679 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
1680 <b>const char **<i>stringptr</i>);</b>
1681 </P>
1682 <P>
1683 To extract a substring by name, you first have to find associated number.
1684 For example, for this pattern
1685 <pre>
1686 (a+)b(?&#60;xxx&#62;\d+)...
1687 </pre>
1688 the number of the subpattern called "xxx" is 2. If the name is known to be
1689 unique (PCRE_DUPNAMES was not set), you can find the number from the name by
1690 calling <b>pcre_get_stringnumber()</b>. The first argument is the compiled
1691 pattern, and the second is the name. The yield of the function is the
1692 subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no subpattern of
1693 that name.
1694 </P>
1695 <P>
1696 Given the number, you can extract the substring directly, or use one of the
1697 functions described in the previous section. For convenience, there are also
1698 two functions that do the whole job.
1699 </P>
1700 <P>
1701 Most of the arguments of <b>pcre_copy_named_substring()</b> and
1702 <b>pcre_get_named_substring()</b> are the same as those for the similarly named
1703 functions that extract by number. As these are described in the previous
1704 section, they are not re-described here. There are just two differences:
1705 </P>
1706 <P>
1707 First, instead of a substring number, a substring name is given. Second, there
1708 is an extra argument, given at the start, which is a pointer to the compiled
1709 pattern. This is needed in order to gain access to the name-to-number
1710 translation table.
1711 </P>
1712 <P>
1713 These functions call <b>pcre_get_stringnumber()</b>, and if it succeeds, they
1714 then call <b>pcre_copy_substring()</b> or <b>pcre_get_substring()</b>, as
1715 appropriate. <b>NOTE:</b> If PCRE_DUPNAMES is set and there are duplicate names,
1716 the behaviour may not be what you want (see the next section).
1717 </P>
1718 <br><a name="SEC17" href="#TOC1">DUPLICATE SUBPATTERN NAMES</a><br>
1719 <P>
1720 <b>int pcre_get_stringtable_entries(const pcre *<i>code</i>,</b>
1721 <b>const char *<i>name</i>, char **<i>first</i>, char **<i>last</i>);</b>
1722 </P>
1723 <P>
1724 When a pattern is compiled with the PCRE_DUPNAMES option, names for subpatterns
1725 are not required to be unique. Normally, patterns with duplicate names are such
1726 that in any one match, only one of the named subpatterns participates. An
1727 example is shown in the
1728 <a href="pcrepattern.html"><b>pcrepattern</b></a>
1729 documentation.
1730 </P>
1731 <P>
1732 When duplicates are present, <b>pcre_copy_named_substring()</b> and
1733 <b>pcre_get_named_substring()</b> return the first substring corresponding to
1734 the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING (-7) is
1735 returned; no data is returned. The <b>pcre_get_stringnumber()</b> function
1736 returns one of the numbers that are associated with the name, but it is not
1737 defined which it is.
1738 </P>
1739 <P>
1740 If you want to get full details of all captured substrings for a given name,
1741 you must use the <b>pcre_get_stringtable_entries()</b> function. The first
1742 argument is the compiled pattern, and the second is the name. The third and
1743 fourth are pointers to variables which are updated by the function. After it
1744 has run, they point to the first and last entries in the name-to-number table
1745 for the given name. The function itself returns the length of each entry, or
1746 PCRE_ERROR_NOSUBSTRING (-7) if there are none. The format of the table is
1747 described above in the section entitled <i>Information about a pattern</i>.
1748 Given all the relevant entries for the name, you can extract each of their
1749 numbers, and hence the captured data, if any.
1750 </P>
1751 <br><a name="SEC18" href="#TOC1">FINDING ALL POSSIBLE MATCHES</a><br>
1752 <P>
1753 The traditional matching function uses a similar algorithm to Perl, which stops
1754 when it finds the first match, starting at a given point in the subject. If you
1755 want to find all possible matches, or the longest possible match, consider
1756 using the alternative matching function (see below) instead. If you cannot use
1757 the alternative function, but still need to find all possible matches, you
1758 can kludge it up by making use of the callout facility, which is described in
1759 the
1760 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1761 documentation.
1762 </P>
1763 <P>
1764 What you have to do is to insert a callout right at the end of the pattern.
1765 When your callout function is called, extract and save the current matched
1766 substring. Then return 1, which forces <b>pcre_exec()</b> to backtrack and try
1767 other alternatives. Ultimately, when it runs out of matches, <b>pcre_exec()</b>
1768 will yield PCRE_ERROR_NOMATCH.
1769 <a name="dfamatch"></a></P>
1770 <br><a name="SEC19" href="#TOC1">MATCHING A PATTERN: THE ALTERNATIVE FUNCTION</a><br>
1771 <P>
1772 <b>int pcre_dfa_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
1773 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
1774 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>,</b>
1775 <b>int *<i>workspace</i>, int <i>wscount</i>);</b>
1776 </P>
1777 <P>
1778 The function <b>pcre_dfa_exec()</b> is called to match a subject string against
1779 a compiled pattern, using a matching algorithm that scans the subject string
1780 just once, and does not backtrack. This has different characteristics to the
1781 normal algorithm, and is not compatible with Perl. Some of the features of PCRE
1782 patterns are not supported. Nevertheless, there are times when this kind of
1783 matching can be useful. For a discussion of the two matching algorithms, see
1784 the
1785 <a href="pcrematching.html"><b>pcrematching</b></a>
1786 documentation.
1787 </P>
1788 <P>
1789 The arguments for the <b>pcre_dfa_exec()</b> function are the same as for
1790 <b>pcre_exec()</b>, plus two extras. The <i>ovector</i> argument is used in a
1791 different way, and this is described below. The other common arguments are used
1792 in the same way as for <b>pcre_exec()</b>, so their description is not repeated
1793 here.
1794 </P>
1795 <P>
1796 The two additional arguments provide workspace for the function. The workspace
1797 vector should contain at least 20 elements. It is used for keeping track of
1798 multiple paths through the pattern tree. More workspace will be needed for
1799 patterns and subjects where there are a lot of potential matches.
1800 </P>
1801 <P>
1802 Here is an example of a simple call to <b>pcre_dfa_exec()</b>:
1803 <pre>
1804 int rc;
1805 int ovector[10];
1806 int wspace[20];
1807 rc = pcre_dfa_exec(
1808 re, /* result of pcre_compile() */
1809 NULL, /* we didn't study the pattern */
1810 "some string", /* the subject string */
1811 11, /* the length of the subject string */
1812 0, /* start at offset 0 in the subject */
1813 0, /* default options */
1814 ovector, /* vector of integers for substring information */
1815 10, /* number of elements (NOT size in bytes) */
1816 wspace, /* working space vector */
1817 20); /* number of elements (NOT size in bytes) */
1818 </PRE>
1819 </P>
1820 <br><b>
1821 Option bits for <b>pcre_dfa_exec()</b>
1822 </b><br>
1823 <P>
1824 The unused bits of the <i>options</i> argument for <b>pcre_dfa_exec()</b> must be
1825 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_<i>xxx</i>,
1827 PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last three of these are
1828 the same as for <b>pcre_exec()</b>, so their description is not repeated here.
1829 <pre>
1831 </pre>
1832 This has the same general effect as it does for <b>pcre_exec()</b>, but the
1833 details are slightly different. When PCRE_PARTIAL is set for
1834 <b>pcre_dfa_exec()</b>, the return code PCRE_ERROR_NOMATCH is converted into
1835 PCRE_ERROR_PARTIAL if the end of the subject is reached, there have been no
1836 complete matches, but there is still at least one matching possibility. The
1837 portion of the string that provided the partial match is set as the first
1838 matching string.
1839 <pre>
1841 </pre>
1842 Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to stop as
1843 soon as it has found one match. Because of the way the alternative algorithm
1844 works, this is necessarily the shortest possible match at the first possible
1845 matching point in the subject string.
1846 <pre>
1848 </pre>
1849 When <b>pcre_dfa_exec()</b> is called with the PCRE_PARTIAL option, and returns
1850 a partial match, it is possible to call it again, with additional subject
1851 characters, and have it continue with the same match. The PCRE_DFA_RESTART
1852 option requests this action; when it is set, the <i>workspace</i> and
1853 <i>wscount</i> options must reference the same vector as before because data
1854 about the match so far is left in them after a partial match. There is more
1855 discussion of this facility in the
1856 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1857 documentation.
1858 </P>
1859 <br><b>
1860 Successful returns from <b>pcre_dfa_exec()</b>
1861 </b><br>
1862 <P>
1863 When <b>pcre_dfa_exec()</b> succeeds, it may have matched more than one
1864 substring in the subject. Note, however, that all the matches from one run of
1865 the function start at the same point in the subject. The shorter matches are
1866 all initial substrings of the longer matches. For example, if the pattern
1867 <pre>
1868 &#60;.*&#62;
1869 </pre>
1870 is matched against the string
1871 <pre>
1872 This is &#60;something&#62; &#60;something else&#62; &#60;something further&#62; no more
1873 </pre>
1874 the three matched strings are
1875 <pre>
1876 &#60;something&#62;
1877 &#60;something&#62; &#60;something else&#62;
1878 &#60;something&#62; &#60;something else&#62; &#60;something further&#62;
1879 </pre>
1880 On success, the yield of the function is a number greater than zero, which is
1881 the number of matched substrings. The substrings themselves are returned in
1882 <i>ovector</i>. Each string uses two elements; the first is the offset to the
1883 start, and the second is the offset to the end. In fact, all the strings have
1884 the same start offset. (Space could have been saved by giving this only once,
1885 but it was decided to retain some compatibility with the way <b>pcre_exec()</b>
1886 returns data, even though the meaning of the strings is different.)
1887 </P>
1888 <P>
1889 The strings are returned in reverse order of length; that is, the longest
1890 matching string is given first. If there were too many matches to fit into
1891 <i>ovector</i>, the yield of the function is zero, and the vector is filled with
1892 the longest matches.
1893 </P>
1894 <br><b>
1895 Error returns from <b>pcre_dfa_exec()</b>
1896 </b><br>
1897 <P>
1898 The <b>pcre_dfa_exec()</b> function returns a negative number when it fails.
1899 Many of the errors are the same as for <b>pcre_exec()</b>, and these are
1900 described
1901 <a href="#errorlist">above.</a>
1902 There are in addition the following errors that are specific to
1903 <b>pcre_dfa_exec()</b>:
1904 <pre>
1906 </pre>
1907 This return is given if <b>pcre_dfa_exec()</b> encounters an item in the pattern
1908 that it does not support, for instance, the use of \C or a back reference.
1909 <pre>
1911 </pre>
1912 This return is given if <b>pcre_dfa_exec()</b> encounters a condition item that
1913 uses a back reference for the condition, or a test for recursion in a specific
1914 group. These are not supported.
1915 <pre>
1917 </pre>
1918 This return is given if <b>pcre_dfa_exec()</b> is called with an <i>extra</i>
1919 block that contains a setting of the <i>match_limit</i> field. This is not
1920 supported (it is meaningless).
1921 <pre>
1923 </pre>
1924 This return is given if <b>pcre_dfa_exec()</b> runs out of space in the
1925 <i>workspace</i> vector.
1926 <pre>
1928 </pre>
1929 When a recursive subpattern is processed, the matching function calls itself
1930 recursively, using private vectors for <i>ovector</i> and <i>workspace</i>. This
1931 error is given if the output vector is not large enough. This should be
1932 extremely rare, as a vector of size 1000 is used.
1933 </P>
1934 <br><a name="SEC20" href="#TOC1">SEE ALSO</a><br>
1935 <P>
1936 <b>pcrebuild</b>(3), <b>pcrecallout</b>(3), <b>pcrecpp(3)</b>(3),
1937 <b>pcrematching</b>(3), <b>pcrepartial</b>(3), <b>pcreposix</b>(3),
1938 <b>pcreprecompile</b>(3), <b>pcresample</b>(3), <b>pcrestack</b>(3).
1939 </P>
1940 <br><a name="SEC21" href="#TOC1">AUTHOR</a><br>
1941 <P>
1942 Philip Hazel
1943 <br>
1944 University Computing Service
1945 <br>
1946 Cambridge CB2 3QH, England.
1947 <br>
1948 </P>
1949 <br><a name="SEC22" href="#TOC1">REVISION</a><br>
1950 <P>
1951 Last updated: 11 September 2007
1952 <br>
1953 Copyright &copy; 1997-2007 University of Cambridge.
1954 <br>
1955 <p>
1956 Return to the <a href="index.html">PCRE index page</a>.
1957 </p>


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