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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. The choice of newline convention does not affect the interpretation of
280 the \n or \r escape sequences.
281 </P>
282 <br><a name="SEC4" href="#TOC1">MULTITHREADING</a><br>
283 <P>
284 The PCRE functions can be used in multi-threading applications, with the
285 proviso that the memory management functions pointed to by <b>pcre_malloc</b>,
286 <b>pcre_free</b>, <b>pcre_stack_malloc</b>, and <b>pcre_stack_free</b>, and the
287 callout function pointed to by <b>pcre_callout</b>, are shared by all threads.
288 </P>
289 <P>
290 The compiled form of a regular expression is not altered during matching, so
291 the same compiled pattern can safely be used by several threads at once.
292 </P>
293 <br><a name="SEC5" href="#TOC1">SAVING PRECOMPILED PATTERNS FOR LATER USE</a><br>
294 <P>
295 The compiled form of a regular expression can be saved and re-used at a later
296 time, possibly by a different program, and even on a host other than the one on
297 which it was compiled. Details are given in the
298 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
299 documentation. However, compiling a regular expression with one version of PCRE
300 for use with a different version is not guaranteed to work and may cause
301 crashes.
302 </P>
303 <br><a name="SEC6" href="#TOC1">CHECKING BUILD-TIME OPTIONS</a><br>
304 <P>
305 <b>int pcre_config(int <i>what</i>, void *<i>where</i>);</b>
306 </P>
307 <P>
308 The function <b>pcre_config()</b> makes it possible for a PCRE client to
309 discover which optional features have been compiled into the PCRE library. The
310 <a href="pcrebuild.html"><b>pcrebuild</b></a>
311 documentation has more details about these optional features.
312 </P>
313 <P>
314 The first argument for <b>pcre_config()</b> is an integer, specifying which
315 information is required; the second argument is a pointer to a variable into
316 which the information is placed. The following information is available:
317 <pre>
319 </pre>
320 The output is an integer that is set to one if UTF-8 support is available;
321 otherwise it is set to zero.
322 <pre>
324 </pre>
325 The output is an integer that is set to one if support for Unicode character
326 properties is available; otherwise it is set to zero.
327 <pre>
329 </pre>
330 The output is an integer whose value specifies the default character sequence
331 that is recognized as meaning "newline". The four values that are supported
332 are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF, and -1 for ANY. The
333 default should normally be the standard sequence for your operating system.
334 <pre>
336 </pre>
337 The output is an integer that contains the number of bytes used for internal
338 linkage in compiled regular expressions. The value is 2, 3, or 4. Larger values
339 allow larger regular expressions to be compiled, at the expense of slower
340 matching. The default value of 2 is sufficient for all but the most massive
341 patterns, since it allows the compiled pattern to be up to 64K in size.
342 <pre>
344 </pre>
345 The output is an integer that contains the threshold above which the POSIX
346 interface uses <b>malloc()</b> for output vectors. Further details are given in
347 the
348 <a href="pcreposix.html"><b>pcreposix</b></a>
349 documentation.
350 <pre>
352 </pre>
353 The output is an integer that gives the default limit for the number of
354 internal matching function calls in a <b>pcre_exec()</b> execution. Further
355 details are given with <b>pcre_exec()</b> below.
356 <pre>
358 </pre>
359 The output is an integer that gives the default limit for the depth of
360 recursion when calling the internal matching function in a <b>pcre_exec()</b>
361 execution. Further details are given with <b>pcre_exec()</b> below.
362 <pre>
364 </pre>
365 The output is an integer that is set to one if internal recursion when running
366 <b>pcre_exec()</b> is implemented by recursive function calls that use the stack
367 to remember their state. This is the usual way that PCRE is compiled. The
368 output is zero if PCRE was compiled to use blocks of data on the heap instead
369 of recursive function calls. In this case, <b>pcre_stack_malloc</b> and
370 <b>pcre_stack_free</b> are called to manage memory blocks on the heap, thus
371 avoiding the use of the stack.
372 </P>
373 <br><a name="SEC7" href="#TOC1">COMPILING A PATTERN</a><br>
374 <P>
375 <b>pcre *pcre_compile(const char *<i>pattern</i>, int <i>options</i>,</b>
376 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
377 <b>const unsigned char *<i>tableptr</i>);</b>
378 <b>pcre *pcre_compile2(const char *<i>pattern</i>, int <i>options</i>,</b>
379 <b>int *<i>errorcodeptr</i>,</b>
380 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
381 <b>const unsigned char *<i>tableptr</i>);</b>
382 </P>
383 <P>
384 Either of the functions <b>pcre_compile()</b> or <b>pcre_compile2()</b> can be
385 called to compile a pattern into an internal form. The only difference between
386 the two interfaces is that <b>pcre_compile2()</b> has an additional argument,
387 <i>errorcodeptr</i>, via which a numerical error code can be returned.
388 </P>
389 <P>
390 The pattern is a C string terminated by a binary zero, and is passed in the
391 <i>pattern</i> argument. A pointer to a single block of memory that is obtained
392 via <b>pcre_malloc</b> is returned. This contains the compiled code and related
393 data. The <b>pcre</b> type is defined for the returned block; this is a typedef
394 for a structure whose contents are not externally defined. It is up to the
395 caller to free the memory (via <b>pcre_free</b>) when it is no longer required.
396 </P>
397 <P>
398 Although the compiled code of a PCRE regex is relocatable, that is, it does not
399 depend on memory location, the complete <b>pcre</b> data block is not
400 fully relocatable, because it may contain a copy of the <i>tableptr</i>
401 argument, which is an address (see below).
402 </P>
403 <P>
404 The <i>options</i> argument contains various bit settings that affect the
405 compilation. It should be zero if no options are required. The available
406 options are described below. Some of them, in particular, those that are
407 compatible with Perl, can also be set and unset from within the pattern (see
408 the detailed description in the
409 <a href="pcrepattern.html"><b>pcrepattern</b></a>
410 documentation). For these options, the contents of the <i>options</i> argument
411 specifies their initial settings at the start of compilation and execution. The
412 PCRE_ANCHORED and PCRE_NEWLINE_<i>xxx</i> options can be set at the time of
413 matching as well as at compile time.
414 </P>
415 <P>
416 If <i>errptr</i> is NULL, <b>pcre_compile()</b> returns NULL immediately.
417 Otherwise, if compilation of a pattern fails, <b>pcre_compile()</b> returns
418 NULL, and sets the variable pointed to by <i>errptr</i> to point to a textual
419 error message. This is a static string that is part of the library. You must
420 not try to free it. The offset from the start of the pattern to the character
421 where the error was discovered is placed in the variable pointed to by
422 <i>erroffset</i>, which must not be NULL. If it is, an immediate error is given.
423 </P>
424 <P>
425 If <b>pcre_compile2()</b> is used instead of <b>pcre_compile()</b>, and the
426 <i>errorcodeptr</i> argument is not NULL, a non-zero error code number is
427 returned via this argument in the event of an error. This is in addition to the
428 textual error message. Error codes and messages are listed below.
429 </P>
430 <P>
431 If the final argument, <i>tableptr</i>, is NULL, PCRE uses a default set of
432 character tables that are built when PCRE is compiled, using the default C
433 locale. Otherwise, <i>tableptr</i> must be an address that is the result of a
434 call to <b>pcre_maketables()</b>. This value is stored with the compiled
435 pattern, and used again by <b>pcre_exec()</b>, unless another table pointer is
436 passed to it. For more discussion, see the section on locale support below.
437 </P>
438 <P>
439 This code fragment shows a typical straightforward call to <b>pcre_compile()</b>:
440 <pre>
441 pcre *re;
442 const char *error;
443 int erroffset;
444 re = pcre_compile(
445 "^A.*Z", /* the pattern */
446 0, /* default options */
447 &error, /* for error message */
448 &erroffset, /* for error offset */
449 NULL); /* use default character tables */
450 </pre>
451 The following names for option bits are defined in the <b>pcre.h</b> header
452 file:
453 <pre>
455 </pre>
456 If this bit is set, the pattern is forced to be "anchored", that is, it is
457 constrained to match only at the first matching point in the string that is
458 being searched (the "subject string"). This effect can also be achieved by
459 appropriate constructs in the pattern itself, which is the only way to do it in
460 Perl.
461 <pre>
463 </pre>
464 If this bit is set, <b>pcre_compile()</b> automatically inserts callout items,
465 all with number 255, before each pattern item. For discussion of the callout
466 facility, see the
467 <a href="pcrecallout.html"><b>pcrecallout</b></a>
468 documentation.
469 <pre>
471 </pre>
472 If this bit is set, letters in the pattern match both upper and lower case
473 letters. It is equivalent to Perl's /i option, and it can be changed within a
474 pattern by a (?i) option setting. In UTF-8 mode, PCRE always understands the
475 concept of case for characters whose values are less than 128, so caseless
476 matching is always possible. For characters with higher values, the concept of
477 case is supported if PCRE is compiled with Unicode property support, but not
478 otherwise. If you want to use caseless matching for characters 128 and above,
479 you must ensure that PCRE is compiled with Unicode property support as well as
480 with UTF-8 support.
481 <pre>
483 </pre>
484 If this bit is set, a dollar metacharacter in the pattern matches only at the
485 end of the subject string. Without this option, a dollar also matches
486 immediately before a newline at the end of the string (but not before any other
487 newlines). The PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is set.
488 There is no equivalent to this option in Perl, and no way to set it within a
489 pattern.
490 <pre>
492 </pre>
493 If this bit is set, a dot metacharater in the pattern matches all characters,
494 including those that indicate newline. Without it, a dot does not match when
495 the current position is at a newline. This option is equivalent to Perl's /s
496 option, and it can be changed within a pattern by a (?s) option setting. A
497 negative class such as [^a] always matches newline characters, independent of
498 the setting of this option.
499 <pre>
501 </pre>
502 If this bit is set, names used to identify capturing subpatterns need not be
503 unique. This can be helpful for certain types of pattern when it is known that
504 only one instance of the named subpattern can ever be matched. There are more
505 details of named subpatterns below; see also the
506 <a href="pcrepattern.html"><b>pcrepattern</b></a>
507 documentation.
508 <pre>
510 </pre>
511 If this bit is set, whitespace data characters in the pattern are totally
512 ignored except when escaped or inside a character class. Whitespace does not
513 include the VT character (code 11). In addition, characters between an
514 unescaped # outside a character class and the next newline, inclusive, are also
515 ignored. This is equivalent to Perl's /x option, and it can be changed within a
516 pattern by a (?x) option setting.
517 </P>
518 <P>
519 This option makes it possible to include comments inside complicated patterns.
520 Note, however, that this applies only to data characters. Whitespace characters
521 may never appear within special character sequences in a pattern, for example
522 within the sequence (?( which introduces a conditional subpattern.
523 <pre>
525 </pre>
526 This option was invented in order to turn on additional functionality of PCRE
527 that is incompatible with Perl, but it is currently of very little use. When
528 set, any backslash in a pattern that is followed by a letter that has no
529 special meaning causes an error, thus reserving these combinations for future
530 expansion. By default, as in Perl, a backslash followed by a letter with no
531 special meaning is treated as a literal. (Perl can, however, be persuaded to
532 give a warning for this.) There are at present no other features controlled by
533 this option. It can also be set by a (?X) option setting within a pattern.
534 <pre>
536 </pre>
537 If this option is set, an unanchored pattern is required to match before or at
538 the first newline in the subject string, though the matched text may continue
539 over the newline.
540 <pre>
542 </pre>
543 By default, PCRE treats the subject string as consisting of a single line of
544 characters (even if it actually contains newlines). The "start of line"
545 metacharacter (^) matches only at the start of the string, while the "end of
546 line" metacharacter ($) matches only at the end of the string, or before a
547 terminating newline (unless PCRE_DOLLAR_ENDONLY is set). This is the same as
548 Perl.
549 </P>
550 <P>
551 When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs
552 match immediately following or immediately before internal newlines in the
553 subject string, respectively, as well as at the very start and end. This is
554 equivalent to Perl's /m option, and it can be changed within a pattern by a
555 (?m) option setting. If there are no newlines in a subject string, or no
556 occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no effect.
557 <pre>
563 </pre>
564 These options override the default newline definition that was chosen when PCRE
565 was built. Setting the first or the second specifies that a newline is
566 indicated by a single character (CR or LF, respectively). Setting
567 PCRE_NEWLINE_CRLF specifies that a newline is indicated by the two-character
568 CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies that any of the three
569 preceding sequences should be recognized. Setting PCRE_NEWLINE_ANY specifies
570 that any Unicode newline sequence should be recognized. The Unicode newline
571 sequences are the three just mentioned, plus the single characters VT (vertical
572 tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS (line
573 separator, U+2028), and PS (paragraph separator, U+2029). The last two are
574 recognized only in UTF-8 mode.
575 </P>
576 <P>
577 The newline setting in the options word uses three bits that are treated
578 as a number, giving eight possibilities. Currently only six are used (default
579 plus the five values above). This means that if you set more than one newline
580 option, the combination may or may not be sensible. For example,
582 other combinations may yield unused numbers and cause an error.
583 </P>
584 <P>
585 The only time that a line break is specially recognized when compiling a
586 pattern is if PCRE_EXTENDED is set, and an unescaped # outside a character
587 class is encountered. This indicates a comment that lasts until after the next
588 line break sequence. In other circumstances, line break sequences are treated
589 as literal data, except that in PCRE_EXTENDED mode, both CR and LF are treated
590 as whitespace characters and are therefore ignored.
591 </P>
592 <P>
593 The newline option that is set at compile time becomes the default that is used
594 for <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b>, but it can be overridden.
595 <pre>
597 </pre>
598 If this option is set, it disables the use of numbered capturing parentheses in
599 the pattern. Any opening parenthesis that is not followed by ? behaves as if it
600 were followed by ?: but named parentheses can still be used for capturing (and
601 they acquire numbers in the usual way). There is no equivalent of this option
602 in Perl.
603 <pre>
605 </pre>
606 This option inverts the "greediness" of the quantifiers so that they are not
607 greedy by default, but become greedy if followed by "?". It is not compatible
608 with Perl. It can also be set by a (?U) option setting within the pattern.
609 <pre>
611 </pre>
612 This option causes PCRE to regard both the pattern and the subject as strings
613 of UTF-8 characters instead of single-byte character strings. However, it is
614 available only when PCRE is built to include UTF-8 support. If not, the use
615 of this option provokes an error. Details of how this option changes the
616 behaviour of PCRE are given in the
617 <a href="pcre.html#utf8support">section on UTF-8 support</a>
618 in the main
619 <a href="pcre.html"><b>pcre</b></a>
620 page.
621 <pre>
623 </pre>
624 When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
625 automatically checked. There is a discussion about the
626 <a href="pcre.html#utf8strings">validity of UTF-8 strings</a>
627 in the main
628 <a href="pcre.html"><b>pcre</b></a>
629 page. If an invalid UTF-8 sequence of bytes is found, <b>pcre_compile()</b>
630 returns an error. If you already know that your pattern is valid, and you want
631 to skip this check for performance reasons, you can set the PCRE_NO_UTF8_CHECK
632 option. When it is set, the effect of passing an invalid UTF-8 string as a
633 pattern is undefined. It may cause your program to crash. Note that this option
634 can also be passed to <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b>, to suppress
635 the UTF-8 validity checking of subject strings.
636 </P>
637 <br><a name="SEC8" href="#TOC1">COMPILATION ERROR CODES</a><br>
638 <P>
639 The following table lists the error codes than may be returned by
640 <b>pcre_compile2()</b>, along with the error messages that may be returned by
641 both compiling functions. As PCRE has developed, some error codes have fallen
642 out of use. To avoid confusion, they have not been re-used.
643 <pre>
644 0 no error
645 1 \ at end of pattern
646 2 \c at end of pattern
647 3 unrecognized character follows \
648 4 numbers out of order in {} quantifier
649 5 number too big in {} quantifier
650 6 missing terminating ] for character class
651 7 invalid escape sequence in character class
652 8 range out of order in character class
653 9 nothing to repeat
654 10 [this code is not in use]
655 11 internal error: unexpected repeat
656 12 unrecognized character after (?
657 13 POSIX named classes are supported only within a class
658 14 missing )
659 15 reference to non-existent subpattern
660 16 erroffset passed as NULL
661 17 unknown option bit(s) set
662 18 missing ) after comment
663 19 [this code is not in use]
664 20 regular expression too large
665 21 failed to get memory
666 22 unmatched parentheses
667 23 internal error: code overflow
668 24 unrecognized character after (?&#60;
669 25 lookbehind assertion is not fixed length
670 26 malformed number or name after (?(
671 27 conditional group contains more than two branches
672 28 assertion expected after (?(
673 29 (?R or (?[+-]digits must be followed by )
674 30 unknown POSIX class name
675 31 POSIX collating elements are not supported
676 32 this version of PCRE is not compiled with PCRE_UTF8 support
677 33 [this code is not in use]
678 34 character value in \x{...} sequence is too large
679 35 invalid condition (?(0)
680 36 \C not allowed in lookbehind assertion
681 37 PCRE does not support \L, \l, \N, \U, or \u
682 38 number after (?C is &#62; 255
683 39 closing ) for (?C expected
684 40 recursive call could loop indefinitely
685 41 unrecognized character after (?P
686 42 syntax error in subpattern name (missing terminator)
687 43 two named subpatterns have the same name
688 44 invalid UTF-8 string
689 45 support for \P, \p, and \X has not been compiled
690 46 malformed \P or \p sequence
691 47 unknown property name after \P or \p
692 48 subpattern name is too long (maximum 32 characters)
693 49 too many named subpatterns (maximum 10,000)
694 50 [this code is not in use]
695 51 octal value is greater than \377 (not in UTF-8 mode)
696 52 internal error: overran compiling workspace
697 53 internal error: previously-checked referenced subpattern not found
698 54 DEFINE group contains more than one branch
699 55 repeating a DEFINE group is not allowed
700 56 inconsistent NEWLINE options"
701 57 \g is not followed by a braced name or an optionally braced
702 non-zero number
703 58 (?+ or (?- or (?(+ or (?(- must be followed by a non-zero number
704 </PRE>
705 </P>
706 <br><a name="SEC9" href="#TOC1">STUDYING A PATTERN</a><br>
707 <P>
708 <b>pcre_extra *pcre_study(const pcre *<i>code</i>, int <i>options</i></b>
709 <b>const char **<i>errptr</i>);</b>
710 </P>
711 <P>
712 If a compiled pattern is going to be used several times, it is worth spending
713 more time analyzing it in order to speed up the time taken for matching. The
714 function <b>pcre_study()</b> takes a pointer to a compiled pattern as its first
715 argument. If studying the pattern produces additional information that will
716 help speed up matching, <b>pcre_study()</b> returns a pointer to a
717 <b>pcre_extra</b> block, in which the <i>study_data</i> field points to the
718 results of the study.
719 </P>
720 <P>
721 The returned value from <b>pcre_study()</b> can be passed directly to
722 <b>pcre_exec()</b>. However, a <b>pcre_extra</b> block also contains other
723 fields that can be set by the caller before the block is passed; these are
724 described
725 <a href="#extradata">below</a>
726 in the section on matching a pattern.
727 </P>
728 <P>
729 If studying the pattern does not produce any additional information
730 <b>pcre_study()</b> returns NULL. In that circumstance, if the calling program
731 wants to pass any of the other fields to <b>pcre_exec()</b>, it must set up its
732 own <b>pcre_extra</b> block.
733 </P>
734 <P>
735 The second argument of <b>pcre_study()</b> contains option bits. At present, no
736 options are defined, and this argument should always be zero.
737 </P>
738 <P>
739 The third argument for <b>pcre_study()</b> is a pointer for an error message. If
740 studying succeeds (even if no data is returned), the variable it points to is
741 set to NULL. Otherwise it is set to point to a textual error message. This is a
742 static string that is part of the library. You must not try to free it. You
743 should test the error pointer for NULL after calling <b>pcre_study()</b>, to be
744 sure that it has run successfully.
745 </P>
746 <P>
747 This is a typical call to <b>pcre_study</b>():
748 <pre>
749 pcre_extra *pe;
750 pe = pcre_study(
751 re, /* result of pcre_compile() */
752 0, /* no options exist */
753 &error); /* set to NULL or points to a message */
754 </pre>
755 At present, studying a pattern is useful only for non-anchored patterns that do
756 not have a single fixed starting character. A bitmap of possible starting
757 bytes is created.
758 <a name="localesupport"></a></P>
759 <br><a name="SEC10" href="#TOC1">LOCALE SUPPORT</a><br>
760 <P>
761 PCRE handles caseless matching, and determines whether characters are letters,
762 digits, or whatever, by reference to a set of tables, indexed by character
763 value. When running in UTF-8 mode, this applies only to characters with codes
764 less than 128. Higher-valued codes never match escapes such as \w or \d, but
765 can be tested with \p if PCRE is built with Unicode character property
766 support. The use of locales with Unicode is discouraged. If you are handling
767 characters with codes greater than 128, you should either use UTF-8 and
768 Unicode, or use locales, but not try to mix the two.
769 </P>
770 <P>
771 PCRE contains an internal set of tables that are used when the final argument
772 of <b>pcre_compile()</b> is NULL. These are sufficient for many applications.
773 Normally, the internal tables recognize only ASCII characters. However, when
774 PCRE is built, it is possible to cause the internal tables to be rebuilt in the
775 default "C" locale of the local system, which may cause them to be different.
776 </P>
777 <P>
778 The internal tables can always be overridden by tables supplied by the
779 application that calls PCRE. These may be created in a different locale from
780 the default. As more and more applications change to using Unicode, the need
781 for this locale support is expected to die away.
782 </P>
783 <P>
784 External tables are built by calling the <b>pcre_maketables()</b> function,
785 which has no arguments, in the relevant locale. The result can then be passed
786 to <b>pcre_compile()</b> or <b>pcre_exec()</b> as often as necessary. For
787 example, to build and use tables that are appropriate for the French locale
788 (where accented characters with values greater than 128 are treated as letters),
789 the following code could be used:
790 <pre>
791 setlocale(LC_CTYPE, "fr_FR");
792 tables = pcre_maketables();
793 re = pcre_compile(..., tables);
794 </pre>
795 The locale name "fr_FR" is used on Linux and other Unix-like systems; if you
796 are using Windows, the name for the French locale is "french".
797 </P>
798 <P>
799 When <b>pcre_maketables()</b> runs, the tables are built in memory that is
800 obtained via <b>pcre_malloc</b>. It is the caller's responsibility to ensure
801 that the memory containing the tables remains available for as long as it is
802 needed.
803 </P>
804 <P>
805 The pointer that is passed to <b>pcre_compile()</b> is saved with the compiled
806 pattern, and the same tables are used via this pointer by <b>pcre_study()</b>
807 and normally also by <b>pcre_exec()</b>. Thus, by default, for any single
808 pattern, compilation, studying and matching all happen in the same locale, but
809 different patterns can be compiled in different locales.
810 </P>
811 <P>
812 It is possible to pass a table pointer or NULL (indicating the use of the
813 internal tables) to <b>pcre_exec()</b>. Although not intended for this purpose,
814 this facility could be used to match a pattern in a different locale from the
815 one in which it was compiled. Passing table pointers at run time is discussed
816 below in the section on matching a pattern.
817 </P>
818 <br><a name="SEC11" href="#TOC1">INFORMATION ABOUT A PATTERN</a><br>
819 <P>
820 <b>int pcre_fullinfo(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
821 <b>int <i>what</i>, void *<i>where</i>);</b>
822 </P>
823 <P>
824 The <b>pcre_fullinfo()</b> function returns information about a compiled
825 pattern. It replaces the obsolete <b>pcre_info()</b> function, which is
826 nevertheless retained for backwards compability (and is documented below).
827 </P>
828 <P>
829 The first argument for <b>pcre_fullinfo()</b> is a pointer to the compiled
830 pattern. The second argument is the result of <b>pcre_study()</b>, or NULL if
831 the pattern was not studied. The third argument specifies which piece of
832 information is required, and the fourth argument is a pointer to a variable
833 to receive the data. The yield of the function is zero for success, or one of
834 the following negative numbers:
835 <pre>
836 PCRE_ERROR_NULL the argument <i>code</i> was NULL
837 the argument <i>where</i> was NULL
838 PCRE_ERROR_BADMAGIC the "magic number" was not found
839 PCRE_ERROR_BADOPTION the value of <i>what</i> was invalid
840 </pre>
841 The "magic number" is placed at the start of each compiled pattern as an simple
842 check against passing an arbitrary memory pointer. Here is a typical call of
843 <b>pcre_fullinfo()</b>, to obtain the length of the compiled pattern:
844 <pre>
845 int rc;
846 size_t length;
847 rc = pcre_fullinfo(
848 re, /* result of pcre_compile() */
849 pe, /* result of pcre_study(), or NULL */
850 PCRE_INFO_SIZE, /* what is required */
851 &length); /* where to put the data */
852 </pre>
853 The possible values for the third argument are defined in <b>pcre.h</b>, and are
854 as follows:
855 <pre>
857 </pre>
858 Return the number of the highest back reference in the pattern. The fourth
859 argument should point to an <b>int</b> variable. Zero is returned if there are
860 no back references.
861 <pre>
863 </pre>
864 Return the number of capturing subpatterns in the pattern. The fourth argument
865 should point to an <b>int</b> variable.
866 <pre>
868 </pre>
869 Return a pointer to the internal default character tables within PCRE. The
870 fourth argument should point to an <b>unsigned char *</b> variable. This
871 information call is provided for internal use by the <b>pcre_study()</b>
872 function. External callers can cause PCRE to use its internal tables by passing
873 a NULL table pointer.
874 <pre>
876 </pre>
877 Return information about the first byte of any matched string, for a
878 non-anchored pattern. The fourth argument should point to an <b>int</b>
879 variable. (This option used to be called PCRE_INFO_FIRSTCHAR; the old name is
880 still recognized for backwards compatibility.)
881 </P>
882 <P>
883 If there is a fixed first byte, for example, from a pattern such as
884 (cat|cow|coyote), its value is returned. Otherwise, if either
885 <br>
886 <br>
887 (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
888 starts with "^", or
889 <br>
890 <br>
891 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
892 (if it were set, the pattern would be anchored),
893 <br>
894 <br>
895 -1 is returned, indicating that the pattern matches only at the start of a
896 subject string or after any newline within the string. Otherwise -2 is
897 returned. For anchored patterns, -2 is returned.
898 <pre>
900 </pre>
901 If the pattern was studied, and this resulted in the construction of a 256-bit
902 table indicating a fixed set of bytes for the first byte in any matching
903 string, a pointer to the table is returned. Otherwise NULL is returned. The
904 fourth argument should point to an <b>unsigned char *</b> variable.
905 <pre>
907 </pre>
908 Return 1 if the pattern contains any explicit matches for CR or LF characters,
909 otherwise 0. The fourth argument should point to an <b>int</b> variable.
910 <pre>
912 </pre>
913 Return 1 if the (?J) option setting is used in the pattern, otherwise 0. The
914 fourth argument should point to an <b>int</b> variable. The (?J) internal option
915 setting changes the local PCRE_DUPNAMES option.
916 <pre>
918 </pre>
919 Return the value of the rightmost literal byte that must exist in any matched
920 string, other than at its start, if such a byte has been recorded. The fourth
921 argument should point to an <b>int</b> variable. If there is no such byte, -1 is
922 returned. For anchored patterns, a last literal byte is recorded only if it
923 follows something of variable length. For example, for the pattern
924 /^a\d+z\d+/ the returned value is "z", but for /^a\dz\d/ the returned value
925 is -1.
926 <pre>
930 </pre>
931 PCRE supports the use of named as well as numbered capturing parentheses. The
932 names are just an additional way of identifying the parentheses, which still
933 acquire numbers. Several convenience functions such as
934 <b>pcre_get_named_substring()</b> are provided for extracting captured
935 substrings by name. It is also possible to extract the data directly, by first
936 converting the name to a number in order to access the correct pointers in the
937 output vector (described with <b>pcre_exec()</b> below). To do the conversion,
938 you need to use the name-to-number map, which is described by these three
939 values.
940 </P>
941 <P>
942 The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives
943 the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each
944 entry; both of these return an <b>int</b> value. The entry size depends on the
945 length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first
946 entry of the table (a pointer to <b>char</b>). The first two bytes of each entry
947 are the number of the capturing parenthesis, most significant byte first. The
948 rest of the entry is the corresponding name, zero terminated. The names are in
949 alphabetical order. When PCRE_DUPNAMES is set, duplicate names are in order of
950 their parentheses numbers. For example, consider the following pattern (assume
951 PCRE_EXTENDED is set, so white space - including newlines - is ignored):
952 <pre>
953 (?&#60;date&#62; (?&#60;year&#62;(\d\d)?\d\d) - (?&#60;month&#62;\d\d) - (?&#60;day&#62;\d\d) )
954 </pre>
955 There are four named subpatterns, so the table has four entries, and each entry
956 in the table is eight bytes long. The table is as follows, with non-printing
957 bytes shows in hexadecimal, and undefined bytes shown as ??:
958 <pre>
959 00 01 d a t e 00 ??
960 00 05 d a y 00 ?? ??
961 00 04 m o n t h 00
962 00 02 y e a r 00 ??
963 </pre>
964 When writing code to extract data from named subpatterns using the
965 name-to-number map, remember that the length of the entries is likely to be
966 different for each compiled pattern.
967 <pre>
969 </pre>
970 Return 1 if the pattern can be used for partial matching, otherwise 0. The
971 fourth argument should point to an <b>int</b> variable. The
972 <a href="pcrepartial.html"><b>pcrepartial</b></a>
973 documentation lists the restrictions that apply to patterns when partial
974 matching is used.
975 <pre>
977 </pre>
978 Return a copy of the options with which the pattern was compiled. The fourth
979 argument should point to an <b>unsigned long int</b> variable. These option bits
980 are those specified in the call to <b>pcre_compile()</b>, modified by any
981 top-level option settings at the start of the pattern itself. In other words,
982 they are the options that will be in force when matching starts. For example,
983 if the pattern /(?im)abc(?-i)d/ is compiled with the PCRE_EXTENDED option, the
985 </P>
986 <P>
987 A pattern is automatically anchored by PCRE if all of its top-level
988 alternatives begin with one of the following:
989 <pre>
990 ^ unless PCRE_MULTILINE is set
991 \A always
992 \G always
993 .* if PCRE_DOTALL is set and there are no back references to the subpattern in which .* appears
994 </pre>
995 For such patterns, the PCRE_ANCHORED bit is set in the options returned by
996 <b>pcre_fullinfo()</b>.
997 <pre>
999 </pre>
1000 Return the size of the compiled pattern, that is, the value that was passed as
1001 the argument to <b>pcre_malloc()</b> when PCRE was getting memory in which to
1002 place the compiled data. The fourth argument should point to a <b>size_t</b>
1003 variable.
1004 <pre>
1006 </pre>
1007 Return the size of the data block pointed to by the <i>study_data</i> field in
1008 a <b>pcre_extra</b> block. That is, it is the value that was passed to
1009 <b>pcre_malloc()</b> when PCRE was getting memory into which to place the data
1010 created by <b>pcre_study()</b>. The fourth argument should point to a
1011 <b>size_t</b> variable.
1012 </P>
1013 <br><a name="SEC12" href="#TOC1">OBSOLETE INFO FUNCTION</a><br>
1014 <P>
1015 <b>int pcre_info(const pcre *<i>code</i>, int *<i>optptr</i>, int</b>
1016 <b>*<i>firstcharptr</i>);</b>
1017 </P>
1018 <P>
1019 The <b>pcre_info()</b> function is now obsolete because its interface is too
1020 restrictive to return all the available data about a compiled pattern. New
1021 programs should use <b>pcre_fullinfo()</b> instead. The yield of
1022 <b>pcre_info()</b> is the number of capturing subpatterns, or one of the
1023 following negative numbers:
1024 <pre>
1025 PCRE_ERROR_NULL the argument <i>code</i> was NULL
1026 PCRE_ERROR_BADMAGIC the "magic number" was not found
1027 </pre>
1028 If the <i>optptr</i> argument is not NULL, a copy of the options with which the
1029 pattern was compiled is placed in the integer it points to (see
1030 PCRE_INFO_OPTIONS above).
1031 </P>
1032 <P>
1033 If the pattern is not anchored and the <i>firstcharptr</i> argument is not NULL,
1034 it is used to pass back information about the first character of any matched
1035 string (see PCRE_INFO_FIRSTBYTE above).
1036 </P>
1037 <br><a name="SEC13" href="#TOC1">REFERENCE COUNTS</a><br>
1038 <P>
1039 <b>int pcre_refcount(pcre *<i>code</i>, int <i>adjust</i>);</b>
1040 </P>
1041 <P>
1042 The <b>pcre_refcount()</b> function is used to maintain a reference count in the
1043 data block that contains a compiled pattern. It is provided for the benefit of
1044 applications that operate in an object-oriented manner, where different parts
1045 of the application may be using the same compiled pattern, but you want to free
1046 the block when they are all done.
1047 </P>
1048 <P>
1049 When a pattern is compiled, the reference count field is initialized to zero.
1050 It is changed only by calling this function, whose action is to add the
1051 <i>adjust</i> value (which may be positive or negative) to it. The yield of the
1052 function is the new value. However, the value of the count is constrained to
1053 lie between 0 and 65535, inclusive. If the new value is outside these limits,
1054 it is forced to the appropriate limit value.
1055 </P>
1056 <P>
1057 Except when it is zero, the reference count is not correctly preserved if a
1058 pattern is compiled on one host and then transferred to a host whose byte-order
1059 is different. (This seems a highly unlikely scenario.)
1060 </P>
1061 <br><a name="SEC14" href="#TOC1">MATCHING A PATTERN: THE TRADITIONAL FUNCTION</a><br>
1062 <P>
1063 <b>int pcre_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
1064 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
1065 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>);</b>
1066 </P>
1067 <P>
1068 The function <b>pcre_exec()</b> is called to match a subject string against a
1069 compiled pattern, which is passed in the <i>code</i> argument. If the
1070 pattern has been studied, the result of the study should be passed in the
1071 <i>extra</i> argument. This function is the main matching facility of the
1072 library, and it operates in a Perl-like manner. For specialist use there is
1073 also an alternative matching function, which is described
1074 <a href="#dfamatch">below</a>
1075 in the section about the <b>pcre_dfa_exec()</b> function.
1076 </P>
1077 <P>
1078 In most applications, the pattern will have been compiled (and optionally
1079 studied) in the same process that calls <b>pcre_exec()</b>. However, it is
1080 possible to save compiled patterns and study data, and then use them later
1081 in different processes, possibly even on different hosts. For a discussion
1082 about this, see the
1083 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
1084 documentation.
1085 </P>
1086 <P>
1087 Here is an example of a simple call to <b>pcre_exec()</b>:
1088 <pre>
1089 int rc;
1090 int ovector[30];
1091 rc = pcre_exec(
1092 re, /* result of pcre_compile() */
1093 NULL, /* we didn't study the pattern */
1094 "some string", /* the subject string */
1095 11, /* the length of the subject string */
1096 0, /* start at offset 0 in the subject */
1097 0, /* default options */
1098 ovector, /* vector of integers for substring information */
1099 30); /* number of elements (NOT size in bytes) */
1100 <a name="extradata"></a></PRE>
1101 </P>
1102 <br><b>
1103 Extra data for <b>pcre_exec()</b>
1104 </b><br>
1105 <P>
1106 If the <i>extra</i> argument is not NULL, it must point to a <b>pcre_extra</b>
1107 data block. The <b>pcre_study()</b> function returns such a block (when it
1108 doesn't return NULL), but you can also create one for yourself, and pass
1109 additional information in it. The <b>pcre_extra</b> block contains the following
1110 fields (not necessarily in this order):
1111 <pre>
1112 unsigned long int <i>flags</i>;
1113 void *<i>study_data</i>;
1114 unsigned long int <i>match_limit</i>;
1115 unsigned long int <i>match_limit_recursion</i>;
1116 void *<i>callout_data</i>;
1117 const unsigned char *<i>tables</i>;
1118 </pre>
1119 The <i>flags</i> field is a bitmap that specifies which of the other fields
1120 are set. The flag bits are:
1121 <pre>
1127 </pre>
1128 Other flag bits should be set to zero. The <i>study_data</i> field is set in the
1129 <b>pcre_extra</b> block that is returned by <b>pcre_study()</b>, together with
1130 the appropriate flag bit. You should not set this yourself, but you may add to
1131 the block by setting the other fields and their corresponding flag bits.
1132 </P>
1133 <P>
1134 The <i>match_limit</i> field provides a means of preventing PCRE from using up a
1135 vast amount of resources when running patterns that are not going to match,
1136 but which have a very large number of possibilities in their search trees. The
1137 classic example is the use of nested unlimited repeats.
1138 </P>
1139 <P>
1140 Internally, PCRE uses a function called <b>match()</b> which it calls repeatedly
1141 (sometimes recursively). The limit set by <i>match_limit</i> is imposed on the
1142 number of times this function is called during a match, which has the effect of
1143 limiting the amount of backtracking that can take place. For patterns that are
1144 not anchored, the count restarts from zero for each position in the subject
1145 string.
1146 </P>
1147 <P>
1148 The default value for the limit can be set when PCRE is built; the default
1149 default is 10 million, which handles all but the most extreme cases. You can
1150 override the default by suppling <b>pcre_exec()</b> with a <b>pcre_extra</b>
1151 block in which <i>match_limit</i> is set, and PCRE_EXTRA_MATCH_LIMIT is set in
1152 the <i>flags</i> field. If the limit is exceeded, <b>pcre_exec()</b> returns
1154 </P>
1155 <P>
1156 The <i>match_limit_recursion</i> field is similar to <i>match_limit</i>, but
1157 instead of limiting the total number of times that <b>match()</b> is called, it
1158 limits the depth of recursion. The recursion depth is a smaller number than the
1159 total number of calls, because not all calls to <b>match()</b> are recursive.
1160 This limit is of use only if it is set smaller than <i>match_limit</i>.
1161 </P>
1162 <P>
1163 Limiting the recursion depth limits the amount of stack that can be used, or,
1164 when PCRE has been compiled to use memory on the heap instead of the stack, the
1165 amount of heap memory that can be used.
1166 </P>
1167 <P>
1168 The default value for <i>match_limit_recursion</i> can be set when PCRE is
1169 built; the default default is the same value as the default for
1170 <i>match_limit</i>. You can override the default by suppling <b>pcre_exec()</b>
1171 with a <b>pcre_extra</b> block in which <i>match_limit_recursion</i> is set, and
1172 PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the <i>flags</i> field. If the limit
1173 is exceeded, <b>pcre_exec()</b> returns PCRE_ERROR_RECURSIONLIMIT.
1174 </P>
1175 <P>
1176 The <i>pcre_callout</i> field is used in conjunction with the "callout" feature,
1177 which is described in the
1178 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1179 documentation.
1180 </P>
1181 <P>
1182 The <i>tables</i> field is used to pass a character tables pointer to
1183 <b>pcre_exec()</b>; this overrides the value that is stored with the compiled
1184 pattern. A non-NULL value is stored with the compiled pattern only if custom
1185 tables were supplied to <b>pcre_compile()</b> via its <i>tableptr</i> argument.
1186 If NULL is passed to <b>pcre_exec()</b> using this mechanism, it forces PCRE's
1187 internal tables to be used. This facility is helpful when re-using patterns
1188 that have been saved after compiling with an external set of tables, because
1189 the external tables might be at a different address when <b>pcre_exec()</b> is
1190 called. See the
1191 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
1192 documentation for a discussion of saving compiled patterns for later use.
1193 <a name="execoptions"></a></P>
1194 <br><b>
1195 Option bits for <b>pcre_exec()</b>
1196 </b><br>
1197 <P>
1198 The unused bits of the <i>options</i> argument for <b>pcre_exec()</b> must be
1199 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_<i>xxx</i>,
1201 <pre>
1203 </pre>
1204 The PCRE_ANCHORED option limits <b>pcre_exec()</b> to matching at the first
1205 matching position. If a pattern was compiled with PCRE_ANCHORED, or turned out
1206 to be anchored by virtue of its contents, it cannot be made unachored at
1207 matching time.
1208 <pre>
1214 </pre>
1215 These options override the newline definition that was chosen or defaulted when
1216 the pattern was compiled. For details, see the description of
1217 <b>pcre_compile()</b> above. During matching, the newline choice affects the
1218 behaviour of the dot, circumflex, and dollar metacharacters. It may also alter
1219 the way the match position is advanced after a match failure for an unanchored
1220 pattern.
1221 </P>
1222 <P>
1224 match attempt for an unanchored pattern fails when the current position is at a
1225 CRLF sequence, and the pattern contains no explicit matches for CR or NL
1226 characters, the match position is advanced by two characters instead of one, in
1227 other words, to after the CRLF.
1228 </P>
1229 <P>
1230 The above rule is a compromise that makes the most common cases work as
1231 expected. For example, if the pattern is .+A (and the PCRE_DOTALL option is not
1232 set), it does not match the string "\r\nA" because, after failing at the
1233 start, it skips both the CR and the LF before retrying. However, the pattern
1234 [\r\n]A does match that string, because it contains an explicit CR or LF
1235 reference, and so advances only by one character after the first failure.
1236 Note than an explicit CR or LF reference occurs for negated character classes
1237 such as [^X] because they can match CR or LF characters.
1238 </P>
1239 <P>
1240 Notwithstanding the above, anomalous effects may still occur when CRLF is a
1241 valid newline sequence and explicit \r or \n escapes appear in the pattern.
1242 <pre>
1244 </pre>
1245 This option specifies that first character of the subject string is not the
1246 beginning of a line, so the circumflex metacharacter should not match before
1247 it. Setting this without PCRE_MULTILINE (at compile time) causes circumflex
1248 never to match. This option affects only the behaviour of the circumflex
1249 metacharacter. It does not affect \A.
1250 <pre>
1252 </pre>
1253 This option specifies that the end of the subject string is not the end of a
1254 line, so the dollar metacharacter should not match it nor (except in multiline
1255 mode) a newline immediately before it. Setting this without PCRE_MULTILINE (at
1256 compile time) causes dollar never to match. This option affects only the
1257 behaviour of the dollar metacharacter. It does not affect \Z or \z.
1258 <pre>
1260 </pre>
1261 An empty string is not considered to be a valid match if this option is set. If
1262 there are alternatives in the pattern, they are tried. If all the alternatives
1263 match the empty string, the entire match fails. For example, if the pattern
1264 <pre>
1265 a?b?
1266 </pre>
1267 is applied to a string not beginning with "a" or "b", it matches the empty
1268 string at the start of the subject. With PCRE_NOTEMPTY set, this match is not
1269 valid, so PCRE searches further into the string for occurrences of "a" or "b".
1270 </P>
1271 <P>
1272 Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a special case
1273 of a pattern match of the empty string within its <b>split()</b> function, and
1274 when using the /g modifier. It is possible to emulate Perl's behaviour after
1275 matching a null string by first trying the match again at the same offset with
1276 PCRE_NOTEMPTY and PCRE_ANCHORED, and then if that fails by advancing the
1277 starting offset (see below) and trying an ordinary match again. There is some
1278 code that demonstrates how to do this in the <i>pcredemo.c</i> sample program.
1279 <pre>
1281 </pre>
1282 When PCRE_UTF8 is set at compile time, the validity of the subject as a UTF-8
1283 string is automatically checked when <b>pcre_exec()</b> is subsequently called.
1284 The value of <i>startoffset</i> is also checked to ensure that it points to the
1285 start of a UTF-8 character. There is a discussion about the validity of UTF-8
1286 strings in the
1287 <a href="pcre.html#utf8strings">section on UTF-8 support</a>
1288 in the main
1289 <a href="pcre.html"><b>pcre</b></a>
1290 page. If an invalid UTF-8 sequence of bytes is found, <b>pcre_exec()</b> returns
1291 the error PCRE_ERROR_BADUTF8. If <i>startoffset</i> contains an invalid value,
1292 PCRE_ERROR_BADUTF8_OFFSET is returned.
1293 </P>
1294 <P>
1295 If you already know that your subject is valid, and you want to skip these
1296 checks for performance reasons, you can set the PCRE_NO_UTF8_CHECK option when
1297 calling <b>pcre_exec()</b>. You might want to do this for the second and
1298 subsequent calls to <b>pcre_exec()</b> if you are making repeated calls to find
1299 all the matches in a single subject string. However, you should be sure that
1300 the value of <i>startoffset</i> points to the start of a UTF-8 character. When
1301 PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid UTF-8 string as a
1302 subject, or a value of <i>startoffset</i> that does not point to the start of a
1303 UTF-8 character, is undefined. Your program may crash.
1304 <pre>
1306 </pre>
1307 This option turns on the partial matching feature. If the subject string fails
1308 to match the pattern, but at some point during the matching process the end of
1309 the subject was reached (that is, the subject partially matches the pattern and
1310 the failure to match occurred only because there were not enough subject
1311 characters), <b>pcre_exec()</b> returns PCRE_ERROR_PARTIAL instead of
1312 PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is used, there are restrictions on what
1313 may appear in the pattern. These are discussed in the
1314 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1315 documentation.
1316 </P>
1317 <br><b>
1318 The string to be matched by <b>pcre_exec()</b>
1319 </b><br>
1320 <P>
1321 The subject string is passed to <b>pcre_exec()</b> as a pointer in
1322 <i>subject</i>, a length in <i>length</i>, and a starting byte offset in
1323 <i>startoffset</i>. In UTF-8 mode, the byte offset must point to the start of a
1324 UTF-8 character. Unlike the pattern string, the subject may contain binary zero
1325 bytes. When the starting offset is zero, the search for a match starts at the
1326 beginning of the subject, and this is by far the most common case.
1327 </P>
1328 <P>
1329 A non-zero starting offset is useful when searching for another match in the
1330 same subject by calling <b>pcre_exec()</b> again after a previous success.
1331 Setting <i>startoffset</i> differs from just passing over a shortened string and
1332 setting PCRE_NOTBOL in the case of a pattern that begins with any kind of
1333 lookbehind. For example, consider the pattern
1334 <pre>
1335 \Biss\B
1336 </pre>
1337 which finds occurrences of "iss" in the middle of words. (\B matches only if
1338 the current position in the subject is not a word boundary.) When applied to
1339 the string "Mississipi" the first call to <b>pcre_exec()</b> finds the first
1340 occurrence. If <b>pcre_exec()</b> is called again with just the remainder of the
1341 subject, namely "issipi", it does not match, because \B is always false at the
1342 start of the subject, which is deemed to be a word boundary. However, if
1343 <b>pcre_exec()</b> is passed the entire string again, but with <i>startoffset</i>
1344 set to 4, it finds the second occurrence of "iss" because it is able to look
1345 behind the starting point to discover that it is preceded by a letter.
1346 </P>
1347 <P>
1348 If a non-zero starting offset is passed when the pattern is anchored, one
1349 attempt to match at the given offset is made. This can only succeed if the
1350 pattern does not require the match to be at the start of the subject.
1351 </P>
1352 <br><b>
1353 How <b>pcre_exec()</b> returns captured substrings
1354 </b><br>
1355 <P>
1356 In general, a pattern matches a certain portion of the subject, and in
1357 addition, further substrings from the subject may be picked out by parts of the
1358 pattern. Following the usage in Jeffrey Friedl's book, this is called
1359 "capturing" in what follows, and the phrase "capturing subpattern" is used for
1360 a fragment of a pattern that picks out a substring. PCRE supports several other
1361 kinds of parenthesized subpattern that do not cause substrings to be captured.
1362 </P>
1363 <P>
1364 Captured substrings are returned to the caller via a vector of integer offsets
1365 whose address is passed in <i>ovector</i>. The number of elements in the vector
1366 is passed in <i>ovecsize</i>, which must be a non-negative number. <b>Note</b>:
1367 this argument is NOT the size of <i>ovector</i> in bytes.
1368 </P>
1369 <P>
1370 The first two-thirds of the vector is used to pass back captured substrings,
1371 each substring using a pair of integers. The remaining third of the vector is
1372 used as workspace by <b>pcre_exec()</b> while matching capturing subpatterns,
1373 and is not available for passing back information. The length passed in
1374 <i>ovecsize</i> should always be a multiple of three. If it is not, it is
1375 rounded down.
1376 </P>
1377 <P>
1378 When a match is successful, information about captured substrings is returned
1379 in pairs of integers, starting at the beginning of <i>ovector</i>, and
1380 continuing up to two-thirds of its length at the most. The first element of a
1381 pair is set to the offset of the first character in a substring, and the second
1382 is set to the offset of the first character after the end of a substring. The
1383 first pair, <i>ovector[0]</i> and <i>ovector[1]</i>, identify the portion of the
1384 subject string matched by the entire pattern. The next pair is used for the
1385 first capturing subpattern, and so on. The value returned by <b>pcre_exec()</b>
1386 is one more than the highest numbered pair that has been set. For example, if
1387 two substrings have been captured, the returned value is 3. If there are no
1388 capturing subpatterns, the return value from a successful match is 1,
1389 indicating that just the first pair of offsets has been set.
1390 </P>
1391 <P>
1392 If a capturing subpattern is matched repeatedly, it is the last portion of the
1393 string that it matched that is returned.
1394 </P>
1395 <P>
1396 If the vector is too small to hold all the captured substring offsets, it is
1397 used as far as possible (up to two-thirds of its length), and the function
1398 returns a value of zero. In particular, if the substring offsets are not of
1399 interest, <b>pcre_exec()</b> may be called with <i>ovector</i> passed as NULL and
1400 <i>ovecsize</i> as zero. However, if the pattern contains back references and
1401 the <i>ovector</i> is not big enough to remember the related substrings, PCRE
1402 has to get additional memory for use during matching. Thus it is usually
1403 advisable to supply an <i>ovector</i>.
1404 </P>
1405 <P>
1406 The <b>pcre_info()</b> function can be used to find out how many capturing
1407 subpatterns there are in a compiled pattern. The smallest size for
1408 <i>ovector</i> that will allow for <i>n</i> captured substrings, in addition to
1409 the offsets of the substring matched by the whole pattern, is (<i>n</i>+1)*3.
1410 </P>
1411 <P>
1412 It is possible for capturing subpattern number <i>n+1</i> to match some part of
1413 the subject when subpattern <i>n</i> has not been used at all. For example, if
1414 the string "abc" is matched against the pattern (a|(z))(bc) the return from the
1415 function is 4, and subpatterns 1 and 3 are matched, but 2 is not. When this
1416 happens, both values in the offset pairs corresponding to unused subpatterns
1417 are set to -1.
1418 </P>
1419 <P>
1420 Offset values that correspond to unused subpatterns at the end of the
1421 expression are also set to -1. For example, if the string "abc" is matched
1422 against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not matched. The
1423 return from the function is 2, because the highest used capturing subpattern
1424 number is 1. However, you can refer to the offsets for the second and third
1425 capturing subpatterns if you wish (assuming the vector is large enough, of
1426 course).
1427 </P>
1428 <P>
1429 Some convenience functions are provided for extracting the captured substrings
1430 as separate strings. These are described below.
1431 <a name="errorlist"></a></P>
1432 <br><b>
1433 Error return values from <b>pcre_exec()</b>
1434 </b><br>
1435 <P>
1436 If <b>pcre_exec()</b> fails, it returns a negative number. The following are
1437 defined in the header file:
1438 <pre>
1440 </pre>
1441 The subject string did not match the pattern.
1442 <pre>
1444 </pre>
1445 Either <i>code</i> or <i>subject</i> was passed as NULL, or <i>ovector</i> was
1446 NULL and <i>ovecsize</i> was not zero.
1447 <pre>
1449 </pre>
1450 An unrecognized bit was set in the <i>options</i> argument.
1451 <pre>
1453 </pre>
1454 PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch
1455 the case when it is passed a junk pointer and to detect when a pattern that was
1456 compiled in an environment of one endianness is run in an environment with the
1457 other endianness. This is the error that PCRE gives when the magic number is
1458 not present.
1459 <pre>
1461 </pre>
1462 While running the pattern match, an unknown item was encountered in the
1463 compiled pattern. This error could be caused by a bug in PCRE or by overwriting
1464 of the compiled pattern.
1465 <pre>
1467 </pre>
1468 If a pattern contains back references, but the <i>ovector</i> that is passed to
1469 <b>pcre_exec()</b> is not big enough to remember the referenced substrings, PCRE
1470 gets a block of memory at the start of matching to use for this purpose. If the
1471 call via <b>pcre_malloc()</b> fails, this error is given. The memory is
1472 automatically freed at the end of matching.
1473 <pre>
1475 </pre>
1476 This error is used by the <b>pcre_copy_substring()</b>,
1477 <b>pcre_get_substring()</b>, and <b>pcre_get_substring_list()</b> functions (see
1478 below). It is never returned by <b>pcre_exec()</b>.
1479 <pre>
1481 </pre>
1482 The backtracking limit, as specified by the <i>match_limit</i> field in a
1483 <b>pcre_extra</b> structure (or defaulted) was reached. See the description
1484 above.
1485 <pre>
1487 </pre>
1488 This error is never generated by <b>pcre_exec()</b> itself. It is provided for
1489 use by callout functions that want to yield a distinctive error code. See the
1490 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1491 documentation for details.
1492 <pre>
1494 </pre>
1495 A string that contains an invalid UTF-8 byte sequence was passed as a subject.
1496 <pre>
1498 </pre>
1499 The UTF-8 byte sequence that was passed as a subject was valid, but the value
1500 of <i>startoffset</i> did not point to the beginning of a UTF-8 character.
1501 <pre>
1503 </pre>
1504 The subject string did not match, but it did match partially. See the
1505 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1506 documentation for details of partial matching.
1507 <pre>
1509 </pre>
1510 The PCRE_PARTIAL option was used with a compiled pattern containing items that
1511 are not supported for partial matching. See the
1512 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1513 documentation for details of partial matching.
1514 <pre>
1516 </pre>
1517 An unexpected internal error has occurred. This error could be caused by a bug
1518 in PCRE or by overwriting of the compiled pattern.
1519 <pre>
1521 </pre>
1522 This error is given if the value of the <i>ovecsize</i> argument is negative.
1523 <pre>
1525 </pre>
1526 The internal recursion limit, as specified by the <i>match_limit_recursion</i>
1527 field in a <b>pcre_extra</b> structure (or defaulted) was reached. See the
1528 description above.
1529 <pre>
1531 </pre>
1532 An invalid combination of PCRE_NEWLINE_<i>xxx</i> options was given.
1533 </P>
1534 <P>
1535 Error numbers -16 to -20 and -22 are not used by <b>pcre_exec()</b>.
1536 </P>
1537 <br><a name="SEC15" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NUMBER</a><br>
1538 <P>
1539 <b>int pcre_copy_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1540 <b>int <i>stringcount</i>, int <i>stringnumber</i>, char *<i>buffer</i>,</b>
1541 <b>int <i>buffersize</i>);</b>
1542 </P>
1543 <P>
1544 <b>int pcre_get_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1545 <b>int <i>stringcount</i>, int <i>stringnumber</i>,</b>
1546 <b>const char **<i>stringptr</i>);</b>
1547 </P>
1548 <P>
1549 <b>int pcre_get_substring_list(const char *<i>subject</i>,</b>
1550 <b>int *<i>ovector</i>, int <i>stringcount</i>, const char ***<i>listptr</i>);</b>
1551 </P>
1552 <P>
1553 Captured substrings can be accessed directly by using the offsets returned by
1554 <b>pcre_exec()</b> in <i>ovector</i>. For convenience, the functions
1555 <b>pcre_copy_substring()</b>, <b>pcre_get_substring()</b>, and
1556 <b>pcre_get_substring_list()</b> are provided for extracting captured substrings
1557 as new, separate, zero-terminated strings. These functions identify substrings
1558 by number. The next section describes functions for extracting named
1559 substrings.
1560 </P>
1561 <P>
1562 A substring that contains a binary zero is correctly extracted and has a
1563 further zero added on the end, but the result is not, of course, a C string.
1564 However, you can process such a string by referring to the length that is
1565 returned by <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>.
1566 Unfortunately, the interface to <b>pcre_get_substring_list()</b> is not adequate
1567 for handling strings containing binary zeros, because the end of the final
1568 string is not independently indicated.
1569 </P>
1570 <P>
1571 The first three arguments are the same for all three of these functions:
1572 <i>subject</i> is the subject string that has just been successfully matched,
1573 <i>ovector</i> is a pointer to the vector of integer offsets that was passed to
1574 <b>pcre_exec()</b>, and <i>stringcount</i> is the number of substrings that were
1575 captured by the match, including the substring that matched the entire regular
1576 expression. This is the value returned by <b>pcre_exec()</b> if it is greater
1577 than zero. If <b>pcre_exec()</b> returned zero, indicating that it ran out of
1578 space in <i>ovector</i>, the value passed as <i>stringcount</i> should be the
1579 number of elements in the vector divided by three.
1580 </P>
1581 <P>
1582 The functions <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>
1583 extract a single substring, whose number is given as <i>stringnumber</i>. A
1584 value of zero extracts the substring that matched the entire pattern, whereas
1585 higher values extract the captured substrings. For <b>pcre_copy_substring()</b>,
1586 the string is placed in <i>buffer</i>, whose length is given by
1587 <i>buffersize</i>, while for <b>pcre_get_substring()</b> a new block of memory is
1588 obtained via <b>pcre_malloc</b>, and its address is returned via
1589 <i>stringptr</i>. The yield of the function is the length of the string, not
1590 including the terminating zero, or one of these error codes:
1591 <pre>
1593 </pre>
1594 The buffer was too small for <b>pcre_copy_substring()</b>, or the attempt to get
1595 memory failed for <b>pcre_get_substring()</b>.
1596 <pre>
1598 </pre>
1599 There is no substring whose number is <i>stringnumber</i>.
1600 </P>
1601 <P>
1602 The <b>pcre_get_substring_list()</b> function extracts all available substrings
1603 and builds a list of pointers to them. All this is done in a single block of
1604 memory that is obtained via <b>pcre_malloc</b>. The address of the memory block
1605 is returned via <i>listptr</i>, which is also the start of the list of string
1606 pointers. The end of the list is marked by a NULL pointer. The yield of the
1607 function is zero if all went well, or the error code
1608 <pre>
1610 </pre>
1611 if the attempt to get the memory block failed.
1612 </P>
1613 <P>
1614 When any of these functions encounter a substring that is unset, which can
1615 happen when capturing subpattern number <i>n+1</i> matches some part of the
1616 subject, but subpattern <i>n</i> has not been used at all, they return an empty
1617 string. This can be distinguished from a genuine zero-length substring by
1618 inspecting the appropriate offset in <i>ovector</i>, which is negative for unset
1619 substrings.
1620 </P>
1621 <P>
1622 The two convenience functions <b>pcre_free_substring()</b> and
1623 <b>pcre_free_substring_list()</b> can be used to free the memory returned by
1624 a previous call of <b>pcre_get_substring()</b> or
1625 <b>pcre_get_substring_list()</b>, respectively. They do nothing more than call
1626 the function pointed to by <b>pcre_free</b>, which of course could be called
1627 directly from a C program. However, PCRE is used in some situations where it is
1628 linked via a special interface to another programming language that cannot use
1629 <b>pcre_free</b> directly; it is for these cases that the functions are
1630 provided.
1631 </P>
1632 <br><a name="SEC16" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NAME</a><br>
1633 <P>
1634 <b>int pcre_get_stringnumber(const pcre *<i>code</i>,</b>
1635 <b>const char *<i>name</i>);</b>
1636 </P>
1637 <P>
1638 <b>int pcre_copy_named_substring(const pcre *<i>code</i>,</b>
1639 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
1640 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
1641 <b>char *<i>buffer</i>, int <i>buffersize</i>);</b>
1642 </P>
1643 <P>
1644 <b>int pcre_get_named_substring(const pcre *<i>code</i>,</b>
1645 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
1646 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
1647 <b>const char **<i>stringptr</i>);</b>
1648 </P>
1649 <P>
1650 To extract a substring by name, you first have to find associated number.
1651 For example, for this pattern
1652 <pre>
1653 (a+)b(?&#60;xxx&#62;\d+)...
1654 </pre>
1655 the number of the subpattern called "xxx" is 2. If the name is known to be
1656 unique (PCRE_DUPNAMES was not set), you can find the number from the name by
1657 calling <b>pcre_get_stringnumber()</b>. The first argument is the compiled
1658 pattern, and the second is the name. The yield of the function is the
1659 subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no subpattern of
1660 that name.
1661 </P>
1662 <P>
1663 Given the number, you can extract the substring directly, or use one of the
1664 functions described in the previous section. For convenience, there are also
1665 two functions that do the whole job.
1666 </P>
1667 <P>
1668 Most of the arguments of <b>pcre_copy_named_substring()</b> and
1669 <b>pcre_get_named_substring()</b> are the same as those for the similarly named
1670 functions that extract by number. As these are described in the previous
1671 section, they are not re-described here. There are just two differences:
1672 </P>
1673 <P>
1674 First, instead of a substring number, a substring name is given. Second, there
1675 is an extra argument, given at the start, which is a pointer to the compiled
1676 pattern. This is needed in order to gain access to the name-to-number
1677 translation table.
1678 </P>
1679 <P>
1680 These functions call <b>pcre_get_stringnumber()</b>, and if it succeeds, they
1681 then call <b>pcre_copy_substring()</b> or <b>pcre_get_substring()</b>, as
1682 appropriate. <b>NOTE:</b> If PCRE_DUPNAMES is set and there are duplicate names,
1683 the behaviour may not be what you want (see the next section).
1684 </P>
1685 <br><a name="SEC17" href="#TOC1">DUPLICATE SUBPATTERN NAMES</a><br>
1686 <P>
1687 <b>int pcre_get_stringtable_entries(const pcre *<i>code</i>,</b>
1688 <b>const char *<i>name</i>, char **<i>first</i>, char **<i>last</i>);</b>
1689 </P>
1690 <P>
1691 When a pattern is compiled with the PCRE_DUPNAMES option, names for subpatterns
1692 are not required to be unique. Normally, patterns with duplicate names are such
1693 that in any one match, only one of the named subpatterns participates. An
1694 example is shown in the
1695 <a href="pcrepattern.html"><b>pcrepattern</b></a>
1696 documentation.
1697 </P>
1698 <P>
1699 When duplicates are present, <b>pcre_copy_named_substring()</b> and
1700 <b>pcre_get_named_substring()</b> return the first substring corresponding to
1701 the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING (-7) is
1702 returned; no data is returned. The <b>pcre_get_stringnumber()</b> function
1703 returns one of the numbers that are associated with the name, but it is not
1704 defined which it is.
1705 </P>
1706 <P>
1707 If you want to get full details of all captured substrings for a given name,
1708 you must use the <b>pcre_get_stringtable_entries()</b> function. The first
1709 argument is the compiled pattern, and the second is the name. The third and
1710 fourth are pointers to variables which are updated by the function. After it
1711 has run, they point to the first and last entries in the name-to-number table
1712 for the given name. The function itself returns the length of each entry, or
1713 PCRE_ERROR_NOSUBSTRING (-7) if there are none. The format of the table is
1714 described above in the section entitled <i>Information about a pattern</i>.
1715 Given all the relevant entries for the name, you can extract each of their
1716 numbers, and hence the captured data, if any.
1717 </P>
1718 <br><a name="SEC18" href="#TOC1">FINDING ALL POSSIBLE MATCHES</a><br>
1719 <P>
1720 The traditional matching function uses a similar algorithm to Perl, which stops
1721 when it finds the first match, starting at a given point in the subject. If you
1722 want to find all possible matches, or the longest possible match, consider
1723 using the alternative matching function (see below) instead. If you cannot use
1724 the alternative function, but still need to find all possible matches, you
1725 can kludge it up by making use of the callout facility, which is described in
1726 the
1727 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1728 documentation.
1729 </P>
1730 <P>
1731 What you have to do is to insert a callout right at the end of the pattern.
1732 When your callout function is called, extract and save the current matched
1733 substring. Then return 1, which forces <b>pcre_exec()</b> to backtrack and try
1734 other alternatives. Ultimately, when it runs out of matches, <b>pcre_exec()</b>
1735 will yield PCRE_ERROR_NOMATCH.
1736 <a name="dfamatch"></a></P>
1737 <br><a name="SEC19" href="#TOC1">MATCHING A PATTERN: THE ALTERNATIVE FUNCTION</a><br>
1738 <P>
1739 <b>int pcre_dfa_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
1740 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
1741 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>,</b>
1742 <b>int *<i>workspace</i>, int <i>wscount</i>);</b>
1743 </P>
1744 <P>
1745 The function <b>pcre_dfa_exec()</b> is called to match a subject string against
1746 a compiled pattern, using a matching algorithm that scans the subject string
1747 just once, and does not backtrack. This has different characteristics to the
1748 normal algorithm, and is not compatible with Perl. Some of the features of PCRE
1749 patterns are not supported. Nevertheless, there are times when this kind of
1750 matching can be useful. For a discussion of the two matching algorithms, see
1751 the
1752 <a href="pcrematching.html"><b>pcrematching</b></a>
1753 documentation.
1754 </P>
1755 <P>
1756 The arguments for the <b>pcre_dfa_exec()</b> function are the same as for
1757 <b>pcre_exec()</b>, plus two extras. The <i>ovector</i> argument is used in a
1758 different way, and this is described below. The other common arguments are used
1759 in the same way as for <b>pcre_exec()</b>, so their description is not repeated
1760 here.
1761 </P>
1762 <P>
1763 The two additional arguments provide workspace for the function. The workspace
1764 vector should contain at least 20 elements. It is used for keeping track of
1765 multiple paths through the pattern tree. More workspace will be needed for
1766 patterns and subjects where there are a lot of potential matches.
1767 </P>
1768 <P>
1769 Here is an example of a simple call to <b>pcre_dfa_exec()</b>:
1770 <pre>
1771 int rc;
1772 int ovector[10];
1773 int wspace[20];
1774 rc = pcre_dfa_exec(
1775 re, /* result of pcre_compile() */
1776 NULL, /* we didn't study the pattern */
1777 "some string", /* the subject string */
1778 11, /* the length of the subject string */
1779 0, /* start at offset 0 in the subject */
1780 0, /* default options */
1781 ovector, /* vector of integers for substring information */
1782 10, /* number of elements (NOT size in bytes) */
1783 wspace, /* working space vector */
1784 20); /* number of elements (NOT size in bytes) */
1785 </PRE>
1786 </P>
1787 <br><b>
1788 Option bits for <b>pcre_dfa_exec()</b>
1789 </b><br>
1790 <P>
1791 The unused bits of the <i>options</i> argument for <b>pcre_dfa_exec()</b> must be
1792 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_<i>xxx</i>,
1794 PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last three of these are
1795 the same as for <b>pcre_exec()</b>, so their description is not repeated here.
1796 <pre>
1798 </pre>
1799 This has the same general effect as it does for <b>pcre_exec()</b>, but the
1800 details are slightly different. When PCRE_PARTIAL is set for
1801 <b>pcre_dfa_exec()</b>, the return code PCRE_ERROR_NOMATCH is converted into
1802 PCRE_ERROR_PARTIAL if the end of the subject is reached, there have been no
1803 complete matches, but there is still at least one matching possibility. The
1804 portion of the string that provided the partial match is set as the first
1805 matching string.
1806 <pre>
1808 </pre>
1809 Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to stop as
1810 soon as it has found one match. Because of the way the alternative algorithm
1811 works, this is necessarily the shortest possible match at the first possible
1812 matching point in the subject string.
1813 <pre>
1815 </pre>
1816 When <b>pcre_dfa_exec()</b> is called with the PCRE_PARTIAL option, and returns
1817 a partial match, it is possible to call it again, with additional subject
1818 characters, and have it continue with the same match. The PCRE_DFA_RESTART
1819 option requests this action; when it is set, the <i>workspace</i> and
1820 <i>wscount</i> options must reference the same vector as before because data
1821 about the match so far is left in them after a partial match. There is more
1822 discussion of this facility in the
1823 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1824 documentation.
1825 </P>
1826 <br><b>
1827 Successful returns from <b>pcre_dfa_exec()</b>
1828 </b><br>
1829 <P>
1830 When <b>pcre_dfa_exec()</b> succeeds, it may have matched more than one
1831 substring in the subject. Note, however, that all the matches from one run of
1832 the function start at the same point in the subject. The shorter matches are
1833 all initial substrings of the longer matches. For example, if the pattern
1834 <pre>
1835 &#60;.*&#62;
1836 </pre>
1837 is matched against the string
1838 <pre>
1839 This is &#60;something&#62; &#60;something else&#62; &#60;something further&#62; no more
1840 </pre>
1841 the three matched strings are
1842 <pre>
1843 &#60;something&#62;
1844 &#60;something&#62; &#60;something else&#62;
1845 &#60;something&#62; &#60;something else&#62; &#60;something further&#62;
1846 </pre>
1847 On success, the yield of the function is a number greater than zero, which is
1848 the number of matched substrings. The substrings themselves are returned in
1849 <i>ovector</i>. Each string uses two elements; the first is the offset to the
1850 start, and the second is the offset to the end. In fact, all the strings have
1851 the same start offset. (Space could have been saved by giving this only once,
1852 but it was decided to retain some compatibility with the way <b>pcre_exec()</b>
1853 returns data, even though the meaning of the strings is different.)
1854 </P>
1855 <P>
1856 The strings are returned in reverse order of length; that is, the longest
1857 matching string is given first. If there were too many matches to fit into
1858 <i>ovector</i>, the yield of the function is zero, and the vector is filled with
1859 the longest matches.
1860 </P>
1861 <br><b>
1862 Error returns from <b>pcre_dfa_exec()</b>
1863 </b><br>
1864 <P>
1865 The <b>pcre_dfa_exec()</b> function returns a negative number when it fails.
1866 Many of the errors are the same as for <b>pcre_exec()</b>, and these are
1867 described
1868 <a href="#errorlist">above.</a>
1869 There are in addition the following errors that are specific to
1870 <b>pcre_dfa_exec()</b>:
1871 <pre>
1873 </pre>
1874 This return is given if <b>pcre_dfa_exec()</b> encounters an item in the pattern
1875 that it does not support, for instance, the use of \C or a back reference.
1876 <pre>
1878 </pre>
1879 This return is given if <b>pcre_dfa_exec()</b> encounters a condition item that
1880 uses a back reference for the condition, or a test for recursion in a specific
1881 group. These are not supported.
1882 <pre>
1884 </pre>
1885 This return is given if <b>pcre_dfa_exec()</b> is called with an <i>extra</i>
1886 block that contains a setting of the <i>match_limit</i> field. This is not
1887 supported (it is meaningless).
1888 <pre>
1890 </pre>
1891 This return is given if <b>pcre_dfa_exec()</b> runs out of space in the
1892 <i>workspace</i> vector.
1893 <pre>
1895 </pre>
1896 When a recursive subpattern is processed, the matching function calls itself
1897 recursively, using private vectors for <i>ovector</i> and <i>workspace</i>. This
1898 error is given if the output vector is not large enough. This should be
1899 extremely rare, as a vector of size 1000 is used.
1900 </P>
1901 <br><a name="SEC20" href="#TOC1">SEE ALSO</a><br>
1902 <P>
1903 <b>pcrebuild</b>(3), <b>pcrecallout</b>(3), <b>pcrecpp(3)</b>(3),
1904 <b>pcrematching</b>(3), <b>pcrepartial</b>(3), <b>pcreposix</b>(3),
1905 <b>pcreprecompile</b>(3), <b>pcresample</b>(3), <b>pcrestack</b>(3).
1906 </P>
1907 <br><a name="SEC21" href="#TOC1">AUTHOR</a><br>
1908 <P>
1909 Philip Hazel
1910 <br>
1911 University Computing Service
1912 <br>
1913 Cambridge CB2 3QH, England.
1914 <br>
1915 </P>
1916 <br><a name="SEC22" href="#TOC1">REVISION</a><br>
1917 <P>
1918 Last updated: 21 August 2007
1919 <br>
1920 Copyright &copy; 1997-2007 University of Cambridge.
1921 <br>
1922 <p>
1923 Return to the <a href="index.html">PCRE index page</a>.
1924 </p>


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