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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 </P>
247 <br><a name="SEC3" href="#TOC1">NEWLINES</a><br>
248 <P>
249 PCRE supports five different conventions for indicating line breaks in
250 strings: a single CR (carriage return) character, a single LF (linefeed)
251 character, the two-character sequence CRLF, any of the three preceding, or any
252 Unicode newline sequence. The Unicode newline sequences are the three just
253 mentioned, plus the single characters VT (vertical tab, U+000B), FF (formfeed,
254 U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS
255 (paragraph separator, U+2029).
256 </P>
257 <P>
258 Each of the first three conventions is used by at least one operating system as
259 its standard newline sequence. When PCRE is built, a default can be specified.
260 The default default is LF, which is the Unix standard. When PCRE is run, the
261 default can be overridden, either when a pattern is compiled, or when it is
262 matched.
263 </P>
264 <P>
265 In the PCRE documentation the word "newline" is used to mean "the character or
266 pair of characters that indicate a line break". The choice of newline
267 convention affects the handling of the dot, circumflex, and dollar
268 metacharacters, the handling of #-comments in /x mode, and, when CRLF is a
269 recognized line ending sequence, the match position advancement for a
270 non-anchored pattern. The choice of newline convention does not affect the
271 interpretation of the \n or \r escape sequences.
272 </P>
273 <br><a name="SEC4" href="#TOC1">MULTITHREADING</a><br>
274 <P>
275 The PCRE functions can be used in multi-threading applications, with the
276 proviso that the memory management functions pointed to by <b>pcre_malloc</b>,
277 <b>pcre_free</b>, <b>pcre_stack_malloc</b>, and <b>pcre_stack_free</b>, and the
278 callout function pointed to by <b>pcre_callout</b>, are shared by all threads.
279 </P>
280 <P>
281 The compiled form of a regular expression is not altered during matching, so
282 the same compiled pattern can safely be used by several threads at once.
283 </P>
284 <br><a name="SEC5" href="#TOC1">SAVING PRECOMPILED PATTERNS FOR LATER USE</a><br>
285 <P>
286 The compiled form of a regular expression can be saved and re-used at a later
287 time, possibly by a different program, and even on a host other than the one on
288 which it was compiled. Details are given in the
289 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
290 documentation. However, compiling a regular expression with one version of PCRE
291 for use with a different version is not guaranteed to work and may cause
292 crashes.
293 </P>
294 <br><a name="SEC6" href="#TOC1">CHECKING BUILD-TIME OPTIONS</a><br>
295 <P>
296 <b>int pcre_config(int <i>what</i>, void *<i>where</i>);</b>
297 </P>
298 <P>
299 The function <b>pcre_config()</b> makes it possible for a PCRE client to
300 discover which optional features have been compiled into the PCRE library. The
301 <a href="pcrebuild.html"><b>pcrebuild</b></a>
302 documentation has more details about these optional features.
303 </P>
304 <P>
305 The first argument for <b>pcre_config()</b> is an integer, specifying which
306 information is required; the second argument is a pointer to a variable into
307 which the information is placed. The following information is available:
308 <pre>
310 </pre>
311 The output is an integer that is set to one if UTF-8 support is available;
312 otherwise it is set to zero.
313 <pre>
315 </pre>
316 The output is an integer that is set to one if support for Unicode character
317 properties is available; otherwise it is set to zero.
318 <pre>
320 </pre>
321 The output is an integer whose value specifies the default character sequence
322 that is recognized as meaning "newline". The four values that are supported
323 are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF, and -1 for ANY. The
324 default should normally be the standard sequence for your operating system.
325 <pre>
327 </pre>
328 The output is an integer that contains the number of bytes used for internal
329 linkage in compiled regular expressions. The value is 2, 3, or 4. Larger values
330 allow larger regular expressions to be compiled, at the expense of slower
331 matching. The default value of 2 is sufficient for all but the most massive
332 patterns, since it allows the compiled pattern to be up to 64K in size.
333 <pre>
335 </pre>
336 The output is an integer that contains the threshold above which the POSIX
337 interface uses <b>malloc()</b> for output vectors. Further details are given in
338 the
339 <a href="pcreposix.html"><b>pcreposix</b></a>
340 documentation.
341 <pre>
343 </pre>
344 The output is an integer that gives the default limit for the number of
345 internal matching function calls in a <b>pcre_exec()</b> execution. Further
346 details are given with <b>pcre_exec()</b> below.
347 <pre>
349 </pre>
350 The output is an integer that gives the default limit for the depth of
351 recursion when calling the internal matching function in a <b>pcre_exec()</b>
352 execution. Further details are given with <b>pcre_exec()</b> below.
353 <pre>
355 </pre>
356 The output is an integer that is set to one if internal recursion when running
357 <b>pcre_exec()</b> is implemented by recursive function calls that use the stack
358 to remember their state. This is the usual way that PCRE is compiled. The
359 output is zero if PCRE was compiled to use blocks of data on the heap instead
360 of recursive function calls. In this case, <b>pcre_stack_malloc</b> and
361 <b>pcre_stack_free</b> are called to manage memory blocks on the heap, thus
362 avoiding the use of the stack.
363 </P>
364 <br><a name="SEC7" href="#TOC1">COMPILING A PATTERN</a><br>
365 <P>
366 <b>pcre *pcre_compile(const char *<i>pattern</i>, int <i>options</i>,</b>
367 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
368 <b>const unsigned char *<i>tableptr</i>);</b>
369 <b>pcre *pcre_compile2(const char *<i>pattern</i>, int <i>options</i>,</b>
370 <b>int *<i>errorcodeptr</i>,</b>
371 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
372 <b>const unsigned char *<i>tableptr</i>);</b>
373 </P>
374 <P>
375 Either of the functions <b>pcre_compile()</b> or <b>pcre_compile2()</b> can be
376 called to compile a pattern into an internal form. The only difference between
377 the two interfaces is that <b>pcre_compile2()</b> has an additional argument,
378 <i>errorcodeptr</i>, via which a numerical error code can be returned.
379 </P>
380 <P>
381 The pattern is a C string terminated by a binary zero, and is passed in the
382 <i>pattern</i> argument. A pointer to a single block of memory that is obtained
383 via <b>pcre_malloc</b> is returned. This contains the compiled code and related
384 data. The <b>pcre</b> type is defined for the returned block; this is a typedef
385 for a structure whose contents are not externally defined. It is up to the
386 caller to free the memory (via <b>pcre_free</b>) when it is no longer required.
387 </P>
388 <P>
389 Although the compiled code of a PCRE regex is relocatable, that is, it does not
390 depend on memory location, the complete <b>pcre</b> data block is not
391 fully relocatable, because it may contain a copy of the <i>tableptr</i>
392 argument, which is an address (see below).
393 </P>
394 <P>
395 The <i>options</i> argument contains various bit settings that affect the
396 compilation. It should be zero if no options are required. The available
397 options are described below. Some of them, in particular, those that are
398 compatible with Perl, can also be set and unset from within the pattern (see
399 the detailed description in the
400 <a href="pcrepattern.html"><b>pcrepattern</b></a>
401 documentation). For these options, the contents of the <i>options</i> argument
402 specifies their initial settings at the start of compilation and execution. The
403 PCRE_ANCHORED and PCRE_NEWLINE_<i>xxx</i> options can be set at the time of
404 matching as well as at compile time.
405 </P>
406 <P>
407 If <i>errptr</i> is NULL, <b>pcre_compile()</b> returns NULL immediately.
408 Otherwise, if compilation of a pattern fails, <b>pcre_compile()</b> returns
409 NULL, and sets the variable pointed to by <i>errptr</i> to point to a textual
410 error message. This is a static string that is part of the library. You must
411 not try to free it. The offset from the start of the pattern to the character
412 where the error was discovered is placed in the variable pointed to by
413 <i>erroffset</i>, which must not be NULL. If it is, an immediate error is given.
414 </P>
415 <P>
416 If <b>pcre_compile2()</b> is used instead of <b>pcre_compile()</b>, and the
417 <i>errorcodeptr</i> argument is not NULL, a non-zero error code number is
418 returned via this argument in the event of an error. This is in addition to the
419 textual error message. Error codes and messages are listed below.
420 </P>
421 <P>
422 If the final argument, <i>tableptr</i>, is NULL, PCRE uses a default set of
423 character tables that are built when PCRE is compiled, using the default C
424 locale. Otherwise, <i>tableptr</i> must be an address that is the result of a
425 call to <b>pcre_maketables()</b>. This value is stored with the compiled
426 pattern, and used again by <b>pcre_exec()</b>, unless another table pointer is
427 passed to it. For more discussion, see the section on locale support below.
428 </P>
429 <P>
430 This code fragment shows a typical straightforward call to <b>pcre_compile()</b>:
431 <pre>
432 pcre *re;
433 const char *error;
434 int erroffset;
435 re = pcre_compile(
436 "^A.*Z", /* the pattern */
437 0, /* default options */
438 &error, /* for error message */
439 &erroffset, /* for error offset */
440 NULL); /* use default character tables */
441 </pre>
442 The following names for option bits are defined in the <b>pcre.h</b> header
443 file:
444 <pre>
446 </pre>
447 If this bit is set, the pattern is forced to be "anchored", that is, it is
448 constrained to match only at the first matching point in the string that is
449 being searched (the "subject string"). This effect can also be achieved by
450 appropriate constructs in the pattern itself, which is the only way to do it in
451 Perl.
452 <pre>
454 </pre>
455 If this bit is set, <b>pcre_compile()</b> automatically inserts callout items,
456 all with number 255, before each pattern item. For discussion of the callout
457 facility, see the
458 <a href="pcrecallout.html"><b>pcrecallout</b></a>
459 documentation.
460 <pre>
462 </pre>
463 If this bit is set, letters in the pattern match both upper and lower case
464 letters. It is equivalent to Perl's /i option, and it can be changed within a
465 pattern by a (?i) option setting. In UTF-8 mode, PCRE always understands the
466 concept of case for characters whose values are less than 128, so caseless
467 matching is always possible. For characters with higher values, the concept of
468 case is supported if PCRE is compiled with Unicode property support, but not
469 otherwise. If you want to use caseless matching for characters 128 and above,
470 you must ensure that PCRE is compiled with Unicode property support as well as
471 with UTF-8 support.
472 <pre>
474 </pre>
475 If this bit is set, a dollar metacharacter in the pattern matches only at the
476 end of the subject string. Without this option, a dollar also matches
477 immediately before a newline at the end of the string (but not before any other
478 newlines). The PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is set.
479 There is no equivalent to this option in Perl, and no way to set it within a
480 pattern.
481 <pre>
483 </pre>
484 If this bit is set, a dot metacharater in the pattern matches all characters,
485 including those that indicate newline. Without it, a dot does not match when
486 the current position is at a newline. This option is equivalent to Perl's /s
487 option, and it can be changed within a pattern by a (?s) option setting. A
488 negative class such as [^a] always matches newline characters, independent of
489 the setting of this option.
490 <pre>
492 </pre>
493 If this bit is set, names used to identify capturing subpatterns need not be
494 unique. This can be helpful for certain types of pattern when it is known that
495 only one instance of the named subpattern can ever be matched. There are more
496 details of named subpatterns below; see also the
497 <a href="pcrepattern.html"><b>pcrepattern</b></a>
498 documentation.
499 <pre>
501 </pre>
502 If this bit is set, whitespace data characters in the pattern are totally
503 ignored except when escaped or inside a character class. Whitespace does not
504 include the VT character (code 11). In addition, characters between an
505 unescaped # outside a character class and the next newline, inclusive, are also
506 ignored. This is equivalent to Perl's /x option, and it can be changed within a
507 pattern by a (?x) option setting.
508 </P>
509 <P>
510 This option makes it possible to include comments inside complicated patterns.
511 Note, however, that this applies only to data characters. Whitespace characters
512 may never appear within special character sequences in a pattern, for example
513 within the sequence (?( which introduces a conditional subpattern.
514 <pre>
516 </pre>
517 This option was invented in order to turn on additional functionality of PCRE
518 that is incompatible with Perl, but it is currently of very little use. When
519 set, any backslash in a pattern that is followed by a letter that has no
520 special meaning causes an error, thus reserving these combinations for future
521 expansion. By default, as in Perl, a backslash followed by a letter with no
522 special meaning is treated as a literal. (Perl can, however, be persuaded to
523 give a warning for this.) There are at present no other features controlled by
524 this option. It can also be set by a (?X) option setting within a pattern.
525 <pre>
527 </pre>
528 If this option is set, an unanchored pattern is required to match before or at
529 the first newline in the subject string, though the matched text may continue
530 over the newline.
531 <pre>
533 </pre>
534 By default, PCRE treats the subject string as consisting of a single line of
535 characters (even if it actually contains newlines). The "start of line"
536 metacharacter (^) matches only at the start of the string, while the "end of
537 line" metacharacter ($) matches only at the end of the string, or before a
538 terminating newline (unless PCRE_DOLLAR_ENDONLY is set). This is the same as
539 Perl.
540 </P>
541 <P>
542 When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs
543 match immediately following or immediately before internal newlines in the
544 subject string, respectively, as well as at the very start and end. This is
545 equivalent to Perl's /m option, and it can be changed within a pattern by a
546 (?m) option setting. If there are no newlines in a subject string, or no
547 occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no effect.
548 <pre>
554 </pre>
555 These options override the default newline definition that was chosen when PCRE
556 was built. Setting the first or the second specifies that a newline is
557 indicated by a single character (CR or LF, respectively). Setting
558 PCRE_NEWLINE_CRLF specifies that a newline is indicated by the two-character
559 CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies that any of the three
560 preceding sequences should be recognized. Setting PCRE_NEWLINE_ANY specifies
561 that any Unicode newline sequence should be recognized. The Unicode newline
562 sequences are the three just mentioned, plus the single characters VT (vertical
563 tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS (line
564 separator, U+2028), and PS (paragraph separator, U+2029). The last two are
565 recognized only in UTF-8 mode.
566 </P>
567 <P>
568 The newline setting in the options word uses three bits that are treated
569 as a number, giving eight possibilities. Currently only six are used (default
570 plus the five values above). This means that if you set more than one newline
571 option, the combination may or may not be sensible. For example,
573 other combinations may yield unused numbers and cause an error.
574 </P>
575 <P>
576 The only time that a line break is specially recognized when compiling a
577 pattern is if PCRE_EXTENDED is set, and an unescaped # outside a character
578 class is encountered. This indicates a comment that lasts until after the next
579 line break sequence. In other circumstances, line break sequences are treated
580 as literal data, except that in PCRE_EXTENDED mode, both CR and LF are treated
581 as whitespace characters and are therefore ignored.
582 </P>
583 <P>
584 The newline option that is set at compile time becomes the default that is used
585 for <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b>, but it can be overridden.
586 <pre>
588 </pre>
589 If this option is set, it disables the use of numbered capturing parentheses in
590 the pattern. Any opening parenthesis that is not followed by ? behaves as if it
591 were followed by ?: but named parentheses can still be used for capturing (and
592 they acquire numbers in the usual way). There is no equivalent of this option
593 in Perl.
594 <pre>
596 </pre>
597 This option inverts the "greediness" of the quantifiers so that they are not
598 greedy by default, but become greedy if followed by "?". It is not compatible
599 with Perl. It can also be set by a (?U) option setting within the pattern.
600 <pre>
602 </pre>
603 This option causes PCRE to regard both the pattern and the subject as strings
604 of UTF-8 characters instead of single-byte character strings. However, it is
605 available only when PCRE is built to include UTF-8 support. If not, the use
606 of this option provokes an error. Details of how this option changes the
607 behaviour of PCRE are given in the
608 <a href="pcre.html#utf8support">section on UTF-8 support</a>
609 in the main
610 <a href="pcre.html"><b>pcre</b></a>
611 page.
612 <pre>
614 </pre>
615 When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
616 automatically checked. There is a discussion about the
617 <a href="pcre.html#utf8strings">validity of UTF-8 strings</a>
618 in the main
619 <a href="pcre.html"><b>pcre</b></a>
620 page. If an invalid UTF-8 sequence of bytes is found, <b>pcre_compile()</b>
621 returns an error. If you already know that your pattern is valid, and you want
622 to skip this check for performance reasons, you can set the PCRE_NO_UTF8_CHECK
623 option. When it is set, the effect of passing an invalid UTF-8 string as a
624 pattern is undefined. It may cause your program to crash. Note that this option
625 can also be passed to <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b>, to suppress
626 the UTF-8 validity checking of subject strings.
627 </P>
628 <br><a name="SEC8" href="#TOC1">COMPILATION ERROR CODES</a><br>
629 <P>
630 The following table lists the error codes than may be returned by
631 <b>pcre_compile2()</b>, along with the error messages that may be returned by
632 both compiling functions. As PCRE has developed, some error codes have fallen
633 out of use. To avoid confusion, they have not been re-used.
634 <pre>
635 0 no error
636 1 \ at end of pattern
637 2 \c at end of pattern
638 3 unrecognized character follows \
639 4 numbers out of order in {} quantifier
640 5 number too big in {} quantifier
641 6 missing terminating ] for character class
642 7 invalid escape sequence in character class
643 8 range out of order in character class
644 9 nothing to repeat
645 10 [this code is not in use]
646 11 internal error: unexpected repeat
647 12 unrecognized character after (?
648 13 POSIX named classes are supported only within a class
649 14 missing )
650 15 reference to non-existent subpattern
651 16 erroffset passed as NULL
652 17 unknown option bit(s) set
653 18 missing ) after comment
654 19 [this code is not in use]
655 20 regular expression too large
656 21 failed to get memory
657 22 unmatched parentheses
658 23 internal error: code overflow
659 24 unrecognized character after (?&#60;
660 25 lookbehind assertion is not fixed length
661 26 malformed number or name after (?(
662 27 conditional group contains more than two branches
663 28 assertion expected after (?(
664 29 (?R or (?[+-]digits must be followed by )
665 30 unknown POSIX class name
666 31 POSIX collating elements are not supported
667 32 this version of PCRE is not compiled with PCRE_UTF8 support
668 33 [this code is not in use]
669 34 character value in \x{...} sequence is too large
670 35 invalid condition (?(0)
671 36 \C not allowed in lookbehind assertion
672 37 PCRE does not support \L, \l, \N, \U, or \u
673 38 number after (?C is &#62; 255
674 39 closing ) for (?C expected
675 40 recursive call could loop indefinitely
676 41 unrecognized character after (?P
677 42 syntax error in subpattern name (missing terminator)
678 43 two named subpatterns have the same name
679 44 invalid UTF-8 string
680 45 support for \P, \p, and \X has not been compiled
681 46 malformed \P or \p sequence
682 47 unknown property name after \P or \p
683 48 subpattern name is too long (maximum 32 characters)
684 49 too many named subpatterns (maximum 10,000)
685 50 [this code is not in use]
686 51 octal value is greater than \377 (not in UTF-8 mode)
687 52 internal error: overran compiling workspace
688 53 internal error: previously-checked referenced subpattern not found
689 54 DEFINE group contains more than one branch
690 55 repeating a DEFINE group is not allowed
691 56 inconsistent NEWLINE options"
692 57 \g is not followed by a braced name or an optionally braced
693 non-zero number
694 58 (?+ or (?- or (?(+ or (?(- must be followed by a non-zero number
695 </PRE>
696 </P>
697 <br><a name="SEC9" href="#TOC1">STUDYING A PATTERN</a><br>
698 <P>
699 <b>pcre_extra *pcre_study(const pcre *<i>code</i>, int <i>options</i></b>
700 <b>const char **<i>errptr</i>);</b>
701 </P>
702 <P>
703 If a compiled pattern is going to be used several times, it is worth spending
704 more time analyzing it in order to speed up the time taken for matching. The
705 function <b>pcre_study()</b> takes a pointer to a compiled pattern as its first
706 argument. If studying the pattern produces additional information that will
707 help speed up matching, <b>pcre_study()</b> returns a pointer to a
708 <b>pcre_extra</b> block, in which the <i>study_data</i> field points to the
709 results of the study.
710 </P>
711 <P>
712 The returned value from <b>pcre_study()</b> can be passed directly to
713 <b>pcre_exec()</b>. However, a <b>pcre_extra</b> block also contains other
714 fields that can be set by the caller before the block is passed; these are
715 described
716 <a href="#extradata">below</a>
717 in the section on matching a pattern.
718 </P>
719 <P>
720 If studying the pattern does not produce any additional information
721 <b>pcre_study()</b> returns NULL. In that circumstance, if the calling program
722 wants to pass any of the other fields to <b>pcre_exec()</b>, it must set up its
723 own <b>pcre_extra</b> block.
724 </P>
725 <P>
726 The second argument of <b>pcre_study()</b> contains option bits. At present, no
727 options are defined, and this argument should always be zero.
728 </P>
729 <P>
730 The third argument for <b>pcre_study()</b> is a pointer for an error message. If
731 studying succeeds (even if no data is returned), the variable it points to is
732 set to NULL. Otherwise it is set to point to a textual error message. This is a
733 static string that is part of the library. You must not try to free it. You
734 should test the error pointer for NULL after calling <b>pcre_study()</b>, to be
735 sure that it has run successfully.
736 </P>
737 <P>
738 This is a typical call to <b>pcre_study</b>():
739 <pre>
740 pcre_extra *pe;
741 pe = pcre_study(
742 re, /* result of pcre_compile() */
743 0, /* no options exist */
744 &error); /* set to NULL or points to a message */
745 </pre>
746 At present, studying a pattern is useful only for non-anchored patterns that do
747 not have a single fixed starting character. A bitmap of possible starting
748 bytes is created.
749 <a name="localesupport"></a></P>
750 <br><a name="SEC10" href="#TOC1">LOCALE SUPPORT</a><br>
751 <P>
752 PCRE handles caseless matching, and determines whether characters are letters,
753 digits, or whatever, by reference to a set of tables, indexed by character
754 value. When running in UTF-8 mode, this applies only to characters with codes
755 less than 128. Higher-valued codes never match escapes such as \w or \d, but
756 can be tested with \p if PCRE is built with Unicode character property
757 support. The use of locales with Unicode is discouraged. If you are handling
758 characters with codes greater than 128, you should either use UTF-8 and
759 Unicode, or use locales, but not try to mix the two.
760 </P>
761 <P>
762 PCRE contains an internal set of tables that are used when the final argument
763 of <b>pcre_compile()</b> is NULL. These are sufficient for many applications.
764 Normally, the internal tables recognize only ASCII characters. However, when
765 PCRE is built, it is possible to cause the internal tables to be rebuilt in the
766 default "C" locale of the local system, which may cause them to be different.
767 </P>
768 <P>
769 The internal tables can always be overridden by tables supplied by the
770 application that calls PCRE. These may be created in a different locale from
771 the default. As more and more applications change to using Unicode, the need
772 for this locale support is expected to die away.
773 </P>
774 <P>
775 External tables are built by calling the <b>pcre_maketables()</b> function,
776 which has no arguments, in the relevant locale. The result can then be passed
777 to <b>pcre_compile()</b> or <b>pcre_exec()</b> as often as necessary. For
778 example, to build and use tables that are appropriate for the French locale
779 (where accented characters with values greater than 128 are treated as letters),
780 the following code could be used:
781 <pre>
782 setlocale(LC_CTYPE, "fr_FR");
783 tables = pcre_maketables();
784 re = pcre_compile(..., tables);
785 </pre>
786 The locale name "fr_FR" is used on Linux and other Unix-like systems; if you
787 are using Windows, the name for the French locale is "french".
788 </P>
789 <P>
790 When <b>pcre_maketables()</b> runs, the tables are built in memory that is
791 obtained via <b>pcre_malloc</b>. It is the caller's responsibility to ensure
792 that the memory containing the tables remains available for as long as it is
793 needed.
794 </P>
795 <P>
796 The pointer that is passed to <b>pcre_compile()</b> is saved with the compiled
797 pattern, and the same tables are used via this pointer by <b>pcre_study()</b>
798 and normally also by <b>pcre_exec()</b>. Thus, by default, for any single
799 pattern, compilation, studying and matching all happen in the same locale, but
800 different patterns can be compiled in different locales.
801 </P>
802 <P>
803 It is possible to pass a table pointer or NULL (indicating the use of the
804 internal tables) to <b>pcre_exec()</b>. Although not intended for this purpose,
805 this facility could be used to match a pattern in a different locale from the
806 one in which it was compiled. Passing table pointers at run time is discussed
807 below in the section on matching a pattern.
808 </P>
809 <br><a name="SEC11" href="#TOC1">INFORMATION ABOUT A PATTERN</a><br>
810 <P>
811 <b>int pcre_fullinfo(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
812 <b>int <i>what</i>, void *<i>where</i>);</b>
813 </P>
814 <P>
815 The <b>pcre_fullinfo()</b> function returns information about a compiled
816 pattern. It replaces the obsolete <b>pcre_info()</b> function, which is
817 nevertheless retained for backwards compability (and is documented below).
818 </P>
819 <P>
820 The first argument for <b>pcre_fullinfo()</b> is a pointer to the compiled
821 pattern. The second argument is the result of <b>pcre_study()</b>, or NULL if
822 the pattern was not studied. The third argument specifies which piece of
823 information is required, and the fourth argument is a pointer to a variable
824 to receive the data. The yield of the function is zero for success, or one of
825 the following negative numbers:
826 <pre>
827 PCRE_ERROR_NULL the argument <i>code</i> was NULL
828 the argument <i>where</i> was NULL
829 PCRE_ERROR_BADMAGIC the "magic number" was not found
830 PCRE_ERROR_BADOPTION the value of <i>what</i> was invalid
831 </pre>
832 The "magic number" is placed at the start of each compiled pattern as an simple
833 check against passing an arbitrary memory pointer. Here is a typical call of
834 <b>pcre_fullinfo()</b>, to obtain the length of the compiled pattern:
835 <pre>
836 int rc;
837 size_t length;
838 rc = pcre_fullinfo(
839 re, /* result of pcre_compile() */
840 pe, /* result of pcre_study(), or NULL */
841 PCRE_INFO_SIZE, /* what is required */
842 &length); /* where to put the data */
843 </pre>
844 The possible values for the third argument are defined in <b>pcre.h</b>, and are
845 as follows:
846 <pre>
848 </pre>
849 Return the number of the highest back reference in the pattern. The fourth
850 argument should point to an <b>int</b> variable. Zero is returned if there are
851 no back references.
852 <pre>
854 </pre>
855 Return the number of capturing subpatterns in the pattern. The fourth argument
856 should point to an <b>int</b> variable.
857 <pre>
859 </pre>
860 Return a pointer to the internal default character tables within PCRE. The
861 fourth argument should point to an <b>unsigned char *</b> variable. This
862 information call is provided for internal use by the <b>pcre_study()</b>
863 function. External callers can cause PCRE to use its internal tables by passing
864 a NULL table pointer.
865 <pre>
867 </pre>
868 Return information about the first byte of any matched string, for a
869 non-anchored pattern. The fourth argument should point to an <b>int</b>
870 variable. (This option used to be called PCRE_INFO_FIRSTCHAR; the old name is
871 still recognized for backwards compatibility.)
872 </P>
873 <P>
874 If there is a fixed first byte, for example, from a pattern such as
875 (cat|cow|coyote), its value is returned. Otherwise, if either
876 <br>
877 <br>
878 (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
879 starts with "^", or
880 <br>
881 <br>
882 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
883 (if it were set, the pattern would be anchored),
884 <br>
885 <br>
886 -1 is returned, indicating that the pattern matches only at the start of a
887 subject string or after any newline within the string. Otherwise -2 is
888 returned. For anchored patterns, -2 is returned.
889 <pre>
891 </pre>
892 If the pattern was studied, and this resulted in the construction of a 256-bit
893 table indicating a fixed set of bytes for the first byte in any matching
894 string, a pointer to the table is returned. Otherwise NULL is returned. The
895 fourth argument should point to an <b>unsigned char *</b> variable.
896 <pre>
898 </pre>
899 Return 1 if the (?J) option setting is used in the pattern, otherwise 0. The
900 fourth argument should point to an <b>int</b> variable. The (?J) internal option
901 setting changes the local PCRE_DUPNAMES option.
902 <pre>
904 </pre>
905 Return the value of the rightmost literal byte that must exist in any matched
906 string, other than at its start, if such a byte has been recorded. The fourth
907 argument should point to an <b>int</b> variable. If there is no such byte, -1 is
908 returned. For anchored patterns, a last literal byte is recorded only if it
909 follows something of variable length. For example, for the pattern
910 /^a\d+z\d+/ the returned value is "z", but for /^a\dz\d/ the returned value
911 is -1.
912 <pre>
916 </pre>
917 PCRE supports the use of named as well as numbered capturing parentheses. The
918 names are just an additional way of identifying the parentheses, which still
919 acquire numbers. Several convenience functions such as
920 <b>pcre_get_named_substring()</b> are provided for extracting captured
921 substrings by name. It is also possible to extract the data directly, by first
922 converting the name to a number in order to access the correct pointers in the
923 output vector (described with <b>pcre_exec()</b> below). To do the conversion,
924 you need to use the name-to-number map, which is described by these three
925 values.
926 </P>
927 <P>
928 The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives
929 the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each
930 entry; both of these return an <b>int</b> value. The entry size depends on the
931 length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first
932 entry of the table (a pointer to <b>char</b>). The first two bytes of each entry
933 are the number of the capturing parenthesis, most significant byte first. The
934 rest of the entry is the corresponding name, zero terminated. The names are in
935 alphabetical order. When PCRE_DUPNAMES is set, duplicate names are in order of
936 their parentheses numbers. For example, consider the following pattern (assume
937 PCRE_EXTENDED is set, so white space - including newlines - is ignored):
938 <pre>
939 (?&#60;date&#62; (?&#60;year&#62;(\d\d)?\d\d) - (?&#60;month&#62;\d\d) - (?&#60;day&#62;\d\d) )
940 </pre>
941 There are four named subpatterns, so the table has four entries, and each entry
942 in the table is eight bytes long. The table is as follows, with non-printing
943 bytes shows in hexadecimal, and undefined bytes shown as ??:
944 <pre>
945 00 01 d a t e 00 ??
946 00 05 d a y 00 ?? ??
947 00 04 m o n t h 00
948 00 02 y e a r 00 ??
949 </pre>
950 When writing code to extract data from named subpatterns using the
951 name-to-number map, remember that the length of the entries is likely to be
952 different for each compiled pattern.
953 <pre>
955 </pre>
956 Return 1 if the pattern can be used for partial matching, otherwise 0. The
957 fourth argument should point to an <b>int</b> variable. The
958 <a href="pcrepartial.html"><b>pcrepartial</b></a>
959 documentation lists the restrictions that apply to patterns when partial
960 matching is used.
961 <pre>
963 </pre>
964 Return a copy of the options with which the pattern was compiled. The fourth
965 argument should point to an <b>unsigned long int</b> variable. These option bits
966 are those specified in the call to <b>pcre_compile()</b>, modified by any
967 top-level option settings at the start of the pattern itself. In other words,
968 they are the options that will be in force when matching starts. For example,
969 if the pattern /(?im)abc(?-i)d/ is compiled with the PCRE_EXTENDED option, the
971 </P>
972 <P>
973 A pattern is automatically anchored by PCRE if all of its top-level
974 alternatives begin with one of the following:
975 <pre>
976 ^ unless PCRE_MULTILINE is set
977 \A always
978 \G always
979 .* if PCRE_DOTALL is set and there are no back references to the subpattern in which .* appears
980 </pre>
981 For such patterns, the PCRE_ANCHORED bit is set in the options returned by
982 <b>pcre_fullinfo()</b>.
983 <pre>
985 </pre>
986 Return the size of the compiled pattern, that is, the value that was passed as
987 the argument to <b>pcre_malloc()</b> when PCRE was getting memory in which to
988 place the compiled data. The fourth argument should point to a <b>size_t</b>
989 variable.
990 <pre>
992 </pre>
993 Return the size of the data block pointed to by the <i>study_data</i> field in
994 a <b>pcre_extra</b> block. That is, it is the value that was passed to
995 <b>pcre_malloc()</b> when PCRE was getting memory into which to place the data
996 created by <b>pcre_study()</b>. The fourth argument should point to a
997 <b>size_t</b> variable.
998 </P>
999 <br><a name="SEC12" href="#TOC1">OBSOLETE INFO FUNCTION</a><br>
1000 <P>
1001 <b>int pcre_info(const pcre *<i>code</i>, int *<i>optptr</i>, int</b>
1002 <b>*<i>firstcharptr</i>);</b>
1003 </P>
1004 <P>
1005 The <b>pcre_info()</b> function is now obsolete because its interface is too
1006 restrictive to return all the available data about a compiled pattern. New
1007 programs should use <b>pcre_fullinfo()</b> instead. The yield of
1008 <b>pcre_info()</b> is the number of capturing subpatterns, or one of the
1009 following negative numbers:
1010 <pre>
1011 PCRE_ERROR_NULL the argument <i>code</i> was NULL
1012 PCRE_ERROR_BADMAGIC the "magic number" was not found
1013 </pre>
1014 If the <i>optptr</i> argument is not NULL, a copy of the options with which the
1015 pattern was compiled is placed in the integer it points to (see
1016 PCRE_INFO_OPTIONS above).
1017 </P>
1018 <P>
1019 If the pattern is not anchored and the <i>firstcharptr</i> argument is not NULL,
1020 it is used to pass back information about the first character of any matched
1021 string (see PCRE_INFO_FIRSTBYTE above).
1022 </P>
1023 <br><a name="SEC13" href="#TOC1">REFERENCE COUNTS</a><br>
1024 <P>
1025 <b>int pcre_refcount(pcre *<i>code</i>, int <i>adjust</i>);</b>
1026 </P>
1027 <P>
1028 The <b>pcre_refcount()</b> function is used to maintain a reference count in the
1029 data block that contains a compiled pattern. It is provided for the benefit of
1030 applications that operate in an object-oriented manner, where different parts
1031 of the application may be using the same compiled pattern, but you want to free
1032 the block when they are all done.
1033 </P>
1034 <P>
1035 When a pattern is compiled, the reference count field is initialized to zero.
1036 It is changed only by calling this function, whose action is to add the
1037 <i>adjust</i> value (which may be positive or negative) to it. The yield of the
1038 function is the new value. However, the value of the count is constrained to
1039 lie between 0 and 65535, inclusive. If the new value is outside these limits,
1040 it is forced to the appropriate limit value.
1041 </P>
1042 <P>
1043 Except when it is zero, the reference count is not correctly preserved if a
1044 pattern is compiled on one host and then transferred to a host whose byte-order
1045 is different. (This seems a highly unlikely scenario.)
1046 </P>
1047 <br><a name="SEC14" href="#TOC1">MATCHING A PATTERN: THE TRADITIONAL FUNCTION</a><br>
1048 <P>
1049 <b>int pcre_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
1050 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
1051 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>);</b>
1052 </P>
1053 <P>
1054 The function <b>pcre_exec()</b> is called to match a subject string against a
1055 compiled pattern, which is passed in the <i>code</i> argument. If the
1056 pattern has been studied, the result of the study should be passed in the
1057 <i>extra</i> argument. This function is the main matching facility of the
1058 library, and it operates in a Perl-like manner. For specialist use there is
1059 also an alternative matching function, which is described
1060 <a href="#dfamatch">below</a>
1061 in the section about the <b>pcre_dfa_exec()</b> function.
1062 </P>
1063 <P>
1064 In most applications, the pattern will have been compiled (and optionally
1065 studied) in the same process that calls <b>pcre_exec()</b>. However, it is
1066 possible to save compiled patterns and study data, and then use them later
1067 in different processes, possibly even on different hosts. For a discussion
1068 about this, see the
1069 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
1070 documentation.
1071 </P>
1072 <P>
1073 Here is an example of a simple call to <b>pcre_exec()</b>:
1074 <pre>
1075 int rc;
1076 int ovector[30];
1077 rc = pcre_exec(
1078 re, /* result of pcre_compile() */
1079 NULL, /* we didn't study the pattern */
1080 "some string", /* the subject string */
1081 11, /* the length of the subject string */
1082 0, /* start at offset 0 in the subject */
1083 0, /* default options */
1084 ovector, /* vector of integers for substring information */
1085 30); /* number of elements (NOT size in bytes) */
1086 <a name="extradata"></a></PRE>
1087 </P>
1088 <br><b>
1089 Extra data for <b>pcre_exec()</b>
1090 </b><br>
1091 <P>
1092 If the <i>extra</i> argument is not NULL, it must point to a <b>pcre_extra</b>
1093 data block. The <b>pcre_study()</b> function returns such a block (when it
1094 doesn't return NULL), but you can also create one for yourself, and pass
1095 additional information in it. The <b>pcre_extra</b> block contains the following
1096 fields (not necessarily in this order):
1097 <pre>
1098 unsigned long int <i>flags</i>;
1099 void *<i>study_data</i>;
1100 unsigned long int <i>match_limit</i>;
1101 unsigned long int <i>match_limit_recursion</i>;
1102 void *<i>callout_data</i>;
1103 const unsigned char *<i>tables</i>;
1104 </pre>
1105 The <i>flags</i> field is a bitmap that specifies which of the other fields
1106 are set. The flag bits are:
1107 <pre>
1113 </pre>
1114 Other flag bits should be set to zero. The <i>study_data</i> field is set in the
1115 <b>pcre_extra</b> block that is returned by <b>pcre_study()</b>, together with
1116 the appropriate flag bit. You should not set this yourself, but you may add to
1117 the block by setting the other fields and their corresponding flag bits.
1118 </P>
1119 <P>
1120 The <i>match_limit</i> field provides a means of preventing PCRE from using up a
1121 vast amount of resources when running patterns that are not going to match,
1122 but which have a very large number of possibilities in their search trees. The
1123 classic example is the use of nested unlimited repeats.
1124 </P>
1125 <P>
1126 Internally, PCRE uses a function called <b>match()</b> which it calls repeatedly
1127 (sometimes recursively). The limit set by <i>match_limit</i> is imposed on the
1128 number of times this function is called during a match, which has the effect of
1129 limiting the amount of backtracking that can take place. For patterns that are
1130 not anchored, the count restarts from zero for each position in the subject
1131 string.
1132 </P>
1133 <P>
1134 The default value for the limit can be set when PCRE is built; the default
1135 default is 10 million, which handles all but the most extreme cases. You can
1136 override the default by suppling <b>pcre_exec()</b> with a <b>pcre_extra</b>
1137 block in which <i>match_limit</i> is set, and PCRE_EXTRA_MATCH_LIMIT is set in
1138 the <i>flags</i> field. If the limit is exceeded, <b>pcre_exec()</b> returns
1140 </P>
1141 <P>
1142 The <i>match_limit_recursion</i> field is similar to <i>match_limit</i>, but
1143 instead of limiting the total number of times that <b>match()</b> is called, it
1144 limits the depth of recursion. The recursion depth is a smaller number than the
1145 total number of calls, because not all calls to <b>match()</b> are recursive.
1146 This limit is of use only if it is set smaller than <i>match_limit</i>.
1147 </P>
1148 <P>
1149 Limiting the recursion depth limits the amount of stack that can be used, or,
1150 when PCRE has been compiled to use memory on the heap instead of the stack, the
1151 amount of heap memory that can be used.
1152 </P>
1153 <P>
1154 The default value for <i>match_limit_recursion</i> can be set when PCRE is
1155 built; the default default is the same value as the default for
1156 <i>match_limit</i>. You can override the default by suppling <b>pcre_exec()</b>
1157 with a <b>pcre_extra</b> block in which <i>match_limit_recursion</i> is set, and
1158 PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the <i>flags</i> field. If the limit
1159 is exceeded, <b>pcre_exec()</b> returns PCRE_ERROR_RECURSIONLIMIT.
1160 </P>
1161 <P>
1162 The <i>pcre_callout</i> field is used in conjunction with the "callout" feature,
1163 which is described in the
1164 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1165 documentation.
1166 </P>
1167 <P>
1168 The <i>tables</i> field is used to pass a character tables pointer to
1169 <b>pcre_exec()</b>; this overrides the value that is stored with the compiled
1170 pattern. A non-NULL value is stored with the compiled pattern only if custom
1171 tables were supplied to <b>pcre_compile()</b> via its <i>tableptr</i> argument.
1172 If NULL is passed to <b>pcre_exec()</b> using this mechanism, it forces PCRE's
1173 internal tables to be used. This facility is helpful when re-using patterns
1174 that have been saved after compiling with an external set of tables, because
1175 the external tables might be at a different address when <b>pcre_exec()</b> is
1176 called. See the
1177 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
1178 documentation for a discussion of saving compiled patterns for later use.
1179 </P>
1180 <br><b>
1181 Option bits for <b>pcre_exec()</b>
1182 </b><br>
1183 <P>
1184 The unused bits of the <i>options</i> argument for <b>pcre_exec()</b> must be
1185 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_<i>xxx</i>,
1187 <pre>
1189 </pre>
1190 The PCRE_ANCHORED option limits <b>pcre_exec()</b> to matching at the first
1191 matching position. If a pattern was compiled with PCRE_ANCHORED, or turned out
1192 to be anchored by virtue of its contents, it cannot be made unachored at
1193 matching time.
1194 <pre>
1200 </pre>
1201 These options override the newline definition that was chosen or defaulted when
1202 the pattern was compiled. For details, see the description of
1203 <b>pcre_compile()</b> above. During matching, the newline choice affects the
1204 behaviour of the dot, circumflex, and dollar metacharacters. It may also alter
1205 the way the match position is advanced after a match failure for an unanchored
1207 set, and a match attempt fails when the current position is at a CRLF sequence,
1208 the match position is advanced by two characters instead of one, in other
1209 words, to after the CRLF.
1210 <pre>
1212 </pre>
1213 This option specifies that first character of the subject string is not the
1214 beginning of a line, so the circumflex metacharacter should not match before
1215 it. Setting this without PCRE_MULTILINE (at compile time) causes circumflex
1216 never to match. This option affects only the behaviour of the circumflex
1217 metacharacter. It does not affect \A.
1218 <pre>
1220 </pre>
1221 This option specifies that the end of the subject string is not the end of a
1222 line, so the dollar metacharacter should not match it nor (except in multiline
1223 mode) a newline immediately before it. Setting this without PCRE_MULTILINE (at
1224 compile time) causes dollar never to match. This option affects only the
1225 behaviour of the dollar metacharacter. It does not affect \Z or \z.
1226 <pre>
1228 </pre>
1229 An empty string is not considered to be a valid match if this option is set. If
1230 there are alternatives in the pattern, they are tried. If all the alternatives
1231 match the empty string, the entire match fails. For example, if the pattern
1232 <pre>
1233 a?b?
1234 </pre>
1235 is applied to a string not beginning with "a" or "b", it matches the empty
1236 string at the start of the subject. With PCRE_NOTEMPTY set, this match is not
1237 valid, so PCRE searches further into the string for occurrences of "a" or "b".
1238 </P>
1239 <P>
1240 Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a special case
1241 of a pattern match of the empty string within its <b>split()</b> function, and
1242 when using the /g modifier. It is possible to emulate Perl's behaviour after
1243 matching a null string by first trying the match again at the same offset with
1244 PCRE_NOTEMPTY and PCRE_ANCHORED, and then if that fails by advancing the
1245 starting offset (see below) and trying an ordinary match again. There is some
1246 code that demonstrates how to do this in the <i>pcredemo.c</i> sample program.
1247 <pre>
1249 </pre>
1250 When PCRE_UTF8 is set at compile time, the validity of the subject as a UTF-8
1251 string is automatically checked when <b>pcre_exec()</b> is subsequently called.
1252 The value of <i>startoffset</i> is also checked to ensure that it points to the
1253 start of a UTF-8 character. There is a discussion about the validity of UTF-8
1254 strings in the
1255 <a href="pcre.html#utf8strings">section on UTF-8 support</a>
1256 in the main
1257 <a href="pcre.html"><b>pcre</b></a>
1258 page. If an invalid UTF-8 sequence of bytes is found, <b>pcre_exec()</b> returns
1259 the error PCRE_ERROR_BADUTF8. If <i>startoffset</i> contains an invalid value,
1260 PCRE_ERROR_BADUTF8_OFFSET is returned.
1261 </P>
1262 <P>
1263 If you already know that your subject is valid, and you want to skip these
1264 checks for performance reasons, you can set the PCRE_NO_UTF8_CHECK option when
1265 calling <b>pcre_exec()</b>. You might want to do this for the second and
1266 subsequent calls to <b>pcre_exec()</b> if you are making repeated calls to find
1267 all the matches in a single subject string. However, you should be sure that
1268 the value of <i>startoffset</i> points to the start of a UTF-8 character. When
1269 PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid UTF-8 string as a
1270 subject, or a value of <i>startoffset</i> that does not point to the start of a
1271 UTF-8 character, is undefined. Your program may crash.
1272 <pre>
1274 </pre>
1275 This option turns on the partial matching feature. If the subject string fails
1276 to match the pattern, but at some point during the matching process the end of
1277 the subject was reached (that is, the subject partially matches the pattern and
1278 the failure to match occurred only because there were not enough subject
1279 characters), <b>pcre_exec()</b> returns PCRE_ERROR_PARTIAL instead of
1280 PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is used, there are restrictions on what
1281 may appear in the pattern. These are discussed in the
1282 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1283 documentation.
1284 </P>
1285 <br><b>
1286 The string to be matched by <b>pcre_exec()</b>
1287 </b><br>
1288 <P>
1289 The subject string is passed to <b>pcre_exec()</b> as a pointer in
1290 <i>subject</i>, a length in <i>length</i>, and a starting byte offset in
1291 <i>startoffset</i>. In UTF-8 mode, the byte offset must point to the start of a
1292 UTF-8 character. Unlike the pattern string, the subject may contain binary zero
1293 bytes. When the starting offset is zero, the search for a match starts at the
1294 beginning of the subject, and this is by far the most common case.
1295 </P>
1296 <P>
1297 A non-zero starting offset is useful when searching for another match in the
1298 same subject by calling <b>pcre_exec()</b> again after a previous success.
1299 Setting <i>startoffset</i> differs from just passing over a shortened string and
1300 setting PCRE_NOTBOL in the case of a pattern that begins with any kind of
1301 lookbehind. For example, consider the pattern
1302 <pre>
1303 \Biss\B
1304 </pre>
1305 which finds occurrences of "iss" in the middle of words. (\B matches only if
1306 the current position in the subject is not a word boundary.) When applied to
1307 the string "Mississipi" the first call to <b>pcre_exec()</b> finds the first
1308 occurrence. If <b>pcre_exec()</b> is called again with just the remainder of the
1309 subject, namely "issipi", it does not match, because \B is always false at the
1310 start of the subject, which is deemed to be a word boundary. However, if
1311 <b>pcre_exec()</b> is passed the entire string again, but with <i>startoffset</i>
1312 set to 4, it finds the second occurrence of "iss" because it is able to look
1313 behind the starting point to discover that it is preceded by a letter.
1314 </P>
1315 <P>
1316 If a non-zero starting offset is passed when the pattern is anchored, one
1317 attempt to match at the given offset is made. This can only succeed if the
1318 pattern does not require the match to be at the start of the subject.
1319 </P>
1320 <br><b>
1321 How <b>pcre_exec()</b> returns captured substrings
1322 </b><br>
1323 <P>
1324 In general, a pattern matches a certain portion of the subject, and in
1325 addition, further substrings from the subject may be picked out by parts of the
1326 pattern. Following the usage in Jeffrey Friedl's book, this is called
1327 "capturing" in what follows, and the phrase "capturing subpattern" is used for
1328 a fragment of a pattern that picks out a substring. PCRE supports several other
1329 kinds of parenthesized subpattern that do not cause substrings to be captured.
1330 </P>
1331 <P>
1332 Captured substrings are returned to the caller via a vector of integer offsets
1333 whose address is passed in <i>ovector</i>. The number of elements in the vector
1334 is passed in <i>ovecsize</i>, which must be a non-negative number. <b>Note</b>:
1335 this argument is NOT the size of <i>ovector</i> in bytes.
1336 </P>
1337 <P>
1338 The first two-thirds of the vector is used to pass back captured substrings,
1339 each substring using a pair of integers. The remaining third of the vector is
1340 used as workspace by <b>pcre_exec()</b> while matching capturing subpatterns,
1341 and is not available for passing back information. The length passed in
1342 <i>ovecsize</i> should always be a multiple of three. If it is not, it is
1343 rounded down.
1344 </P>
1345 <P>
1346 When a match is successful, information about captured substrings is returned
1347 in pairs of integers, starting at the beginning of <i>ovector</i>, and
1348 continuing up to two-thirds of its length at the most. The first element of a
1349 pair is set to the offset of the first character in a substring, and the second
1350 is set to the offset of the first character after the end of a substring. The
1351 first pair, <i>ovector[0]</i> and <i>ovector[1]</i>, identify the portion of the
1352 subject string matched by the entire pattern. The next pair is used for the
1353 first capturing subpattern, and so on. The value returned by <b>pcre_exec()</b>
1354 is one more than the highest numbered pair that has been set. For example, if
1355 two substrings have been captured, the returned value is 3. If there are no
1356 capturing subpatterns, the return value from a successful match is 1,
1357 indicating that just the first pair of offsets has been set.
1358 </P>
1359 <P>
1360 If a capturing subpattern is matched repeatedly, it is the last portion of the
1361 string that it matched that is returned.
1362 </P>
1363 <P>
1364 If the vector is too small to hold all the captured substring offsets, it is
1365 used as far as possible (up to two-thirds of its length), and the function
1366 returns a value of zero. In particular, if the substring offsets are not of
1367 interest, <b>pcre_exec()</b> may be called with <i>ovector</i> passed as NULL and
1368 <i>ovecsize</i> as zero. However, if the pattern contains back references and
1369 the <i>ovector</i> is not big enough to remember the related substrings, PCRE
1370 has to get additional memory for use during matching. Thus it is usually
1371 advisable to supply an <i>ovector</i>.
1372 </P>
1373 <P>
1374 The <b>pcre_info()</b> function can be used to find out how many capturing
1375 subpatterns there are in a compiled pattern. The smallest size for
1376 <i>ovector</i> that will allow for <i>n</i> captured substrings, in addition to
1377 the offsets of the substring matched by the whole pattern, is (<i>n</i>+1)*3.
1378 </P>
1379 <P>
1380 It is possible for capturing subpattern number <i>n+1</i> to match some part of
1381 the subject when subpattern <i>n</i> has not been used at all. For example, if
1382 the string "abc" is matched against the pattern (a|(z))(bc) the return from the
1383 function is 4, and subpatterns 1 and 3 are matched, but 2 is not. When this
1384 happens, both values in the offset pairs corresponding to unused subpatterns
1385 are set to -1.
1386 </P>
1387 <P>
1388 Offset values that correspond to unused subpatterns at the end of the
1389 expression are also set to -1. For example, if the string "abc" is matched
1390 against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not matched. The
1391 return from the function is 2, because the highest used capturing subpattern
1392 number is 1. However, you can refer to the offsets for the second and third
1393 capturing subpatterns if you wish (assuming the vector is large enough, of
1394 course).
1395 </P>
1396 <P>
1397 Some convenience functions are provided for extracting the captured substrings
1398 as separate strings. These are described below.
1399 <a name="errorlist"></a></P>
1400 <br><b>
1401 Error return values from <b>pcre_exec()</b>
1402 </b><br>
1403 <P>
1404 If <b>pcre_exec()</b> fails, it returns a negative number. The following are
1405 defined in the header file:
1406 <pre>
1408 </pre>
1409 The subject string did not match the pattern.
1410 <pre>
1412 </pre>
1413 Either <i>code</i> or <i>subject</i> was passed as NULL, or <i>ovector</i> was
1414 NULL and <i>ovecsize</i> was not zero.
1415 <pre>
1417 </pre>
1418 An unrecognized bit was set in the <i>options</i> argument.
1419 <pre>
1421 </pre>
1422 PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch
1423 the case when it is passed a junk pointer and to detect when a pattern that was
1424 compiled in an environment of one endianness is run in an environment with the
1425 other endianness. This is the error that PCRE gives when the magic number is
1426 not present.
1427 <pre>
1429 </pre>
1430 While running the pattern match, an unknown item was encountered in the
1431 compiled pattern. This error could be caused by a bug in PCRE or by overwriting
1432 of the compiled pattern.
1433 <pre>
1435 </pre>
1436 If a pattern contains back references, but the <i>ovector</i> that is passed to
1437 <b>pcre_exec()</b> is not big enough to remember the referenced substrings, PCRE
1438 gets a block of memory at the start of matching to use for this purpose. If the
1439 call via <b>pcre_malloc()</b> fails, this error is given. The memory is
1440 automatically freed at the end of matching.
1441 <pre>
1443 </pre>
1444 This error is used by the <b>pcre_copy_substring()</b>,
1445 <b>pcre_get_substring()</b>, and <b>pcre_get_substring_list()</b> functions (see
1446 below). It is never returned by <b>pcre_exec()</b>.
1447 <pre>
1449 </pre>
1450 The backtracking limit, as specified by the <i>match_limit</i> field in a
1451 <b>pcre_extra</b> structure (or defaulted) was reached. See the description
1452 above.
1453 <pre>
1455 </pre>
1456 This error is never generated by <b>pcre_exec()</b> itself. It is provided for
1457 use by callout functions that want to yield a distinctive error code. See the
1458 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1459 documentation for details.
1460 <pre>
1462 </pre>
1463 A string that contains an invalid UTF-8 byte sequence was passed as a subject.
1464 <pre>
1466 </pre>
1467 The UTF-8 byte sequence that was passed as a subject was valid, but the value
1468 of <i>startoffset</i> did not point to the beginning of a UTF-8 character.
1469 <pre>
1471 </pre>
1472 The subject string did not match, but it did match partially. See the
1473 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1474 documentation for details of partial matching.
1475 <pre>
1477 </pre>
1478 The PCRE_PARTIAL option was used with a compiled pattern containing items that
1479 are not supported for partial matching. See the
1480 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1481 documentation for details of partial matching.
1482 <pre>
1484 </pre>
1485 An unexpected internal error has occurred. This error could be caused by a bug
1486 in PCRE or by overwriting of the compiled pattern.
1487 <pre>
1489 </pre>
1490 This error is given if the value of the <i>ovecsize</i> argument is negative.
1491 <pre>
1493 </pre>
1494 The internal recursion limit, as specified by the <i>match_limit_recursion</i>
1495 field in a <b>pcre_extra</b> structure (or defaulted) was reached. See the
1496 description above.
1497 <pre>
1499 </pre>
1500 An invalid combination of PCRE_NEWLINE_<i>xxx</i> options was given.
1501 </P>
1502 <P>
1503 Error numbers -16 to -20 and -22 are not used by <b>pcre_exec()</b>.
1504 </P>
1505 <br><a name="SEC15" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NUMBER</a><br>
1506 <P>
1507 <b>int pcre_copy_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1508 <b>int <i>stringcount</i>, int <i>stringnumber</i>, char *<i>buffer</i>,</b>
1509 <b>int <i>buffersize</i>);</b>
1510 </P>
1511 <P>
1512 <b>int pcre_get_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1513 <b>int <i>stringcount</i>, int <i>stringnumber</i>,</b>
1514 <b>const char **<i>stringptr</i>);</b>
1515 </P>
1516 <P>
1517 <b>int pcre_get_substring_list(const char *<i>subject</i>,</b>
1518 <b>int *<i>ovector</i>, int <i>stringcount</i>, const char ***<i>listptr</i>);</b>
1519 </P>
1520 <P>
1521 Captured substrings can be accessed directly by using the offsets returned by
1522 <b>pcre_exec()</b> in <i>ovector</i>. For convenience, the functions
1523 <b>pcre_copy_substring()</b>, <b>pcre_get_substring()</b>, and
1524 <b>pcre_get_substring_list()</b> are provided for extracting captured substrings
1525 as new, separate, zero-terminated strings. These functions identify substrings
1526 by number. The next section describes functions for extracting named
1527 substrings.
1528 </P>
1529 <P>
1530 A substring that contains a binary zero is correctly extracted and has a
1531 further zero added on the end, but the result is not, of course, a C string.
1532 However, you can process such a string by referring to the length that is
1533 returned by <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>.
1534 Unfortunately, the interface to <b>pcre_get_substring_list()</b> is not adequate
1535 for handling strings containing binary zeros, because the end of the final
1536 string is not independently indicated.
1537 </P>
1538 <P>
1539 The first three arguments are the same for all three of these functions:
1540 <i>subject</i> is the subject string that has just been successfully matched,
1541 <i>ovector</i> is a pointer to the vector of integer offsets that was passed to
1542 <b>pcre_exec()</b>, and <i>stringcount</i> is the number of substrings that were
1543 captured by the match, including the substring that matched the entire regular
1544 expression. This is the value returned by <b>pcre_exec()</b> if it is greater
1545 than zero. If <b>pcre_exec()</b> returned zero, indicating that it ran out of
1546 space in <i>ovector</i>, the value passed as <i>stringcount</i> should be the
1547 number of elements in the vector divided by three.
1548 </P>
1549 <P>
1550 The functions <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>
1551 extract a single substring, whose number is given as <i>stringnumber</i>. A
1552 value of zero extracts the substring that matched the entire pattern, whereas
1553 higher values extract the captured substrings. For <b>pcre_copy_substring()</b>,
1554 the string is placed in <i>buffer</i>, whose length is given by
1555 <i>buffersize</i>, while for <b>pcre_get_substring()</b> a new block of memory is
1556 obtained via <b>pcre_malloc</b>, and its address is returned via
1557 <i>stringptr</i>. The yield of the function is the length of the string, not
1558 including the terminating zero, or one of these error codes:
1559 <pre>
1561 </pre>
1562 The buffer was too small for <b>pcre_copy_substring()</b>, or the attempt to get
1563 memory failed for <b>pcre_get_substring()</b>.
1564 <pre>
1566 </pre>
1567 There is no substring whose number is <i>stringnumber</i>.
1568 </P>
1569 <P>
1570 The <b>pcre_get_substring_list()</b> function extracts all available substrings
1571 and builds a list of pointers to them. All this is done in a single block of
1572 memory that is obtained via <b>pcre_malloc</b>. The address of the memory block
1573 is returned via <i>listptr</i>, which is also the start of the list of string
1574 pointers. The end of the list is marked by a NULL pointer. The yield of the
1575 function is zero if all went well, or the error code
1576 <pre>
1578 </pre>
1579 if the attempt to get the memory block failed.
1580 </P>
1581 <P>
1582 When any of these functions encounter a substring that is unset, which can
1583 happen when capturing subpattern number <i>n+1</i> matches some part of the
1584 subject, but subpattern <i>n</i> has not been used at all, they return an empty
1585 string. This can be distinguished from a genuine zero-length substring by
1586 inspecting the appropriate offset in <i>ovector</i>, which is negative for unset
1587 substrings.
1588 </P>
1589 <P>
1590 The two convenience functions <b>pcre_free_substring()</b> and
1591 <b>pcre_free_substring_list()</b> can be used to free the memory returned by
1592 a previous call of <b>pcre_get_substring()</b> or
1593 <b>pcre_get_substring_list()</b>, respectively. They do nothing more than call
1594 the function pointed to by <b>pcre_free</b>, which of course could be called
1595 directly from a C program. However, PCRE is used in some situations where it is
1596 linked via a special interface to another programming language that cannot use
1597 <b>pcre_free</b> directly; it is for these cases that the functions are
1598 provided.
1599 </P>
1600 <br><a name="SEC16" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NAME</a><br>
1601 <P>
1602 <b>int pcre_get_stringnumber(const pcre *<i>code</i>,</b>
1603 <b>const char *<i>name</i>);</b>
1604 </P>
1605 <P>
1606 <b>int pcre_copy_named_substring(const pcre *<i>code</i>,</b>
1607 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
1608 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
1609 <b>char *<i>buffer</i>, int <i>buffersize</i>);</b>
1610 </P>
1611 <P>
1612 <b>int pcre_get_named_substring(const pcre *<i>code</i>,</b>
1613 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
1614 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
1615 <b>const char **<i>stringptr</i>);</b>
1616 </P>
1617 <P>
1618 To extract a substring by name, you first have to find associated number.
1619 For example, for this pattern
1620 <pre>
1621 (a+)b(?&#60;xxx&#62;\d+)...
1622 </pre>
1623 the number of the subpattern called "xxx" is 2. If the name is known to be
1624 unique (PCRE_DUPNAMES was not set), you can find the number from the name by
1625 calling <b>pcre_get_stringnumber()</b>. The first argument is the compiled
1626 pattern, and the second is the name. The yield of the function is the
1627 subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no subpattern of
1628 that name.
1629 </P>
1630 <P>
1631 Given the number, you can extract the substring directly, or use one of the
1632 functions described in the previous section. For convenience, there are also
1633 two functions that do the whole job.
1634 </P>
1635 <P>
1636 Most of the arguments of <b>pcre_copy_named_substring()</b> and
1637 <b>pcre_get_named_substring()</b> are the same as those for the similarly named
1638 functions that extract by number. As these are described in the previous
1639 section, they are not re-described here. There are just two differences:
1640 </P>
1641 <P>
1642 First, instead of a substring number, a substring name is given. Second, there
1643 is an extra argument, given at the start, which is a pointer to the compiled
1644 pattern. This is needed in order to gain access to the name-to-number
1645 translation table.
1646 </P>
1647 <P>
1648 These functions call <b>pcre_get_stringnumber()</b>, and if it succeeds, they
1649 then call <b>pcre_copy_substring()</b> or <b>pcre_get_substring()</b>, as
1650 appropriate. <b>NOTE:</b> If PCRE_DUPNAMES is set and there are duplicate names,
1651 the behaviour may not be what you want (see the next section).
1652 </P>
1653 <br><a name="SEC17" href="#TOC1">DUPLICATE SUBPATTERN NAMES</a><br>
1654 <P>
1655 <b>int pcre_get_stringtable_entries(const pcre *<i>code</i>,</b>
1656 <b>const char *<i>name</i>, char **<i>first</i>, char **<i>last</i>);</b>
1657 </P>
1658 <P>
1659 When a pattern is compiled with the PCRE_DUPNAMES option, names for subpatterns
1660 are not required to be unique. Normally, patterns with duplicate names are such
1661 that in any one match, only one of the named subpatterns participates. An
1662 example is shown in the
1663 <a href="pcrepattern.html"><b>pcrepattern</b></a>
1664 documentation.
1665 </P>
1666 <P>
1667 When duplicates are present, <b>pcre_copy_named_substring()</b> and
1668 <b>pcre_get_named_substring()</b> return the first substring corresponding to
1669 the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING (-7) is
1670 returned; no data is returned. The <b>pcre_get_stringnumber()</b> function
1671 returns one of the numbers that are associated with the name, but it is not
1672 defined which it is.
1673 </P>
1674 <P>
1675 If you want to get full details of all captured substrings for a given name,
1676 you must use the <b>pcre_get_stringtable_entries()</b> function. The first
1677 argument is the compiled pattern, and the second is the name. The third and
1678 fourth are pointers to variables which are updated by the function. After it
1679 has run, they point to the first and last entries in the name-to-number table
1680 for the given name. The function itself returns the length of each entry, or
1681 PCRE_ERROR_NOSUBSTRING (-7) if there are none. The format of the table is
1682 described above in the section entitled <i>Information about a pattern</i>.
1683 Given all the relevant entries for the name, you can extract each of their
1684 numbers, and hence the captured data, if any.
1685 </P>
1686 <br><a name="SEC18" href="#TOC1">FINDING ALL POSSIBLE MATCHES</a><br>
1687 <P>
1688 The traditional matching function uses a similar algorithm to Perl, which stops
1689 when it finds the first match, starting at a given point in the subject. If you
1690 want to find all possible matches, or the longest possible match, consider
1691 using the alternative matching function (see below) instead. If you cannot use
1692 the alternative function, but still need to find all possible matches, you
1693 can kludge it up by making use of the callout facility, which is described in
1694 the
1695 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1696 documentation.
1697 </P>
1698 <P>
1699 What you have to do is to insert a callout right at the end of the pattern.
1700 When your callout function is called, extract and save the current matched
1701 substring. Then return 1, which forces <b>pcre_exec()</b> to backtrack and try
1702 other alternatives. Ultimately, when it runs out of matches, <b>pcre_exec()</b>
1703 will yield PCRE_ERROR_NOMATCH.
1704 <a name="dfamatch"></a></P>
1705 <br><a name="SEC19" href="#TOC1">MATCHING A PATTERN: THE ALTERNATIVE FUNCTION</a><br>
1706 <P>
1707 <b>int pcre_dfa_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
1708 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
1709 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>,</b>
1710 <b>int *<i>workspace</i>, int <i>wscount</i>);</b>
1711 </P>
1712 <P>
1713 The function <b>pcre_dfa_exec()</b> is called to match a subject string against
1714 a compiled pattern, using a matching algorithm that scans the subject string
1715 just once, and does not backtrack. This has different characteristics to the
1716 normal algorithm, and is not compatible with Perl. Some of the features of PCRE
1717 patterns are not supported. Nevertheless, there are times when this kind of
1718 matching can be useful. For a discussion of the two matching algorithms, see
1719 the
1720 <a href="pcrematching.html"><b>pcrematching</b></a>
1721 documentation.
1722 </P>
1723 <P>
1724 The arguments for the <b>pcre_dfa_exec()</b> function are the same as for
1725 <b>pcre_exec()</b>, plus two extras. The <i>ovector</i> argument is used in a
1726 different way, and this is described below. The other common arguments are used
1727 in the same way as for <b>pcre_exec()</b>, so their description is not repeated
1728 here.
1729 </P>
1730 <P>
1731 The two additional arguments provide workspace for the function. The workspace
1732 vector should contain at least 20 elements. It is used for keeping track of
1733 multiple paths through the pattern tree. More workspace will be needed for
1734 patterns and subjects where there are a lot of potential matches.
1735 </P>
1736 <P>
1737 Here is an example of a simple call to <b>pcre_dfa_exec()</b>:
1738 <pre>
1739 int rc;
1740 int ovector[10];
1741 int wspace[20];
1742 rc = pcre_dfa_exec(
1743 re, /* result of pcre_compile() */
1744 NULL, /* we didn't study the pattern */
1745 "some string", /* the subject string */
1746 11, /* the length of the subject string */
1747 0, /* start at offset 0 in the subject */
1748 0, /* default options */
1749 ovector, /* vector of integers for substring information */
1750 10, /* number of elements (NOT size in bytes) */
1751 wspace, /* working space vector */
1752 20); /* number of elements (NOT size in bytes) */
1753 </PRE>
1754 </P>
1755 <br><b>
1756 Option bits for <b>pcre_dfa_exec()</b>
1757 </b><br>
1758 <P>
1759 The unused bits of the <i>options</i> argument for <b>pcre_dfa_exec()</b> must be
1760 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_<i>xxx</i>,
1762 PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last three of these are
1763 the same as for <b>pcre_exec()</b>, so their description is not repeated here.
1764 <pre>
1766 </pre>
1767 This has the same general effect as it does for <b>pcre_exec()</b>, but the
1768 details are slightly different. When PCRE_PARTIAL is set for
1769 <b>pcre_dfa_exec()</b>, the return code PCRE_ERROR_NOMATCH is converted into
1770 PCRE_ERROR_PARTIAL if the end of the subject is reached, there have been no
1771 complete matches, but there is still at least one matching possibility. The
1772 portion of the string that provided the partial match is set as the first
1773 matching string.
1774 <pre>
1776 </pre>
1777 Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to stop as
1778 soon as it has found one match. Because of the way the alternative algorithm
1779 works, this is necessarily the shortest possible match at the first possible
1780 matching point in the subject string.
1781 <pre>
1783 </pre>
1784 When <b>pcre_dfa_exec()</b> is called with the PCRE_PARTIAL option, and returns
1785 a partial match, it is possible to call it again, with additional subject
1786 characters, and have it continue with the same match. The PCRE_DFA_RESTART
1787 option requests this action; when it is set, the <i>workspace</i> and
1788 <i>wscount</i> options must reference the same vector as before because data
1789 about the match so far is left in them after a partial match. There is more
1790 discussion of this facility in the
1791 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1792 documentation.
1793 </P>
1794 <br><b>
1795 Successful returns from <b>pcre_dfa_exec()</b>
1796 </b><br>
1797 <P>
1798 When <b>pcre_dfa_exec()</b> succeeds, it may have matched more than one
1799 substring in the subject. Note, however, that all the matches from one run of
1800 the function start at the same point in the subject. The shorter matches are
1801 all initial substrings of the longer matches. For example, if the pattern
1802 <pre>
1803 &#60;.*&#62;
1804 </pre>
1805 is matched against the string
1806 <pre>
1807 This is &#60;something&#62; &#60;something else&#62; &#60;something further&#62; no more
1808 </pre>
1809 the three matched strings are
1810 <pre>
1811 &#60;something&#62;
1812 &#60;something&#62; &#60;something else&#62;
1813 &#60;something&#62; &#60;something else&#62; &#60;something further&#62;
1814 </pre>
1815 On success, the yield of the function is a number greater than zero, which is
1816 the number of matched substrings. The substrings themselves are returned in
1817 <i>ovector</i>. Each string uses two elements; the first is the offset to the
1818 start, and the second is the offset to the end. In fact, all the strings have
1819 the same start offset. (Space could have been saved by giving this only once,
1820 but it was decided to retain some compatibility with the way <b>pcre_exec()</b>
1821 returns data, even though the meaning of the strings is different.)
1822 </P>
1823 <P>
1824 The strings are returned in reverse order of length; that is, the longest
1825 matching string is given first. If there were too many matches to fit into
1826 <i>ovector</i>, the yield of the function is zero, and the vector is filled with
1827 the longest matches.
1828 </P>
1829 <br><b>
1830 Error returns from <b>pcre_dfa_exec()</b>
1831 </b><br>
1832 <P>
1833 The <b>pcre_dfa_exec()</b> function returns a negative number when it fails.
1834 Many of the errors are the same as for <b>pcre_exec()</b>, and these are
1835 described
1836 <a href="#errorlist">above.</a>
1837 There are in addition the following errors that are specific to
1838 <b>pcre_dfa_exec()</b>:
1839 <pre>
1841 </pre>
1842 This return is given if <b>pcre_dfa_exec()</b> encounters an item in the pattern
1843 that it does not support, for instance, the use of \C or a back reference.
1844 <pre>
1846 </pre>
1847 This return is given if <b>pcre_dfa_exec()</b> encounters a condition item that
1848 uses a back reference for the condition, or a test for recursion in a specific
1849 group. These are not supported.
1850 <pre>
1852 </pre>
1853 This return is given if <b>pcre_dfa_exec()</b> is called with an <i>extra</i>
1854 block that contains a setting of the <i>match_limit</i> field. This is not
1855 supported (it is meaningless).
1856 <pre>
1858 </pre>
1859 This return is given if <b>pcre_dfa_exec()</b> runs out of space in the
1860 <i>workspace</i> vector.
1861 <pre>
1863 </pre>
1864 When a recursive subpattern is processed, the matching function calls itself
1865 recursively, using private vectors for <i>ovector</i> and <i>workspace</i>. This
1866 error is given if the output vector is not large enough. This should be
1867 extremely rare, as a vector of size 1000 is used.
1868 </P>
1869 <br><a name="SEC20" href="#TOC1">SEE ALSO</a><br>
1870 <P>
1871 <b>pcrebuild</b>(3), <b>pcrecallout</b>(3), <b>pcrecpp(3)</b>(3),
1872 <b>pcrematching</b>(3), <b>pcrepartial</b>(3), <b>pcreposix</b>(3),
1873 <b>pcreprecompile</b>(3), <b>pcresample</b>(3), <b>pcrestack</b>(3).
1874 </P>
1875 <br><a name="SEC21" href="#TOC1">AUTHOR</a><br>
1876 <P>
1877 Philip Hazel
1878 <br>
1879 University Computing Service
1880 <br>
1881 Cambridge CB2 3QH, England.
1882 <br>
1883 </P>
1884 <br><a name="SEC22" href="#TOC1">REVISION</a><br>
1885 <P>
1886 Last updated: 09 August 2007
1887 <br>
1888 Copyright &copy; 1997-2007 University of Cambridge.
1889 <br>
1890 <p>
1891 Return to the <a href="index.html">PCRE index page</a>.
1892 </p>


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