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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. If an invalid UTF-8 sequence of bytes is found,
617 <b>pcre_compile()</b> returns an error. If you already know that your pattern is
618 valid, and you want to skip this check for performance reasons, you can set the
619 PCRE_NO_UTF8_CHECK option. When it is set, the effect of passing an invalid
620 UTF-8 string as a pattern is undefined. It may cause your program to crash.
621 Note that this option can also be passed to <b>pcre_exec()</b> and
622 <b>pcre_dfa_exec()</b>, to suppress the UTF-8 validity checking of subject
623 strings.
624 </P>
625 <br><a name="SEC8" href="#TOC1">COMPILATION ERROR CODES</a><br>
626 <P>
627 The following table lists the error codes than may be returned by
628 <b>pcre_compile2()</b>, along with the error messages that may be returned by
629 both compiling functions. As PCRE has developed, some error codes have fallen
630 out of use. To avoid confusion, they have not been re-used.
631 <pre>
632 0 no error
633 1 \ at end of pattern
634 2 \c at end of pattern
635 3 unrecognized character follows \
636 4 numbers out of order in {} quantifier
637 5 number too big in {} quantifier
638 6 missing terminating ] for character class
639 7 invalid escape sequence in character class
640 8 range out of order in character class
641 9 nothing to repeat
642 10 [this code is not in use]
643 11 internal error: unexpected repeat
644 12 unrecognized character after (?
645 13 POSIX named classes are supported only within a class
646 14 missing )
647 15 reference to non-existent subpattern
648 16 erroffset passed as NULL
649 17 unknown option bit(s) set
650 18 missing ) after comment
651 19 [this code is not in use]
652 20 regular expression too large
653 21 failed to get memory
654 22 unmatched parentheses
655 23 internal error: code overflow
656 24 unrecognized character after (?&#60;
657 25 lookbehind assertion is not fixed length
658 26 malformed number or name after (?(
659 27 conditional group contains more than two branches
660 28 assertion expected after (?(
661 29 (?R or (?[+-]digits must be followed by )
662 30 unknown POSIX class name
663 31 POSIX collating elements are not supported
664 32 this version of PCRE is not compiled with PCRE_UTF8 support
665 33 [this code is not in use]
666 34 character value in \x{...} sequence is too large
667 35 invalid condition (?(0)
668 36 \C not allowed in lookbehind assertion
669 37 PCRE does not support \L, \l, \N, \U, or \u
670 38 number after (?C is &#62; 255
671 39 closing ) for (?C expected
672 40 recursive call could loop indefinitely
673 41 unrecognized character after (?P
674 42 syntax error in subpattern name (missing terminator)
675 43 two named subpatterns have the same name
676 44 invalid UTF-8 string
677 45 support for \P, \p, and \X has not been compiled
678 46 malformed \P or \p sequence
679 47 unknown property name after \P or \p
680 48 subpattern name is too long (maximum 32 characters)
681 49 too many named subpatterns (maximum 10,000)
682 50 repeated subpattern is too long
683 51 octal value is greater than \377 (not in UTF-8 mode)
684 52 internal error: overran compiling workspace
685 53 internal error: previously-checked referenced subpattern not found
686 54 DEFINE group contains more than one branch
687 55 repeating a DEFINE group is not allowed
688 56 inconsistent NEWLINE options"
689 57 \g is not followed by a braced name or an optionally braced
690 non-zero number
691 58 (?+ or (?- or (?(+ or (?(- must be followed by a non-zero number
692 </PRE>
693 </P>
694 <br><a name="SEC9" href="#TOC1">STUDYING A PATTERN</a><br>
695 <P>
696 <b>pcre_extra *pcre_study(const pcre *<i>code</i>, int <i>options</i></b>
697 <b>const char **<i>errptr</i>);</b>
698 </P>
699 <P>
700 If a compiled pattern is going to be used several times, it is worth spending
701 more time analyzing it in order to speed up the time taken for matching. The
702 function <b>pcre_study()</b> takes a pointer to a compiled pattern as its first
703 argument. If studying the pattern produces additional information that will
704 help speed up matching, <b>pcre_study()</b> returns a pointer to a
705 <b>pcre_extra</b> block, in which the <i>study_data</i> field points to the
706 results of the study.
707 </P>
708 <P>
709 The returned value from <b>pcre_study()</b> can be passed directly to
710 <b>pcre_exec()</b>. However, a <b>pcre_extra</b> block also contains other
711 fields that can be set by the caller before the block is passed; these are
712 described
713 <a href="#extradata">below</a>
714 in the section on matching a pattern.
715 </P>
716 <P>
717 If studying the pattern does not produce any additional information
718 <b>pcre_study()</b> returns NULL. In that circumstance, if the calling program
719 wants to pass any of the other fields to <b>pcre_exec()</b>, it must set up its
720 own <b>pcre_extra</b> block.
721 </P>
722 <P>
723 The second argument of <b>pcre_study()</b> contains option bits. At present, no
724 options are defined, and this argument should always be zero.
725 </P>
726 <P>
727 The third argument for <b>pcre_study()</b> is a pointer for an error message. If
728 studying succeeds (even if no data is returned), the variable it points to is
729 set to NULL. Otherwise it is set to point to a textual error message. This is a
730 static string that is part of the library. You must not try to free it. You
731 should test the error pointer for NULL after calling <b>pcre_study()</b>, to be
732 sure that it has run successfully.
733 </P>
734 <P>
735 This is a typical call to <b>pcre_study</b>():
736 <pre>
737 pcre_extra *pe;
738 pe = pcre_study(
739 re, /* result of pcre_compile() */
740 0, /* no options exist */
741 &error); /* set to NULL or points to a message */
742 </pre>
743 At present, studying a pattern is useful only for non-anchored patterns that do
744 not have a single fixed starting character. A bitmap of possible starting
745 bytes is created.
746 <a name="localesupport"></a></P>
747 <br><a name="SEC10" href="#TOC1">LOCALE SUPPORT</a><br>
748 <P>
749 PCRE handles caseless matching, and determines whether characters are letters,
750 digits, or whatever, by reference to a set of tables, indexed by character
751 value. When running in UTF-8 mode, this applies only to characters with codes
752 less than 128. Higher-valued codes never match escapes such as \w or \d, but
753 can be tested with \p if PCRE is built with Unicode character property
754 support. The use of locales with Unicode is discouraged. If you are handling
755 characters with codes greater than 128, you should either use UTF-8 and
756 Unicode, or use locales, but not try to mix the two.
757 </P>
758 <P>
759 PCRE contains an internal set of tables that are used when the final argument
760 of <b>pcre_compile()</b> is NULL. These are sufficient for many applications.
761 Normally, the internal tables recognize only ASCII characters. However, when
762 PCRE is built, it is possible to cause the internal tables to be rebuilt in the
763 default "C" locale of the local system, which may cause them to be different.
764 </P>
765 <P>
766 The internal tables can always be overridden by tables supplied by the
767 application that calls PCRE. These may be created in a different locale from
768 the default. As more and more applications change to using Unicode, the need
769 for this locale support is expected to die away.
770 </P>
771 <P>
772 External tables are built by calling the <b>pcre_maketables()</b> function,
773 which has no arguments, in the relevant locale. The result can then be passed
774 to <b>pcre_compile()</b> or <b>pcre_exec()</b> as often as necessary. For
775 example, to build and use tables that are appropriate for the French locale
776 (where accented characters with values greater than 128 are treated as letters),
777 the following code could be used:
778 <pre>
779 setlocale(LC_CTYPE, "fr_FR");
780 tables = pcre_maketables();
781 re = pcre_compile(..., tables);
782 </pre>
783 The locale name "fr_FR" is used on Linux and other Unix-like systems; if you
784 are using Windows, the name for the French locale is "french".
785 </P>
786 <P>
787 When <b>pcre_maketables()</b> runs, the tables are built in memory that is
788 obtained via <b>pcre_malloc</b>. It is the caller's responsibility to ensure
789 that the memory containing the tables remains available for as long as it is
790 needed.
791 </P>
792 <P>
793 The pointer that is passed to <b>pcre_compile()</b> is saved with the compiled
794 pattern, and the same tables are used via this pointer by <b>pcre_study()</b>
795 and normally also by <b>pcre_exec()</b>. Thus, by default, for any single
796 pattern, compilation, studying and matching all happen in the same locale, but
797 different patterns can be compiled in different locales.
798 </P>
799 <P>
800 It is possible to pass a table pointer or NULL (indicating the use of the
801 internal tables) to <b>pcre_exec()</b>. Although not intended for this purpose,
802 this facility could be used to match a pattern in a different locale from the
803 one in which it was compiled. Passing table pointers at run time is discussed
804 below in the section on matching a pattern.
805 </P>
806 <br><a name="SEC11" href="#TOC1">INFORMATION ABOUT A PATTERN</a><br>
807 <P>
808 <b>int pcre_fullinfo(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
809 <b>int <i>what</i>, void *<i>where</i>);</b>
810 </P>
811 <P>
812 The <b>pcre_fullinfo()</b> function returns information about a compiled
813 pattern. It replaces the obsolete <b>pcre_info()</b> function, which is
814 nevertheless retained for backwards compability (and is documented below).
815 </P>
816 <P>
817 The first argument for <b>pcre_fullinfo()</b> is a pointer to the compiled
818 pattern. The second argument is the result of <b>pcre_study()</b>, or NULL if
819 the pattern was not studied. The third argument specifies which piece of
820 information is required, and the fourth argument is a pointer to a variable
821 to receive the data. The yield of the function is zero for success, or one of
822 the following negative numbers:
823 <pre>
824 PCRE_ERROR_NULL the argument <i>code</i> was NULL
825 the argument <i>where</i> was NULL
826 PCRE_ERROR_BADMAGIC the "magic number" was not found
827 PCRE_ERROR_BADOPTION the value of <i>what</i> was invalid
828 </pre>
829 The "magic number" is placed at the start of each compiled pattern as an simple
830 check against passing an arbitrary memory pointer. Here is a typical call of
831 <b>pcre_fullinfo()</b>, to obtain the length of the compiled pattern:
832 <pre>
833 int rc;
834 size_t length;
835 rc = pcre_fullinfo(
836 re, /* result of pcre_compile() */
837 pe, /* result of pcre_study(), or NULL */
838 PCRE_INFO_SIZE, /* what is required */
839 &length); /* where to put the data */
840 </pre>
841 The possible values for the third argument are defined in <b>pcre.h</b>, and are
842 as follows:
843 <pre>
845 </pre>
846 Return the number of the highest back reference in the pattern. The fourth
847 argument should point to an <b>int</b> variable. Zero is returned if there are
848 no back references.
849 <pre>
851 </pre>
852 Return the number of capturing subpatterns in the pattern. The fourth argument
853 should point to an <b>int</b> variable.
854 <pre>
856 </pre>
857 Return a pointer to the internal default character tables within PCRE. The
858 fourth argument should point to an <b>unsigned char *</b> variable. This
859 information call is provided for internal use by the <b>pcre_study()</b>
860 function. External callers can cause PCRE to use its internal tables by passing
861 a NULL table pointer.
862 <pre>
864 </pre>
865 Return information about the first byte of any matched string, for a
866 non-anchored pattern. The fourth argument should point to an <b>int</b>
867 variable. (This option used to be called PCRE_INFO_FIRSTCHAR; the old name is
868 still recognized for backwards compatibility.)
869 </P>
870 <P>
871 If there is a fixed first byte, for example, from a pattern such as
872 (cat|cow|coyote), its value is returned. Otherwise, if either
873 <br>
874 <br>
875 (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
876 starts with "^", or
877 <br>
878 <br>
879 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
880 (if it were set, the pattern would be anchored),
881 <br>
882 <br>
883 -1 is returned, indicating that the pattern matches only at the start of a
884 subject string or after any newline within the string. Otherwise -2 is
885 returned. For anchored patterns, -2 is returned.
886 <pre>
888 </pre>
889 If the pattern was studied, and this resulted in the construction of a 256-bit
890 table indicating a fixed set of bytes for the first byte in any matching
891 string, a pointer to the table is returned. Otherwise NULL is returned. The
892 fourth argument should point to an <b>unsigned char *</b> variable.
893 <pre>
895 </pre>
896 Return 1 if the (?J) option setting is used in the pattern, otherwise 0. The
897 fourth argument should point to an <b>int</b> variable. The (?J) internal option
898 setting changes the local PCRE_DUPNAMES option.
899 <pre>
901 </pre>
902 Return the value of the rightmost literal byte that must exist in any matched
903 string, other than at its start, if such a byte has been recorded. The fourth
904 argument should point to an <b>int</b> variable. If there is no such byte, -1 is
905 returned. For anchored patterns, a last literal byte is recorded only if it
906 follows something of variable length. For example, for the pattern
907 /^a\d+z\d+/ the returned value is "z", but for /^a\dz\d/ the returned value
908 is -1.
909 <pre>
913 </pre>
914 PCRE supports the use of named as well as numbered capturing parentheses. The
915 names are just an additional way of identifying the parentheses, which still
916 acquire numbers. Several convenience functions such as
917 <b>pcre_get_named_substring()</b> are provided for extracting captured
918 substrings by name. It is also possible to extract the data directly, by first
919 converting the name to a number in order to access the correct pointers in the
920 output vector (described with <b>pcre_exec()</b> below). To do the conversion,
921 you need to use the name-to-number map, which is described by these three
922 values.
923 </P>
924 <P>
925 The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives
926 the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each
927 entry; both of these return an <b>int</b> value. The entry size depends on the
928 length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first
929 entry of the table (a pointer to <b>char</b>). The first two bytes of each entry
930 are the number of the capturing parenthesis, most significant byte first. The
931 rest of the entry is the corresponding name, zero terminated. The names are in
932 alphabetical order. When PCRE_DUPNAMES is set, duplicate names are in order of
933 their parentheses numbers. For example, consider the following pattern (assume
934 PCRE_EXTENDED is set, so white space - including newlines - is ignored):
935 <pre>
936 (?&#60;date&#62; (?&#60;year&#62;(\d\d)?\d\d) - (?&#60;month&#62;\d\d) - (?&#60;day&#62;\d\d) )
937 </pre>
938 There are four named subpatterns, so the table has four entries, and each entry
939 in the table is eight bytes long. The table is as follows, with non-printing
940 bytes shows in hexadecimal, and undefined bytes shown as ??:
941 <pre>
942 00 01 d a t e 00 ??
943 00 05 d a y 00 ?? ??
944 00 04 m o n t h 00
945 00 02 y e a r 00 ??
946 </pre>
947 When writing code to extract data from named subpatterns using the
948 name-to-number map, remember that the length of the entries is likely to be
949 different for each compiled pattern.
950 <pre>
952 </pre>
953 Return 1 if the pattern can be used for partial matching, otherwise 0. The
954 fourth argument should point to an <b>int</b> variable. The
955 <a href="pcrepartial.html"><b>pcrepartial</b></a>
956 documentation lists the restrictions that apply to patterns when partial
957 matching is used.
958 <pre>
960 </pre>
961 Return a copy of the options with which the pattern was compiled. The fourth
962 argument should point to an <b>unsigned long int</b> variable. These option bits
963 are those specified in the call to <b>pcre_compile()</b>, modified by any
964 top-level option settings at the start of the pattern itself. In other words,
965 they are the options that will be in force when matching starts. For example,
966 if the pattern /(?im)abc(?-i)d/ is compiled with the PCRE_EXTENDED option, the
968 </P>
969 <P>
970 A pattern is automatically anchored by PCRE if all of its top-level
971 alternatives begin with one of the following:
972 <pre>
973 ^ unless PCRE_MULTILINE is set
974 \A always
975 \G always
976 .* if PCRE_DOTALL is set and there are no back references to the subpattern in which .* appears
977 </pre>
978 For such patterns, the PCRE_ANCHORED bit is set in the options returned by
979 <b>pcre_fullinfo()</b>.
980 <pre>
982 </pre>
983 Return the size of the compiled pattern, that is, the value that was passed as
984 the argument to <b>pcre_malloc()</b> when PCRE was getting memory in which to
985 place the compiled data. The fourth argument should point to a <b>size_t</b>
986 variable.
987 <pre>
989 </pre>
990 Return the size of the data block pointed to by the <i>study_data</i> field in
991 a <b>pcre_extra</b> block. That is, it is the value that was passed to
992 <b>pcre_malloc()</b> when PCRE was getting memory into which to place the data
993 created by <b>pcre_study()</b>. The fourth argument should point to a
994 <b>size_t</b> variable.
995 </P>
996 <br><a name="SEC12" href="#TOC1">OBSOLETE INFO FUNCTION</a><br>
997 <P>
998 <b>int pcre_info(const pcre *<i>code</i>, int *<i>optptr</i>, int</b>
999 <b>*<i>firstcharptr</i>);</b>
1000 </P>
1001 <P>
1002 The <b>pcre_info()</b> function is now obsolete because its interface is too
1003 restrictive to return all the available data about a compiled pattern. New
1004 programs should use <b>pcre_fullinfo()</b> instead. The yield of
1005 <b>pcre_info()</b> is the number of capturing subpatterns, or one of the
1006 following negative numbers:
1007 <pre>
1008 PCRE_ERROR_NULL the argument <i>code</i> was NULL
1009 PCRE_ERROR_BADMAGIC the "magic number" was not found
1010 </pre>
1011 If the <i>optptr</i> argument is not NULL, a copy of the options with which the
1012 pattern was compiled is placed in the integer it points to (see
1013 PCRE_INFO_OPTIONS above).
1014 </P>
1015 <P>
1016 If the pattern is not anchored and the <i>firstcharptr</i> argument is not NULL,
1017 it is used to pass back information about the first character of any matched
1018 string (see PCRE_INFO_FIRSTBYTE above).
1019 </P>
1020 <br><a name="SEC13" href="#TOC1">REFERENCE COUNTS</a><br>
1021 <P>
1022 <b>int pcre_refcount(pcre *<i>code</i>, int <i>adjust</i>);</b>
1023 </P>
1024 <P>
1025 The <b>pcre_refcount()</b> function is used to maintain a reference count in the
1026 data block that contains a compiled pattern. It is provided for the benefit of
1027 applications that operate in an object-oriented manner, where different parts
1028 of the application may be using the same compiled pattern, but you want to free
1029 the block when they are all done.
1030 </P>
1031 <P>
1032 When a pattern is compiled, the reference count field is initialized to zero.
1033 It is changed only by calling this function, whose action is to add the
1034 <i>adjust</i> value (which may be positive or negative) to it. The yield of the
1035 function is the new value. However, the value of the count is constrained to
1036 lie between 0 and 65535, inclusive. If the new value is outside these limits,
1037 it is forced to the appropriate limit value.
1038 </P>
1039 <P>
1040 Except when it is zero, the reference count is not correctly preserved if a
1041 pattern is compiled on one host and then transferred to a host whose byte-order
1042 is different. (This seems a highly unlikely scenario.)
1043 </P>
1044 <br><a name="SEC14" href="#TOC1">MATCHING A PATTERN: THE TRADITIONAL FUNCTION</a><br>
1045 <P>
1046 <b>int pcre_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
1047 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
1048 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>);</b>
1049 </P>
1050 <P>
1051 The function <b>pcre_exec()</b> is called to match a subject string against a
1052 compiled pattern, which is passed in the <i>code</i> argument. If the
1053 pattern has been studied, the result of the study should be passed in the
1054 <i>extra</i> argument. This function is the main matching facility of the
1055 library, and it operates in a Perl-like manner. For specialist use there is
1056 also an alternative matching function, which is described
1057 <a href="#dfamatch">below</a>
1058 in the section about the <b>pcre_dfa_exec()</b> function.
1059 </P>
1060 <P>
1061 In most applications, the pattern will have been compiled (and optionally
1062 studied) in the same process that calls <b>pcre_exec()</b>. However, it is
1063 possible to save compiled patterns and study data, and then use them later
1064 in different processes, possibly even on different hosts. For a discussion
1065 about this, see the
1066 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
1067 documentation.
1068 </P>
1069 <P>
1070 Here is an example of a simple call to <b>pcre_exec()</b>:
1071 <pre>
1072 int rc;
1073 int ovector[30];
1074 rc = pcre_exec(
1075 re, /* result of pcre_compile() */
1076 NULL, /* we didn't study the pattern */
1077 "some string", /* the subject string */
1078 11, /* the length of the subject string */
1079 0, /* start at offset 0 in the subject */
1080 0, /* default options */
1081 ovector, /* vector of integers for substring information */
1082 30); /* number of elements (NOT size in bytes) */
1083 <a name="extradata"></a></PRE>
1084 </P>
1085 <br><b>
1086 Extra data for <b>pcre_exec()</b>
1087 </b><br>
1088 <P>
1089 If the <i>extra</i> argument is not NULL, it must point to a <b>pcre_extra</b>
1090 data block. The <b>pcre_study()</b> function returns such a block (when it
1091 doesn't return NULL), but you can also create one for yourself, and pass
1092 additional information in it. The <b>pcre_extra</b> block contains the following
1093 fields (not necessarily in this order):
1094 <pre>
1095 unsigned long int <i>flags</i>;
1096 void *<i>study_data</i>;
1097 unsigned long int <i>match_limit</i>;
1098 unsigned long int <i>match_limit_recursion</i>;
1099 void *<i>callout_data</i>;
1100 const unsigned char *<i>tables</i>;
1101 </pre>
1102 The <i>flags</i> field is a bitmap that specifies which of the other fields
1103 are set. The flag bits are:
1104 <pre>
1110 </pre>
1111 Other flag bits should be set to zero. The <i>study_data</i> field is set in the
1112 <b>pcre_extra</b> block that is returned by <b>pcre_study()</b>, together with
1113 the appropriate flag bit. You should not set this yourself, but you may add to
1114 the block by setting the other fields and their corresponding flag bits.
1115 </P>
1116 <P>
1117 The <i>match_limit</i> field provides a means of preventing PCRE from using up a
1118 vast amount of resources when running patterns that are not going to match,
1119 but which have a very large number of possibilities in their search trees. The
1120 classic example is the use of nested unlimited repeats.
1121 </P>
1122 <P>
1123 Internally, PCRE uses a function called <b>match()</b> which it calls repeatedly
1124 (sometimes recursively). The limit set by <i>match_limit</i> is imposed on the
1125 number of times this function is called during a match, which has the effect of
1126 limiting the amount of backtracking that can take place. For patterns that are
1127 not anchored, the count restarts from zero for each position in the subject
1128 string.
1129 </P>
1130 <P>
1131 The default value for the limit can be set when PCRE is built; the default
1132 default is 10 million, which handles all but the most extreme cases. You can
1133 override the default by suppling <b>pcre_exec()</b> with a <b>pcre_extra</b>
1134 block in which <i>match_limit</i> is set, and PCRE_EXTRA_MATCH_LIMIT is set in
1135 the <i>flags</i> field. If the limit is exceeded, <b>pcre_exec()</b> returns
1137 </P>
1138 <P>
1139 The <i>match_limit_recursion</i> field is similar to <i>match_limit</i>, but
1140 instead of limiting the total number of times that <b>match()</b> is called, it
1141 limits the depth of recursion. The recursion depth is a smaller number than the
1142 total number of calls, because not all calls to <b>match()</b> are recursive.
1143 This limit is of use only if it is set smaller than <i>match_limit</i>.
1144 </P>
1145 <P>
1146 Limiting the recursion depth limits the amount of stack that can be used, or,
1147 when PCRE has been compiled to use memory on the heap instead of the stack, the
1148 amount of heap memory that can be used.
1149 </P>
1150 <P>
1151 The default value for <i>match_limit_recursion</i> can be set when PCRE is
1152 built; the default default is the same value as the default for
1153 <i>match_limit</i>. You can override the default by suppling <b>pcre_exec()</b>
1154 with a <b>pcre_extra</b> block in which <i>match_limit_recursion</i> is set, and
1155 PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the <i>flags</i> field. If the limit
1156 is exceeded, <b>pcre_exec()</b> returns PCRE_ERROR_RECURSIONLIMIT.
1157 </P>
1158 <P>
1159 The <i>pcre_callout</i> field is used in conjunction with the "callout" feature,
1160 which is described in the
1161 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1162 documentation.
1163 </P>
1164 <P>
1165 The <i>tables</i> field is used to pass a character tables pointer to
1166 <b>pcre_exec()</b>; this overrides the value that is stored with the compiled
1167 pattern. A non-NULL value is stored with the compiled pattern only if custom
1168 tables were supplied to <b>pcre_compile()</b> via its <i>tableptr</i> argument.
1169 If NULL is passed to <b>pcre_exec()</b> using this mechanism, it forces PCRE's
1170 internal tables to be used. This facility is helpful when re-using patterns
1171 that have been saved after compiling with an external set of tables, because
1172 the external tables might be at a different address when <b>pcre_exec()</b> is
1173 called. See the
1174 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
1175 documentation for a discussion of saving compiled patterns for later use.
1176 </P>
1177 <br><b>
1178 Option bits for <b>pcre_exec()</b>
1179 </b><br>
1180 <P>
1181 The unused bits of the <i>options</i> argument for <b>pcre_exec()</b> must be
1182 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_<i>xxx</i>,
1184 <pre>
1186 </pre>
1187 The PCRE_ANCHORED option limits <b>pcre_exec()</b> to matching at the first
1188 matching position. If a pattern was compiled with PCRE_ANCHORED, or turned out
1189 to be anchored by virtue of its contents, it cannot be made unachored at
1190 matching time.
1191 <pre>
1197 </pre>
1198 These options override the newline definition that was chosen or defaulted when
1199 the pattern was compiled. For details, see the description of
1200 <b>pcre_compile()</b> above. During matching, the newline choice affects the
1201 behaviour of the dot, circumflex, and dollar metacharacters. It may also alter
1202 the way the match position is advanced after a match failure for an unanchored
1204 set, and a match attempt fails when the current position is at a CRLF sequence,
1205 the match position is advanced by two characters instead of one, in other
1206 words, to after the CRLF.
1207 <pre>
1209 </pre>
1210 This option specifies that first character of the subject string is not the
1211 beginning of a line, so the circumflex metacharacter should not match before
1212 it. Setting this without PCRE_MULTILINE (at compile time) causes circumflex
1213 never to match. This option affects only the behaviour of the circumflex
1214 metacharacter. It does not affect \A.
1215 <pre>
1217 </pre>
1218 This option specifies that the end of the subject string is not the end of a
1219 line, so the dollar metacharacter should not match it nor (except in multiline
1220 mode) a newline immediately before it. Setting this without PCRE_MULTILINE (at
1221 compile time) causes dollar never to match. This option affects only the
1222 behaviour of the dollar metacharacter. It does not affect \Z or \z.
1223 <pre>
1225 </pre>
1226 An empty string is not considered to be a valid match if this option is set. If
1227 there are alternatives in the pattern, they are tried. If all the alternatives
1228 match the empty string, the entire match fails. For example, if the pattern
1229 <pre>
1230 a?b?
1231 </pre>
1232 is applied to a string not beginning with "a" or "b", it matches the empty
1233 string at the start of the subject. With PCRE_NOTEMPTY set, this match is not
1234 valid, so PCRE searches further into the string for occurrences of "a" or "b".
1235 </P>
1236 <P>
1237 Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a special case
1238 of a pattern match of the empty string within its <b>split()</b> function, and
1239 when using the /g modifier. It is possible to emulate Perl's behaviour after
1240 matching a null string by first trying the match again at the same offset with
1241 PCRE_NOTEMPTY and PCRE_ANCHORED, and then if that fails by advancing the
1242 starting offset (see below) and trying an ordinary match again. There is some
1243 code that demonstrates how to do this in the <i>pcredemo.c</i> sample program.
1244 <pre>
1246 </pre>
1247 When PCRE_UTF8 is set at compile time, the validity of the subject as a UTF-8
1248 string is automatically checked when <b>pcre_exec()</b> is subsequently called.
1249 The value of <i>startoffset</i> is also checked to ensure that it points to the
1250 start of a UTF-8 character. If an invalid UTF-8 sequence of bytes is found,
1251 <b>pcre_exec()</b> returns the error PCRE_ERROR_BADUTF8. If <i>startoffset</i>
1252 contains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
1253 </P>
1254 <P>
1255 If you already know that your subject is valid, and you want to skip these
1256 checks for performance reasons, you can set the PCRE_NO_UTF8_CHECK option when
1257 calling <b>pcre_exec()</b>. You might want to do this for the second and
1258 subsequent calls to <b>pcre_exec()</b> if you are making repeated calls to find
1259 all the matches in a single subject string. However, you should be sure that
1260 the value of <i>startoffset</i> points to the start of a UTF-8 character. When
1261 PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid UTF-8 string as a
1262 subject, or a value of <i>startoffset</i> that does not point to the start of a
1263 UTF-8 character, is undefined. Your program may crash.
1264 <pre>
1266 </pre>
1267 This option turns on the partial matching feature. If the subject string fails
1268 to match the pattern, but at some point during the matching process the end of
1269 the subject was reached (that is, the subject partially matches the pattern and
1270 the failure to match occurred only because there were not enough subject
1271 characters), <b>pcre_exec()</b> returns PCRE_ERROR_PARTIAL instead of
1272 PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is used, there are restrictions on what
1273 may appear in the pattern. These are discussed in the
1274 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1275 documentation.
1276 </P>
1277 <br><b>
1278 The string to be matched by <b>pcre_exec()</b>
1279 </b><br>
1280 <P>
1281 The subject string is passed to <b>pcre_exec()</b> as a pointer in
1282 <i>subject</i>, a length in <i>length</i>, and a starting byte offset in
1283 <i>startoffset</i>. In UTF-8 mode, the byte offset must point to the start of a
1284 UTF-8 character. Unlike the pattern string, the subject may contain binary zero
1285 bytes. When the starting offset is zero, the search for a match starts at the
1286 beginning of the subject, and this is by far the most common case.
1287 </P>
1288 <P>
1289 A non-zero starting offset is useful when searching for another match in the
1290 same subject by calling <b>pcre_exec()</b> again after a previous success.
1291 Setting <i>startoffset</i> differs from just passing over a shortened string and
1292 setting PCRE_NOTBOL in the case of a pattern that begins with any kind of
1293 lookbehind. For example, consider the pattern
1294 <pre>
1295 \Biss\B
1296 </pre>
1297 which finds occurrences of "iss" in the middle of words. (\B matches only if
1298 the current position in the subject is not a word boundary.) When applied to
1299 the string "Mississipi" the first call to <b>pcre_exec()</b> finds the first
1300 occurrence. If <b>pcre_exec()</b> is called again with just the remainder of the
1301 subject, namely "issipi", it does not match, because \B is always false at the
1302 start of the subject, which is deemed to be a word boundary. However, if
1303 <b>pcre_exec()</b> is passed the entire string again, but with <i>startoffset</i>
1304 set to 4, it finds the second occurrence of "iss" because it is able to look
1305 behind the starting point to discover that it is preceded by a letter.
1306 </P>
1307 <P>
1308 If a non-zero starting offset is passed when the pattern is anchored, one
1309 attempt to match at the given offset is made. This can only succeed if the
1310 pattern does not require the match to be at the start of the subject.
1311 </P>
1312 <br><b>
1313 How <b>pcre_exec()</b> returns captured substrings
1314 </b><br>
1315 <P>
1316 In general, a pattern matches a certain portion of the subject, and in
1317 addition, further substrings from the subject may be picked out by parts of the
1318 pattern. Following the usage in Jeffrey Friedl's book, this is called
1319 "capturing" in what follows, and the phrase "capturing subpattern" is used for
1320 a fragment of a pattern that picks out a substring. PCRE supports several other
1321 kinds of parenthesized subpattern that do not cause substrings to be captured.
1322 </P>
1323 <P>
1324 Captured substrings are returned to the caller via a vector of integer offsets
1325 whose address is passed in <i>ovector</i>. The number of elements in the vector
1326 is passed in <i>ovecsize</i>, which must be a non-negative number. <b>Note</b>:
1327 this argument is NOT the size of <i>ovector</i> in bytes.
1328 </P>
1329 <P>
1330 The first two-thirds of the vector is used to pass back captured substrings,
1331 each substring using a pair of integers. The remaining third of the vector is
1332 used as workspace by <b>pcre_exec()</b> while matching capturing subpatterns,
1333 and is not available for passing back information. The length passed in
1334 <i>ovecsize</i> should always be a multiple of three. If it is not, it is
1335 rounded down.
1336 </P>
1337 <P>
1338 When a match is successful, information about captured substrings is returned
1339 in pairs of integers, starting at the beginning of <i>ovector</i>, and
1340 continuing up to two-thirds of its length at the most. The first element of a
1341 pair is set to the offset of the first character in a substring, and the second
1342 is set to the offset of the first character after the end of a substring. The
1343 first pair, <i>ovector[0]</i> and <i>ovector[1]</i>, identify the portion of the
1344 subject string matched by the entire pattern. The next pair is used for the
1345 first capturing subpattern, and so on. The value returned by <b>pcre_exec()</b>
1346 is one more than the highest numbered pair that has been set. For example, if
1347 two substrings have been captured, the returned value is 3. If there are no
1348 capturing subpatterns, the return value from a successful match is 1,
1349 indicating that just the first pair of offsets has been set.
1350 </P>
1351 <P>
1352 If a capturing subpattern is matched repeatedly, it is the last portion of the
1353 string that it matched that is returned.
1354 </P>
1355 <P>
1356 If the vector is too small to hold all the captured substring offsets, it is
1357 used as far as possible (up to two-thirds of its length), and the function
1358 returns a value of zero. In particular, if the substring offsets are not of
1359 interest, <b>pcre_exec()</b> may be called with <i>ovector</i> passed as NULL and
1360 <i>ovecsize</i> as zero. However, if the pattern contains back references and
1361 the <i>ovector</i> is not big enough to remember the related substrings, PCRE
1362 has to get additional memory for use during matching. Thus it is usually
1363 advisable to supply an <i>ovector</i>.
1364 </P>
1365 <P>
1366 The <b>pcre_info()</b> function can be used to find out how many capturing
1367 subpatterns there are in a compiled pattern. The smallest size for
1368 <i>ovector</i> that will allow for <i>n</i> captured substrings, in addition to
1369 the offsets of the substring matched by the whole pattern, is (<i>n</i>+1)*3.
1370 </P>
1371 <P>
1372 It is possible for capturing subpattern number <i>n+1</i> to match some part of
1373 the subject when subpattern <i>n</i> has not been used at all. For example, if
1374 the string "abc" is matched against the pattern (a|(z))(bc) the return from the
1375 function is 4, and subpatterns 1 and 3 are matched, but 2 is not. When this
1376 happens, both values in the offset pairs corresponding to unused subpatterns
1377 are set to -1.
1378 </P>
1379 <P>
1380 Offset values that correspond to unused subpatterns at the end of the
1381 expression are also set to -1. For example, if the string "abc" is matched
1382 against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not matched. The
1383 return from the function is 2, because the highest used capturing subpattern
1384 number is 1. However, you can refer to the offsets for the second and third
1385 capturing subpatterns if you wish (assuming the vector is large enough, of
1386 course).
1387 </P>
1388 <P>
1389 Some convenience functions are provided for extracting the captured substrings
1390 as separate strings. These are described below.
1391 <a name="errorlist"></a></P>
1392 <br><b>
1393 Error return values from <b>pcre_exec()</b>
1394 </b><br>
1395 <P>
1396 If <b>pcre_exec()</b> fails, it returns a negative number. The following are
1397 defined in the header file:
1398 <pre>
1400 </pre>
1401 The subject string did not match the pattern.
1402 <pre>
1404 </pre>
1405 Either <i>code</i> or <i>subject</i> was passed as NULL, or <i>ovector</i> was
1406 NULL and <i>ovecsize</i> was not zero.
1407 <pre>
1409 </pre>
1410 An unrecognized bit was set in the <i>options</i> argument.
1411 <pre>
1413 </pre>
1414 PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch
1415 the case when it is passed a junk pointer and to detect when a pattern that was
1416 compiled in an environment of one endianness is run in an environment with the
1417 other endianness. This is the error that PCRE gives when the magic number is
1418 not present.
1419 <pre>
1421 </pre>
1422 While running the pattern match, an unknown item was encountered in the
1423 compiled pattern. This error could be caused by a bug in PCRE or by overwriting
1424 of the compiled pattern.
1425 <pre>
1427 </pre>
1428 If a pattern contains back references, but the <i>ovector</i> that is passed to
1429 <b>pcre_exec()</b> is not big enough to remember the referenced substrings, PCRE
1430 gets a block of memory at the start of matching to use for this purpose. If the
1431 call via <b>pcre_malloc()</b> fails, this error is given. The memory is
1432 automatically freed at the end of matching.
1433 <pre>
1435 </pre>
1436 This error is used by the <b>pcre_copy_substring()</b>,
1437 <b>pcre_get_substring()</b>, and <b>pcre_get_substring_list()</b> functions (see
1438 below). It is never returned by <b>pcre_exec()</b>.
1439 <pre>
1441 </pre>
1442 The backtracking limit, as specified by the <i>match_limit</i> field in a
1443 <b>pcre_extra</b> structure (or defaulted) was reached. See the description
1444 above.
1445 <pre>
1447 </pre>
1448 This error is never generated by <b>pcre_exec()</b> itself. It is provided for
1449 use by callout functions that want to yield a distinctive error code. See the
1450 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1451 documentation for details.
1452 <pre>
1454 </pre>
1455 A string that contains an invalid UTF-8 byte sequence was passed as a subject.
1456 <pre>
1458 </pre>
1459 The UTF-8 byte sequence that was passed as a subject was valid, but the value
1460 of <i>startoffset</i> did not point to the beginning of a UTF-8 character.
1461 <pre>
1463 </pre>
1464 The subject string did not match, but it did match partially. See the
1465 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1466 documentation for details of partial matching.
1467 <pre>
1469 </pre>
1470 The PCRE_PARTIAL option was used with a compiled pattern containing items that
1471 are not supported for partial matching. See the
1472 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1473 documentation for details of partial matching.
1474 <pre>
1476 </pre>
1477 An unexpected internal error has occurred. This error could be caused by a bug
1478 in PCRE or by overwriting of the compiled pattern.
1479 <pre>
1481 </pre>
1482 This error is given if the value of the <i>ovecsize</i> argument is negative.
1483 <pre>
1485 </pre>
1486 The internal recursion limit, as specified by the <i>match_limit_recursion</i>
1487 field in a <b>pcre_extra</b> structure (or defaulted) was reached. See the
1488 description above.
1489 <pre>
1491 </pre>
1492 An invalid combination of PCRE_NEWLINE_<i>xxx</i> options was given.
1493 </P>
1494 <P>
1495 Error numbers -16 to -20 and -22 are not used by <b>pcre_exec()</b>.
1496 </P>
1497 <br><a name="SEC15" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NUMBER</a><br>
1498 <P>
1499 <b>int pcre_copy_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1500 <b>int <i>stringcount</i>, int <i>stringnumber</i>, char *<i>buffer</i>,</b>
1501 <b>int <i>buffersize</i>);</b>
1502 </P>
1503 <P>
1504 <b>int pcre_get_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1505 <b>int <i>stringcount</i>, int <i>stringnumber</i>,</b>
1506 <b>const char **<i>stringptr</i>);</b>
1507 </P>
1508 <P>
1509 <b>int pcre_get_substring_list(const char *<i>subject</i>,</b>
1510 <b>int *<i>ovector</i>, int <i>stringcount</i>, const char ***<i>listptr</i>);</b>
1511 </P>
1512 <P>
1513 Captured substrings can be accessed directly by using the offsets returned by
1514 <b>pcre_exec()</b> in <i>ovector</i>. For convenience, the functions
1515 <b>pcre_copy_substring()</b>, <b>pcre_get_substring()</b>, and
1516 <b>pcre_get_substring_list()</b> are provided for extracting captured substrings
1517 as new, separate, zero-terminated strings. These functions identify substrings
1518 by number. The next section describes functions for extracting named
1519 substrings.
1520 </P>
1521 <P>
1522 A substring that contains a binary zero is correctly extracted and has a
1523 further zero added on the end, but the result is not, of course, a C string.
1524 However, you can process such a string by referring to the length that is
1525 returned by <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>.
1526 Unfortunately, the interface to <b>pcre_get_substring_list()</b> is not adequate
1527 for handling strings containing binary zeros, because the end of the final
1528 string is not independently indicated.
1529 </P>
1530 <P>
1531 The first three arguments are the same for all three of these functions:
1532 <i>subject</i> is the subject string that has just been successfully matched,
1533 <i>ovector</i> is a pointer to the vector of integer offsets that was passed to
1534 <b>pcre_exec()</b>, and <i>stringcount</i> is the number of substrings that were
1535 captured by the match, including the substring that matched the entire regular
1536 expression. This is the value returned by <b>pcre_exec()</b> if it is greater
1537 than zero. If <b>pcre_exec()</b> returned zero, indicating that it ran out of
1538 space in <i>ovector</i>, the value passed as <i>stringcount</i> should be the
1539 number of elements in the vector divided by three.
1540 </P>
1541 <P>
1542 The functions <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>
1543 extract a single substring, whose number is given as <i>stringnumber</i>. A
1544 value of zero extracts the substring that matched the entire pattern, whereas
1545 higher values extract the captured substrings. For <b>pcre_copy_substring()</b>,
1546 the string is placed in <i>buffer</i>, whose length is given by
1547 <i>buffersize</i>, while for <b>pcre_get_substring()</b> a new block of memory is
1548 obtained via <b>pcre_malloc</b>, and its address is returned via
1549 <i>stringptr</i>. The yield of the function is the length of the string, not
1550 including the terminating zero, or one of these error codes:
1551 <pre>
1553 </pre>
1554 The buffer was too small for <b>pcre_copy_substring()</b>, or the attempt to get
1555 memory failed for <b>pcre_get_substring()</b>.
1556 <pre>
1558 </pre>
1559 There is no substring whose number is <i>stringnumber</i>.
1560 </P>
1561 <P>
1562 The <b>pcre_get_substring_list()</b> function extracts all available substrings
1563 and builds a list of pointers to them. All this is done in a single block of
1564 memory that is obtained via <b>pcre_malloc</b>. The address of the memory block
1565 is returned via <i>listptr</i>, which is also the start of the list of string
1566 pointers. The end of the list is marked by a NULL pointer. The yield of the
1567 function is zero if all went well, or the error code
1568 <pre>
1570 </pre>
1571 if the attempt to get the memory block failed.
1572 </P>
1573 <P>
1574 When any of these functions encounter a substring that is unset, which can
1575 happen when capturing subpattern number <i>n+1</i> matches some part of the
1576 subject, but subpattern <i>n</i> has not been used at all, they return an empty
1577 string. This can be distinguished from a genuine zero-length substring by
1578 inspecting the appropriate offset in <i>ovector</i>, which is negative for unset
1579 substrings.
1580 </P>
1581 <P>
1582 The two convenience functions <b>pcre_free_substring()</b> and
1583 <b>pcre_free_substring_list()</b> can be used to free the memory returned by
1584 a previous call of <b>pcre_get_substring()</b> or
1585 <b>pcre_get_substring_list()</b>, respectively. They do nothing more than call
1586 the function pointed to by <b>pcre_free</b>, which of course could be called
1587 directly from a C program. However, PCRE is used in some situations where it is
1588 linked via a special interface to another programming language that cannot use
1589 <b>pcre_free</b> directly; it is for these cases that the functions are
1590 provided.
1591 </P>
1592 <br><a name="SEC16" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NAME</a><br>
1593 <P>
1594 <b>int pcre_get_stringnumber(const pcre *<i>code</i>,</b>
1595 <b>const char *<i>name</i>);</b>
1596 </P>
1597 <P>
1598 <b>int pcre_copy_named_substring(const pcre *<i>code</i>,</b>
1599 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
1600 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
1601 <b>char *<i>buffer</i>, int <i>buffersize</i>);</b>
1602 </P>
1603 <P>
1604 <b>int pcre_get_named_substring(const pcre *<i>code</i>,</b>
1605 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
1606 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
1607 <b>const char **<i>stringptr</i>);</b>
1608 </P>
1609 <P>
1610 To extract a substring by name, you first have to find associated number.
1611 For example, for this pattern
1612 <pre>
1613 (a+)b(?&#60;xxx&#62;\d+)...
1614 </pre>
1615 the number of the subpattern called "xxx" is 2. If the name is known to be
1616 unique (PCRE_DUPNAMES was not set), you can find the number from the name by
1617 calling <b>pcre_get_stringnumber()</b>. The first argument is the compiled
1618 pattern, and the second is the name. The yield of the function is the
1619 subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no subpattern of
1620 that name.
1621 </P>
1622 <P>
1623 Given the number, you can extract the substring directly, or use one of the
1624 functions described in the previous section. For convenience, there are also
1625 two functions that do the whole job.
1626 </P>
1627 <P>
1628 Most of the arguments of <b>pcre_copy_named_substring()</b> and
1629 <b>pcre_get_named_substring()</b> are the same as those for the similarly named
1630 functions that extract by number. As these are described in the previous
1631 section, they are not re-described here. There are just two differences:
1632 </P>
1633 <P>
1634 First, instead of a substring number, a substring name is given. Second, there
1635 is an extra argument, given at the start, which is a pointer to the compiled
1636 pattern. This is needed in order to gain access to the name-to-number
1637 translation table.
1638 </P>
1639 <P>
1640 These functions call <b>pcre_get_stringnumber()</b>, and if it succeeds, they
1641 then call <b>pcre_copy_substring()</b> or <b>pcre_get_substring()</b>, as
1642 appropriate. <b>NOTE:</b> If PCRE_DUPNAMES is set and there are duplicate names,
1643 the behaviour may not be what you want (see the next section).
1644 </P>
1645 <br><a name="SEC17" href="#TOC1">DUPLICATE SUBPATTERN NAMES</a><br>
1646 <P>
1647 <b>int pcre_get_stringtable_entries(const pcre *<i>code</i>,</b>
1648 <b>const char *<i>name</i>, char **<i>first</i>, char **<i>last</i>);</b>
1649 </P>
1650 <P>
1651 When a pattern is compiled with the PCRE_DUPNAMES option, names for subpatterns
1652 are not required to be unique. Normally, patterns with duplicate names are such
1653 that in any one match, only one of the named subpatterns participates. An
1654 example is shown in the
1655 <a href="pcrepattern.html"><b>pcrepattern</b></a>
1656 documentation. When duplicates are present, <b>pcre_copy_named_substring()</b>
1657 and <b>pcre_get_named_substring()</b> return the first substring corresponding
1658 to the given name that is set. If none are set, an empty string is returned.
1659 The <b>pcre_get_stringnumber()</b> function returns one of the numbers that are
1660 associated with the name, but it is not defined which it is.
1661 <br>
1662 <br>
1663 If you want to get full details of all captured substrings for a given name,
1664 you must use the <b>pcre_get_stringtable_entries()</b> function. The first
1665 argument is the compiled pattern, and the second is the name. The third and
1666 fourth are pointers to variables which are updated by the function. After it
1667 has run, they point to the first and last entries in the name-to-number table
1668 for the given name. The function itself returns the length of each entry, or
1669 PCRE_ERROR_NOSUBSTRING (-7) if there are none. The format of the table is
1670 described above in the section entitled <i>Information about a pattern</i>.
1671 Given all the relevant entries for the name, you can extract each of their
1672 numbers, and hence the captured data, if any.
1673 </P>
1674 <br><a name="SEC18" href="#TOC1">FINDING ALL POSSIBLE MATCHES</a><br>
1675 <P>
1676 The traditional matching function uses a similar algorithm to Perl, which stops
1677 when it finds the first match, starting at a given point in the subject. If you
1678 want to find all possible matches, or the longest possible match, consider
1679 using the alternative matching function (see below) instead. If you cannot use
1680 the alternative function, but still need to find all possible matches, you
1681 can kludge it up by making use of the callout facility, which is described in
1682 the
1683 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1684 documentation.
1685 </P>
1686 <P>
1687 What you have to do is to insert a callout right at the end of the pattern.
1688 When your callout function is called, extract and save the current matched
1689 substring. Then return 1, which forces <b>pcre_exec()</b> to backtrack and try
1690 other alternatives. Ultimately, when it runs out of matches, <b>pcre_exec()</b>
1691 will yield PCRE_ERROR_NOMATCH.
1692 <a name="dfamatch"></a></P>
1693 <br><a name="SEC19" href="#TOC1">MATCHING A PATTERN: THE ALTERNATIVE FUNCTION</a><br>
1694 <P>
1695 <b>int pcre_dfa_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
1696 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
1697 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>,</b>
1698 <b>int *<i>workspace</i>, int <i>wscount</i>);</b>
1699 </P>
1700 <P>
1701 The function <b>pcre_dfa_exec()</b> is called to match a subject string against
1702 a compiled pattern, using a matching algorithm that scans the subject string
1703 just once, and does not backtrack. This has different characteristics to the
1704 normal algorithm, and is not compatible with Perl. Some of the features of PCRE
1705 patterns are not supported. Nevertheless, there are times when this kind of
1706 matching can be useful. For a discussion of the two matching algorithms, see
1707 the
1708 <a href="pcrematching.html"><b>pcrematching</b></a>
1709 documentation.
1710 </P>
1711 <P>
1712 The arguments for the <b>pcre_dfa_exec()</b> function are the same as for
1713 <b>pcre_exec()</b>, plus two extras. The <i>ovector</i> argument is used in a
1714 different way, and this is described below. The other common arguments are used
1715 in the same way as for <b>pcre_exec()</b>, so their description is not repeated
1716 here.
1717 </P>
1718 <P>
1719 The two additional arguments provide workspace for the function. The workspace
1720 vector should contain at least 20 elements. It is used for keeping track of
1721 multiple paths through the pattern tree. More workspace will be needed for
1722 patterns and subjects where there are a lot of potential matches.
1723 </P>
1724 <P>
1725 Here is an example of a simple call to <b>pcre_dfa_exec()</b>:
1726 <pre>
1727 int rc;
1728 int ovector[10];
1729 int wspace[20];
1730 rc = pcre_dfa_exec(
1731 re, /* result of pcre_compile() */
1732 NULL, /* we didn't study the pattern */
1733 "some string", /* the subject string */
1734 11, /* the length of the subject string */
1735 0, /* start at offset 0 in the subject */
1736 0, /* default options */
1737 ovector, /* vector of integers for substring information */
1738 10, /* number of elements (NOT size in bytes) */
1739 wspace, /* working space vector */
1740 20); /* number of elements (NOT size in bytes) */
1741 </PRE>
1742 </P>
1743 <br><b>
1744 Option bits for <b>pcre_dfa_exec()</b>
1745 </b><br>
1746 <P>
1747 The unused bits of the <i>options</i> argument for <b>pcre_dfa_exec()</b> must be
1748 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_<i>xxx</i>,
1750 PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last three of these are
1751 the same as for <b>pcre_exec()</b>, so their description is not repeated here.
1752 <pre>
1754 </pre>
1755 This has the same general effect as it does for <b>pcre_exec()</b>, but the
1756 details are slightly different. When PCRE_PARTIAL is set for
1757 <b>pcre_dfa_exec()</b>, the return code PCRE_ERROR_NOMATCH is converted into
1758 PCRE_ERROR_PARTIAL if the end of the subject is reached, there have been no
1759 complete matches, but there is still at least one matching possibility. The
1760 portion of the string that provided the partial match is set as the first
1761 matching string.
1762 <pre>
1764 </pre>
1765 Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to stop as
1766 soon as it has found one match. Because of the way the alternative algorithm
1767 works, this is necessarily the shortest possible match at the first possible
1768 matching point in the subject string.
1769 <pre>
1771 </pre>
1772 When <b>pcre_dfa_exec()</b> is called with the PCRE_PARTIAL option, and returns
1773 a partial match, it is possible to call it again, with additional subject
1774 characters, and have it continue with the same match. The PCRE_DFA_RESTART
1775 option requests this action; when it is set, the <i>workspace</i> and
1776 <i>wscount</i> options must reference the same vector as before because data
1777 about the match so far is left in them after a partial match. There is more
1778 discussion of this facility in the
1779 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1780 documentation.
1781 </P>
1782 <br><b>
1783 Successful returns from <b>pcre_dfa_exec()</b>
1784 </b><br>
1785 <P>
1786 When <b>pcre_dfa_exec()</b> succeeds, it may have matched more than one
1787 substring in the subject. Note, however, that all the matches from one run of
1788 the function start at the same point in the subject. The shorter matches are
1789 all initial substrings of the longer matches. For example, if the pattern
1790 <pre>
1791 &#60;.*&#62;
1792 </pre>
1793 is matched against the string
1794 <pre>
1795 This is &#60;something&#62; &#60;something else&#62; &#60;something further&#62; no more
1796 </pre>
1797 the three matched strings are
1798 <pre>
1799 &#60;something&#62;
1800 &#60;something&#62; &#60;something else&#62;
1801 &#60;something&#62; &#60;something else&#62; &#60;something further&#62;
1802 </pre>
1803 On success, the yield of the function is a number greater than zero, which is
1804 the number of matched substrings. The substrings themselves are returned in
1805 <i>ovector</i>. Each string uses two elements; the first is the offset to the
1806 start, and the second is the offset to the end. In fact, all the strings have
1807 the same start offset. (Space could have been saved by giving this only once,
1808 but it was decided to retain some compatibility with the way <b>pcre_exec()</b>
1809 returns data, even though the meaning of the strings is different.)
1810 </P>
1811 <P>
1812 The strings are returned in reverse order of length; that is, the longest
1813 matching string is given first. If there were too many matches to fit into
1814 <i>ovector</i>, the yield of the function is zero, and the vector is filled with
1815 the longest matches.
1816 </P>
1817 <br><b>
1818 Error returns from <b>pcre_dfa_exec()</b>
1819 </b><br>
1820 <P>
1821 The <b>pcre_dfa_exec()</b> function returns a negative number when it fails.
1822 Many of the errors are the same as for <b>pcre_exec()</b>, and these are
1823 described
1824 <a href="#errorlist">above.</a>
1825 There are in addition the following errors that are specific to
1826 <b>pcre_dfa_exec()</b>:
1827 <pre>
1829 </pre>
1830 This return is given if <b>pcre_dfa_exec()</b> encounters an item in the pattern
1831 that it does not support, for instance, the use of \C or a back reference.
1832 <pre>
1834 </pre>
1835 This return is given if <b>pcre_dfa_exec()</b> encounters a condition item that
1836 uses a back reference for the condition, or a test for recursion in a specific
1837 group. These are not supported.
1838 <pre>
1840 </pre>
1841 This return is given if <b>pcre_dfa_exec()</b> is called with an <i>extra</i>
1842 block that contains a setting of the <i>match_limit</i> field. This is not
1843 supported (it is meaningless).
1844 <pre>
1846 </pre>
1847 This return is given if <b>pcre_dfa_exec()</b> runs out of space in the
1848 <i>workspace</i> vector.
1849 <pre>
1851 </pre>
1852 When a recursive subpattern is processed, the matching function calls itself
1853 recursively, using private vectors for <i>ovector</i> and <i>workspace</i>. This
1854 error is given if the output vector is not large enough. This should be
1855 extremely rare, as a vector of size 1000 is used.
1856 </P>
1857 <br><a name="SEC20" href="#TOC1">SEE ALSO</a><br>
1858 <P>
1859 <b>pcrebuild</b>(3), <b>pcrecallout</b>(3), <b>pcrecpp(3)</b>(3),
1860 <b>pcrematching</b>(3), <b>pcrepartial</b>(3), <b>pcreposix</b>(3),
1861 <b>pcreprecompile</b>(3), <b>pcresample</b>(3), <b>pcrestack</b>(3).
1862 </P>
1863 <br><a name="SEC21" href="#TOC1">AUTHOR</a><br>
1864 <P>
1865 Philip Hazel
1866 <br>
1867 University Computing Service
1868 <br>
1869 Cambridge CB2 3QH, England.
1870 <br>
1871 </P>
1872 <br><a name="SEC22" href="#TOC1">REVISION</a><br>
1873 <P>
1874 Last updated: 30 July 2007
1875 <br>
1876 Copyright &copy; 1997-2007 University of Cambridge.
1877 <br>
1878 <p>
1879 Return to the <a href="index.html">PCRE index page</a>.
1880 </p>


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