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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 </ul>
37 <br><a name="SEC1" href="#TOC1">PCRE NATIVE API</a><br>
38 <P>
39 <b>#include &#60;pcre.h&#62;</b>
40 </P>
41 <P>
42 <b>pcre *pcre_compile(const char *<i>pattern</i>, int <i>options</i>,</b>
43 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
44 <b>const unsigned char *<i>tableptr</i>);</b>
45 </P>
46 <P>
47 <b>pcre *pcre_compile2(const char *<i>pattern</i>, int <i>options</i>,</b>
48 <b>int *<i>errorcodeptr</i>,</b>
49 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
50 <b>const unsigned char *<i>tableptr</i>);</b>
51 </P>
52 <P>
53 <b>pcre_extra *pcre_study(const pcre *<i>code</i>, int <i>options</i>,</b>
54 <b>const char **<i>errptr</i>);</b>
55 </P>
56 <P>
57 <b>int pcre_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
58 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
59 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>);</b>
60 </P>
61 <P>
62 <b>int pcre_dfa_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
63 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
64 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>,</b>
65 <b>int *<i>workspace</i>, int <i>wscount</i>);</b>
66 </P>
67 <P>
68 <b>int pcre_copy_named_substring(const pcre *<i>code</i>,</b>
69 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
70 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
71 <b>char *<i>buffer</i>, int <i>buffersize</i>);</b>
72 </P>
73 <P>
74 <b>int pcre_copy_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
75 <b>int <i>stringcount</i>, int <i>stringnumber</i>, char *<i>buffer</i>,</b>
76 <b>int <i>buffersize</i>);</b>
77 </P>
78 <P>
79 <b>int pcre_get_named_substring(const pcre *<i>code</i>,</b>
80 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
81 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
82 <b>const char **<i>stringptr</i>);</b>
83 </P>
84 <P>
85 <b>int pcre_get_stringnumber(const pcre *<i>code</i>,</b>
86 <b>const char *<i>name</i>);</b>
87 </P>
88 <P>
89 <b>int pcre_get_stringtable_entries(const pcre *<i>code</i>,</b>
90 <b>const char *<i>name</i>, char **<i>first</i>, char **<i>last</i>);</b>
91 </P>
92 <P>
93 <b>int pcre_get_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
94 <b>int <i>stringcount</i>, int <i>stringnumber</i>,</b>
95 <b>const char **<i>stringptr</i>);</b>
96 </P>
97 <P>
98 <b>int pcre_get_substring_list(const char *<i>subject</i>,</b>
99 <b>int *<i>ovector</i>, int <i>stringcount</i>, const char ***<i>listptr</i>);</b>
100 </P>
101 <P>
102 <b>void pcre_free_substring(const char *<i>stringptr</i>);</b>
103 </P>
104 <P>
105 <b>void pcre_free_substring_list(const char **<i>stringptr</i>);</b>
106 </P>
107 <P>
108 <b>const unsigned char *pcre_maketables(void);</b>
109 </P>
110 <P>
111 <b>int pcre_fullinfo(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
112 <b>int <i>what</i>, void *<i>where</i>);</b>
113 </P>
114 <P>
115 <b>int pcre_info(const pcre *<i>code</i>, int *<i>optptr</i>, int</b>
116 <b>*<i>firstcharptr</i>);</b>
117 </P>
118 <P>
119 <b>int pcre_refcount(pcre *<i>code</i>, int <i>adjust</i>);</b>
120 </P>
121 <P>
122 <b>int pcre_config(int <i>what</i>, void *<i>where</i>);</b>
123 </P>
124 <P>
125 <b>char *pcre_version(void);</b>
126 </P>
127 <P>
128 <b>void *(*pcre_malloc)(size_t);</b>
129 </P>
130 <P>
131 <b>void (*pcre_free)(void *);</b>
132 </P>
133 <P>
134 <b>void *(*pcre_stack_malloc)(size_t);</b>
135 </P>
136 <P>
137 <b>void (*pcre_stack_free)(void *);</b>
138 </P>
139 <P>
140 <b>int (*pcre_callout)(pcre_callout_block *);</b>
141 </P>
142 <br><a name="SEC2" href="#TOC1">PCRE API OVERVIEW</a><br>
143 <P>
144 PCRE has its own native API, which is described in this document. There are
145 also some wrapper functions that correspond to the POSIX regular expression
146 API. These are described in the
147 <a href="pcreposix.html"><b>pcreposix</b></a>
148 documentation. Both of these APIs define a set of C function calls. A C++
149 wrapper is distributed with PCRE. It is documented in the
150 <a href="pcrecpp.html"><b>pcrecpp</b></a>
151 page.
152 </P>
153 <P>
154 The native API C function prototypes are defined in the header file
155 <b>pcre.h</b>, and on Unix systems the library itself is called <b>libpcre</b>.
156 It can normally be accessed by adding <b>-lpcre</b> to the command for linking
157 an application that uses PCRE. The header file defines the macros PCRE_MAJOR
158 and PCRE_MINOR to contain the major and minor release numbers for the library.
159 Applications can use these to include support for different releases of PCRE.
160 </P>
161 <P>
162 The functions <b>pcre_compile()</b>, <b>pcre_compile2()</b>, <b>pcre_study()</b>,
163 and <b>pcre_exec()</b> are used for compiling and matching regular expressions
164 in a Perl-compatible manner. A sample program that demonstrates the simplest
165 way of using them is provided in the file called <i>pcredemo.c</i> in the source
166 distribution. The
167 <a href="pcresample.html"><b>pcresample</b></a>
168 documentation describes how to run it.
169 </P>
170 <P>
171 A second matching function, <b>pcre_dfa_exec()</b>, which is not
172 Perl-compatible, is also provided. This uses a different algorithm for the
173 matching. The alternative algorithm finds all possible matches (at a given
174 point in the subject), and scans the subject just once. However, this algorithm
175 does not return captured substrings. A description of the two matching
176 algorithms and their advantages and disadvantages is given in the
177 <a href="pcrematching.html"><b>pcrematching</b></a>
178 documentation.
179 </P>
180 <P>
181 In addition to the main compiling and matching functions, there are convenience
182 functions for extracting captured substrings from a subject string that is
183 matched by <b>pcre_exec()</b>. They are:
184 <pre>
185 <b>pcre_copy_substring()</b>
186 <b>pcre_copy_named_substring()</b>
187 <b>pcre_get_substring()</b>
188 <b>pcre_get_named_substring()</b>
189 <b>pcre_get_substring_list()</b>
190 <b>pcre_get_stringnumber()</b>
191 <b>pcre_get_stringtable_entries()</b>
192 </pre>
193 <b>pcre_free_substring()</b> and <b>pcre_free_substring_list()</b> are also
194 provided, to free the memory used for extracted strings.
195 </P>
196 <P>
197 The function <b>pcre_maketables()</b> is used to build a set of character tables
198 in the current locale for passing to <b>pcre_compile()</b>, <b>pcre_exec()</b>,
199 or <b>pcre_dfa_exec()</b>. This is an optional facility that is provided for
200 specialist use. Most commonly, no special tables are passed, in which case
201 internal tables that are generated when PCRE is built are used.
202 </P>
203 <P>
204 The function <b>pcre_fullinfo()</b> is used to find out information about a
205 compiled pattern; <b>pcre_info()</b> is an obsolete version that returns only
206 some of the available information, but is retained for backwards compatibility.
207 The function <b>pcre_version()</b> returns a pointer to a string containing the
208 version of PCRE and its date of release.
209 </P>
210 <P>
211 The function <b>pcre_refcount()</b> maintains a reference count in a data block
212 containing a compiled pattern. This is provided for the benefit of
213 object-oriented applications.
214 </P>
215 <P>
216 The global variables <b>pcre_malloc</b> and <b>pcre_free</b> initially contain
217 the entry points of the standard <b>malloc()</b> and <b>free()</b> functions,
218 respectively. PCRE calls the memory management functions via these variables,
219 so a calling program can replace them if it wishes to intercept the calls. This
220 should be done before calling any PCRE functions.
221 </P>
222 <P>
223 The global variables <b>pcre_stack_malloc</b> and <b>pcre_stack_free</b> are also
224 indirections to memory management functions. These special functions are used
225 only when PCRE is compiled to use the heap for remembering data, instead of
226 recursive function calls, when running the <b>pcre_exec()</b> function. See the
227 <a href="pcrebuild.html"><b>pcrebuild</b></a>
228 documentation for details of how to do this. It is a non-standard way of
229 building PCRE, for use in environments that have limited stacks. Because of the
230 greater use of memory management, it runs more slowly. Separate functions are
231 provided so that special-purpose external code can be used for this case. When
232 used, these functions are always called in a stack-like manner (last obtained,
233 first freed), and always for memory blocks of the same size. There is a
234 discussion about PCRE's stack usage in the
235 <a href="pcrestack.html"><b>pcrestack</b></a>
236 documentation.
237 </P>
238 <P>
239 The global variable <b>pcre_callout</b> initially contains NULL. It can be set
240 by the caller to a "callout" function, which PCRE will then call at specified
241 points during a matching operation. Details are given in the
242 <a href="pcrecallout.html"><b>pcrecallout</b></a>
243 documentation.
244 </P>
245 <br><a name="SEC3" href="#TOC1">NEWLINES</a><br>
246 <P>
247 PCRE supports four different conventions for indicating line breaks in
248 strings: a single CR (carriage return) character, a single LF (linefeed)
249 character, the two-character sequence CRLF, or any Unicode newline sequence.
250 The Unicode newline sequences are the three just mentioned, plus the single
251 characters VT (vertical tab, U+000B), FF (formfeed, U+000C), NEL (next line,
252 U+0085), LS (line separator, U+2028), and PS (paragraph separator, U+2029).
253 </P>
254 <P>
255 Each of the first three conventions is used by at least one operating system as
256 its standard newline sequence. When PCRE is built, a default can be specified.
257 The default default is LF, which is the Unix standard. When PCRE is run, the
258 default can be overridden, either when a pattern is compiled, or when it is
259 matched.
260 </P>
261 <P>
262 In the PCRE documentation the word "newline" is used to mean "the character or
263 pair of characters that indicate a line break". The choice of newline
264 convention affects the handling of the dot, circumflex, and dollar
265 metacharacters, the handling of #-comments in /x mode, and, when CRLF is a
266 recognized line ending sequence, the match position advancement for a
267 non-anchored pattern. The choice of newline convention does not affect the
268 interpretation of the \n or \r escape sequences.
269 </P>
270 <br><a name="SEC4" href="#TOC1">MULTITHREADING</a><br>
271 <P>
272 The PCRE functions can be used in multi-threading applications, with the
273 proviso that the memory management functions pointed to by <b>pcre_malloc</b>,
274 <b>pcre_free</b>, <b>pcre_stack_malloc</b>, and <b>pcre_stack_free</b>, and the
275 callout function pointed to by <b>pcre_callout</b>, are shared by all threads.
276 </P>
277 <P>
278 The compiled form of a regular expression is not altered during matching, so
279 the same compiled pattern can safely be used by several threads at once.
280 </P>
281 <br><a name="SEC5" href="#TOC1">SAVING PRECOMPILED PATTERNS FOR LATER USE</a><br>
282 <P>
283 The compiled form of a regular expression can be saved and re-used at a later
284 time, possibly by a different program, and even on a host other than the one on
285 which it was compiled. Details are given in the
286 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
287 documentation.
288 </P>
289 <br><a name="SEC6" href="#TOC1">CHECKING BUILD-TIME OPTIONS</a><br>
290 <P>
291 <b>int pcre_config(int <i>what</i>, void *<i>where</i>);</b>
292 </P>
293 <P>
294 The function <b>pcre_config()</b> makes it possible for a PCRE client to
295 discover which optional features have been compiled into the PCRE library. The
296 <a href="pcrebuild.html"><b>pcrebuild</b></a>
297 documentation has more details about these optional features.
298 </P>
299 <P>
300 The first argument for <b>pcre_config()</b> is an integer, specifying which
301 information is required; the second argument is a pointer to a variable into
302 which the information is placed. The following information is available:
303 <pre>
305 </pre>
306 The output is an integer that is set to one if UTF-8 support is available;
307 otherwise it is set to zero.
308 <pre>
310 </pre>
311 The output is an integer that is set to one if support for Unicode character
312 properties is available; otherwise it is set to zero.
313 <pre>
315 </pre>
316 The output is an integer whose value specifies the default character sequence
317 that is recognized as meaning "newline". The four values that are supported
318 are: 10 for LF, 13 for CR, 3338 for CRLF, and -1 for ANY. The default should
319 normally be the standard sequence for your operating system.
320 <pre>
322 </pre>
323 The output is an integer that contains the number of bytes used for internal
324 linkage in compiled regular expressions. The value is 2, 3, or 4. Larger values
325 allow larger regular expressions to be compiled, at the expense of slower
326 matching. The default value of 2 is sufficient for all but the most massive
327 patterns, since it allows the compiled pattern to be up to 64K in size.
328 <pre>
330 </pre>
331 The output is an integer that contains the threshold above which the POSIX
332 interface uses <b>malloc()</b> for output vectors. Further details are given in
333 the
334 <a href="pcreposix.html"><b>pcreposix</b></a>
335 documentation.
336 <pre>
338 </pre>
339 The output is an integer that gives the default limit for the number of
340 internal matching function calls in a <b>pcre_exec()</b> execution. Further
341 details are given with <b>pcre_exec()</b> below.
342 <pre>
344 </pre>
345 The output is an integer that gives the default limit for the depth of
346 recursion when calling the internal matching function in a <b>pcre_exec()</b>
347 execution. Further details are given with <b>pcre_exec()</b> below.
348 <pre>
350 </pre>
351 The output is an integer that is set to one if internal recursion when running
352 <b>pcre_exec()</b> is implemented by recursive function calls that use the stack
353 to remember their state. This is the usual way that PCRE is compiled. The
354 output is zero if PCRE was compiled to use blocks of data on the heap instead
355 of recursive function calls. In this case, <b>pcre_stack_malloc</b> and
356 <b>pcre_stack_free</b> are called to manage memory blocks on the heap, thus
357 avoiding the use of the stack.
358 </P>
359 <br><a name="SEC7" href="#TOC1">COMPILING A PATTERN</a><br>
360 <P>
361 <b>pcre *pcre_compile(const char *<i>pattern</i>, int <i>options</i>,</b>
362 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
363 <b>const unsigned char *<i>tableptr</i>);</b>
364 <b>pcre *pcre_compile2(const char *<i>pattern</i>, int <i>options</i>,</b>
365 <b>int *<i>errorcodeptr</i>,</b>
366 <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
367 <b>const unsigned char *<i>tableptr</i>);</b>
368 </P>
369 <P>
370 Either of the functions <b>pcre_compile()</b> or <b>pcre_compile2()</b> can be
371 called to compile a pattern into an internal form. The only difference between
372 the two interfaces is that <b>pcre_compile2()</b> has an additional argument,
373 <i>errorcodeptr</i>, via which a numerical error code can be returned.
374 </P>
375 <P>
376 The pattern is a C string terminated by a binary zero, and is passed in the
377 <i>pattern</i> argument. A pointer to a single block of memory that is obtained
378 via <b>pcre_malloc</b> is returned. This contains the compiled code and related
379 data. The <b>pcre</b> type is defined for the returned block; this is a typedef
380 for a structure whose contents are not externally defined. It is up to the
381 caller to free the memory (via <b>pcre_free</b>) when it is no longer required.
382 </P>
383 <P>
384 Although the compiled code of a PCRE regex is relocatable, that is, it does not
385 depend on memory location, the complete <b>pcre</b> data block is not
386 fully relocatable, because it may contain a copy of the <i>tableptr</i>
387 argument, which is an address (see below).
388 </P>
389 <P>
390 The <i>options</i> argument contains various bit settings that affect the
391 compilation. It should be zero if no options are required. The available
392 options are described below. Some of them, in particular, those that are
393 compatible with Perl, can also be set and unset from within the pattern (see
394 the detailed description in the
395 <a href="pcrepattern.html"><b>pcrepattern</b></a>
396 documentation). For these options, the contents of the <i>options</i> argument
397 specifies their initial settings at the start of compilation and execution. The
398 PCRE_ANCHORED and PCRE_NEWLINE_<i>xxx</i> options can be set at the time of
399 matching as well as at compile time.
400 </P>
401 <P>
402 If <i>errptr</i> is NULL, <b>pcre_compile()</b> returns NULL immediately.
403 Otherwise, if compilation of a pattern fails, <b>pcre_compile()</b> returns
404 NULL, and sets the variable pointed to by <i>errptr</i> to point to a textual
405 error message. This is a static string that is part of the library. You must
406 not try to free it. The offset from the start of the pattern to the character
407 where the error was discovered is placed in the variable pointed to by
408 <i>erroffset</i>, which must not be NULL. If it is, an immediate error is given.
409 </P>
410 <P>
411 If <b>pcre_compile2()</b> is used instead of <b>pcre_compile()</b>, and the
412 <i>errorcodeptr</i> argument is not NULL, a non-zero error code number is
413 returned via this argument in the event of an error. This is in addition to the
414 textual error message. Error codes and messages are listed below.
415 </P>
416 <P>
417 If the final argument, <i>tableptr</i>, is NULL, PCRE uses a default set of
418 character tables that are built when PCRE is compiled, using the default C
419 locale. Otherwise, <i>tableptr</i> must be an address that is the result of a
420 call to <b>pcre_maketables()</b>. This value is stored with the compiled
421 pattern, and used again by <b>pcre_exec()</b>, unless another table pointer is
422 passed to it. For more discussion, see the section on locale support below.
423 </P>
424 <P>
425 This code fragment shows a typical straightforward call to <b>pcre_compile()</b>:
426 <pre>
427 pcre *re;
428 const char *error;
429 int erroffset;
430 re = pcre_compile(
431 "^A.*Z", /* the pattern */
432 0, /* default options */
433 &error, /* for error message */
434 &erroffset, /* for error offset */
435 NULL); /* use default character tables */
436 </pre>
437 The following names for option bits are defined in the <b>pcre.h</b> header
438 file:
439 <pre>
441 </pre>
442 If this bit is set, the pattern is forced to be "anchored", that is, it is
443 constrained to match only at the first matching point in the string that is
444 being searched (the "subject string"). This effect can also be achieved by
445 appropriate constructs in the pattern itself, which is the only way to do it in
446 Perl.
447 <pre>
449 </pre>
450 If this bit is set, <b>pcre_compile()</b> automatically inserts callout items,
451 all with number 255, before each pattern item. For discussion of the callout
452 facility, see the
453 <a href="pcrecallout.html"><b>pcrecallout</b></a>
454 documentation.
455 <pre>
457 </pre>
458 If this bit is set, letters in the pattern match both upper and lower case
459 letters. It is equivalent to Perl's /i option, and it can be changed within a
460 pattern by a (?i) option setting. In UTF-8 mode, PCRE always understands the
461 concept of case for characters whose values are less than 128, so caseless
462 matching is always possible. For characters with higher values, the concept of
463 case is supported if PCRE is compiled with Unicode property support, but not
464 otherwise. If you want to use caseless matching for characters 128 and above,
465 you must ensure that PCRE is compiled with Unicode property support as well as
466 with UTF-8 support.
467 <pre>
469 </pre>
470 If this bit is set, a dollar metacharacter in the pattern matches only at the
471 end of the subject string. Without this option, a dollar also matches
472 immediately before a newline at the end of the string (but not before any other
473 newlines). The PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is set.
474 There is no equivalent to this option in Perl, and no way to set it within a
475 pattern.
476 <pre>
478 </pre>
479 If this bit is set, a dot metacharater in the pattern matches all characters,
480 including those that indicate newline. Without it, a dot does not match when
481 the current position is at a newline. This option is equivalent to Perl's /s
482 option, and it can be changed within a pattern by a (?s) option setting. A
483 negative class such as [^a] always matches newline characters, independent of
484 the setting of this option.
485 <pre>
487 </pre>
488 If this bit is set, names used to identify capturing subpatterns need not be
489 unique. This can be helpful for certain types of pattern when it is known that
490 only one instance of the named subpattern can ever be matched. There are more
491 details of named subpatterns below; see also the
492 <a href="pcrepattern.html"><b>pcrepattern</b></a>
493 documentation.
494 <pre>
496 </pre>
497 If this bit is set, whitespace data characters in the pattern are totally
498 ignored except when escaped or inside a character class. Whitespace does not
499 include the VT character (code 11). In addition, characters between an
500 unescaped # outside a character class and the next newline, inclusive, are also
501 ignored. This is equivalent to Perl's /x option, and it can be changed within a
502 pattern by a (?x) option setting.
503 </P>
504 <P>
505 This option makes it possible to include comments inside complicated patterns.
506 Note, however, that this applies only to data characters. Whitespace characters
507 may never appear within special character sequences in a pattern, for example
508 within the sequence (?( which introduces a conditional subpattern.
509 <pre>
511 </pre>
512 This option was invented in order to turn on additional functionality of PCRE
513 that is incompatible with Perl, but it is currently of very little use. When
514 set, any backslash in a pattern that is followed by a letter that has no
515 special meaning causes an error, thus reserving these combinations for future
516 expansion. By default, as in Perl, a backslash followed by a letter with no
517 special meaning is treated as a literal. (Perl can, however, be persuaded to
518 give a warning for this.) There are at present no other features controlled by
519 this option. It can also be set by a (?X) option setting within a pattern.
520 <pre>
522 </pre>
523 If this option is set, an unanchored pattern is required to match before or at
524 the first newline in the subject string, though the matched text may continue
525 over the newline.
526 <pre>
528 </pre>
529 By default, PCRE treats the subject string as consisting of a single line of
530 characters (even if it actually contains newlines). The "start of line"
531 metacharacter (^) matches only at the start of the string, while the "end of
532 line" metacharacter ($) matches only at the end of the string, or before a
533 terminating newline (unless PCRE_DOLLAR_ENDONLY is set). This is the same as
534 Perl.
535 </P>
536 <P>
537 When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs
538 match immediately following or immediately before internal newlines in the
539 subject string, respectively, as well as at the very start and end. This is
540 equivalent to Perl's /m option, and it can be changed within a pattern by a
541 (?m) option setting. If there are no newlines in a subject string, or no
542 occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no effect.
543 <pre>
548 </pre>
549 These options override the default newline definition that was chosen when PCRE
550 was built. Setting the first or the second specifies that a newline is
551 indicated by a single character (CR or LF, respectively). Setting
552 PCRE_NEWLINE_CRLF specifies that a newline is indicated by the two-character
553 CRLF sequence. Setting PCRE_NEWLINE_ANY specifies that any Unicode newline
554 sequence should be recognized. The Unicode newline sequences are the three just
555 mentioned, plus the single characters VT (vertical tab, U+000B), FF (formfeed,
556 U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS
557 (paragraph separator, U+2029). The last two are recognized only in UTF-8 mode.
558 </P>
559 <P>
560 The newline setting in the options word uses three bits that are treated
561 as a number, giving eight possibilities. Currently only five are used (default
562 plus the four values above). This means that if you set more than one newline
563 option, the combination may or may not be sensible. For example,
565 other combinations yield unused numbers and cause an error.
566 </P>
567 <P>
568 The only time that a line break is specially recognized when compiling a
569 pattern is if PCRE_EXTENDED is set, and an unescaped # outside a character
570 class is encountered. This indicates a comment that lasts until after the next
571 line break sequence. In other circumstances, line break sequences are treated
572 as literal data, except that in PCRE_EXTENDED mode, both CR and LF are treated
573 as whitespace characters and are therefore ignored.
574 </P>
575 <P>
576 The newline option that is set at compile time becomes the default that is used
577 for <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b>, but it can be overridden.
578 <pre>
580 </pre>
581 If this option is set, it disables the use of numbered capturing parentheses in
582 the pattern. Any opening parenthesis that is not followed by ? behaves as if it
583 were followed by ?: but named parentheses can still be used for capturing (and
584 they acquire numbers in the usual way). There is no equivalent of this option
585 in Perl.
586 <pre>
588 </pre>
589 This option inverts the "greediness" of the quantifiers so that they are not
590 greedy by default, but become greedy if followed by "?". It is not compatible
591 with Perl. It can also be set by a (?U) option setting within the pattern.
592 <pre>
594 </pre>
595 This option causes PCRE to regard both the pattern and the subject as strings
596 of UTF-8 characters instead of single-byte character strings. However, it is
597 available only when PCRE is built to include UTF-8 support. If not, the use
598 of this option provokes an error. Details of how this option changes the
599 behaviour of PCRE are given in the
600 <a href="pcre.html#utf8support">section on UTF-8 support</a>
601 in the main
602 <a href="pcre.html"><b>pcre</b></a>
603 page.
604 <pre>
606 </pre>
607 When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
608 automatically checked. If an invalid UTF-8 sequence of bytes is found,
609 <b>pcre_compile()</b> returns an error. If you already know that your pattern is
610 valid, and you want to skip this check for performance reasons, you can set the
611 PCRE_NO_UTF8_CHECK option. When it is set, the effect of passing an invalid
612 UTF-8 string as a pattern is undefined. It may cause your program to crash.
613 Note that this option can also be passed to <b>pcre_exec()</b> and
614 <b>pcre_dfa_exec()</b>, to suppress the UTF-8 validity checking of subject
615 strings.
616 </P>
617 <br><a name="SEC8" href="#TOC1">COMPILATION ERROR CODES</a><br>
618 <P>
619 The following table lists the error codes than may be returned by
620 <b>pcre_compile2()</b>, along with the error messages that may be returned by
621 both compiling functions. As PCRE has developed, some error codes have fallen
622 out of use. To avoid confusion, they have not been re-used.
623 <pre>
624 0 no error
625 1 \ at end of pattern
626 2 \c at end of pattern
627 3 unrecognized character follows \
628 4 numbers out of order in {} quantifier
629 5 number too big in {} quantifier
630 6 missing terminating ] for character class
631 7 invalid escape sequence in character class
632 8 range out of order in character class
633 9 nothing to repeat
634 10 [this code is not in use]
635 11 internal error: unexpected repeat
636 12 unrecognized character after (?
637 13 POSIX named classes are supported only within a class
638 14 missing )
639 15 reference to non-existent subpattern
640 16 erroffset passed as NULL
641 17 unknown option bit(s) set
642 18 missing ) after comment
643 19 [this code is not in use]
644 20 regular expression too large
645 21 failed to get memory
646 22 unmatched parentheses
647 23 internal error: code overflow
648 24 unrecognized character after (?&#60;
649 25 lookbehind assertion is not fixed length
650 26 malformed number or name after (?(
651 27 conditional group contains more than two branches
652 28 assertion expected after (?(
653 29 (?R or (?digits must be followed by )
654 30 unknown POSIX class name
655 31 POSIX collating elements are not supported
656 32 this version of PCRE is not compiled with PCRE_UTF8 support
657 33 [this code is not in use]
658 34 character value in \x{...} sequence is too large
659 35 invalid condition (?(0)
660 36 \C not allowed in lookbehind assertion
661 37 PCRE does not support \L, \l, \N, \U, or \u
662 38 number after (?C is &#62; 255
663 39 closing ) for (?C expected
664 40 recursive call could loop indefinitely
665 41 unrecognized character after (?P
666 42 syntax error in subpattern name (missing terminator)
667 43 two named subpatterns have the same name
668 44 invalid UTF-8 string
669 45 support for \P, \p, and \X has not been compiled
670 46 malformed \P or \p sequence
671 47 unknown property name after \P or \p
672 48 subpattern name is too long (maximum 32 characters)
673 49 too many named subpatterns (maximum 10,000)
674 50 repeated subpattern is too long
675 51 octal value is greater than \377 (not in UTF-8 mode)
676 52 internal error: overran compiling workspace
677 53 internal error: previously-checked referenced subpattern not found
678 54 DEFINE group contains more than one branch
679 55 repeating a DEFINE group is not allowed
680 56 inconsistent NEWLINE options"
681 </PRE>
682 </P>
683 <br><a name="SEC9" href="#TOC1">STUDYING A PATTERN</a><br>
684 <P>
685 <b>pcre_extra *pcre_study(const pcre *<i>code</i>, int <i>options</i></b>
686 <b>const char **<i>errptr</i>);</b>
687 </P>
688 <P>
689 If a compiled pattern is going to be used several times, it is worth spending
690 more time analyzing it in order to speed up the time taken for matching. The
691 function <b>pcre_study()</b> takes a pointer to a compiled pattern as its first
692 argument. If studying the pattern produces additional information that will
693 help speed up matching, <b>pcre_study()</b> returns a pointer to a
694 <b>pcre_extra</b> block, in which the <i>study_data</i> field points to the
695 results of the study.
696 </P>
697 <P>
698 The returned value from <b>pcre_study()</b> can be passed directly to
699 <b>pcre_exec()</b>. However, a <b>pcre_extra</b> block also contains other
700 fields that can be set by the caller before the block is passed; these are
701 described
702 <a href="#extradata">below</a>
703 in the section on matching a pattern.
704 </P>
705 <P>
706 If studying the pattern does not produce any additional information
707 <b>pcre_study()</b> returns NULL. In that circumstance, if the calling program
708 wants to pass any of the other fields to <b>pcre_exec()</b>, it must set up its
709 own <b>pcre_extra</b> block.
710 </P>
711 <P>
712 The second argument of <b>pcre_study()</b> contains option bits. At present, no
713 options are defined, and this argument should always be zero.
714 </P>
715 <P>
716 The third argument for <b>pcre_study()</b> is a pointer for an error message. If
717 studying succeeds (even if no data is returned), the variable it points to is
718 set to NULL. Otherwise it is set to point to a textual error message. This is a
719 static string that is part of the library. You must not try to free it. You
720 should test the error pointer for NULL after calling <b>pcre_study()</b>, to be
721 sure that it has run successfully.
722 </P>
723 <P>
724 This is a typical call to <b>pcre_study</b>():
725 <pre>
726 pcre_extra *pe;
727 pe = pcre_study(
728 re, /* result of pcre_compile() */
729 0, /* no options exist */
730 &error); /* set to NULL or points to a message */
731 </pre>
732 At present, studying a pattern is useful only for non-anchored patterns that do
733 not have a single fixed starting character. A bitmap of possible starting
734 bytes is created.
735 <a name="localesupport"></a></P>
736 <br><a name="SEC10" href="#TOC1">LOCALE SUPPORT</a><br>
737 <P>
738 PCRE handles caseless matching, and determines whether characters are letters
739 digits, or whatever, by reference to a set of tables, indexed by character
740 value. When running in UTF-8 mode, this applies only to characters with codes
741 less than 128. Higher-valued codes never match escapes such as \w or \d, but
742 can be tested with \p if PCRE is built with Unicode character property
743 support. The use of locales with Unicode is discouraged.
744 </P>
745 <P>
746 An internal set of tables is created in the default C locale when PCRE is
747 built. This is used when the final argument of <b>pcre_compile()</b> is NULL,
748 and is sufficient for many applications. An alternative set of tables can,
749 however, be supplied. These may be created in a different locale from the
750 default. As more and more applications change to using Unicode, the need for
751 this locale support is expected to die away.
752 </P>
753 <P>
754 External tables are built by calling the <b>pcre_maketables()</b> function,
755 which has no arguments, in the relevant locale. The result can then be passed
756 to <b>pcre_compile()</b> or <b>pcre_exec()</b> as often as necessary. For
757 example, to build and use tables that are appropriate for the French locale
758 (where accented characters with values greater than 128 are treated as letters),
759 the following code could be used:
760 <pre>
761 setlocale(LC_CTYPE, "fr_FR");
762 tables = pcre_maketables();
763 re = pcre_compile(..., tables);
764 </pre>
765 When <b>pcre_maketables()</b> runs, the tables are built in memory that is
766 obtained via <b>pcre_malloc</b>. It is the caller's responsibility to ensure
767 that the memory containing the tables remains available for as long as it is
768 needed.
769 </P>
770 <P>
771 The pointer that is passed to <b>pcre_compile()</b> is saved with the compiled
772 pattern, and the same tables are used via this pointer by <b>pcre_study()</b>
773 and normally also by <b>pcre_exec()</b>. Thus, by default, for any single
774 pattern, compilation, studying and matching all happen in the same locale, but
775 different patterns can be compiled in different locales.
776 </P>
777 <P>
778 It is possible to pass a table pointer or NULL (indicating the use of the
779 internal tables) to <b>pcre_exec()</b>. Although not intended for this purpose,
780 this facility could be used to match a pattern in a different locale from the
781 one in which it was compiled. Passing table pointers at run time is discussed
782 below in the section on matching a pattern.
783 </P>
784 <br><a name="SEC11" href="#TOC1">INFORMATION ABOUT A PATTERN</a><br>
785 <P>
786 <b>int pcre_fullinfo(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
787 <b>int <i>what</i>, void *<i>where</i>);</b>
788 </P>
789 <P>
790 The <b>pcre_fullinfo()</b> function returns information about a compiled
791 pattern. It replaces the obsolete <b>pcre_info()</b> function, which is
792 nevertheless retained for backwards compability (and is documented below).
793 </P>
794 <P>
795 The first argument for <b>pcre_fullinfo()</b> is a pointer to the compiled
796 pattern. The second argument is the result of <b>pcre_study()</b>, or NULL if
797 the pattern was not studied. The third argument specifies which piece of
798 information is required, and the fourth argument is a pointer to a variable
799 to receive the data. The yield of the function is zero for success, or one of
800 the following negative numbers:
801 <pre>
802 PCRE_ERROR_NULL the argument <i>code</i> was NULL
803 the argument <i>where</i> was NULL
804 PCRE_ERROR_BADMAGIC the "magic number" was not found
805 PCRE_ERROR_BADOPTION the value of <i>what</i> was invalid
806 </pre>
807 The "magic number" is placed at the start of each compiled pattern as an simple
808 check against passing an arbitrary memory pointer. Here is a typical call of
809 <b>pcre_fullinfo()</b>, to obtain the length of the compiled pattern:
810 <pre>
811 int rc;
812 size_t length;
813 rc = pcre_fullinfo(
814 re, /* result of pcre_compile() */
815 pe, /* result of pcre_study(), or NULL */
816 PCRE_INFO_SIZE, /* what is required */
817 &length); /* where to put the data */
818 </pre>
819 The possible values for the third argument are defined in <b>pcre.h</b>, and are
820 as follows:
821 <pre>
823 </pre>
824 Return the number of the highest back reference in the pattern. The fourth
825 argument should point to an <b>int</b> variable. Zero is returned if there are
826 no back references.
827 <pre>
829 </pre>
830 Return the number of capturing subpatterns in the pattern. The fourth argument
831 should point to an <b>int</b> variable.
832 <pre>
834 </pre>
835 Return a pointer to the internal default character tables within PCRE. The
836 fourth argument should point to an <b>unsigned char *</b> variable. This
837 information call is provided for internal use by the <b>pcre_study()</b>
838 function. External callers can cause PCRE to use its internal tables by passing
839 a NULL table pointer.
840 <pre>
842 </pre>
843 Return information about the first byte of any matched string, for a
844 non-anchored pattern. The fourth argument should point to an <b>int</b>
845 variable. (This option used to be called PCRE_INFO_FIRSTCHAR; the old name is
846 still recognized for backwards compatibility.)
847 </P>
848 <P>
849 If there is a fixed first byte, for example, from a pattern such as
850 (cat|cow|coyote), its value is returned. Otherwise, if either
851 <br>
852 <br>
853 (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
854 starts with "^", or
855 <br>
856 <br>
857 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
858 (if it were set, the pattern would be anchored),
859 <br>
860 <br>
861 -1 is returned, indicating that the pattern matches only at the start of a
862 subject string or after any newline within the string. Otherwise -2 is
863 returned. For anchored patterns, -2 is returned.
864 <pre>
866 </pre>
867 If the pattern was studied, and this resulted in the construction of a 256-bit
868 table indicating a fixed set of bytes for the first byte in any matching
869 string, a pointer to the table is returned. Otherwise NULL is returned. The
870 fourth argument should point to an <b>unsigned char *</b> variable.
871 <pre>
873 </pre>
874 Return the value of the rightmost literal byte that must exist in any matched
875 string, other than at its start, if such a byte has been recorded. The fourth
876 argument should point to an <b>int</b> variable. If there is no such byte, -1 is
877 returned. For anchored patterns, a last literal byte is recorded only if it
878 follows something of variable length. For example, for the pattern
879 /^a\d+z\d+/ the returned value is "z", but for /^a\dz\d/ the returned value
880 is -1.
881 <pre>
885 </pre>
886 PCRE supports the use of named as well as numbered capturing parentheses. The
887 names are just an additional way of identifying the parentheses, which still
888 acquire numbers. Several convenience functions such as
889 <b>pcre_get_named_substring()</b> are provided for extracting captured
890 substrings by name. It is also possible to extract the data directly, by first
891 converting the name to a number in order to access the correct pointers in the
892 output vector (described with <b>pcre_exec()</b> below). To do the conversion,
893 you need to use the name-to-number map, which is described by these three
894 values.
895 </P>
896 <P>
897 The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives
898 the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each
899 entry; both of these return an <b>int</b> value. The entry size depends on the
900 length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first
901 entry of the table (a pointer to <b>char</b>). The first two bytes of each entry
902 are the number of the capturing parenthesis, most significant byte first. The
903 rest of the entry is the corresponding name, zero terminated. The names are in
904 alphabetical order. When PCRE_DUPNAMES is set, duplicate names are in order of
905 their parentheses numbers. For example, consider the following pattern (assume
906 PCRE_EXTENDED is set, so white space - including newlines - is ignored):
907 <pre>
908 (?&#60;date&#62; (?&#60;year&#62;(\d\d)?\d\d) - (?&#60;month&#62;\d\d) - (?&#60;day&#62;\d\d) )
909 </pre>
910 There are four named subpatterns, so the table has four entries, and each entry
911 in the table is eight bytes long. The table is as follows, with non-printing
912 bytes shows in hexadecimal, and undefined bytes shown as ??:
913 <pre>
914 00 01 d a t e 00 ??
915 00 05 d a y 00 ?? ??
916 00 04 m o n t h 00
917 00 02 y e a r 00 ??
918 </pre>
919 When writing code to extract data from named subpatterns using the
920 name-to-number map, remember that the length of the entries is likely to be
921 different for each compiled pattern.
922 <pre>
924 </pre>
925 Return a copy of the options with which the pattern was compiled. The fourth
926 argument should point to an <b>unsigned long int</b> variable. These option bits
927 are those specified in the call to <b>pcre_compile()</b>, modified by any
928 top-level option settings within the pattern itself.
929 </P>
930 <P>
931 A pattern is automatically anchored by PCRE if all of its top-level
932 alternatives begin with one of the following:
933 <pre>
934 ^ unless PCRE_MULTILINE is set
935 \A always
936 \G always
937 .* if PCRE_DOTALL is set and there are no back references to the subpattern in which .* appears
938 </pre>
939 For such patterns, the PCRE_ANCHORED bit is set in the options returned by
940 <b>pcre_fullinfo()</b>.
941 <pre>
943 </pre>
944 Return the size of the compiled pattern, that is, the value that was passed as
945 the argument to <b>pcre_malloc()</b> when PCRE was getting memory in which to
946 place the compiled data. The fourth argument should point to a <b>size_t</b>
947 variable.
948 <pre>
950 </pre>
951 Return the size of the data block pointed to by the <i>study_data</i> field in
952 a <b>pcre_extra</b> block. That is, it is the value that was passed to
953 <b>pcre_malloc()</b> when PCRE was getting memory into which to place the data
954 created by <b>pcre_study()</b>. The fourth argument should point to a
955 <b>size_t</b> variable.
956 </P>
957 <br><a name="SEC12" href="#TOC1">OBSOLETE INFO FUNCTION</a><br>
958 <P>
959 <b>int pcre_info(const pcre *<i>code</i>, int *<i>optptr</i>, int</b>
960 <b>*<i>firstcharptr</i>);</b>
961 </P>
962 <P>
963 The <b>pcre_info()</b> function is now obsolete because its interface is too
964 restrictive to return all the available data about a compiled pattern. New
965 programs should use <b>pcre_fullinfo()</b> instead. The yield of
966 <b>pcre_info()</b> is the number of capturing subpatterns, or one of the
967 following negative numbers:
968 <pre>
969 PCRE_ERROR_NULL the argument <i>code</i> was NULL
970 PCRE_ERROR_BADMAGIC the "magic number" was not found
971 </pre>
972 If the <i>optptr</i> argument is not NULL, a copy of the options with which the
973 pattern was compiled is placed in the integer it points to (see
975 </P>
976 <P>
977 If the pattern is not anchored and the <i>firstcharptr</i> argument is not NULL,
978 it is used to pass back information about the first character of any matched
979 string (see PCRE_INFO_FIRSTBYTE above).
980 </P>
981 <br><a name="SEC13" href="#TOC1">REFERENCE COUNTS</a><br>
982 <P>
983 <b>int pcre_refcount(pcre *<i>code</i>, int <i>adjust</i>);</b>
984 </P>
985 <P>
986 The <b>pcre_refcount()</b> function is used to maintain a reference count in the
987 data block that contains a compiled pattern. It is provided for the benefit of
988 applications that operate in an object-oriented manner, where different parts
989 of the application may be using the same compiled pattern, but you want to free
990 the block when they are all done.
991 </P>
992 <P>
993 When a pattern is compiled, the reference count field is initialized to zero.
994 It is changed only by calling this function, whose action is to add the
995 <i>adjust</i> value (which may be positive or negative) to it. The yield of the
996 function is the new value. However, the value of the count is constrained to
997 lie between 0 and 65535, inclusive. If the new value is outside these limits,
998 it is forced to the appropriate limit value.
999 </P>
1000 <P>
1001 Except when it is zero, the reference count is not correctly preserved if a
1002 pattern is compiled on one host and then transferred to a host whose byte-order
1003 is different. (This seems a highly unlikely scenario.)
1004 </P>
1005 <br><a name="SEC14" href="#TOC1">MATCHING A PATTERN: THE TRADITIONAL FUNCTION</a><br>
1006 <P>
1007 <b>int pcre_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
1008 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
1009 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>);</b>
1010 </P>
1011 <P>
1012 The function <b>pcre_exec()</b> is called to match a subject string against a
1013 compiled pattern, which is passed in the <i>code</i> argument. If the
1014 pattern has been studied, the result of the study should be passed in the
1015 <i>extra</i> argument. This function is the main matching facility of the
1016 library, and it operates in a Perl-like manner. For specialist use there is
1017 also an alternative matching function, which is described
1018 <a href="#dfamatch">below</a>
1019 in the section about the <b>pcre_dfa_exec()</b> function.
1020 </P>
1021 <P>
1022 In most applications, the pattern will have been compiled (and optionally
1023 studied) in the same process that calls <b>pcre_exec()</b>. However, it is
1024 possible to save compiled patterns and study data, and then use them later
1025 in different processes, possibly even on different hosts. For a discussion
1026 about this, see the
1027 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
1028 documentation.
1029 </P>
1030 <P>
1031 Here is an example of a simple call to <b>pcre_exec()</b>:
1032 <pre>
1033 int rc;
1034 int ovector[30];
1035 rc = pcre_exec(
1036 re, /* result of pcre_compile() */
1037 NULL, /* we didn't study the pattern */
1038 "some string", /* the subject string */
1039 11, /* the length of the subject string */
1040 0, /* start at offset 0 in the subject */
1041 0, /* default options */
1042 ovector, /* vector of integers for substring information */
1043 30); /* number of elements (NOT size in bytes) */
1044 <a name="extradata"></a></PRE>
1045 </P>
1046 <br><b>
1047 Extra data for <b>pcre_exec()</b>
1048 </b><br>
1049 <P>
1050 If the <i>extra</i> argument is not NULL, it must point to a <b>pcre_extra</b>
1051 data block. The <b>pcre_study()</b> function returns such a block (when it
1052 doesn't return NULL), but you can also create one for yourself, and pass
1053 additional information in it. The <b>pcre_extra</b> block contains the following
1054 fields (not necessarily in this order):
1055 <pre>
1056 unsigned long int <i>flags</i>;
1057 void *<i>study_data</i>;
1058 unsigned long int <i>match_limit</i>;
1059 unsigned long int <i>match_limit_recursion</i>;
1060 void *<i>callout_data</i>;
1061 const unsigned char *<i>tables</i>;
1062 </pre>
1063 The <i>flags</i> field is a bitmap that specifies which of the other fields
1064 are set. The flag bits are:
1065 <pre>
1071 </pre>
1072 Other flag bits should be set to zero. The <i>study_data</i> field is set in the
1073 <b>pcre_extra</b> block that is returned by <b>pcre_study()</b>, together with
1074 the appropriate flag bit. You should not set this yourself, but you may add to
1075 the block by setting the other fields and their corresponding flag bits.
1076 </P>
1077 <P>
1078 The <i>match_limit</i> field provides a means of preventing PCRE from using up a
1079 vast amount of resources when running patterns that are not going to match,
1080 but which have a very large number of possibilities in their search trees. The
1081 classic example is the use of nested unlimited repeats.
1082 </P>
1083 <P>
1084 Internally, PCRE uses a function called <b>match()</b> which it calls repeatedly
1085 (sometimes recursively). The limit set by <i>match_limit</i> is imposed on the
1086 number of times this function is called during a match, which has the effect of
1087 limiting the amount of backtracking that can take place. For patterns that are
1088 not anchored, the count restarts from zero for each position in the subject
1089 string.
1090 </P>
1091 <P>
1092 The default value for the limit can be set when PCRE is built; the default
1093 default is 10 million, which handles all but the most extreme cases. You can
1094 override the default by suppling <b>pcre_exec()</b> with a <b>pcre_extra</b>
1095 block in which <i>match_limit</i> is set, and PCRE_EXTRA_MATCH_LIMIT is set in
1096 the <i>flags</i> field. If the limit is exceeded, <b>pcre_exec()</b> returns
1098 </P>
1099 <P>
1100 The <i>match_limit_recursion</i> field is similar to <i>match_limit</i>, but
1101 instead of limiting the total number of times that <b>match()</b> is called, it
1102 limits the depth of recursion. The recursion depth is a smaller number than the
1103 total number of calls, because not all calls to <b>match()</b> are recursive.
1104 This limit is of use only if it is set smaller than <i>match_limit</i>.
1105 </P>
1106 <P>
1107 Limiting the recursion depth limits the amount of stack that can be used, or,
1108 when PCRE has been compiled to use memory on the heap instead of the stack, the
1109 amount of heap memory that can be used.
1110 </P>
1111 <P>
1112 The default value for <i>match_limit_recursion</i> can be set when PCRE is
1113 built; the default default is the same value as the default for
1114 <i>match_limit</i>. You can override the default by suppling <b>pcre_exec()</b>
1115 with a <b>pcre_extra</b> block in which <i>match_limit_recursion</i> is set, and
1116 PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the <i>flags</i> field. If the limit
1117 is exceeded, <b>pcre_exec()</b> returns PCRE_ERROR_RECURSIONLIMIT.
1118 </P>
1119 <P>
1120 The <i>pcre_callout</i> field is used in conjunction with the "callout" feature,
1121 which is described in the
1122 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1123 documentation.
1124 </P>
1125 <P>
1126 The <i>tables</i> field is used to pass a character tables pointer to
1127 <b>pcre_exec()</b>; this overrides the value that is stored with the compiled
1128 pattern. A non-NULL value is stored with the compiled pattern only if custom
1129 tables were supplied to <b>pcre_compile()</b> via its <i>tableptr</i> argument.
1130 If NULL is passed to <b>pcre_exec()</b> using this mechanism, it forces PCRE's
1131 internal tables to be used. This facility is helpful when re-using patterns
1132 that have been saved after compiling with an external set of tables, because
1133 the external tables might be at a different address when <b>pcre_exec()</b> is
1134 called. See the
1135 <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
1136 documentation for a discussion of saving compiled patterns for later use.
1137 </P>
1138 <br><b>
1139 Option bits for <b>pcre_exec()</b>
1140 </b><br>
1141 <P>
1142 The unused bits of the <i>options</i> argument for <b>pcre_exec()</b> must be
1143 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_<i>xxx</i>,
1145 <pre>
1147 </pre>
1148 The PCRE_ANCHORED option limits <b>pcre_exec()</b> to matching at the first
1149 matching position. If a pattern was compiled with PCRE_ANCHORED, or turned out
1150 to be anchored by virtue of its contents, it cannot be made unachored at
1151 matching time.
1152 <pre>
1157 </pre>
1158 These options override the newline definition that was chosen or defaulted when
1159 the pattern was compiled. For details, see the description of
1160 <b>pcre_compile()</b> above. During matching, the newline choice affects the
1161 behaviour of the dot, circumflex, and dollar metacharacters. It may also alter
1162 the way the match position is advanced after a match failure for an unanchored
1163 pattern. When PCRE_NEWLINE_CRLF or PCRE_NEWLINE_ANY is set, and a match attempt
1164 fails when the current position is at a CRLF sequence, the match position is
1165 advanced by two characters instead of one, in other words, to after the CRLF.
1166 <pre>
1168 </pre>
1169 This option specifies that first character of the subject string is not the
1170 beginning of a line, so the circumflex metacharacter should not match before
1171 it. Setting this without PCRE_MULTILINE (at compile time) causes circumflex
1172 never to match. This option affects only the behaviour of the circumflex
1173 metacharacter. It does not affect \A.
1174 <pre>
1176 </pre>
1177 This option specifies that the end of the subject string is not the end of a
1178 line, so the dollar metacharacter should not match it nor (except in multiline
1179 mode) a newline immediately before it. Setting this without PCRE_MULTILINE (at
1180 compile time) causes dollar never to match. This option affects only the
1181 behaviour of the dollar metacharacter. It does not affect \Z or \z.
1182 <pre>
1184 </pre>
1185 An empty string is not considered to be a valid match if this option is set. If
1186 there are alternatives in the pattern, they are tried. If all the alternatives
1187 match the empty string, the entire match fails. For example, if the pattern
1188 <pre>
1189 a?b?
1190 </pre>
1191 is applied to a string not beginning with "a" or "b", it matches the empty
1192 string at the start of the subject. With PCRE_NOTEMPTY set, this match is not
1193 valid, so PCRE searches further into the string for occurrences of "a" or "b".
1194 </P>
1195 <P>
1196 Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a special case
1197 of a pattern match of the empty string within its <b>split()</b> function, and
1198 when using the /g modifier. It is possible to emulate Perl's behaviour after
1199 matching a null string by first trying the match again at the same offset with
1200 PCRE_NOTEMPTY and PCRE_ANCHORED, and then if that fails by advancing the
1201 starting offset (see below) and trying an ordinary match again. There is some
1202 code that demonstrates how to do this in the <i>pcredemo.c</i> sample program.
1203 <pre>
1205 </pre>
1206 When PCRE_UTF8 is set at compile time, the validity of the subject as a UTF-8
1207 string is automatically checked when <b>pcre_exec()</b> is subsequently called.
1208 The value of <i>startoffset</i> is also checked to ensure that it points to the
1209 start of a UTF-8 character. If an invalid UTF-8 sequence of bytes is found,
1210 <b>pcre_exec()</b> returns the error PCRE_ERROR_BADUTF8. If <i>startoffset</i>
1211 contains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
1212 </P>
1213 <P>
1214 If you already know that your subject is valid, and you want to skip these
1215 checks for performance reasons, you can set the PCRE_NO_UTF8_CHECK option when
1216 calling <b>pcre_exec()</b>. You might want to do this for the second and
1217 subsequent calls to <b>pcre_exec()</b> if you are making repeated calls to find
1218 all the matches in a single subject string. However, you should be sure that
1219 the value of <i>startoffset</i> points to the start of a UTF-8 character. When
1220 PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid UTF-8 string as a
1221 subject, or a value of <i>startoffset</i> that does not point to the start of a
1222 UTF-8 character, is undefined. Your program may crash.
1223 <pre>
1225 </pre>
1226 This option turns on the partial matching feature. If the subject string fails
1227 to match the pattern, but at some point during the matching process the end of
1228 the subject was reached (that is, the subject partially matches the pattern and
1229 the failure to match occurred only because there were not enough subject
1230 characters), <b>pcre_exec()</b> returns PCRE_ERROR_PARTIAL instead of
1231 PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is used, there are restrictions on what
1232 may appear in the pattern. These are discussed in the
1233 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1234 documentation.
1235 </P>
1236 <br><b>
1237 The string to be matched by <b>pcre_exec()</b>
1238 </b><br>
1239 <P>
1240 The subject string is passed to <b>pcre_exec()</b> as a pointer in
1241 <i>subject</i>, a length in <i>length</i>, and a starting byte offset in
1242 <i>startoffset</i>. In UTF-8 mode, the byte offset must point to the start of a
1243 UTF-8 character. Unlike the pattern string, the subject may contain binary zero
1244 bytes. When the starting offset is zero, the search for a match starts at the
1245 beginning of the subject, and this is by far the most common case.
1246 </P>
1247 <P>
1248 A non-zero starting offset is useful when searching for another match in the
1249 same subject by calling <b>pcre_exec()</b> again after a previous success.
1250 Setting <i>startoffset</i> differs from just passing over a shortened string and
1251 setting PCRE_NOTBOL in the case of a pattern that begins with any kind of
1252 lookbehind. For example, consider the pattern
1253 <pre>
1254 \Biss\B
1255 </pre>
1256 which finds occurrences of "iss" in the middle of words. (\B matches only if
1257 the current position in the subject is not a word boundary.) When applied to
1258 the string "Mississipi" the first call to <b>pcre_exec()</b> finds the first
1259 occurrence. If <b>pcre_exec()</b> is called again with just the remainder of the
1260 subject, namely "issipi", it does not match, because \B is always false at the
1261 start of the subject, which is deemed to be a word boundary. However, if
1262 <b>pcre_exec()</b> is passed the entire string again, but with <i>startoffset</i>
1263 set to 4, it finds the second occurrence of "iss" because it is able to look
1264 behind the starting point to discover that it is preceded by a letter.
1265 </P>
1266 <P>
1267 If a non-zero starting offset is passed when the pattern is anchored, one
1268 attempt to match at the given offset is made. This can only succeed if the
1269 pattern does not require the match to be at the start of the subject.
1270 </P>
1271 <br><b>
1272 How <b>pcre_exec()</b> returns captured substrings
1273 </b><br>
1274 <P>
1275 In general, a pattern matches a certain portion of the subject, and in
1276 addition, further substrings from the subject may be picked out by parts of the
1277 pattern. Following the usage in Jeffrey Friedl's book, this is called
1278 "capturing" in what follows, and the phrase "capturing subpattern" is used for
1279 a fragment of a pattern that picks out a substring. PCRE supports several other
1280 kinds of parenthesized subpattern that do not cause substrings to be captured.
1281 </P>
1282 <P>
1283 Captured substrings are returned to the caller via a vector of integer offsets
1284 whose address is passed in <i>ovector</i>. The number of elements in the vector
1285 is passed in <i>ovecsize</i>, which must be a non-negative number. <b>Note</b>:
1286 this argument is NOT the size of <i>ovector</i> in bytes.
1287 </P>
1288 <P>
1289 The first two-thirds of the vector is used to pass back captured substrings,
1290 each substring using a pair of integers. The remaining third of the vector is
1291 used as workspace by <b>pcre_exec()</b> while matching capturing subpatterns,
1292 and is not available for passing back information. The length passed in
1293 <i>ovecsize</i> should always be a multiple of three. If it is not, it is
1294 rounded down.
1295 </P>
1296 <P>
1297 When a match is successful, information about captured substrings is returned
1298 in pairs of integers, starting at the beginning of <i>ovector</i>, and
1299 continuing up to two-thirds of its length at the most. The first element of a
1300 pair is set to the offset of the first character in a substring, and the second
1301 is set to the offset of the first character after the end of a substring. The
1302 first pair, <i>ovector[0]</i> and <i>ovector[1]</i>, identify the portion of the
1303 subject string matched by the entire pattern. The next pair is used for the
1304 first capturing subpattern, and so on. The value returned by <b>pcre_exec()</b>
1305 is one more than the highest numbered pair that has been set. For example, if
1306 two substrings have been captured, the returned value is 3. If there are no
1307 capturing subpatterns, the return value from a successful match is 1,
1308 indicating that just the first pair of offsets has been set.
1309 </P>
1310 <P>
1311 If a capturing subpattern is matched repeatedly, it is the last portion of the
1312 string that it matched that is returned.
1313 </P>
1314 <P>
1315 If the vector is too small to hold all the captured substring offsets, it is
1316 used as far as possible (up to two-thirds of its length), and the function
1317 returns a value of zero. In particular, if the substring offsets are not of
1318 interest, <b>pcre_exec()</b> may be called with <i>ovector</i> passed as NULL and
1319 <i>ovecsize</i> as zero. However, if the pattern contains back references and
1320 the <i>ovector</i> is not big enough to remember the related substrings, PCRE
1321 has to get additional memory for use during matching. Thus it is usually
1322 advisable to supply an <i>ovector</i>.
1323 </P>
1324 <P>
1325 The <b>pcre_info()</b> function can be used to find out how many capturing
1326 subpatterns there are in a compiled pattern. The smallest size for
1327 <i>ovector</i> that will allow for <i>n</i> captured substrings, in addition to
1328 the offsets of the substring matched by the whole pattern, is (<i>n</i>+1)*3.
1329 </P>
1330 <P>
1331 It is possible for capturing subpattern number <i>n+1</i> to match some part of
1332 the subject when subpattern <i>n</i> has not been used at all. For example, if
1333 the string "abc" is matched against the pattern (a|(z))(bc) the return from the
1334 function is 4, and subpatterns 1 and 3 are matched, but 2 is not. When this
1335 happens, both values in the offset pairs corresponding to unused subpatterns
1336 are set to -1.
1337 </P>
1338 <P>
1339 Offset values that correspond to unused subpatterns at the end of the
1340 expression are also set to -1. For example, if the string "abc" is matched
1341 against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not matched. The
1342 return from the function is 2, because the highest used capturing subpattern
1343 number is 1. However, you can refer to the offsets for the second and third
1344 capturing subpatterns if you wish (assuming the vector is large enough, of
1345 course).
1346 </P>
1347 <P>
1348 Some convenience functions are provided for extracting the captured substrings
1349 as separate strings. These are described below.
1350 <a name="errorlist"></a></P>
1351 <br><b>
1352 Error return values from <b>pcre_exec()</b>
1353 </b><br>
1354 <P>
1355 If <b>pcre_exec()</b> fails, it returns a negative number. The following are
1356 defined in the header file:
1357 <pre>
1359 </pre>
1360 The subject string did not match the pattern.
1361 <pre>
1363 </pre>
1364 Either <i>code</i> or <i>subject</i> was passed as NULL, or <i>ovector</i> was
1365 NULL and <i>ovecsize</i> was not zero.
1366 <pre>
1368 </pre>
1369 An unrecognized bit was set in the <i>options</i> argument.
1370 <pre>
1372 </pre>
1373 PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch
1374 the case when it is passed a junk pointer and to detect when a pattern that was
1375 compiled in an environment of one endianness is run in an environment with the
1376 other endianness. This is the error that PCRE gives when the magic number is
1377 not present.
1378 <pre>
1380 </pre>
1381 While running the pattern match, an unknown item was encountered in the
1382 compiled pattern. This error could be caused by a bug in PCRE or by overwriting
1383 of the compiled pattern.
1384 <pre>
1386 </pre>
1387 If a pattern contains back references, but the <i>ovector</i> that is passed to
1388 <b>pcre_exec()</b> is not big enough to remember the referenced substrings, PCRE
1389 gets a block of memory at the start of matching to use for this purpose. If the
1390 call via <b>pcre_malloc()</b> fails, this error is given. The memory is
1391 automatically freed at the end of matching.
1392 <pre>
1394 </pre>
1395 This error is used by the <b>pcre_copy_substring()</b>,
1396 <b>pcre_get_substring()</b>, and <b>pcre_get_substring_list()</b> functions (see
1397 below). It is never returned by <b>pcre_exec()</b>.
1398 <pre>
1400 </pre>
1401 The backtracking limit, as specified by the <i>match_limit</i> field in a
1402 <b>pcre_extra</b> structure (or defaulted) was reached. See the description
1403 above.
1404 <pre>
1406 </pre>
1407 This error is never generated by <b>pcre_exec()</b> itself. It is provided for
1408 use by callout functions that want to yield a distinctive error code. See the
1409 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1410 documentation for details.
1411 <pre>
1413 </pre>
1414 A string that contains an invalid UTF-8 byte sequence was passed as a subject.
1415 <pre>
1417 </pre>
1418 The UTF-8 byte sequence that was passed as a subject was valid, but the value
1419 of <i>startoffset</i> did not point to the beginning of a UTF-8 character.
1420 <pre>
1422 </pre>
1423 The subject string did not match, but it did match partially. See the
1424 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1425 documentation for details of partial matching.
1426 <pre>
1428 </pre>
1429 The PCRE_PARTIAL option was used with a compiled pattern containing items that
1430 are not supported for partial matching. See the
1431 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1432 documentation for details of partial matching.
1433 <pre>
1435 </pre>
1436 An unexpected internal error has occurred. This error could be caused by a bug
1437 in PCRE or by overwriting of the compiled pattern.
1438 <pre>
1440 </pre>
1441 This error is given if the value of the <i>ovecsize</i> argument is negative.
1442 <pre>
1444 </pre>
1445 The internal recursion limit, as specified by the <i>match_limit_recursion</i>
1446 field in a <b>pcre_extra</b> structure (or defaulted) was reached. See the
1447 description above.
1448 <pre>
1450 </pre>
1451 When a group that can match an empty substring is repeated with an unbounded
1452 upper limit, the subject position at the start of the group must be remembered,
1453 so that a test for an empty string can be made when the end of the group is
1454 reached. Some workspace is required for this; if it runs out, this error is
1455 given.
1456 <pre>
1458 </pre>
1459 An invalid combination of PCRE_NEWLINE_<i>xxx</i> options was given.
1460 </P>
1461 <P>
1462 Error numbers -16 to -20 are not used by <b>pcre_exec()</b>.
1463 </P>
1464 <br><a name="SEC15" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NUMBER</a><br>
1465 <P>
1466 <b>int pcre_copy_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1467 <b>int <i>stringcount</i>, int <i>stringnumber</i>, char *<i>buffer</i>,</b>
1468 <b>int <i>buffersize</i>);</b>
1469 </P>
1470 <P>
1471 <b>int pcre_get_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1472 <b>int <i>stringcount</i>, int <i>stringnumber</i>,</b>
1473 <b>const char **<i>stringptr</i>);</b>
1474 </P>
1475 <P>
1476 <b>int pcre_get_substring_list(const char *<i>subject</i>,</b>
1477 <b>int *<i>ovector</i>, int <i>stringcount</i>, const char ***<i>listptr</i>);</b>
1478 </P>
1479 <P>
1480 Captured substrings can be accessed directly by using the offsets returned by
1481 <b>pcre_exec()</b> in <i>ovector</i>. For convenience, the functions
1482 <b>pcre_copy_substring()</b>, <b>pcre_get_substring()</b>, and
1483 <b>pcre_get_substring_list()</b> are provided for extracting captured substrings
1484 as new, separate, zero-terminated strings. These functions identify substrings
1485 by number. The next section describes functions for extracting named
1486 substrings.
1487 </P>
1488 <P>
1489 A substring that contains a binary zero is correctly extracted and has a
1490 further zero added on the end, but the result is not, of course, a C string.
1491 However, you can process such a string by referring to the length that is
1492 returned by <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>.
1493 Unfortunately, the interface to <b>pcre_get_substring_list()</b> is not adequate
1494 for handling strings containing binary zeros, because the end of the final
1495 string is not independently indicated.
1496 </P>
1497 <P>
1498 The first three arguments are the same for all three of these functions:
1499 <i>subject</i> is the subject string that has just been successfully matched,
1500 <i>ovector</i> is a pointer to the vector of integer offsets that was passed to
1501 <b>pcre_exec()</b>, and <i>stringcount</i> is the number of substrings that were
1502 captured by the match, including the substring that matched the entire regular
1503 expression. This is the value returned by <b>pcre_exec()</b> if it is greater
1504 than zero. If <b>pcre_exec()</b> returned zero, indicating that it ran out of
1505 space in <i>ovector</i>, the value passed as <i>stringcount</i> should be the
1506 number of elements in the vector divided by three.
1507 </P>
1508 <P>
1509 The functions <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>
1510 extract a single substring, whose number is given as <i>stringnumber</i>. A
1511 value of zero extracts the substring that matched the entire pattern, whereas
1512 higher values extract the captured substrings. For <b>pcre_copy_substring()</b>,
1513 the string is placed in <i>buffer</i>, whose length is given by
1514 <i>buffersize</i>, while for <b>pcre_get_substring()</b> a new block of memory is
1515 obtained via <b>pcre_malloc</b>, and its address is returned via
1516 <i>stringptr</i>. The yield of the function is the length of the string, not
1517 including the terminating zero, or one of these error codes:
1518 <pre>
1520 </pre>
1521 The buffer was too small for <b>pcre_copy_substring()</b>, or the attempt to get
1522 memory failed for <b>pcre_get_substring()</b>.
1523 <pre>
1525 </pre>
1526 There is no substring whose number is <i>stringnumber</i>.
1527 </P>
1528 <P>
1529 The <b>pcre_get_substring_list()</b> function extracts all available substrings
1530 and builds a list of pointers to them. All this is done in a single block of
1531 memory that is obtained via <b>pcre_malloc</b>. The address of the memory block
1532 is returned via <i>listptr</i>, which is also the start of the list of string
1533 pointers. The end of the list is marked by a NULL pointer. The yield of the
1534 function is zero if all went well, or the error code
1535 <pre>
1537 </pre>
1538 if the attempt to get the memory block failed.
1539 </P>
1540 <P>
1541 When any of these functions encounter a substring that is unset, which can
1542 happen when capturing subpattern number <i>n+1</i> matches some part of the
1543 subject, but subpattern <i>n</i> has not been used at all, they return an empty
1544 string. This can be distinguished from a genuine zero-length substring by
1545 inspecting the appropriate offset in <i>ovector</i>, which is negative for unset
1546 substrings.
1547 </P>
1548 <P>
1549 The two convenience functions <b>pcre_free_substring()</b> and
1550 <b>pcre_free_substring_list()</b> can be used to free the memory returned by
1551 a previous call of <b>pcre_get_substring()</b> or
1552 <b>pcre_get_substring_list()</b>, respectively. They do nothing more than call
1553 the function pointed to by <b>pcre_free</b>, which of course could be called
1554 directly from a C program. However, PCRE is used in some situations where it is
1555 linked via a special interface to another programming language that cannot use
1556 <b>pcre_free</b> directly; it is for these cases that the functions are
1557 provided.
1558 </P>
1559 <br><a name="SEC16" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NAME</a><br>
1560 <P>
1561 <b>int pcre_get_stringnumber(const pcre *<i>code</i>,</b>
1562 <b>const char *<i>name</i>);</b>
1563 </P>
1564 <P>
1565 <b>int pcre_copy_named_substring(const pcre *<i>code</i>,</b>
1566 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
1567 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
1568 <b>char *<i>buffer</i>, int <i>buffersize</i>);</b>
1569 </P>
1570 <P>
1571 <b>int pcre_get_named_substring(const pcre *<i>code</i>,</b>
1572 <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
1573 <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
1574 <b>const char **<i>stringptr</i>);</b>
1575 </P>
1576 <P>
1577 To extract a substring by name, you first have to find associated number.
1578 For example, for this pattern
1579 <pre>
1580 (a+)b(?&#60;xxx&#62;\d+)...
1581 </pre>
1582 the number of the subpattern called "xxx" is 2. If the name is known to be
1583 unique (PCRE_DUPNAMES was not set), you can find the number from the name by
1584 calling <b>pcre_get_stringnumber()</b>. The first argument is the compiled
1585 pattern, and the second is the name. The yield of the function is the
1586 subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no subpattern of
1587 that name.
1588 </P>
1589 <P>
1590 Given the number, you can extract the substring directly, or use one of the
1591 functions described in the previous section. For convenience, there are also
1592 two functions that do the whole job.
1593 </P>
1594 <P>
1595 Most of the arguments of <b>pcre_copy_named_substring()</b> and
1596 <b>pcre_get_named_substring()</b> are the same as those for the similarly named
1597 functions that extract by number. As these are described in the previous
1598 section, they are not re-described here. There are just two differences:
1599 </P>
1600 <P>
1601 First, instead of a substring number, a substring name is given. Second, there
1602 is an extra argument, given at the start, which is a pointer to the compiled
1603 pattern. This is needed in order to gain access to the name-to-number
1604 translation table.
1605 </P>
1606 <P>
1607 These functions call <b>pcre_get_stringnumber()</b>, and if it succeeds, they
1608 then call <i>pcre_copy_substring()</i> or <i>pcre_get_substring()</i>, as
1609 appropriate.
1610 </P>
1611 <br><a name="SEC17" href="#TOC1">DUPLICATE SUBPATTERN NAMES</a><br>
1612 <P>
1613 <b>int pcre_get_stringtable_entries(const pcre *<i>code</i>,</b>
1614 <b>const char *<i>name</i>, char **<i>first</i>, char **<i>last</i>);</b>
1615 </P>
1616 <P>
1617 When a pattern is compiled with the PCRE_DUPNAMES option, names for subpatterns
1618 are not required to be unique. Normally, patterns with duplicate names are such
1619 that in any one match, only one of the named subpatterns participates. An
1620 example is shown in the
1621 <a href="pcrepattern.html"><b>pcrepattern</b></a>
1622 documentation. When duplicates are present, <b>pcre_copy_named_substring()</b>
1623 and <b>pcre_get_named_substring()</b> return the first substring corresponding
1624 to the given name that is set. If none are set, an empty string is returned.
1625 The <b>pcre_get_stringnumber()</b> function returns one of the numbers that are
1626 associated with the name, but it is not defined which it is.
1627 <br>
1628 <br>
1629 If you want to get full details of all captured substrings for a given name,
1630 you must use the <b>pcre_get_stringtable_entries()</b> function. The first
1631 argument is the compiled pattern, and the second is the name. The third and
1632 fourth are pointers to variables which are updated by the function. After it
1633 has run, they point to the first and last entries in the name-to-number table
1634 for the given name. The function itself returns the length of each entry, or
1635 PCRE_ERROR_NOSUBSTRING (-7) if there are none. The format of the table is
1636 described above in the section entitled <i>Information about a pattern</i>.
1637 Given all the relevant entries for the name, you can extract each of their
1638 numbers, and hence the captured data, if any.
1639 </P>
1640 <br><a name="SEC18" href="#TOC1">FINDING ALL POSSIBLE MATCHES</a><br>
1641 <P>
1642 The traditional matching function uses a similar algorithm to Perl, which stops
1643 when it finds the first match, starting at a given point in the subject. If you
1644 want to find all possible matches, or the longest possible match, consider
1645 using the alternative matching function (see below) instead. If you cannot use
1646 the alternative function, but still need to find all possible matches, you
1647 can kludge it up by making use of the callout facility, which is described in
1648 the
1649 <a href="pcrecallout.html"><b>pcrecallout</b></a>
1650 documentation.
1651 </P>
1652 <P>
1653 What you have to do is to insert a callout right at the end of the pattern.
1654 When your callout function is called, extract and save the current matched
1655 substring. Then return 1, which forces <b>pcre_exec()</b> to backtrack and try
1656 other alternatives. Ultimately, when it runs out of matches, <b>pcre_exec()</b>
1657 will yield PCRE_ERROR_NOMATCH.
1658 <a name="dfamatch"></a></P>
1659 <br><a name="SEC19" href="#TOC1">MATCHING A PATTERN: THE ALTERNATIVE FUNCTION</a><br>
1660 <P>
1661 <b>int pcre_dfa_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
1662 <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
1663 <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>,</b>
1664 <b>int *<i>workspace</i>, int <i>wscount</i>);</b>
1665 </P>
1666 <P>
1667 The function <b>pcre_dfa_exec()</b> is called to match a subject string against
1668 a compiled pattern, using a matching algorithm that scans the subject string
1669 just once, and does not backtrack. This has different characteristics to the
1670 normal algorithm, and is not compatible with Perl. Some of the features of PCRE
1671 patterns are not supported. Nevertheless, there are times when this kind of
1672 matching can be useful. For a discussion of the two matching algorithms, see
1673 the
1674 <a href="pcrematching.html"><b>pcrematching</b></a>
1675 documentation.
1676 </P>
1677 <P>
1678 The arguments for the <b>pcre_dfa_exec()</b> function are the same as for
1679 <b>pcre_exec()</b>, plus two extras. The <i>ovector</i> argument is used in a
1680 different way, and this is described below. The other common arguments are used
1681 in the same way as for <b>pcre_exec()</b>, so their description is not repeated
1682 here.
1683 </P>
1684 <P>
1685 The two additional arguments provide workspace for the function. The workspace
1686 vector should contain at least 20 elements. It is used for keeping track of
1687 multiple paths through the pattern tree. More workspace will be needed for
1688 patterns and subjects where there are a lot of potential matches.
1689 </P>
1690 <P>
1691 Here is an example of a simple call to <b>pcre_dfa_exec()</b>:
1692 <pre>
1693 int rc;
1694 int ovector[10];
1695 int wspace[20];
1696 rc = pcre_dfa_exec(
1697 re, /* result of pcre_compile() */
1698 NULL, /* we didn't study the pattern */
1699 "some string", /* the subject string */
1700 11, /* the length of the subject string */
1701 0, /* start at offset 0 in the subject */
1702 0, /* default options */
1703 ovector, /* vector of integers for substring information */
1704 10, /* number of elements (NOT size in bytes) */
1705 wspace, /* working space vector */
1706 20); /* number of elements (NOT size in bytes) */
1707 </PRE>
1708 </P>
1709 <br><b>
1710 Option bits for <b>pcre_dfa_exec()</b>
1711 </b><br>
1712 <P>
1713 The unused bits of the <i>options</i> argument for <b>pcre_dfa_exec()</b> must be
1714 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_<i>xxx</i>,
1716 PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last three of these are
1717 the same as for <b>pcre_exec()</b>, so their description is not repeated here.
1718 <pre>
1720 </pre>
1721 This has the same general effect as it does for <b>pcre_exec()</b>, but the
1722 details are slightly different. When PCRE_PARTIAL is set for
1723 <b>pcre_dfa_exec()</b>, the return code PCRE_ERROR_NOMATCH is converted into
1724 PCRE_ERROR_PARTIAL if the end of the subject is reached, there have been no
1725 complete matches, but there is still at least one matching possibility. The
1726 portion of the string that provided the partial match is set as the first
1727 matching string.
1728 <pre>
1730 </pre>
1731 Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to stop as
1732 soon as it has found one match. Because of the way the alternative algorithm
1733 works, this is necessarily the shortest possible match at the first possible
1734 matching point in the subject string.
1735 <pre>
1737 </pre>
1738 When <b>pcre_dfa_exec()</b> is called with the PCRE_PARTIAL option, and returns
1739 a partial match, it is possible to call it again, with additional subject
1740 characters, and have it continue with the same match. The PCRE_DFA_RESTART
1741 option requests this action; when it is set, the <i>workspace</i> and
1742 <i>wscount</i> options must reference the same vector as before because data
1743 about the match so far is left in them after a partial match. There is more
1744 discussion of this facility in the
1745 <a href="pcrepartial.html"><b>pcrepartial</b></a>
1746 documentation.
1747 </P>
1748 <br><b>
1749 Successful returns from <b>pcre_dfa_exec()</b>
1750 </b><br>
1751 <P>
1752 When <b>pcre_dfa_exec()</b> succeeds, it may have matched more than one
1753 substring in the subject. Note, however, that all the matches from one run of
1754 the function start at the same point in the subject. The shorter matches are
1755 all initial substrings of the longer matches. For example, if the pattern
1756 <pre>
1757 &#60;.*&#62;
1758 </pre>
1759 is matched against the string
1760 <pre>
1761 This is &#60;something&#62; &#60;something else&#62; &#60;something further&#62; no more
1762 </pre>
1763 the three matched strings are
1764 <pre>
1765 &#60;something&#62;
1766 &#60;something&#62; &#60;something else&#62;
1767 &#60;something&#62; &#60;something else&#62; &#60;something further&#62;
1768 </pre>
1769 On success, the yield of the function is a number greater than zero, which is
1770 the number of matched substrings. The substrings themselves are returned in
1771 <i>ovector</i>. Each string uses two elements; the first is the offset to the
1772 start, and the second is the offset to the end. In fact, all the strings have
1773 the same start offset. (Space could have been saved by giving this only once,
1774 but it was decided to retain some compatibility with the way <b>pcre_exec()</b>
1775 returns data, even though the meaning of the strings is different.)
1776 </P>
1777 <P>
1778 The strings are returned in reverse order of length; that is, the longest
1779 matching string is given first. If there were too many matches to fit into
1780 <i>ovector</i>, the yield of the function is zero, and the vector is filled with
1781 the longest matches.
1782 </P>
1783 <br><b>
1784 Error returns from <b>pcre_dfa_exec()</b>
1785 </b><br>
1786 <P>
1787 The <b>pcre_dfa_exec()</b> function returns a negative number when it fails.
1788 Many of the errors are the same as for <b>pcre_exec()</b>, and these are
1789 described
1790 <a href="#errorlist">above.</a>
1791 There are in addition the following errors that are specific to
1792 <b>pcre_dfa_exec()</b>:
1793 <pre>
1795 </pre>
1796 This return is given if <b>pcre_dfa_exec()</b> encounters an item in the pattern
1797 that it does not support, for instance, the use of \C or a back reference.
1798 <pre>
1800 </pre>
1801 This return is given if <b>pcre_dfa_exec()</b> encounters a condition item that
1802 uses a back reference for the condition, or a test for recursion in a specific
1803 group. These are not supported.
1804 <pre>
1806 </pre>
1807 This return is given if <b>pcre_dfa_exec()</b> is called with an <i>extra</i>
1808 block that contains a setting of the <i>match_limit</i> field. This is not
1809 supported (it is meaningless).
1810 <pre>
1812 </pre>
1813 This return is given if <b>pcre_dfa_exec()</b> runs out of space in the
1814 <i>workspace</i> vector.
1815 <pre>
1817 </pre>
1818 When a recursive subpattern is processed, the matching function calls itself
1819 recursively, using private vectors for <i>ovector</i> and <i>workspace</i>. This
1820 error is given if the output vector is not large enough. This should be
1821 extremely rare, as a vector of size 1000 is used.
1822 </P>
1823 <br><a name="SEC20" href="#TOC1">SEE ALSO</a><br>
1824 <P>
1825 <b>pcrebuild</b>(3), <b>pcrecallout</b>(3), <b>pcrecpp(3)</b>(3),
1826 <b>pcrematching</b>(3), <b>pcrepartial</b>(3), <b>pcreposix</b>(3),
1827 <b>pcreprecompile</b>(3), <b>pcresample</b>(3), <b>pcrestack</b>(3).
1828 </P>
1829 <P>
1830 Last updated: 30 November 2006
1831 <br>
1832 Copyright &copy; 1997-2006 University of Cambridge.
1833 <p>
1834 Return to the <a href="index.html">PCRE index page</a>.
1835 </p>

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