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Revision 231 - (show annotations)
Tue Sep 11 11:15:33 2007 UTC (13 years, 10 months ago) by ph10
File size: 83813 byte(s)
Add facility to make \R match only CR, LF, or CRLF.
3 PCRE - Perl-compatible regular expressions
5 .rs
6 .sp
7 .B #include <pcre.h>
8 .PP
9 .SM
10 .B pcre *pcre_compile(const char *\fIpattern\fP, int \fIoptions\fP,
11 .ti +5n
12 .B const char **\fIerrptr\fP, int *\fIerroffset\fP,
13 .ti +5n
14 .B const unsigned char *\fItableptr\fP);
15 .PP
16 .B pcre *pcre_compile2(const char *\fIpattern\fP, int \fIoptions\fP,
17 .ti +5n
18 .B int *\fIerrorcodeptr\fP,
19 .ti +5n
20 .B const char **\fIerrptr\fP, int *\fIerroffset\fP,
21 .ti +5n
22 .B const unsigned char *\fItableptr\fP);
23 .PP
24 .B pcre_extra *pcre_study(const pcre *\fIcode\fP, int \fIoptions\fP,
25 .ti +5n
26 .B const char **\fIerrptr\fP);
27 .PP
28 .B int pcre_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
29 .ti +5n
30 .B "const char *\fIsubject\fP," int \fIlength\fP, int \fIstartoffset\fP,
31 .ti +5n
32 .B int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP);
33 .PP
34 .B int pcre_dfa_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
35 .ti +5n
36 .B "const char *\fIsubject\fP," int \fIlength\fP, int \fIstartoffset\fP,
37 .ti +5n
38 .B int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP,
39 .ti +5n
40 .B int *\fIworkspace\fP, int \fIwscount\fP);
41 .PP
42 .B int pcre_copy_named_substring(const pcre *\fIcode\fP,
43 .ti +5n
44 .B const char *\fIsubject\fP, int *\fIovector\fP,
45 .ti +5n
46 .B int \fIstringcount\fP, const char *\fIstringname\fP,
47 .ti +5n
48 .B char *\fIbuffer\fP, int \fIbuffersize\fP);
49 .PP
50 .B int pcre_copy_substring(const char *\fIsubject\fP, int *\fIovector\fP,
51 .ti +5n
52 .B int \fIstringcount\fP, int \fIstringnumber\fP, char *\fIbuffer\fP,
53 .ti +5n
54 .B int \fIbuffersize\fP);
55 .PP
56 .B int pcre_get_named_substring(const pcre *\fIcode\fP,
57 .ti +5n
58 .B const char *\fIsubject\fP, int *\fIovector\fP,
59 .ti +5n
60 .B int \fIstringcount\fP, const char *\fIstringname\fP,
61 .ti +5n
62 .B const char **\fIstringptr\fP);
63 .PP
64 .B int pcre_get_stringnumber(const pcre *\fIcode\fP,
65 .ti +5n
66 .B const char *\fIname\fP);
67 .PP
68 .B int pcre_get_stringtable_entries(const pcre *\fIcode\fP,
69 .ti +5n
70 .B const char *\fIname\fP, char **\fIfirst\fP, char **\fIlast\fP);
71 .PP
72 .B int pcre_get_substring(const char *\fIsubject\fP, int *\fIovector\fP,
73 .ti +5n
74 .B int \fIstringcount\fP, int \fIstringnumber\fP,
75 .ti +5n
76 .B const char **\fIstringptr\fP);
77 .PP
78 .B int pcre_get_substring_list(const char *\fIsubject\fP,
79 .ti +5n
80 .B int *\fIovector\fP, int \fIstringcount\fP, "const char ***\fIlistptr\fP);"
81 .PP
82 .B void pcre_free_substring(const char *\fIstringptr\fP);
83 .PP
84 .B void pcre_free_substring_list(const char **\fIstringptr\fP);
85 .PP
86 .B const unsigned char *pcre_maketables(void);
87 .PP
88 .B int pcre_fullinfo(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
89 .ti +5n
90 .B int \fIwhat\fP, void *\fIwhere\fP);
91 .PP
92 .B int pcre_info(const pcre *\fIcode\fP, int *\fIoptptr\fP, int
93 .B *\fIfirstcharptr\fP);
94 .PP
95 .B int pcre_refcount(pcre *\fIcode\fP, int \fIadjust\fP);
96 .PP
97 .B int pcre_config(int \fIwhat\fP, void *\fIwhere\fP);
98 .PP
99 .B char *pcre_version(void);
100 .PP
101 .B void *(*pcre_malloc)(size_t);
102 .PP
103 .B void (*pcre_free)(void *);
104 .PP
105 .B void *(*pcre_stack_malloc)(size_t);
106 .PP
107 .B void (*pcre_stack_free)(void *);
108 .PP
109 .B int (*pcre_callout)(pcre_callout_block *);
110 .
111 .
113 .rs
114 .sp
115 PCRE has its own native API, which is described in this document. There are
116 also some wrapper functions that correspond to the POSIX regular expression
117 API. These are described in the
118 .\" HREF
119 \fBpcreposix\fP
120 .\"
121 documentation. Both of these APIs define a set of C function calls. A C++
122 wrapper is distributed with PCRE. It is documented in the
123 .\" HREF
124 \fBpcrecpp\fP
125 .\"
126 page.
127 .P
128 The native API C function prototypes are defined in the header file
129 \fBpcre.h\fP, and on Unix systems the library itself is called \fBlibpcre\fP.
130 It can normally be accessed by adding \fB-lpcre\fP to the command for linking
131 an application that uses PCRE. The header file defines the macros PCRE_MAJOR
132 and PCRE_MINOR to contain the major and minor release numbers for the library.
133 Applications can use these to include support for different releases of PCRE.
134 .P
135 The functions \fBpcre_compile()\fP, \fBpcre_compile2()\fP, \fBpcre_study()\fP,
136 and \fBpcre_exec()\fP are used for compiling and matching regular expressions
137 in a Perl-compatible manner. A sample program that demonstrates the simplest
138 way of using them is provided in the file called \fIpcredemo.c\fP in the source
139 distribution. The
140 .\" HREF
141 \fBpcresample\fP
142 .\"
143 documentation describes how to run it.
144 .P
145 A second matching function, \fBpcre_dfa_exec()\fP, which is not
146 Perl-compatible, is also provided. This uses a different algorithm for the
147 matching. The alternative algorithm finds all possible matches (at a given
148 point in the subject), and scans the subject just once. However, this algorithm
149 does not return captured substrings. A description of the two matching
150 algorithms and their advantages and disadvantages is given in the
151 .\" HREF
152 \fBpcrematching\fP
153 .\"
154 documentation.
155 .P
156 In addition to the main compiling and matching functions, there are convenience
157 functions for extracting captured substrings from a subject string that is
158 matched by \fBpcre_exec()\fP. They are:
159 .sp
160 \fBpcre_copy_substring()\fP
161 \fBpcre_copy_named_substring()\fP
162 \fBpcre_get_substring()\fP
163 \fBpcre_get_named_substring()\fP
164 \fBpcre_get_substring_list()\fP
165 \fBpcre_get_stringnumber()\fP
166 \fBpcre_get_stringtable_entries()\fP
167 .sp
168 \fBpcre_free_substring()\fP and \fBpcre_free_substring_list()\fP are also
169 provided, to free the memory used for extracted strings.
170 .P
171 The function \fBpcre_maketables()\fP is used to build a set of character tables
172 in the current locale for passing to \fBpcre_compile()\fP, \fBpcre_exec()\fP,
173 or \fBpcre_dfa_exec()\fP. This is an optional facility that is provided for
174 specialist use. Most commonly, no special tables are passed, in which case
175 internal tables that are generated when PCRE is built are used.
176 .P
177 The function \fBpcre_fullinfo()\fP is used to find out information about a
178 compiled pattern; \fBpcre_info()\fP is an obsolete version that returns only
179 some of the available information, but is retained for backwards compatibility.
180 The function \fBpcre_version()\fP returns a pointer to a string containing the
181 version of PCRE and its date of release.
182 .P
183 The function \fBpcre_refcount()\fP maintains a reference count in a data block
184 containing a compiled pattern. This is provided for the benefit of
185 object-oriented applications.
186 .P
187 The global variables \fBpcre_malloc\fP and \fBpcre_free\fP initially contain
188 the entry points of the standard \fBmalloc()\fP and \fBfree()\fP functions,
189 respectively. PCRE calls the memory management functions via these variables,
190 so a calling program can replace them if it wishes to intercept the calls. This
191 should be done before calling any PCRE functions.
192 .P
193 The global variables \fBpcre_stack_malloc\fP and \fBpcre_stack_free\fP are also
194 indirections to memory management functions. These special functions are used
195 only when PCRE is compiled to use the heap for remembering data, instead of
196 recursive function calls, when running the \fBpcre_exec()\fP function. See the
197 .\" HREF
198 \fBpcrebuild\fP
199 .\"
200 documentation for details of how to do this. It is a non-standard way of
201 building PCRE, for use in environments that have limited stacks. Because of the
202 greater use of memory management, it runs more slowly. Separate functions are
203 provided so that special-purpose external code can be used for this case. When
204 used, these functions are always called in a stack-like manner (last obtained,
205 first freed), and always for memory blocks of the same size. There is a
206 discussion about PCRE's stack usage in the
207 .\" HREF
208 \fBpcrestack\fP
209 .\"
210 documentation.
211 .P
212 The global variable \fBpcre_callout\fP initially contains NULL. It can be set
213 by the caller to a "callout" function, which PCRE will then call at specified
214 points during a matching operation. Details are given in the
215 .\" HREF
216 \fBpcrecallout\fP
217 .\"
218 documentation.
219 .
220 .
221 .\" HTML <a name="newlines"></a>
223 .rs
224 .sp
225 PCRE supports five different conventions for indicating line breaks in
226 strings: a single CR (carriage return) character, a single LF (linefeed)
227 character, the two-character sequence CRLF, any of the three preceding, or any
228 Unicode newline sequence. The Unicode newline sequences are the three just
229 mentioned, plus the single characters VT (vertical tab, U+000B), FF (formfeed,
230 U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS
231 (paragraph separator, U+2029).
232 .P
233 Each of the first three conventions is used by at least one operating system as
234 its standard newline sequence. When PCRE is built, a default can be specified.
235 The default default is LF, which is the Unix standard. When PCRE is run, the
236 default can be overridden, either when a pattern is compiled, or when it is
237 matched.
238 .P
239 At compile time, the newline convention can be specified by the \fIoptions\fP
240 argument of \fBpcre_compile()\fP, or it can be specified by special text at the
241 start of the pattern itself; this overrides any other settings. See the
242 .\" HREF
243 \fBpcrepattern\fP
244 .\"
245 page for details of the special character sequences.
246 .P
247 In the PCRE documentation the word "newline" is used to mean "the character or
248 pair of characters that indicate a line break". The choice of newline
249 convention affects the handling of the dot, circumflex, and dollar
250 metacharacters, the handling of #-comments in /x mode, and, when CRLF is a
251 recognized line ending sequence, the match position advancement for a
252 non-anchored pattern. There is more detail about this in the
253 .\" HTML <a href="#execoptions">
254 .\" </a>
255 section on \fBpcre_exec()\fP options
256 .\"
257 below.
258 .P
259 The choice of newline convention does not affect the interpretation of
260 the \en or \er escape sequences, nor does it affect what \eR matches, which is
261 controlled in a similar way, but by separate options.
262 .
263 .
265 .rs
266 .sp
267 The PCRE functions can be used in multi-threading applications, with the
268 proviso that the memory management functions pointed to by \fBpcre_malloc\fP,
269 \fBpcre_free\fP, \fBpcre_stack_malloc\fP, and \fBpcre_stack_free\fP, and the
270 callout function pointed to by \fBpcre_callout\fP, are shared by all threads.
271 .P
272 The compiled form of a regular expression is not altered during matching, so
273 the same compiled pattern can safely be used by several threads at once.
274 .
275 .
277 .rs
278 .sp
279 The compiled form of a regular expression can be saved and re-used at a later
280 time, possibly by a different program, and even on a host other than the one on
281 which it was compiled. Details are given in the
282 .\" HREF
283 \fBpcreprecompile\fP
284 .\"
285 documentation. However, compiling a regular expression with one version of PCRE
286 for use with a different version is not guaranteed to work and may cause
287 crashes.
288 .
289 .
291 .rs
292 .sp
293 .B int pcre_config(int \fIwhat\fP, void *\fIwhere\fP);
294 .PP
295 The function \fBpcre_config()\fP makes it possible for a PCRE client to
296 discover which optional features have been compiled into the PCRE library. The
297 .\" HREF
298 \fBpcrebuild\fP
299 .\"
300 documentation has more details about these optional features.
301 .P
302 The first argument for \fBpcre_config()\fP is an integer, specifying which
303 information is required; the second argument is a pointer to a variable into
304 which the information is placed. The following information is available:
305 .sp
307 .sp
308 The output is an integer that is set to one if UTF-8 support is available;
309 otherwise it is set to zero.
310 .sp
312 .sp
313 The output is an integer that is set to one if support for Unicode character
314 properties is available; otherwise it is set to zero.
315 .sp
317 .sp
318 The output is an integer whose value specifies the default character sequence
319 that is recognized as meaning "newline". The four values that are supported
320 are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF, and -1 for ANY. The
321 default should normally be the standard sequence for your operating system.
322 .sp
324 .sp
325 The output is an integer whose value indicates what character sequences the \eR
326 escape sequence matches by default. A value of 0 means that \eR matches any
327 Unicode line ending sequence; a value of 1 means that \eR matches only CR, LF,
328 or CRLF. The default can be overridden when a pattern is compiled or matched.
329 .sp
331 .sp
332 The output is an integer that contains the number of bytes used for internal
333 linkage in compiled regular expressions. The value is 2, 3, or 4. Larger values
334 allow larger regular expressions to be compiled, at the expense of slower
335 matching. The default value of 2 is sufficient for all but the most massive
336 patterns, since it allows the compiled pattern to be up to 64K in size.
337 .sp
339 .sp
340 The output is an integer that contains the threshold above which the POSIX
341 interface uses \fBmalloc()\fP for output vectors. Further details are given in
342 the
343 .\" HREF
344 \fBpcreposix\fP
345 .\"
346 documentation.
347 .sp
349 .sp
350 The output is an integer that gives the default limit for the number of
351 internal matching function calls in a \fBpcre_exec()\fP execution. Further
352 details are given with \fBpcre_exec()\fP below.
353 .sp
355 .sp
356 The output is an integer that gives the default limit for the depth of
357 recursion when calling the internal matching function in a \fBpcre_exec()\fP
358 execution. Further details are given with \fBpcre_exec()\fP below.
359 .sp
361 .sp
362 The output is an integer that is set to one if internal recursion when running
363 \fBpcre_exec()\fP is implemented by recursive function calls that use the stack
364 to remember their state. This is the usual way that PCRE is compiled. The
365 output is zero if PCRE was compiled to use blocks of data on the heap instead
366 of recursive function calls. In this case, \fBpcre_stack_malloc\fP and
367 \fBpcre_stack_free\fP are called to manage memory blocks on the heap, thus
368 avoiding the use of the stack.
369 .
370 .
372 .rs
373 .sp
374 .B pcre *pcre_compile(const char *\fIpattern\fP, int \fIoptions\fP,
375 .ti +5n
376 .B const char **\fIerrptr\fP, int *\fIerroffset\fP,
377 .ti +5n
378 .B const unsigned char *\fItableptr\fP);
379 .sp
380 .B pcre *pcre_compile2(const char *\fIpattern\fP, int \fIoptions\fP,
381 .ti +5n
382 .B int *\fIerrorcodeptr\fP,
383 .ti +5n
384 .B const char **\fIerrptr\fP, int *\fIerroffset\fP,
385 .ti +5n
386 .B const unsigned char *\fItableptr\fP);
387 .P
388 Either of the functions \fBpcre_compile()\fP or \fBpcre_compile2()\fP can be
389 called to compile a pattern into an internal form. The only difference between
390 the two interfaces is that \fBpcre_compile2()\fP has an additional argument,
391 \fIerrorcodeptr\fP, via which a numerical error code can be returned.
392 .P
393 The pattern is a C string terminated by a binary zero, and is passed in the
394 \fIpattern\fP argument. A pointer to a single block of memory that is obtained
395 via \fBpcre_malloc\fP is returned. This contains the compiled code and related
396 data. The \fBpcre\fP type is defined for the returned block; this is a typedef
397 for a structure whose contents are not externally defined. It is up to the
398 caller to free the memory (via \fBpcre_free\fP) when it is no longer required.
399 .P
400 Although the compiled code of a PCRE regex is relocatable, that is, it does not
401 depend on memory location, the complete \fBpcre\fP data block is not
402 fully relocatable, because it may contain a copy of the \fItableptr\fP
403 argument, which is an address (see below).
404 .P
405 The \fIoptions\fP argument contains various bit settings that affect the
406 compilation. It should be zero if no options are required. The available
407 options are described below. Some of them, in particular, those that are
408 compatible with Perl, can also be set and unset from within the pattern (see
409 the detailed description in the
410 .\" HREF
411 \fBpcrepattern\fP
412 .\"
413 documentation). For these options, the contents of the \fIoptions\fP argument
414 specifies their initial settings at the start of compilation and execution. The
415 PCRE_ANCHORED and PCRE_NEWLINE_\fIxxx\fP options can be set at the time of
416 matching as well as at compile time.
417 .P
418 If \fIerrptr\fP is NULL, \fBpcre_compile()\fP returns NULL immediately.
419 Otherwise, if compilation of a pattern fails, \fBpcre_compile()\fP returns
420 NULL, and sets the variable pointed to by \fIerrptr\fP to point to a textual
421 error message. This is a static string that is part of the library. You must
422 not try to free it. The offset from the start of the pattern to the character
423 where the error was discovered is placed in the variable pointed to by
424 \fIerroffset\fP, which must not be NULL. If it is, an immediate error is given.
425 .P
426 If \fBpcre_compile2()\fP is used instead of \fBpcre_compile()\fP, and the
427 \fIerrorcodeptr\fP argument is not NULL, a non-zero error code number is
428 returned via this argument in the event of an error. This is in addition to the
429 textual error message. Error codes and messages are listed below.
430 .P
431 If the final argument, \fItableptr\fP, is NULL, PCRE uses a default set of
432 character tables that are built when PCRE is compiled, using the default C
433 locale. Otherwise, \fItableptr\fP must be an address that is the result of a
434 call to \fBpcre_maketables()\fP. This value is stored with the compiled
435 pattern, and used again by \fBpcre_exec()\fP, unless another table pointer is
436 passed to it. For more discussion, see the section on locale support below.
437 .P
438 This code fragment shows a typical straightforward call to \fBpcre_compile()\fP:
439 .sp
440 pcre *re;
441 const char *error;
442 int erroffset;
443 re = pcre_compile(
444 "^A.*Z", /* the pattern */
445 0, /* default options */
446 &error, /* for error message */
447 &erroffset, /* for error offset */
448 NULL); /* use default character tables */
449 .sp
450 The following names for option bits are defined in the \fBpcre.h\fP header
451 file:
452 .sp
454 .sp
455 If this bit is set, the pattern is forced to be "anchored", that is, it is
456 constrained to match only at the first matching point in the string that is
457 being searched (the "subject string"). This effect can also be achieved by
458 appropriate constructs in the pattern itself, which is the only way to do it in
459 Perl.
460 .sp
462 .sp
463 If this bit is set, \fBpcre_compile()\fP automatically inserts callout items,
464 all with number 255, before each pattern item. For discussion of the callout
465 facility, see the
466 .\" HREF
467 \fBpcrecallout\fP
468 .\"
469 documentation.
470 .sp
473 .sp
474 These options (which are mutually exclusive) control what the \eR escape
475 sequence matches. The choice is either to match only CR, LF, or CRLF, or to
476 match any Unicode newline sequence. The default is specified when PCRE is
477 built. It can be overridden from within the pattern, or by setting an option
478 when a compiled pattern is matched.
479 .sp
481 .sp
482 If this bit is set, letters in the pattern match both upper and lower case
483 letters. It is equivalent to Perl's /i option, and it can be changed within a
484 pattern by a (?i) option setting. In UTF-8 mode, PCRE always understands the
485 concept of case for characters whose values are less than 128, so caseless
486 matching is always possible. For characters with higher values, the concept of
487 case is supported if PCRE is compiled with Unicode property support, but not
488 otherwise. If you want to use caseless matching for characters 128 and above,
489 you must ensure that PCRE is compiled with Unicode property support as well as
490 with UTF-8 support.
491 .sp
493 .sp
494 If this bit is set, a dollar metacharacter in the pattern matches only at the
495 end of the subject string. Without this option, a dollar also matches
496 immediately before a newline at the end of the string (but not before any other
497 newlines). The PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is set.
498 There is no equivalent to this option in Perl, and no way to set it within a
499 pattern.
500 .sp
502 .sp
503 If this bit is set, a dot metacharater in the pattern matches all characters,
504 including those that indicate newline. Without it, a dot does not match when
505 the current position is at a newline. This option is equivalent to Perl's /s
506 option, and it can be changed within a pattern by a (?s) option setting. A
507 negative class such as [^a] always matches newline characters, independent of
508 the setting of this option.
509 .sp
511 .sp
512 If this bit is set, names used to identify capturing subpatterns need not be
513 unique. This can be helpful for certain types of pattern when it is known that
514 only one instance of the named subpattern can ever be matched. There are more
515 details of named subpatterns below; see also the
516 .\" HREF
517 \fBpcrepattern\fP
518 .\"
519 documentation.
520 .sp
522 .sp
523 If this bit is set, whitespace data characters in the pattern are totally
524 ignored except when escaped or inside a character class. Whitespace does not
525 include the VT character (code 11). In addition, characters between an
526 unescaped # outside a character class and the next newline, inclusive, are also
527 ignored. This is equivalent to Perl's /x option, and it can be changed within a
528 pattern by a (?x) option setting.
529 .P
530 This option makes it possible to include comments inside complicated patterns.
531 Note, however, that this applies only to data characters. Whitespace characters
532 may never appear within special character sequences in a pattern, for example
533 within the sequence (?( which introduces a conditional subpattern.
534 .sp
536 .sp
537 This option was invented in order to turn on additional functionality of PCRE
538 that is incompatible with Perl, but it is currently of very little use. When
539 set, any backslash in a pattern that is followed by a letter that has no
540 special meaning causes an error, thus reserving these combinations for future
541 expansion. By default, as in Perl, a backslash followed by a letter with no
542 special meaning is treated as a literal. (Perl can, however, be persuaded to
543 give a warning for this.) There are at present no other features controlled by
544 this option. It can also be set by a (?X) option setting within a pattern.
545 .sp
547 .sp
548 If this option is set, an unanchored pattern is required to match before or at
549 the first newline in the subject string, though the matched text may continue
550 over the newline.
551 .sp
553 .sp
554 By default, PCRE treats the subject string as consisting of a single line of
555 characters (even if it actually contains newlines). The "start of line"
556 metacharacter (^) matches only at the start of the string, while the "end of
557 line" metacharacter ($) matches only at the end of the string, or before a
558 terminating newline (unless PCRE_DOLLAR_ENDONLY is set). This is the same as
559 Perl.
560 .P
561 When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs
562 match immediately following or immediately before internal newlines in the
563 subject string, respectively, as well as at the very start and end. This is
564 equivalent to Perl's /m option, and it can be changed within a pattern by a
565 (?m) option setting. If there are no newlines in a subject string, or no
566 occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no effect.
567 .sp
573 .sp
574 These options override the default newline definition that was chosen when PCRE
575 was built. Setting the first or the second specifies that a newline is
576 indicated by a single character (CR or LF, respectively). Setting
577 PCRE_NEWLINE_CRLF specifies that a newline is indicated by the two-character
578 CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies that any of the three
579 preceding sequences should be recognized. Setting PCRE_NEWLINE_ANY specifies
580 that any Unicode newline sequence should be recognized. The Unicode newline
581 sequences are the three just mentioned, plus the single characters VT (vertical
582 tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS (line
583 separator, U+2028), and PS (paragraph separator, U+2029). The last two are
584 recognized only in UTF-8 mode.
585 .P
586 The newline setting in the options word uses three bits that are treated
587 as a number, giving eight possibilities. Currently only six are used (default
588 plus the five values above). This means that if you set more than one newline
589 option, the combination may or may not be sensible. For example,
591 other combinations may yield unused numbers and cause an error.
592 .P
593 The only time that a line break is specially recognized when compiling a
594 pattern is if PCRE_EXTENDED is set, and an unescaped # outside a character
595 class is encountered. This indicates a comment that lasts until after the next
596 line break sequence. In other circumstances, line break sequences are treated
597 as literal data, except that in PCRE_EXTENDED mode, both CR and LF are treated
598 as whitespace characters and are therefore ignored.
599 .P
600 The newline option that is set at compile time becomes the default that is used
601 for \fBpcre_exec()\fP and \fBpcre_dfa_exec()\fP, but it can be overridden.
602 .sp
604 .sp
605 If this option is set, it disables the use of numbered capturing parentheses in
606 the pattern. Any opening parenthesis that is not followed by ? behaves as if it
607 were followed by ?: but named parentheses can still be used for capturing (and
608 they acquire numbers in the usual way). There is no equivalent of this option
609 in Perl.
610 .sp
612 .sp
613 This option inverts the "greediness" of the quantifiers so that they are not
614 greedy by default, but become greedy if followed by "?". It is not compatible
615 with Perl. It can also be set by a (?U) option setting within the pattern.
616 .sp
618 .sp
619 This option causes PCRE to regard both the pattern and the subject as strings
620 of UTF-8 characters instead of single-byte character strings. However, it is
621 available only when PCRE is built to include UTF-8 support. If not, the use
622 of this option provokes an error. Details of how this option changes the
623 behaviour of PCRE are given in the
624 .\" HTML <a href="pcre.html#utf8support">
625 .\" </a>
626 section on UTF-8 support
627 .\"
628 in the main
629 .\" HREF
630 \fBpcre\fP
631 .\"
632 page.
633 .sp
635 .sp
636 When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
637 automatically checked. There is a discussion about the
638 .\" HTML <a href="pcre.html#utf8strings">
639 .\" </a>
640 validity of UTF-8 strings
641 .\"
642 in the main
643 .\" HREF
644 \fBpcre\fP
645 .\"
646 page. If an invalid UTF-8 sequence of bytes is found, \fBpcre_compile()\fP
647 returns an error. If you already know that your pattern is valid, and you want
648 to skip this check for performance reasons, you can set the PCRE_NO_UTF8_CHECK
649 option. When it is set, the effect of passing an invalid UTF-8 string as a
650 pattern is undefined. It may cause your program to crash. Note that this option
651 can also be passed to \fBpcre_exec()\fP and \fBpcre_dfa_exec()\fP, to suppress
652 the UTF-8 validity checking of subject strings.
653 .
654 .
656 .rs
657 .sp
658 The following table lists the error codes than may be returned by
659 \fBpcre_compile2()\fP, along with the error messages that may be returned by
660 both compiling functions. As PCRE has developed, some error codes have fallen
661 out of use. To avoid confusion, they have not been re-used.
662 .sp
663 0 no error
664 1 \e at end of pattern
665 2 \ec at end of pattern
666 3 unrecognized character follows \e
667 4 numbers out of order in {} quantifier
668 5 number too big in {} quantifier
669 6 missing terminating ] for character class
670 7 invalid escape sequence in character class
671 8 range out of order in character class
672 9 nothing to repeat
673 10 [this code is not in use]
674 11 internal error: unexpected repeat
675 12 unrecognized character after (?
676 13 POSIX named classes are supported only within a class
677 14 missing )
678 15 reference to non-existent subpattern
679 16 erroffset passed as NULL
680 17 unknown option bit(s) set
681 18 missing ) after comment
682 19 [this code is not in use]
683 20 regular expression too large
684 21 failed to get memory
685 22 unmatched parentheses
686 23 internal error: code overflow
687 24 unrecognized character after (?<
688 25 lookbehind assertion is not fixed length
689 26 malformed number or name after (?(
690 27 conditional group contains more than two branches
691 28 assertion expected after (?(
692 29 (?R or (?[+-]digits must be followed by )
693 30 unknown POSIX class name
694 31 POSIX collating elements are not supported
695 32 this version of PCRE is not compiled with PCRE_UTF8 support
696 33 [this code is not in use]
697 34 character value in \ex{...} sequence is too large
698 35 invalid condition (?(0)
699 36 \eC not allowed in lookbehind assertion
700 37 PCRE does not support \eL, \el, \eN, \eU, or \eu
701 38 number after (?C is > 255
702 39 closing ) for (?C expected
703 40 recursive call could loop indefinitely
704 41 unrecognized character after (?P
705 42 syntax error in subpattern name (missing terminator)
706 43 two named subpatterns have the same name
707 44 invalid UTF-8 string
708 45 support for \eP, \ep, and \eX has not been compiled
709 46 malformed \eP or \ep sequence
710 47 unknown property name after \eP or \ep
711 48 subpattern name is too long (maximum 32 characters)
712 49 too many named subpatterns (maximum 10,000)
713 50 [this code is not in use]
714 51 octal value is greater than \e377 (not in UTF-8 mode)
715 52 internal error: overran compiling workspace
716 53 internal error: previously-checked referenced subpattern not found
717 54 DEFINE group contains more than one branch
718 55 repeating a DEFINE group is not allowed
719 56 inconsistent NEWLINE options
720 57 \eg is not followed by a braced name or an optionally braced
721 non-zero number
722 58 (?+ or (?- or (?(+ or (?(- must be followed by a non-zero number
723 .
724 .
726 .rs
727 .sp
728 .B pcre_extra *pcre_study(const pcre *\fIcode\fP, int \fIoptions\fP
729 .ti +5n
730 .B const char **\fIerrptr\fP);
731 .PP
732 If a compiled pattern is going to be used several times, it is worth spending
733 more time analyzing it in order to speed up the time taken for matching. The
734 function \fBpcre_study()\fP takes a pointer to a compiled pattern as its first
735 argument. If studying the pattern produces additional information that will
736 help speed up matching, \fBpcre_study()\fP returns a pointer to a
737 \fBpcre_extra\fP block, in which the \fIstudy_data\fP field points to the
738 results of the study.
739 .P
740 The returned value from \fBpcre_study()\fP can be passed directly to
741 \fBpcre_exec()\fP. However, a \fBpcre_extra\fP block also contains other
742 fields that can be set by the caller before the block is passed; these are
743 described
744 .\" HTML <a href="#extradata">
745 .\" </a>
746 below
747 .\"
748 in the section on matching a pattern.
749 .P
750 If studying the pattern does not produce any additional information
751 \fBpcre_study()\fP returns NULL. In that circumstance, if the calling program
752 wants to pass any of the other fields to \fBpcre_exec()\fP, it must set up its
753 own \fBpcre_extra\fP block.
754 .P
755 The second argument of \fBpcre_study()\fP contains option bits. At present, no
756 options are defined, and this argument should always be zero.
757 .P
758 The third argument for \fBpcre_study()\fP is a pointer for an error message. If
759 studying succeeds (even if no data is returned), the variable it points to is
760 set to NULL. Otherwise it is set to point to a textual error message. This is a
761 static string that is part of the library. You must not try to free it. You
762 should test the error pointer for NULL after calling \fBpcre_study()\fP, to be
763 sure that it has run successfully.
764 .P
765 This is a typical call to \fBpcre_study\fP():
766 .sp
767 pcre_extra *pe;
768 pe = pcre_study(
769 re, /* result of pcre_compile() */
770 0, /* no options exist */
771 &error); /* set to NULL or points to a message */
772 .sp
773 At present, studying a pattern is useful only for non-anchored patterns that do
774 not have a single fixed starting character. A bitmap of possible starting
775 bytes is created.
776 .
777 .
778 .\" HTML <a name="localesupport"></a>
780 .rs
781 .sp
782 PCRE handles caseless matching, and determines whether characters are letters,
783 digits, or whatever, by reference to a set of tables, indexed by character
784 value. When running in UTF-8 mode, this applies only to characters with codes
785 less than 128. Higher-valued codes never match escapes such as \ew or \ed, but
786 can be tested with \ep if PCRE is built with Unicode character property
787 support. The use of locales with Unicode is discouraged. If you are handling
788 characters with codes greater than 128, you should either use UTF-8 and
789 Unicode, or use locales, but not try to mix the two.
790 .P
791 PCRE contains an internal set of tables that are used when the final argument
792 of \fBpcre_compile()\fP is NULL. These are sufficient for many applications.
793 Normally, the internal tables recognize only ASCII characters. However, when
794 PCRE is built, it is possible to cause the internal tables to be rebuilt in the
795 default "C" locale of the local system, which may cause them to be different.
796 .P
797 The internal tables can always be overridden by tables supplied by the
798 application that calls PCRE. These may be created in a different locale from
799 the default. As more and more applications change to using Unicode, the need
800 for this locale support is expected to die away.
801 .P
802 External tables are built by calling the \fBpcre_maketables()\fP function,
803 which has no arguments, in the relevant locale. The result can then be passed
804 to \fBpcre_compile()\fP or \fBpcre_exec()\fP as often as necessary. For
805 example, to build and use tables that are appropriate for the French locale
806 (where accented characters with values greater than 128 are treated as letters),
807 the following code could be used:
808 .sp
809 setlocale(LC_CTYPE, "fr_FR");
810 tables = pcre_maketables();
811 re = pcre_compile(..., tables);
812 .sp
813 The locale name "fr_FR" is used on Linux and other Unix-like systems; if you
814 are using Windows, the name for the French locale is "french".
815 .P
816 When \fBpcre_maketables()\fP runs, the tables are built in memory that is
817 obtained via \fBpcre_malloc\fP. It is the caller's responsibility to ensure
818 that the memory containing the tables remains available for as long as it is
819 needed.
820 .P
821 The pointer that is passed to \fBpcre_compile()\fP is saved with the compiled
822 pattern, and the same tables are used via this pointer by \fBpcre_study()\fP
823 and normally also by \fBpcre_exec()\fP. Thus, by default, for any single
824 pattern, compilation, studying and matching all happen in the same locale, but
825 different patterns can be compiled in different locales.
826 .P
827 It is possible to pass a table pointer or NULL (indicating the use of the
828 internal tables) to \fBpcre_exec()\fP. Although not intended for this purpose,
829 this facility could be used to match a pattern in a different locale from the
830 one in which it was compiled. Passing table pointers at run time is discussed
831 below in the section on matching a pattern.
832 .
833 .
835 .rs
836 .sp
837 .B int pcre_fullinfo(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
838 .ti +5n
839 .B int \fIwhat\fP, void *\fIwhere\fP);
840 .PP
841 The \fBpcre_fullinfo()\fP function returns information about a compiled
842 pattern. It replaces the obsolete \fBpcre_info()\fP function, which is
843 nevertheless retained for backwards compability (and is documented below).
844 .P
845 The first argument for \fBpcre_fullinfo()\fP is a pointer to the compiled
846 pattern. The second argument is the result of \fBpcre_study()\fP, or NULL if
847 the pattern was not studied. The third argument specifies which piece of
848 information is required, and the fourth argument is a pointer to a variable
849 to receive the data. The yield of the function is zero for success, or one of
850 the following negative numbers:
851 .sp
852 PCRE_ERROR_NULL the argument \fIcode\fP was NULL
853 the argument \fIwhere\fP was NULL
854 PCRE_ERROR_BADMAGIC the "magic number" was not found
855 PCRE_ERROR_BADOPTION the value of \fIwhat\fP was invalid
856 .sp
857 The "magic number" is placed at the start of each compiled pattern as an simple
858 check against passing an arbitrary memory pointer. Here is a typical call of
859 \fBpcre_fullinfo()\fP, to obtain the length of the compiled pattern:
860 .sp
861 int rc;
862 size_t length;
863 rc = pcre_fullinfo(
864 re, /* result of pcre_compile() */
865 pe, /* result of pcre_study(), or NULL */
866 PCRE_INFO_SIZE, /* what is required */
867 &length); /* where to put the data */
868 .sp
869 The possible values for the third argument are defined in \fBpcre.h\fP, and are
870 as follows:
871 .sp
873 .sp
874 Return the number of the highest back reference in the pattern. The fourth
875 argument should point to an \fBint\fP variable. Zero is returned if there are
876 no back references.
877 .sp
879 .sp
880 Return the number of capturing subpatterns in the pattern. The fourth argument
881 should point to an \fBint\fP variable.
882 .sp
884 .sp
885 Return a pointer to the internal default character tables within PCRE. The
886 fourth argument should point to an \fBunsigned char *\fP variable. This
887 information call is provided for internal use by the \fBpcre_study()\fP
888 function. External callers can cause PCRE to use its internal tables by passing
889 a NULL table pointer.
890 .sp
892 .sp
893 Return information about the first byte of any matched string, for a
894 non-anchored pattern. The fourth argument should point to an \fBint\fP
895 variable. (This option used to be called PCRE_INFO_FIRSTCHAR; the old name is
896 still recognized for backwards compatibility.)
897 .P
898 If there is a fixed first byte, for example, from a pattern such as
899 (cat|cow|coyote), its value is returned. Otherwise, if either
900 .sp
901 (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
902 starts with "^", or
903 .sp
904 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
905 (if it were set, the pattern would be anchored),
906 .sp
907 -1 is returned, indicating that the pattern matches only at the start of a
908 subject string or after any newline within the string. Otherwise -2 is
909 returned. For anchored patterns, -2 is returned.
910 .sp
912 .sp
913 If the pattern was studied, and this resulted in the construction of a 256-bit
914 table indicating a fixed set of bytes for the first byte in any matching
915 string, a pointer to the table is returned. Otherwise NULL is returned. The
916 fourth argument should point to an \fBunsigned char *\fP variable.
917 .sp
919 .sp
920 Return 1 if the pattern contains any explicit matches for CR or LF characters,
921 otherwise 0. The fourth argument should point to an \fBint\fP variable. An
922 explicit match is either a literal CR or LF character, or \er or \en.
923 .sp
925 .sp
926 Return 1 if the (?J) option setting is used in the pattern, otherwise 0. The
927 fourth argument should point to an \fBint\fP variable. The (?J) internal option
928 setting changes the local PCRE_DUPNAMES option.
929 .sp
931 .sp
932 Return the value of the rightmost literal byte that must exist in any matched
933 string, other than at its start, if such a byte has been recorded. The fourth
934 argument should point to an \fBint\fP variable. If there is no such byte, -1 is
935 returned. For anchored patterns, a last literal byte is recorded only if it
936 follows something of variable length. For example, for the pattern
937 /^a\ed+z\ed+/ the returned value is "z", but for /^a\edz\ed/ the returned value
938 is -1.
939 .sp
943 .sp
944 PCRE supports the use of named as well as numbered capturing parentheses. The
945 names are just an additional way of identifying the parentheses, which still
946 acquire numbers. Several convenience functions such as
947 \fBpcre_get_named_substring()\fP are provided for extracting captured
948 substrings by name. It is also possible to extract the data directly, by first
949 converting the name to a number in order to access the correct pointers in the
950 output vector (described with \fBpcre_exec()\fP below). To do the conversion,
951 you need to use the name-to-number map, which is described by these three
952 values.
953 .P
954 The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives
955 the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each
956 entry; both of these return an \fBint\fP value. The entry size depends on the
957 length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first
958 entry of the table (a pointer to \fBchar\fP). The first two bytes of each entry
959 are the number of the capturing parenthesis, most significant byte first. The
960 rest of the entry is the corresponding name, zero terminated. The names are in
961 alphabetical order. When PCRE_DUPNAMES is set, duplicate names are in order of
962 their parentheses numbers. For example, consider the following pattern (assume
963 PCRE_EXTENDED is set, so white space - including newlines - is ignored):
964 .sp
965 .\" JOIN
966 (?<date> (?<year>(\ed\ed)?\ed\ed) -
967 (?<month>\ed\ed) - (?<day>\ed\ed) )
968 .sp
969 There are four named subpatterns, so the table has four entries, and each entry
970 in the table is eight bytes long. The table is as follows, with non-printing
971 bytes shows in hexadecimal, and undefined bytes shown as ??:
972 .sp
973 00 01 d a t e 00 ??
974 00 05 d a y 00 ?? ??
975 00 04 m o n t h 00
976 00 02 y e a r 00 ??
977 .sp
978 When writing code to extract data from named subpatterns using the
979 name-to-number map, remember that the length of the entries is likely to be
980 different for each compiled pattern.
981 .sp
983 .sp
984 Return 1 if the pattern can be used for partial matching, otherwise 0. The
985 fourth argument should point to an \fBint\fP variable. The
986 .\" HREF
987 \fBpcrepartial\fP
988 .\"
989 documentation lists the restrictions that apply to patterns when partial
990 matching is used.
991 .sp
993 .sp
994 Return a copy of the options with which the pattern was compiled. The fourth
995 argument should point to an \fBunsigned long int\fP variable. These option bits
996 are those specified in the call to \fBpcre_compile()\fP, modified by any
997 top-level option settings at the start of the pattern itself. In other words,
998 they are the options that will be in force when matching starts. For example,
999 if the pattern /(?im)abc(?-i)d/ is compiled with the PCRE_EXTENDED option, the
1001 .P
1002 A pattern is automatically anchored by PCRE if all of its top-level
1003 alternatives begin with one of the following:
1004 .sp
1005 ^ unless PCRE_MULTILINE is set
1006 \eA always
1007 \eG always
1008 .\" JOIN
1009 .* if PCRE_DOTALL is set and there are no back
1010 references to the subpattern in which .* appears
1011 .sp
1012 For such patterns, the PCRE_ANCHORED bit is set in the options returned by
1013 \fBpcre_fullinfo()\fP.
1014 .sp
1016 .sp
1017 Return the size of the compiled pattern, that is, the value that was passed as
1018 the argument to \fBpcre_malloc()\fP when PCRE was getting memory in which to
1019 place the compiled data. The fourth argument should point to a \fBsize_t\fP
1020 variable.
1021 .sp
1023 .sp
1024 Return the size of the data block pointed to by the \fIstudy_data\fP field in
1025 a \fBpcre_extra\fP block. That is, it is the value that was passed to
1026 \fBpcre_malloc()\fP when PCRE was getting memory into which to place the data
1027 created by \fBpcre_study()\fP. The fourth argument should point to a
1028 \fBsize_t\fP variable.
1029 .
1030 .
1032 .rs
1033 .sp
1034 .B int pcre_info(const pcre *\fIcode\fP, int *\fIoptptr\fP, int
1035 .B *\fIfirstcharptr\fP);
1036 .PP
1037 The \fBpcre_info()\fP function is now obsolete because its interface is too
1038 restrictive to return all the available data about a compiled pattern. New
1039 programs should use \fBpcre_fullinfo()\fP instead. The yield of
1040 \fBpcre_info()\fP is the number of capturing subpatterns, or one of the
1041 following negative numbers:
1042 .sp
1043 PCRE_ERROR_NULL the argument \fIcode\fP was NULL
1044 PCRE_ERROR_BADMAGIC the "magic number" was not found
1045 .sp
1046 If the \fIoptptr\fP argument is not NULL, a copy of the options with which the
1047 pattern was compiled is placed in the integer it points to (see
1048 PCRE_INFO_OPTIONS above).
1049 .P
1050 If the pattern is not anchored and the \fIfirstcharptr\fP argument is not NULL,
1051 it is used to pass back information about the first character of any matched
1052 string (see PCRE_INFO_FIRSTBYTE above).
1053 .
1054 .
1056 .rs
1057 .sp
1058 .B int pcre_refcount(pcre *\fIcode\fP, int \fIadjust\fP);
1059 .PP
1060 The \fBpcre_refcount()\fP function is used to maintain a reference count in the
1061 data block that contains a compiled pattern. It is provided for the benefit of
1062 applications that operate in an object-oriented manner, where different parts
1063 of the application may be using the same compiled pattern, but you want to free
1064 the block when they are all done.
1065 .P
1066 When a pattern is compiled, the reference count field is initialized to zero.
1067 It is changed only by calling this function, whose action is to add the
1068 \fIadjust\fP value (which may be positive or negative) to it. The yield of the
1069 function is the new value. However, the value of the count is constrained to
1070 lie between 0 and 65535, inclusive. If the new value is outside these limits,
1071 it is forced to the appropriate limit value.
1072 .P
1073 Except when it is zero, the reference count is not correctly preserved if a
1074 pattern is compiled on one host and then transferred to a host whose byte-order
1075 is different. (This seems a highly unlikely scenario.)
1076 .
1077 .
1079 .rs
1080 .sp
1081 .B int pcre_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
1082 .ti +5n
1083 .B "const char *\fIsubject\fP," int \fIlength\fP, int \fIstartoffset\fP,
1084 .ti +5n
1085 .B int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP);
1086 .P
1087 The function \fBpcre_exec()\fP is called to match a subject string against a
1088 compiled pattern, which is passed in the \fIcode\fP argument. If the
1089 pattern has been studied, the result of the study should be passed in the
1090 \fIextra\fP argument. This function is the main matching facility of the
1091 library, and it operates in a Perl-like manner. For specialist use there is
1092 also an alternative matching function, which is described
1093 .\" HTML <a href="#dfamatch">
1094 .\" </a>
1095 below
1096 .\"
1097 in the section about the \fBpcre_dfa_exec()\fP function.
1098 .P
1099 In most applications, the pattern will have been compiled (and optionally
1100 studied) in the same process that calls \fBpcre_exec()\fP. However, it is
1101 possible to save compiled patterns and study data, and then use them later
1102 in different processes, possibly even on different hosts. For a discussion
1103 about this, see the
1104 .\" HREF
1105 \fBpcreprecompile\fP
1106 .\"
1107 documentation.
1108 .P
1109 Here is an example of a simple call to \fBpcre_exec()\fP:
1110 .sp
1111 int rc;
1112 int ovector[30];
1113 rc = pcre_exec(
1114 re, /* result of pcre_compile() */
1115 NULL, /* we didn't study the pattern */
1116 "some string", /* the subject string */
1117 11, /* the length of the subject string */
1118 0, /* start at offset 0 in the subject */
1119 0, /* default options */
1120 ovector, /* vector of integers for substring information */
1121 30); /* number of elements (NOT size in bytes) */
1122 .
1123 .\" HTML <a name="extradata"></a>
1124 .SS "Extra data for \fBpcre_exec()\fR"
1125 .rs
1126 .sp
1127 If the \fIextra\fP argument is not NULL, it must point to a \fBpcre_extra\fP
1128 data block. The \fBpcre_study()\fP function returns such a block (when it
1129 doesn't return NULL), but you can also create one for yourself, and pass
1130 additional information in it. The \fBpcre_extra\fP block contains the following
1131 fields (not necessarily in this order):
1132 .sp
1133 unsigned long int \fIflags\fP;
1134 void *\fIstudy_data\fP;
1135 unsigned long int \fImatch_limit\fP;
1136 unsigned long int \fImatch_limit_recursion\fP;
1137 void *\fIcallout_data\fP;
1138 const unsigned char *\fItables\fP;
1139 .sp
1140 The \fIflags\fP field is a bitmap that specifies which of the other fields
1141 are set. The flag bits are:
1142 .sp
1148 .sp
1149 Other flag bits should be set to zero. The \fIstudy_data\fP field is set in the
1150 \fBpcre_extra\fP block that is returned by \fBpcre_study()\fP, together with
1151 the appropriate flag bit. You should not set this yourself, but you may add to
1152 the block by setting the other fields and their corresponding flag bits.
1153 .P
1154 The \fImatch_limit\fP field provides a means of preventing PCRE from using up a
1155 vast amount of resources when running patterns that are not going to match,
1156 but which have a very large number of possibilities in their search trees. The
1157 classic example is the use of nested unlimited repeats.
1158 .P
1159 Internally, PCRE uses a function called \fBmatch()\fP which it calls repeatedly
1160 (sometimes recursively). The limit set by \fImatch_limit\fP is imposed on the
1161 number of times this function is called during a match, which has the effect of
1162 limiting the amount of backtracking that can take place. For patterns that are
1163 not anchored, the count restarts from zero for each position in the subject
1164 string.
1165 .P
1166 The default value for the limit can be set when PCRE is built; the default
1167 default is 10 million, which handles all but the most extreme cases. You can
1168 override the default by suppling \fBpcre_exec()\fP with a \fBpcre_extra\fP
1169 block in which \fImatch_limit\fP is set, and PCRE_EXTRA_MATCH_LIMIT is set in
1170 the \fIflags\fP field. If the limit is exceeded, \fBpcre_exec()\fP returns
1172 .P
1173 The \fImatch_limit_recursion\fP field is similar to \fImatch_limit\fP, but
1174 instead of limiting the total number of times that \fBmatch()\fP is called, it
1175 limits the depth of recursion. The recursion depth is a smaller number than the
1176 total number of calls, because not all calls to \fBmatch()\fP are recursive.
1177 This limit is of use only if it is set smaller than \fImatch_limit\fP.
1178 .P
1179 Limiting the recursion depth limits the amount of stack that can be used, or,
1180 when PCRE has been compiled to use memory on the heap instead of the stack, the
1181 amount of heap memory that can be used.
1182 .P
1183 The default value for \fImatch_limit_recursion\fP can be set when PCRE is
1184 built; the default default is the same value as the default for
1185 \fImatch_limit\fP. You can override the default by suppling \fBpcre_exec()\fP
1186 with a \fBpcre_extra\fP block in which \fImatch_limit_recursion\fP is set, and
1187 PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the \fIflags\fP field. If the limit
1188 is exceeded, \fBpcre_exec()\fP returns PCRE_ERROR_RECURSIONLIMIT.
1189 .P
1190 The \fIpcre_callout\fP field is used in conjunction with the "callout" feature,
1191 which is described in the
1192 .\" HREF
1193 \fBpcrecallout\fP
1194 .\"
1195 documentation.
1196 .P
1197 The \fItables\fP field is used to pass a character tables pointer to
1198 \fBpcre_exec()\fP; this overrides the value that is stored with the compiled
1199 pattern. A non-NULL value is stored with the compiled pattern only if custom
1200 tables were supplied to \fBpcre_compile()\fP via its \fItableptr\fP argument.
1201 If NULL is passed to \fBpcre_exec()\fP using this mechanism, it forces PCRE's
1202 internal tables to be used. This facility is helpful when re-using patterns
1203 that have been saved after compiling with an external set of tables, because
1204 the external tables might be at a different address when \fBpcre_exec()\fP is
1205 called. See the
1206 .\" HREF
1207 \fBpcreprecompile\fP
1208 .\"
1209 documentation for a discussion of saving compiled patterns for later use.
1210 .
1211 .\" HTML <a name="execoptions"></a>
1212 .SS "Option bits for \fBpcre_exec()\fP"
1213 .rs
1214 .sp
1215 The unused bits of the \fIoptions\fP argument for \fBpcre_exec()\fP must be
1216 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_\fIxxx\fP,
1218 .sp
1220 .sp
1221 The PCRE_ANCHORED option limits \fBpcre_exec()\fP to matching at the first
1222 matching position. If a pattern was compiled with PCRE_ANCHORED, or turned out
1223 to be anchored by virtue of its contents, it cannot be made unachored at
1224 matching time.
1225 .sp
1228 .sp
1229 These options (which are mutually exclusive) control what the \eR escape
1230 sequence matches. The choice is either to match only CR, LF, or CRLF, or to
1231 match any Unicode newline sequence. These options override the choice that was
1232 made or defaulted when the pattern was compiled.
1233 .sp
1239 .sp
1240 These options override the newline definition that was chosen or defaulted when
1241 the pattern was compiled. For details, see the description of
1242 \fBpcre_compile()\fP above. During matching, the newline choice affects the
1243 behaviour of the dot, circumflex, and dollar metacharacters. It may also alter
1244 the way the match position is advanced after a match failure for an unanchored
1245 pattern.
1246 .P
1248 match attempt for an unanchored pattern fails when the current position is at a
1249 CRLF sequence, and the pattern contains no explicit matches for CR or LF
1250 characters, the match position is advanced by two characters instead of one, in
1251 other words, to after the CRLF.
1252 .P
1253 The above rule is a compromise that makes the most common cases work as
1254 expected. For example, if the pattern is .+A (and the PCRE_DOTALL option is not
1255 set), it does not match the string "\er\enA" because, after failing at the
1256 start, it skips both the CR and the LF before retrying. However, the pattern
1257 [\er\en]A does match that string, because it contains an explicit CR or LF
1258 reference, and so advances only by one character after the first failure.
1259 .P
1260 An explicit match for CR of LF is either a literal appearance of one of those
1261 characters, or one of the \er or \en escape sequences. Implicit matches such as
1262 [^X] do not count, nor does \es (which includes CR and LF in the characters
1263 that it matches).
1264 .P
1265 Notwithstanding the above, anomalous effects may still occur when CRLF is a
1266 valid newline sequence and explicit \er or \en escapes appear in the pattern.
1267 .sp
1269 .sp
1270 This option specifies that first character of the subject string is not the
1271 beginning of a line, so the circumflex metacharacter should not match before
1272 it. Setting this without PCRE_MULTILINE (at compile time) causes circumflex
1273 never to match. This option affects only the behaviour of the circumflex
1274 metacharacter. It does not affect \eA.
1275 .sp
1277 .sp
1278 This option specifies that the end of the subject string is not the end of a
1279 line, so the dollar metacharacter should not match it nor (except in multiline
1280 mode) a newline immediately before it. Setting this without PCRE_MULTILINE (at
1281 compile time) causes dollar never to match. This option affects only the
1282 behaviour of the dollar metacharacter. It does not affect \eZ or \ez.
1283 .sp
1285 .sp
1286 An empty string is not considered to be a valid match if this option is set. If
1287 there are alternatives in the pattern, they are tried. If all the alternatives
1288 match the empty string, the entire match fails. For example, if the pattern
1289 .sp
1290 a?b?
1291 .sp
1292 is applied to a string not beginning with "a" or "b", it matches the empty
1293 string at the start of the subject. With PCRE_NOTEMPTY set, this match is not
1294 valid, so PCRE searches further into the string for occurrences of "a" or "b".
1295 .P
1296 Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a special case
1297 of a pattern match of the empty string within its \fBsplit()\fP function, and
1298 when using the /g modifier. It is possible to emulate Perl's behaviour after
1299 matching a null string by first trying the match again at the same offset with
1300 PCRE_NOTEMPTY and PCRE_ANCHORED, and then if that fails by advancing the
1301 starting offset (see below) and trying an ordinary match again. There is some
1302 code that demonstrates how to do this in the \fIpcredemo.c\fP sample program.
1303 .sp
1305 .sp
1306 When PCRE_UTF8 is set at compile time, the validity of the subject as a UTF-8
1307 string is automatically checked when \fBpcre_exec()\fP is subsequently called.
1308 The value of \fIstartoffset\fP is also checked to ensure that it points to the
1309 start of a UTF-8 character. There is a discussion about the validity of UTF-8
1310 strings in the
1311 .\" HTML <a href="pcre.html#utf8strings">
1312 .\" </a>
1313 section on UTF-8 support
1314 .\"
1315 in the main
1316 .\" HREF
1317 \fBpcre\fP
1318 .\"
1319 page. If an invalid UTF-8 sequence of bytes is found, \fBpcre_exec()\fP returns
1320 the error PCRE_ERROR_BADUTF8. If \fIstartoffset\fP contains an invalid value,
1321 PCRE_ERROR_BADUTF8_OFFSET is returned.
1322 .P
1323 If you already know that your subject is valid, and you want to skip these
1324 checks for performance reasons, you can set the PCRE_NO_UTF8_CHECK option when
1325 calling \fBpcre_exec()\fP. You might want to do this for the second and
1326 subsequent calls to \fBpcre_exec()\fP if you are making repeated calls to find
1327 all the matches in a single subject string. However, you should be sure that
1328 the value of \fIstartoffset\fP points to the start of a UTF-8 character. When
1329 PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid UTF-8 string as a
1330 subject, or a value of \fIstartoffset\fP that does not point to the start of a
1331 UTF-8 character, is undefined. Your program may crash.
1332 .sp
1334 .sp
1335 This option turns on the partial matching feature. If the subject string fails
1336 to match the pattern, but at some point during the matching process the end of
1337 the subject was reached (that is, the subject partially matches the pattern and
1338 the failure to match occurred only because there were not enough subject
1339 characters), \fBpcre_exec()\fP returns PCRE_ERROR_PARTIAL instead of
1340 PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is used, there are restrictions on what
1341 may appear in the pattern. These are discussed in the
1342 .\" HREF
1343 \fBpcrepartial\fP
1344 .\"
1345 documentation.
1346 .
1347 .SS "The string to be matched by \fBpcre_exec()\fP"
1348 .rs
1349 .sp
1350 The subject string is passed to \fBpcre_exec()\fP as a pointer in
1351 \fIsubject\fP, a length in \fIlength\fP, and a starting byte offset in
1352 \fIstartoffset\fP. In UTF-8 mode, the byte offset must point to the start of a
1353 UTF-8 character. Unlike the pattern string, the subject may contain binary zero
1354 bytes. When the starting offset is zero, the search for a match starts at the
1355 beginning of the subject, and this is by far the most common case.
1356 .P
1357 A non-zero starting offset is useful when searching for another match in the
1358 same subject by calling \fBpcre_exec()\fP again after a previous success.
1359 Setting \fIstartoffset\fP differs from just passing over a shortened string and
1360 setting PCRE_NOTBOL in the case of a pattern that begins with any kind of
1361 lookbehind. For example, consider the pattern
1362 .sp
1363 \eBiss\eB
1364 .sp
1365 which finds occurrences of "iss" in the middle of words. (\eB matches only if
1366 the current position in the subject is not a word boundary.) When applied to
1367 the string "Mississipi" the first call to \fBpcre_exec()\fP finds the first
1368 occurrence. If \fBpcre_exec()\fP is called again with just the remainder of the
1369 subject, namely "issipi", it does not match, because \eB is always false at the
1370 start of the subject, which is deemed to be a word boundary. However, if
1371 \fBpcre_exec()\fP is passed the entire string again, but with \fIstartoffset\fP
1372 set to 4, it finds the second occurrence of "iss" because it is able to look
1373 behind the starting point to discover that it is preceded by a letter.
1374 .P
1375 If a non-zero starting offset is passed when the pattern is anchored, one
1376 attempt to match at the given offset is made. This can only succeed if the
1377 pattern does not require the match to be at the start of the subject.
1378 .
1379 .SS "How \fBpcre_exec()\fP returns captured substrings"
1380 .rs
1381 .sp
1382 In general, a pattern matches a certain portion of the subject, and in
1383 addition, further substrings from the subject may be picked out by parts of the
1384 pattern. Following the usage in Jeffrey Friedl's book, this is called
1385 "capturing" in what follows, and the phrase "capturing subpattern" is used for
1386 a fragment of a pattern that picks out a substring. PCRE supports several other
1387 kinds of parenthesized subpattern that do not cause substrings to be captured.
1388 .P
1389 Captured substrings are returned to the caller via a vector of integer offsets
1390 whose address is passed in \fIovector\fP. The number of elements in the vector
1391 is passed in \fIovecsize\fP, which must be a non-negative number. \fBNote\fP:
1392 this argument is NOT the size of \fIovector\fP in bytes.
1393 .P
1394 The first two-thirds of the vector is used to pass back captured substrings,
1395 each substring using a pair of integers. The remaining third of the vector is
1396 used as workspace by \fBpcre_exec()\fP while matching capturing subpatterns,
1397 and is not available for passing back information. The length passed in
1398 \fIovecsize\fP should always be a multiple of three. If it is not, it is
1399 rounded down.
1400 .P
1401 When a match is successful, information about captured substrings is returned
1402 in pairs of integers, starting at the beginning of \fIovector\fP, and
1403 continuing up to two-thirds of its length at the most. The first element of a
1404 pair is set to the offset of the first character in a substring, and the second
1405 is set to the offset of the first character after the end of a substring. The
1406 first pair, \fIovector[0]\fP and \fIovector[1]\fP, identify the portion of the
1407 subject string matched by the entire pattern. The next pair is used for the
1408 first capturing subpattern, and so on. The value returned by \fBpcre_exec()\fP
1409 is one more than the highest numbered pair that has been set. For example, if
1410 two substrings have been captured, the returned value is 3. If there are no
1411 capturing subpatterns, the return value from a successful match is 1,
1412 indicating that just the first pair of offsets has been set.
1413 .P
1414 If a capturing subpattern is matched repeatedly, it is the last portion of the
1415 string that it matched that is returned.
1416 .P
1417 If the vector is too small to hold all the captured substring offsets, it is
1418 used as far as possible (up to two-thirds of its length), and the function
1419 returns a value of zero. In particular, if the substring offsets are not of
1420 interest, \fBpcre_exec()\fP may be called with \fIovector\fP passed as NULL and
1421 \fIovecsize\fP as zero. However, if the pattern contains back references and
1422 the \fIovector\fP is not big enough to remember the related substrings, PCRE
1423 has to get additional memory for use during matching. Thus it is usually
1424 advisable to supply an \fIovector\fP.
1425 .P
1426 The \fBpcre_info()\fP function can be used to find out how many capturing
1427 subpatterns there are in a compiled pattern. The smallest size for
1428 \fIovector\fP that will allow for \fIn\fP captured substrings, in addition to
1429 the offsets of the substring matched by the whole pattern, is (\fIn\fP+1)*3.
1430 .P
1431 It is possible for capturing subpattern number \fIn+1\fP to match some part of
1432 the subject when subpattern \fIn\fP has not been used at all. For example, if
1433 the string "abc" is matched against the pattern (a|(z))(bc) the return from the
1434 function is 4, and subpatterns 1 and 3 are matched, but 2 is not. When this
1435 happens, both values in the offset pairs corresponding to unused subpatterns
1436 are set to -1.
1437 .P
1438 Offset values that correspond to unused subpatterns at the end of the
1439 expression are also set to -1. For example, if the string "abc" is matched
1440 against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not matched. The
1441 return from the function is 2, because the highest used capturing subpattern
1442 number is 1. However, you can refer to the offsets for the second and third
1443 capturing subpatterns if you wish (assuming the vector is large enough, of
1444 course).
1445 .P
1446 Some convenience functions are provided for extracting the captured substrings
1447 as separate strings. These are described below.
1448 .
1449 .\" HTML <a name="errorlist"></a>
1450 .SS "Error return values from \fBpcre_exec()\fP"
1451 .rs
1452 .sp
1453 If \fBpcre_exec()\fP fails, it returns a negative number. The following are
1454 defined in the header file:
1455 .sp
1457 .sp
1458 The subject string did not match the pattern.
1459 .sp
1461 .sp
1462 Either \fIcode\fP or \fIsubject\fP was passed as NULL, or \fIovector\fP was
1463 NULL and \fIovecsize\fP was not zero.
1464 .sp
1466 .sp
1467 An unrecognized bit was set in the \fIoptions\fP argument.
1468 .sp
1470 .sp
1471 PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch
1472 the case when it is passed a junk pointer and to detect when a pattern that was
1473 compiled in an environment of one endianness is run in an environment with the
1474 other endianness. This is the error that PCRE gives when the magic number is
1475 not present.
1476 .sp
1478 .sp
1479 While running the pattern match, an unknown item was encountered in the
1480 compiled pattern. This error could be caused by a bug in PCRE or by overwriting
1481 of the compiled pattern.
1482 .sp
1484 .sp
1485 If a pattern contains back references, but the \fIovector\fP that is passed to
1486 \fBpcre_exec()\fP is not big enough to remember the referenced substrings, PCRE
1487 gets a block of memory at the start of matching to use for this purpose. If the
1488 call via \fBpcre_malloc()\fP fails, this error is given. The memory is
1489 automatically freed at the end of matching.
1490 .sp
1492 .sp
1493 This error is used by the \fBpcre_copy_substring()\fP,
1494 \fBpcre_get_substring()\fP, and \fBpcre_get_substring_list()\fP functions (see
1495 below). It is never returned by \fBpcre_exec()\fP.
1496 .sp
1498 .sp
1499 The backtracking limit, as specified by the \fImatch_limit\fP field in a
1500 \fBpcre_extra\fP structure (or defaulted) was reached. See the description
1501 above.
1502 .sp
1504 .sp
1505 This error is never generated by \fBpcre_exec()\fP itself. It is provided for
1506 use by callout functions that want to yield a distinctive error code. See the
1507 .\" HREF
1508 \fBpcrecallout\fP
1509 .\"
1510 documentation for details.
1511 .sp
1513 .sp
1514 A string that contains an invalid UTF-8 byte sequence was passed as a subject.
1515 .sp
1517 .sp
1518 The UTF-8 byte sequence that was passed as a subject was valid, but the value
1519 of \fIstartoffset\fP did not point to the beginning of a UTF-8 character.
1520 .sp
1522 .sp
1523 The subject string did not match, but it did match partially. See the
1524 .\" HREF
1525 \fBpcrepartial\fP
1526 .\"
1527 documentation for details of partial matching.
1528 .sp
1530 .sp
1531 The PCRE_PARTIAL option was used with a compiled pattern containing items that
1532 are not supported for partial matching. See the
1533 .\" HREF
1534 \fBpcrepartial\fP
1535 .\"
1536 documentation for details of partial matching.
1537 .sp
1539 .sp
1540 An unexpected internal error has occurred. This error could be caused by a bug
1541 in PCRE or by overwriting of the compiled pattern.
1542 .sp
1544 .sp
1545 This error is given if the value of the \fIovecsize\fP argument is negative.
1546 .sp
1548 .sp
1549 The internal recursion limit, as specified by the \fImatch_limit_recursion\fP
1550 field in a \fBpcre_extra\fP structure (or defaulted) was reached. See the
1551 description above.
1552 .sp
1554 .sp
1555 An invalid combination of PCRE_NEWLINE_\fIxxx\fP options was given.
1556 .P
1557 Error numbers -16 to -20 and -22 are not used by \fBpcre_exec()\fP.
1558 .
1559 .
1561 .rs
1562 .sp
1563 .B int pcre_copy_substring(const char *\fIsubject\fP, int *\fIovector\fP,
1564 .ti +5n
1565 .B int \fIstringcount\fP, int \fIstringnumber\fP, char *\fIbuffer\fP,
1566 .ti +5n
1567 .B int \fIbuffersize\fP);
1568 .PP
1569 .B int pcre_get_substring(const char *\fIsubject\fP, int *\fIovector\fP,
1570 .ti +5n
1571 .B int \fIstringcount\fP, int \fIstringnumber\fP,
1572 .ti +5n
1573 .B const char **\fIstringptr\fP);
1574 .PP
1575 .B int pcre_get_substring_list(const char *\fIsubject\fP,
1576 .ti +5n
1577 .B int *\fIovector\fP, int \fIstringcount\fP, "const char ***\fIlistptr\fP);"
1578 .PP
1579 Captured substrings can be accessed directly by using the offsets returned by
1580 \fBpcre_exec()\fP in \fIovector\fP. For convenience, the functions
1581 \fBpcre_copy_substring()\fP, \fBpcre_get_substring()\fP, and
1582 \fBpcre_get_substring_list()\fP are provided for extracting captured substrings
1583 as new, separate, zero-terminated strings. These functions identify substrings
1584 by number. The next section describes functions for extracting named
1585 substrings.
1586 .P
1587 A substring that contains a binary zero is correctly extracted and has a
1588 further zero added on the end, but the result is not, of course, a C string.
1589 However, you can process such a string by referring to the length that is
1590 returned by \fBpcre_copy_substring()\fP and \fBpcre_get_substring()\fP.
1591 Unfortunately, the interface to \fBpcre_get_substring_list()\fP is not adequate
1592 for handling strings containing binary zeros, because the end of the final
1593 string is not independently indicated.
1594 .P
1595 The first three arguments are the same for all three of these functions:
1596 \fIsubject\fP is the subject string that has just been successfully matched,
1597 \fIovector\fP is a pointer to the vector of integer offsets that was passed to
1598 \fBpcre_exec()\fP, and \fIstringcount\fP is the number of substrings that were
1599 captured by the match, including the substring that matched the entire regular
1600 expression. This is the value returned by \fBpcre_exec()\fP if it is greater
1601 than zero. If \fBpcre_exec()\fP returned zero, indicating that it ran out of
1602 space in \fIovector\fP, the value passed as \fIstringcount\fP should be the
1603 number of elements in the vector divided by three.
1604 .P
1605 The functions \fBpcre_copy_substring()\fP and \fBpcre_get_substring()\fP
1606 extract a single substring, whose number is given as \fIstringnumber\fP. A
1607 value of zero extracts the substring that matched the entire pattern, whereas
1608 higher values extract the captured substrings. For \fBpcre_copy_substring()\fP,
1609 the string is placed in \fIbuffer\fP, whose length is given by
1610 \fIbuffersize\fP, while for \fBpcre_get_substring()\fP a new block of memory is
1611 obtained via \fBpcre_malloc\fP, and its address is returned via
1612 \fIstringptr\fP. The yield of the function is the length of the string, not
1613 including the terminating zero, or one of these error codes:
1614 .sp
1616 .sp
1617 The buffer was too small for \fBpcre_copy_substring()\fP, or the attempt to get
1618 memory failed for \fBpcre_get_substring()\fP.
1619 .sp
1621 .sp
1622 There is no substring whose number is \fIstringnumber\fP.
1623 .P
1624 The \fBpcre_get_substring_list()\fP function extracts all available substrings
1625 and builds a list of pointers to them. All this is done in a single block of
1626 memory that is obtained via \fBpcre_malloc\fP. The address of the memory block
1627 is returned via \fIlistptr\fP, which is also the start of the list of string
1628 pointers. The end of the list is marked by a NULL pointer. The yield of the
1629 function is zero if all went well, or the error code
1630 .sp
1632 .sp
1633 if the attempt to get the memory block failed.
1634 .P
1635 When any of these functions encounter a substring that is unset, which can
1636 happen when capturing subpattern number \fIn+1\fP matches some part of the
1637 subject, but subpattern \fIn\fP has not been used at all, they return an empty
1638 string. This can be distinguished from a genuine zero-length substring by
1639 inspecting the appropriate offset in \fIovector\fP, which is negative for unset
1640 substrings.
1641 .P
1642 The two convenience functions \fBpcre_free_substring()\fP and
1643 \fBpcre_free_substring_list()\fP can be used to free the memory returned by
1644 a previous call of \fBpcre_get_substring()\fP or
1645 \fBpcre_get_substring_list()\fP, respectively. They do nothing more than call
1646 the function pointed to by \fBpcre_free\fP, which of course could be called
1647 directly from a C program. However, PCRE is used in some situations where it is
1648 linked via a special interface to another programming language that cannot use
1649 \fBpcre_free\fP directly; it is for these cases that the functions are
1650 provided.
1651 .
1652 .
1654 .rs
1655 .sp
1656 .B int pcre_get_stringnumber(const pcre *\fIcode\fP,
1657 .ti +5n
1658 .B const char *\fIname\fP);
1659 .PP
1660 .B int pcre_copy_named_substring(const pcre *\fIcode\fP,
1661 .ti +5n
1662 .B const char *\fIsubject\fP, int *\fIovector\fP,
1663 .ti +5n
1664 .B int \fIstringcount\fP, const char *\fIstringname\fP,
1665 .ti +5n
1666 .B char *\fIbuffer\fP, int \fIbuffersize\fP);
1667 .PP
1668 .B int pcre_get_named_substring(const pcre *\fIcode\fP,
1669 .ti +5n
1670 .B const char *\fIsubject\fP, int *\fIovector\fP,
1671 .ti +5n
1672 .B int \fIstringcount\fP, const char *\fIstringname\fP,
1673 .ti +5n
1674 .B const char **\fIstringptr\fP);
1675 .PP
1676 To extract a substring by name, you first have to find associated number.
1677 For example, for this pattern
1678 .sp
1679 (a+)b(?<xxx>\ed+)...
1680 .sp
1681 the number of the subpattern called "xxx" is 2. If the name is known to be
1682 unique (PCRE_DUPNAMES was not set), you can find the number from the name by
1683 calling \fBpcre_get_stringnumber()\fP. The first argument is the compiled
1684 pattern, and the second is the name. The yield of the function is the
1685 subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no subpattern of
1686 that name.
1687 .P
1688 Given the number, you can extract the substring directly, or use one of the
1689 functions described in the previous section. For convenience, there are also
1690 two functions that do the whole job.
1691 .P
1692 Most of the arguments of \fBpcre_copy_named_substring()\fP and
1693 \fBpcre_get_named_substring()\fP are the same as those for the similarly named
1694 functions that extract by number. As these are described in the previous
1695 section, they are not re-described here. There are just two differences:
1696 .P
1697 First, instead of a substring number, a substring name is given. Second, there
1698 is an extra argument, given at the start, which is a pointer to the compiled
1699 pattern. This is needed in order to gain access to the name-to-number
1700 translation table.
1701 .P
1702 These functions call \fBpcre_get_stringnumber()\fP, and if it succeeds, they
1703 then call \fBpcre_copy_substring()\fP or \fBpcre_get_substring()\fP, as
1704 appropriate. \fBNOTE:\fP If PCRE_DUPNAMES is set and there are duplicate names,
1705 the behaviour may not be what you want (see the next section).
1706 .
1707 .
1709 .rs
1710 .sp
1711 .B int pcre_get_stringtable_entries(const pcre *\fIcode\fP,
1712 .ti +5n
1713 .B const char *\fIname\fP, char **\fIfirst\fP, char **\fIlast\fP);
1714 .PP
1715 When a pattern is compiled with the PCRE_DUPNAMES option, names for subpatterns
1716 are not required to be unique. Normally, patterns with duplicate names are such
1717 that in any one match, only one of the named subpatterns participates. An
1718 example is shown in the
1719 .\" HREF
1720 \fBpcrepattern\fP
1721 .\"
1722 documentation.
1723 .P
1724 When duplicates are present, \fBpcre_copy_named_substring()\fP and
1725 \fBpcre_get_named_substring()\fP return the first substring corresponding to
1726 the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING (-7) is
1727 returned; no data is returned. The \fBpcre_get_stringnumber()\fP function
1728 returns one of the numbers that are associated with the name, but it is not
1729 defined which it is.
1730 .P
1731 If you want to get full details of all captured substrings for a given name,
1732 you must use the \fBpcre_get_stringtable_entries()\fP function. The first
1733 argument is the compiled pattern, and the second is the name. The third and
1734 fourth are pointers to variables which are updated by the function. After it
1735 has run, they point to the first and last entries in the name-to-number table
1736 for the given name. The function itself returns the length of each entry, or
1737 PCRE_ERROR_NOSUBSTRING (-7) if there are none. The format of the table is
1738 described above in the section entitled \fIInformation about a pattern\fP.
1739 Given all the relevant entries for the name, you can extract each of their
1740 numbers, and hence the captured data, if any.
1741 .
1742 .
1744 .rs
1745 .sp
1746 The traditional matching function uses a similar algorithm to Perl, which stops
1747 when it finds the first match, starting at a given point in the subject. If you
1748 want to find all possible matches, or the longest possible match, consider
1749 using the alternative matching function (see below) instead. If you cannot use
1750 the alternative function, but still need to find all possible matches, you
1751 can kludge it up by making use of the callout facility, which is described in
1752 the
1753 .\" HREF
1754 \fBpcrecallout\fP
1755 .\"
1756 documentation.
1757 .P
1758 What you have to do is to insert a callout right at the end of the pattern.
1759 When your callout function is called, extract and save the current matched
1760 substring. Then return 1, which forces \fBpcre_exec()\fP to backtrack and try
1761 other alternatives. Ultimately, when it runs out of matches, \fBpcre_exec()\fP
1762 will yield PCRE_ERROR_NOMATCH.
1763 .
1764 .
1765 .\" HTML <a name="dfamatch"></a>
1767 .rs
1768 .sp
1769 .B int pcre_dfa_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
1770 .ti +5n
1771 .B "const char *\fIsubject\fP," int \fIlength\fP, int \fIstartoffset\fP,
1772 .ti +5n
1773 .B int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP,
1774 .ti +5n
1775 .B int *\fIworkspace\fP, int \fIwscount\fP);
1776 .P
1777 The function \fBpcre_dfa_exec()\fP is called to match a subject string against
1778 a compiled pattern, using a matching algorithm that scans the subject string
1779 just once, and does not backtrack. This has different characteristics to the
1780 normal algorithm, and is not compatible with Perl. Some of the features of PCRE
1781 patterns are not supported. Nevertheless, there are times when this kind of
1782 matching can be useful. For a discussion of the two matching algorithms, see
1783 the
1784 .\" HREF
1785 \fBpcrematching\fP
1786 .\"
1787 documentation.
1788 .P
1789 The arguments for the \fBpcre_dfa_exec()\fP function are the same as for
1790 \fBpcre_exec()\fP, plus two extras. The \fIovector\fP argument is used in a
1791 different way, and this is described below. The other common arguments are used
1792 in the same way as for \fBpcre_exec()\fP, so their description is not repeated
1793 here.
1794 .P
1795 The two additional arguments provide workspace for the function. The workspace
1796 vector should contain at least 20 elements. It is used for keeping track of
1797 multiple paths through the pattern tree. More workspace will be needed for
1798 patterns and subjects where there are a lot of potential matches.
1799 .P
1800 Here is an example of a simple call to \fBpcre_dfa_exec()\fP:
1801 .sp
1802 int rc;
1803 int ovector[10];
1804 int wspace[20];
1805 rc = pcre_dfa_exec(
1806 re, /* result of pcre_compile() */
1807 NULL, /* we didn't study the pattern */
1808 "some string", /* the subject string */
1809 11, /* the length of the subject string */
1810 0, /* start at offset 0 in the subject */
1811 0, /* default options */
1812 ovector, /* vector of integers for substring information */
1813 10, /* number of elements (NOT size in bytes) */
1814 wspace, /* working space vector */
1815 20); /* number of elements (NOT size in bytes) */
1816 .
1817 .SS "Option bits for \fBpcre_dfa_exec()\fP"
1818 .rs
1819 .sp
1820 The unused bits of the \fIoptions\fP argument for \fBpcre_dfa_exec()\fP must be
1821 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_\fIxxx\fP,
1823 PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last three of these are
1824 the same as for \fBpcre_exec()\fP, so their description is not repeated here.
1825 .sp
1827 .sp
1828 This has the same general effect as it does for \fBpcre_exec()\fP, but the
1829 details are slightly different. When PCRE_PARTIAL is set for
1830 \fBpcre_dfa_exec()\fP, the return code PCRE_ERROR_NOMATCH is converted into
1831 PCRE_ERROR_PARTIAL if the end of the subject is reached, there have been no
1832 complete matches, but there is still at least one matching possibility. The
1833 portion of the string that provided the partial match is set as the first
1834 matching string.
1835 .sp
1837 .sp
1838 Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to stop as
1839 soon as it has found one match. Because of the way the alternative algorithm
1840 works, this is necessarily the shortest possible match at the first possible
1841 matching point in the subject string.
1842 .sp
1844 .sp
1845 When \fBpcre_dfa_exec()\fP is called with the PCRE_PARTIAL option, and returns
1846 a partial match, it is possible to call it again, with additional subject
1847 characters, and have it continue with the same match. The PCRE_DFA_RESTART
1848 option requests this action; when it is set, the \fIworkspace\fP and
1849 \fIwscount\fP options must reference the same vector as before because data
1850 about the match so far is left in them after a partial match. There is more
1851 discussion of this facility in the
1852 .\" HREF
1853 \fBpcrepartial\fP
1854 .\"
1855 documentation.
1856 .
1857 .SS "Successful returns from \fBpcre_dfa_exec()\fP"
1858 .rs
1859 .sp
1860 When \fBpcre_dfa_exec()\fP succeeds, it may have matched more than one
1861 substring in the subject. Note, however, that all the matches from one run of
1862 the function start at the same point in the subject. The shorter matches are
1863 all initial substrings of the longer matches. For example, if the pattern
1864 .sp
1865 <.*>
1866 .sp
1867 is matched against the string
1868 .sp
1869 This is <something> <something else> <something further> no more
1870 .sp
1871 the three matched strings are
1872 .sp
1873 <something>
1874 <something> <something else>
1875 <something> <something else> <something further>
1876 .sp
1877 On success, the yield of the function is a number greater than zero, which is
1878 the number of matched substrings. The substrings themselves are returned in
1879 \fIovector\fP. Each string uses two elements; the first is the offset to the
1880 start, and the second is the offset to the end. In fact, all the strings have
1881 the same start offset. (Space could have been saved by giving this only once,
1882 but it was decided to retain some compatibility with the way \fBpcre_exec()\fP
1883 returns data, even though the meaning of the strings is different.)
1884 .P
1885 The strings are returned in reverse order of length; that is, the longest
1886 matching string is given first. If there were too many matches to fit into
1887 \fIovector\fP, the yield of the function is zero, and the vector is filled with
1888 the longest matches.
1889 .
1890 .SS "Error returns from \fBpcre_dfa_exec()\fP"
1891 .rs
1892 .sp
1893 The \fBpcre_dfa_exec()\fP function returns a negative number when it fails.
1894 Many of the errors are the same as for \fBpcre_exec()\fP, and these are
1895 described
1896 .\" HTML <a href="#errorlist">
1897 .\" </a>
1898 above.
1899 .\"
1900 There are in addition the following errors that are specific to
1901 \fBpcre_dfa_exec()\fP:
1902 .sp
1904 .sp
1905 This return is given if \fBpcre_dfa_exec()\fP encounters an item in the pattern
1906 that it does not support, for instance, the use of \eC or a back reference.
1907 .sp
1909 .sp
1910 This return is given if \fBpcre_dfa_exec()\fP encounters a condition item that
1911 uses a back reference for the condition, or a test for recursion in a specific
1912 group. These are not supported.
1913 .sp
1915 .sp
1916 This return is given if \fBpcre_dfa_exec()\fP is called with an \fIextra\fP
1917 block that contains a setting of the \fImatch_limit\fP field. This is not
1918 supported (it is meaningless).
1919 .sp
1921 .sp
1922 This return is given if \fBpcre_dfa_exec()\fP runs out of space in the
1923 \fIworkspace\fP vector.
1924 .sp
1926 .sp
1927 When a recursive subpattern is processed, the matching function calls itself
1928 recursively, using private vectors for \fIovector\fP and \fIworkspace\fP. This
1929 error is given if the output vector is not large enough. This should be
1930 extremely rare, as a vector of size 1000 is used.
1931 .
1932 .
1933 .SH "SEE ALSO"
1934 .rs
1935 .sp
1936 \fBpcrebuild\fP(3), \fBpcrecallout\fP(3), \fBpcrecpp(3)\fP(3),
1937 \fBpcrematching\fP(3), \fBpcrepartial\fP(3), \fBpcreposix\fP(3),
1938 \fBpcreprecompile\fP(3), \fBpcresample\fP(3), \fBpcrestack\fP(3).
1939 .
1940 .
1942 .rs
1943 .sp
1944 .nf
1945 Philip Hazel
1946 University Computing Service
1947 Cambridge CB2 3QH, England.
1948 .fi
1949 .
1950 .
1952 .rs
1953 .sp
1954 .nf
1955 Last updated: 11 September 2007
1956 Copyright (c) 1997-2007 University of Cambridge.
1957 .fi


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