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Revision 801 - (show annotations)
Mon Dec 12 16:23:37 2011 UTC (9 years, 4 months ago) by ph10
File size: 110800 byte(s)
Merge changes from trunk r755 to r800 into the 16-bit branch.
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 void pcre_free_study(pcre_extra *\fIextra\fP);
29 .PP
30 .B int pcre_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
31 .ti +5n
32 .B "const char *\fIsubject\fP," int \fIlength\fP, int \fIstartoffset\fP,
33 .ti +5n
34 .B int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP);
35 .
36 .
38 .rs
39 .sp
40 .B pcre_jit_stack *pcre_jit_stack_alloc(int \fIstartsize\fP, int \fImaxsize\fP);
41 .PP
42 .B void pcre_jit_stack_free(pcre_jit_stack *\fIstack\fP);
43 .PP
44 .B void pcre_assign_jit_stack(pcre_extra *\fIextra\fP,
45 .ti +5n
46 .B pcre_jit_callback \fIcallback\fP, void *\fIdata\fP);
47 .PP
48 .B int pcre_dfa_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
49 .ti +5n
50 .B "const char *\fIsubject\fP," int \fIlength\fP, int \fIstartoffset\fP,
51 .ti +5n
52 .B int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP,
53 .ti +5n
54 .B int *\fIworkspace\fP, int \fIwscount\fP);
55 .PP
56 .B int pcre_copy_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 char *\fIbuffer\fP, int \fIbuffersize\fP);
63 .PP
64 .B int pcre_copy_substring(const char *\fIsubject\fP, int *\fIovector\fP,
65 .ti +5n
66 .B int \fIstringcount\fP, int \fIstringnumber\fP, char *\fIbuffer\fP,
67 .ti +5n
68 .B int \fIbuffersize\fP);
69 .PP
70 .B int pcre_get_named_substring(const pcre *\fIcode\fP,
71 .ti +5n
72 .B const char *\fIsubject\fP, int *\fIovector\fP,
73 .ti +5n
74 .B int \fIstringcount\fP, const char *\fIstringname\fP,
75 .ti +5n
76 .B const char **\fIstringptr\fP);
77 .PP
78 .B int pcre_get_stringnumber(const pcre *\fIcode\fP,
79 .ti +5n
80 .B const char *\fIname\fP);
81 .PP
82 .B int pcre_get_stringtable_entries(const pcre *\fIcode\fP,
83 .ti +5n
84 .B const char *\fIname\fP, char **\fIfirst\fP, char **\fIlast\fP);
85 .PP
86 .B int pcre_get_substring(const char *\fIsubject\fP, int *\fIovector\fP,
87 .ti +5n
88 .B int \fIstringcount\fP, int \fIstringnumber\fP,
89 .ti +5n
90 .B const char **\fIstringptr\fP);
91 .PP
92 .B int pcre_get_substring_list(const char *\fIsubject\fP,
93 .ti +5n
94 .B int *\fIovector\fP, int \fIstringcount\fP, "const char ***\fIlistptr\fP);"
95 .PP
96 .B void pcre_free_substring(const char *\fIstringptr\fP);
97 .PP
98 .B void pcre_free_substring_list(const char **\fIstringptr\fP);
99 .PP
100 .B const unsigned char *pcre_maketables(void);
101 .PP
102 .B int pcre_fullinfo(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
103 .ti +5n
104 .B int \fIwhat\fP, void *\fIwhere\fP);
105 .PP
106 .B int pcre_info(const pcre *\fIcode\fP, int *\fIoptptr\fP, int
107 .B *\fIfirstcharptr\fP);
108 .PP
109 .B int pcre_refcount(pcre *\fIcode\fP, int \fIadjust\fP);
110 .PP
111 .B int pcre_config(int \fIwhat\fP, void *\fIwhere\fP);
112 .PP
113 .B char *pcre_version(void);
114 .
115 .
117 .rs
118 .sp
119 .B void *(*pcre_malloc)(size_t);
120 .PP
121 .B void (*pcre_free)(void *);
122 .PP
123 .B void *(*pcre_stack_malloc)(size_t);
124 .PP
125 .B void (*pcre_stack_free)(void *);
126 .PP
127 .B int (*pcre_callout)(pcre_callout_block *);
128 .
129 .
131 .rs
132 .sp
133 PCRE has its own native API, which is described in this document. There are
134 also some wrapper functions that correspond to the POSIX regular expression
135 API, but they do not give access to all the functionality. They are described
136 in the
137 .\" HREF
138 \fBpcreposix\fP
139 .\"
140 documentation. Both of these APIs define a set of C function calls. A C++
141 wrapper is also distributed with PCRE. It is documented in the
142 .\" HREF
143 \fBpcrecpp\fP
144 .\"
145 page.
146 .P
147 The native API C function prototypes are defined in the header file
148 \fBpcre.h\fP, and on Unix systems the library itself is called \fBlibpcre\fP.
149 It can normally be accessed by adding \fB-lpcre\fP to the command for linking
150 an application that uses PCRE. The header file defines the macros PCRE_MAJOR
151 and PCRE_MINOR to contain the major and minor release numbers for the library.
152 Applications can use these to include support for different releases of PCRE.
153 .P
154 In a Windows environment, if you want to statically link an application program
155 against a non-dll \fBpcre.a\fP file, you must define PCRE_STATIC before
156 including \fBpcre.h\fP or \fBpcrecpp.h\fP, because otherwise the
157 \fBpcre_malloc()\fP and \fBpcre_free()\fP exported functions will be declared
158 \fB__declspec(dllimport)\fP, with unwanted results.
159 .P
160 The functions \fBpcre_compile()\fP, \fBpcre_compile2()\fP, \fBpcre_study()\fP,
161 and \fBpcre_exec()\fP are used for compiling and matching regular expressions
162 in a Perl-compatible manner. A sample program that demonstrates the simplest
163 way of using them is provided in the file called \fIpcredemo.c\fP in the PCRE
164 source distribution. A listing of this program is given in the
165 .\" HREF
166 \fBpcredemo\fP
167 .\"
168 documentation, and the
169 .\" HREF
170 \fBpcresample\fP
171 .\"
172 documentation describes how to compile and run it.
173 .P
174 Just-in-time compiler support is an optional feature of PCRE that can be built
175 in appropriate hardware environments. It greatly speeds up the matching
176 performance of many patterns. Simple programs can easily request that it be
177 used if available, by setting an option that is ignored when it is not
178 relevant. More complicated programs might need to make use of the functions
179 \fBpcre_jit_stack_alloc()\fP, \fBpcre_jit_stack_free()\fP, and
180 \fBpcre_assign_jit_stack()\fP in order to control the JIT code's memory usage.
181 These functions are discussed in the
182 .\" HREF
183 \fBpcrejit\fP
184 .\"
185 documentation.
186 .P
187 A second matching function, \fBpcre_dfa_exec()\fP, which is not
188 Perl-compatible, is also provided. This uses a different algorithm for the
189 matching. The alternative algorithm finds all possible matches (at a given
190 point in the subject), and scans the subject just once (unless there are
191 lookbehind assertions). However, this algorithm does not return captured
192 substrings. A description of the two matching algorithms and their advantages
193 and disadvantages is given in the
194 .\" HREF
195 \fBpcrematching\fP
196 .\"
197 documentation.
198 .P
199 In addition to the main compiling and matching functions, there are convenience
200 functions for extracting captured substrings from a subject string that is
201 matched by \fBpcre_exec()\fP. They are:
202 .sp
203 \fBpcre_copy_substring()\fP
204 \fBpcre_copy_named_substring()\fP
205 \fBpcre_get_substring()\fP
206 \fBpcre_get_named_substring()\fP
207 \fBpcre_get_substring_list()\fP
208 \fBpcre_get_stringnumber()\fP
209 \fBpcre_get_stringtable_entries()\fP
210 .sp
211 \fBpcre_free_substring()\fP and \fBpcre_free_substring_list()\fP are also
212 provided, to free the memory used for extracted strings.
213 .P
214 The function \fBpcre_maketables()\fP is used to build a set of character tables
215 in the current locale for passing to \fBpcre_compile()\fP, \fBpcre_exec()\fP,
216 or \fBpcre_dfa_exec()\fP. This is an optional facility that is provided for
217 specialist use. Most commonly, no special tables are passed, in which case
218 internal tables that are generated when PCRE is built are used.
219 .P
220 The function \fBpcre_fullinfo()\fP is used to find out information about a
221 compiled pattern; \fBpcre_info()\fP is an obsolete version that returns only
222 some of the available information, but is retained for backwards compatibility.
223 The function \fBpcre_version()\fP returns a pointer to a string containing the
224 version of PCRE and its date of release.
225 .P
226 The function \fBpcre_refcount()\fP maintains a reference count in a data block
227 containing a compiled pattern. This is provided for the benefit of
228 object-oriented applications.
229 .P
230 The global variables \fBpcre_malloc\fP and \fBpcre_free\fP initially contain
231 the entry points of the standard \fBmalloc()\fP and \fBfree()\fP functions,
232 respectively. PCRE calls the memory management functions via these variables,
233 so a calling program can replace them if it wishes to intercept the calls. This
234 should be done before calling any PCRE functions.
235 .P
236 The global variables \fBpcre_stack_malloc\fP and \fBpcre_stack_free\fP are also
237 indirections to memory management functions. These special functions are used
238 only when PCRE is compiled to use the heap for remembering data, instead of
239 recursive function calls, when running the \fBpcre_exec()\fP function. See the
240 .\" HREF
241 \fBpcrebuild\fP
242 .\"
243 documentation for details of how to do this. It is a non-standard way of
244 building PCRE, for use in environments that have limited stacks. Because of the
245 greater use of memory management, it runs more slowly. Separate functions are
246 provided so that special-purpose external code can be used for this case. When
247 used, these functions are always called in a stack-like manner (last obtained,
248 first freed), and always for memory blocks of the same size. There is a
249 discussion about PCRE's stack usage in the
250 .\" HREF
251 \fBpcrestack\fP
252 .\"
253 documentation.
254 .P
255 The global variable \fBpcre_callout\fP initially contains NULL. It can be set
256 by the caller to a "callout" function, which PCRE will then call at specified
257 points during a matching operation. Details are given in the
258 .\" HREF
259 \fBpcrecallout\fP
260 .\"
261 documentation.
262 .
263 .
264 .\" HTML <a name="newlines"></a>
266 .rs
267 .sp
268 PCRE supports five different conventions for indicating line breaks in
269 strings: a single CR (carriage return) character, a single LF (linefeed)
270 character, the two-character sequence CRLF, any of the three preceding, or any
271 Unicode newline sequence. The Unicode newline sequences are the three just
272 mentioned, plus the single characters VT (vertical tab, U+000B), FF (formfeed,
273 U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS
274 (paragraph separator, U+2029).
275 .P
276 Each of the first three conventions is used by at least one operating system as
277 its standard newline sequence. When PCRE is built, a default can be specified.
278 The default default is LF, which is the Unix standard. When PCRE is run, the
279 default can be overridden, either when a pattern is compiled, or when it is
280 matched.
281 .P
282 At compile time, the newline convention can be specified by the \fIoptions\fP
283 argument of \fBpcre_compile()\fP, or it can be specified by special text at the
284 start of the pattern itself; this overrides any other settings. See the
285 .\" HREF
286 \fBpcrepattern\fP
287 .\"
288 page for details of the special character sequences.
289 .P
290 In the PCRE documentation the word "newline" is used to mean "the character or
291 pair of characters that indicate a line break". The choice of newline
292 convention affects the handling of the dot, circumflex, and dollar
293 metacharacters, the handling of #-comments in /x mode, and, when CRLF is a
294 recognized line ending sequence, the match position advancement for a
295 non-anchored pattern. There is more detail about this in the
296 .\" HTML <a href="#execoptions">
297 .\" </a>
298 section on \fBpcre_exec()\fP options
299 .\"
300 below.
301 .P
302 The choice of newline convention does not affect the interpretation of
303 the \en or \er escape sequences, nor does it affect what \eR matches, which is
304 controlled in a similar way, but by separate options.
305 .
306 .
308 .rs
309 .sp
310 The PCRE functions can be used in multi-threading applications, with the
311 proviso that the memory management functions pointed to by \fBpcre_malloc\fP,
312 \fBpcre_free\fP, \fBpcre_stack_malloc\fP, and \fBpcre_stack_free\fP, and the
313 callout function pointed to by \fBpcre_callout\fP, are shared by all threads.
314 .P
315 The compiled form of a regular expression is not altered during matching, so
316 the same compiled pattern can safely be used by several threads at once.
317 .P
318 If the just-in-time optimization feature is being used, it needs separate
319 memory stack areas for each thread. See the
320 .\" HREF
321 \fBpcrejit\fP
322 .\"
323 documentation for more details.
324 .
325 .
327 .rs
328 .sp
329 The compiled form of a regular expression can be saved and re-used at a later
330 time, possibly by a different program, and even on a host other than the one on
331 which it was compiled. Details are given in the
332 .\" HREF
333 \fBpcreprecompile\fP
334 .\"
335 documentation. However, compiling a regular expression with one version of PCRE
336 for use with a different version is not guaranteed to work and may cause
337 crashes.
338 .
339 .
341 .rs
342 .sp
343 .B int pcre_config(int \fIwhat\fP, void *\fIwhere\fP);
344 .PP
345 The function \fBpcre_config()\fP makes it possible for a PCRE client to
346 discover which optional features have been compiled into the PCRE library. The
347 .\" HREF
348 \fBpcrebuild\fP
349 .\"
350 documentation has more details about these optional features.
351 .P
352 The first argument for \fBpcre_config()\fP is an integer, specifying which
353 information is required; the second argument is a pointer to a variable into
354 which the information is placed. The following information is available:
355 .sp
357 .sp
358 The output is an integer that is set to one if UTF-8 support is available;
359 otherwise it is set to zero.
360 .sp
362 .sp
363 The output is an integer that is set to one if support for Unicode character
364 properties is available; otherwise it is set to zero.
365 .sp
367 .sp
368 The output is an integer that is set to one if support for just-in-time
369 compiling is available; otherwise it is set to zero.
370 .sp
372 .sp
373 The output is an integer whose value specifies the default character sequence
374 that is recognized as meaning "newline". The four values that are supported
375 are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF, and -1 for ANY.
376 Though they are derived from ASCII, the same values are returned in EBCDIC
377 environments. The default should normally correspond to the standard sequence
378 for your operating system.
379 .sp
381 .sp
382 The output is an integer whose value indicates what character sequences the \eR
383 escape sequence matches by default. A value of 0 means that \eR matches any
384 Unicode line ending sequence; a value of 1 means that \eR matches only CR, LF,
385 or CRLF. The default can be overridden when a pattern is compiled or matched.
386 .sp
388 .sp
389 The output is an integer that contains the number of bytes used for internal
390 linkage in compiled regular expressions. The value is 2, 3, or 4. Larger values
391 allow larger regular expressions to be compiled, at the expense of slower
392 matching. The default value of 2 is sufficient for all but the most massive
393 patterns, since it allows the compiled pattern to be up to 64K in size.
394 .sp
396 .sp
397 The output is an integer that contains the threshold above which the POSIX
398 interface uses \fBmalloc()\fP for output vectors. Further details are given in
399 the
400 .\" HREF
401 \fBpcreposix\fP
402 .\"
403 documentation.
404 .sp
406 .sp
407 The output is a long integer that gives the default limit for the number of
408 internal matching function calls in a \fBpcre_exec()\fP execution. Further
409 details are given with \fBpcre_exec()\fP below.
410 .sp
412 .sp
413 The output is a long integer that gives the default limit for the depth of
414 recursion when calling the internal matching function in a \fBpcre_exec()\fP
415 execution. Further details are given with \fBpcre_exec()\fP below.
416 .sp
418 .sp
419 The output is an integer that is set to one if internal recursion when running
420 \fBpcre_exec()\fP is implemented by recursive function calls that use the stack
421 to remember their state. This is the usual way that PCRE is compiled. The
422 output is zero if PCRE was compiled to use blocks of data on the heap instead
423 of recursive function calls. In this case, \fBpcre_stack_malloc\fP and
424 \fBpcre_stack_free\fP are called to manage memory blocks on the heap, thus
425 avoiding the use of the stack.
426 .
427 .
429 .rs
430 .sp
431 .B pcre *pcre_compile(const char *\fIpattern\fP, int \fIoptions\fP,
432 .ti +5n
433 .B const char **\fIerrptr\fP, int *\fIerroffset\fP,
434 .ti +5n
435 .B const unsigned char *\fItableptr\fP);
436 .sp
437 .B pcre *pcre_compile2(const char *\fIpattern\fP, int \fIoptions\fP,
438 .ti +5n
439 .B int *\fIerrorcodeptr\fP,
440 .ti +5n
441 .B const char **\fIerrptr\fP, int *\fIerroffset\fP,
442 .ti +5n
443 .B const unsigned char *\fItableptr\fP);
444 .P
445 Either of the functions \fBpcre_compile()\fP or \fBpcre_compile2()\fP can be
446 called to compile a pattern into an internal form. The only difference between
447 the two interfaces is that \fBpcre_compile2()\fP has an additional argument,
448 \fIerrorcodeptr\fP, via which a numerical error code can be returned. To avoid
449 too much repetition, we refer just to \fBpcre_compile()\fP below, but the
450 information applies equally to \fBpcre_compile2()\fP.
451 .P
452 The pattern is a C string terminated by a binary zero, and is passed in the
453 \fIpattern\fP argument. A pointer to a single block of memory that is obtained
454 via \fBpcre_malloc\fP is returned. This contains the compiled code and related
455 data. The \fBpcre\fP type is defined for the returned block; this is a typedef
456 for a structure whose contents are not externally defined. It is up to the
457 caller to free the memory (via \fBpcre_free\fP) when it is no longer required.
458 .P
459 Although the compiled code of a PCRE regex is relocatable, that is, it does not
460 depend on memory location, the complete \fBpcre\fP data block is not
461 fully relocatable, because it may contain a copy of the \fItableptr\fP
462 argument, which is an address (see below).
463 .P
464 The \fIoptions\fP argument contains various bit settings that affect the
465 compilation. It should be zero if no options are required. The available
466 options are described below. Some of them (in particular, those that are
467 compatible with Perl, but some others as well) can also be set and unset from
468 within the pattern (see the detailed description in the
469 .\" HREF
470 \fBpcrepattern\fP
471 .\"
472 documentation). For those options that can be different in different parts of
473 the pattern, the contents of the \fIoptions\fP argument specifies their
474 settings at the start of compilation and execution. The PCRE_ANCHORED,
476 PCRE_NO_START_OPT options can be set at the time of matching as well as at
477 compile time.
478 .P
479 If \fIerrptr\fP is NULL, \fBpcre_compile()\fP returns NULL immediately.
480 Otherwise, if compilation of a pattern fails, \fBpcre_compile()\fP returns
481 NULL, and sets the variable pointed to by \fIerrptr\fP to point to a textual
482 error message. This is a static string that is part of the library. You must
483 not try to free it. Normally, the offset from the start of the pattern to the
484 byte that was being processed when the error was discovered is placed in the
485 variable pointed to by \fIerroffset\fP, which must not be NULL (if it is, an
486 immediate error is given). However, for an invalid UTF-8 string, the offset is
487 that of the first byte of the failing character. Also, some errors are not
488 detected until checks are carried out when the whole pattern has been scanned;
489 in these cases the offset passed back is the length of the pattern.
490 .P
491 Note that the offset is in bytes, not characters, even in UTF-8 mode. It may
492 sometimes point into the middle of a UTF-8 character.
493 .P
494 If \fBpcre_compile2()\fP is used instead of \fBpcre_compile()\fP, and the
495 \fIerrorcodeptr\fP argument is not NULL, a non-zero error code number is
496 returned via this argument in the event of an error. This is in addition to the
497 textual error message. Error codes and messages are listed below.
498 .P
499 If the final argument, \fItableptr\fP, is NULL, PCRE uses a default set of
500 character tables that are built when PCRE is compiled, using the default C
501 locale. Otherwise, \fItableptr\fP must be an address that is the result of a
502 call to \fBpcre_maketables()\fP. This value is stored with the compiled
503 pattern, and used again by \fBpcre_exec()\fP, unless another table pointer is
504 passed to it. For more discussion, see the section on locale support below.
505 .P
506 This code fragment shows a typical straightforward call to \fBpcre_compile()\fP:
507 .sp
508 pcre *re;
509 const char *error;
510 int erroffset;
511 re = pcre_compile(
512 "^A.*Z", /* the pattern */
513 0, /* default options */
514 &error, /* for error message */
515 &erroffset, /* for error offset */
516 NULL); /* use default character tables */
517 .sp
518 The following names for option bits are defined in the \fBpcre.h\fP header
519 file:
520 .sp
522 .sp
523 If this bit is set, the pattern is forced to be "anchored", that is, it is
524 constrained to match only at the first matching point in the string that is
525 being searched (the "subject string"). This effect can also be achieved by
526 appropriate constructs in the pattern itself, which is the only way to do it in
527 Perl.
528 .sp
530 .sp
531 If this bit is set, \fBpcre_compile()\fP automatically inserts callout items,
532 all with number 255, before each pattern item. For discussion of the callout
533 facility, see the
534 .\" HREF
535 \fBpcrecallout\fP
536 .\"
537 documentation.
538 .sp
541 .sp
542 These options (which are mutually exclusive) control what the \eR escape
543 sequence matches. The choice is either to match only CR, LF, or CRLF, or to
544 match any Unicode newline sequence. The default is specified when PCRE is
545 built. It can be overridden from within the pattern, or by setting an option
546 when a compiled pattern is matched.
547 .sp
549 .sp
550 If this bit is set, letters in the pattern match both upper and lower case
551 letters. It is equivalent to Perl's /i option, and it can be changed within a
552 pattern by a (?i) option setting. In UTF-8 mode, PCRE always understands the
553 concept of case for characters whose values are less than 128, so caseless
554 matching is always possible. For characters with higher values, the concept of
555 case is supported if PCRE is compiled with Unicode property support, but not
556 otherwise. If you want to use caseless matching for characters 128 and above,
557 you must ensure that PCRE is compiled with Unicode property support as well as
558 with UTF-8 support.
559 .sp
561 .sp
562 If this bit is set, a dollar metacharacter in the pattern matches only at the
563 end of the subject string. Without this option, a dollar also matches
564 immediately before a newline at the end of the string (but not before any other
565 newlines). The PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is set.
566 There is no equivalent to this option in Perl, and no way to set it within a
567 pattern.
568 .sp
570 .sp
571 If this bit is set, a dot metacharacter in the pattern matches a character of
572 any value, including one that indicates a newline. However, it only ever
573 matches one character, even if newlines are coded as CRLF. Without this option,
574 a dot does not match when the current position is at a newline. This option is
575 equivalent to Perl's /s option, and it can be changed within a pattern by a
576 (?s) option setting. A negative class such as [^a] always matches newline
577 characters, independent of the setting of this option.
578 .sp
580 .sp
581 If this bit is set, names used to identify capturing subpatterns need not be
582 unique. This can be helpful for certain types of pattern when it is known that
583 only one instance of the named subpattern can ever be matched. There are more
584 details of named subpatterns below; see also the
585 .\" HREF
586 \fBpcrepattern\fP
587 .\"
588 documentation.
589 .sp
591 .sp
592 If this bit is set, whitespace data characters in the pattern are totally
593 ignored except when escaped or inside a character class. Whitespace does not
594 include the VT character (code 11). In addition, characters between an
595 unescaped # outside a character class and the next newline, inclusive, are also
596 ignored. This is equivalent to Perl's /x option, and it can be changed within a
597 pattern by a (?x) option setting.
598 .P
599 Which characters are interpreted as newlines is controlled by the options
600 passed to \fBpcre_compile()\fP or by a special sequence at the start of the
601 pattern, as described in the section entitled
602 .\" HTML <a href="pcrepattern.html#newlines">
603 .\" </a>
604 "Newline conventions"
605 .\"
606 in the \fBpcrepattern\fP documentation. Note that the end of this type of
607 comment is a literal newline sequence in the pattern; escape sequences that
608 happen to represent a newline do not count.
609 .P
610 This option makes it possible to include comments inside complicated patterns.
611 Note, however, that this applies only to data characters. Whitespace characters
612 may never appear within special character sequences in a pattern, for example
613 within the sequence (?( that introduces a conditional subpattern.
614 .sp
616 .sp
617 This option was invented in order to turn on additional functionality of PCRE
618 that is incompatible with Perl, but it is currently of very little use. When
619 set, any backslash in a pattern that is followed by a letter that has no
620 special meaning causes an error, thus reserving these combinations for future
621 expansion. By default, as in Perl, a backslash followed by a letter with no
622 special meaning is treated as a literal. (Perl can, however, be persuaded to
623 give an error for this, by running it with the -w option.) There are at present
624 no other features controlled by this option. It can also be set by a (?X)
625 option setting within a pattern.
626 .sp
628 .sp
629 If this option is set, an unanchored pattern is required to match before or at
630 the first newline in the subject string, though the matched text may continue
631 over the newline.
632 .sp
634 .sp
635 If this option is set, PCRE's behaviour is changed in some ways so that it is
636 compatible with JavaScript rather than Perl. The changes are as follows:
637 .P
638 (1) A lone closing square bracket in a pattern causes a compile-time error,
639 because this is illegal in JavaScript (by default it is treated as a data
640 character). Thus, the pattern AB]CD becomes illegal when this option is set.
641 .P
642 (2) At run time, a back reference to an unset subpattern group matches an empty
643 string (by default this causes the current matching alternative to fail). A
644 pattern such as (\e1)(a) succeeds when this option is set (assuming it can find
645 an "a" in the subject), whereas it fails by default, for Perl compatibility.
646 .P
647 (3) \eU matches an upper case "U" character; by default \eU causes a compile
648 time error (Perl uses \eU to upper case subsequent characters).
649 .P
650 (4) \eu matches a lower case "u" character unless it is followed by four
651 hexadecimal digits, in which case the hexadecimal number defines the code point
652 to match. By default, \eu causes a compile time error (Perl uses it to upper
653 case the following character).
654 .P
655 (5) \ex matches a lower case "x" character unless it is followed by two
656 hexadecimal digits, in which case the hexadecimal number defines the code point
657 to match. By default, as in Perl, a hexadecimal number is always expected after
658 \ex, but it may have zero, one, or two digits (so, for example, \exz matches a
659 binary zero character followed by z).
660 .sp
662 .sp
663 By default, PCRE treats the subject string as consisting of a single line of
664 characters (even if it actually contains newlines). The "start of line"
665 metacharacter (^) matches only at the start of the string, while the "end of
666 line" metacharacter ($) matches only at the end of the string, or before a
667 terminating newline (unless PCRE_DOLLAR_ENDONLY is set). This is the same as
668 Perl.
669 .P
670 When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs
671 match immediately following or immediately before internal newlines in the
672 subject string, respectively, as well as at the very start and end. This is
673 equivalent to Perl's /m option, and it can be changed within a pattern by a
674 (?m) option setting. If there are no newlines in a subject string, or no
675 occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no effect.
676 .sp
682 .sp
683 These options override the default newline definition that was chosen when PCRE
684 was built. Setting the first or the second specifies that a newline is
685 indicated by a single character (CR or LF, respectively). Setting
686 PCRE_NEWLINE_CRLF specifies that a newline is indicated by the two-character
687 CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies that any of the three
688 preceding sequences should be recognized. Setting PCRE_NEWLINE_ANY specifies
689 that any Unicode newline sequence should be recognized. The Unicode newline
690 sequences are the three just mentioned, plus the single characters VT (vertical
691 tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS (line
692 separator, U+2028), and PS (paragraph separator, U+2029). The last two are
693 recognized only in UTF-8 mode.
694 .P
695 The newline setting in the options word uses three bits that are treated
696 as a number, giving eight possibilities. Currently only six are used (default
697 plus the five values above). This means that if you set more than one newline
698 option, the combination may or may not be sensible. For example,
700 other combinations may yield unused numbers and cause an error.
701 .P
702 The only time that a line break in a pattern is specially recognized when
703 compiling is when PCRE_EXTENDED is set. CR and LF are whitespace characters,
704 and so are ignored in this mode. Also, an unescaped # outside a character class
705 indicates a comment that lasts until after the next line break sequence. In
706 other circumstances, line break sequences in patterns are treated as literal
707 data.
708 .P
709 The newline option that is set at compile time becomes the default that is used
710 for \fBpcre_exec()\fP and \fBpcre_dfa_exec()\fP, but it can be overridden.
711 .sp
713 .sp
714 If this option is set, it disables the use of numbered capturing parentheses in
715 the pattern. Any opening parenthesis that is not followed by ? behaves as if it
716 were followed by ?: but named parentheses can still be used for capturing (and
717 they acquire numbers in the usual way). There is no equivalent of this option
718 in Perl.
719 .sp
721 .sp
722 This is an option that acts at matching time; that is, it is really an option
723 for \fBpcre_exec()\fP or \fBpcre_dfa_exec()\fP. If it is set at compile time,
724 it is remembered with the compiled pattern and assumed at matching time. For
725 details see the discussion of PCRE_NO_START_OPTIMIZE
726 .\" HTML <a href="#execoptions">
727 .\" </a>
728 below.
729 .\"
730 .sp
732 .sp
733 This option changes the way PCRE processes \eB, \eb, \eD, \ed, \eS, \es, \eW,
734 \ew, and some of the POSIX character classes. By default, only ASCII characters
735 are recognized, but if PCRE_UCP is set, Unicode properties are used instead to
736 classify characters. More details are given in the section on
737 .\" HTML <a href="pcre.html#genericchartypes">
738 .\" </a>
739 generic character types
740 .\"
741 in the
742 .\" HREF
743 \fBpcrepattern\fP
744 .\"
745 page. If you set PCRE_UCP, matching one of the items it affects takes much
746 longer. The option is available only if PCRE has been compiled with Unicode
747 property support.
748 .sp
750 .sp
751 This option inverts the "greediness" of the quantifiers so that they are not
752 greedy by default, but become greedy if followed by "?". It is not compatible
753 with Perl. It can also be set by a (?U) option setting within the pattern.
754 .sp
756 .sp
757 This option causes PCRE to regard both the pattern and the subject as strings
758 of UTF-8 characters instead of single-byte character strings. However, it is
759 available only when PCRE is built to include UTF-8 support. If not, the use
760 of this option provokes an error. Details of how this option changes the
761 behaviour of PCRE are given in the
762 .\" HREF
763 \fBpcreunicode\fP
764 .\"
765 page.
766 .sp
768 .sp
769 When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
770 automatically checked. There is a discussion about the
771 .\" HTML <a href="pcre.html#utf8strings">
772 .\" </a>
773 validity of UTF-8 strings
774 .\"
775 in the main
776 .\" HREF
777 \fBpcre\fP
778 .\"
779 page. If an invalid UTF-8 sequence of bytes is found, \fBpcre_compile()\fP
780 returns an error. If you already know that your pattern is valid, and you want
781 to skip this check for performance reasons, you can set the PCRE_NO_UTF8_CHECK
782 option. When it is set, the effect of passing an invalid UTF-8 string as a
783 pattern is undefined. It may cause your program to crash. Note that this option
784 can also be passed to \fBpcre_exec()\fP and \fBpcre_dfa_exec()\fP, to suppress
785 the UTF-8 validity checking of subject strings.
786 .
787 .
789 .rs
790 .sp
791 The following table lists the error codes than may be returned by
792 \fBpcre_compile2()\fP, along with the error messages that may be returned by
793 both compiling functions. As PCRE has developed, some error codes have fallen
794 out of use. To avoid confusion, they have not been re-used.
795 .sp
796 0 no error
797 1 \e at end of pattern
798 2 \ec at end of pattern
799 3 unrecognized character follows \e
800 4 numbers out of order in {} quantifier
801 5 number too big in {} quantifier
802 6 missing terminating ] for character class
803 7 invalid escape sequence in character class
804 8 range out of order in character class
805 9 nothing to repeat
806 10 [this code is not in use]
807 11 internal error: unexpected repeat
808 12 unrecognized character after (? or (?-
809 13 POSIX named classes are supported only within a class
810 14 missing )
811 15 reference to non-existent subpattern
812 16 erroffset passed as NULL
813 17 unknown option bit(s) set
814 18 missing ) after comment
815 19 [this code is not in use]
816 20 regular expression is too large
817 21 failed to get memory
818 22 unmatched parentheses
819 23 internal error: code overflow
820 24 unrecognized character after (?<
821 25 lookbehind assertion is not fixed length
822 26 malformed number or name after (?(
823 27 conditional group contains more than two branches
824 28 assertion expected after (?(
825 29 (?R or (?[+-]digits must be followed by )
826 30 unknown POSIX class name
827 31 POSIX collating elements are not supported
828 32 this version of PCRE is not compiled with PCRE_UTF8 support
829 33 [this code is not in use]
830 34 character value in \ex{...} sequence is too large
831 35 invalid condition (?(0)
832 36 \eC not allowed in lookbehind assertion
833 37 PCRE does not support \eL, \el, \eN{name}, \eU, or \eu
834 38 number after (?C is > 255
835 39 closing ) for (?C expected
836 40 recursive call could loop indefinitely
837 41 unrecognized character after (?P
838 42 syntax error in subpattern name (missing terminator)
839 43 two named subpatterns have the same name
840 44 invalid UTF-8 string
841 45 support for \eP, \ep, and \eX has not been compiled
842 46 malformed \eP or \ep sequence
843 47 unknown property name after \eP or \ep
844 48 subpattern name is too long (maximum 32 characters)
845 49 too many named subpatterns (maximum 10000)
846 50 [this code is not in use]
847 51 octal value is greater than \e377 (not in UTF-8 mode)
848 52 internal error: overran compiling workspace
849 53 internal error: previously-checked referenced subpattern
850 not found
851 54 DEFINE group contains more than one branch
852 55 repeating a DEFINE group is not allowed
853 56 inconsistent NEWLINE options
854 57 \eg is not followed by a braced, angle-bracketed, or quoted
855 name/number or by a plain number
856 58 a numbered reference must not be zero
857 59 an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT)
858 60 (*VERB) not recognized
859 61 number is too big
860 62 subpattern name expected
861 63 digit expected after (?+
862 64 ] is an invalid data character in JavaScript compatibility mode
863 65 different names for subpatterns of the same number are
864 not allowed
865 66 (*MARK) must have an argument
866 67 this version of PCRE is not compiled with PCRE_UCP support
867 68 \ec must be followed by an ASCII character
868 69 \ek is not followed by a braced, angle-bracketed, or quoted name
869 .sp
870 The numbers 32 and 10000 in errors 48 and 49 are defaults; different values may
871 be used if the limits were changed when PCRE was built.
872 .
873 .
874 .\" HTML <a name="studyingapattern"></a>
876 .rs
877 .sp
878 .B pcre_extra *pcre_study(const pcre *\fIcode\fP, int \fIoptions\fP
879 .ti +5n
880 .B const char **\fIerrptr\fP);
881 .PP
882 If a compiled pattern is going to be used several times, it is worth spending
883 more time analyzing it in order to speed up the time taken for matching. The
884 function \fBpcre_study()\fP takes a pointer to a compiled pattern as its first
885 argument. If studying the pattern produces additional information that will
886 help speed up matching, \fBpcre_study()\fP returns a pointer to a
887 \fBpcre_extra\fP block, in which the \fIstudy_data\fP field points to the
888 results of the study.
889 .P
890 The returned value from \fBpcre_study()\fP can be passed directly to
891 \fBpcre_exec()\fP or \fBpcre_dfa_exec()\fP. However, a \fBpcre_extra\fP block
892 also contains other fields that can be set by the caller before the block is
893 passed; these are described
894 .\" HTML <a href="#extradata">
895 .\" </a>
896 below
897 .\"
898 in the section on matching a pattern.
899 .P
900 If studying the pattern does not produce any useful information,
901 \fBpcre_study()\fP returns NULL. In that circumstance, if the calling program
902 wants to pass any of the other fields to \fBpcre_exec()\fP or
903 \fBpcre_dfa_exec()\fP, it must set up its own \fBpcre_extra\fP block.
904 .P
905 The second argument of \fBpcre_study()\fP contains option bits. There is only
906 one option: PCRE_STUDY_JIT_COMPILE. If this is set, and the just-in-time
907 compiler is available, the pattern is further compiled into machine code that
908 executes much faster than the \fBpcre_exec()\fP matching function. If
909 the just-in-time compiler is not available, this option is ignored. All other
910 bits in the \fIoptions\fP argument must be zero.
911 .P
912 JIT compilation is a heavyweight optimization. It can take some time for
913 patterns to be analyzed, and for one-off matches and simple patterns the
914 benefit of faster execution might be offset by a much slower study time.
915 Not all patterns can be optimized by the JIT compiler. For those that cannot be
916 handled, matching automatically falls back to the \fBpcre_exec()\fP
917 interpreter. For more details, see the
918 .\" HREF
919 \fBpcrejit\fP
920 .\"
921 documentation.
922 .P
923 The third argument for \fBpcre_study()\fP is a pointer for an error message. If
924 studying succeeds (even if no data is returned), the variable it points to is
925 set to NULL. Otherwise it is set to point to a textual error message. This is a
926 static string that is part of the library. You must not try to free it. You
927 should test the error pointer for NULL after calling \fBpcre_study()\fP, to be
928 sure that it has run successfully.
929 .P
930 When you are finished with a pattern, you can free the memory used for the
931 study data by calling \fBpcre_free_study()\fP. This function was added to the
932 API for release 8.20. For earlier versions, the memory could be freed with
933 \fBpcre_free()\fP, just like the pattern itself. This will still work in cases
934 where PCRE_STUDY_JIT_COMPILE is not used, but it is advisable to change to the
935 new function when convenient.
936 .P
937 This is a typical way in which \fBpcre_study\fP() is used (except that in a
938 real application there should be tests for errors):
939 .sp
940 int rc;
941 pcre *re;
942 pcre_extra *sd;
943 re = pcre_compile("pattern", 0, &error, &erroroffset, NULL);
944 sd = pcre_study(
945 re, /* result of pcre_compile() */
946 0, /* no options */
947 &error); /* set to NULL or points to a message */
948 rc = pcre_exec( /* see below for details of pcre_exec() options */
949 re, sd, "subject", 7, 0, 0, ovector, 30);
950 ...
951 pcre_free_study(sd);
952 pcre_free(re);
953 .sp
954 Studying a pattern does two things: first, a lower bound for the length of
955 subject string that is needed to match the pattern is computed. This does not
956 mean that there are any strings of that length that match, but it does
957 guarantee that no shorter strings match. The value is used by
958 \fBpcre_exec()\fP and \fBpcre_dfa_exec()\fP to avoid wasting time by trying to
959 match strings that are shorter than the lower bound. You can find out the value
960 in a calling program via the \fBpcre_fullinfo()\fP function.
961 .P
962 Studying a pattern is also useful for non-anchored patterns that do not have a
963 single fixed starting character. A bitmap of possible starting bytes is
964 created. This speeds up finding a position in the subject at which to start
965 matching.
966 .P
967 These two optimizations apply to both \fBpcre_exec()\fP and
968 \fBpcre_dfa_exec()\fP. However, they are not used by \fBpcre_exec()\fP if
969 \fBpcre_study()\fP is called with the PCRE_STUDY_JIT_COMPILE option, and
970 just-in-time compiling is successful. The optimizations can be disabled by
971 setting the PCRE_NO_START_OPTIMIZE option when calling \fBpcre_exec()\fP or
972 \fBpcre_dfa_exec()\fP. You might want to do this if your pattern contains
973 callouts or (*MARK) (which cannot be handled by the JIT compiler), and you want
974 to make use of these facilities in cases where matching fails. See the
975 discussion of PCRE_NO_START_OPTIMIZE
976 .\" HTML <a href="#execoptions">
977 .\" </a>
978 below.
979 .\"
980 .
981 .
982 .\" HTML <a name="localesupport"></a>
984 .rs
985 .sp
986 PCRE handles caseless matching, and determines whether characters are letters,
987 digits, or whatever, by reference to a set of tables, indexed by character
988 value. When running in UTF-8 mode, this applies only to characters with codes
989 less than 128. By default, higher-valued codes never match escapes such as \ew
990 or \ed, but they can be tested with \ep if PCRE is built with Unicode character
991 property support. Alternatively, the PCRE_UCP option can be set at compile
992 time; this causes \ew and friends to use Unicode property support instead of
993 built-in tables. The use of locales with Unicode is discouraged. If you are
994 handling characters with codes greater than 128, you should either use UTF-8
995 and Unicode, or use locales, but not try to mix the two.
996 .P
997 PCRE contains an internal set of tables that are used when the final argument
998 of \fBpcre_compile()\fP is NULL. These are sufficient for many applications.
999 Normally, the internal tables recognize only ASCII characters. However, when
1000 PCRE is built, it is possible to cause the internal tables to be rebuilt in the
1001 default "C" locale of the local system, which may cause them to be different.
1002 .P
1003 The internal tables can always be overridden by tables supplied by the
1004 application that calls PCRE. These may be created in a different locale from
1005 the default. As more and more applications change to using Unicode, the need
1006 for this locale support is expected to die away.
1007 .P
1008 External tables are built by calling the \fBpcre_maketables()\fP function,
1009 which has no arguments, in the relevant locale. The result can then be passed
1010 to \fBpcre_compile()\fP or \fBpcre_exec()\fP as often as necessary. For
1011 example, to build and use tables that are appropriate for the French locale
1012 (where accented characters with values greater than 128 are treated as letters),
1013 the following code could be used:
1014 .sp
1015 setlocale(LC_CTYPE, "fr_FR");
1016 tables = pcre_maketables();
1017 re = pcre_compile(..., tables);
1018 .sp
1019 The locale name "fr_FR" is used on Linux and other Unix-like systems; if you
1020 are using Windows, the name for the French locale is "french".
1021 .P
1022 When \fBpcre_maketables()\fP runs, the tables are built in memory that is
1023 obtained via \fBpcre_malloc\fP. It is the caller's responsibility to ensure
1024 that the memory containing the tables remains available for as long as it is
1025 needed.
1026 .P
1027 The pointer that is passed to \fBpcre_compile()\fP is saved with the compiled
1028 pattern, and the same tables are used via this pointer by \fBpcre_study()\fP
1029 and normally also by \fBpcre_exec()\fP. Thus, by default, for any single
1030 pattern, compilation, studying and matching all happen in the same locale, but
1031 different patterns can be compiled in different locales.
1032 .P
1033 It is possible to pass a table pointer or NULL (indicating the use of the
1034 internal tables) to \fBpcre_exec()\fP. Although not intended for this purpose,
1035 this facility could be used to match a pattern in a different locale from the
1036 one in which it was compiled. Passing table pointers at run time is discussed
1037 below in the section on matching a pattern.
1038 .
1039 .
1040 .\" HTML <a name="infoaboutpattern"></a>
1042 .rs
1043 .sp
1044 .B int pcre_fullinfo(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
1045 .ti +5n
1046 .B int \fIwhat\fP, void *\fIwhere\fP);
1047 .PP
1048 The \fBpcre_fullinfo()\fP function returns information about a compiled
1049 pattern. It replaces the obsolete \fBpcre_info()\fP function, which is
1050 nevertheless retained for backwards compability (and is documented below).
1051 .P
1052 The first argument for \fBpcre_fullinfo()\fP is a pointer to the compiled
1053 pattern. The second argument is the result of \fBpcre_study()\fP, or NULL if
1054 the pattern was not studied. The third argument specifies which piece of
1055 information is required, and the fourth argument is a pointer to a variable
1056 to receive the data. The yield of the function is zero for success, or one of
1057 the following negative numbers:
1058 .sp
1059 PCRE_ERROR_NULL the argument \fIcode\fP was NULL
1060 the argument \fIwhere\fP was NULL
1061 PCRE_ERROR_BADMAGIC the "magic number" was not found
1062 PCRE_ERROR_BADOPTION the value of \fIwhat\fP was invalid
1063 .sp
1064 The "magic number" is placed at the start of each compiled pattern as an simple
1065 check against passing an arbitrary memory pointer. Here is a typical call of
1066 \fBpcre_fullinfo()\fP, to obtain the length of the compiled pattern:
1067 .sp
1068 int rc;
1069 size_t length;
1070 rc = pcre_fullinfo(
1071 re, /* result of pcre_compile() */
1072 sd, /* result of pcre_study(), or NULL */
1073 PCRE_INFO_SIZE, /* what is required */
1074 &length); /* where to put the data */
1075 .sp
1076 The possible values for the third argument are defined in \fBpcre.h\fP, and are
1077 as follows:
1078 .sp
1080 .sp
1081 Return the number of the highest back reference in the pattern. The fourth
1082 argument should point to an \fBint\fP variable. Zero is returned if there are
1083 no back references.
1084 .sp
1086 .sp
1087 Return the number of capturing subpatterns in the pattern. The fourth argument
1088 should point to an \fBint\fP variable.
1089 .sp
1091 .sp
1092 Return a pointer to the internal default character tables within PCRE. The
1093 fourth argument should point to an \fBunsigned char *\fP variable. This
1094 information call is provided for internal use by the \fBpcre_study()\fP
1095 function. External callers can cause PCRE to use its internal tables by passing
1096 a NULL table pointer.
1097 .sp
1099 .sp
1100 Return information about the first byte of any matched string, for a
1101 non-anchored pattern. The fourth argument should point to an \fBint\fP
1102 variable. (This option used to be called PCRE_INFO_FIRSTCHAR; the old name is
1103 still recognized for backwards compatibility.)
1104 .P
1105 If there is a fixed first byte, for example, from a pattern such as
1106 (cat|cow|coyote), its value is returned. Otherwise, if either
1107 .sp
1108 (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
1109 starts with "^", or
1110 .sp
1111 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
1112 (if it were set, the pattern would be anchored),
1113 .sp
1114 -1 is returned, indicating that the pattern matches only at the start of a
1115 subject string or after any newline within the string. Otherwise -2 is
1116 returned. For anchored patterns, -2 is returned.
1117 .sp
1119 .sp
1120 If the pattern was studied, and this resulted in the construction of a 256-bit
1121 table indicating a fixed set of bytes for the first byte in any matching
1122 string, a pointer to the table is returned. Otherwise NULL is returned. The
1123 fourth argument should point to an \fBunsigned char *\fP variable.
1124 .sp
1126 .sp
1127 Return 1 if the pattern contains any explicit matches for CR or LF characters,
1128 otherwise 0. The fourth argument should point to an \fBint\fP variable. An
1129 explicit match is either a literal CR or LF character, or \er or \en.
1130 .sp
1132 .sp
1133 Return 1 if the (?J) or (?-J) option setting is used in the pattern, otherwise
1134 0. The fourth argument should point to an \fBint\fP variable. (?J) and
1135 (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
1136 .sp
1138 .sp
1139 Return 1 if the pattern was studied with the PCRE_STUDY_JIT_COMPILE option, and
1140 just-in-time compiling was successful. The fourth argument should point to an
1141 \fBint\fP variable. A return value of 0 means that JIT support is not available
1142 in this version of PCRE, or that the pattern was not studied with the
1143 PCRE_STUDY_JIT_COMPILE option, or that the JIT compiler could not handle this
1144 particular pattern. See the
1145 .\" HREF
1146 \fBpcrejit\fP
1147 .\"
1148 documentation for details of what can and cannot be handled.
1149 .sp
1151 .sp
1152 If the pattern was successfully studied with the PCRE_STUDY_JIT_COMPILE option,
1153 return the size of the JIT compiled code, otherwise return zero. The fourth
1154 argument should point to a \fBsize_t\fP variable.
1155 .sp
1157 .sp
1158 Return the value of the rightmost literal byte that must exist in any matched
1159 string, other than at its start, if such a byte has been recorded. The fourth
1160 argument should point to an \fBint\fP variable. If there is no such byte, -1 is
1161 returned. For anchored patterns, a last literal byte is recorded only if it
1162 follows something of variable length. For example, for the pattern
1163 /^a\ed+z\ed+/ the returned value is "z", but for /^a\edz\ed/ the returned value
1164 is -1.
1165 .sp
1167 .sp
1168 If the pattern was studied and a minimum length for matching subject strings
1169 was computed, its value is returned. Otherwise the returned value is -1. The
1170 value is a number of characters, not bytes (this may be relevant in UTF-8
1171 mode). The fourth argument should point to an \fBint\fP variable. A
1172 non-negative value is a lower bound to the length of any matching string. There
1173 may not be any strings of that length that do actually match, but every string
1174 that does match is at least that long.
1175 .sp
1179 .sp
1180 PCRE supports the use of named as well as numbered capturing parentheses. The
1181 names are just an additional way of identifying the parentheses, which still
1182 acquire numbers. Several convenience functions such as
1183 \fBpcre_get_named_substring()\fP are provided for extracting captured
1184 substrings by name. It is also possible to extract the data directly, by first
1185 converting the name to a number in order to access the correct pointers in the
1186 output vector (described with \fBpcre_exec()\fP below). To do the conversion,
1187 you need to use the name-to-number map, which is described by these three
1188 values.
1189 .P
1190 The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives
1191 the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each
1192 entry; both of these return an \fBint\fP value. The entry size depends on the
1193 length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first
1194 entry of the table (a pointer to \fBchar\fP). The first two bytes of each entry
1195 are the number of the capturing parenthesis, most significant byte first. The
1196 rest of the entry is the corresponding name, zero terminated.
1197 .P
1198 The names are in alphabetical order. Duplicate names may appear if (?| is used
1199 to create multiple groups with the same number, as described in the
1200 .\" HTML <a href="pcrepattern.html#dupsubpatternnumber">
1201 .\" </a>
1202 section on duplicate subpattern numbers
1203 .\"
1204 in the
1205 .\" HREF
1206 \fBpcrepattern\fP
1207 .\"
1208 page. Duplicate names for subpatterns with different numbers are permitted only
1209 if PCRE_DUPNAMES is set. In all cases of duplicate names, they appear in the
1210 table in the order in which they were found in the pattern. In the absence of
1211 (?| this is the order of increasing number; when (?| is used this is not
1212 necessarily the case because later subpatterns may have lower numbers.
1213 .P
1214 As a simple example of the name/number table, consider the following pattern
1215 (assume PCRE_EXTENDED is set, so white space - including newlines - is
1216 ignored):
1217 .sp
1218 .\" JOIN
1219 (?<date> (?<year>(\ed\ed)?\ed\ed) -
1220 (?<month>\ed\ed) - (?<day>\ed\ed) )
1221 .sp
1222 There are four named subpatterns, so the table has four entries, and each entry
1223 in the table is eight bytes long. The table is as follows, with non-printing
1224 bytes shows in hexadecimal, and undefined bytes shown as ??:
1225 .sp
1226 00 01 d a t e 00 ??
1227 00 05 d a y 00 ?? ??
1228 00 04 m o n t h 00
1229 00 02 y e a r 00 ??
1230 .sp
1231 When writing code to extract data from named subpatterns using the
1232 name-to-number map, remember that the length of the entries is likely to be
1233 different for each compiled pattern.
1234 .sp
1236 .sp
1237 Return 1 if the pattern can be used for partial matching with
1238 \fBpcre_exec()\fP, otherwise 0. The fourth argument should point to an
1239 \fBint\fP variable. From release 8.00, this always returns 1, because the
1240 restrictions that previously applied to partial matching have been lifted. The
1241 .\" HREF
1242 \fBpcrepartial\fP
1243 .\"
1244 documentation gives details of partial matching.
1245 .sp
1247 .sp
1248 Return a copy of the options with which the pattern was compiled. The fourth
1249 argument should point to an \fBunsigned long int\fP variable. These option bits
1250 are those specified in the call to \fBpcre_compile()\fP, modified by any
1251 top-level option settings at the start of the pattern itself. In other words,
1252 they are the options that will be in force when matching starts. For example,
1253 if the pattern /(?im)abc(?-i)d/ is compiled with the PCRE_EXTENDED option, the
1255 .P
1256 A pattern is automatically anchored by PCRE if all of its top-level
1257 alternatives begin with one of the following:
1258 .sp
1259 ^ unless PCRE_MULTILINE is set
1260 \eA always
1261 \eG always
1262 .\" JOIN
1263 .* if PCRE_DOTALL is set and there are no back
1264 references to the subpattern in which .* appears
1265 .sp
1266 For such patterns, the PCRE_ANCHORED bit is set in the options returned by
1267 \fBpcre_fullinfo()\fP.
1268 .sp
1270 .sp
1271 Return the size of the compiled pattern. The fourth argument should point to a
1272 \fBsize_t\fP variable. This value does not include the size of the \fBpcre\fP
1273 structure that is returned by \fBpcre_compile()\fP. The value that is passed as
1274 the argument to \fBpcre_malloc()\fP when \fBpcre_compile()\fP is getting memory
1275 in which to place the compiled data is the value returned by this option plus
1276 the size of the \fBpcre\fP structure. Studying a compiled pattern, with or
1277 without JIT, does not alter the value returned by this option.
1278 .sp
1280 .sp
1281 Return the size of the data block pointed to by the \fIstudy_data\fP field in a
1282 \fBpcre_extra\fP block. If \fBpcre_extra\fP is NULL, or there is no study data,
1283 zero is returned. The fourth argument should point to a \fBsize_t\fP variable.
1284 The \fIstudy_data\fP field is set by \fBpcre_study()\fP to record information
1285 that will speed up matching (see the section entitled
1286 .\" HTML <a href="#studyingapattern">
1287 .\" </a>
1288 "Studying a pattern"
1289 .\"
1290 above). The format of the \fIstudy_data\fP block is private, but its length
1291 is made available via this option so that it can be saved and restored (see the
1292 .\" HREF
1293 \fBpcreprecompile\fP
1294 .\"
1295 documentation for details).
1296 .
1297 .
1299 .rs
1300 .sp
1301 .B int pcre_info(const pcre *\fIcode\fP, int *\fIoptptr\fP, int
1302 .B *\fIfirstcharptr\fP);
1303 .PP
1304 The \fBpcre_info()\fP function is now obsolete because its interface is too
1305 restrictive to return all the available data about a compiled pattern. New
1306 programs should use \fBpcre_fullinfo()\fP instead. The yield of
1307 \fBpcre_info()\fP is the number of capturing subpatterns, or one of the
1308 following negative numbers:
1309 .sp
1310 PCRE_ERROR_NULL the argument \fIcode\fP was NULL
1311 PCRE_ERROR_BADMAGIC the "magic number" was not found
1312 .sp
1313 If the \fIoptptr\fP argument is not NULL, a copy of the options with which the
1314 pattern was compiled is placed in the integer it points to (see
1315 PCRE_INFO_OPTIONS above).
1316 .P
1317 If the pattern is not anchored and the \fIfirstcharptr\fP argument is not NULL,
1318 it is used to pass back information about the first character of any matched
1319 string (see PCRE_INFO_FIRSTBYTE above).
1320 .
1321 .
1323 .rs
1324 .sp
1325 .B int pcre_refcount(pcre *\fIcode\fP, int \fIadjust\fP);
1326 .PP
1327 The \fBpcre_refcount()\fP function is used to maintain a reference count in the
1328 data block that contains a compiled pattern. It is provided for the benefit of
1329 applications that operate in an object-oriented manner, where different parts
1330 of the application may be using the same compiled pattern, but you want to free
1331 the block when they are all done.
1332 .P
1333 When a pattern is compiled, the reference count field is initialized to zero.
1334 It is changed only by calling this function, whose action is to add the
1335 \fIadjust\fP value (which may be positive or negative) to it. The yield of the
1336 function is the new value. However, the value of the count is constrained to
1337 lie between 0 and 65535, inclusive. If the new value is outside these limits,
1338 it is forced to the appropriate limit value.
1339 .P
1340 Except when it is zero, the reference count is not correctly preserved if a
1341 pattern is compiled on one host and then transferred to a host whose byte-order
1342 is different. (This seems a highly unlikely scenario.)
1343 .
1344 .
1346 .rs
1347 .sp
1348 .B int pcre_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
1349 .ti +5n
1350 .B "const char *\fIsubject\fP," int \fIlength\fP, int \fIstartoffset\fP,
1351 .ti +5n
1352 .B int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP);
1353 .P
1354 The function \fBpcre_exec()\fP is called to match a subject string against a
1355 compiled pattern, which is passed in the \fIcode\fP argument. If the
1356 pattern was studied, the result of the study should be passed in the
1357 \fIextra\fP argument. You can call \fBpcre_exec()\fP with the same \fIcode\fP
1358 and \fIextra\fP arguments as many times as you like, in order to match
1359 different subject strings with the same pattern.
1360 .P
1361 This function is the main matching facility of the library, and it operates in
1362 a Perl-like manner. For specialist use there is also an alternative matching
1363 function, which is described
1364 .\" HTML <a href="#dfamatch">
1365 .\" </a>
1366 below
1367 .\"
1368 in the section about the \fBpcre_dfa_exec()\fP function.
1369 .P
1370 In most applications, the pattern will have been compiled (and optionally
1371 studied) in the same process that calls \fBpcre_exec()\fP. However, it is
1372 possible to save compiled patterns and study data, and then use them later
1373 in different processes, possibly even on different hosts. For a discussion
1374 about this, see the
1375 .\" HREF
1376 \fBpcreprecompile\fP
1377 .\"
1378 documentation.
1379 .P
1380 Here is an example of a simple call to \fBpcre_exec()\fP:
1381 .sp
1382 int rc;
1383 int ovector[30];
1384 rc = pcre_exec(
1385 re, /* result of pcre_compile() */
1386 NULL, /* we didn't study the pattern */
1387 "some string", /* the subject string */
1388 11, /* the length of the subject string */
1389 0, /* start at offset 0 in the subject */
1390 0, /* default options */
1391 ovector, /* vector of integers for substring information */
1392 30); /* number of elements (NOT size in bytes) */
1393 .
1394 .
1395 .\" HTML <a name="extradata"></a>
1396 .SS "Extra data for \fBpcre_exec()\fR"
1397 .rs
1398 .sp
1399 If the \fIextra\fP argument is not NULL, it must point to a \fBpcre_extra\fP
1400 data block. The \fBpcre_study()\fP function returns such a block (when it
1401 doesn't return NULL), but you can also create one for yourself, and pass
1402 additional information in it. The \fBpcre_extra\fP block contains the following
1403 fields (not necessarily in this order):
1404 .sp
1405 unsigned long int \fIflags\fP;
1406 void *\fIstudy_data\fP;
1407 void *\fIexecutable_jit\fP;
1408 unsigned long int \fImatch_limit\fP;
1409 unsigned long int \fImatch_limit_recursion\fP;
1410 void *\fIcallout_data\fP;
1411 const unsigned char *\fItables\fP;
1412 unsigned char **\fImark\fP;
1413 .sp
1414 The \fIflags\fP field is a bitmap that specifies which of the other fields
1415 are set. The flag bits are:
1416 .sp
1424 .sp
1425 Other flag bits should be set to zero. The \fIstudy_data\fP field and sometimes
1426 the \fIexecutable_jit\fP field are set in the \fBpcre_extra\fP block that is
1427 returned by \fBpcre_study()\fP, together with the appropriate flag bits. You
1428 should not set these yourself, but you may add to the block by setting the
1429 other fields and their corresponding flag bits.
1430 .P
1431 The \fImatch_limit\fP field provides a means of preventing PCRE from using up a
1432 vast amount of resources when running patterns that are not going to match,
1433 but which have a very large number of possibilities in their search trees. The
1434 classic example is a pattern that uses nested unlimited repeats.
1435 .P
1436 Internally, \fBpcre_exec()\fP uses a function called \fBmatch()\fP, which it
1437 calls repeatedly (sometimes recursively). The limit set by \fImatch_limit\fP is
1438 imposed on the number of times this function is called during a match, which
1439 has the effect of limiting the amount of backtracking that can take place. For
1440 patterns that are not anchored, the count restarts from zero for each position
1441 in the subject string.
1442 .P
1443 When \fBpcre_exec()\fP is called with a pattern that was successfully studied
1444 with the PCRE_STUDY_JIT_COMPILE option, the way that the matching is executed
1445 is entirely different. However, there is still the possibility of runaway
1446 matching that goes on for a very long time, and so the \fImatch_limit\fP value
1447 is also used in this case (but in a different way) to limit how long the
1448 matching can continue.
1449 .P
1450 The default value for the limit can be set when PCRE is built; the default
1451 default is 10 million, which handles all but the most extreme cases. You can
1452 override the default by suppling \fBpcre_exec()\fP with a \fBpcre_extra\fP
1453 block in which \fImatch_limit\fP is set, and PCRE_EXTRA_MATCH_LIMIT is set in
1454 the \fIflags\fP field. If the limit is exceeded, \fBpcre_exec()\fP returns
1456 .P
1457 The \fImatch_limit_recursion\fP field is similar to \fImatch_limit\fP, but
1458 instead of limiting the total number of times that \fBmatch()\fP is called, it
1459 limits the depth of recursion. The recursion depth is a smaller number than the
1460 total number of calls, because not all calls to \fBmatch()\fP are recursive.
1461 This limit is of use only if it is set smaller than \fImatch_limit\fP.
1462 .P
1463 Limiting the recursion depth limits the amount of machine stack that can be
1464 used, or, when PCRE has been compiled to use memory on the heap instead of the
1465 stack, the amount of heap memory that can be used. This limit is not relevant,
1466 and is ignored, if the pattern was successfully studied with
1468 .P
1469 The default value for \fImatch_limit_recursion\fP can be set when PCRE is
1470 built; the default default is the same value as the default for
1471 \fImatch_limit\fP. You can override the default by suppling \fBpcre_exec()\fP
1472 with a \fBpcre_extra\fP block in which \fImatch_limit_recursion\fP is set, and
1473 PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the \fIflags\fP field. If the limit
1474 is exceeded, \fBpcre_exec()\fP returns PCRE_ERROR_RECURSIONLIMIT.
1475 .P
1476 The \fIcallout_data\fP field is used in conjunction with the "callout" feature,
1477 and is described in the
1478 .\" HREF
1479 \fBpcrecallout\fP
1480 .\"
1481 documentation.
1482 .P
1483 The \fItables\fP field is used to pass a character tables pointer to
1484 \fBpcre_exec()\fP; this overrides the value that is stored with the compiled
1485 pattern. A non-NULL value is stored with the compiled pattern only if custom
1486 tables were supplied to \fBpcre_compile()\fP via its \fItableptr\fP argument.
1487 If NULL is passed to \fBpcre_exec()\fP using this mechanism, it forces PCRE's
1488 internal tables to be used. This facility is helpful when re-using patterns
1489 that have been saved after compiling with an external set of tables, because
1490 the external tables might be at a different address when \fBpcre_exec()\fP is
1491 called. See the
1492 .\" HREF
1493 \fBpcreprecompile\fP
1494 .\"
1495 documentation for a discussion of saving compiled patterns for later use.
1496 .P
1497 If PCRE_EXTRA_MARK is set in the \fIflags\fP field, the \fImark\fP field must
1498 be set to point to a \fBchar *\fP variable. If the pattern contains any
1499 backtracking control verbs such as (*MARK:NAME), and the execution ends up with
1500 a name to pass back, a pointer to the name string (zero terminated) is placed
1501 in the variable pointed to by the \fImark\fP field. The names are within the
1502 compiled pattern; if you wish to retain such a name you must copy it before
1503 freeing the memory of a compiled pattern. If there is no name to pass back, the
1504 variable pointed to by the \fImark\fP field set to NULL. For details of the
1505 backtracking control verbs, see the section entitled
1506 .\" HTML <a href="pcrepattern#backtrackcontrol">
1507 .\" </a>
1508 "Backtracking control"
1509 .\"
1510 in the
1511 .\" HREF
1512 \fBpcrepattern\fP
1513 .\"
1514 documentation.
1515 .
1516 .
1517 .\" HTML <a name="execoptions"></a>
1518 .SS "Option bits for \fBpcre_exec()\fP"
1519 .rs
1520 .sp
1521 The unused bits of the \fIoptions\fP argument for \fBpcre_exec()\fP must be
1522 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_\fIxxx\fP,
1526 .P
1527 If the pattern was successfully studied with the PCRE_STUDY_JIT_COMPILE option,
1528 the only supported options for JIT execution are PCRE_NO_UTF8_CHECK,
1530 particular that partial matching is not supported. If an unsupported option is
1531 used, JIT execution is disabled and the normal interpretive code in
1532 \fBpcre_exec()\fP is run.
1533 .sp
1535 .sp
1536 The PCRE_ANCHORED option limits \fBpcre_exec()\fP to matching at the first
1537 matching position. If a pattern was compiled with PCRE_ANCHORED, or turned out
1538 to be anchored by virtue of its contents, it cannot be made unachored at
1539 matching time.
1540 .sp
1543 .sp
1544 These options (which are mutually exclusive) control what the \eR escape
1545 sequence matches. The choice is either to match only CR, LF, or CRLF, or to
1546 match any Unicode newline sequence. These options override the choice that was
1547 made or defaulted when the pattern was compiled.
1548 .sp
1554 .sp
1555 These options override the newline definition that was chosen or defaulted when
1556 the pattern was compiled. For details, see the description of
1557 \fBpcre_compile()\fP above. During matching, the newline choice affects the
1558 behaviour of the dot, circumflex, and dollar metacharacters. It may also alter
1559 the way the match position is advanced after a match failure for an unanchored
1560 pattern.
1561 .P
1563 match attempt for an unanchored pattern fails when the current position is at a
1564 CRLF sequence, and the pattern contains no explicit matches for CR or LF
1565 characters, the match position is advanced by two characters instead of one, in
1566 other words, to after the CRLF.
1567 .P
1568 The above rule is a compromise that makes the most common cases work as
1569 expected. For example, if the pattern is .+A (and the PCRE_DOTALL option is not
1570 set), it does not match the string "\er\enA" because, after failing at the
1571 start, it skips both the CR and the LF before retrying. However, the pattern
1572 [\er\en]A does match that string, because it contains an explicit CR or LF
1573 reference, and so advances only by one character after the first failure.
1574 .P
1575 An explicit match for CR of LF is either a literal appearance of one of those
1576 characters, or one of the \er or \en escape sequences. Implicit matches such as
1577 [^X] do not count, nor does \es (which includes CR and LF in the characters
1578 that it matches).
1579 .P
1580 Notwithstanding the above, anomalous effects may still occur when CRLF is a
1581 valid newline sequence and explicit \er or \en escapes appear in the pattern.
1582 .sp
1584 .sp
1585 This option specifies that first character of the subject string is not the
1586 beginning of a line, so the circumflex metacharacter should not match before
1587 it. Setting this without PCRE_MULTILINE (at compile time) causes circumflex
1588 never to match. This option affects only the behaviour of the circumflex
1589 metacharacter. It does not affect \eA.
1590 .sp
1592 .sp
1593 This option specifies that the end of the subject string is not the end of a
1594 line, so the dollar metacharacter should not match it nor (except in multiline
1595 mode) a newline immediately before it. Setting this without PCRE_MULTILINE (at
1596 compile time) causes dollar never to match. This option affects only the
1597 behaviour of the dollar metacharacter. It does not affect \eZ or \ez.
1598 .sp
1600 .sp
1601 An empty string is not considered to be a valid match if this option is set. If
1602 there are alternatives in the pattern, they are tried. If all the alternatives
1603 match the empty string, the entire match fails. For example, if the pattern
1604 .sp
1605 a?b?
1606 .sp
1607 is applied to a string not beginning with "a" or "b", it matches an empty
1608 string at the start of the subject. With PCRE_NOTEMPTY set, this match is not
1609 valid, so PCRE searches further into the string for occurrences of "a" or "b".
1610 .sp
1612 .sp
1613 This is like PCRE_NOTEMPTY, except that an empty string match that is not at
1614 the start of the subject is permitted. If the pattern is anchored, such a match
1615 can occur only if the pattern contains \eK.
1616 .P
1617 Perl has no direct equivalent of PCRE_NOTEMPTY or PCRE_NOTEMPTY_ATSTART, but it
1618 does make a special case of a pattern match of the empty string within its
1619 \fBsplit()\fP function, and when using the /g modifier. It is possible to
1620 emulate Perl's behaviour after matching a null string by first trying the match
1621 again at the same offset with PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED, and then
1622 if that fails, by advancing the starting offset (see below) and trying an
1623 ordinary match again. There is some code that demonstrates how to do this in
1624 the
1625 .\" HREF
1626 \fBpcredemo\fP
1627 .\"
1628 sample program. In the most general case, you have to check to see if the
1629 newline convention recognizes CRLF as a newline, and if so, and the current
1630 character is CR followed by LF, advance the starting offset by two characters
1631 instead of one.
1632 .sp
1634 .sp
1635 There are a number of optimizations that \fBpcre_exec()\fP uses at the start of
1636 a match, in order to speed up the process. For example, if it is known that an
1637 unanchored match must start with a specific character, it searches the subject
1638 for that character, and fails immediately if it cannot find it, without
1639 actually running the main matching function. This means that a special item
1640 such as (*COMMIT) at the start of a pattern is not considered until after a
1641 suitable starting point for the match has been found. When callouts or (*MARK)
1642 items are in use, these "start-up" optimizations can cause them to be skipped
1643 if the pattern is never actually used. The start-up optimizations are in effect
1644 a pre-scan of the subject that takes place before the pattern is run.
1645 .P
1646 The PCRE_NO_START_OPTIMIZE option disables the start-up optimizations, possibly
1647 causing performance to suffer, but ensuring that in cases where the result is
1648 "no match", the callouts do occur, and that items such as (*COMMIT) and (*MARK)
1649 are considered at every possible starting position in the subject string. If
1650 PCRE_NO_START_OPTIMIZE is set at compile time, it cannot be unset at matching
1651 time.
1652 .P
1653 Setting PCRE_NO_START_OPTIMIZE can change the outcome of a matching operation.
1654 Consider the pattern
1655 .sp
1657 .sp
1658 When this is compiled, PCRE records the fact that a match must start with the
1659 character "A". Suppose the subject string is "DEFABC". The start-up
1660 optimization scans along the subject, finds "A" and runs the first match
1661 attempt from there. The (*COMMIT) item means that the pattern must match the
1662 current starting position, which in this case, it does. However, if the same
1663 match is run with PCRE_NO_START_OPTIMIZE set, the initial scan along the
1664 subject string does not happen. The first match attempt is run starting from
1665 "D" and when this fails, (*COMMIT) prevents any further matches being tried, so
1666 the overall result is "no match". If the pattern is studied, more start-up
1667 optimizations may be used. For example, a minimum length for the subject may be
1668 recorded. Consider the pattern
1669 .sp
1670 (*MARK:A)(X|Y)
1671 .sp
1672 The minimum length for a match is one character. If the subject is "ABC", there
1673 will be attempts to match "ABC", "BC", "C", and then finally an empty string.
1674 If the pattern is studied, the final attempt does not take place, because PCRE
1675 knows that the subject is too short, and so the (*MARK) is never encountered.
1676 In this case, studying the pattern does not affect the overall match result,
1677 which is still "no match", but it does affect the auxiliary information that is
1678 returned.
1679 .sp
1681 .sp
1682 When PCRE_UTF8 is set at compile time, the validity of the subject as a UTF-8
1683 string is automatically checked when \fBpcre_exec()\fP is subsequently called.
1684 The value of \fIstartoffset\fP is also checked to ensure that it points to the
1685 start of a UTF-8 character. There is a discussion about the validity of UTF-8
1686 strings in the
1687 .\" HTML <a href="pcre.html#utf8strings">
1688 .\" </a>
1689 section on UTF-8 support
1690 .\"
1691 in the main
1692 .\" HREF
1693 \fBpcre\fP
1694 .\"
1695 page. If an invalid UTF-8 sequence of bytes is found, \fBpcre_exec()\fP returns
1696 the error PCRE_ERROR_BADUTF8 or, if PCRE_PARTIAL_HARD is set and the problem is
1697 a truncated UTF-8 character at the end of the subject, PCRE_ERROR_SHORTUTF8. In
1698 both cases, information about the precise nature of the error may also be
1699 returned (see the descriptions of these errors in the section entitled \fIError
1700 return values from\fP \fBpcre_exec()\fP
1701 .\" HTML <a href="#errorlist">
1702 .\" </a>
1703 below).
1704 .\"
1705 If \fIstartoffset\fP contains a value that does not point to the start of a
1706 UTF-8 character (or to the end of the subject), PCRE_ERROR_BADUTF8_OFFSET is
1707 returned.
1708 .P
1709 If you already know that your subject is valid, and you want to skip these
1710 checks for performance reasons, you can set the PCRE_NO_UTF8_CHECK option when
1711 calling \fBpcre_exec()\fP. You might want to do this for the second and
1712 subsequent calls to \fBpcre_exec()\fP if you are making repeated calls to find
1713 all the matches in a single subject string. However, you should be sure that
1714 the value of \fIstartoffset\fP points to the start of a UTF-8 character (or the
1715 end of the subject). When PCRE_NO_UTF8_CHECK is set, the effect of passing an
1716 invalid UTF-8 string as a subject or an invalid value of \fIstartoffset\fP is
1717 undefined. Your program may crash.
1718 .sp
1721 .sp
1722 These options turn on the partial matching feature. For backwards
1723 compatibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial match
1724 occurs if the end of the subject string is reached successfully, but there are
1725 not enough subject characters to complete the match. If this happens when
1726 PCRE_PARTIAL_SOFT (but not PCRE_PARTIAL_HARD) is set, matching continues by
1727 testing any remaining alternatives. Only if no complete match can be found is
1728 PCRE_ERROR_PARTIAL returned instead of PCRE_ERROR_NOMATCH. In other words,
1729 PCRE_PARTIAL_SOFT says that the caller is prepared to handle a partial match,
1730 but only if no complete match can be found.
1731 .P
1732 If PCRE_PARTIAL_HARD is set, it overrides PCRE_PARTIAL_SOFT. In this case, if a
1733 partial match is found, \fBpcre_exec()\fP immediately returns
1734 PCRE_ERROR_PARTIAL, without considering any other alternatives. In other words,
1735 when PCRE_PARTIAL_HARD is set, a partial match is considered to be more
1736 important that an alternative complete match.
1737 .P
1738 In both cases, the portion of the string that was inspected when the partial
1739 match was found is set as the first matching string. There is a more detailed
1740 discussion of partial and multi-segment matching, with examples, in the
1741 .\" HREF
1742 \fBpcrepartial\fP
1743 .\"
1744 documentation.
1745 .
1746 .
1747 .SS "The string to be matched by \fBpcre_exec()\fP"
1748 .rs
1749 .sp
1750 The subject string is passed to \fBpcre_exec()\fP as a pointer in
1751 \fIsubject\fP, a length (in bytes) in \fIlength\fP, and a starting byte offset
1752 in \fIstartoffset\fP. If this is negative or greater than the length of the
1753 subject, \fBpcre_exec()\fP returns PCRE_ERROR_BADOFFSET. When the starting
1754 offset is zero, the search for a match starts at the beginning of the subject,
1755 and this is by far the most common case. In UTF-8 mode, the byte offset must
1756 point to the start of a UTF-8 character (or the end of the subject). Unlike the
1757 pattern string, the subject may contain binary zero bytes.
1758 .P
1759 A non-zero starting offset is useful when searching for another match in the
1760 same subject by calling \fBpcre_exec()\fP again after a previous success.
1761 Setting \fIstartoffset\fP differs from just passing over a shortened string and
1762 setting PCRE_NOTBOL in the case of a pattern that begins with any kind of
1763 lookbehind. For example, consider the pattern
1764 .sp
1765 \eBiss\eB
1766 .sp
1767 which finds occurrences of "iss" in the middle of words. (\eB matches only if
1768 the current position in the subject is not a word boundary.) When applied to
1769 the string "Mississipi" the first call to \fBpcre_exec()\fP finds the first
1770 occurrence. If \fBpcre_exec()\fP is called again with just the remainder of the
1771 subject, namely "issipi", it does not match, because \eB is always false at the
1772 start of the subject, which is deemed to be a word boundary. However, if
1773 \fBpcre_exec()\fP is passed the entire string again, but with \fIstartoffset\fP
1774 set to 4, it finds the second occurrence of "iss" because it is able to look
1775 behind the starting point to discover that it is preceded by a letter.
1776 .P
1777 Finding all the matches in a subject is tricky when the pattern can match an
1778 empty string. It is possible to emulate Perl's /g behaviour by first trying the
1779 match again at the same offset, with the PCRE_NOTEMPTY_ATSTART and
1780 PCRE_ANCHORED options, and then if that fails, advancing the starting offset
1781 and trying an ordinary match again. There is some code that demonstrates how to
1782 do this in the
1783 .\" HREF
1784 \fBpcredemo\fP
1785 .\"
1786 sample program. In the most general case, you have to check to see if the
1787 newline convention recognizes CRLF as a newline, and if so, and the current
1788 character is CR followed by LF, advance the starting offset by two characters
1789 instead of one.
1790 .P
1791 If a non-zero starting offset is passed when the pattern is anchored, one
1792 attempt to match at the given offset is made. This can only succeed if the
1793 pattern does not require the match to be at the start of the subject.
1794 .
1795 .
1796 .SS "How \fBpcre_exec()\fP returns captured substrings"
1797 .rs
1798 .sp
1799 In general, a pattern matches a certain portion of the subject, and in
1800 addition, further substrings from the subject may be picked out by parts of the
1801 pattern. Following the usage in Jeffrey Friedl's book, this is called
1802 "capturing" in what follows, and the phrase "capturing subpattern" is used for
1803 a fragment of a pattern that picks out a substring. PCRE supports several other
1804 kinds of parenthesized subpattern that do not cause substrings to be captured.
1805 .P
1806 Captured substrings are returned to the caller via a vector of integers whose
1807 address is passed in \fIovector\fP. The number of elements in the vector is
1808 passed in \fIovecsize\fP, which must be a non-negative number. \fBNote\fP: this
1809 argument is NOT the size of \fIovector\fP in bytes.
1810 .P
1811 The first two-thirds of the vector is used to pass back captured substrings,
1812 each substring using a pair of integers. The remaining third of the vector is
1813 used as workspace by \fBpcre_exec()\fP while matching capturing subpatterns,
1814 and is not available for passing back information. The number passed in
1815 \fIovecsize\fP should always be a multiple of three. If it is not, it is
1816 rounded down.
1817 .P
1818 When a match is successful, information about captured substrings is returned
1819 in pairs of integers, starting at the beginning of \fIovector\fP, and
1820 continuing up to two-thirds of its length at the most. The first element of
1821 each pair is set to the byte offset of the first character in a substring, and
1822 the second is set to the byte offset of the first character after the end of a
1823 substring. \fBNote\fP: these values are always byte offsets, even in UTF-8
1824 mode. They are not character counts.
1825 .P
1826 The first pair of integers, \fIovector[0]\fP and \fIovector[1]\fP, identify the
1827 portion of the subject string matched by the entire pattern. The next pair is
1828 used for the first capturing subpattern, and so on. The value returned by
1829 \fBpcre_exec()\fP is one more than the highest numbered pair that has been set.
1830 For example, if two substrings have been captured, the returned value is 3. If
1831 there are no capturing subpatterns, the return value from a successful match is
1832 1, indicating that just the first pair of offsets has been set.
1833 .P
1834 If a capturing subpattern is matched repeatedly, it is the last portion of the
1835 string that it matched that is returned.
1836 .P
1837 If the vector is too small to hold all the captured substring offsets, it is
1838 used as far as possible (up to two-thirds of its length), and the function
1839 returns a value of zero. If neither the actual string matched not any captured
1840 substrings are of interest, \fBpcre_exec()\fP may be called with \fIovector\fP
1841 passed as NULL and \fIovecsize\fP as zero. However, if the pattern contains
1842 back references and the \fIovector\fP is not big enough to remember the related
1843 substrings, PCRE has to get additional memory for use during matching. Thus it
1844 is usually advisable to supply an \fIovector\fP of reasonable size.
1845 .P
1846 There are some cases where zero is returned (indicating vector overflow) when
1847 in fact the vector is exactly the right size for the final match. For example,
1848 consider the pattern
1849 .sp
1850 (a)(?:(b)c|bd)
1851 .sp
1852 If a vector of 6 elements (allowing for only 1 captured substring) is given
1853 with subject string "abd", \fBpcre_exec()\fP will try to set the second
1854 captured string, thereby recording a vector overflow, before failing to match
1855 "c" and backing up to try the second alternative. The zero return, however,
1856 does correctly indicate that the maximum number of slots (namely 2) have been
1857 filled. In similar cases where there is temporary overflow, but the final
1858 number of used slots is actually less than the maximum, a non-zero value is
1859 returned.
1860 .P
1861 The \fBpcre_fullinfo()\fP function can be used to find out how many capturing
1862 subpatterns there are in a compiled pattern. The smallest size for
1863 \fIovector\fP that will allow for \fIn\fP captured substrings, in addition to
1864 the offsets of the substring matched by the whole pattern, is (\fIn\fP+1)*3.
1865 .P
1866 It is possible for capturing subpattern number \fIn+1\fP to match some part of
1867 the subject when subpattern \fIn\fP has not been used at all. For example, if
1868 the string "abc" is matched against the pattern (a|(z))(bc) the return from the
1869 function is 4, and subpatterns 1 and 3 are matched, but 2 is not. When this
1870 happens, both values in the offset pairs corresponding to unused subpatterns
1871 are set to -1.
1872 .P
1873 Offset values that correspond to unused subpatterns at the end of the
1874 expression are also set to -1. For example, if the string "abc" is matched
1875 against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not matched. The
1876 return from the function is 2, because the highest used capturing subpattern
1877 number is 1, and the offsets for for the second and third capturing subpatterns
1878 (assuming the vector is large enough, of course) are set to -1.
1879 .P
1880 \fBNote\fP: Elements in the first two-thirds of \fIovector\fP that do not
1881 correspond to capturing parentheses in the pattern are never changed. That is,
1882 if a pattern contains \fIn\fP capturing parentheses, no more than
1883 \fIovector[0]\fP to \fIovector[2n+1]\fP are set by \fBpcre_exec()\fP. The other
1884 elements (in the first two-thirds) retain whatever values they previously had.
1885 .P
1886 Some convenience functions are provided for extracting the captured substrings
1887 as separate strings. These are described below.
1888 .
1889 .
1890 .\" HTML <a name="errorlist"></a>
1891 .SS "Error return values from \fBpcre_exec()\fP"
1892 .rs
1893 .sp
1894 If \fBpcre_exec()\fP fails, it returns a negative number. The following are
1895 defined in the header file:
1896 .sp
1898 .sp
1899 The subject string did not match the pattern.
1900 .sp
1902 .sp
1903 Either \fIcode\fP or \fIsubject\fP was passed as NULL, or \fIovector\fP was
1904 NULL and \fIovecsize\fP was not zero.
1905 .sp
1907 .sp
1908 An unrecognized bit was set in the \fIoptions\fP argument.
1909 .sp
1911 .sp
1912 PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch
1913 the case when it is passed a junk pointer and to detect when a pattern that was
1914 compiled in an environment of one endianness is run in an environment with the
1915 other endianness. This is the error that PCRE gives when the magic number is
1916 not present.
1917 .sp
1919 .sp
1920 While running the pattern match, an unknown item was encountered in the
1921 compiled pattern. This error could be caused by a bug in PCRE or by overwriting
1922 of the compiled pattern.
1923 .sp
1925 .sp
1926 If a pattern contains back references, but the \fIovector\fP that is passed to
1927 \fBpcre_exec()\fP is not big enough to remember the referenced substrings, PCRE
1928 gets a block of memory at the start of matching to use for this purpose. If the
1929 call via \fBpcre_malloc()\fP fails, this error is given. The memory is
1930 automatically freed at the end of matching.
1931 .P
1932 This error is also given if \fBpcre_stack_malloc()\fP fails in
1933 \fBpcre_exec()\fP. This can happen only when PCRE has been compiled with
1934 \fB--disable-stack-for-recursion\fP.
1935 .sp
1937 .sp
1938 This error is used by the \fBpcre_copy_substring()\fP,
1939 \fBpcre_get_substring()\fP, and \fBpcre_get_substring_list()\fP functions (see
1940 below). It is never returned by \fBpcre_exec()\fP.
1941 .sp
1943 .sp
1944 The backtracking limit, as specified by the \fImatch_limit\fP field in a
1945 \fBpcre_extra\fP structure (or defaulted) was reached. See the description
1946 above.
1947 .sp
1949 .sp
1950 This error is never generated by \fBpcre_exec()\fP itself. It is provided for
1951 use by callout functions that want to yield a distinctive error code. See the
1952 .\" HREF
1953 \fBpcrecallout\fP
1954 .\"
1955 documentation for details.
1956 .sp
1958 .sp
1959 A string that contains an invalid UTF-8 byte sequence was passed as a subject,
1960 and the PCRE_NO_UTF8_CHECK option was not set. If the size of the output vector
1961 (\fIovecsize\fP) is at least 2, the byte offset to the start of the the invalid
1962 UTF-8 character is placed in the first element, and a reason code is placed in
1963 the second element. The reason codes are listed in the
1964 .\" HTML <a href="#badutf8reasons">
1965 .\" </a>
1966 following section.
1967 .\"
1968 For backward compatibility, if PCRE_PARTIAL_HARD is set and the problem is a
1969 truncated UTF-8 character at the end of the subject (reason codes 1 to 5),
1970 PCRE_ERROR_SHORTUTF8 is returned instead of PCRE_ERROR_BADUTF8.
1971 .sp
1973 .sp
1974 The UTF-8 byte sequence that was passed as a subject was checked and found to
1975 be valid (the PCRE_NO_UTF8_CHECK option was not set), but the value of
1976 \fIstartoffset\fP did not point to the beginning of a UTF-8 character or the
1977 end of the subject.
1978 .sp
1980 .sp
1981 The subject string did not match, but it did match partially. See the
1982 .\" HREF
1983 \fBpcrepartial\fP
1984 .\"
1985 documentation for details of partial matching.
1986 .sp
1988 .sp
1989 This code is no longer in use. It was formerly returned when the PCRE_PARTIAL
1990 option was used with a compiled pattern containing items that were not
1991 supported for partial matching. From release 8.00 onwards, there are no
1992 restrictions on partial matching.
1993 .sp
1995 .sp
1996 An unexpected internal error has occurred. This error could be caused by a bug
1997 in PCRE or by overwriting of the compiled pattern.
1998 .sp
2000 .sp
2001 This error is given if the value of the \fIovecsize\fP argument is negative.
2002 .sp
2004 .sp
2005 The internal recursion limit, as specified by the \fImatch_limit_recursion\fP
2006 field in a \fBpcre_extra\fP structure (or defaulted) was reached. See the
2007 description above.
2008 .sp
2010 .sp
2011 An invalid combination of PCRE_NEWLINE_\fIxxx\fP options was given.
2012 .sp
2014 .sp
2015 The value of \fIstartoffset\fP was negative or greater than the length of the
2016 subject, that is, the value in \fIlength\fP.
2017 .sp
2019 .sp
2020 This error is returned instead of PCRE_ERROR_BADUTF8 when the subject string
2021 ends with a truncated UTF-8 character and the PCRE_PARTIAL_HARD option is set.
2022 Information about the failure is returned as for PCRE_ERROR_BADUTF8. It is in
2023 fact sufficient to detect this case, but this special error code for
2024 PCRE_PARTIAL_HARD precedes the implementation of returned information; it is
2025 retained for backwards compatibility.
2026 .sp
2028 .sp
2029 This error is returned when \fBpcre_exec()\fP detects a recursion loop within
2030 the pattern. Specifically, it means that either the whole pattern or a
2031 subpattern has been called recursively for the second time at the same position
2032 in the subject string. Some simple patterns that might do this are detected and
2033 faulted at compile time, but more complicated cases, in particular mutual
2034 recursions between two different subpatterns, cannot be detected until run
2035 time.
2036 .sp
2038 .sp
2039 This error is returned when a pattern that was successfully studied using the
2040 PCRE_STUDY_JIT_COMPILE option is being matched, but the memory available for
2041 the just-in-time processing stack is not large enough. See the
2042 .\" HREF
2043 \fBpcrejit\fP
2044 .\"
2045 documentation for more details.
2046 .P
2047 Error numbers -16 to -20 and -22 are not used by \fBpcre_exec()\fP.
2048 .
2049 .
2050 .\" HTML <a name="badutf8reasons"></a>
2051 .SS "Reason codes for invalid UTF-8 strings"
2052 .rs
2053 .sp
2054 When \fBpcre_exec()\fP returns either PCRE_ERROR_BADUTF8 or
2055 PCRE_ERROR_SHORTUTF8, and the size of the output vector (\fIovecsize\fP) is at
2056 least 2, the offset of the start of the invalid UTF-8 character is placed in
2057 the first output vector element (\fIovector[0]\fP) and a reason code is placed
2058 in the second element (\fIovector[1]\fP). The reason codes are given names in
2059 the \fBpcre.h\fP header file:
2060 .sp
2066 .sp
2067 The string ends with a truncated UTF-8 character; the code specifies how many
2068 bytes are missing (1 to 5). Although RFC 3629 restricts UTF-8 characters to be
2069 no longer than 4 bytes, the encoding scheme (originally defined by RFC 2279)
2070 allows for up to 6 bytes, and this is checked first; hence the possibility of
2071 4 or 5 missing bytes.
2072 .sp
2077 PCRE_UTF8_ERR10
2078 .sp
2079 The two most significant bits of the 2nd, 3rd, 4th, 5th, or 6th byte of the
2080 character do not have the binary value 0b10 (that is, either the most
2081 significant bit is 0, or the next bit is 1).
2082 .sp
2083 PCRE_UTF8_ERR11
2084 PCRE_UTF8_ERR12
2085 .sp
2086 A character that is valid by the RFC 2279 rules is either 5 or 6 bytes long;
2087 these code points are excluded by RFC 3629.
2088 .sp
2089 PCRE_UTF8_ERR13
2090 .sp
2091 A 4-byte character has a value greater than 0x10fff; these code points are
2092 excluded by RFC 3629.
2093 .sp
2094 PCRE_UTF8_ERR14
2095 .sp
2096 A 3-byte character has a value in the range 0xd800 to 0xdfff; this range of
2097 code points are reserved by RFC 3629 for use with UTF-16, and so are excluded
2098 from UTF-8.
2099 .sp
2100 PCRE_UTF8_ERR15
2101 PCRE_UTF8_ERR16
2102 PCRE_UTF8_ERR17
2103 PCRE_UTF8_ERR18
2104 PCRE_UTF8_ERR19
2105 .sp
2106 A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it codes for a
2107 value that can be represented by fewer bytes, which is invalid. For example,
2108 the two bytes 0xc0, 0xae give the value 0x2e, whose correct coding uses just
2109 one byte.
2110 .sp
2111 PCRE_UTF8_ERR20
2112 .sp
2113 The two most significant bits of the first byte of a character have the binary
2114 value 0b10 (that is, the most significant bit is 1 and the second is 0). Such a
2115 byte can only validly occur as the second or subsequent byte of a multi-byte
2116 character.
2117 .sp
2118 PCRE_UTF8_ERR21
2119 .sp
2120 The first byte of a character has the value 0xfe or 0xff. These values can
2121 never occur in a valid UTF-8 string.
2122 .
2123 .
2125 .rs
2126 .sp
2127 .B int pcre_copy_substring(const char *\fIsubject\fP, int *\fIovector\fP,
2128 .ti +5n
2129 .B int \fIstringcount\fP, int \fIstringnumber\fP, char *\fIbuffer\fP,
2130 .ti +5n
2131 .B int \fIbuffersize\fP);
2132 .PP
2133 .B int pcre_get_substring(const char *\fIsubject\fP, int *\fIovector\fP,
2134 .ti +5n
2135 .B int \fIstringcount\fP, int \fIstringnumber\fP,
2136 .ti +5n
2137 .B const char **\fIstringptr\fP);
2138 .PP
2139 .B int pcre_get_substring_list(const char *\fIsubject\fP,
2140 .ti +5n
2141 .B int *\fIovector\fP, int \fIstringcount\fP, "const char ***\fIlistptr\fP);"
2142 .PP
2143 Captured substrings can be accessed directly by using the offsets returned by
2144 \fBpcre_exec()\fP in \fIovector\fP. For convenience, the functions
2145 \fBpcre_copy_substring()\fP, \fBpcre_get_substring()\fP, and
2146 \fBpcre_get_substring_list()\fP are provided for extracting captured substrings
2147 as new, separate, zero-terminated strings. These functions identify substrings
2148 by number. The next section describes functions for extracting named
2149 substrings.
2150 .P
2151 A substring that contains a binary zero is correctly extracted and has a
2152 further zero added on the end, but the result is not, of course, a C string.
2153 However, you can process such a string by referring to the length that is
2154 returned by \fBpcre_copy_substring()\fP and \fBpcre_get_substring()\fP.
2155 Unfortunately, the interface to \fBpcre_get_substring_list()\fP is not adequate
2156 for handling strings containing binary zeros, because the end of the final
2157 string is not independently indicated.
2158 .P
2159 The first three arguments are the same for all three of these functions:
2160 \fIsubject\fP is the subject string that has just been successfully matched,
2161 \fIovector\fP is a pointer to the vector of integer offsets that was passed to
2162 \fBpcre_exec()\fP, and \fIstringcount\fP is the number of substrings that were
2163 captured by the match, including the substring that matched the entire regular
2164 expression. This is the value returned by \fBpcre_exec()\fP if it is greater
2165 than zero. If \fBpcre_exec()\fP returned zero, indicating that it ran out of
2166 space in \fIovector\fP, the value passed as \fIstringcount\fP should be the
2167 number of elements in the vector divided by three.
2168 .P
2169 The functions \fBpcre_copy_substring()\fP and \fBpcre_get_substring()\fP
2170 extract a single substring, whose number is given as \fIstringnumber\fP. A
2171 value of zero extracts the substring that matched the entire pattern, whereas
2172 higher values extract the captured substrings. For \fBpcre_copy_substring()\fP,
2173 the string is placed in \fIbuffer\fP, whose length is given by
2174 \fIbuffersize\fP, while for \fBpcre_get_substring()\fP a new block of memory is
2175 obtained via \fBpcre_malloc\fP, and its address is returned via
2176 \fIstringptr\fP. The yield of the function is the length of the string, not
2177 including the terminating zero, or one of these error codes:
2178 .sp
2180 .sp
2181 The buffer was too small for \fBpcre_copy_substring()\fP, or the attempt to get
2182 memory failed for \fBpcre_get_substring()\fP.
2183 .sp
2185 .sp
2186 There is no substring whose number is \fIstringnumber\fP.
2187 .P
2188 The \fBpcre_get_substring_list()\fP function extracts all available substrings
2189 and builds a list of pointers to them. All this is done in a single block of
2190 memory that is obtained via \fBpcre_malloc\fP. The address of the memory block
2191 is returned via \fIlistptr\fP, which is also the start of the list of string
2192 pointers. The end of the list is marked by a NULL pointer. The yield of the
2193 function is zero if all went well, or the error code
2194 .sp
2196 .sp
2197 if the attempt to get the memory block failed.
2198 .P
2199 When any of these functions encounter a substring that is unset, which can
2200 happen when capturing subpattern number \fIn+1\fP matches some part of the
2201 subject, but subpattern \fIn\fP has not been used at all, they return an empty
2202 string. This can be distinguished from a genuine zero-length substring by
2203 inspecting the appropriate offset in \fIovector\fP, which is negative for unset
2204 substrings.
2205 .P
2206 The two convenience functions \fBpcre_free_substring()\fP and
2207 \fBpcre_free_substring_list()\fP can be used to free the memory returned by
2208 a previous call of \fBpcre_get_substring()\fP or
2209 \fBpcre_get_substring_list()\fP, respectively. They do nothing more than call
2210 the function pointed to by \fBpcre_free\fP, which of course could be called
2211 directly from a C program. However, PCRE is used in some situations where it is
2212 linked via a special interface to another programming language that cannot use
2213 \fBpcre_free\fP directly; it is for these cases that the functions are
2214 provided.
2215 .
2216 .
2218 .rs
2219 .sp
2220 .B int pcre_get_stringnumber(const pcre *\fIcode\fP,
2221 .ti +5n
2222 .B const char *\fIname\fP);
2223 .PP
2224 .B int pcre_copy_named_substring(const pcre *\fIcode\fP,
2225 .ti +5n
2226 .B const char *\fIsubject\fP, int *\fIovector\fP,
2227 .ti +5n
2228 .B int \fIstringcount\fP, const char *\fIstringname\fP,
2229 .ti +5n
2230 .B char *\fIbuffer\fP, int \fIbuffersize\fP);
2231 .PP
2232 .B int pcre_get_named_substring(const pcre *\fIcode\fP,
2233 .ti +5n
2234 .B const char *\fIsubject\fP, int *\fIovector\fP,
2235 .ti +5n
2236 .B int \fIstringcount\fP, const char *\fIstringname\fP,
2237 .ti +5n
2238 .B const char **\fIstringptr\fP);
2239 .PP
2240 To extract a substring by name, you first have to find associated number.
2241 For example, for this pattern
2242 .sp
2243 (a+)b(?<xxx>\ed+)...
2244 .sp
2245 the number of the subpattern called "xxx" is 2. If the name is known to be
2246 unique (PCRE_DUPNAMES was not set), you can find the number from the name by
2247 calling \fBpcre_get_stringnumber()\fP. The first argument is the compiled
2248 pattern, and the second is the name. The yield of the function is the
2249 subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no subpattern of
2250 that name.
2251 .P
2252 Given the number, you can extract the substring directly, or use one of the
2253 functions described in the previous section. For convenience, there are also
2254 two functions that do the whole job.
2255 .P
2256 Most of the arguments of \fBpcre_copy_named_substring()\fP and
2257 \fBpcre_get_named_substring()\fP are the same as those for the similarly named
2258 functions that extract by number. As these are described in the previous
2259 section, they are not re-described here. There are just two differences:
2260 .P
2261 First, instead of a substring number, a substring name is given. Second, there
2262 is an extra argument, given at the start, which is a pointer to the compiled
2263 pattern. This is needed in order to gain access to the name-to-number
2264 translation table.
2265 .P
2266 These functions call \fBpcre_get_stringnumber()\fP, and if it succeeds, they
2267 then call \fBpcre_copy_substring()\fP or \fBpcre_get_substring()\fP, as
2268 appropriate. \fBNOTE:\fP If PCRE_DUPNAMES is set and there are duplicate names,
2269 the behaviour may not be what you want (see the next section).
2270 .P
2271 \fBWarning:\fP If the pattern uses the (?| feature to set up multiple
2272 subpatterns with the same number, as described in the
2273 .\" HTML <a href="pcrepattern.html#dupsubpatternnumber">
2274 .\" </a>
2275 section on duplicate subpattern numbers
2276 .\"
2277 in the
2278 .\" HREF
2279 \fBpcrepattern\fP
2280 .\"
2281 page, you cannot use names to distinguish the different subpatterns, because
2282 names are not included in the compiled code. The matching process uses only
2283 numbers. For this reason, the use of different names for subpatterns of the
2284 same number causes an error at compile time.
2285 .
2286 .
2288 .rs
2289 .sp
2290 .B int pcre_get_stringtable_entries(const pcre *\fIcode\fP,
2291 .ti +5n
2292 .B const char *\fIname\fP, char **\fIfirst\fP, char **\fIlast\fP);
2293 .PP
2294 When a pattern is compiled with the PCRE_DUPNAMES option, names for subpatterns
2295 are not required to be unique. (Duplicate names are always allowed for
2296 subpatterns with the same number, created by using the (?| feature. Indeed, if
2297 such subpatterns are named, they are required to use the same names.)
2298 .P
2299 Normally, patterns with duplicate names are such that in any one match, only
2300 one of the named subpatterns participates. An example is shown in the
2301 .\" HREF
2302 \fBpcrepattern\fP
2303 .\"
2304 documentation.
2305 .P
2306 When duplicates are present, \fBpcre_copy_named_substring()\fP and
2307 \fBpcre_get_named_substring()\fP return the first substring corresponding to
2308 the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING (-7) is
2309 returned; no data is returned. The \fBpcre_get_stringnumber()\fP function
2310 returns one of the numbers that are associated with the name, but it is not
2311 defined which it is.
2312 .P
2313 If you want to get full details of all captured substrings for a given name,
2314 you must use the \fBpcre_get_stringtable_entries()\fP function. The first
2315 argument is the compiled pattern, and the second is the name. The third and
2316 fourth are pointers to variables which are updated by the function. After it
2317 has run, they point to the first and last entries in the name-to-number table
2318 for the given name. The function itself returns the length of each entry, or
2319 PCRE_ERROR_NOSUBSTRING (-7) if there are none. The format of the table is
2320 described above in the section entitled \fIInformation about a pattern\fP
2321 .\" HTML <a href="#infoaboutpattern">
2322 .\" </a>
2323 above.
2324 .\"
2325 Given all the relevant entries for the name, you can extract each of their
2326 numbers, and hence the captured data, if any.
2327 .
2328 .
2330 .rs
2331 .sp
2332 The traditional matching function uses a similar algorithm to Perl, which stops
2333 when it finds the first match, starting at a given point in the subject. If you
2334 want to find all possible matches, or the longest possible match, consider
2335 using the alternative matching function (see below) instead. If you cannot use
2336 the alternative function, but still need to find all possible matches, you
2337 can kludge it up by making use of the callout facility, which is described in
2338 the
2339 .\" HREF
2340 \fBpcrecallout\fP
2341 .\"
2342 documentation.
2343 .P
2344 What you have to do is to insert a callout right at the end of the pattern.
2345 When your callout function is called, extract and save the current matched
2346 substring. Then return 1, which forces \fBpcre_exec()\fP to backtrack and try
2347 other alternatives. Ultimately, when it runs out of matches, \fBpcre_exec()\fP
2348 will yield PCRE_ERROR_NOMATCH.
2349 .
2350 .
2351 .\" HTML <a name="dfamatch"></a>
2353 .rs
2354 .sp
2355 .B int pcre_dfa_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
2356 .ti +5n
2357 .B "const char *\fIsubject\fP," int \fIlength\fP, int \fIstartoffset\fP,
2358 .ti +5n
2359 .B int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP,
2360 .ti +5n
2361 .B int *\fIworkspace\fP, int \fIwscount\fP);
2362 .P
2363 The function \fBpcre_dfa_exec()\fP is called to match a subject string against
2364 a compiled pattern, using a matching algorithm that scans the subject string
2365 just once, and does not backtrack. This has different characteristics to the
2366 normal algorithm, and is not compatible with Perl. Some of the features of PCRE
2367 patterns are not supported. Nevertheless, there are times when this kind of
2368 matching can be useful. For a discussion of the two matching algorithms, and a
2369 list of features that \fBpcre_dfa_exec()\fP does not support, see the
2370 .\" HREF
2371 \fBpcrematching\fP
2372 .\"
2373 documentation.
2374 .P
2375 The arguments for the \fBpcre_dfa_exec()\fP function are the same as for
2376 \fBpcre_exec()\fP, plus two extras. The \fIovector\fP argument is used in a
2377 different way, and this is described below. The other common arguments are used
2378 in the same way as for \fBpcre_exec()\fP, so their description is not repeated
2379 here.
2380 .P
2381 The two additional arguments provide workspace for the function. The workspace
2382 vector should contain at least 20 elements. It is used for keeping track of
2383 multiple paths through the pattern tree. More workspace will be needed for
2384 patterns and subjects where there are a lot of potential matches.
2385 .P
2386 Here is an example of a simple call to \fBpcre_dfa_exec()\fP:
2387 .sp
2388 int rc;
2389 int ovector[10];
2390 int wspace[20];
2391 rc = pcre_dfa_exec(
2392 re, /* result of pcre_compile() */
2393 NULL, /* we didn't study the pattern */
2394 "some string", /* the subject string */
2395 11, /* the length of the subject string */
2396 0, /* start at offset 0 in the subject */
2397 0, /* default options */
2398 ovector, /* vector of integers for substring information */
2399 10, /* number of elements (NOT size in bytes) */
2400 wspace, /* working space vector */
2401 20); /* number of elements (NOT size in bytes) */
2402 .
2403 .SS "Option bits for \fBpcre_dfa_exec()\fP"
2404 .rs
2405 .sp
2406 The unused bits of the \fIoptions\fP argument for \fBpcre_dfa_exec()\fP must be
2407 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_\fIxxx\fP,
2411 All but the last four of these are exactly the same as for \fBpcre_exec()\fP,
2412 so their description is not repeated here.
2413 .sp
2416 .sp
2417 These have the same general effect as they do for \fBpcre_exec()\fP, but the
2418 details are slightly different. When PCRE_PARTIAL_HARD is set for
2419 \fBpcre_dfa_exec()\fP, it returns PCRE_ERROR_PARTIAL if the end of the subject
2420 is reached and there is still at least one matching possibility that requires
2421 additional characters. This happens even if some complete matches have also
2422 been found. When PCRE_PARTIAL_SOFT is set, the return code PCRE_ERROR_NOMATCH
2423 is converted into PCRE_ERROR_PARTIAL if the end of the subject is reached,
2424 there have been no complete matches, but there is still at least one matching
2425 possibility. The portion of the string that was inspected when the longest
2426 partial match was found is set as the first matching string in both cases.
2427 There is a more detailed discussion of partial and multi-segment matching, with
2428 examples, in the
2429 .\" HREF
2430 \fBpcrepartial\fP
2431 .\"
2432 documentation.
2433 .sp
2435 .sp
2436 Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to stop as
2437 soon as it has found one match. Because of the way the alternative algorithm
2438 works, this is necessarily the shortest possible match at the first possible
2439 matching point in the subject string.
2440 .sp
2442 .sp
2443 When \fBpcre_dfa_exec()\fP returns a partial match, it is possible to call it
2444 again, with additional subject characters, and have it continue with the same
2445 match. The PCRE_DFA_RESTART option requests this action; when it is set, the
2446 \fIworkspace\fP and \fIwscount\fP options must reference the same vector as
2447 before because data about the match so far is left in them after a partial
2448 match. There is more discussion of this facility in the
2449 .\" HREF
2450 \fBpcrepartial\fP
2451 .\"
2452 documentation.
2453 .
2454 .
2455 .SS "Successful returns from \fBpcre_dfa_exec()\fP"
2456 .rs
2457 .sp
2458 When \fBpcre_dfa_exec()\fP succeeds, it may have matched more than one
2459 substring in the subject. Note, however, that all the matches from one run of
2460 the function start at the same point in the subject. The shorter matches are
2461 all initial substrings of the longer matches. For example, if the pattern
2462 .sp
2463 <.*>
2464 .sp
2465 is matched against the string
2466 .sp
2467 This is <something> <something else> <something further> no more
2468 .sp
2469 the three matched strings are
2470 .sp
2471 <something>
2472 <something> <something else>
2473 <something> <something else> <something further>
2474 .sp
2475 On success, the yield of the function is a number greater than zero, which is
2476 the number of matched substrings. The substrings themselves are returned in
2477 \fIovector\fP. Each string uses two elements; the first is the offset to the
2478 start, and the second is the offset to the end. In fact, all the strings have
2479 the same start offset. (Space could have been saved by giving this only once,
2480 but it was decided to retain some compatibility with the way \fBpcre_exec()\fP
2481 returns data, even though the meaning of the strings is different.)
2482 .P
2483 The strings are returned in reverse order of length; that is, the longest
2484 matching string is given first. If there were too many matches to fit into
2485 \fIovector\fP, the yield of the function is zero, and the vector is filled with
2486 the longest matches. Unlike \fBpcre_exec()\fP, \fBpcre_dfa_exec()\fP can use
2487 the entire \fIovector\fP for returning matched strings.
2488 .
2489 .
2490 .SS "Error returns from \fBpcre_dfa_exec()\fP"
2491 .rs
2492 .sp
2493 The \fBpcre_dfa_exec()\fP function returns a negative number when it fails.
2494 Many of the errors are the same as for \fBpcre_exec()\fP, and these are
2495 described
2496 .\" HTML <a href="#errorlist">
2497 .\" </a>
2498 above.
2499 .\"
2500 There are in addition the following errors that are specific to
2501 \fBpcre_dfa_exec()\fP:
2502 .sp
2504 .sp
2505 This return is given if \fBpcre_dfa_exec()\fP encounters an item in the pattern
2506 that it does not support, for instance, the use of \eC or a back reference.
2507 .sp
2509 .sp
2510 This return is given if \fBpcre_dfa_exec()\fP encounters a condition item that
2511 uses a back reference for the condition, or a test for recursion in a specific
2512 group. These are not supported.
2513 .sp
2515 .sp
2516 This return is given if \fBpcre_dfa_exec()\fP is called with an \fIextra\fP
2517 block that contains a setting of the \fImatch_limit\fP or
2518 \fImatch_limit_recursion\fP fields. This is not supported (these fields are
2519 meaningless for DFA matching).
2520 .sp
2522 .sp
2523 This return is given if \fBpcre_dfa_exec()\fP runs out of space in the
2524 \fIworkspace\fP vector.
2525 .sp
2527 .sp
2528 When a recursive subpattern is processed, the matching function calls itself
2529 recursively, using private vectors for \fIovector\fP and \fIworkspace\fP. This
2530 error is given if the output vector is not large enough. This should be
2531 extremely rare, as a vector of size 1000 is used.
2532 .
2533 .
2534 .SH "SEE ALSO"
2535 .rs
2536 .sp
2537 \fBpcrebuild\fP(3), \fBpcrecallout\fP(3), \fBpcrecpp(3)\fP(3),
2538 \fBpcrematching\fP(3), \fBpcrepartial\fP(3), \fBpcreposix\fP(3),
2539 \fBpcreprecompile\fP(3), \fBpcresample\fP(3), \fBpcrestack\fP(3).
2540 .
2541 .
2543 .rs
2544 .sp
2545 .nf
2546 Philip Hazel
2547 University Computing Service
2548 Cambridge CB2 3QH, England.
2549 .fi
2550 .
2551 .
2553 .rs
2554 .sp
2555 .nf
2556 Last updated: 02 December 2011
2557 Copyright (c) 1997-2011 University of Cambridge.
2558 .fi


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