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Add pcredemo man page, containing a listing of pcredemo.c.
3 PCRE - Perl-compatible regular expressions
5 .rs
6 .sp
7 .B #include <pcre.h>
8 .PP
9 .SM
10 .B pcre *pcre_compile(const char *\fIpattern\fP, int \fIoptions\fP,
11 .ti +5n
12 .B const char **\fIerrptr\fP, int *\fIerroffset\fP,
13 .ti +5n
14 .B const unsigned char *\fItableptr\fP);
15 .PP
16 .B pcre *pcre_compile2(const char *\fIpattern\fP, int \fIoptions\fP,
17 .ti +5n
18 .B int *\fIerrorcodeptr\fP,
19 .ti +5n
20 .B const char **\fIerrptr\fP, int *\fIerroffset\fP,
21 .ti +5n
22 .B const unsigned char *\fItableptr\fP);
23 .PP
24 .B pcre_extra *pcre_study(const pcre *\fIcode\fP, int \fIoptions\fP,
25 .ti +5n
26 .B const char **\fIerrptr\fP);
27 .PP
28 .B int pcre_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
29 .ti +5n
30 .B "const char *\fIsubject\fP," int \fIlength\fP, int \fIstartoffset\fP,
31 .ti +5n
32 .B int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP);
33 .PP
34 .B int pcre_dfa_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
35 .ti +5n
36 .B "const char *\fIsubject\fP," int \fIlength\fP, int \fIstartoffset\fP,
37 .ti +5n
38 .B int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP,
39 .ti +5n
40 .B int *\fIworkspace\fP, int \fIwscount\fP);
41 .PP
42 .B int pcre_copy_named_substring(const pcre *\fIcode\fP,
43 .ti +5n
44 .B const char *\fIsubject\fP, int *\fIovector\fP,
45 .ti +5n
46 .B int \fIstringcount\fP, const char *\fIstringname\fP,
47 .ti +5n
48 .B char *\fIbuffer\fP, int \fIbuffersize\fP);
49 .PP
50 .B int pcre_copy_substring(const char *\fIsubject\fP, int *\fIovector\fP,
51 .ti +5n
52 .B int \fIstringcount\fP, int \fIstringnumber\fP, char *\fIbuffer\fP,
53 .ti +5n
54 .B int \fIbuffersize\fP);
55 .PP
56 .B int pcre_get_named_substring(const pcre *\fIcode\fP,
57 .ti +5n
58 .B const char *\fIsubject\fP, int *\fIovector\fP,
59 .ti +5n
60 .B int \fIstringcount\fP, const char *\fIstringname\fP,
61 .ti +5n
62 .B const char **\fIstringptr\fP);
63 .PP
64 .B int pcre_get_stringnumber(const pcre *\fIcode\fP,
65 .ti +5n
66 .B const char *\fIname\fP);
67 .PP
68 .B int pcre_get_stringtable_entries(const pcre *\fIcode\fP,
69 .ti +5n
70 .B const char *\fIname\fP, char **\fIfirst\fP, char **\fIlast\fP);
71 .PP
72 .B int pcre_get_substring(const char *\fIsubject\fP, int *\fIovector\fP,
73 .ti +5n
74 .B int \fIstringcount\fP, int \fIstringnumber\fP,
75 .ti +5n
76 .B const char **\fIstringptr\fP);
77 .PP
78 .B int pcre_get_substring_list(const char *\fIsubject\fP,
79 .ti +5n
80 .B int *\fIovector\fP, int \fIstringcount\fP, "const char ***\fIlistptr\fP);"
81 .PP
82 .B void pcre_free_substring(const char *\fIstringptr\fP);
83 .PP
84 .B void pcre_free_substring_list(const char **\fIstringptr\fP);
85 .PP
86 .B const unsigned char *pcre_maketables(void);
87 .PP
88 .B int pcre_fullinfo(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
89 .ti +5n
90 .B int \fIwhat\fP, void *\fIwhere\fP);
91 .PP
92 .B int pcre_info(const pcre *\fIcode\fP, int *\fIoptptr\fP, int
93 .B *\fIfirstcharptr\fP);
94 .PP
95 .B int pcre_refcount(pcre *\fIcode\fP, int \fIadjust\fP);
96 .PP
97 .B int pcre_config(int \fIwhat\fP, void *\fIwhere\fP);
98 .PP
99 .B char *pcre_version(void);
100 .PP
101 .B void *(*pcre_malloc)(size_t);
102 .PP
103 .B void (*pcre_free)(void *);
104 .PP
105 .B void *(*pcre_stack_malloc)(size_t);
106 .PP
107 .B void (*pcre_stack_free)(void *);
108 .PP
109 .B int (*pcre_callout)(pcre_callout_block *);
110 .
111 .
113 .rs
114 .sp
115 PCRE has its own native API, which is described in this document. There are
116 also some wrapper functions that correspond to the POSIX regular expression
117 API. These are described in the
118 .\" HREF
119 \fBpcreposix\fP
120 .\"
121 documentation. Both of these APIs define a set of C function calls. A C++
122 wrapper is distributed with PCRE. It is documented in the
123 .\" HREF
124 \fBpcrecpp\fP
125 .\"
126 page.
127 .P
128 The native API C function prototypes are defined in the header file
129 \fBpcre.h\fP, and on Unix systems the library itself is called \fBlibpcre\fP.
130 It can normally be accessed by adding \fB-lpcre\fP to the command for linking
131 an application that uses PCRE. The header file defines the macros PCRE_MAJOR
132 and PCRE_MINOR to contain the major and minor release numbers for the library.
133 Applications can use these to include support for different releases of PCRE.
134 .P
135 The functions \fBpcre_compile()\fP, \fBpcre_compile2()\fP, \fBpcre_study()\fP,
136 and \fBpcre_exec()\fP are used for compiling and matching regular expressions
137 in a Perl-compatible manner. A sample program that demonstrates the simplest
138 way of using them is provided in the file called \fIpcredemo.c\fP in the PCRE
139 source distribution. A listing of this program is given in the
140 .\" HREF
141 \fBpcredemo\fP
142 .\"
143 documentation, and the
144 .\" HREF
145 \fBpcresample\fP
146 .\"
147 documentation describes how to compile and run it.
148 .P
149 A second matching function, \fBpcre_dfa_exec()\fP, which is not
150 Perl-compatible, is also provided. This uses a different algorithm for the
151 matching. The alternative algorithm finds all possible matches (at a given
152 point in the subject), and scans the subject just once. However, this algorithm
153 does not return captured substrings. A description of the two matching
154 algorithms and their advantages and disadvantages is given in the
155 .\" HREF
156 \fBpcrematching\fP
157 .\"
158 documentation.
159 .P
160 In addition to the main compiling and matching functions, there are convenience
161 functions for extracting captured substrings from a subject string that is
162 matched by \fBpcre_exec()\fP. They are:
163 .sp
164 \fBpcre_copy_substring()\fP
165 \fBpcre_copy_named_substring()\fP
166 \fBpcre_get_substring()\fP
167 \fBpcre_get_named_substring()\fP
168 \fBpcre_get_substring_list()\fP
169 \fBpcre_get_stringnumber()\fP
170 \fBpcre_get_stringtable_entries()\fP
171 .sp
172 \fBpcre_free_substring()\fP and \fBpcre_free_substring_list()\fP are also
173 provided, to free the memory used for extracted strings.
174 .P
175 The function \fBpcre_maketables()\fP is used to build a set of character tables
176 in the current locale for passing to \fBpcre_compile()\fP, \fBpcre_exec()\fP,
177 or \fBpcre_dfa_exec()\fP. This is an optional facility that is provided for
178 specialist use. Most commonly, no special tables are passed, in which case
179 internal tables that are generated when PCRE is built are used.
180 .P
181 The function \fBpcre_fullinfo()\fP is used to find out information about a
182 compiled pattern; \fBpcre_info()\fP is an obsolete version that returns only
183 some of the available information, but is retained for backwards compatibility.
184 The function \fBpcre_version()\fP returns a pointer to a string containing the
185 version of PCRE and its date of release.
186 .P
187 The function \fBpcre_refcount()\fP maintains a reference count in a data block
188 containing a compiled pattern. This is provided for the benefit of
189 object-oriented applications.
190 .P
191 The global variables \fBpcre_malloc\fP and \fBpcre_free\fP initially contain
192 the entry points of the standard \fBmalloc()\fP and \fBfree()\fP functions,
193 respectively. PCRE calls the memory management functions via these variables,
194 so a calling program can replace them if it wishes to intercept the calls. This
195 should be done before calling any PCRE functions.
196 .P
197 The global variables \fBpcre_stack_malloc\fP and \fBpcre_stack_free\fP are also
198 indirections to memory management functions. These special functions are used
199 only when PCRE is compiled to use the heap for remembering data, instead of
200 recursive function calls, when running the \fBpcre_exec()\fP function. See the
201 .\" HREF
202 \fBpcrebuild\fP
203 .\"
204 documentation for details of how to do this. It is a non-standard way of
205 building PCRE, for use in environments that have limited stacks. Because of the
206 greater use of memory management, it runs more slowly. Separate functions are
207 provided so that special-purpose external code can be used for this case. When
208 used, these functions are always called in a stack-like manner (last obtained,
209 first freed), and always for memory blocks of the same size. There is a
210 discussion about PCRE's stack usage in the
211 .\" HREF
212 \fBpcrestack\fP
213 .\"
214 documentation.
215 .P
216 The global variable \fBpcre_callout\fP initially contains NULL. It can be set
217 by the caller to a "callout" function, which PCRE will then call at specified
218 points during a matching operation. Details are given in the
219 .\" HREF
220 \fBpcrecallout\fP
221 .\"
222 documentation.
223 .
224 .
225 .\" HTML <a name="newlines"></a>
227 .rs
228 .sp
229 PCRE supports five different conventions for indicating line breaks in
230 strings: a single CR (carriage return) character, a single LF (linefeed)
231 character, the two-character sequence CRLF, any of the three preceding, or any
232 Unicode newline sequence. The Unicode newline sequences are the three just
233 mentioned, plus the single characters VT (vertical tab, U+000B), FF (formfeed,
234 U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS
235 (paragraph separator, U+2029).
236 .P
237 Each of the first three conventions is used by at least one operating system as
238 its standard newline sequence. When PCRE is built, a default can be specified.
239 The default default is LF, which is the Unix standard. When PCRE is run, the
240 default can be overridden, either when a pattern is compiled, or when it is
241 matched.
242 .P
243 At compile time, the newline convention can be specified by the \fIoptions\fP
244 argument of \fBpcre_compile()\fP, or it can be specified by special text at the
245 start of the pattern itself; this overrides any other settings. See the
246 .\" HREF
247 \fBpcrepattern\fP
248 .\"
249 page for details of the special character sequences.
250 .P
251 In the PCRE documentation the word "newline" is used to mean "the character or
252 pair of characters that indicate a line break". The choice of newline
253 convention affects the handling of the dot, circumflex, and dollar
254 metacharacters, the handling of #-comments in /x mode, and, when CRLF is a
255 recognized line ending sequence, the match position advancement for a
256 non-anchored pattern. There is more detail about this in the
257 .\" HTML <a href="#execoptions">
258 .\" </a>
259 section on \fBpcre_exec()\fP options
260 .\"
261 below.
262 .P
263 The choice of newline convention does not affect the interpretation of
264 the \en or \er escape sequences, nor does it affect what \eR matches, which is
265 controlled in a similar way, but by separate options.
266 .
267 .
269 .rs
270 .sp
271 The PCRE functions can be used in multi-threading applications, with the
272 proviso that the memory management functions pointed to by \fBpcre_malloc\fP,
273 \fBpcre_free\fP, \fBpcre_stack_malloc\fP, and \fBpcre_stack_free\fP, and the
274 callout function pointed to by \fBpcre_callout\fP, are shared by all threads.
275 .P
276 The compiled form of a regular expression is not altered during matching, so
277 the same compiled pattern can safely be used by several threads at once.
278 .
279 .
281 .rs
282 .sp
283 The compiled form of a regular expression can be saved and re-used at a later
284 time, possibly by a different program, and even on a host other than the one on
285 which it was compiled. Details are given in the
286 .\" HREF
287 \fBpcreprecompile\fP
288 .\"
289 documentation. However, compiling a regular expression with one version of PCRE
290 for use with a different version is not guaranteed to work and may cause
291 crashes.
292 .
293 .
295 .rs
296 .sp
297 .B int pcre_config(int \fIwhat\fP, void *\fIwhere\fP);
298 .PP
299 The function \fBpcre_config()\fP makes it possible for a PCRE client to
300 discover which optional features have been compiled into the PCRE library. The
301 .\" HREF
302 \fBpcrebuild\fP
303 .\"
304 documentation has more details about these optional features.
305 .P
306 The first argument for \fBpcre_config()\fP is an integer, specifying which
307 information is required; the second argument is a pointer to a variable into
308 which the information is placed. The following information is available:
309 .sp
311 .sp
312 The output is an integer that is set to one if UTF-8 support is available;
313 otherwise it is set to zero.
314 .sp
316 .sp
317 The output is an integer that is set to one if support for Unicode character
318 properties is available; otherwise it is set to zero.
319 .sp
321 .sp
322 The output is an integer whose value specifies the default character sequence
323 that is recognized as meaning "newline". The four values that are supported
324 are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF, and -1 for ANY.
325 Though they are derived from ASCII, the same values are returned in EBCDIC
326 environments. The default should normally correspond to the standard sequence
327 for your operating system.
328 .sp
330 .sp
331 The output is an integer whose value indicates what character sequences the \eR
332 escape sequence matches by default. A value of 0 means that \eR matches any
333 Unicode line ending sequence; a value of 1 means that \eR matches only CR, LF,
334 or CRLF. The default can be overridden when a pattern is compiled or matched.
335 .sp
337 .sp
338 The output is an integer that contains the number of bytes used for internal
339 linkage in compiled regular expressions. The value is 2, 3, or 4. Larger values
340 allow larger regular expressions to be compiled, at the expense of slower
341 matching. The default value of 2 is sufficient for all but the most massive
342 patterns, since it allows the compiled pattern to be up to 64K in size.
343 .sp
345 .sp
346 The output is an integer that contains the threshold above which the POSIX
347 interface uses \fBmalloc()\fP for output vectors. Further details are given in
348 the
349 .\" HREF
350 \fBpcreposix\fP
351 .\"
352 documentation.
353 .sp
355 .sp
356 The output is a long integer that gives the default limit for the number of
357 internal matching function calls in a \fBpcre_exec()\fP execution. Further
358 details are given with \fBpcre_exec()\fP below.
359 .sp
361 .sp
362 The output is a long integer that gives the default limit for the depth of
363 recursion when calling the internal matching function in a \fBpcre_exec()\fP
364 execution. Further details are given with \fBpcre_exec()\fP below.
365 .sp
367 .sp
368 The output is an integer that is set to one if internal recursion when running
369 \fBpcre_exec()\fP is implemented by recursive function calls that use the stack
370 to remember their state. This is the usual way that PCRE is compiled. The
371 output is zero if PCRE was compiled to use blocks of data on the heap instead
372 of recursive function calls. In this case, \fBpcre_stack_malloc\fP and
373 \fBpcre_stack_free\fP are called to manage memory blocks on the heap, thus
374 avoiding the use of the stack.
375 .
376 .
378 .rs
379 .sp
380 .B pcre *pcre_compile(const char *\fIpattern\fP, int \fIoptions\fP,
381 .ti +5n
382 .B const char **\fIerrptr\fP, int *\fIerroffset\fP,
383 .ti +5n
384 .B const unsigned char *\fItableptr\fP);
385 .sp
386 .B pcre *pcre_compile2(const char *\fIpattern\fP, int \fIoptions\fP,
387 .ti +5n
388 .B int *\fIerrorcodeptr\fP,
389 .ti +5n
390 .B const char **\fIerrptr\fP, int *\fIerroffset\fP,
391 .ti +5n
392 .B const unsigned char *\fItableptr\fP);
393 .P
394 Either of the functions \fBpcre_compile()\fP or \fBpcre_compile2()\fP can be
395 called to compile a pattern into an internal form. The only difference between
396 the two interfaces is that \fBpcre_compile2()\fP has an additional argument,
397 \fIerrorcodeptr\fP, via which a numerical error code can be returned.
398 .P
399 The pattern is a C string terminated by a binary zero, and is passed in the
400 \fIpattern\fP argument. A pointer to a single block of memory that is obtained
401 via \fBpcre_malloc\fP is returned. This contains the compiled code and related
402 data. The \fBpcre\fP type is defined for the returned block; this is a typedef
403 for a structure whose contents are not externally defined. It is up to the
404 caller to free the memory (via \fBpcre_free\fP) when it is no longer required.
405 .P
406 Although the compiled code of a PCRE regex is relocatable, that is, it does not
407 depend on memory location, the complete \fBpcre\fP data block is not
408 fully relocatable, because it may contain a copy of the \fItableptr\fP
409 argument, which is an address (see below).
410 .P
411 The \fIoptions\fP argument contains various bit settings that affect the
412 compilation. It should be zero if no options are required. The available
413 options are described below. Some of them (in particular, those that are
414 compatible with Perl, but also some others) can also be set and unset from
415 within the pattern (see the detailed description in the
416 .\" HREF
417 \fBpcrepattern\fP
418 .\"
419 documentation). For those options that can be different in different parts of
420 the pattern, the contents of the \fIoptions\fP argument specifies their initial
421 settings at the start of compilation and execution. The PCRE_ANCHORED and
422 PCRE_NEWLINE_\fIxxx\fP options can be set at the time of matching as well as at
423 compile time.
424 .P
425 If \fIerrptr\fP is NULL, \fBpcre_compile()\fP returns NULL immediately.
426 Otherwise, if compilation of a pattern fails, \fBpcre_compile()\fP returns
427 NULL, and sets the variable pointed to by \fIerrptr\fP to point to a textual
428 error message. This is a static string that is part of the library. You must
429 not try to free it. The offset from the start of the pattern to the character
430 where the error was discovered is placed in the variable pointed to by
431 \fIerroffset\fP, which must not be NULL. If it is, an immediate error is given.
432 .P
433 If \fBpcre_compile2()\fP is used instead of \fBpcre_compile()\fP, and the
434 \fIerrorcodeptr\fP argument is not NULL, a non-zero error code number is
435 returned via this argument in the event of an error. This is in addition to the
436 textual error message. Error codes and messages are listed below.
437 .P
438 If the final argument, \fItableptr\fP, is NULL, PCRE uses a default set of
439 character tables that are built when PCRE is compiled, using the default C
440 locale. Otherwise, \fItableptr\fP must be an address that is the result of a
441 call to \fBpcre_maketables()\fP. This value is stored with the compiled
442 pattern, and used again by \fBpcre_exec()\fP, unless another table pointer is
443 passed to it. For more discussion, see the section on locale support below.
444 .P
445 This code fragment shows a typical straightforward call to \fBpcre_compile()\fP:
446 .sp
447 pcre *re;
448 const char *error;
449 int erroffset;
450 re = pcre_compile(
451 "^A.*Z", /* the pattern */
452 0, /* default options */
453 &error, /* for error message */
454 &erroffset, /* for error offset */
455 NULL); /* use default character tables */
456 .sp
457 The following names for option bits are defined in the \fBpcre.h\fP header
458 file:
459 .sp
461 .sp
462 If this bit is set, the pattern is forced to be "anchored", that is, it is
463 constrained to match only at the first matching point in the string that is
464 being searched (the "subject string"). This effect can also be achieved by
465 appropriate constructs in the pattern itself, which is the only way to do it in
466 Perl.
467 .sp
469 .sp
470 If this bit is set, \fBpcre_compile()\fP automatically inserts callout items,
471 all with number 255, before each pattern item. For discussion of the callout
472 facility, see the
473 .\" HREF
474 \fBpcrecallout\fP
475 .\"
476 documentation.
477 .sp
480 .sp
481 These options (which are mutually exclusive) control what the \eR escape
482 sequence matches. The choice is either to match only CR, LF, or CRLF, or to
483 match any Unicode newline sequence. The default is specified when PCRE is
484 built. It can be overridden from within the pattern, or by setting an option
485 when a compiled pattern is matched.
486 .sp
488 .sp
489 If this bit is set, letters in the pattern match both upper and lower case
490 letters. It is equivalent to Perl's /i option, and it can be changed within a
491 pattern by a (?i) option setting. In UTF-8 mode, PCRE always understands the
492 concept of case for characters whose values are less than 128, so caseless
493 matching is always possible. For characters with higher values, the concept of
494 case is supported if PCRE is compiled with Unicode property support, but not
495 otherwise. If you want to use caseless matching for characters 128 and above,
496 you must ensure that PCRE is compiled with Unicode property support as well as
497 with UTF-8 support.
498 .sp
500 .sp
501 If this bit is set, a dollar metacharacter in the pattern matches only at the
502 end of the subject string. Without this option, a dollar also matches
503 immediately before a newline at the end of the string (but not before any other
504 newlines). The PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is set.
505 There is no equivalent to this option in Perl, and no way to set it within a
506 pattern.
507 .sp
509 .sp
510 If this bit is set, a dot metacharater in the pattern matches all characters,
511 including those that indicate newline. Without it, a dot does not match when
512 the current position is at a newline. This option is equivalent to Perl's /s
513 option, and it can be changed within a pattern by a (?s) option setting. A
514 negative class such as [^a] always matches newline characters, independent of
515 the setting of this option.
516 .sp
518 .sp
519 If this bit is set, names used to identify capturing subpatterns need not be
520 unique. This can be helpful for certain types of pattern when it is known that
521 only one instance of the named subpattern can ever be matched. There are more
522 details of named subpatterns below; see also the
523 .\" HREF
524 \fBpcrepattern\fP
525 .\"
526 documentation.
527 .sp
529 .sp
530 If this bit is set, whitespace data characters in the pattern are totally
531 ignored except when escaped or inside a character class. Whitespace does not
532 include the VT character (code 11). In addition, characters between an
533 unescaped # outside a character class and the next newline, inclusive, are also
534 ignored. This is equivalent to Perl's /x option, and it can be changed within a
535 pattern by a (?x) option setting.
536 .P
537 This option makes it possible to include comments inside complicated patterns.
538 Note, however, that this applies only to data characters. Whitespace characters
539 may never appear within special character sequences in a pattern, for example
540 within the sequence (?( which introduces a conditional subpattern.
541 .sp
543 .sp
544 This option was invented in order to turn on additional functionality of PCRE
545 that is incompatible with Perl, but it is currently of very little use. When
546 set, any backslash in a pattern that is followed by a letter that has no
547 special meaning causes an error, thus reserving these combinations for future
548 expansion. By default, as in Perl, a backslash followed by a letter with no
549 special meaning is treated as a literal. (Perl can, however, be persuaded to
550 give a warning for this.) There are at present no other features controlled by
551 this option. It can also be set by a (?X) option setting within a pattern.
552 .sp
554 .sp
555 If this option is set, an unanchored pattern is required to match before or at
556 the first newline in the subject string, though the matched text may continue
557 over the newline.
558 .sp
560 .sp
561 If this option is set, PCRE's behaviour is changed in some ways so that it is
562 compatible with JavaScript rather than Perl. The changes are as follows:
563 .P
564 (1) A lone closing square bracket in a pattern causes a compile-time error,
565 because this is illegal in JavaScript (by default it is treated as a data
566 character). Thus, the pattern AB]CD becomes illegal when this option is set.
567 .P
568 (2) At run time, a back reference to an unset subpattern group matches an empty
569 string (by default this causes the current matching alternative to fail). A
570 pattern such as (\e1)(a) succeeds when this option is set (assuming it can find
571 an "a" in the subject), whereas it fails by default, for Perl compatibility.
572 .sp
574 .sp
575 By default, PCRE treats the subject string as consisting of a single line of
576 characters (even if it actually contains newlines). The "start of line"
577 metacharacter (^) matches only at the start of the string, while the "end of
578 line" metacharacter ($) matches only at the end of the string, or before a
579 terminating newline (unless PCRE_DOLLAR_ENDONLY is set). This is the same as
580 Perl.
581 .P
582 When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs
583 match immediately following or immediately before internal newlines in the
584 subject string, respectively, as well as at the very start and end. This is
585 equivalent to Perl's /m option, and it can be changed within a pattern by a
586 (?m) option setting. If there are no newlines in a subject string, or no
587 occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no effect.
588 .sp
594 .sp
595 These options override the default newline definition that was chosen when PCRE
596 was built. Setting the first or the second specifies that a newline is
597 indicated by a single character (CR or LF, respectively). Setting
598 PCRE_NEWLINE_CRLF specifies that a newline is indicated by the two-character
599 CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies that any of the three
600 preceding sequences should be recognized. Setting PCRE_NEWLINE_ANY specifies
601 that any Unicode newline sequence should be recognized. The Unicode newline
602 sequences are the three just mentioned, plus the single characters VT (vertical
603 tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS (line
604 separator, U+2028), and PS (paragraph separator, U+2029). The last two are
605 recognized only in UTF-8 mode.
606 .P
607 The newline setting in the options word uses three bits that are treated
608 as a number, giving eight possibilities. Currently only six are used (default
609 plus the five values above). This means that if you set more than one newline
610 option, the combination may or may not be sensible. For example,
612 other combinations may yield unused numbers and cause an error.
613 .P
614 The only time that a line break is specially recognized when compiling a
615 pattern is if PCRE_EXTENDED is set, and an unescaped # outside a character
616 class is encountered. This indicates a comment that lasts until after the next
617 line break sequence. In other circumstances, line break sequences are treated
618 as literal data, except that in PCRE_EXTENDED mode, both CR and LF are treated
619 as whitespace characters and are therefore ignored.
620 .P
621 The newline option that is set at compile time becomes the default that is used
622 for \fBpcre_exec()\fP and \fBpcre_dfa_exec()\fP, but it can be overridden.
623 .sp
625 .sp
626 If this option is set, it disables the use of numbered capturing parentheses in
627 the pattern. Any opening parenthesis that is not followed by ? behaves as if it
628 were followed by ?: but named parentheses can still be used for capturing (and
629 they acquire numbers in the usual way). There is no equivalent of this option
630 in Perl.
631 .sp
633 .sp
634 This option inverts the "greediness" of the quantifiers so that they are not
635 greedy by default, but become greedy if followed by "?". It is not compatible
636 with Perl. It can also be set by a (?U) option setting within the pattern.
637 .sp
639 .sp
640 This option causes PCRE to regard both the pattern and the subject as strings
641 of UTF-8 characters instead of single-byte character strings. However, it is
642 available only when PCRE is built to include UTF-8 support. If not, the use
643 of this option provokes an error. Details of how this option changes the
644 behaviour of PCRE are given in the
645 .\" HTML <a href="pcre.html#utf8support">
646 .\" </a>
647 section on UTF-8 support
648 .\"
649 in the main
650 .\" HREF
651 \fBpcre\fP
652 .\"
653 page.
654 .sp
656 .sp
657 When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
658 automatically checked. There is a discussion about the
659 .\" HTML <a href="pcre.html#utf8strings">
660 .\" </a>
661 validity of UTF-8 strings
662 .\"
663 in the main
664 .\" HREF
665 \fBpcre\fP
666 .\"
667 page. If an invalid UTF-8 sequence of bytes is found, \fBpcre_compile()\fP
668 returns an error. If you already know that your pattern is valid, and you want
669 to skip this check for performance reasons, you can set the PCRE_NO_UTF8_CHECK
670 option. When it is set, the effect of passing an invalid UTF-8 string as a
671 pattern is undefined. It may cause your program to crash. Note that this option
672 can also be passed to \fBpcre_exec()\fP and \fBpcre_dfa_exec()\fP, to suppress
673 the UTF-8 validity checking of subject strings.
674 .
675 .
677 .rs
678 .sp
679 The following table lists the error codes than may be returned by
680 \fBpcre_compile2()\fP, along with the error messages that may be returned by
681 both compiling functions. As PCRE has developed, some error codes have fallen
682 out of use. To avoid confusion, they have not been re-used.
683 .sp
684 0 no error
685 1 \e at end of pattern
686 2 \ec at end of pattern
687 3 unrecognized character follows \e
688 4 numbers out of order in {} quantifier
689 5 number too big in {} quantifier
690 6 missing terminating ] for character class
691 7 invalid escape sequence in character class
692 8 range out of order in character class
693 9 nothing to repeat
694 10 [this code is not in use]
695 11 internal error: unexpected repeat
696 12 unrecognized character after (? or (?-
697 13 POSIX named classes are supported only within a class
698 14 missing )
699 15 reference to non-existent subpattern
700 16 erroffset passed as NULL
701 17 unknown option bit(s) set
702 18 missing ) after comment
703 19 [this code is not in use]
704 20 regular expression is too large
705 21 failed to get memory
706 22 unmatched parentheses
707 23 internal error: code overflow
708 24 unrecognized character after (?<
709 25 lookbehind assertion is not fixed length
710 26 malformed number or name after (?(
711 27 conditional group contains more than two branches
712 28 assertion expected after (?(
713 29 (?R or (?[+-]digits must be followed by )
714 30 unknown POSIX class name
715 31 POSIX collating elements are not supported
716 32 this version of PCRE is not compiled with PCRE_UTF8 support
717 33 [this code is not in use]
718 34 character value in \ex{...} sequence is too large
719 35 invalid condition (?(0)
720 36 \eC not allowed in lookbehind assertion
721 37 PCRE does not support \eL, \el, \eN, \eU, or \eu
722 38 number after (?C is > 255
723 39 closing ) for (?C expected
724 40 recursive call could loop indefinitely
725 41 unrecognized character after (?P
726 42 syntax error in subpattern name (missing terminator)
727 43 two named subpatterns have the same name
728 44 invalid UTF-8 string
729 45 support for \eP, \ep, and \eX has not been compiled
730 46 malformed \eP or \ep sequence
731 47 unknown property name after \eP or \ep
732 48 subpattern name is too long (maximum 32 characters)
733 49 too many named subpatterns (maximum 10000)
734 50 [this code is not in use]
735 51 octal value is greater than \e377 (not in UTF-8 mode)
736 52 internal error: overran compiling workspace
737 53 internal error: previously-checked referenced subpattern not found
738 54 DEFINE group contains more than one branch
739 55 repeating a DEFINE group is not allowed
740 56 inconsistent NEWLINE options
741 57 \eg is not followed by a braced, angle-bracketed, or quoted
742 name/number or by a plain number
743 58 a numbered reference must not be zero
744 59 (*VERB) with an argument is not supported
745 60 (*VERB) not recognized
746 61 number is too big
747 62 subpattern name expected
748 63 digit expected after (?+
749 64 ] is an invalid data character in JavaScript compatibility mode
750 .sp
751 The numbers 32 and 10000 in errors 48 and 49 are defaults; different values may
752 be used if the limits were changed when PCRE was built.
753 .
754 .
756 .rs
757 .sp
758 .B pcre_extra *pcre_study(const pcre *\fIcode\fP, int \fIoptions\fP
759 .ti +5n
760 .B const char **\fIerrptr\fP);
761 .PP
762 If a compiled pattern is going to be used several times, it is worth spending
763 more time analyzing it in order to speed up the time taken for matching. The
764 function \fBpcre_study()\fP takes a pointer to a compiled pattern as its first
765 argument. If studying the pattern produces additional information that will
766 help speed up matching, \fBpcre_study()\fP returns a pointer to a
767 \fBpcre_extra\fP block, in which the \fIstudy_data\fP field points to the
768 results of the study.
769 .P
770 The returned value from \fBpcre_study()\fP can be passed directly to
771 \fBpcre_exec()\fP. However, a \fBpcre_extra\fP block also contains other
772 fields that can be set by the caller before the block is passed; these are
773 described
774 .\" HTML <a href="#extradata">
775 .\" </a>
776 below
777 .\"
778 in the section on matching a pattern.
779 .P
780 If studying the pattern does not produce any additional information
781 \fBpcre_study()\fP returns NULL. In that circumstance, if the calling program
782 wants to pass any of the other fields to \fBpcre_exec()\fP, it must set up its
783 own \fBpcre_extra\fP block.
784 .P
785 The second argument of \fBpcre_study()\fP contains option bits. At present, no
786 options are defined, and this argument should always be zero.
787 .P
788 The third argument for \fBpcre_study()\fP is a pointer for an error message. If
789 studying succeeds (even if no data is returned), the variable it points to is
790 set to NULL. Otherwise it is set to point to a textual error message. This is a
791 static string that is part of the library. You must not try to free it. You
792 should test the error pointer for NULL after calling \fBpcre_study()\fP, to be
793 sure that it has run successfully.
794 .P
795 This is a typical call to \fBpcre_study\fP():
796 .sp
797 pcre_extra *pe;
798 pe = pcre_study(
799 re, /* result of pcre_compile() */
800 0, /* no options exist */
801 &error); /* set to NULL or points to a message */
802 .sp
803 At present, studying a pattern is useful only for non-anchored patterns that do
804 not have a single fixed starting character. A bitmap of possible starting
805 bytes is created.
806 .
807 .
808 .\" HTML <a name="localesupport"></a>
810 .rs
811 .sp
812 PCRE handles caseless matching, and determines whether characters are letters,
813 digits, or whatever, by reference to a set of tables, indexed by character
814 value. When running in UTF-8 mode, this applies only to characters with codes
815 less than 128. Higher-valued codes never match escapes such as \ew or \ed, but
816 can be tested with \ep if PCRE is built with Unicode character property
817 support. The use of locales with Unicode is discouraged. If you are handling
818 characters with codes greater than 128, you should either use UTF-8 and
819 Unicode, or use locales, but not try to mix the two.
820 .P
821 PCRE contains an internal set of tables that are used when the final argument
822 of \fBpcre_compile()\fP is NULL. These are sufficient for many applications.
823 Normally, the internal tables recognize only ASCII characters. However, when
824 PCRE is built, it is possible to cause the internal tables to be rebuilt in the
825 default "C" locale of the local system, which may cause them to be different.
826 .P
827 The internal tables can always be overridden by tables supplied by the
828 application that calls PCRE. These may be created in a different locale from
829 the default. As more and more applications change to using Unicode, the need
830 for this locale support is expected to die away.
831 .P
832 External tables are built by calling the \fBpcre_maketables()\fP function,
833 which has no arguments, in the relevant locale. The result can then be passed
834 to \fBpcre_compile()\fP or \fBpcre_exec()\fP as often as necessary. For
835 example, to build and use tables that are appropriate for the French locale
836 (where accented characters with values greater than 128 are treated as letters),
837 the following code could be used:
838 .sp
839 setlocale(LC_CTYPE, "fr_FR");
840 tables = pcre_maketables();
841 re = pcre_compile(..., tables);
842 .sp
843 The locale name "fr_FR" is used on Linux and other Unix-like systems; if you
844 are using Windows, the name for the French locale is "french".
845 .P
846 When \fBpcre_maketables()\fP runs, the tables are built in memory that is
847 obtained via \fBpcre_malloc\fP. It is the caller's responsibility to ensure
848 that the memory containing the tables remains available for as long as it is
849 needed.
850 .P
851 The pointer that is passed to \fBpcre_compile()\fP is saved with the compiled
852 pattern, and the same tables are used via this pointer by \fBpcre_study()\fP
853 and normally also by \fBpcre_exec()\fP. Thus, by default, for any single
854 pattern, compilation, studying and matching all happen in the same locale, but
855 different patterns can be compiled in different locales.
856 .P
857 It is possible to pass a table pointer or NULL (indicating the use of the
858 internal tables) to \fBpcre_exec()\fP. Although not intended for this purpose,
859 this facility could be used to match a pattern in a different locale from the
860 one in which it was compiled. Passing table pointers at run time is discussed
861 below in the section on matching a pattern.
862 .
863 .
865 .rs
866 .sp
867 .B int pcre_fullinfo(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
868 .ti +5n
869 .B int \fIwhat\fP, void *\fIwhere\fP);
870 .PP
871 The \fBpcre_fullinfo()\fP function returns information about a compiled
872 pattern. It replaces the obsolete \fBpcre_info()\fP function, which is
873 nevertheless retained for backwards compability (and is documented below).
874 .P
875 The first argument for \fBpcre_fullinfo()\fP is a pointer to the compiled
876 pattern. The second argument is the result of \fBpcre_study()\fP, or NULL if
877 the pattern was not studied. The third argument specifies which piece of
878 information is required, and the fourth argument is a pointer to a variable
879 to receive the data. The yield of the function is zero for success, or one of
880 the following negative numbers:
881 .sp
882 PCRE_ERROR_NULL the argument \fIcode\fP was NULL
883 the argument \fIwhere\fP was NULL
884 PCRE_ERROR_BADMAGIC the "magic number" was not found
885 PCRE_ERROR_BADOPTION the value of \fIwhat\fP was invalid
886 .sp
887 The "magic number" is placed at the start of each compiled pattern as an simple
888 check against passing an arbitrary memory pointer. Here is a typical call of
889 \fBpcre_fullinfo()\fP, to obtain the length of the compiled pattern:
890 .sp
891 int rc;
892 size_t length;
893 rc = pcre_fullinfo(
894 re, /* result of pcre_compile() */
895 pe, /* result of pcre_study(), or NULL */
896 PCRE_INFO_SIZE, /* what is required */
897 &length); /* where to put the data */
898 .sp
899 The possible values for the third argument are defined in \fBpcre.h\fP, and are
900 as follows:
901 .sp
903 .sp
904 Return the number of the highest back reference in the pattern. The fourth
905 argument should point to an \fBint\fP variable. Zero is returned if there are
906 no back references.
907 .sp
909 .sp
910 Return the number of capturing subpatterns in the pattern. The fourth argument
911 should point to an \fBint\fP variable.
912 .sp
914 .sp
915 Return a pointer to the internal default character tables within PCRE. The
916 fourth argument should point to an \fBunsigned char *\fP variable. This
917 information call is provided for internal use by the \fBpcre_study()\fP
918 function. External callers can cause PCRE to use its internal tables by passing
919 a NULL table pointer.
920 .sp
922 .sp
923 Return information about the first byte of any matched string, for a
924 non-anchored pattern. The fourth argument should point to an \fBint\fP
925 variable. (This option used to be called PCRE_INFO_FIRSTCHAR; the old name is
926 still recognized for backwards compatibility.)
927 .P
928 If there is a fixed first byte, for example, from a pattern such as
929 (cat|cow|coyote), its value is returned. Otherwise, if either
930 .sp
931 (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
932 starts with "^", or
933 .sp
934 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
935 (if it were set, the pattern would be anchored),
936 .sp
937 -1 is returned, indicating that the pattern matches only at the start of a
938 subject string or after any newline within the string. Otherwise -2 is
939 returned. For anchored patterns, -2 is returned.
940 .sp
942 .sp
943 If the pattern was studied, and this resulted in the construction of a 256-bit
944 table indicating a fixed set of bytes for the first byte in any matching
945 string, a pointer to the table is returned. Otherwise NULL is returned. The
946 fourth argument should point to an \fBunsigned char *\fP variable.
947 .sp
949 .sp
950 Return 1 if the pattern contains any explicit matches for CR or LF characters,
951 otherwise 0. The fourth argument should point to an \fBint\fP variable. An
952 explicit match is either a literal CR or LF character, or \er or \en.
953 .sp
955 .sp
956 Return 1 if the (?J) or (?-J) option setting is used in the pattern, otherwise
957 0. The fourth argument should point to an \fBint\fP variable. (?J) and
958 (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
959 .sp
961 .sp
962 Return the value of the rightmost literal byte that must exist in any matched
963 string, other than at its start, if such a byte has been recorded. The fourth
964 argument should point to an \fBint\fP variable. If there is no such byte, -1 is
965 returned. For anchored patterns, a last literal byte is recorded only if it
966 follows something of variable length. For example, for the pattern
967 /^a\ed+z\ed+/ the returned value is "z", but for /^a\edz\ed/ the returned value
968 is -1.
969 .sp
973 .sp
974 PCRE supports the use of named as well as numbered capturing parentheses. The
975 names are just an additional way of identifying the parentheses, which still
976 acquire numbers. Several convenience functions such as
977 \fBpcre_get_named_substring()\fP are provided for extracting captured
978 substrings by name. It is also possible to extract the data directly, by first
979 converting the name to a number in order to access the correct pointers in the
980 output vector (described with \fBpcre_exec()\fP below). To do the conversion,
981 you need to use the name-to-number map, which is described by these three
982 values.
983 .P
984 The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives
985 the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each
986 entry; both of these return an \fBint\fP value. The entry size depends on the
987 length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first
988 entry of the table (a pointer to \fBchar\fP). The first two bytes of each entry
989 are the number of the capturing parenthesis, most significant byte first. The
990 rest of the entry is the corresponding name, zero terminated. The names are in
991 alphabetical order. When PCRE_DUPNAMES is set, duplicate names are in order of
992 their parentheses numbers. For example, consider the following pattern (assume
993 PCRE_EXTENDED is set, so white space - including newlines - is ignored):
994 .sp
995 .\" JOIN
996 (?<date> (?<year>(\ed\ed)?\ed\ed) -
997 (?<month>\ed\ed) - (?<day>\ed\ed) )
998 .sp
999 There are four named subpatterns, so the table has four entries, and each entry
1000 in the table is eight bytes long. The table is as follows, with non-printing
1001 bytes shows in hexadecimal, and undefined bytes shown as ??:
1002 .sp
1003 00 01 d a t e 00 ??
1004 00 05 d a y 00 ?? ??
1005 00 04 m o n t h 00
1006 00 02 y e a r 00 ??
1007 .sp
1008 When writing code to extract data from named subpatterns using the
1009 name-to-number map, remember that the length of the entries is likely to be
1010 different for each compiled pattern.
1011 .sp
1013 .sp
1014 Return 1 if the pattern can be used for partial matching, otherwise 0. The
1015 fourth argument should point to an \fBint\fP variable. From release 8.00, this
1016 always returns 1, because the restrictions that previously applied to partial
1017 matching have been lifted. The
1018 .\" HREF
1019 \fBpcrepartial\fP
1020 .\"
1021 documentation gives details of partial matching.
1022 .sp
1024 .sp
1025 Return a copy of the options with which the pattern was compiled. The fourth
1026 argument should point to an \fBunsigned long int\fP variable. These option bits
1027 are those specified in the call to \fBpcre_compile()\fP, modified by any
1028 top-level option settings at the start of the pattern itself. In other words,
1029 they are the options that will be in force when matching starts. For example,
1030 if the pattern /(?im)abc(?-i)d/ is compiled with the PCRE_EXTENDED option, the
1032 .P
1033 A pattern is automatically anchored by PCRE if all of its top-level
1034 alternatives begin with one of the following:
1035 .sp
1036 ^ unless PCRE_MULTILINE is set
1037 \eA always
1038 \eG always
1039 .\" JOIN
1040 .* if PCRE_DOTALL is set and there are no back
1041 references to the subpattern in which .* appears
1042 .sp
1043 For such patterns, the PCRE_ANCHORED bit is set in the options returned by
1044 \fBpcre_fullinfo()\fP.
1045 .sp
1047 .sp
1048 Return the size of the compiled pattern, that is, the value that was passed as
1049 the argument to \fBpcre_malloc()\fP when PCRE was getting memory in which to
1050 place the compiled data. The fourth argument should point to a \fBsize_t\fP
1051 variable.
1052 .sp
1054 .sp
1055 Return the size of the data block pointed to by the \fIstudy_data\fP field in
1056 a \fBpcre_extra\fP block. That is, it is the value that was passed to
1057 \fBpcre_malloc()\fP when PCRE was getting memory into which to place the data
1058 created by \fBpcre_study()\fP. The fourth argument should point to a
1059 \fBsize_t\fP variable.
1060 .
1061 .
1063 .rs
1064 .sp
1065 .B int pcre_info(const pcre *\fIcode\fP, int *\fIoptptr\fP, int
1066 .B *\fIfirstcharptr\fP);
1067 .PP
1068 The \fBpcre_info()\fP function is now obsolete because its interface is too
1069 restrictive to return all the available data about a compiled pattern. New
1070 programs should use \fBpcre_fullinfo()\fP instead. The yield of
1071 \fBpcre_info()\fP is the number of capturing subpatterns, or one of the
1072 following negative numbers:
1073 .sp
1074 PCRE_ERROR_NULL the argument \fIcode\fP was NULL
1075 PCRE_ERROR_BADMAGIC the "magic number" was not found
1076 .sp
1077 If the \fIoptptr\fP argument is not NULL, a copy of the options with which the
1078 pattern was compiled is placed in the integer it points to (see
1079 PCRE_INFO_OPTIONS above).
1080 .P
1081 If the pattern is not anchored and the \fIfirstcharptr\fP argument is not NULL,
1082 it is used to pass back information about the first character of any matched
1083 string (see PCRE_INFO_FIRSTBYTE above).
1084 .
1085 .
1087 .rs
1088 .sp
1089 .B int pcre_refcount(pcre *\fIcode\fP, int \fIadjust\fP);
1090 .PP
1091 The \fBpcre_refcount()\fP function is used to maintain a reference count in the
1092 data block that contains a compiled pattern. It is provided for the benefit of
1093 applications that operate in an object-oriented manner, where different parts
1094 of the application may be using the same compiled pattern, but you want to free
1095 the block when they are all done.
1096 .P
1097 When a pattern is compiled, the reference count field is initialized to zero.
1098 It is changed only by calling this function, whose action is to add the
1099 \fIadjust\fP value (which may be positive or negative) to it. The yield of the
1100 function is the new value. However, the value of the count is constrained to
1101 lie between 0 and 65535, inclusive. If the new value is outside these limits,
1102 it is forced to the appropriate limit value.
1103 .P
1104 Except when it is zero, the reference count is not correctly preserved if a
1105 pattern is compiled on one host and then transferred to a host whose byte-order
1106 is different. (This seems a highly unlikely scenario.)
1107 .
1108 .
1110 .rs
1111 .sp
1112 .B int pcre_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
1113 .ti +5n
1114 .B "const char *\fIsubject\fP," int \fIlength\fP, int \fIstartoffset\fP,
1115 .ti +5n
1116 .B int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP);
1117 .P
1118 The function \fBpcre_exec()\fP is called to match a subject string against a
1119 compiled pattern, which is passed in the \fIcode\fP argument. If the
1120 pattern has been studied, the result of the study should be passed in the
1121 \fIextra\fP argument. This function is the main matching facility of the
1122 library, and it operates in a Perl-like manner. For specialist use there is
1123 also an alternative matching function, which is described
1124 .\" HTML <a href="#dfamatch">
1125 .\" </a>
1126 below
1127 .\"
1128 in the section about the \fBpcre_dfa_exec()\fP function.
1129 .P
1130 In most applications, the pattern will have been compiled (and optionally
1131 studied) in the same process that calls \fBpcre_exec()\fP. However, it is
1132 possible to save compiled patterns and study data, and then use them later
1133 in different processes, possibly even on different hosts. For a discussion
1134 about this, see the
1135 .\" HREF
1136 \fBpcreprecompile\fP
1137 .\"
1138 documentation.
1139 .P
1140 Here is an example of a simple call to \fBpcre_exec()\fP:
1141 .sp
1142 int rc;
1143 int ovector[30];
1144 rc = pcre_exec(
1145 re, /* result of pcre_compile() */
1146 NULL, /* we didn't study the pattern */
1147 "some string", /* the subject string */
1148 11, /* the length of the subject string */
1149 0, /* start at offset 0 in the subject */
1150 0, /* default options */
1151 ovector, /* vector of integers for substring information */
1152 30); /* number of elements (NOT size in bytes) */
1153 .
1154 .\" HTML <a name="extradata"></a>
1155 .SS "Extra data for \fBpcre_exec()\fR"
1156 .rs
1157 .sp
1158 If the \fIextra\fP argument is not NULL, it must point to a \fBpcre_extra\fP
1159 data block. The \fBpcre_study()\fP function returns such a block (when it
1160 doesn't return NULL), but you can also create one for yourself, and pass
1161 additional information in it. The \fBpcre_extra\fP block contains the following
1162 fields (not necessarily in this order):
1163 .sp
1164 unsigned long int \fIflags\fP;
1165 void *\fIstudy_data\fP;
1166 unsigned long int \fImatch_limit\fP;
1167 unsigned long int \fImatch_limit_recursion\fP;
1168 void *\fIcallout_data\fP;
1169 const unsigned char *\fItables\fP;
1170 .sp
1171 The \fIflags\fP field is a bitmap that specifies which of the other fields
1172 are set. The flag bits are:
1173 .sp
1179 .sp
1180 Other flag bits should be set to zero. The \fIstudy_data\fP field is set in the
1181 \fBpcre_extra\fP block that is returned by \fBpcre_study()\fP, together with
1182 the appropriate flag bit. You should not set this yourself, but you may add to
1183 the block by setting the other fields and their corresponding flag bits.
1184 .P
1185 The \fImatch_limit\fP field provides a means of preventing PCRE from using up a
1186 vast amount of resources when running patterns that are not going to match,
1187 but which have a very large number of possibilities in their search trees. The
1188 classic example is the use of nested unlimited repeats.
1189 .P
1190 Internally, PCRE uses a function called \fBmatch()\fP which it calls repeatedly
1191 (sometimes recursively). The limit set by \fImatch_limit\fP is imposed on the
1192 number of times this function is called during a match, which has the effect of
1193 limiting the amount of backtracking that can take place. For patterns that are
1194 not anchored, the count restarts from zero for each position in the subject
1195 string.
1196 .P
1197 The default value for the limit can be set when PCRE is built; the default
1198 default is 10 million, which handles all but the most extreme cases. You can
1199 override the default by suppling \fBpcre_exec()\fP with a \fBpcre_extra\fP
1200 block in which \fImatch_limit\fP is set, and PCRE_EXTRA_MATCH_LIMIT is set in
1201 the \fIflags\fP field. If the limit is exceeded, \fBpcre_exec()\fP returns
1203 .P
1204 The \fImatch_limit_recursion\fP field is similar to \fImatch_limit\fP, but
1205 instead of limiting the total number of times that \fBmatch()\fP is called, it
1206 limits the depth of recursion. The recursion depth is a smaller number than the
1207 total number of calls, because not all calls to \fBmatch()\fP are recursive.
1208 This limit is of use only if it is set smaller than \fImatch_limit\fP.
1209 .P
1210 Limiting the recursion depth limits the amount of stack that can be used, or,
1211 when PCRE has been compiled to use memory on the heap instead of the stack, the
1212 amount of heap memory that can be used.
1213 .P
1214 The default value for \fImatch_limit_recursion\fP can be set when PCRE is
1215 built; the default default is the same value as the default for
1216 \fImatch_limit\fP. You can override the default by suppling \fBpcre_exec()\fP
1217 with a \fBpcre_extra\fP block in which \fImatch_limit_recursion\fP is set, and
1218 PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the \fIflags\fP field. If the limit
1219 is exceeded, \fBpcre_exec()\fP returns PCRE_ERROR_RECURSIONLIMIT.
1220 .P
1221 The \fIpcre_callout\fP field is used in conjunction with the "callout" feature,
1222 which is described in the
1223 .\" HREF
1224 \fBpcrecallout\fP
1225 .\"
1226 documentation.
1227 .P
1228 The \fItables\fP field is used to pass a character tables pointer to
1229 \fBpcre_exec()\fP; this overrides the value that is stored with the compiled
1230 pattern. A non-NULL value is stored with the compiled pattern only if custom
1231 tables were supplied to \fBpcre_compile()\fP via its \fItableptr\fP argument.
1232 If NULL is passed to \fBpcre_exec()\fP using this mechanism, it forces PCRE's
1233 internal tables to be used. This facility is helpful when re-using patterns
1234 that have been saved after compiling with an external set of tables, because
1235 the external tables might be at a different address when \fBpcre_exec()\fP is
1236 called. See the
1237 .\" HREF
1238 \fBpcreprecompile\fP
1239 .\"
1240 documentation for a discussion of saving compiled patterns for later use.
1241 .
1242 .\" HTML <a name="execoptions"></a>
1243 .SS "Option bits for \fBpcre_exec()\fP"
1244 .rs
1245 .sp
1246 The unused bits of the \fIoptions\fP argument for \fBpcre_exec()\fP must be
1247 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_\fIxxx\fP,
1250 .sp
1252 .sp
1253 The PCRE_ANCHORED option limits \fBpcre_exec()\fP to matching at the first
1254 matching position. If a pattern was compiled with PCRE_ANCHORED, or turned out
1255 to be anchored by virtue of its contents, it cannot be made unachored at
1256 matching time.
1257 .sp
1260 .sp
1261 These options (which are mutually exclusive) control what the \eR escape
1262 sequence matches. The choice is either to match only CR, LF, or CRLF, or to
1263 match any Unicode newline sequence. These options override the choice that was
1264 made or defaulted when the pattern was compiled.
1265 .sp
1271 .sp
1272 These options override the newline definition that was chosen or defaulted when
1273 the pattern was compiled. For details, see the description of
1274 \fBpcre_compile()\fP above. During matching, the newline choice affects the
1275 behaviour of the dot, circumflex, and dollar metacharacters. It may also alter
1276 the way the match position is advanced after a match failure for an unanchored
1277 pattern.
1278 .P
1280 match attempt for an unanchored pattern fails when the current position is at a
1281 CRLF sequence, and the pattern contains no explicit matches for CR or LF
1282 characters, the match position is advanced by two characters instead of one, in
1283 other words, to after the CRLF.
1284 .P
1285 The above rule is a compromise that makes the most common cases work as
1286 expected. For example, if the pattern is .+A (and the PCRE_DOTALL option is not
1287 set), it does not match the string "\er\enA" because, after failing at the
1288 start, it skips both the CR and the LF before retrying. However, the pattern
1289 [\er\en]A does match that string, because it contains an explicit CR or LF
1290 reference, and so advances only by one character after the first failure.
1291 .P
1292 An explicit match for CR of LF is either a literal appearance of one of those
1293 characters, or one of the \er or \en escape sequences. Implicit matches such as
1294 [^X] do not count, nor does \es (which includes CR and LF in the characters
1295 that it matches).
1296 .P
1297 Notwithstanding the above, anomalous effects may still occur when CRLF is a
1298 valid newline sequence and explicit \er or \en escapes appear in the pattern.
1299 .sp
1301 .sp
1302 This option specifies that first character of the subject string is not the
1303 beginning of a line, so the circumflex metacharacter should not match before
1304 it. Setting this without PCRE_MULTILINE (at compile time) causes circumflex
1305 never to match. This option affects only the behaviour of the circumflex
1306 metacharacter. It does not affect \eA.
1307 .sp
1309 .sp
1310 This option specifies that the end of the subject string is not the end of a
1311 line, so the dollar metacharacter should not match it nor (except in multiline
1312 mode) a newline immediately before it. Setting this without PCRE_MULTILINE (at
1313 compile time) causes dollar never to match. This option affects only the
1314 behaviour of the dollar metacharacter. It does not affect \eZ or \ez.
1315 .sp
1317 .sp
1318 An empty string is not considered to be a valid match if this option is set. If
1319 there are alternatives in the pattern, they are tried. If all the alternatives
1320 match the empty string, the entire match fails. For example, if the pattern
1321 .sp
1322 a?b?
1323 .sp
1324 is applied to a string not beginning with "a" or "b", it matches the empty
1325 string at the start of the subject. With PCRE_NOTEMPTY set, this match is not
1326 valid, so PCRE searches further into the string for occurrences of "a" or "b".
1327 .P
1328 Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a special case
1329 of a pattern match of the empty string within its \fBsplit()\fP function, and
1330 when using the /g modifier. It is possible to emulate Perl's behaviour after
1331 matching a null string by first trying the match again at the same offset with
1332 PCRE_NOTEMPTY and PCRE_ANCHORED, and then if that fails by advancing the
1333 starting offset (see below) and trying an ordinary match again. There is some
1334 code that demonstrates how to do this in the
1335 .\" HREF
1336 \fBpcredemo\fP
1337 .\"
1338 sample program.
1339 .sp
1341 .sp
1342 There are a number of optimizations that \fBpcre_exec()\fP uses at the start of
1343 a match, in order to speed up the process. For example, if it is known that a
1344 match must start with a specific character, it searches the subject for that
1345 character, and fails immediately if it cannot find it, without actually running
1346 the main matching function. When callouts are in use, these optimizations can
1347 cause them to be skipped. This option disables the "start-up" optimizations,
1348 causing performance to suffer, but ensuring that the callouts do occur.
1349 .sp
1351 .sp
1352 When PCRE_UTF8 is set at compile time, the validity of the subject as a UTF-8
1353 string is automatically checked when \fBpcre_exec()\fP is subsequently called.
1354 The value of \fIstartoffset\fP is also checked to ensure that it points to the
1355 start of a UTF-8 character. There is a discussion about the validity of UTF-8
1356 strings in the
1357 .\" HTML <a href="pcre.html#utf8strings">
1358 .\" </a>
1359 section on UTF-8 support
1360 .\"
1361 in the main
1362 .\" HREF
1363 \fBpcre\fP
1364 .\"
1365 page. If an invalid UTF-8 sequence of bytes is found, \fBpcre_exec()\fP returns
1366 the error PCRE_ERROR_BADUTF8. If \fIstartoffset\fP contains an invalid value,
1367 PCRE_ERROR_BADUTF8_OFFSET is returned.
1368 .P
1369 If you already know that your subject is valid, and you want to skip these
1370 checks for performance reasons, you can set the PCRE_NO_UTF8_CHECK option when
1371 calling \fBpcre_exec()\fP. You might want to do this for the second and
1372 subsequent calls to \fBpcre_exec()\fP if you are making repeated calls to find
1373 all the matches in a single subject string. However, you should be sure that
1374 the value of \fIstartoffset\fP points to the start of a UTF-8 character. When
1375 PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid UTF-8 string as a
1376 subject, or a value of \fIstartoffset\fP that does not point to the start of a
1377 UTF-8 character, is undefined. Your program may crash.
1378 .sp
1381 .sp
1382 These options turn on the partial matching feature. For backwards
1383 compatibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial match
1384 occurs if the end of the subject string is reached successfully, but there are
1385 not enough subject characters to complete the match. If this happens when
1386 PCRE_PARTIAL_HARD is set, \fBpcre_exec()\fP immediately returns
1387 PCRE_ERROR_PARTIAL. Otherwise, if PCRE_PARTIAL_SOFT is set, matching continues
1388 by testing any other alternatives. Only if they all fail is PCRE_ERROR_PARTIAL
1389 returned (instead of PCRE_ERROR_NOMATCH). The portion of the string that
1390 provided the partial match is set as the first matching string. There is a more
1391 detailed discussion in the
1392 .\" HREF
1393 \fBpcrepartial\fP
1394 .\"
1395 documentation.
1396 .
1397 .SS "The string to be matched by \fBpcre_exec()\fP"
1398 .rs
1399 .sp
1400 The subject string is passed to \fBpcre_exec()\fP as a pointer in
1401 \fIsubject\fP, a length (in bytes) in \fIlength\fP, and a starting byte offset
1402 in \fIstartoffset\fP. In UTF-8 mode, the byte offset must point to the start of
1403 a UTF-8 character. Unlike the pattern string, the subject may contain binary
1404 zero bytes. When the starting offset is zero, the search for a match starts at
1405 the beginning of the subject, and this is by far the most common case.
1406 .P
1407 A non-zero starting offset is useful when searching for another match in the
1408 same subject by calling \fBpcre_exec()\fP again after a previous success.
1409 Setting \fIstartoffset\fP differs from just passing over a shortened string and
1410 setting PCRE_NOTBOL in the case of a pattern that begins with any kind of
1411 lookbehind. For example, consider the pattern
1412 .sp
1413 \eBiss\eB
1414 .sp
1415 which finds occurrences of "iss" in the middle of words. (\eB matches only if
1416 the current position in the subject is not a word boundary.) When applied to
1417 the string "Mississipi" the first call to \fBpcre_exec()\fP finds the first
1418 occurrence. If \fBpcre_exec()\fP is called again with just the remainder of the
1419 subject, namely "issipi", it does not match, because \eB is always false at the
1420 start of the subject, which is deemed to be a word boundary. However, if
1421 \fBpcre_exec()\fP is passed the entire string again, but with \fIstartoffset\fP
1422 set to 4, it finds the second occurrence of "iss" because it is able to look
1423 behind the starting point to discover that it is preceded by a letter.
1424 .P
1425 If a non-zero starting offset is passed when the pattern is anchored, one
1426 attempt to match at the given offset is made. This can only succeed if the
1427 pattern does not require the match to be at the start of the subject.
1428 .
1429 .SS "How \fBpcre_exec()\fP returns captured substrings"
1430 .rs
1431 .sp
1432 In general, a pattern matches a certain portion of the subject, and in
1433 addition, further substrings from the subject may be picked out by parts of the
1434 pattern. Following the usage in Jeffrey Friedl's book, this is called
1435 "capturing" in what follows, and the phrase "capturing subpattern" is used for
1436 a fragment of a pattern that picks out a substring. PCRE supports several other
1437 kinds of parenthesized subpattern that do not cause substrings to be captured.
1438 .P
1439 Captured substrings are returned to the caller via a vector of integers whose
1440 address is passed in \fIovector\fP. The number of elements in the vector is
1441 passed in \fIovecsize\fP, which must be a non-negative number. \fBNote\fP: this
1442 argument is NOT the size of \fIovector\fP in bytes.
1443 .P
1444 The first two-thirds of the vector is used to pass back captured substrings,
1445 each substring using a pair of integers. The remaining third of the vector is
1446 used as workspace by \fBpcre_exec()\fP while matching capturing subpatterns,
1447 and is not available for passing back information. The number passed in
1448 \fIovecsize\fP should always be a multiple of three. If it is not, it is
1449 rounded down.
1450 .P
1451 When a match is successful, information about captured substrings is returned
1452 in pairs of integers, starting at the beginning of \fIovector\fP, and
1453 continuing up to two-thirds of its length at the most. The first element of
1454 each pair is set to the byte offset of the first character in a substring, and
1455 the second is set to the byte offset of the first character after the end of a
1456 substring. \fBNote\fP: these values are always byte offsets, even in UTF-8
1457 mode. They are not character counts.
1458 .P
1459 The first pair of integers, \fIovector[0]\fP and \fIovector[1]\fP, identify the
1460 portion of the subject string matched by the entire pattern. The next pair is
1461 used for the first capturing subpattern, and so on. The value returned by
1462 \fBpcre_exec()\fP is one more than the highest numbered pair that has been set.
1463 For example, if two substrings have been captured, the returned value is 3. If
1464 there are no capturing subpatterns, the return value from a successful match is
1465 1, indicating that just the first pair of offsets has been set.
1466 .P
1467 If a capturing subpattern is matched repeatedly, it is the last portion of the
1468 string that it matched that is returned.
1469 .P
1470 If the vector is too small to hold all the captured substring offsets, it is
1471 used as far as possible (up to two-thirds of its length), and the function
1472 returns a value of zero. If the substring offsets are not of interest,
1473 \fBpcre_exec()\fP may be called with \fIovector\fP passed as NULL and
1474 \fIovecsize\fP as zero. However, if the pattern contains back references and
1475 the \fIovector\fP is not big enough to remember the related substrings, PCRE
1476 has to get additional memory for use during matching. Thus it is usually
1477 advisable to supply an \fIovector\fP.
1478 .P
1479 The \fBpcre_info()\fP function can be used to find out how many capturing
1480 subpatterns there are in a compiled pattern. The smallest size for
1481 \fIovector\fP that will allow for \fIn\fP captured substrings, in addition to
1482 the offsets of the substring matched by the whole pattern, is (\fIn\fP+1)*3.
1483 .P
1484 It is possible for capturing subpattern number \fIn+1\fP to match some part of
1485 the subject when subpattern \fIn\fP has not been used at all. For example, if
1486 the string "abc" is matched against the pattern (a|(z))(bc) the return from the
1487 function is 4, and subpatterns 1 and 3 are matched, but 2 is not. When this
1488 happens, both values in the offset pairs corresponding to unused subpatterns
1489 are set to -1.
1490 .P
1491 Offset values that correspond to unused subpatterns at the end of the
1492 expression are also set to -1. For example, if the string "abc" is matched
1493 against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not matched. The
1494 return from the function is 2, because the highest used capturing subpattern
1495 number is 1. However, you can refer to the offsets for the second and third
1496 capturing subpatterns if you wish (assuming the vector is large enough, of
1497 course).
1498 .P
1499 Some convenience functions are provided for extracting the captured substrings
1500 as separate strings. These are described below.
1501 .
1502 .\" HTML <a name="errorlist"></a>
1503 .SS "Error return values from \fBpcre_exec()\fP"
1504 .rs
1505 .sp
1506 If \fBpcre_exec()\fP fails, it returns a negative number. The following are
1507 defined in the header file:
1508 .sp
1510 .sp
1511 The subject string did not match the pattern.
1512 .sp
1514 .sp
1515 Either \fIcode\fP or \fIsubject\fP was passed as NULL, or \fIovector\fP was
1516 NULL and \fIovecsize\fP was not zero.
1517 .sp
1519 .sp
1520 An unrecognized bit was set in the \fIoptions\fP argument.
1521 .sp
1523 .sp
1524 PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch
1525 the case when it is passed a junk pointer and to detect when a pattern that was
1526 compiled in an environment of one endianness is run in an environment with the
1527 other endianness. This is the error that PCRE gives when the magic number is
1528 not present.
1529 .sp
1531 .sp
1532 While running the pattern match, an unknown item was encountered in the
1533 compiled pattern. This error could be caused by a bug in PCRE or by overwriting
1534 of the compiled pattern.
1535 .sp
1537 .sp
1538 If a pattern contains back references, but the \fIovector\fP that is passed to
1539 \fBpcre_exec()\fP is not big enough to remember the referenced substrings, PCRE
1540 gets a block of memory at the start of matching to use for this purpose. If the
1541 call via \fBpcre_malloc()\fP fails, this error is given. The memory is
1542 automatically freed at the end of matching.
1543 .sp
1545 .sp
1546 This error is used by the \fBpcre_copy_substring()\fP,
1547 \fBpcre_get_substring()\fP, and \fBpcre_get_substring_list()\fP functions (see
1548 below). It is never returned by \fBpcre_exec()\fP.
1549 .sp
1551 .sp
1552 The backtracking limit, as specified by the \fImatch_limit\fP field in a
1553 \fBpcre_extra\fP structure (or defaulted) was reached. See the description
1554 above.
1555 .sp
1557 .sp
1558 This error is never generated by \fBpcre_exec()\fP itself. It is provided for
1559 use by callout functions that want to yield a distinctive error code. See the
1560 .\" HREF
1561 \fBpcrecallout\fP
1562 .\"
1563 documentation for details.
1564 .sp
1566 .sp
1567 A string that contains an invalid UTF-8 byte sequence was passed as a subject.
1568 .sp
1570 .sp
1571 The UTF-8 byte sequence that was passed as a subject was valid, but the value
1572 of \fIstartoffset\fP did not point to the beginning of a UTF-8 character.
1573 .sp
1575 .sp
1576 The subject string did not match, but it did match partially. See the
1577 .\" HREF
1578 \fBpcrepartial\fP
1579 .\"
1580 documentation for details of partial matching.
1581 .sp
1583 .sp
1584 This code is no longer in use. It was formerly returned when the PCRE_PARTIAL
1585 option was used with a compiled pattern containing items that were not
1586 supported for partial matching. From release 8.00 onwards, there are no
1587 restrictions on partial matching.
1588 .sp
1590 .sp
1591 An unexpected internal error has occurred. This error could be caused by a bug
1592 in PCRE or by overwriting of the compiled pattern.
1593 .sp
1595 .sp
1596 This error is given if the value of the \fIovecsize\fP argument is negative.
1597 .sp
1599 .sp
1600 The internal recursion limit, as specified by the \fImatch_limit_recursion\fP
1601 field in a \fBpcre_extra\fP structure (or defaulted) was reached. See the
1602 description above.
1603 .sp
1605 .sp
1606 An invalid combination of PCRE_NEWLINE_\fIxxx\fP options was given.
1607 .P
1608 Error numbers -16 to -20 and -22 are not used by \fBpcre_exec()\fP.
1609 .
1610 .
1612 .rs
1613 .sp
1614 .B int pcre_copy_substring(const char *\fIsubject\fP, int *\fIovector\fP,
1615 .ti +5n
1616 .B int \fIstringcount\fP, int \fIstringnumber\fP, char *\fIbuffer\fP,
1617 .ti +5n
1618 .B int \fIbuffersize\fP);
1619 .PP
1620 .B int pcre_get_substring(const char *\fIsubject\fP, int *\fIovector\fP,
1621 .ti +5n
1622 .B int \fIstringcount\fP, int \fIstringnumber\fP,
1623 .ti +5n
1624 .B const char **\fIstringptr\fP);
1625 .PP
1626 .B int pcre_get_substring_list(const char *\fIsubject\fP,
1627 .ti +5n
1628 .B int *\fIovector\fP, int \fIstringcount\fP, "const char ***\fIlistptr\fP);"
1629 .PP
1630 Captured substrings can be accessed directly by using the offsets returned by
1631 \fBpcre_exec()\fP in \fIovector\fP. For convenience, the functions
1632 \fBpcre_copy_substring()\fP, \fBpcre_get_substring()\fP, and
1633 \fBpcre_get_substring_list()\fP are provided for extracting captured substrings
1634 as new, separate, zero-terminated strings. These functions identify substrings
1635 by number. The next section describes functions for extracting named
1636 substrings.
1637 .P
1638 A substring that contains a binary zero is correctly extracted and has a
1639 further zero added on the end, but the result is not, of course, a C string.
1640 However, you can process such a string by referring to the length that is
1641 returned by \fBpcre_copy_substring()\fP and \fBpcre_get_substring()\fP.
1642 Unfortunately, the interface to \fBpcre_get_substring_list()\fP is not adequate
1643 for handling strings containing binary zeros, because the end of the final
1644 string is not independently indicated.
1645 .P
1646 The first three arguments are the same for all three of these functions:
1647 \fIsubject\fP is the subject string that has just been successfully matched,
1648 \fIovector\fP is a pointer to the vector of integer offsets that was passed to
1649 \fBpcre_exec()\fP, and \fIstringcount\fP is the number of substrings that were
1650 captured by the match, including the substring that matched the entire regular
1651 expression. This is the value returned by \fBpcre_exec()\fP if it is greater
1652 than zero. If \fBpcre_exec()\fP returned zero, indicating that it ran out of
1653 space in \fIovector\fP, the value passed as \fIstringcount\fP should be the
1654 number of elements in the vector divided by three.
1655 .P
1656 The functions \fBpcre_copy_substring()\fP and \fBpcre_get_substring()\fP
1657 extract a single substring, whose number is given as \fIstringnumber\fP. A
1658 value of zero extracts the substring that matched the entire pattern, whereas
1659 higher values extract the captured substrings. For \fBpcre_copy_substring()\fP,
1660 the string is placed in \fIbuffer\fP, whose length is given by
1661 \fIbuffersize\fP, while for \fBpcre_get_substring()\fP a new block of memory is
1662 obtained via \fBpcre_malloc\fP, and its address is returned via
1663 \fIstringptr\fP. The yield of the function is the length of the string, not
1664 including the terminating zero, or one of these error codes:
1665 .sp
1667 .sp
1668 The buffer was too small for \fBpcre_copy_substring()\fP, or the attempt to get
1669 memory failed for \fBpcre_get_substring()\fP.
1670 .sp
1672 .sp
1673 There is no substring whose number is \fIstringnumber\fP.
1674 .P
1675 The \fBpcre_get_substring_list()\fP function extracts all available substrings
1676 and builds a list of pointers to them. All this is done in a single block of
1677 memory that is obtained via \fBpcre_malloc\fP. The address of the memory block
1678 is returned via \fIlistptr\fP, which is also the start of the list of string
1679 pointers. The end of the list is marked by a NULL pointer. The yield of the
1680 function is zero if all went well, or the error code
1681 .sp
1683 .sp
1684 if the attempt to get the memory block failed.
1685 .P
1686 When any of these functions encounter a substring that is unset, which can
1687 happen when capturing subpattern number \fIn+1\fP matches some part of the
1688 subject, but subpattern \fIn\fP has not been used at all, they return an empty
1689 string. This can be distinguished from a genuine zero-length substring by
1690 inspecting the appropriate offset in \fIovector\fP, which is negative for unset
1691 substrings.
1692 .P
1693 The two convenience functions \fBpcre_free_substring()\fP and
1694 \fBpcre_free_substring_list()\fP can be used to free the memory returned by
1695 a previous call of \fBpcre_get_substring()\fP or
1696 \fBpcre_get_substring_list()\fP, respectively. They do nothing more than call
1697 the function pointed to by \fBpcre_free\fP, which of course could be called
1698 directly from a C program. However, PCRE is used in some situations where it is
1699 linked via a special interface to another programming language that cannot use
1700 \fBpcre_free\fP directly; it is for these cases that the functions are
1701 provided.
1702 .
1703 .
1705 .rs
1706 .sp
1707 .B int pcre_get_stringnumber(const pcre *\fIcode\fP,
1708 .ti +5n
1709 .B const char *\fIname\fP);
1710 .PP
1711 .B int pcre_copy_named_substring(const pcre *\fIcode\fP,
1712 .ti +5n
1713 .B const char *\fIsubject\fP, int *\fIovector\fP,
1714 .ti +5n
1715 .B int \fIstringcount\fP, const char *\fIstringname\fP,
1716 .ti +5n
1717 .B char *\fIbuffer\fP, int \fIbuffersize\fP);
1718 .PP
1719 .B int pcre_get_named_substring(const pcre *\fIcode\fP,
1720 .ti +5n
1721 .B const char *\fIsubject\fP, int *\fIovector\fP,
1722 .ti +5n
1723 .B int \fIstringcount\fP, const char *\fIstringname\fP,
1724 .ti +5n
1725 .B const char **\fIstringptr\fP);
1726 .PP
1727 To extract a substring by name, you first have to find associated number.
1728 For example, for this pattern
1729 .sp
1730 (a+)b(?<xxx>\ed+)...
1731 .sp
1732 the number of the subpattern called "xxx" is 2. If the name is known to be
1733 unique (PCRE_DUPNAMES was not set), you can find the number from the name by
1734 calling \fBpcre_get_stringnumber()\fP. The first argument is the compiled
1735 pattern, and the second is the name. The yield of the function is the
1736 subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no subpattern of
1737 that name.
1738 .P
1739 Given the number, you can extract the substring directly, or use one of the
1740 functions described in the previous section. For convenience, there are also
1741 two functions that do the whole job.
1742 .P
1743 Most of the arguments of \fBpcre_copy_named_substring()\fP and
1744 \fBpcre_get_named_substring()\fP are the same as those for the similarly named
1745 functions that extract by number. As these are described in the previous
1746 section, they are not re-described here. There are just two differences:
1747 .P
1748 First, instead of a substring number, a substring name is given. Second, there
1749 is an extra argument, given at the start, which is a pointer to the compiled
1750 pattern. This is needed in order to gain access to the name-to-number
1751 translation table.
1752 .P
1753 These functions call \fBpcre_get_stringnumber()\fP, and if it succeeds, they
1754 then call \fBpcre_copy_substring()\fP or \fBpcre_get_substring()\fP, as
1755 appropriate. \fBNOTE:\fP If PCRE_DUPNAMES is set and there are duplicate names,
1756 the behaviour may not be what you want (see the next section).
1757 .P
1758 \fBWarning:\fP If the pattern uses the "(?|" feature to set up multiple
1759 subpatterns with the same number, you cannot use names to distinguish them,
1760 because names are not included in the compiled code. The matching process uses
1761 only numbers.
1762 .
1764 .rs
1765 .sp
1766 .B int pcre_get_stringtable_entries(const pcre *\fIcode\fP,
1767 .ti +5n
1768 .B const char *\fIname\fP, char **\fIfirst\fP, char **\fIlast\fP);
1769 .PP
1770 When a pattern is compiled with the PCRE_DUPNAMES option, names for subpatterns
1771 are not required to be unique. Normally, patterns with duplicate names are such
1772 that in any one match, only one of the named subpatterns participates. An
1773 example is shown in the
1774 .\" HREF
1775 \fBpcrepattern\fP
1776 .\"
1777 documentation.
1778 .P
1779 When duplicates are present, \fBpcre_copy_named_substring()\fP and
1780 \fBpcre_get_named_substring()\fP return the first substring corresponding to
1781 the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING (-7) is
1782 returned; no data is returned. The \fBpcre_get_stringnumber()\fP function
1783 returns one of the numbers that are associated with the name, but it is not
1784 defined which it is.
1785 .P
1786 If you want to get full details of all captured substrings for a given name,
1787 you must use the \fBpcre_get_stringtable_entries()\fP function. The first
1788 argument is the compiled pattern, and the second is the name. The third and
1789 fourth are pointers to variables which are updated by the function. After it
1790 has run, they point to the first and last entries in the name-to-number table
1791 for the given name. The function itself returns the length of each entry, or
1792 PCRE_ERROR_NOSUBSTRING (-7) if there are none. The format of the table is
1793 described above in the section entitled \fIInformation about a pattern\fP.
1794 Given all the relevant entries for the name, you can extract each of their
1795 numbers, and hence the captured data, if any.
1796 .
1797 .
1799 .rs
1800 .sp
1801 The traditional matching function uses a similar algorithm to Perl, which stops
1802 when it finds the first match, starting at a given point in the subject. If you
1803 want to find all possible matches, or the longest possible match, consider
1804 using the alternative matching function (see below) instead. If you cannot use
1805 the alternative function, but still need to find all possible matches, you
1806 can kludge it up by making use of the callout facility, which is described in
1807 the
1808 .\" HREF
1809 \fBpcrecallout\fP
1810 .\"
1811 documentation.
1812 .P
1813 What you have to do is to insert a callout right at the end of the pattern.
1814 When your callout function is called, extract and save the current matched
1815 substring. Then return 1, which forces \fBpcre_exec()\fP to backtrack and try
1816 other alternatives. Ultimately, when it runs out of matches, \fBpcre_exec()\fP
1817 will yield PCRE_ERROR_NOMATCH.
1818 .
1819 .
1820 .\" HTML <a name="dfamatch"></a>
1822 .rs
1823 .sp
1824 .B int pcre_dfa_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
1825 .ti +5n
1826 .B "const char *\fIsubject\fP," int \fIlength\fP, int \fIstartoffset\fP,
1827 .ti +5n
1828 .B int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP,
1829 .ti +5n
1830 .B int *\fIworkspace\fP, int \fIwscount\fP);
1831 .P
1832 The function \fBpcre_dfa_exec()\fP is called to match a subject string against
1833 a compiled pattern, using a matching algorithm that scans the subject string
1834 just once, and does not backtrack. This has different characteristics to the
1835 normal algorithm, and is not compatible with Perl. Some of the features of PCRE
1836 patterns are not supported. Nevertheless, there are times when this kind of
1837 matching can be useful. For a discussion of the two matching algorithms, see
1838 the
1839 .\" HREF
1840 \fBpcrematching\fP
1841 .\"
1842 documentation.
1843 .P
1844 The arguments for the \fBpcre_dfa_exec()\fP function are the same as for
1845 \fBpcre_exec()\fP, plus two extras. The \fIovector\fP argument is used in a
1846 different way, and this is described below. The other common arguments are used
1847 in the same way as for \fBpcre_exec()\fP, so their description is not repeated
1848 here.
1849 .P
1850 The two additional arguments provide workspace for the function. The workspace
1851 vector should contain at least 20 elements. It is used for keeping track of
1852 multiple paths through the pattern tree. More workspace will be needed for
1853 patterns and subjects where there are a lot of potential matches.
1854 .P
1855 Here is an example of a simple call to \fBpcre_dfa_exec()\fP:
1856 .sp
1857 int rc;
1858 int ovector[10];
1859 int wspace[20];
1860 rc = pcre_dfa_exec(
1861 re, /* result of pcre_compile() */
1862 NULL, /* we didn't study the pattern */
1863 "some string", /* the subject string */
1864 11, /* the length of the subject string */
1865 0, /* start at offset 0 in the subject */
1866 0, /* default options */
1867 ovector, /* vector of integers for substring information */
1868 10, /* number of elements (NOT size in bytes) */
1869 wspace, /* working space vector */
1870 20); /* number of elements (NOT size in bytes) */
1871 .
1872 .SS "Option bits for \fBpcre_dfa_exec()\fP"
1873 .rs
1874 .sp
1875 The unused bits of the \fIoptions\fP argument for \fBpcre_dfa_exec()\fP must be
1876 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_\fIxxx\fP,
1879 four of these are exactly the same as for \fBpcre_exec()\fP, so their
1880 description is not repeated here.
1881 .sp
1884 .sp
1885 These have the same general effect as they do for \fBpcre_exec()\fP, but the
1886 details are slightly different. When PCRE_PARTIAL_HARD is set for
1887 \fBpcre_dfa_exec()\fP, it returns PCRE_ERROR_PARTIAL if the end of the subject
1888 is reached and there is still at least one matching possibility that requires
1889 additional characters. This happens even if some complete matches have also
1890 been found. When PCRE_PARTIAL_SOFT is set, the return code PCRE_ERROR_NOMATCH
1891 is converted into PCRE_ERROR_PARTIAL if the end of the subject is reached,
1892 there have been no complete matches, but there is still at least one matching
1893 possibility. The portion of the string that provided the longest partial match
1894 is set as the first matching string in both cases.
1895 .sp
1897 .sp
1898 Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to stop as
1899 soon as it has found one match. Because of the way the alternative algorithm
1900 works, this is necessarily the shortest possible match at the first possible
1901 matching point in the subject string.
1902 .sp
1904 .sp
1905 When \fBpcre_dfa_exec()\fP returns a partial match, it is possible to call it
1906 again, with additional subject characters, and have it continue with the same
1907 match. The PCRE_DFA_RESTART option requests this action; when it is set, the
1908 \fIworkspace\fP and \fIwscount\fP options must reference the same vector as
1909 before because data about the match so far is left in them after a partial
1910 match. There is more discussion of this facility in the
1911 .\" HREF
1912 \fBpcrepartial\fP
1913 .\"
1914 documentation.
1915 .
1916 .SS "Successful returns from \fBpcre_dfa_exec()\fP"
1917 .rs
1918 .sp
1919 When \fBpcre_dfa_exec()\fP succeeds, it may have matched more than one
1920 substring in the subject. Note, however, that all the matches from one run of
1921 the function start at the same point in the subject. The shorter matches are
1922 all initial substrings of the longer matches. For example, if the pattern
1923 .sp
1924 <.*>
1925 .sp
1926 is matched against the string
1927 .sp
1928 This is <something> <something else> <something further> no more
1929 .sp
1930 the three matched strings are
1931 .sp
1932 <something>
1933 <something> <something else>
1934 <something> <something else> <something further>
1935 .sp
1936 On success, the yield of the function is a number greater than zero, which is
1937 the number of matched substrings. The substrings themselves are returned in
1938 \fIovector\fP. Each string uses two elements; the first is the offset to the
1939 start, and the second is the offset to the end. In fact, all the strings have
1940 the same start offset. (Space could have been saved by giving this only once,
1941 but it was decided to retain some compatibility with the way \fBpcre_exec()\fP
1942 returns data, even though the meaning of the strings is different.)
1943 .P
1944 The strings are returned in reverse order of length; that is, the longest
1945 matching string is given first. If there were too many matches to fit into
1946 \fIovector\fP, the yield of the function is zero, and the vector is filled with
1947 the longest matches.
1948 .
1949 .SS "Error returns from \fBpcre_dfa_exec()\fP"
1950 .rs
1951 .sp
1952 The \fBpcre_dfa_exec()\fP function returns a negative number when it fails.
1953 Many of the errors are the same as for \fBpcre_exec()\fP, and these are
1954 described
1955 .\" HTML <a href="#errorlist">
1956 .\" </a>
1957 above.
1958 .\"
1959 There are in addition the following errors that are specific to
1960 \fBpcre_dfa_exec()\fP:
1961 .sp
1963 .sp
1964 This return is given if \fBpcre_dfa_exec()\fP encounters an item in the pattern
1965 that it does not support, for instance, the use of \eC or a back reference.
1966 .sp
1968 .sp
1969 This return is given if \fBpcre_dfa_exec()\fP encounters a condition item that
1970 uses a back reference for the condition, or a test for recursion in a specific
1971 group. These are not supported.
1972 .sp
1974 .sp
1975 This return is given if \fBpcre_dfa_exec()\fP is called with an \fIextra\fP
1976 block that contains a setting of the \fImatch_limit\fP field. This is not
1977 supported (it is meaningless).
1978 .sp
1980 .sp
1981 This return is given if \fBpcre_dfa_exec()\fP runs out of space in the
1982 \fIworkspace\fP vector.
1983 .sp
1985 .sp
1986 When a recursive subpattern is processed, the matching function calls itself
1987 recursively, using private vectors for \fIovector\fP and \fIworkspace\fP. This
1988 error is given if the output vector is not large enough. This should be
1989 extremely rare, as a vector of size 1000 is used.
1990 .
1991 .
1992 .SH "SEE ALSO"
1993 .rs
1994 .sp
1995 \fBpcrebuild\fP(3), \fBpcrecallout\fP(3), \fBpcrecpp(3)\fP(3),
1996 \fBpcrematching\fP(3), \fBpcrepartial\fP(3), \fBpcreposix\fP(3),
1997 \fBpcreprecompile\fP(3), \fBpcresample\fP(3), \fBpcrestack\fP(3).
1998 .
1999 .
2001 .rs
2002 .sp
2003 .nf
2004 Philip Hazel
2005 University Computing Service
2006 Cambridge CB2 3QH, England.
2007 .fi
2008 .
2009 .
2011 .rs
2012 .sp
2013 .nf
2014 Last updated: 01 September 2009
2015 Copyright (c) 1997-2009 University of Cambridge.
2016 .fi


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