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Tidies and final updates for 7.1.
3 PCRE - Perl-compatible regular expressions
5 .rs
6 .sp
7 .B #include <pcre.h>
8 .PP
9 .SM
10 .B pcre *pcre_compile(const char *\fIpattern\fP, int \fIoptions\fP,
11 .ti +5n
12 .B const char **\fIerrptr\fP, int *\fIerroffset\fP,
13 .ti +5n
14 .B const unsigned char *\fItableptr\fP);
15 .PP
16 .B pcre *pcre_compile2(const char *\fIpattern\fP, int \fIoptions\fP,
17 .ti +5n
18 .B int *\fIerrorcodeptr\fP,
19 .ti +5n
20 .B const char **\fIerrptr\fP, int *\fIerroffset\fP,
21 .ti +5n
22 .B const unsigned char *\fItableptr\fP);
23 .PP
24 .B pcre_extra *pcre_study(const pcre *\fIcode\fP, int \fIoptions\fP,
25 .ti +5n
26 .B const char **\fIerrptr\fP);
27 .PP
28 .B int pcre_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
29 .ti +5n
30 .B "const char *\fIsubject\fP," int \fIlength\fP, int \fIstartoffset\fP,
31 .ti +5n
32 .B int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP);
33 .PP
34 .B int pcre_dfa_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
35 .ti +5n
36 .B "const char *\fIsubject\fP," int \fIlength\fP, int \fIstartoffset\fP,
37 .ti +5n
38 .B int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP,
39 .ti +5n
40 .B int *\fIworkspace\fP, int \fIwscount\fP);
41 .PP
42 .B int pcre_copy_named_substring(const pcre *\fIcode\fP,
43 .ti +5n
44 .B const char *\fIsubject\fP, int *\fIovector\fP,
45 .ti +5n
46 .B int \fIstringcount\fP, const char *\fIstringname\fP,
47 .ti +5n
48 .B char *\fIbuffer\fP, int \fIbuffersize\fP);
49 .PP
50 .B int pcre_copy_substring(const char *\fIsubject\fP, int *\fIovector\fP,
51 .ti +5n
52 .B int \fIstringcount\fP, int \fIstringnumber\fP, char *\fIbuffer\fP,
53 .ti +5n
54 .B int \fIbuffersize\fP);
55 .PP
56 .B int pcre_get_named_substring(const pcre *\fIcode\fP,
57 .ti +5n
58 .B const char *\fIsubject\fP, int *\fIovector\fP,
59 .ti +5n
60 .B int \fIstringcount\fP, const char *\fIstringname\fP,
61 .ti +5n
62 .B const char **\fIstringptr\fP);
63 .PP
64 .B int pcre_get_stringnumber(const pcre *\fIcode\fP,
65 .ti +5n
66 .B const char *\fIname\fP);
67 .PP
68 .B int pcre_get_stringtable_entries(const pcre *\fIcode\fP,
69 .ti +5n
70 .B const char *\fIname\fP, char **\fIfirst\fP, char **\fIlast\fP);
71 .PP
72 .B int pcre_get_substring(const char *\fIsubject\fP, int *\fIovector\fP,
73 .ti +5n
74 .B int \fIstringcount\fP, int \fIstringnumber\fP,
75 .ti +5n
76 .B const char **\fIstringptr\fP);
77 .PP
78 .B int pcre_get_substring_list(const char *\fIsubject\fP,
79 .ti +5n
80 .B int *\fIovector\fP, int \fIstringcount\fP, "const char ***\fIlistptr\fP);"
81 .PP
82 .B void pcre_free_substring(const char *\fIstringptr\fP);
83 .PP
84 .B void pcre_free_substring_list(const char **\fIstringptr\fP);
85 .PP
86 .B const unsigned char *pcre_maketables(void);
87 .PP
88 .B int pcre_fullinfo(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
89 .ti +5n
90 .B int \fIwhat\fP, void *\fIwhere\fP);
91 .PP
92 .B int pcre_info(const pcre *\fIcode\fP, int *\fIoptptr\fP, int
93 .B *\fIfirstcharptr\fP);
94 .PP
95 .B int pcre_refcount(pcre *\fIcode\fP, int \fIadjust\fP);
96 .PP
97 .B int pcre_config(int \fIwhat\fP, void *\fIwhere\fP);
98 .PP
99 .B char *pcre_version(void);
100 .PP
101 .B void *(*pcre_malloc)(size_t);
102 .PP
103 .B void (*pcre_free)(void *);
104 .PP
105 .B void *(*pcre_stack_malloc)(size_t);
106 .PP
107 .B void (*pcre_stack_free)(void *);
108 .PP
109 .B int (*pcre_callout)(pcre_callout_block *);
110 .
111 .
113 .rs
114 .sp
115 PCRE has its own native API, which is described in this document. There are
116 also some wrapper functions that correspond to the POSIX regular expression
117 API. These are described in the
118 .\" HREF
119 \fBpcreposix\fP
120 .\"
121 documentation. Both of these APIs define a set of C function calls. A C++
122 wrapper is distributed with PCRE. It is documented in the
123 .\" HREF
124 \fBpcrecpp\fP
125 .\"
126 page.
127 .P
128 The native API C function prototypes are defined in the header file
129 \fBpcre.h\fP, and on Unix systems the library itself is called \fBlibpcre\fP.
130 It can normally be accessed by adding \fB-lpcre\fP to the command for linking
131 an application that uses PCRE. The header file defines the macros PCRE_MAJOR
132 and PCRE_MINOR to contain the major and minor release numbers for the library.
133 Applications can use these to include support for different releases of PCRE.
134 .P
135 The functions \fBpcre_compile()\fP, \fBpcre_compile2()\fP, \fBpcre_study()\fP,
136 and \fBpcre_exec()\fP are used for compiling and matching regular expressions
137 in a Perl-compatible manner. A sample program that demonstrates the simplest
138 way of using them is provided in the file called \fIpcredemo.c\fP in the source
139 distribution. The
140 .\" HREF
141 \fBpcresample\fP
142 .\"
143 documentation describes how to run it.
144 .P
145 A second matching function, \fBpcre_dfa_exec()\fP, which is not
146 Perl-compatible, is also provided. This uses a different algorithm for the
147 matching. The alternative algorithm finds all possible matches (at a given
148 point in the subject), and scans the subject just once. However, this algorithm
149 does not return captured substrings. A description of the two matching
150 algorithms and their advantages and disadvantages is given in the
151 .\" HREF
152 \fBpcrematching\fP
153 .\"
154 documentation.
155 .P
156 In addition to the main compiling and matching functions, there are convenience
157 functions for extracting captured substrings from a subject string that is
158 matched by \fBpcre_exec()\fP. They are:
159 .sp
160 \fBpcre_copy_substring()\fP
161 \fBpcre_copy_named_substring()\fP
162 \fBpcre_get_substring()\fP
163 \fBpcre_get_named_substring()\fP
164 \fBpcre_get_substring_list()\fP
165 \fBpcre_get_stringnumber()\fP
166 \fBpcre_get_stringtable_entries()\fP
167 .sp
168 \fBpcre_free_substring()\fP and \fBpcre_free_substring_list()\fP are also
169 provided, to free the memory used for extracted strings.
170 .P
171 The function \fBpcre_maketables()\fP is used to build a set of character tables
172 in the current locale for passing to \fBpcre_compile()\fP, \fBpcre_exec()\fP,
173 or \fBpcre_dfa_exec()\fP. This is an optional facility that is provided for
174 specialist use. Most commonly, no special tables are passed, in which case
175 internal tables that are generated when PCRE is built are used.
176 .P
177 The function \fBpcre_fullinfo()\fP is used to find out information about a
178 compiled pattern; \fBpcre_info()\fP is an obsolete version that returns only
179 some of the available information, but is retained for backwards compatibility.
180 The function \fBpcre_version()\fP returns a pointer to a string containing the
181 version of PCRE and its date of release.
182 .P
183 The function \fBpcre_refcount()\fP maintains a reference count in a data block
184 containing a compiled pattern. This is provided for the benefit of
185 object-oriented applications.
186 .P
187 The global variables \fBpcre_malloc\fP and \fBpcre_free\fP initially contain
188 the entry points of the standard \fBmalloc()\fP and \fBfree()\fP functions,
189 respectively. PCRE calls the memory management functions via these variables,
190 so a calling program can replace them if it wishes to intercept the calls. This
191 should be done before calling any PCRE functions.
192 .P
193 The global variables \fBpcre_stack_malloc\fP and \fBpcre_stack_free\fP are also
194 indirections to memory management functions. These special functions are used
195 only when PCRE is compiled to use the heap for remembering data, instead of
196 recursive function calls, when running the \fBpcre_exec()\fP function. See the
197 .\" HREF
198 \fBpcrebuild\fP
199 .\"
200 documentation for details of how to do this. It is a non-standard way of
201 building PCRE, for use in environments that have limited stacks. Because of the
202 greater use of memory management, it runs more slowly. Separate functions are
203 provided so that special-purpose external code can be used for this case. When
204 used, these functions are always called in a stack-like manner (last obtained,
205 first freed), and always for memory blocks of the same size. There is a
206 discussion about PCRE's stack usage in the
207 .\" HREF
208 \fBpcrestack\fP
209 .\"
210 documentation.
211 .P
212 The global variable \fBpcre_callout\fP initially contains NULL. It can be set
213 by the caller to a "callout" function, which PCRE will then call at specified
214 points during a matching operation. Details are given in the
215 .\" HREF
216 \fBpcrecallout\fP
217 .\"
218 documentation.
219 .
220 .
222 .rs
223 .sp
224 PCRE supports five different conventions for indicating line breaks in
225 strings: a single CR (carriage return) character, a single LF (linefeed)
226 character, the two-character sequence CRLF, any of the three preceding, or any
227 Unicode newline sequence. The Unicode newline sequences are the three just
228 mentioned, plus the single characters VT (vertical tab, U+000B), FF (formfeed,
229 U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS
230 (paragraph separator, U+2029).
231 .P
232 Each of the first three conventions is used by at least one operating system as
233 its standard newline sequence. When PCRE is built, a default can be specified.
234 The default default is LF, which is the Unix standard. When PCRE is run, the
235 default can be overridden, either when a pattern is compiled, or when it is
236 matched.
237 .P
238 In the PCRE documentation the word "newline" is used to mean "the character or
239 pair of characters that indicate a line break". The choice of newline
240 convention affects the handling of the dot, circumflex, and dollar
241 metacharacters, the handling of #-comments in /x mode, and, when CRLF is a
242 recognized line ending sequence, the match position advancement for a
243 non-anchored pattern. The choice of newline convention does not affect the
244 interpretation of the \en or \er escape sequences.
245 .
246 .
248 .rs
249 .sp
250 The PCRE functions can be used in multi-threading applications, with the
251 proviso that the memory management functions pointed to by \fBpcre_malloc\fP,
252 \fBpcre_free\fP, \fBpcre_stack_malloc\fP, and \fBpcre_stack_free\fP, and the
253 callout function pointed to by \fBpcre_callout\fP, are shared by all threads.
254 .P
255 The compiled form of a regular expression is not altered during matching, so
256 the same compiled pattern can safely be used by several threads at once.
257 .
258 .
260 .rs
261 .sp
262 The compiled form of a regular expression can be saved and re-used at a later
263 time, possibly by a different program, and even on a host other than the one on
264 which it was compiled. Details are given in the
265 .\" HREF
266 \fBpcreprecompile\fP
267 .\"
268 documentation. However, compiling a regular expression with one version of PCRE
269 for use with a different version is not guaranteed to work and may cause
270 crashes.
271 .
272 .
274 .rs
275 .sp
276 .B int pcre_config(int \fIwhat\fP, void *\fIwhere\fP);
277 .PP
278 The function \fBpcre_config()\fP makes it possible for a PCRE client to
279 discover which optional features have been compiled into the PCRE library. The
280 .\" HREF
281 \fBpcrebuild\fP
282 .\"
283 documentation has more details about these optional features.
284 .P
285 The first argument for \fBpcre_config()\fP is an integer, specifying which
286 information is required; the second argument is a pointer to a variable into
287 which the information is placed. The following information is available:
288 .sp
290 .sp
291 The output is an integer that is set to one if UTF-8 support is available;
292 otherwise it is set to zero.
293 .sp
295 .sp
296 The output is an integer that is set to one if support for Unicode character
297 properties is available; otherwise it is set to zero.
298 .sp
300 .sp
301 The output is an integer whose value specifies the default character sequence
302 that is recognized as meaning "newline". The four values that are supported
303 are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF, and -1 for ANY. The
304 default should normally be the standard sequence for your operating system.
305 .sp
307 .sp
308 The output is an integer that contains the number of bytes used for internal
309 linkage in compiled regular expressions. The value is 2, 3, or 4. Larger values
310 allow larger regular expressions to be compiled, at the expense of slower
311 matching. The default value of 2 is sufficient for all but the most massive
312 patterns, since it allows the compiled pattern to be up to 64K in size.
313 .sp
315 .sp
316 The output is an integer that contains the threshold above which the POSIX
317 interface uses \fBmalloc()\fP for output vectors. Further details are given in
318 the
319 .\" HREF
320 \fBpcreposix\fP
321 .\"
322 documentation.
323 .sp
325 .sp
326 The output is an integer that gives the default limit for the number of
327 internal matching function calls in a \fBpcre_exec()\fP execution. Further
328 details are given with \fBpcre_exec()\fP below.
329 .sp
331 .sp
332 The output is an integer that gives the default limit for the depth of
333 recursion when calling the internal matching function in a \fBpcre_exec()\fP
334 execution. Further details are given with \fBpcre_exec()\fP below.
335 .sp
337 .sp
338 The output is an integer that is set to one if internal recursion when running
339 \fBpcre_exec()\fP is implemented by recursive function calls that use the stack
340 to remember their state. This is the usual way that PCRE is compiled. The
341 output is zero if PCRE was compiled to use blocks of data on the heap instead
342 of recursive function calls. In this case, \fBpcre_stack_malloc\fP and
343 \fBpcre_stack_free\fP are called to manage memory blocks on the heap, thus
344 avoiding the use of the stack.
345 .
346 .
348 .rs
349 .sp
350 .B pcre *pcre_compile(const char *\fIpattern\fP, int \fIoptions\fP,
351 .ti +5n
352 .B const char **\fIerrptr\fP, int *\fIerroffset\fP,
353 .ti +5n
354 .B const unsigned char *\fItableptr\fP);
355 .sp
356 .B pcre *pcre_compile2(const char *\fIpattern\fP, int \fIoptions\fP,
357 .ti +5n
358 .B int *\fIerrorcodeptr\fP,
359 .ti +5n
360 .B const char **\fIerrptr\fP, int *\fIerroffset\fP,
361 .ti +5n
362 .B const unsigned char *\fItableptr\fP);
363 .P
364 Either of the functions \fBpcre_compile()\fP or \fBpcre_compile2()\fP can be
365 called to compile a pattern into an internal form. The only difference between
366 the two interfaces is that \fBpcre_compile2()\fP has an additional argument,
367 \fIerrorcodeptr\fP, via which a numerical error code can be returned.
368 .P
369 The pattern is a C string terminated by a binary zero, and is passed in the
370 \fIpattern\fP argument. A pointer to a single block of memory that is obtained
371 via \fBpcre_malloc\fP is returned. This contains the compiled code and related
372 data. The \fBpcre\fP type is defined for the returned block; this is a typedef
373 for a structure whose contents are not externally defined. It is up to the
374 caller to free the memory (via \fBpcre_free\fP) when it is no longer required.
375 .P
376 Although the compiled code of a PCRE regex is relocatable, that is, it does not
377 depend on memory location, the complete \fBpcre\fP data block is not
378 fully relocatable, because it may contain a copy of the \fItableptr\fP
379 argument, which is an address (see below).
380 .P
381 The \fIoptions\fP argument contains various bit settings that affect the
382 compilation. It should be zero if no options are required. The available
383 options are described below. Some of them, in particular, those that are
384 compatible with Perl, can also be set and unset from within the pattern (see
385 the detailed description in the
386 .\" HREF
387 \fBpcrepattern\fP
388 .\"
389 documentation). For these options, the contents of the \fIoptions\fP argument
390 specifies their initial settings at the start of compilation and execution. The
391 PCRE_ANCHORED and PCRE_NEWLINE_\fIxxx\fP options can be set at the time of
392 matching as well as at compile time.
393 .P
394 If \fIerrptr\fP is NULL, \fBpcre_compile()\fP returns NULL immediately.
395 Otherwise, if compilation of a pattern fails, \fBpcre_compile()\fP returns
396 NULL, and sets the variable pointed to by \fIerrptr\fP to point to a textual
397 error message. This is a static string that is part of the library. You must
398 not try to free it. The offset from the start of the pattern to the character
399 where the error was discovered is placed in the variable pointed to by
400 \fIerroffset\fP, which must not be NULL. If it is, an immediate error is given.
401 .P
402 If \fBpcre_compile2()\fP is used instead of \fBpcre_compile()\fP, and the
403 \fIerrorcodeptr\fP argument is not NULL, a non-zero error code number is
404 returned via this argument in the event of an error. This is in addition to the
405 textual error message. Error codes and messages are listed below.
406 .P
407 If the final argument, \fItableptr\fP, is NULL, PCRE uses a default set of
408 character tables that are built when PCRE is compiled, using the default C
409 locale. Otherwise, \fItableptr\fP must be an address that is the result of a
410 call to \fBpcre_maketables()\fP. This value is stored with the compiled
411 pattern, and used again by \fBpcre_exec()\fP, unless another table pointer is
412 passed to it. For more discussion, see the section on locale support below.
413 .P
414 This code fragment shows a typical straightforward call to \fBpcre_compile()\fP:
415 .sp
416 pcre *re;
417 const char *error;
418 int erroffset;
419 re = pcre_compile(
420 "^A.*Z", /* the pattern */
421 0, /* default options */
422 &error, /* for error message */
423 &erroffset, /* for error offset */
424 NULL); /* use default character tables */
425 .sp
426 The following names for option bits are defined in the \fBpcre.h\fP header
427 file:
428 .sp
430 .sp
431 If this bit is set, the pattern is forced to be "anchored", that is, it is
432 constrained to match only at the first matching point in the string that is
433 being searched (the "subject string"). This effect can also be achieved by
434 appropriate constructs in the pattern itself, which is the only way to do it in
435 Perl.
436 .sp
438 .sp
439 If this bit is set, \fBpcre_compile()\fP automatically inserts callout items,
440 all with number 255, before each pattern item. For discussion of the callout
441 facility, see the
442 .\" HREF
443 \fBpcrecallout\fP
444 .\"
445 documentation.
446 .sp
448 .sp
449 If this bit is set, letters in the pattern match both upper and lower case
450 letters. It is equivalent to Perl's /i option, and it can be changed within a
451 pattern by a (?i) option setting. In UTF-8 mode, PCRE always understands the
452 concept of case for characters whose values are less than 128, so caseless
453 matching is always possible. For characters with higher values, the concept of
454 case is supported if PCRE is compiled with Unicode property support, but not
455 otherwise. If you want to use caseless matching for characters 128 and above,
456 you must ensure that PCRE is compiled with Unicode property support as well as
457 with UTF-8 support.
458 .sp
460 .sp
461 If this bit is set, a dollar metacharacter in the pattern matches only at the
462 end of the subject string. Without this option, a dollar also matches
463 immediately before a newline at the end of the string (but not before any other
464 newlines). The PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is set.
465 There is no equivalent to this option in Perl, and no way to set it within a
466 pattern.
467 .sp
469 .sp
470 If this bit is set, a dot metacharater in the pattern matches all characters,
471 including those that indicate newline. Without it, a dot does not match when
472 the current position is at a newline. This option is equivalent to Perl's /s
473 option, and it can be changed within a pattern by a (?s) option setting. A
474 negative class such as [^a] always matches newline characters, independent of
475 the setting of this option.
476 .sp
478 .sp
479 If this bit is set, names used to identify capturing subpatterns need not be
480 unique. This can be helpful for certain types of pattern when it is known that
481 only one instance of the named subpattern can ever be matched. There are more
482 details of named subpatterns below; see also the
483 .\" HREF
484 \fBpcrepattern\fP
485 .\"
486 documentation.
487 .sp
489 .sp
490 If this bit is set, whitespace data characters in the pattern are totally
491 ignored except when escaped or inside a character class. Whitespace does not
492 include the VT character (code 11). In addition, characters between an
493 unescaped # outside a character class and the next newline, inclusive, are also
494 ignored. This is equivalent to Perl's /x option, and it can be changed within a
495 pattern by a (?x) option setting.
496 .P
497 This option makes it possible to include comments inside complicated patterns.
498 Note, however, that this applies only to data characters. Whitespace characters
499 may never appear within special character sequences in a pattern, for example
500 within the sequence (?( which introduces a conditional subpattern.
501 .sp
503 .sp
504 This option was invented in order to turn on additional functionality of PCRE
505 that is incompatible with Perl, but it is currently of very little use. When
506 set, any backslash in a pattern that is followed by a letter that has no
507 special meaning causes an error, thus reserving these combinations for future
508 expansion. By default, as in Perl, a backslash followed by a letter with no
509 special meaning is treated as a literal. (Perl can, however, be persuaded to
510 give a warning for this.) There are at present no other features controlled by
511 this option. It can also be set by a (?X) option setting within a pattern.
512 .sp
514 .sp
515 If this option is set, an unanchored pattern is required to match before or at
516 the first newline in the subject string, though the matched text may continue
517 over the newline.
518 .sp
520 .sp
521 By default, PCRE treats the subject string as consisting of a single line of
522 characters (even if it actually contains newlines). The "start of line"
523 metacharacter (^) matches only at the start of the string, while the "end of
524 line" metacharacter ($) matches only at the end of the string, or before a
525 terminating newline (unless PCRE_DOLLAR_ENDONLY is set). This is the same as
526 Perl.
527 .P
528 When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs
529 match immediately following or immediately before internal newlines in the
530 subject string, respectively, as well as at the very start and end. This is
531 equivalent to Perl's /m option, and it can be changed within a pattern by a
532 (?m) option setting. If there are no newlines in a subject string, or no
533 occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no effect.
534 .sp
540 .sp
541 These options override the default newline definition that was chosen when PCRE
542 was built. Setting the first or the second specifies that a newline is
543 indicated by a single character (CR or LF, respectively). Setting
544 PCRE_NEWLINE_CRLF specifies that a newline is indicated by the two-character
545 CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies that any of the three
546 preceding sequences should be recognized. Setting PCRE_NEWLINE_ANY specifies
547 that any Unicode newline sequence should be recognized. The Unicode newline
548 sequences are the three just mentioned, plus the single characters VT (vertical
549 tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS (line
550 separator, U+2028), and PS (paragraph separator, U+2029). The last two are
551 recognized only in UTF-8 mode.
552 .P
553 The newline setting in the options word uses three bits that are treated
554 as a number, giving eight possibilities. Currently only six are used (default
555 plus the five values above). This means that if you set more than one newline
556 option, the combination may or may not be sensible. For example,
558 other combinations may yield unused numbers and cause an error.
559 .P
560 The only time that a line break is specially recognized when compiling a
561 pattern is if PCRE_EXTENDED is set, and an unescaped # outside a character
562 class is encountered. This indicates a comment that lasts until after the next
563 line break sequence. In other circumstances, line break sequences are treated
564 as literal data, except that in PCRE_EXTENDED mode, both CR and LF are treated
565 as whitespace characters and are therefore ignored.
566 .P
567 The newline option that is set at compile time becomes the default that is used
568 for \fBpcre_exec()\fP and \fBpcre_dfa_exec()\fP, but it can be overridden.
569 .sp
571 .sp
572 If this option is set, it disables the use of numbered capturing parentheses in
573 the pattern. Any opening parenthesis that is not followed by ? behaves as if it
574 were followed by ?: but named parentheses can still be used for capturing (and
575 they acquire numbers in the usual way). There is no equivalent of this option
576 in Perl.
577 .sp
579 .sp
580 This option inverts the "greediness" of the quantifiers so that they are not
581 greedy by default, but become greedy if followed by "?". It is not compatible
582 with Perl. It can also be set by a (?U) option setting within the pattern.
583 .sp
585 .sp
586 This option causes PCRE to regard both the pattern and the subject as strings
587 of UTF-8 characters instead of single-byte character strings. However, it is
588 available only when PCRE is built to include UTF-8 support. If not, the use
589 of this option provokes an error. Details of how this option changes the
590 behaviour of PCRE are given in the
591 .\" HTML <a href="pcre.html#utf8support">
592 .\" </a>
593 section on UTF-8 support
594 .\"
595 in the main
596 .\" HREF
597 \fBpcre\fP
598 .\"
599 page.
600 .sp
602 .sp
603 When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
604 automatically checked. If an invalid UTF-8 sequence of bytes is found,
605 \fBpcre_compile()\fP returns an error. If you already know that your pattern is
606 valid, and you want to skip this check for performance reasons, you can set the
607 PCRE_NO_UTF8_CHECK option. When it is set, the effect of passing an invalid
608 UTF-8 string as a pattern is undefined. It may cause your program to crash.
609 Note that this option can also be passed to \fBpcre_exec()\fP and
610 \fBpcre_dfa_exec()\fP, to suppress the UTF-8 validity checking of subject
611 strings.
612 .
613 .
615 .rs
616 .sp
617 The following table lists the error codes than may be returned by
618 \fBpcre_compile2()\fP, along with the error messages that may be returned by
619 both compiling functions. As PCRE has developed, some error codes have fallen
620 out of use. To avoid confusion, they have not been re-used.
621 .sp
622 0 no error
623 1 \e at end of pattern
624 2 \ec at end of pattern
625 3 unrecognized character follows \e
626 4 numbers out of order in {} quantifier
627 5 number too big in {} quantifier
628 6 missing terminating ] for character class
629 7 invalid escape sequence in character class
630 8 range out of order in character class
631 9 nothing to repeat
632 10 [this code is not in use]
633 11 internal error: unexpected repeat
634 12 unrecognized character after (?
635 13 POSIX named classes are supported only within a class
636 14 missing )
637 15 reference to non-existent subpattern
638 16 erroffset passed as NULL
639 17 unknown option bit(s) set
640 18 missing ) after comment
641 19 [this code is not in use]
642 20 regular expression too large
643 21 failed to get memory
644 22 unmatched parentheses
645 23 internal error: code overflow
646 24 unrecognized character after (?<
647 25 lookbehind assertion is not fixed length
648 26 malformed number or name after (?(
649 27 conditional group contains more than two branches
650 28 assertion expected after (?(
651 29 (?R or (?digits must be followed by )
652 30 unknown POSIX class name
653 31 POSIX collating elements are not supported
654 32 this version of PCRE is not compiled with PCRE_UTF8 support
655 33 [this code is not in use]
656 34 character value in \ex{...} sequence is too large
657 35 invalid condition (?(0)
658 36 \eC not allowed in lookbehind assertion
659 37 PCRE does not support \eL, \el, \eN, \eU, or \eu
660 38 number after (?C is > 255
661 39 closing ) for (?C expected
662 40 recursive call could loop indefinitely
663 41 unrecognized character after (?P
664 42 syntax error in subpattern name (missing terminator)
665 43 two named subpatterns have the same name
666 44 invalid UTF-8 string
667 45 support for \eP, \ep, and \eX has not been compiled
668 46 malformed \eP or \ep sequence
669 47 unknown property name after \eP or \ep
670 48 subpattern name is too long (maximum 32 characters)
671 49 too many named subpatterns (maximum 10,000)
672 50 repeated subpattern is too long
673 51 octal value is greater than \e377 (not in UTF-8 mode)
674 52 internal error: overran compiling workspace
675 53 internal error: previously-checked referenced subpattern not found
676 54 DEFINE group contains more than one branch
677 55 repeating a DEFINE group is not allowed
678 56 inconsistent NEWLINE options"
679 .
680 .
682 .rs
683 .sp
684 .B pcre_extra *pcre_study(const pcre *\fIcode\fP, int \fIoptions\fP
685 .ti +5n
686 .B const char **\fIerrptr\fP);
687 .PP
688 If a compiled pattern is going to be used several times, it is worth spending
689 more time analyzing it in order to speed up the time taken for matching. The
690 function \fBpcre_study()\fP takes a pointer to a compiled pattern as its first
691 argument. If studying the pattern produces additional information that will
692 help speed up matching, \fBpcre_study()\fP returns a pointer to a
693 \fBpcre_extra\fP block, in which the \fIstudy_data\fP field points to the
694 results of the study.
695 .P
696 The returned value from \fBpcre_study()\fP can be passed directly to
697 \fBpcre_exec()\fP. However, a \fBpcre_extra\fP block also contains other
698 fields that can be set by the caller before the block is passed; these are
699 described
700 .\" HTML <a href="#extradata">
701 .\" </a>
702 below
703 .\"
704 in the section on matching a pattern.
705 .P
706 If studying the pattern does not produce any additional information
707 \fBpcre_study()\fP returns NULL. In that circumstance, if the calling program
708 wants to pass any of the other fields to \fBpcre_exec()\fP, it must set up its
709 own \fBpcre_extra\fP block.
710 .P
711 The second argument of \fBpcre_study()\fP contains option bits. At present, no
712 options are defined, and this argument should always be zero.
713 .P
714 The third argument for \fBpcre_study()\fP is a pointer for an error message. If
715 studying succeeds (even if no data is returned), the variable it points to is
716 set to NULL. Otherwise it is set to point to a textual error message. This is a
717 static string that is part of the library. You must not try to free it. You
718 should test the error pointer for NULL after calling \fBpcre_study()\fP, to be
719 sure that it has run successfully.
720 .P
721 This is a typical call to \fBpcre_study\fP():
722 .sp
723 pcre_extra *pe;
724 pe = pcre_study(
725 re, /* result of pcre_compile() */
726 0, /* no options exist */
727 &error); /* set to NULL or points to a message */
728 .sp
729 At present, studying a pattern is useful only for non-anchored patterns that do
730 not have a single fixed starting character. A bitmap of possible starting
731 bytes is created.
732 .
733 .
734 .\" HTML <a name="localesupport"></a>
736 .rs
737 .sp
738 PCRE handles caseless matching, and determines whether characters are letters,
739 digits, or whatever, by reference to a set of tables, indexed by character
740 value. When running in UTF-8 mode, this applies only to characters with codes
741 less than 128. Higher-valued codes never match escapes such as \ew or \ed, but
742 can be tested with \ep if PCRE is built with Unicode character property
743 support. The use of locales with Unicode is discouraged. If you are handling
744 characters with codes greater than 128, you should either use UTF-8 and
745 Unicode, or use locales, but not try to mix the two.
746 .P
747 PCRE contains an internal set of tables that are used when the final argument
748 of \fBpcre_compile()\fP is NULL. These are sufficient for many applications.
749 Normally, the internal tables recognize only ASCII characters. However, when
750 PCRE is built, it is possible to cause the internal tables to be rebuilt in the
751 default "C" locale of the local system, which may cause them to be different.
752 .P
753 The internal tables can always be overridden by tables supplied by the
754 application that calls PCRE. These may be created in a different locale from
755 the default. As more and more applications change to using Unicode, the need
756 for this locale support is expected to die away.
757 .P
758 External tables are built by calling the \fBpcre_maketables()\fP function,
759 which has no arguments, in the relevant locale. The result can then be passed
760 to \fBpcre_compile()\fP or \fBpcre_exec()\fP as often as necessary. For
761 example, to build and use tables that are appropriate for the French locale
762 (where accented characters with values greater than 128 are treated as letters),
763 the following code could be used:
764 .sp
765 setlocale(LC_CTYPE, "fr_FR");
766 tables = pcre_maketables();
767 re = pcre_compile(..., tables);
768 .sp
769 The locale name "fr_FR" is used on Linux and other Unix-like systems; if you
770 are using Windows, the name for the French locale is "french".
771 .P
772 When \fBpcre_maketables()\fP runs, the tables are built in memory that is
773 obtained via \fBpcre_malloc\fP. It is the caller's responsibility to ensure
774 that the memory containing the tables remains available for as long as it is
775 needed.
776 .P
777 The pointer that is passed to \fBpcre_compile()\fP is saved with the compiled
778 pattern, and the same tables are used via this pointer by \fBpcre_study()\fP
779 and normally also by \fBpcre_exec()\fP. Thus, by default, for any single
780 pattern, compilation, studying and matching all happen in the same locale, but
781 different patterns can be compiled in different locales.
782 .P
783 It is possible to pass a table pointer or NULL (indicating the use of the
784 internal tables) to \fBpcre_exec()\fP. Although not intended for this purpose,
785 this facility could be used to match a pattern in a different locale from the
786 one in which it was compiled. Passing table pointers at run time is discussed
787 below in the section on matching a pattern.
788 .
789 .
791 .rs
792 .sp
793 .B int pcre_fullinfo(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
794 .ti +5n
795 .B int \fIwhat\fP, void *\fIwhere\fP);
796 .PP
797 The \fBpcre_fullinfo()\fP function returns information about a compiled
798 pattern. It replaces the obsolete \fBpcre_info()\fP function, which is
799 nevertheless retained for backwards compability (and is documented below).
800 .P
801 The first argument for \fBpcre_fullinfo()\fP is a pointer to the compiled
802 pattern. The second argument is the result of \fBpcre_study()\fP, or NULL if
803 the pattern was not studied. The third argument specifies which piece of
804 information is required, and the fourth argument is a pointer to a variable
805 to receive the data. The yield of the function is zero for success, or one of
806 the following negative numbers:
807 .sp
808 PCRE_ERROR_NULL the argument \fIcode\fP was NULL
809 the argument \fIwhere\fP was NULL
810 PCRE_ERROR_BADMAGIC the "magic number" was not found
811 PCRE_ERROR_BADOPTION the value of \fIwhat\fP was invalid
812 .sp
813 The "magic number" is placed at the start of each compiled pattern as an simple
814 check against passing an arbitrary memory pointer. Here is a typical call of
815 \fBpcre_fullinfo()\fP, to obtain the length of the compiled pattern:
816 .sp
817 int rc;
818 size_t length;
819 rc = pcre_fullinfo(
820 re, /* result of pcre_compile() */
821 pe, /* result of pcre_study(), or NULL */
822 PCRE_INFO_SIZE, /* what is required */
823 &length); /* where to put the data */
824 .sp
825 The possible values for the third argument are defined in \fBpcre.h\fP, and are
826 as follows:
827 .sp
829 .sp
830 Return the number of the highest back reference in the pattern. The fourth
831 argument should point to an \fBint\fP variable. Zero is returned if there are
832 no back references.
833 .sp
835 .sp
836 Return the number of capturing subpatterns in the pattern. The fourth argument
837 should point to an \fBint\fP variable.
838 .sp
840 .sp
841 Return a pointer to the internal default character tables within PCRE. The
842 fourth argument should point to an \fBunsigned char *\fP variable. This
843 information call is provided for internal use by the \fBpcre_study()\fP
844 function. External callers can cause PCRE to use its internal tables by passing
845 a NULL table pointer.
846 .sp
848 .sp
849 Return information about the first byte of any matched string, for a
850 non-anchored pattern. The fourth argument should point to an \fBint\fP
851 variable. (This option used to be called PCRE_INFO_FIRSTCHAR; the old name is
852 still recognized for backwards compatibility.)
853 .P
854 If there is a fixed first byte, for example, from a pattern such as
855 (cat|cow|coyote), its value is returned. Otherwise, if either
856 .sp
857 (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
858 starts with "^", or
859 .sp
860 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
861 (if it were set, the pattern would be anchored),
862 .sp
863 -1 is returned, indicating that the pattern matches only at the start of a
864 subject string or after any newline within the string. Otherwise -2 is
865 returned. For anchored patterns, -2 is returned.
866 .sp
868 .sp
869 If the pattern was studied, and this resulted in the construction of a 256-bit
870 table indicating a fixed set of bytes for the first byte in any matching
871 string, a pointer to the table is returned. Otherwise NULL is returned. The
872 fourth argument should point to an \fBunsigned char *\fP variable.
873 .sp
875 .sp
876 Return the value of the rightmost literal byte that must exist in any matched
877 string, other than at its start, if such a byte has been recorded. The fourth
878 argument should point to an \fBint\fP variable. If there is no such byte, -1 is
879 returned. For anchored patterns, a last literal byte is recorded only if it
880 follows something of variable length. For example, for the pattern
881 /^a\ed+z\ed+/ the returned value is "z", but for /^a\edz\ed/ the returned value
882 is -1.
883 .sp
887 .sp
888 PCRE supports the use of named as well as numbered capturing parentheses. The
889 names are just an additional way of identifying the parentheses, which still
890 acquire numbers. Several convenience functions such as
891 \fBpcre_get_named_substring()\fP are provided for extracting captured
892 substrings by name. It is also possible to extract the data directly, by first
893 converting the name to a number in order to access the correct pointers in the
894 output vector (described with \fBpcre_exec()\fP below). To do the conversion,
895 you need to use the name-to-number map, which is described by these three
896 values.
897 .P
898 The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives
899 the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each
900 entry; both of these return an \fBint\fP value. The entry size depends on the
901 length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first
902 entry of the table (a pointer to \fBchar\fP). The first two bytes of each entry
903 are the number of the capturing parenthesis, most significant byte first. The
904 rest of the entry is the corresponding name, zero terminated. The names are in
905 alphabetical order. When PCRE_DUPNAMES is set, duplicate names are in order of
906 their parentheses numbers. For example, consider the following pattern (assume
907 PCRE_EXTENDED is set, so white space - including newlines - is ignored):
908 .sp
909 .\" JOIN
910 (?<date> (?<year>(\ed\ed)?\ed\ed) -
911 (?<month>\ed\ed) - (?<day>\ed\ed) )
912 .sp
913 There are four named subpatterns, so the table has four entries, and each entry
914 in the table is eight bytes long. The table is as follows, with non-printing
915 bytes shows in hexadecimal, and undefined bytes shown as ??:
916 .sp
917 00 01 d a t e 00 ??
918 00 05 d a y 00 ?? ??
919 00 04 m o n t h 00
920 00 02 y e a r 00 ??
921 .sp
922 When writing code to extract data from named subpatterns using the
923 name-to-number map, remember that the length of the entries is likely to be
924 different for each compiled pattern.
925 .sp
927 .sp
928 Return a copy of the options with which the pattern was compiled. The fourth
929 argument should point to an \fBunsigned long int\fP variable. These option bits
930 are those specified in the call to \fBpcre_compile()\fP, modified by any
931 top-level option settings within the pattern itself.
932 .P
933 A pattern is automatically anchored by PCRE if all of its top-level
934 alternatives begin with one of the following:
935 .sp
936 ^ unless PCRE_MULTILINE is set
937 \eA always
938 \eG always
939 .\" JOIN
940 .* if PCRE_DOTALL is set and there are no back
941 references to the subpattern in which .* appears
942 .sp
943 For such patterns, the PCRE_ANCHORED bit is set in the options returned by
944 \fBpcre_fullinfo()\fP.
945 .sp
947 .sp
948 Return the size of the compiled pattern, that is, the value that was passed as
949 the argument to \fBpcre_malloc()\fP when PCRE was getting memory in which to
950 place the compiled data. The fourth argument should point to a \fBsize_t\fP
951 variable.
952 .sp
954 .sp
955 Return the size of the data block pointed to by the \fIstudy_data\fP field in
956 a \fBpcre_extra\fP block. That is, it is the value that was passed to
957 \fBpcre_malloc()\fP when PCRE was getting memory into which to place the data
958 created by \fBpcre_study()\fP. The fourth argument should point to a
959 \fBsize_t\fP variable.
960 .
961 .
963 .rs
964 .sp
965 .B int pcre_info(const pcre *\fIcode\fP, int *\fIoptptr\fP, int
966 .B *\fIfirstcharptr\fP);
967 .PP
968 The \fBpcre_info()\fP function is now obsolete because its interface is too
969 restrictive to return all the available data about a compiled pattern. New
970 programs should use \fBpcre_fullinfo()\fP instead. The yield of
971 \fBpcre_info()\fP is the number of capturing subpatterns, or one of the
972 following negative numbers:
973 .sp
974 PCRE_ERROR_NULL the argument \fIcode\fP was NULL
975 PCRE_ERROR_BADMAGIC the "magic number" was not found
976 .sp
977 If the \fIoptptr\fP argument is not NULL, a copy of the options with which the
978 pattern was compiled is placed in the integer it points to (see
980 .P
981 If the pattern is not anchored and the \fIfirstcharptr\fP argument is not NULL,
982 it is used to pass back information about the first character of any matched
983 string (see PCRE_INFO_FIRSTBYTE above).
984 .
985 .
987 .rs
988 .sp
989 .B int pcre_refcount(pcre *\fIcode\fP, int \fIadjust\fP);
990 .PP
991 The \fBpcre_refcount()\fP function is used to maintain a reference count in the
992 data block that contains a compiled pattern. It is provided for the benefit of
993 applications that operate in an object-oriented manner, where different parts
994 of the application may be using the same compiled pattern, but you want to free
995 the block when they are all done.
996 .P
997 When a pattern is compiled, the reference count field is initialized to zero.
998 It is changed only by calling this function, whose action is to add the
999 \fIadjust\fP value (which may be positive or negative) to it. The yield of the
1000 function is the new value. However, the value of the count is constrained to
1001 lie between 0 and 65535, inclusive. If the new value is outside these limits,
1002 it is forced to the appropriate limit value.
1003 .P
1004 Except when it is zero, the reference count is not correctly preserved if a
1005 pattern is compiled on one host and then transferred to a host whose byte-order
1006 is different. (This seems a highly unlikely scenario.)
1007 .
1008 .
1010 .rs
1011 .sp
1012 .B int pcre_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
1013 .ti +5n
1014 .B "const char *\fIsubject\fP," int \fIlength\fP, int \fIstartoffset\fP,
1015 .ti +5n
1016 .B int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP);
1017 .P
1018 The function \fBpcre_exec()\fP is called to match a subject string against a
1019 compiled pattern, which is passed in the \fIcode\fP argument. If the
1020 pattern has been studied, the result of the study should be passed in the
1021 \fIextra\fP argument. This function is the main matching facility of the
1022 library, and it operates in a Perl-like manner. For specialist use there is
1023 also an alternative matching function, which is described
1024 .\" HTML <a href="#dfamatch">
1025 .\" </a>
1026 below
1027 .\"
1028 in the section about the \fBpcre_dfa_exec()\fP function.
1029 .P
1030 In most applications, the pattern will have been compiled (and optionally
1031 studied) in the same process that calls \fBpcre_exec()\fP. However, it is
1032 possible to save compiled patterns and study data, and then use them later
1033 in different processes, possibly even on different hosts. For a discussion
1034 about this, see the
1035 .\" HREF
1036 \fBpcreprecompile\fP
1037 .\"
1038 documentation.
1039 .P
1040 Here is an example of a simple call to \fBpcre_exec()\fP:
1041 .sp
1042 int rc;
1043 int ovector[30];
1044 rc = pcre_exec(
1045 re, /* result of pcre_compile() */
1046 NULL, /* we didn't study the pattern */
1047 "some string", /* the subject string */
1048 11, /* the length of the subject string */
1049 0, /* start at offset 0 in the subject */
1050 0, /* default options */
1051 ovector, /* vector of integers for substring information */
1052 30); /* number of elements (NOT size in bytes) */
1053 .
1054 .\" HTML <a name="extradata"></a>
1055 .SS "Extra data for \fBpcre_exec()\fR"
1056 .rs
1057 .sp
1058 If the \fIextra\fP argument is not NULL, it must point to a \fBpcre_extra\fP
1059 data block. The \fBpcre_study()\fP function returns such a block (when it
1060 doesn't return NULL), but you can also create one for yourself, and pass
1061 additional information in it. The \fBpcre_extra\fP block contains the following
1062 fields (not necessarily in this order):
1063 .sp
1064 unsigned long int \fIflags\fP;
1065 void *\fIstudy_data\fP;
1066 unsigned long int \fImatch_limit\fP;
1067 unsigned long int \fImatch_limit_recursion\fP;
1068 void *\fIcallout_data\fP;
1069 const unsigned char *\fItables\fP;
1070 .sp
1071 The \fIflags\fP field is a bitmap that specifies which of the other fields
1072 are set. The flag bits are:
1073 .sp
1079 .sp
1080 Other flag bits should be set to zero. The \fIstudy_data\fP field is set in the
1081 \fBpcre_extra\fP block that is returned by \fBpcre_study()\fP, together with
1082 the appropriate flag bit. You should not set this yourself, but you may add to
1083 the block by setting the other fields and their corresponding flag bits.
1084 .P
1085 The \fImatch_limit\fP field provides a means of preventing PCRE from using up a
1086 vast amount of resources when running patterns that are not going to match,
1087 but which have a very large number of possibilities in their search trees. The
1088 classic example is the use of nested unlimited repeats.
1089 .P
1090 Internally, PCRE uses a function called \fBmatch()\fP which it calls repeatedly
1091 (sometimes recursively). The limit set by \fImatch_limit\fP is imposed on the
1092 number of times this function is called during a match, which has the effect of
1093 limiting the amount of backtracking that can take place. For patterns that are
1094 not anchored, the count restarts from zero for each position in the subject
1095 string.
1096 .P
1097 The default value for the limit can be set when PCRE is built; the default
1098 default is 10 million, which handles all but the most extreme cases. You can
1099 override the default by suppling \fBpcre_exec()\fP with a \fBpcre_extra\fP
1100 block in which \fImatch_limit\fP is set, and PCRE_EXTRA_MATCH_LIMIT is set in
1101 the \fIflags\fP field. If the limit is exceeded, \fBpcre_exec()\fP returns
1103 .P
1104 The \fImatch_limit_recursion\fP field is similar to \fImatch_limit\fP, but
1105 instead of limiting the total number of times that \fBmatch()\fP is called, it
1106 limits the depth of recursion. The recursion depth is a smaller number than the
1107 total number of calls, because not all calls to \fBmatch()\fP are recursive.
1108 This limit is of use only if it is set smaller than \fImatch_limit\fP.
1109 .P
1110 Limiting the recursion depth limits the amount of stack that can be used, or,
1111 when PCRE has been compiled to use memory on the heap instead of the stack, the
1112 amount of heap memory that can be used.
1113 .P
1114 The default value for \fImatch_limit_recursion\fP can be set when PCRE is
1115 built; the default default is the same value as the default for
1116 \fImatch_limit\fP. You can override the default by suppling \fBpcre_exec()\fP
1117 with a \fBpcre_extra\fP block in which \fImatch_limit_recursion\fP is set, and
1118 PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the \fIflags\fP field. If the limit
1119 is exceeded, \fBpcre_exec()\fP returns PCRE_ERROR_RECURSIONLIMIT.
1120 .P
1121 The \fIpcre_callout\fP field is used in conjunction with the "callout" feature,
1122 which is described in the
1123 .\" HREF
1124 \fBpcrecallout\fP
1125 .\"
1126 documentation.
1127 .P
1128 The \fItables\fP field is used to pass a character tables pointer to
1129 \fBpcre_exec()\fP; this overrides the value that is stored with the compiled
1130 pattern. A non-NULL value is stored with the compiled pattern only if custom
1131 tables were supplied to \fBpcre_compile()\fP via its \fItableptr\fP argument.
1132 If NULL is passed to \fBpcre_exec()\fP using this mechanism, it forces PCRE's
1133 internal tables to be used. This facility is helpful when re-using patterns
1134 that have been saved after compiling with an external set of tables, because
1135 the external tables might be at a different address when \fBpcre_exec()\fP is
1136 called. See the
1137 .\" HREF
1138 \fBpcreprecompile\fP
1139 .\"
1140 documentation for a discussion of saving compiled patterns for later use.
1141 .
1142 .SS "Option bits for \fBpcre_exec()\fP"
1143 .rs
1144 .sp
1145 The unused bits of the \fIoptions\fP argument for \fBpcre_exec()\fP must be
1146 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_\fIxxx\fP,
1148 .sp
1150 .sp
1151 The PCRE_ANCHORED option limits \fBpcre_exec()\fP to matching at the first
1152 matching position. If a pattern was compiled with PCRE_ANCHORED, or turned out
1153 to be anchored by virtue of its contents, it cannot be made unachored at
1154 matching time.
1155 .sp
1161 .sp
1162 These options override the newline definition that was chosen or defaulted when
1163 the pattern was compiled. For details, see the description of
1164 \fBpcre_compile()\fP above. During matching, the newline choice affects the
1165 behaviour of the dot, circumflex, and dollar metacharacters. It may also alter
1166 the way the match position is advanced after a match failure for an unanchored
1168 set, and a match attempt fails when the current position is at a CRLF sequence,
1169 the match position is advanced by two characters instead of one, in other
1170 words, to after the CRLF.
1171 .sp
1173 .sp
1174 This option specifies that first character of the subject string is not the
1175 beginning of a line, so the circumflex metacharacter should not match before
1176 it. Setting this without PCRE_MULTILINE (at compile time) causes circumflex
1177 never to match. This option affects only the behaviour of the circumflex
1178 metacharacter. It does not affect \eA.
1179 .sp
1181 .sp
1182 This option specifies that the end of the subject string is not the end of a
1183 line, so the dollar metacharacter should not match it nor (except in multiline
1184 mode) a newline immediately before it. Setting this without PCRE_MULTILINE (at
1185 compile time) causes dollar never to match. This option affects only the
1186 behaviour of the dollar metacharacter. It does not affect \eZ or \ez.
1187 .sp
1189 .sp
1190 An empty string is not considered to be a valid match if this option is set. If
1191 there are alternatives in the pattern, they are tried. If all the alternatives
1192 match the empty string, the entire match fails. For example, if the pattern
1193 .sp
1194 a?b?
1195 .sp
1196 is applied to a string not beginning with "a" or "b", it matches the empty
1197 string at the start of the subject. With PCRE_NOTEMPTY set, this match is not
1198 valid, so PCRE searches further into the string for occurrences of "a" or "b".
1199 .P
1200 Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a special case
1201 of a pattern match of the empty string within its \fBsplit()\fP function, and
1202 when using the /g modifier. It is possible to emulate Perl's behaviour after
1203 matching a null string by first trying the match again at the same offset with
1204 PCRE_NOTEMPTY and PCRE_ANCHORED, and then if that fails by advancing the
1205 starting offset (see below) and trying an ordinary match again. There is some
1206 code that demonstrates how to do this in the \fIpcredemo.c\fP sample program.
1207 .sp
1209 .sp
1210 When PCRE_UTF8 is set at compile time, the validity of the subject as a UTF-8
1211 string is automatically checked when \fBpcre_exec()\fP is subsequently called.
1212 The value of \fIstartoffset\fP is also checked to ensure that it points to the
1213 start of a UTF-8 character. If an invalid UTF-8 sequence of bytes is found,
1214 \fBpcre_exec()\fP returns the error PCRE_ERROR_BADUTF8. If \fIstartoffset\fP
1215 contains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
1216 .P
1217 If you already know that your subject is valid, and you want to skip these
1218 checks for performance reasons, you can set the PCRE_NO_UTF8_CHECK option when
1219 calling \fBpcre_exec()\fP. You might want to do this for the second and
1220 subsequent calls to \fBpcre_exec()\fP if you are making repeated calls to find
1221 all the matches in a single subject string. However, you should be sure that
1222 the value of \fIstartoffset\fP points to the start of a UTF-8 character. When
1223 PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid UTF-8 string as a
1224 subject, or a value of \fIstartoffset\fP that does not point to the start of a
1225 UTF-8 character, is undefined. Your program may crash.
1226 .sp
1228 .sp
1229 This option turns on the partial matching feature. If the subject string fails
1230 to match the pattern, but at some point during the matching process the end of
1231 the subject was reached (that is, the subject partially matches the pattern and
1232 the failure to match occurred only because there were not enough subject
1233 characters), \fBpcre_exec()\fP returns PCRE_ERROR_PARTIAL instead of
1234 PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is used, there are restrictions on what
1235 may appear in the pattern. These are discussed in the
1236 .\" HREF
1237 \fBpcrepartial\fP
1238 .\"
1239 documentation.
1240 .
1241 .SS "The string to be matched by \fBpcre_exec()\fP"
1242 .rs
1243 .sp
1244 The subject string is passed to \fBpcre_exec()\fP as a pointer in
1245 \fIsubject\fP, a length in \fIlength\fP, and a starting byte offset in
1246 \fIstartoffset\fP. In UTF-8 mode, the byte offset must point to the start of a
1247 UTF-8 character. Unlike the pattern string, the subject may contain binary zero
1248 bytes. When the starting offset is zero, the search for a match starts at the
1249 beginning of the subject, and this is by far the most common case.
1250 .P
1251 A non-zero starting offset is useful when searching for another match in the
1252 same subject by calling \fBpcre_exec()\fP again after a previous success.
1253 Setting \fIstartoffset\fP differs from just passing over a shortened string and
1254 setting PCRE_NOTBOL in the case of a pattern that begins with any kind of
1255 lookbehind. For example, consider the pattern
1256 .sp
1257 \eBiss\eB
1258 .sp
1259 which finds occurrences of "iss" in the middle of words. (\eB matches only if
1260 the current position in the subject is not a word boundary.) When applied to
1261 the string "Mississipi" the first call to \fBpcre_exec()\fP finds the first
1262 occurrence. If \fBpcre_exec()\fP is called again with just the remainder of the
1263 subject, namely "issipi", it does not match, because \eB is always false at the
1264 start of the subject, which is deemed to be a word boundary. However, if
1265 \fBpcre_exec()\fP is passed the entire string again, but with \fIstartoffset\fP
1266 set to 4, it finds the second occurrence of "iss" because it is able to look
1267 behind the starting point to discover that it is preceded by a letter.
1268 .P
1269 If a non-zero starting offset is passed when the pattern is anchored, one
1270 attempt to match at the given offset is made. This can only succeed if the
1271 pattern does not require the match to be at the start of the subject.
1272 .
1273 .SS "How \fBpcre_exec()\fP returns captured substrings"
1274 .rs
1275 .sp
1276 In general, a pattern matches a certain portion of the subject, and in
1277 addition, further substrings from the subject may be picked out by parts of the
1278 pattern. Following the usage in Jeffrey Friedl's book, this is called
1279 "capturing" in what follows, and the phrase "capturing subpattern" is used for
1280 a fragment of a pattern that picks out a substring. PCRE supports several other
1281 kinds of parenthesized subpattern that do not cause substrings to be captured.
1282 .P
1283 Captured substrings are returned to the caller via a vector of integer offsets
1284 whose address is passed in \fIovector\fP. The number of elements in the vector
1285 is passed in \fIovecsize\fP, which must be a non-negative number. \fBNote\fP:
1286 this argument is NOT the size of \fIovector\fP in bytes.
1287 .P
1288 The first two-thirds of the vector is used to pass back captured substrings,
1289 each substring using a pair of integers. The remaining third of the vector is
1290 used as workspace by \fBpcre_exec()\fP while matching capturing subpatterns,
1291 and is not available for passing back information. The length passed in
1292 \fIovecsize\fP should always be a multiple of three. If it is not, it is
1293 rounded down.
1294 .P
1295 When a match is successful, information about captured substrings is returned
1296 in pairs of integers, starting at the beginning of \fIovector\fP, and
1297 continuing up to two-thirds of its length at the most. The first element of a
1298 pair is set to the offset of the first character in a substring, and the second
1299 is set to the offset of the first character after the end of a substring. The
1300 first pair, \fIovector[0]\fP and \fIovector[1]\fP, identify the portion of the
1301 subject string matched by the entire pattern. The next pair is used for the
1302 first capturing subpattern, and so on. The value returned by \fBpcre_exec()\fP
1303 is one more than the highest numbered pair that has been set. For example, if
1304 two substrings have been captured, the returned value is 3. If there are no
1305 capturing subpatterns, the return value from a successful match is 1,
1306 indicating that just the first pair of offsets has been set.
1307 .P
1308 If a capturing subpattern is matched repeatedly, it is the last portion of the
1309 string that it matched that is returned.
1310 .P
1311 If the vector is too small to hold all the captured substring offsets, it is
1312 used as far as possible (up to two-thirds of its length), and the function
1313 returns a value of zero. In particular, if the substring offsets are not of
1314 interest, \fBpcre_exec()\fP may be called with \fIovector\fP passed as NULL and
1315 \fIovecsize\fP as zero. However, if the pattern contains back references and
1316 the \fIovector\fP is not big enough to remember the related substrings, PCRE
1317 has to get additional memory for use during matching. Thus it is usually
1318 advisable to supply an \fIovector\fP.
1319 .P
1320 The \fBpcre_info()\fP function can be used to find out how many capturing
1321 subpatterns there are in a compiled pattern. The smallest size for
1322 \fIovector\fP that will allow for \fIn\fP captured substrings, in addition to
1323 the offsets of the substring matched by the whole pattern, is (\fIn\fP+1)*3.
1324 .P
1325 It is possible for capturing subpattern number \fIn+1\fP to match some part of
1326 the subject when subpattern \fIn\fP has not been used at all. For example, if
1327 the string "abc" is matched against the pattern (a|(z))(bc) the return from the
1328 function is 4, and subpatterns 1 and 3 are matched, but 2 is not. When this
1329 happens, both values in the offset pairs corresponding to unused subpatterns
1330 are set to -1.
1331 .P
1332 Offset values that correspond to unused subpatterns at the end of the
1333 expression are also set to -1. For example, if the string "abc" is matched
1334 against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not matched. The
1335 return from the function is 2, because the highest used capturing subpattern
1336 number is 1. However, you can refer to the offsets for the second and third
1337 capturing subpatterns if you wish (assuming the vector is large enough, of
1338 course).
1339 .P
1340 Some convenience functions are provided for extracting the captured substrings
1341 as separate strings. These are described below.
1342 .
1343 .\" HTML <a name="errorlist"></a>
1344 .SS "Error return values from \fBpcre_exec()\fP"
1345 .rs
1346 .sp
1347 If \fBpcre_exec()\fP fails, it returns a negative number. The following are
1348 defined in the header file:
1349 .sp
1351 .sp
1352 The subject string did not match the pattern.
1353 .sp
1355 .sp
1356 Either \fIcode\fP or \fIsubject\fP was passed as NULL, or \fIovector\fP was
1357 NULL and \fIovecsize\fP was not zero.
1358 .sp
1360 .sp
1361 An unrecognized bit was set in the \fIoptions\fP argument.
1362 .sp
1364 .sp
1365 PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch
1366 the case when it is passed a junk pointer and to detect when a pattern that was
1367 compiled in an environment of one endianness is run in an environment with the
1368 other endianness. This is the error that PCRE gives when the magic number is
1369 not present.
1370 .sp
1372 .sp
1373 While running the pattern match, an unknown item was encountered in the
1374 compiled pattern. This error could be caused by a bug in PCRE or by overwriting
1375 of the compiled pattern.
1376 .sp
1378 .sp
1379 If a pattern contains back references, but the \fIovector\fP that is passed to
1380 \fBpcre_exec()\fP is not big enough to remember the referenced substrings, PCRE
1381 gets a block of memory at the start of matching to use for this purpose. If the
1382 call via \fBpcre_malloc()\fP fails, this error is given. The memory is
1383 automatically freed at the end of matching.
1384 .sp
1386 .sp
1387 This error is used by the \fBpcre_copy_substring()\fP,
1388 \fBpcre_get_substring()\fP, and \fBpcre_get_substring_list()\fP functions (see
1389 below). It is never returned by \fBpcre_exec()\fP.
1390 .sp
1392 .sp
1393 The backtracking limit, as specified by the \fImatch_limit\fP field in a
1394 \fBpcre_extra\fP structure (or defaulted) was reached. See the description
1395 above.
1396 .sp
1398 .sp
1399 This error is never generated by \fBpcre_exec()\fP itself. It is provided for
1400 use by callout functions that want to yield a distinctive error code. See the
1401 .\" HREF
1402 \fBpcrecallout\fP
1403 .\"
1404 documentation for details.
1405 .sp
1407 .sp
1408 A string that contains an invalid UTF-8 byte sequence was passed as a subject.
1409 .sp
1411 .sp
1412 The UTF-8 byte sequence that was passed as a subject was valid, but the value
1413 of \fIstartoffset\fP did not point to the beginning of a UTF-8 character.
1414 .sp
1416 .sp
1417 The subject string did not match, but it did match partially. See the
1418 .\" HREF
1419 \fBpcrepartial\fP
1420 .\"
1421 documentation for details of partial matching.
1422 .sp
1424 .sp
1425 The PCRE_PARTIAL option was used with a compiled pattern containing items that
1426 are not supported for partial matching. See the
1427 .\" HREF
1428 \fBpcrepartial\fP
1429 .\"
1430 documentation for details of partial matching.
1431 .sp
1433 .sp
1434 An unexpected internal error has occurred. This error could be caused by a bug
1435 in PCRE or by overwriting of the compiled pattern.
1436 .sp
1438 .sp
1439 This error is given if the value of the \fIovecsize\fP argument is negative.
1440 .sp
1442 .sp
1443 The internal recursion limit, as specified by the \fImatch_limit_recursion\fP
1444 field in a \fBpcre_extra\fP structure (or defaulted) was reached. See the
1445 description above.
1446 .sp
1448 .sp
1449 When a group that can match an empty substring is repeated with an unbounded
1450 upper limit, the subject position at the start of the group must be remembered,
1451 so that a test for an empty string can be made when the end of the group is
1452 reached. Some workspace is required for this; if it runs out, this error is
1453 given.
1454 .sp
1456 .sp
1457 An invalid combination of PCRE_NEWLINE_\fIxxx\fP options was given.
1458 .P
1459 Error numbers -16 to -20 are not used by \fBpcre_exec()\fP.
1460 .
1461 .
1463 .rs
1464 .sp
1465 .B int pcre_copy_substring(const char *\fIsubject\fP, int *\fIovector\fP,
1466 .ti +5n
1467 .B int \fIstringcount\fP, int \fIstringnumber\fP, char *\fIbuffer\fP,
1468 .ti +5n
1469 .B int \fIbuffersize\fP);
1470 .PP
1471 .B int pcre_get_substring(const char *\fIsubject\fP, int *\fIovector\fP,
1472 .ti +5n
1473 .B int \fIstringcount\fP, int \fIstringnumber\fP,
1474 .ti +5n
1475 .B const char **\fIstringptr\fP);
1476 .PP
1477 .B int pcre_get_substring_list(const char *\fIsubject\fP,
1478 .ti +5n
1479 .B int *\fIovector\fP, int \fIstringcount\fP, "const char ***\fIlistptr\fP);"
1480 .PP
1481 Captured substrings can be accessed directly by using the offsets returned by
1482 \fBpcre_exec()\fP in \fIovector\fP. For convenience, the functions
1483 \fBpcre_copy_substring()\fP, \fBpcre_get_substring()\fP, and
1484 \fBpcre_get_substring_list()\fP are provided for extracting captured substrings
1485 as new, separate, zero-terminated strings. These functions identify substrings
1486 by number. The next section describes functions for extracting named
1487 substrings.
1488 .P
1489 A substring that contains a binary zero is correctly extracted and has a
1490 further zero added on the end, but the result is not, of course, a C string.
1491 However, you can process such a string by referring to the length that is
1492 returned by \fBpcre_copy_substring()\fP and \fBpcre_get_substring()\fP.
1493 Unfortunately, the interface to \fBpcre_get_substring_list()\fP is not adequate
1494 for handling strings containing binary zeros, because the end of the final
1495 string is not independently indicated.
1496 .P
1497 The first three arguments are the same for all three of these functions:
1498 \fIsubject\fP is the subject string that has just been successfully matched,
1499 \fIovector\fP is a pointer to the vector of integer offsets that was passed to
1500 \fBpcre_exec()\fP, and \fIstringcount\fP is the number of substrings that were
1501 captured by the match, including the substring that matched the entire regular
1502 expression. This is the value returned by \fBpcre_exec()\fP if it is greater
1503 than zero. If \fBpcre_exec()\fP returned zero, indicating that it ran out of
1504 space in \fIovector\fP, the value passed as \fIstringcount\fP should be the
1505 number of elements in the vector divided by three.
1506 .P
1507 The functions \fBpcre_copy_substring()\fP and \fBpcre_get_substring()\fP
1508 extract a single substring, whose number is given as \fIstringnumber\fP. A
1509 value of zero extracts the substring that matched the entire pattern, whereas
1510 higher values extract the captured substrings. For \fBpcre_copy_substring()\fP,
1511 the string is placed in \fIbuffer\fP, whose length is given by
1512 \fIbuffersize\fP, while for \fBpcre_get_substring()\fP a new block of memory is
1513 obtained via \fBpcre_malloc\fP, and its address is returned via
1514 \fIstringptr\fP. The yield of the function is the length of the string, not
1515 including the terminating zero, or one of these error codes:
1516 .sp
1518 .sp
1519 The buffer was too small for \fBpcre_copy_substring()\fP, or the attempt to get
1520 memory failed for \fBpcre_get_substring()\fP.
1521 .sp
1523 .sp
1524 There is no substring whose number is \fIstringnumber\fP.
1525 .P
1526 The \fBpcre_get_substring_list()\fP function extracts all available substrings
1527 and builds a list of pointers to them. All this is done in a single block of
1528 memory that is obtained via \fBpcre_malloc\fP. The address of the memory block
1529 is returned via \fIlistptr\fP, which is also the start of the list of string
1530 pointers. The end of the list is marked by a NULL pointer. The yield of the
1531 function is zero if all went well, or the error code
1532 .sp
1534 .sp
1535 if the attempt to get the memory block failed.
1536 .P
1537 When any of these functions encounter a substring that is unset, which can
1538 happen when capturing subpattern number \fIn+1\fP matches some part of the
1539 subject, but subpattern \fIn\fP has not been used at all, they return an empty
1540 string. This can be distinguished from a genuine zero-length substring by
1541 inspecting the appropriate offset in \fIovector\fP, which is negative for unset
1542 substrings.
1543 .P
1544 The two convenience functions \fBpcre_free_substring()\fP and
1545 \fBpcre_free_substring_list()\fP can be used to free the memory returned by
1546 a previous call of \fBpcre_get_substring()\fP or
1547 \fBpcre_get_substring_list()\fP, respectively. They do nothing more than call
1548 the function pointed to by \fBpcre_free\fP, which of course could be called
1549 directly from a C program. However, PCRE is used in some situations where it is
1550 linked via a special interface to another programming language that cannot use
1551 \fBpcre_free\fP directly; it is for these cases that the functions are
1552 provided.
1553 .
1554 .
1556 .rs
1557 .sp
1558 .B int pcre_get_stringnumber(const pcre *\fIcode\fP,
1559 .ti +5n
1560 .B const char *\fIname\fP);
1561 .PP
1562 .B int pcre_copy_named_substring(const pcre *\fIcode\fP,
1563 .ti +5n
1564 .B const char *\fIsubject\fP, int *\fIovector\fP,
1565 .ti +5n
1566 .B int \fIstringcount\fP, const char *\fIstringname\fP,
1567 .ti +5n
1568 .B char *\fIbuffer\fP, int \fIbuffersize\fP);
1569 .PP
1570 .B int pcre_get_named_substring(const pcre *\fIcode\fP,
1571 .ti +5n
1572 .B const char *\fIsubject\fP, int *\fIovector\fP,
1573 .ti +5n
1574 .B int \fIstringcount\fP, const char *\fIstringname\fP,
1575 .ti +5n
1576 .B const char **\fIstringptr\fP);
1577 .PP
1578 To extract a substring by name, you first have to find associated number.
1579 For example, for this pattern
1580 .sp
1581 (a+)b(?<xxx>\ed+)...
1582 .sp
1583 the number of the subpattern called "xxx" is 2. If the name is known to be
1584 unique (PCRE_DUPNAMES was not set), you can find the number from the name by
1585 calling \fBpcre_get_stringnumber()\fP. The first argument is the compiled
1586 pattern, and the second is the name. The yield of the function is the
1587 subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no subpattern of
1588 that name.
1589 .P
1590 Given the number, you can extract the substring directly, or use one of the
1591 functions described in the previous section. For convenience, there are also
1592 two functions that do the whole job.
1593 .P
1594 Most of the arguments of \fBpcre_copy_named_substring()\fP and
1595 \fBpcre_get_named_substring()\fP are the same as those for the similarly named
1596 functions that extract by number. As these are described in the previous
1597 section, they are not re-described here. There are just two differences:
1598 .P
1599 First, instead of a substring number, a substring name is given. Second, there
1600 is an extra argument, given at the start, which is a pointer to the compiled
1601 pattern. This is needed in order to gain access to the name-to-number
1602 translation table.
1603 .P
1604 These functions call \fBpcre_get_stringnumber()\fP, and if it succeeds, they
1605 then call \fBpcre_copy_substring()\fP or \fBpcre_get_substring()\fP, as
1606 appropriate. \fBNOTE:\fP If PCRE_DUPNAMES is set and there are duplicate names,
1607 the behaviour may not be what you want (see the next section).
1608 .
1609 .
1611 .rs
1612 .sp
1613 .B int pcre_get_stringtable_entries(const pcre *\fIcode\fP,
1614 .ti +5n
1615 .B const char *\fIname\fP, char **\fIfirst\fP, char **\fIlast\fP);
1616 .PP
1617 When a pattern is compiled with the PCRE_DUPNAMES option, names for subpatterns
1618 are not required to be unique. Normally, patterns with duplicate names are such
1619 that in any one match, only one of the named subpatterns participates. An
1620 example is shown in the
1621 .\" HREF
1622 \fBpcrepattern\fP
1623 .\"
1624 documentation. When duplicates are present, \fBpcre_copy_named_substring()\fP
1625 and \fBpcre_get_named_substring()\fP return the first substring corresponding
1626 to the given name that is set. If none are set, an empty string is returned.
1627 The \fBpcre_get_stringnumber()\fP function returns one of the numbers that are
1628 associated with the name, but it is not defined which it is.
1629 .sp
1630 If you want to get full details of all captured substrings for a given name,
1631 you must use the \fBpcre_get_stringtable_entries()\fP function. The first
1632 argument is the compiled pattern, and the second is the name. The third and
1633 fourth are pointers to variables which are updated by the function. After it
1634 has run, they point to the first and last entries in the name-to-number table
1635 for the given name. The function itself returns the length of each entry, or
1636 PCRE_ERROR_NOSUBSTRING (-7) if there are none. The format of the table is
1637 described above in the section entitled \fIInformation about a pattern\fP.
1638 Given all the relevant entries for the name, you can extract each of their
1639 numbers, and hence the captured data, if any.
1640 .
1641 .
1643 .rs
1644 .sp
1645 The traditional matching function uses a similar algorithm to Perl, which stops
1646 when it finds the first match, starting at a given point in the subject. If you
1647 want to find all possible matches, or the longest possible match, consider
1648 using the alternative matching function (see below) instead. If you cannot use
1649 the alternative function, but still need to find all possible matches, you
1650 can kludge it up by making use of the callout facility, which is described in
1651 the
1652 .\" HREF
1653 \fBpcrecallout\fP
1654 .\"
1655 documentation.
1656 .P
1657 What you have to do is to insert a callout right at the end of the pattern.
1658 When your callout function is called, extract and save the current matched
1659 substring. Then return 1, which forces \fBpcre_exec()\fP to backtrack and try
1660 other alternatives. Ultimately, when it runs out of matches, \fBpcre_exec()\fP
1661 will yield PCRE_ERROR_NOMATCH.
1662 .
1663 .
1664 .\" HTML <a name="dfamatch"></a>
1666 .rs
1667 .sp
1668 .B int pcre_dfa_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
1669 .ti +5n
1670 .B "const char *\fIsubject\fP," int \fIlength\fP, int \fIstartoffset\fP,
1671 .ti +5n
1672 .B int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP,
1673 .ti +5n
1674 .B int *\fIworkspace\fP, int \fIwscount\fP);
1675 .P
1676 The function \fBpcre_dfa_exec()\fP is called to match a subject string against
1677 a compiled pattern, using a matching algorithm that scans the subject string
1678 just once, and does not backtrack. This has different characteristics to the
1679 normal algorithm, and is not compatible with Perl. Some of the features of PCRE
1680 patterns are not supported. Nevertheless, there are times when this kind of
1681 matching can be useful. For a discussion of the two matching algorithms, see
1682 the
1683 .\" HREF
1684 \fBpcrematching\fP
1685 .\"
1686 documentation.
1687 .P
1688 The arguments for the \fBpcre_dfa_exec()\fP function are the same as for
1689 \fBpcre_exec()\fP, plus two extras. The \fIovector\fP argument is used in a
1690 different way, and this is described below. The other common arguments are used
1691 in the same way as for \fBpcre_exec()\fP, so their description is not repeated
1692 here.
1693 .P
1694 The two additional arguments provide workspace for the function. The workspace
1695 vector should contain at least 20 elements. It is used for keeping track of
1696 multiple paths through the pattern tree. More workspace will be needed for
1697 patterns and subjects where there are a lot of potential matches.
1698 .P
1699 Here is an example of a simple call to \fBpcre_dfa_exec()\fP:
1700 .sp
1701 int rc;
1702 int ovector[10];
1703 int wspace[20];
1704 rc = pcre_dfa_exec(
1705 re, /* result of pcre_compile() */
1706 NULL, /* we didn't study the pattern */
1707 "some string", /* the subject string */
1708 11, /* the length of the subject string */
1709 0, /* start at offset 0 in the subject */
1710 0, /* default options */
1711 ovector, /* vector of integers for substring information */
1712 10, /* number of elements (NOT size in bytes) */
1713 wspace, /* working space vector */
1714 20); /* number of elements (NOT size in bytes) */
1715 .
1716 .SS "Option bits for \fBpcre_dfa_exec()\fP"
1717 .rs
1718 .sp
1719 The unused bits of the \fIoptions\fP argument for \fBpcre_dfa_exec()\fP must be
1720 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_\fIxxx\fP,
1722 PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last three of these are
1723 the same as for \fBpcre_exec()\fP, so their description is not repeated here.
1724 .sp
1726 .sp
1727 This has the same general effect as it does for \fBpcre_exec()\fP, but the
1728 details are slightly different. When PCRE_PARTIAL is set for
1729 \fBpcre_dfa_exec()\fP, the return code PCRE_ERROR_NOMATCH is converted into
1730 PCRE_ERROR_PARTIAL if the end of the subject is reached, there have been no
1731 complete matches, but there is still at least one matching possibility. The
1732 portion of the string that provided the partial match is set as the first
1733 matching string.
1734 .sp
1736 .sp
1737 Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to stop as
1738 soon as it has found one match. Because of the way the alternative algorithm
1739 works, this is necessarily the shortest possible match at the first possible
1740 matching point in the subject string.
1741 .sp
1743 .sp
1744 When \fBpcre_dfa_exec()\fP is called with the PCRE_PARTIAL option, and returns
1745 a partial match, it is possible to call it again, with additional subject
1746 characters, and have it continue with the same match. The PCRE_DFA_RESTART
1747 option requests this action; when it is set, the \fIworkspace\fP and
1748 \fIwscount\fP options must reference the same vector as before because data
1749 about the match so far is left in them after a partial match. There is more
1750 discussion of this facility in the
1751 .\" HREF
1752 \fBpcrepartial\fP
1753 .\"
1754 documentation.
1755 .
1756 .SS "Successful returns from \fBpcre_dfa_exec()\fP"
1757 .rs
1758 .sp
1759 When \fBpcre_dfa_exec()\fP succeeds, it may have matched more than one
1760 substring in the subject. Note, however, that all the matches from one run of
1761 the function start at the same point in the subject. The shorter matches are
1762 all initial substrings of the longer matches. For example, if the pattern
1763 .sp
1764 <.*>
1765 .sp
1766 is matched against the string
1767 .sp
1768 This is <something> <something else> <something further> no more
1769 .sp
1770 the three matched strings are
1771 .sp
1772 <something>
1773 <something> <something else>
1774 <something> <something else> <something further>
1775 .sp
1776 On success, the yield of the function is a number greater than zero, which is
1777 the number of matched substrings. The substrings themselves are returned in
1778 \fIovector\fP. Each string uses two elements; the first is the offset to the
1779 start, and the second is the offset to the end. In fact, all the strings have
1780 the same start offset. (Space could have been saved by giving this only once,
1781 but it was decided to retain some compatibility with the way \fBpcre_exec()\fP
1782 returns data, even though the meaning of the strings is different.)
1783 .P
1784 The strings are returned in reverse order of length; that is, the longest
1785 matching string is given first. If there were too many matches to fit into
1786 \fIovector\fP, the yield of the function is zero, and the vector is filled with
1787 the longest matches.
1788 .
1789 .SS "Error returns from \fBpcre_dfa_exec()\fP"
1790 .rs
1791 .sp
1792 The \fBpcre_dfa_exec()\fP function returns a negative number when it fails.
1793 Many of the errors are the same as for \fBpcre_exec()\fP, and these are
1794 described
1795 .\" HTML <a href="#errorlist">
1796 .\" </a>
1797 above.
1798 .\"
1799 There are in addition the following errors that are specific to
1800 \fBpcre_dfa_exec()\fP:
1801 .sp
1803 .sp
1804 This return is given if \fBpcre_dfa_exec()\fP encounters an item in the pattern
1805 that it does not support, for instance, the use of \eC or a back reference.
1806 .sp
1808 .sp
1809 This return is given if \fBpcre_dfa_exec()\fP encounters a condition item that
1810 uses a back reference for the condition, or a test for recursion in a specific
1811 group. These are not supported.
1812 .sp
1814 .sp
1815 This return is given if \fBpcre_dfa_exec()\fP is called with an \fIextra\fP
1816 block that contains a setting of the \fImatch_limit\fP field. This is not
1817 supported (it is meaningless).
1818 .sp
1820 .sp
1821 This return is given if \fBpcre_dfa_exec()\fP runs out of space in the
1822 \fIworkspace\fP vector.
1823 .sp
1825 .sp
1826 When a recursive subpattern is processed, the matching function calls itself
1827 recursively, using private vectors for \fIovector\fP and \fIworkspace\fP. This
1828 error is given if the output vector is not large enough. This should be
1829 extremely rare, as a vector of size 1000 is used.
1830 .
1831 .
1832 .SH "SEE ALSO"
1833 .rs
1834 .sp
1835 \fBpcrebuild\fP(3), \fBpcrecallout\fP(3), \fBpcrecpp(3)\fP(3),
1836 \fBpcrematching\fP(3), \fBpcrepartial\fP(3), \fBpcreposix\fP(3),
1837 \fBpcreprecompile\fP(3), \fBpcresample\fP(3), \fBpcrestack\fP(3).
1838 .
1839 .
1841 .rs
1842 .sp
1843 .nf
1844 Philip Hazel
1845 University Computing Service
1846 Cambridge CB2 3QH, England.
1847 .fi
1848 .
1849 .
1851 .rs
1852 .sp
1853 .nf
1854 Last updated: 24 April 2007
1855 Copyright (c) 1997-2007 University of Cambridge.
1856 .fi


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