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3 PCRE - Perl-compatible regular expressions
4 .sp
5 .B #include <pcre.h>
6 .
7 .
9 .rs
10 .sp
11 .SM
12 .B pcre *pcre_compile(const char *\fIpattern\fP, int \fIoptions\fP,
13 .ti +5n
14 .B const char **\fIerrptr\fP, int *\fIerroffset\fP,
15 .ti +5n
16 .B const unsigned char *\fItableptr\fP);
17 .PP
18 .B pcre *pcre_compile2(const char *\fIpattern\fP, int \fIoptions\fP,
19 .ti +5n
20 .B int *\fIerrorcodeptr\fP,
21 .ti +5n
22 .B const char **\fIerrptr\fP, int *\fIerroffset\fP,
23 .ti +5n
24 .B const unsigned char *\fItableptr\fP);
25 .PP
26 .B pcre_extra *pcre_study(const pcre *\fIcode\fP, int \fIoptions\fP,
27 .ti +5n
28 .B const char **\fIerrptr\fP);
29 .PP
30 .B void pcre_free_study(pcre_extra *\fIextra\fP);
31 .PP
32 .B int pcre_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
33 .ti +5n
34 .B "const char *\fIsubject\fP," int \fIlength\fP, int \fIstartoffset\fP,
35 .ti +5n
36 .B int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP);
37 .PP
38 .B int pcre_dfa_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
39 .ti +5n
40 .B "const char *\fIsubject\fP," int \fIlength\fP, int \fIstartoffset\fP,
41 .ti +5n
42 .B int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP,
43 .ti +5n
44 .B int *\fIworkspace\fP, int \fIwscount\fP);
45 .
46 .
48 .rs
49 .sp
50 .B int pcre_copy_named_substring(const pcre *\fIcode\fP,
51 .ti +5n
52 .B const char *\fIsubject\fP, int *\fIovector\fP,
53 .ti +5n
54 .B int \fIstringcount\fP, const char *\fIstringname\fP,
55 .ti +5n
56 .B char *\fIbuffer\fP, int \fIbuffersize\fP);
57 .PP
58 .B int pcre_copy_substring(const char *\fIsubject\fP, int *\fIovector\fP,
59 .ti +5n
60 .B int \fIstringcount\fP, int \fIstringnumber\fP, char *\fIbuffer\fP,
61 .ti +5n
62 .B int \fIbuffersize\fP);
63 .PP
64 .B int pcre_get_named_substring(const pcre *\fIcode\fP,
65 .ti +5n
66 .B const char *\fIsubject\fP, int *\fIovector\fP,
67 .ti +5n
68 .B int \fIstringcount\fP, const char *\fIstringname\fP,
69 .ti +5n
70 .B const char **\fIstringptr\fP);
71 .PP
72 .B int pcre_get_stringnumber(const pcre *\fIcode\fP,
73 .ti +5n
74 .B const char *\fIname\fP);
75 .PP
76 .B int pcre_get_stringtable_entries(const pcre *\fIcode\fP,
77 .ti +5n
78 .B const char *\fIname\fP, char **\fIfirst\fP, char **\fIlast\fP);
79 .PP
80 .B int pcre_get_substring(const char *\fIsubject\fP, int *\fIovector\fP,
81 .ti +5n
82 .B int \fIstringcount\fP, int \fIstringnumber\fP,
83 .ti +5n
84 .B const char **\fIstringptr\fP);
85 .PP
86 .B int pcre_get_substring_list(const char *\fIsubject\fP,
87 .ti +5n
88 .B int *\fIovector\fP, int \fIstringcount\fP, "const char ***\fIlistptr\fP);"
89 .PP
90 .B void pcre_free_substring(const char *\fIstringptr\fP);
91 .PP
92 .B void pcre_free_substring_list(const char **\fIstringptr\fP);
93 .
94 .
96 .rs
97 .sp
98 .B pcre_jit_stack *pcre_jit_stack_alloc(int \fIstartsize\fP, int \fImaxsize\fP);
99 .PP
100 .B void pcre_jit_stack_free(pcre_jit_stack *\fIstack\fP);
101 .PP
102 .B void pcre_assign_jit_stack(pcre_extra *\fIextra\fP,
103 .ti +5n
104 .B pcre_jit_callback \fIcallback\fP, void *\fIdata\fP);
105 .PP
106 .B const unsigned char *pcre_maketables(void);
107 .PP
108 .B int pcre_fullinfo(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
109 .ti +5n
110 .B int \fIwhat\fP, void *\fIwhere\fP);
111 .PP
112 .B int pcre_refcount(pcre *\fIcode\fP, int \fIadjust\fP);
113 .PP
114 .B int pcre_config(int \fIwhat\fP, void *\fIwhere\fP);
115 .PP
116 .B const char *pcre_version(void);
117 .PP
118 .B int pcre_pattern_to_host_byte_order(pcre *\fIcode\fP,
119 .ti +5n
120 .B pcre_extra *\fIextra\fP, const unsigned char *\fItables\fP);
121 .
122 .
124 .rs
125 .sp
126 .B void *(*pcre_malloc)(size_t);
127 .PP
128 .B void (*pcre_free)(void *);
129 .PP
130 .B void *(*pcre_stack_malloc)(size_t);
131 .PP
132 .B void (*pcre_stack_free)(void *);
133 .PP
134 .B int (*pcre_callout)(pcre_callout_block *);
135 .
136 .
138 .rs
139 .sp
140 From release 8.30, PCRE can be compiled as a library for handling 16-bit
141 character strings as well as, or instead of, the original library that handles
142 8-bit character strings. To avoid too much complication, this document
143 describes the 8-bit versions of the functions, with only occasional references
144 to the 16-bit library.
145 .P
146 The 16-bit functions operate in the same way as their 8-bit counterparts; they
147 just use different data types for their arguments and results, and their names
148 start with \fBpcre16_\fP instead of \fBpcre_\fP. For every option that has UTF8
149 in its name (for example, PCRE_UTF8), there is a corresponding 16-bit name with
150 UTF8 replaced by UTF16. This facility is in fact just cosmetic; the 16-bit
151 option names define the same bit values.
152 .P
153 References to bytes and UTF-8 in this document should be read as references to
154 16-bit data quantities and UTF-16 when using the 16-bit library, unless
155 specified otherwise. More details of the specific differences for the 16-bit
156 library are given in the
157 .\" HREF
158 \fBpcre16\fP
159 .\"
160 page.
161 .
162 .
164 .rs
165 .sp
166 PCRE has its own native API, which is described in this document. There are
167 also some wrapper functions (for the 8-bit library only) that correspond to the
168 POSIX regular expression API, but they do not give access to all the
169 functionality. They are described in the
170 .\" HREF
171 \fBpcreposix\fP
172 .\"
173 documentation. Both of these APIs define a set of C function calls. A C++
174 wrapper (again for the 8-bit library only) is also distributed with PCRE. It is
175 documented in the
176 .\" HREF
177 \fBpcrecpp\fP
178 .\"
179 page.
180 .P
181 The native API C function prototypes are defined in the header file
182 \fBpcre.h\fP, and on Unix-like systems the (8-bit) library itself is called
183 \fBlibpcre\fP. It can normally be accessed by adding \fB-lpcre\fP to the
184 command for linking an application that uses PCRE. The header file defines the
185 macros PCRE_MAJOR and PCRE_MINOR to contain the major and minor release numbers
186 for the library. Applications can use these to include support for different
187 releases of PCRE.
188 .P
189 In a Windows environment, if you want to statically link an application program
190 against a non-dll \fBpcre.a\fP file, you must define PCRE_STATIC before
191 including \fBpcre.h\fP or \fBpcrecpp.h\fP, because otherwise the
192 \fBpcre_malloc()\fP and \fBpcre_free()\fP exported functions will be declared
193 \fB__declspec(dllimport)\fP, with unwanted results.
194 .P
195 The functions \fBpcre_compile()\fP, \fBpcre_compile2()\fP, \fBpcre_study()\fP,
196 and \fBpcre_exec()\fP are used for compiling and matching regular expressions
197 in a Perl-compatible manner. A sample program that demonstrates the simplest
198 way of using them is provided in the file called \fIpcredemo.c\fP in the PCRE
199 source distribution. A listing of this program is given in the
200 .\" HREF
201 \fBpcredemo\fP
202 .\"
203 documentation, and the
204 .\" HREF
205 \fBpcresample\fP
206 .\"
207 documentation describes how to compile and run it.
208 .P
209 Just-in-time compiler support is an optional feature of PCRE that can be built
210 in appropriate hardware environments. It greatly speeds up the matching
211 performance of many patterns. Simple programs can easily request that it be
212 used if available, by setting an option that is ignored when it is not
213 relevant. More complicated programs might need to make use of the functions
214 \fBpcre_jit_stack_alloc()\fP, \fBpcre_jit_stack_free()\fP, and
215 \fBpcre_assign_jit_stack()\fP in order to control the JIT code's memory usage.
216 These functions are discussed in the
217 .\" HREF
218 \fBpcrejit\fP
219 .\"
220 documentation.
221 .P
222 A second matching function, \fBpcre_dfa_exec()\fP, which is not
223 Perl-compatible, is also provided. This uses a different algorithm for the
224 matching. The alternative algorithm finds all possible matches (at a given
225 point in the subject), and scans the subject just once (unless there are
226 lookbehind assertions). However, this algorithm does not return captured
227 substrings. A description of the two matching algorithms and their advantages
228 and disadvantages is given in the
229 .\" HREF
230 \fBpcrematching\fP
231 .\"
232 documentation.
233 .P
234 In addition to the main compiling and matching functions, there are convenience
235 functions for extracting captured substrings from a subject string that is
236 matched by \fBpcre_exec()\fP. They are:
237 .sp
238 \fBpcre_copy_substring()\fP
239 \fBpcre_copy_named_substring()\fP
240 \fBpcre_get_substring()\fP
241 \fBpcre_get_named_substring()\fP
242 \fBpcre_get_substring_list()\fP
243 \fBpcre_get_stringnumber()\fP
244 \fBpcre_get_stringtable_entries()\fP
245 .sp
246 \fBpcre_free_substring()\fP and \fBpcre_free_substring_list()\fP are also
247 provided, to free the memory used for extracted strings.
248 .P
249 The function \fBpcre_maketables()\fP is used to build a set of character tables
250 in the current locale for passing to \fBpcre_compile()\fP, \fBpcre_exec()\fP,
251 or \fBpcre_dfa_exec()\fP. This is an optional facility that is provided for
252 specialist use. Most commonly, no special tables are passed, in which case
253 internal tables that are generated when PCRE is built are used.
254 .P
255 The function \fBpcre_fullinfo()\fP is used to find out information about a
256 compiled pattern. The function \fBpcre_version()\fP returns a pointer to a
257 string containing the version of PCRE and its date of release.
258 .P
259 The function \fBpcre_refcount()\fP maintains a reference count in a data block
260 containing a compiled pattern. This is provided for the benefit of
261 object-oriented applications.
262 .P
263 The global variables \fBpcre_malloc\fP and \fBpcre_free\fP initially contain
264 the entry points of the standard \fBmalloc()\fP and \fBfree()\fP functions,
265 respectively. PCRE calls the memory management functions via these variables,
266 so a calling program can replace them if it wishes to intercept the calls. This
267 should be done before calling any PCRE functions.
268 .P
269 The global variables \fBpcre_stack_malloc\fP and \fBpcre_stack_free\fP are also
270 indirections to memory management functions. These special functions are used
271 only when PCRE is compiled to use the heap for remembering data, instead of
272 recursive function calls, when running the \fBpcre_exec()\fP function. See the
273 .\" HREF
274 \fBpcrebuild\fP
275 .\"
276 documentation for details of how to do this. It is a non-standard way of
277 building PCRE, for use in environments that have limited stacks. Because of the
278 greater use of memory management, it runs more slowly. Separate functions are
279 provided so that special-purpose external code can be used for this case. When
280 used, these functions are always called in a stack-like manner (last obtained,
281 first freed), and always for memory blocks of the same size. There is a
282 discussion about PCRE's stack usage in the
283 .\" HREF
284 \fBpcrestack\fP
285 .\"
286 documentation.
287 .P
288 The global variable \fBpcre_callout\fP initially contains NULL. It can be set
289 by the caller to a "callout" function, which PCRE will then call at specified
290 points during a matching operation. Details are given in the
291 .\" HREF
292 \fBpcrecallout\fP
293 .\"
294 documentation.
295 .
296 .
297 .\" HTML <a name="newlines"></a>
299 .rs
300 .sp
301 PCRE supports five different conventions for indicating line breaks in
302 strings: a single CR (carriage return) character, a single LF (linefeed)
303 character, the two-character sequence CRLF, any of the three preceding, or any
304 Unicode newline sequence. The Unicode newline sequences are the three just
305 mentioned, plus the single characters VT (vertical tab, U+000B), FF (formfeed,
306 U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS
307 (paragraph separator, U+2029).
308 .P
309 Each of the first three conventions is used by at least one operating system as
310 its standard newline sequence. When PCRE is built, a default can be specified.
311 The default default is LF, which is the Unix standard. When PCRE is run, the
312 default can be overridden, either when a pattern is compiled, or when it is
313 matched.
314 .P
315 At compile time, the newline convention can be specified by the \fIoptions\fP
316 argument of \fBpcre_compile()\fP, or it can be specified by special text at the
317 start of the pattern itself; this overrides any other settings. See the
318 .\" HREF
319 \fBpcrepattern\fP
320 .\"
321 page for details of the special character sequences.
322 .P
323 In the PCRE documentation the word "newline" is used to mean "the character or
324 pair of characters that indicate a line break". The choice of newline
325 convention affects the handling of the dot, circumflex, and dollar
326 metacharacters, the handling of #-comments in /x mode, and, when CRLF is a
327 recognized line ending sequence, the match position advancement for a
328 non-anchored pattern. There is more detail about this in the
329 .\" HTML <a href="#execoptions">
330 .\" </a>
331 section on \fBpcre_exec()\fP options
332 .\"
333 below.
334 .P
335 The choice of newline convention does not affect the interpretation of
336 the \en or \er escape sequences, nor does it affect what \eR matches, which is
337 controlled in a similar way, but by separate options.
338 .
339 .
341 .rs
342 .sp
343 The PCRE functions can be used in multi-threading applications, with the
344 proviso that the memory management functions pointed to by \fBpcre_malloc\fP,
345 \fBpcre_free\fP, \fBpcre_stack_malloc\fP, and \fBpcre_stack_free\fP, and the
346 callout function pointed to by \fBpcre_callout\fP, are shared by all threads.
347 .P
348 The compiled form of a regular expression is not altered during matching, so
349 the same compiled pattern can safely be used by several threads at once.
350 .P
351 If the just-in-time optimization feature is being used, it needs separate
352 memory stack areas for each thread. See the
353 .\" HREF
354 \fBpcrejit\fP
355 .\"
356 documentation for more details.
357 .
358 .
360 .rs
361 .sp
362 The compiled form of a regular expression can be saved and re-used at a later
363 time, possibly by a different program, and even on a host other than the one on
364 which it was compiled. Details are given in the
365 .\" HREF
366 \fBpcreprecompile\fP
367 .\"
368 documentation, which includes a description of the
369 \fBpcre_pattern_to_host_byte_order()\fP function. However, compiling a regular
370 expression with one version of PCRE for use with a different version is not
371 guaranteed to work and may cause crashes.
372 .
373 .
375 .rs
376 .sp
377 .B int pcre_config(int \fIwhat\fP, void *\fIwhere\fP);
378 .PP
379 The function \fBpcre_config()\fP makes it possible for a PCRE client to
380 discover which optional features have been compiled into the PCRE library. The
381 .\" HREF
382 \fBpcrebuild\fP
383 .\"
384 documentation has more details about these optional features.
385 .P
386 The first argument for \fBpcre_config()\fP is an integer, specifying which
387 information is required; the second argument is a pointer to a variable into
388 which the information is placed. The returned value is zero on success, or the
389 negative error code PCRE_ERROR_BADOPTION if the value in the first argument is
390 not recognized. The following information is available:
391 .sp
393 .sp
394 The output is an integer that is set to one if UTF-8 support is available;
395 otherwise it is set to zero. If this option is given to the 16-bit version of
396 this function, \fBpcre16_config()\fP, the result is PCRE_ERROR_BADOPTION.
397 .sp
399 .sp
400 The output is an integer that is set to one if UTF-16 support is available;
401 otherwise it is set to zero. This value should normally be given to the 16-bit
402 version of this function, \fBpcre16_config()\fP. If it is given to the 8-bit
403 version of this function, the result is PCRE_ERROR_BADOPTION.
404 .sp
406 .sp
407 The output is an integer that is set to one if support for Unicode character
408 properties is available; otherwise it is set to zero.
409 .sp
411 .sp
412 The output is an integer that is set to one if support for just-in-time
413 compiling is available; otherwise it is set to zero.
414 .sp
416 .sp
417 The output is a pointer to a zero-terminated "const char *" string. If JIT
418 support is available, the string contains the name of the architecture for
419 which the JIT compiler is configured, for example "x86 32bit (little endian +
420 unaligned)". If JIT support is not available, the result is NULL.
421 .sp
423 .sp
424 The output is an integer whose value specifies the default character sequence
425 that is recognized as meaning "newline". The four values that are supported
426 are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF, and -1 for ANY.
427 Though they are derived from ASCII, the same values are returned in EBCDIC
428 environments. The default should normally correspond to the standard sequence
429 for your operating system.
430 .sp
432 .sp
433 The output is an integer whose value indicates what character sequences the \eR
434 escape sequence matches by default. A value of 0 means that \eR matches any
435 Unicode line ending sequence; a value of 1 means that \eR matches only CR, LF,
436 or CRLF. The default can be overridden when a pattern is compiled or matched.
437 .sp
439 .sp
440 The output is an integer that contains the number of bytes used for internal
441 linkage in compiled regular expressions. For the 8-bit library, the value can
442 be 2, 3, or 4. For the 16-bit library, the value is either 2 or 4 and is still
443 a number of bytes. The default value of 2 is sufficient for all but the most
444 massive patterns, since it allows the compiled pattern to be up to 64K in size.
445 Larger values allow larger regular expressions to be compiled, at the expense
446 of slower matching.
447 .sp
449 .sp
450 The output is an integer that contains the threshold above which the POSIX
451 interface uses \fBmalloc()\fP for output vectors. Further details are given in
452 the
453 .\" HREF
454 \fBpcreposix\fP
455 .\"
456 documentation.
457 .sp
459 .sp
460 The output is a long integer that gives the default limit for the number of
461 internal matching function calls in a \fBpcre_exec()\fP execution. Further
462 details are given with \fBpcre_exec()\fP below.
463 .sp
465 .sp
466 The output is a long integer that gives the default limit for the depth of
467 recursion when calling the internal matching function in a \fBpcre_exec()\fP
468 execution. Further details are given with \fBpcre_exec()\fP below.
469 .sp
471 .sp
472 The output is an integer that is set to one if internal recursion when running
473 \fBpcre_exec()\fP is implemented by recursive function calls that use the stack
474 to remember their state. This is the usual way that PCRE is compiled. The
475 output is zero if PCRE was compiled to use blocks of data on the heap instead
476 of recursive function calls. In this case, \fBpcre_stack_malloc\fP and
477 \fBpcre_stack_free\fP are called to manage memory blocks on the heap, thus
478 avoiding the use of the stack.
479 .
480 .
482 .rs
483 .sp
484 .B pcre *pcre_compile(const char *\fIpattern\fP, int \fIoptions\fP,
485 .ti +5n
486 .B const char **\fIerrptr\fP, int *\fIerroffset\fP,
487 .ti +5n
488 .B const unsigned char *\fItableptr\fP);
489 .sp
490 .B pcre *pcre_compile2(const char *\fIpattern\fP, int \fIoptions\fP,
491 .ti +5n
492 .B int *\fIerrorcodeptr\fP,
493 .ti +5n
494 .B const char **\fIerrptr\fP, int *\fIerroffset\fP,
495 .ti +5n
496 .B const unsigned char *\fItableptr\fP);
497 .P
498 Either of the functions \fBpcre_compile()\fP or \fBpcre_compile2()\fP can be
499 called to compile a pattern into an internal form. The only difference between
500 the two interfaces is that \fBpcre_compile2()\fP has an additional argument,
501 \fIerrorcodeptr\fP, via which a numerical error code can be returned. To avoid
502 too much repetition, we refer just to \fBpcre_compile()\fP below, but the
503 information applies equally to \fBpcre_compile2()\fP.
504 .P
505 The pattern is a C string terminated by a binary zero, and is passed in the
506 \fIpattern\fP argument. A pointer to a single block of memory that is obtained
507 via \fBpcre_malloc\fP is returned. This contains the compiled code and related
508 data. The \fBpcre\fP type is defined for the returned block; this is a typedef
509 for a structure whose contents are not externally defined. It is up to the
510 caller to free the memory (via \fBpcre_free\fP) when it is no longer required.
511 .P
512 Although the compiled code of a PCRE regex is relocatable, that is, it does not
513 depend on memory location, the complete \fBpcre\fP data block is not
514 fully relocatable, because it may contain a copy of the \fItableptr\fP
515 argument, which is an address (see below).
516 .P
517 The \fIoptions\fP argument contains various bit settings that affect the
518 compilation. It should be zero if no options are required. The available
519 options are described below. Some of them (in particular, those that are
520 compatible with Perl, but some others as well) can also be set and unset from
521 within the pattern (see the detailed description in the
522 .\" HREF
523 \fBpcrepattern\fP
524 .\"
525 documentation). For those options that can be different in different parts of
526 the pattern, the contents of the \fIoptions\fP argument specifies their
527 settings at the start of compilation and execution. The PCRE_ANCHORED,
529 PCRE_NO_START_OPTIMIZE options can be set at the time of matching as well as at
530 compile time.
531 .P
532 If \fIerrptr\fP is NULL, \fBpcre_compile()\fP returns NULL immediately.
533 Otherwise, if compilation of a pattern fails, \fBpcre_compile()\fP returns
534 NULL, and sets the variable pointed to by \fIerrptr\fP to point to a textual
535 error message. This is a static string that is part of the library. You must
536 not try to free it. Normally, the offset from the start of the pattern to the
537 byte that was being processed when the error was discovered is placed in the
538 variable pointed to by \fIerroffset\fP, which must not be NULL (if it is, an
539 immediate error is given). However, for an invalid UTF-8 string, the offset is
540 that of the first byte of the failing character.
541 .P
542 Some errors are not detected until the whole pattern has been scanned; in these
543 cases, the offset passed back is the length of the pattern. Note that the
544 offset is in bytes, not characters, even in UTF-8 mode. It may sometimes point
545 into the middle of a UTF-8 character.
546 .P
547 If \fBpcre_compile2()\fP is used instead of \fBpcre_compile()\fP, and the
548 \fIerrorcodeptr\fP argument is not NULL, a non-zero error code number is
549 returned via this argument in the event of an error. This is in addition to the
550 textual error message. Error codes and messages are listed below.
551 .P
552 If the final argument, \fItableptr\fP, is NULL, PCRE uses a default set of
553 character tables that are built when PCRE is compiled, using the default C
554 locale. Otherwise, \fItableptr\fP must be an address that is the result of a
555 call to \fBpcre_maketables()\fP. This value is stored with the compiled
556 pattern, and used again by \fBpcre_exec()\fP, unless another table pointer is
557 passed to it. For more discussion, see the section on locale support below.
558 .P
559 This code fragment shows a typical straightforward call to \fBpcre_compile()\fP:
560 .sp
561 pcre *re;
562 const char *error;
563 int erroffset;
564 re = pcre_compile(
565 "^A.*Z", /* the pattern */
566 0, /* default options */
567 &error, /* for error message */
568 &erroffset, /* for error offset */
569 NULL); /* use default character tables */
570 .sp
571 The following names for option bits are defined in the \fBpcre.h\fP header
572 file:
573 .sp
575 .sp
576 If this bit is set, the pattern is forced to be "anchored", that is, it is
577 constrained to match only at the first matching point in the string that is
578 being searched (the "subject string"). This effect can also be achieved by
579 appropriate constructs in the pattern itself, which is the only way to do it in
580 Perl.
581 .sp
583 .sp
584 If this bit is set, \fBpcre_compile()\fP automatically inserts callout items,
585 all with number 255, before each pattern item. For discussion of the callout
586 facility, see the
587 .\" HREF
588 \fBpcrecallout\fP
589 .\"
590 documentation.
591 .sp
594 .sp
595 These options (which are mutually exclusive) control what the \eR escape
596 sequence matches. The choice is either to match only CR, LF, or CRLF, or to
597 match any Unicode newline sequence. The default is specified when PCRE is
598 built. It can be overridden from within the pattern, or by setting an option
599 when a compiled pattern is matched.
600 .sp
602 .sp
603 If this bit is set, letters in the pattern match both upper and lower case
604 letters. It is equivalent to Perl's /i option, and it can be changed within a
605 pattern by a (?i) option setting. In UTF-8 mode, PCRE always understands the
606 concept of case for characters whose values are less than 128, so caseless
607 matching is always possible. For characters with higher values, the concept of
608 case is supported if PCRE is compiled with Unicode property support, but not
609 otherwise. If you want to use caseless matching for characters 128 and above,
610 you must ensure that PCRE is compiled with Unicode property support as well as
611 with UTF-8 support.
612 .sp
614 .sp
615 If this bit is set, a dollar metacharacter in the pattern matches only at the
616 end of the subject string. Without this option, a dollar also matches
617 immediately before a newline at the end of the string (but not before any other
618 newlines). The PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is set.
619 There is no equivalent to this option in Perl, and no way to set it within a
620 pattern.
621 .sp
623 .sp
624 If this bit is set, a dot metacharacter in the pattern matches a character of
625 any value, including one that indicates a newline. However, it only ever
626 matches one character, even if newlines are coded as CRLF. Without this option,
627 a dot does not match when the current position is at a newline. This option is
628 equivalent to Perl's /s option, and it can be changed within a pattern by a
629 (?s) option setting. A negative class such as [^a] always matches newline
630 characters, independent of the setting of this option.
631 .sp
633 .sp
634 If this bit is set, names used to identify capturing subpatterns need not be
635 unique. This can be helpful for certain types of pattern when it is known that
636 only one instance of the named subpattern can ever be matched. There are more
637 details of named subpatterns below; see also the
638 .\" HREF
639 \fBpcrepattern\fP
640 .\"
641 documentation.
642 .sp
644 .sp
645 If this bit is set, whitespace data characters in the pattern are totally
646 ignored except when escaped or inside a character class. Whitespace does not
647 include the VT character (code 11). In addition, characters between an
648 unescaped # outside a character class and the next newline, inclusive, are also
649 ignored. This is equivalent to Perl's /x option, and it can be changed within a
650 pattern by a (?x) option setting.
651 .P
652 Which characters are interpreted as newlines is controlled by the options
653 passed to \fBpcre_compile()\fP or by a special sequence at the start of the
654 pattern, as described in the section entitled
655 .\" HTML <a href="pcrepattern.html#newlines">
656 .\" </a>
657 "Newline conventions"
658 .\"
659 in the \fBpcrepattern\fP documentation. Note that the end of this type of
660 comment is a literal newline sequence in the pattern; escape sequences that
661 happen to represent a newline do not count.
662 .P
663 This option makes it possible to include comments inside complicated patterns.
664 Note, however, that this applies only to data characters. Whitespace characters
665 may never appear within special character sequences in a pattern, for example
666 within the sequence (?( that introduces a conditional subpattern.
667 .sp
669 .sp
670 This option was invented in order to turn on additional functionality of PCRE
671 that is incompatible with Perl, but it is currently of very little use. When
672 set, any backslash in a pattern that is followed by a letter that has no
673 special meaning causes an error, thus reserving these combinations for future
674 expansion. By default, as in Perl, a backslash followed by a letter with no
675 special meaning is treated as a literal. (Perl can, however, be persuaded to
676 give an error for this, by running it with the -w option.) There are at present
677 no other features controlled by this option. It can also be set by a (?X)
678 option setting within a pattern.
679 .sp
681 .sp
682 If this option is set, an unanchored pattern is required to match before or at
683 the first newline in the subject string, though the matched text may continue
684 over the newline.
685 .sp
687 .sp
688 If this option is set, PCRE's behaviour is changed in some ways so that it is
689 compatible with JavaScript rather than Perl. The changes are as follows:
690 .P
691 (1) A lone closing square bracket in a pattern causes a compile-time error,
692 because this is illegal in JavaScript (by default it is treated as a data
693 character). Thus, the pattern AB]CD becomes illegal when this option is set.
694 .P
695 (2) At run time, a back reference to an unset subpattern group matches an empty
696 string (by default this causes the current matching alternative to fail). A
697 pattern such as (\e1)(a) succeeds when this option is set (assuming it can find
698 an "a" in the subject), whereas it fails by default, for Perl compatibility.
699 .P
700 (3) \eU matches an upper case "U" character; by default \eU causes a compile
701 time error (Perl uses \eU to upper case subsequent characters).
702 .P
703 (4) \eu matches a lower case "u" character unless it is followed by four
704 hexadecimal digits, in which case the hexadecimal number defines the code point
705 to match. By default, \eu causes a compile time error (Perl uses it to upper
706 case the following character).
707 .P
708 (5) \ex matches a lower case "x" character unless it is followed by two
709 hexadecimal digits, in which case the hexadecimal number defines the code point
710 to match. By default, as in Perl, a hexadecimal number is always expected after
711 \ex, but it may have zero, one, or two digits (so, for example, \exz matches a
712 binary zero character followed by z).
713 .sp
715 .sp
716 By default, PCRE treats the subject string as consisting of a single line of
717 characters (even if it actually contains newlines). The "start of line"
718 metacharacter (^) matches only at the start of the string, while the "end of
719 line" metacharacter ($) matches only at the end of the string, or before a
720 terminating newline (unless PCRE_DOLLAR_ENDONLY is set). This is the same as
721 Perl.
722 .P
723 When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs
724 match immediately following or immediately before internal newlines in the
725 subject string, respectively, as well as at the very start and end. This is
726 equivalent to Perl's /m option, and it can be changed within a pattern by a
727 (?m) option setting. If there are no newlines in a subject string, or no
728 occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no effect.
729 .sp
735 .sp
736 These options override the default newline definition that was chosen when PCRE
737 was built. Setting the first or the second specifies that a newline is
738 indicated by a single character (CR or LF, respectively). Setting
739 PCRE_NEWLINE_CRLF specifies that a newline is indicated by the two-character
740 CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies that any of the three
741 preceding sequences should be recognized. Setting PCRE_NEWLINE_ANY specifies
742 that any Unicode newline sequence should be recognized. The Unicode newline
743 sequences are the three just mentioned, plus the single characters VT (vertical
744 tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS (line
745 separator, U+2028), and PS (paragraph separator, U+2029). For the 8-bit
746 library, the last two are recognized only in UTF-8 mode.
747 .P
748 The newline setting in the options word uses three bits that are treated
749 as a number, giving eight possibilities. Currently only six are used (default
750 plus the five values above). This means that if you set more than one newline
751 option, the combination may or may not be sensible. For example,
753 other combinations may yield unused numbers and cause an error.
754 .P
755 The only time that a line break in a pattern is specially recognized when
756 compiling is when PCRE_EXTENDED is set. CR and LF are whitespace characters,
757 and so are ignored in this mode. Also, an unescaped # outside a character class
758 indicates a comment that lasts until after the next line break sequence. In
759 other circumstances, line break sequences in patterns are treated as literal
760 data.
761 .P
762 The newline option that is set at compile time becomes the default that is used
763 for \fBpcre_exec()\fP and \fBpcre_dfa_exec()\fP, but it can be overridden.
764 .sp
766 .sp
767 If this option is set, it disables the use of numbered capturing parentheses in
768 the pattern. Any opening parenthesis that is not followed by ? behaves as if it
769 were followed by ?: but named parentheses can still be used for capturing (and
770 they acquire numbers in the usual way). There is no equivalent of this option
771 in Perl.
772 .sp
774 .sp
775 This is an option that acts at matching time; that is, it is really an option
776 for \fBpcre_exec()\fP or \fBpcre_dfa_exec()\fP. If it is set at compile time,
777 it is remembered with the compiled pattern and assumed at matching time. For
778 details see the discussion of PCRE_NO_START_OPTIMIZE
779 .\" HTML <a href="#execoptions">
780 .\" </a>
781 below.
782 .\"
783 .sp
785 .sp
786 This option changes the way PCRE processes \eB, \eb, \eD, \ed, \eS, \es, \eW,
787 \ew, and some of the POSIX character classes. By default, only ASCII characters
788 are recognized, but if PCRE_UCP is set, Unicode properties are used instead to
789 classify characters. More details are given in the section on
790 .\" HTML <a href="pcre.html#genericchartypes">
791 .\" </a>
792 generic character types
793 .\"
794 in the
795 .\" HREF
796 \fBpcrepattern\fP
797 .\"
798 page. If you set PCRE_UCP, matching one of the items it affects takes much
799 longer. The option is available only if PCRE has been compiled with Unicode
800 property support.
801 .sp
803 .sp
804 This option inverts the "greediness" of the quantifiers so that they are not
805 greedy by default, but become greedy if followed by "?". It is not compatible
806 with Perl. It can also be set by a (?U) option setting within the pattern.
807 .sp
809 .sp
810 This option causes PCRE to regard both the pattern and the subject as strings
811 of UTF-8 characters instead of single-byte strings. However, it is available
812 only when PCRE is built to include UTF support. If not, the use of this option
813 provokes an error. Details of how this option changes the behaviour of PCRE are
814 given in the
815 .\" HREF
816 \fBpcreunicode\fP
817 .\"
818 page.
819 .sp
821 .sp
822 When PCRE_UTF8 is set, the validity of the pattern as a UTF-8
823 string is automatically checked. There is a discussion about the
824 .\" HTML <a href="pcreunicode.html#utf8strings">
825 .\" </a>
826 validity of UTF-8 strings
827 .\"
828 in the
829 .\" HREF
830 \fBpcreunicode\fP
831 .\"
832 page. If an invalid UTF-8 sequence is found, \fBpcre_compile()\fP returns an
833 error. If you already know that your pattern is valid, and you want to skip
834 this check for performance reasons, you can set the PCRE_NO_UTF8_CHECK option.
835 When it is set, the effect of passing an invalid UTF-8 string as a pattern is
836 undefined. It may cause your program to crash. Note that this option can also
837 be passed to \fBpcre_exec()\fP and \fBpcre_dfa_exec()\fP, to suppress the
838 validity checking of subject strings.
839 .
840 .
842 .rs
843 .sp
844 The following table lists the error codes than may be returned by
845 \fBpcre_compile2()\fP, along with the error messages that may be returned by
846 both compiling functions. Note that error messages are always 8-bit ASCII
847 strings, even in 16-bit mode. As PCRE has developed, some error codes have
848 fallen out of use. To avoid confusion, they have not been re-used.
849 .sp
850 0 no error
851 1 \e at end of pattern
852 2 \ec at end of pattern
853 3 unrecognized character follows \e
854 4 numbers out of order in {} quantifier
855 5 number too big in {} quantifier
856 6 missing terminating ] for character class
857 7 invalid escape sequence in character class
858 8 range out of order in character class
859 9 nothing to repeat
860 10 [this code is not in use]
861 11 internal error: unexpected repeat
862 12 unrecognized character after (? or (?-
863 13 POSIX named classes are supported only within a class
864 14 missing )
865 15 reference to non-existent subpattern
866 16 erroffset passed as NULL
867 17 unknown option bit(s) set
868 18 missing ) after comment
869 19 [this code is not in use]
870 20 regular expression is too large
871 21 failed to get memory
872 22 unmatched parentheses
873 23 internal error: code overflow
874 24 unrecognized character after (?<
875 25 lookbehind assertion is not fixed length
876 26 malformed number or name after (?(
877 27 conditional group contains more than two branches
878 28 assertion expected after (?(
879 29 (?R or (?[+-]digits must be followed by )
880 30 unknown POSIX class name
881 31 POSIX collating elements are not supported
882 32 this version of PCRE is compiled without UTF support
883 33 [this code is not in use]
884 34 character value in \ex{...} sequence is too large
885 35 invalid condition (?(0)
886 36 \eC not allowed in lookbehind assertion
887 37 PCRE does not support \eL, \el, \eN{name}, \eU, or \eu
888 38 number after (?C is > 255
889 39 closing ) for (?C expected
890 40 recursive call could loop indefinitely
891 41 unrecognized character after (?P
892 42 syntax error in subpattern name (missing terminator)
893 43 two named subpatterns have the same name
894 44 invalid UTF-8 string (specifically UTF-8)
895 45 support for \eP, \ep, and \eX has not been compiled
896 46 malformed \eP or \ep sequence
897 47 unknown property name after \eP or \ep
898 48 subpattern name is too long (maximum 32 characters)
899 49 too many named subpatterns (maximum 10000)
900 50 [this code is not in use]
901 51 octal value is greater than \e377 in 8-bit non-UTF-8 mode
902 52 internal error: overran compiling workspace
903 53 internal error: previously-checked referenced subpattern
904 not found
905 54 DEFINE group contains more than one branch
906 55 repeating a DEFINE group is not allowed
907 56 inconsistent NEWLINE options
908 57 \eg is not followed by a braced, angle-bracketed, or quoted
909 name/number or by a plain number
910 58 a numbered reference must not be zero
911 59 an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT)
912 60 (*VERB) not recognized
913 61 number is too big
914 62 subpattern name expected
915 63 digit expected after (?+
916 64 ] is an invalid data character in JavaScript compatibility mode
917 65 different names for subpatterns of the same number are
918 not allowed
919 66 (*MARK) must have an argument
920 67 this version of PCRE is not compiled with Unicode property
921 support
922 68 \ec must be followed by an ASCII character
923 69 \ek is not followed by a braced, angle-bracketed, or quoted name
924 70 internal error: unknown opcode in find_fixedlength()
925 71 \eN is not supported in a class
926 72 too many forward references
927 73 disallowed Unicode code point (>= 0xd800 && <= 0xdfff)
928 74 invalid UTF-16 string (specifically UTF-16)
929 .sp
930 The numbers 32 and 10000 in errors 48 and 49 are defaults; different values may
931 be used if the limits were changed when PCRE was built.
932 .
933 .
934 .\" HTML <a name="studyingapattern"></a>
936 .rs
937 .sp
938 .B pcre_extra *pcre_study(const pcre *\fIcode\fP, int \fIoptions\fP
939 .ti +5n
940 .B const char **\fIerrptr\fP);
941 .PP
942 If a compiled pattern is going to be used several times, it is worth spending
943 more time analyzing it in order to speed up the time taken for matching. The
944 function \fBpcre_study()\fP takes a pointer to a compiled pattern as its first
945 argument. If studying the pattern produces additional information that will
946 help speed up matching, \fBpcre_study()\fP returns a pointer to a
947 \fBpcre_extra\fP block, in which the \fIstudy_data\fP field points to the
948 results of the study.
949 .P
950 The returned value from \fBpcre_study()\fP can be passed directly to
951 \fBpcre_exec()\fP or \fBpcre_dfa_exec()\fP. However, a \fBpcre_extra\fP block
952 also contains other fields that can be set by the caller before the block is
953 passed; these are described
954 .\" HTML <a href="#extradata">
955 .\" </a>
956 below
957 .\"
958 in the section on matching a pattern.
959 .P
960 If studying the pattern does not produce any useful information,
961 \fBpcre_study()\fP returns NULL. In that circumstance, if the calling program
962 wants to pass any of the other fields to \fBpcre_exec()\fP or
963 \fBpcre_dfa_exec()\fP, it must set up its own \fBpcre_extra\fP block.
964 .P
965 The second argument of \fBpcre_study()\fP contains option bits. There are three
966 options:
967 .sp
971 .sp
972 If any of these are set, and the just-in-time compiler is available, the
973 pattern is further compiled into machine code that executes much faster than
974 the \fBpcre_exec()\fP interpretive matching function. If the just-in-time
975 compiler is not available, these options are ignored. All other bits in the
976 \fIoptions\fP argument must be zero.
977 .P
978 JIT compilation is a heavyweight optimization. It can take some time for
979 patterns to be analyzed, and for one-off matches and simple patterns the
980 benefit of faster execution might be offset by a much slower study time.
981 Not all patterns can be optimized by the JIT compiler. For those that cannot be
982 handled, matching automatically falls back to the \fBpcre_exec()\fP
983 interpreter. For more details, see the
984 .\" HREF
985 \fBpcrejit\fP
986 .\"
987 documentation.
988 .P
989 The third argument for \fBpcre_study()\fP is a pointer for an error message. If
990 studying succeeds (even if no data is returned), the variable it points to is
991 set to NULL. Otherwise it is set to point to a textual error message. This is a
992 static string that is part of the library. You must not try to free it. You
993 should test the error pointer for NULL after calling \fBpcre_study()\fP, to be
994 sure that it has run successfully.
995 .P
996 When you are finished with a pattern, you can free the memory used for the
997 study data by calling \fBpcre_free_study()\fP. This function was added to the
998 API for release 8.20. For earlier versions, the memory could be freed with
999 \fBpcre_free()\fP, just like the pattern itself. This will still work in cases
1000 where JIT optimization is not used, but it is advisable to change to the new
1001 function when convenient.
1002 .P
1003 This is a typical way in which \fBpcre_study\fP() is used (except that in a
1004 real application there should be tests for errors):
1005 .sp
1006 int rc;
1007 pcre *re;
1008 pcre_extra *sd;
1009 re = pcre_compile("pattern", 0, &error, &erroroffset, NULL);
1010 sd = pcre_study(
1011 re, /* result of pcre_compile() */
1012 0, /* no options */
1013 &error); /* set to NULL or points to a message */
1014 rc = pcre_exec( /* see below for details of pcre_exec() options */
1015 re, sd, "subject", 7, 0, 0, ovector, 30);
1016 ...
1017 pcre_free_study(sd);
1018 pcre_free(re);
1019 .sp
1020 Studying a pattern does two things: first, a lower bound for the length of
1021 subject string that is needed to match the pattern is computed. This does not
1022 mean that there are any strings of that length that match, but it does
1023 guarantee that no shorter strings match. The value is used by
1024 \fBpcre_exec()\fP and \fBpcre_dfa_exec()\fP to avoid wasting time by trying to
1025 match strings that are shorter than the lower bound. You can find out the value
1026 in a calling program via the \fBpcre_fullinfo()\fP function.
1027 .P
1028 Studying a pattern is also useful for non-anchored patterns that do not have a
1029 single fixed starting character. A bitmap of possible starting bytes is
1030 created. This speeds up finding a position in the subject at which to start
1031 matching. (In 16-bit mode, the bitmap is used for 16-bit values less than 256.)
1032 .P
1033 These two optimizations apply to both \fBpcre_exec()\fP and
1034 \fBpcre_dfa_exec()\fP, and the information is also used by the JIT compiler.
1035 The optimizations can be disabled by setting the PCRE_NO_START_OPTIMIZE option
1036 when calling \fBpcre_exec()\fP or \fBpcre_dfa_exec()\fP, but if this is done,
1037 JIT execution is also disabled. You might want to do this if your pattern
1038 contains callouts or (*MARK) and you want to make use of these facilities in
1039 cases where matching fails. See the discussion of PCRE_NO_START_OPTIMIZE
1040 .\" HTML <a href="#execoptions">
1041 .\" </a>
1042 below.
1043 .\"
1044 .
1045 .
1046 .\" HTML <a name="localesupport"></a>
1048 .rs
1049 .sp
1050 PCRE handles caseless matching, and determines whether characters are letters,
1051 digits, or whatever, by reference to a set of tables, indexed by character
1052 value. When running in UTF-8 mode, this applies only to characters
1053 with codes less than 128. By default, higher-valued codes never match escapes
1054 such as \ew or \ed, but they can be tested with \ep if PCRE is built with
1055 Unicode character property support. Alternatively, the PCRE_UCP option can be
1056 set at compile time; this causes \ew and friends to use Unicode property
1057 support instead of built-in tables. The use of locales with Unicode is
1058 discouraged. If you are handling characters with codes greater than 128, you
1059 should either use UTF-8 and Unicode, or use locales, but not try to mix the
1060 two.
1061 .P
1062 PCRE contains an internal set of tables that are used when the final argument
1063 of \fBpcre_compile()\fP is NULL. These are sufficient for many applications.
1064 Normally, the internal tables recognize only ASCII characters. However, when
1065 PCRE is built, it is possible to cause the internal tables to be rebuilt in the
1066 default "C" locale of the local system, which may cause them to be different.
1067 .P
1068 The internal tables can always be overridden by tables supplied by the
1069 application that calls PCRE. These may be created in a different locale from
1070 the default. As more and more applications change to using Unicode, the need
1071 for this locale support is expected to die away.
1072 .P
1073 External tables are built by calling the \fBpcre_maketables()\fP function,
1074 which has no arguments, in the relevant locale. The result can then be passed
1075 to \fBpcre_compile()\fP or \fBpcre_exec()\fP as often as necessary. For
1076 example, to build and use tables that are appropriate for the French locale
1077 (where accented characters with values greater than 128 are treated as letters),
1078 the following code could be used:
1079 .sp
1080 setlocale(LC_CTYPE, "fr_FR");
1081 tables = pcre_maketables();
1082 re = pcre_compile(..., tables);
1083 .sp
1084 The locale name "fr_FR" is used on Linux and other Unix-like systems; if you
1085 are using Windows, the name for the French locale is "french".
1086 .P
1087 When \fBpcre_maketables()\fP runs, the tables are built in memory that is
1088 obtained via \fBpcre_malloc\fP. It is the caller's responsibility to ensure
1089 that the memory containing the tables remains available for as long as it is
1090 needed.
1091 .P
1092 The pointer that is passed to \fBpcre_compile()\fP is saved with the compiled
1093 pattern, and the same tables are used via this pointer by \fBpcre_study()\fP
1094 and normally also by \fBpcre_exec()\fP. Thus, by default, for any single
1095 pattern, compilation, studying and matching all happen in the same locale, but
1096 different patterns can be compiled in different locales.
1097 .P
1098 It is possible to pass a table pointer or NULL (indicating the use of the
1099 internal tables) to \fBpcre_exec()\fP. Although not intended for this purpose,
1100 this facility could be used to match a pattern in a different locale from the
1101 one in which it was compiled. Passing table pointers at run time is discussed
1102 below in the section on matching a pattern.
1103 .
1104 .
1105 .\" HTML <a name="infoaboutpattern"></a>
1107 .rs
1108 .sp
1109 .B int pcre_fullinfo(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
1110 .ti +5n
1111 .B int \fIwhat\fP, void *\fIwhere\fP);
1112 .PP
1113 The \fBpcre_fullinfo()\fP function returns information about a compiled
1114 pattern. It replaces the \fBpcre_info()\fP function, which was removed from the
1115 library at version 8.30, after more than 10 years of obsolescence.
1116 .P
1117 The first argument for \fBpcre_fullinfo()\fP is a pointer to the compiled
1118 pattern. The second argument is the result of \fBpcre_study()\fP, or NULL if
1119 the pattern was not studied. The third argument specifies which piece of
1120 information is required, and the fourth argument is a pointer to a variable
1121 to receive the data. The yield of the function is zero for success, or one of
1122 the following negative numbers:
1123 .sp
1124 PCRE_ERROR_NULL the argument \fIcode\fP was NULL
1125 the argument \fIwhere\fP was NULL
1126 PCRE_ERROR_BADMAGIC the "magic number" was not found
1127 PCRE_ERROR_BADENDIANNESS the pattern was compiled with different
1128 endianness
1129 PCRE_ERROR_BADOPTION the value of \fIwhat\fP was invalid
1130 .sp
1131 The "magic number" is placed at the start of each compiled pattern as an simple
1132 check against passing an arbitrary memory pointer. The endianness error can
1133 occur if a compiled pattern is saved and reloaded on a different host. Here is
1134 a typical call of \fBpcre_fullinfo()\fP, to obtain the length of the compiled
1135 pattern:
1136 .sp
1137 int rc;
1138 size_t length;
1139 rc = pcre_fullinfo(
1140 re, /* result of pcre_compile() */
1141 sd, /* result of pcre_study(), or NULL */
1142 PCRE_INFO_SIZE, /* what is required */
1143 &length); /* where to put the data */
1144 .sp
1145 The possible values for the third argument are defined in \fBpcre.h\fP, and are
1146 as follows:
1147 .sp
1149 .sp
1150 Return the number of the highest back reference in the pattern. The fourth
1151 argument should point to an \fBint\fP variable. Zero is returned if there are
1152 no back references.
1153 .sp
1155 .sp
1156 Return the number of capturing subpatterns in the pattern. The fourth argument
1157 should point to an \fBint\fP variable.
1158 .sp
1160 .sp
1161 Return a pointer to the internal default character tables within PCRE. The
1162 fourth argument should point to an \fBunsigned char *\fP variable. This
1163 information call is provided for internal use by the \fBpcre_study()\fP
1164 function. External callers can cause PCRE to use its internal tables by passing
1165 a NULL table pointer.
1166 .sp
1168 .sp
1169 Return information about the first data unit of any matched string, for a
1170 non-anchored pattern. (The name of this option refers to the 8-bit library,
1171 where data units are bytes.) The fourth argument should point to an \fBint\fP
1172 variable.
1173 .P
1174 If there is a fixed first value, for example, the letter "c" from a pattern
1175 such as (cat|cow|coyote), its value is returned. In the 8-bit library, the
1176 value is always less than 256; in the 16-bit library the value can be up to
1177 0xffff.
1178 .P
1179 If there is no fixed first value, and if either
1180 .sp
1181 (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
1182 starts with "^", or
1183 .sp
1184 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
1185 (if it were set, the pattern would be anchored),
1186 .sp
1187 -1 is returned, indicating that the pattern matches only at the start of a
1188 subject string or after any newline within the string. Otherwise -2 is
1189 returned. For anchored patterns, -2 is returned.
1190 .sp
1192 .sp
1193 If the pattern was studied, and this resulted in the construction of a 256-bit
1194 table indicating a fixed set of values for the first data unit in any matching
1195 string, a pointer to the table is returned. Otherwise NULL is returned. The
1196 fourth argument should point to an \fBunsigned char *\fP variable.
1197 .sp
1199 .sp
1200 Return 1 if the pattern contains any explicit matches for CR or LF characters,
1201 otherwise 0. The fourth argument should point to an \fBint\fP variable. An
1202 explicit match is either a literal CR or LF character, or \er or \en.
1203 .sp
1205 .sp
1206 Return 1 if the (?J) or (?-J) option setting is used in the pattern, otherwise
1207 0. The fourth argument should point to an \fBint\fP variable. (?J) and
1208 (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
1209 .sp
1211 .sp
1212 Return 1 if the pattern was studied with one of the JIT options, and
1213 just-in-time compiling was successful. The fourth argument should point to an
1214 \fBint\fP variable. A return value of 0 means that JIT support is not available
1215 in this version of PCRE, or that the pattern was not studied with a JIT option,
1216 or that the JIT compiler could not handle this particular pattern. See the
1217 .\" HREF
1218 \fBpcrejit\fP
1219 .\"
1220 documentation for details of what can and cannot be handled.
1221 .sp
1223 .sp
1224 If the pattern was successfully studied with a JIT option, return the size of
1225 the JIT compiled code, otherwise return zero. The fourth argument should point
1226 to a \fBsize_t\fP variable.
1227 .sp
1229 .sp
1230 Return the value of the rightmost literal data unit that must exist in any
1231 matched string, other than at its start, if such a value has been recorded. The
1232 fourth argument should point to an \fBint\fP variable. If there is no such
1233 value, -1 is returned. For anchored patterns, a last literal value is recorded
1234 only if it follows something of variable length. For example, for the pattern
1235 /^a\ed+z\ed+/ the returned value is "z", but for /^a\edz\ed/ the returned value
1236 is -1.
1237 .sp
1239 .sp
1240 If the pattern was studied and a minimum length for matching subject strings
1241 was computed, its value is returned. Otherwise the returned value is -1. The
1242 value is a number of characters, which in UTF-8 mode may be different from the
1243 number of bytes. The fourth argument should point to an \fBint\fP variable. A
1244 non-negative value is a lower bound to the length of any matching string. There
1245 may not be any strings of that length that do actually match, but every string
1246 that does match is at least that long.
1247 .sp
1251 .sp
1252 PCRE supports the use of named as well as numbered capturing parentheses. The
1253 names are just an additional way of identifying the parentheses, which still
1254 acquire numbers. Several convenience functions such as
1255 \fBpcre_get_named_substring()\fP are provided for extracting captured
1256 substrings by name. It is also possible to extract the data directly, by first
1257 converting the name to a number in order to access the correct pointers in the
1258 output vector (described with \fBpcre_exec()\fP below). To do the conversion,
1259 you need to use the name-to-number map, which is described by these three
1260 values.
1261 .P
1262 The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives
1263 the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each
1264 entry; both of these return an \fBint\fP value. The entry size depends on the
1265 length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first
1266 entry of the table. This is a pointer to \fBchar\fP in the 8-bit library, where
1267 the first two bytes of each entry are the number of the capturing parenthesis,
1268 most significant byte first. In the 16-bit library, the pointer points to
1269 16-bit data units, the first of which contains the parenthesis number. The rest
1270 of the entry is the corresponding name, zero terminated.
1271 .P
1272 The names are in alphabetical order. Duplicate names may appear if (?| is used
1273 to create multiple groups with the same number, as described in the
1274 .\" HTML <a href="pcrepattern.html#dupsubpatternnumber">
1275 .\" </a>
1276 section on duplicate subpattern numbers
1277 .\"
1278 in the
1279 .\" HREF
1280 \fBpcrepattern\fP
1281 .\"
1282 page. Duplicate names for subpatterns with different numbers are permitted only
1283 if PCRE_DUPNAMES is set. In all cases of duplicate names, they appear in the
1284 table in the order in which they were found in the pattern. In the absence of
1285 (?| this is the order of increasing number; when (?| is used this is not
1286 necessarily the case because later subpatterns may have lower numbers.
1287 .P
1288 As a simple example of the name/number table, consider the following pattern
1289 after compilation by the 8-bit library (assume PCRE_EXTENDED is set, so white
1290 space - including newlines - is ignored):
1291 .sp
1292 .\" JOIN
1293 (?<date> (?<year>(\ed\ed)?\ed\ed) -
1294 (?<month>\ed\ed) - (?<day>\ed\ed) )
1295 .sp
1296 There are four named subpatterns, so the table has four entries, and each entry
1297 in the table is eight bytes long. The table is as follows, with non-printing
1298 bytes shows in hexadecimal, and undefined bytes shown as ??:
1299 .sp
1300 00 01 d a t e 00 ??
1301 00 05 d a y 00 ?? ??
1302 00 04 m o n t h 00
1303 00 02 y e a r 00 ??
1304 .sp
1305 When writing code to extract data from named subpatterns using the
1306 name-to-number map, remember that the length of the entries is likely to be
1307 different for each compiled pattern.
1308 .sp
1310 .sp
1311 Return 1 if the pattern can be used for partial matching with
1312 \fBpcre_exec()\fP, otherwise 0. The fourth argument should point to an
1313 \fBint\fP variable. From release 8.00, this always returns 1, because the
1314 restrictions that previously applied to partial matching have been lifted. The
1315 .\" HREF
1316 \fBpcrepartial\fP
1317 .\"
1318 documentation gives details of partial matching.
1319 .sp
1321 .sp
1322 Return a copy of the options with which the pattern was compiled. The fourth
1323 argument should point to an \fBunsigned long int\fP variable. These option bits
1324 are those specified in the call to \fBpcre_compile()\fP, modified by any
1325 top-level option settings at the start of the pattern itself. In other words,
1326 they are the options that will be in force when matching starts. For example,
1327 if the pattern /(?im)abc(?-i)d/ is compiled with the PCRE_EXTENDED option, the
1329 .P
1330 A pattern is automatically anchored by PCRE if all of its top-level
1331 alternatives begin with one of the following:
1332 .sp
1333 ^ unless PCRE_MULTILINE is set
1334 \eA always
1335 \eG always
1336 .\" JOIN
1337 .* if PCRE_DOTALL is set and there are no back
1338 references to the subpattern in which .* appears
1339 .sp
1340 For such patterns, the PCRE_ANCHORED bit is set in the options returned by
1341 \fBpcre_fullinfo()\fP.
1342 .sp
1344 .sp
1345 Return the size of the compiled pattern in bytes (for both libraries). The
1346 fourth argument should point to a \fBsize_t\fP variable. This value does not
1347 include the size of the \fBpcre\fP structure that is returned by
1348 \fBpcre_compile()\fP. The value that is passed as the argument to
1349 \fBpcre_malloc()\fP when \fBpcre_compile()\fP is getting memory in which to
1350 place the compiled data is the value returned by this option plus the size of
1351 the \fBpcre\fP structure. Studying a compiled pattern, with or without JIT,
1352 does not alter the value returned by this option.
1353 .sp
1355 .sp
1356 Return the size in bytes of the data block pointed to by the \fIstudy_data\fP
1357 field in a \fBpcre_extra\fP block. If \fBpcre_extra\fP is NULL, or there is no
1358 study data, zero is returned. The fourth argument should point to a
1359 \fBsize_t\fP variable. The \fIstudy_data\fP field is set by \fBpcre_study()\fP
1360 to record information that will speed up matching (see the section entitled
1361 .\" HTML <a href="#studyingapattern">
1362 .\" </a>
1363 "Studying a pattern"
1364 .\"
1365 above). The format of the \fIstudy_data\fP block is private, but its length
1366 is made available via this option so that it can be saved and restored (see the
1367 .\" HREF
1368 \fBpcreprecompile\fP
1369 .\"
1370 documentation for details).
1371 .
1372 .
1374 .rs
1375 .sp
1376 .B int pcre_refcount(pcre *\fIcode\fP, int \fIadjust\fP);
1377 .PP
1378 The \fBpcre_refcount()\fP function is used to maintain a reference count in the
1379 data block that contains a compiled pattern. It is provided for the benefit of
1380 applications that operate in an object-oriented manner, where different parts
1381 of the application may be using the same compiled pattern, but you want to free
1382 the block when they are all done.
1383 .P
1384 When a pattern is compiled, the reference count field is initialized to zero.
1385 It is changed only by calling this function, whose action is to add the
1386 \fIadjust\fP value (which may be positive or negative) to it. The yield of the
1387 function is the new value. However, the value of the count is constrained to
1388 lie between 0 and 65535, inclusive. If the new value is outside these limits,
1389 it is forced to the appropriate limit value.
1390 .P
1391 Except when it is zero, the reference count is not correctly preserved if a
1392 pattern is compiled on one host and then transferred to a host whose byte-order
1393 is different. (This seems a highly unlikely scenario.)
1394 .
1395 .
1397 .rs
1398 .sp
1399 .B int pcre_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
1400 .ti +5n
1401 .B "const char *\fIsubject\fP," int \fIlength\fP, int \fIstartoffset\fP,
1402 .ti +5n
1403 .B int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP);
1404 .P
1405 The function \fBpcre_exec()\fP is called to match a subject string against a
1406 compiled pattern, which is passed in the \fIcode\fP argument. If the
1407 pattern was studied, the result of the study should be passed in the
1408 \fIextra\fP argument. You can call \fBpcre_exec()\fP with the same \fIcode\fP
1409 and \fIextra\fP arguments as many times as you like, in order to match
1410 different subject strings with the same pattern.
1411 .P
1412 This function is the main matching facility of the library, and it operates in
1413 a Perl-like manner. For specialist use there is also an alternative matching
1414 function, which is described
1415 .\" HTML <a href="#dfamatch">
1416 .\" </a>
1417 below
1418 .\"
1419 in the section about the \fBpcre_dfa_exec()\fP function.
1420 .P
1421 In most applications, the pattern will have been compiled (and optionally
1422 studied) in the same process that calls \fBpcre_exec()\fP. However, it is
1423 possible to save compiled patterns and study data, and then use them later
1424 in different processes, possibly even on different hosts. For a discussion
1425 about this, see the
1426 .\" HREF
1427 \fBpcreprecompile\fP
1428 .\"
1429 documentation.
1430 .P
1431 Here is an example of a simple call to \fBpcre_exec()\fP:
1432 .sp
1433 int rc;
1434 int ovector[30];
1435 rc = pcre_exec(
1436 re, /* result of pcre_compile() */
1437 NULL, /* we didn't study the pattern */
1438 "some string", /* the subject string */
1439 11, /* the length of the subject string */
1440 0, /* start at offset 0 in the subject */
1441 0, /* default options */
1442 ovector, /* vector of integers for substring information */
1443 30); /* number of elements (NOT size in bytes) */
1444 .
1445 .
1446 .\" HTML <a name="extradata"></a>
1447 .SS "Extra data for \fBpcre_exec()\fR"
1448 .rs
1449 .sp
1450 If the \fIextra\fP argument is not NULL, it must point to a \fBpcre_extra\fP
1451 data block. The \fBpcre_study()\fP function returns such a block (when it
1452 doesn't return NULL), but you can also create one for yourself, and pass
1453 additional information in it. The \fBpcre_extra\fP block contains the following
1454 fields (not necessarily in this order):
1455 .sp
1456 unsigned long int \fIflags\fP;
1457 void *\fIstudy_data\fP;
1458 void *\fIexecutable_jit\fP;
1459 unsigned long int \fImatch_limit\fP;
1460 unsigned long int \fImatch_limit_recursion\fP;
1461 void *\fIcallout_data\fP;
1462 const unsigned char *\fItables\fP;
1463 unsigned char **\fImark\fP;
1464 .sp
1465 In the 16-bit version of this structure, the \fImark\fP field has type
1466 "PCRE_UCHAR16 **".
1467 .P
1468 The \fIflags\fP field is used to specify which of the other fields are set. The
1469 flag bits are:
1470 .sp
1478 .sp
1479 Other flag bits should be set to zero. The \fIstudy_data\fP field and sometimes
1480 the \fIexecutable_jit\fP field are set in the \fBpcre_extra\fP block that is
1481 returned by \fBpcre_study()\fP, together with the appropriate flag bits. You
1482 should not set these yourself, but you may add to the block by setting other
1483 fields and their corresponding flag bits.
1484 .P
1485 The \fImatch_limit\fP field provides a means of preventing PCRE from using up a
1486 vast amount of resources when running patterns that are not going to match,
1487 but which have a very large number of possibilities in their search trees. The
1488 classic example is a pattern that uses nested unlimited repeats.
1489 .P
1490 Internally, \fBpcre_exec()\fP uses a function called \fBmatch()\fP, which it
1491 calls repeatedly (sometimes recursively). The limit set by \fImatch_limit\fP is
1492 imposed on the number of times this function is called during a match, which
1493 has the effect of limiting the amount of backtracking that can take place. For
1494 patterns that are not anchored, the count restarts from zero for each position
1495 in the subject string.
1496 .P
1497 When \fBpcre_exec()\fP is called with a pattern that was successfully studied
1498 with a JIT option, the way that the matching is executed is entirely different.
1499 However, there is still the possibility of runaway matching that goes on for a
1500 very long time, and so the \fImatch_limit\fP value is also used in this case
1501 (but in a different way) to limit how long the matching can continue.
1502 .P
1503 The default value for the limit can be set when PCRE is built; the default
1504 default is 10 million, which handles all but the most extreme cases. You can
1505 override the default by suppling \fBpcre_exec()\fP with a \fBpcre_extra\fP
1506 block in which \fImatch_limit\fP is set, and PCRE_EXTRA_MATCH_LIMIT is set in
1507 the \fIflags\fP field. If the limit is exceeded, \fBpcre_exec()\fP returns
1509 .P
1510 The \fImatch_limit_recursion\fP field is similar to \fImatch_limit\fP, but
1511 instead of limiting the total number of times that \fBmatch()\fP is called, it
1512 limits the depth of recursion. The recursion depth is a smaller number than the
1513 total number of calls, because not all calls to \fBmatch()\fP are recursive.
1514 This limit is of use only if it is set smaller than \fImatch_limit\fP.
1515 .P
1516 Limiting the recursion depth limits the amount of machine stack that can be
1517 used, or, when PCRE has been compiled to use memory on the heap instead of the
1518 stack, the amount of heap memory that can be used. This limit is not relevant,
1519 and is ignored, when matching is done using JIT compiled code.
1520 .P
1521 The default value for \fImatch_limit_recursion\fP can be set when PCRE is
1522 built; the default default is the same value as the default for
1523 \fImatch_limit\fP. You can override the default by suppling \fBpcre_exec()\fP
1524 with a \fBpcre_extra\fP block in which \fImatch_limit_recursion\fP is set, and
1525 PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the \fIflags\fP field. If the limit
1526 is exceeded, \fBpcre_exec()\fP returns PCRE_ERROR_RECURSIONLIMIT.
1527 .P
1528 The \fIcallout_data\fP field is used in conjunction with the "callout" feature,
1529 and is described in the
1530 .\" HREF
1531 \fBpcrecallout\fP
1532 .\"
1533 documentation.
1534 .P
1535 The \fItables\fP field is used to pass a character tables pointer to
1536 \fBpcre_exec()\fP; this overrides the value that is stored with the compiled
1537 pattern. A non-NULL value is stored with the compiled pattern only if custom
1538 tables were supplied to \fBpcre_compile()\fP via its \fItableptr\fP argument.
1539 If NULL is passed to \fBpcre_exec()\fP using this mechanism, it forces PCRE's
1540 internal tables to be used. This facility is helpful when re-using patterns
1541 that have been saved after compiling with an external set of tables, because
1542 the external tables might be at a different address when \fBpcre_exec()\fP is
1543 called. See the
1544 .\" HREF
1545 \fBpcreprecompile\fP
1546 .\"
1547 documentation for a discussion of saving compiled patterns for later use.
1548 .P
1549 If PCRE_EXTRA_MARK is set in the \fIflags\fP field, the \fImark\fP field must
1550 be set to point to a suitable variable. If the pattern contains any
1551 backtracking control verbs such as (*MARK:NAME), and the execution ends up with
1552 a name to pass back, a pointer to the name string (zero terminated) is placed
1553 in the variable pointed to by the \fImark\fP field. The names are within the
1554 compiled pattern; if you wish to retain such a name you must copy it before
1555 freeing the memory of a compiled pattern. If there is no name to pass back, the
1556 variable pointed to by the \fImark\fP field is set to NULL. For details of the
1557 backtracking control verbs, see the section entitled
1558 .\" HTML <a href="pcrepattern#backtrackcontrol">
1559 .\" </a>
1560 "Backtracking control"
1561 .\"
1562 in the
1563 .\" HREF
1564 \fBpcrepattern\fP
1565 .\"
1566 documentation.
1567 .
1568 .
1569 .\" HTML <a name="execoptions"></a>
1570 .SS "Option bits for \fBpcre_exec()\fP"
1571 .rs
1572 .sp
1573 The unused bits of the \fIoptions\fP argument for \fBpcre_exec()\fP must be
1574 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_\fIxxx\fP,
1578 .P
1579 If the pattern was successfully studied with one of the just-in-time (JIT)
1580 compile options, the only supported options for JIT execution are
1583 unsupported option is used, JIT execution is disabled and the normal
1584 interpretive code in \fBpcre_exec()\fP is run.
1585 .sp
1587 .sp
1588 The PCRE_ANCHORED option limits \fBpcre_exec()\fP to matching at the first
1589 matching position. If a pattern was compiled with PCRE_ANCHORED, or turned out
1590 to be anchored by virtue of its contents, it cannot be made unachored at
1591 matching time.
1592 .sp
1595 .sp
1596 These options (which are mutually exclusive) control what the \eR escape
1597 sequence matches. The choice is either to match only CR, LF, or CRLF, or to
1598 match any Unicode newline sequence. These options override the choice that was
1599 made or defaulted when the pattern was compiled.
1600 .sp
1606 .sp
1607 These options override the newline definition that was chosen or defaulted when
1608 the pattern was compiled. For details, see the description of
1609 \fBpcre_compile()\fP above. During matching, the newline choice affects the
1610 behaviour of the dot, circumflex, and dollar metacharacters. It may also alter
1611 the way the match position is advanced after a match failure for an unanchored
1612 pattern.
1613 .P
1615 match attempt for an unanchored pattern fails when the current position is at a
1616 CRLF sequence, and the pattern contains no explicit matches for CR or LF
1617 characters, the match position is advanced by two characters instead of one, in
1618 other words, to after the CRLF.
1619 .P
1620 The above rule is a compromise that makes the most common cases work as
1621 expected. For example, if the pattern is .+A (and the PCRE_DOTALL option is not
1622 set), it does not match the string "\er\enA" because, after failing at the
1623 start, it skips both the CR and the LF before retrying. However, the pattern
1624 [\er\en]A does match that string, because it contains an explicit CR or LF
1625 reference, and so advances only by one character after the first failure.
1626 .P
1627 An explicit match for CR of LF is either a literal appearance of one of those
1628 characters, or one of the \er or \en escape sequences. Implicit matches such as
1629 [^X] do not count, nor does \es (which includes CR and LF in the characters
1630 that it matches).
1631 .P
1632 Notwithstanding the above, anomalous effects may still occur when CRLF is a
1633 valid newline sequence and explicit \er or \en escapes appear in the pattern.
1634 .sp
1636 .sp
1637 This option specifies that first character of the subject string is not the
1638 beginning of a line, so the circumflex metacharacter should not match before
1639 it. Setting this without PCRE_MULTILINE (at compile time) causes circumflex
1640 never to match. This option affects only the behaviour of the circumflex
1641 metacharacter. It does not affect \eA.
1642 .sp
1644 .sp
1645 This option specifies that the end of the subject string is not the end of a
1646 line, so the dollar metacharacter should not match it nor (except in multiline
1647 mode) a newline immediately before it. Setting this without PCRE_MULTILINE (at
1648 compile time) causes dollar never to match. This option affects only the
1649 behaviour of the dollar metacharacter. It does not affect \eZ or \ez.
1650 .sp
1652 .sp
1653 An empty string is not considered to be a valid match if this option is set. If
1654 there are alternatives in the pattern, they are tried. If all the alternatives
1655 match the empty string, the entire match fails. For example, if the pattern
1656 .sp
1657 a?b?
1658 .sp
1659 is applied to a string not beginning with "a" or "b", it matches an empty
1660 string at the start of the subject. With PCRE_NOTEMPTY set, this match is not
1661 valid, so PCRE searches further into the string for occurrences of "a" or "b".
1662 .sp
1664 .sp
1665 This is like PCRE_NOTEMPTY, except that an empty string match that is not at
1666 the start of the subject is permitted. If the pattern is anchored, such a match
1667 can occur only if the pattern contains \eK.
1668 .P
1669 Perl has no direct equivalent of PCRE_NOTEMPTY or PCRE_NOTEMPTY_ATSTART, but it
1670 does make a special case of a pattern match of the empty string within its
1671 \fBsplit()\fP function, and when using the /g modifier. It is possible to
1672 emulate Perl's behaviour after matching a null string by first trying the match
1673 again at the same offset with PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED, and then
1674 if that fails, by advancing the starting offset (see below) and trying an
1675 ordinary match again. There is some code that demonstrates how to do this in
1676 the
1677 .\" HREF
1678 \fBpcredemo\fP
1679 .\"
1680 sample program. In the most general case, you have to check to see if the
1681 newline convention recognizes CRLF as a newline, and if so, and the current
1682 character is CR followed by LF, advance the starting offset by two characters
1683 instead of one.
1684 .sp
1686 .sp
1687 There are a number of optimizations that \fBpcre_exec()\fP uses at the start of
1688 a match, in order to speed up the process. For example, if it is known that an
1689 unanchored match must start with a specific character, it searches the subject
1690 for that character, and fails immediately if it cannot find it, without
1691 actually running the main matching function. This means that a special item
1692 such as (*COMMIT) at the start of a pattern is not considered until after a
1693 suitable starting point for the match has been found. When callouts or (*MARK)
1694 items are in use, these "start-up" optimizations can cause them to be skipped
1695 if the pattern is never actually used. The start-up optimizations are in effect
1696 a pre-scan of the subject that takes place before the pattern is run.
1697 .P
1698 The PCRE_NO_START_OPTIMIZE option disables the start-up optimizations, possibly
1699 causing performance to suffer, but ensuring that in cases where the result is
1700 "no match", the callouts do occur, and that items such as (*COMMIT) and (*MARK)
1701 are considered at every possible starting position in the subject string. If
1702 PCRE_NO_START_OPTIMIZE is set at compile time, it cannot be unset at matching
1703 time. The use of PCRE_NO_START_OPTIMIZE disables JIT execution; when it is set,
1704 matching is always done using interpretively.
1705 .P
1706 Setting PCRE_NO_START_OPTIMIZE can change the outcome of a matching operation.
1707 Consider the pattern
1708 .sp
1710 .sp
1711 When this is compiled, PCRE records the fact that a match must start with the
1712 character "A". Suppose the subject string is "DEFABC". The start-up
1713 optimization scans along the subject, finds "A" and runs the first match
1714 attempt from there. The (*COMMIT) item means that the pattern must match the
1715 current starting position, which in this case, it does. However, if the same
1716 match is run with PCRE_NO_START_OPTIMIZE set, the initial scan along the
1717 subject string does not happen. The first match attempt is run starting from
1718 "D" and when this fails, (*COMMIT) prevents any further matches being tried, so
1719 the overall result is "no match". If the pattern is studied, more start-up
1720 optimizations may be used. For example, a minimum length for the subject may be
1721 recorded. Consider the pattern
1722 .sp
1723 (*MARK:A)(X|Y)
1724 .sp
1725 The minimum length for a match is one character. If the subject is "ABC", there
1726 will be attempts to match "ABC", "BC", "C", and then finally an empty string.
1727 If the pattern is studied, the final attempt does not take place, because PCRE
1728 knows that the subject is too short, and so the (*MARK) is never encountered.
1729 In this case, studying the pattern does not affect the overall match result,
1730 which is still "no match", but it does affect the auxiliary information that is
1731 returned.
1732 .sp
1734 .sp
1735 When PCRE_UTF8 is set at compile time, the validity of the subject as a UTF-8
1736 string is automatically checked when \fBpcre_exec()\fP is subsequently called.
1737 The value of \fIstartoffset\fP is also checked to ensure that it points to the
1738 start of a UTF-8 character. There is a discussion about the validity of UTF-8
1739 strings in the
1740 .\" HREF
1741 \fBpcreunicode\fP
1742 .\"
1743 page. If an invalid sequence of bytes is found, \fBpcre_exec()\fP returns the
1744 error PCRE_ERROR_BADUTF8 or, if PCRE_PARTIAL_HARD is set and the problem is a
1745 truncated character at the end of the subject, PCRE_ERROR_SHORTUTF8. In both
1746 cases, information about the precise nature of the error may also be returned
1747 (see the descriptions of these errors in the section entitled \fIError return
1748 values from\fP \fBpcre_exec()\fP
1749 .\" HTML <a href="#errorlist">
1750 .\" </a>
1751 below).
1752 .\"
1753 If \fIstartoffset\fP contains a value that does not point to the start of a
1754 UTF-8 character (or to the end of the subject), PCRE_ERROR_BADUTF8_OFFSET is
1755 returned.
1756 .P
1757 If you already know that your subject is valid, and you want to skip these
1758 checks for performance reasons, you can set the PCRE_NO_UTF8_CHECK option when
1759 calling \fBpcre_exec()\fP. You might want to do this for the second and
1760 subsequent calls to \fBpcre_exec()\fP if you are making repeated calls to find
1761 all the matches in a single subject string. However, you should be sure that
1762 the value of \fIstartoffset\fP points to the start of a character (or the end
1763 of the subject). When PCRE_NO_UTF8_CHECK is set, the effect of passing an
1764 invalid string as a subject or an invalid value of \fIstartoffset\fP is
1765 undefined. Your program may crash.
1766 .sp
1769 .sp
1770 These options turn on the partial matching feature. For backwards
1771 compatibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial match
1772 occurs if the end of the subject string is reached successfully, but there are
1773 not enough subject characters to complete the match. If this happens when
1774 PCRE_PARTIAL_SOFT (but not PCRE_PARTIAL_HARD) is set, matching continues by
1775 testing any remaining alternatives. Only if no complete match can be found is
1776 PCRE_ERROR_PARTIAL returned instead of PCRE_ERROR_NOMATCH. In other words,
1777 PCRE_PARTIAL_SOFT says that the caller is prepared to handle a partial match,
1778 but only if no complete match can be found.
1779 .P
1780 If PCRE_PARTIAL_HARD is set, it overrides PCRE_PARTIAL_SOFT. In this case, if a
1781 partial match is found, \fBpcre_exec()\fP immediately returns
1782 PCRE_ERROR_PARTIAL, without considering any other alternatives. In other words,
1783 when PCRE_PARTIAL_HARD is set, a partial match is considered to be more
1784 important that an alternative complete match.
1785 .P
1786 In both cases, the portion of the string that was inspected when the partial
1787 match was found is set as the first matching string. There is a more detailed
1788 discussion of partial and multi-segment matching, with examples, in the
1789 .\" HREF
1790 \fBpcrepartial\fP
1791 .\"
1792 documentation.
1793 .
1794 .
1795 .SS "The string to be matched by \fBpcre_exec()\fP"
1796 .rs
1797 .sp
1798 The subject string is passed to \fBpcre_exec()\fP as a pointer in
1799 \fIsubject\fP, a length in bytes in \fIlength\fP, and a starting byte offset
1800 in \fIstartoffset\fP. If this is negative or greater than the length of the
1801 subject, \fBpcre_exec()\fP returns PCRE_ERROR_BADOFFSET. When the starting
1802 offset is zero, the search for a match starts at the beginning of the subject,
1803 and this is by far the most common case. In UTF-8 mode, the byte offset must
1804 point to the start of a UTF-8 character (or the end of the subject). Unlike the
1805 pattern string, the subject may contain binary zero bytes.
1806 .P
1807 A non-zero starting offset is useful when searching for another match in the
1808 same subject by calling \fBpcre_exec()\fP again after a previous success.
1809 Setting \fIstartoffset\fP differs from just passing over a shortened string and
1810 setting PCRE_NOTBOL in the case of a pattern that begins with any kind of
1811 lookbehind. For example, consider the pattern
1812 .sp
1813 \eBiss\eB
1814 .sp
1815 which finds occurrences of "iss" in the middle of words. (\eB matches only if
1816 the current position in the subject is not a word boundary.) When applied to
1817 the string "Mississipi" the first call to \fBpcre_exec()\fP finds the first
1818 occurrence. If \fBpcre_exec()\fP is called again with just the remainder of the
1819 subject, namely "issipi", it does not match, because \eB is always false at the
1820 start of the subject, which is deemed to be a word boundary. However, if
1821 \fBpcre_exec()\fP is passed the entire string again, but with \fIstartoffset\fP
1822 set to 4, it finds the second occurrence of "iss" because it is able to look
1823 behind the starting point to discover that it is preceded by a letter.
1824 .P
1825 Finding all the matches in a subject is tricky when the pattern can match an
1826 empty string. It is possible to emulate Perl's /g behaviour by first trying the
1827 match again at the same offset, with the PCRE_NOTEMPTY_ATSTART and
1828 PCRE_ANCHORED options, and then if that fails, advancing the starting offset
1829 and trying an ordinary match again. There is some code that demonstrates how to
1830 do this in the
1831 .\" HREF
1832 \fBpcredemo\fP
1833 .\"
1834 sample program. In the most general case, you have to check to see if the
1835 newline convention recognizes CRLF as a newline, and if so, and the current
1836 character is CR followed by LF, advance the starting offset by two characters
1837 instead of one.
1838 .P
1839 If a non-zero starting offset is passed when the pattern is anchored, one
1840 attempt to match at the given offset is made. This can only succeed if the
1841 pattern does not require the match to be at the start of the subject.
1842 .
1843 .
1844 .SS "How \fBpcre_exec()\fP returns captured substrings"
1845 .rs
1846 .sp
1847 In general, a pattern matches a certain portion of the subject, and in
1848 addition, further substrings from the subject may be picked out by parts of the
1849 pattern. Following the usage in Jeffrey Friedl's book, this is called
1850 "capturing" in what follows, and the phrase "capturing subpattern" is used for
1851 a fragment of a pattern that picks out a substring. PCRE supports several other
1852 kinds of parenthesized subpattern that do not cause substrings to be captured.
1853 .P
1854 Captured substrings are returned to the caller via a vector of integers whose
1855 address is passed in \fIovector\fP. The number of elements in the vector is
1856 passed in \fIovecsize\fP, which must be a non-negative number. \fBNote\fP: this
1857 argument is NOT the size of \fIovector\fP in bytes.
1858 .P
1859 The first two-thirds of the vector is used to pass back captured substrings,
1860 each substring using a pair of integers. The remaining third of the vector is
1861 used as workspace by \fBpcre_exec()\fP while matching capturing subpatterns,
1862 and is not available for passing back information. The number passed in
1863 \fIovecsize\fP should always be a multiple of three. If it is not, it is
1864 rounded down.
1865 .P
1866 When a match is successful, information about captured substrings is returned
1867 in pairs of integers, starting at the beginning of \fIovector\fP, and
1868 continuing up to two-thirds of its length at the most. The first element of
1869 each pair is set to the byte offset of the first character in a substring, and
1870 the second is set to the byte offset of the first character after the end of a
1871 substring. \fBNote\fP: these values are always byte offsets, even in UTF-8
1872 mode. They are not character counts.
1873 .P
1874 The first pair of integers, \fIovector[0]\fP and \fIovector[1]\fP, identify the
1875 portion of the subject string matched by the entire pattern. The next pair is
1876 used for the first capturing subpattern, and so on. The value returned by
1877 \fBpcre_exec()\fP is one more than the highest numbered pair that has been set.
1878 For example, if two substrings have been captured, the returned value is 3. If
1879 there are no capturing subpatterns, the return value from a successful match is
1880 1, indicating that just the first pair of offsets has been set.
1881 .P
1882 If a capturing subpattern is matched repeatedly, it is the last portion of the
1883 string that it matched that is returned.
1884 .P
1885 If the vector is too small to hold all the captured substring offsets, it is
1886 used as far as possible (up to two-thirds of its length), and the function
1887 returns a value of zero. If neither the actual string matched not any captured
1888 substrings are of interest, \fBpcre_exec()\fP may be called with \fIovector\fP
1889 passed as NULL and \fIovecsize\fP as zero. However, if the pattern contains
1890 back references and the \fIovector\fP is not big enough to remember the related
1891 substrings, PCRE has to get additional memory for use during matching. Thus it
1892 is usually advisable to supply an \fIovector\fP of reasonable size.
1893 .P
1894 There are some cases where zero is returned (indicating vector overflow) when
1895 in fact the vector is exactly the right size for the final match. For example,
1896 consider the pattern
1897 .sp
1898 (a)(?:(b)c|bd)
1899 .sp
1900 If a vector of 6 elements (allowing for only 1 captured substring) is given
1901 with subject string "abd", \fBpcre_exec()\fP will try to set the second
1902 captured string, thereby recording a vector overflow, before failing to match
1903 "c" and backing up to try the second alternative. The zero return, however,
1904 does correctly indicate that the maximum number of slots (namely 2) have been
1905 filled. In similar cases where there is temporary overflow, but the final
1906 number of used slots is actually less than the maximum, a non-zero value is
1907 returned.
1908 .P
1909 The \fBpcre_fullinfo()\fP function can be used to find out how many capturing
1910 subpatterns there are in a compiled pattern. The smallest size for
1911 \fIovector\fP that will allow for \fIn\fP captured substrings, in addition to
1912 the offsets of the substring matched by the whole pattern, is (\fIn\fP+1)*3.
1913 .P
1914 It is possible for capturing subpattern number \fIn+1\fP to match some part of
1915 the subject when subpattern \fIn\fP has not been used at all. For example, if
1916 the string "abc" is matched against the pattern (a|(z))(bc) the return from the
1917 function is 4, and subpatterns 1 and 3 are matched, but 2 is not. When this
1918 happens, both values in the offset pairs corresponding to unused subpatterns
1919 are set to -1.
1920 .P
1921 Offset values that correspond to unused subpatterns at the end of the
1922 expression are also set to -1. For example, if the string "abc" is matched
1923 against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not matched. The
1924 return from the function is 2, because the highest used capturing subpattern
1925 number is 1, and the offsets for for the second and third capturing subpatterns
1926 (assuming the vector is large enough, of course) are set to -1.
1927 .P
1928 \fBNote\fP: Elements in the first two-thirds of \fIovector\fP that do not
1929 correspond to capturing parentheses in the pattern are never changed. That is,
1930 if a pattern contains \fIn\fP capturing parentheses, no more than
1931 \fIovector[0]\fP to \fIovector[2n+1]\fP are set by \fBpcre_exec()\fP. The other
1932 elements (in the first two-thirds) retain whatever values they previously had.
1933 .P
1934 Some convenience functions are provided for extracting the captured substrings
1935 as separate strings. These are described below.
1936 .
1937 .
1938 .\" HTML <a name="errorlist"></a>
1939 .SS "Error return values from \fBpcre_exec()\fP"
1940 .rs
1941 .sp
1942 If \fBpcre_exec()\fP fails, it returns a negative number. The following are
1943 defined in the header file:
1944 .sp
1946 .sp
1947 The subject string did not match the pattern.
1948 .sp
1950 .sp
1951 Either \fIcode\fP or \fIsubject\fP was passed as NULL, or \fIovector\fP was
1952 NULL and \fIovecsize\fP was not zero.
1953 .sp
1955 .sp
1956 An unrecognized bit was set in the \fIoptions\fP argument.
1957 .sp
1959 .sp
1960 PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch
1961 the case when it is passed a junk pointer and to detect when a pattern that was
1962 compiled in an environment of one endianness is run in an environment with the
1963 other endianness. This is the error that PCRE gives when the magic number is
1964 not present.
1965 .sp
1967 .sp
1968 While running the pattern match, an unknown item was encountered in the
1969 compiled pattern. This error could be caused by a bug in PCRE or by overwriting
1970 of the compiled pattern.
1971 .sp
1973 .sp
1974 If a pattern contains back references, but the \fIovector\fP that is passed to
1975 \fBpcre_exec()\fP is not big enough to remember the referenced substrings, PCRE
1976 gets a block of memory at the start of matching to use for this purpose. If the
1977 call via \fBpcre_malloc()\fP fails, this error is given. The memory is
1978 automatically freed at the end of matching.
1979 .P
1980 This error is also given if \fBpcre_stack_malloc()\fP fails in
1981 \fBpcre_exec()\fP. This can happen only when PCRE has been compiled with
1982 \fB--disable-stack-for-recursion\fP.
1983 .sp
1985 .sp
1986 This error is used by the \fBpcre_copy_substring()\fP,
1987 \fBpcre_get_substring()\fP, and \fBpcre_get_substring_list()\fP functions (see
1988 below). It is never returned by \fBpcre_exec()\fP.
1989 .sp
1991 .sp
1992 The backtracking limit, as specified by the \fImatch_limit\fP field in a
1993 \fBpcre_extra\fP structure (or defaulted) was reached. See the description
1994 above.
1995 .sp
1997 .sp
1998 This error is never generated by \fBpcre_exec()\fP itself. It is provided for
1999 use by callout functions that want to yield a distinctive error code. See the
2000 .\" HREF
2001 \fBpcrecallout\fP
2002 .\"
2003 documentation for details.
2004 .sp
2006 .sp
2007 A string that contains an invalid UTF-8 byte sequence was passed as a subject,
2008 and the PCRE_NO_UTF8_CHECK option was not set. If the size of the output vector
2009 (\fIovecsize\fP) is at least 2, the byte offset to the start of the the invalid
2010 UTF-8 character is placed in the first element, and a reason code is placed in
2011 the second element. The reason codes are listed in the
2012 .\" HTML <a href="#badutf8reasons">
2013 .\" </a>
2014 following section.
2015 .\"
2016 For backward compatibility, if PCRE_PARTIAL_HARD is set and the problem is a
2017 truncated UTF-8 character at the end of the subject (reason codes 1 to 5),
2018 PCRE_ERROR_SHORTUTF8 is returned instead of PCRE_ERROR_BADUTF8.
2019 .sp
2021 .sp
2022 The UTF-8 byte sequence that was passed as a subject was checked and found to
2023 be valid (the PCRE_NO_UTF8_CHECK option was not set), but the value of
2024 \fIstartoffset\fP did not point to the beginning of a UTF-8 character or the
2025 end of the subject.
2026 .sp
2028 .sp
2029 The subject string did not match, but it did match partially. See the
2030 .\" HREF
2031 \fBpcrepartial\fP
2032 .\"
2033 documentation for details of partial matching.
2034 .sp
2036 .sp
2037 This code is no longer in use. It was formerly returned when the PCRE_PARTIAL
2038 option was used with a compiled pattern containing items that were not
2039 supported for partial matching. From release 8.00 onwards, there are no
2040 restrictions on partial matching.
2041 .sp
2043 .sp
2044 An unexpected internal error has occurred. This error could be caused by a bug
2045 in PCRE or by overwriting of the compiled pattern.
2046 .sp
2048 .sp
2049 This error is given if the value of the \fIovecsize\fP argument is negative.
2050 .sp
2052 .sp
2053 The internal recursion limit, as specified by the \fImatch_limit_recursion\fP
2054 field in a \fBpcre_extra\fP structure (or defaulted) was reached. See the
2055 description above.
2056 .sp
2058 .sp
2059 An invalid combination of PCRE_NEWLINE_\fIxxx\fP options was given.
2060 .sp
2062 .sp
2063 The value of \fIstartoffset\fP was negative or greater than the length of the
2064 subject, that is, the value in \fIlength\fP.
2065 .sp
2067 .sp
2068 This error is returned instead of PCRE_ERROR_BADUTF8 when the subject string
2069 ends with a truncated UTF-8 character and the PCRE_PARTIAL_HARD option is set.
2070 Information about the failure is returned as for PCRE_ERROR_BADUTF8. It is in
2071 fact sufficient to detect this case, but this special error code for
2072 PCRE_PARTIAL_HARD precedes the implementation of returned information; it is
2073 retained for backwards compatibility.
2074 .sp
2076 .sp
2077 This error is returned when \fBpcre_exec()\fP detects a recursion loop within
2078 the pattern. Specifically, it means that either the whole pattern or a
2079 subpattern has been called recursively for the second time at the same position
2080 in the subject string. Some simple patterns that might do this are detected and
2081 faulted at compile time, but more complicated cases, in particular mutual
2082 recursions between two different subpatterns, cannot be detected until run
2083 time.
2084 .sp
2086 .sp
2087 This error is returned when a pattern that was successfully studied using a
2088 JIT compile option is being matched, but the memory available for the
2089 just-in-time processing stack is not large enough. See the
2090 .\" HREF
2091 \fBpcrejit\fP
2092 .\"
2093 documentation for more details.
2094 .sp
2096 .sp
2097 This error is given if a pattern that was compiled by the 8-bit library is
2098 passed to a 16-bit library function, or vice versa.
2099 .sp
2101 .sp
2102 This error is given if a pattern that was compiled and saved is reloaded on a
2103 host with different endianness. The utility function
2104 \fBpcre_pattern_to_host_byte_order()\fP can be used to convert such a pattern
2105 so that it runs on the new host.
2106 .P
2107 Error numbers -16 to -20 and -22 are not used by \fBpcre_exec()\fP.
2108 .
2109 .
2110 .\" HTML <a name="badutf8reasons"></a>
2111 .SS "Reason codes for invalid UTF-8 strings"
2112 .rs
2113 .sp
2114 This section applies only to the 8-bit library. The corresponding information
2115 for the 16-bit library is given in the
2116 .\" HREF
2117 \fBpcre16\fP
2118 .\"
2119 page.
2120 .P
2121 When \fBpcre_exec()\fP returns either PCRE_ERROR_BADUTF8 or
2122 PCRE_ERROR_SHORTUTF8, and the size of the output vector (\fIovecsize\fP) is at
2123 least 2, the offset of the start of the invalid UTF-8 character is placed in
2124 the first output vector element (\fIovector[0]\fP) and a reason code is placed
2125 in the second element (\fIovector[1]\fP). The reason codes are given names in
2126 the \fBpcre.h\fP header file:
2127 .sp
2133 .sp
2134 The string ends with a truncated UTF-8 character; the code specifies how many
2135 bytes are missing (1 to 5). Although RFC 3629 restricts UTF-8 characters to be
2136 no longer than 4 bytes, the encoding scheme (originally defined by RFC 2279)
2137 allows for up to 6 bytes, and this is checked first; hence the possibility of
2138 4 or 5 missing bytes.
2139 .sp
2144 PCRE_UTF8_ERR10
2145 .sp
2146 The two most significant bits of the 2nd, 3rd, 4th, 5th, or 6th byte of the
2147 character do not have the binary value 0b10 (that is, either the most
2148 significant bit is 0, or the next bit is 1).
2149 .sp
2150 PCRE_UTF8_ERR11
2151 PCRE_UTF8_ERR12
2152 .sp
2153 A character that is valid by the RFC 2279 rules is either 5 or 6 bytes long;
2154 these code points are excluded by RFC 3629.
2155 .sp
2156 PCRE_UTF8_ERR13
2157 .sp
2158 A 4-byte character has a value greater than 0x10fff; these code points are
2159 excluded by RFC 3629.
2160 .sp
2161 PCRE_UTF8_ERR14
2162 .sp
2163 A 3-byte character has a value in the range 0xd800 to 0xdfff; this range of
2164 code points are reserved by RFC 3629 for use with UTF-16, and so are excluded
2165 from UTF-8.
2166 .sp
2167 PCRE_UTF8_ERR15
2168 PCRE_UTF8_ERR16
2169 PCRE_UTF8_ERR17
2170 PCRE_UTF8_ERR18
2171 PCRE_UTF8_ERR19
2172 .sp
2173 A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it codes for a
2174 value that can be represented by fewer bytes, which is invalid. For example,
2175 the two bytes 0xc0, 0xae give the value 0x2e, whose correct coding uses just
2176 one byte.
2177 .sp
2178 PCRE_UTF8_ERR20
2179 .sp
2180 The two most significant bits of the first byte of a character have the binary
2181 value 0b10 (that is, the most significant bit is 1 and the second is 0). Such a
2182 byte can only validly occur as the second or subsequent byte of a multi-byte
2183 character.
2184 .sp
2185 PCRE_UTF8_ERR21
2186 .sp
2187 The first byte of a character has the value 0xfe or 0xff. These values can
2188 never occur in a valid UTF-8 string.
2189 .
2190 .
2192 .rs
2193 .sp
2194 .B int pcre_copy_substring(const char *\fIsubject\fP, int *\fIovector\fP,
2195 .ti +5n
2196 .B int \fIstringcount\fP, int \fIstringnumber\fP, char *\fIbuffer\fP,
2197 .ti +5n
2198 .B int \fIbuffersize\fP);
2199 .PP
2200 .B int pcre_get_substring(const char *\fIsubject\fP, int *\fIovector\fP,
2201 .ti +5n
2202 .B int \fIstringcount\fP, int \fIstringnumber\fP,
2203 .ti +5n
2204 .B const char **\fIstringptr\fP);
2205 .PP
2206 .B int pcre_get_substring_list(const char *\fIsubject\fP,
2207 .ti +5n
2208 .B int *\fIovector\fP, int \fIstringcount\fP, "const char ***\fIlistptr\fP);"
2209 .PP
2210 Captured substrings can be accessed directly by using the offsets returned by
2211 \fBpcre_exec()\fP in \fIovector\fP. For convenience, the functions
2212 \fBpcre_copy_substring()\fP, \fBpcre_get_substring()\fP, and
2213 \fBpcre_get_substring_list()\fP are provided for extracting captured substrings
2214 as new, separate, zero-terminated strings. These functions identify substrings
2215 by number. The next section describes functions for extracting named
2216 substrings.
2217 .P
2218 A substring that contains a binary zero is correctly extracted and has a
2219 further zero added on the end, but the result is not, of course, a C string.
2220 However, you can process such a string by referring to the length that is
2221 returned by \fBpcre_copy_substring()\fP and \fBpcre_get_substring()\fP.
2222 Unfortunately, the interface to \fBpcre_get_substring_list()\fP is not adequate
2223 for handling strings containing binary zeros, because the end of the final
2224 string is not independently indicated.
2225 .P
2226 The first three arguments are the same for all three of these functions:
2227 \fIsubject\fP is the subject string that has just been successfully matched,
2228 \fIovector\fP is a pointer to the vector of integer offsets that was passed to
2229 \fBpcre_exec()\fP, and \fIstringcount\fP is the number of substrings that were
2230 captured by the match, including the substring that matched the entire regular
2231 expression. This is the value returned by \fBpcre_exec()\fP if it is greater
2232 than zero. If \fBpcre_exec()\fP returned zero, indicating that it ran out of
2233 space in \fIovector\fP, the value passed as \fIstringcount\fP should be the
2234 number of elements in the vector divided by three.
2235 .P
2236 The functions \fBpcre_copy_substring()\fP and \fBpcre_get_substring()\fP
2237 extract a single substring, whose number is given as \fIstringnumber\fP. A
2238 value of zero extracts the substring that matched the entire pattern, whereas
2239 higher values extract the captured substrings. For \fBpcre_copy_substring()\fP,
2240 the string is placed in \fIbuffer\fP, whose length is given by
2241 \fIbuffersize\fP, while for \fBpcre_get_substring()\fP a new block of memory is
2242 obtained via \fBpcre_malloc\fP, and its address is returned via
2243 \fIstringptr\fP. The yield of the function is the length of the string, not
2244 including the terminating zero, or one of these error codes:
2245 .sp
2247 .sp
2248 The buffer was too small for \fBpcre_copy_substring()\fP, or the attempt to get
2249 memory failed for \fBpcre_get_substring()\fP.
2250 .sp
2252 .sp
2253 There is no substring whose number is \fIstringnumber\fP.
2254 .P
2255 The \fBpcre_get_substring_list()\fP function extracts all available substrings
2256 and builds a list of pointers to them. All this is done in a single block of
2257 memory that is obtained via \fBpcre_malloc\fP. The address of the memory block
2258 is returned via \fIlistptr\fP, which is also the start of the list of string
2259 pointers. The end of the list is marked by a NULL pointer. The yield of the
2260 function is zero if all went well, or the error code
2261 .sp
2263 .sp
2264 if the attempt to get the memory block failed.
2265 .P
2266 When any of these functions encounter a substring that is unset, which can
2267 happen when capturing subpattern number \fIn+1\fP matches some part of the
2268 subject, but subpattern \fIn\fP has not been used at all, they return an empty
2269 string. This can be distinguished from a genuine zero-length substring by
2270 inspecting the appropriate offset in \fIovector\fP, which is negative for unset
2271 substrings.
2272 .P
2273 The two convenience functions \fBpcre_free_substring()\fP and
2274 \fBpcre_free_substring_list()\fP can be used to free the memory returned by
2275 a previous call of \fBpcre_get_substring()\fP or
2276 \fBpcre_get_substring_list()\fP, respectively. They do nothing more than call
2277 the function pointed to by \fBpcre_free\fP, which of course could be called
2278 directly from a C program. However, PCRE is used in some situations where it is
2279 linked via a special interface to another programming language that cannot use
2280 \fBpcre_free\fP directly; it is for these cases that the functions are
2281 provided.
2282 .
2283 .
2285 .rs
2286 .sp
2287 .B int pcre_get_stringnumber(const pcre *\fIcode\fP,
2288 .ti +5n
2289 .B const char *\fIname\fP);
2290 .PP
2291 .B int pcre_copy_named_substring(const pcre *\fIcode\fP,
2292 .ti +5n
2293 .B const char *\fIsubject\fP, int *\fIovector\fP,
2294 .ti +5n
2295 .B int \fIstringcount\fP, const char *\fIstringname\fP,
2296 .ti +5n
2297 .B char *\fIbuffer\fP, int \fIbuffersize\fP);
2298 .PP
2299 .B int pcre_get_named_substring(const pcre *\fIcode\fP,
2300 .ti +5n
2301 .B const char *\fIsubject\fP, int *\fIovector\fP,
2302 .ti +5n
2303 .B int \fIstringcount\fP, const char *\fIstringname\fP,
2304 .ti +5n
2305 .B const char **\fIstringptr\fP);
2306 .PP
2307 To extract a substring by name, you first have to find associated number.
2308 For example, for this pattern
2309 .sp
2310 (a+)b(?<xxx>\ed+)...
2311 .sp
2312 the number of the subpattern called "xxx" is 2. If the name is known to be
2313 unique (PCRE_DUPNAMES was not set), you can find the number from the name by
2314 calling \fBpcre_get_stringnumber()\fP. The first argument is the compiled
2315 pattern, and the second is the name. The yield of the function is the
2316 subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no subpattern of
2317 that name.
2318 .P
2319 Given the number, you can extract the substring directly, or use one of the
2320 functions described in the previous section. For convenience, there are also
2321 two functions that do the whole job.
2322 .P
2323 Most of the arguments of \fBpcre_copy_named_substring()\fP and
2324 \fBpcre_get_named_substring()\fP are the same as those for the similarly named
2325 functions that extract by number. As these are described in the previous
2326 section, they are not re-described here. There are just two differences:
2327 .P
2328 First, instead of a substring number, a substring name is given. Second, there
2329 is an extra argument, given at the start, which is a pointer to the compiled
2330 pattern. This is needed in order to gain access to the name-to-number
2331 translation table.
2332 .P
2333 These functions call \fBpcre_get_stringnumber()\fP, and if it succeeds, they
2334 then call \fBpcre_copy_substring()\fP or \fBpcre_get_substring()\fP, as
2335 appropriate. \fBNOTE:\fP If PCRE_DUPNAMES is set and there are duplicate names,
2336 the behaviour may not be what you want (see the next section).
2337 .P
2338 \fBWarning:\fP If the pattern uses the (?| feature to set up multiple
2339 subpatterns with the same number, as described in the
2340 .\" HTML <a href="pcrepattern.html#dupsubpatternnumber">
2341 .\" </a>
2342 section on duplicate subpattern numbers
2343 .\"
2344 in the
2345 .\" HREF
2346 \fBpcrepattern\fP
2347 .\"
2348 page, you cannot use names to distinguish the different subpatterns, because
2349 names are not included in the compiled code. The matching process uses only
2350 numbers. For this reason, the use of different names for subpatterns of the
2351 same number causes an error at compile time.
2352 .
2353 .
2355 .rs
2356 .sp
2357 .B int pcre_get_stringtable_entries(const pcre *\fIcode\fP,
2358 .ti +5n
2359 .B const char *\fIname\fP, char **\fIfirst\fP, char **\fIlast\fP);
2360 .PP
2361 When a pattern is compiled with the PCRE_DUPNAMES option, names for subpatterns
2362 are not required to be unique. (Duplicate names are always allowed for
2363 subpatterns with the same number, created by using the (?| feature. Indeed, if
2364 such subpatterns are named, they are required to use the same names.)
2365 .P
2366 Normally, patterns with duplicate names are such that in any one match, only
2367 one of the named subpatterns participates. An example is shown in the
2368 .\" HREF
2369 \fBpcrepattern\fP
2370 .\"
2371 documentation.
2372 .P
2373 When duplicates are present, \fBpcre_copy_named_substring()\fP and
2374 \fBpcre_get_named_substring()\fP return the first substring corresponding to
2375 the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING (-7) is
2376 returned; no data is returned. The \fBpcre_get_stringnumber()\fP function
2377 returns one of the numbers that are associated with the name, but it is not
2378 defined which it is.
2379 .P
2380 If you want to get full details of all captured substrings for a given name,
2381 you must use the \fBpcre_get_stringtable_entries()\fP function. The first
2382 argument is the compiled pattern, and the second is the name. The third and
2383 fourth are pointers to variables which are updated by the function. After it
2384 has run, they point to the first and last entries in the name-to-number table
2385 for the given name. The function itself returns the length of each entry, or
2386 PCRE_ERROR_NOSUBSTRING (-7) if there are none. The format of the table is
2387 described above in the section entitled \fIInformation about a pattern\fP
2388 .\" HTML <a href="#infoaboutpattern">
2389 .\" </a>
2390 above.
2391 .\"
2392 Given all the relevant entries for the name, you can extract each of their
2393 numbers, and hence the captured data, if any.
2394 .
2395 .
2397 .rs
2398 .sp
2399 The traditional matching function uses a similar algorithm to Perl, which stops
2400 when it finds the first match, starting at a given point in the subject. If you
2401 want to find all possible matches, or the longest possible match, consider
2402 using the alternative matching function (see below) instead. If you cannot use
2403 the alternative function, but still need to find all possible matches, you
2404 can kludge it up by making use of the callout facility, which is described in
2405 the
2406 .\" HREF
2407 \fBpcrecallout\fP
2408 .\"
2409 documentation.
2410 .P
2411 What you have to do is to insert a callout right at the end of the pattern.
2412 When your callout function is called, extract and save the current matched
2413 substring. Then return 1, which forces \fBpcre_exec()\fP to backtrack and try
2414 other alternatives. Ultimately, when it runs out of matches, \fBpcre_exec()\fP
2415 will yield PCRE_ERROR_NOMATCH.
2416 .
2417 .
2419 .rs
2420 .sp
2421 Matching certain patterns using \fBpcre_exec()\fP can use a lot of process
2422 stack, which in certain environments can be rather limited in size. Some users
2423 find it helpful to have an estimate of the amount of stack that is used by
2424 \fBpcre_exec()\fP, to help them set recursion limits, as described in the
2425 .\" HREF
2426 \fBpcrestack\fP
2427 .\"
2428 documentation. The estimate that is output by \fBpcretest\fP when called with
2429 the \fB-m\fP and \fB-C\fP options is obtained by calling \fBpcre_exec\fP with
2430 the values NULL, NULL, NULL, -999, and -999 for its first five arguments.
2431 .P
2432 Normally, if its first argument is NULL, \fBpcre_exec()\fP immediately returns
2433 the negative error code PCRE_ERROR_NULL, but with this special combination of
2434 arguments, it returns instead a negative number whose absolute value is the
2435 approximate stack frame size in bytes. (A negative number is used so that it is
2436 clear that no match has happened.) The value is approximate because in some
2437 cases, recursive calls to \fBpcre_exec()\fP occur when there are one or two
2438 additional variables on the stack.
2439 .P
2440 If PCRE has been compiled to use the heap instead of the stack for recursion,
2441 the value returned is the size of each block that is obtained from the heap.
2442 .
2443 .
2444 .\" HTML <a name="dfamatch"></a>
2446 .rs
2447 .sp
2448 .B int pcre_dfa_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
2449 .ti +5n
2450 .B "const char *\fIsubject\fP," int \fIlength\fP, int \fIstartoffset\fP,
2451 .ti +5n
2452 .B int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP,
2453 .ti +5n
2454 .B int *\fIworkspace\fP, int \fIwscount\fP);
2455 .P
2456 The function \fBpcre_dfa_exec()\fP is called to match a subject string against
2457 a compiled pattern, using a matching algorithm that scans the subject string
2458 just once, and does not backtrack. This has different characteristics to the
2459 normal algorithm, and is not compatible with Perl. Some of the features of PCRE
2460 patterns are not supported. Nevertheless, there are times when this kind of
2461 matching can be useful. For a discussion of the two matching algorithms, and a
2462 list of features that \fBpcre_dfa_exec()\fP does not support, see the
2463 .\" HREF
2464 \fBpcrematching\fP
2465 .\"
2466 documentation.
2467 .P
2468 The arguments for the \fBpcre_dfa_exec()\fP function are the same as for
2469 \fBpcre_exec()\fP, plus two extras. The \fIovector\fP argument is used in a
2470 different way, and this is described below. The other common arguments are used
2471 in the same way as for \fBpcre_exec()\fP, so their description is not repeated
2472 here.
2473 .P
2474 The two additional arguments provide workspace for the function. The workspace
2475 vector should contain at least 20 elements. It is used for keeping track of
2476 multiple paths through the pattern tree. More workspace will be needed for
2477 patterns and subjects where there are a lot of potential matches.
2478 .P
2479 Here is an example of a simple call to \fBpcre_dfa_exec()\fP:
2480 .sp
2481 int rc;
2482 int ovector[10];
2483 int wspace[20];
2484 rc = pcre_dfa_exec(
2485 re, /* result of pcre_compile() */
2486 NULL, /* we didn't study the pattern */
2487 "some string", /* the subject string */
2488 11, /* the length of the subject string */
2489 0, /* start at offset 0 in the subject */
2490 0, /* default options */
2491 ovector, /* vector of integers for substring information */
2492 10, /* number of elements (NOT size in bytes) */
2493 wspace, /* working space vector */
2494 20); /* number of elements (NOT size in bytes) */
2495 .
2496 .SS "Option bits for \fBpcre_dfa_exec()\fP"
2497 .rs
2498 .sp
2499 The unused bits of the \fIoptions\fP argument for \fBpcre_dfa_exec()\fP must be
2500 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_\fIxxx\fP,
2504 All but the last four of these are exactly the same as for \fBpcre_exec()\fP,
2505 so their description is not repeated here.
2506 .sp
2509 .sp
2510 These have the same general effect as they do for \fBpcre_exec()\fP, but the
2511 details are slightly different. When PCRE_PARTIAL_HARD is set for
2512 \fBpcre_dfa_exec()\fP, it returns PCRE_ERROR_PARTIAL if the end of the subject
2513 is reached and there is still at least one matching possibility that requires
2514 additional characters. This happens even if some complete matches have also
2515 been found. When PCRE_PARTIAL_SOFT is set, the return code PCRE_ERROR_NOMATCH
2516 is converted into PCRE_ERROR_PARTIAL if the end of the subject is reached,
2517 there have been no complete matches, but there is still at least one matching
2518 possibility. The portion of the string that was inspected when the longest
2519 partial match was found is set as the first matching string in both cases.
2520 There is a more detailed discussion of partial and multi-segment matching, with
2521 examples, in the
2522 .\" HREF
2523 \fBpcrepartial\fP
2524 .\"
2525 documentation.
2526 .sp
2528 .sp
2529 Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to stop as
2530 soon as it has found one match. Because of the way the alternative algorithm
2531 works, this is necessarily the shortest possible match at the first possible
2532 matching point in the subject string.
2533 .sp
2535 .sp
2536 When \fBpcre_dfa_exec()\fP returns a partial match, it is possible to call it
2537 again, with additional subject characters, and have it continue with the same
2538 match. The PCRE_DFA_RESTART option requests this action; when it is set, the
2539 \fIworkspace\fP and \fIwscount\fP options must reference the same vector as
2540 before because data about the match so far is left in them after a partial
2541 match. There is more discussion of this facility in the
2542 .\" HREF
2543 \fBpcrepartial\fP
2544 .\"
2545 documentation.
2546 .
2547 .
2548 .SS "Successful returns from \fBpcre_dfa_exec()\fP"
2549 .rs
2550 .sp
2551 When \fBpcre_dfa_exec()\fP succeeds, it may have matched more than one
2552 substring in the subject. Note, however, that all the matches from one run of
2553 the function start at the same point in the subject. The shorter matches are
2554 all initial substrings of the longer matches. For example, if the pattern
2555 .sp
2556 <.*>
2557 .sp
2558 is matched against the string
2559 .sp
2560 This is <something> <something else> <something further> no more
2561 .sp
2562 the three matched strings are
2563 .sp
2564 <something>
2565 <something> <something else>
2566 <something> <something else> <something further>
2567 .sp
2568 On success, the yield of the function is a number greater than zero, which is
2569 the number of matched substrings. The substrings themselves are returned in
2570 \fIovector\fP. Each string uses two elements; the first is the offset to the
2571 start, and the second is the offset to the end. In fact, all the strings have
2572 the same start offset. (Space could have been saved by giving this only once,
2573 but it was decided to retain some compatibility with the way \fBpcre_exec()\fP
2574 returns data, even though the meaning of the strings is different.)
2575 .P
2576 The strings are returned in reverse order of length; that is, the longest
2577 matching string is given first. If there were too many matches to fit into
2578 \fIovector\fP, the yield of the function is zero, and the vector is filled with
2579 the longest matches. Unlike \fBpcre_exec()\fP, \fBpcre_dfa_exec()\fP can use
2580 the entire \fIovector\fP for returning matched strings.
2581 .
2582 .
2583 .SS "Error returns from \fBpcre_dfa_exec()\fP"
2584 .rs
2585 .sp
2586 The \fBpcre_dfa_exec()\fP function returns a negative number when it fails.
2587 Many of the errors are the same as for \fBpcre_exec()\fP, and these are
2588 described
2589 .\" HTML <a href="#errorlist">
2590 .\" </a>
2591 above.
2592 .\"
2593 There are in addition the following errors that are specific to
2594 \fBpcre_dfa_exec()\fP:
2595 .sp
2597 .sp
2598 This return is given if \fBpcre_dfa_exec()\fP encounters an item in the pattern
2599 that it does not support, for instance, the use of \eC or a back reference.
2600 .sp
2602 .sp
2603 This return is given if \fBpcre_dfa_exec()\fP encounters a condition item that
2604 uses a back reference for the condition, or a test for recursion in a specific
2605 group. These are not supported.
2606 .sp
2608 .sp
2609 This return is given if \fBpcre_dfa_exec()\fP is called with an \fIextra\fP
2610 block that contains a setting of the \fImatch_limit\fP or
2611 \fImatch_limit_recursion\fP fields. This is not supported (these fields are
2612 meaningless for DFA matching).
2613 .sp
2615 .sp
2616 This return is given if \fBpcre_dfa_exec()\fP runs out of space in the
2617 \fIworkspace\fP vector.
2618 .sp
2620 .sp
2621 When a recursive subpattern is processed, the matching function calls itself
2622 recursively, using private vectors for \fIovector\fP and \fIworkspace\fP. This
2623 error is given if the output vector is not large enough. This should be
2624 extremely rare, as a vector of size 1000 is used.
2625 .
2626 .
2627 .SH "SEE ALSO"
2628 .rs
2629 .sp
2630 \fBpcre16\fP(3), \fBpcrebuild\fP(3), \fBpcrecallout\fP(3), \fBpcrecpp(3)\fP(3),
2631 \fBpcrematching\fP(3), \fBpcrepartial\fP(3), \fBpcreposix\fP(3),
2632 \fBpcreprecompile\fP(3), \fBpcresample\fP(3), \fBpcrestack\fP(3).
2633 .
2634 .
2636 .rs
2637 .sp
2638 .nf
2639 Philip Hazel
2640 University Computing Service
2641 Cambridge CB2 3QH, England.
2642 .fi
2643 .
2644 .
2646 .rs
2647 .sp
2648 .nf
2649 Last updated: 22 February 2012
2650 Copyright (c) 1997-2012 University of Cambridge.
2651 .fi


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