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1 .TH PCREAPI 3 "04 May 2012" "PCRE 8.31"
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 75 name is too long in (*MARK), (*PRUNE), (*SKIP), or (*THEN)
930 .sp
931 The numbers 32 and 10000 in errors 48 and 49 are defaults; different values may
932 be used if the limits were changed when PCRE was built.
933 .
934 .
935 .\" HTML <a name="studyingapattern"></a>
937 .rs
938 .sp
939 .B pcre_extra *pcre_study(const pcre *\fIcode\fP, int \fIoptions\fP
940 .ti +5n
941 .B const char **\fIerrptr\fP);
942 .PP
943 If a compiled pattern is going to be used several times, it is worth spending
944 more time analyzing it in order to speed up the time taken for matching. The
945 function \fBpcre_study()\fP takes a pointer to a compiled pattern as its first
946 argument. If studying the pattern produces additional information that will
947 help speed up matching, \fBpcre_study()\fP returns a pointer to a
948 \fBpcre_extra\fP block, in which the \fIstudy_data\fP field points to the
949 results of the study.
950 .P
951 The returned value from \fBpcre_study()\fP can be passed directly to
952 \fBpcre_exec()\fP or \fBpcre_dfa_exec()\fP. However, a \fBpcre_extra\fP block
953 also contains other fields that can be set by the caller before the block is
954 passed; these are described
955 .\" HTML <a href="#extradata">
956 .\" </a>
957 below
958 .\"
959 in the section on matching a pattern.
960 .P
961 If studying the pattern does not produce any useful information,
962 \fBpcre_study()\fP returns NULL. In that circumstance, if the calling program
963 wants to pass any of the other fields to \fBpcre_exec()\fP or
964 \fBpcre_dfa_exec()\fP, it must set up its own \fBpcre_extra\fP block.
965 .P
966 The second argument of \fBpcre_study()\fP contains option bits. There are three
967 options:
968 .sp
972 .sp
973 If any of these are set, and the just-in-time compiler is available, the
974 pattern is further compiled into machine code that executes much faster than
975 the \fBpcre_exec()\fP interpretive matching function. If the just-in-time
976 compiler is not available, these options are ignored. All other bits in the
977 \fIoptions\fP argument must be zero.
978 .P
979 JIT compilation is a heavyweight optimization. It can take some time for
980 patterns to be analyzed, and for one-off matches and simple patterns the
981 benefit of faster execution might be offset by a much slower study time.
982 Not all patterns can be optimized by the JIT compiler. For those that cannot be
983 handled, matching automatically falls back to the \fBpcre_exec()\fP
984 interpreter. For more details, see the
985 .\" HREF
986 \fBpcrejit\fP
987 .\"
988 documentation.
989 .P
990 The third argument for \fBpcre_study()\fP is a pointer for an error message. If
991 studying succeeds (even if no data is returned), the variable it points to is
992 set to NULL. Otherwise it is set to point to a textual error message. This is a
993 static string that is part of the library. You must not try to free it. You
994 should test the error pointer for NULL after calling \fBpcre_study()\fP, to be
995 sure that it has run successfully.
996 .P
997 When you are finished with a pattern, you can free the memory used for the
998 study data by calling \fBpcre_free_study()\fP. This function was added to the
999 API for release 8.20. For earlier versions, the memory could be freed with
1000 \fBpcre_free()\fP, just like the pattern itself. This will still work in cases
1001 where JIT optimization is not used, but it is advisable to change to the new
1002 function when convenient.
1003 .P
1004 This is a typical way in which \fBpcre_study\fP() is used (except that in a
1005 real application there should be tests for errors):
1006 .sp
1007 int rc;
1008 pcre *re;
1009 pcre_extra *sd;
1010 re = pcre_compile("pattern", 0, &error, &erroroffset, NULL);
1011 sd = pcre_study(
1012 re, /* result of pcre_compile() */
1013 0, /* no options */
1014 &error); /* set to NULL or points to a message */
1015 rc = pcre_exec( /* see below for details of pcre_exec() options */
1016 re, sd, "subject", 7, 0, 0, ovector, 30);
1017 ...
1018 pcre_free_study(sd);
1019 pcre_free(re);
1020 .sp
1021 Studying a pattern does two things: first, a lower bound for the length of
1022 subject string that is needed to match the pattern is computed. This does not
1023 mean that there are any strings of that length that match, but it does
1024 guarantee that no shorter strings match. The value is used by
1025 \fBpcre_exec()\fP and \fBpcre_dfa_exec()\fP to avoid wasting time by trying to
1026 match strings that are shorter than the lower bound. You can find out the value
1027 in a calling program via the \fBpcre_fullinfo()\fP function.
1028 .P
1029 Studying a pattern is also useful for non-anchored patterns that do not have a
1030 single fixed starting character. A bitmap of possible starting bytes is
1031 created. This speeds up finding a position in the subject at which to start
1032 matching. (In 16-bit mode, the bitmap is used for 16-bit values less than 256.)
1033 .P
1034 These two optimizations apply to both \fBpcre_exec()\fP and
1035 \fBpcre_dfa_exec()\fP, and the information is also used by the JIT compiler.
1036 The optimizations can be disabled by setting the PCRE_NO_START_OPTIMIZE option
1037 when calling \fBpcre_exec()\fP or \fBpcre_dfa_exec()\fP, but if this is done,
1038 JIT execution is also disabled. You might want to do this if your pattern
1039 contains callouts or (*MARK) and you want to make use of these facilities in
1040 cases where matching fails. See the discussion of PCRE_NO_START_OPTIMIZE
1041 .\" HTML <a href="#execoptions">
1042 .\" </a>
1043 below.
1044 .\"
1045 .
1046 .
1047 .\" HTML <a name="localesupport"></a>
1049 .rs
1050 .sp
1051 PCRE handles caseless matching, and determines whether characters are letters,
1052 digits, or whatever, by reference to a set of tables, indexed by character
1053 value. When running in UTF-8 mode, this applies only to characters
1054 with codes less than 128. By default, higher-valued codes never match escapes
1055 such as \ew or \ed, but they can be tested with \ep if PCRE is built with
1056 Unicode character property support. Alternatively, the PCRE_UCP option can be
1057 set at compile time; this causes \ew and friends to use Unicode property
1058 support instead of built-in tables. The use of locales with Unicode is
1059 discouraged. If you are handling characters with codes greater than 128, you
1060 should either use UTF-8 and Unicode, or use locales, but not try to mix the
1061 two.
1062 .P
1063 PCRE contains an internal set of tables that are used when the final argument
1064 of \fBpcre_compile()\fP is NULL. These are sufficient for many applications.
1065 Normally, the internal tables recognize only ASCII characters. However, when
1066 PCRE is built, it is possible to cause the internal tables to be rebuilt in the
1067 default "C" locale of the local system, which may cause them to be different.
1068 .P
1069 The internal tables can always be overridden by tables supplied by the
1070 application that calls PCRE. These may be created in a different locale from
1071 the default. As more and more applications change to using Unicode, the need
1072 for this locale support is expected to die away.
1073 .P
1074 External tables are built by calling the \fBpcre_maketables()\fP function,
1075 which has no arguments, in the relevant locale. The result can then be passed
1076 to \fBpcre_compile()\fP or \fBpcre_exec()\fP as often as necessary. For
1077 example, to build and use tables that are appropriate for the French locale
1078 (where accented characters with values greater than 128 are treated as letters),
1079 the following code could be used:
1080 .sp
1081 setlocale(LC_CTYPE, "fr_FR");
1082 tables = pcre_maketables();
1083 re = pcre_compile(..., tables);
1084 .sp
1085 The locale name "fr_FR" is used on Linux and other Unix-like systems; if you
1086 are using Windows, the name for the French locale is "french".
1087 .P
1088 When \fBpcre_maketables()\fP runs, the tables are built in memory that is
1089 obtained via \fBpcre_malloc\fP. It is the caller's responsibility to ensure
1090 that the memory containing the tables remains available for as long as it is
1091 needed.
1092 .P
1093 The pointer that is passed to \fBpcre_compile()\fP is saved with the compiled
1094 pattern, and the same tables are used via this pointer by \fBpcre_study()\fP
1095 and normally also by \fBpcre_exec()\fP. Thus, by default, for any single
1096 pattern, compilation, studying and matching all happen in the same locale, but
1097 different patterns can be compiled in different locales.
1098 .P
1099 It is possible to pass a table pointer or NULL (indicating the use of the
1100 internal tables) to \fBpcre_exec()\fP. Although not intended for this purpose,
1101 this facility could be used to match a pattern in a different locale from the
1102 one in which it was compiled. Passing table pointers at run time is discussed
1103 below in the section on matching a pattern.
1104 .
1105 .
1106 .\" HTML <a name="infoaboutpattern"></a>
1108 .rs
1109 .sp
1110 .B int pcre_fullinfo(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
1111 .ti +5n
1112 .B int \fIwhat\fP, void *\fIwhere\fP);
1113 .PP
1114 The \fBpcre_fullinfo()\fP function returns information about a compiled
1115 pattern. It replaces the \fBpcre_info()\fP function, which was removed from the
1116 library at version 8.30, after more than 10 years of obsolescence.
1117 .P
1118 The first argument for \fBpcre_fullinfo()\fP is a pointer to the compiled
1119 pattern. The second argument is the result of \fBpcre_study()\fP, or NULL if
1120 the pattern was not studied. The third argument specifies which piece of
1121 information is required, and the fourth argument is a pointer to a variable
1122 to receive the data. The yield of the function is zero for success, or one of
1123 the following negative numbers:
1124 .sp
1125 PCRE_ERROR_NULL the argument \fIcode\fP was NULL
1126 the argument \fIwhere\fP was NULL
1127 PCRE_ERROR_BADMAGIC the "magic number" was not found
1128 PCRE_ERROR_BADENDIANNESS the pattern was compiled with different
1129 endianness
1130 PCRE_ERROR_BADOPTION the value of \fIwhat\fP was invalid
1131 .sp
1132 The "magic number" is placed at the start of each compiled pattern as an simple
1133 check against passing an arbitrary memory pointer. The endianness error can
1134 occur if a compiled pattern is saved and reloaded on a different host. Here is
1135 a typical call of \fBpcre_fullinfo()\fP, to obtain the length of the compiled
1136 pattern:
1137 .sp
1138 int rc;
1139 size_t length;
1140 rc = pcre_fullinfo(
1141 re, /* result of pcre_compile() */
1142 sd, /* result of pcre_study(), or NULL */
1143 PCRE_INFO_SIZE, /* what is required */
1144 &length); /* where to put the data */
1145 .sp
1146 The possible values for the third argument are defined in \fBpcre.h\fP, and are
1147 as follows:
1148 .sp
1150 .sp
1151 Return the number of the highest back reference in the pattern. The fourth
1152 argument should point to an \fBint\fP variable. Zero is returned if there are
1153 no back references.
1154 .sp
1156 .sp
1157 Return the number of capturing subpatterns in the pattern. The fourth argument
1158 should point to an \fBint\fP variable.
1159 .sp
1161 .sp
1162 Return a pointer to the internal default character tables within PCRE. The
1163 fourth argument should point to an \fBunsigned char *\fP variable. This
1164 information call is provided for internal use by the \fBpcre_study()\fP
1165 function. External callers can cause PCRE to use its internal tables by passing
1166 a NULL table pointer.
1167 .sp
1169 .sp
1170 Return information about the first data unit of any matched string, for a
1171 non-anchored pattern. (The name of this option refers to the 8-bit library,
1172 where data units are bytes.) The fourth argument should point to an \fBint\fP
1173 variable.
1174 .P
1175 If there is a fixed first value, for example, the letter "c" from a pattern
1176 such as (cat|cow|coyote), its value is returned. In the 8-bit library, the
1177 value is always less than 256; in the 16-bit library the value can be up to
1178 0xffff.
1179 .P
1180 If there is no fixed first value, and if either
1181 .sp
1182 (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
1183 starts with "^", or
1184 .sp
1185 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
1186 (if it were set, the pattern would be anchored),
1187 .sp
1188 -1 is returned, indicating that the pattern matches only at the start of a
1189 subject string or after any newline within the string. Otherwise -2 is
1190 returned. For anchored patterns, -2 is returned.
1191 .sp
1193 .sp
1194 If the pattern was studied, and this resulted in the construction of a 256-bit
1195 table indicating a fixed set of values for the first data unit in any matching
1196 string, a pointer to the table is returned. Otherwise NULL is returned. The
1197 fourth argument should point to an \fBunsigned char *\fP variable.
1198 .sp
1200 .sp
1201 Return 1 if the pattern contains any explicit matches for CR or LF characters,
1202 otherwise 0. The fourth argument should point to an \fBint\fP variable. An
1203 explicit match is either a literal CR or LF character, or \er or \en.
1204 .sp
1206 .sp
1207 Return 1 if the (?J) or (?-J) option setting is used in the pattern, otherwise
1208 0. The fourth argument should point to an \fBint\fP variable. (?J) and
1209 (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
1210 .sp
1212 .sp
1213 Return 1 if the pattern was studied with one of the JIT options, and
1214 just-in-time compiling was successful. The fourth argument should point to an
1215 \fBint\fP variable. A return value of 0 means that JIT support is not available
1216 in this version of PCRE, or that the pattern was not studied with a JIT option,
1217 or that the JIT compiler could not handle this particular pattern. See the
1218 .\" HREF
1219 \fBpcrejit\fP
1220 .\"
1221 documentation for details of what can and cannot be handled.
1222 .sp
1224 .sp
1225 If the pattern was successfully studied with a JIT option, return the size of
1226 the JIT compiled code, otherwise return zero. The fourth argument should point
1227 to a \fBsize_t\fP variable.
1228 .sp
1230 .sp
1231 Return the value of the rightmost literal data unit that must exist in any
1232 matched string, other than at its start, if such a value has been recorded. The
1233 fourth argument should point to an \fBint\fP variable. If there is no such
1234 value, -1 is returned. For anchored patterns, a last literal value is recorded
1235 only if it follows something of variable length. For example, for the pattern
1236 /^a\ed+z\ed+/ the returned value is "z", but for /^a\edz\ed/ the returned value
1237 is -1.
1238 .sp
1240 .sp
1241 Return the number of characters (NB not bytes) in the longest lookbehind
1242 assertion in the pattern. Note that the simple assertions \eb and \eB require a
1243 one-character lookbehind. This information is useful when doing multi-segment
1244 matching using the partial matching facilities.
1245 .sp
1247 .sp
1248 If the pattern was studied and a minimum length for matching subject strings
1249 was computed, its value is returned. Otherwise the returned value is -1. The
1250 value is a number of characters, which in UTF-8 mode may be different from the
1251 number of bytes. The fourth argument should point to an \fBint\fP variable. A
1252 non-negative value is a lower bound to the length of any matching string. There
1253 may not be any strings of that length that do actually match, but every string
1254 that does match is at least that long.
1255 .sp
1259 .sp
1260 PCRE supports the use of named as well as numbered capturing parentheses. The
1261 names are just an additional way of identifying the parentheses, which still
1262 acquire numbers. Several convenience functions such as
1263 \fBpcre_get_named_substring()\fP are provided for extracting captured
1264 substrings by name. It is also possible to extract the data directly, by first
1265 converting the name to a number in order to access the correct pointers in the
1266 output vector (described with \fBpcre_exec()\fP below). To do the conversion,
1267 you need to use the name-to-number map, which is described by these three
1268 values.
1269 .P
1270 The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives
1271 the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each
1272 entry; both of these return an \fBint\fP value. The entry size depends on the
1273 length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first
1274 entry of the table. This is a pointer to \fBchar\fP in the 8-bit library, where
1275 the first two bytes of each entry are the number of the capturing parenthesis,
1276 most significant byte first. In the 16-bit library, the pointer points to
1277 16-bit data units, the first of which contains the parenthesis number. The rest
1278 of the entry is the corresponding name, zero terminated.
1279 .P
1280 The names are in alphabetical order. Duplicate names may appear if (?| is used
1281 to create multiple groups with the same number, as described in the
1282 .\" HTML <a href="pcrepattern.html#dupsubpatternnumber">
1283 .\" </a>
1284 section on duplicate subpattern numbers
1285 .\"
1286 in the
1287 .\" HREF
1288 \fBpcrepattern\fP
1289 .\"
1290 page. Duplicate names for subpatterns with different numbers are permitted only
1291 if PCRE_DUPNAMES is set. In all cases of duplicate names, they appear in the
1292 table in the order in which they were found in the pattern. In the absence of
1293 (?| this is the order of increasing number; when (?| is used this is not
1294 necessarily the case because later subpatterns may have lower numbers.
1295 .P
1296 As a simple example of the name/number table, consider the following pattern
1297 after compilation by the 8-bit library (assume PCRE_EXTENDED is set, so white
1298 space - including newlines - is ignored):
1299 .sp
1300 .\" JOIN
1301 (?<date> (?<year>(\ed\ed)?\ed\ed) -
1302 (?<month>\ed\ed) - (?<day>\ed\ed) )
1303 .sp
1304 There are four named subpatterns, so the table has four entries, and each entry
1305 in the table is eight bytes long. The table is as follows, with non-printing
1306 bytes shows in hexadecimal, and undefined bytes shown as ??:
1307 .sp
1308 00 01 d a t e 00 ??
1309 00 05 d a y 00 ?? ??
1310 00 04 m o n t h 00
1311 00 02 y e a r 00 ??
1312 .sp
1313 When writing code to extract data from named subpatterns using the
1314 name-to-number map, remember that the length of the entries is likely to be
1315 different for each compiled pattern.
1316 .sp
1318 .sp
1319 Return 1 if the pattern can be used for partial matching with
1320 \fBpcre_exec()\fP, otherwise 0. The fourth argument should point to an
1321 \fBint\fP variable. From release 8.00, this always returns 1, because the
1322 restrictions that previously applied to partial matching have been lifted. The
1323 .\" HREF
1324 \fBpcrepartial\fP
1325 .\"
1326 documentation gives details of partial matching.
1327 .sp
1329 .sp
1330 Return a copy of the options with which the pattern was compiled. The fourth
1331 argument should point to an \fBunsigned long int\fP variable. These option bits
1332 are those specified in the call to \fBpcre_compile()\fP, modified by any
1333 top-level option settings at the start of the pattern itself. In other words,
1334 they are the options that will be in force when matching starts. For example,
1335 if the pattern /(?im)abc(?-i)d/ is compiled with the PCRE_EXTENDED option, the
1337 .P
1338 A pattern is automatically anchored by PCRE if all of its top-level
1339 alternatives begin with one of the following:
1340 .sp
1341 ^ unless PCRE_MULTILINE is set
1342 \eA always
1343 \eG always
1344 .\" JOIN
1345 .* if PCRE_DOTALL is set and there are no back
1346 references to the subpattern in which .* appears
1347 .sp
1348 For such patterns, the PCRE_ANCHORED bit is set in the options returned by
1349 \fBpcre_fullinfo()\fP.
1350 .sp
1352 .sp
1353 Return the size of the compiled pattern in bytes (for both libraries). The
1354 fourth argument should point to a \fBsize_t\fP variable. This value does not
1355 include the size of the \fBpcre\fP structure that is returned by
1356 \fBpcre_compile()\fP. The value that is passed as the argument to
1357 \fBpcre_malloc()\fP when \fBpcre_compile()\fP is getting memory in which to
1358 place the compiled data is the value returned by this option plus the size of
1359 the \fBpcre\fP structure. Studying a compiled pattern, with or without JIT,
1360 does not alter the value returned by this option.
1361 .sp
1363 .sp
1364 Return the size in bytes of the data block pointed to by the \fIstudy_data\fP
1365 field in a \fBpcre_extra\fP block. If \fBpcre_extra\fP is NULL, or there is no
1366 study data, zero is returned. The fourth argument should point to a
1367 \fBsize_t\fP variable. The \fIstudy_data\fP field is set by \fBpcre_study()\fP
1368 to record information that will speed up matching (see the section entitled
1369 .\" HTML <a href="#studyingapattern">
1370 .\" </a>
1371 "Studying a pattern"
1372 .\"
1373 above). The format of the \fIstudy_data\fP block is private, but its length
1374 is made available via this option so that it can be saved and restored (see the
1375 .\" HREF
1376 \fBpcreprecompile\fP
1377 .\"
1378 documentation for details).
1379 .
1380 .
1382 .rs
1383 .sp
1384 .B int pcre_refcount(pcre *\fIcode\fP, int \fIadjust\fP);
1385 .PP
1386 The \fBpcre_refcount()\fP function is used to maintain a reference count in the
1387 data block that contains a compiled pattern. It is provided for the benefit of
1388 applications that operate in an object-oriented manner, where different parts
1389 of the application may be using the same compiled pattern, but you want to free
1390 the block when they are all done.
1391 .P
1392 When a pattern is compiled, the reference count field is initialized to zero.
1393 It is changed only by calling this function, whose action is to add the
1394 \fIadjust\fP value (which may be positive or negative) to it. The yield of the
1395 function is the new value. However, the value of the count is constrained to
1396 lie between 0 and 65535, inclusive. If the new value is outside these limits,
1397 it is forced to the appropriate limit value.
1398 .P
1399 Except when it is zero, the reference count is not correctly preserved if a
1400 pattern is compiled on one host and then transferred to a host whose byte-order
1401 is different. (This seems a highly unlikely scenario.)
1402 .
1403 .
1405 .rs
1406 .sp
1407 .B int pcre_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
1408 .ti +5n
1409 .B "const char *\fIsubject\fP," int \fIlength\fP, int \fIstartoffset\fP,
1410 .ti +5n
1411 .B int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP);
1412 .P
1413 The function \fBpcre_exec()\fP is called to match a subject string against a
1414 compiled pattern, which is passed in the \fIcode\fP argument. If the
1415 pattern was studied, the result of the study should be passed in the
1416 \fIextra\fP argument. You can call \fBpcre_exec()\fP with the same \fIcode\fP
1417 and \fIextra\fP arguments as many times as you like, in order to match
1418 different subject strings with the same pattern.
1419 .P
1420 This function is the main matching facility of the library, and it operates in
1421 a Perl-like manner. For specialist use there is also an alternative matching
1422 function, which is described
1423 .\" HTML <a href="#dfamatch">
1424 .\" </a>
1425 below
1426 .\"
1427 in the section about the \fBpcre_dfa_exec()\fP function.
1428 .P
1429 In most applications, the pattern will have been compiled (and optionally
1430 studied) in the same process that calls \fBpcre_exec()\fP. However, it is
1431 possible to save compiled patterns and study data, and then use them later
1432 in different processes, possibly even on different hosts. For a discussion
1433 about this, see the
1434 .\" HREF
1435 \fBpcreprecompile\fP
1436 .\"
1437 documentation.
1438 .P
1439 Here is an example of a simple call to \fBpcre_exec()\fP:
1440 .sp
1441 int rc;
1442 int ovector[30];
1443 rc = pcre_exec(
1444 re, /* result of pcre_compile() */
1445 NULL, /* we didn't study the pattern */
1446 "some string", /* the subject string */
1447 11, /* the length of the subject string */
1448 0, /* start at offset 0 in the subject */
1449 0, /* default options */
1450 ovector, /* vector of integers for substring information */
1451 30); /* number of elements (NOT size in bytes) */
1452 .
1453 .
1454 .\" HTML <a name="extradata"></a>
1455 .SS "Extra data for \fBpcre_exec()\fR"
1456 .rs
1457 .sp
1458 If the \fIextra\fP argument is not NULL, it must point to a \fBpcre_extra\fP
1459 data block. The \fBpcre_study()\fP function returns such a block (when it
1460 doesn't return NULL), but you can also create one for yourself, and pass
1461 additional information in it. The \fBpcre_extra\fP block contains the following
1462 fields (not necessarily in this order):
1463 .sp
1464 unsigned long int \fIflags\fP;
1465 void *\fIstudy_data\fP;
1466 void *\fIexecutable_jit\fP;
1467 unsigned long int \fImatch_limit\fP;
1468 unsigned long int \fImatch_limit_recursion\fP;
1469 void *\fIcallout_data\fP;
1470 const unsigned char *\fItables\fP;
1471 unsigned char **\fImark\fP;
1472 .sp
1473 In the 16-bit version of this structure, the \fImark\fP field has type
1474 "PCRE_UCHAR16 **".
1475 .P
1476 The \fIflags\fP field is used to specify which of the other fields are set. The
1477 flag bits are:
1478 .sp
1486 .sp
1487 Other flag bits should be set to zero. The \fIstudy_data\fP field and sometimes
1488 the \fIexecutable_jit\fP field are set in the \fBpcre_extra\fP block that is
1489 returned by \fBpcre_study()\fP, together with the appropriate flag bits. You
1490 should not set these yourself, but you may add to the block by setting other
1491 fields and their corresponding flag bits.
1492 .P
1493 The \fImatch_limit\fP field provides a means of preventing PCRE from using up a
1494 vast amount of resources when running patterns that are not going to match,
1495 but which have a very large number of possibilities in their search trees. The
1496 classic example is a pattern that uses nested unlimited repeats.
1497 .P
1498 Internally, \fBpcre_exec()\fP uses a function called \fBmatch()\fP, which it
1499 calls repeatedly (sometimes recursively). The limit set by \fImatch_limit\fP is
1500 imposed on the number of times this function is called during a match, which
1501 has the effect of limiting the amount of backtracking that can take place. For
1502 patterns that are not anchored, the count restarts from zero for each position
1503 in the subject string.
1504 .P
1505 When \fBpcre_exec()\fP is called with a pattern that was successfully studied
1506 with a JIT option, the way that the matching is executed is entirely different.
1507 However, there is still the possibility of runaway matching that goes on for a
1508 very long time, and so the \fImatch_limit\fP value is also used in this case
1509 (but in a different way) to limit how long the matching can continue.
1510 .P
1511 The default value for the limit can be set when PCRE is built; the default
1512 default is 10 million, which handles all but the most extreme cases. You can
1513 override the default by suppling \fBpcre_exec()\fP with a \fBpcre_extra\fP
1514 block in which \fImatch_limit\fP is set, and PCRE_EXTRA_MATCH_LIMIT is set in
1515 the \fIflags\fP field. If the limit is exceeded, \fBpcre_exec()\fP returns
1517 .P
1518 The \fImatch_limit_recursion\fP field is similar to \fImatch_limit\fP, but
1519 instead of limiting the total number of times that \fBmatch()\fP is called, it
1520 limits the depth of recursion. The recursion depth is a smaller number than the
1521 total number of calls, because not all calls to \fBmatch()\fP are recursive.
1522 This limit is of use only if it is set smaller than \fImatch_limit\fP.
1523 .P
1524 Limiting the recursion depth limits the amount of machine stack that can be
1525 used, or, when PCRE has been compiled to use memory on the heap instead of the
1526 stack, the amount of heap memory that can be used. This limit is not relevant,
1527 and is ignored, when matching is done using JIT compiled code.
1528 .P
1529 The default value for \fImatch_limit_recursion\fP can be set when PCRE is
1530 built; the default default is the same value as the default for
1531 \fImatch_limit\fP. You can override the default by suppling \fBpcre_exec()\fP
1532 with a \fBpcre_extra\fP block in which \fImatch_limit_recursion\fP is set, and
1533 PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the \fIflags\fP field. If the limit
1534 is exceeded, \fBpcre_exec()\fP returns PCRE_ERROR_RECURSIONLIMIT.
1535 .P
1536 The \fIcallout_data\fP field is used in conjunction with the "callout" feature,
1537 and is described in the
1538 .\" HREF
1539 \fBpcrecallout\fP
1540 .\"
1541 documentation.
1542 .P
1543 The \fItables\fP field is used to pass a character tables pointer to
1544 \fBpcre_exec()\fP; this overrides the value that is stored with the compiled
1545 pattern. A non-NULL value is stored with the compiled pattern only if custom
1546 tables were supplied to \fBpcre_compile()\fP via its \fItableptr\fP argument.
1547 If NULL is passed to \fBpcre_exec()\fP using this mechanism, it forces PCRE's
1548 internal tables to be used. This facility is helpful when re-using patterns
1549 that have been saved after compiling with an external set of tables, because
1550 the external tables might be at a different address when \fBpcre_exec()\fP is
1551 called. See the
1552 .\" HREF
1553 \fBpcreprecompile\fP
1554 .\"
1555 documentation for a discussion of saving compiled patterns for later use.
1556 .P
1557 If PCRE_EXTRA_MARK is set in the \fIflags\fP field, the \fImark\fP field must
1558 be set to point to a suitable variable. If the pattern contains any
1559 backtracking control verbs such as (*MARK:NAME), and the execution ends up with
1560 a name to pass back, a pointer to the name string (zero terminated) is placed
1561 in the variable pointed to by the \fImark\fP field. The names are within the
1562 compiled pattern; if you wish to retain such a name you must copy it before
1563 freeing the memory of a compiled pattern. If there is no name to pass back, the
1564 variable pointed to by the \fImark\fP field is set to NULL. For details of the
1565 backtracking control verbs, see the section entitled
1566 .\" HTML <a href="pcrepattern#backtrackcontrol">
1567 .\" </a>
1568 "Backtracking control"
1569 .\"
1570 in the
1571 .\" HREF
1572 \fBpcrepattern\fP
1573 .\"
1574 documentation.
1575 .
1576 .
1577 .\" HTML <a name="execoptions"></a>
1578 .SS "Option bits for \fBpcre_exec()\fP"
1579 .rs
1580 .sp
1581 The unused bits of the \fIoptions\fP argument for \fBpcre_exec()\fP must be
1582 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_\fIxxx\fP,
1586 .P
1587 If the pattern was successfully studied with one of the just-in-time (JIT)
1588 compile options, the only supported options for JIT execution are
1591 unsupported option is used, JIT execution is disabled and the normal
1592 interpretive code in \fBpcre_exec()\fP is run.
1593 .sp
1595 .sp
1596 The PCRE_ANCHORED option limits \fBpcre_exec()\fP to matching at the first
1597 matching position. If a pattern was compiled with PCRE_ANCHORED, or turned out
1598 to be anchored by virtue of its contents, it cannot be made unachored at
1599 matching time.
1600 .sp
1603 .sp
1604 These options (which are mutually exclusive) control what the \eR escape
1605 sequence matches. The choice is either to match only CR, LF, or CRLF, or to
1606 match any Unicode newline sequence. These options override the choice that was
1607 made or defaulted when the pattern was compiled.
1608 .sp
1614 .sp
1615 These options override the newline definition that was chosen or defaulted when
1616 the pattern was compiled. For details, see the description of
1617 \fBpcre_compile()\fP above. During matching, the newline choice affects the
1618 behaviour of the dot, circumflex, and dollar metacharacters. It may also alter
1619 the way the match position is advanced after a match failure for an unanchored
1620 pattern.
1621 .P
1623 match attempt for an unanchored pattern fails when the current position is at a
1624 CRLF sequence, and the pattern contains no explicit matches for CR or LF
1625 characters, the match position is advanced by two characters instead of one, in
1626 other words, to after the CRLF.
1627 .P
1628 The above rule is a compromise that makes the most common cases work as
1629 expected. For example, if the pattern is .+A (and the PCRE_DOTALL option is not
1630 set), it does not match the string "\er\enA" because, after failing at the
1631 start, it skips both the CR and the LF before retrying. However, the pattern
1632 [\er\en]A does match that string, because it contains an explicit CR or LF
1633 reference, and so advances only by one character after the first failure.
1634 .P
1635 An explicit match for CR of LF is either a literal appearance of one of those
1636 characters, or one of the \er or \en escape sequences. Implicit matches such as
1637 [^X] do not count, nor does \es (which includes CR and LF in the characters
1638 that it matches).
1639 .P
1640 Notwithstanding the above, anomalous effects may still occur when CRLF is a
1641 valid newline sequence and explicit \er or \en escapes appear in the pattern.
1642 .sp
1644 .sp
1645 This option specifies that first character of the subject string is not the
1646 beginning of a line, so the circumflex metacharacter should not match before
1647 it. Setting this without PCRE_MULTILINE (at compile time) causes circumflex
1648 never to match. This option affects only the behaviour of the circumflex
1649 metacharacter. It does not affect \eA.
1650 .sp
1652 .sp
1653 This option specifies that the end of the subject string is not the end of a
1654 line, so the dollar metacharacter should not match it nor (except in multiline
1655 mode) a newline immediately before it. Setting this without PCRE_MULTILINE (at
1656 compile time) causes dollar never to match. This option affects only the
1657 behaviour of the dollar metacharacter. It does not affect \eZ or \ez.
1658 .sp
1660 .sp
1661 An empty string is not considered to be a valid match if this option is set. If
1662 there are alternatives in the pattern, they are tried. If all the alternatives
1663 match the empty string, the entire match fails. For example, if the pattern
1664 .sp
1665 a?b?
1666 .sp
1667 is applied to a string not beginning with "a" or "b", it matches an empty
1668 string at the start of the subject. With PCRE_NOTEMPTY set, this match is not
1669 valid, so PCRE searches further into the string for occurrences of "a" or "b".
1670 .sp
1672 .sp
1673 This is like PCRE_NOTEMPTY, except that an empty string match that is not at
1674 the start of the subject is permitted. If the pattern is anchored, such a match
1675 can occur only if the pattern contains \eK.
1676 .P
1677 Perl has no direct equivalent of PCRE_NOTEMPTY or PCRE_NOTEMPTY_ATSTART, but it
1678 does make a special case of a pattern match of the empty string within its
1679 \fBsplit()\fP function, and when using the /g modifier. It is possible to
1680 emulate Perl's behaviour after matching a null string by first trying the match
1681 again at the same offset with PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED, and then
1682 if that fails, by advancing the starting offset (see below) and trying an
1683 ordinary match again. There is some code that demonstrates how to do this in
1684 the
1685 .\" HREF
1686 \fBpcredemo\fP
1687 .\"
1688 sample program. In the most general case, you have to check to see if the
1689 newline convention recognizes CRLF as a newline, and if so, and the current
1690 character is CR followed by LF, advance the starting offset by two characters
1691 instead of one.
1692 .sp
1694 .sp
1695 There are a number of optimizations that \fBpcre_exec()\fP uses at the start of
1696 a match, in order to speed up the process. For example, if it is known that an
1697 unanchored match must start with a specific character, it searches the subject
1698 for that character, and fails immediately if it cannot find it, without
1699 actually running the main matching function. This means that a special item
1700 such as (*COMMIT) at the start of a pattern is not considered until after a
1701 suitable starting point for the match has been found. When callouts or (*MARK)
1702 items are in use, these "start-up" optimizations can cause them to be skipped
1703 if the pattern is never actually used. The start-up optimizations are in effect
1704 a pre-scan of the subject that takes place before the pattern is run.
1705 .P
1706 The PCRE_NO_START_OPTIMIZE option disables the start-up optimizations, possibly
1707 causing performance to suffer, but ensuring that in cases where the result is
1708 "no match", the callouts do occur, and that items such as (*COMMIT) and (*MARK)
1709 are considered at every possible starting position in the subject string. If
1710 PCRE_NO_START_OPTIMIZE is set at compile time, it cannot be unset at matching
1711 time. The use of PCRE_NO_START_OPTIMIZE disables JIT execution; when it is set,
1712 matching is always done using interpretively.
1713 .P
1714 Setting PCRE_NO_START_OPTIMIZE can change the outcome of a matching operation.
1715 Consider the pattern
1716 .sp
1718 .sp
1719 When this is compiled, PCRE records the fact that a match must start with the
1720 character "A". Suppose the subject string is "DEFABC". The start-up
1721 optimization scans along the subject, finds "A" and runs the first match
1722 attempt from there. The (*COMMIT) item means that the pattern must match the
1723 current starting position, which in this case, it does. However, if the same
1724 match is run with PCRE_NO_START_OPTIMIZE set, the initial scan along the
1725 subject string does not happen. The first match attempt is run starting from
1726 "D" and when this fails, (*COMMIT) prevents any further matches being tried, so
1727 the overall result is "no match". If the pattern is studied, more start-up
1728 optimizations may be used. For example, a minimum length for the subject may be
1729 recorded. Consider the pattern
1730 .sp
1731 (*MARK:A)(X|Y)
1732 .sp
1733 The minimum length for a match is one character. If the subject is "ABC", there
1734 will be attempts to match "ABC", "BC", "C", and then finally an empty string.
1735 If the pattern is studied, the final attempt does not take place, because PCRE
1736 knows that the subject is too short, and so the (*MARK) is never encountered.
1737 In this case, studying the pattern does not affect the overall match result,
1738 which is still "no match", but it does affect the auxiliary information that is
1739 returned.
1740 .sp
1742 .sp
1743 When PCRE_UTF8 is set at compile time, the validity of the subject as a UTF-8
1744 string is automatically checked when \fBpcre_exec()\fP is subsequently called.
1745 The entire string is checked before any other processing takes place. The value
1746 of \fIstartoffset\fP is also checked to ensure that it points to the start of a
1747 UTF-8 character. There is a discussion about the
1748 .\" HTML <a href="pcreunicode.html#utf8strings">
1749 .\" </a>
1750 validity of UTF-8 strings
1751 .\"
1752 in the
1753 .\" HREF
1754 \fBpcreunicode\fP
1755 .\"
1756 page. If an invalid sequence of bytes is found, \fBpcre_exec()\fP returns the
1757 error PCRE_ERROR_BADUTF8 or, if PCRE_PARTIAL_HARD is set and the problem is a
1758 truncated character at the end of the subject, PCRE_ERROR_SHORTUTF8. In both
1759 cases, information about the precise nature of the error may also be returned
1760 (see the descriptions of these errors in the section entitled \fIError return
1761 values from\fP \fBpcre_exec()\fP
1762 .\" HTML <a href="#errorlist">
1763 .\" </a>
1764 below).
1765 .\"
1766 If \fIstartoffset\fP contains a value that does not point to the start of a
1767 UTF-8 character (or to the end of the subject), PCRE_ERROR_BADUTF8_OFFSET is
1768 returned.
1769 .P
1770 If you already know that your subject is valid, and you want to skip these
1771 checks for performance reasons, you can set the PCRE_NO_UTF8_CHECK option when
1772 calling \fBpcre_exec()\fP. You might want to do this for the second and
1773 subsequent calls to \fBpcre_exec()\fP if you are making repeated calls to find
1774 all the matches in a single subject string. However, you should be sure that
1775 the value of \fIstartoffset\fP points to the start of a character (or the end
1776 of the subject). When PCRE_NO_UTF8_CHECK is set, the effect of passing an
1777 invalid string as a subject or an invalid value of \fIstartoffset\fP is
1778 undefined. Your program may crash.
1779 .sp
1782 .sp
1783 These options turn on the partial matching feature. For backwards
1784 compatibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial match
1785 occurs if the end of the subject string is reached successfully, but there are
1786 not enough subject characters to complete the match. If this happens when
1787 PCRE_PARTIAL_SOFT (but not PCRE_PARTIAL_HARD) is set, matching continues by
1788 testing any remaining alternatives. Only if no complete match can be found is
1789 PCRE_ERROR_PARTIAL returned instead of PCRE_ERROR_NOMATCH. In other words,
1790 PCRE_PARTIAL_SOFT says that the caller is prepared to handle a partial match,
1791 but only if no complete match can be found.
1792 .P
1793 If PCRE_PARTIAL_HARD is set, it overrides PCRE_PARTIAL_SOFT. In this case, if a
1794 partial match is found, \fBpcre_exec()\fP immediately returns
1795 PCRE_ERROR_PARTIAL, without considering any other alternatives. In other words,
1796 when PCRE_PARTIAL_HARD is set, a partial match is considered to be more
1797 important that an alternative complete match.
1798 .P
1799 In both cases, the portion of the string that was inspected when the partial
1800 match was found is set as the first matching string. There is a more detailed
1801 discussion of partial and multi-segment matching, with examples, in the
1802 .\" HREF
1803 \fBpcrepartial\fP
1804 .\"
1805 documentation.
1806 .
1807 .
1808 .SS "The string to be matched by \fBpcre_exec()\fP"
1809 .rs
1810 .sp
1811 The subject string is passed to \fBpcre_exec()\fP as a pointer in
1812 \fIsubject\fP, a length in bytes in \fIlength\fP, and a starting byte offset
1813 in \fIstartoffset\fP. If this is negative or greater than the length of the
1814 subject, \fBpcre_exec()\fP returns PCRE_ERROR_BADOFFSET. When the starting
1815 offset is zero, the search for a match starts at the beginning of the subject,
1816 and this is by far the most common case. In UTF-8 mode, the byte offset must
1817 point to the start of a UTF-8 character (or the end of the subject). Unlike the
1818 pattern string, the subject may contain binary zero bytes.
1819 .P
1820 A non-zero starting offset is useful when searching for another match in the
1821 same subject by calling \fBpcre_exec()\fP again after a previous success.
1822 Setting \fIstartoffset\fP differs from just passing over a shortened string and
1823 setting PCRE_NOTBOL in the case of a pattern that begins with any kind of
1824 lookbehind. For example, consider the pattern
1825 .sp
1826 \eBiss\eB
1827 .sp
1828 which finds occurrences of "iss" in the middle of words. (\eB matches only if
1829 the current position in the subject is not a word boundary.) When applied to
1830 the string "Mississipi" the first call to \fBpcre_exec()\fP finds the first
1831 occurrence. If \fBpcre_exec()\fP is called again with just the remainder of the
1832 subject, namely "issipi", it does not match, because \eB is always false at the
1833 start of the subject, which is deemed to be a word boundary. However, if
1834 \fBpcre_exec()\fP is passed the entire string again, but with \fIstartoffset\fP
1835 set to 4, it finds the second occurrence of "iss" because it is able to look
1836 behind the starting point to discover that it is preceded by a letter.
1837 .P
1838 Finding all the matches in a subject is tricky when the pattern can match an
1839 empty string. It is possible to emulate Perl's /g behaviour by first trying the
1840 match again at the same offset, with the PCRE_NOTEMPTY_ATSTART and
1841 PCRE_ANCHORED options, and then if that fails, advancing the starting offset
1842 and trying an ordinary match again. There is some code that demonstrates how to
1843 do this in the
1844 .\" HREF
1845 \fBpcredemo\fP
1846 .\"
1847 sample program. In the most general case, you have to check to see if the
1848 newline convention recognizes CRLF as a newline, and if so, and the current
1849 character is CR followed by LF, advance the starting offset by two characters
1850 instead of one.
1851 .P
1852 If a non-zero starting offset is passed when the pattern is anchored, one
1853 attempt to match at the given offset is made. This can only succeed if the
1854 pattern does not require the match to be at the start of the subject.
1855 .
1856 .
1857 .SS "How \fBpcre_exec()\fP returns captured substrings"
1858 .rs
1859 .sp
1860 In general, a pattern matches a certain portion of the subject, and in
1861 addition, further substrings from the subject may be picked out by parts of the
1862 pattern. Following the usage in Jeffrey Friedl's book, this is called
1863 "capturing" in what follows, and the phrase "capturing subpattern" is used for
1864 a fragment of a pattern that picks out a substring. PCRE supports several other
1865 kinds of parenthesized subpattern that do not cause substrings to be captured.
1866 .P
1867 Captured substrings are returned to the caller via a vector of integers whose
1868 address is passed in \fIovector\fP. The number of elements in the vector is
1869 passed in \fIovecsize\fP, which must be a non-negative number. \fBNote\fP: this
1870 argument is NOT the size of \fIovector\fP in bytes.
1871 .P
1872 The first two-thirds of the vector is used to pass back captured substrings,
1873 each substring using a pair of integers. The remaining third of the vector is
1874 used as workspace by \fBpcre_exec()\fP while matching capturing subpatterns,
1875 and is not available for passing back information. The number passed in
1876 \fIovecsize\fP should always be a multiple of three. If it is not, it is
1877 rounded down.
1878 .P
1879 When a match is successful, information about captured substrings is returned
1880 in pairs of integers, starting at the beginning of \fIovector\fP, and
1881 continuing up to two-thirds of its length at the most. The first element of
1882 each pair is set to the byte offset of the first character in a substring, and
1883 the second is set to the byte offset of the first character after the end of a
1884 substring. \fBNote\fP: these values are always byte offsets, even in UTF-8
1885 mode. They are not character counts.
1886 .P
1887 The first pair of integers, \fIovector[0]\fP and \fIovector[1]\fP, identify the
1888 portion of the subject string matched by the entire pattern. The next pair is
1889 used for the first capturing subpattern, and so on. The value returned by
1890 \fBpcre_exec()\fP is one more than the highest numbered pair that has been set.
1891 For example, if two substrings have been captured, the returned value is 3. If
1892 there are no capturing subpatterns, the return value from a successful match is
1893 1, indicating that just the first pair of offsets has been set.
1894 .P
1895 If a capturing subpattern is matched repeatedly, it is the last portion of the
1896 string that it matched that is returned.
1897 .P
1898 If the vector is too small to hold all the captured substring offsets, it is
1899 used as far as possible (up to two-thirds of its length), and the function
1900 returns a value of zero. If neither the actual string matched nor any captured
1901 substrings are of interest, \fBpcre_exec()\fP may be called with \fIovector\fP
1902 passed as NULL and \fIovecsize\fP as zero. However, if the pattern contains
1903 back references and the \fIovector\fP is not big enough to remember the related
1904 substrings, PCRE has to get additional memory for use during matching. Thus it
1905 is usually advisable to supply an \fIovector\fP of reasonable size.
1906 .P
1907 There are some cases where zero is returned (indicating vector overflow) when
1908 in fact the vector is exactly the right size for the final match. For example,
1909 consider the pattern
1910 .sp
1911 (a)(?:(b)c|bd)
1912 .sp
1913 If a vector of 6 elements (allowing for only 1 captured substring) is given
1914 with subject string "abd", \fBpcre_exec()\fP will try to set the second
1915 captured string, thereby recording a vector overflow, before failing to match
1916 "c" and backing up to try the second alternative. The zero return, however,
1917 does correctly indicate that the maximum number of slots (namely 2) have been
1918 filled. In similar cases where there is temporary overflow, but the final
1919 number of used slots is actually less than the maximum, a non-zero value is
1920 returned.
1921 .P
1922 The \fBpcre_fullinfo()\fP function can be used to find out how many capturing
1923 subpatterns there are in a compiled pattern. The smallest size for
1924 \fIovector\fP that will allow for \fIn\fP captured substrings, in addition to
1925 the offsets of the substring matched by the whole pattern, is (\fIn\fP+1)*3.
1926 .P
1927 It is possible for capturing subpattern number \fIn+1\fP to match some part of
1928 the subject when subpattern \fIn\fP has not been used at all. For example, if
1929 the string "abc" is matched against the pattern (a|(z))(bc) the return from the
1930 function is 4, and subpatterns 1 and 3 are matched, but 2 is not. When this
1931 happens, both values in the offset pairs corresponding to unused subpatterns
1932 are set to -1.
1933 .P
1934 Offset values that correspond to unused subpatterns at the end of the
1935 expression are also set to -1. For example, if the string "abc" is matched
1936 against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not matched. The
1937 return from the function is 2, because the highest used capturing subpattern
1938 number is 1, and the offsets for for the second and third capturing subpatterns
1939 (assuming the vector is large enough, of course) are set to -1.
1940 .P
1941 \fBNote\fP: Elements in the first two-thirds of \fIovector\fP that do not
1942 correspond to capturing parentheses in the pattern are never changed. That is,
1943 if a pattern contains \fIn\fP capturing parentheses, no more than
1944 \fIovector[0]\fP to \fIovector[2n+1]\fP are set by \fBpcre_exec()\fP. The other
1945 elements (in the first two-thirds) retain whatever values they previously had.
1946 .P
1947 Some convenience functions are provided for extracting the captured substrings
1948 as separate strings. These are described below.
1949 .
1950 .
1951 .\" HTML <a name="errorlist"></a>
1952 .SS "Error return values from \fBpcre_exec()\fP"
1953 .rs
1954 .sp
1955 If \fBpcre_exec()\fP fails, it returns a negative number. The following are
1956 defined in the header file:
1957 .sp
1959 .sp
1960 The subject string did not match the pattern.
1961 .sp
1963 .sp
1964 Either \fIcode\fP or \fIsubject\fP was passed as NULL, or \fIovector\fP was
1965 NULL and \fIovecsize\fP was not zero.
1966 .sp
1968 .sp
1969 An unrecognized bit was set in the \fIoptions\fP argument.
1970 .sp
1972 .sp
1973 PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch
1974 the case when it is passed a junk pointer and to detect when a pattern that was
1975 compiled in an environment of one endianness is run in an environment with the
1976 other endianness. This is the error that PCRE gives when the magic number is
1977 not present.
1978 .sp
1980 .sp
1981 While running the pattern match, an unknown item was encountered in the
1982 compiled pattern. This error could be caused by a bug in PCRE or by overwriting
1983 of the compiled pattern.
1984 .sp
1986 .sp
1987 If a pattern contains back references, but the \fIovector\fP that is passed to
1988 \fBpcre_exec()\fP is not big enough to remember the referenced substrings, PCRE
1989 gets a block of memory at the start of matching to use for this purpose. If the
1990 call via \fBpcre_malloc()\fP fails, this error is given. The memory is
1991 automatically freed at the end of matching.
1992 .P
1993 This error is also given if \fBpcre_stack_malloc()\fP fails in
1994 \fBpcre_exec()\fP. This can happen only when PCRE has been compiled with
1995 \fB--disable-stack-for-recursion\fP.
1996 .sp
1998 .sp
1999 This error is used by the \fBpcre_copy_substring()\fP,
2000 \fBpcre_get_substring()\fP, and \fBpcre_get_substring_list()\fP functions (see
2001 below). It is never returned by \fBpcre_exec()\fP.
2002 .sp
2004 .sp
2005 The backtracking limit, as specified by the \fImatch_limit\fP field in a
2006 \fBpcre_extra\fP structure (or defaulted) was reached. See the description
2007 above.
2008 .sp
2010 .sp
2011 This error is never generated by \fBpcre_exec()\fP itself. It is provided for
2012 use by callout functions that want to yield a distinctive error code. See the
2013 .\" HREF
2014 \fBpcrecallout\fP
2015 .\"
2016 documentation for details.
2017 .sp
2019 .sp
2020 A string that contains an invalid UTF-8 byte sequence was passed as a subject,
2021 and the PCRE_NO_UTF8_CHECK option was not set. If the size of the output vector
2022 (\fIovecsize\fP) is at least 2, the byte offset to the start of the the invalid
2023 UTF-8 character is placed in the first element, and a reason code is placed in
2024 the second element. The reason codes are listed in the
2025 .\" HTML <a href="#badutf8reasons">
2026 .\" </a>
2027 following section.
2028 .\"
2029 For backward compatibility, if PCRE_PARTIAL_HARD is set and the problem is a
2030 truncated UTF-8 character at the end of the subject (reason codes 1 to 5),
2031 PCRE_ERROR_SHORTUTF8 is returned instead of PCRE_ERROR_BADUTF8.
2032 .sp
2034 .sp
2035 The UTF-8 byte sequence that was passed as a subject was checked and found to
2036 be valid (the PCRE_NO_UTF8_CHECK option was not set), but the value of
2037 \fIstartoffset\fP did not point to the beginning of a UTF-8 character or the
2038 end of the subject.
2039 .sp
2041 .sp
2042 The subject string did not match, but it did match partially. See the
2043 .\" HREF
2044 \fBpcrepartial\fP
2045 .\"
2046 documentation for details of partial matching.
2047 .sp
2049 .sp
2050 This code is no longer in use. It was formerly returned when the PCRE_PARTIAL
2051 option was used with a compiled pattern containing items that were not
2052 supported for partial matching. From release 8.00 onwards, there are no
2053 restrictions on partial matching.
2054 .sp
2056 .sp
2057 An unexpected internal error has occurred. This error could be caused by a bug
2058 in PCRE or by overwriting of the compiled pattern.
2059 .sp
2061 .sp
2062 This error is given if the value of the \fIovecsize\fP argument is negative.
2063 .sp
2065 .sp
2066 The internal recursion limit, as specified by the \fImatch_limit_recursion\fP
2067 field in a \fBpcre_extra\fP structure (or defaulted) was reached. See the
2068 description above.
2069 .sp
2071 .sp
2072 An invalid combination of PCRE_NEWLINE_\fIxxx\fP options was given.
2073 .sp
2075 .sp
2076 The value of \fIstartoffset\fP was negative or greater than the length of the
2077 subject, that is, the value in \fIlength\fP.
2078 .sp
2080 .sp
2081 This error is returned instead of PCRE_ERROR_BADUTF8 when the subject string
2082 ends with a truncated UTF-8 character and the PCRE_PARTIAL_HARD option is set.
2083 Information about the failure is returned as for PCRE_ERROR_BADUTF8. It is in
2084 fact sufficient to detect this case, but this special error code for
2085 PCRE_PARTIAL_HARD precedes the implementation of returned information; it is
2086 retained for backwards compatibility.
2087 .sp
2089 .sp
2090 This error is returned when \fBpcre_exec()\fP detects a recursion loop within
2091 the pattern. Specifically, it means that either the whole pattern or a
2092 subpattern has been called recursively for the second time at the same position
2093 in the subject string. Some simple patterns that might do this are detected and
2094 faulted at compile time, but more complicated cases, in particular mutual
2095 recursions between two different subpatterns, cannot be detected until run
2096 time.
2097 .sp
2099 .sp
2100 This error is returned when a pattern that was successfully studied using a
2101 JIT compile option is being matched, but the memory available for the
2102 just-in-time processing stack is not large enough. See the
2103 .\" HREF
2104 \fBpcrejit\fP
2105 .\"
2106 documentation for more details.
2107 .sp
2109 .sp
2110 This error is given if a pattern that was compiled by the 8-bit library is
2111 passed to a 16-bit library function, or vice versa.
2112 .sp
2114 .sp
2115 This error is given if a pattern that was compiled and saved is reloaded on a
2116 host with different endianness. The utility function
2117 \fBpcre_pattern_to_host_byte_order()\fP can be used to convert such a pattern
2118 so that it runs on the new host.
2119 .P
2120 Error numbers -16 to -20, -22, and -30 are not used by \fBpcre_exec()\fP.
2121 .
2122 .
2123 .\" HTML <a name="badutf8reasons"></a>
2124 .SS "Reason codes for invalid UTF-8 strings"
2125 .rs
2126 .sp
2127 This section applies only to the 8-bit library. The corresponding information
2128 for the 16-bit library is given in the
2129 .\" HREF
2130 \fBpcre16\fP
2131 .\"
2132 page.
2133 .P
2134 When \fBpcre_exec()\fP returns either PCRE_ERROR_BADUTF8 or
2135 PCRE_ERROR_SHORTUTF8, and the size of the output vector (\fIovecsize\fP) is at
2136 least 2, the offset of the start of the invalid UTF-8 character is placed in
2137 the first output vector element (\fIovector[0]\fP) and a reason code is placed
2138 in the second element (\fIovector[1]\fP). The reason codes are given names in
2139 the \fBpcre.h\fP header file:
2140 .sp
2146 .sp
2147 The string ends with a truncated UTF-8 character; the code specifies how many
2148 bytes are missing (1 to 5). Although RFC 3629 restricts UTF-8 characters to be
2149 no longer than 4 bytes, the encoding scheme (originally defined by RFC 2279)
2150 allows for up to 6 bytes, and this is checked first; hence the possibility of
2151 4 or 5 missing bytes.
2152 .sp
2157 PCRE_UTF8_ERR10
2158 .sp
2159 The two most significant bits of the 2nd, 3rd, 4th, 5th, or 6th byte of the
2160 character do not have the binary value 0b10 (that is, either the most
2161 significant bit is 0, or the next bit is 1).
2162 .sp
2163 PCRE_UTF8_ERR11
2164 PCRE_UTF8_ERR12
2165 .sp
2166 A character that is valid by the RFC 2279 rules is either 5 or 6 bytes long;
2167 these code points are excluded by RFC 3629.
2168 .sp
2169 PCRE_UTF8_ERR13
2170 .sp
2171 A 4-byte character has a value greater than 0x10fff; these code points are
2172 excluded by RFC 3629.
2173 .sp
2174 PCRE_UTF8_ERR14
2175 .sp
2176 A 3-byte character has a value in the range 0xd800 to 0xdfff; this range of
2177 code points are reserved by RFC 3629 for use with UTF-16, and so are excluded
2178 from UTF-8.
2179 .sp
2180 PCRE_UTF8_ERR15
2181 PCRE_UTF8_ERR16
2182 PCRE_UTF8_ERR17
2183 PCRE_UTF8_ERR18
2184 PCRE_UTF8_ERR19
2185 .sp
2186 A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it codes for a
2187 value that can be represented by fewer bytes, which is invalid. For example,
2188 the two bytes 0xc0, 0xae give the value 0x2e, whose correct coding uses just
2189 one byte.
2190 .sp
2191 PCRE_UTF8_ERR20
2192 .sp
2193 The two most significant bits of the first byte of a character have the binary
2194 value 0b10 (that is, the most significant bit is 1 and the second is 0). Such a
2195 byte can only validly occur as the second or subsequent byte of a multi-byte
2196 character.
2197 .sp
2198 PCRE_UTF8_ERR21
2199 .sp
2200 The first byte of a character has the value 0xfe or 0xff. These values can
2201 never occur in a valid UTF-8 string.
2202 .
2203 .
2205 .rs
2206 .sp
2207 .B int pcre_copy_substring(const char *\fIsubject\fP, int *\fIovector\fP,
2208 .ti +5n
2209 .B int \fIstringcount\fP, int \fIstringnumber\fP, char *\fIbuffer\fP,
2210 .ti +5n
2211 .B int \fIbuffersize\fP);
2212 .PP
2213 .B int pcre_get_substring(const char *\fIsubject\fP, int *\fIovector\fP,
2214 .ti +5n
2215 .B int \fIstringcount\fP, int \fIstringnumber\fP,
2216 .ti +5n
2217 .B const char **\fIstringptr\fP);
2218 .PP
2219 .B int pcre_get_substring_list(const char *\fIsubject\fP,
2220 .ti +5n
2221 .B int *\fIovector\fP, int \fIstringcount\fP, "const char ***\fIlistptr\fP);"
2222 .PP
2223 Captured substrings can be accessed directly by using the offsets returned by
2224 \fBpcre_exec()\fP in \fIovector\fP. For convenience, the functions
2225 \fBpcre_copy_substring()\fP, \fBpcre_get_substring()\fP, and
2226 \fBpcre_get_substring_list()\fP are provided for extracting captured substrings
2227 as new, separate, zero-terminated strings. These functions identify substrings
2228 by number. The next section describes functions for extracting named
2229 substrings.
2230 .P
2231 A substring that contains a binary zero is correctly extracted and has a
2232 further zero added on the end, but the result is not, of course, a C string.
2233 However, you can process such a string by referring to the length that is
2234 returned by \fBpcre_copy_substring()\fP and \fBpcre_get_substring()\fP.
2235 Unfortunately, the interface to \fBpcre_get_substring_list()\fP is not adequate
2236 for handling strings containing binary zeros, because the end of the final
2237 string is not independently indicated.
2238 .P
2239 The first three arguments are the same for all three of these functions:
2240 \fIsubject\fP is the subject string that has just been successfully matched,
2241 \fIovector\fP is a pointer to the vector of integer offsets that was passed to
2242 \fBpcre_exec()\fP, and \fIstringcount\fP is the number of substrings that were
2243 captured by the match, including the substring that matched the entire regular
2244 expression. This is the value returned by \fBpcre_exec()\fP if it is greater
2245 than zero. If \fBpcre_exec()\fP returned zero, indicating that it ran out of
2246 space in \fIovector\fP, the value passed as \fIstringcount\fP should be the
2247 number of elements in the vector divided by three.
2248 .P
2249 The functions \fBpcre_copy_substring()\fP and \fBpcre_get_substring()\fP
2250 extract a single substring, whose number is given as \fIstringnumber\fP. A
2251 value of zero extracts the substring that matched the entire pattern, whereas
2252 higher values extract the captured substrings. For \fBpcre_copy_substring()\fP,
2253 the string is placed in \fIbuffer\fP, whose length is given by
2254 \fIbuffersize\fP, while for \fBpcre_get_substring()\fP a new block of memory is
2255 obtained via \fBpcre_malloc\fP, and its address is returned via
2256 \fIstringptr\fP. The yield of the function is the length of the string, not
2257 including the terminating zero, or one of these error codes:
2258 .sp
2260 .sp
2261 The buffer was too small for \fBpcre_copy_substring()\fP, or the attempt to get
2262 memory failed for \fBpcre_get_substring()\fP.
2263 .sp
2265 .sp
2266 There is no substring whose number is \fIstringnumber\fP.
2267 .P
2268 The \fBpcre_get_substring_list()\fP function extracts all available substrings
2269 and builds a list of pointers to them. All this is done in a single block of
2270 memory that is obtained via \fBpcre_malloc\fP. The address of the memory block
2271 is returned via \fIlistptr\fP, which is also the start of the list of string
2272 pointers. The end of the list is marked by a NULL pointer. The yield of the
2273 function is zero if all went well, or the error code
2274 .sp
2276 .sp
2277 if the attempt to get the memory block failed.
2278 .P
2279 When any of these functions encounter a substring that is unset, which can
2280 happen when capturing subpattern number \fIn+1\fP matches some part of the
2281 subject, but subpattern \fIn\fP has not been used at all, they return an empty
2282 string. This can be distinguished from a genuine zero-length substring by
2283 inspecting the appropriate offset in \fIovector\fP, which is negative for unset
2284 substrings.
2285 .P
2286 The two convenience functions \fBpcre_free_substring()\fP and
2287 \fBpcre_free_substring_list()\fP can be used to free the memory returned by
2288 a previous call of \fBpcre_get_substring()\fP or
2289 \fBpcre_get_substring_list()\fP, respectively. They do nothing more than call
2290 the function pointed to by \fBpcre_free\fP, which of course could be called
2291 directly from a C program. However, PCRE is used in some situations where it is
2292 linked via a special interface to another programming language that cannot use
2293 \fBpcre_free\fP directly; it is for these cases that the functions are
2294 provided.
2295 .
2296 .
2298 .rs
2299 .sp
2300 .B int pcre_get_stringnumber(const pcre *\fIcode\fP,
2301 .ti +5n
2302 .B const char *\fIname\fP);
2303 .PP
2304 .B int pcre_copy_named_substring(const pcre *\fIcode\fP,
2305 .ti +5n
2306 .B const char *\fIsubject\fP, int *\fIovector\fP,
2307 .ti +5n
2308 .B int \fIstringcount\fP, const char *\fIstringname\fP,
2309 .ti +5n
2310 .B char *\fIbuffer\fP, int \fIbuffersize\fP);
2311 .PP
2312 .B int pcre_get_named_substring(const pcre *\fIcode\fP,
2313 .ti +5n
2314 .B const char *\fIsubject\fP, int *\fIovector\fP,
2315 .ti +5n
2316 .B int \fIstringcount\fP, const char *\fIstringname\fP,
2317 .ti +5n
2318 .B const char **\fIstringptr\fP);
2319 .PP
2320 To extract a substring by name, you first have to find associated number.
2321 For example, for this pattern
2322 .sp
2323 (a+)b(?<xxx>\ed+)...
2324 .sp
2325 the number of the subpattern called "xxx" is 2. If the name is known to be
2326 unique (PCRE_DUPNAMES was not set), you can find the number from the name by
2327 calling \fBpcre_get_stringnumber()\fP. The first argument is the compiled
2328 pattern, and the second is the name. The yield of the function is the
2329 subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no subpattern of
2330 that name.
2331 .P
2332 Given the number, you can extract the substring directly, or use one of the
2333 functions described in the previous section. For convenience, there are also
2334 two functions that do the whole job.
2335 .P
2336 Most of the arguments of \fBpcre_copy_named_substring()\fP and
2337 \fBpcre_get_named_substring()\fP are the same as those for the similarly named
2338 functions that extract by number. As these are described in the previous
2339 section, they are not re-described here. There are just two differences:
2340 .P
2341 First, instead of a substring number, a substring name is given. Second, there
2342 is an extra argument, given at the start, which is a pointer to the compiled
2343 pattern. This is needed in order to gain access to the name-to-number
2344 translation table.
2345 .P
2346 These functions call \fBpcre_get_stringnumber()\fP, and if it succeeds, they
2347 then call \fBpcre_copy_substring()\fP or \fBpcre_get_substring()\fP, as
2348 appropriate. \fBNOTE:\fP If PCRE_DUPNAMES is set and there are duplicate names,
2349 the behaviour may not be what you want (see the next section).
2350 .P
2351 \fBWarning:\fP If the pattern uses the (?| feature to set up multiple
2352 subpatterns with the same number, as described in the
2353 .\" HTML <a href="pcrepattern.html#dupsubpatternnumber">
2354 .\" </a>
2355 section on duplicate subpattern numbers
2356 .\"
2357 in the
2358 .\" HREF
2359 \fBpcrepattern\fP
2360 .\"
2361 page, you cannot use names to distinguish the different subpatterns, because
2362 names are not included in the compiled code. The matching process uses only
2363 numbers. For this reason, the use of different names for subpatterns of the
2364 same number causes an error at compile time.
2365 .
2366 .
2368 .rs
2369 .sp
2370 .B int pcre_get_stringtable_entries(const pcre *\fIcode\fP,
2371 .ti +5n
2372 .B const char *\fIname\fP, char **\fIfirst\fP, char **\fIlast\fP);
2373 .PP
2374 When a pattern is compiled with the PCRE_DUPNAMES option, names for subpatterns
2375 are not required to be unique. (Duplicate names are always allowed for
2376 subpatterns with the same number, created by using the (?| feature. Indeed, if
2377 such subpatterns are named, they are required to use the same names.)
2378 .P
2379 Normally, patterns with duplicate names are such that in any one match, only
2380 one of the named subpatterns participates. An example is shown in the
2381 .\" HREF
2382 \fBpcrepattern\fP
2383 .\"
2384 documentation.
2385 .P
2386 When duplicates are present, \fBpcre_copy_named_substring()\fP and
2387 \fBpcre_get_named_substring()\fP return the first substring corresponding to
2388 the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING (-7) is
2389 returned; no data is returned. The \fBpcre_get_stringnumber()\fP function
2390 returns one of the numbers that are associated with the name, but it is not
2391 defined which it is.
2392 .P
2393 If you want to get full details of all captured substrings for a given name,
2394 you must use the \fBpcre_get_stringtable_entries()\fP function. The first
2395 argument is the compiled pattern, and the second is the name. The third and
2396 fourth are pointers to variables which are updated by the function. After it
2397 has run, they point to the first and last entries in the name-to-number table
2398 for the given name. The function itself returns the length of each entry, or
2399 PCRE_ERROR_NOSUBSTRING (-7) if there are none. The format of the table is
2400 described above in the section entitled \fIInformation about a pattern\fP
2401 .\" HTML <a href="#infoaboutpattern">
2402 .\" </a>
2403 above.
2404 .\"
2405 Given all the relevant entries for the name, you can extract each of their
2406 numbers, and hence the captured data, if any.
2407 .
2408 .
2410 .rs
2411 .sp
2412 The traditional matching function uses a similar algorithm to Perl, which stops
2413 when it finds the first match, starting at a given point in the subject. If you
2414 want to find all possible matches, or the longest possible match, consider
2415 using the alternative matching function (see below) instead. If you cannot use
2416 the alternative function, but still need to find all possible matches, you
2417 can kludge it up by making use of the callout facility, which is described in
2418 the
2419 .\" HREF
2420 \fBpcrecallout\fP
2421 .\"
2422 documentation.
2423 .P
2424 What you have to do is to insert a callout right at the end of the pattern.
2425 When your callout function is called, extract and save the current matched
2426 substring. Then return 1, which forces \fBpcre_exec()\fP to backtrack and try
2427 other alternatives. Ultimately, when it runs out of matches, \fBpcre_exec()\fP
2428 will yield PCRE_ERROR_NOMATCH.
2429 .
2430 .
2432 .rs
2433 .sp
2434 Matching certain patterns using \fBpcre_exec()\fP can use a lot of process
2435 stack, which in certain environments can be rather limited in size. Some users
2436 find it helpful to have an estimate of the amount of stack that is used by
2437 \fBpcre_exec()\fP, to help them set recursion limits, as described in the
2438 .\" HREF
2439 \fBpcrestack\fP
2440 .\"
2441 documentation. The estimate that is output by \fBpcretest\fP when called with
2442 the \fB-m\fP and \fB-C\fP options is obtained by calling \fBpcre_exec\fP with
2443 the values NULL, NULL, NULL, -999, and -999 for its first five arguments.
2444 .P
2445 Normally, if its first argument is NULL, \fBpcre_exec()\fP immediately returns
2446 the negative error code PCRE_ERROR_NULL, but with this special combination of
2447 arguments, it returns instead a negative number whose absolute value is the
2448 approximate stack frame size in bytes. (A negative number is used so that it is
2449 clear that no match has happened.) The value is approximate because in some
2450 cases, recursive calls to \fBpcre_exec()\fP occur when there are one or two
2451 additional variables on the stack.
2452 .P
2453 If PCRE has been compiled to use the heap instead of the stack for recursion,
2454 the value returned is the size of each block that is obtained from the heap.
2455 .
2456 .
2457 .\" HTML <a name="dfamatch"></a>
2459 .rs
2460 .sp
2461 .B int pcre_dfa_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
2462 .ti +5n
2463 .B "const char *\fIsubject\fP," int \fIlength\fP, int \fIstartoffset\fP,
2464 .ti +5n
2465 .B int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP,
2466 .ti +5n
2467 .B int *\fIworkspace\fP, int \fIwscount\fP);
2468 .P
2469 The function \fBpcre_dfa_exec()\fP is called to match a subject string against
2470 a compiled pattern, using a matching algorithm that scans the subject string
2471 just once, and does not backtrack. This has different characteristics to the
2472 normal algorithm, and is not compatible with Perl. Some of the features of PCRE
2473 patterns are not supported. Nevertheless, there are times when this kind of
2474 matching can be useful. For a discussion of the two matching algorithms, and a
2475 list of features that \fBpcre_dfa_exec()\fP does not support, see the
2476 .\" HREF
2477 \fBpcrematching\fP
2478 .\"
2479 documentation.
2480 .P
2481 The arguments for the \fBpcre_dfa_exec()\fP function are the same as for
2482 \fBpcre_exec()\fP, plus two extras. The \fIovector\fP argument is used in a
2483 different way, and this is described below. The other common arguments are used
2484 in the same way as for \fBpcre_exec()\fP, so their description is not repeated
2485 here.
2486 .P
2487 The two additional arguments provide workspace for the function. The workspace
2488 vector should contain at least 20 elements. It is used for keeping track of
2489 multiple paths through the pattern tree. More workspace will be needed for
2490 patterns and subjects where there are a lot of potential matches.
2491 .P
2492 Here is an example of a simple call to \fBpcre_dfa_exec()\fP:
2493 .sp
2494 int rc;
2495 int ovector[10];
2496 int wspace[20];
2497 rc = pcre_dfa_exec(
2498 re, /* result of pcre_compile() */
2499 NULL, /* we didn't study the pattern */
2500 "some string", /* the subject string */
2501 11, /* the length of the subject string */
2502 0, /* start at offset 0 in the subject */
2503 0, /* default options */
2504 ovector, /* vector of integers for substring information */
2505 10, /* number of elements (NOT size in bytes) */
2506 wspace, /* working space vector */
2507 20); /* number of elements (NOT size in bytes) */
2508 .
2509 .SS "Option bits for \fBpcre_dfa_exec()\fP"
2510 .rs
2511 .sp
2512 The unused bits of the \fIoptions\fP argument for \fBpcre_dfa_exec()\fP must be
2513 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_\fIxxx\fP,
2517 All but the last four of these are exactly the same as for \fBpcre_exec()\fP,
2518 so their description is not repeated here.
2519 .sp
2522 .sp
2523 These have the same general effect as they do for \fBpcre_exec()\fP, but the
2524 details are slightly different. When PCRE_PARTIAL_HARD is set for
2525 \fBpcre_dfa_exec()\fP, it returns PCRE_ERROR_PARTIAL if the end of the subject
2526 is reached and there is still at least one matching possibility that requires
2527 additional characters. This happens even if some complete matches have also
2528 been found. When PCRE_PARTIAL_SOFT is set, the return code PCRE_ERROR_NOMATCH
2529 is converted into PCRE_ERROR_PARTIAL if the end of the subject is reached,
2530 there have been no complete matches, but there is still at least one matching
2531 possibility. The portion of the string that was inspected when the longest
2532 partial match was found is set as the first matching string in both cases.
2533 There is a more detailed discussion of partial and multi-segment matching, with
2534 examples, in the
2535 .\" HREF
2536 \fBpcrepartial\fP
2537 .\"
2538 documentation.
2539 .sp
2541 .sp
2542 Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to stop as
2543 soon as it has found one match. Because of the way the alternative algorithm
2544 works, this is necessarily the shortest possible match at the first possible
2545 matching point in the subject string.
2546 .sp
2548 .sp
2549 When \fBpcre_dfa_exec()\fP returns a partial match, it is possible to call it
2550 again, with additional subject characters, and have it continue with the same
2551 match. The PCRE_DFA_RESTART option requests this action; when it is set, the
2552 \fIworkspace\fP and \fIwscount\fP options must reference the same vector as
2553 before because data about the match so far is left in them after a partial
2554 match. There is more discussion of this facility in the
2555 .\" HREF
2556 \fBpcrepartial\fP
2557 .\"
2558 documentation.
2559 .
2560 .
2561 .SS "Successful returns from \fBpcre_dfa_exec()\fP"
2562 .rs
2563 .sp
2564 When \fBpcre_dfa_exec()\fP succeeds, it may have matched more than one
2565 substring in the subject. Note, however, that all the matches from one run of
2566 the function start at the same point in the subject. The shorter matches are
2567 all initial substrings of the longer matches. For example, if the pattern
2568 .sp
2569 <.*>
2570 .sp
2571 is matched against the string
2572 .sp
2573 This is <something> <something else> <something further> no more
2574 .sp
2575 the three matched strings are
2576 .sp
2577 <something>
2578 <something> <something else>
2579 <something> <something else> <something further>
2580 .sp
2581 On success, the yield of the function is a number greater than zero, which is
2582 the number of matched substrings. The substrings themselves are returned in
2583 \fIovector\fP. Each string uses two elements; the first is the offset to the
2584 start, and the second is the offset to the end. In fact, all the strings have
2585 the same start offset. (Space could have been saved by giving this only once,
2586 but it was decided to retain some compatibility with the way \fBpcre_exec()\fP
2587 returns data, even though the meaning of the strings is different.)
2588 .P
2589 The strings are returned in reverse order of length; that is, the longest
2590 matching string is given first. If there were too many matches to fit into
2591 \fIovector\fP, the yield of the function is zero, and the vector is filled with
2592 the longest matches. Unlike \fBpcre_exec()\fP, \fBpcre_dfa_exec()\fP can use
2593 the entire \fIovector\fP for returning matched strings.
2594 .
2595 .
2596 .SS "Error returns from \fBpcre_dfa_exec()\fP"
2597 .rs
2598 .sp
2599 The \fBpcre_dfa_exec()\fP function returns a negative number when it fails.
2600 Many of the errors are the same as for \fBpcre_exec()\fP, and these are
2601 described
2602 .\" HTML <a href="#errorlist">
2603 .\" </a>
2604 above.
2605 .\"
2606 There are in addition the following errors that are specific to
2607 \fBpcre_dfa_exec()\fP:
2608 .sp
2610 .sp
2611 This return is given if \fBpcre_dfa_exec()\fP encounters an item in the pattern
2612 that it does not support, for instance, the use of \eC or a back reference.
2613 .sp
2615 .sp
2616 This return is given if \fBpcre_dfa_exec()\fP encounters a condition item that
2617 uses a back reference for the condition, or a test for recursion in a specific
2618 group. These are not supported.
2619 .sp
2621 .sp
2622 This return is given if \fBpcre_dfa_exec()\fP is called with an \fIextra\fP
2623 block that contains a setting of the \fImatch_limit\fP or
2624 \fImatch_limit_recursion\fP fields. This is not supported (these fields are
2625 meaningless for DFA matching).
2626 .sp
2628 .sp
2629 This return is given if \fBpcre_dfa_exec()\fP runs out of space in the
2630 \fIworkspace\fP vector.
2631 .sp
2633 .sp
2634 When a recursive subpattern is processed, the matching function calls itself
2635 recursively, using private vectors for \fIovector\fP and \fIworkspace\fP. This
2636 error is given if the output vector is not large enough. This should be
2637 extremely rare, as a vector of size 1000 is used.
2638 .sp
2640 .sp
2641 When \fBpcre_dfa_exec()\fP is called with the \fBPCRE_DFA_RESTART\fP option,
2642 some plausibility checks are made on the contents of the workspace, which
2643 should contain data about the previous partial match. If any of these checks
2644 fail, this error is given.
2645 .
2646 .
2647 .SH "SEE ALSO"
2648 .rs
2649 .sp
2650 \fBpcre16\fP(3), \fBpcrebuild\fP(3), \fBpcrecallout\fP(3), \fBpcrecpp(3)\fP(3),
2651 \fBpcrematching\fP(3), \fBpcrepartial\fP(3), \fBpcreposix\fP(3),
2652 \fBpcreprecompile\fP(3), \fBpcresample\fP(3), \fBpcrestack\fP(3).
2653 .
2654 .
2656 .rs
2657 .sp
2658 .nf
2659 Philip Hazel
2660 University Computing Service
2661 Cambridge CB2 3QH, England.
2662 .fi
2663 .
2664 .
2666 .rs
2667 .sp
2668 .nf
2669 Last updated: 04 May 2012
2670 Copyright (c) 1997-2012 University of Cambridge.
2671 .fi


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