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Revision 1404 - (show annotations)
Tue Nov 19 15:36:57 2013 UTC (5 years, 9 months ago) by ph10
File size: 128200 byte(s)
Source tidies for 8.34-RC1.
1 .TH PCREAPI 3 "12 November 2013" "PCRE 8.34"
2 .SH NAME
3 PCRE - Perl-compatible regular expressions
4 .sp
5 .B #include <pcre.h>
6 .
7 .
8 .SH "PCRE NATIVE API BASIC FUNCTIONS"
9 .rs
10 .sp
11 .nf
12 .B pcre *pcre_compile(const char *\fIpattern\fP, int \fIoptions\fP,
13 .B " const char **\fIerrptr\fP, int *\fIerroffset\fP,"
14 .B " const unsigned char *\fItableptr\fP);"
15 .sp
16 .B pcre *pcre_compile2(const char *\fIpattern\fP, int \fIoptions\fP,
17 .B " int *\fIerrorcodeptr\fP,"
18 .B " const char **\fIerrptr\fP, int *\fIerroffset\fP,"
19 .B " const unsigned char *\fItableptr\fP);"
20 .sp
21 .B pcre_extra *pcre_study(const pcre *\fIcode\fP, int \fIoptions\fP,
22 .B " const char **\fIerrptr\fP);"
23 .sp
24 .B void pcre_free_study(pcre_extra *\fIextra\fP);
25 .sp
26 .B int pcre_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
27 .B " const char *\fIsubject\fP, int \fIlength\fP, int \fIstartoffset\fP,"
28 .B " int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP);"
29 .sp
30 .B int pcre_dfa_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
31 .B " const char *\fIsubject\fP, int \fIlength\fP, int \fIstartoffset\fP,"
32 .B " int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP,"
33 .B " int *\fIworkspace\fP, int \fIwscount\fP);"
34 .fi
35 .
36 .
37 .SH "PCRE NATIVE API STRING EXTRACTION FUNCTIONS"
38 .rs
39 .sp
40 .nf
41 .B int pcre_copy_named_substring(const pcre *\fIcode\fP,
42 .B " const char *\fIsubject\fP, int *\fIovector\fP,"
43 .B " int \fIstringcount\fP, const char *\fIstringname\fP,"
44 .B " char *\fIbuffer\fP, int \fIbuffersize\fP);"
45 .sp
46 .B int pcre_copy_substring(const char *\fIsubject\fP, int *\fIovector\fP,
47 .B " int \fIstringcount\fP, int \fIstringnumber\fP, char *\fIbuffer\fP,"
48 .B " int \fIbuffersize\fP);"
49 .sp
50 .B int pcre_get_named_substring(const pcre *\fIcode\fP,
51 .B " const char *\fIsubject\fP, int *\fIovector\fP,"
52 .B " int \fIstringcount\fP, const char *\fIstringname\fP,"
53 .B " const char **\fIstringptr\fP);"
54 .sp
55 .B int pcre_get_stringnumber(const pcre *\fIcode\fP,
56 .B " const char *\fIname\fP);"
57 .sp
58 .B int pcre_get_stringtable_entries(const pcre *\fIcode\fP,
59 .B " const char *\fIname\fP, char **\fIfirst\fP, char **\fIlast\fP);"
60 .sp
61 .B int pcre_get_substring(const char *\fIsubject\fP, int *\fIovector\fP,
62 .B " int \fIstringcount\fP, int \fIstringnumber\fP,"
63 .B " const char **\fIstringptr\fP);"
64 .sp
65 .B int pcre_get_substring_list(const char *\fIsubject\fP,
66 .B " int *\fIovector\fP, int \fIstringcount\fP, const char ***\fIlistptr\fP);"
67 .sp
68 .B void pcre_free_substring(const char *\fIstringptr\fP);
69 .sp
70 .B void pcre_free_substring_list(const char **\fIstringptr\fP);
71 .fi
72 .
73 .
74 .SH "PCRE NATIVE API AUXILIARY FUNCTIONS"
75 .rs
76 .sp
77 .nf
78 .B int pcre_jit_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
79 .B " const char *\fIsubject\fP, int \fIlength\fP, int \fIstartoffset\fP,"
80 .B " int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP,"
81 .B " pcre_jit_stack *\fIjstack\fP);"
82 .sp
83 .B pcre_jit_stack *pcre_jit_stack_alloc(int \fIstartsize\fP, int \fImaxsize\fP);
84 .sp
85 .B void pcre_jit_stack_free(pcre_jit_stack *\fIstack\fP);
86 .sp
87 .B void pcre_assign_jit_stack(pcre_extra *\fIextra\fP,
88 .B " pcre_jit_callback \fIcallback\fP, void *\fIdata\fP);"
89 .sp
90 .B const unsigned char *pcre_maketables(void);
91 .sp
92 .B int pcre_fullinfo(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
93 .B " int \fIwhat\fP, void *\fIwhere\fP);"
94 .sp
95 .B int pcre_refcount(pcre *\fIcode\fP, int \fIadjust\fP);
96 .sp
97 .B int pcre_config(int \fIwhat\fP, void *\fIwhere\fP);
98 .sp
99 .B const char *pcre_version(void);
100 .sp
101 .B int pcre_pattern_to_host_byte_order(pcre *\fIcode\fP,
102 .B " pcre_extra *\fIextra\fP, const unsigned char *\fItables\fP);"
103 .fi
104 .
105 .
106 .SH "PCRE NATIVE API INDIRECTED FUNCTIONS"
107 .rs
108 .sp
109 .nf
110 .B void *(*pcre_malloc)(size_t);
111 .sp
112 .B void (*pcre_free)(void *);
113 .sp
114 .B void *(*pcre_stack_malloc)(size_t);
115 .sp
116 .B void (*pcre_stack_free)(void *);
117 .sp
118 .B int (*pcre_callout)(pcre_callout_block *);
119 .fi
120 .
121 .
122 .SH "PCRE 8-BIT, 16-BIT, AND 32-BIT LIBRARIES"
123 .rs
124 .sp
125 As well as support for 8-bit character strings, PCRE also supports 16-bit
126 strings (from release 8.30) and 32-bit strings (from release 8.32), by means of
127 two additional libraries. They can be built as well as, or instead of, the
128 8-bit library. To avoid too much complication, this document describes the
129 8-bit versions of the functions, with only occasional references to the 16-bit
130 and 32-bit libraries.
131 .P
132 The 16-bit and 32-bit functions operate in the same way as their 8-bit
133 counterparts; they just use different data types for their arguments and
134 results, and their names start with \fBpcre16_\fP or \fBpcre32_\fP instead of
135 \fBpcre_\fP. For every option that has UTF8 in its name (for example,
136 PCRE_UTF8), there are corresponding 16-bit and 32-bit names with UTF8 replaced
137 by UTF16 or UTF32, respectively. This facility is in fact just cosmetic; the
138 16-bit and 32-bit option names define the same bit values.
139 .P
140 References to bytes and UTF-8 in this document should be read as references to
141 16-bit data units and UTF-16 when using the 16-bit library, or 32-bit data
142 units and UTF-32 when using the 32-bit library, unless specified otherwise.
143 More details of the specific differences for the 16-bit and 32-bit libraries
144 are given in the
145 .\" HREF
146 \fBpcre16\fP
147 .\"
148 and
149 .\" HREF
150 \fBpcre32\fP
151 .\"
152 pages.
153 .
154 .
155 .SH "PCRE API OVERVIEW"
156 .rs
157 .sp
158 PCRE has its own native API, which is described in this document. There are
159 also some wrapper functions (for the 8-bit library only) that correspond to the
160 POSIX regular expression API, but they do not give access to all the
161 functionality. They are described in the
162 .\" HREF
163 \fBpcreposix\fP
164 .\"
165 documentation. Both of these APIs define a set of C function calls. A C++
166 wrapper (again for the 8-bit library only) is also distributed with PCRE. It is
167 documented in the
168 .\" HREF
169 \fBpcrecpp\fP
170 .\"
171 page.
172 .P
173 The native API C function prototypes are defined in the header file
174 \fBpcre.h\fP, and on Unix-like systems the (8-bit) library itself is called
175 \fBlibpcre\fP. It can normally be accessed by adding \fB-lpcre\fP to the
176 command for linking an application that uses PCRE. The header file defines the
177 macros PCRE_MAJOR and PCRE_MINOR to contain the major and minor release numbers
178 for the library. Applications can use these to include support for different
179 releases of PCRE.
180 .P
181 In a Windows environment, if you want to statically link an application program
182 against a non-dll \fBpcre.a\fP file, you must define PCRE_STATIC before
183 including \fBpcre.h\fP or \fBpcrecpp.h\fP, because otherwise the
184 \fBpcre_malloc()\fP and \fBpcre_free()\fP exported functions will be declared
185 \fB__declspec(dllimport)\fP, with unwanted results.
186 .P
187 The functions \fBpcre_compile()\fP, \fBpcre_compile2()\fP, \fBpcre_study()\fP,
188 and \fBpcre_exec()\fP are used for compiling and matching regular expressions
189 in a Perl-compatible manner. A sample program that demonstrates the simplest
190 way of using them is provided in the file called \fIpcredemo.c\fP in the PCRE
191 source distribution. A listing of this program is given in the
192 .\" HREF
193 \fBpcredemo\fP
194 .\"
195 documentation, and the
196 .\" HREF
197 \fBpcresample\fP
198 .\"
199 documentation describes how to compile and run it.
200 .P
201 Just-in-time compiler support is an optional feature of PCRE that can be built
202 in appropriate hardware environments. It greatly speeds up the matching
203 performance of many patterns. Simple programs can easily request that it be
204 used if available, by setting an option that is ignored when it is not
205 relevant. More complicated programs might need to make use of the functions
206 \fBpcre_jit_stack_alloc()\fP, \fBpcre_jit_stack_free()\fP, and
207 \fBpcre_assign_jit_stack()\fP in order to control the JIT code's memory usage.
208 .P
209 From release 8.32 there is also a direct interface for JIT execution, which
210 gives improved performance. The JIT-specific functions are discussed in the
211 .\" HREF
212 \fBpcrejit\fP
213 .\"
214 documentation.
215 .P
216 A second matching function, \fBpcre_dfa_exec()\fP, which is not
217 Perl-compatible, is also provided. This uses a different algorithm for the
218 matching. The alternative algorithm finds all possible matches (at a given
219 point in the subject), and scans the subject just once (unless there are
220 lookbehind assertions). However, this algorithm does not return captured
221 substrings. A description of the two matching algorithms and their advantages
222 and disadvantages is given in the
223 .\" HREF
224 \fBpcrematching\fP
225 .\"
226 documentation.
227 .P
228 In addition to the main compiling and matching functions, there are convenience
229 functions for extracting captured substrings from a subject string that is
230 matched by \fBpcre_exec()\fP. They are:
231 .sp
232 \fBpcre_copy_substring()\fP
233 \fBpcre_copy_named_substring()\fP
234 \fBpcre_get_substring()\fP
235 \fBpcre_get_named_substring()\fP
236 \fBpcre_get_substring_list()\fP
237 \fBpcre_get_stringnumber()\fP
238 \fBpcre_get_stringtable_entries()\fP
239 .sp
240 \fBpcre_free_substring()\fP and \fBpcre_free_substring_list()\fP are also
241 provided, to free the memory used for extracted strings.
242 .P
243 The function \fBpcre_maketables()\fP is used to build a set of character tables
244 in the current locale for passing to \fBpcre_compile()\fP, \fBpcre_exec()\fP,
245 or \fBpcre_dfa_exec()\fP. This is an optional facility that is provided for
246 specialist use. Most commonly, no special tables are passed, in which case
247 internal tables that are generated when PCRE is built are used.
248 .P
249 The function \fBpcre_fullinfo()\fP is used to find out information about a
250 compiled pattern. The function \fBpcre_version()\fP returns a pointer to a
251 string containing the version of PCRE and its date of release.
252 .P
253 The function \fBpcre_refcount()\fP maintains a reference count in a data block
254 containing a compiled pattern. This is provided for the benefit of
255 object-oriented applications.
256 .P
257 The global variables \fBpcre_malloc\fP and \fBpcre_free\fP initially contain
258 the entry points of the standard \fBmalloc()\fP and \fBfree()\fP functions,
259 respectively. PCRE calls the memory management functions via these variables,
260 so a calling program can replace them if it wishes to intercept the calls. This
261 should be done before calling any PCRE functions.
262 .P
263 The global variables \fBpcre_stack_malloc\fP and \fBpcre_stack_free\fP are also
264 indirections to memory management functions. These special functions are used
265 only when PCRE is compiled to use the heap for remembering data, instead of
266 recursive function calls, when running the \fBpcre_exec()\fP function. See the
267 .\" HREF
268 \fBpcrebuild\fP
269 .\"
270 documentation for details of how to do this. It is a non-standard way of
271 building PCRE, for use in environments that have limited stacks. Because of the
272 greater use of memory management, it runs more slowly. Separate functions are
273 provided so that special-purpose external code can be used for this case. When
274 used, these functions are always called in a stack-like manner (last obtained,
275 first freed), and always for memory blocks of the same size. There is a
276 discussion about PCRE's stack usage in the
277 .\" HREF
278 \fBpcrestack\fP
279 .\"
280 documentation.
281 .P
282 The global variable \fBpcre_callout\fP initially contains NULL. It can be set
283 by the caller to a "callout" function, which PCRE will then call at specified
284 points during a matching operation. Details are given in the
285 .\" HREF
286 \fBpcrecallout\fP
287 .\"
288 documentation.
289 .
290 .
291 .\" HTML <a name="newlines"></a>
292 .SH NEWLINES
293 .rs
294 .sp
295 PCRE supports five different conventions for indicating line breaks in
296 strings: a single CR (carriage return) character, a single LF (linefeed)
297 character, the two-character sequence CRLF, any of the three preceding, or any
298 Unicode newline sequence. The Unicode newline sequences are the three just
299 mentioned, plus the single characters VT (vertical tab, U+000B), FF (form feed,
300 U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS
301 (paragraph separator, U+2029).
302 .P
303 Each of the first three conventions is used by at least one operating system as
304 its standard newline sequence. When PCRE is built, a default can be specified.
305 The default default is LF, which is the Unix standard. When PCRE is run, the
306 default can be overridden, either when a pattern is compiled, or when it is
307 matched.
308 .P
309 At compile time, the newline convention can be specified by the \fIoptions\fP
310 argument of \fBpcre_compile()\fP, or it can be specified by special text at the
311 start of the pattern itself; this overrides any other settings. See the
312 .\" HREF
313 \fBpcrepattern\fP
314 .\"
315 page for details of the special character sequences.
316 .P
317 In the PCRE documentation the word "newline" is used to mean "the character or
318 pair of characters that indicate a line break". The choice of newline
319 convention affects the handling of the dot, circumflex, and dollar
320 metacharacters, the handling of #-comments in /x mode, and, when CRLF is a
321 recognized line ending sequence, the match position advancement for a
322 non-anchored pattern. There is more detail about this in the
323 .\" HTML <a href="#execoptions">
324 .\" </a>
325 section on \fBpcre_exec()\fP options
326 .\"
327 below.
328 .P
329 The choice of newline convention does not affect the interpretation of
330 the \en or \er escape sequences, nor does it affect what \eR matches, which is
331 controlled in a similar way, but by separate options.
332 .
333 .
334 .SH MULTITHREADING
335 .rs
336 .sp
337 The PCRE functions can be used in multi-threading applications, with the
338 proviso that the memory management functions pointed to by \fBpcre_malloc\fP,
339 \fBpcre_free\fP, \fBpcre_stack_malloc\fP, and \fBpcre_stack_free\fP, and the
340 callout function pointed to by \fBpcre_callout\fP, are shared by all threads.
341 .P
342 The compiled form of a regular expression is not altered during matching, so
343 the same compiled pattern can safely be used by several threads at once.
344 .P
345 If the just-in-time optimization feature is being used, it needs separate
346 memory stack areas for each thread. See the
347 .\" HREF
348 \fBpcrejit\fP
349 .\"
350 documentation for more details.
351 .
352 .
353 .SH "SAVING PRECOMPILED PATTERNS FOR LATER USE"
354 .rs
355 .sp
356 The compiled form of a regular expression can be saved and re-used at a later
357 time, possibly by a different program, and even on a host other than the one on
358 which it was compiled. Details are given in the
359 .\" HREF
360 \fBpcreprecompile\fP
361 .\"
362 documentation, which includes a description of the
363 \fBpcre_pattern_to_host_byte_order()\fP function. However, compiling a regular
364 expression with one version of PCRE for use with a different version is not
365 guaranteed to work and may cause crashes.
366 .
367 .
368 .SH "CHECKING BUILD-TIME OPTIONS"
369 .rs
370 .sp
371 .B int pcre_config(int \fIwhat\fP, void *\fIwhere\fP);
372 .PP
373 The function \fBpcre_config()\fP makes it possible for a PCRE client to
374 discover which optional features have been compiled into the PCRE library. The
375 .\" HREF
376 \fBpcrebuild\fP
377 .\"
378 documentation has more details about these optional features.
379 .P
380 The first argument for \fBpcre_config()\fP is an integer, specifying which
381 information is required; the second argument is a pointer to a variable into
382 which the information is placed. The returned value is zero on success, or the
383 negative error code PCRE_ERROR_BADOPTION if the value in the first argument is
384 not recognized. The following information is available:
385 .sp
386 PCRE_CONFIG_UTF8
387 .sp
388 The output is an integer that is set to one if UTF-8 support is available;
389 otherwise it is set to zero. This value should normally be given to the 8-bit
390 version of this function, \fBpcre_config()\fP. If it is given to the 16-bit
391 or 32-bit version of this function, the result is PCRE_ERROR_BADOPTION.
392 .sp
393 PCRE_CONFIG_UTF16
394 .sp
395 The output is an integer that is set to one if UTF-16 support is available;
396 otherwise it is set to zero. This value should normally be given to the 16-bit
397 version of this function, \fBpcre16_config()\fP. If it is given to the 8-bit
398 or 32-bit version of this function, the result is PCRE_ERROR_BADOPTION.
399 .sp
400 PCRE_CONFIG_UTF32
401 .sp
402 The output is an integer that is set to one if UTF-32 support is available;
403 otherwise it is set to zero. This value should normally be given to the 32-bit
404 version of this function, \fBpcre32_config()\fP. If it is given to the 8-bit
405 or 16-bit version of this function, the result is PCRE_ERROR_BADOPTION.
406 .sp
407 PCRE_CONFIG_UNICODE_PROPERTIES
408 .sp
409 The output is an integer that is set to one if support for Unicode character
410 properties is available; otherwise it is set to zero.
411 .sp
412 PCRE_CONFIG_JIT
413 .sp
414 The output is an integer that is set to one if support for just-in-time
415 compiling is available; otherwise it is set to zero.
416 .sp
417 PCRE_CONFIG_JITTARGET
418 .sp
419 The output is a pointer to a zero-terminated "const char *" string. If JIT
420 support is available, the string contains the name of the architecture for
421 which the JIT compiler is configured, for example "x86 32bit (little endian +
422 unaligned)". If JIT support is not available, the result is NULL.
423 .sp
424 PCRE_CONFIG_NEWLINE
425 .sp
426 The output is an integer whose value specifies the default character sequence
427 that is recognized as meaning "newline". The values that are supported in
428 ASCII/Unicode environments are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for
429 ANYCRLF, and -1 for ANY. In EBCDIC environments, CR, ANYCRLF, and ANY yield the
430 same values. However, the value for LF is normally 21, though some EBCDIC
431 environments use 37. The corresponding values for CRLF are 3349 and 3365. The
432 default should normally correspond to the standard sequence for your operating
433 system.
434 .sp
435 PCRE_CONFIG_BSR
436 .sp
437 The output is an integer whose value indicates what character sequences the \eR
438 escape sequence matches by default. A value of 0 means that \eR matches any
439 Unicode line ending sequence; a value of 1 means that \eR matches only CR, LF,
440 or CRLF. The default can be overridden when a pattern is compiled or matched.
441 .sp
442 PCRE_CONFIG_LINK_SIZE
443 .sp
444 The output is an integer that contains the number of bytes used for internal
445 linkage in compiled regular expressions. For the 8-bit library, the value can
446 be 2, 3, or 4. For the 16-bit library, the value is either 2 or 4 and is still
447 a number of bytes. For the 32-bit library, the value is either 2 or 4 and is
448 still a number of bytes. The default value of 2 is sufficient for all but the
449 most massive patterns, since it allows the compiled pattern to be up to 64K in
450 size. Larger values allow larger regular expressions to be compiled, at the
451 expense of slower matching.
452 .sp
453 PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
454 .sp
455 The output is an integer that contains the threshold above which the POSIX
456 interface uses \fBmalloc()\fP for output vectors. Further details are given in
457 the
458 .\" HREF
459 \fBpcreposix\fP
460 .\"
461 documentation.
462 .sp
463 PCRE_CONFIG_PARENS_LIMIT
464 .sp
465 The output is a long integer that gives the maximum depth of nesting of
466 parentheses (of any kind) in a pattern. This limit is imposed to cap the amount
467 of system stack used when a pattern is compiled. It is specified when PCRE is
468 built; the default is 250.
469 .sp
470 PCRE_CONFIG_MATCH_LIMIT
471 .sp
472 The output is a long integer that gives the default limit for the number of
473 internal matching function calls in a \fBpcre_exec()\fP execution. Further
474 details are given with \fBpcre_exec()\fP below.
475 .sp
476 PCRE_CONFIG_MATCH_LIMIT_RECURSION
477 .sp
478 The output is a long integer that gives the default limit for the depth of
479 recursion when calling the internal matching function in a \fBpcre_exec()\fP
480 execution. Further details are given with \fBpcre_exec()\fP below.
481 .sp
482 PCRE_CONFIG_STACKRECURSE
483 .sp
484 The output is an integer that is set to one if internal recursion when running
485 \fBpcre_exec()\fP is implemented by recursive function calls that use the stack
486 to remember their state. This is the usual way that PCRE is compiled. The
487 output is zero if PCRE was compiled to use blocks of data on the heap instead
488 of recursive function calls. In this case, \fBpcre_stack_malloc\fP and
489 \fBpcre_stack_free\fP are called to manage memory blocks on the heap, thus
490 avoiding the use of the stack.
491 .
492 .
493 .SH "COMPILING A PATTERN"
494 .rs
495 .sp
496 .nf
497 .B pcre *pcre_compile(const char *\fIpattern\fP, int \fIoptions\fP,
498 .B " const char **\fIerrptr\fP, int *\fIerroffset\fP,"
499 .B " const unsigned char *\fItableptr\fP);"
500 .sp
501 .B pcre *pcre_compile2(const char *\fIpattern\fP, int \fIoptions\fP,
502 .B " int *\fIerrorcodeptr\fP,"
503 .B " const char **\fIerrptr\fP, int *\fIerroffset\fP,"
504 .B " const unsigned char *\fItableptr\fP);"
505 .fi
506 .P
507 Either of the functions \fBpcre_compile()\fP or \fBpcre_compile2()\fP can be
508 called to compile a pattern into an internal form. The only difference between
509 the two interfaces is that \fBpcre_compile2()\fP has an additional argument,
510 \fIerrorcodeptr\fP, via which a numerical error code can be returned. To avoid
511 too much repetition, we refer just to \fBpcre_compile()\fP below, but the
512 information applies equally to \fBpcre_compile2()\fP.
513 .P
514 The pattern is a C string terminated by a binary zero, and is passed in the
515 \fIpattern\fP argument. A pointer to a single block of memory that is obtained
516 via \fBpcre_malloc\fP is returned. This contains the compiled code and related
517 data. The \fBpcre\fP type is defined for the returned block; this is a typedef
518 for a structure whose contents are not externally defined. It is up to the
519 caller to free the memory (via \fBpcre_free\fP) when it is no longer required.
520 .P
521 Although the compiled code of a PCRE regex is relocatable, that is, it does not
522 depend on memory location, the complete \fBpcre\fP data block is not
523 fully relocatable, because it may contain a copy of the \fItableptr\fP
524 argument, which is an address (see below).
525 .P
526 The \fIoptions\fP argument contains various bit settings that affect the
527 compilation. It should be zero if no options are required. The available
528 options are described below. Some of them (in particular, those that are
529 compatible with Perl, but some others as well) can also be set and unset from
530 within the pattern (see the detailed description in the
531 .\" HREF
532 \fBpcrepattern\fP
533 .\"
534 documentation). For those options that can be different in different parts of
535 the pattern, the contents of the \fIoptions\fP argument specifies their
536 settings at the start of compilation and execution. The PCRE_ANCHORED,
537 PCRE_BSR_\fIxxx\fP, PCRE_NEWLINE_\fIxxx\fP, PCRE_NO_UTF8_CHECK, and
538 PCRE_NO_START_OPTIMIZE options can be set at the time of matching as well as at
539 compile time.
540 .P
541 If \fIerrptr\fP is NULL, \fBpcre_compile()\fP returns NULL immediately.
542 Otherwise, if compilation of a pattern fails, \fBpcre_compile()\fP returns
543 NULL, and sets the variable pointed to by \fIerrptr\fP to point to a textual
544 error message. This is a static string that is part of the library. You must
545 not try to free it. Normally, the offset from the start of the pattern to the
546 data unit that was being processed when the error was discovered is placed in
547 the variable pointed to by \fIerroffset\fP, which must not be NULL (if it is,
548 an immediate error is given). However, for an invalid UTF-8 or UTF-16 string,
549 the offset is that of the first data unit of the failing character.
550 .P
551 Some errors are not detected until the whole pattern has been scanned; in these
552 cases, the offset passed back is the length of the pattern. Note that the
553 offset is in data units, not characters, even in a UTF mode. It may sometimes
554 point into the middle of a UTF-8 or UTF-16 character.
555 .P
556 If \fBpcre_compile2()\fP is used instead of \fBpcre_compile()\fP, and the
557 \fIerrorcodeptr\fP argument is not NULL, a non-zero error code number is
558 returned via this argument in the event of an error. This is in addition to the
559 textual error message. Error codes and messages are listed below.
560 .P
561 If the final argument, \fItableptr\fP, is NULL, PCRE uses a default set of
562 character tables that are built when PCRE is compiled, using the default C
563 locale. Otherwise, \fItableptr\fP must be an address that is the result of a
564 call to \fBpcre_maketables()\fP. This value is stored with the compiled
565 pattern, and used again by \fBpcre_exec()\fP and \fBpcre_dfa_exec()\fP when the
566 pattern is matched. For more discussion, see the section on locale support
567 below.
568 .P
569 This code fragment shows a typical straightforward call to \fBpcre_compile()\fP:
570 .sp
571 pcre *re;
572 const char *error;
573 int erroffset;
574 re = pcre_compile(
575 "^A.*Z", /* the pattern */
576 0, /* default options */
577 &error, /* for error message */
578 &erroffset, /* for error offset */
579 NULL); /* use default character tables */
580 .sp
581 The following names for option bits are defined in the \fBpcre.h\fP header
582 file:
583 .sp
584 PCRE_ANCHORED
585 .sp
586 If this bit is set, the pattern is forced to be "anchored", that is, it is
587 constrained to match only at the first matching point in the string that is
588 being searched (the "subject string"). This effect can also be achieved by
589 appropriate constructs in the pattern itself, which is the only way to do it in
590 Perl.
591 .sp
592 PCRE_AUTO_CALLOUT
593 .sp
594 If this bit is set, \fBpcre_compile()\fP automatically inserts callout items,
595 all with number 255, before each pattern item. For discussion of the callout
596 facility, see the
597 .\" HREF
598 \fBpcrecallout\fP
599 .\"
600 documentation.
601 .sp
602 PCRE_BSR_ANYCRLF
603 PCRE_BSR_UNICODE
604 .sp
605 These options (which are mutually exclusive) control what the \eR escape
606 sequence matches. The choice is either to match only CR, LF, or CRLF, or to
607 match any Unicode newline sequence. The default is specified when PCRE is
608 built. It can be overridden from within the pattern, or by setting an option
609 when a compiled pattern is matched.
610 .sp
611 PCRE_CASELESS
612 .sp
613 If this bit is set, letters in the pattern match both upper and lower case
614 letters. It is equivalent to Perl's /i option, and it can be changed within a
615 pattern by a (?i) option setting. In UTF-8 mode, PCRE always understands the
616 concept of case for characters whose values are less than 128, so caseless
617 matching is always possible. For characters with higher values, the concept of
618 case is supported if PCRE is compiled with Unicode property support, but not
619 otherwise. If you want to use caseless matching for characters 128 and above,
620 you must ensure that PCRE is compiled with Unicode property support as well as
621 with UTF-8 support.
622 .sp
623 PCRE_DOLLAR_ENDONLY
624 .sp
625 If this bit is set, a dollar metacharacter in the pattern matches only at the
626 end of the subject string. Without this option, a dollar also matches
627 immediately before a newline at the end of the string (but not before any other
628 newlines). The PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is set.
629 There is no equivalent to this option in Perl, and no way to set it within a
630 pattern.
631 .sp
632 PCRE_DOTALL
633 .sp
634 If this bit is set, a dot metacharacter in the pattern matches a character of
635 any value, including one that indicates a newline. However, it only ever
636 matches one character, even if newlines are coded as CRLF. Without this option,
637 a dot does not match when the current position is at a newline. This option is
638 equivalent to Perl's /s option, and it can be changed within a pattern by a
639 (?s) option setting. A negative class such as [^a] always matches newline
640 characters, independent of the setting of this option.
641 .sp
642 PCRE_DUPNAMES
643 .sp
644 If this bit is set, names used to identify capturing subpatterns need not be
645 unique. This can be helpful for certain types of pattern when it is known that
646 only one instance of the named subpattern can ever be matched. There are more
647 details of named subpatterns below; see also the
648 .\" HREF
649 \fBpcrepattern\fP
650 .\"
651 documentation.
652 .sp
653 PCRE_EXTENDED
654 .sp
655 If this bit is set, most white space characters in the pattern are totally
656 ignored except when escaped or inside a character class. However, white space
657 is not allowed within sequences such as (?> that introduce various
658 parenthesized subpatterns, nor within a numerical quantifier such as {1,3}.
659 However, ignorable white space is permitted between an item and a following
660 quantifier and between a quantifier and a following + that indicates
661 possessiveness.
662 .P
663 White space did not used to include the VT character (code 11), because Perl
664 did not treat this character as white space. However, Perl changed at release
665 5.18, so PCRE followed at release 8.34, and VT is now treated as white space.
666 .P
667 PCRE_EXTENDED also causes characters between an unescaped # outside a character
668 class and the next newline, inclusive, to be ignored. PCRE_EXTENDED is
669 equivalent to Perl's /x option, and it can be changed within a pattern by a
670 (?x) option setting.
671 .P
672 Which characters are interpreted as newlines is controlled by the options
673 passed to \fBpcre_compile()\fP or by a special sequence at the start of the
674 pattern, as described in the section entitled
675 .\" HTML <a href="pcrepattern.html#newlines">
676 .\" </a>
677 "Newline conventions"
678 .\"
679 in the \fBpcrepattern\fP documentation. Note that the end of this type of
680 comment is a literal newline sequence in the pattern; escape sequences that
681 happen to represent a newline do not count.
682 .P
683 This option makes it possible to include comments inside complicated patterns.
684 Note, however, that this applies only to data characters. White space characters
685 may never appear within special character sequences in a pattern, for example
686 within the sequence (?( that introduces a conditional subpattern.
687 .sp
688 PCRE_EXTRA
689 .sp
690 This option was invented in order to turn on additional functionality of PCRE
691 that is incompatible with Perl, but it is currently of very little use. When
692 set, any backslash in a pattern that is followed by a letter that has no
693 special meaning causes an error, thus reserving these combinations for future
694 expansion. By default, as in Perl, a backslash followed by a letter with no
695 special meaning is treated as a literal. (Perl can, however, be persuaded to
696 give an error for this, by running it with the -w option.) There are at present
697 no other features controlled by this option. It can also be set by a (?X)
698 option setting within a pattern.
699 .sp
700 PCRE_FIRSTLINE
701 .sp
702 If this option is set, an unanchored pattern is required to match before or at
703 the first newline in the subject string, though the matched text may continue
704 over the newline.
705 .sp
706 PCRE_JAVASCRIPT_COMPAT
707 .sp
708 If this option is set, PCRE's behaviour is changed in some ways so that it is
709 compatible with JavaScript rather than Perl. The changes are as follows:
710 .P
711 (1) A lone closing square bracket in a pattern causes a compile-time error,
712 because this is illegal in JavaScript (by default it is treated as a data
713 character). Thus, the pattern AB]CD becomes illegal when this option is set.
714 .P
715 (2) At run time, a back reference to an unset subpattern group matches an empty
716 string (by default this causes the current matching alternative to fail). A
717 pattern such as (\e1)(a) succeeds when this option is set (assuming it can find
718 an "a" in the subject), whereas it fails by default, for Perl compatibility.
719 .P
720 (3) \eU matches an upper case "U" character; by default \eU causes a compile
721 time error (Perl uses \eU to upper case subsequent characters).
722 .P
723 (4) \eu matches a lower case "u" character unless it is followed by four
724 hexadecimal digits, in which case the hexadecimal number defines the code point
725 to match. By default, \eu causes a compile time error (Perl uses it to upper
726 case the following character).
727 .P
728 (5) \ex matches a lower case "x" character unless it is followed by two
729 hexadecimal digits, in which case the hexadecimal number defines the code point
730 to match. By default, as in Perl, a hexadecimal number is always expected after
731 \ex, but it may have zero, one, or two digits (so, for example, \exz matches a
732 binary zero character followed by z).
733 .sp
734 PCRE_MULTILINE
735 .sp
736 By default, for the purposes of matching "start of line" and "end of line",
737 PCRE treats the subject string as consisting of a single line of characters,
738 even if it actually contains newlines. The "start of line" metacharacter (^)
739 matches only at the start of the string, and the "end of line" metacharacter
740 ($) matches only at the end of the string, or before a terminating newline
741 (except when PCRE_DOLLAR_ENDONLY is set). Note, however, that unless
742 PCRE_DOTALL is set, the "any character" metacharacter (.) does not match at a
743 newline. This behaviour (for ^, $, and dot) is the same as Perl.
744 .P
745 When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs
746 match immediately following or immediately before internal newlines in the
747 subject string, respectively, as well as at the very start and end. This is
748 equivalent to Perl's /m option, and it can be changed within a pattern by a
749 (?m) option setting. If there are no newlines in a subject string, or no
750 occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no effect.
751 .sp
752 PCRE_NEVER_UTF
753 .sp
754 This option locks out interpretation of the pattern as UTF-8 (or UTF-16 or
755 UTF-32 in the 16-bit and 32-bit libraries). In particular, it prevents the
756 creator of the pattern from switching to UTF interpretation by starting the
757 pattern with (*UTF). This may be useful in applications that process patterns
758 from external sources. The combination of PCRE_UTF8 and PCRE_NEVER_UTF also
759 causes an error.
760 .sp
761 PCRE_NEWLINE_CR
762 PCRE_NEWLINE_LF
763 PCRE_NEWLINE_CRLF
764 PCRE_NEWLINE_ANYCRLF
765 PCRE_NEWLINE_ANY
766 .sp
767 These options override the default newline definition that was chosen when PCRE
768 was built. Setting the first or the second specifies that a newline is
769 indicated by a single character (CR or LF, respectively). Setting
770 PCRE_NEWLINE_CRLF specifies that a newline is indicated by the two-character
771 CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies that any of the three
772 preceding sequences should be recognized. Setting PCRE_NEWLINE_ANY specifies
773 that any Unicode newline sequence should be recognized.
774 .P
775 In an ASCII/Unicode environment, the Unicode newline sequences are the three
776 just mentioned, plus the single characters VT (vertical tab, U+000B), FF (form
777 feed, U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS
778 (paragraph separator, U+2029). For the 8-bit library, the last two are
779 recognized only in UTF-8 mode.
780 .P
781 When PCRE is compiled to run in an EBCDIC (mainframe) environment, the code for
782 CR is 0x0d, the same as ASCII. However, the character code for LF is normally
783 0x15, though in some EBCDIC environments 0x25 is used. Whichever of these is
784 not LF is made to correspond to Unicode's NEL character. EBCDIC codes are all
785 less than 256. For more details, see the
786 .\" HREF
787 \fBpcrebuild\fP
788 .\"
789 documentation.
790 .P
791 The newline setting in the options word uses three bits that are treated
792 as a number, giving eight possibilities. Currently only six are used (default
793 plus the five values above). This means that if you set more than one newline
794 option, the combination may or may not be sensible. For example,
795 PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to PCRE_NEWLINE_CRLF, but
796 other combinations may yield unused numbers and cause an error.
797 .P
798 The only time that a line break in a pattern is specially recognized when
799 compiling is when PCRE_EXTENDED is set. CR and LF are white space characters,
800 and so are ignored in this mode. Also, an unescaped # outside a character class
801 indicates a comment that lasts until after the next line break sequence. In
802 other circumstances, line break sequences in patterns are treated as literal
803 data.
804 .P
805 The newline option that is set at compile time becomes the default that is used
806 for \fBpcre_exec()\fP and \fBpcre_dfa_exec()\fP, but it can be overridden.
807 .sp
808 PCRE_NO_AUTO_CAPTURE
809 .sp
810 If this option is set, it disables the use of numbered capturing parentheses in
811 the pattern. Any opening parenthesis that is not followed by ? behaves as if it
812 were followed by ?: but named parentheses can still be used for capturing (and
813 they acquire numbers in the usual way). There is no equivalent of this option
814 in Perl.
815 .sp
816 PCRE_NO_AUTO_POSSESS
817 .sp
818 If this option is set, it disables "auto-possessification". This is an
819 optimization that, for example, turns a+b into a++b in order to avoid
820 backtracks into a+ that can never be successful. However, if callouts are in
821 use, auto-possessification means that some of them are never taken. You can set
822 this option if you want the matching functions to do a full unoptimized search
823 and run all the callouts, but it is mainly provided for testing purposes.
824 .sp
825 PCRE_NO_START_OPTIMIZE
826 .sp
827 This is an option that acts at matching time; that is, it is really an option
828 for \fBpcre_exec()\fP or \fBpcre_dfa_exec()\fP. If it is set at compile time,
829 it is remembered with the compiled pattern and assumed at matching time. This
830 is necessary if you want to use JIT execution, because the JIT compiler needs
831 to know whether or not this option is set. For details see the discussion of
832 PCRE_NO_START_OPTIMIZE
833 .\" HTML <a href="#execoptions">
834 .\" </a>
835 below.
836 .\"
837 .sp
838 PCRE_UCP
839 .sp
840 This option changes the way PCRE processes \eB, \eb, \eD, \ed, \eS, \es, \eW,
841 \ew, and some of the POSIX character classes. By default, only ASCII characters
842 are recognized, but if PCRE_UCP is set, Unicode properties are used instead to
843 classify characters. More details are given in the section on
844 .\" HTML <a href="pcre.html#genericchartypes">
845 .\" </a>
846 generic character types
847 .\"
848 in the
849 .\" HREF
850 \fBpcrepattern\fP
851 .\"
852 page. If you set PCRE_UCP, matching one of the items it affects takes much
853 longer. The option is available only if PCRE has been compiled with Unicode
854 property support.
855 .sp
856 PCRE_UNGREEDY
857 .sp
858 This option inverts the "greediness" of the quantifiers so that they are not
859 greedy by default, but become greedy if followed by "?". It is not compatible
860 with Perl. It can also be set by a (?U) option setting within the pattern.
861 .sp
862 PCRE_UTF8
863 .sp
864 This option causes PCRE to regard both the pattern and the subject as strings
865 of UTF-8 characters instead of single-byte strings. However, it is available
866 only when PCRE is built to include UTF support. If not, the use of this option
867 provokes an error. Details of how this option changes the behaviour of PCRE are
868 given in the
869 .\" HREF
870 \fBpcreunicode\fP
871 .\"
872 page.
873 .sp
874 PCRE_NO_UTF8_CHECK
875 .sp
876 When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
877 automatically checked. There is a discussion about the
878 .\" HTML <a href="pcreunicode.html#utf8strings">
879 .\" </a>
880 validity of UTF-8 strings
881 .\"
882 in the
883 .\" HREF
884 \fBpcreunicode\fP
885 .\"
886 page. If an invalid UTF-8 sequence is found, \fBpcre_compile()\fP returns an
887 error. If you already know that your pattern is valid, and you want to skip
888 this check for performance reasons, you can set the PCRE_NO_UTF8_CHECK option.
889 When it is set, the effect of passing an invalid UTF-8 string as a pattern is
890 undefined. It may cause your program to crash or loop. Note that this option
891 can also be passed to \fBpcre_exec()\fP and \fBpcre_dfa_exec()\fP, to suppress
892 the validity checking of subject strings only. If the same string is being
893 matched many times, the option can be safely set for the second and subsequent
894 matchings to improve performance.
895 .
896 .
897 .SH "COMPILATION ERROR CODES"
898 .rs
899 .sp
900 The following table lists the error codes than may be returned by
901 \fBpcre_compile2()\fP, along with the error messages that may be returned by
902 both compiling functions. Note that error messages are always 8-bit ASCII
903 strings, even in 16-bit or 32-bit mode. As PCRE has developed, some error codes
904 have fallen out of use. To avoid confusion, they have not been re-used.
905 .sp
906 0 no error
907 1 \e at end of pattern
908 2 \ec at end of pattern
909 3 unrecognized character follows \e
910 4 numbers out of order in {} quantifier
911 5 number too big in {} quantifier
912 6 missing terminating ] for character class
913 7 invalid escape sequence in character class
914 8 range out of order in character class
915 9 nothing to repeat
916 10 [this code is not in use]
917 11 internal error: unexpected repeat
918 12 unrecognized character after (? or (?-
919 13 POSIX named classes are supported only within a class
920 14 missing )
921 15 reference to non-existent subpattern
922 16 erroffset passed as NULL
923 17 unknown option bit(s) set
924 18 missing ) after comment
925 19 [this code is not in use]
926 20 regular expression is too large
927 21 failed to get memory
928 22 unmatched parentheses
929 23 internal error: code overflow
930 24 unrecognized character after (?<
931 25 lookbehind assertion is not fixed length
932 26 malformed number or name after (?(
933 27 conditional group contains more than two branches
934 28 assertion expected after (?(
935 29 (?R or (?[+-]digits must be followed by )
936 30 unknown POSIX class name
937 31 POSIX collating elements are not supported
938 32 this version of PCRE is compiled without UTF support
939 33 [this code is not in use]
940 34 character value in \ex{} or \eo{} is too large
941 35 invalid condition (?(0)
942 36 \eC not allowed in lookbehind assertion
943 37 PCRE does not support \eL, \el, \eN{name}, \eU, or \eu
944 38 number after (?C is > 255
945 39 closing ) for (?C expected
946 40 recursive call could loop indefinitely
947 41 unrecognized character after (?P
948 42 syntax error in subpattern name (missing terminator)
949 43 two named subpatterns have the same name
950 44 invalid UTF-8 string (specifically UTF-8)
951 45 support for \eP, \ep, and \eX has not been compiled
952 46 malformed \eP or \ep sequence
953 47 unknown property name after \eP or \ep
954 48 subpattern name is too long (maximum 32 characters)
955 49 too many named subpatterns (maximum 10000)
956 50 [this code is not in use]
957 51 octal value is greater than \e377 in 8-bit non-UTF-8 mode
958 52 internal error: overran compiling workspace
959 53 internal error: previously-checked referenced subpattern
960 not found
961 54 DEFINE group contains more than one branch
962 55 repeating a DEFINE group is not allowed
963 56 inconsistent NEWLINE options
964 57 \eg is not followed by a braced, angle-bracketed, or quoted
965 name/number or by a plain number
966 58 a numbered reference must not be zero
967 59 an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT)
968 60 (*VERB) not recognized or malformed
969 61 number is too big
970 62 subpattern name expected
971 63 digit expected after (?+
972 64 ] is an invalid data character in JavaScript compatibility mode
973 65 different names for subpatterns of the same number are
974 not allowed
975 66 (*MARK) must have an argument
976 67 this version of PCRE is not compiled with Unicode property
977 support
978 68 \ec must be followed by an ASCII character
979 69 \ek is not followed by a braced, angle-bracketed, or quoted name
980 70 internal error: unknown opcode in find_fixedlength()
981 71 \eN is not supported in a class
982 72 too many forward references
983 73 disallowed Unicode code point (>= 0xd800 && <= 0xdfff)
984 74 invalid UTF-16 string (specifically UTF-16)
985 75 name is too long in (*MARK), (*PRUNE), (*SKIP), or (*THEN)
986 76 character value in \eu.... sequence is too large
987 77 invalid UTF-32 string (specifically UTF-32)
988 78 setting UTF is disabled by the application
989 79 non-hex character in \ex{} (closing brace missing?)
990 80 non-octal character in \eo{} (closing brace missing?)
991 81 missing opening brace after \eo
992 82 parentheses are too deeply nested
993 83 invalid range in character class
994 .sp
995 The numbers 32 and 10000 in errors 48 and 49 are defaults; different values may
996 be used if the limits were changed when PCRE was built.
997 .
998 .
999 .\" HTML <a name="studyingapattern"></a>
1000 .SH "STUDYING A PATTERN"
1001 .rs
1002 .sp
1003 .nf
1004 .B pcre_extra *pcre_study(const pcre *\fIcode\fP, int \fIoptions\fP,
1005 .B " const char **\fIerrptr\fP);"
1006 .fi
1007 .PP
1008 If a compiled pattern is going to be used several times, it is worth spending
1009 more time analyzing it in order to speed up the time taken for matching. The
1010 function \fBpcre_study()\fP takes a pointer to a compiled pattern as its first
1011 argument. If studying the pattern produces additional information that will
1012 help speed up matching, \fBpcre_study()\fP returns a pointer to a
1013 \fBpcre_extra\fP block, in which the \fIstudy_data\fP field points to the
1014 results of the study.
1015 .P
1016 The returned value from \fBpcre_study()\fP can be passed directly to
1017 \fBpcre_exec()\fP or \fBpcre_dfa_exec()\fP. However, a \fBpcre_extra\fP block
1018 also contains other fields that can be set by the caller before the block is
1019 passed; these are described
1020 .\" HTML <a href="#extradata">
1021 .\" </a>
1022 below
1023 .\"
1024 in the section on matching a pattern.
1025 .P
1026 If studying the pattern does not produce any useful information,
1027 \fBpcre_study()\fP returns NULL by default. In that circumstance, if the
1028 calling program wants to pass any of the other fields to \fBpcre_exec()\fP or
1029 \fBpcre_dfa_exec()\fP, it must set up its own \fBpcre_extra\fP block. However,
1030 if \fBpcre_study()\fP is called with the PCRE_STUDY_EXTRA_NEEDED option, it
1031 returns a \fBpcre_extra\fP block even if studying did not find any additional
1032 information. It may still return NULL, however, if an error occurs in
1033 \fBpcre_study()\fP.
1034 .P
1035 The second argument of \fBpcre_study()\fP contains option bits. There are three
1036 further options in addition to PCRE_STUDY_EXTRA_NEEDED:
1037 .sp
1038 PCRE_STUDY_JIT_COMPILE
1039 PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE
1040 PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE
1041 .sp
1042 If any of these are set, and the just-in-time compiler is available, the
1043 pattern is further compiled into machine code that executes much faster than
1044 the \fBpcre_exec()\fP interpretive matching function. If the just-in-time
1045 compiler is not available, these options are ignored. All undefined bits in the
1046 \fIoptions\fP argument must be zero.
1047 .P
1048 JIT compilation is a heavyweight optimization. It can take some time for
1049 patterns to be analyzed, and for one-off matches and simple patterns the
1050 benefit of faster execution might be offset by a much slower study time.
1051 Not all patterns can be optimized by the JIT compiler. For those that cannot be
1052 handled, matching automatically falls back to the \fBpcre_exec()\fP
1053 interpreter. For more details, see the
1054 .\" HREF
1055 \fBpcrejit\fP
1056 .\"
1057 documentation.
1058 .P
1059 The third argument for \fBpcre_study()\fP is a pointer for an error message. If
1060 studying succeeds (even if no data is returned), the variable it points to is
1061 set to NULL. Otherwise it is set to point to a textual error message. This is a
1062 static string that is part of the library. You must not try to free it. You
1063 should test the error pointer for NULL after calling \fBpcre_study()\fP, to be
1064 sure that it has run successfully.
1065 .P
1066 When you are finished with a pattern, you can free the memory used for the
1067 study data by calling \fBpcre_free_study()\fP. This function was added to the
1068 API for release 8.20. For earlier versions, the memory could be freed with
1069 \fBpcre_free()\fP, just like the pattern itself. This will still work in cases
1070 where JIT optimization is not used, but it is advisable to change to the new
1071 function when convenient.
1072 .P
1073 This is a typical way in which \fBpcre_study\fP() is used (except that in a
1074 real application there should be tests for errors):
1075 .sp
1076 int rc;
1077 pcre *re;
1078 pcre_extra *sd;
1079 re = pcre_compile("pattern", 0, &error, &erroroffset, NULL);
1080 sd = pcre_study(
1081 re, /* result of pcre_compile() */
1082 0, /* no options */
1083 &error); /* set to NULL or points to a message */
1084 rc = pcre_exec( /* see below for details of pcre_exec() options */
1085 re, sd, "subject", 7, 0, 0, ovector, 30);
1086 ...
1087 pcre_free_study(sd);
1088 pcre_free(re);
1089 .sp
1090 Studying a pattern does two things: first, a lower bound for the length of
1091 subject string that is needed to match the pattern is computed. This does not
1092 mean that there are any strings of that length that match, but it does
1093 guarantee that no shorter strings match. The value is used to avoid wasting
1094 time by trying to match strings that are shorter than the lower bound. You can
1095 find out the value in a calling program via the \fBpcre_fullinfo()\fP function.
1096 .P
1097 Studying a pattern is also useful for non-anchored patterns that do not have a
1098 single fixed starting character. A bitmap of possible starting bytes is
1099 created. This speeds up finding a position in the subject at which to start
1100 matching. (In 16-bit mode, the bitmap is used for 16-bit values less than 256.
1101 In 32-bit mode, the bitmap is used for 32-bit values less than 256.)
1102 .P
1103 These two optimizations apply to both \fBpcre_exec()\fP and
1104 \fBpcre_dfa_exec()\fP, and the information is also used by the JIT compiler.
1105 The optimizations can be disabled by setting the PCRE_NO_START_OPTIMIZE option.
1106 You might want to do this if your pattern contains callouts or (*MARK) and you
1107 want to make use of these facilities in cases where matching fails.
1108 .P
1109 PCRE_NO_START_OPTIMIZE can be specified at either compile time or execution
1110 time. However, if PCRE_NO_START_OPTIMIZE is passed to \fBpcre_exec()\fP, (that
1111 is, after any JIT compilation has happened) JIT execution is disabled. For JIT
1112 execution to work with PCRE_NO_START_OPTIMIZE, the option must be set at
1113 compile time.
1114 .P
1115 There is a longer discussion of PCRE_NO_START_OPTIMIZE
1116 .\" HTML <a href="#execoptions">
1117 .\" </a>
1118 below.
1119 .\"
1120 .
1121 .
1122 .\" HTML <a name="localesupport"></a>
1123 .SH "LOCALE SUPPORT"
1124 .rs
1125 .sp
1126 PCRE handles caseless matching, and determines whether characters are letters,
1127 digits, or whatever, by reference to a set of tables, indexed by character
1128 code point. When running in UTF-8 mode, or in the 16- or 32-bit libraries, this
1129 applies only to characters with code points less than 256. By default,
1130 higher-valued code points never match escapes such as \ew or \ed. However, if
1131 PCRE is built with Unicode property support, all characters can be tested with
1132 \ep and \eP, or, alternatively, the PCRE_UCP option can be set when a pattern
1133 is compiled; this causes \ew and friends to use Unicode property support
1134 instead of the built-in tables.
1135 .P
1136 The use of locales with Unicode is discouraged. If you are handling characters
1137 with code points greater than 128, you should either use Unicode support, or
1138 use locales, but not try to mix the two.
1139 .P
1140 PCRE contains an internal set of tables that are used when the final argument
1141 of \fBpcre_compile()\fP is NULL. These are sufficient for many applications.
1142 Normally, the internal tables recognize only ASCII characters. However, when
1143 PCRE is built, it is possible to cause the internal tables to be rebuilt in the
1144 default "C" locale of the local system, which may cause them to be different.
1145 .P
1146 The internal tables can always be overridden by tables supplied by the
1147 application that calls PCRE. These may be created in a different locale from
1148 the default. As more and more applications change to using Unicode, the need
1149 for this locale support is expected to die away.
1150 .P
1151 External tables are built by calling the \fBpcre_maketables()\fP function,
1152 which has no arguments, in the relevant locale. The result can then be passed
1153 to \fBpcre_compile()\fP as often as necessary. For example, to build and use
1154 tables that are appropriate for the French locale (where accented characters
1155 with values greater than 128 are treated as letters), the following code could
1156 be used:
1157 .sp
1158 setlocale(LC_CTYPE, "fr_FR");
1159 tables = pcre_maketables();
1160 re = pcre_compile(..., tables);
1161 .sp
1162 The locale name "fr_FR" is used on Linux and other Unix-like systems; if you
1163 are using Windows, the name for the French locale is "french".
1164 .P
1165 When \fBpcre_maketables()\fP runs, the tables are built in memory that is
1166 obtained via \fBpcre_malloc\fP. It is the caller's responsibility to ensure
1167 that the memory containing the tables remains available for as long as it is
1168 needed.
1169 .P
1170 The pointer that is passed to \fBpcre_compile()\fP is saved with the compiled
1171 pattern, and the same tables are used via this pointer by \fBpcre_study()\fP
1172 and also by \fBpcre_exec()\fP and \fBpcre_dfa_exec()\fP. Thus, for any single
1173 pattern, compilation, studying and matching all happen in the same locale, but
1174 different patterns can be processed in different locales.
1175 .P
1176 It is possible to pass a table pointer or NULL (indicating the use of the
1177 internal tables) to \fBpcre_exec()\fP or \fBpcre_dfa_exec()\fP (see the
1178 discussion below in the section on matching a pattern). This facility is
1179 provided for use with pre-compiled patterns that have been saved and reloaded.
1180 Character tables are not saved with patterns, so if a non-standard table was
1181 used at compile time, it must be provided again when the reloaded pattern is
1182 matched. Attempting to use this facility to match a pattern in a different
1183 locale from the one in which it was compiled is likely to lead to anomalous
1184 (usually incorrect) results.
1185 .
1186 .
1187 .\" HTML <a name="infoaboutpattern"></a>
1188 .SH "INFORMATION ABOUT A PATTERN"
1189 .rs
1190 .sp
1191 .nf
1192 .B int pcre_fullinfo(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
1193 .B " int \fIwhat\fP, void *\fIwhere\fP);"
1194 .fi
1195 .PP
1196 The \fBpcre_fullinfo()\fP function returns information about a compiled
1197 pattern. It replaces the \fBpcre_info()\fP function, which was removed from the
1198 library at version 8.30, after more than 10 years of obsolescence.
1199 .P
1200 The first argument for \fBpcre_fullinfo()\fP is a pointer to the compiled
1201 pattern. The second argument is the result of \fBpcre_study()\fP, or NULL if
1202 the pattern was not studied. The third argument specifies which piece of
1203 information is required, and the fourth argument is a pointer to a variable
1204 to receive the data. The yield of the function is zero for success, or one of
1205 the following negative numbers:
1206 .sp
1207 PCRE_ERROR_NULL the argument \fIcode\fP was NULL
1208 the argument \fIwhere\fP was NULL
1209 PCRE_ERROR_BADMAGIC the "magic number" was not found
1210 PCRE_ERROR_BADENDIANNESS the pattern was compiled with different
1211 endianness
1212 PCRE_ERROR_BADOPTION the value of \fIwhat\fP was invalid
1213 PCRE_ERROR_UNSET the requested field is not set
1214 .sp
1215 The "magic number" is placed at the start of each compiled pattern as an simple
1216 check against passing an arbitrary memory pointer. The endianness error can
1217 occur if a compiled pattern is saved and reloaded on a different host. Here is
1218 a typical call of \fBpcre_fullinfo()\fP, to obtain the length of the compiled
1219 pattern:
1220 .sp
1221 int rc;
1222 size_t length;
1223 rc = pcre_fullinfo(
1224 re, /* result of pcre_compile() */
1225 sd, /* result of pcre_study(), or NULL */
1226 PCRE_INFO_SIZE, /* what is required */
1227 &length); /* where to put the data */
1228 .sp
1229 The possible values for the third argument are defined in \fBpcre.h\fP, and are
1230 as follows:
1231 .sp
1232 PCRE_INFO_BACKREFMAX
1233 .sp
1234 Return the number of the highest back reference in the pattern. The fourth
1235 argument should point to an \fBint\fP variable. Zero is returned if there are
1236 no back references.
1237 .sp
1238 PCRE_INFO_CAPTURECOUNT
1239 .sp
1240 Return the number of capturing subpatterns in the pattern. The fourth argument
1241 should point to an \fBint\fP variable.
1242 .sp
1243 PCRE_INFO_DEFAULT_TABLES
1244 .sp
1245 Return a pointer to the internal default character tables within PCRE. The
1246 fourth argument should point to an \fBunsigned char *\fP variable. This
1247 information call is provided for internal use by the \fBpcre_study()\fP
1248 function. External callers can cause PCRE to use its internal tables by passing
1249 a NULL table pointer.
1250 .sp
1251 PCRE_INFO_FIRSTBYTE
1252 .sp
1253 Return information about the first data unit of any matched string, for a
1254 non-anchored pattern. (The name of this option refers to the 8-bit library,
1255 where data units are bytes.) The fourth argument should point to an \fBint\fP
1256 variable.
1257 .P
1258 If there is a fixed first value, for example, the letter "c" from a pattern
1259 such as (cat|cow|coyote), its value is returned. In the 8-bit library, the
1260 value is always less than 256. In the 16-bit library the value can be up to
1261 0xffff. In the 32-bit library the value can be up to 0x10ffff.
1262 .P
1263 If there is no fixed first value, and if either
1264 .sp
1265 (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
1266 starts with "^", or
1267 .sp
1268 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
1269 (if it were set, the pattern would be anchored),
1270 .sp
1271 -1 is returned, indicating that the pattern matches only at the start of a
1272 subject string or after any newline within the string. Otherwise -2 is
1273 returned. For anchored patterns, -2 is returned.
1274 .P
1275 Since for the 32-bit library using the non-UTF-32 mode, this function is unable
1276 to return the full 32-bit range of the character, this value is deprecated;
1277 instead the PCRE_INFO_FIRSTCHARACTERFLAGS and PCRE_INFO_FIRSTCHARACTER values
1278 should be used.
1279 .sp
1280 PCRE_INFO_FIRSTTABLE
1281 .sp
1282 If the pattern was studied, and this resulted in the construction of a 256-bit
1283 table indicating a fixed set of values for the first data unit in any matching
1284 string, a pointer to the table is returned. Otherwise NULL is returned. The
1285 fourth argument should point to an \fBunsigned char *\fP variable.
1286 .sp
1287 PCRE_INFO_HASCRORLF
1288 .sp
1289 Return 1 if the pattern contains any explicit matches for CR or LF characters,
1290 otherwise 0. The fourth argument should point to an \fBint\fP variable. An
1291 explicit match is either a literal CR or LF character, or \er or \en.
1292 .sp
1293 PCRE_INFO_JCHANGED
1294 .sp
1295 Return 1 if the (?J) or (?-J) option setting is used in the pattern, otherwise
1296 0. The fourth argument should point to an \fBint\fP variable. (?J) and
1297 (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
1298 .sp
1299 PCRE_INFO_JIT
1300 .sp
1301 Return 1 if the pattern was studied with one of the JIT options, and
1302 just-in-time compiling was successful. The fourth argument should point to an
1303 \fBint\fP variable. A return value of 0 means that JIT support is not available
1304 in this version of PCRE, or that the pattern was not studied with a JIT option,
1305 or that the JIT compiler could not handle this particular pattern. See the
1306 .\" HREF
1307 \fBpcrejit\fP
1308 .\"
1309 documentation for details of what can and cannot be handled.
1310 .sp
1311 PCRE_INFO_JITSIZE
1312 .sp
1313 If the pattern was successfully studied with a JIT option, return the size of
1314 the JIT compiled code, otherwise return zero. The fourth argument should point
1315 to a \fBsize_t\fP variable.
1316 .sp
1317 PCRE_INFO_LASTLITERAL
1318 .sp
1319 Return the value of the rightmost literal data unit that must exist in any
1320 matched string, other than at its start, if such a value has been recorded. The
1321 fourth argument should point to an \fBint\fP variable. If there is no such
1322 value, -1 is returned. For anchored patterns, a last literal value is recorded
1323 only if it follows something of variable length. For example, for the pattern
1324 /^a\ed+z\ed+/ the returned value is "z", but for /^a\edz\ed/ the returned value
1325 is -1.
1326 .P
1327 Since for the 32-bit library using the non-UTF-32 mode, this function is unable
1328 to return the full 32-bit range of characters, this value is deprecated;
1329 instead the PCRE_INFO_REQUIREDCHARFLAGS and PCRE_INFO_REQUIREDCHAR values should
1330 be used.
1331 .sp
1332 PCRE_INFO_MATCH_EMPTY
1333 .sp
1334 Return 1 if the pattern can match an empty string, otherwise 0. The fourth
1335 argument should point to an \fBint\fP variable.
1336 .sp
1337 PCRE_INFO_MATCHLIMIT
1338 .sp
1339 If the pattern set a match limit by including an item of the form
1340 (*LIMIT_MATCH=nnnn) at the start, the value is returned. The fourth argument
1341 should point to an unsigned 32-bit integer. If no such value has been set, the
1342 call to \fBpcre_fullinfo()\fP returns the error PCRE_ERROR_UNSET.
1343 .sp
1344 PCRE_INFO_MAXLOOKBEHIND
1345 .sp
1346 Return the number of characters (NB not data units) in the longest lookbehind
1347 assertion in the pattern. This information is useful when doing multi-segment
1348 matching using the partial matching facilities. Note that the simple assertions
1349 \eb and \eB require a one-character lookbehind. \eA also registers a
1350 one-character lookbehind, though it does not actually inspect the previous
1351 character. This is to ensure that at least one character from the old segment
1352 is retained when a new segment is processed. Otherwise, if there are no
1353 lookbehinds in the pattern, \eA might match incorrectly at the start of a new
1354 segment.
1355 .sp
1356 PCRE_INFO_MINLENGTH
1357 .sp
1358 If the pattern was studied and a minimum length for matching subject strings
1359 was computed, its value is returned. Otherwise the returned value is -1. The
1360 value is a number of characters, which in UTF mode may be different from the
1361 number of data units. The fourth argument should point to an \fBint\fP
1362 variable. A non-negative value is a lower bound to the length of any matching
1363 string. There may not be any strings of that length that do actually match, but
1364 every string that does match is at least that long.
1365 .sp
1366 PCRE_INFO_NAMECOUNT
1367 PCRE_INFO_NAMEENTRYSIZE
1368 PCRE_INFO_NAMETABLE
1369 .sp
1370 PCRE supports the use of named as well as numbered capturing parentheses. The
1371 names are just an additional way of identifying the parentheses, which still
1372 acquire numbers. Several convenience functions such as
1373 \fBpcre_get_named_substring()\fP are provided for extracting captured
1374 substrings by name. It is also possible to extract the data directly, by first
1375 converting the name to a number in order to access the correct pointers in the
1376 output vector (described with \fBpcre_exec()\fP below). To do the conversion,
1377 you need to use the name-to-number map, which is described by these three
1378 values.
1379 .P
1380 The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives
1381 the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each
1382 entry; both of these return an \fBint\fP value. The entry size depends on the
1383 length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first
1384 entry of the table. This is a pointer to \fBchar\fP in the 8-bit library, where
1385 the first two bytes of each entry are the number of the capturing parenthesis,
1386 most significant byte first. In the 16-bit library, the pointer points to
1387 16-bit data units, the first of which contains the parenthesis number. In the
1388 32-bit library, the pointer points to 32-bit data units, the first of which
1389 contains the parenthesis number. The rest of the entry is the corresponding
1390 name, zero terminated.
1391 .P
1392 The names are in alphabetical order. If (?| is used to create multiple groups
1393 with the same number, as described in the
1394 .\" HTML <a href="pcrepattern.html#dupsubpatternnumber">
1395 .\" </a>
1396 section on duplicate subpattern numbers
1397 .\"
1398 in the
1399 .\" HREF
1400 \fBpcrepattern\fP
1401 .\"
1402 page, the groups may be given the same name, but there is only one entry in the
1403 table. Different names for groups of the same number are not permitted.
1404 Duplicate names for subpatterns with different numbers are permitted,
1405 but only if PCRE_DUPNAMES is set. They appear in the table in the order in
1406 which they were found in the pattern. In the absence of (?| this is the order
1407 of increasing number; when (?| is used this is not necessarily the case because
1408 later subpatterns may have lower numbers.
1409 .P
1410 As a simple example of the name/number table, consider the following pattern
1411 after compilation by the 8-bit library (assume PCRE_EXTENDED is set, so white
1412 space - including newlines - is ignored):
1413 .sp
1414 .\" JOIN
1415 (?<date> (?<year>(\ed\ed)?\ed\ed) -
1416 (?<month>\ed\ed) - (?<day>\ed\ed) )
1417 .sp
1418 There are four named subpatterns, so the table has four entries, and each entry
1419 in the table is eight bytes long. The table is as follows, with non-printing
1420 bytes shows in hexadecimal, and undefined bytes shown as ??:
1421 .sp
1422 00 01 d a t e 00 ??
1423 00 05 d a y 00 ?? ??
1424 00 04 m o n t h 00
1425 00 02 y e a r 00 ??
1426 .sp
1427 When writing code to extract data from named subpatterns using the
1428 name-to-number map, remember that the length of the entries is likely to be
1429 different for each compiled pattern.
1430 .sp
1431 PCRE_INFO_OKPARTIAL
1432 .sp
1433 Return 1 if the pattern can be used for partial matching with
1434 \fBpcre_exec()\fP, otherwise 0. The fourth argument should point to an
1435 \fBint\fP variable. From release 8.00, this always returns 1, because the
1436 restrictions that previously applied to partial matching have been lifted. The
1437 .\" HREF
1438 \fBpcrepartial\fP
1439 .\"
1440 documentation gives details of partial matching.
1441 .sp
1442 PCRE_INFO_OPTIONS
1443 .sp
1444 Return a copy of the options with which the pattern was compiled. The fourth
1445 argument should point to an \fBunsigned long int\fP variable. These option bits
1446 are those specified in the call to \fBpcre_compile()\fP, modified by any
1447 top-level option settings at the start of the pattern itself. In other words,
1448 they are the options that will be in force when matching starts. For example,
1449 if the pattern /(?im)abc(?-i)d/ is compiled with the PCRE_EXTENDED option, the
1450 result is PCRE_CASELESS, PCRE_MULTILINE, and PCRE_EXTENDED.
1451 .P
1452 A pattern is automatically anchored by PCRE if all of its top-level
1453 alternatives begin with one of the following:
1454 .sp
1455 ^ unless PCRE_MULTILINE is set
1456 \eA always
1457 \eG always
1458 .\" JOIN
1459 .* if PCRE_DOTALL is set and there are no back
1460 references to the subpattern in which .* appears
1461 .sp
1462 For such patterns, the PCRE_ANCHORED bit is set in the options returned by
1463 \fBpcre_fullinfo()\fP.
1464 .sp
1465 PCRE_INFO_RECURSIONLIMIT
1466 .sp
1467 If the pattern set a recursion limit by including an item of the form
1468 (*LIMIT_RECURSION=nnnn) at the start, the value is returned. The fourth
1469 argument should point to an unsigned 32-bit integer. If no such value has been
1470 set, the call to \fBpcre_fullinfo()\fP returns the error PCRE_ERROR_UNSET.
1471 .sp
1472 PCRE_INFO_SIZE
1473 .sp
1474 Return the size of the compiled pattern in bytes (for all three libraries). The
1475 fourth argument should point to a \fBsize_t\fP variable. This value does not
1476 include the size of the \fBpcre\fP structure that is returned by
1477 \fBpcre_compile()\fP. The value that is passed as the argument to
1478 \fBpcre_malloc()\fP when \fBpcre_compile()\fP is getting memory in which to
1479 place the compiled data is the value returned by this option plus the size of
1480 the \fBpcre\fP structure. Studying a compiled pattern, with or without JIT,
1481 does not alter the value returned by this option.
1482 .sp
1483 PCRE_INFO_STUDYSIZE
1484 .sp
1485 Return the size in bytes (for all three libraries) of the data block pointed to
1486 by the \fIstudy_data\fP field in a \fBpcre_extra\fP block. If \fBpcre_extra\fP
1487 is NULL, or there is no study data, zero is returned. The fourth argument
1488 should point to a \fBsize_t\fP variable. The \fIstudy_data\fP field is set by
1489 \fBpcre_study()\fP to record information that will speed up matching (see the
1490 section entitled
1491 .\" HTML <a href="#studyingapattern">
1492 .\" </a>
1493 "Studying a pattern"
1494 .\"
1495 above). The format of the \fIstudy_data\fP block is private, but its length
1496 is made available via this option so that it can be saved and restored (see the
1497 .\" HREF
1498 \fBpcreprecompile\fP
1499 .\"
1500 documentation for details).
1501 .sp
1502 PCRE_INFO_FIRSTCHARACTERFLAGS
1503 .sp
1504 Return information about the first data unit of any matched string, for a
1505 non-anchored pattern. The fourth argument should point to an \fBint\fP
1506 variable.
1507 .P
1508 If there is a fixed first value, for example, the letter "c" from a pattern
1509 such as (cat|cow|coyote), 1 is returned, and the character value can be
1510 retrieved using PCRE_INFO_FIRSTCHARACTER.
1511 .P
1512 If there is no fixed first value, and if either
1513 .sp
1514 (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
1515 starts with "^", or
1516 .sp
1517 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
1518 (if it were set, the pattern would be anchored),
1519 .sp
1520 2 is returned, indicating that the pattern matches only at the start of a
1521 subject string or after any newline within the string. Otherwise 0 is
1522 returned. For anchored patterns, 0 is returned.
1523 .sp
1524 PCRE_INFO_FIRSTCHARACTER
1525 .sp
1526 Return the fixed first character value in the situation where
1527 PCRE_INFO_FIRSTCHARACTERFLAGS returns 1; otherwise return 0. The fourth
1528 argument should point to an \fBuint_t\fP variable.
1529 .P
1530 In the 8-bit library, the value is always less than 256. In the 16-bit library
1531 the value can be up to 0xffff. In the 32-bit library in UTF-32 mode the value
1532 can be up to 0x10ffff, and up to 0xffffffff when not using UTF-32 mode.
1533 .sp
1534 PCRE_INFO_REQUIREDCHARFLAGS
1535 .sp
1536 Returns 1 if there is a rightmost literal data unit that must exist in any
1537 matched string, other than at its start. The fourth argument should point to
1538 an \fBint\fP variable. If there is no such value, 0 is returned. If returning
1539 1, the character value itself can be retrieved using PCRE_INFO_REQUIREDCHAR.
1540 .P
1541 For anchored patterns, a last literal value is recorded only if it follows
1542 something of variable length. For example, for the pattern /^a\ed+z\ed+/ the
1543 returned value 1 (with "z" returned from PCRE_INFO_REQUIREDCHAR), but for
1544 /^a\edz\ed/ the returned value is 0.
1545 .sp
1546 PCRE_INFO_REQUIREDCHAR
1547 .sp
1548 Return the value of the rightmost literal data unit that must exist in any
1549 matched string, other than at its start, if such a value has been recorded. The
1550 fourth argument should point to an \fBuint32_t\fP variable. If there is no such
1551 value, 0 is returned.
1552 .
1553 .
1554 .SH "REFERENCE COUNTS"
1555 .rs
1556 .sp
1557 .B int pcre_refcount(pcre *\fIcode\fP, int \fIadjust\fP);
1558 .PP
1559 The \fBpcre_refcount()\fP function is used to maintain a reference count in the
1560 data block that contains a compiled pattern. It is provided for the benefit of
1561 applications that operate in an object-oriented manner, where different parts
1562 of the application may be using the same compiled pattern, but you want to free
1563 the block when they are all done.
1564 .P
1565 When a pattern is compiled, the reference count field is initialized to zero.
1566 It is changed only by calling this function, whose action is to add the
1567 \fIadjust\fP value (which may be positive or negative) to it. The yield of the
1568 function is the new value. However, the value of the count is constrained to
1569 lie between 0 and 65535, inclusive. If the new value is outside these limits,
1570 it is forced to the appropriate limit value.
1571 .P
1572 Except when it is zero, the reference count is not correctly preserved if a
1573 pattern is compiled on one host and then transferred to a host whose byte-order
1574 is different. (This seems a highly unlikely scenario.)
1575 .
1576 .
1577 .SH "MATCHING A PATTERN: THE TRADITIONAL FUNCTION"
1578 .rs
1579 .sp
1580 .nf
1581 .B int pcre_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
1582 .B " const char *\fIsubject\fP," int \fIlength\fP, int \fIstartoffset\fP,
1583 .B " int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP);"
1584 .fi
1585 .P
1586 The function \fBpcre_exec()\fP is called to match a subject string against a
1587 compiled pattern, which is passed in the \fIcode\fP argument. If the
1588 pattern was studied, the result of the study should be passed in the
1589 \fIextra\fP argument. You can call \fBpcre_exec()\fP with the same \fIcode\fP
1590 and \fIextra\fP arguments as many times as you like, in order to match
1591 different subject strings with the same pattern.
1592 .P
1593 This function is the main matching facility of the library, and it operates in
1594 a Perl-like manner. For specialist use there is also an alternative matching
1595 function, which is described
1596 .\" HTML <a href="#dfamatch">
1597 .\" </a>
1598 below
1599 .\"
1600 in the section about the \fBpcre_dfa_exec()\fP function.
1601 .P
1602 In most applications, the pattern will have been compiled (and optionally
1603 studied) in the same process that calls \fBpcre_exec()\fP. However, it is
1604 possible to save compiled patterns and study data, and then use them later
1605 in different processes, possibly even on different hosts. For a discussion
1606 about this, see the
1607 .\" HREF
1608 \fBpcreprecompile\fP
1609 .\"
1610 documentation.
1611 .P
1612 Here is an example of a simple call to \fBpcre_exec()\fP:
1613 .sp
1614 int rc;
1615 int ovector[30];
1616 rc = pcre_exec(
1617 re, /* result of pcre_compile() */
1618 NULL, /* we didn't study the pattern */
1619 "some string", /* the subject string */
1620 11, /* the length of the subject string */
1621 0, /* start at offset 0 in the subject */
1622 0, /* default options */
1623 ovector, /* vector of integers for substring information */
1624 30); /* number of elements (NOT size in bytes) */
1625 .
1626 .
1627 .\" HTML <a name="extradata"></a>
1628 .SS "Extra data for \fBpcre_exec()\fR"
1629 .rs
1630 .sp
1631 If the \fIextra\fP argument is not NULL, it must point to a \fBpcre_extra\fP
1632 data block. The \fBpcre_study()\fP function returns such a block (when it
1633 doesn't return NULL), but you can also create one for yourself, and pass
1634 additional information in it. The \fBpcre_extra\fP block contains the following
1635 fields (not necessarily in this order):
1636 .sp
1637 unsigned long int \fIflags\fP;
1638 void *\fIstudy_data\fP;
1639 void *\fIexecutable_jit\fP;
1640 unsigned long int \fImatch_limit\fP;
1641 unsigned long int \fImatch_limit_recursion\fP;
1642 void *\fIcallout_data\fP;
1643 const unsigned char *\fItables\fP;
1644 unsigned char **\fImark\fP;
1645 .sp
1646 In the 16-bit version of this structure, the \fImark\fP field has type
1647 "PCRE_UCHAR16 **".
1648 .sp
1649 In the 32-bit version of this structure, the \fImark\fP field has type
1650 "PCRE_UCHAR32 **".
1651 .P
1652 The \fIflags\fP field is used to specify which of the other fields are set. The
1653 flag bits are:
1654 .sp
1655 PCRE_EXTRA_CALLOUT_DATA
1656 PCRE_EXTRA_EXECUTABLE_JIT
1657 PCRE_EXTRA_MARK
1658 PCRE_EXTRA_MATCH_LIMIT
1659 PCRE_EXTRA_MATCH_LIMIT_RECURSION
1660 PCRE_EXTRA_STUDY_DATA
1661 PCRE_EXTRA_TABLES
1662 .sp
1663 Other flag bits should be set to zero. The \fIstudy_data\fP field and sometimes
1664 the \fIexecutable_jit\fP field are set in the \fBpcre_extra\fP block that is
1665 returned by \fBpcre_study()\fP, together with the appropriate flag bits. You
1666 should not set these yourself, but you may add to the block by setting other
1667 fields and their corresponding flag bits.
1668 .P
1669 The \fImatch_limit\fP field provides a means of preventing PCRE from using up a
1670 vast amount of resources when running patterns that are not going to match,
1671 but which have a very large number of possibilities in their search trees. The
1672 classic example is a pattern that uses nested unlimited repeats.
1673 .P
1674 Internally, \fBpcre_exec()\fP uses a function called \fBmatch()\fP, which it
1675 calls repeatedly (sometimes recursively). The limit set by \fImatch_limit\fP is
1676 imposed on the number of times this function is called during a match, which
1677 has the effect of limiting the amount of backtracking that can take place. For
1678 patterns that are not anchored, the count restarts from zero for each position
1679 in the subject string.
1680 .P
1681 When \fBpcre_exec()\fP is called with a pattern that was successfully studied
1682 with a JIT option, the way that the matching is executed is entirely different.
1683 However, there is still the possibility of runaway matching that goes on for a
1684 very long time, and so the \fImatch_limit\fP value is also used in this case
1685 (but in a different way) to limit how long the matching can continue.
1686 .P
1687 The default value for the limit can be set when PCRE is built; the default
1688 default is 10 million, which handles all but the most extreme cases. You can
1689 override the default by suppling \fBpcre_exec()\fP with a \fBpcre_extra\fP
1690 block in which \fImatch_limit\fP is set, and PCRE_EXTRA_MATCH_LIMIT is set in
1691 the \fIflags\fP field. If the limit is exceeded, \fBpcre_exec()\fP returns
1692 PCRE_ERROR_MATCHLIMIT.
1693 .P
1694 A value for the match limit may also be supplied by an item at the start of a
1695 pattern of the form
1696 .sp
1697 (*LIMIT_MATCH=d)
1698 .sp
1699 where d is a decimal number. However, such a setting is ignored unless d is
1700 less than the limit set by the caller of \fBpcre_exec()\fP or, if no such limit
1701 is set, less than the default.
1702 .P
1703 The \fImatch_limit_recursion\fP field is similar to \fImatch_limit\fP, but
1704 instead of limiting the total number of times that \fBmatch()\fP is called, it
1705 limits the depth of recursion. The recursion depth is a smaller number than the
1706 total number of calls, because not all calls to \fBmatch()\fP are recursive.
1707 This limit is of use only if it is set smaller than \fImatch_limit\fP.
1708 .P
1709 Limiting the recursion depth limits the amount of machine stack that can be
1710 used, or, when PCRE has been compiled to use memory on the heap instead of the
1711 stack, the amount of heap memory that can be used. This limit is not relevant,
1712 and is ignored, when matching is done using JIT compiled code.
1713 .P
1714 The default value for \fImatch_limit_recursion\fP can be set when PCRE is
1715 built; the default default is the same value as the default for
1716 \fImatch_limit\fP. You can override the default by suppling \fBpcre_exec()\fP
1717 with a \fBpcre_extra\fP block in which \fImatch_limit_recursion\fP is set, and
1718 PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the \fIflags\fP field. If the limit
1719 is exceeded, \fBpcre_exec()\fP returns PCRE_ERROR_RECURSIONLIMIT.
1720 .P
1721 A value for the recursion limit may also be supplied by an item at the start of
1722 a pattern of the form
1723 .sp
1724 (*LIMIT_RECURSION=d)
1725 .sp
1726 where d is a decimal number. However, such a setting is ignored unless d is
1727 less than the limit set by the caller of \fBpcre_exec()\fP or, if no such limit
1728 is set, less than the default.
1729 .P
1730 The \fIcallout_data\fP field is used in conjunction with the "callout" feature,
1731 and is described in the
1732 .\" HREF
1733 \fBpcrecallout\fP
1734 .\"
1735 documentation.
1736 .P
1737 The \fItables\fP field is provided for use with patterns that have been
1738 pre-compiled using custom character tables, saved to disc or elsewhere, and
1739 then reloaded, because the tables that were used to compile a pattern are not
1740 saved with it. See the
1741 .\" HREF
1742 \fBpcreprecompile\fP
1743 .\"
1744 documentation for a discussion of saving compiled patterns for later use. If
1745 NULL is passed using this mechanism, it forces PCRE's internal tables to be
1746 used.
1747 .P
1748 \fBWarning:\fP The tables that \fBpcre_exec()\fP uses must be the same as those
1749 that were used when the pattern was compiled. If this is not the case, the
1750 behaviour of \fBpcre_exec()\fP is undefined. Therefore, when a pattern is
1751 compiled and matched in the same process, this field should never be set. In
1752 this (the most common) case, the correct table pointer is automatically passed
1753 with the compiled pattern from \fBpcre_compile()\fP to \fBpcre_exec()\fP.
1754 .P
1755 If PCRE_EXTRA_MARK is set in the \fIflags\fP field, the \fImark\fP field must
1756 be set to point to a suitable variable. If the pattern contains any
1757 backtracking control verbs such as (*MARK:NAME), and the execution ends up with
1758 a name to pass back, a pointer to the name string (zero terminated) is placed
1759 in the variable pointed to by the \fImark\fP field. The names are within the
1760 compiled pattern; if you wish to retain such a name you must copy it before
1761 freeing the memory of a compiled pattern. If there is no name to pass back, the
1762 variable pointed to by the \fImark\fP field is set to NULL. For details of the
1763 backtracking control verbs, see the section entitled
1764 .\" HTML <a href="pcrepattern#backtrackcontrol">
1765 .\" </a>
1766 "Backtracking control"
1767 .\"
1768 in the
1769 .\" HREF
1770 \fBpcrepattern\fP
1771 .\"
1772 documentation.
1773 .
1774 .
1775 .\" HTML <a name="execoptions"></a>
1776 .SS "Option bits for \fBpcre_exec()\fP"
1777 .rs
1778 .sp
1779 The unused bits of the \fIoptions\fP argument for \fBpcre_exec()\fP must be
1780 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_\fIxxx\fP,
1781 PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
1782 PCRE_NO_START_OPTIMIZE, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_HARD, and
1783 PCRE_PARTIAL_SOFT.
1784 .P
1785 If the pattern was successfully studied with one of the just-in-time (JIT)
1786 compile options, the only supported options for JIT execution are
1787 PCRE_NO_UTF8_CHECK, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,
1788 PCRE_NOTEMPTY_ATSTART, PCRE_PARTIAL_HARD, and PCRE_PARTIAL_SOFT. If an
1789 unsupported option is used, JIT execution is disabled and the normal
1790 interpretive code in \fBpcre_exec()\fP is run.
1791 .sp
1792 PCRE_ANCHORED
1793 .sp
1794 The PCRE_ANCHORED option limits \fBpcre_exec()\fP to matching at the first
1795 matching position. If a pattern was compiled with PCRE_ANCHORED, or turned out
1796 to be anchored by virtue of its contents, it cannot be made unachored at
1797 matching time.
1798 .sp
1799 PCRE_BSR_ANYCRLF
1800 PCRE_BSR_UNICODE
1801 .sp
1802 These options (which are mutually exclusive) control what the \eR escape
1803 sequence matches. The choice is either to match only CR, LF, or CRLF, or to
1804 match any Unicode newline sequence. These options override the choice that was
1805 made or defaulted when the pattern was compiled.
1806 .sp
1807 PCRE_NEWLINE_CR
1808 PCRE_NEWLINE_LF
1809 PCRE_NEWLINE_CRLF
1810 PCRE_NEWLINE_ANYCRLF
1811 PCRE_NEWLINE_ANY
1812 .sp
1813 These options override the newline definition that was chosen or defaulted when
1814 the pattern was compiled. For details, see the description of
1815 \fBpcre_compile()\fP above. During matching, the newline choice affects the
1816 behaviour of the dot, circumflex, and dollar metacharacters. It may also alter
1817 the way the match position is advanced after a match failure for an unanchored
1818 pattern.
1819 .P
1820 When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY is set, and a
1821 match attempt for an unanchored pattern fails when the current position is at a
1822 CRLF sequence, and the pattern contains no explicit matches for CR or LF
1823 characters, the match position is advanced by two characters instead of one, in
1824 other words, to after the CRLF.
1825 .P
1826 The above rule is a compromise that makes the most common cases work as
1827 expected. For example, if the pattern is .+A (and the PCRE_DOTALL option is not
1828 set), it does not match the string "\er\enA" because, after failing at the
1829 start, it skips both the CR and the LF before retrying. However, the pattern
1830 [\er\en]A does match that string, because it contains an explicit CR or LF
1831 reference, and so advances only by one character after the first failure.
1832 .P
1833 An explicit match for CR of LF is either a literal appearance of one of those
1834 characters, or one of the \er or \en escape sequences. Implicit matches such as
1835 [^X] do not count, nor does \es (which includes CR and LF in the characters
1836 that it matches).
1837 .P
1838 Notwithstanding the above, anomalous effects may still occur when CRLF is a
1839 valid newline sequence and explicit \er or \en escapes appear in the pattern.
1840 .sp
1841 PCRE_NOTBOL
1842 .sp
1843 This option specifies that first character of the subject string is not the
1844 beginning of a line, so the circumflex metacharacter should not match before
1845 it. Setting this without PCRE_MULTILINE (at compile time) causes circumflex
1846 never to match. This option affects only the behaviour of the circumflex
1847 metacharacter. It does not affect \eA.
1848 .sp
1849 PCRE_NOTEOL
1850 .sp
1851 This option specifies that the end of the subject string is not the end of a
1852 line, so the dollar metacharacter should not match it nor (except in multiline
1853 mode) a newline immediately before it. Setting this without PCRE_MULTILINE (at
1854 compile time) causes dollar never to match. This option affects only the
1855 behaviour of the dollar metacharacter. It does not affect \eZ or \ez.
1856 .sp
1857 PCRE_NOTEMPTY
1858 .sp
1859 An empty string is not considered to be a valid match if this option is set. If
1860 there are alternatives in the pattern, they are tried. If all the alternatives
1861 match the empty string, the entire match fails. For example, if the pattern
1862 .sp
1863 a?b?
1864 .sp
1865 is applied to a string not beginning with "a" or "b", it matches an empty
1866 string at the start of the subject. With PCRE_NOTEMPTY set, this match is not
1867 valid, so PCRE searches further into the string for occurrences of "a" or "b".
1868 .sp
1869 PCRE_NOTEMPTY_ATSTART
1870 .sp
1871 This is like PCRE_NOTEMPTY, except that an empty string match that is not at
1872 the start of the subject is permitted. If the pattern is anchored, such a match
1873 can occur only if the pattern contains \eK.
1874 .P
1875 Perl has no direct equivalent of PCRE_NOTEMPTY or PCRE_NOTEMPTY_ATSTART, but it
1876 does make a special case of a pattern match of the empty string within its
1877 \fBsplit()\fP function, and when using the /g modifier. It is possible to
1878 emulate Perl's behaviour after matching a null string by first trying the match
1879 again at the same offset with PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED, and then
1880 if that fails, by advancing the starting offset (see below) and trying an
1881 ordinary match again. There is some code that demonstrates how to do this in
1882 the
1883 .\" HREF
1884 \fBpcredemo\fP
1885 .\"
1886 sample program. In the most general case, you have to check to see if the
1887 newline convention recognizes CRLF as a newline, and if so, and the current
1888 character is CR followed by LF, advance the starting offset by two characters
1889 instead of one.
1890 .sp
1891 PCRE_NO_START_OPTIMIZE
1892 .sp
1893 There are a number of optimizations that \fBpcre_exec()\fP uses at the start of
1894 a match, in order to speed up the process. For example, if it is known that an
1895 unanchored match must start with a specific character, it searches the subject
1896 for that character, and fails immediately if it cannot find it, without
1897 actually running the main matching function. This means that a special item
1898 such as (*COMMIT) at the start of a pattern is not considered until after a
1899 suitable starting point for the match has been found. Also, when callouts or
1900 (*MARK) items are in use, these "start-up" optimizations can cause them to be
1901 skipped if the pattern is never actually used. The start-up optimizations are
1902 in effect a pre-scan of the subject that takes place before the pattern is run.
1903 .P
1904 The PCRE_NO_START_OPTIMIZE option disables the start-up optimizations, possibly
1905 causing performance to suffer, but ensuring that in cases where the result is
1906 "no match", the callouts do occur, and that items such as (*COMMIT) and (*MARK)
1907 are considered at every possible starting position in the subject string. If
1908 PCRE_NO_START_OPTIMIZE is set at compile time, it cannot be unset at matching
1909 time. The use of PCRE_NO_START_OPTIMIZE at matching time (that is, passing it
1910 to \fBpcre_exec()\fP) disables JIT execution; in this situation, matching is
1911 always done using interpretively.
1912 .P
1913 Setting PCRE_NO_START_OPTIMIZE can change the outcome of a matching operation.
1914 Consider the pattern
1915 .sp
1916 (*COMMIT)ABC
1917 .sp
1918 When this is compiled, PCRE records the fact that a match must start with the
1919 character "A". Suppose the subject string is "DEFABC". The start-up
1920 optimization scans along the subject, finds "A" and runs the first match
1921 attempt from there. The (*COMMIT) item means that the pattern must match the
1922 current starting position, which in this case, it does. However, if the same
1923 match is run with PCRE_NO_START_OPTIMIZE set, the initial scan along the
1924 subject string does not happen. The first match attempt is run starting from
1925 "D" and when this fails, (*COMMIT) prevents any further matches being tried, so
1926 the overall result is "no match". If the pattern is studied, more start-up
1927 optimizations may be used. For example, a minimum length for the subject may be
1928 recorded. Consider the pattern
1929 .sp
1930 (*MARK:A)(X|Y)
1931 .sp
1932 The minimum length for a match is one character. If the subject is "ABC", there
1933 will be attempts to match "ABC", "BC", "C", and then finally an empty string.
1934 If the pattern is studied, the final attempt does not take place, because PCRE
1935 knows that the subject is too short, and so the (*MARK) is never encountered.
1936 In this case, studying the pattern does not affect the overall match result,
1937 which is still "no match", but it does affect the auxiliary information that is
1938 returned.
1939 .sp
1940 PCRE_NO_UTF8_CHECK
1941 .sp
1942 When PCRE_UTF8 is set at compile time, the validity of the subject as a UTF-8
1943 string is automatically checked when \fBpcre_exec()\fP is subsequently called.
1944 The entire string is checked before any other processing takes place. The value
1945 of \fIstartoffset\fP is also checked to ensure that it points to the start of a
1946 UTF-8 character. There is a discussion about the
1947 .\" HTML <a href="pcreunicode.html#utf8strings">
1948 .\" </a>
1949 validity of UTF-8 strings
1950 .\"
1951 in the
1952 .\" HREF
1953 \fBpcreunicode\fP
1954 .\"
1955 page. If an invalid sequence of bytes is found, \fBpcre_exec()\fP returns the
1956 error PCRE_ERROR_BADUTF8 or, if PCRE_PARTIAL_HARD is set and the problem is a
1957 truncated character at the end of the subject, PCRE_ERROR_SHORTUTF8. In both
1958 cases, information about the precise nature of the error may also be returned
1959 (see the descriptions of these errors in the section entitled \fIError return
1960 values from\fP \fBpcre_exec()\fP
1961 .\" HTML <a href="#errorlist">
1962 .\" </a>
1963 below).
1964 .\"
1965 If \fIstartoffset\fP contains a value that does not point to the start of a
1966 UTF-8 character (or to the end of the subject), PCRE_ERROR_BADUTF8_OFFSET is
1967 returned.
1968 .P
1969 If you already know that your subject is valid, and you want to skip these
1970 checks for performance reasons, you can set the PCRE_NO_UTF8_CHECK option when
1971 calling \fBpcre_exec()\fP. You might want to do this for the second and
1972 subsequent calls to \fBpcre_exec()\fP if you are making repeated calls to find
1973 all the matches in a single subject string. However, you should be sure that
1974 the value of \fIstartoffset\fP points to the start of a character (or the end
1975 of the subject). When PCRE_NO_UTF8_CHECK is set, the effect of passing an
1976 invalid string as a subject or an invalid value of \fIstartoffset\fP is
1977 undefined. Your program may crash or loop.
1978 .sp
1979 PCRE_PARTIAL_HARD
1980 PCRE_PARTIAL_SOFT
1981 .sp
1982 These options turn on the partial matching feature. For backwards
1983 compatibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial match
1984 occurs if the end of the subject string is reached successfully, but there are
1985 not enough subject characters to complete the match. If this happens when
1986 PCRE_PARTIAL_SOFT (but not PCRE_PARTIAL_HARD) is set, matching continues by
1987 testing any remaining alternatives. Only if no complete match can be found is
1988 PCRE_ERROR_PARTIAL returned instead of PCRE_ERROR_NOMATCH. In other words,
1989 PCRE_PARTIAL_SOFT says that the caller is prepared to handle a partial match,
1990 but only if no complete match can be found.
1991 .P
1992 If PCRE_PARTIAL_HARD is set, it overrides PCRE_PARTIAL_SOFT. In this case, if a
1993 partial match is found, \fBpcre_exec()\fP immediately returns
1994 PCRE_ERROR_PARTIAL, without considering any other alternatives. In other words,
1995 when PCRE_PARTIAL_HARD is set, a partial match is considered to be more
1996 important that an alternative complete match.
1997 .P
1998 In both cases, the portion of the string that was inspected when the partial
1999 match was found is set as the first matching string. There is a more detailed
2000 discussion of partial and multi-segment matching, with examples, in the
2001 .\" HREF
2002 \fBpcrepartial\fP
2003 .\"
2004 documentation.
2005 .
2006 .
2007 .SS "The string to be matched by \fBpcre_exec()\fP"
2008 .rs
2009 .sp
2010 The subject string is passed to \fBpcre_exec()\fP as a pointer in
2011 \fIsubject\fP, a length in \fIlength\fP, and a starting offset in
2012 \fIstartoffset\fP. The units for \fIlength\fP and \fIstartoffset\fP are bytes
2013 for the 8-bit library, 16-bit data items for the 16-bit library, and 32-bit
2014 data items for the 32-bit library.
2015 .P
2016 If \fIstartoffset\fP is negative or greater than the length of the subject,
2017 \fBpcre_exec()\fP returns PCRE_ERROR_BADOFFSET. When the starting offset is
2018 zero, the search for a match starts at the beginning of the subject, and this
2019 is by far the most common case. In UTF-8 or UTF-16 mode, the offset must point
2020 to the start of a character, or the end of the subject (in UTF-32 mode, one
2021 data unit equals one character, so all offsets are valid). Unlike the pattern
2022 string, the subject may contain binary zeroes.
2023 .P
2024 A non-zero starting offset is useful when searching for another match in the
2025 same subject by calling \fBpcre_exec()\fP again after a previous success.
2026 Setting \fIstartoffset\fP differs from just passing over a shortened string and
2027 setting PCRE_NOTBOL in the case of a pattern that begins with any kind of
2028 lookbehind. For example, consider the pattern
2029 .sp
2030 \eBiss\eB
2031 .sp
2032 which finds occurrences of "iss" in the middle of words. (\eB matches only if
2033 the current position in the subject is not a word boundary.) When applied to
2034 the string "Mississipi" the first call to \fBpcre_exec()\fP finds the first
2035 occurrence. If \fBpcre_exec()\fP is called again with just the remainder of the
2036 subject, namely "issipi", it does not match, because \eB is always false at the
2037 start of the subject, which is deemed to be a word boundary. However, if
2038 \fBpcre_exec()\fP is passed the entire string again, but with \fIstartoffset\fP
2039 set to 4, it finds the second occurrence of "iss" because it is able to look
2040 behind the starting point to discover that it is preceded by a letter.
2041 .P
2042 Finding all the matches in a subject is tricky when the pattern can match an
2043 empty string. It is possible to emulate Perl's /g behaviour by first trying the
2044 match again at the same offset, with the PCRE_NOTEMPTY_ATSTART and
2045 PCRE_ANCHORED options, and then if that fails, advancing the starting offset
2046 and trying an ordinary match again. There is some code that demonstrates how to
2047 do this in the
2048 .\" HREF
2049 \fBpcredemo\fP
2050 .\"
2051 sample program. In the most general case, you have to check to see if the
2052 newline convention recognizes CRLF as a newline, and if so, and the current
2053 character is CR followed by LF, advance the starting offset by two characters
2054 instead of one.
2055 .P
2056 If a non-zero starting offset is passed when the pattern is anchored, one
2057 attempt to match at the given offset is made. This can only succeed if the
2058 pattern does not require the match to be at the start of the subject.
2059 .
2060 .
2061 .SS "How \fBpcre_exec()\fP returns captured substrings"
2062 .rs
2063 .sp
2064 In general, a pattern matches a certain portion of the subject, and in
2065 addition, further substrings from the subject may be picked out by parts of the
2066 pattern. Following the usage in Jeffrey Friedl's book, this is called
2067 "capturing" in what follows, and the phrase "capturing subpattern" is used for
2068 a fragment of a pattern that picks out a substring. PCRE supports several other
2069 kinds of parenthesized subpattern that do not cause substrings to be captured.
2070 .P
2071 Captured substrings are returned to the caller via a vector of integers whose
2072 address is passed in \fIovector\fP. The number of elements in the vector is
2073 passed in \fIovecsize\fP, which must be a non-negative number. \fBNote\fP: this
2074 argument is NOT the size of \fIovector\fP in bytes.
2075 .P
2076 The first two-thirds of the vector is used to pass back captured substrings,
2077 each substring using a pair of integers. The remaining third of the vector is
2078 used as workspace by \fBpcre_exec()\fP while matching capturing subpatterns,
2079 and is not available for passing back information. The number passed in
2080 \fIovecsize\fP should always be a multiple of three. If it is not, it is
2081 rounded down.
2082 .P
2083 When a match is successful, information about captured substrings is returned
2084 in pairs of integers, starting at the beginning of \fIovector\fP, and
2085 continuing up to two-thirds of its length at the most. The first element of
2086 each pair is set to the offset of the first character in a substring, and the
2087 second is set to the offset of the first character after the end of a
2088 substring. These values are always data unit offsets, even in UTF mode. They
2089 are byte offsets in the 8-bit library, 16-bit data item offsets in the 16-bit
2090 library, and 32-bit data item offsets in the 32-bit library. \fBNote\fP: they
2091 are not character counts.
2092 .P
2093 The first pair of integers, \fIovector[0]\fP and \fIovector[1]\fP, identify the
2094 portion of the subject string matched by the entire pattern. The next pair is
2095 used for the first capturing subpattern, and so on. The value returned by
2096 \fBpcre_exec()\fP is one more than the highest numbered pair that has been set.
2097 For example, if two substrings have been captured, the returned value is 3. If
2098 there are no capturing subpatterns, the return value from a successful match is
2099 1, indicating that just the first pair of offsets has been set.
2100 .P
2101 If a capturing subpattern is matched repeatedly, it is the last portion of the
2102 string that it matched that is returned.
2103 .P
2104 If the vector is too small to hold all the captured substring offsets, it is
2105 used as far as possible (up to two-thirds of its length), and the function
2106 returns a value of zero. If neither the actual string matched nor any captured
2107 substrings are of interest, \fBpcre_exec()\fP may be called with \fIovector\fP
2108 passed as NULL and \fIovecsize\fP as zero. However, if the pattern contains
2109 back references and the \fIovector\fP is not big enough to remember the related
2110 substrings, PCRE has to get additional memory for use during matching. Thus it
2111 is usually advisable to supply an \fIovector\fP of reasonable size.
2112 .P
2113 There are some cases where zero is returned (indicating vector overflow) when
2114 in fact the vector is exactly the right size for the final match. For example,
2115 consider the pattern
2116 .sp
2117 (a)(?:(b)c|bd)
2118 .sp
2119 If a vector of 6 elements (allowing for only 1 captured substring) is given
2120 with subject string "abd", \fBpcre_exec()\fP will try to set the second
2121 captured string, thereby recording a vector overflow, before failing to match
2122 "c" and backing up to try the second alternative. The zero return, however,
2123 does correctly indicate that the maximum number of slots (namely 2) have been
2124 filled. In similar cases where there is temporary overflow, but the final
2125 number of used slots is actually less than the maximum, a non-zero value is
2126 returned.
2127 .P
2128 The \fBpcre_fullinfo()\fP function can be used to find out how many capturing
2129 subpatterns there are in a compiled pattern. The smallest size for
2130 \fIovector\fP that will allow for \fIn\fP captured substrings, in addition to
2131 the offsets of the substring matched by the whole pattern, is (\fIn\fP+1)*3.
2132 .P
2133 It is possible for capturing subpattern number \fIn+1\fP to match some part of
2134 the subject when subpattern \fIn\fP has not been used at all. For example, if
2135 the string "abc" is matched against the pattern (a|(z))(bc) the return from the
2136 function is 4, and subpatterns 1 and 3 are matched, but 2 is not. When this
2137 happens, both values in the offset pairs corresponding to unused subpatterns
2138 are set to -1.
2139 .P
2140 Offset values that correspond to unused subpatterns at the end of the
2141 expression are also set to -1. For example, if the string "abc" is matched
2142 against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not matched. The
2143 return from the function is 2, because the highest used capturing subpattern
2144 number is 1, and the offsets for for the second and third capturing subpatterns
2145 (assuming the vector is large enough, of course) are set to -1.
2146 .P
2147 \fBNote\fP: Elements in the first two-thirds of \fIovector\fP that do not
2148 correspond to capturing parentheses in the pattern are never changed. That is,
2149 if a pattern contains \fIn\fP capturing parentheses, no more than
2150 \fIovector[0]\fP to \fIovector[2n+1]\fP are set by \fBpcre_exec()\fP. The other
2151 elements (in the first two-thirds) retain whatever values they previously had.
2152 .P
2153 Some convenience functions are provided for extracting the captured substrings
2154 as separate strings. These are described below.
2155 .
2156 .
2157 .\" HTML <a name="errorlist"></a>
2158 .SS "Error return values from \fBpcre_exec()\fP"
2159 .rs
2160 .sp
2161 If \fBpcre_exec()\fP fails, it returns a negative number. The following are
2162 defined in the header file:
2163 .sp
2164 PCRE_ERROR_NOMATCH (-1)
2165 .sp
2166 The subject string did not match the pattern.
2167 .sp
2168 PCRE_ERROR_NULL (-2)
2169 .sp
2170 Either \fIcode\fP or \fIsubject\fP was passed as NULL, or \fIovector\fP was
2171 NULL and \fIovecsize\fP was not zero.
2172 .sp
2173 PCRE_ERROR_BADOPTION (-3)
2174 .sp
2175 An unrecognized bit was set in the \fIoptions\fP argument.
2176 .sp
2177 PCRE_ERROR_BADMAGIC (-4)
2178 .sp
2179 PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch
2180 the case when it is passed a junk pointer and to detect when a pattern that was
2181 compiled in an environment of one endianness is run in an environment with the
2182 other endianness. This is the error that PCRE gives when the magic number is
2183 not present.
2184 .sp
2185 PCRE_ERROR_UNKNOWN_OPCODE (-5)
2186 .sp
2187 While running the pattern match, an unknown item was encountered in the
2188 compiled pattern. This error could be caused by a bug in PCRE or by overwriting
2189 of the compiled pattern.
2190 .sp
2191 PCRE_ERROR_NOMEMORY (-6)
2192 .sp
2193 If a pattern contains back references, but the \fIovector\fP that is passed to
2194 \fBpcre_exec()\fP is not big enough to remember the referenced substrings, PCRE
2195 gets a block of memory at the start of matching to use for this purpose. If the
2196 call via \fBpcre_malloc()\fP fails, this error is given. The memory is
2197 automatically freed at the end of matching.
2198 .P
2199 This error is also given if \fBpcre_stack_malloc()\fP fails in
2200 \fBpcre_exec()\fP. This can happen only when PCRE has been compiled with
2201 \fB--disable-stack-for-recursion\fP.
2202 .sp
2203 PCRE_ERROR_NOSUBSTRING (-7)
2204 .sp
2205 This error is used by the \fBpcre_copy_substring()\fP,
2206 \fBpcre_get_substring()\fP, and \fBpcre_get_substring_list()\fP functions (see
2207 below). It is never returned by \fBpcre_exec()\fP.
2208 .sp
2209 PCRE_ERROR_MATCHLIMIT (-8)
2210 .sp
2211 The backtracking limit, as specified by the \fImatch_limit\fP field in a
2212 \fBpcre_extra\fP structure (or defaulted) was reached. See the description
2213 above.
2214 .sp
2215 PCRE_ERROR_CALLOUT (-9)
2216 .sp
2217 This error is never generated by \fBpcre_exec()\fP itself. It is provided for
2218 use by callout functions that want to yield a distinctive error code. See the
2219 .\" HREF
2220 \fBpcrecallout\fP
2221 .\"
2222 documentation for details.
2223 .sp
2224 PCRE_ERROR_BADUTF8 (-10)
2225 .sp
2226 A string that contains an invalid UTF-8 byte sequence was passed as a subject,
2227 and the PCRE_NO_UTF8_CHECK option was not set. If the size of the output vector
2228 (\fIovecsize\fP) is at least 2, the byte offset to the start of the the invalid
2229 UTF-8 character is placed in the first element, and a reason code is placed in
2230 the second element. The reason codes are listed in the
2231 .\" HTML <a href="#badutf8reasons">
2232 .\" </a>
2233 following section.
2234 .\"
2235 For backward compatibility, if PCRE_PARTIAL_HARD is set and the problem is a
2236 truncated UTF-8 character at the end of the subject (reason codes 1 to 5),
2237 PCRE_ERROR_SHORTUTF8 is returned instead of PCRE_ERROR_BADUTF8.
2238 .sp
2239 PCRE_ERROR_BADUTF8_OFFSET (-11)
2240 .sp
2241 The UTF-8 byte sequence that was passed as a subject was checked and found to
2242 be valid (the PCRE_NO_UTF8_CHECK option was not set), but the value of
2243 \fIstartoffset\fP did not point to the beginning of a UTF-8 character or the
2244 end of the subject.
2245 .sp
2246 PCRE_ERROR_PARTIAL (-12)
2247 .sp
2248 The subject string did not match, but it did match partially. See the
2249 .\" HREF
2250 \fBpcrepartial\fP
2251 .\"
2252 documentation for details of partial matching.
2253 .sp
2254 PCRE_ERROR_BADPARTIAL (-13)
2255 .sp
2256 This code is no longer in use. It was formerly returned when the PCRE_PARTIAL
2257 option was used with a compiled pattern containing items that were not
2258 supported for partial matching. From release 8.00 onwards, there are no
2259 restrictions on partial matching.
2260 .sp
2261 PCRE_ERROR_INTERNAL (-14)
2262 .sp
2263 An unexpected internal error has occurred. This error could be caused by a bug
2264 in PCRE or by overwriting of the compiled pattern.
2265 .sp
2266 PCRE_ERROR_BADCOUNT (-15)
2267 .sp
2268 This error is given if the value of the \fIovecsize\fP argument is negative.
2269 .sp
2270 PCRE_ERROR_RECURSIONLIMIT (-21)
2271 .sp
2272 The internal recursion limit, as specified by the \fImatch_limit_recursion\fP
2273 field in a \fBpcre_extra\fP structure (or defaulted) was reached. See the
2274 description above.
2275 .sp
2276 PCRE_ERROR_BADNEWLINE (-23)
2277 .sp
2278 An invalid combination of PCRE_NEWLINE_\fIxxx\fP options was given.
2279 .sp
2280 PCRE_ERROR_BADOFFSET (-24)
2281 .sp
2282 The value of \fIstartoffset\fP was negative or greater than the length of the
2283 subject, that is, the value in \fIlength\fP.
2284 .sp
2285 PCRE_ERROR_SHORTUTF8 (-25)
2286 .sp
2287 This error is returned instead of PCRE_ERROR_BADUTF8 when the subject string
2288 ends with a truncated UTF-8 character and the PCRE_PARTIAL_HARD option is set.
2289 Information about the failure is returned as for PCRE_ERROR_BADUTF8. It is in
2290 fact sufficient to detect this case, but this special error code for
2291 PCRE_PARTIAL_HARD precedes the implementation of returned information; it is
2292 retained for backwards compatibility.
2293 .sp
2294 PCRE_ERROR_RECURSELOOP (-26)
2295 .sp
2296 This error is returned when \fBpcre_exec()\fP detects a recursion loop within
2297 the pattern. Specifically, it means that either the whole pattern or a
2298 subpattern has been called recursively for the second time at the same position
2299 in the subject string. Some simple patterns that might do this are detected and
2300 faulted at compile time, but more complicated cases, in particular mutual
2301 recursions between two different subpatterns, cannot be detected until run
2302 time.
2303 .sp
2304 PCRE_ERROR_JIT_STACKLIMIT (-27)
2305 .sp
2306 This error is returned when a pattern that was successfully studied using a
2307 JIT compile option is being matched, but the memory available for the
2308 just-in-time processing stack is not large enough. See the
2309 .\" HREF
2310 \fBpcrejit\fP
2311 .\"
2312 documentation for more details.
2313 .sp
2314 PCRE_ERROR_BADMODE (-28)
2315 .sp
2316 This error is given if a pattern that was compiled by the 8-bit library is
2317 passed to a 16-bit or 32-bit library function, or vice versa.
2318 .sp
2319 PCRE_ERROR_BADENDIANNESS (-29)
2320 .sp
2321 This error is given if a pattern that was compiled and saved is reloaded on a
2322 host with different endianness. The utility function
2323 \fBpcre_pattern_to_host_byte_order()\fP can be used to convert such a pattern
2324 so that it runs on the new host.
2325 .sp
2326 PCRE_ERROR_JIT_BADOPTION
2327 .sp
2328 This error is returned when a pattern that was successfully studied using a JIT
2329 compile option is being matched, but the matching mode (partial or complete
2330 match) does not correspond to any JIT compilation mode. When the JIT fast path
2331 function is used, this error may be also given for invalid options. See the
2332 .\" HREF
2333 \fBpcrejit\fP
2334 .\"
2335 documentation for more details.
2336 .sp
2337 PCRE_ERROR_BADLENGTH (-32)
2338 .sp
2339 This error is given if \fBpcre_exec()\fP is called with a negative value for
2340 the \fIlength\fP argument.
2341 .P
2342 Error numbers -16 to -20, -22, and 30 are not used by \fBpcre_exec()\fP.
2343 .
2344 .
2345 .\" HTML <a name="badutf8reasons"></a>
2346 .SS "Reason codes for invalid UTF-8 strings"
2347 .rs
2348 .sp
2349 This section applies only to the 8-bit library. The corresponding information
2350 for the 16-bit and 32-bit libraries is given in the
2351 .\" HREF
2352 \fBpcre16\fP
2353 .\"
2354 and
2355 .\" HREF
2356 \fBpcre32\fP
2357 .\"
2358 pages.
2359 .P
2360 When \fBpcre_exec()\fP returns either PCRE_ERROR_BADUTF8 or
2361 PCRE_ERROR_SHORTUTF8, and the size of the output vector (\fIovecsize\fP) is at
2362 least 2, the offset of the start of the invalid UTF-8 character is placed in
2363 the first output vector element (\fIovector[0]\fP) and a reason code is placed
2364 in the second element (\fIovector[1]\fP). The reason codes are given names in
2365 the \fBpcre.h\fP header file:
2366 .sp
2367 PCRE_UTF8_ERR1
2368 PCRE_UTF8_ERR2
2369 PCRE_UTF8_ERR3
2370 PCRE_UTF8_ERR4
2371 PCRE_UTF8_ERR5
2372 .sp
2373 The string ends with a truncated UTF-8 character; the code specifies how many
2374 bytes are missing (1 to 5). Although RFC 3629 restricts UTF-8 characters to be
2375 no longer than 4 bytes, the encoding scheme (originally defined by RFC 2279)
2376 allows for up to 6 bytes, and this is checked first; hence the possibility of
2377 4 or 5 missing bytes.
2378 .sp
2379 PCRE_UTF8_ERR6
2380 PCRE_UTF8_ERR7
2381 PCRE_UTF8_ERR8
2382 PCRE_UTF8_ERR9
2383 PCRE_UTF8_ERR10
2384 .sp
2385 The two most significant bits of the 2nd, 3rd, 4th, 5th, or 6th byte of the
2386 character do not have the binary value 0b10 (that is, either the most
2387 significant bit is 0, or the next bit is 1).
2388 .sp
2389 PCRE_UTF8_ERR11
2390 PCRE_UTF8_ERR12
2391 .sp
2392 A character that is valid by the RFC 2279 rules is either 5 or 6 bytes long;
2393 these code points are excluded by RFC 3629.
2394 .sp
2395 PCRE_UTF8_ERR13
2396 .sp
2397 A 4-byte character has a value greater than 0x10fff; these code points are
2398 excluded by RFC 3629.
2399 .sp
2400 PCRE_UTF8_ERR14
2401 .sp
2402 A 3-byte character has a value in the range 0xd800 to 0xdfff; this range of
2403 code points are reserved by RFC 3629 for use with UTF-16, and so are excluded
2404 from UTF-8.
2405 .sp
2406 PCRE_UTF8_ERR15
2407 PCRE_UTF8_ERR16
2408 PCRE_UTF8_ERR17
2409 PCRE_UTF8_ERR18
2410 PCRE_UTF8_ERR19
2411 .sp
2412 A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it codes for a
2413 value that can be represented by fewer bytes, which is invalid. For example,
2414 the two bytes 0xc0, 0xae give the value 0x2e, whose correct coding uses just
2415 one byte.
2416 .sp
2417 PCRE_UTF8_ERR20
2418 .sp
2419 The two most significant bits of the first byte of a character have the binary
2420 value 0b10 (that is, the most significant bit is 1 and the second is 0). Such a
2421 byte can only validly occur as the second or subsequent byte of a multi-byte
2422 character.
2423 .sp
2424 PCRE_UTF8_ERR21
2425 .sp
2426 The first byte of a character has the value 0xfe or 0xff. These values can
2427 never occur in a valid UTF-8 string.
2428 .sp
2429 PCRE_UTF8_ERR22
2430 .sp
2431 This error code was formerly used when the presence of a so-called
2432 "non-character" caused an error. Unicode corrigendum #9 makes it clear that
2433 such characters should not cause a string to be rejected, and so this code is
2434 no longer in use and is never returned.
2435 .
2436 .
2437 .SH "EXTRACTING CAPTURED SUBSTRINGS BY NUMBER"
2438 .rs
2439 .sp
2440 .nf
2441 .B int pcre_copy_substring(const char *\fIsubject\fP, int *\fIovector\fP,
2442 .B " int \fIstringcount\fP, int \fIstringnumber\fP, char *\fIbuffer\fP,"
2443 .B " int \fIbuffersize\fP);"
2444 .sp
2445 .B int pcre_get_substring(const char *\fIsubject\fP, int *\fIovector\fP,
2446 .B " int \fIstringcount\fP, int \fIstringnumber\fP,"
2447 .B " const char **\fIstringptr\fP);"
2448 .sp
2449 .B int pcre_get_substring_list(const char *\fIsubject\fP,
2450 .B " int *\fIovector\fP, int \fIstringcount\fP, const char ***\fIlistptr\fP);"
2451 .fi
2452 .PP
2453 Captured substrings can be accessed directly by using the offsets returned by
2454 \fBpcre_exec()\fP in \fIovector\fP. For convenience, the functions
2455 \fBpcre_copy_substring()\fP, \fBpcre_get_substring()\fP, and
2456 \fBpcre_get_substring_list()\fP are provided for extracting captured substrings
2457 as new, separate, zero-terminated strings. These functions identify substrings
2458 by number. The next section describes functions for extracting named
2459 substrings.
2460 .P
2461 A substring that contains a binary zero is correctly extracted and has a
2462 further zero added on the end, but the result is not, of course, a C string.
2463 However, you can process such a string by referring to the length that is
2464 returned by \fBpcre_copy_substring()\fP and \fBpcre_get_substring()\fP.
2465 Unfortunately, the interface to \fBpcre_get_substring_list()\fP is not adequate
2466 for handling strings containing binary zeros, because the end of the final
2467 string is not independently indicated.
2468 .P
2469 The first three arguments are the same for all three of these functions:
2470 \fIsubject\fP is the subject string that has just been successfully matched,
2471 \fIovector\fP is a pointer to the vector of integer offsets that was passed to
2472 \fBpcre_exec()\fP, and \fIstringcount\fP is the number of substrings that were
2473 captured by the match, including the substring that matched the entire regular
2474 expression. This is the value returned by \fBpcre_exec()\fP if it is greater
2475 than zero. If \fBpcre_exec()\fP returned zero, indicating that it ran out of
2476 space in \fIovector\fP, the value passed as \fIstringcount\fP should be the
2477 number of elements in the vector divided by three.
2478 .P
2479 The functions \fBpcre_copy_substring()\fP and \fBpcre_get_substring()\fP
2480 extract a single substring, whose number is given as \fIstringnumber\fP. A
2481 value of zero extracts the substring that matched the entire pattern, whereas
2482 higher values extract the captured substrings. For \fBpcre_copy_substring()\fP,
2483 the string is placed in \fIbuffer\fP, whose length is given by
2484 \fIbuffersize\fP, while for \fBpcre_get_substring()\fP a new block of memory is
2485 obtained via \fBpcre_malloc\fP, and its address is returned via
2486 \fIstringptr\fP. The yield of the function is the length of the string, not
2487 including the terminating zero, or one of these error codes:
2488 .sp
2489 PCRE_ERROR_NOMEMORY (-6)
2490 .sp
2491 The buffer was too small for \fBpcre_copy_substring()\fP, or the attempt to get
2492 memory failed for \fBpcre_get_substring()\fP.
2493 .sp
2494 PCRE_ERROR_NOSUBSTRING (-7)
2495 .sp
2496 There is no substring whose number is \fIstringnumber\fP.
2497 .P
2498 The \fBpcre_get_substring_list()\fP function extracts all available substrings
2499 and builds a list of pointers to them. All this is done in a single block of
2500 memory that is obtained via \fBpcre_malloc\fP. The address of the memory block
2501 is returned via \fIlistptr\fP, which is also the start of the list of string
2502 pointers. The end of the list is marked by a NULL pointer. The yield of the
2503 function is zero if all went well, or the error code
2504 .sp
2505 PCRE_ERROR_NOMEMORY (-6)
2506 .sp
2507 if the attempt to get the memory block failed.
2508 .P
2509 When any of these functions encounter a substring that is unset, which can
2510 happen when capturing subpattern number \fIn+1\fP matches some part of the
2511 subject, but subpattern \fIn\fP has not been used at all, they return an empty
2512 string. This can be distinguished from a genuine zero-length substring by
2513 inspecting the appropriate offset in \fIovector\fP, which is negative for unset
2514 substrings.
2515 .P
2516 The two convenience functions \fBpcre_free_substring()\fP and
2517 \fBpcre_free_substring_list()\fP can be used to free the memory returned by
2518 a previous call of \fBpcre_get_substring()\fP or
2519 \fBpcre_get_substring_list()\fP, respectively. They do nothing more than call
2520 the function pointed to by \fBpcre_free\fP, which of course could be called
2521 directly from a C program. However, PCRE is used in some situations where it is
2522 linked via a special interface to another programming language that cannot use
2523 \fBpcre_free\fP directly; it is for these cases that the functions are
2524 provided.
2525 .
2526 .
2527 .SH "EXTRACTING CAPTURED SUBSTRINGS BY NAME"
2528 .rs
2529 .sp
2530 .nf
2531 .B int pcre_get_stringnumber(const pcre *\fIcode\fP,
2532 .B " const char *\fIname\fP);"
2533 .sp
2534 .B int pcre_copy_named_substring(const pcre *\fIcode\fP,
2535 .B " const char *\fIsubject\fP, int *\fIovector\fP,"
2536 .B " int \fIstringcount\fP, const char *\fIstringname\fP,"
2537 .B " char *\fIbuffer\fP, int \fIbuffersize\fP);"
2538 .sp
2539 .B int pcre_get_named_substring(const pcre *\fIcode\fP,
2540 .B " const char *\fIsubject\fP, int *\fIovector\fP,"
2541 .B " int \fIstringcount\fP, const char *\fIstringname\fP,"
2542 .B " const char **\fIstringptr\fP);"
2543 .fi
2544 .PP
2545 To extract a substring by name, you first have to find associated number.
2546 For example, for this pattern
2547 .sp
2548 (a+)b(?<xxx>\ed+)...
2549 .sp
2550 the number of the subpattern called "xxx" is 2. If the name is known to be
2551 unique (PCRE_DUPNAMES was not set), you can find the number from the name by
2552 calling \fBpcre_get_stringnumber()\fP. The first argument is the compiled
2553 pattern, and the second is the name. The yield of the function is the
2554 subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no subpattern of
2555 that name.
2556 .P
2557 Given the number, you can extract the substring directly, or use one of the
2558 functions described in the previous section. For convenience, there are also
2559 two functions that do the whole job.
2560 .P
2561 Most of the arguments of \fBpcre_copy_named_substring()\fP and
2562 \fBpcre_get_named_substring()\fP are the same as those for the similarly named
2563 functions that extract by number. As these are described in the previous
2564 section, they are not re-described here. There are just two differences:
2565 .P
2566 First, instead of a substring number, a substring name is given. Second, there
2567 is an extra argument, given at the start, which is a pointer to the compiled
2568 pattern. This is needed in order to gain access to the name-to-number
2569 translation table.
2570 .P
2571 These functions call \fBpcre_get_stringnumber()\fP, and if it succeeds, they
2572 then call \fBpcre_copy_substring()\fP or \fBpcre_get_substring()\fP, as
2573 appropriate. \fBNOTE:\fP If PCRE_DUPNAMES is set and there are duplicate names,
2574 the behaviour may not be what you want (see the next section).
2575 .P
2576 \fBWarning:\fP If the pattern uses the (?| feature to set up multiple
2577 subpatterns with the same number, as described in the
2578 .\" HTML <a href="pcrepattern.html#dupsubpatternnumber">
2579 .\" </a>
2580 section on duplicate subpattern numbers
2581 .\"
2582 in the
2583 .\" HREF
2584 \fBpcrepattern\fP
2585 .\"
2586 page, you cannot use names to distinguish the different subpatterns, because
2587 names are not included in the compiled code. The matching process uses only
2588 numbers. For this reason, the use of different names for subpatterns of the
2589 same number causes an error at compile time.
2590 .
2591 .
2592 .SH "DUPLICATE SUBPATTERN NAMES"
2593 .rs
2594 .sp
2595 .nf
2596 .B int pcre_get_stringtable_entries(const pcre *\fIcode\fP,
2597 .B " const char *\fIname\fP, char **\fIfirst\fP, char **\fIlast\fP);"
2598 .fi
2599 .PP
2600 When a pattern is compiled with the PCRE_DUPNAMES option, names for subpatterns
2601 are not required to be unique. (Duplicate names are always allowed for
2602 subpatterns with the same number, created by using the (?| feature. Indeed, if
2603 such subpatterns are named, they are required to use the same names.)
2604 .P
2605 Normally, patterns with duplicate names are such that in any one match, only
2606 one of the named subpatterns participates. An example is shown in the
2607 .\" HREF
2608 \fBpcrepattern\fP
2609 .\"
2610 documentation.
2611 .P
2612 When duplicates are present, \fBpcre_copy_named_substring()\fP and
2613 \fBpcre_get_named_substring()\fP return the first substring corresponding to
2614 the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING (-7) is
2615 returned; no data is returned. The \fBpcre_get_stringnumber()\fP function
2616 returns one of the numbers that are associated with the name, but it is not
2617 defined which it is.
2618 .P
2619 If you want to get full details of all captured substrings for a given name,
2620 you must use the \fBpcre_get_stringtable_entries()\fP function. The first
2621 argument is the compiled pattern, and the second is the name. The third and
2622 fourth are pointers to variables which are updated by the function. After it
2623 has run, they point to the first and last entries in the name-to-number table
2624 for the given name. The function itself returns the length of each entry, or
2625 PCRE_ERROR_NOSUBSTRING (-7) if there are none. The format of the table is
2626 described above in the section entitled \fIInformation about a pattern\fP
2627 .\" HTML <a href="#infoaboutpattern">
2628 .\" </a>
2629 above.
2630 .\"
2631 Given all the relevant entries for the name, you can extract each of their
2632 numbers, and hence the captured data, if any.
2633 .
2634 .
2635 .SH "FINDING ALL POSSIBLE MATCHES"
2636 .rs
2637 .sp
2638 The traditional matching function uses a similar algorithm to Perl, which stops
2639 when it finds the first match, starting at a given point in the subject. If you
2640 want to find all possible matches, or the longest possible match, consider
2641 using the alternative matching function (see below) instead. If you cannot use
2642 the alternative function, but still need to find all possible matches, you
2643 can kludge it up by making use of the callout facility, which is described in
2644 the
2645 .\" HREF
2646 \fBpcrecallout\fP
2647 .\"
2648 documentation.
2649 .P
2650 What you have to do is to insert a callout right at the end of the pattern.
2651 When your callout function is called, extract and save the current matched
2652 substring. Then return 1, which forces \fBpcre_exec()\fP to backtrack and try
2653 other alternatives. Ultimately, when it runs out of matches, \fBpcre_exec()\fP
2654 will yield PCRE_ERROR_NOMATCH.
2655 .
2656 .
2657 .SH "OBTAINING AN ESTIMATE OF STACK USAGE"
2658 .rs
2659 .sp
2660 Matching certain patterns using \fBpcre_exec()\fP can use a lot of process
2661 stack, which in certain environments can be rather limited in size. Some users
2662 find it helpful to have an estimate of the amount of stack that is used by
2663 \fBpcre_exec()\fP, to help them set recursion limits, as described in the
2664 .\" HREF
2665 \fBpcrestack\fP
2666 .\"
2667 documentation. The estimate that is output by \fBpcretest\fP when called with
2668 the \fB-m\fP and \fB-C\fP options is obtained by calling \fBpcre_exec\fP with
2669 the values NULL, NULL, NULL, -999, and -999 for its first five arguments.
2670 .P
2671 Normally, if its first argument is NULL, \fBpcre_exec()\fP immediately returns
2672 the negative error code PCRE_ERROR_NULL, but with this special combination of
2673 arguments, it returns instead a negative number whose absolute value is the
2674 approximate stack frame size in bytes. (A negative number is used so that it is
2675 clear that no match has happened.) The value is approximate because in some
2676 cases, recursive calls to \fBpcre_exec()\fP occur when there are one or two
2677 additional variables on the stack.
2678 .P
2679 If PCRE has been compiled to use the heap instead of the stack for recursion,
2680 the value returned is the size of each block that is obtained from the heap.
2681 .
2682 .
2683 .\" HTML <a name="dfamatch"></a>
2684 .SH "MATCHING A PATTERN: THE ALTERNATIVE FUNCTION"
2685 .rs
2686 .sp
2687 .nf
2688 .B int pcre_dfa_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
2689 .B " const char *\fIsubject\fP, int \fIlength\fP, int \fIstartoffset\fP,"
2690 .B " int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP,"
2691 .B " int *\fIworkspace\fP, int \fIwscount\fP);"
2692 .fi
2693 .P
2694 The function \fBpcre_dfa_exec()\fP is called to match a subject string against
2695 a compiled pattern, using a matching algorithm that scans the subject string
2696 just once, and does not backtrack. This has different characteristics to the
2697 normal algorithm, and is not compatible with Perl. Some of the features of PCRE
2698 patterns are not supported. Nevertheless, there are times when this kind of
2699 matching can be useful. For a discussion of the two matching algorithms, and a
2700 list of features that \fBpcre_dfa_exec()\fP does not support, see the
2701 .\" HREF
2702 \fBpcrematching\fP
2703 .\"
2704 documentation.
2705 .P
2706 The arguments for the \fBpcre_dfa_exec()\fP function are the same as for
2707 \fBpcre_exec()\fP, plus two extras. The \fIovector\fP argument is used in a
2708 different way, and this is described below. The other common arguments are used
2709 in the same way as for \fBpcre_exec()\fP, so their description is not repeated
2710 here.
2711 .P
2712 The two additional arguments provide workspace for the function. The workspace
2713 vector should contain at least 20 elements. It is used for keeping track of
2714 multiple paths through the pattern tree. More workspace will be needed for
2715 patterns and subjects where there are a lot of potential matches.
2716 .P
2717 Here is an example of a simple call to \fBpcre_dfa_exec()\fP:
2718 .sp
2719 int rc;
2720 int ovector[10];
2721 int wspace[20];
2722 rc = pcre_dfa_exec(
2723 re, /* result of pcre_compile() */
2724 NULL, /* we didn't study the pattern */
2725 "some string", /* the subject string */
2726 11, /* the length of the subject string */
2727 0, /* start at offset 0 in the subject */
2728 0, /* default options */
2729 ovector, /* vector of integers for substring information */
2730 10, /* number of elements (NOT size in bytes) */
2731 wspace, /* working space vector */
2732 20); /* number of elements (NOT size in bytes) */
2733 .
2734 .SS "Option bits for \fBpcre_dfa_exec()\fP"
2735 .rs
2736 .sp
2737 The unused bits of the \fIoptions\fP argument for \fBpcre_dfa_exec()\fP must be
2738 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_\fIxxx\fP,
2739 PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
2740 PCRE_NO_UTF8_CHECK, PCRE_BSR_ANYCRLF, PCRE_BSR_UNICODE, PCRE_NO_START_OPTIMIZE,
2741 PCRE_PARTIAL_HARD, PCRE_PARTIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART.
2742 All but the last four of these are exactly the same as for \fBpcre_exec()\fP,
2743 so their description is not repeated here.
2744 .sp
2745 PCRE_PARTIAL_HARD
2746 PCRE_PARTIAL_SOFT
2747 .sp
2748 These have the same general effect as they do for \fBpcre_exec()\fP, but the
2749 details are slightly different. When PCRE_PARTIAL_HARD is set for
2750 \fBpcre_dfa_exec()\fP, it returns PCRE_ERROR_PARTIAL if the end of the subject
2751 is reached and there is still at least one matching possibility that requires
2752 additional characters. This happens even if some complete matches have also
2753 been found. When PCRE_PARTIAL_SOFT is set, the return code PCRE_ERROR_NOMATCH
2754 is converted into PCRE_ERROR_PARTIAL if the end of the subject is reached,
2755 there have been no complete matches, but there is still at least one matching
2756 possibility. The portion of the string that was inspected when the longest
2757 partial match was found is set as the first matching string in both cases.
2758 There is a more detailed discussion of partial and multi-segment matching, with
2759 examples, in the
2760 .\" HREF
2761 \fBpcrepartial\fP
2762 .\"
2763 documentation.
2764 .sp
2765 PCRE_DFA_SHORTEST
2766 .sp
2767 Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to stop as
2768 soon as it has found one match. Because of the way the alternative algorithm
2769 works, this is necessarily the shortest possible match at the first possible
2770 matching point in the subject string.
2771 .sp
2772 PCRE_DFA_RESTART
2773 .sp
2774 When \fBpcre_dfa_exec()\fP returns a partial match, it is possible to call it
2775 again, with additional subject characters, and have it continue with the same
2776 match. The PCRE_DFA_RESTART option requests this action; when it is set, the
2777 \fIworkspace\fP and \fIwscount\fP options must reference the same vector as
2778 before because data about the match so far is left in them after a partial
2779 match. There is more discussion of this facility in the
2780 .\" HREF
2781 \fBpcrepartial\fP
2782 .\"
2783 documentation.
2784 .
2785 .
2786 .SS "Successful returns from \fBpcre_dfa_exec()\fP"
2787 .rs
2788 .sp
2789 When \fBpcre_dfa_exec()\fP succeeds, it may have matched more than one
2790 substring in the subject. Note, however, that all the matches from one run of
2791 the function start at the same point in the subject. The shorter matches are
2792 all initial substrings of the longer matches. For example, if the pattern
2793 .sp
2794 <.*>
2795 .sp
2796 is matched against the string
2797 .sp
2798 This is <something> <something else> <something further> no more
2799 .sp
2800 the three matched strings are
2801 .sp
2802 <something>
2803 <something> <something else>
2804 <something> <something else> <something further>
2805 .sp
2806 On success, the yield of the function is a number greater than zero, which is
2807 the number of matched substrings. The substrings themselves are returned in
2808 \fIovector\fP. Each string uses two elements; the first is the offset to the
2809 start, and the second is the offset to the end. In fact, all the strings have
2810 the same start offset. (Space could have been saved by giving this only once,
2811 but it was decided to retain some compatibility with the way \fBpcre_exec()\fP
2812 returns data, even though the meaning of the strings is different.)
2813 .P
2814 The strings are returned in reverse order of length; that is, the longest
2815 matching string is given first. If there were too many matches to fit into
2816 \fIovector\fP, the yield of the function is zero, and the vector is filled with
2817 the longest matches. Unlike \fBpcre_exec()\fP, \fBpcre_dfa_exec()\fP can use
2818 the entire \fIovector\fP for returning matched strings.
2819 .P
2820 NOTE: PCRE's "auto-possessification" optimization usually applies to character
2821 repeats at the end of a pattern (as well as internally). For example, the
2822 pattern "a\ed+" is compiled as if it were "a\ed++" because there is no point
2823 even considering the possibility of backtracking into the repeated digits. For
2824 DFA matching, this means that only one possible match is found. If you really
2825 do want multiple matches in such cases, either use an ungreedy repeat
2826 ("a\ed+?") or set the PCRE_NO_AUTO_POSSESS option when compiling.
2827 .
2828 .
2829 .SS "Error returns from \fBpcre_dfa_exec()\fP"
2830 .rs
2831 .sp
2832 The \fBpcre_dfa_exec()\fP function returns a negative number when it fails.
2833 Many of the errors are the same as for \fBpcre_exec()\fP, and these are
2834 described
2835 .\" HTML <a href="#errorlist">
2836 .\" </a>
2837 above.
2838 .\"
2839 There are in addition the following errors that are specific to
2840 \fBpcre_dfa_exec()\fP:
2841 .sp
2842 PCRE_ERROR_DFA_UITEM (-16)
2843 .sp
2844 This return is given if \fBpcre_dfa_exec()\fP encounters an item in the pattern
2845 that it does not support, for instance, the use of \eC or a back reference.
2846 .sp
2847 PCRE_ERROR_DFA_UCOND (-17)
2848 .sp
2849 This return is given if \fBpcre_dfa_exec()\fP encounters a condition item that
2850 uses a back reference for the condition, or a test for recursion in a specific
2851 group. These are not supported.
2852 .sp
2853 PCRE_ERROR_DFA_UMLIMIT (-18)
2854 .sp
2855 This return is given if \fBpcre_dfa_exec()\fP is called with an \fIextra\fP
2856 block that contains a setting of the \fImatch_limit\fP or
2857 \fImatch_limit_recursion\fP fields. This is not supported (these fields are
2858 meaningless for DFA matching).
2859 .sp
2860 PCRE_ERROR_DFA_WSSIZE (-19)
2861 .sp
2862 This return is given if \fBpcre_dfa_exec()\fP runs out of space in the
2863 \fIworkspace\fP vector.
2864 .sp
2865 PCRE_ERROR_DFA_RECURSE (-20)
2866 .sp
2867 When a recursive subpattern is processed, the matching function calls itself
2868 recursively, using private vectors for \fIovector\fP and \fIworkspace\fP. This
2869 error is given if the output vector is not large enough. This should be
2870 extremely rare, as a vector of size 1000 is used.
2871 .sp
2872 PCRE_ERROR_DFA_BADRESTART (-30)
2873 .sp
2874 When \fBpcre_dfa_exec()\fP is called with the \fBPCRE_DFA_RESTART\fP option,
2875 some plausibility checks are made on the contents of the workspace, which
2876 should contain data about the previous partial match. If any of these checks
2877 fail, this error is given.
2878 .
2879 .
2880 .SH "SEE ALSO"
2881 .rs
2882 .sp
2883 \fBpcre16\fP(3), \fBpcre32\fP(3), \fBpcrebuild\fP(3), \fBpcrecallout\fP(3),
2884 \fBpcrecpp(3)\fP(3), \fBpcrematching\fP(3), \fBpcrepartial\fP(3),
2885 \fBpcreposix\fP(3), \fBpcreprecompile\fP(3), \fBpcresample\fP(3),
2886 \fBpcrestack\fP(3).
2887 .
2888 .
2889 .SH AUTHOR
2890 .rs
2891 .sp
2892 .nf
2893 Philip Hazel
2894 University Computing Service
2895 Cambridge CB2 3QH, England.
2896 .fi
2897 .
2898 .
2899 .SH REVISION
2900 .rs
2901 .sp
2902 .nf
2903 Last updated: 12 November 2013
2904 Copyright (c) 1997-2013 University of Cambridge.
2905 .fi

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