/[pcre]/code/trunk/doc/pcre.txt
ViewVC logotype

Diff of /code/trunk/doc/pcre.txt

Parent Directory Parent Directory | Revision Log Revision Log | View Patch Patch

revision 69 by nigel, Sat Feb 24 21:40:18 2007 UTC revision 518 by ph10, Tue May 18 15:47:01 2010 UTC
# Line 1  Line 1 
1    -----------------------------------------------------------------------------
2  This file contains a concatenation of the PCRE man pages, converted to plain  This file contains a concatenation of the PCRE man pages, converted to plain
3  text format for ease of searching with a text editor, or for use on systems  text format for ease of searching with a text editor, or for use on systems
4  that do not have a man page processor. The small individual files that give  that do not have a man page processor. The small individual files that give
5  synopses of each function in the library have not been included. There are  synopses of each function in the library have not been included. Neither has
6  separate text files for the pcregrep and pcretest commands.  the pcredemo program. There are separate text files for the pcregrep and
7    pcretest commands.
8  -----------------------------------------------------------------------------  -----------------------------------------------------------------------------
9    
 NAME  
      PCRE - Perl-compatible regular expressions  
10    
11    PCRE(3)                                                                PCRE(3)
12    
 DESCRIPTION  
13    
14       The PCRE library is a set of functions that implement  regu-  NAME
15       lar  expression  pattern  matching using the same syntax and         PCRE - Perl-compatible regular expressions
      semantics as Perl, with just a few differences. The  current  
      implementation  of  PCRE  (release 4.x) corresponds approxi-  
      mately with Perl 5.8, including support  for  UTF-8  encoded  
      strings.    However,  this  support  has  to  be  explicitly  
      enabled; it is not the default.  
   
      PCRE is written in C and released as a C library. However, a  
      number  of  people  have  written wrappers and interfaces of  
      various kinds. A C++ class is included  in  these  contribu-  
      tions,  which  can  be found in the Contrib directory at the  
      primary FTP site, which is:  
   
      ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre  
   
      Details of exactly which Perl  regular  expression  features  
      are  and  are  not  supported  by PCRE are given in separate  
      documents. See the pcrepattern and pcrecompat pages.  
   
      Some features of PCRE can be included, excluded, or  changed  
      when  the library is built. The pcre_config() function makes  
      it possible for a client  to  discover  which  features  are  
      available.  Documentation  about  building  PCRE for various  
      operating systems can be found in the  README  file  in  the  
      source distribution.  
16    
17    
18  USER DOCUMENTATION  INTRODUCTION
19    
20       The user documentation for PCRE has been  split  up  into  a         The  PCRE  library is a set of functions that implement regular expres-
21       number  of  different sections. In the "man" format, each of         sion pattern matching using the same syntax and semantics as Perl, with
22       these is a separate "man page". In the HTML format, each  is         just  a few differences. Some features that appeared in Python and PCRE
23       a  separate  page,  linked from the index page. In the plain         before they appeared in Perl are also available using the  Python  syn-
24       text format, all the sections are concatenated, for ease  of         tax,  there  is  some  support for one or two .NET and Oniguruma syntax
25       searching. The sections are as follows:         items, and there is an option for requesting some  minor  changes  that
26           give better JavaScript compatibility.
27         pcre              this document  
28         pcreapi           details of PCRE's native API         The  current implementation of PCRE corresponds approximately with Perl
29         pcrebuild         options for building PCRE         5.10/5.11, including support for UTF-8 encoded strings and Unicode gen-
30         pcrecallout       details of the callout feature         eral  category properties. However, UTF-8 and Unicode support has to be
31         pcrecompat        discussion of Perl compatibility         explicitly enabled; it is not the default. The  Unicode  tables  corre-
32         pcregrep          description of the pcregrep command         spond to Unicode release 5.2.0.
33         pcrepattern       syntax and semantics of supported  
34                             regular expressions         In  addition to the Perl-compatible matching function, PCRE contains an
35         pcreperform       discussion of performance issues         alternative function that matches the same compiled patterns in a  dif-
36         pcreposix         the POSIX-compatible API         ferent way. In certain circumstances, the alternative function has some
37         pcresample        discussion of the sample program         advantages.  For a discussion of the two matching algorithms,  see  the
38         pcretest          the pcretest testing command         pcrematching page.
39    
40       In addition, in the "man" and HTML formats, there is a short         PCRE  is  written  in C and released as a C library. A number of people
41       page  for  each  library function, listing its arguments and         have written wrappers and interfaces of various kinds.  In  particular,
42       results.         Google  Inc.   have  provided  a comprehensive C++ wrapper. This is now
43           included as part of the PCRE distribution. The pcrecpp page has details
44           of  this  interface.  Other  people's contributions can be found in the
45           Contrib directory at the primary FTP site, which is:
46    
47           ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
48    
49           Details of exactly which Perl regular expression features are  and  are
50           not supported by PCRE are given in separate documents. See the pcrepat-
51           tern and pcrecompat pages. There is a syntax summary in the  pcresyntax
52           page.
53    
54           Some  features  of  PCRE can be included, excluded, or changed when the
55           library is built. The pcre_config() function makes it  possible  for  a
56           client  to  discover  which  features are available. The features them-
57           selves are described in the pcrebuild page. Documentation about  build-
58           ing  PCRE  for various operating systems can be found in the README and
59           NON-UNIX-USE files in the source distribution.
60    
61           The library contains a number of undocumented  internal  functions  and
62           data  tables  that  are  used by more than one of the exported external
63           functions, but which are not intended  for  use  by  external  callers.
64           Their  names  all begin with "_pcre_", which hopefully will not provoke
65           any name clashes. In some environments, it is possible to control which
66           external  symbols  are  exported when a shared library is built, and in
67           these cases the undocumented symbols are not exported.
68    
69    
70  LIMITATIONS  USER DOCUMENTATION
71    
72       There are some size limitations in PCRE but it is hoped that         The user documentation for PCRE comprises a number  of  different  sec-
73       they will never in practice be relevant.         tions.  In the "man" format, each of these is a separate "man page". In
74           the HTML format, each is a separate page, linked from the  index  page.
75           In  the  plain  text format, all the sections, except the pcredemo sec-
76           tion, are concatenated, for ease of searching. The sections are as fol-
77           lows:
78    
79             pcre              this document
80             pcre-config       show PCRE installation configuration information
81             pcreapi           details of PCRE's native C API
82             pcrebuild         options for building PCRE
83             pcrecallout       details of the callout feature
84             pcrecompat        discussion of Perl compatibility
85             pcrecpp           details of the C++ wrapper
86             pcredemo          a demonstration C program that uses PCRE
87             pcregrep          description of the pcregrep command
88             pcrematching      discussion of the two matching algorithms
89             pcrepartial       details of the partial matching facility
90             pcrepattern       syntax and semantics of supported
91                                 regular expressions
92             pcreperform       discussion of performance issues
93             pcreposix         the POSIX-compatible C API
94             pcreprecompile    details of saving and re-using precompiled patterns
95             pcresample        discussion of the pcredemo program
96             pcrestack         discussion of stack usage
97             pcresyntax        quick syntax reference
98             pcretest          description of the pcretest testing command
99    
100       The maximum length of a  compiled  pattern  is  65539  (sic)         In  addition,  in the "man" and HTML formats, there is a short page for
101       bytes  if PCRE is compiled with the default internal linkage         each C library function, listing its arguments and results.
      size of 2. If you want to process regular  expressions  that  
      are  truly  enormous,  you can compile PCRE with an internal  
      linkage size of 3 or 4 (see the README file  in  the  source  
      distribution  and  the pcrebuild documentation for details).  
      If these cases the limit is substantially larger.   However,  
      the speed of execution will be slower.  
   
      All values in repeating quantifiers must be less than 65536.  
      The maximum number of capturing subpatterns is 65535.  
   
      There is no limit to the  number  of  non-capturing  subpat-  
      terns,  but  the  maximum  depth  of nesting of all kinds of  
      parenthesized subpattern, including  capturing  subpatterns,  
      assertions, and other types of subpattern, is 200.  
   
      The maximum length of a subject string is the largest  posi-  
      tive number that an integer variable can hold. However, PCRE  
      uses recursion to handle subpatterns and indefinite  repeti-  
      tion.  This  means  that the available stack space may limit  
      the size of a subject string that can be processed  by  cer-  
      tain patterns.  
102    
103    
104  UTF-8 SUPPORT  LIMITATIONS
105    
106       Starting at release 3.3, PCRE has had some support for char-         There are some size limitations in PCRE but it is hoped that they  will
107       acter  strings  encoded in the UTF-8 format. For release 4.0         never in practice be relevant.
      this has been greatly extended to cover most common require-  
      ments.  
   
      In order process UTF-8  strings,  you  must  build  PCRE  to  
      include  UTF-8  support  in  the code, and, in addition, you  
      must call pcre_compile() with  the  PCRE_UTF8  option  flag.  
      When  you  do this, both the pattern and any subject strings  
      that are matched against it are  treated  as  UTF-8  strings  
      instead of just strings of bytes.  
   
      If you compile PCRE with UTF-8 support, but do not use it at  
      run  time,  the  library will be a bit bigger, but the addi-  
      tional run time overhead is limited to testing the PCRE_UTF8  
      flag in several places, so should not be very large.  
   
      The following comments apply when PCRE is running  in  UTF-8  
      mode:  
   
      1. PCRE assumes that the strings it is given  contain  valid  
      UTF-8  codes. It does not diagnose invalid UTF-8 strings. If  
      you pass invalid UTF-8 strings  to  PCRE,  the  results  are  
      undefined.  
   
      2. In a pattern, the escape sequence \x{...}, where the con-  
      tents  of  the  braces is a string of hexadecimal digits, is  
      interpreted as a UTF-8 character whose code  number  is  the  
      given  hexadecimal  number, for example: \x{1234}. If a non-  
      hexadecimal digit appears between the braces,  the  item  is  
      not  recognized.  This escape sequence can be used either as  
      a literal, or within a character class.  
   
      3. The original hexadecimal escape sequence, \xhh, matches a  
      two-byte UTF-8 character if the value is greater than 127.  
   
      4. Repeat quantifiers apply to  complete  UTF-8  characters,  
      not to individual bytes, for example: \x{100}{3}.  
   
      5. The dot metacharacter matches one UTF-8 character instead  
      of a single byte.  
   
      6. The escape sequence \C can be used to match a single byte  
      in UTF-8 mode, but its use can lead to some strange effects.  
   
      7. The character escapes \b, \B, \d, \D, \s, \S, \w, and  \W  
      correctly test characters of any code value, but the charac-  
      ters that PCRE recognizes as digits, spaces, or word charac-  
      ters  remain  the  same  set as before, all with values less  
      than 256.  
   
      8. Case-insensitive  matching  applies  only  to  characters  
      whose  values  are  less than 256. PCRE does not support the  
      notion of "case" for higher-valued characters.  
108    
109       9. PCRE does not support the use of Unicode tables and  pro-         The  maximum  length of a compiled pattern is 65539 (sic) bytes if PCRE
110       perties or the Perl escapes \p, \P, and \X.         is compiled with the default internal linkage size of 2. If you want to
111           process  regular  expressions  that are truly enormous, you can compile
112           PCRE with an internal linkage size of 3 or 4 (see the  README  file  in
113           the  source  distribution and the pcrebuild documentation for details).
114           In these cases the limit is substantially larger.  However,  the  speed
115           of execution is slower.
116    
117           All values in repeating quantifiers must be less than 65536.
118    
119           There is no limit to the number of parenthesized subpatterns, but there
120           can be no more than 65535 capturing subpatterns.
121    
122           The maximum length of name for a named subpattern is 32 characters, and
123           the maximum number of named subpatterns is 10000.
124    
125           The  maximum  length of a subject string is the largest positive number
126           that an integer variable can hold. However, when using the  traditional
127           matching function, PCRE uses recursion to handle subpatterns and indef-
128           inite repetition.  This means that the available stack space may  limit
129           the size of a subject string that can be processed by certain patterns.
130           For a discussion of stack issues, see the pcrestack documentation.
131    
132    
133    UTF-8 AND UNICODE PROPERTY SUPPORT
134    
135           From release 3.3, PCRE has  had  some  support  for  character  strings
136           encoded  in the UTF-8 format. For release 4.0 this was greatly extended
137           to cover most common requirements, and in release 5.0  additional  sup-
138           port for Unicode general category properties was added.
139    
140           In  order  process  UTF-8 strings, you must build PCRE to include UTF-8
141           support in the code, and, in addition,  you  must  call  pcre_compile()
142           with  the  PCRE_UTF8  option  flag,  or the pattern must start with the
143           sequence (*UTF8). When either of these is the case,  both  the  pattern
144           and  any  subject  strings  that  are matched against it are treated as
145           UTF-8 strings instead of strings of 1-byte characters.
146    
147           If you compile PCRE with UTF-8 support, but do not use it at run  time,
148           the  library will be a bit bigger, but the additional run time overhead
149           is limited to testing the PCRE_UTF8 flag occasionally, so should not be
150           very big.
151    
152           If PCRE is built with Unicode character property support (which implies
153           UTF-8 support), the escape sequences \p{..}, \P{..}, and  \X  are  sup-
154           ported.  The available properties that can be tested are limited to the
155           general category properties such as Lu for an upper case letter  or  Nd
156           for  a  decimal number, the Unicode script names such as Arabic or Han,
157           and the derived properties Any and L&. A full  list  is  given  in  the
158           pcrepattern documentation. Only the short names for properties are sup-
159           ported. For example, \p{L} matches a letter. Its Perl synonym,  \p{Let-
160           ter},  is  not  supported.   Furthermore,  in Perl, many properties may
161           optionally be prefixed by "Is", for compatibility with Perl  5.6.  PCRE
162           does not support this.
163    
164       Validity of UTF-8 strings
165    
166           When  you  set  the  PCRE_UTF8 flag, the strings passed as patterns and
167           subjects are (by default) checked for validity on entry to the relevant
168           functions.  From  release 7.3 of PCRE, the check is according the rules
169           of RFC 3629, which are themselves derived from the  Unicode  specifica-
170           tion.  Earlier  releases  of PCRE followed the rules of RFC 2279, which
171           allows the full range of 31-bit values (0 to 0x7FFFFFFF).  The  current
172           check allows only values in the range U+0 to U+10FFFF, excluding U+D800
173           to U+DFFF.
174    
175           The excluded code points are the "Low Surrogate Area"  of  Unicode,  of
176           which  the Unicode Standard says this: "The Low Surrogate Area does not
177           contain any  character  assignments,  consequently  no  character  code
178           charts or namelists are provided for this area. Surrogates are reserved
179           for use with UTF-16 and then must be used in pairs."  The  code  points
180           that  are  encoded  by  UTF-16  pairs are available as independent code
181           points in the UTF-8 encoding. (In  other  words,  the  whole  surrogate
182           thing is a fudge for UTF-16 which unfortunately messes up UTF-8.)
183    
184           If  an  invalid  UTF-8  string  is  passed  to  PCRE,  an  error return
185           (PCRE_ERROR_BADUTF8) is given. In some situations, you may already know
186           that your strings are valid, and therefore want to skip these checks in
187           order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag at
188           compile  time  or at run time, PCRE assumes that the pattern or subject
189           it is given (respectively) contains only valid  UTF-8  codes.  In  this
190           case, it does not diagnose an invalid UTF-8 string.
191    
192           If  you  pass  an  invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set,
193           what happens depends on why the string is invalid. If the  string  con-
194           forms to the "old" definition of UTF-8 (RFC 2279), it is processed as a
195           string of characters in the range 0  to  0x7FFFFFFF.  In  other  words,
196           apart from the initial validity test, PCRE (when in UTF-8 mode) handles
197           strings according to the more liberal rules of RFC  2279.  However,  if
198           the  string does not even conform to RFC 2279, the result is undefined.
199           Your program may crash.
200    
201           If you want to process strings  of  values  in  the  full  range  0  to
202           0x7FFFFFFF,  encoded in a UTF-8-like manner as per the old RFC, you can
203           set PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in
204           this situation, you will have to apply your own validity check.
205    
206       General comments about UTF-8 mode
207    
208           1.  An  unbraced  hexadecimal  escape sequence (such as \xb3) matches a
209           two-byte UTF-8 character if the value is greater than 127.
210    
211           2. Octal numbers up to \777 are recognized, and  match  two-byte  UTF-8
212           characters for values greater than \177.
213    
214           3.  Repeat quantifiers apply to complete UTF-8 characters, not to indi-
215           vidual bytes, for example: \x{100}{3}.
216    
217           4. The dot metacharacter matches one UTF-8 character instead of a  sin-
218           gle byte.
219    
220           5.  The  escape sequence \C can be used to match a single byte in UTF-8
221           mode, but its use can lead to some strange effects.  This  facility  is
222           not available in the alternative matching function, pcre_dfa_exec().
223    
224           6.  The  character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
225           test characters of any code value, but, by default, the characters that
226           PCRE  recognizes  as digits, spaces, or word characters remain the same
227           set as before, all with values less than 256. This  remains  true  even
228           when  PCRE  is built to include Unicode property support, because to do
229           otherwise would slow down PCRE in many common  cases.  Note  that  this
230           also applies to \b, because it is defined in terms of \w and \W. If you
231           really want to test for a wider sense of, say,  "digit",  you  can  use
232           explicit  Unicode property tests such as \p{Nd}.  Alternatively, if you
233           set the PCRE_UCP option, the way that the  character  escapes  work  is
234           changed  so that Unicode properties are used to determine which charac-
235           ters match. There are more details in the section on generic  character
236           types in the pcrepattern documentation.
237    
238           7.  Similarly,  characters that match the POSIX named character classes
239           are all low-valued characters, unless the PCRE_UCP option is set.
240    
241           8. However, the Perl 5.10 horizontal and vertical  whitespace  matching
242           escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char-
243           acters, whether or not PCRE_UCP is set.
244    
245           9. Case-insensitive matching applies only to  characters  whose  values
246           are  less than 128, unless PCRE is built with Unicode property support.
247           Even when Unicode property support is available, PCRE  still  uses  its
248           own  character  tables when checking the case of low-valued characters,
249           so as not to degrade performance.  The Unicode property information  is
250           used only for characters with higher values. Even when Unicode property
251           support is available, PCRE supports case-insensitive matching only when
252           there  is  a  one-to-one  mapping between a letter's cases. There are a
253           small number of many-to-one mappings in Unicode;  these  are  not  sup-
254           ported by PCRE.
255    
256    
257  AUTHOR  AUTHOR
258    
259       Philip Hazel <ph10@cam.ac.uk>         Philip Hazel
260       University Computing Service,         University Computing Service
261       Cambridge CB2 3QG, England.         Cambridge CB2 3QH, England.
262       Phone: +44 1223 334714  
263           Putting  an actual email address here seems to have been a spam magnet,
264           so I've taken it away. If you want to email me, use  my  two  initials,
265           followed by the two digits 10, at the domain cam.ac.uk.
266    
267    
268    REVISION
269    
270           Last updated: 12 May 2010
271           Copyright (c) 1997-2010 University of Cambridge.
272    ------------------------------------------------------------------------------
273    
274    
275    PCREBUILD(3)                                                      PCREBUILD(3)
276    
 Last updated: 04 February 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
277    
278  NAME  NAME
279       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
280    
281    
282  PCRE BUILD-TIME OPTIONS  PCRE BUILD-TIME OPTIONS
283    
284       This document describes the optional features of  PCRE  that         This  document  describes  the  optional  features  of PCRE that can be
285       can  be  selected when the library is compiled. They are all         selected when the library is compiled. It assumes use of the  configure
286       selected, or deselected, by providing options to the config-         script,  where the optional features are selected or deselected by pro-
287       ure  script  which  is run before the make command. The com-         viding options to configure before running the make  command.  However,
288       plete list of options  for  configure  (which  includes  the         the  same  options  can be selected in both Unix-like and non-Unix-like
289       standard  ones  such  as  the  selection of the installation         environments using the GUI facility of cmake-gui if you are using CMake
290       directory) can be obtained by running         instead of configure to build PCRE.
291    
292         ./configure --help         There  is  a  lot more information about building PCRE in non-Unix-like
293           environments in the file called NON_UNIX_USE, which is part of the PCRE
294       The following sections describe certain options whose  names         distribution.  You  should consult this file as well as the README file
295       begin  with  --enable  or  --disable. These settings specify         if you are building in a non-Unix-like environment.
296       changes to the defaults for the configure  command.  Because  
297       of  the  way  that  configure  works, --enable and --disable         The complete list of options for configure (which includes the standard
298       always come in pairs, so  the  complementary  option  always         ones  such  as  the  selection  of  the  installation directory) can be
299       exists  as  well, but as it specifies the default, it is not         obtained by running
300       described.  
301             ./configure --help
302    
303           The following sections include  descriptions  of  options  whose  names
304           begin with --enable or --disable. These settings specify changes to the
305           defaults for the configure command. Because of the way  that  configure
306           works,  --enable  and --disable always come in pairs, so the complemen-
307           tary option always exists as well, but as it specifies the default,  it
308           is not described.
309    
310    
311    C++ SUPPORT
312    
313           By default, the configure script will search for a C++ compiler and C++
314           header files. If it finds them, it automatically builds the C++ wrapper
315           library for PCRE. You can disable this by adding
316    
317             --disable-cpp
318    
319           to the configure command.
320    
321    
322  UTF-8 SUPPORT  UTF-8 SUPPORT
323    
324       To build PCRE with support for UTF-8 character strings, add         To build PCRE with support for UTF-8 Unicode character strings, add
325    
326             --enable-utf8
327    
328           to  the  configure  command.  Of  itself, this does not make PCRE treat
329           strings as UTF-8. As well as compiling PCRE with this option, you  also
330           have  have to set the PCRE_UTF8 option when you call the pcre_compile()
331           or pcre_compile2() functions.
332    
333         --enable-utf8         If you set --enable-utf8 when compiling in an EBCDIC environment,  PCRE
334           expects its input to be either ASCII or UTF-8 (depending on the runtime
335           option). It is not possible to support both EBCDIC and UTF-8  codes  in
336           the  same  version  of  the  library.  Consequently,  --enable-utf8 and
337           --enable-ebcdic are mutually exclusive.
338    
339       to the configure command. Of itself, this does not make PCRE  
340       treat  strings as UTF-8. As well as compiling PCRE with this  UNICODE CHARACTER PROPERTY SUPPORT
341       option, you also have have to set the PCRE_UTF8 option  when  
342       you call the pcre_compile() function.         UTF-8 support allows PCRE to process character values greater than  255
343           in  the  strings that it handles. On its own, however, it does not pro-
344           vide any facilities for accessing the properties of such characters. If
345           you  want  to  be able to use the pattern escapes \P, \p, and \X, which
346           refer to Unicode character properties, you must add
347    
348             --enable-unicode-properties
349    
350           to the configure command. This implies UTF-8 support, even if you  have
351           not explicitly requested it.
352    
353           Including  Unicode  property  support  adds around 30K of tables to the
354           PCRE library. Only the general category properties such as  Lu  and  Nd
355           are supported. Details are given in the pcrepattern documentation.
356    
357    
358  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
359    
360       By default, PCRE treats character 10 (linefeed) as the  new-         By  default,  PCRE interprets the linefeed (LF) character as indicating
361       line  character.  This  is  the  normal newline character on         the end of a line. This is the normal newline  character  on  Unix-like
362       Unix-like systems. You can compile PCRE to use character  13         systems.  You  can compile PCRE to use carriage return (CR) instead, by
363       (carriage return) instead by adding         adding
364    
365         --enable-newline-is-cr           --enable-newline-is-cr
366    
367       to the configure command. For completeness there is  also  a         to the  configure  command.  There  is  also  a  --enable-newline-is-lf
368       --enable-newline-is-lf  option,  which  explicitly specifies         option, which explicitly specifies linefeed as the newline character.
369       linefeed as the newline character.  
370           Alternatively, you can specify that line endings are to be indicated by
371           the two character sequence CRLF. If you want this, add
372    
373             --enable-newline-is-crlf
374    
375           to the configure command. There is a fourth option, specified by
376    
377             --enable-newline-is-anycrlf
378    
379           which causes PCRE to recognize any of the three sequences  CR,  LF,  or
380           CRLF as indicating a line ending. Finally, a fifth option, specified by
381    
382             --enable-newline-is-any
383    
384           causes PCRE to recognize any Unicode newline sequence.
385    
386           Whatever  line  ending convention is selected when PCRE is built can be
387           overridden when the library functions are called. At build time  it  is
388           conventional to use the standard for your operating system.
389    
390    
391    WHAT \R MATCHES
392    
393           By  default,  the  sequence \R in a pattern matches any Unicode newline
394           sequence, whatever has been selected as the line  ending  sequence.  If
395           you specify
396    
397             --enable-bsr-anycrlf
398    
399           the  default  is changed so that \R matches only CR, LF, or CRLF. What-
400           ever is selected when PCRE is built can be overridden when the  library
401           functions are called.
402    
403    
404  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
405    
406       The PCRE building process uses libtool to build both  shared         The  PCRE building process uses libtool to build both shared and static
407       and  static  Unix libraries by default. You can suppress one         Unix libraries by default. You can suppress one of these by adding  one
408       of these by adding one of         of
409    
410         --disable-shared           --disable-shared
411         --disable-static           --disable-static
412    
413       to the configure command, as required.         to the configure command, as required.
414    
415    
416  POSIX MALLOC USAGE  POSIX MALLOC USAGE
417    
418       When PCRE is called through the  POSIX  interface  (see  the         When PCRE is called through the POSIX interface (see the pcreposix doc-
419       pcreposix  documentation),  additional  working  storage  is         umentation), additional working storage is  required  for  holding  the
420       required for holding the pointers  to  capturing  substrings         pointers  to capturing substrings, because PCRE requires three integers
421       because  PCRE requires three integers per substring, whereas         per substring, whereas the POSIX interface provides only  two.  If  the
422       the POSIX interface provides only  two.  If  the  number  of         number of expected substrings is small, the wrapper function uses space
423       expected  substrings  is  small,  the  wrapper function uses         on the stack, because this is faster than using malloc() for each call.
424       space on the stack, because this is faster than  using  mal-         The default threshold above which the stack is no longer used is 10; it
425       loc()  for  each call. The default threshold above which the         can be changed by adding a setting such as
426       stack is no longer used is 10; it can be changed by adding a  
427       setting such as           --with-posix-malloc-threshold=20
428    
429         --with-posix-malloc-threshold=20         to the configure command.
430    
431       to the configure command.  
432    HANDLING VERY LARGE PATTERNS
433    
434           Within a compiled pattern, offset values are used  to  point  from  one
435           part  to another (for example, from an opening parenthesis to an alter-
436           nation metacharacter). By default, two-byte values are used  for  these
437           offsets,  leading  to  a  maximum size for a compiled pattern of around
438           64K. This is sufficient to handle all but the most  gigantic  patterns.
439           Nevertheless,  some  people do want to process truyl enormous patterns,
440           so it is possible to compile PCRE to use three-byte or  four-byte  off-
441           sets by adding a setting such as
442    
443             --with-link-size=3
444    
445           to  the  configure  command.  The value given must be 2, 3, or 4. Using
446           longer offsets slows down the operation of PCRE because it has to  load
447           additional bytes when handling them.
448    
449    
450    AVOIDING EXCESSIVE STACK USAGE
451    
452           When matching with the pcre_exec() function, PCRE implements backtrack-
453           ing by making recursive calls to an internal function  called  match().
454           In  environments  where  the size of the stack is limited, this can se-
455           verely limit PCRE's operation. (The Unix environment does  not  usually
456           suffer from this problem, but it may sometimes be necessary to increase
457           the maximum stack size.  There is a discussion in the  pcrestack  docu-
458           mentation.)  An alternative approach to recursion that uses memory from
459           the heap to remember data, instead of using recursive  function  calls,
460           has  been  implemented to work round the problem of limited stack size.
461           If you want to build a version of PCRE that works this way, add
462    
463             --disable-stack-for-recursion
464    
465           to the configure command. With this configuration, PCRE  will  use  the
466           pcre_stack_malloc  and pcre_stack_free variables to call memory manage-
467           ment functions. By default these point to malloc() and free(), but  you
468           can replace the pointers so that your own functions are used instead.
469    
470           Separate  functions  are  provided  rather  than  using pcre_malloc and
471           pcre_free because the  usage  is  very  predictable:  the  block  sizes
472           requested  are  always  the  same,  and  the blocks are always freed in
473           reverse order. A calling program might be able to  implement  optimized
474           functions  that  perform  better  than  malloc()  and free(). PCRE runs
475           noticeably more slowly when built in this way. This option affects only
476           the pcre_exec() function; it is not relevant for pcre_dfa_exec().
477    
478    
479  LIMITING PCRE RESOURCE USAGE  LIMITING PCRE RESOURCE USAGE
480    
481       Internally, PCRE has a  function  called  match()  which  it         Internally,  PCRE has a function called match(), which it calls repeat-
482       calls  repeatedly  (possibly  recursively) when performing a         edly  (sometimes  recursively)  when  matching  a  pattern   with   the
483       matching operation. By limiting the  number  of  times  this         pcre_exec()  function.  By controlling the maximum number of times this
484       function  may  be  called,  a  limit  can  be  placed on the         function may be called during a single matching operation, a limit  can
485       resources used by a single call to  pcre_exec().  The  limit         be  placed  on  the resources used by a single call to pcre_exec(). The
486       can  be  changed  at  run  time, as described in the pcreapi         limit can be changed at run time, as described in the pcreapi  documen-
487       documentation. The default is 10 million, but  this  can  be         tation.  The default is 10 million, but this can be changed by adding a
488       changed by adding a setting such as         setting such as
489    
490         --with-match-limit=500000           --with-match-limit=500000
491    
492       to the configure command.         to  the  configure  command.  This  setting  has  no  effect   on   the
493           pcre_dfa_exec() matching function.
494    
495           In  some  environments  it is desirable to limit the depth of recursive
496           calls of match() more strictly than the total number of calls, in order
497           to  restrict  the maximum amount of stack (or heap, if --disable-stack-
498           for-recursion is specified) that is used. A second limit controls this;
499           it  defaults  to  the  value  that is set for --with-match-limit, which
500           imposes no additional constraints. However, you can set a  lower  limit
501           by adding, for example,
502    
503  HANDLING VERY LARGE PATTERNS           --with-match-limit-recursion=10000
504    
505       Within a compiled pattern, offset values are used  to  point         to  the  configure  command.  This  value can also be overridden at run
506       from  one  part  to  another  (for  example, from an opening         time.
507       parenthesis to an  alternation  metacharacter).  By  default  
508       two-byte  values  are  used  for these offsets, leading to a  
509       maximum size for a compiled pattern of around 64K.  This  is  CREATING CHARACTER TABLES AT BUILD TIME
510       sufficient  to  handle  all  but the most gigantic patterns.  
511       Nevertheless, some people do want to process  enormous  pat-         PCRE uses fixed tables for processing characters whose code values  are
512       terns,  so  it is possible to compile PCRE to use three-byte         less  than 256. By default, PCRE is built with a set of tables that are
513       or four-byte offsets by adding a setting such as         distributed in the file pcre_chartables.c.dist. These  tables  are  for
514           ASCII codes only. If you add
515         --with-link-size=3  
516             --enable-rebuild-chartables
517       to the configure command. The value given must be 2,  3,  or  
518       4.  Using  longer  offsets  slows down the operation of PCRE         to  the  configure  command, the distributed tables are no longer used.
519       because it has to load additional bytes when handling them.         Instead, a program called dftables is compiled and  run.  This  outputs
520           the source for new set of tables, created in the default locale of your
521       If you build PCRE with an increased link size, test  2  (and         C runtime system. (This method of replacing the tables does not work if
522       test 5 if you are using UTF-8) will fail. Part of the output         you  are cross compiling, because dftables is run on the local host. If
523       of these tests is a representation of the compiled  pattern,         you need to create alternative tables when cross  compiling,  you  will
524       and this changes with the link size.         have to do so "by hand".)
525    
526    
527    USING EBCDIC CODE
528    
529           PCRE  assumes  by  default that it will run in an environment where the
530           character code is ASCII (or Unicode, which is  a  superset  of  ASCII).
531           This  is  the  case for most computer operating systems. PCRE can, how-
532           ever, be compiled to run in an EBCDIC environment by adding
533    
534             --enable-ebcdic
535    
536           to the configure command. This setting implies --enable-rebuild-charta-
537           bles.  You  should  only  use  it if you know that you are in an EBCDIC
538           environment (for example,  an  IBM  mainframe  operating  system).  The
539           --enable-ebcdic option is incompatible with --enable-utf8.
540    
541    
542    PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
543    
544           By default, pcregrep reads all files as plain text. You can build it so
545           that it recognizes files whose names end in .gz or .bz2, and reads them
546           with libz or libbz2, respectively, by adding one or both of
547    
548             --enable-pcregrep-libz
549             --enable-pcregrep-libbz2
550    
551           to the configure command. These options naturally require that the rel-
552           evant libraries are installed on your system. Configuration  will  fail
553           if they are not.
554    
555    
556    PCRETEST OPTION FOR LIBREADLINE SUPPORT
557    
558           If you add
559    
560             --enable-pcretest-libreadline
561    
562           to  the  configure  command,  pcretest  is  linked with the libreadline
563           library, and when its input is from a terminal, it reads it  using  the
564           readline() function. This provides line-editing and history facilities.
565           Note that libreadline is GPL-licensed, so if you distribute a binary of
566           pcretest linked in this way, there may be licensing issues.
567    
568           Setting  this  option  causes  the -lreadline option to be added to the
569           pcretest build. In many operating environments with  a  sytem-installed
570           libreadline this is sufficient. However, in some environments (e.g.  if
571           an unmodified distribution version of readline is in use),  some  extra
572           configuration  may  be necessary. The INSTALL file for libreadline says
573           this:
574    
575             "Readline uses the termcap functions, but does not link with the
576             termcap or curses library itself, allowing applications which link
577             with readline the to choose an appropriate library."
578    
579           If your environment has not been set up so that an appropriate  library
580           is automatically included, you may need to add something like
581    
582             LIBS="-ncurses"
583    
584           immediately before the configure command.
585    
586    
587    SEE ALSO
588    
589           pcreapi(3), pcre_config(3).
590    
591    
592    AUTHOR
593    
594           Philip Hazel
595           University Computing Service
596           Cambridge CB2 3QH, England.
597    
598    
599    REVISION
600    
601           Last updated: 29 September 2009
602           Copyright (c) 1997-2009 University of Cambridge.
603    ------------------------------------------------------------------------------
604    
605    
606    PCREMATCHING(3)                                                PCREMATCHING(3)
607    
 Last updated: 21 January 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
608    
609  NAME  NAME
610       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
611    
612    
613    PCRE MATCHING ALGORITHMS
614    
615           This document describes the two different algorithms that are available
616           in PCRE for matching a compiled regular expression against a given sub-
617           ject  string.  The  "standard"  algorithm  is  the  one provided by the
618           pcre_exec() function.  This works in the same was  as  Perl's  matching
619           function, and provides a Perl-compatible matching operation.
620    
621           An  alternative  algorithm is provided by the pcre_dfa_exec() function;
622           this operates in a different way, and is not  Perl-compatible.  It  has
623           advantages  and disadvantages compared with the standard algorithm, and
624           these are described below.
625    
626           When there is only one possible way in which a given subject string can
627           match  a pattern, the two algorithms give the same answer. A difference
628           arises, however, when there are multiple possibilities. For example, if
629           the pattern
630    
631             ^<.*>
632    
633           is matched against the string
634    
635             <something> <something else> <something further>
636    
637           there are three possible answers. The standard algorithm finds only one
638           of them, whereas the alternative algorithm finds all three.
639    
640    
641  SYNOPSIS OF PCRE API  REGULAR EXPRESSIONS AS TREES
642    
643       #include <pcre.h>         The set of strings that are matched by a regular expression can be rep-
644           resented  as  a  tree structure. An unlimited repetition in the pattern
645           makes the tree of infinite size, but it is still a tree.  Matching  the
646           pattern  to a given subject string (from a given starting point) can be
647           thought of as a search of the tree.  There are two  ways  to  search  a
648           tree:  depth-first  and  breadth-first, and these correspond to the two
649           matching algorithms provided by PCRE.
650    
      pcre *pcre_compile(const char *pattern, int options,  
           const char **errptr, int *erroffset,  
           const unsigned char *tableptr);  
651    
652       pcre_extra *pcre_study(const pcre *code, int options,  THE STANDARD MATCHING ALGORITHM
           const char **errptr);  
653    
654       int pcre_exec(const pcre *code, const pcre_extra *extra,         In the terminology of Jeffrey Friedl's book "Mastering Regular  Expres-
655            const char *subject, int length, int startoffset,         sions",  the  standard  algorithm  is an "NFA algorithm". It conducts a
656            int options, int *ovector, int ovecsize);         depth-first search of the pattern tree. That is, it  proceeds  along  a
657           single path through the tree, checking that the subject matches what is
658           required. When there is a mismatch, the algorithm  tries  any  alterna-
659           tives  at  the  current point, and if they all fail, it backs up to the
660           previous branch point in the  tree,  and  tries  the  next  alternative
661           branch  at  that  level.  This often involves backing up (moving to the
662           left) in the subject string as well.  The  order  in  which  repetition
663           branches  are  tried  is controlled by the greedy or ungreedy nature of
664           the quantifier.
665    
666       int pcre_copy_named_substring(const pcre *code,         If a leaf node is reached, a matching string has  been  found,  and  at
667            const char *subject, int *ovector,         that  point the algorithm stops. Thus, if there is more than one possi-
668            int stringcount, const char *stringname,         ble match, this algorithm returns the first one that it finds.  Whether
669            char *buffer, int buffersize);         this  is the shortest, the longest, or some intermediate length depends
670           on the way the greedy and ungreedy repetition quantifiers are specified
671           in the pattern.
672    
673       int pcre_copy_substring(const char *subject, int *ovector,         Because  it  ends  up  with a single path through the tree, it is rela-
674            int stringcount, int stringnumber, char *buffer,         tively straightforward for this algorithm to keep  track  of  the  sub-
675            int buffersize);         strings  that  are  matched  by portions of the pattern in parentheses.
676           This provides support for capturing parentheses and back references.
677    
      int pcre_get_named_substring(const pcre *code,  
           const char *subject, int *ovector,  
           int stringcount, const char *stringname,  
           const char **stringptr);  
678    
679       int pcre_get_stringnumber(const pcre *code,  THE ALTERNATIVE MATCHING ALGORITHM
           const char *name);  
680    
681       int pcre_get_substring(const char *subject, int *ovector,         This algorithm conducts a breadth-first search of  the  tree.  Starting
682            int stringcount, int stringnumber,         from  the  first  matching  point  in the subject, it scans the subject
683            const char **stringptr);         string from left to right, once, character by character, and as it does
684           this,  it remembers all the paths through the tree that represent valid
685           matches. In Friedl's terminology, this is a kind  of  "DFA  algorithm",
686           though  it is not implemented as a traditional finite state machine (it
687           keeps multiple states active simultaneously).
688    
689       int pcre_get_substring_list(const char *subject,         Although the general principle of this matching algorithm  is  that  it
690            int *ovector, int stringcount, const char ***listptr);         scans  the subject string only once, without backtracking, there is one
691           exception: when a lookaround assertion is encountered,  the  characters
692           following  or  preceding  the  current  point  have to be independently
693           inspected.
694    
695       void pcre_free_substring(const char *stringptr);         The scan continues until either the end of the subject is  reached,  or
696           there  are  no more unterminated paths. At this point, terminated paths
697           represent the different matching possibilities (if there are none,  the
698           match  has  failed).   Thus,  if there is more than one possible match,
699           this algorithm finds all of them, and in particular, it finds the long-
700           est.  There  is  an  option to stop the algorithm after the first match
701           (which is necessarily the shortest) is found.
702    
703       void pcre_free_substring_list(const char **stringptr);         Note that all the matches that are found start at the same point in the
704           subject. If the pattern
705    
706       const unsigned char *pcre_maketables(void);           cat(er(pillar)?)
707    
708       int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         is  matched  against the string "the caterpillar catchment", the result
709            int what, void *where);         will be the three strings "cat", "cater", and "caterpillar" that  start
710           at the fourth character of the subject. The algorithm does not automat-
711           ically move on to find matches that start at later positions.
712    
713           There are a number of features of PCRE regular expressions that are not
714           supported by the alternative matching algorithm. They are as follows:
715    
716       int pcre_info(const pcre *code, int *optptr, *firstcharptr);         1.  Because  the  algorithm  finds  all possible matches, the greedy or
717           ungreedy nature of repetition quantifiers is not relevant.  Greedy  and
718           ungreedy quantifiers are treated in exactly the same way. However, pos-
719           sessive quantifiers can make a difference when what follows could  also
720           match what is quantified, for example in a pattern like this:
721    
722       int pcre_config(int what, void *where);           ^a++\w!
723    
724       char *pcre_version(void);         This  pattern matches "aaab!" but not "aaa!", which would be matched by
725           a non-possessive quantifier. Similarly, if an atomic group is  present,
726           it  is matched as if it were a standalone pattern at the current point,
727           and the longest match is then "locked in" for the rest of  the  overall
728           pattern.
729    
730       void *(*pcre_malloc)(size_t);         2. When dealing with multiple paths through the tree simultaneously, it
731           is not straightforward to keep track of  captured  substrings  for  the
732           different  matching  possibilities,  and  PCRE's implementation of this
733           algorithm does not attempt to do this. This means that no captured sub-
734           strings are available.
735    
736       void (*pcre_free)(void *);         3.  Because no substrings are captured, back references within the pat-
737           tern are not supported, and cause errors if encountered.
738    
739       int (*pcre_callout)(pcre_callout_block *);         4. For the same reason, conditional expressions that use  a  backrefer-
740           ence  as  the  condition or test for a specific group recursion are not
741           supported.
742    
743           5. Because many paths through the tree may be  active,  the  \K  escape
744           sequence, which resets the start of the match when encountered (but may
745           be on some paths and not on others), is not  supported.  It  causes  an
746           error if encountered.
747    
748  PCRE API         6.  Callouts  are  supported, but the value of the capture_top field is
749           always 1, and the value of the capture_last field is always -1.
750    
751       PCRE has its own native API,  which  is  described  in  this         7. The \C escape sequence, which (in the standard algorithm) matches  a
752       document.  There  is  also  a  set of wrapper functions that         single  byte, even in UTF-8 mode, is not supported because the alterna-
753       correspond to the POSIX regular expression API.   These  are         tive algorithm moves through the subject  string  one  character  at  a
754       described in the pcreposix documentation.         time, for all active paths through the tree.
755    
756       The native API function prototypes are defined in the header         8.  Except for (*FAIL), the backtracking control verbs such as (*PRUNE)
757       file  pcre.h,  and  on  Unix  systems  the library itself is         are not supported. (*FAIL) is supported, and  behaves  like  a  failing
758       called libpcre.a, so can be accessed by adding -lpcre to the         negative assertion.
      command  for  linking  an  application  which  calls it. The  
      header file defines the macros PCRE_MAJOR and PCRE_MINOR  to  
      contain the major and minor release numbers for the library.  
      Applications can use these to include support for  different  
      releases.  
759    
      The functions pcre_compile(), pcre_study(), and  pcre_exec()  
      are  used  for compiling and matching regular expressions. A  
      sample program that demonstrates the simplest way  of  using  
      them  is  given in the file pcredemo.c. The pcresample docu-  
      mentation describes how to run it.  
760    
761       There are convenience functions for extracting captured sub-  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
      strings from a matched subject string. They are:  
762    
763         pcre_copy_substring()         Using  the alternative matching algorithm provides the following advan-
764         pcre_copy_named_substring()         tages:
        pcre_get_substring()  
        pcre_get_named_substring()  
        pcre_get_substring_list()  
765    
766       pcre_free_substring()  and  pcre_free_substring_list()   are         1. All possible matches (at a single point in the subject) are automat-
767       also  provided,  to  free  the  memory  used  for  extracted         ically  found,  and  in particular, the longest match is found. To find
768       strings.         more than one match using the standard algorithm, you have to do kludgy
769           things with callouts.
770    
771       The function pcre_maketables() is used (optionally) to build         2.  Because  the  alternative  algorithm  scans the subject string just
772       a  set of character tables in the current locale for passing         once, and never needs to backtrack, it is possible to  pass  very  long
773       to pcre_compile().         subject  strings  to  the matching function in several pieces, checking
774           for partial matching each time.  The  pcrepartial  documentation  gives
775           details of partial matching.
776    
      The function pcre_fullinfo() is used to find out information  
      about a compiled pattern; pcre_info() is an obsolete version  
      which returns only some of the available information, but is  
      retained   for   backwards   compatibility.    The  function  
      pcre_version() returns a pointer to a string containing  the  
      version of PCRE and its date of release.  
777    
778       The global variables  pcre_malloc  and  pcre_free  initially  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
      contain the entry points of the standard malloc() and free()  
      functions respectively. PCRE  calls  the  memory  management  
      functions  via  these  variables,  so  a calling program can  
      replace them if it  wishes  to  intercept  the  calls.  This  
      should be done before calling any PCRE functions.  
779    
780       The global variable pcre_callout initially contains NULL. It         The alternative algorithm suffers from a number of disadvantages:
781       can be set by the caller to a "callout" function, which PCRE  
782       will then call at specified points during a matching  opera-         1.  It  is  substantially  slower  than the standard algorithm. This is
783       tion. Details are given in the pcrecallout documentation.         partly because it has to search for all possible matches, but  is  also
784           because it is less susceptible to optimization.
785    
786           2. Capturing parentheses and back references are not supported.
787    
788           3. Although atomic groups are supported, their use does not provide the
789           performance advantage that it does for the standard algorithm.
790    
791    
792    AUTHOR
793    
794           Philip Hazel
795           University Computing Service
796           Cambridge CB2 3QH, England.
797    
798    
799    REVISION
800    
801           Last updated: 29 September 2009
802           Copyright (c) 1997-2009 University of Cambridge.
803    ------------------------------------------------------------------------------
804    
805    
806    PCREAPI(3)                                                          PCREAPI(3)
807    
808    
809    NAME
810           PCRE - Perl-compatible regular expressions
811    
812    
813    PCRE NATIVE API
814    
815           #include <pcre.h>
816    
817           pcre *pcre_compile(const char *pattern, int options,
818                const char **errptr, int *erroffset,
819                const unsigned char *tableptr);
820    
821           pcre *pcre_compile2(const char *pattern, int options,
822                int *errorcodeptr,
823                const char **errptr, int *erroffset,
824                const unsigned char *tableptr);
825    
826           pcre_extra *pcre_study(const pcre *code, int options,
827                const char **errptr);
828    
829           int pcre_exec(const pcre *code, const pcre_extra *extra,
830                const char *subject, int length, int startoffset,
831                int options, int *ovector, int ovecsize);
832    
833           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
834                const char *subject, int length, int startoffset,
835                int options, int *ovector, int ovecsize,
836                int *workspace, int wscount);
837    
838           int pcre_copy_named_substring(const pcre *code,
839                const char *subject, int *ovector,
840                int stringcount, const char *stringname,
841                char *buffer, int buffersize);
842    
843           int pcre_copy_substring(const char *subject, int *ovector,
844                int stringcount, int stringnumber, char *buffer,
845                int buffersize);
846    
847           int pcre_get_named_substring(const pcre *code,
848                const char *subject, int *ovector,
849                int stringcount, const char *stringname,
850                const char **stringptr);
851    
852           int pcre_get_stringnumber(const pcre *code,
853                const char *name);
854    
855           int pcre_get_stringtable_entries(const pcre *code,
856                const char *name, char **first, char **last);
857    
858           int pcre_get_substring(const char *subject, int *ovector,
859                int stringcount, int stringnumber,
860                const char **stringptr);
861    
862           int pcre_get_substring_list(const char *subject,
863                int *ovector, int stringcount, const char ***listptr);
864    
865           void pcre_free_substring(const char *stringptr);
866    
867           void pcre_free_substring_list(const char **stringptr);
868    
869           const unsigned char *pcre_maketables(void);
870    
871           int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
872                int what, void *where);
873    
874           int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
875    
876           int pcre_refcount(pcre *code, int adjust);
877    
878           int pcre_config(int what, void *where);
879    
880           char *pcre_version(void);
881    
882           void *(*pcre_malloc)(size_t);
883    
884           void (*pcre_free)(void *);
885    
886           void *(*pcre_stack_malloc)(size_t);
887    
888           void (*pcre_stack_free)(void *);
889    
890           int (*pcre_callout)(pcre_callout_block *);
891    
892    
893    PCRE API OVERVIEW
894    
895           PCRE has its own native API, which is described in this document. There
896           are also some wrapper functions that correspond to  the  POSIX  regular
897           expression  API.  These  are  described in the pcreposix documentation.
898           Both of these APIs define a set of C function calls. A C++  wrapper  is
899           distributed with PCRE. It is documented in the pcrecpp page.
900    
901           The  native  API  C  function prototypes are defined in the header file
902           pcre.h, and on Unix systems the library itself is called  libpcre.   It
903           can normally be accessed by adding -lpcre to the command for linking an
904           application  that  uses  PCRE.  The  header  file  defines  the  macros
905           PCRE_MAJOR  and  PCRE_MINOR to contain the major and minor release num-
906           bers for the library.  Applications can use these  to  include  support
907           for different releases of PCRE.
908    
909           The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and
910           pcre_exec() are used for compiling and matching regular expressions  in
911           a  Perl-compatible  manner. A sample program that demonstrates the sim-
912           plest way of using them is provided in the file  called  pcredemo.c  in
913           the PCRE source distribution. A listing of this program is given in the
914           pcredemo documentation, and the pcresample documentation describes  how
915           to compile and run it.
916    
917           A second matching function, pcre_dfa_exec(), which is not Perl-compati-
918           ble, is also provided. This uses a different algorithm for  the  match-
919           ing.  The  alternative algorithm finds all possible matches (at a given
920           point in the subject), and scans the subject just  once  (unless  there
921           are  lookbehind  assertions).  However,  this algorithm does not return
922           captured substrings. A description of the two matching  algorithms  and
923           their  advantages  and disadvantages is given in the pcrematching docu-
924           mentation.
925    
926           In addition to the main compiling and  matching  functions,  there  are
927           convenience functions for extracting captured substrings from a subject
928           string that is matched by pcre_exec(). They are:
929    
930             pcre_copy_substring()
931             pcre_copy_named_substring()
932             pcre_get_substring()
933             pcre_get_named_substring()
934             pcre_get_substring_list()
935             pcre_get_stringnumber()
936             pcre_get_stringtable_entries()
937    
938           pcre_free_substring() and pcre_free_substring_list() are also provided,
939           to free the memory used for extracted strings.
940    
941           The  function  pcre_maketables()  is  used  to build a set of character
942           tables  in  the  current  locale   for   passing   to   pcre_compile(),
943           pcre_exec(),  or  pcre_dfa_exec(). This is an optional facility that is
944           provided for specialist use.  Most  commonly,  no  special  tables  are
945           passed,  in  which case internal tables that are generated when PCRE is
946           built are used.
947    
948           The function pcre_fullinfo() is used to find out  information  about  a
949           compiled  pattern; pcre_info() is an obsolete version that returns only
950           some of the available information, but is retained for  backwards  com-
951           patibility.   The function pcre_version() returns a pointer to a string
952           containing the version of PCRE and its date of release.
953    
954           The function pcre_refcount() maintains a  reference  count  in  a  data
955           block  containing  a compiled pattern. This is provided for the benefit
956           of object-oriented applications.
957    
958           The global variables pcre_malloc and pcre_free  initially  contain  the
959           entry  points  of  the  standard malloc() and free() functions, respec-
960           tively. PCRE calls the memory management functions via these variables,
961           so  a  calling  program  can replace them if it wishes to intercept the
962           calls. This should be done before calling any PCRE functions.
963    
964           The global variables pcre_stack_malloc  and  pcre_stack_free  are  also
965           indirections  to  memory  management functions. These special functions
966           are used only when PCRE is compiled to use  the  heap  for  remembering
967           data, instead of recursive function calls, when running the pcre_exec()
968           function. See the pcrebuild documentation for  details  of  how  to  do
969           this.  It  is  a non-standard way of building PCRE, for use in environ-
970           ments that have limited stacks. Because of the greater  use  of  memory
971           management,  it  runs  more  slowly. Separate functions are provided so
972           that special-purpose external code can be  used  for  this  case.  When
973           used,  these  functions  are always called in a stack-like manner (last
974           obtained, first freed), and always for memory blocks of the same  size.
975           There  is  a discussion about PCRE's stack usage in the pcrestack docu-
976           mentation.
977    
978           The global variable pcre_callout initially contains NULL. It can be set
979           by  the  caller  to  a "callout" function, which PCRE will then call at
980           specified points during a matching operation. Details are given in  the
981           pcrecallout documentation.
982    
983    
984    NEWLINES
985    
986           PCRE  supports five different conventions for indicating line breaks in
987           strings: a single CR (carriage return) character, a  single  LF  (line-
988           feed) character, the two-character sequence CRLF, any of the three pre-
989           ceding, or any Unicode newline sequence. The Unicode newline  sequences
990           are  the  three just mentioned, plus the single characters VT (vertical
991           tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS  (line
992           separator, U+2028), and PS (paragraph separator, U+2029).
993    
994           Each  of  the first three conventions is used by at least one operating
995           system as its standard newline sequence. When PCRE is built, a  default
996           can  be  specified.  The default default is LF, which is the Unix stan-
997           dard. When PCRE is run, the default can be overridden,  either  when  a
998           pattern is compiled, or when it is matched.
999    
1000           At compile time, the newline convention can be specified by the options
1001           argument of pcre_compile(), or it can be specified by special  text  at
1002           the start of the pattern itself; this overrides any other settings. See
1003           the pcrepattern page for details of the special character sequences.
1004    
1005           In the PCRE documentation the word "newline" is used to mean "the char-
1006           acter  or pair of characters that indicate a line break". The choice of
1007           newline convention affects the handling of  the  dot,  circumflex,  and
1008           dollar metacharacters, the handling of #-comments in /x mode, and, when
1009           CRLF is a recognized line ending sequence, the match position  advance-
1010           ment for a non-anchored pattern. There is more detail about this in the
1011           section on pcre_exec() options below.
1012    
1013           The choice of newline convention does not affect the interpretation  of
1014           the  \n  or  \r  escape  sequences, nor does it affect what \R matches,
1015           which is controlled in a similar way, but by separate options.
1016    
1017    
1018  MULTITHREADING  MULTITHREADING
1019    
1020       The PCRE functions can be used in  multi-threading  applica-         The PCRE functions can be used in  multi-threading  applications,  with
1021       tions, with the proviso that the memory management functions         the  proviso  that  the  memory  management  functions  pointed  to  by
1022       pointed to by pcre_malloc and  pcre_free,  and  the  callout         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
1023       function  pointed  to  by  pcre_callout,  are  shared by all         callout function pointed to by pcre_callout, are shared by all threads.
1024       threads.  
1025           The  compiled form of a regular expression is not altered during match-
1026       The compiled form of a regular  expression  is  not  altered         ing, so the same compiled pattern can safely be used by several threads
1027       during  matching, so the same compiled pattern can safely be         at once.
1028       used by several threads at once.  
1029    
1030    SAVING PRECOMPILED PATTERNS FOR LATER USE
1031    
1032           The compiled form of a regular expression can be saved and re-used at a
1033           later time, possibly by a different program, and even on a  host  other
1034           than  the  one  on  which  it  was  compiled.  Details are given in the
1035           pcreprecompile documentation. However, compiling a  regular  expression
1036           with  one version of PCRE for use with a different version is not guar-
1037           anteed to work and may cause crashes.
1038    
1039    
1040  CHECKING BUILD-TIME OPTIONS  CHECKING BUILD-TIME OPTIONS
1041    
1042       int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
1043    
1044           The function pcre_config() makes it possible for a PCRE client to  dis-
1045           cover which optional features have been compiled into the PCRE library.
1046           The pcrebuild documentation has more details about these optional  fea-
1047           tures.
1048    
1049           The  first  argument  for pcre_config() is an integer, specifying which
1050           information is required; the second argument is a pointer to a variable
1051           into  which  the  information  is  placed. The following information is
1052           available:
1053    
1054             PCRE_CONFIG_UTF8
1055    
1056           The output is an integer that is set to one if UTF-8 support is  avail-
1057           able; otherwise it is set to zero.
1058    
1059             PCRE_CONFIG_UNICODE_PROPERTIES
1060    
1061       The function pcre_config() makes  it  possible  for  a  PCRE         The  output  is  an  integer  that is set to one if support for Unicode
1062       client  to  discover  which optional features have been com-         character properties is available; otherwise it is set to zero.
      piled into the PCRE library. The pcrebuild documentation has  
      more details about these optional features.  
1063    
1064       The first argument for pcre_config() is an integer, specify-           PCRE_CONFIG_NEWLINE
      ing  which information is required; the second argument is a  
      pointer to a variable into which the information is  placed.  
      The following information is available:  
1065    
1066         PCRE_CONFIG_UTF8         The output is an integer whose value specifies  the  default  character
1067           sequence  that is recognized as meaning "newline". The four values that
1068           are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
1069           and  -1  for  ANY.  Though they are derived from ASCII, the same values
1070           are returned in EBCDIC environments. The default should normally corre-
1071           spond to the standard sequence for your operating system.
1072    
1073       The output is an integer that is set to one if UTF-8 support           PCRE_CONFIG_BSR
      is available; otherwise it is set to zero.  
1074    
1075         PCRE_CONFIG_NEWLINE         The output is an integer whose value indicates what character sequences
1076           the \R escape sequence matches by default. A value of 0 means  that  \R
1077           matches  any  Unicode  line ending sequence; a value of 1 means that \R
1078           matches only CR, LF, or CRLF. The default can be overridden when a pat-
1079           tern is compiled or matched.
1080    
1081       The output is an integer that is set to  the  value  of  the           PCRE_CONFIG_LINK_SIZE
      code  that  is  used for the newline character. It is either  
      linefeed (10) or carriage return (13), and  should  normally  
      be the standard character for your operating system.  
1082    
1083         PCRE_CONFIG_LINK_SIZE         The  output  is  an  integer that contains the number of bytes used for
1084           internal linkage in compiled regular expressions. The value is 2, 3, or
1085           4.  Larger  values  allow larger regular expressions to be compiled, at
1086           the expense of slower matching. The default value of  2  is  sufficient
1087           for  all  but  the  most massive patterns, since it allows the compiled
1088           pattern to be up to 64K in size.
1089    
1090       The output is an integer that contains the number  of  bytes           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
      used  for  internal linkage in compiled regular expressions.  
      The value is 2, 3, or 4. Larger values allow larger  regular  
      expressions  to be compiled, at the expense of slower match-  
      ing. The default value of 2 is sufficient for  all  but  the  
      most  massive patterns, since it allows the compiled pattern  
      to be up to 64K in size.  
1091    
1092         PCRE_CONFIG_POSIX_MALLOC_THRESHOLD         The output is an integer that contains the threshold  above  which  the
1093           POSIX  interface  uses malloc() for output vectors. Further details are
1094           given in the pcreposix documentation.
1095    
1096       The output is an integer that contains the  threshold  above           PCRE_CONFIG_MATCH_LIMIT
      which  the POSIX interface uses malloc() for output vectors.  
      Further details are given in the pcreposix documentation.  
1097    
1098         PCRE_CONFIG_MATCH_LIMIT         The output is a long integer that gives the default limit for the  num-
1099           ber  of  internal  matching  function calls in a pcre_exec() execution.
1100           Further details are given with pcre_exec() below.
1101    
1102       The output is an integer that gives the  default  limit  for           PCRE_CONFIG_MATCH_LIMIT_RECURSION
1103       the   number  of  internal  matching  function  calls  in  a  
1104       pcre_exec()  execution.  Further  details  are  given   with         The output is a long integer that gives the default limit for the depth
1105       pcre_exec() below.         of   recursion  when  calling  the  internal  matching  function  in  a
1106           pcre_exec() execution.  Further  details  are  given  with  pcre_exec()
1107           below.
1108    
1109             PCRE_CONFIG_STACKRECURSE
1110    
1111           The  output is an integer that is set to one if internal recursion when
1112           running pcre_exec() is implemented by recursive function calls that use
1113           the  stack  to remember their state. This is the usual way that PCRE is
1114           compiled. The output is zero if PCRE was compiled to use blocks of data
1115           on  the  heap  instead  of  recursive  function  calls.  In  this case,
1116           pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory
1117           blocks on the heap, thus avoiding the use of the stack.
1118    
1119    
1120  COMPILING A PATTERN  COMPILING A PATTERN
1121    
1122       pcre *pcre_compile(const char *pattern, int options,         pcre *pcre_compile(const char *pattern, int options,
1123            const char **errptr, int *erroffset,              const char **errptr, int *erroffset,
1124            const unsigned char *tableptr);              const unsigned char *tableptr);
1125    
1126       The function pcre_compile() is called to compile  a  pattern         pcre *pcre_compile2(const char *pattern, int options,
1127       into  an internal form. The pattern is a C string terminated              int *errorcodeptr,
1128       by a binary zero, and is passed in the argument  pattern.  A              const char **errptr, int *erroffset,
1129       pointer  to  a  single  block of memory that is obtained via              const unsigned char *tableptr);
1130       pcre_malloc is returned. This contains the compiled code and  
1131       related  data.  The  pcre  type  is defined for the returned         Either of the functions pcre_compile() or pcre_compile2() can be called
1132       block; this is a typedef for a structure whose contents  are         to compile a pattern into an internal form. The only difference between
1133       not  externally  defined. It is up to the caller to free the         the  two interfaces is that pcre_compile2() has an additional argument,
1134       memory when it is no longer required.         errorcodeptr, via which a numerical error  code  can  be  returned.  To
1135           avoid  too  much repetition, we refer just to pcre_compile() below, but
1136       Although the compiled code of a PCRE regex  is  relocatable,         the information applies equally to pcre_compile2().
1137       that is, it does not depend on memory location, the complete  
1138       pcre data block is not fully relocatable,  because  it  con-         The pattern is a C string terminated by a binary zero, and is passed in
1139       tains  a  copy of the tableptr argument, which is an address         the  pattern  argument.  A  pointer to a single block of memory that is
1140       (see below).         obtained via pcre_malloc is returned. This contains the  compiled  code
1141       The options argument contains independent bits  that  affect         and related data. The pcre type is defined for the returned block; this
1142       the  compilation.  It  should  be  zero  if  no  options are         is a typedef for a structure whose contents are not externally defined.
1143       required. Some of the options, in particular, those that are         It is up to the caller to free the memory (via pcre_free) when it is no
1144       compatible  with Perl, can also be set and unset from within         longer required.
1145       the pattern (see the detailed description of regular expres-  
1146       sions  in the pcrepattern documentation). For these options,         Although the compiled code of a PCRE regex is relocatable, that is,  it
1147       the contents of the options argument specifies their initial         does not depend on memory location, the complete pcre data block is not
1148       settings  at  the  start  of  compilation and execution. The         fully relocatable, because it may contain a copy of the tableptr  argu-
1149       PCRE_ANCHORED option can be set at the time of  matching  as         ment, which is an address (see below).
1150       well as at compile time.  
1151           The options argument contains various bit settings that affect the com-
1152       If errptr is NULL, pcre_compile() returns NULL  immediately.         pilation. It should be zero if no options are required.  The  available
1153       Otherwise, if compilation of a pattern fails, pcre_compile()         options  are  described  below. Some of them (in particular, those that
1154       returns NULL, and sets the variable pointed to by errptr  to         are compatible with Perl, but some others as well) can also be set  and
1155       point  to a textual error message. The offset from the start         unset  from  within  the  pattern  (see the detailed description in the
1156       of  the  pattern  to  the  character  where  the  error  was         pcrepattern documentation). For those options that can be different  in
1157       discovered   is   placed  in  the  variable  pointed  to  by         different  parts  of  the pattern, the contents of the options argument
1158       erroffset, which must not be NULL. If it  is,  an  immediate         specifies their settings at the start of compilation and execution. The
1159       error is given.         PCRE_ANCHORED, PCRE_BSR_xxx, and PCRE_NEWLINE_xxx options can be set at
1160           the time of matching as well as at compile time.
1161       If the final  argument,  tableptr,  is  NULL,  PCRE  uses  a  
1162       default  set  of character tables which are built when it is         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1163       compiled, using the default C  locale.  Otherwise,  tableptr         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and
1164       must  be  the result of a call to pcre_maketables(). See the         sets the variable pointed to by errptr to point to a textual error mes-
1165       section on locale support below.         sage. This is a static string that is part of the library. You must not
1166           try to free it. The byte offset from the start of the  pattern  to  the
1167       This code fragment shows a typical straightforward  call  to         character  that  was  being  processed when the error was discovered is
1168       pcre_compile():         placed in the variable pointed to by erroffset, which must not be NULL.
1169           If  it  is,  an  immediate error is given. Some errors are not detected
1170         pcre *re;         until checks are carried out when the whole pattern has  been  scanned;
1171         const char *error;         in this case the offset is set to the end of the pattern.
1172         int erroffset;  
1173         re = pcre_compile(         If  pcre_compile2()  is  used instead of pcre_compile(), and the error-
1174           "^A.*Z",          /* the pattern */         codeptr argument is not NULL, a non-zero error code number is  returned
1175           0,                /* default options */         via  this argument in the event of an error. This is in addition to the
1176           &error,           /* for error message */         textual error message. Error codes and messages are listed below.
1177           &erroffset,       /* for error offset */  
1178           NULL);            /* use default character tables */         If the final argument, tableptr, is NULL, PCRE uses a  default  set  of
1179           character  tables  that  are  built  when  PCRE  is compiled, using the
1180       The following option bits are defined:         default C locale. Otherwise, tableptr must be an address  that  is  the
1181           result  of  a  call to pcre_maketables(). This value is stored with the
1182         PCRE_ANCHORED         compiled pattern, and used again by pcre_exec(), unless  another  table
1183           pointer is passed to it. For more discussion, see the section on locale
1184       If this bit is set, the pattern is forced to be  "anchored",         support below.
1185       that is, it is constrained to match only at the first match-  
1186       ing point in the string which is being searched  (the  "sub-         This code fragment shows a typical straightforward  call  to  pcre_com-
1187       ject string"). This effect can also be achieved by appropri-         pile():
1188       ate constructs in the pattern itself, which is the only  way  
1189       to do it in Perl.           pcre *re;
1190             const char *error;
1191         PCRE_CASELESS           int erroffset;
1192             re = pcre_compile(
1193       If this bit is set, letters in the pattern match both  upper             "^A.*Z",          /* the pattern */
1194       and  lower  case  letters.  It  is  equivalent  to Perl's /i             0,                /* default options */
1195       option, and it can be changed within a  pattern  by  a  (?i)             &error,           /* for error message */
1196       option setting.             &erroffset,       /* for error offset */
1197               NULL);            /* use default character tables */
1198         PCRE_DOLLAR_ENDONLY  
1199           The  following  names  for option bits are defined in the pcre.h header
1200       If this bit is set, a dollar metacharacter  in  the  pattern         file:
1201       matches  only at the end of the subject string. Without this  
1202       option, a dollar also matches immediately before  the  final           PCRE_ANCHORED
1203       character  if it is a newline (but not before any other new-  
1204       lines).  The  PCRE_DOLLAR_ENDONLY  option  is   ignored   if         If this bit is set, the pattern is forced to be "anchored", that is, it
1205       PCRE_MULTILINE is set. There is no equivalent to this option         is  constrained to match only at the first matching point in the string
1206       in Perl, and no way to set it within a pattern.         that is being searched (the "subject string"). This effect can also  be
1207           achieved  by appropriate constructs in the pattern itself, which is the
1208         PCRE_DOTALL         only way to do it in Perl.
1209    
1210       If this bit is  set,  a  dot  metacharater  in  the  pattern           PCRE_AUTO_CALLOUT
1211       matches all characters, including newlines. Without it, new-  
1212       lines are excluded. This option is equivalent to  Perl's  /s         If this bit is set, pcre_compile() automatically inserts callout items,
1213       option,  and  it  can  be changed within a pattern by a (?s)         all  with  number  255, before each pattern item. For discussion of the
1214       option setting. A negative class such as [^a] always matches         callout facility, see the pcrecallout documentation.
1215       a  newline  character,  independent  of  the setting of this  
1216       option.           PCRE_BSR_ANYCRLF
1217             PCRE_BSR_UNICODE
1218         PCRE_EXTENDED  
1219           These options (which are mutually exclusive) control what the \R escape
1220       If this bit is set, whitespace data characters in  the  pat-         sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1221       tern  are  totally  ignored  except when escaped or inside a         or to match any Unicode newline sequence. The default is specified when
1222       character class. Whitespace does not include the VT  charac-         PCRE is built. It can be overridden from within the pattern, or by set-
1223       ter  (code 11). In addition, characters between an unescaped         ting an option when a compiled pattern is matched.
1224       # outside a character class and the next newline  character,  
1225       inclusive, are also ignored. This is equivalent to Perl's /x           PCRE_CASELESS
1226       option, and it can be changed within a  pattern  by  a  (?x)  
1227       option setting.         If this bit is set, letters in the pattern match both upper  and  lower
1228           case  letters.  It  is  equivalent  to  Perl's /i option, and it can be
1229       This option makes it possible  to  include  comments  inside         changed within a pattern by a (?i) option setting. In UTF-8 mode,  PCRE
1230       complicated patterns.  Note, however, that this applies only         always  understands the concept of case for characters whose values are
1231       to data characters. Whitespace characters may  never  appear         less than 128, so caseless matching is always possible. For  characters
1232       within special character sequences in a pattern, for example         with  higher  values,  the concept of case is supported if PCRE is com-
1233       within the sequence (?( which introduces a conditional  sub-         piled with Unicode property support, but not otherwise. If you want  to
1234       pattern.         use  caseless  matching  for  characters 128 and above, you must ensure
1235           that PCRE is compiled with Unicode property support  as  well  as  with
1236         PCRE_EXTRA         UTF-8 support.
1237    
1238       This option was invented in  order  to  turn  on  additional           PCRE_DOLLAR_ENDONLY
1239       functionality of PCRE that is incompatible with Perl, but it  
1240       is currently of very little use. When set, any backslash  in         If  this bit is set, a dollar metacharacter in the pattern matches only
1241       a  pattern  that is followed by a letter that has no special         at the end of the subject string. Without this option,  a  dollar  also
1242       meaning causes an error, thus reserving  these  combinations         matches  immediately before a newline at the end of the string (but not
1243       for  future  expansion.  By default, as in Perl, a backslash         before any other newlines). The PCRE_DOLLAR_ENDONLY option  is  ignored
1244       followed by a letter with no special meaning is treated as a         if  PCRE_MULTILINE  is  set.   There is no equivalent to this option in
1245       literal.  There  are at present no other features controlled         Perl, and no way to set it within a pattern.
1246       by this option. It can also be set by a (?X) option  setting  
1247       within a pattern.           PCRE_DOTALL
1248    
1249         PCRE_MULTILINE         If this bit is set, a dot metacharater in the pattern matches all char-
1250           acters,  including  those that indicate newline. Without it, a dot does
1251       By default, PCRE treats the subject string as consisting  of         not match when the current position is at a  newline.  This  option  is
1252       a  single "line" of characters (even if it actually contains         equivalent  to Perl's /s option, and it can be changed within a pattern
1253       several newlines). The "start  of  line"  metacharacter  (^)         by a (?s) option setting. A negative class such as [^a] always  matches
1254       matches  only  at the start of the string, while the "end of         newline characters, independent of the setting of this option.
1255       line" metacharacter ($) matches  only  at  the  end  of  the  
1256       string,    or   before   a   terminating   newline   (unless           PCRE_DUPNAMES
1257       PCRE_DOLLAR_ENDONLY is set). This is the same as Perl.  
1258           If  this  bit is set, names used to identify capturing subpatterns need
1259       When PCRE_MULTILINE it is set, the "start of line" and  "end         not be unique. This can be helpful for certain types of pattern when it
1260       of  line"  constructs match immediately following or immedi-         is  known  that  only  one instance of the named subpattern can ever be
1261       ately before any newline  in  the  subject  string,  respec-         matched. There are more details of named subpatterns  below;  see  also
1262       tively,  as  well  as  at  the  very  start and end. This is         the pcrepattern documentation.
1263       equivalent to Perl's /m option, and it can be changed within  
1264       a  pattern  by  a  (?m) option setting. If there are no "\n"           PCRE_EXTENDED
1265       characters in a subject string, or no occurrences of ^ or  $  
1266       in a pattern, setting PCRE_MULTILINE has no effect.         If  this  bit  is  set,  whitespace  data characters in the pattern are
1267           totally ignored except when escaped or inside a character class. White-
1268         PCRE_NO_AUTO_CAPTURE         space does not include the VT character (code 11). In addition, charac-
1269           ters between an unescaped # outside a character class and the next new-
1270       If this option is set, it disables the use of numbered  cap-         line,  inclusive,  are  also  ignored.  This is equivalent to Perl's /x
1271       turing  parentheses  in the pattern. Any opening parenthesis         option, and it can be changed within a pattern by a  (?x)  option  set-
1272       that is not followed by ? behaves as if it were followed  by         ting.
1273       ?:  but  named  parentheses  can still be used for capturing  
1274       (and they acquire numbers in the usual  way).  There  is  no         This  option  makes  it possible to include comments inside complicated
1275       equivalent of this option in Perl.         patterns.  Note, however, that this applies only  to  data  characters.
1276           Whitespace   characters  may  never  appear  within  special  character
1277         PCRE_UNGREEDY         sequences in a pattern, for  example  within  the  sequence  (?(  which
1278           introduces a conditional subpattern.
1279       This option inverts the "greediness" of the  quantifiers  so  
1280       that  they  are  not greedy by default, but become greedy if           PCRE_EXTRA
1281       followed by "?". It is not compatible with Perl. It can also  
1282       be set by a (?U) option setting within the pattern.         This  option  was invented in order to turn on additional functionality
1283           of PCRE that is incompatible with Perl, but it  is  currently  of  very
1284         PCRE_UTF8         little  use. When set, any backslash in a pattern that is followed by a
1285           letter that has no special meaning  causes  an  error,  thus  reserving
1286       This option causes PCRE to regard both the pattern  and  the         these  combinations  for  future  expansion.  By default, as in Perl, a
1287       subject  as  strings  of UTF-8 characters instead of single-         backslash followed by a letter with no special meaning is treated as  a
1288       byte character strings. However, it  is  available  only  if         literal. (Perl can, however, be persuaded to give an error for this, by
1289       PCRE  has  been  built to include UTF-8 support. If not, the         running it with the -w option.) There are at present no other  features
1290       use of this option provokes an error. Details  of  how  this         controlled  by this option. It can also be set by a (?X) option setting
1291       option  changes  the behaviour of PCRE are given in the sec-         within a pattern.
1292       tion on UTF-8 support in the main pcre page.  
1293             PCRE_FIRSTLINE
1294    
1295           If this option is set, an  unanchored  pattern  is  required  to  match
1296           before  or  at  the  first  newline  in  the subject string, though the
1297           matched text may continue over the newline.
1298    
1299             PCRE_JAVASCRIPT_COMPAT
1300    
1301           If this option is set, PCRE's behaviour is changed in some ways so that
1302           it  is  compatible with JavaScript rather than Perl. The changes are as
1303           follows:
1304    
1305           (1) A lone closing square bracket in a pattern  causes  a  compile-time
1306           error,  because this is illegal in JavaScript (by default it is treated
1307           as a data character). Thus, the pattern AB]CD becomes illegal when this
1308           option is set.
1309    
1310           (2)  At run time, a back reference to an unset subpattern group matches
1311           an empty string (by default this causes the current  matching  alterna-
1312           tive  to  fail). A pattern such as (\1)(a) succeeds when this option is
1313           set (assuming it can find an "a" in the subject), whereas it  fails  by
1314           default, for Perl compatibility.
1315    
1316             PCRE_MULTILINE
1317    
1318           By  default,  PCRE  treats the subject string as consisting of a single
1319           line of characters (even if it actually contains newlines). The  "start
1320           of  line"  metacharacter  (^)  matches only at the start of the string,
1321           while the "end of line" metacharacter ($) matches only at  the  end  of
1322           the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1323           is set). This is the same as Perl.
1324    
1325           When PCRE_MULTILINE it is set, the "start of line" and  "end  of  line"
1326           constructs  match  immediately following or immediately before internal
1327           newlines in the subject string, respectively, as well as  at  the  very
1328           start  and  end.  This is equivalent to Perl's /m option, and it can be
1329           changed within a pattern by a (?m) option setting. If there are no new-
1330           lines  in  a  subject string, or no occurrences of ^ or $ in a pattern,
1331           setting PCRE_MULTILINE has no effect.
1332    
1333             PCRE_NEWLINE_CR
1334             PCRE_NEWLINE_LF
1335             PCRE_NEWLINE_CRLF
1336             PCRE_NEWLINE_ANYCRLF
1337             PCRE_NEWLINE_ANY
1338    
1339           These options override the default newline definition that  was  chosen
1340           when  PCRE  was built. Setting the first or the second specifies that a
1341           newline is indicated by a single character (CR  or  LF,  respectively).
1342           Setting  PCRE_NEWLINE_CRLF specifies that a newline is indicated by the
1343           two-character CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF  specifies
1344           that any of the three preceding sequences should be recognized. Setting
1345           PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should  be
1346           recognized. The Unicode newline sequences are the three just mentioned,
1347           plus the single characters VT (vertical  tab,  U+000B),  FF  (formfeed,
1348           U+000C),  NEL  (next line, U+0085), LS (line separator, U+2028), and PS
1349           (paragraph separator, U+2029). The last  two  are  recognized  only  in
1350           UTF-8 mode.
1351    
1352           The  newline  setting  in  the  options  word  uses three bits that are
1353           treated as a number, giving eight possibilities. Currently only six are
1354           used  (default  plus the five values above). This means that if you set
1355           more than one newline option, the combination may or may not be  sensi-
1356           ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1357           PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers  and
1358           cause an error.
1359    
1360           The  only time that a line break is specially recognized when compiling
1361           a pattern is if PCRE_EXTENDED is set, and  an  unescaped  #  outside  a
1362           character  class  is  encountered.  This indicates a comment that lasts
1363           until after the next line break sequence. In other circumstances,  line
1364           break   sequences   are   treated  as  literal  data,  except  that  in
1365           PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1366           and are therefore ignored.
1367    
1368           The newline option that is set at compile time becomes the default that
1369           is used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1370    
1371             PCRE_NO_AUTO_CAPTURE
1372    
1373           If this option is set, it disables the use of numbered capturing paren-
1374           theses  in the pattern. Any opening parenthesis that is not followed by
1375           ? behaves as if it were followed by ?: but named parentheses can  still
1376           be  used  for  capturing  (and  they acquire numbers in the usual way).
1377           There is no equivalent of this option in Perl.
1378    
1379             PCRE_UNGREEDY
1380    
1381           This option inverts the "greediness" of the quantifiers  so  that  they
1382           are  not greedy by default, but become greedy if followed by "?". It is
1383           not compatible with Perl. It can also be set by a (?U)  option  setting
1384           within the pattern.
1385    
1386             PCRE_UTF8
1387    
1388           This  option  causes PCRE to regard both the pattern and the subject as
1389           strings of UTF-8 characters instead of single-byte  character  strings.
1390           However,  it is available only when PCRE is built to include UTF-8 sup-
1391           port. If not, the use of this option provokes an error. Details of  how
1392           this  option  changes the behaviour of PCRE are given in the section on
1393           UTF-8 support in the main pcre page.
1394    
1395             PCRE_NO_UTF8_CHECK
1396    
1397           When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
1398           automatically  checked.  There  is  a  discussion about the validity of
1399           UTF-8 strings in the main pcre page. If an invalid  UTF-8  sequence  of
1400           bytes  is  found,  pcre_compile() returns an error. If you already know
1401           that your pattern is valid, and you want to skip this check for perfor-
1402           mance  reasons,  you  can set the PCRE_NO_UTF8_CHECK option. When it is
1403           set, the effect of passing an invalid UTF-8  string  as  a  pattern  is
1404           undefined.  It  may  cause your program to crash. Note that this option
1405           can also be passed to pcre_exec() and pcre_dfa_exec(), to suppress  the
1406           UTF-8 validity checking of subject strings.
1407    
1408    
1409    COMPILATION ERROR CODES
1410    
1411           The  following  table  lists  the  error  codes than may be returned by
1412           pcre_compile2(), along with the error messages that may be returned  by
1413           both  compiling functions. As PCRE has developed, some error codes have
1414           fallen out of use. To avoid confusion, they have not been re-used.
1415    
1416              0  no error
1417              1  \ at end of pattern
1418              2  \c at end of pattern
1419              3  unrecognized character follows \
1420              4  numbers out of order in {} quantifier
1421              5  number too big in {} quantifier
1422              6  missing terminating ] for character class
1423              7  invalid escape sequence in character class
1424              8  range out of order in character class
1425              9  nothing to repeat
1426             10  [this code is not in use]
1427             11  internal error: unexpected repeat
1428             12  unrecognized character after (? or (?-
1429             13  POSIX named classes are supported only within a class
1430             14  missing )
1431             15  reference to non-existent subpattern
1432             16  erroffset passed as NULL
1433             17  unknown option bit(s) set
1434             18  missing ) after comment
1435             19  [this code is not in use]
1436             20  regular expression is too large
1437             21  failed to get memory
1438             22  unmatched parentheses
1439             23  internal error: code overflow
1440             24  unrecognized character after (?<
1441             25  lookbehind assertion is not fixed length
1442             26  malformed number or name after (?(
1443             27  conditional group contains more than two branches
1444             28  assertion expected after (?(
1445             29  (?R or (?[+-]digits must be followed by )
1446             30  unknown POSIX class name
1447             31  POSIX collating elements are not supported
1448             32  this version of PCRE is not compiled with PCRE_UTF8 support
1449             33  [this code is not in use]
1450             34  character value in \x{...} sequence is too large
1451             35  invalid condition (?(0)
1452             36  \C not allowed in lookbehind assertion
1453             37  PCRE does not support \L, \l, \N, \U, or \u
1454             38  number after (?C is > 255
1455             39  closing ) for (?C expected
1456             40  recursive call could loop indefinitely
1457             41  unrecognized character after (?P
1458             42  syntax error in subpattern name (missing terminator)
1459             43  two named subpatterns have the same name
1460             44  invalid UTF-8 string
1461             45  support for \P, \p, and \X has not been compiled
1462             46  malformed \P or \p sequence
1463             47  unknown property name after \P or \p
1464             48  subpattern name is too long (maximum 32 characters)
1465             49  too many named subpatterns (maximum 10000)
1466             50  [this code is not in use]
1467             51  octal value is greater than \377 (not in UTF-8 mode)
1468             52  internal error: overran compiling workspace
1469             53  internal  error:  previously-checked  referenced  subpattern  not
1470           found
1471             54  DEFINE group contains more than one branch
1472             55  repeating a DEFINE group is not allowed
1473             56  inconsistent NEWLINE options
1474             57  \g is not followed by a braced, angle-bracketed, or quoted
1475                   name/number or by a plain number
1476             58  a numbered reference must not be zero
1477             59  an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT)
1478             60  (*VERB) not recognized
1479             61  number is too big
1480             62  subpattern name expected
1481             63  digit expected after (?+
1482             64  ] is an invalid data character in JavaScript compatibility mode
1483             65   different  names  for  subpatterns  of  the  same number are not
1484           allowed
1485             66  (*MARK) must have an argument
1486    
1487           The numbers 32 and 10000 in errors 48 and 49  are  defaults;  different
1488           values may be used if the limits were changed when PCRE was built.
1489    
1490    
1491  STUDYING A PATTERN  STUDYING A PATTERN
1492    
1493       pcre_extra *pcre_study(const pcre *code, int options,         pcre_extra *pcre_study(const pcre *code, int options
1494            const char **errptr);              const char **errptr);
1495    
1496       When a pattern is going to be  used  several  times,  it  is         If  a  compiled  pattern is going to be used several times, it is worth
1497       worth  spending  more time analyzing it in order to speed up         spending more time analyzing it in order to speed up the time taken for
1498       the time taken for matching. The function pcre_study() takes         matching.  The function pcre_study() takes a pointer to a compiled pat-
1499       a  pointer  to  a compiled pattern as its first argument. If         tern as its first argument. If studying the pattern produces additional
1500       studing the pattern  produces  additional  information  that         information  that  will  help speed up matching, pcre_study() returns a
1501       will  help speed up matching, pcre_study() returns a pointer         pointer to a pcre_extra block, in which the study_data field points  to
1502       to a pcre_extra block, in which the study_data field  points         the results of the study.
1503       to the results of the study.  
1504           The  returned  value  from  pcre_study()  can  be  passed  directly  to
1505       The  returned  value  from  a  pcre_study()  can  be  passed         pcre_exec() or pcre_dfa_exec(). However, a pcre_extra block  also  con-
1506       directly  to pcre_exec(). However, the pcre_extra block also         tains  other  fields  that can be set by the caller before the block is
1507       contains other fields that can be set by the  caller  before         passed; these are described below in the section on matching a pattern.
1508       the  block is passed; these are described below. If studying  
1509       the pattern does not  produce  any  additional  information,         If studying the  pattern  does  not  produce  any  useful  information,
1510       pcre_study() returns NULL. In that circumstance, if the cal-         pcre_study() returns NULL. In that circumstance, if the calling program
1511       ling program wants to pass  some  of  the  other  fields  to         wants  to  pass  any  of   the   other   fields   to   pcre_exec()   or
1512       pcre_exec(), it must set up its own pcre_extra block.         pcre_dfa_exec(), it must set up its own pcre_extra block.
1513    
1514       The second argument contains option  bits.  At  present,  no         The  second  argument of pcre_study() contains option bits. At present,
1515       options  are  defined  for  pcre_study(),  and this argument         no options are defined, and this argument should always be zero.
1516       should always be zero.  
1517           The third argument for pcre_study() is a pointer for an error  message.
1518       The third argument for pcre_study()  is  a  pointer  for  an         If  studying  succeeds  (even  if no data is returned), the variable it
1519       error  message.  If  studying  succeeds  (even if no data is         points to is set to NULL. Otherwise it is set to  point  to  a  textual
1520       returned), the variable it points to is set to NULL.  Other-         error message. This is a static string that is part of the library. You
1521       wise it points to a textual error message. You should there-         must not try to free it. You should test the  error  pointer  for  NULL
1522       fore  test  the  error  pointer  for  NULL   after   calling         after calling pcre_study(), to be sure that it has run successfully.
1523       pcre_study(), to be sure that it has run successfully.  
1524           This is a typical call to pcre_study():
1525       This is a typical call to pcre_study():  
1526             pcre_extra *pe;
1527         pcre_extra *pe;           pe = pcre_study(
1528         pe = pcre_study(             re,             /* result of pcre_compile() */
1529           re,             /* result of pcre_compile() */             0,              /* no options exist */
1530           0,              /* no options exist */             &error);        /* set to NULL or points to a message */
1531           &error);        /* set to NULL or points to a message */  
1532           Studying a pattern does two things: first, a lower bound for the length
1533       At present, studying a  pattern  is  useful  only  for  non-         of subject string that is needed to match the pattern is computed. This
1534       anchored  patterns  that do not have a single fixed starting         does not mean that there are any strings of that length that match, but
1535       character. A  bitmap  of  possible  starting  characters  is         it does guarantee that no shorter strings match. The value is  used  by
1536       created.         pcre_exec()  and  pcre_dfa_exec()  to  avoid  wasting time by trying to
1537           match strings that are shorter than the lower bound. You can  find  out
1538           the value in a calling program via the pcre_fullinfo() function.
1539    
1540           Studying a pattern is also useful for non-anchored patterns that do not
1541           have a single fixed starting character. A bitmap of  possible  starting
1542           bytes  is  created. This speeds up finding a position in the subject at
1543           which to start matching.
1544    
1545    
1546  LOCALE SUPPORT  LOCALE SUPPORT
1547    
1548       PCRE handles caseless matching, and determines whether char-         PCRE handles caseless matching, and determines whether  characters  are
1549       acters  are  letters, digits, or whatever, by reference to a         letters,  digits, or whatever, by reference to a set of tables, indexed
1550       set of tables. When running in UTF-8 mode, this applies only         by character value. When running in UTF-8 mode, this  applies  only  to
1551       to characters with codes less than 256. The library contains         characters  with  codes  less than 128. Higher-valued codes never match
1552       a default set of tables that is created  in  the  default  C         escapes such as \w or \d, but can be tested with \p if  PCRE  is  built
1553       locale  when  PCRE  is compiled. This is used when the final         with  Unicode  character property support. The use of locales with Uni-
1554       argument of pcre_compile() is NULL, and  is  sufficient  for         code is discouraged. If you are handling characters with codes  greater
1555       many applications.         than  128, you should either use UTF-8 and Unicode, or use locales, but
1556           not try to mix the two.
1557       An alternative set of tables can, however, be supplied. Such  
1558       tables  are built by calling the pcre_maketables() function,         PCRE contains an internal set of tables that are used  when  the  final
1559       which has no arguments, in the relevant locale.  The  result         argument  of  pcre_compile()  is  NULL.  These  are sufficient for many
1560       can  then be passed to pcre_compile() as often as necessary.         applications.  Normally, the internal tables recognize only ASCII char-
1561       For example, to build and use tables  that  are  appropriate         acters. However, when PCRE is built, it is possible to cause the inter-
1562       for  the French locale (where accented characters with codes         nal tables to be rebuilt in the default "C" locale of the local system,
1563       greater than 128 are treated as letters), the following code         which may cause them to be different.
1564       could be used:  
1565           The  internal tables can always be overridden by tables supplied by the
1566         setlocale(LC_CTYPE, "fr");         application that calls PCRE. These may be created in a different locale
1567         tables = pcre_maketables();         from  the  default.  As more and more applications change to using Uni-
1568         re = pcre_compile(..., tables);         code, the need for this locale support is expected to die away.
1569    
1570       The  tables  are  built  in  memory  that  is  obtained  via         External tables are built by calling  the  pcre_maketables()  function,
1571       pcre_malloc.  The  pointer that is passed to pcre_compile is         which  has no arguments, in the relevant locale. The result can then be
1572       saved with the compiled pattern, and  the  same  tables  are         passed to pcre_compile() or pcre_exec()  as  often  as  necessary.  For
1573       used via this pointer by pcre_study() and pcre_exec(). Thus,         example,  to  build  and use tables that are appropriate for the French
1574       for any single pattern, compilation, studying  and  matching         locale (where accented characters with  values  greater  than  128  are
1575       all happen in the same locale, but different patterns can be         treated as letters), the following code could be used:
1576       compiled in different locales. It is the caller's  responsi-  
1577       bility  to  ensure  that  the  memory  containing the tables           setlocale(LC_CTYPE, "fr_FR");
1578       remains available for as long as it is needed.           tables = pcre_maketables();
1579             re = pcre_compile(..., tables);
1580    
1581           The  locale  name "fr_FR" is used on Linux and other Unix-like systems;
1582           if you are using Windows, the name for the French locale is "french".
1583    
1584           When pcre_maketables() runs, the tables are built  in  memory  that  is
1585           obtained  via  pcre_malloc. It is the caller's responsibility to ensure
1586           that the memory containing the tables remains available for as long  as
1587           it is needed.
1588    
1589           The pointer that is passed to pcre_compile() is saved with the compiled
1590           pattern, and the same tables are used via this pointer by  pcre_study()
1591           and normally also by pcre_exec(). Thus, by default, for any single pat-
1592           tern, compilation, studying and matching all happen in the same locale,
1593           but different patterns can be compiled in different locales.
1594    
1595           It  is  possible to pass a table pointer or NULL (indicating the use of
1596           the internal tables) to pcre_exec(). Although  not  intended  for  this
1597           purpose,  this facility could be used to match a pattern in a different
1598           locale from the one in which it was compiled. Passing table pointers at
1599           run time is discussed below in the section on matching a pattern.
1600    
1601    
1602  INFORMATION ABOUT A PATTERN  INFORMATION ABOUT A PATTERN
1603    
1604       int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1605            int what, void *where);              int what, void *where);
1606    
1607       The pcre_fullinfo() function  returns  information  about  a         The  pcre_fullinfo() function returns information about a compiled pat-
1608       compiled pattern. It replaces the obsolete pcre_info() func-         tern. It replaces the obsolete pcre_info() function, which is neverthe-
1609       tion, which is nevertheless retained for backwards compabil-         less retained for backwards compability (and is documented below).
1610       ity (and is documented below).  
1611           The  first  argument  for  pcre_fullinfo() is a pointer to the compiled
1612       The first argument for pcre_fullinfo() is a pointer  to  the         pattern. The second argument is the result of pcre_study(), or NULL  if
1613       compiled  pattern.  The  second  argument  is  the result of         the  pattern  was not studied. The third argument specifies which piece
1614       pcre_study(), or NULL if the pattern was  not  studied.  The         of information is required, and the fourth argument is a pointer  to  a
1615       third  argument  specifies  which  piece  of  information is         variable  to  receive  the  data. The yield of the function is zero for
1616       required, and the fourth argument is a pointer to a variable         success, or one of the following negative numbers:
1617       to  receive  the data. The yield of the function is zero for  
1618       success, or one of the following negative numbers:           PCRE_ERROR_NULL       the argument code was NULL
1619                                   the argument where was NULL
1620         PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1621                               the argument where was NULL           PCRE_ERROR_BADOPTION  the value of what was invalid
1622         PCRE_ERROR_BADMAGIC   the "magic number" was not found  
1623         PCRE_ERROR_BADOPTION  the value of what was invalid         The "magic number" is placed at the start of each compiled  pattern  as
1624           an  simple check against passing an arbitrary memory pointer. Here is a
1625       Here is a typical call of  pcre_fullinfo(),  to  obtain  the         typical call of pcre_fullinfo(), to obtain the length of  the  compiled
1626       length of the compiled pattern:         pattern:
1627    
1628         int rc;           int rc;
1629         unsigned long int length;           size_t length;
1630         rc = pcre_fullinfo(           rc = pcre_fullinfo(
1631           re,               /* result of pcre_compile() */             re,               /* result of pcre_compile() */
1632           pe,               /* result of pcre_study(), or NULL */             pe,               /* result of pcre_study(), or NULL */
1633           PCRE_INFO_SIZE,   /* what is required */             PCRE_INFO_SIZE,   /* what is required */
1634           &length);         /* where to put the data */             &length);         /* where to put the data */
1635    
1636       The possible values for the third argument  are  defined  in         The  possible  values for the third argument are defined in pcre.h, and
1637       pcre.h, and are as follows:         are as follows:
1638    
1639         PCRE_INFO_BACKREFMAX           PCRE_INFO_BACKREFMAX
1640    
1641       Return the number of the highest back reference in the  pat-         Return the number of the highest back reference  in  the  pattern.  The
1642       tern.  The  fourth argument should point to an int variable.         fourth  argument  should  point to an int variable. Zero is returned if
1643       Zero is returned if there are no back references.         there are no back references.
1644    
1645         PCRE_INFO_CAPTURECOUNT           PCRE_INFO_CAPTURECOUNT
1646    
1647       Return the number of capturing subpatterns in  the  pattern.         Return the number of capturing subpatterns in the pattern.  The  fourth
1648       The fourth argument should point to an int variable.         argument should point to an int variable.
1649    
1650         PCRE_INFO_FIRSTBYTE           PCRE_INFO_DEFAULT_TABLES
1651    
1652       Return information about  the  first  byte  of  any  matched         Return  a pointer to the internal default character tables within PCRE.
1653       string,  for a non-anchored pattern. (This option used to be         The fourth argument should point to an unsigned char *  variable.  This
1654       called PCRE_INFO_FIRSTCHAR; the old name is still recognized         information call is provided for internal use by the pcre_study() func-
1655       for backwards compatibility.)         tion. External callers can cause PCRE to use  its  internal  tables  by
1656           passing a NULL table pointer.
1657       If there is a fixed first byte, e.g. from a pattern such  as  
1658       (cat|cow|coyote),  it  is returned in the integer pointed to           PCRE_INFO_FIRSTBYTE
1659       by where. Otherwise, if either  
1660           Return  information  about  the first byte of any matched string, for a
1661       (a) the pattern was compiled with the PCRE_MULTILINE option,         non-anchored pattern. The fourth argument should point to an int  vari-
1662       and every branch starts with "^", or         able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
1663           is still recognized for backwards compatibility.)
1664       (b) every  branch  of  the  pattern  starts  with  ".*"  and  
1665       PCRE_DOTALL is not set (if it were set, the pattern would be         If there is a fixed first byte, for example, from  a  pattern  such  as
1666       anchored),         (cat|cow|coyote), its value is returned. Otherwise, if either
1667    
1668       -1 is returned, indicating that the pattern matches only  at         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every
1669       the  start  of  a subject string or after any newline within         branch starts with "^", or
1670       the string. Otherwise -2 is returned. For anchored patterns,  
1671       -2 is returned.         (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
1672           set (if it were set, the pattern would be anchored),
1673         PCRE_INFO_FIRSTTABLE  
1674           -1  is  returned, indicating that the pattern matches only at the start
1675       If the pattern was studied, and this resulted  in  the  con-         of a subject string or after any newline within the  string.  Otherwise
1676       struction of a 256-bit table indicating a fixed set of bytes         -2 is returned. For anchored patterns, -2 is returned.
1677       for the first byte in any matching string, a pointer to  the  
1678       table  is  returned.  Otherwise NULL is returned. The fourth           PCRE_INFO_FIRSTTABLE
1679       argument should point to an unsigned char * variable.  
1680           If  the pattern was studied, and this resulted in the construction of a
1681         PCRE_INFO_LASTLITERAL         256-bit table indicating a fixed set of bytes for the first byte in any
1682           matching  string, a pointer to the table is returned. Otherwise NULL is
1683       Return the value of the rightmost  literal  byte  that  must         returned. The fourth argument should point to an unsigned char *  vari-
1684       exist  in  any  matched  string, other than at its start, if         able.
1685       such a byte has been recorded. The  fourth  argument  should  
1686       point  to  an  int variable. If there is no such byte, -1 is           PCRE_INFO_HASCRORLF
1687       returned. For anchored patterns,  a  last  literal  byte  is  
1688       recorded  only  if  it follows something of variable length.         Return  1  if  the  pattern  contains any explicit matches for CR or LF
1689       For example, for the pattern /^a\d+z\d+/ the returned  value         characters, otherwise 0. The fourth argument should  point  to  an  int
1690       is "z", but for /^a\dz\d/ the returned value is -1.         variable.  An explicit match is either a literal CR or LF character, or
1691           \r or \n.
1692         PCRE_INFO_NAMECOUNT  
1693         PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_JCHANGED
1694         PCRE_INFO_NAMETABLE  
1695           Return 1 if the (?J) or (?-J) option setting is used  in  the  pattern,
1696       PCRE supports the use of named as well as numbered capturing         otherwise  0. The fourth argument should point to an int variable. (?J)
1697       parentheses. The names are just an additional way of identi-         and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
1698       fying the parentheses,  which  still  acquire  a  number.  A  
1699       caller  that  wants  to extract data from a named subpattern           PCRE_INFO_LASTLITERAL
1700       must convert the name to a number in  order  to  access  the  
1701       correct  pointers  in  the  output  vector  (described  with         Return the value of the rightmost literal byte that must exist  in  any
1702       pcre_exec() below). In order to do this, it must  first  use         matched  string,  other  than  at  its  start,  if such a byte has been
1703       these  three  values  to  obtain  the name-to-number mapping         recorded. The fourth argument should point to an int variable. If there
1704       table for the pattern.         is  no such byte, -1 is returned. For anchored patterns, a last literal
1705           byte is recorded only if it follows something of variable  length.  For
1706       The  map  consists  of  a  number  of  fixed-size   entries.         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
1707       PCRE_INFO_NAMECOUNT   gives   the  number  of  entries,  and         /^a\dz\d/ the returned value is -1.
1708       PCRE_INFO_NAMEENTRYSIZE gives the size of each  entry;  both  
1709       of  these return an int value. The entry size depends on the           PCRE_INFO_MINLENGTH
1710       length of the longest name.  PCRE_INFO_NAMETABLE  returns  a  
1711       pointer to the first entry of the table (a pointer to char).         If the pattern was studied and a minimum length  for  matching  subject
1712       The first two bytes of each entry are the number of the cap-         strings  was  computed,  its  value is returned. Otherwise the returned
1713       turing parenthesis, most significant byte first. The rest of         value is -1. The value is a number of characters, not bytes  (this  may
1714       the entry is the corresponding name,  zero  terminated.  The         be  relevant in UTF-8 mode). The fourth argument should point to an int
1715       names  are  in alphabetical order. For example, consider the         variable. A non-negative value is a lower bound to the  length  of  any
1716       following pattern (assume PCRE_EXTENDED  is  set,  so  white         matching  string.  There  may not be any strings of that length that do
1717       space - including newlines - is ignored):         actually match, but every string that does match is at least that long.
1718    
1719         (?P<date> (?P<year>(\d\d)?\d\d) -           PCRE_INFO_NAMECOUNT
1720         (?P<month>\d\d) - (?P<day>\d\d) )           PCRE_INFO_NAMEENTRYSIZE
1721             PCRE_INFO_NAMETABLE
1722       There are four named subpatterns,  so  the  table  has  four  
1723       entries,  and  each  entry in the table is eight bytes long.         PCRE supports the use of named as well as numbered capturing  parenthe-
1724       The table is as follows, with non-printing  bytes  shows  in         ses.  The names are just an additional way of identifying the parenthe-
1725       hex, and undefined bytes shown as ??:         ses, which still acquire numbers. Several convenience functions such as
1726           pcre_get_named_substring()  are  provided  for extracting captured sub-
1727         00 01 d  a  t  e  00 ??         strings by name. It is also possible to extract the data  directly,  by
1728         00 05 d  a  y  00 ?? ??         first  converting  the  name to a number in order to access the correct
1729         00 04 m  o  n  t  h  00         pointers in the output vector (described with pcre_exec() below). To do
1730         00 02 y  e  a  r  00 ??         the  conversion,  you  need  to  use  the  name-to-number map, which is
1731           described by these three values.
1732       When writing code to extract data  from  named  subpatterns,  
1733       remember  that the length of each entry may be different for         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
1734       each compiled pattern.         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1735           of each entry; both of these  return  an  int  value.  The  entry  size
1736         PCRE_INFO_OPTIONS         depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns
1737           a pointer to the first entry of the table  (a  pointer  to  char).  The
1738       Return a copy of the options with which the pattern was com-         first two bytes of each entry are the number of the capturing parenthe-
1739       piled.  The fourth argument should point to an unsigned long         sis, most significant byte first. The rest of the entry is  the  corre-
1740       int variable. These option bits are those specified  in  the         sponding name, zero terminated.
1741       call  to  pcre_compile(),  modified  by any top-level option  
1742       settings within the pattern itself.         The  names are in alphabetical order. Duplicate names may appear if (?|
1743           is used to create multiple groups with the same number, as described in
1744       A pattern is automatically anchored by PCRE if  all  of  its         the  section  on  duplicate subpattern numbers in the pcrepattern page.
1745       top-level alternatives begin with one of the following:         Duplicate names for subpatterns with different  numbers  are  permitted
1746           only  if  PCRE_DUPNAMES  is  set. In all cases of duplicate names, they
1747         ^     unless PCRE_MULTILINE is set         appear in the table in the order in which they were found in  the  pat-
1748         \A    always         tern.  In  the  absence  of (?| this is the order of increasing number;
1749         \G    always         when (?| is used this is not necessarily the case because later subpat-
1750         .*    if PCRE_DOTALL is set and there are no back         terns may have lower numbers.
1751                 references to the subpattern in which .* appears  
1752           As  a  simple  example of the name/number table, consider the following
1753       For such patterns, the  PCRE_ANCHORED  bit  is  set  in  the         pattern (assume PCRE_EXTENDED is set, so white space -  including  new-
1754       options returned by pcre_fullinfo().         lines - is ignored):
1755    
1756         PCRE_INFO_SIZE           (?<date> (?<year>(\d\d)?\d\d) -
1757             (?<month>\d\d) - (?<day>\d\d) )
1758       Return the size of the compiled pattern, that is, the  value  
1759       that  was  passed as the argument to pcre_malloc() when PCRE         There  are  four  named subpatterns, so the table has four entries, and
1760       was getting memory in which to place the compiled data.  The         each entry in the table is eight bytes long. The table is  as  follows,
1761       fourth argument should point to a size_t variable.         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1762           as ??:
1763         PCRE_INFO_STUDYSIZE  
1764             00 01 d  a  t  e  00 ??
1765       Returns the size  of  the  data  block  pointed  to  by  the           00 05 d  a  y  00 ?? ??
1766       study_data  field  in a pcre_extra block. That is, it is the           00 04 m  o  n  t  h  00
1767       value that was passed to pcre_malloc() when PCRE was getting           00 02 y  e  a  r  00 ??
1768       memory into which to place the data created by pcre_study().  
1769       The fourth argument should point to a size_t variable.         When writing code to extract data  from  named  subpatterns  using  the
1770           name-to-number  map,  remember that the length of the entries is likely
1771           to be different for each compiled pattern.
1772    
1773             PCRE_INFO_OKPARTIAL
1774    
1775           Return 1  if  the  pattern  can  be  used  for  partial  matching  with
1776           pcre_exec(),  otherwise  0.  The fourth argument should point to an int
1777           variable. From  release  8.00,  this  always  returns  1,  because  the
1778           restrictions  that  previously  applied  to  partial matching have been
1779           lifted. The pcrepartial documentation gives details of  partial  match-
1780           ing.
1781    
1782             PCRE_INFO_OPTIONS
1783    
1784           Return  a  copy of the options with which the pattern was compiled. The
1785           fourth argument should point to an unsigned long  int  variable.  These
1786           option bits are those specified in the call to pcre_compile(), modified
1787           by any top-level option settings at the start of the pattern itself. In
1788           other  words,  they are the options that will be in force when matching
1789           starts. For example, if the pattern /(?im)abc(?-i)d/ is  compiled  with
1790           the  PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,
1791           and PCRE_EXTENDED.
1792    
1793           A pattern is automatically anchored by PCRE if  all  of  its  top-level
1794           alternatives begin with one of the following:
1795    
1796             ^     unless PCRE_MULTILINE is set
1797             \A    always
1798             \G    always
1799             .*    if PCRE_DOTALL is set and there are no back
1800                     references to the subpattern in which .* appears
1801    
1802           For such patterns, the PCRE_ANCHORED bit is set in the options returned
1803           by pcre_fullinfo().
1804    
1805             PCRE_INFO_SIZE
1806    
1807           Return the size of the compiled pattern, that is, the  value  that  was
1808           passed as the argument to pcre_malloc() when PCRE was getting memory in
1809           which to place the compiled data. The fourth argument should point to a
1810           size_t variable.
1811    
1812             PCRE_INFO_STUDYSIZE
1813    
1814           Return the size of the data block pointed to by the study_data field in
1815           a pcre_extra block. That is,  it  is  the  value  that  was  passed  to
1816           pcre_malloc() when PCRE was getting memory into which to place the data
1817           created by pcre_study(). If pcre_extra is NULL, or there  is  no  study
1818           data,  zero  is  returned. The fourth argument should point to a size_t
1819           variable.
1820    
1821    
1822  OBSOLETE INFO FUNCTION  OBSOLETE INFO FUNCTION
1823    
1824       int pcre_info(const pcre *code, int *optptr, *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1825    
1826       The pcre_info() function is now obsolete because its  inter-         The pcre_info() function is now obsolete because its interface  is  too
1827       face  is  too  restrictive  to return all the available data         restrictive  to return all the available data about a compiled pattern.
1828       about  a  compiled  pattern.   New   programs   should   use         New  programs  should  use  pcre_fullinfo()  instead.  The   yield   of
1829       pcre_fullinfo()  instead.  The  yield  of pcre_info() is the         pcre_info()  is the number of capturing subpatterns, or one of the fol-
1830       number of capturing subpatterns, or  one  of  the  following         lowing negative numbers:
1831       negative numbers:  
1832             PCRE_ERROR_NULL       the argument code was NULL
1833         PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1834         PCRE_ERROR_BADMAGIC   the "magic number" was not found  
1835           If the optptr argument is not NULL, a copy of the  options  with  which
1836       If the optptr argument is not NULL, a copy  of  the  options         the  pattern  was  compiled  is placed in the integer it points to (see
1837       with which the pattern was compiled is placed in the integer         PCRE_INFO_OPTIONS above).
1838       it points to (see PCRE_INFO_OPTIONS above).  
1839           If the pattern is not anchored and the  firstcharptr  argument  is  not
1840       If the pattern is not anchored and the firstcharptr argument         NULL,  it is used to pass back information about the first character of
1841       is  not  NULL, it is used to pass back information about the         any matched string (see PCRE_INFO_FIRSTBYTE above).
1842       first    character    of    any    matched    string    (see  
1843       PCRE_INFO_FIRSTBYTE above).  
1844    REFERENCE COUNTS
1845    
1846           int pcre_refcount(pcre *code, int adjust);
1847    
1848           The pcre_refcount() function is used to maintain a reference  count  in
1849           the data block that contains a compiled pattern. It is provided for the
1850           benefit of applications that  operate  in  an  object-oriented  manner,
1851           where different parts of the application may be using the same compiled
1852           pattern, but you want to free the block when they are all done.
1853    
1854           When a pattern is compiled, the reference count field is initialized to
1855           zero.   It is changed only by calling this function, whose action is to
1856           add the adjust value (which may be positive or  negative)  to  it.  The
1857           yield of the function is the new value. However, the value of the count
1858           is constrained to lie between 0 and 65535, inclusive. If the new  value
1859           is outside these limits, it is forced to the appropriate limit value.
1860    
1861           Except  when it is zero, the reference count is not correctly preserved
1862           if a pattern is compiled on one host and then  transferred  to  a  host
1863           whose byte-order is different. (This seems a highly unlikely scenario.)
1864    
1865    
1866    MATCHING A PATTERN: THE TRADITIONAL FUNCTION
1867    
1868           int pcre_exec(const pcre *code, const pcre_extra *extra,
1869                const char *subject, int length, int startoffset,
1870                int options, int *ovector, int ovecsize);
1871    
1872           The  function pcre_exec() is called to match a subject string against a
1873           compiled pattern, which is passed in the code argument. If the  pattern
1874           was  studied,  the  result  of  the study should be passed in the extra
1875           argument. This function is the main matching facility of  the  library,
1876           and it operates in a Perl-like manner. For specialist use there is also
1877           an alternative matching function, which is described below in the  sec-
1878           tion about the pcre_dfa_exec() function.
1879    
1880           In  most applications, the pattern will have been compiled (and option-
1881           ally studied) in the same process that calls pcre_exec().  However,  it
1882           is possible to save compiled patterns and study data, and then use them
1883           later in different processes, possibly even on different hosts.  For  a
1884           discussion about this, see the pcreprecompile documentation.
1885    
1886           Here is an example of a simple call to pcre_exec():
1887    
1888             int rc;
1889             int ovector[30];
1890             rc = pcre_exec(
1891               re,             /* result of pcre_compile() */
1892               NULL,           /* we didn't study the pattern */
1893               "some string",  /* the subject string */
1894               11,             /* the length of the subject string */
1895               0,              /* start at offset 0 in the subject */
1896               0,              /* default options */
1897               ovector,        /* vector of integers for substring information */
1898               30);            /* number of elements (NOT size in bytes) */
1899    
1900       Extra data for pcre_exec()
1901    
1902           If  the  extra argument is not NULL, it must point to a pcre_extra data
1903           block. The pcre_study() function returns such a block (when it  doesn't
1904           return  NULL), but you can also create one for yourself, and pass addi-
1905           tional information in it. The pcre_extra block contains  the  following
1906           fields (not necessarily in this order):
1907    
1908             unsigned long int flags;
1909             void *study_data;
1910             unsigned long int match_limit;
1911             unsigned long int match_limit_recursion;
1912             void *callout_data;
1913             const unsigned char *tables;
1914             unsigned char **mark;
1915    
1916           The  flags  field  is a bitmap that specifies which of the other fields
1917           are set. The flag bits are:
1918    
1919             PCRE_EXTRA_STUDY_DATA
1920             PCRE_EXTRA_MATCH_LIMIT
1921             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1922             PCRE_EXTRA_CALLOUT_DATA
1923             PCRE_EXTRA_TABLES
1924             PCRE_EXTRA_MARK
1925    
1926           Other flag bits should be set to zero. The study_data field is  set  in
1927           the  pcre_extra  block  that is returned by pcre_study(), together with
1928           the appropriate flag bit. You should not set this yourself, but you may
1929           add  to  the  block by setting the other fields and their corresponding
1930           flag bits.
1931    
1932           The match_limit field provides a means of preventing PCRE from using up
1933           a  vast amount of resources when running patterns that are not going to
1934           match, but which have a very large number  of  possibilities  in  their
1935           search  trees. The classic example is a pattern that uses nested unlim-
1936           ited repeats.
1937    
1938           Internally, PCRE uses a function called match() which it calls  repeat-
1939           edly  (sometimes  recursively). The limit set by match_limit is imposed
1940           on the number of times this function is called during  a  match,  which
1941           has  the  effect  of  limiting the amount of backtracking that can take
1942           place. For patterns that are not anchored, the count restarts from zero
1943           for each position in the subject string.
1944    
1945           The  default  value  for  the  limit can be set when PCRE is built; the
1946           default default is 10 million, which handles all but the  most  extreme
1947           cases.  You  can  override  the  default by suppling pcre_exec() with a
1948           pcre_extra    block    in    which    match_limit    is    set,     and
1949           PCRE_EXTRA_MATCH_LIMIT  is  set  in  the  flags  field. If the limit is
1950           exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1951    
1952           The match_limit_recursion field is similar to match_limit, but  instead
1953           of limiting the total number of times that match() is called, it limits
1954           the depth of recursion. The recursion depth is a  smaller  number  than
1955           the  total number of calls, because not all calls to match() are recur-
1956           sive.  This limit is of use only if it is set smaller than match_limit.
1957    
1958           Limiting the recursion depth limits the amount of  stack  that  can  be
1959           used, or, when PCRE has been compiled to use memory on the heap instead
1960           of the stack, the amount of heap memory that can be used.
1961    
1962           The default value for match_limit_recursion can be  set  when  PCRE  is
1963           built;  the  default  default  is  the  same  value  as the default for
1964           match_limit. You can override the default by suppling pcre_exec()  with
1965           a   pcre_extra   block  in  which  match_limit_recursion  is  set,  and
1966           PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in  the  flags  field.  If  the
1967           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1968    
1969           The  callout_data  field is used in conjunction with the "callout" fea-
1970           ture, and is described in the pcrecallout documentation.
1971    
1972           The tables field  is  used  to  pass  a  character  tables  pointer  to
1973           pcre_exec();  this overrides the value that is stored with the compiled
1974           pattern. A non-NULL value is stored with the compiled pattern  only  if
1975           custom  tables  were  supplied to pcre_compile() via its tableptr argu-
1976           ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
1977           PCRE's  internal  tables  to be used. This facility is helpful when re-
1978           using patterns that have been saved after compiling  with  an  external
1979           set  of  tables,  because  the  external tables might be at a different
1980           address when pcre_exec() is called. See the  pcreprecompile  documenta-
1981           tion for a discussion of saving compiled patterns for later use.
1982    
1983           If  PCRE_EXTRA_MARK  is  set in the flags field, the mark field must be
1984           set to point to a char * variable. If the pattern  contains  any  back-
1985           tracking  control verbs such as (*MARK:NAME), and the execution ends up
1986           with a name to pass back, a pointer to the  name  string  (zero  termi-
1987           nated)  is  placed  in  the  variable pointed to by the mark field. The
1988           names are within the compiled pattern; if you wish  to  retain  such  a
1989           name  you must copy it before freeing the memory of a compiled pattern.
1990           If there is no name to pass back, the variable pointed to by  the  mark
1991           field  set  to NULL. For details of the backtracking control verbs, see
1992           the section entitled "Backtracking control" in the pcrepattern documen-
1993           tation.
1994    
1995       Option bits for pcre_exec()
1996    
1997           The  unused  bits of the options argument for pcre_exec() must be zero.
1998           The only bits that may  be  set  are  PCRE_ANCHORED,  PCRE_NEWLINE_xxx,
1999           PCRE_NOTBOL,    PCRE_NOTEOL,    PCRE_NOTEMPTY,   PCRE_NOTEMPTY_ATSTART,
2000           PCRE_NO_START_OPTIMIZE,  PCRE_NO_UTF8_CHECK,   PCRE_PARTIAL_SOFT,   and
2001           PCRE_PARTIAL_HARD.
2002    
2003             PCRE_ANCHORED
2004    
2005           The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first
2006           matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or
2007           turned  out to be anchored by virtue of its contents, it cannot be made
2008           unachored at matching time.
2009    
2010             PCRE_BSR_ANYCRLF
2011             PCRE_BSR_UNICODE
2012    
2013           These options (which are mutually exclusive) control what the \R escape
2014           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
2015           or to match any Unicode newline sequence. These  options  override  the
2016           choice that was made or defaulted when the pattern was compiled.
2017    
2018             PCRE_NEWLINE_CR
2019             PCRE_NEWLINE_LF
2020             PCRE_NEWLINE_CRLF
2021             PCRE_NEWLINE_ANYCRLF
2022             PCRE_NEWLINE_ANY
2023    
2024           These  options  override  the  newline  definition  that  was chosen or
2025           defaulted when the pattern was compiled. For details, see the  descrip-
2026           tion  of  pcre_compile()  above.  During  matching,  the newline choice
2027           affects the behaviour of the dot, circumflex,  and  dollar  metacharac-
2028           ters.  It may also alter the way the match position is advanced after a
2029           match failure for an unanchored pattern.
2030    
2031           When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF,  or  PCRE_NEWLINE_ANY  is
2032           set,  and a match attempt for an unanchored pattern fails when the cur-
2033           rent position is at a  CRLF  sequence,  and  the  pattern  contains  no
2034           explicit  matches  for  CR  or  LF  characters,  the  match position is
2035           advanced by two characters instead of one, in other words, to after the
2036           CRLF.
2037    
2038           The above rule is a compromise that makes the most common cases work as
2039           expected. For example, if the  pattern  is  .+A  (and  the  PCRE_DOTALL
2040           option is not set), it does not match the string "\r\nA" because, after
2041           failing at the start, it skips both the CR and the LF before  retrying.
2042           However,  the  pattern  [\r\n]A does match that string, because it con-
2043           tains an explicit CR or LF reference, and so advances only by one char-
2044           acter after the first failure.
2045    
2046           An explicit match for CR of LF is either a literal appearance of one of
2047           those characters, or one of the \r or  \n  escape  sequences.  Implicit
2048           matches  such  as [^X] do not count, nor does \s (which includes CR and
2049           LF in the characters that it matches).
2050    
2051           Notwithstanding the above, anomalous effects may still occur when  CRLF
2052           is a valid newline sequence and explicit \r or \n escapes appear in the
2053           pattern.
2054    
2055             PCRE_NOTBOL
2056    
2057           This option specifies that first character of the subject string is not
2058           the  beginning  of  a  line, so the circumflex metacharacter should not
2059           match before it. Setting this without PCRE_MULTILINE (at compile  time)
2060           causes  circumflex  never to match. This option affects only the behav-
2061           iour of the circumflex metacharacter. It does not affect \A.
2062    
2063             PCRE_NOTEOL
2064    
2065           This option specifies that the end of the subject string is not the end
2066           of  a line, so the dollar metacharacter should not match it nor (except
2067           in multiline mode) a newline immediately before it. Setting this  with-
2068           out PCRE_MULTILINE (at compile time) causes dollar never to match. This
2069           option affects only the behaviour of the dollar metacharacter. It  does
2070           not affect \Z or \z.
2071    
2072             PCRE_NOTEMPTY
2073    
2074           An empty string is not considered to be a valid match if this option is
2075           set. If there are alternatives in the pattern, they are tried.  If  all
2076           the  alternatives  match  the empty string, the entire match fails. For
2077           example, if the pattern
2078    
2079             a?b?
2080    
2081           is applied to a string not beginning with "a" or  "b",  it  matches  an
2082           empty  string at the start of the subject. With PCRE_NOTEMPTY set, this
2083           match is not valid, so PCRE searches further into the string for occur-
2084           rences of "a" or "b".
2085    
2086             PCRE_NOTEMPTY_ATSTART
2087    
2088           This  is  like PCRE_NOTEMPTY, except that an empty string match that is
2089           not at the start of  the  subject  is  permitted.  If  the  pattern  is
2090           anchored, such a match can occur only if the pattern contains \K.
2091    
2092           Perl     has    no    direct    equivalent    of    PCRE_NOTEMPTY    or
2093           PCRE_NOTEMPTY_ATSTART, but it does make a special  case  of  a  pattern
2094           match  of  the empty string within its split() function, and when using
2095           the /g modifier. It is  possible  to  emulate  Perl's  behaviour  after
2096           matching a null string by first trying the match again at the same off-
2097           set with PCRE_NOTEMPTY_ATSTART and  PCRE_ANCHORED,  and  then  if  that
2098           fails, by advancing the starting offset (see below) and trying an ordi-
2099           nary match again. There is some code that demonstrates how to  do  this
2100           in the pcredemo sample program.
2101    
2102             PCRE_NO_START_OPTIMIZE
2103    
2104           There  are a number of optimizations that pcre_exec() uses at the start
2105           of a match, in order to speed up the process. For  example,  if  it  is
2106           known  that  a  match must start with a specific character, it searches
2107           the subject for that character, and fails immediately if it cannot find
2108           it,  without actually running the main matching function. When callouts
2109           are in use, these optimizations can cause  them  to  be  skipped.  This
2110           option  disables  the  "start-up" optimizations, causing performance to
2111           suffer, but ensuring that the callouts do occur.
2112    
2113             PCRE_NO_UTF8_CHECK
2114    
2115           When PCRE_UTF8 is set at compile time, the validity of the subject as a
2116           UTF-8  string is automatically checked when pcre_exec() is subsequently
2117           called.  The value of startoffset is also checked  to  ensure  that  it
2118           points  to  the start of a UTF-8 character. There is a discussion about
2119           the validity of UTF-8 strings in the section on UTF-8  support  in  the
2120           main  pcre  page.  If  an  invalid  UTF-8  sequence  of bytes is found,
2121           pcre_exec() returns the error PCRE_ERROR_BADUTF8. If  startoffset  con-
2122           tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
2123    
2124           If  you  already  know that your subject is valid, and you want to skip
2125           these   checks   for   performance   reasons,   you   can    set    the
2126           PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to
2127           do this for the second and subsequent calls to pcre_exec() if  you  are
2128           making  repeated  calls  to  find  all  the matches in a single subject
2129           string. However, you should be  sure  that  the  value  of  startoffset
2130           points  to  the  start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is
2131           set, the effect of passing an invalid UTF-8 string as a subject,  or  a
2132           value  of startoffset that does not point to the start of a UTF-8 char-
2133           acter, is undefined. Your program may crash.
2134    
2135             PCRE_PARTIAL_HARD
2136             PCRE_PARTIAL_SOFT
2137    
2138           These options turn on the partial matching feature. For backwards  com-
2139           patibility,  PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial
2140           match occurs if the end of the subject string is reached  successfully,
2141           but  there  are not enough subject characters to complete the match. If
2142           this happens when PCRE_PARTIAL_HARD  is  set,  pcre_exec()  immediately
2143           returns  PCRE_ERROR_PARTIAL.  Otherwise,  if  PCRE_PARTIAL_SOFT is set,
2144           matching continues by testing any other alternatives. Only if they  all
2145           fail  is  PCRE_ERROR_PARTIAL  returned (instead of PCRE_ERROR_NOMATCH).
2146           The portion of the string that was inspected when the partial match was
2147           found  is  set  as  the first matching string. There is a more detailed
2148           discussion in the pcrepartial documentation.
2149    
2150       The string to be matched by pcre_exec()
2151    
2152           The subject string is passed to pcre_exec() as a pointer in subject,  a
2153           length (in bytes) in length, and a starting byte offset in startoffset.
2154           In UTF-8 mode, the byte offset must point to the start of a UTF-8 char-
2155           acter.  Unlike  the pattern string, the subject may contain binary zero
2156           bytes. When the starting offset is zero, the search for a match  starts
2157           at  the  beginning  of  the subject, and this is by far the most common
2158           case.
2159    
2160           A non-zero starting offset is useful when searching for  another  match
2161           in  the same subject by calling pcre_exec() again after a previous suc-
2162           cess.  Setting startoffset differs from just passing over  a  shortened
2163           string  and  setting  PCRE_NOTBOL  in the case of a pattern that begins
2164           with any kind of lookbehind. For example, consider the pattern
2165    
2166             \Biss\B
2167    
2168           which finds occurrences of "iss" in the middle of  words.  (\B  matches
2169           only  if  the  current position in the subject is not a word boundary.)
2170           When applied to the string "Mississipi" the first call  to  pcre_exec()
2171           finds  the  first  occurrence. If pcre_exec() is called again with just
2172           the remainder of the subject,  namely  "issipi",  it  does  not  match,
2173           because \B is always false at the start of the subject, which is deemed
2174           to be a word boundary. However, if pcre_exec()  is  passed  the  entire
2175           string again, but with startoffset set to 4, it finds the second occur-
2176           rence of "iss" because it is able to look behind the starting point  to
2177           discover that it is preceded by a letter.
2178    
2179           If  a  non-zero starting offset is passed when the pattern is anchored,
2180           one attempt to match at the given offset is made. This can only succeed
2181           if  the  pattern  does  not require the match to be at the start of the
2182           subject.
2183    
2184       How pcre_exec() returns captured substrings
2185    
2186           In general, a pattern matches a certain portion of the subject, and  in
2187           addition,  further  substrings  from  the  subject may be picked out by
2188           parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,
2189           this  is  called "capturing" in what follows, and the phrase "capturing
2190           subpattern" is used for a fragment of a pattern that picks out  a  sub-
2191           string.  PCRE  supports several other kinds of parenthesized subpattern
2192           that do not cause substrings to be captured.
2193    
2194           Captured substrings are returned to the caller via a vector of integers
2195           whose  address is passed in ovector. The number of elements in the vec-
2196           tor is passed in ovecsize, which must be a non-negative  number.  Note:
2197           this argument is NOT the size of ovector in bytes.
2198    
2199           The  first  two-thirds of the vector is used to pass back captured sub-
2200           strings, each substring using a pair of integers. The  remaining  third
2201           of  the  vector is used as workspace by pcre_exec() while matching cap-
2202           turing subpatterns, and is not available for passing back  information.
2203           The  number passed in ovecsize should always be a multiple of three. If
2204           it is not, it is rounded down.
2205    
2206           When a match is successful, information about  captured  substrings  is
2207           returned  in  pairs  of integers, starting at the beginning of ovector,
2208           and continuing up to two-thirds of its length at the  most.  The  first
2209           element  of  each pair is set to the byte offset of the first character
2210           in a substring, and the second is set to the byte offset of  the  first
2211           character  after  the end of a substring. Note: these values are always
2212           byte offsets, even in UTF-8 mode. They are not character counts.
2213    
2214           The first pair of integers, ovector[0]  and  ovector[1],  identify  the
2215           portion  of  the subject string matched by the entire pattern. The next
2216           pair is used for the first capturing subpattern, and so on.  The  value
2217           returned by pcre_exec() is one more than the highest numbered pair that
2218           has been set.  For example, if two substrings have been  captured,  the
2219           returned  value is 3. If there are no capturing subpatterns, the return
2220           value from a successful match is 1, indicating that just the first pair
2221           of offsets has been set.
2222    
2223           If a capturing subpattern is matched repeatedly, it is the last portion
2224           of the string that it matched that is returned.
2225    
2226           If the vector is too small to hold all the captured substring  offsets,
2227           it is used as far as possible (up to two-thirds of its length), and the
2228           function returns a value of zero. If the substring offsets are  not  of
2229           interest,  pcre_exec()  may  be  called with ovector passed as NULL and
2230           ovecsize as zero. However, if the pattern contains back references  and
2231           the  ovector is not big enough to remember the related substrings, PCRE
2232           has to get additional memory for use during matching. Thus it  is  usu-
2233           ally advisable to supply an ovector.
2234    
2235           The pcre_fullinfo() function can be used to find out how many capturing
2236           subpatterns there are in a compiled  pattern.  The  smallest  size  for
2237           ovector  that  will allow for n captured substrings, in addition to the
2238           offsets of the substring matched by the whole pattern, is (n+1)*3.
2239    
2240           It is possible for capturing subpattern number n+1 to match  some  part
2241           of the subject when subpattern n has not been used at all. For example,
2242           if the string "abc" is matched  against  the  pattern  (a|(z))(bc)  the
2243           return from the function is 4, and subpatterns 1 and 3 are matched, but
2244           2 is not. When this happens, both values in  the  offset  pairs  corre-
2245           sponding to unused subpatterns are set to -1.
2246    
2247           Offset  values  that correspond to unused subpatterns at the end of the
2248           expression are also set to -1. For example,  if  the  string  "abc"  is
2249           matched  against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
2250           matched. The return from the function is 2, because  the  highest  used
2251           capturing subpattern number is 1. However, you can refer to the offsets
2252           for the second and third capturing subpatterns if  you  wish  (assuming
2253           the vector is large enough, of course).
2254    
2255           Some  convenience  functions  are  provided for extracting the captured
2256           substrings as separate strings. These are described below.
2257    
2258       Error return values from pcre_exec()
2259    
2260           If pcre_exec() fails, it returns a negative number. The  following  are
2261           defined in the header file:
2262    
2263             PCRE_ERROR_NOMATCH        (-1)
2264    
2265           The subject string did not match the pattern.
2266    
2267             PCRE_ERROR_NULL           (-2)
2268    
2269           Either  code  or  subject  was  passed as NULL, or ovector was NULL and
2270           ovecsize was not zero.
2271    
2272             PCRE_ERROR_BADOPTION      (-3)
2273    
2274           An unrecognized bit was set in the options argument.
2275    
2276             PCRE_ERROR_BADMAGIC       (-4)
2277    
2278           PCRE stores a 4-byte "magic number" at the start of the compiled  code,
2279           to catch the case when it is passed a junk pointer and to detect when a
2280           pattern that was compiled in an environment of one endianness is run in
2281           an  environment  with the other endianness. This is the error that PCRE
2282           gives when the magic number is not present.
2283    
2284             PCRE_ERROR_UNKNOWN_OPCODE (-5)
2285    
2286           While running the pattern match, an unknown item was encountered in the
2287           compiled  pattern.  This  error  could be caused by a bug in PCRE or by
2288           overwriting of the compiled pattern.
2289    
2290             PCRE_ERROR_NOMEMORY       (-6)
2291    
2292           If a pattern contains back references, but the ovector that  is  passed
2293           to pcre_exec() is not big enough to remember the referenced substrings,
2294           PCRE gets a block of memory at the start of matching to  use  for  this
2295           purpose.  If the call via pcre_malloc() fails, this error is given. The
2296           memory is automatically freed at the end of matching.
2297    
2298             PCRE_ERROR_NOSUBSTRING    (-7)
2299    
2300           This error is used by the pcre_copy_substring(),  pcre_get_substring(),
2301           and  pcre_get_substring_list()  functions  (see  below).  It  is  never
2302           returned by pcre_exec().
2303    
2304             PCRE_ERROR_MATCHLIMIT     (-8)
2305    
2306           The backtracking limit, as specified by  the  match_limit  field  in  a
2307           pcre_extra  structure  (or  defaulted) was reached. See the description
2308           above.
2309    
2310             PCRE_ERROR_CALLOUT        (-9)
2311    
2312           This error is never generated by pcre_exec() itself. It is provided for
2313           use  by  callout functions that want to yield a distinctive error code.
2314           See the pcrecallout documentation for details.
2315    
2316             PCRE_ERROR_BADUTF8        (-10)
2317    
2318           A string that contains an invalid UTF-8 byte sequence was passed  as  a
2319           subject.
2320    
2321             PCRE_ERROR_BADUTF8_OFFSET (-11)
2322    
2323           The UTF-8 byte sequence that was passed as a subject was valid, but the
2324           value of startoffset did not point to the beginning of a UTF-8  charac-
2325           ter.
2326    
2327             PCRE_ERROR_PARTIAL        (-12)
2328    
2329           The  subject  string did not match, but it did match partially. See the
2330           pcrepartial documentation for details of partial matching.
2331    
2332             PCRE_ERROR_BADPARTIAL     (-13)
2333    
2334           This code is no longer in  use.  It  was  formerly  returned  when  the
2335           PCRE_PARTIAL  option  was used with a compiled pattern containing items
2336           that were  not  supported  for  partial  matching.  From  release  8.00
2337           onwards, there are no restrictions on partial matching.
2338    
2339             PCRE_ERROR_INTERNAL       (-14)
2340    
2341           An  unexpected  internal error has occurred. This error could be caused
2342           by a bug in PCRE or by overwriting of the compiled pattern.
2343    
2344             PCRE_ERROR_BADCOUNT       (-15)
2345    
2346           This error is given if the value of the ovecsize argument is negative.
2347    
2348             PCRE_ERROR_RECURSIONLIMIT (-21)
2349    
2350           The internal recursion limit, as specified by the match_limit_recursion
2351           field  in  a  pcre_extra  structure (or defaulted) was reached. See the
2352           description above.
2353    
2354             PCRE_ERROR_BADNEWLINE     (-23)
2355    
2356  MATCHING A PATTERN         An invalid combination of PCRE_NEWLINE_xxx options was given.
2357    
2358       int pcre_exec(const pcre *code, const pcre_extra *extra,         Error numbers -16 to -20 and -22 are not used by pcre_exec().
           const char *subject, int length, int startoffset,  
           int options, int *ovector, int ovecsize);  
   
      The function pcre_exec() is called to match a subject string  
      against  a pre-compiled pattern, which is passed in the code  
      argument. If the pattern has been studied, the result of the  
      study should be passed in the extra argument.  
   
      Here is an example of a simple call to pcre_exec():  
   
        int rc;  
        int ovector[30];  
        rc = pcre_exec(  
          re,             /* result of pcre_compile() */  
          NULL,           /* we didn't study the pattern */  
          "some string",  /* the subject string */  
          11,             /* the length of the subject string */  
          0,              /* start at offset 0 in the subject */  
          0,              /* default options */  
          ovector,        /* vector for substring information */  
          30);            /* number of elements in the vector */  
   
      If the extra argument is  not  NULL,  it  must  point  to  a  
      pcre_extra  data  block.  The  pcre_study() function returns  
      such a block (when it doesn't return NULL), but you can also  
      create  one for yourself, and pass additional information in  
      it. The fields in the block are as follows:  
   
        unsigned long int flags;  
        void *study_data;  
        unsigned long int match_limit;  
        void *callout_data;  
   
      The flags field is a bitmap  that  specifies  which  of  the  
      other fields are set. The flag bits are:  
   
        PCRE_EXTRA_STUDY_DATA  
        PCRE_EXTRA_MATCH_LIMIT  
        PCRE_EXTRA_CALLOUT_DATA  
   
      Other flag bits should be set to zero. The study_data  field  
      is   set  in  the  pcre_extra  block  that  is  returned  by  
      pcre_study(), together with the appropriate  flag  bit.  You  
      should  not  set this yourself, but you can add to the block  
      by setting the other fields.  
   
      The match_limit field provides a means  of  preventing  PCRE  
      from  using  up a vast amount of resources when running pat-  
      terns that are not going to match, but  which  have  a  very  
      large  number  of  possibilities  in their search trees. The  
      classic example is the  use  of  nested  unlimited  repeats.  
      Internally,  PCRE  uses  a  function called match() which it  
      calls  repeatedly  (sometimes  recursively).  The  limit  is  
      imposed  on the number of times this function is called dur-  
      ing a match, which has the effect of limiting the amount  of  
      recursion and backtracking that can take place. For patterns  
      that are not anchored, the count starts from zero  for  each  
      position in the subject string.  
   
      The default limit for the library can be set  when  PCRE  is  
      built;  the default default is 10 million, which handles all  
      but the most extreme cases. You can reduce  the  default  by  
      suppling  pcre_exec()  with  a  pcre_extra  block  in  which  
      match_limit   is   set   to    a    smaller    value,    and  
      PCRE_EXTRA_MATCH_LIMIT  is  set  in  the flags field. If the  
      limit      is      exceeded,       pcre_exec()       returns  
      PCRE_ERROR_MATCHLIMIT.  
   
      The pcre_callout field is used in conjunction with the "cal-  
      lout"  feature,  which is described in the pcrecallout docu-  
      mentation.  
   
      The PCRE_ANCHORED option can be passed in the options  argu-  
      ment,   whose   unused   bits  must  be  zero.  This  limits  
      pcre_exec() to matching at the first matching position. How-  
      ever,  if  a  pattern  was  compiled  with PCRE_ANCHORED, or  
      turned out to be anchored by virtue of its contents, it can-  
      not be made unachored at matching time.  
   
      There are also three further options that can be set only at  
      matching time:  
   
        PCRE_NOTBOL  
   
      The first character of the string is not the beginning of  a  
      line,  so  the  circumflex  metacharacter  should  not match  
      before it. Setting this without PCRE_MULTILINE  (at  compile  
      time) causes circumflex never to match.  
   
        PCRE_NOTEOL  
   
      The end of the string is not the end of a line, so the  dol-  
      lar  metacharacter should not match it nor (except in multi-  
      line mode) a newline immediately  before  it.  Setting  this  
      without PCRE_MULTILINE (at compile time) causes dollar never  
      to match.  
   
        PCRE_NOTEMPTY  
   
      An empty string is not considered to be  a  valid  match  if  
      this  option  is  set. If there are alternatives in the pat-  
      tern, they are tried. If  all  the  alternatives  match  the  
      empty  string,  the  entire match fails. For example, if the  
      pattern  
   
        a?b?  
   
      is applied to a string not beginning with  "a"  or  "b",  it  
      matches  the  empty string at the start of the subject. With  
      PCRE_NOTEMPTY set, this match is not valid, so PCRE searches  
      further into the string for occurrences of "a" or "b".  
   
      Perl has no direct equivalent of PCRE_NOTEMPTY, but it  does  
      make  a  special case of a pattern match of the empty string  
      within its split() function, and when using the /g modifier.  
      It  is possible to emulate Perl's behaviour after matching a  
      null string by first trying the  match  again  at  the  same  
      offset  with  PCRE_NOTEMPTY  set,  and then if that fails by  
      advancing the starting offset  (see  below)  and  trying  an  
      ordinary match again.  
   
      The subject string is passed to pcre_exec() as a pointer  in  
      subject,  a length in length, and a starting offset in star-  
      toffset. Unlike the pattern string, the subject may  contain  
      binary  zero  bytes.  When  the starting offset is zero, the  
      search for a match starts at the beginning of  the  subject,  
      and this is by far the most common case.  
   
      If the pattern was compiled with the PCRE_UTF8  option,  the  
      subject  must  be  a sequence of bytes that is a valid UTF-8  
      string.  If  an  invalid  UTF-8  string  is  passed,  PCRE's  
      behaviour is not defined.  
   
      A non-zero starting offset  is  useful  when  searching  for  
      another  match  in  the  same subject by calling pcre_exec()  
      again after a previous success.  Setting startoffset differs  
      from  just  passing  over  a  shortened  string  and setting  
      PCRE_NOTBOL in the case of a pattern that  begins  with  any  
      kind of lookbehind. For example, consider the pattern  
   
        \Biss\B  
   
      which finds occurrences of "iss" in the middle of words. (\B  
      matches only if the current position in the subject is not a  
      word boundary.) When applied to the string "Mississipi"  the  
      first  call  to  pcre_exec()  finds the first occurrence. If  
      pcre_exec() is called again with just the remainder  of  the  
      subject,  namely  "issipi", it does not match, because \B is  
      always false at the start of the subject, which is deemed to  
      be  a  word  boundary. However, if pcre_exec() is passed the  
      entire string again, but with startoffset set to 4, it finds  
      the  second  occurrence  of "iss" because it is able to look  
      behind the starting point to discover that it is preceded by  
      a letter.  
   
      If a non-zero starting offset is passed when the pattern  is  
      anchored, one attempt to match at the given offset is tried.  
      This can only succeed if the pattern does  not  require  the  
      match to be at the start of the subject.  
   
      In general, a pattern matches a certain portion of the  sub-  
      ject,  and  in addition, further substrings from the subject  
      may be picked out by parts of  the  pattern.  Following  the  
      usage  in  Jeffrey Friedl's book, this is called "capturing"  
      in what follows, and the phrase  "capturing  subpattern"  is  
      used for a fragment of a pattern that picks out a substring.  
      PCRE supports several other kinds of  parenthesized  subpat-  
      tern that do not cause substrings to be captured.  
   
      Captured substrings are returned to the caller via a  vector  
      of  integer  offsets whose address is passed in ovector. The  
      number of elements in the vector is passed in ovecsize.  The  
      first two-thirds of the vector is used to pass back captured  
      substrings, each substring using a  pair  of  integers.  The  
      remaining  third  of  the  vector  is  used  as workspace by  
      pcre_exec() while matching capturing subpatterns, and is not  
      available for passing back information. The length passed in  
      ovecsize should always be a multiple of three. If it is not,  
      it is rounded down.  
   
      When a match has been successful, information about captured  
      substrings is returned in pairs of integers, starting at the  
      beginning of ovector, and continuing up to two-thirds of its  
      length  at  the  most. The first element of a pair is set to  
      the offset of the first character in a  substring,  and  the  
      second is set to the offset of the first character after the  
      end of a substring. The first  pair,  ovector[0]  and  ovec-  
      tor[1],  identify  the portion of the subject string matched  
      by the entire pattern. The next pair is used for  the  first  
      capturing  subpattern,  and  so  on.  The  value returned by  
      pcre_exec() is the number of pairs that have  been  set.  If  
      there  are no capturing subpatterns, the return value from a  
      successful match is 1, indicating that just the  first  pair  
      of offsets has been set.  
   
      Some convenience functions are provided for  extracting  the  
      captured substrings as separate strings. These are described  
      in the following section.  
   
      It is possible for an capturing  subpattern  number  n+1  to  
      match  some  part  of  the subject when subpattern n has not  
      been used at all.  For  example,  if  the  string  "abc"  is  
      matched  against the pattern (a|(z))(bc) subpatterns 1 and 3  
      are matched, but 2 is not. When this  happens,  both  offset  
      values corresponding to the unused subpattern are set to -1.  
   
      If a capturing subpattern is matched repeatedly, it  is  the  
      last  portion  of  the  string  that  it  matched  that gets  
      returned.  
   
      If the vector is too small to hold  all  the  captured  sub-  
      strings,  it is used as far as possible (up to two-thirds of  
      its length), and the function returns a value  of  zero.  In  
      particular,  if  the  substring offsets are not of interest,  
      pcre_exec() may be called with ovector passed  as  NULL  and  
      ovecsize  as  zero.  However,  if  the pattern contains back  
      references and the ovector isn't big enough to remember  the  
      related  substrings,  PCRE  has to get additional memory for  
      use during matching. Thus it is usually advisable to  supply  
      an ovector.  
   
      Note that pcre_info() can be used to find out how many  cap-  
      turing  subpatterns  there  are  in  a compiled pattern. The  
      smallest size for ovector that will  allow  for  n  captured  
      substrings,  in  addition  to  the  offsets of the substring  
      matched by the whole pattern, is (n+1)*3.  
   
      If pcre_exec() fails, it returns a negative number. The fol-  
      lowing are defined in the header file:  
   
        PCRE_ERROR_NOMATCH        (-1)  
   
      The subject string did not match the pattern.  
   
        PCRE_ERROR_NULL           (-2)  
   
      Either code or subject was passed as NULL,  or  ovector  was  
      NULL and ovecsize was not zero.  
   
        PCRE_ERROR_BADOPTION      (-3)  
   
      An unrecognized bit was set in the options argument.  
   
        PCRE_ERROR_BADMAGIC       (-4)  
   
      PCRE stores a 4-byte "magic number" at the start of the com-  
      piled  code,  to  catch  the  case  when it is passed a junk  
      pointer. This is the error it gives when  the  magic  number  
      isn't present.  
   
        PCRE_ERROR_UNKNOWN_NODE   (-5)  
   
      While running the pattern match, an unknown item was encoun-  
      tered in the compiled pattern. This error could be caused by  
      a bug in PCRE or by overwriting of the compiled pattern.  
   
        PCRE_ERROR_NOMEMORY       (-6)  
   
      If a pattern contains back references, but the ovector  that  
      is  passed  to pcre_exec() is not big enough to remember the  
      referenced substrings, PCRE gets a block of  memory  at  the  
      start  of  matching to use for this purpose. If the call via  
      pcre_malloc() fails, this error  is  given.  The  memory  is  
      freed at the end of matching.  
   
        PCRE_ERROR_NOSUBSTRING    (-7)  
   
      This   error   is   used   by   the   pcre_copy_substring(),  
      pcre_get_substring(),  and  pcre_get_substring_list()  func-  
      tions (see below). It is never returned by pcre_exec().  
   
        PCRE_ERROR_MATCHLIMIT     (-8)  
   
      The recursion and backtracking limit, as  specified  by  the  
      match_limit  field  in a pcre_extra structure (or defaulted)  
      was reached. See the description above.  
   
        PCRE_ERROR_CALLOUT        (-9)  
   
      This error is never generated by pcre_exec() itself.  It  is  
      provided  for  use by callout functions that want to yield a  
      distinctive error code. See  the  pcrecallout  documentation  
      for details.  
2359    
2360    
2361  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2362    
2363       int pcre_copy_substring(const char *subject, int *ovector,         int pcre_copy_substring(const char *subject, int *ovector,
2364            int stringcount, int stringnumber, char *buffer,              int stringcount, int stringnumber, char *buffer,
2365            int buffersize);              int buffersize);
2366    
2367       int pcre_get_substring(const char *subject, int *ovector,         int pcre_get_substring(const char *subject, int *ovector,
2368            int stringcount, int stringnumber,              int stringcount, int stringnumber,
2369            const char **stringptr);              const char **stringptr);
2370    
2371       int pcre_get_substring_list(const char *subject,         int pcre_get_substring_list(const char *subject,
2372            int *ovector, int stringcount, const char ***listptr);              int *ovector, int stringcount, const char ***listptr);
2373    
2374       Captured substrings can be accessed directly  by  using  the         Captured substrings can be  accessed  directly  by  using  the  offsets
2375       offsets returned by pcre_exec() in ovector. For convenience,         returned  by  pcre_exec()  in  ovector.  For convenience, the functions
2376       the functions  pcre_copy_substring(),  pcre_get_substring(),         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
2377       and  pcre_get_substring_list()  are  provided for extracting         string_list()  are  provided for extracting captured substrings as new,
2378       captured  substrings  as  new,   separate,   zero-terminated         separate, zero-terminated strings. These functions identify  substrings
2379       strings.  These functions identify substrings by number. The         by  number.  The  next section describes functions for extracting named
2380       next section describes functions for extracting  named  sub-         substrings.
2381       strings.   A  substring  that  contains  a  binary  zero  is  
2382       correctly extracted and has a further zero added on the end,         A substring that contains a binary zero is correctly extracted and  has
2383       but the result is not, of course, a C string.         a  further zero added on the end, but the result is not, of course, a C
2384           string.  However, you can process such a string  by  referring  to  the
2385       The first three arguments are the  same  for  all  three  of         length  that  is  returned  by  pcre_copy_substring() and pcre_get_sub-
2386       these  functions:   subject  is the subject string which has         string().  Unfortunately, the interface to pcre_get_substring_list() is
2387       just been successfully matched, ovector is a pointer to  the         not  adequate for handling strings containing binary zeros, because the
2388       vector  of  integer  offsets that was passed to pcre_exec(),         end of the final string is not independently indicated.
2389       and stringcount is the number of substrings that  were  cap-  
2390       tured by the match, including the substring that matched the         The first three arguments are the same for all  three  of  these  func-
2391       entire regular expression. This is  the  value  returned  by         tions:  subject  is  the subject string that has just been successfully
2392       pcre_exec  if  it  is  greater  than  zero.  If  pcre_exec()         matched, ovector is a pointer to the vector of integer offsets that was
2393       returned zero, indicating that it ran out of space in  ovec-         passed to pcre_exec(), and stringcount is the number of substrings that
2394       tor,  the  value passed as stringcount should be the size of         were captured by the match, including the substring  that  matched  the
2395       the vector divided by three.         entire regular expression. This is the value returned by pcre_exec() if
2396           it is greater than zero. If pcre_exec() returned zero, indicating  that
2397       The functions pcre_copy_substring() and pcre_get_substring()         it  ran out of space in ovector, the value passed as stringcount should
2398       extract a single substring, whose number is given as string-         be the number of elements in the vector divided by three.
2399       number. A value of zero extracts the substring that  matched  
2400       the entire pattern, while higher values extract the captured         The functions pcre_copy_substring() and pcre_get_substring() extract  a
2401       substrings. For pcre_copy_substring(), the string is  placed         single  substring,  whose  number  is given as stringnumber. A value of
2402       in  buffer,  whose  length is given by buffersize, while for         zero extracts the substring that matched the  entire  pattern,  whereas
2403       pcre_get_substring() a new block of memory is  obtained  via         higher  values  extract  the  captured  substrings.  For pcre_copy_sub-
2404       pcre_malloc,  and its address is returned via stringptr. The         string(), the string is placed in buffer,  whose  length  is  given  by
2405       yield of the function is  the  length  of  the  string,  not         buffersize,  while  for  pcre_get_substring()  a new block of memory is
2406       including the terminating zero, or one of         obtained via pcre_malloc, and its address is  returned  via  stringptr.
2407           The  yield  of  the function is the length of the string, not including
2408         PCRE_ERROR_NOMEMORY       (-6)         the terminating zero, or one of these error codes:
2409    
2410       The buffer was too small for pcre_copy_substring(),  or  the           PCRE_ERROR_NOMEMORY       (-6)
2411       attempt to get memory failed for pcre_get_substring().  
2412           The buffer was too small for pcre_copy_substring(), or the  attempt  to
2413         PCRE_ERROR_NOSUBSTRING    (-7)         get memory failed for pcre_get_substring().
2414    
2415       There is no substring whose number is stringnumber.           PCRE_ERROR_NOSUBSTRING    (-7)
2416    
2417       The pcre_get_substring_list() function extracts  all  avail-         There is no substring whose number is stringnumber.
2418       able  substrings  and builds a list of pointers to them. All  
2419       this is done in a single block of memory which  is  obtained         The  pcre_get_substring_list()  function  extracts  all  available sub-
2420       via pcre_malloc. The address of the memory block is returned         strings and builds a list of pointers to them. All this is  done  in  a
2421       via listptr, which is also the start of the list  of  string         single block of memory that is obtained via pcre_malloc. The address of
2422       pointers.  The  end of the list is marked by a NULL pointer.         the memory block is returned via listptr, which is also  the  start  of
2423       The yield of the function is zero if all went well, or         the  list  of  string pointers. The end of the list is marked by a NULL
2424           pointer. The yield of the function is zero if all  went  well,  or  the
2425         PCRE_ERROR_NOMEMORY       (-6)         error code
2426    
2427       if the attempt to get the memory block failed.           PCRE_ERROR_NOMEMORY       (-6)
2428    
2429       When any of these functions encounter a  substring  that  is         if the attempt to get the memory block failed.
2430       unset, which can happen when capturing subpattern number n+1  
2431       matches some part of the subject, but subpattern n  has  not         When  any of these functions encounter a substring that is unset, which
2432       been  used  at all, they return an empty string. This can be         can happen when capturing subpattern number n+1 matches  some  part  of
2433       distinguished  from  a  genuine  zero-length  substring   by         the  subject, but subpattern n has not been used at all, they return an
2434       inspecting the appropriate offset in ovector, which is nega-         empty string. This can be distinguished from a genuine zero-length sub-
2435       tive for unset substrings.         string  by inspecting the appropriate offset in ovector, which is nega-
2436           tive for unset substrings.
2437       The  two  convenience  functions  pcre_free_substring()  and  
2438       pcre_free_substring_list()  can  be  used to free the memory         The two convenience functions pcre_free_substring() and  pcre_free_sub-
2439       returned by  a  previous  call  of  pcre_get_substring()  or         string_list()  can  be  used  to free the memory returned by a previous
2440       pcre_get_substring_list(),  respectively.  They  do  nothing         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2441       more than call the function pointed to by  pcre_free,  which         tively.  They  do  nothing  more  than  call the function pointed to by
2442       of  course  could  be called directly from a C program. How-         pcre_free, which of course could be called directly from a  C  program.
2443       ever, PCRE is used in some situations where it is linked via         However,  PCRE is used in some situations where it is linked via a spe-
2444       a  special  interface  to another programming language which         cial  interface  to  another  programming  language  that  cannot   use
2445       cannot use pcre_free directly; it is for  these  cases  that         pcre_free  directly;  it is for these cases that the functions are pro-
2446       the functions are provided.         vided.
2447    
2448    
2449  EXTRACTING CAPTURED SUBSTRINGS BY NAME  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2450    
2451       int pcre_copy_named_substring(const pcre *code,         int pcre_get_stringnumber(const pcre *code,
2452            const char *subject, int *ovector,              const char *name);
2453            int stringcount, const char *stringname,  
2454            char *buffer, int buffersize);         int pcre_copy_named_substring(const pcre *code,
2455                const char *subject, int *ovector,
2456       int pcre_get_stringnumber(const pcre *code,              int stringcount, const char *stringname,
2457            const char *name);              char *buffer, int buffersize);
2458    
2459       int pcre_get_named_substring(const pcre *code,         int pcre_get_named_substring(const pcre *code,
2460            const char *subject, int *ovector,              const char *subject, int *ovector,
2461            int stringcount, const char *stringname,              int stringcount, const char *stringname,
2462            const char **stringptr);              const char **stringptr);
2463    
2464       To extract a substring by name, you first have to find asso-         To extract a substring by name, you first have to find associated  num-
2465       ciated    number.    This    can    be   done   by   calling         ber.  For example, for this pattern
2466       pcre_get_stringnumber(). The first argument is the  compiled  
2467       pattern,  and  the second is the name. For example, for this           (a+)b(?<xxx>\d+)...
2468       pattern  
2469           the number of the subpattern called "xxx" is 2. If the name is known to
2470         ab(?<xxx>\d+)...         be unique (PCRE_DUPNAMES was not set), you can find the number from the
2471           name by calling pcre_get_stringnumber(). The first argument is the com-
2472       the number of the subpattern called "xxx" is  1.  Given  the         piled pattern, and the second is the name. The yield of the function is
2473       number,  you can then extract the substring directly, or use         the  subpattern  number,  or PCRE_ERROR_NOSUBSTRING (-7) if there is no
2474       one of the functions described in the previous section.  For         subpattern of that name.
2475       convenience,  there are also two functions that do the whole  
2476       job.         Given the number, you can extract the substring directly, or use one of
2477           the functions described in the previous section. For convenience, there
2478       Most of the  arguments  of  pcre_copy_named_substring()  and         are also two functions that do the whole job.
2479       pcre_get_named_substring()  are  the  same  as those for the  
2480       functions that  extract  by  number,  and  so  are  not  re-         Most   of   the   arguments    of    pcre_copy_named_substring()    and
2481       described here. There are just two differences.         pcre_get_named_substring()  are  the  same  as  those for the similarly
2482           named functions that extract by number. As these are described  in  the
2483       First, instead of a substring number, a  substring  name  is         previous  section,  they  are not re-described here. There are just two
2484       given.  Second,  there  is  an  extra argument, given at the         differences:
2485       start, which is a pointer to the compiled pattern.  This  is  
2486       needed  in order to gain access to the name-to-number trans-         First, instead of a substring number, a substring name is  given.  Sec-
2487       lation table.         ond, there is an extra argument, given at the start, which is a pointer
2488           to the compiled pattern. This is needed in order to gain access to  the
2489       These functions  call  pcre_get_stringnumber(),  and  if  it         name-to-number translation table.
2490       succeeds,    they   then   call   pcre_copy_substring()   or  
2491       pcre_get_substring(), as appropriate.         These  functions call pcre_get_stringnumber(), and if it succeeds, they
2492           then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-
2493           ate.  NOTE:  If PCRE_DUPNAMES is set and there are duplicate names, the
2494           behaviour may not be what you want (see the next section).
2495    
2496           Warning: If the pattern uses the (?| feature to set up multiple subpat-
2497           terns  with  the  same number, as described in the section on duplicate
2498           subpattern numbers in the pcrepattern page, you  cannot  use  names  to
2499           distinguish  the  different subpatterns, because names are not included
2500           in the compiled code. The matching process uses only numbers. For  this
2501           reason,  the  use of different names for subpatterns of the same number
2502           causes an error at compile time.
2503    
2504    
2505    DUPLICATE SUBPATTERN NAMES
2506    
2507           int pcre_get_stringtable_entries(const pcre *code,
2508                const char *name, char **first, char **last);
2509    
2510           When a pattern is compiled with the  PCRE_DUPNAMES  option,  names  for
2511           subpatterns  are not required to be unique. (Duplicate names are always
2512           allowed for subpatterns with the same number, created by using the  (?|
2513           feature.  Indeed,  if  such subpatterns are named, they are required to
2514           use the same names.)
2515    
2516           Normally, patterns with duplicate names are such that in any one match,
2517           only  one of the named subpatterns participates. An example is shown in
2518           the pcrepattern documentation.
2519    
2520           When   duplicates   are   present,   pcre_copy_named_substring()    and
2521           pcre_get_named_substring()  return the first substring corresponding to
2522           the given name that is set. If  none  are  set,  PCRE_ERROR_NOSUBSTRING
2523           (-7)  is  returned;  no  data  is returned. The pcre_get_stringnumber()
2524           function returns one of the numbers that are associated with the  name,
2525           but it is not defined which it is.
2526    
2527           If  you want to get full details of all captured substrings for a given
2528           name, you must use  the  pcre_get_stringtable_entries()  function.  The
2529           first argument is the compiled pattern, and the second is the name. The
2530           third and fourth are pointers to variables which  are  updated  by  the
2531           function. After it has run, they point to the first and last entries in
2532           the name-to-number table  for  the  given  name.  The  function  itself
2533           returns  the  length  of  each entry, or PCRE_ERROR_NOSUBSTRING (-7) if
2534           there are none. The format of the table is described above in the  sec-
2535           tion  entitled  Information  about  a  pattern.  Given all the relevant
2536           entries for the name, you can extract each of their numbers, and  hence
2537           the captured data, if any.
2538    
2539    
2540    FINDING ALL POSSIBLE MATCHES
2541    
2542           The  traditional  matching  function  uses a similar algorithm to Perl,
2543           which stops when it finds the first match, starting at a given point in
2544           the  subject.  If you want to find all possible matches, or the longest
2545           possible match, consider using the alternative matching  function  (see
2546           below)  instead.  If you cannot use the alternative function, but still
2547           need to find all possible matches, you can kludge it up by  making  use
2548           of the callout facility, which is described in the pcrecallout documen-
2549           tation.
2550    
2551           What you have to do is to insert a callout right at the end of the pat-
2552           tern.   When your callout function is called, extract and save the cur-
2553           rent matched substring. Then return  1,  which  forces  pcre_exec()  to
2554           backtrack  and  try other alternatives. Ultimately, when it runs out of
2555           matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2556    
2557    
2558    MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
2559    
2560           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
2561                const char *subject, int length, int startoffset,
2562                int options, int *ovector, int ovecsize,
2563                int *workspace, int wscount);
2564    
2565           The function pcre_dfa_exec()  is  called  to  match  a  subject  string
2566           against  a  compiled pattern, using a matching algorithm that scans the
2567           subject string just once, and does not backtrack.  This  has  different
2568           characteristics  to  the  normal  algorithm, and is not compatible with
2569           Perl. Some of the features of PCRE patterns are not  supported.  Never-
2570           theless,  there are times when this kind of matching can be useful. For
2571           a discussion of the two matching algorithms, and  a  list  of  features
2572           that  pcre_dfa_exec() does not support, see the pcrematching documenta-
2573           tion.
2574    
2575           The arguments for the pcre_dfa_exec() function  are  the  same  as  for
2576           pcre_exec(), plus two extras. The ovector argument is used in a differ-
2577           ent way, and this is described below. The other  common  arguments  are
2578           used  in  the  same way as for pcre_exec(), so their description is not
2579           repeated here.
2580    
2581           The two additional arguments provide workspace for  the  function.  The
2582           workspace  vector  should  contain at least 20 elements. It is used for
2583           keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2584           workspace  will  be  needed for patterns and subjects where there are a
2585           lot of potential matches.
2586    
2587           Here is an example of a simple call to pcre_dfa_exec():
2588    
2589             int rc;
2590             int ovector[10];
2591             int wspace[20];
2592             rc = pcre_dfa_exec(
2593               re,             /* result of pcre_compile() */
2594               NULL,           /* we didn't study the pattern */
2595               "some string",  /* the subject string */
2596               11,             /* the length of the subject string */
2597               0,              /* start at offset 0 in the subject */
2598               0,              /* default options */
2599               ovector,        /* vector of integers for substring information */
2600               10,             /* number of elements (NOT size in bytes) */
2601               wspace,         /* working space vector */
2602               20);            /* number of elements (NOT size in bytes) */
2603    
2604       Option bits for pcre_dfa_exec()
2605    
2606           The unused bits of the options argument  for  pcre_dfa_exec()  must  be
2607           zero.  The  only  bits  that  may  be  set are PCRE_ANCHORED, PCRE_NEW-
2608           LINE_xxx,        PCRE_NOTBOL,        PCRE_NOTEOL,        PCRE_NOTEMPTY,
2609           PCRE_NOTEMPTY_ATSTART, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_HARD, PCRE_PAR-
2610           TIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All  but  the  last
2611           four  of  these  are  exactly  the  same  as  for pcre_exec(), so their
2612           description is not repeated here.
2613    
2614             PCRE_PARTIAL_HARD
2615             PCRE_PARTIAL_SOFT
2616    
2617           These have the same general effect as they do for pcre_exec(), but  the
2618           details  are  slightly  different.  When  PCRE_PARTIAL_HARD  is set for
2619           pcre_dfa_exec(), it returns PCRE_ERROR_PARTIAL if the end of  the  sub-
2620           ject  is  reached  and there is still at least one matching possibility
2621           that requires additional characters. This happens even if some complete
2622           matches have also been found. When PCRE_PARTIAL_SOFT is set, the return
2623           code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end
2624           of  the  subject  is  reached, there have been no complete matches, but
2625           there is still at least one matching possibility. The  portion  of  the
2626           string  that  was inspected when the longest partial match was found is
2627           set as the first matching string in both cases.
2628    
2629             PCRE_DFA_SHORTEST
2630    
2631           Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to
2632           stop as soon as it has found one match. Because of the way the alterna-
2633           tive algorithm works, this is necessarily the shortest  possible  match
2634           at the first possible matching point in the subject string.
2635    
2636             PCRE_DFA_RESTART
2637    
2638           When pcre_dfa_exec() returns a partial match, it is possible to call it
2639           again, with additional subject characters, and have  it  continue  with
2640           the  same match. The PCRE_DFA_RESTART option requests this action; when
2641           it is set, the workspace and wscount options must  reference  the  same
2642           vector  as  before  because data about the match so far is left in them
2643           after a partial match. There is more discussion of this facility in the
2644           pcrepartial documentation.
2645    
2646       Successful returns from pcre_dfa_exec()
2647    
2648           When  pcre_dfa_exec()  succeeds, it may have matched more than one sub-
2649           string in the subject. Note, however, that all the matches from one run
2650           of  the  function  start  at the same point in the subject. The shorter
2651           matches are all initial substrings of the longer matches. For  example,
2652           if the pattern
2653    
2654             <.*>
2655    
2656           is matched against the string
2657    
2658             This is <something> <something else> <something further> no more
2659    
2660           the three matched strings are
2661    
2662             <something>
2663             <something> <something else>
2664             <something> <something else> <something further>
2665    
2666           On  success,  the  yield of the function is a number greater than zero,
2667           which is the number of matched substrings.  The  substrings  themselves
2668           are  returned  in  ovector. Each string uses two elements; the first is
2669           the offset to the start, and the second is the offset to  the  end.  In
2670           fact,  all  the  strings  have the same start offset. (Space could have
2671           been saved by giving this only once, but it was decided to retain  some
2672           compatibility  with  the  way pcre_exec() returns data, even though the
2673           meaning of the strings is different.)
2674    
2675           The strings are returned in reverse order of length; that is, the long-
2676           est  matching  string is given first. If there were too many matches to
2677           fit into ovector, the yield of the function is zero, and the vector  is
2678           filled with the longest matches.
2679    
2680       Error returns from pcre_dfa_exec()
2681    
2682           The  pcre_dfa_exec()  function returns a negative number when it fails.
2683           Many of the errors are the same  as  for  pcre_exec(),  and  these  are
2684           described  above.   There are in addition the following errors that are
2685           specific to pcre_dfa_exec():
2686    
2687             PCRE_ERROR_DFA_UITEM      (-16)
2688    
2689           This return is given if pcre_dfa_exec() encounters an item in the  pat-
2690           tern  that  it  does not support, for instance, the use of \C or a back
2691           reference.
2692    
2693             PCRE_ERROR_DFA_UCOND      (-17)
2694    
2695           This return is given if pcre_dfa_exec()  encounters  a  condition  item
2696           that  uses  a back reference for the condition, or a test for recursion
2697           in a specific group. These are not supported.
2698    
2699             PCRE_ERROR_DFA_UMLIMIT    (-18)
2700    
2701           This return is given if pcre_dfa_exec() is called with an  extra  block
2702           that contains a setting of the match_limit field. This is not supported
2703           (it is meaningless).
2704    
2705             PCRE_ERROR_DFA_WSSIZE     (-19)
2706    
2707           This return is given if  pcre_dfa_exec()  runs  out  of  space  in  the
2708           workspace vector.
2709    
2710             PCRE_ERROR_DFA_RECURSE    (-20)
2711    
2712           When  a  recursive subpattern is processed, the matching function calls
2713           itself recursively, using private vectors for  ovector  and  workspace.
2714           This  error  is  given  if  the output vector is not large enough. This
2715           should be extremely rare, as a vector of size 1000 is used.
2716    
2717    
2718    SEE ALSO
2719    
2720           pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-
2721           tial(3), pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2722    
2723    
2724    AUTHOR
2725    
2726           Philip Hazel
2727           University Computing Service
2728           Cambridge CB2 3QH, England.
2729    
2730    
2731    REVISION
2732    
2733           Last updated: 03 May 2010
2734           Copyright (c) 1997-2010 University of Cambridge.
2735    ------------------------------------------------------------------------------
2736    
2737    
2738    PCRECALLOUT(3)                                                  PCRECALLOUT(3)
2739    
 Last updated: 03 February 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
2740    
2741  NAME  NAME
2742       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2743    
2744    
2745  PCRE CALLOUTS  PCRE CALLOUTS
2746    
2747       int (*pcre_callout)(pcre_callout_block *);         int (*pcre_callout)(pcre_callout_block *);
   
      PCRE provides a feature called "callout", which is  a  means  
      of  temporarily passing control to the caller of PCRE in the  
      middle of pattern matching. The caller of PCRE  provides  an  
      external  function  by putting its entry point in the global  
      variable pcre_callout. By default,  this  variable  contains  
      NULL, which disables all calling out.  
   
      Within a regular expression, (?C) indicates  the  points  at  
      which  the external function is to be called. Different cal-  
      lout points can be identified by putting a number less  than  
      256  after  the  letter  C.  The default value is zero.  For  
      example, this pattern has two callout points:  
   
        (?C1)9abc(?C2)def  
   
      During matching, when PCRE  reaches  a  callout  point  (and  
      pcre_callout  is  set), the external function is called. Its  
      only argument is a pointer to  a  pcre_callout  block.  This  
      contains the following variables:  
   
        int          version;  
        int          callout_number;  
        int         *offset_vector;  
        const char  *subject;  
        int          subject_length;  
        int          start_match;  
        int          current_position;  
        int          capture_top;  
        int          capture_last;  
        void        *callout_data;  
   
      The version field  is  an  integer  containing  the  version  
      number of the block format. The current version is zero. The  
      version number may change in future if additional fields are  
      added,  but  the  intention  is  never  to remove any of the  
      existing fields.  
   
      The callout_number field contains the number of the callout,  
      as compiled into the pattern (that is, the number after ?C).  
   
      The offset_vector field  is  a  pointer  to  the  vector  of  
      offsets  that  was  passed by the caller to pcre_exec(). The  
      contents can be inspected in  order  to  extract  substrings  
      that  have  been  matched  so  far,  in  the same way as for  
      extracting substrings after a match has completed.  
      The subject and subject_length  fields  contain  copies  the  
      values that were passed to pcre_exec().  
   
      The start_match field contains the offset within the subject  
      at  which  the current match attempt started. If the pattern  
      is not anchored, the callout function may be called  several  
      times for different starting points.  
   
      The current_position field contains the  offset  within  the  
      subject of the current match pointer.  
   
      The capture_top field contains the  number  of  the  highest  
      captured substring so far.  
   
      The capture_last field  contains  the  number  of  the  most  
      recently captured substring.  
   
      The callout_data field contains a value that  is  passed  to  
      pcre_exec()  by  the  caller  specifically so that it can be  
      passed back in callouts. It is passed  in  the  pcre_callout  
      field  of the pcre_extra data structure. If no such data was  
      passed, the value of callout_data in a pcre_callout block is  
      NULL.  There is a description of the pcre_extra structure in  
      the pcreapi documentation.  
2748    
2749           PCRE provides a feature called "callout", which is a means of temporar-
2750           ily passing control to the caller of PCRE  in  the  middle  of  pattern
2751           matching.  The  caller of PCRE provides an external function by putting
2752           its entry point in the global variable pcre_callout. By  default,  this
2753           variable contains NULL, which disables all calling out.
2754    
2755           Within  a  regular  expression,  (?C) indicates the points at which the
2756           external function is to be called.  Different  callout  points  can  be
2757           identified  by  putting  a number less than 256 after the letter C. The
2758           default value is zero.  For  example,  this  pattern  has  two  callout
2759           points:
2760    
2761             (?C1)abc(?C2)def
2762    
2763           If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() or
2764           pcre_compile2() is called, PCRE  automatically  inserts  callouts,  all
2765           with  number  255,  before  each  item  in the pattern. For example, if
2766           PCRE_AUTO_CALLOUT is used with the pattern
2767    
2768             A(\d{2}|--)
2769    
2770           it is processed as if it were
2771    
2772           (?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255)
2773    
2774           Notice that there is a callout before and after  each  parenthesis  and
2775           alternation  bar.  Automatic  callouts  can  be  used  for tracking the
2776           progress of pattern matching. The pcretest command has an  option  that
2777           sets  automatic callouts; when it is used, the output indicates how the
2778           pattern is matched. This is useful information when you are  trying  to
2779           optimize the performance of a particular pattern.
2780    
2781    
2782    MISSING CALLOUTS
2783    
2784           You  should  be  aware  that,  because of optimizations in the way PCRE
2785           matches patterns by default, callouts  sometimes  do  not  happen.  For
2786           example, if the pattern is
2787    
2788             ab(?C4)cd
2789