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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    
10    
11    PCRE(3)                                                                PCRE(3)
12    
13    
14  NAME  NAME
15       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
16    
17    
18  DESCRIPTION  INTRODUCTION
19    
20       The PCRE library is a set of functions that implement  regu-         The  PCRE  library is a set of functions that implement regular expres-
21       lar  expression  pattern  matching using the same syntax and         sion pattern matching using the same syntax and semantics as Perl, with
22       semantics as Perl, with just a few differences. The  current         just  a few differences. Some features that appeared in Python and PCRE
23       implementation  of  PCRE  (release 4.x) corresponds approxi-         before they appeared in Perl are also available using the  Python  syn-
24       mately with Perl 5.8, including support  for  UTF-8  encoded         tax,  there  is  some  support for one or two .NET and Oniguruma syntax
25       strings.    However,  this  support  has  to  be  explicitly         items, and there is an option for requesting some  minor  changes  that
26       enabled; it is not the default.         give better JavaScript compatibility.
27    
28       PCRE is written in C and released as a C library. However, a         The  current implementation of PCRE corresponds approximately with Perl
29       number  of  people  have  written wrappers and interfaces of         5.10, including support for UTF-8 encoded strings and  Unicode  general
30       various kinds. A C++ class is included  in  these  contribu-         category  properties.  However,  UTF-8  and  Unicode  support has to be
31       tions,  which  can  be found in the Contrib directory at the         explicitly enabled; it is not the default. The  Unicode  tables  corre-
32       primary FTP site, which is:         spond to Unicode release 5.1.
33    
34       ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre         In  addition to the Perl-compatible matching function, PCRE contains an
35           alternative function that matches the same compiled patterns in a  dif-
36       Details of exactly which Perl  regular  expression  features         ferent way. In certain circumstances, the alternative function has some
37       are  and  are  not  supported  by PCRE are given in separate         advantages.  For a discussion of the two matching algorithms,  see  the
38       documents. See the pcrepattern and pcrecompat pages.         pcrematching page.
39    
40       Some features of PCRE can be included, excluded, or  changed         PCRE  is  written  in C and released as a C library. A number of people
41       when  the library is built. The pcre_config() function makes         have written wrappers and interfaces of various kinds.  In  particular,
42       it possible for a client  to  discover  which  features  are         Google  Inc.   have  provided  a comprehensive C++ wrapper. This is now
43       available.  Documentation  about  building  PCRE for various         included as part of the PCRE distribution. The pcrecpp page has details
44       operating systems can be found in the  README  file  in  the         of  this  interface.  Other  people's contributions can be found in the
45       source distribution.         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  USER DOCUMENTATION  USER DOCUMENTATION
71    
72       The user documentation for PCRE has been  split  up  into  a         The user documentation for PCRE comprises a number  of  different  sec-
73       number  of  different sections. In the "man" format, each of         tions.  In the "man" format, each of these is a separate "man page". In
74       these is a separate "man page". In the HTML format, each  is         the HTML format, each is a separate page, linked from the  index  page.
75       a  separate  page,  linked from the index page. In the plain         In  the  plain  text format, all the sections, except the pcredemo sec-
76       text format, all the sections are concatenated, for ease  of         tion, are concatenated, for ease of searching. The sections are as fol-
77       searching. The sections are as follows:         lows:
78    
79         pcre              this document           pcre              this document
80         pcreapi           details of PCRE's native API           pcre-config       show PCRE installation configuration information
81         pcrebuild         options for building PCRE           pcreapi           details of PCRE's native C API
82         pcrecallout       details of the callout feature           pcrebuild         options for building PCRE
83         pcrecompat        discussion of Perl compatibility           pcrecallout       details of the callout feature
84         pcregrep          description of the pcregrep command           pcrecompat        discussion of Perl compatibility
85         pcrepattern       syntax and semantics of supported           pcrecpp           details of the C++ wrapper
86                             regular expressions           pcredemo          a demonstration C program that uses PCRE
87         pcreperform       discussion of performance issues           pcregrep          description of the pcregrep command
88         pcreposix         the POSIX-compatible API           pcrematching      discussion of the two matching algorithms
89         pcresample        discussion of the sample program           pcrepartial       details of the partial matching facility
90         pcretest          the pcretest testing command           pcrepattern       syntax and semantics of supported
91                                 regular expressions
92       In addition, in the "man" and HTML formats, there is a short           pcreperform       discussion of performance issues
93       page  for  each  library function, listing its arguments and           pcreposix         the POSIX-compatible C API
94       results.           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           In  addition,  in the "man" and HTML formats, there is a short page for
101           each C library function, listing its arguments and results.
102    
103    
104  LIMITATIONS  LIMITATIONS
105    
106       There are some size limitations in PCRE but it is hoped that         There are some size limitations in PCRE but it is hoped that they  will
107       they will never in practice be relevant.         never in practice be relevant.
108    
109       The maximum length of a  compiled  pattern  is  65539  (sic)         The  maximum  length of a compiled pattern is 65539 (sic) bytes if PCRE
110       bytes  if PCRE is compiled with the default internal linkage         is compiled with the default internal linkage size of 2. If you want to
111       size of 2. If you want to process regular  expressions  that         process  regular  expressions  that are truly enormous, you can compile
112       are  truly  enormous,  you can compile PCRE with an internal         PCRE with an internal linkage size of 3 or 4 (see the  README  file  in
113       linkage size of 3 or 4 (see the README file  in  the  source         the  source  distribution and the pcrebuild documentation for details).
114       distribution  and  the pcrebuild documentation for details).         In these cases the limit is substantially larger.  However,  the  speed
115       If these cases the limit is substantially larger.   However,         of execution is slower.
116       the speed of execution will be slower.  
117           All values in repeating quantifiers must be less than 65536.
118       All values in repeating quantifiers must be less than 65536.  
119       The maximum number of capturing subpatterns is 65535.         There is no limit to the number of parenthesized subpatterns, but there
120           can be no more than 65535 capturing subpatterns.
121       There is no limit to the  number  of  non-capturing  subpat-  
122       terns,  but  the  maximum  depth  of nesting of all kinds of         The maximum length of name for a named subpattern is 32 characters, and
123       parenthesized subpattern, including  capturing  subpatterns,         the maximum number of named subpatterns is 10000.
124       assertions, and other types of subpattern, is 200.  
125           The  maximum  length of a subject string is the largest positive number
126       The maximum length of a subject string is the largest  posi-         that an integer variable can hold. However, when using the  traditional
127       tive number that an integer variable can hold. However, PCRE         matching function, PCRE uses recursion to handle subpatterns and indef-
128       uses recursion to handle subpatterns and indefinite  repeti-         inite repetition.  This means that the available stack space may  limit
129       tion.  This  means  that the available stack space may limit         the size of a subject string that can be processed by certain patterns.
130       the size of a subject string that can be processed  by  cer-         For a discussion of stack issues, see the pcrestack documentation.
131       tain patterns.  
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 the characters that PCRE  recog-
226           nizes  as  digits,  spaces,  or  word characters remain the same set as
227           before, all with values less than 256. This remains true even when PCRE
228           includes  Unicode  property support, because to do otherwise would slow
229           down PCRE in many common cases. If you really want to test for a  wider
230           sense  of,  say,  "digit",  you must use Unicode property tests such as
231           \p{Nd}. Note that this also applies to \b, because  it  is  defined  in
232           terms of \w and \W.
233    
234           7.  Similarly,  characters that match the POSIX named character classes
235           are all low-valued characters.
236    
237           8. However, the Perl 5.10 horizontal and vertical  whitespace  matching
238           escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char-
239           acters.
240    
241           9. Case-insensitive matching applies only to  characters  whose  values
242           are  less than 128, unless PCRE is built with Unicode property support.
243           Even when Unicode property support is available, PCRE  still  uses  its
244           own  character  tables when checking the case of low-valued characters,
245           so as not to degrade performance.  The Unicode property information  is
246           used only for characters with higher values. Even when Unicode property
247           support is available, PCRE supports case-insensitive matching only when
248           there  is  a  one-to-one  mapping between a letter's cases. There are a
249           small number of many-to-one mappings in Unicode;  these  are  not  sup-
250           ported by PCRE.
251    
252    
253  UTF-8 SUPPORT  AUTHOR
254    
255       Starting at release 3.3, PCRE has had some support for char-         Philip Hazel
256       acter  strings  encoded in the UTF-8 format. For release 4.0         University Computing Service
257       this has been greatly extended to cover most common require-         Cambridge CB2 3QH, England.
      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.  
258    
259       9. PCRE does not support the use of Unicode tables and  pro-         Putting  an actual email address here seems to have been a spam magnet,
260       perties or the Perl escapes \p, \P, and \X.         so I've taken it away. If you want to email me, use  my  two  initials,
261           followed by the two digits 10, at the domain cam.ac.uk.
262    
263    
264  AUTHOR  REVISION
265    
266       Philip Hazel <ph10@cam.ac.uk>         Last updated: 28 September 2009
267       University Computing Service,         Copyright (c) 1997-2009 University of Cambridge.
268       Cambridge CB2 3QG, England.  ------------------------------------------------------------------------------
269       Phone: +44 1223 334714  
270    
271    PCREBUILD(3)                                                      PCREBUILD(3)
272    
 Last updated: 04 February 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
273    
274  NAME  NAME
275       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
276    
277    
278  PCRE BUILD-TIME OPTIONS  PCRE BUILD-TIME OPTIONS
279    
280       This document describes the optional features of  PCRE  that         This  document  describes  the  optional  features  of PCRE that can be
281       can  be  selected when the library is compiled. They are all         selected when the library is compiled. It assumes use of the  configure
282       selected, or deselected, by providing options to the config-         script,  where the optional features are selected or deselected by pro-
283       ure  script  which  is run before the make command. The com-         viding options to configure before running the make  command.  However,
284       plete list of options  for  configure  (which  includes  the         the  same  options  can be selected in both Unix-like and non-Unix-like
285       standard  ones  such  as  the  selection of the installation         environments using the GUI facility of cmake-gui if you are using CMake
286       directory) can be obtained by running         instead of configure to build PCRE.
287    
288         ./configure --help         There  is  a  lot more information about building PCRE in non-Unix-like
289           environments in the file called NON_UNIX_USE, which is part of the PCRE
290       The following sections describe certain options whose  names         distribution.  You  should consult this file as well as the README file
291       begin  with  --enable  or  --disable. These settings specify         if you are building in a non-Unix-like environment.
292       changes to the defaults for the configure  command.  Because  
293       of  the  way  that  configure  works, --enable and --disable         The complete list of options for configure (which includes the standard
294       always come in pairs, so  the  complementary  option  always         ones  such  as  the  selection  of  the  installation directory) can be
295       exists  as  well, but as it specifies the default, it is not         obtained by running
296       described.  
297             ./configure --help
298    
299           The following sections include  descriptions  of  options  whose  names
300           begin with --enable or --disable. These settings specify changes to the
301           defaults for the configure command. Because of the way  that  configure
302           works,  --enable  and --disable always come in pairs, so the complemen-
303           tary option always exists as well, but as it specifies the default,  it
304           is not described.
305    
306    
307    C++ SUPPORT
308    
309           By default, the configure script will search for a C++ compiler and C++
310           header files. If it finds them, it automatically builds the C++ wrapper
311           library for PCRE. You can disable this by adding
312    
313             --disable-cpp
314    
315           to the configure command.
316    
317    
318  UTF-8 SUPPORT  UTF-8 SUPPORT
319    
320       To build PCRE with support for UTF-8 character strings, add         To build PCRE with support for UTF-8 Unicode character strings, add
321    
322             --enable-utf8
323    
324         --enable-utf8         to  the  configure  command.  Of  itself, this does not make PCRE treat
325           strings as UTF-8. As well as compiling PCRE with this option, you  also
326           have  have to set the PCRE_UTF8 option when you call the pcre_compile()
327           or pcre_compile2() functions.
328    
329       to the configure command. Of itself, this does not make PCRE         If you set --enable-utf8 when compiling in an EBCDIC environment,  PCRE
330       treat  strings as UTF-8. As well as compiling PCRE with this         expects its input to be either ASCII or UTF-8 (depending on the runtime
331       option, you also have have to set the PCRE_UTF8 option  when         option). It is not possible to support both EBCDIC and UTF-8  codes  in
332       you call the pcre_compile() function.         the  same  version  of  the  library.  Consequently,  --enable-utf8 and
333           --enable-ebcdic are mutually exclusive.
334    
335    
336    UNICODE CHARACTER PROPERTY SUPPORT
337    
338           UTF-8 support allows PCRE to process character values greater than  255
339           in  the  strings that it handles. On its own, however, it does not pro-
340           vide any facilities for accessing the properties of such characters. If
341           you  want  to  be able to use the pattern escapes \P, \p, and \X, which
342           refer to Unicode character properties, you must add
343    
344             --enable-unicode-properties
345    
346           to the configure command. This implies UTF-8 support, even if you  have
347           not explicitly requested it.
348    
349           Including  Unicode  property  support  adds around 30K of tables to the
350           PCRE library. Only the general category properties such as  Lu  and  Nd
351           are supported. Details are given in the pcrepattern documentation.
352    
353    
354  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
355    
356       By default, PCRE treats character 10 (linefeed) as the  new-         By  default,  PCRE interprets the linefeed (LF) character as indicating
357       line  character.  This  is  the  normal newline character on         the end of a line. This is the normal newline  character  on  Unix-like
358       Unix-like systems. You can compile PCRE to use character  13         systems.  You  can compile PCRE to use carriage return (CR) instead, by
359       (carriage return) instead by adding         adding
360    
361         --enable-newline-is-cr           --enable-newline-is-cr
362    
363       to the configure command. For completeness there is  also  a         to the  configure  command.  There  is  also  a  --enable-newline-is-lf
364       --enable-newline-is-lf  option,  which  explicitly specifies         option, which explicitly specifies linefeed as the newline character.
365       linefeed as the newline character.  
366           Alternatively, you can specify that line endings are to be indicated by
367           the two character sequence CRLF. If you want this, add
368    
369             --enable-newline-is-crlf
370    
371           to the configure command. There is a fourth option, specified by
372    
373             --enable-newline-is-anycrlf
374    
375           which causes PCRE to recognize any of the three sequences  CR,  LF,  or
376           CRLF as indicating a line ending. Finally, a fifth option, specified by
377    
378             --enable-newline-is-any
379    
380           causes PCRE to recognize any Unicode newline sequence.
381    
382           Whatever  line  ending convention is selected when PCRE is built can be
383           overridden when the library functions are called. At build time  it  is
384           conventional to use the standard for your operating system.
385    
386    
387    WHAT \R MATCHES
388    
389           By  default,  the  sequence \R in a pattern matches any Unicode newline
390           sequence, whatever has been selected as the line  ending  sequence.  If
391           you specify
392    
393             --enable-bsr-anycrlf
394    
395           the  default  is changed so that \R matches only CR, LF, or CRLF. What-
396           ever is selected when PCRE is built can be overridden when the  library
397           functions are called.
398    
399    
400  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
401    
402       The PCRE building process uses libtool to build both  shared         The  PCRE building process uses libtool to build both shared and static
403       and  static  Unix libraries by default. You can suppress one         Unix libraries by default. You can suppress one of these by adding  one
404       of these by adding one of         of
405    
406         --disable-shared           --disable-shared
407         --disable-static           --disable-static
408    
409       to the configure command, as required.         to the configure command, as required.
410    
411    
412  POSIX MALLOC USAGE  POSIX MALLOC USAGE
413    
414       When PCRE is called through the  POSIX  interface  (see  the         When PCRE is called through the POSIX interface (see the pcreposix doc-
415       pcreposix  documentation),  additional  working  storage  is         umentation), additional working storage is  required  for  holding  the
416       required for holding the pointers  to  capturing  substrings         pointers  to capturing substrings, because PCRE requires three integers
417       because  PCRE requires three integers per substring, whereas         per substring, whereas the POSIX interface provides only  two.  If  the
418       the POSIX interface provides only  two.  If  the  number  of         number of expected substrings is small, the wrapper function uses space
419       expected  substrings  is  small,  the  wrapper function uses         on the stack, because this is faster than using malloc() for each call.
420       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
421       loc()  for  each call. The default threshold above which the         can be changed by adding a setting such as
      stack is no longer used is 10; it can be changed by adding a  
      setting such as  
422    
423         --with-posix-malloc-threshold=20           --with-posix-malloc-threshold=20
424    
425       to the configure command.         to the configure command.
426    
427    
428    HANDLING VERY LARGE PATTERNS
429    
430           Within a compiled pattern, offset values are used  to  point  from  one
431           part  to another (for example, from an opening parenthesis to an alter-
432           nation metacharacter). By default, two-byte values are used  for  these
433           offsets,  leading  to  a  maximum size for a compiled pattern of around
434           64K. This is sufficient to handle all but the most  gigantic  patterns.
435           Nevertheless,  some  people do want to process truyl enormous patterns,
436           so it is possible to compile PCRE to use three-byte or  four-byte  off-
437           sets by adding a setting such as
438    
439             --with-link-size=3
440    
441           to  the  configure  command.  The value given must be 2, 3, or 4. Using
442           longer offsets slows down the operation of PCRE because it has to  load
443           additional bytes when handling them.
444    
445    
446    AVOIDING EXCESSIVE STACK USAGE
447    
448           When matching with the pcre_exec() function, PCRE implements backtrack-
449           ing by making recursive calls to an internal function  called  match().
450           In  environments  where  the size of the stack is limited, this can se-
451           verely limit PCRE's operation. (The Unix environment does  not  usually
452           suffer from this problem, but it may sometimes be necessary to increase
453           the maximum stack size.  There is a discussion in the  pcrestack  docu-
454           mentation.)  An alternative approach to recursion that uses memory from
455           the heap to remember data, instead of using recursive  function  calls,
456           has  been  implemented to work round the problem of limited stack size.
457           If you want to build a version of PCRE that works this way, add
458    
459             --disable-stack-for-recursion
460    
461           to the configure command. With this configuration, PCRE  will  use  the
462           pcre_stack_malloc  and pcre_stack_free variables to call memory manage-
463           ment functions. By default these point to malloc() and free(), but  you
464           can replace the pointers so that your own functions are used instead.
465    
466           Separate  functions  are  provided  rather  than  using pcre_malloc and
467           pcre_free because the  usage  is  very  predictable:  the  block  sizes
468           requested  are  always  the  same,  and  the blocks are always freed in
469           reverse order. A calling program might be able to  implement  optimized
470           functions  that  perform  better  than  malloc()  and free(). PCRE runs
471           noticeably more slowly when built in this way. This option affects only
472           the pcre_exec() function; it is not relevant for pcre_dfa_exec().
473    
474    
475  LIMITING PCRE RESOURCE USAGE  LIMITING PCRE RESOURCE USAGE
476    
477       Internally, PCRE has a  function  called  match()  which  it         Internally,  PCRE has a function called match(), which it calls repeat-
478       calls  repeatedly  (possibly  recursively) when performing a         edly  (sometimes  recursively)  when  matching  a  pattern   with   the
479       matching operation. By limiting the  number  of  times  this         pcre_exec()  function.  By controlling the maximum number of times this
480       function  may  be  called,  a  limit  can  be  placed on the         function may be called during a single matching operation, a limit  can
481       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
482       can  be  changed  at  run  time, as described in the pcreapi         limit can be changed at run time, as described in the pcreapi  documen-
483       documentation. The default is 10 million, but  this  can  be         tation.  The default is 10 million, but this can be changed by adding a
484       changed by adding a setting such as         setting such as
485    
486         --with-match-limit=500000           --with-match-limit=500000
487    
488       to the configure command.         to  the  configure  command.  This  setting  has  no  effect   on   the
489           pcre_dfa_exec() matching function.
490    
491           In  some  environments  it is desirable to limit the depth of recursive
492           calls of match() more strictly than the total number of calls, in order
493           to  restrict  the maximum amount of stack (or heap, if --disable-stack-
494           for-recursion is specified) that is used. A second limit controls this;
495           it  defaults  to  the  value  that is set for --with-match-limit, which
496           imposes no additional constraints. However, you can set a  lower  limit
497           by adding, for example,
498    
499  HANDLING VERY LARGE PATTERNS           --with-match-limit-recursion=10000
500    
501       Within a compiled pattern, offset values are used  to  point         to  the  configure  command.  This  value can also be overridden at run
502       from  one  part  to  another  (for  example, from an opening         time.
503       parenthesis to an  alternation  metacharacter).  By  default  
504       two-byte  values  are  used  for these offsets, leading to a  
505       maximum size for a compiled pattern of around 64K.  This  is  CREATING CHARACTER TABLES AT BUILD TIME
506       sufficient  to  handle  all  but the most gigantic patterns.  
507       Nevertheless, some people do want to process  enormous  pat-         PCRE uses fixed tables for processing characters whose code values  are
508       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
509       or four-byte offsets by adding a setting such as         distributed in the file pcre_chartables.c.dist. These  tables  are  for
510           ASCII codes only. If you add
511         --with-link-size=3  
512             --enable-rebuild-chartables
513       to the configure command. The value given must be 2,  3,  or  
514       4.  Using  longer  offsets  slows down the operation of PCRE         to  the  configure  command, the distributed tables are no longer used.
515       because it has to load additional bytes when handling them.         Instead, a program called dftables is compiled and  run.  This  outputs
516           the source for new set of tables, created in the default locale of your
517       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
518       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
519       of these tests is a representation of the compiled  pattern,         you need to create alternative tables when cross  compiling,  you  will
520       and this changes with the link size.         have to do so "by hand".)
521    
522    
523    USING EBCDIC CODE
524    
525           PCRE  assumes  by  default that it will run in an environment where the
526           character code is ASCII (or Unicode, which is  a  superset  of  ASCII).
527           This  is  the  case for most computer operating systems. PCRE can, how-
528           ever, be compiled to run in an EBCDIC environment by adding
529    
530             --enable-ebcdic
531    
532           to the configure command. This setting implies --enable-rebuild-charta-
533           bles.  You  should  only  use  it if you know that you are in an EBCDIC
534           environment (for example,  an  IBM  mainframe  operating  system).  The
535           --enable-ebcdic option is incompatible with --enable-utf8.
536    
537    
538    PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
539    
540           By default, pcregrep reads all files as plain text. You can build it so
541           that it recognizes files whose names end in .gz or .bz2, and reads them
542           with libz or libbz2, respectively, by adding one or both of
543    
544             --enable-pcregrep-libz
545             --enable-pcregrep-libbz2
546    
547           to the configure command. These options naturally require that the rel-
548           evant libraries are installed on your system. Configuration  will  fail
549           if they are not.
550    
551    
552    PCRETEST OPTION FOR LIBREADLINE SUPPORT
553    
554           If you add
555    
556             --enable-pcretest-libreadline
557    
558           to  the  configure  command,  pcretest  is  linked with the libreadline
559           library, and when its input is from a terminal, it reads it  using  the
560           readline() function. This provides line-editing and history facilities.
561           Note that libreadline is GPL-licensed, so if you distribute a binary of
562           pcretest linked in this way, there may be licensing issues.
563    
564           Setting  this  option  causes  the -lreadline option to be added to the
565           pcretest build. In many operating environments with  a  sytem-installed
566           libreadline this is sufficient. However, in some environments (e.g.  if
567           an unmodified distribution version of readline is in use),  some  extra
568           configuration  may  be necessary. The INSTALL file for libreadline says
569           this:
570    
571             "Readline uses the termcap functions, but does not link with the
572             termcap or curses library itself, allowing applications which link
573             with readline the to choose an appropriate library."
574    
575           If your environment has not been set up so that an appropriate  library
576           is automatically included, you may need to add something like
577    
578             LIBS="-ncurses"
579    
580           immediately before the configure command.
581    
582    
583    SEE ALSO
584    
585           pcreapi(3), pcre_config(3).
586    
587    
588    AUTHOR
589    
590           Philip Hazel
591           University Computing Service
592           Cambridge CB2 3QH, England.
593    
594    
595    REVISION
596    
597           Last updated: 29 September 2009
598           Copyright (c) 1997-2009 University of Cambridge.
599    ------------------------------------------------------------------------------
600    
601    
602    PCREMATCHING(3)                                                PCREMATCHING(3)
603    
 Last updated: 21 January 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
604    
605  NAME  NAME
606       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
607    
608    
609    PCRE MATCHING ALGORITHMS
610    
611           This document describes the two different algorithms that are available
612           in PCRE for matching a compiled regular expression against a given sub-
613           ject  string.  The  "standard"  algorithm  is  the  one provided by the
614           pcre_exec() function.  This works in the same was  as  Perl's  matching
615           function, and provides a Perl-compatible matching operation.
616    
617           An  alternative  algorithm is provided by the pcre_dfa_exec() function;
618           this operates in a different way, and is not  Perl-compatible.  It  has
619           advantages  and disadvantages compared with the standard algorithm, and
620           these are described below.
621    
622           When there is only one possible way in which a given subject string can
623           match  a pattern, the two algorithms give the same answer. A difference
624           arises, however, when there are multiple possibilities. For example, if
625           the pattern
626    
627             ^<.*>
628    
629           is matched against the string
630    
631             <something> <something else> <something further>
632    
633           there are three possible answers. The standard algorithm finds only one
634           of them, whereas the alternative algorithm finds all three.
635    
636    
637    REGULAR EXPRESSIONS AS TREES
638    
639           The set of strings that are matched by a regular expression can be rep-
640           resented  as  a  tree structure. An unlimited repetition in the pattern
641           makes the tree of infinite size, but it is still a tree.  Matching  the
642           pattern  to a given subject string (from a given starting point) can be
643           thought of as a search of the tree.  There are two  ways  to  search  a
644           tree:  depth-first  and  breadth-first, and these correspond to the two
645           matching algorithms provided by PCRE.
646    
 SYNOPSIS OF PCRE API  
647    
648       #include <pcre.h>  THE STANDARD MATCHING ALGORITHM
649    
650       pcre *pcre_compile(const char *pattern, int options,         In the terminology of Jeffrey Friedl's book "Mastering Regular  Expres-
651            const char **errptr, int *erroffset,         sions",  the  standard  algorithm  is an "NFA algorithm". It conducts a
652            const unsigned char *tableptr);         depth-first search of the pattern tree. That is, it  proceeds  along  a
653           single path through the tree, checking that the subject matches what is
654           required. When there is a mismatch, the algorithm  tries  any  alterna-
655           tives  at  the  current point, and if they all fail, it backs up to the
656           previous branch point in the  tree,  and  tries  the  next  alternative
657           branch  at  that  level.  This often involves backing up (moving to the
658           left) in the subject string as well.  The  order  in  which  repetition
659           branches  are  tried  is controlled by the greedy or ungreedy nature of
660           the quantifier.
661    
662       pcre_extra *pcre_study(const pcre *code, int options,         If a leaf node is reached, a matching string has  been  found,  and  at
663            const char **errptr);         that  point the algorithm stops. Thus, if there is more than one possi-
664           ble match, this algorithm returns the first one that it finds.  Whether
665           this  is the shortest, the longest, or some intermediate length depends
666           on the way the greedy and ungreedy repetition quantifiers are specified
667           in the pattern.
668    
669       int pcre_exec(const pcre *code, const pcre_extra *extra,         Because  it  ends  up  with a single path through the tree, it is rela-
670            const char *subject, int length, int startoffset,         tively straightforward for this algorithm to keep  track  of  the  sub-
671            int options, int *ovector, int ovecsize);         strings  that  are  matched  by portions of the pattern in parentheses.
672           This provides support for capturing parentheses and back references.
673    
      int pcre_copy_named_substring(const pcre *code,  
           const char *subject, int *ovector,  
           int stringcount, const char *stringname,  
           char *buffer, int buffersize);  
674    
675       int pcre_copy_substring(const char *subject, int *ovector,  THE ALTERNATIVE MATCHING ALGORITHM
           int stringcount, int stringnumber, char *buffer,  
           int buffersize);  
676    
677       int pcre_get_named_substring(const pcre *code,         This algorithm conducts a breadth-first search of  the  tree.  Starting
678            const char *subject, int *ovector,         from  the  first  matching  point  in the subject, it scans the subject
679            int stringcount, const char *stringname,         string from left to right, once, character by character, and as it does
680            const char **stringptr);         this,  it remembers all the paths through the tree that represent valid
681           matches. In Friedl's terminology, this is a kind  of  "DFA  algorithm",
682           though  it is not implemented as a traditional finite state machine (it
683           keeps multiple states active simultaneously).
684    
685       int pcre_get_stringnumber(const pcre *code,         Although the general principle of this matching algorithm  is  that  it
686            const char *name);         scans  the subject string only once, without backtracking, there is one
687           exception: when a lookaround assertion is encountered,  the  characters
688           following  or  preceding  the  current  point  have to be independently
689           inspected.
690    
691       int pcre_get_substring(const char *subject, int *ovector,         The scan continues until either the end of the subject is  reached,  or
692            int stringcount, int stringnumber,         there  are  no more unterminated paths. At this point, terminated paths
693            const char **stringptr);         represent the different matching possibilities (if there are none,  the
694           match  has  failed).   Thus,  if there is more than one possible match,
695           this algorithm finds all of them, and in particular, it finds the long-
696           est.  There  is  an  option to stop the algorithm after the first match
697           (which is necessarily the shortest) is found.
698    
699       int pcre_get_substring_list(const char *subject,         Note that all the matches that are found start at the same point in the
700            int *ovector, int stringcount, const char ***listptr);         subject. If the pattern
701    
702       void pcre_free_substring(const char *stringptr);           cat(er(pillar)?)
703    
704       void pcre_free_substring_list(const char **stringptr);         is  matched  against the string "the caterpillar catchment", the result
705           will be the three strings "cat", "cater", and "caterpillar" that  start
706           at the fourth character of the subject. The algorithm does not automat-
707           ically move on to find matches that start at later positions.
708    
709       const unsigned char *pcre_maketables(void);         There are a number of features of PCRE regular expressions that are not
710           supported by the alternative matching algorithm. They are as follows:
711    
712       int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         1.  Because  the  algorithm  finds  all possible matches, the greedy or
713            int what, void *where);         ungreedy nature of repetition quantifiers is not relevant.  Greedy  and
714           ungreedy quantifiers are treated in exactly the same way. However, pos-
715           sessive quantifiers can make a difference when what follows could  also
716           match what is quantified, for example in a pattern like this:
717    
718             ^a++\w!
719    
720       int pcre_info(const pcre *code, int *optptr, *firstcharptr);         This  pattern matches "aaab!" but not "aaa!", which would be matched by
721           a non-possessive quantifier. Similarly, if an atomic group is  present,
722           it  is matched as if it were a standalone pattern at the current point,
723           and the longest match is then "locked in" for the rest of  the  overall
724           pattern.
725    
726       int pcre_config(int what, void *where);         2. When dealing with multiple paths through the tree simultaneously, it
727           is not straightforward to keep track of  captured  substrings  for  the
728           different  matching  possibilities,  and  PCRE's implementation of this
729           algorithm does not attempt to do this. This means that no captured sub-
730           strings are available.
731    
732       char *pcre_version(void);         3.  Because no substrings are captured, back references within the pat-
733           tern are not supported, and cause errors if encountered.
734    
735       void *(*pcre_malloc)(size_t);         4. For the same reason, conditional expressions that use  a  backrefer-
736           ence  as  the  condition or test for a specific group recursion are not
737           supported.
738    
739       void (*pcre_free)(void *);         5. Because many paths through the tree may be  active,  the  \K  escape
740           sequence, which resets the start of the match when encountered (but may
741           be on some paths and not on others), is not  supported.  It  causes  an
742           error if encountered.
743    
744       int (*pcre_callout)(pcre_callout_block *);         6.  Callouts  are  supported, but the value of the capture_top field is
745           always 1, and the value of the capture_last field is always -1.
746    
747           7. The \C escape sequence, which (in the standard algorithm) matches  a
748           single  byte, even in UTF-8 mode, is not supported because the alterna-
749           tive algorithm moves through the subject  string  one  character  at  a
750           time, for all active paths through the tree.
751    
752  PCRE API         8.  Except for (*FAIL), the backtracking control verbs such as (*PRUNE)
753           are not supported. (*FAIL) is supported, and  behaves  like  a  failing
754           negative assertion.
755    
      PCRE has its own native API,  which  is  described  in  this  
      document.  There  is  also  a  set of wrapper functions that  
      correspond to the POSIX regular expression API.   These  are  
      described in the pcreposix documentation.  
756    
757       The native API function prototypes are defined in the header  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
      file  pcre.h,  and  on  Unix  systems  the library itself is  
      called libpcre.a, so can be accessed by adding -lpcre to the  
      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.  
758    
759       The functions pcre_compile(), pcre_study(), and  pcre_exec()         Using  the alternative matching algorithm provides the following advan-
760       are  used  for compiling and matching regular expressions. A         tages:
      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.  
761    
762       There are convenience functions for extracting captured sub-         1. All possible matches (at a single point in the subject) are automat-
763       strings from a matched subject string. They are:         ically  found,  and  in particular, the longest match is found. To find
764           more than one match using the standard algorithm, you have to do kludgy
765           things with callouts.
766    
767         pcre_copy_substring()         2.  Because  the  alternative  algorithm  scans the subject string just
768         pcre_copy_named_substring()         once, and never needs to backtrack, it is possible to  pass  very  long
769         pcre_get_substring()         subject  strings  to  the matching function in several pieces, checking
770         pcre_get_named_substring()         for partial matching each time.  The  pcrepartial  documentation  gives
771         pcre_get_substring_list()         details of partial matching.
772    
      pcre_free_substring()  and  pcre_free_substring_list()   are  
      also  provided,  to  free  the  memory  used  for  extracted  
      strings.  
773    
774       The function pcre_maketables() is used (optionally) to build  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
      a  set of character tables in the current locale for passing  
      to pcre_compile().  
775    
776       The function pcre_fullinfo() is used to find out information         The alternative algorithm suffers from a number of disadvantages:
      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         1.  It  is  substantially  slower  than the standard algorithm. This is
779       contain the entry points of the standard malloc() and free()         partly because it has to search for all possible matches, but  is  also
780       functions respectively. PCRE  calls  the  memory  management         because it is less susceptible to optimization.
      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.  
781    
782       The global variable pcre_callout initially contains NULL. It         2. Capturing parentheses and back references are not supported.
783       can be set by the caller to a "callout" function, which PCRE  
784       will then call at specified points during a matching  opera-         3. Although atomic groups are supported, their use does not provide the
785       tion. Details are given in the pcrecallout documentation.         performance advantage that it does for the standard algorithm.
786    
787    
788    AUTHOR
789    
790           Philip Hazel
791           University Computing Service
792           Cambridge CB2 3QH, England.
793    
794    
795    REVISION
796    
797           Last updated: 29 September 2009
798           Copyright (c) 1997-2009 University of Cambridge.
799    ------------------------------------------------------------------------------
800    
801    
802    PCREAPI(3)                                                          PCREAPI(3)
803    
804    
805    NAME
806           PCRE - Perl-compatible regular expressions
807    
808    
809    PCRE NATIVE API
810    
811           #include <pcre.h>
812    
813           pcre *pcre_compile(const char *pattern, int options,
814                const char **errptr, int *erroffset,
815                const unsigned char *tableptr);
816    
817           pcre *pcre_compile2(const char *pattern, int options,
818                int *errorcodeptr,
819                const char **errptr, int *erroffset,
820                const unsigned char *tableptr);
821    
822           pcre_extra *pcre_study(const pcre *code, int options,
823                const char **errptr);
824    
825           int pcre_exec(const pcre *code, const pcre_extra *extra,
826                const char *subject, int length, int startoffset,
827                int options, int *ovector, int ovecsize);
828    
829           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
830                const char *subject, int length, int startoffset,
831                int options, int *ovector, int ovecsize,
832                int *workspace, int wscount);
833    
834           int pcre_copy_named_substring(const pcre *code,
835                const char *subject, int *ovector,
836                int stringcount, const char *stringname,
837                char *buffer, int buffersize);
838    
839           int pcre_copy_substring(const char *subject, int *ovector,
840                int stringcount, int stringnumber, char *buffer,
841                int buffersize);
842    
843           int pcre_get_named_substring(const pcre *code,
844                const char *subject, int *ovector,
845                int stringcount, const char *stringname,
846                const char **stringptr);
847    
848           int pcre_get_stringnumber(const pcre *code,
849                const char *name);
850    
851           int pcre_get_stringtable_entries(const pcre *code,
852                const char *name, char **first, char **last);
853    
854           int pcre_get_substring(const char *subject, int *ovector,
855                int stringcount, int stringnumber,
856                const char **stringptr);
857    
858           int pcre_get_substring_list(const char *subject,
859                int *ovector, int stringcount, const char ***listptr);
860    
861           void pcre_free_substring(const char *stringptr);
862    
863           void pcre_free_substring_list(const char **stringptr);
864    
865           const unsigned char *pcre_maketables(void);
866    
867           int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
868                int what, void *where);
869    
870           int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
871    
872           int pcre_refcount(pcre *code, int adjust);
873    
874           int pcre_config(int what, void *where);
875    
876           char *pcre_version(void);
877    
878           void *(*pcre_malloc)(size_t);
879    
880           void (*pcre_free)(void *);
881    
882           void *(*pcre_stack_malloc)(size_t);
883    
884           void (*pcre_stack_free)(void *);
885    
886           int (*pcre_callout)(pcre_callout_block *);
887    
888    
889    PCRE API OVERVIEW
890    
891           PCRE has its own native API, which is described in this document. There
892           are also some wrapper functions that correspond to  the  POSIX  regular
893           expression  API.  These  are  described in the pcreposix documentation.
894           Both of these APIs define a set of C function calls. A C++  wrapper  is
895           distributed with PCRE. It is documented in the pcrecpp page.
896    
897           The  native  API  C  function prototypes are defined in the header file
898           pcre.h, and on Unix systems the library itself is called  libpcre.   It
899           can normally be accessed by adding -lpcre to the command for linking an
900           application  that  uses  PCRE.  The  header  file  defines  the  macros
901           PCRE_MAJOR  and  PCRE_MINOR to contain the major and minor release num-
902           bers for the library.  Applications can use these  to  include  support
903           for different releases of PCRE.
904    
905           The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and
906           pcre_exec() are used for compiling and matching regular expressions  in
907           a  Perl-compatible  manner. A sample program that demonstrates the sim-
908           plest way of using them is provided in the file  called  pcredemo.c  in
909           the PCRE source distribution. A listing of this program is given in the
910           pcredemo documentation, and the pcresample documentation describes  how
911           to compile and run it.
912    
913           A second matching function, pcre_dfa_exec(), which is not Perl-compati-
914           ble, is also provided. This uses a different algorithm for  the  match-
915           ing.  The  alternative algorithm finds all possible matches (at a given
916           point in the subject), and scans the subject just  once  (unless  there
917           are  lookbehind  assertions).  However,  this algorithm does not return
918           captured substrings. A description of the two matching  algorithms  and
919           their  advantages  and disadvantages is given in the pcrematching docu-
920           mentation.
921    
922           In addition to the main compiling and  matching  functions,  there  are
923           convenience functions for extracting captured substrings from a subject
924           string that is matched by pcre_exec(). They are:
925    
926             pcre_copy_substring()
927             pcre_copy_named_substring()
928             pcre_get_substring()
929             pcre_get_named_substring()
930             pcre_get_substring_list()
931             pcre_get_stringnumber()
932             pcre_get_stringtable_entries()
933    
934           pcre_free_substring() and pcre_free_substring_list() are also provided,
935           to free the memory used for extracted strings.
936    
937           The  function  pcre_maketables()  is  used  to build a set of character
938           tables  in  the  current  locale   for   passing   to   pcre_compile(),
939           pcre_exec(),  or  pcre_dfa_exec(). This is an optional facility that is
940           provided for specialist use.  Most  commonly,  no  special  tables  are
941           passed,  in  which case internal tables that are generated when PCRE is
942           built are used.
943    
944           The function pcre_fullinfo() is used to find out  information  about  a
945           compiled  pattern; pcre_info() is an obsolete version that returns only
946           some of the available information, but is retained for  backwards  com-
947           patibility.   The function pcre_version() returns a pointer to a string
948           containing the version of PCRE and its date of release.
949    
950           The function pcre_refcount() maintains a  reference  count  in  a  data
951           block  containing  a compiled pattern. This is provided for the benefit
952           of object-oriented applications.
953    
954           The global variables pcre_malloc and pcre_free  initially  contain  the
955           entry  points  of  the  standard malloc() and free() functions, respec-
956           tively. PCRE calls the memory management functions via these variables,
957           so  a  calling  program  can replace them if it wishes to intercept the
958           calls. This should be done before calling any PCRE functions.
959    
960           The global variables pcre_stack_malloc  and  pcre_stack_free  are  also
961           indirections  to  memory  management functions. These special functions
962           are used only when PCRE is compiled to use  the  heap  for  remembering
963           data, instead of recursive function calls, when running the pcre_exec()
964           function. See the pcrebuild documentation for  details  of  how  to  do
965           this.  It  is  a non-standard way of building PCRE, for use in environ-
966           ments that have limited stacks. Because of the greater  use  of  memory
967           management,  it  runs  more  slowly. Separate functions are provided so
968           that special-purpose external code can be  used  for  this  case.  When
969           used,  these  functions  are always called in a stack-like manner (last
970           obtained, first freed), and always for memory blocks of the same  size.
971           There  is  a discussion about PCRE's stack usage in the pcrestack docu-
972           mentation.
973    
974           The global variable pcre_callout initially contains NULL. It can be set
975           by  the  caller  to  a "callout" function, which PCRE will then call at
976           specified points during a matching operation. Details are given in  the
977           pcrecallout documentation.
978    
979    
980    NEWLINES
981    
982           PCRE  supports five different conventions for indicating line breaks in
983           strings: a single CR (carriage return) character, a  single  LF  (line-
984           feed) character, the two-character sequence CRLF, any of the three pre-
985           ceding, or any Unicode newline sequence. The Unicode newline  sequences
986           are  the  three just mentioned, plus the single characters VT (vertical
987           tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS  (line
988           separator, U+2028), and PS (paragraph separator, U+2029).
989    
990           Each  of  the first three conventions is used by at least one operating
991           system as its standard newline sequence. When PCRE is built, a  default
992           can  be  specified.  The default default is LF, which is the Unix stan-
993           dard. When PCRE is run, the default can be overridden,  either  when  a
994           pattern is compiled, or when it is matched.
995    
996           At compile time, the newline convention can be specified by the options
997           argument of pcre_compile(), or it can be specified by special  text  at
998           the start of the pattern itself; this overrides any other settings. See
999           the pcrepattern page for details of the special character sequences.
1000    
1001           In the PCRE documentation the word "newline" is used to mean "the char-
1002           acter  or pair of characters that indicate a line break". The choice of
1003           newline convention affects the handling of  the  dot,  circumflex,  and
1004           dollar metacharacters, the handling of #-comments in /x mode, and, when
1005           CRLF is a recognized line ending sequence, the match position  advance-
1006           ment for a non-anchored pattern. There is more detail about this in the
1007           section on pcre_exec() options below.
1008    
1009           The choice of newline convention does not affect the interpretation  of
1010           the  \n  or  \r  escape  sequences, nor does it affect what \R matches,
1011           which is controlled in a similar way, but by separate options.
1012    
1013    
1014  MULTITHREADING  MULTITHREADING
1015    
1016       The PCRE functions can be used in  multi-threading  applica-         The PCRE functions can be used in  multi-threading  applications,  with
1017       tions, with the proviso that the memory management functions         the  proviso  that  the  memory  management  functions  pointed  to  by
1018       pointed to by pcre_malloc and  pcre_free,  and  the  callout         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
1019       function  pointed  to  by  pcre_callout,  are  shared by all         callout function pointed to by pcre_callout, are shared by all threads.
1020       threads.  
1021           The  compiled form of a regular expression is not altered during match-
1022       The compiled form of a regular  expression  is  not  altered         ing, so the same compiled pattern can safely be used by several threads
1023       during  matching, so the same compiled pattern can safely be         at once.
1024       used by several threads at once.  
1025    
1026    SAVING PRECOMPILED PATTERNS FOR LATER USE
1027    
1028           The compiled form of a regular expression can be saved and re-used at a
1029           later time, possibly by a different program, and even on a  host  other
1030           than  the  one  on  which  it  was  compiled.  Details are given in the
1031           pcreprecompile documentation. However, compiling a  regular  expression
1032           with  one version of PCRE for use with a different version is not guar-
1033           anteed to work and may cause crashes.
1034    
1035    
1036  CHECKING BUILD-TIME OPTIONS  CHECKING BUILD-TIME OPTIONS
1037    
1038       int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
1039    
1040           The function pcre_config() makes it possible for a PCRE client to  dis-
1041           cover which optional features have been compiled into the PCRE library.
1042           The pcrebuild documentation has more details about these optional  fea-
1043           tures.
1044    
1045           The  first  argument  for pcre_config() is an integer, specifying which
1046           information is required; the second argument is a pointer to a variable
1047           into  which  the  information  is  placed. The following information is
1048           available:
1049    
1050             PCRE_CONFIG_UTF8
1051    
1052           The output is an integer that is set to one if UTF-8 support is  avail-
1053           able; otherwise it is set to zero.
1054    
1055             PCRE_CONFIG_UNICODE_PROPERTIES
1056    
1057       The function pcre_config() makes  it  possible  for  a  PCRE         The  output  is  an  integer  that is set to one if support for Unicode
1058       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.  
1059    
1060       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:  
1061    
1062         PCRE_CONFIG_UTF8         The output is an integer whose value specifies  the  default  character
1063           sequence  that is recognized as meaning "newline". The four values that
1064           are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
1065           and  -1  for  ANY.  Though they are derived from ASCII, the same values
1066           are returned in EBCDIC environments. The default should normally corre-
1067           spond to the standard sequence for your operating system.
1068    
1069       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.  
1070    
1071         PCRE_CONFIG_NEWLINE         The output is an integer whose value indicates what character sequences
1072           the \R escape sequence matches by default. A value of 0 means  that  \R
1073           matches  any  Unicode  line ending sequence; a value of 1 means that \R
1074           matches only CR, LF, or CRLF. The default can be overridden when a pat-
1075           tern is compiled or matched.
1076    
1077       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.  
1078    
1079         PCRE_CONFIG_LINK_SIZE         The  output  is  an  integer that contains the number of bytes used for
1080           internal linkage in compiled regular expressions. The value is 2, 3, or
1081           4.  Larger  values  allow larger regular expressions to be compiled, at
1082           the expense of slower matching. The default value of  2  is  sufficient
1083           for  all  but  the  most massive patterns, since it allows the compiled
1084           pattern to be up to 64K in size.
1085    
1086       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.  
1087    
1088         PCRE_CONFIG_POSIX_MALLOC_THRESHOLD         The output is an integer that contains the threshold  above  which  the
1089           POSIX  interface  uses malloc() for output vectors. Further details are
1090           given in the pcreposix documentation.
1091    
1092       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.  
1093    
1094         PCRE_CONFIG_MATCH_LIMIT         The output is a long integer that gives the default limit for the  num-
1095           ber  of  internal  matching  function calls in a pcre_exec() execution.
1096           Further details are given with pcre_exec() below.
1097    
1098       The output is an integer that gives the  default  limit  for           PCRE_CONFIG_MATCH_LIMIT_RECURSION
1099       the   number  of  internal  matching  function  calls  in  a  
1100       pcre_exec()  execution.  Further  details  are  given   with         The output is a long integer that gives the default limit for the depth
1101       pcre_exec() below.         of   recursion  when  calling  the  internal  matching  function  in  a
1102           pcre_exec() execution.  Further  details  are  given  with  pcre_exec()
1103           below.
1104    
1105             PCRE_CONFIG_STACKRECURSE
1106    
1107           The  output is an integer that is set to one if internal recursion when
1108           running pcre_exec() is implemented by recursive function calls that use
1109           the  stack  to remember their state. This is the usual way that PCRE is
1110           compiled. The output is zero if PCRE was compiled to use blocks of data
1111           on  the  heap  instead  of  recursive  function  calls.  In  this case,
1112           pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory
1113           blocks on the heap, thus avoiding the use of the stack.
1114    
1115    
1116  COMPILING A PATTERN  COMPILING A PATTERN
1117    
1118       pcre *pcre_compile(const char *pattern, int options,         pcre *pcre_compile(const char *pattern, int options,
1119            const char **errptr, int *erroffset,              const char **errptr, int *erroffset,
1120            const unsigned char *tableptr);              const unsigned char *tableptr);
1121    
1122       The function pcre_compile() is called to compile  a  pattern         pcre *pcre_compile2(const char *pattern, int options,
1123       into  an internal form. The pattern is a C string terminated              int *errorcodeptr,
1124       by a binary zero, and is passed in the argument  pattern.  A              const char **errptr, int *erroffset,
1125       pointer  to  a  single  block of memory that is obtained via              const unsigned char *tableptr);
1126       pcre_malloc is returned. This contains the compiled code and  
1127       related  data.  The  pcre  type  is defined for the returned         Either of the functions pcre_compile() or pcre_compile2() can be called
1128       block; this is a typedef for a structure whose contents  are         to compile a pattern into an internal form. The only difference between
1129       not  externally  defined. It is up to the caller to free the         the  two interfaces is that pcre_compile2() has an additional argument,
1130       memory when it is no longer required.         errorcodeptr, via which a numerical error  code  can  be  returned.  To
1131           avoid  too  much repetition, we refer just to pcre_compile() below, but
1132       Although the compiled code of a PCRE regex  is  relocatable,         the information applies equally to pcre_compile2().
1133       that is, it does not depend on memory location, the complete  
1134       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
1135       tains  a  copy of the tableptr argument, which is an address         the  pattern  argument.  A  pointer to a single block of memory that is
1136       (see below).         obtained via pcre_malloc is returned. This contains the  compiled  code
1137       The options argument contains independent bits  that  affect         and related data. The pcre type is defined for the returned block; this
1138       the  compilation.  It  should  be  zero  if  no  options are         is a typedef for a structure whose contents are not externally defined.
1139       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
1140       compatible  with Perl, can also be set and unset from within         longer required.
1141       the pattern (see the detailed description of regular expres-  
1142       sions  in the pcrepattern documentation). For these options,         Although the compiled code of a PCRE regex is relocatable, that is,  it
1143       the contents of the options argument specifies their initial         does not depend on memory location, the complete pcre data block is not
1144       settings  at  the  start  of  compilation and execution. The         fully relocatable, because it may contain a copy of the tableptr  argu-
1145       PCRE_ANCHORED option can be set at the time of  matching  as         ment, which is an address (see below).
1146       well as at compile time.  
1147           The options argument contains various bit settings that affect the com-
1148       If errptr is NULL, pcre_compile() returns NULL  immediately.         pilation. It should be zero if no options are required.  The  available
1149       Otherwise, if compilation of a pattern fails, pcre_compile()         options  are  described  below. Some of them (in particular, those that
1150       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
1151       point  to a textual error message. The offset from the start         unset  from  within  the  pattern  (see the detailed description in the
1152       of  the  pattern  to  the  character  where  the  error  was         pcrepattern documentation). For those options that can be different  in
1153       discovered   is   placed  in  the  variable  pointed  to  by         different  parts  of  the pattern, the contents of the options argument
1154       erroffset, which must not be NULL. If it  is,  an  immediate         specifies their settings at the start of compilation and execution. The
1155       error is given.         PCRE_ANCHORED, PCRE_BSR_xxx, and PCRE_NEWLINE_xxx options can be set at
1156           the time of matching as well as at compile time.
1157       If the final  argument,  tableptr,  is  NULL,  PCRE  uses  a  
1158       default  set  of character tables which are built when it is         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1159       compiled, using the default C  locale.  Otherwise,  tableptr         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and
1160       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-
1161       section on locale support below.         sage. This is a static string that is part of the library. You must not
1162           try to free it. The byte offset from the start of the  pattern  to  the
1163       This code fragment shows a typical straightforward  call  to         character  that  was  being  processed when the error was discovered is
1164       pcre_compile():         placed in the variable pointed to by erroffset, which must not be NULL.
1165           If  it  is,  an  immediate error is given. Some errors are not detected
1166         pcre *re;         until checks are carried out when the whole pattern has  been  scanned;
1167         const char *error;         in this case the offset is set to the end of the pattern.
1168         int erroffset;  
1169         re = pcre_compile(         If  pcre_compile2()  is  used instead of pcre_compile(), and the error-
1170           "^A.*Z",          /* the pattern */         codeptr argument is not NULL, a non-zero error code number is  returned
1171           0,                /* default options */         via  this argument in the event of an error. This is in addition to the
1172           &error,           /* for error message */         textual error message. Error codes and messages are listed below.
1173           &erroffset,       /* for error offset */  
1174           NULL);            /* use default character tables */         If the final argument, tableptr, is NULL, PCRE uses a  default  set  of
1175           character  tables  that  are  built  when  PCRE  is compiled, using the
1176       The following option bits are defined:         default C locale. Otherwise, tableptr must be an address  that  is  the
1177           result  of  a  call to pcre_maketables(). This value is stored with the
1178         PCRE_ANCHORED         compiled pattern, and used again by pcre_exec(), unless  another  table
1179           pointer is passed to it. For more discussion, see the section on locale
1180       If this bit is set, the pattern is forced to be  "anchored",         support below.
1181       that is, it is constrained to match only at the first match-  
1182       ing point in the string which is being searched  (the  "sub-         This code fragment shows a typical straightforward  call  to  pcre_com-
1183       ject string"). This effect can also be achieved by appropri-         pile():
1184       ate constructs in the pattern itself, which is the only  way  
1185       to do it in Perl.           pcre *re;
1186             const char *error;
1187         PCRE_CASELESS           int erroffset;
1188             re = pcre_compile(
1189       If this bit is set, letters in the pattern match both  upper             "^A.*Z",          /* the pattern */
1190       and  lower  case  letters.  It  is  equivalent  to Perl's /i             0,                /* default options */
1191       option, and it can be changed within a  pattern  by  a  (?i)             &error,           /* for error message */
1192       option setting.             &erroffset,       /* for error offset */
1193               NULL);            /* use default character tables */
1194         PCRE_DOLLAR_ENDONLY  
1195           The  following  names  for option bits are defined in the pcre.h header
1196       If this bit is set, a dollar metacharacter  in  the  pattern         file:
1197       matches  only at the end of the subject string. Without this  
1198       option, a dollar also matches immediately before  the  final           PCRE_ANCHORED
1199       character  if it is a newline (but not before any other new-  
1200       lines).  The  PCRE_DOLLAR_ENDONLY  option  is   ignored   if         If this bit is set, the pattern is forced to be "anchored", that is, it
1201       PCRE_MULTILINE is set. There is no equivalent to this option         is  constrained to match only at the first matching point in the string
1202       in Perl, and no way to set it within a pattern.         that is being searched (the "subject string"). This effect can also  be
1203           achieved  by appropriate constructs in the pattern itself, which is the
1204         PCRE_DOTALL         only way to do it in Perl.
1205    
1206       If this bit is  set,  a  dot  metacharater  in  the  pattern           PCRE_AUTO_CALLOUT
1207       matches all characters, including newlines. Without it, new-  
1208       lines are excluded. This option is equivalent to  Perl's  /s         If this bit is set, pcre_compile() automatically inserts callout items,
1209       option,  and  it  can  be changed within a pattern by a (?s)         all  with  number  255, before each pattern item. For discussion of the
1210       option setting. A negative class such as [^a] always matches         callout facility, see the pcrecallout documentation.
1211       a  newline  character,  independent  of  the setting of this  
1212       option.           PCRE_BSR_ANYCRLF
1213             PCRE_BSR_UNICODE
1214         PCRE_EXTENDED  
1215           These options (which are mutually exclusive) control what the \R escape
1216       If this bit is set, whitespace data characters in  the  pat-         sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1217       tern  are  totally  ignored  except when escaped or inside a         or to match any Unicode newline sequence. The default is specified when
1218       character class. Whitespace does not include the VT  charac-         PCRE is built. It can be overridden from within the pattern, or by set-
1219       ter  (code 11). In addition, characters between an unescaped         ting an option when a compiled pattern is matched.
1220       # outside a character class and the next newline  character,  
1221       inclusive, are also ignored. This is equivalent to Perl's /x           PCRE_CASELESS
1222       option, and it can be changed within a  pattern  by  a  (?x)  
1223       option setting.         If this bit is set, letters in the pattern match both upper  and  lower
1224           case  letters.  It  is  equivalent  to  Perl's /i option, and it can be
1225       This option makes it possible  to  include  comments  inside         changed within a pattern by a (?i) option setting. In UTF-8 mode,  PCRE
1226       complicated patterns.  Note, however, that this applies only         always  understands the concept of case for characters whose values are
1227       to data characters. Whitespace characters may  never  appear         less than 128, so caseless matching is always possible. For  characters
1228       within special character sequences in a pattern, for example         with  higher  values,  the concept of case is supported if PCRE is com-
1229       within the sequence (?( which introduces a conditional  sub-         piled with Unicode property support, but not otherwise. If you want  to
1230       pattern.         use  caseless  matching  for  characters 128 and above, you must ensure
1231           that PCRE is compiled with Unicode property support  as  well  as  with
1232         PCRE_EXTRA         UTF-8 support.
1233    
1234       This option was invented in  order  to  turn  on  additional           PCRE_DOLLAR_ENDONLY
1235       functionality of PCRE that is incompatible with Perl, but it  
1236       is currently of very little use. When set, any backslash  in         If  this bit is set, a dollar metacharacter in the pattern matches only
1237       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
1238       meaning causes an error, thus reserving  these  combinations         matches  immediately before a newline at the end of the string (but not
1239       for  future  expansion.  By default, as in Perl, a backslash         before any other newlines). The PCRE_DOLLAR_ENDONLY option  is  ignored
1240       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
1241       literal.  There  are at present no other features controlled         Perl, and no way to set it within a pattern.
1242       by this option. It can also be set by a (?X) option  setting  
1243       within a pattern.           PCRE_DOTALL
1244    
1245         PCRE_MULTILINE         If this bit is set, a dot metacharater in the pattern matches all char-
1246           acters,  including  those that indicate newline. Without it, a dot does
1247       By default, PCRE treats the subject string as consisting  of         not match when the current position is at a  newline.  This  option  is
1248       a  single "line" of characters (even if it actually contains         equivalent  to Perl's /s option, and it can be changed within a pattern
1249       several newlines). The "start  of  line"  metacharacter  (^)         by a (?s) option setting. A negative class such as [^a] always  matches
1250       matches  only  at the start of the string, while the "end of         newline characters, independent of the setting of this option.
1251       line" metacharacter ($) matches  only  at  the  end  of  the  
1252       string,    or   before   a   terminating   newline   (unless           PCRE_DUPNAMES
1253       PCRE_DOLLAR_ENDONLY is set). This is the same as Perl.  
1254           If  this  bit is set, names used to identify capturing subpatterns need
1255       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
1256       of  line"  constructs match immediately following or immedi-         is  known  that  only  one instance of the named subpattern can ever be
1257       ately before any newline  in  the  subject  string,  respec-         matched. There are more details of named subpatterns  below;  see  also
1258       tively,  as  well  as  at  the  very  start and end. This is         the pcrepattern documentation.
1259       equivalent to Perl's /m option, and it can be changed within  
1260       a  pattern  by  a  (?m) option setting. If there are no "\n"           PCRE_EXTENDED
1261       characters in a subject string, or no occurrences of ^ or  $  
1262       in a pattern, setting PCRE_MULTILINE has no effect.         If  this  bit  is  set,  whitespace  data characters in the pattern are
1263           totally ignored except when escaped or inside a character class. White-
1264         PCRE_NO_AUTO_CAPTURE         space does not include the VT character (code 11). In addition, charac-
1265           ters between an unescaped # outside a character class and the next new-
1266       If this option is set, it disables the use of numbered  cap-         line,  inclusive,  are  also  ignored.  This is equivalent to Perl's /x
1267       turing  parentheses  in the pattern. Any opening parenthesis         option, and it can be changed within a pattern by a  (?x)  option  set-
1268       that is not followed by ? behaves as if it were followed  by         ting.
1269       ?:  but  named  parentheses  can still be used for capturing  
1270       (and they acquire numbers in the usual  way).  There  is  no         This  option  makes  it possible to include comments inside complicated
1271       equivalent of this option in Perl.         patterns.  Note, however, that this applies only  to  data  characters.
1272           Whitespace   characters  may  never  appear  within  special  character
1273         PCRE_UNGREEDY         sequences in a pattern, for  example  within  the  sequence  (?(  which
1274           introduces a conditional subpattern.
1275       This option inverts the "greediness" of the  quantifiers  so  
1276       that  they  are  not greedy by default, but become greedy if           PCRE_EXTRA
1277       followed by "?". It is not compatible with Perl. It can also  
1278       be set by a (?U) option setting within the pattern.         This  option  was invented in order to turn on additional functionality
1279           of PCRE that is incompatible with Perl, but it  is  currently  of  very
1280         PCRE_UTF8         little  use. When set, any backslash in a pattern that is followed by a
1281           letter that has no special meaning  causes  an  error,  thus  reserving
1282       This option causes PCRE to regard both the pattern  and  the         these  combinations  for  future  expansion.  By default, as in Perl, a
1283       subject  as  strings  of UTF-8 characters instead of single-         backslash followed by a letter with no special meaning is treated as  a
1284       byte character strings. However, it  is  available  only  if         literal.  (Perl can, however, be persuaded to give a warning for this.)
1285       PCRE  has  been  built to include UTF-8 support. If not, the         There are at present no other features controlled by  this  option.  It
1286       use of this option provokes an error. Details  of  how  this         can also be set by a (?X) option setting within a pattern.
1287       option  changes  the behaviour of PCRE are given in the sec-  
1288       tion on UTF-8 support in the main pcre page.           PCRE_FIRSTLINE
1289    
1290           If  this  option  is  set,  an  unanchored pattern is required to match
1291           before or at the first  newline  in  the  subject  string,  though  the
1292           matched text may continue over the newline.
1293    
1294             PCRE_JAVASCRIPT_COMPAT
1295    
1296           If this option is set, PCRE's behaviour is changed in some ways so that
1297           it is compatible with JavaScript rather than Perl. The changes  are  as
1298           follows:
1299    
1300           (1)  A  lone  closing square bracket in a pattern causes a compile-time
1301           error, because this is illegal in JavaScript (by default it is  treated
1302           as a data character). Thus, the pattern AB]CD becomes illegal when this
1303           option is set.
1304    
1305           (2) At run time, a back reference to an unset subpattern group  matches
1306           an  empty  string (by default this causes the current matching alterna-
1307           tive to fail). A pattern such as (\1)(a) succeeds when this  option  is
1308           set  (assuming  it can find an "a" in the subject), whereas it fails by
1309           default, for Perl compatibility.
1310    
1311             PCRE_MULTILINE
1312    
1313           By default, PCRE treats the subject string as consisting  of  a  single
1314           line  of characters (even if it actually contains newlines). The "start
1315           of line" metacharacter (^) matches only at the  start  of  the  string,
1316           while  the  "end  of line" metacharacter ($) matches only at the end of
1317           the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1318           is set). This is the same as Perl.
1319    
1320           When  PCRE_MULTILINE  it  is set, the "start of line" and "end of line"
1321           constructs match immediately following or immediately  before  internal
1322           newlines  in  the  subject string, respectively, as well as at the very
1323           start and end. This is equivalent to Perl's /m option, and  it  can  be
1324           changed within a pattern by a (?m) option setting. If there are no new-
1325           lines in a subject string, or no occurrences of ^ or $  in  a  pattern,
1326           setting PCRE_MULTILINE has no effect.
1327    
1328             PCRE_NEWLINE_CR
1329             PCRE_NEWLINE_LF
1330             PCRE_NEWLINE_CRLF
1331             PCRE_NEWLINE_ANYCRLF
1332             PCRE_NEWLINE_ANY
1333    
1334           These  options  override the default newline definition that was chosen
1335           when PCRE was built. Setting the first or the second specifies  that  a
1336           newline  is  indicated  by a single character (CR or LF, respectively).
1337           Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the
1338           two-character  CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF specifies
1339           that any of the three preceding sequences should be recognized. Setting
1340           PCRE_NEWLINE_ANY  specifies that any Unicode newline sequence should be
1341           recognized. The Unicode newline sequences are the three just mentioned,
1342           plus  the  single  characters  VT (vertical tab, U+000B), FF (formfeed,
1343           U+000C), NEL (next line, U+0085), LS (line separator, U+2028),  and  PS
1344           (paragraph  separator,  U+2029).  The  last  two are recognized only in
1345           UTF-8 mode.
1346    
1347           The newline setting in the  options  word  uses  three  bits  that  are
1348           treated as a number, giving eight possibilities. Currently only six are
1349           used (default plus the five values above). This means that if  you  set
1350           more  than one newline option, the combination may or may not be sensi-
1351           ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1352           PCRE_NEWLINE_CRLF,  but other combinations may yield unused numbers and
1353           cause an error.
1354    
1355           The only time that a line break is specially recognized when  compiling
1356           a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a
1357           character class is encountered. This indicates  a  comment  that  lasts
1358           until  after the next line break sequence. In other circumstances, line
1359           break  sequences  are  treated  as  literal  data,   except   that   in
1360           PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1361           and are therefore ignored.
1362    
1363           The newline option that is set at compile time becomes the default that
1364           is used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1365    
1366             PCRE_NO_AUTO_CAPTURE
1367    
1368           If this option is set, it disables the use of numbered capturing paren-
1369           theses in the pattern. Any opening parenthesis that is not followed  by
1370           ?  behaves as if it were followed by ?: but named parentheses can still
1371           be used for capturing (and they acquire  numbers  in  the  usual  way).
1372           There is no equivalent of this option in Perl.
1373    
1374             PCRE_UNGREEDY
1375    
1376           This  option  inverts  the "greediness" of the quantifiers so that they
1377           are not greedy by default, but become greedy if followed by "?". It  is
1378           not  compatible  with Perl. It can also be set by a (?U) option setting
1379           within the pattern.
1380    
1381             PCRE_UTF8
1382    
1383           This option causes PCRE to regard both the pattern and the  subject  as
1384           strings  of  UTF-8 characters instead of single-byte character strings.
1385           However, it is available only when PCRE is built to include UTF-8  sup-
1386           port.  If not, the use of this option provokes an error. Details of how
1387           this option changes the behaviour of PCRE are given in the  section  on
1388           UTF-8 support in the main pcre page.
1389    
1390             PCRE_NO_UTF8_CHECK
1391    
1392           When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
1393           automatically checked. There is a  discussion  about  the  validity  of
1394           UTF-8  strings  in  the main pcre page. If an invalid UTF-8 sequence of
1395           bytes is found, pcre_compile() returns an error. If  you  already  know
1396           that your pattern is valid, and you want to skip this check for perfor-
1397           mance reasons, you can set the PCRE_NO_UTF8_CHECK option.  When  it  is
1398           set,  the  effect  of  passing  an invalid UTF-8 string as a pattern is
1399           undefined. It may cause your program to crash. Note  that  this  option
1400           can  also be passed to pcre_exec() and pcre_dfa_exec(), to suppress the
1401           UTF-8 validity checking of subject strings.
1402    
1403    
1404    COMPILATION ERROR CODES
1405    
1406           The following table lists the error  codes  than  may  be  returned  by
1407           pcre_compile2(),  along with the error messages that may be returned by
1408           both compiling functions. As PCRE has developed, some error codes  have
1409           fallen out of use. To avoid confusion, they have not been re-used.
1410    
1411              0  no error
1412              1  \ at end of pattern
1413              2  \c at end of pattern
1414              3  unrecognized character follows \
1415              4  numbers out of order in {} quantifier
1416              5  number too big in {} quantifier
1417              6  missing terminating ] for character class
1418              7  invalid escape sequence in character class
1419              8  range out of order in character class
1420              9  nothing to repeat
1421             10  [this code is not in use]
1422             11  internal error: unexpected repeat
1423             12  unrecognized character after (? or (?-
1424             13  POSIX named classes are supported only within a class
1425             14  missing )
1426             15  reference to non-existent subpattern
1427             16  erroffset passed as NULL
1428             17  unknown option bit(s) set
1429             18  missing ) after comment
1430             19  [this code is not in use]
1431             20  regular expression is too large
1432             21  failed to get memory
1433             22  unmatched parentheses
1434             23  internal error: code overflow
1435             24  unrecognized character after (?<
1436             25  lookbehind assertion is not fixed length
1437             26  malformed number or name after (?(
1438             27  conditional group contains more than two branches
1439             28  assertion expected after (?(
1440             29  (?R or (?[+-]digits must be followed by )
1441             30  unknown POSIX class name
1442             31  POSIX collating elements are not supported
1443             32  this version of PCRE is not compiled with PCRE_UTF8 support
1444             33  [this code is not in use]
1445             34  character value in \x{...} sequence is too large
1446             35  invalid condition (?(0)
1447             36  \C not allowed in lookbehind assertion
1448             37  PCRE does not support \L, \l, \N, \U, or \u
1449             38  number after (?C is > 255
1450             39  closing ) for (?C expected
1451             40  recursive call could loop indefinitely
1452             41  unrecognized character after (?P
1453             42  syntax error in subpattern name (missing terminator)
1454             43  two named subpatterns have the same name
1455             44  invalid UTF-8 string
1456             45  support for \P, \p, and \X has not been compiled
1457             46  malformed \P or \p sequence
1458             47  unknown property name after \P or \p
1459             48  subpattern name is too long (maximum 32 characters)
1460             49  too many named subpatterns (maximum 10000)
1461             50  [this code is not in use]
1462             51  octal value is greater than \377 (not in UTF-8 mode)
1463             52  internal error: overran compiling workspace
1464             53   internal  error:  previously-checked  referenced  subpattern not
1465           found
1466             54  DEFINE group contains more than one branch
1467             55  repeating a DEFINE group is not allowed
1468             56  inconsistent NEWLINE options
1469             57  \g is not followed by a braced, angle-bracketed, or quoted
1470                   name/number or by a plain number
1471             58  a numbered reference must not be zero
1472             59  (*VERB) with an argument is not supported
1473             60  (*VERB) not recognized
1474             61  number is too big
1475             62  subpattern name expected
1476             63  digit expected after (?+
1477             64  ] is an invalid data character in JavaScript compatibility mode
1478    
1479           The numbers 32 and 10000 in errors 48 and 49  are  defaults;  different
1480           values may be used if the limits were changed when PCRE was built.
1481    
1482    
1483  STUDYING A PATTERN  STUDYING A PATTERN
1484    
1485       pcre_extra *pcre_study(const pcre *code, int options,         pcre_extra *pcre_study(const pcre *code, int options
1486            const char **errptr);              const char **errptr);
1487    
1488       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
1489       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
1490       the time taken for matching. The function pcre_study() takes         matching.  The function pcre_study() takes a pointer to a compiled pat-
1491       a  pointer  to  a compiled pattern as its first argument. If         tern as its first argument. If studying the pattern produces additional
1492       studing the pattern  produces  additional  information  that         information  that  will  help speed up matching, pcre_study() returns a
1493       will  help speed up matching, pcre_study() returns a pointer         pointer to a pcre_extra block, in which the study_data field points  to
1494       to a pcre_extra block, in which the study_data field  points         the results of the study.
1495       to the results of the study.  
1496           The  returned  value  from  pcre_study()  can  be  passed  directly  to
1497       The  returned  value  from  a  pcre_study()  can  be  passed         pcre_exec() or pcre_dfa_exec(). However, a pcre_extra block  also  con-
1498       directly  to pcre_exec(). However, the pcre_extra block also         tains  other  fields  that can be set by the caller before the block is
1499       contains other fields that can be set by the  caller  before         passed; these are described below in the section on matching a pattern.
1500       the  block is passed; these are described below. If studying  
1501       the pattern does not  produce  any  additional  information,         If studying the  pattern  does  not  produce  any  useful  information,
1502       pcre_study() returns NULL. In that circumstance, if the cal-         pcre_study() returns NULL. In that circumstance, if the calling program
1503       ling program wants to pass  some  of  the  other  fields  to         wants  to  pass  any  of   the   other   fields   to   pcre_exec()   or
1504       pcre_exec(), it must set up its own pcre_extra block.         pcre_dfa_exec(), it must set up its own pcre_extra block.
1505    
1506       The second argument contains option  bits.  At  present,  no         The  second  argument of pcre_study() contains option bits. At present,
1507       options  are  defined  for  pcre_study(),  and this argument         no options are defined, and this argument should always be zero.
1508       should always be zero.  
1509           The third argument for pcre_study() is a pointer for an error  message.
1510       The third argument for pcre_study()  is  a  pointer  for  an         If  studying  succeeds  (even  if no data is returned), the variable it
1511       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
1512       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
1513       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
1514       fore  test  the  error  pointer  for  NULL   after   calling         after calling pcre_study(), to be sure that it has run successfully.
1515       pcre_study(), to be sure that it has run successfully.  
1516           This is a typical call to pcre_study():
1517       This is a typical call to pcre_study():  
1518             pcre_extra *pe;
1519         pcre_extra *pe;           pe = pcre_study(
1520         pe = pcre_study(             re,             /* result of pcre_compile() */
1521           re,             /* result of pcre_compile() */             0,              /* no options exist */
1522           0,              /* no options exist */             &error);        /* set to NULL or points to a message */
1523           &error);        /* set to NULL or points to a message */  
1524           Studying a pattern does two things: first, a lower bound for the length
1525       At present, studying a  pattern  is  useful  only  for  non-         of subject string that is needed to match the pattern is computed. This
1526       anchored  patterns  that do not have a single fixed starting         does not mean that there are any strings of that length that match, but
1527       character. A  bitmap  of  possible  starting  characters  is         it does guarantee that no shorter strings match. The value is  used  by
1528       created.         pcre_exec()  and  pcre_dfa_exec()  to  avoid  wasting time by trying to
1529           match strings that are shorter than the lower bound. You can  find  out
1530           the value in a calling program via the pcre_fullinfo() function.
1531    
1532           Studying a pattern is also useful for non-anchored patterns that do not
1533           have a single fixed starting character. A bitmap of  possible  starting
1534           bytes  is  created. This speeds up finding a position in the subject at
1535           which to start matching.
1536    
1537    
1538  LOCALE SUPPORT  LOCALE SUPPORT
1539    
1540       PCRE handles caseless matching, and determines whether char-         PCRE handles caseless matching, and determines whether  characters  are
1541       acters  are  letters, digits, or whatever, by reference to a         letters,  digits, or whatever, by reference to a set of tables, indexed
1542       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
1543       to characters with codes less than 256. The library contains         characters  with  codes  less than 128. Higher-valued codes never match
1544       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
1545       locale  when  PCRE  is compiled. This is used when the final         with  Unicode  character property support. The use of locales with Uni-
1546       argument of pcre_compile() is NULL, and  is  sufficient  for         code is discouraged. If you are handling characters with codes  greater
1547       many applications.         than  128, you should either use UTF-8 and Unicode, or use locales, but
1548           not try to mix the two.
1549       An alternative set of tables can, however, be supplied. Such  
1550       tables  are built by calling the pcre_maketables() function,         PCRE contains an internal set of tables that are used  when  the  final
1551       which has no arguments, in the relevant locale.  The  result         argument  of  pcre_compile()  is  NULL.  These  are sufficient for many
1552       can  then be passed to pcre_compile() as often as necessary.         applications.  Normally, the internal tables recognize only ASCII char-
1553       For example, to build and use tables  that  are  appropriate         acters. However, when PCRE is built, it is possible to cause the inter-
1554       for  the French locale (where accented characters with codes         nal tables to be rebuilt in the default "C" locale of the local system,
1555       greater than 128 are treated as letters), the following code         which may cause them to be different.
1556       could be used:  
1557           The  internal tables can always be overridden by tables supplied by the
1558         setlocale(LC_CTYPE, "fr");         application that calls PCRE. These may be created in a different locale
1559         tables = pcre_maketables();         from  the  default.  As more and more applications change to using Uni-
1560         re = pcre_compile(..., tables);         code, the need for this locale support is expected to die away.
1561    
1562       The  tables  are  built  in  memory  that  is  obtained  via         External tables are built by calling  the  pcre_maketables()  function,
1563       pcre_malloc.  The  pointer that is passed to pcre_compile is         which  has no arguments, in the relevant locale. The result can then be
1564       saved with the compiled pattern, and  the  same  tables  are         passed to pcre_compile() or pcre_exec()  as  often  as  necessary.  For
1565       used via this pointer by pcre_study() and pcre_exec(). Thus,         example,  to  build  and use tables that are appropriate for the French
1566       for any single pattern, compilation, studying  and  matching         locale (where accented characters with  values  greater  than  128  are
1567       all happen in the same locale, but different patterns can be         treated as letters), the following code could be used:
1568       compiled in different locales. It is the caller's  responsi-  
1569       bility  to  ensure  that  the  memory  containing the tables           setlocale(LC_CTYPE, "fr_FR");
1570       remains available for as long as it is needed.           tables = pcre_maketables();
1571             re = pcre_compile(..., tables);
1572    
1573           The  locale  name "fr_FR" is used on Linux and other Unix-like systems;
1574           if you are using Windows, the name for the French locale is "french".
1575    
1576           When pcre_maketables() runs, the tables are built  in  memory  that  is
1577           obtained  via  pcre_malloc. It is the caller's responsibility to ensure
1578           that the memory containing the tables remains available for as long  as
1579           it is needed.
1580    
1581           The pointer that is passed to pcre_compile() is saved with the compiled
1582           pattern, and the same tables are used via this pointer by  pcre_study()
1583           and normally also by pcre_exec(). Thus, by default, for any single pat-
1584           tern, compilation, studying and matching all happen in the same locale,
1585           but different patterns can be compiled in different locales.
1586    
1587           It  is  possible to pass a table pointer or NULL (indicating the use of
1588           the internal tables) to pcre_exec(). Although  not  intended  for  this
1589           purpose,  this facility could be used to match a pattern in a different
1590           locale from the one in which it was compiled. Passing table pointers at
1591           run time is discussed below in the section on matching a pattern.
1592    
1593    
1594  INFORMATION ABOUT A PATTERN  INFORMATION ABOUT A PATTERN
1595    
1596       int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1597            int what, void *where);              int what, void *where);
1598    
1599       The pcre_fullinfo() function  returns  information  about  a         The  pcre_fullinfo() function returns information about a compiled pat-
1600       compiled pattern. It replaces the obsolete pcre_info() func-         tern. It replaces the obsolete pcre_info() function, which is neverthe-
1601       tion, which is nevertheless retained for backwards compabil-         less retained for backwards compability (and is documented below).
1602       ity (and is documented below).  
1603           The  first  argument  for  pcre_fullinfo() is a pointer to the compiled
1604       The first argument for pcre_fullinfo() is a pointer  to  the         pattern. The second argument is the result of pcre_study(), or NULL  if
1605       compiled  pattern.  The  second  argument  is  the result of         the  pattern  was not studied. The third argument specifies which piece
1606       pcre_study(), or NULL if the pattern was  not  studied.  The         of information is required, and the fourth argument is a pointer  to  a
1607       third  argument  specifies  which  piece  of  information is         variable  to  receive  the  data. The yield of the function is zero for
1608       required, and the fourth argument is a pointer to a variable         success, or one of the following negative numbers:
1609       to  receive  the data. The yield of the function is zero for  
1610       success, or one of the following negative numbers:           PCRE_ERROR_NULL       the argument code was NULL
1611                                   the argument where was NULL
1612         PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1613                               the argument where was NULL           PCRE_ERROR_BADOPTION  the value of what was invalid
1614         PCRE_ERROR_BADMAGIC   the "magic number" was not found  
1615         PCRE_ERROR_BADOPTION  the value of what was invalid         The "magic number" is placed at the start of each compiled  pattern  as
1616           an  simple check against passing an arbitrary memory pointer. Here is a
1617       Here is a typical call of  pcre_fullinfo(),  to  obtain  the         typical call of pcre_fullinfo(), to obtain the length of  the  compiled
1618       length of the compiled pattern:         pattern:
1619    
1620         int rc;           int rc;
1621         unsigned long int length;           size_t length;
1622         rc = pcre_fullinfo(           rc = pcre_fullinfo(
1623           re,               /* result of pcre_compile() */             re,               /* result of pcre_compile() */
1624           pe,               /* result of pcre_study(), or NULL */             pe,               /* result of pcre_study(), or NULL */
1625           PCRE_INFO_SIZE,   /* what is required */             PCRE_INFO_SIZE,   /* what is required */
1626           &length);         /* where to put the data */             &length);         /* where to put the data */
1627    
1628       The possible values for the third argument  are  defined  in         The  possible  values for the third argument are defined in pcre.h, and
1629       pcre.h, and are as follows:         are as follows:
1630    
1631         PCRE_INFO_BACKREFMAX           PCRE_INFO_BACKREFMAX
1632    
1633       Return the number of the highest back reference in the  pat-         Return the number of the highest back reference  in  the  pattern.  The
1634       tern.  The  fourth argument should point to an int variable.         fourth  argument  should  point to an int variable. Zero is returned if
1635       Zero is returned if there are no back references.         there are no back references.
1636    
1637         PCRE_INFO_CAPTURECOUNT           PCRE_INFO_CAPTURECOUNT
1638    
1639       Return the number of capturing subpatterns in  the  pattern.         Return the number of capturing subpatterns in the pattern.  The  fourth
1640       The fourth argument should point to an int variable.         argument should point to an int variable.
1641    
1642         PCRE_INFO_FIRSTBYTE           PCRE_INFO_DEFAULT_TABLES
1643    
1644       Return information about  the  first  byte  of  any  matched         Return  a pointer to the internal default character tables within PCRE.
1645       string,  for a non-anchored pattern. (This option used to be         The fourth argument should point to an unsigned char *  variable.  This
1646       called PCRE_INFO_FIRSTCHAR; the old name is still recognized         information call is provided for internal use by the pcre_study() func-
1647       for backwards compatibility.)         tion. External callers can cause PCRE to use  its  internal  tables  by
1648           passing a NULL table pointer.
1649       If there is a fixed first byte, e.g. from a pattern such  as  
1650       (cat|cow|coyote),  it  is returned in the integer pointed to           PCRE_INFO_FIRSTBYTE
1651       by where. Otherwise, if either  
1652           Return  information  about  the first byte of any matched string, for a
1653       (a) the pattern was compiled with the PCRE_MULTILINE option,         non-anchored pattern. The fourth argument should point to an int  vari-
1654       and every branch starts with "^", or         able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
1655           is still recognized for backwards compatibility.)
1656       (b) every  branch  of  the  pattern  starts  with  ".*"  and  
1657       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
1658       anchored),         (cat|cow|coyote), its value is returned. Otherwise, if either
1659    
1660       -1 is returned, indicating that the pattern matches only  at         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every
1661       the  start  of  a subject string or after any newline within         branch starts with "^", or
1662       the string. Otherwise -2 is returned. For anchored patterns,  
1663       -2 is returned.         (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
1664           set (if it were set, the pattern would be anchored),
1665         PCRE_INFO_FIRSTTABLE  
1666           -1  is  returned, indicating that the pattern matches only at the start
1667       If the pattern was studied, and this resulted  in  the  con-         of a subject string or after any newline within the  string.  Otherwise
1668       struction of a 256-bit table indicating a fixed set of bytes         -2 is returned. For anchored patterns, -2 is returned.
1669       for the first byte in any matching string, a pointer to  the  
1670       table  is  returned.  Otherwise NULL is returned. The fourth           PCRE_INFO_FIRSTTABLE
1671       argument should point to an unsigned char * variable.  
1672           If  the pattern was studied, and this resulted in the construction of a
1673         PCRE_INFO_LASTLITERAL         256-bit table indicating a fixed set of bytes for the first byte in any
1674           matching  string, a pointer to the table is returned. Otherwise NULL is
1675       Return the value of the rightmost  literal  byte  that  must         returned. The fourth argument should point to an unsigned char *  vari-
1676       exist  in  any  matched  string, other than at its start, if         able.
1677       such a byte has been recorded. The  fourth  argument  should  
1678       point  to  an  int variable. If there is no such byte, -1 is           PCRE_INFO_HASCRORLF
1679       returned. For anchored patterns,  a  last  literal  byte  is  
1680       recorded  only  if  it follows something of variable length.         Return  1  if  the  pattern  contains any explicit matches for CR or LF
1681       For example, for the pattern /^a\d+z\d+/ the returned  value         characters, otherwise 0. The fourth argument should  point  to  an  int
1682       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
1683           \r or \n.
1684         PCRE_INFO_NAMECOUNT  
1685         PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_JCHANGED
1686         PCRE_INFO_NAMETABLE  
1687           Return 1 if the (?J) or (?-J) option setting is used  in  the  pattern,
1688       PCRE supports the use of named as well as numbered capturing         otherwise  0. The fourth argument should point to an int variable. (?J)
1689       parentheses. The names are just an additional way of identi-         and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
1690       fying the parentheses,  which  still  acquire  a  number.  A  
1691       caller  that  wants  to extract data from a named subpattern           PCRE_INFO_LASTLITERAL
1692       must convert the name to a number in  order  to  access  the  
1693       correct  pointers  in  the  output  vector  (described  with         Return the value of the rightmost literal byte that must exist  in  any
1694       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
1695       these  three  values  to  obtain  the name-to-number mapping         recorded. The fourth argument should point to an int variable. If there
1696       table for the pattern.         is  no such byte, -1 is returned. For anchored patterns, a last literal
1697           byte is recorded only if it follows something of variable  length.  For
1698       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
1699       PCRE_INFO_NAMECOUNT   gives   the  number  of  entries,  and         /^a\dz\d/ the returned value is -1.
1700       PCRE_INFO_NAMEENTRYSIZE gives the size of each  entry;  both  
1701       of  these return an int value. The entry size depends on the           PCRE_INFO_MINLENGTH
1702       length of the longest name.  PCRE_INFO_NAMETABLE  returns  a  
1703       pointer to the first entry of the table (a pointer to char).         If the pattern was studied and a minimum length  for  matching  subject
1704       The first two bytes of each entry are the number of the cap-         strings  was  computed,  its  value is returned. Otherwise the returned
1705       turing parenthesis, most significant byte first. The rest of         value is -1. The value is a number of characters, not bytes  (this  may
1706       the entry is the corresponding name,  zero  terminated.  The         be  relevant in UTF-8 mode). The fourth argument should point to an int
1707       names  are  in alphabetical order. For example, consider the         variable. A non-negative value is a lower bound to the  length  of  any
1708       following pattern (assume PCRE_EXTENDED  is  set,  so  white         matching  string.  There  may not be any strings of that length that do
1709       space - including newlines - is ignored):         actually match, but every string that does match is at least that long.
1710    
1711         (?P<date> (?P<year>(\d\d)?\d\d) -           PCRE_INFO_NAMECOUNT
1712         (?P<month>\d\d) - (?P<day>\d\d) )           PCRE_INFO_NAMEENTRYSIZE
1713             PCRE_INFO_NAMETABLE
1714       There are four named subpatterns,  so  the  table  has  four  
1715       entries,  and  each  entry in the table is eight bytes long.         PCRE supports the use of named as well as numbered capturing  parenthe-
1716       The table is as follows, with non-printing  bytes  shows  in         ses.  The names are just an additional way of identifying the parenthe-
1717       hex, and undefined bytes shown as ??:         ses, which still acquire numbers. Several convenience functions such as
1718           pcre_get_named_substring()  are  provided  for extracting captured sub-
1719         00 01 d  a  t  e  00 ??         strings by name. It is also possible to extract the data  directly,  by
1720         00 05 d  a  y  00 ?? ??         first  converting  the  name to a number in order to access the correct
1721         00 04 m  o  n  t  h  00         pointers in the output vector (described with pcre_exec() below). To do
1722         00 02 y  e  a  r  00 ??         the  conversion,  you  need  to  use  the  name-to-number map, which is
1723           described by these three values.
1724       When writing code to extract data  from  named  subpatterns,  
1725       remember  that the length of each entry may be different for         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
1726       each compiled pattern.         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1727           of each entry; both of these  return  an  int  value.  The  entry  size
1728         PCRE_INFO_OPTIONS         depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns
1729           a pointer to the first entry of the table  (a  pointer  to  char).  The
1730       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-
1731       piled.  The fourth argument should point to an unsigned long         sis, most significant byte first. The rest of the entry is  the  corre-
1732       int variable. These option bits are those specified  in  the         sponding name, zero terminated.
1733       call  to  pcre_compile(),  modified  by any top-level option  
1734       settings within the pattern itself.         The  names are in alphabetical order. Duplicate names may appear if (?|
1735           is used to create multiple groups with the same number, as described in
1736       A pattern is automatically anchored by PCRE if  all  of  its         the  section  on  duplicate subpattern numbers in the pcrepattern page.
1737       top-level alternatives begin with one of the following:         Duplicate names for subpatterns with different  numbers  are  permitted
1738           only  if  PCRE_DUPNAMES  is  set. In all cases of duplicate names, they
1739         ^     unless PCRE_MULTILINE is set         appear in the table in the order in which they were found in  the  pat-
1740         \A    always         tern.  In  the  absence  of (?| this is the order of increasing number;
1741         \G    always         when (?| is used this is not necessarily the case because later subpat-
1742         .*    if PCRE_DOTALL is set and there are no back         terns may have lower numbers.
1743                 references to the subpattern in which .* appears  
1744           As  a  simple  example of the name/number table, consider the following
1745       For such patterns, the  PCRE_ANCHORED  bit  is  set  in  the         pattern (assume PCRE_EXTENDED is set, so white space -  including  new-
1746       options returned by pcre_fullinfo().         lines - is ignored):
1747    
1748         PCRE_INFO_SIZE           (?<date> (?<year>(\d\d)?\d\d) -
1749             (?<month>\d\d) - (?<day>\d\d) )
1750       Return the size of the compiled pattern, that is, the  value  
1751       that  was  passed as the argument to pcre_malloc() when PCRE         There  are  four  named subpatterns, so the table has four entries, and
1752       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,
1753       fourth argument should point to a size_t variable.         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1754           as ??:
1755         PCRE_INFO_STUDYSIZE  
1756             00 01 d  a  t  e  00 ??
1757       Returns the size  of  the  data  block  pointed  to  by  the           00 05 d  a  y  00 ?? ??
1758       study_data  field  in a pcre_extra block. That is, it is the           00 04 m  o  n  t  h  00
1759       value that was passed to pcre_malloc() when PCRE was getting           00 02 y  e  a  r  00 ??
1760       memory into which to place the data created by pcre_study().  
1761       The fourth argument should point to a size_t variable.         When writing code to extract data  from  named  subpatterns  using  the
1762           name-to-number  map,  remember that the length of the entries is likely
1763           to be different for each compiled pattern.
1764    
1765             PCRE_INFO_OKPARTIAL
1766    
1767           Return 1  if  the  pattern  can  be  used  for  partial  matching  with
1768           pcre_exec(),  otherwise  0.  The fourth argument should point to an int
1769           variable. From  release  8.00,  this  always  returns  1,  because  the
1770           restrictions  that  previously  applied  to  partial matching have been
1771           lifted. The pcrepartial documentation gives details of  partial  match-
1772           ing.
1773    
1774             PCRE_INFO_OPTIONS
1775    
1776           Return  a  copy of the options with which the pattern was compiled. The
1777           fourth argument should point to an unsigned long  int  variable.  These
1778           option bits are those specified in the call to pcre_compile(), modified
1779           by any top-level option settings at the start of the pattern itself. In
1780           other  words,  they are the options that will be in force when matching
1781           starts. For example, if the pattern /(?im)abc(?-i)d/ is  compiled  with
1782           the  PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,
1783           and PCRE_EXTENDED.
1784    
1785           A pattern is automatically anchored by PCRE if  all  of  its  top-level
1786           alternatives begin with one of the following:
1787    
1788             ^     unless PCRE_MULTILINE is set
1789             \A    always
1790             \G    always
1791             .*    if PCRE_DOTALL is set and there are no back
1792                     references to the subpattern in which .* appears
1793    
1794           For such patterns, the PCRE_ANCHORED bit is set in the options returned
1795           by pcre_fullinfo().
1796    
1797             PCRE_INFO_SIZE
1798    
1799           Return the size of the compiled pattern, that is, the  value  that  was
1800           passed as the argument to pcre_malloc() when PCRE was getting memory in
1801           which to place the compiled data. The fourth argument should point to a
1802           size_t variable.
1803    
1804             PCRE_INFO_STUDYSIZE
1805    
1806           Return the size of the data block pointed to by the study_data field in
1807           a pcre_extra block. That is,  it  is  the  value  that  was  passed  to
1808           pcre_malloc() when PCRE was getting memory into which to place the data
1809           created by pcre_study(). If pcre_extra is NULL, or there  is  no  study
1810           data,  zero  is  returned. The fourth argument should point to a size_t
1811           variable.
1812    
1813    
1814  OBSOLETE INFO FUNCTION  OBSOLETE INFO FUNCTION
1815    
1816       int pcre_info(const pcre *code, int *optptr, *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1817    
1818       The pcre_info() function is now obsolete because its  inter-         The pcre_info() function is now obsolete because its interface  is  too
1819       face  is  too  restrictive  to return all the available data         restrictive  to return all the available data about a compiled pattern.
1820       about  a  compiled  pattern.   New   programs   should   use         New  programs  should  use  pcre_fullinfo()  instead.  The   yield   of
1821       pcre_fullinfo()  instead.  The  yield  of pcre_info() is the         pcre_info()  is the number of capturing subpatterns, or one of the fol-
1822       number of capturing subpatterns, or  one  of  the  following         lowing negative numbers:
1823       negative numbers:  
1824             PCRE_ERROR_NULL       the argument code was NULL
1825         PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1826         PCRE_ERROR_BADMAGIC   the "magic number" was not found  
1827           If the optptr argument is not NULL, a copy of the  options  with  which
1828       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
1829       with which the pattern was compiled is placed in the integer         PCRE_INFO_OPTIONS above).
1830       it points to (see PCRE_INFO_OPTIONS above).  
1831           If the pattern is not anchored and the  firstcharptr  argument  is  not
1832       If the pattern is not anchored and the firstcharptr argument         NULL,  it is used to pass back information about the first character of
1833       is  not  NULL, it is used to pass back information about the         any matched string (see PCRE_INFO_FIRSTBYTE above).
1834       first    character    of    any    matched    string    (see  
1835       PCRE_INFO_FIRSTBYTE above).  
1836    REFERENCE COUNTS
1837    
1838           int pcre_refcount(pcre *code, int adjust);
1839    
1840           The pcre_refcount() function is used to maintain a reference  count  in
1841           the data block that contains a compiled pattern. It is provided for the
1842           benefit of applications that  operate  in  an  object-oriented  manner,
1843           where different parts of the application may be using the same compiled
1844           pattern, but you want to free the block when they are all done.
1845    
1846           When a pattern is compiled, the reference count field is initialized to
1847           zero.   It is changed only by calling this function, whose action is to
1848           add the adjust value (which may be positive or  negative)  to  it.  The
1849           yield of the function is the new value. However, the value of the count
1850           is constrained to lie between 0 and 65535, inclusive. If the new  value
1851           is outside these limits, it is forced to the appropriate limit value.
1852    
1853           Except  when it is zero, the reference count is not correctly preserved
1854           if a pattern is compiled on one host and then  transferred  to  a  host
1855           whose byte-order is different. (This seems a highly unlikely scenario.)
1856    
1857    
1858    MATCHING A PATTERN: THE TRADITIONAL FUNCTION
1859    
1860           int pcre_exec(const pcre *code, const pcre_extra *extra,
1861                const char *subject, int length, int startoffset,
1862                int options, int *ovector, int ovecsize);
1863    
1864           The  function pcre_exec() is called to match a subject string against a
1865           compiled pattern, which is passed in the code argument. If the  pattern
1866           was  studied,  the  result  of  the study should be passed in the extra
1867           argument. This function is the main matching facility of  the  library,
1868           and it operates in a Perl-like manner. For specialist use there is also
1869           an alternative matching function, which is described below in the  sec-
1870           tion about the pcre_dfa_exec() function.
1871    
1872           In  most applications, the pattern will have been compiled (and option-
1873           ally studied) in the same process that calls pcre_exec().  However,  it
1874           is possible to save compiled patterns and study data, and then use them
1875           later in different processes, possibly even on different hosts.  For  a
1876           discussion about this, see the pcreprecompile documentation.
1877    
1878           Here is an example of a simple call to pcre_exec():
1879    
1880             int rc;
1881             int ovector[30];
1882             rc = pcre_exec(
1883               re,             /* result of pcre_compile() */
1884               NULL,           /* we didn't study the pattern */
1885               "some string",  /* the subject string */
1886               11,             /* the length of the subject string */
1887               0,              /* start at offset 0 in the subject */
1888               0,              /* default options */
1889               ovector,        /* vector of integers for substring information */
1890               30);            /* number of elements (NOT size in bytes) */
1891    
1892       Extra data for pcre_exec()
1893    
1894           If  the  extra argument is not NULL, it must point to a pcre_extra data
1895           block. The pcre_study() function returns such a block (when it  doesn't
1896           return  NULL), but you can also create one for yourself, and pass addi-
1897           tional information in it. The pcre_extra block contains  the  following
1898           fields (not necessarily in this order):
1899    
1900             unsigned long int flags;
1901             void *study_data;
1902             unsigned long int match_limit;
1903             unsigned long int match_limit_recursion;
1904             void *callout_data;
1905             const unsigned char *tables;
1906    
1907           The  flags  field  is a bitmap that specifies which of the other fields
1908           are set. The flag bits are:
1909    
1910             PCRE_EXTRA_STUDY_DATA
1911             PCRE_EXTRA_MATCH_LIMIT
1912             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1913             PCRE_EXTRA_CALLOUT_DATA
1914             PCRE_EXTRA_TABLES
1915    
1916           Other flag bits should be set to zero. The study_data field is  set  in
1917           the  pcre_extra  block  that is returned by pcre_study(), together with
1918           the appropriate flag bit. You should not set this yourself, but you may
1919           add  to  the  block by setting the other fields and their corresponding
1920           flag bits.
1921    
1922           The match_limit field provides a means of preventing PCRE from using up
1923           a  vast amount of resources when running patterns that are not going to
1924           match, but which have a very large number  of  possibilities  in  their
1925           search  trees. The classic example is a pattern that uses nested unlim-
1926           ited repeats.
1927    
1928           Internally, PCRE uses a function called match() which it calls  repeat-
1929           edly  (sometimes  recursively). The limit set by match_limit is imposed
1930           on the number of times this function is called during  a  match,  which
1931           has  the  effect  of  limiting the amount of backtracking that can take
1932           place. For patterns that are not anchored, the count restarts from zero
1933           for each position in the subject string.
1934    
1935           The  default  value  for  the  limit can be set when PCRE is built; the
1936           default default is 10 million, which handles all but the  most  extreme
1937           cases.  You  can  override  the  default by suppling pcre_exec() with a
1938           pcre_extra    block    in    which    match_limit    is    set,     and
1939           PCRE_EXTRA_MATCH_LIMIT  is  set  in  the  flags  field. If the limit is
1940           exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1941    
1942           The match_limit_recursion field is similar to match_limit, but  instead
1943           of limiting the total number of times that match() is called, it limits
1944           the depth of recursion. The recursion depth is a  smaller  number  than
1945           the  total number of calls, because not all calls to match() are recur-
1946           sive.  This limit is of use only if it is set smaller than match_limit.
1947    
1948           Limiting the recursion depth limits the amount of  stack  that  can  be
1949           used, or, when PCRE has been compiled to use memory on the heap instead
1950           of the stack, the amount of heap memory that can be used.
1951    
1952           The default value for match_limit_recursion can be  set  when  PCRE  is
1953           built;  the  default  default  is  the  same  value  as the default for
1954           match_limit. You can override the default by suppling pcre_exec()  with
1955           a   pcre_extra   block  in  which  match_limit_recursion  is  set,  and
1956           PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in  the  flags  field.  If  the
1957           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1958    
1959           The  callout_data  field is used in conjunction with the "callout" fea-
1960           ture, and is described in the pcrecallout documentation.
1961    
1962           The tables field  is  used  to  pass  a  character  tables  pointer  to
1963           pcre_exec();  this overrides the value that is stored with the compiled
1964           pattern. A non-NULL value is stored with the compiled pattern  only  if
1965           custom  tables  were  supplied to pcre_compile() via its tableptr argu-
1966           ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
1967           PCRE's  internal  tables  to be used. This facility is helpful when re-
1968           using patterns that have been saved after compiling  with  an  external
1969           set  of  tables,  because  the  external tables might be at a different
1970           address when pcre_exec() is called. See the  pcreprecompile  documenta-
1971           tion for a discussion of saving compiled patterns for later use.
1972    
1973       Option bits for pcre_exec()
1974    
1975           The  unused  bits of the options argument for pcre_exec() must be zero.
1976           The only bits that may  be  set  are  PCRE_ANCHORED,  PCRE_NEWLINE_xxx,
1977           PCRE_NOTBOL,    PCRE_NOTEOL,    PCRE_NOTEMPTY,   PCRE_NOTEMPTY_ATSTART,
1978           PCRE_NO_START_OPTIMIZE,  PCRE_NO_UTF8_CHECK,   PCRE_PARTIAL_SOFT,   and
1979           PCRE_PARTIAL_HARD.
1980    
1981             PCRE_ANCHORED
1982    
1983           The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first
1984           matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or
1985           turned  out to be anchored by virtue of its contents, it cannot be made
1986           unachored at matching time.
1987    
1988             PCRE_BSR_ANYCRLF
1989             PCRE_BSR_UNICODE
1990    
1991           These options (which are mutually exclusive) control what the \R escape
1992           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1993           or to match any Unicode newline sequence. These  options  override  the
1994           choice that was made or defaulted when the pattern was compiled.
1995    
1996             PCRE_NEWLINE_CR
1997             PCRE_NEWLINE_LF
1998             PCRE_NEWLINE_CRLF
1999             PCRE_NEWLINE_ANYCRLF
2000             PCRE_NEWLINE_ANY
2001    
2002           These  options  override  the  newline  definition  that  was chosen or
2003           defaulted when the pattern was compiled. For details, see the  descrip-
2004           tion  of  pcre_compile()  above.  During  matching,  the newline choice
2005           affects the behaviour of the dot, circumflex,  and  dollar  metacharac-
2006           ters.  It may also alter the way the match position is advanced after a
2007           match failure for an unanchored pattern.
2008    
2009           When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF,  or  PCRE_NEWLINE_ANY  is
2010           set,  and a match attempt for an unanchored pattern fails when the cur-
2011           rent position is at a  CRLF  sequence,  and  the  pattern  contains  no
2012           explicit  matches  for  CR  or  LF  characters,  the  match position is
2013           advanced by two characters instead of one, in other words, to after the
2014           CRLF.
2015    
2016           The above rule is a compromise that makes the most common cases work as
2017           expected. For example, if the  pattern  is  .+A  (and  the  PCRE_DOTALL
2018           option is not set), it does not match the string "\r\nA" because, after
2019           failing at the start, it skips both the CR and the LF before  retrying.
2020           However,  the  pattern  [\r\n]A does match that string, because it con-
2021           tains an explicit CR or LF reference, and so advances only by one char-
2022           acter after the first failure.
2023    
2024           An explicit match for CR of LF is either a literal appearance of one of
2025           those characters, or one of the \r or  \n  escape  sequences.  Implicit
2026           matches  such  as [^X] do not count, nor does \s (which includes CR and
2027           LF in the characters that it matches).
2028    
2029           Notwithstanding the above, anomalous effects may still occur when  CRLF
2030           is a valid newline sequence and explicit \r or \n escapes appear in the
2031           pattern.
2032    
2033             PCRE_NOTBOL
2034    
2035           This option specifies that first character of the subject string is not
2036           the  beginning  of  a  line, so the circumflex metacharacter should not
2037           match before it. Setting this without PCRE_MULTILINE (at compile  time)
2038           causes  circumflex  never to match. This option affects only the behav-
2039           iour of the circumflex metacharacter. It does not affect \A.
2040    
2041             PCRE_NOTEOL
2042    
2043           This option specifies that the end of the subject string is not the end
2044           of  a line, so the dollar metacharacter should not match it nor (except
2045           in multiline mode) a newline immediately before it. Setting this  with-
2046           out PCRE_MULTILINE (at compile time) causes dollar never to match. This
2047           option affects only the behaviour of the dollar metacharacter. It  does
2048           not affect \Z or \z.
2049    
2050             PCRE_NOTEMPTY
2051    
2052           An empty string is not considered to be a valid match if this option is
2053           set. If there are alternatives in the pattern, they are tried.  If  all
2054           the  alternatives  match  the empty string, the entire match fails. For
2055           example, if the pattern
2056    
2057             a?b?
2058    
2059           is applied to a string not beginning with "a" or  "b",  it  matches  an
2060           empty  string at the start of the subject. With PCRE_NOTEMPTY set, this
2061           match is not valid, so PCRE searches further into the string for occur-
2062           rences of "a" or "b".
2063    
2064             PCRE_NOTEMPTY_ATSTART
2065    
2066           This  is  like PCRE_NOTEMPTY, except that an empty string match that is
2067           not at the start of  the  subject  is  permitted.  If  the  pattern  is
2068           anchored, such a match can occur only if the pattern contains \K.
2069    
2070           Perl     has    no    direct    equivalent    of    PCRE_NOTEMPTY    or
2071           PCRE_NOTEMPTY_ATSTART, but it does make a special  case  of  a  pattern
2072           match  of  the empty string within its split() function, and when using
2073           the /g modifier. It is  possible  to  emulate  Perl's  behaviour  after
2074           matching a null string by first trying the match again at the same off-
2075           set with PCRE_NOTEMPTY_ATSTART and  PCRE_ANCHORED,  and  then  if  that
2076           fails, by advancing the starting offset (see below) and trying an ordi-
2077           nary match again. There is some code that demonstrates how to  do  this
2078           in the pcredemo sample program.
2079    
2080             PCRE_NO_START_OPTIMIZE
2081    
2082           There  are a number of optimizations that pcre_exec() uses at the start
2083           of a match, in order to speed up the process. For  example,  if  it  is
2084           known  that  a  match must start with a specific character, it searches
2085           the subject for that character, and fails immediately if it cannot find
2086           it,  without actually running the main matching function. When callouts
2087           are in use, these optimizations can cause  them  to  be  skipped.  This
2088           option  disables  the  "start-up" optimizations, causing performance to
2089           suffer, but ensuring that the callouts do occur.
2090    
2091             PCRE_NO_UTF8_CHECK
2092    
2093           When PCRE_UTF8 is set at compile time, the validity of the subject as a
2094           UTF-8  string is automatically checked when pcre_exec() is subsequently
2095           called.  The value of startoffset is also checked  to  ensure  that  it
2096           points  to  the start of a UTF-8 character. There is a discussion about
2097           the validity of UTF-8 strings in the section on UTF-8  support  in  the
2098           main  pcre  page.  If  an  invalid  UTF-8  sequence  of bytes is found,
2099           pcre_exec() returns the error PCRE_ERROR_BADUTF8. If  startoffset  con-
2100           tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
2101    
2102           If  you  already  know that your subject is valid, and you want to skip
2103           these   checks   for   performance   reasons,   you   can    set    the
2104           PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to
2105           do this for the second and subsequent calls to pcre_exec() if  you  are
2106           making  repeated  calls  to  find  all  the matches in a single subject
2107           string. However, you should be  sure  that  the  value  of  startoffset
2108           points  to  the  start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is
2109           set, the effect of passing an invalid UTF-8 string as a subject,  or  a
2110           value  of startoffset that does not point to the start of a UTF-8 char-
2111           acter, is undefined. Your program may crash.
2112    
2113             PCRE_PARTIAL_HARD
2114             PCRE_PARTIAL_SOFT
2115    
2116           These options turn on the partial matching feature. For backwards  com-
2117           patibility,  PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial
2118           match occurs if the end of the subject string is reached  successfully,
2119           but  there  are not enough subject characters to complete the match. If
2120           this happens when PCRE_PARTIAL_HARD  is  set,  pcre_exec()  immediately
2121           returns  PCRE_ERROR_PARTIAL.  Otherwise,  if  PCRE_PARTIAL_SOFT is set,
2122           matching continues by testing any other alternatives. Only if they  all
2123           fail  is  PCRE_ERROR_PARTIAL  returned (instead of PCRE_ERROR_NOMATCH).
2124           The portion of the string that was inspected when the partial match was
2125           found  is  set  as  the first matching string. There is a more detailed
2126           discussion in the pcrepartial documentation.
2127    
2128       The string to be matched by pcre_exec()
2129    
2130           The subject string is passed to pcre_exec() as a pointer in subject,  a
2131           length (in bytes) in length, and a starting byte offset in startoffset.
2132           In UTF-8 mode, the byte offset must point to the start of a UTF-8 char-
2133           acter.  Unlike  the pattern string, the subject may contain binary zero
2134           bytes. When the starting offset is zero, the search for a match  starts
2135           at  the  beginning  of  the subject, and this is by far the most common
2136           case.
2137    
2138           A non-zero starting offset is useful when searching for  another  match
2139           in  the same subject by calling pcre_exec() again after a previous suc-
2140           cess.  Setting startoffset differs from just passing over  a  shortened
2141           string  and  setting  PCRE_NOTBOL  in the case of a pattern that begins
2142           with any kind of lookbehind. For example, consider the pattern
2143    
2144             \Biss\B
2145    
2146           which finds occurrences of "iss" in the middle of  words.  (\B  matches
2147           only  if  the  current position in the subject is not a word boundary.)
2148           When applied to the string "Mississipi" the first call  to  pcre_exec()
2149           finds  the  first  occurrence. If pcre_exec() is called again with just
2150           the remainder of the subject,  namely  "issipi",  it  does  not  match,
2151           because \B is always false at the start of the subject, which is deemed
2152           to be a word boundary. However, if pcre_exec()  is  passed  the  entire
2153           string again, but with startoffset set to 4, it finds the second occur-
2154           rence of "iss" because it is able to look behind the starting point  to
2155           discover that it is preceded by a letter.
2156    
2157           If  a  non-zero starting offset is passed when the pattern is anchored,
2158           one attempt to match at the given offset is made. This can only succeed
2159           if  the  pattern  does  not require the match to be at the start of the
2160           subject.
2161    
2162       How pcre_exec() returns captured substrings
2163    
2164           In general, a pattern matches a certain portion of the subject, and  in
2165           addition,  further  substrings  from  the  subject may be picked out by
2166           parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,
2167           this  is  called "capturing" in what follows, and the phrase "capturing
2168           subpattern" is used for a fragment of a pattern that picks out  a  sub-
2169           string.  PCRE  supports several other kinds of parenthesized subpattern
2170           that do not cause substrings to be captured.
2171    
2172           Captured substrings are returned to the caller via a vector of integers
2173           whose  address is passed in ovector. The number of elements in the vec-
2174           tor is passed in ovecsize, which must be a non-negative  number.  Note:
2175           this argument is NOT the size of ovector in bytes.
2176    
2177           The  first  two-thirds of the vector is used to pass back captured sub-
2178           strings, each substring using a pair of integers. The  remaining  third
2179           of  the  vector is used as workspace by pcre_exec() while matching cap-
2180           turing subpatterns, and is not available for passing back  information.
2181           The  number passed in ovecsize should always be a multiple of three. If
2182           it is not, it is rounded down.
2183    
2184           When a match is successful, information about  captured  substrings  is
2185           returned  in  pairs  of integers, starting at the beginning of ovector,
2186           and continuing up to two-thirds of its length at the  most.  The  first
2187           element  of  each pair is set to the byte offset of the first character
2188           in a substring, and the second is set to the byte offset of  the  first
2189           character  after  the end of a substring. Note: these values are always
2190           byte offsets, even in UTF-8 mode. They are not character counts.
2191    
2192           The first pair of integers, ovector[0]  and  ovector[1],  identify  the
2193           portion  of  the subject string matched by the entire pattern. The next
2194           pair is used for the first capturing subpattern, and so on.  The  value
2195           returned by pcre_exec() is one more than the highest numbered pair that
2196           has been set.  For example, if two substrings have been  captured,  the
2197           returned  value is 3. If there are no capturing subpatterns, the return
2198           value from a successful match is 1, indicating that just the first pair
2199           of offsets has been set.
2200    
2201           If a capturing subpattern is matched repeatedly, it is the last portion
2202           of the string that it matched that is returned.
2203    
2204           If the vector is too small to hold all the captured substring  offsets,
2205           it is used as far as possible (up to two-thirds of its length), and the
2206           function returns a value of zero. If the substring offsets are  not  of
2207           interest,  pcre_exec()  may  be  called with ovector passed as NULL and
2208           ovecsize as zero. However, if the pattern contains back references  and
2209           the  ovector is not big enough to remember the related substrings, PCRE
2210           has to get additional memory for use during matching. Thus it  is  usu-
2211           ally advisable to supply an ovector.
2212    
2213           The pcre_fullinfo() function can be used to find out how many capturing
2214           subpatterns there are in a compiled  pattern.  The  smallest  size  for
2215           ovector  that  will allow for n captured substrings, in addition to the
2216           offsets of the substring matched by the whole pattern, is (n+1)*3.
2217    
2218           It is possible for capturing subpattern number n+1 to match  some  part
2219           of the subject when subpattern n has not been used at all. For example,
2220           if the string "abc" is matched  against  the  pattern  (a|(z))(bc)  the
2221           return from the function is 4, and subpatterns 1 and 3 are matched, but
2222           2 is not. When this happens, both values in  the  offset  pairs  corre-
2223           sponding to unused subpatterns are set to -1.
2224    
2225           Offset  values  that correspond to unused subpatterns at the end of the
2226           expression are also set to -1. For example,  if  the  string  "abc"  is
2227           matched  against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
2228           matched. The return from the function is 2, because  the  highest  used
2229           capturing subpattern number is 1. However, you can refer to the offsets
2230           for the second and third capturing subpatterns if  you  wish  (assuming
2231           the vector is large enough, of course).
2232    
2233           Some  convenience  functions  are  provided for extracting the captured
2234           substrings as separate strings. These are described below.
2235    
2236       Error return values from pcre_exec()
2237    
2238           If pcre_exec() fails, it returns a negative number. The  following  are
2239           defined in the header file:
2240    
2241             PCRE_ERROR_NOMATCH        (-1)
2242    
2243           The subject string did not match the pattern.
2244    
2245             PCRE_ERROR_NULL           (-2)
2246    
2247           Either  code  or  subject  was  passed as NULL, or ovector was NULL and
2248           ovecsize was not zero.
2249    
2250             PCRE_ERROR_BADOPTION      (-3)
2251    
2252           An unrecognized bit was set in the options argument.
2253    
2254             PCRE_ERROR_BADMAGIC       (-4)
2255    
2256           PCRE stores a 4-byte "magic number" at the start of the compiled  code,
2257           to catch the case when it is passed a junk pointer and to detect when a
2258           pattern that was compiled in an environment of one endianness is run in
2259           an  environment  with the other endianness. This is the error that PCRE
2260           gives when the magic number is not present.
2261    
2262             PCRE_ERROR_UNKNOWN_OPCODE (-5)
2263    
2264           While running the pattern match, an unknown item was encountered in the
2265           compiled  pattern.  This  error  could be caused by a bug in PCRE or by
2266           overwriting of the compiled pattern.
2267    
2268             PCRE_ERROR_NOMEMORY       (-6)
2269    
2270           If a pattern contains back references, but the ovector that  is  passed
2271           to pcre_exec() is not big enough to remember the referenced substrings,
2272           PCRE gets a block of memory at the start of matching to  use  for  this
2273           purpose.  If the call via pcre_malloc() fails, this error is given. The
2274           memory is automatically freed at the end of matching.
2275    
2276             PCRE_ERROR_NOSUBSTRING    (-7)
2277    
2278           This error is used by the pcre_copy_substring(),  pcre_get_substring(),
2279           and  pcre_get_substring_list()  functions  (see  below).  It  is  never
2280           returned by pcre_exec().
2281    
2282             PCRE_ERROR_MATCHLIMIT     (-8)
2283    
2284           The backtracking limit, as specified by  the  match_limit  field  in  a
2285           pcre_extra  structure  (or  defaulted) was reached. See the description
2286           above.
2287    
2288             PCRE_ERROR_CALLOUT        (-9)
2289    
2290           This error is never generated by pcre_exec() itself. It is provided for
2291           use  by  callout functions that want to yield a distinctive error code.
2292           See the pcrecallout documentation for details.
2293    
2294             PCRE_ERROR_BADUTF8        (-10)
2295    
2296           A string that contains an invalid UTF-8 byte sequence was passed  as  a
2297           subject.
2298    
2299             PCRE_ERROR_BADUTF8_OFFSET (-11)
2300    
2301           The UTF-8 byte sequence that was passed as a subject was valid, but the
2302           value of startoffset did not point to the beginning of a UTF-8  charac-
2303           ter.
2304    
2305             PCRE_ERROR_PARTIAL        (-12)
2306    
2307           The  subject  string did not match, but it did match partially. See the
2308           pcrepartial documentation for details of partial matching.
2309    
2310             PCRE_ERROR_BADPARTIAL     (-13)
2311    
2312           This code is no longer in  use.  It  was  formerly  returned  when  the
2313           PCRE_PARTIAL  option  was used with a compiled pattern containing items
2314           that were  not  supported  for  partial  matching.  From  release  8.00
2315           onwards, there are no restrictions on partial matching.
2316    
2317             PCRE_ERROR_INTERNAL       (-14)
2318    
2319           An  unexpected  internal error has occurred. This error could be caused
2320           by a bug in PCRE or by overwriting of the compiled pattern.
2321    
2322             PCRE_ERROR_BADCOUNT       (-15)
2323    
2324           This error is given if the value of the ovecsize argument is negative.
2325    
2326             PCRE_ERROR_RECURSIONLIMIT (-21)
2327    
2328           The internal recursion limit, as specified by the match_limit_recursion
2329           field  in  a  pcre_extra  structure (or defaulted) was reached. See the
2330           description above.
2331    
2332             PCRE_ERROR_BADNEWLINE     (-23)
2333    
2334  MATCHING A PATTERN         An invalid combination of PCRE_NEWLINE_xxx options was given.
2335    
2336       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.  
2337    
2338    
2339  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2340    
2341       int pcre_copy_substring(const char *subject, int *ovector,         int pcre_copy_substring(const char *subject, int *ovector,
2342            int stringcount, int stringnumber, char *buffer,              int stringcount, int stringnumber, char *buffer,
2343            int buffersize);              int buffersize);
2344    
2345       int pcre_get_substring(const char *subject, int *ovector,         int pcre_get_substring(const char *subject, int *ovector,
2346            int stringcount, int stringnumber,              int stringcount, int stringnumber,
2347            const char **stringptr);              const char **stringptr);
2348    
2349       int pcre_get_substring_list(const char *subject,         int pcre_get_substring_list(const char *subject,
2350            int *ovector, int stringcount, const char ***listptr);              int *ovector, int stringcount, const char ***listptr);
2351    
2352       Captured substrings can be accessed directly  by  using  the         Captured substrings can be  accessed  directly  by  using  the  offsets
2353       offsets returned by pcre_exec() in ovector. For convenience,         returned  by  pcre_exec()  in  ovector.  For convenience, the functions
2354       the functions  pcre_copy_substring(),  pcre_get_substring(),         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
2355       and  pcre_get_substring_list()  are  provided for extracting         string_list()  are  provided for extracting captured substrings as new,
2356       captured  substrings  as  new,   separate,   zero-terminated         separate, zero-terminated strings. These functions identify  substrings
2357       strings.  These functions identify substrings by number. The         by  number.  The  next section describes functions for extracting named
2358       next section describes functions for extracting  named  sub-         substrings.
2359       strings.   A  substring  that  contains  a  binary  zero  is  
2360       correctly extracted and has a further zero added on the end,         A substring that contains a binary zero is correctly extracted and  has
2361       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
2362           string.  However, you can process such a string  by  referring  to  the
2363       The first three arguments are the  same  for  all  three  of         length  that  is  returned  by  pcre_copy_substring() and pcre_get_sub-
2364       these  functions:   subject  is the subject string which has         string().  Unfortunately, the interface to pcre_get_substring_list() is
2365       just been successfully matched, ovector is a pointer to  the         not  adequate for handling strings containing binary zeros, because the
2366       vector  of  integer  offsets that was passed to pcre_exec(),         end of the final string is not independently indicated.
2367       and stringcount is the number of substrings that  were  cap-  
2368       tured by the match, including the substring that matched the         The first three arguments are the same for all  three  of  these  func-
2369       entire regular expression. This is  the  value  returned  by         tions:  subject  is  the subject string that has just been successfully
2370       pcre_exec  if  it  is  greater  than  zero.  If  pcre_exec()         matched, ovector is a pointer to the vector of integer offsets that was
2371       returned zero, indicating that it ran out of space in  ovec-         passed to pcre_exec(), and stringcount is the number of substrings that
2372       tor,  the  value passed as stringcount should be the size of         were captured by the match, including the substring  that  matched  the
2373       the vector divided by three.         entire regular expression. This is the value returned by pcre_exec() if
2374           it is greater than zero. If pcre_exec() returned zero, indicating  that
2375       The functions pcre_copy_substring() and pcre_get_substring()         it  ran out of space in ovector, the value passed as stringcount should
2376       extract a single substring, whose number is given as string-         be the number of elements in the vector divided by three.
2377       number. A value of zero extracts the substring that  matched  
2378       the entire pattern, while higher values extract the captured         The functions pcre_copy_substring() and pcre_get_substring() extract  a
2379       substrings. For pcre_copy_substring(), the string is  placed         single  substring,  whose  number  is given as stringnumber. A value of
2380       in  buffer,  whose  length is given by buffersize, while for         zero extracts the substring that matched the  entire  pattern,  whereas
2381       pcre_get_substring() a new block of memory is  obtained  via         higher  values  extract  the  captured  substrings.  For pcre_copy_sub-
2382       pcre_malloc,  and its address is returned via stringptr. The         string(), the string is placed in buffer,  whose  length  is  given  by
2383       yield of the function is  the  length  of  the  string,  not         buffersize,  while  for  pcre_get_substring()  a new block of memory is
2384       including the terminating zero, or one of         obtained via pcre_malloc, and its address is  returned  via  stringptr.
2385           The  yield  of  the function is the length of the string, not including
2386         PCRE_ERROR_NOMEMORY       (-6)         the terminating zero, or one of these error codes:
2387    
2388       The buffer was too small for pcre_copy_substring(),  or  the           PCRE_ERROR_NOMEMORY       (-6)
2389       attempt to get memory failed for pcre_get_substring().  
2390           The buffer was too small for pcre_copy_substring(), or the  attempt  to
2391         PCRE_ERROR_NOSUBSTRING    (-7)         get memory failed for pcre_get_substring().
2392    
2393       There is no substring whose number is stringnumber.           PCRE_ERROR_NOSUBSTRING    (-7)
2394    
2395       The pcre_get_substring_list() function extracts  all  avail-         There is no substring whose number is stringnumber.
2396       able  substrings  and builds a list of pointers to them. All  
2397       this is done in a single block of memory which  is  obtained         The  pcre_get_substring_list()  function  extracts  all  available sub-
2398       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
2399       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
2400       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
2401       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
2402           pointer. The yield of the function is zero if all  went  well,  or  the
2403         PCRE_ERROR_NOMEMORY       (-6)         error code
2404    
2405       if the attempt to get the memory block failed.           PCRE_ERROR_NOMEMORY       (-6)
2406    
2407       When any of these functions encounter a  substring  that  is         if the attempt to get the memory block failed.
2408       unset, which can happen when capturing subpattern number n+1  
2409       matches some part of the subject, but subpattern n  has  not         When  any of these functions encounter a substring that is unset, which
2410       been  used  at all, they return an empty string. This can be         can happen when capturing subpattern number n+1 matches  some  part  of
2411       distinguished  from  a  genuine  zero-length  substring   by         the  subject, but subpattern n has not been used at all, they return an
2412       inspecting the appropriate offset in ovector, which is nega-         empty string. This can be distinguished from a genuine zero-length sub-
2413       tive for unset substrings.         string  by inspecting the appropriate offset in ovector, which is nega-
2414           tive for unset substrings.
2415       The  two  convenience  functions  pcre_free_substring()  and  
2416       pcre_free_substring_list()  can  be  used to free the memory         The two convenience functions pcre_free_substring() and  pcre_free_sub-
2417       returned by  a  previous  call  of  pcre_get_substring()  or         string_list()  can  be  used  to free the memory returned by a previous
2418       pcre_get_substring_list(),  respectively.  They  do  nothing         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2419       more than call the function pointed to by  pcre_free,  which         tively.  They  do  nothing  more  than  call the function pointed to by
2420       of  course  could  be called directly from a C program. How-         pcre_free, which of course could be called directly from a  C  program.
2421       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-
2422       a  special  interface  to another programming language which         cial  interface  to  another  programming  language  that  cannot   use
2423       cannot use pcre_free directly; it is for  these  cases  that         pcre_free  directly;  it is for these cases that the functions are pro-
2424       the functions are provided.         vided.
2425    
2426    
2427  EXTRACTING CAPTURED SUBSTRINGS BY NAME  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2428    
2429       int pcre_copy_named_substring(const pcre *code,         int pcre_get_stringnumber(const pcre *code,
2430            const char *subject, int *ovector,              const char *name);
2431            int stringcount, const char *stringname,  
2432            char *buffer, int buffersize);         int pcre_copy_named_substring(const pcre *code,
2433                const char *subject, int *ovector,
2434       int pcre_get_stringnumber(const pcre *code,              int stringcount, const char *stringname,
2435            const char *name);              char *buffer, int buffersize);
2436    
2437       int pcre_get_named_substring(const pcre *code,         int pcre_get_named_substring(const pcre *code,
2438            const char *subject, int *ovector,              const char *subject, int *ovector,
2439            int stringcount, const char *stringname,              int stringcount, const char *stringname,
2440            const char **stringptr);              const char **stringptr);
2441    
2442       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-
2443       ciated    number.    This    can    be   done   by   calling         ber.  For example, for this pattern
2444       pcre_get_stringnumber(). The first argument is the  compiled  
2445       pattern,  and  the second is the name. For example, for this           (a+)b(?<xxx>\d+)...
2446       pattern  
2447           the number of the subpattern called "xxx" is 2. If the name is known to
2448         ab(?<xxx>\d+)...         be unique (PCRE_DUPNAMES was not set), you can find the number from the
2449           name by calling pcre_get_stringnumber(). The first argument is the com-
2450       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
2451       number,  you can then extract the substring directly, or use         the  subpattern  number,  or PCRE_ERROR_NOSUBSTRING (-7) if there is no
2452       one of the functions described in the previous section.  For         subpattern of that name.
2453       convenience,  there are also two functions that do the whole  
2454       job.         Given the number, you can extract the substring directly, or use one of
2455           the functions described in the previous section. For convenience, there
2456       Most of the  arguments  of  pcre_copy_named_substring()  and         are also two functions that do the whole job.
2457       pcre_get_named_substring()  are  the  same  as those for the  
2458       functions that  extract  by  number,  and  so  are  not  re-         Most   of   the   arguments    of    pcre_copy_named_substring()    and
2459       described here. There are just two differences.         pcre_get_named_substring()  are  the  same  as  those for the similarly
2460           named functions that extract by number. As these are described  in  the
2461       First, instead of a substring number, a  substring  name  is         previous  section,  they  are not re-described here. There are just two
2462       given.  Second,  there  is  an  extra argument, given at the         differences:
2463       start, which is a pointer to the compiled pattern.  This  is  
2464       needed  in order to gain access to the name-to-number trans-         First, instead of a substring number, a substring name is  given.  Sec-
2465       lation table.         ond, there is an extra argument, given at the start, which is a pointer
2466           to the compiled pattern. This is needed in order to gain access to  the
2467       These functions  call  pcre_get_stringnumber(),  and  if  it         name-to-number translation table.
2468       succeeds,    they   then   call   pcre_copy_substring()   or  
2469       pcre_get_substring(), as appropriate.         These  functions call pcre_get_stringnumber(), and if it succeeds, they
2470           then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-
2471           ate.  NOTE:  If PCRE_DUPNAMES is set and there are duplicate names, the
2472           behaviour may not be what you want (see the next section).
2473    
2474           Warning: If the pattern uses the (?| feature to set up multiple subpat-
2475           terns  with  the  same number, as described in the section on duplicate
2476           subpattern numbers in the pcrepattern page, you  cannot  use  names  to
2477           distinguish  the  different subpatterns, because names are not included
2478           in the compiled code. The matching process uses only numbers. For  this
2479           reason,  the  use of different names for subpatterns of the same number
2480           causes an error at compile time.
2481    
2482    
2483    DUPLICATE SUBPATTERN NAMES
2484    
2485           int pcre_get_stringtable_entries(const pcre *code,
2486                const char *name, char **first, char **last);
2487    
2488           When a pattern is compiled with the  PCRE_DUPNAMES  option,  names  for
2489           subpatterns  are not required to be unique. (Duplicate names are always
2490           allowed for subpatterns with the same number, created by using the  (?|
2491           feature.  Indeed,  if  such subpatterns are named, they are required to
2492           use the same names.)
2493    
2494           Normally, patterns with duplicate names are such that in any one match,
2495           only  one of the named subpatterns participates. An example is shown in
2496           the pcrepattern documentation.
2497    
2498           When   duplicates   are   present,   pcre_copy_named_substring()    and
2499           pcre_get_named_substring()  return the first substring corresponding to
2500           the given name that is set. If  none  are  set,  PCRE_ERROR_NOSUBSTRING
2501           (-7)  is  returned;  no  data  is returned. The pcre_get_stringnumber()
2502           function returns one of the numbers that are associated with the  name,
2503           but it is not defined which it is.
2504    
2505           If  you want to get full details of all captured substrings for a given
2506           name, you must use  the  pcre_get_stringtable_entries()  function.  The
2507           first argument is the compiled pattern, and the second is the name. The
2508           third and fourth are pointers to variables which  are  updated  by  the
2509           function. After it has run, they point to the first and last entries in
2510           the name-to-number table  for  the  given  name.  The  function  itself
2511           returns  the  length  of  each entry, or PCRE_ERROR_NOSUBSTRING (-7) if
2512           there are none. The format of the table is described above in the  sec-
2513           tion  entitled  Information  about  a  pattern.  Given all the relevant
2514           entries for the name, you can extract each of their numbers, and  hence
2515           the captured data, if any.
2516    
2517    
2518    FINDING ALL POSSIBLE MATCHES
2519    
2520           The  traditional  matching  function  uses a similar algorithm to Perl,
2521           which stops when it finds the first match, starting at a given point in
2522           the  subject.  If you want to find all possible matches, or the longest
2523           possible match, consider using the alternative matching  function  (see
2524           below)  instead.  If you cannot use the alternative function, but still
2525           need to find all possible matches, you can kludge it up by  making  use
2526           of the callout facility, which is described in the pcrecallout documen-
2527           tation.
2528    
2529           What you have to do is to insert a callout right at the end of the pat-
2530           tern.   When your callout function is called, extract and save the cur-
2531           rent matched substring. Then return  1,  which  forces  pcre_exec()  to
2532           backtrack  and  try other alternatives. Ultimately, when it runs out of
2533           matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2534    
2535    
2536    MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
2537    
2538           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
2539                const char *subject, int length, int startoffset,
2540                int options, int *ovector, int ovecsize,
2541                int *workspace, int wscount);
2542    
2543           The function pcre_dfa_exec()  is  called  to  match  a  subject  string
2544           against  a  compiled pattern, using a matching algorithm that scans the
2545           subject string just once, and does not backtrack.  This  has  different
2546           characteristics  to  the  normal  algorithm, and is not compatible with
2547           Perl. Some of the features of PCRE patterns are not  supported.  Never-
2548           theless,  there are times when this kind of matching can be useful. For
2549           a discussion of the two matching algorithms, and  a  list  of  features
2550           that  pcre_dfa_exec() does not support, see the pcrematching documenta-
2551           tion.
2552    
2553           The arguments for the pcre_dfa_exec() function  are  the  same  as  for
2554           pcre_exec(), plus two extras. The ovector argument is used in a differ-
2555           ent way, and this is described below. The other  common  arguments  are
2556           used  in  the  same way as for pcre_exec(), so their description is not
2557           repeated here.
2558    
2559           The two additional arguments provide workspace for  the  function.  The
2560           workspace  vector  should  contain at least 20 elements. It is used for
2561           keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2562           workspace  will  be  needed for patterns and subjects where there are a
2563           lot of potential matches.
2564    
2565           Here is an example of a simple call to pcre_dfa_exec():
2566    
2567             int rc;
2568             int ovector[10];
2569             int wspace[20];
2570             rc = pcre_dfa_exec(
2571               re,             /* result of pcre_compile() */
2572               NULL,           /* we didn't study the pattern */
2573               "some string",  /* the subject string */
2574               11,             /* the length of the subject string */
2575               0,              /* start at offset 0 in the subject */
2576               0,              /* default options */
2577               ovector,        /* vector of integers for substring information */
2578               10,             /* number of elements (NOT size in bytes) */
2579               wspace,         /* working space vector */
2580               20);            /* number of elements (NOT size in bytes) */
2581    
2582       Option bits for pcre_dfa_exec()
2583    
2584           The unused bits of the options argument  for  pcre_dfa_exec()  must  be
2585           zero.  The  only  bits  that  may  be  set are PCRE_ANCHORED, PCRE_NEW-
2586           LINE_xxx,        PCRE_NOTBOL,        PCRE_NOTEOL,        PCRE_NOTEMPTY,
2587           PCRE_NOTEMPTY_ATSTART, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_HARD, PCRE_PAR-
2588           TIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All  but  the  last
2589           four  of  these  are  exactly  the  same  as  for pcre_exec(), so their
2590           description is not repeated here.
2591    
2592             PCRE_PARTIAL_HARD
2593             PCRE_PARTIAL_SOFT
2594    
2595           These have the same general effect as they do for pcre_exec(), but  the
2596           details  are  slightly  different.  When  PCRE_PARTIAL_HARD  is set for
2597           pcre_dfa_exec(), it returns PCRE_ERROR_PARTIAL if the end of  the  sub-
2598           ject  is  reached  and there is still at least one matching possibility
2599           that requires additional characters. This happens even if some complete
2600           matches have also been found. When PCRE_PARTIAL_SOFT is set, the return
2601           code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end
2602           of  the  subject  is  reached, there have been no complete matches, but
2603           there is still at least one matching possibility. The  portion  of  the
2604           string  that  was inspected when the longest partial match was found is
2605           set as the first matching string in both cases.
2606    
2607             PCRE_DFA_SHORTEST
2608    
2609           Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to
2610           stop as soon as it has found one match. Because of the way the alterna-
2611           tive algorithm works, this is necessarily the shortest  possible  match
2612           at the first possible matching point in the subject string.
2613    
2614             PCRE_DFA_RESTART
2615    
2616           When pcre_dfa_exec() returns a partial match, it is possible to call it
2617           again, with additional subject characters, and have  it  continue  with
2618           the  same match. The PCRE_DFA_RESTART option requests this action; when
2619           it is set, the workspace and wscount options must  reference  the  same
2620           vector  as  before  because data about the match so far is left in them
2621           after a partial match. There is more discussion of this facility in the
2622           pcrepartial documentation.
2623    
2624       Successful returns from pcre_dfa_exec()
2625    
2626           When  pcre_dfa_exec()  succeeds, it may have matched more than one sub-
2627           string in the subject. Note, however, that all the matches from one run
2628           of  the  function  start  at the same point in the subject. The shorter
2629           matches are all initial substrings of the longer matches. For  example,
2630           if the pattern
2631    
2632             <.*>
2633    
2634           is matched against the string
2635    
2636             This is <something> <something else> <something further> no more
2637    
2638           the three matched strings are
2639    
2640             <something>
2641             <something> <something else>
2642             <something> <something else> <something further>
2643    
2644           On  success,  the  yield of the function is a number greater than zero,
2645           which is the number of matched substrings.  The  substrings  themselves
2646           are  returned  in  ovector. Each string uses two elements; the first is
2647           the offset to the start, and the second is the offset to  the  end.  In
2648           fact,  all  the  strings  have the same start offset. (Space could have
2649           been saved by giving this only once, but it was decided to retain  some
2650           compatibility  with  the  way pcre_exec() returns data, even though the
2651           meaning of the strings is different.)
2652    
2653           The strings are returned in reverse order of length; that is, the long-
2654           est  matching  string is given first. If there were too many matches to
2655           fit into ovector, the yield of the function is zero, and the vector  is
2656           filled with the longest matches.
2657    
2658       Error returns from pcre_dfa_exec()
2659    
2660           The  pcre_dfa_exec()  function returns a negative number when it fails.
2661           Many of the errors are the same  as  for  pcre_exec(),  and  these  are
2662           described  above.   There are in addition the following errors that are
2663           specific to pcre_dfa_exec():
2664    
2665             PCRE_ERROR_DFA_UITEM      (-16)
2666    
2667           This return is given if pcre_dfa_exec() encounters an item in the  pat-
2668           tern  that  it  does not support, for instance, the use of \C or a back
2669           reference.
2670    
2671             PCRE_ERROR_DFA_UCOND      (-17)
2672    
2673           This return is given if pcre_dfa_exec()  encounters  a  condition  item
2674           that  uses  a back reference for the condition, or a test for recursion
2675           in a specific group. These are not supported.
2676    
2677             PCRE_ERROR_DFA_UMLIMIT    (-18)
2678    
2679           This return is given if pcre_dfa_exec() is called with an  extra  block
2680           that contains a setting of the match_limit field. This is not supported
2681           (it is meaningless).
2682    
2683             PCRE_ERROR_DFA_WSSIZE     (-19)
2684    
2685           This return is given if  pcre_dfa_exec()  runs  out  of  space  in  the
2686           workspace vector.
2687    
2688             PCRE_ERROR_DFA_RECURSE    (-20)
2689    
2690           When  a  recursive subpattern is processed, the matching function calls
2691           itself recursively, using private vectors for  ovector  and  workspace.
2692           This  error  is  given  if  the output vector is not large enough. This
2693           should be extremely rare, as a vector of size 1000 is used.
2694    
2695    
2696    SEE ALSO
2697    
2698           pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-
2699           tial(3), pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2700    
2701    
2702    AUTHOR
2703    
2704           Philip Hazel
2705           University Computing Service
2706           Cambridge CB2 3QH, England.
2707    
2708    
2709    REVISION
2710    
2711           Last updated: 03 October 2009
2712           Copyright (c) 1997-2009 University of Cambridge.
2713    ------------------------------------------------------------------------------
2714    
2715    
2716    PCRECALLOUT(3)                                                  PCRECALLOUT(3)
2717    
 Last updated: 03 February 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
2718    
2719  NAME  NAME
2720       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2721    
2722    
2723  PCRE CALLOUTS  PCRE CALLOUTS
2724    
2725       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.  
2726    
2727           PCRE provides a feature called "callout", which is a means of temporar-
2728           ily passing control to the caller of PCRE  in  the  middle  of  pattern
2729           matching.  The  caller of PCRE provides an external function by putting
2730           its entry point in the global variable pcre_callout. By  default,  this
2731           variable contains NULL, which disables all calling out.
2732    
2733           Within  a  regular  expression,  (?C) indicates the points at which the
2734           external function is to be called.  Different  callout  points  can  be
2735           identified  by  putting  a number less than 256 after the letter C. The
2736           default value is zero.  For  example,  this  pattern  has  two  callout
2737           points:
2738    
2739             (?C1)abc(?C2)def
2740    
2741           If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() or
2742           pcre_compile2() is called, PCRE  automatically  inserts  callouts,  all
2743           with  number  255,  before  each  item  in the pattern. For example, if
2744           PCRE_AUTO_CALLOUT is used with the pattern
2745    
2746             A(\d{2}|--)
2747    
2748           it is processed as if it were
2749    
2750           (?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255)
2751    
2752           Notice that there is a callout before and after  each  parenthesis  and
2753           alternation  bar.  Automatic  callouts  can  be  used  for tracking the
2754           progress of pattern matching. The pcretest command has an  option  that
2755           sets  automatic callouts; when it is used, the output indicates how the
2756           pattern is matched. This is useful information when you are  trying  to
2757           optimize the performance of a particular pattern.
2758    
2759    
2760    MISSING CALLOUTS
2761    
2762           You  should  be  aware  that,  because of optimizations in the way PCRE
2763           matches patterns by default, callouts  sometimes  do  not  happen.  For
2764           example, if the pattern is
2765    
2766             ab(?C4)cd
2767    
2768           PCRE knows that any matching string must contain the letter "d". If the
2769           subject string is "abyz", the lack of "d" means that  matching  doesn't
2770           ever  start,  and  the  callout is never reached. However, with "abyd",
2771           though the result is still no match, the callout is obeyed.
2772    
2773           If the pattern is studied, PCRE knows the minimum length of a  matching
2774           string,  and will immediately give a "no match" return without actually
2775           running a match if the subject is not long enough, or,  for  unanchored
2776           patterns, if it has been scanned far enough.
2777    
2778           You  can disable these optimizations by passing the PCRE_NO_START_OPTI-
2779           MIZE option to pcre_exec() or  pcre_dfa_exec().  This  slows  down  the
2780           matching  process,  but  does  ensure that callouts such as the example
2781           above are obeyed.
2782    
2783    
2784    THE CALLOUT INTERFACE
2785    
2786           During matching, when PCRE reaches a callout point, the external  func-
2787           tion  defined by pcre_callout is called (if it is set). This applies to
2788           both the pcre_exec() and the pcre_dfa_exec()  matching  functions.  The
2789           only  argument  to  the callout function is a pointer to a pcre_callout
2790           block. This structure contains the following fields:
2791    
2792             int          version;
2793             int          callout_number;
2794             int         *offset_vector;
2795             const char  *subject;
2796             int          subject_length;
2797             int          start_match;
2798             int          current_position;
2799             int          capture_top;
2800             int          capture_last;
2801             void        *callout_data;
2802