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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    
 NAME  
      PCRE - Perl-compatible regular expressions  
10    
11    PCRE(3)                                                                PCRE(3)
12    
 DESCRIPTION  
13    
14       The PCRE library is a set of functions that implement  regu-  NAME
15       lar  expression  pattern  matching using the same syntax and         PCRE - Perl-compatible regular expressions
      semantics as Perl, with just a few differences. The  current  
      implementation  of  PCRE  (release 4.x) corresponds approxi-  
      mately with Perl 5.8, including support  for  UTF-8  encoded  
      strings.    However,  this  support  has  to  be  explicitly  
      enabled; it is not the default.  
   
      PCRE is written in C and released as a C library. However, a  
      number  of  people  have  written wrappers and interfaces of  
      various kinds. A C++ class is included  in  these  contribu-  
      tions,  which  can  be found in the Contrib directory at the  
      primary FTP site, which is:  
   
      ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre  
   
      Details of exactly which Perl  regular  expression  features  
      are  and  are  not  supported  by PCRE are given in separate  
      documents. See the pcrepattern and pcrecompat pages.  
   
      Some features of PCRE can be included, excluded, or  changed  
      when  the library is built. The pcre_config() function makes  
      it possible for a client  to  discover  which  features  are  
      available.  Documentation  about  building  PCRE for various  
      operating systems can be found in the  README  file  in  the  
      source distribution.  
16    
17    
18  USER DOCUMENTATION  INTRODUCTION
19    
20       The user documentation for PCRE has been  split  up  into  a         The  PCRE  library is a set of functions that implement regular expres-
21       number  of  different sections. In the "man" format, each of         sion pattern matching using the same syntax and semantics as Perl, with
22       these is a separate "man page". In the HTML format, each  is         just  a  few  differences. Certain features that appeared in Python and
23       a  separate  page,  linked from the index page. In the plain         PCRE before they appeared in Perl are also available using  the  Python
24       text format, all the sections are concatenated, for ease  of         syntax.  There is also some support for certain .NET and Oniguruma syn-
25       searching. The sections are as follows:         tax items, and there is an option for  requesting  some  minor  changes
26           that give better JavaScript compatibility.
27         pcre              this document  
28         pcreapi           details of PCRE's native API         The  current implementation of PCRE (release 8.xx) corresponds approxi-
29         pcrebuild         options for building PCRE         mately with Perl 5.10, including support for UTF-8 encoded strings  and
30         pcrecallout       details of the callout feature         Unicode general category properties. However, UTF-8 and Unicode support
31         pcrecompat        discussion of Perl compatibility         has to be explicitly enabled; it is not the default. The Unicode tables
32         pcregrep          description of the pcregrep command         correspond to Unicode release 5.1.
33         pcrepattern       syntax and semantics of supported  
34                             regular expressions         In  addition to the Perl-compatible matching function, PCRE contains an
35         pcreperform       discussion of performance issues         alternative matching function that matches the same  compiled  patterns
36         pcreposix         the POSIX-compatible API         in  a different way. In certain circumstances, the alternative function
37         pcresample        discussion of the sample program         has some advantages. For a discussion of the two  matching  algorithms,
38         pcretest          the pcretest testing command         see the pcrematching page.
39    
40       In addition, in the "man" and HTML formats, there is a short         PCRE  is  written  in C and released as a C library. A number of people
41       page  for  each  library function, listing its arguments and         have written wrappers and interfaces of various kinds.  In  particular,
42       results.         Google  Inc.   have  provided  a comprehensive C++ wrapper. This is now
43           included as part of the PCRE distribution. The pcrecpp page has details
44           of  this  interface.  Other  people's contributions can be found in the
45           Contrib directory at the primary FTP site, which is:
46    
47           ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
48    
49           Details of exactly which Perl regular expression features are  and  are
50           not supported by PCRE are given in separate documents. See the pcrepat-
51           tern and pcrecompat pages. There is a syntax summary in the  pcresyntax
52           page.
53    
54           Some  features  of  PCRE can be included, excluded, or changed when the
55           library is built. The pcre_config() function makes it  possible  for  a
56           client  to  discover  which  features are available. The features them-
57           selves are described in the pcrebuild page. Documentation about  build-
58           ing  PCRE for various operating systems can be found in the README file
59           in the source distribution.
60    
61           The library contains a number of undocumented  internal  functions  and
62           data  tables  that  are  used by more than one of the exported external
63           functions, but which are not intended  for  use  by  external  callers.
64           Their  names  all begin with "_pcre_", which hopefully will not provoke
65           any name clashes. In some environments, it is possible to control which
66           external  symbols  are  exported when a shared library is built, and in
67           these cases the undocumented symbols are not exported.
68    
69    
70  LIMITATIONS  USER DOCUMENTATION
71    
72       There are some size limitations in PCRE but it is hoped that         The user documentation for PCRE comprises a number  of  different  sec-
73       they will never in practice be relevant.         tions.  In the "man" format, each of these is a separate "man page". In
74           the HTML format, each is a separate page, linked from the  index  page.
75           In  the  plain  text format, all the sections, except the pcredemo sec-
76           tion, are concatenated, for ease of searching. The sections are as fol-
77           lows:
78    
79             pcre              this document
80             pcre-config       show PCRE installation configuration information
81             pcreapi           details of PCRE's native C API
82             pcrebuild         options for building PCRE
83             pcrecallout       details of the callout feature
84             pcrecompat        discussion of Perl compatibility
85             pcrecpp           details of the C++ wrapper
86             pcredemo          a demonstration C program that uses PCRE
87             pcregrep          description of the pcregrep command
88             pcrematching      discussion of the two matching algorithms
89             pcrepartial       details of the partial matching facility
90             pcrepattern       syntax and semantics of supported
91                                 regular expressions
92             pcresyntax        quick syntax reference
93             pcreperform       discussion of performance issues
94             pcreposix         the POSIX-compatible C API
95             pcreprecompile    details of saving and re-using precompiled patterns
96             pcresample        discussion of the pcredemo program
97             pcrestack         discussion of stack usage
98             pcretest          description of the pcretest testing command
99    
100       The maximum length of a  compiled  pattern  is  65539  (sic)         In  addition,  in the "man" and HTML formats, there is a short page for
101       bytes  if PCRE is compiled with the default internal linkage         each C library function, listing its arguments and results.
      size of 2. If you want to process regular  expressions  that  
      are  truly  enormous,  you can compile PCRE with an internal  
      linkage size of 3 or 4 (see the README file  in  the  source  
      distribution  and  the pcrebuild documentation for details).  
      If these cases the limit is substantially larger.   However,  
      the speed of execution will be slower.  
   
      All values in repeating quantifiers must be less than 65536.  
      The maximum number of capturing subpatterns is 65535.  
   
      There is no limit to the  number  of  non-capturing  subpat-  
      terns,  but  the  maximum  depth  of nesting of all kinds of  
      parenthesized subpattern, including  capturing  subpatterns,  
      assertions, and other types of subpattern, is 200.  
   
      The maximum length of a subject string is the largest  posi-  
      tive number that an integer variable can hold. However, PCRE  
      uses recursion to handle subpatterns and indefinite  repeti-  
      tion.  This  means  that the available stack space may limit  
      the size of a subject string that can be processed  by  cer-  
      tain patterns.  
102    
103    
104  UTF-8 SUPPORT  LIMITATIONS
105    
106       Starting at release 3.3, PCRE has had some support for char-         There are some size limitations in PCRE but it is hoped that they  will
107       acter  strings  encoded in the UTF-8 format. For release 4.0         never in practice be relevant.
      this has been greatly extended to cover most common require-  
      ments.  
   
      In order process UTF-8  strings,  you  must  build  PCRE  to  
      include  UTF-8  support  in  the code, and, in addition, you  
      must call pcre_compile() with  the  PCRE_UTF8  option  flag.  
      When  you  do this, both the pattern and any subject strings  
      that are matched against it are  treated  as  UTF-8  strings  
      instead of just strings of bytes.  
   
      If you compile PCRE with UTF-8 support, but do not use it at  
      run  time,  the  library will be a bit bigger, but the addi-  
      tional run time overhead is limited to testing the PCRE_UTF8  
      flag in several places, so should not be very large.  
   
      The following comments apply when PCRE is running  in  UTF-8  
      mode:  
   
      1. PCRE assumes that the strings it is given  contain  valid  
      UTF-8  codes. It does not diagnose invalid UTF-8 strings. If  
      you pass invalid UTF-8 strings  to  PCRE,  the  results  are  
      undefined.  
   
      2. In a pattern, the escape sequence \x{...}, where the con-  
      tents  of  the  braces is a string of hexadecimal digits, is  
      interpreted as a UTF-8 character whose code  number  is  the  
      given  hexadecimal  number, for example: \x{1234}. If a non-  
      hexadecimal digit appears between the braces,  the  item  is  
      not  recognized.  This escape sequence can be used either as  
      a literal, or within a character class.  
   
      3. The original hexadecimal escape sequence, \xhh, matches a  
      two-byte UTF-8 character if the value is greater than 127.  
   
      4. Repeat quantifiers apply to  complete  UTF-8  characters,  
      not to individual bytes, for example: \x{100}{3}.  
   
      5. The dot metacharacter matches one UTF-8 character instead  
      of a single byte.  
   
      6. The escape sequence \C can be used to match a single byte  
      in UTF-8 mode, but its use can lead to some strange effects.  
   
      7. The character escapes \b, \B, \d, \D, \s, \S, \w, and  \W  
      correctly test characters of any code value, but the charac-  
      ters that PCRE recognizes as digits, spaces, or word charac-  
      ters  remain  the  same  set as before, all with values less  
      than 256.  
   
      8. Case-insensitive  matching  applies  only  to  characters  
      whose  values  are  less than 256. PCRE does not support the  
      notion of "case" for higher-valued characters.  
108    
109       9. PCRE does not support the use of Unicode tables and  pro-         The  maximum  length of a compiled pattern is 65539 (sic) bytes if PCRE
110       perties or the Perl escapes \p, \P, and \X.         is compiled with the default internal linkage size of 2. If you want to
111           process  regular  expressions  that are truly enormous, you can compile
112           PCRE with an internal linkage size of 3 or 4 (see the  README  file  in
113           the  source  distribution and the pcrebuild documentation for details).
114           In these cases the limit is substantially larger.  However,  the  speed
115           of execution is slower.
116    
117           All values in repeating quantifiers must be less than 65536.
118    
119           There is no limit to the number of parenthesized subpatterns, but there
120           can be no more than 65535 capturing subpatterns.
121    
122           The maximum length of name for a named subpattern is 32 characters, and
123           the maximum number of named subpatterns is 10000.
124    
125           The  maximum  length of a subject string is the largest positive number
126           that an integer variable can hold. However, when using the  traditional
127           matching function, PCRE uses recursion to handle subpatterns and indef-
128           inite repetition.  This means that the available stack space may  limit
129           the size of a subject string that can be processed by certain patterns.
130           For a discussion of stack issues, see the pcrestack documentation.
131    
132    
133    UTF-8 AND UNICODE PROPERTY SUPPORT
134    
135           From release 3.3, PCRE has  had  some  support  for  character  strings
136           encoded  in the UTF-8 format. For release 4.0 this was greatly extended
137           to cover most common requirements, and in release 5.0  additional  sup-
138           port for Unicode general category properties was added.
139    
140           In  order  process  UTF-8 strings, you must build PCRE to include UTF-8
141           support in the code, and, in addition,  you  must  call  pcre_compile()
142           with  the  PCRE_UTF8  option  flag,  or the pattern must start with the
143           sequence (*UTF8). When either of these is the case,  both  the  pattern
144           and  any  subject  strings  that  are matched against it are treated as
145           UTF-8 strings instead of just strings of bytes.
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  AUTHOR  AUTHOR
254    
255       Philip Hazel <ph10@cam.ac.uk>         Philip Hazel
256       University Computing Service,         University Computing Service
257       Cambridge CB2 3QG, England.         Cambridge CB2 3QH, England.
258       Phone: +44 1223 334714  
259           Putting  an actual email address here seems to have been a spam magnet,
260           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    REVISION
265    
266           Last updated: 01 September 2009
267           Copyright (c) 1997-2009 University of Cambridge.
268    ------------------------------------------------------------------------------
269    
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           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           function.
328    
329           If you set --enable-utf8 when compiling in an EBCDIC environment,  PCRE
330           expects its input to be either ASCII or UTF-8 (depending on the runtime
331           option). It is not possible to support both EBCDIC and UTF-8  codes  in
332           the  same  version  of  the  library.  Consequently,  --enable-utf8 and
333           --enable-ebcdic are mutually exclusive.
334    
        --enable-utf8  
335    
336       to the configure command. Of itself, this does not make PCRE  UNICODE CHARACTER PROPERTY SUPPORT
337       treat  strings as UTF-8. As well as compiling PCRE with this  
338       option, you also have have to set the PCRE_UTF8 option  when         UTF-8 support allows PCRE to process character values greater than  255
339       you call the pcre_compile() function.         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.
426    
427    
428    HANDLING VERY LARGE PATTERNS
429    
430       to the configure command.         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 enormous patterns, so it
436           is possible to compile PCRE to use three-byte or four-byte  offsets  by
437           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.
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  the  the
473           pcre_dfa_exec() function.
474    
475    
476  LIMITING PCRE RESOURCE USAGE  LIMITING PCRE RESOURCE USAGE
477    
478       Internally, PCRE has a  function  called  match()  which  it         Internally, PCRE has a function called match(), which it calls  repeat-
479       calls  repeatedly  (possibly  recursively) when performing a         edly   (sometimes   recursively)  when  matching  a  pattern  with  the
480       matching operation. By limiting the  number  of  times  this         pcre_exec() function. By controlling the maximum number of  times  this
481       function  may  be  called,  a  limit  can  be  placed on the         function  may be called during a single matching operation, a limit can
482       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
483       can  be  changed  at  run  time, as described in the pcreapi         limit  can be changed at run time, as described in the pcreapi documen-
484       documentation. The default is 10 million, but  this  can  be         tation. The default is 10 million, but this can be changed by adding  a
485       changed by adding a setting such as         setting such as
486    
487         --with-match-limit=500000           --with-match-limit=500000
488    
489       to the configure command.         to   the   configure  command.  This  setting  has  no  effect  on  the
490           pcre_dfa_exec() matching function.
491    
492           In some environments it is desirable to limit the  depth  of  recursive
493           calls of match() more strictly than the total number of calls, in order
494           to restrict the maximum amount of stack (or heap,  if  --disable-stack-
495           for-recursion is specified) that is used. A second limit controls this;
496           it defaults to the value that  is  set  for  --with-match-limit,  which
497           imposes  no  additional constraints. However, you can set a lower limit
498           by adding, for example,
499    
500  HANDLING VERY LARGE PATTERNS           --with-match-limit-recursion=10000
501    
502       Within a compiled pattern, offset values are used  to  point         to the configure command. This value can  also  be  overridden  at  run
503       from  one  part  to  another  (for  example, from an opening         time.
504       parenthesis to an  alternation  metacharacter).  By  default  
505       two-byte  values  are  used  for these offsets, leading to a  
506       maximum size for a compiled pattern of around 64K.  This  is  CREATING CHARACTER TABLES AT BUILD TIME
507       sufficient  to  handle  all  but the most gigantic patterns.  
508       Nevertheless, some people do want to process  enormous  pat-         PCRE  uses fixed tables for processing characters whose code values are
509       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
510       or four-byte offsets by adding a setting such as         distributed  in  the  file pcre_chartables.c.dist. These tables are for
511           ASCII codes only. If you add
512         --with-link-size=3  
513             --enable-rebuild-chartables
514       to the configure command. The value given must be 2,  3,  or  
515       4.  Using  longer  offsets  slows down the operation of PCRE         to the configure command, the distributed tables are  no  longer  used.
516       because it has to load additional bytes when handling them.         Instead,  a  program  called dftables is compiled and run. This outputs
517           the source for new set of tables, created in the default locale of your
518       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
519       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
520       of these tests is a representation of the compiled  pattern,         you  need  to  create alternative tables when cross compiling, you will
521       and this changes with the link size.         have to do so "by hand".)
522    
523    
524    USING EBCDIC CODE
525    
526           PCRE assumes by default that it will run in an  environment  where  the
527           character  code  is  ASCII  (or Unicode, which is a superset of ASCII).
528           This is the case for most computer operating systems.  PCRE  can,  how-
529           ever, be compiled to run in an EBCDIC environment by adding
530    
531             --enable-ebcdic
532    
533           to the configure command. This setting implies --enable-rebuild-charta-
534           bles. You should only use it if you know that  you  are  in  an  EBCDIC
535           environment  (for  example,  an  IBM  mainframe  operating system). The
536           --enable-ebcdic option is incompatible with --enable-utf8.
537    
538    
539    PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
540    
541           By default, pcregrep reads all files as plain text. You can build it so
542           that it recognizes files whose names end in .gz or .bz2, and reads them
543           with libz or libbz2, respectively, by adding one or both of
544    
545             --enable-pcregrep-libz
546             --enable-pcregrep-libbz2
547    
548           to the configure command. These options naturally require that the rel-
549           evant  libraries  are installed on your system. Configuration will fail
550           if they are not.
551    
552    
553    PCRETEST OPTION FOR LIBREADLINE SUPPORT
554    
555           If you add
556    
557             --enable-pcretest-libreadline
558    
559           to the configure command,  pcretest  is  linked  with  the  libreadline
560           library,  and  when its input is from a terminal, it reads it using the
561           readline() function. This provides line-editing and history facilities.
562           Note that libreadline is GPL-licenced, so if you distribute a binary of
563           pcretest linked in this way, there may be licensing issues.
564    
565           Setting this option causes the -lreadline option to  be  added  to  the
566           pcretest  build.  In many operating environments with a sytem-installed
567           libreadline this is sufficient. However, in some environments (e.g.  if
568           an  unmodified  distribution version of readline is in use), some extra
569           configuration may be necessary. The INSTALL file for  libreadline  says
570           this:
571    
572             "Readline uses the termcap functions, but does not link with the
573             termcap or curses library itself, allowing applications which link
574             with readline the to choose an appropriate library."
575    
576           If  your environment has not been set up so that an appropriate library
577           is automatically included, you may need to add something like
578    
579             LIBS="-ncurses"
580    
581           immediately before the configure command.
582    
583    
584    SEE ALSO
585    
586           pcreapi(3), pcre_config(3).
587    
588    
589    AUTHOR
590    
591           Philip Hazel
592           University Computing Service
593           Cambridge CB2 3QH, England.
594    
595    
596    REVISION
597    
598           Last updated: 06 September 2009
599           Copyright (c) 1997-2009 University of Cambridge.
600    ------------------------------------------------------------------------------
601    
602    
603    PCREMATCHING(3)                                                PCREMATCHING(3)
604    
 Last updated: 21 January 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
605    
606  NAME  NAME
607       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
608    
609    
610    PCRE MATCHING ALGORITHMS
611    
612           This document describes the two different algorithms that are available
613           in PCRE for matching a compiled regular expression against a given sub-
614           ject  string.  The  "standard"  algorithm  is  the  one provided by the
615           pcre_exec() function.  This works in the same was  as  Perl's  matching
616           function, and provides a Perl-compatible matching operation.
617    
618           An  alternative  algorithm is provided by the pcre_dfa_exec() function;
619           this operates in a different way, and is not  Perl-compatible.  It  has
620           advantages  and disadvantages compared with the standard algorithm, and
621           these are described below.
622    
623           When there is only one possible way in which a given subject string can
624           match  a pattern, the two algorithms give the same answer. A difference
625           arises, however, when there are multiple possibilities. For example, if
626           the pattern
627    
628             ^<.*>
629    
630           is matched against the string
631    
632             <something> <something else> <something further>
633    
634           there are three possible answers. The standard algorithm finds only one
635           of them, whereas the alternative algorithm finds all three.
636    
637    
638    REGULAR EXPRESSIONS AS TREES
639    
640           The set of strings that are matched by a regular expression can be rep-
641           resented  as  a  tree structure. An unlimited repetition in the pattern
642           makes the tree of infinite size, but it is still a tree.  Matching  the
643           pattern  to a given subject string (from a given starting point) can be
644           thought of as a search of the tree.  There are two  ways  to  search  a
645           tree:  depth-first  and  breadth-first, and these correspond to the two
646           matching algorithms provided by PCRE.
647    
648    
649    THE STANDARD MATCHING ALGORITHM
650    
651           In the terminology of Jeffrey Friedl's book "Mastering Regular  Expres-
652           sions",  the  standard  algorithm  is an "NFA algorithm". It conducts a
653           depth-first search of the pattern tree. That is, it  proceeds  along  a
654           single path through the tree, checking that the subject matches what is
655           required. When there is a mismatch, the algorithm  tries  any  alterna-
656           tives  at  the  current point, and if they all fail, it backs up to the
657           previous branch point in the  tree,  and  tries  the  next  alternative
658           branch  at  that  level.  This often involves backing up (moving to the
659           left) in the subject string as well.  The  order  in  which  repetition
660           branches  are  tried  is controlled by the greedy or ungreedy nature of
661           the quantifier.
662    
663  SYNOPSIS OF PCRE API         If a leaf node is reached, a matching string has  been  found,  and  at
664           that  point the algorithm stops. Thus, if there is more than one possi-
665           ble match, this algorithm returns the first one that it finds.  Whether
666           this  is the shortest, the longest, or some intermediate length depends
667           on the way the greedy and ungreedy repetition quantifiers are specified
668           in the pattern.
669    
670       #include <pcre.h>         Because  it  ends  up  with a single path through the tree, it is rela-
671           tively straightforward for this algorithm to keep  track  of  the  sub-
672           strings  that  are  matched  by portions of the pattern in parentheses.
673           This provides support for capturing parentheses and back references.
674    
      pcre *pcre_compile(const char *pattern, int options,  
           const char **errptr, int *erroffset,  
           const unsigned char *tableptr);  
675    
676       pcre_extra *pcre_study(const pcre *code, int options,  THE ALTERNATIVE MATCHING ALGORITHM
           const char **errptr);  
677    
678       int pcre_exec(const pcre *code, const pcre_extra *extra,         This algorithm conducts a breadth-first search of  the  tree.  Starting
679            const char *subject, int length, int startoffset,         from  the  first  matching  point  in the subject, it scans the subject
680            int options, int *ovector, int ovecsize);         string from left to right, once, character by character, and as it does
681           this,  it remembers all the paths through the tree that represent valid
682           matches. In Friedl's terminology, this is a kind  of  "DFA  algorithm",
683           though  it is not implemented as a traditional finite state machine (it
684           keeps multiple states active simultaneously).
685    
686       int pcre_copy_named_substring(const pcre *code,         The scan continues until either the end of the subject is  reached,  or
687            const char *subject, int *ovector,         there  are  no more unterminated paths. At this point, terminated paths
688            int stringcount, const char *stringname,         represent the different matching possibilities (if there are none,  the
689            char *buffer, int buffersize);         match  has  failed).   Thus,  if there is more than one possible match,
690           this algorithm finds all of them, and in particular, it finds the long-
691           est.  In PCRE, there is an option to stop the algorithm after the first
692           match (which is necessarily the shortest) has been found.
693    
694       int pcre_copy_substring(const char *subject, int *ovector,         Note that all the matches that are found start at the same point in the
695            int stringcount, int stringnumber, char *buffer,         subject. If the pattern
           int buffersize);  
696    
697       int pcre_get_named_substring(const pcre *code,           cat(er(pillar)?)
           const char *subject, int *ovector,  
           int stringcount, const char *stringname,  
           const char **stringptr);  
698    
699       int pcre_get_stringnumber(const pcre *code,         is  matched  against the string "the caterpillar catchment", the result
700            const char *name);         will be the three strings "cat", "cater", and "caterpillar" that  start
701           at the fourth character of the subject. The algorithm does not automat-
702           ically move on to find matches that start at later positions.
703    
704       int pcre_get_substring(const char *subject, int *ovector,         Although the general principle of this matching algorithm  is  that  it
705            int stringcount, int stringnumber,         scans  the subject string only once, without backtracking, there is one
706            const char **stringptr);         exception: when a lookbehind assertion is  encountered,  the  preceding
707           characters have to be re-inspected.
708    
709       int pcre_get_substring_list(const char *subject,         There are a number of features of PCRE regular expressions that are not
710            int *ovector, int stringcount, const char ***listptr);         supported by the alternative matching algorithm. They are as follows:
711    
712       void pcre_free_substring(const char *stringptr);         1. Because the algorithm finds all  possible  matches,  the  greedy  or
713           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       void pcre_free_substring_list(const char **stringptr);           ^a++\w!
719    
720       const unsigned char *pcre_maketables(void);         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_fullinfo(const pcre *code, const pcre_extra *extra,         2. When dealing with multiple paths through the tree simultaneously, it
727            int what, void *where);         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           3. Because no substrings are captured, back references within the  pat-
733           tern are not supported, and cause errors if encountered.
734    
735       int pcre_info(const pcre *code, int *optptr, *firstcharptr);         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       int pcre_config(int what, void *where);         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       char *pcre_version(void);         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       void *(*pcre_malloc)(size_t);         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       void (*pcre_free)(void *);         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    
      int (*pcre_callout)(pcre_callout_block *);  
756    
757    ADVANTAGES OF THE ALTERNATIVE ALGORITHM
758    
759  PCRE API         Using the alternative matching algorithm provides the following  advan-
760           tages:
761    
762       PCRE has its own native API,  which  is  described  in  this         1. All possible matches (at a single point in the subject) are automat-
763       document.  There  is  also  a  set of wrapper functions that         ically found, and in particular, the longest match is  found.  To  find
764       correspond to the POSIX regular expression API.   These  are         more than one match using the standard algorithm, you have to do kludgy
765       described in the pcreposix documentation.         things with callouts.
766    
767       The native API function prototypes are defined in the header         2. Because the alternative algorithm  scans  the  subject  string  just
768       file  pcre.h,  and  on  Unix  systems  the library itself is         once,  and  never  needs to backtrack, it is possible to pass very long
769       called libpcre.a, so can be accessed by adding -lpcre to the         subject strings to the matching function in  several  pieces,  checking
770       command  for  linking  an  application  which  calls it. The         for partial matching each time.
      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.  
771    
      The functions pcre_compile(), pcre_study(), and  pcre_exec()  
      are  used  for compiling and matching regular expressions. A  
      sample program that demonstrates the simplest way  of  using  
      them  is  given in the file pcredemo.c. The pcresample docu-  
      mentation describes how to run it.  
772    
773       There are convenience functions for extracting captured sub-  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
      strings from a matched subject string. They are:  
774    
775         pcre_copy_substring()         The alternative algorithm suffers from a number of disadvantages:
        pcre_copy_named_substring()  
        pcre_get_substring()  
        pcre_get_named_substring()  
        pcre_get_substring_list()  
776    
777       pcre_free_substring()  and  pcre_free_substring_list()   are         1.  It  is  substantially  slower  than the standard algorithm. This is
778       also  provided,  to  free  the  memory  used  for  extracted         partly because it has to search for all possible matches, but  is  also
779       strings.         because it is less susceptible to optimization.
780    
781       The function pcre_maketables() is used (optionally) to build         2. Capturing parentheses and back references are not supported.
      a  set of character tables in the current locale for passing  
      to pcre_compile().  
782    
783       The function pcre_fullinfo() is used to find out information         3. Although atomic groups are supported, their use does not provide the
784       about a compiled pattern; pcre_info() is an obsolete version         performance advantage that it does for the standard algorithm.
      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.  
785    
      The global variables  pcre_malloc  and  pcre_free  initially  
      contain the entry points of the standard malloc() and free()  
      functions respectively. PCRE  calls  the  memory  management  
      functions  via  these  variables,  so  a calling program can  
      replace them if it  wishes  to  intercept  the  calls.  This  
      should be done before calling any PCRE functions.  
786    
787       The global variable pcre_callout initially contains NULL. It  AUTHOR
788       can be set by the caller to a "callout" function, which PCRE  
789       will then call at specified points during a matching  opera-         Philip Hazel
790       tion. Details are given in the pcrecallout documentation.         University Computing Service
791           Cambridge CB2 3QH, England.
792    
793    
794    REVISION
795    
796           Last updated: 05 September 2009
797           Copyright (c) 1997-2009 University of Cambridge.
798    ------------------------------------------------------------------------------
799    
800    
801    PCREAPI(3)                                                          PCREAPI(3)
802    
803    
804    NAME
805           PCRE - Perl-compatible regular expressions
806    
807    
808    PCRE NATIVE API
809    
810           #include <pcre.h>
811    
812           pcre *pcre_compile(const char *pattern, int options,
813                const char **errptr, int *erroffset,
814                const unsigned char *tableptr);
815    
816           pcre *pcre_compile2(const char *pattern, int options,
817                int *errorcodeptr,
818                const char **errptr, int *erroffset,
819                const unsigned char *tableptr);
820    
821           pcre_extra *pcre_study(const pcre *code, int options,
822                const char **errptr);
823    
824           int pcre_exec(const pcre *code, const pcre_extra *extra,
825                const char *subject, int length, int startoffset,
826                int options, int *ovector, int ovecsize);
827    
828           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
829                const char *subject, int length, int startoffset,
830                int options, int *ovector, int ovecsize,
831                int *workspace, int wscount);
832    
833           int pcre_copy_named_substring(const pcre *code,
834                const char *subject, int *ovector,
835                int stringcount, const char *stringname,
836                char *buffer, int buffersize);
837    
838           int pcre_copy_substring(const char *subject, int *ovector,
839                int stringcount, int stringnumber, char *buffer,
840                int buffersize);
841    
842           int pcre_get_named_substring(const pcre *code,
843                const char *subject, int *ovector,
844                int stringcount, const char *stringname,
845                const char **stringptr);
846    
847           int pcre_get_stringnumber(const pcre *code,
848                const char *name);
849    
850           int pcre_get_stringtable_entries(const pcre *code,
851                const char *name, char **first, char **last);
852    
853           int pcre_get_substring(const char *subject, int *ovector,
854                int stringcount, int stringnumber,
855                const char **stringptr);
856    
857           int pcre_get_substring_list(const char *subject,
858                int *ovector, int stringcount, const char ***listptr);
859    
860           void pcre_free_substring(const char *stringptr);
861    
862           void pcre_free_substring_list(const char **stringptr);
863    
864           const unsigned char *pcre_maketables(void);
865    
866           int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
867                int what, void *where);
868    
869           int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
870    
871           int pcre_refcount(pcre *code, int adjust);
872    
873           int pcre_config(int what, void *where);
874    
875           char *pcre_version(void);
876    
877           void *(*pcre_malloc)(size_t);
878    
879           void (*pcre_free)(void *);
880    
881           void *(*pcre_stack_malloc)(size_t);
882    
883           void (*pcre_stack_free)(void *);
884    
885           int (*pcre_callout)(pcre_callout_block *);
886    
887    
888    PCRE API OVERVIEW
889    
890           PCRE has its own native API, which is described in this document. There
891           are also some wrapper functions that correspond to  the  POSIX  regular
892           expression  API.  These  are  described in the pcreposix documentation.
893           Both of these APIs define a set of C function calls. A C++  wrapper  is
894           distributed with PCRE. It is documented in the pcrecpp page.
895    
896           The  native  API  C  function prototypes are defined in the header file
897           pcre.h, and on Unix systems the library itself is called  libpcre.   It
898           can normally be accessed by adding -lpcre to the command for linking an
899           application  that  uses  PCRE.  The  header  file  defines  the  macros
900           PCRE_MAJOR  and  PCRE_MINOR to contain the major and minor release num-
901           bers for the library.  Applications can use these  to  include  support
902           for different releases of PCRE.
903    
904           The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and
905           pcre_exec() are used for compiling and matching regular expressions  in
906           a  Perl-compatible  manner. A sample program that demonstrates the sim-
907           plest way of using them is provided in the file  called  pcredemo.c  in
908           the PCRE source distribution. A listing of this program is given in the
909           pcredemo documentation, and the pcresample documentation describes  how
910           to compile and run it.
911    
912           A second matching function, pcre_dfa_exec(), which is not Perl-compati-
913           ble, is also provided. This uses a different algorithm for  the  match-
914           ing.  The  alternative algorithm finds all possible matches (at a given
915           point in the subject), and scans the subject just  once  (unless  there
916           are  lookbehind  assertions).  However,  this algorithm does not return
917           captured substrings. A description of the two matching  algorithms  and
918           their  advantages  and disadvantages is given in the pcrematching docu-
919           mentation.
920    
921           In addition to the main compiling and  matching  functions,  there  are
922           convenience functions for extracting captured substrings from a subject
923           string that is matched by pcre_exec(). They are:
924    
925             pcre_copy_substring()
926             pcre_copy_named_substring()
927             pcre_get_substring()
928             pcre_get_named_substring()
929             pcre_get_substring_list()
930             pcre_get_stringnumber()
931             pcre_get_stringtable_entries()
932    
933           pcre_free_substring() and pcre_free_substring_list() are also provided,
934           to free the memory used for extracted strings.
935    
936           The  function  pcre_maketables()  is  used  to build a set of character
937           tables  in  the  current  locale   for   passing   to   pcre_compile(),
938           pcre_exec(),  or  pcre_dfa_exec(). This is an optional facility that is
939           provided for specialist use.  Most  commonly,  no  special  tables  are
940           passed,  in  which case internal tables that are generated when PCRE is
941           built are used.
942    
943           The function pcre_fullinfo() is used to find out  information  about  a
944           compiled  pattern; pcre_info() is an obsolete version that returns only
945           some of the available information, but is retained for  backwards  com-
946           patibility.   The function pcre_version() returns a pointer to a string
947           containing the version of PCRE and its date of release.
948    
949           The function pcre_refcount() maintains a  reference  count  in  a  data
950           block  containing  a compiled pattern. This is provided for the benefit
951           of object-oriented applications.
952    
953           The global variables pcre_malloc and pcre_free  initially  contain  the
954           entry  points  of  the  standard malloc() and free() functions, respec-
955           tively. PCRE calls the memory management functions via these variables,
956           so  a  calling  program  can replace them if it wishes to intercept the
957           calls. This should be done before calling any PCRE functions.
958    
959           The global variables pcre_stack_malloc  and  pcre_stack_free  are  also
960           indirections  to  memory  management functions. These special functions
961           are used only when PCRE is compiled to use  the  heap  for  remembering
962           data, instead of recursive function calls, when running the pcre_exec()
963           function. See the pcrebuild documentation for  details  of  how  to  do
964           this.  It  is  a non-standard way of building PCRE, for use in environ-
965           ments that have limited stacks. Because of the greater  use  of  memory
966           management,  it  runs  more  slowly. Separate functions are provided so
967           that special-purpose external code can be  used  for  this  case.  When
968           used,  these  functions  are always called in a stack-like manner (last
969           obtained, first freed), and always for memory blocks of the same  size.
970           There  is  a discussion about PCRE's stack usage in the pcrestack docu-
971           mentation.
972    
973           The global variable pcre_callout initially contains NULL. It can be set
974           by  the  caller  to  a "callout" function, which PCRE will then call at
975           specified points during a matching operation. Details are given in  the
976           pcrecallout documentation.
977    
978    
979    NEWLINES
980    
981           PCRE  supports five different conventions for indicating line breaks in
982           strings: a single CR (carriage return) character, a  single  LF  (line-
983           feed) character, the two-character sequence CRLF, any of the three pre-
984           ceding, or any Unicode newline sequence. The Unicode newline  sequences
985           are  the  three just mentioned, plus the single characters VT (vertical
986           tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS  (line
987           separator, U+2028), and PS (paragraph separator, U+2029).
988    
989           Each  of  the first three conventions is used by at least one operating
990           system as its standard newline sequence. When PCRE is built, a  default
991           can  be  specified.  The default default is LF, which is the Unix stan-
992           dard. When PCRE is run, the default can be overridden,  either  when  a
993           pattern is compiled, or when it is matched.
994    
995           At compile time, the newline convention can be specified by the options
996           argument of pcre_compile(), or it can be specified by special  text  at
997           the start of the pattern itself; this overrides any other settings. See
998           the pcrepattern page for details of the special character sequences.
999    
1000           In the PCRE documentation the word "newline" is used to mean "the char-
1001           acter  or pair of characters that indicate a line break". The choice of
1002           newline convention affects the handling of  the  dot,  circumflex,  and
1003           dollar metacharacters, the handling of #-comments in /x mode, and, when
1004           CRLF is a recognized line ending sequence, the match position  advance-
1005           ment for a non-anchored pattern. There is more detail about this in the
1006           section on pcre_exec() options below.
1007    
1008           The choice of newline convention does not affect the interpretation  of
1009           the  \n  or  \r  escape  sequences, nor does it affect what \R matches,
1010           which is controlled in a similar way, but by separate options.
1011    
1012    
1013  MULTITHREADING  MULTITHREADING
1014    
1015       The PCRE functions can be used in  multi-threading  applica-         The PCRE functions can be used in  multi-threading  applications,  with
1016       tions, with the proviso that the memory management functions         the  proviso  that  the  memory  management  functions  pointed  to  by
1017       pointed to by pcre_malloc and  pcre_free,  and  the  callout         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
1018       function  pointed  to  by  pcre_callout,  are  shared by all         callout function pointed to by pcre_callout, are shared by all threads.
1019       threads.  
1020           The  compiled form of a regular expression is not altered during match-
1021       The compiled form of a regular  expression  is  not  altered         ing, so the same compiled pattern can safely be used by several threads
1022       during  matching, so the same compiled pattern can safely be         at once.
1023       used by several threads at once.  
1024    
1025    SAVING PRECOMPILED PATTERNS FOR LATER USE
1026    
1027           The compiled form of a regular expression can be saved and re-used at a
1028           later time, possibly by a different program, and even on a  host  other
1029           than  the  one  on  which  it  was  compiled.  Details are given in the
1030           pcreprecompile documentation. However, compiling a  regular  expression
1031           with  one version of PCRE for use with a different version is not guar-
1032           anteed to work and may cause crashes.
1033    
1034    
1035  CHECKING BUILD-TIME OPTIONS  CHECKING BUILD-TIME OPTIONS
1036    
1037       int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
1038    
1039           The function pcre_config() makes it possible for a PCRE client to  dis-
1040           cover which optional features have been compiled into the PCRE library.
1041           The pcrebuild documentation has more details about these optional  fea-
1042           tures.
1043    
1044           The  first  argument  for pcre_config() is an integer, specifying which
1045           information is required; the second argument is a pointer to a variable
1046           into  which  the  information  is  placed. The following information is
1047           available:
1048    
1049             PCRE_CONFIG_UTF8
1050    
1051           The output is an integer that is set to one if UTF-8 support is  avail-
1052           able; otherwise it is set to zero.
1053    
1054       The function pcre_config() makes  it  possible  for  a  PCRE           PCRE_CONFIG_UNICODE_PROPERTIES
      client  to  discover  which optional features have been com-  
      piled into the PCRE library. The pcrebuild documentation has  
      more details about these optional features.  
1055    
1056       The first argument for pcre_config() is an integer, specify-         The  output  is  an  integer  that is set to one if support for Unicode
1057       ing  which information is required; the second argument is a         character properties is available; otherwise it is set to zero.
      pointer to a variable into which the information is  placed.  
      The following information is available:  
1058    
1059         PCRE_CONFIG_UTF8           PCRE_CONFIG_NEWLINE
1060    
1061       The output is an integer that is set to one if UTF-8 support         The output is an integer whose value specifies  the  default  character
1062       is available; otherwise it is set to zero.         sequence  that is recognized as meaning "newline". The four values that
1063           are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
1064           and  -1  for  ANY.  Though they are derived from ASCII, the same values
1065           are returned in EBCDIC environments. The default should normally corre-
1066           spond to the standard sequence for your operating system.
1067    
1068         PCRE_CONFIG_NEWLINE           PCRE_CONFIG_BSR
1069    
1070       The output is an integer that is set to  the  value  of  the         The output is an integer whose value indicates what character sequences
1071       code  that  is  used for the newline character. It is either         the \R escape sequence matches by default. A value of 0 means  that  \R
1072       linefeed (10) or carriage return (13), and  should  normally         matches  any  Unicode  line ending sequence; a value of 1 means that \R
1073       be the standard character for your operating system.         matches only CR, LF, or CRLF. The default can be overridden when a pat-
1074           tern is compiled or matched.
1075    
1076         PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
1077    
1078       The output is an integer that contains the number  of  bytes         The  output  is  an  integer that contains the number of bytes used for
1079       used  for  internal linkage in compiled regular expressions.         internal linkage in compiled regular expressions. The value is 2, 3, or
1080       The value is 2, 3, or 4. Larger values allow larger  regular         4.  Larger  values  allow larger regular expressions to be compiled, at
1081       expressions  to be compiled, at the expense of slower match-         the expense of slower matching. The default value of  2  is  sufficient
1082       ing. The default value of 2 is sufficient for  all  but  the         for  all  but  the  most massive patterns, since it allows the compiled
1083       most  massive patterns, since it allows the compiled pattern         pattern to be up to 64K in size.
      to be up to 64K in size.  
1084    
1085         PCRE_CONFIG_POSIX_MALLOC_THRESHOLD           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
1086    
1087       The output is an integer that contains the  threshold  above         The output is an integer that contains the threshold  above  which  the
1088       which  the POSIX interface uses malloc() for output vectors.         POSIX  interface  uses malloc() for output vectors. Further details are
1089       Further details are given in the pcreposix documentation.         given in the pcreposix documentation.
1090    
1091         PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_MATCH_LIMIT
1092    
1093       The output is an integer that gives the  default  limit  for         The output is a long integer that gives the default limit for the  num-
1094       the   number  of  internal  matching  function  calls  in  a         ber  of  internal  matching  function calls in a pcre_exec() execution.
1095       pcre_exec()  execution.  Further  details  are  given   with         Further details are given with pcre_exec() below.
1096       pcre_exec() below.  
1097             PCRE_CONFIG_MATCH_LIMIT_RECURSION
1098    
1099           The output is a long integer that gives the default limit for the depth
1100           of   recursion  when  calling  the  internal  matching  function  in  a
1101           pcre_exec() execution.  Further  details  are  given  with  pcre_exec()
1102           below.
1103    
1104             PCRE_CONFIG_STACKRECURSE
1105    
1106           The  output is an integer that is set to one if internal recursion when
1107           running pcre_exec() is implemented by recursive function calls that use
1108           the  stack  to remember their state. This is the usual way that PCRE is
1109           compiled. The output is zero if PCRE was compiled to use blocks of data
1110           on  the  heap  instead  of  recursive  function  calls.  In  this case,
1111           pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory
1112           blocks on the heap, thus avoiding the use of the stack.
1113    
1114    
1115  COMPILING A PATTERN  COMPILING A PATTERN
1116    
1117       pcre *pcre_compile(const char *pattern, int options,         pcre *pcre_compile(const char *pattern, int options,
1118            const char **errptr, int *erroffset,              const char **errptr, int *erroffset,
1119            const unsigned char *tableptr);              const unsigned char *tableptr);
1120    
1121       The function pcre_compile() is called to compile  a  pattern         pcre *pcre_compile2(const char *pattern, int options,
1122       into  an internal form. The pattern is a C string terminated              int *errorcodeptr,
1123       by a binary zero, and is passed in the argument  pattern.  A              const char **errptr, int *erroffset,
1124       pointer  to  a  single  block of memory that is obtained via              const unsigned char *tableptr);
1125       pcre_malloc is returned. This contains the compiled code and  
1126       related  data.  The  pcre  type  is defined for the returned         Either of the functions pcre_compile() or pcre_compile2() can be called
1127       block; this is a typedef for a structure whose contents  are         to compile a pattern into an internal form. The only difference between
1128       not  externally  defined. It is up to the caller to free the         the  two interfaces is that pcre_compile2() has an additional argument,
1129       memory when it is no longer required.         errorcodeptr, via which a numerical error code can be returned.
1130    
1131       Although the compiled code of a PCRE regex  is  relocatable,         The pattern is a C string terminated by a binary zero, and is passed in
1132       that is, it does not depend on memory location, the complete         the  pattern  argument.  A  pointer to a single block of memory that is
1133       pcre data block is not fully relocatable,  because  it  con-         obtained via pcre_malloc is returned. This contains the  compiled  code
1134       tains  a  copy of the tableptr argument, which is an address         and related data. The pcre type is defined for the returned block; this
1135       (see below).         is a typedef for a structure whose contents are not externally defined.
1136       The options argument contains independent bits  that  affect         It is up to the caller to free the memory (via pcre_free) when it is no
1137       the  compilation.  It  should  be  zero  if  no  options are         longer required.
1138       required. Some of the options, in particular, those that are  
1139       compatible  with Perl, can also be set and unset from within         Although the compiled code of a PCRE regex is relocatable, that is,  it
1140       the pattern (see the detailed description of regular expres-         does not depend on memory location, the complete pcre data block is not
1141       sions  in the pcrepattern documentation). For these options,         fully relocatable, because it may contain a copy of the tableptr  argu-
1142       the contents of the options argument specifies their initial         ment, which is an address (see below).
1143       settings  at  the  start  of  compilation and execution. The  
1144       PCRE_ANCHORED option can be set at the time of  matching  as         The options argument contains various bit settings that affect the com-
1145       well as at compile time.         pilation. It should be zero if no options are required.  The  available
1146           options  are  described  below. Some of them (in particular, those that
1147       If errptr is NULL, pcre_compile() returns NULL  immediately.         are compatible with Perl, but also some others) can  also  be  set  and
1148       Otherwise, if compilation of a pattern fails, pcre_compile()         unset  from  within  the  pattern  (see the detailed description in the
1149       returns NULL, and sets the variable pointed to by errptr  to         pcrepattern documentation). For those options that can be different  in
1150       point  to a textual error message. The offset from the start         different  parts  of  the pattern, the contents of the options argument
1151       of  the  pattern  to  the  character  where  the  error  was         specifies their initial settings at the start of compilation and execu-
1152       discovered   is   placed  in  the  variable  pointed  to  by         tion.  The PCRE_ANCHORED and PCRE_NEWLINE_xxx options can be set at the
1153       erroffset, which must not be NULL. If it  is,  an  immediate         time of matching as well as at compile time.
1154       error is given.  
1155           If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1156       If the final  argument,  tableptr,  is  NULL,  PCRE  uses  a         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and
1157       default  set  of character tables which are built when it is         sets the variable pointed to by errptr to point to a textual error mes-
1158       compiled, using the default C  locale.  Otherwise,  tableptr         sage. This is a static string that is part of the library. You must not
1159       must  be  the result of a call to pcre_maketables(). See the         try to free it. The byte offset from the start of the  pattern  to  the
1160       section on locale support below.         character  that  was  being  processes when the error was discovered is
1161           placed in the variable pointed to by erroffset, which must not be NULL.
1162       This code fragment shows a typical straightforward  call  to         If  it  is,  an  immediate error is given. Some errors are not detected
1163       pcre_compile():         until checks are carried out when the whole pattern has  been  scanned;
1164           in this case the offset is set to the end of the pattern.
1165         pcre *re;  
1166         const char *error;         If  pcre_compile2()  is  used instead of pcre_compile(), and the error-
1167         int erroffset;         codeptr argument is not NULL, a non-zero error code number is  returned
1168         re = pcre_compile(         via  this argument in the event of an error. This is in addition to the
1169           "^A.*Z",          /* the pattern */         textual error message. Error codes and messages are listed below.
1170           0,                /* default options */  
1171           &error,           /* for error message */         If the final argument, tableptr, is NULL, PCRE uses a  default  set  of
1172           &erroffset,       /* for error offset */         character  tables  that  are  built  when  PCRE  is compiled, using the
1173           NULL);            /* use default character tables */         default C locale. Otherwise, tableptr must be an address  that  is  the
1174           result  of  a  call to pcre_maketables(). This value is stored with the
1175       The following option bits are defined:         compiled pattern, and used again by pcre_exec(), unless  another  table
1176           pointer is passed to it. For more discussion, see the section on locale
1177         PCRE_ANCHORED         support below.
1178    
1179       If this bit is set, the pattern is forced to be  "anchored",         This code fragment shows a typical straightforward  call  to  pcre_com-
1180       that is, it is constrained to match only at the first match-         pile():
1181       ing point in the string which is being searched  (the  "sub-  
1182       ject string"). This effect can also be achieved by appropri-           pcre *re;
1183       ate constructs in the pattern itself, which is the only  way           const char *error;
1184       to do it in Perl.           int erroffset;
1185             re = pcre_compile(
1186         PCRE_CASELESS             "^A.*Z",          /* the pattern */
1187               0,                /* default options */
1188       If this bit is set, letters in the pattern match both  upper             &error,           /* for error message */
1189       and  lower  case  letters.  It  is  equivalent  to Perl's /i             &erroffset,       /* for error offset */
1190       option, and it can be changed within a  pattern  by  a  (?i)             NULL);            /* use default character tables */
1191       option setting.  
1192           The  following  names  for option bits are defined in the pcre.h header
1193         PCRE_DOLLAR_ENDONLY         file:
1194    
1195       If this bit is set, a dollar metacharacter  in  the  pattern           PCRE_ANCHORED
1196       matches  only at the end of the subject string. Without this  
1197       option, a dollar also matches immediately before  the  final         If this bit is set, the pattern is forced to be "anchored", that is, it
1198       character  if it is a newline (but not before any other new-         is  constrained to match only at the first matching point in the string
1199       lines).  The  PCRE_DOLLAR_ENDONLY  option  is   ignored   if         that is being searched (the "subject string"). This effect can also  be
1200       PCRE_MULTILINE is set. There is no equivalent to this option         achieved  by appropriate constructs in the pattern itself, which is the
1201       in Perl, and no way to set it within a pattern.         only way to do it in Perl.
1202    
1203         PCRE_DOTALL           PCRE_AUTO_CALLOUT
1204    
1205       If this bit is  set,  a  dot  metacharater  in  the  pattern         If this bit is set, pcre_compile() automatically inserts callout items,
1206       matches all characters, including newlines. Without it, new-         all  with  number  255, before each pattern item. For discussion of the
1207       lines are excluded. This option is equivalent to  Perl's  /s         callout facility, see the pcrecallout documentation.
1208       option,  and  it  can  be changed within a pattern by a (?s)  
1209       option setting. A negative class such as [^a] always matches           PCRE_BSR_ANYCRLF
1210       a  newline  character,  independent  of  the setting of this           PCRE_BSR_UNICODE
1211       option.  
1212           These options (which are mutually exclusive) control what the \R escape
1213         PCRE_EXTENDED         sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1214           or to match any Unicode newline sequence. The default is specified when
1215       If this bit is set, whitespace data characters in  the  pat-         PCRE is built. It can be overridden from within the pattern, or by set-
1216       tern  are  totally  ignored  except when escaped or inside a         ting an option when a compiled pattern is matched.
1217       character class. Whitespace does not include the VT  charac-  
1218       ter  (code 11). In addition, characters between an unescaped           PCRE_CASELESS
1219       # outside a character class and the next newline  character,  
1220       inclusive, are also ignored. This is equivalent to Perl's /x         If this bit is set, letters in the pattern match both upper  and  lower
1221       option, and it can be changed within a  pattern  by  a  (?x)         case  letters.  It  is  equivalent  to  Perl's /i option, and it can be
1222       option setting.         changed within a pattern by a (?i) option setting. In UTF-8 mode,  PCRE
1223           always  understands the concept of case for characters whose values are
1224       This option makes it possible  to  include  comments  inside         less than 128, so caseless matching is always possible. For  characters
1225       complicated patterns.  Note, however, that this applies only         with  higher  values,  the concept of case is supported if PCRE is com-
1226       to data characters. Whitespace characters may  never  appear         piled with Unicode property support, but not otherwise. If you want  to
1227       within special character sequences in a pattern, for example         use  caseless  matching  for  characters 128 and above, you must ensure
1228       within the sequence (?( which introduces a conditional  sub-         that PCRE is compiled with Unicode property support  as  well  as  with
1229       pattern.         UTF-8 support.
1230    
1231         PCRE_EXTRA           PCRE_DOLLAR_ENDONLY
1232    
1233       This option was invented in  order  to  turn  on  additional         If  this bit is set, a dollar metacharacter in the pattern matches only
1234       functionality of PCRE that is incompatible with Perl, but it         at the end of the subject string. Without this option,  a  dollar  also
1235       is currently of very little use. When set, any backslash  in         matches  immediately before a newline at the end of the string (but not
1236       a  pattern  that is followed by a letter that has no special         before any other newlines). The PCRE_DOLLAR_ENDONLY option  is  ignored
1237       meaning causes an error, thus reserving  these  combinations         if  PCRE_MULTILINE  is  set.   There is no equivalent to this option in
1238       for  future  expansion.  By default, as in Perl, a backslash         Perl, and no way to set it within a pattern.
1239       followed by a letter with no special meaning is treated as a  
1240       literal.  There  are at present no other features controlled           PCRE_DOTALL
1241       by this option. It can also be set by a (?X) option  setting  
1242       within a pattern.         If this bit is set, a dot metacharater in the pattern matches all char-
1243           acters,  including  those that indicate newline. Without it, a dot does
1244         PCRE_MULTILINE         not match when the current position is at a  newline.  This  option  is
1245           equivalent  to Perl's /s option, and it can be changed within a pattern
1246       By default, PCRE treats the subject string as consisting  of         by a (?s) option setting. A negative class such as [^a] always  matches
1247       a  single "line" of characters (even if it actually contains         newline characters, independent of the setting of this option.
1248       several newlines). The "start  of  line"  metacharacter  (^)  
1249       matches  only  at the start of the string, while the "end of           PCRE_DUPNAMES
1250       line" metacharacter ($) matches  only  at  the  end  of  the  
1251       string,    or   before   a   terminating   newline   (unless         If  this  bit is set, names used to identify capturing subpatterns need
1252       PCRE_DOLLAR_ENDONLY is set). This is the same as Perl.         not be unique. This can be helpful for certain types of pattern when it
1253           is  known  that  only  one instance of the named subpattern can ever be
1254       When PCRE_MULTILINE it is set, the "start of line" and  "end         matched. There are more details of named subpatterns  below;  see  also
1255       of  line"  constructs match immediately following or immedi-         the pcrepattern documentation.
1256       ately before any newline  in  the  subject  string,  respec-  
1257       tively,  as  well  as  at  the  very  start and end. This is           PCRE_EXTENDED
1258       equivalent to Perl's /m option, and it can be changed within  
1259       a  pattern  by  a  (?m) option setting. If there are no "\n"         If  this  bit  is  set,  whitespace  data characters in the pattern are
1260       characters in a subject string, or no occurrences of ^ or  $         totally ignored except when escaped or inside a character class. White-
1261       in a pattern, setting PCRE_MULTILINE has no effect.         space does not include the VT character (code 11). In addition, charac-
1262           ters between an unescaped # outside a character class and the next new-
1263         PCRE_NO_AUTO_CAPTURE         line,  inclusive,  are  also  ignored.  This is equivalent to Perl's /x
1264           option, and it can be changed within a pattern by a  (?x)  option  set-
1265       If this option is set, it disables the use of numbered  cap-         ting.
1266       turing  parentheses  in the pattern. Any opening parenthesis  
1267       that is not followed by ? behaves as if it were followed  by         This  option  makes  it possible to include comments inside complicated
1268       ?:  but  named  parentheses  can still be used for capturing         patterns.  Note, however, that this applies only  to  data  characters.
1269       (and they acquire numbers in the usual  way).  There  is  no         Whitespace   characters  may  never  appear  within  special  character
1270       equivalent of this option in Perl.         sequences in a pattern, for  example  within  the  sequence  (?(  which
1271           introduces a conditional subpattern.
1272         PCRE_UNGREEDY  
1273             PCRE_EXTRA
1274       This option inverts the "greediness" of the  quantifiers  so  
1275       that  they  are  not greedy by default, but become greedy if         This  option  was invented in order to turn on additional functionality
1276       followed by "?". It is not compatible with Perl. It can also         of PCRE that is incompatible with Perl, but it  is  currently  of  very
1277       be set by a (?U) option setting within the pattern.         little  use. When set, any backslash in a pattern that is followed by a
1278           letter that has no special meaning  causes  an  error,  thus  reserving
1279         PCRE_UTF8         these  combinations  for  future  expansion.  By default, as in Perl, a
1280           backslash followed by a letter with no special meaning is treated as  a
1281       This option causes PCRE to regard both the pattern  and  the         literal.  (Perl can, however, be persuaded to give a warning for this.)
1282       subject  as  strings  of UTF-8 characters instead of single-         There are at present no other features controlled by  this  option.  It
1283       byte character strings. However, it  is  available  only  if         can also be set by a (?X) option setting within a pattern.
1284       PCRE  has  been  built to include UTF-8 support. If not, the  
1285       use of this option provokes an error. Details  of  how  this           PCRE_FIRSTLINE
1286       option  changes  the behaviour of PCRE are given in the sec-  
1287       tion on UTF-8 support in the main pcre page.         If  this  option  is  set,  an  unanchored pattern is required to match
1288           before or at the first  newline  in  the  subject  string,  though  the
1289           matched text may continue over the newline.
1290    
1291             PCRE_JAVASCRIPT_COMPAT
1292    
1293           If this option is set, PCRE's behaviour is changed in some ways so that
1294           it is compatible with JavaScript rather than Perl. The changes  are  as
1295           follows:
1296    
1297           (1)  A  lone  closing square bracket in a pattern causes a compile-time
1298           error, because this is illegal in JavaScript (by default it is  treated
1299           as a data character). Thus, the pattern AB]CD becomes illegal when this
1300           option is set.
1301    
1302           (2) At run time, a back reference to an unset subpattern group  matches
1303           an  empty  string (by default this causes the current matching alterna-
1304           tive to fail). A pattern such as (\1)(a) succeeds when this  option  is
1305           set  (assuming  it can find an "a" in the subject), whereas it fails by
1306           default, for Perl compatibility.
1307    
1308             PCRE_MULTILINE
1309    
1310           By default, PCRE treats the subject string as consisting  of  a  single
1311           line  of characters (even if it actually contains newlines). The "start
1312           of line" metacharacter (^) matches only at the  start  of  the  string,
1313           while  the  "end  of line" metacharacter ($) matches only at the end of
1314           the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1315           is set). This is the same as Perl.
1316    
1317           When  PCRE_MULTILINE  it  is set, the "start of line" and "end of line"
1318           constructs match immediately following or immediately  before  internal
1319           newlines  in  the  subject string, respectively, as well as at the very
1320           start and end. This is equivalent to Perl's /m option, and  it  can  be
1321           changed within a pattern by a (?m) option setting. If there are no new-
1322           lines in a subject string, or no occurrences of ^ or $  in  a  pattern,
1323           setting PCRE_MULTILINE has no effect.
1324    
1325             PCRE_NEWLINE_CR
1326             PCRE_NEWLINE_LF
1327             PCRE_NEWLINE_CRLF
1328             PCRE_NEWLINE_ANYCRLF
1329             PCRE_NEWLINE_ANY
1330    
1331           These  options  override the default newline definition that was chosen
1332           when PCRE was built. Setting the first or the second specifies  that  a
1333           newline  is  indicated  by a single character (CR or LF, respectively).
1334           Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the
1335           two-character  CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF specifies
1336           that any of the three preceding sequences should be recognized. Setting
1337           PCRE_NEWLINE_ANY  specifies that any Unicode newline sequence should be
1338           recognized. The Unicode newline sequences are the three just mentioned,
1339           plus  the  single  characters  VT (vertical tab, U+000B), FF (formfeed,
1340           U+000C), NEL (next line, U+0085), LS (line separator, U+2028),  and  PS
1341           (paragraph  separator,  U+2029).  The  last  two are recognized only in
1342           UTF-8 mode.
1343    
1344           The newline setting in the  options  word  uses  three  bits  that  are
1345           treated as a number, giving eight possibilities. Currently only six are
1346           used (default plus the five values above). This means that if  you  set
1347           more  than one newline option, the combination may or may not be sensi-
1348           ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1349           PCRE_NEWLINE_CRLF,  but other combinations may yield unused numbers and
1350           cause an error.
1351    
1352           The only time that a line break is specially recognized when  compiling
1353           a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a
1354           character class is encountered. This indicates  a  comment  that  lasts
1355           until  after the next line break sequence. In other circumstances, line
1356           break  sequences  are  treated  as  literal  data,   except   that   in
1357           PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1358           and are therefore ignored.
1359    
1360           The newline option that is set at compile time becomes the default that
1361           is used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1362    
1363             PCRE_NO_AUTO_CAPTURE
1364    
1365           If this option is set, it disables the use of numbered capturing paren-
1366           theses in the pattern. Any opening parenthesis that is not followed  by
1367           ?  behaves as if it were followed by ?: but named parentheses can still
1368           be used for capturing (and they acquire  numbers  in  the  usual  way).
1369           There is no equivalent of this option in Perl.
1370    
1371             PCRE_UNGREEDY
1372    
1373           This  option  inverts  the "greediness" of the quantifiers so that they
1374           are not greedy by default, but become greedy if followed by "?". It  is
1375           not  compatible  with Perl. It can also be set by a (?U) option setting
1376           within the pattern.
1377    
1378             PCRE_UTF8
1379    
1380           This option causes PCRE to regard both the pattern and the  subject  as
1381           strings  of  UTF-8 characters instead of single-byte character strings.
1382           However, it is available only when PCRE is built to include UTF-8  sup-
1383           port.  If not, the use of this option provokes an error. Details of how
1384           this option changes the behaviour of PCRE are given in the  section  on
1385           UTF-8 support in the main pcre page.
1386    
1387             PCRE_NO_UTF8_CHECK
1388    
1389           When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
1390           automatically checked. There is a  discussion  about  the  validity  of
1391           UTF-8  strings  in  the main pcre page. If an invalid UTF-8 sequence of
1392           bytes is found, pcre_compile() returns an error. If  you  already  know
1393           that your pattern is valid, and you want to skip this check for perfor-
1394           mance reasons, you can set the PCRE_NO_UTF8_CHECK option.  When  it  is
1395           set,  the  effect  of  passing  an invalid UTF-8 string as a pattern is
1396           undefined. It may cause your program to crash. Note  that  this  option
1397           can  also be passed to pcre_exec() and pcre_dfa_exec(), to suppress the
1398           UTF-8 validity checking of subject strings.
1399    
1400    
1401    COMPILATION ERROR CODES
1402    
1403           The following table lists the error  codes  than  may  be  returned  by
1404           pcre_compile2(),  along with the error messages that may be returned by
1405           both compiling functions. As PCRE has developed, some error codes  have
1406           fallen out of use. To avoid confusion, they have not been re-used.
1407    
1408              0  no error
1409              1  \ at end of pattern
1410              2  \c at end of pattern
1411              3  unrecognized character follows \
1412              4  numbers out of order in {} quantifier
1413              5  number too big in {} quantifier
1414              6  missing terminating ] for character class
1415              7  invalid escape sequence in character class
1416              8  range out of order in character class
1417              9  nothing to repeat
1418             10  [this code is not in use]
1419             11  internal error: unexpected repeat
1420             12  unrecognized character after (? or (?-
1421             13  POSIX named classes are supported only within a class
1422             14  missing )
1423             15  reference to non-existent subpattern
1424             16  erroffset passed as NULL
1425             17  unknown option bit(s) set
1426             18  missing ) after comment
1427             19  [this code is not in use]
1428             20  regular expression is too large
1429             21  failed to get memory
1430             22  unmatched parentheses
1431             23  internal error: code overflow
1432             24  unrecognized character after (?<
1433             25  lookbehind assertion is not fixed length
1434             26  malformed number or name after (?(
1435             27  conditional group contains more than two branches
1436             28  assertion expected after (?(
1437             29  (?R or (?[+-]digits must be followed by )
1438             30  unknown POSIX class name
1439             31  POSIX collating elements are not supported
1440             32  this version of PCRE is not compiled with PCRE_UTF8 support
1441             33  [this code is not in use]
1442             34  character value in \x{...} sequence is too large
1443             35  invalid condition (?(0)
1444             36  \C not allowed in lookbehind assertion
1445             37  PCRE does not support \L, \l, \N, \U, or \u
1446             38  number after (?C is > 255
1447             39  closing ) for (?C expected
1448             40  recursive call could loop indefinitely
1449             41  unrecognized character after (?P
1450             42  syntax error in subpattern name (missing terminator)
1451             43  two named subpatterns have the same name
1452             44  invalid UTF-8 string
1453             45  support for \P, \p, and \X has not been compiled
1454             46  malformed \P or \p sequence
1455             47  unknown property name after \P or \p
1456             48  subpattern name is too long (maximum 32 characters)
1457             49  too many named subpatterns (maximum 10000)
1458             50  [this code is not in use]
1459             51  octal value is greater than \377 (not in UTF-8 mode)
1460             52  internal error: overran compiling workspace
1461             53   internal  error:  previously-checked  referenced  subpattern not
1462           found
1463             54  DEFINE group contains more than one branch
1464             55  repeating a DEFINE group is not allowed
1465             56  inconsistent NEWLINE options
1466             57  \g is not followed by a braced, angle-bracketed, or quoted
1467                   name/number or by a plain number
1468             58  a numbered reference must not be zero
1469             59  (*VERB) with an argument is not supported
1470             60  (*VERB) not recognized
1471             61  number is too big
1472             62  subpattern name expected
1473             63  digit expected after (?+
1474             64  ] is an invalid data character in JavaScript compatibility mode
1475    
1476           The numbers 32 and 10000 in errors 48 and 49  are  defaults;  different
1477           values may be used if the limits were changed when PCRE was built.
1478    
1479    
1480  STUDYING A PATTERN  STUDYING A PATTERN
1481    
1482       pcre_extra *pcre_study(const pcre *code, int options,         pcre_extra *pcre_study(const pcre *code, int options
1483            const char **errptr);              const char **errptr);
1484    
1485       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
1486       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
1487       the time taken for matching. The function pcre_study() takes         matching.  The function pcre_study() takes a pointer to a compiled pat-
1488       a  pointer  to  a compiled pattern as its first argument. If         tern as its first argument. If studying the pattern produces additional
1489       studing the pattern  produces  additional  information  that         information  that  will  help speed up matching, pcre_study() returns a
1490       will  help speed up matching, pcre_study() returns a pointer         pointer to a pcre_extra block, in which the study_data field points  to
1491       to a pcre_extra block, in which the study_data field  points         the results of the study.
1492       to the results of the study.  
1493           The  returned  value  from  pcre_study()  can  be  passed  directly  to
1494       The  returned  value  from  a  pcre_study()  can  be  passed         pcre_exec(). However, a pcre_extra block  also  contains  other  fields
1495       directly  to pcre_exec(). However, the pcre_extra block also         that  can  be  set  by the caller before the block is passed; these are
1496       contains other fields that can be set by the  caller  before         described below in the section on matching a pattern.
1497       the  block is passed; these are described below. If studying  
1498       the pattern does not  produce  any  additional  information,         If studying the pattern does not  produce  any  additional  information
1499       pcre_study() returns NULL. In that circumstance, if the cal-         pcre_study() returns NULL. In that circumstance, if the calling program
1500       ling program wants to pass  some  of  the  other  fields  to         wants to pass any of the other fields to pcre_exec(), it  must  set  up
1501       pcre_exec(), it must set up its own pcre_extra block.         its own pcre_extra block.
1502    
1503       The second argument contains option  bits.  At  present,  no         The  second  argument of pcre_study() contains option bits. At present,
1504       options  are  defined  for  pcre_study(),  and this argument         no options are defined, and this argument should always be zero.
1505       should always be zero.  
1506           The third argument for pcre_study() is a pointer for an error  message.
1507       The third argument for pcre_study()  is  a  pointer  for  an         If  studying  succeeds  (even  if no data is returned), the variable it
1508       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
1509       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
1510       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
1511       fore  test  the  error  pointer  for  NULL   after   calling         after calling pcre_study(), to be sure that it has run successfully.
1512       pcre_study(), to be sure that it has run successfully.  
1513           This is a typical call to pcre_study():
1514       This is a typical call to pcre_study():  
1515             pcre_extra *pe;
1516         pcre_extra *pe;           pe = pcre_study(
1517         pe = pcre_study(             re,             /* result of pcre_compile() */
1518           re,             /* result of pcre_compile() */             0,              /* no options exist */
1519           0,              /* no options exist */             &error);        /* set to NULL or points to a message */
1520           &error);        /* set to NULL or points to a message */  
1521           At present, studying a pattern is useful only for non-anchored patterns
1522       At present, studying a  pattern  is  useful  only  for  non-         that do not have a single fixed starting character. A bitmap of  possi-
1523       anchored  patterns  that do not have a single fixed starting         ble starting bytes is created.
      character. A  bitmap  of  possible  starting  characters  is  
      created.  
1524    
1525    
1526  LOCALE SUPPORT  LOCALE SUPPORT
1527    
1528       PCRE handles caseless matching, and determines whether char-         PCRE  handles  caseless matching, and determines whether characters are
1529       acters  are  letters, digits, or whatever, by reference to a         letters, digits, or whatever, by reference to a set of tables,  indexed
1530       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
1531       to characters with codes less than 256. The library contains         characters with codes less than 128. Higher-valued  codes  never  match
1532       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
1533       locale  when  PCRE  is compiled. This is used when the final         with Unicode character property support. The use of locales  with  Uni-
1534       argument of pcre_compile() is NULL, and  is  sufficient  for         code  is discouraged. If you are handling characters with codes greater
1535       many applications.         than 128, you should either use UTF-8 and Unicode, or use locales,  but
1536           not try to mix the two.
1537       An alternative set of tables can, however, be supplied. Such  
1538       tables  are built by calling the pcre_maketables() function,         PCRE  contains  an  internal set of tables that are used when the final
1539       which has no arguments, in the relevant locale.  The  result         argument of pcre_compile() is  NULL.  These  are  sufficient  for  many
1540       can  then be passed to pcre_compile() as often as necessary.         applications.  Normally, the internal tables recognize only ASCII char-
1541       For example, to build and use tables  that  are  appropriate         acters. However, when PCRE is built, it is possible to cause the inter-
1542       for  the French locale (where accented characters with codes         nal tables to be rebuilt in the default "C" locale of the local system,
1543       greater than 128 are treated as letters), the following code         which may cause them to be different.
1544       could be used:  
1545           The internal tables can always be overridden by tables supplied by  the
1546         setlocale(LC_CTYPE, "fr");         application that calls PCRE. These may be created in a different locale
1547         tables = pcre_maketables();         from the default. As more and more applications change  to  using  Uni-
1548         re = pcre_compile(..., tables);         code, the need for this locale support is expected to die away.
1549    
1550       The  tables  are  built  in  memory  that  is  obtained  via         External  tables  are  built by calling the pcre_maketables() function,
1551       pcre_malloc.  The  pointer that is passed to pcre_compile is         which has no arguments, in the relevant locale. The result can then  be
1552       saved with the compiled pattern, and  the  same  tables  are         passed  to  pcre_compile()  or  pcre_exec()  as often as necessary. For
1553       used via this pointer by pcre_study() and pcre_exec(). Thus,         example, to build and use tables that are appropriate  for  the  French
1554       for any single pattern, compilation, studying  and  matching         locale  (where  accented  characters  with  values greater than 128 are
1555       all happen in the same locale, but different patterns can be         treated as letters), the following code could be used:
1556       compiled in different locales. It is the caller's  responsi-  
1557       bility  to  ensure  that  the  memory  containing the tables           setlocale(LC_CTYPE, "fr_FR");
1558       remains available for as long as it is needed.           tables = pcre_maketables();
1559             re = pcre_compile(..., tables);
1560    
1561           The locale name "fr_FR" is used on Linux and other  Unix-like  systems;
1562           if you are using Windows, the name for the French locale is "french".
1563    
1564           When  pcre_maketables()  runs,  the  tables are built in memory that is
1565           obtained via pcre_malloc. It is the caller's responsibility  to  ensure
1566           that  the memory containing the tables remains available for as long as
1567           it is needed.
1568    
1569           The pointer that is passed to pcre_compile() is saved with the compiled
1570           pattern,  and the same tables are used via this pointer by pcre_study()
1571           and normally also by pcre_exec(). Thus, by default, for any single pat-
1572           tern, compilation, studying and matching all happen in the same locale,
1573           but different patterns can be compiled in different locales.
1574    
1575           It is possible to pass a table pointer or NULL (indicating the  use  of
1576           the  internal  tables)  to  pcre_exec(). Although not intended for this
1577           purpose, this facility could be used to match a pattern in a  different
1578           locale from the one in which it was compiled. Passing table pointers at
1579           run time is discussed below in the section on matching a pattern.
1580    
1581    
1582  INFORMATION ABOUT A PATTERN  INFORMATION ABOUT A PATTERN
1583    
1584       int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1585            int what, void *where);              int what, void *where);
1586    
1587       The pcre_fullinfo() function  returns  information  about  a         The pcre_fullinfo() function returns information about a compiled  pat-
1588       compiled pattern. It replaces the obsolete pcre_info() func-         tern. It replaces the obsolete pcre_info() function, which is neverthe-
1589       tion, which is nevertheless retained for backwards compabil-         less retained for backwards compability (and is documented below).
1590       ity (and is documented below).  
1591           The first argument for pcre_fullinfo() is a  pointer  to  the  compiled
1592       The first argument for pcre_fullinfo() is a pointer  to  the         pattern.  The second argument is the result of pcre_study(), or NULL if
1593       compiled  pattern.  The  second  argument  is  the result of         the pattern was not studied. The third argument specifies  which  piece
1594       pcre_study(), or NULL if the pattern was  not  studied.  The         of  information  is required, and the fourth argument is a pointer to a
1595       third  argument  specifies  which  piece  of  information is         variable to receive the data. The yield of the  function  is  zero  for
1596       required, and the fourth argument is a pointer to a variable         success, or one of the following negative numbers:
1597       to  receive  the data. The yield of the function is zero for  
1598       success, or one of the following negative numbers:           PCRE_ERROR_NULL       the argument code was NULL
1599                                   the argument where was NULL
1600         PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1601                               the argument where was NULL           PCRE_ERROR_BADOPTION  the value of what was invalid
1602         PCRE_ERROR_BADMAGIC   the "magic number" was not found  
1603         PCRE_ERROR_BADOPTION  the value of what was invalid         The  "magic  number" is placed at the start of each compiled pattern as
1604           an simple check against passing an arbitrary memory pointer. Here is  a
1605       Here is a typical call of  pcre_fullinfo(),  to  obtain  the         typical  call  of pcre_fullinfo(), to obtain the length of the compiled
1606       length of the compiled pattern:         pattern:
1607    
1608         int rc;           int rc;
1609         unsigned long int length;           size_t length;
1610         rc = pcre_fullinfo(           rc = pcre_fullinfo(
1611           re,               /* result of pcre_compile() */             re,               /* result of pcre_compile() */
1612           pe,               /* result of pcre_study(), or NULL */             pe,               /* result of pcre_study(), or NULL */
1613           PCRE_INFO_SIZE,   /* what is required */             PCRE_INFO_SIZE,   /* what is required */
1614           &length);         /* where to put the data */             &length);         /* where to put the data */
1615    
1616       The possible values for the third argument  are  defined  in         The possible values for the third argument are defined in  pcre.h,  and
1617       pcre.h, and are as follows:         are as follows:
1618    
1619         PCRE_INFO_BACKREFMAX           PCRE_INFO_BACKREFMAX
1620    
1621       Return the number of the highest back reference in the  pat-         Return  the  number  of  the highest back reference in the pattern. The
1622       tern.  The  fourth argument should point to an int variable.         fourth argument should point to an int variable. Zero  is  returned  if
1623       Zero is returned if there are no back references.         there are no back references.
1624    
1625         PCRE_INFO_CAPTURECOUNT           PCRE_INFO_CAPTURECOUNT
1626    
1627       Return the number of capturing subpatterns in  the  pattern.         Return  the  number of capturing subpatterns in the pattern. The fourth
1628       The fourth argument should point to an int variable.         argument should point to an int variable.
1629    
1630         PCRE_INFO_FIRSTBYTE           PCRE_INFO_DEFAULT_TABLES
1631    
1632       Return information about  the  first  byte  of  any  matched         Return a pointer to the internal default character tables within  PCRE.
1633       string,  for a non-anchored pattern. (This option used to be         The  fourth  argument should point to an unsigned char * variable. This
1634       called PCRE_INFO_FIRSTCHAR; the old name is still recognized         information call is provided for internal use by the pcre_study() func-
1635       for backwards compatibility.)         tion.  External  callers  can  cause PCRE to use its internal tables by
1636           passing a NULL table pointer.
1637       If there is a fixed first byte, e.g. from a pattern such  as  
1638       (cat|cow|coyote),  it  is returned in the integer pointed to           PCRE_INFO_FIRSTBYTE
1639       by where. Otherwise, if either  
1640           Return information about the first byte of any matched  string,  for  a
1641       (a) the pattern was compiled with the PCRE_MULTILINE option,         non-anchored  pattern. The fourth argument should point to an int vari-
1642       and every branch starts with "^", or         able. (This option used to be called PCRE_INFO_FIRSTCHAR; the old  name
1643           is still recognized for backwards compatibility.)
1644       (b) every  branch  of  the  pattern  starts  with  ".*"  and  
1645       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
1646       anchored),         (cat|cow|coyote), its value is returned. Otherwise, if either
1647    
1648       -1 is returned, indicating that the pattern matches only  at         (a) the pattern was compiled with the PCRE_MULTILINE option, and  every
1649       the  start  of  a subject string or after any newline within         branch starts with "^", or
1650       the string. Otherwise -2 is returned. For anchored patterns,  
1651       -2 is returned.         (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
1652           set (if it were set, the pattern would be anchored),
1653         PCRE_INFO_FIRSTTABLE  
1654           -1 is returned, indicating that the pattern matches only at  the  start
1655       If the pattern was studied, and this resulted  in  the  con-         of  a  subject string or after any newline within the string. Otherwise
1656       struction of a 256-bit table indicating a fixed set of bytes         -2 is returned. For anchored patterns, -2 is returned.
1657       for the first byte in any matching string, a pointer to  the  
1658       table  is  returned.  Otherwise NULL is returned. The fourth           PCRE_INFO_FIRSTTABLE
1659       argument should point to an unsigned char * variable.  
1660           If the pattern was studied, and this resulted in the construction of  a
1661         PCRE_INFO_LASTLITERAL         256-bit table indicating a fixed set of bytes for the first byte in any
1662           matching string, a pointer to the table is returned. Otherwise NULL  is
1663       Return the value of the rightmost  literal  byte  that  must         returned.  The fourth argument should point to an unsigned char * vari-
1664       exist  in  any  matched  string, other than at its start, if         able.
1665       such a byte has been recorded. The  fourth  argument  should  
1666       point  to  an  int variable. If there is no such byte, -1 is           PCRE_INFO_HASCRORLF
1667       returned. For anchored patterns,  a  last  literal  byte  is  
1668       recorded  only  if  it follows something of variable length.         Return 1 if the pattern contains any explicit  matches  for  CR  or  LF
1669       For example, for the pattern /^a\d+z\d+/ the returned  value         characters,  otherwise  0.  The  fourth argument should point to an int
1670       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
1671           \r or \n.
1672         PCRE_INFO_NAMECOUNT  
1673         PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_JCHANGED
1674         PCRE_INFO_NAMETABLE  
1675           Return  1  if  the (?J) or (?-J) option setting is used in the pattern,
1676       PCRE supports the use of named as well as numbered capturing         otherwise 0. The fourth argument should point to an int variable.  (?J)
1677       parentheses. The names are just an additional way of identi-         and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
1678       fying the parentheses,  which  still  acquire  a  number.  A  
1679       caller  that  wants  to extract data from a named subpattern           PCRE_INFO_LASTLITERAL
1680       must convert the name to a number in  order  to  access  the  
1681       correct  pointers  in  the  output  vector  (described  with         Return  the  value of the rightmost literal byte that must exist in any
1682       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
1683       these  three  values  to  obtain  the name-to-number mapping         recorded. The fourth argument should point to an int variable. If there
1684       table for the pattern.         is no such byte, -1 is returned. For anchored patterns, a last  literal
1685           byte  is  recorded only if it follows something of variable length. For
1686       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
1687       PCRE_INFO_NAMECOUNT   gives   the  number  of  entries,  and         /^a\dz\d/ the returned value is -1.
1688       PCRE_INFO_NAMEENTRYSIZE gives the size of each  entry;  both  
1689       of  these return an int value. The entry size depends on the           PCRE_INFO_NAMECOUNT
1690       length of the longest name.  PCRE_INFO_NAMETABLE  returns  a           PCRE_INFO_NAMEENTRYSIZE
1691       pointer to the first entry of the table (a pointer to char).           PCRE_INFO_NAMETABLE
1692       The first two bytes of each entry are the number of the cap-  
1693       turing parenthesis, most significant byte first. The rest of         PCRE  supports the use of named as well as numbered capturing parenthe-
1694       the entry is the corresponding name,  zero  terminated.  The         ses. The names are just an additional way of identifying the  parenthe-
1695       names  are  in alphabetical order. For example, consider the         ses, which still acquire numbers. Several convenience functions such as
1696       following pattern (assume PCRE_EXTENDED  is  set,  so  white         pcre_get_named_substring() are provided for  extracting  captured  sub-
1697       space - including newlines - is ignored):         strings  by  name. It is also possible to extract the data directly, by
1698           first converting the name to a number in order to  access  the  correct
1699         (?P<date> (?P<year>(\d\d)?\d\d) -         pointers in the output vector (described with pcre_exec() below). To do
1700         (?P<month>\d\d) - (?P<day>\d\d) )         the conversion, you need  to  use  the  name-to-number  map,  which  is
1701           described by these three values.
1702       There are four named subpatterns,  so  the  table  has  four  
1703       entries,  and  each  entry in the table is eight bytes long.         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
1704       The table is as follows, with non-printing  bytes  shows  in         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1705       hex, and undefined bytes shown as ??:         of  each  entry;  both  of  these  return  an int value. The entry size
1706           depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns
1707         00 01 d  a  t  e  00 ??         a  pointer  to  the  first  entry of the table (a pointer to char). The
1708         00 05 d  a  y  00 ?? ??         first two bytes of each entry are the number of the capturing parenthe-
1709         00 04 m  o  n  t  h  00         sis,  most  significant byte first. The rest of the entry is the corre-
1710         00 02 y  e  a  r  00 ??         sponding name, zero terminated. The names are  in  alphabetical  order.
1711           When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1712       When writing code to extract data  from  named  subpatterns,         theses numbers. For example, consider  the  following  pattern  (assume
1713       remember  that the length of each entry may be different for         PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is
1714       each compiled pattern.         ignored):
1715    
1716         PCRE_INFO_OPTIONS           (?<date> (?<year>(\d\d)?\d\d) -
1717             (?<month>\d\d) - (?<day>\d\d) )
1718       Return a copy of the options with which the pattern was com-  
1719       piled.  The fourth argument should point to an unsigned long         There are four named subpatterns, so the table has  four  entries,  and
1720       int variable. These option bits are those specified  in  the         each  entry  in the table is eight bytes long. The table is as follows,
1721       call  to  pcre_compile(),  modified  by any top-level option         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1722       settings within the pattern itself.         as ??:
1723    
1724       A pattern is automatically anchored by PCRE if  all  of  its           00 01 d  a  t  e  00 ??
1725       top-level alternatives begin with one of the following:           00 05 d  a  y  00 ?? ??
1726             00 04 m  o  n  t  h  00
1727         ^     unless PCRE_MULTILINE is set           00 02 y  e  a  r  00 ??
1728         \A    always  
1729         \G    always         When  writing  code  to  extract  data from named subpatterns using the
1730         .*    if PCRE_DOTALL is set and there are no back         name-to-number map, remember that the length of the entries  is  likely
1731                 references to the subpattern in which .* appears         to be different for each compiled pattern.
1732    
1733       For such patterns, the  PCRE_ANCHORED  bit  is  set  in  the           PCRE_INFO_OKPARTIAL
1734       options returned by pcre_fullinfo().  
1735           Return  1  if  the  pattern  can  be  used  for  partial  matching with
1736         PCRE_INFO_SIZE         pcre_exec(), otherwise 0. The fourth argument should point  to  an  int
1737           variable.  From  release  8.00,  this  always  returns  1,  because the
1738       Return the size of the compiled pattern, that is, the  value         restrictions that previously applied  to  partial  matching  have  been
1739       that  was  passed as the argument to pcre_malloc() when PCRE         lifted.  The  pcrepartial documentation gives details of partial match-
1740       was getting memory in which to place the compiled data.  The         ing.
1741       fourth argument should point to a size_t variable.  
1742             PCRE_INFO_OPTIONS
1743         PCRE_INFO_STUDYSIZE  
1744           Return a copy of the options with which the pattern was  compiled.  The
1745       Returns the size  of  the  data  block  pointed  to  by  the         fourth  argument  should  point to an unsigned long int variable. These
1746       study_data  field  in a pcre_extra block. That is, it is the         option bits are those specified in the call to pcre_compile(), modified
1747       value that was passed to pcre_malloc() when PCRE was getting         by any top-level option settings at the start of the pattern itself. In
1748       memory into which to place the data created by pcre_study().         other words, they are the options that will be in force  when  matching
1749       The fourth argument should point to a size_t variable.         starts.  For  example, if the pattern /(?im)abc(?-i)d/ is compiled with
1750           the PCRE_EXTENDED option, the result is PCRE_CASELESS,  PCRE_MULTILINE,
1751           and PCRE_EXTENDED.
1752    
1753           A  pattern  is  automatically  anchored by PCRE if all of its top-level
1754           alternatives begin with one of the following:
1755    
1756             ^     unless PCRE_MULTILINE is set
1757             \A    always
1758             \G    always
1759             .*    if PCRE_DOTALL is set and there are no back
1760                     references to the subpattern in which .* appears
1761    
1762           For such patterns, the PCRE_ANCHORED bit is set in the options returned
1763           by pcre_fullinfo().
1764    
1765             PCRE_INFO_SIZE
1766    
1767           Return  the  size  of the compiled pattern, that is, the value that was
1768           passed as the argument to pcre_malloc() when PCRE was getting memory in
1769           which to place the compiled data. The fourth argument should point to a
1770           size_t variable.
1771    
1772             PCRE_INFO_STUDYSIZE
1773    
1774           Return the size of the data block pointed to by the study_data field in
1775           a  pcre_extra  block.  That  is,  it  is  the  value that was passed to
1776           pcre_malloc() when PCRE was getting memory into which to place the data
1777           created  by  pcre_study(). The fourth argument should point to a size_t
1778           variable.
1779    
1780    
1781  OBSOLETE INFO FUNCTION  OBSOLETE INFO FUNCTION
1782    
1783       int pcre_info(const pcre *code, int *optptr, *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1784    
1785       The pcre_info() function is now obsolete because its  inter-         The pcre_info() function is now obsolete because its interface  is  too
1786       face  is  too  restrictive  to return all the available data         restrictive  to return all the available data about a compiled pattern.
1787       about  a  compiled  pattern.   New   programs   should   use         New  programs  should  use  pcre_fullinfo()  instead.  The   yield   of
1788       pcre_fullinfo()  instead.  The  yield  of pcre_info() is the         pcre_info()  is the number of capturing subpatterns, or one of the fol-
1789       number of capturing subpatterns, or  one  of  the  following         lowing negative numbers:
1790       negative numbers:  
1791             PCRE_ERROR_NULL       the argument code was NULL
1792         PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1793         PCRE_ERROR_BADMAGIC   the "magic number" was not found  
1794           If the optptr argument is not NULL, a copy of the  options  with  which
1795       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
1796       with which the pattern was compiled is placed in the integer         PCRE_INFO_OPTIONS above).
1797       it points to (see PCRE_INFO_OPTIONS above).  
1798           If the pattern is not anchored and the  firstcharptr  argument  is  not
1799       If the pattern is not anchored and the firstcharptr argument         NULL,  it is used to pass back information about the first character of
1800       is  not  NULL, it is used to pass back information about the         any matched string (see PCRE_INFO_FIRSTBYTE above).
1801       first    character    of    any    matched    string    (see  
1802       PCRE_INFO_FIRSTBYTE above).  
1803    REFERENCE COUNTS
1804    
1805           int pcre_refcount(pcre *code, int adjust);
1806    
1807           The pcre_refcount() function is used to maintain a reference  count  in
1808           the data block that contains a compiled pattern. It is provided for the
1809           benefit of applications that  operate  in  an  object-oriented  manner,
1810           where different parts of the application may be using the same compiled
1811           pattern, but you want to free the block when they are all done.
1812    
1813           When a pattern is compiled, the reference count field is initialized to
1814           zero.   It is changed only by calling this function, whose action is to
1815           add the adjust value (which may be positive or  negative)  to  it.  The
1816           yield of the function is the new value. However, the value of the count
1817           is constrained to lie between 0 and 65535, inclusive. If the new  value
1818           is outside these limits, it is forced to the appropriate limit value.
1819    
1820           Except  when it is zero, the reference count is not correctly preserved
1821           if a pattern is compiled on one host and then  transferred  to  a  host
1822           whose byte-order is different. (This seems a highly unlikely scenario.)
1823    
1824    
1825    MATCHING A PATTERN: THE TRADITIONAL FUNCTION
1826    
1827           int pcre_exec(const pcre *code, const pcre_extra *extra,
1828                const char *subject, int length, int startoffset,
1829                int options, int *ovector, int ovecsize);
1830    
1831           The  function pcre_exec() is called to match a subject string against a
1832           compiled pattern, which is passed in the code argument. If the  pattern
1833           has been studied, the result of the study should be passed in the extra
1834           argument. This function is the main matching facility of  the  library,
1835           and it operates in a Perl-like manner. For specialist use there is also
1836           an alternative matching function, which is described below in the  sec-
1837           tion about the pcre_dfa_exec() function.
1838    
1839           In  most applications, the pattern will have been compiled (and option-
1840           ally studied) in the same process that calls pcre_exec().  However,  it
1841           is possible to save compiled patterns and study data, and then use them
1842           later in different processes, possibly even on different hosts.  For  a
1843           discussion about this, see the pcreprecompile documentation.
1844    
1845           Here is an example of a simple call to pcre_exec():
1846    
1847             int rc;
1848             int ovector[30];
1849             rc = pcre_exec(
1850               re,             /* result of pcre_compile() */
1851               NULL,           /* we didn't study the pattern */
1852               "some string",  /* the subject string */
1853               11,             /* the length of the subject string */
1854               0,              /* start at offset 0 in the subject */
1855               0,              /* default options */
1856               ovector,        /* vector of integers for substring information */
1857               30);            /* number of elements (NOT size in bytes) */
1858    
1859       Extra data for pcre_exec()
1860    
1861           If  the  extra argument is not NULL, it must point to a pcre_extra data
1862           block. The pcre_study() function returns such a block (when it  doesn't
1863           return  NULL), but you can also create one for yourself, and pass addi-
1864           tional information in it. The pcre_extra block contains  the  following
1865           fields (not necessarily in this order):
1866    
1867             unsigned long int flags;
1868             void *study_data;
1869             unsigned long int match_limit;
1870             unsigned long int match_limit_recursion;
1871             void *callout_data;
1872             const unsigned char *tables;
1873    
1874           The  flags  field  is a bitmap that specifies which of the other fields
1875           are set. The flag bits are:
1876    
1877             PCRE_EXTRA_STUDY_DATA
1878             PCRE_EXTRA_MATCH_LIMIT
1879             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1880             PCRE_EXTRA_CALLOUT_DATA
1881             PCRE_EXTRA_TABLES
1882    
1883           Other flag bits should be set to zero. The study_data field is  set  in
1884           the  pcre_extra  block  that is returned by pcre_study(), together with
1885           the appropriate flag bit. You should not set this yourself, but you may
1886           add  to  the  block by setting the other fields and their corresponding
1887           flag bits.
1888    
1889           The match_limit field provides a means of preventing PCRE from using up
1890           a  vast amount of resources when running patterns that are not going to
1891           match, but which have a very large number  of  possibilities  in  their
1892           search  trees.  The  classic  example  is  the  use of nested unlimited
1893           repeats.
1894    
1895           Internally, PCRE uses a function called match() which it calls  repeat-
1896           edly  (sometimes  recursively). The limit set by match_limit is imposed
1897           on the number of times this function is called during  a  match,  which
1898           has  the  effect  of  limiting the amount of backtracking that can take
1899           place. For patterns that are not anchored, the count restarts from zero
1900           for each position in the subject string.
1901    
1902           The  default  value  for  the  limit can be set when PCRE is built; the
1903           default default is 10 million, which handles all but the  most  extreme
1904           cases.  You  can  override  the  default by suppling pcre_exec() with a
1905           pcre_extra    block    in    which    match_limit    is    set,     and
1906           PCRE_EXTRA_MATCH_LIMIT  is  set  in  the  flags  field. If the limit is
1907           exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1908    
1909           The match_limit_recursion field is similar to match_limit, but  instead
1910           of limiting the total number of times that match() is called, it limits
1911           the depth of recursion. The recursion depth is a  smaller  number  than
1912           the  total number of calls, because not all calls to match() are recur-
1913           sive.  This limit is of use only if it is set smaller than match_limit.
1914    
1915           Limiting the recursion depth limits the amount of  stack  that  can  be
1916           used, or, when PCRE has been compiled to use memory on the heap instead
1917           of the stack, the amount of heap memory that can be used.
1918    
1919           The default value for match_limit_recursion can be  set  when  PCRE  is
1920           built;  the  default  default  is  the  same  value  as the default for
1921           match_limit. You can override the default by suppling pcre_exec()  with
1922           a   pcre_extra   block  in  which  match_limit_recursion  is  set,  and
1923           PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in  the  flags  field.  If  the
1924           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1925    
1926           The  callout_data  field is used in conjunction with the "callout" fea-
1927           ture, and is described in the pcrecallout documentation.
1928    
1929           The tables field  is  used  to  pass  a  character  tables  pointer  to
1930           pcre_exec();  this overrides the value that is stored with the compiled
1931           pattern. A non-NULL value is stored with the compiled pattern  only  if
1932           custom  tables  were  supplied to pcre_compile() via its tableptr argu-
1933           ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
1934           PCRE's  internal  tables  to be used. This facility is helpful when re-
1935           using patterns that have been saved after compiling  with  an  external
1936           set  of  tables,  because  the  external tables might be at a different
1937           address when pcre_exec() is called. See the  pcreprecompile  documenta-
1938           tion for a discussion of saving compiled patterns for later use.
1939    
1940       Option bits for pcre_exec()
1941    
1942           The  unused  bits of the options argument for pcre_exec() must be zero.
1943           The only bits that may  be  set  are  PCRE_ANCHORED,  PCRE_NEWLINE_xxx,
1944           PCRE_NOTBOL,    PCRE_NOTEOL,    PCRE_NOTEMPTY,   PCRE_NOTEMPTY_ATSTART,
1945           PCRE_NO_START_OPTIMIZE,  PCRE_NO_UTF8_CHECK,   PCRE_PARTIAL_SOFT,   and
1946           PCRE_PARTIAL_HARD.
1947    
1948             PCRE_ANCHORED
1949    
1950           The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first
1951           matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or
1952           turned  out to be anchored by virtue of its contents, it cannot be made
1953           unachored at matching time.
1954    
1955             PCRE_BSR_ANYCRLF
1956             PCRE_BSR_UNICODE
1957    
1958           These options (which are mutually exclusive) control what the \R escape
1959           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1960           or to match any Unicode newline sequence. These  options  override  the
1961           choice that was made or defaulted when the pattern was compiled.
1962    
1963             PCRE_NEWLINE_CR
1964             PCRE_NEWLINE_LF
1965             PCRE_NEWLINE_CRLF
1966             PCRE_NEWLINE_ANYCRLF
1967             PCRE_NEWLINE_ANY
1968    
1969           These  options  override  the  newline  definition  that  was chosen or
1970           defaulted when the pattern was compiled. For details, see the  descrip-
1971           tion  of  pcre_compile()  above.  During  matching,  the newline choice
1972           affects the behaviour of the dot, circumflex,  and  dollar  metacharac-
1973           ters.  It may also alter the way the match position is advanced after a
1974           match failure for an unanchored pattern.
1975    
1976           When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF,  or  PCRE_NEWLINE_ANY  is
1977           set,  and a match attempt for an unanchored pattern fails when the cur-
1978           rent position is at a  CRLF  sequence,  and  the  pattern  contains  no
1979           explicit  matches  for  CR  or  LF  characters,  the  match position is
1980           advanced by two characters instead of one, in other words, to after the
1981           CRLF.
1982    
1983           The above rule is a compromise that makes the most common cases work as
1984           expected. For example, if the  pattern  is  .+A  (and  the  PCRE_DOTALL
1985           option is not set), it does not match the string "\r\nA" because, after
1986           failing at the start, it skips both the CR and the LF before  retrying.
1987           However,  the  pattern  [\r\n]A does match that string, because it con-
1988           tains an explicit CR or LF reference, and so advances only by one char-
1989           acter after the first failure.
1990    
1991           An explicit match for CR of LF is either a literal appearance of one of
1992           those characters, or one of the \r or  \n  escape  sequences.  Implicit
1993           matches  such  as [^X] do not count, nor does \s (which includes CR and
1994           LF in the characters that it matches).
1995    
1996           Notwithstanding the above, anomalous effects may still occur when  CRLF
1997           is a valid newline sequence and explicit \r or \n escapes appear in the
1998           pattern.
1999    
2000             PCRE_NOTBOL
2001    
2002           This option specifies that first character of the subject string is not
2003           the  beginning  of  a  line, so the circumflex metacharacter should not
2004           match before it. Setting this without PCRE_MULTILINE (at compile  time)
2005           causes  circumflex  never to match. This option affects only the behav-
2006           iour of the circumflex metacharacter. It does not affect \A.
2007    
2008             PCRE_NOTEOL
2009    
2010           This option specifies that the end of the subject string is not the end
2011           of  a line, so the dollar metacharacter should not match it nor (except
2012           in multiline mode) a newline immediately before it. Setting this  with-
2013           out PCRE_MULTILINE (at compile time) causes dollar never to match. This
2014           option affects only the behaviour of the dollar metacharacter. It  does
2015           not affect \Z or \z.
2016    
2017             PCRE_NOTEMPTY
2018    
2019           An empty string is not considered to be a valid match if this option is
2020           set. If there are alternatives in the pattern, they are tried.  If  all
2021           the  alternatives  match  the empty string, the entire match fails. For
2022           example, if the pattern
2023    
2024             a?b?
2025    
2026           is applied to a string not beginning with "a" or  "b",  it  matches  an
2027           empty  string at the start of the subject. With PCRE_NOTEMPTY set, this
2028           match is not valid, so PCRE searches further into the string for occur-
2029           rences of "a" or "b".
2030    
2031             PCRE_NOTEMPTY_ATSTART
2032    
2033           This  is  like PCRE_NOTEMPTY, except that an empty string match that is
2034           not at the start of  the  subject  is  permitted.  If  the  pattern  is
2035           anchored, such a match can occur only if the pattern contains \K.
2036    
2037           Perl     has    no    direct    equivalent    of    PCRE_NOTEMPTY    or
2038           PCRE_NOTEMPTY_ATSTART, but it does make a special  case  of  a  pattern
2039           match  of  the empty string within its split() function, and when using
2040           the /g modifier. It is  possible  to  emulate  Perl's  behaviour  after
2041           matching a null string by first trying the match again at the same off-
2042           set with PCRE_NOTEMPTY_ATSTART and  PCRE_ANCHORED,  and  then  if  that
2043           fails, by advancing the starting offset (see below) and trying an ordi-
2044           nary match again. There is some code that demonstrates how to  do  this
2045           in the pcredemo sample program.
2046    
2047             PCRE_NO_START_OPTIMIZE
2048    
2049           There  are a number of optimizations that pcre_exec() uses at the start
2050           of a match, in order to speed up the process. For  example,  if  it  is
2051           known  that  a  match must start with a specific character, it searches
2052           the subject for that character, and fails immediately if it cannot find
2053           it,  without actually running the main matching function. When callouts
2054           are in use, these optimizations can cause  them  to  be  skipped.  This
2055           option  disables  the  "start-up" optimizations, causing performance to
2056           suffer, but ensuring that the callouts do occur.
2057    
2058             PCRE_NO_UTF8_CHECK
2059    
2060           When PCRE_UTF8 is set at compile time, the validity of the subject as a
2061           UTF-8  string is automatically checked when pcre_exec() is subsequently
2062           called.  The value of startoffset is also checked  to  ensure  that  it
2063           points  to  the start of a UTF-8 character. There is a discussion about
2064           the validity of UTF-8 strings in the section on UTF-8  support  in  the
2065           main  pcre  page.  If  an  invalid  UTF-8  sequence  of bytes is found,
2066           pcre_exec() returns the error PCRE_ERROR_BADUTF8. If  startoffset  con-
2067           tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
2068    
2069           If  you  already  know that your subject is valid, and you want to skip
2070           these   checks   for   performance   reasons,   you   can    set    the
2071           PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to
2072           do this for the second and subsequent calls to pcre_exec() if  you  are
2073           making  repeated  calls  to  find  all  the matches in a single subject
2074           string. However, you should be  sure  that  the  value  of  startoffset
2075           points  to  the  start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is
2076           set, the effect of passing an invalid UTF-8 string as a subject,  or  a
2077           value  of startoffset that does not point to the start of a UTF-8 char-
2078           acter, is undefined. Your program may crash.
2079    
2080             PCRE_PARTIAL_HARD
2081             PCRE_PARTIAL_SOFT
2082    
2083           These options turn on the partial matching feature. For backwards  com-
2084           patibility,  PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial
2085           match occurs if the end of the subject string is reached  successfully,
2086           but  there  are not enough subject characters to complete the match. If
2087           this happens when PCRE_PARTIAL_HARD  is  set,  pcre_exec()  immediately
2088           returns  PCRE_ERROR_PARTIAL.  Otherwise,  if  PCRE_PARTIAL_SOFT is set,
2089           matching continues by testing any other alternatives. Only if they  all
2090           fail  is  PCRE_ERROR_PARTIAL  returned (instead of PCRE_ERROR_NOMATCH).
2091           The portion of the string that was inspected when the partial match was
2092           found  is  set  as  the first matching string. There is a more detailed
2093           discussion in the pcrepartial documentation.
2094    
2095       The string to be matched by pcre_exec()
2096    
2097           The subject string is passed to pcre_exec() as a pointer in subject,  a
2098           length (in bytes) in length, and a starting byte offset in startoffset.
2099           In UTF-8 mode, the byte offset must point to the start of a UTF-8 char-
2100           acter.  Unlike  the pattern string, the subject may contain binary zero
2101           bytes. When the starting offset is zero, the search for a match  starts
2102           at  the  beginning  of  the subject, and this is by far the most common
2103           case.
2104    
2105           A non-zero starting offset is useful when searching for  another  match
2106           in  the same subject by calling pcre_exec() again after a previous suc-
2107           cess.  Setting startoffset differs from just passing over  a  shortened
2108           string  and  setting  PCRE_NOTBOL  in the case of a pattern that begins
2109           with any kind of lookbehind. For example, consider the pattern
2110    
2111             \Biss\B
2112    
2113           which finds occurrences of "iss" in the middle of  words.  (\B  matches
2114           only  if  the  current position in the subject is not a word boundary.)
2115           When applied to the string "Mississipi" the first call  to  pcre_exec()
2116           finds  the  first  occurrence. If pcre_exec() is called again with just
2117           the remainder of the subject,  namely  "issipi",  it  does  not  match,
2118           because \B is always false at the start of the subject, which is deemed
2119           to be a word boundary. However, if pcre_exec()  is  passed  the  entire
2120           string again, but with startoffset set to 4, it finds the second occur-
2121           rence of "iss" because it is able to look behind the starting point  to
2122           discover that it is preceded by a letter.
2123    
2124           If  a  non-zero starting offset is passed when the pattern is anchored,
2125           one attempt to match at the given offset is made. This can only succeed
2126           if  the  pattern  does  not require the match to be at the start of the
2127           subject.
2128    
2129       How pcre_exec() returns captured substrings
2130    
2131           In general, a pattern matches a certain portion of the subject, and  in
2132           addition,  further  substrings  from  the  subject may be picked out by
2133           parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,
2134           this  is  called "capturing" in what follows, and the phrase "capturing
2135           subpattern" is used for a fragment of a pattern that picks out  a  sub-
2136           string.  PCRE  supports several other kinds of parenthesized subpattern
2137           that do not cause substrings to be captured.
2138    
2139           Captured substrings are returned to the caller via a vector of integers
2140           whose  address is passed in ovector. The number of elements in the vec-
2141           tor is passed in ovecsize, which must be a non-negative  number.  Note:
2142           this argument is NOT the size of ovector in bytes.
2143    
2144           The  first  two-thirds of the vector is used to pass back captured sub-
2145           strings, each substring using a pair of integers. The  remaining  third
2146           of  the  vector is used as workspace by pcre_exec() while matching cap-
2147           turing subpatterns, and is not available for passing back  information.
2148           The  number passed in ovecsize should always be a multiple of three. If
2149           it is not, it is rounded down.
2150    
2151           When a match is successful, information about  captured  substrings  is
2152           returned  in  pairs  of integers, starting at the beginning of ovector,
2153           and continuing up to two-thirds of its length at the  most.  The  first
2154           element  of  each pair is set to the byte offset of the first character
2155           in a substring, and the second is set to the byte offset of  the  first
2156           character  after  the end of a substring. Note: these values are always
2157           byte offsets, even in UTF-8 mode. They are not character counts.
2158    
2159           The first pair of integers, ovector[0]  and  ovector[1],  identify  the
2160           portion  of  the subject string matched by the entire pattern. The next
2161           pair is used for the first capturing subpattern, and so on.  The  value
2162           returned by pcre_exec() is one more than the highest numbered pair that
2163           has been set.  For example, if two substrings have been  captured,  the
2164           returned  value is 3. If there are no capturing subpatterns, the return
2165           value from a successful match is 1, indicating that just the first pair
2166           of offsets has been set.
2167    
2168           If a capturing subpattern is matched repeatedly, it is the last portion
2169           of the string that it matched that is returned.
2170    
2171           If the vector is too small to hold all the captured substring  offsets,
2172           it is used as far as possible (up to two-thirds of its length), and the
2173           function returns a value of zero. If the substring offsets are  not  of
2174           interest,  pcre_exec()  may  be  called with ovector passed as NULL and
2175           ovecsize as zero. However, if the pattern contains back references  and
2176           the  ovector is not big enough to remember the related substrings, PCRE
2177           has to get additional memory for use during matching. Thus it  is  usu-
2178           ally advisable to supply an ovector.
2179    
2180           The  pcre_info()  function  can  be used to find out how many capturing
2181           subpatterns there are in a compiled  pattern.  The  smallest  size  for
2182           ovector  that  will allow for n captured substrings, in addition to the
2183           offsets of the substring matched by the whole pattern, is (n+1)*3.
2184    
2185           It is possible for capturing subpattern number n+1 to match  some  part
2186           of the subject when subpattern n has not been used at all. For example,
2187           if the string "abc" is matched  against  the  pattern  (a|(z))(bc)  the
2188           return from the function is 4, and subpatterns 1 and 3 are matched, but
2189           2 is not. When this happens, both values in  the  offset  pairs  corre-
2190           sponding to unused subpatterns are set to -1.
2191    
2192           Offset  values  that correspond to unused subpatterns at the end of the
2193           expression are also set to -1. For example,  if  the  string  "abc"  is
2194           matched  against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
2195           matched. The return from the function is 2, because  the  highest  used
2196           capturing subpattern number is 1. However, you can refer to the offsets
2197           for the second and third capturing subpatterns if  you  wish  (assuming
2198           the vector is large enough, of course).
2199    
2200           Some  convenience  functions  are  provided for extracting the captured
2201           substrings as separate strings. These are described below.
2202    
2203       Error return values from pcre_exec()
2204    
2205           If pcre_exec() fails, it returns a negative number. The  following  are
2206           defined in the header file:
2207    
2208             PCRE_ERROR_NOMATCH        (-1)
2209    
2210           The subject string did not match the pattern.
2211    
2212             PCRE_ERROR_NULL           (-2)
2213    
2214           Either  code  or  subject  was  passed as NULL, or ovector was NULL and
2215           ovecsize was not zero.
2216    
2217             PCRE_ERROR_BADOPTION      (-3)
2218    
2219           An unrecognized bit was set in the options argument.
2220    
2221             PCRE_ERROR_BADMAGIC       (-4)
2222    
2223           PCRE stores a 4-byte "magic number" at the start of the compiled  code,
2224           to catch the case when it is passed a junk pointer and to detect when a
2225           pattern that was compiled in an environment of one endianness is run in
2226           an  environment  with the other endianness. This is the error that PCRE
2227           gives when the magic number is not present.
2228    
2229             PCRE_ERROR_UNKNOWN_OPCODE (-5)
2230    
2231           While running the pattern match, an unknown item was encountered in the
2232           compiled  pattern.  This  error  could be caused by a bug in PCRE or by
2233           overwriting of the compiled pattern.
2234    
2235             PCRE_ERROR_NOMEMORY       (-6)
2236    
2237           If a pattern contains back references, but the ovector that  is  passed
2238           to pcre_exec() is not big enough to remember the referenced substrings,
2239           PCRE gets a block of memory at the start of matching to  use  for  this
2240           purpose.  If the call via pcre_malloc() fails, this error is given. The
2241           memory is automatically freed at the end of matching.
2242    
2243             PCRE_ERROR_NOSUBSTRING    (-7)
2244    
2245           This error is used by the pcre_copy_substring(),  pcre_get_substring(),
2246           and  pcre_get_substring_list()  functions  (see  below).  It  is  never
2247           returned by pcre_exec().
2248    
2249             PCRE_ERROR_MATCHLIMIT     (-8)
2250    
2251           The backtracking limit, as specified by  the  match_limit  field  in  a
2252           pcre_extra  structure  (or  defaulted) was reached. See the description
2253           above.
2254    
2255             PCRE_ERROR_CALLOUT        (-9)
2256    
2257           This error is never generated by pcre_exec() itself. It is provided for
2258           use  by  callout functions that want to yield a distinctive error code.
2259           See the pcrecallout documentation for details.
2260    
2261             PCRE_ERROR_BADUTF8        (-10)
2262    
2263           A string that contains an invalid UTF-8 byte sequence was passed  as  a
2264           subject.
2265    
2266             PCRE_ERROR_BADUTF8_OFFSET (-11)
2267    
2268           The UTF-8 byte sequence that was passed as a subject was valid, but the
2269           value of startoffset did not point to the beginning of a UTF-8  charac-
2270           ter.
2271    
2272             PCRE_ERROR_PARTIAL        (-12)
2273    
2274           The  subject  string did not match, but it did match partially. See the
2275           pcrepartial documentation for details of partial matching.
2276    
2277             PCRE_ERROR_BADPARTIAL     (-13)
2278    
2279           This code is no longer in  use.  It  was  formerly  returned  when  the
2280           PCRE_PARTIAL  option  was used with a compiled pattern containing items
2281           that were  not  supported  for  partial  matching.  From  release  8.00
2282           onwards, there are no restrictions on partial matching.
2283    
2284             PCRE_ERROR_INTERNAL       (-14)
2285    
2286           An  unexpected  internal error has occurred. This error could be caused
2287           by a bug in PCRE or by overwriting of the compiled pattern.
2288    
2289             PCRE_ERROR_BADCOUNT       (-15)
2290    
2291           This error is given if the value of the ovecsize argument is negative.
2292    
2293             PCRE_ERROR_RECURSIONLIMIT (-21)
2294    
2295           The internal recursion limit, as specified by the match_limit_recursion
2296           field  in  a  pcre_extra  structure (or defaulted) was reached. See the
2297           description above.
2298    
2299             PCRE_ERROR_BADNEWLINE     (-23)
2300    
2301  MATCHING A PATTERN         An invalid combination of PCRE_NEWLINE_xxx options was given.
2302    
2303       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.  
2304    
2305    
2306  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2307    
2308       int pcre_copy_substring(const char *subject, int *ovector,         int pcre_copy_substring(const char *subject, int *ovector,
2309            int stringcount, int stringnumber, char *buffer,              int stringcount, int stringnumber, char *buffer,
2310            int buffersize);              int buffersize);
2311    
2312       int pcre_get_substring(const char *subject, int *ovector,         int pcre_get_substring(const char *subject, int *ovector,
2313            int stringcount, int stringnumber,              int stringcount, int stringnumber,
2314            const char **stringptr);              const char **stringptr);
2315    
2316       int pcre_get_substring_list(const char *subject,         int pcre_get_substring_list(const char *subject,
2317            int *ovector, int stringcount, const char ***listptr);              int *ovector, int stringcount, const char ***listptr);
2318    
2319       Captured substrings can be accessed directly  by  using  the         Captured substrings can be  accessed  directly  by  using  the  offsets
2320       offsets returned by pcre_exec() in ovector. For convenience,         returned  by  pcre_exec()  in  ovector.  For convenience, the functions
2321       the functions  pcre_copy_substring(),  pcre_get_substring(),         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
2322       and  pcre_get_substring_list()  are  provided for extracting         string_list()  are  provided for extracting captured substrings as new,
2323       captured  substrings  as  new,   separate,   zero-terminated         separate, zero-terminated strings. These functions identify  substrings
2324       strings.  These functions identify substrings by number. The         by  number.  The  next section describes functions for extracting named
2325       next section describes functions for extracting  named  sub-         substrings.
2326       strings.   A  substring  that  contains  a  binary  zero  is  
2327       correctly extracted and has a further zero added on the end,         A substring that contains a binary zero is correctly extracted and  has
2328       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
2329           string.  However, you can process such a string  by  referring  to  the
2330       The first three arguments are the  same  for  all  three  of         length  that  is  returned  by  pcre_copy_substring() and pcre_get_sub-
2331       these  functions:   subject  is the subject string which has         string().  Unfortunately, the interface to pcre_get_substring_list() is
2332       just been successfully matched, ovector is a pointer to  the         not  adequate for handling strings containing binary zeros, because the
2333       vector  of  integer  offsets that was passed to pcre_exec(),         end of the final string is not independently indicated.
2334       and stringcount is the number of substrings that  were  cap-  
2335       tured by the match, including the substring that matched the         The first three arguments are the same for all  three  of  these  func-
2336       entire regular expression. This is  the  value  returned  by         tions:  subject  is  the subject string that has just been successfully
2337       pcre_exec  if  it  is  greater  than  zero.  If  pcre_exec()         matched, ovector is a pointer to the vector of integer offsets that was
2338       returned zero, indicating that it ran out of space in  ovec-         passed to pcre_exec(), and stringcount is the number of substrings that
2339       tor,  the  value passed as stringcount should be the size of         were captured by the match, including the substring  that  matched  the
2340       the vector divided by three.         entire regular expression. This is the value returned by pcre_exec() if
2341           it is greater than zero. If pcre_exec() returned zero, indicating  that
2342       The functions pcre_copy_substring() and pcre_get_substring()         it  ran out of space in ovector, the value passed as stringcount should
2343       extract a single substring, whose number is given as string-         be the number of elements in the vector divided by three.
2344       number. A value of zero extracts the substring that  matched  
2345       the entire pattern, while higher values extract the captured         The functions pcre_copy_substring() and pcre_get_substring() extract  a
2346       substrings. For pcre_copy_substring(), the string is  placed         single  substring,  whose  number  is given as stringnumber. A value of
2347       in  buffer,  whose  length is given by buffersize, while for         zero extracts the substring that matched the  entire  pattern,  whereas
2348       pcre_get_substring() a new block of memory is  obtained  via         higher  values  extract  the  captured  substrings.  For pcre_copy_sub-
2349       pcre_malloc,  and its address is returned via stringptr. The         string(), the string is placed in buffer,  whose  length  is  given  by
2350       yield of the function is  the  length  of  the  string,  not         buffersize,  while  for  pcre_get_substring()  a new block of memory is
2351       including the terminating zero, or one of         obtained via pcre_malloc, and its address is  returned  via  stringptr.
2352           The  yield  of  the function is the length of the string, not including
2353         PCRE_ERROR_NOMEMORY       (-6)         the terminating zero, or one of these error codes:
2354    
2355       The buffer was too small for pcre_copy_substring(),  or  the           PCRE_ERROR_NOMEMORY       (-6)
2356       attempt to get memory failed for pcre_get_substring().  
2357           The buffer was too small for pcre_copy_substring(), or the  attempt  to
2358         PCRE_ERROR_NOSUBSTRING    (-7)         get memory failed for pcre_get_substring().
2359    
2360       There is no substring whose number is stringnumber.           PCRE_ERROR_NOSUBSTRING    (-7)
2361    
2362       The pcre_get_substring_list() function extracts  all  avail-         There is no substring whose number is stringnumber.
2363       able  substrings  and builds a list of pointers to them. All  
2364       this is done in a single block of memory which  is  obtained         The  pcre_get_substring_list()  function  extracts  all  available sub-
2365       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
2366       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
2367       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
2368       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
2369           pointer. The yield of the function is zero if all  went  well,  or  the
2370         PCRE_ERROR_NOMEMORY       (-6)         error code
2371    
2372       if the attempt to get the memory block failed.           PCRE_ERROR_NOMEMORY       (-6)
2373    
2374       When any of these functions encounter a  substring  that  is         if the attempt to get the memory block failed.
2375       unset, which can happen when capturing subpattern number n+1  
2376       matches some part of the subject, but subpattern n  has  not         When  any of these functions encounter a substring that is unset, which
2377       been  used  at all, they return an empty string. This can be         can happen when capturing subpattern number n+1 matches  some  part  of
2378       distinguished  from  a  genuine  zero-length  substring   by         the  subject, but subpattern n has not been used at all, they return an
2379       inspecting the appropriate offset in ovector, which is nega-         empty string. This can be distinguished from a genuine zero-length sub-
2380       tive for unset substrings.         string  by inspecting the appropriate offset in ovector, which is nega-
2381           tive for unset substrings.
2382       The  two  convenience  functions  pcre_free_substring()  and  
2383       pcre_free_substring_list()  can  be  used to free the memory         The two convenience functions pcre_free_substring() and  pcre_free_sub-
2384       returned by  a  previous  call  of  pcre_get_substring()  or         string_list()  can  be  used  to free the memory returned by a previous
2385       pcre_get_substring_list(),  respectively.  They  do  nothing         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2386       more than call the function pointed to by  pcre_free,  which         tively.  They  do  nothing  more  than  call the function pointed to by
2387       of  course  could  be called directly from a C program. How-         pcre_free, which of course could be called directly from a  C  program.
2388       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-
2389       a  special  interface  to another programming language which         cial  interface  to  another  programming  language  that  cannot   use
2390       cannot use pcre_free directly; it is for  these  cases  that         pcre_free  directly;  it is for these cases that the functions are pro-
2391       the functions are provided.         vided.
2392    
2393    
2394  EXTRACTING CAPTURED SUBSTRINGS BY NAME  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2395    
2396       int pcre_copy_named_substring(const pcre *code,         int pcre_get_stringnumber(const pcre *code,
2397            const char *subject, int *ovector,              const char *name);
2398            int stringcount, const char *stringname,  
2399            char *buffer, int buffersize);         int pcre_copy_named_substring(const pcre *code,
2400                const char *subject, int *ovector,
2401       int pcre_get_stringnumber(const pcre *code,              int stringcount, const char *stringname,
2402            const char *name);              char *buffer, int buffersize);
2403    
2404       int pcre_get_named_substring(const pcre *code,         int pcre_get_named_substring(const pcre *code,
2405            const char *subject, int *ovector,              const char *subject, int *ovector,
2406            int stringcount, const char *stringname,              int stringcount, const char *stringname,
2407            const char **stringptr);              const char **stringptr);
2408    
2409       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-
2410       ciated    number.    This    can    be   done   by   calling         ber.  For example, for this pattern
2411       pcre_get_stringnumber(). The first argument is the  compiled  
2412       pattern,  and  the second is the name. For example, for this           (a+)b(?<xxx>\d+)...
2413       pattern  
2414           the number of the subpattern called "xxx" is 2. If the name is known to
2415         ab(?<xxx>\d+)...         be unique (PCRE_DUPNAMES was not set), you can find the number from the
2416           name by calling pcre_get_stringnumber(). The first argument is the com-
2417       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
2418       number,  you can then extract the substring directly, or use         the  subpattern  number,  or PCRE_ERROR_NOSUBSTRING (-7) if there is no
2419       one of the functions described in the previous section.  For         subpattern of that name.
2420       convenience,  there are also two functions that do the whole  
2421       job.         Given the number, you can extract the substring directly, or use one of
2422           the functions described in the previous section. For convenience, there
2423       Most of the  arguments  of  pcre_copy_named_substring()  and         are also two functions that do the whole job.
2424       pcre_get_named_substring()  are  the  same  as those for the  
2425       functions that  extract  by  number,  and  so  are  not  re-         Most   of   the   arguments    of    pcre_copy_named_substring()    and
2426       described here. There are just two differences.         pcre_get_named_substring()  are  the  same  as  those for the similarly
2427           named functions that extract by number. As these are described  in  the
2428       First, instead of a substring number, a  substring  name  is         previous  section,  they  are not re-described here. There are just two
2429       given.  Second,  there  is  an  extra argument, given at the         differences:
2430       start, which is a pointer to the compiled pattern.  This  is  
2431       needed  in order to gain access to the name-to-number trans-         First, instead of a substring number, a substring name is  given.  Sec-
2432       lation table.         ond, there is an extra argument, given at the start, which is a pointer
2433           to the compiled pattern. This is needed in order to gain access to  the
2434       These functions  call  pcre_get_stringnumber(),  and  if  it         name-to-number translation table.
2435       succeeds,    they   then   call   pcre_copy_substring()   or  
2436       pcre_get_substring(), as appropriate.         These  functions call pcre_get_stringnumber(), and if it succeeds, they
2437           then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-
2438           ate.  NOTE:  If PCRE_DUPNAMES is set and there are duplicate names, the
2439           behaviour may not be what you want (see the next section).
2440    
2441           Warning: If the pattern uses the "(?|" feature to set up multiple  sub-
2442           patterns  with  the  same  number,  you cannot use names to distinguish
2443           them, because names are not included in the compiled code. The matching
2444           process uses only numbers.
2445    
2446    
2447    DUPLICATE SUBPATTERN NAMES
2448    
2449           int pcre_get_stringtable_entries(const pcre *code,
2450                const char *name, char **first, char **last);
2451    
2452           When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for
2453           subpatterns are not required to  be  unique.  Normally,  patterns  with
2454           duplicate  names  are such that in any one match, only one of the named
2455           subpatterns participates. An example is shown in the pcrepattern  docu-
2456           mentation.
2457    
2458           When    duplicates   are   present,   pcre_copy_named_substring()   and
2459           pcre_get_named_substring() return the first substring corresponding  to
2460           the  given  name  that  is set. If none are set, PCRE_ERROR_NOSUBSTRING
2461           (-7) is returned; no  data  is  returned.  The  pcre_get_stringnumber()
2462           function  returns one of the numbers that are associated with the name,
2463           but it is not defined which it is.
2464    
2465           If you want to get full details of all captured substrings for a  given
2466           name,  you  must  use  the pcre_get_stringtable_entries() function. The
2467           first argument is the compiled pattern, and the second is the name. The
2468           third  and  fourth  are  pointers to variables which are updated by the
2469           function. After it has run, they point to the first and last entries in
2470           the  name-to-number  table  for  the  given  name.  The function itself
2471           returns the length of each entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if
2472           there  are none. The format of the table is described above in the sec-
2473           tion entitled Information about a  pattern.   Given  all  the  relevant
2474           entries  for the name, you can extract each of their numbers, and hence
2475           the captured data, if any.
2476    
2477    
2478    FINDING ALL POSSIBLE MATCHES
2479    
2480           The traditional matching function uses a  similar  algorithm  to  Perl,
2481           which stops when it finds the first match, starting at a given point in
2482           the subject. If you want to find all possible matches, or  the  longest
2483           possible  match,  consider using the alternative matching function (see
2484           below) instead. If you cannot use the alternative function,  but  still
2485           need  to  find all possible matches, you can kludge it up by making use
2486           of the callout facility, which is described in the pcrecallout documen-
2487           tation.
2488    
2489           What you have to do is to insert a callout right at the end of the pat-
2490           tern.  When your callout function is called, extract and save the  cur-
2491           rent  matched  substring.  Then  return  1, which forces pcre_exec() to
2492           backtrack and try other alternatives. Ultimately, when it runs  out  of
2493           matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2494    
2495    
2496    MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
2497    
2498           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
2499                const char *subject, int length, int startoffset,
2500                int options, int *ovector, int ovecsize,
2501                int *workspace, int wscount);
2502    
2503           The  function  pcre_dfa_exec()  is  called  to  match  a subject string
2504           against a compiled pattern, using a matching algorithm that  scans  the
2505           subject  string  just  once, and does not backtrack. This has different
2506           characteristics to the normal algorithm, and  is  not  compatible  with
2507           Perl.  Some  of the features of PCRE patterns are not supported. Never-
2508           theless, there are times when this kind of matching can be useful.  For
2509           a  discussion  of  the  two matching algorithms, and a list of features
2510           that pcre_dfa_exec() does not support, see the pcrematching  documenta-
2511           tion.
2512    
2513           The  arguments  for  the  pcre_dfa_exec()  function are the same as for
2514           pcre_exec(), plus two extras. The ovector argument is used in a differ-
2515           ent  way,  and  this is described below. The other common arguments are
2516           used in the same way as for pcre_exec(), so their  description  is  not
2517           repeated here.
2518    
2519           The  two  additional  arguments provide workspace for the function. The
2520           workspace vector should contain at least 20 elements. It  is  used  for
2521           keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2522           workspace will be needed for patterns and subjects where  there  are  a
2523           lot of potential matches.
2524    
2525           Here is an example of a simple call to pcre_dfa_exec():
2526    
2527             int rc;
2528             int ovector[10];
2529             int wspace[20];
2530             rc = pcre_dfa_exec(
2531               re,             /* result of pcre_compile() */
2532               NULL,           /* we didn't study the pattern */
2533               "some string",  /* the subject string */
2534               11,             /* the length of the subject string */
2535               0,              /* start at offset 0 in the subject */
2536               0,              /* default options */
2537               ovector,        /* vector of integers for substring information */
2538               10,             /* number of elements (NOT size in bytes) */
2539               wspace,         /* working space vector */
2540               20);            /* number of elements (NOT size in bytes) */
2541    
2542       Option bits for pcre_dfa_exec()
2543    
2544           The  unused  bits  of  the options argument for pcre_dfa_exec() must be
2545           zero. The only bits  that  may  be  set  are  PCRE_ANCHORED,  PCRE_NEW-
2546           LINE_xxx,        PCRE_NOTBOL,        PCRE_NOTEOL,        PCRE_NOTEMPTY,
2547           PCRE_NOTEMPTY_ATSTART, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_HARD, PCRE_PAR-
2548           TIAL_SOFT,  PCRE_DFA_SHORTEST,  and  PCRE_DFA_RESTART. All but the last
2549           four of these are  exactly  the  same  as  for  pcre_exec(),  so  their
2550           description is not repeated here.
2551    
2552             PCRE_PARTIAL_HARD
2553             PCRE_PARTIAL_SOFT
2554    
2555           These  have the same general effect as they do for pcre_exec(), but the
2556           details are slightly  different.  When  PCRE_PARTIAL_HARD  is  set  for
2557           pcre_dfa_exec(),  it  returns PCRE_ERROR_PARTIAL if the end of the sub-
2558           ject is reached and there is still at least  one  matching  possibility
2559           that requires additional characters. This happens even if some complete
2560           matches have also been found. When PCRE_PARTIAL_SOFT is set, the return
2561           code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end
2562           of the subject is reached, there have been  no  complete  matches,  but
2563           there  is  still  at least one matching possibility. The portion of the
2564           string that was inspected when the longest partial match was  found  is
2565           set as the first matching string in both cases.
2566    
2567             PCRE_DFA_SHORTEST
2568    
2569           Setting  the  PCRE_DFA_SHORTEST option causes the matching algorithm to
2570           stop as soon as it has found one match. Because of the way the alterna-
2571           tive  algorithm  works, this is necessarily the shortest possible match
2572           at the first possible matching point in the subject string.
2573    
2574             PCRE_DFA_RESTART
2575    
2576           When pcre_dfa_exec() returns a partial match, it is possible to call it
2577           again,  with  additional  subject characters, and have it continue with
2578           the same match. The PCRE_DFA_RESTART option requests this action;  when
2579           it  is  set,  the workspace and wscount options must reference the same
2580           vector as before because data about the match so far is  left  in  them
2581           after a partial match. There is more discussion of this facility in the
2582           pcrepartial documentation.
2583    
2584       Successful returns from pcre_dfa_exec()
2585    
2586           When pcre_dfa_exec() succeeds, it may have matched more than  one  sub-
2587           string in the subject. Note, however, that all the matches from one run
2588           of the function start at the same point in  the  subject.  The  shorter
2589           matches  are all initial substrings of the longer matches. For example,
2590           if the pattern
2591    
2592             <.*>
2593    
2594           is matched against the string
2595    
2596             This is <something> <something else> <something further> no more
2597    
2598           the three matched strings are
2599    
2600             <something>
2601             <something> <something else>
2602             <something> <something else> <something further>
2603    
2604           On success, the yield of the function is a number  greater  than  zero,
2605           which  is  the  number of matched substrings. The substrings themselves
2606           are returned in ovector. Each string uses two elements;  the  first  is
2607           the  offset  to  the start, and the second is the offset to the end. In
2608           fact, all the strings have the same start  offset.  (Space  could  have
2609           been  saved by giving this only once, but it was decided to retain some
2610           compatibility with the way pcre_exec() returns data,  even  though  the
2611           meaning of the strings is different.)
2612    
2613           The strings are returned in reverse order of length; that is, the long-
2614           est matching string is given first. If there were too many  matches  to
2615           fit  into ovector, the yield of the function is zero, and the vector is
2616           filled with the longest matches.
2617    
2618       Error returns from pcre_dfa_exec()
2619    
2620           The pcre_dfa_exec() function returns a negative number when  it  fails.
2621           Many  of  the  errors  are  the  same as for pcre_exec(), and these are
2622           described above.  There are in addition the following errors  that  are
2623           specific to pcre_dfa_exec():
2624    
2625             PCRE_ERROR_DFA_UITEM      (-16)
2626    
2627           This  return is given if pcre_dfa_exec() encounters an item in the pat-
2628           tern that it does not support, for instance, the use of \C  or  a  back
2629           reference.
2630    
2631             PCRE_ERROR_DFA_UCOND      (-17)
2632    
2633           This  return  is  given  if pcre_dfa_exec() encounters a condition item
2634           that uses a back reference for the condition, or a test  for  recursion
2635           in a specific group. These are not supported.
2636    
2637             PCRE_ERROR_DFA_UMLIMIT    (-18)
2638    
2639           This  return  is given if pcre_dfa_exec() is called with an extra block
2640           that contains a setting of the match_limit field. This is not supported
2641           (it is meaningless).
2642    
2643             PCRE_ERROR_DFA_WSSIZE     (-19)
2644    
2645           This  return  is  given  if  pcre_dfa_exec()  runs  out of space in the
2646           workspace vector.
2647    
2648             PCRE_ERROR_DFA_RECURSE    (-20)
2649    
2650           When a recursive subpattern is processed, the matching  function  calls
2651           itself  recursively,  using  private vectors for ovector and workspace.
2652           This error is given if the output vector  is  not  large  enough.  This
2653           should be extremely rare, as a vector of size 1000 is used.
2654    
2655    
2656    SEE ALSO
2657    
2658           pcrebuild(3),  pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar-
2659           tial(3), pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2660    
2661    
2662    AUTHOR
2663    
2664           Philip Hazel
2665           University Computing Service
2666           Cambridge CB2 3QH, England.
2667    
2668    
2669    REVISION
2670    
2671           Last updated: 22 September 2009
2672           Copyright (c) 1997-2009 University of Cambridge.
2673    ------------------------------------------------------------------------------
2674    
2675    
2676    PCRECALLOUT(3)                                                  PCRECALLOUT(3)
2677    
 Last updated: 03 February 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
2678    
2679  NAME  NAME
2680       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2681    
2682    
2683  PCRE CALLOUTS  PCRE CALLOUTS
2684    
2685       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.  
2686    
2687           PCRE provides a feature called "callout", which is a means of temporar-
2688           ily passing control to the caller of PCRE  in  the  middle  of  pattern
2689           matching.  The  caller of PCRE provides an external function by putting
2690           its entry point in the global variable pcre_callout. By  default,  this
2691           variable contains NULL, which disables all calling out.
2692    
2693           Within  a  regular  expression,  (?C) indicates the points at which the
2694           external function is to be called.  Different  callout  points  can  be
2695           identified  by  putting  a number less than 256 after the letter C. The
2696           default value is zero.  For  example,  this  pattern  has  two  callout
2697           points:
2698    
2699             (?C1)abc(?C2)def
2700    
2701           If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is
2702           called, PCRE automatically  inserts  callouts,  all  with  number  255,
2703           before  each  item in the pattern. For example, if PCRE_AUTO_CALLOUT is
2704           used with the pattern
2705    
2706             A(\d{2}|--)
2707    
2708           it is processed as if it were
2709    
2710           (?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255)
2711    
2712           Notice that there is a callout before and after  each  parenthesis  and
2713           alternation  bar.  Automatic  callouts  can  be  used  for tracking the
2714           progress of pattern matching. The pcretest command has an  option  that
2715           sets  automatic callouts; when it is used, the output indicates how the
2716           pattern is matched. This is useful information when you are  trying  to
2717           optimize the performance of a particular pattern.
2718    
2719    
2720    MISSING CALLOUTS
2721    
2722           You  should  be  aware  that,  because of optimizations in the way PCRE
2723           matches patterns by default, callouts  sometimes  do  not  happen.  For
2724           example, if the pattern is
2725    
2726             ab(?C4)cd
2727    
2728           PCRE knows that any matching string must contain the letter "d". If the
2729           subject string is "abyz", the lack of "d" means that  matching  doesn't
2730           ever  start,  and  the  callout is never reached. However, with "abyd",
2731           though the result is still no match, the callout is obeyed.
2732    
2733           You can disable these optimizations by passing the  PCRE_NO_START_OPTI-
2734           MIZE  option  to  pcre_exec()  or  pcre_dfa_exec(). This slows down the
2735           matching process, but does ensure that callouts  such  as  the  example
2736           above are obeyed.
2737    
2738    
2739    THE CALLOUT INTERFACE
2740    
2741           During  matching, when PCRE reaches a callout point, the external func-
2742           tion defined by pcre_callout is called (if it is set). This applies  to
2743           both  the  pcre_exec()  and the pcre_dfa_exec() matching functions. The
2744           only argument to the callout function is a pointer  to  a  pcre_callout
2745           block. This structure contains the following fields:
2746    
2747             int          version;
2748             int          callout_number;
2749             int         *offset_vector;
2750             const char  *subject;
2751             int          subject_length;
2752             int          start_match;
2753             int          current_position;
2754             int          capture_top;
2755             int          capture_last;
2756             void        *callout_data;
2757             int          pattern_position;
2758             int          next_item_length;
2759    
2760           The  version  field  is an integer containing the version number of the
2761           block format. The initial version was 0; the current version is 1.  The
2762           version  number  will  change  again in future if additional fields are
2763           added, but the intention is never to remove any of the existing fields.
2764    
2765           The callout_number field contains the number of the  callout,  as  com-
2766           piled  into  the pattern (that is, the number after ?C for manual call-
2767           outs, and 255 for automatically generated callouts).
2768    
2769           The offset_vector field is a pointer to the vector of offsets that  was
2770           passed   by   the   caller  to  pcre_exec()  or  pcre_dfa_exec().  When
2771           pcre_exec() is used, the contents can be inspected in order to  extract
2772           substrings  that  have  been  matched  so  far,  in the same way as for
2773           extracting substrings after a match has completed. For  pcre_dfa_exec()
2774           this field is not useful.
2775    
2776           The subject and subject_length fields contain copies of the values that
2777           were passed to pcre_exec().
2778    
2779           The start_match field normally contains the offset within  the  subject
2780           at  which  the  current  match  attempt started. However, if the escape
2781           sequence \K has been encountered, this value is changed to reflect  the
2782           modified  starting  point.  If the pattern is not anchored, the callout
2783           function may be called several times from the same point in the pattern
2784           for different starting points in the subject.
2785    
2786           The  current_position  field  contains the offset within the subject of
2787           the current match pointer.
2788    
2789           When the pcre_exec() function is used, the capture_top  field  contains
2790           one  more than the number of the highest numbered captured substring so
2791           far. If no substrings have been captured, the value of  capture_top  is
2792           one.  This  is always the case when pcre_dfa_exec() is used, because it
2793           does not support captured substrings.
2794    
2795           The capture_last field contains the number of the  most  recently  cap-
2796           tured  substring. If no substrings have been captured, its value is -1.
2797           This is always the case when pcre_dfa_exec() is used.
2798