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NAME

       PCRE - Perl-compatible regular expressions


PCRE NATIVE API


       #include <pcre.h>

       pcre *pcre_compile(const char *pattern, int options,
            const char **errptr, int *erroffset,
            const unsigned char *tableptr);

       pcre *pcre_compile2(const char *pattern, int options,
            int *errorcodeptr,
            const char **errptr, int *erroffset,
            const unsigned char *tableptr);

       pcre_extra *pcre_study(const pcre *code, int options,
            const char **errptr);

       int pcre_exec(const pcre *code, const pcre_extra *extra,
            const char *subject, int length, int startoffset,
            int options, int *ovector, int ovecsize);

       int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
            const char *subject, int length, int startoffset,
            int options, int *ovector, int ovecsize,
            int *workspace, int wscount);

       int pcre_copy_named_substring(const pcre *code,
            const char *subject, int *ovector,
            int stringcount, const char *stringname,
            char *buffer, int buffersize);

       int pcre_copy_substring(const char *subject, int *ovector,
            int stringcount, int stringnumber, char *buffer,
            int buffersize);

       int pcre_get_named_substring(const pcre *code,
            const char *subject, int *ovector,
            int stringcount, const char *stringname,
            const char **stringptr);

       int pcre_get_stringnumber(const pcre *code,
            const char *name);

       int pcre_get_substring(const char *subject, int *ovector,
            int stringcount, int stringnumber,
            const char **stringptr);

       int pcre_get_substring_list(const char *subject,
            int *ovector, int stringcount, const char ***listptr);

       void pcre_free_substring(const char *stringptr);

       void pcre_free_substring_list(const char **stringptr);

       const unsigned char *pcre_maketables(void);

       int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
            int what, void *where);

       int pcre_info(const pcre *code, int *optptr, int *firstcharptr);

       int pcre_refcount(pcre *code, int adjust);

       int pcre_config(int what, void *where);

       char *pcre_version(void);

       void *(*pcre_malloc)(size_t);

       void (*pcre_free)(void *);

       void *(*pcre_stack_malloc)(size_t);

       void (*pcre_stack_free)(void *);

       int (*pcre_callout)(pcre_callout_block *);


PCRE API OVERVIEW


       PCRE has its own native API, which is described in this document. There
       is also a set of wrapper functions that correspond to the POSIX regular
       expression  API.  These  are  described in the pcreposix documentation.
       Both of these APIs define a set of C function calls. A C++  wrapper  is
       distributed with PCRE. It is documented in the pcrecpp page.

       The  native  API  C  function prototypes are defined in the header file
       pcre.h, and on Unix systems the library itself is called  libpcre.   It
       can normally be accessed by adding -lpcre to the command for linking an
       application  that  uses  PCRE.  The  header  file  defines  the  macros
       PCRE_MAJOR  and  PCRE_MINOR to contain the major and minor release num-
       bers for the library.  Applications can use these  to  include  support
       for different releases of PCRE.

       The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and
       pcre_exec() are used for compiling and matching regular expressions  in
       a  Perl-compatible  manner. A sample program that demonstrates the sim-
       plest way of using them is provided in the file  called  pcredemo.c  in
       the  source distribution. The pcresample documentation describes how to
       run it.

       A second matching function, pcre_dfa_exec(), which is not Perl-compati-
       ble,  is  also provided. This uses a different algorithm for the match-
       ing. This allows it to find all possible matches (at a given  point  in
       the  subject),  not  just  one. However, this algorithm does not return
       captured substrings. A description of the two matching  algorithms  and
       their  advantages  and disadvantages is given in the pcrematching docu-
       mentation.

       In addition to the main compiling and  matching  functions,  there  are
       convenience functions for extracting captured substrings from a subject
       string that is matched by pcre_exec(). They are:

         pcre_copy_substring()
         pcre_copy_named_substring()
         pcre_get_substring()
         pcre_get_named_substring()
         pcre_get_substring_list()
         pcre_get_stringnumber()

       pcre_free_substring() and pcre_free_substring_list() are also provided,
       to free the memory used for extracted strings.

       The  function  pcre_maketables()  is  used  to build a set of character
       tables  in  the  current  locale   for   passing   to   pcre_compile(),
       pcre_exec(),  or  pcre_dfa_exec(). This is an optional facility that is
       provided for specialist use.  Most  commonly,  no  special  tables  are
       passed,  in  which case internal tables that are generated when PCRE is
       built are used.

       The function pcre_fullinfo() is used to find out  information  about  a
       compiled  pattern; pcre_info() is an obsolete version that returns only
       some of the available information, but is retained for  backwards  com-
       patibility.   The function pcre_version() returns a pointer to a string
       containing the version of PCRE and its date of release.

       The function pcre_refcount() maintains a  reference  count  in  a  data
       block  containing  a compiled pattern. This is provided for the benefit
       of object-oriented applications.

       The global variables pcre_malloc and pcre_free  initially  contain  the
       entry  points  of  the  standard malloc() and free() functions, respec-
       tively. 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.

       The global variables pcre_stack_malloc  and  pcre_stack_free  are  also
       indirections  to  memory  management functions. These special functions
       are used only when PCRE is compiled to use  the  heap  for  remembering
       data, instead of recursive function calls, when running the pcre_exec()
       function. This is a non-standard way of building PCRE, for use in envi-
       ronments that have limited stacks. Because of the greater use of memory
       management, it runs more slowly.  Separate functions  are  provided  so
       that  special-purpose  external  code  can  be used for this case. When
       used, these functions are always called in a  stack-like  manner  (last
       obtained,  first freed), and always for memory blocks of the same size.

       The global variable pcre_callout initially contains NULL. It can be set
       by  the  caller  to  a "callout" function, which PCRE will then call at
       specified points during a matching operation. Details are given in  the
       pcrecallout documentation.


MULTITHREADING


       The  PCRE  functions  can be used in multi-threading applications, with
       the  proviso  that  the  memory  management  functions  pointed  to  by
       pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
       callout function pointed to by pcre_callout, are shared by all threads.

       The  compiled form of a regular expression is not altered during match-
       ing, so the same compiled pattern can safely be used by several threads
       at once.


SAVING PRECOMPILED PATTERNS FOR LATER USE


       The compiled form of a regular expression can be saved and re-used at a
       later time, possibly by a different program, and even on a  host  other
       than  the  one  on  which  it  was  compiled.  Details are given in the
       pcreprecompile documentation.


CHECKING BUILD-TIME OPTIONS


       int pcre_config(int what, void *where);

       The function pcre_config() makes it possible for a PCRE client to  dis-
       cover which optional features have been compiled into the PCRE library.
       The pcrebuild documentation has more details about these optional  fea-
       tures.

       The  first  argument  for pcre_config() is an integer, specifying which
       information is required; the second argument is a pointer to a variable
       into  which  the  information  is  placed. The following information is
       available:

         PCRE_CONFIG_UTF8

       The output is an integer that is set to one if UTF-8 support is  avail-
       able; otherwise it is set to zero.

         PCRE_CONFIG_UNICODE_PROPERTIES

       The  output  is  an  integer  that is set to one if support for Unicode
       character properties is available; otherwise it is set to zero.

         PCRE_CONFIG_NEWLINE

       The output is an integer that is set to the value of the code  that  is
       used  for the newline character. It is either linefeed (10) or carriage
       return (13), and should normally be the  standard  character  for  your
       operating system.

         PCRE_CONFIG_LINK_SIZE

       The  output  is  an  integer that contains the number of bytes used for
       internal linkage in compiled regular expressions. The value is 2, 3, or
       4.  Larger  values  allow larger regular expressions to be compiled, at
       the expense of slower matching. The default value of  2  is  sufficient
       for  all  but  the  most massive patterns, since it allows the compiled
       pattern to be up to 64K in size.

         PCRE_CONFIG_POSIX_MALLOC_THRESHOLD

       The output is an integer that contains the threshold  above  which  the
       POSIX  interface  uses malloc() for output vectors. Further details are
       given in the pcreposix documentation.

         PCRE_CONFIG_MATCH_LIMIT

       The output is an integer that gives the default limit for the number of
       internal  matching  function  calls in a pcre_exec() execution. Further
       details are given with pcre_exec() below.

         PCRE_CONFIG_STACKRECURSE

       The output is an integer that is set to one if internal recursion  when
       running pcre_exec() is implemented by recursive function calls that use
       the stack to remember their state. This is the usual way that  PCRE  is
       compiled. The output is zero if PCRE was compiled to use blocks of data
       on the  heap  instead  of  recursive  function  calls.  In  this  case,
       pcre_stack_malloc  and  pcre_stack_free  are  called  to  manage memory
       blocks on the heap, thus avoiding the use of the stack.


COMPILING A PATTERN


       pcre *pcre_compile(const char *pattern, int options,
            const char **errptr, int *erroffset,
            const unsigned char *tableptr);

       pcre *pcre_compile2(const char *pattern, int options,
            int *errorcodeptr,
            const char **errptr, int *erroffset,
            const unsigned char *tableptr);

       Either of the functions pcre_compile() or pcre_compile2() can be called
       to compile a pattern into an internal form. The only difference between
       the two interfaces is that pcre_compile2() has an additional  argument,
       errorcodeptr, via which a numerical error code can be returned.

       The pattern is a C string terminated by a binary zero, and is passed in
       the pattern argument. A pointer to a single block  of  memory  that  is
       obtained  via  pcre_malloc is returned. This contains the compiled code
       and related data. The pcre type is defined for the returned block; this
       is a typedef for a structure whose contents are not externally defined.
       It is up to the caller  to  free  the  memory  when  it  is  no  longer
       required.

       Although  the compiled code of a PCRE regex is relocatable, that is, it
       does not depend on memory location, the complete pcre data block is not
       fully  relocatable, because it may contain a copy of the tableptr argu-
       ment, which is an address (see below).

       The options argument contains independent bits that affect the compila-
       tion.  It  should  be  zero  if  no options are required. The available
       options are described below. Some of them, in  particular,  those  that
       are  compatible  with  Perl,  can also be set and unset from within the
       pattern (see the detailed description  in  the  pcrepattern  documenta-
       tion).  For  these options, the contents of the options argument speci-
       fies their initial settings at the start of compilation and  execution.
       The  PCRE_ANCHORED option can be set at the time of matching as well as
       at compile time.

       If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
       if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and
       sets the variable pointed to by errptr to point to a textual error mes-
       sage.  The  offset from the start of the pattern to the character where
       the error was discovered is  placed  in  the  variable  pointed  to  by
       erroffset,  which  must  not  be  NULL. If it is, an immediate error is
       given.

       If pcre_compile2() is used instead of pcre_compile(),  and  the  error-
       codeptr  argument is not NULL, a non-zero error code number is returned
       via this argument in the event of an error. This is in addition to  the
       textual error message. Error codes and messages are listed below.

       If  the  final  argument, tableptr, is NULL, PCRE uses a default set of
       character tables that are  built  when  PCRE  is  compiled,  using  the
       default  C  locale.  Otherwise, tableptr must be an address that is the
       result of a call to pcre_maketables(). This value is  stored  with  the
       compiled  pattern,  and used again by pcre_exec(), unless another table
       pointer is passed to it. For more discussion, see the section on locale
       support below.

       This  code  fragment  shows a typical straightforward call to pcre_com-
       pile():

         pcre *re;
         const char *error;
         int erroffset;
         re = pcre_compile(
           "^A.*Z",          /* the pattern */
           0,                /* default options */
           &error,           /* for error message */
           &erroffset,       /* for error offset */
           NULL);            /* use default character tables */

       The following names for option bits are defined in  the  pcre.h  header
       file:

         PCRE_ANCHORED

       If this bit is set, the pattern is forced to be "anchored", that is, it
       is constrained to match only at the first matching point in the  string
       that  is being searched (the "subject string"). This effect can also be
       achieved by appropriate constructs in the pattern itself, which is  the
       only way to do it in Perl.

         PCRE_AUTO_CALLOUT

       If this bit is set, pcre_compile() automatically inserts callout items,
       all with number 255, before each pattern item. For  discussion  of  the
       callout facility, see the pcrecallout documentation.

         PCRE_CASELESS

       If  this  bit is set, letters in the pattern match both upper and lower
       case letters. It is equivalent to Perl's  /i  option,  and  it  can  be
       changed  within a pattern by a (?i) option setting. In UTF-8 mode, PCRE
       always understands the concept of case for characters whose values  are
       less  than 128, so caseless matching is always possible. For characters
       with higher values, the concept of case is supported if  PCRE  is  com-
       piled  with Unicode property support, but not otherwise. If you want to
       use caseless matching for characters 128 and  above,  you  must  ensure
       that  PCRE  is  compiled  with Unicode property support as well as with
       UTF-8 support.

         PCRE_DOLLAR_ENDONLY

       If this bit is set, a dollar metacharacter in the pattern matches  only
       at  the  end  of the subject string. Without this option, a dollar also
       matches immediately before the final character if it is a newline  (but
       not  before  any  other  newlines).  The  PCRE_DOLLAR_ENDONLY option is
       ignored if PCRE_MULTILINE is set. There is no equivalent to this option
       in Perl, and no way to set it within a pattern.

         PCRE_DOTALL

       If this bit is set, a dot metacharater in the pattern matches all char-
       acters, including newlines. Without it,  newlines  are  excluded.  This
       option  is equivalent to Perl's /s option, and it can be changed within
       a pattern by a (?s) option setting.  A  negative  class  such  as  [^a]
       always  matches a newline character, independent of the setting of this
       option.

         PCRE_EXTENDED

       If this bit is set, whitespace  data  characters  in  the  pattern  are
       totally ignored except when escaped or inside a character class. White-
       space does not include the VT character (code 11). In addition, charac-
       ters between an unescaped # outside a character class and the next new-
       line character, inclusive, are also  ignored.  This  is  equivalent  to
       Perl's  /x  option,  and  it  can be changed within a pattern by a (?x)
       option setting.

       This option makes it possible to include  comments  inside  complicated
       patterns.   Note,  however,  that this applies only to data characters.
       Whitespace  characters  may  never  appear  within  special   character
       sequences  in  a  pattern,  for  example  within the sequence (?( which
       introduces a conditional subpattern.

         PCRE_EXTRA

       This option was invented in order to turn on  additional  functionality
       of  PCRE  that  is  incompatible with Perl, but it is currently of very
       little use. When set, any backslash in a pattern that is followed by  a
       letter  that  has  no  special  meaning causes an error, thus reserving
       these combinations for future expansion. By  default,  as  in  Perl,  a
       backslash  followed by a letter with no special meaning is treated as a
       literal. There are at present no  other  features  controlled  by  this
       option. It can also be set by a (?X) option setting within a pattern.

         PCRE_FIRSTLINE

       If  this  option  is  set,  an  unanchored pattern is required to match
       before or at the first newline character in the subject string,  though
       the matched text may continue over the newline.

         PCRE_MULTILINE

       By  default,  PCRE  treats the subject string as consisting of a single
       line of characters (even if it actually contains newlines). The  "start
       of  line"  metacharacter  (^)  matches only at the start of the string,
       while the "end of line" metacharacter ($) matches only at  the  end  of
       the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
       is set). This is the same as Perl.

       When PCRE_MULTILINE it is set, the "start of line" and  "end  of  line"
       constructs  match  immediately following or immediately before any new-
       line in the subject string, respectively, as well as at the very  start
       and  end. This is equivalent to Perl's /m option, and it can be changed
       within a pattern by a (?m) option setting. If there are no "\n" charac-
       ters  in  a  subject  string, or no occurrences of ^ or $ in a pattern,
       setting PCRE_MULTILINE has no effect.

         PCRE_NO_AUTO_CAPTURE

       If this option is set, it disables the use of numbered capturing paren-
       theses  in the pattern. Any opening parenthesis that is not followed by
       ? behaves as if it were followed by ?: but named parentheses can  still
       be  used  for  capturing  (and  they acquire numbers in the usual way).
       There is no equivalent of this option in Perl.

         PCRE_UNGREEDY

       This option inverts the "greediness" of the quantifiers  so  that  they
       are  not greedy by default, but become greedy if followed by "?". It is
       not compatible with Perl. It can also be set by a (?U)  option  setting
       within the pattern.

         PCRE_UTF8

       This  option  causes PCRE to regard both the pattern and the subject as
       strings of UTF-8 characters instead of single-byte  character  strings.
       However,  it is available only when PCRE is built to include UTF-8 sup-
       port. If not, the use of this option provokes an error. Details of  how
       this  option  changes the behaviour of PCRE are given in the section on
       UTF-8 support in the main pcre page.

         PCRE_NO_UTF8_CHECK

       When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
       automatically  checked. If an invalid UTF-8 sequence of bytes is found,
       pcre_compile() returns an error. If you already know that your  pattern
       is  valid, and you want to skip this check for performance reasons, you
       can set the PCRE_NO_UTF8_CHECK option. When it is set,  the  effect  of
       passing an invalid UTF-8 string as a pattern is undefined. It may cause
       your program to crash.  Note that this option can  also  be  passed  to
       pcre_exec()  and pcre_dfa_exec(), to suppress the UTF-8 validity check-
       ing of subject strings.


COMPILATION ERROR CODES


       The following table lists the error  codes  than  may  be  returned  by
       pcre_compile2(),  along with the error messages that may be returned by
       both compiling functions.

          0  no error
          1  \ at end of pattern
          2  \c at end of pattern
          3  unrecognized character follows \
          4  numbers out of order in {} quantifier
          5  number too big in {} quantifier
          6  missing terminating ] for character class
          7  invalid escape sequence in character class
          8  range out of order in character class
          9  nothing to repeat
         10  operand of unlimited repeat could match the empty string
         11  internal error: unexpected repeat
         12  unrecognized character after (?
         13  POSIX named classes are supported only within a class
         14  missing )
         15  reference to non-existent subpattern
         16  erroffset passed as NULL
         17  unknown option bit(s) set
         18  missing ) after comment
         19  parentheses nested too deeply
         20  regular expression too large
         21  failed to get memory
         22  unmatched parentheses
         23  internal error: code overflow
         24  unrecognized character after (?<
         25  lookbehind assertion is not fixed length
         26  malformed number after (?(
         27  conditional group contains more than two branches
         28  assertion expected after (?(
         29  (?R or (?digits must be followed by )
         30  unknown POSIX class name
         31  POSIX collating elements are not supported
         32  this version of PCRE is not compiled with PCRE_UTF8 support
         33  spare error
         34  character value in \x{...} sequence is too large
         35  invalid condition (?(0)
         36  \C not allowed in lookbehind assertion
         37  PCRE does not support \L, \l, \N, \U, or \u
         38  number after (?C is > 255
         39  closing ) for (?C expected
         40  recursive call could loop indefinitely
         41  unrecognized character after (?P
         42  syntax error after (?P
         43  two named groups have the same name
         44  invalid UTF-8 string
         45  support for \P, \p, and \X has not been compiled
         46  malformed \P or \p sequence
         47  unknown property name after \P or \p


STUDYING A PATTERN


       pcre_extra *pcre_study(const pcre *code, int options
            const char **errptr);

       If a compiled pattern is going to be used several times,  it  is  worth
       spending more time analyzing it in order to speed up the time taken for
       matching. The function pcre_study() takes a pointer to a compiled  pat-
       tern as its first argument. If studying the pattern produces additional
       information that will help speed up matching,  pcre_study()  returns  a
       pointer  to a pcre_extra block, in which the study_data field points to
       the results of the study.

       The  returned  value  from  pcre_study()  can  be  passed  directly  to
       pcre_exec().  However,  a  pcre_extra  block also contains other fields
       that can be set by the caller before the block  is  passed;  these  are
       described below in the section on matching a pattern.

       If  studying  the  pattern  does not produce any additional information
       pcre_study() returns NULL. In that circumstance, if the calling program
       wants  to  pass  any of the other fields to pcre_exec(), it must set up
       its own pcre_extra block.

       The second argument of pcre_study() contains option bits.  At  present,
       no options are defined, and this argument should always be zero.

       The  third argument for pcre_study() is a pointer for an error message.
       If studying succeeds (even if no data is  returned),  the  variable  it
       points  to  is set to NULL. Otherwise it points to a textual error mes-
       sage. You should therefore test the error pointer for NULL after  call-
       ing pcre_study(), to be sure that it has run successfully.

       This is a typical call to pcre_study():

         pcre_extra *pe;
         pe = pcre_study(
           re,             /* result of pcre_compile() */
           0,              /* no options exist */
           &error);        /* set to NULL or points to a message */

       At present, studying a pattern is useful only for non-anchored patterns
       that do not have a single fixed starting character. A bitmap of  possi-
       ble starting bytes is created.


LOCALE SUPPORT


       PCRE  handles  caseless matching, and determines whether characters are
       letters digits, or whatever, by reference to a set of  tables,  indexed
       by  character  value.  When running in UTF-8 mode, this applies only to
       characters with codes less than 128. Higher-valued  codes  never  match
       escapes  such  as  \w or \d, but can be tested with \p if PCRE is built
       with Unicode character property support.

       An internal set of tables is created in the default C locale when  PCRE
       is  built.  This  is  used when the final argument of pcre_compile() is
       NULL, and is sufficient for many applications. An  alternative  set  of
       tables  can,  however, be supplied. These may be created in a different
       locale from the default. As more and more applications change to  using
       Unicode, the need for this locale support is expected to die away.

       External  tables  are  built by calling the pcre_maketables() function,
       which has no arguments, in the relevant locale. The result can then  be
       passed  to  pcre_compile()  or  pcre_exec()  as often as necessary. For
       example, to build and use tables that are appropriate  for  the  French
       locale  (where  accented  characters  with  values greater than 128 are
       treated as letters), the following code could be used:

         setlocale(LC_CTYPE, "fr_FR");
         tables = pcre_maketables();
         re = pcre_compile(..., tables);

       When pcre_maketables() runs, the tables are built  in  memory  that  is
       obtained  via  pcre_malloc. It is the caller's responsibility to ensure
       that the memory containing the tables remains available for as long  as
       it is needed.

       The pointer that is passed to pcre_compile() is saved with the compiled
       pattern, and the same tables are used via this pointer by  pcre_study()
       and normally also by pcre_exec(). Thus, by default, for any single pat-
       tern, compilation, studying and matching all happen in the same locale,
       but different patterns can be compiled in different locales.

       It  is  possible to pass a table pointer or NULL (indicating the use of
       the internal tables) to pcre_exec(). Although  not  intended  for  this
       purpose,  this facility could be used to match a pattern in a different
       locale from the one in which it was compiled. Passing table pointers at
       run time is discussed below in the section on matching a pattern.


INFORMATION ABOUT A PATTERN


       int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
            int what, void *where);

       The  pcre_fullinfo() function returns information about a compiled pat-
       tern. It replaces the obsolete pcre_info() function, which is neverthe-
       less retained for backwards compability (and is documented below).

       The  first  argument  for  pcre_fullinfo() is a pointer to the compiled
       pattern. The second argument is the result of pcre_study(), or NULL  if
       the  pattern  was not studied. The third argument specifies which piece
       of information is required, and the fourth argument is a pointer  to  a
       variable  to  receive  the  data. The yield of the function is zero for
       success, or one of the following negative numbers:

         PCRE_ERROR_NULL       the argument code was NULL
                               the argument where was NULL
         PCRE_ERROR_BADMAGIC   the "magic number" was not found
         PCRE_ERROR_BADOPTION  the value of what was invalid

       The "magic number" is placed at the start of each compiled  pattern  as
       an  simple check against passing an arbitrary memory pointer. Here is a
       typical call of pcre_fullinfo(), to obtain the length of  the  compiled
       pattern:

         int rc;
         unsigned long int length;
         rc = pcre_fullinfo(
           re,               /* result of pcre_compile() */
           pe,               /* result of pcre_study(), or NULL */
           PCRE_INFO_SIZE,   /* what is required */
           &length);         /* where to put the data */

       The  possible  values for the third argument are defined in pcre.h, and
       are as follows:

         PCRE_INFO_BACKREFMAX

       Return the number of the highest back reference  in  the  pattern.  The
       fourth  argument  should  point to an int variable. Zero is returned if
       there are no back references.

         PCRE_INFO_CAPTURECOUNT

       Return the number of capturing subpatterns in the pattern.  The  fourth
       argument should point to an int variable.

         PCRE_INFO_DEFAULT_TABLES

       Return  a pointer to the internal default character tables within PCRE.
       The fourth argument should point to an unsigned char *  variable.  This
       information call is provided for internal use by the pcre_study() func-
       tion. External callers can cause PCRE to use  its  internal  tables  by
       passing a NULL table pointer.

         PCRE_INFO_FIRSTBYTE

       Return  information  about  the first byte of any matched string, for a
       non-anchored   pattern.   (This    option    used    to    be    called
       PCRE_INFO_FIRSTCHAR;  the  old  name  is still recognized for backwards
       compatibility.)

       If there is a fixed first byte, for example, from  a  pattern  such  as
       (cat|cow|coyote),  it  is  returned in the integer pointed to by where.
       Otherwise, if either

       (a) the pattern was compiled with the PCRE_MULTILINE option, and  every
       branch starts with "^", or

       (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
       set (if it were set, the pattern would be anchored),

       -1 is returned, indicating that the pattern matches only at  the  start
       of  a  subject string or after any newline within the string. Otherwise
       -2 is returned. For anchored patterns, -2 is returned.

         PCRE_INFO_FIRSTTABLE

       If the pattern was studied, and this resulted in the construction of  a
       256-bit table indicating a fixed set of bytes for the first byte in any
       matching string, a pointer to the table is returned. Otherwise NULL  is
       returned.  The fourth argument should point to an unsigned char * vari-
       able.

         PCRE_INFO_LASTLITERAL

       Return the value of the rightmost literal byte that must exist  in  any
       matched  string,  other  than  at  its  start,  if such a byte has been
       recorded. The fourth argument should point to an int variable. If there
       is  no such byte, -1 is returned. For anchored patterns, a last literal
       byte is recorded only if it follows something of variable  length.  For
       example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
       /^a\dz\d/ the returned value is -1.

         PCRE_INFO_NAMECOUNT
         PCRE_INFO_NAMEENTRYSIZE
         PCRE_INFO_NAMETABLE

       PCRE supports the use of named as well as numbered capturing  parenthe-
       ses.  The names are just an additional way of identifying the parenthe-
       ses,  which  still  acquire  numbers.  A  convenience  function  called
       pcre_get_named_substring()  is  provided  for  extracting an individual
       captured substring by name. It is also possible  to  extract  the  data
       directly,  by  first converting the name to a number in order to access
       the correct pointers in the output vector (described  with  pcre_exec()
       below).  To  do the conversion, you need to use the name-to-number map,
       which is described by these three values.

       The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
       gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
       of each entry; both of these  return  an  int  value.  The  entry  size
       depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns
       a pointer to the first entry of the table  (a  pointer  to  char).  The
       first two bytes of each entry are the number of the capturing parenthe-
       sis, most significant byte first. The rest of the entry is  the  corre-
       sponding  name,  zero  terminated. The names are in alphabetical order.
       For example, consider the following pattern  (assume  PCRE_EXTENDED  is
       set, so white space - including newlines - is ignored):

         (?P<date> (?P<year>(\d\d)?\d\d) -
         (?P<month>\d\d) - (?P<day>\d\d) )

       There  are  four  named subpatterns, so the table has four entries, and
       each entry in the table is eight bytes long. The table is  as  follows,
       with non-printing bytes shows in hexadecimal, and undefined bytes shown
       as ??:

         00 01 d  a  t  e  00 ??
         00 05 d  a  y  00 ?? ??
         00 04 m  o  n  t  h  00
         00 02 y  e  a  r  00 ??

       When writing code to extract data  from  named  subpatterns  using  the
       name-to-number map, remember that the length of each entry is likely to
       be different for each compiled pattern.

         PCRE_INFO_OPTIONS

       Return a copy of the options with which the pattern was  compiled.  The
       fourth  argument  should  point to an unsigned long int variable. These
       option bits are those specified in the call to pcre_compile(), modified
       by any top-level option settings within the pattern itself.

       A  pattern  is  automatically  anchored by PCRE if all of its top-level
       alternatives begin with one of the following:

         ^     unless PCRE_MULTILINE is set
         \A    always
         \G    always
         .*    if PCRE_DOTALL is set and there are no back
                 references to the subpattern in which .* appears

       For such patterns, the PCRE_ANCHORED bit is set in the options returned
       by pcre_fullinfo().

         PCRE_INFO_SIZE

       Return  the  size  of the compiled pattern, that is, the value that was
       passed as the argument to pcre_malloc() when PCRE was getting memory in
       which to place the compiled data. The fourth argument should point to a
       size_t variable.

         PCRE_INFO_STUDYSIZE

       Return the size of the data block pointed to by the study_data field in
       a  pcre_extra  block.  That  is,  it  is  the  value that was passed to
       pcre_malloc() when PCRE was getting memory into which to place the data
       created  by  pcre_study(). The fourth argument should point to a size_t
       variable.


OBSOLETE INFO FUNCTION


       int pcre_info(const pcre *code, int *optptr, int *firstcharptr);

       The pcre_info() function is now obsolete because its interface  is  too
       restrictive  to return all the available data about a compiled pattern.
       New  programs  should  use  pcre_fullinfo()  instead.  The   yield   of
       pcre_info()  is the number of capturing subpatterns, or one of the fol-
       lowing negative numbers:

         PCRE_ERROR_NULL       the argument code was NULL
         PCRE_ERROR_BADMAGIC   the "magic number" was not found

       If the optptr argument is not NULL, a copy of the  options  with  which
       the  pattern  was  compiled  is placed in the integer it points to (see
       PCRE_INFO_OPTIONS above).

       If the pattern is not anchored and the  firstcharptr  argument  is  not
       NULL,  it is used to pass back information about the first character of
       any matched string (see PCRE_INFO_FIRSTBYTE above).


REFERENCE COUNTS


       int pcre_refcount(pcre *code, int adjust);

       The pcre_refcount() function is used to maintain a reference  count  in
       the data block that contains a compiled pattern. It is provided for the
       benefit of applications that  operate  in  an  object-oriented  manner,
       where different parts of the application may be using the same compiled
       pattern, but you want to free the block when they are all done.

       When a pattern is compiled, the reference count field is initialized to
       zero.   It is changed only by calling this function, whose action is to
       add the adjust value (which may be positive or  negative)  to  it.  The
       yield of the function is the new value. However, the value of the count
       is constrained to lie between 0 and 65535, inclusive. If the new  value
       is outside these limits, it is forced to the appropriate limit value.

       Except  when it is zero, the reference count is not correctly preserved
       if a pattern is compiled on one host and then  transferred  to  a  host
       whose byte-order is different. (This seems a highly unlikely scenario.)


MATCHING A PATTERN: THE TRADITIONAL FUNCTION


       int pcre_exec(const pcre *code, const pcre_extra *extra,
            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
       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.  This  function is the main matching facility of the library,
       and it operates in a Perl-like manner. For specialist use there is also
       an  alternative matching function, which is described below in the sec-
       tion about the pcre_dfa_exec() function.

       In most applications, the pattern will have been compiled (and  option-
       ally  studied)  in the same process that calls pcre_exec(). However, it
       is possible to save compiled patterns and study data, and then use them
       later  in  different processes, possibly even on different hosts. For a
       discussion about this, see the pcreprecompile documentation.

       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 of integers for substring information */
           30);            /* number of elements (NOT size in bytes) */

   Extra data for pcre_exec()

       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  addi-
       tional  information in it. The fields in a pcre_extra block are as fol-
       lows:

         unsigned long int flags;
         void *study_data;
         unsigned long int match_limit;
         void *callout_data;
         const unsigned char *tables;

       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
         PCRE_EXTRA_TABLES

       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 may
       add to the block by setting the other fields  and  their  corresponding
       flag bits.

       The match_limit field provides a means of preventing PCRE from using up
       a vast amount of resources when running patterns 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 repeat-
       edly (sometimes recursively). The limit is imposed  on  the  number  of
       times  this  function is called during 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 "callout" fea-
       ture, which is described in the pcrecallout documentation.

       The tables field  is  used  to  pass  a  character  tables  pointer  to
       pcre_exec();  this overrides the value that is stored with the compiled
       pattern. A non-NULL value is stored with the compiled pattern  only  if
       custom  tables  were  supplied to pcre_compile() via its tableptr argu-
       ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
       PCRE's  internal  tables  to be used. This facility is helpful when re-
       using patterns that have been saved after compiling  with  an  external
       set  of  tables,  because  the  external tables might be at a different
       address when pcre_exec() is called. See the  pcreprecompile  documenta-
       tion for a discussion of saving compiled patterns for later use.

   Option bits for pcre_exec()

       The  unused  bits of the options argument for pcre_exec() must be zero.
       The  only  bits  that  may  be  set  are  PCRE_ANCHORED,   PCRE_NOTBOL,
       PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK and PCRE_PARTIAL.

         PCRE_ANCHORED

       The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first
       matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or
       turned  out to be anchored by virtue of its contents, it cannot be made
       unachored at matching time.

         PCRE_NOTBOL

       This option specifies that first character of the subject 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. This option affects only the behav-
       iour of the circumflex metacharacter. It does not affect \A.

         PCRE_NOTEOL

       This option specifies that the end of the subject string is not the end
       of  a line, so the dollar metacharacter should not match it nor (except
       in multiline mode) a newline immediately before it. Setting this  with-
       out PCRE_MULTILINE (at compile time) causes dollar never to match. This
       option affects only the behaviour of the dollar metacharacter. It  does
       not affect \Z or \z.

         PCRE_NOTEMPTY

       An empty string is not considered to be a valid match if this option is
       set. If there are alternatives in the pattern, 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 occur-
       rences of "a" or "b".

       Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-
       cial 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 and PCRE_ANCHORED, and then
       if that fails by advancing the starting offset (see below)  and  trying
       an ordinary match again. There is some code that demonstrates how to do
       this in the pcredemo.c sample program.

         PCRE_NO_UTF8_CHECK

       When PCRE_UTF8 is set at compile time, the validity of the subject as a
       UTF-8  string is automatically checked when pcre_exec() is subsequently
       called.  The value of startoffset is also checked  to  ensure  that  it
       points  to the start of a UTF-8 character. If an invalid UTF-8 sequence
       of bytes is found, pcre_exec() returns the error PCRE_ERROR_BADUTF8. If
       startoffset  contains  an  invalid  value, PCRE_ERROR_BADUTF8_OFFSET is
       returned.

       If you already know that your subject is valid, and you  want  to  skip
       these    checks    for   performance   reasons,   you   can   set   the
       PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to
       do  this  for the second and subsequent calls to pcre_exec() if you are
       making repeated calls to find all  the  matches  in  a  single  subject
       string.  However,  you  should  be  sure  that the value of startoffset
       points to the start of a UTF-8 character.  When  PCRE_NO_UTF8_CHECK  is
       set,  the  effect of passing an invalid UTF-8 string as a subject, or a
       value of startoffset that does not point to the start of a UTF-8  char-
       acter, is undefined. Your program may crash.

         PCRE_PARTIAL

       This  option  turns  on  the  partial  matching feature. If the subject
       string fails to match the pattern, but at some point during the  match-
       ing  process  the  end of the subject was reached (that is, the subject
       partially matches the pattern and the failure to  match  occurred  only
       because  there were not enough subject characters), pcre_exec() returns
       PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is
       used,  there  are restrictions on what may appear in the pattern. These
       are discussed in the pcrepartial documentation.

   The string to be matched by pcre_exec()

       The subject string is passed to pcre_exec() as a pointer in subject,  a
       length  in  length, and a starting byte offset in startoffset. In UTF-8
       mode, the byte offset must point to the start  of  a  UTF-8  character.
       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.

       A  non-zero  starting offset is useful when searching for another match
       in the same subject by calling pcre_exec() again after a previous  suc-
       cess.   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 occur-
       rence  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 made. This can only succeed
       if the pattern does not require the match to be at  the  start  of  the
       subject.

   How pcre_exec() returns captured substrings

       In  general, a pattern matches a certain portion of the subject, 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 sub-
       string. PCRE supports several other kinds of  parenthesized  subpattern
       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, which must be a non-negative number.
       Note: this argument is NOT the size of ovector in bytes.

       The first two-thirds of the vector is used to pass back  captured  sub-
       strings,  each  substring using a pair of integers. The remaining third
       of the vector is used as workspace by pcre_exec() while  matching  cap-
       turing  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  is 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 sub-
       string,  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  subpat-
       tern,  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 is returned.

       If  the vector is too small to hold all the captured substring offsets,
       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 off-
       sets 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 is not 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  capturing  sub-
       patterns 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.

   Return values from pcre_exec()

       If  pcre_exec()  fails, it returns a negative number. The following 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 compiled code,
       to catch the case when it is passed a junk pointer and to detect when a
       pattern that was compiled in an environment of one endianness is run in
       an environment with the other endianness. This is the error  that  PCRE
       gives when the magic number is not present.

         PCRE_ERROR_UNKNOWN_NODE   (-5)

       While running the pattern match, an unknown item was encountered 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 automatically 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()  functions  (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.

         PCRE_ERROR_BADUTF8        (-10)

       A  string  that contains an invalid UTF-8 byte sequence was passed as a
       subject.

         PCRE_ERROR_BADUTF8_OFFSET (-11)

       The UTF-8 byte sequence that was passed as a subject was valid, but the
       value  of startoffset did not point to the beginning of a UTF-8 charac-
       ter.

         PCRE_ERROR_PARTIAL        (-12)

       The subject string did not match, but it did match partially.  See  the
       pcrepartial documentation for details of partial matching.

         PCRE_ERROR_BADPARTIAL     (-13)

       The  PCRE_PARTIAL  option  was  used with a compiled pattern containing
       items that are not supported for partial matching. See the  pcrepartial
       documentation for details of partial matching.

         PCRE_ERROR_INTERNAL       (-14)

       An  unexpected  internal error has occurred. This error could be caused
       by a bug in PCRE or by overwriting of the compiled pattern.

         PCRE_ERROR_BADCOUNT       (-15)

       This error is given if the value of the ovecsize argument is  negative.


EXTRACTING CAPTURED SUBSTRINGS BY NUMBER


       int pcre_copy_substring(const char *subject, int *ovector,
            int stringcount, int stringnumber, char *buffer,
            int buffersize);

       int pcre_get_substring(const char *subject, int *ovector,
            int stringcount, int stringnumber,
            const char **stringptr);

       int pcre_get_substring_list(const char *subject,
            int *ovector, int stringcount, const char ***listptr);

       Captured  substrings  can  be  accessed  directly  by using the offsets
       returned by pcre_exec() in  ovector.  For  convenience,  the  functions
       pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
       string_list() are provided for extracting captured substrings  as  new,
       separate,  zero-terminated strings. These functions identify substrings
       by number. The next section describes functions  for  extracting  named
       substrings.  A  substring  that  contains  a  binary  zero is correctly
       extracted and has a further zero added on the end, but  the  result  is
       not, of course, a C string.

       The  first  three  arguments  are the same for all three of these func-
       tions: subject is the subject string that has  just  been  successfully
       matched, ovector is a pointer to the vector of integer offsets that was
       passed to pcre_exec(), and stringcount is the number of substrings that
       were  captured  by  the match, including the substring that matched the
       entire regular expression. This is the value returned by pcre_exec() if
       it  is greater than zero. If pcre_exec() returned zero, indicating that
       it ran out of space in ovector, the value passed as stringcount  should
       be the number of elements in the vector divided by three.

       The  functions pcre_copy_substring() and pcre_get_substring() extract a
       single substring, whose number is given as  stringnumber.  A  value  of
       zero  extracts  the  substring that matched the entire pattern, whereas
       higher values  extract  the  captured  substrings.  For  pcre_copy_sub-
       string(),  the  string  is  placed  in buffer, whose length is given by
       buffersize, while for pcre_get_substring() a new  block  of  memory  is
       obtained  via  pcre_malloc,  and its address is returned via stringptr.
       The yield of the function is the length of the  string,  not  including
       the terminating zero, or one of

         PCRE_ERROR_NOMEMORY       (-6)

       The  buffer  was too small for pcre_copy_substring(), or the attempt to
       get memory failed for pcre_get_substring().

         PCRE_ERROR_NOSUBSTRING    (-7)

       There is no substring whose number is stringnumber.

       The pcre_get_substring_list()  function  extracts  all  available  sub-
       strings  and  builds  a list of pointers to them. All this is done in a
       single block of memory that is obtained via pcre_malloc. The address of
       the  memory  block  is returned via listptr, which is also the start of
       the list of string pointers. The end of the list is marked  by  a  NULL
       pointer. The yield of the function is zero if all went well, or

         PCRE_ERROR_NOMEMORY       (-6)

       if the attempt to get the memory block failed.

       When  any of these functions encounter a substring that is unset, which
       can happen when capturing subpattern number n+1 matches  some  part  of
       the  subject, but subpattern n has not been used at all, they return an
       empty string. This can be distinguished from a genuine zero-length sub-
       string  by inspecting the appropriate offset in ovector, which is nega-
       tive for unset substrings.

       The two convenience functions pcre_free_substring() and  pcre_free_sub-
       string_list()  can  be  used  to free the memory returned by a previous
       call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
       tively.  They  do  nothing  more  than  call the function pointed to by
       pcre_free, which of course could be called directly from a  C  program.
       However,  PCRE is used in some situations where it is linked via a spe-
       cial  interface  to  another  programming  language  which  cannot  use
       pcre_free  directly;  it is for these cases that the functions are pro-
       vided.


EXTRACTING CAPTURED SUBSTRINGS BY NAME


       int pcre_get_stringnumber(const pcre *code,
            const char *name);

       int pcre_copy_named_substring(const pcre *code,
            const char *subject, int *ovector,
            int stringcount, const char *stringname,
            char *buffer, int buffersize);

       int pcre_get_named_substring(const pcre *code,
            const char *subject, int *ovector,
            int stringcount, const char *stringname,
            const char **stringptr);

       To extract a substring by name, you first have to find associated  num-
       ber.  For example, for this pattern

         (a+)b(?P<xxx>\d+)...

       the number of the subpattern called "xxx" is 2. You can find the number
       from the name by calling pcre_get_stringnumber(). The first argument is
       the  compiled  pattern,  and  the  second is the name. The yield of the
       function is the subpattern number, or  PCRE_ERROR_NOSUBSTRING  (-7)  if
       there is no subpattern of that name.

       Given the number, you can extract the substring directly, or use one of
       the functions described in the previous section. For convenience, there
       are also two functions that do the whole job.

       Most    of    the    arguments   of   pcre_copy_named_substring()   and
       pcre_get_named_substring() are the same  as  those  for  the  similarly
       named  functions  that extract by number. As these are described in the
       previous section, they are not re-described here. There  are  just  two
       differences:

       First,  instead  of a substring number, a substring name is given. Sec-
       ond, there is an extra argument, given at the start, which is a pointer
       to  the compiled pattern. This is needed in order to gain access to the
       name-to-number translation table.

       These functions call pcre_get_stringnumber(), and if it succeeds,  they
       then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-
       ate.


FINDING ALL POSSIBLE MATCHES


       The traditional matching function uses a  similar  algorithm  to  Perl,
       which stops when it finds the first match, starting at a given point in
       the subject. If you want to find all possible matches, or  the  longest
       possible  match,  consider using the alternative matching function (see
       below) instead. If you cannot use the alternative function,  but  still
       need  to  find all possible matches, you can kludge it up by making use
       of the callout facility, which is described in the pcrecallout documen-
       tation.

       What you have to do is to insert a callout right at the end of the pat-
       tern.  When your callout function is called, extract and save the  cur-
       rent  matched  substring.  Then  return  1, which forces pcre_exec() to
       backtrack and try other alternatives. Ultimately, when it runs  out  of
       matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.


MATCHING A PATTERN: THE ALTERNATIVE FUNCTION


       int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
            const char *subject, int length, int startoffset,
            int options, int *ovector, int ovecsize,
            int *workspace, int wscount);

       The  function  pcre_dfa_exec()  is  called  to  match  a subject string
       against a compiled pattern, using a "DFA" matching algorithm. This  has
       different  characteristics to the normal algorithm, and is not compati-
       ble with Perl. Some of the features of PCRE patterns are not supported.
       Nevertheless, there are times when this kind of matching can be useful.
       For a discussion of the two matching algorithms, see  the  pcrematching
       documentation.

       The  arguments  for  the  pcre_dfa_exec()  function are the same as for
       pcre_exec(), plus two extras. The ovector argument is used in a differ-
       ent  way,  and  this is described below. The other common arguments are
       used in the same way as for pcre_exec(), so their  description  is  not
       repeated here.

       The  two  additional  arguments provide workspace for the function. The
       workspace vector should contain at least 20 elements. It  is  used  for
       keeping  track  of  multiple  paths  through  the  pattern  tree.  More
       workspace will be needed for patterns and subjects where  there  are  a
       lot of possible matches.

       Here is an example of a simple call to pcre_exec():

         int rc;
         int ovector[10];
         int wspace[20];
         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 of integers for substring information */
           10,             /* number of elements (NOT size in bytes) */
           wspace,         /* working space vector */
           20);            /* number of elements (NOT size in bytes) */

   Option bits for pcre_dfa_exec()

       The  unused  bits  of  the options argument for pcre_dfa_exec() must be
       zero. The only bits that may be  set  are  PCRE_ANCHORED,  PCRE_NOTBOL,
       PCRE_NOTEOL,     PCRE_NOTEMPTY,    PCRE_NO_UTF8_CHECK,    PCRE_PARTIAL,
       PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All  but  the  last  three  of
       these  are  the  same  as  for pcre_exec(), so their description is not
       repeated here.

         PCRE_PARTIAL

       This has the same general effect as it does for  pcre_exec(),  but  the
       details   are   slightly   different.  When  PCRE_PARTIAL  is  set  for
       pcre_dfa_exec(), the return code PCRE_ERROR_NOMATCH is  converted  into
       PCRE_ERROR_PARTIAL  if  the  end  of the subject is reached, there have
       been no complete matches, but there is still at least one matching pos-
       sibility.  The portion of the string that provided the partial match is
       set as the first matching string.

         PCRE_DFA_SHORTEST

       Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to
       stop  as  soon  as  it  has found one match. Because of the way the DFA
       algorithm works, this is necessarily the shortest possible match at the
       first possible matching point in the subject string.

         PCRE_DFA_RESTART

       When  pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option, and
       returns a partial match, it is possible to call it  again,  with  addi-
       tional  subject  characters,  and have it continue with the same match.
       The PCRE_DFA_RESTART option requests this action; when it is  set,  the
       workspace  and wscount options must reference the same vector as before
       because data about the match so far is left in  them  after  a  partial
       match.  There  is  more  discussion of this facility in the pcrepartial
       documentation.

   Successful returns from pcre_dfa_exec()

       When pcre_dfa_exec() succeeds, it may have matched more than  one  sub-
       string in the subject. Note, however, that all the matches from one run
       of the function start at the same point in  the  subject.  The  shorter
       matches  are all initial substrings of the longer matches. For example,
       if the pattern

         <.*>

       is matched against the string

         This is <something> <something else> <something further> no more

       the three matched strings are

         <something>
         <something> <something else>
         <something> <something else> <something further>

       On success, the yield of the function is a number  greater  than  zero,
       which  is  the  number of matched substrings. The substrings themselves
       are returned in ovector. Each string uses two elements;  the  first  is
       the  offset  to the start, and the second is the offset to the end. All
       the strings have the same start offset. (Space could have been saved by
       giving  this only once, but it was decided to retain some compatibility
       with the way pcre_exec() returns data, even though the meaning  of  the
       strings is different.)

       The strings are returned in reverse order of length; that is, the long-
       est matching string is given first. If there were too many  matches  to
       fit  into ovector, the yield of the function is zero, and the vector is
       filled with the longest matches.

   Error returns from pcre_dfa_exec()

       The pcre_dfa_exec() function returns a negative number when  it  fails.
       Many  of  the  errors  are  the  same as for pcre_exec(), and these are
       described above.  There are in addition the following errors  that  are
       specific to pcre_dfa_exec():

         PCRE_ERROR_DFA_UITEM      (-16)

       This  return is given if pcre_dfa_exec() encounters an item in the pat-
       tern that it does not support, for instance, the use of \C  or  a  back
       reference.

         PCRE_ERROR_DFA_UCOND      (-17)

       This  return is given if pcre_dfa_exec() encounters a condition item in
       a pattern that uses a back reference for the  condition.  This  is  not
       supported.

         PCRE_ERROR_DFA_UMLIMIT    (-18)

       This  return  is given if pcre_dfa_exec() is called with an extra block
       that contains a setting of the match_limit field. This is not supported
       (it is meaningless).

         PCRE_ERROR_DFA_WSSIZE     (-19)

       This  return  is  given  if  pcre_dfa_exec()  runs  out of space in the
       workspace vector.

         PCRE_ERROR_DFA_RECURSE    (-20)

       When a recursive subpattern is processed, the matching  function  calls
       itself  recursively,  using  private vectors for ovector and workspace.
       This error is given if the output vector  is  not  large  enough.  This
       should be extremely rare, as a vector of size 1000 is used.

Last updated: 16 May 2005
Copyright (c) 1997-2005 University of Cambridge.

                                                                    PCREAPI(3)

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