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PCREAPI(3)                           Library Functions Manual                          PCREAPI(3)



NAME
       PCRE - Perl-compatible regular expressions

       #include <pcre.h>

PCRE NATIVE API BASIC FUNCTIONS

       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);

       void pcre_free_study(pcre_extra *extra);

       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);

PCRE NATIVE API STRING EXTRACTION FUNCTIONS

       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_stringtable_entries(const pcre *code,
            const char *name, char **first, char **last);

       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);

PCRE NATIVE API AUXILIARY FUNCTIONS

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

       pcre_jit_stack *pcre_jit_stack_alloc(int startsize, int maxsize);

       void pcre_jit_stack_free(pcre_jit_stack *stack);

       void pcre_assign_jit_stack(pcre_extra *extra,
            pcre_jit_callback callback, void *data);

       const unsigned char *pcre_maketables(void);

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

       int pcre_refcount(pcre *code, int adjust);

       int pcre_config(int what, void *where);

       const char *pcre_version(void);

       int pcre_pattern_to_host_byte_order(pcre *code,
            pcre_extra *extra, const unsigned char *tables);

PCRE NATIVE API INDIRECTED FUNCTIONS

       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 8-BIT, 16-BIT, AND 32-BIT LIBRARIES

       As  well  as  support for 8-bit character strings, PCRE also supports 16-bit strings (from
       release 8.30) and  32-bit  strings  (from  release  8.32),  by  means  of  two  additional
       libraries.  They  can  be built as well as, or instead of, the 8-bit library. To avoid too
       much complication, this document describes the 8-bit versions of the functions, with  only
       occasional references to the 16-bit and 32-bit libraries.

       The  16-bit and 32-bit functions operate in the same way as their 8-bit counterparts; they
       just use different data types for their arguments and results, and their names start  with
       pcre16_ or pcre32_ instead of pcre_. For every option that has UTF8 in its name (for exam-
       ple, PCRE_UTF8), there are corresponding 16-bit and 32-bit names  with  UTF8  replaced  by
       UTF16  or  UTF32,  respectively.  This  facility  is in fact just cosmetic; the 16-bit and
       32-bit option names define the same bit values.

       References to bytes and UTF-8 in this document should be read as references to 16-bit data
       quantities  and UTF-16 when using the 16-bit library, or 32-bit data quantities and UTF-32
       when using the 32-bit library, unless specified otherwise. More details  of  the  specific
       differences for the 16-bit and 32-bit libraries are given in the pcre16 and pcre32 pages.

PCRE API OVERVIEW

       PCRE  has  its  own  native  API, which is described in this document. There are also some
       wrapper functions (for the 8-bit library  only)  that  correspond  to  the  POSIX  regular
       expression  API,  but they do not give access to all the functionality. They are described
       in the pcreposix documentation. Both of these APIs define a set of C function calls. A C++
       wrapper (again for the 8-bit library only) is also 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-
       like  systems the (8-bit) 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.

       In  a Windows environment, if you want to statically link an application program against a
       non-dll pcre.a file, you must define PCRE_STATIC before  including  pcre.h  or  pcrecpp.h,
       because  otherwise  the  pcre_malloc() and pcre_free() exported functions will be declared
       __declspec(dllimport), with unwanted results.

       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 simplest way of using them is provided in the file called pcredemo.c
       in  the PCRE source distribution. A listing of this program is given in the pcredemo docu-
       mentation, and the pcresample documentation describes how to compile and run it.

       Just-in-time compiler support is an optional feature of PCRE that can be built  in  appro-
       priate  hardware  environments. It greatly speeds up the matching performance of many pat-
       terns. Simple programs can easily request that it be used  if  available,  by  setting  an
       option  that  is  ignored when it is not relevant. More complicated programs might need to
       make   use   of   the   functions   pcre_jit_stack_alloc(),   pcre_jit_stack_free(),   and
       pcre_assign_jit_stack() in order to control the JIT code's memory usage.

       From release 8.32 there is also a direct interface for JIT execution, which gives improved
       performance. The JIT-specific functions are discussed in the pcrejit documentation.

       A second matching function, pcre_dfa_exec(), which is not Perl-compatible,  is  also  pro-
       vided.  This  uses a different algorithm for the matching. The alternative algorithm finds
       all possible matches (at a given point in the subject), and scans the  subject  just  once
       (unless there are lookbehind assertions). However, this algorithm does not return captured
       substrings. A description of the two matching algorithms and their advantages  and  disad-
       vantages is given in the pcrematching documentation.

       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_get_stringtable_entries()

       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. 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 com-
       piled 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, 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.

       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. See the pcrebuild documentation for details of how to do this. It is
       a  non-standard  way  of  building PCRE, for use in environments 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. There is a discussion about PCRE's stack usage
       in the pcrestack documentation.

       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 opera-
       tion. Details are given in the pcrecallout documentation.

NEWLINES

       PCRE supports five different conventions for indicating line breaks in strings:  a  single
       CR  (carriage  return)  character,  a  single  LF  (linefeed) character, the two-character
       sequence CRLF, any of the three preceding, or any Unicode newline  sequence.  The  Unicode
       newline  sequences  are  the three just mentioned, plus the single characters VT (vertical
       tab, U+000B), FF (form feed,  U+000C),  NEL  (next  line,  U+0085),  LS  (line  separator,
       U+2028), and PS (paragraph separator, U+2029).

       Each  of the first three conventions is used by at least one operating system as its stan-
       dard newline sequence. When PCRE is built,  a  default  can  be  specified.   The  default
       default  is  LF, which is the Unix standard. When PCRE is run, the default can be overrid-
       den, either when a pattern is compiled, or when it is matched.

       At compile time, the newline convention can  be  specified  by  the  options  argument  of
       pcre_compile(), or it can be specified by special text at the start of the pattern itself;
       this overrides any other settings. See the pcrepattern page for  details  of  the  special
       character sequences.

       In  the  PCRE  documentation  the word "newline" is used to mean "the character or pair of
       characters that indicate a line break". The choice of newline convention affects the  han-
       dling  of the dot, circumflex, and dollar metacharacters, the handling of #-comments in /x
       mode, and, when CRLF is a recognized line ending sequence, the match position  advancement
       for  a non-anchored pattern. There is more detail about this in the section on pcre_exec()
       options below.

       The choice of newline convention does not affect the interpretation of the \n or \r escape
       sequences,  nor  does it affect what \R matches, which is controlled in a similar way, but
       by separate options.

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 matching, so the same com-
       piled pattern can safely be used by several threads at once.

       If the just-in-time optimization feature is being used, it  needs  separate  memory  stack
       areas for each thread. See the pcrejit documentation for more details.

SAVING PRECOMPILED PATTERNS FOR LATER USE

       The compiled form of a regular expression can be saved and re-used at a later time, possi-
       bly by a different program, and even on a host other than the one on  which  it  was  com-
       piled. Details are given in the pcreprecompile documentation, which includes a description
       of the pcre_pattern_to_host_byte_order() function. However, compiling a regular expression
       with  one  version  of PCRE for use with a different version is not guaranteed to work and
       may cause crashes.

CHECKING BUILD-TIME OPTIONS

       int pcre_config(int what, void *where);

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

       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  returned  value  is  zero  on  success,   or   the   negative   error   code
       PCRE_ERROR_BADOPTION  if  the value in the first argument is not recognized. The following
       information is available:

         PCRE_CONFIG_UTF8

       The output is an integer that is set to one if UTF-8 support is available; otherwise it is
       set  to  zero.  This value should normally be given to the 8-bit version of this function,
       pcre_config(). If it is given to the 16-bit or 32-bit version of this function, the result
       is PCRE_ERROR_BADOPTION.

         PCRE_CONFIG_UTF16

       The  output  is an integer that is set to one if UTF-16 support is available; otherwise it
       is set to zero. This value should normally be given to the 16-bit version  of  this  func-
       tion, pcre16_config(). If it is given to the 8-bit or 32-bit version of this function, the
       result is PCRE_ERROR_BADOPTION.

         PCRE_CONFIG_UTF32

       The output is an integer that is set to one if UTF-32 support is available;  otherwise  it
       is  set  to  zero. This value should normally be given to the 32-bit version of this func-
       tion, pcre32_config(). If it is given to the 8-bit or 16-bit version of this function, the
       result is PCRE_ERROR_BADOPTION.

         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_JIT

       The output is an integer that is set to one  if  support  for  just-in-time  compiling  is
       available; otherwise it is set to zero.

         PCRE_CONFIG_JITTARGET

       The  output  is  a  pointer  to a zero-terminated "const char *" string. If JIT support is
       available, the string contains the name of the architecture for which the JIT compiler  is
       configured,  for  example  "x86  32bit (little endian + unaligned)". If JIT support is not
       available, the result is NULL.

         PCRE_CONFIG_NEWLINE

       The output is an integer whose value specifies the default character sequence that is rec-
       ognized  as meaning "newline". The values that are supported in ASCII/Unicode environments
       are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF, and -1 for ANY. In EBCDIC  envi-
       ronments,  CR,  ANYCRLF,  and ANY yield the same values. However, the value for LF is nor-
       mally 21, though some EBCDIC environments use 37. The corresponding values  for  CRLF  are
       3349  and  3365.  The default should normally correspond to the standard sequence for your
       operating system.

         PCRE_CONFIG_BSR

       The output is an integer whose value indicates what  character  sequences  the  \R  escape
       sequence  matches  by  default. A value of 0 means that \R matches any Unicode line ending
       sequence; a value of 1 means that \R matches only CR, LF, or  CRLF.  The  default  can  be
       overridden when a pattern is compiled or matched.

         PCRE_CONFIG_LINK_SIZE

       The  output  is  an integer that contains the number of bytes used for internal linkage in
       compiled regular expressions. For the 8-bit library, the value can be 2, 3, or 4. For  the
       16-bit  library, the value is either 2 or 4 and is still a number of bytes. For the 32-bit
       library, the value is either 2 or 4 and is still a number of bytes. 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. Larger values allow larger regular expressions to be compiled, at
       the expense of slower matching.

         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 a long 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_MATCH_LIMIT_RECURSION

       The output is a long integer that gives the default limit for the depth of recursion  when
       calling  the  internal  matching  function 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 pat-
       tern 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. To avoid too much repetition, we refer just to pcre_compile() below,  but
       the information applies equally to pcre_compile2().

       The  pattern is a C string terminated by a binary zero, and is passed in the pattern argu-
       ment. 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 (via pcre_free) 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 argument, which is an address (see below).

       The options argument contains various bit settings that affect the compilation. 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, but some  others  as  well)  can
       also  be  set  and  unset  from  within  the  pattern (see the detailed description in the
       pcrepattern documentation). For those options that can be different in different parts  of
       the pattern, the contents of the options argument specifies their settings at the start of
       compilation   and   execution.   The   PCRE_ANCHORED,   PCRE_BSR_xxx,    PCRE_NEWLINE_xxx,
       PCRE_NO_UTF8_CHECK,  and PCRE_NO_START_OPTIMIZE options 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 message. This is a static string that is part of the  library.
       You  must  not  try  to free it. Normally, the offset from the start of the pattern to the
       byte that was being processed when 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).
       However, for an invalid UTF-8 string, the offset is that of the first byte of the  failing
       character.

       Some errors are not detected until the whole pattern has been scanned; in these cases, the
       offset passed back is the length of the pattern. Note that the offset  is  in  bytes,  not
       characters,  even in UTF-8 mode. It may sometimes point into the middle of a UTF-8 charac-
       ter.

       If pcre_compile2() is used instead of pcre_compile(), and the errorcodeptr 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_compile():

         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_BSR_ANYCRLF
         PCRE_BSR_UNICODE

       These options (which are mutually exclusive) control what the \R escape sequence  matches.
       The  choice  is  either  to  match  only  CR, LF, or CRLF, or to match any Unicode newline
       sequence. The default is specified when PCRE is built. It can be  overridden  from  within
       the pattern, or by setting an option when a compiled pattern is matched.

         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 compiled 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 a newline at
       the end of the string (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 metacharacter in the pattern matches a character of  any  value,
       including  one that indicates a newline. However, it only ever matches one character, even
       if newlines are coded as CRLF. Without this option, a dot does not match when the  current
       position  is  at  a  newline. 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 newline characters, independent of the setting of this option.

         PCRE_DUPNAMES

       If  this bit is set, names used to identify capturing subpatterns need not be unique. This
       can be helpful for certain types of pattern when it is known that only one instance of the
       named  subpattern  can ever be matched. There are more details of named subpatterns below;
       see also the pcrepattern documentation.

         PCRE_EXTENDED

       If this bit is set, white space 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, characters between an unescaped # outside a  character  class  and
       the next newline, 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.

       Which characters are interpreted as newlines  is  controlled  by  the  options  passed  to
       pcre_compile()  or  by a special sequence at the start of the pattern, as described in the
       section entitled "Newline conventions" in the pcrepattern documentation. Note that the end
       of  this  type  of  comment is a literal newline sequence in the pattern; escape sequences
       that happen to represent a newline do not count.

       This option makes it possible to include comments inside complicated patterns.  Note, how-
       ever,  that  this applies only to data characters. White space characters may never appear
       within special character sequences in a pattern, for example within the sequence (?(  that
       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. (Perl can, however,
       be persuaded to give an error for this, by running it with the -w option.)  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 in the subject string, though the matched text may continue over the newline.

         PCRE_JAVASCRIPT_COMPAT

       If  this  option is set, PCRE's behaviour is changed in some ways so that it is compatible
       with JavaScript rather than Perl. The changes are as follows:

       (1) A lone closing square bracket in a pattern causes a compile-time error,  because  this
       is illegal in JavaScript (by default it is treated as a data character). Thus, the pattern
       AB]CD becomes illegal when this option is set.

       (2) At run time, a back reference to an unset subpattern group matches an empty string (by
       default  this  causes the current matching alternative to fail). A pattern such as (\1)(a)
       succeeds when this option is set (assuming it can find an "a" in the subject), whereas  it
       fails by default, for Perl compatibility.

       (3)  \U  matches  an  upper  case "U" character; by default \U causes a compile time error
       (Perl uses \U to upper case subsequent characters).

       (4) \u matches a lower case "u" character unless it is followed by four  hexadecimal  dig-
       its,  in which case the hexadecimal number defines the code point to match. By default, \u
       causes a compile time error (Perl uses it to upper case the following character).

       (5) \x matches a lower case "x" character unless it is followed by two hexadecimal digits,
       in  which  case  the hexadecimal number defines the code point to match. By default, as in
       Perl, a hexadecimal number is always expected after \x, but it may have zero, one, or  two
       digits (so, for example, \xz matches a binary zero character followed by z).

         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  internal  newlines  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
       newlines  in a subject string, or no occurrences of ^ or $ in a pattern, setting PCRE_MUL-
       TILINE has no effect.

         PCRE_NEWLINE_CR
         PCRE_NEWLINE_LF
         PCRE_NEWLINE_CRLF
         PCRE_NEWLINE_ANYCRLF
         PCRE_NEWLINE_ANY

       These options override the default newline definition that was chosen when PCRE was built.
       Setting  the first or the second specifies that a newline is indicated by a single charac-
       ter (CR or LF, respectively). Setting PCRE_NEWLINE_CRLF specifies that a newline is  indi-
       cated  by the two-character CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies that any
       of the three preceding sequences should be recognized. Setting PCRE_NEWLINE_ANY  specifies
       that any Unicode newline sequence should be recognized.

       In  an  ASCII/Unicode  environment,  the Unicode newline sequences are the three just men-
       tioned, plus the single characters VT (vertical tab, U+000B), FF (form feed, U+000C),  NEL
       (next  line,  U+0085),  LS (line separator, U+2028), and PS (paragraph separator, U+2029).
       For the 8-bit library, the last two are recognized only in UTF-8 mode.

       When PCRE is compiled to run in an EBCDIC (mainframe) environment,  the  code  for  CR  is
       0x0d,  the  same  as ASCII. However, the character code for LF is normally 0x15, though in
       some EBCDIC environments 0x25 is used. Whichever of these is not LF is made to  correspond
       to  Unicode's NEL character. EBCDIC codes are all less than 256. For more details, see the
       pcrebuild documentation.

       The newline setting in the options word uses three bits that are treated as a number, giv-
       ing eight possibilities. Currently only six are used (default plus the five values above).
       This means that if you set more than one newline option, the combination may or may not be
       sensible.  For  example,  PCRE_NEWLINE_CR  with PCRE_NEWLINE_LF is equivalent to PCRE_NEW-
       LINE_CRLF, but other combinations may yield unused numbers and cause an error.

       The only time that a line break in a pattern is specially  recognized  when  compiling  is
       when  PCRE_EXTENDED  is  set.  CR and LF are white space characters, and so are ignored in
       this mode. Also, an unescaped # outside a character class indicates a comment  that  lasts
       until  after the next line break sequence. In other circumstances, line break sequences in
       patterns are treated as literal data.

       The newline option that is set at compile time  becomes  the  default  that  is  used  for
       pcre_exec() and pcre_dfa_exec(), but it can be overridden.

         PCRE_NO_AUTO_CAPTURE

       If  this  option is set, it disables the use of numbered capturing parentheses in the pat-
       tern. 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.

         NO_START_OPTIMIZE

       This is an option that acts at matching  time;  that  is,  it  is  really  an  option  for
       pcre_exec()  or  pcre_dfa_exec().  If it is set at compile time, it is remembered with the
       compiled pattern and  assumed  at  matching  time.  For  details  see  the  discussion  of
       PCRE_NO_START_OPTIMIZE below.

         PCRE_UCP

       This option changes the way PCRE processes \B, \b, \D, \d, \S, \s, \W, \w, and some of the
       POSIX character classes. By default, only ASCII characters are recognized, but if PCRE_UCP
       is set, Unicode properties are used instead to classify characters. More details are given
       in the section on generic character types in the pcrepattern page. If  you  set  PCRE_UCP,
       matching  one  of  the items it affects takes much longer. The option is available only if
       PCRE has been compiled with Unicode property support.

         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  strings.  However, it is available only when PCRE is
       built to include UTF support. If not, the use of this option provokes an error. Details of
       how this option changes the behaviour of PCRE are given in the pcreunicode page.

         PCRE_NO_UTF8_CHECK

       When  PCRE_UTF8  is  set,  the  validity of the pattern as a UTF-8 string is automatically
       checked. There is a discussion about the validity of  UTF-8  strings  in  the  pcreunicode
       page.  If  an  invalid  UTF-8  sequence  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 validity checking of subject strings only. If the same string is  being  matched  many
       times,  the  option  can  be safely set for the second and subsequent matchings to improve
       performance.

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. Note that error
       messages are always 8-bit ASCII strings, even in 16-bit or 32-bit mode. As PCRE has devel-
       oped,  some error codes have fallen out of use. To avoid confusion, they have not been re-
       used.

          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  [this code is not in use]
         11  internal error: unexpected repeat
         12  unrecognized character after (? or (?-
         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  [this code is not in use]
         20  regular expression is 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 or name 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 compiled without UTF support
         33  [this code is not in use]
         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{name}, \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 in subpattern name (missing terminator)
         43  two named subpatterns have the same name
         44  invalid UTF-8 string (specifically UTF-8)
         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
         48  subpattern name is too long (maximum 32 characters)
         49  too many named subpatterns (maximum 10000)
         50  [this code is not in use]
         51  octal value is greater than \377 in 8-bit non-UTF-8 mode
         52  internal error: overran compiling workspace
         53  internal error: previously-checked referenced subpattern
               not found
         54  DEFINE group contains more than one branch
         55  repeating a DEFINE group is not allowed
         56  inconsistent NEWLINE options
         57  \g is not followed by a braced, angle-bracketed, or quoted
               name/number or by a plain number
         58  a numbered reference must not be zero
         59  an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT)
         60  (*VERB) not recognized
         61  number is too big
         62  subpattern name expected
         63  digit expected after (?+
         64  ] is an invalid data character in JavaScript compatibility mode
         65  different names for subpatterns of the same number are
               not allowed
         66  (*MARK) must have an argument
         67  this version of PCRE is not compiled with Unicode property
               support
         68  \c must be followed by an ASCII character
         69  \k is not followed by a braced, angle-bracketed, or quoted name
         70  internal error: unknown opcode in find_fixedlength()
         71  \N is not supported in a class
         72  too many forward references
         73  disallowed Unicode code point (>= 0xd800 && <= 0xdfff)
         74  invalid UTF-16 string (specifically UTF-16)
         75  name is too long in (*MARK), (*PRUNE), (*SKIP), or (*THEN)
         76  character value in \u.... sequence is too large
         77  invalid UTF-32 string (specifically UTF-32)

       The numbers 32 and 10000 in errors 48 and 49 are defaults; different values may be used if
       the limits were changed when PCRE was built.

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 pattern as its first argument. If studying the pattern pro-
       duces 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()   or
       pcre_dfa_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  match-
       ing a pattern.

       If studying the pattern does not produce any useful information, pcre_study() returns NULL
       by default. In that circumstance, if the calling program wants to pass any  of  the  other
       fields  to  pcre_exec()  or pcre_dfa_exec(), it must set up its own pcre_extra block. How-
       ever, if pcre_study() is called with the  PCRE_STUDY_EXTRA_NEEDED  option,  it  returns  a
       pcre_extra  block  even  if studying did not find any additional information. It may still
       return NULL, however, if an error occurs in pcre_study().

       The second argument of pcre_study() contains option bits. There are three further  options
       in addition to PCRE_STUDY_EXTRA_NEEDED:

         PCRE_STUDY_JIT_COMPILE
         PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE
         PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE

       If  any  of these are set, and the just-in-time compiler is available, the pattern is fur-
       ther compiled into machine code that executes much faster than the  pcre_exec()  interpre-
       tive  matching  function. If the just-in-time compiler is not available, these options are
       ignored. All undefined bits in the options argument must be zero.

       JIT compilation is a heavyweight optimization. It can take some time for  patterns  to  be
       analyzed,  and  for  one-off  matches  and simple patterns the benefit of faster execution
       might be offset by a much slower study time.  Not all patterns can be optimized by the JIT
       compiler.  For  those  that  cannot  be  handled, matching automatically falls back to the
       pcre_exec() interpreter. For more details, see the pcrejit documentation.

       The third argument for pcre_study() is a pointer for an error message.  If  studying  suc-
       ceeds  (even  if no data is returned), the variable it points to is set to NULL. Otherwise
       it is set to point to a textual error message. This is a static string that is part of the
       library.  You  must  not  try to free it. You should test the error pointer for NULL after
       calling pcre_study(), to be sure that it has run successfully.

       When you are finished with a pattern, you can free the memory used for the study  data  by
       calling  pcre_free_study().  This function was added to the API for release 8.20. For ear-
       lier versions, the memory could be freed with pcre_free(), just like the  pattern  itself.
       This  will  still work in cases where JIT optimization is not used, but it is advisable to
       change to the new function when convenient.

       This is a typical way in which pcre_study() is used (except that  in  a  real  application
       there should be tests for errors):

         int rc;
         pcre *re;
         pcre_extra *sd;
         re = pcre_compile("pattern", 0, &error, &erroroffset, NULL);
         sd = pcre_study(
           re,             /* result of pcre_compile() */
           0,              /* no options */
           &error);        /* set to NULL or points to a message */
         rc = pcre_exec(   /* see below for details of pcre_exec() options */
           re, sd, "subject", 7, 0, 0, ovector, 30);
         ...
         pcre_free_study(sd);
         pcre_free(re);

       Studying  a pattern does two things: first, a lower bound for the length of subject string
       that is needed to match the pattern is computed. This does not mean  that  there  are  any
       strings  of  that  length that match, but it does guarantee that no shorter strings match.
       The value is used to avoid wasting time by trying to match strings that are  shorter  than
       the  lower  bound. You can find out the value in a calling program via the pcre_fullinfo()
       function.

       Studying a pattern is also useful for non-anchored patterns that  do  not  have  a  single
       fixed  starting  character. A bitmap of possible starting bytes is created. This speeds up
       finding a position in the subject at which to start matching. (In 16-bit mode, the  bitmap
       is  used  for  16-bit values less than 256.  In 32-bit mode, the bitmap is used for 32-bit
       values less than 256.)

       These two optimizations apply to both pcre_exec() and pcre_dfa_exec(), and the information
       is  also  used  by  the  JIT  compiler.   The optimizations can be disabled by setting the
       PCRE_NO_START_OPTIMIZE option when calling pcre_exec() or pcre_dfa_exec(), but if this  is
       done,  JIT  execution is also disabled. You might want to do this if your pattern contains
       callouts or (*MARK) and you want to make use of these facilities in cases  where  matching
       fails. See the discussion of PCRE_NO_START_OPTIMIZE below.

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. By default, higher-
       valued codes never match escapes such as \w or \d, but they can be tested with \p if  PCRE
       is  built  with Unicode character property support. Alternatively, the PCRE_UCP option can
       be set at compile time; this causes \w and friends to use Unicode property support instead
       of  built-in  tables.  The use of locales with Unicode is discouraged. If you are handling
       characters with codes greater than 128, you should either use UTF-8 and  Unicode,  or  use
       locales, but not try to mix the two.

       PCRE contains an internal set of tables that are used when the final argument of pcre_com-
       pile() is NULL. These are sufficient for many applications.  Normally, the internal tables
       recognize  only ASCII characters. However, when PCRE is built, it is possible to cause the
       internal tables to be rebuilt in the default "C" locale of the  local  system,  which  may
       cause them to be different.

       The  internal  tables  can always be overridden by tables supplied by the application that
       calls PCRE. 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  argu-
       ments,  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 appropri-
       ate  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);

       The locale name "fr_FR" is used on Linux and other Unix-like systems;  if  you  are  using
       Windows, the name for the French locale is "french".

       When pcre_maketables() runs, the tables are built in memory that is obtained via pcre_mal-
       loc. 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 pattern, 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 pattern. It replaces the
       pcre_info() function, which was removed from the library at version 8.30, after more  than
       10 years of obsolescence.

       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_BADENDIANNESS  the pattern was compiled with different
                                   endianness
         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. The endianness error can occur if a  compiled
       pattern  is  saved  and  reloaded  on  a  different  host.  Here  is  a  typical  call  of
       pcre_fullinfo(), to obtain the length of the compiled pattern:

         int rc;
         size_t length;
         rc = pcre_fullinfo(
           re,               /* result of pcre_compile() */
           sd,               /* 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 inter-
       nal use by the pcre_study() function. External callers can cause PCRE to use its  internal
       tables by passing a NULL table pointer.

         PCRE_INFO_FIRSTBYTE

       Return  information  about  the  first data unit of any matched string, for a non-anchored
       pattern. (The name of this option refers to  the  8-bit  library,  where  data  units  are
       bytes.) The fourth argument should point to an int variable.

       If  there  is  a  fixed  first  value,  for example, the letter "c" from a pattern such as
       (cat|cow|coyote), its value is returned. In the 8-bit library, the value  is  always  less
       than  256.  In the 16-bit library the value can be up to 0xffff. In the 32-bit library the
       value can be up to 0x10ffff.

       If there is no fixed first value, and 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.

       Since for the 32-bit library using the non-UTF-32 mode, this function is unable to  return
       the   full  32-bit  range  of  the  character,  this  value  is  deprecated;  instead  the
       PCRE_INFO_FIRSTCHARACTERFLAGS and PCRE_INFO_FIRSTCHARACTER values should be used.

         PCRE_INFO_FIRSTTABLE

       If the pattern was studied, and this resulted in the construction of a 256-bit table indi-
       cating  a fixed set of values for the first data unit in any matching string, a pointer to
       the table is returned. Otherwise NULL is returned. The fourth argument should point to  an
       unsigned char * variable.

         PCRE_INFO_HASCRORLF

       Return  1  if the pattern contains any explicit matches for CR or LF characters, otherwise
       0. The fourth argument should point to an int variable. An explicit match is either a lit-
       eral CR or LF character, or \r or \n.

         PCRE_INFO_JCHANGED

       Return  1  if  the  (?J)  or (?-J) option setting is used in the pattern, otherwise 0. The
       fourth argument should point to an int variable. (?J) and (?-J) set and  unset  the  local
       PCRE_DUPNAMES option, respectively.

         PCRE_INFO_JIT

       Return  1 if the pattern was studied with one of the JIT options, and just-in-time compil-
       ing was successful. The fourth argument should point to an int variable. A return value of
       0 means that JIT support is not available in this version of PCRE, or that the pattern was
       not studied with a JIT option, or that the JIT compiler could not handle  this  particular
       pattern. See the pcrejit documentation for details of what can and cannot be handled.

         PCRE_INFO_JITSIZE

       If the pattern was successfully studied with a JIT option, return the size of the JIT com-
       piled code, otherwise return zero. The fourth argument should point to a size_t variable.

         PCRE_INFO_LASTLITERAL

       Return the value of the rightmost literal data unit that must exist in any matched string,
       other  than  at  its  start, if such a value has been recorded. The fourth argument should
       point to an int variable. If there is no such value, -1 is  returned.  For  anchored  pat-
       terns,  a  last literal value 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.

       Since  for the 32-bit library using the non-UTF-32 mode, this function is unable to return
       the  full  32-bit  range  of  the  character,  this  value  is  deprecated;  instead   the
       PCRE_INFO_REQUIREDCHARFLAGS and PCRE_INFO_REQUIREDCHAR values should be used.

         PCRE_INFO_MAXLOOKBEHIND

       Return  the number of characters (NB not bytes) in the longest lookbehind assertion in the
       pattern. Note that the simple assertions \b and \B  require  a  one-character  lookbehind.
       This  information  is  useful when doing multi-segment matching using the partial matching
       facilities.

         PCRE_INFO_MINLENGTH

       If the pattern was studied and a minimum length for matching subject strings was computed,
       its  value is returned. Otherwise the returned value is -1. The value is a number of char-
       acters, which in UTF-8 mode may be different from the number of bytes. The fourth argument
       should  point  to  an int variable. A non-negative value is a lower bound to the length of
       any matching string. There may not be any strings of that length that do  actually  match,
       but every string that does match is at least that long.

         PCRE_INFO_NAMECOUNT
         PCRE_INFO_NAMEENTRYSIZE
         PCRE_INFO_NAMETABLE

       PCRE  supports  the  use of named as well as numbered capturing parentheses. The names are
       just an additional way of identifying the parentheses, which still acquire  numbers.  Sev-
       eral  convenience functions such as pcre_get_named_substring() are provided for extracting
       captured substrings 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 vec-
       tor (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. This is  a  pointer
       to  char  in  the 8-bit library, where the first two bytes of each entry are the number of
       the capturing parenthesis, most significant byte first. In the 16-bit library, the pointer
       points  to  16-bit data units, the first of which contains the parenthesis number.  In the
       32-bit library, the pointer points to 32-bit data units, the first of which  contains  the
       parenthesis number. The rest of the entry is the corresponding name, zero terminated.

       The  names  are in alphabetical order. Duplicate names may appear if (?| is used to create
       multiple groups with the same number, as described in the section on duplicate  subpattern
       numbers  in  the  pcrepattern page. Duplicate names for subpatterns with different numbers
       are permitted only if PCRE_DUPNAMES is set. In all cases of duplicate names,  they  appear
       in  the  table in the order in which they were found in the pattern. In the absence of (?|
       this is the order of increasing number; when (?| is used this is not necessarily the  case
       because later subpatterns may have lower numbers.

       As  a simple example of the name/number table, consider the following pattern after compi-
       lation by the 8-bit library (assume PCRE_EXTENDED is set, so white space - including  new-
       lines - is ignored):

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

       There are four named subpatterns, so the table has four entries, and each entry in the ta-
       ble is eight bytes long. The table is as follows, with non-printing bytes shows  in  hexa-
       decimal, 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 the entries is likely to be different for each  compiled  pat-
       tern.

         PCRE_INFO_OKPARTIAL

       Return  1  if  the pattern can be used for partial matching with pcre_exec(), otherwise 0.
       The fourth argument should point to an  int  variable.  From  release  8.00,  this  always
       returns  1, because the restrictions that previously applied to partial matching have been
       lifted. The pcrepartial documentation gives details of partial matching.

         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 at the start of  the
       pattern  itself.  In other words, they are the options that will be in force when matching
       starts. For example, if the pattern /(?im)abc(?-i)d/ is compiled  with  the  PCRE_EXTENDED
       option, the result is PCRE_CASELESS, PCRE_MULTILINE, and PCRE_EXTENDED.

       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 in bytes (for both libraries). The fourth argument
       should point to a size_t variable. This value does not include the size of the pcre struc-
       ture  that  is  returned  by  pcre_compile().  The value that is passed as the argument to
       pcre_malloc() when pcre_compile() is getting memory in which to place the compiled data is
       the value returned by this option plus the size of the pcre structure. Studying a compiled
       pattern, with or without JIT, does not alter the value returned by this option.

         PCRE_INFO_STUDYSIZE

       Return the size in bytes of the data block  pointed  to  by  the  study_data  field  in  a
       pcre_extra  block. If pcre_extra is NULL, or there is no study data, zero is returned. The
       fourth argument should point to  a  size_t  variable.  The  study_data  field  is  set  by
       pcre_study()  to  record information that will speed up matching (see the section entitled
       "Studying a pattern" above). The format of the study_data block is private, but its length
       is  made  available via this option so that it can be saved and restored (see the pcrepre-
       compile documentation for details).

         PCRE_INFO_FIRSTCHARACTERFLAGS

       Return information about the first data unit of any matched  string,  for  a  non-anchored
       pattern. The fourth argument should point to an int variable.

       If  there  is  a  fixed  first  value,  for example, the letter "c" from a pattern such as
       (cat|cow|coyote),  1  is  returned,  and  the  character  value  can  be  retrieved  using
       PCRE_INFO_FIRSTCHARACTER.

       If there is no fixed first value, and 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),

       2  is  returned, indicating that the pattern matches only at the start of a subject string
       or after any newline within the string. Otherwise 0 is returned. For anchored patterns,  0
       is returned.

         PCRE_INFO_FIRSTCHARACTER

       Return  the fixed first character value, if PCRE_INFO_FIRSTCHARACTERFLAGS returned 1; oth-
       erwise returns 0. The fourth argument should point to an uint_t variable.

       In the 8-bit library, the value is always less than 256. In the 16-bit library  the  value
       can be up to 0xffff. In the 32-bit library in UTF-32 mode the value can be up to 0x10ffff,
       and up to 0xffffffff when not using UTF-32 mode.

       If there is no fixed first value, and 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_REQUIREDCHARFLAGS

       Returns 1 if there is a rightmost literal data unit that must exist in any matched string,
       other than at its start. The fourth argument should  point to an int variable. If there is
       no such value, 0 is returned. If returning 1, the character value itself can be  retrieved
       using PCRE_INFO_REQUIREDCHAR.

       For  anchored  patterns,  a last literal value is recorded only if it follows something of
       variable length. For example, for the pattern /^a\d+z\d+/ the returned value 1  (with  "z"
       returned from PCRE_INFO_REQUIREDCHAR), but for /^a\dz\d/ the returned value is 0.

         PCRE_INFO_REQUIREDCHAR

       Return the value of the rightmost literal data unit that must exist in any matched string,
       other than at its start, if such a value has been recorded.  The  fourth  argument  should
       point to an uint32_t variable. If there is no such value, 0 is returned.

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 was studied, the result of the study
       should be passed in the extra argument. You can call pcre_exec() with the  same  code  and
       extra  arguments  as  many  times as you like, in order to match different subject strings
       with the same pattern.

       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 section about the pcre_dfa_exec() function.

       In most applications, the pattern will have been compiled (and optionally 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 additional information in it. The pcre_extra block con-
       tains the following fields (not necessarily in this order):

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

       In the 16-bit version of this structure, the mark field has type "PCRE_UCHAR16 **".

       In the 32-bit version of this structure, the mark field has type "PCRE_UCHAR32 **".

       The flags field is used to specify which of the other fields are set. The flag bits are:

         PCRE_EXTRA_CALLOUT_DATA
         PCRE_EXTRA_EXECUTABLE_JIT
         PCRE_EXTRA_MARK
         PCRE_EXTRA_MATCH_LIMIT
         PCRE_EXTRA_MATCH_LIMIT_RECURSION
         PCRE_EXTRA_STUDY_DATA
         PCRE_EXTRA_TABLES

       Other flag bits should be set to  zero.  The  study_data  field  and  sometimes  the  exe-
       cutable_jit  field  are  set  in  the  pcre_extra  block that is returned by pcre_study(),
       together with the appropriate flag bits. You should not set these yourself,  but  you  may
       add to the block by setting 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 a pattern that uses
       nested unlimited repeats.

       Internally, pcre_exec() uses a function called match(), which it calls  repeatedly  (some-
       times  recursively).  The  limit set by match_limit is imposed on the number of times this
       function is called during a match, which has the effect of limiting the  amount  of  back-
       tracking  that can take place. For patterns that are not anchored, the count restarts from
       zero for each position in the subject string.

       When pcre_exec() is called with a pattern that was successfully studied with a JIT option,
       the  way that the matching is executed is entirely different.  However, there is still the
       possibility of runaway matching that goes on for a very long time, and so the  match_limit
       value  is  also  used in this case (but in a different way) to limit how long the matching
       can continue.

       The default value for the limit can be set when PCRE is built; the default default  is  10
       million,  which  handles  all  but the most extreme cases. You can override the default by
       suppling  pcre_exec()  with  a  pcre_extra  block  in  which  match_limit  is   set,   and
       PCRE_EXTRA_MATCH_LIMIT  is  set  in the flags field. If the limit is exceeded, pcre_exec()
       returns PCRE_ERROR_MATCHLIMIT.

       The match_limit_recursion field is similar to match_limit, but  instead  of  limiting  the
       total number of times that match() is called, it limits the depth of recursion. The recur-
       sion depth is a smaller number than the total number of calls, because not  all  calls  to
       match() are recursive.  This limit is of use only if it is set smaller than match_limit.

       Limiting the recursion depth limits the amount of machine stack that can be used, or, when
       PCRE has been compiled to use memory on the heap instead of the stack, the amount of  heap
       memory that can be used. This limit is not relevant, and is ignored, when matching is done
       using JIT compiled code.

       The default value for match_limit_recursion can be set when PCRE  is  built;  the  default
       default  is the same value as the default for match_limit. You can override the default by
       suppling pcre_exec() with a pcre_extra block in which match_limit_recursion  is  set,  and
       PCRE_EXTRA_MATCH_LIMIT_RECURSION  is  set  in  the  flags field. If the limit is exceeded,
       pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.

       The callout_data field is used in conjunction with the "callout" feature, and 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
       argument.  If NULL is passed to pcre_exec() using this mechanism, it forces PCRE's  inter-
       nal  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 documentation
       for a discussion of saving compiled patterns for later use.

       If PCRE_EXTRA_MARK is set in the flags field, the mark field must be set  to  point  to  a
       suitable  variable.  If  the  pattern  contains  any  backtracking  control  verbs such as
       (*MARK:NAME), and the execution ends up with a name to pass back, a pointer  to  the  name
       string (zero terminated) is placed in the variable pointed to by the mark field. The names
       are within the compiled pattern; if you wish to retain such a name you must copy it before
       freeing  the  memory of a compiled pattern. If there is no name to pass back, the variable
       pointed to by the mark field is set to NULL.  For  details  of  the  backtracking  control
       verbs, see the section entitled "Backtracking control" in the pcrepattern documentation.

   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_NEWLINE_xxx, PCRE_NOTBOL,  PCRE_NOTEOL,  PCRE_NOTEMPTY,
       PCRE_NOTEMPTY_ATSTART,  PCRE_NO_START_OPTIMIZE, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_HARD, and
       PCRE_PARTIAL_SOFT.

       If the pattern was successfully  studied  with  one  of  the  just-in-time  (JIT)  compile
       options, the only supported options for JIT execution are PCRE_NO_UTF8_CHECK, PCRE_NOTBOL,
       PCRE_NOTEOL,  PCRE_NOTEMPTY,  PCRE_NOTEMPTY_ATSTART,  PCRE_PARTIAL_HARD,   and   PCRE_PAR-
       TIAL_SOFT.  If  an  unsupported  option  is used, JIT execution is disabled and the normal
       interpretive code in pcre_exec() is run.

         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_BSR_ANYCRLF
         PCRE_BSR_UNICODE

       These options (which are mutually exclusive) control what the \R escape sequence  matches.
       The  choice  is  either  to  match  only  CR, LF, or CRLF, or to match any Unicode newline
       sequence. These options override the choice that was made or defaulted  when  the  pattern
       was compiled.

         PCRE_NEWLINE_CR
         PCRE_NEWLINE_LF
         PCRE_NEWLINE_CRLF
         PCRE_NEWLINE_ANYCRLF
         PCRE_NEWLINE_ANY

       These  options  override the newline definition that was chosen or defaulted when the pat-
       tern was compiled. For details, see the description of pcre_compile() above. During match-
       ing, the newline choice affects the behaviour of the dot, circumflex, and dollar metachar-
       acters. It may also alter the way the match position is advanced after a match failure for
       an unanchored pattern.

       When  PCRE_NEWLINE_CRLF,  PCRE_NEWLINE_ANYCRLF,  or  PCRE_NEWLINE_ANY  is set, and a match
       attempt for an unanchored pattern fails when the current position is at a  CRLF  sequence,
       and  the  pattern contains no explicit matches for CR or LF characters, the match position
       is advanced by two characters instead of one, in other words, to after the CRLF.

       The above rule is a compromise that makes the most common  cases  work  as  expected.  For
       example,  if the pattern is .+A (and the PCRE_DOTALL option is not set), it does not match
       the string "\r\nA" because, after failing at the start, it skips both the CR  and  the  LF
       before  retrying. However, the pattern [\r\n]A does match that string, because it contains
       an explicit CR or LF reference, and so advances only by  one  character  after  the  first
       failure.

       An  explicit match for CR of LF is either a literal appearance of one of those characters,
       or one of the \r or \n escape sequences. Implicit matches such as [^X] do not  count,  nor
       does \s (which includes CR and LF in the characters that it matches).

       Notwithstanding  the above, anomalous effects may still occur when CRLF is a valid newline
       sequence and explicit \r or \n escapes appear in the pattern.

         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 behaviour 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  immedi-
       ately before it. Setting this without 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 an 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".

         PCRE_NOTEMPTY_ATSTART

       This  is like PCRE_NOTEMPTY, except that an empty string match that is not at the start of
       the subject is permitted. If the pattern is anchored, such a match can occur only  if  the
       pattern contains \K.

       Perl  has no direct equivalent of PCRE_NOTEMPTY or PCRE_NOTEMPTY_ATSTART, 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_ATSTART
       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  sample  program.  In the most general case, you have to check to see if the
       newline convention recognizes CRLF as a newline, and if so, and the current  character  is
       CR followed by LF, advance the starting offset by two characters instead of one.

         PCRE_NO_START_OPTIMIZE

       There  are  a  number  of  optimizations that pcre_exec() uses at the start of a match, in
       order to speed up the process. For example, if it is known that an unanchored  match  must
       start  with  a  specific  character, it searches the subject for that character, and fails
       immediately if it cannot find it, without actually running  the  main  matching  function.
       This  means that a special item such as (*COMMIT) at the start of a pattern is not consid-
       ered until after a suitable starting point for the match has been found. When callouts  or
       (*MARK)  items  are in use, these "start-up" optimizations can cause them to be skipped if
       the pattern is never actually used. The start-up optimizations are in effect a pre-scan of
       the subject that takes place before the pattern is run.

       The  PCRE_NO_START_OPTIMIZE  option  disables the start-up optimizations, possibly causing
       performance to suffer, but ensuring that in cases where the  result  is  "no  match",  the
       callouts  do  occur,  and that items such as (*COMMIT) and (*MARK) are considered at every
       possible starting position in the subject string. If PCRE_NO_START_OPTIMIZE is set at com-
       pile time, it cannot be unset at matching time. The use of PCRE_NO_START_OPTIMIZE disables
       JIT execution; when it is set, matching is always done using interpretively.

       Setting PCRE_NO_START_OPTIMIZE can change the outcome of a matching  operation.   Consider
       the pattern

         (*COMMIT)ABC

       When  this  is  compiled, PCRE records the fact that a match must start with the character
       "A". Suppose the subject string is "DEFABC". The start-up  optimization  scans  along  the
       subject,  finds  "A" and runs the first match attempt from there. The (*COMMIT) item means
       that the pattern must match the current starting position, which in this  case,  it  does.
       However,  if the same match is run with PCRE_NO_START_OPTIMIZE set, the initial scan along
       the subject string does not happen. The first match attempt is run starting from  "D"  and
       when this fails, (*COMMIT) prevents any further matches being tried, so the overall result
       is "no match". If the pattern is studied, more start-up optimizations  may  be  used.  For
       example, a minimum length for the subject may be recorded. Consider the pattern

         (*MARK:A)(X|Y)

       The  minimum  length  for a match is one character. If the subject is "ABC", there will be
       attempts to match "ABC", "BC", "C", and then finally an empty string.  If the  pattern  is
       studied, the final attempt does not take place, because PCRE knows that the subject is too
       short, and so the (*MARK) is never encountered.  In this case, studying the  pattern  does
       not  affect  the  overall  match result, which is still "no match", but it does affect the
       auxiliary information that is returned.

         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 entire string is
       checked before any other processing takes place. The value of startoffset is also  checked
       to  ensure  that  it points to the start of a UTF-8 character. There is a discussion about
       the validity of UTF-8 strings in the pcreunicode page. If an invalid sequence of bytes  is
       found,  pcre_exec()  returns  the error PCRE_ERROR_BADUTF8 or, if PCRE_PARTIAL_HARD is set
       and the problem is a truncated character at the end of the subject,  PCRE_ERROR_SHORTUTF8.
       In both cases, information about the precise nature of the error may also be returned (see
       the descriptions of these  errors  in  the  section  entitled  Error  return  values  from
       pcre_exec() below).  If startoffset contains a value that does not point to the start of a
       UTF-8 character (or to the end of the subject), PCRE_ERROR_BADUTF8_OFFSET is returned.

       If you already know that your subject is valid, and you want to skip these checks for per-
       formance  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 character (or the end  of  the
       subject).  When  PCRE_NO_UTF8_CHECK  is  set, the effect of passing an invalid string as a
       subject or an invalid value of startoffset is undefined. Your program may crash.

         PCRE_PARTIAL_HARD
         PCRE_PARTIAL_SOFT

       These options turn on the partial matching feature. For backwards compatibility, PCRE_PAR-
       TIAL  is a synonym for PCRE_PARTIAL_SOFT. A partial match occurs if the end of the subject
       string is reached successfully, but there are not enough subject  characters  to  complete
       the  match.  If  this  happens  when PCRE_PARTIAL_SOFT (but not PCRE_PARTIAL_HARD) is set,
       matching continues by testing any remaining alternatives. Only if no complete match can be
       found  is  PCRE_ERROR_PARTIAL  returned  instead  of  PCRE_ERROR_NOMATCH.  In other words,
       PCRE_PARTIAL_SOFT says that the caller is prepared to handle a partial match, but only  if
       no complete match can be found.

       If  PCRE_PARTIAL_HARD  is  set, it overrides PCRE_PARTIAL_SOFT. In this case, if a partial
       match is found, pcre_exec() immediately returns  PCRE_ERROR_PARTIAL,  without  considering
       any  other alternatives. In other words, when PCRE_PARTIAL_HARD is set, a partial match is
       considered to be more important that an alternative complete match.

       In both cases, the portion of the string that was inspected when  the  partial  match  was
       found  is set as the first matching string. There is a more detailed discussion of partial
       and multi-segment matching, with examples, 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 bytes  in
       length, and a starting byte offset in startoffset. If this is negative or greater than the
       length of the subject, pcre_exec() returns PCRE_ERROR_BADOFFSET. 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. In UTF-8 mode, the byte offset must point to the start  of  a  UTF-8
       character  (or the end of the subject). Unlike the pattern string, the subject may contain
       binary zero bytes.

       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.

       Finding all the matches in a subject is tricky when the pattern can match an empty string.
       It  is possible to emulate Perl's /g behaviour by first trying the match again at the same
       offset, with the PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED options, and then if that  fails,
       advancing  the starting offset and trying an ordinary match again. There is some code that
       demonstrates how to do this in the pcredemo sample program. In the most general case,  you
       have  to  check  to see if the newline convention recognizes CRLF as a newline, and if so,
       and the current character is CR followed by LF, advance the starting offset by two charac-
       ters instead of one.

       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 "cap-
       turing subpattern" is used for a fragment of a pattern that picks out  a  substring.  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 integers 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  substrings,  each  sub-
       string 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 number 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 each pair is set to the byte offset of the  first
       character  in a substring, and the second is set to the byte offset of the first character
       after the end of a substring. Note: these values are always byte offsets,  even  in  UTF-8
       mode. They are not character counts.

       The first pair of integers, ovector[0] and ovector[1], identify the portion of the subject
       string matched by the entire pattern. The next pair is used for the first  capturing  sub-
       pattern,  and  so  on. The value returned by pcre_exec() is one more than the highest num-
       bered pair that has been set.  For example, if two  substrings  have  been  captured,  the
       returned  value  is 3. If there are no capturing subpatterns, the return value from a suc-
       cessful match is 1, indicating that just the first pair of offsets has been set.

       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. If
       neither the actual string matched nor any captured substrings are 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 sub-
       strings, PCRE has to get additional memory for use during matching.  Thus  it  is  usually
       advisable to supply an ovector of reasonable size.

       There  are some cases where zero is returned (indicating vector overflow) when in fact the
       vector is exactly the right size for the final match. For example, consider the pattern

         (a)(?:(b)c|bd)

       If a vector of 6 elements (allowing for only 1 captured substring) is given  with  subject
       string  "abd", pcre_exec() will try to set the second captured string, thereby recording a
       vector overflow, before failing to match "c" and backing up to try the second alternative.
       The zero return, however, does correctly indicate that the maximum number of slots (namely
       2) have been filled. In similar cases where there is temporary  overflow,  but  the  final
       number of used slots is actually less than the maximum, a non-zero value is returned.

       The  pcre_fullinfo() function can be used to find out how many capturing 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.

       It is possible for 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) the return from the function is 4, and subpatterns  1  and  3  are
       matched, but 2 is not. When this happens, both values in the offset pairs corresponding to
       unused subpatterns are set to -1.

       Offset values that correspond to unused subpatterns at the end of the expression are  also
       set  to -1. For example, if the string "abc" is matched against the pattern (abc)(x(yz)?)?
       subpatterns 2 and 3 are not matched. The return from the function is 2, because the  high-
       est  used  capturing  subpattern number is 1, and the offsets for for the second and third
       capturing subpatterns (assuming the vector is large enough, of course) are set to -1.

       Note: Elements in the first two-thirds of ovector that  do  not  correspond  to  capturing
       parentheses  in  the pattern are never changed. That is, if a pattern contains n capturing
       parentheses, no more than ovector[0] to ovector[2n+1] are set by  pcre_exec().  The  other
       elements (in the first two-thirds) retain whatever values they previously had.

       Some convenience functions are provided for extracting the captured substrings as separate
       strings. These are described below.

   Error 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_OPCODE (-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.

       This error is also given if pcre_stack_malloc() fails in pcre_exec(). This can happen only
       when PCRE has been compiled with --disable-stack-for-recursion.

         PCRE_ERROR_NOSUBSTRING    (-7)

       This  error  is used by the pcre_copy_substring(), pcre_get_substring(), and pcre_get_sub-
       string_list() functions (see below). It is never returned by pcre_exec().

         PCRE_ERROR_MATCHLIMIT     (-8)

       The 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, and the
       PCRE_NO_UTF8_CHECK option was not set. If the size of the output vector (ovecsize)  is  at
       least  2, the byte offset to the start of the the invalid UTF-8 character is placed in the
       first element, and a reason code is placed in the second element.  The  reason  codes  are
       listed  in the following section.  For backward compatibility, if PCRE_PARTIAL_HARD is set
       and the problem is a truncated UTF-8 character at the end of the subject (reason  codes  1
       to 5), PCRE_ERROR_SHORTUTF8 is returned instead of PCRE_ERROR_BADUTF8.

         PCRE_ERROR_BADUTF8_OFFSET (-11)

       The  UTF-8  byte  sequence  that was passed as a subject was checked and found to be valid
       (the PCRE_NO_UTF8_CHECK option was not set), but the value of startoffset did not point to
       the beginning of a UTF-8 character or the end of the subject.

         PCRE_ERROR_PARTIAL        (-12)

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

         PCRE_ERROR_BADPARTIAL     (-13)

       This code is no longer in use. It was formerly returned when the PCRE_PARTIAL  option  was
       used  with  a compiled pattern containing items that were not supported for partial match-
       ing. From release 8.00 onwards, there are no restrictions on 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.

         PCRE_ERROR_RECURSIONLIMIT (-21)

       The  internal  recursion  limit,  as  specified  by  the  match_limit_recursion field in a
       pcre_extra structure (or defaulted) was reached. See the description above.

         PCRE_ERROR_BADNEWLINE     (-23)

       An invalid combination of PCRE_NEWLINE_xxx options was given.

         PCRE_ERROR_BADOFFSET      (-24)

       The value of startoffset was negative or greater than the length of the subject, that  is,
       the value in length.

         PCRE_ERROR_SHORTUTF8      (-25)

       This  error  is returned instead of PCRE_ERROR_BADUTF8 when the subject string ends with a
       truncated UTF-8 character and the PCRE_PARTIAL_HARD option is set.  Information about  the
       failure  is  returned  as  for PCRE_ERROR_BADUTF8. It is in fact sufficient to detect this
       case, but this special error code for PCRE_PARTIAL_HARD  precedes  the  implementation  of
       returned information; it is retained for backwards compatibility.

         PCRE_ERROR_RECURSELOOP    (-26)

       This  error  is  returned  when  pcre_exec()  detects a recursion loop within the pattern.
       Specifically, it means that either the whole pattern  or  a  subpattern  has  been  called
       recursively  for  the  second time at the same position in the subject string. Some simple
       patterns that might do this are detected and faulted at compile time, but more complicated
       cases,  in  particular  mutual  recursions  between  two  different subpatterns, cannot be
       detected until run time.

         PCRE_ERROR_JIT_STACKLIMIT (-27)

       This error is returned when a pattern that was successfully studied using  a  JIT  compile
       option is being matched, but the memory available for the just-in-time processing stack is
       not large enough. See the pcrejit documentation for more details.

         PCRE_ERROR_BADMODE        (-28)

       This error is given if a pattern that was compiled by the 8-bit library  is  passed  to  a
       16-bit or 32-bit library function, or vice versa.

         PCRE_ERROR_BADENDIANNESS  (-29)

       This  error  is  given if a pattern that was compiled and saved is reloaded on a host with
       different endianness. The utility function pcre_pattern_to_host_byte_order() can  be  used
       to convert such a pattern so that it runs on the new host.

         PCRE_ERROR_JIT_BADOPTION

       This  error  is  returned when a pattern that was successfully studied using a JIT compile
       option is being matched, but the matching mode (partial or complete match) does not corre-
       spond to any JIT compilation mode. When the JIT fast path function is used, this error may
       be also given for invalid options. See the pcrejit documentation for more details.

         PCRE_ERROR_BADLENGTH      (-32)

       This error is given if pcre_exec() is called with a negative value for  the  length  argu-
       ment.

       Error numbers -16 to -20, -22, and 30 are not used by pcre_exec().

   Reason codes for invalid UTF-8 strings

       This  section  applies  only  to  the 8-bit library. The corresponding information for the
       16-bit and 32-bit libraries is given in the pcre16 and pcre32 pages.

       When pcre_exec() returns either PCRE_ERROR_BADUTF8 or PCRE_ERROR_SHORTUTF8, and  the  size
       of  the  output  vector  (ovecsize)  is at least 2, the offset of the start of the invalid
       UTF-8 character is placed in the first output vector element  (ovector[0])  and  a  reason
       code is placed in the second element (ovector[1]). The reason codes are given names in the
       pcre.h header file:

         PCRE_UTF8_ERR1
         PCRE_UTF8_ERR2
         PCRE_UTF8_ERR3
         PCRE_UTF8_ERR4
         PCRE_UTF8_ERR5

       The string ends with a truncated UTF-8 character; the code specifies how  many  bytes  are
       missing  (1  to  5).  Although  RFC 3629 restricts UTF-8 characters to be no longer than 4
       bytes, the encoding scheme (originally defined by RFC 2279) allows for up to 6 bytes,  and
       this is checked first; hence the possibility of 4 or 5 missing bytes.

         PCRE_UTF8_ERR6
         PCRE_UTF8_ERR7
         PCRE_UTF8_ERR8
         PCRE_UTF8_ERR9
         PCRE_UTF8_ERR10

       The  two  most significant bits of the 2nd, 3rd, 4th, 5th, or 6th byte of the character do
       not have the binary value 0b10 (that is, either the most significant bit is 0, or the next
       bit is 1).

         PCRE_UTF8_ERR11
         PCRE_UTF8_ERR12

       A  character  that  is valid by the RFC 2279 rules is either 5 or 6 bytes long; these code
       points are excluded by RFC 3629.

         PCRE_UTF8_ERR13

       A 4-byte character has a value greater than 0x10fff; these code points are excluded by RFC
       3629.

         PCRE_UTF8_ERR14

       A  3-byte  character  has a value in the range 0xd800 to 0xdfff; this range of code points
       are reserved by RFC 3629 for use with UTF-16, and so are excluded from UTF-8.

         PCRE_UTF8_ERR15
         PCRE_UTF8_ERR16
         PCRE_UTF8_ERR17
         PCRE_UTF8_ERR18
         PCRE_UTF8_ERR19

       A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it codes for  a  value  that
       can be represented by fewer bytes, which is invalid. For example, the two bytes 0xc0, 0xae
       give the value 0x2e, whose correct coding uses just one byte.

         PCRE_UTF8_ERR20

       The two most significant bits of the first byte of a character have the binary value  0b10
       (that is, the most significant bit is 1 and the second is 0). Such a byte can only validly
       occur as the second or subsequent byte of a multi-byte character.

         PCRE_UTF8_ERR21

       The first byte of a character has the value 0xfe or 0xff. These values can never occur  in
       a valid UTF-8 string.

         PCRE_UTF8_ERR2

       Non-character.  These  are the last two characters in each plane (0xfffe, 0xffff, 0x1fffe,
       0x1ffff .. 0x10fffe, 0x10ffff), and the characters 0xfdd0..0xfdef.

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_substring_list() are provided for extracting captured substrings as new, sep-
       arate,  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.  However, you can process
       such a string by referring to the length that is  returned  by  pcre_copy_substring()  and
       pcre_get_substring().   Unfortunately,  the  interface to pcre_get_substring_list() is not
       adequate for handling strings containing binary zeros, because the end of the final string
       is not independently indicated.

       The  first  three  arguments are the same for all three of these functions: 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 sub-
       strings 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_substring(), the string is placed in buffer, whose length is  given  by  buffer-
       size,  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 these error codes:

         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 substrings 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 the error code

         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  substring  by inspecting the appropriate offset in ovector, which is negative
       for unset substrings.

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

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  number.   For  example,
       for this pattern

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

       the  number  of  the  subpattern  called  "xxx"  is  2.  If the name is known to be unique
       (PCRE_DUPNAMES  was  not  set),  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 dif-
       ferences:

       First, instead of a substring number, a substring name is given. Second, 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 appropriate. NOTE: If PCRE_DUPNAMES is
       set and there are duplicate names, the behaviour may not be what you want  (see  the  next
       section).

       Warning:  If the pattern uses the (?| feature to set up multiple subpatterns with the same
       number, as described in the section on duplicate subpattern  numbers  in  the  pcrepattern
       page, you cannot use names to distinguish the different subpatterns, because names are not
       included in the compiled code. The matching process uses only numbers.  For  this  reason,
       the  use  of different names for subpatterns of the same number causes an error at compile
       time.

DUPLICATE SUBPATTERN NAMES

       int pcre_get_stringtable_entries(const pcre *code,
            const char *name, char **first, char **last);

       When a pattern is compiled with the PCRE_DUPNAMES option, names for  subpatterns  are  not
       required  to  be unique. (Duplicate names are always allowed for subpatterns with the same
       number, created by using the (?| feature. Indeed, if such subpatterns are named, they  are
       required to use the same names.)

       Normally,  patterns  with  duplicate names are such that in any one match, only one of the
       named subpatterns participates. An example is shown in the pcrepattern documentation.

       When duplicates are present,  pcre_copy_named_substring()  and  pcre_get_named_substring()
       return  the  first substring corresponding to the given name that is set. If none are set,
       PCRE_ERROR_NOSUBSTRING (-7) is returned; no data is returned. The  pcre_get_stringnumber()
       function  returns  one  of  the  numbers  that are associated with the name, but it is not
       defined which it is.

       If you want to get full details of all captured substrings for a given name, you must  use
       the  pcre_get_stringtable_entries()  function. The first argument is the compiled pattern,
       and the second is the name. The third and fourth  are  pointers  to  variables  which  are
       updated by the function. After it has run, they point to the first and last entries in the
       name-to-number table for the given name. The function itself returns the  length  of  each
       entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if  there  are  none. The format of the table is
       described above in the section entitled Information about a pattern above.  Given all  the
       relevant  entries  for the name, you can extract each of their numbers, and hence the cap-
       tured data, if any.

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 documentation.

       What  you  have  to  do is to insert a callout right at the end of the pattern.  When your
       callout function is called, extract and save the current 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.

OBTAINING AN ESTIMATE OF STACK USAGE

       Matching certain patterns using pcre_exec() can use a lot of process stack, which in  cer-
       tain  environments  can  be  rather limited in size. Some users find it helpful to have an
       estimate of the amount of stack that is used by pcre_exec(), to help  them  set  recursion
       limits,  as  described  in  the  pcrestack  documentation.  The estimate that is output by
       pcretest when called with the -m and -C options is obtained by calling pcre_exec with  the
       values NULL, NULL, NULL, -999, and -999 for its first five arguments.

       Normally,  if  its  first  argument  is NULL, pcre_exec() immediately returns the negative
       error code PCRE_ERROR_NULL, but with this special combination  of  arguments,  it  returns
       instead  a  negative  number  whose  absolute value is the approximate stack frame size in
       bytes. (A negative number is used so that it is clear that no  match  has  happened.)  The
       value  is  approximate  because  in  some cases, recursive calls to pcre_exec() occur when
       there are one or two additional variables on the stack.

       If PCRE has been compiled to use the heap instead of the stack for  recursion,  the  value
       returned is the size of each block that is obtained from the heap.

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 pat-
       tern, using a matching algorithm that scans the subject string just  once,  and  does  not
       backtrack. 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, and a list of features that pcre_dfa_exec() does not support, 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 different 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 potential matches.

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

         int rc;
         int ovector[10];
         int wspace[20];
         rc = pcre_dfa_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_NEWLINE_xxx,   PCRE_NOTBOL,   PCRE_NOTEOL,
       PCRE_NOTEMPTY,  PCRE_NOTEMPTY_ATSTART, PCRE_NO_UTF8_CHECK, PCRE_BSR_ANYCRLF, PCRE_BSR_UNI-
       CODE, PCRE_NO_START_OPTIMIZE, PCRE_PARTIAL_HARD, PCRE_PARTIAL_SOFT, PCRE_DFA_SHORTEST, and
       PCRE_DFA_RESTART.  All but the last four of these are exactly the same as for pcre_exec(),
       so their description is not repeated here.

         PCRE_PARTIAL_HARD
         PCRE_PARTIAL_SOFT

       These have the same general effect as  they  do  for  pcre_exec(),  but  the  details  are
       slightly  different.  When  PCRE_PARTIAL_HARD  is  set  for  pcre_dfa_exec(),  it  returns
       PCRE_ERROR_PARTIAL if the end of the subject is reached and there is still  at  least  one
       matching  possibility  that requires additional characters. This happens even if some com-
       plete matches have also been  found.  When  PCRE_PARTIAL_SOFT  is  set,  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
       possibility.  The  portion of the string that was inspected when the longest partial match
       was found is set as the first matching string in both cases.  There  is  a  more  detailed
       discussion  of partial and multi-segment matching, with examples, in the pcrepartial docu-
       mentation.

         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 alternative algorithm works, this is necessar-
       ily the shortest possible match at the  first  possible  matching  point  in  the  subject
       string.

         PCRE_DFA_RESTART

       When  pcre_dfa_exec() 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 refer-
       ence 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 substring 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.  In fact, 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 longest matching string
       is given first. If there were too many matches to fit into ovector, the yield of the func-
       tion  is  zero,  and  the  vector  is filled with the longest matches. Unlike pcre_exec(),
       pcre_dfa_exec() can use the entire ovector for returning matched strings.

   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 pattern 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 that uses a back ref-
       erence for the condition, or a test for recursion in a specific group. These are not  sup-
       ported.

         PCRE_ERROR_DFA_UMLIMIT    (-18)

       This return is given if pcre_dfa_exec() is called with an extra block that contains a set-
       ting of the match_limit or match_limit_recursion fields.  This  is  not  supported  (these
       fields are meaningless for DFA matching).

         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.

         PCRE_ERROR_DFA_BADRESTART (-30)

       When  pcre_dfa_exec() is called with the PCRE_DFA_RESTART option, some plausibility checks
       are made on the contents of the workspace, which should contain data  about  the  previous
       partial match. If any of these checks fail, this error is given.

SEE ALSO

       pcre16(3),   pcre32(3),   pcrebuild(3),  pcrecallout(3),  pcrecpp(3)(3),  pcrematching(3),
       pcrepartial(3), pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).

AUTHOR

       Philip Hazel
       University Computing Service
       Cambridge CB2 3QH, England.

REVISION

       Last updated: 08 November 2012
       Copyright (c) 1997-2012 University of Cambridge.



PCRE 8.32                                08 November 2012                              PCREAPI(3)

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