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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 *);

       int (*pcre_stack_guard)(void);

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  example,  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  units  and
       UTF-16  when  using  the  16-bit  library, or 32-bit data units 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 numbers 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 documentation, 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  appropriate  hardware
       environments.  It greatly speeds up the matching performance of many patterns. 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 provided. 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 disadvantages 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 compiled pattern.
       This is provided for the benefit of object-oriented applications.

       The global variables pcre_malloc and pcre_free  initially  contain  the  entry  points  of  the  standard
       malloc()  and  free()  functions,  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 always allocate 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 operation. Details are given in
       the pcrecallout documentation.

       The global variable pcre_stack_guard initially contains NULL. It can be set by the caller to  a  function
       that  is called by PCRE whenever it starts to compile a parenthesized part of a pattern. When parentheses
       are nested, PCRE uses recursive function calls, which use up the system stack. This function is  provided
       so  that  applications  with  restricted  stacks can force a compilation error if the stack runs out. The
       function should return zero if all is well, or non-zero to force an error.

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  standard  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 overridden, 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 handling 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 and stack-checking functions pointed to by pcre_callout and pcre_stack_guard, are  shared  by
       all threads.

       The  compiled  form  of a regular expression is not altered during matching, so the same compiled 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, possibly by a
       different program, and even on a host other than the one on which it was compiled. Details are  given  in
       the  pcreprecompile  documentation, 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 function, 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 function, 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  recognized  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 environments, CR, ANYCRLF,  and  ANY  yield  the
       same  values.  However,  the  value  for  LF  is normally 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_PARENS_LIMIT

       The  output  is  a long integer that gives the maximum depth of nesting of parentheses (of any kind) in a
       pattern. This limit is imposed to cap the amount of system stack used when a pattern is compiled.  It  is
       specified  when  PCRE  is built; the default is 250. This limit does not take into account the stack that
       may already be used by the calling application. For finer control over compilation stack usage,  you  can
       set a pointer to an external checking function in pcre_stack_guard.

         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 pattern into an
       internal form. The only difference between the two interfaces is that pcre_compile2() has  an  additional
       argument,  errorcodeptr,  via which a numerical error code can be returned. 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 argument.  A  pointer
       to a single block of memory that is obtained via pcre_malloc is returned. This contains the compiled code
       and related data. The pcre type is defined for the returned block; this is  a  typedef  for  a  structure
       whose contents are not externally defined. It is up to the caller to free the memory (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 data unit 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 or UTF-16 string, the offset is that  of  the
       first data unit 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 data units, not characters, even in  a  UTF
       mode. It may sometimes point into the middle of a UTF-8 or UTF-16 character.

       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() and pcre_dfa_exec() when the pattern is matched. 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, most white space characters in the pattern are totally ignored except when escaped or
       inside a character class. However, white space is not allowed within sequences such as (?> that introduce
       various parenthesized subpatterns, nor within a numerical quantifier such as {1,3}.   However,  ignorable
       white  space  is  permitted  between  an  item  and a following quantifier and between a quantifier and a
       following + that indicates possessiveness.

       White space did not used to include the VT character (code 11), because Perl did not treat this character
       as  white  space.  However, Perl changed at release 5.18, so PCRE followed at release 8.34, and VT is now
       treated as white space.

       PCRE_EXTENDED also causes characters between an unescaped #  outside  a  character  class  and  the  next
       newline, inclusive, to be ignored. PCRE_EXTENDED 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, however, 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 digits, 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,  for  the  purposes  of  matching "start of line" and "end of line", 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, and the "end of line" metacharacter ($)
       matches only at the end of the string, or before a terminating newline (except  when  PCRE_DOLLAR_ENDONLY
       is  set).  Note,  however, that unless PCRE_DOTALL is set, the "any character" metacharacter (.) does not
       match at a newline. This behaviour (for ^, $, and dot) 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_MULTILINE has no effect.

         PCRE_NEVER_UTF

       This option locks out interpretation of the pattern as UTF-8 (or UTF-16  or  UTF-32  in  the  16-bit  and
       32-bit  libraries).  In  particular,  it  prevents  the  creator  of  the  pattern  from switching to UTF
       interpretation by starting the pattern with (*UTF). This may  be  useful  in  applications  that  process
       patterns from external sources. The combination of PCRE_UTF8 and PCRE_NEVER_UTF also causes an error.

         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 character (CR or LF, respectively).
       Setting  PCRE_NEWLINE_CRLF  specifies  that  a  newline  is indicated 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 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).  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, giving 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_NEWLINE_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 pattern. Any opening
       parenthesis that is not followed by ? behaves as if it were followed by  ?:  but  named  parentheses  can
       still  be  used for capturing (and they acquire numbers in the usual way). There is no equivalent of this
       option in Perl.

         PCRE_NO_AUTO_POSSESS

       If this option is set, it disables "auto-possessification". This is an optimization  that,  for  example,
       turns  a+b  into  a++b  in  order  to  avoid backtracks into a+ that can never be successful. However, if
       callouts are in use, auto-possessification means that some of them are never  taken.  You  can  set  this
       option  if  you want the matching functions to do a full unoptimized search and run all the callouts, but
       it is mainly provided for testing purposes.

         PCRE_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. This is necessary if you want to use JIT execution, because the JIT compiler needs to know
       whether or not this option is set. 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
       or  loop.  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 developed, 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{} or \o{} 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 or malformed
         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)
         78  setting UTF is disabled by the application
         79  non-hex character in \x{} (closing brace missing?)
         80  non-octal character in \o{} (closing brace missing?)
         81  missing opening brace after \o
         82  parentheses are too deeply nested
         83  invalid range in character class
         84  group name must start with a non-digit
         85  parentheses are too deeply nested (stack check)

       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 produces additional information that will help
       speed up matching, pcre_study() returns a pointer to a pcre_extra block, in which  the  study_data  field
       points to the results of the study.

       The returned value from pcre_study() can be passed directly to pcre_exec() 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 matching 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. However, 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 further compiled into
       machine  code that executes much faster than the pcre_exec() interpretive 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 succeeds (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 earlier 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.
       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.

       PCRE_NO_START_OPTIMIZE  can  be  specified  at  either  compile  time  or  execution  time.  However,  if
       PCRE_NO_START_OPTIMIZE is passed to pcre_exec(), (that is, after any JIT compilation  has  happened)  JIT
       execution  is  disabled. For JIT execution to work with PCRE_NO_START_OPTIMIZE, the option must be set at
       compile time.

       There is a longer 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 code point. When running in UTF-8 mode, or in the 16-
       or 32-bit libraries, this applies only to characters with code points less than 256. By default,  higher-
       valued  code points never match escapes such as \w or \d. However, if PCRE is built with Unicode property
       support, all characters can be tested with \p and \P, or, alternatively, the PCRE_UCP option can  be  set
       when  a  pattern  is  compiled; this causes \w and friends to use Unicode property support instead of the
       built-in tables.

       The use of locales with Unicode is discouraged. If you are handling characters with code  points  greater
       than 128, you should either use Unicode support, 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_compile() 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  arguments,  in  the
       relevant  locale.  The result can then be passed to pcre_compile() as often as necessary. For example, to
       build and use tables that are appropriate for the French locale (where accented  characters  with  values
       greater than 128 are treated as letters), the following code could be used:

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

       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_malloc. It  is  the
       caller's  responsibility to ensure that the memory containing the tables remains available for as long as
       it is needed.

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

       It is possible to pass a table pointer or NULL (indicating the use of the internal tables) to pcre_exec()
       or pcre_dfa_exec() (see the discussion below in the section on matching  a  pattern).  This  facility  is
       provided  for use with pre-compiled patterns that have been saved and reloaded.  Character tables are not
       saved with patterns, so if a non-standard table was used at compile time, it must be provided again  when
       the reloaded pattern is matched. Attempting to use this facility to match a pattern in a different locale
       from the one in which it was compiled is likely to lead to anomalous (usually incorrect) results.

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
         PCRE_ERROR_UNSET          the requested field is not set

       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 internal 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 (deprecated)

       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. Negative values are used for special cases. However, this means that when the  32-bit
       library  is  in non-UTF-32 mode, the full 32-bit range of characters cannot be returned. For this reason,
       this value is deprecated; use PCRE_INFO_FIRSTCHARACTERFLAGS and PCRE_INFO_FIRSTCHARACTER instead.

       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.

         PCRE_INFO_FIRSTCHARACTER

       Return the value of the first data unit (non-UTF character) of any matched string in the situation  where
       PCRE_INFO_FIRSTCHARACTERFLAGS  returns  1;  otherwise  return  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.

         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_FIRSTTABLE

       If  the  pattern was studied, and this resulted in the construction of a 256-bit table indicating 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 literal 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 compiling 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 compiled 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 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 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   characters,   this   value   is  deprecated;  instead  the  PCRE_INFO_REQUIREDCHARFLAGS  and
       PCRE_INFO_REQUIREDCHAR values should be used.

         PCRE_INFO_MATCH_EMPTY

       Return 1 if the pattern can match an empty string, otherwise 0. The fourth argument should  point  to  an
       int variable.

         PCRE_INFO_MATCHLIMIT

       If  the  pattern set a match limit by including an item of the form (*LIMIT_MATCH=nnnn) at the start, the
       value is returned. The fourth argument should point to an unsigned 32-bit integer. If no such  value  has
       been set, the call to pcre_fullinfo() returns the error PCRE_ERROR_UNSET.

         PCRE_INFO_MAXLOOKBEHIND

       Return  the  number of characters (NB not data units) in the longest lookbehind assertion in the pattern.
       This information is useful when doing multi-segment matching using the partial matching facilities.  Note
       that  the  simple  assertions  \b  and  \B  require  a one-character lookbehind. \A also registers a one-
       character lookbehind, though it does not actually inspect the previous character. This is to ensure  that
       at  least  one  character from the old segment is retained when a new segment is processed. Otherwise, if
       there are no lookbehinds in the pattern, \A might match incorrectly at the start of a new segment.

         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 characters, which in UTF mode may
       be different from the number of data units. 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. Several 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 vector (described with pcre_exec() below). To do the conversion, you  need
       to use the name-to-number map, which is described by these three values.

       The  map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives the number of entries, and
       PCRE_INFO_NAMEENTRYSIZE gives the size of each entry; both of these return an int value. The  entry  size
       depends  on  the  length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first entry of
       the table. 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. If (?| is used to create multiple groups with the  same  number,  as
       described in the section on duplicate subpattern numbers in the pcrepattern page, the groups may be given
       the same name, but there is only one entry in the table. Different names for groups of  the  same  number
       are  not  permitted.   Duplicate  names for subpatterns with different numbers are permitted, but only if
       PCRE_DUPNAMES is set. 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  compilation  by  the
       8-bit library (assume PCRE_EXTENDED is set, so white space - including newlines - 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 table is eight
       bytes long. The table is as follows, with non-printing bytes shows in hexadecimal,  and  undefined  bytes
       shown as ??:

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

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

         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_RECURSIONLIMIT

       If the pattern set a recursion limit by including an item of  the  form  (*LIMIT_RECURSION=nnnn)  at  the
       start,  the value is returned. The fourth argument should point to an unsigned 32-bit integer. If no such
       value has been set, the call to pcre_fullinfo() returns the error PCRE_ERROR_UNSET.

         PCRE_INFO_SIZE

       Return the size of the compiled pattern in bytes (for all three libraries). The  fourth  argument  should
       point  to  a size_t variable. This value does not include the size of the pcre structure 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 (for all three libraries) 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 pcreprecompile documentation for details).

         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 contains 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  executable_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  (sometimes
       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 backtracking 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.

       A value for the match limit may also be supplied by an item at the start of a pattern of the form

         (*LIMIT_MATCH=d)

       where d is a decimal number. However, such a setting is ignored unless d is less than the  limit  set  by
       the caller of pcre_exec() or, if no such limit is set, less than the default.

       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 recursion 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.

       A value for the recursion limit may also be supplied by an item at the start of a pattern of the form

         (*LIMIT_RECURSION=d)

       where  d  is  a decimal number. However, such a setting is ignored unless d is less than the limit set by
       the caller of pcre_exec() or, if no such limit is set, less than the default.

       The callout_data field is used in conjunction with  the  "callout"  feature,  and  is  described  in  the
       pcrecallout documentation.

       The  tables  field  is  provided for use with patterns that have been pre-compiled using custom character
       tables, saved to disc or elsewhere, and then reloaded, because the tables that were  used  to  compile  a
       pattern  are  not saved with it. See the pcreprecompile documentation for a discussion of saving compiled
       patterns for later use. If NULL is passed using this mechanism, it forces PCRE's internal  tables  to  be
       used.

       Warning:  The  tables that pcre_exec() uses must be the same as those that were used when the pattern was
       compiled. If this is not the case, the behaviour of pcre_exec() is undefined. Therefore, when  a  pattern
       is  compiled  and  matched in the same process, this field should never be set. In this (the most common)
       case, the correct table pointer is automatically passed with the compiled pattern from pcre_compile()  to
       pcre_exec().

       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_PARTIAL_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 pattern was compiled.
       For details, see the description of pcre_compile() above. During matching, the newline choice affects the
       behaviour of the dot, circumflex, and dollar metacharacters. 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 immediately 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 considered until after a suitable starting point for the match has been found. Also, 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  compile  time,  it  cannot be unset at matching time. The use of
       PCRE_NO_START_OPTIMIZE at matching time (that is, passing it to pcre_exec()) disables JIT  execution;  in
       this situation, 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 performance
       reasons, you can set the PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might want  to  do  this
       for  the  second  and  subsequent  calls  to pcre_exec() if you are making repeated calls to find all the
       matches in a single subject string. However, you should be sure that the value of startoffset  points  to
       the  start  of  a  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 or loop.

         PCRE_PARTIAL_HARD
         PCRE_PARTIAL_SOFT

       These  options  turn  on  the  partial  matching  feature. For backwards compatibility, PCRE_PARTIAL 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 length, and  a  starting
       offset  in startoffset. The units for length and startoffset are bytes for the 8-bit library, 16-bit data
       items for the 16-bit library, and 32-bit data items for the 32-bit library.

       If  startoffset  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 or UTF-16 mode, the offset must  point  to
       the  start of a character, or the end of the subject (in UTF-32 mode, one data unit equals one character,
       so all offsets are valid). Unlike the pattern string, the subject may contain binary zeroes.

       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 characters 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 "capturing 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 substring using a pair
       of integers. The remaining third of the vector  is  used  as  workspace  by  pcre_exec()  while  matching
       capturing  subpatterns,  and is not available for passing back information. The 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 offset of the first character in a substring, and the second  is
       set  to the offset of the first character after the end of a substring. These values are always data unit
       offsets, even in UTF mode. They are byte offsets in the 8-bit library, 16-bit data item  offsets  in  the
       16-bit library, and 32-bit data item offsets in the 32-bit library. Note: 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 subpattern, and  so  on.  The  value
       returned  by  pcre_exec()  is one more than the highest numbered 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 successful 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 substrings, 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 highest 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_substring_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  documentation  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  matching.  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 correspond  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 argument.

       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_ERR22

       This  error  code  was  formerly  used  when the presence of a so-called "non-character" caused an error.
       Unicode corrigendum #9 makes it clear that such characters should not cause a string to be rejected,  and
       so this code is no longer in use and is never returned.

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, separate, zero-terminated strings. These functions
       identify substrings by number. The next section describes functions for extracting named substrings.

       A substring that contains a binary zero is correctly extracted and has a further zero added on  the  end,
       but the result is not, of course, a C string.  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 substrings  that  were  captured  by  the  match,
       including  the  substring  that  matched  the  entire  regular  expression. This is the value returned by
       pcre_exec() if it is greater than zero. If pcre_exec() returned zero, indicating that it ran out of space
       in  ovector,  the  value  passed as stringcount should be the number of elements in the vector divided by
       three.

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

       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  captured
       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 certain 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 pattern, 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 compatible 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_UNICODE,   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 complete 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 documentation.

         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 necessarily 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  additional  subject
       characters,  and  have it continue with the same match. The PCRE_DFA_RESTART option requests this action;
       when it is set, the workspace and wscount options must reference the same vector as before  because  data
       about  the  match so far is left in them after a partial match. There is more discussion of this facility
       in the pcrepartial documentation.

   Successful returns from pcre_dfa_exec()

       When pcre_dfa_exec() succeeds, it may have matched more than one 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 function 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.

       NOTE: PCRE's "auto-possessification" optimization usually applies to character repeats at the  end  of  a
       pattern  (as  well  as  internally).  For  example,  the pattern "a\d+" is compiled as if it were "a\d++"
       because there is no point even considering the possibility of backtracking into the repeated digits.  For
       DFA matching, this means that only one possible match is found. If you really do want multiple matches in
       such cases, either use  an  ungreedy  repeat  ("a\d+?")  or  set  the  PCRE_NO_AUTO_POSSESS  option  when
       compiling.

   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  reference  for  the
       condition, or a test for recursion in a specific group. These are not supported.

         PCRE_ERROR_DFA_UMLIMIT    (-18)

       This  return  is  given  if  pcre_dfa_exec() is called with an extra block that contains a setting of the
       match_limit 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: 18 December 2015
       Copyright (c) 1997-2015 University of Cambridge.