Provided by: libpcre3-dev_8.39-9_amd64 bug

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.