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pcreapi

       #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);

       pcre_jit_stack *pcre_jit_stack_alloc(int startsize, int maxsize);

       void pcre_jit_stack_free(pcre_jit_stack *stack);

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

       const unsigned char *pcre_maketables(void);

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

       int pcre_refcount(pcre *code, int adjust);

       int pcre_config(int what, void *where);

       const char *pcre_version(void);

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


PCRE NATIVE API INDIRECTED FUNCTIONS


       void *(*pcre_malloc)(size_t);

       void (*pcre_free)(void *);

       void *(*pcre_stack_malloc)(size_t);

       void (*pcre_stack_free)(void *);

       int (*pcre_callout)(pcre_callout_block *);


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


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

       The 16-bit and 32-bit functions operate in the same way as their  8-bit
       counterparts;  they  just  use different data types for their arguments
       and results, and their names start with pcre16_ or pcre32_  instead  of
       pcre_.  For  every  option  that  has  UTF8  in  its name (for 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  val-
       ues.

       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_mal-
       loc()   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  sim-
       plest  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  dis-
       cussed in the pcrejit documentation.

       A second matching function, pcre_dfa_exec(), which is not Perl-compati-
       ble, is also provided. This uses a different algorithm for  the  match-
       ing.  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 docu-
       mentation.

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

         pcre_copy_substring()

       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, respec-
       tively. PCRE calls the memory management functions via these variables,
       so  a  calling  program  can replace them if it wishes to intercept the
       calls. This should be done before calling any PCRE functions.

       The global variables pcre_stack_malloc  and  pcre_stack_free  are  also
       indirections  to  memory  management functions. These special functions
       are used only when PCRE is compiled to use  the  heap  for  remembering
       data, instead of recursive function calls, when running the pcre_exec()
       function. See the pcrebuild documentation for  details  of  how  to  do
       this.  It  is  a non-standard way of building PCRE, for use in environ-
       ments that have limited stacks. Because of the greater  use  of  memory
       management,  it  runs  more  slowly. Separate functions are provided so
       that special-purpose external code can be  used  for  this  case.  When
       used,  these  functions  are always called in a stack-like manner (last
       obtained, first freed), and always for memory blocks of the same  size.
       There  is  a discussion about PCRE's stack usage in the pcrestack docu-
       mentation.

       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.


NEWLINES


       PCRE  supports five different conventions for indicating line breaks in
       strings: a single CR (carriage return) character, a  single  LF  (line-
       feed) character, the two-character sequence CRLF, any of the three pre-
       ceding, 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 stan-
       dard. When PCRE is run, the default can be overridden,  either  when  a
       pattern is compiled, or when it is matched.

       the  \n  or  \r  escape  sequences, nor does it affect what \R matches,
       which is controlled in a similar way, but by separate options.


MULTITHREADING


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

       The  compiled form of a regular expression is not altered during match-
       ing, 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 sepa-
       rate 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 regu-
       lar expression with one version of PCRE for use with a  different  ver-
       sion 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 dis-
       cover which optional features have been compiled into the PCRE library.
       The  pcrebuild documentation has more details about these optional fea-
       tures.

       The first argument for pcre_config() is an  integer,  specifying  which
       information is required; the second argument is a pointer to a variable
       into which the information is placed. The 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 avail-
       able; 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_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 architec-
       ture  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 corre-
       spond 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 pat-
       tern 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

       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  argu-
       ment, which is an address (see below).

       The options argument contains various bit settings that affect the com-
       pilation. 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

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

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

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

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

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

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

         PCRE_ANCHORED

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

         PCRE_AUTO_CALLOUT

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

         PCRE_BSR_ANYCRLF
         PCRE_BSR_UNICODE

       piled  with Unicode property support, but not otherwise. If you want to
       use caseless matching for characters 128 and  above,  you  must  ensure
       that  PCRE  is  compiled  with Unicode property support as well as with
       UTF-8 support.

         PCRE_DOLLAR_ENDONLY

       If this bit is set, a dollar metacharacter in the pattern matches  only
       at  the  end  of the subject string. Without this option, a dollar also
       matches immediately before 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 char-
       acter 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 set-
       ting of this option.

         PCRE_DUPNAMES

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

         PCRE_EXTENDED

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

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

       When PCRE_MULTILINE it is set, the "start of line" and  "end  of  line"
       constructs  match  immediately following or immediately before internal
       newlines in the subject string, respectively, as well as  at  the  very
       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 sep-
       arator, 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 sensi-
       ble. 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 #  out-
       side  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 paren-
       theses  in the pattern. Any opening parenthesis that is not followed by
       ? behaves as if it were followed by ?: but named parentheses can  still
       be  used  for  capturing  (and  they acquire numbers in the usual way).
       There is no equivalent of this option in Perl.

         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  match-
       ing  time.  For  details  see  the discussion of PCRE_NO_START_OPTIMIZE
       below.
       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  rea-
       sons,  you  can set the PCRE_NO_UTF8_CHECK option.  When it is set, the
       effect of passing an invalid UTF-8 string as a pattern is undefined. It
       may  cause  your  program  to  crash. Note that this option can also be
       passed to pcre_exec() and pcre_dfa_exec(),  to  suppress  the  validity
       checking  of  subject strings only. If the same string is being matched
       many times, the option can be safely set for the second and  subsequent
       matchings to improve performance.


COMPILATION ERROR CODES


       The  following  table  lists  the  error  codes than may be returned by
       pcre_compile2(), along with the error messages that may be returned  by
       both  compiling  functions.  Note  that error messages are always 8-bit
       ASCII strings, even in 16-bit or 32-bit mode. As  PCRE  has  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 )
         29  (?R or (?[+-]digits must be followed by )
         30  unknown POSIX class name
         31  POSIX collating elements are not supported
         32  this version of PCRE is compiled without UTF support
         33  [this code is not in use]
         34  character value in \x{...} sequence is too large
         35  invalid condition (?(0)
         36  \C not allowed in lookbehind assertion
         37  PCRE does not support \L, \l, \N{name}, \U, or \u
         38  number after (?C is > 255
         39  closing ) for (?C expected
         40  recursive call could loop indefinitely
         41  unrecognized character after (?P
         42  syntax error in subpattern name (missing terminator)
         43  two named subpatterns have the same name
         44  invalid UTF-8 string (specifically UTF-8)
         45  support for \P, \p, and \X has not been compiled
         46  malformed \P or \p sequence
         47  unknown property name after \P or \p
         48  subpattern name is too long (maximum 32 characters)
         49  too many named subpatterns (maximum 10000)
         50  [this code is not in use]
         51  octal value is greater than \377 in 8-bit non-UTF-8 mode
         52  internal error: overran compiling workspace
         53  internal error: previously-checked referenced subpattern
               not found
         54  DEFINE group contains more than one branch
         55  repeating a DEFINE group is not allowed
         56  inconsistent NEWLINE options
         57  \g is not followed by a braced, angle-bracketed, or quoted
               name/number or by a plain number
         58  a numbered reference must not be zero
         59  an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT)
         60  (*VERB) not recognized
         61  number is too big
         62  subpattern name expected
         63  digit expected after (?+
         64  ] is an invalid data character in JavaScript compatibility mode
         65  different names for subpatterns of the same number are
               not allowed
         66  (*MARK) must have an argument
         67  this version of PCRE is not compiled with Unicode property
               support
         68  \c must be followed by an ASCII character
         69  \k is not followed by a braced, angle-bracketed, or quoted name
         70  internal error: unknown opcode in find_fixedlength()
         71  \N is not supported in a class
         72  too many forward references
         73  disallowed Unicode code point (>= 0xd800 && <= 0xdfff)
         74  invalid UTF-16 string (specifically UTF-16)
         75  name is too long in (*MARK), (*PRUNE), (*SKIP), or (*THEN)
         76  character value in \u.... sequence is too large

       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  con-
       tains  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 pat-
       terns 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 documenta-
       tion.

       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.
         ...
         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 optimiza-
       tions can be disabled by setting the PCRE_NO_START_OPTIMIZE option when
       calling pcre_exec() or pcre_dfa_exec(), but if this is done, JIT execu-
       tion is also disabled. You might want to do this if your  pattern  con-
       tains  callouts or (*MARK) and you want to make use of these facilities
       in   cases   where   matching   fails.   See    the    discussion    of
       PCRE_NO_START_OPTIMIZE below.


LOCALE SUPPORT


       PCRE  handles  caseless matching, and determines whether characters are
       letters, digits, or whatever, by reference to a set of tables,  indexed
       by  character  value.  When running in UTF-8 mode, this applies only to
       characters with codes less than 128. By  default,  higher-valued  codes
       never match escapes such as \w or \d, but they can be tested with \p if
       PCRE is built with Unicode character property  support.  Alternatively,
       the  PCRE_UCP  option  can  be  set at compile time; this causes \w and
       friends to use Unicode property support instead of built-in tables. The
       use of locales with Unicode is discouraged. If you are handling charac-
       ters with codes greater than 128, you should either use UTF-8 and  Uni-
       code, 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 char-
       acters. However, when PCRE is built, it is possible to cause the inter-
       nal 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  Uni-
       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 normally also by pcre_exec(). Thus, by default, for any single pat-
       tern, compilation, studying and matching all happen in the same locale,
       but different patterns can be compiled in different locales.

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


INFORMATION ABOUT A PATTERN


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

       The pcre_fullinfo() function returns information about a compiled  pat-
       tern.  It replaces the pcre_info() function, which was removed from the
       library at version 8.30, after more than 10 years of obsolescence.

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

         PCRE_ERROR_NULL           the argument code was NULL
                                   the argument where was NULL
         PCRE_ERROR_BADMAGIC       the "magic number" was not found
         PCRE_ERROR_BADENDIANNESS  the pattern was compiled with different
                                   endianness
         PCRE_ERROR_BADOPTION      the value of what was invalid

       The  "magic  number" is placed at the start of each compiled pattern as
       an simple check against passing an arbitrary memory pointer. The  endi-
       anness 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() */

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

         PCRE_INFO_DEFAULT_TABLES

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

         PCRE_INFO_FIRSTBYTE

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

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

       If there is no fixed first value, and if either

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

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

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

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

         PCRE_INFO_FIRSTTABLE

       If  the pattern was studied, and this resulted in the construction of a
       256-bit table 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

       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  par-
       ticular  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 argu-
       ment 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 the character, this value
       is   deprecated;   instead    the    PCRE_INFO_REQUIREDCHARFLAGS    and
       PCRE_INFO_REQUIREDCHAR values should be used.

         PCRE_INFO_MAXLOOKBEHIND

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

         PCRE_INFO_MINLENGTH

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

         PCRE_INFO_NAMECOUNT
         PCRE_INFO_NAMEENTRYSIZE
         PCRE_INFO_NAMETABLE

       PCRE  supports the use of named as well as numbered capturing parenthe-
       ses. The names are just an additional way of identifying the  parenthe-
       ber  of  the capturing parenthesis, most significant byte first. In the
       16-bit library, the pointer points to 16-bit data units, the  first  of
       which  contains  the  parenthesis  number.   In the 32-bit library, the
       pointer points to 32-bit data units, the first of  which  contains  the
       parenthesis  number.  The  rest of the entry is the corresponding name,
       zero terminated.

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

         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

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

         PCRE_INFO_SIZE

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

         PCRE_INFO_STUDYSIZE

       Return the size in bytes of the data block pointed to by the study_data
       field  in  a  pcre_extra  block.  If pcre_extra is NULL, or there is no
       study data, zero is returned. The fourth argument  should  point  to  a
       size_t  variable. The study_data field is set by pcre_study() to record
       information that will speed  up  matching  (see  the  section  entitled
       "Studying a pattern" above). The format of the study_data block is pri-
       vate, 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_FIRSTCHARACTERFLAGS

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

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

       If there is no fixed first value, and if either

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

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

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

         PCRE_INFO_FIRSTCHARACTER

       Return the fixed first character  value,  if  PCRE_INFO_FIRSTCHARACTER-
       set (if it were set, the pattern would be anchored),

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

         PCRE_INFO_REQUIREDCHARFLAGS

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

       For anchored patterns, a last literal value is recorded only if it fol-
       lows 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);

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

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

         int rc;
         int ovector[30];
         rc = pcre_exec(
           re,             /* result of pcre_compile() */
           NULL,           /* we didn't study the pattern */
           "some string",  /* the subject string */
           11,             /* the length of the subject string */
           0,              /* start at offset 0 in the subject */
           0,              /* default options */
           ovector,        /* vector of integers for substring information */
           30);            /* number of elements (NOT size in bytes) */

   Extra data for pcre_exec()

       If the extra argument is not NULL, it must point to a  pcre_extra  data
       block.  The pcre_study() function returns such a block (when it doesn't
       return NULL), but you can also create one for yourself, and pass  addi-
       tional  information  in it. The 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

       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 match-
       ing can continue.

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

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

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

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

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

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

       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 descrip-
       tion of pcre_compile()  above.  During  matching,  the  newline  choice
       affects  the  behaviour  of the dot, circumflex, and dollar metacharac-
       ters. 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  cur-
       rent  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
         PCRE_NOTBOL

       This option specifies that first character of the subject string is not
       the beginning of a line, so the  circumflex  metacharacter  should  not
       match  before it. Setting this without PCRE_MULTILINE (at compile time)
       causes circumflex never to match. This option affects only  the  behav-
       iour of the circumflex metacharacter. It does not affect \A.

         PCRE_NOTEOL

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

         PCRE_NOTEMPTY

       An empty string is not considered to be a valid match if this option is
       set.  If  there are alternatives in the pattern, they are tried. If all
       the alternatives match the empty string, the entire  match  fails.  For
       example, if the pattern

         a?b?

       is  applied  to  a  string not beginning with "a" or "b", it matches 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 occur-
       rences 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 off-
       set  with  PCRE_NOTEMPTY_ATSTART  and  PCRE_ANCHORED,  and then if that
       fails, by advancing the starting offset (see below) and trying an ordi-
       nary  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

       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 disables JIT execution; when it is set, matching
       is always done using interpretively.

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

         (*COMMIT)ABC

       When  this  is  compiled, PCRE records the fact that a match must start
       with the character "A". Suppose the subject  string  is  "DEFABC".  The
       start-up  optimization  scans along the subject, finds "A" and runs the
       first match attempt from there. The (*COMMIT) item means that the  pat-
       tern  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  opti-
       mizations  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  enti-
       tled  Error return values from pcre_exec() below).  If startoffset con-
       tains 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.

       These options turn on the partial matching feature. For backwards  com-
       patibility,  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  consid-
       ered to be more important that an alternative complete match.

       In  both  cases,  the portion of the string that was inspected when the
       partial match was found is set as the first matching string. There is a
       more  detailed  discussion  of partial and multi-segment matching, with
       examples, in the pcrepartial documentation.

   The string to be matched by pcre_exec()

       The subject string is passed to pcre_exec() as a pointer in subject,  a
       length  in  bytes in length, and a starting byte offset in startoffset.
       If this is  negative  or  greater  than  the  length  of  the  subject,
       pcre_exec()  returns  PCRE_ERROR_BADOFFSET. When the starting offset is
       zero, the search for a match starts at the beginning  of  the  subject,
       and this is by far the most common case. In UTF-8 mode, the byte offset
       must point to the start of a UTF-8 character (or the end  of  the  sub-
       ject).  Unlike  the pattern string, the subject may contain binary zero
       bytes.

       A non-zero starting offset is useful when searching for  another  match
       in  the same subject by calling pcre_exec() again after a previous suc-
       cess.  Setting startoffset differs from just passing over  a  shortened
       string  and  setting  PCRE_NOTBOL  in the case of a pattern that begins
       with any kind of lookbehind. For example, consider the pattern

         \Biss\B

       which finds occurrences of "iss" in the middle of  words.  (\B  matches
       only  if  the  current position in the subject is not a word boundary.)
       When applied to the string "Mississipi" the first call  to  pcre_exec()
       finds  the  first  occurrence. If pcre_exec() is called again with just
       the remainder of the subject,  namely  "issipi",  it  does  not  match,
       because \B is always false at the start of the subject, which is deemed
       to be a word boundary. However, if pcre_exec()  is  passed  the  entire
       string again, but with startoffset set to 4, it finds the second occur-
       rence of "iss" because it is able to look behind the starting point  to
       discover that it is preceded by a letter.
       if the pattern does not require the match to be at  the  start  of  the
       subject.

   How pcre_exec() returns captured substrings

       In  general, a pattern matches a certain portion of the subject, and in
       addition, further substrings from the subject  may  be  picked  out  by
       parts  of  the  pattern.  Following the usage in Jeffrey Friedl's book,
       this is called "capturing" in what follows, and the  phrase  "capturing
       subpattern"  is  used for a fragment of a pattern that picks out a sub-
       string. PCRE supports several other kinds of  parenthesized  subpattern
       that do not cause substrings to be captured.

       Captured substrings are returned to the caller via a vector of integers
       whose address is passed in ovector. The number of elements in the  vec-
       tor  is  passed in ovecsize, which must be a non-negative number. Note:
       this argument is NOT the size of ovector in bytes.

       The first two-thirds of the vector is used to pass back  captured  sub-
       strings,  each  substring using a pair of integers. The remaining third
       of the vector is used as workspace by pcre_exec() while  matching  cap-
       turing  subpatterns, and is not available for passing back information.
       The number passed in ovecsize should always be a multiple of three.  If
       it is not, it is rounded down.

       When  a  match  is successful, information about captured substrings is
       returned in pairs of integers, starting at the  beginning  of  ovector,
       and  continuing  up  to two-thirds of its length at the most. The first
       element of each pair is set to the byte offset of the  first  character
       in  a  substring, and the second is set to the byte offset of the first
       character after the end of a substring. Note: these values  are  always
       byte offsets, even in UTF-8 mode. They are not character counts.

       The  first  pair  of  integers, ovector[0] and ovector[1], identify the
       portion of the subject string matched by the entire pattern.  The  next
       pair  is  used for the first capturing 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 pat-
       tern contains back references and the ovector  is  not  big  enough  to
       remember  the related substrings, PCRE has to get additional memory for
       slots (namely 2) have been filled. In similar cases where there is tem-
       porary  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 corre-
       sponding 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  corre-
       spond  to  capturing parentheses in the pattern are never changed. That
       is, if a pattern contains n capturing parentheses, no more  than  ovec-
       tor[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)

       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  ele-
       ment,  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 char-
       acter  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 charac-
       ter 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.

       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  implementa-
       tion  of returned information; it is retained for backwards compatibil-
       ity.

         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, can-
       not 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)

         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_SHORT-
       UTF8, 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  (origi-
       nally  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.
       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  cor-
       rect 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  sec-
       ond  is  0). Such a byte can only validly occur as the second or subse-
       quent byte of a multi-byte character.

         PCRE_UTF8_ERR21

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

         PCRE_UTF8_ERR2

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


EXTRACTING CAPTURED SUBSTRINGS BY NUMBER


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

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

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

       Captured  substrings  can  be  accessed  directly  by using the offsets
       returned by pcre_exec() in  ovector.  For  convenience,  the  functions
       pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
       string_list() are provided for extracting captured substrings  as  new,
       separate,  zero-terminated strings. These functions identify substrings
       by number. The next section describes functions  for  extracting  named
       substrings.

       A  substring that contains a binary zero is correctly extracted and has
       a further zero added on the end, but the result is not, of course, a  C
       string.   However,  you  can  process such a string by referring to the
       length that is  returned  by  pcre_copy_substring()  and  pcre_get_sub-
       string().  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 func-
       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  sub-
       strings  and  builds  a list of pointers to them. All this is done in a
       single block of memory that is obtained via pcre_malloc. The address of
       the  memory  block  is returned via listptr, which is also the start of
       the list of string pointers. The end of the list is marked  by  a  NULL
       pointer.  The  yield  of  the function is zero if all went well, or 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 sub-
       string by inspecting the appropriate offset in ovector, which is  nega-
       tive for unset substrings.

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


EXTRACTING CAPTURED SUBSTRINGS BY NAME


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

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

       piled pattern, and the second is the name. The yield of the function is
       the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if  there  is  no
       subpattern of that name.

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

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

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

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


FINDING ALL POSSIBLE MATCHES


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

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


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 call-
       ing  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 nega-
       tive 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
       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_NEW-
       LINE_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_PAR-
       TIAL_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  sub-
       ject  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 exam-
       ples, in the pcrepartial documentation.

         PCRE_DFA_SHORTEST

       Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to

   Successful returns from pcre_dfa_exec()

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

         <.*>

       is matched against the string

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

       the three matched strings are

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

       On  success,  the  yield of the function is a number greater than zero,
       which is the number of matched substrings.  The  substrings  themselves
       are  returned  in  ovector. Each string uses two elements; the first is
       the offset to the start, and the second is the offset to  the  end.  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 long-
       est  matching  string is given first. If there were too many matches to
       fit into ovector, the yield of the function is zero, and the vector  is
       filled  with  the  longest matches. Unlike pcre_exec(), pcre_dfa_exec()
       can use the entire ovector for returning matched strings.

   Error returns from pcre_dfa_exec()

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

         PCRE_ERROR_DFA_UITEM      (-16)

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

         PCRE_ERROR_DFA_UCOND      (-17)

       This  return  is  given  if pcre_dfa_exec() encounters a condition item
       that uses a back reference for the condition, or a test  for  recursion
         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), pcre-
       sample(3), pcrestack(3).


AUTHOR


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


REVISION


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


PCRE 8.32 08 November 2012 PCREAPI(3)



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