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PCREAPI(3)                                                          PCREAPI(3)



NAME
       PCRE - Perl-compatible regular expressions

PCRE NATIVE API BASIC FUNCTIONS

       #include <pcre.h>

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

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

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

       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);

PCRE NATIVE API AUXILIARY FUNCTIONS

       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);

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

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

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

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

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

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

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

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

       void pcre_free_substring(const char *stringptr);

       void pcre_free_substring_list(const char **stringptr);

       const unsigned char *pcre_maketables(void);

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

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

       int pcre_refcount(pcre *code, int adjust);

       int pcre_config(int what, void *where);

       char *pcre_version(void);

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 API OVERVIEW

       PCRE  has  its  own native API, which is described in this document. There are also some wrapper functions that
       correspond to the POSIX regular expression API, but they do not give access to all the functionality. They  are
       described in the pcreposix documentation. Both of these APIs define a set of C function calls. A C++ wrapper 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  systems  the  library
       itself  is called libpcre.  It can normally be accessed by adding -lpcre to the command for linking an applica-
       tion that uses PCRE. The header file defines the macros PCRE_MAJOR and PCRE_MINOR  to  contain  the  major  and
       minor release numbers for the library.  Applications can use these to include support for different releases of
       PCRE.

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

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

       Just-in-time compiler support is an optional feature of PCRE that can be built in appropriate hardware environ-
       ments. 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 pro-
       grams  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.  These functions are discussed in the
       pcrejit documentation.

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

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

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

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

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

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

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

       The  global variables pcre_malloc and pcre_free initially contain the entry points of the standard malloc() and
       free() functions, respectively. PCRE calls the memory management functions via these variables,  so  a  calling
       program can replace them if it wishes to intercept the calls. This should be done before calling any PCRE func-
       tions.

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

       The  global variable pcre_callout initially contains NULL. It can be set by the caller to a "callout" function,
       which PCRE will then call at specified points during a matching 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 (linefeed) character, the two-character sequence CRLF, any of the  three  preceding,  or
       any Unicode newline sequence. The Unicode newline sequences are the three just mentioned, plus the single char-
       acters VT (vertical tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS (line separator,  U+2028),
       and PS (paragraph separator, U+2029).

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

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

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

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

MULTITHREADING

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

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

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

SAVING PRECOMPILED PATTERNS FOR LATER USE

       The compiled form of a regular expression can be saved and re-used at a later time,  possibly  by  a  different
       program,  and  even on a host other than the one on which it was compiled. Details are given in the pcreprecom-
       pile documentation. However, compiling a regular expression with one version of PCRE for use with  a  different
       version is not guaranteed to work and may cause crashes.

CHECKING BUILD-TIME OPTIONS

       int pcre_config(int what, void *where);

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

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

         PCRE_CONFIG_UTF8

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

         PCRE_CONFIG_UNICODE_PROPERTIES

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

         PCRE_CONFIG_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_NEWLINE

       The  output  is  an  integer whose value specifies the default character sequence that is recognized as meaning
       "newline". The four values that are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF, and  -1
       for  ANY.  Though they are derived from ASCII, the same values are returned in EBCDIC environments. The default
       should normally correspond to the standard sequence for your operating system.

         PCRE_CONFIG_BSR

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

         PCRE_CONFIG_LINK_SIZE

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

         PCRE_CONFIG_POSIX_MALLOC_THRESHOLD

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

         PCRE_CONFIG_MATCH_LIMIT

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

         PCRE_CONFIG_MATCH_LIMIT_RECURSION

       The  output is a long integer that gives the default limit for the depth of recursion when calling the internal
       matching function in a pcre_exec() execution. Further details are given with pcre_exec() below.

         PCRE_CONFIG_STACKRECURSE

       The output is an integer that is set to one if internal recursion when running pcre_exec()  is  implemented  by
       recursive  function  calls  that use the stack to remember their state. This is the usual way that PCRE is com-
       piled. 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, error-
       codeptr, via which a numerical error code can be returned. To avoid too  much  repetition,  we  refer  just  to
       pcre_compile() below, but the information applies equally to pcre_compile2().

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

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

       The options argument contains various bit settings that affect the compilation. It should be zero if no options
       are required. The available options are described below. Some of them (in particular, those that are compatible
       with  Perl,  but  some  others  as  well)  can  also be set and unset from within the pattern (see the detailed
       description in the pcrepattern documentation). For those options that can be different in  different  parts  of
       the pattern, the contents of the options argument specifies their settings at the start of compilation and exe-
       cution. The PCRE_ANCHORED, PCRE_BSR_xxx, PCRE_NEWLINE_xxx, PCRE_NO_UTF8_CHECK,  and  PCRE_NO_START_OPT  options
       can be set at the time of matching as well as at compile time.

       If  errptr  is  NULL,  pcre_compile()  returns NULL immediately.  Otherwise, if compilation of a pattern fails,
       pcre_compile() returns NULL, and sets the variable pointed to by errptr to point to a  textual  error  message.
       This is a static string that is part of the library. You must not try to free it. Normally, the offset from the
       start of the pattern to the byte that was being processed when the error was discovered is placed in the  vari-
       able  pointed  to by erroffset, which must not be NULL (if it is, an immediate error is given). However, for an
       invalid UTF-8 string, the offset is that of the first byte of the failing character. Also, some errors are  not
       detected until checks are carried out when 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 errorcodeptr argument is not NULL, a non-zero
       error code number is returned via this argument in the event of an error. This is in addition  to  the  textual
       error message. Error codes and messages are listed below.

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

       This code fragment shows a typical straightforward call to pcre_compile():

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

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

         PCRE_ANCHORED

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

         PCRE_AUTO_CALLOUT

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

         PCRE_BSR_ANYCRLF
         PCRE_BSR_UNICODE

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

         PCRE_CASELESS

       If this bit is set, letters in the pattern match both upper and lower case letters. It is equivalent to  Perl's
       /i  option,  and it can be changed within a pattern by a (?i) option setting. In UTF-8 mode, PCRE always under-
       stands the concept of case for characters whose values are less than 128, so caseless matching is always possi-
       ble. For characters with higher values, the concept of case is supported if PCRE is compiled with Unicode prop-
       erty 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. With-
       out 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 equiva-
       lent to this option in Perl, and no way to set it within a pattern.

         PCRE_DOTALL

       If this bit is set, a dot metacharacter in the pattern matches a character of any  value,  including  one  that
       indicates  a  newline. However, it only ever matches one character, even if newlines are coded as CRLF. Without
       this option, a dot does not match when the current position is at a  newline.  This  option  is  equivalent  to
       Perl's  /s  option,  and  it can be changed within a pattern by a (?s) option setting. A negative class such as
       [^a] always matches newline characters, independent of the setting of this option.

         PCRE_DUPNAMES

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

         PCRE_EXTENDED

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

       Which characters are interpreted as newlines is controlled by the options passed to pcre_compile() or by a spe-
       cial sequence at the start of the pattern, as described in the section entitled "Newline  conventions"  in  the
       pcrepattern  documentation. Note that the end of this type of comment is a literal newline sequence in the pat-
       tern; 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. Whitespace characters may never appear within special character sequences in a
       pattern, for example within the sequence (?( that introduces a conditional subpattern.

         PCRE_EXTRA

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

         PCRE_FIRSTLINE

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

         PCRE_JAVASCRIPT_COMPAT

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

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

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

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

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

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

         PCRE_MULTILINE

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

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

         PCRE_NEWLINE_CR
         PCRE_NEWLINE_LF
         PCRE_NEWLINE_CRLF
         PCRE_NEWLINE_ANYCRLF
         PCRE_NEWLINE_ANY

       These options override the default newline definition that was chosen when PCRE was built. Setting the first or
       the  second  specifies  that  a  newline  is  indicated by a single character (CR or LF, respectively). Setting
       PCRE_NEWLINE_CRLF specifies that a newline is indicated by the two-character CRLF sequence.  Setting  PCRE_NEW-
       LINE_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. The Unicode newline sequences are  the  three
       just  mentioned,  plus  the single characters VT (vertical tab, U+000B), FF (formfeed, U+000C), NEL (next line,
       U+0085), LS (line separator, U+2028), and PS (paragraph separator, U+2029). The last two are recognized only in
       UTF-8 mode.

       The  newline  setting in the options word uses three bits that are treated as a number, giving eight possibili-
       ties. Currently only six are used (default plus the five values above). This means that if you  set  more  than
       one  newline  option,  the  combination may or may not be sensible. For example, PCRE_NEWLINE_CR with PCRE_NEW-
       LINE_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 whitespace characters, and so are ignored in this mode. Also, an unescaped # outside a char-
       acter  class  indicates  a comment that lasts until after the next line break sequence. In other circumstances,
       line break sequences in patterns are treated as literal data.

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

         PCRE_NO_AUTO_CAPTURE

       If this option is set, it disables the use of numbered capturing parentheses in the pattern. Any opening paren-
       thesis 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.

         PCRE_UCP

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

         PCRE_UNGREEDY

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

         PCRE_UTF8

       This  option  causes  PCRE to regard both the pattern and the subject as strings of UTF-8 characters instead of
       single-byte character strings. However, it is available only when PCRE is built to include  UTF-8  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  dis-
       cussion  about  the  validity  of UTF-8 strings in the main pcre page. If an invalid UTF-8 sequence of bytes is
       found, pcre_compile() returns an error. If you already know that your pattern is valid, and you  want  to  skip
       this  check  for  performance reasons, you can set the PCRE_NO_UTF8_CHECK option. When it is set, the effect of
       passing an invalid UTF-8 string as a pattern is undefined. It may cause your program to crash. Note  that  this
       option  can  also be passed to pcre_exec() and pcre_dfa_exec(), to suppress the UTF-8 validity checking of sub-
       ject strings.

COMPILATION ERROR CODES

       The following table lists the error codes than may be returned by pcre_compile2(), along with  the  error  mes-
       sages that may be returned by both compiling functions. As PCRE has developed, some error codes have fallen out
       of use. To avoid confusion, they have not been re-used.

          0  no error
          1  \ at end of pattern
          2  \c at end of pattern
          3  unrecognized character follows \
          4  numbers out of order in {} quantifier
          5  number too big in {} quantifier
          6  missing terminating ] for character class
          7  invalid escape sequence in character class
          8  range out of order in character class
          9  nothing to repeat
         10  [this code is not in use]
         11  internal error: unexpected repeat
         12  unrecognized character after (? or (?-
         13  POSIX named classes are supported only within a class
         14  missing )
         15  reference to non-existent subpattern
         16  erroffset passed as NULL
         17  unknown option bit(s) set
         18  missing ) after comment
         19  [this code is not in use]
         20  regular expression is too large
         21  failed to get memory
         22  unmatched parentheses
         23  internal error: code overflow
         24  unrecognized character after (?<
         25  lookbehind assertion is not fixed length
         26  malformed number or name after (?(
         27  conditional group contains more than two branches
         28  assertion expected after (?(
         29  (?R or (?[+-]digits must be followed by )
         30  unknown POSIX class name
         31  POSIX collating elements are not supported
         32  this version of PCRE is not compiled with PCRE_UTF8 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
         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 (not in 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 PCRE_UCP support
         68  \c must be followed by an ASCII character
         69  \k is not followed by a braced, angle-bracketed, or quoted name

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

STUDYING A PATTERN

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

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

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

       If  studying  the  pattern  does not produce any useful information, pcre_study() returns NULL. In that circum-
       stance, 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.

       The  second argument of pcre_study() contains option bits. There is only one option: PCRE_STUDY_JIT_COMPILE. If
       this is 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() matching function. If the just-in-time compiler is not available,
       this option is ignored. All other bits in the options argument must be zero.

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

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

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

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

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

       Studying a pattern does two things: first, a lower bound for the length of subject string  that  is  needed  to
       match  the pattern is computed. This does not mean that there are any strings of that length that match, but it
       does guarantee that no shorter strings match. The value is used by pcre_exec()  and  pcre_dfa_exec()  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.

       These two optimizations apply  to  both  pcre_exec()  and  pcre_dfa_exec().  However,  they  are  not  used  by
       pcre_exec()  if  pcre_study()  is  called with the PCRE_STUDY_JIT_COMPILE option, and just-in-time compiling is
       successful. The optimizations can be  disabled  by  setting  the  PCRE_NO_START_OPTIMIZE  option  when  calling
       pcre_exec()  or  pcre_dfa_exec(). You might want to do this if your pattern contains callouts or (*MARK) (which
       cannot be handled by the JIT compiler), 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 refer-
       ence to a set of tables, indexed by character value. When running in UTF-8 mode, this applies only  to  charac-
       ters  with  codes less than 128. By default, higher-valued codes never match escapes such as \w or \d, but they
       can be tested with \p if PCRE is built with Unicode character property  support.  Alternatively,  the  PCRE_UCP
       option can be set at compile time; this causes \w and friends to use Unicode property support instead of built-
       in tables. The use of locales with Unicode is discouraged. If you are handling characters  with  codes  greater
       than 128, you should either use UTF-8 and Unicode, or use locales, but not try to mix the two.

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

       The internal tables can always be overridden by tables supplied by the application that calls PCRE.  These  may
       be  created  in a different locale from the default. As more and more applications change to using Unicode, the
       need for this locale support is expected to die away.

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

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

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

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

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

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

INFORMATION ABOUT A PATTERN

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

       The pcre_fullinfo() function returns information about a compiled pattern. It replaces the obsolete pcre_info()
       function, which is nevertheless retained for backwards compability (and is documented below).

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

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

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

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

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

         PCRE_INFO_BACKREFMAX

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

         PCRE_INFO_CAPTURECOUNT

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

         PCRE_INFO_DEFAULT_TABLES

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

         PCRE_INFO_FIRSTBYTE

       Return  information about the first byte of any matched string, for a non-anchored pattern. The fourth argument
       should point to an int variable. (This option used to be called PCRE_INFO_FIRSTCHAR; the old name is still rec-
       ognized for backwards compatibility.)

       If  there  is  a fixed first byte, for example, from a pattern such as (cat|cow|coyote), its value is returned.
       Otherwise, if either

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

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

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

         PCRE_INFO_FIRSTTABLE

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

         PCRE_INFO_HASCRORLF

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

         PCRE_INFO_JCHANGED

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

         PCRE_INFO_JIT

       Return 1 if the pattern was studied with the PCRE_STUDY_JIT_COMPILE option, and just-in-time compiling was suc-
       cessful. 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 the PCRE_STUDY_JIT_COMPILE  option,
       or that the JIT compiler could not handle this particular pattern. See the pcrejit documentation for details of
       what can and cannot be handled.

         PCRE_INFO_JITSIZE

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

         PCRE_INFO_LASTLITERAL

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

         PCRE_INFO_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, not bytes (this may be rele-
       vant in UTF-8 mode). The fourth argument should point to an int variable. A non-negative value is a lower bound
       to the length of any matching string. There may not be any strings of that length that do actually  match,  but
       every string that does match is at least that long.

         PCRE_INFO_NAMECOUNT
         PCRE_INFO_NAMEENTRYSIZE
         PCRE_INFO_NAMETABLE

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

       The map consists of a number of fixed-size entries.  PCRE_INFO_NAMECOUNT  gives  the  number  of  entries,  and
       PCRE_INFO_NAMEENTRYSIZE gives the size of each entry; both of these return an int value. The entry size depends
       on the length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first entry  of  the  table  (a
       pointer  to char). The first two bytes of each entry are the number of the capturing parenthesis, most signifi-
       cant byte first. 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 dupli-
       cate  names,  they  appear in the table in the order in which they were found in the pattern. In the absence of
       (?| this is the order of increasing number; when (?| is used this is not necessarily  the  case  because  later
       subpatterns may have lower numbers.

       As  a  simple example of the name/number table, consider the following pattern (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 previ-
       ously applied to partial matching have been lifted. The pcrepartial  documentation  gives  details  of  partial
       matching.

         PCRE_INFO_OPTIONS

       Return  a  copy  of  the  options  with  which the pattern was compiled. The fourth argument should point to an
       unsigned long int variable. These option bits are those specified in the call to  pcre_compile(),  modified  by
       any  top-level  option  settings  at the start of the pattern itself. In other words, they are the options that
       will be in force when matching starts. For example, if  the  pattern  /(?im)abc(?-i)d/  is  compiled  with  the
       PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE, and PCRE_EXTENDED.

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

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

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

         PCRE_INFO_SIZE

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

         PCRE_INFO_STUDYSIZE

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

OBSOLETE INFO FUNCTION

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

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

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

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

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

REFERENCE COUNTS

       int pcre_refcount(pcre *code, int adjust);

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

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

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

MATCHING A PATTERN: THE TRADITIONAL FUNCTION

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

       The function pcre_exec() is called to match a subject string against a compiled pattern, which is passed in the
       code  argument. If the pattern was studied, the result of the study should be passed in the extra argument. You
       can call pcre_exec() with the same code and extra arguments as many times as you like, in order to  match  dif-
       ferent subject strings with the same pattern.

       This function is the main matching facility of the library, and it operates in a Perl-like manner. For special-
       ist use there is also an alternative matching function, which is described  below  in  the  section  about  the
       pcre_dfa_exec() function.

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

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

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

   Extra data for pcre_exec()

       If the extra argument is not NULL, it must point to a pcre_extra data block. The pcre_study() function  returns
       such  a  block  (when  it  doesn't  return NULL), but you can also create one for yourself, and pass additional
       information in it. The pcre_extra block contains the following fields (not necessarily in this order):

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

       The flags field is a bitmap that specifies which of the other fields are set. The flag bits are:

         PCRE_EXTRA_STUDY_DATA
         PCRE_EXTRA_EXECUTABLE_JIT
         PCRE_EXTRA_MATCH_LIMIT
         PCRE_EXTRA_MATCH_LIMIT_RECURSION
         PCRE_EXTRA_CALLOUT_DATA
         PCRE_EXTRA_TABLES
         PCRE_EXTRA_MARK

       Other flag bits should be set to zero. The study_data field and sometimes the executable_jit field are  set  in
       the  pcre_extra block that is returned by pcre_study(), together with the appropriate flag bits. You should not
       set these yourself, but you may add to the block by setting the other fields and their corresponding flag bits.

       The match_limit field provides a means of preventing PCRE from using up a vast amount of resources when running
       patterns that are not going to match, but which have a very large  number  of  possibilities  in  their  search
       trees. The classic example is a pattern that uses nested unlimited repeats.

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

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

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

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

       Limiting  the  recursion depth limits the amount of machine stack that can be used, or, when PCRE has been com-
       piled 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, if the pattern was successfully studied with PCRE_STUDY_JIT_COMPILE.

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

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

       The  tables  field  is used to pass a character tables pointer to pcre_exec(); this overrides the value that is
       stored with the compiled pattern. A non-NULL value is stored with the compiled pattern only  if  custom  tables
       were  supplied to pcre_compile() via its tableptr argument.  If NULL is passed to pcre_exec() using this mecha-
       nism, 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 documentation for a discussion  of  saving  compiled
       patterns for later use.

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

   Option bits for pcre_exec()

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

       If  the pattern was successfully studied with the PCRE_STUDY_JIT_COMPILE option, the only supported options for
       JIT execution are PCRE_NO_UTF8_CHECK, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NOTEMPTY_ATSTART.  Note
       in  particular  that partial matching is not supported. If an unsupported option is used, JIT execution is dis-
       abled 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  com-
       piled  with  PCRE_ANCHORED, or turned out to be anchored by virtue of its contents, it cannot be made unachored
       at matching time.

         PCRE_BSR_ANYCRLF
         PCRE_BSR_UNICODE

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

         PCRE_NEWLINE_CR
         PCRE_NEWLINE_LF
         PCRE_NEWLINE_CRLF
         PCRE_NEWLINE_ANYCRLF
         PCRE_NEWLINE_ANY

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

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

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

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

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

         PCRE_NOTBOL

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

         PCRE_NOTEOL

       This option specifies that the end of the subject string is not the end of a line, so the dollar  metacharacter
       should  not  match  it  nor  (except  in  multiline mode) a newline immediately before it. Setting this without
       PCRE_MULTILINE (at compile time) causes dollar never to match. This option affects only the  behaviour  of  the
       dollar metacharacter. It does not affect \Z or \z.

         PCRE_NOTEMPTY

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

         a?b?

       is  applied  to a string not beginning with "a" or "b", it matches an empty string at the start of the subject.
       With PCRE_NOTEMPTY set, this match is not valid, so PCRE searches further into the string  for  occurrences  of
       "a" or "b".

         PCRE_NOTEMPTY_ATSTART

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

       Perl has no direct equivalent of PCRE_NOTEMPTY or PCRE_NOTEMPTY_ATSTART, but it does make a special case  of  a
       pattern  match  of the empty string within its split() function, and when using the /g modifier. It is possible
       to emulate Perl's behaviour after matching a null string by first trying the match again  at  the  same  offset
       with  PCRE_NOTEMPTY_ATSTART  and  PCRE_ANCHORED,  and then if that fails, by advancing the starting offset (see
       below) and trying an ordinary match again. There is some code that demonstrates how to do this in the  pcredemo
       sample program. In the most general case, you have to check to see if the newline convention recognizes CRLF as
       a newline, and if so, and the current character is CR followed by LF, advance the starting offset by two  char-
       acters instead of one.

         PCRE_NO_START_OPTIMIZE

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

       The  PCRE_NO_START_OPTIMIZE option disables the start-up optimizations, possibly causing performance to suffer,
       but ensuring that in cases where the result is "no match", the callouts do occur, and that items such as (*COM-
       MIT)   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.

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

         (*MARK:A)(X|Y)

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

         PCRE_NO_UTF8_CHECK

       When  PCRE_UTF8  is set at compile time, the validity of the subject as a UTF-8 string is automatically checked
       when pcre_exec() is subsequently called.  The 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 section on
       UTF-8 support in the main pcre page. If an invalid UTF-8 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 UTF-8 character at the
       end of the subject, PCRE_ERROR_SHORTUTF8. In both cases, information about the precise nature of the error  may
       also  be  returned  (see  the  descriptions  of  these  errors in the section entitled Error return values from
       pcre_exec() below).  If startoffset contains a value that does not point to the start of a UTF-8 character  (or
       to the end of the subject), PCRE_ERROR_BADUTF8_OFFSET is returned.

       If  you already know that your subject is valid, and you want to skip these checks for performance reasons, you
       can set the PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might want to do this for  the  second  and
       subsequent  calls  to  pcre_exec() if you are making repeated calls to find all the matches in a single subject
       string. However, you should be sure that the value of startoffset points to the start of a UTF-8 character  (or
       the  end  of  the  subject). When PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid UTF-8 string as a
       subject or an invalid value of startoffset is undefined. Your program may crash.

         PCRE_PARTIAL_HARD
         PCRE_PARTIAL_SOFT

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

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

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

   The string to be matched by pcre_exec()

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

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

         \Biss\B

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

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

       If  a non-zero starting offset is passed when the pattern is anchored, one attempt to match at the given offset
       is made. This can only succeed if the pattern does not require the match to be at the start of the subject.

   How pcre_exec() returns captured substrings

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

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

       The first two-thirds of the vector is used to pass back captured substrings, each substring  using  a  pair  of
       integers.  The  remaining third of the vector is used as workspace by pcre_exec() while matching capturing sub-
       patterns, 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 success-
       ful 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 not
       any captured substrings are of interest, pcre_exec() may be called with ovector passed as NULL and ovecsize  as
       zero.  However,  if  the  pattern  contains  back  references and the ovector is not big enough to remember the
       related substrings, PCRE has to get additional memory for use during matching. Thus it is usually advisable  to
       supply an ovector of reasonable size.

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

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

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

       The pcre_fullinfo() function can be used to find out how many capturing subpatterns there  are  in  a  compiled
       pattern. The smallest size for ovector that will allow for n captured substrings, in addition to the offsets of
       the substring matched by the whole pattern, is (n+1)*3.

       It is possible for capturing subpattern number n+1 to match some part of the subject when subpattern n has  not
       been  used  at all. For example, if the string "abc" is matched against the pattern (a|(z))(bc) the return from
       the function is 4, and subpatterns 1 and 3 are matched, but 2 is not. When this happens,  both  values  in  the
       offset pairs corresponding to unused subpatterns are set to -1.

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

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

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

   Error return values from pcre_exec()

       If pcre_exec() fails, it returns a negative number. The following are defined in the header file:

         PCRE_ERROR_NOMATCH        (-1)

       The subject string did not match the pattern.

         PCRE_ERROR_NULL           (-2)

       Either code or subject was passed as NULL, or ovector was NULL and ovecsize was not zero.

         PCRE_ERROR_BADOPTION      (-3)

       An unrecognized bit was set in the options argument.

         PCRE_ERROR_BADMAGIC       (-4)

       PCRE  stores  a  4-byte "magic number" at the start of the compiled code, to catch the case when it is passed a
       junk pointer and to detect when a pattern that was compiled in an environment of one endianness is  run  in  an
       environment  with the other endianness. This is the error that PCRE gives when the magic number is not present.

         PCRE_ERROR_UNKNOWN_OPCODE (-5)

       While running the pattern match, an unknown item was encountered in the compiled pattern. This error  could  be
       caused by a bug in PCRE or by overwriting of the compiled pattern.

         PCRE_ERROR_NOMEMORY       (-6)

       If  a  pattern  contains  back  references,  but the ovector that is passed to pcre_exec() is not big enough to
       remember the referenced substrings, PCRE gets a block of memory at the start of matching to use for  this  pur-
       pose. If the call via pcre_malloc() fails, this error is given. The memory is automatically freed at the end of
       matching.

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

         PCRE_ERROR_NOSUBSTRING    (-7)

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

         PCRE_ERROR_MATCHLIMIT     (-8)

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

         PCRE_ERROR_CALLOUT        (-9)

       This  error  is never generated by pcre_exec() itself. It is provided for use by callout functions that want to
       yield a distinctive error code. See the pcrecallout documentation for details.

         PCRE_ERROR_BADUTF8        (-10)

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

         PCRE_ERROR_BADUTF8_OFFSET (-11)

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

         PCRE_ERROR_PARTIAL        (-12)

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

         PCRE_ERROR_BADPARTIAL     (-13)

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

         PCRE_ERROR_INTERNAL       (-14)

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

         PCRE_ERROR_BADCOUNT       (-15)

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

         PCRE_ERROR_RECURSIONLIMIT (-21)

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

         PCRE_ERROR_BADNEWLINE     (-23)

       An invalid combination of PCRE_NEWLINE_xxx options was given.

         PCRE_ERROR_BADOFFSET      (-24)

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

         PCRE_ERROR_SHORTUTF8      (-25)

       This  error is returned instead of PCRE_ERROR_BADUTF8 when the subject string ends with a truncated UTF-8 char-
       acter  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_PAR-
       TIAL_HARD precedes the implementation of returned information; it is retained for backwards compatibility.

         PCRE_ERROR_RECURSELOOP    (-26)

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

         PCRE_ERROR_JIT_STACKLIMIT (-27)

       This error is returned when a pattern that was successfully studied using the PCRE_STUDY_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.

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

   Reason codes for invalid UTF-8 strings

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

         PCRE_UTF8_ERR1
         PCRE_UTF8_ERR2
         PCRE_UTF8_ERR3
         PCRE_UTF8_ERR4
         PCRE_UTF8_ERR5

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

         PCRE_UTF8_ERR6
         PCRE_UTF8_ERR7
         PCRE_UTF8_ERR8
         PCRE_UTF8_ERR9
         PCRE_UTF8_ERR10

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

         PCRE_UTF8_ERR11
         PCRE_UTF8_ERR12

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

         PCRE_UTF8_ERR13

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

         PCRE_UTF8_ERR14

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

         PCRE_UTF8_ERR15
         PCRE_UTF8_ERR16
         PCRE_UTF8_ERR17
         PCRE_UTF8_ERR18
         PCRE_UTF8_ERR19

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

         PCRE_UTF8_ERR20

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

         PCRE_UTF8_ERR21

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

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  con-
       venience, the functions pcre_copy_substring(), pcre_get_substring(), and pcre_get_substring_list() are provided
       for extracting captured substrings as new, separate, zero-terminated strings.  These  functions  identify  sub-
       strings by number. The next section describes functions for extracting named substrings.

       A substring that contains a binary zero is correctly extracted and has a further zero added on the end, but the
       result is not, of course, a C string.  However, you can process such a string by referring to the  length  that
       is  returned  by pcre_copy_substring() and pcre_get_substring().  Unfortunately, the interface to pcre_get_sub-
       string_list() is not adequate for handling strings containing binary zeros, because the end of the final string
       is not independently indicated.

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

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

         PCRE_ERROR_NOMEMORY       (-6)

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

         PCRE_ERROR_NOSUBSTRING    (-7)

       There is no substring whose number is stringnumber.

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

         PCRE_ERROR_NOMEMORY       (-6)

       if the attempt to get the memory block failed.

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

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

EXTRACTING CAPTURED SUBSTRINGS BY NAME

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

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

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

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

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

       the number of the subpattern called "xxx" is 2. If the name is known to be unique (PCRE_DUPNAMES was not  set),
       you  can  find  the number from the name by calling pcre_get_stringnumber(). The first argument is the compiled
       pattern, and the second is the name. The yield of the function is the subpattern number,  or  PCRE_ERROR_NOSUB-
       STRING (-7) if there is no subpattern of that name.

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

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

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

       These functions call pcre_get_stringnumber(), and if it  succeeds,  they  then  call  pcre_copy_substring()  or
       pcre_get_substring(),  as  appropriate.  NOTE:  If  PCRE_DUPNAMES  is  set  and  there are duplicate names, the
       behaviour may not be what you want (see the next section).

       Warning: If the pattern uses the (?| feature to set up multiple subpatterns with the same number, as  described
       in the section on duplicate subpattern numbers in the pcrepattern page, you cannot use names to distinguish the
       different subpatterns, because names are not included in the compiled code. The matching process uses only num-
       bers. 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  par-
       ticipates. An example is shown in the pcrepattern documentation.

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

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

FINDING ALL POSSIBLE MATCHES

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

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

MATCHING A PATTERN: THE ALTERNATIVE FUNCTION

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

       The  function  pcre_dfa_exec() is called to match a subject string against a compiled pattern, using a matching
       algorithm that scans the subject string just once, and does not backtrack. This has  different  characteristics
       to  the  normal  algorithm, and is not compatible with Perl. Some of the features of PCRE patterns are not sup-
       ported. Nevertheless, there are times when this kind of matching can be useful. For a  discussion  of  the  two
       matching  algorithms,  and a list of features that pcre_dfa_exec() does not support, see the pcrematching docu-
       mentation.

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

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

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

         int rc;
         int ovector[10];
         int wspace[20];
         rc = pcre_dfa_exec(
           re,             /* result of pcre_compile() */
           NULL,           /* we didn't study the pattern */
           "some string",  /* the subject string */
           11,             /* the length of the subject string */
           0,              /* start at offset 0 in the subject */
           0,              /* default options */
           ovector,        /* vector of integers for substring information */
           10,             /* number of elements (NOT size in bytes) */
           wspace,         /* working space vector */
           20);            /* number of elements (NOT size in bytes) */

   Option bits for pcre_dfa_exec()

       The unused bits of the options argument for pcre_dfa_exec() must be zero. The only bits that  may  be  set  are
       PCRE_ANCHORED,    PCRE_NEWLINE_xxx,    PCRE_NOTBOL,    PCRE_NOTEOL,    PCRE_NOTEMPTY,    PCRE_NOTEMPTY_ATSTART,
       PCRE_NO_UTF8_CHECK, PCRE_BSR_ANYCRLF, PCRE_BSR_UNICODE,  PCRE_NO_START_OPTIMIZE,  PCRE_PARTIAL_HARD,  PCRE_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 subject is
       reached and there is still at least one matching possibility that requires additional characters. This  happens
       even  if  some  complete  matches  have  also  been  found.  When  PCRE_PARTIAL_SOFT  is  set,  the return code
       PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end of the subject is reached, there  have  been
       no  complete  matches, but there is still at least one matching possibility. The portion of the string that was
       inspected when the longest partial match was found is set as the first matching string in both cases.  There is
       a  more detailed discussion of partial and multi-segment matching, with examples, in the pcrepartial documenta-
       tion.

         PCRE_DFA_SHORTEST

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

         PCRE_DFA_RESTART

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

   Successful returns from pcre_dfa_exec()

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

         <.*>

       is matched against the string

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

       the three matched strings are

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

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

       The strings are returned in reverse order of length; that is, the longest matching string is  given  first.  If
       there  were  too  many matches to fit into ovector, the yield of the function is zero, and the vector is filled
       with the longest matches. Unlike pcre_exec(), pcre_dfa_exec() can use the entire ovector for returning  matched
       strings.

   Error returns from pcre_dfa_exec()

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

         PCRE_ERROR_DFA_UITEM      (-16)

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

         PCRE_ERROR_DFA_UCOND      (-17)

       This return is given if pcre_dfa_exec() encounters a condition item that uses a back reference for  the  condi-
       tion, or a test for recursion in a specific group. These are not supported.

         PCRE_ERROR_DFA_UMLIMIT    (-18)

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

         PCRE_ERROR_DFA_WSSIZE     (-19)

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

         PCRE_ERROR_DFA_RECURSE    (-20)

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

SEE ALSO

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

AUTHOR

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

REVISION

       Last updated: 02 December 2011
       Copyright (c) 1997-2011 University of Cambridge.



                                                                    PCREAPI(3)