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    Command:

    pcreapi

    
    
    

    PCRE NATIVE API

    
           #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);
    
           int pcre_exec(const pcre *code, const pcre_extra *extra,
                const char *subject, int length, int startoffset,
                int options, int *ovector, int ovecsize);
    
           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
                const char *subject, int length, int startoffset,
                int options, int *ovector, int ovecsize,
                int *workspace, int wscount);
    
           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);
    
    
           char *pcre_version(void);
    
           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.  These  are  described in the pcreposix documentation.
           Both of these APIs define a set of C function calls. A C++  wrapper  is
           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
           application  that  uses  PCRE.  The  header  file  defines  the  macros
           PCRE_MAJOR  and  PCRE_MINOR to contain the major and minor release num-
           bers for the library.  Applications can use these  to  include  support
           for different releases of PCRE.
    
           The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and
           pcre_exec() are used for compiling and matching regular expressions  in
           a  Perl-compatible  manner. A sample program that demonstrates the sim-
           plest way of using them is provided in the file  called  pcredemo.c  in
           the  source distribution. The pcresample documentation describes how to
           compile and run it.
    
           A second matching function, pcre_dfa_exec(), which is not Perl-compati-
           ble,  is  also provided. This uses a different algorithm for the match-
           ing. The alternative algorithm finds all possible matches (at  a  given
           point  in  the subject), and scans the subject just once. However, this
           algorithm does not return captured substrings. A description of the two
           matching  algorithms and their advantages and disadvantages is given in
           the pcrematching documentation.
    
           In addition to the main compiling and  matching  functions,  there  are
           convenience functions for extracting captured substrings from a subject
           string that is matched by pcre_exec(). They are:
    
             pcre_copy_substring()
             pcre_copy_named_substring()
             pcre_get_substring()
             pcre_get_named_substring()
    
           The function pcre_fullinfo() is used to find out  information  about  a
           compiled  pattern; pcre_info() is an obsolete version that returns only
           some of the available information, but is retained for  backwards  com-
           patibility.   The function pcre_version() returns a pointer to a string
           containing the version of PCRE and its date of release.
    
           The function pcre_refcount() maintains a  reference  count  in  a  data
           block  containing  a compiled pattern. This is provided for the benefit
           of object-oriented applications.
    
           The global variables pcre_malloc and pcre_free  initially  contain  the
           entry  points  of  the  standard malloc() and free() functions, respec-
           tively. PCRE calls the memory management functions via these variables,
           so  a  calling  program  can replace them if it wishes to intercept the
           calls. This should be done before calling any PCRE functions.
    
           The global variables pcre_stack_malloc  and  pcre_stack_free  are  also
           indirections  to  memory  management functions. These special functions
           are used only when PCRE is compiled to use  the  heap  for  remembering
           data, instead of recursive function calls, when running the pcre_exec()
           function. See the pcrebuild documentation for  details  of  how  to  do
           this.  It  is  a non-standard way of building PCRE, for use in environ-
           ments that have limited stacks. Because of the greater  use  of  memory
           management,  it  runs  more  slowly. Separate functions are provided so
           that special-purpose external code can be  used  for  this  case.  When
           used,  these  functions  are always called in a stack-like manner (last
           obtained, first freed), and always for memory blocks of the same  size.
           There  is  a discussion about PCRE's stack usage in the pcrestack docu-
           mentation.
    
           The global variable pcre_callout initially contains NULL. It can be set
           by  the  caller  to  a "callout" function, which PCRE will then call at
           specified points during a matching operation. Details are given in  the
           pcrecallout documentation.
    
    
    

    NEWLINES

    
           PCRE  supports five different conventions for indicating line breaks in
           strings: a single CR (carriage return) character, a  single  LF  (line-
           feed) character, the two-character sequence CRLF, any of the three pre-
           ceding, or any Unicode newline sequence. The Unicode newline  sequences
           are  the  three just mentioned, plus the single characters VT (vertical
           tab, U+000B), FF (form feed, U+000C), NEL (next line, U+0085), LS (line
           separator, U+2028), and PS (paragraph separator, U+2029).
    
           Each  of  the first three conventions is used by at least one operating
           system as its standard newline sequence. When PCRE is built, a  default
           can  be  specified.  The default default is LF, which is the Unix stan-
           dard. When PCRE is run, the default can be overridden,  either  when  a
           pattern is compiled, or when it is matched.
    
           At compile time, the newline convention can be specified by the options
           which is controlled in a similar way, but by separate options.
    
    
    

    MULTITHREADING

    
           The PCRE functions can be used in  multi-threading  applications,  with
           the  proviso  that  the  memory  management  functions  pointed  to  by
           pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
           callout function pointed to by pcre_callout, are shared by all threads.
    
           The compiled form of a regular expression is not altered during  match-
           ing, so the same compiled pattern can safely be used by several threads
           at once.
    
    
    

    SAVING PRECOMPILED PATTERNS FOR LATER USE

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

    CHECKING BUILD-TIME OPTIONS

    
           int pcre_config(int what, void *where);
    
           The  function pcre_config() makes it possible for a PCRE client to dis-
           cover which optional features have been compiled into the PCRE library.
           The  pcrebuild documentation has more details about these optional fea-
           tures.
    
           The first argument for pcre_config() is an  integer,  specifying  which
           information is required; the second argument is a pointer to a variable
           into which the information is  placed.  The  following  information  is
           available:
    
             PCRE_CONFIG_UTF8
    
           The  output is an integer that is set to one if UTF-8 support is avail-
           able; otherwise it is set to zero.
    
             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_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. The default should normally be  the  standard  sequence
           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 an 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 an integer that gives the default limit for the depth  of
           recursion  when calling the internal matching function in a pcre_exec()
           execution. Further details are given with pcre_exec() below.
    
             PCRE_CONFIG_STACKRECURSE
    
           The output is an integer that is set to one if internal recursion  when
           running pcre_exec() is implemented by recursive function calls that use
           the stack to remember their state. This is the usual way that  PCRE  is
           compiled. The output is zero if PCRE was compiled to use blocks of data
           on the  heap  instead  of  recursive  function  calls.  In  this  case,
           pcre_stack_malloc  and  pcre_stack_free  are  called  to  manage memory
           blocks on the heap, thus avoiding the use of the stack.
    
    
    

    COMPILING A PATTERN

    
           pcre *pcre_compile(const char *pattern, int options,
                const char **errptr, int *erroffset,
                const unsigned char *tableptr);
    
           pcre *pcre_compile2(const char *pattern, int options,
                int *errorcodeptr,
                const char **errptr, int *erroffset,
                const unsigned char *tableptr);
    
           Either of the functions pcre_compile() or pcre_compile2() can be called
           to compile a pattern into an internal form. The only difference between
           the two interfaces is that pcre_compile2() has an additional  argument,
           errorcodeptr, via which a numerical error code can be returned.
    
           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
           pattern (see the detailed description  in  the  pcrepattern  documenta-
           tion).  For  these options, the contents of the options argument speci-
           fies their initial settings at the start of compilation and  execution.
           The  PCRE_ANCHORED  and PCRE_NEWLINE_xxx 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 mes-
           sage. This is a static string that is part of the library. You must not
           try to free it. Normally, the offset from the start of the  pattern  to
           the  byte  that  was  being  processed when the error was discovered is
           placed in the variable pointed to by erroffset, which must not be  NULL
           (if  it is, an immediate error is given). However, for an invalid UTF-8
           string, the offset is that of the first byte of the failing  character.
           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  error-
           codeptr  argument is not NULL, a non-zero error code number is returned
           via this argument in the event of an error. This is in addition to  the
           textual error message. Error codes and messages are listed below.
    
           If  the  final  argument, tableptr, is NULL, PCRE uses a default set of
           character tables that are  built  when  PCRE  is  compiled,  using  the
           default  C  locale.  Otherwise, tableptr must be an address that is the
           result of a call to pcre_maketables(). This value is  stored  with  the
           compiled  pattern,  and used again by pcre_exec(), unless another table
           pointer is passed to it. For more discussion, see the section on locale
           support below.
    
           This  code  fragment  shows a typical straightforward call to pcre_com-
           pile():
    
             pcre *re;
             const char *error;
             int erroffset;
             re = pcre_compile(
               "^A.*Z",          /* the pattern */
               0,                /* default options */
               &error,           /* for error message */
               &erroffset,       /* for error offset */
               NULL);            /* use default character tables */
    
           The following names for option bits are defined in  the  pcre.h  header
           file:
    
             PCRE_ANCHORED
             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 set-
           ting an option when a compiled pattern is matched.
    
             PCRE_CASELESS
    
           If  this  bit is set, letters in the pattern match both upper and lower
           case letters. It is equivalent to Perl's  /i  option,  and  it  can  be
           changed  within a pattern by a (?i) option setting. In UTF-8 mode, PCRE
           always understands the concept of case for characters whose values  are
           less  than 128, so caseless matching is always possible. For characters
           with higher values, the concept of case is supported if  PCRE  is  com-
           piled  with Unicode property support, but not otherwise. If you want to
           use caseless matching for characters 128 and  above,  you  must  ensure
           that  PCRE  is  compiled  with Unicode property support as well as with
           UTF-8 support.
    
             PCRE_DOLLAR_ENDONLY
    
           If this bit is set, a dollar metacharacter in the pattern matches  only
           at  the  end  of the subject string. Without this option, a dollar also
           matches immediately before a newline at the end of the string (but  not
           before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored
           if PCRE_MULTILINE is set.  There is no equivalent  to  this  option  in
           Perl, and no way to set it within a pattern.
    
             PCRE_DOTALL
    
           If this bit is set, a dot metacharater in the pattern matches all char-
           acters, including those that indicate newline. Without it, a  dot  does
           not  match  when  the  current position is at a newline. This option is
           equivalent to Perl's /s option, and it can be changed within a  pattern
           by  a (?s) option setting. A negative class such as [^a] always matches
           newline characters, independent of the setting of this option.
    
             PCRE_DUPNAMES
    
           If this bit is set, names used to identify capturing  subpatterns  need
           not be unique. This can be helpful for certain types of pattern when it
           is known that only one instance of the named  subpattern  can  ever  be
           matched.  There  are  more details of named subpatterns below; see also
           the pcrepattern documentation.
    
             PCRE_EXTENDED
    
           If this bit is set, white space data  characters  in  the  pattern  are
           totally  ignored except when escaped or inside a character class. White
           space does not include the VT character (code 11). In addition, charac-
           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 a warning for  this.)
           There  are  at  present no other features controlled by this option. It
           can also be set by a (?X) option setting within a pattern.
    
             PCRE_FIRSTLINE
    
           If this option is set, an  unanchored  pattern  is  required  to  match
           before  or  at  the  first  newline  in  the subject string, though the
           matched text may continue over the newline.
    
             PCRE_JAVASCRIPT_COMPAT
    
           If this option is set, PCRE's behaviour is changed in some ways so that
           it  is  compatible with JavaScript rather than Perl. The changes are as
           follows:
    
           (1) A lone closing square bracket in a pattern  causes  a  compile-time
           error,  because this is illegal in JavaScript (by default it is treated
           as a data character). Thus, the pattern AB]CD becomes illegal when this
           option is set.
    
           (2)  At run time, a back reference to an unset subpattern group matches
           an empty string (by default this causes the current  matching  alterna-
           tive  to  fail). A pattern such as (\1)(a) succeeds when this option is
           set (assuming it can find an "a" in the subject), whereas it  fails  by
           default, for Perl compatibility.
    
             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 new-
           lines  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
    
           UTF-8 mode.
    
           The  newline  setting  in  the  options  word  uses three bits that are
           treated as a number, giving eight possibilities. Currently only six are
           used  (default  plus the five values above). This means that if you set
           more than one newline option, the combination may or may not be  sensi-
           ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
           PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers  and
           cause an error.
    
           The  only time that a line break is specially recognized when compiling
           a pattern is if PCRE_EXTENDED is set, and  an  unescaped  #  outside  a
           character  class  is  encountered.  This indicates a comment that lasts
           until after the next line break sequence. In other circumstances,  line
           break   sequences   are   treated  as  literal  data,  except  that  in
           PCRE_EXTENDED mode, both CR and LF are treated as white  space  charac-
           ters and are therefore ignored.
    
           The newline option that is set at compile time becomes the default that
           is used for pcre_exec() and pcre_dfa_exec(), but it can be  overridden.
    
             PCRE_NO_AUTO_CAPTURE
    
           If this option is set, it disables the use of numbered capturing paren-
           theses in the pattern. Any opening parenthesis that is not followed  by
           ?  behaves as if it were followed by ?: but named parentheses can still
           be used for capturing (and they acquire  numbers  in  the  usual  way).
           There is no equivalent of this option in Perl.
    
             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  sup-
           port.  If not, the use of this option provokes an error. Details of how
           this option changes the behaviour of PCRE are given in the  section  on
           UTF-8 support in the main pcre page.
    
             PCRE_NO_UTF8_CHECK
    
           When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
           automatically checked. There is a  discussion  about  the  validity  of
           UTF-8  strings  in  the 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 perfor-
              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, \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
    
           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 pat-
           tern 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(). 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  additional  information
           pcre_study() returns NULL. In that circumstance, if the calling program
           wants to pass any of the other fields to pcre_exec(), it  must  set  up
           its own pcre_extra block.
    
           The  second  argument of pcre_study() contains option bits. At present,
           no options are defined, and this argument should always be zero.
    
           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.
    
           This is a typical call to pcre_study():
    
             pcre_extra *pe;
             pe = pcre_study(
               re,             /* result of pcre_compile() */
               0,              /* no options exist */
               &error);        /* set to NULL or points to a message */
    
           At present, studying a pattern is useful only for non-anchored patterns
           that do not have a single fixed starting character. A bitmap of  possi-
           ble starting bytes is created.
    
    
    

    LOCALE SUPPORT

    
           PCRE  handles  caseless matching, and determines whether characters are
           system, which may cause them to be different.
    
           The internal tables can always be overridden by tables supplied by  the
           application that calls PCRE. These may be created in a different locale
           from the default. As more and more applications change  to  using  Uni-
           code, 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 pat-
           tern, compilation, studying and matching all happen in the same locale,
           but different patterns can be compiled in different locales.
    
           It is possible to pass a table pointer or NULL (indicating the  use  of
           the  internal  tables)  to  pcre_exec(). Although not intended for this
           purpose, this facility could be used to match a pattern in a  different
           locale from the one in which it was compiled. Passing table pointers at
           run time is discussed below in the section on matching a pattern.
    
    
    

    INFORMATION ABOUT A PATTERN

    
           int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
                int what, void *where);
    
           The pcre_fullinfo() function returns information about a compiled  pat-
           tern. It replaces the obsolete pcre_info() function, which is neverthe-
           less 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  information  is required, and the fourth argument is a pointer to a
           variable to receive the data. The yield of the  function  is  zero  for
             rc = pcre_fullinfo(
               re,               /* result of pcre_compile() */
               pe,               /* 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() func-
           tion.  External  callers  can  cause PCRE to use its internal tables by
           passing a NULL table pointer.
    
             PCRE_INFO_FIRSTBYTE
    
           Return information about the first byte of any matched  string,  for  a
           non-anchored  pattern. The fourth argument should point to an int vari-
           able. (This option used to be called PCRE_INFO_FIRSTCHAR; the old  name
           is still recognized 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
           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_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_NAMECOUNT
             PCRE_INFO_NAMEENTRYSIZE
             PCRE_INFO_NAMETABLE
    
           PCRE  supports the use of named as well as numbered capturing parenthe-
           ses. The names are just an additional way of identifying the  parenthe-
           ses, which still acquire numbers. Several convenience functions such as
           pcre_get_named_substring() are provided for  extracting  captured  sub-
           strings  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 parenthe-
           sis,  most  significant byte first. The rest of the entry is the corre-
           sponding name, zero terminated. The names are  in  alphabetical  order.
           When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
           theses numbers. For example, 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 ??
    
           Return a copy of the options with which the pattern was  compiled.  The
           fourth  argument  should  point to an unsigned long int variable. These
           option bits are those specified in the call to pcre_compile(), modified
           by any top-level option settings at the start of the pattern itself. In
           other words, they are the options that will be in force  when  matching
           starts.  For  example, if the pattern /(?im)abc(?-i)d/ is compiled with
           the PCRE_EXTENDED option, the result is PCRE_CASELESS,  PCRE_MULTILINE,
           and PCRE_EXTENDED.
    
           A  pattern  is  automatically  anchored by PCRE if all of its top-level
           alternatives begin with one of the following:
    
             ^     unless PCRE_MULTILINE is set
             \A    always
             \G    always
             .*    if PCRE_DOTALL is set and there are no back
                     references to the subpattern in which .* appears
    
           For such patterns, the PCRE_ANCHORED bit is set in the options returned
           by pcre_fullinfo().
    
             PCRE_INFO_SIZE
    
           Return  the  size  of the compiled pattern, that is, the value that was
           passed as the argument to pcre_malloc() when PCRE was getting memory in
           which to place the compiled data. The fourth argument should point to a
           size_t variable.
    
             PCRE_INFO_STUDYSIZE
    
           Return the size of the data block pointed to by the study_data field in
           a  pcre_extra  block.  That  is,  it  is  the  value that was passed to
           pcre_malloc() when PCRE was getting memory into which to place the data
           created  by  pcre_study(). The fourth argument should point to a size_t
           variable.
    
    
    

    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 fol-
           lowing 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).
    
           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
           has been studied, the result of the study should be passed in the extra
           argument.  This  function is the main matching facility of the library,
           and it operates in a Perl-like manner. For specialist use there is also
           an  alternative matching function, which is described below in the sec-
           tion about the pcre_dfa_exec() function.
    
           In most applications, the pattern will have been compiled (and  option-
           ally  studied)  in the same process that calls pcre_exec(). However, it
           is possible to save compiled patterns and study data, and then use them
           later  in  different processes, possibly even on different hosts. For a
           discussion about this, see the pcreprecompile documentation.
    
           Here is an example of a simple call to pcre_exec():
    
             int rc;
             int ovector[30];
             rc = pcre_exec(
               re,             /* result of pcre_compile() */
               NULL,           /* we didn't study the pattern */
               "some string",  /* the subject string */
               11,             /* the length of the subject string */
               0,              /* start at offset 0 in the subject */
               0,              /* default options */
               ovector,        /* vector of integers for substring information */
               30);            /* number of elements (NOT size in bytes) */
    
       Extra data for pcre_exec()
    
           If the extra argument is not NULL, it must point to a  pcre_extra  data
           block.  The pcre_study() function returns such a block (when it doesn't
           return NULL), but you can also create one for yourself, and pass  addi-
           tional  information  in it. The pcre_extra block contains the following
             PCRE_EXTRA_MATCH_LIMIT_RECURSION
             PCRE_EXTRA_CALLOUT_DATA
             PCRE_EXTRA_TABLES
    
           Other  flag  bits should be set to zero. The study_data field is set in
           the pcre_extra block that is returned by  pcre_study(),  together  with
           the appropriate flag bit. You should not set this 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  the  use  of  nested  unlimited
           repeats.
    
           Internally,  PCRE uses a function called match() which it calls repeat-
           edly (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.
    
           The default value for the limit can be set  when  PCRE  is  built;  the
           default  default  is 10 million, which handles all but the most extreme
           cases. You can override the default  by  suppling  pcre_exec()  with  a
           pcre_extra     block    in    which    match_limit    is    set,    and
           PCRE_EXTRA_MATCH_LIMIT is set in the  flags  field.  If  the  limit  is
           exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
    
           The  match_limit_recursion field is similar to match_limit, but instead
           of limiting the total number of times that match() is called, it limits
           the  depth  of  recursion. The recursion depth is a smaller number than
           the total number of calls, because not all calls to match() are  recur-
           sive.  This limit is of use only if it is set smaller than match_limit.
    
           Limiting the recursion depth limits the amount of  stack  that  can  be
           used, or, when PCRE has been compiled to use memory on the heap instead
           of the stack, the amount of heap memory that can be used.
    
           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  pcre_callout  field is used in conjunction with the "callout" fea-
           ture, which 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
           PCRE_PARTIAL.
    
             PCRE_ANCHORED
    
           The PCRE_ANCHORED option limits pcre_exec() to matching  at  the  first
           matching  position.  If  a  pattern was compiled with PCRE_ANCHORED, or
           turned out to be anchored by virtue of its contents, it cannot be  made
           unachored at matching time.
    
             PCRE_BSR_ANYCRLF
             PCRE_BSR_UNICODE
    
           These options (which are mutually exclusive) control what the \R escape
           sequence matches. The choice is either to match only CR, LF,  or  CRLF,
           or  to  match  any Unicode newline sequence. These options override the
           choice that was made or defaulted when the pattern was compiled.
    
             PCRE_NEWLINE_CR
             PCRE_NEWLINE_LF
             PCRE_NEWLINE_CRLF
             PCRE_NEWLINE_ANYCRLF
             PCRE_NEWLINE_ANY
    
           These options override  the  newline  definition  that  was  chosen  or
           defaulted  when the pattern was compiled. For details, see the descrip-
           tion of pcre_compile()  above.  During  matching,  the  newline  choice
           affects  the  behaviour  of the dot, circumflex, and dollar metacharac-
           ters. It may also alter the way the match position is advanced after  a
           match failure for an unanchored pattern.
    
           When  PCRE_NEWLINE_CRLF,  PCRE_NEWLINE_ANYCRLF,  or PCRE_NEWLINE_ANY is
           set, and a match attempt for an unanchored pattern fails when the  cur-
           rent  position  is  at  a  CRLF  sequence,  and the pattern contains no
           explicit matches for  CR  or  LF  characters,  the  match  position  is
           advanced by two characters instead of one, in other words, to after the
           CRLF.
    
           The above rule is a compromise that makes the most common cases work as
           expected.  For  example,  if  the  pattern  is .+A (and the PCRE_DOTALL
           option is not set), it does not match the string "\r\nA" because, after
           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  con-
           tains an explicit CR or LF reference, and so advances only by one char-
           acter 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
           in  multiline mode) a newline immediately before it. Setting this with-
           out PCRE_MULTILINE (at compile time) causes dollar never to match. This
           option  affects only the behaviour of the dollar metacharacter. It does
           not affect \Z or \z.
    
             PCRE_NOTEMPTY
    
           An empty string is not considered to be a valid match if this option is
           set.  If  there are alternatives in the pattern, they are tried. If all
           the alternatives match the empty string, the entire  match  fails.  For
           example, if the pattern
    
             a?b?
    
           is  applied  to  a string not beginning with "a" or "b", it matches the
           empty string at the start of the subject. With PCRE_NOTEMPTY set,  this
           match is not valid, so PCRE searches further into the string for occur-
           rences of "a" or "b".
    
           Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-
           cial  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 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.c sample program.
    
             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. 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.
    
           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.
    
           In UTF-8 mode, the byte offset must point to the start of a UTF-8 char-
           acter (or the end of the subject). Unlike the pattern string, the  sub-
           ject  may  contain binary zero bytes. 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.
    
           A  non-zero  starting offset is useful when searching for another match
           in the same subject by calling pcre_exec() again after a previous  suc-
           cess.   Setting  startoffset differs from just passing over a shortened
           string and setting PCRE_NOTBOL in the case of  a  pattern  that  begins
           with any kind of lookbehind. For example, consider the pattern
    
             \Biss\B
    
           which  finds  occurrences  of "iss" in the middle of words. (\B matches
           only if the current position in the subject is not  a  word  boundary.)
           When  applied  to the string "Mississipi" the first call to pcre_exec()
           finds the first occurrence. If pcre_exec() is called  again  with  just
           the  remainder  of  the  subject,  namely  "issipi", it does not match,
           because \B is always false at the start of the subject, which is deemed
           to  be  a  word  boundary. However, if pcre_exec() is passed the entire
           string again, but with startoffset set to 4, it finds the second occur-
           rence  of "iss" because it is able to look behind the starting point to
           discover that it is preceded by a letter.
    
           If 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 sub-
           string. PCRE supports several other kinds of  parenthesized  subpattern
           that do not cause substrings to be captured.
    
           Captured substrings are returned to the caller via a vector of integers
           whose address is passed in ovector. The number of elements in the  vec-
           tor  is  passed in ovecsize, which must be a non-negative number. Note:
           this argument is NOT the size of ovector in bytes.
    
           The first two-thirds of the vector is used to pass back  captured  sub-
           The  first  pair  of  integers, ovector[0] and ovector[1], identify the
           portion of the subject string matched by the entire pattern.  The  next
           pair  is  used for the first capturing subpattern, and so on. The value
           returned by pcre_exec() is one more than the highest numbered pair that
           has  been  set.  For example, if two substrings have been captured, the
           returned value is 3. If there are no capturing subpatterns, the  return
           value from a successful match is 1, indicating that just the first pair
           of offsets has been set.
    
           If a capturing subpattern is matched repeatedly, it is the last portion
           of the string that it matched that is returned.
    
           If  the vector is too small to hold all the captured substring offsets,
           it is used as far as possible (up to two-thirds of its length), and the
           function  returns  a value of zero. If the substring offsets are not 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 usu-
           ally advisable to supply an ovector.
    
           The pcre_info() function can be used to find  out  how  many  capturing
           subpatterns  there  are  in  a  compiled pattern. The smallest size for
           ovector that will allow for n captured substrings, in addition  to  the
           offsets of the substring matched by the whole pattern, is (n+1)*3.
    
           It  is  possible for capturing subpattern number n+1 to match some part
           of the subject when subpattern n has not been used at all. For example,
           if  the  string  "abc"  is  matched against the pattern (a|(z))(bc) the
           return from the function is 4, and subpatterns 1 and 3 are matched, but
           2  is  not.  When  this happens, both values in the offset pairs corre-
           sponding to unused subpatterns are set to -1.
    
           Offset values that correspond to unused subpatterns at the end  of  the
           expression  are  also  set  to  -1. For example, if the string "abc" is
           matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are  not
           matched.  The  return  from the function is 2, because the highest used
           capturing subpattern number is 1. However, you can refer to the offsets
           for  the  second  and third capturing subpatterns if you wish (assuming
           the vector is large enough, of course).
    
           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.
           pattern that was compiled in an environment of one endianness is run in
           an environment with the other endianness. This is the error  that  PCRE
           gives when the magic number is not present.
    
             PCRE_ERROR_UNKNOWN_OPCODE (-5)
    
           While running the pattern match, an unknown item was encountered in the
           compiled pattern. This error could be caused by a bug  in  PCRE  or  by
           overwriting of the compiled pattern.
    
             PCRE_ERROR_NOMEMORY       (-6)
    
           If  a  pattern contains back references, but the ovector that is passed
           to pcre_exec() is not big enough to remember the referenced substrings,
           PCRE  gets  a  block of memory at the start of matching to use for this
           purpose. If the call via pcre_malloc() fails, this error is given.  The
           memory is automatically freed at the end of matching.
    
             PCRE_ERROR_NOSUBSTRING    (-7)
    
           This  error is used by the pcre_copy_substring(), pcre_get_substring(),
           and  pcre_get_substring_list()  functions  (see  below).  It  is  never
           returned by pcre_exec().
    
             PCRE_ERROR_MATCHLIMIT     (-8)
    
           The  backtracking  limit,  as  specified  by the match_limit field in a
           pcre_extra structure (or defaulted) was reached.  See  the  description
           above.
    
             PCRE_ERROR_CALLOUT        (-9)
    
           This error is never generated by pcre_exec() itself. It is provided for
           use by callout functions that want to yield a distinctive  error  code.
           See the pcrecallout documentation for details.
    
             PCRE_ERROR_BADUTF8        (-10)
    
           A  string  that contains an invalid UTF-8 byte sequence was passed as a
           subject, and the PCRE_NO_UTF8_CHECK option was not set. If the size  of
           the  output  vector  (ovecsize)  is  at least 2, the byte offset to the
           start of the the invalid UTF-8 character is placed in  the  first  ele-
           ment,  and  a  reason  code is placed in the second element. The reason
           codes are listed in the following section.
    
             PCRE_ERROR_BADUTF8_OFFSET (-11)
    
           The UTF-8 byte sequence that was passed as a subject  was  checked  and
           found  to be valid (the PCRE_NO_UTF8_CHECK option was not set), but the
           value of startoffset did not point to the beginning of a UTF-8  charac-
           ter.
    
           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.
    
           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_SHORT-
           UTF8, and the size of the output vector (ovecsize) is at least  2,  the
           offset  of  the  start  of the invalid UTF-8 character is placed in the
           first output vector element (ovector[0]) and a reason code is placed in
           the  second  element  (ovector[1]). The reason codes are given names in
           the pcre.h header file:
    
             PCRE_UTF8_ERR1
             PCRE_UTF8_ERR2
             PCRE_UTF8_ERR3
             PCRE_UTF8_ERR4
             PCRE_UTF8_ERR5
    
           The string ends with a truncated UTF-8 character;  the  code  specifies
           how  many bytes are missing (1 to 5). Although RFC 3629 restricts UTF-8
           characters to be no longer than 4 bytes, the  encoding  scheme  (origi-
           nally  defined  by  RFC  2279)  allows  for  up to 6 bytes, and this is
           checked first; hence the possibility of 4 or 5 missing bytes.
    
             PCRE_UTF8_ERR6
             PCRE_UTF8_ERR7
             PCRE_UTF8_ERR8
             PCRE_UTF8_ERR9
             PCRE_UTF8_ERR10
    
           The two most significant bits of the 2nd, 3rd, 4th, 5th, or 6th byte of
           the  character  do  not have the binary value 0b10 (that is, either the
    
           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  cor-
           rect coding uses just one byte.
    
             PCRE_UTF8_ERR20
    
           The two most significant bits of the first byte of a character have the
           binary value 0b10 (that is, the most significant bit is 1 and the  sec-
           ond  is  0). Such a byte can only validly occur as the second or subse-
           quent byte of a multi-byte character.
    
             PCRE_UTF8_ERR21
    
           The first byte of a character has the value 0xfe or 0xff. These  values
           can never occur in a valid UTF-8 string.
    
    
    

    EXTRACTING CAPTURED SUBSTRINGS BY NUMBER

    
           int pcre_copy_substring(const char *subject, int *ovector,
                int stringcount, int stringnumber, char *buffer,
                int buffersize);
    
           int pcre_get_substring(const char *subject, int *ovector,
                int stringcount, int stringnumber,
                const char **stringptr);
    
           int pcre_get_substring_list(const char *subject,
                int *ovector, int stringcount, const char ***listptr);
    
           Captured  substrings  can  be  accessed  directly  by using the offsets
           returned by pcre_exec() in  ovector.  For  convenience,  the  functions
           pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
           string_list() are provided for extracting captured substrings  as  new,
           separate,  zero-terminated strings. These functions identify substrings
           by number. The next section describes functions  for  extracting  named
           substrings.
    
           A  substring that contains a binary zero is correctly extracted and has
           a further zero added on the end, but the result is not, of course, a  C
           string.   However,  you  can  process such a string by referring to the
    
           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_sub-
           string(),  the  string  is  placed  in buffer, whose length is given by
           buffersize, while for pcre_get_substring() a new  block  of  memory  is
           obtained  via  pcre_malloc,  and its address is returned via stringptr.
           The yield of the function is the length of the  string,  not  including
           the terminating zero, or one of these error codes:
    
             PCRE_ERROR_NOMEMORY       (-6)
    
           The  buffer  was too small for pcre_copy_substring(), or the attempt to
           get memory failed for pcre_get_substring().
    
             PCRE_ERROR_NOSUBSTRING    (-7)
    
           There is no substring whose number is stringnumber.
    
           The pcre_get_substring_list()  function  extracts  all  available  sub-
           strings  and  builds  a list of pointers to them. All this is done in a
           single block of memory that is obtained via pcre_malloc. The address of
           the  memory  block  is returned via listptr, which is also the start of
           the list of string pointers. The end of the list is marked  by  a  NULL
           pointer.  The  yield  of  the function is zero if all went well, or the
           error code
    
             PCRE_ERROR_NOMEMORY       (-6)
    
           if the attempt to get the memory block failed.
    
           When any of these functions encounter a substring that is unset,  which
           can  happen  when  capturing subpattern number n+1 matches some part of
           the subject, but subpattern n has not been used at all, they return  an
           empty string. This can be distinguished from a genuine zero-length sub-
           string by inspecting the appropriate offset in ovector, which is  nega-
           tive for unset substrings.
    
           The  two convenience functions pcre_free_substring() and pcre_free_sub-
           string_list() can be used to free the memory  returned  by  a  previous
           call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
           tively. They do nothing more than  call  the  function  pointed  to  by
           pcre_free,  which  of course could be called directly from a C program.
           However, PCRE is used in some situations where it is linked via a  spe-
           cial   interface  to  another  programming  language  that  cannot  use
           pcre_free directly; it is for these cases that the functions  are  pro-
           vided.
    
    
    

    EXTRACTING CAPTURED SUBSTRINGS BY NAME

    
           int pcre_get_stringnumber(const pcre *code,
    
             (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 com-
           piled pattern, and the second is the name. The yield of the function is
           the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if  there  is  no
           subpattern of that name.
    
           Given the number, you can extract the substring directly, or use one of
           the functions described in the previous section. For convenience, there
           are also two functions that do the whole job.
    
           Most    of    the    arguments   of   pcre_copy_named_substring()   and
           pcre_get_named_substring() are the same  as  those  for  the  similarly
           named  functions  that extract by number. As these are described in the
           previous section, they are not re-described here. There  are  just  two
           differences:
    
           First,  instead  of a substring number, a substring name is given. Sec-
           ond, there is an extra argument, given at the start, which is a pointer
           to  the compiled pattern. This is needed in order to gain access to the
           name-to-number translation table.
    
           These functions call pcre_get_stringnumber(), and if it succeeds,  they
           then    call    pcre_copy_substring()   or   pcre_get_substring(),   as
           appropriate. NOTE: If PCRE_DUPNAMES is  set  and  there  are  duplicate
           names, the behaviour may not be what you want (see the next section).
    
    
    

    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.  Normally,  patterns  with
           duplicate  names  are such that in any one match, only one of the named
           subpatterns participates. An example is shown in the pcrepattern  docu-
           mentation.
    
           When    duplicates   are   present,   pcre_copy_named_substring()   and
           pcre_get_named_substring() return the first substring corresponding  to
           the  given  name  that  is set. If none are set, PCRE_ERROR_NOSUBSTRING
           (-7) is returned; no  data  is  returned.  The  pcre_get_stringnumber()
           function  returns one of the numbers that are associated with the name,
           but it is not defined which it is.
    
           If you want to get full details of all captured substrings for a  given
           name,  you  must  use  the pcre_get_stringtable_entries() function. The
           first argument is the compiled pattern, and the second is the name. The
           third  and  fourth  are  pointers to variables which are updated by the
           possible match, consider using the alternative matching  function  (see
           below)  instead.  If you cannot use the alternative function, but still
           need to find all possible matches, you can kludge it up by  making  use
           of the callout facility, which is described in the pcrecallout documen-
           tation.
    
           What you have to do is to insert a callout right at the end of the pat-
           tern.   When your callout function is called, extract and save the cur-
           rent matched substring. Then return  1,  which  forces  pcre_exec()  to
           backtrack  and  try other alternatives. Ultimately, when it runs out of
           matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
    
    
    

    MATCHING A PATTERN: THE ALTERNATIVE FUNCTION

    
           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
                const char *subject, int length, int startoffset,
                int options, int *ovector, int ovecsize,
                int *workspace, int wscount);
    
           The function pcre_dfa_exec()  is  called  to  match  a  subject  string
           against  a  compiled pattern, using a matching algorithm that scans the
           subject string just once, and does not backtrack.  This  has  different
           characteristics  to  the  normal  algorithm, and is not compatible with
           Perl. Some of the features of PCRE patterns are not  supported.  Never-
           theless,  there are times when this kind of matching can be useful. For
           a discussion of the two matching algorithms, 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 differ-
           ent  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 */
    
             PCRE_PARTIAL
    
           This has the same general effect as it does for  pcre_exec(),  but  the
           details   are   slightly   different.  When  PCRE_PARTIAL  is  set  for
           pcre_dfa_exec(), 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 pos-
           sibility.  The portion of the string that provided the partial match is
           set as the first matching string.
    
             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 alterna-
           tive 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()  is  called  with  the  PCRE_PARTIAL  option, and
           returns a partial match, it is possible to call it  again,  with  addi-
           tional  subject  characters,  and have it continue with the same match.
           The PCRE_DFA_RESTART option requests this action; when it is  set,  the
           workspace  and wscount options must reference the same vector as before
           because data about the match so far is left in  them  after  a  partial
           match.  There  is  more  discussion of this facility in the pcrepartial
           documentation.
    
       Successful returns from pcre_dfa_exec()
    
           When pcre_dfa_exec() succeeds,  it  may  have  matched  more  than  one
           substring  in the subject. Note, however, that all the matches from one
           run of the function start at the same point in the subject. The shorter
           matches  are all initial substrings of the longer matches. For example,
           if the pattern
    
             <.*>
    
           is matched against the string
    
             This is <something> <something else> <something further> no more
    
           the three matched strings are
    
             <something>
             <something> <something else>
             <something> <something else> <something further>
    
           On success, the yield of the function is a number  greater  than  zero,
           which  is  the  number of matched substrings. The substrings themselves
           are returned in ovector. Each string uses two elements;  the  first  is
           the  offset  to  the start, and the second is the offset to the end. In
           described above.  There are in addition the following errors  that  are
           specific to pcre_dfa_exec():
    
             PCRE_ERROR_DFA_UITEM      (-16)
    
           This  return is given if pcre_dfa_exec() encounters an item in the pat-
           tern that it does not support, for instance, the use of \C  or  a  back
           reference.
    
             PCRE_ERROR_DFA_UCOND      (-17)
    
           This  return  is  given  if pcre_dfa_exec() encounters a condition item
           that uses a back reference for the condition, or a test  for  recursion
           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 field. This is not supported
           (it is meaningless).
    
             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), pcrepar-
           tial(3), pcreposix(3), pcreprecompile(3), pcresample(3),  pcrestack(3).
    
    
    

    AUTHOR

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

    REVISION

    
           Last updated: 24 August 2008
           Copyright (c) 1997-2011 University of Cambridge.
    
                                                                        PCREAPI(3)
    
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