pcreapi man page on NetBSD

Man page or keyword search:  
man Server   9087 pages
apropos Keyword Search (all sections)
Output format
NetBSD logo
[printable version]

PCREAPI(3)							    PCREAPI(3)

NAME
       PCRE - Perl-compatible regular expressions

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);

       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);

       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 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.

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

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

	 pcre_copy_substring()
	 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 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 (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 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
       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 char‐
       acter  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  advance‐
       ment 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 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.  Though they are derived from ASCII, the same values
       are returned in EBCDIC environments. The default should normally corre‐
       spond to the standard sequence for your operating system.

	 PCRE_CONFIG_BSR

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

	 PCRE_CONFIG_LINK_SIZE

       The  output  is	an  integer that contains the number of bytes used for
       internal linkage in compiled regular expressions. 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  num‐
       ber  of	internal  matching  function calls in a pcre_exec() execution.
       Further details are given with pcre_exec() below.

	 PCRE_CONFIG_MATCH_LIMIT_RECURSION

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

	 PCRE_CONFIG_STACKRECURSE

       The  output is an integer that is set to one if internal recursion when
       running pcre_exec() is implemented by recursive function calls that use
       the  stack  to remember their state. This is the usual way that PCRE is
       compiled. The output is zero if PCRE was compiled to use blocks of data
       on  the	heap  instead  of  recursive  function	calls.	In  this case,
       pcre_stack_malloc and  pcre_stack_free  are  called  to	manage	memory
       blocks on the heap, thus avoiding the use of the stack.

COMPILING A PATTERN

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

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

       Either of the functions pcre_compile() or pcre_compile2() can be called
       to compile a pattern into an internal form. The only difference between
       the  two interfaces is that pcre_compile2() has an additional argument,
       errorcodeptr, via which a numerical error  code	can  be	 returned.  To
       avoid  too  much repetition, we refer just to pcre_compile() below, but
       the information applies equally to pcre_compile2().

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

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

       The options argument contains various bit settings that affect the com‐
       pilation. It should be zero if no options are required.	The  available
       options	are  described	below. Some of them (in particular, those that
       are compatible with Perl, but some others as well) can also be set  and
       unset  from  within  the	 pattern  (see the detailed description in the
       pcrepattern documentation). For those options that can be different  in
       different  parts	 of  the pattern, the contents of the options argument
       specifies their settings at the start of compilation and execution. The
       PCRE_ANCHORED, PCRE_BSR_xxx, 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. The byte offset from the start of the  pattern  to  the
       character  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. Some errors are not detected
       until checks are carried out when the whole pattern has	been  scanned;
       in this case the offset is set to the end of the pattern.

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

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

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

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

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

	 PCRE_ANCHORED

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

	 PCRE_AUTO_CALLOUT

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

	 PCRE_BSR_ANYCRLF
	 PCRE_BSR_UNICODE

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

       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  (?(	 which
       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 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
	 PCRE_NEWLINE_ANYCRLF
	 PCRE_NEWLINE_ANY

       These  options  override the default newline definition that was chosen
       when PCRE was built. Setting the first or the second specifies  that  a
       newline	is  indicated  by a single character (CR or LF, respectively).
       Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the
       two-character  CRLF  sequence.  Setting	PCRE_NEWLINE_ANYCRLF specifies
       that any of the three preceding sequences should be recognized. Setting
       PCRE_NEWLINE_ANY	 specifies that any Unicode newline sequence should be
       recognized. 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 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 whitespace characters
       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‐
       mance 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 subject strings.

COMPILATION ERROR CODES

       The following table lists the error  codes  than	 may  be  returned  by
       pcre_compile2(),	 along with the error messages that may be returned by
       both compiling functions. 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, \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  (*VERB) with an argument is not supported
	 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

       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() or pcre_dfa_exec(). However, a pcre_extra block  also  con‐
       tains  other  fields  that can be set by the caller before the block is
       passed; these are described below in the section on matching a pattern.

       If studying the	pattern	 does  not  produce  any  useful  information,
       pcre_study() returns NULL. In that circumstance, if the calling program
       wants  to  pass	any  of	  the	other	fields	 to   pcre_exec()   or
       pcre_dfa_exec(), it must set up its own pcre_extra block.

       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 */

       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.

LOCALE SUPPORT

       PCRE handles caseless matching, and determines whether  characters  are
       letters,	 digits, or whatever, by reference to a set of tables, indexed
       by character value. When running in UTF-8 mode, this  applies  only  to
       characters  with	 codes	less than 128. Higher-valued codes never match
       escapes such as \w or \d, but can be tested with \p if  PCRE  is	 built
       with  Unicode  character property support. The use of locales with Uni‐
       code 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 char‐
       acters. However, when PCRE is built, it is possible to cause the inter‐
       nal tables to be rebuilt in the default "C" locale of the local system,
       which may cause them to be different.

       The  internal tables can always be overridden by tables supplied by the
       application that calls PCRE. These may be created in a different locale
       from  the  default.  As more and more applications change to using Uni‐
       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
       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 arbitrary 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() */
	   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
       matching	 string, a pointer to the table is returned. Otherwise NULL is
       returned. The fourth argument should point to an unsigned char *	 vari‐
       able.

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

       As  a  simple  example of the name/number table, consider the following
       pattern (assume PCRE_EXTENDED is set, so white space -  including  new‐
       lines - is ignored):

	 (?<date> (?<year>(\d\d)?\d\d) -
	 (?<month>\d\d) - (?<day>\d\d) )

       There  are  four	 named subpatterns, so the table has four entries, and
       each entry in the table is eight bytes long. The table is  as  follows,
       with non-printing bytes shows in hexadecimal, and undefined bytes shown
       as ??:

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

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

	 PCRE_INFO_OKPARTIAL

       Return 1	 if  the  pattern  can	be  used  for  partial	matching  with
       pcre_exec(),  otherwise	0.  The fourth argument should point to an int
       variable. From  release	8.00,  this  always  returns  1,  because  the
       restrictions  that  previously  applied	to  partial matching have been
       lifted. The pcrepartial documentation gives details of  partial	match‐
       ing.

	 PCRE_INFO_OPTIONS

       Return  a  copy of the options with which the pattern was compiled. The
       fourth argument should point to an unsigned long	 int  variable.	 These
       option bits are those specified in the call to pcre_compile(), modified
       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(). If pcre_extra is NULL, or there	 is  no	 study
       data,  zero  is	returned. 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).

       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 different parts of the application may be using the same compiled
       pattern, but you want to free the block when they are all done.

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

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

MATCHING A PATTERN: THE TRADITIONAL FUNCTION

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

       The  function pcre_exec() is called to match a subject string against a
       compiled pattern, which is passed in the code argument. If the  pattern
       was  studied,  the  result  of  the study should be passed in the extra
       argument. 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
       fields (not necessarily in this order):

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

       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_MATCH_LIMIT
	 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 a pattern that uses nested unlim‐
       ited 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  callout_data  field is used in conjunction with the "callout" fea‐
       ture, and is described in the pcrecallout documentation.

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

   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.

	 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
       pattern.

	 PCRE_NOTBOL

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

	 PCRE_NOTEOL

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

	 PCRE_NOTEMPTY

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

	 a?b?

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

	 PCRE_NOTEMPTY_ATSTART

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

       Perl	has    no    direct    equivalent    of	   PCRE_NOTEMPTY    or
       PCRE_NOTEMPTY_ATSTART, but it does make a special  case	of  a  pattern
       match  of  the empty string within its split() function, and when using
       the /g modifier. It is  possible	 to  emulate  Perl's  behaviour	 after
       matching a null string by first trying the match again at the same off‐
       set with PCRE_NOTEMPTY_ATSTART and  PCRE_ANCHORED,  and	then  if  that
       fails, by advancing the starting offset (see below) and trying an ordi‐
       nary match again. There is some code that demonstrates how to  do  this
       in the pcredemo sample program.

	 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  a  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. When callouts
       are in use, these optimizations can cause  them	to  be	skipped.  This
       option  disables	 the  "start-up" optimizations, causing performance to
       suffer, but ensuring that the callouts do occur.

	 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. If  startoffset  con‐
       tains an invalid value, 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. When PCRE_NO_UTF8_CHECK is
       set, the effect of passing an invalid UTF-8 string as a subject,	 or  a
       value  of startoffset that does not point to the start of a UTF-8 char‐
       acter, is undefined. Your program may crash.

	 PCRE_PARTIAL_HARD
	 PCRE_PARTIAL_SOFT

       These options turn on the partial matching feature. For backwards  com‐
       patibility,  PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial
       match occurs if the end of the subject string is reached	 successfully,
       but  there  are not enough subject characters to complete the match. If
       this happens when PCRE_PARTIAL_HARD  is	set,  pcre_exec()  immediately
       returns	PCRE_ERROR_PARTIAL.  Otherwise,	 if  PCRE_PARTIAL_SOFT is set,
       matching continues by testing any other alternatives. Only if they  all
       fail  is	 PCRE_ERROR_PARTIAL  returned (instead of PCRE_ERROR_NOMATCH).
       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 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.
       In UTF-8 mode, the byte offset must point to the start of a UTF-8 char‐
       acter.  Unlike  the pattern string, the subject 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‐
       strings, each substring using a pair of integers. The  remaining	 third
       of  the	vector is used as workspace by pcre_exec() while matching cap‐
       turing subpatterns, and is not available for passing back  information.
       The  number passed in ovecsize should always be a multiple of three. If
       it is not, it is rounded down.

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

       The first pair of integers, ovector[0]  and  ovector[1],	 identify  the
       portion	of  the subject string matched by the entire pattern. The next
       pair is used for the first capturing subpattern, and so on.  The	 value
       returned by pcre_exec() is one more than the highest numbered pair that
       has been set.  For example, if two substrings have been	captured,  the
       returned	 value is 3. If there are no capturing subpatterns, the return
       value from a successful match is 1, indicating that just the first pair
       of offsets has been set.

       If a capturing subpattern is matched repeatedly, it is the last portion
       of the string that it matched that is returned.

       If the vector is too small to hold all the captured substring  offsets,
       it is used as far as possible (up to two-thirds of its length), and the
       function returns a value of zero. If 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_fullinfo() function can be used to find out how many capturing
       subpatterns there are in a compiled  pattern.  The  smallest  size  for
       ovector	that  will allow for n captured substrings, in addition to the
       offsets of the substring matched by the whole pattern, is (n+1)*3.

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

       Offset  values  that correspond to unused subpatterns at the end of the
       expression are also set to -1. For example,  if	the  string  "abc"  is
       matched	against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
       matched. The return from the function is 2, because  the	 highest  used
       capturing subpattern number is 1. 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.

	 PCRE_ERROR_NULL	   (-2)

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

	 PCRE_ERROR_BADOPTION	   (-3)

       An unrecognized bit was set in the options argument.

	 PCRE_ERROR_BADMAGIC	   (-4)

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

	 PCRE_ERROR_UNKNOWN_OPCODE (-5)

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

	 PCRE_ERROR_NOMEMORY	   (-6)

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

	 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.

	 PCRE_ERROR_BADUTF8_OFFSET (-11)

       The UTF-8 byte sequence that was passed as a subject was valid, but the
       value of startoffset did not point to the beginning of a UTF-8  charac‐
       ter.

	 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.

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

EXTRACTING CAPTURED SUBSTRINGS BY NUMBER

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

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

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

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

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

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

       The functions pcre_copy_substring() and pcre_get_substring() extract  a
       single  substring,  whose  number  is given as stringnumber. A value of
       zero extracts the substring that matched the  entire  pattern,  whereas
       higher  values  extract	the  captured  substrings.  For pcre_copy_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,
	    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  num‐
       ber.  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 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  appropri‐
       ate.  NOTE:  If PCRE_DUPNAMES is set and there are duplicate names, the
       behaviour may not be what you want (see the next section).

       Warning: If the pattern uses the (?| feature to set up multiple subpat‐
       terns  with  the	 same number, as described in the section on duplicate
       subpattern numbers in the pcrepattern page, you	cannot	use  names  to
       distinguish  the	 different subpatterns, because names are not included
       in the compiled code. The matching process uses only numbers. For  this
       reason,	the  use of different names for subpatterns of the same number
       causes an error at compile time.

DUPLICATE SUBPATTERN NAMES

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

       When a pattern is compiled with the  PCRE_DUPNAMES  option,  names  for
       subpatterns  are not required to be unique. (Duplicate names are always
       allowed for subpatterns with the same number, created by using the  (?|
       feature.	 Indeed,  if  such subpatterns are named, they are required to
       use the same names.)

       Normally, patterns with duplicate names are such that in any one match,
       only  one of the named subpatterns participates. An example is shown in
       the pcrepattern documentation.

       When   duplicates   are	 present,   pcre_copy_named_substring()	   and
       pcre_get_named_substring()  return the first substring corresponding to
       the given name that is set. If  none  are  set,	PCRE_ERROR_NOSUBSTRING
       (-7)  is	 returned;  no	data  is returned. The pcre_get_stringnumber()
       function returns one of the numbers that are associated with the	 name,
       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  sec‐
       tion  entitled  Information  about  a  pattern.	Given all the relevant
       entries for the name, you can extract each of their numbers, and	 hence
       the captured data, if any.

FINDING ALL POSSIBLE MATCHES

       The  traditional	 matching  function  uses a similar algorithm to Perl,
       which stops when it finds the first match, starting at a given point in
       the  subject.  If you want to find all possible matches, or the longest
       possible match, consider using the alternative matching	function  (see
       below)  instead.	 If you cannot use the alternative function, but still
       need to find all possible matches, you can kludge it up by  making  use
       of the callout facility, which is described in the pcrecallout 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, and	 a  list  of  features
       that  pcre_dfa_exec() does not support, see the pcrematching documenta‐
       tion.

       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 */
	   ovector,	   /* vector of integers for substring information */
	   10,		   /* number of elements (NOT size in bytes) */
	   wspace,	   /* working space vector */
	   20);		   /* number of elements (NOT size in bytes) */

   Option bits for pcre_dfa_exec()

       The unused bits of the options argument	for  pcre_dfa_exec()  must  be
       zero.  The  only	 bits  that  may  be  set are PCRE_ANCHORED, PCRE_NEW‐
       LINE_xxx,	PCRE_NOTBOL,	    PCRE_NOTEOL,	PCRE_NOTEMPTY,
       PCRE_NOTEMPTY_ATSTART, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_HARD, PCRE_PAR‐
       TIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All	but  the  last
       four  of	 these	are  exactly  the  same	 as  for pcre_exec(), so their
       description is not repeated here.

	 PCRE_PARTIAL_HARD
	 PCRE_PARTIAL_SOFT

       These have the same general effect as they do for pcre_exec(), but  the
       details	are  slightly  different.  When	 PCRE_PARTIAL_HARD  is set for
       pcre_dfa_exec(), it returns PCRE_ERROR_PARTIAL if the end of  the  sub‐
       ject  is	 reached  and there is still at least one matching possibility
       that requires additional characters. This happens even if some complete
       matches have also been found. When PCRE_PARTIAL_SOFT is set, the return
       code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end
       of  the	subject	 is  reached, there have been no complete matches, but
       there is still at least one matching possibility. The  portion  of  the
       string  that  was inspected when the longest partial match was found is
       set as the first matching string in both cases.

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

   Successful returns from pcre_dfa_exec()

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

	 <.*>

       is matched against the string

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

       the three matched strings are

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

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

       The strings are returned in reverse order of length; that is, the long‐
       est  matching  string is given first. If there were too many matches to
       fit into ovector, the yield of the function is zero, and the vector  is
       filled with the longest matches.

   Error returns from pcre_dfa_exec()

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

	 PCRE_ERROR_DFA_UITEM	   (-16)

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

	 PCRE_ERROR_DFA_UCOND	   (-17)

       This return is given if pcre_dfa_exec()	encounters  a  condition  item
       that  uses  a back reference for the condition, or a test for recursion
       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: 03 October 2009
       Copyright (c) 1997-2009 University of Cambridge.

								    PCREAPI(3)
[top]
                             _         _         _ 
                            | |       | |       | |     
                            | |       | |       | |     
                         __ | | __ __ | | __ __ | | __  
                         \ \| |/ / \ \| |/ / \ \| |/ /  
                          \ \ / /   \ \ / /   \ \ / /   
                           \   /     \   /     \   /    
                            \_/       \_/       \_/ 
More information is available in HTML format for server NetBSD

List of man pages available for NetBSD

Copyright (c) for man pages and the logo by the respective OS vendor.

For those who want to learn more, the polarhome community provides shell access and support.

[legal] [privacy] [GNU] [policy] [cookies] [netiquette] [sponsors] [FAQ]
Tweet
Polarhome, production since 1999.
Member of Polarhome portal.
Based on Fawad Halim's script.
....................................................................
Vote for polarhome
Free Shell Accounts :: the biggest list on the net