NAME | PCRE NATIVE API BASIC FUNCTIONS | PCRE NATIVE API STRING EXTRACTION FUNCTIONS | PCRE NATIVE API AUXILIARY FUNCTIONS | PCRE NATIVE API INDIRECTED FUNCTIONS | PCRE 8-BIT, 16-BIT, AND 32-BIT LIBRARIES | PCRE API OVERVIEW | NEWLINES | MULTITHREADING | SAVING PRECOMPILED PATTERNS FOR LATER USE | CHECKING BUILD-TIME OPTIONS | COMPILING A PATTERN | COMPILATION ERROR CODES | STUDYING A PATTERN | LOCALE SUPPORT | INFORMATION ABOUT A PATTERN | REFERENCE COUNTS | MATCHING A PATTERN: THE TRADITIONAL FUNCTION | EXTRACTING CAPTURED SUBSTRINGS BY NUMBER | EXTRACTING CAPTURED SUBSTRINGS BY NAME | DUPLICATE SUBPATTERN NAMES | FINDING ALL POSSIBLE MATCHES | OBTAINING AN ESTIMATE OF STACK USAGE | MATCHING A PATTERN: THE ALTERNATIVE FUNCTION | SEE ALSO | AUTHOR | REVISION | COLOPHON

PCREAPI(3)                Library Functions Manual                PCREAPI(3)

NAME         top

       PCRE - Perl-compatible regular expressions

       #include <pcre.h>

PCRE NATIVE API BASIC FUNCTIONS         top


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

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

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

       void pcre_free_study(pcre_extra *extra);

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

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

PCRE NATIVE API STRING EXTRACTION FUNCTIONS         top


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

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

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

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

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

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

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

       void pcre_free_substring(const char *stringptr);

       void pcre_free_substring_list(const char **stringptr);

PCRE NATIVE API AUXILIARY FUNCTIONS         top


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

       pcre_jit_stack *pcre_jit_stack_alloc(int startsize, int maxsize);

       void pcre_jit_stack_free(pcre_jit_stack *stack);

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

       const unsigned char *pcre_maketables(void);

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

       int pcre_refcount(pcre *code, int adjust);

       int pcre_config(int what, void *where);

       const char *pcre_version(void);

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

PCRE NATIVE API INDIRECTED FUNCTIONS         top


       void *(*pcre_malloc)(size_t);

       void (*pcre_free)(void *);

       void *(*pcre_stack_malloc)(size_t);

       void (*pcre_stack_free)(void *);

       int (*pcre_callout)(pcre_callout_block *);

       int (*pcre_stack_guard)(void);

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


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

       The 16-bit and 32-bit functions operate in the same way as their
       8-bit counterparts; they just use different data types for their
       arguments and results, and their names start with pcre16_ or pcre32_
       instead of pcre_. For every option that has UTF8 in its name (for
       example, PCRE_UTF8), there are corresponding 16-bit and 32-bit names
       with UTF8 replaced by UTF16 or UTF32, respectively. This facility is
       in fact just cosmetic; the 16-bit and 32-bit option names define the
       same bit values.

       References to bytes and UTF-8 in this document should be read as
       references to 16-bit data units and UTF-16 when using the 16-bit
       library, or 32-bit data units and UTF-32 when using the 32-bit
       library, unless specified otherwise.  More details of the specific
       differences for the 16-bit and 32-bit libraries are given in the
       pcre16 and pcre32 pages.

PCRE API OVERVIEW         top


       PCRE has its own native API, which is described in this document.
       There are also some wrapper functions (for the 8-bit library only)
       that correspond to the POSIX regular expression API, but they do not
       give access to all the functionality. They are described in the
       pcreposix documentation. Both of these APIs define a set of C
       function calls. A C++ wrapper (again for the 8-bit library only) is
       also distributed with PCRE. It is documented in the pcrecpp page.

       The native API C function prototypes are defined in the header file
       pcre.h, and on Unix-like systems the (8-bit) library itself is called
       libpcre. It can normally be accessed by adding -lpcre to the command
       for linking an application that uses PCRE. The header file defines
       the macros PCRE_MAJOR and PCRE_MINOR to contain the major and minor
       release numbers for the library. Applications can use these to
       include support for different releases of PCRE.

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

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

       Just-in-time compiler support is an optional feature of PCRE that can
       be built in appropriate hardware environments. It greatly speeds up
       the matching performance of many patterns. Simple programs can easily
       request that it be used if available, by setting an option that is
       ignored when it is not relevant. More complicated programs might need
       to make use of the functions pcre_jit_stack_alloc(),
       pcre_jit_stack_free(), and pcre_assign_jit_stack() in order to
       control the JIT code's memory usage.

       From release 8.32 there is also a direct interface for JIT execution,
       which gives improved performance. The JIT-specific functions are
       discussed in the pcrejit documentation.

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

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

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

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

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

       The function pcre_fullinfo() is used to find out information about a
       compiled pattern. The function pcre_version() returns a pointer to a
       string containing the version of PCRE and its date of release.

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

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

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

       The global variable pcre_callout initially contains NULL. It can be
       set by the caller to a "callout" function, which PCRE will then call
       at specified points during a matching operation. Details are given in
       the pcrecallout documentation.

       The global variable pcre_stack_guard initially contains NULL. It can
       be set by the caller to a function that is called by PCRE whenever it
       starts to compile a parenthesized part of a pattern. When parentheses
       are nested, PCRE uses recursive function calls, which use up the
       system stack. This function is provided so that applications with
       restricted stacks can force a compilation error if the stack runs
       out. The function should return zero if all is well, or non-zero to
       force an error.

NEWLINES         top


       PCRE supports five different conventions for indicating line breaks
       in strings: a single CR (carriage return) character, a single LF
       (linefeed) character, the two-character sequence CRLF, any of the
       three preceding, or any Unicode newline sequence. The Unicode newline
       sequences are the three just mentioned, plus the single characters VT
       (vertical tab, U+000B), FF (form feed, U+000C), NEL (next line,
       U+0085), LS (line separator, U+2028), and PS (paragraph separator,
       U+2029).

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

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

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

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

MULTITHREADING         top


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

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

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

SAVING PRECOMPILED PATTERNS FOR LATER USE         top


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

CHECKING BUILD-TIME OPTIONS         top


       int pcre_config(int what, void *where);

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

       The first argument for pcre_config() is an integer, specifying which
       information is required; the second argument is a pointer to a
       variable into which the information is placed. The returned value is
       zero on success, or the negative error code PCRE_ERROR_BADOPTION if
       the value in the first argument is not recognized. The following
       information is available:

         PCRE_CONFIG_UTF8

       The output is an integer that is set to one if UTF-8 support is
       available; otherwise it is set to zero. This value should normally be
       given to the 8-bit version of this function, pcre_config(). If it is
       given to the 16-bit or 32-bit version of this function, the result is
       PCRE_ERROR_BADOPTION.

         PCRE_CONFIG_UTF16

       The output is an integer that is set to one if UTF-16 support is
       available; otherwise it is set to zero. This value should normally be
       given to the 16-bit version of this function, pcre16_config(). If it
       is given to the 8-bit or 32-bit version of this function, the result
       is PCRE_ERROR_BADOPTION.

         PCRE_CONFIG_UTF32

       The output is an integer that is set to one if UTF-32 support is
       available; otherwise it is set to zero. This value should normally be
       given to the 32-bit version of this function, pcre32_config(). If it
       is given to the 8-bit or 16-bit version of this function, the result
       is PCRE_ERROR_BADOPTION.

         PCRE_CONFIG_UNICODE_PROPERTIES

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

         PCRE_CONFIG_JIT

       The output is an integer that is set to one if support for just-in-
       time compiling is available; otherwise it is set to zero.

         PCRE_CONFIG_JITTARGET

       The output is a pointer to a zero-terminated "const char *" string.
       If JIT support is available, the string contains the name of the
       architecture for which the JIT compiler is configured, for example
       "x86 32bit (little endian + unaligned)". If JIT support is not
       available, the result is NULL.

         PCRE_CONFIG_NEWLINE

       The output is an integer whose value specifies the default character
       sequence that is recognized as meaning "newline". The values that are
       supported in ASCII/Unicode environments are: 10 for LF, 13 for CR,
       3338 for CRLF, -2 for ANYCRLF, and -1 for ANY. In EBCDIC
       environments, CR, ANYCRLF, and ANY yield the same values. However,
       the value for LF is normally 21, though some EBCDIC environments use
       37. The corresponding values for CRLF are 3349 and 3365. The default
       should normally correspond to the standard sequence for your
       operating system.

         PCRE_CONFIG_BSR

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

         PCRE_CONFIG_LINK_SIZE

       The output is an integer that contains the number of bytes used for
       internal linkage in compiled regular expressions. For the 8-bit
       library, the value can be 2, 3, or 4. For the 16-bit library, the
       value is either 2 or 4 and is still a number of bytes. For the 32-bit
       library, the value is either 2 or 4 and is still a number of bytes.
       The default value of 2 is sufficient for all but the most massive
       patterns, since it allows the compiled pattern to be up to 64K in
       size. Larger values allow larger regular expressions to be compiled,
       at the expense of slower matching.

         PCRE_CONFIG_POSIX_MALLOC_THRESHOLD

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

         PCRE_CONFIG_PARENS_LIMIT

       The output is a long integer that gives the maximum depth of nesting
       of parentheses (of any kind) in a pattern. This limit is imposed to
       cap the amount of system stack used when a pattern is compiled. It is
       specified when PCRE is built; the default is 250. This limit does not
       take into account the stack that may already be used by the calling
       application. For finer control over compilation stack usage, you can
       set a pointer to an external checking function in pcre_stack_guard.

         PCRE_CONFIG_MATCH_LIMIT

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

         PCRE_CONFIG_MATCH_LIMIT_RECURSION

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

         PCRE_CONFIG_STACKRECURSE

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

COMPILING A PATTERN         top


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

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

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

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

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

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

       If errptr is NULL, pcre_compile() returns NULL immediately.
       Otherwise, if compilation of a pattern fails, pcre_compile() returns
       NULL, and sets the variable pointed to by errptr to point to a
       textual error message. This is a static string that is part of the
       library. You must not try to free it. Normally, the offset from the
       start of the pattern to the data unit that was being processed when
       the error was discovered is placed in the variable pointed to by
       erroffset, which must not be NULL (if it is, an immediate error is
       given). However, for an invalid UTF-8 or UTF-16 string, the offset is
       that of the first data unit of the failing character.

       Some errors are not detected until the whole pattern has been
       scanned; in these cases, the offset passed back is the length of the
       pattern. Note that the offset is in data units, not characters, even
       in a UTF mode. It may sometimes point into the middle of a UTF-8 or
       UTF-16 character.

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

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

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

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

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

         PCRE_ANCHORED

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

         PCRE_AUTO_CALLOUT

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

         PCRE_BSR_ANYCRLF
         PCRE_BSR_UNICODE

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

         PCRE_CASELESS

       If this bit is set, letters in the pattern match both upper and lower
       case letters. It is equivalent to Perl's /i option, and it can be
       changed within a pattern by a (?i) option setting. In UTF-8 mode,
       PCRE always understands the concept of case for characters whose
       values are less than 128, so caseless matching is always possible.
       For characters with higher values, the concept of case is supported
       if PCRE is compiled with Unicode property support, but not otherwise.
       If you want to use caseless matching for characters 128 and above,
       you must ensure that PCRE is compiled with Unicode property support
       as well as with UTF-8 support.

         PCRE_DOLLAR_ENDONLY

       If this bit is set, a dollar metacharacter in the pattern matches
       only at the end of the subject string. Without this option, a dollar
       also matches immediately before a newline at the end of the string
       (but not before any other newlines). The PCRE_DOLLAR_ENDONLY option
       is ignored if PCRE_MULTILINE is set.  There is no equivalent to this
       option in Perl, and no way to set it within a pattern.

         PCRE_DOTALL

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

         PCRE_DUPNAMES

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

         PCRE_EXTENDED

       If this bit is set, most white space characters in the pattern are
       totally ignored except when escaped or inside a character class.
       However, white space is not allowed within sequences such as (?> that
       introduce various parenthesized subpatterns, nor within a numerical
       quantifier such as {1,3}.  However, ignorable white space is
       permitted between an item and a following quantifier and between a
       quantifier and a following + that indicates possessiveness.

       White space did not used to include the VT character (code 11),
       because Perl did not treat this character as white space. However,
       Perl changed at release 5.18, so PCRE followed at release 8.34, and
       VT is now treated as white space.

       PCRE_EXTENDED also causes characters between an unescaped # outside a
       character class and the next newline, inclusive, to be ignored.
       PCRE_EXTENDED is equivalent to Perl's /x option, and it can be
       changed within a pattern by a (?x) option setting.

       Which characters are interpreted as newlines is controlled by the
       options passed to pcre_compile() or by a special sequence at the
       start of the pattern, as described in the section entitled "Newline
       conventions" in the pcrepattern documentation. Note that the end of
       this type of comment is a literal newline sequence in the pattern;
       escape sequences that happen to represent a newline do not count.

       This option makes it possible to include comments inside complicated
       patterns.  Note, however, that this applies only to data characters.
       White space characters may never appear within special character
       sequences in a pattern, for example within the sequence (?( that
       introduces a conditional subpattern.

         PCRE_EXTRA

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

         PCRE_FIRSTLINE

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

         PCRE_JAVASCRIPT_COMPAT

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

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

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

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

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

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

         PCRE_MULTILINE

       By default, for the purposes of matching "start of line" and "end of
       line", PCRE treats the subject string as consisting of a single line
       of characters, even if it actually contains newlines. The "start of
       line" metacharacter (^) matches only at the start of the string, and
       the "end of line" metacharacter ($) matches only at the end of the
       string, or before a terminating newline (except when
       PCRE_DOLLAR_ENDONLY is set). Note, however, that unless PCRE_DOTALL
       is set, the "any character" metacharacter (.) does not match at a
       newline. This behaviour (for ^, $, and dot) is the same as Perl.

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

         PCRE_NEVER_UTF

       This option locks out interpretation of the pattern as UTF-8 (or
       UTF-16 or UTF-32 in the 16-bit and 32-bit libraries). In particular,
       it prevents the creator of the pattern from switching to UTF
       interpretation by starting the pattern with (*UTF). This may be
       useful in applications that process patterns from external sources.
       The combination of PCRE_UTF8 and PCRE_NEVER_UTF also causes an error.

         PCRE_NEWLINE_CR
         PCRE_NEWLINE_LF
         PCRE_NEWLINE_CRLF
         PCRE_NEWLINE_ANYCRLF
         PCRE_NEWLINE_ANY

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

       In an ASCII/Unicode environment, the Unicode newline sequences are
       the three just mentioned, plus the single characters VT (vertical
       tab, U+000B), FF (form feed, U+000C), NEL (next line, U+0085), LS
       (line separator, U+2028), and PS (paragraph separator, U+2029). For
       the 8-bit library, the last two are recognized only in UTF-8 mode.

       When PCRE is compiled to run in an EBCDIC (mainframe) environment,
       the code for CR is 0x0d, the same as ASCII. However, the character
       code for LF is normally 0x15, though in some EBCDIC environments 0x25
       is used. Whichever of these is not LF is made to correspond to
       Unicode's NEL character. EBCDIC codes are all less than 256. For more
       details, see the pcrebuild documentation.

       The newline setting in the options word uses three bits that are
       treated as a number, giving eight possibilities. Currently only six
       are used (default plus the five values above). This means that if you
       set more than one newline option, the combination may or may not be
       sensible. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is
       equivalent to PCRE_NEWLINE_CRLF, but other combinations may yield
       unused numbers and cause an error.

       The only time that a line break in a pattern is specially recognized
       when compiling is when PCRE_EXTENDED is set. CR and LF are white
       space characters, and so are ignored in this mode. Also, an unescaped
       # outside a character class indicates a comment that lasts until
       after the next line break sequence. In other circumstances, line
       break sequences in patterns are treated as literal data.

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

         PCRE_NO_AUTO_CAPTURE

       If this option is set, it disables the use of numbered capturing
       parentheses in the pattern. Any opening parenthesis that is not
       followed by ? behaves as if it were followed by ?: but named
       parentheses can still be used for capturing (and they acquire numbers
       in the usual way). There is no equivalent of this option in Perl.

         PCRE_NO_AUTO_POSSESS

       If this option is set, it disables "auto-possessification". This is
       an optimization that, for example, turns a+b into a++b in order to
       avoid backtracks into a+ that can never be successful. However, if
       callouts are in use, auto-possessification means that some of them
       are never taken. You can set this option if you want the matching
       functions to do a full unoptimized search and run all the callouts,
       but it is mainly provided for testing purposes.

         PCRE_NO_START_OPTIMIZE

       This is an option that acts at matching time; that is, it is really
       an option for pcre_exec() or pcre_dfa_exec(). If it is set at compile
       time, it is remembered with the compiled pattern and assumed at
       matching time. This is necessary if you want to use JIT execution,
       because the JIT compiler needs to know whether or not this option is
       set. For details see the discussion of PCRE_NO_START_OPTIMIZE below.

         PCRE_UCP

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

         PCRE_UNGREEDY

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

         PCRE_UTF8

       This option causes PCRE to regard both the pattern and the subject as
       strings of UTF-8 characters instead of single-byte strings. However,
       it is available only when PCRE is built to include UTF support. If
       not, the use of this option provokes an error. Details of how this
       option changes the behaviour of PCRE are given in the pcreunicode
       page.

         PCRE_NO_UTF8_CHECK

       When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string
       is automatically checked. There is a discussion about the validity of
       UTF-8 strings in the pcreunicode page. If an invalid UTF-8 sequence
       is found, pcre_compile() returns an error. If you already know that
       your pattern is valid, and you want to skip this check for
       performance reasons, you can set the PCRE_NO_UTF8_CHECK option.  When
       it is set, the effect of passing an invalid UTF-8 string as a pattern
       is undefined. It may cause your program to crash or loop. Note that
       this option can also be passed to pcre_exec() and pcre_dfa_exec(), to
       suppress the validity checking of subject strings only. If the same
       string is being matched many times, the option can be safely set for
       the second and subsequent matchings to improve performance.

COMPILATION ERROR CODES         top


       The following table lists the error codes than may be returned by
       pcre_compile2(), along with the error messages that may be returned
       by both compiling functions. Note that error messages are always
       8-bit ASCII strings, even in 16-bit or 32-bit mode. As PCRE has
       developed, some error codes have fallen out of use. To avoid
       confusion, they have not been re-used.

          0  no error
          1  \ at end of pattern
          2  \c at end of pattern
          3  unrecognized character follows \
          4  numbers out of order in {} quantifier
          5  number too big in {} quantifier
          6  missing terminating ] for character class
          7  invalid escape sequence in character class
          8  range out of order in character class
          9  nothing to repeat
         10  [this code is not in use]
         11  internal error: unexpected repeat
         12  unrecognized character after (? or (?-
         13  POSIX named classes are supported only within a class
         14  missing )
         15  reference to non-existent subpattern
         16  erroffset passed as NULL
         17  unknown option bit(s) set
         18  missing ) after comment
         19  [this code is not in use]
         20  regular expression is too large
         21  failed to get memory
         22  unmatched parentheses
         23  internal error: code overflow
         24  unrecognized character after (?<
         25  lookbehind assertion is not fixed length
         26  malformed number or name after (?(
         27  conditional group contains more than two branches
         28  assertion expected after (?(
         29  (?R or (?[+-]digits must be followed by )
         30  unknown POSIX class name
         31  POSIX collating elements are not supported
         32  this version of PCRE is compiled without UTF support
         33  [this code is not in use]
         34  character value in \x{} or \o{} is too large
         35  invalid condition (?(0)
         36  \C not allowed in lookbehind assertion
         37  PCRE does not support \L, \l, \N{name}, \U, or \u
         38  number after (?C is > 255
         39  closing ) for (?C expected
         40  recursive call could loop indefinitely
         41  unrecognized character after (?P
         42  syntax error in subpattern name (missing terminator)
         43  two named subpatterns have the same name
         44  invalid UTF-8 string (specifically UTF-8)
         45  support for \P, \p, and \X has not been compiled
         46  malformed \P or \p sequence
         47  unknown property name after \P or \p
         48  subpattern name is too long (maximum 32 characters)
         49  too many named subpatterns (maximum 10000)
         50  [this code is not in use]
         51  octal value is greater than \377 in 8-bit non-UTF-8 mode
         52  internal error: overran compiling workspace
         53  internal error: previously-checked referenced subpattern
               not found
         54  DEFINE group contains more than one branch
         55  repeating a DEFINE group is not allowed
         56  inconsistent NEWLINE options
         57  \g is not followed by a braced, angle-bracketed, or quoted
               name/number or by a plain number
         58  a numbered reference must not be zero
         59  an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT)
         60  (*VERB) not recognized or malformed
         61  number is too big
         62  subpattern name expected
         63  digit expected after (?+
         64  ] is an invalid data character in JavaScript compatibility mode
         65  different names for subpatterns of the same number are
               not allowed
         66  (*MARK) must have an argument
         67  this version of PCRE is not compiled with Unicode property
               support
         68  \c must be followed by an ASCII character
         69  \k is not followed by a braced, angle-bracketed, or quoted name
         70  internal error: unknown opcode in find_fixedlength()
         71  \N is not supported in a class
         72  too many forward references
         73  disallowed Unicode code point (>= 0xd800 && <= 0xdfff)
         74  invalid UTF-16 string (specifically UTF-16)
         75  name is too long in (*MARK), (*PRUNE), (*SKIP), or (*THEN)
         76  character value in \u.... sequence is too large
         77  invalid UTF-32 string (specifically UTF-32)
         78  setting UTF is disabled by the application
         79  non-hex character in \x{} (closing brace missing?)
         80  non-octal character in \o{} (closing brace missing?)
         81  missing opening brace after \o
         82  parentheses are too deeply nested
         83  invalid range in character class
         84  group name must start with a non-digit
         85  parentheses are too deeply nested (stack check)

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

STUDYING A PATTERN         top


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

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

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

       If studying the pattern does not produce any useful information,
       pcre_study() returns NULL by default. In that circumstance, if the
       calling program wants to pass any of the other fields to pcre_exec()
       or pcre_dfa_exec(), it must set up its own pcre_extra block. However,
       if pcre_study() is called with the PCRE_STUDY_EXTRA_NEEDED option, it
       returns a pcre_extra block even if studying did not find any
       additional information. It may still return NULL, however, if an
       error occurs in pcre_study().

       The second argument of pcre_study() contains option bits. There are
       three further options in addition to PCRE_STUDY_EXTRA_NEEDED:

         PCRE_STUDY_JIT_COMPILE
         PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE
         PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE

       If any of these are set, and the just-in-time compiler is available,
       the pattern is further compiled into machine code that executes much
       faster than the pcre_exec() interpretive matching function. If the
       just-in-time compiler is not available, these options are ignored.
       All undefined bits in the options argument must be zero.

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

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

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

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

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

       Studying a pattern does two things: first, a lower bound for the
       length of subject string that is needed to match the pattern is
       computed. This does not mean that there are any strings of that
       length that match, but it does guarantee that no shorter strings
       match. The value is used to avoid wasting time by trying to match
       strings that are shorter than the lower bound. You can find out the
       value in a calling program via the pcre_fullinfo() function.

       Studying a pattern is also useful for non-anchored patterns that do
       not have a single fixed starting character. A bitmap of possible
       starting bytes is created. This speeds up finding a position in the
       subject at which to start matching. (In 16-bit mode, the bitmap is
       used for 16-bit values less than 256.  In 32-bit mode, the bitmap is
       used for 32-bit values less than 256.)

       These two optimizations apply to both pcre_exec() and
       pcre_dfa_exec(), and the information is also used by the JIT
       compiler.  The optimizations can be disabled by setting the
       PCRE_NO_START_OPTIMIZE option.  You might want to do this if your
       pattern contains callouts or (*MARK) and you want to make use of
       these facilities in cases where matching fails.

       PCRE_NO_START_OPTIMIZE can be specified at either compile time or
       execution time. However, if PCRE_NO_START_OPTIMIZE is passed to
       pcre_exec(), (that is, after any JIT compilation has happened) JIT
       execution is disabled. For JIT execution to work with
       PCRE_NO_START_OPTIMIZE, the option must be set at compile time.

       There is a longer discussion of PCRE_NO_START_OPTIMIZE below.

LOCALE SUPPORT         top


       PCRE handles caseless matching, and determines whether characters are
       letters, digits, or whatever, by reference to a set of tables,
       indexed by character code point. When running in UTF-8 mode, or in
       the 16- or 32-bit libraries, this applies only to characters with
       code points less than 256. By default, higher-valued code points
       never match escapes such as \w or \d. However, if PCRE is built with
       Unicode property support, all characters can be tested with \p and
       \P, or, alternatively, the PCRE_UCP option can be set when a pattern
       is compiled; this causes \w and friends to use Unicode property
       support instead of the built-in tables.

       The use of locales with Unicode is discouraged. If you are handling
       characters with code points greater than 128, you should either use
       Unicode support, or use locales, but not try to mix the two.

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

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

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

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

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

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

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

       It is possible to pass a table pointer or NULL (indicating the use of
       the internal tables) to pcre_exec() or pcre_dfa_exec() (see the
       discussion below in the section on matching a pattern). This facility
       is provided for use with pre-compiled patterns that have been saved
       and reloaded.  Character tables are not saved with patterns, so if a
       non-standard table was used at compile time, it must be provided
       again when the reloaded pattern is matched. Attempting to use this
       facility to match a pattern in a different locale from the one in
       which it was compiled is likely to lead to anomalous (usually
       incorrect) results.

INFORMATION ABOUT A PATTERN         top


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

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

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

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

       The "magic number" is placed at the start of each compiled pattern as
       an simple check against passing an arbitrary memory pointer. The
       endianness error can occur if a compiled pattern is saved and
       reloaded on a different host. Here is a typical call of
       pcre_fullinfo(), to obtain the length of the compiled pattern:

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

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

         PCRE_INFO_BACKREFMAX

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

         PCRE_INFO_CAPTURECOUNT

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

         PCRE_INFO_DEFAULT_TABLES

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

         PCRE_INFO_FIRSTBYTE (deprecated)

       Return information about the first data unit of any matched string,
       for a non-anchored pattern. The name of this option refers to the
       8-bit library, where data units are bytes. The fourth argument should
       point to an int variable. Negative values are used for special cases.
       However, this means that when the 32-bit library is in non-UTF-32
       mode, the full 32-bit range of characters cannot be returned. For
       this reason, this value is deprecated; use
       PCRE_INFO_FIRSTCHARACTERFLAGS and PCRE_INFO_FIRSTCHARACTER instead.

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

       If there is no fixed first value, and if either

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

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

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

         PCRE_INFO_FIRSTCHARACTER

       Return the value of the first data unit (non-UTF character) of any
       matched string in the situation where PCRE_INFO_FIRSTCHARACTERFLAGS
       returns 1; otherwise return 0. The fourth argument should point to an
       uint_t variable.

       In the 8-bit library, the value is always less than 256. In the
       16-bit library the value can be up to 0xffff. In the 32-bit library
       in UTF-32 mode the value can be up to 0x10ffff, and up to 0xffffffff
       when not using UTF-32 mode.

         PCRE_INFO_FIRSTCHARACTERFLAGS

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

       If there is a fixed first value, for example, the letter "c" from a
       pattern such as (cat|cow|coyote), 1 is returned, and the character
       value can be retrieved using PCRE_INFO_FIRSTCHARACTER. If there is no
       fixed first value, and if either

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

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

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

         PCRE_INFO_FIRSTTABLE

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

         PCRE_INFO_HASCRORLF

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

         PCRE_INFO_JCHANGED

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

         PCRE_INFO_JIT

       Return 1 if the pattern was studied with one of the JIT options, and
       just-in-time compiling was successful. The fourth argument should
       point to an int variable. A return value of 0 means that JIT support
       is not available in this version of PCRE, or that the pattern was not
       studied with a JIT option, or that the JIT compiler could not handle
       this particular pattern. See the pcrejit documentation for details of
       what can and cannot be handled.

         PCRE_INFO_JITSIZE

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

         PCRE_INFO_LASTLITERAL

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

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

         PCRE_INFO_MATCH_EMPTY

       Return 1 if the pattern can match an empty string, otherwise 0. The
       fourth argument should point to an int variable.

         PCRE_INFO_MATCHLIMIT

       If the pattern set a match limit by including an item of the form
       (*LIMIT_MATCH=nnnn) at the start, the value is returned. The fourth
       argument should point to an unsigned 32-bit integer. If no such value
       has been set, the call to pcre_fullinfo() returns the error
       PCRE_ERROR_UNSET.

         PCRE_INFO_MAXLOOKBEHIND

       Return the number of characters (NB not data units) in the longest
       lookbehind assertion in the pattern. This information is useful when
       doing multi-segment matching using the partial matching facilities.
       Note that the simple assertions \b and \B require a one-character
       lookbehind. \A also registers a one-character lookbehind, though it
       does not actually inspect the previous character. This is to ensure
       that at least one character from the old segment is retained when a
       new segment is processed. Otherwise, if there are no lookbehinds in
       the pattern, \A might match incorrectly at the start of a new
       segment.

         PCRE_INFO_MINLENGTH

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

         PCRE_INFO_NAMECOUNT
         PCRE_INFO_NAMEENTRYSIZE
         PCRE_INFO_NAMETABLE

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

       The map consists of a number of fixed-size entries.
       PCRE_INFO_NAMECOUNT gives the number of entries, and
       PCRE_INFO_NAMEENTRYSIZE gives the size of each entry; both of these
       return an int value. The entry size depends on the length of the
       longest name. PCRE_INFO_NAMETABLE returns a pointer to the first
       entry of the table. This is a pointer to char in the 8-bit library,
       where the first two bytes of each entry are the number of the
       capturing parenthesis, most significant byte first. In the 16-bit
       library, the pointer points to 16-bit data units, the first of which
       contains the parenthesis number. In the 32-bit library, the pointer
       points to 32-bit data units, the first of which contains the
       parenthesis number. The rest of the entry is the corresponding name,
       zero terminated.

       The names are in alphabetical order. If (?| is used to create
       multiple groups with the same number, as described in the section on
       duplicate subpattern numbers in the pcrepattern page, the groups may
       be given the same name, but there is only one entry in the table.
       Different names for groups of the same number are not permitted.
       Duplicate names for subpatterns with different numbers are permitted,
       but only if PCRE_DUPNAMES is set. They appear in the table in the
       order in which they were found in the pattern. In the absence of (?|
       this is the order of increasing number; when (?| is used this is not
       necessarily the case because later subpatterns may have lower
       numbers.

       As a simple example of the name/number table, consider the following
       pattern after compilation by the 8-bit library (assume PCRE_EXTENDED
       is set, so white space - including newlines - is ignored):

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

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

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

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

         PCRE_INFO_OKPARTIAL

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

         PCRE_INFO_OPTIONS

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

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

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

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

         PCRE_INFO_RECURSIONLIMIT

       If the pattern set a recursion limit by including an item of the form
       (*LIMIT_RECURSION=nnnn) at the start, the value is returned. The
       fourth argument should point to an unsigned 32-bit integer. If no
       such value has been set, the call to pcre_fullinfo() returns the
       error PCRE_ERROR_UNSET.

         PCRE_INFO_SIZE

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

         PCRE_INFO_STUDYSIZE

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

         PCRE_INFO_REQUIREDCHARFLAGS

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

       For anchored patterns, a last literal value is recorded only if it
       follows something of variable length. For example, for the pattern
       /^a\d+z\d+/ the returned value 1 (with "z" returned from
       PCRE_INFO_REQUIREDCHAR), but for /^a\dz\d/ the returned value is 0.

         PCRE_INFO_REQUIREDCHAR

       Return the value of the rightmost literal data unit that must exist
       in any matched string, other than at its start, if such a value has
       been recorded. The fourth argument should point to an uint32_t
       variable. If there is no such value, 0 is returned.

REFERENCE COUNTS         top


       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         top


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

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

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

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

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

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

   Extra data for pcre_exec()

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

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

       In the 16-bit version of this structure, the mark field has type
       "PCRE_UCHAR16 **".

       In the 32-bit version of this structure, the mark field has type
       "PCRE_UCHAR32 **".

       The flags field is used to specify which of the other fields are set.
       The flag bits are:

         PCRE_EXTRA_CALLOUT_DATA
         PCRE_EXTRA_EXECUTABLE_JIT
         PCRE_EXTRA_MARK
         PCRE_EXTRA_MATCH_LIMIT
         PCRE_EXTRA_MATCH_LIMIT_RECURSION
         PCRE_EXTRA_STUDY_DATA
         PCRE_EXTRA_TABLES

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

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

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

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

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

       A value for the match limit may also be supplied by an item at the
       start of a pattern of the form

         (*LIMIT_MATCH=d)

       where d is a decimal number. However, such a setting is ignored
       unless d is less than the limit set by the caller of pcre_exec() or,
       if no such limit is set, less than the default.

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

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

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

       A value for the recursion limit may also be supplied by an item at
       the start of a pattern of the form

         (*LIMIT_RECURSION=d)

       where d is a decimal number. However, such a setting is ignored
       unless d is less than the limit set by the caller of pcre_exec() or,
       if no such limit is set, less than the default.

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

       The tables field is provided for use with patterns that have been
       pre-compiled using custom character tables, saved to disc or
       elsewhere, and then reloaded, because the tables that were used to
       compile a pattern are not saved with it. See the pcreprecompile
       documentation for a discussion of saving compiled patterns for later
       use. If NULL is passed using this mechanism, it forces PCRE's
       internal tables to be used.

       Warning: The tables that pcre_exec() uses must be the same as those
       that were used when the pattern was compiled. If this is not the
       case, the behaviour of pcre_exec() is undefined. Therefore, when a
       pattern is compiled and matched in the same process, this field
       should never be set. In this (the most common) case, the correct
       table pointer is automatically passed with the compiled pattern from
       pcre_compile() to pcre_exec().

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

   Option bits for pcre_exec()

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

       If the pattern was successfully studied with one of the just-in-time
       (JIT) compile options, the only supported options for JIT execution
       are PCRE_NO_UTF8_CHECK, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,
       PCRE_NOTEMPTY_ATSTART, PCRE_PARTIAL_HARD, and PCRE_PARTIAL_SOFT. If
       an unsupported option is used, JIT execution is disabled and the
       normal interpretive code in pcre_exec() is run.

         PCRE_ANCHORED

       The PCRE_ANCHORED option limits pcre_exec() to matching at the first
       matching position. If a pattern was compiled with PCRE_ANCHORED, or
       turned out to be anchored by virtue of its contents, it cannot be
       made unachored at matching time.

         PCRE_BSR_ANYCRLF
         PCRE_BSR_UNICODE

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

         PCRE_NEWLINE_CR
         PCRE_NEWLINE_LF
         PCRE_NEWLINE_CRLF
         PCRE_NEWLINE_ANYCRLF
         PCRE_NEWLINE_ANY

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

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

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

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

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

         PCRE_NOTBOL

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

         PCRE_NOTEOL

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

         PCRE_NOTEMPTY

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

         a?b?

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

         PCRE_NOTEMPTY_ATSTART

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

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

         PCRE_NO_START_OPTIMIZE

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

       The PCRE_NO_START_OPTIMIZE option disables the start-up
       optimizations, possibly causing performance to suffer, but ensuring
       that in cases where the result is "no match", the callouts do occur,
       and that items such as (*COMMIT) and (*MARK) are considered at every
       possible starting position in the subject string. If
       PCRE_NO_START_OPTIMIZE is set at compile time, it cannot be unset at
       matching time. The use of PCRE_NO_START_OPTIMIZE at matching time
       (that is, passing it to pcre_exec()) disables JIT execution; in this
       situation, matching is always done using interpretively.

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

         (*COMMIT)ABC

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

         (*MARK:A)(X|Y)

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

         PCRE_NO_UTF8_CHECK

       When PCRE_UTF8 is set at compile time, the validity of the subject as
       a UTF-8 string is automatically checked when pcre_exec() is
       subsequently called.  The entire string is checked before any other
       processing takes place. The value of startoffset is also checked to
       ensure that it points to the start of a UTF-8 character. There is a
       discussion about the validity of UTF-8 strings in the pcreunicode
       page. If an invalid sequence of bytes is found, pcre_exec() returns
       the error PCRE_ERROR_BADUTF8 or, if PCRE_PARTIAL_HARD is set and the
       problem is a truncated character at the end of the subject,
       PCRE_ERROR_SHORTUTF8. In both cases, information about the precise
       nature of the error may also be returned (see the descriptions of
       these errors in the section entitled Error return values from
       pcre_exec() below).  If startoffset contains a value that does not
       point to the start of a UTF-8 character (or to the end of the
       subject), PCRE_ERROR_BADUTF8_OFFSET is returned.

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

         PCRE_PARTIAL_HARD
         PCRE_PARTIAL_SOFT

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

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

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

   The string to be matched by pcre_exec()

       The subject string is passed to pcre_exec() as a pointer in subject,
       a length in length, and a starting offset in startoffset. The units
       for length and startoffset are bytes for the 8-bit library, 16-bit
       data items for the 16-bit library, and 32-bit data items for the
       32-bit library.

       If startoffset is negative or greater than the length of the subject,
       pcre_exec() returns PCRE_ERROR_BADOFFSET. When the starting offset is
       zero, the search for a match starts at the beginning of the subject,
       and this is by far the most common case. In UTF-8 or UTF-16 mode, the
       offset must point to the start of a character, or the end of the
       subject (in UTF-32 mode, one data unit equals one character, so all
       offsets are valid). Unlike the pattern string, the subject may
       contain binary zeroes.

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

         \Biss\B

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

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

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

   How pcre_exec() returns captured substrings

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

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

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

       When a match is successful, information about captured substrings is
       returned in pairs of integers, starting at the beginning of ovector,
       and continuing up to two-thirds of its length at the most. The first
       element of each pair is set to the offset of the first character in a
       substring, and the second is set to the offset of the first character
       after the end of a substring. These values are always data unit
       offsets, even in UTF mode. They are byte offsets in the 8-bit
       library, 16-bit data item offsets in the 16-bit library, and 32-bit
       data item offsets in the 32-bit library. Note: they are not character
       counts.

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

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

       If the vector is too small to hold all the captured substring
       offsets, it is used as far as possible (up to two-thirds of its
       length), and the function returns a value of zero. If neither the
       actual string matched nor any captured substrings are of interest,
       pcre_exec() may be called with ovector passed as NULL and ovecsize as
       zero. However, if the pattern contains back references and the
       ovector is not big enough to remember the related substrings, PCRE
       has to get additional memory for use during matching. Thus it is
       usually advisable to supply an ovector of reasonable size.

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

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

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

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

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

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

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

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

   Error return values from pcre_exec()

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

         PCRE_ERROR_NOMATCH        (-1)

       The subject string did not match the pattern.

         PCRE_ERROR_NULL           (-2)

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

         PCRE_ERROR_BADOPTION      (-3)

       An unrecognized bit was set in the options argument.

         PCRE_ERROR_BADMAGIC       (-4)

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

         PCRE_ERROR_UNKNOWN_OPCODE (-5)

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

         PCRE_ERROR_NOMEMORY       (-6)

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

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

         PCRE_ERROR_NOSUBSTRING    (-7)

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

         PCRE_ERROR_MATCHLIMIT     (-8)

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

         PCRE_ERROR_CALLOUT        (-9)

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

         PCRE_ERROR_BADUTF8        (-10)

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

         PCRE_ERROR_BADUTF8_OFFSET (-11)

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

         PCRE_ERROR_PARTIAL        (-12)

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

         PCRE_ERROR_BADPARTIAL     (-13)

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

         PCRE_ERROR_INTERNAL       (-14)

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

         PCRE_ERROR_BADCOUNT       (-15)

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

         PCRE_ERROR_RECURSIONLIMIT (-21)

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

         PCRE_ERROR_BADNEWLINE     (-23)

       An invalid combination of PCRE_NEWLINE_xxx options was given.

         PCRE_ERROR_BADOFFSET      (-24)

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

         PCRE_ERROR_SHORTUTF8      (-25)

       This error is returned instead of PCRE_ERROR_BADUTF8 when the subject
       string ends with a truncated UTF-8 character and the
       PCRE_PARTIAL_HARD option is set.  Information about the failure is
       returned as for PCRE_ERROR_BADUTF8. It is in fact sufficient to
       detect this case, but this special error code for PCRE_PARTIAL_HARD
       precedes the implementation of returned information; it is retained
       for backwards compatibility.

         PCRE_ERROR_RECURSELOOP    (-26)

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

         PCRE_ERROR_JIT_STACKLIMIT (-27)

       This error is returned when a pattern that was successfully studied
       using a JIT compile option is being matched, but the memory available
       for the just-in-time processing stack is not large enough. See the
       pcrejit documentation for more details.

         PCRE_ERROR_BADMODE        (-28)

       This error is given if a pattern that was compiled by the 8-bit
       library is passed to a 16-bit or 32-bit library function, or vice
       versa.

         PCRE_ERROR_BADENDIANNESS  (-29)

       This error is given if a pattern that was compiled and saved is
       reloaded on a host with different endianness. The utility function
       pcre_pattern_to_host_byte_order() can be used to convert such a
       pattern so that it runs on the new host.

         PCRE_ERROR_JIT_BADOPTION

       This error is returned when a pattern that was successfully studied
       using a JIT compile option is being matched, but the matching mode
       (partial or complete match) does not correspond to any JIT
       compilation mode. When the JIT fast path function is used, this error
       may be also given for invalid options. See the pcrejit documentation
       for more details.

         PCRE_ERROR_BADLENGTH      (-32)

       This error is given if pcre_exec() is called with a negative value
       for the length argument.

       Error numbers -16 to -20, -22, and 30 are not used by pcre_exec().

   Reason codes for invalid UTF-8 strings

       This section applies only to the 8-bit library. The corresponding
       information for the 16-bit and 32-bit libraries is given in the
       pcre16 and pcre32 pages.

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

         PCRE_UTF8_ERR1
         PCRE_UTF8_ERR2
         PCRE_UTF8_ERR3
         PCRE_UTF8_ERR4
         PCRE_UTF8_ERR5

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

         PCRE_UTF8_ERR6
         PCRE_UTF8_ERR7
         PCRE_UTF8_ERR8
         PCRE_UTF8_ERR9
         PCRE_UTF8_ERR10

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

         PCRE_UTF8_ERR11
         PCRE_UTF8_ERR12

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

         PCRE_UTF8_ERR13

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

         PCRE_UTF8_ERR14

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

         PCRE_UTF8_ERR15
         PCRE_UTF8_ERR16
         PCRE_UTF8_ERR17
         PCRE_UTF8_ERR18
         PCRE_UTF8_ERR19

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

         PCRE_UTF8_ERR20

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

         PCRE_UTF8_ERR21

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

         PCRE_UTF8_ERR22

       This error code was formerly used when the presence of a so-called
       "non-character" caused an error. Unicode corrigendum #9 makes it
       clear that such characters should not cause a string to be rejected,
       and so this code is no longer in use and is never returned.

EXTRACTING CAPTURED SUBSTRINGS BY NUMBER         top


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

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

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

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

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

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

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

         PCRE_ERROR_NOMEMORY       (-6)

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

         PCRE_ERROR_NOSUBSTRING    (-7)

       There is no substring whose number is stringnumber.

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

         PCRE_ERROR_NOMEMORY       (-6)

       if the attempt to get the memory block failed.

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

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

EXTRACTING CAPTURED SUBSTRINGS BY NAME         top


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

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

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

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

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

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

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

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

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

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

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

DUPLICATE SUBPATTERN NAMES         top


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

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

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

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

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

FINDING ALL POSSIBLE MATCHES         top


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

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

OBTAINING AN ESTIMATE OF STACK USAGE         top


       Matching certain patterns using pcre_exec() can use a lot of process
       stack, which in certain environments can be rather limited in size.
       Some users find it helpful to have an estimate of the amount of stack
       that is used by pcre_exec(), to help them set recursion limits, as
       described in the pcrestack documentation. The estimate that is output
       by pcretest when called with the -m and -C options is obtained by
       calling pcre_exec with the values NULL, NULL, NULL, -999, and -999
       for its first five arguments.

       Normally, if its first argument is NULL, pcre_exec() immediately
       returns the negative error code PCRE_ERROR_NULL, but with this
       special combination of arguments, it returns instead a negative
       number whose absolute value is the approximate stack frame size in
       bytes. (A negative number is used so that it is clear that no match
       has happened.) The value is approximate because in some cases,
       recursive calls to pcre_exec() occur when there are one or two
       additional variables on the stack.

       If PCRE has been compiled to use the heap instead of the stack for
       recursion, the value returned is the size of each block that is
       obtained from the heap.

MATCHING A PATTERN: THE ALTERNATIVE FUNCTION         top


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

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

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

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

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

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

   Option bits for pcre_dfa_exec()

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

         PCRE_PARTIAL_HARD
         PCRE_PARTIAL_SOFT

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

         PCRE_DFA_SHORTEST

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

         PCRE_DFA_RESTART

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

   Successful returns from pcre_dfa_exec()

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

         <.*>

       is matched against the string

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

       the three matched strings are

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

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

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

       NOTE: PCRE's "auto-possessification" optimization usually applies to
       character repeats at the end of a pattern (as well as internally).
       For example, the pattern "a\d+" is compiled as if it were "a\d++"
       because there is no point even considering the possibility of
       backtracking into the repeated digits. For DFA matching, this means
       that only one possible match is found. If you really do want multiple
       matches in such cases, either use an ungreedy repeat ("a\d+?") or set
       the PCRE_NO_AUTO_POSSESS option when compiling.

   Error returns from pcre_dfa_exec()

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

         PCRE_ERROR_DFA_UITEM      (-16)

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

         PCRE_ERROR_DFA_UCOND      (-17)

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

         PCRE_ERROR_DFA_UMLIMIT    (-18)

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

         PCRE_ERROR_DFA_WSSIZE     (-19)

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

         PCRE_ERROR_DFA_RECURSE    (-20)

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

         PCRE_ERROR_DFA_BADRESTART (-30)

       When pcre_dfa_exec() is called with the PCRE_DFA_RESTART option, some
       plausibility checks are made on the contents of the workspace, which
       should contain data about the previous partial match. If any of these
       checks fail, this error is given.

SEE ALSO         top


       pcre16(3), pcre32(3), pcrebuild(3), pcrecallout(3), pcrecpp(3)(3),
       pcrematching(3), pcrepartial(3), pcreposix(3), pcreprecompile(3),
       pcresample(3), pcrestack(3).

AUTHOR         top


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

REVISION         top


       Last updated: 18 December 2015
       Copyright (c) 1997-2015 University of Cambridge.

COLOPHON         top

       This page is part of the PCRE (Perl Compatible Regular Expressions)
       project.  Information about the project can be found at 
       ⟨http://www.pcre.org/⟩.  If you have a bug report for this manual
       page, see ⟨http://bugs.exim.org/enter_bug.cgi?product=PCRE⟩.  This
       page was obtained from the tarball pcre-8.41.tar.gz fetched from 
       ⟨ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/⟩ on
       2017-09-15.  If you discover any rendering problems in this HTML ver‐
       sion of the page, or you believe there is a better or more up-to-date
       source for the page, or you have corrections or improvements to the
       information in this COLOPHON (which is not part of the original man‐
       ual page), send a mail to man-pages@man7.org

PCRE 8.39                     18 December 2015                    PCREAPI(3)

Pages that refer to this page: pcretest(1)pcrebuild(3)pcrejit(3)pcrepattern(3)pcresyntax(3)