pcreapi(3) — Linux manual page

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 a 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 a 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 a
       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-8.44.tar.gz fetched from
       ⟨ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/⟩ on
       2021-04-01.  If you discover any rendering problems in this HTML
       version 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 manual 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)