pcre2api


       PCRE2  is  a  new API for PCRE, starting at release 10.0. This document
       contains a description of all its native functions. See the pcre2 docu-
       ment for an overview of all the PCRE2 documentation.

PCRE2 NATIVE API BASIC FUNCTIONS

       pcre2_code *pcre2_compile(PCRE2_SPTR pattern, PCRE2_SIZE length,
         uint32_t options, int *errorcode, PCRE2_SIZE *erroroffset,
         pcre2_compile_context *ccontext);

       void pcre2_code_free(pcre2_code *code);

       pcre2_match_data *pcre2_match_data_create(uint32_t ovecsize,
         pcre2_general_context *gcontext);

       pcre2_match_data *pcre2_match_data_create_from_pattern(
         const pcre2_code *code, pcre2_general_context *gcontext);

       int pcre2_match(const pcre2_code *code, PCRE2_SPTR subject,
         PCRE2_SIZE length, PCRE2_SIZE startoffset,
         uint32_t options, pcre2_match_data *match_data,
         pcre2_match_context *mcontext);

       int pcre2_dfa_match(const pcre2_code *code, PCRE2_SPTR subject,
         PCRE2_SIZE length, PCRE2_SIZE startoffset,
         uint32_t options, pcre2_match_data *match_data,
         pcre2_match_context *mcontext,
         int *workspace, PCRE2_SIZE wscount);

       void pcre2_match_data_free(pcre2_match_data *match_data);

PCRE2 NATIVE API AUXILIARY MATCH FUNCTIONS

       PCRE2_SPTR pcre2_get_mark(pcre2_match_data *match_data);

       uint32_t pcre2_get_ovector_count(pcre2_match_data *match_data);

       PCRE2_SIZE *pcre2_get_ovector_pointer(pcre2_match_data *match_data);

       PCRE2_SIZE pcre2_get_startchar(pcre2_match_data *match_data);

PCRE2 NATIVE API GENERAL CONTEXT FUNCTIONS

       pcre2_general_context *pcre2_general_context_create(
         void *(*private_malloc)(PCRE2_SIZE, void *),
         void (*private_free)(void *, void *), void *memory_data);

       pcre2_general_context *pcre2_general_context_copy(
         pcre2_general_context *gcontext);

       void pcre2_general_context_free(pcre2_general_context *gcontext);

PCRE2 NATIVE API COMPILE CONTEXT FUNCTIONS
       int pcre2_set_character_tables(pcre2_compile_context *ccontext,
         const unsigned char *tables);

       int pcre2_set_compile_extra_options(pcre2_compile_context *ccontext,
         uint32_t extra_options);

       int pcre2_set_max_pattern_length(pcre2_compile_context *ccontext,
         PCRE2_SIZE value);

       int pcre2_set_newline(pcre2_compile_context *ccontext,
         uint32_t value);

       int pcre2_set_parens_nest_limit(pcre2_compile_context *ccontext,
         uint32_t value);

       int pcre2_set_compile_recursion_guard(pcre2_compile_context *ccontext,
         int (*guard_function)(uint32_t, void *), void *user_data);

PCRE2 NATIVE API MATCH CONTEXT FUNCTIONS

       pcre2_match_context *pcre2_match_context_create(
         pcre2_general_context *gcontext);

       pcre2_match_context *pcre2_match_context_copy(
         pcre2_match_context *mcontext);

       void pcre2_match_context_free(pcre2_match_context *mcontext);

       int pcre2_set_callout(pcre2_match_context *mcontext,
         int (*callout_function)(pcre2_callout_block *, void *),
         void *callout_data);

       int pcre2_set_substitute_callout(pcre2_match_context *mcontext,
         int (*callout_function)(pcre2_substitute_callout_block *, void *),
         void *callout_data);

       int pcre2_set_offset_limit(pcre2_match_context *mcontext,
         PCRE2_SIZE value);

       int pcre2_set_heap_limit(pcre2_match_context *mcontext,
         uint32_t value);

       int pcre2_set_match_limit(pcre2_match_context *mcontext,
         uint32_t value);

       int pcre2_set_depth_limit(pcre2_match_context *mcontext,
         uint32_t value);

PCRE2 NATIVE API STRING EXTRACTION FUNCTIONS

       int pcre2_substring_copy_byname(pcre2_match_data *match_data,
         PCRE2_SPTR name, PCRE2_UCHAR *buffer, PCRE2_SIZE *bufflen);

       int pcre2_substring_copy_bynumber(pcre2_match_data *match_data,
       int pcre2_substring_length_byname(pcre2_match_data *match_data,
         PCRE2_SPTR name, PCRE2_SIZE *length);

       int pcre2_substring_length_bynumber(pcre2_match_data *match_data,
         uint32_t number, PCRE2_SIZE *length);

       int pcre2_substring_nametable_scan(const pcre2_code *code,
         PCRE2_SPTR name, PCRE2_SPTR *first, PCRE2_SPTR *last);

       int pcre2_substring_number_from_name(const pcre2_code *code,
         PCRE2_SPTR name);

       void pcre2_substring_list_free(PCRE2_SPTR *list);

       int pcre2_substring_list_get(pcre2_match_data *match_data,
         PCRE2_UCHAR ***listptr, PCRE2_SIZE **lengthsptr);

PCRE2 NATIVE API STRING SUBSTITUTION FUNCTION

       int pcre2_substitute(const pcre2_code *code, PCRE2_SPTR subject,
         PCRE2_SIZE length, PCRE2_SIZE startoffset,
         uint32_t options, pcre2_match_data *match_data,
         pcre2_match_context *mcontext, PCRE2_SPTR replacementzfP,
         PCRE2_SIZE rlength, PCRE2_UCHAR *outputbuffer,
         PCRE2_SIZE *outlengthptr);

PCRE2 NATIVE API JIT FUNCTIONS

       int pcre2_jit_compile(pcre2_code *code, uint32_t options);

       int pcre2_jit_match(const pcre2_code *code, PCRE2_SPTR subject,
         PCRE2_SIZE length, PCRE2_SIZE startoffset,
         uint32_t options, pcre2_match_data *match_data,
         pcre2_match_context *mcontext);

       void pcre2_jit_free_unused_memory(pcre2_general_context *gcontext);

       pcre2_jit_stack *pcre2_jit_stack_create(PCRE2_SIZE startsize,
         PCRE2_SIZE maxsize, pcre2_general_context *gcontext);

       void pcre2_jit_stack_assign(pcre2_match_context *mcontext,
         pcre2_jit_callback callback_function, void *callback_data);

       void pcre2_jit_stack_free(pcre2_jit_stack *jit_stack);

PCRE2 NATIVE API SERIALIZATION FUNCTIONS

       int32_t pcre2_serialize_decode(pcre2_code **codes,
         int32_t number_of_codes, const uint8_t *bytes,
         pcre2_general_context *gcontext);

       int32_t pcre2_serialize_encode(const pcre2_code **codes,
         int32_t number_of_codes, uint8_t **serialized_bytes,
         PCRE2_SIZE *serialized_size, pcre2_general_context *gcontext);
         PCRE2_SIZE bufflen);

       const unsigned char *pcre2_maketables(pcre2_general_context *gcontext);

       int pcre2_pattern_info(const pcre2_code *code, uint32_t what,
         void *where);

       int pcre2_callout_enumerate(const pcre2_code *code,
         int (*callback)(pcre2_callout_enumerate_block *, void *),
         void *user_data);

       int pcre2_config(uint32_t what, void *where);

PCRE2 NATIVE API OBSOLETE FUNCTIONS

       int pcre2_set_recursion_limit(pcre2_match_context *mcontext,
         uint32_t value);

       int pcre2_set_recursion_memory_management(
         pcre2_match_context *mcontext,
         void *(*private_malloc)(PCRE2_SIZE, void *),
         void (*private_free)(void *, void *), void *memory_data);

       These  functions became obsolete at release 10.30 and are retained only
       for backward compatibility. They should not be used in  new  code.  The
       first  is  replaced by pcre2_set_depth_limit(); the second is no longer
       needed and has no effect (it always returns zero).

PCRE2 EXPERIMENTAL PATTERN CONVERSION FUNCTIONS

       pcre2_convert_context *pcre2_convert_context_create(
         pcre2_general_context *gcontext);

       pcre2_convert_context *pcre2_convert_context_copy(
         pcre2_convert_context *cvcontext);

       void pcre2_convert_context_free(pcre2_convert_context *cvcontext);

       int pcre2_set_glob_escape(pcre2_convert_context *cvcontext,
         uint32_t escape_char);

       int pcre2_set_glob_separator(pcre2_convert_context *cvcontext,
         uint32_t separator_char);

       int pcre2_pattern_convert(PCRE2_SPTR pattern, PCRE2_SIZE length,
         uint32_t options, PCRE2_UCHAR **buffer,
         PCRE2_SIZE *blength, pcre2_convert_context *cvcontext);

       void pcre2_converted_pattern_free(PCRE2_UCHAR *converted_pattern);

       These functions provide a way of  converting  non-PCRE2  patterns  into
       patterns  that  can  be  processed by pcre2_compile(). This facility is
       experimental and may be changed in future releases. At present, "globs"
       and  POSIX  basic  and  extended patterns can be converted. Details are
       Character strings are passed to and from a PCRE2 library as a  sequence
       of  unsigned  integers  in  code  units of the appropriate width. Every
       PCRE2 function comes in three different forms, one  for  each  library,
       for example:

         pcre2_compile_8()
         pcre2_compile_16()
         pcre2_compile_32()

       There are also three different sets of data types:

         PCRE2_UCHAR8, PCRE2_UCHAR16, PCRE2_UCHAR32
         PCRE2_SPTR8,  PCRE2_SPTR16,  PCRE2_SPTR32

       The  UCHAR  types define unsigned code units of the appropriate widths.
       For example, PCRE2_UCHAR16 is usually defined as `uint16_t'.  The  SPTR
       types  are  constant  pointers  to the equivalent UCHAR types, that is,
       they are pointers to vectors of unsigned code units.

       Many applications use only one code unit width. For their  convenience,
       macros are defined whose names are the generic forms such as pcre2_com-
       pile() and  PCRE2_SPTR.  These  macros  use  the  value  of  the  macro
       PCRE2_CODE_UNIT_WIDTH  to generate the appropriate width-specific func-
       tion and macro names.  PCRE2_CODE_UNIT_WIDTH is not defined by default.
       An  application  must  define  it  to  be 8, 16, or 32 before including
       pcre2.h in order to make use of the generic names.

       Applications that use more than one code unit width can be linked  with
       more  than  one PCRE2 library, but must define PCRE2_CODE_UNIT_WIDTH to
       be 0 before including pcre2.h, and then use the  real  function  names.
       Any  code  that  is to be included in an environment where the value of
       PCRE2_CODE_UNIT_WIDTH is unknown should  also  use  the  real  function
       names. (Unfortunately, it is not possible in C code to save and restore
       the value of a macro.)

       If PCRE2_CODE_UNIT_WIDTH is not defined  before  including  pcre2.h,  a
       compiler error occurs.

       When  using  multiple  libraries  in an application, you must take care
       when processing any particular pattern to use  only  functions  from  a
       single  library.   For example, if you want to run a match using a pat-
       tern that was compiled with pcre2_compile_16(), you  must  do  so  with
       pcre2_match_16(), not pcre2_match_8() or pcre2_match_32().

       In  the  function summaries above, and in the rest of this document and
       other PCRE2 documents, functions and data  types  are  described  using
       their generic names, without the _8, _16, or _32 suffix.

PCRE2 API OVERVIEW

       PCRE2  has  its  own  native  API, which is described in this document.
       There are also some wrapper functions for the 8-bit library that corre-
       spond  to the POSIX regular expression API, but they do not give access
       to all the functionality of PCRE2. They are described in the pcre2posix
       The  functions pcre2_compile() and pcre2_match() 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 pcre2demo.c in the PCRE2 source distribution. A listing
       of  this  program  is  given  in  the  pcre2demo documentation, and the
       pcre2sample documentation describes how to compile and run it.

       The compiling and matching functions recognize various options that are
       passed as bits in an options argument. There are also some more compli-
       cated  parameters  such  as  custom  memory  management  functions  and
       resource  limits  that  are passed in "contexts" (which are just memory
       blocks, described below). Simple applications do not need to  make  use
       of contexts.

       Just-in-time  (JIT)  compiler  support  is an optional feature of PCRE2
       that can be built in  appropriate  hardware  environments.  It  greatly
       speeds  up  the  matching  performance  of  many patterns. Programs can
       request that it be used if  available  by  calling  pcre2_jit_compile()
       after a pattern has been successfully compiled by pcre2_compile(). This
       does nothing if JIT support is not available.

       More complicated programs might need to  make  use  of  the  specialist
       functions    pcre2_jit_stack_create(),    pcre2_jit_stack_free(),   and
       pcre2_jit_stack_assign() in order to  control  the  JIT  code's  memory
       usage.

       JIT matching is automatically used by pcre2_match() if it is available,
       unless the PCRE2_NO_JIT option is set. There is also a direct interface
       for  JIT  matching,  which gives improved performance at the expense of
       less sanity checking. The JIT-specific functions are discussed  in  the
       pcre2jit documentation.

       A  second  matching function, pcre2_dfa_match(), which is not Perl-com-
       patible, 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  lookaround  assertions).  However,  this algorithm does not
       return captured substrings. A description of  the  two  matching  algo-
       rithms   and  their  advantages  and  disadvantages  is  given  in  the
       pcre2matching   documentation.   There   is   no   JIT   support    for
       pcre2_dfa_match().

       In  addition  to  the  main compiling and matching functions, there are
       convenience functions for extracting captured substrings from a subject
       string that has been matched by pcre2_match(). They are:

         pcre2_substring_copy_byname()
         pcre2_substring_copy_bynumber()
         pcre2_substring_get_byname()
         pcre2_substring_get_bynumber()
         pcre2_substring_list_get()
         pcre2_substring_length_byname()
         pcre2_substring_length_bynumber()
         pcre2_substring_nametable_scan()

       compiled patterns on disc or elsewhere, and reloading them later.

       Finally,  there  are functions for finding out information about a com-
       piled pattern (pcre2_pattern_info()) and about the  configuration  with
       which PCRE2 was built (pcre2_config()).

       Functions  with  names  ending with _free() are used for freeing memory
       blocks of various sorts. In all cases, if one  of  these  functions  is
       called with a NULL argument, it does nothing.

STRING LENGTHS AND OFFSETS

       The  PCRE2  API  uses  string  lengths and offsets into strings of code
       units in several places. These values are always  of  type  PCRE2_SIZE,
       which  is an unsigned integer type, currently always defined as size_t.
       The largest  value  that  can  be  stored  in  such  a  type  (that  is
       ~(PCRE2_SIZE)0)  is reserved as a special indicator for zero-terminated
       strings and unset offsets.  Therefore, the longest string that  can  be
       handled is one less than this maximum.

NEWLINES

       PCRE2 supports five different conventions for indicating line breaks in
       strings: a single CR (carriage return) character, a  single  LF  (line-
       feed) character, the two-character sequence CRLF, any of the three pre-
       ceding, or any Unicode newline sequence. The Unicode newline  sequences
       are  the  three just mentioned, plus the single characters VT (vertical
       tab, U+000B), FF (form feed, U+000C), NEL (next line, U+0085), LS (line
       separator, U+2028), and PS (paragraph separator, U+2029).

       Each  of  the first three conventions is used by at least one operating
       system as its standard newline sequence. When PCRE2 is built, a default
       can be specified.  If it is not, the default is set to LF, which is the
       Unix standard. However, the newline convention can  be  changed  by  an
       application  when  calling  pcre2_compile(),  or it can be specified by
       special text at the start of the pattern  itself;  this  overrides  any
       other  settings.  See  the pcre2pattern page for details of the special
       character sequences.

       In the PCRE2 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  advance-
       ment for a non-anchored pattern. There is more detail about this in the
       section on pcre2_match() 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; this
       has its own separate convention.

MULTITHREADING

       In a multithreaded application it is important to keep  thread-specific
       when pcre2_compile() is successful. The data in the compiled pattern is
       fixed, and does not change when the pattern is matched.  Therefore,  it
       is  thread-safe, that is, the same compiled pattern can be used by more
       than one thread simultaneously. For example, an application can compile
       all its patterns at the start, before forking off multiple threads that
       use them. However, if the just-in-time (JIT)  optimization  feature  is
       being  used,  it needs separate memory stack areas for each thread. See
       the pcre2jit documentation for more details.

       In a more complicated situation, where patterns are compiled only  when
       they  are  first needed, but are still shared between threads, pointers
       to compiled patterns must be protected  from  simultaneous  writing  by
       multiple threads, at least until a pattern has been compiled. The logic
       can be something like this:

         Get a read-only (shared) lock (mutex) for pointer
         if (pointer == NULL)
           {
           Get a write (unique) lock for pointer
           pointer = pcre2_compile(...
           }
         Release the lock
         Use pointer in pcre2_match()

       Of course, testing for compilation errors should also  be  included  in
       the code.

       If JIT is being used, but the JIT compilation is not being done immedi-
       ately, (perhaps waiting to see if the pattern  is  used  often  enough)
       similar logic is required. JIT compilation updates a pointer within the
       compiled code block, so a thread must gain unique write access  to  the
       pointer     before    calling    pcre2_jit_compile().    Alternatively,
       pcre2_code_copy()  or  pcre2_code_copy_with_tables()  can  be  used  to
       obtain  a private copy of the compiled code before calling the JIT com-
       piler.

   Context blocks

       The next main section below introduces the idea of "contexts" in  which
       PCRE2 functions are called. A context is nothing more than a collection
       of parameters that control the way PCRE2 operates. Grouping a number of
       parameters together in a context is a convenient way of passing them to
       a PCRE2 function without using lots of arguments. The  parameters  that
       are  stored  in  contexts  are in some sense "advanced features" of the
       API. Many straightforward applications will not need to use contexts.

       In a multithreaded application, if the parameters in a context are val-
       ues  that  are  never  changed, the same context can be used by all the
       threads. However, if any thread needs to change any value in a context,
       it must make its own thread-specific copy.

   Match blocks

       The  matching  functions need a block of memory for storing the results
       that holds the parameter values.  Applications  that  do  not  need  to
       adjust  any  of  the  context  parameters  can pass NULL when a context
       pointer is required.

       There are three different types of context: a general context  that  is
       relevant  for  several  PCRE2 operations, a compile-time context, and a
       match-time context.

   The general context

       At present, this context just  contains  pointers  to  (and  data  for)
       external  memory  management  functions  that  are  called from several
       places in the PCRE2 library. The context is named `general' rather than
       specifically  `memory'  because in future other fields may be added. If
       you do not want to supply your own custom memory management  functions,
       you  do not need to bother with a general context. A general context is
       created by:

       pcre2_general_context *pcre2_general_context_create(
         void *(*private_malloc)(PCRE2_SIZE, void *),
         void (*private_free)(void *, void *), void *memory_data);

       The two function pointers specify custom memory  management  functions,
       whose prototypes are:

         void *private_malloc(PCRE2_SIZE, void *);
         void  private_free(void *, void *);

       Whenever code in PCRE2 calls these functions, the final argument is the
       value of memory_data. Either of the first two arguments of the creation
       function  may be NULL, in which case the system memory management func-
       tions malloc() and free() are used. (This is not currently  useful,  as
       there  are  no  other  fields in a general context, but in future there
       might be.)  The private_malloc() function  is  used  (if  supplied)  to
       obtain  memory  for storing the context, and all three values are saved
       as part of the context.

       Whenever PCRE2 creates a data block of any kind, the block  contains  a
       pointer  to the free() function that matches the malloc() function that
       was used. When the time comes to  free  the  block,  this  function  is
       called.

       A general context can be copied by calling:

       pcre2_general_context *pcre2_general_context_copy(
         pcre2_general_context *gcontext);

       The memory used for a general context should be freed by calling:

       void pcre2_general_context_free(pcre2_general_context *gcontext);

       If  this  function  is  passed  a NULL argument, it returns immediately
       without doing anything.


       A compile context is also required if you are using custom memory  man-
       agement.   If  none of these apply, just pass NULL as the context argu-
       ment of pcre2_compile().

       A compile context is created, copied, and freed by the following  func-
       tions:

       pcre2_compile_context *pcre2_compile_context_create(
         pcre2_general_context *gcontext);

       pcre2_compile_context *pcre2_compile_context_copy(
         pcre2_compile_context *ccontext);

       void pcre2_compile_context_free(pcre2_compile_context *ccontext);

       A  compile  context  is created with default values for its parameters.
       These can be changed by calling the following functions, which return 0
       on success, or PCRE2_ERROR_BADDATA if invalid data is detected.

       int pcre2_set_bsr(pcre2_compile_context *ccontext,
         uint32_t value);

       The  value  must  be PCRE2_BSR_ANYCRLF, to specify that \R matches only
       CR, LF, or CRLF, or PCRE2_BSR_UNICODE, to specify that \R  matches  any
       Unicode line ending sequence. The value is used by the JIT compiler and
       by  the  two  interpreted   matching   functions,   pcre2_match()   and
       pcre2_dfa_match().

       int pcre2_set_character_tables(pcre2_compile_context *ccontext,
         const unsigned char *tables);

       The  value  must  be  the result of a call to pcre2_maketables(), whose
       only argument is a general context. This function builds a set of char-
       acter tables in the current locale.

       int pcre2_set_compile_extra_options(pcre2_compile_context *ccontext,
         uint32_t extra_options);

       As  PCRE2  has developed, almost all the 32 option bits that are avail-
       able in the options argument of pcre2_compile() have been used  up.  To
       avoid  running  out, the compile context contains a set of extra option
       bits which are used for some newer, assumed rarer, options. This  func-
       tion  sets  those bits. It always sets all the bits (either on or off).
       It does not modify any existing  setting.  The  available  options  are
       defined in the section entitled "Extra compile options" below.

       int pcre2_set_max_pattern_length(pcre2_compile_context *ccontext,
         PCRE2_SIZE value);

       This  sets a maximum length, in code units, for any pattern string that
       is compiled with this context. If the pattern is longer,  an  error  is
       generated.   This facility is provided so that applications that accept
       patterns from external sources can limit their size. The default is the

       A pattern can override the value set in the compile context by starting
       with a sequence such as (*CRLF). See the pcre2pattern page for details.

       When   a   pattern   is   compiled   with   the    PCRE2_EXTENDED    or
       PCRE2_EXTENDED_MORE option, the newline convention affects the recogni-
       tion of the end of internal comments starting  with  #.  The  value  is
       saved  with the compiled pattern for subsequent use by the JIT compiler
       and by  the  two  interpreted  matching  functions,  pcre2_match()  and
       pcre2_dfa_match().

       int pcre2_set_parens_nest_limit(pcre2_compile_context *ccontext,
         uint32_t value);

       This  parameter  adjusts  the  limit,  set when PCRE2 is built (default
       250), on the depth of parenthesis nesting  in  a  pattern.  This  limit
       stops  rogue  patterns  using  up too much system stack when being com-
       piled. The limit applies to parentheses of all kinds, not just  captur-
       ing parentheses.

       int pcre2_set_compile_recursion_guard(pcre2_compile_context *ccontext,
         int (*guard_function)(uint32_t, void *), void *user_data);

       There  is at least one application that runs PCRE2 in threads with very
       limited system stack, where running out of stack is to  be  avoided  at
       all  costs. The parenthesis limit above cannot take account of how much
       stack is actually available during compilation. For  a  finer  control,
       you  can  supply  a  function  that  is called whenever pcre2_compile()
       starts to compile a parenthesized part of a pattern. This function  can
       check  the  actual  stack  size  (or anything else that it wants to, of
       course).

       The first argument to the callout function gives the current  depth  of
       nesting,  and  the second is user data that is set up by the last argu-
       ment  of  pcre2_set_compile_recursion_guard().  The  callout   function
       should return zero if all is well, or non-zero to force an error.

   The match context

       A match context is required if you want to:

         Set up a callout function
         Set an offset limit for matching an unanchored pattern
         Change the limit on the amount of heap used when matching
         Change the backtracking match limit
         Change the backtracking depth limit
         Set custom memory management specifically for the match

       If  none  of  these  apply,  just  pass NULL as the context argument of
       pcre2_match(), pcre2_dfa_match(), or pcre2_jit_match().

       A match context is created, copied, and freed by  the  following  func-
       tions:

       int pcre2_set_callout(pcre2_match_context *mcontext,
         int (*callout_function)(pcre2_callout_block *, void *),
         void *callout_data);

       This  sets  up a callout function for PCRE2 to call at specified points
       during a matching operation. Details are given in the pcre2callout doc-
       umentation.

       int pcre2_set_substitute_callout(pcre2_match_context *mcontext,
         int (*callout_function)(pcre2_substitute_callout_block *, void *),
         void *callout_data);

       This  sets up a callout function for PCRE2 to call after each substitu-
       tion made by pcre2_substitute(). Details are given in the section enti-
       tled "Creating a new string with substitutions" below.

       int pcre2_set_offset_limit(pcre2_match_context *mcontext,
         PCRE2_SIZE value);

       The  offset_limit  parameter  limits  how  far an unanchored search can
       advance in the subject string. The default value  is  PCRE2_UNSET.  The
       pcre2_match()      and      pcre2_dfa_match()      functions     return
       PCRE2_ERROR_NOMATCH if a match with a starting point before or  at  the
       given  offset  is  not  found. The pcre2_substitute() function makes no
       more substitutions.

       For example, if the pattern /abc/ is matched against "123abc"  with  an
       offset  limit  less  than 3, the result is PCRE2_ERROR_NOMATCH. A match
       can never be  found  if  the  startoffset  argument  of  pcre2_match(),
       pcre2_dfa_match(),  or  pcre2_substitute()  is  greater than the offset
       limit set in the match context.

       When using this  facility,  you  must  set  the  PCRE2_USE_OFFSET_LIMIT
       option when calling pcre2_compile() so that when JIT is in use, differ-
       ent code can be compiled. If a match  is  started  with  a  non-default
       match  limit when PCRE2_USE_OFFSET_LIMIT is not set, an error is gener-
       ated.

       The offset limit facility can be used to track progress when  searching
       large  subject  strings or to limit the extent of global substitutions.
       See also the PCRE2_FIRSTLINE option, which requires a  match  to  start
       before  or  at  the first newline that follows the start of matching in
       the subject. If this is set with an offset limit, a match must occur in
       the first line and also within the offset limit. In other words, which-
       ever limit comes first is used.

       int pcre2_set_heap_limit(pcre2_match_context *mcontext,
         uint32_t value);

       The heap_limit parameter specifies, in units of kibibytes (1024 bytes),
       the  maximum  amount  of heap memory that pcre2_match() may use to hold
       backtracking information when running an interpretive match. This limit
       also applies to pcre2_dfa_match(), which may use the heap when process-
       ing patterns with a lot of nested pattern recursion or  lookarounds  or
       where  ddd  is  a  decimal  number.  However, such a setting is ignored
       unless ddd is less than the limit set by the  caller  of  pcre2_match()
       or, if no such limit is set, less than the default.

       The  pcre2_match() function starts out using a 20KiB vector on the sys-
       tem stack for recording backtracking points. The more nested backtrack-
       ing  points  there  are (that is, the deeper the search tree), the more
       memory is needed.  Heap memory is used only if the  initial  vector  is
       too small. If the heap limit is set to a value less than 21 (in partic-
       ular, zero) no heap memory will be used. In this  case,  only  patterns
       that  do not have a lot of nested backtracking can be successfully pro-
       cessed.

       Similarly, for pcre2_dfa_match(), a vector on the system stack is  used
       when  processing pattern recursions, lookarounds, or atomic groups, and
       only if this is not big enough is heap memory used. In this case,  too,
       setting a value of zero disables the use of the heap.

       int pcre2_set_match_limit(pcre2_match_context *mcontext,
         uint32_t value);

       The  match_limit  parameter  provides  a means of preventing PCRE2 from
       using up too many computing resources when processing 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.

       There  is an internal counter in pcre2_match() that is incremented each
       time round its main matching loop. If  this  value  reaches  the  match
       limit, pcre2_match() returns the negative value PCRE2_ERROR_MATCHLIMIT.
       This 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. This limit  also  applies
       to pcre2_dfa_match(), though the counting is done in a different way.

       When  pcre2_match() is called with a pattern that was successfully pro-
       cessed by pcre2_jit_compile(), the way in which 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  PCRE2  is  built;  the
       default  default  is 10 million, which handles all but the most extreme
       cases. A value for the match limit may also be supplied by an  item  at
       the start of a pattern of the form

         (*LIMIT_MATCH=ddd)

       where  ddd  is  a  decimal  number.  However, such a setting is ignored
       unless ddd is less than the limit set by the caller of pcre2_match() or
       pcre2_dfa_match() or, if no such limit is set, less than the default.

       int pcre2_set_depth_limit(pcre2_match_context *mcontext,
       using JIT compiled code. However, it is supported by pcre2_dfa_match(),
       which uses it to limit the depth of nested internal recursive  function
       calls  that implement atomic groups, lookaround assertions, and pattern
       recursions. This limits, indirectly, the amount of system stack that is
       used.  It  was  more useful in versions before 10.32, when stack memory
       was used for local workspace vectors for recursive function calls. From
       version  10.32,  only local variables are allocated on the stack and as
       each call uses only a few hundred bytes, even a small stack can support
       quite a lot of recursion.

       If  the  depth  of  internal  recursive function calls is great enough,
       local workspace vectors are allocated on the heap  from  version  10.32
       onwards,  so  the depth limit also indirectly limits the amount of heap
       memory that is used. A recursive pattern such as /(.(?2))((?1)|)/, when
       matched  to a very long string using pcre2_dfa_match(), can use a great
       deal of memory. However, it is probably  better  to  limit  heap  usage
       directly by calling pcre2_set_heap_limit().

       The  default  value for the depth limit can be set when PCRE2 is built;
       if it is not, the default is set to the same value as the  default  for
       the   match   limit.   If  the  limit  is  exceeded,  pcre2_match()  or
       pcre2_dfa_match() returns PCRE2_ERROR_DEPTHLIMIT. A value for the depth
       limit  may also be supplied by an item at the start of a pattern of the
       form

         (*LIMIT_DEPTH=ddd)

       where ddd is a decimal number.  However,  such  a  setting  is  ignored
       unless ddd is less than the limit set by the caller of pcre2_match() or
       pcre2_dfa_match() or, if no such limit is set, less than the default.

CHECKING BUILD-TIME OPTIONS

       int pcre2_config(uint32_t what, void *where);

       The function pcre2_config() makes it possible for  a  PCRE2  client  to
       discover  which  optional  features  have  been compiled into the PCRE2
       library. The pcre2build documentation  has  more  details  about  these
       optional features.

       The  first  argument  for pcre2_config() specifies which information is
       required. The second argument is a pointer to  memory  into  which  the
       information  is  placed.  If  NULL  is passed, the function returns the
       amount of memory that is needed  for  the  requested  information.  For
       calls  that  return  numerical  values,  the  value  is  in bytes; when
       requesting these values, where should point  to  appropriately  aligned
       memory.  For calls that return strings, the required length is given in
       code units, not counting the terminating zero.

       When requesting information, the returned value from pcre2_config()  is
       non-negative  on success, or the negative error code PCRE2_ERROR_BADOP-
       TION if the value in the first argument is not recognized. The  follow-
       ing information is available:

       8-bit  support, and the 2-bit and 4-bit indicate 16-bit and 32-bit sup-
       port, respectively.

         PCRE2_CONFIG_DEPTHLIMIT

       The output is a uint32_t integer that gives the default limit  for  the
       depth  of  nested  backtracking in pcre2_match() or the depth of nested
       recursions, lookarounds, and atomic groups in  pcre2_dfa_match().  Fur-
       ther details are given with pcre2_set_depth_limit() above.

         PCRE2_CONFIG_HEAPLIMIT

       The  output is a uint32_t integer that gives, in kibibytes, the default
       limit  for  the  amount  of  heap  memory  used  by  pcre2_match()   or
       pcre2_dfa_match().      Further      details     are     given     with
       pcre2_set_heap_limit() above.

         PCRE2_CONFIG_JIT

       The output is a uint32_t integer that is set  to  one  if  support  for
       just-in-time compiling is available; otherwise it is set to zero.

         PCRE2_CONFIG_JITTARGET

       The  where  argument  should point to a buffer that is at least 48 code
       units long.  (The  exact  length  required  can  be  found  by  calling
       pcre2_config()  with  where  set  to NULL.) The buffer is filled with a
       string that 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, PCRE2_ERROR_BADOPTION  is
       returned,  otherwise the number of code units used is returned. This is
       the length of the string, plus one unit for the terminating zero.

         PCRE2_CONFIG_LINKSIZE

       The output is a uint32_t integer that contains the number of bytes used
       for  internal  linkage  in  compiled regular expressions. When PCRE2 is
       configured, the value can be set to 2, 3, or 4, with the default  being
       2.  This is the value that is returned by pcre2_config(). However, when
       the 16-bit library is compiled, a value of 3 is rounded up  to  4,  and
       when  the  32-bit  library  is compiled, internal linkages always use 4
       bytes, so the configured value is not relevant.

       The default value of 2 for the 8-bit and 16-bit libraries is sufficient
       for  all but the most massive patterns, since it allows the size of the
       compiled pattern to be up to 65535  code  units.  Larger  values  allow
       larger  regular  expressions to be compiled by those two libraries, but
       at the expense of slower matching.

         PCRE2_CONFIG_MATCHLIMIT

       The output is a uint32_t integer that gives the default match limit for
       pcre2_match().  Further  details are given with pcre2_set_match_limit()
       above.
         PCRE2_NEWLINE_NUL      The NUL character (binary zero)

       The default should normally correspond to  the  standard  sequence  for
       your operating system.

         PCRE2_CONFIG_NEVER_BACKSLASH_C

       The  output  is  a uint32_t integer that is set to one if the use of \C
       was permanently disabled when PCRE2 was built; otherwise it is  set  to
       zero.

         PCRE2_CONFIG_PARENSLIMIT

       The  output is a uint32_t integer that gives the maximum depth of nest-
       ing 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 PCRE2 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,  see
       pcre2_set_compile_recursion_guard().

         PCRE2_CONFIG_STACKRECURSE

       This parameter is obsolete and should not be used in new code. The out-
       put is a uint32_t integer that is always set to zero.

         PCRE2_CONFIG_UNICODE_VERSION

       The where argument should point to a buffer that is at  least  24  code
       units  long.  (The  exact  length  required  can  be  found  by calling
       pcre2_config() with where set to NULL.)  If  PCRE2  has  been  compiled
       without  Unicode  support,  the buffer is filled with the text "Unicode
       not supported". Otherwise, the Unicode  version  string  (for  example,
       "8.0.0")  is  inserted. The number of code units used is returned. This
       is the length of the string plus one unit for the terminating zero.

         PCRE2_CONFIG_UNICODE

       The output is a uint32_t integer that is set to one if Unicode  support
       is  available; otherwise it is set to zero. Unicode support implies UTF
       support.

         PCRE2_CONFIG_VERSION

       The where argument should point to a buffer that is at  least  24  code
       units  long.  (The  exact  length  required  can  be  found  by calling
       pcre2_config() with where set to NULL.) The buffer is filled  with  the
       PCRE2 version string, zero-terminated. The number of code units used is
       returned. This is the length of the string plus one unit for the termi-
       nating zero.

COMPILING A PATTERN

       pcre2_code *pcre2_compile(PCRE2_SPTR pattern, PCRE2_SIZE length,
       can be specified  as  PCRE2_ZERO_TERMINATED.  The  function  returns  a
       pointer  to  a  block  of memory that contains the compiled pattern and
       related data, or NULL if an error occurred.

       If the compile context argument ccontext is NULL, memory for  the  com-
       piled  pattern  is  obtained  by  calling  malloc().  Otherwise,  it is
       obtained from the same memory function that was used  for  the  compile
       context.  The  caller must free the memory by calling pcre2_code_free()
       when it is no longer needed.  If pcre2_code_free()  is  called  with  a
       NULL argument, it returns immediately, without doing anything.

       The function pcre2_code_copy() makes a copy of the compiled code in new
       memory, using the same memory allocator as was used for  the  original.
       However,  if  the  code  has  been  processed  by the JIT compiler (see
       below), the JIT information cannot be copied (because it  is  position-
       dependent).  The new copy can initially be used only for non-JIT match-
       ing, though it can be passed to  pcre2_jit_compile()  if  required.  If
       pcre2_code_copy() is called with a NULL argument, it returns NULL.

       The pcre2_code_copy() function provides a way for individual threads in
       a multithreaded application to acquire a private copy  of  shared  com-
       piled  code.   However, it does not make a copy of the character tables
       used by the compiled pattern; the new pattern code points to  the  same
       tables  as  the original code.  (See "Locale Support" below for details
       of these character tables.) In many applications the  same  tables  are
       used  throughout, so this behaviour is appropriate. Nevertheless, there
       are occasions when a copy of a compiled pattern and the relevant tables
       are  needed.  The pcre2_code_copy_with_tables() provides this facility.
       Copies of both the code and the tables are  made,  with  the  new  code
       pointing  to the new tables. The memory for the new tables is automati-
       cally freed when pcre2_code_free() is called for the new  copy  of  the
       compiled  code.  If pcre2_code_copy_with_tables() is called with a NULL
       argument, it returns NULL.

       NOTE: When one of the matching functions is  called,  pointers  to  the
       compiled pattern and the subject string are set in the match data block
       so that they can be referenced by the  substring  extraction  functions
       after  a  successful match.  After running a match, you must not free a
       compiled pattern or a subject string until after all operations on  the
       match  data  block have taken place, unless, in the case of the subject
       string, you have used the PCRE2_COPY_MATCHED_SUBJECT option,  which  is
       described  in  the  section  entitled  "Option  bits for pcre2_match()"
       below.

       The options argument for pcre2_compile() contains various bit  settings
       that  affect  the  compilation.  It  should be zero if none of them 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 pcre2pattern documentation).

       For  those options that can be different in different parts of the pat-
       tern, the contents of the options argument specifies their settings  at
       the  start  of  compilation. The PCRE2_ANCHORED, PCRE2_ENDANCHORED, and
       cessful and pcre2_compile() returns a non-NULL value.

       There are nearly 100 positive  error  codes  that  pcre2_compile()  may
       return  if  it finds an error in the pattern. There are also some nega-
       tive error codes that are used for invalid UTF strings. These  are  the
       same as given by pcre2_match() and pcre2_dfa_match(), and are described
       in the pcre2unicode page. There is no separate  documentation  for  the
       positive  error  codes,  because  the  textual  error messages that are
       obtained  by  calling  the  pcre2_get_error_message()   function   (see
       "Obtaining  a textual error message" below) should be self-explanatory.
       Macro names starting with PCRE2_ERROR_ are defined  for  both  positive
       and negative error codes in pcre2.h.

       The value returned in erroroffset is an indication of where in the pat-
       tern the error occurred. It is not necessarily the  furthest  point  in
       the  pattern  that  was  read. For example, after the error "lookbehind
       assertion is not fixed length", the error offset points to the start of
       the  failing assertion. For an invalid UTF-8 or UTF-16 string, the off-
       set is that of the first code 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 code units, not characters, even  in  a  UTF
       mode. It may sometimes point into the middle of a UTF-8 or UTF-16 char-
       acter.

       This code fragment shows a typical straightforward call  to  pcre2_com-
       pile():

         pcre2_code *re;
         PCRE2_SIZE erroffset;
         int errorcode;
         re = pcre2_compile(
           "^A.*Z",                /* the pattern */
           PCRE2_ZERO_TERMINATED,  /* the pattern is zero-terminated */
           0,                      /* default options */
           &errorcode,             /* for error code */
           &erroffset,             /* for error offset */
           NULL);                  /* no compile context */

   Main compile options

       The  following  names for option bits are defined in the pcre2.h header
       file:

         PCRE2_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.

         PCRE2_ALLOW_EMPTY_CLASS

       (1) \U matches an upper case "U" character; by default \U causes a com-
       pile time error (Perl uses \U to upper case subsequent characters).

       (2) \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).

       (3)  \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).

       ECMAscript 6 added additional functionality to \u. This can be accessed
       using  the  PCRE2_EXTRA_ALT_BSUX  extra  option  (see  "Extra   compile
       options"  below).   Note  that this alternative escape handling applies
       only to patterns. Neither of these options affects  the  processing  of
       replacement strings passed to pcre2_substitute().

         PCRE2_ALT_CIRCUMFLEX

       In  multiline  mode  (when  PCRE2_MULTILINE  is  set),  the  circumflex
       metacharacter matches at the start of the subject (unless  PCRE2_NOTBOL
       is  set),  and  also  after  any internal newline. However, it does not
       match after a newline at the end of the subject, for compatibility with
       Perl.  If  you want a multiline circumflex also to match after a termi-
       nating newline, you must set PCRE2_ALT_CIRCUMFLEX.

         PCRE2_ALT_VERBNAMES

       By default, for compatibility with Perl, the name in any verb  sequence
       such  as  (*MARK:NAME)  is  any  sequence  of  characters that does not
       include a closing parenthesis. The name is not processed  in  any  way,
       and  it  is  not possible to include a closing parenthesis in the name.
       However, if the PCRE2_ALT_VERBNAMES option  is  set,  normal  backslash
       processing  is  applied  to  verb  names  and only an unescaped closing
       parenthesis terminates the name. A closing parenthesis can be  included
       in  a  name either as \) or between \Q and \E. If the PCRE2_EXTENDED or
       PCRE2_EXTENDED_MORE option is set with  PCRE2_ALT_VERBNAMES,  unescaped
       whitespace  in  verb  names  is  skipped and #-comments are recognized,
       exactly as in the rest of the pattern.

         PCRE2_AUTO_CALLOUT

       If this bit  is  set,  pcre2_compile()  automatically  inserts  callout
       items,  all  with  number 255, before each pattern item, except immedi-
       ately before or after an explicit callout in the pattern.  For  discus-
       sion of the callout facility, see the pcre2callout documentation.

         PCRE2_CASELESS

       If  this  bit is set, letters in the pattern match both upper and lower
       case letters in the subject. It is equivalent to Perl's /i option,  and
       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 PCRE2_DOLLAR_ENDONLY option is ignored
       if PCRE2_MULTILINE is set. There is no equivalent  to  this  option  in
       Perl, and no way to set it within a pattern.

         PCRE2_DOTALL

       If  this  bit  is  set,  a dot metacharacter in the pattern matches any
       character, 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 in the sub-
       ject  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 neg-
       ative  class such as [^a] always matches newline characters, and the \N
       escape sequence always matches a non-newline character, independent  of
       the setting of PCRE2_DOTALL.

         PCRE2_DUPNAMES

       If  this  bit is set, names used to identify capture groups need not be
       unique.  This can be helpful for certain types of pattern  when  it  is
       known  that  only  one instance of the named group can ever be matched.
       There are more details of named capture  groups  below;  see  also  the
       pcre2pattern documentation.

         PCRE2_ENDANCHORED

       If  this  bit is set, the end of any pattern match must be right at the
       end of the string being searched (the "subject string"). If the pattern
       match succeeds by reaching (*ACCEPT), but does not reach the end of the
       subject, the match fails at the current starting point. For  unanchored
       patterns,  a  new  match is then tried at the next starting point. How-
       ever, if the match succeeds by reaching the end of the pattern, but not
       the  end  of  the subject, backtracking occurs and an alternative match
       may be found. Consider these two patterns:

         .(*ACCEPT)|..
         .|..

       If matched against "abc" with PCRE2_ENDANCHORED set, the first  matches
       "c"  whereas  the  second matches "bc". The effect of PCRE2_ENDANCHORED
       can also be achieved by appropriate constructs in the  pattern  itself,
       which is the only way to do it in Perl.

       For DFA matching with pcre2_dfa_match(), PCRE2_ENDANCHORED applies only
       to the first (that is, the  longest)  matched  string.  Other  parallel
       matches,  which are necessarily substrings of the first one, must obvi-
       ously end before the end of the subject.

         PCRE2_EXTENDED

       If this bit is set, most white space  characters  in  the  pattern  are
       totally  ignored  except when escaped or inside a character class. How-
       function to identify space characters. In most ASCII environments,  the
       relevant  characters  are  those  with code points 0x0009 (tab), 0x000A
       (linefeed), 0x000B (vertical tab), 0x000C (formfeed), 0x000D  (carriage
       return), and 0x0020 (space).

       When PCRE2 is compiled with Unicode support, in addition to these char-
       acters, five more Unicode "Pattern White Space" characters  are  recog-
       nized by PCRE2_EXTENDED. These are U+0085 (next line), U+200E (left-to-
       right mark), U+200F (right-to-left mark), U+2028 (line separator),  and
       U+2029  (paragraph  separator).  This  set of characters is the same as
       recognized by Perl's /x option. Note that the horizontal  and  vertical
       space  characters that are matched by the \h and \v escapes in patterns
       are a much bigger set.

       As well as ignoring most white space, PCRE2_EXTENDED also causes  char-
       acters  between  an  unescaped # outside a character class and the next
       newline, inclusive, to be ignored, which makes it possible  to  include
       comments inside complicated patterns. 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.

       Which characters are interpreted as newlines can be specified by a set-
       ting in the compile context that is passed to pcre2_compile() or  by  a
       special  sequence at the start of the pattern, as described in the sec-
       tion entitled "Newline conventions" in the pcre2pattern  documentation.
       A default is defined when PCRE2 is built.

         PCRE2_EXTENDED_MORE

       This  option  has  the  effect  of  PCRE2_EXTENDED,  but,  in addition,
       unescaped space and horizontal tab  characters  are  ignored  inside  a
       character  class.  Note: only these two characters are ignored, not the
       full set of pattern white space characters that are ignored  outside  a
       character  class.  PCRE2_EXTENDED_MORE  is  equivalent  to  Perl's  /xx
       option, and it can be changed within a pattern by a (?xx)  option  set-
       ting.

         PCRE2_FIRSTLINE

       If this option is set, the start of an unanchored pattern match must be
       before or at the first newline in  the  subject  string  following  the
       start  of  matching, though the matched text may continue over the new-
       line. If startoffset is non-zero, the limiting newline is not necessar-
       ily  the  first  newline  in  the  subject. For example, if the subject
       string is "abc\nxyz" (where \n represents a single-character newline) a
       pattern  match for "yz" succeeds with PCRE2_FIRSTLINE if startoffset is
       greater than 3. See also PCRE2_USE_OFFSET_LIMIT, which provides a  more
       general  limiting  facility.  If  PCRE2_FIRSTLINE is set with an offset
       limit, a match must occur in the first line and also within the  offset
       limit. In other words, whichever limit comes first is used.

         PCRE2_LITERAL

       If this option is set, all meta-characters in the pattern are disabled,

       If  this  option  is  set,  a  backreference  to an unset capture 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. Setting this option makes
       PCRE2 behave more like ECMAscript (aka JavaScript).

         PCRE2_MULTILINE

       By default, for the purposes of matching "start of line"  and  "end  of
       line",  PCRE2  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  PCRE2_DOL-
       LAR_ENDONLY is set). Note, however, that unless  PCRE2_DOTALL  is  set,
       the "any character" metacharacter (.) does not match at a newline. This
       behaviour (for ^, $, and dot) is the same as Perl.

       When PCRE2_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. Note that the "start
       of line" metacharacter does not match after a newline at the end of the
       subject, for compatibility with Perl.  However, you can change this  by
       setting  the PCRE2_ALT_CIRCUMFLEX option. If there are no newlines in a
       subject string, or no occurrences of ^  or  $  in  a  pattern,  setting
       PCRE2_MULTILINE has no effect.

         PCRE2_NEVER_BACKSLASH_C

       This  option  locks out the use of \C in the pattern that is being com-
       piled.  This escape can  cause  unpredictable  behaviour  in  UTF-8  or
       UTF-16  modes,  because  it may leave the current matching point in the
       middle of a multi-code-unit character. This option  may  be  useful  in
       applications  that  process  patterns  from external sources. Note that
       there is also a build-time option that permanently locks out the use of
       \C.

         PCRE2_NEVER_UCP

       This  option  locks  out the use of Unicode properties for handling \B,
       \b, \D, \d, \S, \s, \W, \w, and some of the POSIX character classes, as
       described  for  the  PCRE2_UCP option below. In particular, it prevents
       the creator of the pattern from enabling this facility by starting  the
       pattern  with  (*UCP).  This  option may be useful in applications that
       process patterns from external sources. The option combination PCRE_UCP
       and PCRE_NEVER_UCP causes an error.

         PCRE2_NEVER_UTF

       This  option  locks out interpretation of the pattern as UTF-8, UTF-16,
       is the same as Perl's /n option.  Note that, when this option  is  set,
       references  to  capture  groups (backreferences or recursion/subroutine
       calls) may only refer to named groups, though the reference can  be  by
       name or by number.

         PCRE2_NO_AUTO_POSSESS

       If this option is set, it disables "auto-possessification", which 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  callouts  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.

         PCRE2_NO_DOTSTAR_ANCHOR

       If this option is set, it disables an optimization that is applied when
       .* is the first significant item in a top-level branch  of  a  pattern,
       and  all  the  other branches also start with .* or with \A or \G or ^.
       The optimization is automatically disabled for .* if it  is  inside  an
       atomic group or a capture group that is the subject of a backreference,
       or if the pattern contains (*PRUNE) or (*SKIP). When  the  optimization
       is   not   disabled,  such  a  pattern  is  automatically  anchored  if
       PCRE2_DOTALL is set for all the .* items and PCRE2_MULTILINE is not set
       for  any  ^ items. Otherwise, the fact that any match must start either
       at the start of the subject or following a newline is remembered.  Like
       other optimizations, this can cause callouts to be skipped.

         PCRE2_NO_START_OPTIMIZE

       This  is  an  option whose main effect is at matching time. It does not
       change what pcre2_compile() generates, but it does affect the output of
       the JIT compiler.

       There  are  a  number of optimizations that may occur 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 code unit value,
       the matching code searches the subject for that value, and fails  imme-
       diately  if it cannot find it, without actually running the main match-
       ing 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  optimiza-
       tions  are  in effect a pre-scan of the subject that takes place before
       the pattern is run.

       The PCRE2_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.

       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".

       There are also other start-up optimizations.  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", and "C". An attempt
       to match an empty string at the end of the subject does not take place,
       because PCRE2 knows that the subject is  now  too  short,  and  so  the
       (*MARK)  is  never encountered. In this case, the optimization does not
       affect the overall match result, which is still "no match", but it does
       affect the auxiliary information that is returned.

         PCRE2_NO_UTF_CHECK

       When  PCRE2_UTF  is set, the validity of the pattern as a UTF string is
       automatically checked. There are  discussions  about  the  validity  of
       UTF-8  strings,  UTF-16 strings, and UTF-32 strings in the pcre2unicode
       document. If an invalid UTF sequence is found, pcre2_compile()  returns
       a negative error code.

       If  you  know  that your pattern is a valid UTF string, and you want to
       skip  this  check  for   performance   reasons,   you   can   set   the
       PCRE2_NO_UTF_CHECK  option.  When  it  is set, the effect of passing an
       invalid UTF string as a pattern is undefined. It may cause your program
       to crash or loop.

       Note  that  this  option  can  also  be  passed  to  pcre2_match()  and
       pcre_dfa_match(), to suppress UTF  validity  checking  of  the  subject
       string.

       Note also that setting PCRE2_NO_UTF_CHECK at compile time does not dis-
       able the error that is given if an escape sequence for an invalid  Uni-
       code  code  point is encountered in the pattern. In particular, the so-
       called "surrogate" code points (0xd800 to 0xdfff) are invalid.  If  you
       want  to  allow  escape  sequences  such  as  \x{d800}  you can set the
       PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES extra option, as described  in  the
       section  entitled "Extra compile options" below.  However, this is pos-
       sible only in UTF-8 and UTF-32 modes, because these values are not rep-
       resentable in UTF-16.

         PCRE2_UCP

       This option changes the way PCRE2 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 PCRE2_UCP is set, Unicode properties
       are used instead to classify characters. More details are given in  the
       section on generic character types in the pcre2pattern page. If you set
       PCRE2_UCP, matching one of the items it affects takes much longer.  The
       option  is  available only if PCRE2 has been compiled with Unicode sup-
       is going to be used to set a non-default offset limit in a  match  con-
       text  for  matches  that  use this pattern. An error is generated if an
       offset limit is set without this option.  For  more  details,  see  the
       description  of  pcre2_set_offset_limit() in the section that describes
       match contexts. See also the PCRE2_FIRSTLINE option above.

         PCRE2_UTF

       This option causes PCRE2 to regard both the  pattern  and  the  subject
       strings  that  are  subsequently processed as strings of UTF characters
       instead of single-code-unit strings. It  is  available  when  PCRE2  is
       built  to  include  Unicode  support (which is the default). If Unicode
       support is not available, the use of this  option  provokes  an  error.
       Details  of  how  PCRE2_UTF changes the behaviour of PCRE2 are given in
       the pcre2unicode page. In particular, note  that  it  changes  the  way
       PCRE2_CASELESS handles characters with code points greater than 127.

   Extra compile options

       The  option  bits  that  can be set in a compile context by calling the
       pcre2_set_compile_extra_options() function are as follows:

         PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES

       This option applies when compiling a pattern in UTF-8 or  UTF-32  mode.
       It  is  forbidden in UTF-16 mode, and ignored in non-UTF modes. Unicode
       "surrogate" code points in the range 0xd800 to 0xdfff are used in pairs
       in  UTF-16  to  encode  code points with values in the range 0x10000 to
       0x10ffff. The surrogates cannot therefore  be  represented  in  UTF-16.
       They can be represented in UTF-8 and UTF-32, but are defined as invalid
       code points, and cause errors if  encountered  in  a  UTF-8  or  UTF-32
       string that is being checked for validity by PCRE2.

       These  values also cause errors if encountered in escape sequences such
       as \x{d912} within a pattern. However, it seems that some applications,
       when  using  PCRE2  to  check for unwanted characters in UTF-8 strings,
       explicitly  test  for  the  surrogates  using  escape  sequences.   The
       PCRE2_NO_UTF_CHECK  option  does  not  disable  the  error that occurs,
       because it applies only to the testing of input strings for UTF  valid-
       ity.

       If  the extra option PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES is set, surro-
       gate code point values in UTF-8 and UTF-32 patterns no  longer  provoke
       errors  and are incorporated in the compiled pattern. However, they can
       only match subject characters if the matching function is  called  with
       PCRE2_NO_UTF_CHECK set.

         PCRE2_EXTRA_ALT_BSUX

       The  original option PCRE2_ALT_BSUX causes PCRE2 to process \U, \u, and
       \x in the way that ECMAscript (aka JavaScript) does.  Additional  func-
       tionality was defined by ECMAscript 6; setting PCRE2_EXTRA_ALT_BSUX has
       the effect of PCRE2_ALT_BSUX, but in addition it  recognizes  \u{hhh..}
       as a hexadecimal character code, where hhh.. is any number of hexadeci-

       If  the  PCRE2_EXTRA_BAD_ESCAPE_IS_LITERAL  extra  option  is passed to
       pcre2_compile(), all unrecognized or  malformed  escape  sequences  are
       treated  as  single-character escapes. For example, \j is a literal "j"
       and \x{2z} is treated as  the  literal  string  "x{2z}".  Setting  this
       option  means  that  typos in patterns may go undetected and have unex-
       pected results. Also note that a sequence such as [\N{] is  interpreted
       as  a  malformed attempt at [\N{...}] and so is treated as [N{] whereas
       [\N] gives an error  because  an  unqualified  \N  is  a  valid  escape
       sequence  but is not supported in a character class. To reiterate: this
       is a dangerous option. Use with great care.

         PCRE2_EXTRA_ESCAPED_CR_IS_LF

       There are some legacy applications where the escape sequence  \r  in  a
       pattern  is expected to match a newline. If this option is set, \r in a
       pattern is converted to \n so that it matches a LF  (linefeed)  instead
       of  a CR (carriage return) character. The option does not affect a lit-
       eral CR in the pattern, nor does it affect CR specified as an  explicit
       code point such as \x{0D}.

         PCRE2_EXTRA_MATCH_LINE

       This  option  is  provided  for  use  by the -x option of pcre2grep. It
       causes the pattern only to match complete lines. This  is  achieved  by
       automatically  inserting  the  code for "^(?:" at the start of the com-
       piled pattern and ")$" at the end. Thus, when PCRE2_MULTILINE  is  set,
       the  matched  line  may  be  in  the middle of the subject string. This
       option can be used with PCRE2_LITERAL.

         PCRE2_EXTRA_MATCH_WORD

       This option is provided for use by  the  -w  option  of  pcre2grep.  It
       causes  the  pattern only to match strings that have a word boundary at
       the start and the end. This is achieved by automatically inserting  the
       code  for "\b(?:" at the start of the compiled pattern and ")\b" at the
       end. The option may be used with PCRE2_LITERAL. However, it is  ignored
       if PCRE2_EXTRA_MATCH_LINE is also set.

JUST-IN-TIME (JIT) COMPILATION

       int pcre2_jit_compile(pcre2_code *code, uint32_t options);

       int pcre2_jit_match(const pcre2_code *code, PCRE2_SPTR subject,
         PCRE2_SIZE length, PCRE2_SIZE startoffset,
         uint32_t options, pcre2_match_data *match_data,
         pcre2_match_context *mcontext);

       void pcre2_jit_free_unused_memory(pcre2_general_context *gcontext);

       pcre2_jit_stack *pcre2_jit_stack_create(PCRE2_SIZE startsize,
         PCRE2_SIZE maxsize, pcre2_general_context *gcontext);

       void pcre2_jit_stack_assign(pcre2_match_context *mcontext,
       terns  the benefit of faster execution might be offset by a much slower
       compilation time.  Most (but not all) patterns can be optimized by  the
       JIT compiler.

LOCALE SUPPORT

       PCRE2  handles caseless matching, and determines whether characters are
       letters, digits, or whatever, by reference to a set of tables,  indexed
       by  character  code  point.  This applies only to characters whose code
       points are less than 256. By default, higher-valued code  points  never
       match  escapes  such as \w or \d.  However, if PCRE2 is built with Uni-
       code support, all characters can be tested with \p and \P, or, alterna-
       tively,  the  PCRE2_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.

       PCRE2  contains  an  internal  set of character tables that are used by
       default.  These are sufficient for  many  applications.  Normally,  the
       internal tables recognize only ASCII characters. However, when PCRE2 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 dif-
       ferent.

       The internal tables can be overridden by tables supplied by the  appli-
       cation  that  calls  PCRE2.  These may be created in a different locale
       from the default.  As more and more applications change to  using  Uni-
       code, the need for this locale support is expected to die away.

       External  tables  are built by calling the pcre2_maketables() function,
       in the relevant locale. The result can be passed to pcre2_compile()  as
       often   as  necessary,  by  creating  a  compile  context  and  calling
       pcre2_set_character_tables() to set the  tables  pointer  therein.  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 = pcre2_maketables(NULL);
         ccontext = pcre2_compile_context_create(NULL);
         pcre2_set_character_tables(ccontext, tables);
         re = pcre2_compile(..., ccontext);

       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".
       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 (via the compile context) to pcre2_compile()
       is  saved  with  the  compiled pattern, and the same tables are used by
       pcre2_match() and pcre_dfa_match(). Thus, for any single pattern,  com-
       receive  the data. If the third argument is NULL, the first argument is
       ignored, and the function returns the size in  bytes  of  the  variable
       that is required for the information requested. Otherwise, the yield of
       the function is zero for success, or one of the following negative num-
       bers:

         PCRE2_ERROR_NULL           the argument code was NULL
         PCRE2_ERROR_BADMAGIC       the "magic number" was not found
         PCRE2_ERROR_BADOPTION      the value of what was invalid
         PCRE2_ERROR_UNSET          the requested field is not set

       The  "magic  number" is placed at the start of each compiled pattern as
       an simple check against passing an arbitrary memory pointer. Here is  a
       typical  call of pcre2_pattern_info(), to obtain the length of the com-
       piled pattern:

         int rc;
         size_t length;
         rc = pcre2_pattern_info(
           re,               /* result of pcre2_compile() */
           PCRE2_INFO_SIZE,  /* what is required */
           &length);         /* where to put the data */

       The possible values for the second argument are defined in pcre2.h, and
       are as follows:

         PCRE2_INFO_ALLOPTIONS
         PCRE2_INFO_ARGOPTIONS
         PCRE2_INFO_EXTRAOPTIONS

       Return copies of the pattern's options. The third argument should point
       to a  uint32_t  variable.  PCRE2_INFO_ARGOPTIONS  returns  exactly  the
       options  that were passed to pcre2_compile(), whereas PCRE2_INFO_ALLOP-
       TIONS returns the compile options as modified by any  top-level  (*XXX)
       option  settings  such  as  (*UTF)  at the start of the pattern itself.
       PCRE2_INFO_EXTRAOPTIONS returns the extra options that were set in  the
       compile  context by calling the pcre2_set_compile_extra_options() func-
       tion.

       For  example,  if  the  pattern  /(*UTF)abc/  is  compiled   with   the
       PCRE2_EXTENDED   option,   the   result  for  PCRE2_INFO_ALLOPTIONS  is
       PCRE2_EXTENDED and PCRE2_UTF.  Option settings such as  (?i)  that  can
       change  within  a pattern do not affect the result of PCRE2_INFO_ALLOP-
       TIONS, even if they appear right at the start of the pattern. (This was
       different in some earlier releases.)

       A  pattern compiled without PCRE2_ANCHORED is automatically anchored by
       PCRE2 if the first significant item in every top-level branch is one of
       the following:

         ^     unless PCRE2_MULTILINE is set
         \A    always
         \G    always
         .*    sometimes - see below

       the options returned for PCRE2_INFO_ALLOPTIONS.

         PCRE2_INFO_BACKREFMAX

       Return  the  number  of  the  highest backreference in the pattern. The
       third argument should point to  an  uint32_t  variable.  Named  capture
       groups  acquire  numbers  as well as names, and these count towards the
       highest backreference. Backreferences such as \4 or  \g{12}  match  the
       captured characters of the given group, but in addition, the check that
       a capture group is set in a conditional group such as (?(3)a|b) is also
       a backreference.  Zero is returned if there are no backreferences.

         PCRE2_INFO_BSR

       The  output  is a uint32_t integer whose value indicates what character
       sequences the \R escape sequence matches. A value of  PCRE2_BSR_UNICODE
       means  that  \R  matches  any  Unicode line ending sequence; a value of
       PCRE2_BSR_ANYCRLF means that \R matches only CR, LF, or CRLF.

         PCRE2_INFO_CAPTURECOUNT

       Return the highest capture group number in  the  pattern.  In  patterns
       where (?| is not used, this is also the total number of capture groups.
       The third argument should point to an uint32_t variable.

         PCRE2_INFO_DEPTHLIMIT

       If the pattern set a backtracking depth limit by including an  item  of
       the  form  (*LIMIT_DEPTH=nnnn) at the start, the value is returned. The
       third argument should point to a uint32_t integer. If no such value has
       been   set,   the   call  to  pcre2_pattern_info()  returns  the  error
       PCRE2_ERROR_UNSET. Note that this limit will only be used during match-
       ing  if it is less than the limit set or defaulted by the caller of the
       match function.

         PCRE2_INFO_FIRSTBITMAP

       In the absence of a single first code unit for a non-anchored  pattern,
       pcre2_compile()  may construct a 256-bit table that defines a fixed set
       of values for the first code unit in any match. For example, a  pattern
       that  starts  with  [abc]  results in a table with three bits set. When
       code unit values greater than 255 are supported, the flag bit  for  255
       means  "any  code unit of value 255 or above". If such a table was con-
       structed, a pointer to it is returned. Otherwise NULL is returned.  The
       third argument should point to a const uint8_t * variable.

         PCRE2_INFO_FIRSTCODETYPE

       Return information about the first code unit of any matched string, for
       a non-anchored pattern. The third argument should point to an  uint32_t
       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  value
       can  be  retrieved using PCRE2_INFO_FIRSTCODEUNIT. If there is no fixed
       first value, but it is known that a match can occur only at  the  start

         PCRE2_INFO_FRAMESIZE

       Return the size (in bytes) of the data frames that are used to remember
       backtracking  positions  when the pattern is processed by pcre2_match()
       without the use of JIT. The third argument should  point  to  a  size_t
       variable. The frame size depends on the number of capturing parentheses
       in the pattern. Each additional capture group adds two PCRE2_SIZE vari-
       ables.

         PCRE2_INFO_HASBACKSLASHC

       Return  1 if the pattern contains any instances of \C, otherwise 0. The
       third argument should point to an uint32_t variable.

         PCRE2_INFO_HASCRORLF

       Return 1 if the pattern contains any explicit  matches  for  CR  or  LF
       characters, otherwise 0. The third argument should point to an uint32_t
       variable. An explicit match is either a literal CR or LF character,  or
       \r  or  \n  or  one  of  the  equivalent  hexadecimal  or  octal escape
       sequences.

         PCRE2_INFO_HEAPLIMIT

       If the pattern set a heap memory limit by including an item of the form
       (*LIMIT_HEAP=nnnn) at the start, the value is returned. The third argu-
       ment should point to a uint32_t integer. If no such value has been set,
       the  call  to pcre2_pattern_info() returns the error PCRE2_ERROR_UNSET.
       Note that this limit will only be used during matching if  it  is  less
       than the limit set or defaulted by the caller of the match function.

         PCRE2_INFO_JCHANGED

       Return  1  if  the (?J) or (?-J) option setting is used in the pattern,
       otherwise 0. The third argument should point to an  uint32_t  variable.
       (?J)  and  (?-J) set and unset the local PCRE2_DUPNAMES option, respec-
       tively.

         PCRE2_INFO_JITSIZE

       If the compiled pattern was successfully  processed  by  pcre2_jit_com-
       pile(),  return  the  size  of  the JIT compiled code, otherwise return
       zero. The third argument should point to a size_t variable.

         PCRE2_INFO_LASTCODETYPE

       Returns 1 if there is a rightmost literal code unit that must exist  in
       any  matched string, other than at its start. The third argument should
       point to an uint32_t  variable.  If  there  is  no  such  value,  0  is
       returned.  When  1  is  returned,  the  code  unit  value itself can be
       retrieved using PCRE2_INFO_LASTCODEUNIT. 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
       Return  1  if the pattern might match an empty string, otherwise 0. The
       third argument should point to an uint32_t  variable.  When  a  pattern
       contains recursive subroutine calls it is not always possible to deter-
       mine whether or not it can match an empty string. PCRE2  takes  a  cau-
       tious approach and returns 1 in such cases.

         PCRE2_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  third
       argument  should point to a uint32_t integer. If no such value has been
       set,   the   call   to   pcre2_pattern_info()   returns    the    error
       PCRE2_ERROR_UNSET. Note that this limit will only be used during match-
       ing if it is less than the limit set or defaulted by the caller of  the
       match function.

         PCRE2_INFO_MAXLOOKBEHIND

       Return the number of characters (not code units) in the longest lookbe-
       hind assertion in the pattern. The third argument  should  point  to  a
       uint32_t  integer.  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 regis-
       ters 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.  Oth-
       erwise,  if  there  are  no  lookbehinds in the pattern, \A might match
       incorrectly at the start of a second or subsequent segment.

         PCRE2_INFO_MINLENGTH

       If a minimum length for matching  subject  strings  was  computed,  its
       value  is  returned.  Otherwise the returned value is 0. The value is a
       number of characters, which in UTF mode may be different from the  num-
       ber  of  code  units.   The  third argument should point to an uint32_t
       variable. The 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.

         PCRE2_INFO_NAMECOUNT
         PCRE2_INFO_NAMEENTRYSIZE
         PCRE2_INFO_NAMETABLE

       PCRE2 supports the use of named as well as numbered capturing parenthe-
       ses.  The names are just an additional way of identifying the parenthe-
       ses, which still acquire numbers. Several convenience functions such as
       pcre2_substring_get_byname()  are provided for extracting captured sub-
       strings by name. It is also possible to extract the data  directly,  by
       first  converting  the  name to a number in order to access the correct
       pointers in the output vector (described with pcre2_match() 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.  PCRE2_INFO_NAME-

       The names are in alphabetical order. If (?| is used to create  multiple
       capture  groups  with  the  same number, as described in the section on
       duplicate group numbers in the pcre2pattern page,  the  groups  may  be
       given  the same name, but there is only one entry in the table. Differ-
       ent names for groups of the same number are not permitted.

       Duplicate names for capture groups with different numbers  are  permit-
       ted, but only if PCRE2_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 capture groups may have  lower  num-
       bers.

       As  a  simple  example of the name/number table, consider the following
       pattern after compilation by the 8-bit library  (assume  PCRE2_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 capture groups, 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 capture groups  using  the
       name-to-number  map,  remember that the length of the entries is likely
       to be different for each compiled pattern.

         PCRE2_INFO_NEWLINE

       The output is one of the following uint32_t values:

         PCRE2_NEWLINE_CR       Carriage return (CR)
         PCRE2_NEWLINE_LF       Linefeed (LF)
         PCRE2_NEWLINE_CRLF     Carriage return, linefeed (CRLF)
         PCRE2_NEWLINE_ANY      Any Unicode line ending
         PCRE2_NEWLINE_ANYCRLF  Any of CR, LF, or CRLF
         PCRE2_NEWLINE_NUL      The NUL character (binary zero)

       This identifies the character sequence that will be recognized as mean-
       ing "newline" while matching.

         PCRE2_INFO_SIZE

       Return  the  size  of  the  compiled  pattern  in  bytes (for all three
       libraries). The third argument should point to a size_t variable.  This
       value  includes  the  size  of the general data block that precedes the

       A script language that supports the use of string arguments in callouts
       might like to scan all the callouts in a  pattern  before  running  the
       match. This can be done by calling pcre2_callout_enumerate(). The first
       argument is a pointer to a compiled pattern, the  second  points  to  a
       callback  function,  and the third is arbitrary user data. The callback
       function is called for every callout in the pattern  in  the  order  in
       which they appear. Its first argument is a pointer to a callout enumer-
       ation block, and its second argument is the user_data  value  that  was
       passed  to  pcre2_callout_enumerate(). The contents of the callout enu-
       meration block are described in the pcre2callout  documentation,  which
       also gives further details about callouts.

SERIALIZATION AND PRECOMPILING

       It  is  possible  to  save  compiled patterns on disc or elsewhere, and
       reload them later, subject to a number of  restrictions.  The  host  on
       which  the  patterns  are  reloaded must be running the same version of
       PCRE2, with the same code unit width, and must also have the same endi-
       anness,  pointer  width,  and PCRE2_SIZE type. Before compiled patterns
       can be saved, they must be converted to a "serialized" form,  which  in
       the  case of PCRE2 is really just a bytecode dump.  The functions whose
       names begin with pcre2_serialize_ are used for converting to  and  from
       the  serialized form. They are described in the pcre2serialize documen-
       tation. Note that PCRE2 serialization does not  convert  compiled  pat-
       terns to an abstract format like Java or .NET serialization.

THE MATCH DATA BLOCK

       pcre2_match_data *pcre2_match_data_create(uint32_t ovecsize,
         pcre2_general_context *gcontext);

       pcre2_match_data *pcre2_match_data_create_from_pattern(
         const pcre2_code *code, pcre2_general_context *gcontext);

       void pcre2_match_data_free(pcre2_match_data *match_data);

       Information  about  a  successful  or unsuccessful match is placed in a
       match data block, which is an opaque  structure  that  is  accessed  by
       function  calls.  In particular, the match data block contains a vector
       of offsets into the subject string that define the matched part of  the
       subject  and  any  substrings  that were captured. This is known as the
       ovector.

       Before calling pcre2_match(), pcre2_dfa_match(),  or  pcre2_jit_match()
       you must create a match data block by calling one of the creation func-
       tions above. For pcre2_match_data_create(), the first argument  is  the
       number  of  pairs  of  offsets  in  the ovector. One pair of offsets is
       required to identify the string that matched the whole pattern, with an
       additional  pair for each captured substring. For example, a value of 4
       creates enough space to record the matched portion of the subject  plus
       three  captured  substrings. A minimum of at least 1 pair is imposed by
       pcre2_match_data_create(), so it is always possible to return the over-
       all matched string.

       A  match  data block can be used many times, with the same or different
       compiled patterns. You can extract information from a match data  block
       after  a  match  operation  has  finished,  using  functions  that  are
       described in the sections on  matched  strings  and  other  match  data
       below.

       When  a  call  of  pcre2_match()  fails, valid data is available in the
       match   block   only   when   the   error    is    PCRE2_ERROR_NOMATCH,
       PCRE2_ERROR_PARTIAL,  or  one  of  the  error  codes for an invalid UTF
       string. Exactly what is available depends on the error, and is detailed
       below.

       When  one of the matching functions is called, pointers to the compiled
       pattern and the subject string are set in the match data block so  that
       they  can  be referenced by the extraction functions after a successful
       match. After running a match, you must not free a compiled pattern or a
       subject  string until after all operations on the match data block (for
       that match) have taken place,  unless,  in  the  case  of  the  subject
       string,  you  have used the PCRE2_COPY_MATCHED_SUBJECT option, which is
       described in the  section  entitled  "Option  bits  for  pcre2_match()"
       below.

       When  a match data block itself is no longer needed, it should be freed
       by calling pcre2_match_data_free(). If this function is called  with  a
       NULL argument, it returns immediately, without doing anything.

MATCHING A PATTERN: THE TRADITIONAL FUNCTION

       int pcre2_match(const pcre2_code *code, PCRE2_SPTR subject,
         PCRE2_SIZE length, PCRE2_SIZE startoffset,
         uint32_t options, pcre2_match_data *match_data,
         pcre2_match_context *mcontext);

       The  function pcre2_match() is called to match a subject string against
       a compiled pattern, which is passed in the code argument. You can  call
       pcre2_match() with the same code argument as many times as you like, in
       order to find multiple matches in the subject string or to  match  dif-
       ferent subject strings with the same pattern.

       This  function  is  the  main  matching facility of the library, and it
       operates in a Perl-like manner. For specialist use  there  is  also  an
       alternative  matching function, which is described below in the section
       about the pcre2_dfa_match() function.

       Here is an example of a simple call to pcre2_match():

         pcre2_match_data *md = pcre2_match_data_create(4, NULL);
         int rc = pcre2_match(
           re,             /* result of pcre2_compile() */
           "some string",  /* the subject string */
           11,             /* the length of the subject string */
           0,              /* start at offset 0 in the subject */
           0,              /* default options */

       and  offset  are  in  code units, not characters.  That is, they are in
       bytes for the 8-bit library, 16-bit code units for the 16-bit  library,
       and  32-bit  code units for the 32-bit library, whether or not UTF pro-
       cessing is enabled.

       If startoffset is greater than the length of the subject, pcre2_match()
       returns  PCRE2_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 starting off-
       set must point to the start of a character, or to the end of  the  sub-
       ject  (in  UTF-32 mode, one code unit equals one character, so all off-
       sets are valid). Like the  pattern  string,  the  subject  may  contain
       binary zeros.

       A  non-zero  starting offset is useful when searching for another match
       in the same subject by calling pcre2_match()  again  after  a  previous
       success.   Setting  startoffset  differs  from passing over a shortened
       string and setting PCRE2_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 pcre2_match()
       finds the first occurrence. If pcre2_match() 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 pcre2_match() is passed the entire
       string again, but with startoffset set to 4, it finds the second occur-
       rence  of "iss" because it is able to look behind the starting point to
       discover that it is preceded by a letter.

       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
       PCRE2_NOTEMPTY_ATSTART  and  PCRE2_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
       pcre2demo 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  start-
       ing offset by two characters instead of one.

       If a non-zero starting offset is passed when the pattern is anchored, a
       single attempt to match at the given offset is made. This can only suc-
       ceed  if  the  pattern does not require the match to be at the start of
       the subject. In other words, the anchoring must be the result  of  set-
       ting  the PCRE2_ANCHORED option or the use of .* with PCRE2_DOTALL, not
       by starting the pattern with ^ or \A.

   Option bits for pcre2_match()

       The unused bits of the options argument for pcre2_match() must be zero.
         PCRE2_ANCHORED

       The PCRE2_ANCHORED option limits pcre2_match() to matching at the first
       matching position. If a pattern was compiled  with  PCRE2_ANCHORED,  or
       turned  out to be anchored by virtue of its contents, it cannot be made
       unachored at matching time. Note that setting the option at match  time
       disables JIT matching.

         PCRE2_COPY_MATCHED_SUBJECT

       By  default,  a  pointer to the subject is remembered in the match data
       block so that, after a successful match, it can be  referenced  by  the
       substring  extraction  functions.  This means that the subject's memory
       must not be freed until all such  operations  are  complete.  For  some
       applications  where  the  lifetime of the subject string is not guaran-
       teed, it may be necessary to make a copy of the subject string, but  it
       is wasteful to do this unless the match is successful. After a success-
       ful match, if PCRE2_COPY_MATCHED_SUBJECT is set, the subject is  copied
       and  the  new  pointer is remembered in the match data block instead of
       the original subject pointer. The memory allocator that  was  used  for
       the  match  block  itself is used. The copy is automatically freed when
       pcre2_match_data_free() is called to free the match data block.  It  is
       also automatically freed if the match data block is re-used for another
       match operation.

         PCRE2_ENDANCHORED

       If the PCRE2_ENDANCHORED option is set, any string  that  pcre2_match()
       matches  must be right at the end of the subject string. Note that set-
       ting the option at match time disables JIT matching.

         PCRE2_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  having  set  PCRE2_MULTILINE  at
       compile time causes circumflex never to match. This option affects only
       the behaviour of the circumflex metacharacter. It does not affect \A.

         PCRE2_NOTEOL

       This option specifies that the end of the subject string is not the end
       of  a line, so the dollar metacharacter should not match it nor (except
       in multiline mode) a newline immediately before it. Setting this  with-
       out  having  set PCRE2_MULTILINE at compile time causes dollar never to
       match. This option affects only the behaviour of the dollar metacharac-
       ter. It does not affect \Z or \z.

         PCRE2_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
       subject  plus  the  starting offset. An empty string match later in the
       subject is permitted.  If the pattern is anchored,  such  a  match  can
       occur only if the pattern contains \K.

         PCRE2_NO_JIT

       By   default,   if   a  pattern  has  been  successfully  processed  by
       pcre2_jit_compile(), JIT is automatically used  when  pcre2_match()  is
       called  with  options  that JIT supports. Setting PCRE2_NO_JIT disables
       the use of JIT; it forces matching to be done by the interpreter.

         PCRE2_NO_UTF_CHECK

       When PCRE2_UTF is set at compile time, the validity of the subject as a
       UTF  string  is  checked  by default when pcre2_match() is subsequently
       called.  If a non-zero starting offset is given, the check  is  applied
       only  to that part of the subject that could be inspected during match-
       ing, and there is a check that the starting offset points to the  first
       code  unit of a character or to the end of the subject. If there are no
       lookbehind assertions in the pattern, the check starts at the  starting
       offset.  Otherwise,  it  starts at the length of the longest lookbehind
       before the starting offset, or at the start of the subject if there are
       not  that  many  characters  before  the starting offset. Note that the
       sequences \b and \B are one-character lookbehinds.

       The check is carried out before any other processing takes place, and a
       negative  error  code is returned if the check fails. There are several
       UTF error codes for each code unit width,  corresponding  to  different
       problems  with  the code unit sequence. There are discussions about the
       validity of UTF-8 strings, UTF-16 strings, and UTF-32  strings  in  the
       pcre2unicode page.

       If  you  know  that  your  subject is valid, and you want to skip these
       checks for performance reasons,  you  can  set  the  PCRE2_NO_UTF_CHECK
       option  when  calling  pcre2_match(). You might want to do this for the
       second and subsequent calls to pcre2_match() if you are making repeated
       calls to find other matches in the same subject string.

       Warning:  When  PCRE2_NO_UTF_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 indefinitely.

         PCRE2_PARTIAL_HARD
         PCRE2_PARTIAL_SOFT

       These  options  turn  on  the partial matching feature. 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 PCRE2_PARTIAL_SOFT (but not  PCRE2_PARTIAL_HARD)  is  set,
       matching  continues  by  testing any remaining alternatives. Only if no
       complete match can be found is PCRE2_ERROR_PARTIAL returned instead  of
       PCRE2_ERROR_NOMATCH.  In other words, PCRE2_PARTIAL_SOFT specifies that
       the caller is prepared to handle a partial match, but only if  no  com-
       plete match can be found.
       When PCRE2 is built, a default newline convention is set; this is  usu-
       ally  the standard convention for the operating system. The default can
       be overridden in a compile context by calling  pcre2_set_newline().  It
       can  also be overridden by starting a pattern string with, for example,
       (*CRLF), as described in the section  on  newline  conventions  in  the
       pcre2pattern  page. During matching, the newline choice affects the be-
       haviour of the dot, circumflex, and dollar metacharacters. It may  also
       alter  the  way  the  match starting position is advanced after a match
       failure for an unanchored pattern.

       When PCRE2_NEWLINE_CRLF, PCRE2_NEWLINE_ANYCRLF, or PCRE2_NEWLINE_ANY is
       set  as  the  newline convention, and a match attempt for an unanchored
       pattern fails when the current starting 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  PCRE2_DOTALL
       option is not set), it does not match the string "\r\nA" because, after
       failing at the start, it skips both the CR and the LF before  retrying.
       However,  the  pattern  [\r\n]A does match that string, because it con-
       tains an explicit CR or LF reference, and so advances only by one char-
       acter after the first failure.

       An explicit match for CR of LF is either a literal appearance of one of
       those characters in the pattern, or one of the \r or \n  or  equivalent
       octal or hexadecimal escape sequences. Implicit matches such as [^X] do
       not count, nor does \s, even though it includes CR and LF in the  char-
       acters 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.

HOW PCRE2_MATCH() RETURNS A STRING AND CAPTURED SUBSTRINGS

       uint32_t pcre2_get_ovector_count(pcre2_match_data *match_data);

       PCRE2_SIZE *pcre2_get_ovector_pointer(pcre2_match_data *match_data);

       In  general, a pattern matches a certain portion of the subject, and in
       addition, further substrings from the subject  may  be  picked  out  by
       parenthesized  parts  of  the  pattern.  Following the usage in Jeffrey
       Friedl's book, this is called "capturing"  in  what  follows,  and  the
       phrase  "capture  group" (Perl terminology) is used for a fragment of a
       pattern that picks out a substring. PCRE2 supports several other  kinds
       of parenthesized group that do not cause substrings to be captured. The
       pcre2_pattern_info() function can be used to find out how many  capture
       groups there are in a compiled pattern.

       You  can  use  auxiliary functions for accessing captured substrings by
       number or by name, as described in sections below.

       library, and 32-bit offsets in the 32-bit library.

       After a partial match  (error  return  PCRE2_ERROR_PARTIAL),  only  the
       first  pair  of  offsets  (that is, ovector[0] and ovector[1]) are set.
       They identify the part of the subject that was partially  matched.  See
       the pcre2partial documentation for details of partial matching.

       After  a  fully  successful match, the first pair of offsets identifies
       the portion of the subject string that was matched by the  entire  pat-
       tern.  The  next  pair is used for the first captured substring, and so
       on. The value returned by pcre2_match() 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  captured  sub-
       strings, the return value from a successful match is 1, indicating that
       just the first pair of offsets has been set.

       If a pattern uses the \K escape sequence within a  positive  assertion,
       the reported start of a successful match can be greater than the end of
       the match.  For example, if the pattern  (?=ab\K)  is  matched  against
       "ab", the start and end offset values for the match are 2 and 0.

       If  a  capture group is matched repeatedly within a single match opera-
       tion, it is the last portion of the subject that  it  matched  that  is
       returned.

       If the ovector is too small to hold all the captured substring offsets,
       as much as possible is filled in, and the function returns a  value  of
       zero.  If captured substrings are not of interest, pcre2_match() may be
       called with a match data block whose ovector is of minimum length (that
       is, one pair).

       It  is  possible for capture group number n+1 to match some part of the
       subject when group 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 groups 1 and 3 are matched, but 2 is  not.  When
       this  happens,  both values in the offset pairs corresponding to unused
       groups are set to PCRE2_UNSET.

       Offset values that correspond to  unused  groups  at  the  end  of  the
       expression  are  also  set  to  PCRE2_UNSET. For example, if the string
       "abc" is matched against the pattern (abc)(x(yz)?)? groups 2 and 3  are
       not  matched.  The  return  from the function is 2, because the highest
       used capture group number is 1. The offsets  for  for  the  second  and
       third  capture groupss (assuming the vector is large enough, of course)
       are set to PCRE2_UNSET.

       Elements in the ovector that do not correspond to capturing parentheses
       in the pattern are never changed. That is, if a pattern contains n cap-
       turing parentheses, no more than ovector[0] to ovector[2n+1] are set by
       pcre2_match().  The  other  elements retain whatever values they previ-
       ously had. After a failed match attempt, the contents  of  the  ovector
       are unchanged.

OTHER INFORMATION ABOUT A MATCH
       The function pcre2_get_mark() can be called to access this name,  which
       can  be  specified  in  the  pattern by any of the backtracking control
       verbs, not just (*MARK). The same function applies to all the verbs. It
       returns a pointer to the zero-terminated name, which is within the com-
       piled pattern. If no name is available, NULL is returned. The length of
       the  name  (excluding  the terminating zero) is stored in the code unit
       that precedes the name. You should use this length instead  of  relying
       on the terminating zero if the name might contain a binary zero.

       After  a  successful  match, the name that is returned is the last mark
       name encountered on the matching path through the pattern. Instances of
       backtracking  verbs  without  names do not count. Thus, for example, if
       the matching path contains (*MARK:A)(*PRUNE), the name "A" is returned.
       After  a  "no  match"  or a partial match, the last encountered name is
       returned. For example, consider this pattern:

         ^(*MARK:A)((*MARK:B)a|b)c

       When it matches "bc", the returned name is A. The B mark is  "seen"  in
       the  first  branch of the group, but it is not on the matching path. On
       the other hand, when this pattern fails to  match  "bx",  the  returned
       name is B.

       Warning:  By  default, certain start-of-match optimizations are used to
       give a fast "no match" result in some situations. For example,  if  the
       anchoring  is removed from the pattern above, there is an initial check
       for the presence of "c" in the  subject  before  running  the  matching
       engine. This check fails for "bx", causing a match failure without see-
       ing any marks. You can disable the start-of-match optimizations by set-
       ting  the  PCRE2_NO_START_OPTIMIZE  option  for  pcre2_compile()  or by
       starting the pattern with (*NO_START_OPT).

       After a successful match, a partial match, or one of  the  invalid  UTF
       errors  (for example, PCRE2_ERROR_UTF8_ERR5), pcre2_get_startchar() can
       be called. After a successful or partial match it returns the code unit
       offset  of  the character at which the match started. For a non-partial
       match, this can be different to the value of ovector[0] if the  pattern
       contains  the  \K escape sequence. After a partial match, however, this
       value is always the same as ovector[0] because \K does not  affect  the
       result of a partial match.

       After  a UTF check failure, pcre2_get_startchar() can be used to obtain
       the code unit offset of the invalid UTF character. Details are given in
       the pcre2unicode page.

ERROR RETURNS FROM pcre2_match()

       If  pcre2_match() fails, it returns a negative number. This can be con-
       verted to a text string by calling the pcre2_get_error_message()  func-
       tion  (see  "Obtaining a textual error message" below).  Negative error
       codes are also returned by other functions,  and  are  documented  with
       them.  The codes are given names in the header file. If UTF checking is
       in force and an invalid UTF subject string is detected, one of a number
       of  UTF-specific negative error codes is returned. Details are given in
         PCRE2_ERROR_BADMAGIC

       PCRE2 stores a 4-byte "magic number" at the start of the compiled code,
       to  catch  the case when it is passed a junk pointer. This is the error
       that is returned when the magic number is not present.

         PCRE2_ERROR_BADMODE

       This error is given when a compiled pattern is passed to a function  in
       a  library  of a different code unit width, for example, a pattern com-
       piled by the 8-bit library is passed to  a  16-bit  or  32-bit  library
       function.

         PCRE2_ERROR_BADOFFSET

       The value of startoffset was greater than the length of the subject.

         PCRE2_ERROR_BADOPTION

       An unrecognized bit was set in the options argument.

         PCRE2_ERROR_BADUTFOFFSET

       The UTF code unit sequence that was passed as a subject was checked and
       found to be valid (the PCRE2_NO_UTF_CHECK option was not set), but  the
       value  of startoffset did not point to the beginning of a UTF character
       or the end of the subject.

         PCRE2_ERROR_CALLOUT

       This error is never generated by pcre2_match() itself. It  is  provided
       for  use  by  callout  functions  that  want  to cause pcre2_match() or
       pcre2_callout_enumerate() to return a distinctive error code.  See  the
       pcre2callout documentation for details.

         PCRE2_ERROR_DEPTHLIMIT

       The nested backtracking depth limit was reached.

         PCRE2_ERROR_HEAPLIMIT

       The heap limit was reached.

         PCRE2_ERROR_INTERNAL

       An  unexpected  internal error has occurred. This error could be caused
       by a bug in PCRE2 or by overwriting of the compiled pattern.

         PCRE2_ERROR_JIT_STACKLIMIT

       This error is returned when a pattern  that  was  successfully  studied
       using  JIT  is being matched, but the memory available for the just-in-
       time processing stack is not large enough. See the pcre2jit  documenta-
       tion for more details.
       PCRE2_COPY_MATCHED_SUBJECT is set and memory allocation fails.

         PCRE2_ERROR_NULL

       Either the code, subject, or match_data argument was passed as NULL.

         PCRE2_ERROR_RECURSELOOP

       This error is returned when  pcre2_match()  detects  a  recursion  loop
       within  the  pattern. Specifically, it means that either the whole pat-
       tern or a capture group 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  com-
       plicated  cases,  in particular mutual recursions between two different
       groups, cannot be detected until matching is attempted.

OBTAINING A TEXTUAL ERROR MESSAGE

       int pcre2_get_error_message(int errorcode, PCRE2_UCHAR *buffer,
         PCRE2_SIZE bufflen);

       A text message for an error code  from  any  PCRE2  function  (compile,
       match,  or  auxiliary)  can be obtained by calling pcre2_get_error_mes-
       sage(). The code is passed as the first argument,  with  the  remaining
       two  arguments  specifying  a  code  unit buffer and its length in code
       units, into which the text message is placed. The message  is  returned
       in  code  units  of the appropriate width for the library that is being
       used.

       The returned message is terminated with a trailing zero, and the  func-
       tion  returns  the  number  of  code units used, excluding the trailing
       zero.  If  the  error  number  is  unknown,  the  negative  error  code
       PCRE2_ERROR_BADDATA  is  returned. If the buffer is too small, the mes-
       sage is truncated (but still with a trailing zero),  and  the  negative
       error  code PCRE2_ERROR_NOMEMORY is returned.  None of the messages are
       very long; a buffer size of 120 code units is ample.

EXTRACTING CAPTURED SUBSTRINGS BY NUMBER

       int pcre2_substring_length_bynumber(pcre2_match_data *match_data,
         uint32_t number, PCRE2_SIZE *length);

       int pcre2_substring_copy_bynumber(pcre2_match_data *match_data,
         uint32_t number, PCRE2_UCHAR *buffer,
         PCRE2_SIZE *bufflen);

       int pcre2_substring_get_bynumber(pcre2_match_data *match_data,
         uint32_t number, PCRE2_UCHAR **bufferptr,
         PCRE2_SIZE *bufflen);

       void pcre2_substring_free(PCRE2_UCHAR *buffer);

       Captured substrings can be accessed directly by using  the  ovector  as
       described above.  For convenience, auxiliary functions are provided for
       If a pattern uses the \K escape sequence within a  positive  assertion,
       the reported start of a successful match can be greater than the end of
       the match.  For example, if the pattern  (?=ab\K)  is  matched  against
       "ab",  the  start  and  end offset values for the match are 2 and 0. In
       this situation, calling these functions with a  zero  substring  number
       extracts a zero-length empty string.

       You  can  find the length in code units of a captured substring without
       extracting it by calling pcre2_substring_length_bynumber().  The  first
       argument  is a pointer to the match data block, the second is the group
       number, and the third is a pointer to a variable into which the  length
       is  placed.  If  you just want to know whether or not the substring has
       been captured, you can pass the third argument as NULL.

       The pcre2_substring_copy_bynumber() function  copies  a  captured  sub-
       string  into  a supplied buffer, whereas pcre2_substring_get_bynumber()
       copies it into new memory, obtained using the  same  memory  allocation
       function  that  was  used for the match data block. The first two argu-
       ments of these functions are a pointer to the match data  block  and  a
       capture group number.

       The final arguments of pcre2_substring_copy_bynumber() are a pointer to
       the buffer and a pointer to a variable that contains its length in code
       units.  This is updated to contain the actual number of code units used
       for the extracted substring, excluding the terminating zero.

       For pcre2_substring_get_bynumber() the third and fourth arguments point
       to  variables that are updated with a pointer to the new memory and the
       number of code units that comprise the substring, again  excluding  the
       terminating  zero.  When  the substring is no longer needed, the memory
       should be freed by calling pcre2_substring_free().

       The return value from all these functions is zero  for  success,  or  a
       negative  error  code.  If  the pattern match failed, the match failure
       code is returned.  If a substring number  greater  than  zero  is  used
       after  a partial match, PCRE2_ERROR_PARTIAL is returned. Other possible
       error codes are:

         PCRE2_ERROR_NOMEMORY

       The buffer was too small for  pcre2_substring_copy_bynumber(),  or  the
       attempt to get memory failed for pcre2_substring_get_bynumber().

         PCRE2_ERROR_NOSUBSTRING

       There  is  no  substring  with that number in the pattern, that is, the
       number is greater than the number of capturing parentheses.

         PCRE2_ERROR_UNAVAILABLE

       The substring number, though not greater than the number of captures in
       the pattern, is greater than the number of slots in the ovector, so the
       substring could not be captured.


       The pcre2_substring_list_get() function  extracts  all  available  sub-
       strings  and  builds  a  list of pointers to them. It also (optionally)
       builds a second list that  contains  their  lengths  (in  code  units),
       excluding a terminating zero that is added to each of them. All this is
       done in a single block of memory that is obtained using the same memory
       allocation function that was used to get the match data block.

       This  function  must be called only after a successful match. If called
       after a partial match, the error code PCRE2_ERROR_PARTIAL is returned.

       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 address of the list of lengths is  returned  via
       lengthsptr.  If your strings do not contain binary zeros and you do not
       therefore need the lengths, you may supply NULL as the lengthsptr argu-
       ment  to  disable  the  creation of a list of lengths. The yield of the
       function is zero if all went well, or PCRE2_ERROR_NOMEMORY if the  mem-
       ory  block could not be obtained. When the list is no longer needed, it
       should be freed by calling pcre2_substring_list_free().

       If this function encounters a substring that is unset, which can happen
       when  capture  group  number  n+1 matches some part of the subject, but
       group n has not been used at all, it returns an empty string. This  can
       be distinguished from a genuine zero-length substring by inspecting the
       appropriate offset in the ovector, which contain PCRE2_UNSET for  unset
       substrings, or by calling pcre2_substring_length_bynumber().

EXTRACTING CAPTURED SUBSTRINGS BY NAME

       int pcre2_substring_number_from_name(const pcre2_code *code,
         PCRE2_SPTR name);

       int pcre2_substring_length_byname(pcre2_match_data *match_data,
         PCRE2_SPTR name, PCRE2_SIZE *length);

       int pcre2_substring_copy_byname(pcre2_match_data *match_data,
         PCRE2_SPTR name, PCRE2_UCHAR *buffer, PCRE2_SIZE *bufflen);

       int pcre2_substring_get_byname(pcre2_match_data *match_data,
         PCRE2_SPTR name, PCRE2_UCHAR **bufferptr, PCRE2_SIZE *bufflen);

       void pcre2_substring_free(PCRE2_UCHAR *buffer);

       To  extract a substring by name, you first have to find associated num-
       ber.  For example, for this pattern:

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

       the number of the capture group called "xxx" is 2. If the name is known
       to be unique (PCRE2_DUPNAMES was not set), you can find the number from
       the name by calling pcre2_substring_number_from_name(). The first argu-
       ment  is the compiled pattern, and the second is the name. The yield of
       the function is the group number, PCRE2_ERROR_NOSUBSTRING if  there  is
       If  there are no groups with the given name, PCRE2_ERROR_NOSUBSTRING is
       returned. If all groups with the name have  numbers  that  are  greater
       than  the  number  of  slots in the ovector, PCRE2_ERROR_UNAVAILABLE is
       returned. If there is at least one group with a slot  in  the  ovector,
       but no group is found to be set, PCRE2_ERROR_UNSET is returned.

       Warning: If the pattern uses the (?| feature to set up multiple capture
       groups with the same number, as described in the section  on  duplicate
       group numbers in the pcre2pattern page, you cannot use names to distin-
       guish the different capture groups, because names are not  included  in
       the  compiled  code.  The  matching process uses only numbers. For this
       reason, the use of different names for  groups  with  the  same  number
       causes an error at compile time.

CREATING A NEW STRING WITH SUBSTITUTIONS

       int pcre2_substitute(const pcre2_code *code, PCRE2_SPTR subject,
         PCRE2_SIZE length, PCRE2_SIZE startoffset,
         uint32_t options, pcre2_match_data *match_data,
         pcre2_match_context *mcontext, PCRE2_SPTR replacement,
         PCRE2_SIZE rlength, PCRE2_UCHAR *outputbuffer,
         PCRE2_SIZE *outlengthptr);

       This  function calls pcre2_match() and then makes a copy of the subject
       string in outputbuffer, replacing one or more parts that  were  matched
       with the replacement string, whose length is supplied in rlength.  This
       can be given as PCRE2_ZERO_TERMINATED  for  a  zero-terminated  string.
       The  default is to perform just one replacement, but there is an option
       that requests multiple replacements (see PCRE2_SUBSTITUTE_GLOBAL  below
       for details).

       Matches  in  which  a  \K item in a lookahead in the pattern causes the
       match to end before it starts are not supported, and give  rise  to  an
       error return. For global replacements, matches in which \K in a lookbe-
       hind causes the match to start earlier than the point that was  reached
       in the previous iteration are also not supported.

       The  first  seven  arguments  of pcre2_substitute() are the same as for
       pcre2_match(), except that the partial matching options are not permit-
       ted,  and  match_data may be passed as NULL, in which case a match data
       block is obtained and freed within this function, using memory  manage-
       ment  functions from the match context, if provided, or else those that
       were used to allocate memory for the compiled code.

       If an external match_data block is provided,  its  contents  afterwards
       are  those  set by the final call to pcre2_match(). For global changes,
       this will have ended in a matching error. The contents of  the  ovector
       within the match data block may or may not have been changed.

       The  outlengthptr  argument  must point to a variable that contains the
       length, in code units, of the output buffer. If the  function  is  suc-
       cessful,  the value is updated to contain the length of the new string,
       excluding the trailing zero that is automatically added.

       In the replacement string, which is interpreted as a UTF string in  UTF
       mode,  and  is  checked  for UTF validity unless the PCRE2_NO_UTF_CHECK
       option is set, a dollar character is an escape character that can spec-
       ify  the  insertion  of  characters  from  capture groups or names from
       (*MARK) or other control verbs in the pattern. The following forms  are
       always recognized:

         $$                  insert a dollar character
         $<n> or ${<n>}      insert the contents of group <n>
         $*MARK or ${*MARK}  insert a control verb name

       Either  a  group  number  or  a  group name can be given for <n>. Curly
       brackets are required only if the following character would  be  inter-
       preted as part of the number or name. The number may be zero to include
       the entire matched string.   For  example,  if  the  pattern  a(b)c  is
       matched  with "=abc=" and the replacement string "+$1$0$1+", the result
       is "=+babcb+=".

       $*MARK inserts the name from the last encountered backtracking  control
       verb  on the matching path that has a name. (*MARK) must always include
       a name, but the other verbs need not.  For  example,  in  the  case  of
       (*MARK:A)(*PRUNE) the name inserted is "A", but for (*MARK:A)(*PRUNE:B)
       the relevant name is "B". This facility can be used to  perform  simple
       simultaneous substitutions, as this pcre2test example shows:

         /(*MARK:pear)apple|(*MARK:orange)lemon/g,replace=${*MARK}
             apple lemon
          2: pear orange

       As  well as the usual options for pcre2_match(), a number of additional
       options can be set in the options argument of pcre2_substitute().

       PCRE2_SUBSTITUTE_GLOBAL causes the function to iterate over the subject
       string,  replacing every matching substring. If this option is not set,
       only the first matching substring is replaced. The search  for  matches
       takes  place in the original subject string (that is, previous replace-
       ments do not affect it).  Iteration is  implemented  by  advancing  the
       startoffset  value  for  each search, which is always passed the entire
       subject string. If an offset limit is set in the match context, search-
       ing stops when that limit is reached.

       You  can  restrict  the effect of a global substitution to a portion of
       the subject string by setting either or both of startoffset and an off-
       set limit. Here is a pcre2test example:

         /B/g,replace=!,use_offset_limit
         ABC ABC ABC ABC\=offset=3,offset_limit=12
          2: ABC A!C A!C ABC

       When  continuing  with  global substitutions after matching a substring
       with zero length, an attempt to find a non-empty match at the same off-
       set is performed.  If this is not successful, the offset is advanced by
       one character except when CRLF is a valid newline sequence and the next
       two  characters are CR, LF. In this case, the offset is advanced by two
       much memory is needed for given substitution. However, this  does  mean
       that the entire operation is carried out twice. Depending on the appli-
       cation, it may be more efficient to allocate a large  buffer  and  free
       the   excess   afterwards,   instead  of  using  PCRE2_SUBSTITUTE_OVER-
       FLOW_LENGTH.

       PCRE2_SUBSTITUTE_UNKNOWN_UNSET causes references to capture groups that
       do not appear in the pattern to be treated as unset groups. This option
       should be used with care, because it means that a typo in a group  name
       or number no longer causes the PCRE2_ERROR_NOSUBSTRING error.

       PCRE2_SUBSTITUTE_UNSET_EMPTY  causes  unset  capture  groups (including
       unknown  groups  when  PCRE2_SUBSTITUTE_UNKNOWN_UNSET  is  set)  to  be
       treated  as  empty  strings  when  inserted as described above. If this
       option is not set, an attempt to  insert  an  unset  group  causes  the
       PCRE2_ERROR_UNSET  error.  This  option does not influence the extended
       substitution syntax described below.

       PCRE2_SUBSTITUTE_EXTENDED causes extra processing to be applied to  the
       replacement  string.  Without this option, only the dollar character is
       special, and only the group insertion forms  listed  above  are  valid.
       When PCRE2_SUBSTITUTE_EXTENDED is set, two things change:

       Firstly,  backslash in a replacement string is interpreted as an escape
       character. The usual forms such as \n or \x{ddd} can be used to specify
       particular  character codes, and backslash followed by any non-alphanu-
       meric character quotes that character. Extended quoting  can  be  coded
       using \Q...\E, exactly as in pattern strings.

       There  are  also four escape sequences for forcing the case of inserted
       letters.  The insertion mechanism has three states:  no  case  forcing,
       force upper case, and force lower case. The escape sequences change the
       current state: \U and \L change to upper or lower case forcing, respec-
       tively,  and  \E (when not terminating a \Q quoted sequence) reverts to
       no case forcing. The sequences \u and \l force the next  character  (if
       it  is  a  letter)  to  upper or lower case, respectively, and then the
       state automatically reverts to no case forcing. Case forcing applies to
       all  inserted  characters, including those from capture groups and let-
       ters within \Q...\E quoted sequences.

       Note that case forcing sequences such as \U...\E do not nest. For exam-
       ple,  the  result of processing "\Uaa\LBB\Ecc\E" is "AAbbcc"; the final
       \E  has  no   effect.   Note   also   that   the   PCRE2_ALT_BSUX   and
       PCRE2_EXTRA_ALT_BSUX  options  do not apply to not apply to replacement
       strings.

       The second effect of setting PCRE2_SUBSTITUTE_EXTENDED is to  add  more
       flexibility  to  capture  group  substitution. The syntax is similar to
       that used by Bash:

         ${<n>:-<string>}
         ${<n>:+<string1>:<string2>}

       As before, <n> may be a group number or a name. The first  form  speci-

         /(some)?(body)/substitute_extended,replace=${1:+\U:\L}HeLLo
             body
          1: hello
             somebody
          1: HELLO

       The PCRE2_SUBSTITUTE_UNSET_EMPTY option does not affect these  extended
       substitutions.   However,   PCRE2_SUBSTITUTE_UNKNOWN_UNSET  does  cause
       unknown groups in the extended syntax forms to be treated as unset.

       If successful, pcre2_substitute()  returns  the  number  of  successful
       matches.  This  may  be  zero  if  no  matches were found, and is never
       greater than 1 unless PCRE2_SUBSTITUTE_GLOBAL is set.

       In the event of an error, a negative error code is returned. Except for
       PCRE2_ERROR_NOMATCH    (which   is   never   returned),   errors   from
       pcre2_match() are passed straight back.

       PCRE2_ERROR_NOSUBSTRING is returned for a non-existent substring inser-
       tion, unless PCRE2_SUBSTITUTE_UNKNOWN_UNSET is set.

       PCRE2_ERROR_UNSET is returned for an unset substring insertion (includ-
       ing an unknown substring when  PCRE2_SUBSTITUTE_UNKNOWN_UNSET  is  set)
       when  the  simple  (non-extended)  syntax  is  used  and  PCRE2_SUBSTI-
       TUTE_UNSET_EMPTY is not set.

       PCRE2_ERROR_NOMEMORY is returned  if  the  output  buffer  is  not  big
       enough. If the PCRE2_SUBSTITUTE_OVERFLOW_LENGTH option is set, the size
       of buffer that is needed is returned via outlengthptr. Note  that  this
       does not happen by default.

       PCRE2_ERROR_BADREPLACEMENT  is  used for miscellaneous syntax errors in
       the   replacement   string,   with   more   particular   errors   being
       PCRE2_ERROR_BADREPESCAPE  (invalid  escape  sequence), PCRE2_ERROR_REP-
       MISSINGBRACE (closing curly bracket not found),  PCRE2_ERROR_BADSUBSTI-
       TUTION   (syntax   error   in   extended   group   substitution),   and
       PCRE2_ERROR_BADSUBSPATTERN (the pattern match ended before  it  started
       or  the match started earlier than the current position in the subject,
       which can happen if \K is used in an assertion).

       As for all PCRE2 errors, a text message that describes the error can be
       obtained   by   calling  the  pcre2_get_error_message()  function  (see
       "Obtaining a textual error message" above).

   Substitution callouts

       int pcre2_set_substitute_callout(pcre2_match_context *mcontext,
         int (*callout_function)(pcre2_substitute_callout_block *, void *),
         void *callout_data);

       The pcre2_set_substitution_callout() function can be used to specify  a
       callout  function for pcre2_substitute(). This information is passed in
       a match context. The callout function is called after each substitution
         PCRE2_SIZE *ovector;
         uint32_t    oveccount;
         PCRE2_SIZE  output_offsets[2];

       The  version field contains the version number of the block format. The
       current version is 0. The version number will  increase  in  future  if
       more  fields are added, but the intention is never to remove any of the
       existing fields.

       The subscount field is the number of the current match. It is 1 for the
       first callout, 2 for the second, and so on. The input and output point-
       ers are copies of the values passed to pcre2_substitute().

       The ovector field points to the ovector, which contains the  result  of
       the most recent match. The oveccount field contains the number of pairs
       that are set in the ovector, and is always greater than zero.

       The output_offsets vector contains the offsets of  the  replacement  in
       the  output  string. This has already been processed for dollar and (if
       requested) backslash substitutions as described above.

       The second argument of the callout function  is  the  value  passed  as
       callout_data  when  the  function was registered. The value returned by
       the callout function is interpreted as follows:

       If the value is zero, the replacement is accepted, and,  if  PCRE2_SUB-
       STITUTE_GLOBAL  is set, processing continues with a search for the next
       match. If the value  is  not  zero,  the  current  replacement  is  not
       accepted.  If the value is greater than zero, processing continues when
       PCRE2_SUBSTITUTE_GLOBAL is set. Otherwise (the value is less than  zero
       or  PCRE2_SUBSTITUTE_GLOBAL  is  not set), the the rest of the input is
       copied to the output and the call to pcre2_substitute() exits,  return-
       ing the number of matches so far.

DUPLICATE CAPTURE GROUP NAMES

       int pcre2_substring_nametable_scan(const pcre2_code *code,
         PCRE2_SPTR name, PCRE2_SPTR *first, PCRE2_SPTR *last);

       When  a  pattern  is compiled with the PCRE2_DUPNAMES option, names for
       capture groups are not required  to  be  unique.  Duplicate  names  are
       always  allowed  for  groups with the same number, created by using the
       (?| feature. Indeed, if such groups are named, they are required to use
       the same names.

       Normally,  patterns  that  use duplicate names are such that in any one
       match, only one of each set of identically-named  groups  participates.
       An example is shown in the pcre2pattern documentation.

       When   duplicates   are   present,   pcre2_substring_copy_byname()  and
       pcre2_substring_get_byname() return the first  substring  corresponding
       to   the   given   name   that   is  set.  Only  if  none  are  set  is
       PCRE2_ERROR_UNSET is returned.  The  pcre2_substring_number_from_name()
       function returns the error PCRE2_ERROR_NOUNIQUESUBSTRING when there are
       units. In both cases, PCRE2_ERROR_NOSUBSTRING is returned if there  are
       no entries for the given name.

       The format of the name table is described above in the section entitled
       Information about a pattern. Given all the  relevant  entries  for  the
       name,  you  can  extract  each of their numbers, and hence the captured
       data.

FINDING ALL POSSIBLE MATCHES AT ONE POSITION

       The traditional matching function uses a  similar  algorithm  to  Perl,
       which  stops when it finds the first match at a given point in the sub-
       ject. If you want to find all possible matches, or the longest possible
       match  at  a  given  position,  consider using the alternative matching
       function (see below) instead. If you cannot use the  alternative  func-
       tion, you can kludge it up by making use of the callout facility, which
       is described in the pcre2callout documentation.

       What you have to do is to insert a callout right at the end of the pat-
       tern.   When your callout function is called, extract and save the cur-
       rent matched substring. Then return 1, which  forces  pcre2_match()  to
       backtrack  and  try other alternatives. Ultimately, when it runs out of
       matches, pcre2_match() will yield PCRE2_ERROR_NOMATCH.

MATCHING A PATTERN: THE ALTERNATIVE FUNCTION

       int pcre2_dfa_match(const pcre2_code *code, PCRE2_SPTR subject,
         PCRE2_SIZE length, PCRE2_SIZE startoffset,
         uint32_t options, pcre2_match_data *match_data,
         pcre2_match_context *mcontext,
         int *workspace, PCRE2_SIZE wscount);

       The function pcre2_dfa_match() is called  to  match  a  subject  string
       against  a  compiled pattern, using a matching algorithm that scans the
       subject string just once (not counting lookaround assertions), and does
       not  backtrack.  This has different characteristics to the normal algo-
       rithm, and is not compatible with Perl. Some of the features  of  PCRE2
       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 pcre2_dfa_match() does not sup-
       port, see the pcre2matching documentation.

       The arguments for the pcre2_dfa_match() function are the  same  as  for
       pcre2_match(), plus two extras. The ovector within the match data block
       is used in a different way, and this is described below. The other com-
       mon  arguments  are used in the same way as for pcre2_match(), 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  is needed for patterns and subjects where there are a lot of
       potential matches.

           wspace,         /* working space vector */
           20);            /* number of elements (NOT size in bytes) */

   Option bits for pcre_dfa_match()

       The unused bits of the options argument for pcre2_dfa_match()  must  be
       zero.   The   only   bits   that   may   be   set  are  PCRE2_ANCHORED,
       PCRE2_COPY_MATCHED_SUBJECT,      PCRE2_ENDANCHORED,       PCRE2_NOTBOL,
       PCRE2_NOTEOL,          PCRE2_NOTEMPTY,          PCRE2_NOTEMPTY_ATSTART,
       PCRE2_NO_UTF_CHECK,       PCRE2_PARTIAL_HARD,       PCRE2_PARTIAL_SOFT,
       PCRE2_DFA_SHORTEST,  and  PCRE2_DFA_RESTART.  All  but the last four of
       these are exactly the same as for pcre2_match(), so  their  description
       is not repeated here.

         PCRE2_PARTIAL_HARD
         PCRE2_PARTIAL_SOFT

       These  have  the  same general effect as they do for pcre2_match(), but
       the details are slightly different. When PCRE2_PARTIAL_HARD is set  for
       pcre2_dfa_match(),  it  returns  PCRE2_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 already been found. When PCRE2_PARTIAL_SOFT  is  set,  the
       return  code  PCRE2_ERROR_NOMATCH is converted into PCRE2_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 por-
       tion 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 pcre2partial documentation.

         PCRE2_DFA_SHORTEST

       Setting  the PCRE2_DFA_SHORTEST option causes the matching algorithm to
       stop as soon as it has found one match. Because of the way the alterna-
       tive  algorithm  works, this is necessarily the shortest possible match
       at the first possible matching point in the subject string.

         PCRE2_DFA_RESTART

       When pcre2_dfa_match() returns a partial match, it is possible to  call
       it again, with additional subject characters, and have it continue with
       the same match. The PCRE2_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
       pcre2partial documentation.

   Successful returns from pcre2_dfa_match()

       When pcre2_dfa_match() succeeds, it may have matched more than one sub-
       string in the subject. Note, however, that all the matches from one run
       of the function start at the same point in  the  subject.  The  shorter
       matches  are all initial substrings of the longer matches. For example,
         <something>

       On success, the yield of the function is a number  greater  than  zero,
       which  is  the  number  of  matched substrings. The offsets of the sub-
       strings are returned in the ovector, and can be extracted by number  in
       the  same way as for pcre2_match(), but the numbers bear no relation to
       any capture groups that may exist in the pattern, because DFA  matching
       does not support capturing.

       Calls  to  the  convenience  functions  that extract substrings by name
       return the error PCRE2_ERROR_DFA_UFUNC (unsupported function)  if  used
       after a DFA match. The convenience functions that extract substrings by
       number never return PCRE2_ERROR_NOSUBSTRING.

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

       NOTE:  PCRE2'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++". 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 such as "a\d+?" or set  the  PCRE2_NO_AUTO_POSSESS  option  when
       compiling.

   Error returns from pcre2_dfa_match()

       The pcre2_dfa_match() function returns a negative number when it fails.
       Many of the errors are the same  as  for  pcre2_match(),  as  described
       above.  There are in addition the following errors that are specific to
       pcre2_dfa_match():

         PCRE2_ERROR_DFA_UITEM

       This return is given if pcre2_dfa_match() encounters  an  item  in  the
       pattern  that it does not support, for instance, the use of \C in a UTF
       mode or a backreference.

         PCRE2_ERROR_DFA_UCOND

       This return is given if pcre2_dfa_match() encounters a  condition  item
       that uses a backreference for the condition, or a test for recursion in
       a specific capture group. These are not supported.

         PCRE2_ERROR_DFA_WSSIZE

       This return is given if pcre2_dfa_match() runs  out  of  space  in  the
       workspace vector.

         PCRE2_ERROR_DFA_RECURSE

       When a recursion or subroutine call is processed, the matching function

SEE ALSO

       pcre2build(3),   pcre2callout(3),    pcre2demo(3),    pcre2matching(3),
       pcre2partial(3), pcre2posix(3), pcre2sample(3), pcre2unicode(3).

AUTHOR

       Philip Hazel
       University Computing Service
       Cambridge, England.

REVISION

       Last updated: 14 February 2019
       Copyright (c) 1997-2019 University of Cambridge.

PCRE2 10.33                    14 February 2019                    PCRE2API(3)
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