# pcre2api

## NAME



           PCRE2 - Perl-compatible regular expressions (revised API)
    
           **#include <pcre2.h>**
    
           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** document 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_**);**
    
           **PCRE2_SIZE pcre2_get_match_data_size(pcre2_match_data ***_match_data_**);**
    
           **PCRE2_SIZE pcre2_get_match_data_heapframes_size(**
             **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



    
           **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_**);**
    
           **int pcre2_set_bsr(pcre2_compile_context ***_ccontext_**,**
             **uint32_t** _value_**);**
    
           **int pcre2_set_character_tables(pcre2_compile_context ***_ccontext_**,**
             **const uint8_t ***_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_max_pattern_compiled_length(**
             **pcre2_compile_context ***_ccontext_**, PCRE2_SIZE** _value_**);**
    
           **int pcre2_set_max_varlookbehind(pcre2_compile_contest ***_ccontext_**,**
             **uint32_t** _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_**);**
    
           **int pcre2_set_optimize(pcre2_compile_context ***_ccontext_**,**
             **uint32_t** _directive_**);**
    


## 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_substitute_case_callout(pcre2_match_context ***_mcontext_**,**
             **PCRE2_SIZE (***_callout_function_**)(PCRE2_SPTR, PCRE2_SIZE,**
                                            **PCRE2_UCHAR *, PCRE2_SIZE,**
                                            **int, 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_**,**
             **uint32_t** _number_**, PCRE2_UCHAR ***_buffer_**,**
             **PCRE2_SIZE ***_bufflen_**);**
    
           **void pcre2_substring_free(PCRE2_UCHAR ***_buffer_**);**
    
           **int pcre2_substring_get_byname(pcre2_match_data ***_match_data_**,**
             **PCRE2_SPTR** _name_**, PCRE2_UCHAR ****_bufferptr_**, PCRE2_SIZE ***_bufflen_**);**
    
           **int pcre2_substring_get_bynumber(pcre2_match_data ***_match_data_**,**
             **uint32_t** _number_**, PCRE2_UCHAR ****_bufferptr_**,**
             **PCRE2_SIZE ***_bufflen_**);**
    
           **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_UCHAR ****_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** _replacement_**,**
             **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(size_t** _startsize_**,**
             **size_t** _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_**);**
    
           **void pcre2_serialize_free(uint8_t ***_bytes_**);**
    
           **int32_t pcre2_serialize_get_number_of_codes(const uint8_t ***_bytes_**);**
    


## PCRE2 NATIVE API AUXILIARY FUNCTIONS



    
           **pcre2_code *pcre2_code_copy(const pcre2_code ***_code_**);**
    
           **pcre2_code *pcre2_code_copy_with_tables(const pcre2_code ***_code_**);**
    
           **int pcre2_get_error_message(int** _errorcode_**, PCRE2_UCHAR ***_buffer_**,**
             **PCRE2_SIZE** _bufflen_**);**
    
           **const uint8_t *pcre2_maketables(pcre2_general_context ***_gcontext_**);**
    
           **void pcre2_maketables_free(pcre2_general_context ***_gcontext_**,**
             **const uint8_t ***_tables_**);**
    
           **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_**)(size_t, 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 given in the **pcre2convert** documentation.
    


## PCRE2 8-BIT, 16-BIT, AND 32-BIT LIBRARIES



    
           There are three PCRE2 libraries, supporting 8-bit, 16-bit, and
           32-bit code units, respectively. However, there is just one header
           file, **pcre2.h**.  This contains the function prototypes and other
           definitions for all three libraries. One, two, or all three can be
           installed simultaneously. On Unix-like systems the libraries are
           called **libpcre2-8** , **libpcre2-16** , and **libpcre2-32** , and they can also
           co-exist with the original PCRE libraries.  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 pointers to constants of the
           equivalent UCHAR types, that is, they are pointers to vectors of
           unsigned code units.
    
           Character strings are passed to a PCRE2 library as sequences of
           unsigned integers in code units of the appropriate width. The
           length of a string may be given as a number of code units, or the
           string may be specified as zero-terminated.
    
           Many applications use only one code unit width. For their
           convenience, macros are defined whose names are the generic forms
           such as **pcre2_compile()** and PCRE2_SPTR. These macros use the value
           of the macro PCRE2_CODE_UNIT_WIDTH to generate the appropriate
           width-specific function 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 pattern 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
           correspond to the POSIX regular expression API, but they do not
           give access to all the functionality of PCRE2 and they are not
           thread-safe. They are described in the **pcre2posix** documentation.
           Both these APIs define a set of C function calls.
    
           The native API C data types, function prototypes, option values,
           and error codes are defined in the header file **pcre2.h** , which also
           contains definitions of PCRE2_MAJOR and PCRE2_MINOR, the major and
           minor release numbers for the library. Applications can use these
           to include support for different releases of PCRE2.
    
           In a Windows environment, if you want to statically link an
           application program against a non-dll PCRE2 library, you must
           define PCRE2_STATIC before including **pcre2.h**.
    
           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 complicated 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-
           compatible, is also provided. This uses a different algorithm for
           the matching. The alternative algorithm finds all possible matches
           (at a given point in the subject), and scans the subject just once
           (unless there are lookaround assertions). However, this algorithm
           does not return captured substrings. A description of the two
           matching algorithms and their advantages and disadvantages is
           given in the **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()**
             **pcre2_substring_number_from_name()**
    
           **pcre2_substring_free()** and **pcre2_substring_list_free()** are also
           provided, to free memory used for extracted strings. If either of
           these functions is called with a NULL argument, the function
           returns immediately without doing anything.
    
           The function **pcre2_substitute()** can be called to match a pattern
           and return a copy of the subject string with substitutions for
           parts that were matched.
    
           Functions whose names begin with **pcre2_serialize_** are used for
           saving compiled patterns on disc or elsewhere, and reloading them
           later.
    
           Finally, there are functions for finding out information about a
           compiled 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.
           Note that string lengths are always given in code units. Only in
           the 8-bit library is such a length the same as the number of bytes
           in the string.
    


## NEWLINES



    
           PCRE2 supports five different conventions for indicating line
           breaks in strings: a single CR (carriage return) character, a
           single LF (linefeed) character, the two-character sequence CRLF,
           any of the three preceding, or any Unicode newline sequence. The
           Unicode newline sequences are the three just mentioned, plus the
           single characters VT (vertical tab, U+000B), FF (form feed,
           U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and
           PS (paragraph separator, U+2029).
    
           Each of the first three conventions is used by at least one
           operating system as its standard newline sequence. When 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 advancement 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 data separate from data that can be shared between
           threads. The PCRE2 library code itself is thread-safe: it contains
           no static or global variables. The API is designed to be fairly
           simple for non-threaded applications while at the same time
           ensuring that multithreaded applications can use it.
    
           There are several different blocks of data that are used to pass
           information between the application and the PCRE2 libraries.
    
       **The compiled pattern**
    
           A pointer to the compiled form of a pattern is returned to the
           user 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. This is somewhat tricky to do
           correctly. If you know that writing to a pointer is atomic in your
           environment, you can use logic like this:
    
             Get a read-only (shared) lock (mutex) for pointer
             if (pointer == NULL)
               {
               Get a write (unique) lock for pointer
               if (pointer == NULL) pointer = pcre2_compile(...
               }
             Release the lock
             Use pointer in pcre2_match()
    
           Of course, testing for compilation errors should also be included
           in the code.
    
           The reason for checking the pointer a second time is as follows:
           Several threads may have acquired the shared lock and tested the
           pointer for being NULL, but only one of them will be given the
           write lock, with the rest kept waiting. The winning thread will
           compile the pattern and store the result.  After this thread
           releases the write lock, another thread will get it, and if it
           does not retest pointer for being NULL, will recompile the pattern
           and overwrite the pointer, creating a memory leak and possibly
           causing other issues.
    
           In an environment where writing to a pointer may not be atomic,
           the above logic is not sufficient. The thread that is doing the
           compiling may be descheduled after writing only part of the
           pointer, which could cause other threads to use an invalid value.
           Instead of checking the pointer itself, a separate "pointer is
           valid" flag (that can be updated atomically) must be used:
    
             Get a read-only (shared) lock (mutex) for pointer
             if (!pointer_is_valid)
               {
               Get a write (unique) lock for pointer
               if (!pointer_is_valid)
                 {
                 pointer = pcre2_compile(...
                 pointer_is_valid = TRUE
                 }
               }
             Release the lock
             Use pointer in pcre2_match()
    
           If JIT is being used, but the JIT compilation is not being done
           immediately (perhaps waiting to see if the pattern is used often
           enough), similar logic is required. JIT compilation updates a
           value 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 compiler.
    
       **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
           values 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 of a match. This includes details of what was matched, as
           well as additional information such as the name of a (*MARK)
           setting. Each thread must provide its own copy of this memory.
    


## PCRE2 CONTEXTS



    
           Some PCRE2 functions have a lot of parameters, many of which are
           used only by specialist applications, for example, those that use
           custom memory management or non-standard character tables. To keep
           function argument lists at a reasonable size, and at the same time
           to keep the API extensible, "uncommon" parameters are passed to
           certain functions in a **context** instead of directly. A context is
           just a block of memory 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 functions _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.
    
       **The compile context**
    
           A compile context is required if you want to provide an external
           function for stack checking during compilation or to change the
           default values of any of the following compile-time parameters:
    
             What \R matches (Unicode newlines or CR, LF, CRLF only)
             PCRE2's character tables
             The newline character sequence
             The compile time nested parentheses limit
             The maximum length of the pattern string
             The extra options bits (none set by default)
             Which performance optimizations the compiler should apply
    
           A compile context is also required if you are using custom memory
           management.  If none of these apply, just pass NULL as the context
           argument of _pcre2_compile()_.
    
           A compile context is created, copied, and freed by the following
           functions:
    
           **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 uint8_t ***_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 character 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
           available 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 function 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 largest number that a PCRE2_SIZE
           variable can hold, which is effectively unlimited.
    
           **int pcre2_set_max_pattern_compiled_length(**
             **pcre2_compile_context ***_ccontext_**, PCRE2_SIZE** _value_**);**
    
           This sets a maximum size, in bytes, for the memory needed to hold
           the compiled version of a pattern that is compiled with this
           context. If the pattern needs more memory, an error is generated.
           This facility is provided so that applications that accept
           patterns from external sources can limit the amount of memory they
           use. The default is the largest number that a PCRE2_SIZE variable
           can hold, which is effectively unlimited.
    
           **int pcre2_set_max_varlookbehind(pcre2_compile_contest ***_ccontext_**,**
             **uint32_t** _value_**);**
    
           This sets a maximum length for the number of characters matched by
           a variable-length lookbehind assertion. The default is set when
           PCRE2 is built, with the ultimate default being 255, the same as
           Perl. Lookbehind assertions without a bounding length are not
           supported.
    
           **int pcre2_set_newline(pcre2_compile_context ***_ccontext_**,**
             **uint32_t** _value_**);**
    
           This specifies which characters or character sequences are to be
           recognized as newlines. The value must be one of PCRE2_NEWLINE_CR
           (carriage return only), PCRE2_NEWLINE_LF (linefeed only),
           PCRE2_NEWLINE_CRLF (the two-character sequence CR followed by LF),
           PCRE2_NEWLINE_ANYCRLF (any of the above), PCRE2_NEWLINE_ANY (any
           Unicode newline sequence), or PCRE2_NEWLINE_NUL (the NUL
           character, that is a binary zero).
    
           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
           recognition 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
           compiled. The limit applies to parentheses of all kinds, not just
           capturing 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
           argument of **pcre2_set_compile_recursion_guard()**. The callout
           function should return zero if all is well, or non-zero to force
           an error.
    
           **int pcre2_set_optimize(pcre2_compile_context ***_ccontext_**,**
             **uint32_t** _directive_**);**
    
           PCRE2 can apply various performance optimizations during
           compilation, in order to make matching faster. For example, the
           compiler might convert some regex constructs into an equivalent
           construct which **pcre2_match()** can execute faster. By default, all
           available optimizations are enabled. However, in rare cases, one
           might wish to disable specific optimizations. For example, if it
           is known that some optimizations cannot benefit a certain regex,
           it might be desirable to disable them, in order to speed up
           compilation.
    
           The permitted values of _directive_ are as follows:
    
             PCRE2_OPTIMIZATION_FULL
    
           Enable all optional performance optimizations. This is the default
           value.
    
             PCRE2_OPTIMIZATION_NONE
    
           Disable all optional performance optimizations.
    
             PCRE2_AUTO_POSSESS
             PCRE2_AUTO_POSSESS_OFF
    
           Enable/disable "auto-possessification" of variable quantifiers
           such as * and +.  This optimization, 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 disable this
           optimization if you want the matching functions to do a full,
           unoptimized search and run all the callouts.
    
             PCRE2_DOTSTAR_ANCHOR
             PCRE2_DOTSTAR_ANCHOR_OFF
    
           Enable/disable 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 ^. 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.
    
           Dotstar anchor 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).
    
             PCRE2_START_OPTIMIZE
             PCRE2_START_OPTIMIZE_OFF
    
           Enable/disable optimizations which cause matching functions to
           scan the subject string for specific code unit values before
           attempting a match. For example, if it is known that an unanchored
           match must start with a specific value, the matching code searches
           the subject for that value, and fails immediately if it cannot
           find it, without actually running the main matching function. This
           means that a special item such as (*COMMIT) at the start of a
           pattern is not considered until after a suitable starting point
           for the match has been found.  Also, when callouts or (*MARK)
           items are in use, these "start-up" optimizations can cause them to
           be skipped if the pattern is never actually used. The start-up
           optimizations are in effect a pre-scan of the subject that takes
           place before the pattern is run.
    
           Disabling start-up optimizations ensures 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.
    
           Disabling start-up optimizations may change the outcome of a
           matching operation.  Consider the pattern
    
             (*COMMIT)ABC
    
           When this is compiled, PCRE2 records the fact that a match must
           start with the character "A". Suppose the subject string is
           "DEFABC". The start-up optimization scans along the subject, finds
           "A" and runs the first match attempt from there. The (*COMMIT)
           item means that the pattern must match the current starting
           position, which in this case, it does. However, if the same match
           is run without start-up optimizations, the initial scan along the
           subject string does not happen. The first match attempt is run
           starting from "D" and when this fails, (*COMMIT) prevents any
           further matches being tried, so the overall result is "no match".
    
           Another start-up optimization makes use of a minimum length for a
           matching subject, which is recorded when possible. Consider the
           pattern
    
             (*MARK:1)B(*MARK:2)(X|Y)
    
           The minimum length for a match is two characters. If the subject
           is "XXBB", the "starting character" optimization skips "XX", then
           tries to match "BB", which is long enough. In the process,
           (*MARK:2) is encountered and remembered. When the match attempt
           fails, the next "B" is found, but there is only one character
           left, so there are no more attempts, and "no match" is returned
           with the "last mark seen" set to "2". Without start-up
           optimizations, however, matches are tried at every possible
           starting position, including at the end of the subject, where
           (*MARK:1) is encountered, but there is no "B", so the "last mark
           seen" that is returned is "1". In this case, the optimizations do
           not affect the overall match result, which is still "no match",
           but they do affect the auxiliary information that is returned.
    
       **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
           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_**);**
    
           A match 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_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** documentation.
    
           **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
           substitution made by **pcre2_substitute()**. Details are given in the
           section entitled "Creating a new string with substitutions" below.
    
           **int pcre2_set_substitute_case_callout(pcre2_match_context ***_mcontext_**,**
             **PCRE2_SIZE (***_callout_function_**)(PCRE2_SPTR, PCRE2_SIZE,**
                                            **PCRE2_UCHAR *, PCRE2_SIZE,**
                                            **int, void *),**
             **void ***_callout_data_**);**
    
           This sets up a callout function for PCRE2 to call when performing
           case transformations inside **pcre2_substitute()**. Details are given
           in the section entitled "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,
           different 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 generated.
    
           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, whichever 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 processing patterns with a lot of nested pattern
           recursion or lookarounds or atomic groups. This limit does not
           apply to matching with the JIT optimization, which has its own
           memory control arrangements (see the **pcre2jit** documentation for
           more details). If the limit is reached, the negative error code
           PCRE2_ERROR_HEAPLIMIT is returned. The default limit can be set
           when PCRE2 is built; if it is not, the default is set very large
           and is essentially unlimited.
    
           A value for the heap limit may also be supplied by an item at the
           start of a pattern of the form
    
             (*LIMIT_HEAP=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, if no such limit is set, less than the default.
    
           The **pcre2_match()** function always needs some heap memory, so
           setting a value of zero guarantees a "heap limit exceeded" error.
           Details of how **pcre2_match()** uses the heap are given in the
           **pcre2perform** documentation.
    
           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,
           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
           processed 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 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_**,**
             **uint32_t** _value_**);**
    
           This parameter limits the depth of nested backtracking in
           **pcre2_match()**.  Each time a nested backtracking point is passed, a
           new memory frame is used to remember the state of matching at that
           point. Thus, this parameter indirectly limits the amount of memory
           that is used in a match. However, because the size of each memory
           frame depends on the number of capturing parentheses, the actual
           memory limit varies from pattern to pattern. This limit was more
           useful in versions before 10.30, where function recursion was used
           for backtracking.
    
           The depth limit is not relevant, and is ignored, when matching is
           done 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 find the value of certain configuration parameters and to
           discover which optional features have been compiled into the PCRE2
           library. The **pcre2build** documentation has more details about these
           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_BADOPTION if the value in the first argument is
           not recognized. The following information is available:
    
             PCRE2_CONFIG_BSR
    
           The output is a uint32_t integer whose value indicates what
           character sequences the \R escape sequence matches by default. 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. The default can be overridden when a
           pattern is compiled.
    
             PCRE2_CONFIG_COMPILED_WIDTHS
    
           The output is a uint32_t integer whose lower bits indicate which
           code unit widths were selected when PCRE2 was built. The 1-bit
           indicates 8-bit support, and the 2-bit and 4-bit indicate 16-bit
           and 32-bit support, 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()**. Further 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 included in the library; otherwise it is
           set to zero. Note that having the support in the library does not
           guarantee that JIT will be used for any given match, and neither
           does it guarantee that JIT will actually be able to function,
           because it may not be able to allocate executable memory in some
           environments. There is a special call to **pcre2_jit_compile()** that
           can be used to check this. See the **pcre2jit** documentation for more
           details.
    
             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_CONFIG_NEWLINE
    
           The output is a uint32_t integer whose value specifies the default
           character sequence that is recognized as meaning "newline". The
           values are:
    
             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)
    
           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
           nesting of parentheses (of any kind) in a pattern. This limit is
           imposed to cap the amount of system stack used when a pattern is
           compiled. It is specified when 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
           output is a uint32_t integer that is always set to zero.
    
             PCRE2_CONFIG_TABLES_LENGTH
    
           The output is a uint32_t integer that gives the length of PCRE2's
           character processing tables in bytes. For details of these tables
           see the section on locale support below.
    
             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 terminating zero.
    


## COMPILING A PATTERN



    
           **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_code *pcre2_code_copy(const pcre2_code ***_code_**);**
    
           **pcre2_code *pcre2_code_copy_with_tables(const pcre2_code ***_code_**);**
    
           The **pcre2_compile()** function compiles a pattern into an internal
           form.  The pattern is defined by a pointer to a string of code
           units and a length in code units. If the pattern is zero-
           terminated, the length can be specified as PCRE2_ZERO_TERMINATED.
           A NULL pattern pointer with a length of zero is treated as an
           empty string (NULL with a non-zero length causes an error return).
           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
           compiled 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 matching, 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 compiled 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 automatically
           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
           pattern, the contents of the _options_ argument specifies their
           settings at the start of compilation. The PCRE2_ANCHORED,
           PCRE2_ENDANCHORED, and PCRE2_NO_UTF_CHECK options can be set at
           the time of matching as well as at compile time.
    
           Some additional options and less frequently required compile-time
           parameters (for example, the newline setting) can be provided in a
           compile context (as described above).
    
           If _errorcode_ or _erroroffset_ is NULL, **pcre2_compile()** returns NULL
           immediately. Otherwise, the variables to which these point are set
           to an error code and an offset (number of code units) within the
           pattern, respectively, when **pcre2_compile()** returns NULL because a
           compilation error has occurred.
    
           There are over 100 positive error codes that **pcre2_compile()** may
           return if it finds an error in the pattern. There are also some
           negative error codes that are used for invalid UTF strings when
           validity checking is in force. These are the same as given by
           **pcre2_match()** and **pcre2_dfa_match()** , and are described in the
           **pcre2unicode** documentation. 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**. When
           compilation is successful _errorcode_ is set to a value that returns
           the message "no error" if passed to **pcre2_get_error_message()**.
    
           The value returned in _erroroffset_ is an indication of where in the
           pattern an error occurred. When there is no error, zero is
           returned. A non-zero value 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 offset 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 character.
    
           This code fragment shows a typical straightforward call to
           **pcre2_compile()** :
    
             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
    
           By default, for compatibility with Perl, a closing square bracket
           that immediately follows an opening one is treated as a data
           character for the class. When PCRE2_ALLOW_EMPTY_CLASS is set, it
           terminates the class, which therefore contains no characters and
           so can never match.
    
             PCRE2_ALT_BSUX
    
           This option request alternative handling of three escape
           sequences, which makes PCRE2's behaviour more like ECMAscript (aka
           JavaScript). When it is set:
    
           (1) \U matches an upper case "U" character; by default \U causes a
           compile 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
           one or two digits.
    
           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 terminating newline, you must set
           PCRE2_ALT_CIRCUMFLEX.
    
             PCRE2_ALT_EXTENDED_CLASS
    
           Alters the parsing of character classes to follow the extended
           syntax described by Unicode UTS#18. The PCRE2_ALT_EXTENDED_CLASS
           option has no impact on the behaviour of the Perl-specific
           "(?[...])" syntax for extended classes, but instead enables the
           alternative syntax of extended class behaviour inside ordinary
           "[...]" character classes. See the **pcre2pattern** documentation for
           details of the character classes supported.
    
             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 white space 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
           immediately before or after an explicit callout in the pattern.
           For discussion 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 it can be changed within a pattern by a (?i) option
           setting. If either PCRE2_UTF or PCRE2_UCP is set, Unicode
           properties are used for all characters with more than one other
           case, and for all characters whose code points are greater than
           U+007F.
    
           Note that there are two ASCII characters, K and S, that, in
           addition to their lower case ASCII equivalents, are case-
           equivalent with U+212A (Kelvin sign) and U+017F (long S)
           respectively. If you do not want this case equivalence, you can
           suppress it by setting PCRE2_EXTRA_CASELESS_RESTRICT.
    
           One language family, Turkish and Azeri, has its own case-
           insensitivity rules, which can be selected by setting
           PCRE2_EXTRA_TURKISH_CASING. This alters the behaviour of the 'i',
           'I', U+0130 (capital I with dot above), and U+0131 (small dotless
           i) characters.
    
           For lower valued characters with only one other case, a lookup
           table is used for speed. When neither PCRE2_UTF nor PCRE2_UCP is
           set, a lookup table is used for all code points less than 256, and
           higher code points (available only in 16-bit or 32-bit mode) are
           treated as not having another case.
    
           From release 10.45 PCRE2_CASELESS also affects what some of the
           letter-related Unicode property escapes (\p and \P) match. The
           properties Lu (upper case letter), Ll (lower case letter), and Lt
           (title case letter) are all treated as LC (cased letter) when
           PCRE2_CASELESS is set.
    
             PCRE2_DOLLAR_ENDONLY
    
           If this bit is set, a dollar metacharacter in the pattern matches
           only at the end of the subject string. Without this option, a
           dollar also matches immediately before a newline at the end of the
           string (but not before any other newlines). The
           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 subject is at a newline. This option is equivalent
           to Perl's /s option, and it can be changed within a pattern by a
           (?s) option setting. A negative class such as [^a] always matches
           newline characters, 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. However, 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 obviously 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, inside a character class, or
           inside a \Q...\E sequence. However, white space is not allowed
           within sequences such as (?> that introduce various parenthesized
           groups, nor within numerical quantifiers such as {1,3}. Ignorable
           white space is permitted between an item and a following
           quantifier and between a quantifier and a following + that
           indicates possessiveness. PCRE2_EXTENDED is equivalent to Perl's
           /x option, and it can be changed within a pattern by a (?x) option
           setting.
    
           When PCRE2 is compiled without Unicode support, PCRE2_EXTENDED
           recognizes as white space only those characters with code points
           less than 256 that are flagged as white space in its low-character
           table. The table is normally created by **pcre2_maketables()** , which
           uses the **isspace()** 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
           characters, five more Unicode "Pattern White Space" characters are
           recognized 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
           characters 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
           setting 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 section 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 setting.
    
             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 newline. If _startoffset_ is non-zero, the
           limiting newline is not necessarily 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. This
           option has no effect for anchored patterns.
    
             PCRE2_LITERAL
    
           If this option is set, all meta-characters in the pattern are
           disabled, and it is treated as a literal string. Matching literal
           strings with a regular expression engine is not the most efficient
           way of doing it. If you are doing a lot of literal matching and
           are worried about efficiency, you should consider using other
           approaches. The only other main options that are allowed with
           PCRE2_LITERAL are: PCRE2_ANCHORED, PCRE2_ENDANCHORED,
           PCRE2_AUTO_CALLOUT, PCRE2_CASELESS, PCRE2_FIRSTLINE,
           PCRE2_MATCH_INVALID_UTF, PCRE2_NO_START_OPTIMIZE,
           PCRE2_NO_UTF_CHECK, PCRE2_UTF, and PCRE2_USE_OFFSET_LIMIT. The
           extra options PCRE2_EXTRA_MATCH_LINE and PCRE2_EXTRA_MATCH_WORD
           are also supported. Any other options cause an error.
    
             PCRE2_MATCH_INVALID_UTF
    
           This option forces PCRE2_UTF (see below) and also enables support
           for matching by **pcre2_match()** in subject strings that contain
           invalid UTF sequences.  Note, however, that the 16-bit and 32-bit
           PCRE2 libraries process strings as sequences of uint16_t or
           uint32_t code points. They cannot find valid UTF sequences within
           an arbitrary string of bytes unless such sequences are suitably
           aligned. This facility is not supported for DFA matching. For
           details, see the **pcre2unicode** documentation.
    
             PCRE2_MATCH_UNSET_BACKREF
    
           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_DOLLAR_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
           compiled.  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 PCRE2_UCP and PCRE2_NEVER_UCP
           causes an error.
    
             PCRE2_NEVER_UTF
    
           This option locks out interpretation of the pattern as UTF-8,
           UTF-16, or UTF-32, depending on which library is in use. In
           particular, it prevents the creator of the pattern from switching
           to UTF interpretation by starting the pattern with (*UTF). This
           option may be useful in applications that process patterns from
           external sources. The combination of PCRE2_UTF and PCRE2_NEVER_UTF
           causes an error.
    
             PCRE2_NO_AUTO_CAPTURE
    
           If this option is set, it disables the use of numbered capturing
           parentheses in the pattern. Any opening parenthesis that is not
           followed by ? behaves as if it were followed by ?: but named
           parentheses can still be used for capturing (and they acquire
           numbers in the usual way). This 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 (deprecated) 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.
    
           If a compile context is available, it is recommended to use
           **pcre2_set_optimize()** with the _directive_ PCRE2_AUTO_POSSESS_OFF
           rather than the compile option PCRE2_NO_AUTO_POSSESS. Note that
           PCRE2_NO_AUTO_POSSESS takes precedence over the
           **pcre2_set_optimize()** optimization directives PCRE2_AUTO_POSSESS
           and PCRE2_AUTO_POSSESS_OFF.
    
             PCRE2_NO_DOTSTAR_ANCHOR
    
           If this (deprecated) 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.  (If a
           compile context is available, it is recommended to use
           **pcre2_set_optimize()** with the _directive_ PCRE2_DOTSTAR_ANCHOR_OFF
           instead.)
    
             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. Setting this option is equivalent to
           calling **pcre2_set_optimize()** with the _directive_ parameter set to
           PCRE2_START_OPTIMIZE_OFF.
    
           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 immediately if it cannot find it, without actually
           running the main matching function. The start-up optimizations are
           in effect a pre-scan of the subject that takes place before the
           pattern is run.
    
           Disabling the start-up optimizations may cause performance to
           suffer. However, this may be desirable for patterns which contain
           callouts or items such as (*COMMIT) and (*MARK). See the above
           description of PCRE2_START_OPTIMIZE_OFF for further details.
    
             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
           **pcre2_dfa_match()** , to suppress UTF validity checking of the
           subject string.
    
           Note also that setting PCRE2_NO_UTF_CHECK at compile time does not
           disable the error that is given if an escape sequence for an
           invalid Unicode 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 possible only in UTF-8 and
           UTF-32 modes, because these values are not representable in
           UTF-16.
    
             PCRE2_UCP
    
           This option has two effects. Firstly, it change 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
           to classify characters. There are some PCRE2_EXTRA options (see
           below) that add finer control to this behaviour. More details are
           given in the section on generic character types in the
           **pcre2pattern** page.
    
           The second effect of PCRE2_UCP is to force the use of Unicode
           properties for upper/lower casing operations, even when PCRE2_UTF
           is not set. This makes it possible to process strings in the
           16-bit UCS-2 code. This option is available only if PCRE2 has been
           compiled with Unicode support (which is the default).
    
           The PCRE2_EXTRA_CASELESS_RESTRICT option (see above) restricts
           caseless matching such that ASCII characters match only ASCII
           characters and non-ASCII characters match only non-ASCII
           characters. The PCRE2_EXTRA_TURKISH_CASING option (see above)
           alters the matching of the 'i' characters to follow their
           behaviour in Turkish and Azeri languages. For further details on
           PCRE2_EXTRA_CASELESS_RESTRICT and PCRE2_EXTRA_TURKISH_CASING, see
           the **pcre2unicode** page.
    
             PCRE2_UNGREEDY
    
           This option inverts the "greediness" of the quantifiers so that
           they are not greedy by default, but become greedy if followed by
           "?". It is not compatible with Perl. It can also be set by a (?U)
           option setting within the pattern.
    
             PCRE2_USE_OFFSET_LIMIT
    
           This option must be set for **pcre2_compile()** if
           **pcre2_set_offset_limit()** is going to be used to set a non-default
           offset limit in a match context 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 works.
    
       **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_LOOKAROUND_BSK
    
           Since release 10.38 PCRE2 has forbidden the use of \K within
           lookaround assertions, following Perl's lead. This option is
           provided to re-enable the previous behaviour (act in positive
           lookarounds, ignore in negative ones) in case anybody is relying
           on it.
    
             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 validity.
    
           If the extra option PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES is set,
           surrogate 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 functionality 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 hexadecimal digits.
    
             PCRE2_EXTRA_ASCII_BSD
    
           This option forces \d to match only ASCII digits, even when
           PCRE2_UCP is set.  It can be changed within a pattern by means of
           the (?aD) option setting.
    
             PCRE2_EXTRA_ASCII_BSS
    
           This option forces \s to match only ASCII space characters, even
           when PCRE2_UCP is set. It can be changed within a pattern by means
           of the (?aS) option setting.
    
             PCRE2_EXTRA_ASCII_BSW
    
           This option forces \w to match only ASCII word characters, even
           when PCRE2_UCP is set. It can be changed within a pattern by means
           of the (?aW) option setting.
    
             PCRE2_EXTRA_ASCII_DIGIT
    
           This option forces the POSIX character classes [:digit:] and
           [:xdigit:] to match only ASCII digits, even when PCRE2_UCP is set.
           It can be changed within a pattern by means of the (?aT) option
           setting.
    
             PCRE2_EXTRA_ASCII_POSIX
    
           This option forces all the POSIX character classes, including
           [:digit:] and [:xdigit:], to match only ASCII characters, even
           when PCRE2_UCP is set. It can be changed within a pattern by means
           of the (?aP) option setting, but note that this also sets
           PCRE2_EXTRA_ASCII_DIGIT in order to ensure that (?-aP) unsets all
           ASCII restrictions for POSIX classes.
    
             PCRE2_EXTRA_BAD_ESCAPE_IS_LITERAL
    
           This is a dangerous option. Use with care. By default, an
           unrecognized escape such as \j or a malformed one such as \x{2z}
           causes a compile-time error when detected by **pcre2_compile()**. Perl
           is somewhat inconsistent in handling such items: for example, \j
           is treated as a literal "j", and non-hexadecimal digits in \x{}
           are just ignored, though warnings are given in both cases if
           Perl's warning switch is enabled. However, a malformed octal
           number after \o{ always causes an error in Perl.
    
           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 unexpected 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_CASELESS_RESTRICT
    
           When either PCRE2_UCP or PCRE2_UTF is set, caseless matching
           follows Unicode rules, which allow for more than two cases per
           character. There are two case-equivalent character sets that
           contain both ASCII and non-ASCII characters. The ASCII letter S is
           case-equivalent to U+017f (long S) and the ASCII letter K is case-
           equivalent to U+212a (Kelvin sign). This option disables
           recognition of case-equivalences that cross the ASCII/non-ASCII
           boundary. In a caseless match, both characters must either be
           ASCII or non-ASCII. The option can be changed within a pattern by
           the (*CASELESS_RESTRICT) or (?r) option settings.
    
             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 literal 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
           compiled 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.
    
             PCRE2_EXTRA_NO_BS0
    
           If this option is set (note that its final character is the digit
           0) it locks out the use of the sequence \0 unless at least one
           more octal digit follows.
    
             PCRE2_EXTRA_PYTHON_OCTAL
    
           If this option is set, PCRE2 follows Python's rules for
           interpreting octal escape sequences. The rules for handling
           sequences such as \14, which could be an octal number or a back
           reference are different. Details are given in the **pcre2pattern**
           documentation.
    
             PCRE2_EXTRA_NEVER_CALLOUT
    
           If this option is set, PCRE2 treats callouts in the pattern as a
           syntax error, returning PCRE2_ERROR_CALLOUT_CALLER_DISABLED. This
           is useful if the application knows that a callout will not be
           provided to **pcre2_match()** , so that callouts in the pattern are not
           silently ignored.
    
             PCRE2_EXTRA_TURKISH_CASING
    
           This option alters case-equivalence of the 'i' letters to follow
           the alphabet used by Turkish and Azeri languages. The option can
           be changed within a pattern by the (*TURKISH_CASING) start-of-
           pattern setting. Either the UTF or UCP options must be set. In the
           8-bit library, UTF must be set. This option cannot be combined
           with PCRE2_EXTRA_CASELESS_RESTRICT.
    


## 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(size_t** _startsize_**,**
             **size_t** _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_**);**
    
           These functions provide support for JIT compilation, which, if the
           just-in-time compiler is available, further processes a compiled
           pattern into machine code that executes much faster than the
           **pcre2_match()** interpretive matching function. Full details are
           given in the **pcre2jit** documentation.
    
           JIT compilation is a heavyweight optimization. It can take some
           time for patterns to be analyzed, and for one-off matches and
           simple patterns the benefit of faster execution might be offset by
           a much slower compilation time.  Most (but not all) patterns can
           be optimized by the JIT compiler.
    


## LOCALE SUPPORT



    
           **const uint8_t *pcre2_maketables(pcre2_general_context ***_gcontext_**);**
    
           **void pcre2_maketables_free(pcre2_general_context ***_gcontext_**,**
             **const uint8_t ***_tables_**);**
    
           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. However, 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.
    
           When PCRE2 is built with Unicode support (the default), certain
           Unicode character properties can be tested with \p and \P, or,
           alternatively, 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.  PCRE2_UCP also causes
           upper/lower casing operations on characters with code points
           greater than 127 to use Unicode properties. These effects apply
           even when PCRE2_UTF is not set. There are, however, some
           PCRE2_EXTRA options (see above) that can be used to modify or
           suppress them.
    
           The use of locales with Unicode is discouraged. If you are
           handling characters with code points greater than 127, you should
           either use Unicode support, or use locales, but not try to mix the
           two.
    
           PCRE2 contains a built-in 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 different.
    
           The built-in tables can be overridden by tables supplied by the
           application that calls PCRE2. These may be created in a different
           locale from the default.  As more and more applications change to
           using Unicode, the need for this locale support is expected to die
           away.
    
           External tables are built by calling the **pcre2_maketables()**
           function, in the relevant locale. The only argument to this
           function is a general context, which can be used to pass a custom
           memory allocator. If the argument is NULL, the system **malloc()** is
           used. 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
           127 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".
    
           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 the matching functions. Thus, for any single
           pattern, compilation and matching both happen in the same locale,
           but different patterns can be processed in different locales.
    
           It is the caller's responsibility to ensure that the memory
           containing the tables remains available while they are still in
           use. When they are no longer needed, you can discard them using
           **pcre2_maketables_free()** , which should pass as its first parameter
           the same global context that was used to create the tables.
    
       **Saving locale tables**
    
           The tables described above are just a sequence of binary bytes,
           which makes them independent of hardware characteristics such as
           endianness or whether the processor is 32-bit or 64-bit. A copy of
           the result of **pcre2_maketables()** can therefore be saved in a file
           or elsewhere and re-used later, even in a different program or on
           another computer. The size of the tables (number of bytes) must be
           obtained by calling **pcre2_config()** with the
           PCRE2_CONFIG_TABLES_LENGTH option because **pcre2_maketables()** does
           not return this value. Note that the **pcre2_dftables** program, which
           is part of the PCRE2 build system, can be used stand-alone to
           create a file that contains a set of binary tables. See the
           **pcre2build** documentation for details.
    


## INFORMATION ABOUT A COMPILED PATTERN



    
           **int pcre2_pattern_info(const pcre2 ***_code_**, uint32_t** _what_**, void ***_where_**);**
    
           The **pcre2_pattern_info()** function returns general information
           about a compiled pattern. For information about callouts, see the
           next section.  The first argument for **pcre2_pattern_info()** is a
           pointer to the compiled pattern. The second argument specifies
           which piece of information is required, and the third argument is
           a pointer to a variable to 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 numbers:
    
             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 a simple check against passing an arbitrary memory pointer.
           Here is a typical call of **pcre2_pattern_info()** , to obtain the
           length of the compiled 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_ALLOPTIONS 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() function.
    
           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_ALLOPTIONS, 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
    
           When .* is the first significant item, anchoring is possible only
           when all the following are true:
    
             .* is not in an atomic group
             .* is not in a capture group that is the subject
                  of a backreference
             PCRE2_DOTALL is in force for .*
             Neither (*PRUNE) nor (*SKIP) appears in the pattern
             PCRE2_NO_DOTSTAR_ANCHOR is not set
             Dotstar anchoring has not been disabled with
           PCRE2_DOTSTAR_ANCHOR_OFF
    
           For patterns that are auto-anchored, the PCRE2_ANCHORED bit is set
           in 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 a **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 a **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 matching 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 constructed, 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 a **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 of the subject
           or following a newline in the subject, 2 is returned. Otherwise,
           and for anchored patterns, 0 is returned.
    
             PCRE2_INFO_FIRSTCODEUNIT
    
           Return the value of the first code unit of any matched string for
           a pattern where PCRE2_INFO_FIRSTCODETYPE returns 1; otherwise
           return 0. The third argument should point to a **uint32_t** variable.
           In the 8-bit library, the value is always less than 256. In the
           16-bit library the value can be up to 0xffff. In the 32-bit
           library in UTF-32 mode the value can be up to 0x10ffff, and up to
           0xffffffff when not using UTF-32 mode.
    
             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 variables.
    
             PCRE2_INFO_HASBACKSLASHC
    
           Return 1 if the pattern contains any instances of \C, otherwise 0.
           The third argument should point to a **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 a
           **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 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 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 a
           **uint32_t** variable. (?J) and (?-J) set and unset the local
           PCRE2_DUPNAMES option, respectively.
    
             PCRE2_INFO_JITSIZE
    
           If the compiled pattern was successfully processed by
           **pcre2_jit_compile()** , 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 a **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 1 (with "z" returned from
           PCRE2_INFO_LASTCODEUNIT), but for /^a\dz\d/ the returned value is
           0.
    
             PCRE2_INFO_LASTCODEUNIT
    
           Return the value of the rightmost literal code unit that must
           exist in any matched string, other than at its start, for a
           pattern where PCRE2_INFO_LASTCODETYPE returns 1. Otherwise, return
           0. The third argument should point to a **uint32_t** variable.
    
             PCRE2_INFO_MATCHEMPTY
    
           Return 1 if the pattern might match an empty string, otherwise 0.
           The third argument should point to a **uint32_t** variable. When a
           pattern contains recursive subroutine calls it is not always
           possible to determine whether or not it can match an empty string.
           PCRE2 takes a cautious 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
           matching if it is less than the limit set or defaulted by the
           caller of the match function.
    
             PCRE2_INFO_MAXLOOKBEHIND
    
           A lookbehind assertion moves back a certain number of characters
           (not code units) when it starts to process each of its branches.
           This request returns the largest of these backward moves. The
           third argument should point to a uint32_t integer. The simple
           assertions \b and \B require a one-character lookbehind and cause
           PCRE2_INFO_MAXLOOKBEHIND to return 1 in the absence of anything
           longer. \A also registers a one-character lookbehind, though it
           does not actually inspect the previous character.
    
           Note that this information is useful for multi-segment matching
           only if the pattern contains no nested lookbehinds. For example,
           the pattern (?<=a(?<=ba)c) returns a maximum lookbehind of 2, but
           when it is processed, the first lookbehind moves back by two
           characters, matches one character, then the nested lookbehind also
           moves back by two characters. This puts the matching point three
           characters earlier than it was at the start.
           PCRE2_INFO_MAXLOOKBEHIND is really only useful as a debugging
           tool. See the **pcre2partial** documentation for a discussion of
           multi-segment matching.
    
             PCRE2_INFO_MINLENGTH
    
           If a minimum length for matching subject strings was computed, its
           value is returned. Otherwise the returned value is 0. This value
           is not computed when PCRE2_NO_START_OPTIMIZE is set. The value is
           a number of characters, which in UTF mode may be different from
           the number of code units. The third argument should point to a
           **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
           parentheses. The names are just an additional way of identifying
           the parentheses, which still acquire numbers. Several convenience
           functions such as **pcre2_substring_get_byname()** are provided for
           extracting captured substrings by name. It is also possible to
           extract the data directly, by first converting the name to a
           number in order to access the correct pointers in the output
           vector (described with **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_NAMECOUNT gives the number of entries, and
           PCRE2_INFO_NAMEENTRYSIZE gives the size of each entry in code
           units; both of these return a **uint32_t** value. The entry size
           depends on the length of the longest name.
    
           PCRE2_INFO_NAMETABLE returns a pointer to the first entry of the
           table. This is a PCRE2_SPTR pointer to a block of code units. In
           the 8-bit library, the first two bytes of each entry are the
           number of the capturing parenthesis, most significant byte first.
           In the 16-bit library, the pointer points to 16-bit code units,
           the first of which contains the parenthesis number. In the 32-bit
           library, the pointer points to 32-bit code units, the first of
           which contains the parenthesis number. The rest of the entry is
           the corresponding name, zero terminated.
    
           The names are in alphabetical order. If (?| is used to create
           multiple 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. Different names for groups of the same number are not
           permitted.
    
           Duplicate names for capture groups with different numbers are
           permitted, 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 numbers.
    
           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
           meaning "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 code units of the compiled pattern itself. The value
           that is used when **pcre2_compile()** is getting memory in which to
           place the compiled pattern may be slightly larger than the value
           returned by this option, because there are cases where the code
           that calculates the size has to over-estimate. Processing a
           pattern with the JIT compiler does not alter the value returned by
           this option.
    


## INFORMATION ABOUT A PATTERN'S CALLOUTS



    
           **int pcre2_callout_enumerate(const pcre2_code ***_code_**,**
             **int (***_callback_**)(pcre2_callout_enumerate_block *, void *),**
             **void ***_user_data_**);**
    
           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 enumeration
           block, and its second argument is the _user_data_ value that was
           passed to **pcre2_callout_enumerate()**. The contents of the callout
           enumeration 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 endianness, 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**
           documentation. Note that PCRE2 serialization does not convert
           compiled patterns 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
           parts of the subject. 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 functions above. For
           **pcre2_match_data_create()** , the first argument is the number of
           pairs of offsets in the _ovector_.
    
           When using **pcre2_match()** , 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.
    
           When using **pcre2_dfa_match()** there may be multiple matched
           substrings of different lengths at the same point in the subject.
           The ovector should be made large enough to hold as many as are
           expected.
    
           A minimum of at least 1 pair is imposed by
           **pcre2_match_data_create()** , so it is always possible to return the
           overall matched string in the case of **pcre2_match()** or the longest
           match in the case of **pcre2_dfa_match()**. The maximum number of
           pairs is 65535; if the first argument of **pcre2_match_data_create()**
           is greater than this, 65535 is used.
    
           The second argument of **pcre2_match_data_create()** is a pointer to a
           general context, which can specify custom memory management for
           obtaining the memory for the match data block. If you are not
           using custom memory management, pass NULL, which causes **malloc()**
           to be used.
    
           For **pcre2_match_data_create_from_pattern()** , the first argument is
           a pointer to a compiled pattern. The ovector is created to be
           exactly the right size to hold all the substrings a pattern might
           capture when matched using **pcre2_match()**. You should not use this
           call when matching with **pcre2_dfa_match()**. The second argument is
           again a pointer to a general context, but in this case if NULL is
           passed, the memory is obtained using the same allocator that was
           used for the compiled pattern (custom or default).
    
           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.
    


## MEMORY USE FOR MATCH DATA BLOCKS



    
           **PCRE2_SIZE pcre2_get_match_data_size(pcre2_match_data ***_match_data_**);**
    
           **PCRE2_SIZE pcre2_get_match_data_heapframes_size(**
             **pcre2_match_data ***_match_data_**);**
    
           The size of a match data block depends on the size of the ovector
           that it contains. The function **pcre2_get_match_data_size()** returns
           the size, in bytes, of the block that is its argument.
    
           When **pcre2_match()** runs interpretively (that is, without using
           JIT), it makes use of a vector of data frames for remembering
           backtracking positions.  The size of each individual frame depends
           on the number of capturing parentheses in the pattern and can be
           obtained by calling **pcre2_pattern_info()** with the
           PCRE2_INFO_FRAMESIZE option (see the section entitled "Information
           about a compiled pattern" above).
    
           Heap memory is used for the frames vector; if the initial memory
           block turns out to be too small during matching, it is
           automatically expanded. When **pcre2_match()** returns, the memory is
           not freed, but remains attached to the match data block, for use
           by any subsequent matches that use the same block. It is
           automatically freed when the match data block itself is freed.
    
           You can find the current size of the frames vector that a match
           data block owns by calling **pcre2_get_match_data_heapframes_size()**.
           For a newly created match data block the size will be zero. Some
           types of match may require a lot of frames and thus a large
           vector; applications that run in environments where memory is
           constrained can check this and free the match data block if the
           heap frames vector has become too big.
    


## 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 different subject strings with the same
           pattern.
    
           This function is the main matching facility of the library, and it
           operates in a Perl-like manner. For specialist use there is also
           an alternative matching function, which is described below in the
           section about the **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 */
               md,             /* the match data block */
               NULL);          /* a match context; NULL means use defaults */
    
           If the subject string is zero-terminated, the length can be given
           as PCRE2_ZERO_TERMINATED. A match context must be provided if
           certain less common matching parameters are to be changed. For
           details, see the section on the match context above.
    
       **The string to be matched by pcre2_match()**
    
           The subject string is passed to **pcre2_match()** as a pointer in
           _subject_ , a length in _length_ , and a starting offset in _startoffset_.
           The length 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 processing is enabled. As a special case, if
           _subject_ is NULL and _length_ is zero, the subject is assumed to be
           an empty string. If _length_ is non-zero, an error occurs if _subject_
           is NULL.
    
           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 offset must point to the start of a
           character, or to the end of the subject (in UTF-32 mode, one code
           unit equals one character, so all offsets 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 "Mississippi" the first call
           to **pcre2_match()** finds the first occurrence. If **pcre2_match()** is
           called again with just the remainder of the subject, namely
           "issippi", 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 occurrence of "iss"
           because it is able to look behind the starting point to discover
           that it is preceded by a letter.
    
           Finding all the matches in a subject is tricky when the pattern
           can match an empty string. PCRE2 includes a helper API to assist
           with this; see the section entitled "Iterating over all matches"
           below for details.
    
           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 succeed 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 setting 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. The only bits that may be set are PCRE2_ANCHORED,
           PCRE2_COPY_MATCHED_SUBJECT, PCRE2_DISABLE_RECURSELOOP_CHECK,
           PCRE2_ENDANCHORED, PCRE2_NOTBOL, PCRE2_NOTEOL, PCRE2_NOTEMPTY,
           PCRE2_NOTEMPTY_ATSTART, PCRE2_NO_JIT, PCRE2_NO_UTF_CHECK,
           PCRE2_PARTIAL_HARD, and PCRE2_PARTIAL_SOFT.  Their action is
           described below.
    
           Setting PCRE2_ANCHORED or PCRE2_ENDANCHORED at match time is not
           supported by the just-in-time (JIT) compiler. If it is set, JIT
           matching is disabled and the interpretive code in **pcre2_match()** is
           run.  PCRE2_DISABLE_RECURSELOOP_CHECK is ignored by JIT, but apart
           from PCRE2_NO_JIT (obviously), the remaining options are supported
           for JIT matching.
    
             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 unanchored 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 guaranteed, 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 successful 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_DISABLE_RECURSELOOP_CHECK
    
           This option is relevant only to **pcre2_match()** for interpretive
           matching.  It is ignored when JIT is used, and is forbidden for
           **pcre2_dfa_match()**.
    
           The use of recursion in patterns can lead to infinite loops. In
           the interpretive matcher these would be eventually caught by the
           match or heap limits, but this could take a long time and/or use a
           lot of memory if the limits are large. There is therefore a check
           at the start of each recursion.  If the same group is still active
           from a previous call, and the current subject pointer is the same
           as it was at the start of that group, and the furthest inspected
           character of the subject has not changed, an error is generated.
    
           There are rare cases of matches that would complete, but
           nevertheless trigger this error. This option disables the check.
           It is provided mainly for testing when comparing JIT and
           interpretive behaviour.
    
             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 setting 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 without having set PCRE2_MULTILINE at compile time
           causes dollar never to match. This option affects only the
           behaviour of the dollar metacharacter. It does not affect \Z or
           \z.
    
             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
    
             a?b?
    
           is applied to a string not beginning with "a" or "b", it matches
           an empty string at the start of the subject. With PCRE2_NOTEMPTY
           set, this match is not valid, so **pcre2_match()** searches further
           into the string for occurrences of "a" or "b".
    
             PCRE2_NOTEMPTY_ATSTART
    
           This is like PCRE2_NOTEMPTY, except that it locks out an empty
           string match only at the first matching position, that is, at the
           start of the 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 unless PCRE2_NO_UTF_CHECK is passed to
           **pcre2_match()** or PCRE2_MATCH_INVALID_UTF was passed to
           **pcre2_compile()**. The latter special case is discussed in detail in
           the **pcre2unicode** documentation.
    
           In the default case, if a non-zero starting offset is given, the
           check is applied only to that part of the subject that could be
           inspected during matching, 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** documentation.
    
           If you know that your subject is valid, and you want to skip this
           check 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 multiple matches in the same subject
           string.
    
           **Warning:** Unless PCRE2_MATCH_INVALID_UTF was set at compile time,
           when PCRE2_NO_UTF_CHECK is set at match time 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 or give wrong results.
    
             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. In addition, either at least one character
           must have been inspected or the pattern must contain a lookbehind,
           or the pattern must be one that could match an empty string.
    
           If this situation arises 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 complete match
           can be found.
    
           If PCRE2_PARTIAL_HARD is set, it overrides PCRE2_PARTIAL_SOFT. In
           this case, if a partial match is found, **pcre2_match()** immediately
           returns PCRE2_ERROR_PARTIAL, without considering any other
           alternatives. In other words, when PCRE2_PARTIAL_HARD is set, a
           partial match is considered to be more important than an
           alternative complete match.
    
           There is a more detailed discussion of partial and multi-segment
           matching, with examples, in the **pcre2partial** documentation.
    


## NEWLINE HANDLING WHEN MATCHING



    
           When PCRE2 is built, a default newline convention is set; this is
           usually 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 behaviour 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 contains an explicit CR or LF
           reference, and so advances only by one character after the first
           failure.
    
           An explicit match for CR of LF is either a literal appearance of
           one of those characters 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 characters that it matches.
    
           Notwithstanding the above, anomalous effects may still occur when
           CRLF is a valid newline sequence and explicit \r or \n escapes
           appear in the pattern.
    


## 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.
    
           Alternatively, you can make direct use of the vector of PCRE2_SIZE
           values, called the **ovector** , which contains the offsets of captured
           strings. It is part of the match data block.  The function
           **pcre2_get_ovector_pointer()** returns the address of the ovector,
           and **pcre2_get_ovector_count()** returns the number of pairs of
           values it contains.
    
           Within the ovector, the first in each pair of values is set to the
           offset of the first code unit of a substring, and the second is
           set to the offset of the first code unit after the end of a
           substring. These values are always code unit offsets, not
           character offsets. That is, they are byte offsets in the 8-bit
           library, 16-bit offsets in the 16-bit 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 pattern. 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 substrings, 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
           lookahead 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
           operation, 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 the second
           and third capture groups (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_ capturing parentheses, no more than _ovector[0]_
           to _ovector[2n+1]_ are set by **pcre2_match()**. The other elements
           retain whatever values they previously had. After a failed match
           attempt, the contents of the ovector are unchanged.
    


## OTHER INFORMATION ABOUT A MATCH



    
           **PCRE2_SPTR pcre2_get_mark(pcre2_match_data ***_match_data_**);**
    
           **PCRE2_SIZE pcre2_get_startchar(pcre2_match_data ***_match_data_**);**
    
           As well as the offsets in the ovector, other information about a
           match is retained in the match data block and can be retrieved by
           the above functions in appropriate circumstances. If they are
           called at other times, the result is undefined.
    
           After a successful match, a partial match (PCRE2_ERROR_PARTIAL),
           or a failure to match (PCRE2_ERROR_NOMATCH), a mark name may be
           available. 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 compiled 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 seeing any marks. You can disable the start-
           of-match optimizations by setting 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
           converted to a text string by calling the
           **pcre2_get_error_message()** function (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 the
           **pcre2unicode** page. The following are the other errors that may be
           returned by **pcre2_match()** :
    
             PCRE2_ERROR_NOMATCH
    
           The subject string did not match the pattern.
    
             PCRE2_ERROR_PARTIAL
    
           The subject string did not match, but it did match partially. See
           the **pcre2partial** documentation for details of partial matching.
    
             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 compiled 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** documentation for more details.
    
             PCRE2_ERROR_MATCHLIMIT
    
           The backtracking match limit was reached.
    
             PCRE2_ERROR_NOMEMORY
    
           Heap memory is used to remember backtracking points. This error is
           given when the memory allocation function (default or custom)
           fails. Note that a different error, PCRE2_ERROR_HEAPLIMIT, is
           given if the amount of memory needed exceeds the heap limit.
           PCRE2_ERROR_NOMEMORY is also returned if
           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
           pattern 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 complicated 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_message()**. 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
           function 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 message is truncated (but still with a trailing zero), and the
           negative error code PCRE2_ERROR_NOMEMORY is returned.  None of the
           messages is very long; a buffer size of 120 code units is ample.
    


## ITERATING OVER ALL MATCHES



    
           **int pcre2_next_match(pcre2_match_data ***_match_data_**,**
             **PCRE2_SIZE ***_pstart_offset_**, uint32_t ***_poptions_**);**
    
           A common task for applications is to implement "global" matching
           behaviour, for example, replacing all matches in the subject;
           splitting the subject on all matches; or simply counting the
           number of matches. The **pcre2_next_match()** function helps with this
           task by providing the appropriate parameters for the next match
           attempt (available since PCRE2 10.46).
    
           First, a match attempt should be made using one of the matching
           functions (**pcre2_match()** , **pcre2_dfa_match()** , or
           **pcre2_jit_match()**).  Then, **pcre2_next_match()** can be called,
           providing the same _match_data_ parameter.
    
           It returns 0 ("false") if there is no need to make a further match
           attempt, or 1 ("true") if another match should be attempted.
           Returning 1 does not imply that there is another match, only that
           another match should be attempted (which may return
           PCRE2_ERROR_NOMATCH).
    
           The *_pstart_offset_ and *_poptions_ are set if the function returns
           1.  The *_pstart_offset_ should be passed to the next match attempt
           directly, and the *_poptions_ should be passed to the next match
           attempt by combining with the application's match options using
           OR.
    
           There is some code that demonstrates how to do this in the
           **pcre2demo** sample program. The general pattern is:
    
             uint32_t app_options = ...;
             uint32_t global_options = 0;
             PCRE2_SIZE start_offset = 0;
             while (1)
               {
               int rc = pcre2_match(re, subject, subject_len, start_offset,
                                    app_options | global_options, match_data,
                                    match_context);
    
               if (rc == PCRE2_ERROR_NOMATCH) break; /* no match, and no more attempts */
               if (rc < 0) { ... exit }
    
               ...handle the match
    
               if (!pcre2_next_match(match_data, &start_offset, &global_options))
                 break; /* no more attempts */
               }
    
           The guarantees provided by **pcre2_next_match()** are that the
           start_offset will advance, so the loop will definitely terminate.
           The conditions which ensure this are that either: (a)
           pcre2_next_match() returns 0 (false); or (b) the returned
           *_pstart_offset_ is strictly greater than the previous start_offset;
           or (c) if the previous match was a successful match of the empty
           string then the returned *_pstart_offset_ is equal to the previous
           ovector[1], and *_poptions_ will be set to PCRE2_NOTEMPTY_ATSTART to
           prevent another empty match from being returned.
    
           A loop implemented as shown above will always terminate, unless
           there is a bug in PCRE2. As a measure of "defensive programming",
           applications are encouraged to add an assertion or check to break
           their loop if it does not make progress (and report the issue as a
           bug).
    
           If an application does not use the flag
           PCRE2_EXTRA_ALLOW_LOOKAROUND_BSK, then each match is "well-
           behaved" and satisfies:
    
             start_offset <= ovector[0] <= ovector[1].
    
           In this case, the matches found by pcre2_match() with
           pcre2_next_match() will be sorted, non-overlapping (possibly
           touching), and with no duplicates.
    
           Otherwise, if PCRE2_EXTRA_ALLOW_LOOKAROUND_BSK is used, then the
           guarantees are considerably weaker. We do not guarantee that the
           matches will always advance: only that the start_offset will. The
           matches found by pcre2_match() with pcre2_next_match() will be a
           finite sequence (as pcre2_next_match() ensures that start_offset
           advances, so the search will terminate). The matches can however
           be overlapping, can contain duplicates, and (in truly pathological
           examples) may not even be sorted by ovector[0]. Additionally, each
           match itself can end before it starts (ovector[1] < ovector[0]).
           We recommend that applications do not set
           PCRE2_EXTRA_ALLOW_LOOKAROUND_BSK.
    


## 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 extracting captured substrings as new, separate,
           zero-terminated strings. A substring that contains a binary zero
           is correctly extracted and has a further zero added on the end,
           but the result is not, of course, a C string.
    
           The functions in this section identify substrings by number. The
           number zero refers to the entire matched substring, with higher
           numbers referring to substrings captured by parenthesized groups.
           After a partial match, only substring zero is available. An
           attempt to extract any other substring gives the error
           PCRE2_ERROR_PARTIAL. The next section describes similar functions
           for extracting captured substrings by name.
    
           If a pattern uses the \K escape sequence within a positive
           lookahead 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
           substring 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 arguments 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.
    
             PCRE2_ERROR_UNSET
    
           The substring did not participate in the match. For example, if
           the pattern is (abc)|(def) and the subject is "def", and the
           ovector contains at least two capturing slots, substring number 1
           is unset.
    


## EXTRACTING A LIST OF ALL CAPTURED SUBSTRINGS



    
           **int pcre2_substring_list_get(pcre2_match_data ***_match_data_**,**
             **PCRE2_UCHAR *****_listptr_**, PCRE2_SIZE ****_lengthsptr_**);**
    
           **void pcre2_substring_list_free(PCRE2_UCHAR ****_list_**);**
    
           The **pcre2_substring_list_get()** function extracts all available
           substrings 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** argument 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 memory 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
           number.  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 argument 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
           no group with that name, or PCRE2_ERROR_NOUNIQUESUBSTRING if there
           is more than one group with that name.  Given the number, you can
           extract the substring directly from the ovector, or use one of the
           "bynumber" functions described above.
    
           For convenience, there are also "byname" functions that correspond
           to the "bynumber" functions, the only difference being that the
           second argument is a name instead of a number. If PCRE2_DUPNAMES
           is set and there are duplicate names, these functions scan all the
           groups with the given name, and return the captured substring from
           the first named group that is set.
    
           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 distinguish 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 optionally calls **pcre2_match()** and then makes a copy
           of the subject string in _outputbuffer_ , replacing parts that were
           matched with the _replacement_ string, whose length is supplied in
           **rlength** , which can be given as PCRE2_ZERO_TERMINATED for a zero-
           terminated string. As a special case, if _replacement_ is NULL and
           _rlength_ is zero, the replacement is assumed to be an empty string.
           If _rlength_ is non-zero, an error occurs if _replacement_ is NULL.
    
           There is an option (see PCRE2_SUBSTITUTE_REPLACEMENT_ONLY below)
           to return just the replacement string(s). The default action is to
           perform just one replacement if the pattern matches, but there is
           an option that requests multiple replacements (see
           PCRE2_SUBSTITUTE_GLOBAL below).
    
           If successful, **pcre2_substitute()** returns the number of
           substitutions that were carried out. This may be zero if no match
           was found, and is never greater than one unless
           PCRE2_SUBSTITUTE_GLOBAL is set. A negative value is returned if an
           error is detected.
    
           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 lookbehind causes the match to start earlier than the point
           that was reached in the previous iteration are also not supported.
           (These cases are only possible if the pattern was compiled with
           the backwards-compatibility option
           PCRE2_EXTRA_ALLOW_LOOKAROUND_BSK.)
    
           The first seven arguments of **pcre2_substitute()** are the same as
           for **pcre2_match()** , except that the partial matching options are
           not permitted, and _match_data_ may be passed as NULL, in which case
           a match data block is obtained and freed within this function,
           using memory management functions from the match context, if
           provided, or else those that were used to allocate memory for the
           compiled code.
    
           If _match_data_ is not NULL and PCRE2_SUBSTITUTE_MATCHED is not set,
           the provided block is used for all calls to **pcre2_match()** , and its
           contents afterwards are the result of the final call. For global
           changes, this will always be a no-match error. The contents of the
           ovector within the match data block may or may not have been
           changed.
    
           As well as the usual options for **pcre2_match()** , a number of
           additional options can be set in the _options_ argument of
           **pcre2_substitute()**.  One such option is PCRE2_SUBSTITUTE_MATCHED.
           When this is set, an external _match_data_ block must be provided,
           and it must have already been used for an external call to
           **pcre2_match()** with the same pattern and subject arguments. The
           data in the _match_data_ block (return code, offset vector) is then
           used for the first substitution instead of calling **pcre2_match()**
           from within **pcre2_substitute()**. This allows an application to
           check for a match before choosing to substitute, without having to
           repeat the match.
    
           The contents of the externally supplied match data block are not
           changed when PCRE2_SUBSTITUTE_MATCHED is set. If
           PCRE2_SUBSTITUTE_GLOBAL is also set, **pcre2_match()** is called after
           the first substitution to check for further matches, but this is
           done using an internally obtained match data block, thus always
           leaving the external block unchanged.
    
           The _code_ argument is not used for matching before the first
           substitution when PCRE2_SUBSTITUTE_MATCHED is set, but it must be
           provided, even when PCRE2_SUBSTITUTE_GLOBAL is not set, because it
           contains information such as the UTF setting and the number of
           capturing parentheses in the pattern.
    
           The default action of **pcre2_substitute()** is to return a copy of
           the subject string with matched substrings replaced. However, if
           PCRE2_SUBSTITUTE_REPLACEMENT_ONLY is set, only the replacement
           substrings are returned. In the global case, multiple replacements
           are concatenated in the output buffer. Substitution callouts (see
           below) can be used to separate them if necessary.
    
           The _outlengthptr_ argument of **pcre2_substitute()** must point to a
           variable that contains the length, in code units, of the output
           buffer. If the function is successful, the value is updated to
           contain the length in code units of the new string, excluding the
           trailing zero that is automatically added.
    
           If the function is not successful, the value set via _outlengthptr_
           depends on the type of error. For syntax errors in the replacement
           string, the value is the offset in the replacement string where
           the error was detected. For other errors, the value is PCRE2_UNSET
           by default. This includes the case of the output buffer being too
           small, unless PCRE2_SUBSTITUTE_OVERFLOW_LENGTH is set.
    
           PCRE2_SUBSTITUTE_OVERFLOW_LENGTH changes what happens when the
           output buffer is too small. The default action is to return
           PCRE2_ERROR_NOMEMORY immediately. If this option is set, however,
           **pcre2_substitute()** continues to go through the motions of matching
           and substituting (without, of course, writing anything) in order
           to compute the size of buffer that is needed, which will include
           the extra space for the terminating NUL. This value is passed back
           via the _outlengthptr_ variable, with the result of the function
           still being PCRE2_ERROR_NOMEMORY.
    
           Passing a buffer size of zero is a permitted way of finding out
           how much memory is needed for given substitution. However, this
           does mean that the entire operation is carried out twice.
           Depending on the application, it may be more efficient to allocate
           a large buffer and free the excess afterwards, instead of using
           PCRE2_SUBSTITUTE_OVERFLOW_LENGTH.
    
           The replacement string, which is interpreted as a UTF string in
           UTF mode, is checked for UTF validity unless PCRE2_NO_UTF_CHECK is
           set. An invalid UTF replacement string causes an immediate return
           with the relevant UTF error code.
    
           If PCRE2_SUBSTITUTE_LITERAL is set, the replacement string is not
           interpreted in any way. By default, however, a dollar character is
           an escape character that can specify the insertion of characters
           from capture groups and names from (*MARK) or other control verbs
           in the pattern. Dollar is the only escape character (backslash is
           treated as literal). The following forms are recognized:
    
             $$                  insert a dollar character
             $n or ${n}          insert the contents of group _n_
             $0 or $&            insert the entire matched substring
             $`                  insert the substring that precedes the match
             $'                  insert the substring that follows the match
             $_                  insert the entire input string
             $*MARK or ${*MARK}  insert a control verb name
    
           Either a group number or a group name can be given for _n_ , for
           example $2 or $NAME. Curly brackets are required only if the
           following character would be interpreted 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+=".
    
           The JavaScript form $<name>, where the angle brackets are part of
           the syntax, is also recognized for group names, but not for group
           numbers or *MARK.
    
           $*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
    
           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 replacements 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, searching stops when that limit
           is reached.
    
           Because global substitutions apply the pattern repeatedly to the
           subject string, and always iterate over non-overlapping matches,
           the substitutions done by **pcre2_substitute()** do not match and
           substitute text inside the replacement strings themselves (no
           recursive/iterative substitution). However, applications can
           easily implement other alternative replacement strategies, such as
           iteratively replacing, then matching and replacing on the result.
           The replacement loop inside **pcre2_substitute()** is simple and can
           be emulated in client code by allocating a buffer, searching for
           matches in a loop, and calling **pcre2_substitute()** with
           PCRE2_SUBSTITUTE_REPLACEMENT_ONLY an PCRE2_SUBSTITUTE_MATCHED, and
           without PCRE2_SUBSTITUTE_GLOBAL.
    
           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 offset 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 offset 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 characters.
    
           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, several
           things change:
    
           Firstly, backslash in a replacement string is interpreted as an
           escape character. The usual forms such as \x{ddd} can be used to
           specify particular character codes, and backslash followed by any
           non-alphanumeric character quotes that character. Extended quoting
           can be coded using \Q...\E, exactly as in pattern strings. The
           escapes \b and \v are interpreted as the characters backspace and
           vertical tab, respectively.
    
           The interpretation of backslash followed by one or more digits is
           the same as in a pattern, which in Perl has some ambiguities.
           Details are given in the **pcre2pattern** page.
    
           The Python form \g<n>, where the angle brackets are part of the
           syntax and _n_ is either a group name or number, is recognized as an
           alternative way of inserting the contents of a group, for example
           \g<3>.
    
           There are also four escape sequences for forcing the case of
           inserted letters.  Case forcing applies to all inserted
           characters, including those from capture groups and letters within
           \Q...\E quoted sequences. 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, respectively, 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.
    
           However, if \u is immediately followed by \L or \l is immediately
           followed by \U, the next character's case is forced by the first
           escape sequence, and subsequent characters by the second. This
           provides a "title casing" facility that can be applied to group
           captures. For example, if group 1 has captured "heLLo", the
           replacement string "\u\L$1" becomes "Hello".
    
           If either PCRE2_UTF or PCRE2_UCP was set when the pattern was
           compiled, Unicode properties are used for case forcing characters
           whose code points are greater than 127. However, only simple case
           folding, as determined by the Unicode file **CaseFolding.txt** is
           supported. PCRE2 does not support language-specific special casing
           rules such as using different lower case Greek sigmas in the
           middle and ends of words (as defined in the Unicode file
           **SpecialCasing.txt**).
    
           Note that case forcing sequences such as \U...\E do not nest. For
           example, 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 replacement strings.
    
           The final 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 in the simple case, _n_ may be a group number or a name. The
           first form specifies a default value. If group _n_ is set, its value
           is inserted; if not, the string is expanded and the result
           inserted. The second form specifies strings that are expanded and
           inserted when group _n_ is set or unset, respectively. The first
           form is just a convenient shorthand for
    
             ${n:+${n}:string}
    
           Backslash can be used to escape colons and closing curly brackets
           in the replacement strings. A change of the case forcing state
           within a replacement string remains in force afterwards, as shown
           in this **pcre2test** example:
    
             /(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 PCRE2_SUBSTITUTE_LITERAL is set,
           PCRE2_SUBSTITUTE_UNKNOWN_UNSET, PCRE2_SUBSTITUTE_UNSET_EMPTY, and
           PCRE2_SUBSTITUTE_EXTENDED are irrelevant and are ignored.
    
       **Substitution errors**
    
           In the event of an error, **pcre2_substitute()** returns a negative
           error code. 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
           insertion, unless PCRE2_SUBSTITUTE_UNKNOWN_UNSET is set.
    
           PCRE2_ERROR_UNSET is returned for an unset substring insertion
           (including an unknown substring when
           PCRE2_SUBSTITUTE_UNKNOWN_UNSET is set) when the simple (non-
           extended) syntax is used and PCRE2_SUBSTITUTE_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_NULL is returned if PCRE2_SUBSTITUTE_MATCHED is set
           but the _match_data_ argument is NULL or if the _subject_ or
           _replacement_ arguments are NULL. For backward compatibility reasons
           an exception is made for the _replacement_ argument if the _rlength_
           argument is also 0.
    
           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_REPMISSINGBRACE (closing curly bracket not found),
           PCRE2_ERROR_BADSUBSTITUTION (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
           a lookaround 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_substitute_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 has been processed, but it can cause the
           replacement not to happen.
    
           The callout function is not called for simulated substitutions
           that happen as a result of the PCRE2_SUBSTITUTE_OVERFLOW_LENGTH
           option. In this mode, when substitution processing exceeds the
           buffer space provided by the caller, processing continues by
           counting code units. The simulation is unable to populate the
           callout block, and so the simulation is pessimistic about the
           required buffer size. Whichever is larger of accepted or rejected
           substitution is reported as the required size. Therefore, the
           returned buffer length may be an overestimate (without a
           substitution callout, it is normally an exact measurement).
    
           The first argument of the callout function is a pointer to a
           substitute callout block structure, which contains the following
           fields, not necessarily in this order:
    
             uint32_t    _version_ ;
             uint32_t    _subscount_ ;
             PCRE2_SPTR  _input_ ;
             PCRE2_SPTR  _output_ ;
             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_ pointers 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_SUBSTITUTE_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 rest of the input is copied to the output and the
           call to **pcre2_substitute()** exits, returning the number of matches
           so far.
    
       **Substitution case callouts**
    
           **int pcre2_set_substitute_case_callout(pcre2_match_context ***_mcontext_**,**
             **PCRE2_SIZE (***_callout_function_**)(PCRE2_SPTR, PCRE2_SIZE,**
                                            **PCRE2_UCHAR *, PCRE2_SIZE,**
                                            **int, void *),**
             **void ***_callout_data_**);**
    
           The **pcre2_set_substitute_case_callout()** function can be used to
           specify a callout function for **pcre2_substitute()** to use when
           performing case transformations. This does not affect any case
           insensitivity behaviour when performing a match, but only the
           user-visible transformations performed when processing a
           substitution such as:
    
               pcre2_substitute(..., "\\U$1", ...)
    
           The default case transformations applied by PCRE2 are reasonably
           complete, and, in UTF or UCP mode, perform the simple locale-
           invariant case transformations as specified by Unicode. This is
           suitable for the internal (invisible) case-equivalence procedures
           used during pattern matching, but an application may wish to use
           more sophisticated locale-aware processing for the user-visible
           substitution transformations.
    
           One example implementation of the _callout_function_ using the ICU
           library would be:
    
               PCRE2_SIZE
               icu_case_callout(
                 PCRE2_SPTR input, PCRE2_SIZE input_len,
                 PCRE2_UCHAR *output, PCRE2_SIZE output_cap,
                 int to_case, void *data_ptr)
               {
                 UErrorCode err = U_ZERO_ERROR;
                 int32_t r = to_case == PCRE2_SUBSTITUTE_CASE_LOWER
                   ? u_strToLower(output, output_cap, input, input_len, NULL, &err)
                   : to_case == PCRE2_SUBSTITUTE_CASE_UPPER
                   ? u_strToUpper(output, output_cap, input, input_len, NULL, &err)
                   : u_strToTitle(output, output_cap, input, input_len, &first_char_only,
                                  NULL, &err);
                 if (U_FAILURE(err)) return (~(PCRE2_SIZE)0);
                 return r;
               }
    
           The first and second arguments of the case callout function are
           the Unicode string to transform.
    
           The third and fourth arguments are the output buffer and its
           capacity.
    
           The fifth is one of the constants PCRE2_SUBSTITUTE_CASE_LOWER,
           PCRE2_SUBSTITUTE_CASE_UPPER, or PCRE2_SUBSTITUTE_CASE_TITLE_FIRST.
           PCRE2_SUBSTITUTE_CASE_LOWER and PCRE2_SUBSTITUTE_CASE_UPPER are
           passed to the callout to indicate that the case of the entire
           callout input should be case-transformed.
           PCRE2_SUBSTITUTE_CASE_TITLE_FIRST is passed to indicate that only
           the first character or glyph should be transformed to Unicode
           titlecase and the rest to Unicode lowercase (note that titlecasing
           sometimes uses Unicode properties to titlecase each word in a
           string; but PCRE2 is requesting that only the single leading
           character is to be titlecased).
    
           The sixth argument is the _callout_data_ supplied to
           **pcre2_set_substitute_case_callout()**.
    
           The resulting string in the destination buffer may be larger or
           smaller than the input, if the casing rules merge or split
           characters. The return value is the length required for the output
           string. If a buffer of sufficient size was provided to the
           callout, then the result must be written to the buffer and the
           number of code units returned. If the result does not fit in the
           provided buffer, then the required capacity must be returned and
           PCRE2 will not make use of the output buffer. PCRE2 provides input
           and output buffers which overlap, so the callout must support this
           by suitable internal buffering.
    
           Alternatively, if the callout wishes to indicate an error, then it
           may return (~(PCRE2_SIZE)0). In this case pcre2_substitute() will
           immediately fail with error PCRE2_ERROR_REPLACECASE.
    
           When a case callout is combined with the
           PCRE2_SUBSTITUTE_OVERFLOW_LENGTH option, there are situations when
           pcre2_substitute() will return an underestimate of the required
           buffer size. If you call pcre2_substitute() once with
           PCRE2_SUBSTITUTE_OVERFLOW_LENGTH, and the input buffer is too
           small for the replacement string to be constructed, then instead
           of calling the case callout, pcre2_substitute() will make an
           estimate of the required buffer size.  The second call should also
           pass PCRE2_SUBSTITUTE_OVERFLOW_LENGTH, because that second call is
           not guaranteed to succeed either, if the case callout requires
           more buffer space than expected. The caller must make repeated
           attempts in a loop.
    


## 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 duplicate names.
    
           If you want to get full details of all captured substrings for a
           given name, you must use the **pcre2_substring_nametable_scan()**
           function. The first argument is the compiled pattern, and the
           second is the name. If the third and fourth arguments are NULL,
           the function returns a group number for a unique name, or
           PCRE2_ERROR_NOUNIQUESUBSTRING otherwise.
    
           When the third and fourth arguments are not NULL, they must be
           pointers to variables that are updated by the function. After it
           has run, they point to the first and last entries in the name-to-
           number table for the given name, and the function returns the
           length of each entry in code 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 subject. 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 function, 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
           pattern.  When your callout function is called, extract and save
           the current 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 (except when processing lookaround
           assertions). This has different characteristics to the normal
           algorithm, 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 support, 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 common 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.
    
           Here is an example of a simple call to **pcre2_dfa_match()** :
    
             int wspace[20];
             pcre2_match_data *md = pcre2_match_data_create(4, NULL);
             int rc = pcre2_dfa_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 */
               md,             /* the match data block */
               NULL,           /* a match context; NULL means use defaults */
               wspace,         /* working space vector */
               20);            /* number of elements (NOT size in bytes) */
    
       **Option bits for pcre2_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
           portion of the string that was inspected when the longest partial
           match was found is set as the first matching string in both cases.
           There is a more detailed discussion of partial and multi-segment
           matching, with examples, in the **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 alternative 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
           substring in the subject. Note, however, that all the matches from
           one run of the function start at the same point in the subject.
           The shorter matches are all initial substrings of the longer
           matches. For example, if the pattern
    
             <.*>
    
           is matched against the string
    
             This is <something> <something else> <something further> no more
    
           the three matched strings are
    
             <something> <something else> <something further>
             <something> <something else>
             <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 substrings 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_UINVALID_UTF
    
           This return is given if **pcre2_dfa_match()** is called for a pattern
           that was compiled with PCRE2_MATCH_INVALID_UTF. This is not
           supported for DFA matching.
    
             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 calls itself recursively, using private memory for the
           ovector and _workspace_.  This error is given if the internal
           ovector is not large enough. This should be extremely rare, as a
           vector of size 1000 is used.
    
             PCRE2_ERROR_DFA_BADRESTART
    
           When **pcre2_dfa_match()** is called with the **PCRE2_DFA_RESTART**
           option, some plausibility checks are made on the contents of the
           workspace, which should contain data about the previous partial
           match. If any of these checks fail, this error is given.
    


## REVISION



    
           Last updated: 26 December 2024
           Copyright (c) 1997-2024 University of Cambridge.
    


* * *