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<html><head><title>pcre2api specification</title></head><body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB"><h1>pcre2api man page</h1><p>Return to the <a href="index.html">PCRE2 index page</a>.</p><p>This page is part of the PCRE2 HTML documentation. It was generatedautomatically from the original man page. If there is any nonsense in it,please consult the man page, in case the conversion went wrong.<br><ul><li><a name="TOC1" href="#SEC1">PCRE2 NATIVE API BASIC FUNCTIONS</a><li><a name="TOC2" href="#SEC2">PCRE2 NATIVE API AUXILIARY MATCH FUNCTIONS</a><li><a name="TOC3" href="#SEC3">PCRE2 NATIVE API GENERAL CONTEXT FUNCTIONS</a><li><a name="TOC4" href="#SEC4">PCRE2 NATIVE API COMPILE CONTEXT FUNCTIONS</a><li><a name="TOC5" href="#SEC5">PCRE2 NATIVE API MATCH CONTEXT FUNCTIONS</a><li><a name="TOC6" href="#SEC6">PCRE2 NATIVE API STRING EXTRACTION FUNCTIONS</a><li><a name="TOC7" href="#SEC7">PCRE2 NATIVE API STRING SUBSTITUTION FUNCTION</a><li><a name="TOC8" href="#SEC8">PCRE2 NATIVE API JIT FUNCTIONS</a><li><a name="TOC9" href="#SEC9">PCRE2 NATIVE API SERIALIZATION FUNCTIONS</a><li><a name="TOC10" href="#SEC10">PCRE2 NATIVE API AUXILIARY FUNCTIONS</a><li><a name="TOC11" href="#SEC11">PCRE2 NATIVE API OBSOLETE FUNCTIONS</a><li><a name="TOC12" href="#SEC12">PCRE2 EXPERIMENTAL PATTERN CONVERSION FUNCTIONS</a><li><a name="TOC13" href="#SEC13">PCRE2 8-BIT, 16-BIT, AND 32-BIT LIBRARIES</a><li><a name="TOC14" href="#SEC14">PCRE2 API OVERVIEW</a><li><a name="TOC15" href="#SEC15">STRING LENGTHS AND OFFSETS</a><li><a name="TOC16" href="#SEC16">NEWLINES</a><li><a name="TOC17" href="#SEC17">MULTITHREADING</a><li><a name="TOC18" href="#SEC18">PCRE2 CONTEXTS</a><li><a name="TOC19" href="#SEC19">CHECKING BUILD-TIME OPTIONS</a><li><a name="TOC20" href="#SEC20">COMPILING A PATTERN</a><li><a name="TOC21" href="#SEC21">JUST-IN-TIME (JIT) COMPILATION</a><li><a name="TOC22" href="#SEC22">LOCALE SUPPORT</a><li><a name="TOC23" href="#SEC23">INFORMATION ABOUT A COMPILED PATTERN</a><li><a name="TOC24" href="#SEC24">INFORMATION ABOUT A PATTERN'S CALLOUTS</a><li><a name="TOC25" href="#SEC25">SERIALIZATION AND PRECOMPILING</a><li><a name="TOC26" href="#SEC26">THE MATCH DATA BLOCK</a><li><a name="TOC27" href="#SEC27">MEMORY USE FOR MATCH DATA BLOCKS</a><li><a name="TOC28" href="#SEC28">MATCHING A PATTERN: THE TRADITIONAL FUNCTION</a><li><a name="TOC29" href="#SEC29">NEWLINE HANDLING WHEN MATCHING</a><li><a name="TOC30" href="#SEC30">HOW PCRE2_MATCH() RETURNS A STRING AND CAPTURED SUBSTRINGS</a><li><a name="TOC31" href="#SEC31">OTHER INFORMATION ABOUT A MATCH</a><li><a name="TOC32" href="#SEC32">ERROR RETURNS FROM <b>pcre2_match()</b></a><li><a name="TOC33" href="#SEC33">OBTAINING A TEXTUAL ERROR MESSAGE</a><li><a name="TOC34" href="#SEC34">EXTRACTING CAPTURED SUBSTRINGS BY NUMBER</a><li><a name="TOC35" href="#SEC35">EXTRACTING A LIST OF ALL CAPTURED SUBSTRINGS</a><li><a name="TOC36" href="#SEC36">EXTRACTING CAPTURED SUBSTRINGS BY NAME</a><li><a name="TOC37" href="#SEC37">CREATING A NEW STRING WITH SUBSTITUTIONS</a><li><a name="TOC38" href="#SEC38">DUPLICATE CAPTURE GROUP NAMES</a><li><a name="TOC39" href="#SEC39">FINDING ALL POSSIBLE MATCHES AT ONE POSITION</a><li><a name="TOC40" href="#SEC40">MATCHING A PATTERN: THE ALTERNATIVE FUNCTION</a><li><a name="TOC41" href="#SEC41">SEE ALSO</a><li><a name="TOC42" href="#SEC42">AUTHOR</a><li><a name="TOC43" href="#SEC43">REVISION</a></ul><P><b>#include <pcre2.h></b><br><br>PCRE2 is a new API for PCRE, starting at release 10.0. This document contains adescription of all its native functions. See the<a href="pcre2.html"><b>pcre2</b></a>document for an overview of all the PCRE2 documentation.</P><br><a name="SEC1" href="#TOC1">PCRE2 NATIVE API BASIC FUNCTIONS</a><br><P><b>pcre2_code *pcre2_compile(PCRE2_SPTR <i>pattern</i>, PCRE2_SIZE <i>length</i>,</b><b> uint32_t <i>options</i>, int *<i>errorcode</i>, PCRE2_SIZE *<i>erroroffset,</i></b><b> pcre2_compile_context *<i>ccontext</i>);</b><br><br><b>void pcre2_code_free(pcre2_code *<i>code</i>);</b><br><br><b>pcre2_match_data *pcre2_match_data_create(uint32_t <i>ovecsize</i>,</b><b> pcre2_general_context *<i>gcontext</i>);</b><br><br><b>pcre2_match_data *pcre2_match_data_create_from_pattern(</b><b> const pcre2_code *<i>code</i>, pcre2_general_context *<i>gcontext</i>);</b><br><br><b>int pcre2_match(const pcre2_code *<i>code</i>, PCRE2_SPTR <i>subject</i>,</b><b> PCRE2_SIZE <i>length</i>, PCRE2_SIZE <i>startoffset</i>,</b><b> uint32_t <i>options</i>, pcre2_match_data *<i>match_data</i>,</b><b> pcre2_match_context *<i>mcontext</i>);</b><br><br><b>int pcre2_dfa_match(const pcre2_code *<i>code</i>, PCRE2_SPTR <i>subject</i>,</b><b> PCRE2_SIZE <i>length</i>, PCRE2_SIZE <i>startoffset</i>,</b><b> uint32_t <i>options</i>, pcre2_match_data *<i>match_data</i>,</b><b> pcre2_match_context *<i>mcontext</i>,</b><b> int *<i>workspace</i>, PCRE2_SIZE <i>wscount</i>);</b><br><br><b>void pcre2_match_data_free(pcre2_match_data *<i>match_data</i>);</b></P><br><a name="SEC2" href="#TOC1">PCRE2 NATIVE API AUXILIARY MATCH FUNCTIONS</a><br><P><b>PCRE2_SPTR pcre2_get_mark(pcre2_match_data *<i>match_data</i>);</b><br><br><b>PCRE2_SIZE pcre2_get_match_data_size(pcre2_match_data *<i>match_data</i>);</b><br><br><b>PCRE2_SIZE pcre2_get_match_data_heapframes_size(</b><b> pcre2_match_data *<i>match_data</i>);</b><br><br><b>uint32_t pcre2_get_ovector_count(pcre2_match_data *<i>match_data</i>);</b><br><br><b>PCRE2_SIZE *pcre2_get_ovector_pointer(pcre2_match_data *<i>match_data</i>);</b><br><br><b>PCRE2_SIZE pcre2_get_startchar(pcre2_match_data *<i>match_data</i>);</b></P><br><a name="SEC3" href="#TOC1">PCRE2 NATIVE API GENERAL CONTEXT FUNCTIONS</a><br><P><b>pcre2_general_context *pcre2_general_context_create(</b><b> void *(*<i>private_malloc</i>)(PCRE2_SIZE, void *),</b><b> void (*<i>private_free</i>)(void *, void *), void *<i>memory_data</i>);</b><br><br><b>pcre2_general_context *pcre2_general_context_copy(</b><b> pcre2_general_context *<i>gcontext</i>);</b><br><br><b>void pcre2_general_context_free(pcre2_general_context *<i>gcontext</i>);</b></P><br><a name="SEC4" href="#TOC1">PCRE2 NATIVE API COMPILE CONTEXT FUNCTIONS</a><br><P><b>pcre2_compile_context *pcre2_compile_context_create(</b><b> pcre2_general_context *<i>gcontext</i>);</b><br><br><b>pcre2_compile_context *pcre2_compile_context_copy(</b><b> pcre2_compile_context *<i>ccontext</i>);</b><br><br><b>void pcre2_compile_context_free(pcre2_compile_context *<i>ccontext</i>);</b><br><br><b>int pcre2_set_bsr(pcre2_compile_context *<i>ccontext</i>,</b><b> uint32_t <i>value</i>);</b><br><br><b>int pcre2_set_character_tables(pcre2_compile_context *<i>ccontext</i>,</b><b> const uint8_t *<i>tables</i>);</b><br><br><b>int pcre2_set_compile_extra_options(pcre2_compile_context *<i>ccontext</i>,</b><b> uint32_t <i>extra_options</i>);</b><br><br><b>int pcre2_set_max_pattern_length(pcre2_compile_context *<i>ccontext</i>,</b><b> PCRE2_SIZE <i>value</i>);</b><br><br><b>int pcre2_set_max_pattern_compiled_length(</b><b> pcre2_compile_context *<i>ccontext</i>, PCRE2_SIZE <i>value</i>);</b><br><br><b>int pcre2_set_max_varlookbehind(pcre2_compile_contest *<i>ccontext</i>,</b><b>" uint32_t <i>value</i>);</b><br><br><b>int pcre2_set_newline(pcre2_compile_context *<i>ccontext</i>,</b><b> uint32_t <i>value</i>);</b><br><br><b>int pcre2_set_parens_nest_limit(pcre2_compile_context *<i>ccontext</i>,</b><b> uint32_t <i>value</i>);</b><br><br><b>int pcre2_set_compile_recursion_guard(pcre2_compile_context *<i>ccontext</i>,</b><b> int (*<i>guard_function</i>)(uint32_t, void *), void *<i>user_data</i>);</b></P><br><a name="SEC5" href="#TOC1">PCRE2 NATIVE API MATCH CONTEXT FUNCTIONS</a><br><P><b>pcre2_match_context *pcre2_match_context_create(</b><b> pcre2_general_context *<i>gcontext</i>);</b><br><br><b>pcre2_match_context *pcre2_match_context_copy(</b><b> pcre2_match_context *<i>mcontext</i>);</b><br><br><b>void pcre2_match_context_free(pcre2_match_context *<i>mcontext</i>);</b><br><br><b>int pcre2_set_callout(pcre2_match_context *<i>mcontext</i>,</b><b> int (*<i>callout_function</i>)(pcre2_callout_block *, void *),</b><b> void *<i>callout_data</i>);</b><br><br><b>int pcre2_set_substitute_callout(pcre2_match_context *<i>mcontext</i>,</b><b> int (*<i>callout_function</i>)(pcre2_substitute_callout_block *, void *),</b><b> void *<i>callout_data</i>);</b><br><br><b>int pcre2_set_offset_limit(pcre2_match_context *<i>mcontext</i>,</b><b> PCRE2_SIZE <i>value</i>);</b><br><br><b>int pcre2_set_heap_limit(pcre2_match_context *<i>mcontext</i>,</b><b> uint32_t <i>value</i>);</b><br><br><b>int pcre2_set_match_limit(pcre2_match_context *<i>mcontext</i>,</b><b> uint32_t <i>value</i>);</b><br><br><b>int pcre2_set_depth_limit(pcre2_match_context *<i>mcontext</i>,</b><b> uint32_t <i>value</i>);</b></P><br><a name="SEC6" href="#TOC1">PCRE2 NATIVE API STRING EXTRACTION FUNCTIONS</a><br><P><b>int pcre2_substring_copy_byname(pcre2_match_data *<i>match_data</i>,</b><b> PCRE2_SPTR <i>name</i>, PCRE2_UCHAR *<i>buffer</i>, PCRE2_SIZE *<i>bufflen</i>);</b><br><br><b>int pcre2_substring_copy_bynumber(pcre2_match_data *<i>match_data</i>,</b><b> uint32_t <i>number</i>, PCRE2_UCHAR *<i>buffer</i>,</b><b> PCRE2_SIZE *<i>bufflen</i>);</b><br><br><b>void pcre2_substring_free(PCRE2_UCHAR *<i>buffer</i>);</b><br><br><b>int pcre2_substring_get_byname(pcre2_match_data *<i>match_data</i>,</b><b> PCRE2_SPTR <i>name</i>, PCRE2_UCHAR **<i>bufferptr</i>, PCRE2_SIZE *<i>bufflen</i>);</b><br><br><b>int pcre2_substring_get_bynumber(pcre2_match_data *<i>match_data</i>,</b><b> uint32_t <i>number</i>, PCRE2_UCHAR **<i>bufferptr</i>,</b><b> PCRE2_SIZE *<i>bufflen</i>);</b><br><br><b>int pcre2_substring_length_byname(pcre2_match_data *<i>match_data</i>,</b><b> PCRE2_SPTR <i>name</i>, PCRE2_SIZE *<i>length</i>);</b><br><br><b>int pcre2_substring_length_bynumber(pcre2_match_data *<i>match_data</i>,</b><b> uint32_t <i>number</i>, PCRE2_SIZE *<i>length</i>);</b><br><br><b>int pcre2_substring_nametable_scan(const pcre2_code *<i>code</i>,</b><b> PCRE2_SPTR <i>name</i>, PCRE2_SPTR *<i>first</i>, PCRE2_SPTR *<i>last</i>);</b><br><br><b>int pcre2_substring_number_from_name(const pcre2_code *<i>code</i>,</b><b> PCRE2_SPTR <i>name</i>);</b><br><br><b>void pcre2_substring_list_free(PCRE2_UCHAR **<i>list</i>);</b><br><br><b>int pcre2_substring_list_get(pcre2_match_data *<i>match_data</i>,</b><b>" PCRE2_UCHAR ***<i>listptr</i>, PCRE2_SIZE **<i>lengthsptr</i>);</b></P><br><a name="SEC7" href="#TOC1">PCRE2 NATIVE API STRING SUBSTITUTION FUNCTION</a><br><P><b>int pcre2_substitute(const pcre2_code *<i>code</i>, PCRE2_SPTR <i>subject</i>,</b><b> PCRE2_SIZE <i>length</i>, PCRE2_SIZE <i>startoffset</i>,</b><b> uint32_t <i>options</i>, pcre2_match_data *<i>match_data</i>,</b><b> pcre2_match_context *<i>mcontext</i>, PCRE2_SPTR <i>replacementz</i>,</b><b> PCRE2_SIZE <i>rlength</i>, PCRE2_UCHAR *<i>outputbuffer</i>,</b><b> PCRE2_SIZE *<i>outlengthptr</i>);</b></P><br><a name="SEC8" href="#TOC1">PCRE2 NATIVE API JIT FUNCTIONS</a><br><P><b>int pcre2_jit_compile(pcre2_code *<i>code</i>, uint32_t <i>options</i>);</b><br><br><b>int pcre2_jit_match(const pcre2_code *<i>code</i>, PCRE2_SPTR <i>subject</i>,</b><b> PCRE2_SIZE <i>length</i>, PCRE2_SIZE <i>startoffset</i>,</b><b> uint32_t <i>options</i>, pcre2_match_data *<i>match_data</i>,</b><b> pcre2_match_context *<i>mcontext</i>);</b><br><br><b>void pcre2_jit_free_unused_memory(pcre2_general_context *<i>gcontext</i>);</b><br><br><b>pcre2_jit_stack *pcre2_jit_stack_create(size_t <i>startsize</i>,</b><b> size_t <i>maxsize</i>, pcre2_general_context *<i>gcontext</i>);</b><br><br><b>void pcre2_jit_stack_assign(pcre2_match_context *<i>mcontext</i>,</b><b> pcre2_jit_callback <i>callback_function</i>, void *<i>callback_data</i>);</b><br><br><b>void pcre2_jit_stack_free(pcre2_jit_stack *<i>jit_stack</i>);</b></P><br><a name="SEC9" href="#TOC1">PCRE2 NATIVE API SERIALIZATION FUNCTIONS</a><br><P><b>int32_t pcre2_serialize_decode(pcre2_code **<i>codes</i>,</b><b> int32_t <i>number_of_codes</i>, const uint8_t *<i>bytes</i>,</b><b> pcre2_general_context *<i>gcontext</i>);</b><br><br><b>int32_t pcre2_serialize_encode(const pcre2_code **<i>codes</i>,</b><b> int32_t <i>number_of_codes</i>, uint8_t **<i>serialized_bytes</i>,</b><b> PCRE2_SIZE *<i>serialized_size</i>, pcre2_general_context *<i>gcontext</i>);</b><br><br><b>void pcre2_serialize_free(uint8_t *<i>bytes</i>);</b><br><br><b>int32_t pcre2_serialize_get_number_of_codes(const uint8_t *<i>bytes</i>);</b></P><br><a name="SEC10" href="#TOC1">PCRE2 NATIVE API AUXILIARY FUNCTIONS</a><br><P><b>pcre2_code *pcre2_code_copy(const pcre2_code *<i>code</i>);</b><br><br><b>pcre2_code *pcre2_code_copy_with_tables(const pcre2_code *<i>code</i>);</b><br><br><b>int pcre2_get_error_message(int <i>errorcode</i>, PCRE2_UCHAR *<i>buffer</i>,</b><b> PCRE2_SIZE <i>bufflen</i>);</b><br><br><b>const uint8_t *pcre2_maketables(pcre2_general_context *<i>gcontext</i>);</b><br><br><b>void pcre2_maketables_free(pcre2_general_context *<i>gcontext</i>,</b><b> const uint8_t *<i>tables</i>);</b><br><br><b>int pcre2_pattern_info(const pcre2_code *<i>code</i>, uint32_t <i>what</i>,</b><b> void *<i>where</i>);</b><br><br><b>int pcre2_callout_enumerate(const pcre2_code *<i>code</i>,</b><b> int (*<i>callback</i>)(pcre2_callout_enumerate_block *, void *),</b><b> void *<i>user_data</i>);</b><br><br><b>int pcre2_config(uint32_t <i>what</i>, void *<i>where</i>);</b></P><br><a name="SEC11" href="#TOC1">PCRE2 NATIVE API OBSOLETE FUNCTIONS</a><br><P><b>int pcre2_set_recursion_limit(pcre2_match_context *<i>mcontext</i>,</b><b> uint32_t <i>value</i>);</b><br><br><b>int pcre2_set_recursion_memory_management(</b><b> pcre2_match_context *<i>mcontext</i>,</b><b> void *(*<i>private_malloc</i>)(size_t, void *),</b><b> void (*<i>private_free</i>)(void *, void *), void *<i>memory_data</i>);</b><br><br>These functions became obsolete at release 10.30 and are retained only forbackward compatibility. They should not be used in new code. The first isreplaced by <b>pcre2_set_depth_limit()</b>; the second is no longer needed andhas no effect (it always returns zero).</P><br><a name="SEC12" href="#TOC1">PCRE2 EXPERIMENTAL PATTERN CONVERSION FUNCTIONS</a><br><P><b>pcre2_convert_context *pcre2_convert_context_create(</b><b> pcre2_general_context *<i>gcontext</i>);</b><br><br><b>pcre2_convert_context *pcre2_convert_context_copy(</b><b> pcre2_convert_context *<i>cvcontext</i>);</b><br><br><b>void pcre2_convert_context_free(pcre2_convert_context *<i>cvcontext</i>);</b><br><br><b>int pcre2_set_glob_escape(pcre2_convert_context *<i>cvcontext</i>,</b><b> uint32_t <i>escape_char</i>);</b><br><br><b>int pcre2_set_glob_separator(pcre2_convert_context *<i>cvcontext</i>,</b><b> uint32_t <i>separator_char</i>);</b><br><br><b>int pcre2_pattern_convert(PCRE2_SPTR <i>pattern</i>, PCRE2_SIZE <i>length</i>,</b><b> uint32_t <i>options</i>, PCRE2_UCHAR **<i>buffer</i>,</b><b> PCRE2_SIZE *<i>blength</i>, pcre2_convert_context *<i>cvcontext</i>);</b><br><br><b>void pcre2_converted_pattern_free(PCRE2_UCHAR *<i>converted_pattern</i>);</b><br><br>These functions provide a way of converting non-PCRE2 patterns intopatterns that can be processed by <b>pcre2_compile()</b>. This facility isexperimental and may be changed in future releases. At present, "globs" andPOSIX basic and extended patterns can be converted. Details are given in the<a href="pcre2convert.html"><b>pcre2convert</b></a>documentation.</P><br><a name="SEC13" href="#TOC1">PCRE2 8-BIT, 16-BIT, AND 32-BIT LIBRARIES</a><br><P>There are three PCRE2 libraries, supporting 8-bit, 16-bit, and 32-bit codeunits, respectively. However, there is just one header file, <b>pcre2.h</b>.This contains the function prototypes and other definitions for all threelibraries. One, two, or all three can be installed simultaneously. On Unix-likesystems the libraries are called <b>libpcre2-8</b>, <b>libpcre2-16</b>, and<b>libpcre2-32</b>, and they can also co-exist with the original PCRE libraries.Every PCRE2 function comes in three different forms, one for each library, forexample:<pre> <b>pcre2_compile_8()</b> <b>pcre2_compile_16()</b> <b>pcre2_compile_32()</b></pre>There are also three different sets of data types:<pre> <b>PCRE2_UCHAR8, PCRE2_UCHAR16, PCRE2_UCHAR32</b> <b>PCRE2_SPTR8, PCRE2_SPTR16, PCRE2_SPTR32</b></pre>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.</P><P>Character strings are passed to a PCRE2 library as sequences of unsignedintegers in code units of the appropriate width. The length of a string maybe given as a number of code units, or the string may be specified aszero-terminated.</P><P>Many applications use only one code unit width. For their convenience, macrosare defined whose names are the generic forms such as <b>pcre2_compile()</b> andPCRE2_SPTR. These macros use the value of the macro PCRE2_CODE_UNIT_WIDTH togenerate the appropriate width-specific function and macro names.PCRE2_CODE_UNIT_WIDTH is not defined by default. An application must define itto be 8, 16, or 32 before including <b>pcre2.h</b> in order to make use of thegeneric names.</P><P>Applications that use more than one code unit width can be linked with morethan one PCRE2 library, but must define PCRE2_CODE_UNIT_WIDTH to be 0 beforeincluding <b>pcre2.h</b>, and then use the real function names. Any code that isto be included in an environment where the value of PCRE2_CODE_UNIT_WIDTH isunknown should also use the real function names. (Unfortunately, it is notpossible in C code to save and restore the value of a macro.)</P><P>If PCRE2_CODE_UNIT_WIDTH is not defined before including <b>pcre2.h</b>, acompiler error occurs.</P><P>When using multiple libraries in an application, you must take care whenprocessing 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<b>pcre2_compile_16()</b>, you must do so with <b>pcre2_match_16()</b>, not<b>pcre2_match_8()</b> or <b>pcre2_match_32()</b>.</P><P>In the function summaries above, and in the rest of this document and otherPCRE2 documents, functions and data types are described using their genericnames, without the _8, _16, or _32 suffix.</P><br><a name="SEC14" href="#TOC1">PCRE2 API OVERVIEW</a><br><P>PCRE2 has its own native API, which is described in this document. There arealso some wrapper functions for the 8-bit library that correspond to thePOSIX regular expression API, but they do not give access to all thefunctionality of PCRE2 and they are not thread-safe. They are described in the<a href="pcre2posix.html"><b>pcre2posix</b></a>documentation. Both these APIs define a set of C function calls.</P><P>The native API C data types, function prototypes, option values, and errorcodes are defined in the header file <b>pcre2.h</b>, which also containsdefinitions of PCRE2_MAJOR and PCRE2_MINOR, the major and minor release numbersfor the library. Applications can use these to include support for differentreleases of PCRE2.</P><P>In a Windows environment, if you want to statically link an application programagainst a non-dll PCRE2 library, you must define PCRE2_STATIC before including<b>pcre2.h</b>.</P><P>The functions <b>pcre2_compile()</b> and <b>pcre2_match()</b> are used forcompiling and matching regular expressions in a Perl-compatible manner. Asample program that demonstrates the simplest way of using them is provided inthe file called <i>pcre2demo.c</i> in the PCRE2 source distribution. A listingof this program is given in the<a href="pcre2demo.html"><b>pcre2demo</b></a>documentation, and the<a href="pcre2sample.html"><b>pcre2sample</b></a>documentation describes how to compile and run it.</P><P>The compiling and matching functions recognize various options that are passedas bits in an options argument. There are also some more complicated parameterssuch as custom memory management functions and resource limits that are passedin "contexts" (which are just memory blocks, described below). Simpleapplications do not need to make use of contexts.</P><P>Just-in-time (JIT) compiler support is an optional feature of PCRE2 that can bebuilt in appropriate hardware environments. It greatly speeds up the matchingperformance of many patterns. Programs can request that it be used ifavailable by calling <b>pcre2_jit_compile()</b> after a pattern has beensuccessfully compiled by <b>pcre2_compile()</b>. This does nothing if JITsupport is not available.</P><P>More complicated programs might need to make use of the specialist functions<b>pcre2_jit_stack_create()</b>, <b>pcre2_jit_stack_free()</b>, and<b>pcre2_jit_stack_assign()</b> in order to control the JIT code's memory usage.</P><P>JIT matching is automatically used by <b>pcre2_match()</b> if it is available,unless the PCRE2_NO_JIT option is set. There is also a direct interface for JITmatching, which gives improved performance at the expense of less sanitychecking. The JIT-specific functions are discussed in the<a href="pcre2jit.html"><b>pcre2jit</b></a>documentation.</P><P>A second matching function, <b>pcre2_dfa_match()</b>, which is notPerl-compatible, is also provided. This uses a different algorithm for thematching. The alternative algorithm finds all possible matches (at a givenpoint in the subject), and scans the subject just once (unless there arelookaround assertions). However, this algorithm does not return capturedsubstrings. A description of the two matching algorithms and their advantagesand disadvantages is given in the<a href="pcre2matching.html"><b>pcre2matching</b></a>documentation. There is no JIT support for <b>pcre2_dfa_match()</b>.</P><P>In addition to the main compiling and matching functions, there are conveniencefunctions for extracting captured substrings from a subject string that hasbeen matched by <b>pcre2_match()</b>. They are:<pre> <b>pcre2_substring_copy_byname()</b> <b>pcre2_substring_copy_bynumber()</b> <b>pcre2_substring_get_byname()</b> <b>pcre2_substring_get_bynumber()</b> <b>pcre2_substring_list_get()</b> <b>pcre2_substring_length_byname()</b> <b>pcre2_substring_length_bynumber()</b> <b>pcre2_substring_nametable_scan()</b> <b>pcre2_substring_number_from_name()</b></pre><b>pcre2_substring_free()</b> and <b>pcre2_substring_list_free()</b> are alsoprovided, to free memory used for extracted strings. If either of thesefunctions is called with a NULL argument, the function returns immediatelywithout doing anything.</P><P>The function <b>pcre2_substitute()</b> can be called to match a pattern andreturn a copy of the subject string with substitutions for parts that werematched.</P><P>Functions whose names begin with <b>pcre2_serialize_</b> are used for savingcompiled patterns on disc or elsewhere, and reloading them later.</P><P>Finally, there are functions for finding out information about a compiledpattern (<b>pcre2_pattern_info()</b>) and about the configuration with whichPCRE2 was built (<b>pcre2_config()</b>).</P><P>Functions with names ending with <b>_free()</b> are used for freeing memoryblocks of various sorts. In all cases, if one of these functions is called witha NULL argument, it does nothing.</P><br><a name="SEC15" href="#TOC1">STRING LENGTHS AND OFFSETS</a><br><P>The PCRE2 API uses string lengths and offsets into strings of code units inseveral places. These values are always of type PCRE2_SIZE, which is anunsigned integer type, currently always defined as <i>size_t</i>. The largestvalue that can be stored in such a type (that is ~(PCRE2_SIZE)0) is reservedas a special indicator for zero-terminated strings and unset offsets.Therefore, the longest string that can be handled is one less than thismaximum. Note that string lengths are always given in code units. Only in the8-bit library is such a length the same as the number of bytes in the string.<a name="newlines"></a></P><br><a name="SEC16" href="#TOC1">NEWLINES</a><br><P>PCRE2 supports five different conventions for indicating line breaks instrings: a single CR (carriage return) character, a single LF (linefeed)character, the two-character sequence CRLF, any of the three preceding, or anyUnicode newline sequence. The Unicode newline sequences are the three justmentioned, 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).</P><P>Each of the first three conventions is used by at least one operating system asits 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<b>pcre2_compile()</b>, or it can be specified by special text at the start ofthe pattern itself; this overrides any other settings. See the<a href="pcre2pattern.html"><b>pcre2pattern</b></a>page for details of the special character sequences.</P><P>In the PCRE2 documentation the word "newline" is used to mean "the character orpair of characters that indicate a line break". The choice of newlineconvention affects the handling of the dot, circumflex, and dollarmetacharacters, the handling of #-comments in /x mode, and, when CRLF is arecognized line ending sequence, the match position advancement for anon-anchored pattern. There is more detail about this in the<a href="#matchoptions">section on <b>pcre2_match()</b> options</a>below.</P><P>The choice of newline convention does not affect the interpretation ofthe \n or \r escape sequences, nor does it affect what \R matches; this hasits own separate convention.</P><br><a name="SEC17" href="#TOC1">MULTITHREADING</a><br><P>In a multithreaded application it is important to keep thread-specific dataseparate from data that can be shared between threads. The PCRE2 library codeitself is thread-safe: it contains no static or global variables. The API isdesigned to be fairly simple for non-threaded applications while at the sametime ensuring that multithreaded applications can use it.</P><P>There are several different blocks of data that are used to pass informationbetween the application and the PCRE2 libraries.</P><br><b>The compiled pattern</b><br><P>A pointer to the compiled form of a pattern is returned to the user when<b>pcre2_compile()</b> 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 threadsimultaneously. For example, an application can compile all its patterns at thestart, before forking off multiple threads that use them. However, if thejust-in-time (JIT) optimization feature is being used, it needs separate memorystack areas for each thread. See the<a href="pcre2jit.html"><b>pcre2jit</b></a>documentation for more details.</P><P>In a more complicated situation, where patterns are compiled only when they arefirst needed, but are still shared between threads, pointers to compiledpatterns must be protected from simultaneous writing by multiple threads. Thisis somewhat tricky to do correctly. If you know that writing to a pointer isatomic in your environment, you can use logic like this:<pre> 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()</pre>Of course, testing for compilation errors should also be included in the code.</P><P>The reason for checking the pointer a second time is as follows: Severalthreads may have acquired the shared lock and tested the pointer for beingNULL, but only one of them will be given the write lock, with the rest keptwaiting. The winning thread will compile the pattern and store the result.After this thread releases the write lock, another thread will get it, and ifit does not retest pointer for being NULL, will recompile the pattern andoverwrite the pointer, creating a memory leak and possibly causing otherissues.</P><P>In an environment where writing to a pointer may not be atomic, the above logicis not sufficient. The thread that is doing the compiling may be descheduledafter writing only part of the pointer, which could cause other threads to usean invalid value. Instead of checking the pointer itself, a separate "pointeris valid" flag (that can be updated atomically) must be used:<pre> 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()</pre>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 isrequired. JIT compilation updates a value within the compiled code block, so athread must gain unique write access to the pointer before calling<b>pcre2_jit_compile()</b>. Alternatively, <b>pcre2_code_copy()</b> or<b>pcre2_code_copy_with_tables()</b> can be used to obtain a private copy of thecompiled code before calling the JIT compiler.</P><br><b>Context blocks</b><br><P>The next main section below introduces the idea of "contexts" in which PCRE2functions are called. A context is nothing more than a collection of parametersthat control the way PCRE2 operates. Grouping a number of parameters togetherin a context is a convenient way of passing them to a PCRE2 function withoutusing lots of arguments. The parameters that are stored in contexts are in somesense "advanced features" of the API. Many straightforward applications willnot need to use contexts.</P><P>In a multithreaded application, if the parameters in a context are values thatare never changed, the same context can be used by all the threads. However, ifany thread needs to change any value in a context, it must make its ownthread-specific copy.</P><br><b>Match blocks</b><br><P>The matching functions need a block of memory for storing the results of amatch. This includes details of what was matched, as well as additionalinformation such as the name of a (*MARK) setting. Each thread must provide itsown copy of this memory.</P><br><a name="SEC18" href="#TOC1">PCRE2 CONTEXTS</a><br><P>Some PCRE2 functions have a lot of parameters, many of which are used only byspecialist applications, for example, those that use custom memory managementor non-standard character tables. To keep function argument lists at areasonable size, and at the same time to keep the API extensible, "uncommon"parameters are passed to certain functions in a <b>context</b> instead ofdirectly. 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 passNULL when a context pointer is required.</P><P>There are three different types of context: a general context that is relevantfor several PCRE2 operations, a compile-time context, and a match-time context.</P><br><b>The general context</b><br><P>At present, this context just contains pointers to (and data for) externalmemory management functions that are called from several places in the PCRE2library. The context is named `general' rather than specifically `memory'because in future other fields may be added. If you do not want to supply yourown custom memory management functions, you do not need to bother with ageneral context. A general context is created by:<br><br><b>pcre2_general_context *pcre2_general_context_create(</b><b> void *(*<i>private_malloc</i>)(PCRE2_SIZE, void *),</b><b> void (*<i>private_free</i>)(void *, void *), void *<i>memory_data</i>);</b><br><br>The two function pointers specify custom memory management functions, whoseprototypes are:<pre> <b>void *private_malloc(PCRE2_SIZE, void *);</b> <b>void private_free(void *, void *);</b></pre>Whenever code in PCRE2 calls these functions, the final argument is the valueof <i>memory_data</i>. Either of the first two arguments of the creationfunction may be NULL, in which case the system memory management functions<i>malloc()</i> and <i>free()</i> are used. (This is not currently useful, asthere are no other fields in a general context, but in future there might be.)The <i>private_malloc()</i> function is used (if supplied) to obtain memory forstoring the context, and all three values are saved as part of the context.</P><P>Whenever PCRE2 creates a data block of any kind, the block contains a pointerto the <i>free()</i> function that matches the <i>malloc()</i> function that wasused. When the time comes to free the block, this function is called.</P><P>A general context can be copied by calling:<br><br><b>pcre2_general_context *pcre2_general_context_copy(</b><b> pcre2_general_context *<i>gcontext</i>);</b><br><br>The memory used for a general context should be freed by calling:<br><br><b>void pcre2_general_context_free(pcre2_general_context *<i>gcontext</i>);</b><br><br>If this function is passed a NULL argument, it returns immediately withoutdoing anything.<a name="compilecontext"></a></P><br><b>The compile context</b><br><P>A compile context is required if you want to provide an external function forstack checking during compilation or to change the default values of any of thefollowing compile-time parameters:<pre> 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)</pre>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<i>pcre2_compile()</i>.</P><P>A compile context is created, copied, and freed by the following functions:<br><br><b>pcre2_compile_context *pcre2_compile_context_create(</b><b> pcre2_general_context *<i>gcontext</i>);</b><br><br><b>pcre2_compile_context *pcre2_compile_context_copy(</b><b> pcre2_compile_context *<i>ccontext</i>);</b><br><br><b>void pcre2_compile_context_free(pcre2_compile_context *<i>ccontext</i>);</b><br><br>A compile context is created with default values for its parameters. These canbe changed by calling the following functions, which return 0 on success, orPCRE2_ERROR_BADDATA if invalid data is detected.<br><br><b>int pcre2_set_bsr(pcre2_compile_context *<i>ccontext</i>,</b><b> uint32_t <i>value</i>);</b><br><br>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 lineending sequence. The value is used by the JIT compiler and by the twointerpreted matching functions, <i>pcre2_match()</i> and<i>pcre2_dfa_match()</i>.<br><br><b>int pcre2_set_character_tables(pcre2_compile_context *<i>ccontext</i>,</b><b> const uint8_t *<i>tables</i>);</b><br><br>The value must be the result of a call to <b>pcre2_maketables()</b>, whose onlyargument is a general context. This function builds a set of character tablesin the current locale.<br><br><b>int pcre2_set_compile_extra_options(pcre2_compile_context *<i>ccontext</i>,</b><b> uint32_t <i>extra_options</i>);</b><br><br>As PCRE2 has developed, almost all the 32 option bits that are available inthe <i>options</i> argument of <b>pcre2_compile()</b> have been used up. To avoidrunning out, the compile context contains a set of extra option bits which areused for some newer, assumed rarer, options. This function sets those bits. Italways sets all the bits (either on or off). It does not modify any existingsetting. The available options are defined in the section entitled "Extracompile options"<a href="#extracompileoptions">below.</a><br><br><b>int pcre2_set_max_pattern_length(pcre2_compile_context *<i>ccontext</i>,</b><b> PCRE2_SIZE <i>value</i>);</b><br><br>This sets a maximum length, in code units, for any pattern string that iscompiled with this context. If the pattern is longer, an error is generated.This facility is provided so that applications that accept patterns fromexternal sources can limit their size. The default is the largest number that aPCRE2_SIZE variable can hold, which is effectively unlimited.<br><br><b>int pcre2_set_max_pattern_compiled_length(</b><b> pcre2_compile_context *<i>ccontext</i>, PCRE2_SIZE <i>value</i>);</b><br><br>This sets a maximum size, in bytes, for the memory needed to hold the compiledversion of a pattern that is compiled with this context. If the pattern needsmore memory, an error is generated. This facility is provided so thatapplications that accept patterns from external sources can limit the amount ofmemory they use. The default is the largest number that a PCRE2_SIZE variablecan hold, which is effectively unlimited.<br><br><b>int pcre2_set_max_varlookbehind(pcre2_compile_contest *<i>ccontext</i>,</b><b>" uint32_t <i>value</i>);</b><br><br>This sets a maximum length for the number of characters matched by avariable-length lookbehind assertion. The default is set when PCRE2 is built,with the ultimate default being 255, the same as Perl. Lookbehind assertionswithout a bounding length are not supported.<br><br><b>int pcre2_set_newline(pcre2_compile_context *<i>ccontext</i>,</b><b> uint32_t <i>value</i>);</b><br><br>This specifies which characters or character sequences are to be recognized asnewlines. The value must be one of PCRE2_NEWLINE_CR (carriage return only),PCRE2_NEWLINE_LF (linefeed only), PCRE2_NEWLINE_CRLF (the two-charactersequence CR followed by LF), PCRE2_NEWLINE_ANYCRLF (any of the above),PCRE2_NEWLINE_ANY (any Unicode newline sequence), or PCRE2_NEWLINE_NUL (theNUL character, that is a binary zero).</P><P>A pattern can override the value set in the compile context by starting with asequence such as (*CRLF). See the<a href="pcre2pattern.html"><b>pcre2pattern</b></a>page for details.</P><P>When a pattern is compiled with the PCRE2_EXTENDED or PCRE2_EXTENDED_MOREoption, the newline convention affects the recognition of the end of internalcomments starting with #. The value is saved with the compiled pattern forsubsequent use by the JIT compiler and by the two interpreted matchingfunctions, <i>pcre2_match()</i> and <i>pcre2_dfa_match()</i>.<br><br><b>int pcre2_set_parens_nest_limit(pcre2_compile_context *<i>ccontext</i>,</b><b> uint32_t <i>value</i>);</b><br><br>This parameter adjusts the limit, set when PCRE2 is built (default 250), on thedepth of parenthesis nesting in a pattern. This limit stops rogue patternsusing up too much system stack when being compiled. The limit applies toparentheses of all kinds, not just capturing parentheses.<br><br><b>int pcre2_set_compile_recursion_guard(pcre2_compile_context *<i>ccontext</i>,</b><b> int (*<i>guard_function</i>)(uint32_t, void *), void *<i>user_data</i>);</b><br><br>There is at least one application that runs PCRE2 in threads with very limitedsystem stack, where running out of stack is to be avoided at all costs. Theparenthesis limit above cannot take account of how much stack is actuallyavailable during compilation. For a finer control, you can supply a functionthat is called whenever <b>pcre2_compile()</b> starts to compile a parenthesizedpart of a pattern. This function can check the actual stack size (or anythingelse that it wants to, of course).</P><P>The first argument to the callout function gives the current depth ofnesting, and the second is user data that is set up by the last argument of<b>pcre2_set_compile_recursion_guard()</b>. The callout function should returnzero if all is well, or non-zero to force an error.<a name="matchcontext"></a></P><br><b>The match context</b><br><P>A match context is required if you want to:<pre> 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</pre>If none of these apply, just pass NULL as the context argument of<b>pcre2_match()</b>, <b>pcre2_dfa_match()</b>, or <b>pcre2_jit_match()</b>.</P><P>A match context is created, copied, and freed by the following functions:<br><br><b>pcre2_match_context *pcre2_match_context_create(</b><b> pcre2_general_context *<i>gcontext</i>);</b><br><br><b>pcre2_match_context *pcre2_match_context_copy(</b><b> pcre2_match_context *<i>mcontext</i>);</b><br><br><b>void pcre2_match_context_free(pcre2_match_context *<i>mcontext</i>);</b><br><br>A match context is created with default values for its parameters. These canbe changed by calling the following functions, which return 0 on success, orPCRE2_ERROR_BADDATA if invalid data is detected.<br><br><b>int pcre2_set_callout(pcre2_match_context *<i>mcontext</i>,</b><b> int (*<i>callout_function</i>)(pcre2_callout_block *, void *),</b><b> void *<i>callout_data</i>);</b><br><br>This sets up a callout function for PCRE2 to call at specified pointsduring a matching operation. Details are given in the<a href="pcre2callout.html"><b>pcre2callout</b></a>documentation.<br><br><b>int pcre2_set_substitute_callout(pcre2_match_context *<i>mcontext</i>,</b><b> int (*<i>callout_function</i>)(pcre2_substitute_callout_block *, void *),</b><b> void *<i>callout_data</i>);</b><br><br>This sets up a callout function for PCRE2 to call after each substitutionmade by <b>pcre2_substitute()</b>. Details are given in the section entitled"Creating a new string with substitutions"<a href="#substitutions">below.</a><br><br><b>int pcre2_set_offset_limit(pcre2_match_context *<i>mcontext</i>,</b><b> PCRE2_SIZE <i>value</i>);</b><br><br>The <i>offset_limit</i> parameter limits how far an unanchored search canadvance in the subject string. The default value is PCRE2_UNSET. The<b>pcre2_match()</b> and <b>pcre2_dfa_match()</b> functions returnPCRE2_ERROR_NOMATCH if a match with a starting point before or at the givenoffset is not found. The <b>pcre2_substitute()</b> function makes no moresubstitutions.</P><P>For example, if the pattern /abc/ is matched against "123abc" with an offsetlimit less than 3, the result is PCRE2_ERROR_NOMATCH. A match can never befound if the <i>startoffset</i> argument of <b>pcre2_match()</b>,<b>pcre2_dfa_match()</b>, or <b>pcre2_substitute()</b> is greater than the offsetlimit set in the match context.</P><P>When using this facility, you must set the PCRE2_USE_OFFSET_LIMIT option whencalling <b>pcre2_compile()</b> so that when JIT is in use, different code can becompiled. If a match is started with a non-default match limit whenPCRE2_USE_OFFSET_LIMIT is not set, an error is generated.</P><P>The offset limit facility can be used to track progress when searching largesubject strings or to limit the extent of global substitutions. See also thePCRE2_FIRSTLINE option, which requires a match to start before or at the firstnewline that follows the start of matching in the subject. If this is set withan offset limit, a match must occur in the first line and also within theoffset limit. In other words, whichever limit comes first is used.<br><br><b>int pcre2_set_heap_limit(pcre2_match_context *<i>mcontext</i>,</b><b> uint32_t <i>value</i>);</b><br><br>The <i>heap_limit</i> parameter specifies, in units of kibibytes (1024 bytes),the maximum amount of heap memory that <b>pcre2_match()</b> may use to holdbacktracking information when running an interpretive match. This limit alsoapplies to <b>pcre2_dfa_match()</b>, which may use the heap when processingpatterns with a lot of nested pattern recursion or lookarounds or atomicgroups. This limit does not apply to matching with the JIT optimization, whichhas its own memory control arrangements (see the<a href="pcre2jit.html"><b>pcre2jit</b></a>documentation for more details). If the limit is reached, the negative errorcode PCRE2_ERROR_HEAPLIMIT is returned. The default limit can be set when PCRE2is built; if it is not, the default is set very large and is essentiallyunlimited.</P><P>A value for the heap limit may also be supplied by an item at the start of apattern of the form<pre> (*LIMIT_HEAP=ddd)</pre>where ddd is a decimal number. However, such a setting is ignored unless ddd isless than the limit set by the caller of <b>pcre2_match()</b> or, if no suchlimit is set, less than the default.</P><P>The <b>pcre2_match()</b> function always needs some heap memory, so setting avalue of zero guarantees a "heap limit exceeded" error. Details of how<b>pcre2_match()</b> uses the heap are given in the<a href="pcre2perform.html"><b>pcre2perform</b></a>documentation.</P><P>For <b>pcre2_dfa_match()</b>, a vector on the system stack is used whenprocessing pattern recursions, lookarounds, or atomic groups, and only if thisis not big enough is heap memory used. In this case, setting a value of zerodisables the use of the heap.<br><br><b>int pcre2_set_match_limit(pcre2_match_context *<i>mcontext</i>,</b><b> uint32_t <i>value</i>);</b><br><br>The <i>match_limit</i> parameter provides a means of preventing PCRE2 from usingup too many computing resources when processing patterns that are not going tomatch, but which have a very large number of possibilities in their searchtrees. The classic example is a pattern that uses nested unlimited repeats.</P><P>There is an internal counter in <b>pcre2_match()</b> that is incremented eachtime round its main matching loop. If this value reaches the match limit,<b>pcre2_match()</b> returns the negative value PCRE2_ERROR_MATCHLIMIT. This hasthe effect of limiting the amount of backtracking that can take place. Forpatterns that are not anchored, the count restarts from zero for each positionin the subject string. This limit also applies to <b>pcre2_dfa_match()</b>,though the counting is done in a different way.</P><P>When <b>pcre2_match()</b> is called with a pattern that was successfullyprocessed by <b>pcre2_jit_compile()</b>, the way in which matching is executedis entirely different. However, there is still the possibility of runawaymatching that goes on for a very long time, and so the <i>match_limit</i> valueis also used in this case (but in a different way) to limit how long thematching can continue.</P><P>The default value for the limit can be set when PCRE2 is built; the default is10 million, which handles all but the most extreme cases. A value for the matchlimit may also be supplied by an item at the start of a pattern of the form<pre> (*LIMIT_MATCH=ddd)</pre>where ddd is a decimal number. However, such a setting is ignored unless ddd isless than the limit set by the caller of <b>pcre2_match()</b> or<b>pcre2_dfa_match()</b> or, if no such limit is set, less than the default.<br><br><b>int pcre2_set_depth_limit(pcre2_match_context *<i>mcontext</i>,</b><b> uint32_t <i>value</i>);</b><br><br>This parameter limits the depth of nested backtracking in <b>pcre2_match()</b>.Each time a nested backtracking point is passed, a new memory frame is usedto remember the state of matching at that point. Thus, this parameterindirectly limits the amount of memory that is used in a match. However,because the size of each memory frame depends on the number of capturingparentheses, the actual memory limit varies from pattern to pattern. This limitwas more useful in versions before 10.30, where function recursion was used forbacktracking.</P><P>The depth limit is not relevant, and is ignored, when matching is done usingJIT compiled code. However, it is supported by <b>pcre2_dfa_match()</b>, whichuses it to limit the depth of nested internal recursive function calls thatimplement atomic groups, lookaround assertions, and pattern recursions. Thislimits, indirectly, the amount of system stack that is used. It was more usefulin versions before 10.32, when stack memory was used for local workspacevectors for recursive function calls. From version 10.32, only local variablesare allocated on the stack and as each call uses only a few hundred bytes, evena small stack can support quite a lot of recursion.</P><P>If the depth of internal recursive function calls is great enough, localworkspace vectors are allocated on the heap from version 10.32 onwards, so thedepth limit also indirectly limits the amount of heap memory that is used. Arecursive pattern such as /(.(?2))((?1)|)/, when matched to a very long stringusing <b>pcre2_dfa_match()</b>, can use a great deal of memory. However, it isprobably better to limit heap usage directly by calling<b>pcre2_set_heap_limit()</b>.</P><P>The default value for the depth limit can be set when PCRE2 is built; if it isnot, the default is set to the same value as the default for the match limit.If the limit is exceeded, <b>pcre2_match()</b> or <b>pcre2_dfa_match()</b>returns PCRE2_ERROR_DEPTHLIMIT. A value for the depth limit may also besupplied by an item at the start of a pattern of the form<pre> (*LIMIT_DEPTH=ddd)</pre>where ddd is a decimal number. However, such a setting is ignored unless ddd isless than the limit set by the caller of <b>pcre2_match()</b> or<b>pcre2_dfa_match()</b> or, if no such limit is set, less than the default.</P><br><a name="SEC19" href="#TOC1">CHECKING BUILD-TIME OPTIONS</a><br><P><b>int pcre2_config(uint32_t <i>what</i>, void *<i>where</i>);</b></P><P>The function <b>pcre2_config()</b> makes it possible for a PCRE2 client to findthe value of certain configuration parameters and to discover which optionalfeatures have been compiled into the PCRE2 library. The<a href="pcre2build.html"><b>pcre2build</b></a>documentation has more details about these features.</P><P>The first argument for <b>pcre2_config()</b> specifies which information isrequired. The second argument is a pointer to memory into which the informationis placed. If NULL is passed, the function returns the amount of memory that isneeded for the requested information. For calls that return numerical values,the value is in bytes; when requesting these values, <i>where</i> should pointto appropriately aligned memory. For calls that return strings, the requiredlength is given in code units, not counting the terminating zero.</P><P>When requesting information, the returned value from <b>pcre2_config()</b> isnon-negative on success, or the negative error code PCRE2_ERROR_BADOPTION ifthe value in the first argument is not recognized. The following information isavailable:<pre> PCRE2_CONFIG_BSR</pre>The output is a uint32_t integer whose value indicates what charactersequences the \R escape sequence matches by default. A value ofPCRE2_BSR_UNICODE means that \R matches any Unicode line ending sequence; avalue of PCRE2_BSR_ANYCRLF means that \R matches only CR, LF, or CRLF. Thedefault can be overridden when a pattern is compiled.<pre> PCRE2_CONFIG_COMPILED_WIDTHS</pre>The output is a uint32_t integer whose lower bits indicate which code unitwidths 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.<pre> PCRE2_CONFIG_DEPTHLIMIT</pre>The output is a uint32_t integer that gives the default limit for the depth ofnested backtracking in <b>pcre2_match()</b> or the depth of nested recursions,lookarounds, and atomic groups in <b>pcre2_dfa_match()</b>. Further details aregiven with <b>pcre2_set_depth_limit()</b> above.<pre> PCRE2_CONFIG_HEAPLIMIT</pre>The output is a uint32_t integer that gives, in kibibytes, the default limitfor the amount of heap memory used by <b>pcre2_match()</b> or<b>pcre2_dfa_match()</b>. Further details are given with<b>pcre2_set_heap_limit()</b> above.<pre> PCRE2_CONFIG_JIT</pre>The output is a uint32_t integer that is set to one if support for just-in-timecompiling is included in the library; otherwise it is set to zero. Note thathaving the support in the library does not guarantee that JIT will be used forany given match. See the<a href="pcre2jit.html"><b>pcre2jit</b></a>documentation for more details.<pre> PCRE2_CONFIG_JITTARGET</pre>The <i>where</i> argument should point to a buffer that is at least 48 codeunits long. (The exact length required can be found by calling<b>pcre2_config()</b> with <b>where</b> set to NULL.) The buffer is filled with astring that contains the name of the architecture for which the JIT compiler isconfigured, for example "x86 32bit (little endian + unaligned)". If JIT supportis not available, PCRE2_ERROR_BADOPTION is returned, otherwise the number ofcode units used is returned. This is the length of the string, plus one unitfor the terminating zero.<pre> PCRE2_CONFIG_LINKSIZE</pre>The output is a uint32_t integer that contains the number of bytes used forinternal linkage in compiled regular expressions. When PCRE2 is configured, thevalue can be set to 2, 3, or 4, with the default being 2. This is the valuethat is returned by <b>pcre2_config()</b>. However, when the 16-bit library iscompiled, a value of 3 is rounded up to 4, and when the 32-bit library iscompiled, internal linkages always use 4 bytes, so the configured value is notrelevant.</P><P>The default value of 2 for the 8-bit and 16-bit libraries is sufficient for allbut the most massive patterns, since it allows the size of the compiled patternto be up to 65535 code units. Larger values allow larger regular expressions tobe compiled by those two libraries, but at the expense of slower matching.<pre> PCRE2_CONFIG_MATCHLIMIT</pre>The output is a uint32_t integer that gives the default match limit for<b>pcre2_match()</b>. Further details are given with<b>pcre2_set_match_limit()</b> above.<pre> PCRE2_CONFIG_NEWLINE</pre>The output is a uint32_t integer whose value specifies the default charactersequence that is recognized as meaning "newline". The values are:<pre> 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)</pre>The default should normally correspond to the standard sequence for youroperating system.<pre> PCRE2_CONFIG_NEVER_BACKSLASH_C</pre>The output is a uint32_t integer that is set to one if the use of \C waspermanently disabled when PCRE2 was built; otherwise it is set to zero.<pre> PCRE2_CONFIG_PARENSLIMIT</pre>The output is a uint32_t integer that gives the maximum depth of nestingof parentheses (of any kind) in a pattern. This limit is imposed to cap theamount of system stack used when a pattern is compiled. It is specified whenPCRE2 is built; the default is 250. This limit does not take into account thestack that may already be used by the calling application. For finer controlover compilation stack usage, see <b>pcre2_set_compile_recursion_guard()</b>.<pre> PCRE2_CONFIG_STACKRECURSE</pre>This parameter is obsolete and should not be used in new code. The output is auint32_t integer that is always set to zero.<pre> PCRE2_CONFIG_TABLES_LENGTH</pre>The output is a uint32_t integer that gives the length of PCRE2's characterprocessing tables in bytes. For details of these tables see the<a href="#localesupport">section on locale support</a>below.<pre> PCRE2_CONFIG_UNICODE_VERSION</pre>The <i>where</i> argument should point to a buffer that is at least 24 codeunits long. (The exact length required can be found by calling<b>pcre2_config()</b> with <b>where</b> set to NULL.) If PCRE2 has been compiledwithout Unicode support, the buffer is filled with the text "Unicode notsupported". Otherwise, the Unicode version string (for example, "8.0.0") isinserted. The number of code units used is returned. This is the length of thestring plus one unit for the terminating zero.<pre> PCRE2_CONFIG_UNICODE</pre>The output is a uint32_t integer that is set to one if Unicode support isavailable; otherwise it is set to zero. Unicode support implies UTF support.<pre> PCRE2_CONFIG_VERSION</pre>The <i>where</i> argument should point to a buffer that is at least 24 codeunits long. (The exact length required can be found by calling<b>pcre2_config()</b> with <b>where</b> set to NULL.) The buffer is filled withthe PCRE2 version string, zero-terminated. The number of code units used isreturned. This is the length of the string plus one unit for the terminatingzero.<a name="compiling"></a></P><br><a name="SEC20" href="#TOC1">COMPILING A PATTERN</a><br><P><b>pcre2_code *pcre2_compile(PCRE2_SPTR <i>pattern</i>, PCRE2_SIZE <i>length</i>,</b><b> uint32_t <i>options</i>, int *<i>errorcode</i>, PCRE2_SIZE *<i>erroroffset,</i></b><b> pcre2_compile_context *<i>ccontext</i>);</b><br><br><b>void pcre2_code_free(pcre2_code *<i>code</i>);</b><br><br><b>pcre2_code *pcre2_code_copy(const pcre2_code *<i>code</i>);</b><br><br><b>pcre2_code *pcre2_code_copy_with_tables(const pcre2_code *<i>code</i>);</b></P><P>The <b>pcre2_compile()</b> function compiles a pattern into an internal form.The pattern is defined by a pointer to a string of code units and a length incode units. If the pattern is zero-terminated, the length can be specified asPCRE2_ZERO_TERMINATED. A NULL pattern pointer with a length of zero is treatedas an empty string (NULL with a non-zero length causes an error return). Thefunction returns a pointer to a block of memory that contains the compiledpattern and related data, or NULL if an error occurred.</P><P>If the compile context argument <i>ccontext</i> is NULL, memory for the compiledpattern is obtained by calling <b>malloc()</b>. Otherwise, it is obtained fromthe same memory function that was used for the compile context. The caller mustfree the memory by calling <b>pcre2_code_free()</b> when it is no longer needed.If <b>pcre2_code_free()</b> is called with a NULL argument, it returnsimmediately, without doing anything.</P><P>The function <b>pcre2_code_copy()</b> makes a copy of the compiled code in newmemory, using the same memory allocator as was used for the original. However,if the code has been processed by the JIT compiler (see<a href="#jitcompiling">below),</a>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 bepassed to <b>pcre2_jit_compile()</b> if required. If <b>pcre2_code_copy()</b> iscalled with a NULL argument, it returns NULL.</P><P>The <b>pcre2_code_copy()</b> function provides a way for individual threads in amultithreaded application to acquire a private copy of shared compiled code.However, it does not make a copy of the character tables used by the compiledpattern; the new pattern code points to the same tables as the original code.(See<a href="#jitcompiling">"Locale Support"</a>below for details of these character tables.) In many applications the sametables are used throughout, so this behaviour is appropriate. Nevertheless,there are occasions when a copy of a compiled pattern and the relevant tablesare needed. The <b>pcre2_code_copy_with_tables()</b> provides this facility.Copies of both the code and the tables are made, with the new code pointing tothe new tables. The memory for the new tables is automatically freed when<b>pcre2_code_free()</b> is called for the new copy of the compiled code. If<b>pcre2_code_copy_with_tables()</b> is called with a NULL argument, it returnsNULL.</P><P>NOTE: When one of the matching functions is called, pointers to the compiledpattern and the subject string are set in the match data block so that they canbe referenced by the substring extraction functions after a successful match.After running a match, you must not free a compiled pattern or a subject stringuntil after all operations on the<a href="#matchdatablock">match data block</a>have taken place, unless, in the case of the subject string, you have used thePCRE2_COPY_MATCHED_SUBJECT option, which is described in the section entitled"Option bits for <b>pcre2_match()</b>"<a href="#matchoptions>">below.</a></P><P>The <i>options</i> argument for <b>pcre2_compile()</b> contains various bitsettings that affect the compilation. It should be zero if none of them arerequired. The available options are described below. Some of them (inparticular, those that are compatible with Perl, but some others as well) canalso be set and unset from within the pattern (see the detailed description inthe<a href="pcre2pattern.html"><b>pcre2pattern</b></a>documentation).</P><P>For those options that can be different in different parts of the pattern, thecontents of the <i>options</i> argument specifies their settings at the start ofcompilation. The PCRE2_ANCHORED, PCRE2_ENDANCHORED, and PCRE2_NO_UTF_CHECKoptions can be set at the time of matching as well as at compile time.</P><P>Some additional options and less frequently required compile-time parameters(for example, the newline setting) can be provided in a compile context (asdescribed<a href="#compilecontext">above).</a></P><P>If <i>errorcode</i> or <i>erroroffset</i> is NULL, <b>pcre2_compile()</b> returnsNULL immediately. Otherwise, the variables to which these point are set to anerror code and an offset (number of code units) within the pattern,respectively, when <b>pcre2_compile()</b> returns NULL because a compilationerror has occurred.</P><P>There are nearly 100 positive error codes that <b>pcre2_compile()</b> may returnif it finds an error in the pattern. There are also some negative error codesthat are used for invalid UTF strings when validity checking is in force. Theseare the same as given by <b>pcre2_match()</b> and <b>pcre2_dfa_match()</b>, andare described in the<a href="pcre2unicode.html"><b>pcre2unicode</b></a>documentation. There is no separate documentation for the positive error codes,because the textual error messages that are obtained by calling the<b>pcre2_get_error_message()</b> function (see "Obtaining a textual errormessage"<a href="#geterrormessage">below)</a>should be self-explanatory. Macro names starting with PCRE2_ERROR_ are definedfor both positive and negative error codes in <b>pcre2.h</b>. When compilationis successful <i>errorcode</i> is set to a value that returns the message "noerror" if passed to <b>pcre2_get_error_message()</b>.</P><P>The value returned in <i>erroroffset</i> is an indication of where in thepattern an error occurred. When there is no error, zero is returned. A non-zerovalue is not necessarily the furthest point in the pattern that was read. Forexample, after the error "lookbehind assertion is not fixed length", the erroroffset points to the start of the failing assertion. For an invalid UTF-8 orUTF-16 string, the offset is that of the first code unit of the failingcharacter.</P><P>Some errors are not detected until the whole pattern has been scanned; in thesecases, the offset passed back is the length of the pattern. Note that theoffset is in code units, not characters, even in a UTF mode. It may sometimespoint into the middle of a UTF-8 or UTF-16 character.</P><P>This code fragment shows a typical straightforward call to<b>pcre2_compile()</b>:<pre> 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 */
</PRE></P><br><b>Main compile options</b><br><P>The following names for option bits are defined in the <b>pcre2.h</b> headerfile:<pre> PCRE2_ANCHORED</pre>If this bit is set, the pattern is forced to be "anchored", that is, it isconstrained to match only at the first matching point in the string that isbeing searched (the "subject string"). This effect can also be achieved byappropriate constructs in the pattern itself, which is the only way to do it inPerl.<pre> PCRE2_ALLOW_EMPTY_CLASS</pre>By default, for compatibility with Perl, a closing square bracket thatimmediately follows an opening one is treated as a data character for theclass. When PCRE2_ALLOW_EMPTY_CLASS is set, it terminates the class, whichtherefore contains no characters and so can never match.<pre> PCRE2_ALT_BSUX</pre>This option request alternative handling of three escape sequences, whichmakes PCRE2's behaviour more like ECMAscript (aka JavaScript). When it is set:</P><P>(1) \U matches an upper case "U" character; by default \U causes a compiletime error (Perl uses \U to upper case subsequent characters).</P><P>(2) \u matches a lower case "u" character unless it is followed by fourhexadecimal digits, in which case the hexadecimal number defines the code pointto match. By default, \u causes a compile time error (Perl uses it to uppercase the following character).</P><P>(3) \x matches a lower case "x" character unless it is followed by twohexadecimal digits, in which case the hexadecimal number defines the code pointto match. By default, as in Perl, a hexadecimal number is always expected after\x, but it may have zero, one, or two digits (so, for example, \xz matches abinary zero character followed by z).</P><P>ECMAscript 6 added additional functionality to \u. This can be accessed usingthe PCRE2_EXTRA_ALT_BSUX extra option (see "Extra compile options"<a href="#extracompileoptions">below).</a>Note that this alternative escape handling applies only to patterns. Neither ofthese options affects the processing of replacement strings passed to<b>pcre2_substitute()</b>.<pre> PCRE2_ALT_CIRCUMFLEX</pre>In multiline mode (when PCRE2_MULTILINE is set), the circumflex metacharactermatches at the start of the subject (unless PCRE2_NOTBOL is set), and alsoafter any internal newline. However, it does not match after a newline at theend of the subject, for compatibility with Perl. If you want a multilinecircumflex also to match after a terminating newline, you must setPCRE2_ALT_CIRCUMFLEX.<pre> PCRE2_ALT_VERBNAMES</pre>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 closingparenthesis. The name is not processed in any way, and it is not possible toinclude a closing parenthesis in the name. However, if the PCRE2_ALT_VERBNAMESoption is set, normal backslash processing is applied to verb names and only anunescaped closing parenthesis terminates the name. A closing parenthesis can beincluded in a name either as \) or between \Q and \E. If the PCRE2_EXTENDEDor PCRE2_EXTENDED_MORE option is set with PCRE2_ALT_VERBNAMES, unescapedwhitespace in verb names is skipped and #-comments are recognized, exactly asin the rest of the pattern.<pre> PCRE2_AUTO_CALLOUT</pre>If this bit is set, <b>pcre2_compile()</b> automatically inserts callout items,all with number 255, before each pattern item, except immediately before orafter an explicit callout in the pattern. For discussion of the calloutfacility, see the<a href="pcre2callout.html"><b>pcre2callout</b></a>documentation.<pre> PCRE2_CASELESS</pre>If this bit is set, letters in the pattern match both upper and lower caseletters in the subject. It is equivalent to Perl's /i option, and it can bechanged within a pattern by a (?i) option setting. If either PCRE2_UTF orPCRE2_UCP is set, Unicode properties are used for all characters with more thanone other case, and for all characters whose code points are greater thanU+007F. Note that there are two ASCII characters, K and S, that, in addition totheir lower case ASCII equivalents, are case-equivalent with U+212A (Kelvinsign) and U+017F (long S) respectively. If you do not want this caseequivalence, you can suppress it by setting PCRE2_EXTRA_CASELESS_RESTRICT.</P><P>For lower valued characters with only one other case, a lookup table is usedfor speed. When neither PCRE2_UTF nor PCRE2_UCP is set, a lookup table is usedfor all code points less than 256, and higher code points (available only in16-bit or 32-bit mode) are treated as not having another case.<pre> PCRE2_DOLLAR_ENDONLY</pre>If this bit is set, a dollar metacharacter in the pattern matches only at theend of the subject string. Without this option, a dollar also matchesimmediately before a newline at the end of the string (but not before any othernewlines). The PCRE2_DOLLAR_ENDONLY option is ignored if PCRE2_MULTILINE isset. There is no equivalent to this option in Perl, and no way to set it withina pattern.<pre> PCRE2_DOTALL</pre>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 onecharacter, even if newlines are coded as CRLF. Without this option, a dot doesnot match when the current position in the subject is at a newline. This optionis 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 newlinecharacters, and the \N escape sequence always matches a non-newline character,independent of the setting of PCRE2_DOTALL.<pre> PCRE2_DUPNAMES</pre>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 oneinstance of the named group can ever be matched. There are more details ofnamed capture groups below; see also the<a href="pcre2pattern.html"><b>pcre2pattern</b></a>documentation.<pre> PCRE2_ENDANCHORED</pre>If this bit is set, the end of any pattern match must be right at the end ofthe string being searched (the "subject string"). If the pattern matchsucceeds by reaching (*ACCEPT), but does not reach the end of the subject, thematch fails at the current starting point. For unanchored patterns, a new matchis then tried at the next starting point. However, if the match succeeds byreaching the end of the pattern, but not the end of the subject, backtrackingoccurs and an alternative match may be found. Consider these two patterns:<pre> .(*ACCEPT)|.. .|..</pre>If matched against "abc" with PCRE2_ENDANCHORED set, the first matches "c"whereas the second matches "bc". The effect of PCRE2_ENDANCHORED can also beachieved by appropriate constructs in the pattern itself, which is the only wayto do it in Perl.</P><P>For DFA matching with <b>pcre2_dfa_match()</b>, PCRE2_ENDANCHORED applies onlyto the first (that is, the longest) matched string. Other parallel matches,which are necessarily substrings of the first one, must obviously end beforethe end of the subject.<pre> PCRE2_EXTENDED</pre>If this bit is set, most white space characters in the pattern are totallyignored except when escaped, inside a character class, or inside a \Q...\Esequence. However, white space is not allowed within sequences such as (?> thatintroduce various parenthesized groups, nor within numerical quantifiers suchas {1,3}. Ignorable white space is permitted between an item and a followingquantifier and between a quantifier and a following + that indicatespossessiveness. PCRE2_EXTENDED is equivalent to Perl's /x option, and it can bechanged within a pattern by a (?x) option setting.</P><P>When PCRE2 is compiled without Unicode support, PCRE2_EXTENDED recognizes aswhite space only those characters with code points less than 256 that areflagged as white space in its low-character table. The table is normallycreated by<a href="pcre2_maketables.html"><b>pcre2_maketables()</b>,</a>which uses the <b>isspace()</b> function to identify space characters. In mostASCII environments, the relevant characters are those with code points 0x0009(tab), 0x000A (linefeed), 0x000B (vertical tab), 0x000C (formfeed), 0x000D(carriage return), and 0x0020 (space).</P><P>When PCRE2 is compiled with Unicode support, in addition to these characters,five more Unicode "Pattern White Space" characters are recognized byPCRE2_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 (paragraphseparator). This set of characters is the same as recognized by Perl's /xoption. Note that the horizontal and vertical space characters that are matchedby the \h and \v escapes in patterns are a much bigger set.</P><P>As well as ignoring most white space, PCRE2_EXTENDED also causes charactersbetween an unescaped # outside a character class and the next newline,inclusive, to be ignored, which makes it possible to include comments insidecomplicated patterns. Note that the end of this type of comment is a literalnewline sequence in the pattern; escape sequences that happen to represent anewline do not count.</P><P>Which characters are interpreted as newlines can be specified by a setting inthe compile context that is passed to <b>pcre2_compile()</b> or by a specialsequence at the start of the pattern, as described in the section entitled<a href="pcre2pattern.html#newlines">"Newline conventions"</a>in the <b>pcre2pattern</b> documentation. A default is defined when PCRE2 isbuilt.<pre> PCRE2_EXTENDED_MORE</pre>This option has the effect of PCRE2_EXTENDED, but, in addition, unescaped spaceand horizontal tab characters are ignored inside a character class. Note: onlythese two characters are ignored, not the full set of pattern white spacecharacters that are ignored outside a character class. PCRE2_EXTENDED_MORE isequivalent to Perl's /xx option, and it can be changed within a pattern by a(?xx) option setting.<pre> PCRE2_FIRSTLINE</pre>If this option is set, the start of an unanchored pattern match must be beforeor at the first newline in the subject string following the start of matching,though the matched text may continue over the newline. If <i>startoffset</i> isnon-zero, the limiting newline is not necessarily the first newline in thesubject. For example, if the subject string is "abc\nxyz" (where \nrepresents a single-character newline) a pattern match for "yz" succeeds withPCRE2_FIRSTLINE if <i>startoffset</i> is greater than 3. See alsoPCRE2_USE_OFFSET_LIMIT, which provides a more general limiting facility. IfPCRE2_FIRSTLINE is set with an offset limit, a match must occur in the firstline and also within the offset limit. In other words, whichever limit comesfirst is used. This option has no effect for anchored patterns.<pre> PCRE2_LITERAL</pre>If this option is set, all meta-characters in the pattern are disabled, and itis treated as a literal string. Matching literal strings with a regularexpression engine is not the most efficient way of doing it. If you are doing alot of literal matching and are worried about efficiency, you should considerusing other approaches. The only other main options that are allowed withPCRE2_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, andPCRE2_USE_OFFSET_LIMIT. The extra options PCRE2_EXTRA_MATCH_LINE andPCRE2_EXTRA_MATCH_WORD are also supported. Any other options cause an error.<pre> PCRE2_MATCH_INVALID_UTF</pre>This option forces PCRE2_UTF (see below) and also enables support for matchingby <b>pcre2_match()</b> in subject strings that contain invalid UTF sequences.Note, however, that the 16-bit and 32-bit PCRE2 libraries process strings assequences of uint16_t or uint32_t code points. They cannot find valid UTFsequences within an arbitrary string of bytes unless such sequences aresuitably aligned. This facility is not supported for DFA matching. For details,see the<a href="pcre2unicode.html"><b>pcre2unicode</b></a>documentation.<pre> PCRE2_MATCH_UNSET_BACKREF</pre>If this option is set, a backreference to an unset capture group matches anempty 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 canfind an "a" in the subject), whereas it fails by default, for Perlcompatibility. Setting this option makes PCRE2 behave more like ECMAscript (akaJavaScript).<pre> PCRE2_MULTILINE</pre>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 unlessPCRE2_DOTALL is set, the "any character" metacharacter (.) does not match at anewline. This behaviour (for ^, $, and dot) is the same as Perl.</P><P>When PCRE2_MULTILINE it is set, the "start of line" and "end of line"constructs match immediately following or immediately before internal newlinesin the subject string, respectively, as well as at the very start and end. Thisis 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 matchafter a newline at the end of the subject, for compatibility with Perl.However, you can change this by setting the PCRE2_ALT_CIRCUMFLEX option. Ifthere are no newlines in a subject string, or no occurrences of ^ or $ in apattern, setting PCRE2_MULTILINE has no effect.<pre> PCRE2_NEVER_BACKSLASH_C</pre>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, becauseit may leave the current matching point in the middle of a multi-code-unitcharacter. This option may be useful in applications that process patterns fromexternal sources. Note that there is also a build-time option that permanentlylocks out the use of \C.<pre> PCRE2_NEVER_UCP</pre>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 describedfor the PCRE2_UCP option below. In particular, it prevents the creator of thepattern from enabling this facility by starting the pattern with (*UCP). Thisoption may be useful in applications that process patterns from externalsources. The option combination PCRE_UCP and PCRE_NEVER_UCP causes an error.<pre> PCRE2_NEVER_UTF</pre>This option locks out interpretation of the pattern as UTF-8, UTF-16, orUTF-32, depending on which library is in use. In particular, it prevents thecreator of the pattern from switching to UTF interpretation by starting thepattern with (*UTF). This option may be useful in applications that processpatterns from external sources. The combination of PCRE2_UTF andPCRE2_NEVER_UTF causes an error.<pre> PCRE2_NO_AUTO_CAPTURE</pre>If this option is set, it disables the use of numbered capturing parentheses inthe pattern. Any opening parenthesis that is not followed by ? behaves as if itwere followed by ?: but named parentheses can still be used for capturing (andthey 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.<pre> PCRE2_NO_AUTO_POSSESS</pre>If this option is set, it disables "auto-possessification", which is anoptimization that, for example, turns a+b into a++b in order to avoidbacktracks into a+ that can never be successful. However, if callouts are inuse, auto-possessification means that some callouts are never taken. You canset this option if you want the matching functions to do a full unoptimizedsearch and run all the callouts, but it is mainly provided for testingpurposes.<pre> PCRE2_NO_DOTSTAR_ANCHOR</pre>If this option is set, it disables an optimization that is applied when .* isthe first significant item in a top-level branch of a pattern, and all theother branches also start with .* or with \A or \G or ^. The optimization isautomatically disabled for .* if it is inside an atomic group or a capturegroup that is the subject of a backreference, or if the pattern contains(*PRUNE) or (*SKIP). When the optimization is not disabled, such a pattern isautomatically anchored if PCRE2_DOTALL is set for all the .* items andPCRE2_MULTILINE is not set for any ^ items. Otherwise, the fact that any matchmust start either at the start of the subject or following a newline isremembered. Like other optimizations, this can cause callouts to be skipped.<pre> PCRE2_NO_START_OPTIMIZE</pre>This is an option whose main effect is at matching time. It does not changewhat <b>pcre2_compile()</b> generates, but it does affect the output of the JITcompiler.</P><P>There are a number of optimizations that may occur at the start of a match, inorder to speed up the process. For example, if it is known that an unanchoredmatch must start with a specific code unit value, the matching code searchesthe subject for that value, and fails immediately if it cannot find it, withoutactually running the main matching function. This means that a special itemsuch as (*COMMIT) at the start of a pattern is not considered until after asuitable 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 beskipped if the pattern is never actually used. The start-up optimizations arein effect a pre-scan of the subject that takes place before the pattern is run.</P><P>The PCRE2_NO_START_OPTIMIZE option disables the start-up optimizations,possibly causing performance to suffer, but ensuring that in cases where theresult is "no match", the callouts do occur, and that items such as (*COMMIT)and (*MARK) are considered at every possible starting position in the subjectstring.</P><P>Setting PCRE2_NO_START_OPTIMIZE may change the outcome of a matching operation.Consider the pattern<pre> (*COMMIT)ABC</pre>When this is compiled, PCRE2 records the fact that a match must start with thecharacter "A". Suppose the subject string is "DEFABC". The start-upoptimization scans along the subject, finds "A" and runs the first matchattempt from there. The (*COMMIT) item means that the pattern must match thecurrent starting position, which in this case, it does. However, if the samematch is run with PCRE2_NO_START_OPTIMIZE set, the initial scan along thesubject string does not happen. The first match attempt is run starting from"D" and when this fails, (*COMMIT) prevents any further matches being tried, sothe overall result is "no match".</P><P>As another start-up optimization makes use of a minimum length for a matchingsubject, which is recorded when possible. Consider the pattern<pre> (*MARK:1)B(*MARK:2)(X|Y)</pre>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", whichis long enough. In the process, (*MARK:2) is encountered and remembered. Whenthe match attempt fails, the next "B" is found, but there is only one characterleft, so there are no more attempts, and "no match" is returned with the "lastmark seen" set to "2". If NO_START_OPTIMIZE is set, however, matches are triedat 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 isreturned is "1". In this case, the optimizations do not affect the overallmatch result, which is still "no match", but they do affect the auxiliaryinformation that is returned.<pre> PCRE2_NO_UTF_CHECK</pre>When PCRE2_UTF is set, the validity of the pattern as a UTF string isautomatically checked. There are discussions about the validity of<a href="pcre2unicode.html#utf8strings">UTF-8 strings,</a><a href="pcre2unicode.html#utf16strings">UTF-16 strings,</a>and<a href="pcre2unicode.html#utf32strings">UTF-32 strings</a>in the<a href="pcre2unicode.html"><b>pcre2unicode</b></a>document. If an invalid UTF sequence is found, <b>pcre2_compile()</b> returns anegative error code.</P><P>If you know that your pattern is a valid UTF string, and you want to skip thischeck for performance reasons, you can set the PCRE2_NO_UTF_CHECK option. Whenit is set, the effect of passing an invalid UTF string as a pattern isundefined. It may cause your program to crash or loop.</P><P>Note that this option can also be passed to <b>pcre2_match()</b> and<b>pcre2_dfa_match()</b>, to suppress UTF validity checking of the subjectstring.</P><P>Note also that setting PCRE2_NO_UTF_CHECK at compile time does not disable theerror that is given if an escape sequence for an invalid Unicode code point isencountered in the pattern. In particular, the so-called "surrogate" codepoints (0xd800 to 0xdfff) are invalid. If you want to allow escape sequencessuch as \x{d800} you can set the PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES extraoption, as described in the section entitled "Extra compile options"<a href="#extracompileoptions">below.</a>However, this is possible only in UTF-8 and UTF-32 modes, because these valuesare not representable in UTF-16.<pre> PCRE2_UCP</pre>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. Bydefault, only ASCII characters are recognized, but if PCRE2_UCP is set, Unicodeproperties are used to classify characters. There are some PCRE2_EXTRAoptions (see below) that add finer control to this behaviour. More details aregiven in the section on<a href="pcre2pattern.html#genericchartypes">generic character types</a>in the<a href="pcre2pattern.html"><b>pcre2pattern</b></a>page.</P><P>The second effect of PCRE2_UCP is to force the use of Unicode properties forupper/lower casing operations, even when PCRE2_UTF is not set. This makes itpossible to process strings in the 16-bit UCS-2 code. This option is availableonly if PCRE2 has been compiled with Unicode support (which is the default).The PCRE2_EXTRA_CASELESS_RESTRICT option (see below) restricts caselessmatching such that ASCII characters match only ASCII characters and non-ASCIIcharacters match only non-ASCII characters.<pre> PCRE2_UNGREEDY</pre>This option inverts the "greediness" of the quantifiers so that they are notgreedy by default, but become greedy if followed by "?". It is not compatiblewith Perl. It can also be set by a (?U) option setting within the pattern.<pre> PCRE2_USE_OFFSET_LIMIT</pre>This option must be set for <b>pcre2_compile()</b> if<b>pcre2_set_offset_limit()</b> is going to be used to set a non-default offsetlimit in a match context for matches that use this pattern. An error isgenerated if an offset limit is set without this option. For more details, seethe description of <b>pcre2_set_offset_limit()</b> in the<a href="#matchcontext">section</a>that describes match contexts. See also the PCRE2_FIRSTLINEoption above.<pre> PCRE2_UTF</pre>This option causes PCRE2 to regard both the pattern and the subject stringsthat are subsequently processed as strings of UTF characters instead ofsingle-code-unit strings. It is available when PCRE2 is built to includeUnicode 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 thebehaviour of PCRE2 are given in the<a href="pcre2unicode.html"><b>pcre2unicode</b></a>page. In particular, note that it changes the way PCRE2_CASELESS works.<a name="extracompileoptions"></a></P><br><b>Extra compile options</b><br><P>The option bits that can be set in a compile context by calling the<b>pcre2_set_compile_extra_options()</b> function are as follows:<pre> PCRE2_EXTRA_ALLOW_LOOKAROUND_BSK</pre>Since release 10.38 PCRE2 has forbidden the use of \K within lookaroundassertions, following Perl's lead. This option is provided to re-enable theprevious behaviour (act in positive lookarounds, ignore in negative ones) incase anybody is relying on it.<pre> PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES</pre>This option applies when compiling a pattern in UTF-8 or UTF-32 mode. It isforbidden 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 encodecode points with values in the range 0x10000 to 0x10ffff. The surrogates cannottherefore be represented in UTF-16. They can be represented in UTF-8 andUTF-32, but are defined as invalid code points, and cause errors if encounteredin a UTF-8 or UTF-32 string that is being checked for validity by PCRE2.</P><P>These values also cause errors if encountered in escape sequences such as\x{d912} within a pattern. However, it seems that some applications, whenusing PCRE2 to check for unwanted characters in UTF-8 strings, explicitly testfor the surrogates using escape sequences. The PCRE2_NO_UTF_CHECK option doesnot disable the error that occurs, because it applies only to the testing ofinput strings for UTF validity.</P><P>If the extra option PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES is set, surrogate codepoint values in UTF-8 and UTF-32 patterns no longer provoke errors and areincorporated in the compiled pattern. However, they can only match subjectcharacters if the matching function is called with PCRE2_NO_UTF_CHECK set.<pre> PCRE2_EXTRA_ALT_BSUX</pre>The original option PCRE2_ALT_BSUX causes PCRE2 to process \U, \u, and \x inthe way that ECMAscript (aka JavaScript) does. Additional functionality wasdefined by ECMAscript 6; setting PCRE2_EXTRA_ALT_BSUX has the effect ofPCRE2_ALT_BSUX, but in addition it recognizes \u{hhh..} as a hexadecimalcharacter code, where hhh.. is any number of hexadecimal digits.<pre> PCRE2_EXTRA_ASCII_BSD</pre>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.<pre> PCRE2_EXTRA_ASCII_BSS</pre>This option forces \s to match only ASCII space characters, even whenPCRE2_UCP is set. It can be changed within a pattern by means of the (?aS)option setting.<pre> PCRE2_EXTRA_ASCII_BSW</pre>This option forces \w to match only ASCII word characters, even when PCRE2_UCPis set. It can be changed within a pattern by means of the (?aW) optionsetting.<pre> PCRE2_EXTRA_ASCII_DIGIT</pre>This option forces the POSIX character classes [:digit:] and [:xdigit:] tomatch only ASCII digits, even when PCRE2_UCP is set. It can be changed withina pattern by means of the (?aT) option setting.<pre> PCRE2_EXTRA_ASCII_POSIX</pre>This option forces all the POSIX character classes, including [:digit:] and[:xdigit:], to match only ASCII characters, even when PCRE2_UCP is set. It canbe changed within a pattern by means of the (?aP) option setting, but note thatthis also sets PCRE2_EXTRA_ASCII_DIGIT in order to ensure that (?-aP) unsetsall ASCII restrictions for POSIX classes.<pre> PCRE2_EXTRA_BAD_ESCAPE_IS_LITERAL</pre>This is a dangerous option. Use with care. By default, an unrecognized escapesuch as \j or a malformed one such as \x{2z} causes a compile-time error whendetected by <b>pcre2_compile()</b>. Perl is somewhat inconsistent in handlingsuch items: for example, \j is treated as a literal "j", and non-hexadecimaldigits in \x{} are just ignored, though warnings are given in both cases ifPerl's warning switch is enabled. However, a malformed octal number after \o{always causes an error in Perl.</P><P>If the PCRE2_EXTRA_BAD_ESCAPE_IS_LITERAL extra option is passed to<b>pcre2_compile()</b>, all unrecognized or malformed escape sequences aretreated 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 meansthat typos in patterns may go undetected and have unexpected results. Also notethat 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 anunqualified \N is a valid escape sequence but is not supported in a characterclass. To reiterate: this is a dangerous option. Use with great care.<pre> PCRE2_EXTRA_CASELESS_RESTRICT</pre>When either PCRE2_UCP or PCRE2_UTF is set, caseless matching follows Unicoderules, which allow for more than two cases per character. There are twocase-equivalent character sets that contain both ASCII and non-ASCIIcharacters. The ASCII letter S is case-equivalent to U+017f (long S) and theASCII letter K is case-equivalent to U+212a (Kelvin sign). This option disablesrecognition of case-equivalences that cross the ASCII/non-ASCII boundary. In acaseless match, both characters must either be ASCII or non-ASCII. The optioncan be changed with a pattern by the (?r) option setting.<pre> PCRE2_EXTRA_ESCAPED_CR_IS_LF</pre>There are some legacy applications where the escape sequence \r in a patternis expected to match a newline. If this option is set, \r in a pattern isconverted to \n so that it matches a LF (linefeed) instead of a CR (carriagereturn) character. The option does not affect a literal CR in the pattern, nordoes it affect CR specified as an explicit code point such as \x{0D}.<pre> PCRE2_EXTRA_MATCH_LINE</pre>This option is provided for use by the <b>-x</b> option of <b>pcre2grep</b>. Itcauses the pattern only to match complete lines. This is achieved byautomatically inserting the code for "^(?:" at the start of the compiledpattern and ")$" at the end. Thus, when PCRE2_MULTILINE is set, the matchedline may be in the middle of the subject string. This option can be used withPCRE2_LITERAL.<pre> PCRE2_EXTRA_MATCH_WORD</pre>This option is provided for use by the <b>-w</b> option of <b>pcre2grep</b>. Itcauses the pattern only to match strings that have a word boundary at the startand 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 beused with PCRE2_LITERAL. However, it is ignored if PCRE2_EXTRA_MATCH_LINE isalso set.<a name="jitcompiling"></a></P><br><a name="SEC21" href="#TOC1">JUST-IN-TIME (JIT) COMPILATION</a><br><P><b>int pcre2_jit_compile(pcre2_code *<i>code</i>, uint32_t <i>options</i>);</b><br><br><b>int pcre2_jit_match(const pcre2_code *<i>code</i>, PCRE2_SPTR <i>subject</i>,</b><b> PCRE2_SIZE <i>length</i>, PCRE2_SIZE <i>startoffset</i>,</b><b> uint32_t <i>options</i>, pcre2_match_data *<i>match_data</i>,</b><b> pcre2_match_context *<i>mcontext</i>);</b><br><br><b>void pcre2_jit_free_unused_memory(pcre2_general_context *<i>gcontext</i>);</b><br><br><b>pcre2_jit_stack *pcre2_jit_stack_create(size_t <i>startsize</i>,</b><b> size_t <i>maxsize</i>, pcre2_general_context *<i>gcontext</i>);</b><br><br><b>void pcre2_jit_stack_assign(pcre2_match_context *<i>mcontext</i>,</b><b> pcre2_jit_callback <i>callback_function</i>, void *<i>callback_data</i>);</b><br><br><b>void pcre2_jit_stack_free(pcre2_jit_stack *<i>jit_stack</i>);</b></P><P>These functions provide support for JIT compilation, which, if the just-in-timecompiler is available, further processes a compiled pattern into machine codethat executes much faster than the <b>pcre2_match()</b> interpretive matchingfunction. Full details are given in the<a href="pcre2jit.html"><b>pcre2jit</b></a>documentation.</P><P>JIT compilation is a heavyweight optimization. It can take some time forpatterns to be analyzed, and for one-off matches and simple patterns thebenefit of faster execution might be offset by a much slower compilation time.Most (but not all) patterns can be optimized by the JIT compiler.<a name="localesupport"></a></P><br><a name="SEC22" href="#TOC1">LOCALE SUPPORT</a><br><P><b>const uint8_t *pcre2_maketables(pcre2_general_context *<i>gcontext</i>);</b><br><br><b>void pcre2_maketables_free(pcre2_general_context *<i>gcontext</i>,</b><b> const uint8_t *<i>tables</i>);</b></P><P>PCRE2 handles caseless matching, and determines whether characters are letters,digits, or whatever, by reference to a set of tables, indexed by character codepoint. However, this applies only to characters whose code points are less than256. By default, higher-valued code points never match escapes such as \w or\d.</P><P>When PCRE2 is built with Unicode support (the default), certain Unicodecharacter properties can be tested with \p and \P, or, alternatively, thePCRE2_UCP option can be set when a pattern is compiled; this causes \w andfriends to use Unicode property support instead of the built-in tables.PCRE2_UCP also causes upper/lower casing operations on characters with codepoints greater than 127 to use Unicode properties. These effects apply evenwhen PCRE2_UTF is not set. There are, however, some PCRE2_EXTRA options (seeabove) that can be used to modify or suppress them.</P><P>The use of locales with Unicode is discouraged. If you are handling characterswith code points greater than 127, you should either use Unicode support, oruse locales, but not try to mix the two.</P><P>PCRE2 contains a built-in set of character tables that are used by default.These are sufficient for many applications. Normally, the internal tablesrecognize only ASCII characters. However, when PCRE2 is built, it is possibleto cause the internal tables to be rebuilt in the default "C" locale of thelocal system, which may cause them to be different.</P><P>The built-in tables can be overridden by tables supplied by the applicationthat 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 localesupport is expected to die away.</P><P>External tables are built by calling the <b>pcre2_maketables()</b> function, inthe 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 <b>malloc()</b> is used. The result can be passed to<b>pcre2_compile()</b> as often as necessary, by creating a compile context andcalling <b>pcre2_set_character_tables()</b> to set the tables pointer therein.</P><P>For example, to build and use tables that are appropriate for the French locale(where accented characters with values greater than 127 are treated asletters), the following code could be used:<pre> 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);</pre>The locale name "fr_FR" is used on Linux and other Unix-like systems; if youare using Windows, the name for the French locale is "french".</P><P>The pointer that is passed (via the compile context) to <b>pcre2_compile()</b>is saved with the compiled pattern, and the same tables are used by thematching functions. Thus, for any single pattern, compilation and matching bothhappen in the same locale, but different patterns can be processed in differentlocales.</P><P>It is the caller's responsibility to ensure that the memory containing thetables remains available while they are still in use. When they are no longerneeded, you can discard them using <b>pcre2_maketables_free()</b>, which shouldpass as its first parameter the same global context that was used to create thetables.</P><br><b>Saving locale tables</b><br><P>The tables described above are just a sequence of binary bytes, which makesthem independent of hardware characteristics such as endianness or whether theprocessor is 32-bit or 64-bit. A copy of the result of <b>pcre2_maketables()</b>can therefore be saved in a file or elsewhere and re-used later, even in adifferent program or on another computer. The size of the tables (number ofbytes) must be obtained by calling <b>pcre2_config()</b> with thePCRE2_CONFIG_TABLES_LENGTH option because <b>pcre2_maketables()</b> does notreturn this value. Note that the <b>pcre2_dftables</b> program, which is part ofthe PCRE2 build system, can be used stand-alone to create a file that containsa set of binary tables. See the<a href="pcre2build.html#createtables"><b>pcre2build</b></a>documentation for details.<a name="infoaboutpattern"></a></P><br><a name="SEC23" href="#TOC1">INFORMATION ABOUT A COMPILED PATTERN</a><br><P><b>int pcre2_pattern_info(const pcre2 *<i>code</i>, uint32_t <i>what</i>, void *<i>where</i>);</b></P><P>The <b>pcre2_pattern_info()</b> function returns general information about acompiled pattern. For information about callouts, see the<a href="#infoaboutcallouts">next section.</a>The first argument for <b>pcre2_pattern_info()</b> is a pointer to the compiledpattern. 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 thethird argument is NULL, the first argument is ignored, and the function returnsthe size in bytes of the variable that is required for the informationrequested. Otherwise, the yield of the function is zero for success, or one ofthe following negative numbers:<pre> PCRE2_ERROR_NULL the argument <i>code</i> was NULL PCRE2_ERROR_BADMAGIC the "magic number" was not found PCRE2_ERROR_BADOPTION the value of <i>what</i> was invalid PCRE2_ERROR_UNSET the requested field is not set</pre>The "magic number" is placed at the start of each compiled pattern as a simplecheck against passing an arbitrary memory pointer. Here is a typical call of<b>pcre2_pattern_info()</b>, to obtain the length of the compiled pattern:<pre> 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 */</pre>The possible values for the second argument are defined in <b>pcre2.h</b>, andare as follows:<pre> PCRE2_INFO_ALLOPTIONS PCRE2_INFO_ARGOPTIONS PCRE2_INFO_EXTRAOPTIONS</pre>Return copies of the pattern's options. The third argument should point to a<b>uint32_t</b> variable. PCRE2_INFO_ARGOPTIONS returns exactly the options thatwere passed to <b>pcre2_compile()</b>, whereas PCRE2_INFO_ALLOPTIONS returnsthe 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 theextra options that were set in the compile context by calling thepcre2_set_compile_extra_options() function.</P><P>For example, if the pattern /(*UTF)abc/ is compiled with the PCRE2_EXTENDEDoption, 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 theresult of PCRE2_INFO_ALLOPTIONS, even if they appear right at the start of thepattern. (This was different in some earlier releases.)</P><P>A pattern compiled without PCRE2_ANCHORED is automatically anchored by PCRE2 ifthe first significant item in every top-level branch is one of the following:<pre> ^ unless PCRE2_MULTILINE is set \A always \G always .* sometimes - see below</pre>When .* is the first significant item, anchoring is possible only when all thefollowing are true:<pre> .* 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</pre>For patterns that are auto-anchored, the PCRE2_ANCHORED bit is set in theoptions returned for PCRE2_INFO_ALLOPTIONS.<pre> PCRE2_INFO_BACKREFMAX</pre>Return the number of the highest backreference in the pattern. The thirdargument should point to a <b>uint32_t</b> variable. Named capture groupsacquire numbers as well as names, and these count towards the highestbackreference. Backreferences such as \4 or \g{12} match the capturedcharacters of the given group, but in addition, the check that a capturegroup is set in a conditional group such as (?(3)a|b) is also a backreference.Zero is returned if there are no backreferences.<pre> PCRE2_INFO_BSR</pre>The output is a uint32_t integer whose value indicates what character sequencesthe \R escape sequence matches. A value of PCRE2_BSR_UNICODE means that \Rmatches any Unicode line ending sequence; a value of PCRE2_BSR_ANYCRLF meansthat \R matches only CR, LF, or CRLF.<pre> PCRE2_INFO_CAPTURECOUNT</pre>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 thirdargument should point to a <b>uint32_t</b> variable.<pre> PCRE2_INFO_DEPTHLIMIT</pre>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 argumentshould point to a uint32_t integer. If no such value has been set, the call to<b>pcre2_pattern_info()</b> returns the error PCRE2_ERROR_UNSET. Note that thislimit will only be used during matching if it is less than the limit set ordefaulted by the caller of the match function.<pre> PCRE2_INFO_FIRSTBITMAP</pre>In the absence of a single first code unit for a non-anchored pattern,<b>pcre2_compile()</b> may construct a 256-bit table that defines a fixed set ofvalues for the first code unit in any match. For example, a pattern that startswith [abc] results in a table with three bits set. When code unit valuesgreater than 255 are supported, the flag bit for 255 means "any code unit ofvalue 255 or above". If such a table was constructed, a pointer to it isreturned. Otherwise NULL is returned. The third argument should point to a<b>const uint8_t *</b> variable.<pre> PCRE2_INFO_FIRSTCODETYPE</pre>Return information about the first code unit of any matched string, for anon-anchored pattern. The third argument should point to a <b>uint32_t</b>variable. If there is a fixed first value, for example, the letter "c" from apattern such as (cat|cow|coyote), 1 is returned, and the value can be retrievedusing PCRE2_INFO_FIRSTCODEUNIT. If there is no fixed first value, but it isknown that a match can occur only at the start of the subject or following anewline in the subject, 2 is returned. Otherwise, and for anchored patterns, 0is returned.<pre> PCRE2_INFO_FIRSTCODEUNIT</pre>Return the value of the first code unit of any matched string for a patternwhere PCRE2_INFO_FIRSTCODETYPE returns 1; otherwise return 0. The thirdargument should point to a <b>uint32_t</b> variable. In the 8-bit library, thevalue is always less than 256. In the 16-bit library the value can be up to0xffff. 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.<pre> PCRE2_INFO_FRAMESIZE</pre>Return the size (in bytes) of the data frames that are used to rememberbacktracking positions when the pattern is processed by <b>pcre2_match()</b>without the use of JIT. The third argument should point to a <b>size_t</b>variable. The frame size depends on the number of capturing parentheses in thepattern. Each additional capture group adds two PCRE2_SIZE variables.<pre> PCRE2_INFO_HASBACKSLASHC</pre>Return 1 if the pattern contains any instances of \C, otherwise 0. The thirdargument should point to a <b>uint32_t</b> variable.<pre> PCRE2_INFO_HASCRORLF</pre>Return 1 if the pattern contains any explicit matches for CR or LF characters,otherwise 0. The third argument should point to a <b>uint32_t</b> variable. Anexplicit match is either a literal CR or LF character, or \r or \n or one ofthe equivalent hexadecimal or octal escape sequences.<pre> PCRE2_INFO_HEAPLIMIT</pre>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 argumentshould point to a uint32_t integer. If no such value has been set, the call to<b>pcre2_pattern_info()</b> returns the error PCRE2_ERROR_UNSET. Note that thislimit will only be used during matching if it is less than the limit set ordefaulted by the caller of the match function.<pre> PCRE2_INFO_JCHANGED</pre>Return 1 if the (?J) or (?-J) option setting is used in the pattern, otherwise0. The third argument should point to a <b>uint32_t</b> variable. (?J) and(?-J) set and unset the local PCRE2_DUPNAMES option, respectively.<pre> PCRE2_INFO_JITSIZE</pre>If the compiled pattern was successfully processed by<b>pcre2_jit_compile()</b>, return the size of the JIT compiled code, otherwisereturn zero. The third argument should point to a <b>size_t</b> variable.<pre> PCRE2_INFO_LASTCODETYPE</pre>Returns 1 if there is a rightmost literal code unit that must exist in anymatched string, other than at its start. The third argument should point to a<b>uint32_t</b> variable. If there is no such value, 0 is returned. When 1 isreturned, the code unit value itself can be retrieved usingPCRE2_INFO_LASTCODEUNIT. For anchored patterns, a last literal value isrecorded only if it follows something of variable length. For example, for thepattern /^a\d+z\d+/ the returned value is 1 (with "z" returned fromPCRE2_INFO_LASTCODEUNIT), but for /^a\dz\d/ the returned value is 0.<pre> PCRE2_INFO_LASTCODEUNIT</pre>Return the value of the rightmost literal code unit that must exist in anymatched string, other than at its start, for a pattern wherePCRE2_INFO_LASTCODETYPE returns 1. Otherwise, return 0. The third argumentshould point to a <b>uint32_t</b> variable.<pre> PCRE2_INFO_MATCHEMPTY</pre>Return 1 if the pattern might match an empty string, otherwise 0. The thirdargument should point to a <b>uint32_t</b> variable. When a pattern containsrecursive subroutine calls it is not always possible to determine whether ornot it can match an empty string. PCRE2 takes a cautious approach and returns 1in such cases.<pre> PCRE2_INFO_MATCHLIMIT</pre>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 argumentshould point to a uint32_t integer. If no such value has been set, the call to<b>pcre2_pattern_info()</b> returns the error PCRE2_ERROR_UNSET. Note that thislimit will only be used during matching if it is less than the limit set ordefaulted by the caller of the match function.<pre> PCRE2_INFO_MAXLOOKBEHIND</pre>A lookbehind assertion moves back a certain number of characters (not codeunits) when it starts to process each of its branches. This request returns thelargest of these backward moves. The third argument should point to a uint32_tinteger. The simple assertions \b and \B require a one-character lookbehindand cause PCRE2_INFO_MAXLOOKBEHIND to return 1 in the absence of anythinglonger. \A also registers a one-character lookbehind, though it does notactually inspect the previous character.</P><P>Note that this information is useful for multi-segment matching onlyif the pattern contains no nested lookbehinds. For example, the pattern(?<=a(?<=ba)c) returns a maximum lookbehind of 2, but when it is processed, thefirst lookbehind moves back by two characters, matches one character, then thenested lookbehind also moves back by two characters. This puts the matchingpoint three characters earlier than it was at the start.PCRE2_INFO_MAXLOOKBEHIND is really only useful as a debugging tool. See the<a href="pcre2partial.html"><b>pcre2partial</b></a>documentation for a discussion of multi-segment matching.<pre> PCRE2_INFO_MINLENGTH</pre>If a minimum length for matching subject strings was computed, its value isreturned. Otherwise the returned value is 0. This value is not computed whenPCRE2_NO_START_OPTIMIZE is set. The value is a number of characters, which inUTF mode may be different from the number of code units. The third argumentshould point to a <b>uint32_t</b> variable. The value is a lower bound to thelength of any matching string. There may not be any strings of that length thatdo actually match, but every string that does match is at least that long.<pre> PCRE2_INFO_NAMECOUNT PCRE2_INFO_NAMEENTRYSIZE PCRE2_INFO_NAMETABLE</pre>PCRE2 supports the use of named as well as numbered capturing parentheses. Thenames are just an additional way of identifying the parentheses, which stillacquire numbers. Several convenience functions such as<b>pcre2_substring_get_byname()</b> are provided for extracting capturedsubstrings by name. It is also possible to extract the data directly, by firstconverting the name to a number in order to access the correct pointers in theoutput vector (described with <b>pcre2_match()</b> below). To do the conversion,you need to use the name-to-number map, which is described by these threevalues.</P><P>The map consists of a number of fixed-size entries. PCRE2_INFO_NAMECOUNT givesthe number of entries, and PCRE2_INFO_NAMEENTRYSIZE gives the size of eachentry in code units; both of these return a <b>uint32_t</b> value. The entrysize depends on the length of the longest name.</P><P>PCRE2_INFO_NAMETABLE returns a pointer to the first entry of the table. This isa PCRE2_SPTR pointer to a block of code units. In the 8-bit library, the firsttwo bytes of each entry are the number of the capturing parenthesis, mostsignificant byte first. In the 16-bit library, the pointer points to 16-bitcode units, the first of which contains the parenthesis number. In the 32-bitlibrary, the pointer points to 32-bit code units, the first of which containsthe parenthesis number. The rest of the entry is the corresponding name, zeroterminated.</P><P>The names are in alphabetical order. If (?| is used to create multiple capturegroups with the same number, as described in the<a href="pcre2pattern.html#dupgroupnumber">section on duplicate group numbers</a>in the<a href="pcre2pattern.html"><b>pcre2pattern</b></a>page, the groups may be given the same name, but there is only one entry in thetable. Different names for groups of the same number are not permitted.</P><P>Duplicate names for capture groups with different numbers are permitted, butonly if PCRE2_DUPNAMES is set. They appear in the table in the order in whichthey were found in the pattern. In the absence of (?| this is the order ofincreasing number; when (?| is used this is not necessarily the case becauselater capture groups may have lower numbers.</P><P>As a simple example of the name/number table, consider the following patternafter compilation by the 8-bit library (assume PCRE2_EXTENDED is set, so whitespace - including newlines - is ignored):<pre> (?<date> (?<year>(\d\d)?\d\d) - (?<month>\d\d) - (?<day>\d\d) )</pre>There are four named capture groups, so the table has four entries, and eachentry in the table is eight bytes long. The table is as follows, withnon-printing bytes shows in hexadecimal, and undefined bytes shown as ??:<pre> 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 ??</pre>When writing code to extract data from named capture groups using thename-to-number map, remember that the length of the entries is likely to bedifferent for each compiled pattern.<pre> PCRE2_INFO_NEWLINE</pre>The output is one of the following <b>uint32_t</b> values:<pre> 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)</pre>This identifies the character sequence that will be recognized as meaning"newline" while matching.<pre> PCRE2_INFO_SIZE</pre>Return the size of the compiled pattern in bytes (for all three libraries). Thethird argument should point to a <b>size_t</b> variable. This value includes thesize of the general data block that precedes the code units of the compiledpattern itself. The value that is used when <b>pcre2_compile()</b> is gettingmemory in which to place the compiled pattern may be slightly larger than thevalue returned by this option, because there are cases where the code thatcalculates the size has to over-estimate. Processing a pattern with the JITcompiler does not alter the value returned by this option.<a name="infoaboutcallouts"></a></P><br><a name="SEC24" href="#TOC1">INFORMATION ABOUT A PATTERN'S CALLOUTS</a><br><P><b>int pcre2_callout_enumerate(const pcre2_code *<i>code</i>,</b><b> int (*<i>callback</i>)(pcre2_callout_enumerate_block *, void *),</b><b> void *<i>user_data</i>);</b><br><br>A script language that supports the use of string arguments in callouts mightlike to scan all the callouts in a pattern before running the match. This canbe done by calling <b>pcre2_callout_enumerate()</b>. The first argument is apointer to a compiled pattern, the second points to a callback function, andthe third is arbitrary user data. The callback function is called for everycallout in the pattern in the order in which they appear. Its first argument isa pointer to a callout enumeration block, and its second argument is the<i>user_data</i> value that was passed to <b>pcre2_callout_enumerate()</b>. Thecontents of the callout enumeration block are described in the<a href="pcre2callout.html"><b>pcre2callout</b></a>documentation, which also gives further details about callouts.</P><br><a name="SEC25" href="#TOC1">SERIALIZATION AND PRECOMPILING</a><br><P>It is possible to save compiled patterns on disc or elsewhere, and reload themlater, subject to a number of restrictions. The host on which the patterns arereloaded must be running the same version of PCRE2, with the same code unitwidth, and must also have the same endianness, pointer width, and PCRE2_SIZEtype. 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 <b>pcre2_serialize_</b> are used forconverting to and from the serialized form. They are described in the<a href="pcre2serialize.html"><b>pcre2serialize</b></a>documentation. Note that PCRE2 serialization does not convert compiled patternsto an abstract format like Java or .NET serialization.<a name="matchdatablock"></a></P><br><a name="SEC26" href="#TOC1">THE MATCH DATA BLOCK</a><br><P><b>pcre2_match_data *pcre2_match_data_create(uint32_t <i>ovecsize</i>,</b><b> pcre2_general_context *<i>gcontext</i>);</b><br><br><b>pcre2_match_data *pcre2_match_data_create_from_pattern(</b><b> const pcre2_code *<i>code</i>, pcre2_general_context *<i>gcontext</i>);</b><br><br><b>void pcre2_match_data_free(pcre2_match_data *<i>match_data</i>);</b></P><P>Information about a successful or unsuccessful match is placed in a matchdata block, which is an opaque structure that is accessed by function calls. Inparticular, the match data block contains a vector of offsets into the subjectstring that define the matched parts of the subject. This is known as the<i>ovector</i>.</P><P>Before calling <b>pcre2_match()</b>, <b>pcre2_dfa_match()</b>, or<b>pcre2_jit_match()</b> you must create a match data block by calling one ofthe creation functions above. For <b>pcre2_match_data_create()</b>, the firstargument is the number of pairs of offsets in the <i>ovector</i>.</P><P>When using <b>pcre2_match()</b>, one pair of offsets is required to identify thestring that matched the whole pattern, with an additional pair for eachcaptured substring. For example, a value of 4 creates enough space to recordthe matched portion of the subject plus three captured substrings.</P><P>When using <b>pcre2_dfa_match()</b> there may be multiple matched substrings ofdifferent lengths at the same point in the subject. The ovector should be madelarge enough to hold as many as are expected.</P><P>A minimum of at least 1 pair is imposed by <b>pcre2_match_data_create()</b>, soit is always possible to return the overall matched string in the case of<b>pcre2_match()</b> or the longest match in the case of<b>pcre2_dfa_match()</b>. The maximum number of pairs is 65535; if the firstargument of <b>pcre2_match_data_create()</b> is greater than this, 65535 isused.</P><P>The second argument of <b>pcre2_match_data_create()</b> is a pointer to ageneral context, which can specify custom memory management for obtaining thememory for the match data block. If you are not using custom memory management,pass NULL, which causes <b>malloc()</b> to be used.</P><P>For <b>pcre2_match_data_create_from_pattern()</b>, the first argument is apointer to a compiled pattern. The ovector is created to be exactly the rightsize to hold all the substrings a pattern might capture when matched using<b>pcre2_match()</b>. You should not use this call when matching with<b>pcre2_dfa_match()</b>. The second argument is again a pointer to a generalcontext, but in this case if NULL is passed, the memory is obtained using thesame allocator that was used for the compiled pattern (custom or default).</P><P>A match data block can be used many times, with the same or different compiledpatterns. You can extract information from a match data block after a matchoperation has finished, using functions that are described in the sections on<a href="#matchedstrings">matched strings</a>and<a href="#matchotherdata">other match data</a>below.</P><P>When a call of <b>pcre2_match()</b> fails, valid data is available in the matchblock only when the error is PCRE2_ERROR_NOMATCH, PCRE2_ERROR_PARTIAL, or oneof the error codes for an invalid UTF string. Exactly what is available dependson the error, and is detailed below.</P><P>When one of the matching functions is called, pointers to the compiled patternand the subject string are set in the match data block so that they can bereferenced by the extraction functions after a successful match. After runninga match, you must not free a compiled pattern or a subject string until afterall operations on the match data block (for that match) have taken place,unless, in the case of the subject string, you have used thePCRE2_COPY_MATCHED_SUBJECT option, which is described in the section entitled"Option bits for <b>pcre2_match()</b>"<a href="#matchoptions>">below.</a></P><P>When a match data block itself is no longer needed, it should be freed bycalling <b>pcre2_match_data_free()</b>. If this function is called with a NULLargument, it returns immediately, without doing anything.</P><br><a name="SEC27" href="#TOC1">MEMORY USE FOR MATCH DATA BLOCKS</a><br><P><b>PCRE2_SIZE pcre2_get_match_data_size(pcre2_match_data *<i>match_data</i>);</b><br><br><b>PCRE2_SIZE pcre2_get_match_data_heapframes_size(</b><b> pcre2_match_data *<i>match_data</i>);</b></P><P>The size of a match data block depends on the size of the ovector that itcontains. The function <b>pcre2_get_match_data_size()</b> returns the size, inbytes, of the block that is its argument.</P><P>When <b>pcre2_match()</b> runs interpretively (that is, without using JIT), itmakes use of a vector of data frames for remembering backtracking positions.The size of each individual frame depends on the number of capturingparentheses in the pattern and can be obtained by calling<b>pcre2_pattern_info()</b> with the PCRE2_INFO_FRAMESIZE option (see thesection entitled "Information about a compiled pattern"<a href="#infoaboutpattern>">above).</a></P><P>Heap memory is used for the frames vector; if the initial memory block turnsout to be too small during matching, it is automatically expanded. When<b>pcre2_match()</b> returns, the memory is not freed, but remains attached tothe match data block, for use by any subsequent matches that use the sameblock. It is automatically freed when the match data block itself is freed.</P><P>You can find the current size of the frames vector that a match data block ownsby calling <b>pcre2_get_match_data_heapframes_size()</b>. For a newly createdmatch data block the size will be zero. Some types of match may require a lotof frames and thus a large vector; applications that run in environments wherememory is constrained can check this and free the match data block if the heapframes vector has become too big.</P><br><a name="SEC28" href="#TOC1">MATCHING A PATTERN: THE TRADITIONAL FUNCTION</a><br><P><b>int pcre2_match(const pcre2_code *<i>code</i>, PCRE2_SPTR <i>subject</i>,</b><b> PCRE2_SIZE <i>length</i>, PCRE2_SIZE <i>startoffset</i>,</b><b> uint32_t <i>options</i>, pcre2_match_data *<i>match_data</i>,</b><b> pcre2_match_context *<i>mcontext</i>);</b></P><P>The function <b>pcre2_match()</b> is called to match a subject string against acompiled pattern, which is passed in the <i>code</i> argument. You can call<b>pcre2_match()</b> with the same <i>code</i> argument as many times as youlike, in order to find multiple matches in the subject string or to matchdifferent subject strings with the same pattern.</P><P>This function is the main matching facility of the library, and it operates ina Perl-like manner. For specialist use there is also an alternative matchingfunction, which is described<a href="#dfamatch">below</a>in the section about the <b>pcre2_dfa_match()</b> function.</P><P>Here is an example of a simple call to <b>pcre2_match()</b>:<pre> 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 */</pre>If the subject string is zero-terminated, the length can be given asPCRE2_ZERO_TERMINATED. A match context must be provided if certain less commonmatching parameters are to be changed. For details, see the section on<a href="#matchcontext">the match context</a>above.</P><br><b>The string to be matched by <b>pcre2_match()</b></b><br><P>The subject string is passed to <b>pcre2_match()</b> as a pointer in<i>subject</i>, a length in <i>length</i>, and a starting offset in<i>startoffset</i>. 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 the16-bit library, and 32-bit code units for the 32-bit library, whether or notUTF processing is enabled. As a special case, if <i>subject</i> is NULL and<i>length</i> is zero, the subject is assumed to be an empty string. If<i>length</i> is non-zero, an error occurs if <i>subject</i> is NULL.</P><P>If <i>startoffset</i> is greater than the length of the subject,<b>pcre2_match()</b> returns PCRE2_ERROR_BADOFFSET. When the starting offset iszero, the search for a match starts at the beginning of the subject, and thisis by far the most common case. In UTF-8 or UTF-16 mode, the starting offsetmust point to the start of a character, or to the end of the subject (in UTF-32mode, one code unit equals one character, so all offsets are valid). Like thepattern string, the subject may contain binary zeros.</P><P>A non-zero starting offset is useful when searching for another match in thesame subject by calling <b>pcre2_match()</b> again after a previous success.Setting <i>startoffset</i> differs from passing over a shortened string andsetting PCRE2_NOTBOL in the case of a pattern that begins with any kind oflookbehind. For example, consider the pattern<pre> \Biss\B</pre>which finds occurrences of "iss" in the middle of words. (\B matches only ifthe current position in the subject is not a word boundary.) When applied tothe string "Mississippi" the first call to <b>pcre2_match()</b> finds the firstoccurrence. If <b>pcre2_match()</b> is called again with just the remainder ofthe subject, namely "issippi", it does not match, because \B is always falseat the start of the subject, which is deemed to be a word boundary. However, if<b>pcre2_match()</b> is passed the entire string again, but with<i>startoffset</i> set to 4, it finds the second occurrence of "iss" because itis able to look behind the starting point to discover that it is preceded by aletter.</P><P>Finding all the matches in a subject is tricky when the pattern can match anempty string. It is possible to emulate Perl's /g behaviour by first trying thematch again at the same offset, with the PCRE2_NOTEMPTY_ATSTART andPCRE2_ANCHORED options, and then if that fails, advancing the starting offsetand trying an ordinary match again. There is some code that demonstrates how todo this in the<a href="pcre2demo.html"><b>pcre2demo</b></a>sample program. In the most general case, you have to check to see if thenewline convention recognizes CRLF as a newline, and if so, and the currentcharacter is CR followed by LF, advance the starting offset by two charactersinstead of one.</P><P>If a non-zero starting offset is passed when the pattern is anchored, a singleattempt to match at the given offset is made. This can only succeed if thepattern does not require the match to be at the start of the subject. In otherwords, the anchoring must be the result of setting the PCRE2_ANCHORED option orthe use of .* with PCRE2_DOTALL, not by starting the pattern with ^ or \A.<a name="matchoptions"></a></P><br><b>Option bits for <b>pcre2_match()</b></b><br><P>The unused bits of the <i>options</i> argument for <b>pcre2_match()</b> must bezero. 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.</P><P>Setting PCRE2_ANCHORED or PCRE2_ENDANCHORED at match time is not supported bythe just-in-time (JIT) compiler. If it is set, JIT matching is disabled and theinterpretive code in <b>pcre2_match()</b> 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.<pre> PCRE2_ANCHORED</pre>The PCRE2_ANCHORED option limits <b>pcre2_match()</b> to matching at the firstmatching position. If a pattern was compiled with PCRE2_ANCHORED, or turned outto be anchored by virtue of its contents, it cannot be made unachored atmatching time. Note that setting the option at match time disables JITmatching.<pre> PCRE2_COPY_MATCHED_SUBJECT</pre>By default, a pointer to the subject is remembered in the match data block sothat, after a successful match, it can be referenced by the substringextraction functions. This means that the subject's memory must not be freeduntil all such operations are complete. For some applications where thelifetime of the subject string is not guaranteed, it may be necessary to make acopy of the subject string, but it is wasteful to do this unless the match issuccessful. After a successful match, if PCRE2_COPY_MATCHED_SUBJECT is set, thesubject is copied and the new pointer is remembered in the match data blockinstead of the original subject pointer. The memory allocator that was used forthe match block itself is used. The copy is automatically freed when<b>pcre2_match_data_free()</b> is called to free the match data block. It is alsoautomatically freed if the match data block is re-used for another matchoperation.<pre> PCRE2_DISABLE_RECURSELOOP_CHECK</pre>This option is relevant only to <b>pcre2_match()</b> for interpretive matching.It is ignored when JIT is used, and is forbidden for <b>pcre2_dfa_match()</b>.</P><P>The use of recursion in patterns can lead to infinite loops. In theinterpretive matcher these would be eventually caught by the match or heaplimits, but this could take a long time and/or use a lot of memory if thelimits 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 subjectpointer is the same as it was at the start of that group, and the furthestinspected character of the subject has not changed, an error is generated.</P><P>There are rare cases of matches that would complete, but nevertheless triggerthis error. This option disables the check. It is provided mainly for testingwhen comparing JIT and interpretive behaviour.<pre> PCRE2_ENDANCHORED</pre>If the PCRE2_ENDANCHORED option is set, any string that <b>pcre2_match()</b>matches must be right at the end of the subject string. Note that setting theoption at match time disables JIT matching.<pre> PCRE2_NOTBOL</pre>This option specifies that first character of the subject string is not thebeginning of a line, so the circumflex metacharacter should not match beforeit. Setting this without having set PCRE2_MULTILINE at compile time causescircumflex never to match. This option affects only the behaviour of thecircumflex metacharacter. It does not affect \A.<pre> PCRE2_NOTEOL</pre>This option specifies that the end of the subject string is not the end of aline, so the dollar metacharacter should not match it nor (except in multilinemode) a newline immediately before it. Setting this without having setPCRE2_MULTILINE at compile time causes dollar never to match. This optionaffects only the behaviour of the dollar metacharacter. It does not affect \Zor \z.<pre> PCRE2_NOTEMPTY</pre>An empty string is not considered to be a valid match if this option is set. Ifthere are alternatives in the pattern, they are tried. If all the alternativesmatch the empty string, the entire match fails. For example, if the pattern<pre> a?b?</pre>is applied to a string not beginning with "a" or "b", it matches an emptystring at the start of the subject. With PCRE2_NOTEMPTY set, this match is notvalid, so <b>pcre2_match()</b> searches further into the string for occurrencesof "a" or "b".<pre> PCRE2_NOTEMPTY_ATSTART</pre>This is like PCRE2_NOTEMPTY, except that it locks out an empty string matchonly at the first matching position, that is, at the start of the subject plusthe 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.<pre> PCRE2_NO_JIT</pre>By default, if a pattern has been successfully processed by<b>pcre2_jit_compile()</b>, JIT is automatically used when <b>pcre2_match()</b>is called with options that JIT supports. Setting PCRE2_NO_JIT disables the useof JIT; it forces matching to be done by the interpreter.<pre> PCRE2_NO_UTF_CHECK</pre>When PCRE2_UTF is set at compile time, the validity of the subject as a UTFstring is checked unless PCRE2_NO_UTF_CHECK is passed to <b>pcre2_match()</b> orPCRE2_MATCH_INVALID_UTF was passed to <b>pcre2_compile()</b>. The latter specialcase is discussed in detail in the<a href="pcre2unicode.html"><b>pcre2unicode</b></a>documentation.</P><P>In the default case, if a non-zero starting offset is given, the check isapplied only to that part of the subject that could be inspected duringmatching, and there is a check that the starting offset points to the firstcode unit of a character or to the end of the subject. If there are nolookbehind assertions in the pattern, the check starts at the starting offset.Otherwise, it starts at the length of the longest lookbehind before thestarting offset, or at the start of the subject if there are not that manycharacters before the starting offset. Note that the sequences \b and \B areone-character lookbehinds.</P><P>The check is carried out before any other processing takes place, and anegative error code is returned if the check fails. There are several UTF errorcodes for each code unit width, corresponding to different problems with thecode unit sequence. There are discussions about the validity of<a href="pcre2unicode.html#utf8strings">UTF-8 strings,</a><a href="pcre2unicode.html#utf16strings">UTF-16 strings,</a>and<a href="pcre2unicode.html#utf32strings">UTF-32 strings</a>in the<a href="pcre2unicode.html"><b>pcre2unicode</b></a>documentation.</P><P>If you know that your subject is valid, and you want to skip this check forperformance reasons, you can set the PCRE2_NO_UTF_CHECK option when calling<b>pcre2_match()</b>. You might want to do this for the second and subsequentcalls to <b>pcre2_match()</b> if you are making repeated calls to find multiplematches in the same subject string.</P><P><b>Warning:</b> Unless PCRE2_MATCH_INVALID_UTF was set at compile time, whenPCRE2_NO_UTF_CHECK is set at match time the effect of passing an invalidstring as a subject, or an invalid value of <i>startoffset</i>, is undefined.Your program may crash or loop indefinitely or give wrong results.<pre> PCRE2_PARTIAL_HARD PCRE2_PARTIAL_SOFT</pre>These options turn on the partial matching feature. A partial match occurs ifthe end of the subject string is reached successfully, but there are not enoughsubject characters to complete the match. In addition, either at least onecharacter must have been inspected or the pattern must contain a lookbehind, orthe pattern must be one that could match an empty string.</P><P>If this situation arises when PCRE2_PARTIAL_SOFT (but not PCRE2_PARTIAL_HARD)is set, matching continues by testing any remaining alternatives. Only if nocomplete match can be found is PCRE2_ERROR_PARTIAL returned instead ofPCRE2_ERROR_NOMATCH. In other words, PCRE2_PARTIAL_SOFT specifies that thecaller is prepared to handle a partial match, but only if no complete match canbe found.</P><P>If PCRE2_PARTIAL_HARD is set, it overrides PCRE2_PARTIAL_SOFT. In this case, ifa partial match is found, <b>pcre2_match()</b> immediately returnsPCRE2_ERROR_PARTIAL, without considering any other alternatives. In otherwords, when PCRE2_PARTIAL_HARD is set, a partial match is considered to be moreimportant that an alternative complete match.</P><P>There is a more detailed discussion of partial and multi-segment matching, withexamples, in the<a href="pcre2partial.html"><b>pcre2partial</b></a>documentation.</P><br><a name="SEC29" href="#TOC1">NEWLINE HANDLING WHEN MATCHING</a><br><P>When PCRE2 is built, a default newline convention is set; this is usually thestandard convention for the operating system. The default can be overridden ina<a href="#compilecontext">compile context</a>by calling <b>pcre2_set_newline()</b>. It can also be overridden by starting apattern string with, for example, (*CRLF), as described in the<a href="pcre2pattern.html#newlines">section on newline conventions</a>in the<a href="pcre2pattern.html"><b>pcre2pattern</b></a>page. During matching, the newline choice affects the behaviour of the dot,circumflex, and dollar metacharacters. It may also alter the way the matchstarting position is advanced after a match failure for an unanchored pattern.</P><P>When PCRE2_NEWLINE_CRLF, PCRE2_NEWLINE_ANYCRLF, or PCRE2_NEWLINE_ANY is set asthe newline convention, and a match attempt for an unanchored pattern failswhen the current starting position is at a CRLF sequence, and the patterncontains no explicit matches for CR or LF characters, the match position isadvanced by two characters instead of one, in other words, to after the CRLF.</P><P>The above rule is a compromise that makes the most common cases work asexpected. For example, if the pattern is .+A (and the PCRE2_DOTALL option isnot set), it does not match the string "\r\nA" because, after failing at thestart, 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 LFreference, and so advances only by one character after the first failure.</P><P>An explicit match for CR of LF is either a literal appearance of one of thosecharacters in the pattern, or one of the \r or \n or equivalent octal orhexadecimal escape sequences. Implicit matches such as [^X] do not count, nordoes \s, even though it includes CR and LF in the characters that it matches.</P><P>Notwithstanding the above, anomalous effects may still occur when CRLF is avalid newline sequence and explicit \r or \n escapes appear in the pattern.<a name="matchedstrings"></a></P><br><a name="SEC30" href="#TOC1">HOW PCRE2_MATCH() RETURNS A STRING AND CAPTURED SUBSTRINGS</a><br><P><b>uint32_t pcre2_get_ovector_count(pcre2_match_data *<i>match_data</i>);</b><br><br><b>PCRE2_SIZE *pcre2_get_ovector_pointer(pcre2_match_data *<i>match_data</i>);</b></P><P>In general, a pattern matches a certain portion of the subject, and inaddition, further substrings from the subject may be picked out byparenthesized parts of the pattern. Following the usage in Jeffrey Friedl'sbook, this is called "capturing" in what follows, and the phrase "capturegroup" (Perl terminology) is used for a fragment of a pattern that picks out asubstring. PCRE2 supports several other kinds of parenthesized group that donot cause substrings to be captured. The <b>pcre2_pattern_info()</b> functioncan be used to find out how many capture groups there are in a compiledpattern.</P><P>You can use auxiliary functions for accessing captured substrings<a href="#extractbynumber">by number</a>or<a href="#extractbyname">by name,</a>as described in sections below.</P><P>Alternatively, you can make direct use of the vector of PCRE2_SIZE values,called the <b>ovector</b>, which contains the offsets of captured strings. It ispart of the<a href="#matchdatablock">match data block.</a>The function <b>pcre2_get_ovector_pointer()</b> returns the address of theovector, and <b>pcre2_get_ovector_count()</b> returns the number of pairs ofvalues it contains.</P><P>Within the ovector, the first in each pair of values is set to the offset ofthe first code unit of a substring, and the second is set to the offset of thefirst code unit after the end of a substring. These values are always code unitoffsets, not character offsets. That is, they are byte offsets in the 8-bitlibrary, 16-bit offsets in the 16-bit library, and 32-bit offsets in the 32-bitlibrary.</P><P>After a partial match (error return PCRE2_ERROR_PARTIAL), only the first pairof offsets (that is, <i>ovector[0]</i> and <i>ovector[1]</i>) are set. Theyidentify the part of the subject that was partially matched. See the<a href="pcre2partial.html"><b>pcre2partial</b></a>documentation for details of partial matching.</P><P>After a fully successful match, the first pair of offsets identifies theportion of the subject string that was matched by the entire pattern. The nextpair is used for the first captured substring, and so on. The value returned by<b>pcre2_match()</b> is one more than the highest numbered pair that has beenset. For example, if two substrings have been captured, the returned value is3. If there are no captured substrings, the return value from a successfulmatch is 1, indicating that just the first pair of offsets has been set.</P><P>If a pattern uses the \K escape sequence within a positive assertion, thereported 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 andend offset values for the match are 2 and 0.</P><P>If a capture group is matched repeatedly within a single match operation, it isthe last portion of the subject that it matched that is returned.</P><P>If the ovector is too small to hold all the captured substring offsets, as muchas possible is filled in, and the function returns a value of zero. If capturedsubstrings are not of interest, <b>pcre2_match()</b> may be called with a matchdata block whose ovector is of minimum length (that is, one pair).</P><P>It is possible for capture group number <i>n+1</i> to match some part of thesubject when group <i>n</i> has not been used at all. For example, if the string"abc" is matched against the pattern (a|(z))(bc) the return from the functionis 4, and groups 1 and 3 are matched, but 2 is not. When this happens, bothvalues in the offset pairs corresponding to unused groups are set toPCRE2_UNSET.</P><P>Offset values that correspond to unused groups at the end of the expression arealso set to PCRE2_UNSET. For example, if the string "abc" is matched againstthe pattern (abc)(x(yz)?)? groups 2 and 3 are not matched. The return from thefunction is 2, because the highest used capture group number is 1. The offsetsfor the second and third capture groups (assuming the vector is large enough,of course) are set to PCRE2_UNSET.</P><P>Elements in the ovector that do not correspond to capturing parentheses in thepattern are never changed. That is, if a pattern contains <i>n</i> capturingparentheses, no more than <i>ovector[0]</i> to <i>ovector[2n+1]</i> are set by<b>pcre2_match()</b>. The other elements retain whatever values they previouslyhad. After a failed match attempt, the contents of the ovector are unchanged.<a name="matchotherdata"></a></P><br><a name="SEC31" href="#TOC1">OTHER INFORMATION ABOUT A MATCH</a><br><P><b>PCRE2_SPTR pcre2_get_mark(pcre2_match_data *<i>match_data</i>);</b><br><br><b>PCRE2_SIZE pcre2_get_startchar(pcre2_match_data *<i>match_data</i>);</b></P><P>As well as the offsets in the ovector, other information about a match isretained in the match data block and can be retrieved by the above functions inappropriate circumstances. If they are called at other times, the result isundefined.</P><P>After a successful match, a partial match (PCRE2_ERROR_PARTIAL), or a failureto match (PCRE2_ERROR_NOMATCH), a mark name may be available. The function<b>pcre2_get_mark()</b> can be called to access this name, which can bespecified 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 tothe zero-terminated name, which is within the compiled pattern. If no name isavailable, NULL is returned. The length of the name (excluding the terminatingzero) is stored in the code unit that precedes the name. You should use thislength instead of relying on the terminating zero if the name might contain abinary zero.</P><P>After a successful match, the name that is returned is the last mark nameencountered on the matching path through the pattern. Instances of backtrackingverbs without names do not count. Thus, for example, if the matching pathcontains (*MARK:A)(*PRUNE), the name "A" is returned. After a "no match" or apartial match, the last encountered name is returned. For example, considerthis pattern:<pre> ^(*MARK:A)((*MARK:B)a|b)c</pre>When it matches "bc", the returned name is A. The B mark is "seen" in the firstbranch 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.</P><P><b>Warning:</b> By default, certain start-of-match optimizations are used togive a fast "no match" result in some situations. For example, if the anchoringis removed from the pattern above, there is an initial check for the presenceof "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 thestart-of-match optimizations by setting the PCRE2_NO_START_OPTIMIZE option for<b>pcre2_compile()</b> or by starting the pattern with (*NO_START_OPT).</P><P>After a successful match, a partial match, or one of the invalid UTF errors(for example, PCRE2_ERROR_UTF8_ERR5), <b>pcre2_get_startchar()</b> can becalled. After a successful or partial match it returns the code unit offset ofthe character at which the match started. For a non-partial match, this can bedifferent to the value of <i>ovector[0]</i> if the pattern contains the \Kescape sequence. After a partial match, however, this value is always the sameas <i>ovector[0]</i> because \K does not affect the result of a partial match.</P><P>After a UTF check failure, <b>pcre2_get_startchar()</b> can be used to obtainthe code unit offset of the invalid UTF character. Details are given in the<a href="pcre2unicode.html"><b>pcre2unicode</b></a>page.<a name="errorlist"></a></P><br><a name="SEC32" href="#TOC1">ERROR RETURNS FROM <b>pcre2_match()</b></a><br><P>If <b>pcre2_match()</b> fails, it returns a negative number. This can beconverted to a text string by calling the <b>pcre2_get_error_message()</b>function (see "Obtaining a textual error message"<a href="#geterrormessage">below).</a>Negative error codes are also returned by other functions, and are documentedwith them. The codes are given names in the header file. If UTF checking is inforce and an invalid UTF subject string is detected, one of a number ofUTF-specific negative error codes is returned. Details are given in the<a href="pcre2unicode.html"><b>pcre2unicode</b></a>page. The following are the other errors that may be returned by<b>pcre2_match()</b>:<pre> PCRE2_ERROR_NOMATCH</pre>The subject string did not match the pattern.<pre> PCRE2_ERROR_PARTIAL</pre>The subject string did not match, but it did match partially. See the<a href="pcre2partial.html"><b>pcre2partial</b></a>documentation for details of partial matching.<pre> PCRE2_ERROR_BADMAGIC</pre>PCRE2 stores a 4-byte "magic number" at the start of the compiled code, tocatch the case when it is passed a junk pointer. This is the error that isreturned when the magic number is not present.<pre> PCRE2_ERROR_BADMODE</pre>This error is given when a compiled pattern is passed to a function in alibrary of a different code unit width, for example, a pattern compiled bythe 8-bit library is passed to a 16-bit or 32-bit library function.<pre> PCRE2_ERROR_BADOFFSET</pre>The value of <i>startoffset</i> was greater than the length of the subject.<pre> PCRE2_ERROR_BADOPTION</pre>An unrecognized bit was set in the <i>options</i> argument.<pre> PCRE2_ERROR_BADUTFOFFSET</pre>The UTF code unit sequence that was passed as a subject was checked and foundto be valid (the PCRE2_NO_UTF_CHECK option was not set), but the value of<i>startoffset</i> did not point to the beginning of a UTF character or the endof the subject.<pre> PCRE2_ERROR_CALLOUT</pre>This error is never generated by <b>pcre2_match()</b> itself. It is provided foruse by callout functions that want to cause <b>pcre2_match()</b> or<b>pcre2_callout_enumerate()</b> to return a distinctive error code. See the<a href="pcre2callout.html"><b>pcre2callout</b></a>documentation for details.<pre> PCRE2_ERROR_DEPTHLIMIT</pre>The nested backtracking depth limit was reached.<pre> PCRE2_ERROR_HEAPLIMIT</pre>The heap limit was reached.<pre> PCRE2_ERROR_INTERNAL</pre>An unexpected internal error has occurred. This error could be caused by a bugin PCRE2 or by overwriting of the compiled pattern.<pre> PCRE2_ERROR_JIT_STACKLIMIT</pre>This error is returned when a pattern that was successfully studied using JITis being matched, but the memory available for the just-in-time processingstack is not large enough. See the<a href="pcre2jit.html"><b>pcre2jit</b></a>documentation for more details.<pre> PCRE2_ERROR_MATCHLIMIT</pre>The backtracking match limit was reached.<pre> PCRE2_ERROR_NOMEMORY</pre>Heap memory is used to remember backtracking points. This error is given whenthe memory allocation function (default or custom) fails. Note that a differenterror, PCRE2_ERROR_HEAPLIMIT, is given if the amount of memory needed exceedsthe heap limit. PCRE2_ERROR_NOMEMORY is also returned ifPCRE2_COPY_MATCHED_SUBJECT is set and memory allocation fails.<pre> PCRE2_ERROR_NULL</pre>Either the <i>code</i>, <i>subject</i>, or <i>match_data</i> argument was passedas NULL.<pre> PCRE2_ERROR_RECURSELOOP</pre>This error is returned when <b>pcre2_match()</b> detects a recursion loop withinthe pattern. Specifically, it means that either the whole pattern or acapture group has been called recursively for the second time at the sameposition in the subject string. Some simple patterns that might do this aredetected and faulted at compile time, but more complicated cases, in particularmutual recursions between two different groups, cannot be detected untilmatching is attempted.<a name="geterrormessage"></a></P><br><a name="SEC33" href="#TOC1">OBTAINING A TEXTUAL ERROR MESSAGE</a><br><P><b>int pcre2_get_error_message(int <i>errorcode</i>, PCRE2_UCHAR *<i>buffer</i>,</b><b> PCRE2_SIZE <i>bufflen</i>);</b></P><P>A text message for an error code from any PCRE2 function (compile, match, orauxiliary) can be obtained by calling <b>pcre2_get_error_message()</b>. The codeis passed as the first argument, with the remaining two arguments specifying acode unit buffer and its length in code units, into which the text message isplaced. The message is returned in code units of the appropriate width for thelibrary that is being used.</P><P>The returned message is terminated with a trailing zero, and the functionreturns the number of code units used, excluding the trailing zero. If theerror number is unknown, the negative error code PCRE2_ERROR_BADDATA isreturned. If the buffer is too small, the message is truncated (but still witha trailing zero), and the negative error code PCRE2_ERROR_NOMEMORY is returned.None of the messages are very long; a buffer size of 120 code units is ample.<a name="extractbynumber"></a></P><br><a name="SEC34" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NUMBER</a><br><P><b>int pcre2_substring_length_bynumber(pcre2_match_data *<i>match_data</i>,</b><b> uint32_t <i>number</i>, PCRE2_SIZE *<i>length</i>);</b><br><br><b>int pcre2_substring_copy_bynumber(pcre2_match_data *<i>match_data</i>,</b><b> uint32_t <i>number</i>, PCRE2_UCHAR *<i>buffer</i>,</b><b> PCRE2_SIZE *<i>bufflen</i>);</b><br><br><b>int pcre2_substring_get_bynumber(pcre2_match_data *<i>match_data</i>,</b><b> uint32_t <i>number</i>, PCRE2_UCHAR **<i>bufferptr</i>,</b><b> PCRE2_SIZE *<i>bufflen</i>);</b><br><br><b>void pcre2_substring_free(PCRE2_UCHAR *<i>buffer</i>);</b></P><P>Captured substrings can be accessed directly by using the ovector as described<a href="#matchedstrings">above.</a>For convenience, auxiliary functions are provided for extracting capturedsubstrings as new, separate, zero-terminated strings. A substring that containsa binary zero is correctly extracted and has a further zero added on the end,but the result is not, of course, a C string.</P><P>The functions in this section identify substrings by number. The number zerorefers to the entire matched substring, with higher numbers referring tosubstrings captured by parenthesized groups. After a partial match, onlysubstring zero is available. An attempt to extract any other substring givesthe error PCRE2_ERROR_PARTIAL. The next section describes similar functions forextracting captured substrings by name.</P><P>If a pattern uses the \K escape sequence within a positive assertion, thereported 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 andend offset values for the match are 2 and 0. In this situation, calling thesefunctions with a zero substring number extracts a zero-length empty string.</P><P>You can find the length in code units of a captured substring withoutextracting it by calling <b>pcre2_substring_length_bynumber()</b>. The firstargument 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. Ifyou just want to know whether or not the substring has been captured, you canpass the third argument as NULL.</P><P>The <b>pcre2_substring_copy_bynumber()</b> function copies a captured substringinto a supplied buffer, whereas <b>pcre2_substring_get_bynumber()</b> copies itinto new memory, obtained using the same memory allocation function that wasused for the match data block. The first two arguments of these functions are apointer to the match data block and a capture group number.</P><P>The final arguments of <b>pcre2_substring_copy_bynumber()</b> are a pointer tothe 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 theextracted substring, excluding the terminating zero.</P><P>For <b>pcre2_substring_get_bynumber()</b> the third and fourth arguments pointto variables that are updated with a pointer to the new memory and the numberof code units that comprise the substring, again excluding the terminatingzero. When the substring is no longer needed, the memory should be freed bycalling <b>pcre2_substring_free()</b>.</P><P>The return value from all these functions is zero for success, or a negativeerror 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:<pre> PCRE2_ERROR_NOMEMORY</pre>The buffer was too small for <b>pcre2_substring_copy_bynumber()</b>, or theattempt to get memory failed for <b>pcre2_substring_get_bynumber()</b>.<pre> PCRE2_ERROR_NOSUBSTRING</pre>There is no substring with that number in the pattern, that is, the number isgreater than the number of capturing parentheses.<pre> PCRE2_ERROR_UNAVAILABLE</pre>The substring number, though not greater than the number of captures in thepattern, is greater than the number of slots in the ovector, so the substringcould not be captured.<pre> PCRE2_ERROR_UNSET</pre>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 twocapturing slots, substring number 1 is unset.</P><br><a name="SEC35" href="#TOC1">EXTRACTING A LIST OF ALL CAPTURED SUBSTRINGS</a><br><P><b>int pcre2_substring_list_get(pcre2_match_data *<i>match_data</i>,</b><b>" PCRE2_UCHAR ***<i>listptr</i>, PCRE2_SIZE **<i>lengthsptr</i>);</b><br><br><b>void pcre2_substring_list_free(PCRE2_UCHAR **<i>list</i>);</b></P><P>The <b>pcre2_substring_list_get()</b> function extracts all available substringsand builds a list of pointers to them. It also (optionally) builds a secondlist that contains their lengths (in code units), excluding a terminating zerothat is added to each of them. All this is done in a single block of memorythat is obtained using the same memory allocation function that was used to getthe match data block.</P><P>This function must be called only after a successful match. If called after apartial match, the error code PCRE2_ERROR_PARTIAL is returned.</P><P>The address of the memory block is returned via <i>listptr</i>, which is alsothe start of the list of string pointers. The end of the list is marked by aNULL pointer. The address of the list of lengths is returned via<i>lengthsptr</i>. If your strings do not contain binary zeros and you do nottherefore need the lengths, you may supply NULL as the <b>lengthsptr</b>argument to disable the creation of a list of lengths. The yield of thefunction is zero if all went well, or PCRE2_ERROR_NOMEMORY if the memory blockcould not be obtained. When the list is no longer needed, it should be freed bycalling <b>pcre2_substring_list_free()</b>.</P><P>If this function encounters a substring that is unset, which can happen whencapture group number <i>n+1</i> matches some part of the subject, but group<i>n</i> has not been used at all, it returns an empty string. This can bedistinguished from a genuine zero-length substring by inspecting theappropriate offset in the ovector, which contain PCRE2_UNSET for unsetsubstrings, or by calling <b>pcre2_substring_length_bynumber()</b>.<a name="extractbyname"></a></P><br><a name="SEC36" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NAME</a><br><P><b>int pcre2_substring_number_from_name(const pcre2_code *<i>code</i>,</b><b> PCRE2_SPTR <i>name</i>);</b><br><br><b>int pcre2_substring_length_byname(pcre2_match_data *<i>match_data</i>,</b><b> PCRE2_SPTR <i>name</i>, PCRE2_SIZE *<i>length</i>);</b><br><br><b>int pcre2_substring_copy_byname(pcre2_match_data *<i>match_data</i>,</b><b> PCRE2_SPTR <i>name</i>, PCRE2_UCHAR *<i>buffer</i>, PCRE2_SIZE *<i>bufflen</i>);</b><br><br><b>int pcre2_substring_get_byname(pcre2_match_data *<i>match_data</i>,</b><b> PCRE2_SPTR <i>name</i>, PCRE2_UCHAR **<i>bufferptr</i>, PCRE2_SIZE *<i>bufflen</i>);</b><br><br><b>void pcre2_substring_free(PCRE2_UCHAR *<i>buffer</i>);</b></P><P>To extract a substring by name, you first have to find associated number.For example, for this pattern:<pre> (a+)b(?<xxx>\d+)...</pre>the number of the capture group called "xxx" is 2. If the name is known to beunique (PCRE2_DUPNAMES was not set), you can find the number from the name bycalling <b>pcre2_substring_number_from_name()</b>. The first argument is thecompiled pattern, and the second is the name. The yield of the function is thegroup number, PCRE2_ERROR_NOSUBSTRING if there is no group with that name, orPCRE2_ERROR_NOUNIQUESUBSTRING if there is more than one group with that name.Given the number, you can extract the substring directly from the ovector, oruse one of the "bynumber" functions described above.</P><P>For convenience, there are also "byname" functions that correspond to the"bynumber" functions, the only difference being that the second argument is aname instead of a number. If PCRE2_DUPNAMES is set and there are duplicatenames, these functions scan all the groups with the given name, and return thecaptured substring from the first named group that is set.</P><P>If there are no groups with the given name, PCRE2_ERROR_NOSUBSTRING isreturned. If all groups with the name have numbers that are greater than thenumber of slots in the ovector, PCRE2_ERROR_UNAVAILABLE is returned. If thereis at least one group with a slot in the ovector, but no group is found to beset, PCRE2_ERROR_UNSET is returned.</P><P><b>Warning:</b> If the pattern uses the (?| feature to set up multiplecapture groups with the same number, as described in the<a href="pcre2pattern.html#dupgroupnumber">section on duplicate group numbers</a>in the<a href="pcre2pattern.html"><b>pcre2pattern</b></a>page, you cannot use names to distinguish the different capture groups, becausenames are not included in the compiled code. The matching process uses onlynumbers. For this reason, the use of different names for groups with thesame number causes an error at compile time.<a name="substitutions"></a></P><br><a name="SEC37" href="#TOC1">CREATING A NEW STRING WITH SUBSTITUTIONS</a><br><P><b>int pcre2_substitute(const pcre2_code *<i>code</i>, PCRE2_SPTR <i>subject</i>,</b><b> PCRE2_SIZE <i>length</i>, PCRE2_SIZE <i>startoffset</i>,</b><b> uint32_t <i>options</i>, pcre2_match_data *<i>match_data</i>,</b><b> pcre2_match_context *<i>mcontext</i>, PCRE2_SPTR <i>replacement</i>,</b><b> PCRE2_SIZE <i>rlength</i>, PCRE2_UCHAR *<i>outputbuffer</i>,</b><b> PCRE2_SIZE *<i>outlengthptr</i>);</b></P><P>This function optionally calls <b>pcre2_match()</b> and then makes a copy of thesubject string in <i>outputbuffer</i>, replacing parts that were matched withthe <i>replacement</i> string, whose length is supplied in <b>rlength</b>, whichcan be given as PCRE2_ZERO_TERMINATED for a zero-terminated string. As aspecial case, if <i>replacement</i> is NULL and <i>rlength</i> is zero, thereplacement is assumed to be an empty string. If <i>rlength</i> is non-zero, anerror occurs if <i>replacement</i> is NULL.</P><P>There is an option (see PCRE2_SUBSTITUTE_REPLACEMENT_ONLY below) to return justthe replacement string(s). The default action is to perform just onereplacement if the pattern matches, but there is an option that requestsmultiple replacements (see PCRE2_SUBSTITUTE_GLOBAL below).</P><P>If successful, <b>pcre2_substitute()</b> returns the number of substitutionsthat were carried out. This may be zero if no match was found, and is nevergreater than one unless PCRE2_SUBSTITUTE_GLOBAL is set. A negative value isreturned if an error is detected.</P><P>Matches in which a \K item in a lookahead in the pattern causes the match toend before it starts are not supported, and give rise to an error return. Forglobal replacements, matches in which \K in a lookbehind causes the match tostart earlier than the point that was reached in the previous iteration arealso not supported.</P><P>The first seven arguments of <b>pcre2_substitute()</b> are the same as for<b>pcre2_match()</b>, except that the partial matching options are notpermitted, and <i>match_data</i> may be passed as NULL, in which case a matchdata block is obtained and freed within this function, using memory managementfunctions from the match context, if provided, or else those that were used toallocate memory for the compiled code.</P><P>If <i>match_data</i> is not NULL and PCRE2_SUBSTITUTE_MATCHED is not set, theprovided block is used for all calls to <b>pcre2_match()</b>, and its contentsafterwards are the result of the final call. For global changes, this willalways be a no-match error. The contents of the ovector within the match datablock may or may not have been changed.</P><P>As well as the usual options for <b>pcre2_match()</b>, a number of additionaloptions can be set in the <i>options</i> argument of <b>pcre2_substitute()</b>.One such option is PCRE2_SUBSTITUTE_MATCHED. When this is set, an external<i>match_data</i> block must be provided, and it must have already been used foran external call to <b>pcre2_match()</b> with the same pattern and subjectarguments. The data in the <i>match_data</i> block (return code, offset vector)is then used for the first substitution instead of calling <b>pcre2_match()</b>from within <b>pcre2_substitute()</b>. This allows an application to check for amatch before choosing to substitute, without having to repeat the match.</P><P>The contents of the externally supplied match data block are not changed whenPCRE2_SUBSTITUTE_MATCHED is set. If PCRE2_SUBSTITUTE_GLOBAL is also set,<b>pcre2_match()</b> is called after the first substitution to check for furthermatches, but this is done using an internally obtained match data block, thusalways leaving the external block unchanged.</P><P>The <i>code</i> argument is not used for matching before the first substitutionwhen PCRE2_SUBSTITUTE_MATCHED is set, but it must be provided, even whenPCRE2_SUBSTITUTE_GLOBAL is not set, because it contains information such as theUTF setting and the number of capturing parentheses in the pattern.</P><P>The default action of <b>pcre2_substitute()</b> is to return a copy of thesubject string with matched substrings replaced. However, ifPCRE2_SUBSTITUTE_REPLACEMENT_ONLY is set, only the replacement substrings arereturned. In the global case, multiple replacements are concatenated in theoutput buffer. Substitution callouts (see<a href="#subcallouts">below)</a>can be used to separate them if necessary.</P><P>The <i>outlengthptr</i> argument of <b>pcre2_substitute()</b> must point to avariable that contains the length, in code units, of the output buffer. If thefunction is successful, the value is updated to contain the length in codeunits of the new string, excluding the trailing zero that is automaticallyadded.</P><P>If the function is not successful, the value set via <i>outlengthptr</i> dependson the type of error. For syntax errors in the replacement string, the value isthe offset in the replacement string where the error was detected. For othererrors, the value is PCRE2_UNSET by default. This includes the case of theoutput buffer being too small, unless PCRE2_SUBSTITUTE_OVERFLOW_LENGTH is set.</P><P>PCRE2_SUBSTITUTE_OVERFLOW_LENGTH changes what happens when the output buffer istoo small. The default action is to return PCRE2_ERROR_NOMEMORY immediately. Ifthis option is set, however, <b>pcre2_substitute()</b> continues to go throughthe motions of matching and substituting (without, of course, writing anything)in order to compute the size of buffer that is needed. This value is passedback via the <i>outlengthptr</i> variable, with the result of the function stillbeing PCRE2_ERROR_NOMEMORY.</P><P>Passing a buffer size of zero is a permitted way of finding out how much memoryis needed for given substitution. However, this does mean that the entireoperation is carried out twice. Depending on the application, it may be moreefficient to allocate a large buffer and free the excess afterwards, instead ofusing PCRE2_SUBSTITUTE_OVERFLOW_LENGTH.</P><P>The replacement string, which is interpreted as a UTF string in UTF mode, ischecked for UTF validity unless PCRE2_NO_UTF_CHECK is set. An invalid UTFreplacement string causes an immediate return with the relevant UTF error code.</P><P>If PCRE2_SUBSTITUTE_LITERAL is set, the replacement string is not interpretedin any way. By default, however, a dollar character is an escape character thatcan specify the insertion of characters from capture groups and names from(*MARK) or other control verbs in the pattern. Dollar is the only escapecharacter (backslash is treated as literal). The following forms are alwaysrecognized:<pre> $$ insert a dollar character $<n> or ${<n>} insert the contents of group <n> $*MARK or ${*MARK} insert a control verb name</pre>Either a group number or a group name can be given for <n>. Curly brackets arerequired only if the following character would be interpreted as part of thenumber 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 replacementstring "+$1$0$1+", the result is "=+babcb+=".</P><P>$*MARK inserts the name from the last encountered backtracking control verb onthe matching path that has a name. (*MARK) must always include a name, but theother verbs need not. For example, in the case of (*MARK:A)(*PRUNE) the nameinserted is "A", but for (*MARK:A)(*PRUNE:B) the relevant name is "B". Thisfacility can be used to perform simple simultaneous substitutions, as this<b>pcre2test</b> example shows:<pre> /(*MARK:pear)apple|(*MARK:orange)lemon/g,replace=${*MARK} apple lemon 2: pear orange</pre>PCRE2_SUBSTITUTE_GLOBAL causes the function to iterate over the subject string,replacing every matching substring. If this option is not set, only the firstmatching substring is replaced. The search for matches takes place in theoriginal subject string (that is, previous replacements do not affect it).Iteration is implemented by advancing the <i>startoffset</i> value for eachsearch, which is always passed the entire subject string. If an offset limit isset in the match context, searching stops when that limit is reached.</P><P>You can restrict the effect of a global substitution to a portion of thesubject string by setting either or both of <i>startoffset</i> and an offsetlimit. Here is a <b>pcre2test</b> example:<pre> /B/g,replace=!,use_offset_limit ABC ABC ABC ABC\=offset=3,offset_limit=12 2: ABC A!C A!C ABC</pre>When continuing with global substitutions after matching a substring with zerolength, 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 whenCRLF is a valid newline sequence and the next two characters are CR, LF. Inthis case, the offset is advanced by two characters.</P><P>PCRE2_SUBSTITUTE_UNKNOWN_UNSET causes references to capture groups that donot appear in the pattern to be treated as unset groups. This option should beused with care, because it means that a typo in a group name or number nolonger causes the PCRE2_ERROR_NOSUBSTRING error.</P><P>PCRE2_SUBSTITUTE_UNSET_EMPTY causes unset capture groups (including unknowngroups when PCRE2_SUBSTITUTE_UNKNOWN_UNSET is set) to be treated as emptystrings when inserted as described above. If this option is not set, an attemptto insert an unset group causes the PCRE2_ERROR_UNSET error. This option doesnot influence the extended substitution syntax described below.</P><P>PCRE2_SUBSTITUTE_EXTENDED causes extra processing to be applied to thereplacement string. Without this option, only the dollar character is special,and only the group insertion forms listed above are valid. WhenPCRE2_SUBSTITUTE_EXTENDED is set, two things change:</P><P>Firstly, backslash in a replacement string is interpreted as an escapecharacter. The usual forms such as \n or \x{ddd} can be used to specifyparticular character codes, and backslash followed by any non-alphanumericcharacter quotes that character. Extended quoting can be coded using \Q...\E,exactly as in pattern strings.</P><P>There are also four escape sequences for forcing the case of inserted letters.The insertion mechanism has three states: no case forcing, force upper case,and force lower case. The escape sequences change the current state: \U and\L change to upper or lower case forcing, respectively, and \E (when notterminating 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 lowercase, respectively, and then the state automatically reverts to no caseforcing. Case forcing applies to all inserted characters, including those fromcapture groups and letters within \Q...\E quoted sequences. If eitherPCRE2_UTF or PCRE2_UCP was set when the pattern was compiled, Unicodeproperties are used for case forcing characters whose code points are greaterthan 127.</P><P>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 noeffect. Note also that the PCRE2_ALT_BSUX and PCRE2_EXTRA_ALT_BSUX options donot apply to replacement strings.</P><P>The second effect of setting PCRE2_SUBSTITUTE_EXTENDED is to add moreflexibility to capture group substitution. The syntax is similar to that usedby Bash:<pre> ${<n>:-<string>} ${<n>:+<string1>:<string2>}</pre>As before, <n> may be a group number or a name. The first form specifies adefault value. If group <n> is set, its value is inserted; if not, <string> isexpanded and the result inserted. The second form specifies strings that areexpanded and inserted when group <n> is set or unset, respectively. The firstform is just a convenient shorthand for<pre> ${<n>:+${<n>}:<string>}</pre>Backslash can be used to escape colons and closing curly brackets in thereplacement strings. A change of the case forcing state within a replacementstring remains in force afterwards, as shown in this <b>pcre2test</b> example:<pre> /(some)?(body)/substitute_extended,replace=${1:+\U:\L}HeLLo body 1: hello somebody 1: HELLO</pre>The PCRE2_SUBSTITUTE_UNSET_EMPTY option does not affect these extendedsubstitutions. However, PCRE2_SUBSTITUTE_UNKNOWN_UNSET does cause unknowngroups in the extended syntax forms to be treated as unset.</P><P>If PCRE2_SUBSTITUTE_LITERAL is set, PCRE2_SUBSTITUTE_UNKNOWN_UNSET,PCRE2_SUBSTITUTE_UNSET_EMPTY, and PCRE2_SUBSTITUTE_EXTENDED are irrelevant andare ignored.</P><br><b>Substitution errors</b><br><P>In the event of an error, <b>pcre2_substitute()</b> returns a negative errorcode. Except for PCRE2_ERROR_NOMATCH (which is never returned), errors from<b>pcre2_match()</b> are passed straight back.</P><P>PCRE2_ERROR_NOSUBSTRING is returned for a non-existent substring insertion,unless PCRE2_SUBSTITUTE_UNKNOWN_UNSET is set.</P><P>PCRE2_ERROR_UNSET is returned for an unset substring insertion (including anunknown substring when PCRE2_SUBSTITUTE_UNKNOWN_UNSET is set) when the simple(non-extended) syntax is used and PCRE2_SUBSTITUTE_UNSET_EMPTY is not set.</P><P>PCRE2_ERROR_NOMEMORY is returned if the output buffer is not big enough. If thePCRE2_SUBSTITUTE_OVERFLOW_LENGTH option is set, the size of buffer that isneeded is returned via <i>outlengthptr</i>. Note that this does not happen bydefault.</P><P>PCRE2_ERROR_NULL is returned if PCRE2_SUBSTITUTE_MATCHED is set but the<i>match_data</i> argument is NULL or if the <i>subject</i> or <i>replacement</i>arguments are NULL. For backward compatibility reasons an exception is made forthe <i>replacement</i> argument if the <i>rlength</i> argument is also 0.</P><P>PCRE2_ERROR_BADREPLACEMENT is used for miscellaneous syntax errors in thereplacement string, with more particular errors being PCRE2_ERROR_BADREPESCAPE(invalid escape sequence), PCRE2_ERROR_REPMISSINGBRACE (closing curly bracketnot found), PCRE2_ERROR_BADSUBSTITUTION (syntax error in extended groupsubstitution), and PCRE2_ERROR_BADSUBSPATTERN (the pattern match ended beforeit started or the match started earlier than the current position in thesubject, which can happen if \K is used in an assertion).</P><P>As for all PCRE2 errors, a text message that describes the error can beobtained by calling the <b>pcre2_get_error_message()</b> function (see"Obtaining a textual error message"<a href="#geterrormessage">above).</a><a name="subcallouts"></a></P><br><b>Substitution callouts</b><br><P><b>int pcre2_set_substitute_callout(pcre2_match_context *<i>mcontext</i>,</b><b> int (*<i>callout_function</i>)(pcre2_substitute_callout_block *, void *),</b><b> void *<i>callout_data</i>);</b><br><br>The <b>pcre2_set_substitution_callout()</b> function can be used to specify acallout function for <b>pcre2_substitute()</b>. This information is passed ina match context. The callout function is called after each substitution hasbeen processed, but it can cause the replacement not to happen. The calloutfunction is not called for simulated substitutions that happen as a result ofthe PCRE2_SUBSTITUTE_OVERFLOW_LENGTH option.</P><P>The first argument of the callout function is a pointer to a substitute calloutblock structure, which contains the following fields, not necessarily in thisorder:<pre> uint32_t <i>version</i>; uint32_t <i>subscount</i>; PCRE2_SPTR <i>input</i>; PCRE2_SPTR <i>output</i>; PCRE2_SIZE <i>*ovector</i>; uint32_t <i>oveccount</i>; PCRE2_SIZE <i>output_offsets[2]</i>;</pre>The <i>version</i> field contains the version number of the block format. Thecurrent version is 0. The version number will increase in future if more fieldsare added, but the intention is never to remove any of the existing fields.</P><P>The <i>subscount</i> field is the number of the current match. It is 1 for thefirst callout, 2 for the second, and so on. The <i>input</i> and <i>output</i>pointers are copies of the values passed to <b>pcre2_substitute()</b>.</P><P>The <i>ovector</i> field points to the ovector, which contains the result of themost recent match. The <i>oveccount</i> field contains the number of pairs thatare set in the ovector, and is always greater than zero.</P><P>The <i>output_offsets</i> vector contains the offsets of the replacement in theoutput string. This has already been processed for dollar and (if requested)backslash substitutions as described above.</P><P>The second argument of the callout function is the value passed as<i>callout_data</i> when the function was registered. The value returned by thecallout function is interpreted as follows:</P><P>If the value is zero, the replacement is accepted, and, ifPCRE2_SUBSTITUTE_GLOBAL is set, processing continues with a search for the nextmatch. If the value is not zero, the current replacement is not accepted. Ifthe value is greater than zero, processing continues whenPCRE2_SUBSTITUTE_GLOBAL is set. Otherwise (the value is less than zero orPCRE2_SUBSTITUTE_GLOBAL is not set), the rest of the input is copied to theoutput and the call to <b>pcre2_substitute()</b> exits, returning the number ofmatches so far.</P><br><a name="SEC38" href="#TOC1">DUPLICATE CAPTURE GROUP NAMES</a><br><P><b>int pcre2_substring_nametable_scan(const pcre2_code *<i>code</i>,</b><b> PCRE2_SPTR <i>name</i>, PCRE2_SPTR *<i>first</i>, PCRE2_SPTR *<i>last</i>);</b></P><P>When a pattern is compiled with the PCRE2_DUPNAMES option, names for capturegroups are not required to be unique. Duplicate names are always allowed forgroups with the same number, created by using the (?| feature. Indeed, if suchgroups are named, they are required to use the same names.</P><P>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 isshown in the<a href="pcre2pattern.html"><b>pcre2pattern</b></a>documentation.</P><P>When duplicates are present, <b>pcre2_substring_copy_byname()</b> and<b>pcre2_substring_get_byname()</b> return the first substring corresponding tothe given name that is set. Only if none are set is PCRE2_ERROR_UNSET isreturned. The <b>pcre2_substring_number_from_name()</b> function returns theerror PCRE2_ERROR_NOUNIQUESUBSTRING when there are duplicate names.</P><P>If you want to get full details of all captured substrings for a given name,you must use the <b>pcre2_substring_nametable_scan()</b> function. The firstargument is the compiled pattern, and the second is the name. If the third andfourth arguments are NULL, the function returns a group number for a uniquename, or PCRE2_ERROR_NOUNIQUESUBSTRING otherwise.</P><P>When the third and fourth arguments are not NULL, they must be pointers tovariables that are updated by the function. After it has run, they point to thefirst and last entries in the name-to-number table for the given name, and thefunction 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.</P><P>The format of the name table is described<a href="#infoaboutpattern">above</a>in the section entitled <i>Information about a pattern</i>. Given all therelevant entries for the name, you can extract each of their numbers, and hencethe captured data.</P><br><a name="SEC39" href="#TOC1">FINDING ALL POSSIBLE MATCHES AT ONE POSITION</a><br><P>The traditional matching function uses a similar algorithm to Perl, which stopswhen it finds the first match at a given point in the subject. If you want tofind all possible matches, or the longest possible match at a given position,consider using the alternative matching function (see below) instead. If youcannot use the alternative function, you can kludge it up by making use of thecallout facility, which is described in the<a href="pcre2callout.html"><b>pcre2callout</b></a>documentation.</P><P>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 matchedsubstring. Then return 1, which forces <b>pcre2_match()</b> to backtrack and tryother alternatives. Ultimately, when it runs out of matches,<b>pcre2_match()</b> will yield PCRE2_ERROR_NOMATCH.<a name="dfamatch"></a></P><br><a name="SEC40" href="#TOC1">MATCHING A PATTERN: THE ALTERNATIVE FUNCTION</a><br><P><b>int pcre2_dfa_match(const pcre2_code *<i>code</i>, PCRE2_SPTR <i>subject</i>,</b><b> PCRE2_SIZE <i>length</i>, PCRE2_SIZE <i>startoffset</i>,</b><b> uint32_t <i>options</i>, pcre2_match_data *<i>match_data</i>,</b><b> pcre2_match_context *<i>mcontext</i>,</b><b> int *<i>workspace</i>, PCRE2_SIZE <i>wscount</i>);</b></P><P>The function <b>pcre2_dfa_match()</b> is called to match a subject stringagainst a compiled pattern, using a matching algorithm that scans the subjectstring just once (not counting lookaround assertions), and does not backtrack(except when processing lookaround assertions). This has differentcharacteristics to the normal algorithm, and is not compatible with Perl. Someof the features of PCRE2 patterns are not supported. Nevertheless, there aretimes when this kind of matching can be useful. For a discussion of the twomatching algorithms, and a list of features that <b>pcre2_dfa_match()</b> doesnot support, see the<a href="pcre2matching.html"><b>pcre2matching</b></a>documentation.</P><P>The arguments for the <b>pcre2_dfa_match()</b> function are the same as for<b>pcre2_match()</b>, plus two extras. The ovector within the match data blockis used in a different way, and this is described below. The other commonarguments are used in the same way as for <b>pcre2_match()</b>, so theirdescription is not repeated here.</P><P>The two additional arguments provide workspace for the function. The workspacevector should contain at least 20 elements. It is used for keeping track ofmultiple paths through the pattern tree. More workspace is needed for patternsand subjects where there are a lot of potential matches.</P><P>Here is an example of a simple call to <b>pcre2_dfa_match()</b>:<pre> 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) */</PRE></P><br><b>Option bits for <b>pcre2_dfa_match()</b></b><br><P>The unused bits of the <i>options</i> argument for <b>pcre2_dfa_match()</b> mustbe 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 lastfour of these are exactly the same as for <b>pcre2_match()</b>, so theirdescription is not repeated here.<pre> PCRE2_PARTIAL_HARD PCRE2_PARTIAL_SOFT</pre>These have the same general effect as they do for <b>pcre2_match()</b>, but thedetails are slightly different. When PCRE2_PARTIAL_HARD is set for<b>pcre2_dfa_match()</b>, it returns PCRE2_ERROR_PARTIAL if the end of thesubject is reached and there is still at least one matching possibility thatrequires additional characters. This happens even if some complete matches havealready been found. When PCRE2_PARTIAL_SOFT is set, the return codePCRE2_ERROR_NOMATCH is converted into PCRE2_ERROR_PARTIAL if the end of thesubject is reached, there have been no complete matches, but there is still atleast one matching possibility. The portion of the string that was inspectedwhen the longest partial match was found is set as the first matching string inboth cases. There is a more detailed discussion of partial and multi-segmentmatching, with examples, in the<a href="pcre2partial.html"><b>pcre2partial</b></a>documentation.<pre> PCRE2_DFA_SHORTEST</pre>Setting the PCRE2_DFA_SHORTEST option causes the matching algorithm to stop assoon as it has found one match. Because of the way the alternative algorithmworks, this is necessarily the shortest possible match at the first possiblematching point in the subject string.<pre> PCRE2_DFA_RESTART</pre>When <b>pcre2_dfa_match()</b> returns a partial match, it is possible to call itagain, with additional subject characters, and have it continue with the samematch. The PCRE2_DFA_RESTART option requests this action; when it is set, the<i>workspace</i> and <i>wscount</i> options must reference the same vector asbefore because data about the match so far is left in them after a partialmatch. There is more discussion of this facility in the<a href="pcre2partial.html"><b>pcre2partial</b></a>documentation.</P><br><b>Successful returns from <b>pcre2_dfa_match()</b></b><br><P>When <b>pcre2_dfa_match()</b> succeeds, it may have matched more than onesubstring in the subject. Note, however, that all the matches from one run ofthe function start at the same point in the subject. The shorter matches areall initial substrings of the longer matches. For example, if the pattern<pre> <.*></pre>is matched against the string<pre> This is <something> <something else> <something further> no more</pre>the three matched strings are<pre> <something> <something else> <something further> <something> <something else> <something></pre>On success, the yield of the function is a number greater than zero, which isthe number of matched substrings. The offsets of the substrings are returned inthe ovector, and can be extracted by number in the same way as for<b>pcre2_match()</b>, but the numbers bear no relation to any capture groupsthat may exist in the pattern, because DFA matching does not support capturing.</P><P>Calls to the convenience functions that extract substrings by namereturn the error PCRE2_ERROR_DFA_UFUNC (unsupported function) if used after aDFA match. The convenience functions that extract substrings by number neverreturn PCRE2_ERROR_NOSUBSTRING.</P><P>The matched strings are stored in the ovector in reverse order of length; thatis, the longest matching string is first. If there were too many matches to fitinto the ovector, the yield of the function is zero, and the vector is filledwith the longest matches.</P><P>NOTE: PCRE2's "auto-possessification" optimization usually applies to characterrepeats at the end of a pattern (as well as internally). For example, thepattern "a\d+" is compiled as if it were "a\d++". For DFA matching, thismeans that only one possible match is found. If you really do want multiplematches in such cases, either use an ungreedy repeat such as "a\d+?" or setthe PCRE2_NO_AUTO_POSSESS option when compiling.</P><br><b>Error returns from <b>pcre2_dfa_match()</b></b><br><P>The <b>pcre2_dfa_match()</b> function returns a negative number when it fails.Many of the errors are the same as for <b>pcre2_match()</b>, as described<a href="#errorlist">above.</a>There are in addition the following errors that are specific to<b>pcre2_dfa_match()</b>:<pre> PCRE2_ERROR_DFA_UITEM</pre>This return is given if <b>pcre2_dfa_match()</b> encounters an item in thepattern that it does not support, for instance, the use of \C in a UTF mode ora backreference.<pre> PCRE2_ERROR_DFA_UCOND</pre>This return is given if <b>pcre2_dfa_match()</b> encounters a condition itemthat uses a backreference for the condition, or a test for recursion in aspecific capture group. These are not supported.<pre> PCRE2_ERROR_DFA_UINVALID_UTF</pre>This return is given if <b>pcre2_dfa_match()</b> is called for a pattern thatwas compiled with PCRE2_MATCH_INVALID_UTF. This is not supported for DFAmatching.<pre> PCRE2_ERROR_DFA_WSSIZE</pre>This return is given if <b>pcre2_dfa_match()</b> runs out of space in the<i>workspace</i> vector.<pre> PCRE2_ERROR_DFA_RECURSE</pre>When a recursion or subroutine call is processed, the matching function callsitself recursively, using private memory for the ovector and <i>workspace</i>.This error is given if the internal ovector is not large enough. This should beextremely rare, as a vector of size 1000 is used.<pre> PCRE2_ERROR_DFA_BADRESTART</pre>When <b>pcre2_dfa_match()</b> is called with the <b>PCRE2_DFA_RESTART</b> option,some plausibility checks are made on the contents of the workspace, whichshould contain data about the previous partial match. If any of these checksfail, this error is given.</P><br><a name="SEC41" href="#TOC1">SEE ALSO</a><br><P><b>pcre2build</b>(3), <b>pcre2callout</b>(3), <b>pcre2demo(3)</b>,<b>pcre2matching</b>(3), <b>pcre2partial</b>(3), <b>pcre2posix</b>(3),<b>pcre2sample</b>(3), <b>pcre2unicode</b>(3).</P><br><a name="SEC42" href="#TOC1">AUTHOR</a><br><P>Philip Hazel<br>Retired from University Computing Service<br>Cambridge, England.<br></P><br><a name="SEC43" href="#TOC1">REVISION</a><br><P>Last updated: 24 April 2024<br>Copyright © 1997-2024 University of Cambridge.<br><p>Return to the <a href="index.html">PCRE2 index page</a>.</p>
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