NAME

PCRE2 - Perl-compatible regular expressions (revised API)

#include <pcre2.h>

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

PCRE2 NATIVE API BASIC FUNCTIONS

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

void pcre2_code_free(pcre2_code *code);

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

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

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

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

void pcre2_match_data_free(pcre2_match_data *match_data);

PCRE2 NATIVE API AUXILIARY MATCH FUNCTIONS

PCRE2_SPTR pcre2_get_mark(pcre2_match_data *match_data);

PCRE2_SIZE pcre2_get_match_data_size(pcre2_match_data *match_data);

PCRE2_SIZE pcre2_get_match_data_heapframes_size(
  pcre2_match_data *match_data);

uint32_t pcre2_get_ovector_count(pcre2_match_data *match_data);

PCRE2_SIZE *pcre2_get_ovector_pointer(pcre2_match_data *match_data);

PCRE2_SIZE pcre2_get_startchar(pcre2_match_data *match_data);

PCRE2 NATIVE API GENERAL CONTEXT FUNCTIONS

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

pcre2_general_context *pcre2_general_context_copy(
  pcre2_general_context *gcontext);

void pcre2_general_context_free(pcre2_general_context *gcontext);

PCRE2 NATIVE API COMPILE CONTEXT FUNCTIONS

pcre2_compile_context *pcre2_compile_context_create(
  pcre2_general_context *gcontext);

pcre2_compile_context *pcre2_compile_context_copy(
  pcre2_compile_context *ccontext);

void pcre2_compile_context_free(pcre2_compile_context *ccontext);

int pcre2_set_bsr(pcre2_compile_context *ccontext,
  uint32_t value);

int pcre2_set_character_tables(pcre2_compile_context *ccontext,
  const uint8_t *tables);

int pcre2_set_compile_extra_options(pcre2_compile_context *ccontext,
  uint32_t extra_options);

int pcre2_set_max_pattern_length(pcre2_compile_context *ccontext,
  PCRE2_SIZE value);

int pcre2_set_max_pattern_compiled_length(
  pcre2_compile_context *ccontext, PCRE2_SIZE value);

int pcre2_set_max_varlookbehind(pcre2_compile_contest *ccontext,
  uint32_t value);

int pcre2_set_newline(pcre2_compile_context *ccontext,
  uint32_t value);

int pcre2_set_parens_nest_limit(pcre2_compile_context *ccontext,
  uint32_t value);

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

PCRE2 NATIVE API MATCH CONTEXT FUNCTIONS

pcre2_match_context *pcre2_match_context_create(
  pcre2_general_context *gcontext);

pcre2_match_context *pcre2_match_context_copy(
  pcre2_match_context *mcontext);

void pcre2_match_context_free(pcre2_match_context *mcontext);

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

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

int pcre2_set_offset_limit(pcre2_match_context *mcontext,
  PCRE2_SIZE value);

int pcre2_set_heap_limit(pcre2_match_context *mcontext,
  uint32_t value);

int pcre2_set_match_limit(pcre2_match_context *mcontext,
  uint32_t value);

int pcre2_set_depth_limit(pcre2_match_context *mcontext,
  uint32_t value);

PCRE2 NATIVE API STRING EXTRACTION FUNCTIONS

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

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

void pcre2_substring_free(PCRE2_UCHAR *buffer);

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

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

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

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

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

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

void pcre2_substring_list_free(PCRE2_UCHAR **list);

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

PCRE2 NATIVE API STRING SUBSTITUTION FUNCTION

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

PCRE2 NATIVE API JIT FUNCTIONS

int pcre2_jit_compile(pcre2_code *code, uint32_t options);

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

void pcre2_jit_free_unused_memory(pcre2_general_context *gcontext);

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

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

void pcre2_jit_stack_free(pcre2_jit_stack *jit_stack);

PCRE2 NATIVE API SERIALIZATION FUNCTIONS

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

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

void pcre2_serialize_free(uint8_t *bytes);

int32_t pcre2_serialize_get_number_of_codes(const uint8_t *bytes);

PCRE2 NATIVE API AUXILIARY FUNCTIONS

pcre2_code *pcre2_code_copy(const pcre2_code *code);

pcre2_code *pcre2_code_copy_with_tables(const pcre2_code *code);

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

const uint8_t *pcre2_maketables(pcre2_general_context *gcontext);

void pcre2_maketables_free(pcre2_general_context *gcontext,
  const uint8_t *tables);

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

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

int pcre2_config(uint32_t what, void *where);

PCRE2 NATIVE API OBSOLETE FUNCTIONS

int pcre2_set_recursion_limit(pcre2_match_context *mcontext,
  uint32_t value);

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

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

PCRE2 EXPERIMENTAL PATTERN CONVERSION FUNCTIONS

pcre2_convert_context *pcre2_convert_context_create(
  pcre2_general_context *gcontext);

pcre2_convert_context *pcre2_convert_context_copy(
  pcre2_convert_context *cvcontext);

void pcre2_convert_context_free(pcre2_convert_context *cvcontext);

int pcre2_set_glob_escape(pcre2_convert_context *cvcontext,
  uint32_t escape_char);

int pcre2_set_glob_separator(pcre2_convert_context *cvcontext,
  uint32_t separator_char);

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

void pcre2_converted_pattern_free(PCRE2_UCHAR *converted_pattern);

These functions provide a way of converting non-PCRE2 patterns into patterns that can be processed by pcre2_compile(). This facility is experimental and may be changed in future releases. At present, "globs" and POSIX basic and extended patterns can be converted. Details are given in the pcre2convert documentation.

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

There are three PCRE2 libraries, supporting 8-bit, 16-bit, and 32-bit code units, respectively. However, there is just one header file, pcre2.h. This contains the function prototypes and other definitions for all three libraries. One, two, or all three can be installed simultaneously. On Unix-like systems the libraries are called libpcre2-8, libpcre2-16, and libpcre2-32, and they can also co-exist with the original PCRE libraries. Every PCRE2 function comes in three different forms, one for each library, for example:

pcre2_compile_8()
pcre2_compile_16()
pcre2_compile_32()

There are also three different sets of data types:

PCRE2_UCHAR8, PCRE2_UCHAR16, PCRE2_UCHAR32
PCRE2_SPTR8, PCRE2_SPTR16, PCRE2_SPTR32

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

Character strings are passed to a PCRE2 library as sequences of unsigned integers in code units of the appropriate width. The length of a string may be given as a number of code units, or the string may be specified as zero-terminated.

Many applications use only one code unit width. For their convenience, macros are defined whose names are the generic forms such as pcre2_compile() and PCRE2_SPTR. These macros use the value of the macro PCRE2_CODE_UNIT_WIDTH to generate the appropriate width-specific function and macro names. PCRE2_CODE_UNIT_WIDTH is not defined by default. An application must define it to be 8, 16, or 32 before including pcre2.h in order to make use of the generic names.

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

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

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

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

PCRE2 API OVERVIEW

PCRE2 has its own native API, which is described in this document. There are also some wrapper functions for the 8-bit library that correspond to the POSIX regular expression API, but they do not give access to all the functionality of PCRE2 and they are not thread-safe. They are described in the pcre2posix documentation. Both these APIs define a set of C function calls.

The native API C data types, function prototypes, option values, and error codes are defined in the header file pcre2.h, which also contains definitions of PCRE2_MAJOR and PCRE2_MINOR, the major and minor release numbers for the library. Applications can use these to include support for different releases of PCRE2.

In a Windows environment, if you want to statically link an application program against a non-dll PCRE2 library, you must define PCRE2_STATIC before including pcre2.h.

The functions pcre2_compile() and pcre2_match() are used for compiling and matching regular expressions in a Perl-compatible manner. A sample program that demonstrates the simplest way of using them is provided in the file called pcre2demo.c in the PCRE2 source distribution. A listing of this program is given in the pcre2demo documentation, and the pcre2sample documentation describes how to compile and run it.

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

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

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

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

A second matching function, pcre2_dfa_match(), which is not Perl-compatible, is also provided. This uses a different algorithm for the matching. The alternative algorithm finds all possible matches (at a given point in the subject), and scans the subject just once (unless there are lookaround assertions). However, this algorithm does not return captured substrings. A description of the two matching algorithms and their advantages and disadvantages is given in the pcre2matching documentation. There is no JIT support for pcre2_dfa_match().

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

pcre2_substring_copy_byname()
pcre2_substring_copy_bynumber()
pcre2_substring_get_byname()
pcre2_substring_get_bynumber()
pcre2_substring_list_get()
pcre2_substring_length_byname()
pcre2_substring_length_bynumber()
pcre2_substring_nametable_scan()
pcre2_substring_number_from_name()

pcre2_substring_free() and pcre2_substring_list_free() are also provided, to free memory used for extracted strings. If either of these functions is called with a NULL argument, the function returns immediately without doing anything.

The function pcre2_substitute() can be called to match a pattern and return a copy of the subject string with substitutions for parts that were matched.

Functions whose names begin with pcre2_serialize_ are used for saving compiled patterns on disc or elsewhere, and reloading them later.

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

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

STRING LENGTHS AND OFFSETS

The PCRE2 API uses string lengths and offsets into strings of code units in several places. These values are always of type PCRE2_SIZE, which is an unsigned integer type, currently always defined as size_t. The largest value that can be stored in such a type (that is ~(PCRE2_SIZE)0) is reserved as a special indicator for zero-terminated strings and unset offsets. Therefore, the longest string that can be handled is one less than this maximum. Note that string lengths are always given in code units. Only in the 8-bit library is such a length the same as the number of bytes in the string.

NEWLINES

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

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

In the PCRE2 documentation the word "newline" is used to mean "the character or pair of characters that indicate a line break". The choice of newline convention affects the handling of the dot, circumflex, and dollar metacharacters, the handling of #-comments in /x mode, and, when CRLF is a recognized line ending sequence, the match position advancement for a non-anchored pattern. There is more detail about this in the section on pcre2_match() options below.

The choice of newline convention does not affect the interpretation of the \n or \r escape sequences, nor does it affect what \R matches; this has its own separate convention.

MULTITHREADING

In a multithreaded application it is important to keep thread-specific data separate from data that can be shared between threads. The PCRE2 library code itself is thread-safe: it contains no static or global variables. The API is designed to be fairly simple for non-threaded applications while at the same time ensuring that multithreaded applications can use it.

There are several different blocks of data that are used to pass information between the application and the PCRE2 libraries.

PCRE2 CONTEXTS

Some PCRE2 functions have a lot of parameters, many of which are used only by specialist applications, for example, those that use custom memory management or non-standard character tables. To keep function argument lists at a reasonable size, and at the same time to keep the API extensible, "uncommon" parameters are passed to certain functions in a context instead of directly. A context is just a block of memory that holds the parameter values. Applications that do not need to adjust any of the context parameters can pass NULL when a context pointer is required.

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

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

pcre2_general_context *pcre2_general_context_copy(
  pcre2_general_context *gcontext);

void pcre2_general_context_free(pcre2_general_context *gcontext);

pcre2_compile_context *pcre2_compile_context_create(
  pcre2_general_context *gcontext);

pcre2_compile_context *pcre2_compile_context_copy(
  pcre2_compile_context *ccontext);

void pcre2_compile_context_free(pcre2_compile_context *ccontext);

int pcre2_set_bsr(pcre2_compile_context *ccontext,
  uint32_t value);

int pcre2_set_character_tables(pcre2_compile_context *ccontext,
  const uint8_t *tables);

int pcre2_set_compile_extra_options(pcre2_compile_context *ccontext,
  uint32_t extra_options);

int pcre2_set_max_pattern_length(pcre2_compile_context *ccontext,
  PCRE2_SIZE value);

int pcre2_set_max_pattern_compiled_length(
  pcre2_compile_context *ccontext, PCRE2_SIZE value);

int pcre2_set_max_varlookbehind(pcre2_compile_contest *ccontext,
  uint32_t value);

int pcre2_set_newline(pcre2_compile_context *ccontext,
  uint32_t value);

int pcre2_set_parens_nest_limit(pcre2_compile_context *ccontext,
  uint32_t value);

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

pcre2_match_context *pcre2_match_context_create(
  pcre2_general_context *gcontext);

pcre2_match_context *pcre2_match_context_copy(
  pcre2_match_context *mcontext);

void pcre2_match_context_free(pcre2_match_context *mcontext);

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

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

int pcre2_set_offset_limit(pcre2_match_context *mcontext,
  PCRE2_SIZE value);

int pcre2_set_heap_limit(pcre2_match_context *mcontext,
  uint32_t value);

int pcre2_set_match_limit(pcre2_match_context *mcontext,
  uint32_t value);

int pcre2_set_depth_limit(pcre2_match_context *mcontext,
  uint32_t value);

CHECKING BUILD-TIME OPTIONS

int pcre2_config(uint32_t what, void *where);

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

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

When requesting information, the returned value from pcre2_config() is non-negative on success, or the negative error code PCRE2_ERROR_BADOPTION if the value in the first argument is not recognized. The following information is available:

PCRE2_CONFIG_BSR

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

PCRE2_CONFIG_COMPILED_WIDTHS

The output is a uint32_t integer whose lower bits indicate which code unit widths were selected when PCRE2 was built. The 1-bit indicates 8-bit support, and the 2-bit and 4-bit indicate 16-bit and 32-bit support, respectively.

PCRE2_CONFIG_DEPTHLIMIT

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

PCRE2_CONFIG_HEAPLIMIT

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

PCRE2_CONFIG_JIT

The output is a uint32_t integer that is set to one if support for just-in-time compiling is included in the library; otherwise it is set to zero. Note that having the support in the library does not guarantee that JIT will be used for any given match. See the pcre2jit documentation for more details.

PCRE2_CONFIG_JITTARGET

The where argument should point to a buffer that is at least 48 code units long. (The exact length required can be found by calling pcre2_config() with where set to NULL.) The buffer is filled with a string that contains the name of the architecture for which the JIT compiler is configured, for example "x86 32bit (little endian + unaligned)". If JIT support is not available, PCRE2_ERROR_BADOPTION is returned, otherwise the number of code units used is returned. This is the length of the string, plus one unit for the terminating zero.

PCRE2_CONFIG_LINKSIZE

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

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

PCRE2_CONFIG_MATCHLIMIT

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

PCRE2_CONFIG_NEWLINE

The output is a uint32_t integer whose value specifies the default character sequence that is recognized as meaning "newline". The values are:

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

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

PCRE2_CONFIG_NEVER_BACKSLASH_C

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

PCRE2_CONFIG_PARENSLIMIT

The output is a uint32_t integer that gives the maximum depth of nesting of parentheses (of any kind) in a pattern. This limit is imposed to cap the amount of system stack used when a pattern is compiled. It is specified when PCRE2 is built; the default is 250. This limit does not take into account the stack that may already be used by the calling application. For finer control over compilation stack usage, see pcre2_set_compile_recursion_guard().

PCRE2_CONFIG_STACKRECURSE

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

PCRE2_CONFIG_TABLES_LENGTH

The output is a uint32_t integer that gives the length of PCRE2's character processing tables in bytes. For details of these tables see the section on locale support below.

PCRE2_CONFIG_UNICODE_VERSION

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

PCRE2_CONFIG_UNICODE

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

PCRE2_CONFIG_VERSION

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

COMPILING A PATTERN

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

void pcre2_code_free(pcre2_code *code);

pcre2_code *pcre2_code_copy(const pcre2_code *code);

pcre2_code *pcre2_code_copy_with_tables(const pcre2_code *code);

The pcre2_compile() function compiles a pattern into an internal form. The pattern is defined by a pointer to a string of code units and a length in code units. If the pattern is zero-terminated, the length can be specified as PCRE2_ZERO_TERMINATED. A NULL pattern pointer with a length of zero is treated as an empty string (NULL with a non-zero length causes an error return). The function returns a pointer to a block of memory that contains the compiled pattern and related data, or NULL if an error occurred.

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

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

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

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

The options argument for pcre2_compile() contains various bit settings that affect the compilation. It should be zero if none of them are required. The available options are described below. Some of them (in particular, those that are compatible with Perl, but some others as well) can also be set and unset from within the pattern (see the detailed description in the pcre2pattern documentation).

For those options that can be different in different parts of the pattern, the contents of the options argument specifies their settings at the start of compilation. The PCRE2_ANCHORED, PCRE2_ENDANCHORED, and PCRE2_NO_UTF_CHECK options can be set at the time of matching as well as at compile time.

Some additional options and less frequently required compile-time parameters (for example, the newline setting) can be provided in a compile context (as described above).

If errorcode or erroroffset is NULL, pcre2_compile() returns NULL immediately. Otherwise, the variables to which these point are set to an error code and an offset (number of code units) within the pattern, respectively, when pcre2_compile() returns NULL because a compilation error has occurred.

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

The value returned in erroroffset is an indication of where in the pattern an error occurred. When there is no error, zero is returned. A non-zero value is not necessarily the furthest point in the pattern that was read. For example, after the error "lookbehind assertion is not fixed length", the error offset points to the start of the failing assertion. For an invalid UTF-8 or UTF-16 string, the offset is that of the first code unit of the failing character.

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

This code fragment shows a typical straightforward call to pcre2_compile():

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

JUST-IN-TIME (JIT) COMPILATION

int pcre2_jit_compile(pcre2_code *code, uint32_t options);

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

void pcre2_jit_free_unused_memory(pcre2_general_context *gcontext);

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

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

void pcre2_jit_stack_free(pcre2_jit_stack *jit_stack);

These functions provide support for JIT compilation, which, if the just-in-time compiler is available, further processes a compiled pattern into machine code that executes much faster than the pcre2_match() interpretive matching function. Full details are given in the pcre2jit documentation.

JIT compilation is a heavyweight optimization. It can take some time for patterns to be analyzed, and for one-off matches and simple patterns the benefit of faster execution might be offset by a much slower compilation time. Most (but not all) patterns can be optimized by the JIT compiler.

LOCALE SUPPORT

const uint8_t *pcre2_maketables(pcre2_general_context *gcontext);

void pcre2_maketables_free(pcre2_general_context *gcontext,
  const uint8_t *tables);

PCRE2 handles caseless matching, and determines whether characters are letters, digits, or whatever, by reference to a set of tables, indexed by character code point. However, this applies only to characters whose code points are less than 256. By default, higher-valued code points never match escapes such as \w or \d.

When PCRE2 is built with Unicode support (the default), certain Unicode character properties can be tested with \p and \P, or, alternatively, the PCRE2_UCP option can be set when a pattern is compiled; this causes \w and friends to use Unicode property support instead of the built-in tables. PCRE2_UCP also causes upper/lower casing operations on characters with code points greater than 127 to use Unicode properties. These effects apply even when PCRE2_UTF is not set. There are, however, some PCRE2_EXTRA options (see above) that can be used to modify or suppress them.

The use of locales with Unicode is discouraged. If you are handling characters with code points greater than 127, you should either use Unicode support, or use locales, but not try to mix the two.

PCRE2 contains a built-in set of character tables that are used by default. These are sufficient for many applications. Normally, the internal tables recognize only ASCII characters. However, when PCRE2 is built, it is possible to cause the internal tables to be rebuilt in the default "C" locale of the local system, which may cause them to be different.

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

External tables are built by calling the pcre2_maketables() function, in the relevant locale. The only argument to this function is a general context, which can be used to pass a custom memory allocator. If the argument is NULL, the system malloc() is used. The result can be passed to pcre2_compile() as often as necessary, by creating a compile context and calling pcre2_set_character_tables() to set the tables pointer therein.

For example, to build and use tables that are appropriate for the French locale (where accented characters with values greater than 127 are treated as letters), the following code could be used:

setlocale(LC_CTYPE, "fr_FR");
tables = pcre2_maketables(NULL);
ccontext = pcre2_compile_context_create(NULL);
pcre2_set_character_tables(ccontext, tables);
re = pcre2_compile(..., ccontext);

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

The pointer that is passed (via the compile context) to pcre2_compile() is saved with the compiled pattern, and the same tables are used by the matching functions. Thus, for any single pattern, compilation and matching both happen in the same locale, but different patterns can be processed in different locales.

It is the caller's responsibility to ensure that the memory containing the tables remains available while they are still in use. When they are no longer needed, you can discard them using pcre2_maketables_free(), which should pass as its first parameter the same global context that was used to create the tables.

INFORMATION ABOUT A COMPILED PATTERN

int pcre2_pattern_info(const pcre2 *code, uint32_t what, void *where);

The pcre2_pattern_info() function returns general information about a compiled pattern. For information about callouts, see the next section. The first argument for pcre2_pattern_info() is a pointer to the compiled pattern. The second argument specifies which piece of information is required, and the third argument is a pointer to a variable to receive the data. If the third argument is NULL, the first argument is ignored, and the function returns the size in bytes of the variable that is required for the information requested. Otherwise, the yield of the function is zero for success, or one of the following negative numbers:

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

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

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

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

PCRE2_INFO_ALLOPTIONS
PCRE2_INFO_ARGOPTIONS
PCRE2_INFO_EXTRAOPTIONS

Return copies of the pattern's options. The third argument should point to a uint32_t variable. PCRE2_INFO_ARGOPTIONS returns exactly the options that were passed to pcre2_compile(), whereas PCRE2_INFO_ALLOPTIONS returns the compile options as modified by any top-level (*XXX) option settings such as (*UTF) at the start of the pattern itself. PCRE2_INFO_EXTRAOPTIONS returns the extra options that were set in the compile context by calling the pcre2_set_compile_extra_options() function.

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

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

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

When .* is the first significant item, anchoring is possible only when all the following are true:

.* is not in an atomic group
.* is not in a capture group that is the subject
of a backreference
PCRE2_DOTALL is in force for .*
Neither (*PRUNE) nor (*SKIP) appears in the pattern
PCRE2_NO_DOTSTAR_ANCHOR is not set

For patterns that are auto-anchored, the PCRE2_ANCHORED bit is set in the options returned for PCRE2_INFO_ALLOPTIONS.

PCRE2_INFO_BACKREFMAX

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

PCRE2_INFO_BSR

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

PCRE2_INFO_CAPTURECOUNT

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

PCRE2_INFO_DEPTHLIMIT

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

PCRE2_INFO_FIRSTBITMAP

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

PCRE2_INFO_FIRSTCODETYPE

Return information about the first code unit of any matched string, for a non-anchored pattern. The third argument should point to a uint32_t variable. If there is a fixed first value, for example, the letter "c" from a pattern such as (cat|cow|coyote), 1 is returned, and the value can be retrieved using PCRE2_INFO_FIRSTCODEUNIT. If there is no fixed first value, but it is known that a match can occur only at the start of the subject or following a newline in the subject, 2 is returned. Otherwise, and for anchored patterns, 0 is returned.

PCRE2_INFO_FIRSTCODEUNIT

Return the value of the first code unit of any matched string for a pattern where PCRE2_INFO_FIRSTCODETYPE returns 1; otherwise return 0. The third argument should point to a uint32_t variable. In the 8-bit library, the value is always less than 256. In the 16-bit library the value can be up to 0xffff. In the 32-bit library in UTF-32 mode the value can be up to 0x10ffff, and up to 0xffffffff when not using UTF-32 mode.

PCRE2_INFO_FRAMESIZE

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

PCRE2_INFO_HASBACKSLASHC

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

PCRE2_INFO_HASCRORLF

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

PCRE2_INFO_HEAPLIMIT

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

PCRE2_INFO_JCHANGED

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

PCRE2_INFO_JITSIZE

If the compiled pattern was successfully processed by pcre2_jit_compile(), return the size of the JIT compiled code, otherwise return zero. The third argument should point to a size_t variable.

PCRE2_INFO_LASTCODETYPE

Returns 1 if there is a rightmost literal code unit that must exist in any matched string, other than at its start. The third argument should point to a uint32_t variable. If there is no such value, 0 is returned. When 1 is returned, the code unit value itself can be retrieved using PCRE2_INFO_LASTCODEUNIT. For anchored patterns, a last literal value is recorded only if it follows something of variable length. For example, for the pattern /^a\d+z\d+/ the returned value is 1 (with "z" returned from PCRE2_INFO_LASTCODEUNIT), but for /^a\dz\d/ the returned value is 0.

PCRE2_INFO_LASTCODEUNIT

Return the value of the rightmost literal code unit that must exist in any matched string, other than at its start, for a pattern where PCRE2_INFO_LASTCODETYPE returns 1. Otherwise, return 0. The third argument should point to a uint32_t variable.

PCRE2_INFO_MATCHEMPTY

Return 1 if the pattern might match an empty string, otherwise 0. The third argument should point to a uint32_t variable. When a pattern contains recursive subroutine calls it is not always possible to determine whether or not it can match an empty string. PCRE2 takes a cautious approach and returns 1 in such cases.

PCRE2_INFO_MATCHLIMIT

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

PCRE2_INFO_MAXLOOKBEHIND

A lookbehind assertion moves back a certain number of characters (not code units) when it starts to process each of its branches. This request returns the largest of these backward moves. The third argument should point to a uint32_t integer. The simple assertions \b and \B require a one-character lookbehind and cause PCRE2_INFO_MAXLOOKBEHIND to return 1 in the absence of anything longer. \A also registers a one-character lookbehind, though it does not actually inspect the previous character.

Note that this information is useful for multi-segment matching only if the pattern contains no nested lookbehinds. For example, the pattern (?<=a(?<=ba)c) returns a maximum lookbehind of 2, but when it is processed, the first lookbehind moves back by two characters, matches one character, then the nested lookbehind also moves back by two characters. This puts the matching point three characters earlier than it was at the start. PCRE2_INFO_MAXLOOKBEHIND is really only useful as a debugging tool. See the pcre2partial documentation for a discussion of multi-segment matching.

PCRE2_INFO_MINLENGTH

If a minimum length for matching subject strings was computed, its value is returned. Otherwise the returned value is 0. This value is not computed when PCRE2_NO_START_OPTIMIZE is set. The value is a number of characters, which in UTF mode may be different from the number of code units. The third argument should point to a uint32_t variable. The value is a lower bound to the length of any matching string. There may not be any strings of that length that do actually match, but every string that does match is at least that long.

PCRE2_INFO_NAMECOUNT
PCRE2_INFO_NAMEENTRYSIZE
PCRE2_INFO_NAMETABLE

PCRE2 supports the use of named as well as numbered capturing parentheses. The names are just an additional way of identifying the parentheses, which still acquire numbers. Several convenience functions such as pcre2_substring_get_byname() are provided for extracting captured substrings by name. It is also possible to extract the data directly, by first converting the name to a number in order to access the correct pointers in the output vector (described with pcre2_match() below). To do the conversion, you need to use the name-to-number map, which is described by these three values.

The map consists of a number of fixed-size entries. PCRE2_INFO_NAMECOUNT gives the number of entries, and PCRE2_INFO_NAMEENTRYSIZE gives the size of each entry in code units; both of these return a uint32_t value. The entry size depends on the length of the longest name.

PCRE2_INFO_NAMETABLE returns a pointer to the first entry of the table. This is a PCRE2_SPTR pointer to a block of code units. In the 8-bit library, the first two bytes of each entry are the number of the capturing parenthesis, most significant byte first. In the 16-bit library, the pointer points to 16-bit code units, the first of which contains the parenthesis number. In the 32-bit library, the pointer points to 32-bit code units, the first of which contains the parenthesis number. The rest of the entry is the corresponding name, zero terminated.

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

Duplicate names for capture groups with different numbers are permitted, but only if PCRE2_DUPNAMES is set. They appear in the table in the order in which they were found in the pattern. In the absence of (?| this is the order of increasing number; when (?| is used this is not necessarily the case because later capture groups may have lower numbers.

As a simple example of the name/number table, consider the following pattern after compilation by the 8-bit library (assume PCRE2_EXTENDED is set, so white space - including newlines - is ignored):

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

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

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

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

PCRE2_INFO_NEWLINE

The output is one of the following uint32_t values:

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

This identifies the character sequence that will be recognized as meaning "newline" while matching.

PCRE2_INFO_SIZE

Return the size of the compiled pattern in bytes (for all three libraries). The third argument should point to a size_t variable. This value includes the size of the general data block that precedes the code units of the compiled pattern itself. The value that is used when pcre2_compile() is getting memory in which to place the compiled pattern may be slightly larger than the value returned by this option, because there are cases where the code that calculates the size has to over-estimate. Processing a pattern with the JIT compiler does not alter the value returned by this option.

INFORMATION ABOUT A PATTERN'S CALLOUTS

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

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

SERIALIZATION AND PRECOMPILING

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

THE MATCH DATA BLOCK

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

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

void pcre2_match_data_free(pcre2_match_data *match_data);

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

Before calling pcre2_match(), pcre2_dfa_match(), or pcre2_jit_match() you must create a match data block by calling one of the creation functions above. For pcre2_match_data_create(), the first argument is the number of pairs of offsets in the ovector.

When using pcre2_match(), one pair of offsets is required to identify the string that matched the whole pattern, with an additional pair for each captured substring. For example, a value of 4 creates enough space to record the matched portion of the subject plus three captured substrings.

When using pcre2_dfa_match() there may be multiple matched substrings of different lengths at the same point in the subject. The ovector should be made large enough to hold as many as are expected.

A minimum of at least 1 pair is imposed by pcre2_match_data_create(), so it is always possible to return the overall matched string in the case of pcre2_match() or the longest match in the case of pcre2_dfa_match(). The maximum number of pairs is 65535; if the first argument of pcre2_match_data_create() is greater than this, 65535 is used.

The second argument of pcre2_match_data_create() is a pointer to a general context, which can specify custom memory management for obtaining the memory for the match data block. If you are not using custom memory management, pass NULL, which causes malloc() to be used.

For pcre2_match_data_create_from_pattern(), the first argument is a pointer to a compiled pattern. The ovector is created to be exactly the right size to hold all the substrings a pattern might capture when matched using pcre2_match(). You should not use this call when matching with pcre2_dfa_match(). The second argument is again a pointer to a general context, but in this case if NULL is passed, the memory is obtained using the same allocator that was used for the compiled pattern (custom or default).

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

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

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

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

MEMORY USE FOR MATCH DATA BLOCKS

PCRE2_SIZE pcre2_get_match_data_size(pcre2_match_data *match_data);

PCRE2_SIZE pcre2_get_match_data_heapframes_size(
  pcre2_match_data *match_data);

The size of a match data block depends on the size of the ovector that it contains. The function pcre2_get_match_data_size() returns the size, in bytes, of the block that is its argument.

When pcre2_match() runs interpretively (that is, without using JIT), it makes use of a vector of data frames for remembering backtracking positions. The size of each individual frame depends on the number of capturing parentheses in the pattern and can be obtained by calling pcre2_pattern_info() with the PCRE2_INFO_FRAMESIZE option (see the section entitled "Information about a compiled pattern" above).

Heap memory is used for the frames vector; if the initial memory block turns out to be too small during matching, it is automatically expanded. When pcre2_match() returns, the memory is not freed, but remains attached to the match data block, for use by any subsequent matches that use the same block. It is automatically freed when the match data block itself is freed.

You can find the current size of the frames vector that a match data block owns by calling pcre2_get_match_data_heapframes_size(). For a newly created match data block the size will be zero. Some types of match may require a lot of frames and thus a large vector; applications that run in environments where memory is constrained can check this and free the match data block if the heap frames vector has become too big.

MATCHING A PATTERN: THE TRADITIONAL FUNCTION

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

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

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

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

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

If the subject string is zero-terminated, the length can be given as PCRE2_ZERO_TERMINATED. A match context must be provided if certain less common matching parameters are to be changed. For details, see the section on the match context above.

NEWLINE HANDLING WHEN MATCHING

When PCRE2 is built, a default newline convention is set; this is usually the standard convention for the operating system. The default can be overridden in a compile context by calling pcre2_set_newline(). It can also be overridden by starting a pattern string with, for example, (*CRLF), as described in the section on newline conventions in the pcre2pattern page. During matching, the newline choice affects the behaviour of the dot, circumflex, and dollar metacharacters. It may also alter the way the match starting position is advanced after a match failure for an unanchored pattern.

When PCRE2_NEWLINE_CRLF, PCRE2_NEWLINE_ANYCRLF, or PCRE2_NEWLINE_ANY is set as the newline convention, and a match attempt for an unanchored pattern fails when the current starting position is at a CRLF sequence, and the pattern contains no explicit matches for CR or LF characters, the match position is advanced by two characters instead of one, in other words, to after the CRLF.

The above rule is a compromise that makes the most common cases work as expected. For example, if the pattern is .+A (and the PCRE2_DOTALL option is not set), it does not match the string "\r\nA" because, after failing at the start, it skips both the CR and the LF before retrying. However, the pattern [\r\n]A does match that string, because it contains an explicit CR or LF reference, and so advances only by one character after the first failure.

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

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

HOW PCRE2_MATCH() RETURNS A STRING AND CAPTURED SUBSTRINGS

uint32_t pcre2_get_ovector_count(pcre2_match_data *match_data);

PCRE2_SIZE *pcre2_get_ovector_pointer(pcre2_match_data *match_data);

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

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

Alternatively, you can make direct use of the vector of PCRE2_SIZE values, called the ovector, which contains the offsets of captured strings. It is part of the match data block. The function pcre2_get_ovector_pointer() returns the address of the ovector, and pcre2_get_ovector_count() returns the number of pairs of values it contains.

Within the ovector, the first in each pair of values is set to the offset of the first code unit of a substring, and the second is set to the offset of the first code unit after the end of a substring. These values are always code unit offsets, not character offsets. That is, they are byte offsets in the 8-bit library, 16-bit offsets in the 16-bit library, and 32-bit offsets in the 32-bit library.

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

After a fully successful match, the first pair of offsets identifies the portion of the subject string that was matched by the entire pattern. The next pair is used for the first captured substring, and so on. The value returned by pcre2_match() is one more than the highest numbered pair that has been set. For example, if two substrings have been captured, the returned value is 3. If there are no captured substrings, the return value from a successful match is 1, indicating that just the first pair of offsets has been set.

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

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

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

It is possible for capture group number n+1 to match some part of the subject when group n has not been used at all. For example, if the string "abc" is matched against the pattern (a|(z))(bc) the return from the function is 4, and groups 1 and 3 are matched, but 2 is not. When this happens, both values in the offset pairs corresponding to unused groups are set to PCRE2_UNSET.

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

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

OTHER INFORMATION ABOUT A MATCH

PCRE2_SPTR pcre2_get_mark(pcre2_match_data *match_data);

PCRE2_SIZE pcre2_get_startchar(pcre2_match_data *match_data);

As well as the offsets in the ovector, other information about a match is retained in the match data block and can be retrieved by the above functions in appropriate circumstances. If they are called at other times, the result is undefined.

After a successful match, a partial match (PCRE2_ERROR_PARTIAL), or a failure to match (PCRE2_ERROR_NOMATCH), a mark name may be available. The function pcre2_get_mark() can be called to access this name, which can be specified in the pattern by any of the backtracking control verbs, not just (*MARK). The same function applies to all the verbs. It returns a pointer to the zero-terminated name, which is within the compiled pattern. If no name is available, NULL is returned. The length of the name (excluding the terminating zero) is stored in the code unit that precedes the name. You should use this length instead of relying on the terminating zero if the name might contain a binary zero.

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

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

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

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

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

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

ERROR RETURNS FROM pcre2_match()

If pcre2_match() fails, it returns a negative number. This can be converted to a text string by calling the pcre2_get_error_message() function (see "Obtaining a textual error message" below). Negative error codes are also returned by other functions, and are documented with them. The codes are given names in the header file. If UTF checking is in force and an invalid UTF subject string is detected, one of a number of UTF-specific negative error codes is returned. Details are given in the pcre2unicode page. The following are the other errors that may be returned by pcre2_match():

PCRE2_ERROR_NOMATCH

The subject string did not match the pattern.

PCRE2_ERROR_PARTIAL

The subject string did not match, but it did match partially. See the pcre2partial documentation for details of partial matching.

PCRE2_ERROR_BADMAGIC

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

PCRE2_ERROR_BADMODE

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

PCRE2_ERROR_BADOFFSET

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

PCRE2_ERROR_BADOPTION

An unrecognized bit was set in the options argument.

PCRE2_ERROR_BADUTFOFFSET

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

PCRE2_ERROR_CALLOUT

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

PCRE2_ERROR_DEPTHLIMIT

The nested backtracking depth limit was reached.

PCRE2_ERROR_HEAPLIMIT

The heap limit was reached.

PCRE2_ERROR_INTERNAL

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

PCRE2_ERROR_JIT_STACKLIMIT

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

PCRE2_ERROR_MATCHLIMIT

The backtracking match limit was reached.

PCRE2_ERROR_NOMEMORY

Heap memory is used to remember backtracking points. This error is given when the memory allocation function (default or custom) fails. Note that a different error, PCRE2_ERROR_HEAPLIMIT, is given if the amount of memory needed exceeds the heap limit. PCRE2_ERROR_NOMEMORY is also returned if PCRE2_COPY_MATCHED_SUBJECT is set and memory allocation fails.

PCRE2_ERROR_NULL

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

PCRE2_ERROR_RECURSELOOP

This error is returned when pcre2_match() detects a recursion loop within the pattern. Specifically, it means that either the whole pattern or a capture group has been called recursively for the second time at the same position in the subject string. Some simple patterns that might do this are detected and faulted at compile time, but more complicated cases, in particular mutual recursions between two different groups, cannot be detected until matching is attempted.

OBTAINING A TEXTUAL ERROR MESSAGE

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

A text message for an error code from any PCRE2 function (compile, match, or auxiliary) can be obtained by calling pcre2_get_error_message(). The code is passed as the first argument, with the remaining two arguments specifying a code unit buffer and its length in code units, into which the text message is placed. The message is returned in code units of the appropriate width for the library that is being used.

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

EXTRACTING CAPTURED SUBSTRINGS BY NUMBER

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

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

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

void pcre2_substring_free(PCRE2_UCHAR *buffer);

Captured substrings can be accessed directly by using the ovector as described above. For convenience, auxiliary functions are provided for extracting captured substrings as new, separate, zero-terminated strings. A substring that contains a binary zero is correctly extracted and has a further zero added on the end, but the result is not, of course, a C string.

The functions in this section identify substrings by number. The number zero refers to the entire matched substring, with higher numbers referring to substrings captured by parenthesized groups. After a partial match, only substring zero is available. An attempt to extract any other substring gives the error PCRE2_ERROR_PARTIAL. The next section describes similar functions for extracting captured substrings by name.

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

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

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

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

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

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

PCRE2_ERROR_NOMEMORY

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

PCRE2_ERROR_NOSUBSTRING

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

PCRE2_ERROR_UNAVAILABLE

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

PCRE2_ERROR_UNSET

The substring did not participate in the match. For example, if the pattern is (abc)|(def) and the subject is "def", and the ovector contains at least two capturing slots, substring number 1 is unset.

EXTRACTING A LIST OF ALL CAPTURED SUBSTRINGS

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

void pcre2_substring_list_free(PCRE2_UCHAR **list);

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

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

The address of the memory block is returned via listptr, which is also the start of the list of string pointers. The end of the list is marked by a NULL pointer. The address of the list of lengths is returned via lengthsptr. If your strings do not contain binary zeros and you do not therefore need the lengths, you may supply NULL as the lengthsptr argument to disable the creation of a list of lengths. The yield of the function is zero if all went well, or PCRE2_ERROR_NOMEMORY if the memory block could not be obtained. When the list is no longer needed, it should be freed by calling pcre2_substring_list_free().

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

EXTRACTING CAPTURED SUBSTRINGS BY NAME

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

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

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

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

void pcre2_substring_free(PCRE2_UCHAR *buffer);

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

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

the number of the capture group called "xxx" is 2. If the name is known to be unique (PCRE2_DUPNAMES was not set), you can find the number from the name by calling pcre2_substring_number_from_name(). The first argument is the compiled pattern, and the second is the name. The yield of the function is the group number, PCRE2_ERROR_NOSUBSTRING if there is no group with that name, or PCRE2_ERROR_NOUNIQUESUBSTRING if there is more than one group with that name. Given the number, you can extract the substring directly from the ovector, or use one of the "bynumber" functions described above.

For convenience, there are also "byname" functions that correspond to the "bynumber" functions, the only difference being that the second argument is a name instead of a number. If PCRE2_DUPNAMES is set and there are duplicate names, these functions scan all the groups with the given name, and return the captured substring from the first named group that is set.

If there are no groups with the given name, PCRE2_ERROR_NOSUBSTRING is returned. If all groups with the name have numbers that are greater than the number of slots in the ovector, PCRE2_ERROR_UNAVAILABLE is returned. If there is at least one group with a slot in the ovector, but no group is found to be set, PCRE2_ERROR_UNSET is returned.

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

CREATING A NEW STRING WITH SUBSTITUTIONS

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

This function optionally calls pcre2_match() and then makes a copy of the subject string in outputbuffer, replacing parts that were matched with the replacement string, whose length is supplied in rlength, which can be given as PCRE2_ZERO_TERMINATED for a zero-terminated string. As a special case, if replacement is NULL and rlength is zero, the replacement is assumed to be an empty string. If rlength is non-zero, an error occurs if replacement is NULL.

There is an option (see PCRE2_SUBSTITUTE_REPLACEMENT_ONLY below) to return just the replacement string(s). The default action is to perform just one replacement if the pattern matches, but there is an option that requests multiple replacements (see PCRE2_SUBSTITUTE_GLOBAL below).

If successful, pcre2_substitute() returns the number of substitutions that were carried out. This may be zero if no match was found, and is never greater than one unless PCRE2_SUBSTITUTE_GLOBAL is set. A negative value is returned if an error is detected.

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

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

If match_data is not NULL and PCRE2_SUBSTITUTE_MATCHED is not set, the provided block is used for all calls to pcre2_match(), and its contents afterwards are the result of the final call. For global changes, this will always be a no-match error. The contents of the ovector within the match data block may or may not have been changed.

As well as the usual options for pcre2_match(), a number of additional options can be set in the options argument of pcre2_substitute(). One such option is PCRE2_SUBSTITUTE_MATCHED. When this is set, an external match_data block must be provided, and it must have already been used for an external call to pcre2_match() with the same pattern and subject arguments. The data in the match_data block (return code, offset vector) is then used for the first substitution instead of calling pcre2_match() from within pcre2_substitute(). This allows an application to check for a match before choosing to substitute, without having to repeat the match.

The contents of the externally supplied match data block are not changed when PCRE2_SUBSTITUTE_MATCHED is set. If PCRE2_SUBSTITUTE_GLOBAL is also set, pcre2_match() is called after the first substitution to check for further matches, but this is done using an internally obtained match data block, thus always leaving the external block unchanged.

The code argument is not used for matching before the first substitution when PCRE2_SUBSTITUTE_MATCHED is set, but it must be provided, even when PCRE2_SUBSTITUTE_GLOBAL is not set, because it contains information such as the UTF setting and the number of capturing parentheses in the pattern.

The default action of pcre2_substitute() is to return a copy of the subject string with matched substrings replaced. However, if PCRE2_SUBSTITUTE_REPLACEMENT_ONLY is set, only the replacement substrings are returned. In the global case, multiple replacements are concatenated in the output buffer. Substitution callouts (see below) can be used to separate them if necessary.

The outlengthptr argument of pcre2_substitute() must point to a variable that contains the length, in code units, of the output buffer. If the function is successful, the value is updated to contain the length in code units of the new string, excluding the trailing zero that is automatically added.

If the function is not successful, the value set via outlengthptr depends on the type of error. For syntax errors in the replacement string, the value is the offset in the replacement string where the error was detected. For other errors, the value is PCRE2_UNSET by default. This includes the case of the output buffer being too small, unless PCRE2_SUBSTITUTE_OVERFLOW_LENGTH is set.

PCRE2_SUBSTITUTE_OVERFLOW_LENGTH changes what happens when the output buffer is too small. The default action is to return PCRE2_ERROR_NOMEMORY immediately. If this option is set, however, pcre2_substitute() continues to go through the motions of matching and substituting (without, of course, writing anything) in order to compute the size of buffer that is needed. This value is passed back via the outlengthptr variable, with the result of the function still being PCRE2_ERROR_NOMEMORY.

Passing a buffer size of zero is a permitted way of finding out how much memory is needed for given substitution. However, this does mean that the entire operation is carried out twice. Depending on the application, it may be more efficient to allocate a large buffer and free the excess afterwards, instead of using PCRE2_SUBSTITUTE_OVERFLOW_LENGTH.

The replacement string, which is interpreted as a UTF string in UTF mode, is checked for UTF validity unless PCRE2_NO_UTF_CHECK is set. An invalid UTF replacement string causes an immediate return with the relevant UTF error code.

If PCRE2_SUBSTITUTE_LITERAL is set, the replacement string is not interpreted in any way. By default, however, a dollar character is an escape character that can specify the insertion of characters from capture groups and names from (*MARK) or other control verbs in the pattern. Dollar is the only escape character (backslash is treated as literal). The following forms are always recognized:

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

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

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

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

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

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

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

When continuing with global substitutions after matching a substring with zero length, an attempt to find a non-empty match at the same offset is performed. If this is not successful, the offset is advanced by one character except when CRLF is a valid newline sequence and the next two characters are CR, LF. In this case, the offset is advanced by two characters.

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

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

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

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

There are also four escape sequences for forcing the case of inserted letters. The insertion mechanism has three states: no case forcing, force upper case, and force lower case. The escape sequences change the current state: \U and \L change to upper or lower case forcing, respectively, and \E (when not terminating a \Q quoted sequence) reverts to no case forcing. The sequences \u and \l force the next character (if it is a letter) to upper or lower case, respectively, and then the state automatically reverts to no case forcing. Case forcing applies to all inserted characters, including those from capture groups and letters within \Q...\E quoted sequences. If either PCRE2_UTF or PCRE2_UCP was set when the pattern was compiled, Unicode properties are used for case forcing characters whose code points are greater than 127.

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

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

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

As before, <n> may be a group number or a name. The first form specifies a default value. If group <n> is set, its value is inserted; if not, <string> is expanded and the result inserted. The second form specifies strings that are expanded and inserted when group <n> is set or unset, respectively. The first form is just a convenient shorthand for

${<n>:+${<n>}:<string>}

Backslash can be used to escape colons and closing curly brackets in the replacement strings. A change of the case forcing state within a replacement string remains in force afterwards, as shown in this pcre2test example:

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

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

If PCRE2_SUBSTITUTE_LITERAL is set, PCRE2_SUBSTITUTE_UNKNOWN_UNSET, PCRE2_SUBSTITUTE_UNSET_EMPTY, and PCRE2_SUBSTITUTE_EXTENDED are irrelevant and are ignored.

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

DUPLICATE CAPTURE GROUP NAMES

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

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

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

When duplicates are present, pcre2_substring_copy_byname() and pcre2_substring_get_byname() return the first substring corresponding to the given name that is set. Only if none are set is PCRE2_ERROR_UNSET is returned. The pcre2_substring_number_from_name() function returns the error PCRE2_ERROR_NOUNIQUESUBSTRING when there are duplicate names.

If you want to get full details of all captured substrings for a given name, you must use the pcre2_substring_nametable_scan() function. The first argument is the compiled pattern, and the second is the name. If the third and fourth arguments are NULL, the function returns a group number for a unique name, or PCRE2_ERROR_NOUNIQUESUBSTRING otherwise.

When the third and fourth arguments are not NULL, they must be pointers to variables that are updated by the function. After it has run, they point to the first and last entries in the name-to-number table for the given name, and the function returns the length of each entry in code units. In both cases, PCRE2_ERROR_NOSUBSTRING is returned if there are no entries for the given name.

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

FINDING ALL POSSIBLE MATCHES AT ONE POSITION

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

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

MATCHING A PATTERN: THE ALTERNATIVE FUNCTION

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

The function pcre2_dfa_match() is called to match a subject string against a compiled pattern, using a matching algorithm that scans the subject string just once (not counting lookaround assertions), and does not backtrack (except when processing lookaround assertions). This has different characteristics to the normal algorithm, and is not compatible with Perl. Some of the features of PCRE2 patterns are not supported. Nevertheless, there are times when this kind of matching can be useful. For a discussion of the two matching algorithms, and a list of features that pcre2_dfa_match() does not support, see the pcre2matching documentation.

The arguments for the pcre2_dfa_match() function are the same as for pcre2_match(), plus two extras. The ovector within the match data block is used in a different way, and this is described below. The other common arguments are used in the same way as for pcre2_match(), so their description is not repeated here.

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

Here is an example of a simple call to pcre2_dfa_match():

int wspace[20];
pcre2_match_data *md = pcre2_match_data_create(4, NULL);
int rc = pcre2_dfa_match(
re, /* result of pcre2_compile() */
"some string", /* the subject string */
11, /* the length of the subject string */
0, /* start at offset 0 in the subject */
0, /* default options */
md, /* the match data block */
NULL, /* a match context; NULL means use defaults */
wspace, /* working space vector */
20); /* number of elements (NOT size in bytes) */

SEE ALSO

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

AUTHOR

Philip Hazel
Retired from University Computing Service
Cambridge, England.

REVISION

Last updated: 24 April 2024
Copyright (c) 1997-2024 University of Cambridge.