pcre2api man page

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• PCRE2 NATIVE API BASIC FUNCTIONS
• PCRE2 NATIVE API AUXILIARY MATCH FUNCTIONS
• PCRE2 NATIVE API GENERAL CONTEXT FUNCTIONS
• PCRE2 NATIVE API COMPILE CONTEXT FUNCTIONS
• PCRE2 NATIVE API MATCH CONTEXT FUNCTIONS
• PCRE2 NATIVE API STRING EXTRACTION FUNCTIONS
• PCRE2 NATIVE API STRING SUBSTITUTION FUNCTION
• PCRE2 NATIVE API JIT FUNCTIONS
• PCRE2 NATIVE API SERIALIZATION FUNCTIONS
• PCRE2 NATIVE API AUXILIARY FUNCTIONS
• PCRE2 NATIVE API OBSOLETE FUNCTIONS
• PCRE2 8-BIT, 16-BIT, AND 32-BIT LIBRARIES
• PCRE2 API OVERVIEW
• STRING LENGTHS AND OFFSETS
• NEWLINES
• MULTITHREADING
• PCRE2 CONTEXTS
• CHECKING BUILD-TIME OPTIONS
• COMPILING A PATTERN
• COMPILATION ERROR CODES
• JUST-IN-TIME (JIT) COMPILATION
• LOCALE SUPPORT
• INFORMATION ABOUT A COMPILED PATTERN
• INFORMATION ABOUT A PATTERN'S CALLOUTS
• SERIALIZATION AND PRECOMPILING
• THE MATCH DATA BLOCK
• MATCHING A PATTERN: THE TRADITIONAL FUNCTION
• NEWLINE HANDLING WHEN MATCHING
• HOW PCRE2_MATCH() RETURNS A STRING AND CAPTURED SUBSTRINGS
• OTHER INFORMATION ABOUT A MATCH
• ERROR RETURNS FROM pcre2_match()
• OBTAINING A TEXTUAL ERROR MESSAGE
• EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
• EXTRACTING A LIST OF ALL CAPTURED SUBSTRINGS
• EXTRACTING CAPTURED SUBSTRINGS BY NAME
• CREATING A NEW STRING WITH SUBSTITUTIONS
• DUPLICATE SUBPATTERN NAMES
• FINDING ALL POSSIBLE MATCHES AT ONE POSITION
• MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
• SEE ALSO
• AUTHOR
• REVISION

#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_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_SPTR pcre2_get_mark(pcre2_match_data *match_data);

uint32_t pcre2_get_ovector_count(pcre2_match_data *match_data);

PCRE2_SIZE *pcre2_get_ovector_pointer(pcre2_match_data *match_data);

PCRE2_SIZE pcre2_get_startchar(pcre2_match_data *match_data);

pcre2_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 unsigned char *tables);

int pcre2_set_compile_extra_options(pcre2_compile_context *ccontext, uint32_t extra_options);

int pcre2_set_max_pattern_length(pcre2_compile_context *ccontext, PCRE2_SIZE value);

int pcre2_set_newline(pcre2_compile_context *ccontext, uint32_t value);

int pcre2_set_parens_nest_limit(pcre2_compile_context *ccontext, uint32_t value);

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

pcre2_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_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);

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_SPTR *list);

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

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 \fIreplacementzfP, PCRE2_SIZE rlength, PCRE2_UCHAR *outputbuffer, PCRE2_SIZE *outlengthptr);

int pcre2_jit_compile(pcre2_code *code, uint32_t options);

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

void pcre2_jit_free_unused_memory(pcre2_general_context *gcontext);

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

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

void pcre2_jit_stack_free(pcre2_jit_stack *jit_stack);

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_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 unsigned char *pcre2_maketables(pcre2_general_context *gcontext);

int pcre2_pattern_info(const pcre2 *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);

int pcre2_set_recursion_limit(pcre2_match_context *mcontext, uint32_t value);

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

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

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.

Character strings are passed to and from a PCRE2 library as a sequence of unsigned integers in code units of the appropriate width. Every PCRE2 function comes in three different forms, one for each library, for example:

  pcre2_compile_8()
  pcre2_compile_16()
  pcre2_compile_32()

  PCRE2_UCHAR8, PCRE2_UCHAR16, PCRE2_UCHAR32
  PCRE2_SPTR8,  PCRE2_SPTR16,  PCRE2_SPTR32

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 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. 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()

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.

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.

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. The default default is 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.

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.

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

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

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

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

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

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

The matching functions need a block of memory for storing the results of a match. This includes details of what was matched, as well as additional information such as the name of a (*MARK) setting. Each thread must provide its own copy of this memory.

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.

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

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

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

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

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

A general context can be copied by calling:

pcre2_general_context *pcre2_general_context_copy( pcre2_general_context *gcontext);

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

void pcre2_general_context_free(pcre2_general_context *gcontext);

A compile context is required if you want to provide an external function for stack checking during compilation or to change the default values of any of the following compile-time parameters:

  What \R matches (Unicode newlines or CR, LF, CRLF only)
  PCRE2's character tables
  The newline character sequence
  The compile time nested parentheses limit
  The maximum length of the pattern string
  The extra options bits (none set by default) 

A compile context is created, copied, and freed by the following functions:

pcre2_compile_context *pcre2_compile_context_create( pcre2_general_context *gcontext);

pcre2_compile_context *pcre2_compile_context_copy( pcre2_compile_context *ccontext);

void pcre2_compile_context_free(pcre2_compile_context *ccontext);

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

int pcre2_set_bsr(pcre2_compile_context *ccontext, uint32_t value);

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

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

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

int pcre2_set_compile_extra_options(pcre2_compile_context *ccontext, uint32_t extra_options);

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

int pcre2_set_max_pattern_length(pcre2_compile_context *ccontext, PCRE2_SIZE value);

This sets a maximum length, in code units, for any pattern string that is compiled with this context. If the pattern is longer, an error is generated. This facility is provided so that applications that accept patterns from external sources can limit their size. The default is the largest number that a PCRE2_SIZE variable can hold, which is effectively unlimited.

int pcre2_set_newline(pcre2_compile_context *ccontext, uint32_t value);

This specifies which characters or character sequences are to be recognized as newlines. The value must be one of PCRE2_NEWLINE_CR (carriage return only), PCRE2_NEWLINE_LF (linefeed only), PCRE2_NEWLINE_CRLF (the two-character sequence CR followed by LF), PCRE2_NEWLINE_ANYCRLF (any of the above), PCRE2_NEWLINE_ANY (any Unicode newline sequence), or PCRE2_NEWLINE_NUL (the NUL character, that is a binary zero).

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

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

int pcre2_set_parens_nest_limit(pcre2_compile_context *ccontext, uint32_t value);

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

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

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

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

A match context is required if you want to:

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

A match context is created, copied, and freed by the following functions:

pcre2_match_context *pcre2_match_context_create( pcre2_general_context *gcontext);

pcre2_match_context *pcre2_match_context_copy( pcre2_match_context *mcontext);

void pcre2_match_context_free(pcre2_match_context *mcontext);

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

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

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

int pcre2_set_offset_limit(pcre2_match_context *mcontext, PCRE2_SIZE value);

The offset_limit parameter limits how far an unanchored search can advance in the subject string. The default value is PCRE2_UNSET. The pcre2_match() and pcre2_dfa_match() functions return PCRE2_ERROR_NOMATCH if a match with a starting point before or at the given offset is not found. For example, if the pattern /abc/ is matched against "123abc" with an offset limit less than 3, the result is PCRE2_ERROR_NO_MATCH. A match can never be found if the startoffset argument of pcre2_match() or pcre2_dfa_match() is greater than the offset limit.

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

The offset limit facility can be used to track progress when searching large subject strings. See also the PCRE2_FIRSTLINE option, which requires a match to start within the first line of the subject. If this is set with an offset limit, a match must occur in the first line and also within the offset limit. In other words, whichever limit comes first is used.

int pcre2_set_heap_limit(pcre2_match_context *mcontext, uint32_t value);

The heap_limit parameter specifies, in units of kilobytes, the maximum amount of heap memory that pcre2_match() may use to hold backtracking information when running an interpretive match. This limit does not apply to matching with the JIT optimization, which has its own memory control arrangements (see the pcre2jit documentation for more details), nor does it apply to pcre2_dfa_match(). If the limit is reached, the negative error code PCRE2_ERROR_HEAPLIMIT is returned. The default limit is set when PCRE2 is built; the default default is very large and is essentially "unlimited".

A value for the heap limit may also be supplied by an item at the start of a pattern of the form

  (*LIMIT_HEAP=ddd)

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

int pcre2_set_match_limit(pcre2_match_context *mcontext, uint32_t value);

The match_limit parameter provides a means of preventing PCRE2 from using up too many computing resources when processing patterns that are not going to match, but which have a very large number of possibilities in their search trees. The classic example is a pattern that uses nested unlimited repeats.

There is an internal counter in pcre2_match() that is incremented each time round its main matching loop. If this value reaches the match limit, pcre2_match() returns the negative value PCRE2_ERROR_MATCHLIMIT. This has the effect of limiting the amount of backtracking that can take place. For patterns that are not anchored, the count restarts from zero for each position in the subject string. This limit is not relevant to pcre2_dfa_match(), which ignores it.

When pcre2_match() is called with a pattern that was successfully processed by pcre2_jit_compile(), the way in which matching is executed is entirely different. However, there is still the possibility of runaway matching that goes on for a very long time, and so the match_limit value is also used in this case (but in a different way) to limit how long the matching can continue.

The default value for the limit can be set when PCRE2 is built; the default default is 10 million, which handles all but the most extreme cases. A value for the match limit may also be supplied by an item at the start of a pattern of the form

  (*LIMIT_MATCH=ddd)

The depth limit is not relevant, and is ignored, when matching is done using JIT compiled code. However, it is supported by pcre2_dfa_match(), which uses it to limit the depth of internal recursive function calls that implement atomic groups, lookaround assertions, and pattern recursions. This is, therefore, an indirect limit on the amount of system stack that is used. A recursive pattern such as /(.)(?1)/, when matched to a very long string using pcre2_dfa_match(), can use a great deal of stack.

The default value for the depth limit can be set when PCRE2 is built; the default default is the same value as the default for the match limit. If the limit is exceeded, pcre2_match() or pcre2_dfa_match() returns PCRE2_ERROR_DEPTHLIMIT. A value for the depth limit may also be supplied by an item at the start of a pattern of the form

  (*LIMIT_DEPTH=ddd)

int pcre2_config(uint32_t what, void *where);

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

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

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

  PCRE2_CONFIG_BSR

  PCRE2_CONFIG_DEPTHLIMIT

  PCRE2_CONFIG_HEAPLIMIT

  PCRE2_CONFIG_JIT

  PCRE2_CONFIG_JITTARGET

  PCRE2_CONFIG_LINKSIZE

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 64K 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

  PCRE2_CONFIG_NEWLINE

  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) 

  PCRE2_CONFIG_PARENSLIMIT

  PCRE2_CONFIG_STACKRECURSE

  PCRE2_CONFIG_UNICODE_VERSION

  PCRE2_CONFIG_UNICODE

  PCRE2_CONFIG_VERSION

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. If the pattern is zero-terminated, the length can be specified as PCRE2_ZERO_TERMINATED. The function returns a pointer to a block of memory that contains the compiled pattern and related data, or NULL if an error occurred.

If the compile context argument ccontext is NULL, memory for the 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.

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.

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.

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 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.

The options argument for pcre2_compile() contains various bit settings that affect the compilation. It should be zero if no options are required. The available options are described below. Some of them (in particular, those that are compatible with Perl, but some others as well) can also be set and unset from within the pattern (see the detailed description in the 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.

Other, 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. The values are not defined when compilation is successful and pcre2_compile() returns a non-NULL value.

The value returned in erroroffset is an indication of where in the pattern the error occurred. It is not necessarily the furthest point in the pattern that was read. For example, after the error "lookbehind assertion is not fixed length", the error offset points to the start of the failing assertion.

The pcre2_get_error_message() function (see "Obtaining a textual error message" below) provides a textual message for each error code. Compilation errors have positive error codes; UTF formatting error codes are negative. 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 */

  PCRE2_ANCHORED

  PCRE2_ALLOW_EMPTY_CLASS

  PCRE2_ALT_BSUX

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

(2) \u matches a lower case "u" character unless it is followed by four hexadecimal digits, in which case the hexadecimal number defines the code point to match. By default, \u causes a compile time error (Perl uses it to upper case the following character).

(3) \x matches a lower case "x" character unless it is followed by two hexadecimal digits, in which case the hexadecimal number defines the code point to match. By default, as in Perl, a hexadecimal number is always expected after \x, but it may have zero, one, or two digits (so, for example, \xz matches a binary zero character followed by z).

  PCRE2_ALT_CIRCUMFLEX

  PCRE2_ALT_VERBNAMES

  PCRE2_AUTO_CALLOUT

  PCRE2_CASELESS

  PCRE2_DOLLAR_ENDONLY

  PCRE2_DOTALL

  PCRE2_DUPNAMES

  PCRE2_ENDANCHORED

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

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

  PCRE2_EXTENDED

PCRE2_EXTENDED also causes characters between an unescaped # outside a character class and the next newline, inclusive, to be ignored, which makes it possible to include comments inside complicated patterns. Note that the end of this type of comment is a literal newline sequence in the pattern; escape sequences that happen to represent a newline do not count. PCRE2_EXTENDED is equivalent to Perl's /x option, and it can be changed within a pattern by a (?x) option setting.

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

  PCRE2_EXTENDED_MORE

  PCRE2_FIRSTLINE

  PCRE2_MATCH_UNSET_BACKREF

  PCRE2_MULTILINE

When PCRE2_MULTILINE it is set, the "start of line" and "end of line" constructs match immediately following or immediately before internal newlines in the subject string, respectively, as well as at the very start and end. This is equivalent to Perl's /m option, and it can be changed within a pattern by a (?m) option setting. Note that the "start of line" metacharacter does not match after a newline at the end of the subject, for compatibility with Perl. However, you can change this by setting the PCRE2_ALT_CIRCUMFLEX option. If there are no newlines in a subject string, or no occurrences of ^ or $ in a pattern, setting PCRE2_MULTILINE has no effect.

  PCRE2_NEVER_BACKSLASH_C

  PCRE2_NEVER_UCP

  PCRE2_NEVER_UTF

  PCRE2_NO_AUTO_CAPTURE

  PCRE2_NO_AUTO_POSSESS

  PCRE2_NO_DOTSTAR_ANCHOR

  PCRE2_NO_START_OPTIMIZE

There are a number of optimizations that may occur at the start of a match, in order to speed up the process. For example, if it is known that an unanchored match must start with a specific code unit value, the matching code searches the subject for that value, and fails immediately if it cannot find it, without actually running the main matching function. This means that a special item such as (*COMMIT) at the start of a pattern is not considered until after a suitable starting point for the match has been found. Also, when callouts or (*MARK) items are in use, these "start-up" optimizations can cause them to be skipped if the pattern is never actually used. The start-up optimizations are in effect a pre-scan of the subject that takes place before the pattern is run.

The PCRE2_NO_START_OPTIMIZE option disables the start-up optimizations, possibly causing performance to suffer, but ensuring that in cases where the result is "no match", the callouts do occur, and that items such as (*COMMIT) and (*MARK) are considered at every possible starting position in the subject string.

Setting PCRE2_NO_START_OPTIMIZE may change the outcome of a matching operation. Consider the pattern

  (*COMMIT)ABC

There are also other start-up optimizations. For example, a minimum length for the subject may be recorded. Consider the pattern

  (*MARK:A)(X|Y)

  PCRE2_NO_UTF_CHECK

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

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

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

  PCRE2_UCP

  PCRE2_UNGREEDY

  PCRE2_USE_OFFSET_LIMIT

  PCRE2_UTF

Unlike the main compile-time options, the extra options are not saved with the compiled pattern. The option bits that can be set in a compile context by calling the pcre2_set_compile_extra_options() function are as follows:

  PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES

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

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

There are nearly 100 positive error codes that pcre2_compile() may return (via errorcode) if it finds an error in the pattern. There are also some negative error codes that are used for invalid UTF strings. These are the same as given by pcre2_match() and pcre2_dfa_match(), and are described in the pcre2unicode page. The pcre2_get_error_message() function (see "Obtaining a textual error message" below) can be called to obtain a textual error message from any error code.

int pcre2_jit_compile(pcre2_code *code, uint32_t options);

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

void pcre2_jit_free_unused_memory(pcre2_general_context *gcontext);

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

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

void pcre2_jit_stack_free(pcre2_jit_stack *jit_stack);

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.

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

The use of locales with Unicode is discouraged. If you are handling characters with code points greater than 128, you should either use Unicode support, or use locales, but not try to mix the two.

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

The internal 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 result can be passed to pcre2_compile() as often as necessary, by creating a compile context and calling pcre2_set_character_tables() to set the tables pointer therein. For example, to build and use tables that are appropriate for the French locale (where accented characters with values greater than 128 are treated as letters), the following code could be used:

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

The pointer that is passed (via the compile context) to pcre2_compile() is saved with the compiled pattern, and the same tables are used by pcre2_match() and pcre_dfa_match(). Thus, for any single pattern, compilation and matching both happen in the same locale, but different patterns can be processed in different locales.

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

  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 */

  PCRE2_INFO_ALLOPTIONS
  PCRE2_INFO_ARGOPTIONS

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

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

  PCRE2_INFO_BACKREFMAX

  PCRE2_INFO_BSR

  PCRE2_INFO_CAPTURECOUNT

  PCRE2_INFO_DEPTHLIMIT

  PCRE2_INFO_FIRSTBITMAP

  PCRE2_INFO_FIRSTCODETYPE

  PCRE2_INFO_FIRSTCODEUNIT

  PCRE2_INFO_FRAMESIZE

  PCRE2_INFO_HASBACKSLASHC

  PCRE2_INFO_HASCRORLF

  PCRE2_INFO_HEAPLIMIT

  PCRE2_INFO_JCHANGED

  PCRE2_INFO_JITSIZE

  PCRE2_INFO_LASTCODETYPE

  PCRE2_INFO_LASTCODEUNIT

  PCRE2_INFO_MATCHEMPTY

  PCRE2_INFO_MATCHLIMIT

  PCRE2_INFO_MAXLOOKBEHIND

  PCRE2_INFO_MINLENGTH

  PCRE2_INFO_NAMECOUNT
  PCRE2_INFO_NAMEENTRYSIZE
  PCRE2_INFO_NAMETABLE

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 groups with the same number, as described in the section on duplicate subpattern 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 subpatterns 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 subpatterns may have lower numbers.

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

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

  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 ??

  PCRE2_INFO_NEWLINE

  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) 

  PCRE2_INFO_SIZE

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.

It is possible to save compiled patterns on disc or elsewhere, and reload them later, subject to a number of restrictions. The functions whose names begin with pcre2_serialize_ are used for this purpose. They are described in the pcre2serialize documentation.

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

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

void pcre2_match_data_free(pcre2_match_data *match_data);

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

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

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. 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 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.

When a match data block itself is no longer needed, it should be freed by calling pcre2_match_data_free().

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 */
    match_data,     /* the match data block */
    NULL);          /* a match context; NULL means use defaults */

The subject string is passed to pcre2_match() as a pointer in subject, a length in length, and a starting offset in startoffset. The length and offset are in code units, not characters. That is, they are in bytes for the 8-bit library, 16-bit code units for the 16-bit library, and 32-bit code units for the 32-bit library, whether or not UTF processing is enabled.

If startoffset is greater than the length of the subject, pcre2_match() returns PCRE2_ERROR_BADOFFSET. When the starting offset is zero, the search for a match starts at the beginning of the subject, and this is by far the most common case. In UTF-8 or UTF-16 mode, the starting offset must point to the start of a character, or to the end of the subject (in UTF-32 mode, one code unit equals one character, so all offsets are valid). Like the pattern string, the subject may contain binary zeroes.

A non-zero starting offset is useful when searching for another match in the same subject by calling pcre2_match() again after a previous success. Setting startoffset differs from passing over a shortened string and setting PCRE2_NOTBOL in the case of a pattern that begins with any kind of lookbehind. For example, consider the pattern

  \Biss\B

Finding all the matches in a subject is tricky when the pattern can match an empty string. It is possible to emulate Perl's /g behaviour by first trying the match again at the same offset, with the PCRE2_NOTEMPTY_ATSTART and PCRE2_ANCHORED options, and then if that fails, advancing the starting offset and trying an ordinary match again. There is some code that demonstrates how to do this in the pcre2demo sample program. In the most general case, you have to check to see if the newline convention recognizes CRLF as a newline, and if so, and the current character is CR followed by LF, advance the starting offset by two characters instead of one.

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

The unused bits of the options argument for pcre2_match() must be zero. The only bits that may be set are PCRE2_ANCHORED, PCRE2_ENDANCHORED, PCRE2_NOTBOL, PCRE2_NOTEOL, PCRE2_NOTEMPTY, PCRE2_NOTEMPTY_ATSTART, PCRE2_NO_JIT, PCRE2_NO_UTF_CHECK, PCRE2_PARTIAL_HARD, and PCRE2_PARTIAL_SOFT. Their action is described below.

Setting PCRE2_ANCHORED or PCRE2_ENDANCHORED at match time is not supported by the just-in-time (JIT) compiler. If it is set, JIT matching is disabled and the interpretive code in pcre2_match() is run. Apart from PCRE2_NO_JIT (obviously), the remaining options are supported for JIT matching.

  PCRE2_ANCHORED

  PCRE2_ENDANCHORED

  PCRE2_NOTBOL

  PCRE2_NOTEOL

  PCRE2_NOTEMPTY

  a?b?

  PCRE2_NOTEMPTY_ATSTART

  PCRE2_NO_JIT

  PCRE2_NO_UTF_CHECK

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

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

WARNING: When PCRE2_NO_UTF_CHECK is set, the effect of passing an invalid string as a subject, or an invalid value of startoffset, is undefined. Your program may crash or loop indefinitely.

  PCRE2_PARTIAL_HARD
  PCRE2_PARTIAL_SOFT

If PCRE2_PARTIAL_HARD is set, it overrides PCRE2_PARTIAL_SOFT. In this case, if a partial match is found, pcre2_match() immediately returns PCRE2_ERROR_PARTIAL, without considering any other alternatives. In other words, when PCRE2_PARTIAL_HARD is set, a partial match is considered to be more important that an alternative complete match.

There is a more detailed discussion of partial and multi-segment matching, with examples, in the pcre2partial documentation.

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.

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 "capturing subpattern" or "capturing group" is used for a fragment of a pattern that picks out a substring. PCRE2 supports several other kinds of parenthesized subpattern that do not cause substrings to be captured. The pcre2_pattern_info() function can be used to find out how many capturing subpatterns 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 capturing subpattern 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 capturing subpattern number n+1 to match some part of the subject when subpattern n has not been used at all. For example, if the string "abc" is matched against the pattern (a|(z))(bc) the return from the function is 4, and subpatterns 1 and 3 are matched, but 2 is not. When this happens, both values in the offset pairs corresponding to unused subpatterns are set to PCRE2_UNSET.

Offset values that correspond to unused subpatterns 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)?)? subpatterns 2 and 3 are not matched. The return from the function is 2, because the highest used capturing subpattern number is 1. The offsets for for the second and third capturing subpatterns (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.

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, and pcre2_get_mark() can be called. It returns a pointer to the zero-terminated name, which is within the compiled pattern. Otherwise NULL is returned. The length of the (*MARK) name (excluding the terminating zero) is stored in the code unit that preceeds the name. You should use this instead of relying on the terminating zero if the (*MARK) name might contain a binary zero.

After a successful match, the (*MARK) name that is returned is the last one encountered on the matching path through the pattern. After a "no match" or a partial match, the last encountered (*MARK) name is returned. For example, consider this pattern:

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

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.

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

  PCRE2_ERROR_PARTIAL

  PCRE2_ERROR_BADMAGIC

  PCRE2_ERROR_BADMODE

  PCRE2_ERROR_BADOFFSET

  PCRE2_ERROR_BADOPTION

  PCRE2_ERROR_BADUTFOFFSET

  PCRE2_ERROR_CALLOUT

  PCRE2_ERROR_DEPTHLIMIT

  PCRE2_ERROR_HEAPLIMIT

  PCRE2_ERROR_INTERNAL

  PCRE2_ERROR_JIT_STACKLIMIT

  PCRE2_ERROR_MATCHLIMIT

  PCRE2_ERROR_NOMEMORY

  PCRE2_ERROR_NULL

  PCRE2_ERROR_RECURSELOOP

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.

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 capturing 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

  PCRE2_ERROR_NOSUBSTRING

  PCRE2_ERROR_UNAVAILABLE

  PCRE2_ERROR_UNSET

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

void pcre2_substring_list_free(PCRE2_SPTR *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 capturing subpattern number n+1 matches some part of the subject, but subpattern 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().

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+)...

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 first named string 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 subpatterns with the same number, as described in the section on duplicate subpattern numbers in the pcre2pattern page, you cannot use names to distinguish the different subpatterns, because names are not included in the compiled code. The matching process uses only numbers. For this reason, the use of different names for subpatterns of the same number causes an error at compile time.

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 *\fIoutputbuffer\zfP, PCRE2_SIZE *outlengthptr);

This function calls pcre2_match() and then makes a copy of the subject string in outputbuffer, replacing the part that was matched with the replacement string, whose length is supplied in rlength. This can be given as PCRE2_ZERO_TERMINATED for a zero-terminated string. 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.

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.

The outlengthptr argument 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 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 (see below), in which case the value is the minimum length needed, including space for the trailing zero. Note that in order to compute the required length, pcre2_substitute() has to simulate all the matching and copying, instead of giving an error return as soon as the buffer overflows. Note also that the length is in code units, not bytes.

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

  $$                  insert a dollar character
  $<n> or ${<n>}      insert the contents of group <n>
  $*MARK or ${*MARK}  insert the name of the last (*MARK) encountered

The facility for inserting a (*MARK) name can be used to perform simple simultaneous substitutions, as this pcre2test example shows:

  /(*:pear)apple|(*: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 is not set, only the first matching substring is replaced. If any matched substring has zero length, after the substitution has happened, an attempt to find a non-empty match at the same position is performed. If this is not successful, the current position 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 current position is advanced by two characters.

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.

PCRE2_SUBSTITUTE_UNKNOWN_UNSET causes references to capturing 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 capturing 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 captured groups and letters within \Q...\E quoted sequences.

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.

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

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

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

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

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

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

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

PCRE2_ERROR_UNSET is returned for an unset substring insertion (including an unknown substring when PCRE2_SUBSTITUTE_UNKNOWN_UNSET is set) when the simple (non-extended) syntax is used and PCRE2_SUBSTITUTE_UNSET_EMPTY is not set.

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

PCRE2_ERROR_BADREPLACEMENT is used for miscellaneous syntax errors in the replacement string, with more particular errors being PCRE2_ERROR_BADREPESCAPE (invalid escape sequence), PCRE2_ERROR_REPMISSING_BRACE (closing curly bracket not found), PCRE2_BADSUBSTITUTION (syntax error in extended group substitution), and PCRE2_BADSUBPATTERN (the pattern match ended before it started, which can happen if \K is used in an assertion).

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

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 subpatterns are not required to be unique. Duplicate names are always allowed for subpatterns with the same number, created by using the (?| feature. Indeed, if such subpatterns are named, they are required to use the same names.

Normally, patterns with duplicate names are such that in any one match, only one of the named subpatterns participates. An example is shown in the 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.

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.

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

The function pcre2_dfa_match() is called to match a subject string against a compiled pattern, using a matching algorithm that scans the subject string just once (not counting lookaround assertions), and does not backtrack. This has different characteristics to the normal 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 */
    match_data,     /* the match data block */
    NULL,           /* a match context; NULL means use defaults */
    wspace,         /* working space vector */
    20);            /* number of elements (NOT size in bytes) */

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

  PCRE2_PARTIAL_HARD
  PCRE2_PARTIAL_SOFT

  PCRE2_DFA_SHORTEST

  PCRE2_DFA_RESTART

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

  <.*>

  This is <something> <something else> <something further> no more

  <something> <something else> <something further>
  <something> <something else>
  <something>

Calls to the convenience functions that extract substrings by name return the error PCRE2_ERROR_DFA_UFUNC (unsupported function) if used after a DFA match. The convenience functions that extract substrings by number never return PCRE2_ERROR_NOSUBSTRING, and the meanings of some other errors are slightly different:

  PCRE2_ERROR_UNAVAILABLE

  PCRE2_ERROR_UNSET

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

NOTE: PCRE2's "auto-possessification" optimization usually applies to character repeats at the end of a pattern (as well as internally). For example, the pattern "a\d+" is compiled as if it were "a\d++". For DFA matching, this means that only one possible match is found. If you really do want multiple matches in such cases, either use an ungreedy repeat such as "a\d+?" or set the PCRE2_NO_AUTO_POSSESS option when compiling.

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

  PCRE2_ERROR_DFA_UITEM

  PCRE2_ERROR_DFA_UCOND

  PCRE2_ERROR_DFA_WSSIZE

  PCRE2_ERROR_DFA_RECURSE

  PCRE2_ERROR_DFA_BADRESTART

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

Philip Hazel
University Computing Service
Cambridge, England.

Last updated: 26 May 2017
Copyright © 1997-2017 University of Cambridge.

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