pcre2

----------------------------------------------------------------------------- This file contains a concatenation of the PCRE2 man pages, converted to plain text format for ease of searching with a text editor, or for use on systems that do not have a man page processor. The small individual files that give synopses of each function in the library have not been included. Neither has the pcre2demo program. There are separate text files for the pcre2grep and pcre2test commands. ----------------------------------------------------------------------------- PCRE2(3) Library Functions Manual PCRE2(3) NAME PCRE2 - Perl-compatible regular expressions (revised API) INTRODUCTION PCRE2 is the name used for a revised API for the PCRE library, which is a set of functions, written in C, that implement regular expression pattern matching using the same syntax and semantics as Perl, with just a few differences. After nearly two decades, the limitations of the original API were making development increasingly difficult. The new API is more extensible, and it was simplified by abolishing the sepa- rate "study" optimizing function; in PCRE2, patterns are automatically optimized where possible. Since forking from PCRE1, the code has been extensively refactored and new features introduced. As well as Perl-style regular expression patterns, some features that appeared in Python and the original PCRE before they appeared in Perl are available using the Python syntax. There is also some support for one or two .NET and Oniguruma syntax items, and there are options for requesting some minor changes that give better ECMAScript (aka Java- Script) compatibility. The source code for PCRE2 can be compiled to support 8-bit, 16-bit, or 32-bit code units, which means that up to three separate libraries may be installed. The original work to extend PCRE to 16-bit and 32-bit code units was done by Zoltan Herczeg and Christian Persch, respec- tively. In all three cases, strings can be interpreted either as one character per code unit, or as UTF-encoded Unicode, with support for Unicode general category properties. Unicode support is optional at build time (but is the default). However, processing strings as UTF code units must be enabled explicitly at run time. The version of Uni- code in use can be discovered by running pcre2test -C The three libraries contain identical sets of functions, with names ending in _8, _16, or _32, respectively (for example, pcre2_com- pile_8()). However, by defining PCRE2_CODE_UNIT_WIDTH to be 8, 16, or 32, a program that uses just one code unit width can be written using generic names such as pcre2_compile(), and the documentation is written assuming that this is the case. In addition to the Perl-compatible matching function, PCRE2 contains an alternative function that matches the same compiled patterns in a dif- ferent way. In certain circumstances, the alternative function has some advantages. For a discussion of the two matching algorithms, see the pcre2matching page. Details of exactly which Perl regular expression features are and are not supported by PCRE2 are given in separate documents. See the pcre2pattern and pcre2compat pages. There is a syntax summary in the pcre2syntax page. Some features of PCRE2 can be included, excluded, or changed when the library is built. The pcre2_config() function makes it possible for a client to discover which features are available. The features them- selves are described in the pcre2build page. Documentation about build- ing PCRE2 for various operating systems can be found in the README and NON-AUTOTOOLS_BUILD files in the source distribution. The libraries contains a number of undocumented internal functions and data tables that are used by more than one of the exported external functions, but which are not intended for use by external callers. Their names all begin with "_pcre2", which hopefully will not provoke any name clashes. In some environments, it is possible to control which external symbols are exported when a shared library is built, and in these cases the undocumented symbols are not exported. SECURITY CONSIDERATIONS If you are using PCRE2 in a non-UTF application that permits users to supply arbitrary patterns for compilation, you should be aware of a feature that allows users to turn on UTF support from within a pattern. For example, an 8-bit pattern that begins with "(*UTF)" turns on UTF-8 mode, which interprets patterns and subjects as strings of UTF-8 code units instead of individual 8-bit characters. This causes both the pat- tern and any data against which it is matched to be checked for UTF-8 validity. If the data string is very long, such a check might use suf- ficiently many resources as to cause your application to lose perfor- mance. One way of guarding against this possibility is to use the pcre2_pat- tern_info() function to check the compiled pattern's options for PCRE2_UTF. Alternatively, you can set the PCRE2_NEVER_UTF option when calling pcre2_compile(). This causes a compile time error if the pat- tern contains a UTF-setting sequence. The use of Unicode properties for character types such as \d can also be enabled from within the pattern, by specifying "(*UCP)". This fea- ture can be disallowed by setting the PCRE2_NEVER_UCP option. If your application is one that supports UTF, be aware that validity checking can take time. If the same data string is to be matched many times, you can use the PCRE2_NO_UTF_CHECK option for the second and subsequent matches to avoid running redundant checks. The use of the \C escape sequence in a UTF-8 or UTF-16 pattern can lead to problems, because it may leave the current matching point in the middle of a multi-code-unit character. The PCRE2_NEVER_BACKSLASH_C op- tion can be used by an application to lock out the use of \C, causing a compile-time error if it is encountered. It is also possible to build PCRE2 with the use of \C permanently disabled. Another way that performance can be hit is by running a pattern that has a very large search tree against a string that will never match. Nested unlimited repeats in a pattern are a common example. PCRE2 pro- vides some protection against this: see the pcre2_set_match_limit() function in the pcre2api page. There is a similar function called pcre2_set_depth_limit() that can be used to restrict the amount of mem- ory that is used. USER DOCUMENTATION The user documentation for PCRE2 comprises a number of different sec- tions. In the "man" format, each of these is a separate "man page". In the HTML format, each is a separate page, linked from the index page. In the plain text format, the descriptions of the pcre2grep and pcre2test programs are in files called pcre2grep.txt and pcre2test.txt, respectively. The remaining sections, except for the pcre2demo section (which is a program listing), and the short pages for individual func- tions, are concatenated in pcre2.txt, for ease of searching. The sec- tions are as follows: pcre2 this document pcre2-config show PCRE2 installation configuration information pcre2api details of PCRE2's native C API pcre2build building PCRE2 pcre2callout details of the pattern callout feature pcre2compat discussion of Perl compatibility pcre2convert details of pattern conversion functions pcre2demo a demonstration C program that uses PCRE2 pcre2grep description of the pcre2grep command (8-bit only) pcre2jit discussion of just-in-time optimization support pcre2limits details of size and other limits pcre2matching discussion of the two matching algorithms pcre2partial details of the partial matching facility pcre2pattern syntax and semantics of supported regular expression patterns pcre2perform discussion of performance issues pcre2posix the POSIX-compatible C API for the 8-bit library pcre2sample discussion of the pcre2demo program pcre2serialize details of pattern serialization pcre2syntax quick syntax reference pcre2test description of the pcre2test command pcre2unicode discussion of Unicode and UTF support In the "man" and HTML formats, there is also a short page for each C library function, listing its arguments and results. AUTHOR Philip Hazel University Computing Service Cambridge, England. Putting an actual email address here is a spam magnet. If you want to email me, use my two initials, followed by the two digits 10, at the domain cam.ac.uk. REVISION Last updated: 17 September 2018 Copyright (c) 1997-2018 University of Cambridge. ------------------------------------------------------------------------------ PCRE2API(3) Library Functions Manual PCRE2API(3) NAME PCRE2 - Perl-compatible regular expressions (revised API) #include <pcre2.h> PCRE2 is a new API for PCRE, starting at release 10.0. This document contains a description of all its native functions. See the pcre2 docu- ment for an overview of all the PCRE2 documentation. PCRE2 NATIVE API BASIC FUNCTIONS pcre2_code *pcre2_compile(PCRE2_SPTR pattern, PCRE2_SIZE length, uint32_t options, int *errorcode, PCRE2_SIZE *erroroffset, pcre2_compile_context *ccontext); void pcre2_code_free(pcre2_code *code); pcre2_match_data *pcre2_match_data_create(uint32_t ovecsize, pcre2_general_context *gcontext); pcre2_match_data *pcre2_match_data_create_from_pattern( const pcre2_code *code, pcre2_general_context *gcontext); int pcre2_match(const pcre2_code *code, PCRE2_SPTR subject, PCRE2_SIZE length, PCRE2_SIZE startoffset, uint32_t options, pcre2_match_data *match_data, pcre2_match_context *mcontext); int pcre2_dfa_match(const pcre2_code *code, PCRE2_SPTR subject, PCRE2_SIZE length, PCRE2_SIZE startoffset, uint32_t options, pcre2_match_data *match_data, pcre2_match_context *mcontext, int *workspace, PCRE2_SIZE wscount); void pcre2_match_data_free(pcre2_match_data *match_data); PCRE2 NATIVE API AUXILIARY MATCH FUNCTIONS PCRE2_SPTR pcre2_get_mark(pcre2_match_data *match_data); uint32_t pcre2_get_ovector_count(pcre2_match_data *match_data); PCRE2_SIZE *pcre2_get_ovector_pointer(pcre2_match_data *match_data); PCRE2_SIZE pcre2_get_startchar(pcre2_match_data *match_data); PCRE2 NATIVE API GENERAL CONTEXT FUNCTIONS pcre2_general_context *pcre2_general_context_create( void *(*private_malloc)(PCRE2_SIZE, void *), void (*private_free)(void *, void *), void *memory_data); pcre2_general_context *pcre2_general_context_copy( pcre2_general_context *gcontext); void pcre2_general_context_free(pcre2_general_context *gcontext); PCRE2 NATIVE API COMPILE CONTEXT FUNCTIONS pcre2_compile_context *pcre2_compile_context_create( pcre2_general_context *gcontext); pcre2_compile_context *pcre2_compile_context_copy( pcre2_compile_context *ccontext); void pcre2_compile_context_free(pcre2_compile_context *ccontext); int pcre2_set_bsr(pcre2_compile_context *ccontext, uint32_t value); int pcre2_set_character_tables(pcre2_compile_context *ccontext, const uint8_t *tables); int pcre2_set_compile_extra_options(pcre2_compile_context *ccontext, uint32_t extra_options); int pcre2_set_max_pattern_length(pcre2_compile_context *ccontext, PCRE2_SIZE value); int pcre2_set_newline(pcre2_compile_context *ccontext, uint32_t value); int pcre2_set_parens_nest_limit(pcre2_compile_context *ccontext, uint32_t value); int pcre2_set_compile_recursion_guard(pcre2_compile_context *ccontext, int (*guard_function)(uint32_t, void *), void *user_data); PCRE2 NATIVE API MATCH CONTEXT FUNCTIONS pcre2_match_context *pcre2_match_context_create( pcre2_general_context *gcontext); pcre2_match_context *pcre2_match_context_copy( pcre2_match_context *mcontext); void pcre2_match_context_free(pcre2_match_context *mcontext); int pcre2_set_callout(pcre2_match_context *mcontext, int (*callout_function)(pcre2_callout_block *, void *), void *callout_data); int pcre2_set_substitute_callout(pcre2_match_context *mcontext, int (*callout_function)(pcre2_substitute_callout_block *, void *), void *callout_data); int pcre2_set_offset_limit(pcre2_match_context *mcontext, PCRE2_SIZE value); int pcre2_set_heap_limit(pcre2_match_context *mcontext, uint32_t value); int pcre2_set_match_limit(pcre2_match_context *mcontext, uint32_t value); int pcre2_set_depth_limit(pcre2_match_context *mcontext, uint32_t value); PCRE2 NATIVE API STRING EXTRACTION FUNCTIONS int pcre2_substring_copy_byname(pcre2_match_data *match_data, PCRE2_SPTR name, PCRE2_UCHAR *buffer, PCRE2_SIZE *bufflen); int pcre2_substring_copy_bynumber(pcre2_match_data *match_data, uint32_t number, PCRE2_UCHAR *buffer, PCRE2_SIZE *bufflen); void pcre2_substring_free(PCRE2_UCHAR *buffer); int pcre2_substring_get_byname(pcre2_match_data *match_data, PCRE2_SPTR name, PCRE2_UCHAR **bufferptr, PCRE2_SIZE *bufflen); int pcre2_substring_get_bynumber(pcre2_match_data *match_data, uint32_t number, PCRE2_UCHAR **bufferptr, PCRE2_SIZE *bufflen); int pcre2_substring_length_byname(pcre2_match_data *match_data, PCRE2_SPTR name, PCRE2_SIZE *length); int pcre2_substring_length_bynumber(pcre2_match_data *match_data, uint32_t number, PCRE2_SIZE *length); int pcre2_substring_nametable_scan(const pcre2_code *code, PCRE2_SPTR name, PCRE2_SPTR *first, PCRE2_SPTR *last); int pcre2_substring_number_from_name(const pcre2_code *code, PCRE2_SPTR name); void pcre2_substring_list_free(PCRE2_SPTR *list); int pcre2_substring_list_get(pcre2_match_data *match_data, PCRE2_UCHAR ***listptr, PCRE2_SIZE **lengthsptr); PCRE2 NATIVE API STRING SUBSTITUTION FUNCTION int pcre2_substitute(const pcre2_code *code, PCRE2_SPTR subject, PCRE2_SIZE length, PCRE2_SIZE startoffset, uint32_t options, pcre2_match_data *match_data, pcre2_match_context *mcontext, PCRE2_SPTR replacementz, PCRE2_SIZE rlength, PCRE2_UCHAR *outputbuffer, PCRE2_SIZE *outlengthptr); PCRE2 NATIVE API JIT FUNCTIONS int pcre2_jit_compile(pcre2_code *code, uint32_t options); int pcre2_jit_match(const pcre2_code *code, PCRE2_SPTR subject, PCRE2_SIZE length, PCRE2_SIZE startoffset, uint32_t options, pcre2_match_data *match_data, pcre2_match_context *mcontext); void pcre2_jit_free_unused_memory(pcre2_general_context *gcontext); pcre2_jit_stack *pcre2_jit_stack_create(PCRE2_SIZE startsize, PCRE2_SIZE maxsize, pcre2_general_context *gcontext); void pcre2_jit_stack_assign(pcre2_match_context *mcontext, pcre2_jit_callback callback_function, void *callback_data); void pcre2_jit_stack_free(pcre2_jit_stack *jit_stack); PCRE2 NATIVE API SERIALIZATION FUNCTIONS int32_t pcre2_serialize_decode(pcre2_code **codes, int32_t number_of_codes, const uint8_t *bytes, pcre2_general_context *gcontext); int32_t pcre2_serialize_encode(const pcre2_code **codes, int32_t number_of_codes, uint8_t **serialized_bytes, PCRE2_SIZE *serialized_size, pcre2_general_context *gcontext); void pcre2_serialize_free(uint8_t *bytes); int32_t pcre2_serialize_get_number_of_codes(const uint8_t *bytes); PCRE2 NATIVE API AUXILIARY FUNCTIONS pcre2_code *pcre2_code_copy(const pcre2_code *code); pcre2_code *pcre2_code_copy_with_tables(const pcre2_code *code); int pcre2_get_error_message(int errorcode, PCRE2_UCHAR *buffer, PCRE2_SIZE bufflen); const uint8_t *pcre2_maketables(pcre2_general_context *gcontext); void pcre2_maketables_free(pcre2_general_context *gcontext, const uint8_t *tables); int pcre2_pattern_info(const pcre2_code *code, uint32_t what, void *where); int pcre2_callout_enumerate(const pcre2_code *code, int (*callback)(pcre2_callout_enumerate_block *, void *), void *user_data); int pcre2_config(uint32_t what, void *where); PCRE2 NATIVE API OBSOLETE FUNCTIONS int pcre2_set_recursion_limit(pcre2_match_context *mcontext, uint32_t value); int pcre2_set_recursion_memory_management( pcre2_match_context *mcontext, void *(*private_malloc)(PCRE2_SIZE, void *), void (*private_free)(void *, void *), void *memory_data); These functions became obsolete at release 10.30 and are retained only for backward compatibility. They should not be used in new code. The first is replaced by pcre2_set_depth_limit(); the second is no longer needed and has no effect (it always returns zero). PCRE2 EXPERIMENTAL PATTERN CONVERSION FUNCTIONS pcre2_convert_context *pcre2_convert_context_create( pcre2_general_context *gcontext); pcre2_convert_context *pcre2_convert_context_copy( pcre2_convert_context *cvcontext); void pcre2_convert_context_free(pcre2_convert_context *cvcontext); int pcre2_set_glob_escape(pcre2_convert_context *cvcontext, uint32_t escape_char); int pcre2_set_glob_separator(pcre2_convert_context *cvcontext, uint32_t separator_char); int pcre2_pattern_convert(PCRE2_SPTR pattern, PCRE2_SIZE length, uint32_t options, PCRE2_UCHAR **buffer, PCRE2_SIZE *blength, pcre2_convert_context *cvcontext); void pcre2_converted_pattern_free(PCRE2_UCHAR *converted_pattern); These functions provide a way of converting non-PCRE2 patterns into patterns that can be processed by pcre2_compile(). This facility is ex- perimental and may be changed in future releases. At present, "globs" and POSIX basic and extended patterns can be converted. Details are given in the pcre2convert documentation. PCRE2 8-BIT, 16-BIT, AND 32-BIT LIBRARIES There are three PCRE2 libraries, supporting 8-bit, 16-bit, and 32-bit code units, respectively. However, there is just one header file, pcre2.h. This contains the function prototypes and other definitions for all three libraries. One, two, or all three can be installed simul- taneously. On Unix-like systems the libraries are called libpcre2-8, libpcre2-16, and libpcre2-32, and they can also co-exist with the orig- inal 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() There are also three different sets of data types: PCRE2_UCHAR8, PCRE2_UCHAR16, PCRE2_UCHAR32 PCRE2_SPTR8, PCRE2_SPTR16, PCRE2_SPTR32 The UCHAR types define unsigned code units of the appropriate widths. For example, PCRE2_UCHAR16 is usually defined as `uint16_t'. The SPTR types are constant pointers to the equivalent UCHAR types, that is, they are pointers to vectors of unsigned code units. Many applications use only one code unit width. For their convenience, macros are defined whose names are the generic forms such as pcre2_com- pile() and PCRE2_SPTR. These macros use the value of the macro PCRE2_CODE_UNIT_WIDTH to generate the appropriate width-specific func- tion and macro names. PCRE2_CODE_UNIT_WIDTH is not defined by default. An application must define it to be 8, 16, or 32 before including pcre2.h in order to make use of the generic names. Applications that use more than one code unit width can be linked with more than one PCRE2 library, but must define PCRE2_CODE_UNIT_WIDTH to be 0 before including pcre2.h, and then use the real function names. Any code that is to be included in an environment where the value of PCRE2_CODE_UNIT_WIDTH is unknown should also use the real function names. (Unfortunately, it is not possible in C code to save and restore the value of a macro.) If PCRE2_CODE_UNIT_WIDTH is not defined before including pcre2.h, a compiler error occurs. When using multiple libraries in an application, you must take care when processing any particular pattern to use only functions from a single library. For example, if you want to run a match using a pat- tern that was compiled with pcre2_compile_16(), you must do so with pcre2_match_16(), not pcre2_match_8() or pcre2_match_32(). In the function summaries above, and in the rest of this document and other PCRE2 documents, functions and data types are described using their generic names, without the _8, _16, or _32 suffix. PCRE2 API OVERVIEW PCRE2 has its own native API, which is described in this document. There are also some wrapper functions for the 8-bit library that corre- spond to the POSIX regular expression API, but they do not give access to all the functionality of PCRE2. They are described in the pcre2posix 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 compli- cated parameters such as custom memory management functions and re- source 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 re- quest 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 us- age. JIT matching is automatically used by pcre2_match() if it is available, unless the PCRE2_NO_JIT option is set. There is also a direct interface for JIT matching, which gives improved performance at the expense of less sanity checking. The JIT-specific functions are discussed in the pcre2jit documentation. A second matching function, pcre2_dfa_match(), which is not Perl-com- patible, is also provided. This uses a different algorithm for the matching. The alternative algorithm finds all possible matches (at a given point in the subject), and scans the subject just once (unless there are lookaround assertions). However, this algorithm does not re- turn captured substrings. A description of the two matching algorithms and their advantages and disadvantages is given in the pcre2matching documentation. There is no JIT support for pcre2_dfa_match(). In addition to the main compiling and matching functions, there are convenience functions for extracting captured substrings from a subject string that has been matched by pcre2_match(). They are: pcre2_substring_copy_byname() pcre2_substring_copy_bynumber() pcre2_substring_get_byname() pcre2_substring_get_bynumber() pcre2_substring_list_get() pcre2_substring_length_byname() pcre2_substring_length_bynumber() pcre2_substring_nametable_scan() pcre2_substring_number_from_name() pcre2_substring_free() and pcre2_substring_list_free() are also pro- vided, to free memory used for extracted strings. If either of these functions is called with a NULL argument, the function returns immedi- ately without doing anything. The function pcre2_substitute() can be called to match a pattern and return a copy of the subject string with substitutions for parts that were matched. Functions whose names begin with pcre2_serialize_ are used for saving compiled patterns on disc or elsewhere, and reloading them later. Finally, there are functions for finding out information about a com- piled pattern (pcre2_pattern_info()) and about the configuration with which PCRE2 was built (pcre2_config()). Functions with names ending with _free() are used for freeing memory blocks of various sorts. In all cases, if one of these functions is called with a NULL argument, it does nothing. STRING LENGTHS AND OFFSETS The PCRE2 API uses string lengths and offsets into strings of code units in several places. These values are always of type PCRE2_SIZE, which is an unsigned integer type, currently always defined as size_t. The largest value that can be stored in such a type (that is ~(PCRE2_SIZE)0) is reserved as a special indicator for zero-terminated strings and unset offsets. Therefore, the longest string that can be handled is one less than this maximum. NEWLINES PCRE2 supports five different conventions for indicating line breaks in strings: a single CR (carriage return) character, a single LF (line- feed) character, the two-character sequence CRLF, any of the three pre- ceding, or any Unicode newline sequence. The Unicode newline sequences are the three just mentioned, plus the single characters VT (vertical tab, U+000B), FF (form feed, U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS (paragraph separator, U+2029). Each of the first three conventions is used by at least one operating system as its standard newline sequence. When PCRE2 is built, a default can be specified. If it is not, the default is set to LF, which is the Unix standard. However, the newline convention can be changed by an ap- plication when calling pcre2_compile(), or it can be specified by spe- cial text at the start of the pattern itself; this overrides any other settings. See the pcre2pattern page for details of the special charac- ter sequences. In the PCRE2 documentation the word "newline" is used to mean "the character or pair of characters that indicate a line break". The choice of newline convention affects the handling of the dot, circumflex, and dollar metacharacters, the handling of #-comments in /x mode, and, when CRLF is a recognized line ending sequence, the match position advance- ment for a non-anchored pattern. There is more detail about this in the section on pcre2_match() options below. The choice of newline convention does not affect the interpretation of the \n or \r escape sequences, nor does it affect what \R matches; this has its own separate convention. MULTITHREADING In a multithreaded application it is important to keep thread-specific 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 ap- plications while at the same time ensuring that multithreaded applica- tions can use it. There are several different blocks of data that are used to pass infor- mation between the application and the PCRE2 libraries. The compiled pattern A pointer to the compiled form of a pattern is returned to the user when pcre2_compile() is successful. The data in the compiled pattern is fixed, and does not change when the pattern is matched. Therefore, it is thread-safe, that is, the same compiled pattern can be used by more than one thread simultaneously. For example, an application can compile all its patterns at the start, before forking off multiple threads that use them. However, if the just-in-time (JIT) optimization feature is being used, it needs separate memory stack areas for each thread. See the pcre2jit documentation for more details. In a more complicated situation, where patterns are compiled only when they are first needed, but are still shared between threads, pointers to compiled patterns must be protected from simultaneous writing by multiple threads. This is somewhat tricky to do correctly. If you know that writing to a pointer is atomic in your environment, you can use logic like this: Get a read-only (shared) lock (mutex) for pointer if (pointer == NULL) { Get a write (unique) lock for pointer if (pointer == NULL) pointer = pcre2_compile(... } Release the lock Use pointer in pcre2_match() Of course, testing for compilation errors should also be included in the code. The reason for checking the pointer a second time is as follows: Sev- eral threads may have acquired the shared lock and tested the pointer for being NULL, but only one of them will be given the write lock, with the rest kept waiting. The winning thread will compile the pattern and store the result. After this thread releases the write lock, another thread will get it, and if it does not retest pointer for being NULL, will recompile the pattern and overwrite the pointer, creating a memory leak and possibly causing other issues. In an environment where writing to a pointer may not be atomic, the above logic is not sufficient. The thread that is doing the compiling may be descheduled after writing only part of the pointer, which could cause other threads to use an invalid value. Instead of checking the pointer itself, a separate "pointer is valid" flag (that can be updated atomically) must be used: Get a read-only (shared) lock (mutex) for pointer if (!pointer_is_valid) { Get a write (unique) lock for pointer if (!pointer_is_valid) { pointer = pcre2_compile(... pointer_is_valid = TRUE } } Release the lock Use pointer in pcre2_match() If JIT is being used, but the JIT compilation is not being done immedi- ately (perhaps waiting to see if the pattern is used often enough), similar logic is required. JIT compilation updates a value within the compiled code block, so a thread must gain unique write access to the pointer before calling pcre2_jit_compile(). Alternatively, pcre2_code_copy() or pcre2_code_copy_with_tables() can be used to ob- tain a private copy of the compiled code before calling the JIT com- piler. Context blocks The next main section below introduces the idea of "contexts" in which PCRE2 functions are called. A context is nothing more than a collection of parameters that control the way PCRE2 operates. Grouping a number of parameters together in a context is a convenient way of passing them to a PCRE2 function without using lots of arguments. The parameters that are stored in contexts are in some sense "advanced features" of the API. Many straightforward applications will not need to use contexts. In a multithreaded application, if the parameters in a context are val- ues that are never changed, the same context can be used by all the threads. However, if any thread needs to change any value in a context, it must make its own thread-specific copy. Match blocks The matching functions need a block of memory for storing the results of a match. This includes details of what was matched, as well as addi- tional information such as the name of a (*MARK) setting. Each thread must provide its own copy of this memory. PCRE2 CONTEXTS Some PCRE2 functions have a lot of parameters, many of which are used only by specialist applications, for example, those that use custom memory management or non-standard character tables. To keep function argument lists at a reasonable size, and at the same time to keep the API extensible, "uncommon" parameters are passed to certain functions in a context instead of directly. A context is just a block of memory that holds the parameter values. Applications that do not need to ad- just any of the context parameters can pass NULL when a context pointer is required. There are three different types of context: a general context that is relevant for several PCRE2 operations, a compile-time context, and a match-time context. The general context At present, this context just contains pointers to (and data for) ex- ternal memory management functions that are called from several places in the PCRE2 library. The context is named `general' rather than specifically `memory' because in future other fields may be added. If you do not want to supply your own custom memory management functions, you do not need to bother with a general context. A general context is created by: pcre2_general_context *pcre2_general_context_create( void *(*private_malloc)(PCRE2_SIZE, void *), void (*private_free)(void *, void *), void *memory_data); The two function pointers specify custom memory management functions, whose prototypes are: void *private_malloc(PCRE2_SIZE, void *); void private_free(void *, void *); Whenever code in PCRE2 calls these functions, the final argument is the value of memory_data. Either of the first two arguments of the creation function may be NULL, in which case the system memory management func- tions malloc() and free() are used. (This is not currently useful, as there are no other fields in a general context, but in future there might be.) The private_malloc() function is used (if supplied) to ob- tain memory for storing the context, and all three values are saved as part of the context. Whenever PCRE2 creates a data block of any kind, the block contains a pointer to the free() function that matches the malloc() function that was used. When the time comes to free the block, this function is called. A general context can be copied by calling: pcre2_general_context *pcre2_general_context_copy( pcre2_general_context *gcontext); The memory used for a general context should be freed by calling: void pcre2_general_context_free(pcre2_general_context *gcontext); If this function is passed a NULL argument, it returns immediately without doing anything. The compile context A compile context is required if you want to provide an external func- tion 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 also required if you are using custom memory man- agement. If none of these apply, just pass NULL as the context argu- ment of pcre2_compile(). A compile context is created, copied, and freed by the following func- tions: pcre2_compile_context *pcre2_compile_context_create( pcre2_general_context *gcontext); pcre2_compile_context *pcre2_compile_context_copy( pcre2_compile_context *ccontext); void pcre2_compile_context_free(pcre2_compile_context *ccontext); A compile context is created with default values for its parameters. These can be changed by calling the following functions, which return 0 on success, or PCRE2_ERROR_BADDATA if invalid data is detected. int pcre2_set_bsr(pcre2_compile_context *ccontext, uint32_t value); The value must be PCRE2_BSR_ANYCRLF, to specify that \R matches only CR, LF, or CRLF, or PCRE2_BSR_UNICODE, to specify that \R matches any Unicode line ending sequence. The value is used by the JIT compiler and by the two interpreted matching functions, pcre2_match() and pcre2_dfa_match(). int pcre2_set_character_tables(pcre2_compile_context *ccontext, const uint8_t *tables); The value must be the result of a call to pcre2_maketables(), whose only argument is a general context. This function builds a set of char- acter tables in the current locale. int pcre2_set_compile_extra_options(pcre2_compile_context *ccontext, uint32_t extra_options); As PCRE2 has developed, almost all the 32 option bits that are avail- able in the options argument of pcre2_compile() have been used up. To avoid running out, the compile context contains a set of extra option bits which are used for some newer, assumed rarer, options. This func- tion sets those bits. It always sets all the bits (either on or off). It does not modify any existing setting. The available options are de- fined 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 effec- tively unlimited. int pcre2_set_newline(pcre2_compile_context *ccontext, uint32_t value); This specifies which characters or character sequences are to be recog- nized 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_EX- TENDED_MORE option, the newline convention affects the recognition of the end of internal comments starting with #. The value is saved with the compiled pattern for subsequent use by the JIT compiler and by the two interpreted matching functions, pcre2_match() and pcre2_dfa_match(). int pcre2_set_parens_nest_limit(pcre2_compile_context *ccontext, uint32_t value); This parameter adjusts the limit, set when PCRE2 is built (default 250), on the depth of parenthesis nesting in a pattern. This limit stops rogue patterns using up too much system stack when being com- piled. The limit applies to parentheses of all kinds, not just captur- ing parentheses. int pcre2_set_compile_recursion_guard(pcre2_compile_context *ccontext, int (*guard_function)(uint32_t, void *), void *user_data); There is at least one application that runs PCRE2 in threads with very limited system stack, where running out of stack is to be avoided at all costs. The parenthesis limit above cannot take account of how much stack is actually available during compilation. For a finer control, you can supply a function that is called whenever pcre2_compile() starts to compile a parenthesized part of a pattern. This function can check the actual stack size (or anything else that it wants to, of course). The first argument to the callout function gives the current depth of nesting, and the second is user data that is set up by the last argu- ment of pcre2_set_compile_recursion_guard(). The callout function should return zero if all is well, or non-zero to force an error. The match context A match context is required if you want to: Set up a callout function Set an offset limit for matching an unanchored pattern Change the limit on the amount of heap used when matching Change the backtracking match limit Change the backtracking depth limit Set custom memory management specifically for the match If none of these apply, just pass NULL as the context argument of pcre2_match(), pcre2_dfa_match(), or pcre2_jit_match(). A match context is created, copied, and freed by the following func- tions: 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 doc- umentation. int pcre2_set_substitute_callout(pcre2_match_context *mcontext, int (*callout_function)(pcre2_substitute_callout_block *, void *), void *callout_data); This sets up a callout function for PCRE2 to call after each substitu- tion made by pcre2_substitute(). Details are given in the section enti- tled "Creating a new string with substitutions" below. int pcre2_set_offset_limit(pcre2_match_context *mcontext, PCRE2_SIZE value); The offset_limit parameter limits how far an unanchored search can ad- vance in the subject string. The default value is PCRE2_UNSET. The pcre2_match() and pcre2_dfa_match() functions return PCRE2_ERROR_NO- MATCH if a match with a starting point before or at the given offset is not found. The pcre2_substitute() function makes no more substitutions. For example, if the pattern /abc/ is matched against "123abc" with an offset limit less than 3, the result is PCRE2_ERROR_NOMATCH. A match can never be found if the startoffset argument of pcre2_match(), pcre2_dfa_match(), or pcre2_substitute() is greater than the offset limit set in the match context. When using this facility, you must set the PCRE2_USE_OFFSET_LIMIT op- tion when calling pcre2_compile() so that when JIT is in use, different code can be compiled. If a match is started with a non-default match limit when PCRE2_USE_OFFSET_LIMIT is not set, an error is generated. The offset limit facility can be used to track progress when searching large subject strings or to limit the extent of global substitutions. See also the PCRE2_FIRSTLINE option, which requires a match to start before or at the first newline that follows the start of matching in the subject. If this is set with an offset limit, a match must occur in the first line and also within the offset limit. In other words, which- ever limit comes first is used. int pcre2_set_heap_limit(pcre2_match_context *mcontext, uint32_t value); The heap_limit parameter specifies, in units of kibibytes (1024 bytes), the maximum amount of heap memory that pcre2_match() may use to hold backtracking information when running an interpretive match. This limit also applies to pcre2_dfa_match(), which may use the heap when process- ing patterns with a lot of nested pattern recursion or lookarounds or atomic groups. This limit does not apply to matching with the JIT opti- mization, which has its own memory control arrangements (see the pcre2jit documentation for more details). If the limit is reached, the negative error code PCRE2_ERROR_HEAPLIMIT is returned. The default limit can be set when PCRE2 is built; if it is not, the default is set very large and is essentially "unlimited". A value for the heap limit may also be supplied by an item at the start of a pattern of the form (*LIMIT_HEAP=ddd) where ddd is a decimal number. However, such a setting is ignored un- less ddd is less than the limit set by the caller of pcre2_match() or, if no such limit is set, less than the default. The pcre2_match() function starts out using a 20KiB vector on the sys- tem stack for recording backtracking points. The more nested backtrack- ing points there are (that is, the deeper the search tree), the more memory is needed. Heap memory is used only if the initial vector is too small. If the heap limit is set to a value less than 21 (in partic- ular, zero) no heap memory will be used. In this case, only patterns that do not have a lot of nested backtracking can be successfully pro- cessed. Similarly, for pcre2_dfa_match(), a vector on the system stack is used when processing pattern recursions, lookarounds, or atom