----------------------------------------------------------------------------- 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. ----------------------------------------------------------------------------- PCRE2API(3) Library Functions Manual PCRE2API(3) NAME PCRE2 - Perl-compatible regular expressions (revised API) #include PCRE2 is a new API for PCRE. This document contains a description of all its functions. See the pcre2 document for an overview of all the PCRE2 documentation. PCRE2 NATIVE API BASIC FUNCTIONS pcre2_code *pcre2_compile(PCRE2_SPTR pattern, PCRE2_SIZE length, uint32_t options, int *errorcode, PCRE2_SIZE *erroroffset, pcre2_compile_context *ccontext); pcre2_code_free(pcre2_code *code); pcre2_match_data_create(uint32_t ovecsize, pcre2_general_context *gcontext); pcre2_match_data_create_from_pattern(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_SIZE pcre2_get_leftchar(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_rightchar(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_compile(pcre2_compile_context *ccontext, uint32_t value); int pcre2_set_character_tables(pcre2_compile_context *ccontext, const unsigned char *tables); int pcre2_set_newline_compile(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)); 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_bsr_match(pcre2_match_context *mcontext, uint32_t value); int pcre2_set_callout(pcre2_match_context *mcontext, int (*callout_function)(pcre2_callout_block *), void *callout_data); int pcre2_set_match_limit(pcre2_match_context *mcontext, uint32_t value); int pcre2_set_newline_match(pcre2_match_context *mcontext, uint32_t value); 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); 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, unsigned int 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, unsigned int 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, unsigned int 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 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, pcre2_jit_stack *jit_stack); void pcre2_jit_free_unused_memory(pcre2_general_context *gcontext); pcre2_jit_stack *pcre2_jit_stack_alloc(pcre2_general_context *gcontext, PCRE2_SIZE startsize, PCRE2_SIZE maxsize); void pcre2_jit_stack_assign(const pcre2_code *code, pcre2_jit_callback callback_function, void *callback_data); void pcre2_jit_stack_free(pcre2_jit_stack *jit_stack); PCRE2 NATIVE API AUXILIARY FUNCTIONS 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_config(uint32_t what, void *where, PCRE2_SIZE length); 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(). 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. They are described in the pcre2posix documen- tation. 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 contains def- initions 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. Just-in-time 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_alloc(), 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. There is also a direct interface for JIT matching, which gives improved performance. The JIT-specific functions are discussed in the pcre2jit documentation. A second matching function, pcre2_dfa_exec(), which is not Perl-compat- ible, is also provided. This uses a different algorithm for the match- ing. The alternative algorithm finds all possible matches (at a given point in the subject), and scans the subject just once (unless there are lookbehind 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 docu- mentation. 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 is 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 the memory used for extracted strings. There are functions for finding out information about a compiled pat- tern (pcre2_pattern_info()) and about the configuration with which PCRE2 was built (pcre2_config()). 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. The default default is LF, which is the Unix stan- dard. When PCRE2 is run, the default can be overridden, either when a pattern is compiled, or when it is matched. The newline convention can be changed 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 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, which has its own separate control. MULTITHREADING In a multithreaded application it is important to keep thread-specific data separate from data that can be shared between threads. The PCRE2 library code itself is thread-safe: it contains no static or global variables. The API is designed to be fairly simple for non-threaded applications while at the same time ensuring that multithreaded appli- cations can use it. There are several different blocks of data that are used to pass infor- mation between the application and the PCRE libraries. (1) 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. An application can compile all its pat- terns at the start, before forking off multiple threads that use them. However, if the just-in-time optimization feature is being used, it needs separate memory stack areas for each thread. See the pcre2jit documentation for more details. (2) The next 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. (3) The matching functions need a block of memory for working space and 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 version of this mem- ory. PCRE2 CONTEXTS Some PCRE2 functions have a lot of parameters, many of which are used only by specialist applications, for example, those that use custom memory management or non-standard character tables. To keep function argument lists at a reasonable size, and at the same time to keep the API extensible, "uncommon" parameters are passed to certain functions in a context instead of directly. A context is just a block of memory that holds the parameter values. Applications that do not need to adjust any of the context parameters can pass NULL when a context pointer is required. There are three different types of context: a general context that is relevant for several PCRE2 operations, a compile-time context, and a match-time context. The general context At present, this context just contains pointers to (and data for) external memory management functions that are called from several places in the PCRE2 library. The context is named `general' rather than specifically `memory' because in future other fields may be added. If you do not want to supply your own custom memory management functions, you do not need to bother with a general context. A general context is created by: pcre2_general_context *pcre2_general_context_create( void *(*private_malloc)(PCRE2_SIZE, void *), void (*private_free)(void *, void *), void *memory_data); The two function pointers specify custom memory management functions, whose prototypes are: void *private_malloc(PCRE2_SIZE, void *); void private_free(void *, void *); Whenever code in PCRE2 calls these functions, the final argument is the value of memory_data. Either of the first two arguments of the creation function may be NULL, in which case the system memory management 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 obtain memory for storing the context, and all three values are saved as part of the context. Whenever PCRE2 creates a data block of any kind, the block contains a pointer to the free() function that matches the malloc() function that was used. When the time comes to free the block, this function is called. A general context can be copied by calling: pcre2_general_context *pcre2_general_context_copy( pcre2_general_context *gcontext); The memory used for a general context should be freed by calling: void pcre2_general_context_free(pcre2_general_context *gcontext); The compile context A compile context is required if you want 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; An external function for stack checking. 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_compile(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 of this parameter does not affect what is compiled; it is just saved with the compiled pattern. The value is used by the JIT compiler and by the two interpreted match- ing functions, pcre2_match() and pcre2_dfa_match(). You can change the value when calling these functions, but doing so disables the use of JIT. 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 char- acter tables in the current locale. int pcre2_set_newline_compile(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), or PCRE2_NEWLINE_ANY (any Unicode newline sequence). When a pattern is compiled with the PCRE2_EXTENDED option, the value of this parameter 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 inter- preted matching functions, pcre2_match() and pcre2_dfa_match(). You can change the value when calling these functions, but doing so disables the use of JIT. 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. int pcre2_set_compile_recursion_guard(pcre2_compile_context *ccontext, int (*guard_function)(uint32_t)); 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. For a finer control, you can supply a function that is called whenever pcre2_compile() starts to compile a parenthesized part of a pattern. The argument to the function gives the current depth of nesting. The 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 change the default values of any of the following match-time parameters: What \R matches (Unicode newlines or CR, LF, CRLF only); A callout function; The limit for calling match(); The limit for calling match() recursively; The newline character sequence; A match context is also required if you are using custom memory manage- ment. If none of these apply, just pass NULL as the context argument of pcre2_match(), pcre2_dfa_match(), or pcre2_jit_match(). Changing the newline value or what \R matches at match time disables the use of JIT via pcre2_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_bsr_match(pcre2_match_context *mcontext, 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. If you want to make use of JIT matching, you should not use this function, but instead set the value in a com- pile context. int pcre2_set_callout(pcre2_match_context *mcontext, int (*callout_function)(pcre2_callout_block *), void *callout_data); This sets up a "callout" function, which PCRE2 will call at specified points during a matching operation. Details are given in the pcre2call- out documentation. 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 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 unlim- ited repeats. Internally, pcre2_match() uses a function called match(), which it calls repeatedly (sometimes recursively). The limit set by match_limit is imposed on the number of times this function is called during a match, which 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 stud- ied with pcre2_jit_compile(), the way that the 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. If the limit is exceeded, pcre2_match() returns PCRE2_ERROR_MATCHLIMIT. A value for the match limit may also be sup- plied by an item at the start of a pattern of the form (*LIMIT_MATCH=ddd) where ddd is a decimal number. However, such a setting is ignored unless ddd is less than the limit set by the caller of pcre2_match() or, if no such limit is set, less than the default. int pcre2_set_recursion_limit(pcre2_match_context *mcontext, uint32_t value); The recursion_limit parameter is similar to match_limit, but instead of limiting the total number of times that match() is called, it limits the depth of recursion. The recursion depth is a smaller number than the total number of calls, because not all calls to match() are recur- sive. This limit is of use only if it is set smaller than match_limit. Limiting the recursion depth limits the amount of system stack that can be used, or, when PCRE2 has been compiled to use memory on the heap instead of the stack, the amount of heap memory that can be used. This limit is not relevant, and is ignored, when matching is done using JIT compiled code or by the pcre2_dfa_match() function. The default value for recursion_limit can be set when PCRE2 is built; the default default is the same value as the default for match_limit. If the limit is exceeded, pcre2_match() returns PCRE2_ERROR_RECURSION- LIMIT. A value for the recursion limit may also be supplied by an item at the start of a pattern of the form (*LIMIT_RECURSION=ddd) where ddd is a decimal number. However, such a setting is ignored unless ddd is less than the limit set by the caller of pcre2_match() or, if no such limit is set, less than the default. int pcre2_set_newline_match(pcre2_match_context *mcontext, 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), or PCRE2_NEWLINE_ANY (any Unicode newline sequence). If you want to make use of JIT matching, you should not use this function, but instead set the value in a compile context. int pcre2_set_recursion_memory_management( pcre2_match_context *mcontext, void *(*private_malloc)(PCRE2_SIZE, void *), void (*private_free)(void *, void *), void *memory_data); This function sets up two additional custom memory management functions for use by pcre2_match() when PCRE2 is compiled to use the heap for remembering backtracking data, instead of recursive function calls that use the system stack. There is a discussion about PCRE2's stack usage in the pcre2stack documentation. See the pcre2build documentation for details of how to build PCRE2. Using the heap for recursion is a non- standard way of building PCRE2, for use in environments that have lim- ited stacks. Because of the greater use of memory management, pcre2_match() runs more slowly. Functions that are different to the general custom memory functions are provided so that special-purpose external code can be used for this case, because the memory blocks are all the same size. The blocks are retained by pcre2_match() until it is about to exit so that they can be re-used when possible during the match. In the absence of these functions, the normal custom memory man- agement functions are used, if supplied, otherwise the system func- tions. CHECKING BUILD-TIME OPTIONS int pcre2_config(uint32_t what, void *where, PCRE2_SIZE length); 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, with the final argument giving the length of this memory in bytes. For calls that return numerical values, where should point to appropriately aligned memory, with length set to at least the "sizeof" the data type. The returned value from pcre2_config() is zero on success, or the nega- tive error code PCRE2_ERROR_BADOPTION if the value in the first argu- ment is not recognized. The following information is available: PCRE2_CONFIG_BSR The output is an integer whose value indicates what character sequences the \R escape sequence matches by default. A value of 0 means that \R matches any Unicode line ending sequence; a value of 1 means that \R matches only CR, LF, or CRLF. The default can be overridden when a pat- tern is compiled or matched. PCRE2_CONFIG_JIT The output is an integer that is set to one if support for just-in-time compiling is available; otherwise it is set to zero. PCRE2_CONFIG_JITTARGET FIXME: this needs sorting out once JIT is implemented. If JIT support is available, the string contains the name of the architecture for which the JIT compiler is configured, for example "x86 32bit (little endian + unaligned)". If JIT support is not available, FIXME. PCRE2_CONFIG_LINKSIZE The output is an integer that contains the number of bytes used for internal linkage in compiled regular expressions. When PCRE2 is config- ured, the value can be set to 2, 3, or 4, with the default being 2. This is the value that is returned by pcre2_config(). However, when the 16-bit library is compiled, a value of 3 is rounded up to 4, and when the 32-bit library is compiled, internal linkages always use 4 bytes, so the configured value is not relevant. The default value of 2 for the 8-bit and 16-bit libraries is sufficient for all but the most massive patterns, since it allows the size of the compiled pattern to be up to 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 The output is an unsigned long integer that gives the default limit for the number of internal matching function calls in a pcre2_match() exe- cution. Further details are given with pcre2_match() below. PCRE2_CONFIG_NEWLINE The output is an integer whose value specifies the default character sequence that is recognized as meaning "newline". The values are: 1 Carriage return (CR) 2 Linefeed (LF) 3 Carriage return, linefeed (CRLF) 4 Any Unicode line ending 5 Any of CR, LF, or CRLF The default should normally correspond to the standard sequence for your operating system. PCRE2_CONFIG_PARENSLIMIT The output is an unsigned long integer that gives the maximum depth of nesting of parentheses (of any kind) in a pattern. This limit is imposed to cap the amount of system stack used when a pattern is com- piled. It is specified when PCRE2 is built; the default is 250. This limit does not take into account the stack that may already be used by the calling application. For finer control over compilation stack usage, see pcre2_set_compile_recursion_guard(). PCRE2_CONFIG_RECURSIONLIMIT The output is an unsigned long integer that gives the default limit for the depth of recursion when calling the internal matching function in a pcre2_match() execution. Further details are given with pcre2_match() below. PCRE2_CONFIG_STACKRECURSE The output is an integer that is set to one if internal recursion when running pcre2_match() is implemented by recursive function calls that use the system stack to remember their state. This is the usual way that PCRE2 is compiled. The output is zero if PCRE2 was compiled to use blocks of data on the heap instead of recursive function calls. PCRE2_CONFIG_UNICODE_VERSION The where argument should point to a buffer that is at least 24 code units long. If PCRE2 has been compiled without Unicode support, this is filled with the text "Unicode not supported". Otherwise, the Unicode version string (for example, "7.0.0") is returnd. The string is zero- terminated. PCRE2_CONFIG_UNICODE The output is an integer that is set to one if Unicode support is available; otherwise it is set to zero. Unicode support implies UTF support. PCRE2_CONFIG_VERSION The where argument should point to a buffer that is at least 12 code units long. It is filled with the PCRE2 version string, zero-termi- nated. COMPILING A PATTERN pcre2_code *pcre2_compile(PCRE2_SPTR pattern, PCRE2_SIZE length, uint32_t options, int *errorcode, PCRE2_SIZE *erroroffset, pcre2_compile_context *ccontext); pcre2_code_free(pcre2_code *code); This function compiles a pattern, defined by a pointer to a string of code units and a length, into an internal form. If the pattern is zero- terminated, the length should be specified as PCRE2_ZERO_TERMINATED. The function returns a pointer to a block of memory that contains the compiled pattern and related data. The caller must free the memory by calling pcre2_code_free() when it is no longer needed. If the compile context argument ccontext is NULL, the memory is obtained by calling malloc(). Otherwise, it is obtained from the same memory function that was used for the compile context. The options argument contains various bit settings that affect the com- pilation. 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 pat- tern, the contents of the options argument specifies their settings at the start of compilation. The PCRE2_ANCHORED, PCRE2_NO_UTF_CHECK, and PCRE2_NO_START_OPTIMIZE 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 imme- diately. Otherwise, if compilation of a pattern fails, pcre2_compile() returns NULL, having set these variables to an error code and an offset (number of code units) within the pattern, respectively. The pcre2_get_error_message() function provides a textual message for each error code. Compilation errors are positive numbers, but UTF formatting errors are negative numbers. 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 char- acter. This code fragment shows a typical straightforward call to pcre2_com- pile(): 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 */ The following names for option bits are defined in the pcre2.h header file: PCRE2_ANCHORED If this bit is set, the pattern is forced to be "anchored", that is, it is constrained to match only at the first matching point in the string that is being searched (the "subject string"). This effect can also be achieved by appropriate constructs in the pattern itself, which is the only way to do it in Perl. PCRE2_ALLOW_EMPTY_CLASS By default, for compatibility with Perl, a closing square bracket that immediately follows an opening one is treated as a data character for the class. When PCRE2_ALLOW_EMPTY_CLASS is set, it terminates the class, which therefore contains no characters and so can never match. PCRE2_ALT_BSUX This option request alternative handling of three escape sequences, which makes PCRE2's behaviour more like ECMAscript (aka JavaScript). When it is set: (1) \U matches an upper case "U" character; by default \U causes a com- pile 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_AUTO_CALLOUT If this bit is set, pcre2_compile() automatically inserts callout items, all with number 255, before each pattern item. For discussion of the callout facility, see the pcre2callout documentation. PCRE2_CASELESS If this bit is set, letters in the pattern match both upper and lower case letters in the subject. It is equivalent to Perl's /i option, and it can be changed within a pattern by a (?i) option setting. PCRE2_DOLLAR_ENDONLY If this bit is set, a dollar metacharacter in the pattern matches only at the end of the subject string. Without this option, a dollar also matches immediately before a newline at the end of the string (but not before any other newlines). The PCRE2_DOLLAR_ENDONLY option is ignored if PCRE2_MULTILINE is set. There is no equivalent to this option in Perl, and no way to set it within a pattern. PCRE2_DOTALL If this bit is set, a dot metacharacter in the pattern matches any character, including one that indicates a newline. However, it only ever matches one character, even if newlines are coded as CRLF. Without this option, a dot does not match when the current position in the sub- ject is at a newline. This option is equivalent to Perl's /s option, and it can be changed within a pattern by a (?s) option setting. A neg- ative class such as [^a] always matches newline characters, independent of the setting of this option. PCRE2_DUPNAMES If this bit is set, names used to identify capturing subpatterns need not be unique. This can be helpful for certain types of pattern when it is known that only one instance of the named subpattern can ever be matched. There are more details of named subpatterns below; see also the pcre2pattern documentation. PCRE2_EXTENDED If this bit is set, most white space characters in the pattern are totally ignored except when escaped or inside a character class. How- ever, white space is not allowed within sequences such as (?> that introduce various parenthesized subpatterns, nor within numerical quan- tifiers such as {1,3}. Ignorable white space is permitted between an item and a following quantifier and between a quantifier and a follow- ing + that indicates possessiveness. 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 set- ting 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 sec- tion entitled "Newline conventions" in the pcre2pattern documentation. A default is defined when PCRE2 is built. PCRE2_FIRSTLINE If this option is set, an unanchored pattern is required to match before or at the first newline in the subject string, though the matched text may continue over the newline. PCRE2_MATCH_UNSET_BACKREF If this option is set, a back reference to an unset subpattern group matches an empty string (by default this causes the current matching alternative to fail). A pattern such as (\1)(a) succeeds when this option is set (assuming it can find an "a" in the subject), whereas it fails by default, for Perl compatibility. Setting this option makes PCRE2 behave more like ECMAscript (aka JavaScript). PCRE2_MULTILINE By default, for the purposes of matching "start of line" and "end of line", PCRE2 treats the subject string as consisting of a single line of characters, even if it actually contains newlines. The "start of line" metacharacter (^) matches only at the start of the string, and the "end of line" metacharacter ($) matches only at the end of the string, or before a terminating newline (except when PCRE2_DOL- LAR_ENDONLY is set). Note, however, that unless PCRE2_DOTALL is set, the "any character" metacharacter (.) does not match at a newline. This behaviour (for ^, $, and dot) is the same as Perl. When PCRE2_MULTILINE it is set, the "start of line" and "end of line" constructs match immediately following or immediately before internal newlines in the subject string, respectively, as well as at the very start and end. This is equivalent to Perl's /m option, and it can be changed within a pattern by a (?m) option setting. If there are no new- lines in a subject string, or no occurrences of ^ or $ in a pattern, setting PCRE2_MULTILINE has no effect. PCRE2_NEVER_UCP This option locks out the use of Unicode properties for handling \B, \b, \D, \d, \S, \s, \W, \w, and some of the POSIX character classes, as described for the PCRE2_UCP option below. In particular, it prevents the creator of the pattern from enabling this facility by starting the pattern with (*UCP). This may be useful in applications that process patterns from external sources. The option combination PCRE_UCP and PCRE_NEVER_UCP causes an error. PCRE2_NEVER_UTF This option locks out interpretation of the pattern as UTF-8, UTF-16, or UTF-32, depending on which library is in use. In particular, it pre- vents the creator of the pattern from switching to UTF interpretation by starting the pattern with (*UTF). This may be useful in applications that process patterns from external sources. The combination of PCRE2_UTF and PCRE2_NEVER_UTF causes an error. PCRE2_NO_AUTO_CAPTURE If this option is set, it disables the use of numbered capturing paren- theses in the pattern. Any opening parenthesis that is not followed by ? behaves as if it were followed by ?: but named parentheses can still be used for capturing (and they acquire numbers in the usual way). There is no equivalent of this option in Perl. PCRE2_NO_AUTO_POSSESS If this option is set, it disables "auto-possessification", which is an optimization that, for example, turns a+b into a++b in order to avoid backtracks into a+ that can never be successful. However, if callouts are in use, auto-possessification means that some callouts are never taken. You can set this option if you want the matching functions to do a full unoptimized search and run all the callouts, but it is mainly provided for testing purposes. PCRE2_NO_START_OPTIMIZE This is an option that acts at matching time; that is, it is really an option for pcre2_match() or pcre_dfa_match(). If it is set at compile time, it is remembered with the compiled pattern and assumed at match- ing time. This is necessary if you want to use JIT execution, because the JIT compiler needs to know whether or not this option is set. For details, see the discussion of PCRE2_NO_START_OPTIMIZE in the section on pcre2_match() options below. PCRE2_NO_UTF_CHECK When PCRE2_UTF is set, the validity of the pattern as a UTF string is automatically checked. There are discussions about the validity of UTF-8 strings, UTF-16 strings, and UTF-32 strings in the pcre2unicode document. If an invalid UTF sequence is found, pcre2_compile() returns a negative error code. If you know that your pattern is valid, 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 pat- tern 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 validity checking of the subject string. PCRE2_UCP This option changes the way PCRE2 processes \B, \b, \D, \d, \S, \s, \W, \w, and some of the POSIX character classes. By default, only ASCII characters are recognized, but if PCRE2_UCP is set, Unicode properties are used instead to classify characters. More details are given in the section on generic character types in the pcre2pattern page. If you set PCRE2_UCP, matching one of the items it affects takes much longer. The option is available only if PCRE2 has been compiled with UTF support. PCRE2_UNGREEDY This option inverts the "greediness" of the quantifiers so that they are not greedy by default, but become greedy if followed by "?". It is not compatible with Perl. It can also be set by a (?U) option setting within the pattern. PCRE2_UTF This option causes PCRE2 to regard both the pattern and the subject strings that are subsequently processed as strings of UTF characters instead of single-code-unit strings. However, it is available only when PCRE2 is built to include UTF support. If not, the use of this option provokes an error. Details of how this option changes the behaviour of PCRE2 are given in the pcre2unicode page. COMPILATION ERROR CODES There are over 80 positive error codes that pcre2_compile() may return if it finds an error in the pattern. There are also some negative error codes that are used for invalid UTF strings. 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 can be called to obtain a textual error message from any error code. JUST-IN-TIME (JIT) COMPILATION int pcre2_jit_compile(pcre2_code *code, uint32_t options); int pcre2_jit_match(const pcre2_code *code, PCRE2_SPTR subject, PCRE2_SIZE length, PCRE2_SIZE startoffset, uint32_t options, pcre2_match_data *match_data, pcre2_match_context *mcontext, pcre2_jit_stack *jit_stack); void pcre2_jit_free_unused_memory(pcre2_general_context *gcontext); pcre2_jit_stack *pcre2_jit_stack_alloc(pcre2_general_context *gcontext, PCRE2_SIZE startsize, PCRE2_SIZE maxsize); void pcre2_jit_stack_assign(const pcre2_code *code, 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 pat- tern 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 pat- terns the benefit of faster execution might be offset by a much slower compilation time. Most, but not all patterns can be optimized by the JIT compiler. LOCALE SUPPORT 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. When running in UTF-8 mode, or using the 16-bit or 32-bit libraries, this applies only to characters with code points less than 256. By default, higher-valued code points never match escapes such as \w or \d. However, if PCRE2 is built with UTF 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 dif- ferent. The internal tables can be overridden by tables supplied by the appli- cation that calls PCRE2. These may be created in a different locale from the default. As more and more applications change to using Uni- code, 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 locale name "fr_FR" is used on Linux and other Unix-like systems; if you are using Windows, the name for the French locale is "french". It is the caller's responsibility to ensure that the memory containing the tables remains available for as long as it is needed. 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, com- pilation, and matching all happen in the same locale, but different patterns can be processed in different locales. INFORMATION ABOUT A COMPILED PATTERN int pcre2_pattern_info(const pcre2 *code, uint32_t what, void *where); The pcre2_pattern_info() function returns information about a compiled pattern. The first argument 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. The yield of the function is zero for success, or one of the following neg- ative numbers: PCRE2_ERROR_NULL the argument code was NULL the argument where was NULL PCRE2_ERROR_BADMAGIC the "magic number" was not found PCRE2_ERROR_BADOPTION the value of what was invalid PCRE2_ERROR_UNSET the requested field is not set The "magic number" is placed at the start of each compiled pattern as an simple check against passing an arbitrary memory pointer. Here is a typical call of pcre2_pattern_info(), to obtain the length of the com- piled pattern: int rc; size_t length; rc = pcre2_pattern_info( re, /* result of pcre2_compile() */ PCRE2_INFO_SIZE, /* what is required */ &length); /* where to put the data */ The possible values for the second argument are defined in pcre2.h, and are as follows: PCRE2_INFO_ALLOPTIONS PCRE2_INFO_ARGOPTIONS Return a copy of the pattern's options. The third argument should point to a uint32_t variable. PCRE2_INFO_ARGOPTIONS returns exactly the options that were passed to pcre2_compile(), whereas PCRE2_INFO_ALLOP- TIONS returns the compile options as modified by any top-level option settings at the start of the pattern itself. In other words, they are the options that will be in force when matching starts. For example, if the pattern /(?im)abc(?-i)d/ is compiled with the PCRE2_EXTENDED option, the result is PCRE2_CASELESS, PCRE2_MULTILINE, and PCRE2_EXTENDED. A pattern is automatically anchored by PCRE2 if all of its top-level alternatives begin with one of the following: ^ unless PCRE2_MULTILINE is set \A always \G always .* if PCRE2_DOTALL is set and there are no back references to the subpattern in which .* appears For such patterns, the PCRE2_ANCHORED bit is set in the options returned for PCRE2_INFO_ALLOPTIONS. PCRE2_INFO_BACKREFMAX Return the number of the highest back reference in the pattern. The third argument should point to an uint32_t variable. Zero is returned if there are no back references. PCRE2_INFO_BSR The output is a uint32_t whose value indicates what character sequences the \R escape sequence matches by default. A value of 0 means that \R matches any Unicode line ending sequence; a value of 1 means that \R matches only CR, LF, or CRLF. The default can be overridden when a pat- tern is matched. PCRE2_INFO_CAPTURECOUNT Return the number of capturing subpatterns in the pattern. The third argument should point to an uint32_t variable. PCRE2_INFO_FIRSTCODETYPE Return information about the first code unit of any matched string, for a non-anchored pattern. The third argument should point to an uint32_t variable. If there is a fixed first value, for example, the letter "c" from a pattern such as (cat|cow|coyote), 1 is returned, and the character value can be retrieved using PCRE2_INFO_FIRSTCODEUNIT. If there is no fixed first value, and if either (a) the pattern was compiled with the PCRE2_MULTILINE option, and every branch starts with "^", or (b) every branch of the pattern starts with ".*" and PCRE2_DOTALL is not set (if it were set, the pattern would be anchored), 2 is returned, indicating that the pattern matches only at the start of a subject string or after any newline within the string. Otherwise 0 is returned. For anchored patterns, 0 is returned. PCRE2_INFO_FIRSTCODEUNIT Return the value of the first code unit of any matched string in the situation where PCRE2_INFO_FIRSTCODETYPE returns 1; otherwise return 0. The third argument should point to an uint32_t variable. In the 8-bit library, the value is always less than 256. In the 16-bit library the value can be up to 0xffff. In the 32-bit library in UTF-32 mode the value can be up to 0x10ffff, and up to 0xffffffff when not using UTF-32 mode. PCRE2_INFO_FIRSTBITMAP In the absence of a single first code unit for a non-anchored pattern, pcre2_compile() may construct a 256-bit table that defines a fixed set of values for the first code unit in any match. For example, a pattern that starts with [abc] results in a table with three bits set. When code unit values greater than 255 are supported, the flag bit for 255 means "any code unit of value 255 or above". If such a table was con- structed, a pointer to it is returned. Otherwise NULL is returned. The third argument should point to an const uint8_t * variable. PCRE2_INFO_HASCRORLF Return 1 if the pattern contains any explicit matches for CR or LF characters, otherwise 0. The third argument should point to an uint32_t variable. An explicit match is either a literal CR or LF character, or \r or \n. PCRE2_INFO_JCHANGED Return 1 if the (?J) or (?-J) option setting is used in the pattern, otherwise 0. The third argument should point to an uint32_t variable. (?J) and (?-J) set and unset the local PCRE2_DUPNAMES option, respec- tively. PCRE2_INFO_JITSIZE If the compiled pattern was successfully processed by pcre2_jit_com- pile(), return the size of the JIT compiled code, otherwise return zero. The third argument should point to a size_t variable. PCRE2_INFO_LASTCODETYPE Returns 1 if there is a rightmost literal code unit that must exist in any matched string, other than at its start. The third argument should point to an uint32_t variable. If there is no such value, 0 is returned. When 1 is returned, the code unit value itself can be retrieved using PCRE2_INFO_LASTCODEUNIT. For anchored patterns, a last literal value is recorded only if it fol- lows something of variable length. For example, for the pattern /^a\d+z\d+/ the returned value is 1 (with "z" returned from PCRE2_INFO_LASTCODEUNIT), but for /^a\dz\d/ the returned value is 0. PCRE2_INFO_LASTCODEUNIT Return the value of the rightmost literal data unit that must exist in any matched string, other than at its start, if such a value has been recorded. The third argument should point to an uint32_t variable. If there is no such value, 0 is returned. PCRE2_INFO_MATCHEMPTY Return 1 if the pattern can match an empty string, otherwise 0. The third argument should point to an uint32_t variable. PCRE2_INFO_MATCHLIMIT If the pattern set a match limit by including an item of the form (*LIMIT_MATCH=nnnn) at the start, the value is returned. The third argument should point to an unsigned 32-bit integer. If no such value has been set, the call to pcre2_pattern_info() returns the error PCRE2_ERROR_UNSET. PCRE2_INFO_MAXLOOKBEHIND Return the number of characters (not code units) in the longest lookbe- hind assertion in the pattern. The third argument should point to an unsigned 32-bit integer. This information is useful when doing multi- segment matching using the partial matching facilities. Note that the simple assertions \b and \B require a one-character lookbehind. \A also registers a one-character lookbehind, though it does not actually inspect the previous character. This is to ensure that at least one character from the old segment is retained when a new segment is pro- cessed. Otherwise, if there are no lookbehinds in the pattern, \A might match incorrectly at the start of a new segment. PCRE2_INFO_MINLENGTH If a minimum length for matching subject strings was computed, its value is returned. Otherwise the returned value is 0. The value is a number of characters, which in UTF mode may be different from the num- ber of code units. The third argument should point to an uint32_t variable. The value is a lower bound to the length of any matching string. There may not be any strings of that length that do actually match, but every string that does match is at least that long. PCRE2_INFO_NAMECOUNT PCRE2_INFO_NAMEENTRYSIZE PCRE2_INFO_NAMETABLE PCRE2 supports the use of named as well as numbered capturing parenthe- ses. The names are just an additional way of identifying the parenthe- ses, which still acquire numbers. Several convenience functions such as pcre2_substring_get_byname() are provided for extracting captured sub- strings by name. It is also possible to extract the data directly, by first converting the name to a number in order to access the correct pointers in the output vector (described with pcre2_match() below). To do the conversion, you need to use the name-to-number map, which is described by these three values. The map consists of a number of fixed-size entries. PCRE2_INFO_NAME- COUNT gives the number of entries, and PCRE2_INFO_NAMEENTRYSIZE gives the size of each entry; 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 cap- turing parenthesis, most significant byte first. In the 16-bit library, the pointer points to 16-bit data units, the first of which contains the parenthesis number. In the 32-bit library, the pointer points to 32-bit data 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): (? (?(\d\d)?\d\d) - (?\d\d) - (?\d\d) ) There are four named subpatterns, so the table has four entries, and each entry in the table is eight bytes long. The table is as follows, with non-printing bytes shows in hexadecimal, and undefined bytes shown as ??: 00 01 d a t e 00 ?? 00 05 d a y 00 ?? ?? 00 04 m o n t h 00 00 02 y e a r 00 ?? When writing code to extract data from named subpatterns using the name-to-number map, remember that the length of the entries is likely to be different for each compiled pattern. PCRE2_INFO_NEWLINE The output is a uint32_t whose value specifies the default character sequence that will be recognized as meaning "newline" while matching. The values are: 1 Carriage return (CR) 2 Linefeed (LF) 3 Carriage return, linefeed (CRLF) 4 Any Unicode line ending 5 Any of CR, LF, or CRLF The default can be overridden when a pattern is matched. PCRE2_INFO_RECURSIONLIMIT If the pattern set a recursion limit by including an item of the form (*LIMIT_RECURSION=nnnn) at the start, the value is returned. The third argument should point to an unsigned 32-bit integer. If no such value has been set, the call to pcre2_pattern_info() returns the error PCRE2_ERROR_UNSET. PCRE2_INFO_SIZE Return the size of the compiled pattern in bytes (for all three libraries). The third argument should point to a size_t variable. This value does not include the size of the pcre2_code structure that is returned by pcre_compile(). The value that is used when pcre2_compile() is getting memory in which to place the compiled data is the value returned by this option plus the size of the pcre2_code structure. Pro- cessing a pattern with the JIT compiler does not alter the value returned by this option. THE MATCH DATA BLOCK pcre2_match_data_create(uint32_t ovecsize, pcre2_general_context *gcontext); pcre2_match_data_create_from_pattern(pcre2_code *code, pcre2_general_context *gcontext); void pcre2_match_data_free(pcre2_match_data *match_data); Information about successful and unsuccessful matches 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 capured. This is know as the ovec- tor. Before calling pcre2_match() or pcre2_dfa_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 another pair for each cap- tured substring. For example, a value of 4 creates enough space to record the matched portion of the subject plus three captured sub- strings. For pcre2_match_data_create_from_pattern(), the first argument is a pointer to a compiled pattern. In this case the ovector is created to be exactly the right size to hold all the substrings a pattern might capture. The second argument of both these functions ia 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. A match data block can be used many times, with the same or different compiled patterns. When it is no longer needed, it should be freed by calling pcre2_match_data_free(). How to extract information from a match data block after a match operation is described in the sections on matched strings and other match data below. MATCHING A PATTERN: THE TRADITIONAL FUNCTION int pcre2_match(const pcre2_code *code, PCRE2_SPTR subject, PCRE2_SIZE length, PCRE2_SIZE startoffset, uint32_t options, pcre2_match_data *match_data, pcre2_match_context *mcontext); The function pcre2_match() is called to match a subject string against a compiled pattern, which is passed in the code argument. You can call pcre2_match() with the same code argument as many times as you like, in order to find multiple matches in the subject string or to match dif- ferent 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 */ If the subject string is zero-terminated, the length can be given as PCRE2_ZERO_TERMINATED. A match context must be provided if certain less common matching parameters are to be changed. For details, see the sec- tion on the match context above. The string to be matched by pcre2_match() The subject string is passed to pcre2_match() as a pointer in subject, a length in length, and a starting offset in startoffset. The length and offset are in code units, not characters. That is, they are in bytes for the 8-bit library, 16-bit code units for the 16-bit library, and 32-bit code units for the 32-bit library, whether or not UTF pro- cessing 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 off- set must point to the start of a character, or to the end of the sub- ject (in UTF-32 mode, one code unit equals one character, so all off- sets 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 which finds occurrences of "iss" in the middle of words. (\B matches only if the current position in the subject is not a word boundary.) When applied to the string "Mississipi" the first call to pcre2_match() finds the first occurrence. If pcre2_match() is called again with just the remainder of the subject, namely "issipi", it does not match, because \B is always false at the start of the subject, which is deemed to be a word boundary. However, if pcre2_match() is passed the entire string again, but with startoffset set to 4, it finds the second occur- rence of "iss" because it is able to look behind the starting point to discover that it is preceded by a letter. Finding all the matches in a subject is tricky when the pattern can match an empty string. 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 start- ing offset by two characters instead of one. If a non-zero starting offset is passed when the pattern is anchored, one 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. Option bits for pcre2_match() The unused bits of the options argument for pcre2_match() must be zero. The only bits that may be set are PCRE2_ANCHORED, PCRE2_NOTBOL, PCRE2_NOTEOL, PCRE2_NOTEMPTY, PCRE2_NOTEMPTY_ATSTART, PCRE2_NO_START_OPTIMIZE, PCRE2_NO_UTF_CHECK, PCRE2_PARTIAL_HARD, and PCRE2_PARTIAL_SOFT. Their action is described below. If the pattern was successfully processed by the just-in-time (JIT) compiler, the only supported options for matching using the JIT code are PCRE2_NOTBOL, PCRE2_NOTEOL, PCRE2_NOTEMPTY, PCRE2_NOTEMPTY_ATSTART, PCRE2_NO_UTF_CHECK, PCRE2_PARTIAL_HARD, and PCRE2_PARTIAL_SOFT. If an unsupported option is used, JIT matching is disabled and the normal interpretive code in pcre2_match() is run. PCRE2_ANCHORED The PCRE2_ANCHORED option limits pcre2_match() to matching at the first matching position. If a pattern was compiled with PCRE2_ANCHORED, or turned out to be anchored by virtue of its contents, it cannot be made unachored at matching time. Note that setting the option at match time disables JIT matching. PCRE2_NOTBOL This option specifies that first character of the subject string is not the beginning of a line, so the circumflex metacharacter should not match before it. Setting this without PCRE2_MULTILINE (at compile time) causes circumflex never to match. This option affects only the behav- iour of the circumflex metacharacter. It does not affect \A. PCRE2_NOTEOL This option specifies that the end of the subject string is not the end of a line, so the dollar metacharacter should not match it nor (except in multiline mode) a newline immediately before it. Setting this with- out PCRE2_MULTILINE (at compile time) causes dollar never to match. This option affects only the behaviour of the dollar metacharacter. It does not affect \Z or \z. PCRE2_NOTEMPTY An empty string is not considered to be a valid match if this option is set. If there are alternatives in the pattern, they are tried. If all the alternatives match the empty string, the entire match fails. For example, if the pattern a?b? is applied to a string not beginning with "a" or "b", it matches an empty string at the start of the subject. With PCRE2_NOTEMPTY set, this match is not valid, so PCRE2 searches further into the string for occurrences of "a" or "b". PCRE2_NOTEMPTY_ATSTART This is like PCRE2_NOTEMPTY, except that an empty string match that is not at the start of the subject is permitted. If the pattern is anchored, such a match can occur only if the pattern contains \K. PCRE2_NO_START_OPTIMIZE There are a number of optimizations that pcre2_match() uses 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 character, it searches the subject for that character, 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 pat- tern 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 pat- tern 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. If PCRE2_NO_START_OPTIMIZE is set at compile time, it cannot be unset at matching time. The use of PCRE2_NO_START_OPTIMIZE at matching time (that is, passing it to pcre2_match()) disables JIT execution; in this situation, matching is always done using interpretively. Setting PCRE2_NO_START_OPTIMIZE can change the outcome of a matching operation. Consider the pattern (*COMMIT)ABC When this is compiled, PCRE2 records the fact that a match must start with the character "A". Suppose the subject string is "DEFABC". The start-up optimization scans along the subject, finds "A" and runs the first match attempt from there. The (*COMMIT) item means that the pat- tern must match the current starting position, which in this case, it does. However, if the same match is run with PCRE2_NO_START_OPTIMIZE set, the initial scan along the subject string does not happen. The first match attempt is run starting from "D" and when this fails, (*COMMIT) prevents any further matches being tried, so the overall result is "no match". 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) The minimum length for a match is one character. If the subject is "ABC", there will be attempts to match "ABC", "BC", and "C". An attempt to match an empty string at the end of the subject does not take place, because PCRE2 knows that the subject is now too short, and so the (*MARK) is never encountered. In this case, the optimization does not affect the overall match result, which is still "no match", but it does affect the auxiliary information that is returned. PCRE2_NO_UTF_CHECK When PCRE2_UTF is set at compile time, the validity of the subject as a UTF string is checked by default when pcre2_match() is subsequently called. The entire string is checked 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. The value of startoff- set is also checked, to ensure that it points to the start of a charac- ter or to the end of the subject. 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 all the matches in a single subject string. NOTE: 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 These options turn on the partial matching feature. A partial match occurs if the end of the subject string is reached successfully, but there are not enough subject characters to complete the match. If this happens when PCRE2_PARTIAL_SOFT (but not PCRE2_PARTIAL_HARD) is set, matching continues by testing any remaining alternatives. Only if no complete match can be found is PCRE2_ERROR_PARTIAL returned instead of PCRE2_ERROR_NOMATCH. In other words, PCRE2_PARTIAL_SOFT says that the caller is prepared to handle a partial match, but only if no complete match can be found. If PCRE2_PARTIAL_HARD is set, it overrides PCRE2_PARTIAL_SOFT. In this case, if a partial match is found, pcre2_match() immediately returns PCRE2_ERROR_PARTIAL, without considering any other alternatives. In other words, when PCRE2_PARTIAL_HARD is set, a partial match is consid- ered to be more important that an alternative complete match. There is a more detailed discussion of partial and multi-segment match- ing, with examples, in the pcre2partial documentation. NEWLINE HANDLING WHEN MATCHING When PCRE2 is built, a default newline convention is set; this is usu- ally the standard convention for the operating system. The default can be overridden in either a compile context or a match context. However, changing the newline convention at match time disables JIT matching. During matching, the newline choice affects the behaviour of the dot, circumflex, and dollar metacharacters. It may also alter the way the match position is advanced after a match failure for an unanchored pat- tern. When PCRE2_NEWLINE_CRLF, PCRE2_NEWLINE_ANYCRLF, or PCRE2_NEWLINE_ANY is set, and a match attempt for an unanchored pattern fails when the cur- rent 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 con- tains an explicit CR or LF reference, and so advances only by one char- acter 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 escape sequences. Implicit matches such as [^X] do not count, nor does \s (which includes CR and LF in the characters that it matches). Notwithstanding the above, anomalous effects may still occur when CRLF is a valid newline sequence and explicit \r or \n escapes appear in the pattern. HOW PCRE2_MATCH() RETURNS A STRING AND CAPTURED SUBSTRINGS uint32_t pcre2_get_ovector_count(pcre2_match_data *match_data); PCRE2_SIZE *pcre2_get_ovector_pointer(pcre2_match_data *match_data); In general, a pattern matches a certain portion of the subject, and in addition, further substrings from the subject may be picked out by parenthesized parts of the pattern. Following the usage in Jeffrey Friedl's book, this is called "capturing" in what follows, and the phrase "capturing subpattern" is used for a fragment of a pattern that picks out a substring. PCRE2 supports several other kinds of parenthe- sized subpattern that do not cause substrings to be captured. The pcre2_pattern_info() function can be used to find out how many captur- ing subpatterns there are in a compiled pattern. The overall matched string and any captured substrings are returned to the caller via a vector of PCRE2_SIZE values, called the ovector. This is contained within the match data block. You can obtain direct access to the ovector by calling pcre2_get_ovector_pointer() to find its address, and pcre2_get_ovector_count() to find the number of pairs of values it contains. Alternatively, you can use the auxiliary functions for accessing captured substrings by number or by name (see below). Within the ovector, the first in each pair of values is set to the off- set 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 val- ues 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. The first pair of offsets (that is, ovector[0] and ovector[1]) identi- fies the portion of the subject string that was matched by the entire pattern. The next pair is used for the first capturing subpattern, and so on. The value returned by pcre2_match() is one more than the high- est numbered pair that has been set. For example, if two substrings have been captured, the returned value is 3. If there are no capturing subpatterns, the return value from a successful match is 1, indicating that just the first pair of offsets has been set. If a capturing subpattern is matched repeatedly within a single match operation, it is the last portion of the string 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 neither the actual string matched nor any captured substrings are of interest, pcre2_match() may be called with a match data block whose ovector is of zero length. However, if the pattern contains back references and the ovector is not big enough to remember the related substrings, PCRE2 has to get additional memory for use during matching. Thus it is usually advisable to set up a match data block containing an ovector of reasonable size. 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 corre- sponding 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 high- est used capturing subpattern number is 1. The offsets for for the sec- ond 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 cap- turing parentheses, no more than ovector[0] to ovector[2n+1] are set by pcre2_match(). The other elements retain whatever values they previ- ously had. Other information about the match PCRE2_SPTR pcre2_get_mark(pcre2_match_data *match_data); PCRE2_SIZE pcre2_get_leftchar(pcre2_match_data *match_data); PCRE2_SIZE pcre2_get_rightchar(pcre2_match_data *match_data); PCRE2_SIZE pcre2_get_startchar(pcre2_match_data *match_data); In addition to 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. When a (*MARK) name is to be passed back, pcre2_get_mark() returns a pointer to the zero-terminated name, which is within the compiled pat- tern. Otherwise NULL is returned. A (*MARK) name may be available after a failed match or a partial match, as well as after a successful one. The other three functions yield values that give information about the part of the subject string that was inspected during a successful match or a partial match. Their results are undefined after a failed match. They return the following values, respectively: (1) The offset of the leftmost character that was inspected during the match. This can be earlier than the point at which the match started if the pattern contains lookbehind assertions or \b or \B at the start. (2) The offset of the character that follows the rightmost character that was inspected during the match. This can be after the end of the match if the pattern contains lookahead assertions. (3) The offset of the character at which the successful or partial match started. This can be different to the value of ovector[0] if the pattern contains the \K escape sequence. For example, if the pattern (?<=abc)xx\Kyy(?=def) is matched against the string "123abcxxyydef123", the resulting offsets are: ovector[0] 8 ovector[1] 10 leftchar 3 rightchar 13 startchar 6 The allusedtext modifier in pcre2test can be used to display a longer string that shows the leftmost and rightmost characters in a match instead of just the matched string. Error return values from pcre2_match() If pcre2_match() fails, it returns a negative number. This can be con- verted to a text string by calling pcre2_get_error_message(). 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 check- ing is in force and an invalid UTF subject string is detected, one of a number of UTF-specific negative error codes is returned. Details are given in the pcre2unicode page. The following are the other errors that may be returned by pcre2_match(): PCRE2_ERROR_NOMATCH The subject string did not match the pattern. PCRE2_ERROR_PARTIAL The subject string did not match, but it did match partially. See the pcre2partial documentation for details of partial matching. PCRE2_ERROR_BADMAGIC PCRE2 stores a 4-byte "magic number" at the start of the compiled code, to catch the case when it is passed a junk pointer. This is the error that is returned when the magic number is not present. PCRE2_ERROR_BADMODE This error is given when a pattern that was compiled by the 8-bit library is passed to a 16-bit or 32-bit library function, or vice versa. PCRE2_ERROR_BADOFFSET The value of startoffset greater than the length of the subject. PCRE2_ERROR_BADOPTION An unrecognized bit was set in the options argument. PCRE2_ERROR_BADUTFOFFSET The UTF code unit sequence that was passed as a subject was checked and found to be valid (the PCRE2_NO_UTF_CHECK option was not set), but the value of startoffset did not point to the beginning of a UTF character or the end of the subject. PCRE2_ERROR_CALLOUT This error is never generated by pcre2_match() itself. It is provided for use by callout functions that want to cause pcre2_match() to return a distinctive error code. See the pcre2callout documentation for details. PCRE2_ERROR_INTERNAL An unexpected internal error has occurred. This error could be caused by a bug in PCRE2 or by overwriting of the compiled pattern. PCRE2_ERROR_JIT_BADOPTION This error is returned when a pattern that was successfully studied using JIT is being matched, but the matching mode (partial or complete match) does not correspond to any JIT compilation mode. When the JIT fast path function is used, this error may be also given for invalid options. See the pcre2jit documentation for more details. PCRE2_ERROR_JIT_STACKLIMIT This error is returned when a pattern that was successfully studied using JIT is being matched, but the memory available for the just-in- time processing stack is not large enough. See the pcre2jit documenta- tion for more details. PCRE2_ERROR_MATCHLIMIT The backtracking limit was reached. PCRE2_ERROR_NOMEMORY If a pattern contains back references, but the ovector is not big enough to remember the referenced substrings, PCRE2 gets a block of memory at the start of matching to use for this purpose. There are some other special cases where extra memory is needed during matching. This error is given when memory cannot be obtained. PCRE2_ERROR_NULL Either the code, subject, or match_data argument was passed as NULL. PCRE2_ERROR_RECURSELOOP This error is returned when pcre2_match() detects a recursion loop within the pattern. Specifically, it means that either the whole pat- tern or a subpattern has been called recursively for the second time at the same position in the subject string. Some simple patterns that might do this are detected and faulted at compile time, but more com- plicated cases, in particular mutual recursions between two different subpatterns, cannot be detected until run time. PCRE2_ERROR_RECURSIONLIMIT The internal recursion limit was reached. EXTRACTING CAPTURED SUBSTRINGS BY NUMBER int pcre2_substring_length_bynumber(pcre2_match_data *match_data, unsigned int number, PCRE2_SIZE *length); int pcre2_substring_copy_bynumber(pcre2_match_data *match_data, unsigned int number, PCRE2_UCHAR *buffer, PCRE2_SIZE *bufflen); int pcre2_substring_get_bynumber(pcre2_match_data *match_data, unsigned int 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. The functions in this section identify substrings by number. The next section describes similar functions for extracting substrings by name. 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. 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. The pcre2_substring_copy_bynumber() function copies one string 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 func- tions are a pointer to the match data block and a capturing group num- ber. A group number of zero extracts the substring that matched the entire pattern, and higher values extract the captured substrings. 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, 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 these functions is zero for success, or one of these error codes: PCRE2_ERROR_NOMEMORY The buffer was too small for pcre2_substring_copy_bynumber(), or the attempt to get memory failed for pcre2_substring_get_bynumber(). PCRE2_ERROR_NOSUBSTRING No substring with the given number was captured. This could be because there is no capturing group of that number in the pattern, or because the group with that number did not participate in the match, or because the ovector was too small to capture that group. EXTRACTING A LIST OF ALL CAPTURED SUBSTRINGS int pcre2_substring_list_get(pcre2_match_data *match_data, PCRE2_UCHAR ***listptr, PCRE2_SIZE **lengthsptr); void pcre2_substring_list_free(PCRE2_SPTR *list); The pcre2_substring_list_get() function extracts all available sub- strings and builds a list of pointers to them, and 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. 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 argu- ment 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 mem- ory 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 contains PCRE2_UNSET for unset substrings. EXTRACTING CAPTURED SUBSTRINGS BY NAME int pcre2_substring_number_from_name(const pcre2_code *code, PCRE2_SPTR name); int pcre2_substring_length_byname(pcre2_match_data *match_data, PCRE2_SPTR name, PCRE2_SIZE *length); int pcre2_substring_copy_byname(pcre2_match_data *match_data, PCRE2_SPTR name, PCRE2_UCHAR *buffer, PCRE2_SIZE *bufflen); int pcre2_substring_get_byname(pcre2_match_data *match_data, PCRE2_SPTR name, PCRE2_UCHAR **bufferptr, PCRE2_SIZE *bufflen); void pcre2_substring_free(PCRE2_UCHAR *buffer); To extract a substring by name, you first have to find associated num- ber. For example, for this pattern: (a+)b(?\d+)... the number of the subpattern called "xxx" is 2. If the name is known to be unique (PCRE2_DUPNAMES was not set), you can find the number from the name by calling pcre2_substring_number_from_name(). The first argu- ment is the compiled pattern, and the second is the name. The yield of the function is the subpattern number, or PCRE2_ERROR_NOSUBSTRING if there is no subpattern of that name. Given the number, you can extract the substring directly, or use one of the functions described in the previous section. For convenience, there are also "byname" functions that correspond to the "bynumber" func- tions, the only difference being that the second argument is a name instead of a number. However, if PCRE2_DUPNAMES is set and there are duplicate names, the behaviour may not be what you want (see the next section). Warning: If the pattern uses the (?| feature to set up multiple subpat- terns 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. DUPLICATE SUBPATTERN NAMES int pcre2_substring_nametable_scan(const pcre2_code *code, PCRE2_SPTR name, PCRE2_SPTR *first, PCRE2_SPTR *last); When a pattern is compiled with the PCRE2_DUPNAMES option, names for 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. If none are set, PCRE2_ERROR_NOSUBSTRING is returned. The pcre2_substring_number_from_name() function returns one of the numbers that are associated with the name, but it is not defined which it is. 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 (it is not defined which). Otherwise, the third and fourth argu- ments 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 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 above. Given all the relevant entries for the name, you can extract each of their numbers, and hence the captured data. FINDING ALL POSSIBLE MATCHES The traditional matching function uses a similar algorithm to Perl, which stops when it finds the first match, starting 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 alterna- tive function, you can kludge it up by making use of the callout facil- ity, which is described in the pcre2callout documentation. What you have to do is to insert a callout right at the end of the pat- tern. When your callout function is called, extract and save the cur- rent matched substring. Then return 1, which forces pcre2_match() to backtrack and try other alternatives. Ultimately, when it runs out of matches, pcre2_match() will yield PCRE2_ERROR_NOMATCH. MATCHING A PATTERN: THE ALTERNATIVE FUNCTION int pcre2_dfa_match(const pcre2_code *code, PCRE2_SPTR subject, PCRE2_SIZE length, PCRE2_SIZE startoffset, uint32_t options, pcre2_match_data *match_data, pcre2_match_context *mcontext, int *workspace, PCRE2_SIZE wscount); The function pcre2_dfa_match() is called to match a subject string against a compiled pattern, using a matching algorithm that scans the subject string just once, 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. Never- theless, 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 documen- tation. 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 com- mon 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) */ Option bits for pcre_dfa_match() The unused bits of the options argument for pcre2_dfa_match() must be zero. The only bits that may be set are PCRE2_ANCHORED, PCRE2_NOTBOL, PCRE2_NOTEOL, PCRE2_NOTEMPTY, PCRE2_NOTEMPTY_ATSTART, PCRE2_NO_UTF_CHECK, PCRE2_NO_START_OPTIMIZE, PCRE2_PARTIAL_HARD, PCRE2_PARTIAL_SOFT, PCRE2_DFA_SHORTEST, and PCRE2_DFA_RESTART. All but the last four of these are exactly the same as for pcre2_match(), so their description is not repeated here. PCRE2_PARTIAL_HARD PCRE2_PARTIAL_SOFT These have the same general effect as they do for pcre2_match(), but the details are slightly different. When PCRE2_PARTIAL_HARD is set for pcre2_dfa_match(), it returns PCRE2_ERROR_PARTIAL if the end of the subject is reached and there is still at least one matching possibility that requires additional characters. This happens even if some complete matches have already been found. When PCRE2_PARTIAL_SOFT is set, the return code PCRE2_ERROR_NOMATCH is converted into PCRE2_ERROR_PARTIAL if the end of the subject is reached, there have been no complete matches, but there is still at least one matching possibility. The por- tion of the string that was inspected when the longest partial match was found is set as the first matching string in both cases. There is a more detailed discussion of partial and multi-segment matching, with examples, in the pcre2partial documentation. PCRE2_DFA_SHORTEST Setting the PCRE2_DFA_SHORTEST option causes the matching algorithm to stop as soon as it has found one match. Because of the way the alterna- tive algorithm works, this is necessarily the shortest possible match at the first possible matching point in the subject string. PCRE2_DFA_RESTART When pcre2_dfa_match() returns a partial match, it is possible to call it again, with additional subject characters, and have it continue with the same match. The PCRE2_DFA_RESTART option requests this action; when it is set, the workspace and wscount options must reference the same vector as before because data about the match so far is left in them after a partial match. There is more discussion of this facility in the pcre2partial documentation. Successful returns from pcre2_dfa_match() When pcre2_dfa_match() succeeds, it may have matched more than one sub- string in the subject. Note, however, that all the matches from one run of the function start at the same point in the subject. The shorter matches are all initial substrings of the longer matches. For example, if the pattern <.*> is matched against the string This is no more the three matched strings are On success, the yield of the function is a number greater than zero, which is the number of matched substrings. The offsets of the sub- strings are returned in the ovector, and can be extracted in the same way as for pcre2_match(). They are returned in reverse order of length; that is, the longest matching string is given first. If there were too many matches to fit into the ovector, the yield of the func- tion 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++" because there is no point in backtracking into the repeated digits. 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 ("a\d+?") or set the PCRE2_NO_AUTO_POSSESS option when compil- ing. Error returns from pcre2_dfa_match() The pcre2_dfa_match() function returns a negative number when it fails. Many of the errors are the same as for pcre2_match(), as described above. There are in addition the following errors that are specific to pcre2_dfa_match(): PCRE2_ERROR_DFA_UITEM This return is given if pcre2_dfa_match() encounters an item in the pattern that it does not support, for instance, the use of \C or a back reference. PCRE2_ERROR_DFA_UCOND This return is given if pcre2_dfa_match() encounters a condition item that uses a back reference for the condition, or a test for recursion in a specific group. These are not supported. PCRE2_ERROR_DFA_WSSIZE This return is given if pcre2_dfa_match() runs out of space in the workspace vector. PCRE2_ERROR_DFA_RECURSE When a recursive subpattern is processed, the matching function calls itself recursively, using private memory for the ovector and workspace. This error is given if the internal ovector is not large enough. This should be extremely rare, as a vector of size 1000 is used. PCRE2_ERROR_DFA_BADRESTART When pcre2_dfa_match() is called with the pcre2_dfa_RESTART option, some plausibility checks are made on the contents of the workspace, which should contain data about the previous partial match. If any of these checks fail, this error is given. SEE ALSO pcre2build(3), pcre2libs(3), pcre2callout(3), pcre2matching(3), pcre2partial(3), pcre2posix(3), pcre2demo(3), pcre2sample(3), pcre2stack(3). AUTHOR Philip Hazel University Computing Service Cambridge CB2 3QH, England. REVISION Last updated: 16 September 2014 Copyright (c) 1997-2014 University of Cambridge. ------------------------------------------------------------------------------ PCRE2CALLOUT(3) Library Functions Manual PCRE2CALLOUT(3) NAME PCRE2 - Perl-compatible regular expressions (revised API) SYNOPSIS #include int (*pcre2_callout)(pcre2_callout_block *); DESCRIPTION PCRE2 provides a feature called "callout", which is a means of tempo- rarily passing control to the caller of PCRE2 in the middle of pattern matching. The caller of PCRE2 provides an external function by putting its entry point in a match context (see pcre2_set_callout()) in the pcre2api documentation). Within a regular expression, (?C) indicates the points at which the external function is to be called. Different callout points can be identified by putting a number less than 256 after the letter C. The default value is zero. For example, this pattern has two callout points: (?C1)abc(?C2)def If the PCRE2_AUTO_CALLOUT option bit is set when a pattern is compiled, PCRE2 automatically inserts callouts, all with number 255, before each item in the pattern. For example, if PCRE2_AUTO_CALLOUT is used with the pattern A(\d{2}|--) it is processed as if it were (?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255) Notice that there is a callout before and after each parenthesis and alternation bar. If the pattern contains a conditional group whose con- dition is an assertion, an automatic callout is inserted immediately before the condition. Such a callout may also be inserted explicitly, for example: (?(?C9)(?=a)ab|de) This applies only to assertion conditions (because they are themselves independent groups). Automatic callouts can be used for tracking the progress of pattern matching. The pcre2test program has a pattern qualifier (/auto_call- out) that sets automatic callouts; when it is used, the output indi- cates how the pattern is being matched. This is useful information when you are trying to optimize the performance of a particular pattern. MISSING CALLOUTS You should be aware that, because of optimizations in the way PCRE2 compiles and matches patterns, callouts sometimes do not happen exactly as you might expect. At compile time, PCRE2 "auto-possessifies" repeated items when it knows that what follows cannot be part of the repeat. For example, a+[bc] is compiled as if it were a++[bc]. The pcre2test output when this pattern is anchored and then applied with automatic callouts to the string "aaaa" is: --->aaaa +0 ^ ^ +1 ^ a+ +3 ^ ^ [bc] No match This indicates that when matching [bc] fails, there is no backtracking into a+ and therefore the callouts that would be taken for the back- tracks do not occur. You can disable the auto-possessify feature by passing PCRE2_NO_AUTO_POSSESS to pcre2_compile(), or starting the pat- tern with (*NO_AUTO_POSSESS). If this is done in pcre2test (using the /no_auto_possess qualifier), the output changes to this: --->aaaa +0 ^ ^ +1 ^ a+ +3 ^ ^ [bc] +3 ^ ^ [bc] +3 ^ ^ [bc] +3 ^^ [bc] No match This time, when matching [bc] fails, the matcher backtracks into a+ and tries again, repeatedly, until a+ itself fails. Other optimizations that provide fast "no match" results also affect callouts. For example, if the pattern is ab(?C4)cd PCRE2 knows that any matching string must contain the letter "d". If the subject string is "abyz", the lack of "d" means that matching doesn't ever start, and the callout is never reached. However, with "abyd", though the result is still no match, the callout is obeyed. PCRE2 also knows the minimum length of a matching string, and will immediately give a "no match" return without actually running a match if the subject is not long enough, or, for unanchored patterns, if it has been scanned far enough. You can disable these optimizations by passing the PCRE2_NO_START_OPTI- MIZE option to the matching function, or by starting the pattern with (*NO_START_OPT). This slows down the matching process, but does ensure that callouts such as the example above are obeyed. THE CALLOUT INTERFACE During matching, when PCRE2 reaches a callout point, the external func- tion that is set in the match context is called (if it is set). This applies to both normal and DFA matching. The only argument to the call- out function is a pointer to a pcre2_callout block. This structure con- tains the following fields: uint32_t version; uint32_t callout_number; uint32_t capture_top; uint32_t capture_last; void *callout_data; PCRE2_SIZE *offset_vector; PCRE2_SPTR mark; PCRE2_SPTR subject; PCRE2_SIZE subject_length; PCRE2_SIZE start_match; PCRE2_SIZE current_position; PCRE2_SIZE pattern_position; PCRE2_SIZE next_item_length; The version field contains the version number of the block format. The current version is 0. The version number will change in future if addi- tional fields are added, but the intention is never to remove any of the existing fields. The callout_number field contains the number of the callout, as com- piled into the pattern (that is, the number after ?C for manual call- outs, and 255 for automatically generated callouts). The offset_vector field is a pointer to the vector of capturing offsets (the "ovector") that was passed to the matching function in the match data block. When pcre2_match() is used, the contents can be inspected, in order to extract substrings that have been matched so far, in the same way as for extracting substrings after a match has completed. For the DFA matching function, this field is not useful. The subject and subject_length fields contain copies of the values that were passed to the matching function. The start_match field normally contains the offset within the subject at which the current match attempt started. However, if the escape sequence \K has been encountered, this value is changed to reflect the modified starting point. If the pattern is not anchored, the callout function may be called several times from the same point in the pattern for different starting points in the subject. The current_position field contains the offset within the subject of the current match pointer. When the pcre2_match() is used, the capture_top field contains one more than the number of the highest numbered captured substring so far. If no substrings have been captured, the value of capture_top is one. This is always the case when the DFA functions are used, because they do not support captured substrings. The capture_last field contains the number of the most recently cap- tured substring. However, when a recursion exits, the value reverts to what it was outside the recursion, as do the values of all captured substrings. If no substrings have been captured, the value of cap- ture_last is 0. This is always the case for the DFA matching functions. The callout_data field contains a value that is passed to a matching function specifically so that it can be passed back in callouts. It is set in the match context when the callout is set up by calling pcre2_set_callout() (see the pcre2api documentation). The pattern_position field contains the offset to the next item to be matched in the pattern string. The next_item_length field contains the length of the next item to be matched in the pattern string. When the callout immediately precedes an alternation bar, a closing parenthesis, or the end of the pattern, the length is zero. When the callout precedes an opening parenthesis, the length is that of the entire subpattern. The pattern_position and next_item_length fields are intended to help in distinguishing between different automatic callouts, which all have the same callout number. However, they are set for all callouts. In callouts from pcre2_match() the mark field contains a pointer to the zero-terminated name of the most recently passed (*MARK), (*PRUNE), or (*THEN) item in the match, or NULL if no such items have been passed. Instances of (*PRUNE) or (*THEN) without a name do not obliterate a previous (*MARK). In callouts from the DFA matching function this field always contains NULL. RETURN VALUES The external callout function returns an integer to PCRE2. If the value is zero, matching proceeds as normal. If the value is greater than zero, matching fails at the current point, but the testing of other matching possibilities goes ahead, just as if a lookahead assertion had failed. If the value is less than zero, the match is abandoned, and the matching function returns the negative value. Negative values should normally be chosen from the set of PCRE2_ERROR_xxx values. In particular, PCRE2_ERROR_NOMATCH forces a standard "no match" failure. The error number PCRE2_ERROR_CALLOUT is reserved for use by callout functions; it will never be used by PCRE2 itself. AUTHOR Philip Hazel University Computing Service Cambridge CB2 3QH, England. REVISION Last updated: 19 October 2014 Copyright (c) 1997-2014 University of Cambridge. ------------------------------------------------------------------------------ PCRE2UNICODE(3) Library Functions Manual PCRE2UNICODE(3) NAME PCRE - Perl-compatible regular expressions (revised API) UNICODE AND UTF SUPPORT When PCRE2 is built with Unicode support, it acquires knowledge of Uni- code character properties and can process text strings in UTF-8, UTF-16, or UTF-32 format (depending on the code unit width). By default, PCRE2 assumes that one code unit is one character. To process a pattern as a UTF string, where a character may require more than one code unit, you must call pcre2_compile() with the PCRE2_UTF option flag, or the pattern must start with the sequence (*UTF). When either of these is the case, both the pattern and any subject strings that are matched against it are treated as UTF strings instead of strings of individual one-code-unit characters. If you build PCRE2 with Unicode support, the library will be bigger, but the additional run time overhead is limited to testing the PCRE2_UTF flag occasionally, so should not be very much. UNICODE PROPERTY SUPPORT When PCRE2 is built with Unicode support, the escape sequences \p{..}, \P{..}, and \X can be used. The Unicode properties that can be tested are limited to the general category properties such as Lu for an upper case letter or Nd for a decimal number, the Unicode script names such as Arabic or Han, and the derived properties Any and L&. Full lists are given in the pcre2pattern and pcre2syntax documentation. Only the short names for properties are supported. For example, \p{L} matches a let- ter. Its Perl synonym, \p{Letter}, is not supported. Furthermore, in Perl, many properties may optionally be prefixed by "Is", for compati- bility with Perl 5.6. PCRE does not support this. WIDE CHARACTERS AND UTF MODES Codepoints less than 256 can be specified in patterns by either braced or unbraced hexadecimal escape sequences (for example, \x{b3} or \xb3). Larger values have to use braced sequences. Unbraced octal code points up to \777 are also recognized; larger ones can be coded using \o{...}. In UTF modes, repeat quantifiers apply to complete UTF characters, not to individual code units. In UTF modes, the dot metacharacter matches one UTF character instead of a single code unit. The escape sequence \C can be used to match a single code unit, in a UTF mode, but its use can lead to some strange effects because it breaks up multi-unit characters (see the description of \C in the pcre2pattern documentation). The use of \C is not supported in the alternative matching function pcre2_dfa_exec(), nor is it supported in UTF mode by the JIT optimization. If JIT optimization is requested for a UTF pattern that contains \C, it will not succeed, and so the match- ing will be carried out by the normal interpretive function. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly test characters of any code value, but, by default, the characters that PCRE2 recognizes as digits, spaces, or word characters remain the same set as in non-UTF mode, all with code points less than 256. This remains true even when PCRE2 is built to include Unicode support, because to do otherwise would slow down matching in many common cases. Note that this also applies to \b and \B, because they are defined in terms of \w and \W. If you want to test for a wider sense of, say, "digit", you can use explicit Unicode property tests such as \p{Nd}. Alternatively, if you set the PCRE2_UCP option, the way that the char- acter escapes work is changed so that Unicode properties are used to determine which characters match. There are more details in the section on generic character types in the pcre2pattern documentation. Similarly, characters that match the POSIX named character classes are all low-valued characters, unless the PCRE2_UCP option is set. However, the special horizontal and vertical white space matching escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char- acters, whether or not PCRE2_UCP is set. Case-insensitive matching in UTF mode makes use of Unicode properties. A few Unicode characters such as Greek sigma have more than two code- points that are case-equivalent, and these are treated as such. VALIDITY OF UTF STRINGS When the PCRE2_UTF option is set, the strings passed as patterns and subjects are (by default) checked for validity on entry to the relevant functions. If an invalid UTF string is passed, an error return is given. UTF-16 and UTF-32 strings can indicate their endianness by special code knows as a byte-order mark (BOM). The PCRE2 functions do not handle this, expecting strings to be in host byte order. The entire string is checked before any other processing takes place. In addition to checking the format of the string, there is a check to ensure that all code points lie in the range U+0 to U+10FFFF, excluding the surrogate area. The so-called "non-character" code points are not excluded because Unicode corrigendum #9 makes it clear that they should not be. Characters in the "Surrogate Area" of Unicode are reserved for use by UTF-16, where they are used in pairs to encode code points with values greater than 0xFFFF. The code points that are encoded by UTF-16 pairs are available independently in the UTF-8 and UTF-32 encodings. (In other words, the whole surrogate thing is a fudge for UTF-16 which unfortunately messes up UTF-8 and UTF-32.) In some situations, you may already know that your strings are valid, and therefore want to skip these checks in order to improve perfor- mance, for example in the case of a long subject string that is being scanned repeatedly. If you set the PCRE2_NO_UTF_CHECK flag at compile time or at run time, PCRE2 assumes that the pattern or subject it is given (respectively) contains only valid UTF code unit sequences. Passing PCRE2_NO_UTF_CHECK to pcre2_compile() just disables the check for the pattern; it does not also apply to subject strings. If you want to disable the check for a subject string you must pass this option to pcre2_exec() or pcre2_dfa_exec(). If you pass an invalid UTF string when PCRE2_NO_UTF_CHECK is set, the result is undefined and your program may crash or loop indefinitely. Errors in UTF-8 strings The following negative error codes are given for invalid UTF-8 strings: PCRE2_ERROR_UTF8_ERR1 PCRE2_ERROR_UTF8_ERR2 PCRE2_ERROR_UTF8_ERR3 PCRE2_ERROR_UTF8_ERR4 PCRE2_ERROR_UTF8_ERR5 The string ends with a truncated UTF-8 character; the code specifies how many bytes are missing (1 to 5). Although RFC 3629 restricts UTF-8 characters to be no longer than 4 bytes, the encoding scheme (origi- nally defined by RFC 2279) allows for up to 6 bytes, and this is checked first; hence the possibility of 4 or 5 missing bytes. PCRE2_ERROR_UTF8_ERR6 PCRE2_ERROR_UTF8_ERR7 PCRE2_ERROR_UTF8_ERR8 PCRE2_ERROR_UTF8_ERR9 PCRE2_ERROR_UTF8_ERR10 The two most significant bits of the 2nd, 3rd, 4th, 5th, or 6th byte of the character do not have the binary value 0b10 (that is, either the most significant bit is 0, or the next bit is 1). PCRE2_ERROR_UTF8_ERR11 PCRE2_ERROR_UTF8_ERR12 A character that is valid by the RFC 2279 rules is either 5 or 6 bytes long; these code points are excluded by RFC 3629. PCRE2_ERROR_UTF8_ERR13 A 4-byte character has a value greater than 0x10fff; these code points are excluded by RFC 3629. PCRE2_ERROR_UTF8_ERR14 A 3-byte character has a value in the range 0xd800 to 0xdfff; this range of code points are reserved by RFC 3629 for use with UTF-16, and so are excluded from UTF-8. PCRE2_ERROR_UTF8_ERR15 PCRE2_ERROR_UTF8_ERR16 PCRE2_ERROR_UTF8_ERR17 PCRE2_ERROR_UTF8_ERR18 PCRE2_ERROR_UTF8_ERR19 A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it codes for a value that can be represented by fewer bytes, which is invalid. For example, the two bytes 0xc0, 0xae give the value 0x2e, whose cor- rect coding uses just one byte. PCRE2_ERROR_UTF8_ERR20 The two most significant bits of the first byte of a character have the binary value 0b10 (that is, the most significant bit is 1 and the sec- ond is 0). Such a byte can only validly occur as the second or subse- quent byte of a multi-byte character. PCRE2_ERROR_UTF8_ERR21 The first byte of a character has the value 0xfe or 0xff. These values can never occur in a valid UTF-8 string. Errors in UTF-16 strings The following negative error codes are given for invalid UTF-16 strings: PCRE_UTF16_ERR1 Missing low surrogate at end of string PCRE_UTF16_ERR2 Invalid low surrogate follows high surrogate PCRE_UTF16_ERR3 Isolated low surrogate Errors in UTF-32 strings The following negative error codes are given for invalid UTF-32 strings: PCRE_UTF32_ERR1 Surrogate character (range from 0xd800 to 0xdfff) PCRE_UTF32_ERR2 Code point is greater than 0x10ffff AUTHOR Philip Hazel University Computing Service Cambridge CB2 3QH, England. REVISION Last updated: 16 September 2014 Copyright (c) 1997-2014 University of Cambridge. ------------------------------------------------------------------------------