Provided by: libpcre2-dev_10.21-1_amd64 
NAME
PCRE2 - Perl-compatible regular expressions (revised API)
#include <pcre2.h>
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);
void pcre2_code_free(pcre2_code *code);
pcre2_match_data *pcre2_match_data_create(uint32_t ovecsize,
pcre2_general_context *gcontext);
pcre2_match_data *pcre2_match_data_create_from_pattern(
const pcre2_code *code, pcre2_general_context *gcontext);
int pcre2_match(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext);
int pcre2_dfa_match(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext,
int *workspace, PCRE2_SIZE wscount);
void pcre2_match_data_free(pcre2_match_data *match_data);
PCRE2 NATIVE API AUXILIARY MATCH FUNCTIONS
PCRE2_SPTR pcre2_get_mark(pcre2_match_data *match_data);
uint32_t pcre2_get_ovector_count(pcre2_match_data *match_data);
PCRE2_SIZE *pcre2_get_ovector_pointer(pcre2_match_data *match_data);
PCRE2_SIZE pcre2_get_startchar(pcre2_match_data *match_data);
PCRE2 NATIVE API GENERAL CONTEXT FUNCTIONS
pcre2_general_context *pcre2_general_context_create(
void *(*private_malloc)(PCRE2_SIZE, void *),
void (*private_free)(void *, void *), void *memory_data);
pcre2_general_context *pcre2_general_context_copy(
pcre2_general_context *gcontext);
void pcre2_general_context_free(pcre2_general_context *gcontext);
PCRE2 NATIVE API COMPILE CONTEXT FUNCTIONS
pcre2_compile_context *pcre2_compile_context_create(
pcre2_general_context *gcontext);
pcre2_compile_context *pcre2_compile_context_copy(
pcre2_compile_context *ccontext);
void pcre2_compile_context_free(pcre2_compile_context *ccontext);
int pcre2_set_bsr(pcre2_compile_context *ccontext,
uint32_t value);
int pcre2_set_character_tables(pcre2_compile_context *ccontext,
const unsigned char *tables);
int pcre2_set_max_pattern_length(pcre2_compile_context *ccontext,
PCRE2_SIZE value);
int pcre2_set_newline(pcre2_compile_context *ccontext,
uint32_t value);
int pcre2_set_parens_nest_limit(pcre2_compile_context *ccontext,
uint32_t value);
int pcre2_set_compile_recursion_guard(pcre2_compile_context *ccontext,
int (*guard_function)(uint32_t, void *), void *user_data);
PCRE2 NATIVE API MATCH CONTEXT FUNCTIONS
pcre2_match_context *pcre2_match_context_create(
pcre2_general_context *gcontext);
pcre2_match_context *pcre2_match_context_copy(
pcre2_match_context *mcontext);
void pcre2_match_context_free(pcre2_match_context *mcontext);
int pcre2_set_callout(pcre2_match_context *mcontext,
int (*callout_function)(pcre2_callout_block *, void *),
void *callout_data);
int pcre2_set_match_limit(pcre2_match_context *mcontext,
uint32_t value);
int pcre2_set_offset_limit(pcre2_match_context *mcontext,
PCRE2_SIZE 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,
uint32_t number, PCRE2_UCHAR *buffer,
PCRE2_SIZE *bufflen);
void pcre2_substring_free(PCRE2_UCHAR *buffer);
int pcre2_substring_get_byname(pcre2_match_data *match_data,
PCRE2_SPTR name, PCRE2_UCHAR **bufferptr, PCRE2_SIZE *bufflen);
int pcre2_substring_get_bynumber(pcre2_match_data *match_data,
uint32_t number, PCRE2_UCHAR **bufferptr,
PCRE2_SIZE *bufflen);
int pcre2_substring_length_byname(pcre2_match_data *match_data,
PCRE2_SPTR name, PCRE2_SIZE *length);
int pcre2_substring_length_bynumber(pcre2_match_data *match_data,
uint32_t number, PCRE2_SIZE *length);
int pcre2_substring_nametable_scan(const pcre2_code *code,
PCRE2_SPTR name, PCRE2_SPTR *first, PCRE2_SPTR *last);
int pcre2_substring_number_from_name(const pcre2_code *code,
PCRE2_SPTR name);
void pcre2_substring_list_free(PCRE2_SPTR *list);
int pcre2_substring_list_get(pcre2_match_data *match_data,
PCRE2_UCHAR ***listptr, PCRE2_SIZE **lengthsptr);
PCRE2 NATIVE API STRING SUBSTITUTION FUNCTION
int pcre2_substitute(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext, PCRE2_SPTR replacementzfP,
PCRE2_SIZE rlength, PCRE2_UCHAR *outputbuffer,
PCRE2_SIZE *outlengthptr);
PCRE2 NATIVE API JIT FUNCTIONS
int pcre2_jit_compile(pcre2_code *code, uint32_t options);
int pcre2_jit_match(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext);
void pcre2_jit_free_unused_memory(pcre2_general_context *gcontext);
pcre2_jit_stack *pcre2_jit_stack_create(PCRE2_SIZE startsize,
PCRE2_SIZE maxsize, pcre2_general_context *gcontext);
void pcre2_jit_stack_assign(pcre2_match_context *mcontext,
pcre2_jit_callback callback_function, void *callback_data);
void pcre2_jit_stack_free(pcre2_jit_stack *jit_stack);
PCRE2 NATIVE API SERIALIZATION FUNCTIONS
int32_t pcre2_serialize_decode(pcre2_code **codes,
int32_t number_of_codes, const uint8_t *bytes,
pcre2_general_context *gcontext);
int32_t pcre2_serialize_encode(const pcre2_code **codes,
int32_t number_of_codes, uint8_t **serialized_bytes,
PCRE2_SIZE *serialized_size, pcre2_general_context *gcontext);
void pcre2_serialize_free(uint8_t *bytes);
int32_t pcre2_serialize_get_number_of_codes(const uint8_t *bytes);
PCRE2 NATIVE API AUXILIARY FUNCTIONS
int pcre2_get_error_message(int errorcode, PCRE2_UCHAR *buffer,
PCRE2_SIZE bufflen);
const unsigned char *pcre2_maketables(pcre2_general_context *gcontext);
int pcre2_pattern_info(const pcre2 *code, uint32_t what, void *where);
int pcre2_callout_enumerate(const pcre2_code *code,
int (*callback)(pcre2_callout_enumerate_block *, void *),
void *user_data);
int pcre2_config(uint32_t what, void *where);
PCRE2 8-BIT, 16-BIT, AND 32-BIT LIBRARIES
There are three PCRE2 libraries, supporting 8-bit, 16-bit, and 32-bit code units,
respectively. However, there is just one header file, pcre2.h. This contains the function
prototypes and other definitions for all three libraries. One, two, or all three can be
installed simultaneously. On Unix-like systems the libraries are called libpcre2-8,
libpcre2-16, and libpcre2-32, and they can also co-exist with the original PCRE libraries.
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_compile() and PCRE2_SPTR. These macros use
the value of the macro PCRE2_CODE_UNIT_WIDTH to generate the appropriate width-specific
function and macro names. PCRE2_CODE_UNIT_WIDTH is not defined by default. An application
must define it to be 8, 16, or 32 before including pcre2.h in order to make use of the
generic names.
Applications that use more than one code unit width can be linked with more than one PCRE2
library, but must define PCRE2_CODE_UNIT_WIDTH to be 0 before including pcre2.h, and then
use the real function names. Any code that is to be included in an environment where the
value of PCRE2_CODE_UNIT_WIDTH is unknown should also use the real function names.
(Unfortunately, it is not possible in C code to save and restore the value of a macro.)
If PCRE2_CODE_UNIT_WIDTH is not defined before including pcre2.h, a compiler error occurs.
When using multiple libraries in an application, you must take care when processing any
particular pattern to use only functions from a single library. For example, if you want
to run a match using a pattern that was compiled with pcre2_compile_16(), you must do so
with pcre2_match_16(), not pcre2_match_8().
In the function summaries above, and in the rest of this document and other PCRE2
documents, functions and data types are described using their generic names, without the
8, 16, or 32 suffix.
PCRE2 API OVERVIEW
PCRE2 has its own native API, which is described in this document. There are also some
wrapper functions for the 8-bit library that correspond to the POSIX regular expression
API, but they do not give access to all the functionality. They are described in the
pcre2posix documentation. Both these APIs define a set of C function calls.
The native API C data types, function prototypes, option values, and error codes are
defined in the header file pcre2.h, which contains definitions of PCRE2_MAJOR and
PCRE2_MINOR, the major and minor release numbers for the library. Applications can use
these to include support for different releases of PCRE2.
In a Windows environment, if you want to statically link an application program against a
non-dll PCRE2 library, you must define PCRE2_STATIC before including pcre2.h.
The functions pcre2_compile(), and pcre2_match() are used for compiling and matching
regular expressions in a Perl-compatible manner. A sample program that demonstrates the
simplest way of using them is provided in the file called pcre2demo.c in the PCRE2 source
distribution. A listing of this program is given in the pcre2demo documentation, and the
pcre2sample documentation describes how to compile and run it.
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_create(), pcre2_jit_stack_free(), and pcre2_jit_stack_assign() in order to
control the JIT code's memory usage.
JIT matching is automatically used by pcre2_match() if it is available. 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_match(), which is not Perl-compatible, is also
provided. This uses a different algorithm for the matching. The alternative algorithm
finds all possible matches (at a given point in the subject), and scans the subject just
once (unless there are 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 documentation. There is no JIT support for
pcre2_dfa_match().
In addition to the main compiling and matching functions, there are convenience functions
for extracting captured substrings from a subject string that has been matched by
pcre2_match(). They are:
pcre2_substring_copy_byname()
pcre2_substring_copy_bynumber()
pcre2_substring_get_byname()
pcre2_substring_get_bynumber()
pcre2_substring_list_get()
pcre2_substring_length_byname()
pcre2_substring_length_bynumber()
pcre2_substring_nametable_scan()
pcre2_substring_number_from_name()
pcre2_substring_free() and pcre2_substring_list_free() are also provided, to free the
memory used for extracted strings.
The function pcre2_substitute() can be called to match a pattern and return a copy of the
subject string with substitutions for parts that were matched.
Finally, there are functions for finding out information about a compiled pattern
(pcre2_pattern_info()) and about the configuration with which PCRE2 was built
(pcre2_config()).
STRING LENGTHS AND OFFSETS
The PCRE2 API uses string lengths and offsets into strings of code units in several
places. These values are always of type PCRE2_SIZE, which is an unsigned integer type,
currently always defined as size_t. The largest value that can be stored in such a type
(that is ~(PCRE2_SIZE)0) is reserved as a special indicator for zero-terminated strings
and unset offsets. Therefore, the longest string that can be handled is one less than
this maximum.
NEWLINES
PCRE2 supports five different conventions for indicating line breaks in strings: a single
CR (carriage return) character, a single LF (linefeed) character, the two-character
sequence CRLF, any of the three preceding, or any Unicode newline sequence. The Unicode
newline sequences are the three just mentioned, plus the single characters VT (vertical
tab, U+000B), FF (form feed, U+000C), NEL (next line, U+0085), LS (line separator,
U+2028), and PS (paragraph separator, U+2029).
Each of the first three conventions is used by at least one operating system as its
standard newline sequence. When PCRE2 is built, a default can be specified. The default
default is LF, which is the Unix standard. However, the newline convention can be changed
by an application when calling pcre2_compile(), or it can be specified by special text at
the start of the pattern itself; this overrides any other settings. See the pcre2pattern
page for details of the special character sequences.
In the PCRE2 documentation the word "newline" is used to mean "the character or pair of
characters that indicate a line break". The choice of newline convention affects the
handling of the dot, circumflex, and dollar metacharacters, the handling of #-comments in
/x mode, and, when CRLF is a recognized line ending sequence, the match position
advancement for a non-anchored pattern. There is more detail about this in the section on
pcre2_match() options below.
The choice of newline convention does not affect the interpretation of the \n or \r escape
sequences, nor does it affect what \R matches; this has its own separate convention.
MULTITHREADING
In a multithreaded application it is important to keep thread-specific data separate from
data that can be shared between threads. The PCRE2 library code itself is thread-safe: it
contains no static or global variables. The API is designed to be fairly simple for non-
threaded applications while at the same time ensuring that multithreaded applications can
use it.
There are several different blocks of data that are used to pass information between the
application and the PCRE2 libraries.
(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 patterns 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 values that are never
changed, the same context can be used by all the threads. However, if any thread needs to
change any value in a context, it must make its own thread-specific copy.
(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 memory.
PCRE2 CONTEXTS
Some PCRE2 functions have a lot of parameters, many of which are used only by specialist
applications, for example, those that use custom memory management or non-standard
character tables. To keep function argument lists at a reasonable size, and at the same
time to keep the API extensible, "uncommon" parameters are passed to certain functions in
a context instead of directly. A context is just a block of memory that holds the
parameter values. Applications that do not need to 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 functions 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
The maximum length of the pattern string
An external function for stack checking
A compile context is also required if you are using custom memory management. If none of
these apply, just pass NULL as the context argument of pcre2_compile().
A compile context is created, copied, and freed by the following functions:
pcre2_compile_context *pcre2_compile_context_create(
pcre2_general_context *gcontext);
pcre2_compile_context *pcre2_compile_context_copy(
pcre2_compile_context *ccontext);
void pcre2_compile_context_free(pcre2_compile_context *ccontext);
A compile context is created with default values for its parameters. These can be changed
by calling the following functions, which return 0 on success, or PCRE2_ERROR_BADDATA if
invalid data is detected.
int pcre2_set_bsr(pcre2_compile_context *ccontext,
uint32_t value);
The value must be PCRE2_BSR_ANYCRLF, to specify that \R matches only CR, LF, or CRLF, or
PCRE2_BSR_UNICODE, to specify that \R matches any Unicode line ending sequence. The value
is used by the JIT compiler and by the two interpreted matching functions, pcre2_match()
and pcre2_dfa_match().
int pcre2_set_character_tables(pcre2_compile_context *ccontext,
const unsigned char *tables);
The value must be the result of a call to pcre2_maketables(), whose only argument is a
general context. This function builds a set of character tables in the current locale.
int pcre2_set_max_pattern_length(pcre2_compile_context *ccontext,
PCRE2_SIZE value);
This sets a maximum length, in code units, for the pattern string that is to be compiled.
If the pattern is longer, an error is generated. This facility is provided so that
applications that accept patterns from external sources can limit their size. The default
is the largest number that a PCRE2_SIZE variable can hold, which is effectively unlimited.
int pcre2_set_newline(pcre2_compile_context *ccontext,
uint32_t value);
This specifies which characters or character sequences are to be recognized as newlines.
The value must be one of PCRE2_NEWLINE_CR (carriage return only), PCRE2_NEWLINE_LF
(linefeed only), PCRE2_NEWLINE_CRLF (the two-character sequence CR followed by LF),
PCRE2_NEWLINE_ANYCRLF (any of the above), 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 interpreted matching functions, pcre2_match() and pcre2_dfa_match().
int pcre2_set_parens_nest_limit(pcre2_compile_context *ccontext,
uint32_t value);
This parameter ajusts the limit, set when PCRE2 is built (default 250), on the depth of
parenthesis nesting in a pattern. This limit stops rogue patterns using up too much system
stack when being compiled.
int pcre2_set_compile_recursion_guard(pcre2_compile_context *ccontext,
int (*guard_function)(uint32_t, void *), void *user_data);
There is at least one application that runs PCRE2 in threads with very limited system
stack, where running out of stack is to be avoided at all costs. The parenthesis limit
above cannot take account of how much stack is actually available. For a finer control,
you can supply a function that is called whenever pcre2_compile() starts to compile a
parenthesized part of a pattern. This function can check the actual stack size (or
anything else that it wants to, of course).
The first argument to the callout function gives the current depth of nesting, and the
second is user data that is set up by the last argument of
pcre2_set_compile_recursion_guard(). The callout function should return zero if all is
well, or non-zero to force an error.
The match context
A match context is required if you want to change the default values of any of the
following match-time parameters:
A callout function
The offset limit for matching an unanchored pattern
The limit for calling match() (see below)
The limit for calling match() recursively
A match context is also required if you are using custom memory management. If none of
these apply, just pass NULL as the context argument of pcre2_match(), pcre2_dfa_match(),
or pcre2_jit_match().
A match context is created, copied, and freed by the following functions:
pcre2_match_context *pcre2_match_context_create(
pcre2_general_context *gcontext);
pcre2_match_context *pcre2_match_context_copy(
pcre2_match_context *mcontext);
void pcre2_match_context_free(pcre2_match_context *mcontext);
A match context is created with default values for its parameters. These can be changed by
calling the following functions, which return 0 on success, or PCRE2_ERROR_BADDATA if
invalid data is detected.
int pcre2_set_callout(pcre2_match_context *mcontext,
int (*callout_function)(pcre2_callout_block *, void *),
void *callout_data);
This sets up a "callout" function, which PCRE2 will call at specified points during a
matching operation. Details are given in the pcre2callout documentation.
int pcre2_set_offset_limit(pcre2_match_context *mcontext,
PCRE2_SIZE value);
The offset_limit parameter limits how far an unanchored search can advance in the subject
string. The default value is PCRE2_UNSET. The pcre2_match() and pcre2_dfa_match()
functions return PCRE2_ERROR_NOMATCH if a match with a starting point before or at the
given offset is not found. For example, if the pattern /abc/ is matched against "123abc"
with an offset limit less than 3, the result is PCRE2_ERROR_NO_MATCH. A match can never
be found if the startoffset argument of pcre2_match() or pcre2_dfa_match() is greater than
the offset limit.
When using this facility, you must set PCRE2_USE_OFFSET_LIMIT when calling pcre2_compile()
so that when JIT is in use, different code can be compiled. If a match is started with a
non-default match limit when PCRE2_USE_OFFSET_LIMIT is not set, an error is generated.
The offset limit facility can be used to track progress when searching large subject
strings. See also the PCRE2_FIRSTLINE option, which requires a match to start within the
first line of the subject. If this is set with an offset limit, a match must occur in the
first line and also within the offset limit. In other words, whichever limit comes first
is used.
int pcre2_set_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 unlimited 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 processed by
pcre2_jit_compile(), the way in which matching is executed is entirely different. However,
there is still the possibility of runaway matching that goes on for a very long time, and
so the match_limit value is also used in this case (but in a different way) to limit how
long the matching can continue.
The default value for the limit can be set when PCRE2 is built; the default default is 10
million, which handles all but the most extreme cases. If the limit is exceeded,
pcre2_match() returns PCRE2_ERROR_MATCHLIMIT. A value for the match limit may also be
supplied by an item at the start of a pattern of the form
(*LIMIT_MATCH=ddd)
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 recursive. 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_RECURSIONLIMIT. 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_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 limited 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 management functions are used, if
supplied, otherwise the system functions.
CHECKING BUILD-TIME OPTIONS
int pcre2_config(uint32_t what, void *where);
The function pcre2_config() makes it possible for a PCRE2 client to discover which
optional features have been compiled into the PCRE2 library. The pcre2build documentation
has more details about these optional features.
The first argument for pcre2_config() specifies which information is required. The second
argument is a pointer to memory into which the information is placed. If NULL is passed,
the function returns the amount of memory that is needed for the requested information.
For calls that return numerical values, the value is in bytes; when requesting these
values, where should point to appropriately aligned memory. For calls that return strings,
the required length is given in code units, not counting the terminating zero.
When requesting information, the returned value from pcre2_config() is non-negative on
success, or the negative error code PCRE2_ERROR_BADOPTION if the value in the first
argument is not recognized. The following information is available:
PCRE2_CONFIG_BSR
The output is a uint32_t integer whose value indicates what character sequences the \R
escape sequence matches by default. A value of PCRE2_BSR_UNICODE means that \R matches any
Unicode line ending sequence; a value of PCRE2_BSR_ANYCRLF means that \R matches only CR,
LF, or CRLF. The default can be overridden when a pattern is compiled.
PCRE2_CONFIG_JIT
The output is a uint32_t integer that is set to one if support for just-in-time compiling
is available; otherwise it is set to zero.
PCRE2_CONFIG_JITTARGET
The where argument should point to a buffer that is at least 48 code units long. (The
exact length required can be found by calling pcre2_config() with where set to NULL.) The
buffer is filled with a string that contains the name of the architecture for which the
JIT compiler is configured, for example "x86 32bit (little endian + unaligned)". If JIT
support is not available, PCRE2_ERROR_BADOPTION is returned, otherwise the number of code
units used is returned. This is the length of the string, plus one unit for the
terminating zero.
PCRE2_CONFIG_LINKSIZE
The output is a uint32_t integer that contains the number of bytes used for internal
linkage in compiled regular expressions. When PCRE2 is configured, the value can be set to
2, 3, or 4, with the default being 2. This is the value that is returned by
pcre2_config(). However, when the 16-bit library is compiled, a value of 3 is rounded up
to 4, and when the 32-bit library is compiled, internal linkages always use 4 bytes, so
the configured value is not relevant.
The default value of 2 for the 8-bit and 16-bit libraries is sufficient for all but the
most massive patterns, since it allows the size of the compiled pattern to be up to 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 a uint32_t integer that gives the default limit for the number of internal
matching function calls in a pcre2_match() execution. Further details are given with
pcre2_match() below.
PCRE2_CONFIG_NEWLINE
The output is a uint32_t integer whose value specifies the default character sequence that
is recognized as meaning "newline". The values are:
PCRE2_NEWLINE_CR Carriage return (CR)
PCRE2_NEWLINE_LF Linefeed (LF)
PCRE2_NEWLINE_CRLF Carriage return, linefeed (CRLF)
PCRE2_NEWLINE_ANY Any Unicode line ending
PCRE2_NEWLINE_ANYCRLF Any of CR, LF, or CRLF
The default should normally correspond to the standard sequence for your operating system.
PCRE2_CONFIG_PARENSLIMIT
The output is a uint32_t integer that gives the maximum depth of nesting of parentheses
(of any kind) in a pattern. This limit is imposed to cap the amount of system stack used
when a pattern is compiled. It is specified when PCRE2 is built; the default is 250. This
limit does not take into account the stack that may already be used by the calling
application. For finer control over compilation stack usage, see
pcre2_set_compile_recursion_guard().
PCRE2_CONFIG_RECURSIONLIMIT
The output is a uint32_t 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 a uint32_t 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. (The
exact length required can be found by calling pcre2_config() with where set to NULL.) If
PCRE2 has been compiled without Unicode support, the buffer is filled with the text
"Unicode not supported". Otherwise, the Unicode version string (for example, "8.0.0") is
inserted. The number of code units used is returned. This is the length of the string plus
one unit for the terminating zero.
PCRE2_CONFIG_UNICODE
The output is a uint32_t integer that is set to one if Unicode support is available;
otherwise it is set to zero. Unicode support implies UTF support.
PCRE2_CONFIG_VERSION
The where argument should point to a buffer that is at least 12 code units long. (The
exact length required can be found by calling pcre2_config() with where set to NULL.) The
buffer is filled with the PCRE2 version string, zero-terminated. The number of code units
used is returned. This is the length of the string plus one unit for the terminating zero.
COMPILING A PATTERN
pcre2_code *pcre2_compile(PCRE2_SPTR pattern, PCRE2_SIZE length,
uint32_t options, int *errorcode, PCRE2_SIZE *erroroffset,
pcre2_compile_context *ccontext);
void pcre2_code_free(pcre2_code *code);
The pcre2_compile() function compiles a pattern into an internal form. The pattern is
defined by a pointer to a string of code units and a length, If the pattern is zero-
terminated, the length can be specified as PCRE2_ZERO_TERMINATED. The function returns a
pointer to a block of memory that contains the compiled pattern and related data. The
caller must free the memory by calling pcre2_code_free() when it is no longer needed.
NOTE: When one of the matching functions is called, pointers to the compiled pattern and
the subject string are set in the match data block so that they can be referenced by the
extraction functions. After running a match, you must not free a compiled pattern (or a
subject string) until after all operations on the match data block have taken place.
If the compile context argument ccontext is NULL, memory for the compiled pattern is
obtained by calling malloc(). Otherwise, it is obtained from the same memory function that
was used for the compile context.
The options argument contains various bit settings that affect the compilation. It should
be zero if no options are required. The available options are described below. Some of
them (in particular, those that are compatible with Perl, but some others as well) can
also be set and unset from within the pattern (see the detailed description in the
pcre2pattern documentation).
For those options that can be different in different parts of the pattern, the contents of
the options argument specifies their settings at the start of compilation. The
PCRE2_ANCHORED and PCRE2_NO_UTF_CHECK options can be set at the time of matching as well
as at compile time.
Other, less frequently required compile-time parameters (for example, the newline setting)
can be provided in a compile context (as described above).
If errorcode or erroroffset is NULL, pcre2_compile() returns NULL immediately. Otherwise,
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 character.
This code fragment shows a typical straightforward call to pcre2_compile():
pcre2_code *re;
PCRE2_SIZE erroffset;
int errorcode;
re = pcre2_compile(
"^A.*Z", /* the pattern */
PCRE2_ZERO_TERMINATED, /* the pattern is zero-terminated */
0, /* default options */
&errorcode, /* for error code */
&erroffset, /* for error offset */
NULL); /* no compile context */
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 compile time error
(Perl uses \U to upper case subsequent characters).
(2) \u matches a lower case "u" character unless it is followed by four hexadecimal
digits, in which case the hexadecimal number defines the code point to match. By default,
\u causes a compile time error (Perl uses it to upper case the following character).
(3) \x matches a lower case "x" character unless it is followed by two hexadecimal digits,
in which case the hexadecimal number defines the code point to match. By default, as in
Perl, a hexadecimal number is always expected after \x, but it may have zero, one, or two
digits (so, for example, \xz matches a binary zero character followed by z).
PCRE2_ALT_CIRCUMFLEX
In multiline mode (when PCRE2_MULTILINE is set), the circumflex metacharacter matches at
the start of the subject (unless PCRE2_NOTBOL is set), and also after any internal
newline. However, it does not match after a newline at the end of the subject, for
compatibility with Perl. If you want a multiline circumflex also to match after a
terminating newline, you must set PCRE2_ALT_CIRCUMFLEX.
PCRE2_ALT_VERBNAMES
By default, for compatibility with Perl, the name in any verb sequence such as
(*MARK:NAME) is any sequence of characters that does not include a closing parenthesis.
The name is not processed in any way, and it is not possible to include a closing
parenthesis in the name. However, if the PCRE2_ALT_VERBNAMES option is set, normal
backslash processing is applied to verb names and only an unescaped closing parenthesis
terminates the name. A closing parenthesis can be included in a name either as \) or
between \Q and \E. If the PCRE2_EXTENDED option is set, unescaped whitespace in verb names
is skipped and #-comments are recognized, exactly as in the rest of the pattern.
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 subject 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 negative 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. However, white space is not allowed within
sequences such as (?> that introduce various parenthesized subpatterns, nor within
numerical quantifiers such as {1,3}. Ignorable white space is permitted between an item
and a following quantifier and between a quantifier and a following + 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 setting in the compile
context that is passed to pcre2_compile() or by a special sequence at the start of the
pattern, as described in the section entitled "Newline conventions" in the pcre2pattern
documentation. A default is defined when PCRE2 is built.
PCRE2_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. See
also PCRE2_USE_OFFSET_LIMIT, which provides a more general limiting facility. If
PCRE2_FIRSTLINE is set with an offset limit, a match must occur in the first line and also
within the offset limit. In other words, whichever limit comes first is used.
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_DOLLAR_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. Note that the
"start of line" metacharacter does not match after a newline at the end of the subject,
for compatibility with Perl. However, you can change this by setting the
PCRE2_ALT_CIRCUMFLEX option. If there are no newlines in a subject string, or no
occurrences of ^ or $ in a pattern, setting PCRE2_MULTILINE has no effect.
PCRE2_NEVER_BACKSLASH_C
This option locks out the use of \C in the pattern that is being compiled. This escape
can cause unpredictable behaviour in UTF-8 or UTF-16 modes, because it may leave the
current matching point in the middle of a multi-code-unit character. This option may be
useful in applications that process patterns from external sources. Note that there is
also a build-time option that permanently locks out the use of \C.
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 option 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 prevents the creator of the pattern from
switching to UTF interpretation by starting the pattern with (*UTF). This option 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 parentheses 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_DOTSTAR_ANCHOR
If this option is set, it disables an optimization that is applied when .* is the first
significant item in a top-level branch of a pattern, and all the other branches also start
with .* or with \A or \G or ^. The optimization is automatically disabled for .* if it is
inside an atomic group or a capturing group that is the subject of a back reference, or if
the pattern contains (*PRUNE) or (*SKIP). When the optimization is not disabled, such a
pattern is automatically anchored if PCRE2_DOTALL is set for all the .* items and
PCRE2_MULTILINE is not set for any ^ items. Otherwise, the fact that any match must start
either at the start of the subject or following a newline is remembered. Like other
optimizations, this can cause callouts to be skipped.
PCRE2_NO_START_OPTIMIZE
This is an option whose main effect is at matching time. It does not change what
pcre2_compile() generates, but it does affect the output of the JIT compiler.
There are a number of optimizations that may occur at the start of a match, in order to
speed up the process. For example, if it is known that an unanchored match must start with
a specific character, the matching code 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 pattern is not
considered until after a suitable starting point for the match has been found. Also, when
callouts or (*MARK) items are in use, these "start-up" optimizations can cause them to be
skipped if the pattern is never actually used. The start-up optimizations are in effect a
pre-scan of the subject that takes place before the pattern is run.
The PCRE2_NO_START_OPTIMIZE option disables the start-up optimizations, possibly causing
performance to suffer, but ensuring that in cases where the result is "no match", the
callouts do occur, and that items such as (*COMMIT) and (*MARK) are considered at every
possible starting position in the subject string.
Setting PCRE2_NO_START_OPTIMIZE may change the outcome of a matching operation. Consider
the pattern
(*COMMIT)ABC
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 pattern 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, 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 pattern is undefined. It may cause your program to crash or
loop. Note that this option can also be passed to pcre2_match() and pcre_dfa_match(), to
suppress 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 Unicode 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_USE_OFFSET_LIMIT
This option must be set for pcre2_compile() if pcre2_set_offset_limit() is going to be
used to set a non-default offset limit in a match context for matches that use this
pattern. An error is generated if an offset limit is set without this option. For more
details, see the description of pcre2_set_offset_limit() in the section that describes
match contexts. See also the PCRE2_FIRSTLINE option above.
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.
It is available when PCRE2 is built to include Unicode support (which is the default). If
Unicode support is not available, 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);
void pcre2_jit_free_unused_memory(pcre2_general_context *gcontext);
pcre2_jit_stack *pcre2_jit_stack_create(PCRE2_SIZE startsize,
PCRE2_SIZE maxsize, pcre2_general_context *gcontext);
void pcre2_jit_stack_assign(pcre2_match_context *mcontext,
pcre2_jit_callback callback_function, void *callback_data);
void pcre2_jit_stack_free(pcre2_jit_stack *jit_stack);
These functions provide support for JIT compilation, which, if the just-in-time compiler
is available, further processes a compiled pattern into machine code that executes much
faster than the pcre2_match() interpretive matching function. Full details are given in
the pcre2jit documentation.
JIT compilation is a heavyweight optimization. It can take some time for patterns to be
analyzed, and for one-off matches and simple patterns the benefit of faster execution
might be offset by a much slower compilation time. Most, but not all patterns can be
optimized by the JIT compiler.
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. This applies
only to characters whose code points are less than 256. By default, higher-valued code
points never match escapes such as \w or \d. However, if PCRE2 is built with 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
different.
The internal tables can be overridden by tables supplied by the application that calls
PCRE2. These may be created in a different locale from the default. As more and more
applications change to using Unicode, the need for this locale support is expected to die
away.
External tables are built by calling the pcre2_maketables() function, in the relevant
locale. The result can be passed to pcre2_compile() as often as necessary, by creating a
compile context and calling pcre2_set_character_tables() to set the tables pointer
therein. For example, to build and use tables that are appropriate for the French locale
(where accented characters with values greater than 128 are treated as letters), the
following code could be used:
setlocale(LC_CTYPE, "fr_FR");
tables = pcre2_maketables(NULL);
ccontext = pcre2_compile_context_create(NULL);
pcre2_set_character_tables(ccontext, tables);
re = pcre2_compile(..., ccontext);
The 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, compilation, 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 general information about a compiled pattern.
For information about callouts, see the next section. The first argument for
pcre2_pattern_info() is a pointer to the compiled pattern. The second argument specifies
which piece of information is required, and the third argument is a pointer to a variable
to receive the data. If the third argument is NULL, the first argument is ignored, and the
function returns the size in bytes of the variable that is required for the information
requested. Otherwise, The yield of the function is zero for success, or one of the
following negative numbers:
PCRE2_ERROR_NULL the argument code was NULL
PCRE2_ERROR_BADMAGIC the "magic number" was not found
PCRE2_ERROR_BADOPTION the value of what was invalid
PCRE2_ERROR_UNSET the requested field is not set
The "magic number" is placed at the start of each compiled pattern as an simple check
against passing an arbitrary memory pointer. Here is a typical call of
pcre2_pattern_info(), to obtain the length of the compiled pattern:
int rc;
size_t length;
rc = pcre2_pattern_info(
re, /* result of pcre2_compile() */
PCRE2_INFO_SIZE, /* what is required */
&length); /* where to put the data */
The possible values for the second argument are defined in pcre2.h, and are as follows:
PCRE2_INFO_ALLOPTIONS
PCRE2_INFO_ARGOPTIONS
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_ALLOPTIONS returns the compile options as modified by
any top-level option settings such as (*UTF) at the start of the pattern itself. For
example, if the pattern /(*UTF)abc/ is compiled with the PCRE2_EXTENDED option, the result
is PCRE2_EXTENDED and PCRE2_UTF.
A pattern compiled without PCRE2_ANCHORED is automatically anchored by PCRE2 if the first
significant item in every top-level branch is one of the following:
^ unless PCRE2_MULTILINE is set
\A always
\G always
.* sometimes - see below
When .* is the first significant item, anchoring is possible only when all the following
are true:
.* is not in an atomic group
.* is not in a capturing group that is the subject
of a back reference
PCRE2_DOTALL is in force for .*
Neither (*PRUNE) nor (*SKIP) appears in the pattern.
PCRE2_NO_DOTSTAR_ANCHOR is not set.
For patterns that are auto-anchored, the PCRE2_ANCHORED bit is set in the options returned
for PCRE2_INFO_ALLOPTIONS.
PCRE2_INFO_BACKREFMAX
Return the number of the highest back reference in the pattern. The third argument should
point to an uint32_t variable. Named subpatterns acquire numbers as well as names, and
these count towards the highest back reference. Back references such as \4 or \g{12}
match the captured characters of the given group, but in addition, the check that a
capturing group is set in a conditional subpattern such as (?(3)a|b) is also a back
reference. 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. A value of PCRE2_BSR_UNICODE means that \R matches any Unicode line
ending sequence; a value of PCRE2_BSR_ANYCRLF means that \R matches only CR, LF, or CRLF.
PCRE2_INFO_CAPTURECOUNT
Return the highest capturing subpattern number in the pattern. In patterns where (?| is
not used, this is also the total number of capturing subpatterns. The third argument
should point to an uint32_t variable.
PCRE2_INFO_FIRSTBITMAP
In the absence of a single first code unit for a non-anchored pattern, pcre2_compile() may
construct a 256-bit table that defines a fixed set of values for the first code unit in
any match. For example, a pattern that starts with [abc] results in a table with three
bits set. When code unit values greater than 255 are supported, the flag bit for 255 means
"any code unit of value 255 or above". If such a table was constructed, a pointer to it is
returned. Otherwise NULL is returned. The third argument should point to an const uint8_t
* variable.
PCRE2_INFO_FIRSTCODETYPE
Return information about the first code unit of any matched string, for a non-anchored
pattern. The third argument should point to 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, but it is known that a match can occur only at the start of
the subject or following a newline in the subject, 2 is returned. Otherwise, and for
anchored patterns, 0 is returned.
PCRE2_INFO_FIRSTCODEUNIT
Return the value of the first code unit of any matched string 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_HASBACKSLASHC
Return 1 if the pattern contains any instances of \C, otherwise 0. The third argument
should point to an uint32_t variable.
PCRE2_INFO_HASCRORLF
Return 1 if the pattern contains any explicit matches for CR or LF characters, otherwise
0. The third argument should point to 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, respectively.
PCRE2_INFO_JITSIZE
If the compiled pattern was successfully processed by pcre2_jit_compile(), return the size
of the JIT compiled code, otherwise return zero. The third argument should point to a
size_t variable.
PCRE2_INFO_LASTCODETYPE
Returns 1 if there is a rightmost literal code unit that must exist in any matched string,
other than at its start. The third argument should point to 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 follows something of variable length. For example, for the pattern
/^a\d+z\d+/ the returned value is 1 (with "z" returned from PCRE2_INFO_LASTCODEUNIT), but
for /^a\dz\d/ the returned value is 0.
PCRE2_INFO_LASTCODEUNIT
Return the value of the rightmost literal 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 might match an empty string, otherwise 0. The third argument
should point to an uint32_t variable. When a pattern contains recursive subroutine calls
it is not always possible to determine whether or not it can match an empty string. PCRE2
takes a cautious approach and returns 1 in such cases.
PCRE2_INFO_MATCHLIMIT
If the pattern set a match limit by including an item of the form (*LIMIT_MATCH=nnnn) at
the start, the value is returned. The third argument should point to 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 lookbehind 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 processed. 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 number 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 parentheses. The names are
just an additional way of identifying the parentheses, which still acquire numbers.
Several convenience functions such as pcre2_substring_get_byname() are provided for
extracting captured substrings by name. It is also possible to extract the data directly,
by first converting the name to a number in order to access the correct pointers in the
output vector (described with pcre2_match() below). To do the conversion, you need to use
the name-to-number map, which is described by these three values.
The map consists of a number of fixed-size entries. PCRE2_INFO_NAMECOUNT gives the number
of entries, and PCRE2_INFO_NAMEENTRYSIZE gives the size of each entry in code units; both
of these return a uint32_t value. The entry size depends on the length of the longest
name.
PCRE2_INFO_NAMETABLE returns a pointer to the first entry of the table. This is a
PCRE2_SPTR pointer to a block of code units. In the 8-bit library, the first two bytes of
each entry are the number of the capturing parenthesis, most significant byte first. In
the 16-bit library, the pointer points to 16-bit code units, the first of which contains
the parenthesis number. In the 32-bit library, the pointer points to 32-bit code units,
the first of which contains the parenthesis number. The rest of the entry is the
corresponding name, zero terminated.
The names are in alphabetical order. If (?| is used to create multiple groups with the
same number, as described in the section on duplicate subpattern numbers in the
pcre2pattern page, the groups may be given the same name, but there is only one entry in
the table. Different names for groups of the same number are not permitted.
Duplicate names for subpatterns with different numbers are permitted, but only if
PCRE2_DUPNAMES is set. They appear in the table in the order in which they were found in
the pattern. In the absence of (?| this is the order of increasing number; when (?| is
used this is not necessarily the case because later subpatterns may have lower numbers.
As a simple example of the name/number table, consider the following pattern after
compilation by the 8-bit library (assume PCRE2_EXTENDED is set, so white space - including
newlines - is ignored):
(?<date> (?<year>(\d\d)?\d\d) -
(?<month>\d\d) - (?<day>\d\d) )
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 with one of the following values:
PCRE2_NEWLINE_CR Carriage return (CR)
PCRE2_NEWLINE_LF Linefeed (LF)
PCRE2_NEWLINE_CRLF Carriage return, linefeed (CRLF)
PCRE2_NEWLINE_ANY Any Unicode line ending
PCRE2_NEWLINE_ANYCRLF Any of CR, LF, or CRLF
This specifies the default character sequence that will be recognized as meaning "newline"
while matching.
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 includes the size of the general
data block that precedes the code units of the compiled pattern itself. The value that is
used when pcre2_compile() is getting memory in which to place the compiled pattern may be
slightly larger than the value returned by this option, because there are cases where the
code that calculates the size has to over-estimate. Processing a pattern with the JIT
compiler does not alter the value returned by this option.
INFORMATION ABOUT A PATTERN'S CALLOUTS
int pcre2_callout_enumerate(const pcre2_code *code,
int (*callback)(pcre2_callout_enumerate_block *, void *),
void *user_data);
A script language that supports the use of string arguments in callouts might like to scan
all the callouts in a pattern before running the match. This can be done by calling
pcre2_callout_enumerate(). The first argument is a pointer to a compiled pattern, the
second points to a callback function, and the third is arbitrary user data. The callback
function is called for every callout in the pattern in the order in which they appear. Its
first argument is a pointer to a callout enumeration block, and its second argument is the
user_data value that was passed to pcre2_callout_enumerate(). The contents of the callout
enumeration block are described in the pcre2callout documentation, which also gives
further details about callouts.
SERIALIZATION AND PRECOMPILING
It is possible to save compiled patterns on disc or elsewhere, and reload them later,
subject to a number of restrictions. The functions whose names begin with pcre2_serialize_
are used for this purpose. They are described in the pcre2serialize documentation.
THE MATCH DATA BLOCK
pcre2_match_data *pcre2_match_data_create(uint32_t ovecsize,
pcre2_general_context *gcontext);
pcre2_match_data *pcre2_match_data_create_from_pattern(
const pcre2_code *code, pcre2_general_context *gcontext);
void pcre2_match_data_free(pcre2_match_data *match_data);
Information about a successful or unsuccessful match is placed in a match data block,
which is an opaque structure that is accessed by function calls. In particular, the match
data block contains a vector of offsets into the subject string that define the matched
part of the subject and any substrings that were captured. This is know as the ovector.
Before calling pcre2_match(), pcre2_dfa_match(), or pcre2_jit_match() you must create a
match data block by calling one of the creation functions above. For
pcre2_match_data_create(), the first argument is the number of pairs of offsets in the
ovector. One pair of offsets is required to identify the string that matched the whole
pattern, with another pair for each captured substring. For example, a value of 4 creates
enough space to record the matched portion of the subject plus three captured substrings.
A minimum of at least 1 pair is imposed by pcre2_match_data_create(), so it is always
possible to return the overall matched string.
The second argument of pcre2_match_data_create() is a pointer to a general context, which
can specify custom memory management for obtaining the memory for the match data block. If
you are not using custom memory management, pass NULL, which causes malloc() to be used.
For pcre2_match_data_create_from_pattern(), the first argument is a pointer to a compiled
pattern. The ovector is created to be exactly the right size to hold all the substrings a
pattern might capture. The second argument is again a pointer to a general context, but in
this case if NULL is passed, the memory is obtained using the same allocator that was used
for the compiled pattern (custom or default).
A match data block can be used many times, with the same or different compiled patterns.
You can extract information from a match data block after a match operation has finished,
using functions that are described in the sections on matched strings and other match data
below.
When a call of pcre2_match() fails, valid data is available in the match block only when
the error is PCRE2_ERROR_NOMATCH, PCRE2_ERROR_PARTIAL, or one of the error codes for an
invalid UTF string. Exactly what is available depends on the error, and is detailed below.
When one of the matching functions is called, pointers to the compiled pattern and the
subject string are set in the match data block so that they can be referenced by the
extraction functions. After running a match, you must not free a compiled pattern or a
subject string until after all operations on the match data block (for that match) have
taken place.
When a match data block itself is no longer needed, it should be freed by calling
pcre2_match_data_free().
MATCHING A PATTERN: THE TRADITIONAL FUNCTION
int pcre2_match(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext);
The function pcre2_match() is called to match a subject string against a compiled pattern,
which is passed in the code argument. You can call pcre2_match() with the same code
argument as many times as you like, in order to find multiple matches in the subject
string or to match different subject strings with the same pattern.
This function is the main matching facility of the library, and it operates in a Perl-like
manner. For specialist use there is also an alternative matching function, which is
described below in the section about the pcre2_dfa_match() function.
Here is an example of a simple call to pcre2_match():
pcre2_match_data *md = pcre2_match_data_create(4, NULL);
int rc = pcre2_match(
re, /* result of pcre2_compile() */
"some string", /* the subject string */
11, /* the length of the subject string */
0, /* start at offset 0 in the subject */
0, /* default options */
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 section 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
processing is enabled.
If startoffset is greater than the length of the subject, pcre2_match() returns
PCRE2_ERROR_BADOFFSET. When the starting offset is zero, the search for a match starts at
the beginning of the subject, and this is by far the most common case. In UTF-8 or UTF-16
mode, the starting offset must point to the start of a character, or to the end of the
subject (in UTF-32 mode, one code unit equals one character, so all offsets are valid).
Like the pattern string, the subject may contain binary zeroes.
A non-zero starting offset is useful when searching for another match in the same subject
by calling pcre2_match() again after a previous success. Setting startoffset differs from
passing over a shortened string and setting PCRE2_NOTBOL in the case of a pattern that
begins with any kind of lookbehind. For example, consider the pattern
\Biss\B
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 occurrence 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 starting 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_UTF_CHECK, PCRE2_PARTIAL_HARD, and PCRE2_PARTIAL_SOFT.
Their action is described below.
Setting PCRE2_ANCHORED at match time is not supported by the just-in-time (JIT) compiler.
If it is set, JIT matching is disabled and the normal interpretive code in pcre2_match()
is run. The remaining options are supported for JIT matching.
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
having set PCRE2_MULTILINE at compile time causes circumflex never to match. This option
affects only the behaviour 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 without having set 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_match()
searches further into the string for occurrences of "a" or "b".
PCRE2_NOTEMPTY_ATSTART
This is like PCRE2_NOTEMPTY, except that it locks out an empty string match only at the
first matching position, that is, at the start of the subject plus the starting offset. An
empty string match later in the subject is permitted. If the pattern is anchored, such a
match can occur only if the pattern contains \K.
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. If a non-zero starting
offset is given, the check is applied only to that part of the subject that could be
inspected during matching, and there is a check that the starting offset points to the
first code unit of a character or to the end of the subject. If there are no lookbehind
assertions in the pattern, the check starts at the starting offset. Otherwise, it starts
at the length of the longest lookbehind before the starting offset, or at the start of the
subject if there are not that many characters before the starting offset. Note that the
sequences \b and \B are one-character lookbehinds.
The check is carried out before any other processing takes place, and a negative error
code is returned if the check fails. There are several UTF error codes for each code unit
width, corresponding to different problems with the code unit sequence. There are
discussions about the validity of UTF-8 strings, UTF-16 strings, and UTF-32 strings in the
pcre2unicode page.
If you know that your subject is valid, and you want to skip these checks for performance
reasons, you can set the PCRE2_NO_UTF_CHECK option when calling pcre2_match(). You might
want to do this for the second and subsequent calls to pcre2_match() if you are making
repeated calls to find 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 specifies 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
considered to be more important that an alternative complete match.
There is a more detailed discussion of partial and multi-segment matching, with examples,
in the pcre2partial documentation.
NEWLINE HANDLING WHEN MATCHING
When PCRE2 is built, a default newline convention is set; this is usually the standard
convention for the operating system. The default can be overridden in a compile context by
calling pcre2_set_newline(). It can also be overridden by starting a pattern string with,
for example, (*CRLF), as described in the section on newline conventions in the
pcre2pattern page. During matching, the newline choice affects the behaviour of the dot,
circumflex, and dollar metacharacters. It may also alter the way the match starting
position is advanced after a match failure for an unanchored pattern.
When PCRE2_NEWLINE_CRLF, PCRE2_NEWLINE_ANYCRLF, or PCRE2_NEWLINE_ANY is set as the newline
convention, and a match attempt for an unanchored pattern fails when the current starting
position is at a CRLF sequence, and the pattern contains no explicit matches for CR or LF
characters, the match position is advanced by two characters instead of one, in other
words, to after the CRLF.
The above rule is a compromise that makes the most common cases work as expected. For
example, if the pattern is .+A (and the PCRE2_DOTALL option is not set), it does not match
the string "\r\nA" because, after failing at the start, it skips both the CR and the LF
before retrying. However, the pattern [\r\n]A does match that string, because it contains
an explicit CR or LF reference, and so advances only by one character after the first
failure.
An explicit match for CR of LF is either a literal appearance of one of those characters
in the pattern, or one of the \r or \n escape sequences. Implicit matches such as [^X] do
not count, nor does \s, even though it includes CR and LF in the characters that it
matches.
Notwithstanding the above, anomalous effects may still occur when CRLF is a valid newline
sequence and explicit \r or \n escapes appear in the pattern.
HOW PCRE2_MATCH() RETURNS A STRING AND CAPTURED SUBSTRINGS
uint32_t pcre2_get_ovector_count(pcre2_match_data *match_data);
PCRE2_SIZE *pcre2_get_ovector_pointer(pcre2_match_data *match_data);
In general, a pattern matches a certain portion of the subject, and in addition, further
substrings from the subject may be picked out by parenthesized parts of the pattern.
Following the usage in Jeffrey Friedl's book, this is called "capturing" in what follows,
and the phrase "capturing subpattern" or "capturing group" is used for a fragment of a
pattern that picks out a substring. PCRE2 supports several other kinds of parenthesized
subpattern that do not cause substrings to be captured. The pcre2_pattern_info() function
can be used to find out how many capturing subpatterns there are in a compiled pattern.
You can use auxiliary functions for accessing captured substrings by number or by name, as
described in sections below.
Alternatively, you can make direct use of the vector of PCRE2_SIZE values, called the
ovector, which contains the offsets of captured strings. It is part of the match data
block. The function pcre2_get_ovector_pointer() returns the address of the ovector, and
pcre2_get_ovector_count() returns the number of pairs of values it contains.
Within the ovector, the first in each pair of values is set to the offset of the first
code unit of a substring, and the second is set to the offset of the first code unit after
the end of a substring. These values are always code unit offsets, not character offsets.
That is, they are byte offsets in the 8-bit library, 16-bit offsets in the 16-bit library,
and 32-bit offsets in the 32-bit library.
After a partial match (error return PCRE2_ERROR_PARTIAL), only the first pair of offsets
(that is, ovector[0] and ovector[1]) are set. They identify the part of the subject that
was partially matched. See the pcre2partial documentation for details of partial matching.
After a successful match, the first pair of offsets identifies the portion of the subject
string that was matched by the entire pattern. The next pair is used for the first
capturing subpattern, and so on. The value returned by pcre2_match() is one more than the
highest numbered pair that has been set. For example, if two substrings have been
captured, the returned value is 3. If there are no capturing subpatterns, the return value
from a successful match is 1, indicating that just the first pair of offsets has been set.
If a pattern uses the \K escape sequence within a positive assertion, the reported start
of a successful match can be greater than the end of the match. For example, if the
pattern (?=ab\K) is matched against "ab", the start and end offset values for the match
are 2 and 0.
If a capturing subpattern group is matched repeatedly within a single match operation, it
is the last portion of the subject that it matched that is returned.
If the ovector is too small to hold all the captured substring offsets, as much as
possible is filled in, and the function returns a value of zero. If captured substrings
are not of interest, pcre2_match() may be called with a match data block whose ovector is
of minimum length (that is, one pair). 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 corresponding to
unused subpatterns are set to PCRE2_UNSET.
Offset values that correspond to unused subpatterns at the end of the expression are also
set to PCRE2_UNSET. For example, if the string "abc" is matched against the pattern
(abc)(x(yz)?)? subpatterns 2 and 3 are not matched. The return from the function is 2,
because the highest used capturing subpattern number is 1. The offsets for for the second
and third capturing subpatterns (assuming the vector is large enough, of course) are set
to PCRE2_UNSET.
Elements in the ovector that do not correspond to capturing parentheses in the pattern are
never changed. That is, if a pattern contains n capturing parentheses, no more than
ovector[0] to ovector[2n+1] are set by pcre2_match(). The other elements retain whatever
values they previously had.
OTHER INFORMATION ABOUT A MATCH
PCRE2_SPTR pcre2_get_mark(pcre2_match_data *match_data);
PCRE2_SIZE pcre2_get_startchar(pcre2_match_data *match_data);
As well as the offsets in the ovector, other information about a match is retained in the
match data block and can be retrieved by the above functions in appropriate circumstances.
If they are called at other times, the result is undefined.
After a successful match, a partial match (PCRE2_ERROR_PARTIAL), or a failure to match
(PCRE2_ERROR_NOMATCH), a (*MARK) name may be available, and pcre2_get_mark() can be
called. It returns a pointer to the zero-terminated name, which is within the compiled
pattern. Otherwise NULL is returned. The length of the (*MARK) name (excluding the
terminating zero) is stored in the code unit that preceeds the name. You should use this
instead of relying on the terminating zero if the (*MARK) name might contain a binary
zero.
After a successful match, the (*MARK) name that is returned is the last one encountered on
the matching path through the pattern. After a "no match" or a partial match, the last
encountered (*MARK) name is returned. For example, consider this pattern:
^(*MARK:A)((*MARK:B)a|b)c
When it matches "bc", the returned mark is A. The B mark is "seen" in the first branch of
the group, but it is not on the matching path. On the other hand, when this pattern fails
to match "bx", the returned mark is B.
After a successful match, a partial match, or one of the invalid UTF errors (for example,
PCRE2_ERROR_UTF8_ERR5), pcre2_get_startchar() can be called. After a successful or partial
match it returns the code unit offset of the character at which the match started. For a
non-partial match, this can be different to the value of ovector[0] if the pattern
contains the \K escape sequence. After a partial match, however, this value is always the
same as ovector[0] because \K does not affect the result of a partial match.
After a UTF check failure, pcre2_get_startchar() can be used to obtain the code unit
offset of the invalid UTF character. Details are given in the pcre2unicode page.
ERROR RETURNS FROM pcre2_match()
If pcre2_match() fails, it returns a negative number. This can be converted to a text
string by calling 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 checking is in force and an invalid UTF subject string is detected, one of a
number of UTF-specific negative error codes is returned. Details are given in the
pcre2unicode page. The following are the other errors that may be returned by
pcre2_match():
PCRE2_ERROR_NOMATCH
The subject string did not match the pattern.
PCRE2_ERROR_PARTIAL
The subject string did not match, but it did match partially. See the pcre2partial
documentation for details of partial matching.
PCRE2_ERROR_BADMAGIC
PCRE2 stores a 4-byte "magic number" at the start of the compiled code, to catch the case
when it is passed a junk pointer. This is the error that is returned when the magic number
is not present.
PCRE2_ERROR_BADMODE
This error is given when a 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 was greater than the length of the subject.
PCRE2_ERROR_BADOPTION
An unrecognized bit was set in the options argument.
PCRE2_ERROR_BADUTFOFFSET
The UTF code unit sequence that was passed as a subject was checked and found to be valid
(the PCRE2_NO_UTF_CHECK option was not set), but the value of startoffset did not point to
the beginning of a UTF character or the end of the subject.
PCRE2_ERROR_CALLOUT
This error is never generated by pcre2_match() itself. It is provided for use by callout
functions that want to cause pcre2_match() or pcre2_callout_enumerate() to return a
distinctive error code. See the pcre2callout documentation for details.
PCRE2_ERROR_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 documentation 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 pattern 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 complicated
cases, in particular mutual recursions between two different subpatterns, cannot be
detected until matching is attempted.
PCRE2_ERROR_RECURSIONLIMIT
The internal recursion limit was reached.
EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
int pcre2_substring_length_bynumber(pcre2_match_data *match_data,
uint32_t number, PCRE2_SIZE *length);
int pcre2_substring_copy_bynumber(pcre2_match_data *match_data,
uint32_t number, PCRE2_UCHAR *buffer,
PCRE2_SIZE *bufflen);
int pcre2_substring_get_bynumber(pcre2_match_data *match_data,
uint32_t number, PCRE2_UCHAR **bufferptr,
PCRE2_SIZE *bufflen);
void pcre2_substring_free(PCRE2_UCHAR *buffer);
Captured substrings can be accessed directly by using the ovector as described above. For
convenience, auxiliary functions are provided for extracting captured substrings as new,
separate, zero-terminated strings. A substring that contains a binary zero is correctly
extracted and has a further zero added on the end, but the result is not, of course, a C
string.
The functions in this section identify substrings by number. The number zero refers to the
entire matched substring, with higher numbers referring to substrings captured by
parenthesized groups. After a partial match, only substring zero is available. An attempt
to extract any other substring gives the error PCRE2_ERROR_PARTIAL. The next section
describes similar functions for extracting captured substrings by name.
If a pattern uses the \K escape sequence within a positive assertion, the reported start
of a successful match can be greater than the end of the match. For example, if the
pattern (?=ab\K) is matched against "ab", the start and end offset values for the match
are 2 and 0. In this situation, calling these functions with a zero substring number
extracts a zero-length empty string.
You can find the length in code units of a captured substring without extracting it by
calling pcre2_substring_length_bynumber(). The first argument is a pointer to the match
data block, the second is the group number, and the third is a pointer to a variable into
which the length is placed. If you just want to know whether or not the substring has been
captured, you can pass the third argument as NULL.
The pcre2_substring_copy_bynumber() function copies a captured substring into a supplied
buffer, whereas pcre2_substring_get_bynumber() copies it into new memory, obtained using
the same memory allocation function that was used for the match data block. The first two
arguments of these functions are a pointer to the match data block and a capturing group
number.
The final arguments of pcre2_substring_copy_bynumber() are a pointer to the buffer and a
pointer to a variable that contains its length in code units. This is updated to contain
the actual number of code units used for the extracted substring, excluding the
terminating zero.
For pcre2_substring_get_bynumber() the third and fourth arguments point to variables that
are updated with a pointer to the new memory and the number of code units that comprise
the substring, again excluding the terminating zero. When the substring is no longer
needed, the memory should be freed by calling pcre2_substring_free().
The return value from all these functions is zero for success, or a negative error code.
If the pattern match failed, the match failure code is returned. If a substring number
greater than zero is used after a partial match, PCRE2_ERROR_PARTIAL is returned. Other
possible error codes are:
PCRE2_ERROR_NOMEMORY
The buffer was too small for pcre2_substring_copy_bynumber(), or the attempt to get memory
failed for pcre2_substring_get_bynumber().
PCRE2_ERROR_NOSUBSTRING
There is no substring with that number in the pattern, that is, the number is greater than
the number of capturing parentheses.
PCRE2_ERROR_UNAVAILABLE
The substring number, though not greater than the number of captures in the pattern, is
greater than the number of slots in the ovector, so the substring could not be captured.
PCRE2_ERROR_UNSET
The substring did not participate in the match. For example, if the pattern is (abc)|(def)
and the subject is "def", and the ovector contains at least two capturing slots, substring
number 1 is unset.
EXTRACTING A LIST OF ALL CAPTURED SUBSTRINGS
int pcre2_substring_list_get(pcre2_match_data *match_data,
PCRE2_UCHAR ***listptr, PCRE2_SIZE **lengthsptr);
void pcre2_substring_list_free(PCRE2_SPTR *list);
The pcre2_substring_list_get() function extracts all available substrings and builds a
list of pointers to them. It also (optionally) builds a second list that contains their
lengths (in code units), excluding a terminating zero that is added to each of them. All
this is done in a single block of memory that is obtained using the same memory allocation
function that was used to get the match data block.
This function must be called only after a successful match. If called after a partial
match, the error code PCRE2_ERROR_PARTIAL is returned.
The address of the memory block is returned via listptr, which is also the start of the
list of string pointers. The end of the list is marked by a NULL pointer. The address of
the list of lengths is returned via lengthsptr. If your strings do not contain binary
zeros and you do not therefore need the lengths, you may supply NULL as the lengthsptr
argument to disable the creation of a list of lengths. The yield of the function is zero
if all went well, or PCRE2_ERROR_NOMEMORY if the memory block could not be obtained. When
the list is no longer needed, it should be freed by calling pcre2_substring_list_free().
If this function encounters a substring that is unset, which can happen when capturing
subpattern number n+1 matches some part of the subject, but subpattern n has not been used
at all, it returns an empty string. This can be distinguished from a genuine zero-length
substring by inspecting the appropriate offset in the ovector, which contain PCRE2_UNSET
for unset substrings, or by calling pcre2_substring_length_bynumber().
EXTRACTING CAPTURED SUBSTRINGS BY NAME
int pcre2_substring_number_from_name(const pcre2_code *code,
PCRE2_SPTR name);
int pcre2_substring_length_byname(pcre2_match_data *match_data,
PCRE2_SPTR name, PCRE2_SIZE *length);
int pcre2_substring_copy_byname(pcre2_match_data *match_data,
PCRE2_SPTR name, PCRE2_UCHAR *buffer, PCRE2_SIZE *bufflen);
int pcre2_substring_get_byname(pcre2_match_data *match_data,
PCRE2_SPTR name, PCRE2_UCHAR **bufferptr, PCRE2_SIZE *bufflen);
void pcre2_substring_free(PCRE2_UCHAR *buffer);
To extract a substring by name, you first have to find associated number. For example,
for this pattern:
(a+)b(?<xxx>\d+)...
the number of the 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 argument is the compiled pattern, and the
second is the name. The yield of the function is the subpattern number,
PCRE2_ERROR_NOSUBSTRING if there is no subpattern of that name, or
PCRE2_ERROR_NOUNIQUESUBSTRING if there is more than one subpattern of that name. Given the
number, you can extract the substring directly, or use one of the functions described
above.
For convenience, there are also "byname" functions that correspond to the "bynumber"
functions, the only difference being that the second argument is a name instead of a
number. If PCRE2_DUPNAMES is set and there are duplicate names, these functions scan all
the groups with the given name, and return the first named string that is set.
If there are no groups with the given name, PCRE2_ERROR_NOSUBSTRING is returned. If all
groups with the name have numbers that are greater than the number of slots in the
ovector, PCRE2_ERROR_UNAVAILABLE is returned. If there is at least one group with a slot
in the ovector, but no group is found to be set, PCRE2_ERROR_UNSET is returned.
Warning: If the pattern uses the (?| feature to set up multiple subpatterns with the same
number, as described in the section on duplicate subpattern numbers in the pcre2pattern
page, you cannot use names to distinguish the different subpatterns, because names are not
included in the compiled code. The matching process uses only numbers. For this reason,
the use of different names for subpatterns of the same number causes an error at compile
time.
CREATING A NEW STRING WITH SUBSTITUTIONS
int pcre2_substitute(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext, PCRE2_SPTR replacement,
PCRE2_SIZE rlength, PCRE2_UCHAR *outputbufferfP,
PCRE2_SIZE *outlengthptr);
This function calls pcre2_match() and then makes a copy of the subject string in
outputbuffer, replacing the part that was matched with the replacement string, whose
length is supplied in rlength. This can be given as PCRE2_ZERO_TERMINATED for a zero-
terminated string. Matches in which a \K item in a lookahead in the pattern causes the
match to end before it starts are not supported, and give rise to an error return.
The first seven arguments of pcre2_substitute() are the same as for pcre2_match(), except
that the partial matching options are not permitted, and match_data may be passed as NULL,
in which case a match data block is obtained and freed within this function, using memory
management functions from the match context, if provided, or else those that were used to
allocate memory for the compiled code.
The outlengthptr argument must point to a variable that contains the length, in code
units, of the output buffer. If the function is successful, the value is updated to
contain the length of the new string, excluding the trailing zero that is automatically
added.
If the function is not successful, the value set via outlengthptr depends on the type of
error. For syntax errors in the replacement string, the value is the offset in the
replacement string where the error was detected. For other errors, the value is
PCRE2_UNSET by default. This includes the case of the output buffer being too small,
unless PCRE2_SUBSTITUTE_OVERFLOW_LENGTH is set (see below), in which case the value is the
minimum length needed, including space for the trailing zero. Note that in order to
compute the required length, pcre2_substitute() has to simulate all the matching and
copying, instead of giving an error return as soon as the buffer overflows. Note also that
the length is in code units, not bytes.
In the replacement string, which is interpreted as a UTF string in UTF mode, and is
checked for UTF validity unless the PCRE2_NO_UTF_CHECK option is set, a dollar character
is an escape character that can specify the insertion of characters from capturing groups
or (*MARK) items in the pattern. The following forms are always recognized:
$$ insert a dollar character
$<n> or ${<n>} insert the contents of group <n>
$*MARK or ${*MARK} insert the name of the last (*MARK) encountered
Either a group number or a group name can be given for <n>. Curly brackets are required
only if the following character would be interpreted as part of the number or name. The
number may be zero to include the entire matched string. For example, if the pattern
a(b)c is matched with "=abc=" and the replacement string "+$1$0$1+", the result is
"=+babcb+=".
The facility for inserting a (*MARK) name can be used to perform simple simultaneous
substitutions, as this pcre2test example shows:
/(*:pear)apple|(*:orange)lemon/g,replace=${*MARK}
apple lemon
2: pear orange
As well as the usual options for pcre2_match(), a number of additional options can be set
in the options argument.
PCRE2_SUBSTITUTE_GLOBAL causes the function to iterate over the subject string, replacing
every matching substring. If this is not set, only the first matching substring is
replaced. If any matched substring has zero length, after the substitution has happened,
an attempt to find a non-empty match at the same position is performed. If this is not
successful, the current position is advanced by one character except when CRLF is a valid
newline sequence and the next two characters are CR, LF. In this case, the current
position is advanced by two characters.
PCRE2_SUBSTITUTE_OVERFLOW_LENGTH changes what happens when the output buffer is too small.
The default action is to return PCRE2_ERROR_NOMEMORY immediately. If this option is set,
however, pcre2_substitute() continues to go through the motions of matching and
substituting (without, of course, writing anything) in order to compute the size of buffer
that is needed. This value is passed back via the outlengthptr variable, with the result
of the function still being PCRE2_ERROR_NOMEMORY.
Passing a buffer size of zero is a permitted way of finding out how much memory is needed
for given substitution. However, this does mean that the entire operation is carried out
twice. Depending on the application, it may be more efficient to allocate a large buffer
and free the excess afterwards, instead of using PCRE2_SUBSTITUTE_OVERFLOW_LENGTH.
PCRE2_SUBSTITUTE_UNKNOWN_UNSET causes references to capturing groups that do not appear in
the pattern to be treated as unset groups. This option should be used with care, because
it means that a typo in a group name or number no longer causes the
PCRE2_ERROR_NOSUBSTRING error.
PCRE2_SUBSTITUTE_UNSET_EMPTY causes unset capturing groups (including unknown groups when
PCRE2_SUBSTITUTE_UNKNOWN_UNSET is set) to be treated as empty strings when inserted as
described above. If this option is not set, an attempt to insert an unset group causes the
PCRE2_ERROR_UNSET error. This option does not influence the extended substitution syntax
described below.
PCRE2_SUBSTITUTE_EXTENDED causes extra processing to be applied to the replacement string.
Without this option, only the dollar character is special, and only the group insertion
forms listed above are valid. When PCRE2_SUBSTITUTE_EXTENDED is set, two things change:
Firstly, backslash in a replacement string is interpreted as an escape character. The
usual forms such as \n or \x{ddd} can be used to specify particular character codes, and
backslash followed by any non-alphanumeric character quotes that character. Extended
quoting can be coded using \Q...\E, exactly as in pattern strings.
There are also four escape sequences for forcing the case of inserted letters. The
insertion mechanism has three states: no case forcing, force upper case, and force lower
case. The escape sequences change the current state: \U and \L change to upper or lower
case forcing, respectively, and \E (when not terminating a \Q quoted sequence) reverts to
no case forcing. The sequences \u and \l force the next character (if it is a letter) to
upper or lower case, respectively, and then the state automatically reverts to no case
forcing. Case forcing applies to all inserted characters, including those from captured
groups and letters within \Q...\E quoted sequences.
Note that case forcing sequences such as \U...\E do not nest. For example, the result of
processing "\Uaa\LBB\Ecc\E" is "AAbbcc"; the final \E has no effect.
The second effect of setting PCRE2_SUBSTITUTE_EXTENDED is to add more flexibility to group
substitution. The syntax is similar to that used by Bash:
${<n>:-<string>}
${<n>:+<string1>:<string2>}
As before, <n> may be a group number or a name. The first form specifies a default value.
If group <n> is set, its value is inserted; if not, <string> is expanded and the result
inserted. The second form specifies strings that are expanded and inserted when group <n>
is set or unset, respectively. The first form is just a convenient shorthand for
${<n>:+${<n>}:<string>}
Backslash can be used to escape colons and closing curly brackets in the replacement
strings. A change of the case forcing state within a replacement string remains in force
afterwards, as shown in this pcre2test example:
/(some)?(body)/substitute_extended,replace=${1:+\U:\L}HeLLo
body
1: hello
somebody
1: HELLO
The PCRE2_SUBSTITUTE_UNSET_EMPTY option does not affect these extended substitutions.
However, PCRE2_SUBSTITUTE_UNKNOWN_UNSET does cause unknown groups in the extended syntax
forms to be treated as unset.
If successful, pcre2_substitute() returns the number of replacements that were made. This
may be zero if no matches were found, and is never greater than 1 unless
PCRE2_SUBSTITUTE_GLOBAL is set.
In the event of an error, a negative error code is returned. Except for
PCRE2_ERROR_NOMATCH (which is never returned), errors from pcre2_match() are passed
straight back.
PCRE2_ERROR_NOSUBSTRING is returned for a non-existent substring insertion, unless
PCRE2_SUBSTITUTE_UNKNOWN_UNSET is set.
PCRE2_ERROR_UNSET is returned for an unset substring insertion (including an unknown
substring when PCRE2_SUBSTITUTE_UNKNOWN_UNSET is set) when the simple (non-extended)
syntax is used and PCRE2_SUBSTITUTE_UNSET_EMPTY is not set.
PCRE2_ERROR_NOMEMORY is returned if the output buffer is not big enough. If the
PCRE2_SUBSTITUTE_OVERFLOW_LENGTH option is set, the size of buffer that is needed is
returned via outlengthptr. Note that this does not happen by default.
PCRE2_ERROR_BADREPLACEMENT is used for miscellaneous syntax errors in the replacement
string, with more particular errors being PCRE2_ERROR_BADREPESCAPE (invalid escape
sequence), PCRE2_ERROR_REPMISSING_BRACE (closing curly bracket not found),
PCRE2_BADSUBSTITUTION (syntax error in extended group substitution), and
PCRE2_BADSUBPATTERN (the pattern match ended before it started, which can happen if \K is
used in an assertion).
As for all PCRE2 errors, a text message that describes the error can be obtained by
calling pcre2_get_error_message().
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. Only if none are set is PCRE2_ERROR_UNSET is returned. The
pcre2_substring_number_from_name() function returns the error
PCRE2_ERROR_NOUNIQUESUBSTRING when there are duplicate names.
If you want to get full details of all captured substrings for a given name, you must use
the pcre2_substring_nametable_scan() function. The first argument is the compiled pattern,
and the second is the name. If the third and fourth arguments are NULL, the function
returns a group number for a unique name, or PCRE2_ERROR_NOUNIQUESUBSTRING otherwise.
When the third and fourth arguments are not NULL, they must be pointers to variables that
are updated by the function. After it has run, they point to the first and last entries in
the name-to-number table for the given name, and the function returns the length of each
entry in code units. In both cases, PCRE2_ERROR_NOSUBSTRING is returned if there are no
entries for the given name.
The format of the name table is described above in the section entitled Information about
a pattern. Given all the relevant entries for the name, you can extract each of their
numbers, and hence the captured data.
FINDING ALL POSSIBLE MATCHES AT ONE POSITION
The traditional matching function uses a similar algorithm to Perl, which stops when it
finds the first match at a given point in the subject. If you want to find all possible
matches, or the longest possible match at a given position, consider using the alternative
matching function (see below) instead. If you cannot use the alternative function, you can
kludge it up by making use of the callout facility, which is described in the pcre2callout
documentation.
What you have to do is to insert a callout right at the end of the pattern. When your
callout function is called, extract and save the current matched substring. Then return 1,
which forces pcre2_match() to backtrack and try other alternatives. Ultimately, when it
runs out of matches, pcre2_match() will yield PCRE2_ERROR_NOMATCH.
MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
int pcre2_dfa_match(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext,
int *workspace, PCRE2_SIZE wscount);
The function pcre2_dfa_match() is called to match a subject string against a compiled
pattern, using a matching algorithm that scans the subject string just once, and does not
backtrack. This has different characteristics to the normal algorithm, and is not
compatible with Perl. Some of the features of PCRE2 patterns are not supported.
Nevertheless, there are times when this kind of matching can be useful. For a discussion
of the two matching algorithms, and a list of features that pcre2_dfa_match() does not
support, see the pcre2matching documentation.
The arguments for the pcre2_dfa_match() function are the same as for pcre2_match(), plus
two extras. The ovector within the match data block is used in a different way, and this
is described below. The other common arguments are used in the same way as for
pcre2_match(), so their description is not repeated here.
The two additional arguments provide workspace for the function. The workspace vector
should contain at least 20 elements. It is used for keeping track of multiple paths
through the pattern tree. More workspace is needed for patterns and subjects where there
are a lot of potential matches.
Here is an example of a simple call to pcre2_dfa_match():
int wspace[20];
pcre2_match_data *md = pcre2_match_data_create(4, NULL);
int rc = pcre2_dfa_match(
re, /* result of pcre2_compile() */
"some string", /* the subject string */
11, /* the length of the subject string */
0, /* start at offset 0 in the subject */
0, /* default options */
match_data, /* the match data block */
NULL, /* a match context; NULL means use defaults */
wspace, /* working space vector */
20); /* number of elements (NOT size in bytes) */
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_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 portion 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 alternative 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 substring in the
subject. Note, however, that all the matches from one run of the function start at the
same point in the subject. The shorter matches are all initial substrings of the longer
matches. For example, if the pattern
<.*>
is matched against the string
This is <something> <something else> <something further> no more
the three matched strings are
<something> <something else> <something further>
<something> <something else>
<something>
On success, the yield of the function is a number greater than zero, which is the number
of matched substrings. The offsets of the substrings are returned in the ovector, and can
be extracted by number in the same way as for pcre2_match(), but the numbers bear no
relation to any capturing groups that may exist in the pattern, because DFA matching does
not support group capture.
Calls to the convenience functions that extract substrings by name return the error
PCRE2_ERROR_DFA_UFUNC (unsupported function) if used after a DFA match. The convenience
functions that extract substrings by number never return PCRE2_ERROR_NOSUBSTRING, and the
meanings of some other errors are slightly different:
PCRE2_ERROR_UNAVAILABLE
The ovector is not big enough to include a slot for the given substring number.
PCRE2_ERROR_UNSET
There is a slot in the ovector for this substring, but there were insufficient matches to
fill it.
The matched strings are stored in the ovector in reverse order of length; that is, the
longest matching string is first. If there were too many matches to fit into the ovector,
the yield of the function is zero, and the vector is filled with the longest matches.
NOTE: PCRE2's "auto-possessification" optimization usually applies to character repeats at
the end of a pattern (as well as internally). For example, the pattern "a\d+" is compiled
as if it were "a\d++". For DFA matching, this means that only one possible match is found.
If you really do want multiple matches in such cases, either use an ungreedy repeat auch
as "a\d+?" or set the PCRE2_NO_AUTO_POSSESS option when compiling.
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 in a UTF mode 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), pcre2callout(3), pcre2demo(3), pcre2matching(3), pcre2partial(3),
pcre2posix(3), pcre2sample(3), pcre2stack(3), pcre2unicode(3).
AUTHOR
Philip Hazel
University Computing Service
Cambridge, England.
REVISION
Last updated: 16 December 2015
Copyright (c) 1997-2015 University of Cambridge.