pcre2api(3) Library Functions Manual pcre2api(3)
NAME
PCRE2 - Perl-compatible regular expressions (revised API)
#include <pcre2.h>
PCRE2 is a new API for PCRE, starting at release 10.0. This document
contains a description of all its native functions. See the pcre2
document for an overview of all the PCRE2 documentation.
PCRE2 NATIVE API BASIC FUNCTIONS
pcre2_code *pcre2_compile(PCRE2_SPTR pattern, PCRE2_SIZE length,
uint32_t options, int *errorcode, PCRE2_SIZE *erroroffset,
pcre2_compile_context *ccontext);
void pcre2_code_free(pcre2_code *code);
pcre2_match_data *pcre2_match_data_create(uint32_t ovecsize,
pcre2_general_context *gcontext);
pcre2_match_data *pcre2_match_data_create_from_pattern(
const pcre2_code *code, pcre2_general_context *gcontext);
int pcre2_match(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext);
int pcre2_dfa_match(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext,
int *workspace, PCRE2_SIZE wscount);
void pcre2_match_data_free(pcre2_match_data *match_data);
PCRE2 NATIVE API AUXILIARY MATCH FUNCTIONS
PCRE2_SPTR pcre2_get_mark(pcre2_match_data *match_data);
PCRE2_SIZE pcre2_get_match_data_size(pcre2_match_data *match_data);
PCRE2_SIZE pcre2_get_match_data_heapframes_size(
pcre2_match_data *match_data);
uint32_t pcre2_get_ovector_count(pcre2_match_data *match_data);
PCRE2_SIZE *pcre2_get_ovector_pointer(pcre2_match_data *match_data);
PCRE2_SIZE pcre2_get_startchar(pcre2_match_data *match_data);
PCRE2 NATIVE API GENERAL CONTEXT FUNCTIONS
pcre2_general_context *pcre2_general_context_create(
void *(*private_malloc)(PCRE2_SIZE, void *),
void (*private_free)(void *, void *), void *memory_data);
pcre2_general_context *pcre2_general_context_copy(
pcre2_general_context *gcontext);
void pcre2_general_context_free(pcre2_general_context *gcontext);
PCRE2 NATIVE API COMPILE CONTEXT FUNCTIONS
pcre2_compile_context *pcre2_compile_context_create(
pcre2_general_context *gcontext);
pcre2_compile_context *pcre2_compile_context_copy(
pcre2_compile_context *ccontext);
void pcre2_compile_context_free(pcre2_compile_context *ccontext);
int pcre2_set_bsr(pcre2_compile_context *ccontext,
uint32_t value);
int pcre2_set_character_tables(pcre2_compile_context *ccontext,
const uint8_t *tables);
int pcre2_set_compile_extra_options(pcre2_compile_context *ccontext,
uint32_t extra_options);
int pcre2_set_max_pattern_length(pcre2_compile_context *ccontext,
PCRE2_SIZE value);
int pcre2_set_max_pattern_compiled_length(
pcre2_compile_context *ccontext, PCRE2_SIZE value);
int pcre2_set_max_varlookbehind(pcre2_compile_contest *ccontext,
uint32_t value);
int pcre2_set_newline(pcre2_compile_context *ccontext,
uint32_t value);
int pcre2_set_parens_nest_limit(pcre2_compile_context *ccontext,
uint32_t value);
int pcre2_set_compile_recursion_guard(pcre2_compile_context *ccontext,
int (*guard_function)(uint32_t, void *), void *user_data);
PCRE2 NATIVE API MATCH CONTEXT FUNCTIONS
pcre2_match_context *pcre2_match_context_create(
pcre2_general_context *gcontext);
pcre2_match_context *pcre2_match_context_copy(
pcre2_match_context *mcontext);
void pcre2_match_context_free(pcre2_match_context *mcontext);
int pcre2_set_callout(pcre2_match_context *mcontext,
int (*callout_function)(pcre2_callout_block *, void *),
void *callout_data);
int pcre2_set_substitute_callout(pcre2_match_context *mcontext,
int (*callout_function)(pcre2_substitute_callout_block *, void *),
void *callout_data);
int pcre2_set_offset_limit(pcre2_match_context *mcontext,
PCRE2_SIZE value);
int pcre2_set_heap_limit(pcre2_match_context *mcontext,
uint32_t value);
int pcre2_set_match_limit(pcre2_match_context *mcontext,
uint32_t value);
int pcre2_set_depth_limit(pcre2_match_context *mcontext,
uint32_t value);
PCRE2 NATIVE API STRING EXTRACTION FUNCTIONS
int pcre2_substring_copy_byname(pcre2_match_data *match_data,
PCRE2_SPTR name, PCRE2_UCHAR *buffer, PCRE2_SIZE *bufflen);
int pcre2_substring_copy_bynumber(pcre2_match_data *match_data,
uint32_t number, PCRE2_UCHAR *buffer,
PCRE2_SIZE *bufflen);
void pcre2_substring_free(PCRE2_UCHAR *buffer);
int pcre2_substring_get_byname(pcre2_match_data *match_data,
PCRE2_SPTR name, PCRE2_UCHAR **bufferptr, PCRE2_SIZE *bufflen);
int pcre2_substring_get_bynumber(pcre2_match_data *match_data,
uint32_t number, PCRE2_UCHAR **bufferptr,
PCRE2_SIZE *bufflen);
int pcre2_substring_length_byname(pcre2_match_data *match_data,
PCRE2_SPTR name, PCRE2_SIZE *length);
int pcre2_substring_length_bynumber(pcre2_match_data *match_data,
uint32_t number, PCRE2_SIZE *length);
int pcre2_substring_nametable_scan(const pcre2_code *code,
PCRE2_SPTR name, PCRE2_SPTR *first, PCRE2_SPTR *last);
int pcre2_substring_number_from_name(const pcre2_code *code,
PCRE2_SPTR name);
void pcre2_substring_list_free(PCRE2_UCHAR **list);
int pcre2_substring_list_get(pcre2_match_data *match_data,
PCRE2_UCHAR ***listptr, PCRE2_SIZE **lengthsptr);
PCRE2 NATIVE API STRING SUBSTITUTION FUNCTION
int pcre2_substitute(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext, PCRE2_SPTR replacementz,
PCRE2_SIZE rlength, PCRE2_UCHAR *outputbuffer,
PCRE2_SIZE *outlengthptr);
PCRE2 NATIVE API JIT FUNCTIONS
int pcre2_jit_compile(pcre2_code *code, uint32_t options);
int pcre2_jit_match(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext);
void pcre2_jit_free_unused_memory(pcre2_general_context *gcontext);
pcre2_jit_stack *pcre2_jit_stack_create(size_t startsize,
size_t maxsize, pcre2_general_context *gcontext);
void pcre2_jit_stack_assign(pcre2_match_context *mcontext,
pcre2_jit_callback callback_function, void *callback_data);
void pcre2_jit_stack_free(pcre2_jit_stack *jit_stack);
PCRE2 NATIVE API SERIALIZATION FUNCTIONS
int32_t pcre2_serialize_decode(pcre2_code **codes,
int32_t number_of_codes, const uint8_t *bytes,
pcre2_general_context *gcontext);
int32_t pcre2_serialize_encode(const pcre2_code **codes,
int32_t number_of_codes, uint8_t **serialized_bytes,
PCRE2_SIZE *serialized_size, pcre2_general_context *gcontext);
void pcre2_serialize_free(uint8_t *bytes);
int32_t pcre2_serialize_get_number_of_codes(const uint8_t *bytes);
PCRE2 NATIVE API AUXILIARY FUNCTIONS
pcre2_code *pcre2_code_copy(const pcre2_code *code);
pcre2_code *pcre2_code_copy_with_tables(const pcre2_code *code);
int pcre2_get_error_message(int errorcode, PCRE2_UCHAR *buffer,
PCRE2_SIZE bufflen);
const uint8_t *pcre2_maketables(pcre2_general_context *gcontext);
void pcre2_maketables_free(pcre2_general_context *gcontext,
const uint8_t *tables);
int pcre2_pattern_info(const pcre2_code *code, uint32_t what,
void *where);
int pcre2_callout_enumerate(const pcre2_code *code,
int (*callback)(pcre2_callout_enumerate_block *, void *),
void *user_data);
int pcre2_config(uint32_t what, void *where);
PCRE2 NATIVE API OBSOLETE FUNCTIONS
int pcre2_set_recursion_limit(pcre2_match_context *mcontext,
uint32_t value);
int pcre2_set_recursion_memory_management(
pcre2_match_context *mcontext,
void *(*private_malloc)(size_t, void *),
void (*private_free)(void *, void *), void *memory_data);
These functions became obsolete at release 10.30 and are retained only
for backward compatibility. They should not be used in new code. The
first is replaced by pcre2_set_depth_limit(); the second is no longer
needed and has no effect (it always returns zero).
PCRE2 EXPERIMENTAL PATTERN CONVERSION FUNCTIONS
pcre2_convert_context *pcre2_convert_context_create(
pcre2_general_context *gcontext);
pcre2_convert_context *pcre2_convert_context_copy(
pcre2_convert_context *cvcontext);
void pcre2_convert_context_free(pcre2_convert_context *cvcontext);
int pcre2_set_glob_escape(pcre2_convert_context *cvcontext,
uint32_t escape_char);
int pcre2_set_glob_separator(pcre2_convert_context *cvcontext,
uint32_t separator_char);
int pcre2_pattern_convert(PCRE2_SPTR pattern, PCRE2_SIZE length,
uint32_t options, PCRE2_UCHAR **buffer,
PCRE2_SIZE *blength, pcre2_convert_context *cvcontext);
void pcre2_converted_pattern_free(PCRE2_UCHAR *converted_pattern);
These functions provide a way of converting non-PCRE2 patterns into
patterns that can be processed by pcre2_compile(). This facility is
experimental and may be changed in future releases. At present, "globs"
and POSIX basic and extended patterns can be converted. Details are
given in the pcre2convert documentation.
PCRE2 8-BIT, 16-BIT, AND 32-BIT LIBRARIES
There are three PCRE2 libraries, supporting 8-bit, 16-bit, and 32-bit
code units, respectively. However, there is just one header file,
pcre2.h. This contains the function prototypes and other definitions
for all three libraries. One, two, or all three can be installed
simultaneously. On Unix-like systems the libraries are called
libpcre2-8, libpcre2-16, and libpcre2-32, and they can also co-exist
with the original PCRE libraries. Every PCRE2 function comes in three
different forms, one for each library, for example:
pcre2_compile_8()
pcre2_compile_16()
pcre2_compile_32()
There are also three different sets of data types:
PCRE2_UCHAR8, PCRE2_UCHAR16, PCRE2_UCHAR32
PCRE2_SPTR8, PCRE2_SPTR16, PCRE2_SPTR32
The UCHAR types define unsigned code units of the appropriate widths.
For example, PCRE2_UCHAR16 is usually defined as `uint16_t'. The SPTR
types are pointers to constants of the equivalent UCHAR types, that is,
they are pointers to vectors of unsigned code units.
Character strings are passed to a PCRE2 library as sequences of
unsigned integers in code units of the appropriate width. The length of
a string may be given as a number of code units, or the string may be
specified as zero-terminated.
Many applications use only one code unit width. For their convenience,
macros are defined whose names are the generic forms such as
pcre2_compile() and PCRE2_SPTR. These macros use the value of the macro
PCRE2_CODE_UNIT_WIDTH to generate the appropriate width-specific
function and macro names. PCRE2_CODE_UNIT_WIDTH is not defined by
default. An application must define it to be 8, 16, or 32 before
including pcre2.h in order to make use of the generic names.
Applications that use more than one code unit width can be linked with
more than one PCRE2 library, but must define PCRE2_CODE_UNIT_WIDTH to
be 0 before including pcre2.h, and then use the real function names.
Any code that is to be included in an environment where the value of
PCRE2_CODE_UNIT_WIDTH is unknown should also use the real function
names. (Unfortunately, it is not possible in C code to save and restore
the value of a macro.)
If PCRE2_CODE_UNIT_WIDTH is not defined before including pcre2.h, a
compiler error occurs.
When using multiple libraries in an application, you must take care
when processing any particular pattern to use only functions from a
single library. For example, if you want to run a match using a
pattern that was compiled with pcre2_compile_16(), you must do so with
pcre2_match_16(), not pcre2_match_8() or pcre2_match_32().
In the function summaries above, and in the rest of this document and
other PCRE2 documents, functions and data types are described using
their generic names, without the _8, _16, or _32 suffix.
PCRE2 API OVERVIEW
PCRE2 has its own native API, which is described in this document.
There are also some wrapper functions for the 8-bit library that
correspond to the POSIX regular expression API, but they do not give
access to all the functionality of PCRE2 and they are not thread-safe.
They are described in the pcre2posix documentation. Both these APIs
define a set of C function calls.
The native API C data types, function prototypes, option values, and
error codes are defined in the header file pcre2.h, which also contains
definitions of PCRE2_MAJOR and PCRE2_MINOR, the major and minor release
numbers for the library. Applications can use these to include support
for different releases of PCRE2.
In a Windows environment, if you want to statically link an application
program against a non-dll PCRE2 library, you must define PCRE2_STATIC
before including pcre2.h.
The functions pcre2_compile() and pcre2_match() are used for compiling
and matching regular expressions in a Perl-compatible manner. A sample
program that demonstrates the simplest way of using them is provided in
the file called pcre2demo.c in the PCRE2 source distribution. A listing
of this program is given in the pcre2demo documentation, and the
pcre2sample documentation describes how to compile and run it.
The compiling and matching functions recognize various options that are
passed as bits in an options argument. There are also some more
complicated parameters such as custom memory management functions and
resource limits that are passed in "contexts" (which are just memory
blocks, described below). Simple applications do not need to make use
of contexts.
Just-in-time (JIT) compiler support is an optional feature of PCRE2
that can be built in appropriate hardware environments. It greatly
speeds up the matching performance of many patterns. Programs can
request that it be used if available by calling pcre2_jit_compile()
after a pattern has been successfully compiled by pcre2_compile(). This
does nothing if JIT support is not available.
More complicated programs might need to make use of the specialist
functions pcre2_jit_stack_create(), pcre2_jit_stack_free(), and
pcre2_jit_stack_assign() in order to control the JIT code's memory
usage.
JIT matching is automatically used by pcre2_match() if it is available,
unless the PCRE2_NO_JIT option is set. There is also a direct interface
for JIT matching, which gives improved performance at the expense of
less sanity checking. The JIT-specific functions are discussed in the
pcre2jit documentation.
A second matching function, pcre2_dfa_match(), which is not Perl-
compatible, is also provided. This uses a different algorithm for the
matching. The alternative algorithm finds all possible matches (at a
given point in the subject), and scans the subject just once (unless
there are lookaround assertions). However, this algorithm does not
return captured substrings. A description of the two matching
algorithms and their advantages and disadvantages is given in the
pcre2matching documentation. There is no JIT support for
pcre2_dfa_match().
In addition to the main compiling and matching functions, there are
convenience functions for extracting captured substrings from a subject
string that has been matched by pcre2_match(). They are:
pcre2_substring_copy_byname()
pcre2_substring_copy_bynumber()
pcre2_substring_get_byname()
pcre2_substring_get_bynumber()
pcre2_substring_list_get()
pcre2_substring_length_byname()
pcre2_substring_length_bynumber()
pcre2_substring_nametable_scan()
pcre2_substring_number_from_name()
pcre2_substring_free() and pcre2_substring_list_free() are also
provided, to free memory used for extracted strings. If either of these
functions is called with a NULL argument, the function returns
immediately without doing anything.
The function pcre2_substitute() can be called to match a pattern and
return a copy of the subject string with substitutions for parts that
were matched.
Functions whose names begin with pcre2_serialize_ are used for saving
compiled patterns on disc or elsewhere, and reloading them later.
Finally, there are functions for finding out information about a
compiled pattern (pcre2_pattern_info()) and about the configuration
with which PCRE2 was built (pcre2_config()).
Functions with names ending with _free() are used for freeing memory
blocks of various sorts. In all cases, if one of these functions is
called with a NULL argument, it does nothing.
STRING LENGTHS AND OFFSETS
The PCRE2 API uses string lengths and offsets into strings of code
units in several places. These values are always of type PCRE2_SIZE,
which is an unsigned integer type, currently always defined as size_t.
The largest value that can be stored in such a type (that is
~(PCRE2_SIZE)0) is reserved as a special indicator for zero-terminated
strings and unset offsets. Therefore, the longest string that can be
handled is one less than this maximum. Note that string lengths are
always given in code units. Only in the 8-bit library is such a length
the same as the number of bytes in the string.
NEWLINES
PCRE2 supports five different conventions for indicating line breaks in
strings: a single CR (carriage return) character, a single LF
(linefeed) character, the two-character sequence CRLF, any of the three
preceding, or any Unicode newline sequence. The Unicode newline
sequences are the three just mentioned, plus the single characters VT
(vertical tab, U+000B), FF (form feed, U+000C), NEL (next line,
U+0085), LS (line separator, U+2028), and PS (paragraph separator,
U+2029).
Each of the first three conventions is used by at least one operating
system as its standard newline sequence. When PCRE2 is built, a default
can be specified. If it is not, the default is set to LF, which is the
Unix standard. However, the newline convention can be changed by an
application when calling pcre2_compile(), or it can be specified by
special text at the start of the pattern itself; this overrides any
other settings. See the pcre2pattern page for details of the special
character sequences.
In the PCRE2 documentation the word "newline" is used to mean "the
character or pair of characters that indicate a line break". The choice
of newline convention affects the handling of the dot, circumflex, and
dollar metacharacters, the handling of #-comments in /x mode, and, when
CRLF is a recognized line ending sequence, the match position
advancement for a non-anchored pattern. There is more detail about this
in the section on pcre2_match() options below.
The choice of newline convention does not affect the interpretation of
the \n or \r escape sequences, nor does it affect what \R matches; this
has its own separate convention.
MULTITHREADING
In a multithreaded application it is important to keep thread-specific
data separate from data that can be shared between threads. The PCRE2
library code itself is thread-safe: it contains no static or global
variables. The API is designed to be fairly simple for non-threaded
applications while at the same time ensuring that multithreaded
applications can use it.
There are several different blocks of data that are used to pass
information between the application and the PCRE2 libraries.
The compiled pattern
A pointer to the compiled form of a pattern is returned to the user
when pcre2_compile() is successful. The data in the compiled pattern is
fixed, and does not change when the pattern is matched. Therefore, it
is thread-safe, that is, the same compiled pattern can be used by more
than one thread simultaneously. For example, an application can compile
all its patterns at the start, before forking off multiple threads that
use them. However, if the just-in-time (JIT) optimization feature is
being used, it needs separate memory stack areas for each thread. See
the pcre2jit documentation for more details.
In a more complicated situation, where patterns are compiled only when
they are first needed, but are still shared between threads, pointers
to compiled patterns must be protected from simultaneous writing by
multiple threads. This is somewhat tricky to do correctly. If you know
that writing to a pointer is atomic in your environment, you can use
logic like this:
Get a read-only (shared) lock (mutex) for pointer
if (pointer == NULL)
{
Get a write (unique) lock for pointer
if (pointer == NULL) pointer = pcre2_compile(...
}
Release the lock
Use pointer in pcre2_match()
Of course, testing for compilation errors should also be included in
the code.
The reason for checking the pointer a second time is as follows:
Several threads may have acquired the shared lock and tested the
pointer for being NULL, but only one of them will be given the write
lock, with the rest kept waiting. The winning thread will compile the
pattern and store the result. After this thread releases the write
lock, another thread will get it, and if it does not retest pointer for
being NULL, will recompile the pattern and overwrite the pointer,
creating a memory leak and possibly causing other issues.
In an environment where writing to a pointer may not be atomic, the
above logic is not sufficient. The thread that is doing the compiling
may be descheduled after writing only part of the pointer, which could
cause other threads to use an invalid value. Instead of checking the
pointer itself, a separate "pointer is valid" flag (that can be updated
atomically) must be used:
Get a read-only (shared) lock (mutex) for pointer
if (!pointer_is_valid)
{
Get a write (unique) lock for pointer
if (!pointer_is_valid)
{
pointer = pcre2_compile(...
pointer_is_valid = TRUE
}
}
Release the lock
Use pointer in pcre2_match()
If JIT is being used, but the JIT compilation is not being done
immediately (perhaps waiting to see if the pattern is used often
enough), similar logic is required. JIT compilation updates a value
within the compiled code block, so a thread must gain unique write
access to the pointer before calling pcre2_jit_compile().
Alternatively, pcre2_code_copy() or pcre2_code_copy_with_tables() can
be used to obtain a private copy of the compiled code before calling
the JIT compiler.
Context blocks
The next main section below introduces the idea of "contexts" in which
PCRE2 functions are called. A context is nothing more than a collection
of parameters that control the way PCRE2 operates. Grouping a number of
parameters together in a context is a convenient way of passing them to
a PCRE2 function without using lots of arguments. The parameters that
are stored in contexts are in some sense "advanced features" of the
API. Many straightforward applications will not need to use contexts.
In a multithreaded application, if the parameters in a context are
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.
Match blocks
The matching functions need a block of memory for storing the results
of a match. This includes details of what was matched, as well as
additional information such as the name of a (*MARK) setting. Each
thread must provide its own copy of this memory.
PCRE2 CONTEXTS
Some PCRE2 functions have a lot of parameters, many of which are used
only by specialist applications, for example, those that use custom
memory management or non-standard character tables. To keep function
argument lists at a reasonable size, and at the same time to keep the
API extensible, "uncommon" parameters are passed to certain functions
in a context instead of directly. A context is just a block of memory
that holds the parameter values. Applications that do not need to
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);
If this function is passed a NULL argument, it returns immediately
without doing anything.
The compile context
A compile context is required if you want to provide an external
function for stack checking during compilation or to change the default
values of any of the following compile-time parameters:
What \R matches (Unicode newlines or CR, LF, CRLF only)
PCRE2's character tables
The newline character sequence
The compile time nested parentheses limit
The maximum length of the pattern string
The extra options bits (none set by default)
A compile context is 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 uint8_t *tables);
The value must be the result of a call to pcre2_maketables(), whose
only argument is a general context. This function builds a set of
character tables in the current locale.
int pcre2_set_compile_extra_options(pcre2_compile_context *ccontext,
uint32_t extra_options);
As PCRE2 has developed, almost all the 32 option bits that are
available in the options argument of pcre2_compile() have been used up.
To avoid running out, the compile context contains a set of extra
option bits which are used for some newer, assumed rarer, options. This
function sets those bits. It always sets all the bits (either on or
off). It does not modify any existing setting. The available options
are defined in the section entitled "Extra compile options" below.
int pcre2_set_max_pattern_length(pcre2_compile_context *ccontext,
PCRE2_SIZE value);
This sets a maximum length, in code units, for any pattern string that
is compiled with this context. If the pattern is longer, an error is
generated. This facility is provided so that applications that accept
patterns from external sources can limit their size. The default is the
largest number that a PCRE2_SIZE variable can hold, which is
effectively unlimited.
int pcre2_set_max_pattern_compiled_length(
pcre2_compile_context *ccontext, PCRE2_SIZE value);
This sets a maximum size, in bytes, for the memory needed to hold the
compiled version of a pattern that is compiled with this context. If
the pattern needs more memory, an error is generated. This facility is
provided so that applications that accept patterns from external
sources can limit the amount of memory they use. The default is the
largest number that a PCRE2_SIZE variable can hold, which is
effectively unlimited.
int pcre2_set_max_varlookbehind(pcre2_compile_contest *ccontext,
uint32_t value);
This sets a maximum length for the number of characters matched by a
variable-length lookbehind assertion. The default is set when PCRE2 is
built, with the ultimate default being 255, the same as Perl.
Lookbehind assertions without a bounding length are not supported.
int pcre2_set_newline(pcre2_compile_context *ccontext,
uint32_t value);
This specifies which characters or character sequences are to be
recognized as newlines. The value must be one of PCRE2_NEWLINE_CR
(carriage return only), PCRE2_NEWLINE_LF (linefeed only),
PCRE2_NEWLINE_CRLF (the two-character sequence CR followed by LF),
PCRE2_NEWLINE_ANYCRLF (any of the above), PCRE2_NEWLINE_ANY (any
Unicode newline sequence), or PCRE2_NEWLINE_NUL (the NUL character,
that is a binary zero).
A pattern can override the value set in the compile context by starting
with a sequence such as (*CRLF). See the pcre2pattern page for details.
When a pattern is compiled with the PCRE2_EXTENDED or
PCRE2_EXTENDED_MORE option, the newline convention affects the
recognition of the end of internal comments starting with #. The value
is saved with the compiled pattern for subsequent use by the JIT
compiler and by the two interpreted matching functions, pcre2_match()
and pcre2_dfa_match().
int pcre2_set_parens_nest_limit(pcre2_compile_context *ccontext,
uint32_t value);
This parameter adjusts the limit, set when PCRE2 is built (default
250), on the depth of parenthesis nesting in a pattern. This limit
stops rogue patterns using up too much system stack when being
compiled. The limit applies to parentheses of all kinds, not just
capturing parentheses.
int pcre2_set_compile_recursion_guard(pcre2_compile_context *ccontext,
int (*guard_function)(uint32_t, void *), void *user_data);
There is at least one application that runs PCRE2 in threads with very
limited system stack, where running out of stack is to be avoided at
all costs. The parenthesis limit above cannot take account of how much
stack is actually available during compilation. For a finer control,
you can supply a function that is called whenever pcre2_compile()
starts to compile a parenthesized part of a pattern. This function can
check the actual stack size (or anything else that it wants to, of
course).
The first argument to the callout function gives the current depth of
nesting, and the second is user data that is set up by the last
argument of pcre2_set_compile_recursion_guard(). The callout function
should return zero if all is well, or non-zero to force an error.
The match context
A match context is required if you want to:
Set up a callout function
Set an offset limit for matching an unanchored pattern
Change the limit on the amount of heap used when matching
Change the backtracking match limit
Change the backtracking depth limit
Set custom memory management specifically for the match
If none of these apply, just pass NULL as the context argument of
pcre2_match(), pcre2_dfa_match(), or pcre2_jit_match().
A match context is created, copied, and freed by the following
functions:
pcre2_match_context *pcre2_match_context_create(
pcre2_general_context *gcontext);
pcre2_match_context *pcre2_match_context_copy(
pcre2_match_context *mcontext);
void pcre2_match_context_free(pcre2_match_context *mcontext);
A match context is created with default values for its parameters.
These can be changed by calling the following functions, which return 0
on success, or PCRE2_ERROR_BADDATA if invalid data is detected.
int pcre2_set_callout(pcre2_match_context *mcontext,
int (*callout_function)(pcre2_callout_block *, void *),
void *callout_data);
This sets up a callout function for PCRE2 to call at specified points
during a matching operation. Details are given in the pcre2callout
documentation.
int pcre2_set_substitute_callout(pcre2_match_context *mcontext,
int (*callout_function)(pcre2_substitute_callout_block *, void *),
void *callout_data);
This sets up a callout function for PCRE2 to call after each
substitution made by pcre2_substitute(). Details are given in the
section entitled "Creating a new string with substitutions" below.
int pcre2_set_offset_limit(pcre2_match_context *mcontext,
PCRE2_SIZE value);
The offset_limit parameter limits how far an unanchored search can
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. The pcre2_substitute() function makes no
more substitutions.
For example, if the pattern /abc/ is matched against "123abc" with an
offset limit less than 3, the result is PCRE2_ERROR_NOMATCH. A match
can never be found if the startoffset argument of pcre2_match(),
pcre2_dfa_match(), or pcre2_substitute() is greater than the offset
limit set in the match context.
When using this facility, you must set the PCRE2_USE_OFFSET_LIMIT
option when calling pcre2_compile() so that when JIT is in use,
different code can be compiled. If a match is started with a non-
default match limit when PCRE2_USE_OFFSET_LIMIT is not set, an error is
generated.
The offset limit facility can be used to track progress when searching
large subject strings or to limit the extent of global substitutions.
See also the PCRE2_FIRSTLINE option, which requires a match to start
before or at the first newline that follows the start of matching in
the subject. If this is set with an offset limit, a match must occur in
the first line and also within the offset limit. In other words,
whichever limit comes first is used.
int pcre2_set_heap_limit(pcre2_match_context *mcontext,
uint32_t value);
The heap_limit parameter specifies, in units of kibibytes (1024 bytes),
the maximum amount of heap memory that pcre2_match() may use to hold
backtracking information when running an interpretive match. This limit
also applies to pcre2_dfa_match(), which may use the heap when
processing patterns with a lot of nested pattern recursion or
lookarounds or atomic groups. This limit does not apply to matching
with the JIT optimization, which has its own memory control
arrangements (see the pcre2jit documentation for more details). If the
limit is reached, the negative error code PCRE2_ERROR_HEAPLIMIT is
returned. The default limit can be set when PCRE2 is built; if it is
not, the default is set very large and is essentially unlimited.
A value for the heap limit may also be supplied by an item at the start
of a pattern of the form
(*LIMIT_HEAP=ddd)
where ddd is a decimal number. However, such a setting is ignored
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.
The pcre2_match() function always needs some heap memory, so setting a
value of zero guarantees a "heap limit exceeded" error. Details of how
pcre2_match() uses the heap are given in the pcre2perform
documentation.
For pcre2_dfa_match(), a vector on the system stack is used when
processing pattern recursions, lookarounds, or atomic groups, and only
if this is not big enough is heap memory used. In this case, setting a
value of zero disables the use of the heap.
int pcre2_set_match_limit(pcre2_match_context *mcontext,
uint32_t value);
The match_limit parameter provides a means of preventing PCRE2 from
using up too many computing resources when processing patterns that are
not going to match, but which have a very large number of possibilities
in their search trees. The classic example is a pattern that uses
nested unlimited repeats.
There is an internal counter in pcre2_match() that is incremented each
time round its main matching loop. If this value reaches the match
limit, pcre2_match() returns the negative value PCRE2_ERROR_MATCHLIMIT.
This has the effect of limiting the amount of backtracking that can
take place. For patterns that are not anchored, the count restarts from
zero for each position in the subject string. This limit also applies
to pcre2_dfa_match(), though the counting is done in a different way.
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 is 10 million, which handles all but the most extreme cases. A
value for the match limit may also be supplied by an item at the start
of a pattern of the form
(*LIMIT_MATCH=ddd)
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
pcre2_dfa_match() or, if no such limit is set, less than the default.
int pcre2_set_depth_limit(pcre2_match_context *mcontext,
uint32_t value);
This parameter limits the depth of nested backtracking in
pcre2_match(). Each time a nested backtracking point is passed, a new
memory frame is used to remember the state of matching at that point.
Thus, this parameter indirectly limits the amount of memory that is
used in a match. However, because the size of each memory frame depends
on the number of capturing parentheses, the actual memory limit varies
from pattern to pattern. This limit was more useful in versions before
10.30, where function recursion was used for backtracking.
The depth limit is not relevant, and is ignored, when matching is done
using JIT compiled code. However, it is supported by pcre2_dfa_match(),
which uses it to limit the depth of nested internal recursive function
calls that implement atomic groups, lookaround assertions, and pattern
recursions. This limits, indirectly, the amount of system stack that is
used. It was more useful in versions before 10.32, when stack memory
was used for local workspace vectors for recursive function calls. From
version 10.32, only local variables are allocated on the stack and as
each call uses only a few hundred bytes, even a small stack can support
quite a lot of recursion.
If the depth of internal recursive function calls is great enough,
local workspace vectors are allocated on the heap from version 10.32
onwards, so the depth limit also indirectly limits the amount of heap
memory that is used. A recursive pattern such as /(.(?2))((?1)|)/, when
matched to a very long string using pcre2_dfa_match(), can use a great
deal of memory. However, it is probably better to limit heap usage
directly by calling pcre2_set_heap_limit().
The default value for the depth limit can be set when PCRE2 is built;
if it is not, the default is set to the same value as the default for
the match limit. If the limit is exceeded, pcre2_match() or
pcre2_dfa_match() returns PCRE2_ERROR_DEPTHLIMIT. A value for the depth
limit may also be supplied by an item at the start of a pattern of the
form
(*LIMIT_DEPTH=ddd)
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
pcre2_dfa_match() or, if no such limit is set, less than the default.
CHECKING BUILD-TIME OPTIONS
int pcre2_config(uint32_t what, void *where);
The function pcre2_config() makes it possible for a PCRE2 client to
find the value of certain configuration parameters and to discover
which optional features have been compiled into the PCRE2 library. The
pcre2build documentation has more details about these features.
The first argument for pcre2_config() specifies which information is
required. The second argument is a pointer to memory into which the
information is placed. If NULL is passed, the function returns the
amount of memory that is needed for the requested information. For
calls that return numerical values, the value is in bytes; when
requesting these values, where should point to appropriately aligned
memory. For calls that return strings, the required length is given in
code units, not counting the terminating zero.
When requesting information, the returned value from pcre2_config() is
non-negative on success, or the negative error code
PCRE2_ERROR_BADOPTION if the value in the first argument is not
recognized. The following information is available:
PCRE2_CONFIG_BSR
The output is a uint32_t integer whose value indicates what character
sequences the \R escape sequence matches by default. A value of
PCRE2_BSR_UNICODE means that \R matches any Unicode line ending
sequence; a value of PCRE2_BSR_ANYCRLF means that \R matches only CR,
LF, or CRLF. The default can be overridden when a pattern is compiled.
PCRE2_CONFIG_COMPILED_WIDTHS
The output is a uint32_t integer whose lower bits indicate which code
unit widths were selected when PCRE2 was built. The 1-bit indicates
8-bit support, and the 2-bit and 4-bit indicate 16-bit and 32-bit
support, respectively.
PCRE2_CONFIG_DEPTHLIMIT
The output is a uint32_t integer that gives the default limit for the
depth of nested backtracking in pcre2_match() or the depth of nested
recursions, lookarounds, and atomic groups in pcre2_dfa_match().
Further details are given with pcre2_set_depth_limit() above.
PCRE2_CONFIG_HEAPLIMIT
The output is a uint32_t integer that gives, in kibibytes, the default
limit for the amount of heap memory used by pcre2_match() or
pcre2_dfa_match(). Further details are given with
pcre2_set_heap_limit() above.
PCRE2_CONFIG_JIT
The output is a uint32_t integer that is set to one if support for
just-in-time compiling is included in the library; otherwise it is set
to zero. Note that having the support in the library does not guarantee
that JIT will be used for any given match. See the pcre2jit
documentation for more details.
PCRE2_CONFIG_JITTARGET
The where argument should point to a buffer that is at least 48 code
units long. (The exact length required can be found by calling
pcre2_config() with where set to NULL.) The buffer is filled with a
string that contains the name of the architecture for which the JIT
compiler is configured, for example "x86 32bit (little endian +
unaligned)". If JIT support is not available, PCRE2_ERROR_BADOPTION is
returned, otherwise the number of code units used is returned. This is
the length of the string, plus one unit for the terminating zero.
PCRE2_CONFIG_LINKSIZE
The output is a uint32_t integer that contains the number of bytes used
for internal linkage in compiled regular expressions. When PCRE2 is
configured, the value can be set to 2, 3, or 4, with the default being
2. This is the value that is returned by pcre2_config(). However, when
the 16-bit library is compiled, a value of 3 is rounded up to 4, and
when the 32-bit library is compiled, internal linkages always use 4
bytes, so the configured value is not relevant.
The default value of 2 for the 8-bit and 16-bit libraries is sufficient
for all but the most massive patterns, since it allows the size of the
compiled pattern to be up to 65535 code units. Larger values allow
larger regular expressions to be compiled by those two libraries, but
at the expense of slower matching.
PCRE2_CONFIG_MATCHLIMIT
The output is a uint32_t integer that gives the default match limit for
pcre2_match(). Further details are given with pcre2_set_match_limit()
above.
PCRE2_CONFIG_NEWLINE
The output is a uint32_t integer whose value specifies the default
character sequence that is recognized as meaning "newline". The values
are:
PCRE2_NEWLINE_CR Carriage return (CR)
PCRE2_NEWLINE_LF Linefeed (LF)
PCRE2_NEWLINE_CRLF Carriage return, linefeed (CRLF)
PCRE2_NEWLINE_ANY Any Unicode line ending
PCRE2_NEWLINE_ANYCRLF Any of CR, LF, or CRLF
PCRE2_NEWLINE_NUL The NUL character (binary zero)
The default should normally correspond to the standard sequence for
your operating system.
PCRE2_CONFIG_NEVER_BACKSLASH_C
The output is a uint32_t integer that is set to one if the use of \C
was permanently disabled when PCRE2 was built; otherwise it is set to
zero.
PCRE2_CONFIG_PARENSLIMIT
The output is a uint32_t integer that gives the maximum depth of
nesting of parentheses (of any kind) in a pattern. This limit is
imposed to cap the amount of system stack used when a pattern is
compiled. It is specified when PCRE2 is built; the default is 250. This
limit does not take into account the stack that may already be used by
the calling application. For finer control over compilation stack
usage, see pcre2_set_compile_recursion_guard().
PCRE2_CONFIG_STACKRECURSE
This parameter is obsolete and should not be used in new code. The
output is a uint32_t integer that is always set to zero.
PCRE2_CONFIG_TABLES_LENGTH
The output is a uint32_t integer that gives the length of PCRE2's
character processing tables in bytes. For details of these tables see
the section on locale support below.
PCRE2_CONFIG_UNICODE_VERSION
The where argument should point to a buffer that is at least 24 code
units long. (The exact length required can be found by calling
pcre2_config() with where set to NULL.) If PCRE2 has been compiled
without Unicode support, the buffer is filled with the text "Unicode
not supported". Otherwise, the Unicode version string (for example,
"8.0.0") is inserted. The number of code units used is returned. This
is the length of the string plus one unit for the terminating zero.
PCRE2_CONFIG_UNICODE
The output is a uint32_t integer that is set to one if Unicode support
is available; otherwise it is set to zero. Unicode support implies UTF
support.
PCRE2_CONFIG_VERSION
The where argument should point to a buffer that is at least 24 code
units long. (The exact length required can be found by calling
pcre2_config() with where set to NULL.) The buffer is filled with the
PCRE2 version string, zero-terminated. The number of code units used is
returned. This is the length of the string plus one unit for the
terminating zero.
COMPILING A PATTERN
pcre2_code *pcre2_compile(PCRE2_SPTR pattern, PCRE2_SIZE length,
uint32_t options, int *errorcode, PCRE2_SIZE *erroroffset,
pcre2_compile_context *ccontext);
void pcre2_code_free(pcre2_code *code);
pcre2_code *pcre2_code_copy(const pcre2_code *code);
pcre2_code *pcre2_code_copy_with_tables(const pcre2_code *code);
The pcre2_compile() function compiles a pattern into an internal form.
The pattern is defined by a pointer to a string of code units and a
length in code units. If the pattern is zero-terminated, the length can
be specified as PCRE2_ZERO_TERMINATED. A NULL pattern pointer with a
length of zero is treated as an empty string (NULL with a non-zero
length causes an error return). The function returns a pointer to a
block of memory that contains the compiled pattern and related data, or
NULL if an error occurred.
If the compile context argument ccontext is NULL, memory for the
compiled pattern is obtained by calling malloc(). Otherwise, it is
obtained from the same memory function that was used for the compile
context. The caller must free the memory by calling pcre2_code_free()
when it is no longer needed. If pcre2_code_free() is called with a
NULL argument, it returns immediately, without doing anything.
The function pcre2_code_copy() makes a copy of the compiled code in new
memory, using the same memory allocator as was used for the original.
However, if the code has been processed by the JIT compiler (see
below), the JIT information cannot be copied (because it is position-
dependent). The new copy can initially be used only for non-JIT
matching, though it can be passed to pcre2_jit_compile() if required.
If pcre2_code_copy() is called with a NULL argument, it returns NULL.
The pcre2_code_copy() function provides a way for individual threads in
a multithreaded application to acquire a private copy of shared
compiled code. However, it does not make a copy of the character
tables used by the compiled pattern; the new pattern code points to the
same tables as the original code. (See "Locale Support" below for
details of these character tables.) In many applications the same
tables are used throughout, so this behaviour is appropriate.
Nevertheless, there are occasions when a copy of a compiled pattern and
the relevant tables are needed. The pcre2_code_copy_with_tables()
provides this facility. Copies of both the code and the tables are
made, with the new code pointing to the new tables. The memory for the
new tables is automatically freed when pcre2_code_free() is called for
the new copy of the compiled code. If pcre2_code_copy_with_tables() is
called with a NULL argument, it returns NULL.
NOTE: When one of the matching functions is called, pointers to the
compiled pattern and the subject string are set in the match data block
so that they can be referenced by the substring extraction functions
after a successful match. After running a match, you must not free a
compiled pattern or a subject string until after all operations on the
match data block have taken place, unless, in the case of the subject
string, you have used the PCRE2_COPY_MATCHED_SUBJECT option, which is
described in the section entitled "Option bits for pcre2_match()"
below.
The options argument for pcre2_compile() contains various bit settings
that affect the compilation. It should be zero if none of them are
required. The available options are described below. Some of them (in
particular, those that are compatible with Perl, but some others as
well) can also be set and unset from within the pattern (see the
detailed description in the pcre2pattern documentation).
For those options that can be different in different parts of the
pattern, the contents of the options argument specifies their settings
at the start of compilation. The PCRE2_ANCHORED, PCRE2_ENDANCHORED, and
PCRE2_NO_UTF_CHECK options can be set at the time of matching as well
as at compile time.
Some additional options and less frequently required compile-time
parameters (for example, the newline setting) can be provided in a
compile context (as described above).
If errorcode or erroroffset is NULL, pcre2_compile() returns NULL
immediately. Otherwise, the variables to which these point are set to
an error code and an offset (number of code units) within the pattern,
respectively, when pcre2_compile() returns NULL because a compilation
error has occurred.
There are nearly 100 positive error codes that pcre2_compile() may
return if it finds an error in the pattern. There are also some
negative error codes that are used for invalid UTF strings when
validity checking is in force. These are the same as given by
pcre2_match() and pcre2_dfa_match(), and are described in the
pcre2unicode documentation. There is no separate documentation for the
positive error codes, because the textual error messages that are
obtained by calling the pcre2_get_error_message() function (see
"Obtaining a textual error message" below) should be self-explanatory.
Macro names starting with PCRE2_ERROR_ are defined for both positive
and negative error codes in pcre2.h. When compilation is successful
errorcode is set to a value that returns the message "no error" if
passed to pcre2_get_error_message().
The value returned in erroroffset is an indication of where in the
pattern an error occurred. When there is no error, zero is returned. A
non-zero value is not necessarily the furthest point in the pattern
that was read. For example, after the error "lookbehind assertion is
not fixed length", the error offset points to the start of the failing
assertion. For an invalid UTF-8 or UTF-16 string, the offset is that of
the first code unit of the failing character.
Some errors are not detected until the whole pattern has been scanned;
in these cases, the offset passed back is the length of the pattern.
Note that the offset is in code units, not characters, even in a UTF
mode. It may sometimes point into the middle of a UTF-8 or UTF-16
character.
This code fragment shows a typical straightforward call to
pcre2_compile():
pcre2_code *re;
PCRE2_SIZE erroffset;
int errorcode;
re = pcre2_compile(
"^A.*Z", /* the pattern */
PCRE2_ZERO_TERMINATED, /* the pattern is zero-terminated */
0, /* default options */
&errorcode, /* for error code */
&erroffset, /* for error offset */
NULL); /* no compile context */
Main compile options
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).
ECMAscript 6 added additional functionality to \u. This can be accessed
using the PCRE2_EXTRA_ALT_BSUX extra option (see "Extra compile
options" below). Note that this alternative escape handling applies
only to patterns. Neither of these options affects the processing of
replacement strings passed to pcre2_substitute().
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 or
PCRE2_EXTENDED_MORE option is set with PCRE2_ALT_VERBNAMES, 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, except
immediately before or after an explicit callout in the pattern. 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. If either
PCRE2_UTF or PCRE2_UCP is set, Unicode properties are used for all
characters with more than one other case, and for all characters whose
code points are greater than U+007F. Note that there are two ASCII
characters, K and S, that, in addition to their lower case ASCII
equivalents, are case-equivalent with U+212A (Kelvin sign) and U+017F
(long S) respectively. If you do not want this case equivalence, you
can suppress it by setting PCRE2_EXTRA_CASELESS_RESTRICT.
For lower valued characters with only one other case, a lookup table is
used for speed. When neither PCRE2_UTF nor PCRE2_UCP is set, a lookup
table is used for all code points less than 256, and higher code points
(available only in 16-bit or 32-bit mode) are treated as not having
another case.
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, and the
\N escape sequence always matches a non-newline character, independent
of the setting of PCRE2_DOTALL.
PCRE2_DUPNAMES
If this bit is set, names used to identify capture groups need not be
unique. This can be helpful for certain types of pattern when it is
known that only one instance of the named group can ever be matched.
There are more details of named capture groups below; see also the
pcre2pattern documentation.
PCRE2_ENDANCHORED
If this bit is set, the end of any pattern match must be right at the
end of the string being searched (the "subject string"). If the pattern
match succeeds by reaching (*ACCEPT), but does not reach the end of the
subject, the match fails at the current starting point. For unanchored
patterns, a new match is then tried at the next starting point.
However, if the match succeeds by reaching the end of the pattern, but
not the end of the subject, backtracking occurs and an alternative
match may be found. Consider these two patterns:
.(*ACCEPT)|..
.|..
If matched against "abc" with PCRE2_ENDANCHORED set, the first matches
"c" whereas the second matches "bc". The effect of PCRE2_ENDANCHORED
can also be achieved by appropriate constructs in the pattern itself,
which is the only way to do it in Perl.
For DFA matching with pcre2_dfa_match(), PCRE2_ENDANCHORED applies only
to the first (that is, the longest) matched string. Other parallel
matches, which are necessarily substrings of the first one, must
obviously end before the end of the subject.
PCRE2_EXTENDED
If this bit is set, most white space characters in the pattern are
totally ignored except when escaped, inside a character class, or
inside a \Q...\E sequence. However, white space is not allowed within
sequences such as (?> that introduce various parenthesized groups, 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 is equivalent to Perl's /x option, and it can be changed
within a pattern by a (?x) option setting.
When PCRE2 is compiled without Unicode support, PCRE2_EXTENDED
recognizes as white space only those characters with code points less
than 256 that are flagged as white space in its low-character table.
The table is normally created by pcre2_maketables(), which uses the
isspace() function to identify space characters. In most ASCII
environments, the relevant characters are those with code points 0x0009
(tab), 0x000A (linefeed), 0x000B (vertical tab), 0x000C (formfeed),
0x000D (carriage return), and 0x0020 (space).
When PCRE2 is compiled with Unicode support, in addition to these
characters, five more Unicode "Pattern White Space" characters are
recognized by PCRE2_EXTENDED. These are U+0085 (next line), U+200E
(left-to-right mark), U+200F (right-to-left mark), U+2028 (line
separator), and U+2029 (paragraph separator). This set of characters is
the same as recognized by Perl's /x option. Note that the horizontal
and vertical space characters that are matched by the \h and \v escapes
in patterns are a much bigger set.
As well as ignoring most white space, 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.
Which characters are interpreted as newlines can be specified by a
setting in the compile context that is passed to pcre2_compile() or by
a special sequence at the start of the pattern, as described in the
section entitled "Newline conventions" in the pcre2pattern
documentation. A default is defined when PCRE2 is built.
PCRE2_EXTENDED_MORE
This option has the effect of PCRE2_EXTENDED, but, in addition,
unescaped space and horizontal tab characters are ignored inside a
character class. Note: only these two characters are ignored, not the
full set of pattern white space characters that are ignored outside a
character class. PCRE2_EXTENDED_MORE is equivalent to Perl's /xx
option, and it can be changed within a pattern by a (?xx) option
setting.
PCRE2_FIRSTLINE
If this option is set, the start of an unanchored pattern match must be
before or at the first newline in the subject string following the
start of matching, though the matched text may continue over the
newline. If startoffset is non-zero, the limiting newline is not
necessarily the first newline in the subject. For example, if the
subject string is "abc\nxyz" (where \n represents a single-character
newline) a pattern match for "yz" succeeds with PCRE2_FIRSTLINE if
startoffset is greater than 3. 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. This option has no effect for anchored patterns.
PCRE2_LITERAL
If this option is set, all meta-characters in the pattern are disabled,
and it is treated as a literal string. Matching literal strings with a
regular expression engine is not the most efficient way of doing it. If
you are doing a lot of literal matching and are worried about
efficiency, you should consider using other approaches. The only other
main options that are allowed with PCRE2_LITERAL are: PCRE2_ANCHORED,
PCRE2_ENDANCHORED, PCRE2_AUTO_CALLOUT, PCRE2_CASELESS, PCRE2_FIRSTLINE,
PCRE2_MATCH_INVALID_UTF, PCRE2_NO_START_OPTIMIZE, PCRE2_NO_UTF_CHECK,
PCRE2_UTF, and PCRE2_USE_OFFSET_LIMIT. The extra options
PCRE2_EXTRA_MATCH_LINE and PCRE2_EXTRA_MATCH_WORD are also supported.
Any other options cause an error.
PCRE2_MATCH_INVALID_UTF
This option forces PCRE2_UTF (see below) and also enables support for
matching by pcre2_match() in subject strings that contain invalid UTF
sequences. Note, however, that the 16-bit and 32-bit PCRE2 libraries
process strings as sequences of uint16_t or uint32_t code points. They
cannot find valid UTF sequences within an arbitrary string of bytes
unless such sequences are suitably aligned. This facility is not
supported for DFA matching. For details, see the pcre2unicode
documentation.
PCRE2_MATCH_UNSET_BACKREF
If this option is set, a backreference to an unset capture 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). This is the same as Perl's /n option. Note that,
when this option is set, references to capture groups (backreferences
or recursion/subroutine calls) may only refer to named groups, though
the reference can be by name or by number.
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 capture group that is the subject of a backreference,
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 code unit value,
the matching code searches the subject for that value, and fails
immediately if it cannot find it, without actually running the main
matching function. This means that a special item such as (*COMMIT) at
the start of a pattern is not considered until after a suitable
starting point for the match has been found. Also, when callouts or
(*MARK) items are in use, these "start-up" optimizations can cause them
to be skipped if the pattern is never actually used. The start-up
optimizations are in effect a pre-scan of the subject that takes place
before the pattern is run.
The PCRE2_NO_START_OPTIMIZE option disables the start-up optimizations,
possibly causing performance to suffer, but ensuring that in cases
where the result is "no match", the callouts do occur, and that items
such as (*COMMIT) and (*MARK) are considered at every possible starting
position in the subject string.
Setting PCRE2_NO_START_OPTIMIZE may change the outcome of a matching
operation. Consider the pattern
(*COMMIT)ABC
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".
As another start-up optimization makes use of a minimum length for a
matching subject, which is recorded when possible. Consider the pattern
(*MARK:1)B(*MARK:2)(X|Y)
The minimum length for a match is two characters. If the subject is
"XXBB", the "starting character" optimization skips "XX", then tries to
match "BB", which is long enough. In the process, (*MARK:2) is
encountered and remembered. When the match attempt fails, the next "B"
is found, but there is only one character left, so there are no more
attempts, and "no match" is returned with the "last mark seen" set to
"2". If NO_START_OPTIMIZE is set, however, matches are tried at every
possible starting position, including at the end of the subject, where
(*MARK:1) is encountered, but there is no "B", so the "last mark seen"
that is returned is "1". In this case, the optimizations do not affect
the overall match result, which is still "no match", but they do 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 a valid UTF string, and you want to
skip this check for performance reasons, you can set the
PCRE2_NO_UTF_CHECK option. When it is set, the effect of passing an
invalid UTF string as a pattern is undefined. It may cause your program
to crash or loop.
Note that this option can also be passed to pcre2_match() and
pcre2_dfa_match(), to suppress UTF validity checking of the subject
string.
Note also that setting PCRE2_NO_UTF_CHECK at compile time does not
disable the error that is given if an escape sequence for an invalid
Unicode code point is encountered in the pattern. In particular, the
so-called "surrogate" code points (0xd800 to 0xdfff) are invalid. If
you want to allow escape sequences such as \x{d800} you can set the
PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES extra option, as described in the
section entitled "Extra compile options" below. However, this is
possible only in UTF-8 and UTF-32 modes, because these values are not
representable in UTF-16.
PCRE2_UCP
This option has two effects. Firstly, it change 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 to classify characters.
There are some PCRE2_EXTRA options (see below) that add finer control
to this behaviour. More details are given in the section on generic
character types in the pcre2pattern page.
The second effect of PCRE2_UCP is to force the use of Unicode
properties for upper/lower casing operations, even when PCRE2_UTF is
not set. This makes it possible to process strings in the 16-bit UCS-2
code. This option is available only if PCRE2 has been compiled with
Unicode support (which is the default). The
PCRE2_EXTRA_CASELESS_RESTRICT option (see below) restricts caseless
matching such that ASCII characters match only ASCII characters and
non-ASCII characters match only non-ASCII characters.
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 PCRE2_UTF changes the behaviour of PCRE2 are given in
the pcre2unicode page. In particular, note that it changes the way
PCRE2_CASELESS works.
Extra compile options
The option bits that can be set in a compile context by calling the
pcre2_set_compile_extra_options() function are as follows:
PCRE2_EXTRA_ALLOW_LOOKAROUND_BSK
Since release 10.38 PCRE2 has forbidden the use of \K within lookaround
assertions, following Perl's lead. This option is provided to re-enable
the previous behaviour (act in positive lookarounds, ignore in negative
ones) in case anybody is relying on it.
PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES
This option applies when compiling a pattern in UTF-8 or UTF-32 mode.
It is forbidden in UTF-16 mode, and ignored in non-UTF modes. Unicode
"surrogate" code points in the range 0xd800 to 0xdfff are used in pairs
in UTF-16 to encode code points with values in the range 0x10000 to
0x10ffff. The surrogates cannot therefore be represented in UTF-16.
They can be represented in UTF-8 and UTF-32, but are defined as invalid
code points, and cause errors if encountered in a UTF-8 or UTF-32
string that is being checked for validity by PCRE2.
These values also cause errors if encountered in escape sequences such
as \x{d912} within a pattern. However, it seems that some applications,
when using PCRE2 to check for unwanted characters in UTF-8 strings,
explicitly test for the surrogates using escape sequences. The
PCRE2_NO_UTF_CHECK option does not disable the error that occurs,
because it applies only to the testing of input strings for UTF
validity.
If the extra option PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES is set,
surrogate code point values in UTF-8 and UTF-32 patterns no longer
provoke errors and are incorporated in the compiled pattern. However,
they can only match subject characters if the matching function is
called with PCRE2_NO_UTF_CHECK set.
PCRE2_EXTRA_ALT_BSUX
The original option PCRE2_ALT_BSUX causes PCRE2 to process \U, \u, and
\x in the way that ECMAscript (aka JavaScript) does. Additional
functionality was defined by ECMAscript 6; setting PCRE2_EXTRA_ALT_BSUX
has the effect of PCRE2_ALT_BSUX, but in addition it recognizes
\u{hhh..} as a hexadecimal character code, where hhh.. is any number of
hexadecimal digits.
PCRE2_EXTRA_ASCII_BSD
This option forces \d to match only ASCII digits, even when PCRE2_UCP
is set. It can be changed within a pattern by means of the (?aD)
option setting.
PCRE2_EXTRA_ASCII_BSS
This option forces \s to match only ASCII space characters, even when
PCRE2_UCP is set. It can be changed within a pattern by means of the
(?aS) option setting.
PCRE2_EXTRA_ASCII_BSW
This option forces \w to match only ASCII word characters, even when
PCRE2_UCP is set. It can be changed within a pattern by means of the
(?aW) option setting.
PCRE2_EXTRA_ASCII_DIGIT
This option forces the POSIX character classes [:digit:] and [:xdigit:]
to match only ASCII digits, even when PCRE2_UCP is set. It can be
changed within a pattern by means of the (?aT) option setting.
PCRE2_EXTRA_ASCII_POSIX
This option forces all the POSIX character classes, including [:digit:]
and [:xdigit:], to match only ASCII characters, even when PCRE2_UCP is
set. It can be changed within a pattern by means of the (?aP) option
setting, but note that this also sets PCRE2_EXTRA_ASCII_DIGIT in order
to ensure that (?-aP) unsets all ASCII restrictions for POSIX classes.
PCRE2_EXTRA_BAD_ESCAPE_IS_LITERAL
This is a dangerous option. Use with care. By default, an unrecognized
escape such as \j or a malformed one such as \x{2z} causes a compile-
time error when detected by pcre2_compile(). Perl is somewhat
inconsistent in handling such items: for example, \j is treated as a
literal "j", and non-hexadecimal digits in \x{} are just ignored,
though warnings are given in both cases if Perl's warning switch is
enabled. However, a malformed octal number after \o{ always causes an
error in Perl.
If the PCRE2_EXTRA_BAD_ESCAPE_IS_LITERAL extra option is passed to
pcre2_compile(), all unrecognized or malformed escape sequences are
treated as single-character escapes. For example, \j is a literal "j"
and \x{2z} is treated as the literal string "x{2z}". Setting this
option means that typos in patterns may go undetected and have
unexpected results. Also note that a sequence such as [\N{] is
interpreted as a malformed attempt at [\N{...}] and so is treated as
[N{] whereas [\N] gives an error because an unqualified \N is a valid
escape sequence but is not supported in a character class. To
reiterate: this is a dangerous option. Use with great care.
PCRE2_EXTRA_CASELESS_RESTRICT
When either PCRE2_UCP or PCRE2_UTF is set, caseless matching follows
Unicode rules, which allow for more than two cases per character. There
are two case-equivalent character sets that contain both ASCII and non-
ASCII characters. The ASCII letter S is case-equivalent to U+017f (long
S) and the ASCII letter K is case-equivalent to U+212a (Kelvin sign).
This option disables recognition of case-equivalences that cross the
ASCII/non-ASCII boundary. In a caseless match, both characters must
either be ASCII or non-ASCII. The option can be changed with a pattern
by the (?r) option setting.
PCRE2_EXTRA_ESCAPED_CR_IS_LF
There are some legacy applications where the escape sequence \r in a
pattern is expected to match a newline. If this option is set, \r in a
pattern is converted to \n so that it matches a LF (linefeed) instead
of a CR (carriage return) character. The option does not affect a
literal CR in the pattern, nor does it affect CR specified as an
explicit code point such as \x{0D}.
PCRE2_EXTRA_MATCH_LINE
This option is provided for use by the -x option of pcre2grep. It
causes the pattern only to match complete lines. This is achieved by
automatically inserting the code for "^(?:" at the start of the
compiled pattern and ")$" at the end. Thus, when PCRE2_MULTILINE is
set, the matched line may be in the middle of the subject string. This
option can be used with PCRE2_LITERAL.
PCRE2_EXTRA_MATCH_WORD
This option is provided for use by the -w option of pcre2grep. It
causes the pattern only to match strings that have a word boundary at
the start and the end. This is achieved by automatically inserting the
code for "\b(?:" at the start of the compiled pattern and ")\b" at the
end. The option may be used with PCRE2_LITERAL. However, it is ignored
if PCRE2_EXTRA_MATCH_LINE is also set.
JUST-IN-TIME (JIT) COMPILATION
int pcre2_jit_compile(pcre2_code *code, uint32_t options);
int pcre2_jit_match(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext);
void pcre2_jit_free_unused_memory(pcre2_general_context *gcontext);
pcre2_jit_stack *pcre2_jit_stack_create(size_t startsize,
size_t maxsize, pcre2_general_context *gcontext);
void pcre2_jit_stack_assign(pcre2_match_context *mcontext,
pcre2_jit_callback callback_function, void *callback_data);
void pcre2_jit_stack_free(pcre2_jit_stack *jit_stack);
These functions provide support for JIT compilation, which, if the
just-in-time compiler is available, further processes a compiled
pattern into machine code that executes much faster than the
pcre2_match() interpretive matching function. Full details are given in
the pcre2jit documentation.
JIT compilation is a heavyweight optimization. It can take some time
for patterns to be analyzed, and for one-off matches and simple
patterns the benefit of faster execution might be offset by a much
slower compilation time. Most (but not all) patterns can be optimized
by the JIT compiler.
LOCALE SUPPORT
const uint8_t *pcre2_maketables(pcre2_general_context *gcontext);
void pcre2_maketables_free(pcre2_general_context *gcontext,
const uint8_t *tables);
PCRE2 handles caseless matching, and determines whether characters are
letters, digits, or whatever, by reference to a set of tables, indexed
by character code point. However, this applies only to characters whose
code points are less than 256. By default, higher-valued code points
never match escapes such as \w or \d.
When PCRE2 is built with Unicode support (the default), certain Unicode
character properties can be tested with \p and \P, or, alternatively,
the PCRE2_UCP option can be set when a pattern is compiled; this causes
\w and friends to use Unicode property support instead of the built-in
tables. PCRE2_UCP also causes upper/lower casing operations on
characters with code points greater than 127 to use Unicode properties.
These effects apply even when PCRE2_UTF is not set. There are, however,
some PCRE2_EXTRA options (see above) that can be used to modify or
suppress them.
The use of locales with Unicode is discouraged. If you are handling
characters with code points greater than 127, you should either use
Unicode support, or use locales, but not try to mix the two.
PCRE2 contains a built-in set of character tables that are used by
default. These are sufficient for many applications. Normally, the
internal tables recognize only ASCII characters. However, when PCRE2 is
built, it is possible to cause the internal tables to be rebuilt in the
default "C" locale of the local system, which may cause them to be
different.
The built-in tables can be overridden by tables supplied by the
application that calls PCRE2. These may be created in a different
locale from the default. As more and more applications change to using
Unicode, the need for this locale support is expected to die away.
External tables are built by calling the pcre2_maketables() function,
in the relevant locale. The only argument to this function is a general
context, which can be used to pass a custom memory allocator. If the
argument is NULL, the system malloc() is used. The result can be passed
to pcre2_compile() as often as necessary, by creating a compile context
and calling pcre2_set_character_tables() to set the tables pointer
therein.
For example, to build and use tables that are appropriate for the
French locale (where accented characters with values greater than 127
are treated as letters), the following code could be used:
setlocale(LC_CTYPE, "fr_FR");
tables = pcre2_maketables(NULL);
ccontext = pcre2_compile_context_create(NULL);
pcre2_set_character_tables(ccontext, tables);
re = pcre2_compile(..., ccontext);
The locale name "fr_FR" is used on Linux and other Unix-like systems;
if you are using Windows, the name for the French locale is "french".
The pointer that is passed (via the compile context) to pcre2_compile()
is saved with the compiled pattern, and the same tables are used by the
matching functions. Thus, for any single pattern, compilation and
matching both happen in the same locale, but different patterns can be
processed in different locales.
It is the caller's responsibility to ensure that the memory containing
the tables remains available while they are still in use. When they are
no longer needed, you can discard them using pcre2_maketables_free(),
which should pass as its first parameter the same global context that
was used to create the tables.
Saving locale tables
The tables described above are just a sequence of binary bytes, which
makes them independent of hardware characteristics such as endianness
or whether the processor is 32-bit or 64-bit. A copy of the result of
pcre2_maketables() can therefore be saved in a file or elsewhere and
re-used later, even in a different program or on another computer. The
size of the tables (number of bytes) must be obtained by calling
pcre2_config() with the PCRE2_CONFIG_TABLES_LENGTH option because
pcre2_maketables() does not return this value. Note that the
pcre2_dftables program, which is part of the PCRE2 build system, can be
used stand-alone to create a file that contains a set of binary tables.
See the pcre2build documentation for details.
INFORMATION ABOUT A COMPILED PATTERN
int pcre2_pattern_info(const pcre2 *code, uint32_t what, void *where);
The pcre2_pattern_info() function returns general information about a
compiled pattern. For information about callouts, see the next section.
The first argument for pcre2_pattern_info() is a pointer to the
compiled pattern. The second argument specifies which piece of
information is required, and the third argument is a pointer to a
variable to receive the data. If the third argument is NULL, the first
argument is ignored, and the function returns the size in bytes of the
variable that is required for the information requested. Otherwise, the
yield of the function is zero for success, or one of the following
negative numbers:
PCRE2_ERROR_NULL the argument code was NULL
PCRE2_ERROR_BADMAGIC the "magic number" was not found
PCRE2_ERROR_BADOPTION the value of what was invalid
PCRE2_ERROR_UNSET the requested field is not set
The "magic number" is placed at the start of each compiled pattern as a
simple check against passing an arbitrary memory pointer. Here is a
typical call of pcre2_pattern_info(), to obtain the length of the
compiled pattern:
int rc;
size_t length;
rc = pcre2_pattern_info(
re, /* result of pcre2_compile() */
PCRE2_INFO_SIZE, /* what is required */
&length); /* where to put the data */
The possible values for the second argument are defined in pcre2.h, and
are as follows:
PCRE2_INFO_ALLOPTIONS
PCRE2_INFO_ARGOPTIONS
PCRE2_INFO_EXTRAOPTIONS
Return copies of the pattern's options. The third argument should point
to a uint32_t variable. PCRE2_INFO_ARGOPTIONS returns exactly the
options that were passed to pcre2_compile(), whereas
PCRE2_INFO_ALLOPTIONS returns the compile options as modified by any
top-level (*XXX) option settings such as (*UTF) at the start of the
pattern itself. PCRE2_INFO_EXTRAOPTIONS returns the extra options that
were set in the compile context by calling the
pcre2_set_compile_extra_options() function.
For example, if the pattern /(*UTF)abc/ is compiled with the
PCRE2_EXTENDED option, the result for PCRE2_INFO_ALLOPTIONS is
PCRE2_EXTENDED and PCRE2_UTF. Option settings such as (?i) that can
change within a pattern do not affect the result of
PCRE2_INFO_ALLOPTIONS, even if they appear right at the start of the
pattern. (This was different in some earlier releases.)
A pattern compiled without PCRE2_ANCHORED is automatically anchored by
PCRE2 if the first significant item in every top-level branch is one of
the following:
^ unless PCRE2_MULTILINE is set
\A always
\G always
.* sometimes - see below
When .* is the first significant item, anchoring is possible only when
all the following are true:
.* is not in an atomic group
.* is not in a capture group that is the subject
of a backreference
PCRE2_DOTALL is in force for .*
Neither (*PRUNE) nor (*SKIP) appears in the pattern
PCRE2_NO_DOTSTAR_ANCHOR is not set
For patterns that are auto-anchored, the PCRE2_ANCHORED bit is set in
the options returned for PCRE2_INFO_ALLOPTIONS.
PCRE2_INFO_BACKREFMAX
Return the number of the highest backreference in the pattern. The
third argument should point to a uint32_t variable. Named capture
groups acquire numbers as well as names, and these count towards the
highest backreference. Backreferences such as \4 or \g{12} match the
captured characters of the given group, but in addition, the check that
a capture group is set in a conditional group such as (?(3)a|b) is also
a backreference. Zero is returned if there are no backreferences.
PCRE2_INFO_BSR
The output is a uint32_t integer whose value indicates what character
sequences the \R escape sequence matches. A value of PCRE2_BSR_UNICODE
means that \R matches any Unicode line ending sequence; a value of
PCRE2_BSR_ANYCRLF means that \R matches only CR, LF, or CRLF.
PCRE2_INFO_CAPTURECOUNT
Return the highest capture group number in the pattern. In patterns
where (?| is not used, this is also the total number of capture groups.
The third argument should point to a uint32_t variable.
PCRE2_INFO_DEPTHLIMIT
If the pattern set a backtracking depth limit by including an item of
the form (*LIMIT_DEPTH=nnnn) at the start, the value is returned. The
third argument should point to a uint32_t integer. If no such value has
been set, the call to pcre2_pattern_info() returns the error
PCRE2_ERROR_UNSET. Note that this limit will only be used during
matching if it is less than the limit set or defaulted by the caller of
the match function.
PCRE2_INFO_FIRSTBITMAP
In the absence of a single first code unit for a non-anchored pattern,
pcre2_compile() may construct a 256-bit table that defines a fixed set
of values for the first code unit in any match. For example, a pattern
that starts with [abc] results in a table with three bits set. When
code unit values greater than 255 are supported, the flag bit for 255
means "any code unit of value 255 or above". If such a table was
constructed, a pointer to it is returned. Otherwise NULL is returned.
The third argument should point to a const uint8_t * variable.
PCRE2_INFO_FIRSTCODETYPE
Return information about the first code unit of any matched string, for
a non-anchored pattern. The third argument should point to a uint32_t
variable. If there is a fixed first value, for example, the letter "c"
from a pattern such as (cat|cow|coyote), 1 is returned, and the value
can be retrieved using PCRE2_INFO_FIRSTCODEUNIT. If there is no fixed
first value, but it is known that a match can occur only at the start
of the subject or following a newline in the subject, 2 is returned.
Otherwise, and for anchored patterns, 0 is returned.
PCRE2_INFO_FIRSTCODEUNIT
Return the value of the first code unit of any matched string for a
pattern where PCRE2_INFO_FIRSTCODETYPE returns 1; otherwise return 0.
The third argument should point to a uint32_t variable. In the 8-bit
library, the value is always less than 256. In the 16-bit library the
value can be up to 0xffff. In the 32-bit library in UTF-32 mode the
value can be up to 0x10ffff, and up to 0xffffffff when not using UTF-32
mode.
PCRE2_INFO_FRAMESIZE
Return the size (in bytes) of the data frames that are used to remember
backtracking positions when the pattern is processed by pcre2_match()
without the use of JIT. The third argument should point to a size_t
variable. The frame size depends on the number of capturing parentheses
in the pattern. Each additional capture group adds two PCRE2_SIZE
variables.
PCRE2_INFO_HASBACKSLASHC
Return 1 if the pattern contains any instances of \C, otherwise 0. The
third argument should point to a uint32_t variable.
PCRE2_INFO_HASCRORLF
Return 1 if the pattern contains any explicit matches for CR or LF
characters, otherwise 0. The third argument should point to a uint32_t
variable. An explicit match is either a literal CR or LF character, or
\r or \n or one of the equivalent hexadecimal or octal escape
sequences.
PCRE2_INFO_HEAPLIMIT
If the pattern set a heap memory limit by including an item of the form
(*LIMIT_HEAP=nnnn) at the start, the value is returned. The third
argument should point to a uint32_t integer. If no such value has been
set, the call to pcre2_pattern_info() returns the error
PCRE2_ERROR_UNSET. Note that this limit will only be used during
matching if it is less than the limit set or defaulted by the caller of
the match function.
PCRE2_INFO_JCHANGED
Return 1 if the (?J) or (?-J) option setting is used in the pattern,
otherwise 0. The third argument should point to a uint32_t variable.
(?J) and (?-J) set and unset the local PCRE2_DUPNAMES option,
respectively.
PCRE2_INFO_JITSIZE
If the compiled pattern was successfully processed by
pcre2_jit_compile(), return the size of the JIT compiled code,
otherwise return zero. The third argument should point to a size_t
variable.
PCRE2_INFO_LASTCODETYPE
Returns 1 if there is a rightmost literal code unit that must exist in
any matched string, other than at its start. The third argument should
point to a uint32_t variable. If there is no such value, 0 is returned.
When 1 is returned, the code unit value itself can be retrieved using
PCRE2_INFO_LASTCODEUNIT. For anchored patterns, a last literal value is
recorded only if it follows something of variable length. For example,
for the pattern /^a\d+z\d+/ the returned value is 1 (with "z" returned
from PCRE2_INFO_LASTCODEUNIT), but for /^a\dz\d/ the returned value is
0.
PCRE2_INFO_LASTCODEUNIT
Return the value of the rightmost literal code unit that must exist in
any matched string, other than at its start, for a pattern where
PCRE2_INFO_LASTCODETYPE returns 1. Otherwise, return 0. The third
argument should point to a uint32_t variable.
PCRE2_INFO_MATCHEMPTY
Return 1 if the pattern might match an empty string, otherwise 0. The
third argument should point to a uint32_t variable. When a pattern
contains recursive subroutine calls it is not always possible to
determine whether or not it can match an empty string. PCRE2 takes a
cautious approach and returns 1 in such cases.
PCRE2_INFO_MATCHLIMIT
If the pattern set a match limit by including an item of the form
(*LIMIT_MATCH=nnnn) at the start, the value is returned. The third
argument should point to a uint32_t integer. If no such value has been
set, the call to pcre2_pattern_info() returns the error
PCRE2_ERROR_UNSET. Note that this limit will only be used during
matching if it is less than the limit set or defaulted by the caller of
the match function.
PCRE2_INFO_MAXLOOKBEHIND
A lookbehind assertion moves back a certain number of characters (not
code units) when it starts to process each of its branches. This
request returns the largest of these backward moves. The third argument
should point to a uint32_t integer. The simple assertions \b and \B
require a one-character lookbehind and cause PCRE2_INFO_MAXLOOKBEHIND
to return 1 in the absence of anything longer. \A also registers a one-
character lookbehind, though it does not actually inspect the previous
character.
Note that this information is useful for multi-segment matching only if
the pattern contains no nested lookbehinds. For example, the pattern
(?<=a(?<=ba)c) returns a maximum lookbehind of 2, but when it is
processed, the first lookbehind moves back by two characters, matches
one character, then the nested lookbehind also moves back by two
characters. This puts the matching point three characters earlier than
it was at the start. PCRE2_INFO_MAXLOOKBEHIND is really only useful as
a debugging tool. See the pcre2partial documentation for a discussion
of multi-segment matching.
PCRE2_INFO_MINLENGTH
If a minimum length for matching subject strings was computed, its
value is returned. Otherwise the returned value is 0. This value is not
computed when PCRE2_NO_START_OPTIMIZE is set. The value is a number of
characters, which in UTF mode may be different from the number of code
units. The third argument should point to a uint32_t variable. The
value is a lower bound to the length of any matching string. There may
not be any strings of that length that do actually match, but every
string that does match is at least that long.
PCRE2_INFO_NAMECOUNT
PCRE2_INFO_NAMEENTRYSIZE
PCRE2_INFO_NAMETABLE
PCRE2 supports the use of named as well as numbered capturing
parentheses. The names are just an additional way of identifying the
parentheses, which still acquire numbers. Several convenience functions
such as pcre2_substring_get_byname() are provided for extracting
captured substrings by name. It is also possible to extract the data
directly, by first converting the name to a number in order to access
the correct pointers in the output vector (described with pcre2_match()
below). To do the conversion, you need to use the name-to-number map,
which is described by these three values.
The map consists of a number of fixed-size entries.
PCRE2_INFO_NAMECOUNT gives the number of entries, and
PCRE2_INFO_NAMEENTRYSIZE gives the size of each entry in code units;
both of these return a uint32_t value. The entry size depends on the
length of the longest name.
PCRE2_INFO_NAMETABLE returns a pointer to the first entry of the table.
This is a PCRE2_SPTR pointer to a block of code units. In the 8-bit
library, the first two bytes of each entry are the number of the
capturing parenthesis, most significant byte first. In the 16-bit
library, the pointer points to 16-bit code units, the first of which
contains the parenthesis number. In the 32-bit library, the pointer
points to 32-bit code units, the first of which contains the
parenthesis number. The rest of the entry is the corresponding name,
zero terminated.
The names are in alphabetical order. If (?| is used to create multiple
capture groups with the same number, as described in the section on
duplicate group numbers in the pcre2pattern page, the groups may be
given the same name, but there is only one entry in the table.
Different names for groups of the same number are not permitted.
Duplicate names for capture groups with different numbers are
permitted, but only if PCRE2_DUPNAMES is set. They appear in the table
in the order in which they were found in the pattern. In the absence of
(?| this is the order of increasing number; when (?| is used this is
not necessarily the case because later capture groups may have lower
numbers.
As a simple example of the name/number table, consider the following
pattern after compilation by the 8-bit library (assume PCRE2_EXTENDED
is set, so white space - including newlines - is ignored):
(?<date> (?<year>(\d\d)?\d\d) -
(?<month>\d\d) - (?<day>\d\d) )
There are four named capture groups, so the table has four entries, and
each entry in the table is eight bytes long. The table is as follows,
with non-printing bytes shows in hexadecimal, and undefined bytes shown
as ??:
00 01 d a t e 00 ??
00 05 d a y 00 ?? ??
00 04 m o n t h 00
00 02 y e a r 00 ??
When writing code to extract data from named capture groups using the
name-to-number map, remember that the length of the entries is likely
to be different for each compiled pattern.
PCRE2_INFO_NEWLINE
The output is one of the following uint32_t values:
PCRE2_NEWLINE_CR Carriage return (CR)
PCRE2_NEWLINE_LF Linefeed (LF)
PCRE2_NEWLINE_CRLF Carriage return, linefeed (CRLF)
PCRE2_NEWLINE_ANY Any Unicode line ending
PCRE2_NEWLINE_ANYCRLF Any of CR, LF, or CRLF
PCRE2_NEWLINE_NUL The NUL character (binary zero)
This identifies the character sequence that will be recognized as
meaning "newline" while matching.
PCRE2_INFO_SIZE
Return the size of the compiled pattern in bytes (for all three
libraries). The third argument should point to a size_t variable. This
value includes the size of the general data block that precedes the
code units of the compiled pattern itself. The value that is used when
pcre2_compile() is getting memory in which to place the compiled
pattern may be slightly larger than the value returned by this option,
because there are cases where the code that calculates the size has to
over-estimate. Processing a pattern with the JIT compiler does not
alter the value returned by this option.
INFORMATION ABOUT A PATTERN'S CALLOUTS
int pcre2_callout_enumerate(const pcre2_code *code,
int (*callback)(pcre2_callout_enumerate_block *, void *),
void *user_data);
A script language that supports the use of string arguments in callouts
might like to scan all the callouts in a pattern before running the
match. This can be done by calling pcre2_callout_enumerate(). The first
argument is a pointer to a compiled pattern, the second points to a
callback function, and the third is arbitrary user data. The callback
function is called for every callout in the pattern in the order in
which they appear. Its first argument is a pointer to a callout
enumeration block, and its second argument is the user_data value that
was passed to pcre2_callout_enumerate(). The contents of the callout
enumeration block are described in the pcre2callout documentation,
which also gives further details about callouts.
SERIALIZATION AND PRECOMPILING
It is possible to save compiled patterns on disc or elsewhere, and
reload them later, subject to a number of restrictions. The host on
which the patterns are reloaded must be running the same version of
PCRE2, with the same code unit width, and must also have the same
endianness, pointer width, and PCRE2_SIZE type. Before compiled
patterns can be saved, they must be converted to a "serialized" form,
which in the case of PCRE2 is really just a bytecode dump. The
functions whose names begin with pcre2_serialize_ are used for
converting to and from the serialized form. They are described in the
pcre2serialize documentation. Note that PCRE2 serialization does not
convert compiled patterns to an abstract format like Java or .NET
serialization.
THE MATCH DATA BLOCK
pcre2_match_data *pcre2_match_data_create(uint32_t ovecsize,
pcre2_general_context *gcontext);
pcre2_match_data *pcre2_match_data_create_from_pattern(
const pcre2_code *code, pcre2_general_context *gcontext);
void pcre2_match_data_free(pcre2_match_data *match_data);
Information about a successful or unsuccessful match is placed in a
match data block, which is an opaque structure that is accessed by
function calls. In particular, the match data block contains a vector
of offsets into the subject string that define the matched parts of the
subject. This is known as the ovector.
Before calling pcre2_match(), pcre2_dfa_match(), or pcre2_jit_match()
you must create a match data block by calling one of the creation
functions above. For pcre2_match_data_create(), the first argument is
the number of pairs of offsets in the ovector.
When using pcre2_match(), one pair of offsets is required to identify
the string that matched the whole pattern, with an additional pair for
each captured substring. For example, a value of 4 creates enough space
to record the matched portion of the subject plus three captured
substrings.
When using pcre2_dfa_match() there may be multiple matched substrings
of different lengths at the same point in the subject. The ovector
should be made large enough to hold as many as are expected.
A minimum of at least 1 pair is imposed by pcre2_match_data_create(),
so it is always possible to return the overall matched string in the
case of pcre2_match() or the longest match in the case of
pcre2_dfa_match(). The maximum number of pairs is 65535; if the first
argument of pcre2_match_data_create() is greater than this, 65535 is
used.
The second argument of pcre2_match_data_create() is a pointer to a
general context, which can specify custom memory management for
obtaining the memory for the match data block. If you are not using
custom memory management, pass NULL, which causes malloc() to be used.
For pcre2_match_data_create_from_pattern(), the first argument is a
pointer to a compiled pattern. The ovector is created to be exactly the
right size to hold all the substrings a pattern might capture when
matched using pcre2_match(). You should not use this call when matching
with pcre2_dfa_match(). The second argument is again a pointer to a
general context, but in this case if NULL is passed, the memory is
obtained using the same allocator that was used for the compiled
pattern (custom or default).
A match data block can be used many times, with the same or different
compiled patterns. You can extract information from a match data block
after a match operation has finished, using functions that are
described in the sections on matched strings and other match data
below.
When a call of pcre2_match() fails, valid data is available in the
match block only when the error is PCRE2_ERROR_NOMATCH,
PCRE2_ERROR_PARTIAL, or one of the error codes for an invalid UTF
string. Exactly what is available depends on the error, and is detailed
below.
When one of the matching functions is called, pointers to the compiled
pattern and the subject string are set in the match data block so that
they can be referenced by the extraction functions after a successful
match. After running a match, you must not free a compiled pattern or a
subject string until after all operations on the match data block (for
that match) have taken place, unless, in the case of the subject
string, you have used the PCRE2_COPY_MATCHED_SUBJECT option, which is
described in the section entitled "Option bits for pcre2_match()"
below.
When a match data block itself is no longer needed, it should be freed
by calling pcre2_match_data_free(). If this function is called with a
NULL argument, it returns immediately, without doing anything.
MEMORY USE FOR MATCH DATA BLOCKS
PCRE2_SIZE pcre2_get_match_data_size(pcre2_match_data *match_data);
PCRE2_SIZE pcre2_get_match_data_heapframes_size(
pcre2_match_data *match_data);
The size of a match data block depends on the size of the ovector that
it contains. The function pcre2_get_match_data_size() returns the size,
in bytes, of the block that is its argument.
When pcre2_match() runs interpretively (that is, without using JIT), it
makes use of a vector of data frames for remembering backtracking
positions. The size of each individual frame depends on the number of
capturing parentheses in the pattern and can be obtained by calling
pcre2_pattern_info() with the PCRE2_INFO_FRAMESIZE option (see the
section entitled "Information about a compiled pattern" above).
Heap memory is used for the frames vector; if the initial memory block
turns out to be too small during matching, it is automatically
expanded. When pcre2_match() returns, the memory is not freed, but
remains attached to the match data block, for use by any subsequent
matches that use the same block. It is automatically freed when the
match data block itself is freed.
You can find the current size of the frames vector that a match data
block owns by calling pcre2_get_match_data_heapframes_size(). For a
newly created match data block the size will be zero. Some types of
match may require a lot of frames and thus a large vector; applications
that run in environments where memory is constrained can check this and
free the match data block if the heap frames vector has become too big.
MATCHING A PATTERN: THE TRADITIONAL FUNCTION
int pcre2_match(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext);
The function pcre2_match() is called to match a subject string against
a compiled pattern, which is passed in the code argument. You can call
pcre2_match() with the same code argument as many times as you like, in
order to find multiple matches in the subject string or to match
different subject strings with the same pattern.
This function is the main matching facility of the library, and it
operates in a Perl-like manner. For specialist use there is also an
alternative matching function, which is described below in the section
about the pcre2_dfa_match() function.
Here is an example of a simple call to pcre2_match():
pcre2_match_data *md = pcre2_match_data_create(4, NULL);
int rc = pcre2_match(
re, /* result of pcre2_compile() */
"some string", /* the subject string */
11, /* the length of the subject string */
0, /* start at offset 0 in the subject */
0, /* default options */
md, /* the match data block */
NULL); /* a match context; NULL means use defaults */
If the subject string is zero-terminated, the length can be given as
PCRE2_ZERO_TERMINATED. A match context must be provided if certain less
common matching parameters are to be changed. For details, see the
section on the match context above.
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. As a special case, if subject is NULL and length
is zero, the subject is assumed to be an empty string. If length is
non-zero, an error occurs if subject is NULL.
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 zeros.
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 "Mississippi" the first call to
pcre2_match() finds the first occurrence. If pcre2_match() is called
again with just the remainder of the subject, namely "issippi", 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, a
single attempt to match at the given offset is made. This can only
succeed if the pattern does not require the match to be at the start of
the subject. In other words, the anchoring must be the result of
setting the PCRE2_ANCHORED option or the use of .* with PCRE2_DOTALL,
not by starting the pattern with ^ or \A.
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_COPY_MATCHED_SUBJECT, PCRE2_DISABLE_RECURSELOOP_CHECK,
PCRE2_ENDANCHORED, PCRE2_NOTBOL, PCRE2_NOTEOL, PCRE2_NOTEMPTY,
PCRE2_NOTEMPTY_ATSTART, PCRE2_NO_JIT, PCRE2_NO_UTF_CHECK,
PCRE2_PARTIAL_HARD, and PCRE2_PARTIAL_SOFT. Their action is described
below.
Setting PCRE2_ANCHORED or PCRE2_ENDANCHORED at match time is not
supported by the just-in-time (JIT) compiler. If it is set, JIT
matching is disabled and the interpretive code in pcre2_match() is run.
PCRE2_DISABLE_RECURSELOOP_CHECK is ignored by JIT, but apart from
PCRE2_NO_JIT (obviously), 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_COPY_MATCHED_SUBJECT
By default, a pointer to the subject is remembered in the match data
block so that, after a successful match, it can be referenced by the
substring extraction functions. This means that the subject's memory
must not be freed until all such operations are complete. For some
applications where the lifetime of the subject string is not
guaranteed, it may be necessary to make a copy of the subject string,
but it is wasteful to do this unless the match is successful. After a
successful match, if PCRE2_COPY_MATCHED_SUBJECT is set, the subject is
copied and the new pointer is remembered in the match data block
instead of the original subject pointer. The memory allocator that was
used for the match block itself is used. The copy is automatically
freed when pcre2_match_data_free() is called to free the match data
block. It is also automatically freed if the match data block is re-
used for another match operation.
PCRE2_DISABLE_RECURSELOOP_CHECK
This option is relevant only to pcre2_match() for interpretive
matching. It is ignored when JIT is used, and is forbidden for
pcre2_dfa_match().
The use of recursion in patterns can lead to infinite loops. In the
interpretive matcher these would be eventually caught by the match or
heap limits, but this could take a long time and/or use a lot of memory
if the limits are large. There is therefore a check at the start of
each recursion. If the same group is still active from a previous
call, and the current subject pointer is the same as it was at the
start of that group, and the furthest inspected character of the
subject has not changed, an error is generated.
There are rare cases of matches that would complete, but nevertheless
trigger this error. This option disables the check. It is provided
mainly for testing when comparing JIT and interpretive behaviour.
PCRE2_ENDANCHORED
If the PCRE2_ENDANCHORED option is set, any string that pcre2_match()
matches must be right at the end of the subject string. 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_JIT
By default, if a pattern has been successfully processed by
pcre2_jit_compile(), JIT is automatically used when pcre2_match() is
called with options that JIT supports. Setting PCRE2_NO_JIT disables
the use of JIT; it forces matching to be done by the interpreter.
PCRE2_NO_UTF_CHECK
When PCRE2_UTF is set at compile time, the validity of the subject as a
UTF string is checked unless PCRE2_NO_UTF_CHECK is passed to
pcre2_match() or PCRE2_MATCH_INVALID_UTF was passed to pcre2_compile().
The latter special case is discussed in detail in the pcre2unicode
documentation.
In the default case, 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 documentation.
If you know that your subject is valid, and you want to skip this check
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 multiple matches in the same subject string.
Warning: Unless PCRE2_MATCH_INVALID_UTF was set at compile time, when
PCRE2_NO_UTF_CHECK is set at match time 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 or give wrong
results.
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. In
addition, either at least one character must have been inspected or the
pattern must contain a lookbehind, or the pattern must be one that
could match an empty string.
If this situation arises 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 or equivalent
octal or hexadecimal escape sequences. Implicit matches such as [^X] do
not count, nor does \s, even though it includes CR and LF in the
characters that it matches.
Notwithstanding the above, anomalous effects may still occur when CRLF
is a valid newline sequence and explicit \r or \n escapes appear in the
pattern.
HOW PCRE2_MATCH() RETURNS A STRING AND CAPTURED SUBSTRINGS
uint32_t pcre2_get_ovector_count(pcre2_match_data *match_data);
PCRE2_SIZE *pcre2_get_ovector_pointer(pcre2_match_data *match_data);
In general, a pattern matches a certain portion of the subject, and in
addition, further substrings from the subject may be picked out by
parenthesized parts of the pattern. Following the usage in Jeffrey
Friedl's book, this is called "capturing" in what follows, and the
phrase "capture group" (Perl terminology) is used for a fragment of a
pattern that picks out a substring. PCRE2 supports several other kinds
of parenthesized group that do not cause substrings to be captured. The
pcre2_pattern_info() function can be used to find out how many capture
groups there are in a compiled pattern.
You can use auxiliary functions for accessing captured substrings by
number or by name, as described in sections below.
Alternatively, you can make direct use of the vector of PCRE2_SIZE
values, called the ovector, which contains the offsets of captured
strings. It is part of the match data block. The function
pcre2_get_ovector_pointer() returns the address of the ovector, and
pcre2_get_ovector_count() returns the number of pairs of values it
contains.
Within the ovector, the first in each pair of values is set to the
offset of the first code unit of a substring, and the second is set to
the offset of the first code unit after the end of a substring. These
values are always code unit offsets, not character offsets. That is,
they are byte offsets in the 8-bit library, 16-bit offsets in the
16-bit library, and 32-bit offsets in the 32-bit library.
After a partial match (error return PCRE2_ERROR_PARTIAL), only the
first pair of offsets (that is, ovector[0] and ovector[1]) are set.
They identify the part of the subject that was partially matched. See
the pcre2partial documentation for details of partial matching.
After a fully successful match, the first pair of offsets identifies
the portion of the subject string that was matched by the entire
pattern. The next pair is used for the first captured substring, and so
on. The value returned by pcre2_match() is one more than the highest
numbered pair that has been set. For example, if two substrings have
been captured, the returned value is 3. If there are no captured
substrings, the return value from a successful match is 1, indicating
that just the first pair of offsets has been set.
If a pattern uses the \K escape sequence within a positive assertion,
the reported start of a successful match can be greater than the end of
the match. For example, if the pattern (?=ab\K) is matched against
"ab", the start and end offset values for the match are 2 and 0.
If a capture group is matched repeatedly within a single match
operation, it is the last portion of the subject that it matched that
is returned.
If the ovector is too small to hold all the captured substring offsets,
as much as possible is filled in, and the function returns a value of
zero. If captured substrings are not of interest, pcre2_match() may be
called with a match data block whose ovector is of minimum length (that
is, one pair).
It is possible for capture group number n+1 to match some part of the
subject when group n has not been used at all. For example, if the
string "abc" is matched against the pattern (a|(z))(bc) the return from
the function is 4, and groups 1 and 3 are matched, but 2 is not. When
this happens, both values in the offset pairs corresponding to unused
groups are set to PCRE2_UNSET.
Offset values that correspond to unused groups at the end of the
expression are also set to PCRE2_UNSET. For example, if the string
"abc" is matched against the pattern (abc)(x(yz)?)? groups 2 and 3 are
not matched. The return from the function is 2, because the highest
used capture group number is 1. The offsets for the second and third
capture groups (assuming the vector is large enough, of course) are set
to PCRE2_UNSET.
Elements in the ovector that do not correspond to capturing parentheses
in the pattern are never changed. That is, if a pattern contains n
capturing parentheses, no more than ovector[0] to ovector[2n+1] are set
by pcre2_match(). The other elements retain whatever values they
previously had. After a failed match attempt, the contents of the
ovector are unchanged.
OTHER INFORMATION ABOUT A MATCH
PCRE2_SPTR pcre2_get_mark(pcre2_match_data *match_data);
PCRE2_SIZE pcre2_get_startchar(pcre2_match_data *match_data);
As well as the offsets in the ovector, other information about a match
is retained in the match data block and can be retrieved by the above
functions in appropriate circumstances. If they are called at other
times, the result is undefined.
After a successful match, a partial match (PCRE2_ERROR_PARTIAL), or a
failure to match (PCRE2_ERROR_NOMATCH), a mark name may be available.
The function pcre2_get_mark() can be called to access this name, which
can be specified in the pattern by any of the backtracking control
verbs, not just (*MARK). The same function applies to all the verbs. It
returns a pointer to the zero-terminated name, which is within the
compiled pattern. If no name is available, NULL is returned. The length
of the name (excluding the terminating zero) is stored in the code unit
that precedes the name. You should use this length instead of relying
on the terminating zero if the name might contain a binary zero.
After a successful match, the name that is returned is the last mark
name encountered on the matching path through the pattern. Instances of
backtracking verbs without names do not count. Thus, for example, if
the matching path contains (*MARK:A)(*PRUNE), the name "A" is returned.
After a "no match" or a partial match, the last encountered name is
returned. For example, consider this pattern:
^(*MARK:A)((*MARK:B)a|b)c
When it matches "bc", the returned name is A. The B mark is "seen" in
the first branch of the group, but it is not on the matching path. On
the other hand, when this pattern fails to match "bx", the returned
name is B.
Warning: By default, certain start-of-match optimizations are used to
give a fast "no match" result in some situations. For example, if the
anchoring is removed from the pattern above, there is an initial check
for the presence of "c" in the subject before running the matching
engine. This check fails for "bx", causing a match failure without
seeing any marks. You can disable the start-of-match optimizations by
setting the PCRE2_NO_START_OPTIMIZE option for pcre2_compile() or by
starting the pattern with (*NO_START_OPT).
After a successful match, a partial match, or one of the invalid UTF
errors (for example, PCRE2_ERROR_UTF8_ERR5), pcre2_get_startchar() can
be called. After a successful or partial match it returns the code unit
offset of the character at which the match started. For a non-partial
match, this can be different to the value of ovector[0] if the pattern
contains the \K escape sequence. After a partial match, however, this
value is always the same as ovector[0] because \K does not affect the
result of a partial match.
After a UTF check failure, pcre2_get_startchar() can be used to obtain
the code unit offset of the invalid UTF character. Details are given in
the pcre2unicode page.
ERROR RETURNS FROM pcre2_match()
If pcre2_match() fails, it returns a negative number. This can be
converted to a text string by calling the pcre2_get_error_message()
function (see "Obtaining a textual error message" below). Negative
error codes are also returned by other functions, and are documented
with them. The codes are given names in the header file. If UTF
checking is in force and an invalid UTF subject string is detected, one
of a number of UTF-specific negative error codes is returned. Details
are given in the pcre2unicode page. The following are the other errors
that may be returned by pcre2_match():
PCRE2_ERROR_NOMATCH
The subject string did not match the pattern.
PCRE2_ERROR_PARTIAL
The subject string did not match, but it did match partially. See the
pcre2partial documentation for details of partial matching.
PCRE2_ERROR_BADMAGIC
PCRE2 stores a 4-byte "magic number" at the start of the compiled code,
to catch the case when it is passed a junk pointer. This is the error
that is returned when the magic number is not present.
PCRE2_ERROR_BADMODE
This error is given when a compiled pattern is passed to a function in
a library of a different code unit width, for example, a pattern
compiled by the 8-bit library is passed to a 16-bit or 32-bit library
function.
PCRE2_ERROR_BADOFFSET
The value of startoffset was greater than the length of the subject.
PCRE2_ERROR_BADOPTION
An unrecognized bit was set in the options argument.
PCRE2_ERROR_BADUTFOFFSET
The UTF code unit sequence that was passed as a subject was checked and
found to be valid (the PCRE2_NO_UTF_CHECK option was not set), but the
value of startoffset did not point to the beginning of a UTF character
or the end of the subject.
PCRE2_ERROR_CALLOUT
This error is never generated by pcre2_match() itself. It is provided
for use by callout functions that want to cause pcre2_match() or
pcre2_callout_enumerate() to return a distinctive error code. See the
pcre2callout documentation for details.
PCRE2_ERROR_DEPTHLIMIT
The nested backtracking depth limit was reached.
PCRE2_ERROR_HEAPLIMIT
The heap limit was reached.
PCRE2_ERROR_INTERNAL
An unexpected internal error has occurred. This error could be caused
by a bug in PCRE2 or by overwriting of the compiled pattern.
PCRE2_ERROR_JIT_STACKLIMIT
This error is returned when a pattern that was successfully studied
using JIT is being matched, but the memory available for the just-in-
time processing stack is not large enough. See the pcre2jit
documentation for more details.
PCRE2_ERROR_MATCHLIMIT
The backtracking match limit was reached.
PCRE2_ERROR_NOMEMORY
Heap memory is used to remember backtracking points. This error is
given when the memory allocation function (default or custom) fails.
Note that a different error, PCRE2_ERROR_HEAPLIMIT, is given if the
amount of memory needed exceeds the heap limit. PCRE2_ERROR_NOMEMORY is
also returned if PCRE2_COPY_MATCHED_SUBJECT is set and memory
allocation fails.
PCRE2_ERROR_NULL
Either the code, subject, or match_data argument was passed as NULL.
PCRE2_ERROR_RECURSELOOP
This error is returned when pcre2_match() detects a recursion loop
within the pattern. Specifically, it means that either the whole
pattern or a capture group has been called recursively for the second
time at the same position in the subject string. Some simple patterns
that might do this are detected and faulted at compile time, but more
complicated cases, in particular mutual recursions between two
different groups, cannot be detected until matching is attempted.
OBTAINING A TEXTUAL ERROR MESSAGE
int pcre2_get_error_message(int errorcode, PCRE2_UCHAR *buffer,
PCRE2_SIZE bufflen);
A text message for an error code from any PCRE2 function (compile,
match, or auxiliary) can be obtained by calling
pcre2_get_error_message(). The code is passed as the first argument,
with the remaining two arguments specifying a code unit buffer and its
length in code units, into which the text message is placed. The
message is returned in code units of the appropriate width for the
library that is being used.
The returned message is terminated with a trailing zero, and the
function returns the number of code units used, excluding the trailing
zero. If the error number is unknown, the negative error code
PCRE2_ERROR_BADDATA is returned. If the buffer is too small, the
message is truncated (but still with a trailing zero), and the negative
error code PCRE2_ERROR_NOMEMORY is returned. None of the messages are
very long; a buffer size of 120 code units is ample.
EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
int pcre2_substring_length_bynumber(pcre2_match_data *match_data,
uint32_t number, PCRE2_SIZE *length);
int pcre2_substring_copy_bynumber(pcre2_match_data *match_data,
uint32_t number, PCRE2_UCHAR *buffer,
PCRE2_SIZE *bufflen);
int pcre2_substring_get_bynumber(pcre2_match_data *match_data,
uint32_t number, PCRE2_UCHAR **bufferptr,
PCRE2_SIZE *bufflen);
void pcre2_substring_free(PCRE2_UCHAR *buffer);
Captured substrings can be accessed directly by using the ovector as
described above. For convenience, auxiliary functions are provided for
extracting captured substrings as new, separate, zero-terminated
strings. A substring that contains a binary zero is correctly extracted
and has a further zero added on the end, but the result is not, of
course, a C string.
The functions in this section identify substrings by number. The number
zero refers to the entire matched substring, with higher numbers
referring to substrings captured by parenthesized groups. After a
partial match, only substring zero is available. An attempt to extract
any other substring gives the error PCRE2_ERROR_PARTIAL. The next
section describes similar functions for extracting captured substrings
by name.
If a pattern uses the \K escape sequence within a positive assertion,
the reported start of a successful match can be greater than the end of
the match. For example, if the pattern (?=ab\K) is matched against
"ab", the start and end offset values for the match are 2 and 0. In
this situation, calling these functions with a zero substring number
extracts a zero-length empty string.
You can find the length in code units of a captured substring without
extracting it by calling pcre2_substring_length_bynumber(). The first
argument is a pointer to the match data block, the second is the group
number, and the third is a pointer to a variable into which the length
is placed. If you just want to know whether or not the substring has
been captured, you can pass the third argument as NULL.
The pcre2_substring_copy_bynumber() function copies a captured
substring into a supplied buffer, whereas
pcre2_substring_get_bynumber() copies it into new memory, obtained
using the same memory allocation function that was used for the match
data block. The first two arguments of these functions are a pointer to
the match data block and a capture group number.
The final arguments of pcre2_substring_copy_bynumber() are a pointer to
the buffer and a pointer to a variable that contains its length in code
units. This is updated to contain the actual number of code units used
for the extracted substring, excluding the terminating zero.
For pcre2_substring_get_bynumber() the third and fourth arguments point
to variables that are updated with a pointer to the new memory and the
number of code units that comprise the substring, again excluding the
terminating zero. When the substring is no longer needed, the memory
should be freed by calling pcre2_substring_free().
The return value from all these functions is zero for success, or a
negative error code. If the pattern match failed, the match failure
code is returned. If a substring number greater than zero is used
after a partial match, PCRE2_ERROR_PARTIAL is returned. Other possible
error codes are:
PCRE2_ERROR_NOMEMORY
The buffer was too small for pcre2_substring_copy_bynumber(), or the
attempt to get memory failed for pcre2_substring_get_bynumber().
PCRE2_ERROR_NOSUBSTRING
There is no substring with that number in the pattern, that is, the
number is greater than the number of capturing parentheses.
PCRE2_ERROR_UNAVAILABLE
The substring number, though not greater than the number of captures in
the pattern, is greater than the number of slots in the ovector, so the
substring could not be captured.
PCRE2_ERROR_UNSET
The substring did not participate in the match. For example, if the
pattern is (abc)|(def) and the subject is "def", and the ovector
contains at least two capturing slots, substring number 1 is unset.
EXTRACTING A LIST OF ALL CAPTURED SUBSTRINGS
int pcre2_substring_list_get(pcre2_match_data *match_data,
PCRE2_UCHAR ***listptr, PCRE2_SIZE **lengthsptr);
void pcre2_substring_list_free(PCRE2_UCHAR **list);
The pcre2_substring_list_get() function extracts all available
substrings and builds a list of pointers to them. It also (optionally)
builds a second list that contains their lengths (in code units),
excluding a terminating zero that is added to each of them. All this is
done in a single block of memory that is obtained using the same memory
allocation function that was used to get the match data block.
This function must be called only after a successful match. If called
after a partial match, the error code PCRE2_ERROR_PARTIAL is returned.
The address of the memory block is returned via listptr, which is also
the start of the list of string pointers. The end of the list is marked
by a NULL pointer. The address of the list of lengths is returned via
lengthsptr. If your strings do not contain binary zeros and you do not
therefore need the lengths, you may supply NULL as the lengthsptr
argument to disable the creation of a list of lengths. The yield of the
function is zero if all went well, or PCRE2_ERROR_NOMEMORY if the
memory block could not be obtained. When the list is no longer needed,
it should be freed by calling pcre2_substring_list_free().
If this function encounters a substring that is unset, which can happen
when capture group number n+1 matches some part of the subject, but
group n has not been used at all, it returns an empty string. This can
be distinguished from a genuine zero-length substring by inspecting the
appropriate offset in the ovector, which contain PCRE2_UNSET for unset
substrings, or by calling pcre2_substring_length_bynumber().
EXTRACTING CAPTURED SUBSTRINGS BY NAME
int pcre2_substring_number_from_name(const pcre2_code *code,
PCRE2_SPTR name);
int pcre2_substring_length_byname(pcre2_match_data *match_data,
PCRE2_SPTR name, PCRE2_SIZE *length);
int pcre2_substring_copy_byname(pcre2_match_data *match_data,
PCRE2_SPTR name, PCRE2_UCHAR *buffer, PCRE2_SIZE *bufflen);
int pcre2_substring_get_byname(pcre2_match_data *match_data,
PCRE2_SPTR name, PCRE2_UCHAR **bufferptr, PCRE2_SIZE *bufflen);
void pcre2_substring_free(PCRE2_UCHAR *buffer);
To extract a substring by name, you first have to find associated
number. For example, for this pattern:
(a+)b(?<xxx>\d+)...
the number of the capture group called "xxx" is 2. If the name is known
to be unique (PCRE2_DUPNAMES was not set), you can find the number from
the name by calling pcre2_substring_number_from_name(). The first
argument is the compiled pattern, and the second is the name. The yield
of the function is the group number, PCRE2_ERROR_NOSUBSTRING if there
is no group with that name, or PCRE2_ERROR_NOUNIQUESUBSTRING if there
is more than one group with that name. Given the number, you can
extract the substring directly from the ovector, or use one of the
"bynumber" functions described above.
For convenience, there are also "byname" functions that correspond to
the "bynumber" functions, the only difference being that the second
argument is a name instead of a number. If PCRE2_DUPNAMES is set and
there are duplicate names, these functions scan all the groups with the
given name, and return the captured substring from the first named
group that is set.
If there are no groups with the given name, PCRE2_ERROR_NOSUBSTRING is
returned. If all groups with the name have numbers that are greater
than the number of slots in the ovector, PCRE2_ERROR_UNAVAILABLE is
returned. If there is at least one group with a slot in the ovector,
but no group is found to be set, PCRE2_ERROR_UNSET is returned.
Warning: If the pattern uses the (?| feature to set up multiple capture
groups with the same number, as described in the section on duplicate
group numbers in the pcre2pattern page, you cannot use names to
distinguish the different capture groups, because names are not
included in the compiled code. The matching process uses only numbers.
For this reason, the use of different names for groups with the same
number causes an error at compile time.
CREATING A NEW STRING WITH SUBSTITUTIONS
int pcre2_substitute(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext, PCRE2_SPTR replacement,
PCRE2_SIZE rlength, PCRE2_UCHAR *outputbuffer,
PCRE2_SIZE *outlengthptr);
This function optionally calls pcre2_match() and then makes a copy of
the subject string in outputbuffer, replacing parts that were matched
with the replacement string, whose length is supplied in rlength, which
can be given as PCRE2_ZERO_TERMINATED for a zero-terminated string. As
a special case, if replacement is NULL and rlength is zero, the
replacement is assumed to be an empty string. If rlength is non-zero,
an error occurs if replacement is NULL.
There is an option (see PCRE2_SUBSTITUTE_REPLACEMENT_ONLY below) to
return just the replacement string(s). The default action is to perform
just one replacement if the pattern matches, but there is an option
that requests multiple replacements (see PCRE2_SUBSTITUTE_GLOBAL
below).
If successful, pcre2_substitute() returns the number of substitutions
that were carried out. This may be zero if no match was found, and is
never greater than one unless PCRE2_SUBSTITUTE_GLOBAL is set. A
negative value is returned if an error is detected.
Matches in which a \K item in a lookahead in the pattern causes the
match to end before it starts are not supported, and give rise to an
error return. For global replacements, matches in which \K in a
lookbehind causes the match to start earlier than the point that was
reached in the previous iteration are also not supported.
The first seven arguments of pcre2_substitute() are the same as for
pcre2_match(), except that the partial matching options are not
permitted, and match_data may be passed as NULL, in which case a match
data block is obtained and freed within this function, using memory
management functions from the match context, if provided, or else those
that were used to allocate memory for the compiled code.
If match_data is not NULL and PCRE2_SUBSTITUTE_MATCHED is not set, the
provided block is used for all calls to pcre2_match(), and its contents
afterwards are the result of the final call. For global changes, this
will always be a no-match error. The contents of the ovector within the
match data block may or may not have been changed.
As well as the usual options for pcre2_match(), a number of additional
options can be set in the options argument of pcre2_substitute(). One
such option is PCRE2_SUBSTITUTE_MATCHED. When this is set, an external
match_data block must be provided, and it must have already been used
for an external call to pcre2_match() with the same pattern and subject
arguments. The data in the match_data block (return code, offset
vector) is then used for the first substitution instead of calling
pcre2_match() from within pcre2_substitute(). This allows an
application to check for a match before choosing to substitute, without
having to repeat the match.
The contents of the externally supplied match data block are not
changed when PCRE2_SUBSTITUTE_MATCHED is set. If
PCRE2_SUBSTITUTE_GLOBAL is also set, pcre2_match() is called after the
first substitution to check for further matches, but this is done using
an internally obtained match data block, thus always leaving the
external block unchanged.
The code argument is not used for matching before the first
substitution when PCRE2_SUBSTITUTE_MATCHED is set, but it must be
provided, even when PCRE2_SUBSTITUTE_GLOBAL is not set, because it
contains information such as the UTF setting and the number of
capturing parentheses in the pattern.
The default action of pcre2_substitute() is to return a copy of the
subject string with matched substrings replaced. However, if
PCRE2_SUBSTITUTE_REPLACEMENT_ONLY is set, only the replacement
substrings are returned. In the global case, multiple replacements are
concatenated in the output buffer. Substitution callouts (see below)
can be used to separate them if necessary.
The outlengthptr argument of pcre2_substitute() must point to a
variable that contains the length, in code units, of the output buffer.
If the function is successful, the value is updated to contain the
length in code units of the new string, excluding the trailing zero
that is automatically added.
If the function is not successful, the value set via outlengthptr
depends on the type of error. For syntax errors in the replacement
string, the value is the offset in the replacement string where the
error was detected. For other errors, the value is PCRE2_UNSET by
default. This includes the case of the output buffer being too small,
unless PCRE2_SUBSTITUTE_OVERFLOW_LENGTH is set.
PCRE2_SUBSTITUTE_OVERFLOW_LENGTH changes what happens when the output
buffer is too small. The default action is to return
PCRE2_ERROR_NOMEMORY immediately. If this option is set, however,
pcre2_substitute() continues to go through the motions of matching and
substituting (without, of course, writing anything) in order to compute
the size of buffer that is needed. This value is passed back via the
outlengthptr variable, with the result of the function still being
PCRE2_ERROR_NOMEMORY.
Passing a buffer size of zero is a permitted way of finding out how
much memory is needed for given substitution. However, this does mean
that the entire operation is carried out twice. Depending on the
application, it may be more efficient to allocate a large buffer and
free the excess afterwards, instead of using
PCRE2_SUBSTITUTE_OVERFLOW_LENGTH.
The replacement string, which is interpreted as a UTF string in UTF
mode, is checked for UTF validity unless PCRE2_NO_UTF_CHECK is set. An
invalid UTF replacement string causes an immediate return with the
relevant UTF error code.
If PCRE2_SUBSTITUTE_LITERAL is set, the replacement string is not
interpreted in any way. By default, however, a dollar character is an
escape character that can specify the insertion of characters from
capture groups and names from (*MARK) or other control verbs in the
pattern. Dollar is the only escape character (backslash is treated as
literal). The following forms are always recognized:
$$ insert a dollar character
$<n> or ${<n>} insert the contents of group <n>
$*MARK or ${*MARK} insert a control verb name
Either a group number or a group name can be given for <n>. Curly
brackets are required only if the following character would be
interpreted as part of the number or name. The number may be zero to
include the entire matched string. For example, if the pattern a(b)c
is matched with "=abc=" and the replacement string "+$1$0$1+", the
result is "=+babcb+=".
$*MARK inserts the name from the last encountered backtracking control
verb on the matching path that has a name. (*MARK) must always include
a name, but the other verbs need not. For example, in the case of
(*MARK:A)(*PRUNE) the name inserted is "A", but for (*MARK:A)(*PRUNE:B)
the relevant name is "B". This facility can be used to perform simple
simultaneous substitutions, as this pcre2test example shows:
/(*MARK:pear)apple|(*MARK:orange)lemon/g,replace=${*MARK}
apple lemon
2: pear orange
PCRE2_SUBSTITUTE_GLOBAL causes the function to iterate over the subject
string, replacing every matching substring. If this option is not set,
only the first matching substring is replaced. The search for matches
takes place in the original subject string (that is, previous
replacements do not affect it). Iteration is implemented by advancing
the startoffset value for each search, which is always passed the
entire subject string. If an offset limit is set in the match context,
searching stops when that limit is reached.
You can restrict the effect of a global substitution to a portion of
the subject string by setting either or both of startoffset and an
offset limit. Here is a pcre2test example:
/B/g,replace=!,use_offset_limit
ABC ABC ABC ABC\=offset=3,offset_limit=12
2: ABC A!C A!C ABC
When continuing with global substitutions after matching a substring
with zero length, an attempt to find a non-empty match at the same
offset is performed. If this is not successful, the offset is advanced
by one character except when CRLF is a valid newline sequence and the
next two characters are CR, LF. In this case, the offset is advanced by
two characters.
PCRE2_SUBSTITUTE_UNKNOWN_UNSET causes references to capture groups that
do not appear in the pattern to be treated as unset groups. This option
should be used with care, because it means that a typo in a group name
or number no longer causes the PCRE2_ERROR_NOSUBSTRING error.
PCRE2_SUBSTITUTE_UNSET_EMPTY causes unset capture groups (including
unknown groups when PCRE2_SUBSTITUTE_UNKNOWN_UNSET is set) to be
treated as empty strings when inserted as described above. If this
option is not set, an attempt to insert an unset group causes the
PCRE2_ERROR_UNSET error. This option does not influence the extended
substitution syntax described below.
PCRE2_SUBSTITUTE_EXTENDED causes extra processing to be applied to the
replacement string. Without this option, only the dollar character is
special, and only the group insertion forms listed above are valid.
When PCRE2_SUBSTITUTE_EXTENDED is set, two things change:
Firstly, backslash in a replacement string is interpreted as an escape
character. The usual forms such as \n or \x{ddd} can be used to specify
particular character codes, and backslash followed by any non-
alphanumeric character quotes that character. Extended quoting can be
coded using \Q...\E, exactly as in pattern strings.
There are also four escape sequences for forcing the case of inserted
letters. The insertion mechanism has three states: no case forcing,
force upper case, and force lower case. The escape sequences change the
current state: \U and \L change to upper or lower case forcing,
respectively, and \E (when not terminating a \Q quoted sequence)
reverts to no case forcing. The sequences \u and \l force the next
character (if it is a letter) to upper or lower case, respectively, and
then the state automatically reverts to no case forcing. Case forcing
applies to all inserted characters, including those from capture groups
and letters within \Q...\E quoted sequences. If either PCRE2_UTF or
PCRE2_UCP was set when the pattern was compiled, Unicode properties are
used for case forcing characters whose code points are greater than
127.
Note that case forcing sequences such as \U...\E do not nest. For
example, the result of processing "\Uaa\LBB\Ecc\E" is "AAbbcc"; the
final \E has no effect. Note also that the PCRE2_ALT_BSUX and
PCRE2_EXTRA_ALT_BSUX options do not apply to replacement strings.
The second effect of setting PCRE2_SUBSTITUTE_EXTENDED is to add more
flexibility to capture group substitution. The syntax is similar to
that used by Bash:
${<n>:-<string>}
${<n>:+<string1>:<string2>}
As before, <n> may be a group number or a name. The first form
specifies a default value. If group <n> is set, its value is inserted;
if not, <string> is expanded and the result inserted. The second form
specifies strings that are expanded and inserted when group <n> is set
or unset, respectively. The first form is just a convenient shorthand
for
${<n>:+${<n>}:<string>}
Backslash can be used to escape colons and closing curly brackets in
the replacement strings. A change of the case forcing state within a
replacement string remains in force afterwards, as shown in this
pcre2test example:
/(some)?(body)/substitute_extended,replace=${1:+\U:\L}HeLLo
body
1: hello
somebody
1: HELLO
The PCRE2_SUBSTITUTE_UNSET_EMPTY option does not affect these extended
substitutions. However, PCRE2_SUBSTITUTE_UNKNOWN_UNSET does cause
unknown groups in the extended syntax forms to be treated as unset.
If PCRE2_SUBSTITUTE_LITERAL is set, PCRE2_SUBSTITUTE_UNKNOWN_UNSET,
PCRE2_SUBSTITUTE_UNSET_EMPTY, and PCRE2_SUBSTITUTE_EXTENDED are
irrelevant and are ignored.
Substitution errors
In the event of an error, pcre2_substitute() returns a negative error
code. 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_NULL is returned if PCRE2_SUBSTITUTE_MATCHED is set but the
match_data argument is NULL or if the subject or replacement arguments
are NULL. For backward compatibility reasons an exception is made for
the replacement argument if the rlength argument is also 0.
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_REPMISSINGBRACE (closing curly bracket not found),
PCRE2_ERROR_BADSUBSTITUTION (syntax error in extended group
substitution), and PCRE2_ERROR_BADSUBSPATTERN (the pattern match ended
before it started or the match started earlier than the current
position in the subject, which can happen if \K is used in an
assertion).
As for all PCRE2 errors, a text message that describes the error can be
obtained by calling the pcre2_get_error_message() function (see
"Obtaining a textual error message" above).
Substitution callouts
int pcre2_set_substitute_callout(pcre2_match_context *mcontext,
int (*callout_function)(pcre2_substitute_callout_block *, void *),
void *callout_data);
The pcre2_set_substitution_callout() function can be used to specify a
callout function for pcre2_substitute(). This information is passed in
a match context. The callout function is called after each substitution
has been processed, but it can cause the replacement not to happen. The
callout function is not called for simulated substitutions that happen
as a result of the PCRE2_SUBSTITUTE_OVERFLOW_LENGTH option.
The first argument of the callout function is a pointer to a substitute
callout block structure, which contains the following fields, not
necessarily in this order:
uint32_t version;
uint32_t subscount;
PCRE2_SPTR input;
PCRE2_SPTR output;
PCRE2_SIZE *ovector;
uint32_t oveccount;
PCRE2_SIZE output_offsets[2];
The version field contains the version number of the block format. The
current version is 0. The version number will increase in future if
more fields are added, but the intention is never to remove any of the
existing fields.
The subscount field is the number of the current match. It is 1 for the
first callout, 2 for the second, and so on. The input and output
pointers are copies of the values passed to pcre2_substitute().
The ovector field points to the ovector, which contains the result of
the most recent match. The oveccount field contains the number of pairs
that are set in the ovector, and is always greater than zero.
The output_offsets vector contains the offsets of the replacement in
the output string. This has already been processed for dollar and (if
requested) backslash substitutions as described above.
The second argument of the callout function is the value passed as
callout_data when the function was registered. The value returned by
the callout function is interpreted as follows:
If the value is zero, the replacement is accepted, and, if
PCRE2_SUBSTITUTE_GLOBAL is set, processing continues with a search for
the next match. If the value is not zero, the current replacement is
not accepted. If the value is greater than zero, processing continues
when PCRE2_SUBSTITUTE_GLOBAL is set. Otherwise (the value is less than
zero or PCRE2_SUBSTITUTE_GLOBAL is not set), the rest of the input is
copied to the output and the call to pcre2_substitute() exits,
returning the number of matches so far.
DUPLICATE CAPTURE GROUP NAMES
int pcre2_substring_nametable_scan(const pcre2_code *code,
PCRE2_SPTR name, PCRE2_SPTR *first, PCRE2_SPTR *last);
When a pattern is compiled with the PCRE2_DUPNAMES option, names for
capture groups are not required to be unique. Duplicate names are
always allowed for groups with the same number, created by using the
(?| feature. Indeed, if such groups are named, they are required to use
the same names.
Normally, patterns that use duplicate names are such that in any one
match, only one of each set of identically-named groups participates.
An example is shown in the pcre2pattern documentation.
When duplicates are present, pcre2_substring_copy_byname() and
pcre2_substring_get_byname() return the first substring corresponding
to the given name that is set. Only if none are set is
PCRE2_ERROR_UNSET is returned. The pcre2_substring_number_from_name()
function returns the error PCRE2_ERROR_NOUNIQUESUBSTRING when there are
duplicate names.
If you want to get full details of all captured substrings for a given
name, you must use the pcre2_substring_nametable_scan() function. The
first argument is the compiled pattern, and the second is the name. If
the third and fourth arguments are NULL, the function returns a group
number for a unique name, or PCRE2_ERROR_NOUNIQUESUBSTRING otherwise.
When the third and fourth arguments are not NULL, they must be pointers
to variables that are updated by the function. After it has run, they
point to the first and last entries in the name-to-number table for the
given name, and the function returns the length of each entry in code
units. In both cases, PCRE2_ERROR_NOSUBSTRING is returned if there are
no entries for the given name.
The format of the name table is described above in the section entitled
Information about a pattern. Given all the relevant entries for the
name, you can extract each of their numbers, and hence the captured
data.
FINDING ALL POSSIBLE MATCHES AT ONE POSITION
The traditional matching function uses a similar algorithm to Perl,
which stops when it finds the first match at a given point in the
subject. If you want to find all possible matches, or the longest
possible match at a given position, consider using the alternative
matching function (see below) instead. If you cannot use the
alternative function, you can kludge it up by making use of the callout
facility, which is described in the pcre2callout documentation.
What you have to do is to insert a callout right at the end of the
pattern. When your callout function is called, extract and save the
current matched substring. Then return 1, which forces pcre2_match() to
backtrack and try other alternatives. Ultimately, when it runs out of
matches, pcre2_match() will yield PCRE2_ERROR_NOMATCH.
MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
int pcre2_dfa_match(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext,
int *workspace, PCRE2_SIZE wscount);
The function pcre2_dfa_match() is called to match a subject string
against a compiled pattern, using a matching algorithm that scans the
subject string just once (not counting lookaround assertions), and does
not backtrack (except when processing lookaround assertions). This has
different characteristics to the normal algorithm, and is not
compatible with Perl. Some of the features of PCRE2 patterns are not
supported. Nevertheless, there are times when this kind of matching can
be useful. For a discussion of the two matching algorithms, and a list
of features that pcre2_dfa_match() does not support, see the
pcre2matching documentation.
The arguments for the pcre2_dfa_match() function are the same as for
pcre2_match(), plus two extras. The ovector within the match data block
is used in a different way, and this is described below. The other
common arguments are used in the same way as for pcre2_match(), so
their description is not repeated here.
The two additional arguments provide workspace for the function. The
workspace vector should contain at least 20 elements. It is used for
keeping track of multiple paths through the pattern tree. More
workspace is needed for patterns and subjects where there are a lot of
potential matches.
Here is an example of a simple call to pcre2_dfa_match():
int wspace[20];
pcre2_match_data *md = pcre2_match_data_create(4, NULL);
int rc = pcre2_dfa_match(
re, /* result of pcre2_compile() */
"some string", /* the subject string */
11, /* the length of the subject string */
0, /* start at offset 0 in the subject */
0, /* default options */
md, /* the match data block */
NULL, /* a match context; NULL means use defaults */
wspace, /* working space vector */
20); /* number of elements (NOT size in bytes) */
Option bits for pcre2_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_COPY_MATCHED_SUBJECT, PCRE2_ENDANCHORED, PCRE2_NOTBOL,
PCRE2_NOTEOL, PCRE2_NOTEMPTY, PCRE2_NOTEMPTY_ATSTART,
PCRE2_NO_UTF_CHECK, PCRE2_PARTIAL_HARD, PCRE2_PARTIAL_SOFT,
PCRE2_DFA_SHORTEST, and PCRE2_DFA_RESTART. All but the last four of
these are exactly the same as for pcre2_match(), so their description
is not repeated here.
PCRE2_PARTIAL_HARD
PCRE2_PARTIAL_SOFT
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 capture groups that may exist in the pattern, because DFA
matching does not support capturing.
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.
The matched strings are stored in the ovector in reverse order of
length; that is, the longest matching string is first. If there were
too many matches to fit into the ovector, the yield of the function is
zero, and the vector is filled with the longest matches.
NOTE: PCRE2's "auto-possessification" optimization usually applies to
character repeats at the end of a pattern (as well as internally). For
example, the pattern "a\d+" is compiled as if it were "a\d++". For DFA
matching, this means that only one possible match is found. If you
really do want multiple matches in such cases, either use an ungreedy
repeat such as "a\d+?" or set the PCRE2_NO_AUTO_POSSESS option when
compiling.
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 backreference.
PCRE2_ERROR_DFA_UCOND
This return is given if pcre2_dfa_match() encounters a condition item
that uses a backreference for the condition, or a test for recursion in
a specific capture group. These are not supported.
PCRE2_ERROR_DFA_UINVALID_UTF
This return is given if pcre2_dfa_match() is called for a pattern that
was compiled with PCRE2_MATCH_INVALID_UTF. This is not supported for
DFA matching.
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 recursion or subroutine call 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), pcre2unicode(3).
AUTHOR
Philip Hazel
Retired from University Computing Service
Cambridge, England.
REVISION
Last updated: 24 April 2024
Copyright (c) 1997-2024 University of Cambridge.
PCRE2 10.44 24 April 2024 pcre2api(3)
pcre2 10.44 - Generated Mon Jun 17 07:26:46 CDT 2024