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PCRE2API(3) Library Functions Manual PCRE2API(3)
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_code *pcre2_compile(PCRE2_SPTR pattern, PCRE2_SIZE length,
uint32_t options, int *errorcode, PCRE2_SIZE *erroroffset,
pcre2_compile_context *ccontext);
void pcre2_code_free(pcre2_code *code);
pcre2_match_data *pcre2_match_data_create(uint32_t ovecsize,
pcre2_general_context *gcontext);
pcre2_match_data *pcre2_match_data_create_from_pattern(
const pcre2_code *code, pcre2_general_context *gcontext);
int pcre2_match(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext);
int pcre2_dfa_match(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext,
int *workspace, PCRE2_SIZE wscount);
void pcre2_match_data_free(pcre2_match_data *match_data);
PCRE2_SPTR pcre2_get_mark(pcre2_match_data *match_data);
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_general_context *pcre2_general_context_create(
void *(*private_malloc)(PCRE2_SIZE, void *),
void (*private_free)(void *, void *), void *memory_data);
pcre2_general_context *pcre2_general_context_copy(
pcre2_general_context *gcontext);
void pcre2_general_context_free(pcre2_general_context *gcontext);
pcre2_compile_context *pcre2_compile_context_create(
pcre2_general_context *gcontext);
pcre2_compile_context *pcre2_compile_context_copy(
pcre2_compile_context *ccontext);
void pcre2_compile_context_free(pcre2_compile_context *ccontext);
int pcre2_set_bsr(pcre2_compile_context *ccontext,
uint32_t value);
int pcre2_set_character_tables(pcre2_compile_context *ccontext,
const 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);
int pcre2_set_optimize(pcre2_compile_context *ccontext,
uint32_t directive);
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_substitute_case_callout(pcre2_match_context *mcontext,
PCRE2_SIZE (*callout_function)(PCRE2_SPTR, PCRE2_SIZE,
PCRE2_UCHAR *, PCRE2_SIZE,
int, void *),
void *callout_data);
int pcre2_set_offset_limit(pcre2_match_context *mcontext,
PCRE2_SIZE value);
int pcre2_set_heap_limit(pcre2_match_context *mcontext,
uint32_t value);
int pcre2_set_match_limit(pcre2_match_context *mcontext,
uint32_t value);
int pcre2_set_depth_limit(pcre2_match_context *mcontext,
uint32_t value);
int pcre2_substring_copy_byname(pcre2_match_data *match_data,
PCRE2_SPTR name, PCRE2_UCHAR *buffer, PCRE2_SIZE *bufflen);
int pcre2_substring_copy_bynumber(pcre2_match_data *match_data,
uint32_t number, PCRE2_UCHAR *buffer,
PCRE2_SIZE *bufflen);
void pcre2_substring_free(PCRE2_UCHAR *buffer);
int pcre2_substring_get_byname(pcre2_match_data *match_data,
PCRE2_SPTR name, PCRE2_UCHAR **bufferptr, PCRE2_SIZE *bufflen);
int pcre2_substring_get_bynumber(pcre2_match_data *match_data,
uint32_t number, PCRE2_UCHAR **bufferptr,
PCRE2_SIZE *bufflen);
int pcre2_substring_length_byname(pcre2_match_data *match_data,
PCRE2_SPTR name, PCRE2_SIZE *length);
int pcre2_substring_length_bynumber(pcre2_match_data *match_data,
uint32_t number, PCRE2_SIZE *length);
int pcre2_substring_nametable_scan(const pcre2_code *code,
PCRE2_SPTR name, PCRE2_SPTR *first, PCRE2_SPTR *last);
int pcre2_substring_number_from_name(const pcre2_code *code,
PCRE2_SPTR name);
void pcre2_substring_list_free(PCRE2_UCHAR **list);
int pcre2_substring_list_get(pcre2_match_data *match_data,
PCRE2_UCHAR ***listptr, PCRE2_SIZE **lengthsptr);
int pcre2_substitute(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext, PCRE2_SPTR replacement,
PCRE2_SIZE rlength, PCRE2_UCHAR *outputbuffer,
PCRE2_SIZE *outlengthptr);
int pcre2_jit_compile(pcre2_code *code, uint32_t options);
int pcre2_jit_match(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext);
void pcre2_jit_free_unused_memory(pcre2_general_context *gcontext);
pcre2_jit_stack *pcre2_jit_stack_create(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);
int32_t pcre2_serialize_decode(pcre2_code **codes,
int32_t number_of_codes, const uint8_t *bytes,
pcre2_general_context *gcontext);
int32_t pcre2_serialize_encode(const pcre2_code **codes,
int32_t number_of_codes, uint8_t **serialized_bytes,
PCRE2_SIZE *serialized_size, pcre2_general_context *gcontext);
void pcre2_serialize_free(uint8_t *bytes);
int32_t pcre2_serialize_get_number_of_codes(const uint8_t *bytes);
pcre2_code *pcre2_code_copy(const pcre2_code *code);
pcre2_code *pcre2_code_copy_with_tables(const pcre2_code *code);
int pcre2_get_error_message(int errorcode, PCRE2_UCHAR *buffer,
PCRE2_SIZE bufflen);
const 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);
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_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.
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 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.
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.
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.
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.
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)
Which performance optimizations the compiler should apply
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.
int pcre2_set_optimize(pcre2_compile_context *ccontext,
uint32_t directive);
PCRE2 can apply various performance optimizations during
compilation, in order to make matching faster. For example, the
compiler might convert some regex constructs into an equivalent
construct which pcre2_match() can execute faster. By default, all
available optimizations are enabled. However, in rare cases, one
might wish to disable specific optimizations. For example, if it
is known that some optimizations cannot benefit a certain regex,
it might be desirable to disable them, in order to speed up
compilation.
The permitted values of directive are as follows:
PCRE2_OPTIMIZATION_FULL
Enable all optional performance optimizations. This is the default
value.
PCRE2_OPTIMIZATION_NONE
Disable all optional performance optimizations.
PCRE2_AUTO_POSSESS
PCRE2_AUTO_POSSESS_OFF
Enable/disable "auto-possessification" of variable quantifiers
such as * and +. This optimization, 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 disable this
optimization if you want the matching functions to do a full,
unoptimized search and run all the callouts.
PCRE2_DOTSTAR_ANCHOR
PCRE2_DOTSTAR_ANCHOR_OFF
Enable/disable 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 ^. 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.
Dotstar anchor 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).
PCRE2_START_OPTIMIZE
PCRE2_START_OPTIMIZE_OFF
Enable/disable optimizations which cause matching functions to
scan the subject string for specific code unit values before
attempting a match. For example, if it is known that an unanchored
match must start with a specific 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.
Disabling start-up optimizations ensures 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.
Disabling start-up optimizations 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 without start-up optimizations, 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".
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". Without start-up
optimizations, 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.
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_substitute_case_callout(pcre2_match_context *mcontext,
PCRE2_SIZE (*callout_function)(PCRE2_SPTR, PCRE2_SIZE,
PCRE2_UCHAR *, PCRE2_SIZE,
int, void *),
void *callout_data);
This sets up a callout function for PCRE2 to call when performing
case transformations inside 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.
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, and neither
does it guarantee that JIT will actually be able to function,
because it may not be able to allocate executable memory in some
environments. There is a special call to pcre2_jit_compile() that
can be used to check this. 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.
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 over 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
one or two digits.
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_EXTENDED_CLASS
Alters the parsing of character classes to follow the extended
syntax described by Unicode UTS#18. The PCRE2_ALT_EXTENDED_CLASS
option has no impact on the behaviour of the Perl-specific
"(?[...])" syntax for extended classes, but instead enables the
alternative syntax of extended class behaviour inside ordinary
"[...]" character classes. See the pcre2pattern documentation for
details of the character classes supported.
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 white space 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.
One language family, Turkish and Azeri, has its own case-
insensitivity rules, which can be selected by setting
PCRE2_EXTRA_TURKISH_CASING. This alters the behaviour of the 'i',
'I', U+0130 (capital I with dot above), and U+0131 (small dotless
i) characters.
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.
From release 10.45 PCRE2_CASELESS also affects what some of the
letter-related Unicode property escapes (\p and \P) match. The
properties Lu (upper case letter), Ll (lower case letter), and Lt
(title case letter) are all treated as LC (cased letter) when
PCRE2_CASELESS is set.
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 PCRE2_UCP and PCRE2_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 (deprecated) 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.
If a compile context is available, it is recommended to use
pcre2_set_optimize() with the directive PCRE2_AUTO_POSSESS_OFF
rather than the compile option PCRE2_NO_AUTO_POSSESS. Note that
PCRE2_NO_AUTO_POSSESS takes precedence over the
pcre2_set_optimize() optimization directives PCRE2_AUTO_POSSESS
and PCRE2_AUTO_POSSESS_OFF.
PCRE2_NO_DOTSTAR_ANCHOR
If this (deprecated) 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. (If a
compile context is available, it is recommended to use
pcre2_set_optimize() with the directive PCRE2_DOTSTAR_ANCHOR_OFF
instead.)
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. Setting this option is equivalent to
calling pcre2_set_optimize() with the directive parameter set to
PCRE2_START_OPTIMIZE_OFF.
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. The start-up optimizations are
in effect a pre-scan of the subject that takes place before the
pattern is run.
Disabling the start-up optimizations may cause performance to
suffer. However, this may be desirable for patterns which contain
callouts or items such as (*COMMIT) and (*MARK). See the above
description of PCRE2_START_OPTIMIZE_OFF for further details.
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 above) restricts
caseless matching such that ASCII characters match only ASCII
characters and non-ASCII characters match only non-ASCII
characters. The PCRE2_EXTRA_TURKISH_CASING option (see above)
alters the matching of the 'i' characters to follow their
behaviour in Turkish and Azeri languages. For further details on
PCRE2_EXTRA_CASELESS_RESTRICT and PCRE2_EXTRA_TURKISH_CASING, see
the pcre2unicode page.
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 within a pattern by
the (*CASELESS_RESTRICT) or (?r) option settings.
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.
PCRE2_EXTRA_NO_BS0
If this option is set (note that its final character is the digit
0) it locks out the use of the sequence \0 unless at least one
more octal digit follows.
PCRE2_EXTRA_PYTHON_OCTAL
If this option is set, PCRE2 follows Python's rules for
interpreting octal escape sequences. The rules for handling
sequences such as \14, which could be an octal number or a back
reference are different. Details are given in the pcre2pattern
documentation.
PCRE2_EXTRA_NEVER_CALLOUT
If this option is set, PCRE2 treats callouts in the pattern as a
syntax error, returning PCRE2_ERROR_CALLOUT_CALLER_DISABLED. This
is useful if the application knows that a callout will not be
provided to pcre2_match(), so that callouts in the pattern are not
silently ignored.
PCRE2_EXTRA_TURKISH_CASING
This option alters case-equivalence of the 'i' letters to follow
the alphabet used by Turkish and Azeri languages. The option can
be changed within a pattern by the (*TURKISH_CASING) start-of-
pattern setting. Either the UTF or UCP options must be set. In the
8-bit library, UTF must be set. This option cannot be combined
with PCRE2_EXTRA_CASELESS_RESTRICT.
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.
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.
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
Dotstar anchoring has not been disabled with
PCRE2_DOTSTAR_ANCHOR_OFF
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.
int pcre2_callout_enumerate(const pcre2_code *code,
int (*callback)(pcre2_callout_enumerate_block *, void *),
void *user_data);
A script language that supports the use of string arguments in
callouts might like to scan all the callouts in a pattern before
running the match. This can be done by calling
pcre2_callout_enumerate(). The first argument is a pointer to a
compiled pattern, the second points to a callback function, and
the third is arbitrary user data. The callback function is called
for every callout in the pattern in the order in which they
appear. Its first argument is a pointer to a callout enumeration
block, and its second argument is the user_data value that was
passed to pcre2_callout_enumerate(). The contents of the callout
enumeration block are described in the pcre2callout documentation,
which also gives further details about callouts.
It is possible to save compiled patterns on disc or elsewhere, and
reload them later, subject to a number of restrictions. The 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.
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.
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.
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. PCRE2 includes a helper API to assist
with this; see the section entitled "Iterating over all matches"
below for details.
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 unanchored 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 than an
alternative complete match.
There is a more detailed discussion of partial and multi-segment
matching, with examples, in the pcre2partial documentation.
When PCRE2 is built, a default newline convention is set; this is
usually the standard convention for the operating system. The
default can be overridden in a compile context by calling
pcre2_set_newline(). It can also be overridden by starting a
pattern string with, for example, (*CRLF), as described in the
section on newline conventions in the pcre2pattern page. During
matching, the newline choice affects the behaviour of the dot,
circumflex, and dollar metacharacters. It may also alter the way
the match starting position is advanced after a match failure for
an unanchored pattern.
When PCRE2_NEWLINE_CRLF, PCRE2_NEWLINE_ANYCRLF, or
PCRE2_NEWLINE_ANY is set as the newline convention, and a match
attempt for an unanchored pattern fails when the current starting
position is at a CRLF sequence, and the pattern contains no
explicit matches for CR or LF characters, the match position is
advanced by two characters instead of one, in other words, to
after the CRLF.
The above rule is a compromise that makes the most common cases
work as expected. For example, if the pattern is .+A (and the
PCRE2_DOTALL option is not set), it does not match the string
"\r\nA" because, after failing at the start, it skips both the CR
and the LF before retrying. However, the pattern [\r\n]A does
match that string, because it contains an explicit CR or LF
reference, and so advances only by one character after the first
failure.
An explicit match for CR of LF is either a literal appearance of
one of those characters in the pattern, or one of the \r or \n or
equivalent octal or hexadecimal escape sequences. Implicit matches
such as [^X] do not count, nor does \s, even though it includes CR
and LF in the characters that it matches.
Notwithstanding the above, anomalous effects may still occur when
CRLF is a valid newline sequence and explicit \r or \n escapes
appear in the pattern.
uint32_t pcre2_get_ovector_count(pcre2_match_data *match_data);
PCRE2_SIZE *pcre2_get_ovector_pointer(pcre2_match_data *match_data);
In general, a pattern matches a certain portion of the subject,
and in addition, further substrings from the subject may be picked
out by parenthesized parts of the pattern. Following the usage in
Jeffrey Friedl's book, this is called "capturing" in what follows,
and the phrase "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
lookahead 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.
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.
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.
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 is very long; a buffer size of 120 code units is ample.
int pcre2_next_match(pcre2_match_data *match_data,
PCRE2_SIZE *pstart_offset, uint32_t *poptions);
A common task for applications is to implement "global" matching
behaviour, for example, replacing all matches in the subject;
splitting the subject on all matches; or simply counting the
number of matches. The pcre2_next_match() function helps with this
task by providing the appropriate parameters for the next match
attempt (available since PCRE2 10.46).
First, a match attempt should be made using one of the matching
functions (pcre2_match(), pcre2_dfa_match(), or
pcre2_jit_match()). Then, pcre2_next_match() can be called,
providing the same match_data parameter.
It returns 0 ("false") if there is no need to make a further match
attempt, or 1 ("true") if another match should be attempted.
Returning 1 does not imply that there is another match, only that
another match should be attempted (which may return
PCRE2_ERROR_NOMATCH).
The *pstart_offset and *poptions are set if the function returns
1. The *pstart_offset should be passed to the next match attempt
directly, and the *poptions should be passed to the next match
attempt by combining with the application's match options using
OR.
There is some code that demonstrates how to do this in the
pcre2demo sample program. The general pattern is:
uint32_t app_options = ...;
uint32_t global_options = 0;
PCRE2_SIZE start_offset = 0;
while (1)
{
int rc = pcre2_match(re, subject, subject_len, start_offset,
app_options | global_options, match_data,
match_context);
if (rc == PCRE2_ERROR_NOMATCH) break; /* no match, and no more attempts */
if (rc < 0) { ... exit }
...handle the match
if (!pcre2_next_match(match_data, &start_offset, &global_options))
break; /* no more attempts */
}
The guarantees provided by pcre2_next_match() are that the
start_offset will advance, so the loop will definitely terminate.
The conditions which ensure this are that either: (a)
pcre2_next_match() returns 0 (false); or (b) the returned
*pstart_offset is strictly greater than the previous start_offset;
or (c) if the previous match was a successful match of the empty
string then the returned *pstart_offset is equal to the previous
ovector[1], and *poptions will be set to PCRE2_NOTEMPTY_ATSTART to
prevent another empty match from being returned.
A loop implemented as shown above will always terminate, unless
there is a bug in PCRE2. As a measure of "defensive programming",
applications are encouraged to add an assertion or check to break
their loop if it does not make progress (and report the issue as a
bug).
If an application does not use the flag
PCRE2_EXTRA_ALLOW_LOOKAROUND_BSK, then each match is "well-
behaved" and satisfies:
start_offset <= ovector[0] <= ovector[1].
In this case, the matches found by pcre2_match() with
pcre2_next_match() will be sorted, non-overlapping (possibly
touching), and with no duplicates.
Otherwise, if PCRE2_EXTRA_ALLOW_LOOKAROUND_BSK is used, then the
guarantees are considerably weaker. We do not guarantee that the
matches will always advance: only that the start_offset will. The
matches found by pcre2_match() with pcre2_next_match() will be a
finite sequence (as pcre2_next_match() ensures that start_offset
advances, so the search will terminate). The matches can however
be overlapping, can contain duplicates, and (in truly pathological
examples) may not even be sorted by ovector[0]. Additionally, each
match itself can end before it starts (ovector[1] < ovector[0]).
We recommend that applications do not set
PCRE2_EXTRA_ALLOW_LOOKAROUND_BSK.
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
lookahead 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.
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().
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.
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.
(These cases are only possible if the pattern was compiled with
the backwards-compatibility option
PCRE2_EXTRA_ALLOW_LOOKAROUND_BSK.)
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, which will include
the extra space for the terminating NUL. 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 recognized:
$$ insert a dollar character
$n or ${n} insert the contents of group n
$0 or $& insert the entire matched substring
$` insert the substring that precedes the match
$' insert the substring that follows the match
$_ insert the entire input string
$*MARK or ${*MARK} insert a control verb name
Either a group number or a group name can be given for n, for
example $2 or $NAME. Curly brackets are required only if the
following character would be interpreted as part of the number or
name. The number may be zero to include the entire matched string.
For example, if the pattern a(b)c is matched with "=abc=" and the
replacement string "+$1$0$1+", the result is "=+babcb+=".
The JavaScript form $<name>, where the angle brackets are part of
the syntax, is also recognized for group names, but not for group
numbers or *MARK.
$*MARK inserts the name from the last encountered backtracking
control verb on the matching path that has a name. (*MARK) must
always include a name, but the other verbs need not. For example,
in the case of (*MARK:A)(*PRUNE) the name inserted is "A", but for
(*MARK:A)(*PRUNE:B) the relevant name is "B". This facility can be
used to perform simple simultaneous substitutions, as this
pcre2test example shows:
/(*MARK:pear)apple|(*MARK:orange)lemon/g,replace=${*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.
Because global substitutions apply the pattern repeatedly to the
subject string, and always iterate over non-overlapping matches,
the substitutions done by pcre2_substitute() do not match and
substitute text inside the replacement strings themselves (no
recursive/iterative substitution). However, applications can
easily implement other alternative replacement strategies, such as
iteratively replacing, then matching and replacing on the result.
The replacement loop inside pcre2_substitute() is simple and can
be emulated in client code by allocating a buffer, searching for
matches in a loop, and calling pcre2_substitute() with
PCRE2_SUBSTITUTE_REPLACEMENT_ONLY an PCRE2_SUBSTITUTE_MATCHED, and
without PCRE2_SUBSTITUTE_GLOBAL.
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, several
things change:
Firstly, backslash in a replacement string is interpreted as an
escape character. The usual forms such as \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. The
escapes \b and \v are interpreted as the characters backspace and
vertical tab, respectively.
The interpretation of backslash followed by one or more digits is
the same as in a pattern, which in Perl has some ambiguities.
Details are given in the pcre2pattern page.
The Python form \g<n>, where the angle brackets are part of the
syntax and n is either a group name or number, is recognized as an
alternative way of inserting the contents of a group, for example
\g<3>.
There are also four escape sequences for forcing the case of
inserted letters. Case forcing applies to all inserted
characters, including those from capture groups and letters within
\Q...\E quoted sequences. 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.
However, if \u is immediately followed by \L or \l is immediately
followed by \U, the next character's case is forced by the first
escape sequence, and subsequent characters by the second. This
provides a "title casing" facility that can be applied to group
captures. For example, if group 1 has captured "heLLo", the
replacement string "\u\L$1" becomes "Hello".
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. However, only simple case
folding, as determined by the Unicode file CaseFolding.txt is
supported. PCRE2 does not support language-specific special casing
rules such as using different lower case Greek sigmas in the
middle and ends of words (as defined in the Unicode file
SpecialCasing.txt).
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 final 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 in the simple case, 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, the 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
a lookaround 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_substitute_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. In this mode, when substitution processing exceeds the
buffer space provided by the caller, processing continues by
counting code units. The simulation is unable to populate the
callout block, and so the simulation is pessimistic about the
required buffer size. Whichever is larger of accepted or rejected
substitution is reported as the required size. Therefore, the
returned buffer length may be an overestimate (without a
substitution callout, it is normally an exact measurement).
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.
Substitution case callouts
int pcre2_set_substitute_case_callout(pcre2_match_context *mcontext,
PCRE2_SIZE (*callout_function)(PCRE2_SPTR, PCRE2_SIZE,
PCRE2_UCHAR *, PCRE2_SIZE,
int, void *),
void *callout_data);
The pcre2_set_substitute_case_callout() function can be used to
specify a callout function for pcre2_substitute() to use when
performing case transformations. This does not affect any case
insensitivity behaviour when performing a match, but only the
user-visible transformations performed when processing a
substitution such as:
pcre2_substitute(..., "\\U$1", ...)
The default case transformations applied by PCRE2 are reasonably
complete, and, in UTF or UCP mode, perform the simple locale-
invariant case transformations as specified by Unicode. This is
suitable for the internal (invisible) case-equivalence procedures
used during pattern matching, but an application may wish to use
more sophisticated locale-aware processing for the user-visible
substitution transformations.
One example implementation of the callout_function using the ICU
library would be:
PCRE2_SIZE
icu_case_callout(
PCRE2_SPTR input, PCRE2_SIZE input_len,
PCRE2_UCHAR *output, PCRE2_SIZE output_cap,
int to_case, void *data_ptr)
{
UErrorCode err = U_ZERO_ERROR;
int32_t r = to_case == PCRE2_SUBSTITUTE_CASE_LOWER
? u_strToLower(output, output_cap, input, input_len, NULL, &err)
: to_case == PCRE2_SUBSTITUTE_CASE_UPPER
? u_strToUpper(output, output_cap, input, input_len, NULL, &err)
: u_strToTitle(output, output_cap, input, input_len, &first_char_only,
NULL, &err);
if (U_FAILURE(err)) return (~(PCRE2_SIZE)0);
return r;
}
The first and second arguments of the case callout function are
the Unicode string to transform.
The third and fourth arguments are the output buffer and its
capacity.
The fifth is one of the constants PCRE2_SUBSTITUTE_CASE_LOWER,
PCRE2_SUBSTITUTE_CASE_UPPER, or PCRE2_SUBSTITUTE_CASE_TITLE_FIRST.
PCRE2_SUBSTITUTE_CASE_LOWER and PCRE2_SUBSTITUTE_CASE_UPPER are
passed to the callout to indicate that the case of the entire
callout input should be case-transformed.
PCRE2_SUBSTITUTE_CASE_TITLE_FIRST is passed to indicate that only
the first character or glyph should be transformed to Unicode
titlecase and the rest to Unicode lowercase (note that titlecasing
sometimes uses Unicode properties to titlecase each word in a
string; but PCRE2 is requesting that only the single leading
character is to be titlecased).
The sixth argument is the callout_data supplied to
pcre2_set_substitute_case_callout().
The resulting string in the destination buffer may be larger or
smaller than the input, if the casing rules merge or split
characters. The return value is the length required for the output
string. If a buffer of sufficient size was provided to the
callout, then the result must be written to the buffer and the
number of code units returned. If the result does not fit in the
provided buffer, then the required capacity must be returned and
PCRE2 will not make use of the output buffer. PCRE2 provides input
and output buffers which overlap, so the callout must support this
by suitable internal buffering.
Alternatively, if the callout wishes to indicate an error, then it
may return (~(PCRE2_SIZE)0). In this case pcre2_substitute() will
immediately fail with error PCRE2_ERROR_REPLACECASE.
When a case callout is combined with the
PCRE2_SUBSTITUTE_OVERFLOW_LENGTH option, there are situations when
pcre2_substitute() will return an underestimate of the required
buffer size. If you call pcre2_substitute() once with
PCRE2_SUBSTITUTE_OVERFLOW_LENGTH, and the input buffer is too
small for the replacement string to be constructed, then instead
of calling the case callout, pcre2_substitute() will make an
estimate of the required buffer size. The second call should also
pass PCRE2_SUBSTITUTE_OVERFLOW_LENGTH, because that second call is
not guaranteed to succeed either, if the case callout requires
more buffer space than expected. The caller must make repeated
attempts in a loop.
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.
The traditional matching function uses a similar algorithm to
Perl, which stops when it finds the first match at a given point
in the subject. If you want to find all possible matches, or the
longest possible match at a given position, consider using the
alternative matching function (see below) instead. If you cannot
use the alternative function, you can kludge it up by making use
of the callout facility, which is described in the pcre2callout
documentation.
What you have to do is to insert a callout right at the end of the
pattern. When your callout function is called, extract and save
the current matched substring. Then return 1, which forces
pcre2_match() to backtrack and try other alternatives. Ultimately,
when it runs out of matches, pcre2_match() will yield
PCRE2_ERROR_NOMATCH.
int pcre2_dfa_match(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext,
int *workspace, PCRE2_SIZE wscount);
The function pcre2_dfa_match() is called to match a subject string
against a compiled pattern, using a matching algorithm that scans
the subject string just once (not counting lookaround assertions),
and does not backtrack (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.
pcre2build(3), pcre2callout(3), pcre2demo(3), pcre2matching(3),
pcre2partial(3), pcre2posix(3), pcre2sample(3), pcre2unicode(3).
Philip Hazel
Retired from University Computing Service
Cambridge, England.
Last updated: 26 December 2024
Copyright (c) 1997-2024 University of Cambridge.
This page is part of the PCRE (Perl Compatible Regular
Expressions) project. Information about the project can be found
at ⟨http://www.pcre.org/⟩. If you have a bug report for this
manual page, see
⟨http://bugs.exim.org/enter_bug.cgi?product=PCRE⟩. This page was
obtained from the tarball fetched from
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page, or you have corrections or improvements to the information
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send a mail to man-pages@man7.org
PCRE2 10.46-DEV 26 December 2024 PCRE2API(3)
Pages that refer to this page: pcre2test(1), pcre2build(3), pcre2jit(3), pcre2pattern(3), pcre2syntax(3)
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