PCRE2API(3) Introduction to Library Functions PCRE2API(3)

NAME

PCRE2 - Perl-compatible regular expressions (revised API)

#include <pcre2.h>

PCRE2 is a new API for PCRE, starting at release 10.0. This document
contains a description of all its native functions. See the pcre2
document for an overview of all the PCRE2 documentation.

PCRE2 NATIVE API BASIC FUNCTIONS
pcre2_code *pcre2_compile(PCRE2_SPTR pattern, PCRE2_SIZE length,
uint32_t options, int *errorcode, PCRE2_SIZE *erroroffset,
pcre2_compile_context *ccontext);

void pcre2_code_free(pcre2_code *code);

pcre2_match_data *pcre2_match_data_create(uint32_t ovecsize,
pcre2_general_context *gcontext);

pcre2_match_data *pcre2_match_data_create_from_pattern(
const pcre2_code *code, pcre2_general_context *gcontext);

int pcre2_match(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext);

int pcre2_dfa_match(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext,
int *workspace, PCRE2_SIZE wscount);

void pcre2_match_data_free(pcre2_match_data *match_data);

PCRE2 NATIVE API AUXILIARY MATCH FUNCTIONS
PCRE2_SPTR pcre2_get_mark(pcre2_match_data *match_data);

PCRE2_SIZE pcre2_get_match_data_size(pcre2_match_data *match_data);

PCRE2_SIZE pcre2_get_match_data_heapframes_size(
pcre2_match_data *match_data);

uint32_t pcre2_get_ovector_count(pcre2_match_data *match_data);

PCRE2_SIZE *pcre2_get_ovector_pointer(pcre2_match_data *match_data);

PCRE2_SIZE pcre2_get_startchar(pcre2_match_data *match_data);

PCRE2 NATIVE API GENERAL CONTEXT FUNCTIONS
pcre2_general_context *pcre2_general_context_create(
void *(*private_malloc)(PCRE2_SIZE, void *),
void (*private_free)(void *, void *), void *memory_data);

pcre2_general_context *pcre2_general_context_copy(
pcre2_general_context *gcontext);

void pcre2_general_context_free(pcre2_general_context *gcontext);

PCRE2 NATIVE API COMPILE CONTEXT FUNCTIONS
pcre2_compile_context *pcre2_compile_context_create(
pcre2_general_context *gcontext);

pcre2_compile_context *pcre2_compile_context_copy(
pcre2_compile_context *ccontext);

void pcre2_compile_context_free(pcre2_compile_context *ccontext);

int pcre2_set_bsr(pcre2_compile_context *ccontext,
uint32_t value);

int pcre2_set_character_tables(pcre2_compile_context *ccontext,
const uint8_t *tables);

int pcre2_set_compile_extra_options(pcre2_compile_context *ccontext,
uint32_t extra_options);

int pcre2_set_max_pattern_length(pcre2_compile_context *ccontext,
PCRE2_SIZE value);

int pcre2_set_max_pattern_compiled_length(
pcre2_compile_context *ccontext, PCRE2_SIZE value);

int pcre2_set_max_varlookbehind(pcre2_compile_contest *ccontext,
uint32_t value);

int pcre2_set_newline(pcre2_compile_context *ccontext,
uint32_t value);

int pcre2_set_parens_nest_limit(pcre2_compile_context *ccontext,
uint32_t value);

int pcre2_set_compile_recursion_guard(pcre2_compile_context *ccontext,
int (*guard_function)(uint32_t, void *), void *user_data);

int pcre2_set_optimize(pcre2_compile_context *ccontext,
uint32_t directive);

PCRE2 NATIVE API MATCH CONTEXT FUNCTIONS
pcre2_match_context *pcre2_match_context_create(
pcre2_general_context *gcontext);

pcre2_match_context *pcre2_match_context_copy(
pcre2_match_context *mcontext);

void pcre2_match_context_free(pcre2_match_context *mcontext);

int pcre2_set_callout(pcre2_match_context *mcontext,
int (*callout_function)(pcre2_callout_block *, void *),
void *callout_data);

int pcre2_set_substitute_callout(pcre2_match_context *mcontext,
int (*callout_function)(pcre2_substitute_callout_block *, void *),
void *callout_data);

int pcre2_set_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);

PCRE2 NATIVE API STRING EXTRACTION FUNCTIONS
int pcre2_substring_copy_byname(pcre2_match_data *match_data,
PCRE2_SPTR name, PCRE2_UCHAR *buffer, PCRE2_SIZE *bufflen);

int pcre2_substring_copy_bynumber(pcre2_match_data *match_data,
uint32_t number, PCRE2_UCHAR *buffer,
PCRE2_SIZE *bufflen);

void pcre2_substring_free(PCRE2_UCHAR *buffer);

int pcre2_substring_get_byname(pcre2_match_data *match_data,
PCRE2_SPTR name, PCRE2_UCHAR **bufferptr, PCRE2_SIZE *bufflen);

int pcre2_substring_get_bynumber(pcre2_match_data *match_data,
uint32_t number, PCRE2_UCHAR **bufferptr,
PCRE2_SIZE *bufflen);

int pcre2_substring_length_byname(pcre2_match_data *match_data,
PCRE2_SPTR name, PCRE2_SIZE *length);

int pcre2_substring_length_bynumber(pcre2_match_data *match_data,
uint32_t number, PCRE2_SIZE *length);

int pcre2_substring_nametable_scan(const pcre2_code *code,
PCRE2_SPTR name, PCRE2_SPTR *first, PCRE2_SPTR *last);

int pcre2_substring_number_from_name(const pcre2_code *code,
PCRE2_SPTR name);

void pcre2_substring_list_free(PCRE2_UCHAR **list);

int pcre2_substring_list_get(pcre2_match_data *match_data,
PCRE2_UCHAR ***listptr, PCRE2_SIZE **lengthsptr);

PCRE2 NATIVE API STRING SUBSTITUTION FUNCTION
int pcre2_substitute(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext, PCRE2_SPTR replacementz,
PCRE2_SIZE rlength, PCRE2_UCHAR *outputbuffer,
PCRE2_SIZE *outlengthptr);

PCRE2 NATIVE API JIT FUNCTIONS
int pcre2_jit_compile(pcre2_code *code, uint32_t options);

int pcre2_jit_match(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext);

void pcre2_jit_free_unused_memory(pcre2_general_context *gcontext);

pcre2_jit_stack *pcre2_jit_stack_create(size_t startsize,
size_t maxsize, pcre2_general_context *gcontext);

void pcre2_jit_stack_assign(pcre2_match_context *mcontext,
pcre2_jit_callback callback_function, void *callback_data);

void pcre2_jit_stack_free(pcre2_jit_stack *jit_stack);

PCRE2 NATIVE API SERIALIZATION FUNCTIONS
int32_t pcre2_serialize_decode(pcre2_code **codes,
int32_t number_of_codes, const uint8_t *bytes,
pcre2_general_context *gcontext);

int32_t pcre2_serialize_encode(const pcre2_code **codes,
int32_t number_of_codes, uint8_t **serialized_bytes,
PCRE2_SIZE *serialized_size, pcre2_general_context *gcontext);

void pcre2_serialize_free(uint8_t *bytes);

int32_t pcre2_serialize_get_number_of_codes(const uint8_t *bytes);

PCRE2 NATIVE API AUXILIARY FUNCTIONS
pcre2_code *pcre2_code_copy(const pcre2_code *code);

pcre2_code *pcre2_code_copy_with_tables(const pcre2_code *code);

int pcre2_get_error_message(int errorcode, PCRE2_UCHAR *buffer,
PCRE2_SIZE bufflen);

const uint8_t *pcre2_maketables(pcre2_general_context *gcontext);

void pcre2_maketables_free(pcre2_general_context *gcontext,
const uint8_t *tables);

int pcre2_pattern_info(const pcre2_code *code, uint32_t what,
void *where);

int pcre2_callout_enumerate(const pcre2_code *code,
int (*callback)(pcre2_callout_enumerate_block *, void *),
void *user_data);

int pcre2_config(uint32_t what, void *where);

PCRE2 NATIVE API OBSOLETE FUNCTIONS
int pcre2_set_recursion_limit(pcre2_match_context *mcontext,
uint32_t value);

int pcre2_set_recursion_memory_management(
pcre2_match_context *mcontext,
void *(*private_malloc)(size_t, void *),
void (*private_free)(void *, void *), void *memory_data);

These functions became obsolete at release 10.30 and are retained
only for backward compatibility. They should not be used in new code.
The first is replaced by pcre2_set_depth_limit(); the second is no
longer needed and has no effect (it always returns zero).

PCRE2 EXPERIMENTAL PATTERN CONVERSION FUNCTIONS
pcre2_convert_context *pcre2_convert_context_create(
pcre2_general_context *gcontext);

pcre2_convert_context *pcre2_convert_context_copy(
pcre2_convert_context *cvcontext);

void pcre2_convert_context_free(pcre2_convert_context *cvcontext);

int pcre2_set_glob_escape(pcre2_convert_context *cvcontext,
uint32_t escape_char);

int pcre2_set_glob_separator(pcre2_convert_context *cvcontext,
uint32_t separator_char);

int pcre2_pattern_convert(PCRE2_SPTR pattern, PCRE2_SIZE length,
uint32_t options, PCRE2_UCHAR **buffer,
PCRE2_SIZE *blength, pcre2_convert_context *cvcontext);

void pcre2_converted_pattern_free(PCRE2_UCHAR *converted_pattern);

These functions provide a way of converting non-PCRE2 patterns into
patterns that can be processed by pcre2_compile(). This facility is
experimental and may be changed in future releases. At present,
"globs" and POSIX basic and extended patterns can be converted.
Details are given in the pcre2convert documentation.

PCRE2 8-BIT, 16-BIT, AND 32-BIT LIBRARIES
There are three PCRE2 libraries, supporting 8-bit, 16-bit, and 32-bit
code units, respectively. However, there is just one header file,
pcre2.h. This contains the function prototypes and other definitions
for all three libraries. One, two, or all three can be installed
simultaneously. On Unix-like systems the libraries are called
libpcre2-8, libpcre2-16, and libpcre2-32, and they can also co-exist
with the original PCRE libraries. Every PCRE2 function comes in
three different forms, one for each library, for example:

pcre2_compile_8()
pcre2_compile_16()
pcre2_compile_32()

There are also three different sets of data types:

PCRE2_UCHAR8, PCRE2_UCHAR16, PCRE2_UCHAR32
PCRE2_SPTR8, PCRE2_SPTR16, PCRE2_SPTR32

The UCHAR types define unsigned code units of the appropriate widths.
For example, PCRE2_UCHAR16 is usually defined as `uint16_t'. The
SPTR types are pointers to constants of the equivalent UCHAR types,
that is, they are pointers to vectors of unsigned code units.

Character strings are passed to a PCRE2 library as sequences of
unsigned integers in code units of the appropriate width. The length
of a string may be given as a number of code units, or the string may
be specified as zero-terminated.

Many applications use only one code unit width. For their
convenience, macros are defined whose names are the generic forms
such as pcre2_compile() and PCRE2_SPTR. These macros use the value of
the macro PCRE2_CODE_UNIT_WIDTH to generate the appropriate width-
specific function and macro names. PCRE2_CODE_UNIT_WIDTH is not
defined by default. An application must define it to be 8, 16, or 32
before including pcre2.h in order to make use of the generic names.

Applications that use more than one code unit width can be linked
with more than one PCRE2 library, but must define
PCRE2_CODE_UNIT_WIDTH to be 0 before including pcre2.h, and then use
the real function names. Any code that is to be included in an
environment where the value of PCRE2_CODE_UNIT_WIDTH is unknown
should also use the real function names. (Unfortunately, it is not
possible in C code to save and restore the value of a macro.)

If PCRE2_CODE_UNIT_WIDTH is not defined before including pcre2.h, a
compiler error occurs.

When using multiple libraries in an application, you must take care
when processing any particular pattern to use only functions from a
single library. For example, if you want to run a match using a
pattern that was compiled with pcre2_compile_16(), you must do so
with pcre2_match_16(), not pcre2_match_8() or pcre2_match_32().

In the function summaries above, and in the rest of this document and
other PCRE2 documents, functions and data types are described using
their generic names, without the _8, _16, or _32 suffix.

PCRE2 API OVERVIEW
PCRE2 has its own native API, which is described in this document.
There are also some wrapper functions for the 8-bit library that
correspond to the POSIX regular expression API, but they do not give
access to all the functionality of PCRE2 and they are not thread-
safe. They are described in the pcre2posix documentation. Both these
APIs define a set of C function calls.

The native API C data types, function prototypes, option values, and
error codes are defined in the header file pcre2.h, which also
contains definitions of PCRE2_MAJOR and PCRE2_MINOR, the major and
minor release numbers for the library. Applications can use these to
include support for different releases of PCRE2.

In a Windows environment, if you want to statically link an
application program against a non-dll PCRE2 library, you must define
PCRE2_STATIC before including pcre2.h.

The functions pcre2_compile() and pcre2_match() are used for
compiling and matching regular expressions in a Perl-compatible
manner. A sample program that demonstrates the simplest way of using
them is provided in the file called pcre2demo.c in the PCRE2 source
distribution. A listing of this program is given in the pcre2demo
documentation, and the pcre2sample documentation describes how to
compile and run it.

The compiling and matching functions recognize various options that
are passed as bits in an options argument. There are also some more
complicated parameters such as custom memory management functions and
resource limits that are passed in "contexts" (which are just memory
blocks, described below). Simple applications do not need to make use
of contexts.

Just-in-time (JIT) compiler support is an optional feature of PCRE2
that can be built in appropriate hardware environments. It greatly
speeds up the matching performance of many patterns. Programs can
request that it be used if available by calling pcre2_jit_compile()
after a pattern has been successfully compiled by pcre2_compile().
This does nothing if JIT support is not available.

More complicated programs might need to make use of the specialist
functions pcre2_jit_stack_create(), pcre2_jit_stack_free(), and
pcre2_jit_stack_assign() in order to control the JIT code's memory
usage.

JIT matching is automatically used by pcre2_match() if it is
available, unless the PCRE2_NO_JIT option is set. There is also a
direct interface for JIT matching, which gives improved performance
at the expense of less sanity checking. The JIT-specific functions
are discussed in the pcre2jit documentation.

A second matching function, pcre2_dfa_match(), which is not Perl-
compatible, is also provided. This uses a different algorithm for the
matching. The alternative algorithm finds all possible matches (at a
given point in the subject), and scans the subject just once (unless
there are lookaround assertions). However, this algorithm does not
return captured substrings. A description of the two matching
algorithms and their advantages and disadvantages is given in the
pcre2matching documentation. There is no JIT support for
pcre2_dfa_match().

In addition to the main compiling and matching functions, there are
convenience functions for extracting captured substrings from a
subject string that has been matched by pcre2_match(). They are:

pcre2_substring_copy_byname()
pcre2_substring_copy_bynumber()
pcre2_substring_get_byname()
pcre2_substring_get_bynumber()
pcre2_substring_list_get()
pcre2_substring_length_byname()
pcre2_substring_length_bynumber()
pcre2_substring_nametable_scan()
pcre2_substring_number_from_name()

pcre2_substring_free() and pcre2_substring_list_free() are also
provided, to free memory used for extracted strings. If either of
these functions is called with a NULL argument, the function returns
immediately without doing anything.

The function pcre2_substitute() can be called to match a pattern and
return a copy of the subject string with substitutions for parts that
were matched.

Functions whose names begin with pcre2_serialize_ are used for saving
compiled patterns on disc or elsewhere, and reloading them later.

Finally, there are functions for finding out information about a
compiled pattern (pcre2_pattern_info()) and about the configuration
with which PCRE2 was built (pcre2_config()).

Functions with names ending with _free() are used for freeing memory
blocks of various sorts. In all cases, if one of these functions is
called with a NULL argument, it does nothing.

STRING LENGTHS AND OFFSETS

The PCRE2 API uses string lengths and offsets into strings of code
units in several places. These values are always of type PCRE2_SIZE,
which is an unsigned integer type, currently always defined as
size_t. The largest value that can be stored in such a type (that is
~(PCRE2_SIZE)0) is reserved as a special indicator for zero-
terminated strings and unset offsets. Therefore, the longest string
that can be handled is one less than this maximum. Note that string
lengths are always given in code units. Only in the 8-bit library is
such a length the same as the number of bytes in the string.

NEWLINES

PCRE2 supports five different conventions for indicating line breaks
in strings: a single CR (carriage return) character, a single LF
(linefeed) character, the two-character sequence CRLF, any of the
three preceding, or any Unicode newline sequence. The Unicode newline
sequences are the three just mentioned, plus the single characters VT
(vertical tab, U+000B), FF (form feed, U+000C), NEL (next line,
U+0085), LS (line separator, U+2028), and PS (paragraph separator,
U+2029).

Each of the first three conventions is used by at least one operating
system as its standard newline sequence. When PCRE2 is built, a
default can be specified. If it is not, the default is set to LF,
which is the Unix standard. However, the newline convention can be
changed by an application when calling pcre2_compile(), or it can be
specified by special text at the start of the pattern itself; this
overrides any other settings. See the pcre2pattern page for details
of the special character sequences.

In the PCRE2 documentation the word "newline" is used to mean "the
character or pair of characters that indicate a line break". The
choice of newline convention affects the handling of the dot,
circumflex, and dollar metacharacters, the handling of #-comments in
/x mode, and, when CRLF is a recognized line ending sequence, the
match position advancement for a non-anchored pattern. There is more
detail about this in the section on pcre2_match() options below.

The choice of newline convention does not affect the interpretation
of the \n or \r escape sequences, nor does it affect what \R matches;
this has its own separate convention.

MULTITHREADING

In a multithreaded application it is important to keep thread-
specific data separate from data that can be shared between threads.
The PCRE2 library code itself is thread-safe: it contains no static
or global variables. The API is designed to be fairly simple for non-
threaded applications while at the same time ensuring that
multithreaded applications can use it.

There are several different blocks of data that are used to pass
information between the application and the PCRE2 libraries.

The compiled pattern

A pointer to the compiled form of a pattern is returned to the user
when pcre2_compile() is successful. The data in the compiled pattern
is fixed, and does not change when the pattern is matched. Therefore,
it is thread-safe, that is, the same compiled pattern can be used by
more than one thread simultaneously. For example, an application can
compile all its patterns at the start, before forking off multiple
threads that use them. However, if the just-in-time (JIT)
optimization feature is being used, it needs separate memory stack
areas for each thread. See the pcre2jit documentation for more
details.

In a more complicated situation, where patterns are compiled only
when they are first needed, but are still shared between threads,
pointers to compiled patterns must be protected from simultaneous
writing by multiple threads. This is somewhat tricky to do correctly.
If you know that writing to a pointer is atomic in your environment,
you can use logic like this:

Get a read-only (shared) lock (mutex) for pointer
if (pointer == NULL)
{
Get a write (unique) lock for pointer
if (pointer == NULL) pointer = pcre2_compile(...
}
Release the lock
Use pointer in pcre2_match()

Of course, testing for compilation errors should also be included in
the code.

The reason for checking the pointer a second time is as follows:
Several threads may have acquired the shared lock and tested the
pointer for being NULL, but only one of them will be given the write
lock, with the rest kept waiting. The winning thread will compile the
pattern and store the result. After this thread releases the write
lock, another thread will get it, and if it does not retest pointer
for being NULL, will recompile the pattern and overwrite the pointer,
creating a memory leak and possibly causing other issues.

In an environment where writing to a pointer may not be atomic, the
above logic is not sufficient. The thread that is doing the compiling
may be descheduled after writing only part of the pointer, which
could cause other threads to use an invalid value. Instead of
checking the pointer itself, a separate "pointer is valid" flag (that
can be updated atomically) must be used:

Get a read-only (shared) lock (mutex) for pointer
if (!pointer_is_valid)
{
Get a write (unique) lock for pointer
if (!pointer_is_valid)
{
pointer = pcre2_compile(...
pointer_is_valid = TRUE
}
}
Release the lock
Use pointer in pcre2_match()

If JIT is being used, but the JIT compilation is not being done
immediately (perhaps waiting to see if the pattern is used often
enough), similar logic is required. JIT compilation updates a value
within the compiled code block, so a thread must gain unique write
access to the pointer before calling pcre2_jit_compile().
Alternatively, pcre2_code_copy() or pcre2_code_copy_with_tables() can
be used to obtain a private copy of the compiled code before calling
the JIT compiler.

Context blocks

The next main section below introduces the idea of "contexts" in
which PCRE2 functions are called. A context is nothing more than a
collection of parameters that control the way PCRE2 operates.
Grouping a number of parameters together in a context is a convenient
way of passing them to a PCRE2 function without using lots of
arguments. The parameters that are stored in contexts are in some
sense "advanced features" of the API. Many straightforward
applications will not need to use contexts.

In a multithreaded application, if the parameters in a context are
values that are never changed, the same context can be used by all
the threads. However, if any thread needs to change any value in a
context, it must make its own thread-specific copy.

Match blocks

The matching functions need a block of memory for storing the results
of a match. This includes details of what was matched, as well as
additional information such as the name of a (*MARK) setting. Each
thread must provide its own copy of this memory.

PCRE2 CONTEXTS
Some PCRE2 functions have a lot of parameters, many of which are used
only by specialist applications, for example, those that use custom
memory management or non-standard character tables. To keep function
argument lists at a reasonable size, and at the same time to keep the
API extensible, "uncommon" parameters are passed to certain functions
in a context instead of directly. A context is just a block of memory
that holds the parameter values. Applications that do not need to
adjust any of the context parameters can pass NULL when a context
pointer is required.

There are three different types of context: a general context that is
relevant for several PCRE2 operations, a compile-time context, and a
match-time context.

The general context

At present, this context just contains pointers to (and data for)
external memory management functions that are called from several
places in the PCRE2 library. The context is named `general' rather
than specifically `memory' because in future other fields may be
added. If you do not want to supply your own custom memory management
functions, you do not need to bother with a general context. A
general context is created by:

pcre2_general_context *pcre2_general_context_create(
void *(*private_malloc)(PCRE2_SIZE, void *),
void (*private_free)(void *, void *), void *memory_data);

The two function pointers specify custom memory management functions,
whose prototypes are:

void *private_malloc(PCRE2_SIZE, void *);
void private_free(void *, void *);

Whenever code in PCRE2 calls these functions, the final argument is
the value of memory_data. Either of the first two arguments of the
creation function may be NULL, in which case the system memory
management functions malloc() and free() are used. (This is not
currently useful, as there are no other fields in a general context,
but in future there might be.) The private_malloc() function is used
(if supplied) to obtain memory for storing the context, and all three
values are saved as part of the context.

Whenever PCRE2 creates a data block of any kind, the block contains a
pointer to the free() function that matches the malloc() function
that was used. When the time comes to free the block, this function
is called.

A general context can be copied by calling:

pcre2_general_context *pcre2_general_context_copy(
pcre2_general_context *gcontext);

The memory used for a general context should be freed by calling:

void pcre2_general_context_free(pcre2_general_context *gcontext);

If this function is passed a NULL argument, it returns immediately
without doing anything.

The compile context

A compile context is required if you want to provide an external
function for stack checking during compilation or to change the
default values of any of the following compile-time parameters:

What \R matches (Unicode newlines or CR, LF, CRLF only)
PCRE2's character tables
The newline character sequence
The compile time nested parentheses limit
The maximum length of the pattern string
The extra options bits (none set by default)
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.

CHECKING BUILD-TIME OPTIONS
int pcre2_config(uint32_t what, void *where);

The function pcre2_config() makes it possible for a PCRE2 client to
find the value of certain configuration parameters and to discover
which optional features have been compiled into the PCRE2 library.
The pcre2build documentation has more details about these features.

The first argument for pcre2_config() specifies which information is
required. The second argument is a pointer to memory into which the
information is placed. If NULL is passed, the function returns the
amount of memory that is needed for the requested information. For
calls that return numerical values, the value is in bytes; when
requesting these values, where should point to appropriately aligned
memory. For calls that return strings, the required length is given
in code units, not counting the terminating zero.

When requesting information, the returned value from pcre2_config()
is non-negative on success, or the negative error code
PCRE2_ERROR_BADOPTION if the value in the first argument is not
recognized. The following information is available:

PCRE2_CONFIG_BSR

The output is a uint32_t integer whose value indicates what character
sequences the \R escape sequence matches by default. A value of
PCRE2_BSR_UNICODE means that \R matches any Unicode line ending
sequence; a value of PCRE2_BSR_ANYCRLF means that \R matches only CR,
LF, or CRLF. The default can be overridden when a pattern is
compiled.

PCRE2_CONFIG_COMPILED_WIDTHS

The output is a uint32_t integer whose lower bits indicate which code
unit widths were selected when PCRE2 was built. The 1-bit indicates
8-bit support, and the 2-bit and 4-bit indicate 16-bit and 32-bit
support, respectively.

PCRE2_CONFIG_DEPTHLIMIT

The output is a uint32_t integer that gives the default limit for the
depth of nested backtracking in pcre2_match() or the depth of nested
recursions, lookarounds, and atomic groups in pcre2_dfa_match().
Further details are given with pcre2_set_depth_limit() above.

PCRE2_CONFIG_HEAPLIMIT

The output is a uint32_t integer that gives, in kibibytes, the
default limit for the amount of heap memory used by pcre2_match() or
pcre2_dfa_match(). Further details are given with
pcre2_set_heap_limit() above.

PCRE2_CONFIG_JIT

The output is a uint32_t integer that is set to one if support for
just-in-time compiling is included in the library; otherwise it is
set to zero. Note that having the support in the library does not
guarantee that JIT will be used for any given match, 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.

COMPILING A PATTERN

pcre2_code *pcre2_compile(PCRE2_SPTR pattern, PCRE2_SIZE length,
uint32_t options, int *errorcode, PCRE2_SIZE *erroroffset,
pcre2_compile_context *ccontext);

void pcre2_code_free(pcre2_code *code);

pcre2_code *pcre2_code_copy(const pcre2_code *code);

pcre2_code *pcre2_code_copy_with_tables(const pcre2_code *code);

The pcre2_compile() function compiles a pattern into an internal
form. The pattern is defined by a pointer to a string of code units
and a length in code units. If the pattern is zero-terminated, the
length can be specified as PCRE2_ZERO_TERMINATED. A NULL pattern
pointer with a length of zero is treated as an empty string (NULL
with a non-zero length causes an error return). The function returns
a pointer to a block of memory that contains the compiled pattern and
related data, or NULL if an error occurred.

If the compile context argument ccontext is NULL, memory for the
compiled pattern is obtained by calling malloc(). Otherwise, it is
obtained from the same memory function that was used for the compile
context. The caller must free the memory by calling pcre2_code_free()
when it is no longer needed. If pcre2_code_free() is called with a
NULL argument, it returns immediately, without doing anything.

The function pcre2_code_copy() makes a copy of the compiled code in
new memory, using the same memory allocator as was used for the
original. However, if the code has been processed by the JIT compiler
(see below), the JIT information cannot be copied (because it is
position-dependent). The new copy can initially be used only for
non-JIT matching, though it can be passed to pcre2_jit_compile() if
required. If pcre2_code_copy() is called with a NULL argument, it
returns NULL.

The pcre2_code_copy() function provides a way for individual threads
in a multithreaded application to acquire a private copy of shared
compiled code. However, it does not make a copy of the character
tables used by the compiled pattern; the new pattern code points to
the same tables as the original code. (See "Locale Support" below
for details of these character tables.) In many applications the same
tables are used throughout, so this behaviour is appropriate.
Nevertheless, there are occasions when a copy of a compiled pattern
and the relevant tables are needed. The pcre2_code_copy_with_tables()
provides this facility. Copies of both the code and the tables are
made, with the new code pointing to the new tables. The memory for
the new tables is automatically freed when pcre2_code_free() is
called for the new copy of the compiled code. If
pcre2_code_copy_with_tables() is called with a NULL argument, it
returns NULL.

NOTE: When one of the matching functions is called, pointers to the
compiled pattern and the subject string are set in the match data
block so that they can be referenced by the substring extraction
functions after a successful match. After running a match, you must
not free a compiled pattern or a subject string until after all
operations on the match data block have taken place, unless, in the
case of the subject string, you have used the
PCRE2_COPY_MATCHED_SUBJECT option, which is described in the section
entitled "Option bits for pcre2_match()" below.

The options argument for pcre2_compile() contains various bit
settings that affect the compilation. It should be zero if none of
them are required. The available options are described below. Some of
them (in particular, those that are compatible with Perl, but some
others as well) can also be set and unset from within the pattern
(see the detailed description in the pcre2pattern documentation).

For those options that can be different in different parts of the
pattern, the contents of the options argument specifies their
settings at the start of compilation. The PCRE2_ANCHORED,
PCRE2_ENDANCHORED, and PCRE2_NO_UTF_CHECK options can be set at the
time of matching as well as at compile time.

Some additional options and less frequently required compile-time
parameters (for example, the newline setting) can be provided in a
compile context (as described above).

If errorcode or erroroffset is NULL, pcre2_compile() returns NULL
immediately. Otherwise, the variables to which these point are set to
an error code and an offset (number of code units) within the
pattern, respectively, when pcre2_compile() returns NULL because a
compilation error has occurred.

There are 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 zero, one, or two digits
(so, for example, \xz matches a binary zero character followed by z).

ECMAscript 6 added additional functionality to \u. This can be
accessed using the PCRE2_EXTRA_ALT_BSUX extra option (see "Extra
compile options" below). Note that this alternative escape handling
applies only to patterns. Neither of these options affects the
processing of replacement strings passed to pcre2_substitute().

PCRE2_ALT_CIRCUMFLEX

In multiline mode (when PCRE2_MULTILINE is set), the circumflex
metacharacter matches at the start of the subject (unless
PCRE2_NOTBOL is set), and also after any internal newline. However,
it does not match after a newline at the end of the subject, for
compatibility with Perl. If you want a multiline circumflex also to
match after a terminating newline, you must set PCRE2_ALT_CIRCUMFLEX.

PCRE2_ALT_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 whitespace in verb names is skipped
and #-comments are recognized, exactly as in the rest of the pattern.

PCRE2_AUTO_CALLOUT

If this bit is set, pcre2_compile() automatically inserts callout
items, all with number 255, before each pattern item, except
immediately before or after an explicit callout in the pattern. For
discussion of the callout facility, see the pcre2callout
documentation.

PCRE2_CASELESS

If this bit is set, letters in the pattern match both upper and lower
case letters in the subject. It is equivalent to Perl's /i option,
and it can be changed within a pattern by a (?i) option setting. If
either PCRE2_UTF or PCRE2_UCP is set, Unicode properties are used for
all characters with more than one other case, and for all characters
whose code points are greater than U+007F.

Note that there are two ASCII characters, K and S, that, in addition
to their lower case ASCII equivalents, are case-equivalent with
U+212A (Kelvin sign) and U+017F (long S) respectively. If you do not
want this case equivalence, you can suppress it by setting
PCRE2_EXTRA_CASELESS_RESTRICT.

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.

JUST-IN-TIME (JIT) COMPILATION
int pcre2_jit_compile(pcre2_code *code, uint32_t options);

int pcre2_jit_match(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext);

void pcre2_jit_free_unused_memory(pcre2_general_context *gcontext);

pcre2_jit_stack *pcre2_jit_stack_create(size_t startsize,
size_t maxsize, pcre2_general_context *gcontext);

void pcre2_jit_stack_assign(pcre2_match_context *mcontext,
pcre2_jit_callback callback_function, void *callback_data);

void pcre2_jit_stack_free(pcre2_jit_stack *jit_stack);

These functions provide support for JIT compilation, which, if the
just-in-time compiler is available, further processes a compiled
pattern into machine code that executes much faster than the
pcre2_match() interpretive matching function. Full details are given
in the pcre2jit documentation.

JIT compilation is a heavyweight optimization. It can take some time
for patterns to be analyzed, and for one-off matches and simple
patterns the benefit of faster execution might be offset by a much
slower compilation time. Most (but not all) patterns can be
optimized by the JIT compiler.

LOCALE SUPPORT

const uint8_t *pcre2_maketables(pcre2_general_context *gcontext);

void pcre2_maketables_free(pcre2_general_context *gcontext,
const uint8_t *tables);

PCRE2 handles caseless matching, and determines whether characters
are letters, digits, or whatever, by reference to a set of tables,
indexed by character code point. However, this applies only to
characters whose code points are less than 256. By default, higher-
valued code points never match escapes such as \w or \d.

When PCRE2 is built with Unicode support (the default), certain
Unicode character properties can be tested with \p and \P, or,
alternatively, the PCRE2_UCP option can be set when a pattern is
compiled; this causes \w and friends to use Unicode property support
instead of the built-in tables. PCRE2_UCP also causes upper/lower
casing operations on characters with code points greater than 127 to
use Unicode properties. These effects apply even when PCRE2_UTF is
not set. There are, however, some PCRE2_EXTRA options (see above)
that can be used to modify or suppress them.

The use of locales with Unicode is discouraged. If you are handling
characters with code points greater than 127, you should either use
Unicode support, or use locales, but not try to mix the two.

PCRE2 contains a built-in set of character tables that are used by
default. These are sufficient for many applications. Normally, the
internal tables recognize only ASCII characters. However, when PCRE2
is built, it is possible to cause the internal tables to be rebuilt
in the default "C" locale of the local system, which may cause them
to be different.

The built-in tables can be overridden by tables supplied by the
application that calls PCRE2. These may be created in a different
locale from the default. As more and more applications change to
using Unicode, the need for this locale support is expected to die
away.

External tables are built by calling the pcre2_maketables() function,
in the relevant locale. The only argument to this function is a
general context, which can be used to pass a custom memory allocator.
If the argument is NULL, the system malloc() is used. The result can
be passed to pcre2_compile() as often as necessary, by creating a
compile context and calling pcre2_set_character_tables() to set the
tables pointer therein.

For example, to build and use tables that are appropriate for the
French locale (where accented characters with values greater than 127
are treated as letters), the following code could be used:

setlocale(LC_CTYPE, "fr_FR");
tables = pcre2_maketables(NULL);
ccontext = pcre2_compile_context_create(NULL);
pcre2_set_character_tables(ccontext, tables);
re = pcre2_compile(..., ccontext);

The locale name "fr_FR" is used on Linux and other Unix-like systems;
if you are using Windows, the name for the French locale is "french".

The pointer that is passed (via the compile context) to
pcre2_compile() is saved with the compiled pattern, and the same
tables are used by the matching functions. Thus, for any single
pattern, compilation and matching both happen in the same locale, but
different patterns can be processed in different locales.

It is the caller's responsibility to ensure that the memory
containing the tables remains available while they are still in use.
When they are no longer needed, you can discard them using
pcre2_maketables_free(), which should pass as its first parameter the
same global context that was used to create the tables.

Saving locale tables

The tables described above are just a sequence of binary bytes, which
makes them independent of hardware characteristics such as endianness
or whether the processor is 32-bit or 64-bit. A copy of the result of
pcre2_maketables() can therefore be saved in a file or elsewhere and
re-used later, even in a different program or on another computer.
The size of the tables (number of bytes) must be obtained by calling
pcre2_config() with the PCRE2_CONFIG_TABLES_LENGTH option because
pcre2_maketables() does not return this value. Note that the
pcre2_dftables program, which is part of the PCRE2 build system, can
be used stand-alone to create a file that contains a set of binary
tables. See the pcre2build documentation for details.

INFORMATION ABOUT A COMPILED PATTERN

int pcre2_pattern_info(const pcre2 *code, uint32_t what, void *where);

The pcre2_pattern_info() function returns general information about a
compiled pattern. For information about callouts, see the next
section. The first argument for pcre2_pattern_info() is a pointer to
the compiled pattern. The second argument specifies which piece of
information is required, and the third argument is a pointer to a
variable to receive the data. If the third argument is NULL, the
first argument is ignored, and the function returns the size in bytes
of the variable that is required for the information requested.
Otherwise, the yield of the function is zero for success, or one of
the following negative numbers:

PCRE2_ERROR_NULL the argument code was NULL
PCRE2_ERROR_BADMAGIC the "magic number" was not found
PCRE2_ERROR_BADOPTION the value of what was invalid
PCRE2_ERROR_UNSET the requested field is not set

The "magic number" is placed at the start of each compiled pattern as
a simple check against passing an arbitrary memory pointer. Here is a
typical call of pcre2_pattern_info(), to obtain the length of the
compiled pattern:

int rc;
size_t length;
rc = pcre2_pattern_info(
re, /* result of pcre2_compile() */
PCRE2_INFO_SIZE, /* what is required */
&length); /* where to put the data */

The possible values for the second argument are defined in pcre2.h,
and are as follows:

PCRE2_INFO_ALLOPTIONS
PCRE2_INFO_ARGOPTIONS
PCRE2_INFO_EXTRAOPTIONS

Return copies of the pattern's options. The third argument should
point to a uint32_t variable. PCRE2_INFO_ARGOPTIONS returns exactly
the options that were passed to pcre2_compile(), whereas
PCRE2_INFO_ALLOPTIONS returns the compile options as modified by any
top-level (*XXX) option settings such as (*UTF) at the start of the
pattern itself. PCRE2_INFO_EXTRAOPTIONS returns the extra options
that were set in the compile context by calling the
pcre2_set_compile_extra_options() function.

For example, if the pattern /(*UTF)abc/ is compiled with the
PCRE2_EXTENDED option, the result for PCRE2_INFO_ALLOPTIONS is
PCRE2_EXTENDED and PCRE2_UTF. Option settings such as (?i) that can
change within a pattern do not affect the result of
PCRE2_INFO_ALLOPTIONS, even if they appear right at the start of the
pattern. (This was different in some earlier releases.)

A pattern compiled without PCRE2_ANCHORED is automatically anchored
by PCRE2 if the first significant item in every top-level branch is
one of the following:

^ unless PCRE2_MULTILINE is set
\A always
\G always
.* sometimes - see below

When .* is the first significant item, anchoring is possible only
when all the following are true:

.* is not in an atomic group
.* is not in a capture group that is the subject
of a backreference
PCRE2_DOTALL is in force for .*
Neither (*PRUNE) nor (*SKIP) appears in the pattern
PCRE2_NO_DOTSTAR_ANCHOR is not set
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.

INFORMATION ABOUT A PATTERN'S CALLOUTS
int pcre2_callout_enumerate(const pcre2_code *code,
int (*callback)(pcre2_callout_enumerate_block *, void *),
void *user_data);

A script language that supports the use of string arguments in
callouts might like to scan all the callouts in a pattern before
running the match. This can be done by calling
pcre2_callout_enumerate(). The first argument is a pointer to a
compiled pattern, the second points to a callback function, and the
third is arbitrary user data. The callback function is called for
every callout in the pattern in the order in which they appear. Its
first argument is a pointer to a callout enumeration block, and its
second argument is the user_data value that was passed to
pcre2_callout_enumerate(). The contents of the callout enumeration
block are described in the pcre2callout documentation, which also
gives further details about callouts.

SERIALIZATION AND PRECOMPILING

It is possible to save compiled patterns on disc or elsewhere, and
reload them later, subject to a number of restrictions. The host on
which the patterns are reloaded must be running the same version of
PCRE2, with the same code unit width, and must also have the same
endianness, pointer width, and PCRE2_SIZE type. Before compiled
patterns can be saved, they must be converted to a "serialized" form,
which in the case of PCRE2 is really just a bytecode dump. The
functions whose names begin with pcre2_serialize_ are used for
converting to and from the serialized form. They are described in the
pcre2serialize documentation. Note that PCRE2 serialization does not
convert compiled patterns to an abstract format like Java or .NET
serialization.

THE MATCH DATA BLOCK

pcre2_match_data *pcre2_match_data_create(uint32_t ovecsize,
pcre2_general_context *gcontext);

pcre2_match_data *pcre2_match_data_create_from_pattern(
const pcre2_code *code, pcre2_general_context *gcontext);

void pcre2_match_data_free(pcre2_match_data *match_data);

Information about a successful or unsuccessful match is placed in a
match data block, which is an opaque structure that is accessed by
function calls. In particular, the match data block contains a vector
of offsets into the subject string that define the matched parts of
the subject. This is known as the ovector.

Before calling pcre2_match(), pcre2_dfa_match(), or pcre2_jit_match()
you must create a match data block by calling one of the creation
functions above. For pcre2_match_data_create(), the first argument is
the number of pairs of offsets in the ovector.

When using pcre2_match(), one pair of offsets is required to identify
the string that matched the whole pattern, with an additional pair
for each captured substring. For example, a value of 4 creates enough
space to record the matched portion of the subject plus three
captured substrings.

When using pcre2_dfa_match() there may be multiple matched substrings
of different lengths at the same point in the subject. The ovector
should be made large enough to hold as many as are expected.

A minimum of at least 1 pair is imposed by pcre2_match_data_create(),
so it is always possible to return the overall matched string in the
case of pcre2_match() or the longest match in the case of
pcre2_dfa_match(). The maximum number of pairs is 65535; if the first
argument of pcre2_match_data_create() is greater than this, 65535 is
used.

The second argument of pcre2_match_data_create() is a pointer to a
general context, which can specify custom memory management for
obtaining the memory for the match data block. If you are not using
custom memory management, pass NULL, which causes malloc() to be
used.

For pcre2_match_data_create_from_pattern(), the first argument is a
pointer to a compiled pattern. The ovector is created to be exactly
the right size to hold all the substrings a pattern might capture
when matched using pcre2_match(). You should not use this call when
matching with pcre2_dfa_match(). The second argument is again a
pointer to a general context, but in this case if NULL is passed, the
memory is obtained using the same allocator that was used for the
compiled pattern (custom or default).

A match data block can be used many times, with the same or different
compiled patterns. You can extract information from a match data
block after a match operation has finished, using functions that are
described in the sections on matched strings and other match data
below.

When a call of pcre2_match() fails, valid data is available in the
match block only when the error is PCRE2_ERROR_NOMATCH,
PCRE2_ERROR_PARTIAL, or one of the error codes for an invalid UTF
string. Exactly what is available depends on the error, and is
detailed below.

When one of the matching functions is called, pointers to the
compiled pattern and the subject string are set in the match data
block so that they can be referenced by the extraction functions
after a successful match. After running a match, you must not free a
compiled pattern or a subject string until after all operations on
the match data block (for that match) have taken place, unless, in
the case of the subject string, you have used the
PCRE2_COPY_MATCHED_SUBJECT option, which is described in the section
entitled "Option bits for pcre2_match()" below.

When a match data block itself is no longer needed, it should be
freed by calling pcre2_match_data_free(). If this function is called
with a NULL argument, it returns immediately, without doing anything.

MEMORY USE FOR MATCH DATA BLOCKS

PCRE2_SIZE pcre2_get_match_data_size(pcre2_match_data *match_data);

PCRE2_SIZE pcre2_get_match_data_heapframes_size(
pcre2_match_data *match_data);

The size of a match data block depends on the size of the ovector
that it contains. The function pcre2_get_match_data_size() returns
the size, in bytes, of the block that is its argument.

When pcre2_match() runs interpretively (that is, without using JIT),
it makes use of a vector of data frames for remembering backtracking
positions. The size of each individual frame depends on the number
of capturing parentheses in the pattern and can be obtained by
calling pcre2_pattern_info() with the PCRE2_INFO_FRAMESIZE option
(see the section entitled "Information about a compiled pattern"
above).

Heap memory is used for the frames vector; if the initial memory
block turns out to be too small during matching, it is automatically
expanded. When pcre2_match() returns, the memory is not freed, but
remains attached to the match data block, for use by any subsequent
matches that use the same block. It is automatically freed when the
match data block itself is freed.

You can find the current size of the frames vector that a match data
block owns by calling pcre2_get_match_data_heapframes_size(). For a
newly created match data block the size will be zero. Some types of
match may require a lot of frames and thus a large vector;
applications that run in environments where memory is constrained can
check this and free the match data block if the heap frames vector
has become too big.

MATCHING A PATTERN: THE TRADITIONAL FUNCTION
int pcre2_match(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext);

The function pcre2_match() is called to match a subject string
against a compiled pattern, which is passed in the code argument. You
can call pcre2_match() with the same code argument as many times as
you like, in order to find multiple matches in the subject string or
to match different subject strings with the same pattern.

This function is the main matching facility of the library, and it
operates in a Perl-like manner. For specialist use there is also an
alternative matching function, which is described below in the
section about the pcre2_dfa_match() function.

Here is an example of a simple call to pcre2_match():

pcre2_match_data *md = pcre2_match_data_create(4, NULL);
int rc = pcre2_match(
re, /* result of pcre2_compile() */
"some string", /* the subject string */
11, /* the length of the subject string */
0, /* start at offset 0 in the subject */
0, /* default options */
md, /* the match data block */
NULL); /* a match context; NULL means use defaults */

If the subject string is zero-terminated, the length can be given as
PCRE2_ZERO_TERMINATED. A match context must be provided if certain
less common matching parameters are to be changed. For details, see
the section on the match context above.

The string to be matched by pcre2_match()
The subject string is passed to pcre2_match() as a pointer in
subject, a length in length, and a starting offset in startoffset.
The length and offset are in code units, not characters. That is,
they are in bytes for the 8-bit library, 16-bit code units for the
16-bit library, and 32-bit code units for the 32-bit library, whether
or not UTF processing is enabled. As a special case, if subject is
NULL and length is zero, the subject is assumed to be an empty
string. If length is non-zero, an error occurs if subject is NULL.

If startoffset is greater than the length of the subject,
pcre2_match() returns PCRE2_ERROR_BADOFFSET. When the starting offset
is zero, the search for a match starts at the beginning of the
subject, and this is by far the most common case. In UTF-8 or UTF-16
mode, the starting offset must point to the start of a character, or
to the end of the subject (in UTF-32 mode, one code unit equals one
character, so all offsets are valid). Like the pattern string, the
subject may contain binary zeros.

A non-zero starting offset is useful when searching for another match
in the same subject by calling pcre2_match() again after a previous
success. Setting startoffset differs from passing over a shortened
string and setting PCRE2_NOTBOL in the case of a pattern that begins
with any kind of lookbehind. For example, consider the pattern

\Biss\B

which finds occurrences of "iss" in the middle of words. (\B matches
only if the current position in the subject is not a word boundary.)
When applied to the string "Mississippi" the first call to
pcre2_match() finds the first occurrence. If pcre2_match() is called
again with just the remainder of the subject, namely "issippi", it
does not match, because \B is always false at the start of the
subject, which is deemed to be a word boundary. However, if
pcre2_match() is passed the entire string again, but with startoffset
set to 4, it finds the second occurrence of "iss" because it is able
to look behind the starting point to discover that it is preceded by
a letter.

Finding all the matches in a subject is tricky when the pattern can
match an empty string. It is possible to emulate Perl's /g behaviour
by first trying the match again at the same offset, with the
PCRE2_NOTEMPTY_ATSTART and PCRE2_ANCHORED options, and then if that
fails, advancing the starting offset and trying an ordinary match
again. There is some code that demonstrates how to do this in the
pcre2demo sample program. In the most general case, you have to check
to see if the newline convention recognizes CRLF as a newline, and if
so, and the current character is CR followed by LF, advance the
starting offset by two characters instead of one.

If a non-zero starting offset is passed when the pattern is anchored,
a single attempt to match at the given offset is made. This can only
succeed if the pattern does not require the match to be at the start
of the subject. In other words, the anchoring must be the result of
setting the PCRE2_ANCHORED option or the use of .* with PCRE2_DOTALL,
not by starting the pattern with ^ or \A.

Option bits for pcre2_match()
The unused bits of the options argument for pcre2_match() must be
zero. The only bits that may be set are PCRE2_ANCHORED,
PCRE2_COPY_MATCHED_SUBJECT, PCRE2_DISABLE_RECURSELOOP_CHECK,
PCRE2_ENDANCHORED, PCRE2_NOTBOL, PCRE2_NOTEOL, PCRE2_NOTEMPTY,
PCRE2_NOTEMPTY_ATSTART, PCRE2_NO_JIT, PCRE2_NO_UTF_CHECK,
PCRE2_PARTIAL_HARD, and PCRE2_PARTIAL_SOFT. Their action is
described below.

Setting PCRE2_ANCHORED or PCRE2_ENDANCHORED at match time is not
supported by the just-in-time (JIT) compiler. If it is set, JIT
matching is disabled and the interpretive code in pcre2_match() is
run. PCRE2_DISABLE_RECURSELOOP_CHECK is ignored by JIT, but apart
from PCRE2_NO_JIT (obviously), the remaining options are supported
for JIT matching.

PCRE2_ANCHORED

The PCRE2_ANCHORED option limits pcre2_match() to matching at the
first matching position. If a pattern was compiled with
PCRE2_ANCHORED, or turned out to be anchored by virtue of its
contents, it cannot be made unachored at matching time. Note that
setting the option at match time disables JIT matching.

PCRE2_COPY_MATCHED_SUBJECT

By default, a pointer to the subject is remembered in the match data
block so that, after a successful match, it can be referenced by the
substring extraction functions. This means that the subject's memory
must not be freed until all such operations are complete. For some
applications where the lifetime of the subject string is not
guaranteed, it may be necessary to make a copy of the subject string,
but it is wasteful to do this unless the match is successful. After a
successful match, if PCRE2_COPY_MATCHED_SUBJECT is set, the subject
is copied and the new pointer is remembered in the match data block
instead of the original subject pointer. The memory allocator that
was used for the match block itself is used. The copy is
automatically freed when pcre2_match_data_free() is called to free
the match data block. It is also automatically freed if the match
data block is re-used for another match operation.

PCRE2_DISABLE_RECURSELOOP_CHECK

This option is relevant only to pcre2_match() for interpretive
matching. It is ignored when JIT is used, and is forbidden for
pcre2_dfa_match().

The use of recursion in patterns can lead to infinite loops. In the
interpretive matcher these would be eventually caught by the match or
heap limits, but this could take a long time and/or use a lot of
memory if the limits are large. There is therefore a check at the
start of each recursion. If the same group is still active from a
previous call, and the current subject pointer is the same as it was
at the start of that group, and the furthest inspected character of
the subject has not changed, an error is generated.

There are rare cases of matches that would complete, but nevertheless
trigger this error. This option disables the check. It is provided
mainly for testing when comparing JIT and interpretive behaviour.

PCRE2_ENDANCHORED

If the PCRE2_ENDANCHORED option is set, any string that pcre2_match()
matches must be right at the end of the subject string. Note that
setting the option at match time disables JIT matching.

PCRE2_NOTBOL

This option specifies that first character of the subject string is
not the beginning of a line, so the circumflex metacharacter should
not match before it. Setting this without having set PCRE2_MULTILINE
at compile time causes circumflex never to match. This option affects
only the behaviour of the circumflex metacharacter. It does not
affect \A.

PCRE2_NOTEOL

This option specifies that the end of the subject string is not the
end of a line, so the dollar metacharacter should not match it nor
(except in multiline mode) a newline immediately before it. Setting
this without having set PCRE2_MULTILINE at compile time causes dollar
never to match. This option affects only the behaviour of the dollar
metacharacter. It does not affect \Z or \z.

PCRE2_NOTEMPTY

An empty string is not considered to be a valid match if this option
is set. If there are alternatives in the pattern, they are tried. If
all the alternatives match the empty string, the entire match fails.
For example, if the pattern

a?b?

is applied to a string not beginning with "a" or "b", it matches an
empty string at the start of the subject. With PCRE2_NOTEMPTY set,
this match is not valid, so pcre2_match() searches further into the
string for occurrences of "a" or "b".

PCRE2_NOTEMPTY_ATSTART

This is like PCRE2_NOTEMPTY, except that it locks out an empty string
match only at the first matching position, that is, at the start of
the subject plus the starting offset. An empty string match later in
the subject is permitted. If the pattern is anchored, such a match
can occur only if the pattern contains \K.

PCRE2_NO_JIT

By default, if a pattern has been successfully processed by
pcre2_jit_compile(), JIT is automatically used when pcre2_match() is
called with options that JIT supports. Setting PCRE2_NO_JIT disables
the use of JIT; it forces matching to be done by the interpreter.

PCRE2_NO_UTF_CHECK

When PCRE2_UTF is set at compile time, the validity of the subject as
a UTF string is checked unless PCRE2_NO_UTF_CHECK is passed to
pcre2_match() or PCRE2_MATCH_INVALID_UTF was passed to
pcre2_compile(). The latter special case is discussed in detail in
the pcre2unicode documentation.

In the default case, if a non-zero starting offset is given, the
check is applied only to that part of the subject that could be
inspected during matching, and there is a check that the starting
offset points to the first code unit of a character or to the end of
the subject. If there are no lookbehind assertions in the pattern,
the check starts at the starting offset. Otherwise, it starts at the
length of the longest lookbehind before the starting offset, or at
the start of the subject if there are not that many characters before
the starting offset. Note that the sequences \b and \B are one-
character lookbehinds.

The check is carried out before any other processing takes place, and
a negative error code is returned if the check fails. There are
several UTF error codes for each code unit width, corresponding to
different problems with the code unit sequence. There are discussions
about the validity of UTF-8 strings, UTF-16 strings, and UTF-32
strings in the pcre2unicode documentation.

If you know that your subject is valid, and you want to skip this
check for performance reasons, you can set the PCRE2_NO_UTF_CHECK
option when calling pcre2_match(). You might want to do this for the
second and subsequent calls to pcre2_match() if you are making
repeated calls to find multiple matches in the same subject string.

Warning: Unless PCRE2_MATCH_INVALID_UTF was set at compile time, when
PCRE2_NO_UTF_CHECK is set at match time the effect of passing an
invalid string as a subject, or an invalid value of startoffset, is
undefined. Your program may crash or loop indefinitely or give wrong
results.

PCRE2_PARTIAL_HARD
PCRE2_PARTIAL_SOFT

These options turn on the partial matching feature. A partial match
occurs if the end of the subject string is reached successfully, but
there are not enough subject characters to complete the match. In
addition, either at least one character must have been inspected or
the pattern must contain a lookbehind, or the pattern must be one
that could match an empty string.

If this situation arises when PCRE2_PARTIAL_SOFT (but not
PCRE2_PARTIAL_HARD) is set, matching continues by testing any
remaining alternatives. Only if no complete match can be found is
PCRE2_ERROR_PARTIAL returned instead of PCRE2_ERROR_NOMATCH. In other
words, PCRE2_PARTIAL_SOFT specifies that the caller is prepared to
handle a partial match, but only if no complete match can be found.

If PCRE2_PARTIAL_HARD is set, it overrides PCRE2_PARTIAL_SOFT. In
this case, if a partial match is found, pcre2_match() immediately
returns PCRE2_ERROR_PARTIAL, without considering any other
alternatives. In other words, when PCRE2_PARTIAL_HARD is set, a
partial match is considered to be more important that an alternative
complete match.

There is a more detailed discussion of partial and multi-segment
matching, with examples, in the pcre2partial documentation.

NEWLINE HANDLING WHEN MATCHING

When PCRE2 is built, a default newline convention is set; this is
usually the standard convention for the operating system. The default
can be overridden in a compile context by calling
pcre2_set_newline(). It can also be overridden by starting a pattern
string with, for example, (*CRLF), as described in the section on
newline conventions in the pcre2pattern page. During matching, the
newline choice affects the behaviour of the dot, circumflex, and
dollar metacharacters. It may also alter the way the match starting
position is advanced after a match failure for an unanchored pattern.

When PCRE2_NEWLINE_CRLF, PCRE2_NEWLINE_ANYCRLF, or PCRE2_NEWLINE_ANY
is set as the newline convention, and a match attempt for an
unanchored pattern fails when the current starting position is at a
CRLF sequence, and the pattern contains no explicit matches for CR or
LF characters, the match position is advanced by two characters
instead of one, in other words, to after the CRLF.

The above rule is a compromise that makes the most common cases work
as expected. For example, if the pattern is .+A (and the PCRE2_DOTALL
option is not set), it does not match the string "\r\nA" because,
after failing at the start, it skips both the CR and the LF before
retrying. However, the pattern [\r\n]A does match that string,
because it contains an explicit CR or LF reference, and so advances
only by one character after the first failure.

An explicit match for CR of LF is either a literal appearance of one
of those characters in the pattern, or one of the \r or \n or
equivalent octal or hexadecimal escape sequences. Implicit matches
such as [^X] do not count, nor does \s, even though it includes CR
and LF in the characters that it matches.

Notwithstanding the above, anomalous effects may still occur when
CRLF is a valid newline sequence and explicit \r or \n escapes appear
in the pattern.

HOW PCRE2_MATCH() RETURNS A STRING AND CAPTURED SUBSTRINGS
uint32_t pcre2_get_ovector_count(pcre2_match_data *match_data);

PCRE2_SIZE *pcre2_get_ovector_pointer(pcre2_match_data *match_data);

In general, a pattern matches a certain portion of the subject, and
in addition, further substrings from the subject may be picked out by
parenthesized parts of the pattern. Following the usage in Jeffrey
Friedl's book, this is called "capturing" in what follows, and the
phrase "capture group" (Perl terminology) is used for a fragment of a
pattern that picks out a substring. PCRE2 supports several other
kinds of parenthesized group that do not cause substrings to be
captured. The pcre2_pattern_info() function can be used to find out
how many capture groups there are in a compiled pattern.

You can use auxiliary functions for accessing captured substrings by
number or by name, as described in sections below.

Alternatively, you can make direct use of the vector of PCRE2_SIZE
values, called the ovector, which contains the offsets of captured
strings. It is part of the match data block. The function
pcre2_get_ovector_pointer() returns the address of the ovector, and
pcre2_get_ovector_count() returns the number of pairs of values it
contains.

Within the ovector, the first in each pair of values is set to the
offset of the first code unit of a substring, and the second is set
to the offset of the first code unit after the end of a substring.
These values are always code unit offsets, not character offsets.
That is, they are byte offsets in the 8-bit library, 16-bit offsets
in the 16-bit library, and 32-bit offsets in the 32-bit library.

After a partial match (error return PCRE2_ERROR_PARTIAL), only the
first pair of offsets (that is, ovector[0] and ovector[1]) are set.
They identify the part of the subject that was partially matched. See
the pcre2partial documentation for details of partial matching.

After a fully successful match, the first pair of offsets identifies
the portion of the subject string that was matched by the entire
pattern. The next pair is used for the first captured substring, and
so on. The value returned by pcre2_match() is one more than the
highest numbered pair that has been set. For example, if two
substrings have been captured, the returned value is 3. If there are
no captured substrings, the return value from a successful match is
1, indicating that just the first pair of offsets has been set.

If a pattern uses the \K escape sequence within a positive assertion,
the reported start of a successful match can be greater than the end
of the match. For example, if the pattern (?=ab\K) is matched
against "ab", the start and end offset values for the match are 2 and
0.

If a capture group is matched repeatedly within a single match
operation, it is the last portion of the subject that it matched that
is returned.

If the ovector is too small to hold all the captured substring
offsets, as much as possible is filled in, and the function returns a
value of zero. If captured substrings are not of interest,
pcre2_match() may be called with a match data block whose ovector is
of minimum length (that is, one pair).

It is possible for capture group number n+1 to match some part of the
subject when group n has not been used at all. For example, if the
string "abc" is matched against the pattern (a|(z))(bc) the return
from the function is 4, and groups 1 and 3 are matched, but 2 is not.
When this happens, both values in the offset pairs corresponding to
unused groups are set to PCRE2_UNSET.

Offset values that correspond to unused groups at the end of the
expression are also set to PCRE2_UNSET. For example, if the string
"abc" is matched against the pattern (abc)(x(yz)?)? groups 2 and 3
are not matched. The return from the function is 2, because the
highest used capture group number is 1. The offsets for the second
and third capture groups (assuming the vector is large enough, of
course) are set to PCRE2_UNSET.

Elements in the ovector that do not correspond to capturing
parentheses in the pattern are never changed. That is, if a pattern
contains n capturing parentheses, no more than ovector[0] to
ovector[2n+1] are set by pcre2_match(). The other elements retain
whatever values they previously had. After a failed match attempt,
the contents of the ovector are unchanged.

OTHER INFORMATION ABOUT A MATCH

PCRE2_SPTR pcre2_get_mark(pcre2_match_data *match_data);

PCRE2_SIZE pcre2_get_startchar(pcre2_match_data *match_data);

As well as the offsets in the ovector, other information about a
match is retained in the match data block and can be retrieved by the
above functions in appropriate circumstances. If they are called at
other times, the result is undefined.

After a successful match, a partial match (PCRE2_ERROR_PARTIAL), or a
failure to match (PCRE2_ERROR_NOMATCH), a mark name may be available.
The function pcre2_get_mark() can be called to access this name,
which can be specified in the pattern by any of the backtracking
control verbs, not just (*MARK). The same function applies to all the
verbs. It returns a pointer to the zero-terminated name, which is
within the compiled pattern. If no name is available, NULL is
returned. The length of the name (excluding the terminating zero) is
stored in the code unit that precedes the name. You should use this
length instead of relying on the terminating zero if the name might
contain a binary zero.

After a successful match, the name that is returned is the last mark
name encountered on the matching path through the pattern. Instances
of backtracking verbs without names do not count. Thus, for example,
if the matching path contains (*MARK:A)(*PRUNE), the name "A" is
returned. After a "no match" or a partial match, the last encountered
name is returned. For example, consider this pattern:

^(*MARK:A)((*MARK:B)a|b)c

When it matches "bc", the returned name is A. The B mark is "seen" in
the first branch of the group, but it is not on the matching path. On
the other hand, when this pattern fails to match "bx", the returned
name is B.

Warning: By default, certain start-of-match optimizations are used to
give a fast "no match" result in some situations. For example, if the
anchoring is removed from the pattern above, there is an initial
check for the presence of "c" in the subject before running the
matching engine. This check fails for "bx", causing a match failure
without seeing any marks. You can disable the start-of-match
optimizations by setting the PCRE2_NO_START_OPTIMIZE option for
pcre2_compile() or by starting the pattern with (*NO_START_OPT).

After a successful match, a partial match, or one of the invalid UTF
errors (for example, PCRE2_ERROR_UTF8_ERR5), pcre2_get_startchar()
can be called. After a successful or partial match it returns the
code unit offset of the character at which the match started. For a
non-partial match, this can be different to the value of ovector[0]
if the pattern contains the \K escape sequence. After a partial
match, however, this value is always the same as ovector[0] because
\K does not affect the result of a partial match.

After a UTF check failure, pcre2_get_startchar() can be used to
obtain the code unit offset of the invalid UTF character. Details are
given in the pcre2unicode page.

ERROR RETURNS FROM pcre2_match()
If pcre2_match() fails, it returns a negative number. This can be
converted to a text string by calling the pcre2_get_error_message()
function (see "Obtaining a textual error message" below). Negative
error codes are also returned by other functions, and are documented
with them. The codes are given names in the header file. If UTF
checking is in force and an invalid UTF subject string is detected,
one of a number of UTF-specific negative error codes is returned.
Details are given in the pcre2unicode page. The following are the
other errors that may be returned by pcre2_match():

PCRE2_ERROR_NOMATCH

The subject string did not match the pattern.

PCRE2_ERROR_PARTIAL

The subject string did not match, but it did match partially. See the
pcre2partial documentation for details of partial matching.

PCRE2_ERROR_BADMAGIC

PCRE2 stores a 4-byte "magic number" at the start of the compiled
code, to catch the case when it is passed a junk pointer. This is the
error that is returned when the magic number is not present.

PCRE2_ERROR_BADMODE

This error is given when a compiled pattern is passed to a function
in a library of a different code unit width, for example, a pattern
compiled by the 8-bit library is passed to a 16-bit or 32-bit library
function.

PCRE2_ERROR_BADOFFSET

The value of startoffset was greater than the length of the subject.

PCRE2_ERROR_BADOPTION

An unrecognized bit was set in the options argument.

PCRE2_ERROR_BADUTFOFFSET

The UTF code unit sequence that was passed as a subject was checked
and found to be valid (the PCRE2_NO_UTF_CHECK option was not set),
but the value of startoffset did not point to the beginning of a UTF
character or the end of the subject.

PCRE2_ERROR_CALLOUT

This error is never generated by pcre2_match() itself. It is provided
for use by callout functions that want to cause pcre2_match() or
pcre2_callout_enumerate() to return a distinctive error code. See the
pcre2callout documentation for details.

PCRE2_ERROR_DEPTHLIMIT

The nested backtracking depth limit was reached.

PCRE2_ERROR_HEAPLIMIT

The heap limit was reached.

PCRE2_ERROR_INTERNAL

An unexpected internal error has occurred. This error could be caused
by a bug in PCRE2 or by overwriting of the compiled pattern.

PCRE2_ERROR_JIT_STACKLIMIT

This error is returned when a pattern that was successfully studied
using JIT is being matched, but the memory available for the just-in-
time processing stack is not large enough. See the pcre2jit
documentation for more details.

PCRE2_ERROR_MATCHLIMIT

The backtracking match limit was reached.

PCRE2_ERROR_NOMEMORY

Heap memory is used to remember backtracking points. This error is
given when the memory allocation function (default or custom) fails.
Note that a different error, PCRE2_ERROR_HEAPLIMIT, is given if the
amount of memory needed exceeds the heap limit. PCRE2_ERROR_NOMEMORY
is also returned if PCRE2_COPY_MATCHED_SUBJECT is set and memory
allocation fails.

PCRE2_ERROR_NULL

Either the code, subject, or match_data argument was passed as NULL.

PCRE2_ERROR_RECURSELOOP

This error is returned when pcre2_match() detects a recursion loop
within the pattern. Specifically, it means that either the whole
pattern or a capture group has been called recursively for the second
time at the same position in the subject string. Some simple patterns
that might do this are detected and faulted at compile time, but more
complicated cases, in particular mutual recursions between two
different groups, cannot be detected until matching is attempted.

OBTAINING A TEXTUAL ERROR MESSAGE

int pcre2_get_error_message(int errorcode, PCRE2_UCHAR *buffer,
PCRE2_SIZE bufflen);

A text message for an error code from any PCRE2 function (compile,
match, or auxiliary) can be obtained by calling
pcre2_get_error_message(). The code is passed as the first argument,
with the remaining two arguments specifying a code unit buffer and
its length in code units, into which the text message is placed. The
message is returned in code units of the appropriate width for the
library that is being used.

The returned message is terminated with a trailing zero, and the
function returns the number of code units used, excluding the
trailing zero. If the error number is unknown, the negative error
code PCRE2_ERROR_BADDATA is returned. If the buffer is too small, the
message is truncated (but still with a trailing zero), and the
negative error code PCRE2_ERROR_NOMEMORY is returned. None of the
messages are very long; a buffer size of 120 code units is ample.

EXTRACTING CAPTURED SUBSTRINGS BY NUMBER

int pcre2_substring_length_bynumber(pcre2_match_data *match_data,
uint32_t number, PCRE2_SIZE *length);

int pcre2_substring_copy_bynumber(pcre2_match_data *match_data,
uint32_t number, PCRE2_UCHAR *buffer,
PCRE2_SIZE *bufflen);

int pcre2_substring_get_bynumber(pcre2_match_data *match_data,
uint32_t number, PCRE2_UCHAR **bufferptr,
PCRE2_SIZE *bufflen);

void pcre2_substring_free(PCRE2_UCHAR *buffer);

Captured substrings can be accessed directly by using the ovector as
described above. For convenience, auxiliary functions are provided
for extracting captured substrings as new, separate, zero-terminated
strings. A substring that contains a binary zero is correctly
extracted and has a further zero added on the end, but the result is
not, of course, a C string.

The functions in this section identify substrings by number. The
number zero refers to the entire matched substring, with higher
numbers referring to substrings captured by parenthesized groups.
After a partial match, only substring zero is available. An attempt
to extract any other substring gives the error PCRE2_ERROR_PARTIAL.
The next section describes similar functions for extracting captured
substrings by name.

If a pattern uses the \K escape sequence within a positive assertion,
the reported start of a successful match can be greater than the end
of the match. For example, if the pattern (?=ab\K) is matched
against "ab", the start and end offset values for the match are 2 and
0. In this situation, calling these functions with a zero substring
number extracts a zero-length empty string.

You can find the length in code units of a captured substring without
extracting it by calling pcre2_substring_length_bynumber(). The first
argument is a pointer to the match data block, the second is the
group number, and the third is a pointer to a variable into which the
length is placed. If you just want to know whether or not the
substring has been captured, you can pass the third argument as NULL.

The pcre2_substring_copy_bynumber() function copies a captured
substring into a supplied buffer, whereas
pcre2_substring_get_bynumber() copies it into new memory, obtained
using the same memory allocation function that was used for the match
data block. The first two arguments of these functions are a pointer
to the match data block and a capture group number.

The final arguments of pcre2_substring_copy_bynumber() are a pointer
to the buffer and a pointer to a variable that contains its length in
code units. This is updated to contain the actual number of code
units used for the extracted substring, excluding the terminating
zero.

For pcre2_substring_get_bynumber() the third and fourth arguments
point to variables that are updated with a pointer to the new memory
and the number of code units that comprise the substring, again
excluding the terminating zero. When the substring is no longer
needed, the memory should be freed by calling pcre2_substring_free().

The return value from all these functions is zero for success, or a
negative error code. If the pattern match failed, the match failure
code is returned. If a substring number greater than zero is used
after a partial match, PCRE2_ERROR_PARTIAL is returned. Other
possible error codes are:

PCRE2_ERROR_NOMEMORY

The buffer was too small for pcre2_substring_copy_bynumber(), or the
attempt to get memory failed for pcre2_substring_get_bynumber().

PCRE2_ERROR_NOSUBSTRING

There is no substring with that number in the pattern, that is, the
number is greater than the number of capturing parentheses.

PCRE2_ERROR_UNAVAILABLE

The substring number, though not greater than the number of captures
in the pattern, is greater than the number of slots in the ovector,
so the substring could not be captured.

PCRE2_ERROR_UNSET

The substring did not participate in the match. For example, if the
pattern is (abc)|(def) and the subject is "def", and the ovector
contains at least two capturing slots, substring number 1 is unset.

EXTRACTING A LIST OF ALL CAPTURED SUBSTRINGS

int pcre2_substring_list_get(pcre2_match_data *match_data,
PCRE2_UCHAR ***listptr, PCRE2_SIZE **lengthsptr);

void pcre2_substring_list_free(PCRE2_UCHAR **list);

The pcre2_substring_list_get() function extracts all available
substrings and builds a list of pointers to them. It also
(optionally) builds a second list that contains their lengths (in
code units), excluding a terminating zero that is added to each of
them. All this is done in a single block of memory that is obtained
using the same memory allocation function that was used to get the
match data block.

This function must be called only after a successful match. If called
after a partial match, the error code PCRE2_ERROR_PARTIAL is
returned.

The address of the memory block is returned via listptr, which is
also the start of the list of string pointers. The end of the list is
marked by a NULL pointer. The address of the list of lengths is
returned via lengthsptr. If your strings do not contain binary zeros
and you do not therefore need the lengths, you may supply NULL as the
lengthsptr argument to disable the creation of a list of lengths. The
yield of the function is zero if all went well, or
PCRE2_ERROR_NOMEMORY if the memory block could not be obtained. When
the list is no longer needed, it should be freed by calling
pcre2_substring_list_free().

If this function encounters a substring that is unset, which can
happen when capture group number n+1 matches some part of the
subject, but group n has not been used at all, it returns an empty
string. This can be distinguished from a genuine zero-length
substring by inspecting the appropriate offset in the ovector, which
contain PCRE2_UNSET for unset substrings, or by calling
pcre2_substring_length_bynumber().

EXTRACTING CAPTURED SUBSTRINGS BY NAME

int pcre2_substring_number_from_name(const pcre2_code *code,
PCRE2_SPTR name);

int pcre2_substring_length_byname(pcre2_match_data *match_data,
PCRE2_SPTR name, PCRE2_SIZE *length);

int pcre2_substring_copy_byname(pcre2_match_data *match_data,
PCRE2_SPTR name, PCRE2_UCHAR *buffer, PCRE2_SIZE *bufflen);

int pcre2_substring_get_byname(pcre2_match_data *match_data,
PCRE2_SPTR name, PCRE2_UCHAR **bufferptr, PCRE2_SIZE *bufflen);

void pcre2_substring_free(PCRE2_UCHAR *buffer);

To extract a substring by name, you first have to find associated
number. For example, for this pattern:

(a+)b(?<xxx>\d+)...

the number of the capture group called "xxx" is 2. If the name is
known to be unique (PCRE2_DUPNAMES was not set), you can find the
number from the name by calling pcre2_substring_number_from_name().
The first argument is the compiled pattern, and the second is the
name. The yield of the function is the group number,
PCRE2_ERROR_NOSUBSTRING if there is no group with that name, or
PCRE2_ERROR_NOUNIQUESUBSTRING if there is more than one group with
that name. Given the number, you can extract the substring directly
from the ovector, or use one of the "bynumber" functions described
above.

For convenience, there are also "byname" functions that correspond to
the "bynumber" functions, the only difference being that the second
argument is a name instead of a number. If PCRE2_DUPNAMES is set and
there are duplicate names, these functions scan all the groups with
the given name, and return the captured substring from the first
named group that is set.

If there are no groups with the given name, PCRE2_ERROR_NOSUBSTRING
is returned. If all groups with the name have numbers that are
greater than the number of slots in the ovector,
PCRE2_ERROR_UNAVAILABLE is returned. If there is at least one group
with a slot in the ovector, but no group is found to be set,
PCRE2_ERROR_UNSET is returned.

Warning: If the pattern uses the (?| feature to set up multiple
capture groups with the same number, as described in the section on
duplicate group numbers in the pcre2pattern page, you cannot use
names to distinguish the different capture groups, because names are
not included in the compiled code. The matching process uses only
numbers. For this reason, the use of different names for groups with
the same number causes an error at compile time.

CREATING A NEW STRING WITH SUBSTITUTIONS

int pcre2_substitute(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext, PCRE2_SPTR replacement,
PCRE2_SIZE rlength, PCRE2_UCHAR *outputbuffer,
PCRE2_SIZE *outlengthptr);

This function optionally calls pcre2_match() and then makes a copy of
the subject string in outputbuffer, replacing parts that were matched
with the replacement string, whose length is supplied in rlength,
which can be given as PCRE2_ZERO_TERMINATED for a zero-terminated
string. As a special case, if replacement is NULL and rlength is
zero, the replacement is assumed to be an empty string. If rlength is
non-zero, an error occurs if replacement is NULL.

There is an option (see PCRE2_SUBSTITUTE_REPLACEMENT_ONLY below) to
return just the replacement string(s). The default action is to
perform just one replacement if the pattern matches, but there is an
option that requests multiple replacements (see
PCRE2_SUBSTITUTE_GLOBAL below).

If successful, pcre2_substitute() returns the number of substitutions
that were carried out. This may be zero if no match was found, and is
never greater than one unless PCRE2_SUBSTITUTE_GLOBAL is set. A
negative value is returned if an error is detected.

Matches in which a \K item in a lookahead in the pattern causes the
match to end before it starts are not supported, and give rise to an
error return. For global replacements, matches in which \K in a
lookbehind causes the match to start earlier than the point that was
reached in the previous iteration are also not supported.

The first seven arguments of pcre2_substitute() are the same as for
pcre2_match(), except that the partial matching options are not
permitted, and match_data may be passed as NULL, in which case a
match data block is obtained and freed within this function, using
memory management functions from the match context, if provided, or
else those that were used to allocate memory for the compiled code.

If match_data is not NULL and PCRE2_SUBSTITUTE_MATCHED is not set,
the provided block is used for all calls to pcre2_match(), and its
contents afterwards are the result of the final call. For global
changes, this will always be a no-match error. The contents of the
ovector within the match data block may or may not have been changed.

As well as the usual options for pcre2_match(), a number of
additional options can be set in the options argument of
pcre2_substitute(). One such option is PCRE2_SUBSTITUTE_MATCHED.
When this is set, an external match_data block must be provided, and
it must have already been used for an external call to pcre2_match()
with the same pattern and subject arguments. The data in the
match_data block (return code, offset vector) is then used for the
first substitution instead of calling pcre2_match() from within
pcre2_substitute(). This allows an application to check for a match
before choosing to substitute, without having to repeat the match.

The contents of the externally supplied match data block are not
changed when PCRE2_SUBSTITUTE_MATCHED is set. If
PCRE2_SUBSTITUTE_GLOBAL is also set, pcre2_match() is called after
the first substitution to check for further matches, but this is done
using an internally obtained match data block, thus always leaving
the external block unchanged.

The code argument is not used for matching before the first
substitution when PCRE2_SUBSTITUTE_MATCHED is set, but it must be
provided, even when PCRE2_SUBSTITUTE_GLOBAL is not set, because it
contains information such as the UTF setting and the number of
capturing parentheses in the pattern.

The default action of pcre2_substitute() is to return a copy of the
subject string with matched substrings replaced. However, if
PCRE2_SUBSTITUTE_REPLACEMENT_ONLY is set, only the replacement
substrings are returned. In the global case, multiple replacements
are concatenated in the output buffer. Substitution callouts (see
below) can be used to separate them if necessary.

The outlengthptr argument of pcre2_substitute() must point to a
variable that contains the length, in code units, of the output
buffer. If the function is successful, the value is updated to
contain the length in code units of the new string, excluding the
trailing zero that is automatically added.

If the function is not successful, the value set via outlengthptr
depends on the type of error. For syntax errors in the replacement
string, the value is the offset in the replacement string where the
error was detected. For other errors, the value is PCRE2_UNSET by
default. This includes the case of the output buffer being too small,
unless PCRE2_SUBSTITUTE_OVERFLOW_LENGTH is set.

PCRE2_SUBSTITUTE_OVERFLOW_LENGTH changes what happens when the output
buffer is too small. The default action is to return
PCRE2_ERROR_NOMEMORY immediately. If this option is set, however,
pcre2_substitute() continues to go through the motions of matching
and substituting (without, of course, writing anything) in order to
compute the size of buffer that is needed, 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.

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
altertive 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 an
assertion).

As for all PCRE2 errors, a text message that describes the error can
be obtained by calling the pcre2_get_error_message() function (see
"Obtaining a textual error message" above).

Substitution callouts

int pcre2_set_substitute_callout(pcre2_match_context *mcontext,
int (*callout_function)(pcre2_substitute_callout_block *, void *),
void *callout_data);

The pcre2_set_substitution_callout() function can be used to specify
a callout function for pcre2_substitute(). This information is passed
in a match context. The callout function is called after each
substitution has been processed, but it can cause the replacement not
to happen.

The callout function is not called for simulated substitutions that
happen as a result of the PCRE2_SUBSTITUTE_OVERFLOW_LENGTH option. 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_substitution_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.

DUPLICATE CAPTURE GROUP NAMES

int pcre2_substring_nametable_scan(const pcre2_code *code,
PCRE2_SPTR name, PCRE2_SPTR *first, PCRE2_SPTR *last);

When a pattern is compiled with the PCRE2_DUPNAMES option, names for
capture groups are not required to be unique. Duplicate names are
always allowed for groups with the same number, created by using the
(?| feature. Indeed, if such groups are named, they are required to
use the same names.

Normally, patterns that use duplicate names are such that in any one
match, only one of each set of identically-named groups participates.
An example is shown in the pcre2pattern documentation.

When duplicates are present, pcre2_substring_copy_byname() and
pcre2_substring_get_byname() return the first substring corresponding
to the given name that is set. Only if none are set is
PCRE2_ERROR_UNSET is returned. The pcre2_substring_number_from_name()
function returns the error PCRE2_ERROR_NOUNIQUESUBSTRING when there
are duplicate names.

If you want to get full details of all captured substrings for a
given name, you must use the pcre2_substring_nametable_scan()
function. The first argument is the compiled pattern, and the second
is the name. If the third and fourth arguments are NULL, the function
returns a group number for a unique name, or
PCRE2_ERROR_NOUNIQUESUBSTRING otherwise.

When the third and fourth arguments are not NULL, they must be
pointers to variables that are updated by the function. After it has
run, they point to the first and last entries in the name-to-number
table for the given name, and the function returns the length of each
entry in code units. In both cases, PCRE2_ERROR_NOSUBSTRING is
returned if there are no entries for the given name.

The format of the name table is described above in the section
entitled Information about a pattern. Given all the relevant entries
for the name, you can extract each of their numbers, and hence the
captured data.

FINDING ALL POSSIBLE MATCHES AT ONE POSITION

The traditional matching function uses a similar algorithm to Perl,
which stops when it finds the first match at a given point in the
subject. If you want to find all possible matches, or the longest
possible match at a given position, consider using the alternative
matching function (see below) instead. If you cannot use the
alternative function, you can kludge it up by making use of the
callout facility, which is described in the pcre2callout
documentation.

What you have to do is to insert a callout right at the end of the
pattern. When your callout function is called, extract and save the
current matched substring. Then return 1, which forces pcre2_match()
to backtrack and try other alternatives. Ultimately, when it runs out
of matches, pcre2_match() will yield PCRE2_ERROR_NOMATCH.

MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
int pcre2_dfa_match(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext,
int *workspace, PCRE2_SIZE wscount);

The function pcre2_dfa_match() is called to match a subject string
against a compiled pattern, using a matching algorithm that scans the
subject string just once (not counting lookaround assertions), and
does not backtrack (except when processing lookaround assertions).
This has different characteristics to the normal algorithm, and is
not compatible with Perl. Some of the features of PCRE2 patterns are
not supported. Nevertheless, there are times when this kind of
matching can be useful. For a discussion of the two matching
algorithms, and a list of features that pcre2_dfa_match() does not
support, see the pcre2matching documentation.

The arguments for the pcre2_dfa_match() function are the same as for
pcre2_match(), plus two extras. The ovector within the match data
block is used in a different way, and this is described below. The
other common arguments are used in the same way as for pcre2_match(),
so their description is not repeated here.

The two additional arguments provide workspace for the function. The
workspace vector should contain at least 20 elements. It is used for
keeping track of multiple paths through the pattern tree. More
workspace is needed for patterns and subjects where there are a lot
of potential matches.

Here is an example of a simple call to pcre2_dfa_match():

int wspace[20];
pcre2_match_data *md = pcre2_match_data_create(4, NULL);
int rc = pcre2_dfa_match(
re, /* result of pcre2_compile() */
"some string", /* the subject string */
11, /* the length of the subject string */
0, /* start at offset 0 in the subject */
0, /* default options */
md, /* the match data block */
NULL, /* a match context; NULL means use defaults */
wspace, /* working space vector */
20); /* number of elements (NOT size in bytes) */

Option bits for pcre2_dfa_match()
The unused bits of the options argument for pcre2_dfa_match() must be
zero. The only bits that may be set are PCRE2_ANCHORED,
PCRE2_COPY_MATCHED_SUBJECT, PCRE2_ENDANCHORED, PCRE2_NOTBOL,
PCRE2_NOTEOL, PCRE2_NOTEMPTY, PCRE2_NOTEMPTY_ATSTART,
PCRE2_NO_UTF_CHECK, PCRE2_PARTIAL_HARD, PCRE2_PARTIAL_SOFT,
PCRE2_DFA_SHORTEST, and PCRE2_DFA_RESTART. All but the last four of
these are exactly the same as for pcre2_match(), so their description
is not repeated here.

PCRE2_PARTIAL_HARD
PCRE2_PARTIAL_SOFT

These have the same general effect as they do for pcre2_match(), but
the details are slightly different. When PCRE2_PARTIAL_HARD is set
for pcre2_dfa_match(), it returns PCRE2_ERROR_PARTIAL if the end of
the subject is reached and there is still at least one matching
possibility that requires additional characters. This happens even if
some complete matches have already been found. When
PCRE2_PARTIAL_SOFT is set, the return code PCRE2_ERROR_NOMATCH is
converted into PCRE2_ERROR_PARTIAL if the end of the subject is
reached, there have been no complete matches, but there is still at
least one matching possibility. The portion of the string that was
inspected when the longest partial match was found is set as the
first matching string in both cases. There is a more detailed
discussion of partial and multi-segment matching, with examples, in
the pcre2partial documentation.

PCRE2_DFA_SHORTEST

Setting the PCRE2_DFA_SHORTEST option causes the matching algorithm
to stop as soon as it has found one match. Because of the way the
alternative algorithm works, this is necessarily the shortest
possible match at the first possible matching point in the subject
string.

PCRE2_DFA_RESTART

When pcre2_dfa_match() returns a partial match, it is possible to
call it again, with additional subject characters, and have it
continue with the same match. The PCRE2_DFA_RESTART option requests
this action; when it is set, the workspace and wscount options must
reference the same vector as before because data about the match so
far is left in them after a partial match. There is more discussion
of this facility in the pcre2partial documentation.

Successful returns from pcre2_dfa_match()
When pcre2_dfa_match() succeeds, it may have matched more than one
substring in the subject. Note, however, that all the matches from
one run of the function start at the same point in the subject. The
shorter matches are all initial substrings of the longer matches. For
example, if the pattern

<.*>

is matched against the string

This is <something> <something else> <something further> no more

the three matched strings are

<something> <something else> <something further>
<something> <something else>
<something>

On success, the yield of the function is a number greater than zero,
which is the number of matched substrings. The offsets of the
substrings are returned in the ovector, and can be extracted by
number in the same way as for pcre2_match(), but the numbers bear no
relation to any capture groups that may exist in the pattern, because
DFA matching does not support capturing.

Calls to the convenience functions that extract substrings by name
return the error PCRE2_ERROR_DFA_UFUNC (unsupported function) if used
after a DFA match. The convenience functions that extract substrings
by number never return PCRE2_ERROR_NOSUBSTRING.

The matched strings are stored in the ovector in reverse order of
length; that is, the longest matching string is first. If there were
too many matches to fit into the ovector, the yield of the function
is zero, and the vector is filled with the longest matches.

NOTE: PCRE2's "auto-possessification" optimization usually applies to
character repeats at the end of a pattern (as well as internally).
For example, the pattern "a\d+" is compiled as if it were "a\d++".
For DFA matching, this means that only one possible match is found.
If you really do want multiple matches in such cases, either use an
ungreedy repeat such as "a\d+?" or set the PCRE2_NO_AUTO_POSSESS
option when compiling.

Error returns from pcre2_dfa_match()
The pcre2_dfa_match() function returns a negative number when it
fails. Many of the errors are the same as for pcre2_match(), as
described above. There are in addition the following errors that are
specific to pcre2_dfa_match():

PCRE2_ERROR_DFA_UITEM

This return is given if pcre2_dfa_match() encounters an item in the
pattern that it does not support, for instance, the use of \C in a
UTF mode or a backreference.

PCRE2_ERROR_DFA_UCOND

This return is given if pcre2_dfa_match() encounters a condition item
that uses a backreference for the condition, or a test for recursion
in a specific capture group. These are not supported.

PCRE2_ERROR_DFA_UINVALID_UTF

This return is given if pcre2_dfa_match() is called for a pattern
that was compiled with PCRE2_MATCH_INVALID_UTF. This is not supported
for DFA matching.

PCRE2_ERROR_DFA_WSSIZE

This return is given if pcre2_dfa_match() runs out of space in the
workspace vector.

PCRE2_ERROR_DFA_RECURSE

When a recursion or subroutine call is processed, the matching
function calls itself recursively, using private memory for the
ovector and workspace. This error is given if the internal ovector
is not large enough. This should be extremely rare, as a vector of
size 1000 is used.

PCRE2_ERROR_DFA_BADRESTART

When pcre2_dfa_match() is called with the PCRE2_DFA_RESTART option,
some plausibility checks are made on the contents of the workspace,
which should contain data about the previous partial match. If any of
these checks fail, this error is given.

SEE ALSO

pcre2build(3), pcre2callout(3), pcre2demo(3), pcre2matching(3),
pcre2partial(3), pcre2posix(3), pcre2sample(3), pcre2unicode(3).

AUTHOR

Philip Hazel
Retired from University Computing Service
Cambridge, England.

REVISION

Last updated: 26 December 2024
Copyright (c) 1997-2024 University of Cambridge.

PCRE2 10.45 26 December 2024 PCRE2API(3)