PCREAPI(3) Library Functions Manual PCREAPI(3)
PCRE - Perl-compatible regular expressions
#include <pcre.h>
pcre *pcre_compile(const char *pattern, int options,
const char **errptr, int *erroffset,
const unsigned char *tableptr);
pcre *pcre_compile2(const char *pattern, int options,
int *errorcodeptr,
const char **errptr, int *erroffset,
const unsigned char *tableptr);
pcre_extra *pcre_study(const pcre *code, int options,
const char **errptr);
void pcre_free_study(pcre_extra *extra);
int pcre_exec(const pcre *code, const pcre_extra *extra,
const char *subject, int length, int startoffset,
int options, int *ovector, int ovecsize);
int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
const char *subject, int length, int startoffset,
int options, int *ovector, int ovecsize,
int *workspace, int wscount);
int pcre_copy_named_substring(const pcre *code,
const char *subject, int *ovector,
int stringcount, const char *stringname,
char *buffer, int buffersize);
int pcre_copy_substring(const char *subject, int *ovector,
int stringcount, int stringnumber, char *buffer,
int buffersize);
int pcre_get_named_substring(const pcre *code,
const char *subject, int *ovector,
int stringcount, const char *stringname,
const char **stringptr);
int pcre_get_stringnumber(const pcre *code,
const char *name);
int pcre_get_stringtable_entries(const pcre *code,
const char *name, char **first, char **last);
int pcre_get_substring(const char *subject, int *ovector,
int stringcount, int stringnumber,
const char **stringptr);
int pcre_get_substring_list(const char *subject,
int *ovector, int stringcount, const char ***listptr);
void pcre_free_substring(const char *stringptr);
void pcre_free_substring_list(const char **stringptr);
int pcre_jit_exec(const pcre *code, const pcre_extra *extra,
const char *subject, int length, int startoffset,
int options, int *ovector, int ovecsize,
pcre_jit_stack *jstack);
pcre_jit_stack *pcre_jit_stack_alloc(int startsize, int maxsize);
void pcre_jit_stack_free(pcre_jit_stack *stack);
void pcre_assign_jit_stack(pcre_extra *extra,
pcre_jit_callback callback, void *data);
const unsigned char *pcre_maketables(void);
int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
int what, void *where);
int pcre_refcount(pcre *code, int adjust);
int pcre_config(int what, void *where);
const char *pcre_version(void);
int pcre_pattern_to_host_byte_order(pcre *code,
pcre_extra *extra, const unsigned char *tables);
void *(*pcre_malloc)(size_t);
void (*pcre_free)(void *);
void *(*pcre_stack_malloc)(size_t);
void (*pcre_stack_free)(void *);
int (*pcre_callout)(pcre_callout_block *);
int (*pcre_stack_guard)(void);
As well as support for 8-bit character strings, PCRE also
supports 16-bit strings (from release 8.30) and 32-bit strings
(from release 8.32), by means of two additional libraries. They
can be built as well as, or instead of, the 8-bit library. To
avoid too much complication, this document describes the 8-bit
versions of the functions, with only occasional references to the
16-bit and 32-bit libraries.
The 16-bit and 32-bit functions operate in the same way as their
8-bit counterparts; they just use different data types for their
arguments and results, and their names start with pcre16_ or
pcre32_ instead of pcre_. For every option that has UTF8 in its
name (for example, PCRE_UTF8), there are corresponding 16-bit and
32-bit names with UTF8 replaced by UTF16 or UTF32, respectively.
This facility is in fact just cosmetic; the 16-bit and 32-bit
option names define the same bit values.
References to bytes and UTF-8 in this document should be read as
references to 16-bit data units and UTF-16 when using the 16-bit
library, or 32-bit data units and UTF-32 when using the 32-bit
library, unless specified otherwise. More details of the
specific differences for the 16-bit and 32-bit libraries are
given in the pcre16 and pcre32 pages.
PCRE has its own native API, which is described in this document.
There are also some wrapper functions (for the 8-bit library
only) that correspond to the POSIX regular expression API, but
they do not give access to all the functionality. They are
described in the pcreposix documentation. Both of these APIs
define a set of C function calls. A C++ wrapper (again for the
8-bit library only) is also distributed with PCRE. It is
documented in the pcrecpp page.
The native API C function prototypes are defined in the header
file pcre.h, and on Unix-like systems the (8-bit) library itself
is called libpcre. It can normally be accessed by adding -lpcre
to the command for linking an application that uses PCRE. The
header file defines the macros PCRE_MAJOR and PCRE_MINOR to
contain the major and minor release numbers for the library.
Applications can use these to include support for different
releases of PCRE.
In a Windows environment, if you want to statically link an
application program against a non-dll pcre.a file, you must
define PCRE_STATIC before including pcre.h or pcrecpp.h, because
otherwise the pcre_malloc() and pcre_free() exported functions
will be declared __declspec(dllimport), with unwanted results.
The functions pcre_compile(), pcre_compile2(), pcre_study(), and
pcre_exec() 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 pcredemo.c in the PCRE source distribution. A listing
of this program is given in the pcredemo documentation, and the
pcresample documentation describes how to compile and run it.
Just-in-time compiler support is an optional feature of PCRE that
can be built in appropriate hardware environments. It greatly
speeds up the matching performance of many patterns. Simple
programs can easily request that it be used if available, by
setting an option that is ignored when it is not relevant. More
complicated programs might need to make use of the functions
pcre_jit_stack_alloc(), pcre_jit_stack_free(), and
pcre_assign_jit_stack() in order to control the JIT code's memory
usage.
From release 8.32 there is also a direct interface for JIT
execution, which gives improved performance. The JIT-specific
functions are discussed in the pcrejit documentation.
A second matching function, pcre_dfa_exec(), which is not Perl-
compatible, is also provided. This uses a different algorithm for
the matching. The alternative algorithm finds all possible
matches (at a given point in the subject), and scans the subject
just once (unless there are lookbehind assertions). However, this
algorithm does not return captured substrings. A description of
the two matching algorithms and their advantages and
disadvantages is given in the pcrematching documentation.
In addition to the main compiling and matching functions, there
are convenience functions for extracting captured substrings from
a subject string that is matched by pcre_exec(). They are:
pcre_copy_substring()
pcre_copy_named_substring()
pcre_get_substring()
pcre_get_named_substring()
pcre_get_substring_list()
pcre_get_stringnumber()
pcre_get_stringtable_entries()
pcre_free_substring() and pcre_free_substring_list() are also
provided, to free the memory used for extracted strings.
The function pcre_maketables() is used to build a set of
character tables in the current locale for passing to
pcre_compile(), pcre_exec(), or pcre_dfa_exec(). This is an
optional facility that is provided for specialist use. Most
commonly, no special tables are passed, in which case internal
tables that are generated when PCRE is built are used.
The function pcre_fullinfo() is used to find out information
about a compiled pattern. The function pcre_version() returns a
pointer to a string containing the version of PCRE and its date
of release.
The function pcre_refcount() maintains a reference count in a
data block containing a compiled pattern. This is provided for
the benefit of object-oriented applications.
The global variables pcre_malloc and pcre_free initially contain
the entry points of the standard malloc() and free() functions,
respectively. PCRE calls the memory management functions via
these variables, so a calling program can replace them if it
wishes to intercept the calls. This should be done before calling
any PCRE functions.
The global variables pcre_stack_malloc and pcre_stack_free are
also indirections to memory management functions. These special
functions are used only when PCRE is compiled to use the heap for
remembering data, instead of recursive function calls, when
running the pcre_exec() function. See the pcrebuild documentation
for details of how to do this. It is a non-standard way of
building PCRE, for use in environments that have limited stacks.
Because of the greater use of memory management, it runs more
slowly. Separate functions are provided so that special-purpose
external code can be used for this case. When used, these
functions always allocate memory blocks of the same size. There
is a discussion about PCRE's stack usage in the pcrestack
documentation.
The global variable pcre_callout initially contains NULL. It can
be set by the caller to a "callout" function, which PCRE will
then call at specified points during a matching operation.
Details are given in the pcrecallout documentation.
The global variable pcre_stack_guard initially contains NULL. It
can be set by the caller to a function that is called by PCRE
whenever it starts to compile a parenthesized part of a pattern.
When parentheses are nested, PCRE uses recursive function calls,
which use up the system stack. This function is provided so that
applications with restricted stacks can force a compilation error
if the stack runs out. The function should return zero if all is
well, or non-zero to force an error.
PCRE 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 PCRE is
built, a default can be specified. The default default is LF,
which is the Unix standard. When PCRE is run, the default can be
overridden, either when a pattern is compiled, or when it is
matched.
At compile time, the newline convention can be specified by the
options argument of pcre_compile(), or it can be specified by
special text at the start of the pattern itself; this overrides
any other settings. See the pcrepattern page for details of the
special character sequences.
In the PCRE 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 pcre_exec() options
below.
The choice of newline convention does not affect the
interpretation of the \n or \r escape sequences, nor does it
affect what \R matches, which is controlled in a similar way, but
by separate options.
The PCRE functions can be used in multi-threading applications,
with the proviso that the memory management functions pointed to
by pcre_malloc, pcre_free, pcre_stack_malloc, and
pcre_stack_free, and the callout and stack-checking functions
pointed to by pcre_callout and pcre_stack_guard, are shared by
all threads.
The compiled form of a regular expression is not altered during
matching, so the same compiled pattern can safely be used by
several threads at once.
If the just-in-time optimization feature is being used, it needs
separate memory stack areas for each thread. See the pcrejit
documentation for more details.
The compiled form of a regular expression can be saved and re-
used at a later time, possibly by a different program, and even
on a host other than the one on which it was compiled. Details
are given in the pcreprecompile documentation, which includes a
description of the pcre_pattern_to_host_byte_order() function.
However, compiling a regular expression with one version of PCRE
for use with a different version is not guaranteed to work and
may cause crashes.
int pcre_config(int what, void *where);
The function pcre_config() makes it possible for a PCRE client to
discover which optional features have been compiled into the PCRE
library. The pcrebuild documentation has more details about these
optional features.
The first argument for pcre_config() is an integer, specifying
which information is required; the second argument is a pointer
to a variable into which the information is placed. The returned
value is zero on success, or the negative error code
PCRE_ERROR_BADOPTION if the value in the first argument is not
recognized. The following information is available:
PCRE_CONFIG_UTF8
The output is an integer that is set to one if UTF-8 support is
available; otherwise it is set to zero. This value should
normally be given to the 8-bit version of this function,
pcre_config(). If it is given to the 16-bit or 32-bit version of
this function, the result is PCRE_ERROR_BADOPTION.
PCRE_CONFIG_UTF16
The output is an integer that is set to one if UTF-16 support is
available; otherwise it is set to zero. This value should
normally be given to the 16-bit version of this function,
pcre16_config(). If it is given to the 8-bit or 32-bit version of
this function, the result is PCRE_ERROR_BADOPTION.
PCRE_CONFIG_UTF32
The output is an integer that is set to one if UTF-32 support is
available; otherwise it is set to zero. This value should
normally be given to the 32-bit version of this function,
pcre32_config(). If it is given to the 8-bit or 16-bit version of
this function, the result is PCRE_ERROR_BADOPTION.
PCRE_CONFIG_UNICODE_PROPERTIES
The output is an integer that is set to one if support for
Unicode character properties is available; otherwise it is set to
zero.
PCRE_CONFIG_JIT
The output is an integer that is set to one if support for just-
in-time compiling is available; otherwise it is set to zero.
PCRE_CONFIG_JITTARGET
The output is a pointer to a zero-terminated "const char *"
string. If JIT support is available, the string contains the name
of the architecture for which the JIT compiler is configured, for
example "x86 32bit (little endian + unaligned)". If JIT support
is not available, the result is NULL.
PCRE_CONFIG_NEWLINE
The output is an integer whose value specifies the default
character sequence that is recognized as meaning "newline". The
values that are supported in ASCII/Unicode environments are: 10
for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF, and -1 for ANY.
In EBCDIC environments, CR, ANYCRLF, and ANY yield the same
values. However, the value for LF is normally 21, though some
EBCDIC environments use 37. The corresponding values for CRLF are
3349 and 3365. The default should normally correspond to the
standard sequence for your operating system.
PCRE_CONFIG_BSR
The output is an integer whose value indicates what character
sequences the \R escape sequence matches by default. A value of 0
means that \R matches any Unicode line ending sequence; a value
of 1 means that \R matches only CR, LF, or CRLF. The default can
be overridden when a pattern is compiled or matched.
PCRE_CONFIG_LINK_SIZE
The output is an integer that contains the number of bytes used
for internal linkage in compiled regular expressions. For the
8-bit library, the value can be 2, 3, or 4. For the 16-bit
library, the value is either 2 or 4 and is still a number of
bytes. For the 32-bit library, the value is either 2 or 4 and is
still a number of bytes. The default value of 2 is sufficient for
all but the most massive patterns, since it allows the compiled
pattern to be up to 64K in size. Larger values allow larger
regular expressions to be compiled, at the expense of slower
matching.
PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
The output is an integer that contains the threshold above which
the POSIX interface uses malloc() for output vectors. Further
details are given in the pcreposix documentation.
PCRE_CONFIG_PARENS_LIMIT
The output is a long integer that gives the maximum depth of
nesting of parentheses (of any kind) in a pattern. This limit is
imposed to cap the amount of system stack used when a pattern is
compiled. It is specified when PCRE 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, you can set a pointer to an external
checking function in pcre_stack_guard.
PCRE_CONFIG_MATCH_LIMIT
The output is a long integer that gives the default limit for the
number of internal matching function calls in a pcre_exec()
execution. Further details are given with pcre_exec() below.
PCRE_CONFIG_MATCH_LIMIT_RECURSION
The output is a long integer that gives the default limit for the
depth of recursion when calling the internal matching function in
a pcre_exec() execution. Further details are given with
pcre_exec() below.
PCRE_CONFIG_STACKRECURSE
The output is an integer that is set to one if internal recursion
when running pcre_exec() is implemented by recursive function
calls that use the stack to remember their state. This is the
usual way that PCRE is compiled. The output is zero if PCRE was
compiled to use blocks of data on the heap instead of recursive
function calls. In this case, pcre_stack_malloc and
pcre_stack_free are called to manage memory blocks on the heap,
thus avoiding the use of the stack.
pcre *pcre_compile(const char *pattern, int options,
const char **errptr, int *erroffset,
const unsigned char *tableptr);
pcre *pcre_compile2(const char *pattern, int options,
int *errorcodeptr,
const char **errptr, int *erroffset,
const unsigned char *tableptr);
Either of the functions pcre_compile() or pcre_compile2() can be
called to compile a pattern into an internal form. The only
difference between the two interfaces is that pcre_compile2() has
an additional argument, errorcodeptr, via which a numerical error
code can be returned. To avoid too much repetition, we refer just
to pcre_compile() below, but the information applies equally to
pcre_compile2().
The pattern is a C string terminated by a binary zero, and is
passed in the pattern argument. A pointer to a single block of
memory that is obtained via pcre_malloc is returned. This
contains the compiled code and related data. The pcre type is
defined for the returned block; this is a typedef for a structure
whose contents are not externally defined. It is up to the caller
to free the memory (via pcre_free) when it is no longer required.
Although the compiled code of a PCRE regex is relocatable, that
is, it does not depend on memory location, the complete pcre data
block is not fully relocatable, because it may contain a copy of
the tableptr argument, which is an address (see below).
The options argument contains various bit settings that affect
the compilation. It should be zero if no options are required.
The available options are described below. Some of them (in
particular, those that are compatible with Perl, but some others
as well) can also be set and unset from within the pattern (see
the detailed description in the pcrepattern 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 and execution. The
PCRE_ANCHORED, PCRE_BSR_xxx, PCRE_NEWLINE_xxx,
PCRE_NO_UTF8_CHECK, and PCRE_NO_START_OPTIMIZE options can be set
at the time of matching as well as at compile time.
If errptr is NULL, pcre_compile() returns NULL immediately.
Otherwise, if compilation of a pattern fails, pcre_compile()
returns NULL, and sets the variable pointed to by errptr to point
to a textual error message. This is a static string that is part
of the library. You must not try to free it. Normally, the offset
from the start of the pattern to the data unit that was being
processed when the error was discovered is placed in the variable
pointed to by erroffset, which must not be NULL (if it is, an
immediate error is given). However, for an invalid UTF-8 or
UTF-16 string, the offset is that of the first data 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 data units, not
characters, even in a UTF mode. It may sometimes point into the
middle of a UTF-8 or UTF-16 character.
If pcre_compile2() is used instead of pcre_compile(), and the
errorcodeptr argument is not NULL, a non-zero error code number
is returned via this argument in the event of an error. This is
in addition to the textual error message. Error codes and
messages are listed below.
If the final argument, tableptr, is NULL, PCRE uses a default set
of character tables that are built when PCRE is compiled, using
the default C locale. Otherwise, tableptr must be an address that
is the result of a call to pcre_maketables(). This value is
stored with the compiled pattern, and used again by pcre_exec()
and pcre_dfa_exec() when the pattern is matched. For more
discussion, see the section on locale support below.
This code fragment shows a typical straightforward call to
pcre_compile():
pcre *re;
const char *error;
int erroffset;
re = pcre_compile(
"^A.*Z", /* the pattern */
0, /* default options */
&error, /* for error message */
&erroffset, /* for error offset */
NULL); /* use default character tables */
The following names for option bits are defined in the pcre.h
header file:
PCRE_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.
PCRE_AUTO_CALLOUT
If this bit is set, pcre_compile() automatically inserts callout
items, all with number 255, before each pattern item. For
discussion of the callout facility, see the pcrecallout
documentation.
PCRE_BSR_ANYCRLF
PCRE_BSR_UNICODE
These options (which are mutually exclusive) control what the \R
escape sequence matches. The choice is either to match only CR,
LF, or CRLF, or to match any Unicode newline sequence. The
default is specified when PCRE is built. It can be overridden
from within the pattern, or by setting an option when a compiled
pattern is matched.
PCRE_CASELESS
If this bit is set, letters in the pattern match both upper and
lower case letters. It is equivalent to Perl's /i option, and it
can be changed within a pattern by a (?i) option setting. In
UTF-8 mode, PCRE always understands the concept of case for
characters whose values are less than 128, so caseless matching
is always possible. For characters with higher values, the
concept of case is supported if PCRE is compiled with Unicode
property support, but not otherwise. If you want to use caseless
matching for characters 128 and above, you must ensure that PCRE
is compiled with Unicode property support as well as with UTF-8
support.
PCRE_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
PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is set.
There is no equivalent to this option in Perl, and no way to set
it within a pattern.
PCRE_DOTALL
If this bit is set, a dot metacharacter in the pattern matches a
character of any value, 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 is at a newline. This option is equivalent to
Perl's /s option, and it can be changed within a pattern by a
(?s) option setting. A negative class such as [^a] always matches
newline characters, independent of the setting of this option.
PCRE_DUPNAMES
If this bit is set, names used to identify capturing subpatterns
need not be unique. This can be helpful for certain types of
pattern when it is known that only one instance of the named
subpattern can ever be matched. There are more details of named
subpatterns below; see also the pcrepattern documentation.
PCRE_EXTENDED
If this bit is set, most white space characters in the pattern
are totally ignored except when escaped or inside a character
class. However, white space is not allowed within sequences such
as (?> that introduce various parenthesized subpatterns, nor
within a numerical quantifier such as {1,3}. However, ignorable
white space is permitted between an item and a following
quantifier and between a quantifier and a following + that
indicates possessiveness.
White space did not used to include the VT character (code 11),
because Perl did not treat this character as white space.
However, Perl changed at release 5.18, so PCRE followed at
release 8.34, and VT is now treated as white space.
PCRE_EXTENDED also causes characters between an unescaped #
outside a character class and the next newline, inclusive, to be
ignored. PCRE_EXTENDED is equivalent to Perl's /x option, and it
can be changed within a pattern by a (?x) option setting.
Which characters are interpreted as newlines is controlled by the
options passed to pcre_compile() or by a special sequence at the
start of the pattern, as described in the section entitled
"Newline conventions" in the pcrepattern documentation. 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.
This option makes it possible to include comments inside
complicated patterns. Note, however, that this applies only to
data characters. White space characters may never appear within
special character sequences in a pattern, for example within the
sequence (?( that introduces a conditional subpattern.
PCRE_EXTRA
This option was invented in order to turn on additional
functionality of PCRE that is incompatible with Perl, but it is
currently of very little use. When set, any backslash in a
pattern that is followed by a letter that has no special meaning
causes an error, thus reserving these combinations for future
expansion. By default, as in Perl, a backslash followed by a
letter with no special meaning is treated as a literal. (Perl
can, however, be persuaded to give an error for this, by running
it with the -w option.) There are at present no other features
controlled by this option. It can also be set by a (?X) option
setting within a pattern.
PCRE_FIRSTLINE
If this option is set, an unanchored pattern is required to match
before or at the first newline in the subject string, though the
matched text may continue over the newline.
PCRE_JAVASCRIPT_COMPAT
If this option is set, PCRE's behaviour is changed in some ways
so that it is compatible with JavaScript rather than Perl. The
changes are as follows:
(1) A lone closing square bracket in a pattern causes a compile-
time error, because this is illegal in JavaScript (by default it
is treated as a data character). Thus, the pattern AB]CD becomes
illegal when this option is set.
(2) At run time, a back reference to an unset subpattern group
matches an empty string (by default this causes the current
matching alternative to fail). A pattern such as (\1)(a) succeeds
when this option is set (assuming it can find an "a" in the
subject), whereas it fails by default, for Perl compatibility.
(3) \U matches an upper case "U" character; by default \U causes
a compile time error (Perl uses \U to upper case subsequent
characters).
(4) \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).
(5) \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).
PCRE_MULTILINE
By default, for the purposes of matching "start of line" and "end
of line", PCRE 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 PCRE_DOLLAR_ENDONLY is set). Note, however, that
unless PCRE_DOTALL is set, the "any character" metacharacter (.)
does not match at a newline. This behaviour (for ^, $, and dot)
is the same as Perl.
When PCRE_MULTILINE it is set, the "start of line" and "end of
line" constructs match immediately following or immediately
before internal newlines in the subject string, respectively, as
well as at the very start and end. This is equivalent to Perl's
/m option, and it can be changed within a pattern by a (?m)
option setting. If there are no newlines in a subject string, or
no occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has
no effect.
PCRE_NEVER_UTF
This option locks out interpretation of the pattern as UTF-8 (or
UTF-16 or UTF-32 in the 16-bit and 32-bit libraries). In
particular, it prevents the creator of the pattern from switching
to UTF interpretation by starting the pattern with (*UTF). This
may be useful in applications that process patterns from external
sources. The combination of PCRE_UTF8 and PCRE_NEVER_UTF also
causes an error.
PCRE_NEWLINE_CR
PCRE_NEWLINE_LF
PCRE_NEWLINE_CRLF
PCRE_NEWLINE_ANYCRLF
PCRE_NEWLINE_ANY
These options override the default newline definition that was
chosen when PCRE was built. Setting the first or the second
specifies that a newline is indicated by a single character (CR
or LF, respectively). Setting PCRE_NEWLINE_CRLF specifies that a
newline is indicated by the two-character CRLF sequence. Setting
PCRE_NEWLINE_ANYCRLF specifies that any of the three preceding
sequences should be recognized. Setting PCRE_NEWLINE_ANY
specifies that any Unicode newline sequence should be recognized.
In an ASCII/Unicode environment, 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). For the 8-bit library, the last two are
recognized only in UTF-8 mode.
When PCRE is compiled to run in an EBCDIC (mainframe)
environment, the code for CR is 0x0d, the same as ASCII. However,
the character code for LF is normally 0x15, though in some EBCDIC
environments 0x25 is used. Whichever of these is not LF is made
to correspond to Unicode's NEL character. EBCDIC codes are all
less than 256. For more details, see the pcrebuild documentation.
The newline setting in the options word uses three bits that are
treated as a number, giving eight possibilities. Currently only
six are used (default plus the five values above). This means
that if you set more than one newline option, the combination may
or may not be sensible. For example, PCRE_NEWLINE_CR with
PCRE_NEWLINE_LF is equivalent to PCRE_NEWLINE_CRLF, but other
combinations may yield unused numbers and cause an error.
The only time that a line break in a pattern is specially
recognized when compiling is when PCRE_EXTENDED is set. CR and LF
are white space characters, and so are ignored in this mode.
Also, an unescaped # outside a character class indicates a
comment that lasts until after the next line break sequence. In
other circumstances, line break sequences in patterns are treated
as literal data.
The newline option that is set at compile time becomes the
default that is used for pcre_exec() and pcre_dfa_exec(), but it
can be overridden.
PCRE_NO_AUTO_CAPTURE
If this option is set, it disables the use of numbered capturing
parentheses in the pattern. Any opening parenthesis that is not
followed by ? behaves as if it were followed by ?: but named
parentheses can still be used for capturing (and they acquire
numbers in the usual way). There is no equivalent of this option
in Perl.
PCRE_NO_AUTO_POSSESS
If this option is set, it disables "auto-possessification". This
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 of them 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.
PCRE_NO_START_OPTIMIZE
This is an option that acts at matching time; that is, it is
really an option for pcre_exec() or pcre_dfa_exec(). If it is set
at compile time, it is remembered with the compiled pattern and
assumed at matching time. This is necessary if you want to use
JIT execution, because the JIT compiler needs to know whether or
not this option is set. For details see the discussion of
PCRE_NO_START_OPTIMIZE below.
PCRE_UCP
This option changes the way PCRE 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 PCRE_UCP is set,
Unicode properties are used instead to classify characters. More
details are given in the section on generic character types in
the pcrepattern page. If you set PCRE_UCP, matching one of the
items it affects takes much longer. The option is available only
if PCRE has been compiled with Unicode property support.
PCRE_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.
PCRE_UTF8
This option causes PCRE to regard both the pattern and the
subject as strings of UTF-8 characters instead of single-byte
strings. However, it is available only when PCRE is built to
include UTF support. If not, the use of this option provokes an
error. Details of how this option changes the behaviour of PCRE
are given in the pcreunicode page.
PCRE_NO_UTF8_CHECK
When PCRE_UTF8 is set, the validity of the pattern as a UTF-8
string is automatically checked. There is a discussion about the
validity of UTF-8 strings in the pcreunicode page. If an invalid
UTF-8 sequence is found, pcre_compile() returns an error. If you
already know that your pattern is valid, and you want to skip
this check for performance reasons, you can set the
PCRE_NO_UTF8_CHECK option. When it is set, the effect of passing
an invalid UTF-8 string as a pattern is undefined. It may cause
your program to crash or loop. Note that this option can also be
passed to pcre_exec() and pcre_dfa_exec(), to suppress the
validity checking of subject strings only. If the same string is
being matched many times, the option can be safely set for the
second and subsequent matchings to improve performance.
The following table lists the error codes than may be returned by
pcre_compile2(), along with the error messages that may be
returned by both compiling functions. Note that error messages
are always 8-bit ASCII strings, even in 16-bit or 32-bit mode. As
PCRE has developed, some error codes have fallen out of use. To
avoid confusion, they have not been re-used.
0 no error
1 \ at end of pattern
2 \c at end of pattern
3 unrecognized character follows \
4 numbers out of order in {} quantifier
5 number too big in {} quantifier
6 missing terminating ] for character class
7 invalid escape sequence in character class
8 range out of order in character class
9 nothing to repeat
10 [this code is not in use]
11 internal error: unexpected repeat
12 unrecognized character after (? or (?-
13 POSIX named classes are supported only within a class
14 missing )
15 reference to non-existent subpattern
16 erroffset passed as NULL
17 unknown option bit(s) set
18 missing ) after comment
19 [this code is not in use]
20 regular expression is too large
21 failed to get memory
22 unmatched parentheses
23 internal error: code overflow
24 unrecognized character after (?<
25 lookbehind assertion is not fixed length
26 malformed number or name after (?(
27 conditional group contains more than two branches
28 assertion expected after (?(
29 (?R or (?[+-]digits must be followed by )
30 unknown POSIX class name
31 POSIX collating elements are not supported
32 this version of PCRE is compiled without UTF support
33 [this code is not in use]
34 character value in \x{} or \o{} is too large
35 invalid condition (?(0)
36 \C not allowed in lookbehind assertion
37 PCRE does not support \L, \l, \N{name}, \U, or \u
38 number after (?C is > 255
39 closing ) for (?C expected
40 recursive call could loop indefinitely
41 unrecognized character after (?P
42 syntax error in subpattern name (missing terminator)
43 two named subpatterns have the same name
44 invalid UTF-8 string (specifically UTF-8)
45 support for \P, \p, and \X has not been compiled
46 malformed \P or \p sequence
47 unknown property name after \P or \p
48 subpattern name is too long (maximum 32 characters)
49 too many named subpatterns (maximum 10000)
50 [this code is not in use]
51 octal value is greater than \377 in 8-bit non-UTF-8 mode
52 internal error: overran compiling workspace
53 internal error: previously-checked referenced subpattern
not found
54 DEFINE group contains more than one branch
55 repeating a DEFINE group is not allowed
56 inconsistent NEWLINE options
57 \g is not followed by a braced, angle-bracketed, or quoted
name/number or by a plain number
58 a numbered reference must not be zero
59 an argument is not allowed for (*ACCEPT), (*FAIL), or
(*COMMIT)
60 (*VERB) not recognized or malformed
61 number is too big
62 subpattern name expected
63 digit expected after (?+
64 ] is an invalid data character in JavaScript compatibility
mode
65 different names for subpatterns of the same number are
not allowed
66 (*MARK) must have an argument
67 this version of PCRE is not compiled with Unicode property
support
68 \c must be followed by an ASCII character
69 \k is not followed by a braced, angle-bracketed, or quoted
name
70 internal error: unknown opcode in find_fixedlength()
71 \N is not supported in a class
72 too many forward references
73 disallowed Unicode code point (>= 0xd800 && <= 0xdfff)
74 invalid UTF-16 string (specifically UTF-16)
75 name is too long in (*MARK), (*PRUNE), (*SKIP), or (*THEN)
76 character value in \u.... sequence is too large
77 invalid UTF-32 string (specifically UTF-32)
78 setting UTF is disabled by the application
79 non-hex character in \x{} (closing brace missing?)
80 non-octal character in \o{} (closing brace missing?)
81 missing opening brace after \o
82 parentheses are too deeply nested
83 invalid range in character class
84 group name must start with a non-digit
85 parentheses are too deeply nested (stack check)
The numbers 32 and 10000 in errors 48 and 49 are defaults;
different values may be used if the limits were changed when PCRE
was built.
pcre_extra *pcre_study(const pcre *code, int options,
const char **errptr);
If a compiled pattern is going to be used several times, it is
worth spending more time analyzing it in order to speed up the
time taken for matching. The function pcre_study() takes a
pointer to a compiled pattern as its first argument. If studying
the pattern produces additional information that will help speed
up matching, pcre_study() returns a pointer to a pcre_extra
block, in which the study_data field points to the results of the
study.
The returned value from pcre_study() can be passed directly to
pcre_exec() or pcre_dfa_exec(). However, a pcre_extra block also
contains other fields that can be set by the caller before the
block is passed; these are described below in the section on
matching a pattern.
If studying the pattern does not produce any useful information,
pcre_study() returns NULL by default. In that circumstance, if
the calling program wants to pass any of the other fields to
pcre_exec() or pcre_dfa_exec(), it must set up its own pcre_extra
block. However, if pcre_study() is called with the
PCRE_STUDY_EXTRA_NEEDED option, it returns a pcre_extra block
even if studying did not find any additional information. It may
still return NULL, however, if an error occurs in pcre_study().
The second argument of pcre_study() contains option bits. There
are three further options in addition to PCRE_STUDY_EXTRA_NEEDED:
PCRE_STUDY_JIT_COMPILE
PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE
PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE
If any of these are set, and the just-in-time compiler is
available, the pattern is further compiled into machine code that
executes much faster than the pcre_exec() interpretive matching
function. If the just-in-time compiler is not available, these
options are ignored. All undefined bits in the options argument
must be zero.
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 study time. Not all patterns can be optimized
by the JIT compiler. For those that cannot be handled, matching
automatically falls back to the pcre_exec() interpreter. For more
details, see the pcrejit documentation.
The third argument for pcre_study() is a pointer for an error
message. If studying succeeds (even if no data is returned), the
variable it points to is set to NULL. Otherwise it is set to
point to a textual error message. This is a static string that is
part of the library. You must not try to free it. You should test
the error pointer for NULL after calling pcre_study(), to be sure
that it has run successfully.
When you are finished with a pattern, you can free the memory
used for the study data by calling pcre_free_study(). This
function was added to the API for release 8.20. For earlier
versions, the memory could be freed with pcre_free(), just like
the pattern itself. This will still work in cases where JIT
optimization is not used, but it is advisable to change to the
new function when convenient.
This is a typical way in which pcre_study() is used (except that
in a real application there should be tests for errors):
int rc;
pcre *re;
pcre_extra *sd;
re = pcre_compile("pattern", 0, &error, &erroroffset, NULL);
sd = pcre_study(
re, /* result of pcre_compile() */
0, /* no options */
&error); /* set to NULL or points to a message */
rc = pcre_exec( /* see below for details of pcre_exec()
options */
re, sd, "subject", 7, 0, 0, ovector, 30);
...
pcre_free_study(sd);
pcre_free(re);
Studying a pattern does two things: first, a lower bound for the
length of subject string that is needed to match the pattern is
computed. This does not mean that there are any strings of that
length that match, but it does guarantee that no shorter strings
match. The value is used to avoid wasting time by trying to match
strings that are shorter than the lower bound. You can find out
the value in a calling program via the pcre_fullinfo() function.
Studying a pattern is also useful for non-anchored patterns that
do not have a single fixed starting character. A bitmap of
possible starting bytes is created. This speeds up finding a
position in the subject at which to start matching. (In 16-bit
mode, the bitmap is used for 16-bit values less than 256. In
32-bit mode, the bitmap is used for 32-bit values less than 256.)
These two optimizations apply to both pcre_exec() and
pcre_dfa_exec(), and the information is also used by the JIT
compiler. The optimizations can be disabled by setting the
PCRE_NO_START_OPTIMIZE option. You might want to do this if your
pattern contains callouts or (*MARK) and you want to make use of
these facilities in cases where matching fails.
PCRE_NO_START_OPTIMIZE can be specified at either compile time or
execution time. However, if PCRE_NO_START_OPTIMIZE is passed to
pcre_exec(), (that is, after any JIT compilation has happened)
JIT execution is disabled. For JIT execution to work with
PCRE_NO_START_OPTIMIZE, the option must be set at compile time.
There is a longer discussion of PCRE_NO_START_OPTIMIZE below.
PCRE handles caseless matching, and determines whether characters
are letters, digits, or whatever, by reference to a set of
tables, indexed by character code point. When running in UTF-8
mode, or in the 16- or 32-bit libraries, this applies only to
characters with code points less than 256. By default, higher-
valued code points never match escapes such as \w or \d. However,
if PCRE is built with Unicode property support, all characters
can be tested with \p and \P, or, alternatively, the PCRE_UCP
option can be set when a pattern is compiled; this causes \w and
friends to use Unicode property support instead of the built-in
tables.
The use of locales with Unicode is discouraged. If you are
handling characters with code points greater than 128, you should
either use Unicode support, or use locales, but not try to mix
the two.
PCRE contains an internal set of tables that are used when the
final argument of pcre_compile() is NULL. These are sufficient
for many applications. Normally, the internal tables recognize
only ASCII characters. However, when PCRE is built, it is
possible to cause the internal tables to be rebuilt in the
default "C" locale of the local system, which may cause them to
be different.
The internal tables can always be overridden by tables supplied
by the application that calls PCRE. 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 pcre_maketables()
function, which has no arguments, in the relevant locale. The
result can then be passed to pcre_compile() as often as
necessary. For example, to build and use tables that are
appropriate for the French locale (where accented characters with
values greater than 128 are treated as letters), the following
code could be used:
setlocale(LC_CTYPE, "fr_FR");
tables = pcre_maketables();
re = pcre_compile(..., tables);
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".
When pcre_maketables() runs, the tables are built in memory that
is obtained via pcre_malloc. It is the caller's responsibility to
ensure that the memory containing the tables remains available
for as long as it is needed.
The pointer that is passed to pcre_compile() is saved with the
compiled pattern, and the same tables are used via this pointer
by pcre_study() and also by pcre_exec() and pcre_dfa_exec().
Thus, for any single pattern, compilation, studying and matching
all happen in the same locale, but different patterns can be
processed in different locales.
It is possible to pass a table pointer or NULL (indicating the
use of the internal tables) to pcre_exec() or pcre_dfa_exec()
(see the discussion below in the section on matching a pattern).
This facility is provided for use with pre-compiled patterns that
have been saved and reloaded. Character tables are not saved
with patterns, so if a non-standard table was used at compile
time, it must be provided again when the reloaded pattern is
matched. Attempting to use this facility to match a pattern in a
different locale from the one in which it was compiled is likely
to lead to anomalous (usually incorrect) results.
int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
int what, void *where);
The pcre_fullinfo() function returns information about a compiled
pattern. It replaces the pcre_info() function, which was removed
from the library at version 8.30, after more than 10 years of
obsolescence.
The first argument for pcre_fullinfo() is a pointer to the
compiled pattern. The second argument is the result of
pcre_study(), or NULL if the pattern was not studied. The third
argument specifies which piece of information is required, and
the fourth argument is a pointer to a variable to receive the
data. The yield of the function is zero for success, or one of
the following negative numbers:
PCRE_ERROR_NULL the argument code was NULL
the argument where was NULL
PCRE_ERROR_BADMAGIC the "magic number" was not found
PCRE_ERROR_BADENDIANNESS the pattern was compiled with
different
endianness
PCRE_ERROR_BADOPTION the value of what was invalid
PCRE_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. The endianness error can occur if a compiled pattern is
saved and reloaded on a different host. Here is a typical call of
pcre_fullinfo(), to obtain the length of the compiled pattern:
int rc;
size_t length;
rc = pcre_fullinfo(
re, /* result of pcre_compile() */
sd, /* result of pcre_study(), or NULL */
PCRE_INFO_SIZE, /* what is required */
&length); /* where to put the data */
The possible values for the third argument are defined in pcre.h,
and are as follows:
PCRE_INFO_BACKREFMAX
Return the number of the highest back reference in the pattern.
The fourth argument should point to an int variable. Zero is
returned if there are no back references.
PCRE_INFO_CAPTURECOUNT
Return the number of capturing subpatterns in the pattern. The
fourth argument should point to an int variable.
PCRE_INFO_DEFAULT_TABLES
Return a pointer to the internal default character tables within
PCRE. The fourth argument should point to an unsigned char *
variable. This information call is provided for internal use by
the pcre_study() function. External callers can cause PCRE to use
its internal tables by passing a NULL table pointer.
PCRE_INFO_FIRSTBYTE (deprecated)
Return information about the first data unit of any matched
string, for a non-anchored pattern. The name of this option
refers to the 8-bit library, where data units are bytes. The
fourth argument should point to an int variable. Negative values
are used for special cases. However, this means that when the
32-bit library is in non-UTF-32 mode, the full 32-bit range of
characters cannot be returned. For this reason, this value is
deprecated; use PCRE_INFO_FIRSTCHARACTERFLAGS and
PCRE_INFO_FIRSTCHARACTER instead.
If there is a fixed first value, for example, the letter "c" from
a pattern such as (cat|cow|coyote), its value is returned. 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 the
value can be up to 0x10ffff.
If there is no fixed first value, and if either
(a) the pattern was compiled with the PCRE_MULTILINE option, and
every branch starts with "^", or
(b) every branch of the pattern starts with ".*" and PCRE_DOTALL
is not set (if it were set, the pattern would be anchored),
-1 is returned, indicating that the pattern matches only at the
start of a subject string or after any newline within the string.
Otherwise -2 is returned. For anchored patterns, -2 is returned.
PCRE_INFO_FIRSTCHARACTER
Return the value of the first data unit (non-UTF character) of
any matched string in the situation where
PCRE_INFO_FIRSTCHARACTERFLAGS returns 1; otherwise return 0. The
fourth argument should point to a uint_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.
PCRE_INFO_FIRSTCHARACTERFLAGS
Return information about the first data unit of any matched
string, for a non-anchored pattern. The fourth argument should
point to an int variable.
If there is a fixed first value, for example, the letter "c" from
a pattern such as (cat|cow|coyote), 1 is returned, and the
character value can be retrieved using PCRE_INFO_FIRSTCHARACTER.
If there is no fixed first value, and if either
(a) the pattern was compiled with the PCRE_MULTILINE option, and
every branch starts with "^", or
(b) every branch of the pattern starts with ".*" and PCRE_DOTALL
is not set (if it were set, the pattern would be anchored),
2 is returned, indicating that the pattern matches only at the
start of a subject string or after any newline within the string.
Otherwise 0 is returned. For anchored patterns, 0 is returned.
PCRE_INFO_FIRSTTABLE
If the pattern was studied, and this resulted in the construction
of a 256-bit table indicating a fixed set of values for the first
data unit in any matching string, a pointer to the table is
returned. Otherwise NULL is returned. The fourth argument should
point to an unsigned char * variable.
PCRE_INFO_HASCRORLF
Return 1 if the pattern contains any explicit matches for CR or
LF characters, otherwise 0. The fourth argument should point to
an int variable. An explicit match is either a literal CR or LF
character, or \r or \n.
PCRE_INFO_JCHANGED
Return 1 if the (?J) or (?-J) option setting is used in the
pattern, otherwise 0. The fourth argument should point to an int
variable. (?J) and (?-J) set and unset the local PCRE_DUPNAMES
option, respectively.
PCRE_INFO_JIT
Return 1 if the pattern was studied with one of the JIT options,
and just-in-time compiling was successful. The fourth argument
should point to an int variable. A return value of 0 means that
JIT support is not available in this version of PCRE, or that the
pattern was not studied with a JIT option, or that the JIT
compiler could not handle this particular pattern. See the
pcrejit documentation for details of what can and cannot be
handled.
PCRE_INFO_JITSIZE
If the pattern was successfully studied with a JIT option, return
the size of the JIT compiled code, otherwise return zero. The
fourth argument should point to a size_t variable.
PCRE_INFO_LASTLITERAL
Return the value of the rightmost literal data unit that must
exist in any matched string, other than at its start, if such a
value has been recorded. The fourth argument should point to an
int variable. If there is no such value, -1 is returned. 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 "z", but for /^a\dz\d/
the returned value is -1.
Since for the 32-bit library using the non-UTF-32 mode, this
function is unable to return the full 32-bit range of characters,
this value is deprecated; instead the PCRE_INFO_REQUIREDCHARFLAGS
and PCRE_INFO_REQUIREDCHAR values should be used.
PCRE_INFO_MATCH_EMPTY
Return 1 if the pattern can match an empty string, otherwise 0.
The fourth argument should point to an int variable.
PCRE_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
fourth argument should point to an unsigned 32-bit integer. If no
such value has been set, the call to pcre_fullinfo() returns the
error PCRE_ERROR_UNSET.
PCRE_INFO_MAXLOOKBEHIND
Return the number of characters (NB not data units) in the
longest lookbehind assertion in the pattern. This information is
useful when doing multi-segment matching using the partial
matching facilities. Note that the simple assertions \b and \B
require a one-character lookbehind. \A also registers a one-
character lookbehind, though it does not actually inspect the
previous character. This is to ensure that at least one character
from the old segment is retained when a new segment is processed.
Otherwise, if there are no lookbehinds in the pattern, \A might
match incorrectly at the start of a new segment.
PCRE_INFO_MINLENGTH
If the pattern was studied and a minimum length for matching
subject strings was computed, its value is returned. Otherwise
the returned value is -1. The value is a number of characters,
which in UTF mode may be different from the number of data units.
The fourth argument should point to an int variable. A non-
negative 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.
PCRE_INFO_NAMECOUNT
PCRE_INFO_NAMEENTRYSIZE
PCRE_INFO_NAMETABLE
PCRE 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 pcre_get_named_substring() 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 pcre_exec() 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.
PCRE_INFO_NAMECOUNT gives the number of entries, and
PCRE_INFO_NAMEENTRYSIZE gives the size of each entry; both of
these return an int value. The entry size depends on the length
of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the
first entry of the table. This is a pointer to char in the 8-bit
library, where 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 data units, the
first of which contains the parenthesis number. In the 32-bit
library, the pointer points to 32-bit data units, the first of
which contains the parenthesis number. The rest of the entry is
the corresponding name, zero terminated.
The names are in alphabetical order. If (?| is used to create
multiple groups with the same number, as described in the section
on duplicate subpattern numbers in the pcrepattern page, the
groups may be given the same name, but there is only one entry in
the table. Different names for groups of the same number are not
permitted. Duplicate names for subpatterns with different
numbers are permitted, but only if PCRE_DUPNAMES is set. They
appear in the table in the order in which they were found in the
pattern. In the absence of (?| this is the order of increasing
number; when (?| is used this is not necessarily the case because
later subpatterns may have lower numbers.
As a simple example of the name/number table, consider the
following pattern after compilation by the 8-bit library (assume
PCRE_EXTENDED is set, so white space - including newlines - is
ignored):
(?<date> (?<year>(\d\d)?\d\d) -
(?<month>\d\d) - (?<day>\d\d) )
There are four named subpatterns, so the table has four entries,
and each entry in the table is eight bytes long. The table is as
follows, with non-printing bytes shows in hexadecimal, and
undefined bytes shown as ??:
00 01 d a t e 00 ??
00 05 d a y 00 ?? ??
00 04 m o n t h 00
00 02 y e a r 00 ??
When writing code to extract data from named subpatterns using
the name-to-number map, remember that the length of the entries
is likely to be different for each compiled pattern.
PCRE_INFO_OKPARTIAL
Return 1 if the pattern can be used for partial matching with
pcre_exec(), otherwise 0. The fourth argument should point to an
int variable. From release 8.00, this always returns 1, because
the restrictions that previously applied to partial matching have
been lifted. The pcrepartial documentation gives details of
partial matching.
PCRE_INFO_OPTIONS
Return a copy of the options with which the pattern was compiled.
The fourth argument should point to an unsigned long int
variable. These option bits are those specified in the call to
pcre_compile(), modified by any top-level option settings at the
start of the pattern itself. In other words, they are the options
that will be in force when matching starts. For example, if the
pattern /(?im)abc(?-i)d/ is compiled with the PCRE_EXTENDED
option, the result is PCRE_CASELESS, PCRE_MULTILINE, and
PCRE_EXTENDED.
A pattern is automatically anchored by PCRE if all of its top-
level alternatives begin with one of the following:
^ unless PCRE_MULTILINE is set
\A always
\G always
.* if PCRE_DOTALL is set and there are no back
references to the subpattern in which .* appears
For such patterns, the PCRE_ANCHORED bit is set in the options
returned by pcre_fullinfo().
PCRE_INFO_RECURSIONLIMIT
If the pattern set a recursion limit by including an item of the
form (*LIMIT_RECURSION=nnnn) at the start, the value is returned.
The fourth argument should point to an unsigned 32-bit integer.
If no such value has been set, the call to pcre_fullinfo()
returns the error PCRE_ERROR_UNSET.
PCRE_INFO_SIZE
Return the size of the compiled pattern in bytes (for all three
libraries). The fourth argument should point to a size_t
variable. This value does not include the size of the pcre
structure that is returned by pcre_compile(). The value that is
passed as the argument to pcre_malloc() when pcre_compile() is
getting memory in which to place the compiled data is the value
returned by this option plus the size of the pcre structure.
Studying a compiled pattern, with or without JIT, does not alter
the value returned by this option.
PCRE_INFO_STUDYSIZE
Return the size in bytes (for all three libraries) of the data
block pointed to by the study_data field in a pcre_extra block.
If pcre_extra is NULL, or there is no study data, zero is
returned. The fourth argument should point to a size_t variable.
The study_data field is set by pcre_study() to record information
that will speed up matching (see the section entitled "Studying a
pattern" above). The format of the study_data block is private,
but its length is made available via this option so that it can
be saved and restored (see the pcreprecompile documentation for
details).
PCRE_INFO_REQUIREDCHARFLAGS
Returns 1 if there is a rightmost literal data unit that must
exist in any matched string, other than at its start. The fourth
argument should point to an int variable. If there is no such
value, 0 is returned. If returning 1, the character value itself
can be retrieved using PCRE_INFO_REQUIREDCHAR.
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 1 (with "z" returned from
PCRE_INFO_REQUIREDCHAR), but for /^a\dz\d/ the returned value is
0.
PCRE_INFO_REQUIREDCHAR
Return the value of the rightmost literal data unit that must
exist in any matched string, other than at its start, if such a
value has been recorded. The fourth argument should point to a
uint32_t variable. If there is no such value, 0 is returned.
int pcre_refcount(pcre *code, int adjust);
The pcre_refcount() function is used to maintain a reference
count in the data block that contains a compiled pattern. It is
provided for the benefit of applications that operate in an
object-oriented manner, where different parts of the application
may be using the same compiled pattern, but you want to free the
block when they are all done.
When a pattern is compiled, the reference count field is
initialized to zero. It is changed only by calling this
function, whose action is to add the adjust value (which may be
positive or negative) to it. The yield of the function is the new
value. However, the value of the count is constrained to lie
between 0 and 65535, inclusive. If the new value is outside these
limits, it is forced to the appropriate limit value.
Except when it is zero, the reference count is not correctly
preserved if a pattern is compiled on one host and then
transferred to a host whose byte-order is different. (This seems
a highly unlikely scenario.)
int pcre_exec(const pcre *code, const pcre_extra *extra,
const char *subject, int length, int startoffset,
int options, int *ovector, int ovecsize);
The function pcre_exec() is called to match a subject string
against a compiled pattern, which is passed in the code argument.
If the pattern was studied, the result of the study should be
passed in the extra argument. You can call pcre_exec() with the
same code and extra arguments as many times as you like, in order
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 pcre_dfa_exec() function.
In most applications, the pattern will have been compiled (and
optionally studied) in the same process that calls pcre_exec().
However, it is possible to save compiled patterns and study data,
and then use them later in different processes, possibly even on
different hosts. For a discussion about this, see the
pcreprecompile documentation.
Here is an example of a simple call to pcre_exec():
int rc;
int ovector[30];
rc = pcre_exec(
re, /* result of pcre_compile() */
NULL, /* we didn't study the pattern */
"some string", /* the subject string */
11, /* the length of the subject string */
0, /* start at offset 0 in the subject */
0, /* default options */
ovector, /* vector of integers for substring
information */
30); /* number of elements (NOT size in bytes) */
Extra data for pcre_exec()
If the extra argument is not NULL, it must point to a pcre_extra
data block. The pcre_study() function returns such a block (when
it doesn't return NULL), but you can also create one for
yourself, and pass additional information in it. The pcre_extra
block contains the following fields (not necessarily in this
order):
unsigned long int flags;
void *study_data;
void *executable_jit;
unsigned long int match_limit;
unsigned long int match_limit_recursion;
void *callout_data;
const unsigned char *tables;
unsigned char **mark;
In the 16-bit version of this structure, the mark field has type
"PCRE_UCHAR16 **".
In the 32-bit version of this structure, the mark field has type
"PCRE_UCHAR32 **".
The flags field is used to specify which of the other fields are
set. The flag bits are:
PCRE_EXTRA_CALLOUT_DATA
PCRE_EXTRA_EXECUTABLE_JIT
PCRE_EXTRA_MARK
PCRE_EXTRA_MATCH_LIMIT
PCRE_EXTRA_MATCH_LIMIT_RECURSION
PCRE_EXTRA_STUDY_DATA
PCRE_EXTRA_TABLES
Other flag bits should be set to zero. The study_data field and
sometimes the executable_jit field are set in the pcre_extra
block that is returned by pcre_study(), together with the
appropriate flag bits. You should not set these yourself, but you
may add to the block by setting other fields and their
corresponding flag bits.
The match_limit field provides a means of preventing PCRE from
using up a vast amount of resources when running patterns that
are not going to match, but which have a very large number of
possibilities in their search trees. The classic example is a
pattern that uses nested unlimited repeats.
Internally, pcre_exec() uses a function called match(), which it
calls repeatedly (sometimes recursively). The limit set by
match_limit is imposed on the number of times this function is
called during a match, which has the effect of limiting the
amount of backtracking that can take place. For patterns that are
not anchored, the count restarts from zero for each position in
the subject string.
When pcre_exec() is called with a pattern that was successfully
studied with a JIT option, the way that the matching is executed
is entirely different. However, there is still the possibility
of runaway matching that goes on for a very long time, and so the
match_limit value is also used in this case (but in a different
way) to limit how long the matching can continue.
The default value for the limit can be set when PCRE is built;
the default default is 10 million, which handles all but the most
extreme cases. You can override the default by supplying
pcre_exec() with a pcre_extra block in which match_limit is set,
and PCRE_EXTRA_MATCH_LIMIT is set in the flags field. If the
limit is exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
A value for the match limit may also be supplied by an item at
the start of a pattern of the form
(*LIMIT_MATCH=d)
where d is a decimal number. However, such a setting is ignored
unless d is less than the limit set by the caller of pcre_exec()
or, if no such limit is set, less than the default.
The match_limit_recursion field is similar to match_limit, but
instead of limiting the total number of times that match() is
called, it limits the depth of recursion. The recursion depth is
a smaller number than the total number of calls, because not all
calls to match() are recursive. This limit is of use only if it
is set smaller than match_limit.
Limiting the recursion depth limits the amount of machine stack
that can be used, or, when PCRE has been compiled to use memory
on the heap instead of the stack, the amount of heap memory that
can be used. This limit is not relevant, and is ignored, when
matching is done using JIT compiled code.
The default value for match_limit_recursion can be set when PCRE
is built; the default default is the same value as the default
for match_limit. You can override the default by supplying
pcre_exec() with a pcre_extra block in which
match_limit_recursion is set, and
PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the flags field. If
the limit is exceeded, pcre_exec() returns
PCRE_ERROR_RECURSIONLIMIT.
A value for the recursion limit may also be supplied by an item
at the start of a pattern of the form
(*LIMIT_RECURSION=d)
where d is a decimal number. However, such a setting is ignored
unless d is less than the limit set by the caller of pcre_exec()
or, if no such limit is set, less than the default.
The callout_data field is used in conjunction with the "callout"
feature, and is described in the pcrecallout documentation.
The tables field is provided for use with patterns that have been
pre-compiled using custom character tables, saved to disc or
elsewhere, and then reloaded, because the tables that were used
to compile a pattern are not saved with it. See the
pcreprecompile documentation for a discussion of saving compiled
patterns for later use. If NULL is passed using this mechanism,
it forces PCRE's internal tables to be used.
Warning: The tables that pcre_exec() uses must be the same as
those that were used when the pattern was compiled. If this is
not the case, the behaviour of pcre_exec() is undefined.
Therefore, when a pattern is compiled and matched in the same
process, this field should never be set. In this (the most
common) case, the correct table pointer is automatically passed
with the compiled pattern from pcre_compile() to pcre_exec().
If PCRE_EXTRA_MARK is set in the flags field, the mark field must
be set to point to a suitable variable. If the pattern contains
any backtracking control verbs such as (*MARK:NAME), and the
execution ends up with a name to pass back, a pointer to the name
string (zero terminated) is placed in the variable pointed to by
the mark field. The names are within the compiled pattern; if you
wish to retain such a name you must copy it before freeing the
memory of a compiled pattern. If there is no name to pass back,
the variable pointed to by the mark field is set to NULL. For
details of the backtracking control verbs, see the section
entitled "Backtracking control" in the pcrepattern documentation.
Option bits for pcre_exec()
The unused bits of the options argument for pcre_exec() must be
zero. The only bits that may be set are PCRE_ANCHORED,
PCRE_NEWLINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,
PCRE_NOTEMPTY_ATSTART, PCRE_NO_START_OPTIMIZE,
PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_HARD, and PCRE_PARTIAL_SOFT.
If the pattern was successfully studied with one of the just-in-
time (JIT) compile options, the only supported options for JIT
execution are PCRE_NO_UTF8_CHECK, PCRE_NOTBOL, PCRE_NOTEOL,
PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART, PCRE_PARTIAL_HARD, and
PCRE_PARTIAL_SOFT. If an unsupported option is used, JIT
execution is disabled and the normal interpretive code in
pcre_exec() is run.
PCRE_ANCHORED
The PCRE_ANCHORED option limits pcre_exec() to matching at the
first matching position. If a pattern was compiled with
PCRE_ANCHORED, or turned out to be anchored by virtue of its
contents, it cannot be made unachored at matching time.
PCRE_BSR_ANYCRLF
PCRE_BSR_UNICODE
These options (which are mutually exclusive) control what the \R
escape sequence matches. The choice is either to match only CR,
LF, or CRLF, or to match any Unicode newline sequence. These
options override the choice that was made or defaulted when the
pattern was compiled.
PCRE_NEWLINE_CR
PCRE_NEWLINE_LF
PCRE_NEWLINE_CRLF
PCRE_NEWLINE_ANYCRLF
PCRE_NEWLINE_ANY
These options override the newline definition that was chosen or
defaulted when the pattern was compiled. For details, see the
description of pcre_compile() above. During matching, the newline
choice affects the behaviour of the dot, circumflex, and dollar
metacharacters. It may also alter the way the match position is
advanced after a match failure for an unanchored pattern.
When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY
is set, and a match attempt for an unanchored pattern fails when
the current 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
PCRE_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, or one of the \r or \n escape sequences.
Implicit matches such as [^X] do not count, nor does \s (which
includes CR and LF in the characters that it matches).
Notwithstanding the above, anomalous effects may still occur when
CRLF is a valid newline sequence and explicit \r or \n escapes
appear in the pattern.
PCRE_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 PCRE_MULTILINE
(at compile time) causes circumflex never to match. This option
affects only the behaviour of the circumflex metacharacter. It
does not affect \A.
PCRE_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 PCRE_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.
PCRE_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 PCRE_NOTEMPTY
set, this match is not valid, so PCRE searches further into the
string for occurrences of "a" or "b".
PCRE_NOTEMPTY_ATSTART
This is like PCRE_NOTEMPTY, except that an empty string match
that is not at the start of the subject is permitted. If the
pattern is anchored, such a match can occur only if the pattern
contains \K.
Perl has no direct equivalent of PCRE_NOTEMPTY or
PCRE_NOTEMPTY_ATSTART, but it does make a special case of a
pattern match of the empty string within its split() function,
and when using the /g modifier. It is possible to emulate Perl's
behaviour after matching a null string by first trying the match
again at the same offset with PCRE_NOTEMPTY_ATSTART and
PCRE_ANCHORED, and then if that fails, by advancing the starting
offset (see below) and trying an ordinary match again. There is
some code that demonstrates how to do this in the pcredemo 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.
PCRE_NO_START_OPTIMIZE
There are a number of optimizations that pcre_exec() uses at the
start of a match, in order to speed up the process. For example,
if it is known that an unanchored match must start with a
specific character, it searches the subject for that character,
and fails immediately if it cannot find it, without actually
running the main matching function. This means that a special
item such as (*COMMIT) at the start of a pattern is not
considered until after a suitable starting point for the match
has been found. Also, when callouts or (*MARK) items are in use,
these "start-up" optimizations can cause them to be skipped if
the pattern is never actually used. The start-up optimizations
are in effect a pre-scan of the subject that takes place before
the pattern is run.
The PCRE_NO_START_OPTIMIZE option disables the start-up
optimizations, possibly causing performance to suffer, but
ensuring that in cases where the result is "no match", the
callouts do occur, and that items such as (*COMMIT) and (*MARK)
are considered at every possible starting position in the subject
string. If PCRE_NO_START_OPTIMIZE is set at compile time, it
cannot be unset at matching time. The use of
PCRE_NO_START_OPTIMIZE at matching time (that is, passing it to
pcre_exec()) disables JIT execution; in this situation, matching
is always done using interpretively.
Setting PCRE_NO_START_OPTIMIZE can change the outcome of a
matching operation. Consider the pattern
(*COMMIT)ABC
When this is compiled, PCRE records the fact that a match must
start with the character "A". Suppose the subject string is
"DEFABC". The start-up optimization scans along the subject,
finds "A" and runs the first match attempt from there. The
(*COMMIT) item means that the pattern must match the current
starting position, which in this case, it does. However, if the
same match is run with PCRE_NO_START_OPTIMIZE set, the initial
scan along the subject string does not happen. The first match
attempt is run starting from "D" and when this fails, (*COMMIT)
prevents any further matches being tried, so the overall result
is "no match". If the pattern is studied, more start-up
optimizations may be used. For example, a minimum length for the
subject may be recorded. Consider the pattern
(*MARK:A)(X|Y)
The minimum length for a match is one character. If the subject
is "ABC", there will be attempts to match "ABC", "BC", "C", and
then finally an empty string. If the pattern is studied, the
final attempt does not take place, because PCRE knows that the
subject is too short, and so the (*MARK) is never encountered.
In this case, studying the pattern does not affect the overall
match result, which is still "no match", but it does affect the
auxiliary information that is returned.
PCRE_NO_UTF8_CHECK
When PCRE_UTF8 is set at compile time, the validity of the
subject as a UTF-8 string is automatically checked when
pcre_exec() is subsequently called. The entire string is checked
before any other processing takes place. The value of startoffset
is also checked to ensure that it points to the start of a UTF-8
character. There is a discussion about the validity of UTF-8
strings in the pcreunicode page. If an invalid sequence of bytes
is found, pcre_exec() returns the error PCRE_ERROR_BADUTF8 or, if
PCRE_PARTIAL_HARD is set and the problem is a truncated character
at the end of the subject, PCRE_ERROR_SHORTUTF8. In both cases,
information about the precise nature of the error may also be
returned (see the descriptions of these errors in the section
entitled Error return values from pcre_exec() below). If
startoffset contains a value that does not point to the start of
a UTF-8 character (or to the end of the subject),
PCRE_ERROR_BADUTF8_OFFSET is returned.
If you already know that your subject is valid, and you want to
skip these checks for performance reasons, you can set the
PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might
want to do this for the second and subsequent calls to
pcre_exec() if you are making repeated calls to find all the
matches in a single subject string. However, you should be sure
that the value of startoffset points to the start of a character
(or the end of the subject). When PCRE_NO_UTF8_CHECK is set, the
effect of passing an invalid string as a subject or an invalid
value of startoffset is undefined. Your program may crash or
loop.
PCRE_PARTIAL_HARD
PCRE_PARTIAL_SOFT
These options turn on the partial matching feature. For backwards
compatibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A
partial match occurs if the end of the subject string is reached
successfully, but there are not enough subject characters to
complete the match. If this happens when PCRE_PARTIAL_SOFT (but
not PCRE_PARTIAL_HARD) is set, matching continues by testing any
remaining alternatives. Only if no complete match can be found is
PCRE_ERROR_PARTIAL returned instead of PCRE_ERROR_NOMATCH. In
other words, PCRE_PARTIAL_SOFT says that the caller is prepared
to handle a partial match, but only if no complete match can be
found.
If PCRE_PARTIAL_HARD is set, it overrides PCRE_PARTIAL_SOFT. In
this case, if a partial match is found, pcre_exec() immediately
returns PCRE_ERROR_PARTIAL, without considering any other
alternatives. In other words, when PCRE_PARTIAL_HARD is set, a
partial match is considered to be more important that an
alternative complete match.
In both cases, the portion of the string that was inspected when
the partial match was found is set as the first matching string.
There is a more detailed discussion of partial and multi-segment
matching, with examples, in the pcrepartial documentation.
The string to be matched by pcre_exec()
The subject string is passed to pcre_exec() as a pointer in
subject, a length in length, and a starting offset in
startoffset. The units for length and startoffset are bytes for
the 8-bit library, 16-bit data items for the 16-bit library, and
32-bit data items for the 32-bit library.
If startoffset is negative or greater than the length of the
subject, pcre_exec() returns PCRE_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 offset must point to the start
of a character, or the end of the subject (in UTF-32 mode, one
data unit equals one character, so all offsets are valid). Unlike
the pattern string, the subject may contain binary zeroes.
A non-zero starting offset is useful when searching for another
match in the same subject by calling pcre_exec() again after a
previous success. Setting startoffset differs from just passing
over a shortened string and setting PCRE_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 pcre_exec() finds the first occurrence. If pcre_exec() 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 pcre_exec() 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 PCRE_NOTEMPTY_ATSTART and PCRE_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 pcredemo sample program. In the most general case,
you have to check to see if the newline convention recognizes
CRLF as a newline, and if so, and the current character is CR
followed by LF, advance the starting offset by two characters
instead of one.
If a non-zero starting offset is passed when the pattern is
anchored, one attempt to match at the given offset is made. This
can only succeed if the pattern does not require the match to be
at the start of the subject.
How pcre_exec() returns captured substrings
In general, a pattern matches a certain portion of the subject,
and in addition, further substrings from the subject may be
picked out by parts of the pattern. Following the usage in
Jeffrey Friedl's book, this is called "capturing" in what
follows, and the phrase "capturing subpattern" is used for a
fragment of a pattern that picks out a substring. PCRE supports
several other kinds of parenthesized subpattern that do not cause
substrings to be captured.
Captured substrings are returned to the caller via a vector of
integers whose address is passed in ovector. The number of
elements in the vector is passed in ovecsize, which must be a
non-negative number. Note: this argument is NOT the size of
ovector in bytes.
The first two-thirds of the vector is used to pass back captured
substrings, each substring using a pair of integers. The
remaining third of the vector is used as workspace by pcre_exec()
while matching capturing subpatterns, and is not available for
passing back information. The number passed in ovecsize should
always be a multiple of three. If it is not, it is rounded down.
When a match is successful, information about captured substrings
is returned in pairs of integers, starting at the beginning of
ovector, and continuing up to two-thirds of its length at the
most. The first element of each pair is set to the offset of the
first character in a substring, and the second is set to the
offset of the first character after the end of a substring. These
values are always data unit offsets, even in UTF mode. They are
byte offsets in the 8-bit library, 16-bit data item offsets in
the 16-bit library, and 32-bit data item offsets in the 32-bit
library. Note: they are not character counts.
The first pair of integers, ovector[0] and ovector[1], identify
the portion of the subject string matched by the entire pattern.
The next pair is used for the first capturing subpattern, and so
on. The value returned by pcre_exec() is one more than the
highest numbered pair that has been set. For example, if two
substrings have been captured, the returned value is 3. If there
are no capturing subpatterns, the return value from a successful
match is 1, indicating that just the first pair of offsets has
been set.
If a capturing subpattern is matched repeatedly, it is the last
portion of the string that it matched that is returned.
If the vector is too small to hold all the captured substring
offsets, it is used as far as possible (up to two-thirds of its
length), and the function returns a value of zero. If neither the
actual string matched nor any captured substrings are of
interest, pcre_exec() may be called with ovector passed as NULL
and ovecsize as zero. However, if the pattern contains back
references and the ovector is not big enough to remember the
related substrings, PCRE has to get additional memory for use
during matching. Thus it is usually advisable to supply an
ovector of reasonable size.
There are some cases where zero is returned (indicating vector
overflow) when in fact the vector is exactly the right size for
the final match. For example, consider the pattern
(a)(?:(b)c|bd)
If a vector of 6 elements (allowing for only 1 captured
substring) is given with subject string "abd", pcre_exec() will
try to set the second captured string, thereby recording a vector
overflow, before failing to match "c" and backing up to try the
second alternative. The zero return, however, does correctly
indicate that the maximum number of slots (namely 2) have been
filled. In similar cases where there is temporary overflow, but
the final number of used slots is actually less than the maximum,
a non-zero value is returned.
The pcre_fullinfo() function can be used to find out how many
capturing subpatterns there are in a compiled pattern. The
smallest size for ovector that will allow for n captured
substrings, in addition to the offsets of the substring matched
by the whole pattern, is (n+1)*3.
It is possible for capturing subpattern number n+1 to match some
part of the subject when subpattern n has not been used at all.
For example, if the string "abc" is matched against the pattern
(a|(z))(bc) the return from the function is 4, and subpatterns 1
and 3 are matched, but 2 is not. When this happens, both values
in the offset pairs corresponding to unused subpatterns are set
to -1.
Offset values that correspond to unused subpatterns at the end of
the expression are also set to -1. For example, if the string
"abc" is matched against the pattern (abc)(x(yz)?)? subpatterns 2
and 3 are not matched. The return from the function is 2, because
the highest used capturing subpattern number is 1, and the
offsets for for the second and third capturing subpatterns
(assuming the vector is large enough, of course) are set to -1.
Note: Elements in the first two-thirds of 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 pcre_exec().
The other elements (in the first two-thirds) retain whatever
values they previously had.
Some convenience functions are provided for extracting the
captured substrings as separate strings. These are described
below.
Error return values from pcre_exec()
If pcre_exec() fails, it returns a negative number. The following
are defined in the header file:
PCRE_ERROR_NOMATCH (-1)
The subject string did not match the pattern.
PCRE_ERROR_NULL (-2)
Either code or subject was passed as NULL, or ovector was NULL
and ovecsize was not zero.
PCRE_ERROR_BADOPTION (-3)
An unrecognized bit was set in the options argument.
PCRE_ERROR_BADMAGIC (-4)
PCRE stores a 4-byte "magic number" at the start of the compiled
code, to catch the case when it is passed a junk pointer and to
detect when a pattern that was compiled in an environment of one
endianness is run in an environment with the other endianness.
This is the error that PCRE gives when the magic number is not
present.
PCRE_ERROR_UNKNOWN_OPCODE (-5)
While running the pattern match, an unknown item was encountered
in the compiled pattern. This error could be caused by a bug in
PCRE or by overwriting of the compiled pattern.
PCRE_ERROR_NOMEMORY (-6)
If a pattern contains back references, but the ovector that is
passed to pcre_exec() is not big enough to remember the
referenced substrings, PCRE gets a block of memory at the start
of matching to use for this purpose. If the call via
pcre_malloc() fails, this error is given. The memory is
automatically freed at the end of matching.
This error is also given if pcre_stack_malloc() fails in
pcre_exec(). This can happen only when PCRE has been compiled
with --disable-stack-for-recursion.
PCRE_ERROR_NOSUBSTRING (-7)
This error is used by the pcre_copy_substring(),
pcre_get_substring(), and pcre_get_substring_list() functions
(see below). It is never returned by pcre_exec().
PCRE_ERROR_MATCHLIMIT (-8)
The backtracking limit, as specified by the match_limit field in
a pcre_extra structure (or defaulted) was reached. See the
description above.
PCRE_ERROR_CALLOUT (-9)
This error is never generated by pcre_exec() itself. It is
provided for use by callout functions that want to yield a
distinctive error code. See the pcrecallout documentation for
details.
PCRE_ERROR_BADUTF8 (-10)
A string that contains an invalid UTF-8 byte sequence was passed
as a subject, and the PCRE_NO_UTF8_CHECK option was not set. If
the size of the output vector (ovecsize) is at least 2, the byte
offset to the start of the the invalid UTF-8 character is placed
in the first element, and a reason code is placed in the second
element. The reason codes are listed in the following section.
For backward compatibility, if PCRE_PARTIAL_HARD is set and the
problem is a truncated UTF-8 character at the end of the subject
(reason codes 1 to 5), PCRE_ERROR_SHORTUTF8 is returned instead
of PCRE_ERROR_BADUTF8.
PCRE_ERROR_BADUTF8_OFFSET (-11)
The UTF-8 byte sequence that was passed as a subject was checked
and found to be valid (the PCRE_NO_UTF8_CHECK option was not
set), but the value of startoffset did not point to the beginning
of a UTF-8 character or the end of the subject.
PCRE_ERROR_PARTIAL (-12)
The subject string did not match, but it did match partially. See
the pcrepartial documentation for details of partial matching.
PCRE_ERROR_BADPARTIAL (-13)
This code is no longer in use. It was formerly returned when the
PCRE_PARTIAL option was used with a compiled pattern containing
items that were not supported for partial matching. From release
8.00 onwards, there are no restrictions on partial matching.
PCRE_ERROR_INTERNAL (-14)
An unexpected internal error has occurred. This error could be
caused by a bug in PCRE or by overwriting of the compiled
pattern.
PCRE_ERROR_BADCOUNT (-15)
This error is given if the value of the ovecsize argument is
negative.
PCRE_ERROR_RECURSIONLIMIT (-21)
The internal recursion limit, as specified by the
match_limit_recursion field in a pcre_extra structure (or
defaulted) was reached. See the description above.
PCRE_ERROR_BADNEWLINE (-23)
An invalid combination of PCRE_NEWLINE_xxx options was given.
PCRE_ERROR_BADOFFSET (-24)
The value of startoffset was negative or greater than the length
of the subject, that is, the value in length.
PCRE_ERROR_SHORTUTF8 (-25)
This error is returned instead of PCRE_ERROR_BADUTF8 when the
subject string ends with a truncated UTF-8 character and the
PCRE_PARTIAL_HARD option is set. Information about the failure
is returned as for PCRE_ERROR_BADUTF8. It is in fact sufficient
to detect this case, but this special error code for
PCRE_PARTIAL_HARD precedes the implementation of returned
information; it is retained for backwards compatibility.
PCRE_ERROR_RECURSELOOP (-26)
This error is returned when pcre_exec() detects a recursion loop
within the pattern. Specifically, it means that either the whole
pattern or a subpattern has been called recursively for the
second time at the same position in the subject string. Some
simple patterns that might do this are detected and faulted at
compile time, but more complicated cases, in particular mutual
recursions between two different subpatterns, cannot be detected
until run time.
PCRE_ERROR_JIT_STACKLIMIT (-27)
This error is returned when a pattern that was successfully
studied using a JIT compile option is being matched, but the
memory available for the just-in-time processing stack is not
large enough. See the pcrejit documentation for more details.
PCRE_ERROR_BADMODE (-28)
This error is given if a pattern that was compiled by the 8-bit
library is passed to a 16-bit or 32-bit library function, or vice
versa.
PCRE_ERROR_BADENDIANNESS (-29)
This error is given if a pattern that was compiled and saved is
reloaded on a host with different endianness. The utility
function pcre_pattern_to_host_byte_order() can be used to convert
such a pattern so that it runs on the new host.
PCRE_ERROR_JIT_BADOPTION
This error is returned when a pattern that was successfully
studied using a JIT compile option is being matched, but the
matching mode (partial or complete match) does not correspond to
any JIT compilation mode. When the JIT fast path function is
used, this error may be also given for invalid options. See the
pcrejit documentation for more details.
PCRE_ERROR_BADLENGTH (-32)
This error is given if pcre_exec() is called with a negative
value for the length argument.
Error numbers -16 to -20, -22, and 30 are not used by
pcre_exec().
Reason codes for invalid UTF-8 strings
This section applies only to the 8-bit library. The corresponding
information for the 16-bit and 32-bit libraries is given in the
pcre16 and pcre32 pages.
When pcre_exec() returns either PCRE_ERROR_BADUTF8 or
PCRE_ERROR_SHORTUTF8, and the size of the output vector
(ovecsize) is at least 2, the offset of the start of the invalid
UTF-8 character is placed in the first output vector element
(ovector[0]) and a reason code is placed in the second element
(ovector[1]). The reason codes are given names in the pcre.h
header file:
PCRE_UTF8_ERR1
PCRE_UTF8_ERR2
PCRE_UTF8_ERR3
PCRE_UTF8_ERR4
PCRE_UTF8_ERR5
The string ends with a truncated UTF-8 character; the code
specifies how many bytes are missing (1 to 5). Although RFC 3629
restricts UTF-8 characters to be no longer than 4 bytes, the
encoding scheme (originally defined by RFC 2279) allows for up to
6 bytes, and this is checked first; hence the possibility of 4 or
5 missing bytes.
PCRE_UTF8_ERR6
PCRE_UTF8_ERR7
PCRE_UTF8_ERR8
PCRE_UTF8_ERR9
PCRE_UTF8_ERR10
The two most significant bits of the 2nd, 3rd, 4th, 5th, or 6th
byte of the character do not have the binary value 0b10 (that is,
either the most significant bit is 0, or the next bit is 1).
PCRE_UTF8_ERR11
PCRE_UTF8_ERR12
A character that is valid by the RFC 2279 rules is either 5 or 6
bytes long; these code points are excluded by RFC 3629.
PCRE_UTF8_ERR13
A 4-byte character has a value greater than 0x10fff; these code
points are excluded by RFC 3629.
PCRE_UTF8_ERR14
A 3-byte character has a value in the range 0xd800 to 0xdfff;
this range of code points are reserved by RFC 3629 for use with
UTF-16, and so are excluded from UTF-8.
PCRE_UTF8_ERR15
PCRE_UTF8_ERR16
PCRE_UTF8_ERR17
PCRE_UTF8_ERR18
PCRE_UTF8_ERR19
A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it
codes for a value that can be represented by fewer bytes, which
is invalid. For example, the two bytes 0xc0, 0xae give the value
0x2e, whose correct coding uses just one byte.
PCRE_UTF8_ERR20
The two most significant bits of the first byte of a character
have the binary value 0b10 (that is, the most significant bit is
1 and the second is 0). Such a byte can only validly occur as the
second or subsequent byte of a multi-byte character.
PCRE_UTF8_ERR21
The first byte of a character has the value 0xfe or 0xff. These
values can never occur in a valid UTF-8 string.
PCRE_UTF8_ERR22
This error code was formerly used when the presence of a so-
called "non-character" caused an error. Unicode corrigendum #9
makes it clear that such characters should not cause a string to
be rejected, and so this code is no longer in use and is never
returned.
int pcre_copy_substring(const char *subject, int *ovector,
int stringcount, int stringnumber, char *buffer,
int buffersize);
int pcre_get_substring(const char *subject, int *ovector,
int stringcount, int stringnumber,
const char **stringptr);
int pcre_get_substring_list(const char *subject,
int *ovector, int stringcount, const char ***listptr);
Captured substrings can be accessed directly by using the offsets
returned by pcre_exec() in ovector. For convenience, the
functions pcre_copy_substring(), pcre_get_substring(), and
pcre_get_substring_list() are provided for extracting captured
substrings as new, separate, zero-terminated strings. These
functions identify substrings by number. The next section
describes functions for extracting named substrings.
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. However, you can process such a string by
referring to the length that is returned by pcre_copy_substring()
and pcre_get_substring(). Unfortunately, the interface to
pcre_get_substring_list() is not adequate for handling strings
containing binary zeros, because the end of the final string is
not independently indicated.
The first three arguments are the same for all three of these
functions: subject is the subject string that has just been
successfully matched, ovector is a pointer to the vector of
integer offsets that was passed to pcre_exec(), and stringcount
is the number of substrings that were captured by the match,
including the substring that matched the entire regular
expression. This is the value returned by pcre_exec() if it is
greater than zero. If pcre_exec() returned zero, indicating that
it ran out of space in ovector, the value passed as stringcount
should be the number of elements in the vector divided by three.
The functions pcre_copy_substring() and pcre_get_substring()
extract a single substring, whose number is given as
stringnumber. A value of zero extracts the substring that matched
the entire pattern, whereas higher values extract the captured
substrings. For pcre_copy_substring(), the string is placed in
buffer, whose length is given by buffersize, while for
pcre_get_substring() a new block of memory is obtained via
pcre_malloc, and its address is returned via stringptr. The yield
of the function is the length of the string, not including the
terminating zero, or one of these error codes:
PCRE_ERROR_NOMEMORY (-6)
The buffer was too small for pcre_copy_substring(), or the
attempt to get memory failed for pcre_get_substring().
PCRE_ERROR_NOSUBSTRING (-7)
There is no substring whose number is stringnumber.
The pcre_get_substring_list() function extracts all available
substrings and builds a list of pointers to them. All this is
done in a single block of memory that is obtained via
pcre_malloc. 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 yield of the
function is zero if all went well, or the error code
PCRE_ERROR_NOMEMORY (-6)
if the attempt to get the memory block failed.
When any of these functions encounter a substring that is unset,
which can happen when capturing subpattern number n+1 matches
some part of the subject, but subpattern n has not been used at
all, they return an empty string. This can be distinguished from
a genuine zero-length substring by inspecting the appropriate
offset in ovector, which is negative for unset substrings.
The two convenience functions pcre_free_substring() and
pcre_free_substring_list() can be used to free the memory
returned by a previous call of pcre_get_substring() or
pcre_get_substring_list(), respectively. They do nothing more
than call the function pointed to by pcre_free, which of course
could be called directly from a C program. However, PCRE is used
in some situations where it is linked via a special interface to
another programming language that cannot use pcre_free directly;
it is for these cases that the functions are provided.
int pcre_get_stringnumber(const pcre *code,
const char *name);
int pcre_copy_named_substring(const pcre *code,
const char *subject, int *ovector,
int stringcount, const char *stringname,
char *buffer, int buffersize);
int pcre_get_named_substring(const pcre *code,
const char *subject, int *ovector,
int stringcount, const char *stringname,
const char **stringptr);
To extract a substring by name, you first have to find associated
number. For example, for this pattern
(a+)b(?<xxx>\d+)...
the number of the subpattern called "xxx" is 2. If the name is
known to be unique (PCRE_DUPNAMES was not set), you can find the
number from the name by calling pcre_get_stringnumber(). The
first argument is the compiled pattern, and the second is the
name. The yield of the function is the subpattern number, or
PCRE_ERROR_NOSUBSTRING (-7) if there is no subpattern of that
name.
Given the number, you can extract the substring directly, or use
one of the functions described in the previous section. For
convenience, there are also two functions that do the whole job.
Most of the arguments of pcre_copy_named_substring() and
pcre_get_named_substring() are the same as those for the
similarly named functions that extract by number. As these are
described in the previous section, they are not re-described
here. There are just two differences:
First, instead of a substring number, a substring name is given.
Second, there is an extra argument, given at the start, which is
a pointer to the compiled pattern. This is needed in order to
gain access to the name-to-number translation table.
These functions call pcre_get_stringnumber(), and if it succeeds,
they then call pcre_copy_substring() or pcre_get_substring(), as
appropriate. NOTE: If PCRE_DUPNAMES is set and there are
duplicate names, the behaviour may not be what you want (see the
next section).
Warning: If the pattern uses the (?| feature to set up multiple
subpatterns with the same number, as described in the section on
duplicate subpattern numbers in the pcrepattern page, you cannot
use names to distinguish the different subpatterns, because names
are not included in the compiled code. The matching process uses
only numbers. For this reason, the use of different names for
subpatterns of the same number causes an error at compile time.
int pcre_get_stringtable_entries(const pcre *code,
const char *name, char **first, char **last);
When a pattern is compiled with the PCRE_DUPNAMES option, names
for subpatterns are not required to be unique. (Duplicate names
are always allowed for subpatterns with the same number, created
by using the (?| feature. Indeed, if such subpatterns are named,
they are required to use the same names.)
Normally, patterns with duplicate names are such that in any one
match, only one of the named subpatterns participates. An example
is shown in the pcrepattern documentation.
When duplicates are present, pcre_copy_named_substring() and
pcre_get_named_substring() return the first substring
corresponding to the given name that is set. If none are set,
PCRE_ERROR_NOSUBSTRING (-7) is returned; no data is returned. The
pcre_get_stringnumber() function returns one of the numbers that
are associated with the name, but it is not defined which it is.
If you want to get full details of all captured substrings for a
given name, you must use the pcre_get_stringtable_entries()
function. The first argument is the compiled pattern, and the
second is the name. The third and fourth are pointers to
variables which 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. The function itself returns the length
of each entry, or PCRE_ERROR_NOSUBSTRING (-7) if there are none.
The format of the table is described above in the section
entitled Information about a pattern above. Given all the
relevant entries for the name, you can extract each of their
numbers, and hence the captured data, if any.
The traditional matching function uses a similar algorithm to
Perl, which stops when it finds the first match, starting at a
given point in the subject. If you want to find all possible
matches, or the longest possible match, consider using the
alternative matching function (see below) instead. If you cannot
use the alternative function, but still need to find all possible
matches, you can kludge it up by making use of the callout
facility, which is described in the pcrecallout 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
pcre_exec() to backtrack and try other alternatives. Ultimately,
when it runs out of matches, pcre_exec() will yield
PCRE_ERROR_NOMATCH.
Matching certain patterns using pcre_exec() can use a lot of
process stack, which in certain environments can be rather
limited in size. Some users find it helpful to have an estimate
of the amount of stack that is used by pcre_exec(), to help them
set recursion limits, as described in the pcrestack
documentation. The estimate that is output by pcretest when
called with the -m and -C options is obtained by calling
pcre_exec with the values NULL, NULL, NULL, -999, and -999 for
its first five arguments.
Normally, if its first argument is NULL, pcre_exec() immediately
returns the negative error code PCRE_ERROR_NULL, but with this
special combination of arguments, it returns instead a negative
number whose absolute value is the approximate stack frame size
in bytes. (A negative number is used so that it is clear that no
match has happened.) The value is approximate because in some
cases, recursive calls to pcre_exec() occur when there are one or
two additional variables on the stack.
If PCRE has been compiled to use the heap instead of the stack
for recursion, the value returned is the size of each block that
is obtained from the heap.
int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
const char *subject, int length, int startoffset,
int options, int *ovector, int ovecsize,
int *workspace, int wscount);
The function pcre_dfa_exec() is called to match a subject string
against a compiled pattern, using a matching algorithm that scans
the subject string just once, and does not backtrack. This has
different characteristics to the normal algorithm, and is not
compatible with Perl. Some of the features of PCRE 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 pcre_dfa_exec() does not
support, see the pcrematching documentation.
The arguments for the pcre_dfa_exec() function are the same as
for pcre_exec(), plus two extras. The ovector argument is used in
a different way, and this is described below. The other common
arguments are used in the same way as for pcre_exec(), 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 will be needed for patterns and subjects
where there are a lot of potential matches.
Here is an example of a simple call to pcre_dfa_exec():
int rc;
int ovector[10];
int wspace[20];
rc = pcre_dfa_exec(
re, /* result of pcre_compile() */
NULL, /* we didn't study the pattern */
"some string", /* the subject string */
11, /* the length of the subject string */
0, /* start at offset 0 in the subject */
0, /* default options */
ovector, /* vector of integers for substring
information */
10, /* number of elements (NOT size in bytes) */
wspace, /* working space vector */
20); /* number of elements (NOT size in bytes) */
Option bits for pcre_dfa_exec()
The unused bits of the options argument for pcre_dfa_exec() must
be zero. The only bits that may be set are PCRE_ANCHORED,
PCRE_NEWLINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,
PCRE_NOTEMPTY_ATSTART, PCRE_NO_UTF8_CHECK, PCRE_BSR_ANYCRLF,
PCRE_BSR_UNICODE, PCRE_NO_START_OPTIMIZE, PCRE_PARTIAL_HARD,
PCRE_PARTIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All
but the last four of these are exactly the same as for
pcre_exec(), so their description is not repeated here.
PCRE_PARTIAL_HARD
PCRE_PARTIAL_SOFT
These have the same general effect as they do for pcre_exec(),
but the details are slightly different. When PCRE_PARTIAL_HARD is
set for pcre_dfa_exec(), it returns PCRE_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 also been found. When
PCRE_PARTIAL_SOFT is set, the return code PCRE_ERROR_NOMATCH is
converted into PCRE_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 pcrepartial documentation.
PCRE_DFA_SHORTEST
Setting the PCRE_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.
PCRE_DFA_RESTART
When pcre_dfa_exec() returns a partial match, it is possible to
call it again, with additional subject characters, and have it
continue with the same match. The PCRE_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 pcrepartial
documentation.
Successful returns from pcre_dfa_exec()
When pcre_dfa_exec() 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> <something else>
<something> <something else> <something further>
On success, the yield of the function is a number greater than
zero, which is the number of matched substrings. The substrings
themselves are returned in ovector. Each string uses two
elements; the first is the offset to the start, and the second is
the offset to the end. In fact, all the strings have the same
start offset. (Space could have been saved by giving this only
once, but it was decided to retain some compatibility with the
way pcre_exec() returns data, even though the meaning of the
strings is different.)
The strings are returned in reverse order of length; that is, the
longest matching string is given first. If there were too many
matches to fit into ovector, the yield of the function is zero,
and the vector is filled with the longest matches. Unlike
pcre_exec(), pcre_dfa_exec() can use the entire ovector for
returning matched strings.
NOTE: PCRE's "auto-possessification" optimization usually applies
to character repeats at the end of a pattern (as well as
internally). For example, the pattern "a\d+" is compiled as if it
were "a\d++" because there is no point even considering the
possibility of backtracking into the repeated digits. For DFA
matching, this means that only one possible match is found. If
you really do want multiple matches in such cases, either use an
ungreedy repeat ("a\d+?") or set the PCRE_NO_AUTO_POSSESS option
when compiling.
Error returns from pcre_dfa_exec()
The pcre_dfa_exec() function returns a negative number when it
fails. Many of the errors are the same as for pcre_exec(), and
these are described above. There are in addition the following
errors that are specific to pcre_dfa_exec():
PCRE_ERROR_DFA_UITEM (-16)
This return is given if pcre_dfa_exec() encounters an item in the
pattern that it does not support, for instance, the use of \C or
a back reference.
PCRE_ERROR_DFA_UCOND (-17)
This return is given if pcre_dfa_exec() encounters a condition
item that uses a back reference for the condition, or a test for
recursion in a specific group. These are not supported.
PCRE_ERROR_DFA_UMLIMIT (-18)
This return is given if pcre_dfa_exec() is called with an extra
block that contains a setting of the match_limit or
match_limit_recursion fields. This is not supported (these fields
are meaningless for DFA matching).
PCRE_ERROR_DFA_WSSIZE (-19)
This return is given if pcre_dfa_exec() runs out of space in the
workspace vector.
PCRE_ERROR_DFA_RECURSE (-20)
When a recursive subpattern is processed, the matching function
calls itself recursively, using private vectors for ovector and
workspace. This error is given if the output vector is not large
enough. This should be extremely rare, as a vector of size 1000
is used.
PCRE_ERROR_DFA_BADRESTART (-30)
When pcre_dfa_exec() is called with the PCRE_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.
pcre16(3), pcre32(3), pcrebuild(3), pcrecallout(3),
pcrecpp(3)(3), pcrematching(3), pcrepartial(3), pcreposix(3),
pcreprecompile(3), pcresample(3), pcrestack(3).
Philip Hazel
University Computing Service
Cambridge CB2 3QH, England.
Last updated: 18 December 2015
Copyright (c) 1997-2015 University of Cambridge.
This page is part of the PCRE (Perl Compatible Regular
Expressions) project. Information about the project can be found
at ⟨http://www.pcre.org/⟩. If you have a bug report for this
manual page, see
⟨http://bugs.exim.org/enter_bug.cgi?product=PCRE⟩. This page was
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man-pages@man7.org
PCRE 8.39 18 December 2015 PCREAPI(3)
Pages that refer to this page: pcretest(1), pcrebuild(3), pcrejit(3), pcrepattern(3), pcresyntax(3)
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