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) ; |
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) ; |
const
unsigned char *pcre_maketables( |
void) ; |
int
pcre_fullinfo( |
const pcre * | code, |
const pcre_extra * | extra, | |
int | what, | |
void * | where) ; |
int
pcre_info( |
const pcre * | code, |
int * | optptr, | |
int* | firstcharptr) ; |
int
pcre_refcount( |
pcre * | code, |
int | adjust) ; |
int
pcre_config( |
int | what, |
void * | where) ; |
char
*pcre_version( |
void) ; |
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
*) ; |
PCRE has its own native API, which is described in this
document. There are also some wrapper functions that
correspond to the POSIX regular expression API. These are
described in the pcreposix
documentation. Both of these APIs define a set of C function
calls. A C++ wrapper is 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 systems the 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.
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
source distribution. The pcresample
documentation describes how to
run it.
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. 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; pcre_info()
is an obsolete
version that returns only some of the available information,
but is retained for backwards compatibility. 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 are always called in a stack-like
manner (last obtained, first freed), and always for 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.
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 (formfeed, 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.
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. The choice of newline convention does not affect the interpretation of the \n or \r escape sequences.
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 function pointed to by pcre_callout
, 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.
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. 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 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.
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_NEWLINE
The output is an integer whose value specifies the default character sequence that is recognized as meaning "newline". The four values that are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF, and -1 for ANY. The default should normally be the standard sequence for your operating system.
PCRE_CONFIG_LINK_SIZE
The output is an integer that contains the number of bytes used for internal linkage in compiled regular expressions. The value is 2, 3, or 4. Larger values allow larger regular expressions to be compiled, at the expense of slower matching. 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.
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_MATCH_LIMIT
The output is an 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 an 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.
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, can also be
set and unset from within the pattern (see the detailed
description in the pcrepattern
documentation). For these options, the contents of the
options
argument
specifies their initial settings at the start of compilation
and execution. The PCRE_ANCHORED and PCRE_NEWLINE_xxx
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. The offset from the
start of the pattern to the character where 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.
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()
, unless
another table pointer is passed to it. 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_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 metacharater in the pattern matches all characters, including those that indicate newline. Without it, 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, whitespace data characters in the pattern are totally ignored except when escaped or inside a character class. Whitespace does not include the VT character (code 11). In addition, characters between an unescaped # outside a character class and the next newline, inclusive, are also ignored. This is equivalent to Perl's /x option, and it can be changed within a pattern by a (?x) option setting.
This option makes it possible to include comments inside complicated patterns. Note, however, that this applies only to data characters. Whitespace characters may never appear within special character sequences in a pattern, for example within the sequence (?( which 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 a warning for this.) 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_MULTILINE
By default, 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, while the "end of line" metacharacter ($) matches only at the end of the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY is set). This 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_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. The Unicode newline sequences are the three just mentioned, plus the single characters VT (vertical tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS (paragraph separator, U+2029). The last two are recognized only in UTF-8 mode.
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 is specially recognized when compiling a pattern is if PCRE_EXTENDED is set, and an unescaped # outside a character class is encountered. This indicates a comment that lasts until after the next line break sequence. In other circumstances, line break sequences are treated as literal data, except that in PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters and are therefore ignored.
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_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 character strings. However, it is
available only when PCRE is built to include UTF-8
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 section on UTF-8 support in
the main pcre
page.
PCRE_NO_UTF8_CHECK
When PCRE_UTF8 is set, the validity of the pattern
as a UTF-8 string is automatically checked. If an
invalid UTF-8 sequence of bytes 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. Note that this option can also be
passed to pcre_exec()
and
pcre_dfa_exec()
, to
suppress the UTF-8 validity checking of subject
strings.
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. 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 (? 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 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 not compiled with PCRE_UTF8 support 33 [this code is not in use] 34 character value in \x{...} sequence is too large 35 invalid condition (?(0) 36 \C not allowed in lookbehind assertion 37 PCRE does not support \L, \l, \N, \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 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 10,000) 50 repeated subpattern is too long 51 octal value is greater than \377 (not in 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 name or an optionally braced non-zero number 58 (?+ or (?- or (?(+ or (?(- must be followed by a non-zero number
pcre_extra *pcre_study( |
const pcre * | code, |
int optionsconst 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()
. 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 additional
information pcre_study()
returns NULL. In
that circumstance, if the calling program wants to pass any
of the other fields to pcre_exec()
, it must set up
its own pcre_extra
block.
The second argument of pcre_study()
contains option
bits. At present, no options are defined, and this argument
should always be zero.
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.
This is a typical call to pcre_study
():
pcre_extra *pe; pe = pcre_study( re, /* result of pcre_compile() */ 0, /* no options exist */ &error); /* set to NULL or points to a message */
At present, studying a pattern is useful only for non-anchored patterns that do not have a single fixed starting character. A bitmap of possible starting bytes is created.
PCRE handles caseless matching, and determines whether characters are letters, digits, or whatever, by reference to a set of tables, indexed by character value. When running in UTF-8 mode, this applies only to characters with codes less than 128. Higher-valued codes never match escapes such as \w or \d, but can be tested with \p if PCRE is built with Unicode character property support. The use of locales with Unicode is discouraged. If you are handling characters with codes greater than 128, you should either use UTF-8 and Unicode, 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()
or pcre_exec()
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 normally
also by pcre_exec()
. Thus, by
default, for any single pattern, compilation, studying and
matching all happen in the same locale, but different
patterns can be compiled in different locales.
It is possible to pass a table pointer or NULL (indicating
the use of the internal tables) to pcre_exec()
. Although not
intended for this purpose, this facility could be used to
match a pattern in a different locale from the one in which
it was compiled. Passing table pointers at run time is
discussed below in the section on matching a pattern.
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
obsolete pcre_info()
function, which
is nevertheless retained for backwards compability (and is
documented below).
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 argumentcode
was NULL the argumentwhere
was NULL PCRE_ERROR_BADMAGIC the "magic number" was not found PCRE_ERROR_BADOPTION the value ofwhat
was invalid
The "magic number" is placed at the start of each compiled
pattern as an simple check against passing an arbitrary
memory pointer. Here is a typical call of pcre_fullinfo()
, to obtain
the length of the compiled pattern:
int rc; size_t length; rc = pcre_fullinfo( re, /* result of pcre_compile() */ pe, /* 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
Return information about the first byte of any
matched string, for a non-anchored pattern. The fourth
argument should point to an int
variable. (This
option used to be called PCRE_INFO_FIRSTCHAR; the old
name is still recognized for backwards
compatibility.)
If there is a fixed first byte, for example, from a pattern such as (cat|cow|coyote), its value is returned. Otherwise, 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_FIRSTTABLE
If the pattern was studied, and this resulted in the construction of a 256-bit table indicating a fixed set of bytes for the first byte 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_JCHANGED
Return 1 if the (?J) option setting is used in the
pattern, otherwise 0. The fourth argument should point
to an int
variable. The (?J) internal option setting changes the
local PCRE_DUPNAMES option.
PCRE_INFO_LASTLITERAL
Return the value of the rightmost literal byte that
must exist in any matched string, other than at its
start, if such a byte has been recorded. The fourth
argument should point to an int
variable. If there
is no such byte, -1 is returned. For anchored patterns,
a last literal byte 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.
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 (a pointer to char
). The first two bytes of
each entry are the number of the capturing parenthesis, most
significant byte first. The rest of the entry is the
corresponding name, zero terminated. The names are in
alphabetical order. When PCRE_DUPNAMES is set, duplicate
names are in order of their parentheses numbers. For example,
consider the following pattern (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, otherwise 0. The fourth argument should point
to an int
variable. The pcrepartial
documentation lists the restrictions that apply to
patterns when partial matching is used.
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 within the
pattern itself.
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_SIZE
Return the size of the compiled pattern, that is,
the value that was passed as the argument to pcre_malloc()
when PCRE
was getting memory in which to place the compiled data.
The fourth argument should point to a size_t
variable.
PCRE_INFO_STUDYSIZE
Return the size of the data block pointed to by the
study_data
field in a pcre_extra
block. That
is, it is the value that was passed to pcre_malloc()
when PCRE
was getting memory into which to place the data created
by pcre_study()
. The
fourth argument should point to a size_t
variable.
int
pcre_info( |
const pcre * | code, |
int * | optptr, | |
int* | firstcharptr) ; |
The pcre_info()
function is now obsolete because its interface is too
restrictive to return all the available data about a compiled
pattern. New programs should use pcre_fullinfo()
instead. The
yield of pcre_info()
is the number of
capturing subpatterns, or one of the following negative
numbers:
PCRE_ERROR_NULL the argument code
was NULL
PCRE_ERROR_BADMAGIC the "magic number" was not found
If the optptr
argument is not NULL, a copy of the options with which the
pattern was compiled is placed in the integer it points to
(see PCRE_INFO_OPTIONS above).
If the pattern is not anchored and the firstcharptr
argument is not
NULL, it is used to pass back information about the first
character of any matched string (see PCRE_INFO_FIRSTBYTE
above).
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 has been studied, the result of the
study should be passed in the extra
argument. 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) */
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 intflags
; void *study_data
; unsigned long intmatch_limit
; unsigned long intmatch_limit_recursion
; void *callout_data
; const unsigned char *tables
;
The flags
field is a bitmap that specifies which of the other fields
are set. The flag bits are:
PCRE_EXTRA_STUDY_DATA PCRE_EXTRA_MATCH_LIMIT PCRE_EXTRA_MATCH_LIMIT_RECURSION PCRE_EXTRA_CALLOUT_DATA PCRE_EXTRA_TABLES
Other flag bits should be set to zero. The study_data
field is set in
the pcre_extra
block that is returned by pcre_study()
, together with
the appropriate flag bit. You should not set this yourself,
but you may add to the block by setting the 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 the use of
nested unlimited repeats.
Internally, PCRE 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.
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
suppling 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.
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 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.
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 suppling 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.
The pcre_callout
field is used
in conjunction with the "callout" feature, which is
described in the pcrecallout
documentation.
The tables
field is used to pass a character tables pointer to
pcre_exec()
; this
overrides the value that is stored with the compiled
pattern. A non-NULL value is stored with the compiled
pattern only if custom tables were supplied to pcre_compile()
via its
tableptr
argument. If NULL is passed to pcre_exec()
using this
mechanism, it forces PCRE's internal tables to be used.
This facility is helpful when re-using patterns that have
been saved after compiling with an external set of tables,
because the external tables might be at a different address
when pcre_exec()
is called. See the pcreprecompile
documentation for a
discussion of saving compiled patterns for later use.
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_NO_UTF8_CHECK
and PCRE_PARTIAL.
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_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 fails when the current position is at
a CRLF sequence, the match position is advanced by
two characters instead of one, in other words, to
after the CRLF.
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 the 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".
Perl has no direct equivalent of PCRE_NOTEMPTY, 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 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.c
sample program.
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 value of startoffset
is also
checked to ensure that it points to the start of a
UTF-8 character. If an invalid UTF-8 sequence of
bytes is found, pcre_exec()
returns
the error PCRE_ERROR_BADUTF8. If startoffset
contains
an invalid value, 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 UTF-8 character. When PCRE_NO_UTF8_CHECK is set,
the effect of passing an invalid UTF-8 string as a subject,
or a value of startoffset
that does not
point to the start of a UTF-8 character, is undefined. Your
program may crash.
PCRE_PARTIAL
This option turns on the partial matching feature.
If the subject string fails to match the pattern, but
at some point during the matching process the end of
the subject was reached (that is, the subject
partially matches the pattern and the failure to
match occurred only because there were not enough
subject characters), pcre_exec()
returns
PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH.
When PCRE_PARTIAL is used, there are restrictions on
what may appear in the pattern. These are discussed
in the pcrepartial
documentation.
pcre_exec()
The subject string is passed to pcre_exec()
as a pointer in
subject
, a length
in length
, and a
starting byte offset in startoffset
. In UTF-8 mode,
the byte offset must point to the start of a UTF-8
character. Unlike the pattern string, the subject may
contain binary zero bytes. 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.
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
"Mississipi" the first call to pcre_exec()
finds the first
occurrence. If pcre_exec()
is called again
with just the remainder of the subject, namely "issipi", it
does not match, because \B is always false at the start of
the subject, which is deemed to be a word boundary.
However, if 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.
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.
pcre_exec()
returns
captured substringsIn 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 integer offsets 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 length 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 a 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. The first pair,
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. In particular, if the substring offsets are not 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
.
The pcre_info()
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. However, you can refer to the offsets for the second and third capturing subpatterns if you wish (assuming the vector is large enough, of course).
Some convenience functions are provided for extracting the captured substrings as separate strings. These are described below.
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.
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.
PCRE_ERROR_BADUTF8_OFFSET (-11)
The UTF-8 byte sequence that was passed as a subject was
valid, but the value of startoffset
did not point
to the beginning of a UTF-8 character.
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)
The PCRE_PARTIAL option was used with a compiled pattern
containing items that are not supported for partial
matching. See the pcrepartial
documentation for details of 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_NULLWSLIMIT (-22)
When a group that can match an empty substring is repeated with an unbounded upper limit, the subject position at the start of the group must be remembered, so that a test for an empty string can be made when the end of the group is reached. Some workspace is required for this; if it runs out, this error is given.
PCRE_ERROR_BADNEWLINE (-23)
An invalid combination of PCRE_NEWLINE_xxx
options was given.
Error numbers -16 to -20 are not used by pcre_exec()
.
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).
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.
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, an empty string 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. 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.
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,
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) */
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_NO_UTF8_CHECK,
PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All
but the last three of these are the same as for pcre_exec()
, so their
description is not repeated here.
PCRE_PARTIAL
This has the same general effect as it does for
pcre_exec()
, but the
details are slightly different. When PCRE_PARTIAL is
set for pcre_dfa_exec()
, 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 provided the partial match
is set as the first matching string.
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()
is
called with the PCRE_PARTIAL option, and 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.
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.
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
field. This is
not supported (it is meaningless).
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.
pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepartial(3), pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
Last updated: 13 June 2007 Copyright (c) 1997-2007 University of Cambridge.
COPYRIGHT |
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This manual page is taken from the PCRE library, which is distributed under the BSD license. |