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version 1.1, 2012/02/21 23:05:52	version 1.1.1.3, 2012/10/09 09:19:17
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.TH PCRECALLOUT 3	.TH PCRECALLOUT 3 "08 January 2012" "PCRE 8.30"
.SH NAME	.SH NAME
PCRE - Perl-compatible regular expressions	PCRE - Perl-compatible regular expressions
.SH "PCRE CALLOUTS"	.SH "PCRE CALLOUTS"
Line 6 PCRE - Perl-compatible regular expressions	Line 6 PCRE - Perl-compatible regular expressions
.sp	.sp
.B int (pcre_callout)(pcre_callout_block );	.B int (pcre_callout)(pcre_callout_block );
.PP	.PP
	.B int (pcre16_callout)(pcre16_callout_block );
	.PP
PCRE provides a feature called "callout", which is a means of temporarily	PCRE provides a feature called "callout", which is a means of temporarily
passing control to the caller of PCRE in the middle of pattern matching. The	passing control to the caller of PCRE in the middle of pattern matching. The
caller of PCRE provides an external function by putting its entry point in the	caller of PCRE provides an external function by putting its entry point in the
global variable \fIpcre_callout\fP. By default, this variable contains NULL,	global variable \fIpcre_callout\fP (\fIpcre16_callout\fP for the 16-bit
which disables all calling out.	library). By default, this variable contains NULL, which disables all calling
	out.
.P	.P
Within a regular expression, (?C) indicates the points at which the external	Within a regular expression, (?C) indicates the points at which the external
function is to be called. Different callout points can be identified by putting	function is to be called. Different callout points can be identified by putting
Line 19 For example, this pattern has two callout points:	Line 22 For example, this pattern has two callout points:
.sp	.sp
(?C1)abc(?C2)def	(?C1)abc(?C2)def
.sp	.sp
If the PCRE_AUTO_CALLOUT option bit is set when \fBpcre_compile()\fP or	If the PCRE_AUTO_CALLOUT option bit is set when a pattern is compiled, PCRE
\fBpcre_compile2()\fP is called, PCRE automatically inserts callouts, all with	automatically inserts callouts, all with number 255, before each item in the
number 255, before each item in the pattern. For example, if PCRE_AUTO_CALLOUT	pattern. For example, if PCRE_AUTO_CALLOUT is used with the pattern
is used with the pattern
.sp	.sp
A(\ed{2}\|--)	A(\ed{2}\|--)
.sp	.sp
Line 65 if the subject is not long enough, or, for unanchored	Line 67 if the subject is not long enough, or, for unanchored
been scanned far enough.	been scanned far enough.
.P	.P
You can disable these optimizations by passing the PCRE_NO_START_OPTIMIZE	You can disable these optimizations by passing the PCRE_NO_START_OPTIMIZE
option to \fBpcre_compile()\fP, \fBpcre_exec()\fP, or \fBpcre_dfa_exec()\fP,	option to the matching function, or by starting the pattern with
or by starting the pattern with (*NO_START_OPT). This slows down the matching	(*NO_START_OPT). This slows down the matching process, but does ensure that
process, but does ensure that callouts such as the example above are obeyed.	callouts such as the example above are obeyed.
.	.
.	.
.SH "THE CALLOUT INTERFACE"	.SH "THE CALLOUT INTERFACE"
.rs	.rs
.sp	.sp
During matching, when PCRE reaches a callout point, the external function	During matching, when PCRE reaches a callout point, the external function
defined by \fIpcre_callout\fP is called (if it is set). This applies to both	defined by \fIpcre_callout\fP or \fIpcre16_callout\fP is called (if it is set).
the \fBpcre_exec()\fP and the \fBpcre_dfa_exec()\fP matching functions. The	This applies to both normal and DFA matching. The only argument to the callout
only argument to the callout function is a pointer to a \fBpcre_callout\fP	function is a pointer to a \fBpcre_callout\fP or \fBpcre16_callout\fP block.
block. This structure contains the following fields:	These structures contains the following fields:
.sp	.sp
int \fIversion\fP;	int \fIversion\fP;
int \fIcallout_number\fP;	int \fIcallout_number\fP;
int *\fIoffset_vector\fP;	int *\fIoffset_vector\fP;
const char *\fIsubject\fP;	const char *\fIsubject\fP; (8-bit version)
int \fIsubject_length\fP;	PCRE_SPTR16 \fIsubject\fP; (16-bit version)
int \fIstart_match\fP;	int \fIsubject_length\fP;
int \fIcurrent_position\fP;	int \fIstart_match\fP;
int \fIcapture_top\fP;	int \fIcurrent_position\fP;
int \fIcapture_last\fP;	int \fIcapture_top\fP;
void *\fIcallout_data\fP;	int \fIcapture_last\fP;
int \fIpattern_position\fP;	void *\fIcallout_data\fP;
int \fInext_item_length\fP;	.sp
const unsigned char *\fImark\fP;	int \fInext_item_length\fP;
	const unsigned char *\fImark\fP; (8-bit version)
	const PCRE_UCHAR16 *\fImark\fP; (16-bit version)
.sp	.sp
The \fIversion\fP field is an integer containing the version number of the	The \fIversion\fP field is an integer containing the version number of the
block format. The initial version was 0; the current version is 2. The version	block format. The initial version was 0; the current version is 2. The version
Line 103 into the pattern (that is, the number after ?C for man	Line 107 into the pattern (that is, the number after ?C for man
automatically generated callouts).	automatically generated callouts).
.P	.P
The \fIoffset_vector\fP field is a pointer to the vector of offsets that was	The \fIoffset_vector\fP field is a pointer to the vector of offsets that was
passed by the caller to \fBpcre_exec()\fP or \fBpcre_dfa_exec()\fP. When	passed by the caller to the matching function. When \fBpcre_exec()\fP or
\fBpcre_exec()\fP is used, the contents can be inspected in order to extract	\fBpcre16_exec()\fP is used, the contents can be inspected, in order to extract
substrings that have been matched so far, in the same way as for extracting	substrings that have been matched so far, in the same way as for extracting
substrings after a match has completed. For \fBpcre_dfa_exec()\fP this field is	substrings after a match has completed. For the DFA matching functions, this
not useful.	field is not useful.
.P	.P
The \fIsubject\fP and \fIsubject_length\fP fields contain copies of the values	The \fIsubject\fP and \fIsubject_length\fP fields contain copies of the values
that were passed to \fBpcre_exec()\fP.	that were passed to the matching function.
.P	.P
The \fIstart_match\fP field normally contains the offset within the subject at	The \fIstart_match\fP field normally contains the offset within the subject at
which the current match attempt started. However, if the escape sequence \eK	which the current match attempt started. However, if the escape sequence \eK
Line 122 in the subject.	Line 126 in the subject.
The \fIcurrent_position\fP field contains the offset within the subject of the	The \fIcurrent_position\fP field contains the offset within the subject of the
current match pointer.	current match pointer.
.P	.P
When the \fBpcre_exec()\fP function is used, the \fIcapture_top\fP field	When the \fBpcre_exec()\fP or \fBpcre16_exec()\fP is used, the
contains one more than the number of the highest numbered captured substring so	\fIcapture_top\fP field contains one more than the number of the highest
far. If no substrings have been captured, the value of \fIcapture_top\fP is	numbered captured substring so far. If no substrings have been captured, the
one. This is always the case when \fBpcre_dfa_exec()\fP is used, because it	value of \fIcapture_top\fP is one. This is always the case when the DFA
does not support captured substrings.	functions are used, because they do not support captured substrings.
.P	.P
The \fIcapture_last\fP field contains the number of the most recently captured	The \fIcapture_last\fP field contains the number of the most recently captured
substring. If no substrings have been captured, its value is -1. This is always	substring. If no substrings have been captured, its value is -1. This is always
the case when \fBpcre_dfa_exec()\fP is used.	the case for the DFA matching functions.
.P	.P
The \fIcallout_data\fP field contains a value that is passed to	The \fIcallout_data\fP field contains a value that is passed to a matching
\fBpcre_exec()\fP or \fBpcre_dfa_exec()\fP specifically so that it can be	function specifically so that it can be passed back in callouts. It is passed
passed back in callouts. It is passed in the \fIpcre_callout\fP field of the	in the \fIcallout_data\fP field of a \fBpcre_extra\fP or \fBpcre16_extra\fP
\fBpcre_extra\fP data structure. If no such data was passed, the value of	data structure. If no such data was passed, the value of \fIcallout_data\fP in
\fIcallout_data\fP in a \fBpcre_callout\fP block is NULL. There is a	a callout block is NULL. There is a description of the \fBpcre_extra\fP
description of the \fBpcre_extra\fP structure in the	structure in the
.\" HREF	.\" HREF
\fBpcreapi\fP	\fBpcreapi\fP
.\"	.\"
documentation.	documentation.
.P	.P
The \fIpattern_position\fP field is present from version 1 of the	The \fIpattern_position\fP field is present from version 1 of the callout
\fIpcre_callout\fP structure. It contains the offset to the next item to be	structure. It contains the offset to the next item to be matched in the pattern
matched in the pattern string.	string.
.P	.P
The \fInext_item_length\fP field is present from version 1 of the	The \fInext_item_length\fP field is present from version 1 of the callout
\fIpcre_callout\fP structure. It contains the length of the next item to be	structure. It contains the length of the next item to be matched in the pattern
matched in the pattern string. When the callout immediately precedes an	string. When the callout immediately precedes an alternation bar, a closing
alternation bar, a closing parenthesis, or the end of the pattern, the length	parenthesis, or the end of the pattern, the length is zero. When the callout
is zero. When the callout precedes an opening parenthesis, the length is that	precedes an opening parenthesis, the length is that of the entire subpattern.
of the entire subpattern.
.P	.P
The \fIpattern_position\fP and \fInext_item_length\fP fields are intended to	The \fIpattern_position\fP and \fInext_item_length\fP fields are intended to
help in distinguishing between different automatic callouts, which all have the	help in distinguishing between different automatic callouts, which all have the
same callout number. However, they are set for all callouts.	same callout number. However, they are set for all callouts.
.P	.P
The \fImark\fP field is present from version 2 of the \fIpcre_callout\fP	The \fImark\fP field is present from version 2 of the callout structure. In
structure. In callouts from \fBpcre_exec()\fP it contains a pointer to the	callouts from \fBpcre_exec()\fP or \fBpcre16_exec()\fP it contains a pointer to
zero-terminated name of the most recently passed (MARK), (PRUNE), or (*THEN)	the zero-terminated name of the most recently passed (MARK), (PRUNE), or
item in the match, or NULL if no such items have been passed. Instances of	(*THEN) item in the match, or NULL if no such items have been passed. Instances
(PRUNE) or (THEN) without a name do not obliterate a previous (*MARK). In	of (PRUNE) or (THEN) without a name do not obliterate a previous (*MARK). In
callouts from \fBpcre_dfa_exec()\fP this field always contains NULL.	callouts from the DFA matching functions this field always contains NULL.
.	.
.	.
.SH "RETURN VALUES"	.SH "RETURN VALUES"
Line 173 The external callout function returns an integer to PC	Line 176 The external callout function returns an integer to PC
matching proceeds as normal. If the value is greater than zero, matching fails	matching proceeds as normal. If the value is greater than zero, matching fails
at the current point, but the testing of other matching possibilities goes	at the current point, but the testing of other matching possibilities goes
ahead, just as if a lookahead assertion had failed. If the value is less than	ahead, just as if a lookahead assertion had failed. If the value is less than
zero, the match is abandoned, and \fBpcre_exec()\fP or \fBpcre_dfa_exec()\fP	zero, the match is abandoned, the matching function returns the negative value.
returns the negative value.
.P	.P
Negative values should normally be chosen from the set of PCRE_ERROR_xxx	Negative values should normally be chosen from the set of PCRE_ERROR_xxx
values. In particular, PCRE_ERROR_NOMATCH forces a standard "no match" failure.	values. In particular, PCRE_ERROR_NOMATCH forces a standard "no match" failure.
Line 196 Cambridge CB2 3QH, England.	Line 198 Cambridge CB2 3QH, England.
.rs	.rs
.sp	.sp
.nf	.nf
Last updated: 30 November 2011	Last updated: 08 Janurary 2012
Copyright (c) 1997-2011 University of Cambridge.	Copyright (c) 1997-2012 University of Cambridge.
.fi	.fi

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