244 lines
9.9 KiB
HTML
244 lines
9.9 KiB
HTML
<html>
|
|
<head>
|
|
<title>pcrecallout specification</title>
|
|
</head>
|
|
<body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
|
|
<h1>pcrecallout man page</h1>
|
|
<p>
|
|
Return to the <a href="index.html">PCRE index page</a>.
|
|
</p>
|
|
<p>
|
|
This page is part of the PCRE HTML documentation. It was generated automatically
|
|
from the original man page. If there is any nonsense in it, please consult the
|
|
man page, in case the conversion went wrong.
|
|
<br>
|
|
<ul>
|
|
<li><a name="TOC1" href="#SEC1">SYNOPSIS</a>
|
|
<li><a name="TOC2" href="#SEC2">DESCRIPTION</a>
|
|
<li><a name="TOC3" href="#SEC3">MISSING CALLOUTS</a>
|
|
<li><a name="TOC4" href="#SEC4">THE CALLOUT INTERFACE</a>
|
|
<li><a name="TOC5" href="#SEC5">RETURN VALUES</a>
|
|
<li><a name="TOC6" href="#SEC6">AUTHOR</a>
|
|
<li><a name="TOC7" href="#SEC7">REVISION</a>
|
|
</ul>
|
|
<br><a name="SEC1" href="#TOC1">SYNOPSIS</a><br>
|
|
<P>
|
|
<b>#include <pcre.h></b>
|
|
</P>
|
|
<P>
|
|
<b>int (*pcre_callout)(pcre_callout_block *);</b>
|
|
</P>
|
|
<P>
|
|
<b>int (*pcre16_callout)(pcre16_callout_block *);</b>
|
|
</P>
|
|
<P>
|
|
<b>int (*pcre32_callout)(pcre32_callout_block *);</b>
|
|
</P>
|
|
<br><a name="SEC2" href="#TOC1">DESCRIPTION</a><br>
|
|
<P>
|
|
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
|
|
caller of PCRE provides an external function by putting its entry point in the
|
|
global variable <i>pcre_callout</i> (<i>pcre16_callout</i> for the 16-bit
|
|
library, <i>pcre32_callout</i> for the 32-bit 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
|
|
function is to be called. Different callout points can be identified by putting
|
|
a number less than 256 after the letter C. The default value is zero.
|
|
For example, this pattern has two callout points:
|
|
<pre>
|
|
(?C1)abc(?C2)def
|
|
</pre>
|
|
If the PCRE_AUTO_CALLOUT option bit is set when a pattern is compiled, PCRE
|
|
automatically inserts callouts, all with number 255, before each item in the
|
|
pattern. For example, if PCRE_AUTO_CALLOUT is used with the pattern
|
|
<pre>
|
|
A(\d{2}|--)
|
|
</pre>
|
|
it is processed as if it were
|
|
<br>
|
|
<br>
|
|
(?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255)
|
|
<br>
|
|
<br>
|
|
Notice that there is a callout before and after each parenthesis and
|
|
alternation bar. Automatic callouts can be used for tracking the progress of
|
|
pattern matching. The
|
|
<a href="pcretest.html"><b>pcretest</b></a>
|
|
command has an option that sets automatic callouts; when it is used, the output
|
|
indicates how the pattern is matched. This is useful information when you are
|
|
trying to optimize the performance of a particular pattern.
|
|
</P>
|
|
<P>
|
|
The use of callouts in a pattern makes it ineligible for optimization by the
|
|
just-in-time compiler. Studying such a pattern with the PCRE_STUDY_JIT_COMPILE
|
|
option always fails.
|
|
</P>
|
|
<br><a name="SEC3" href="#TOC1">MISSING CALLOUTS</a><br>
|
|
<P>
|
|
You should be aware that, because of optimizations in the way PCRE matches
|
|
patterns by default, callouts sometimes do not happen. For example, if the
|
|
pattern is
|
|
<pre>
|
|
ab(?C4)cd
|
|
</pre>
|
|
PCRE knows that any matching string must contain the letter "d". If the subject
|
|
string is "abyz", the lack of "d" means that matching doesn't ever start, and
|
|
the callout is never reached. However, with "abyd", though the result is still
|
|
no match, the callout is obeyed.
|
|
</P>
|
|
<P>
|
|
If the pattern is studied, PCRE knows the minimum length of a matching string,
|
|
and will immediately give a "no match" return without actually running a match
|
|
if the subject is not long enough, or, for unanchored patterns, if it has
|
|
been scanned far enough.
|
|
</P>
|
|
<P>
|
|
You can disable these optimizations by passing the PCRE_NO_START_OPTIMIZE
|
|
option to the matching function, or by starting the pattern with
|
|
(*NO_START_OPT). This slows down the matching process, but does ensure that
|
|
callouts such as the example above are obeyed.
|
|
</P>
|
|
<br><a name="SEC4" href="#TOC1">THE CALLOUT INTERFACE</a><br>
|
|
<P>
|
|
During matching, when PCRE reaches a callout point, the external function
|
|
defined by <i>pcre_callout</i> or <i>pcre[16|32]_callout</i> is called
|
|
(if it is set). This applies to both normal and DFA matching. The only
|
|
argument to the callout function is a pointer to a <b>pcre_callout</b>
|
|
or <b>pcre[16|32]_callout</b> block.
|
|
These structures contains the following fields:
|
|
<pre>
|
|
int <i>version</i>;
|
|
int <i>callout_number</i>;
|
|
int *<i>offset_vector</i>;
|
|
const char *<i>subject</i>; (8-bit version)
|
|
PCRE_SPTR16 <i>subject</i>; (16-bit version)
|
|
PCRE_SPTR32 <i>subject</i>; (32-bit version)
|
|
int <i>subject_length</i>;
|
|
int <i>start_match</i>;
|
|
int <i>current_position</i>;
|
|
int <i>capture_top</i>;
|
|
int <i>capture_last</i>;
|
|
void *<i>callout_data</i>;
|
|
int <i>pattern_position</i>;
|
|
int <i>next_item_length</i>;
|
|
const unsigned char *<i>mark</i>; (8-bit version)
|
|
const PCRE_UCHAR16 *<i>mark</i>; (16-bit version)
|
|
const PCRE_UCHAR32 *<i>mark</i>; (32-bit version)
|
|
</pre>
|
|
The <i>version</i> field is an integer containing the version number of the
|
|
block format. The initial version was 0; the current version is 2. The version
|
|
number will change again in future if additional fields are added, but the
|
|
intention is never to remove any of the existing fields.
|
|
</P>
|
|
<P>
|
|
The <i>callout_number</i> field contains the number of the callout, as compiled
|
|
into the pattern (that is, the number after ?C for manual callouts, and 255 for
|
|
automatically generated callouts).
|
|
</P>
|
|
<P>
|
|
The <i>offset_vector</i> field is a pointer to the vector of offsets that was
|
|
passed by the caller to the matching function. When <b>pcre_exec()</b> or
|
|
<b>pcre[16|32]_exec()</b> 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 after a match has completed. For the DFA matching functions, this
|
|
field is not useful.
|
|
</P>
|
|
<P>
|
|
The <i>subject</i> and <i>subject_length</i> fields contain copies of the values
|
|
that were passed to the matching function.
|
|
</P>
|
|
<P>
|
|
The <i>start_match</i> field normally contains the offset within the subject at
|
|
which the current match attempt started. However, if the escape sequence \K
|
|
has been encountered, this value is changed to reflect the modified starting
|
|
point. If the pattern is not anchored, the callout function may be called
|
|
several times from the same point in the pattern for different starting points
|
|
in the subject.
|
|
</P>
|
|
<P>
|
|
The <i>current_position</i> field contains the offset within the subject of the
|
|
current match pointer.
|
|
</P>
|
|
<P>
|
|
When the <b>pcre_exec()</b> or <b>pcre[16|32]_exec()</b> is used, the
|
|
<i>capture_top</i> field contains one more than the number of the highest
|
|
numbered captured substring so far. If no substrings have been captured, the
|
|
value of <i>capture_top</i> is one. This is always the case when the DFA
|
|
functions are used, because they do not support captured substrings.
|
|
</P>
|
|
<P>
|
|
The <i>capture_last</i> field contains the number of the most recently captured
|
|
substring. If no substrings have been captured, its value is -1. This is always
|
|
the case for the DFA matching functions.
|
|
</P>
|
|
<P>
|
|
The <i>callout_data</i> field contains a value that is passed to a matching
|
|
function specifically so that it can be passed back in callouts. It is passed
|
|
in the <i>callout_data</i> field of a <b>pcre_extra</b> or <b>pcre[16|32]_extra</b>
|
|
data structure. If no such data was passed, the value of <i>callout_data</i> in
|
|
a callout block is NULL. There is a description of the <b>pcre_extra</b>
|
|
structure in the
|
|
<a href="pcreapi.html"><b>pcreapi</b></a>
|
|
documentation.
|
|
</P>
|
|
<P>
|
|
The <i>pattern_position</i> field is present from version 1 of the callout
|
|
structure. It contains the offset to the next item to be matched in the pattern
|
|
string.
|
|
</P>
|
|
<P>
|
|
The <i>next_item_length</i> field is present from version 1 of the callout
|
|
structure. It contains the length of the next item to be matched in the pattern
|
|
string. When the callout immediately precedes an alternation bar, a closing
|
|
parenthesis, or the end of the pattern, the length is zero. When the callout
|
|
precedes an opening parenthesis, the length is that of the entire subpattern.
|
|
</P>
|
|
<P>
|
|
The <i>pattern_position</i> and <i>next_item_length</i> fields are intended to
|
|
help in distinguishing between different automatic callouts, which all have the
|
|
same callout number. However, they are set for all callouts.
|
|
</P>
|
|
<P>
|
|
The <i>mark</i> field is present from version 2 of the callout structure. In
|
|
callouts from <b>pcre_exec()</b> or <b>pcre[16|32]_exec()</b> it contains a pointer to
|
|
the zero-terminated name of the most recently passed (*MARK), (*PRUNE), or
|
|
(*THEN) item in the match, or NULL if no such items have been passed. Instances
|
|
of (*PRUNE) or (*THEN) without a name do not obliterate a previous (*MARK). In
|
|
callouts from the DFA matching functions this field always contains NULL.
|
|
</P>
|
|
<br><a name="SEC5" href="#TOC1">RETURN VALUES</a><br>
|
|
<P>
|
|
The external callout function returns an integer to PCRE. If the value is zero,
|
|
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
|
|
ahead, just as if a lookahead assertion had failed. If the value is less than
|
|
zero, the match is abandoned, the matching function returns the negative value.
|
|
</P>
|
|
<P>
|
|
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.
|
|
The error number PCRE_ERROR_CALLOUT is reserved for use by callout functions;
|
|
it will never be used by PCRE itself.
|
|
</P>
|
|
<br><a name="SEC6" href="#TOC1">AUTHOR</a><br>
|
|
<P>
|
|
Philip Hazel
|
|
<br>
|
|
University Computing Service
|
|
<br>
|
|
Cambridge CB2 3QH, England.
|
|
<br>
|
|
</P>
|
|
<br><a name="SEC7" href="#TOC1">REVISION</a><br>
|
|
<P>
|
|
Last updated: 24 June 2012
|
|
<br>
|
|
Copyright © 1997-2012 University of Cambridge.
|
|
<br>
|
|
<p>
|
|
Return to the <a href="index.html">PCRE index page</a>.
|
|
</p>
|