version 1.1.1.2, 2012/02/21 23:50:25
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version 1.1.1.4, 2014/06/15 19:46:05
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Line 13 from the original man page. If there is any nonsense i
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Line 13 from the original man page. If there is any nonsense i
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man page, in case the conversion went wrong. |
man page, in case the conversion went wrong. |
<br> |
<br> |
<ul> |
<ul> |
<li><a name="TOC1" href="#SEC1">PCRE CALLOUTS</a> | <li><a name="TOC1" href="#SEC1">SYNOPSIS</a> |
<li><a name="TOC2" href="#SEC2">MISSING CALLOUTS</a> | <li><a name="TOC2" href="#SEC2">DESCRIPTION</a> |
<li><a name="TOC3" href="#SEC3">THE CALLOUT INTERFACE</a> | <li><a name="TOC3" href="#SEC3">MISSING CALLOUTS</a> |
<li><a name="TOC4" href="#SEC4">RETURN VALUES</a> | <li><a name="TOC4" href="#SEC4">THE CALLOUT INTERFACE</a> |
<li><a name="TOC5" href="#SEC5">AUTHOR</a> | <li><a name="TOC5" href="#SEC5">RETURN VALUES</a> |
<li><a name="TOC6" href="#SEC6">REVISION</a> | <li><a name="TOC6" href="#SEC6">AUTHOR</a> |
| <li><a name="TOC7" href="#SEC7">REVISION</a> |
</ul> |
</ul> |
<br><a name="SEC1" href="#TOC1">PCRE CALLOUTS</a><br> | <br><a name="SEC1" href="#TOC1">SYNOPSIS</a><br> |
<P> |
<P> |
|
<b>#include <pcre.h></b> |
|
</P> |
|
<P> |
<b>int (*pcre_callout)(pcre_callout_block *);</b> |
<b>int (*pcre_callout)(pcre_callout_block *);</b> |
</P> |
</P> |
<P> |
<P> |
<b>int (*pcre16_callout)(pcre16_callout_block *);</b> |
<b>int (*pcre16_callout)(pcre16_callout_block *);</b> |
</P> |
</P> |
<P> |
<P> |
|
<b>int (*pcre32_callout)(pcre32_callout_block *);</b> |
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</P> |
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<br><a name="SEC2" href="#TOC1">DESCRIPTION</a><br> |
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<P> |
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 <i>pcre_callout</i> (<i>pcre16_callout</i> for the 16-bit |
global variable <i>pcre_callout</i> (<i>pcre16_callout</i> for the 16-bit |
library). By default, this variable contains NULL, which disables all calling | library, <i>pcre32_callout</i> for the 32-bit library). By default, this |
out. | variable contains NULL, which disables all calling out. |
</P> |
</P> |
<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 |
Line 56 it is processed as if it were
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Line 64 it is processed as if it were
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<br> |
<br> |
<br> |
<br> |
Notice that there is a callout before and after each parenthesis and |
Notice that there is a callout before and after each parenthesis and |
alternation bar. Automatic callouts can be used for tracking the progress of | alternation bar. If the pattern contains a conditional group whose condition is |
pattern matching. The | an assertion, an automatic callout is inserted immediately before the |
| condition. Such a callout may also be inserted explicitly, for example: |
| <pre> |
| (?(?C9)(?=a)ab|de) |
| </pre> |
| This applies only to assertion conditions (because they are themselves |
| independent groups). |
| </P> |
| <P> |
| Automatic callouts can be used for tracking the progress of pattern matching. |
| The |
<a href="pcretest.html"><b>pcretest</b></a> |
<a href="pcretest.html"><b>pcretest</b></a> |
command has an option that sets automatic callouts; when it is used, the output | program has a pattern qualifier (/C) that sets automatic callouts; when it is |
indicates how the pattern is matched. This is useful information when you are | used, the output indicates how the pattern is being matched. This is useful |
trying to optimize the performance of a particular pattern. | information when you are trying to optimize the performance of a particular |
| pattern. |
</P> |
</P> |
|
<br><a name="SEC3" href="#TOC1">MISSING CALLOUTS</a><br> |
<P> |
<P> |
The use of callouts in a pattern makes it ineligible for optimization by the | You should be aware that, because of optimizations in the way PCRE compiles and |
just-in-time compiler. Studying such a pattern with the PCRE_STUDY_JIT_COMPILE | matches patterns, callouts sometimes do not happen exactly as you might expect. |
option always fails. | |
</P> |
</P> |
<br><a name="SEC2" href="#TOC1">MISSING CALLOUTS</a><br> |
|
<P> |
<P> |
You should be aware that, because of optimizations in the way PCRE matches | At compile time, PCRE "auto-possessifies" repeated items when it knows that |
patterns by default, callouts sometimes do not happen. For example, if the | what follows cannot be part of the repeat. For example, a+[bc] is compiled as |
pattern is | if it were a++[bc]. The <b>pcretest</b> output when this pattern is anchored and |
| then applied with automatic callouts to the string "aaaa" is: |
<pre> |
<pre> |
|
--->aaaa |
|
+0 ^ ^ |
|
+1 ^ a+ |
|
+3 ^ ^ [bc] |
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No match |
|
</pre> |
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This indicates that when matching [bc] fails, there is no backtracking into a+ |
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and therefore the callouts that would be taken for the backtracks do not occur. |
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You can disable the auto-possessify feature by passing PCRE_NO_AUTO_POSSESS |
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to <b>pcre_compile()</b>, or starting the pattern with (*NO_AUTO_POSSESS). If |
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this is done in <b>pcretest</b> (using the /O qualifier), the output changes to |
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this: |
|
<pre> |
|
--->aaaa |
|
+0 ^ ^ |
|
+1 ^ a+ |
|
+3 ^ ^ [bc] |
|
+3 ^ ^ [bc] |
|
+3 ^ ^ [bc] |
|
+3 ^^ [bc] |
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No match |
|
</pre> |
|
This time, when matching [bc] fails, the matcher backtracks into a+ and tries |
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again, repeatedly, until a+ itself fails. |
|
</P> |
|
<P> |
|
Other optimizations that provide fast "no match" results also affect callouts. |
|
For example, if the pattern is |
|
<pre> |
ab(?C4)cd |
ab(?C4)cd |
</pre> |
</pre> |
PCRE knows that any matching string must contain the letter "d". If the subject |
PCRE knows that any matching string must contain the letter "d". If the subject |
Line 93 option to the matching function, or by starting the pa
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Line 141 option to the matching function, or by starting the pa
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(*NO_START_OPT). This slows down the matching process, but does ensure that |
(*NO_START_OPT). This slows down the matching process, but does ensure that |
callouts such as the example above are obeyed. |
callouts such as the example above are obeyed. |
</P> |
</P> |
<br><a name="SEC3" href="#TOC1">THE CALLOUT INTERFACE</a><br> | <br><a name="SEC4" href="#TOC1">THE CALLOUT INTERFACE</a><br> |
<P> |
<P> |
During matching, when PCRE reaches a callout point, the external function |
During matching, when PCRE reaches a callout point, the external function |
defined by <i>pcre_callout</i> or <i>pcre16_callout</i> is called (if it is set). | defined by <i>pcre_callout</i> or <i>pcre[16|32]_callout</i> is called (if it is |
This applies to both normal and DFA matching. The only argument to the callout | set). This applies to both normal and DFA matching. The only argument to the |
function is a pointer to a <b>pcre_callout</b> or <b>pcre16_callout</b> block. | callout function is a pointer to a <b>pcre_callout</b> or |
These structures contains the following fields: | <b>pcre[16|32]_callout</b> block. These structures contains the following |
| fields: |
<pre> |
<pre> |
int <i>version</i>; |
int <i>version</i>; |
int <i>callout_number</i>; |
int <i>callout_number</i>; |
int *<i>offset_vector</i>; |
int *<i>offset_vector</i>; |
const char *<i>subject</i>; (8-bit version) |
const char *<i>subject</i>; (8-bit version) |
PCRE_SPTR16 <i>subject</i>; (16-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>subject_length</i>; |
int <i>start_match</i>; |
int <i>start_match</i>; |
int <i>current_position</i>; |
int <i>current_position</i>; |
Line 116 These structures contains the following fields:
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Line 166 These structures contains the following fields:
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int <i>next_item_length</i>; |
int <i>next_item_length</i>; |
const unsigned char *<i>mark</i>; (8-bit version) |
const unsigned char *<i>mark</i>; (8-bit version) |
const PCRE_UCHAR16 *<i>mark</i>; (16-bit version) |
const PCRE_UCHAR16 *<i>mark</i>; (16-bit version) |
|
const PCRE_UCHAR32 *<i>mark</i>; (32-bit version) |
</pre> |
</pre> |
The <i>version</i> field is an integer containing the version number of the |
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 |
block format. The initial version was 0; the current version is 2. The version |
Line 130 automatically generated callouts).
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Line 181 automatically generated callouts).
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<P> |
<P> |
The <i>offset_vector</i> field is a pointer to the vector of offsets that was |
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 |
passed by the caller to the matching function. When <b>pcre_exec()</b> or |
<b>pcre16_exec()</b> is used, the contents can be inspected, in order to extract | <b>pcre[16|32]_exec()</b> is used, the contents can be inspected, in order to |
substrings that have been matched so far, in the same way as for extracting | extract substrings that have been matched so far, in the same way as for |
substrings after a match has completed. For the DFA matching functions, this | extracting substrings after a match has completed. For the DFA matching |
field is not useful. | functions, this field is not useful. |
</P> |
</P> |
<P> |
<P> |
The <i>subject</i> and <i>subject_length</i> fields contain copies of the values |
The <i>subject</i> and <i>subject_length</i> fields contain copies of the values |
Line 152 The <i>current_position</i> field contains the offset
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Line 203 The <i>current_position</i> field contains the offset
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current match pointer. |
current match pointer. |
</P> |
</P> |
<P> |
<P> |
When the <b>pcre_exec()</b> or <b>pcre16_exec()</b> is used, the | 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 |
<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 |
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 |
value of <i>capture_top</i> is one. This is always the case when the DFA |
Line 160 functions are used, because they do not support captur
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Line 211 functions are used, because they do not support captur
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</P> |
</P> |
<P> |
<P> |
The <i>capture_last</i> field contains the number of the most recently captured |
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 | substring. However, when a recursion exits, the value reverts to what it was |
the case for the DFA matching functions. | outside the recursion, as do the values of all captured substrings. If no |
| substrings have been captured, the value of <i>capture_last</i> is -1. This is |
| always the case for the DFA matching functions. |
</P> |
</P> |
<P> |
<P> |
The <i>callout_data</i> field contains a value that is passed to a matching |
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 |
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>pcre16_extra</b> | 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 |
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> |
a callout block is NULL. There is a description of the <b>pcre_extra</b> |
structure in the |
structure in the |
Line 192 same callout number. However, they are set for all cal
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Line 245 same callout number. However, they are set for all cal
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</P> |
</P> |
<P> |
<P> |
The <i>mark</i> field is present from version 2 of the callout structure. In |
The <i>mark</i> field is present from version 2 of the callout structure. In |
callouts from <b>pcre_exec()</b> or <b>pcre16_exec()</b> it contains a pointer to | callouts from <b>pcre_exec()</b> or <b>pcre[16|32]_exec()</b> it contains a |
the zero-terminated name of the most recently passed (*MARK), (*PRUNE), or | pointer to the zero-terminated name of the most recently passed (*MARK), |
(*THEN) item in the match, or NULL if no such items have been passed. Instances | (*PRUNE), or (*THEN) item in the match, or NULL if no such items have been |
of (*PRUNE) or (*THEN) without a name do not obliterate a previous (*MARK). In | passed. Instances of (*PRUNE) or (*THEN) without a name do not obliterate a |
callouts from the DFA matching functions this field always contains NULL. | previous (*MARK). In callouts from the DFA matching functions this field always |
| contains NULL. |
</P> |
</P> |
<br><a name="SEC4" href="#TOC1">RETURN VALUES</a><br> | <br><a name="SEC5" href="#TOC1">RETURN VALUES</a><br> |
<P> |
<P> |
The external callout function returns an integer to PCRE. If the value is zero, |
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 |
matching proceeds as normal. If the value is greater than zero, matching fails |
Line 212 values. In particular, PCRE_ERROR_NOMATCH forces a sta
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Line 266 values. In particular, PCRE_ERROR_NOMATCH forces a sta
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The error number PCRE_ERROR_CALLOUT is reserved for use by callout functions; |
The error number PCRE_ERROR_CALLOUT is reserved for use by callout functions; |
it will never be used by PCRE itself. |
it will never be used by PCRE itself. |
</P> |
</P> |
<br><a name="SEC5" href="#TOC1">AUTHOR</a><br> | <br><a name="SEC6" href="#TOC1">AUTHOR</a><br> |
<P> |
<P> |
Philip Hazel |
Philip Hazel |
<br> |
<br> |
Line 221 University Computing Service
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Line 275 University Computing Service
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Cambridge CB2 3QH, England. |
Cambridge CB2 3QH, England. |
<br> |
<br> |
</P> |
</P> |
<br><a name="SEC6" href="#TOC1">REVISION</a><br> | <br><a name="SEC7" href="#TOC1">REVISION</a><br> |
<P> |
<P> |
Last updated: 08 Janurary 2012 | Last updated: 12 November 2013 |
<br> |
<br> |
Copyright © 1997-2012 University of Cambridge. | Copyright © 1997-2013 University of Cambridge. |
<br> |
<br> |
<p> |
<p> |
Return to the <a href="index.html">PCRE index page</a>. |
Return to the <a href="index.html">PCRE index page</a>. |