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<title>pcrecallout specification</title> |
<title>pcrecallout specification</title> |
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This HTML document has been generated automatically from the original man page. |
<h1>pcrecallout man page</h1> |
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If there is any nonsense in it, please consult the man page, in case the |
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conversion went wrong.<br> |
Return to the <a href="index.html">PCRE index page</a>. |
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</p> |
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This page is part of the PCRE HTML documentation. It was generated automatically |
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from the original man page. If there is any nonsense in it, please consult the |
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man page, in case the conversion went wrong. |
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<br> |
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<ul> |
<ul> |
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<li><a name="TOC1" href="#SEC1">PCRE CALLOUTS</a> |
<li><a name="TOC1" href="#SEC1">PCRE CALLOUTS</a> |
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<li><a name="TOC2" href="#SEC2">RETURN VALUES</a> |
<li><a name="TOC2" href="#SEC2">MISSING CALLOUTS</a> |
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<li><a name="TOC3" href="#SEC3">THE CALLOUT INTERFACE</a> |
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<li><a name="TOC4" href="#SEC4">RETURN VALUES</a> |
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<li><a name="TOC5" href="#SEC5">AUTHOR</a> |
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<li><a name="TOC6" href="#SEC6">REVISION</a> |
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</ul> |
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<br><a name="SEC1" href="#TOC1">PCRE CALLOUTS</a><br> |
<br><a name="SEC1" href="#TOC1">PCRE CALLOUTS</a><br> |
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<P> |
<P> |
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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 |
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a number less than 256 after the letter C. The default value is zero. |
a number less than 256 after the letter C. The default value is zero. |
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For example, this pattern has two callout points: |
For example, this pattern has two callout points: |
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<pre> |
<pre> |
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(?C1)\dabc(?C2)def |
(?C1)abc(?C2)def |
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</PRE> |
</pre> |
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</P> |
If the PCRE_AUTO_CALLOUT option bit is set when <b>pcre_compile()</b> is called, |
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<P> |
PCRE automatically inserts callouts, all with number 255, before each item in |
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During matching, when PCRE reaches a callout point (and <i>pcre_callout</i> is |
the pattern. For example, if PCRE_AUTO_CALLOUT is used with the pattern |
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set), the external function is called. Its only argument is a pointer to a |
<pre> |
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<b>pcre_callout</b> block. This contains the following variables: |
A(\d{2}|--) |
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</pre> |
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it is processed as if it were |
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(?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255) |
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Notice that there is a callout before and after each parenthesis and |
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alternation bar. Automatic callouts can be used for tracking the progress of |
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pattern matching. The |
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<a href="pcretest.html"><b>pcretest</b></a> |
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command has an option that sets automatic callouts; when it is used, the output |
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indicates how the pattern is matched. This is useful information when you are |
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trying to optimize the performance of a particular pattern. |
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</P> |
</P> |
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<br><a name="SEC2" href="#TOC1">MISSING CALLOUTS</a><br> |
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<P> |
<P> |
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You should be aware that, because of optimizations in the way PCRE matches |
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patterns, callouts sometimes do not happen. For example, if the pattern is |
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<pre> |
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ab(?C4)cd |
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</pre> |
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PCRE knows that any matching string must contain the letter "d". If the subject |
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string is "abyz", the lack of "d" means that matching doesn't ever start, and |
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the callout is never reached. However, with "abyd", though the result is still |
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no match, the callout is obeyed. |
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</P> |
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<br><a name="SEC3" href="#TOC1">THE CALLOUT INTERFACE</a><br> |
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<P> |
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During matching, when PCRE reaches a callout point, the external function |
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defined by <i>pcre_callout</i> is called (if it is set). This applies to both |
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the <b>pcre_exec()</b> and the <b>pcre_dfa_exec()</b> matching functions. The |
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only argument to the callout function is a pointer to a <b>pcre_callout</b> |
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block. This structure contains the following fields: |
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<pre> |
<pre> |
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int <i>version</i>; |
int <i>version</i>; |
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int <i>callout_number</i>; |
int <i>callout_number</i>; |
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int <i>capture_top</i>; |
int <i>capture_top</i>; |
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int <i>capture_last</i>; |
int <i>capture_last</i>; |
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void *<i>callout_data</i>; |
void *<i>callout_data</i>; |
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</PRE> |
int <i>pattern_position</i>; |
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</P> |
int <i>next_item_length</i>; |
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<P> |
</pre> |
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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 |
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block format. The current version is zero. The version number may change in |
block format. The initial version was 0; the current version is 1. The version |
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future if additional fields are added, but the intention is never to remove any |
number will change again in future if additional fields are added, but the |
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of the existing fields. |
intention is never to remove any of the existing fields. |
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</P> |
</P> |
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<P> |
<P> |
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The <i>callout_number</i> field contains the number of the callout, as compiled |
The <i>callout_number</i> field contains the number of the callout, as compiled |
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into the pattern (that is, the number after ?C). |
into the pattern (that is, the number after ?C for manual callouts, and 255 for |
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automatically generated callouts). |
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</P> |
</P> |
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<P> |
<P> |
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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 |
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passed by the caller to <b>pcre_exec()</b>. The contents can be inspected in |
passed by the caller to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b>. When |
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order to extract substrings that have been matched so far, in the same way as |
<b>pcre_exec()</b> is used, the contents can be inspected in order to extract |
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for extracting substrings after a match has completed. |
substrings that have been matched so far, in the same way as for extracting |
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substrings after a match has completed. For <b>pcre_dfa_exec()</b> this field is |
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not useful. |
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</P> |
</P> |
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<P> |
<P> |
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The <i>subject</i> and <i>subject_length</i> fields contain copies the values |
The <i>subject</i> and <i>subject_length</i> fields contain copies of the values |
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that were passed to <b>pcre_exec()</b>. |
that were passed to <b>pcre_exec()</b>. |
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</P> |
</P> |
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<P> |
<P> |
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The <i>start_match</i> field contains the offset within the subject at which the |
The <i>start_match</i> field normally contains the offset within the subject at |
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current match attempt started. If the pattern is not anchored, the callout |
which the current match attempt started. However, if the escape sequence \K |
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function may be called several times for different starting points. |
has been encountered, this value is changed to reflect the modified starting |
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point. If the pattern is not anchored, the callout function may be called |
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several times from the same point in the pattern for different starting points |
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in the subject. |
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</P> |
</P> |
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<P> |
<P> |
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The <i>current_position</i> field contains the offset within the subject of the |
The <i>current_position</i> field contains the offset within the subject of the |
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current match pointer. |
current match pointer. |
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</P> |
</P> |
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<P> |
<P> |
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The <i>capture_top</i> field contains one more than the number of the highest |
When the <b>pcre_exec()</b> function is used, the <i>capture_top</i> field |
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numbered captured substring so far. If no substrings have been captured, |
contains one more than the number of the highest numbered captured substring so |
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the value of <i>capture_top</i> is one. |
far. If no substrings have been captured, the value of <i>capture_top</i> is |
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one. This is always the case when <b>pcre_dfa_exec()</b> is used, because it |
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does not support captured substrings. |
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</P> |
</P> |
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<P> |
<P> |
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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 |
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substring. |
substring. If no substrings have been captured, its value is -1. This is always |
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the case when <b>pcre_dfa_exec()</b> is used. |
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</P> |
</P> |
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<P> |
<P> |
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The <i>callout_data</i> field contains a value that is passed to |
The <i>callout_data</i> field contains a value that is passed to |
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<b>pcre_exec()</b> by the caller specifically so that it can be passed back in |
<b>pcre_exec()</b> or <b>pcre_dfa_exec()</b> specifically so that it can be |
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callouts. It is passed in the <i>pcre_callout</i> field of the <b>pcre_extra</b> |
passed back in callouts. It is passed in the <i>pcre_callout</i> field of the |
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data structure. If no such data was passed, the value of <i>callout_data</i> in |
<b>pcre_extra</b> data structure. If no such data was passed, the value of |
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a <b>pcre_callout</b> block is NULL. There is a description of the |
<i>callout_data</i> in a <b>pcre_callout</b> block is NULL. There is a |
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<b>pcre_extra</b> structure in the <b>pcreapi</b> documentation. |
description of the <b>pcre_extra</b> structure in the |
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</P> |
<a href="pcreapi.html"><b>pcreapi</b></a> |
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<br><a name="SEC2" href="#TOC1">RETURN VALUES</a><br> |
documentation. |
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<P> |
</P> |
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The callout function returns an integer. If the value is zero, matching |
<P> |
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proceeds as normal. If the value is greater than zero, matching fails at the |
The <i>pattern_position</i> field is present from version 1 of the |
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current point, but backtracking to test other possibilities goes ahead, just as |
<i>pcre_callout</i> structure. It contains the offset to the next item to be |
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if a lookahead assertion had failed. If the value is less than zero, the match |
matched in the pattern string. |
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is abandoned, and <b>pcre_exec()</b> returns the value. |
</P> |
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<P> |
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The <i>next_item_length</i> field is present from version 1 of the |
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<i>pcre_callout</i> structure. It contains the length of the next item to be |
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matched in the pattern string. When the callout immediately precedes an |
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alternation bar, a closing parenthesis, or the end of the pattern, the length |
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is zero. When the callout precedes an opening parenthesis, the length is that |
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of the entire subpattern. |
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</P> |
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<P> |
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The <i>pattern_position</i> and <i>next_item_length</i> fields are intended to |
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help in distinguishing between different automatic callouts, which all have the |
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same callout number. However, they are set for all callouts. |
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</P> |
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<br><a name="SEC4" href="#TOC1">RETURN VALUES</a><br> |
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<P> |
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The external callout function returns an integer to PCRE. If the value is zero, |
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matching proceeds as normal. If the value is greater than zero, matching fails |
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at the current point, but the testing of other matching possibilities goes |
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ahead, just as if a lookahead assertion had failed. If the value is less than |
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zero, the match is abandoned, and <b>pcre_exec()</b> (or <b>pcre_dfa_exec()</b>) |
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returns the negative value. |
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</P> |
</P> |
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<P> |
<P> |
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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 |
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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; |
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it will never be used by PCRE itself. |
it will never be used by PCRE itself. |
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</P> |
</P> |
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<br><a name="SEC5" href="#TOC1">AUTHOR</a><br> |
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<P> |
<P> |
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Last updated: 21 January 2003 |
Philip Hazel |
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University Computing Service |
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Cambridge CB2 3QH, England. |
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<br> |
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</P> |
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<br><a name="SEC6" href="#TOC1">REVISION</a><br> |
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<P> |
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Last updated: 29 May 2007 |
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<br> |
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Copyright © 1997-2007 University of Cambridge. |
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<br> |
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Copyright © 1997-2003 University of Cambridge. |
<p> |
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Return to the <a href="index.html">PCRE index page</a>. |
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</p> |