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3  <title>pcrecallout specification</title>  <title>pcrecallout specification</title>
4  </head>  </head>
5  <body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">  <body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
6  This HTML document has been generated automatically from the original man page.  <h1>pcrecallout man page</h1>
7  If there is any nonsense in it, please consult the man page, in case the  <p>
8  conversion went wrong.<br>  Return to the <a href="index.html">PCRE index page</a>.
9    </p>
10    <p>
11    This page is part of the PCRE HTML documentation. It was generated automatically
12    from the original man page. If there is any nonsense in it, please consult the
13    man page, in case the conversion went wrong.
14    <br>
15  <ul>  <ul>
16  <li><a name="TOC1" href="#SEC1">PCRE CALLOUTS</a>  <li><a name="TOC1" href="#SEC1">PCRE CALLOUTS</a>
17  <li><a name="TOC2" href="#SEC2">RETURN VALUES</a>  <li><a name="TOC2" href="#SEC2">MISSING CALLOUTS</a>
18    <li><a name="TOC3" href="#SEC3">THE CALLOUT INTERFACE</a>
19    <li><a name="TOC4" href="#SEC4">RETURN VALUES</a>
20  </ul>  </ul>
21  <br><a name="SEC1" href="#TOC1">PCRE CALLOUTS</a><br>  <br><a name="SEC1" href="#TOC1">PCRE CALLOUTS</a><br>
22  <P>  <P>
# Line 26  Within a regular expression, (?C) indica Line 34  Within a regular expression, (?C) indica
34  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
35  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.
36  For example, this pattern has two callout points:  For example, this pattern has two callout points:
 </P>  
 <P>  
37  <pre>  <pre>
38    (?C1)\dabc(?C2)def    (?C1)\deabc(?C2)def
39  </PRE>  </pre>
40  </P>  If the PCRE_AUTO_CALLOUT option bit is set when <b>pcre_compile()</b> is called,
41  <P>  PCRE automatically inserts callouts, all with number 255, before each item in
42  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
43  set), the external function is called. Its only argument is a pointer to a  <pre>
44  <b>pcre_callout</b> block. This contains the following variables:    A(\d{2}|--)
45    </pre>
46    it is processed as if it were
47    <br>
48    <br>
49    (?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255)
50    <br>
51    <br>
52    Notice that there is a callout before and after each parenthesis and
53    alternation bar. Automatic callouts can be used for tracking the progress of
54    pattern matching. The
55    <a href="pcretest.html"><b>pcretest</b></a>
56    command has an option that sets automatic callouts; when it is used, the output
57    indicates how the pattern is matched. This is useful information when you are
58    trying to optimize the performance of a particular pattern.
59  </P>  </P>
60    <br><a name="SEC2" href="#TOC1">MISSING CALLOUTS</a><br>
61  <P>  <P>
62    You should be aware that, because of optimizations in the way PCRE matches
63    patterns, callouts sometimes do not happen. For example, if the pattern is
64    <pre>
65      ab(?C4)cd
66    </pre>
67    PCRE knows that any matching string must contain the letter "d". If the subject
68    string is "abyz", the lack of "d" means that matching doesn't ever start, and
69    the callout is never reached. However, with "abyd", though the result is still
70    no match, the callout is obeyed.
71    </P>
72    <br><a name="SEC3" href="#TOC1">THE CALLOUT INTERFACE</a><br>
73    <P>
74    During matching, when PCRE reaches a callout point, the external function
75    defined by <i>pcre_callout</i> is called (if it is set). The only argument is a
76    pointer to a <b>pcre_callout</b> block. This structure contains the following
77    fields:
78  <pre>  <pre>
79    int          <i>version</i>;    int          <i>version</i>;
80    int          <i>callout_number</i>;    int          <i>callout_number</i>;
# Line 49  set), the external function is called. I Line 86  set), the external function is called. I
86    int          <i>capture_top</i>;    int          <i>capture_top</i>;
87    int          <i>capture_last</i>;    int          <i>capture_last</i>;
88    void        *<i>callout_data</i>;    void        *<i>callout_data</i>;
89  </PRE>    int          <i>pattern_position</i>;
90  </P>    int          <i>next_item_length</i>;
91  <P>  </pre>
92  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
93  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
94  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
95  of the existing fields.  intention is never to remove any of the existing fields.
96  </P>  </P>
97  <P>  <P>
98  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
99  into the pattern (that is, the number after ?C).  into the pattern (that is, the number after ?C for manual callouts, and 255 for
100    automatically generated callouts).
101  </P>  </P>
102  <P>  <P>
103  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
# Line 68  order to extract substrings that have be Line 106  order to extract substrings that have be
106  for extracting substrings after a match has completed.  for extracting substrings after a match has completed.
107  </P>  </P>
108  <P>  <P>
109  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
110  that were passed to <b>pcre_exec()</b>.  that were passed to <b>pcre_exec()</b>.
111  </P>  </P>
112  <P>  <P>
113  The <i>start_match</i> field contains the offset within the subject at which the  The <i>start_match</i> field contains the offset within the subject at which the
114  current match attempt started. If the pattern is not anchored, the callout  current match attempt started. If the pattern is not anchored, the callout
115  function may be called several times for different starting points.  function may be called several times from the same point in the pattern for
116    different starting points in the subject.
117  </P>  </P>
118  <P>  <P>
119  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
# Line 87  the value of <i>capture_top</i> is one. Line 126  the value of <i>capture_top</i> is one.
126  </P>  </P>
127  <P>  <P>
128  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
129  substring.  substring. If no substrings have been captured, its value is -1.
130  </P>  </P>
131  <P>  <P>
132  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
# Line 95  The <i>callout_data</i> field contains a Line 134  The <i>callout_data</i> field contains a
134  callouts. It is passed in the <i>pcre_callout</i> field of the <b>pcre_extra</b>  callouts. It is passed in the <i>pcre_callout</i> field of the <b>pcre_extra</b>
135  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
136  a <b>pcre_callout</b> block is NULL. There is a description of the  a <b>pcre_callout</b> block is NULL. There is a description of the
137  <b>pcre_extra</b> structure in the <b>pcreapi</b> documentation.  <b>pcre_extra</b> structure in the
138    <a href="pcreapi.html"><b>pcreapi</b></a>
139    documentation.
140    </P>
141    <P>
142    The <i>pattern_position</i> field is present from version 1 of the
143    <i>pcre_callout</i> structure. It contains the offset to the next item to be
144    matched in the pattern string.
145    </P>
146    <P>
147    The <i>next_item_length</i> field is present from version 1 of the
148    <i>pcre_callout</i> structure. It contains the length of the next item to be
149    matched in the pattern string. When the callout immediately precedes an
150    alternation bar, a closing parenthesis, or the end of the pattern, the length
151    is zero. When the callout precedes an opening parenthesis, the length is that
152    of the entire subpattern.
153    </P>
154    <P>
155    The <i>pattern_position</i> and <i>next_item_length</i> fields are intended to
156    help in distinguishing between different automatic callouts, which all have the
157    same callout number. However, they are set for all callouts.
158  </P>  </P>
159  <br><a name="SEC2" href="#TOC1">RETURN VALUES</a><br>  <br><a name="SEC4" href="#TOC1">RETURN VALUES</a><br>
160  <P>  <P>
161  The callout function returns an integer. If the value is zero, matching  The external callout function returns an integer to PCRE. If the value is zero,
162  proceeds as normal. If the value is greater than zero, matching fails at the  matching proceeds as normal. If the value is greater than zero, matching fails
163  current point, but backtracking to test other possibilities goes ahead, just as  at the current point, but backtracking to test other matching possibilities
164  if a lookahead assertion had failed. If the value is less than zero, the match  goes ahead, just as if a lookahead assertion had failed. If the value is less
165  is abandoned, and <b>pcre_exec()</b> returns the value.  than zero, the match is abandoned, and <b>pcre_exec()</b> returns the negative
166    value.
167  </P>  </P>
168  <P>  <P>
169  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
# Line 112  The error number PCRE_ERROR_CALLOUT is r Line 172  The error number PCRE_ERROR_CALLOUT is r
172  it will never be used by PCRE itself.  it will never be used by PCRE itself.
173  </P>  </P>
174  <P>  <P>
175  Last updated: 21 January 2003  Last updated: 09 September 2004
176  <br>  <br>
177  Copyright &copy; 1997-2003 University of Cambridge.  Copyright &copy; 1997-2004 University of Cambridge.
178    <p>
179    Return to the <a href="index.html">PCRE index page</a>.
180    </p>

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