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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    <li><a name="TOC5" href="#SEC5">AUTHOR</a>
21    <li><a name="TOC6" href="#SEC6">REVISION</a>
22  </ul>  </ul>
23  <br><a name="SEC1" href="#TOC1">PCRE CALLOUTS</a><br>  <br><a name="SEC1" href="#TOC1">PCRE CALLOUTS</a><br>
24  <P>  <P>
# Line 26  Within a regular expression, (?C) indica Line 36  Within a regular expression, (?C) indica
36  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
37  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.
38  For example, this pattern has two callout points:  For example, this pattern has two callout points:
 </P>  
 <P>  
39  <pre>  <pre>
40    (?C1)\dabc(?C2)def    (?C1)abc(?C2)def
41  </PRE>  </pre>
42  </P>  If the PCRE_AUTO_CALLOUT option bit is set when <b>pcre_compile()</b> is called,
43  <P>  PCRE automatically inserts callouts, all with number 255, before each item in
44  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
45  set), the external function is called. Its only argument is a pointer to a  <pre>
46  <b>pcre_callout</b> block. This contains the following variables:    A(\d{2}|--)
47  </P>  </pre>
48  <P>  it is processed as if it were
49    <br>
50    <br>
51    (?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255)
52    <br>
53    <br>
54    Notice that there is a callout before and after each parenthesis and
55    alternation bar. Automatic callouts can be used for tracking the progress of
56    pattern matching. The
57    <a href="pcretest.html"><b>pcretest</b></a>
58    command has an option that sets automatic callouts; when it is used, the output
59    indicates how the pattern is matched. This is useful information when you are
60    trying to optimize the performance of a particular pattern.
61    </P>
62    <br><a name="SEC2" href="#TOC1">MISSING CALLOUTS</a><br>
63    <P>
64    You should be aware that, because of optimizations in the way PCRE matches
65    patterns by default, callouts sometimes do not happen. For example, if the
66    pattern is
67    <pre>
68      ab(?C4)cd
69    </pre>
70    PCRE knows that any matching string must contain the letter "d". If the subject
71    string is "abyz", the lack of "d" means that matching doesn't ever start, and
72    the callout is never reached. However, with "abyd", though the result is still
73    no match, the callout is obeyed.
74    </P>
75    <P>
76    You can disable these optimizations by passing the PCRE_NO_START_OPTIMIZE
77    option to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b>. This slows down the
78    matching process, but does ensure that callouts such as the example above are
79    obeyed.
80    </P>
81    <br><a name="SEC3" href="#TOC1">THE CALLOUT INTERFACE</a><br>
82    <P>
83    During matching, when PCRE reaches a callout point, the external function
84    defined by <i>pcre_callout</i> is called (if it is set). This applies to both
85    the <b>pcre_exec()</b> and the <b>pcre_dfa_exec()</b> matching functions. The
86    only argument to the callout function is a pointer to a <b>pcre_callout</b>
87    block. This structure contains the following fields:
88  <pre>  <pre>
89    int          <i>version</i>;    int          <i>version</i>;
90    int          <i>callout_number</i>;    int          <i>callout_number</i>;
# Line 49  set), the external function is called. I Line 96  set), the external function is called. I
96    int          <i>capture_top</i>;    int          <i>capture_top</i>;
97    int          <i>capture_last</i>;    int          <i>capture_last</i>;
98    void        *<i>callout_data</i>;    void        *<i>callout_data</i>;
99  </PRE>    int          <i>pattern_position</i>;
100  </P>    int          <i>next_item_length</i>;
101  <P>  </pre>
102  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
103  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
104  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
105  of the existing fields.  intention is never to remove any of the existing fields.
106  </P>  </P>
107  <P>  <P>
108  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
109  into the pattern (that is, the number after ?C).  into the pattern (that is, the number after ?C for manual callouts, and 255 for
110    automatically generated callouts).
111  </P>  </P>
112  <P>  <P>
113  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
114  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
115  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
116  for extracting substrings after a match has completed.  substrings that have been matched so far, in the same way as for extracting
117    substrings after a match has completed. For <b>pcre_dfa_exec()</b> this field is
118    not useful.
119  </P>  </P>
120  <P>  <P>
121  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
122  that were passed to <b>pcre_exec()</b>.  that were passed to <b>pcre_exec()</b>.
123  </P>  </P>
124  <P>  <P>
125  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
126  current match attempt started. If the pattern is not anchored, the callout  which the current match attempt started. However, if the escape sequence \K
127  function may be called several times for different starting points.  has been encountered, this value is changed to reflect the modified starting
128    point. If the pattern is not anchored, the callout function may be called
129    several times from the same point in the pattern for different starting points
130    in the subject.
131  </P>  </P>
132  <P>  <P>
133  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
134  current match pointer.  current match pointer.
135  </P>  </P>
136  <P>  <P>
137  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
138  numbered captured substring so far. If no substrings have been captured,  contains one more than the number of the highest numbered captured substring so
139  the value of <i>capture_top</i> is one.  far. If no substrings have been captured, the value of <i>capture_top</i> is
140    one. This is always the case when <b>pcre_dfa_exec()</b> is used, because it
141    does not support captured substrings.
142  </P>  </P>
143  <P>  <P>
144  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
145  substring.  substring. If no substrings have been captured, its value is -1. This is always
146    the case when <b>pcre_dfa_exec()</b> is used.
147  </P>  </P>
148  <P>  <P>
149  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
150  <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
151  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
152  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
153  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
154  <b>pcre_extra</b> structure in the <b>pcreapi</b> documentation.  description of the <b>pcre_extra</b> structure in the
155  </P>  <a href="pcreapi.html"><b>pcreapi</b></a>
156  <br><a name="SEC2" href="#TOC1">RETURN VALUES</a><br>  documentation.
157  <P>  </P>
158  The callout function returns an integer. If the value is zero, matching  <P>
159  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
160  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
161  if a lookahead assertion had failed. If the value is less than zero, the match  matched in the pattern string.
162  is abandoned, and <b>pcre_exec()</b> returns the value.  </P>
163    <P>
164    The <i>next_item_length</i> field is present from version 1 of the
165    <i>pcre_callout</i> structure. It contains the length of the next item to be
166    matched in the pattern string. When the callout immediately precedes an
167    alternation bar, a closing parenthesis, or the end of the pattern, the length
168    is zero. When the callout precedes an opening parenthesis, the length is that
169    of the entire subpattern.
170    </P>
171    <P>
172    The <i>pattern_position</i> and <i>next_item_length</i> fields are intended to
173    help in distinguishing between different automatic callouts, which all have the
174    same callout number. However, they are set for all callouts.
175    </P>
176    <br><a name="SEC4" href="#TOC1">RETURN VALUES</a><br>
177    <P>
178    The external callout function returns an integer to PCRE. If the value is zero,
179    matching proceeds as normal. If the value is greater than zero, matching fails
180    at the current point, but the testing of other matching possibilities goes
181    ahead, just as if a lookahead assertion had failed. If the value is less than
182    zero, the match is abandoned, and <b>pcre_exec()</b> (or <b>pcre_dfa_exec()</b>)
183    returns the negative value.
184  </P>  </P>
185  <P>  <P>
186  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 111  values. In particular, PCRE_ERROR_NOMATC Line 188  values. In particular, PCRE_ERROR_NOMATC
188  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;
189  it will never be used by PCRE itself.  it will never be used by PCRE itself.
190  </P>  </P>
191    <br><a name="SEC5" href="#TOC1">AUTHOR</a><br>
192    <P>
193    Philip Hazel
194    <br>
195    University Computing Service
196    <br>
197    Cambridge CB2 3QH, England.
198    <br>
199    </P>
200    <br><a name="SEC6" href="#TOC1">REVISION</a><br>
201  <P>  <P>
202  Last updated: 21 January 2003  Last updated: 15 March 2009
203    <br>
204    Copyright &copy; 1997-2009 University of Cambridge.
205  <br>  <br>
206  Copyright &copy; 1997-2003 University of Cambridge.  <p>
207    Return to the <a href="index.html">PCRE index page</a>.
208    </p>

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