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revision 96 by nigel, Fri Mar 2 13:10:43 2007 UTC revision 654 by ph10, Tue Aug 2 11:00:40 2011 UTC
# Line 17  man page, in case the conversion went wr Line 17  man page, in case the conversion went wr
17  <li><a name="TOC2" href="#SEC2">MISSING CALLOUTS</a>  <li><a name="TOC2" href="#SEC2">MISSING CALLOUTS</a>
18  <li><a name="TOC3" href="#SEC3">THE CALLOUT INTERFACE</a>  <li><a name="TOC3" href="#SEC3">THE CALLOUT INTERFACE</a>
19  <li><a name="TOC4" href="#SEC4">RETURN VALUES</a>  <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 35  function is to be called. Different call Line 37  function is to be called. Different call
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:
39  <pre>  <pre>
40    (?C1)\deabc(?C2)def    (?C1)abc(?C2)def
41  </pre>  </pre>
42  If the PCRE_AUTO_CALLOUT option bit is set when <b>pcre_compile()</b> is called,  If the PCRE_AUTO_CALLOUT option bit is set when <b>pcre_compile()</b> or
43  PCRE automatically inserts callouts, all with number 255, before each item in  <b>pcre_compile2()</b> is called, PCRE automatically inserts callouts, all with
44  the pattern. For example, if PCRE_AUTO_CALLOUT is used with the pattern  number 255, before each item in the pattern. For example, if PCRE_AUTO_CALLOUT
45    is used with the pattern
46  <pre>  <pre>
47    A(\d{2}|--)    A(\d{2}|--)
48  </pre>  </pre>
# Line 60  trying to optimize the performance of a Line 63  trying to optimize the performance of a
63  <br><a name="SEC2" href="#TOC1">MISSING CALLOUTS</a><br>  <br><a name="SEC2" href="#TOC1">MISSING CALLOUTS</a><br>
64  <P>  <P>
65  You should be aware that, because of optimizations in the way PCRE matches  You should be aware that, because of optimizations in the way PCRE matches
66  patterns, callouts sometimes do not happen. For example, if the pattern is  patterns by default, callouts sometimes do not happen. For example, if the
67    pattern is
68  <pre>  <pre>
69    ab(?C4)cd    ab(?C4)cd
70  </pre>  </pre>
# Line 69  string is "abyz", the lack of "d" means Line 73  string is "abyz", the lack of "d" means
73  the callout is never reached. However, with "abyd", though the result is still  the callout is never reached. However, with "abyd", though the result is still
74  no match, the callout is obeyed.  no match, the callout is obeyed.
75  </P>  </P>
76    <P>
77    If the pattern is studied, PCRE knows the minimum length of a matching string,
78    and will immediately give a "no match" return without actually running a match
79    if the subject is not long enough, or, for unanchored patterns, if it has
80    been scanned far enough.
81    </P>
82    <P>
83    You can disable these optimizations by passing the PCRE_NO_START_OPTIMIZE
84    option to <b>pcre_compile()</b>, <b>pcre_exec()</b>, or <b>pcre_dfa_exec()</b>,
85    or by starting the pattern with (*NO_START_OPT). This slows down the matching
86    process, but does ensure that callouts such as the example above are obeyed.
87    </P>
88  <br><a name="SEC3" href="#TOC1">THE CALLOUT INTERFACE</a><br>  <br><a name="SEC3" href="#TOC1">THE CALLOUT INTERFACE</a><br>
89  <P>  <P>
90  During matching, when PCRE reaches a callout point, the external function  During matching, when PCRE reaches a callout point, the external function
# Line 77  the <b>pcre_exec()</b> and the <b>pcre_d Line 93  the <b>pcre_exec()</b> and the <b>pcre_d
93  only argument to the callout function is a pointer to a <b>pcre_callout</b>  only argument to the callout function is a pointer to a <b>pcre_callout</b>
94  block. This structure contains the following fields:  block. This structure contains the following fields:
95  <pre>  <pre>
96    int          <i>version</i>;    int         <i>version</i>;
97    int          <i>callout_number</i>;    int         <i>callout_number</i>;
98    int         *<i>offset_vector</i>;    int        *<i>offset_vector</i>;
99    const char  *<i>subject</i>;    const char *<i>subject</i>;
100    int          <i>subject_length</i>;    int         <i>subject_length</i>;
101    int          <i>start_match</i>;    int         <i>start_match</i>;
102    int          <i>current_position</i>;    int         <i>current_position</i>;
103    int          <i>capture_top</i>;    int         <i>capture_top</i>;
104    int          <i>capture_last</i>;    int         <i>capture_last</i>;
105    void        *<i>callout_data</i>;    void       *<i>callout_data</i>;
106    int          <i>pattern_position</i>;    int         <i>pattern_position</i>;
107    int          <i>next_item_length</i>;    int         <i>next_item_length</i>;
108      const unsigned char *<i>mark</i>;
109  </pre>  </pre>
110  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
111  block format. The initial version was 0; the current version is 1. The version  block format. The initial version was 0; the current version is 2. The version
112  number will change again in future if additional fields are added, but the  number will change again in future if additional fields are added, but the
113  intention is never to remove any of the existing fields.  intention is never to remove any of the existing fields.
114  </P>  </P>
# Line 113  The <i>subject</i> and <i>subject_length Line 130  The <i>subject</i> and <i>subject_length
130  that were passed to <b>pcre_exec()</b>.  that were passed to <b>pcre_exec()</b>.
131  </P>  </P>
132  <P>  <P>
133  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
134  current match attempt started. If the pattern is not anchored, the callout  which the current match attempt started. However, if the escape sequence \K
135  function may be called several times from the same point in the pattern for  has been encountered, this value is changed to reflect the modified starting
136  different starting points in the subject.  point. If the pattern is not anchored, the callout function may be called
137    several times from the same point in the pattern for different starting points
138    in the subject.
139  </P>  </P>
140  <P>  <P>
141  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 162  The <i>pattern_position</i> and <i>next_ Line 181  The <i>pattern_position</i> and <i>next_
181  help in distinguishing between different automatic callouts, which all have the  help in distinguishing between different automatic callouts, which all have the
182  same callout number. However, they are set for all callouts.  same callout number. However, they are set for all callouts.
183  </P>  </P>
184    <P>
185    The <i>mark</i> field is present from version 2 of the <i>pcre_callout</i>
186    structure. In callouts from <b>pcre_exec()</b> it contains a pointer to the
187    zero-terminated name of the most recently passed (*MARK) item in the match, or
188    NULL if there are no (*MARK)s in the current matching path. In callouts from
189    <b>pcre_dfa_exec()</b> this field always contains NULL.
190    </P>
191  <br><a name="SEC4" href="#TOC1">RETURN VALUES</a><br>  <br><a name="SEC4" href="#TOC1">RETURN VALUES</a><br>
192  <P>  <P>
193  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,
194  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
195  at the current point, but the testing of other matching possibilities goes  at the current point, but the testing of other matching possibilities goes
196  ahead, just as if a lookahead assertion had failed. If the value is less than  ahead, just as if a lookahead assertion had failed. If the value is less than
197  zero, the match is abandoned, and <b>pcre_exec()</b> (or <b>pcre_dfa_exec()</b>)  zero, the match is abandoned, and <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b>
198  returns the negative value.  returns the negative value.
199  </P>  </P>
200  <P>  <P>
# Line 177  values. In particular, PCRE_ERROR_NOMATC Line 203  values. In particular, PCRE_ERROR_NOMATC
203  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;
204  it will never be used by PCRE itself.  it will never be used by PCRE itself.
205  </P>  </P>
206    <br><a name="SEC5" href="#TOC1">AUTHOR</a><br>
207  <P>  <P>
208  Last updated: 28 February 2005  Philip Hazel
209    <br>
210    University Computing Service
211    <br>
212    Cambridge CB2 3QH, England.
213    <br>
214    </P>
215    <br><a name="SEC6" href="#TOC1">REVISION</a><br>
216    <P>
217    Last updated: 31 July 2011
218    <br>
219    Copyright &copy; 1997-2011 University of Cambridge.
220  <br>  <br>
 Copyright &copy; 1997-2005 University of Cambridge.  
221  <p>  <p>
222  Return to the <a href="index.html">PCRE index page</a>.  Return to the <a href="index.html">PCRE index page</a>.
223  </p>  </p>

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