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revision 77 by nigel, Sat Feb 24 21:40:45 2007 UTC revision 788 by ph10, Tue Dec 6 15:38:01 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 57  command has an option that sets automati Line 60  command has an option that sets automati
60  indicates how the pattern is matched. This is useful information when you are  indicates how the pattern is matched. This is useful information when you are
61  trying to optimize the performance of a particular pattern.  trying to optimize the performance of a particular pattern.
62  </P>  </P>
63    <P>
64    The use of callouts in a pattern makes it ineligible for optimization by the
65    just-in-time compiler. Studying such a pattern with the PCRE_STUDY_JIT_COMPILE
66    option always fails.
67    </P>
68  <br><a name="SEC2" href="#TOC1">MISSING CALLOUTS</a><br>  <br><a name="SEC2" href="#TOC1">MISSING CALLOUTS</a><br>
69  <P>  <P>
70  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
71  patterns, callouts sometimes do not happen. For example, if the pattern is  patterns by default, callouts sometimes do not happen. For example, if the
72    pattern is
73  <pre>  <pre>
74    ab(?C4)cd    ab(?C4)cd
75  </pre>  </pre>
# Line 69  string is "abyz", the lack of "d" means Line 78  string is "abyz", the lack of "d" means
78  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
79  no match, the callout is obeyed.  no match, the callout is obeyed.
80  </P>  </P>
81    <P>
82    If the pattern is studied, PCRE knows the minimum length of a matching string,
83    and will immediately give a "no match" return without actually running a match
84    if the subject is not long enough, or, for unanchored patterns, if it has
85    been scanned far enough.
86    </P>
87    <P>
88    You can disable these optimizations by passing the PCRE_NO_START_OPTIMIZE
89    option to <b>pcre_compile()</b>, <b>pcre_exec()</b>, or <b>pcre_dfa_exec()</b>,
90    or by starting the pattern with (*NO_START_OPT). This slows down the matching
91    process, but does ensure that callouts such as the example above are obeyed.
92    </P>
93  <br><a name="SEC3" href="#TOC1">THE CALLOUT INTERFACE</a><br>  <br><a name="SEC3" href="#TOC1">THE CALLOUT INTERFACE</a><br>
94  <P>  <P>
95  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 98  the <b>pcre_exec()</b> and the <b>pcre_d
98  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>
99  block. This structure contains the following fields:  block. This structure contains the following fields:
100  <pre>  <pre>
101    int          <i>version</i>;    int         <i>version</i>;
102    int          <i>callout_number</i>;    int         <i>callout_number</i>;
103    int         *<i>offset_vector</i>;    int        *<i>offset_vector</i>;
104    const char  *<i>subject</i>;    const char *<i>subject</i>;
105    int          <i>subject_length</i>;    int         <i>subject_length</i>;
106    int          <i>start_match</i>;    int         <i>start_match</i>;
107    int          <i>current_position</i>;    int         <i>current_position</i>;
108    int          <i>capture_top</i>;    int         <i>capture_top</i>;
109    int          <i>capture_last</i>;    int         <i>capture_last</i>;
110    void        *<i>callout_data</i>;    void       *<i>callout_data</i>;
111    int          <i>pattern_position</i>;    int         <i>pattern_position</i>;
112    int          <i>next_item_length</i>;    int         <i>next_item_length</i>;
113      const unsigned char *<i>mark</i>;
114  </pre>  </pre>
115  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
116  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
117  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
118  intention is never to remove any of the existing fields.  intention is never to remove any of the existing fields.
119  </P>  </P>
# Line 113  The <i>subject</i> and <i>subject_length Line 135  The <i>subject</i> and <i>subject_length
135  that were passed to <b>pcre_exec()</b>.  that were passed to <b>pcre_exec()</b>.
136  </P>  </P>
137  <P>  <P>
138  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
139  current match attempt started. If the pattern is not anchored, the callout  which the current match attempt started. However, if the escape sequence \K
140  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
141  different starting points in the subject.  point. If the pattern is not anchored, the callout function may be called
142    several times from the same point in the pattern for different starting points
143    in the subject.
144  </P>  </P>
145  <P>  <P>
146  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 186  The <i>pattern_position</i> and <i>next_
186  help in distinguishing between different automatic callouts, which all have the  help in distinguishing between different automatic callouts, which all have the
187  same callout number. However, they are set for all callouts.  same callout number. However, they are set for all callouts.
188  </P>  </P>
189    <P>
190    The <i>mark</i> field is present from version 2 of the <i>pcre_callout</i>
191    structure. In callouts from <b>pcre_exec()</b> it contains a pointer to the
192    zero-terminated name of the most recently passed (*MARK), (*PRUNE), or (*THEN)
193    item in the match, or NULL if no such items have been passed. Instances of
194    (*PRUNE) or (*THEN) without a name do not obliterate a previous (*MARK). In
195    callouts from <b>pcre_dfa_exec()</b> this field always contains NULL.
196    </P>
197  <br><a name="SEC4" href="#TOC1">RETURN VALUES</a><br>  <br><a name="SEC4" href="#TOC1">RETURN VALUES</a><br>
198  <P>  <P>
199  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,
200  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
201  at the current point, but the testing of other matching possibilities goes  at the current point, but the testing of other matching possibilities goes
202  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
203  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>
204  returns the negative value.  returns the negative value.
205  </P>  </P>
206  <P>  <P>
# Line 177  values. In particular, PCRE_ERROR_NOMATC Line 209  values. In particular, PCRE_ERROR_NOMATC
209  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;
210  it will never be used by PCRE itself.  it will never be used by PCRE itself.
211  </P>  </P>
212    <br><a name="SEC5" href="#TOC1">AUTHOR</a><br>
213  <P>  <P>
214  Last updated: 28 February 2005  Philip Hazel
215    <br>
216    University Computing Service
217    <br>
218    Cambridge CB2 3QH, England.
219    <br>
220    </P>
221    <br><a name="SEC6" href="#TOC1">REVISION</a><br>
222    <P>
223    Last updated: 30 November 2011
224    <br>
225    Copyright &copy; 1997-2011 University of Cambridge.
226  <br>  <br>
 Copyright &copy; 1997-2005 University of Cambridge.  
227  <p>  <p>
228  Return to the <a href="index.html">PCRE index page</a>.  Return to the <a href="index.html">PCRE index page</a>.
229  </p>  </p>

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