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revision 172 by ph10, Tue Jun 5 10:40:13 2007 UTC revision 691 by ph10, Sun Sep 11 14:31:21 2011 UTC
# Line 39  For example, this pattern has two callou Line 39  For example, this pattern has two callou
39  <pre>  <pre>
40    (?C1)abc(?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 59  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 71  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 79  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 166  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) item in the match, or
193    NULL if there are no (*MARK)s in the current matching path. In callouts from
194    <b>pcre_dfa_exec()</b> this field always contains NULL.
195    </P>
196  <br><a name="SEC4" href="#TOC1">RETURN VALUES</a><br>  <br><a name="SEC4" href="#TOC1">RETURN VALUES</a><br>
197  <P>  <P>
198  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,
199  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
200  at the current point, but the testing of other matching possibilities goes  at the current point, but the testing of other matching possibilities goes
201  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
202  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>
203  returns the negative value.  returns the negative value.
204  </P>  </P>
205  <P>  <P>
# Line 192  Cambridge CB2 3QH, England. Line 219  Cambridge CB2 3QH, England.
219  </P>  </P>
220  <br><a name="SEC6" href="#TOC1">REVISION</a><br>  <br><a name="SEC6" href="#TOC1">REVISION</a><br>
221  <P>  <P>
222  Last updated: 29 May 2007  Last updated: 26 August 2011
223  <br>  <br>
224  Copyright &copy; 1997-2007 University of Cambridge.  Copyright &copy; 1997-2011 University of Cambridge.
225  <br>  <br>
226  <p>  <p>
227  Return to the <a href="index.html">PCRE index page</a>.  Return to the <a href="index.html">PCRE index page</a>.

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