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revision 172 by ph10, Tue Jun 5 10:40:13 2007 UTC revision 654 by ph10, Tue Aug 2 11:00:40 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 62  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 71  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 79  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 166  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 192  Cambridge CB2 3QH, England. Line 214  Cambridge CB2 3QH, England.
214  </P>  </P>
215  <br><a name="SEC6" href="#TOC1">REVISION</a><br>  <br><a name="SEC6" href="#TOC1">REVISION</a><br>
216  <P>  <P>
217  Last updated: 29 May 2007  Last updated: 31 July 2011
218  <br>  <br>
219  Copyright &copy; 1997-2007 University of Cambridge.  Copyright &copy; 1997-2011 University of Cambridge.
220  <br>  <br>
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>.

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