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revision 75 by nigel, Sat Feb 24 21:40:37 2007 UTC revision 691 by ph10, Sun Sep 11 14:31:21 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
96  defined by <i>pcre_callout</i> is called (if it is set). The only argument is a  defined by <i>pcre_callout</i> is called (if it is set). This applies to both
97  pointer to a <b>pcre_callout</b> block. This structure contains the following  the <b>pcre_exec()</b> and the <b>pcre_dfa_exec()</b> matching functions. The
98  fields:  only argument to the callout function is a pointer to a <b>pcre_callout</b>
99    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 101  automatically generated callouts). Line 124  automatically generated callouts).
124  </P>  </P>
125  <P>  <P>
126  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
127  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
128  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
129  for extracting substrings after a match has completed.  substrings that have been matched so far, in the same way as for extracting
130    substrings after a match has completed. For <b>pcre_dfa_exec()</b> this field is
131    not useful.
132  </P>  </P>
133  <P>  <P>
134  The <i>subject</i> and <i>subject_length</i> fields contain copies of the values  The <i>subject</i> and <i>subject_length</i> fields contain copies of the values
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
147  current match pointer.  current match pointer.
148  </P>  </P>
149  <P>  <P>
150  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
151  numbered captured substring so far. If no substrings have been captured,  contains one more than the number of the highest numbered captured substring so
152  the value of <i>capture_top</i> is one.  far. If no substrings have been captured, the value of <i>capture_top</i> is
153    one. This is always the case when <b>pcre_dfa_exec()</b> is used, because it
154    does not support captured substrings.
155  </P>  </P>
156  <P>  <P>
157  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
158  substring. If no substrings have been captured, its value is -1.  substring. If no substrings have been captured, its value is -1. This is always
159    the case when <b>pcre_dfa_exec()</b> is used.
160  </P>  </P>
161  <P>  <P>
162  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
163  <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
164  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
165  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
166  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
167  <b>pcre_extra</b> structure in the  description of the <b>pcre_extra</b> structure in the
168  <a href="pcreapi.html"><b>pcreapi</b></a>  <a href="pcreapi.html"><b>pcreapi</b></a>
169  documentation.  documentation.
170  </P>  </P>
# Line 156  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 backtracking to test other matching possibilities  at the current point, but the testing of other matching possibilities goes
201  goes ahead, just as if a lookahead assertion had failed. If the value is less  ahead, just as if a lookahead assertion had failed. If the value is less than
202  than zero, the match is abandoned, and <b>pcre_exec()</b> returns the negative  zero, the match is abandoned, and <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b>
203  value.  returns the negative value.
204  </P>  </P>
205  <P>  <P>
206  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 171  values. In particular, PCRE_ERROR_NOMATC Line 208  values. In particular, PCRE_ERROR_NOMATC
208  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;
209  it will never be used by PCRE itself.  it will never be used by PCRE itself.
210  </P>  </P>
211    <br><a name="SEC5" href="#TOC1">AUTHOR</a><br>
212  <P>  <P>
213  Last updated: 09 September 2004  Philip Hazel
214    <br>
215    University Computing Service
216    <br>
217    Cambridge CB2 3QH, England.
218    <br>
219    </P>
220    <br><a name="SEC6" href="#TOC1">REVISION</a><br>
221    <P>
222    Last updated: 26 August 2011
223    <br>
224    Copyright &copy; 1997-2011 University of Cambridge.
225  <br>  <br>
 Copyright &copy; 1997-2004 University of Cambridge.  
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>.
228  </p>  </p>
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