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2: <head>
3: <title>pcrecallout specification</title>
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6: <h1>pcrecallout man page</h1>
7: <p>
8: Return to the <a href="index.html">PCRE index page</a>.
9: </p>
10: <p>
11: This page is part of the PCRE HTML documentation. It was generated automatically
12: from the original man page. If there is any nonsense in it, please consult the
13: man page, in case the conversion went wrong.
14: <br>
15: <ul>
1.1.1.3 ! misho 16: <li><a name="TOC1" href="#SEC1">SYNOPSIS</a>
! 17: <li><a name="TOC2" href="#SEC2">DESCRIPTION</a>
! 18: <li><a name="TOC3" href="#SEC3">MISSING CALLOUTS</a>
! 19: <li><a name="TOC4" href="#SEC4">THE CALLOUT INTERFACE</a>
! 20: <li><a name="TOC5" href="#SEC5">RETURN VALUES</a>
! 21: <li><a name="TOC6" href="#SEC6">AUTHOR</a>
! 22: <li><a name="TOC7" href="#SEC7">REVISION</a>
1.1 misho 23: </ul>
1.1.1.3 ! misho 24: <br><a name="SEC1" href="#TOC1">SYNOPSIS</a><br>
! 25: <P>
! 26: <b>#include <pcre.h></b>
! 27: </P>
1.1 misho 28: <P>
29: <b>int (*pcre_callout)(pcre_callout_block *);</b>
30: </P>
31: <P>
1.1.1.2 misho 32: <b>int (*pcre16_callout)(pcre16_callout_block *);</b>
33: </P>
34: <P>
1.1.1.3 ! misho 35: <b>int (*pcre32_callout)(pcre32_callout_block *);</b>
! 36: </P>
! 37: <br><a name="SEC2" href="#TOC1">DESCRIPTION</a><br>
! 38: <P>
1.1 misho 39: PCRE provides a feature called "callout", which is a means of temporarily
40: passing control to the caller of PCRE in the middle of pattern matching. The
41: caller of PCRE provides an external function by putting its entry point in the
1.1.1.2 misho 42: global variable <i>pcre_callout</i> (<i>pcre16_callout</i> for the 16-bit
1.1.1.3 ! misho 43: library, <i>pcre32_callout</i> for the 32-bit library). By default, this
! 44: variable contains NULL, which disables all calling out.
1.1 misho 45: </P>
46: <P>
47: Within a regular expression, (?C) indicates the points at which the external
48: function is to be called. Different callout points can be identified by putting
49: a number less than 256 after the letter C. The default value is zero.
50: For example, this pattern has two callout points:
51: <pre>
52: (?C1)abc(?C2)def
53: </pre>
1.1.1.2 misho 54: If the PCRE_AUTO_CALLOUT option bit is set when a pattern is compiled, PCRE
55: automatically inserts callouts, all with number 255, before each item in the
56: pattern. For example, if PCRE_AUTO_CALLOUT is used with the pattern
1.1 misho 57: <pre>
58: A(\d{2}|--)
59: </pre>
60: it is processed as if it were
61: <br>
62: <br>
63: (?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255)
64: <br>
65: <br>
66: Notice that there is a callout before and after each parenthesis and
1.1.1.3 ! misho 67: alternation bar. If the pattern contains a conditional group whose condition is
! 68: an assertion, an automatic callout is inserted immediately before the
! 69: condition. Such a callout may also be inserted explicitly, for example:
! 70: <pre>
! 71: (?(?C9)(?=a)ab|de)
! 72: </pre>
! 73: This applies only to assertion conditions (because they are themselves
! 74: independent groups).
! 75: </P>
! 76: <P>
! 77: Automatic callouts can be used for tracking the progress of pattern matching.
! 78: The
1.1 misho 79: <a href="pcretest.html"><b>pcretest</b></a>
80: command has an option that sets automatic callouts; when it is used, the output
81: indicates how the pattern is matched. This is useful information when you are
82: trying to optimize the performance of a particular pattern.
83: </P>
1.1.1.3 ! misho 84: <br><a name="SEC3" href="#TOC1">MISSING CALLOUTS</a><br>
1.1 misho 85: <P>
86: You should be aware that, because of optimizations in the way PCRE matches
87: patterns by default, callouts sometimes do not happen. For example, if the
88: pattern is
89: <pre>
90: ab(?C4)cd
91: </pre>
92: PCRE knows that any matching string must contain the letter "d". If the subject
93: string is "abyz", the lack of "d" means that matching doesn't ever start, and
94: the callout is never reached. However, with "abyd", though the result is still
95: no match, the callout is obeyed.
96: </P>
97: <P>
98: If the pattern is studied, PCRE knows the minimum length of a matching string,
99: and will immediately give a "no match" return without actually running a match
100: if the subject is not long enough, or, for unanchored patterns, if it has
101: been scanned far enough.
102: </P>
103: <P>
104: You can disable these optimizations by passing the PCRE_NO_START_OPTIMIZE
1.1.1.2 misho 105: option to the matching function, or by starting the pattern with
106: (*NO_START_OPT). This slows down the matching process, but does ensure that
107: callouts such as the example above are obeyed.
1.1 misho 108: </P>
1.1.1.3 ! misho 109: <br><a name="SEC4" href="#TOC1">THE CALLOUT INTERFACE</a><br>
1.1 misho 110: <P>
111: During matching, when PCRE reaches a callout point, the external function
1.1.1.3 ! misho 112: defined by <i>pcre_callout</i> or <i>pcre[16|32]_callout</i> is called
! 113: (if it is set). This applies to both normal and DFA matching. The only
! 114: argument to the callout function is a pointer to a <b>pcre_callout</b>
! 115: or <b>pcre[16|32]_callout</b> block.
1.1.1.2 misho 116: These structures contains the following fields:
1.1 misho 117: <pre>
1.1.1.2 misho 118: int <i>version</i>;
119: int <i>callout_number</i>;
120: int *<i>offset_vector</i>;
121: const char *<i>subject</i>; (8-bit version)
122: PCRE_SPTR16 <i>subject</i>; (16-bit version)
1.1.1.3 ! misho 123: PCRE_SPTR32 <i>subject</i>; (32-bit version)
1.1.1.2 misho 124: int <i>subject_length</i>;
125: int <i>start_match</i>;
126: int <i>current_position</i>;
127: int <i>capture_top</i>;
128: int <i>capture_last</i>;
129: void *<i>callout_data</i>;
130: int <i>pattern_position</i>;
131: int <i>next_item_length</i>;
132: const unsigned char *<i>mark</i>; (8-bit version)
133: const PCRE_UCHAR16 *<i>mark</i>; (16-bit version)
1.1.1.3 ! misho 134: const PCRE_UCHAR32 *<i>mark</i>; (32-bit version)
1.1 misho 135: </pre>
136: The <i>version</i> field is an integer containing the version number of the
137: block format. The initial version was 0; the current version is 2. The version
138: number will change again in future if additional fields are added, but the
139: intention is never to remove any of the existing fields.
140: </P>
141: <P>
142: The <i>callout_number</i> field contains the number of the callout, as compiled
143: into the pattern (that is, the number after ?C for manual callouts, and 255 for
144: automatically generated callouts).
145: </P>
146: <P>
147: The <i>offset_vector</i> field is a pointer to the vector of offsets that was
1.1.1.2 misho 148: passed by the caller to the matching function. When <b>pcre_exec()</b> or
1.1.1.3 ! misho 149: <b>pcre[16|32]_exec()</b> is used, the contents can be inspected, in order to
! 150: extract substrings that have been matched so far, in the same way as for
! 151: extracting substrings after a match has completed. For the DFA matching
! 152: functions, this field is not useful.
1.1 misho 153: </P>
154: <P>
155: The <i>subject</i> and <i>subject_length</i> fields contain copies of the values
1.1.1.2 misho 156: that were passed to the matching function.
1.1 misho 157: </P>
158: <P>
159: The <i>start_match</i> field normally contains the offset within the subject at
160: which the current match attempt started. However, if the escape sequence \K
161: has been encountered, this value is changed to reflect the modified starting
162: point. If the pattern is not anchored, the callout function may be called
163: several times from the same point in the pattern for different starting points
164: in the subject.
165: </P>
166: <P>
167: The <i>current_position</i> field contains the offset within the subject of the
168: current match pointer.
169: </P>
170: <P>
1.1.1.3 ! misho 171: When the <b>pcre_exec()</b> or <b>pcre[16|32]_exec()</b> is used, the
1.1.1.2 misho 172: <i>capture_top</i> field contains one more than the number of the highest
173: numbered captured substring so far. If no substrings have been captured, the
174: value of <i>capture_top</i> is one. This is always the case when the DFA
175: functions are used, because they do not support captured substrings.
1.1 misho 176: </P>
177: <P>
178: The <i>capture_last</i> field contains the number of the most recently captured
1.1.1.3 ! misho 179: substring. However, when a recursion exits, the value reverts to what it was
! 180: outside the recursion, as do the values of all captured substrings. If no
! 181: substrings have been captured, the value of <i>capture_last</i> is -1. This is
! 182: always the case for the DFA matching functions.
1.1 misho 183: </P>
184: <P>
1.1.1.2 misho 185: The <i>callout_data</i> field contains a value that is passed to a matching
186: function specifically so that it can be passed back in callouts. It is passed
1.1.1.3 ! misho 187: in the <i>callout_data</i> field of a <b>pcre_extra</b> or <b>pcre[16|32]_extra</b>
1.1.1.2 misho 188: data structure. If no such data was passed, the value of <i>callout_data</i> in
189: a callout block is NULL. There is a description of the <b>pcre_extra</b>
190: structure in the
1.1 misho 191: <a href="pcreapi.html"><b>pcreapi</b></a>
192: documentation.
193: </P>
194: <P>
1.1.1.2 misho 195: The <i>pattern_position</i> field is present from version 1 of the callout
196: structure. It contains the offset to the next item to be matched in the pattern
197: string.
1.1 misho 198: </P>
199: <P>
1.1.1.2 misho 200: The <i>next_item_length</i> field is present from version 1 of the callout
201: structure. It contains the length of the next item to be matched in the pattern
202: string. When the callout immediately precedes an alternation bar, a closing
203: parenthesis, or the end of the pattern, the length is zero. When the callout
204: precedes an opening parenthesis, the length is that of the entire subpattern.
1.1 misho 205: </P>
206: <P>
207: The <i>pattern_position</i> and <i>next_item_length</i> fields are intended to
208: help in distinguishing between different automatic callouts, which all have the
209: same callout number. However, they are set for all callouts.
210: </P>
211: <P>
1.1.1.2 misho 212: The <i>mark</i> field is present from version 2 of the callout structure. In
1.1.1.3 ! misho 213: callouts from <b>pcre_exec()</b> or <b>pcre[16|32]_exec()</b> it contains a
! 214: pointer to the zero-terminated name of the most recently passed (*MARK),
! 215: (*PRUNE), or (*THEN) item in the match, or NULL if no such items have been
! 216: passed. Instances of (*PRUNE) or (*THEN) without a name do not obliterate a
! 217: previous (*MARK). In callouts from the DFA matching functions this field always
! 218: contains NULL.
1.1 misho 219: </P>
1.1.1.3 ! misho 220: <br><a name="SEC5" href="#TOC1">RETURN VALUES</a><br>
1.1 misho 221: <P>
222: The external callout function returns an integer to PCRE. If the value is zero,
223: matching proceeds as normal. If the value is greater than zero, matching fails
224: at the current point, but the testing of other matching possibilities goes
225: ahead, just as if a lookahead assertion had failed. If the value is less than
1.1.1.2 misho 226: zero, the match is abandoned, the matching function returns the negative value.
1.1 misho 227: </P>
228: <P>
229: Negative values should normally be chosen from the set of PCRE_ERROR_xxx
230: values. In particular, PCRE_ERROR_NOMATCH forces a standard "no match" failure.
231: The error number PCRE_ERROR_CALLOUT is reserved for use by callout functions;
232: it will never be used by PCRE itself.
233: </P>
1.1.1.3 ! misho 234: <br><a name="SEC6" href="#TOC1">AUTHOR</a><br>
1.1 misho 235: <P>
236: Philip Hazel
237: <br>
238: University Computing Service
239: <br>
240: Cambridge CB2 3QH, England.
241: <br>
242: </P>
1.1.1.3 ! misho 243: <br><a name="SEC7" href="#TOC1">REVISION</a><br>
1.1 misho 244: <P>
1.1.1.3 ! misho 245: Last updated: 03 March 2013
1.1 misho 246: <br>
1.1.1.3 ! misho 247: Copyright © 1997-2013 University of Cambridge.
1.1 misho 248: <br>
249: <p>
250: Return to the <a href="index.html">PCRE index page</a>.
251: </p>
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