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1  .TH PCRE 3  .TH PCRE 3
2  .SH NAME  .SH NAME
3  PCRE - Perl-compatible regular expressions  PCRE - Perl-compatible regular expressions
4  .SH PCRE CALLOUTS  .SH "PCRE CALLOUTS"
5  .rs  .rs
6  .sp  .sp
7  .B int (*pcre_callout)(pcre_callout_block *);  .B int (*pcre_callout)(pcre_callout_block *);
# Line 9  PCRE - Perl-compatible regular expressio Line 9  PCRE - Perl-compatible regular expressio
9  PCRE provides a feature called "callout", which is a means of temporarily  PCRE provides a feature called "callout", which is a means of temporarily
10  passing control to the caller of PCRE in the middle of pattern matching. The  passing control to the caller of PCRE in the middle of pattern matching. The
11  caller of PCRE provides an external function by putting its entry point in the  caller of PCRE provides an external function by putting its entry point in the
12  global variable \fIpcre_callout\fR. By default, this variable contains NULL,  global variable \fIpcre_callout\fP. By default, this variable contains NULL,
13  which disables all calling out.  which disables all calling out.
14    .P
15  Within a regular expression, (?C) indicates the points at which the external  Within a regular expression, (?C) indicates the points at which the external
16  function is to be called. Different callout points can be identified by putting  function is to be called. Different callout points can be identified by putting
17  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.
18  For example, this pattern has two callout points:  For example, this pattern has two callout points:
19    .sp
20    (?C1)\dabc(?C2)def    (?C1)\deabc(?C2)def
21    .sp
22  During matching, when PCRE reaches a callout point (and \fIpcre_callout\fR is  If the PCRE_AUTO_CALLOUT option bit is set when \fBpcre_compile()\fP is called,
23  set), the external function is called. Its only argument is a pointer to a  PCRE automatically inserts callouts, all with number 255, before each item in
24  \fBpcre_callout\fR block. This contains the following variables:  the pattern. For example, if PCRE_AUTO_CALLOUT is used with the pattern
25    .sp
26    int          \fIversion\fR;    A(\ed{2}|--)
27    int          \fIcallout_number\fR;  .sp
28    int         *\fIoffset_vector\fR;  it is processed as if it were
29    const char  *\fIsubject\fR;  .sp
30    int          \fIsubject_length\fR;  (?C255)A(?C255)((?C255)\ed{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255)
31    int          \fIstart_match\fR;  .sp
32    int          \fIcurrent_position\fR;  Notice that there is a callout before and after each parenthesis and
33    int          \fIcapture_top\fR;  alternation bar. Automatic callouts can be used for tracking the progress of
34    int          \fIcapture_last\fR;  pattern matching. The
35    void        *\fIcallout_data\fR;  .\" HREF
36    \fBpcretest\fP
37  The \fIversion\fR field is an integer containing the version number of the  .\"
38  block format. The current version is zero. The version number may change in  command has an option that sets automatic callouts; when it is used, the output
39  future if additional fields are added, but the intention is never to remove any  indicates how the pattern is matched. This is useful information when you are
40  of the existing fields.  trying to optimize the performance of a particular pattern.
41    .
42  The \fIcallout_number\fR field contains the number of the callout, as compiled  .
43  into the pattern (that is, the number after ?C).  .SH "MISSING CALLOUTS"
44    .rs
45  The \fIoffset_vector\fR field is a pointer to the vector of offsets that was  .sp
46  passed by the caller to \fBpcre_exec()\fR. The contents can be inspected in  You should be aware that, because of optimizations in the way PCRE matches
47  order to extract substrings that have been matched so far, in the same way as  patterns, callouts sometimes do not happen. For example, if the pattern is
48  for extracting substrings after a match has completed.  .sp
49      ab(?C4)cd
50  The \fIsubject\fR and \fIsubject_length\fR fields contain copies the values  .sp
51  that were passed to \fBpcre_exec()\fR.  PCRE knows that any matching string must contain the letter "d". If the subject
52    string is "abyz", the lack of "d" means that matching doesn't ever start, and
53  The \fIstart_match\fR field contains the offset within the subject at which the  the callout is never reached. However, with "abyd", though the result is still
54    no match, the callout is obeyed.
55    .
56    .
57    .SH "THE CALLOUT INTERFACE"
58    .rs
59    .sp
60    During matching, when PCRE reaches a callout point, the external function
61    defined by \fIpcre_callout\fP is called (if it is set). This applies to both
62    the \fBpcre_exec()\fP and the \fBpcre_dfa_exec()\fP matching functions. The
63    only argument to the callout function is a pointer to a \fBpcre_callout\fP
64    block. This structure contains the following fields:
65    .sp
66      int          \fIversion\fP;
67      int          \fIcallout_number\fP;
68      int         *\fIoffset_vector\fP;
69      const char  *\fIsubject\fP;
70      int          \fIsubject_length\fP;
71      int          \fIstart_match\fP;
72      int          \fIcurrent_position\fP;
73      int          \fIcapture_top\fP;
74      int          \fIcapture_last\fP;
75      void        *\fIcallout_data\fP;
76      int          \fIpattern_position\fP;
77      int          \fInext_item_length\fP;
78    .sp
79    The \fIversion\fP field is an integer containing the version number of the
80    block format. The initial version was 0; the current version is 1. The version
81    number will change again in future if additional fields are added, but the
82    intention is never to remove any of the existing fields.
83    .P
84    The \fIcallout_number\fP field contains the number of the callout, as compiled
85    into the pattern (that is, the number after ?C for manual callouts, and 255 for
86    automatically generated callouts).
87    .P
88    The \fIoffset_vector\fP field is a pointer to the vector of offsets that was
89    passed by the caller to \fBpcre_exec()\fP or \fBpcre_dfa_exec()\fP. When
90    \fBpcre_exec()\fP is used, the contents can be inspected in order to extract
91    substrings that have been matched so far, in the same way as for extracting
92    substrings after a match has completed. For \fBpcre_dfa_exec()\fP this field is
93    not useful.
94    .P
95    The \fIsubject\fP and \fIsubject_length\fP fields contain copies of the values
96    that were passed to \fBpcre_exec()\fP.
97    .P
98    The \fIstart_match\fP field contains the offset within the subject at which the
99  current match attempt started. If the pattern is not anchored, the callout  current match attempt started. If the pattern is not anchored, the callout
100  function may be called several times for different starting points.  function may be called several times from the same point in the pattern for
101    different starting points in the subject.
102  The \fIcurrent_position\fR field contains the offset within the subject of the  .P
103    The \fIcurrent_position\fP field contains the offset within the subject of the
104  current match pointer.  current match pointer.
105    .P
106  The \fIcapture_top\fR field contains one more than the number of the highest  When the \fBpcre_exec()\fP function is used, the \fIcapture_top\fP field
107  numbered captured substring so far. If no substrings have been captured,  contains one more than the number of the highest numbered captured substring so
108  the value of \fIcapture_top\fR is one.  far. If no substrings have been captured, the value of \fIcapture_top\fP is
109    one. This is always the case when \fBpcre_dfa_exec()\fP is used, because it
110  The \fIcapture_last\fR field contains the number of the most recently captured  does not support captured substrings.
111  substring.  .P
112    The \fIcapture_last\fP field contains the number of the most recently captured
113  The \fIcallout_data\fR field contains a value that is passed to  substring. If no substrings have been captured, its value is -1. This is always
114  \fBpcre_exec()\fR by the caller specifically so that it can be passed back in  the case when \fBpcre_dfa_exec()\fP is used.
115  callouts. It is passed in the \fIpcre_callout\fR field of the \fBpcre_extra\fR  .P
116  data structure. If no such data was passed, the value of \fIcallout_data\fR in  The \fIcallout_data\fP field contains a value that is passed to
117  a \fBpcre_callout\fR block is NULL. There is a description of the  \fBpcre_exec()\fP or \fBpcre_dfa_exec()\fP specifically so that it can be
118  \fBpcre_extra\fR structure in the \fBpcreapi\fR documentation.  passed back in callouts. It is passed in the \fIpcre_callout\fP field of the
119    \fBpcre_extra\fP data structure. If no such data was passed, the value of
120    \fIcallout_data\fP in a \fBpcre_callout\fP block is NULL. There is a
121  .SH RETURN VALUES  description of the \fBpcre_extra\fP structure in the
122    .\" HREF
123    \fBpcreapi\fP
124    .\"
125    documentation.
126    .P
127    The \fIpattern_position\fP field is present from version 1 of the
128    \fIpcre_callout\fP structure. It contains the offset to the next item to be
129    matched in the pattern string.
130    .P
131    The \fInext_item_length\fP field is present from version 1 of the
132    \fIpcre_callout\fP structure. It contains the length of the next item to be
133    matched in the pattern string. When the callout immediately precedes an
134    alternation bar, a closing parenthesis, or the end of the pattern, the length
135    is zero. When the callout precedes an opening parenthesis, the length is that
136    of the entire subpattern.
137    .P
138    The \fIpattern_position\fP and \fInext_item_length\fP fields are intended to
139    help in distinguishing between different automatic callouts, which all have the
140    same callout number. However, they are set for all callouts.
141    .
142    .
143    .SH "RETURN VALUES"
144  .rs  .rs
145  .sp  .sp
146  The callout function returns an integer. If the value is zero, matching  The external callout function returns an integer to PCRE. If the value is zero,
147  proceeds as normal. If the value is greater than zero, matching fails at the  matching proceeds as normal. If the value is greater than zero, matching fails
148  current point, but backtracking to test other possibilities goes ahead, just as  at the current point, but the testing of other matching possibilities goes
149  if a lookahead assertion had failed. If the value is less than zero, the match  ahead, just as if a lookahead assertion had failed. If the value is less than
150  is abandoned, and \fBpcre_exec()\fR returns the value.  zero, the match is abandoned, and \fBpcre_exec()\fP (or \fBpcre_dfa_exec()\fP)
151    returns the negative value.
152    .P
153  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
154  values. In particular, PCRE_ERROR_NOMATCH forces a standard "no match" failure.  values. In particular, PCRE_ERROR_NOMATCH forces a standard "no match" failure.
155  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;
156  it will never be used by PCRE itself.  it will never be used by PCRE itself.
157    .P
158  .in 0  .in 0
159  Last updated: 21 January 2003  Last updated: 28 February 2005
160  .br  .br
161  Copyright (c) 1997-2003 University of Cambridge.  Copyright (c) 1997-2005 University of Cambridge.

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