Diff for /embedaddon/pcre/doc/html/pcrecallout.html between versions 1.1 and 1.1.1.4

version 1.1, 2012/02/21 23:05:52 version 1.1.1.4, 2014/06/15 19:46:05
Line 13  from the original man page. If there is any nonsense i Line 13  from the original man page. If there is any nonsense i
 man page, in case the conversion went wrong.  man page, in case the conversion went wrong.
 <br>  <br>
 <ul>  <ul>
<li><a name="TOC1" href="#SEC1">PCRE CALLOUTS</a><li><a name="TOC1" href="#SEC1">SYNOPSIS</a>
<li><a name="TOC2" href="#SEC2">MISSING CALLOUTS</a><li><a name="TOC2" href="#SEC2">DESCRIPTION</a>
<li><a name="TOC3" href="#SEC3">THE CALLOUT INTERFACE</a><li><a name="TOC3" href="#SEC3">MISSING CALLOUTS</a>
<li><a name="TOC4" href="#SEC4">RETURN VALUES</a><li><a name="TOC4" href="#SEC4">THE CALLOUT INTERFACE</a>
<li><a name="TOC5" href="#SEC5">AUTHOR</a><li><a name="TOC5" href="#SEC5">RETURN VALUES</a>
<li><a name="TOC6" href="#SEC6">REVISION</a><li><a name="TOC6" href="#SEC6">AUTHOR</a>
 <li><a name="TOC7" href="#SEC7">REVISION</a>
 </ul>  </ul>
<br><a name="SEC1" href="#TOC1">PCRE CALLOUTS</a><br><br><a name="SEC1" href="#TOC1">SYNOPSIS</a><br>
 <P>  <P>
   <b>#include &#60;pcre.h&#62;</b>
   </P>
   <P>
 <b>int (*pcre_callout)(pcre_callout_block *);</b>  <b>int (*pcre_callout)(pcre_callout_block *);</b>
 </P>  </P>
 <P>  <P>
   <b>int (*pcre16_callout)(pcre16_callout_block *);</b>
   </P>
   <P>
   <b>int (*pcre32_callout)(pcre32_callout_block *);</b>
   </P>
   <br><a name="SEC2" href="#TOC1">DESCRIPTION</a><br>
   <P>
 PCRE provides a feature called "callout", which is a means of temporarily  PCRE provides a feature called "callout", which is a means of temporarily
 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
 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
global variable <i>pcre_callout</i>. By default, this variable contains NULL,global variable <i>pcre_callout</i> (<i>pcre16_callout</i> for the 16-bit
which disables all calling out.library, <i>pcre32_callout</i> for the 32-bit library). By default, this
 variable contains NULL, which disables all calling out.
 </P>  </P>
 <P>  <P>
 Within a regular expression, (?C) indicates the points at which the external  Within a regular expression, (?C) indicates the points at which the external
Line 39  For example, this pattern has two callout points: Line 51  For example, this pattern has two callout points:
 <pre>  <pre>
   (?C1)abc(?C2)def    (?C1)abc(?C2)def
 </pre>  </pre>
If the PCRE_AUTO_CALLOUT option bit is set when <b>pcre_compile()</b> orIf the PCRE_AUTO_CALLOUT option bit is set when a pattern is compiled, PCRE
<b>pcre_compile2()</b> is called, PCRE automatically inserts callouts, all withautomatically inserts callouts, all with number 255, before each item in the
number 255, before each item in the pattern. For example, if PCRE_AUTO_CALLOUTpattern. For example, if PCRE_AUTO_CALLOUT is used with the pattern
is used with the pattern 
 <pre>  <pre>
   A(\d{2}|--)    A(\d{2}|--)
 </pre>  </pre>
Line 53  it is processed as if it were Line 64  it is processed as if it were
 <br>  <br>
 <br>  <br>
 Notice that there is a callout before and after each parenthesis and  Notice that there is a callout before and after each parenthesis and
alternation bar. Automatic callouts can be used for tracking the progress ofalternation bar. If the pattern contains a conditional group whose condition is
pattern matching. Thean assertion, an automatic callout is inserted immediately before the
 condition. Such a callout may also be inserted explicitly, for example:
 <pre>
   (?(?C9)(?=a)ab|de)
 </pre>
 This applies only to assertion conditions (because they are themselves
 independent groups).
 </P>
 <P>
 Automatic callouts can be used for tracking the progress of pattern matching.
 The
 <a href="pcretest.html"><b>pcretest</b></a>  <a href="pcretest.html"><b>pcretest</b></a>
command has an option that sets automatic callouts; when it is used, the outputprogram has a pattern qualifier (/C) that sets automatic callouts; when it is
indicates how the pattern is matched. This is useful information when you areused, the output indicates how the pattern is being matched. This is useful
trying to optimize the performance of a particular pattern.information when you are trying to optimize the performance of a particular
 pattern.
 </P>  </P>
   <br><a name="SEC3" href="#TOC1">MISSING CALLOUTS</a><br>
 <P>  <P>
The use of callouts in a pattern makes it ineligible for optimization by theYou should be aware that, because of optimizations in the way PCRE compiles and
just-in-time compiler. Studying such a pattern with the PCRE_STUDY_JIT_COMPILEmatches patterns, callouts sometimes do not happen exactly as you might expect.
option always fails. 
 </P>  </P>
 <br><a name="SEC2" href="#TOC1">MISSING CALLOUTS</a><br>  
 <P>  <P>
You should be aware that, because of optimizations in the way PCRE matchesAt compile time, PCRE "auto-possessifies" repeated items when it knows that
patterns by default, callouts sometimes do not happen. For example, if thewhat follows cannot be part of the repeat. For example, a+[bc] is compiled as
pattern isif it were a++[bc]. The <b>pcretest</b> output when this pattern is anchored and
 then applied with automatic callouts to the string "aaaa" is:
 <pre>  <pre>
     ---&#62;aaaa
      +0 ^        ^
      +1 ^        a+
      +3 ^   ^    [bc]
     No match
   </pre>
   This indicates that when matching [bc] fails, there is no backtracking into a+
   and therefore the callouts that would be taken for the backtracks do not occur.
   You can disable the auto-possessify feature by passing PCRE_NO_AUTO_POSSESS
   to <b>pcre_compile()</b>, or starting the pattern with (*NO_AUTO_POSSESS). If
   this is done in <b>pcretest</b> (using the /O qualifier), the output changes to
   this:
   <pre>
     ---&#62;aaaa
      +0 ^        ^
      +1 ^        a+
      +3 ^   ^    [bc]
      +3 ^  ^     [bc]
      +3 ^ ^      [bc]
      +3 ^^       [bc]
     No match
   </pre>
   This time, when matching [bc] fails, the matcher backtracks into a+ and tries
   again, repeatedly, until a+ itself fails.
   </P>
   <P>
   Other optimizations that provide fast "no match" results also affect callouts.
   For example, if the pattern is
   <pre>
   ab(?C4)cd    ab(?C4)cd
 </pre>  </pre>
 PCRE knows that any matching string must contain the letter "d". If the subject  PCRE knows that any matching string must contain the letter "d". If the subject
Line 86  been scanned far enough. Line 137  been scanned far enough.
 </P>  </P>
 <P>  <P>
 You can disable these optimizations by passing the PCRE_NO_START_OPTIMIZE  You can disable these optimizations by passing the PCRE_NO_START_OPTIMIZE
option to <b>pcre_compile()</b>, <b>pcre_exec()</b>, or <b>pcre_dfa_exec()</b>,option to the matching function, or by starting the pattern with
or by starting the pattern with (*NO_START_OPT). This slows down the matching(*NO_START_OPT). This slows down the matching process, but does ensure that
process, but does ensure that callouts such as the example above are obeyed.callouts such as the example above are obeyed.
 </P>  </P>
<br><a name="SEC3" href="#TOC1">THE CALLOUT INTERFACE</a><br><br><a name="SEC4" href="#TOC1">THE CALLOUT INTERFACE</a><br>
 <P>  <P>
 During matching, when PCRE reaches a callout point, the external function  During matching, when PCRE reaches a callout point, the external function
defined by <i>pcre_callout</i> is called (if it is set). This applies to bothdefined by <i>pcre_callout</i> or <i>pcre[16|32]_callout</i> is called (if it is
the <b>pcre_exec()</b> and the <b>pcre_dfa_exec()</b> matching functions. Theset). This applies to both normal and DFA matching. The only argument to the
only argument to the callout function is a pointer to a <b>pcre_callout</b>callout function is a pointer to a <b>pcre_callout</b> or
block. This structure contains the following fields:<b>pcre[16|32]_callout</b> block. These structures contains the following
 fields:
 <pre>  <pre>
  int         <i>version</i>;  int           <i>version</i>;
  int         <i>callout_number</i>;  int           <i>callout_number</i>;
  int        *<i>offset_vector</i>;  int          *<i>offset_vector</i>;
  const char *<i>subject</i>;  const char   *<i>subject</i>;           (8-bit version)
  int         <i>subject_length</i>;  PCRE_SPTR16   <i>subject</i>;           (16-bit version)
  int         <i>start_match</i>;  PCRE_SPTR32   <i>subject</i>;           (32-bit version)
  int         <i>current_position</i>;  int           <i>subject_length</i>;
  int         <i>capture_top</i>;  int           <i>start_match</i>;
  int         <i>capture_last</i>;  int           <i>current_position</i>;
  void       *<i>callout_data</i>;  int           <i>capture_top</i>;
  int         <i>pattern_position</i>;  int           <i>capture_last</i>;
  int         <i>next_item_length</i>; </pre>
  const unsigned char *<i>mark</i>;  int           <i>pattern_position</i>;
   int           <i>next_item_length</i>;
   const unsigned char *<i>mark</i>;       (8-bit version)
   const PCRE_UCHAR16  *<i>mark</i>;       (16-bit version)
   const PCRE_UCHAR32  *<i>mark</i>;       (32-bit version)
 </pre>  </pre>
 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
 block format. The initial version was 0; the current version is 2. The version  block format. The initial version was 0; the current version is 2. The version
Line 124  automatically generated callouts). Line 180  automatically generated callouts).
 </P>  </P>
 <P>  <P>
 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
passed by the caller to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b>. Whenpassed by the caller to the matching function. When <b>pcre_exec()</b> or
<b>pcre_exec()</b> is used, the contents can be inspected in order to extract<b>pcre[16|32]_exec()</b> is used, the contents can be inspected, in order to
substrings that have been matched so far, in the same way as for extractingextract substrings that have been matched so far, in the same way as for
substrings after a match has completed. For <b>pcre_dfa_exec()</b> this field isextracting substrings after a match has completed. For the DFA matching
not useful.functions, this field is not useful.
 </P>  </P>
 <P>  <P>
 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
that were passed to <b>pcre_exec()</b>.that were passed to the matching function.
 </P>  </P>
 <P>  <P>
 The <i>start_match</i> field normally contains the offset within the subject at  The <i>start_match</i> field normally contains the offset within the subject at
Line 147  The <i>current_position</i> field contains the offset  Line 203  The <i>current_position</i> field contains the offset 
 current match pointer.  current match pointer.
 </P>  </P>
 <P>  <P>
When the <b>pcre_exec()</b> function is used, the <i>capture_top</i> fieldWhen the <b>pcre_exec()</b> or <b>pcre[16|32]_exec()</b> is used, the
contains one more than the number of the highest numbered captured substring so<i>capture_top</i> field contains one more than the number of the highest
far. If no substrings have been captured, the value of <i>capture_top</i> isnumbered captured substring so far. If no substrings have been captured, the
one. This is always the case when <b>pcre_dfa_exec()</b> is used, because itvalue of <i>capture_top</i> is one. This is always the case when the DFA
does not support captured substrings.functions are used, because they do not support captured substrings.
 </P>  </P>
 <P>  <P>
 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
substring. If no substrings have been captured, its value is -1. This is alwayssubstring. However, when a recursion exits, the value reverts to what it was
the case when <b>pcre_dfa_exec()</b> is used.outside the recursion, as do the values of all captured substrings. If no
 substrings have been captured, the value of <i>capture_last</i> is -1. This is
 always the case for the DFA matching functions.
 </P>  </P>
 <P>  <P>
The <i>callout_data</i> field contains a value that is passed toThe <i>callout_data</i> field contains a value that is passed to a matching
<b>pcre_exec()</b> or <b>pcre_dfa_exec()</b> specifically so that it can befunction specifically so that it can be passed back in callouts. It is passed
passed back in callouts. It is passed in the <i>pcre_callout</i> field of thein the <i>callout_data</i> field of a <b>pcre_extra</b> or <b>pcre[16|32]_extra</b>
<b>pcre_extra</b> data structure. If no such data was passed, the value ofdata structure. If no such data was passed, the value of <i>callout_data</i> in
<i>callout_data</i> in a <b>pcre_callout</b> block is NULL. There is aa callout block is NULL. There is a description of the <b>pcre_extra</b>
description of the <b>pcre_extra</b> structure in thestructure in the
 <a href="pcreapi.html"><b>pcreapi</b></a>  <a href="pcreapi.html"><b>pcreapi</b></a>
 documentation.  documentation.
 </P>  </P>
 <P>  <P>
The <i>pattern_position</i> field is present from version 1 of theThe <i>pattern_position</i> field is present from version 1 of the callout
<i>pcre_callout</i> structure. It contains the offset to the next item to bestructure. It contains the offset to the next item to be matched in the pattern
matched in the pattern string.string.
 </P>  </P>
 <P>  <P>
The <i>next_item_length</i> field is present from version 1 of theThe <i>next_item_length</i> field is present from version 1 of the callout
<i>pcre_callout</i> structure. It contains the length of the next item to bestructure. It contains the length of the next item to be matched in the pattern
matched in the pattern string. When the callout immediately precedes anstring. When the callout immediately precedes an alternation bar, a closing
alternation bar, a closing parenthesis, or the end of the pattern, the lengthparenthesis, or the end of the pattern, the length is zero. When the callout
is zero. When the callout precedes an opening parenthesis, the length is thatprecedes an opening parenthesis, the length is that of the entire subpattern.
of the entire subpattern. 
 </P>  </P>
 <P>  <P>
 The <i>pattern_position</i> and <i>next_item_length</i> fields are intended to  The <i>pattern_position</i> and <i>next_item_length</i> fields are intended to
Line 187  help in distinguishing between different automatic cal Line 244  help in distinguishing between different automatic cal
 same callout number. However, they are set for all callouts.  same callout number. However, they are set for all callouts.
 </P>  </P>
 <P>  <P>
The <i>mark</i> field is present from version 2 of the <i>pcre_callout</i>The <i>mark</i> field is present from version 2 of the callout structure. In
structure. In callouts from <b>pcre_exec()</b> it contains a pointer to thecallouts from <b>pcre_exec()</b> or <b>pcre[16|32]_exec()</b> it contains a
zero-terminated name of the most recently passed (*MARK), (*PRUNE), or (*THEN)pointer to the zero-terminated name of the most recently passed (*MARK),
item in the match, or NULL if no such items have been passed. Instances of(*PRUNE), or (*THEN) item in the match, or NULL if no such items have been
(*PRUNE) or (*THEN) without a name do not obliterate a previous (*MARK). Inpassed. Instances of (*PRUNE) or (*THEN) without a name do not obliterate a
callouts from <b>pcre_dfa_exec()</b> this field always contains NULL.previous (*MARK). In callouts from the DFA matching functions this field always
 contains NULL.
 </P>  </P>
<br><a name="SEC4" href="#TOC1">RETURN VALUES</a><br><br><a name="SEC5" href="#TOC1">RETURN VALUES</a><br>
 <P>  <P>
 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,
 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
 at the current point, but the testing of other matching possibilities goes  at the current point, but the testing of other matching possibilities goes
 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
zero, the match is abandoned, and <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b>zero, the match is abandoned, the matching function returns the negative value.
returns the negative value. 
 </P>  </P>
 <P>  <P>
 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 209  values. In particular, PCRE_ERROR_NOMATCH forces a sta Line 266  values. In particular, PCRE_ERROR_NOMATCH forces a sta
 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;
 it will never be used by PCRE itself.  it will never be used by PCRE itself.
 </P>  </P>
<br><a name="SEC5" href="#TOC1">AUTHOR</a><br><br><a name="SEC6" href="#TOC1">AUTHOR</a><br>
 <P>  <P>
 Philip Hazel  Philip Hazel
 <br>  <br>
Line 218  University Computing Service Line 275  University Computing Service
 Cambridge CB2 3QH, England.  Cambridge CB2 3QH, England.
 <br>  <br>
 </P>  </P>
<br><a name="SEC6" href="#TOC1">REVISION</a><br><br><a name="SEC7" href="#TOC1">REVISION</a><br>
 <P>  <P>
Last updated: 30 November 2011Last updated: 12 November 2013
 <br>  <br>
Copyright &copy; 1997-2011 University of Cambridge.Copyright &copy; 1997-2013 University of Cambridge.
 <br>  <br>
 <p>  <p>
 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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