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revision 929 by ph10, Sat Jan 21 16:37:17 2012 UTC revision 930 by ph10, Fri Feb 24 12:05:54 2012 UTC
# Line 2565  characters that does not include a closi Line 2565  characters that does not include a closi
2565  that is, if the closing parenthesis immediately follows the colon, the effect  that is, if the closing parenthesis immediately follows the colon, the effect
2566  is as if the colon were not there. Any number of these verbs may occur in a  is as if the colon were not there. Any number of these verbs may occur in a
2567  pattern.  pattern.
2568  </P>  <a name="nooptimize"></a></P>
2569    <br><b>
2570    Optimizations that affect backtracking verbs
2571    </b><br>
2572  <P>  <P>
2573  PCRE contains some optimizations that are used to speed up matching by running  PCRE contains some optimizations that are used to speed up matching by running
2574  some checks at the start of each match attempt. For example, it may know the  some checks at the start of each match attempt. For example, it may know the
# Line 2574  present. When one of these optimizations Line 2577  present. When one of these optimizations
2577  included backtracking verbs will not, of course, be processed. You can suppress  included backtracking verbs will not, of course, be processed. You can suppress
2578  the start-of-match optimizations by setting the PCRE_NO_START_OPTIMIZE option  the start-of-match optimizations by setting the PCRE_NO_START_OPTIMIZE option
2579  when calling <b>pcre_compile()</b> or <b>pcre_exec()</b>, or by starting the  when calling <b>pcre_compile()</b> or <b>pcre_exec()</b>, or by starting the
2580  pattern with (*NO_START_OPT).  pattern with (*NO_START_OPT). There is more discussion of this option in the
2581    section entitled
2582    <a href="pcreapi.html#execoptions">"Option bits for <b>pcre_exec()</b>"</a>
2583    in the
2584    <a href="pcreapi.html"><b>pcreapi</b></a>
2585    documentation.
2586  </P>  </P>
2587  <P>  <P>
2588  Experiments with Perl suggest that it too has similar optimizations, sometimes  Experiments with Perl suggest that it too has similar optimizations, sometimes
# Line 2662  After a partial match or a failed match, Line 2670  After a partial match or a failed match,
2670    No match, mark = B    No match, mark = B
2671  </pre>  </pre>
2672  Note that in this unanchored example the mark is retained from the match  Note that in this unanchored example the mark is retained from the match
2673  attempt that started at the letter "X". Subsequent match attempts starting at  attempt that started at the letter "X" in the subject. Subsequent match
2674  "P" and then with an empty string do not get as far as the (*MARK) item, but  attempts starting at "P" and then with an empty string do not get as far as the
2675  nevertheless do not reset it.  (*MARK) item, but nevertheless do not reset it.
2676    </P>
2677    <P>
2678    If you are interested in (*MARK) values after failed matches, you should
2679    probably set the PCRE_NO_START_OPTIMIZE option
2680    <a href="#nooptimize">(see above)</a>
2681    to ensure that the match is always attempted.
2682  </P>  </P>
2683  <br><b>  <br><b>
2684  Verbs that act after backtracking  Verbs that act after backtracking
# Line 2843  Cambridge CB2 3QH, England. Line 2857  Cambridge CB2 3QH, England.
2857  </P>  </P>
2858  <br><a name="SEC28" href="#TOC1">REVISION</a><br>  <br><a name="SEC28" href="#TOC1">REVISION</a><br>
2859  <P>  <P>
2860  Last updated: 09 January 2012  Last updated: 24 February 2012
2861  <br>  <br>
2862  Copyright &copy; 1997-2012 University of Cambridge.  Copyright &copy; 1997-2012 University of Cambridge.
2863  <br>  <br>

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