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Diffstat (limited to 'pcre/doc/html/pcrepattern.html')
| -rw-r--r-- | pcre/doc/html/pcrepattern.html | 25 |
1 files changed, 15 insertions, 10 deletions
diff --git a/pcre/doc/html/pcrepattern.html b/pcre/doc/html/pcrepattern.html index 624cb447238..c06d1e03f11 100644 --- a/pcre/doc/html/pcrepattern.html +++ b/pcre/doc/html/pcrepattern.html @@ -1003,7 +1003,9 @@ matches "foobar", the first substring is still set to "foo". <P> Perl documents that the use of \K within assertions is "not well defined". In PCRE, \K is acted upon when it occurs inside positive assertions, but is -ignored in negative assertions. +ignored in negative assertions. Note that when a pattern such as (?=ab\K) +matches, the reported start of the match can be greater than the end of the +match. <a name="smallassertions"></a></P> <br><b> Simple assertions @@ -2990,19 +2992,22 @@ match does not always guarantee that a match must be at this starting point. <P> Note that (*COMMIT) at the start of a pattern is not the same as an anchor, unless PCRE's start-of-match optimizations are turned off, as shown in this -<b>pcretest</b> example: +output from <b>pcretest</b>: <pre> re> /(*COMMIT)abc/ data> xyzabc 0: abc - xyzabc\Y + data> xyzabc\Y No match </pre> -PCRE knows that any match must start with "a", so the optimization skips along -the subject to "a" before running the first match attempt, which succeeds. When -the optimization is disabled by the \Y escape in the second subject, the match -starts at "x" and so the (*COMMIT) causes it to fail without trying any other -starting points. +For this pattern, PCRE knows that any match must start with "a", so the +optimization skips along the subject to "a" before applying the pattern to the +first set of data. The match attempt then succeeds. In the second set of data, +the escape sequence \Y is interpreted by the <b>pcretest</b> program. It causes +the PCRE_NO_START_OPTIMIZE option to be set when <b>pcre_exec()</b> is called. +This disables the optimization that skips along to the first character. The +pattern is now applied starting at "x", and so the (*COMMIT) causes the match +to fail without trying any other starting points. <pre> (*PRUNE) or (*PRUNE:NAME) </pre> @@ -3221,9 +3226,9 @@ Cambridge CB2 3QH, England. </P> <br><a name="SEC30" href="#TOC1">REVISION</a><br> <P> -Last updated: 03 December 2013 +Last updated: 08 January 2014 <br> -Copyright © 1997-2013 University of Cambridge. +Copyright © 1997-2014 University of Cambridge. <br> <p> Return to the <a href="index.html">PCRE index page</a>. |