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| <a name="boost_regex.syntax.leftmost_longest_rule"></a><a class="link" href="leftmost_longest_rule.html" title="The Leftmost Longest Rule"> The Leftmost |
| Longest Rule</a> |
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| <p> |
| Often there is more than one way of matching a regular expression at a particular |
| location, for POSIX basic and extended regular expressions, the "best" |
| match is determined as follows: |
| </p> |
| <div class="orderedlist"><ol type="1"> |
| <li> |
| Find the leftmost match, if there is only one match possible at this |
| location then return it. |
| </li> |
| <li> |
| Find the longest of the possible matches, along with any ties. If there |
| is only one such possible match then return it. |
| </li> |
| <li> |
| If there are no marked sub-expressions, then all the remaining alternatives |
| are indistinguishable; return the first of these found. |
| </li> |
| <li> |
| Find the match which has matched the first sub-expression in the leftmost |
| position, along with any ties. If there is only on such match possible |
| then return it. |
| </li> |
| <li> |
| Find the match which has the longest match for the first sub-expression, |
| along with any ties. If there is only one such match then return it. |
| </li> |
| <li> |
| Repeat steps 4 and 5 for each additional marked sub-expression. |
| </li> |
| <li> |
| If there is still more than one possible match remaining, then they are |
| indistinguishable; return the first one found. |
| </li> |
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| <td align="right"><div class="copyright-footer">Copyright © 1998 -2010 John Maddock<p> |
| Distributed under the Boost Software License, Version 1.0. (See accompanying |
| file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) |
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