33 lines
1.3 KiB
Plaintext
33 lines
1.3 KiB
Plaintext
[/
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Copyright 2006-2007 John Maddock.
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE_1_0.txt or copy at
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http://www.boost.org/LICENSE_1_0.txt).
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]
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[section:leftmost_longest_rule The Leftmost Longest Rule]
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Often there is more than one way of matching a regular expression at a
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particular location, for POSIX basic and extended regular expressions,
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the "best" match is determined as follows:
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# Find the leftmost match, if there is only one match possible at
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this location then return it.
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# Find the longest of the possible matches, along with any ties.
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If there is only one such possible match then return it.
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# If there are no marked sub-expressions, then all the remaining
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alternatives are indistinguishable; return the first of these found.
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# Find the match which has matched the first sub-expression in the
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leftmost position, along with any ties. If there is only on such
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match possible then return it.
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# Find the match which has the longest match for the first sub-expression,
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along with any ties. If there is only one such match then return it.
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# Repeat steps 4 and 5 for each additional marked sub-expression.
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# If there is still more than one possible match remaining, then they are
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indistinguishable; return the first one found.
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[endsect]
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