Boost C++ Libraries: Ticket #4309: Negative lookbehind assertion error

Steven Watanabe — Mon, 07 Jun 2010 23:33:22 GMT

According to http://perldoc.perl.org/perlre.html#Extended-Patterns, the latter two are not allowed. (I believe that the default behavior of Boost.Regex is to match perl)

anonymous — Tue, 08 Jun 2010 10:20:22 GMT

I wouldn't be too sure.

(?<!pattern) A zero-width negative look-behind assertion. For example /(?<!bar)foo/ matches any occurrence of "foo" that does not follow "bar". Works only for fixed-width look-behind.

Both foo and bar are fixed-width, so ORing them should also be fixed width. There is no quantifier used in the sample.

For comparison, in .NET, System.Text.RegularExpressions.Regex does it 'right'. The .NET regular expression engine is designed to be mostly compatible with Perl 5 regular expressions. Hmmm?

anonymous — Tue, 08 Jun 2010 12:20:20 GMT

Expressions 2 and 3 should have been rejected - they're not supported either by Perl or by Boost.Regex. Will fix shortly, John.

status changed; resolution set

John Maddock — Tue, 08 Jun 2010 12:41:46 GMT

status new → closed
resolution → fixed

(In [62563]) Some lookbehind assertions were accepted when they should not have been. Fixes #4309.