Re: [Boost-users] Lookbehind assertions problem with 1.33

From: John Maddock (john_at_[hidden])
Date: 2005-07-15 04:37:39

> I'm trying to use lookbehind assertions, and here's a problem: the
> following syntax
>
> (?<=^.{2}).{4}
>
> gives me the error:
>
> '(?<=^.{2}).{4}' is a bad regular expression: Unmatched [ or [^
>
> while the following works:
>
> (?<=^..).{4}
>
> matching, as I expected, 4 characters after the first 2 characters
> in a line.
>
> Shouldn't the above two regexes work the same way?

Probably, but the lookbehind assertion code is pretty dumb at present: it 
needs to be able to figure out exactly how many characters to look behind in 
advance, and currently bounded repeats aren't supported.  It's probably not 
too hard to support that case, but it's too late for 1.33 I'm afraid.

John.