Re: [boost] [regex] Support for Perl's (*SKIP)

Subject: Re: [boost] [regex] Support for Perl's (*SKIP)
From: John Maddock (jz.maddock_at_[hidden])
Date: 2015-04-19 06:55:35

> Without (*SKIP), it can be done only by calling regex::search multiple
> times, using an expression like this:
>
>    (?-s)//.*+|/\*[\S\s]*?\*/|"(?:\\.|[^"\n])*+"|(\bfoo\b)
>
> and ignoring every match where group 1 wasn't matched. That's presumed
> to be slower, and certainly more inconvenient for the programmer.

I've added a bug report for this: 
https://svn.boost.org/trac/boost/ticket/11205

However, in the mean time, there is a much simpler workaround, if you use:

   (?x-s)                 (?# free spacing, dot doesn't match newline)
   (?://.*+               (?# eat single-line comment text)
     |/\*[\S\s]*?\*/      (?# eat multi-line comment text)
     |"(?:\\.|[^"\n])*+"  (?# eat string text)
   )                      (?# skip these)
   |\b(foo)\b             (?# match this)

And if $1 matched, then you have what you were looking for, otherwise 
discard.  It's not as "neat" as the original, but is no less/more efficient.

HTH, John.