Re: [Boost-users] Re: [regex] Is there any function to know where the input fails to match a regex?

From: Stuart Dootson (stuart.dootson_at_[hidden])
Date: 2005-02-14 07:40:44

On Mon, 14 Feb 2005 12:48:48 +0100, jordi <jordil2_at_[hidden]> wrote:
> John Maddock wrote:
> >> With my undefined funtion I would obtain:
> >>
> >> - Input text:"123 hello abc"
> >> - Latest rigth Regular expression: "(\d)+\s+(\w)+\s+" Matches: "123
> >> hello "
> >> - First wrong regex: "(\d)+\s+(\w)+\s+(\d)+" does not match.
> >>
> >> -> So, "(\d)+" does not match "abc"
> >>
> >> I understand that usually this is not as easy as I write in my simple
> >> example because of the power of regular expressions but I think a
> >> function like that would improve a lot the error reporting
> >> capabilities. Is there any way to do what I need or I must to write my
> >> own check function?
> >
> >
> > That would indeed be useful: actually what we really need is a regular
> > expression debugger, but both need a fully instrumented regex engine to
> > associate states in the machine with characters in the original
> > expression (so you know where the failure occurred).
> >
> > I'm afraid there's no way to do what you want at present, it's always
> > been on my TO-DO list, but never seems to have surfaced !
> >
> > John.
> Does anyone know any application/utility that includes this feature (or
> a regular expression debugger)?  At least this utility would be easier
> to define (and check) a regular expression against a difficult input.
> 
> Thanks anyway,
> 
> Jordi
> 

Try 'The Regex Coach' @ http://weitz.de/regex-coach/ - that's my
favourite. Built on a Lisp port of PCRE, it uses Lisp's macro feature
to build instrumentation into the library. The syntax is different in
places to Boost.Regex, but it's close enough for development work.

HTH

Stuart Dootson