Re: Help with bit-field semantics in C and C++

[Mark Mitchell <mark at codesourcery dot com>]

David Carlton wrote:

> On Tue, 24 Aug 2004 14:11:17 -0700, Mark Mitchell <mark@codesourcery.com> said:
>
>  
>
> > The standard is just plain not clear here.  There's nothing that says
> > definitively what should happen, either with the conversion or with
> > the subsequent use, assuming that conversion to a value outside the
> > enum range is permitted.
> >    
>
> But that last assumption isn't correct, is it?  I don't see how that's
> consistent with 7.2p9: it talks about "the resulting enumeration
> value", which should surely mean that a value outside the enum range
> _isn't_ permitted.
I think you're reading too cleverly.

When reading the C++ standard, it pays to remember that it's big, 
complex, and some parts are better written than others.  The people 
writing it just didn't think of all the corner cases, whichi is not to 
criticize; it's just a fact.  I know of no compilers that do as you 
suggest, and I think it would disappoint users to have extra conversion 
instructions inserted.  Since EDG passes basically every known 
testsuite, that means no testsuites agree with your interpretation.  If 
we did as you suggest, we'd end up with -ffast-enums to get the behavior 
everyone expects.

--
Mark Mitchell
CodeSourcery, LLC
(916) 791-8304
mark@codesourcery.com