xml-dev - Re: SAX/C++: First interface draft

[James Clark <jjc@jclark.com>]

Steinar Bang wrote:
> 
> >>>>> James Clark <jjc@jclark.com>:
> 
> > One interesting issue is whether to provide a virtual destructor.  I
> > think the safest solution is not to provide a virtual destructor but
> > instead to declare but not define a private operator delete.  This
> > makes it a compile time error to do:
> 
> >   DTDHandler *p;
> >   // ...
> >   delete p;
> 
> Hm... not defining a virtual destructor for a class with virtual
> functions gives me warnings in "gcc -Wall".  Will a private operator
> delete do anything about these warnings, I wonder...?

If not, gcc should be fixed, because there's no legitimate reason to
give a warning. I got this technique from

  http://www.develop.com/dbox/cxx/SmartPtr.htm#Obvious

I've also verified that this complies with the C++ standard (the
relevant clause is 12.5p4).  gcc 2.95.1 correctly gives a compile-error
if you try to delete such a class. Visual C++ 6 doesn't catch this at
compile, but you'll still get a link-time error.

The other possible technique is a protected virtual destructor with an
empty implementation.

James



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