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In article <4gbilr$38m@dub-news-svc-1.compuserve.com> 71247.3221@compuserve.com (Don Wallace) writes:

[example of derived class calling pure virtual function in base class]
 
> I suspect that this is perfectly legal C++ code. Every statement taken
> individually is correct. But even if it linked, the net effect of
> calling bar.foo() would be to attempt to activate a pure virtual
> function (In Borland C++ this generates a RTL program halt - it says
> 'pure virtual function called'.)
> 
> The statement/function 
> 
> >    int foo() { return Foo::foo(); }
> 
> refers to Foo::foo() which is inherently not defined. Hence the link
> error.

This is a common misconception: a pure virtual function may or may
not have a definition. It it doesn't have a definition and you try to 
call it anyway, you will probably get a link-time- or run-time error or
your program could just go haywire; if it does have a definition, then
calling it is perfectly OK. The canonical example of a pure virtual
function that does have a definition is a pure virtual destructor: 
without a body, such a class would not be very useful.

- Wil

Wil Evers, ITT Publitec Research and Development, <wil@ittpub.nl>
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