Thread: non-pure virtual function in C++ interface

Hello everyone,


Seems when using __interface to define a C++ interface in Visual Studio, we can provide non-pure virtual function. Previously I think in interface, only pure virtual function is allowed. Seems there is no such restriction now.

Correct?


thanks in advance,
George

Yes, laserlight. I have read thay link before asking this question, but it seems the code can compile in Visual Studio 2008. Looks strange.

BTW: in COM, the interface should be struct, not __interface, right?

Originally Posted by laserlight

According to MSDN, a Visual C++ interface "can only contain public, pure virtual methods".

regards,
George

Thanks CornedBee,

Originally Posted by CornedBee

__interface is just an alias for struct with a __declspec(novtable) attribute attached.

Therefore, whatever the documentation might say about what an interface may contain, this is not actually enforced by the compiler. It's just part of the COM rules: if you interface contains anything besides public, pure virtual functions, you violate these rules and interoperability is no longer guaranteed.

I have got your point. Your suggestion is trying best not to violate the rule and put non-virtual function into __interface, right? :-)


regards,
George

Thanks CornedBee!


What is it -- "that's a different issue"? :-)

Originally Posted by CornedBee

Yes.

Well, actually I'd simply not use __interface, but that's a different issue.

regards,
George

Hi CornedBee,


If you are using COM, how could you avoid using interface -- as C++ extension?

Originally Posted by CornedBee

Means even when I'm using MS's COM, doesn't mean I'm going to use MS's language extension.

regards,
George

Thanks CornedBee,


My question is answered.

Originally Posted by CornedBee

By using class or struct. Duh.

regards,
George