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

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

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?

Quote:

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Originally Posted by laserlight

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

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regards,
George

__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.

Thanks CornedBee,

Quote:

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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.

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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

Yes.

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

Thanks CornedBee!


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

Quote:

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Originally Posted by CornedBee

Yes.

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

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regards,
George

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

Hi CornedBee,


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

Quote:

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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.

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regards,
George

By using class or struct. Duh.

Thanks CornedBee,


My question is answered.

Quote:

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Originally Posted by CornedBee

By using class or struct. Duh.

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regards,
George