QueryInterface - Quiz Results

The answers you selected are indicated below, along with text that explains the correct answers.

1.	When asked for `IUnknown`, an object's implementation of `QueryInterface` can: Please select the best answer.
	A.	Return any COM interface to the caller because all COM interfaces implement `IUnknown`
	B.	Return `E_NOINTERFACE`
	C.	Always return the same interface pointer as its implementation of `IUnknown`

	The correct answer is C.All requests for `IUnknown` must return the same value.

2.	Read the following code carefully. Which of the following are problems with the code?

		Please select all the correct answers.
	A.	`if (riid == IID_IMyComInterface \|\| riid == IID_IUnknown)`
	B.	`else if (riid == IID_IYourComInterface)`
	C.	`ppv = (IMyComInterface ) this;`
	D.	`AddRef--i.e., (*ppv)->AddRef()`--is not called.

	The correct answers are C and D.The cast on line 11 is wrong. It should be `(IYourInterface )`. The result of using the wrong cast is to return the wrong `vtable` to the client. Also, `AddRef`, i.e., `(ppv)->AddRef()` is not called.