If you could ask a C++ programmer one question to measure their C++ skills, what would it be?

The question I think is best is: Can you call "delete this;" inside a member function? (I put this as a link so you can think it through first, then go to The Best C++ Interview Question – Ever! to see the correct answer.)

I don't ask this because I expect most people to know the answer. If they did it would not be that useful a question. I ask to see if they can work their way to the correct answer and how they do so.