I'd rather ask you about what you've done. Then I'd drill down into the specific tools you used to get that thing done. I'd talk to you most likely from a position of knowing probably nothing about your problem domain, and maybe something about the solution domain. In either case, I'd expect you to be able to teach me about the problem, the solution, its technical details, tradeoffs, etc. I want to leave the interview satisfied that I learned something from you. This might even be if we discovered something together. I want to ask a lot of questions exploring my curiosity about your projects in a lot of depth and judge whether I think you are passionate, knowledgeable, and appreciate other people's curiosity. The technical knowledge too is only part of this process--I also want to judge how entusiastic you are to share your past cool work. In addition I want to thoroughly explore "team player" oriented questions such as how you dealt with management, other team members, frustrating situations, etc.
Specifically quizzing you on the STL, boost, or any specific library--stuff you can google--is useless to me. I generally expect people to know how to look that kind of stuff up. There is no typical programmer set of memorized libraries that I expect people to know. And especially when it comes to C++, almost every organization seems to do things very differently. The one exception I make to this is I expect C++ programmers to thoroughly understand pointers and manual memory management. etc.
Note, though, that this is only part of the interview I would administer. I'd expect you to demonstrate competency in data structures, object oriented concepts, threading/os concepts, etc. I'd expect basic competence in the basic syntax of your language--enough to write some basic programs (foobar, etc) for me. However I wouldn't care if you learned about mutexes through Win32, posix, or boost. The concepts are very portable but extremely important. If I tell you a std::list is a linked list, I expect you to be able to instantly grasp the trade offs.