Interestingly, here's what I get when I feed it your exact question:

    In C++, what happens when you call pop_back() on an empty vector?

    When you call pop_back() on an empty vector in C++, an std::out_of_range exception is thrown. The pop_back() function removes the last element of a vector and it is undefined behavior to call it on an empty vector. Attempting to do so will result in the exception being thrown.

So it basically claims both that an exception is thrown, and that it's undefined behavior. At least in this case, one would know something is up.