It copies on the third line prior to C++0x, and unfortunately not everyone can rely on move semantics yet.

Actually in this particular case that "copy" is allowed to be elided even in C++98, as the copy constructor of person produces no side effects. It would be hard to notice if the optimizer is that smart or not either way though, since it will be optimized by redundant load/store elimination even if it was initially generated without optimization.

And that's the other reason of not using C++ sometimes - you just don't know exactly what happens.