When a structure, union, or enumeration declaration or a function prototype or a C++ class declaration appears in a manually produced .h file, that declaration is copied into the automatically ...

Basically once you've put a using namespace std; in your header, and someone has included your header, there's no way to undo the using. This can reduce your options when a name conflict occurs.

My question was both dumber and smarter than I thought, and you were able to get to the heart of it. It was not clear to me that the compiler looked at a header file for stuff to compile. I ...