Thread: Linking My Project

You have to have one place where the vector is actually declared. Using extern tells the compiler to just pretend the variable exists because you plan for it to be linked to this module later. So the compiler is all happy to pretend your vector exists and can spit out an intermediate file for you (ie. a .o file), but the linker is what puts everything together.

The linker sees all the extern declarations and has to match them with the actual declaration of the vector, which you should have somewhere. If you have a .cpp file that implements your header file, then you could and/or should declare the variable there.