Upon your request, I wrote a small but complete program that demonstrates the issue. This program consists of 5 source code files:

1) main.cpp 2) StateMachine.hpp 3) StateMachine.cpp 4) SuperState.hpp 5) SubState.hpp

You've got a compiler error, not a linker one, right? If so, why do you need 2 translation units and 5 files to reproduce it? I belive, you can reproduce it in one single file, which we could just copy&paste into an empty file, and try to compile. It should go like this: // states definition... // machine definition... int main() { // machine instantiation }