C++ Every single function in another file is 'undefined'

I've just migrated a project over from Eclipse C++, and upon building the compiler completely fails to recognise any function that is not stored in Main.cpp

The 2 relevant headers are included- though the 2nd shows as 'unused', and the files are added to the CMakeList:

add_executable(Proj Main.cpp Main.h EA.cpp EA.h ED.cpp ED.h)

Both share the same namespace and I'm referring to the functions as I have been for the past few weeks this has been compiling fine in Eclipse:

namespace::function(parameter)

The functions are definitely defined in the header files as well. Any help is appreciated, thanks.