Add existing cpp file to visual studio C++ project

Question

I've tried: "source files > add > existing item" and selected the .cpp/.h files but I get still a linker error (possibly because my .cpp files didn't get passed into compiler):

error LNK2001: unresolved external symbol "struct Mem mem" (?mem@@3UMem@@A)

How do I fix it?

Answer 1

I found the solution. I have extern struct Foo in header file which I forget to give an actual definition in some .cpp file.