what compiler are you using?

e.g. on microsoft you have to do something like __declspec(dllexport) and have some code in .cpp file for .lib file to be made. otherwise the library is "header only" and you must include the header and not dll/lib.

Essentially, you got linker error because you either:
- had nothing in the library to link with -> build/compile problem with the dll.
- did not properly configure your project to link with the correctly built library