When I try to create an object I get a LNK2001 error in Visual Studio, it\'s a problem with the constructor I think since changing the constructor changes the error.
If you have linking error then syntactically your code is OK otherwise you'll get compiler errors.
What you should check(or add) is path in Dependencies property of the project that uses Customer class. In VS you can find it "Project Properties->Configuration Properties->Linker->Input->Additional Dependencies". Seems that linker can't find the external library with Customer implementation. You can successfully compile your project cause all #include are correct but you fail on the stage of linking just because of dependencies.