Calling convention in making DLL

[jdy0803]

I'm trying making DLL which is compatible with Visual Studio 6.0 from Visual Studio 2010.
In case of Visual Studio 6.0, there was no calling convention in the properties but I was able to set calling convention to each functions respectively like following.

extern "C" __declspec (dllexport) int __stdcall MyFunc( int num );

So I could use __stdcall for the functions to be called from VB6 and __cdecl for internal used function.

However, there's calling convention option in the Project Properties > Configuration Properties > C/C++ > Advanced > Calling Convention.
If I choose one,for example, __stdcall, "unresolved exter variables"error occurs at internal function(__cdecl).

How to use Calling Convention in Visual Studio 2010?