Unreferenced external symbol during DLL function call

I'm having problems in implementing a class in a DLL in the same way it is explained here . I have my interface with all the methods declared as virtual, I have my class that implements the interface and I have the method that should create the object of the class. The problem is here, when I try to use it I get a "unreferenced external symbol" error. Why?

class IXYZ
{
    virtual void XXX() = 0;
};

class XYZ : public IXYZ
{
    void XXX();
}

#ifdef __cplusplus
    extern "C" __declspec(dllexport) IXYZ* __stdcall GetIXYZ();
#endif
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and I use it inside my win32 program with:

IXYZ *myvar = GetIXYZ();

In my exe program I've included the .h file of the dll

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If you've correctly defined the function in the DLL, and it is exported properly, then the only plausible explanation is that there is something wrong with your use of the .lib file in the application that uses the DLL.