C#

class ClassA
{
    ClassA(){n = 0;}
    int n;
    void F(){n++;}
};

extern "C"
{
    __declspec(dllexport) void ExportedFunc(ClassA** ppA)
    {
        ClassA* pA = *ppA;
        pA->F();
        }
    }

[StructLayout(LayoutKind.Sequential, CharSet=CharSet.Unicode)]
public class ClassA
{
    int n;
}

class DLLImports
{
    [DllImport("ExportFuncs.dll",
        EntryPoint="ExportedFunc",
        SetLastError=true,CharSet=CharSet.Unicode,
        ExactSpelling=true,
        CallingConvention=CallingConvention.StdCall)]
    public static extern void ExportedFunc(ref ClassA refA);
}

{
    .
    .

    ClassA refA = new classA();
    DLLImports.ExportedFunc(ref refA);
    .
    .
}

class ClassA
{
    ClassA(){n = 0;}
    virtual ~ClassA(){}
    int n;
    void F(){n++;}
};