class _declspec(dllexport) MyClass{
public:
    int multiply(int x, int y) const;
    char* get_name() const;
};

_declspec(dllexport) void* createMyClass();
_declspec(dllexport) void destroyMyClass(void* objptr);
_declspec(dllexport) int MyClass_multiply(void* objptr, int x, int y);

int MyClass::multiply(int x, int y) const
{
    return x * y;
}

char* MyClass::get_name() const
{
    return "jensa";
}

void* createMyClass()
{
    return new MyClass;
}

void destroyMyClass(void* objptr)
{
    delete static_cast<MyClass*>(objptr);
}

int MyClass_multiply(void* objptr, int x, int y)
{
    std::ofstream fout("jojo.txt", std::ios::out);
    fout << x << std::endl;
    fout << y << std::endl;
    MyClass* p = (MyClass*)(objptr); // Explicit type cast
    fout << p->get_name() << std::endl;
    fout.close();
    return p->multiply(x,y);
}

<DllImport(Constants.DLL_PATH, EntryPoint:="MyClass_multiply",  CallingConvention:=CallingConvention.Cdecl)>
Private Shared Function MyClass_multiply(ByVal objptr As Long, ByVal x As Long, ByVal y As Long) As Long
End Function

Dim objptr As Long = createMyClass()
Me.TextBox3.Text = MyClass_multiply(objptr, 2, 3)