downcast

My objective is to do a deep copy of a class, but a virtual class is causing trouble. #include<iostream> using namespace std; class Vir//pure virtual class { public: virtual void hi()=0; }; class Handler:public Vir { public: int i; Handler() {} Handler(int val):i(val) {} void hi() {cout<<"Value of i="<<i<<endl;} int getI() const {return i;} void setI(int j) {i=j;} }; class ControlPanel { public: Vir *v; ControlPanel(const ControlPanel& c)//copy constructor { v=new Handler; v->setI(c.getI()); } int getI()const {return v->getI();} void initialize() {v=new Handler(10);} void hi() {v->hi();}

Is there a way to downcast from a virtual base class to a derived class when there are no virtual functions involved? Here's some code to demonstrate what I'm talking about: struct Base1 { int data; }; struct Base2 { char odd_size[9]; }; struct ViBase { double value; }; struct MostDerived : Base1, Base2, virtual ViBase { bool ok; }; void foo(ViBase &v) { MostDerived &md = somehow_cast<MostDerived&>(v); //but HOW? md.ok = true; } int main() { MostDerived md; foo(md); } Please note that the code is for demonstration only. My real scenario is fairly complex and involves template parameters and

I have an implementation of a State Pattern where each state handles events it gets from a event queue. Base State class therefore has a pure virtual method void handleEvent(const Event*) . Events inherit base Event class but each event contains its data that can be of a different type (e.g. int, string...or whatever). handleEvent has to determine the runtime type of the received event and then perform downcast in order to extract event data. Events are dynamically created and stored in a queue (so upcasting takes place here...). I know that downcasting is a sign of a bad design but is it