You could make things more safe if you are willing to pay the price. Introduce your own pointer safety by using something like a singleton to register your class instances with.
Give or take typing mistakes
template <class T> class Watcher{ static set<T *> instanceList;// Prevent other instances of this class Watcher() { } Watcher(const Watcher &) { }public: static void Register(T* instance) { Watcher<T>::instanceList.insert(instance); // cout << "Registering" << endl; } static void Unregister(T* instance) { Watcher<T>::instanceList.erase(instance); // cout << "Unregistering" << endl; } static bool IsLegal(T* instance) { return (Watcher<T>::instanceList.count(instance) == 1) ? true : false; } static T *GetLegal(T* instance) { if( IsLegal(instance) == true ) return instance; else return NULL; } static int Size() { return Watcher<T>::instanceList.size(); }};
Then you just bung
class Base{public: Base() { Watcher<Base>::Register(this); } ~Base() { Watcher<Base>::Unregister(this); }};class Derived : public Base{public: Derived() { Watcher<Derived>::Register(this); } ~Derived() { Watcher<Derived>::Unregister(this); }};int main(int argc, char* argv[]){ Base one; Derived two; Watcher<Base>::Size(); // the answer is 2Watcher<Derived>::Size(); // the answer is 1 Watcher<Base>::IsLegal(&one + 1) ); // Answer: False Watcher<Derived>::IsLegal(&two); // Answer: True - &two is a valid Derived pointerWatcher<Base>::IsLegal(&two); // Answer: True - &two is a valid Base pointer return 0;}
I wrote a little test program and it does compile and do what I think you want. I may have missed an issue or two here it''s off the top of my head.
There are various adaptations you could make to this - eg not registering etc class in a seperate instanceList. Maybe you want a Register class to inherit from or similar - which checks that the pointer is valid but not if the type conversion is.
I guess this is some form of homebrew RTTI.
There was something else too...but I''ve forgotten it.
Oh well hoped that helped,
Chris
