Use code such as this to prevent subclasses from deriving from a base class:
class myclass;
class my_lock {
friend class myclass;
private:
my_lock() {}
my_lock(const my_lock&) {}
};
class myclass : public virtual my_lock {
// ...
public:
myclass();
myclass(char*);
// ...
};
myclass m;
class Der : public myclass { };
Der dd; // error Der::dd() cannot access
// my_lock::my_lock(): private member
