c++ - converting a base class pointer to a derived class pointer

Question

#include 
using namespace std;

class Base {
public:
  Base() {};
  ~Base() {};
};

template
class Derived: public Base {
  T _val;
public         


        

Answer 1

You must change the base type to be polymorphic:

class Base {
public:
    Base() {};
    virtual ~Base(){};
};

To cast from some supertype to some derived type, you should use dynamic_cast:

Base *b = new Derived(1);
Derived *d = dynamic_cast *>(b);

Using dynamic_cast here checks that the typecast is possible. If there is no need to do that check (because the cast cannot fail), you can also use static_cast:

Base *b = new Derived(1);
Derived *d = static_cast *>(b);