#include <cstdio>
class A
{
   public:
     virtual void p(int n = 0) { printf("%d",n); }
};

class B : public A
{
   public:
     virtual void p(int n = 2) { printf("%d",n); }
};

int main()
{
   A* my = new B();
   my->p(); // it out "0"
   delete my;
   return 0;
}