#include <iostream>
using namespace std;
class base 
{
 public:
  virtual ~base(){}
};
class derv: public base 
{
 public:
   void f() { cout << "derv is called" <<endl;}
};
int main() {
  base* p = new base();
  derv *d1 = dynamic_cast<derv*>(p);
  if(d1 == nullptr)
  {
  	std::cout << "nullptr\n";
  }
 
 // Since p point to base , so d1 should return nullptr 
 //calling any function using d1, should fail/crash 
 //but why the following line is working ?? 
 
 d1->f();
}

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