xyz.cpp

int main() {
  
  A x;
  B y;
  A z = y;
 
  std::cout << "x.what() = " << x.what() << std::endl;
  std::cout << "y.what() = " << y.what() << std::endl;
  std::cout << "z.what() = " << z.what() << std::endl;
 
  return 0;
}