将子类对象赋值给父类变量后执行虚函数结果

#include <iostream>

using namespace std;

class shape {
public:
	virtual Sum()
	{
		cout << "sum in shape is " << a  << endl;
	}
public:
	int a{5};
	int b{6};
};

class circle : public shape {
public:
	circle()
	{
		a = 20;
		b = 30;
	}

	Sum() final
	{
		cout << "sum in circle is " << d  << endl;
	}
public:
	int c{99};
	int d{100};
};

shape create_shape()
{
  return circle();
}

int main()
{
	shape s = create_shape();

	s.Sum();
	return 0;
}

执行结果：

$ ./chlid_to_parent_obj.exe
sum in shape is 20
 

和预想的一样，变量赋值的确不能实现多态，但是可以看到a的值已经修改为20.