这里根本没有继承.
您只是在创建class A的对象作为class B的成员变量.
这与在类内部或main函数中的class B对象中创建std::string对象的方式相同.
因此，例如，您将无法执行任何多态性.
A* ptr = new B;将引发错误，因为这需要继承.

There is no inheritance here at all.
You''re simply creating an object of class A as a member variable of class B.
This is the same as how you created a std::string object inside the class or an object of class B in the main function.
So, for example, you will not be able to perform any polymorphism.
A* ptr = new B; will throw an error because this needs inheritance.