A: There is nothing like Virtual Constructor. The Constructor can’t be virtual as the constructor is a code which is responsible for creating an instance of a class and it can’t be delegated to any other object by virtual keyword means.
Shortly, friend class or function is a class or a function that declared friend of an other class. The idea behind friend class is to provide the access to the private and protected members or member functions of the friend class. There is a lot of controversial opinions on this topic and you should not usually use friends as it is a hole in your design. One of the examples where it's used is a momento design pattern.