你称之为成员函数的成员函数是什么？如何编写成员函数？

Question

What do you call function that follows a member function and modifies the return value and how do I write one?

In other words how do I successfully write:

std::cout << box.getVolume().inCubicFeet();

std::cout << box.getVolume().inCubicCentimeters();

Answer 1

For that to work getVolume() needs to return an object of type Volume ( or even a reference to an object of type Volume & ), so that whatever method follows you are able to invoke it on said object. For instance:

class Volume{
    ...
    int inCubicFeet() const {
        //convert it and return it
    }
    int inCubicCentimeters() const {
        //convert it and return it
    }
};


class Box{
    Volume v; //volume object that is initialized somewhere 
              //(either in the constructor of Box or in a method like setVolume)
    ...
    Volume const& getVolume() const {
        return v;
    }
};

Answer 2

box.getVolume() needs to return an object of a class for which a function inCubicFeet() is defined which returns a value for which std::ostream has an overloaded << operator (although you are allowed to define your own overloads). For that second part, a double would suffice.

Answer 3

It is called "member function of the return type". There is nothing special about those methods. The code could be written like this:

const Volume& v = box.getVolume();    // my guess on what the return type is
std::cout << v.inCubicFeet();