operation overloading operator++()

Question

class Point{
private:
    int xpos, ypos;
public:
    Point(int x=0, int y=0) : xpos(x), ypos(y) { }
    void showPosition() const {
        cout<<"["<<xpos<<", "<<ypos<<"]"<<endl;
    } 
    Point& operator++(){  //Point operator++()
        xpos+=1;
        ypos+=1;
        return *this;
    }
};

For operator++() I know Point& is the right return type, but I don't get why Point return type would not also work.

    Point operator++(){ 
        xpos+=1;
        ypos+=1;
        return *this;
    }

when I use this to perform

Point pos(1,3);
++(++pos);

I get

[2,4]

not

[3,5] //which is what I should be getting.

I think operator++() without the reference should still give the same result, as it would implicitly call its copy constructor, so albeit slower, I think it should give the same result.

Answer 1

When ++ returns a copy, then the second ++ in ++(++pos) calls operator++ on the copy returned by the first ++ , not on the original pos . Thus the original pos is only incremented once.

Answer 2

Point& operator++()

should return by reference to non-const so as to let us do ,

Point p;
++++p;

Had it returned Point , you would be trying to modify the temporary which is not the behavior you want.