Operator keyword c++

Question

We have following class. I need explanation of some parts of code.

class CPoint3D
    {
    public:
      double x, y, z;

      CPoint3D (double dX = 0.0, double dY = 0.0, double dZ = 0.0) 
              : x(dX), y(dY), z(dZ) {}
      //what means these lines of    code?
      CPoint3D operator + (const CPoint3D& point) const;
      CPoint3D operator - (const CPoint3D& point) const;
      CPoint3D operator * (double dFactor) const;
      CPoint3D operator / (double dFactor) const;
};

I guess using

CPoint3D operator + (const CPoint3D& point) const;

function I can easily add/subtract/multiply/divide instances of CPoint3D class?

Can someone explain this with examples ? Thanks!

Answer 1

There are millions of examples and/or articles of this on the web (including this one) so I won't re-iterate them here.

Suffice to say that when you add together two CPoint3D objects with obj1 + obj2, the function that gets called is operator+ for that class, with one object being this and the other being point.

Your code is responsible for creating another object containing the addition of those two, then returning it.

Ditto for the subtraction. The multiplicative operators are slightly different since they use a double as the other argument - presumably while it makes some sense to add/subtract individual members of your class for the additive operators, that's not as useful for the multiplicative ones.