Question

The following code prints:

2
1

instead of

2
2

Why is my setter not adjusting the value?

Main

Vector location = camera.get_location();
camera.get_location().set_y(location.get_y() + 1);
std::cout << location.get_y() + 1 << std::endl;
std::cout << camera.get_location().get_y() << std::endl;

camera.h

#ifndef CAMERA_H
#define CAMERA_H

#include "vector.h"

class Camera {
 private:
  Vector location;
 public:
  Vector get_location();
  void set_location(Vector);
};

#endif

camera.cpp

#include "camera.h"

Vector Camera::get_location() { return location; }
void Camera::set_location(Vector l) { location = l; }

Answer 1

camera.get_location().set_y(location.get_y() + 1);

get_location returns a copy of the original object. So set_y does modify y but it is modiying the copy of the original location. If you want the above to work as you expect, then return reference:

Vector & get_location();

The function-body will be same as before:

Vector& Camera::get_location() { return location; }

Now it will work the way you expected.

You could write the code as:

Vector  & location = camera.get_location(); //save the reference
location.set_y(location.get_y() + 1);

It modifies the camera‘s location object.

Compare the above code with this:

Vector location = camera.get_location(); //save the copy!
location.set_y(location.get_y() + 1);

It does NOT modify camera‘s location object! It modifies the copy, not the original.

Hope that helps.