8. Static data members

• Class members may be declared static

• Static data members belong to the class, not to any object...

  • ...so they don't take up space in objects.

• All objects share static variables just like global variables, but in the class scope:

  
      // point.h
      class Point
      {
          static int x_origin;
          static int y_origin;
          int m_x;
          int m_y;
          //...
      };
  
      // point.cpp:
      int Point::x_origin = 0; // initialization of private (!) static members
      int Point::y_origin = 0;