Aiming Derived-Class Pointers at Base-Class Objects

• Previous example
  • Aimed base-class pointer at derived object; Circle "is a" Point
• Aim a derived-class pointer at a base-class object
  • Compiler error
    • No "is a" relationship
    • Point is not a Circle
    • Circle has data/functions that Point does not
      • setRadius (defined in Circle) not defined in Point
  • Can cast base-object"s address to derived-class pointer
    • Called downcasting (more in 10.9)
    • Allows derived-class functionality

Figure 5.7: Aiming a derived-class pointer at a base-class object.