Constructors and Destructors in Derived Classes

• Instantiating derived-class object
  • Chain of constructor calls
    • Derived-class constructor invokes base class constructor
      • Implicitly or explicitly
    • Base of inheritance hierarchy
      • Last constructor called in chain
      • First constructor body to finish executing
      • Example: Point3/Circle4/Cylinder hierarchy
        Point3 constructor called last
        Point3 constructor body finishes execution first
    • Initializing data members
      • Each base-class constructor initializes data members
        Inherited by derived class
• Destroying derived-class object
  • Chain of destructor calls
    • Reverse order of constructor chain
    • Destructor of derived-class called first
    • Destructor of next base class up hierarchy next
      • Continue up hierarchy until final base reached; After final base-class destructor, object removed from memory
• Base-class constructors, destructors, assignment operators
  • Not inherited by derived classes
  • Derived class constructors, assignment operators can call
    • Constructors
    • Assignment operators

Next example revisits the point/circle hierarchy by defining class Point4 (4.30-4.31) and class Circle5 (4.32-4.34) that contain constructors and destructors, each of which prints a message when it is invoked.

Figure 4.30: Point4 class header file and Point4 base class contains a constructor and a destructor. (part 1 of 2)

Figure 4.31: Point4 base class contains a constructor and a destructor. (part 2of 2)

Figure 4.32: Circle5 class header file.

Figure 4.33: Circle5 class inherits from class Point4. (part 1 of 2)

Figure 4.34: Circle5 class inherits from class Point4. (part 2 of 2)

Figure 4.35: Constructor and destructor call order.