Unit 3: Inheritance

Inheritance is the mechanism by which a derived (child) class acquires the data and functions of a base (parent) class. Syntax: class Derived : mode Base { … };

cppclass Student {                       // base
protected:
    int roll;
public:
    void getRoll(int r) { roll = r; }
};
class Exam : public Student {         // multilevel: level 2
protected:
    int m1, m2;
public:
    void getMarks(int a, int b) { m1 = a; m2 = b; }
};
class Result : public Exam {          // level 3
public:
    void show() { cout << roll << " total = " << m1 + m2; }
};

Ambiguity in multiple and hybrid inheritance: if two base classes inherit from the same grandparent, the derived class gets two copies (the diamond problem). It is solved with a virtual base class: class B : virtual public A.

When a derived object is created, the base class constructor runs first, then the derived class constructor. Destructors run in the reverse order. Arguments are passed to the base constructor in the derived constructor's initialiser list: Derived(int a, int b) : Base(a) { … }.

Function overriding means a derived class provides its own version of a function that already exists in the base class, with the same name and same parameters. The derived version hides the base version for derived objects. The base version can still be called with Base::show();.