Inheritance

Inheritance

Create new classes from existing ones

Reuse existing code

Make available to others for additions and extensions without relinquishing control over existing class features

RECALL: Objects as Members of Classes

A class can have objects of other classes as members
class date{
    private:
       int month, day, year;
   };
class Employee{
    private:
      char ssn[9];
      char name[40];
      date birthdate;
       float pay_rate;
    public:
      Employee(); //constructor
      int set_number(char *);
      float calc_pay(float, float);
};

Inheritance - not same as objects as members

Deriving one class from another

Initial class is called the base class, parent class or superclass

Derived class is also called child class or subclass

Derived class is completely new class

Incorporates all data members and operations of base class

Usually adds data members and operations

Can override base class functions

Syntax

The derived class specification line is extended to include : class access base-class-name

Class access can be public, private or protected

In general - most restrictive access used

Protected - also accessible by member functions and member functions of a "derived" class
Constructor initializer must add on the
: base_cls_name(var_list)
after the cls_name::cls_name
class HourlyWorker :public Employee
{
...
};
Can call base class functions - use ::
Base-class :: base-fn();

Inherited Access Restrictions

Base Class Member	Derived Class Access	Derived Class Member
private	: private	inaccessible
protected	: private	private
public	: private	private

private	: public	inaccessible
protected	: public	protected
public	: public	public

private	: protected	inaccessible
protected	: protected	protected
public	: protected	protected

Simple and Multiple Inheritance

Derived type has one parent type

Derived type as multiple parents