Inheritance in C++

Inheritance in C++
OOP Feature - New classes are created from the existing classes
Dr. K. Veningston
Department of Computer Science and Engineering
National Institute of Technology Srinagar
veningstonk@nitsri.ac.in
Inheritance
• When we create a class D, deriving the features of the class B
in class D is called inheritance.
class B Base class/Parent class/Super class
class D Derived class/Child class/Sub class
• This feature is supported by all the OOP languages.

Inheritance in C++
• In C++, inheritance is a process in which one object acquires all the
properties and behaviours of its parent object automatically.
• In such a way, you can reuse, extend or modify the attributes and
behaviours which are defined in other class.
– We need not inherit all the attributes and behaviours. We can suppress
some of them.
• In C++, the class which inherits the members of another class is
called derived class and the class whose members are inherited is
called base class.
– The derived class (child class) is the specialized class for the base class
(parent class).
Example 1
PERSON
EMPLOYEE
MANAGER
Properties: name,
Properties: empID,
UID, DoB, height,
General Properties
department, Properties: DeptID

weight,
designation,
bloodGroup,BP,
off_email, salary Behaviours:
bodyTemp,
attendanceReport(),
qualification,
Behaviours: performanceAppraisal(),
parentage, 10th
getSalary(),
mark, 12th mark,
#projects()
email, address, etc.
specialized class
Example 2 BIKE
specialized versions of Vehicle

Properties: # gears,
• Any object of class price,
CAR can access VEHICLE

Behaviours: start(),
maxSpeed()
attributes and
Properties: # tyres,
methods inside seatingCapacity,
color, weight, CAR
class CAR, as well as mileage
the attributes and Behaviours:
Properties: # gears, price,
legRoom,
methods in class travel() groundClearance,
bootSpace, # airBags,
VEHICLE. type
Behaviours: start(),
accelerate(), decelerate()
Derived Classes
• A derived class is defined as the class derived from the base class.
– Exploit the properties of the base class
• Syntax: How to make a derived class?
class derived_class_name : visibility-mode base_class_name {
//body of the derived class
}
– Visibility mode: The visibility mode specifies whether the features of the base
class are publicly inherited or privately inherited. It can be public or private or
protected.
– We cannot access all the attributes and methods present in the base class.
– Visibility mode decides what attributes and methods are inherited and what are
not.
Visibility-modes
public, protected, and private inheritance
• Public inheritance makes public members of the base class
public in the derived class, and the protected members of the
base class remain protected in the derived class.
– NOTE: Private attributes and methods cannot be inherited as they
cannot be accessed outside the class.
• Protected inheritance makes the public and protected
members of the base class protected in the derived class.
• Private inheritance makes the public and protected members
of the base class private in the derived class.
Access specifiers - Summary
Access specifier of Accessed

Class Inherited
Class members outside the class
private ❌ ❌
In Base class public ✓ ✓
✓
❌
protected (acts like private)
Visibility modes - Summary
public (least constraint) < protected < private (more constraint)
Access specifier of Derived class
Access specifier of Base Visibility members
class members mode Security(derived class members) = max(access
specifier, visibility mode)
private ❌ (inaccessible)
public (least constraint) public public
protected protected
public (least constraint) protected protected
protected protected
public (least constraint) private private
protected private
Visibility of Inherited members
Base class Derived class visibility

access
modifier public protected private
public public protected private
protected protected protected private
private ❌(not inherited) ❌ (not inherited) ❌ (not inherited)

Example (Access specifier vs. Visibility mode)
class A { class B : protected A {
public: //a becomes protected here.
int a; …
… }
}
(ii) Multi-level inheritance
class D : private/protected/public C { class C : private B {

//a becomes inaccessible here. //a becomes private here.
//methods here cannot see any attribute named a …
} }
Objects created of class C outside class C
cannot access the attribute a.
Types of Inheritance
• Single inheritance
• Multi-level inheritance
• Multiple inheritance
• Hierarchical inheritance
• Hybrid inheritance
(i) Single Inheritance
• Single inheritance is defined as the inheritance in which a
derived class is inherited from the only one base class.
class Base
class Derived
(i) Single Inheritance
• We can inherit methods as well.
class Base
class Derived
d1.mul(4,5); will result in Error.

(ii) Multi-level Inheritance
• Multilevel inheritance is a process of deriving a class from
another derived class.
• Inheritance is transitive, so the last derived class acquires all
the members of all its base classes.
class Base
class Derived1: Base
class Derived2:Derived1
(ii) Multi-level Inheritance
class Base
class Derived1: Base
class Derived2:Derived1
(iii) Multiple Inheritance
• Multiple inheritance is the process of deriving a new class that
inherits the attributes from two or more classes.
• Syntax: class Base1 class Base2
class derived : visibility base1, visibility base2, …{
//body of the derived class
} class Derived: Base1, Base 2
• What if both Base1 and Base2 has a member int a?

– Both int a will be inherited in the derived class. Besides this, derived
class can have its own int a.
– We have 3 copies of int a, and we can access all 3 of them.
• Ambiguity in Multiple Inheritance
– Ambiguity can be occurred in using the multiple inheritance when a
variable/function with the same name occurs in more than one base
classes.
• Compiler does not know
which display() to invoke
• Ambiguity
Resolution in
Multiple
Inheritance
– Compiler cannot
resolve this
ambiguity.
– When there is
ambiguity, we have
to resolve the scope
for the compiler.
• Ambiguity
Resolution in
Multiple
Inheritance
– Compiler cannot
resolve this
ambiguity.
– When there is
ambiguity, we have
to resolve the
scope for the
compiler.
(iv) Hierarchical Inheritance
• More than one sub-class inherits the property of a single base
class.
class A
class B : A class C : A class D : A
class E : B class F : B
(v) Hybrid Inheritance
• Hybrid inheritance is a class A
combination of more than one
type of inheritance.
class B : A class C : A
• Dirty Inheritance
class D : B class E : B, C
class F : D, E
Topics to be Covered
• Compile-time Polymorphism
– Operator overloading
• Virtual class, virtual methods, Abstract classes
• Run-time Polymorphism
• Real-life Project using OOP principles.

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Inheritance in C++

class B Base class/Parent class/Super class

class D Derived class/Child class/Sub class

• This feature is supported by all the OOP languages.

department, Properties: DeptID

specialized versions of Vehicle

CAR can access VEHICLE

Access specifier of Accessed

In Base class public ✓ ✓

Base class Derived class visibility

public public protected private

protected protected protected private

private ❌(not inherited) ❌ (not inherited) ❌ (not inherited)

(ii) Multi-level inheritance

class D : private/protected/public C { class C : private B {

d1.mul(4,5); will result in Error.

class Derived1: Base

class Derived1: Base

• What if both Base1 and Base2 has a member int a?

class B : A class C : A class D : A

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