pointers,virtual functions and polymorphism

Dr. BABASAHEB AMBEDKAR TECHNOLOGICAL UNIVERSITY

Presentation on

Pointers , Virtual Functions and Polymorphism. By ,

Ruturaj Nalawade

Sanjay Bidkar

Swapnil Sarwade

Under the Guidance of ,

Mrs . Ladda

POINTERS

INTRODUCTION

Pointers are the variables which holds the addresses of other variables.

Pointer variables are denoted by

‘ * ptr ’

Pointers are the derived data types.

INTRODUCTION – CONT.E.g. :={

int i , *j;i = 3 ; j = & i ;cout<<“The value of i is \t”<<i<<endl;

cout<<“The value of *j is \t”<<*j;}

Output : :

The value of i is 3The value of *j is 3

INTRODUCTION – CONT.E.g. :={

int i , *j;i = 3 ; j = & i ;cout<<“The value of i is \t”<<i<<endl;

cout<<“The value of *j is \t”<<*j;}

Output : :

The value of i is 3The value of *j is 3

* j

Introduction - Cont. How the *j gets the value of i ?int i , *j ;

Variable Names

i j

Value

MemoryAddress

65524 65522

Introduction - Cont. How the *j gets the value of i ?int i , *j ;i = 3 ;

Variable Names

i j

Value

MemoryAddress

65524 65522

3

Introduction - Cont. How the *j gets the value of i ?int i , *j ;i = 3 ;j = & i ;

Variable Names

i j

Value 3

MemoryAddress

65524 65522

65524

*j refers to the value at address j.

INTRODUCTION – CONT.

Pointers are used for memory management and achieving polymorphism.

C++ adds the concept of

CONSTANT POINTER & POINTER TO A CONSTANT . :=

INTRODUCTION - CONT.

1.Constant Pointer ::

Declaration =

data type * const pointer

2.Pointer to a Constant ::

data type const * pointer

3.const data type * const pointer

INTRODUCTION - CONT.

POINTERS TO OBJECTS -

Pointers can point to an object created by class .

Declaration : classname object; classname * pointer; Definition : pointer = & object;

POINTERS TO OBJECTS - CONT.

Object pointers are useful in creating objects at run time.

We can also use an object pointer to access the public members & member function of an object , by using ‘->’ operator and the object pointer .

POINTERS TO OBJECTS –CONT.

E.g.pointer -> getdata( );

We can also use

( * pointer ) . function( );

THIS POINTER

C++ uses keyword ‘ this ’ to represent an object that invokes a member function.

E.g. The function call A. max( ) will set the pointer this to the address of the object A.

E.g. To access private variables inside a member function

a=123; or

this -> a = 123;

THIS POINTER - APPLICATIONS

In operator overloading using member function we use implicitly 'this’ pointer.

The another important application of the pointer 'this' is to return the object it points to .

POINTERS TO DERIVED CLASS

Pointers to objects of a base class are type compatible with pointers to objects of a derived class.

A single pointer variable can be made to point to objects belonging to different classes.

POINTERS TO DERIVED CLASS – CONT.

e.g. B *cptr; B b; D d; cptr = & b; we can also make cptr to point to the

object d as follows: cptr = & d

POINTERS TO DERIVED CLASS – CONT.

Base Class

Public: a , bPrivate / Protected:c , d

Derived Class

Public / Private / Protected :

e , f , g , h

If cptr = & d;

cptr a , b

POINTERS TO DERIVED CLASS – CONT.

This shows that , although a base pointer can be made to point to any number of derived objects, it can not directly access the members defined by a derived class.

To access the members defined by a derived class , cast base pointer to the derived class type.

POINTERS TO DERIVED CLASS – CONT.

E.g . Casting

dptr -> show ( ) ;

( ( DC * ) bptr ) -> show ( ) ;

VIRTUAL FUNCTIONS

VIRTUAL FUNCTION

The application of polymorphism is the ability to refer the objects without any regard to their classes.

This necessitates the use of a single pointer variable to refer to the objects of different classes.

VIRTUAL FUNCTION – CONT.

By making the function 'virtual' in base class C++ determines which function to use at run time based on the type of object pointed to by the base pointer , rather than the type of the pointer.

Runtime polymorphism is achieved only when a virtual function is accessed through a pointer to the base class.

VIRTUAL FUNCTIONS - RULES

1. The virtual functions must be members of some class.

2. They cannot be static members.3. They are accessed by using object

pointers.4. A virtual function can be friend of other

function.5. A virtual function in a base class must

be defined , even though it may not be used.

RULES –CONT.

6. We cannot have a virtual constructors, but we can have virtual destructors.

7. While a base pointer can point to any type of derived object, the reverse is not true.

RULES –CONT.

8. The prototypes of the base class version of a virtual function and all the derived class versions must be identical.

9. When a base pointer points to a derived class , incrementing or decrementing it will not make it to point to the next object of the derived class.

RULES –CONT.

10.If a virtual function is define in the base class ,it need not be necessarily redefined in the derived class.

POLYMORPHISM

POLYMORPHISM

Polymorphism is crucial feature of Object Oriented Programming.

Polymorphism simply means one name having multiple forms.

POLYMORPHISM - CONT.

“Polymorphism is the genie in OOP

who takes instruction from clients and

properly interprets their wishes.”

– Ira Pohl, “Object Oriented

Programming using C++”.

POLYMORPHISM – CONT.

Definition:

Polymorphism is the ability to create a variable, a function or an object that has more than one form.

EXAMPLE:

For example:

The + (plus) operator in C++:4 + 5 <-- Integer addition3.14 + 2.0 <-- Floating point

additions1 + "bar" <-- String

concatenation!

TYPES OF POLYMORPHISM

Compile-time

Polymorphism

Polymorphism

Run-time Polymorphis

m

Function Overloading

Operator Overloadin

g

Virtual Function

TYPES OF POLYMORPHISM

In compile time polymorphism, compiler is able to select the appropriate function a particular call at the compile time.

In run time polymorphism, an appropriate member function is selected while the program is running.

BENEFITS OF POLYMORPHISM

Simplicity:This makes your code easier for you to

write and easier for others to understand.

Extensibility:Polymorphism design and implements

system that are more extensible.

REFERENCES :

Let us C++ – by Yeshwant Kanetkar.

Object Oriented Programming with C++

–by E . BALAGURUSAMY.

Internet.

THANK YOU !!