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

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 3
The value of *j is 3

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 3
The value of *j is 3
* j

Introduction - Cont.
 How the *j gets the value of i ?
int i , *j ;
Variable
Names
i j
Value
Memory
Address
65524 65522

int i , *j ;
i = 3 ;
Variable
Names
i j
Value
Memory
Address
65524 65522
3

int i , *j ;
i = 3 ;
j = & i ;
Variable
Names
i j
Value 3
Memory
Address
65524 65522
65524
*j refers to the value at address j.

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

Base Class
Public:
a , b
Private /
Protected:
c , d
Derived Class
Public / Private /
Protected :
e , f , g , h
If cptr = & d;
cptr a , b

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.

 E.g . Casting
dptr -> show ( ) ;
( ( DC * ) bptr ) -> show ( ) ;

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 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 addition
3.14 + 2.0 <-- Floating point addition
s1 + "bar" <-- String concatenation!

TYPES OF POLYMORPHISM
Compile-time
Polymorphism
Run-time
Polymorphism

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.

Polymorphism

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