Inheritance 1 & 2

7/31/2019 Inheritance 1 & 2

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Inheritance

6/04/11 & 08/04/11


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Definition

It is the process of reusing existing class

program which is already been debugged and

tested without any modification.

The new class is called derived class and the

existing class is called base class.


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Types of Inheritance

Single Inheritance

Multiple Inheritance

Multi-Level Inheritance


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Single Inheritance

When a class inherits a single class it is called

single inheritance.

Ex : class D is the derived class and class B is the

base class

base class

access_specifiers (public or protected or private)Derived class

Class B

Class D


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Declaration Syntax

In case of single inheritance, the derived class

is declared as :

class D : access_specifier B

The access specifier is either public or

protected or private.

ex: for public inheritance the code fordeclaration of class D be :

class D : public B


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Single Public Inheritance

In this kind of inheritance the public function

of base class may be accessed directly by

derived class members, i.e. derived class

inherits these functions.

The objects of derived class can directly access

the public function of base class.


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Example

#include

using namespace std;

class B

{

public :

int m, a ;

int product1() { return a*m ; }

}; // end of base class


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Contd..

class D : public B // declaration of derived class D

{

public :int n;

int Product2() { return n*Product1() ; }

}; // end of class D


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Contd..

int main()

{

D C1 ; //C1 is an object of class D

C1.m = 5; //data directly accessed by object

C1.a = 4;C1.n = 3;

cout


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Base class has public and protected

members

Out of private and protected members of

base class, only protected members may be

accessed by derived class through its own

public function members while the private

members of base class are not visible in

derived class.


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Example

#include


class B //declaration of class B

{

protected :int m ;

public :

int k ;

int square(){return k*k ; }int Product(){return k*m; }

}; // end of class B


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Contd..

class D : public B //class D inherited from class B

{

public :void setvalue1(int a)//public function to access m of B

{ m = a ; }



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Contd..

int main()

{

D C; //C is declared an object of D

C.k = 9 // Direct access to k of class BC.setvalue1(6); //Access to m through public

// member of D

cout


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Public inheritance with base class

having private data

#include

using namespace std ;

class B{

private : // private access

int m ;}; //end of class B


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Contd..

class D : public B // Declaration of class D

{

public :

int a;

void setvalue() // function for accessing m of class B

{

m = a;

}

int n ;



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Contd..

int main()

{ D C ; // Cis an object of class D

C.a = 5;

C.n = 4;

int product = C.a*C.n ;

cout


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Output

Cannot access private member declared in class B

To access the private data members or privatefunction members of base class, corresponding

public function which provide access to private

members of base class


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Contd..

The private members of a base class can only

be accessed through public and protected

functions of base class or by friend functions

of base class.

But friend functions are not inherited.


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Contd..

#include


class B { //base class B

private :int x; // private member of B

int Square() { return x*x ; }//private member of

//class B

public :

void setvalue (int p) ; // setvalue()- a public member//for accessing the private member x of B


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Contd..

int Psquare() { return Square (); } // A public

//member of B to access private member Square()

int m ;


void B : setvalue (int p) { x = p ; };

//definition of setvalue()

class D : public B // declaration of D with public

// inheritance

{

public :int n ;

} ; // end of class D


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Contd..

int main ()

{ D C // C is an object of class D

C.setvalue(5) ; // accessing x of B through setvalue()

C.m = 4; // accessing public member of B directly.C.n = 3; // accessing public member of D directly.

cout


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Single Protected Inheritance

In case of protected inheritance the public

members and the protected members of base

class become members of derived class .

The private members of base class are not

visible to derived class.

They can only be accessed through public and

protected member functions of base class.


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Example

#include


class B {

protected : //Access protected

int m;int Square () { return m*m;}

public : //Access public

int k ;

product() { return k*m;}}; // end of class B


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Contd..

class D : protected B // Inheritance protected

{ public :

void setvalue1(int a) // public member to access m

{ m = a; }

void setvalue2(int p) { k = p ; }//public member to

//access k

int dsquare()

{return B :: Square();} //For accessing Square()


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Example

#include

using namespace std ;

class B { //base class

private :

int m; //private member data

int Square() {

return m*m ;

} // private member function


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Contd..

public :

void setvalueb (int a)

{ m = a ; } // public member to access m

int bSquare()

{

return Square();

} // for accessing Square()

int k ;

int product () { return k*k ;}



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Contd..

class D : protected B //protected inheritance

{

public :

void setvalued (int n) { setvalueb(n); }

void setvalue2 (int p) { k = p ; }//For accessing k

int dbsquare() {

return bSquare() ;

} // For accessing bSquare

int dproduct() {

return product();} // for accessing product()



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Contd..

int main()

{

D C; //C is an object of class D

C.setvalue2(10);C.setvalued(5);

cout


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Single private inheritance

With private inheritance the public and protectedmembers of base class become private membersof derived class.

Hence they cannot be accessed through directly

by an object of derived class. However, they can be accessed through public

function members of derived class.

The private members of base class are not visiblein the derived class, they can be accessed onlythrough public and protected member functionsof the base class.

l f bli d d


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Example for public and protected

members of base class become private

members in derived class#include


class B{protected :

int m ;

public :int k;



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contd..

class D : private B // private inheritance

{

public :

int a;

void setvalue(){ m = a ; }

int n ;}; // end of class D


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Contd..

int main()

{

D C; //C is an object of class D

C.k = 6 ;

C.a = 5 ;

C.n = 4 ;

int product = C.a * C.n ;

cout


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Expected output

An error massage that k cannot be accessed

directly.

k ; cannot access public member declared in

class B


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Example for private inheritance

#include


class B {

protected :

int m ;

public :

int k;

int Square() { return k*k; }

int msquare () { return m*m; }



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Contd..

class D : private B // private inheritance{

public :

int a ;

void setvalue1() // public member of D to access

{ m = a ; } // protected member of B

void setvalue2 (int b) { k = b ;}

// public member of D required to access public

//member of B. Because of private inheritance. Same applies

//to following also.int dmsquare() { return msquare () ; }

int Dsquare() { return B : Square () ; }

};


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Contd..

int main()

{ D C; // C is an object of class D

C.setvalue2(6);

C.a = 5 ;

cout

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Inheritance 1 & 2

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