Class Constructor and Desturctor Function

7/31/2019 Class Constructor and Desturctor Function

1/27

Class Constructor & Destructor

Function

02/02/11 & 03/02/11


2/27

Initialization of Data in Class

Class car

{

private :

int x, y ;

public :

car ()

{

x = 10;y = 20;

}

car (int i )

{

x = i ;

y = i + 50;}

car (int i, int j )

{

x = i ;

y = j ;

}};

main ()

{

car c ;

car m(70);

car k( 5, 10);

.

.

.

.}

CONSTRUCTOR

Default Constructor

Parameterized

Constructor

10 20


3/27

Class Constructor

A Constructor function is a public function andhas same name as that of the class.

General Characteristics of constructor function:

(i) Constructor has same name as that of the class.

(ii) It is declared as a public function.

(iii) It may be defined inside the class or outside

the the class .If it is defined outside the class its

prototype must be declared in the class body.


4/27

Contd..

(iv) It does not return any value, nor it is of type

void .So no type is written for it.

(v) The constructor is automatically calledwhenever an object is created.


5/27

Example

#includeusing namespace std;

class Cubicle

{private :

int x, y, z;

public :

Cubicle( int, int, int ) ;

int volume () { return (x*y*z); }

};


6/27

Contd..Cubicle :: Cubicle(int a, int b, int c)

{ x = a, y = b, z = c ;

cout


7/27

Contd..

The expected output is given below:

constructor called

constructor calledconstructor called

Volume of cube1 = 27

Volume of cube2 = 120Volume of cube3 = 40


8/27

Types of Constructors

A program may have more than one constructor

functions provided their arguments are

different.

Different types of Constructors are :

(i) Constructor with default values

(ii) Constructor with parameters(iii) Copy constructor


9/27

Example

#includeusing namespace std;

class Cubicle

{

private :int x, y, z;

public :

Cubicle() { x = 3, y = 4, z = 2 ;}

Cubicle( int a) { x = a, y = 2, z = 3 ;cout


10/27

Contd..

Cubicle( int m, int k) { x = 3, y = m, z = k ;

cout


11/27

Contd..int main()

{

Cubicle cube2(3);

{Cubicle cube1 ;

cout


12/27

Destructor Functions

A destructor function removes the object from

the computer memory after its relevance is over.

For local object the destructor is called at the end

of the block enclosed by the pair of braces { }wherein the object is created and for a static

object is called at the end of main() function.

The destructor function also has the same nameas class but it is preceded by the tilde symbol (~)

and has no parameters.


13/27

Contd..

#include

using namespace std;

class Cubicle

{

private :int x, y, z;

public :

Cubicle() { x = 3, y = 4, z = 2 ;

cout


14/27

Contd..

Cubicle ( Cubicle &cubeA)

{ x = cubeA.x, y = cubeA.y, z = cubeA.z ;

cout


15/27

int main()

{Cubicle cube2(3);

{Cubicle cube1 ;

cout


16/27

Expected Output..

Constructor with one parameter used.


Destructor used to remove object.


Constructor with two parameters used.


Destructor used to remove object.


Destructor called to remove object.

Destructor called to remove object.


17/27

Accessing private function members of

a class

#include


class Cuboid

{

private :

int surface_area();

int volume();

int x, y, z ;

public :

Cuboid(int L, int W, int H) { x = L; y = W ; z = H ; }

} ;


18/27

Cond..

int Cuboid :: surface_area(){ return 2*(x*y + y*z + z*x ); }

int Cuboid :: volume ()

{ return x*y*z ; }

int main ()

{

Cuboid C1(5,6,4) ;

cout


19/27

Expected output

error: cannot access private member declared in class

Cuboid

error: cannot access private member declared in classCuboid


20/27

Accessing private function member

through a public member function

#include


class Cuboid

{

private :

int surface_area();

int volume();

int x, y, z ;

public :

Cuboid(int L, int W, int H) { x = L; y = W ; z = H ; }


21/27

Contd..

int Surface_area () { return surface_area (); }

int Volume () { return volume() ; }

};int Cuboid :: surface_area()

{ return 2*(x*y + y*z + z*x ); }

int Cuboid :: volume (){ return x*y*z ; }


22/27

Contd..

int main(){

Cuboid C1(5,6,4) ;

cout


23/27

Expected output

Volume of cuboid C1 120

Surface area of C1 = 148


24/27

Local Classes

A class may be declared inside a function, in

which it is called local class.

The scope of a local class is up to the function

definition.


25/27

Classes local to a function

#include

using namespace std ;

int Function ()

{ class X

{ private :

int x ;

public :

X ( int a ) { x = a ; }

int getx() { return x ; }

} x_object(5);


26/27

Contd..

class Y

{

private :

int y ;

public :

Y(int b ) { y = b ;}

int gety () { return y ; }

} y_object (10) ;

return (x_object.getx() * (y_object.gety() ) ) ;

}


27/27

Contd..

void main ()

{

cout

Documents

Class Constructor and Desturctor Function