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CONSTRUCTORS

&DESTRUCTORS

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Constructor

Special Member Function used for Initialization -- Same Name as theClass Name

Does NOT Return a Value

Cannot be virtual and static

Implicitly Invoked When Objects are Created or Copied

Can Have Arguments

Cannot be Explicitly Called

Multiple Constructors are Allowed

Default Constructor -- No Arguments -- Explicit or Implicit

Copy Constructor -- Explicit or Implicit

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What is a constructor?

It is a member function which initializes a class.

A constructor has:

(i) the same name as the class itself(ii) no return type

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Constructor

Constructorwhats this?

method used for initializing objects (of certain class)

a recipe for creating object of a given class

Constructordo we need it?

do the class variables need initialization?

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Constructoran unusual method

We cannot not specify the return value (even: no

void).

We cannot call it for the already constructedobject.

We cannot get its address.

It is not even visible in the class scope and has no

name (according to ANSI).

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ConstructorExample 1

/* A Simple Date Class With Constructors */#define size 50

class date{

private:int day, month, year;

char *string_date;

public:

date(); //defaultdate(int ip_day, int ip_month, int ip_year);

date(char *ip_date);

};

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Types of Constructors

Default Constructor : - A constructor that

accepts no arguments is called the default

constructor.

eg: - x::x()

If no such constructor is defined, then the

compiler supplies a default constructor

Parameterized Constructor: -The constructor

that can take arguments are called

parameterized constructor.

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Example Default Constructor

class integer

{ int m,n;

public:integer( ); // default constructor declared

void getinfo( );

};

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Simple Program

// default constructor

#includeUsing namespace std;

class integer

{

int m,n;public:

integer(void); // constructor declared

void getinfo( );

};

integer :: integer void( ) // constructor defined

{

m= 0;

n=0;

}

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Example: parameterized

constructor

class ABC{ int i;

public:

float j; char k;ABC(int a, float b, char c) //parameterized

{ i=a;

j=b;k=c; }

:

};

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Class integer

{

Int m, n;

Public :

Integer (int x, int y);

};

Integer :: integer(int x,int y)

{m= x;

n=y;

}

By Calling the Constructor explicitly

By Calling the consructor implicitly

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We must pass the initial values as arguments

to the constructor function when an object is

declared. This can be done in two ways:

(1) by calling the function explicitly

eg: integer int1 = integer(0,100);

(2) by calling the function implicitly

eg: integer int1(0,100);

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Copy Constructor

Used to declare & initialize object from

another object.

eg: integer L2(L1);

would define the object L2 & at the same

time initialize it to the values of L1.Another

form of this statement is

integer L2 = L1;

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Copy Constructor

1. The syntax for a copy constructor declaration is

class_name :: class_name (class_name &ptr)2. The Copy Constructor may be used in the following

format also using a const keyword.

class_name :: class_name (const class_name & ptr)

3. Copy Constructor are always used when the compiler hasto create a temporary object of a class object.The copyconstructor are used in the following situations:-

4. The Initialization of an object by another object of thesame class.

5. Return of object as a function value.6. Stating the object as by value parameters of a function.

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Copy Constructor Example with Program

//fibonacci series using copy constructor

#include

Using namespaces std ;

Class fibonacci {

Private :

Unsigned long int f0,f1,fib;

Public :

Fiboancci () // constructor

{F0=0;

F1=1;

Fib=f0+f1;

}

Fibonacci (fibonacci &ptr) // copy construtor

{

F0=ptr.f0;

F1=ptr.f1;

Fib=prt.fib;

}

Void increment ( )

{

F0=f1;

F1=fib;

Fib=f0+f1;}

Void display ( )

{

Cout

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Dynamic Constructor

Used to allocate memory while creatingobjects. This will enable the system to

allocate the right amount of memory for each

object when the objects are not of the same

memory.

Allocation of memory to object at the time of

their construction is known as dynamic

construction of objects. The memory is allocated with the help of the

new operator.

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Destructor

What is the destructor?

Easy to guess

When do we need it?

Even easier

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Destructor

Special Member Function used for Clean-up -- Same Nameas the Class Name with a ~

One Single Destructor

Invoked When an Object Goes Out of Scope

Can be Explicitly Called -- Unusual

Cannot Accept Parameters and Does Not Return A Value

Cannot be Declared static, const or volatile

Can be virtual

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DestructorExample 1

/* A Simple Date Class With a Destructor */

#define size 50

class date{

private:

int day, month, year; char *string_date;

public:

date(char *ip_date);~date(); //Destructor

};

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Destructor

as opposed to constructor it is in the class scope

we may call it

destructor, if not defined by programmer, is

generated by compiler it has empty body, but

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Order of calling constructors and

destructors

Constructors

1. base class (classes in order of declaration)

2. class members in order of declaration

3. constructors body

Destructorssimply opposite order

1. destructors body

2. destructors of class members (order opposite todeclaration)

3. destructor of the base class (classes in order opposite todeclaration)

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Thank You!!!