Class Constructors and Destructors
What is a Constructor?
A class constructor is a special function in a class that is called when a new object of the class is declared. It therefore provides the opportunity to initialize objects as they are created and to ensure that data members only contain valid values.
· constructor purpose is to initialize data members
· it is not explecitly call
· It is automatically call so it have no return type
· Constructor does not have return type
· It has same name as class name
You have no leeway in naming a class constructor - it always has the same name as the class in which it is defined.. It also has no return type. It's wrong to specify a return type for a constructor; you must not even write it as void. The primary function of a class constructor is to assign initial values to the data elements of the class, and no return type is necessary .
Constructor for class rational is
rational ( ):num( 1 ) , denum( 1 )
{ }
Constructor for class distance is
distance ( ): feet( 0) , inches ( 0.0 )
{ }
Here an example of rational class will clear your idea , very easy
#include <iostream>
using namespace std;
class rational
{
private:
int num;
int dnum;
public:
rational():num(1),dnum(1)
{}
void get ()
{
cout<<"enter numerator";
cin>>num;
cout<<"enter denomenator";
cin>>dnum;
}
void print ()
{
cout<<num<<"/"<<dnum<<endl;
}
};
void main ()
{
rational r1;
r1.get();
r1.print();
}
This example will clear your idea about constructor which initializes values to data members as we first use setval( ) function.
Destructor:
A constructor _ is called automatically when an object is first created. you can guess that another function is called automatically when an object is destroyed .such a function is called destructor.
· It is automatically call
· No return type
· same name as class name which same as constructor but with a tilde sign
· It does not take any parameter so it can not be overloaded. // can destructor be overloaded ?
A destructor has same name as constructor which is same as class name but destructor is repersented by sign tilde ( ~ ).
Class foo
{
private:
int data;
public:
foo ( ) : data ( 0 ) // constructor
{ }
~ foo ( ) // destructor , it does not take any parameter
{ }
};
