Constructor and Destructor functions are Member Functions of a class having
some special property.
Constructor function gets invoked when an object of a class is constructed
(declared) and destructor function gets invoked when the object is destructed
(goes out of scope).
Use of Constructor and Destructor function of a class
Constructor function is used to initialize member variables to pre-defined
values as soon as an object of a class is declared.Constructor function having parameters is used to initialize the data members
to the values passed values, upon declaration.Generally, the destructor function is needed only when constructor has
allocated dynamic memory.
Defining Constructor and Destructor functions
The example below illustrates how constructor and destructor functions are
defined:
class myclass
{
private:
int number;
public:
myclass()//constructor
{
number=10;
}
~myclass()//destructor
{
//nothing needed
}
};
A few points to note:
Both of the functions have the same name as that of the class, destructor
function having (~) before its name.Both constructor and destructor functions should not be preceded by any
data type (not even void).These functions do not (and cannot) return any values.
We can have only the constructor function in a class without destructor
function or vice-versa.Constructor function can take arguments but destructors cannot.
Constructor function can be overloaded as usual functions.
Example 1: Using constructor function to initialize data members
to pre-defined values
//Example Program in C++
#include<iostream.h>
class myclass
{
private:
int a;
int b;
public:
myclass()
{
//here constructor function is used to
//initialize data members to pre-def
//values
a=10;
b=10;
}
int add(void)
{
return a+b;
}
};
void main(void)
{
myclass a;
cout<<a.add();
}
Example 2: Using constructor function to initialize data members
to values passed as arguments
//Example Program in C++
#include<iostream.h>
class myclass
{
private:
int a;
int b;
public:
myclass(int i, int j)
{
a=i;
b=j;
}
int add(void)
{
return a+b;
}
};
void main(void)
{
//notice how the object of the class
//has been declared
//it can be thought as
// myclass a;
// a=myclass(10,20)
myclass a(10,20);
cout<<a.add();
}Notice that there is no destructor function in both the examples, just because
we don’t need them.
I will discuss destructor functions in detail in the coming articles.
So, keep checking!
Related Articles: