Constructor And Destructor in C++
Constructor(declaration and definition)
A constructor is a member function of a class; it
automatically called every time when the object is created.
The main use of constructor is to initialize the object. The
constructor has the same name as that of class; it does not have any return
type.
Syntax
<class name>{arguments};
§ Define
it in a public.
§ There
are several form of constructors
1. Default
constructor
2. Parameterized constructor
3. Copy constructor
1. Default constructor
Default constructor is also called as no argument
constructor. x:x() is a default constructor for class x since it takes no
argument.
2. Parameterized constructor
A constructor that can take arguments are called
parameterized constructor.
3. Copy Constructor
Copy constructor is used to declare and initialize an object
from another object.
For ex. abc c2(c1);
Would define an object c2 and at the same time initialize it
to the value of c1.
Ex. class abc{
int a,b;
public:
abc(int x, int y)
{
a=x;
b=y;
}
abc( abc &p)
{
a=p.a;
b=p.b;
cout<<”\n Copy constructor working”;
}
void show()
{
cout<<a<<” “<<b<<endl;
}
};
void main()
{
abc
c1(10,20);
abc
c2(c1);
abc c3=c1;
}
Copy constructor is called in two situations.
1.
When an object is passed by value
2.
When a function return object
· Overloaded constructor
1.
One constructor overload another constructor is
called constructor overloading.
2.
It has the same name of class.
3.
It must be public member and no return type.
4.
Default constructors are called when
constructors are not defined for the class.
Ex.
#include<iostream.h>
class Example {
int a,b;
public:
Example( )
{
a=50;
b=100;
cout<<”\n Im Constructor;”
}
Example
(int x,int y)
{
a=x;
b=y;
cout<<”\n Im constructor”;
}
void
Display()
{
cout<< “\n
Values:”<<a<<”\t”<<b;
}
};
void main()
{
Example obj(10,20);
Example obj2;
obj.Display();
obj2.Display ();
}
Output:
Im Constructor
Im Constructor
Values: 10 20
Values: 50
100
·
Constructor with default argument
It is possible to define constructor with
default arguments.
Default argument is an argument to a
function that a programmer is not required to specify.
·
Destructor
Just as object are created, so are they
destroyed .Destructor is used to destroy the object that has been created by
constructor and release the memory.
Syntax
~classname
();
The name of destructor is same as class
name and protected by (~) tilde.
Ex. class creat
{
private:
int yearOfBirth;
public:
creat()
{
yearOfBirth=1970;
cout<<”Constructor called”<<endl;
}
~creat()
{
cout<<”Destructor
called”;
}
};
void
main()
{
creat obj;
cout<<”main start”<<endl;
}
·
Characteristics of destructor
·
Take the same name as class name.
·
Defined in the public.
·
Destructors cannot be overloaded.
·
No return type is specified.
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