CHAPTER 8: OPERATOR OVERLOADING
Meaning and importance of operator overloading
Operator overloading is an important concept in C++. It is a type of polymorphism in
which an operator is overloaded to give user defined meaning to it. Overloaded
operator is used to perform operation on user-defined data type. For example '+'
operator can be overloaded to perform addition on various data types, like for Integer,
String(concatenation) etc.
Almost any operator can be overloaded in C++. However there are few operator which
can not be overloaded. Operator that are not overloaded are follows
1. scope operator - ::
2. sizeof
3. member selector - .
4. member pointer selector - *
5. ternary operator - ?:
Operator Overloading Syntax
Implementing Operator Overloading
Operator overloading can be done by implementing a function which can be :
1. Member Function
2. Non-Member Function
3. Friend Function
Operator overloading function can be a member function if the Left operand is an
Object of that class, but if the Left operand is different, then Operator overloading
function must be a non-member function.
Operator overloading function can be made friend function if it needs access to the
private and protected members of class.
Restrictions on Operator Overloading
Following are some restrictions to be kept in mind while implementing operator
overloading.
1. Precedence and Associativity of an operator cannot be changed.
2. Arity (numbers of Operands) cannot be changed. Unary operator remains unary,
binary remains binary etc.
3. No new operators can be created, only existing operators can be overloaded.
Cannot redefine the meaning of a procedure. You cannot change how integers are
added.
Operator Overloading Examples
Almost all the operators can be overloaded in infinite different ways. Following are
some examples to learn more about operator overloading. All the examples are closely
connected.
Overloading Arithmetic Operator
Arithmetic operator are most commonly used operator in C++. Almost all arithmetic
operator can be overloaded to perform arithmetic operation on user-defined data type.
In the below example we have overridden the + operator, to add to Time (hh:mm:ss)
objects.
Example: overloading '+' Operator to add two time object
#include< iostream.h>
#include< conio.h>
class time
{
int h,m,s;
public:
time()
{
h=0, m=0; s=0;
}
void getTime();
void show()
{
cout<< h<< ":"<< m<< ":"<< s;
}
time operator+(time); //overloading '+' operator
};
time time::operator+(time t1) //operator function
{
time t;
int a,b;
a=s+t1.s;
t.s=a%60;
b=(a/60)+m+t1.m;
t.m=b%60;
t.h=(b/60)+h+t1.h;
t.h=t.h%12;
return t;
}
void time::getTime()
{
cout<<"\n Enter the hour(0-11) ";
cin>>h;
cout<<"\n Enter the minute(0-59) ";
cin>>m;
cout<<"\n Enter the second(0-59) ";
cin>>s;
}
void main()
{
clrscr();
time t1,t2,t3;
cout<<"\n Enter the first time ";
t1.getTime();
cout<<"\n Enter the second time ";
t2.getTime();
t3=t1+t2; <font color="green">//adding of two time object using '+' operator
cout<<"\n First time ";
t1.show();
cout<<"\n Second time ";
t2.show();
cout<<"\n Sum of times ";
t3.show();
getch();
}
Overloading I/O operator
1. Overloaded to perform input/output for user defined datatypes.
2. Left Operand will be of types ostream& and istream&
3. Function overloading this operator must be a Non-Member function because left
operand is not an Object of the class.
4. It must be a friend function to access private data members.
You have seen above that operator is overloaded with ostream class object
cout to print primitive type value output to the screen. Similarly you can overload
operator in your class to print user-defined type to screen. For example we will
