Unary operators are those which operate on a single variable. Overloading unary operator means extending the operator’s original functionality to operate upon object of the class. The declaration of a overloaded unary operator function precedes the word operator.

For example, consider class 3D which has data members x, y and z and overloaded increment operators:

class 3D
{
int x, y, z;
public:
3D (int a=0, int b=0, int c=0)
{
x = a;
y = b;
z = c;
}
3D operator ++() //unary operator ++ overloaded
{
x = x + 1;
y = y + 1;
z = z + 1;
return *this; //this pointer which points to the caller object
}
3D operator ++(int) //use of dummy argument for post increment
operator
{
3D t = *this;
x = x + 1;
y = y + 1;
z = z + 1;
return t; //return the original object
}
3D show()
{
cout<<”The elements are:\n”
cout<<”x:”<<this->x<<”, y:<this->y <<”, z:”<<this->z;
}
};
int main()
{
3D pt1(2,4,5), pt2(7,1,3);
cout<<”Point one’s dimensions before increment are:”<< pt1.show();
++pt1; //The overloaded operator function ++() will return object’s this pointer
cout<<”Point one’s dimensions after increment are:”<< pt1.show();
cout<<”Point two’s dimensions before increment are:”<< pt2.show();
pt2++; //The overloaded operator function ++() will return object’s this pointer
cout<<”Point two’s dimensions after increment are:”<< pt2.show();
return 0;
}

The o/p would be:
Point one’s dimensions before increment are:
x:2, y:4, z:5
Point one’s dimensions after increment are:
x:3, y:5, z:6
Point two’s dimensions before increment are:
x:7, y:1, z:3
Point two’s dimensions after increment are:
x:7, y:1, z:3

Please note in case of post increment, the operator function increments the value; but returns the original value since it is post increment.