Overloading Unary Operators ( member functions )
Let us consider the unary minus operator. A minus operator, when used as a unary, takes just one operand. We will see here how to overload this operator so that it can be applied to an object in much the same way as is applied to an int or float variable. The unary minus when applied to an object should change the sign of each of its data items.
For Example,
class X
{
int a ;
int b ;
public :
void get ( int m, int n ) ;
void display ( void ) ;
void operator - ( ) ; // overloaded unary minus
} ;
void X : : get ( int m, int n )
{
a = m ;
b = n ;
}
void X : : display ( void )
{
cout << a << " " ;
cout << b << " " ;
}
void X : : operator - ( )
{
a = -a ;
b = -b ;
}
int main ( )
{
X x ;
x . get ( 10, 20 ) ;
- x ; // calls operator - ( )
x . display ( ) ;
return 0 ;
}
This program produces the output -10 -20.
Note that the function operator - ( ) takes no argument. It changes the sign of data members of the object x. Since this function is a member function of the same class, it can directly access the members of the object which activated it.
Overloading Unary Operators ( Friend functions )
It is possible to overload a unary minus operator using a friend function.
friend void operator - ( X & obj ) ; // declaration
void operator - ( X & obj )
{
obj . a = - obj . a ;
obj . b = - obj . b ;
}
Note that the argument is passed by reference. It will not work if we pass argument by value because only a copy of the object that activated the call is passed to operator - ( ) . Therefore, the changes made inside the operator function will not reflect in the called object.