Lecture 8: Operator Overloading

Definition of Operator Overloading

Up to this point in the discussion of C++, the programmer could define operations on structure instance and class objects by using a function. For example:

 c = add(a,b); 

where a, b and c are instances of some structure or a class. However, this is using non-standard operators. C++ permits the programmer to use some of the standard operators in a more natural way using what is called: operator overloading. However, to do this requires that the programmer observe some restrictions.

To define operator overloading on class objects requires that the operator:

• is a system operator.

• maintains the system order of precedence

• can not change type: i.e. between unary and binary operators

• has at least one operand that is a class object.

• is non static.

• has in the operator's definition the keyword: operator

In addition, the programmer should take care how the operators are defined and that the operators should model their real world use. The permissible operators for overloading are:

Open table as spreadsheet

OVERLOADABLE OPERATORS
+	-	*	/	%
^	&	|	~	!
,	=	<	>	<=
>=	++	--	_	<<
>>	==	!=	&&	||
+=	-=	/=	<<=	>>=
[ ]	( )	->	->*
new	delete

While most of the C++ operators can be overloaded, the dot operator (.) and some other operators can not be overloaded. The discussion in this lecture will only cover a few of the operators above.