Overloading Operators

To overload an operator, you define an operator function whose name has the form
operatorsymbol where symbol is the operator you want to overload
i.e. for an assignment operator, you name the function operator= and declare one argument: the object that is to be copied. For example, to provide an assignment operator for the class numArray, you would add the declaration
virtual void operator=(const numArray& Arr) to the class definition.
This overloaded assignment operator is used whenever you assign one object to another.

Guidelines for Overloading Operators

1. You can overload any C++ operator except  .  .*  ::  ?:  sizeof
2. You cannot define new operators by overloading symbols that are not already operators in C++
3. You cannot change the standard precedence of a C++ operator or the number of its operands
4. At least one operand of an overloaded operator must be an instance of a class
5. A typical class should overload at least the assignment(=) and the equality (==) operators

Example:

void NumArray::operator=(const NumArray& NArr)
	// assigns the contents of NArr to the object of class NumArray
{
	size = NArr.size; 	// copy size of old array

	// copies all of the elements of the old array
	for (int count = 0; count < size; count++)
	{
		ele[count] = NArr.ele[count];
	}
}

Friends or Members?

• The operator is a binary operator and the left-hand operand is not an instance of the class.
• The operator is a binary operator and you want to allow the left-hand operand not to be an instance of the class.

• The operator is a unary operator.
• the operator is a binary operator, the left-hand operand is an instance of the class, and the operator generates a side effect on its left-hand operator.