10 Rules of Operator Overloading in C++

Every programmer knows the concept of operation overloading in C++. Although it looks simple to redefine the operators in operator overloading, there are certain restrictions and limitation in overloading the operators. Some of them are listed below:

1. Only existing operators can be overloaded. New operators cannot be overloaded.

2. The overloaded operator must have at least one operand that is of user defined type.

3. We cannot change the basic meaning of an operator. That is to say, We cannot redefine the plus(+) operator to subtract one value from the other.

4. Overloaded operators follow the syntax rules of the original operators. They cannot be overridden.

5. There are some operators that cannot be overloaded like size of operator(sizeof), membership operator(.), pointer to member operator(.*), scope resolution operator(::), conditional operators(?:) etc

6. We cannot use “friend” functions to overload certain operators.However, member function can be used to overload them. Friend Functions can not be used with assignment operator(=), function call operator(()), subscripting operator([]), class member access operator(->) etc. 

7. Unary operators, overloaded by means of a member function, take no explicit arguments and return no explicit values, but, those overloaded by means of a friend function, take one reference argument (the object of the relevent class).

8. Binary operators overloaded through a member function take one explicit argument and those which are overloaded through a friend function take two explicit arguments.

9. When using binary operators overloaded through a member function, the left hand operand must be an object of the relevant class.

10. Binary arithmetic operators such as +,-,* and / must explicitly return a value. They must not attempt to change their own arguments.