Operator Overloading

The operators such as +, -, *, /, >, < etc is pre-defined in programming languages. They can perform the operations on built-in (standard) data types only. They do not work for user-defined data types such as objects.

C++ allows programmers to perform the operations on user-defined data types called objects. This feature called operator overloading.

With operator overloading, a programmer is allowed to provide his own definition for an operator to a class.

Like function overloading, operator overloading is also a form of compile time polymorphism.

The operator overloading function is preceded by the keyword operator followed by an operator.

Operator overloading function must be defined in public section of the class.

Syntax:-

class class_name

{

public:

returntype operator op (args_list)

{

statements;

}

};

Here, op is the operator that has to be overloaded

The following operators can be used in operator overloading.

         a) Unary operators - ++, --, -, !

         b) Binary operators – arithmetic, relational, and logical operators

         c) Other operators – [], (), =>, ->, new and delete operators

The operators that cannot be overloaded

         a) Scope resolution operator (: :)

         b) Member selection operator (.)

         c) Ternary operator (? : )

 

Implementing Operator Overloading

Operator overloading is usually implemented in two ways.

1) Through member function

2) Through friend function

1) Through Member Function

 

·     Number of explicit parameters is reduced by one, because calling object implicitly supplies one operand.

·         Unary operators take no explicit parameter.

·         Binary operators take one explicit parameter.

·         Left-hand operand has to be the calling object.

·         Obj2=obj1+10 is permissible, but obj2=10+obj1 is not permissible.

 

2) Through Friend Function

 

·         Number of explicit parameters is more.

·         Unary operators take only one parameter.

·         Binary operators take two parameters.

·         Left-hand operand need not be an object.

·         Obj2=obj1+10 as well as obj2=10+obj1 is permissible.