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TITLE

C++ & OOPS

SESSION 10

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OPERATOR OVERLOADING The mechanism of giving special meanings to

an operator is known as Operator Overloading.

This is one of the exciting features of C++. This technique has enhanced the power of

extensibility of C++. This technique permits to add two user

defined variables with the same syntax that isapplied to basic types. Provides the new definitions for most of the

C++ operators .

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We can overload all the C++ operatorsexcept

Class member access operators ( . , .* ).

Scope resolution operator ( : : )

Sizeof operator ( sizeof)

Conditional operator ( ? : )

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DEFINING OPERATOR OVERLOADINGReturn type class name :: operatorop (arg

list )

{ function body

}

return type is the type of the value returned

by the function

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op is the operator being overloaded.The op is preceded by the key word

operator

operatorop is the function name

Operator function must be either

member function or friend function

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RULES FOR OVERLOADING OPERATORS

Only existing operators can be overloaded

The operator must have at least one

operand of user defined type.New operators cannot be created.

We cannot change the basic meaning of

an operator.

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That can not be overriddenWhen binary operators overloaded through

member function, the left hand operand

must be an object of the relevant class.

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They follow the syntax rules of originaloperators.

Some operators cannot be overloaded.

Unary operators overloaded by a member

function takes no explicit arguments.

Binary operators overloaded by a member

function takes one explicit argument.

Binary operators must explicitly return avalue.

They must not attempt to change their own

arguments.

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OVERLOADING UNARY OPERATOR

A unary operator takes just one operand.

Overloading unary minus operator.

A unary minus operator changes the signof an operand when applied to a basic

data type.

It should change the sign of data memberswhen applied to an object.

The function directly accesses the

members of the object.

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Ex: class test{ int x,y;

public:

void getdata(); void operator-();

void display (); };//defining the function overloading

operator void test :: operator-()

{ x = -x ; y = -y ; }if S is an object of class test,

the statement -S;

changes the sign of data members of S ;

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OVERLOADING BINARY OPERATORA binary operator takes two operands

Function overloading binary operator will

have one explicit argument.Ex: overloading binary + operator

testoperator +(testobj);

If test is name of the class and obj1 ,obj2

and obj3 are the objects oftestthen the expression

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obj3 = obj1 + obj2; invokes the functionoverloading binary + operator.

obj1 invokes the function and obj2 will be

passed as an argument.

The function returns the sum of obj1 and

obj2 and is assigned to obj3.

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CONCLUSION

What we have learnt this session?Overloading unary and binary operators

using member function.

What we will discuss next session?Type conversions.