Declaration And Definition Of Overloading

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class to which it (the operator) is applied. The operator function helps us in doing so.
The Syntax of declaration of an Operator function is as follows:

Operator Operator_name

For example, suppose that we want to declare an Operator function for ‘=’. We can do it as follows:

operator =

A Binary Operator can be defined either a member function taking one argument or a global function taking one arguments. For a Binary Operator X, a X b can be interpreted as either an operator X (b) or operator X (a, b).

For a Prefix unary operator Y, Ya can be interpreted as either a.operator Y ( ) or Operator Y (a).
For a Postfix unary operator Z, aZ can be interpreted as either a.operator Z(int) or Operator (Z(a),int).

The operator functions namely operator=, operator [ ], operator ( ) and operator? must be nonstatic member functions. Due to this, their first operands will be lvalues.

An operator function should be either a member or take at least one class object argument. The
operators new and delete need not follow the rule. Also, an operator function, which needs to
accept a basic type as its first argument, cannot be a member function.

Some examples of declarations of operator functions are given below:

class P
{
 P operator ++ (int);//Postfix increment
 P operator ++ ( ); //Prefix increment
 P operator || (P); //Binary OR
}

Some examples of Global Operator Functions are given below:

P operator – (P); // Prefix Unary minus
P operator – (P, P); // Binary “minus”
P operator - - (P &, int); // Postfix Decrement

We can declare these Global Operator Functions as being friends of any other class.

Examples of operator overloading:

Operator overloading using friend.

Class time
{
 int r;
 int i;
 public:
 friend time operator + (const time &x, const time &y );
 // operator overloading using friend
 time ( ) { r = i = 0;}
 time (int x, int y) {r = x; i = y;}
 };
 time operator + (const time &x, const time &y)
 {
 time z; 
 z.r = x.r +y.r;
 z.i = x.i + y.i;
 return z;
 }

 main ( )
 {
 time x,y,z;
 x = time (5,6);
 y = time (7,8);
 z = time (9, 10);
 z = x+y; // addition using friend function +
 }


Operator overloading using member function:

Class abc
 {
 char * str;
 int len ; // Present length of the string
 int max_length; // (maximum space allocated to string)
 public:
 abc ( ); // black string of length 0 of maximum allowed length of size 10.
 abc (const abc &s ) ;// copy constructor
 ~ abc ( ) {delete str;}
 int operator = = (const abc &s ) const; // check for equality
 abc & operator = (const abc &s );
 // overloaded assignment operator
 friend abc operator + (const abc &s1, const abc &s2);
 } // string concatenation
 abc:: abc ()
 {
 max_length = 10;
 str = new char [ max_length];
 len = 0;
 str [0] = ‘\0’;
 }
 abc :: abc (const abc &s )
 {
 len = s. len;
 max_length = s.max_length;
 str = new char [max_length];
 strcpy (str, s.str); // physical copying in the new location.
 }

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