Operator Overloading: Friend Functions, Special Forms and Global Overloading, Slides of Computer Science

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Operator Overloading

Friend Functions & Special Forms

Operator Overloading Using a Friend Function

• Number of Parameters Accepted by an Overloaded Friend Operator Function

Depend Upon the Operator Type -- One for Unary Operators and Two for Binary

Operators

class complex{

int re, im;

public:

complex(int ip1 = 0, int ip2 = 0)

:re(ip1), im(ip2){}

friend complex operator+(complex, complex);

//Friend Operator + Function

complex operator+(complex a, complex b)

{return complex(a.re+b.re, a.im+b.im);}

main(){

complex one(1,1), two(2,2), three;

three = one + two; //three = operator+(one, two)

} Is a friend function necessary in this case?

No because LH operand is an instance of the class.

• Similar toGlobal Operator Overloading friend Function Overloading, Except the Keyword friend is Omitted and Global Functions

CANNOT ACCESS private Members

class complex{ //All Public Members!

public:

int re, im;

complex(int ip1 = 0, int ip2 = 0)

:re(ip1), im(ip2){}

void operator!(complex a)

int temp = a.re; a.re = a.im; a.im = temp;

cout << "Real: " << a.re << endl;

cout << "Imaginary: " << a.im << endl;

main()

complex one(1,2);

!one;

Overloading of Operators Having a Variable Arity

• Operators Such as - Can be Unary or Binary
• Overloading of Such Operators Involves Creating a Unary Function (One Operand)

and a Binary Function (Two Operands)

• Only if Both the Forms are Used, They Need to be Implemented

class number{

int n;

public:

number(int x = 0):n(x){}

number operator-(){n = -n; return *this;}

number operator-(number ip)

{n = n – ip.n; return *this;}

main(){

number one(1), two(2), three;

one = -one; //unary operator

three = one - two; //three.n = -

Prefix Overloaded Function -- Example

class number{

int n;

public:

number(int x):n(x){}; //Constructor

//prefix operator -- unary

number operator++();

};

number number::operator++(){

n++; return *this;}

main(){

number one(10); //one.n = 10

++one; //one.n = 11

}

Postfix Overloaded Function -- Example

• Postfix Operator is Implemented as a Binary Operator with an int Argument

with a Default Value of 0. When specifying an overloaded operator for the postfix form of the increment or decrement operator, the additional argument

must be of type int; specifying any other type generates an error.

class number{

int n;

public:

number(int x):n(x){}; //Constructor

//postfix operator -- binary -- int argument

number operator++(int);

};

number number::operator++(int y)

{if (y != 0) n += y; else n++; return *this;}

Special Overloading Forms

A Few Operators Require Special Treatments

During Overloading

Conversion Operator

const Array Operator

Function Call -- Parenthesis Operator

Stream Insertion -- << Operator

Stream Extraction -- >> Operator

Pointer to Member -- -> Operator

Assignment Operator

new Operator

delete Operator

Overloading Stream-Insertion and Stream-Extraction Operators

• Overloaded << and >> operators
  • Must have left operand of types ostream &,

istream & respectively

• It must be a non-member function (left operand

not an object of the class)

• It must be a friend function if it accesses

private data members

31 output << "(" << num.areaCode << ") "

32 << num.exchange << "-" << num.line;

33 return output; // enables cout << a << b << c;

34 }

35

36 istream &operator>>( istream &input, PhoneNumber &num )

37 {

38 input.ignore(); // skip (

39 input >> setw( 4 ) >> num.areaCode; // input area code

40 input.ignore( 2 ); // skip ) and space

41 input >> setw( 4 ) >> num.exchange; // input exchange

42 input.ignore(); // skip dash (-)

43 input >> setw( 5 ) >> num.line; // input line

44 return input; // enables cin >> a >> b >> c;

45 }

46

47 int main()

48 {

49 PhoneNumber phone; // create object phone

50

51 cout << "Enter phone number in the form (123) 456-7890:\n";

52

53 // cin >> phone invokes operator>> function by

54 // issuing the call operator>>( cin, phone ).

55 cin >> phone;

56

57 // cout << phone invokes operator<< function by

58 // issuing the call operator<<( cout, phone ).

59 cout << "The phone number entered was: " << phone << endl;

60 return 0;

61 }

Docsity.com

Enter phone number in the form (123) 456-7890: (800) 555- The phone number entered was: (800) 555-

Converting between Types (cont)

• The compiler can call these functions to create

temporary objects.

• If s is not of type char *

Calls A::operator char *() const; for

cout << s;

Special overloading forms - Example

• Special Forms Example