c++ notes by vikas sharma

8/14/2019 c++ notes by vikas sharma

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1Dale Roberts

Operator OverloadingOperator Overloading

Friend Functions & Special FormsFriend Functions & Special Forms

Dale Roberts, Lecturer

Computer Science, IUPUI

E-mail: [email protected]

Department of Computer and Information Science,

School of Science, IUPUI


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Dale Roberts 2

Operator Overloading Using a Friend FunctionOperator Overloading Using a Friend Function

Number of Parameters Accepted by an Overloaded Friend OperatorNumber of Parameters Accepted by an Overloaded Friend OperatorFunction Depend Upon the Operator Type -- One for Unary Operators andFunction Depend Upon the Operator Type -- One for Unary Operators and

Two for Binary OperatorsTwo for Binary Operators

class complex{class complex{int re, im;int re, im;

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

:re(ip1), im(ip2){}:re(ip1), im(ip2){}friend complex operator+(complex, complex);friend complex operator+(complex, complex);};};//Friend Operator + Function//Friend Operator + Functioncomplex operator+(complex a, complex b)complex operator+(complex a, complex b)

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

main(){main(){complex one(1,1), two(2,2), three;complex one(1,1), two(2,2), three;three = one + two; //three = operator+(one, two)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.


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Dale Roberts 3

Operator Functions as Class Members vs. asOperator Functions as Class Members vs. as friendfriend FunctionsFunctions

Non-member overloaded operator functionsNon-member overloaded operator functions

Enable the operator to be commutativeEnable the operator to be commutative

HugeInteger bigInteger;HugeInteger bigInteger;

int integer;int integer;bigInteger = integer + bigInteger;bigInteger = integer + bigInteger;

oror

bigInteger = bigInteger + integer;bigInteger = bigInteger + integer;


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Dale Roberts 4

Global Operator OverloadingGlobal Operator OverloadingSimilar toSimilar to friendfriendFunction Overloading, Except the KeywordFunction Overloading, Except the Keyword friendfriend is Omitted andis Omitted andGlobal Functions CANNOT ACCESSGlobal Functions CANNOT ACCESS privateprivate MembersMembers

class complex{ //All Public Members!class complex{ //All Public Members!public:public:int re, im;int re, im;complex(int ip1 = 0, int ip2 = 0)complex(int ip1 = 0, int ip2 = 0)

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

void operator!(complex a)void operator!(complex a){{

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


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Dale Roberts 5

Overloading of Operators Having a Variable ArityOverloading of Operators Having a Variable Arity

Operators Such asOperators Such as --Can be Unary or BinaryCan be Unary or Binary

Overloading of Such Operators Involves Creating a Unary Function (OneOverloading of Such Operators Involves Creating a Unary Function (One

Operand) and a Binary Function (Two Operands)Operand) and a Binary Function (Two Operands)Only if Both the Forms are Used, They Need to be ImplementedOnly if Both the Forms are Used, They Need to be Implemented

class number{class number{int n;int n;

public:public:

number(int x = 0):n(x){}number(int x = 0):n(x){}number operator-(){n = -n; return *this;}number operator-(){n = -n; return *this;}number operator-(number ip)number operator-(number ip){n = n ip.n; return *this;}{n = n ip.n; return *this;}

};};main(){main(){

number one(1), two(2), three;number one(1), two(2), three;one = -one; //unary operatorone = -one; //unary operatorthree = one - two; //three.n = -3three = one - two; //three.n = -3

}}


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Dale Roberts 6

Operators with Prefix and Postfix FormsOperators with Prefix and Postfix Forms

Separate Functions for Each -- Prefix andSeparate Functions for Each -- Prefix and

Postfix -- Forms are NeededPostfix -- Forms are NeededPrefix Form is Treated as an Unary OperatorPrefix Form is Treated as an Unary Operator

Postfix Form is Treated as a Binary OperatorPostfix Form is Treated as a Binary Operator


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Prefix Overloaded Function -- ExamplePrefix Overloaded Function -- Example

class number{class number{

int n;int n;public:public:

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

//prefix operator -- unary//prefix operator -- unary

number operator++();number operator++();};};

number number::operator++(){number number::operator++(){

n++; return *this;}n++; return *this;}

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

++one; //one.n = 11++one; //one.n = 11

}}


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Postfix Overloaded Function -- ExamplePostfix Overloaded Function -- Example

Postfix Operator is Implemented as a Binary Operator with anPostfix Operator is Implemented as a Binary Operator with an intintArgument with a Default Value of 0 . When specifying anArgument with a Default Value of 0 . When specifying an

overloaded operator for the postfix form of the increment oroverloaded operator for the postfix form of the increment ordecrement operator, the additional argument must be of type int;decrement operator, the additional argument must be of type int;specifying any other type generates an error.specifying any other type generates an error.

class number{class number{

int n;int n;

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

//postfix operator -- binary -- int argument//postfix operator -- binary -- int argument

number operator++(int);number operator++(int);

};};

number number::operator++(int y)number number::operator++(int y)

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


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Postfix overloaded functionExample (Cont)Postfix overloaded functionExample (Cont)

main()main()

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

one++; // one.n = 11one++; // one.n = 11

one.operator++(2); // one.n = 13one.operator++(2); // one.n = 13

}}

There is no syntax for using the increment or decrementThere is no syntax for using the increment or decrement

operators to pass these values other than explicit invocation, asoperators to pass these values other than explicit invocation, as

shown in the preceding code. A more straightforward way toshown in the preceding code. A more straightforward way to

implement this functionality is to overload theimplement this functionality is to overload the

addition/assignment operator (+=).addition/assignment operator (+=).


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Special Overloading FormsSpecial Overloading Forms

A Few Operators Require Special Treatments DuringA Few Operators Require Special Treatments During

OverloadingOverloadingConversion OperatorConversion Operator

constconstArray OperatorArray Operator

Function Call -- Parenthesis OperatorFunction Call -- Parenthesis Operator

Stream Insertion --Stream Insertion -- > OperatorOperator

Pointer to Member --Pointer to Member -- ->-> OperatorOperator

Assignment OperatorAssignment Operator

newnewOperatorOperator

deletedelete OperatorOperator



Overloading Stream-Insertion and Stream-Extraction OperatorsOverloading Stream-Insertion and Stream-Extraction Operators

OverloadedOverloaded > operatorsoperators

Must have left operand of typesMust have left operand of types ostreamostream&&,, istreamistream&&respectivelyrespectively

It must be a non-member function (left operand not anIt must be a non-member function (left operand not an

object of the class)object of the class)

It must be aIt must be a friendfriendfunction if it accesses private datafunction if it accesses private datamembersmembers



1 // Fig. 18.3: fig18_03.cpp

2 // Overloading the stream-insertion and

3 // stream-extraction operators.

4 #include

5

6 using std::cout;

7 using std::cin;8 using std::endl;

9 using std::ostream;

10 using std::istream;

11

12 #include

13

14 using std::setw;

15

16 class PhoneNumber {

17 friendostream &operator( istream&, PhoneNumber & );

19

20private:

21 char areaCode[ 4 ]; // 3-digit area code and null

22 char exchange[ 4 ]; // 3-digit exchange and null

23 char line[ 5 ]; // 4-digit line and null

24 };

25

26 // Overloaded stream-insertion operator (cannot be

27 // a member function if we would like to invoke it with

28 // cout



31 output > 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 > phone invokes operator>> function by

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

55 cin >> phone;

56

57 // cout



Enter phone number in the form (123) 456-7890:

(800) 555-1212The phone number entered was: (800) 555-1212



Converting between TypesConverting between Types

Cast operatorCast operator

Convert objects into built-in types or other objectsConvert objects into built-in types or other objectsConversion operator must be a non-Conversion operator must be a non-staticstatic member function.member function.

Cannot be aCannot be a friendfriendfunctionfunction

Do not specify return typeDo not specify return typeFor user-defined classFor user-defined classAA

A::operator char *() const; // A to char A::operator char *() const; // A to char A::operator int() const; //A to int A::operator int() const; //A to int

A::operator otherClass() const; //A to otherClassA::operator otherClass() const; //A to otherClass

When compiler seesWhen compiler sees (char *) s(char *) s it callsit calls

s.operator char*()s.operator char*()



Converting between Types (cont)Converting between Types (cont)

The compiler can call these functions to createThe compiler can call these functions to create

temporary objects.temporary objects.IfIfss is not of typeis not of type char *char *

CallsCallsA::operator char *() const;A::operator char *() const; forforcout



Special overloading forms - ExampleSpecial overloading forms - Example

Special Forms ExampleSpecial Forms Example
http://t08specialoverridingformsexample.html/http://t08specialoverridingformsexample.html/http://t08specialoverridingformsexample.html/


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Dale Roberts 18

AcknowledgementsAcknowledgements

These slides were originally development by Dr. Uday Murthy and Dr. Rajeev

Raje.

Some contents comes from the Deitel slides that accompany your text.

Some information regarding the postfix form the increment and decrement

operators comes from MSDN.

c++ notes by vikas sharma

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