Chuong VIII Da Nang Hoa Toan Tu

7/28/2019 Chuong VIII Da Nang Hoa Toan Tu

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Operator Overloading


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8.1 Introduction

Thao tc trn cc i tng ca lp c thc hin bi gicc thng ip ti cc i tng.

K php gi hm ny cng knh, c bit l cc lp ton hc.Nn s dng tp cc ton t c sn ca C++ ch r ccthao tc ca i tng => gi l a nng ha ton t

(operator overloading). Ton t > cng c a nng ha. : ton t trch dng(stream-extraction) v ton t dch chuyn phi.

C++ cho php a nng ha hu ht cc ton t . Trnh bindch pht sinh on m thch hp da trn kiu m trong ton t c s dng. Mt vi ton t c a nng hathng xuyn, c bit l ton t gn v cc ton t s hcnh + v -.


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8.2 CC NGUYN TC C BN CA A NNG HA TON T

C th s dng cc kiu c sn v c th nh ngha cc kiu mi. Cckiu c th c s dng vi tp cc ton t phong ph.

C th s dng cc ton t vi cc kiu do ngi dng nh ngha.C++ khng cho php tocc ton t mi, nhng cho php a nng hacc ton t tn ti khi s dng vi cc i tng ca lp, chngc ngha thch hp vicc kiu mi =>im mnh ca C++.

Cc ton t c a nng ha bng cch vit mt nh ngha hm nh

khi chng ta vit mt hm bnh thng, ngoi tr tn hm l t khaoperatortheo sau bi k hiu ca ton t c a nng ha. Prototypeca n c dng nh sau:

typeoperator operator_symbol ( parameter_list); s dng mt ton t cho cc i tng ca lp, ton t phi c

a nng ha ngoi tr hai iu. Ton t gn c th s dng vi mi lp m khng cn a nng ha. Ton t a ch (&) cng c th c s dng vi cc i tng

ca bt k lp no m khng cn a nng ha;


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8.3 CC GII HN CA A NNG HA TON T

Phn ln cc ton t ca C++ c th c anng ha.

+ - * / % ^ & |

~ ! = += -= *=

/= %= ^= &= |= >>=

[] () new delete

Cc ton t khng th a nng ha

. .* :: ?: sizeof


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Ton t ngoc trn () l ton t gi hm. Sau tn hm c th chanhiu tham s => ton t nhiu ngi.

Th t u tin ca mt ton t khng th c thay i bi a nngha.

Tnh kt hp ca mt ton t khng th c thay i bi a nngha.

Khng th thay i s cc ton hng m mt ton t yu cu: a nngha cc ton t mt ngi vn l cc ton t mt ngi..

Ton t ba ngi duy nht (?:) ca C++ khng th a nng ha. Cc

ton t &, *, + vmi ton t c cc phin bn mt v hai ngi.;Cc phin bn mt v hai ngi ny c th c a nng ha ring bit. Vic a nng ha ton t ch lm vic vi cc i tng ca cc kiu

do ngi dng nh ngha hoc vi mt s pha trn ca mt i tngca kiu do ngi dng nh ngha v mt i tng ca mt kiu csn.

a nng ha mt ton t gn v mt ton t cng cho php cclnh nh l: object2 = object2 + object1 khng bao hm ton t+= cng c a nng ha php cc lnh nh l: object2 +=object1

_=>Cn a nng ha r rng ton t += cho lp .


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8.4 HM TON T L CC THNH VIN CA LPHOC KHNG L CC THNH VIN

Hm ton t c th l hm thnh vin hoc khng thnh vin; hm khngthnh vin thng l friend. Cc hm thnh vin s dng ngm con trthis cha mt trong cc tham s i tng lp ca chng. Tham s lp phi c lit k mt cch tng minh trong li gi hm khng thnhvin.

Khi a nng ha (), [], -> hoc =,hm a nng ha ton tphi c khaibo nh mt thnh vin lp. i vi cc ton t khc, cc hm a nng ha

ton t c th l cc hm khng thnh vin (thng l Friend). D ton t c ci t nh th no, ton t vn c s dng cng cchtrong biu thc. Vy cch ci t no tt nht?

Khi c ci t nh mt hm thnh vin, ton hng cc tri phi l mti tng lp ca ton t. Nu ton hng bn tri phi l mt i tng calp khc hoc mt kiu c snth hm ton t nyphi c ci t nhhm khng thnh vin. Mt hm ton t ci t nh hm khng thnh vincn l mt friendnu hm phi truy cp n cc thnh vin private hocprotected.

Cc hm thnh vin ch c gi khi ton hng tri ca mt ton t haingi l mt i tng c th ca lp , hoc khi ton hng n ca mt

ton t mt ngi l mt i tng ca lp .


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V d :xy dng lp s phc vi tn lp lComplexv a nng ha ton t +

#include

class Complex {private: double R, I;

public: Complex(double R=0.0,double I=0.0);// Constructor mc nhvoid Print(); // Hin th s phcComplex operator+(Complex Z); // Php cng gia hai s phc

Complex operator+(double R); // Php cng mt s phc vi mt s thc};

Complex::Complex(double T,double A) {

R = T; I = A; }

void Complex::Print() {

cout


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Complex Complex::operator + (double T) {

Complex Tmp;

Tmp.R = R + T;

Tmp.I = I;return Tmp; }

int main() {

Complex X,Y(4.3,8.2),Z(3.3,1.1);

cout


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Do a nng ha ton t + trn lp Complex v d trn, chng ta c th vit:X = Y + Z;

Cu lnh ny c trnh bin dch hiu:X = Y.operator + (Z);

Nh vy, trong biu thc Y + Zi tng bn tri ton t + (l i tng Y)l i tng m qua , hm thnh vin ton t operator + ()c gi. Do hm thnh vin ton t + ch nhn mt tham s l i tng bn phiton t v i tng bn tri ton t l i tng to li gi cho hm ton tv c truyn bi con tr this.

Hm operator + () tr v mt i tng Complex. Do vy chng ta c thvit:(Y + Z).Print();

in trn mn hnh s phc ca i tng c tr v. i tng do Y + Zsinh ra nh vy l mt i tng tm thi. N s khng tn ti khi hm

thnhPrint() kt thc. Ton t +cho php mt chui php cng. Nn chng ta cng c th vit:X = X + Y + Z;

Tuy nhin chng ta khng th no vit c cu lnh sau:X = 3.5 + Y; // Li !!! Lam the nao ?


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cch a nng ha ton t

Biu thc Hm thnh vin Hm khng thnh vina#b a.operator#(b) operator#(a,b)

#a a.operator#() operator#(a)

a=b a.operator=(b)

a[b] a.operator[](b)

a(b) a.operator()(b)

a-> a.operator->()

a++ a.operator++(0) operator++(a,0)a-- a.operator--(0) operator--(a,0)


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12V d : xy dng lp Complexv a nng ha ccton t + - += -= v == != > >= <


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// Cc ton t so snhint operator == (Complex Z);

int operator != (Complex Z);

int operator > (Complex Z);

int operator >= (Complex Z);

int operator < (Complex Z);

int operator


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Complex::Complex() {

R = 0.0;

I = 0.0; }

Complex::Complex(double T,double A) {

R = T;

I = A;}

Complex::Complex(const Complex & Z) {

R = Z.R;

I = Z.I; }

Complex::Complex(double T) {

R = T;

I = 0.0; }

void Complex::Print() {

cout


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Complex Complex::operator + (Complex Z) {

Complex Tmp;

Tmp.R = R + Z.R;

Tmp.I = I + Z.I;return Tmp; }

Complex Complex::operator - (Complex Z) {

Complex Tmp;

Tmp.R = R - Z.R;

Tmp.I = I - Z.I;

return Tmp; }

Complex Complex::operator += (Complex Z) {

R += Z.R;

I += Z.I;return *this; }

Complex Complex::operator -= (Complex Z) {

R -= Z.R;

I -= Z.I;

return *this; }

16


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int Complex::operator == (Complex Z) {

return (R == Z.R) && (I == Z.I); }

int Complex::operator != (Complex Z) {

return (R != Z.R) || (I != Z.I); }

int Complex::operator > (Complex Z) {

return Abs() > Z.Abs(); }

int Complex::operator >= (Complex Z) {return Abs() >= Z.Abs(); }

int Complex::operator < (Complex Z) {

return Abs() < Z.Abs(); }

int Complex::operator


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int main() {

Complex X, Y(4.3,8.2), Z(3.3,1.1), T;

cout


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18cout


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20


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Dng cc hm ton t +, - v cc hm tont so snh l hm khng thnh vin.

class Complex {

private: double Real,Imaginary;public: Complex(); // Constructor mc nh

Complex(double R,double I);

Complex (const Complex & Z); // Constructor sao chp

Complex (double R); // Constructor chuyn i

void Print(); // Hin th s phcfriend Complex operator + (Complex Z1,Complex Z2);friend Complex operator - (Complex Z1,Complex Z2);

Complex operator += (Complex Z);

Complex operator -= (Complex Z);

friend int operator == (Complex Z1,Complex Z2);friend int operator != (Complex Z1,Complex Z2);

friend int operator > (Complex Z1,Complex Z2);

friend int operator >= (Complex Z1,Complex Z2);

friend int operator < (Complex Z1,Complex Z2);

friend int operator


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Complex::Complex() {

Real = 0.0; Imaginary = 0.0; }

Complex::Complex(double R,double I) {

Real = R; Imaginary = I; }Complex::Complex(const Complex & Z) {

Real = Z.Real; Imaginary = Z.Imaginary; }

Complex::Complex(double R) {

Real = R; Imaginary = 0.0; }void Complex::Print() {

cout


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Complex operator - (Complex Z1,Complex Z2) {

Complex Tmp;

Tmp.Real = Z1.Real - Z2.Real;Tmp.Imaginary = Z1.Imaginary - Z2.Imaginary;

return Tmp; }

Complex Complex::operator += (Complex Z) {

Real += Z.Real;

Imaginary += Z.Imaginary;

return *this; }

Complex Complex::operator -= (Complex Z) {Real -= Z.Real;

Imaginary -= Z.Imaginary;

return *this; }

23


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int operator == (Complex Z1,Complex Z2) {

return (Z1.Real == Z2.Real) && (Z1.Imaginary ==Z2.Imaginary); }

int operator != (Complex Z1,Complex Z2) {

return (Z1.Real != Z2.Real) || (Z1.Imaginary !=Z2.Imaginary); }

int operator > (Complex Z1,Complex Z2) {

return Z1.Abs() > Z2.Abs(); }int operator >= (Complex Z1,Complex Z2) {

return Z1.Abs() >= Z2.Abs(); }

int operator < (Complex Z1,Complex Z2) {

return Z1.Abs() < Z2.Abs(); }int operator


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8.6 A NNG HA CC TON T MT NGI

Ton t mt ngi ca lp c a nng ha nhmt hm thnh vin khng c tham s hoc nhmt hm khng thnh vin vi mt tham s; Thams phi hoc l mt i tng lp hoc l mttham chiu n i tng lp.

Ton t V d Ton t V d

+ +c ~ ~c- -c ! !a

* *c ++ ++c, c++

& &c -- --c, c--

-> c->

27


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V d :thm ton t du tr mt ngi volp Complex

Thm vo nh ngha lp Complex dng sauComplex operator();

V phnnh ngha cc hm v ton t ca lp

ta thmComplex Complex::operator - () {

Complex Tmp;

Tmp.R = -R;

Tmp.I = -I;

return Tmp; }

28


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8.7 A NNG HA MT S TON T C BIT

Trong phn ny chng ta s tm hiu cch ci tmt vi ton t c bit nh () [] ++ -- , = ->

Ton t []: Khi ci t cc lp vector hoc chui k t, chng

ta cn phi truy cp n tng phn t ca chng,trong ngn ng C/C++ c ton t [] truy cpn mt phn t ca mng. y l ton t haingi, c dng a[b] v khi a nng ton t ny th

hm ton t tng ng phi l thnh vin ca mtlp. V d : a nng ha ton t [] truy cp n

mt phn t ca vector.

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http://localhost/var/www/apps/conversion/lthdt/Htm/Source/CT4_5.CPPhttp://localhost/var/www/apps/conversion/lthdt/Htm/Source/CT4_5.CPPhttp://localhost/var/www/apps/conversion/lthdt/Htm/Source/CT4_5.CPPhttp://localhost/var/www/apps/conversion/lthdt/Htm/Source/CT4_5.CPP


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#include

class Vector {

private: int Size;

int *Data;

public: Vector(int S=2,int V=0);

~Vector();

void Print() const;int & operator [] (int I);

};

Vector::Vector(int S,int V) {

Size = S;Data=new int[Size];

for(int I=0;I


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Vector::~Vector() {

delete []Data;

}void Vector::Print() const {

cout


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int main() {

Vector V(5,1);

V.Print();for(int I=0;I


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Ton t ()

Ton t () c dng gi hm, ton t ny gm

hai ton hng: ton hng u tin l tn hm, tonhng th hai l danh sch cc tham s ca hm.Ton t ny c dng ging nh ton t [] v khia nng ton t ny th hm ton t tng ng

phi l thnh vin ca mt lp. V d :a nng ha ton t () truy cp n

phn t ca ma trn.

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http://localhost/var/www/apps/conversion/lthdt/Htm/Source/CT4_7.CPPhttp://localhost/var/www/apps/conversion/lthdt/Htm/Source/CT4_7.CPP


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#include

class Matrix {

private: int Rows,Cols;

int **Data;

public:

Matrix(int R=2,int C=2,int V=0);

~Matrix();

void Print() const;int & operator () (int R,int C);

};

34Matrix::Matrix(int R int C int V) {


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Matrix::Matrix(int R,int C,int V) {

int I,J;

Rows=R;

Cols=C;

Data = new int *[Rows];

int *Temp=new int[Rows*Cols];

for(I=0;I


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void Matrix::Print() const {

int I,J;

for(I=0;I


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int main() {

int I,J;

Matrix M(2,3,1);cout


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Point::Point(int A,int B) {

X = A;

Y = B; }Point Point::operator++() {

++X;

++Y;

return *this; }

Point Point::operator++(int){

Point Tmp=*this; //Sao chp tng ang xt

// vo tng tm thi trc khi thay i++X;

++Y;

return Tmp; }

40


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Point Point::operator--() {

--X;

--Y;return *this; }

Point Point::operator--(int) {

Point Tmp=*this; //Sao chp i tng ang xt vo

//i tngtm thi trc khi thay i--X;

--Y;

return Tmp; }void Point::Print() const {

cout


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int main() {

Point P1(2,6),P2(5,8),P3,P4;

cout


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Ton t xut


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Ti nh ngha ton t nhp >>

nh ngha hm ton cc:istream& operator >> (istream&, Class&);

class Point {

public:

Point (int x=0, int y=0)

{ Point::x = x; Point::y = y; }

friend istream& operator >>

(istream& is, Point& p)

{ coutp.x;coutp.y;

}

// ..private:

int x, y;

};

void main() {

Point p1, p2;coutp1;

coutp2;

}

g

44

Khi t h


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Khi to ngm nh

c nh ngha sn trong ngn ng:VD: Point p1(10,20); Point p2 = p1;

S gy ra li (kt qu SAI) khi bn trong i tng c thnhphn d liu l con tr.

VD: Matrix m(5,6); Matrix n = m;

Li s xy ra do

khi to ngmbng cch gntng ng tng

thnh phn.

45Chng 8


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Khi to ngm nh (cont..)

Khi lp c thnh phn d liu con tr, phi nhngha hm Khi to sao chp

class Point {

int x, y;

public:

Point (int =0; int =0 );

// Khong can th iet DN

Point (const Point& p) {

x= p.x;

y = p.y;

}

// ..};

//

class Vector {

//

Vector(const Vector&);

};

Vector:: Vector (const Vector &m)

{

Size = m.Size;

Data=new int[Size];

for(int i=0;i


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Gn ngm nh

c nh ngha sn trong ngn ng: Gn tng ng tng thnh phn. ngkhi i tng khng c d liu con tr.

VD: Point p1(10,20); Point p2; p2 = p1;

Khi thnh phn d liu c con tr, bt buc phi nh

ngha php gn = cho lp.class Vector{

//.Vector& operator = (const Vector &m) {

if (Size == m.Size) { // phi khp

for (int i = 0; i < Size; ++i) // sao chp cc phn tdata[i] = m.Data[i];}return *this;

}};

Hm

thnh

vin

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8.8 Case Study: Array class

Arrays in C++No range checking Cannot be compared meaningfully with ==

No array assignment (array names const pointers)

Cannot input/output entire arrays at once One element at a time

Example:Implement anArray class with Range checking

Array assignment Arrays that know their size Outputting/inputting entire arrays with>

Array comparisons with == and !=

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8.8 Case Study: Array class

Copy constructor Used whenever copy of object needed

Passing by value (return value or parameter)

Initializing an object with a copy of anotherArray newArray( oldArray );

newArray copy ofoldArray

Prototype for classArrayArray( const Array & );

Musttake reference

Otherwise, pass by value

Tries to make copy by calling copy constructor

Infinite loop

Outline49

1 // Fig. 8.4: array1.h
http://localhost/var/www/apps/conversion/lthdt/Htm/Source/CT4_5.CPP


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2003 Prentice Hall, Inc.All rights reserved.

Outline

array1.h (1 of 2)

2 // Array class for storing arrays of integers.

3 #ifndefARRAY1_H

4 #defineARRAY1_H

5

6 #include

7

8 using std::ostream;

9 using std::istream;

10

11 class Array {

12 friendostream &operator( istream &, Array & );

14

15 public:

16 Array( int = 10 ); // default constructor

17 Array( const Array & ); // copy constructor

18 ~Array(); // destructor

19 int getSize() const; // return size

20

21 // assignment operator

22 const Array &operator=( const Array & );23

24 // equality operator

25 booloperator==( const Array & ) const;

26

Most operators overloaded asmember functions (except, which must be non-

member functions).

Prototype for copy constructor.

Outline50

27 // inequality operator; returns opposite of == operator


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Outline

array1.h (2 of 2)

28 booloperator!=( const Array &right ) const

29 {

30 return ! ( *this == right ); // invokes Array::operator==

31

32 } // end function operator!=

33

34 // subscript operator for non-const objects returns lvalue

35 int &operator[]( int );

36

37 // subscript operator for const objects returns rvalue

38 constint &operator[]( int ) const;

39

40 private:

41 int size; // array size

42 int *ptr; // pointer to first element of array

43

44 }; // end class Array

45

46 #endif

!= operator simply returns

opposite of== operator. Thus,only need to define the ==

operator.

Outline51

1 // Fig 8.5: array1.cpp


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Outline

array1.cpp (1 of 7)

2 // Member function definitions for class Array

3 #include

4

5 using std::cout;

6 using std::cin;

7 using std::endl;

8

9 #include

10

11 using std::setw;

12

13 #include // C++ standard "new" operator

14

15 #include // exit function prototype

16

17 #include"array1.h" // Array class definition

18

19 // default constructor for class Array (default size 10)

20 Array::Array( int arraySize )

21 {

22 // validate arraySize23 size = ( arraySize >0 ? arraySize : 10 );

24

25 ptr = new int[ size ]; // create space for array

26


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Outline53

51 // return size of array

52


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Outline

array1.cpp (3 of 7)

52 int Array::getSize() const

53 {

54 return size;

55

56 } // end function getSize

57

58 // overloaded assignment operator;

59 // const return avoids: ( a1 = a2 ) = a3

60 const Array &Array::operator=( const Array &right )

61 {

62 if ( &right != this ) { // check for self-assignment

63

64 // for arrays of different sizes, deallocate original

65 // left-side array, then allocate new left-side array

66 if ( size != right.size ) {

67 delete [] ptr; // reclaim space

68 size = right.size; // resize this object

69 ptr = newint[ size ]; // create space for array copy

70

71 } // end inner if

7273 for (int i = 0; i < size; i++ )

74 ptr[ i ] = right.ptr[ i ]; // copy array into object

75

76 } // end outer if

Want to avoid self-assignment.

Outline54

77

78 * hi // bl f l


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Outline

array1.cpp (4 of 7)

78 return *this; // enables x = y = z, for example

79

80 } // end function operator=

81

82 // determine if two arrays are equal and

83 // return true, otherwise return false

84 bool Array::operator==( const Array &right ) const

85 {

86 if ( size != right.size )

87 returnfalse; // arrays of different sizes

88

89 for ( int i = 0; i < size; i++ )

90

91 if ( ptr[ i ] != right.ptr[ i ] )92 return false; // arrays are not equal

93

94 returntrue; // arrays are equal

95

96 } // end function operator==

97

Outline55

98 // overloaded subscript operator for non-const Arrays

99 // f t t l l


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array1.cpp (5 of 7)

99 // reference return creates an lvalue

100 int &Array::operator[]( int subscript )

101 {

102 // check for subscript out of range error

103 if ( subscript < 0 || subscript >= size ) {

104 cout


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array1.cpp (6 of 7)

116 // const reference return creates an rvalue

117 const int &Array::operator[]( int subscript ) const

118 {

119 // check for subscript out of range error

120 if ( subscript < 0 || subscript >= size ) {

121 cout a.ptr[ i ];

138

139 return input; // enables cin >> x >> y;

140

141 } // end function

Outline57

142

143 // l d d t t t f l A
http://localhost/var/www/apps/conversion/lthdt/Htm/Source/CT4_7.CPPhttp://localhost/var/www/apps/conversion/lthdt/Htm/Source/CT4_7.CPPhttp://localhost/var/www/apps/conversion/lthdt/Htm/Source/CT4_5.CPP


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array1.cpp (7 of 7)

143 // overloaded output operator for class Array

144 ostream &operator


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fig08_06.cpp

(1 of 3)

2 // Array class test program.

3 #include

4

5 using std::cout;

6 using std::cin;

7 using std::endl;

8

9 #include "array1.h"

10

11 int main()

12 {

13 Array integers1( 7 ); // seven-element Array

14 Array integers2; // 10-element Array by default

1516 // print integers1 size and contents

17 cout


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fig08_06.cpp

(2 of 3)

27 cout > integers1 >> integers2;

29

30 cout


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fig08_06.cpp

(3 of 3)

49 cout


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fig08_06.cpp

output (1 of 3)

Size of array integers1 is 7

Array after initialization:

0 0 0 0

0 0 0



0 0 0 0

0 0 0 0

0 0

Input 17 integers:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

After input, the arrays contain:

integers1:

1 2 3 4

5 6 7

integers2:

8 9 10 11

12 13 14 15

Outline62Evaluating: integers1 != integers2

integers1 and integers2 are not equal


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fig08_06.cpp

output (2 of 3)

integers1 and integers2 are not equal



1 2 3 4

5 6 7

Assigning integers2 to integers1:

integers1:

8 9 10 11

12 13 14 15

16 17

integers2:

8 9 10 1112 13 14 15

16 17

Evaluating: integers1 == integers2

integers1 and integers2 are equal

integers1[5] is 13


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64

8 11 O erloading ++ and


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8.11 Overloading ++ and --

Increment/decrement operators can be overloaded Add 1 to a Date object, d1

Prototype (member function) Date &operator++();

++d1 same as d1.operator++()

Prototype (non-member) Friend Date &operator++( Date &);

++d1 same as operator++( d1 )


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66

8 11 Overloading ++ and


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8.11 Overloading ++ and --

Return values Preincrement

Returns by reference (Date &)

lvalue (can be assigned)

Postincrement

Returns by value

Returns temporary object with old value

rvalue (cannot be on left side of assignment)

Decrement operator analogous

67

8 12 Case Study: A Date Class


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8.12 Case Study: A Date Class

Example Date class Overloaded increment operator

Change day, month and year

Overloaded += operator

Function to test for leap years

Function to determine if day is last of month

Outline68

1 // Fig. 8.10: date1.h

2 // D t l d fi iti


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All rights reserved.

date1.h (1 of 2)

2 // Date class definition.

3 #ifndef DATE1_H

4 #define DATE1_H

5 #include

67 using std::ostream;

8

9 class Date {

10 friendostream &operator


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date1.h (2 of 2)

24 private:

25 int month;

26 int day;

27 int year;

2829 static const int days[]; // array of days per month

30 voidhelpIncrement(); // utility function

31

32 }; // end class Date

33

34 #endif

Outline70

1 // Fig. 8.11: date1.cpp

2 // Date class member function definitions


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date1.cpp (1 of 5)

2 // Date class member function definitions.

3 #include

4 #include "date1.h"

5

6 // initialize static member at file scope;7 // one class-wide copy

8 const int Date::days[] =

9 { 0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };

10

11// Date constructor

12 Date::Date( int m, int d, int y )

13 {

14 setDate( m, d, y );

15

16 } // end Date constructor

17

18 // set month, day and year

19 voidDate::setDate( int mm, int dd, int yy )

20 {

21 month = ( mm >= 1 && mm = 1900 && yy


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date1.cpp (2 of 5)

26 day = ( dd >= 1 && dd = 1 && dd


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date1.cpp (3 of 5)

53 // add specified number of days to date

54 const Date &Date::operator+=( int additionalDays )

55 {

56 for ( int i = 0; i < additionalDays; i++ )

57 helpIncrement();

58

59 return *this; // enables cascading

60

61 } // end function operator+=

62

63 // if the year is a leap year, return true;

64 // otherwise, return false65 bool Date::leapYear( int testYear ) const

66 {

67 if ( testYear % 400 == 0 ||

68 ( testYear % 100 != 0 && testYear % 4 == 0 ) )

69 returntrue; // a leap year

70 else71 returnfalse; // not a leap year

72

73 } // end function leapYear

74

Outline73

75 // determine whether the day is the last day of the month

76 bool Date::endOfMonth( int testDay ) const


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date1.cpp (4 of 5)

( y )

77 {

78 if ( month == 2 && leapYear( year ) )

79 return testDay == 29; // last day of Feb. in leap year

80 else

81 return testDay == days[ month ];

82

83 } // end function endOfMonth

84

85 // function to help increment the date

86 voidDate::helpIncrement()

87 {88 // day is not end of month

89 if ( !endOfMonth( day ) )

90 ++day;

91

92 else

9394 // day is end of month and month < 12

95 if ( month < 12 ) {

96 ++month;

97 day = 1;

98 }

99

Outline74

100 // last day of year

101 else {


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date1.cpp (5 of 5)

{

102 ++year;

103 month = 1;

104 day = 1;

105 }

106

107 } // end function helpIncrement

108

109 // overloaded output operator

110 ostream &operator


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fig08_12.cpp

(1 of 2)

p g

3 #include

4

5 using std::cout;

6 using std::endl;

7

8 #include"date1.h" // Date class definition

9

10 int main()

11 {

12 Date d1; // defaults to January 1, 1900

13 Date d2( 12, 27, 1992 );14 Date d3( 0, 99, 8045 ); // invalid date

15

16 cout


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fig08_12.cpp

(2 of 2)

27 cout


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fig08_12.cpp

output (1 of 1)

d2 is December 27, 1992

d3 is January 1, 1900

d2 += 7 is January 3, 1993

d3 is February 28, 1992

++d3 is February 29, 1992

Testing the preincrement operator:

d4 is July 13, 2002

++d4 is July 14, 2002

d4 is July 14, 2002

Testing the postincrement operator:

d4 is July 14, 2002

d4++ is July 14, 2002d4 is July 15, 2002

Chuong VIII Da Nang Hoa Toan Tu

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