cs342 data structure

CS342 Data Structure

Review of C++: Overriding base-class functions

Overriding Base-Class Members in a Derived Class

• To override a base-class member function – In the derived class, supply a new version of that

function with the same signature• same function name, different definition

– When the function is then mentioned by name in the derived class, the derived version is automatically called

– The scope-resolution operator may be used to access the base class version from the derived class

1. Employee class

definition

-----------------------

1. Load

header

1.1 Functi

on definitions

1 // Fig. 9.5: employ.h2 // Definition of class Employee3 #ifndef EMPLOY_H4 #define EMPLOY_H56 class Employee {7 public:8 Employee( const char *, const char * ); // constructor9 void print() const; // output first and last name10 ~Employee(); // destructor11 private:12 char *firstName; // dynamically allocated string13 char *lastName; // dynamically allocated string14 };1516 #endif17 // Fig. 9.5: employ.cpp

18 // Member function definitions for class Employee

19 #include <iostream>

20

21 using std::cout;

22

23 #include <cstring>

24 #include <cassert>

25 #include "employ.h"

26

27 // Constructor dynamically allocates space for the

28 // first and last name and uses strcpy to copy

29 // the first and last names into the object.

30 Employee::Employee( const char *first, const char *last )

31 {

32 firstName = new char[ strlen( first ) + 1 ];

1.1 Function definitions

---------------------

1. HourlyWorker class definition

33 assert( firstName != 0 ); // terminate if not allocated34 strcpy( firstName, first );3536 lastName = new char[ strlen( last ) + 1 ];37 assert( lastName != 0 ); // terminate if not allocated38 strcpy( lastName, last );39 }4041 // Output employee name42 void Employee::print() const43 { cout << firstName << ' ' << lastName; }4445 // Destructor deallocates dynamically allocated memory46 Employee::~Employee()47 {48 delete [] firstName; // reclaim dynamic memory49 delete [] lastName; // reclaim dynamic memory50 }51 // Fig. 9.5: hourly.h

52 // Definition of class HourlyWorker

53 #ifndef HOURLY_H

54 #define HOURLY_H

55

56 #include "employ.h"

57

58 class HourlyWorker : public Employee {

59 public:

60 HourlyWorker( const char*, const char*, double, double );

61 double getPay() const; // calculate and return salary

62 void print() const; // overridden base-class print

63 private:

HourlyWorker inherits from Employee.

HourlyWorker will override the print function.

1. Load header


64 double wage; // wage per hour65 double hours; // hours worked for week66 };6768 #endif69 // Fig. 9.5: hourly.cpp

70 // Member function definitions for class HourlyWorker


72

73 using std::cout;

74 using std::endl;

75

76 #include <iomanip>

77

78 using std::ios;

79 using std::setiosflags;

80 using std::setprecision;

81

82 #include "hourly.h"

83

84 // Constructor for class HourlyWorker

85 HourlyWorker::HourlyWorker( const char *first,

86 const char *last,

87 double initHours, double initWage )

88 : Employee( first, last ) // call base-class constructor

89 {

90 hours = initHours; // should validate

91 wage = initWage; // should validate

92 }

93

94 // Get the HourlyWorker's pay

95 double HourlyWorker::getPay() const { return wage * hours; }

1.1 Function Definitions

--------------------

1. Load header

1.1 Initialize object

2. Function call

Program Output

96

97 // Print the HourlyWorker's name and pay

98 void HourlyWorker::print() const

99 {

100 cout << "HourlyWorker::print() is executing\n\n";

101 Employee::print(); // call base-class print function

102

103 cout << " is an hourly worker with pay of $"

104 << setiosflags( ios::fixed | ios::showpoint )

105 << setprecision( 2 ) << getPay() << endl;

106}107// Fig. 9.5: fig09_05.cpp

108// Overriding a base-class member function in a

109// derived class.

110#include "hourly.h"

111

112int main()

113{

114 HourlyWorker h( "Bob", "Smith", 40.0, 10.00 );

115 h.print();

116 return 0;

117}

HourlyWorker::print() is executing Bob Smith is an hourly worker with pay of $400.00

The print function is overriden in HourlyWorker. However, the new function still can call the original print function using ::

Implicit Derived-Class Object to Base-Class

Object Conversion • Assignment of derived and base classes

– Derived-class type and base-class type are different– Derived-class object can be treated as a base-class object

• Derived class has members corresponding to all of the base class’s members

• Derived-class has more members than the base-class object• Derived-class object can be assigned to a base-class object

– Base-class object cannot be treated as a derived-class object

• Would leave additional derived class members undefined• Base-class object cannot be assigned to a derived class object

unless the assignment operator is overloaded to allow such an assignment

Implicit Derived-Class Object to Base-Class Object Conversion continued

• Mixing base and derived class pointers and objects– Referring to a base-class object with a base-class pointer

• Allowed

– Referring to a derived-class object with a derived-class pointer

• Allowed

– Referring to a derived-class object with a base-class pointer

• Possible syntax error• Code can only refer to base-class members, or syntax error

– Referring to a base-class object with a derived-class pointer

• Syntax error, unless• The derived-class pointer must first be cast to a base-class pointer

Down-casting Base-Class Pointers to Derived Class Pointers

• Derived classes relationships to base classes– Objects of a derived class can be treated as objects of the

base class• Reverse not true — base class objects cannot be derived-class objects

• Down-casting a pointer– Use an explicit cast to convert a base-class pointer to a

derived-class pointer

– If pointer is going to be de-referenced, the type of the pointer must match the type of object to which the pointer points

– Format:

derivedPtr = static_cast< DerivedClass * > basePtr;

Down-casting Base-Class Pointers to Derived-Class Pointers continued

• The following example: point (base class) circle (derived class)– Demonstrates the down-casting of base class

pointers to derived class pointers– Class Circle is derived from class Point– A pointer of type Point is used to reference a Circle object, and a pointer to type Circle is used to reference a Point object

Example highlight: point (base) class and circle (derived) class

pointPtr = &c; // Assign address of circle object to pointPtr is OK!

// Treat a circle as a point (see only the point base class part)

// i.e., *pointPtr refers to the point (base class) object.

circlePtr = &p; // Assign address of a point object to a circlePtr is not allowed

circlePtr = static_cast< Circle * >( pointPtr ); // if pointPtr = &c; then // *circlePtr refers to the circle object!

pointPtr = &p; // Assign address of point object to pointPtr is OK.

circlePtr = static_cast< Circle * >( pointPtr ); // here *circlePtr refers to a

// circle (derived class) object, however, the data members

// defined in the circle class are undefined!!!

Full example follows

1. Point class

definition

-------------

1. Load header


1 // Fig. 9.4: point.h

2 // Definition of class Point3 #ifndef POINT_H4 #define POINT_H56 #include <iostream>78 using std::ostream;910 class Point {11 friend ostream &operator<<( ostream &, const Point & );12 public:13 Point( int = 0, int = 0 ); // default constructor14 void setPoint( int, int ); // set coordinates15 int getX() const { return x; } // get x coordinate16 int getY() const { return y; } // get y coordinate17 protected: // accessible by derived classes18 int x, y; // x and y coordinates of the Point19 };2021 #endif22 // Fig. 9.4: point.cpp23 // Member functions for class Point24 #include <iostream>25 #include "point.h"2627 // Constructor for class Point28 Point::Point( int a, int b ) { setPoint( a, b ); }2930 // Set x and y coordinates of Point31 void Point::setPoint( int a, int b )32 {33 x = a;


---------------------

1. Circle class

definition

34 y = b;35 }3637 // Output Point (with overloaded stream insertion operator)38 ostream &operator<<( ostream &output, const Point &p )39 {40 output << '[' << p.x << ", " << p.y << ']';4142 return output; // enables cascaded calls43 }44 // Fig. 9.4: circle.h

45 // Definition of class Circle

46 #ifndef CIRCLE_H

47 #define CIRCLE_H

48


50

51 using std::ostream;

52

53 #include <iomanip>

54

55 using std::ios;

56 using std::setiosflags;

57 using std::setprecision;

58

59 #include "point.h"

60

61 class Circle : public Point { // Circle inherits from Point

62 friend ostream &operator<<( ostream &, const Circle & );

63 public:

64 // default constructor

Class Circle publicly inherits from class Point, so it will have class Point's public and protected member functions and data.

1. Circle definition

--------------------

1. Load header


65 Circle( double r = 0.0, int x = 0, int y = 0 );

66

67 void setRadius( double ); // set radius

68 double getRadius() const; // return radius

69 double area() const; // calculate area

70 protected:

71 double radius;

72 };

73

74 #endif

75 // Fig. 9.4: circle.cpp

76 // Member function definitions for class Circle

77 #include "circle.h"

78

79 // Constructor for Circle calls constructor for Point

80 // with a member initializer then initializes radius.

81 Circle::Circle( double r, int a, int b )

82 : Point( a, b ) // call base-class constructor

83 { setRadius( r ); }

84

85 // Set radius of Circle

86 void Circle::setRadius( double r )

87 { radius = ( r >= 0 ? r : 0 ); }

88

Circle inherits from Point, and has Point's data members (which are set by calling Point's constructor).

1. 1 Function Definitions

----------------------

Driver

1. Load headers

1.1 Initialize objects

89 // Get radius of Circle90 double Circle::getRadius() const { return radius; }9192 // Calculate area of Circle93 double Circle::area() const94 { return 3.14159 * radius * radius; }9596 // Output a Circle in the form:97 // Center = [x, y]; Radius = #.##98 ostream &operator<<( ostream &output, const Circle &c )99 {100 output << "Center = " << static_cast< Point >( c ) 101 << "; Radius = " 102 << setiosflags( ios::fixed | ios::showpoint )103 << setprecision( 2 ) << c.radius;104105 return output; // enables cascaded calls106}107// Fig. 9.4: fig09_04.cpp

108// Casting base-class pointers to derived-class pointers

109#include <iostream>

110

111using std::cout;

112using std::endl;

113

114#include <iomanip>

115

116#include "point.h"

117#include "circle.h"

118

119int main()

120{

121 Point *pointPtr = 0, p( 30, 50 );


1.2 Assign objects

2. Function calls

134 cout << "\nCircle c (via *circlePtr):\n" << *circlePtr

135 << "\nArea of c (via circlePtr): "

136 << circlePtr->area() << '\n';

137

138 // DANGEROUS: Treat a Point as a Circle

139 pointPtr = &p; // assign address of Point to pointPtr

140

141 // cast base-class pointer to derived-class pointer

142 circlePtr = static_cast< Circle * >( pointPtr );

143 cout << "\nPoint p (via *circlePtr):\n" << *circlePtr

144 << "\nArea of object circlePtr points to: "

145 << circlePtr->area() << endl;

146 return 0;

147}

122 Circle *circlePtr = 0, c( 2.7, 120, 89 );

123

124 cout << "Point p: " << p << "\nCircle c: " << c << '\n';

125

126 // Treat a Circle as a Point (see only the base class part)

127 pointPtr = &c; // assign address of Circle to pointPtr

128 cout << "\nCircle c (via *pointPtr): "

129 << *pointPtr << '\n';

130

131 // Treat a Circle as a Circle (with some casting)

132 // cast base-class pointer to derived-class pointer

133 circlePtr = static_cast< Circle * >( pointPtr );

Assign derived-class pointer (&c) to base class pointer pointPtr.

The base class pointer only "sees" the base-class part of the object it points to.

Cast pointPtr into a Circle * , and assign to circlePtr.

circlePtr will treat c (the object to which it points) as a Circle.

Point p: [30, 50]

Circle c: Center = [120, 89]; Radius = 2.70

Circle c (via *pointPtr): [120, 89]

Circle c (via *circlePtr):

Center = [120, 89]; Radius = 2.70

Area of c (via circlePtr): 22.90

Assign pointPtr to a Point object. It has no derived-class information.

When it is cast to a Circle *, circlePtr is really assigned to a base-class object with no derived-class information. This is dangerous.

Point p (via *circlePtr):

Center = [30, 50]; Radius = 0.00

Area of object circlePtr points to: 0.00

Program Output

Point p: [30, 50]Circle c: Center = [120, 89]; Radius = 2.70 Circle c (via *pointPtr): [120, 89] Circle c (via *circlePtr):Center = [120, 89]; Radius = 2.70Area of c (via circlePtr): 22.90 Point p (via *circlePtr):Center = [30, 50]; Radius = 0.00Area of object circlePtr points to: 0.00

Virtual Functions• virtual functions

– Suppose a set of shape classes such as Circle, Triangle, etc.

– Every shape has own unique draw function but possible to call them by calling the draw function of base class Shape

• Compiler determines dynamically (i.e., at run time) which to call

– In base-class declare draw to be virtual– Override draw in each of the derived classes– virtual declaration:

• Keyword virtual before function prototype in base-classvirtual void draw() const;

– A base-class pointer to a derived class object will call the correct draw function

ShapePtr->draw();

– If a derived class does not define a virtual function, the function is inherited from the base class

Virtual Functions

ShapePtr->Draw();

– Compiler implements dynamic binding – Function determined during execution time

ShapeObject.Draw();

– Compiler implements static binding – Function determined during compile-time

Abstract and Concrete Classes

• Abstract classes – Sole purpose is to provide a base class for other classes– No objects of an abstract base class can be instantiated

• Too generic to define real objects (i.e., TwoDimensionalShape)• Can have pointers and references

• Concrete classes – Classes that can instantiate objects– Provide specifics to make real objects (i.e., Square, Circle)

• Making abstract classes– Declare one or more virtual functions as “pure” by

initializing the function to zero– Example of a pure virtual function:

virtual double earnings() const = 0;

Polymorphism

• Polymorphism– Ability for objects of different classes to respond differently to the

same function call– Implemented through virtual functions

• Base-class pointer (or reference) calls a virtual function• C++ chooses the correct overridden function in object

– If non-virtual member function defined in multiple classes and called from base-class pointer then the base-class version is used

• If called from derived-class pointer then derived-class version is used

– Suppose print is not a virtual functionEmployee e, *ePtr = &e;HourlyWorker h, *hPtr = &h;ePtr->print(); // call base-class print functionhPtr->print(); // call derived-class print functionePtr=&h; // allowable implicit conversionePtr->print(); // still calls base-class print

New Classes and Dynamic Binding

• Polymorphism and virtual functions– Work well when all classes are not known in

advance– Use dynamic binding to accommodate new

classes being added to a system

• Dynamic binding (late binding) – Object's type need not be know at compile time

for a virtual function– virtual function call is matched at run time

An example// Drozdek example p20#include <iostream.h>class c1{public:

virtual void f( ){cout << "F( ) in c1\n";}void g( ){cout << "G( ) in c1\n";}

};class c2{public:

virtual void f( ){cout << "F( ) in c2\n";}void g( ){cout << "G( ) in c2\n";}

};class c3{public:

virtual void f( ){cout << "F( ) in c3\n";}};

Example continuedvoid main()

{

c1 o1, *p;

c2 o2;

c3 o3;

p = &o1;

p -> f(); // f in c1

p -> g(); // g in c1

p = (c1 *)&o2; // casting: old style; new style: p = static_cast< c1 * >( &o2 );

p -> f(); // f in c2 since g is virtual: dynamic binding on c2 obj

p -> g(); // g in c1 since g is not virtual: static binding on p

p = (c1 *)&o3;

p -> f(); // f in c3 since g is virtual: dynamic binding on c3 obj

p -> g(); // g in c1 since c3 has no definition for g

}

Case Study: A Payroll System Using Polymorphism

• The following example is a payroll system– Uses virtual functions and polymorphism to

perform payroll calculations based on the type of an employee

1. Employee Definition

(base class)

1 // Fig. 10.1: employ2.h

2 // Abstract base class Employee

3 #ifndef EMPLOY2_H

4 #define EMPLOY2_H

5

6 class Employee {

7 public:

8 Employee( const char *, const char * );

9 ~Employee(); // destructor reclaims memory

10 const char *getFirstName() const;

11 const char *getLastName() const;

12

13 // Pure virtual function makes Employee abstract base class

14 virtual double earnings() const = 0; // pure virtual

15 virtual void print() const; // virtual

16 private:

17 char *firstName;

18 char *lastName;

19 };

20

21 #endif

earnings is declared pure virtual because the implementation will depend on which derived class it will be used in.

Employee is an abstract base class.


22 // Fig. 10.1: employ2.cpp23 // Member function definitions for24 // abstract base class Employee.25 // Note: No definitions given for pure virtual functions.26 #include <iostream>2728 using std::cout;2930 #include <cstring>31 #include <cassert>32 #include "employ2.h"3334 // Constructor dynamically allocates space for the35 // first and last name and uses strcpy to copy36 // the first and last names into the object.37 Employee::Employee( const char *first, const char *last )38 {39 firstName = new char[ strlen( first ) + 1 ];40 assert( firstName != 0 ); // test that new worked41 strcpy( firstName, first );4243 lastName = new char[ strlen( last ) + 1 ];44 assert( lastName != 0 ); // test that new worked45 strcpy( lastName, last );46 }4748 // Destructor deallocates dynamically allocated memory49 Employee::~Employee()50 {51 delete [] firstName;52 delete [] lastName;53 }


54

55 // Return a pointer to the first name

56 // Const return type prevents caller from modifying private

57 // data. Caller should copy returned string before destructor

58 // deletes dynamic storage to prevent undefined pointer.

59 const char *Employee::getFirstName() const

60 {

61 return firstName; // caller must delete memory

62 }

63

64 // Return a pointer to the last name

65 // Const return type prevents caller from modifying private

66 // data. Caller should copy returned string before destructor

67 // deletes dynamic storage to prevent undefined pointer.

68 const char *Employee::getLastName() const

69 {

70 return lastName; // caller must delete memory

71 }

72

73 // Print the name of the Employee

74 void Employee::print() const

75 { cout << firstName << ' ' << lastName; }

1. Boss Definition

(derived class)

76 // Fig. 10.1: boss1.h

77 // Boss class derived from Employee

78 #ifndef BOSS1_H

79 #define BOSS1_H

80 #include "employ2.h"

81

82 class Boss : public Employee {

83 public:

84 Boss( const char *, const char *, double = 0.0 );

85 void setWeeklySalary( double );

86 virtual double earnings() const;

87 virtual void print() const;

88 private:

89 double weeklySalary;

90 };

91

92 #endif


93 // Fig. 10.1: boss1.cpp

94 // Member function definitions for class Boss


96

97 using std::cout;

98

99 #include "boss1.h"

100

101// Constructor function for class Boss

102Boss::Boss( const char *first, const char *last, double s )


104{ setWeeklySalary( s ); }

105

106// Set the Boss's salary

107void Boss::setWeeklySalary( double s )

108 { weeklySalary = s > 0 ? s : 0; }

109

110// Get the Boss's pay

111double Boss::earnings() const { return weeklySalary; }

112

113// Print the Boss's name

114void Boss::print() const

115{

116 cout << "\n Boss: ";

117 Employee::print();

118}

Notice the overriden earnings and print functions.

They were declared virtual in the base class.

1. CommissionWorker Definition (derived

class)

119// Fig. 10.1: commis1.h

120// CommissionWorker class derived from Employee

121#ifndef COMMIS1_H

122#define COMMIS1_H

123#include "employ2.h"

124

125class CommissionWorker : public Employee {

126public:

127 CommissionWorker( const char *, const char *,

128 double = 0.0, double = 0.0,

129 int = 0 );

130 void setSalary( double );

131 void setCommission( double );

132 void setQuantity( int );



135private:

136 double salary; // base salary per week

137 double commission; // amount per item sold

138 int quantity; // total items sold for week

139};

140

141#endif


142// Fig. 10.1: commis1.cpp

143// Member function definitions for class CommissionWorker


145

146using std::cout;

147

148#include "commis1.h"

149

150// Constructor for class CommissionWorker

151CommissionWorker::CommissionWorker( const char *first,

152 const char *last, double s, double c, int q )


154{

155 setSalary( s );

156 setCommission( c );

157 setQuantity( q );

158}

159

160// Set CommissionWorker's weekly base salary

161void CommissionWorker::setSalary( double s )

162 { salary = s > 0 ? s : 0; }


163

164// Set CommissionWorker's commission

165void CommissionWorker::setCommission( double c )

166 { commission = c > 0 ? c : 0; }

167

168// Set CommissionWorker's quantity sold

169void CommissionWorker::setQuantity( int q )

170 { quantity = q > 0 ? q : 0; }

171

172// Determine CommissionWorker's earnings

173double CommissionWorker::earnings() const

174 { return salary + commission * quantity; }

175

176// Print the CommissionWorker's name

177void CommissionWorker::print() const

178{

179 cout << "\nCommission worker: ";


181}

Notice the overriden earnings and print functions.


1. PieceWork

er Definition (derived

class)

182// Fig. 10.1: piece1.h

183// PieceWorker class derived from Employee

184#ifndef PIECE1_H

185#define PIECE1_H


187

188class PieceWorker : public Employee {

189public:

190 PieceWorker( const char *, const char *,

191 double = 0.0, int = 0);

192 void setWage( double );

193 void setQuantity( int );



196private:

197 double wagePerPiece; // wage for each piece output

198 int quantity; // output for week

199};

200

201#endif


202// Fig. 10.1: piece1.cpp203// Member function definitions for class PieceWorker204#include <iostream>205206using std::cout;207208#include "piece1.h"209210// Constructor for class PieceWorker211PieceWorker::PieceWorker( const char *first, const char *last, 212 double w, int q )213 : Employee( first, last ) // call base-class constructor214{215 setWage( w );216 setQuantity( q );217}218219// Set the wage220void PieceWorker::setWage( double w ) 221 { wagePerPiece = w > 0 ? w : 0; }222223// Set the number of items output224void PieceWorker::setQuantity( int q ) 225 { quantity = q > 0 ? q : 0; }226227// Determine the PieceWorker's earnings228double PieceWorker::earnings() const229 { return quantity * wagePerPiece; }230231// Print the PieceWorker's name 232void PieceWorker::print() const233{234 cout << "\n Piece worker: ";235 Employee::print();236}

Again, notice the overridden earnings and print functions.


1. HourlyWor

ker Definition (derived

class)

237// Fig. 10.1: hourly1.h

238// Definition of class HourlyWorker

239#ifndef HOURLY1_H

240#define HOURLY1_H


242

243class HourlyWorker : public Employee {

244public:

245 HourlyWorker( const char *, const char *,

246 double = 0.0, double = 0.0);

247 void setWage( double );

248 void setHours( double );



251private:

252 double wage; // wage per hour

253 double hours; // hours worked for week

254};

255

256#endif


257// Fig. 10.1: hourly1.cpp

258// Member function definitions for class HourlyWorker


260

261using std::cout;

262

263#include "hourly1.h"

264

265// Constructor for class HourlyWorker

266HourlyWorker::HourlyWorker( const char *first,

267 const char *last,

268 double w, double h )


270{

271 setWage( w );

272 setHours( h );

273}

274

275// Set the wage

276void HourlyWorker::setWage( double w )

277 { wage = w > 0 ? w : 0; }


278

279// Set the hours worked

280void HourlyWorker::setHours( double h )

281 { hours = h >= 0 && h < 168 ? h : 0; }

282

283// Get the HourlyWorker's pay

284double HourlyWorker::earnings() const

285{

286 if ( hours <= 40 ) // no overtime

287 return wage * hours;

288 else // overtime is paid at wage * 1.5

289 return 40 * wage + ( hours - 40 ) * wage * 1.5;

290}

291

292// Print the HourlyWorker's name

293void HourlyWorker::print() const

294{

295 cout << "\n Hourly worker: ";


297}

Overridden functions.

1. Load headers

298// Fig. 10.1: fig10_01.cpp

299// Driver for Employee hierarchy


301

302using std::cout;

303using std::endl;

304

305#include <iomanip>

306

307using std::ios;

308using std::setiosflags;

309using std::setprecision;

310


312#include "boss1.h"

313#include "commis1.h"

314#include "piece1.h"

315#include "hourly1.h"

316

317void virtualViaPointer( const Employee * );

318void virtualViaReference( const Employee & );

319

320int main()

321{

322 // set output formatting

323 cout << setiosflags( ios::fixed | ios::showpoint )

324 << setprecision( 2 );

325


2. Print

326 Boss b( "John", "Smith", 800.00 );327 b.print(); // static binding328 cout << " earned $" << b.earnings(); // static binding329 virtualViaPointer( &b ); // uses dynamic binding330 virtualViaReference( b ); // uses dynamic binding331332 CommissionWorker c( "Sue", "Jones", 200.0, 3.0, 150 );333 c.print(); // static binding334 cout << " earned $" << c.earnings(); // static binding335 virtualViaPointer( &c ); // uses dynamic binding336 virtualViaReference( c ); // uses dynamic binding337338 PieceWorker p( "Bob", "Lewis", 2.5, 200 );339 p.print(); // static binding340 cout << " earned $" << p.earnings(); // static binding341 virtualViaPointer( &p ); // uses dynamic binding342 virtualViaReference( p ); // uses dynamic binding343344 HourlyWorker h( "Karen", "Price", 13.75, 40 );345 h.print(); // static binding346 cout << " earned $" << h.earnings(); // static binding347 virtualViaPointer( &h ); // uses dynamic binding348 virtualViaReference( h ); // uses dynamic binding349 cout << endl;350 return 0;351}352353// Make virtual function calls off a base-class pointer354// using dynamic binding.355void virtualViaPointer( const Employee *baseClassPtr )356{357 baseClassPtr->print();358 cout << " earned $" << baseClassPtr->earnings();359}

Boss: John Smith earned $800.00

Call function print using the object itself.

Call function print, using a base-class pointer.

This uses virtual functions and dynamic binding.

Call function print, using a base-class reference.

This uses virtual functions and dynamic binding.



Commission worker: Sue Jones earned $650.00



Piece worker: Bob Lewis earned $500.00



Hourly worker: Karen Price earned $550.00



Take in a baseclass pointer, call the virtual function print.

3. Function Definitions

Program Output

360

361// Make virtual function calls off a base-class reference

362// using dynamic binding.

363void virtualViaReference( const Employee &baseClassRef )

364{

365 baseClassRef.print();

366 cout << " earned $" << baseClassRef.earnings();

367}

Boss: John Smith earned $800.00 Boss: John Smith earned $800.00 Boss: John Smith earned $800.00Commission worker: Sue Jones earned $650.00Commission worker: Sue Jones earned $650.00Commission worker: Sue Jones earned $650.00 Piece worker: Bob Lewis earned $500.00 Piece worker: Bob Lewis earned $500.00 Piece worker: Bob Lewis earned $500.00 Hourly worker: Karen Price earned $550.00 Hourly worker: Karen Price earned $550.00 Hourly worker: Karen Price earned $550.00

Take in base class reference, call the virtual function print.

cs342 data structure

Documents

baseclass objectderived

derived class object

baseclass type

base class version

class objectsdown

derivedclass objectwould

implicit derivedclass

differentderivedclass