C大学教程C++部分23章到25章

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chapter 23 Objected-oriented Programming :inheritance

Base Classes and Derived Classes

• often , an object of one class is an object of another classes.in C++, class Rectangle can be said to inherit from class quadrilateral, in this context , class Quadrilateral is a base class, and class Rectangle is a derived class.
• because every derived-class object is an object of its base.and one base class can have many derived classes,the set objects represented by a base class typically is arger than the set of objects represented by any of its derived classes.
• inheritance releationship form treelike hierarchical structures.
• to specify that class TwoDimensionShape is derived from the class shape ,class TwoDimensionShape could be defined in C++ as follows:

class TwoDimensionShape:public shape;

• this is an example of public inheritance,the most commonly used form, we also will discuss private inheritance and protected inheritance,with all forms of inheritance , private members of a base class are not accessible directly from that class’s derived classes, but these private base-class members are sti;; inherited (they are still considered parts of the derived classes), with public inheritance,all other basic-class members retained their original member access when they become members of the derived class,through these inherited base-class members , the derived class can manipulate private members of the base class(if these inherited members provide such functionality in the base class).note that friend function is not inherited.

23.3 protected Members

• a base class’s public members are accessible within the body of that base class and any where that the program has a handle (i.e a name , reference or pointer) to an object of the that base class or one of the derived class, a base class’s private members are accessible only withon the body of that base class and that friend base.

• using protected access offers an intermediate level of protection between public and private access.

  23.4.1

  代码部分

//CommissionEmployee.h#pragma once#ifndef COMMISSION_H#define COMMISSION_H#include<string>using namespace std;class CommissionEmployee {public:    //constructor while initialing    CommissionEmployee(const string &, const string &, const string &, double = 0.0, double = 0.0);    //set the first name    void setFirstName(const string &);       //return first name    string getFirstName() const;    //set the last name    void setLastName(const string &);    //get the last name    string getLastName() const;    //set SSN    void setSocialSecruityNumber(const string &);    //get the SSN    string getSocialSecruityNumber() const;    //set gross sales amount;    void setGrossSales(double);    //get gross sales amount    double getGrossSales() const;    //set setCommisionRate    void setCommisionRate(double);    //double getCommisionRate    double getCommisionRate() const;    //earning    double earnings() const;    void print() const;private:    string firstName;    string lastName;    string socialSecruityNumber;    double grossSales;    double commisionRate;};#endif

//CommissionEmployee.cpp#include<iostream>#include<string>#include"CommissionEmployee.h"using namespace std;CommissionEmployee::CommissionEmployee(const string &first, const string &last, const string &SSN, double sales, double rate) {    firstName = first;    lastName = last;    socialSecruityNumber = SSN;    setGrossSales(sales);    setCommisionRate(rate);}void CommissionEmployee::setFirstName(const string & first) {    firstName = first;}void CommissionEmployee::setLastName(const string & last) {    lastName = last;}string CommissionEmployee::getFirstName() const {    return firstName;}string CommissionEmployee::getLastName() const{    return lastName;}void CommissionEmployee::setSocialSecruityNumber(const string &ssn) {    socialSecruityNumber = ssn;}string CommissionEmployee::getSocialSecruityNumber() const {    return socialSecruityNumber;}void CommissionEmployee::setGrossSales(double sales) {    grossSales = sales;}double CommissionEmployee::getGrossSales() const {    return grossSales;}void CommissionEmployee::setCommisionRate(double rate) {    commisionRate = (rate > 0.0 && rate < 1.0) ? rate:0.0;}double CommissionEmployee::getCommisionRate() const {    return commisionRate;}double CommissionEmployee::earnings() const {    return commisionRate * grossSales;}void CommissionEmployee::print() const{    cout << "commission employee: " << firstName << " " << lastName        << "\nsocial security number: " << socialSecruityNumber        << "\ngross sales: " << grossSales        << "\ncommission rate: " << commisionRate << endl;}

23.4.2 Creating a class without using inheritance.

the code

//BasePlus.h#pragma once#ifndef COMMISSION_H#define COMMISSION_H#include<string>using namespace std;class BasePlusCommissionEmployee {public:    //constructor while initialing    BasePlusCommissionEmployee(const string &, const string &, const string &, double = 0.0, double = 0.0, double = 0.0);    //set the first name    void setFirstName(const string &);    //return first name    string getFirstName() const;    //set the last name    void setLastName(const string &);    //get the last name    string getLastName() const;    //set SSN    void setSocialSecruityNumber(const string &);    //get the SSN    string getSocialSecruityNumber() const;    //set gross sales amount;    void setGrossSales(double);    //get gross sales amount    double getGrossSales() const;    //set setCommisionRate    void setCommisionRate(double);    //double getCommisionRate    double getCommisionRate() const;    //earning    double earnings() const;    void print() const;    //set the baseSalary    void BasePlusCommissionEmployee::setBaseSalary(double);    double BasePlusCommissionEmployee::getBaseSalary() const;private:    string firstName;    string lastName;    string socialSecruityNumber;    double grossSales;    double commisionRate;    double baseSalary;};#endif//Baseplus.cpp#include<iostream>#include<string>#include"BasePlus.h"using namespace std;BasePlusCommissionEmployee::BasePlusCommissionEmployee(const string &first, const string &last, const string &SSN, double sales, double rate, double salary) {    firstName = first;    lastName = last;    socialSecruityNumber = SSN;    setGrossSales(sales);    setCommisionRate(rate);    setBaseSalary(salary);}void BasePlusCommissionEmployee::setFirstName(const string & first) {    firstName = first;}void BasePlusCommissionEmployee::setLastName(const string & last) {    lastName = last;}string BasePlusCommissionEmployee::getFirstName() const {    return firstName;}string BasePlusCommissionEmployee::getLastName() const {    return lastName;}void BasePlusCommissionEmployee::setSocialSecruityNumber(const string &ssn) {    socialSecruityNumber = ssn;}string BasePlusCommissionEmployee::getSocialSecruityNumber() const {    return socialSecruityNumber;}void BasePlusCommissionEmployee::setGrossSales(double sales) {    grossSales = sales;}double BasePlusCommissionEmployee::getGrossSales() const {    return grossSales;}void BasePlusCommissionEmployee::setCommisionRate(double rate) {    commisionRate = (rate > 0.0 && rate < 1.0) ? rate : 0.0;}double BasePlusCommissionEmployee::getCommisionRate() const {    return commisionRate;}double BasePlusCommissionEmployee::earnings() const {    return commisionRate * grossSales + baseSalary;}void BasePlusCommissionEmployee::print() const{    cout << "commission employee: " << firstName << " " << lastName        << "\nsocial security number: " << socialSecruityNumber        << "\ngross sales: " << grossSales        << "\ncommission rate: " << commisionRate << endl;}void BasePlusCommissionEmployee::setBaseSalary(double salary) {    baseSalary = (salary<0.0) ? 0.0 : salary;}double BasePlusCommissionEmployee::getBaseSalary() const {    return baseSalary;}//test.cpp#include<iostream>#include<iomanip>using namespace std;#include"BasePlus.h"int main() {    BasePlusCommissionEmployee employee("Bob", "lewis", "333-33-3333", 5000, 0.04, 300);    //set floating-point output formatting    cout << fixed << setprecision(2);    //get commission employee data    cout << "\nFirst information detained by get function: \n"        << "\nFirst name is " << employee.getFirstName()        << "\nlast name is " << employee.getLastName()        << "\nsocial security number is " << employee.getSocialSecruityNumber()        << "\ngross sales is " << employee.getGrossSales()        << "\ncommission rate is " << employee.getCommisionRate()        << "\nbase salary id " << employee.getBaseSalary() << endl << endl;    employee.setBaseSalary(1000);    cout << "\nupdated employee information output by print function: " << endl << endl;    employee.print();    cout << "\n\nemployee's earning: $" << employee.earnings() << endl;    return 0;}

• in fact , it is boring and a waste of time.

23.4.3creating a commissionEmployee-basePlusCommissionEmployee inheritance.

• now we create and test a new version of class BasePlusCommissionEmployee that derives from class CommissionEmployee
• in this example , a BasePlusCommissionEmployee object is a CommissionEmployee.
• keyword public indicates the type of inheritance, as a derived class(formed with public inheritance) BasePlusCommissionEmployee inherits all the members of class CommissionEmployee,except for the constructor-each class provides its own constructors that are specific to the class.

//CommissionEmployee.h#pragma once#ifndef COMMISSION_H#define COMMISSION_H#include<string>using namespace std;class CommissionEmployee {public:    //constructor while initialing    CommissionEmployee(const string &, const string &, const string &, double = 0.0, double = 0.0);    //set the first name    void setFirstName(const string &);    //return first name    string getFirstName() const;    //set the last name    void setLastName(const string &);    //get the last name    string getLastName() const;    //set SSN    void setSocialSecruityNumber(const string &);    //get the SSN    string getSocialSecruityNumber() const;    //set gross sales amount;    void setGrossSales(double);    //get gross sales amount    double getGrossSales() const;    //set setCommisionRate    void setCommisionRate(double);    //double getCommisionRate    double getCommisionRate() const;    //earning    double earnings() const;    void print() const;protected:    string firstName;    string lastName;    string socialSecruityNumber;    double grossSales;    double commisionRate;};#endif#pragma once//BasePlus.h#ifndef BASEPLUS_H#define BASEPLUS_H#include<string>using namespace std;#include"CommissionEmployee.h"class BasePlusCommissionEmployee :public CommissionEmployee {public:    //constructor while initialing    BasePlusCommissionEmployee(const string &, const string &, const string &, double = 0.0, double = 0.0, double = 0.0);    //set the baseSalary    void BasePlusCommissionEmployee::setBaseSalary(double);    //get it    double BasePlusCommissionEmployee::getBaseSalary() const;    //earning    double earnings() const;private:    double baseSalary;};#endif//CommissionEmployee.cpp#include<iostream>#include<string>#include"CommissionEmployee.h"using namespace std;CommissionEmployee::CommissionEmployee(const string &first, const string &last, const string &SSN, double sales, double rate) {    firstName = first;    lastName = last;    socialSecruityNumber = SSN;    setGrossSales(sales);    setCommisionRate(rate);}void CommissionEmployee::setFirstName(const string & first) {    firstName = first;}void CommissionEmployee::setLastName(const string & last) {    lastName = last;}string CommissionEmployee::getFirstName() const {    return firstName;}string CommissionEmployee::getLastName() const {    return lastName;}void CommissionEmployee::setSocialSecruityNumber(const string &ssn) {    socialSecruityNumber = ssn;}string CommissionEmployee::getSocialSecruityNumber() const {    return socialSecruityNumber;}void CommissionEmployee::setGrossSales(double sales) {    grossSales = sales;}double CommissionEmployee::getGrossSales() const {    return grossSales;}void CommissionEmployee::setCommisionRate(double rate) {    commisionRate = (rate > 0.0 && rate < 1.0) ? rate : 0.0;}double CommissionEmployee::getCommisionRate() const {    return commisionRate;}double CommissionEmployee::earnings() const {    return commisionRate * grossSales;}void CommissionEmployee::print() const{    cout << "commission employee: " << firstName << " " << lastName        << "\nsocial security number: " << socialSecruityNumber        << "\ngross sales: " << grossSales        << "\ncommission rate: " << commisionRate << endl;}#include<iostream>using namespace std;//BasePlus.cpp#include"BasePlus.h"#include"CommissionEmployee.h"BasePlusCommissionEmployee::BasePlusCommissionEmployee(const string &first, const string &last, const string &SSN, double sales, double rate, double salary)    :CommissionEmployee(first, last, SSN, sales, rate){    setBaseSalary(salary);}double BasePlusCommissionEmployee::earnings() const {    return commisionRate * grossSales + baseSalary;}void BasePlusCommissionEmployee::setBaseSalary(double salary) {    baseSalary = (salary<0.0) ? 0.0 : salary;}double BasePlusCommissionEmployee::getBaseSalary() const {    return baseSalary;}//test.cpp#include<iostream>#include<iomanip>using namespace std;#include"BasePlus.h"int main() {    BasePlusCommissionEmployee employee("Bob", "lewis", "333-33-3333", 5000, 0.04, 300);    //set floating-point output formatting    cout << fixed << setprecision(2);    //get commission employee data    cout << "\nFirst information detained by get function: \n"        << "\nFirst name is " << employee.getFirstName()        << "\nlast name is " << employee.getLastName()        << "\nsocial security number is " << employee.getSocialSecruityNumber()        << "\ngross sales is " << employee.getGrossSales()        << "\ncommission rate is " << employee.getCommisionRate()        << "\nbase salary id " << employee.getBaseSalary() << endl << endl;    employee.setBaseSalary(1000);    cout << "\nupdated employee information output by print function: " << endl << endl;    employee.print();    cout << "\n\nemployee's earning: $" << employee.earnings() << endl;    return 0;}

• C++ requires a derived-class constructor to call its base-class constructor to initialize the base-class data members that are inherited into the derived class..
• as you can see, C++ regidly enforces restriction on private data members.
• another reason to include the base-class header file is that the compiler uses a class definition to determine the size of an object of that class, a client program that creates an object of an class must #include the class definition to enable the compiler to reverse the proper amount of memory for te object,whenusing inheritance, a derived-class object’s size depends on the data members declared explicitly in its class definitionand the data members.

23.3.4 CommissionEmployee-BasePlusCommissionEmployee inheritance hierarchy using protected Data.

• same as the code above.
• to enable class BasePlusCommissionEmployee to directly access CommissionEmployee data members firstName,lastName and so on , we can declare those members as protected in the base class.as we discussed before , a vase’s classs protected members can be accessed by members and friends of any classes derived from that base class.
• notes on using protected Data.
• in most cases,however , it is better to use private data members to encourage proper software engineering , and leave code optimization issues to the compiler,your code will be easier to maintain ,modify and debug.
• problems.
  

  a derived-class object can assign a negative value to the protected data member,thus leaving the object in an inconsistent state.

23.4.5CommissionEmployee-BasePlusCommissionEmployee inheritance Hierarchy using private Data

• final version

//CommissionEmployee.h#pragma once#ifndef COMMISSION_H#define COMMISSION_H#include<string>using namespace std;class CommissionEmployee {public:    //constructor while initialing    CommissionEmployee(const string &, const string &, const string &, double = 0.0, double = 0.0);    //set the first name    void setFirstName(const string &);    //return first name    string getFirstName() const;    //set the last name    void setLastName(const string &);    //get the last name    string getLastName() const;    //set SSN    void setSocialSecruityNumber(const string &);    //get the SSN    string getSocialSecruityNumber() const;    //set gross sales amount;    void setGrossSales(double);    //get gross sales amount    double getGrossSales() const;    //set setCommisionRate    void setCommisionRate(double);    //double getCommisionRate    double getCommisionRate() const;    //earning    double earnings() const;    void print() const;private:    string firstName;    string lastName;    string socialSecruityNumber;    double grossSales;    double commisionRate;};#endif#pragma once//BasePlus.h#ifndef BASEPLUS_H#define BASEPLUS_H#include<string>using namespace std;#include"CommissionEmployee.h"class BasePlusCommissionEmployee :public CommissionEmployee {public:    //constructor while initialing    BasePlusCommissionEmployee(const string &, const string &, const string &, double = 0.0, double = 0.0, double = 0.0);    //set the baseSalary    void BasePlusCommissionEmployee::setBaseSalary(double);    //get it    double BasePlusCommissionEmployee::getBaseSalary() const;    //earning    double earnings() const;private:    double baseSalary;};#endif//CommissionEmployee.cpp#include<iostream>#include<string>#include"CommissionEmployee.h"using namespace std;CommissionEmployee::CommissionEmployee(const string &first, const string &last, const string &SSN, double sales, double rate) :firstName(first),lastName(last),socialSecruityNumber(SSN){    //firstName = first;    //lastName = last;    //socialSecruityNumber = SSN;    setGrossSales(sales);    setCommisionRate(rate);}void CommissionEmployee::setFirstName(const string & first) {    firstName = first;}void CommissionEmployee::setLastName(const string & last) {    lastName = last;}string CommissionEmployee::getFirstName() const {    return firstName;}string CommissionEmployee::getLastName() const {    return lastName;}void CommissionEmployee::setSocialSecruityNumber(const string &ssn) {    socialSecruityNumber = ssn;}string CommissionEmployee::getSocialSecruityNumber() const {    return socialSecruityNumber;}void CommissionEmployee::setGrossSales(double sales) {    grossSales = sales;}double CommissionEmployee::getGrossSales() const {    return grossSales;}void CommissionEmployee::setCommisionRate(double rate) {    commisionRate = (rate > 0.0 && rate < 1.0) ? rate : 0.0;}double CommissionEmployee::getCommisionRate() const {    return commisionRate;}double CommissionEmployee::earnings() const {    return commisionRate * grossSales;}void CommissionEmployee::print() const{    cout << "commission employee: " << firstName << " " << lastName        << "\nsocial security number: " << socialSecruityNumber        << "\ngross sales: " << grossSales        << "\ncommission rate: " << commisionRate << endl;}#include<iostream>using namespace std;//BasePlus.cpp#include"BasePlus.h"#include"CommissionEmployee.h"BasePlusCommissionEmployee::BasePlusCommissionEmployee(const string &first, const string &last, const string &SSN, double sales, double rate, double salary)    :CommissionEmployee(first, last, SSN, sales, rate){    setBaseSalary(salary);}double BasePlusCommissionEmployee::earnings() const {    return CommissionEmployee::earnings() + baseSalary;}void BasePlusCommissionEmployee::setBaseSalary(double salary) {    baseSalary = (salary<0.0) ? 0.0 : salary;}double BasePlusCommissionEmployee::getBaseSalary() const {    return baseSalary;}//test.cpp#include<iostream>#include<iomanip>using namespace std;#include"BasePlus.h"int main() {    BasePlusCommissionEmployee employee("Bob", "lewis", "333-33-3333", 5000, 0.04, 300);    //set floating-point output formatting    cout << fixed << setprecision(2);    //get commission employee data    cout << "\nFirst information detained by get function: \n"        << "\nFirst name is " << employee.getFirstName()        << "\nlast name is " << employee.getLastName()        << "\nsocial security number is " << employee.getSocialSecruityNumber()        << "\ngross sales is " << employee.getGrossSales()        << "\ncommission rate is " << employee.getCommisionRate()        << "\nbase salary id " << employee.getBaseSalary() << endl << endl;    employee.setBaseSalary(1000);    cout << "\nupdated employee information output by print function: " << endl << endl;    employee.print();    cout << "\n\nemployee's earning: $" << employee.earnings() << endl;    return 0;}

chapter 24

24.2 Polymorphism Examples

• With polymorphism , one function can cause different actions to occur , depending on the type of the object on which the function is invoked,this gives the programmer tremendous expressive capability ,
• the polymorphism occurs when a program invokes a virtue function through a base-class pointer or reference - C++ dynamically chooses the correct function for the class from which the object was instantiated ,

24.3 Relationships among objects in an inheritance hierarchy

24.3.1 Invoking Base-Class Functions from Derived-Class Objects.