• 第13章 类继承

    13.1 一个简单的基类

    从一个类派生出另一个类，原始类成为基类，继承类称为派生类。

    13.2 继承:is-a关系

    • 共有继承   is-a
    • 保护继承
    • 私有继承

    13.3多态公有继承

    虚函数：无virtual 程序根据引用类型或指针类型选择方法，有virtual程序将根据引用或指针指向的对象的类型做选择。

    支票代码如下：

    brass.h

    1. #ifndef BRASS_H_
    2. #define BRASS_H_
    3.  
    4. #include <string>
    5.  
    6. using std::string;
    7.  
    8. class Brass
    9. {
    10.     private:
    11.         string fullName;
    12.         long acctNum;
    13.         double balance;
    14.     public:
    15.         Brass(const string &s = "NullBody",long an = -1,double bal = 0.0);
    16.         void Deposit(double amt);
    17.         virtual void Withdraw(double amt);
    18.         double Balance() const;
    19.         virtual void ViewAcct() const;
    20.         virtual ~Brass() {};
    21. };
    22.  
    23. class BrassPlus : public Brass
    24. {
    25.     private:
    26.         double maxLoan;
    27.         double rate;
    28.         double owesBank;
    29.     public:
    30.         BrassPlus(const string &s= "NullBody",long an = -1,double bal = 0.0,double ml =500,double r = 0.11125 );
    31.         BrassPlus(const Brass &ba,double ml = 500,double r = 0.11125);
    32.         virtual void ViewAcct() const;
    33.         virtual void Withdraw(double amt);
    34.         void ResetMax(double m) {maxLoan = m;}
    35.         void ResetRate(double r) {rate = r;}
    36.         void ResetOwes() {owesBank = 0;}
    37. };
    38.  
    39. #endif

    brass.cpp

    1. #include <iostream>
    2. #include "brass.h"
    3.  
    4. using namespace std;
    5.  
    6. typedef ios_base::fmtflags format;
    7. typedef streamsize precis;
    8. format setFormat();
    9. void restore(format f,precis p);
    10.  
    11. Brass::Brass(const string &s,long an,double bal)
    12. {
    13.     fullName = s;
    14.     acctNum = an;
    15.     balance = bal;
    16. }
    17.  
    18. void Brass::Deposit(double amt)
    19. {
    20.     if(amt < 0)
    21.         cout << "Negative deposit, deposit is cancelled.\n";
    22.     else
    23.         balance += amt;
    24. }
    25.  
    26. void Brass::Withdraw(double amt)
    27. {
    28.     format initState = setFormat();
    29.     precis prec = cout.precision(2);
    30.  
    31.     if(amt < 0)
    32.         cout << "Withdraw canceled\n";
    33.     else if(amt <= balance)
    34.         balance -= amt;
    35.     else
    36.         cout << "Withdraw amount of $" << amt << " exceeds your balance.\n" << "Withdraw canceled\n";
    37.     restore(initState,prec);
    38. }
    39.  
    40. double Brass::Balance() const
    41. {
    42.     return balance;
    43. }
    44.  
    45. void Brass::ViewAcct() const
    46. {
    47.     format initialstate = setFormat();
    48.     precis prec = cout.precision(2);
    49.     cout << "Client: " << fullName << endl;
    50.     cout << "Account Number:" << acctNum << endl;
    51.     cout << "Balance: $" << balance << endl;
    52.     restore(initialstate,prec);
    53. }
    54.  
    55. BrassPlus::BrassPlus(const string &s,long an,double bal,double ml,double r):Brass(s,an,bal)
    56. {
    57.     maxLoan = ml;
    58.     owesBank = 0.0;
    59.     rate = r;
    60. }
    61.  
    62. BrassPlus::BrassPlus(const Brass & ba,double ml,double r) : Brass(ba)
    63. {
    64.     maxLoan = ml;
    65.     owesBank = 0.0;
    66.     rate = r;
    67. }
    68.  
    69. void BrassPlus::ViewAcct() const
    70. {
    71.     format initialstate = setFormat();
    72.     precis prec = cout.precision(2);
    73.  
    74.     Brass::ViewAcct();
    75.     cout << "Maxinum loan:$" << maxLoan <<endl;
    76.     cout << "Owed to bank:$" << owesBank << endl;
    77.     cout.precision(3);
    78.     cout << "Loan Rate: "  << 100*rate << "%\n";
    79.     restore(initialstate,prec);
    80. }
    81.  
    82. void BrassPlus::Withdraw(double amt)
    83. {
    84.     format initialstate = setFormat();
    85.     precis prec = cout.precision(2);
    86.  
    87.     double bal = Balance();
    88.     if(amt <= bal)
    89.         Brass::Withdraw(amt);
    90.     else if(amt <= bal + maxLoan - owesBank)
    91.     {
    92.         double advance = amt - bal;
    93.         owesBank += advance * (1.0 + rate);
    94.         cout << "Bank advance:$" << advance << endl;
    95.         cout << "Finance charge:$" << advance * rate << endl;
    96.         Deposit(advance);
    97.         Brass::Withdraw(amt);
    98.     }
    99.     else 
    100.         cout << "Transaction cancelled.\n";
    101.     restore(initialstate,prec);
    102. }
    103.  
    104. format setFormat()
    105. {
    106.     return cout.setf(ios_base::fixed,ios_base::floatfield);
    107. }
    108.  
    109. void restore(format f,precis p)
    110. {
    111.     cout.setf(f,ios_base::floatfield);
    112.     cout.precision(p);
    113. }

    usebrass1.cpp

    1. #include <iostream>
    2. #include "brass.h"
    3.  
    4. using namespace std;
    5.  
    6. int main()
    7. {
    8.     Brass pig("pigg",381299,4000.00);
    9.     BrassPlus Hoggy("Hogg",382288,3000.00);
    10.     pig.ViewAcct();
    11.     cout << endl;
    12.     Hoggy.ViewAcct();
    13.     cout << endl;
    14.     cout << "Hogg + 1000$\n";
    15.     Hoggy.Deposit(1000);
    16.     cout << "Hoggy bal:$" << Hoggy.Balance() << endl;
    17.     cout <<"withdeaw $4200 from pig\n";
    18.     pig.Withdraw(4200);
    19.     cout <<"pig bal:$" << pig.Balance() << endl;
    20.     cout <<"withdraw $4200 from Hogg\n";
    21.     Hoggy.Withdraw(4200);
    22.     Hoggy.ViewAcct();
    23.     return 0;
    24. }

    虚方法行为  多态性

    usebrass2.cpp

    1. #include <iostream>
    2. #include <string>
    3. #include "brass.h"
    4.  
    5. const int CLIENTS = 4;
    6. using namespace std;
    7.  
    8. int main()
    9. {
    10.     Brass* p_client[CLIENTS];
    11.     string temp;
    12.     long tempnum;
    13.     double tempbal;
    14.     char kind;
    15.  
    16.     for(int i=0;i<CLIENTS;i++)
    17.     {
    18.         cout << "enter client's name:";
    19.         getline(cin,temp);
    20.         cout << "enter client's accout number:";
    21.         cin >> tempnum;
    22.         cout << "enter opening balance:$";
    23.         cin >> tempbal;
    24.         cout << "enter 1 for brass accout or 2 for brassplus accout:";
    25.         while(cin >> kind && (kind != '1' && kind != '2'))
    26.             cout << "enter 1 or 2:";
    27.         if(kind == '1')
    28.             p_client[i] = new Brass(temp,tempnum,tempbal);
    29.         else
    30.         {
    31.             double tmax,trate;
    32.             cout << "enter overdraft limit:&";
    33.             cin >> tmax;
    34.             cout << "enter the rate:";
    35.             cin >> trate;
    36.             p_client[i] = new BrassPlus(temp,tempnum,tempbal,tmax,trate);
    37.         
    38.         }
    39.         while(cin.get() != '\n')
    40.             continue;
    41.     }
    42.     cout << endl;
    43.     for(int i =0;i<CLIENTS;i++)
    44.     {
    45.         p_client[i]->ViewAcct();
    46.         cout << endl;
    47.         delete p_client[i];
    48.     }
    49.     cout << "Done!\n";
    50.     return 0;
    51. }

    运行结果：

    1. enter client's name:harry
    2. enter client's accout number:112233
    3. enter opening balance:$1500
    4. enter 1 for brass accout or 2 for brassplus accout:1
    5. enter client's name:dinah
    6. enter client's accout number:121213
    7. enter opening balance:$1800
    8. enter 1 for brass accout or 2 for brassplus accout:2
    9. enter overdraft limit:&350
    10. enter the rate:0.12
    11. enter client's name:brenda
    12. enter client's accout number:212118
    13. enter opening balance:$5200
    14. enter 1 for brass accout or 2 for brassplus accout:2
    15. enter overdraft limit:&800
    16. enter the rate:0.1
    17. enter client's name:tim
    18. enter client's accout number:233255
    19. enter opening balance:$688
    20. enter 1 for brass accout or 2 for brassplus accout:1
    21.  
    22. Client: harry
    23. Account Number:112233
    24. Balance: $1500.00
    25.  
    26. Client: dinah
    27. Account Number:121213
    28. Balance: $1800.00
    29. Maxinum loan:$350.00
    30. Owed to bank:$0.00
    31. Loan Rate: 12.000%
    32.  
    33. Client: brenda
    34. Account Number:212118
    35. Balance: $5200.00
    36. Maxinum loan:$800.00
    37. Owed to bank:$0.00
    38. Loan Rate: 10.000%
    39.  
    40. Client: tim
    41. Account Number:233255
    42. Balance: $688.00
    43.  
    44. Done!

    注意虚函数viewAcct()的调用。

    基类的虚析构函数是很有必要的。

    13.4 静态联编和动态联编

    程序中有重载函数时，编译器根据参数完成函数对应，会再编译过程中完成联编，称为静态联编。

    增加虚函数后，编译器需要在程序运行时对应函数，称为动态联编。

    将派生类引用或指针 转换为 基类引用或者指针 称为向上强制转换，这使公有继承不需要进行显示类型转换。is-a规则

    1. void fr(Brass &rb); //uses rb.ViewAcct()
    2. void fp(Brass *rp); //uses rp->ViewAcct()
    3. void fv(Brass &b); //uses b.ViewAcct()
    4. int main()
    5. {
    6.     Brass b("bill",123432,10000);
    7.     BrassPlus bp("betty",232323,12345);
    8.     fr(b);  //uses Brass::ViewAcct()
    9.     fr(bp); //uses BrassPlus::ViewAcct()
    10.     fp(b);  //uses Brass::ViewAcct()
    11.     fp(bp); //uses BrassPlus::ViewAcct()
    12.     fv(b);  //uses Brass::ViewAcct()
    13.     fv(bp); //uses Brass::ViewAcct()
    14. }

    虚函数在内存和执行速度方面有一定成本：

    • 每个对象都将增大，增大量为储存地址的空间
    • 对于没个类，编译器都创建一个虚函数地址表
    • 对于每个函数调用，都需执行一项额外操作：表中查找地址

    虚函数还需注意事项

    • 构造函数不能为虚函数
    • 析构函数应该时虚函数，除非类不用做基类
    • 友元不能为虚函数
    • 派生类没有定义函数，会使用基类函数
    • 重新定义将被隐藏方法

    13.5 访问控制：protected

    派生类可以直接访问基类保护成员。

    最好对数据成员采用私有访问控制，不要使用保护控制。

    13.6抽象基类

    abstract base class ABC

    在函数原型中使用=0指出类时一个抽象基类，在类中可以不定义该函数

    代码示例

    acctabc.h

    1. #ifndef ACCTABC_H_
    2. #define ACCTABC_H_
    3. #include <iostream>
    4. #include <string>
    5.  
    6. class AcctABC
    7. {
    8. private:
    9.     std::string fullName;
    10.     long acctNum;
    11.     double balance;
    12. protected:
    13.     struct Formatting
    14.     {
    15.         std::ios_base::fmtflags flag;
    16.         std::streamsize pr;
    17.     };
    18.     const std::string &FullName() const {return fullName;}
    19.     long AcctNum() const {return acctNum;}
    20.     Formatting SetFormat() const;
    21.     void Restore(Formatting &f) const;
    22. public:
    23.     AcctABC(const std::string &s = "Nullbody",long an = -1,double bal = 0.0);
    24.     void Deposit(double amt);
    25.     virtual void Withdraw(double amt) = 0;
    26.     double Balance() const {return balance;}
    27.     virtual void ViewAcct() const =0;
    28.     virtual ~AcctABC() {};
    29. };
    30.  
    31. class Brass:public AcctABC
    32. {
    33. public:
    34.     Brass(const std::string &s = "Nullbody",long an = -1,double bal = 0.0):AcctABC(s,an,bal) {}
    35.     virtual void Withdraw(double amt);
    36.     virtual void ViewAcct() const;
    37.     virtual ~Brass() {};
    38. };
    39.  
    40. class BrassPlus:public AcctABC
    41. {
    42. private:
    43.     double maxLoan;
    44.     double rate;
    45.     double owesBank;
    46. public:
    47.     BrassPlus(const std::string &s = "Nullbody",long an=-1,double bal = 0.0,double ml = 500,double r=1.10);
    48.     BrassPlus(const Brass &ba,double ml = 500,double r = 0.1);
    49.     virtual void ViewAcct() const;
    50.     virtual void Withdraw(double amt); 
    51.     void ResetMax(double m) {maxLoan = m;}
    52.     void ResetRate(double r) {rate = r;}
    53.     void ResetOwes() {owesBank = 0;}
    54. };
    55.  
    56. #endif

    acctabc.cpp

    1. #include <iostream>
    2. #include "acctabc.h"
    3.  
    4. using namespace std;
    5.  
    6. AcctABC::AcctABC(const string &s,long an,double bal)
    7. {
    8.     fullName = s;
    9.     acctNum = an;
    10.     balance = bal;
    11. }
    12.  
    13. void AcctABC::Deposit(double amt)
    14. {
    15.     if(amt < 0)
    16.         cout << "Negative deposit, deposit is cancelled.\n";
    17.     else
    18.         balance += amt;
    19. }
    20.  
    21. void AcctABC::Withdraw(double amt)
    22. {
    23.     balance -= amt;
    24. }
    25.  
    26. AcctABC::Formatting AcctABC::SetFormat() const
    27. {
    28.     Formatting f;
    29.     f.flag = cout.setf(ios_base::fixed,ios_base::floatfield);
    30.     f.pr = cout.precision(2);
    31.     return f;
    32. }
    33.  
    34. void AcctABC::Restore(Formatting &f) const
    35. {
    36.     cout.setf(f.flag,ios_base::floatfield);
    37.     cout.precision(f.pr);
    38. }
    39.  
    40. void Brass::Withdraw(double amt)
    41. {
    42.     if(amt < 0)
    43.         cout << "Withdraw canceled\n";
    44.     else if(amt <= Balance())
    45.         AcctABC::Withdraw(amt);
    46.     else
    47.         cout << "Withdraw amount of $" << amt << " exceeds your balance.\n" << "Withdraw canceled\n";
    48. }
    49.  
    50. void Brass::ViewAcct() const
    51. {
    52.     Formatting f = SetFormat();
    53.     cout << "Client: " << FullName() << endl;
    54.     cout << "Account Number:" << AcctNum() << endl;
    55.     cout << "Balance: $" << Balance() << endl;
    56.     Restore(f);
    57. }
    58.  
    59. BrassPlus::BrassPlus(const string &s,long an,double bal,double ml,double r):AcctABC(s,an,bal)
    60. {
    61.     maxLoan = ml;
    62.     owesBank = 0.0;
    63.     rate = r;
    64. }
    65.  
    66. BrassPlus::BrassPlus(const Brass & ba,double ml,double r) : AcctABC(ba)
    67. {
    68.     maxLoan = ml;
    69.     owesBank = 0.0;
    70.     rate = r;
    71. }
    72.  
    73. void BrassPlus::ViewAcct() const
    74. {
    75.     Formatting f = SetFormat();
    76.  
    77.     cout << "Client: " << FullName() << endl;
    78.     cout << "Account Number:" << AcctNum() << endl;
    79.     cout << "Balance: $" << Balance() << endl;
    80.     cout << "Maxinum loan:$" << maxLoan <<endl;
    81.     cout << "Owed to bank:$" << owesBank << endl;
    82.     cout.precision(3);
    83.     cout << "Loan Rate: "  << 100*rate << "%\n";
    84.     Restore(f);
    85. }
    86.  
    87. void BrassPlus::Withdraw(double amt)
    88. {
    89.     Formatting f = SetFormat();
    90.  
    91.     double bal = Balance();
    92.     if(amt <= bal)
    93.         AcctABC::Withdraw(amt);
    94.     else if(amt <= bal + maxLoan - owesBank)
    95.     {
    96.         double advance = amt - bal;
    97.         owesBank += advance * (1.0 + rate);
    98.         cout << "Bank advance:$" << advance << endl;
    99.         cout << "Finance charge:$" << advance * rate << endl;
    100.         Deposit(advance);
    101.         AcctABC::Withdraw(amt);
    102.     }
    103.     else 
    104.         cout << "Transaction cancelled.\n";
    105.     Restore(f);
    106. }

    usebrass3.cpp

    1. #include <iostream>
    2. #include <string>
    3. #include "acctabc.h"
    4.  
    5. const int CLIENTS = 4;
    6. using namespace std;
    7.  
    8. int main()
    9. {
    10.     AcctABC* p_client[CLIENTS];
    11.     string temp;
    12.     long tempnum;
    13.     double tempbal;
    14.     char kind;
    15.  
    16.     for(int i=0;i<CLIENTS;i++)
    17.     {
    18.         cout << "enter client's name:";
    19.         getline(cin,temp);
    20.         cout << "enter client's accout number:";
    21.         cin >> tempnum;
    22.         cout << "enter opening balance:$";
    23.         cin >> tempbal;
    24.         cout << "enter 1 for brass accout or 2 for brassplus accout:";
    25.         while(cin >> kind && (kind != '1' && kind != '2'))
    26.             cout << "enter 1 or 2:";
    27.         if(kind == '1')
    28.             p_client[i] = new Brass(temp,tempnum,tempbal);
    29.         else
    30.         {
    31.             double tmax,trate;
    32.             cout << "enter overdraft limit:&";
    33.             cin >> tmax;
    34.             cout << "enter the rate:";
    35.             cin >> trate;
    36.             p_client[i] = new BrassPlus(temp,tempnum,tempbal,tmax,trate);
    37.         
    38.         }
    39.         while(cin.get() != '\n')
    40.             continue;
    41.     }
    42.     cout << endl;
    43.     for(int i =0;i<CLIENTS;i++)
    44.     {
    45.         p_client[i]->ViewAcct();
    46.         cout << endl;
    47.         delete p_client[i];
    48.     }
    49.     cout << "Done!\n";
    50.     return 0;
    51. }

    3.7继承和动态内存分配

    未完待续

  • 相关阅读:
    EasyExcel完成excel文件的导入导出
    怎样从零开始训练一个AI车手？
    Servlet面试题
    Python 编程语言的介绍
    图像分割 - 线检测
    在微信小程序中如何引入iconfont
    【Linux私房菜】第三期——实用指令
    CSP测试中完善程序题目的解题经验与运用
    【无标题】
    Git安装
  • 原文地址：https://blog.csdn.net/m0_59666413/article/details/125472723