• 第11章 使用类

    11.1 运算符重载

    11.2 计算时间：一个运算符重载示例

    mytime.h

    1. #ifndef MYTIME_H_
    2. #define MYTIME_H_
    3.  
    4. class Time
    5. {
    6.     private:
    7.         int hours;
    8.         int minutes;
    9.     public:
    10.         Time();
    11.         Time(int h,int m = 0);
    12.         void AddMin(int m);
    13.         void AddHr(int h);
    14.         void Reset(int h=0,int m=0);
    15.         Time Sum(const Time &t) const;
    16.         Time operator+(const Time &t) const;
    17.         Time operator*(double m) const;
    18.         friend Time operator*(double m,const Time &t);
    19.         void Show() const;
    20. };
    21.  
    22. #endif

    mytime.cpp

    1. #include <iostream>
    2. #include "mytime.h"
    3.  
    4. Time::Time()
    5. {
    6.     hours = minutes = 0;
    7. }
    8.  
    9. Time::Time(int h,int m)
    10. {
    11.     hours = h;
    12.     minutes = m;
    13. }
    14.  
    15. void Time::AddMin(int m)
    16. {
    17.     minutes += m;
    18.     hours +=minutes/60;
    19.     minutes = minutes%60;
    20. }
    21.  
    22. void Time::AddHr(int h)
    23. {
    24.     hours +=h;
    25. }
    26.  
    27. void Time::Reset(int h,int m)
    28. {
    29.     hours = h;
    30.     minutes = m;
    31. }
    32.  
    33. Time Time::Sum(const Time &t) const
    34. {
    35.     Time sum;
    36.     sum.minutes = minutes + t.minutes;
    37.     sum.hours = t.hours +hours +  sum.minutes/60;
    38.     sum.minutes %= 60;
    39.     return sum;
    40. }
    41.  
    42. Time Time::operator+(const Time &t) const
    43. {
    44.     Time sum;
    45.     sum.minutes = minutes + t.minutes;
    46.     sum.hours = t.hours +hours +  sum.minutes/60;
    47.     sum.minutes %= 60;
    48.     return sum;
    49. }
    50.  
    51. Time Time::operator*(double m) const
    52. {
    53.     Time result;
    54.     long totalmin = hours*60*m + minutes*m;
    55.     result.hours = totalmin/60;
    56.     result.minutes = totalmin%60;
    57.     return result;
    58. }
    59.  
    60. Time operator*(double m,const Time &t)
    61. {
    62.     /*Time result;
    63.     long totalmin = t.hours*60*m + t.minutes*m;
    64.     result.hours = totalmin/60;
    65.     result.minutes = totalmin%60;*/
    66.     return t*m;
    67. }
    68.  
    69. void Time::Show() const
    70. {
    71.     std::cout <<hours << " hours, " << minutes << " min\n";
    72. }

    usetime.cpp

    1. #include <iostream>
    2. #include "mytime.h"
    3.  
    4. Time::Time()
    5. {
    6.     hours = minutes = 0;
    7. }
    8.  
    9. Time::Time(int h,int m)
    10. {
    11.     hours = h;
    12.     minutes = m;
    13. }
    14.  
    15. void Time::AddMin(int m)
    16. {
    17.     minutes += m;
    18.     hours +=minutes/60;
    19.     minutes = minutes%60;
    20. }
    21.  
    22. void Time::AddHr(int h)
    23. {
    24.     hours +=h;
    25. }
    26.  
    27. void Time::Reset(int h,int m)
    28. {
    29.     hours = h;
    30.     minutes = m;
    31. }
    32.  
    33. Time Time::Sum(const Time &t) const
    34. {
    35.     Time sum;
    36.     sum.minutes = minutes + t.minutes;
    37.     sum.hours = t.hours +hours +  sum.minutes/60;
    38.     sum.minutes %= 60;
    39.     return sum;
    40. }
    41.  
    42. Time Time::operator+(const Time &t) const
    43. {
    44.     Time sum;
    45.     sum.minutes = minutes + t.minutes;
    46.     sum.hours = t.hours +hours +  sum.minutes/60;
    47.     sum.minutes %= 60;
    48.     return sum;
    49. }
    50.  
    51. Time Time::operator*(double m) const
    52. {
    53.     Time result;
    54.     long totalmin = hours*60*m + minutes*m;
    55.     result.hours = totalmin/60;
    56.     result.minutes = totalmin%60;
    57.     return result;
    58. }
    59.  
    60. Time operator*(double m,const Time &t)
    61. {
    62.     /*Time result;
    63.     long totalmin = t.hours*60*m + t.minutes*m;
    64.     result.hours = totalmin/60;
    65.     result.minutes = totalmin%60;*/
    66.     return t*m;
    67. }
    68.  
    69. void Time::Show() const
    70. {
    71.     std::cout <<hours << " hours, " << minutes << " min\n";
    72. }

    执行结果：

    1. planning time:0 hours, 0 min
    2. coding  time:2 hours, 40 min
    3. fixing time:5 hours, 55 min
    4. total time:8 hours, 35 min
    5. total time * 1.1:9 hours, 26 min

    11.3 友元

    • 友元函数
    • 友元类
    • 友元成员函数

    创建友元

    友元函数是非成员函数，但范文权限和成员函数相同

    1、将其原型放在类声明中，并在原型声明前加上关键字friend

            friend Time operator*(double m,const Time &t);

    2、编写函数定义，应为不是成员函数，不加类限定符(time::)，定义中不用关键字friend。

    程序用例：

    mytime3.h

    1. #ifndef MYTIME3_H_
    2. #define MYTIME3_H_
    3. #include <iostream>
    4. class Time
    5. {
    6.     private:
    7.         int hours;
    8.         int minutes;
    9.     public:
    10.         Time();
    11.         Time(int h,int m = 0);
    12.         void AddMin(int m);
    13.         void AddHr(int h);
    14.         void Reset(int h=0,int m=0);
    15.         Time Sum(const Time &t) const;
    16.         Time operator+(const Time &t) const;
    17.         Time operator*(double m) const;
    18.         friend Time operator*(double m,const Time &t)
    19.             {return t*m;}
    20.         //void Show() const;
    21.         friend std::ostream &operator<<(std::ostream &os,const Time &t);
    22. };
    23.  
    24. #endif

    mytime3.cpp

    1.  
    2. #include "mytime3.h"
    3.  
    4. Time::Time()
    5. {
    6.     hours = minutes = 0;
    7. }
    8.  
    9. Time::Time(int h,int m)
    10. {
    11.     hours = h;
    12.     minutes = m;
    13. }
    14.  
    15. void Time::AddMin(int m)
    16. {
    17.     minutes += m;
    18.     hours +=minutes/60;
    19.     minutes = minutes%60;
    20. }
    21.  
    22. void Time::AddHr(int h)
    23. {
    24.     hours +=h;
    25. }
    26.  
    27. void Time::Reset(int h,int m)
    28. {
    29.     hours = h;
    30.     minutes = m;
    31. }
    32.  
    33. Time Time::Sum(const Time &t) const
    34. {
    35.     Time sum;
    36.     sum.minutes = minutes + t.minutes;
    37.     sum.hours = t.hours +hours +  sum.minutes/60;
    38.     sum.minutes %= 60;
    39.     return sum;
    40. }
    41.  
    42. Time Time::operator+(const Time &t) const
    43. {
    44.     Time sum;
    45.     sum.minutes = minutes + t.minutes;
    46.     sum.hours = t.hours +hours +  sum.minutes/60;
    47.     sum.minutes %= 60;
    48.     return sum;
    49. }
    50.  
    51. Time Time::operator*(double m) const
    52. {
    53.     Time result;
    54.     long totalmin = hours*60*m + minutes*m;
    55.     result.hours = totalmin/60;
    56.     result.minutes = totalmin%60;
    57.     return result;
    58. }
    59.  
    60. /*Time operator*(double m,const Time &t)
    61. {
    62.     Time result;
    63.     long totalmin = t.hours*60*m + t.minutes*m;
    64.     result.hours = totalmin/60;
    65.     result.minutes = totalmin%60;
    66.     return t*m;
    67. }*/
    68.  
    69. /*void Time::Show() const
    70. {
    71.     std::cout <<hours << " hours, " << minutes << " min\n";
    72. }*/
    73.  
    74. std::ostream &operator<<(std::ostream &os,const Time &t)
    75. {
    76.     os << t.hours << " hours," << t.minutes << " minutes";
    77.     return os;
    78. }

    usetime3.cpp

    1. #include <iostream>
    2. #include "mytime3.h"
    3.  
    4. using  namespace std;
    5.  
    6. int main()
    7. {
    8.     Time coding(3,35);
    9.     Time fixing(2,48);
    10.     Time total;
    11.  
    12.     cout << "coding and fixing:" ;
    13.     cout << coding << ";" << fixing << endl;
    14.  
    15.     total = coding + fixing;
    16.     cout << "coding + fixing:" << total << endl;
    17.  
    18.     total = coding*1.17;
    19.     cout << "coding*1.17:" << total << endl;
    20.  
    21.     cout << "10.0*fixing" << 10.0*fixing << endl;
    22.  
    23.     return 0;
    24. }

    运行结果：

    1. coding and fixing:3 hours,35 minutes;2 hours,48 minutes
    2. coding + fixing:6 hours,23 minutes
    3. coding*1.17:4 hours,11 minutes
    4. 10.0*fixing28 hours,0 minutes

    11.4重载运算符：作为成员函数还是非成员函数

    11.5再谈重载：一个矢量类

    示例：

    vector.h

    1. #ifndef VECTOR_H_
    2. #define VECTOR_H_
    3. #include <iostream>
    4.  
    5. namespace VECTOR
    6. {
    7.     class Vector
    8.     {
    9.         public:
    10.             enum Mode{RECT,POL};  //状态成员 RECT直角坐标模式 POL极坐标模式
    11.         private:
    12.             double x;
    13.             double y;
    14.             double mag;
    15.             double ang;
    16.             Mode mode;
    17.             void set_mag();
    18.             void set_ang();
    19.             void set_x();
    20.             void set_y();
    21.  
    22.         public:
    23.             Vector();
    24.             Vector(double n1,double n2,Mode form = RECT);
    25.             void reset(double n1,double n2,Mode form = RECT);
    26.             ~Vector();
    27.             double xval() const {return x;}
    28.             double yval() const {return y;}
    29.             double magval() const {return mag;}
    30.             double angval() const {return ang;}
    31.             void polar_mode();
    32.             void rect_mode();
    33.             Vector operator+(const Vector &b) const;
    34.             Vector operator-(const Vector &b) const;
    35.             Vector operator-() const;
    36.             Vector operator*(double n) const;
    37.             friend Vector operator*(double n,const Vector &a);
    38.             friend std::ostream &operator<<(std::ostream &os,const Vector &v);
    39.     };
    40. }
    41. #endif

    vector.cpp

    1. #include "vector.h"
    2. #include <cmath>
    3.  
    4. using namespace std;
    5.  
    6. namespace VECTOR
    7. {
    8.    const double Rad_to_deg = 45.0/atan(1.0);
    9.    void Vector::set_mag()
    10.    {
    11.        mag = sqrt(x*x+y*y);
    12.    } 
    13.  
    14.    void Vector::set_ang()
    15.    {
    16.         if(x == 0 && y == 0)
    17.             ang = 0;
    18.         else
    19.             ang = atan2(y,x);
    20.    }
    21.  
    22.    void Vector::set_x()
    23.    {
    24.        x = mag*cos(ang);
    25.    }
    26.  
    27.    void Vector::set_y()
    28.    {
    29.        y = mag*sin(ang);
    30.    }
    31.  
    32.    Vector::Vector()
    33.    {
    34.        x = y =mag = ang = 0;
    35.        mode = RECT;
    36.    }
    37.  
    38.    Vector::Vector(double n1,double n2,Mode form)
    39.    {
    40.        mode = form;
    41.        if(form == RECT)
    42.        {
    43.            x= n1;
    44.            y =n2;
    45.            set_mag();
    46.             set_ang();
    47.        }
    48.        else if(form == POL)
    49.        {
    50.            mag = n1;
    51.            ang = n2;
    52.            set_x();
    53.            set_y();
    54.        }
    55.        else
    56.        {
    57.            cout << "incorrect argument\n";
    58.            cout << "vector set to 0";
    59.            x = y =mag = ang = 0;
    60.             mode = RECT;
    61.        }
    62.    }
    63.    
    64.    void Vector::reset(double n1,double n2,Mode form)
    65.    {
    66.        mode = form;
    67.        if(form == RECT)
    68.        {
    69.            x= n1;
    70.            y =n2;
    71.            set_mag();
    72.             set_ang();
    73.        }
    74.        else if(form == POL)
    75.        {
    76.            mag = n1;
    77.            ang = n2;
    78.            set_x();
    79.            set_y();
    80.        }
    81.        else
    82.        {
    83.            cout << "incorrect argument\n";
    84.            cout << "vector set to 0";
    85.            x = y =mag = ang = 0;
    86.             mode = RECT;
    87.        }
    88.    }
    89.  
    90.    Vector::~Vector()
    91.    {
    92.  
    93.    }
    94.  
    95.    void Vector::polar_mode()
    96.    {
    97.        mode = POL;
    98.    }
    99.  
    100.    void Vector::rect_mode()
    101.    {
    102.        mode = RECT;
    103.    }
    104.  
    105.    Vector Vector::operator+(const Vector &b) const
    106.    {
    107.        return Vector((x+b.x),(y+b.y));
    108.    }
    109.  
    110.    Vector Vector::operator-(const Vector &b) const
    111.    {
    112.        return Vector((x-b.x),(y-b.y));
    113.    }
    114.  
    115.    Vector Vector::operator-() const
    116.    {
    117.        return Vector((-x),(-y));
    118.    }
    119.  
    120.    Vector Vector::operator*(double n) const
    121.    {
    122.        return Vector(n*x,n*y);
    123.    }
    124.  
    125.    Vector operator*(double n,const Vector &a) 
    126.    {
    127.        return a*n;
    128.    }
    129.  
    130.    std::ostream &operator<< (std::ostream &os,const Vector &v)
    131.    {
    132.        //
    133.        if(v.mode == Vector::RECT)
    134.             os << "(x,y) = (" << v.x << "," << v.y <<")";
    135.         else if(v.mode == Vector::POL)
    136.         {
    137.             os << "(m,a) = (" << v.mag << "," << v.ang <<")";
    138.         }
    139.         else
    140.             os << "vector is invalid";
    141.  
    142.         return os; 
    143.    }
    144. }

    随即漫步（醉鬼走路）：

    randwalk.cpp

    1. #include "vector.h"
    2. #include <cstdlib>
    3. #include <ctime>
    4.  
    5. using namespace std;
    6.  
    7. int main()
    8. {
    9.     using VECTOR::Vector;
    10.     srand(time(0));
    11.     double direction;
    12.     Vector step;
    13.     Vector result(0.0,0.0);
    14.     unsigned long steps = 0;
    15.     double target;
    16.     double dstep;
    17.     cout <<"enter target distance (q to quite):";
    18.     while(cin >> target)
    19.     {
    20.         cout << "enter step length:";
    21.         if(!(cin >> dstep))
    22.         {
    23.             break;
    24.         }
    25.         while(result.magval() < target)
    26.         {
    27.             direction = rand()%360;
    28.             step.reset(dstep,direction,Vector::POL);
    29.             result = result + step;
    30.             steps++;
    31.         }
    32.         cout << "after " << steps << " steps,the subject has the following location:\n";
    33.         cout << result << endl;
    34.         result.polar_mode();
    35.         cout << "or\n" << result << endl;
    36.         cout << "average outward distance per step = " << result.magval()/steps << endl;
    37.         steps = 0;
    38.         result.reset(0.0,0.0);
    39.         cout << "enter target distance(q to quit):";
    40.     }
    41.     cout << "Byte!\n";
    42.     cin.clear();
    43.     while(cin.get()!='\n')
    44.         continue;
    45.     return 0;
    46. }

    运行结果：

    1. enter target distance (q to quite):10
    2. enter step length:1
    3. after 116 steps,the subject has the following location:
    4. (x,y) = (-3.42834,-9.68444)
    5. or
    6. (m,a) = (10.2734,-1.91104)
    7. average outward distance per step = 0.0885634
    8. enter target distance(q to quit):20
    9. enter step length:2
    10. after 117 steps,the subject has the following location:
    11. (x,y) = (6.30402,19.1596)
    12. or
    13. (m,a) = (20.17,1.25293)
    14. average outward distance per step = 0.172393
    15. enter target distance(q to quit):q
    16. Byte!

    11.6类的自动转换和强制类型转换

    stonewt.h

    1. #ifndef STONEWT_H_
    2. #define STONEWT_H_
    3.  
    4. class Stonewt
    5. {
    6.     private:
    7.         enum {Labs_per_stn = 14};
    8.         int stone;
    9.         double pds_left;
    10.         double pounds;
    11.     public:
    12.         Stonewt(double lbs);
    13.         Stonewt(int stn,double lbs);
    14.         Stonewt();
    15.         ~Stonewt();
    16.         void show_lbs() const;
    17.         void show_stn() const;
    18. };
    19.  
    20. #endif

    stonewt.cpp

    1. #include <iostream>
    2. #include "stonewt.h"
    3.  
    4. using namespace std;
    5.  
    6. Stonewt::Stonewt(double lbs)
    7. {
    8.     stone = int (lbs)/Labs_per_stn;
    9.     pds_left = int (lbs)%Labs_per_stn +lbs - int(lbs);
    10.     pounds = lbs;
    11. }
    12.  
    13. Stonewt::Stonewt(int stn,double lbs)
    14. {
    15.     stone = stn;
    16.     pds_left = lbs;
    17.     pounds = stn*Labs_per_stn + lbs;
    18. }
    19.  
    20. Stonewt::Stonewt()
    21. {
    22.     stone = pounds = pds_left = 0;
    23. }
    24.  
    25. Stonewt::~Stonewt()
    26. {
    27.  
    28. }
    29.  
    30. void Stonewt::show_stn() const
    31. {
    32.     cout << stone << "stone," << pds_left << "pounds\n";
    33. }
    34.  
    35. void Stonewt::show_lbs() const
    36. {
    37.     cout << pounds << "pounds\n";
    38. }

    explicit:只能用于显示转换，不能用于隐式转换。

    stone.cpp

    1. #include <iostream>
    2. #include "stonewt.h"
    3.  
    4. using namespace std;
    5.  
    6. void display(const Stonewt &st,int n);
    7.  
    8. int main()
    9. {
    10.     Stonewt incognito = 275;
    11.     Stonewt wolfe(285.7);
    12.     Stonewt taft(21,8);
    13.  
    14.     cout << "the celebrity weighed ";
    15.     incognito.show_stn();
    16.     cout << "the detective weighed ";
    17.     wolfe.show_stn();
    18.      cout << "the president weighed ";
    19.     taft.show_lbs();
    20.     incognito = 276.8;
    21.     taft = 325;
    22.     cout << "after dinner,the celebrity weighed ";
    23.     incognito.show_stn();
    24.     cout << "after dinner,the president weighed ";
    25.     taft.show_lbs();
    26.     display(taft,2);
    27.     cout << "the wrestler weiged even more.\n";
    28.     display(422,2);
    29.     cout << "No stone left unearned\n";
    30.     return 0;
    31. }
    32.  
    33. void display(const Stonewt &st,int n)
    34. {
    35.     for(int i = 0;i<n;i++)
    36.     {
    37.         cout << "Wow| ";
    38.         st.show_stn();
    39.     }
    40. }

    运行结果：

    1. the celebrity weighed 19stone,9pounds
    2. the detective weighed 20stone,5.7pounds
    3. the president weighed 302pounds
    4. after dinner,the celebrity weighed 19stone,10.8pounds
    5. after dinner,the president weighed 325pounds
    6. Wow| 23stone,3pounds
    7. Wow| 23stone,3pounds
    8. the wrestler weiged even more.
    9. Wow| 30stone,2pounds
    10. Wow| 30stone,2pounds
    11. No stone left unearned

    转换函数：

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  • 原文地址：https://blog.csdn.net/m0_59666413/article/details/125454375