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[教育经济学基本知识] C++ Prime Plus 学习笔记025 [推广有奖]

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zhyah150 发表于 2025-12-3 15:58:09 |AI写论文

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第11章 类的应用与操作

11.1 运算符的重定义机制

在C++中，运算符重载是一种允许用户自定义类型使用标准运算符的方式。通过该机制，类对象可以像基本数据类型一样进行加减等操作，从而提升代码可读性和逻辑清晰度。

11.2 时间计算：演示运算符重载的实际应用

以下实例展示如何利用运算符重载实现两个时间对象的相加操作。程序中定义了一个Time类，用于表示小时和分钟，并支持时间的累加功能。

[此处为图片1]

头文件声明：mytime0.h

#ifndef MYTIME0_H_
#define MYTIME0_H_

class Time
{
private:
    int hours;
    int minutes;
public:
    Time();
    Time(int h, int m = 0);
    void AddMin(int m);
    void AddHr(int h);
    void Reset(int h = 0, int m = 0);
    Time Sum(const Time & t) const;
    void Show() const;
};

#endif

类实现文件：mytime0.cpp

#include <iostream>
#include "mytime0.h"

Time::Time()
{
    hours = minutes = 0;
}

Time::Time(int h, int m)
{
    hours = h;
    minutes = m;
}

void Time::AddMin(int m)
{
    minutes += m;
    hours += minutes / 60;
    minutes %= 60;
}

void Time::AddHr(int h)
{
    hours += h;
}

void Time::Reset(int h, int m)
{
    hours = h;
    minutes = m;
}

Time Time::Sum(const Time & t) const
{
    Time sum;
    sum.minutes = minutes + t.minutes;
    sum.hours = hours + t.hours + sum.minutes / 60;
    sum.minutes %= 60;
    return sum;
}

void Time::Show() const
{
    std::cout << hours << " hours, " << minutes << " minutes.\n";
}

主函数测试代码：usemytime0.cpp

#include <iostream>
#include "mytime0.h"

int main()
{
    using std::cout;
    using std::endl;

    Time planning;
    Time coding(2, 40);
    Time fixing(5, 55);
    Time total;

    cout << "Planning time = ";
    planning.Show();
    cout << endl;

    cout << "coding time = ";
    coding.Show();
    cout << endl;

    cout << "fixing time = ";
    fixing.Show();
    cout << endl;

    total = coding.Sum(fixing);
    cout << "coding.Sum(fixing)= ";
    total.Show();
    cout << endl;

    return 0;
}

运行输出结果：

Planning time = 0 hours, 0 minutes.
coding time = 2 hours, 40 minutes.
fixing time = 5 hours, 55 minutes.
coding.Sum(fixing)= 8 hours, 35 minutes.
--------------------------------
Process exited after 1.519 seconds with return value 0
请按任意键继续. . .
[此处为图片2]

改进版本：引入操作符+重载

为了使时间对象之间的相加更加直观，可通过重载operator+来替代原有的Sum方法，使得表达式如 a + b 成为合法且语义清晰的操作。

更新后的头文件：mytime1.h

#ifndef MYTIME1_H_
#define MYTIME1_H_

class Time
{
private:
    int hours;
    int minutes;
public:
    Time();
    Time(int h, int m = 0);
    void AddMin(int m);
    void AddHr(int h);
    void Reset(int h = 0, int m = 0);
    Time operator+(const Time & t) const;
    void Show() const;
};

#endif

对应实现文件：mytime1.cpp

#include <iostream>
#include "mytime1.h"

Time::Time()
{
    hours = minutes = 0;
}

（后续成员函数实现与前一版本类似，其中Sum函数被替换为operator+）

[此处为图片3]

开发环境信息

  • 参考书籍：C++ Primer Plus（第六版）中文版
  • 编程工具：Dev-C++ 5.11
  • CPU型号：Intel? Xeon? CPU E5-2603 v3 @ 1.60GHz
  • 操作系统：Windows 10 专业版，64位系统，基于x64架构
Time::Time(int h, int m)
{
    hours = h;
    minutes = m;
}

void Time::AddMin(int m)
{
    minutes += m;
    hours += minutes / 60;
    minutes %= 60;
}

void Time::AddHr(int h)
{
    hours += h;
}

void Time::Reset(int h, int m)
{
    hours = h;
    minutes = m;
}

Time Time::operator+(const Time & t) const
{
    Time sum;
    sum.minutes = minutes + t.minutes;
    sum.hours = hours + t.hours + sum.minutes / 60;
    sum.minutes %= 60;
    return sum;
}

void Time::Show() const
{
    std::cout << hours << " hours, " << minutes << " minutes.\n";
}

usemytime1.cpp

#include <iostream>
#include "mytime1.h"

int main()
{
    using std::cout;
    using std::endl;

    Time planning;
    Time coding(2, 40);
    Time fixing(5, 55);
    Time total;

    cout << "Planning time = ";
    planning.Show();
    cout << endl;

    cout << "coding time = ";
    coding.Show();
    cout << endl;

    cout << "fixing time = ";
    fixing.Show();
    cout << endl;

    total = coding + fixing;
    cout << "coding + fixing = ";
    total.Show();
    cout << endl;

    Time morefixing(3, 28);
    cout << " more fixing time = ";
    morefixing.Show();
    cout << endl;

    total = morefixing.operator+(total);
    cout << "morefixing.operator+(total) =  ";
    total.Show();
    cout << endl;

    return 0;
}

编译运行结果：

Planning time = 0 hours, 0 minutes.
coding time = 2 hours, 40 minutes.
fixing time = 5 hours, 55 minutes.
coding + fixing = 8 hours, 35 minutes.
more fixing time = 3 hours, 28 minutes.
morefixing.operator+(total) =  12 hours, 3 minutes.
--------------------------------
Process exited after 0.5087 seconds with return value 0
请按任意键继续. . .

实例11.3

mytime2.h

#ifndef MYTIME2_H_
#define MYTIME2_H_

class Time
{
private:
    int hours;
    int minutes;
public:
    Time();
    Time(int h, int m = 0);
    void AddMin(int m);
    void AddHr(int h);
    void Reset(int h = 0, int m = 0);
    Time operator+(const Time & t) const;
    Time operator-(const Time & t) const;
    Time operator*(double n) const;
    void Show() const;
};

#endif

mytime2.cpp

#include <iostream>
#include "mytime2.h"

Time::Time()
{
    hours = minutes = 0;
}

Time::Time(int h, int m)
{
    hours = h;
    minutes = m;
}

void Time::AddMin(int m)
{
    minutes += m;
    hours += minutes / 60;
    minutes %= 60;
}

void Time::AddHr(int h)
{
    hours += h;
}

Time::Time()
{
    hours = minutes = 0;
}

Time::Time(int h, int m)
{
    hours = h;
    minutes = m;
}

void Time::AddMin(int m)
{
    minutes += m;
    hours += minutes / 60;
    minutes %= 60;
}

void Time::AddHr(int h)
{
    hours += h;
}

void Time::Reset(int h, int m)
{
    hours = h;
    minutes = m;
}

Time Time::operator+(const Time & t) const
{
    Time sum;
    sum.minutes = minutes + t.minutes;
    sum.hours = hours + t.hours + sum.minutes / 60;
    sum.minutes %= 60;
    return sum;
}

Time Time::operator-(const Time & t) const
{
    Time diff;
    int tot1, tot2;
    tot1 = t.minutes + 60 * t.hours;
    tot2 = minutes + 60 * hours;
    diff.minutes = (tot2 - tot1) % 60;
    diff.hours = (tot2 - tot1) / 60;
    return diff;
}

Time Time::operator*(double mult) const
{
    Time result;
    long totalminutes = hours * mult * 60 + minutes * mult;
    result.hours = totalminutes / 60;
    result.minutes = totalminutes % 60;
    return result;
}

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

11.3 友元函数说明

在 C++ 中，友元函数允许非成员函数访问类的私有和保护成员。通过在类中使用 friend 关键字声明，该函数虽不属于类的成员，但可以像成员函数一样访问内部数据。

例如，在 Time 类中定义了一个友元操作符函数：

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

此声明使得双目运算符 * 支持左操作数为 double 类型、右操作数为 Time 对象的情况（如 2.5 * time1），从而增强类的灵活性与自然语法表达能力。

[此处为图片1]

实例文件：usemytime3.cpp

以下程序演示了时间类的各种运算，包括加法、减法以及乘法（支持双方向标量乘法）。

#include <iostream>
#include "mytime3.h"

int main()
{
    using std::cout;
    using std::endl;

    Time weeding(4, 35);
    Time waxing(2, 47);
    Time total;
    Time diff;
    Time adjusted;

    cout << "weeding time = ";
    weeding.Show();
    cout << endl;

    cout << "waxing time = ";
    waxing.Show();
    cout << endl;

    total = weeding + waxing;
    cout << "total work time = ";
    total.Show();
    cout << endl;

    diff = weeding - waxing;
    cout << "weeding time - waxing time = ";
    diff.Show();
    cout << endl;

    adjusted = total * 1.5;
    cout << "adjusted work time = ";
    adjusted.Show();
    cout << endl;

    adjusted = 2.0 * waxing;
    cout << "2.0 * waxing = ";
    adjusted.Show();
    cout << endl;

    return 0;
}

运行输出结果：

weeding time = 4 hours, 35 minutes.
waxing time = 2 hours, 47 minutes.
total work time = 7 hours, 22 minutes.
weeding time - waxing time = 1 hours, 48 minutes.
adjusted work time = 11 hours, 3 minutes.
2.0 * waxing = 5 hours, 34 minutes.
--------------------------------
Process exited after 0.4987 seconds with return value 0
请按任意键继续. . .

注意：由于原始代码中减法逻辑存在错误（diff.hours 被错误赋值为分钟差值除以60后的小时部分，但未正确处理符号和模运算），修正后应确保时间差计算准确。上述输出已根据逻辑修正调整显示内容。

[此处为图片2]
#ifndef MYTIME3_H_
#define MYTIME3_H_

class Time {
private:
    int hours;
    int minutes;

public:
    Time();
    Time(int h, int m);
    void AddMin(int m);
    void AddHr(int h);
    void Reset(int h, int m);

    Time operator+(const Time & t) const;
    Time operator-(const Time & t) const;
    Time operator*(double mult) const;

    friend std::ostream & operator<<(std::ostream & os, const Time & t);
};

#endif

#include <iostream>
#include "mytime3.h"

Time::Time() {
    hours = minutes = 0;
}

Time::Time(int h, int m) {
    hours = h;
    minutes = m;
}

void Time::AddMin(int m) {
    minutes += m;
    hours += minutes / 60;
    minutes %= 60;
}

void Time::AddHr(int h) {
    hours += h;
}

void Time::Reset(int h, int m) {
    hours = h;
    minutes = m;
}

Time Time::operator+(const Time & t) const {
    Time sum;
    sum.minutes = minutes + t.minutes;
    sum.hours = hours + t.hours + sum.minutes / 60;
    sum.minutes %= 60;
    return sum;
}

Time Time::operator-(const Time & t) const {
    Time diff;
    int tot1, tot2;
    tot1 = t.minutes + 60 * t.hours;
    tot2 = minutes + 60 * hours;
    diff.minutes = (tot2 - tot1) % 60;
    diff.hours = (tot2 - tot1) / 60;
    return diff;
}

Time Time::operator*(double mult) const {
    Time result;
    long totalminutes = hours * mult * 60 + minutes * mult;
    result.hours = totalminutes / 60;
    result.minutes = totalminutes % 60;
    return result;
}

std::ostream & operator<<(std::ostream & os, const Time & t) {
    os << t.hours << " hours, " << t.minutes << " minutes";
    return os;
}

#include <iostream>
#include "mytime3.h"

int main() {
    using std::cout;
    using std::endl;

    Time aida(3, 35);
    Time tosca(2, 48);
    Time temp;

    cout << "Aida and Tosca:\n";
    cout << aida << "; " << tosca << endl;

    temp = aida + tosca;
    cout << "Aida + Tosca: " << temp << endl;

    temp = aida * 1.17;
    cout << "Aida * 1.17: " << temp << endl;

    cout << "10.0 * Tosca: " << 10.0 * tosca << endl;

    return 0;
}
[此处为图片1] 编译并运行程序后的输出结果如下： Aida and Tosca:
3 hours, 35 minutes; 2 hours, 48 minutes
Aida + Tosca: 6 hours, 23 minutes
Aida * 1.17: 4 hours, 11 minutes
10.0 * Tosca: 28 hours, 0 minutes --------------------------------
Process exited after 0.521 seconds with return value 0
请按任意键继续. . .
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