Test2

任务一

源代码

T.h

点击查看代码

#pragma once

#include <string>

// 类T: 声明
class T
{
    // 对象属性、方法
public:
    T(int x = 0, int y = 0); // 普通构造函数
    T(const T &t);           // 复制构造函数
    T(T &&t);                // 移动构造函数
    ~T();                    // 析构函数

    void adjust(int ratio); // 按系数成倍调整数据
    void display() const;   // 以(m1, m2)形式显示T类对象信息

private:
    int m1, m2;

    // 类属性、方法
public:
    static int get_cnt(); // 显示当前T类对象总数

public:
    static const std::string doc; // 类T的描述信息
    static const int max_cnt;     // 类T对象上限

private:
    static int cnt; // 当前T类对象数目

    // 类T友元函数声明
    friend void func();
};

// 普通函数声明
void func();

T.cpp

点击查看代码

#include "T.h"
#include <iostream>
#include <string>

// 类T实现

// static成员数据类外初始化
const std::string T::doc{"a simple class sample"};
const int T::max_cnt = 999;
int T::cnt = 0;

// 类方法
int T::get_cnt()
{
    return cnt;
}

// 对象方法
T::T(int x, int y) : m1{x}, m2{y}
{
    ++cnt;
    std::cout << "T constructor called.\n";
}

T::T(const T &t) : m1{t.m1}, m2{t.m2}
{
    ++cnt;
    std::cout << "T copy constructor called.\n";
}

T::T(T &&t) : m1{t.m1}, m2{t.m2}
{
    ++cnt;
    std::cout << "T move constructor called.\n";
}

T::~T()
{
    --cnt;
    std::cout << "T destructor called.\n";
}

void T::adjust(int ratio)
{
    m1 *= ratio;
    m2 *= ratio;
}

void T::display() const
{
    std::cout << "(" << m1 << ", " << m2 << ")";
}

// 普通函数实现
void func()
{
    T t5(42);
    t5.m2 = 2049;
    std::cout << "t5 = ";
    t5.display();
    std::cout << '\n';
}

task1.cpp

点击查看代码

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

void test_T();

int main()
{
    std::cout << "test Class T: \n";
    test_T();

    std::cout << "\ntest friend func: \n";
    func();
}

void test_T()
{
    using std::cout;
    using std::endl;

    cout << "T info: " << T::doc << endl;
    cout << "T objects'max count: " << T::max_cnt << endl;
    cout << "T objects'current count: " << T::get_cnt() << endl
         << endl;

    T t1;
    cout << "t1 = ";
    t1.display();
    cout << endl;

    T t2(3, 4);
    cout << "t2 = ";
    t2.display();
    cout << endl;

    T t3(t2);
    t3.adjust(2);
    cout << "t3 = ";
    t3.display();
    cout << endl;

    T t4(std::move(t2));
    cout << "t4 = ";
    t4.display();
    cout << endl;

    cout << "test: T objects'current count: " << T::get_cnt() << endl;
}

实验结果

测试结论

问题1：T.h中，在类T内部，已声明func()是T的友元函数。去掉line36，重新编译，程序是否能正常运行？如果能，回答YES;如果不能，以截图形式提供编译报错信息，说明原因。

答：
YES(dev-c)。
NO(vscode)。

原因：未找到func()声明。

问题2：T.h中，line9-12给出了各种构造函数、析构函数。总结它们各自的功能、调用时机。

答：
1.T(int x = 0, int y = 0)用给定的参数初始化新的对象，含有默认参数，无参数传入就默认构造；一般在直接定义时调用。
2.T(const T &t)用一个已经存在的对象复制给一个新对象；一般在左值初始化时调用。
3.T(T &&t)用一个将亡对象构造一个新对象；一般在右值初始化时调用。
4.~T()对象生命周期结束时进行资源释放；一般在对象被销毁或失去作用时调用。

问题3：T.cpp中，line13-15，剪切到T.h的末尾，重新编译，程序能否正确编译。如不能，以截图形式给出报错信息，分析原因。

答:
YES(dev-c)。
NO(vscode)。

原因：头文件 T.h 里定义了静态数据成员，这个头又被多个.cpp 同时包含，导致每个翻译单元各自生成一份同名符号，链接时冲突。

任务二

源代码

Complex.h

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#include <string>

class Complex
{
public:
    Complex(float x = 0, float y = 0);
    Complex(Complex &t);
    ~Complex();
    float get_real() const;
    float get_imag() const;
    void add(Complex t);
    static std::string doc;

private:
    float real, imag;

    friend void output(const Complex &t);
    friend float abs(Complex t);
    friend Complex add(Complex t1, Complex t2);
    friend bool is_equal(Complex t1, Complex t2);
    friend bool is_not_equal(Complex t1, Complex t2);
};

Complex.cpp

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#include "Complex.h"
#include <iostream>
#include <cmath>

std::string Complex::doc = "A simplified Complex class";

Complex::Complex(float x, float y) : real(x), imag(y) {}

Complex::Complex(Complex &t) : real(t.real), imag(t.imag) {}

Complex::~Complex() = default;

float Complex::get_real() const { return real; }

float Complex::get_imag() const { return imag; }

void Complex::add(Complex t)
{
    real += t.real;
    imag += t.imag;
}

void output(const Complex &t)
{
    std::cout << t.real << (t.imag >= 0 ? "+" : "") << t.imag << "i";
}

float abs(Complex t)
{
    return std::sqrt(t.real * t.real + t.imag * t.imag);
}

Complex add(Complex t1, Complex t2)
{
    Complex tmp(t1.real + t2.real, t1.imag + t2.imag);
    return tmp;
}

bool is_equal(Complex t1, Complex t2)
{
    return t1.real == t2.real && t1.imag == t2.imag;
}

bool is_not_equal(Complex t1, Complex t2)
{
    return !is_equal(t1, t2);
}

task2.cpp

点击查看代码

#include "Complex.h"
#include <iostream>
#include <iomanip>
#include <complex>

void test_Complex();
void test_std_complex();

int main()
{
    std::cout << "*******测试1: 自定义类Complex*******\n";
    test_Complex();

    std::cout << "\n*******测试2: 标准库模板类complex*******\n";
    test_std_complex();
}

void test_Complex()
{
    using std::boolalpha;
    using std::cout;
    using std::endl;

    cout << "类成员测试: " << endl;
    cout << Complex::doc << endl
         << endl;

    cout << "Complex对象测试: " << endl;
    Complex c1;
    Complex c2(3, -4);
    Complex c3(c2);
    Complex c4 = c2;
    const Complex c5(3.5);

    cout << "c1 = ";
    output(c1);
    cout << endl;
    cout << "c2 = ";
    output(c2);
    cout << endl;
    cout << "c3 = ";
    output(c3);
    cout << endl;
    cout << "c4 = ";
    output(c4);
    cout << endl;
    cout << "c5.real = " << c5.get_real()
         << ", c5.imag = " << c5.get_imag() << endl
         << endl;

    cout << "复数运算测试: " << endl;
    cout << "abs(c2) = " << abs(c2) << endl;
    c1.add(c2);
    cout << "c1 += c2, c1 = ";
    output(c1);
    cout << endl;
    cout << boolalpha;
    cout << "c1 == c2 : " << is_equal(c1, c2) << endl;
    cout << "c1 != c2 : " << is_not_equal(c1, c2) << endl;
    c4 = add(c2, c3);
    cout << "c4 = c2 + c3, c4 = ";
    output(c4);
    cout << endl;
}

void test_std_complex()
{
    using std::boolalpha;
    using std::cout;
    using std::endl;

    cout << "std::complex<double>对象测试: " << endl;
    std::complex<double> c1;
    std::complex<double> c2(3, -4);
    std::complex<double> c3(c2);
    std::complex<double> c4 = c2;
    const std::complex<double> c5(3.5);

    cout << "c1 = " << c1 << endl;
    cout << "c2 = " << c2 << endl;
    cout << "c3 = " << c3 << endl;
    cout << "c4 = " << c4 << endl;

    cout << "c5.real = " << c5.real()
         << ", c5.imag = " << c5.imag() << endl
         << endl;

    cout << "复数运算测试: " << endl;
    cout << "abs(c2) = " << abs(c2) << endl;
    c1 += c2;
    cout << "c1 += c2, c1 = " << c1 << endl;
    cout << boolalpha;
    cout << "c1 == c2 : " << (c1 == c2) << endl;
    cout << "c1 != c2 : " << (c1 != c2) << endl;
    c4 = c2 + c3;
    cout << "c4 = c2 + c3, c4 = " << c4 << endl;
}

实验结果

测试结论

问题1：比较自定义类Complex和标准库模板类complex的用法，在使用形式上，哪一种更简洁？函数和运算内在有关联吗？

自定义类 Complex	标准库模板类 std::complex
c1.add(c2)	c1 += c2
c4 = add(c2, c3)	c4 = c2 + c3
is_equal(c1, c2)	c1 == c2
is_not_equal(c1, c2)	c1 != c2
output(c1)	cout << c1
abs(c2)	abs(c2)

答：标准库模板更加简洁。表达同一语义，在表达形式上有区别罢了。

问题2：

1）自定义Complex中,output/abs/add/等均设为友元，它们真的需要访问私有数据吗？（回答“是/否”并给出理由）

答：不需要。依靠Complex中的公共接口也能实现output/abs/add/，没有必要设置为友元。

2）标准库std::complex是否把abs设为友元？

答：否。

3) 什么时候才考虑使用friend？总结你的思考。

答：1，需要外部函数访问类的私有状态，并且不想把这些信息公开为接口；
2，为了数据共享，提高部分程序的效率和可读性。

问题3：如果构造对象时禁用=形式，即遇到Complex c4 = c2; 编译报错，类Complex的设计应如何调整？

答：把Complex设计成“值类型”，按规则恢复默认的拷贝/移动语义。

任务三

源代码

PlayerControl.h

点击查看代码

#pragma once
#include <string>

enum class ControlType
{
    Play,
    Pause,
    Next,
    Prev,
    Stop,
    Unknown
};

class PlayerControl
{
public:
    PlayerControl();

    ControlType parse(const std::string &control_str); // 实现std::string --> ControlType转换
    void execute(ControlType cmd) const;               // 执行控制操作（以打印输出模拟）

    static int get_cnt();

private:
    static int total_cnt;
};

PlayerControl.cpp

点击查看代码

#include "PlayerControl.h"
#include <iostream>
#include <algorithm>

int PlayerControl::total_cnt = 0;

PlayerControl::PlayerControl() {}

// 待补足
// 1. 将输入字符串转为小写，实现大小写不敏感
// 2. 匹配"play"/"pause"/"next"/"prev"/"stop"并返回对应枚举
// 3. 未匹配的字符串返回ControlType::Unknown
// 4. 每次成功调用parse时递增total_cnt
ControlType PlayerControl::parse(const std::string &control_str)
{
    std::string cmd = control_str;
    std::transform(cmd.begin(), cmd.end(), cmd.begin(), ::tolower);

    if (cmd == "play")
    {
        ++total_cnt;
        return ControlType::Play;
    }
    else if (cmd == "pause")
    {
        ++total_cnt;
        return ControlType::Pause;
    }
    else if (cmd == "next")
    {
        ++total_cnt;
        return ControlType::Next;
    }
    else if (cmd == "prev")
    {
        ++total_cnt;
        return ControlType::Prev;
    }
    else if (cmd == "stop")
    {
        ++total_cnt;
        return ControlType::Stop;
    }
    else
    {
        return ControlType::Unknown;
    }
}

void PlayerControl::execute(ControlType cmd) const
{
    switch (cmd)
    {
    case ControlType::Play:
        std::cout << "🎵 Playing music...\n";
        break;
    case ControlType::Pause:
        std::cout << "⏸ Music paused\n";
        break;
    case ControlType::Next:
        std::cout << "⏭ Skipping to next track\n";
        break;
    case ControlType::Prev:
        std::cout << "⏮ Back to previous track\n";
        break;
    case ControlType::Stop:
        std::cout << "⏹ Music stopped\n";
        break;
    default:
        std::cout << "[Error] unknown control\n";
        break;
    }
}

int PlayerControl::get_cnt()
{
    return total_cnt;
}

task3.cpp

点击查看代码

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

void test()
{
    PlayerControl controller;
    std::string control_str;
    std::cout << "Enter Control: (play/pause/next/prev/stop/quit):\n";

    while (std::cin >> control_str)
    {
        if (control_str == "quit")
            break;

        ControlType cmd = controller.parse(control_str);
        controller.execute(cmd);
        std::cout << "Current Player control: " << PlayerControl::get_cnt() << "\n\n";
    }
}

int main()
{
    test();
}

实验结果

任务四

源代码

Fraction.h

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#include <string>
class Fraction
{
public:
    static const std::string doc;

    Fraction(int up = 0, int down = 1);
    Fraction(const Fraction &f);

    int get_up() const;
    int get_down() const;

    Fraction negative() const;

private:
    int up;   // 分子
    int down; // 分母
};

void output(const Fraction &f);                       // 输出 f
Fraction add(const Fraction &f1, const Fraction &f2); // f1 + f2
Fraction sub(const Fraction &f1, const Fraction &f2); // f1 - f2
Fraction mul(const Fraction &f1, const Fraction &f2); // f1 * f2
Fraction div(const Fraction &f1, const Fraction &f2); // f1 / f2

Fraction.cpp

点击查看代码

#include "Fraction.h"
#include <iostream>
#include <numeric>
#include <cmath>

const std::string Fraction::doc =
    "Fraction类 v 0.01版。"
    "目前仅支持分数对象的构造、输出、加/减/乘/除运算。";

Fraction::Fraction(int up, int down)
{
    this->up = up;
    this->down = down;
    int gcd = std::gcd(up, down);
    if (gcd != 0)
    {
        this->up /= gcd;
        this->down /= gcd;
    }
}

Fraction::Fraction(const Fraction &f) : up(f.up), down(f.down) {}

int Fraction::get_up() const
{
    return up;
}

int Fraction::get_down() const
{
    return down;
}

Fraction Fraction::negative() const
{
    return Fraction(-up, down);
}

void output(const Fraction &f)
{
    if (f.get_down() == 0)
    {
        std::cout << "分母不能为0!";
        return;
    }
    if (f.get_up() * f.get_down() < 0)
    {
        if (f.get_down() == 1 || f.get_down() == -1)
        {
            std::cout << '-' << std::abs(f.get_up());
            return;
        }
        std::cout << '-' << std::abs(f.get_up()) << "/" << std::abs(f.get_down());
    }
    else
    {
        if (f.get_down() == 1 || f.get_down() == -1)
        {
            std::cout << std::abs(f.get_up());
            return;
        }
        std::cout << std::abs(f.get_up()) << "/" << std::abs(f.get_down());
    }
}

Fraction add(const Fraction &f1, const Fraction &f2)
{
    int new_up = f1.get_up() * f2.get_down() + f2.get_up() * f1.get_down();
    int new_down = f1.get_down() * f2.get_down();
    return Fraction(new_up, new_down);
}

Fraction sub(const Fraction &f1, const Fraction &f2)
{
    int new_up = f1.get_up() * f2.get_down() - f2.get_up() * f1.get_down();
    int new_down = f1.get_down() * f2.get_down();
    return Fraction(new_up, new_down);
}

Fraction mul(const Fraction &f1, const Fraction &f2)
{
    int new_up = f1.get_up() * f2.get_up();
    int new_down = f1.get_down() * f2.get_down();
    return Fraction(new_up, new_down);
}

Fraction div(const Fraction &f1, const Fraction &f2)
{
    int new_up = f1.get_up() * f2.get_down();
    int new_down = f1.get_down() * f2.get_up();
    if (new_down == 0)
    {
        return Fraction(0, 0);
    }
    return Fraction(new_up, new_down);
}

task4.cpp

点击查看代码

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

void test1();
void test2();

int main()
{
    std::cout << "测试1: Fraction类基础功能测试\n";
    test1();

    std::cout << "\n测试2: 分母为0测试: \n";
    test2();
}

void test1()
{
    using std::cout;
    using std::endl;

    cout << "Fraction类测试: " << endl;
    cout << Fraction::doc << endl
         << endl;

    Fraction f1(5);
    Fraction f2(3, -4), f3(-18, 12);
    Fraction f4(f3);
    cout << "f1 = ";
    output(f1);
    cout << endl;
    cout << "f2 = ";
    output(f2);
    cout << endl;
    cout << "f3 = ";
    output(f3);
    cout << endl;
    cout << "f4 = ";
    output(f4);
    cout << endl;

    const Fraction f5(f4.negative());
    cout << "f5 = ";
    output(f5);
    cout << endl;
    cout << "f5.get_up() = " << f5.get_up()
         << ", f5.get_down() = " << f5.get_down() << endl;

    cout << "f1 + f2 = ";
    output(add(f1, f2));
    cout << endl;
    cout << "f1 - f2 = ";
    output(sub(f1, f2));
    cout << endl;
    cout << "f1 * f2 = ";
    output(mul(f1, f2));
    cout << endl;
    cout << "f1 / f2 = ";
    output(div(f1, f2));
    cout << endl;
    cout << "f4 + f5 = ";
    output(add(f4, f5));
    cout << endl;
}

void test2()
{
    using std::cout;
    using std::endl;

    Fraction f6(42, 55), f7(0, 3);
    cout << "f6 = ";
    output(f6);
    cout << endl;
    cout << "f7 = ";
    output(f7);
    cout << endl;
    cout << "f6 / f7 = ";
    output(div(f6, f7));
    cout << endl;
}

实验结果

测试结论

问题1:分数的输出和计算， output/add/sub/mul/div ，你选择的是哪一种设计方案？（友元/自由函数/命名空间+自由函数/类+static)

你的决策理由？如友元方案的优缺点、静态成员函数方案的适用场景、命名空间方案的考虑因素等。

答：我选择了自由函数。
优点：通过类内公共接口进行运算，不必访问私有成员；实现较为轻松；不依赖类定义位置，编译耦合小。
缺点：全局命名污染；可读性差，没有归属性。