实验二

1、实验任务一

源代码：

#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';
}

#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();

#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;
}

测试结果：

 问题一：T.h中，在类T内部，已声明 func 是T的友元函数。在类外部，去掉line36，重新编译，程序能否正常运行。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：

 不能正常运行，因为在类内友元声明只是声明这个函数是T的友元函数，函数本身没声明。

问题二：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）普通构造函数：初始化m1与m2的值，如果没有输入参数则m1=m2=0，如果输入一个参数则m1为输入的参数，m2=0，如果输入两个参数，则m1,m2分别对应输入的参数；直接定义时调用；

（2）复制构造函数：用已有的对象初始化新对象；左赋值时调用；

（3）移动构造函数：用右值对象初始化新对象；右赋值时使用；

（4）析构函数：释放对象资源；对象生命周期结束时调用。

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：

 静态成员函数的定义必须只在一个源文件中实现，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，导致链接时重复定义，出现冲突。

2、实验任务二

源代码：

#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);
};

#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);
}

#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：

问题一：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？

答：标准库模板类更简洁，有关联。

问题二：

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：否，通过Complex中的公共接口也可以实现output/abs/add/；

2-2：标准库 std::complex 是否把 abs 设为友元？

答：否；

2-3：什么时候才考虑使用 friend？总结你的思考。

答：（1）外部函数或者类需要访问当前的私有成员；

（2）无法通过公有接口实现。

 

3、实验任务三

源代码：

#pragma once
#include <string>
enum class ControlType { Play, Pause, Next, Prev, Stop, Unknown };
class PlayerControl {
public:
    PlayerControl();
    ControlType parse(const std::string& control_str); 
        void execute(ControlType cmd) const; 
    static int get_cnt();
private:
    static int total_cnt;
};

#include "PlayerControl.h"
#include <iostream>
#include <algorithm>
int PlayerControl::total_cnt = 0;
PlayerControl::PlayerControl() {}
ControlType PlayerControl::parse(const std::string& control_str) {
    std::string s;
    for (auto c : control_str)
        s += std::tolower(c);
    if (s == "play")
    {
        total_cnt++;
        return ControlType::Play;
    }

    else if (s == "pause")
    {
        total_cnt++;
        return ControlType::Pause;
    }

    else if (s == "next")
    {
        total_cnt++;
        return ControlType::Next;
    }

    else if (s == "prev")
    {
        total_cnt++;
        return ControlType::Prev;
    }

    else if (s == "stop")
    {
        total_cnt++;
        return ControlType::Stop;
    }

    else
    {
        return ControlType::Unknown;
    }
}
void PlayerControl::execute(ControlType cmd) const {
    switch (cmd) {
    case ControlType::Play: std::cout << "[play] Playing music...\n"; break;
    case ControlType::Pause: std::cout << "[Pause] Music paused\n"; break;
    case ControlType::Next: std::cout << "[Next] Skipping to next track\n"; break;
    case ControlType::Prev: std::cout << "[Prev] Back to previous track\n"; break;
    case ControlType::Stop: std::cout << "[Stop] Music stopped\n"; break;
    default: std::cout << "[Error] unknown control\n"; break;
    }
}
int PlayerControl::get_cnt() {
    return total_cnt;
}

#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：

 

4、实验任务四

源代码：

#pragma once
#include<string.h>
#include<iostream>
class Fraction
{
public:
    static const std::string doc;

    Fraction(int u = 0, int d = 1);
    Fraction(const Fraction& f);

    int get_up() const;
    int get_down() const;
    Fraction negative() const;
private:
    int up, down;

    friend void output(const Fraction &f);
    friend Fraction add(const Fraction &f1,const Fraction &f2);
    friend Fraction sub(const Fraction& f1, const Fraction& f2);
    friend Fraction mul(const Fraction& f1, const Fraction& f2);
    friend Fraction div(const Fraction& f1, const Fraction& f2);
};

void output(const Fraction &f);
Fraction add(const Fraction& f1, const Fraction& f2);
Fraction sub(const Fraction& f1, const Fraction& f2);
Fraction mul(const Fraction& f1, const Fraction& f2);
Fraction div(const Fraction& f1, const Fraction& f2);

int gcd(int a, int b);

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

//类说明
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" };

//构造函数
Fraction::Fraction(int u, int d)
{
    //约分
    //计算最大公约数
    int g = gcd(abs(u), abs(d));

    u /= g;
    d /= g;

    //把符号体现在分子上
    if (d < 0)
    {
        down = -d;
        up = -u;
    }

    else
    {
        down = d;
        up = u;
    }
}
Fraction::Fraction(const Fraction& f) :up{ f.up }, down{ f.down } {}


//公有函数实现
int Fraction::get_up() const
{
    return abs(up);
}

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

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

//求最大公约数函数
int gcd(int a, int b)
{
    while (b != 0)
    {
        int temp = b;
        b = a % b;
        a = temp;
    }
    return a;
}

void output(const Fraction& f)
{
    //分子或分母为0
    if (f.up * f.down == 0)
    {
        if (f.down == 0)
        {
            std::cout << "分母不能为0";
        }
        else
        {
            std::cout << 0;
        }
    }

    //分子分母不为0
    else
    {
        //计算最大公约数
        int g = gcd(abs(f.up), abs(f.down));

        int new_up = f.up / g;
        int new_down = f.down / g;

        //整除
        if (new_up % new_down == 0)
        {
            std::cout << new_up / new_down;
        }

        //不整除
        else
        {
            //符号为正
            if (new_up > 0)
            {
                std::cout << abs(new_up) << '/' << abs(new_down);


            }
            //符号为负
            else
            {
                std::cout << '-' << abs(new_up) << '/' << abs(new_down);
            }
        }
    }
}

Fraction add(const Fraction& f1, const Fraction& f2)
{
    int new_up = f1.up * f2.down + f2.up * f1.down;
    int new_down = f1.down * f2.down;

    //计算最大公约数
    int g = gcd(abs(new_up), abs(new_down));

    new_up /= g;
    new_down /= g;

    Fraction f(new_up, new_down);
    return f;
}

Fraction sub(const Fraction& f1, const Fraction& f2)
{
    int new_up = f1.up * f2.down - f2.up * f1.down;
    int new_down = f1.down * f2.down;

    //计算最大公约数
    int g = gcd(abs(new_up), abs(new_down));

    new_up /= g;
    new_down /= g;

    Fraction f(new_up, new_down);
    return f;
}

Fraction mul(const Fraction& f1, const Fraction& f2)
{
    int new_up = f1.up * f2.up;
    int new_down = f1.down * f2.down;

    //计算最大公约数
    int g = gcd(abs(new_up), abs(new_down));

    new_up /= g;
    new_down /= g;

    Fraction f(new_up, new_down);
    return f;
}

Fraction div(const Fraction& f1, const Fraction& f2)
{
    int new_up = f1.up * f2.down;
    int new_down = f1.down * f2.up;

    //计算最大公约数
    int g = gcd(abs(new_up), abs(new_down));

    new_up /= g;
    new_down /= g;

    Fraction f(new_up, new_down);
    return f;
}

#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;
}

测试结果：

问题一： 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：我选择的是友元；static 更适合描述类的共性，比如统计对象数量，但分数的分子分母都是独立的，用不上；自由函数的话，每次都得写 f.get_up () 这类代码，太麻烦；命名空间会削弱封装性，也不好。友元确实有缺点，会破坏封装，类里的属性一改，友元函数都得跟着改，耦合度高，但相比下来，还是友元更合适些。