实验2

任务1：

源代码：

#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();

#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';
}

#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;
}

截图：

 

Q1：重新编译后，会出现以下报错。原因是去掉该声明，在main函数中调用func()时，编译器无法识别func函数。

Q2：

①普通构造函数功能是初始化对象的m1和m2成员，调用时机是创建普通的对象。 

②拷贝构造函数功能是用已有对象t的m1和m2初始化新对象，调用时机是用一个已存在的对象初始化新对象。

③移动构造函数功能是利用右值对象t的m1和m2初始化新对象，调用时机是用右值对象初始化新对象。

④析构函数功能是在对象销毁，调用时机是对象生命周期结束时。

Q3：重新编译会出现多重定义错误，因为 T.h 中已经声明了get_cnt()

 

任务2：

源代码：

#pragma once

#include <string>
#include <iostream>

class Complex {
public:
    //类属性
    static const std::string doc;

    //构造函数
    Complex(double r=0.0, double i=0.0);
    Complex(const Complex &t); 
    

    //返回复数实部和虚部
    double get_real() const;
    double get_imag() const;

    //加法 
    void add(const Complex &t);

    //友元函数
    friend void output(const Complex &c);
    friend double abs(const Complex &c);
    friend Complex add(const Complex &a, const Complex &b);
    friend bool is_equal(const Complex &a, const Complex &b);
    friend bool is_not_equal(const Complex &a, const Complex &b);
    
    //对象属性
private:
    double real;
    double imag;
};

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

//类属性 
const std::string Complex::doc = "a simplified complex class";

//构造函数
Complex::Complex(double r, double i) : real(r), imag(i) {}

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

//返回复数实部
double Complex::get_real() const {
    return real;
}

//返回复数虚部
double Complex::get_imag() const {
    return imag;
}

//加法
void Complex::add(const Complex &t) {
    real += t.real;
    imag += t.imag;
}

//友元函数
void output(const Complex &c) {
    if (c.imag >= 0) {
        std::cout << c.real << " + " << c.imag << "i";
    } else {
        std::cout << c.real << " - " << -c.imag << "i";
    }
}

double abs(const Complex &c) {
    return std::sqrt(c.real * c.real + c.imag * c.imag);
}

Complex add(const Complex &a, const Complex &b) {
    return Complex(a.real + b.real, a.imag + b.imag);
}

bool is_equal(const Complex &a, const Complex &b) {
    return (a.real==b.real) && (a.imag==b.imag);
}

bool is_not_equal(const Complex &a, const Complex &b) {
    return !is_equal(a, b);
}

#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::cout;
    using std::endl;
    using std::boolalpha;

    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::cout;
    using std::endl;
    using std::boolalpha;

    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;
}

截图：

 

Q1：标准库模板类 complex 的用法更简洁，函数和运算内在逻辑一致。

Q2-1：是，因这些函数需直接访问私有成员 real 和 imag 以实现各自功能。

Q2-2：是，std::abs (std::complex) 需访问其私有成员，故设为友元。

Q2-3：当外部函数、类需访问类的私有成员且无法通过公有接口实现时使用。

Q3：将拷贝构造函数声明为私有即可禁用该形式。

 

 任务3：

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);   // 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;   
};

#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 lower_str;
    for (auto c : control_str) {
        lower_str += static_cast<char>(tolower(c));
    }
    
    total_cnt++;
    if (lower_str == "play") {
        return ControlType::Play;
    } else if (lower_str == "pause") {
        return ControlType::Pause;
    } else if (lower_str == "next") {
        return ControlType::Next;
    } else if (lower_str == "prev") {
        return ControlType::Prev;
    } else if (lower_str == "stop") {
        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();
}

截图：

 

选做：可以使用使用 Unicode 编码实现。

 

任务4：

源代码：

#pragma once

#include <string>
#include <iostream>

class Fraction {
public:
    static const std::string doc;

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

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

    Fraction negative() const;

private:
    int up;
    int down;

    int gcd(int a, int b) const;
};

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);

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

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


Fraction::Fraction(int u, int d) : up(u), down(d) {
    if (down < 0) {
        up *= -1;
        down *= -1;
    }
    int common = gcd(up, down);
    if (common != 0) {
        up /= common;
        down /= common;
    }
}

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

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

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

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

//辗转相除法求最大公约数 
int Fraction::gcd(int a, int b) const {
    a = std::abs(a);
    b = std::abs(b);
    while (b != 0) {
        int temp = b;
        b = a % b;
        a = temp;
    }
    return a;
}


void output(const Fraction& f) {
    if(f.get_down()==1){
        std::cout << f.get_up();
    }else if(f.get_down()==0){
        std::cout << "分母不能为0" << std::endl;
    }else
        std::cout << f.get_up() << "/" << 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) {
    return add(f1, f2.negative());
}

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

#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;
}

截图：

 

Q：选择自由函数方案。

理由：自由函数无需依赖类的内部实现细节，相比友元更易维护，比静态成员函数更体现运算的独立性，无需额外命名空间即可清晰组织。

 

实验总结：
~加深了我对类中属性、函数的认识，清楚了友元/自由函数/命名空间/类的区别。