实验二

实验任务一

T.h源码

#pragma once
#include <string>

class T {

public:
    T(int x = 0, int y = 0); 
    T(const T &t);  
    T(T &&t);    
    ~T();    

    void adjust(int ratio);    
    void display() const;      

private:
    int m1, m2;

public:
    static int get_cnt();     

public:
    static const std::string doc;     
    static const int max_cnt;        

private:
    static int cnt;        

    friend void func();
};

void func();

T.cpp源码

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

const std::string T::doc{"a simple class sample"};
const int T::max_cnt = 999;
int T::cnt = 0;

int T::get_cnt() {
   return cnt;
}

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 << ")" ;
}     

void func() {
    T t5(42);
    t5.m2 = 2049;
    std::cout << "t5 = "; t5.display(); std::cout << '\n';
}

task1.cpp源码

#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;
}

运行结果截图

 问题回答

问题1：

　　YES，T.h中类内的友元声明不会将func暴露到全局作用域，但此处编译器没有报错，这是Dev-C++对友元声明的宽松处理。

问题2：

（1）普通构造函数：

　　　功能：初始化T类对象，为成员变量赋初始值

　　　调用时机：创建T对象时调用

（2）复制构造函数：

　　　功能：用已存在的T类对象，初始化新的T类对象

　　　调用时机：用一个T对象初始化另一个T对象时调用

（3）移动构造函数：

　　　功能：用右值引用的T对象初始化新对象，同时递增计数

　　　调用时机：用右值初始化T对象时调用

（4）析构函数：

　　　功能：递减对象计数，释放对象资源

　　　调用时机：T对象生命周期结束时调用

问题3：

　　在Dev-C++中可以编译运行，但在其他编译器终不可以，因为类的静态成员必须在类外的全局作用域单独定义，如果剪切到末尾，会出　　　　现“重复定义”的问题。

 

实验任务二：

Complex.h源码：

#pragma once
#include <string>

class Complex {
public:

    static const std::string doc;

    Complex(double real = 0.0, double imag = 0.0); 
    Complex(const Complex& other);

    double get_real() const;
    double get_imag() const;

    void add(const Complex& other);

    friend void output(const Complex& c);
    friend double abs(const Complex& c);
    friend Complex add(const Complex& c1, const Complex& c2);
    friend bool is_equal(const Complex& c1, const Complex& c2);
    friend bool is_not_equal(const Complex& c1, const Complex& c2);

private:

    double real_;
    double imag_;
};

Complex.cpp源码：

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

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

Complex::Complex(double real, double imag) : real_(real), imag_(imag) {}

Complex::Complex(const Complex& other) : real_(other.real_), imag_(other.imag_) {}

double Complex::get_real() const {
    return real_;
}

double Complex::get_imag() const {
    return imag_;
}

void Complex::add(const Complex& other) {
    real_ += other.real_;
    imag_ += other.imag_;
}

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& c1, const Complex& c2) {
    return Complex(c1.real_ + c2.real_, c1.imag_ + c2.imag_);
}

bool is_equal(const Complex& c1, const Complex& c2) {
    return (c1.real_ == c2.real_) && (c1.imag_ == c2.imag_);
}

bool is_not_equal(const Complex& c1, const Complex& c2) {
    return !is_equal(c1, c2);
}

task2.cpp源码：

#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::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;
}

运行结果截图：

问题回答：

问题1：

　　标准库complex用法更简洁，通过运算符重载实现了更自然的语法，而自定义类需通过函数调用实现。

问题2：

　　2-1：需要。这些函数需要访问Complex的私有成员来完成输出、计算模长、相加等操作，因此必须声明为友元以突破访问权限限制。

　　2-2：否。标准库std::complex的abs是全局函数，通过complex的公有成员函数获取实部、虚部，无需设为友元。

　　2-3：当外部函数或者类需要访问当前类的私有成员，且无法通过公有接口间接实现时，可将其声明为友元。

问题3：

　　可以改成Complex(const Complex&) = delete，使其无法被调用。

 

实验任务三：

 PlayerControl.h源码：

#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源码：

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

int PlayerControl::total_cnt = 0;

PlayerControl::PlayerControl() {}

ControlType PlayerControl::parse(const std::string& control_str) {
    std::string lower_str = control_str;
    std::transform(lower_str.begin(), lower_str.end(), lower_str.begin(),
                   [](unsigned char c) { return std::tolower(c); });
    if (lower_str == "play") {
        total_cnt++; 
        return ControlType::Play;
    } else if (lower_str == "pause") {
        total_cnt++;
        return ControlType::Pause;
    } else if (lower_str == "next") {
        total_cnt++;
        return ControlType::Next;
    } else if (lower_str == "prev") {
        total_cnt++;
        return ControlType::Prev;
    } else if (lower_str == "stop") {
        total_cnt++;
        return ControlType::Stop;
    } else {
        total_cnt++;
        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;
}

task3.cpp源码：

#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();
}

运行结果截图：

 思考：

　　只需修改execute方法的输出内容，替换为带 emoji 的字符串即可。

 

实验任务四：

Fraction.h源码：

#pragma once
#include <string>

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

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

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

    Fraction negative() const;

    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);

private:
    int up_;
    int down_;

    void simplify();
    static int gcd(int a, int b);
};

Fraction.cpp源码：

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

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 up, int down) : up_(up), down_(down) {
    if (down == 0) {
        throw std::invalid_argument("分母不能为0");
    }
    if (down_ < 0) {
        up_ = -up_;
        down_ = -down_;
    }
    simplify(); 
}

Fraction::Fraction(const Fraction& other) : up_(other.up_), down_(other.down_) {}

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

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

Fraction Fraction::negative() const {
    return Fraction(-up_, down_);
}

int Fraction::gcd(int a, int b) {
    a = std::abs(a);
    b = std::abs(b);
    while (b != 0) {
        int temp = b;
        b = a % b;
        a = temp;
    }
    return a;
}

void Fraction::simplify() {
    int common_divisor = gcd(up_, down_);
    up_ /= common_divisor;
    down_ /= common_divisor;
}

void output(const Fraction& f) {
    if (f.down_ == 1) {
        std::cout << f.up_;
    } else {
        std::cout << f.up_ << "/" << f.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_;
    return Fraction(new_up, new_down);
}

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_;
    return Fraction(new_up, new_down);
}

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

Fraction div(const Fraction& f1, const Fraction& f2) {
    if (f2.up_ == 0) {
        throw std::invalid_argument("分母不能为0");
    }
    int new_up = f1.up_ * f2.down_;
    int new_down = f1.down_ * f2.up_;
    return Fraction(new_up, new_down);
}

task4.cpp源码：

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

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;

    try {
        cout << "f6 / f7 = "; 
        output(div(f6, f7)); 
        cout << endl;
    } catch (const std::invalid_argument& e) {
        cout << e.what() << endl;
    }
}

运行结果截图：

 问题回答：

 　　友元。

　　　　优势：可直接访问Fraction的私有成员，无需通过get_up()或者get_down()间接获取，简化代码逻辑；

　　　　缺点：一定程度上破坏了类的封装性，需谨慎控制友元的使用范围。