实验二

任务一：

1.源代码：

（1）T.h:

#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();

（2）T.cpp:

#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';
    std::cout << "func: T objects'current count: " << T::get_cnt() << std::endl;
}

（3）task1.cpp:

#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;
}

2.实验测试代码运行结果如下：

3.问题回答：

（1）YES;

（2）普通构造函数（line 9）是利用两个默认值为0的int类型的数据创建一个T类对象；复制构造函数（line 10）是将已有对象的属性拷贝到一个新的对象，相当于赋值操作；移动构造函数（line 11）是将该T类参数的所有资源等转移到新对象中，原对象变为空，类似剪切操作；析构函数（line 12）是将创建的对象销毁。至于调用时机，构造函数就看提供的参数是否对应上述函数参数类型，而析构函数在程序运行结束（释放内存空间）之前自动调用；

（3）YES，能够正常运行且结果不改变。

任务二：

1.源代码：

（1）Complex.h:

#pragma once

#include <string>

class Complex{
public:
    Complex(double a = 0,double b = 0);
    Complex(const Complex &c);
    ~Complex(); 
    double get_real() const;
    double get_imag() const;
    void add(Complex c);
    
private:
    double real,imag;
    friend void output(Complex c);
    friend double abs(Complex c);
    friend Complex add(Complex a,Complex b);
    friend bool is_equal(Complex a,Complex b);
    friend bool is_not_equal(Complex a,Complex b);
    
public:
    static const std::string doc;
};

（2）Complex.cpp:

#include "Complex.h"

#include <iostream>
#include <cmath>
const std::string Complex::doc{"a simple class sample"};

Complex::Complex(double a,double b): real{a},imag{b}{}
Complex::Complex(const Complex &c): real{c.real},imag{c.imag}{}
Complex::~Complex(){
} 
double Complex::get_real() const{
    return real;
}
double Complex::get_imag() const{
    return imag;
}
void Complex::add(Complex c){
    real += c.get_real();
    imag += c.get_imag();
}
void output(Complex c){
    if(c.get_imag() >= 0)
        std::cout << c.get_real() << " + " << c.get_imag() << "i";
    else
        std::cout << c.get_real() << " - " << (0-c.get_imag()) << "i";
}
double abs(Complex c){
    double abs = sqrt(c.get_real() * c.get_real() + c.get_imag() * c.get_imag());
    return abs;
}
Complex add(Complex a,Complex b){
    double c_r = a.get_real() + b.get_real();
    double c_i = a.get_imag() + b.get_imag();
    Complex c(c_r,c_i);
    return c;
}
bool is_equal(Complex a,Complex b){
    if(a.get_real() == b.get_real() && a.get_imag() == b.get_imag())
        return true;
    return false;
}
bool is_not_equal(Complex a,Complex b){
    if(is_equal(a,b))
        return false;
    return true;
}

（3）task2.cpp:

// 待补足头文件
// xxx
#include "Complex.h"
#include <iostream>
#include <iomanip>
#include <complex>
#include <string>

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;
}

2.实验代码运行结果如下：

3.问题回答：

问题一：

　　标准库模板类更简洁；函数能实现运算功能，但是不能直观的去表示运行，只能通过函数名来尽可能的理解功能，但是能够表达运算功能，但反观标准库，这样的表达更符合数学语言；

问题二：

（1）否。因为这些函数可以在public中也能实现。

（2）否。

（3）个人认为，当要多次访问私有属性时，可以使用友元，或者友元之间关系紧密时，可以使用；当一个功能可以通过公共接口实现，可以不用友元。

问题三：

　　可以通过在复制构造函数前加上explicit去实现。

 

任务三：

1.源代码：

（1）PlayerControl.h:

#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;   
};

（2）PlayerControl.cpp:

#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) {
    // xxx
    total_cnt++;
    std::string s = control_str;
    for(auto &a : s){
        a = std::tolower(a);
    }
    if(s == "play")
        return ControlType::Play;
    else if(s == "pause")
        return ControlType::Play;
    else if(s == "next")
        return ControlType::Next;
    else if(s == "prev")
        return ControlType::Prev;
    else if(s == "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;
}

（3）task3.cpp:

#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();
}

2.实验代码运行结果如下：

任务四：

1.源代码：

（1）Fraction.h:

#pragma once

#include <string>
int find_max(int a,int b);
class Fraction{
public:
    Fraction(int u,int d = 1);
    Fraction(const Fraction &f);
    ~Fraction();
    int get_up() const;
    int get_down() const;
    Fraction negative() const;
    static const std::string doc;
private:
    int up,down;
    friend void output(Fraction f);
    friend Fraction add(Fraction a,Fraction b);
    friend Fraction sub(Fraction a,Fraction b);
    friend Fraction mul(Fraction a,Fraction b);
    friend Fraction div(Fraction a,Fraction b);
};

（2）Fraction.cpp:

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

Fraction::Fraction(int u,int d ){
    int a ;
    a = find_max(u,d);
    up = u / a;
    down = d / a;
}
Fraction::Fraction(const Fraction &f): up{f.up},down{f.down}{}
Fraction::~Fraction(){
}

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."};
int Fraction::get_up() const{

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

    return down;
}
Fraction Fraction::negative() const{
    return Fraction(-up,down);
}
void output(Fraction f){
    if(f.down == 0){
        std::cout << "分母不能为0";
        return; 
    }
    if(f.up % f.down == 0){
        std::cout << f.up/f.down;
        return;
    }
    if(f.down < 0){
        std::cout << -f.up << "/" << -f.down;
    }else{
        std::cout << f.up << "/" << f.down;    
    }
    
    
}
Fraction add(Fraction a,Fraction b){
    int down1 = a.down * b.down;
    int up1 = a.up * b.down + b.up * a.down;
    return Fraction(up1,down1);
}
Fraction sub(Fraction a,Fraction b){
    int down1 = a.down * b.down;
    int up1 = a.up * b.down - b.up * a.down;
    return Fraction(up1,down1);
}
Fraction mul(Fraction a,Fraction b){
    int down1 = a.down * b.down;
    int up1 = a.up *b.up;
    return Fraction(up1,down1);
}
Fraction div(Fraction a,Fraction b){
    int down1 = a.down * b.up;
    int up1 = a.up *b.down;
    return Fraction(up1,down1);
}

int find_max(int a,int b){
    while(b != 0){
        int temp = b;
        b = a % b;
        a = temp;
    }
    return a;
}

（3）task4.cpp:

#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;
}

 2.实验代码运行结果如下：

3.问题回答：

　　我选择了友元方案。因为这些计算是基本上都是同一类对象之间的运算，而且基本只用到了内部的私有属性，更加方便书写代码以及逻辑，以达到提高性能的作用；但这样却提高了耦合度，如果友元出错，则需要更改部分较多代码，可维护性较差，但是介于项目逻辑简单且代码数量较少，可以选择此方法。

实验总结：

　　对于类对象功能的实现，有许多办法，需要合理利用这些方法的优缺点根据实际情况去选择，以优化代码，提高代码可读性，并且便于后期维护。