实验二

实验任务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;
}

问题：

1.YES

2.普通构造函数：初始化T的对象，为m1,m2赋值，创建类的新对象时调用，复制构造函数：复制已存在的T对象的成员变量初始化新对象，在用已有对象初始化新对象时调用，移动构造函数：将临时的T对象转移来初始化新对象，用右值初始化新对象时调用，析构函数：销毁T对象释放资源，对象周期结束时调用

3.不能

移动函数会被重复定义

实验任务2：

源代码：

#pragma once
#include<iostream>
#include<string>
#include<cmath>
#include<algorithm>
class Complex{
    public:
        static const std::string doc;
        Complex();
        Complex(double real);
        Complex(double real,double imag);
        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;
        
};

#include"Complex.h"
const std::string Complex::doc="a simplified complex class";
Complex::Complex():real(0.0),imag(0.0){}
Complex::Complex(double real):real(real),imag(0.0){}
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){
    std::cout<<c.real<<(c.imag>=0?"+":"")<<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);
}

#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;
}

问题：

1.标准库模板更符合日常复数运算的逻辑思考，更简洁；有关联，函数的内在逻辑和运算的逻辑很相似

2.1否，类complex中有相应的get接口可供获取数据值，无需访问私有数据

2.2否

2.3当必须要访问私有成员且无法通过公有接口访问时使用友元

3.可在复制构造函数前加上explicit

实验任务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 = control_str; 
    for (auto& c : lower_str) {           
        c = std::tolower(c);             
    }
    ControlType type = ControlType::Unknown;
    if (lower_str == "play") {
        type = ControlType::Play;
    } else if (lower_str == "pause") {
        type = ControlType::Pause;
    } else if (lower_str == "next") {
        type = ControlType::Next;
    } else if (lower_str == "prev") {
        type = ControlType::Prev;
    } else if (lower_str == "stop") {
        type = ControlType::Stop;
    }
    if (type != ControlType::Unknown) {
        total_cnt++;
    }
    return type; 
}

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();
}

实验任务4：

源代码：

#include<iostream>
#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);
        int gcd(int a, int b) const;
        void simplify();
    
    private:    
        
        int up;
        int down;
};

#include "Fraction.h"
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";
//构造函数 
Fraction::Fraction(int up,int down):up(up),down(down){
    if(down==0){
    std::cout<<"分母不能为0"<<std::endl;
    exit(1);
    }    
    simplify();
}
Fraction::Fraction(const Fraction& other):up(other.up),down(other.down){}
//接口 
int Fraction::get_up() const {
    return up;
}
int Fraction::get_down() const {
    return down;
}
Fraction Fraction::negative() const {
    return Fraction(-up, down);
}
//工具函数
//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;
}
//化简 
void Fraction::simplify() {
    //正负号 
    if (down < 0) {
        up = -up;
        down = -down;
    }
    //约分 
    int g = gcd(up, down);
    if (g != 0) {
        up /= g;
        down /= g;
    }
}
//输出 
void output(const Fraction& f){
    if(f.up==0) 
    std::cout << f.up;
    else 
    std::cout << f.up << "/" << f.down;
        }
//加法 
Fraction add(const Fraction& f1, const Fraction& f2){
    int newUp = f1.up * f2.down + f2.up * f1.down;
    int newDown = f1.down * f2.down;
    Fraction result(newUp, newDown);
    return result;
    }
//减法 
Fraction sub(const Fraction& f1, const Fraction& f2){
    int newUp = f1.up * f2.down - f2.up * f1.down;
    int newDown = f1.down * f2.down;
    Fraction result(newUp, newDown);
    return result;
        }
//乘法 
Fraction mul(const Fraction& f1, const Fraction& f2){
    int newUp = f1.up * f2.up;
    int newDown = f1.down * f2.down;
    Fraction result(newUp, newDown);
    return result;
        }
//除法 
Fraction div(const Fraction& f1, const Fraction& f2){
    int newUp = f1.up * f2.down;
    int newDown = f1.down * f2.up;
    Fraction result(newUp, newDown);
    return result;
        }

#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;
}

问题：

选择友元，优点是友元可直接访问私有成员，代码简洁，缺点是友元可能被滥用