实验二 现代C++编程初体验

任务一： 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>

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;
}

#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';
}

 问题一：能成功运行

问题二：普通构造函数：初始化对象成员，所以在创建对象时调用

              复制构造函数：用已有左值对象拷贝初始化新对象，在对象拷贝时调用

              移动构造函数：用右值对象初始化新对象，在右值对象初始化时调用

              析构函数：减少对象计数、释放资源，在对象作用结束时调用

问题三：能成功运行

 

任务二：

task2.cpp代码:

#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;
}

Complex.h代码：

#pragma once
#include <iostream>
#include <string>
#include <cmath>

class Complex {
private:
    double real;
    double imag;

public:

    static const std::string doc;
    Complex(double r = 0.0, double i = 0.0) : real(r), imag(i) {}
    double get_real() const { return real; }
    double get_imag() const { return imag; }

    void add(const Complex& other) {
        real += other.real;
        imag += other.imag;
    }

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

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

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

complex.h的实现代码：

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

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 sqrt(c.real * c.real + c.imag * c.imag);
}

bool is_equal(const Complex& c1, const Complex& c2) {
    const double eps = 1e-9;
    return (fabs(c1.real - c2.real) < eps) && (fabs(c1.imag - c2.imag) < eps);
}

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

Complex add(const Complex& c1, const Complex& c2) {
    return Complex(c1.real + c2.real, c1.imag + c2.imag);
}

问题一：使用标准库模板类 complex更简洁

问题二：1.是的

               2.否

               3.当函数需要直接访问类的私有成员，且该函数不是类的成员函数的时候

 

任务三：

PlayerControl.cpp代码:

#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;
    std::transform(lower_str.begin(), lower_str.end(), lower_str.begin(), ::tolower);
    
    ControlType result = ControlType::Unknown;
    if (lower_str == "play") {
        result = ControlType::Play;
    } else if (lower_str == "pause") {
        result = ControlType::Pause;
    } else if (lower_str == "next") {
        result = ControlType::Next;
    } else if (lower_str == "prev") {
        result = ControlType::Prev;
    } else if (lower_str == "stop") {
        result = ControlType::Stop;
    } else {
        result = ControlType::Unknown;
    }
    
    total_cnt++;
    
    return result;
}

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;
}

 

任务：四：

Fraction.h代码：

#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;
}

Fraction.cpp代码：

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

// 静态成员初始化
const std::string Fraction::doc = "Fraction类v0.01版. 目前仅支持分数对象的构造、输出、加/减/乘/除运算.";

// 构造函数实现
Fraction::Fraction(int u, int d) : up(u), down(d) {
    if (down == 0) {
        std::cerr << "Error: zero denominator not permitted!" << std::endl;
        exit(1); // 分母为0直接终止程序（或可抛异常，此处简化处理）
    }
    normalize();
}

Fraction::Fraction(const Fraction& other) : up(other.up), down(other.down) {
    // 拷贝构造时已保证规范化，无需额外处理
}

// 辅助函数：最大公约数（欧几里得算法）
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;
}

// 辅助函数：分数规范化（约分、符号统一）
void Fraction::normalize() {
    if (down < 0) { // 分母为负，符号转移到分子
        up = -up;
        down = -down;
    }
    int g = gcd(up, down);
    if (g != 0) {
        up /= g;
        down /= g;
    }
}

// 成员方法：返回自身的负数
Fraction Fraction::negative() const {
    return Fraction(-up, down);
}

// 友元函数：输出分数
void output(const Fraction& f) {
    if (f.down == 1) {
        std::cout << f.up;
    } else {
        std::cout << f.up << "/" << f.down;
    }
}

// 友元函数：分数加法
Fraction add(const Fraction& f1, const Fraction& f2) {
    int u = f1.up * f2.down + f2.up * f1.down;
    int d = f1.down * f2.down;
    return Fraction(u, d); // 构造时自动规范化
}

// 友元函数：分数减法
Fraction sub(const Fraction& f1, const Fraction& f2) {
    int u = f1.up * f2.down - f2.up * f1.down;
    int d = f1.down * f2.down;
    return Fraction(u, d);
}

// 友元函数：分数乘法
Fraction mul(const Fraction& f1, const Fraction& f2) {
    int u = f1.up * f2.up;
    int d = f1.down * f2.down;
    return Fraction(u, d);
}

// 友元函数：分数除法
Fraction div(const Fraction& f1, const Fraction& f2) {
    if (f2.up == 0) {
        std::cerr << "Error: division by zero!" << std::endl;
        exit(1);
    }
    int u = f1.up * f2.down;
    int d = f1.down * f2.up;
    return Fraction(u, d);
}

 问题：用的是友元函数来解决问题。友元方案的优势：可以直接访问类的私有成员，更加简洁高效。  友元方案的缺点：一定程度上破坏了类的封装性，因为友元函数可以直接操作私有成员。