实验二

任务一

 

#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;
}

 

运行结果:

 问题1不能

 从编译错误信息可知，在 main 函数中调用 funcT() 时，该函数未被声明。

问题2:

普通构造函数:

作用:创建T类的新对象,使用参数x和y初始化对象的成员,变量参数有默认值，可以作为默认构造函数使用

调用时机:创建对象时

复制构造函数:

作用:通过已有对象创建新对象的副本,保证新对象与源对象有相同的数据但独立的内存

调用时机:对象初始化,函数参数按值传递,函数返回对象值时

移动构造函数:

作用:从临时对象或即将销毁的对象"窃取"资源,将源对象的资源所有权转移给新对象

调用时机:使用std::move时

析构函数:

作用:清理对象占用的资源,释放动态分配的内存

调用时机:对象离开作用域时

问题3:不能

 编译报错显示 T::doc,T::max_cnt,T::cnt 这些符号在task1.cpp和T.cpp中被多次定义。

任务二:

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

using namespace std;

// 静态成员初始化
const string Complex::doc = "a simplified Complex class";

// 构造函数实现
Complex::Complex() : real(0.0), imag(0.0) {}

Complex::Complex(double r) : real(r), imag(0.0) {}

Complex::Complex(double r, double i) : real(r), imag(i) {}

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

// 成员函数实现
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;
}

// 全局函数实现
void output(const Complex& c) {
    cout << c.get_real();
    if (c.get_imag() >= 0) {
        cout << " + " << c.get_imag() << "i";
    } else {
        cout << " - " << -c.get_imag() << "i";
    }
}

double abs(const Complex& c) {
    return sqrt(c.get_real() * c.get_real() + c.get_imag() * c.get_imag());
}

Complex add(const Complex& c1, const Complex& c2) {
    return Complex(c1.get_real() + c2.get_real(), c1.get_imag() + c2.get_imag());
}

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

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

#ifndef COMPLEX_H
#define COMPLEX_H

#include <string>

class Complex {
private:
    double real;
    double imag;

public:
    static const std::string doc;

    // 构造函数
    Complex();
    Complex(double r);
    Complex(double r, double i);
    Complex(const Complex& other);

    // 获取实部和虚部
    double get_real() const;
    double get_imag() const;

    // 复数加法
    void add(const Complex& other);
};

// 全局函数声明
void output(const Complex& c);
double abs(const Complex& c);
Complex add(const Complex& c1, const Complex& c2);
bool is_equal(const Complex& c1, const Complex& c2);
bool is_not_equal(const Complex& c1, const Complex& c2);

#endif

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

using namespace std;

void test_Complex();
void test_std_complex();

int main() {
    cout << "*******测试1: 自定义类Complex*******\n";
    test_Complex();
    cout << "\n*******测试2: 标准库模板类complex*******\n";
    test_std_complex();
    return 0;
}

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:

问题1:标准库更简洁;有关联,这些函数本质上都是数学运算，使用运算符重载更符合数学直觉和编程习惯

问题2:2.1 是,理由:output(),abs(),add(),is_equal()和is_not_equal()函数需要直接访问real和imag来格式化输出,如果不使用友元，这些函数只能通过公有接口get_real()和get_imag()来访问数据，但这样效率太低

2.2 否,根据cppreference.com：std::abs(std::complex)是一个非成员函数,它通过公有接口real()和imag()来访问复数的实部和虚部,标准库设计遵循"除非必要，否则不使用友元"的原则

2.3 必要的时候：1.当函数确实需要直接访问类的私有成员，且无法通过公有接口有效实现时

2.运算符重载：特别是需要访问两个或多个对象私有数据的二元运算符

3.紧密相关的工具函数：如输入输出函数、类型转换函数等

问题3:在Complex.h中添加：

class Complex {
private:
    Complex& operator=(const Complex&);
    ...
public:
    ...
};

任务三:

#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() {}

ControlType PlayerControl::parse(const std::string& control_str) {
    // 1. 将输入字符串转为小写，实现大小写不敏感
    std::string lower_str = control_str;
    std::transform(lower_str.begin(), lower_str.end(), lower_str.begin(),
                   [](unsigned char c) { return std::tolower(c); });

    // 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
    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;
    }

    // 4. 每次成功调用parse时递增total_cnt
    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;
}

#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();
    return 0;
}

运行结果:

 

 任务四:

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

using namespace std;

// 静态成员初始化
const 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.";

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

// 约分函数
void Fraction::reduce() {
    if (down == 0) {
        throw runtime_error("分母不能为0");
    }

    // 处理符号：让分母始终为正
    if (down < 0) {
        up = -up;
        down = -down;
    }

    // 约分
    int common = gcd(up, down);
    if (common != 0) {
        up /= common;
        down /= common;
    }

    // 如果分子为0，分母设为1
    if (up == 0) {
        down = 1;
    }
}

// 构造函数
Fraction::Fraction(int numerator, int denominator) : up(numerator), down(denominator) {
    reduce();
}

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

// 成员函数实现
int Fraction::get_up() const {
    return up;
}

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

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

// 工具函数实现
void output(const Fraction& f) {
    if (f.get_down() == 1) {
        cout << f.get_up();
    } else {
        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) {
    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 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) {
    if (f2.get_up() == 0) {
        cout << "分母不能为0";
        return Fraction(0, 1); // 返回一个默认值
    }
    int new_up = f1.get_up() * f2.get_down();
    int new_down = f1.get_down() * f2.get_up();
    return Fraction(new_up, new_down);
}

#pragma once
#include <string>

class Fraction {
private:
    int up;     // 分子
    int down;   // 分母

    // 内部工具函数：约分
    void reduce();
    // 内部工具函数：求最大公约数
    int gcd(int a, int b) const;

public:
    static const std::string doc;

    // 构造函数
    Fraction(int numerator = 0, int denominator = 1);
    Fraction(const Fraction& other);

    // 获取分子分母
    int get_up() const;
    int get_down() const;

    // 求负运算
    Fraction negative() const;
};

// 工具函数声明
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 <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();
    return 0;
}

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;
}

运行结果:

问题:

我选择的是自由函数方案,理由:友元方案可以直接访问类的私有成员，效率较高,但是破坏封装性,且维护困难;静态成员函数适用于函数与类紧密相关,但不需要特定对象实例,而这些数学运算函数本质上是通用的，不属于某个特定类;在小型项目中，命名空间可能带来不必要的复杂性