实验2

#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();

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

#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;
}

问题一：no ，func() 是类外定义的友元函数，需要先声明，否则找不到标识符

问题二：1：普通构造函数，初始化类T的对象，为成员变量m1、m2赋初始值 2：复制构造函数，用已存在的T类对象深拷贝创建新对象，复制其成员变量值

               3：移动构造函数，用已存在的T类对象转移资源创建新对象，“窃取” 其成员变量的资源   4.析构函数，释放对象占用的资源，在对象生命周期结束时做清理工作         

问题三：不可以，静态函数如果在类内会重复定义

 

 

实验任务二：

#include <string>
class Complex {
public:
    static const std::string doc;
    Complex();
    Complex(double r);
    Complex(double r, double i);
    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"
#include <iostream>
#include <cmath>
const std::string Complex::doc = "a simplified complex class";
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) {}
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);
}

#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;
}

问题一：标准库模板类complex更简洁。有内在关联，两者都是为了实现复数的运算和操作，功能逻辑一致。

问题二： 1：是，因为output、abs、add需要访问私有成员real和imag才能实现功能。

               2：否。

               3：当外部函数必须访问类私有成员且合理时才用friend，避免过度使用破坏封装。

问题三：把拷贝构造函数设为私有就会编译报错

 

 

实验任务三：

#pragma once
#include <string>

enum class ControlType {Play, Pause, Next, Prev, Stop, Unknown};

class PlayerControl {
public:
    PlayerControl();
    ControlType parse(const std::string& control_str);
    void execute(ControlType cmd) const;
    static int get_cnt();
private:
    static int total_cnt;
};

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

int PlayerControl::total_cnt = 0;

PlayerControl::PlayerControl() {}

ControlType PlayerControl::parse(const std::string& control_str) {
    std::string str = control_str;
    std::transform(str.begin(), str.end(), str.begin(), ::tolower);
    total_cnt++;
    if (str == "play") return ControlType::Play;
    else if (str == "pause") return ControlType::Pause;
    else if (str == "next") return ControlType::Next;
    else if (str == "prev") return ControlType::Prev;
    else if (str == "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;
}

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

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;
}

 

 

实验任务四：

#pragma once
#include <string>

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

    Fraction(int up = 0, 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();
    int gcd(int a, int b);
};

#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");
    }
    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);
}

void Fraction::simplify() {
    if (down < 0) {
        up = -up;
        down = -down;
    }
    int g = gcd(std::abs(up), down);
    if (g != 0) {
        up /= g;
        down /= g;
    }
}

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

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 up = f1.up * f2.down + f2.up * f1.down;
    int down = f1.down * f2.down;
    return Fraction(up, down);
}

Fraction sub(const Fraction &f1, const Fraction &f2) {
    int up = f1.up * f2.down - f2.up * f1.down;
    int down = f1.down * f2.down;
    return Fraction(up, down);
}

Fraction mul(const Fraction &f1, const Fraction &f2) {
    int up = f1.up * f2.up;
    int down = f1.down * f2.down;
    return Fraction(up, down);
}

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

#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;
}

决策理由：友元可直接访问分数类私有成员，实现输出、运算时无需通过公共接口间接获取数据，简化逻辑且保证效率。

友元优点：访问私有成员便捷，代码实现简洁；缺点：一定程度破坏封装性。

静态成员函数适用于与类紧密相关、无需访问对象私有数据的场景（如类级别的工具方法）；命名空间方案适合组织多个类的通用工具函数，此处仅为分数类服务，友元更直接。