实验二

任务1

T.h

#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();

T.cpp

#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';
}

 

task1.cpp

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;}

 

 

运行结果如图：

问题1：不能

在类T内部，func()被称为友元函数，如果去掉line36的普通函数说明，在task1.cpp中调用func()时，编译器会找不到这个函数的声明

问题2：

line9:功能：普通构造函数，创建新对象并初始化数据成员         调用时机： 创建新对象：T t1

line10:功能：复制构造函数，用已有对象创建新对象        调用时机： 对象初始化：T t3(t2);

line11:功能：移动构造函数，避免不必要的拷贝     调用时机：使用std::move：T t4(std::move(t2));

line12:功能：析构函数   调用时机：对象离开作用域

问题3：不能

static成员在类中只是声明，需要在类外单独定义。如果将这些初始化语句从T.cpp移到T.h中，会导致重复定义错误

任务2：

task2.cpp

 Complex.h

#pragma once
#include <string>

class Complex {
public:
    Complex(double real = 0.0, double imag = 0.0);
    Complex(const Complex& other);  
    double get_real() const;
    double get_imag() const;
    void add(const Complex& other);
    
    static const std::string doc;
    
private:
    double real_;
    double imag_;
};

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);

Complex.cpp

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

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

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_;
    if (c.imag_ >= 0) {
        std::cout << " + " << c.imag_ << "i";
    } else {
        std::cout << " - " << -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);
}

task2.cpp

#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;
}

运行结果如图：

问题1：标准库模板类complex更简洁

自定义类的函数名与数学运算有关联，但不够直观，标准库让代码更接近数学表达式

问题2：

2-1  否   output()、abs()、add()、is_equal()、is_not_equal()这些函数都可以通过公有接口get_real()和get_imag()实现，不需要直接访问私有数据

2-2   否   std::abs(std::complex)是一个非成员函数模板，不是友元函数

2-3   当函数需要频繁访问多个私有成员，且通过公有接口会导致性能问题

问题3：使用移动语义

class Complex {
public:
Complex(const Complex& other) = delete; 
Complex(Complex&& other) noexcept; 】
};

任务3

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);
    void execute(ControlType cmd) const;
    
    static int get_cnt();
    
private:
    static int total_cnt;
};

 

PlayerControl.cpp

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

int PlayerControl::total_cnt = 0;

PlayerControl::PlayerControl() {}

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(),
                   [](unsigned char c) { return std::tolower(c); });

    ControlType result;
    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;
    }
    if (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;
}

task3.cpp源码

#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;
}

运行结果如图：

任务4

Fraction.h

#pragma once
#include <string>

class Fraction {
public:
    Fraction(int up = 0, int down = 1);
    Fraction(const Fraction& other);
    
    int get_up() const;
    int get_down() const;
    Fraction negative() const;
    
    static const std::string doc;
    
private:
    int up_;  
    int down_;  
    
    void simplify();
    static int gcd(int a, int b);
};

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);

Fraction.cpp

#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");
    }
    
    if (down_ < 0) {
        up_ = -up_;
        down_ = -down_;
    }
    
    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_);
}

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;
}

void Fraction::simplify() {
    if (up_ == 0) {
        down_ = 1;
        return;
    }
    
    int common_divisor = gcd(up_, down_);
    up_ /= common_divisor;
    down_ /= common_divisor;
    
    if (down_ < 0) {
        up_ = -up_;
        down_ = -down_;
    }
}

void output(const Fraction& f) {
    if (f.get_down() == 1) {
        std::cout << f.get_up();
    } else {
        std::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) {
        throw std::invalid_argument("分母不能为0");
    }
    int new_up = f1.get_up() * f2.get_down();
    int new_down = f1.get_down() * f2.get_up();
    return Fraction(new_up, new_down);
}

task4.cpp源码

#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 << 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;
    
    try {
        cout << "f6 / f7 = "; output(div(f6, f7)); cout << endl;
    } catch (const std::exception& e) {
        cout << e.what() << endl;
    }
}

运行结果如图：

问题：自由函数   逻辑分组清晰；避免命名冲突；扩展性好

友元函数优点是可以直接访问私有成员，性能稍好；代码实现简单。缺点是破坏了封装性，增加了耦合度