实验二

1实验任务一

T.h

#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();

T.cpp

#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';
}

task1.cpp

#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：
不能，在 C++ 中，友元函数的声明只是表明该函数是类的友元，虽然在函数内部，但只是表示可以访问类的私有成员，友元函数本身是全局函数，需要在类外部有独立的声明或者定义

 问题2：
普通股构造函数T(int x=0, int y=0)：创建T类对象时初始化数据成员，两个参数都有默认值，可以接受0个、1个或2个参数，执行对象的初始化工作。调用时机：创建新对象时
复制构造函数T(const T &t)：用一个已存在的同类型对象来替代新对象，const引用参数确保不会修改原对象。调用时机：对象复制时
移动构造函数T(T &&t)：利用右值引用，将临时对象或即将销毁的对象的资源窃取到新的创建的对象中。调用时机：临时对象移动时
析构函数~T();对象生命周期结束时清理资源。调用时机：对象销毁时
问题三：
不能

因为成员定义放在头文件中后，cpp文件包含头文件导致多次被定义。

 

2实验任务二

Complex.h

#pragma once
#include<string>

class Complex{
    public:
        static const std::string doc;
        Complex();
        Complex(double Real);
        Complex(double Real,double Imag);
        Complex(const Complex &other);
        Complex &operator=(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,imag;
};

Complex.cpp

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

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) {
}
Complex &Complex::operator=(const Complex &other) {
    if(this!=&other) {
        real=other.real;
        imag=other.imag;
    }
    return *this;
}
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 if(c.imag<0){
        std::cout << "-" << -c.imag << "i";
    }
}
double abs(const Complex &c){
    return sqrt(c.real*c.real+c.imag*c.imag);
}
Complex add(const Complex &c1,const Complex &c2){
    Complex result;
    result.real=c1.real+c2.real;
    result.imag=c1.imag+c2.imag;
    return result;
}
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);
}

task.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;
}

问题1：

在使用形式上，标准库模板类 complex 更简洁。函数和运算内在有关联：标准库的运算本质是通过重载运算符函数实现的，只是语法形式更接近自然运算。

问题2：

2-1：是。output 需要输出 real / imag ， abs 需要计算 real²+imag² ， add 需要获取 real / imag 做加法——这些操作都依赖类的私有成员 real 和 imag ，因此需要设为友元来访问私有数据。

2-2：否。标准库 std::complex 的 abs 函数并非友元，而是通过类的公共接口获取实部、虚部后计算的。

2-3：函数/类需要访问当前类的私有/保护成员，且无法通过公共接口实现；实现不同类之间的协作。

问题3：

为 Complex 类添加拷贝构造函数。

 

3实验任务三

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);   // 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;   
};

PlayerControl.cpp

#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           
    );
    total_cnt++;
    if (lower_str == "play") 
        return ControlType::Play;
    else if (lower_str == "pause") 
        return ControlType::Pause;
    else if (lower_str == "next") 
        return ControlType::Next;
    else if (lower_str == "prev") 
        return ControlType::Prev;
    else if (lower_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;
}

task3.cpp

#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();
}

 

 

4实验任务四

Fraction.h

#include <string>

class Fraction 
{
private:
    int up;   
    int down; 

    int gcd(int a, int b) const;
    void simplify();

public:
    static const std::string doc;

    Fraction(int up_val);
    Fraction(int up_val, int down_val);
    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);
};

Fraction.cpp

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

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.";

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;
}

void Fraction::simplify() 
{
    if (down < 0) 
    {
        up = -up;
        down = -down;
    }

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

Fraction::Fraction(int up_val) : up(up_val), down(1) 
{
    simplify();
}

Fraction::Fraction(int up_val, int down_val) : up(up_val), down(down_val) 
{
    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 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 new_up = f1.up * f2.down + f2.up * f1.down;
    int new_down = f1.down * f2.down;
    return Fraction(new_up, new_down); 
}

Fraction sub(const Fraction& f1, const Fraction& f2) 
{
    return add(f1, f2.negative());
}

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

Fraction div(const Fraction& f1, const Fraction& f2) 
{
    if (f2.up == 0) 
    {
        std::cerr << "分母不能为0" << std::endl;
        exit(1); 
    }
    return mul(f1, Fraction(f2.down, f2.up));
}

task4.cpp

#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

1.友元

2.直接访问私有成员，避免冗余接口。