实验2

task1:

源代码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;
}

运行结果截图

回答问题

问题1：T.h中，在类T内部，已声明 func 是T的友元函数。在类外部，去掉line36，重新编译，程序能否正常运行。

如果能，回答YES；如果不能，以截图形式提供编译报错信息，说明原因。

答：

 void func()是全局函数声明，删除后其他代码无法调用func

问题2：

T.h中，line9-12给出了各种构造函数、析构函数。总结它们各自的功能、调用时机。

line9普通构造函数，用于创建T类型对象时，初始化对象的成员函数m1和m2,若创建对象不传入实参，m1和m2初始化为0

当使用T类类型定义一个新对象时会被调用

line10复制构造函数，用一个已存在的T类对象去初始化另一个T类对象

用一个已存在的T类对象去初始化另一个T类对象时会被调用

line11移动构造函数，将原对象的资源转移给新对象，将原对象的资源置空避免重复释放

当右值初始化为源时会被调用

line12析构函数，用于释放对象所占用的资源

在T类对象的生命周期结束后被调用

T.cpp中，line13-15，剪切到T.h的末尾，重新编译，程序能否正确编译。

如不能，以截图形式给出报错信息，分析原因。

 static成员变量的定义必须放在T.cpp中，避免重复定义

 

 

task2:

源代码Complex.h

#pragma once
#include<string>

class Complex {
public:
    Complex(double real = 0, double imag = 0);
    Complex(const Complex& c);
    //~Complex();


public:
    static const std::string doc;

public:
    double get_real() const;
    double get_imag() const;
    void add(const Complex& c);

    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(double x, double y) :real{ x }, imag{ y }
{
}

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

double Complex::get_real() const {
    return real;
}
double Complex::get_imag() const {
    return imag;
}
void Complex::add(const Complex& c1) {
    real += c1.real;
    imag += c1.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 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) {
    if (c1.real == c2.real && c1.imag == c2.imag) return true;
    else return false;
}

bool is_not_equal(const Complex& c1, const Complex& c2) {
    if (c1.real == c2.real && c1.imag == c2.imag) return false;
    else return true;
}

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;
}

运行结果截图

 回答问题

2-1：自定义 Complex 中, output/abs/add/ 等均设为友元，它们真的需要访问 私有数据 吗？（回答“是/否”并

给出理由）

是 这些函数都需要输出私有数据或使用私有数据进行一些计算

2-2：标准库 std::complex 是否把 abs 设为友元？（查阅 cppreference后回答）

否

2-3：什么时候才考虑使用 friend？总结你的思考。

当外部代码或类需要访问类内的私有成员时，需用到友元

如果构造对象时禁用=形式，即遇到 Complex c4 = c2; 编译报错，类Complex的设计应如何调整？

Complex(const Complex&) = delete

 

 

 

task3:

源代码PlayControl.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;   
};

PlayControl.cpp

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

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(), ::tolower);
    if (lower_str == "play") {
        total_cnt++;
        return ControlType::Play;
    }
    else if (lower_str == "pause") {
        total_cnt++;
        return ControlType::Pause;
    }
    else if (lower_str == "next") {
        total_cnt++;
        return ControlType::Next;
    }
    else if (lower_str == "prev") {
        total_cnt++;
        return ControlType::Prev;
    }
    else if (lower_str == "stop") {
        total_cnt++;
        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();
}

运行结果截图

 

 

 

 

task4:

源代码Fraction.h

#pragma once
#include<string>
class Fraction {
public:
    Fraction(int x, int y = 1);
    Fraction(const Fraction& f);
    ~Fraction();

    static const std::string doc;

public:
    int get_up() const;
    int get_down() const;
    Fraction negative();

    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,down;
};

Fraction.cpp

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

int gcd(int a, int b) {
    a = abs(a);
    b = abs(b);
    while (b != 0) {
        int t = b;
        b = a % b;
        a = t;
    }
    return a;
}
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 x, int y)  {
    if (y == 0) {
        std::cout << "分母不能为0";
        exit(1);
    }
    if (y < 0) {
        x = -x;
        y = -y;
    }
    int a = x, b = y;
    up = x/gcd(a, b);
    down = y/gcd(a, b);
}
Fraction::Fraction(const Fraction& f) {
    up = f.up;
    down = f.down;
}
Fraction::~Fraction() {
}

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

void output(Fraction const& f) {
    if (f.up == 0) std::cout << 0;
    else if (f.down == 1)std::cout << f.up;
    else std::cout << f.up << "/" << f.down;
}
Fraction add(Fraction const& f1, Fraction const& f2) {
    int x = f1.up * f2.down + f2.up * f1.down;
    int y = f1.down * f2.down;
    int a = x, b = y;
    x /= gcd(a, b);
    y /= gcd(a, b);
    return Fraction(x, y);
}
Fraction sub(Fraction const& f1, Fraction const& f2) {
    int x = f1.up * f2.down - f2.up * f1.down;
    int y = f1.down * f2.down;
    int a = x, b = y;
    x /= gcd(a, b);
    y /= gcd(a, b);
    return Fraction(x, y);
}
Fraction mul(Fraction const& f1, Fraction const& f2) {
    int x = f1.up * f2.up;
    int y = f1.down * f2.down;
    int a = x, b = y;
    x /= gcd(a, b);
    y /= gcd(a, b);
    return Fraction(x, y);
}
Fraction div(Fraction const& f1, Fraction const& f2) {
        int x = f1.up * f2.down;
        int y = f1.down * f2.up;
        int a = x, b = y;
        x /= gcd(a, b);
        y /= gcd(a, b);
        return Fraction(x, y);
}

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;
}

运行结果截图

 问题回答

分数的输出和计算， output/add/sub/mul/div ，你选择的是哪一种设计方案？（友元/自由函数/命名

空间+自由函数/类+static)

你的决策理由？如友元方案的优缺点、静态成员函数方案的适用场景、命名空间方案的考虑因素等。

友元 友元函数可以直接操纵私有成员，减少中间环节，提高效率