OOP实验2

实验任务一：

T.h源码：

#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源码：

#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;

//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 copy 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源码：

#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; 
}

运行测试结果截图：

 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：YES。我认为是因为友元函数func只需要在类外声明并定义就可以，在T.cpp中对友元函数func已经做了定义，所以T.h中有没有声明不影响程序正常运行。

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。

答：①普通构造函数

功能：创建类的对象，并对对象的数据成员初始化

调用时机：以直接初始化的方式创建对象时时，系统选择符合初始化参数的形参类型的普通构造函数；使用new运算符动态创建对象时

②复制构造函数

功能：创建类的对象，该对象是另一个已存在对象复制过来的副本，它会将已有对象的数据成员的值逐一复制到新创建的对象中

调用时机：参数按值传递时；使用拷贝初始化方式创建对象时

③移动构造函数

功能：创建类的对象，直接移动（相当于窃取）另一个已存在对象的数据成员至新的对象中

调用时机：使用右值引用初始化对象时

④析构函数

功能：用于在对象生命周期结束时释放对象所占用的资源

调用时机：函数执行完毕；使用delete运算符释放通过new创建的对象；容器中的元素被移除或者容器本身被销毁时

问题3： 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。

答：能正确编译

实验任务二：

Complex.h源码：

#include<iostream>
#include<string>
using namespace std;

//类声明 
class Complex{
    //类属性 
    public:
        static const string doc;//类Complex的描述信息 
    //对象属性、方法 
    private:
            double real,imag;
    public:
        Complex (double r=0,double i=0);//普通构造函数
        Complex (const Complex &other);//复制构造函数 
        ~Complex ();//析构函数 
    //接口 
    public:
        double get_real() const;
        double get_imag() const;
        void add(Complex &other) ; //函数声明 
    //友元函数 
    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);
};

Complex.cpp源码：

#include<iostream>
#include<string>
#include<cmath>
#include "Complex.h" 
    
    //static成员数据类外初始化 
    const std::string Complex::doc{"a simplified Complex class"};
    
    //对象方法 
    Complex::Complex(double r,double i){
        real=r,imag=i;
    }
    Complex::Complex(const Complex& other) {
        real = other.real;
        imag = other.imag;
    }
    Complex::~Complex(){};
    //接口 
    double Complex::get_real() const {
            return real;
        }
        
    double Complex::get_imag() const {
            return imag;
        }
        
    void Complex::add(Complex &other){
            real+=other.real;
            imag+=other.imag;
        }
    //友元函数
    void output(const Complex &c){
        if(c.imag >= 0)
            cout << c.get_real() << " + " << c.get_imag() << "i" ;
        else
            cout << c.get_real() << " - " << -c.get_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){
        double real_sum=c1.get_real()+c2.get_real();
        double imag_sum=c1.get_imag()+c2.get_imag();
        Complex c3(real_sum,imag_sum);
        return c3;
    }
    
    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);
    }

task2.cpp源码：

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

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();
    cout << ", 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;
}

运行测试结果截图：

回答问题：

问题1：比较自定义类Complex和标准库模板类complex的用法，在使用形式上，哪一种更简洁？函数和运算内在有关联吗？

自定义类 Complex	标准库模板类 complex
c1.add(c2)	c1+=c2
c4=add(c2,c3)	c4=c2+c3
is_equal(c1,c2)	c1==c2
is_not_equal(c1,c2)	c1!=c2
output(c1)	cout<<c1
abs(c2)	abc(c2)

答：（1）使用形式上标准库模板类complex更简洁，因为它的使用形式和逻辑表达式基本一致，直观简洁。

　　（2）函数和运算存在内在关联。自定义类Complex中，成员函数是实现运算的具体手段；而标准库模板类complex里“+=”、“==”等运算符，是通过运算符重载函数来完成运算的，本质上也是通过函数实现运算。

问题2：

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）

答：是。他们需要访问Complex类中的real和imag数据完成运算。

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

答：标准库模板类complex把abs设为友元函数。

2-3：什么时候才考虑使用 friend？总结你的思考。 

答：类外的函数需要使用类内私有和保护类型的数据时需要使用friend。相当于类内public对所有外部函数开放，但私有和保护的数据只对于特定的friend函数开放。

问题3： 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？

答：我觉得可以通过普通构造函数把c2的值传进去，或者场景允许的话直接使用移动构造函数把c2的数据给c4。因为“=”是通过拷贝构造函数复制c2产生c4，禁用拷贝构造函数后就会报错。

实验任务三：

PlayerControl.h源码：

#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源码：

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

int PlayerControl::total_cnt=0;
    
PlayerControl::PlayerControl() {}
    
ControlType PlayerControl::parse(const std::string& control_str){
    std::string ans;
    ans.reserve(control_str.size());
    
    for(unsigned char ch:control_str) 
        ans+=std::tolower(ch);
    if(ans=="play"){
        total_cnt++;
    return ControlType::Play;
    }
    else if (ans=="pause"){
        total_cnt++;
    return ControlType::Pause;
    }
    else if (ans=="next"){
        total_cnt++;
    return ControlType::Next;
    }
    else if(ans=="prev"){
        total_cnt++;
    return ControlType::Prev;
    }
    else if(ans=="stop"){
        total_cnt++;
        return ControlType::Stop;
    }
    else{
        total_cnt++;
        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();
}

运行测试结果截图：

实验任务四：

 Fraction.h源码：

#pragma once
#include <string>
using namespace std;

class Fraction {
public:
    static const 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 reduce();
};

Fraction.cpp源码：

#include "Fraction.h"
#include <iostream>
#include <string>
using namespace std;

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

Fraction::Fraction(int up, int down) : up(up), down(down) {
    if(down==0){
        cout << "分母不能为0" << endl;
        this->up = 0;
        this->down = 1;
    }
    else{
        reduce();
    }
}

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::reduce() {
    if (up == 0) {
        down = 1;
        return;
    }
    int gcd_val = gcd(abs(up), abs(down));
    up /= gcd_val;
    down /= gcd_val;
    if (down < 0) {
        up = -up;
        down = -down;
    }
}

void output(const Fraction& f) {
    if(f.down==1)
    cout << f.up ;
    else
    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;
    if(new_up==0)
    {
        return 0;
    }
    else{
        Fraction res(new_up, new_down);
        res.reduce();
        return res;
    }
}

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

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

Fraction div(const Fraction& f1, const Fraction& f2) {
    if (f2.up == 0) {
        cerr << "分母不能为0" << endl;
        return Fraction(0, 1);
    }
    int new_up = f1.up * f2.down;
    int new_down = f1.down * f2.up;
    Fraction res(new_up, new_down);
    res.reduce();
    return res;
}

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;
    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;
}

 运行测试结果截图：

回答问题：

问题：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。 

答：我选择的方案是友元函数。决策理由是它能直接访问分数类的私有成员，简化了逻辑、提升了效率；虽然友元存在破坏封装、扩展性弱的缺点，但对于本次实验很实用，而静态成员函数更适合逻辑性、扩展性强的场景，命名空间+自由函数则多用于多模块命场景。