OOP-实验2
实验任务1
源代码T.h,T.cpp,task1.cpp
点击查看代码 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();
点击查看代码 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';
}
点击查看代码 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;
}
运行测试截图
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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。 -
回答：编译报错信息见下图，产生原因是
func声明在类T内部，在task1.cpp中调用func时，找不到func的声明。在VSCode上使用C++11标准，为func添加类型为T的参数，则可以正常运行，据此猜测编译器可以通过func的参数，寻找到类T中func的声明。
-
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。
-
回答：line9的函数为普通构造函数，功能是以传入的参数x，y构造类T的对象，在传入0或1或2个int类型的参数时调用；line10的函数是复制构造函数，功能是创建一个和t一样的对象，在需要拷贝对象t时调用；line11的函数是移动构造函数，功能是创建一个新的对象管理t的资源，在不需要t或减少资源开销时调用；line12的函数是析构函数，功能是销毁对象，释放资源，在对象的生命周期结束后自动调用。
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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。
-
回答：不能正确编译，原因是
T.cpp和task1.cpp都#include "T.h"，line13-15代码被多次定义。
实验任务2
源代码Complex.h,Complex.cpp,task2.cpp
点击查看代码 Complex.h
#pragma once
#include <string>
class Complex
{
public:
Complex(double _real = 0, double _imag = 0);
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, imag;
public:
static const std::string doc;
};
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);
点击查看代码 Complex.cpp
#include <iostream>
#include <cmath>
#include "Complex.h"
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)
{
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);
}
点击查看代码 task2.cpp
// 待补足头文件
#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::boolalpha;
using std::cout;
using std::endl;
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::boolalpha;
using std::cout;
using std::endl;
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;
}
运行测试截图
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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？ -
回答：后者更简洁，函数和运算有内在关联，二者都是对功能进行封装，后者只是将我们常用的运算封装为运算符，可以认为后者蕴含于前者。
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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） -
回答：否，显然
output/abs/add/可以使用接口get_real\get_imag，不需要访问私有数据。 -
问题2-2：标准库
std::complex是否把abs设为友元？（查阅cppreference后回答） -
回答：否。
-
问题2-3：什么时候才考虑使用friend？总结你的思考。
-
回答：函数需要调用类的私有方法或者修改类的私有成员变量时使用friend。
-
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？ -
回答：禁用拷贝构造，即
Complex(const Complex &other) = default;。
实验任务3
源代码PlayControl.h,PlayerControl.cpp,task3.cpp
点击查看代码 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;
};
点击查看代码 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 cmd_lower;
for (const auto &ch : control_str)
{
cmd_lower += std::tolower(ch);
}
++total_cnt;
if (cmd_lower == "play")
return ControlType::Play;
else if (cmd_lower == "pause")
return ControlType::Pause;
else if (cmd_lower == "next")
return ControlType::Next;
else if (cmd_lower == "prev")
return ControlType::Prev;
else if (cmd_lower == "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;
}
点击查看代码 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();
}
运行测试截图
实现emoji输出
修改PlayerControl.cpp，其余同上
点击查看代码 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 cmd_lower;
for (const auto &ch : control_str)
{
cmd_lower += std::tolower(ch);
}
++total_cnt;
if (cmd_lower == "play")
return ControlType::Play;
else if (cmd_lower == "pause")
return ControlType::Pause;
else if (cmd_lower == "next")
return ControlType::Next;
else if (cmd_lower == "prev")
return ControlType::Prev;
else if (cmd_lower == "stop")
return ControlType::Stop;
else
return ControlType::Unknown;
}
void PlayerControl::execute(ControlType cmd) const
{
switch (cmd)
{
case ControlType::Play:
std::cout << "▶️ Playing music...\n";
break;
case ControlType::Pause:
std::cout << "⏸️ Music paused\n";
break;
case ControlType::Next:
std::cout << "⏭️ Skipping to next track\n";
break;
case ControlType::Prev:
std::cout << "⏮️ Back to previous track\n";
break;
case ControlType::Stop:
std::cout << "⏹️ Music stopped\n";
break;
default:
std::cout << "❓ unknown control\n";
break;
}
}
int PlayerControl::get_cnt()
{
return total_cnt;
}
运行测试截图
实验任务4
源代码Fraction.h,Fraction.cpp,task4.cpp
点击查看代码 Fraction.h
#pragma once
#include <string>
class Fraction
{
public:
Fraction(int _up, int _down = 1);
Fraction(const Fraction &f);
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, down;
public:
static const std::string doc;
};
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);
点击查看代码 Fraction.cpp
#include <iostream>
#include <algorithm>
#include "Fraction.h"
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)
{
int num_gcd = std::__gcd(abs(up), abs(down));
up /= num_gcd;
down /= num_gcd;
}
Fraction::Fraction(const Fraction &f)
: up(f.up), down(f.down)
{
int num_gcd = std::__gcd(abs(up), abs(down));
up /= num_gcd;
down /= num_gcd;
}
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)
{
bool is_negative = (f.up > 0) ^ (f.down > 0);
int num_gcd = std::__gcd(abs(f.up), abs(f.down));
int new_up = abs(f.up) / num_gcd;
int new_down = abs(f.down) / num_gcd;
if (new_down == 0)
{
std::cout << "分母不能为0";
return;
}
if (new_up == 0)
{
std::cout << "0";
return;
}
if (is_negative)
std::cout << "-";
if (new_down == 1)
{
std::cout << new_up;
return;
}
std::cout << new_up << "/" << new_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;
int num_gcd = std::__gcd(abs(new_up), abs(new_down));
return Fraction(new_up / num_gcd, new_down / num_gcd);
}
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;
int num_gcd = std::__gcd(abs(new_up), abs(new_down));
return Fraction(new_up / num_gcd, new_down / num_gcd);
}
Fraction mul(const Fraction &f1, const Fraction &f2)
{
int new_up = f1.up * f2.up;
int new_down = f1.down * f2.down;
int num_gcd = std::__gcd(abs(new_up), abs(new_down));
return Fraction(new_up / num_gcd, new_down / num_gcd);
}
Fraction div(const Fraction &f1, const Fraction &f2)
{
int new_up = f1.up * f2.down;
int new_down = f1.down * f2.up;
int num_gcd = std::__gcd(abs(new_up), abs(new_down));
return Fraction(new_up / num_gcd, new_down / num_gcd);
}
点击查看代码 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;
}
运行测试截图
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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。 -
回答：友元函数。考虑到分数在计算后可能出现需要化简的情况，且最简分数的存储优于非最简分数（数值可能越界），因此使用友元函数以实现计算后对分数进行简化；由于友元函数可以访问私有成员，故类的安全性有所降低，存在数据被非法修改的风险。综合以上两点，采用友元函数的方案或许更优。
实验总结
-
task1中删去友元函数func的普通声明，则编译报错；但是在如task2中删去友元函数output的普通声明，则编译不会报错。结合以上两种情况，发现后者编译不会报错的原因是output有类Complex的参数，使得编译器可以找到其声明。 -
对于
task4，在构造或计算完成后，都应判断分母是否为非0，且进行化简。 -
诸如
output/add/sub/mul/div，可以通过重载运算符实现。
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