试验2
实验任务1
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：
-
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。
![1 报错信息]()
不能，友元函数仅在作用域内有效，不会在全局作用域中引入函数声明。
-
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。
第一个是普通构造函数，可以用两个值来初始化对象，第二行为复制构造函数，可以用另一个已经存在的对象来初始化一个新对象。第三行为移动构造函数，"窃取"临时对象（右值）的资源，避免不必要的深拷贝。第四个是析构函数，会释放对象占用的资源。对象生命周期结束后自动调用。
-
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。不能，头文件不能在类外定义函数。
![1 报错二]()
实验任务二
Complex.h
#pragma once
#include <string>
class Complex
{
public:
const static std::string doc;
private:
double real, imag;
public:
Complex(double x = 0, double y = 0);
Complex(const Complex &c);
Complex(Complex &&c);
Complex &operator=(const Complex &c);
public:
double get_real() const;
double get_imag() const;
void add(Complex c2);
friend void output(Complex c1);
friend double abs(Complex c1);
friend Complex add(Complex c1, Complex c2);
friend bool is_equal(Complex c1, Complex c2);
friend bool is_not_equal(Complex c1, Complex c2);
};
void output(Complex c1);
double abs(Complex c1);
Complex add(Complex c1, Complex c2);
bool is_equal(Complex c1, Complex c2);
bool is_not_equal(Complex c1, Complex c2);
Complex.cpp
#include "Complex.h"
#include <iostream>
#include <cmath>
#include <string>
#include <iomanip>
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} {}
Complex::Complex(Complex &&c) : real{c.real}, imag{c.imag} {}
Complex &Complex::operator=(const Complex &c)
{
if (this != &c)
{
real = c.real;
imag = c.imag;
}
return *this;
}
double Complex::get_real() const { return real; }
double Complex::get_imag() const { return imag; }
void Complex::add(Complex c2)
{
real += c2.real;
imag += c2.imag;
}
void output(Complex c1)
{
if (c1.imag >= 0)
std::cout << c1.real << " + " << c1.imag << 'i' << '\n';
else
std::cout << c1.real << " - " << -c1.imag << 'i' << '\n';
}
double abs(Complex c1)
{
return sqrt(c1.real * c1.real + c1.imag * c1.imag);
}
Complex add(Complex c1, Complex c2)
{
return {c1.real + c2.real, c1.imag + c2.imag};
}
bool is_equal(Complex c1, Complex c2)
{
return (c1.real == c2.real) & (c1.imag == c2.imag);
}
bool is_not_equal(Complex c1, Complex c2)
{
return !((c1.real == c2.real) & (c1.imag == c2.imag));
}
task2.cpp
#include <iostream>
#include <iomanip>
#include "Complex.h"
#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;
}
运行结果截图
回答问题
-
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？后者更加简洁。有关联。
-
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，output/abs/add/均需要复数的实部和虚部。
2-2：标准库 std::complex 是否把 abs 设为友元？（查阅 cppreference后回答）
没有。
2-3：什么时候才考虑使用 friend？总结你的思考。
在函数需要访问私有数据时。
-
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？
改为Complex(const Complex &&c) = delete;
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>
#include <cstring>
#include <cctype>
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 t_str=control_str;
std::transform(control_str.begin(), control_str.end(), t_str.begin(), tolower);
std::string S[5] = {"play", "pause", "next", "prev", "stop"};
for (int i = 0; i < 5; i++)
if (t_str == S[i]){
total_cnt++;
return static_cast<ControlType>(i);
}
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
实验任务四
Fraction.h
#include <iostream>
#include <cmath>
#include <string>
class Fraction
{
public:
const static std::string doc;
private:
int up, down;
public:
Fraction(int x, int y = 1);
Fraction(const Fraction &x);
int get_up() const;
int get_down() const;
Fraction negative();
friend Fraction simp(Fraction f);
friend void output(Fraction f);
friend Fraction add(Fraction f1, Fraction f2);
friend Fraction sub(Fraction f1, Fraction f2);
friend Fraction mul(Fraction f1, Fraction f2);
friend Fraction div(Fraction f1, Fraction f2);
};
int gcd(int x, int y);
Fraction simp(Fraction f);
void output(Fraction f);
Fraction add(Fraction f1, Fraction f2);
Fraction sub(Fraction f1, Fraction f2);
Fraction mul(Fraction f1, Fraction f2);
Fraction div(Fraction f1, Fraction f2);
Fraction.cpp
#include "Fraction.h"
#include <cmath>
const std::string Fraction::doc{"a simplified fraction class"};
Fraction::Fraction(int x, int y) : up{x / gcd(x, y)}, down{y / gcd(x, y)} {}
Fraction::Fraction(const Fraction &x) : up{x.up}, down{x.down} {}
int Fraction::get_up() const
{
return up;
}
int Fraction::get_down() const
{
return down;
}
Fraction Fraction::negative()
{
return {-1 * up, down};
}
int gcd(int x, int y)
{
return (y == 0) ? (x) : (gcd(y, x % y));
}
Fraction simp(Fraction f)
{
if (f.down == 0)
return f;
Fraction res(f);
int fla = 1;
if (res.down < 0)
res.down *= -1, fla *= -1;
int gc = gcd(abs(res.up), res.down);
res.up *= fla, res.up /= gc, res.down /= gc;
return res;
}
void output(Fraction f)
{
Fraction t(simp(f));
if (t.down == 0)
{
std::cout << "分母不能为0";
return;
}
std::cout << t.up;
if (t.down != 1 && t.up != 0)
std::cout << "/" << t.down;
}
Fraction add(Fraction f1, Fraction f2)
{
Fraction res(f1.up * f2.down + f2.up * f1.down, f1.down * f2.down);
return simp(res);
}
Fraction sub(Fraction f1, Fraction f2)
{
Fraction res(f1.up * f2.down - f2.up * f1.down, f1.down * f2.down);
return simp(res);
}
Fraction mul(Fraction f1, Fraction f2)
{
Fraction res(f1.up * f2.up, f1.down * f2.down);
return simp(res);
}
Fraction div(Fraction f1, Fraction f2)
{
Fraction res(f1.up * f2.down, f1.down * f2.up);
return simp(res);
}
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
回答问题
- 分数的输出和计算， output/add/sub/mul/div ，你选择是哪一种设计方案？（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。
友元函数+自由函数，友元函数会破坏封装性。
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