实验二：现代C++编程初体验

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;
}

 

问题一：会出错，

原因：类里面的声明只是说func是T的友元函数，但是并没有在命名空间里生成一个可用的符号声明

 

问题二：1：初始化类时调用，初始化x，y参数，默认为0

2：复制构造函数，将括号里的类复制到目标类中，当括号内是已有对象时调用

3：移动构造函数，将括号内的类资源移动到目标类，一般括号内是临时值时调用

4：析构函数，在类被销毁时触发

问题三：

不能，

static属于一个类，两个cpp文件都包含h头文件，会出现重复定义，但是static对象是不能重复定义的

 Complex.h

#pragma once
#include<string>class Complex
{
private:double real, imag;
public:static const std::string doc;Complex& operator=(const Complex&) = default;Complex(double a = 0, double b = 0);Complex(const Complex &t);Complex(Complex&& t);~Complex();double get_real() const;double get_imag() const;Complex& add(const Complex &t);friend  void output(const Complex &t);friend double abs(const Complex &t);friend Complex add(const Complex& a, const Complex& b);friend bool is_equal(const Complex& a, const Complex& b);friend bool is_not_equal(const Complex& a, const Complex& b);
};void output(const Complex &t);
double abs(const Complex& t);
Complex add(const Complex& a, const Complex& b);
bool is_equal(const Complex& a, const Complex& b);
bool is_not_equal(const Complex& a, const Complex& b);

Complex.cpp

#include "Complex.h"
#include <iostream>
#include <cmath>const std::string Complex::doc{ "a simplified complex class" };Complex::Complex(double a, double b) :real{ a }, imag{ b } {}
Complex::Complex(const Complex& t) : real{t.real}, imag{ t.imag } {}
Complex::Complex(Complex&& t) : real{ t.real }, imag{ t.imag } {}
Complex::~Complex() {}double Complex:: get_imag()const {return imag;
}double Complex::get_real()const {return real;
}Complex& Complex::add(const Complex& t){real += t.real;imag += t.imag;return *this;
}void output(const Complex &t) {std::cout << t.real ;if (t.imag >= 0)std::cout << '+';std::cout<< t.imag << 'i';
}double abs(const Complex& t) {double c = t.imag * t.imag + t.real * t.real;return sqrt(c);
}Complex add(const Complex& a, const Complex& b) {Complex t3;t3.imag = a.imag + b.imag;t3.real = a.real + b.real;return t3;
}bool is_equal(const Complex& a, const Complex& b) {if (a.imag == b.imag && a.real == b.real)return true;return false;
}bool is_not_equal(const Complex& a, const Complex& b) {if (a.imag != b.imag || a.real != b.real)return true;return false;
}

task2.cpp

#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()<< ", 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;
}

 

 

 

问题一：标准库更简洁，有关联

问题二：是，都使用了private数据

否。

一些私有数据没有对外接口时，使用友元函数

问题三：显示写拷贝构造函数

 

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 <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 str = control_str;std::transform(str.begin(), str.end(), str.begin(), ::tolower);PlayerControl::total_cnt++;if (str == "play") return ControlType::Play;else if (str == "pause") return ControlType::Pause;else if (str == "next") return ControlType::Next;else if (str == "prev") return ControlType::Prev;else if (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();
}

思考题：将所有文件已UTF-8带签名保存，

在main后面加上SetConsoleOutputCP(CP_UTF8);

cout<<u8"emoji";可输出emoji

或者UTF-8无签名保存

在main后面加上SetConsoleOutputCP(CP_UTF8);

cout<<"emoji";

 

Fraction.h

 

#pragma once
#include <string>class Fraction {
public:Fraction(int a = 0, int b = 1);Fraction(const Fraction& );int get_up() const;int get_down() const;Fraction negative()const;static const std::string doc;void simplify();int gcd(int a, int b);
private:int up, down;static int gcd2(int a, int b);};void output(const Fraction&);Fraction add(const Fraction&, const Fraction&);Fraction sub(const Fraction&, const Fraction&);Fraction mul(const Fraction&, const Fraction&);Fraction div(const Fraction&, const Fraction&);

 

Fraction.cpp

#include "Fraction.h"
#include <iostream>
#include <string>const std::string Fraction::doc = "Fraction类 v 0.01版. 目前仅支持分数对象的构造、输出、加 / 减 / 乘 / 除运算.";int Fraction::gcd2(int a, int b)
{while (b != 0){int t = b;b = a % b;a = t;}return a;
}Fraction::Fraction(int a, int b) : up { a }, down{b}{}
Fraction::Fraction(const Fraction& other) :up{ other.up }, down{ other.down } {}
int Fraction::get_up()const {int g = gcd2(abs(up), abs(down));return up/g;
}
int Fraction::get_down()const {int g = gcd2(abs(up), abs(down));return down/g;
}Fraction Fraction::negative() const {return Fraction(-up, down);
}void output(const Fraction& f) {Fraction temp = f;temp.simplify();if (temp.get_up() == 0 && temp.get_down() != 0)std::cout << 0;else if (temp.get_down() == 1)std::cout << temp.get_up();else if (temp.get_down() != 0 && temp.get_up() != 0)std::cout << temp.get_up() << "/" << temp.get_down();elsestd::cout << "分母不能为0";
}Fraction add(const Fraction& a, const Fraction& b) {int u = a.get_up() * b.get_down() + b.get_up() * a.get_down();int d = a.get_down() * b.get_down();return Fraction(u, d);
}Fraction sub(const Fraction& a, const Fraction& b) {int u = a.get_up() * b.get_down() - b.get_up() * a.get_down();int d = a.get_down() * b.get_down();return Fraction(u, d);
}Fraction mul(const Fraction& a, const Fraction& b) {return Fraction(a.get_up() * b.get_up(), a.get_down() * b.get_down());
}Fraction div(const Fraction& a, const Fraction& b) {if (b.get_up() == 0) return Fraction(a.get_up() * b.get_down(), 0);return Fraction(a.get_up() * b.get_down(), a.get_down() * b.get_up());
}
void Fraction::simplify() {int g = gcd(abs(up), abs(down));up /= g;down /= g;if (down < 0){up = -up;down = -down;}
}int Fraction::gcd(int a, int b) {while (b != 0) {int t = a % b;a = b;b = t;}return a;
}

 

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：自由函数/命名空间

友元函数权限过高不安全，静态成员函数只能通过传递参数或者使用静态数据，使用麻烦