1.实验任务1
#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();
#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; int T::get_cnt() {return cnt; } 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 << ")"; } void func() {T t5(42);t5.m2 = 2049;std::cout << "t5 = "; t5.display(); std::cout << '\n';std::cout << "test: T objects'current count: " << T::get_cnt() << std::endl; }
#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.不能，func函数未声明，找不到
二.1：普通构造函数，初始化类T的对象，为成员变量m1、m2赋初始值 2：复制构造函数，用已存在的T类对象深拷贝创建新对象，复制其成员变量值
3：移动构造函数，用已存在的T类对象转移资源创建新对象，“窃取” 其成员变量的资源 4.析构函数，释放对象占用的资源，在对象生命周期结束时做清理工作
三.不可以，静态函数如果在类内会重复定义
2.实验任务2
#include <string> class Complex { public:static const std::string doc;Complex();Complex(double r);Complex(double r, double i);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;double imag; };
#include "Complex.h" #include <iostream> #include <cmath> const std::string Complex::doc = "a simplified complex class"; Complex::Complex() : real(0.0), imag(0.0) {} Complex::Complex(double r) : real(r), imag(0.0) {} Complex::Complex(double r, double i) : real(r), imag(i) {} 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); }
#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; }
问题
一.标准库模板类complex更简洁。有内在关联，两者都是为了实现复数的运算和操作，功能逻辑一致。
二.1.是，它们需要访问real和imag来进行计算和输出
2.否，abs通过real()和imag()成员函数来获取实部和虚部
3.在需要多次访问私有成员时可以用友元
三.可以通过在复制构造函数前加上explicit去实现。
3.实验任务3
#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; };
#include "PlayerControl.h" #include <iostream> #include <algorithm> #include <string>int PlayerControl::total_cnt = 0;PlayerControl::PlayerControl() {}ControlType PlayerControl::parse(const std::string& control_str) {std::string str = control_str;std::transform(str.begin(), str.end(), str.begin(), ::tolower);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; }
#include "PlayerControl.h" #include <iostream> #include <string>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();return 0; }
4.实验任务4
#pragma once #include <string>class Fraction { public:static const std::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 simplify();int gcd(int a, int b); };
#include "Fraction.h" #include <iostream> #include <stdexcept>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) {if (down == 0) {throw std::invalid_argument("分母不能为0");}simplify(); }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::simplify() {if (down < 0) {up = -up;down = -down;}int g = gcd(std::abs(up), down);if (g != 0) {up /= g;down /= g;} }int Fraction::gcd(int a, int b) {while (b != 0) {int temp = b;b = a % b;a = temp;}return a; }void output(const Fraction &f) {if (f.down == 1) {std::cout << f.up;} else {std::cout << f.up << "/" << f.down;} }Fraction add(const Fraction &f1, const Fraction &f2) {int up = f1.up * f2.down + f2.up * f1.down;int down = f1.down * f2.down;return Fraction(up, down); }Fraction sub(const Fraction &f1, const Fraction &f2) {int up = f1.up * f2.down - f2.up * f1.down;int down = f1.down * f2.down;return Fraction(up, down); }Fraction mul(const Fraction &f1, const Fraction &f2) {int up = f1.up * f2.up;int down = f1.down * f2.down;return Fraction(up, down); }Fraction div(const Fraction &f1, const Fraction &f2) {if (f2.up == 0) {throw std::invalid_argument("分母不能为0");}int up = f1.up * f2.down;int down = f1.down * f2.up;return Fraction(up, down); }
#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
一.决策理由：友元可直接访问分数类私有成员，实现输出、运算时无需通过公共接口间接获取数据，简化逻辑且保证效率。
友元优点：访问私有成员便捷，代码实现简洁；缺点：一定程度破坏封装性。
静态成员函数适用于与类紧密相关、无需访问对象私有数据的场景（如类级别的工具方法）；命名空间方案适合组织多个类的通用工具函数，此处仅为分数类服务，友元更直接。
实验总结
1.对于类对象功能的实现，有许多办法，需要合理利用这些方法的优缺点根据实际情况去选择，以优化代码，提高代码可读性，并且便于后期维护。
2.对于友元函数的使用以及认识都更深一些，理解其优缺点及使用条件。
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