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" ;elsecout << 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 ;elsecout << 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。