实验二
task1：
代码组织：
T.h 内容：类T的声明、友元函数声明
T.cpp 内容：类T的实现、友元函数实现
task1.cpp 内容：测试模块、main函数
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：
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。
不能。友元函数声明只是授予函数访问类私有成员的权限，但函数本身没有声明，因此main函数无法找到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。
构造函数的功能是创建新的类对象，当构造类T的对象时，若传入整形参数或者不传入参数，则调用普通构造函数；若传入的参数是类T的对象，则调用复制构造函数；当传入的参数是右值（如临时对象等）时，调用移动构造函数；在创建的对象要结束其生命周期时，析构函数被自动调用，用来释放对象拥有的资源。
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。
程序不能正常运行。因为此时静态成员的定义（初始化）被放在了头文件里，而多个.cpp文件调用头文件的时候，会导致静态变量被重复定义，违反了C++的语法规则，因此报错。
task2：
多文件组织：
Complex.h
#ifndef COMPLEX_H #define COMPLEX_H #include <string> class Complex{ public: static const std::string doc; Complex(double r=0.0,double i=0.0); 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 isequal(const Complex& c1,const Complex& c2); friend bool is_not_equal(const Complex& c1,const Complex& c2); private: double real,imag; }; void output(const Complex &c); double abs(const Complex& c); Complex add(const Complex& c1,const Complex& c2); bool isequal(const Complex& c1,const Complex& c2); bool is_not_equal(const Complex& c1,const Complex& c2); #endif
Complex.cpp
#include "Complex.h" #include <string> #include <iostream> #include <cmath> using namespace std; const string Complex::doc="a simplified complex class"; 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) { cout << c.real; if (c.imag >= 0) { cout << " + " << c.imag << "i"<<endl; } else { cout << " - " << -c.imag << "i"<<endl; } } double abs(const Complex& c){ double r,i; r=c.real;i=c.imag; return sqrt(r*r+i*i); } Complex add(const Complex& c1,const Complex& c2){ double r,i; r=c1.real+c2.real; i=c1.imag+c2.imag; return Complex(r,i); } bool isequal(const Complex& c1,const Complex& c2){ if(c1.real==c2.real&&c1.imag==c2.imag) return true; return false; } bool is_not_equal(const Complex& c1,const Complex& c2){ if(!isequal(c1,c2)) return true; return false; }
task2.cpp
#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 : " << isequal(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;
}
运行结果：
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？
标准库模板类complex更简洁一点。函数和运算有非常紧密的内在关联。加法运算可以用自定义类的add函数或者是标准库中的运算符+来完成，并且标准库提供了完整的运算符重载。
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）
否。虽然output/abs/add/函数需要访问实部和虚部来进行输出，但是可以根据公共接口get_real（）和get_imag（）来访问实部和虚部。
2-2：标准库 std::complex 是否把 abs 设为友元？（查阅 cppreference后回答）
标准库std::complex没有把abs 设为友元。
2-3：什么时候才考虑使用 friend？总结你的思考。
如果需要访问多个类的私有成员或者要实现类的非成员运算符重载，即当需要调用多次公共接口才能实现功能，导致效率较低的时候，考虑友元函数简化操作，提高效率。
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？
将复制构造函数声明为 explicit，可以防止意外的资源拷贝，但不影响其他的构造对象的方式。
task3：
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> int PlayerControl::total_cnt = 0; PlayerControl::PlayerControl() {} ControlType PlayerControl::parse(const std::string& control_str) { std::string lower_str = control_str; std::transform(lower_str.begin(), lower_str.end(), lower_str.begin(), [](unsigned char c) { return std::tolower(c); }); ControlType result = ControlType::Unknown; if (lower_str == "play") { result = ControlType::Play; } else if (lower_str == "pause") { result = ControlType::Pause; } else if (lower_str == "next") { result = ControlType::Next; } else if (lower_str == "prev") { result = ControlType::Prev; } else if (lower_str == "stop") { result = ControlType::Stop; } else { result = ControlType::Unknown; } total_cnt++; return result; } 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：
task4：
Fraction.h
#ifndef FRACTION_H #define FRACTION_H #include <string> class Fraction{ public: static const std::string doc; Fraction(int u=1,int d=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,down; void simple(); }; 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); #endif
Fraction.cpp
#include "Fraction.h" #include <cmath> #include <iostream> #include <stdexcept> using namespace std; int gcd(int a,int b){ a=abs(a); b=abs(b); int temp; while(b!=0) { temp=b; b=a%b; a=temp; } return a; } void Fraction::simple(){ int com; if(down==0) return ; com=gcd(up,down); up=up/com; down=down/com; } const 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(const Fraction& other):up(other.up),down(other.down){} Fraction::Fraction(int u,int d):up(u),down(d){ if(down<0) { up=-up; down=-down; } simple(); } 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){ if(f.down==1) cout<<f.up<<endl; else if(f.down==0){ cout<<"分母不能为0"<<endl; } else{ cout<<f.up<<'/'<<f.down<<endl; } } Fraction add(const Fraction& f1,const Fraction& f2){ int a=f1.up*f2.down+f1.down*f2.up; int b=f1.down*f2.down; return Fraction(a,b); } Fraction sub(const Fraction& f1,const Fraction& f2){ int a=f1.up*f2.down-f1.down*f2.up; int b=f1.down*f2.down; return Fraction(a,b); } Fraction mul(const Fraction& f1,const Fraction& f2){ int a=f1.up*f2.up; int b=f1.down*f2.down; return Fraction(a,b); } Fraction div(const Fraction& f1,const Fraction& f2){ int a=f1.up*f2.down; int b=f1.down*f2.up; if(a!=0) return Fraction(a,b); }
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：
问题回答：
1.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)
我选择的是用友元函数实现。
2.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。
原因如下：首先，友元函数可以直接访问类的私有成员，使程序更简洁高效。其次，add等函数式二元操作函数，使用友元函数保持了运算的对称性。
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