现代C++编程初体验
##实验任务1
##代码
#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
#include "Fraction.h" #include <iostream> // 初始化类属性 const std::string Fraction::doc = "Fraction类 v0.01版.\n目前仅支持分数对象的构造、输出、加/减/乘/除运算."; // 构造函数 Fraction::Fraction(int up, int down) : up(up), down(down) { if (down == 0) { std::cerr << "分母不能为0" << std::endl; // 分母为0时，默认初始化为0/1 this->up = 0; this->down = 1; } else { simplify(); } } // 拷贝构造函数 Fraction::Fraction(const Fraction& other) : up(other.up), down(other.down) {} // 获取分子 int Fraction::get_up() const { return up; } // 获取分母 int Fraction::get_down() const { return down; } // 求负 Fraction Fraction::negative() const { return Fraction(-up, down); } // 化简分数 void Fraction::simplify() { if (up == 0) { down = 1; return; } int sign = 1; if (up < 0) { sign *= -1; up = -up; } if (down < 0) { sign *= -1; down = -down; } int g = gcd(up, down); up = sign * (up / g); down = down / g; } // 求最大公约数 int Fraction::gcd(int a, int b) { return b == 0 ? a : gcd(b, a % b); } // 输出分数 void output(const Fraction& frac) { if (frac.down == 1) { std::cout << frac.up; } else { std::cout << frac.up << "/" << frac.down; } } // 分数相加 Fraction add(const Fraction& f1, const Fraction& f2) { int up = f1.up * f2.down + f2.up * f1.down; int down = f1.down * f2.down; Fraction result(up, down); result.simplify(); return result; } // 分数相减 Fraction sub(const Fraction& f1, const Fraction& f2) { int up = f1.up * f2.down - f2.up * f1.down; int down = f1.down * f2.down; Fraction result(up, down); result.simplify(); return result; } // 分数相乘 Fraction mul(const Fraction& f1, const Fraction& f2) { int up = f1.up * f2.up; int down = f1.down * f2.down; Fraction result(up, down); result.simplify(); return result; } // 分数相除 Fraction div(const Fraction& f1, const Fraction& f2) { if (f2.up == 0) { std::cerr << "分母不能为0" << std::endl; return Fraction(0, 1); } int up = f1.up * f2.down; int down = f1.down * f2.up; Fraction result(up, down); result.simplify(); return result; }
#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(); return 0; } 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; }
friend void func(); }; // 普通函数声明 void func();
#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;
}
1.YES
2.
普通构造函数 功能：初始化对象的数据成员 调用时机：创建新对象时
复制构造函数 功能：通过拷贝另一个同类对象来初始化新对象 调用时机：用已有对象初始化新对象时 对象作为值参数传递给函数时
移动构造函数 功能调用时机用:高效转移资源，右值（临时对象）初始化新对象时。
3.能正确编译。
##实验任务2
##代码
##Complex.h
#ifndef COMPLEX_H #define COMPLEX_H #include <string> class Complex { public: static const std::string doc; // 类说明文档 // 构造函数 Complex(); // 默认构造函数，创建0+0i Complex(double real); // 用实部创建复数，虚部为0 Complex(double real, double imag); // 用实部和虚部创建复数 Complex(const Complex& other); // 拷贝构造函数 // 成员函数 double get_real() const; // 获取实部 double get_imag() const; // 获取虚部 void add(const Complex& other); // 复数加法，相当于+= // 友元函数 friend void output(const Complex& c); // 输出复数 friend double abs(const Complex& c); // 取模 friend Complex add(const Complex& c1, const Complex& c2); // 复数相加 friend bool is_equal(const Complex& c1, const Complex& c2); // 判断相等 friend bool is_not_equal(const Complex& c1, const Complex& c2); // 判断不等 private: double real_; // 实部 double imag_; // 虚部 }; #endif // COMPLEX_H
##task2.cpp
#include "Complex.h" #include <iostream> #include <iomanip> #include <complex> using namespace std; void test_Complex(); void test_std_complex(); int main() { cout << "*******测试1: 自定义类Complex*******\n"; test_Complex(); cout << "\n*******测试2: 标准库模板类complex*******\n"; test_std_complex(); return 0; } 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; }
标准库模板类complex明显更简洁，标准库使用自然的数学运算符，自定义类complex需要专门的输出函数；
函数和运算在功能上是完全等价的，只是标准库的写法更接近数学表达式，直观易懂，标准库的设计通过运算符重载实现了更优雅的语法。
##问题2
2.1是，列如，如果仅通过 get_real()和 get_imag()获取数据，output()需要额外逻辑拼接字符串，不如直接访问私有变量高效，如果不直接访问私有数据，可能会导致性能损失，代码冗余，封装性降低等，因此，友元函数是合理的设计选择。
2.2标准库 std::complex没有将 abs()设为友元函数，std::abs(std::complex)是独立函数，它不依赖友元访问 std::complex的私有数据，而是通过 real()和 imag()这两个公共成员函数获取实部和虚部。
2.3需要访问私有数据，但无法通过公有接口高校实现；需要支持运算符重载，但运算符函数不能是成员。
##问题3
Complex c4 = c2是拷贝初始化，如果编译失败，那么使用直接初始化Complex c3(c2)。
##实验任务3
##代码
#pragma once #include <string> enum class ControlType {Play, Pause, Next, Prev, Stop, Unknown}; class PlayerControl { public: PlayerControl(); ControlType parse(const std::string& control_str); // 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; };
#include "PlayerControl.h" #include <iostream> #include <algorithm> #include <cctype> int PlayerControl::total_cnt = 0; PlayerControl::PlayerControl() {} ControlType PlayerControl::parse(const std::string& control_str) { // 1. 将输入字符串转为小写（实现大小写不敏感） std::string lower_str = control_str; std::transform(lower_str.begin(), lower_str.end(), lower_str.begin(), [](unsigned char c) { return std::tolower(c); }); // 2. 匹配命令并返回对应枚举 ControlType cmd = ControlType::Unknown; if (lower_str == "play") { cmd = ControlType::Play; } else if (lower_str == "pause") { cmd = ControlType::Pause; } else if (lower_str == "next") { cmd = ControlType::Next; } else if (lower_str == "prev") { cmd = ControlType::Prev; } else if (lower_str == "stop") { cmd = ControlType::Stop; } // 3. 成功匹配时，递增总操作次数 if (cmd != ControlType::Unknown) { total_cnt++; } return cmd; } 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> 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
##实验任务4
##代码
##Fraction.h
#ifndef FRACTION_H #define FRACTION_H #include <string> class Fraction { public: // 类属性，用于类说明 static const std::string doc; // 构造函数 Fraction(int up = 0, int down = 1); Fraction(const Fraction& other); // 接口 int get_up() const; int get_down() const; Fraction negative() const; // 友元函数声明（工具函数） friend void output(const Fraction& frac); 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: // 对象属性：分子和分母 int up; int down; // 内部工具函数：化简分数 void simplify(); // 内部工具函数：求最大公约数 int gcd(int a, int b); }; #endif // FRACTION_H
友元函数.友元函数可以直接访问分子分母这些私有成员，无需通过类的接口间接获取；静态成员函数需要通过类名或对象来调用，而不能直接访问私有成员；命名空间方案的自由函数也无法直接访问类的私有成员，必须通过类提供的公有接口来获取分子分母；
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