实验2

1.cpp

#include "t.h"

#include <iostream>
#include <stdexcept>
#include <string>

// static成员数据: 类内声明、类外初始化
const std::string T::doc{"a simple class sample"};
const int T::MAX_CNT = 999;
int T::current_cnt = 0;

// 对象方法
T::T(int x, int y): m1{x}, m2{y} { 
    if(current_cnt == MAX_CNT) {
        throw std::runtime_error("T: maximum object count exceeded");
    }

    ++current_cnt; 
    std::cout << "T constructor called.\n";
} 

T::T(const T &t): m1{t.m1}, m2{t.m2} {
    if(current_cnt == MAX_CNT) {
        throw std::runtime_error("T: maximum object count exceeded");
    }

    ++current_cnt;
    std::cout << "T copy constructor called.\n";
}

T::T(T &&t): m1{t.m1}, m2{t.m2} {
    if(current_cnt == MAX_CNT) {
        throw std::runtime_error("T: maximum object count exceeded");
    }

    ++current_cnt;
    std::cout << "T move constructor called.\n";
}    

T::~T() {
    --current_cnt;
    std::cout << "T destructor called.\n";
}           

void T::adjust(int ratio) {
    m1 *= ratio;
    m2 *= ratio;
}      

// 类方法
int T::get_cnt() {
   return current_cnt;
}

// 友元
void output(const T &t) {
    std::cout << "(" << t.m1 << ", " << t.m2 << ")";
}

1.h

#pragma once

#include <string>

class T {
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

    static int get_cnt();          // 显示当前T类对象总数

    friend void output(const T &t); // 友元, 以(m1, m2)形式输出对象t

    static const std::string doc;       // 类T的描述信息
    static const int MAX_CNT;           // 类T对象上限

private:
    int m1, m2;  // 对象数据成员

    static int current_cnt;    // 当前T类对象数目
};

task1

#include <iostream>
#include <utility>

#include "t.h"

void test() {
    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 = "; output(t1); cout << endl;

        T t2(3, 4);
        cout << "t2 = "; output(t2); cout << endl;

        T t3(t2);
        t3.adjust(2);
        cout << "t3 = "; output(t3); cout << endl;

        T t4(std::move(t2));
        cout << "t4 = "; output(t4); cout << endl;

        cout << "test: T objects'current count: " << T::get_cnt() << endl;
    }
    cout << "test: T objects'current count: " << T::get_cnt() << endl;
}

int main() {
    std::cout << "test Class T: \n";
    test();
}

截图

屏幕截图 2026-11-13 231636

问题回答

    • 问题1
      普通构造函数是是对变量直接赋值，在t2中，输入（3，4），则t2的两个int值则为3和4，如果没有输入任何数值则默认T中的2个变量为0，例如t1，未写任何值两个变量默认为0，复制构造函数是将其他同类的变量复制一遍在赋予到当前的变量中，例如t3，就是将t2的进行了复制，移动构造函数是将同类的变量直接移动到新变量中而不是复制，t4则是将t2的值直接移动到了t4中，析构函数的作用是在生命周期结束的变量进行清除，避免内存占用。

    • 问题2
      不能
      image
      报错显示了重复定义，这违反了C++的单一定义原则，因为变量是在头文件中所定义，且被t.cpp与task1.cpp同时定义了一次，所以编译错误。

    • 问题3
      这4个变量属于局部作用域，生命周期为自动存储期。在t1期间，不能访问t1，t2的变量，因为他们属于private，不可访问，这体现了类的封装与访问控制。

    • 问题4
      image
      会被正常销毁，在出现异常时，析构函数依然会调用，在异常结果报告出来前将其正常销毁，避免内存的占用。

    • 实验任务2

      源代码

      • Complex.h
      #pragma once

#include<string>

class Complex{
public:
	Complex(double r=0.0,double i=0.0);
	Complex(const Complex &com);
	~Complex();
	
	static const std::string doc;
	double real() const;
	double imag() const;
	
	void add(const Complex &com);
	
	friend void output(const Complex &com);
	friend double abs(const Complex &com);
	friend Complex add(const Complex &com1,const Complex &com2);
	friend bool is_equal(const Complex &com1,const Complex &com2);
	friend bool is_not_equal(const Complex &com1,const Complex &com2);
	

private:
	double re;
	double im;
};
      • Complex.cpp
      #include<iostream>
#include<string>
#include<cmath>
#include<iomanip>
#include "Complex.h"

const std::string Complex::doc{"a simplified complex class"};

Complex::Complex(double r,double i):re{r},im{i}{}

Complex::Complex(const Complex &com):re{com.re},im{com.im}{}

Complex::~Complex(){}

double Complex::real() const{
    return re;
}

double Complex::imag() const{
    return im;
}

void Complex::add(const Complex &com){
    re+=com.re;
    im+=com.im;
}

void output(const Complex &com){
    using namespace std;
	if(com.im>=0) cout<<com.re<<" + "<<com.im<<"i"<<endl;
	else cout<<com.re<<" - "<<-com.im<<"i"<<endl;
    
}

double abs(const Complex &com){
    using namespace std;
    double ab=sqrt(com.re*com.re+com.im*com.im);
    return ab;
}

Complex add(const Complex &com1,const Complex &com2){
    Complex com3;
    com3.re=com1.re+com2.re;
    com3.im=com1.im+com2.im;

    return com3;
}

bool is_equal(const Complex &com1,const Complex &com2){
    if(com1.re==com2.re&&com1.im==com2.im) return true;
    else return false;
}

bool is_not_equal(const Complex &com1,const Complex &com2){
    if(com1.re==com2.re&&com1.im==com2.im) return false;
    else return true;
}
      • task2.cpp
      #include <iomanip>
#include <iostream>
#include <complex>

#include "Complex.h"

// 测试自定义类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);
    const Complex c6 = 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 = "; output(c5); cout << endl;
    cout << "c6.real = " << c6.real() 
         << ", c6.imag = " << c6.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;
}

// 测试标准库类模板complex
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;
    std::complex<double> c5 = 3.5;
    const std::complex<double> c6(3.5);

    cout << "c1 = " << c1 << endl;
    cout << "c2 = " << c2 << endl;
    cout << "c3 = " << c3 << endl;
    cout << "c4 = " << c4 << endl;
    cout << "c5 = " << c5 << endl;

    cout << "c6.real = " << c6.real() 
         << ", c6.imag = " << c6.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;
}

int main() {
    std::cout << "*******测试1: 自定义类Complex*******\n";
    test_Complex();

    std::cout << "\n*******测试2: 标准库类模板complex*******\n";
    test_std_complex();
}

      运行截图

      image

      问题回答

      • 问题1
        1.1 在返回real和imag的函数中，后面需要加上const。如果不加，则有报错：
        image
        图像中的则表示一个const常量去调用一个非const成员函数，有修改值的可能性，从而导致编译错误。
        1.2不能通过，因为c6是const，如果add则会触发常量被修改的风险，这体现了类的数据保护机制。

      • 问题2
        标准库的用法更加简洁，其中的运算符与函数名称定义基本相同。

      • 问题3
        必须的，因为类中的两个变量是私有的，如果不加friend的话是无法直接访问到类中的2个变量的，所以必须加上friend，以共享自己的private变量，方便运算。

      实验任务3

      源代码

      • 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 <algorithm>  
#include <iostream>
int PlayerControl::total_cnt = 0;
PlayerControl::PlayerControl() {}
// 待补足
// 1. 将输入字符串统一成转为小写，实现大小写不敏感
// 2. 匹配"play"/"pause"/"next"/"prev"/"stop"并返回对应枚举；
//    未匹配的字符串返回ControlType::Unknown
ControlType PlayerControl::parse(const std::string& control_str) {
	std::string s,s1;
	s1=control_str;
	int len=s1.length();
	for(int i=0;i<len;i++) s+=tolower(s1[i]);
	if(s=="play") return ControlType::Play;
	else if(s=="pause") return ControlType::Pause;
	else if(s=="next") return ControlType::Next;
	else if(s=="prev") return ControlType::Prev;
	else if(s=="stop") return ControlType::Stop;
	else return ControlType::Unknown;
	
}
void PlayerControl::execute(ControlType cmd) const {
	// 每执行一次控制操作（含未知命令），total_cnt自增 1
	++total_cnt; 
	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 <algorithm>  
#include <iostream>
int PlayerControl::total_cnt = 0;
PlayerControl::PlayerControl() {}
// 待补足
// 1. 将输入字符串统一成转为小写，实现大小写不敏感
// 2. 匹配"play"/"pause"/"next"/"prev"/"stop"并返回对应枚举；
//    未匹配的字符串返回ControlType::Unknown
ControlType PlayerControl::parse(const std::string& control_str) {
	std::string s,s1;
	s1=control_str;
	int len=s1.length();
	for(int i=0;i<len;i++) s+=tolower(s1[i]);
	if(s=="play") return ControlType::Play;
	else if(s=="pause") return ControlType::Pause;
	else if(s=="next") return ControlType::Next;
	else if(s=="prev") return ControlType::Prev;
	else if(s=="stop") return ControlType::Stop;
	else return ControlType::Unknown;
	
}
void PlayerControl::execute(ControlType cmd) const {
	// 每执行一次控制操作（含未知命令），total_cnt自增 1
	++total_cnt; 
	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;
}

      运行截图

      image

      问题回答

      由于const保护的是对象自身的非静态成员函数，而static数据是独立于对象而存在的，在任何地方或者函数中都可以被操作修改。

      实验任务4

      源代码

      • Fraction.h
      #pragma once

#include<string>

class Fraction{
public:
	Fraction(int up0=1,int down0=1);
	Fraction(const Fraction &fra);
	~Fraction();
	
	static const std::string doc;
	
	int get_up() const;
	int get_down() const;
	
	Fraction negative();
	
	friend void output(const Fraction &fra);
	friend Fraction add(const Fraction &fra1,const Fraction &fra2);
	friend Fraction sub(const Fraction &fra1,const Fraction &fra2);
	friend Fraction mul(const Fraction &fra1,const Fraction &fra2);
	friend Fraction div(const Fraction &fra1,const Fraction &fra2);
	
private:
	int up;
	int down;
};
      • Fraction.cpp
      #include <iostream>
#include <stdexcept>
#include "Fraction.h"

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 gcd(int a,int b){
	a=std::abs(a);
	b=std::abs(b);
	while(b!=0){
		int tmp=b;
		b=a%b;
		a=tmp;
	}
	return a;
}

Fraction::Fraction(int up0,int down0):up{up0},down{down0}{
    if(down==0)
      throw std::invalid_argument("Fraction: 分母不能为0");
    if(up*down<0){
        down=std::abs(down);
        up=up<0?up:-up;
    }
}

Fraction::Fraction(const Fraction &fra):up{fra.up},down{fra.down}{}

Fraction::~Fraction(){}

int Fraction::get_up() const{
    return up/gcd(up,down);
}

int Fraction::get_down() const{
    return down/gcd(up,down);
}

Fraction Fraction::negative(){
    Fraction fra;
    fra.up=-up;
    fra.down=down;
    return fra;
}

void output(const Fraction &fra){
    int up=fra.up,down=fra.down;
    int yueshu=gcd(up,down);
    up/=yueshu;
    down/=yueshu;
    if(up*down>=0){
        up=std::abs(up);
        down=std::abs(down);
    }
	if(down==0) throw std::invalid_argument("Fraction: 分母不能为0");
    else if(down!=1) std::cout<<up<<"/"<<down<<std::endl;
	else std::cout<<up<<std::endl;
}

Fraction add(const Fraction &fra1,const Fraction &fra2){
    Fraction fra;
    int up1=fra1.up,down1=fra1.down;
    int up2=fra2.up,down2=fra2.down;
    int down=down1*down2;
    int up=up1*down2+up2*down1;
    fra.up=up;
    fra.down=down;
    return fra;
}

Fraction sub(const Fraction &fra1,const Fraction &fra2){
    Fraction fra;
    int up1=fra1.up,down1=fra1.down;
    int up2=fra2.up,down2=fra2.down;
    int down=down1*down2;
    int up=up1*down2-up2*down1;
    fra.up=up;
    fra.down=down;
    return fra;
}

Fraction mul(const Fraction &fra1,const Fraction &fra2){
    Fraction fra;
    int up1=fra1.up,down1=fra1.down;
    int up2=fra2.up,down2=fra2.down;
    int down=down1*down2;
    int up=up1*up2;
    fra.up=up;
    fra.down=down;
    return fra;
}

Fraction div(const Fraction &fra1,const Fraction &fra2){
    Fraction fra;
    int up1=fra1.up,down1=fra1.down;
    int up2=fra2.down,down2=fra2.up;
	if(up2*down2<0){
		down2=std::abs(down2);
		up2=up2<0?up2:-up2;
	}
    int down=down1*down2;
    int up=up1*up2;
    fra.up=up;
    fra.down=down;
    return fra;
}
      • task4.cpp
      #include <iostream>

#include "Fraction.h"

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;
}

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();
}

      运行截图

      image

      问题回答

      我选择的是分数类加友元函数。因为要操作的函数很多，所以需要进行分离，让Fraction这个类只负责数据的承接载体，有友元函数来完成加减乘除的操作，这样做可以将运算和输出分离出类，让类内部更加简洁。

posted @ 2026-11-13 23:20  肖义耀  阅读(4)  评论(0)    收藏  举报