实验5 多态

实验任务1：

1.源代码

#include <iostream>
#include <string>
#include "publisher.hpp"

// Publisher类：实现
Publisher::Publisher(const std::string &name_): name {name_} {
}


// Book类: 实现
Book::Book(const std::string &name_ , const std::string &author_ ): Publisher{name_}, author{author_} {
}

void Book::publish() const {
    std::cout << "Publishing book《" << name << "》 by " << author << '\n';
}

void Book::use() const {
    std::cout << "Reading book 《" << name << "》 by " << author << '\n';
}


// Film类：实现
Film::Film(const std::string &name_, const std::string &director_):Publisher{name_},director{director_} {
}

void Film::publish() const {
    std::cout << "Publishing film <" << name << "> directed by " << director << '\n';
}

void Film::use() const {
    std::cout << "Watching film <" << name << "> directed by " << director << '\n';
}


// Music类：实现
Music::Music(const std::string &name_, const std::string &artist_): Publisher{name_}, artist{artist_} {
}

void Music::publish() const {
    std::cout << "Publishing music <" << name << "> by " << artist << '\n';
}

void Music::use() const {
    std::cout << "Listening to music <" << name << "> by " << artist << '\n';
}

#pragma once

#include <string>

// 发行/出版物类：Publisher （抽象类）
class Publisher {
public:
    Publisher(const std::string &name_ = "");            // 构造函数
    virtual ~Publisher() = default;

public:
    virtual void publish() const = 0;                 // 纯虚函数，作为接口继承
    virtual void use() const = 0;                     // 纯虚函数，作为接口继承

protected:
    std::string name;    // 发行/出版物名称
};

// 图书类: Book
class Book: public Publisher {
public:
    Book(const std::string &name_ = "", const std::string &author_ = "");  // 构造函数

public:
    void publish() const override;        // 接口
    void use() const override;            // 接口

private:
    std::string author;          // 作者
};

// 电影类: Film
class Film: public Publisher {
public:
    Film(const std::string &name_ = "", const std::string &director_ = "");   // 构造函数

public:
    void publish() const override;    // 接口
    void use() const override;        // 接口            

private:
    std::string director;        // 导演
};


// 音乐类：Music
class Music: public Publisher {
public:
    Music(const std::string &name_ = "", const std::string &artist_ = "");

public:
    void publish() const override;        // 接口
    void use() const override;            // 接口

private:
    std::string artist;      // 音乐艺术家名称
};

#include <memory>
#include <iostream>
#include <vector>
#include "publisher.hpp"

void test1() {
   std::vector<Publisher *> v;

   v.push_back(new Book("Harry Potter", "J.K. Rowling"));
   v.push_back(new Film("The Godfather", "Francis Ford Coppola"));
   v.push_back(new Music("Blowing in the wind", "Bob Dylan"));

   for(Publisher *ptr: v) {
        ptr->publish();
        ptr->use();
        std::cout << '\n';
        delete ptr;
   }
}

void test2() {
    std::vector<std::unique_ptr<Publisher>> v;

    v.push_back(std::make_unique<Book>("Harry Potter", "J.K. Rowling"));
    v.push_back(std::make_unique<Film>("The Godfather", "Francis Ford Coppola"));
    v.push_back(std::make_unique<Music>("Blowing in the wind", "Bob Dylan"));

    for(const auto &ptr: v) {
        ptr->publish();
        ptr->use();
        std::cout << '\n';
    }
}

void test3() {
    Book book("A Philosophy of Software Design", "John Ousterhout");
    book.publish();
    book.use();
}

int main() {
    std::cout << "运行时多态：纯虚函数、抽象类\n";

    std::cout << "\n测试1: 使用原始指针\n";
    test1();

    std::cout << "\n测试2: 使用智能指针\n";

    test2();

    std::cout << "\n测试3: 直接使用类\n";
    test3();
}

2.运行测试截图

3.问题回答

问题一：

答：

（1）Publisher类中包含了纯虚函数,所以它是抽象类。具体依据是 在Publisher类的声明中,有纯虚函数:virtual void publish() const=0; 和 virtual void use() const=0

（2）不能，抽象类不能实例化对象。

问题二：

答：

（1）必须实现publish() 和 use() 这两个纯虚函数。

void publish() const override;

void use() const override;

 （2）报错信息会提示函数签名不匹配,因为基类中的虚函数是const成员函数,派生类中的重写版本必须保持const属性。报错信息error: 'virtual void Film::publish()' marked 'override', but does not override 因为去掉const后,函数签名与基类不同,不能重写基类的纯虚函数。

问题三：

答：

（1）ptr 的声明类型是Publisher*，指向 Publish基类的指针

（2）Book,Film,Music

 （3）声明为 virtual 是为了实现多态销毁，确保通过基类指针删除派生类对象时，能够正确调用派生类的析构函数。

如果删除 virtual：当执行 delete ptr; 时，只会调用基类 Publisher 的析构函数，派生类（Book、Film、Music）的析构函数不会被调用可能导致派生类资源无法正确释放，造成内存泄漏

 

实验任务2：

1.源代码

#include <iomanip>
#include <iostream>
#include <string>
#include "book.hpp"


// 图书描述信息类Book: 实现
Book::Book(const std::string &name_, 
          const std::string &author_, 
          const std::string &translator_, 
          const std::string &isbn_, 
          double price_):name{name_}, author{author_}, translator{translator_}, isbn{isbn_}, price{price_} {
}

// 运算符<<重载实现
std::ostream& operator<<(std::ostream &out, const Book &book) {
    using std::left;
    using std::setw;
    
    out << left;
    out << setw(15) << "书名:" << book.name << '\n'
        << setw(15) << "作者:" << book.author << '\n'
        << setw(15) << "译者:" << book.translator << '\n'
        << setw(15) << "ISBN:" << book.isbn << '\n'
        << setw(15) << "定价:" << book.price;

    return out;
}

#pragma once
#include <string>

// 图书描述信息类Book: 声明
class Book {
public:
    Book(const std::string &name_, 
         const std::string &author_, 
         const std::string &translator_, 
         const std::string &isbn_, 
         double price_);

    friend std::ostream& operator<<(std::ostream &out, const Book &book);

private:
    std::string name;        // 书名
    std::string author;      // 作者
    std::string translator;  // 译者
    std::string isbn;        // isbn号
    double price;        // 定价
};

#include <iomanip>
#include <iostream>
#include <string>
#include "booksale.hpp"

// 图书销售记录类BookSales：实现
BookSale::BookSale(const Book &rb_, 
                   double sales_price_, 
                   int sales_amount_): rb{rb_}, sales_price{sales_price_}, sales_amount{sales_amount_} {
}

int BookSale::get_amount() const {
    return sales_amount;
}

double BookSale::get_revenue() const {
    return sales_amount * sales_price;
}

// 运算符<<重载实现
std::ostream& operator<<(std::ostream &out, const BookSale &item) {
    using std::left;
    using std::setw;
    
    out << left;
    out << item.rb << '\n'
        << setw(15) << "售价:" << item.sales_price << '\n'
        << setw(15) << "销售数量:" << item.sales_amount << '\n'
        << setw(15) << "营收:" << item.get_revenue();

    return out;
}

#pragma once

#include <string>
#include "book.hpp"

// 图书销售记录类BookSales：声明
class BookSale {
public:
    BookSale(const Book &rb_, double sales_price_, int sales_amount_);
    int get_amount() const;   // 返回销售数量
    double get_revenue() const;   // 返回营收
    
    friend std::ostream& operator<<(std::ostream &out, const BookSale &item);

private:
    Book rb;         
    double sales_price;      // 售价
    int sales_amount;       // 销售数量
};

#include <algorithm>
#include <iomanip>
#include <iostream>
#include <string>
#include <vector>
#include "booksale.hpp"

// 按图书销售数量比较
bool compare_by_amount(const BookSale &x1, const BookSale &x2) {
    return x1.get_amount() > x2.get_amount();
}

void test() {
    using std::cin;
    using std::cout;
    using std::getline;
    using std::sort;
    using std::string;
    using std::vector;
    using std::ws;

    vector<BookSale> sales_records;         // 图书销售记录表

    int books_number;
    cout << "录入图书数量: ";
    cin >> books_number;

    cout << "录入图书销售记录\n";
    for(int i = 0; i < books_number; ++i) {
        string name, author, translator, isbn;
        double price;
        cout << string(20, '-') << "第" << i+1 << "本图书信息录入" << string(20, '-') << '\n';
        cout << "录入书名: "; getline(cin>>ws, name);
        cout << "录入作者: "; getline(cin>>ws, author);
        cout << "录入译者: "; getline(cin>>ws, translator);
        cout << "录入isbn: "; getline(cin>>ws, isbn);
        cout << "录入定价: "; cin >> price;

        Book book(name, author, translator, isbn, price);

        double sales_price;
        int sales_amount;

        cout << "录入售价: "; cin >> sales_price;
        cout << "录入销售数量: "; cin >> sales_amount;

        BookSale record(book, sales_price, sales_amount);
        sales_records.push_back(record);
    }

    // 按销售册数排序
    sort(sales_records.begin(), sales_records.end(), compare_by_amount);

    // 按销售册数降序输出图书销售信息
    cout << string(20, '=') <<  "图书销售统计" << string(20, '=') << '\n';
    for(auto &record: sales_records) {
        cout << record << '\n';
        cout << string(40, '-') << '\n';
    }
}

int main() {
    test();
}

2.运行测试截图

 3.问题回答

问题一：

答：

（1）运算符<<被重载了两处，

第一处:在book.hpp中声明,在book.cpp中实现,用于输出Book类对象。

第二处:在booksale.hpp中声明,在booksale.cpp中实现,用于输出BookSale类对象。

 （2）在task2.cpp的test()函数中，使用重载<<输出BookSale对象的代码：

for(auto &t: sales_Ist) {
　　cout << t << endl;
　　cout << string(40, '-') << endl;
}

问题二：

（1）1. 定义比较函数：

bool compare_by_amount(const BookSale &x1, const BookSale &x2) {
　　return x1.get_amount() > x2.get_amount();
｝

该函数通过比较get_amount()返回值实现降序排序

2. 使用标准库sort函数排序：

sort(sales_Ist.begin(), sales_Ist.end(), compare_by_amount);

将比较函数作为第三个参数传递给sort()函数

（2）使用lambda表达式替代单独的比较函数：

sort(sales_Ist.begin(), sales_Ist.end(),
　　[](const BookSale &x1, const BookSale &x2) {
　　return x1.get_amount() > x2.get_amount();
　});

这样可以省去单独定义compare_by_amount函数的步骤，使代码更简洁，逻辑更集中。

 

实验任务3:

Task3_1

1.源代码

#include <iostream>

// 类A的定义
class A {
public:
    A(int x0, int y0);
    void display() const;

private:
    int x, y;
};

A::A(int x0, int y0): x{x0}, y{y0} {
}

void A::display() const {
    std::cout << x << ", " << y << '\n';
}

// 类B的定义
class B {
public:
    B(double x0, double y0);
    void display() const;

private:
    double x, y;
};

B::B(double x0, double y0): x{x0}, y{y0} {
}

void B::display() const {
    std::cout << x << ", " << y << '\n';
}

void test() {
    std::cout << "测试类A: " << '\n';
    A a(3, 4);
    a.display();

    std::cout << "\n测试类B: " << '\n';
    B b(3.2, 5.6);
    b.display();
}

int main() {
    test();
}

2.运行测试截图

 Task3_2

1.源代码

#include <iostream>
#include <string>

// 定义类模板
template<typename T>
class X{
public:
    X(T x0, T y0);
    void display();

private:
    T x, y;
};

template<typename T>
X<T>::X(T x0, T y0): x{x0}, y{y0} {
}

template<typename T>
void X<T>::display() {
    std::cout << x << ", " << y << '\n';
}


void test() {
    std::cout << "测试1: 用int实例化类模板X" << '\n';
    X<int> x1(3, 4);
    x1.display();

    std::cout << "\n测试2:用double实例化类模板X" << '\n';
    X<double> x2(3.2, 5.6);
    x2.display();

    std::cout << "\n测试3: 用string实例化类模板X" << '\n';
    X<std::string> x3("hello", "oop");
    x3.display();
}

int main() {
    test();
}

2.运行测试截图

 

实验任务4：

1.源代码

#ifndef PET_HPP
#define PET_HPP

#include <string>
#include <iostream>

// 抽象基类：机器宠物类 MachinePet
class MachinePet {
private:
    std::string nickname; 
public:
    MachinePet(const std::string& name) : nickname(name) {}

    virtual ~MachinePet() = default;

    std::string get_nickname() const {
        return nickname;
    }

    virtual std::string talk() const = 0;
};

// 电子宠物猫类：继承自 MachinePet
class PetCat : public MachinePet {
public:
    PetCat(const std::string& name) : MachinePet(name) {}

    std::string talk() const override {
        return "miao wu~";
    }
};

// 电子宠物狗类：继承自 MachinePet
class PetDog : public MachinePet {
public:
    PetDog(const std::string& name) : MachinePet(name) {}

    std::string talk() const override {
        return "wang wang~";
    }
};

#include <iostream>
#include <memory>
#include <vector>
#include "pet.hpp"

void test1() {
    std::vector<MachinePet *> pets;

    pets.push_back(new PetCat("miku"));
    pets.push_back(new PetDog("da huang"));

    for(MachinePet *ptr: pets) {
        std::cout << ptr->get_nickname() << " says " << ptr->talk() << '\n';
        delete ptr;  // 须手动释放资源
    }   
}

void test2() {
    std::vector<std::unique_ptr<MachinePet>> pets;

    pets.push_back(std::unique_ptr<MachinePet>(new PetCat("miku")));
    pets.push_back(std::unique_ptr<MachinePet>(new PetDog("da huang")));

    for(auto const &ptr: pets)
        std::cout << ptr->get_nickname() << " says " << ptr->talk() << '\n';
}

void test3() {
    // MachinePet pet("little cutie");   // 编译报错：无法定义抽象类对象

    const PetCat cat("miku");
    std::cout << cat.get_nickname() << " says " << cat.talk() << '\n';

    const PetDog dog("da huang");
    std::cout << dog.get_nickname() << " says " << dog.talk() << '\n';
}

int main() {
    std::cout << "测试1: 使用原始指针\n";
    test1();

    std::cout << "\n测试2: 使用智能指针\n";
    test2();

    std::cout << "\n测试3: 直接使用类\n";
    test3();
}

2.运行测试截图

 实验任务5：

1.源代码

#ifndef COMPLEX_HPP
#define COMPLEX_HPP

#include <iostream>

template <typename T>
class Complex {
private:
    T real;   
    T image;  
public:
    Complex() : real(0), image(0) {}
    Complex(T r, T i) : real(r), image(i) {}
    Complex(const Complex& other) : real(other.real), image(other.image) {}

    T get_real() const { return real; }
    T get_image() const { return image; }

    Complex& operator+=(const Complex& other) {
        real += other.real;
        image += other.image;
        return *this;
    }

    bool operator==(const Complex& other) const {
        return (real == other.real) && (image == other.image);
    }

    template <typename U>
    friend Complex<U> operator+(const Complex<U>& c1, const Complex<U>& c2);

    template <typename U>
    friend std::ostream& operator<<(std::ostream& os, const Complex<U>& c);

    template <typename U>
    friend std::istream& operator>>(std::istream& is, Complex<U>& c);
};

template <typename U>
Complex<U> operator+(const Complex<U>& c1, const Complex<U>& c2) {
    Complex<U> res(c1);
    res += c2;
    return res;
}

template <typename U>
std::ostream& operator<<(std::ostream& os, const Complex<U>& c) {
    os << c.real;
    if (c.image >= 0) {
        os << " + " << c.image << "i";
    } else {
        os << " - " << -c.image << "i";
    }
    return os;
}

template <typename U>
std::istream& operator>>(std::istream& is, Complex<U>& c) {
    is >> c.real >> c.image;
    return is;
}

#include <iostream>
#include "Complex.hpp"

void test1() {
    using std::cout;
    using std::boolalpha;
    
    Complex<int> c1(2, -5), c2(c1);

    cout << "c1 = " << c1 << '\n';
    cout << "c2 = " << c2 << '\n';
    cout << "c1 + c2 = " << c1 + c2 << '\n';
    
    c1 += c2;
    cout << "c1 = " << c1 << '\n';
    cout << boolalpha << (c1 == c2) << '\n';
}

void test2() {
    using std::cin;
    using std::cout;

    Complex<double> c1, c2;
    cout << "Enter c1 and c2: ";
    cin >> c1 >> c2;
    cout << "c1 = " << c1 << '\n';
    cout << "c2 = " << c2 << '\n';

    const Complex<double> c3(c1);
    cout << "c3.real = " << c3.get_real() << '\n';
    cout << "c3.imag = " << c3.get_image() << '\n';
}

int main() {
    std::cout << "自定义类模板Complex测试1: \n";
    test1();

    std::cout << "\n自定义类模板Complex测试2: \n";
    test2();
}

2.运行测试截图