实验5 多态

实验任务一：

源代码：

 

#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 <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';
}

#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();
}

 

 

运行结果截图：

 

 回答问题：

问题1：抽象类机制

（1）是什么决定了 Publisher 是抽象类？用一句话说明，并指出代码中的具体依据。

　　含有纯虚函数。

　　代码中的依据：virtual void publish() const = 0

　　　　　　　　　virtual void use() const = 0

　　声明了两个纯虚函数，因此是抽象类。

 

（2）如果在 main.cpp 里直接写 Publisher p; 能否编译通过？为什么？

　　不能编译通过。因为 Publisher 是抽象类，抽象类无法实例化对象。

 

问题2：纯虚函数与接口继承

（1） Book 、 Film 、 Music 必须实现哪两个函数才能通过编译？请写出其完整函数声明。

　　void publish() const override;
　　void use() const override;

 

（2） 在 publisher.cpp 的 Film 类实现中，把两个成员函数实现里的 const 去掉（保持函数体不变），重新 编译，报错信息是什么？

 　　对非静态成员“Publisher::name”的非法引用。

 

问题3：运行时多态与虚析构

（1）在 test1() 里，for (Publisher *ptr : v) 中 ptr 的声明类型是什么？

　　Publisher 类的指针：Publisher*

（2）当循环执行到 ptr->publish(); 时，ptr 实际指向的对象类型分别有哪些？（按循环顺序写出）

　　Book、Film、Music。

（3）基类 Publisher 的析构函数为何声明为 virtual？若删除 virtual，执行 delete ptr; 会出现什么 问题？

　　 基类Publisher的析构函数声明为 virtual 是为了实现多态析构，确保能够正确删除派生类对象，避免内存泄漏。若删除 virtual，执行 delete ptr 时只会调用基类的析构函数，派生类的成员不会被删除，导致内存泄漏。

 

实验任务二：

源代码：

#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
};

#pragma once

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

// 图书销售记录类BookSale: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;                // 图书信息
    double sales_price;     // 售价
    int sales_amount;       // 销售数量
};

#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;
}

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

// 图书销售记录类BookSale: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;
}

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

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

void test() {
    using namespace std;

    vector<BookSale> sales_lst; // 存放图书销售记录

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

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

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

        float 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_lst.push_back(record);
    }

    // 按销售册数排序
    sort(sales_lst.begin(), sales_lst.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, '=') << endl;
    for (auto& t : sales_lst) {
        cout << t << endl;
        cout << string(40, '-') << endl;
    }
}

int main() {
    test();
}

运行结果截图：

回答问题：

问题1：重载运算符<<
（1）找出运算符<<被重载了几处？分别用于什么类型？

　　两处；Book和Booksale类型。
（2）找出使用重载<<输出对象的代码，写在下面。

 book.cpp中
std::ostream& operator<<(std::ostream &out, const Book &book);

booksale.cpp中
std::ostream& operator<<(std::ostream &out, const BookSale &item);

task2.cpp中调用
cout << t << endl; 

问题2：图书销售统计
（1）图书销售记录"按销售数量降序排序"，代码是如何实现的？

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

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

　　使用标准库函数sort和自定义函数compare_by_amount实现按销售数量降序排序。
（2）拓展（选答*）：如果使用lambda表达式，如何实现"按销售数量降序排序"？

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

实验任务三：

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();
}

#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();
}

运行结果截图：

 

 实验任务四：

源代码：

#pragma once

#include<string>
using namespace std;

class MachinePet {
private:
    string nickname;
public:
    MachinePet(const string name):nickname{name} {}
    virtual ~MachinePet() = default;

    string get_nickname() const{
        return nickname;
    }
    virtual string talk() const = 0;
};
class PetCat : public MachinePet {
public:
   
    PetCat(const string& nickname_) : MachinePet( nickname_ ) {}

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

class PetDog : public MachinePet {
public:
   
    PetDog(const string& nickname_) : MachinePet(nickname_ ) {}

    
    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::make_unique<PetCat>("miku"));
    pets.push_back(std::make_unique<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();
}

 

运行结果截图：

 

实验任务五：

源代码：

 

#pragma once

#include<iostream>
using namespace std;

template<typename T>

class Complex {
private:
    T real, imag;
public:
    Complex(T a=0,T b=0):real{a},imag{b} {}
    Complex(const Complex& c) {
        real = c.real;
        imag = c.imag;
    }
    ~Complex() = default;

    T get_real() const {
        return real;
    }
    T get_imag() const {
        return imag;
    }
    void operator+=(const Complex& other) {
        this->real += other.real;
        this->imag += other.imag;
    }

    friend Complex operator+(const Complex& c1, const Complex& c2) {
        Complex temp;
        temp.real = c1.real + c2.real;
        temp.imag = c1.imag + c2.imag;
        return temp;
    }

    friend bool operator==(const Complex& c1, const Complex& c2) {
        return (c1.real == c2.real) && (c1.imag == c2.imag);
    }

    
    friend ostream& operator<<(ostream& out, const Complex& c) {
        
        if (c.imag >= 0) {
            out <<c.real<< "+" << c.imag << "i";
        }
        else {
            out <<c.real<< c.imag << "i";
        }
        return out;
    }

     friend istream& operator>>(istream& in, Complex& c) {
        in >> c.real >> c.imag;
        return in;
    }

};

#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_imag() << '\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();
}

 

运行结果截图：

 

 

实验总结：

 

1.深入理解了抽象类与纯虚函数的机制：抽象类通过纯虚函数定义接口，强制派生类实现具体功能，有效规范了类的继承体系，同时抽象类无法实例化的特性避免了不合理的对象创建。

2.复习了运算符重载相关代码。

3.重温了类模板的定义与使用，类模板将类型参数化，有效减少了代码量。