Test5

任务一

源代码

publisher.hpp

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#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
};

publisher.cpp

点我展开代码

#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';
}

task1

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#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();
}

结果展示

实验结论

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。

答：该类里面有纯虚函数。

virtual void publish() const = 0;
virtual void use() const = 0;

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

答：不能编译通过。
因为Publisher类是抽象类，无法实例化。

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

答：publish()和use()函数必须实现。

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？

答：前后声明不一致。

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？

答: 基类指针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）

答：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？

答：为了确保通过基类指针调用派生类的析构函数删除派生类对象。基类对象被删除，而派生类对象无法删除，造成内存泄漏。

任务二

源代码

book.hpp

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#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
};

book.cpp

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#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;
}

booksale.hpp

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#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
};

booksale.cpp

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#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;
}

task2.cpp

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#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();
}

结果展示

实验结论

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？

答：两次。分别用于Book和Booksale类型。

（2）找出使用重载<<输出对象的代码，写在下面。

答：

out << item.rb << '\n' 第一处输出Book
cout << record << '\n' 第二处输出Booksale

问题2：图书销售统计

（1）"按销售数量降序排序"，描述降序排序实现方式。

答：std::sort()配合自定义比较函数compare_by_amount实现降序排序。
compare_by_amount函数在task2.cpp中已经提前实现。

（2）拓展（选答*）：如果使用lambda表达式，如何实现？

答：

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

任务四

源代码

pet.hpp

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#pragma once
#include <string>
#include <iostream>
using namespace std;

class MachinePet
{
public:
    virtual ~MachinePet() = default;
    virtual const char *get_nickname() const = 0;
    virtual const char *talk() const = 0;
};
class PetCat : public MachinePet
{
public:
    PetCat(const char *name) : nickname(name) {}
    const char *get_nickname() const override
    {
        return nickname.c_str();
    }
    const char *talk() const override
    {
        return "miao miao";
    }

private:
    string nickname;
};
class PetDog : public MachinePet
{
public:
    PetDog(const char *name) : nickname(name) {}
    const char *get_nickname() const override
    {
        return nickname.c_str();
    }
    const char *talk() const override
    {
        return "wang wang";
    }

private:
    string nickname;
};

task4.cpp

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#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();
}

结果展示

任务五

源代码

Complex.hpp

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#pragma once
#include <iostream>

template <typename T>
class Complex
{
public:
    Complex(T r = 0, T i = 0) : real(r), imag(i) {}
    Complex(const Complex &c) : real(c.real), imag(c.imag) {}

    T get_real() const { return real; }
    T get_imag() const { return imag; }

    Complex operator+(const Complex &c) const
    {
        return Complex(real + c.real, imag + c.imag);
    }

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

    bool operator==(const Complex &c) const
    {
        return real == c.real && imag == c.imag;
    }

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

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

private:
    T real, imag;
};

template <typename T>
std::ostream &operator<<(std::ostream &out, const Complex<T> &c)
{
    out << c.real << c.imag << 'i';
    return out;
}

template <typename T>
std::istream &operator>>(std::istream &in, Complex<T> &c)
{
    in >> c.real >> c.imag;
    return in;
}

task5.cpp

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#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();
}

结果展示