实验五

实验任务1

源代码如下：

publisher.hpp

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#pragma once
#include <string>

class Publisher {
public:
    Publisher(const std::string &name_ = "");           
    virtual ~Publisher() = default;

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

protected:
    std::string name;    
};

class Book: public Publisher {
public:
    Book(const std::string &name_ = "", const std::string &author_ = "");  

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

private:
    std::string author;          
};

class Film: public Publisher {
public:
    Film(const std::string &name_ = "", const std::string &director_ = "");   

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

private:
    std::string director;        
};

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

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

private:
    std::string artist;      
};

publisher.cpp

点击查看代码

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

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

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::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::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.cpp

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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();
}

运行截图：

问题回答：

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。
包含纯虚函数，Publisher中有virtual void publish() const = 0和virtual void use() const = 0两个纯虚函数。
（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，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。
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？
成员函数与基类纯虚函数声明不匹配，缺少const修饰。
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基类指针。
（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？
为了实现析构函数的多态，确保删除基类指针时调用派生类析构函数。
若删除virtual，仅调用基类析构函数，会导致派生类资源泄漏。

实验任务2

源代码如下：

book.hpp

点击查看代码

#pragma once
#include <string>

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;        
    std::string author;     
    std::string translator;  
    std::string isbn;        
    double price;      
};

book.cpp

点击查看代码

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

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_} {
}

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

点击查看代码

#pragma once

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

class BookSale {
public:
    BookSale(const Book &rb_, double sales_price_, int sales_amount_);
    int get_amount() const;   
    double get_revenue() const;   
    
    friend std::ostream& operator<<(std::ostream &out, const BookSale &item);

private:
    Book rb;         
    double sales_price;      
    int sales_amount;     
};

booksale.cpp

点击查看代码

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

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;
}

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"

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;         

    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);
    }

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

    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();
}

运行截图：

问题回答：

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？
2 处重载，分别用于Book类型和BookSale类型。
（2）找出使用重载 << 输出对象的代码，写在下面。
cout << item.rb << '\n'（book.cpp）；
cout << t << endl（task2.cpp）；
cout << item << '\n'（booksale.cpp）。
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？
定义比较函数compare_by_amount(),调用sort( sales_lst.begin(),sales_lst.end(),compare_by_amount)实现降序排序。

实验任务4

源代码如下：

pet.hpp

点击查看代码

#pragma once
#include <string>

class MachinePet {
public:
    MachinePet(const std::string &nickname_) : nickname(nickname_) {}
    virtual ~MachinePet() = default; 

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

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

protected:
    std::string nickname;
};

class PetCat : public MachinePet {
public:
    PetCat(const std::string &nickname_) : MachinePet(nickname_) {}
    std::string talk() const override {
        return "miao wu~";
    }
};

class PetDog : public MachinePet {
public:
    PetDog(const std::string &nickname_) : MachinePet(nickname_) {}
    std::string talk() const override {
        return "wang wang~";
    }
};

task4.cpp

点击查看代码

#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;  
    }   
}

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();
}

运行截图：

实验任务5

源代码如下：

Complex.hpp

点击查看代码

#pragma once
#include <iostream>

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

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

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

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

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

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

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

private:
    T real; 
    T imag; 
};

task5.cpp

点击查看代码

#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();
}

运行截图：