实验五

实验五

实验任务一

源代码：

#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();
}

#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';
}

运行结果：

 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：

含有纯虚函数的类为抽象类，Publisher 类中声明了virtual void publish() const = 0和virtual void use() const = 0两个纯虚函数，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？

答：

不能编译通过。因为 Publisher 是抽象类，抽象类的核心特性是不能实例化对象，直接声明Publisher p;会触发编译错误。

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：

void publish() const override和 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：

 

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：

ptr 的声明类型是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）

答：

实际指向的对象类型按顺序为：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：

基类析构函数声明为 virtual 是为了实现多态析构；若删除 virtual，执行delete ptr;时仅调用基类析构函数，派生类的资源无法释放，造成内存泄漏。

 

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
};

#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>
#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 <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;
}

#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();
}

运行结果：

 

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：

重载了 2 处，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。

答：

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：cout << record << '\n';（record 为 BookSale 对象，内部调用 Book 的 << 重载）

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？

答：

首先定义比较函数compare_by_amount，该函数接收两个BookSale对象，返回第一个对象的销售数量大于第二个对象的销售数量；然后调用标准库sort函数，传入销售记录向量的起始迭代器、结束迭代器和比较函数，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"？ 

答：

lambda 表达式实现：sort(sales_records.begin(), sales_records.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();
}

运行结果：

#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：

 

实验任务四

源代码：

#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~"; }
};

#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：

 

实验任务五

源代码：

#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) {
        Complex temp = c1;
        temp += c2;
        return temp;
    }
    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 << "+" << c.imag << "i";
        } else {
            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; 
};

#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();
}

测试结果：