实验5 多态

实验5

实验任务1

源代码

 1 #pragma once
 2 
 3 #include <string>
 4 
 5 // 发行/出版物类：Publisher （抽象类）
 6 class Publisher {
 7 public:
 8     Publisher(const std::string &name_ = "");            // 构造函数
 9     virtual ~Publisher() = default;
10 
11 public:
12     virtual void publish() const = 0;                 // 纯虚函数，作为接口继承
13     virtual void use() const = 0;                     // 纯虚函数，作为接口继承
14 
15 protected:
16     std::string name;    // 发行/出版物名称
17 };
18 
19 // 图书类: Book
20 class Book: public Publisher {
21 public:
22     Book(const std::string &name_ = "", const std::string &author_ = "");  // 构造函数
23 
24 public:
25     void publish() const override;        // 接口
26     void use() const override;            // 接口
27 
28 private:
29     std::string author;          // 作者
30 };
31 
32 // 电影类: Film
33 class Film: public Publisher {
34 public:
35     Film(const std::string &name_ = "", const std::string &director_ = "");   // 构造函数
36 
37 public:
38     void publish() const override;    // 接口
39     void use() const override;        // 接口            
40 
41 private:
42     std::string director;        // 导演
43 };
44 
45 
46 // 音乐类：Music
47 class Music: public Publisher {
48 public:
49     Music(const std::string &name_ = "", const std::string &artist_ = "");
50 
51 public:
52     void publish() const override;        // 接口
53     void use() const override;            // 接口
54 
55 private:
56     std::string artist;      // 音乐艺术家名称
57 };
publisher.hpp
 1 #include <iostream>
 2 #include <string>
 3 #include "publisher.hpp"
 4 
 5 // Publisher类：实现
 6 Publisher::Publisher(const std::string &name_): name {name_} {
 7 }
 8 
 9 
10 // Book类: 实现
11 Book::Book(const std::string &name_ , const std::string &author_ ): Publisher{name_}, author{author_} {
12 }
13 
14 void Book::publish() const {
15     std::cout << "Publishing book《" << name << "》 by " << author << '\n';
16 }
17 
18 void Book::use() const {
19     std::cout << "Reading book 《" << name << "》 by " << author << '\n';
20 }
21 
22 
23 // Film类：实现
24 Film::Film(const std::string &name_, const std::string &director_):Publisher{name_},director{director_} {
25 }
26 
27 void Film::publish() const {
28     std::cout << "Publishing film <" << name << "> directed by " << director << '\n';
29 }
30 
31 void Film::use() const {
32     std::cout << "Watching film <" << name << "> directed by " << director << '\n';
33 }
34 
35 
36 // Music类：实现
37 Music::Music(const std::string &name_, const std::string &artist_): Publisher{name_}, artist{artist_} {
38 }
39 
40 void Music::publish() const {
41     std::cout << "Publishing music <" << name << "> by " << artist << '\n';
42 }
43 
44 void Music::use() const {
45     std::cout << "Listening to music <" << name << "> by " << artist << '\n';
46 }
publisher.cpp
 1 #include <memory>
 2 #include <iostream>
 3 #include <vector>
 4 #include "publisher.hpp"
 5 
 6 void test1() {
 7    std::vector<Publisher *> v;
 8 
 9    v.push_back(new Book("Harry Potter", "J.K. Rowling"));
10    v.push_back(new Film("The Godfather", "Francis Ford Coppola"));
11    v.push_back(new Music("Blowing in the wind", "Bob Dylan"));
12 
13    for(Publisher *ptr: v) {
14         ptr->publish();
15         ptr->use();
16         std::cout << '\n';
17         delete ptr;
18    }
19 }
20 
21 void test2() {
22     std::vector<std::unique_ptr<Publisher>> v;
23 
24     v.push_back(std::make_unique<Book>("Harry Potter", "J.K. Rowling"));
25     v.push_back(std::make_unique<Film>("The Godfather", "Francis Ford Coppola"));
26     v.push_back(std::make_unique<Music>("Blowing in the wind", "Bob Dylan"));
27 
28     for(const auto &ptr: v) {
29         ptr->publish();
30         ptr->use();
31         std::cout << '\n';
32     }
33 }
34 
35 void test3() {
36     Book book("A Philosophy of Software Design", "John Ousterhout");
37     book.publish();
38     book.use();
39 }
40 
41 int main() {
42     std::cout << "运行时多态：纯虚函数、抽象类\n";
43 
44     std::cout << "\n测试1: 使用原始指针\n";
45     test1();
46 
47     std::cout << "\n测试2: 使用智能指针\n";
48     test2();
49 
50     std::cout << "\n测试3: 直接使用类\n";
51     test3();
52 }
task1.cpp

运行结果

image

问题解答

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。
含有纯虚函数的类是抽象类，Publisher类中声明了publish() 和use() 两个纯虚函数，所以是抽象类。
依据：
1 virtual void publish() const = 0；
2 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？
不能编译通过，Publisher含有纯虚函数（publish()和use()），因此是抽象类，抽象类不能实例化，因此会产生错误。
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。
继承自 Publisher 的两个纯虚函数publish()const和use()const:
1     void publish() const override;        // 接口
2     void use() const override;            // 接口
（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？

报错信息：

image

原因：基类Publisher的publish()和use()声明为const成员函数，派生类Film去掉 const，其导致函数签名与基类不匹配。

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？
声明类型：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？
原因：这样有利于实现实现多态析构，确保通过基类指针删除派生类对象时，会先调用派生类析构函数，再调用基类析构函数，从而避免内存泄漏的问题。

删除virtual的问题：析构函数不再具备多态性，通过Publisher* 指针删除派生类对象时，只会调用基类Publisher的析构函数，派生类特有的成员不会被正确析构，则会导致内存泄漏。

 

实验任务2

源代码

 1 #pragma once
 2 #include <string>
 3 
 4 // 图书描述信息类Book: 声明
 5 class Book {
 6 public:
 7     Book(const std::string &name_, 
 8          const std::string &author_, 
 9          const std::string &translator_, 
10          const std::string &isbn_, 
11          double price_);
12 
13     friend std::ostream& operator<<(std::ostream &out, const Book &book);
14 
15 private:
16     std::string name;        // 书名
17     std::string author;      // 作者
18     std::string translator;  // 译者
19     std::string isbn;        // isbn号
20     double price;        // 定价
21 };
book.hpp
 1 #pragma once
 2 
 3 #include <string>
 4 #include "book.hpp"
 5 
 6 // 图书销售记录类BookSales：声明
 7 class BookSale {
 8 public:
 9     BookSale(const Book &rb_, double sales_price_, int sales_amount_);
10     int get_amount() const;   // 返回销售数量
11     double get_revenue() const;   // 返回营收
12     
13     friend std::ostream& operator<<(std::ostream &out, const BookSale &item);
14 
15 private:
16     Book rb;         
17     double sales_price;      // 售价
18     int sales_amount;       // 销售数量
19 };
booksale.hpp
 1 #include <iomanip>
 2 #include <iostream>
 3 #include <string>
 4 #include "book.hpp"
 5 
 6 
 7 // 图书描述信息类Book: 实现
 8 Book::Book(const std::string &name_, 
 9           const std::string &author_, 
10           const std::string &translator_, 
11           const std::string &isbn_, 
12           double price_):name{name_}, author{author_}, translator{translator_}, isbn{isbn_}, price{price_} {
13 }
14 
15 // 运算符<<重载实现
16 std::ostream& operator<<(std::ostream &out, const Book &book) {
17     using std::left;
18     using std::setw;
19     
20     out << left;
21     out << setw(15) << "书名:" << book.name << '\n'
22         << setw(15) << "作者:" << book.author << '\n'
23         << setw(15) << "译者:" << book.translator << '\n'
24         << setw(15) << "ISBN:" << book.isbn << '\n'
25         << setw(15) << "定价:" << book.price;
26 
27     return out;
28 }
book.cpp
 1 #include <iomanip>
 2 #include <iostream>
 3 #include <string>
 4 #include "booksale.hpp"
 5 
 6 // 图书销售记录类BookSales：实现
 7 BookSale::BookSale(const Book &rb_, 
 8                    double sales_price_, 
 9                    int sales_amount_): rb{rb_}, sales_price{sales_price_}, sales_amount{sales_amount_} {
10 }
11 
12 int BookSale::get_amount() const {
13     return sales_amount;
14 }
15 
16 double BookSale::get_revenue() const {
17     return sales_amount * sales_price;
18 }
19 
20 // 运算符<<重载实现
21 std::ostream& operator<<(std::ostream &out, const BookSale &item) {
22     using std::left;
23     using std::setw;
24     
25     out << left;
26     out << item.rb << '\n'
27         << setw(15) << "售价:" << item.sales_price << '\n'
28         << setw(15) << "销售数量:" << item.sales_amount << '\n'
29         << setw(15) << "营收:" << item.get_revenue();
30 
31     return out;
32 }
booksale.cpp
 1 #include <algorithm>
 2 #include <iomanip>
 3 #include <iostream>
 4 #include <string>
 5 #include <vector>
 6 #include "booksale.hpp"
 7 
 8 // 按图书销售数量比较
 9 bool compare_by_amount(const BookSale &x1, const BookSale &x2) {
10     return x1.get_amount() > x2.get_amount();
11 }
12 
13 void test() {
14     using std::cin;
15     using std::cout;
16     using std::getline;
17     using std::sort;
18     using std::string;
19     using std::vector;
20     using std::ws;
21 
22     vector<BookSale> sales_records;         // 图书销售记录表
23 
24     int books_number;
25     cout << "录入图书数量: ";
26     cin >> books_number;
27 
28     cout << "录入图书销售记录\n";
29     for(int i = 0; i < books_number; ++i) {
30         string name, author, translator, isbn;
31         double price;
32         cout << string(20, '-') << "第" << i+1 << "本图书信息录入" << string(20, '-') << '\n';
33         cout << "录入书名: "; getline(cin>>ws, name);
34         cout << "录入作者: "; getline(cin>>ws, author);
35         cout << "录入译者: "; getline(cin>>ws, translator);
36         cout << "录入isbn: "; getline(cin>>ws, isbn);
37         cout << "录入定价: "; cin >> price;
38 
39         Book book(name, author, translator, isbn, price);
40 
41         double sales_price;
42         int sales_amount;
43 
44         cout << "录入售价: "; cin >> sales_price;
45         cout << "录入销售数量: "; cin >> sales_amount;
46 
47         BookSale record(book, sales_price, sales_amount);
48         sales_records.push_back(record);
49     }
50 
51     // 按销售册数排序
52     sort(sales_records.begin(), sales_records.end(), compare_by_amount);
53 
54     // 按销售册数降序输出图书销售信息
55     cout << string(20, '=') <<  "图书销售统计" << string(20, '=') << '\n';
56     for(auto &record: sales_records) {
57         cout << record << '\n';
58         cout << string(40, '-') << '\n';
59     }
60 }
61 
62 int main() {
63     test();
64 }
task2.cpp

运行结果

image

问题解答

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？
Book类：
std::ostream& operator<<(std::ostream &out, const Book &book)

Booksale类：

std::ostream& operator<<(std::ostream &out, const BookSale &item)
（2）找出使用重载 << 输出对象的代码，写在下面。
输出Book对象：
out << item.rb << '\n';

输出BookSale对象：

for(auto &record: sales_records) {
    cout << record << '\n';
    cout << string(40, '-') << '\n';
}
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？
主要分为两步，使用了标准库sort函数和自定义函数：
1.自定义降序比较函数：
bool compare_by_amount(const BookSale &x1, const BookSale &x2) {
    return x1.get_amount() > x2.get_amount();
}

2.使用标准库sort函数完成排序：

sort(sales_records.begin(), sales_records.end(), compare_by_amount);
 
（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"？
不用再定义一个compare_by_amount函数，直接将lambda表达式作为sort的第三个参数就行，lambda表达式的参数列表(const BookSale &x1, const BookSale &x2)对应比较函数的参数，函数体return x1.get_amount() > x2.get_amount()与原先比较函数逻辑一致，就实现降序排序，代码：
1 sort(sales_records.begin(), sales_records.end(), 
2      [](const BookSale &x1, const BookSale &x2) { 
3          return x1.get_amount() > x2.get_amount(); 
4      });

 

实验任务3

（自行练习，无需写入实验博客文档）
 

实验任务4

 源代码

 1 #ifndef PET_HPP
 2 #define PET_HPP
 3 
 4 #include <string>
 5 
 6 class MachinePet {
 7 private:
 8     std::string nickname;  
 9 
10 public:
11     MachinePet(const std::string& name) : nickname(name) {}
12     std::string get_nickname() const {
13         return nickname;
14     }
15 
16     virtual std::string talk() const = 0;
17     virtual ~MachinePet() = default;
18 };
19 
20 class PetCat : public MachinePet {
21 public:
22     PetCat(const std::string& name) : MachinePet(name) {}
23     std::string talk() const override {
24         return "喵喵~";  // 可根据需求修改为 "meow" 等
25     }
26 };
27 
28 class PetDog : public MachinePet {
29 public:
30     PetDog(const std::string& name) : MachinePet(name) {}
31     std::string talk() const override {
32         return "汪汪！";  // 可根据需求修改为 "woof" 等
33     }
34 };
35 #endif  // PET_HPP
pet.hpp
 1 #include <iostream>
 2 #include <memory>
 3 #include <vector>
 4 #include <vector>
 5 #include "pet.hpp"
 6 
 7 void test1() {
 8     std::vector<MachinePet*> pets;
 9 
10     pets.push_back(new PetCat("miku"));
11     pets.push_back(new PetDog("da huang"));
12 
13     for (MachinePet* ptr : pets) {
14         std::cout << ptr->get_nickname() << " says " << ptr->talk() << '\n';
15         delete ptr; // 须手动释放资源
16     }
17 }
18 
19 void test2() {
20     std::vector<std::unique_ptr<MachinePet>> pets;
21 
22     pets.push_back(std::make_unique<PetCat>("miku"));
23     pets.push_back(std::make_unique<PetDog>("da huang"));
24 
25     for (auto const& ptr : pets)
26         std::cout << ptr->get_nickname() << " says " << ptr->talk() << '\n';
27 }
28 
29 void test3() {
30     // MachinePet pet("little cutie"); // 编译报错：无法定义抽象类对象
31 
32     const PetCat cat("miku");
33     std::cout << cat.get_nickname() << " says " << cat.talk() << '\n';
34 
35     const PetDog dog("da huang");
36     std::cout << dog.get_nickname() << " says " << dog.talk() << '\n';
37 }
38 
39 int main() {
40     std::cout << "测试1：使用原始指针\n";
41     test1();
42 
43     std::cout << "\n测试2：使用智能指针\n";
44     test2();
45 
46     std::cout << "\n测试3：直接使用类\n";
47     test3();
48 }
task4.cpp

运行结果

image

 

实验任务4

源代码

 1 #ifndef COMPLEX_HPP
 2 #define COMPLEX_HPP
 3 
 4 #include <iostream>
 5 
 6 template<typename T>
 7 class Complex;
 8 
 9 template<typename T>
10 Complex<T> operator+(const Complex<T>& a, const Complex<T>& b);
11 
12 template<typename T>
13 bool operator==(const Complex<T>& a, const Complex<T>& b);
14 
15 template<typename T>
16 std::ostream& operator<<(std::ostream& os, const Complex<T>& c);
17 
18 template<typename T>
19 std::istream& operator>>(std::istream& is, Complex<T>& c);
20 
21 template<typename T>
22 class Complex {
23 private:
24     T real;
25     T imag;
26 
27 public:
28     Complex() : real(0), imag(0) {}
29     Complex(T r, T i) : real(r), imag(i) {}
30     Complex(const Complex<T>& other) : real(other.real), imag(other.imag) {}
31 
32     T get_real() const { return real; }
33     T get_imag() const { return imag; }
34 
35     Complex<T>& operator+=(const Complex<T>& other) {
36         real += other.real;
37         imag += other.imag;
38         return *this;
39     }
40 
41     friend Complex<T> operator+ <>(const Complex<T>& a, const Complex<T>& b);
42     friend bool operator== <>(const Complex<T>& a, const Complex<T>& b);
43     friend std::ostream& operator<< <>(std::ostream& os, const Complex<T>& c);
44     friend std::istream& operator>> <>(std::istream& is, Complex<T>& c);
45 };
46 
47 template<typename T>
48 Complex<T> operator+(const Complex<T>& a, const Complex<T>& b) {
49     return Complex<T>(a.real + b.real, a.imag + b.imag);
50 }
51 
52 template<typename T>
53 bool operator==(const Complex<T>& a, const Complex<T>& b) {
54     return (a.real == b.real) && (a.imag == b.imag);
55 }
56 
57 template<typename T>
58 std::ostream& operator<<(std::ostream& os, const Complex<T>& c) {
59     os << c.real; // 先输出实部
60     if (c.imag > 0) {
61         os << " + " << c.imag << "i"; 
62     }
63     else if (c.imag < 0) {
64         os << " - " << (-c.imag) << "i"; 
65     }
66     return os;
67 }
68 
69 template<typename T>
70 std::istream& operator>>(std::istream& is, Complex<T>& c) {
71     is >> c.real >> c.imag;
72     return is;
73 }
74 
75 #endif  // COMPLEX_HPP
Complex.hpp
 1 #include <iostream>
 2 #include "Complex.hpp"
 3 
 4 void test1() {
 5     using std::cout;
 6     using std::boolalpha;
 7 
 8     Complex<int> c1(2, -5), c2(c1);
 9 
10     cout << "c1 = " << c1 << '\n';
11     cout << "c2 = " << c2 << '\n';
12     cout << "c1 + c2 = " << c1 + c2 << '\n';
13 
14     c1 += c2;
15     cout << "c1 = " << c1 << '\n';
16     cout << boolalpha << (c1 == c2) << '\n';
17 }
18 
19 void test2() {
20     using std::cin;
21     using std::cout;
22 
23     Complex<double> c1, c2;
24     cout << "Enter c1 and c2: ";
25     cin >> c1 >> c2;
26     cout << "c1 = " << c1 << '\n';
27     cout << "c2 = " << c2 << '\n';
28 
29     const Complex<double> c3(c1);
30     cout << "c3.real = " << c3.get_real() << '\n';
31     cout << "c3.imag = " << c3.get_imag() << '\n';
32 }
33 
34 int main() {
35     std::cout << "自定义类模板Complex测试1: \n";
36     test1();
37 
38     std::cout << "\n自定义类模板Complex测试2: \n";
39     test2();
40 }
task5.cpp

运行结果

image

 

实验总结

本次实验通过在继承的基础上运用了类模板的定义与实例化方法，实践了运算符重载，明白了编译器将表达式转换为运算符函数调用的规则，同时学会了（纯）虚函数和抽象类的定义与使用，还能结合具体的继承场景如出版物类和模拟宠物类，通过继承、虚函数与抽象类实现接口继承和运行时多态的综合运用，基本能够完成实验任务。

 

 

posted @ 2025-12-16 21:48  景思翰  阅读(5)  评论(0)    收藏  举报