实验5 多态

一、实验任务1

源代码task1

 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

运行结果截图

1eaeea14bf5f135503ff918fbaca0b8b

 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。

Publisher 类包含纯虚函数是其成为抽象类的核心原因；代码依据为virtual void publish() const = 0;和virtual void use() const = 0;这两个纯虚函数声明。

（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。因为抽象类包含纯虚函数，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。

必须实现publish和use函数，完整声明为：

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？

b03809e534296673d9daed9127c68220

函数定义与声明不匹配，导致报错。

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？

ptr 的声明类型是Publisher*（指向 Publisher 基类的指针）。

（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？

Publisher 析构函数声明为virtual是为了通过基类指针删除派生类对象时，能正确调用派生类析构函数；若删除virtual，执行delete ptr;；只会调用基类析构函数，派生类的资源无法释放，导致内存泄漏。

 

二、实验任务2

源代码task2

 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 #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 #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 "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

运行结果截图

087ac95cbe2ddf0e58f5af89107045cf

 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？

运算符<<被重载了 2 处；分别用于Book类（输出图书基础信息）和BookSale类（输出图书销售记录信息）。

（2）找出使用重载 << 输出对象的代码，写在下面。

// 遍历销售记录，输出BookSale对象（内部嵌套输出Book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？

代码通过调用<algorithm>库的sort函数，传入自定义的比较函数compare_by_amount作为排序规则，实现按销售数量降序排序：

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

// 比较函数核心逻辑：return x1.get_amount() > x2.get_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"？

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

    [](const BookSale &x1, const BookSale &x2) {

        return x1.get_amount() > x2.get_amount();

    });

 

三、实验任务3

源代码task3

 1 #include <iostream>
 2 
 3 // 类A的定义
 4 class A {
 5 public:
 6     A(int x0, int y0);
 7     void display() const;
 8 
 9 private:
10     int x, y;
11 };
12 
13 A::A(int x0, int y0): x{x0}, y{y0} {
14 }
15 
16 void A::display() const {
17     std::cout << x << ", " << y << '\n';
18 }
19 
20 // 类B的定义
21 class B {
22 public:
23     B(double x0, double y0);
24     void display() const;
25 
26 private:
27     double x, y;
28 };
29 
30 B::B(double x0, double y0): x{x0}, y{y0} {
31 }
32 
33 void B::display() const {
34     std::cout << x << ", " << y << '\n';
35 }
36 
37 void test() {
38     std::cout << "测试类A: " << '\n';
39     A a(3, 4);
40     a.display();
41 
42     std::cout << "\n测试类B: " << '\n';
43     B b(3.2, 5.6);
44     b.display();
45 }
46 
47 int main() {
48     test();
49 }
task3_1.cpp
task3_2.cpp

 运行结果截图

bc482872d9f688c54dfcb4722fbc5a2b

68083bf941c2dde07e677273b28f95ba

 

四、实验任务4

源代码task4

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

4e7052b870ec12935887919d3dcfccf8

 

五、实验任务5

源代码task5

 1 #pragma once
 2 #include <iostream>
 3 #include <cmath>
 4 
 5 template <typename T>
 6 class Complex {
 7 public:
 8     Complex(T r = T(), T i = T()) : real(r), imag(i) {}
 9     Complex(const Complex<T>& other) : real(other.real), imag(other.imag) {}
10 
11     T get_real() const { return real; }
12     T get_imag() const { return imag; }
13 
14     Complex<T> operator+(const Complex<T>& other) const {
15         return Complex<T>(real + other.real, imag + other.imag);
16     }
17 
18     Complex<T>& operator+=(const Complex<T>& other) {
19         real += other.real;
20         imag += other.imag;
21         return *this;
22     }
23 
24     bool operator==(const Complex<T>& other) const {
25         return real == other.real && imag == other.imag;
26     }
27 
28     friend std::ostream& operator<<(std::ostream& os, const Complex<T>& c) {
29         os << c.real;
30         if (c.imag >= 0) {
31             os << " + " << c.imag << "i";
32         } else {
33             os << " - " << std::abs(c.imag) << "i";
34         }
35         return os;
36     }
37 
38     friend std::istream& operator>>(std::istream& is, Complex<T>& c) {
39         is >> c.real >> c.imag;
40         return is;
41     }
42 
43 private:
44     T real;
45     T imag;
46 };
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

2acb33b01fde2d70fee038ca0fea2abe

 

实验总结：
1.本次实验掌握了 C++ 多态的两种核心实现：类模板、运算符重载实现编译时多态，继承 + 虚函数 + 抽象类实现运行时多态。

2.类模板需注意：成员函数类外实现要加模板头和完整类名X<T>，模板函数需在头文件完整定义，不可拆分至.cpp 文件；模板友元函数可类内直接定义，或通过前向声明在类外实现。

3.模板类构造函数参数默认值建议用T()而非固定值（如 0/0.0），避免类型不匹配问题。

4.抽象类可规范接口，智能指针能自动释放资源，运算符重载让自定义类型使用更贴合原生语法，这些特性提升了代码的通用性和可维护性。 

posted @ 2025-12-10 08:42  htsjubbymjeymsy  阅读(5)  评论(0)    收藏  举报