实验五
一、试验任务一
验证性实验。综合应用组合、继承、多态实现出版物的分类管理。
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 };
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 }
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 test3() { 22 Book book("A Philosophy of Software Design", "John Ousterhout"); 23 book.publish(); 24 book.use(); 25 } 26 27 int main() { 28 std::cout << "运行时多态：纯虚函数、抽象类\n"; 29 30 std::cout << "\n测试1: 使用原始指针\n"; 31 test1(); 32 33 std::cout << "\n测试3: 直接使用类\n"; 34 test3(); 35 }
运行截图：
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类中声明了纯虚函数：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？
不能，Publisher是抽象类，只能设置一个Publisher类指针，不可实例化。
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？
函数实现和函数声明不匹配，hpp中函数声明是const类型。
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*基类指针类型
（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？
为了派生类对象正常析构的时候，不调用基类析构函数，防止内存泄漏；会出现只调用基类析构函数，派生类动态分配的内存无法正常释放，导致内存泄漏
二、试验任务二
验证性实验。综合应用运算符重载、组合、标准库实现图书销售统计。
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 };
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 }
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 };
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 }
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 }
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，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。
for(auto &record: sales_records) {
cout << record << '\n'; //重载<<
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？
bool compare_by_amount(const BookSale &x1, const BookSale &x2) {
return x1.get_amount() > x2.get_amount();
}
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"？
sort(sales_records.begin(), sales_records.end(), [](const BookSale &x1, const BookSale &x2) { return x1.get_amount() > x2.get_amount(); });
三、实验任务三
验证性实验：类模板定义和使用。阅读、理解代码，结合运行回答问题
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 }
1 #include <iostream> 2 #include <string> 3 4 // 定义类模板 5 template<typename T> 6 class X{ 7 public: 8 X(T x0, T y0); 9 void display(); 10 11 private: 12 T x, y; 13 }; 14 15 template<typename T> 16 X<T>::X(T x0, T y0): x{x0}, y{y0} { 17 } 18 19 template<typename T> 20 void X<T>::display() { 21 std::cout << x << ", " << y << '\n'; 22 } 23 24 25 void test() { 26 std::cout << "测试1: 用int实例化类模板X" << '\n'; 27 X<int> x1(3, 4); 28 x1.display(); 29 30 std::cout << "\n测试2:用double实例化类模板X" << '\n'; 31 X<double> x2(3.2, 5.6); 32 x2.display(); 33 34 std::cout << "\n测试3: 用string实例化类模板X" << '\n'; 35 X<std::string> x3("hello", "oop"); 36 x3.display(); 37 } 38 39 int main() { 40 test(); 41 }
四、试验任务四
设计性实验。综合应用继承、多态，模拟简单机器宠物。
1 #include <iostream > 2 #include <stdio.h> 3 #include <string.h> 4 using namespace std; 5 6 class MachinePet { 7 public: 8 MachinePet(const string& nickname_):nickname{nickname_}{} 9 virtual ~MachinePet() = default; 10 virtual string talk()const = 0; 11 string get_nickname()const { 12 return nickname; 13 } 14 private: 15 string nickname; 16 }; 17 18 class PetCat:public MachinePet{ 19 public: 20 PetCat(const string& nickname_):MachinePet(nickname_){} 21 string talk()const override{return "miao wu ~";} 22 }; 23 24 class PetDog:public MachinePet{ 25 public: 26 PetDog(const string& nickname_):MachinePet(nickname_){} 27 string talk()const override{return "wang wang ~";} 28 };
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 }
五、试验任务五
设计性实验。综合应用运算符重载、类模板实现编译时多态。
1 #include <iostream> 2 #include <stdio.h> 3 #include <string.h> 4 #include <iomanip> 5 using namespace std; 6 7 template <typename T> 8 9 class Complex{ 10 public: 11 Complex():x{0},y{0}{} 12 Complex(T x_,T y_):x{x_},y{y_}{} 13 Complex(const Complex<T>& c):x{c.x},y{c.y}{} 14 15 ~Complex()= default; 16 T get_real()const {return x;} 17 T get_imag()const {return y;} 18 19 friend ostream& operator<<(ostream& out ,const Complex<T>& c){ 20 if(c.y>0) 21 out<<c.x<<" + "<< c.y <<"i"; 22 else out <<c.x<<" - "<<-c.y<<"i"; 23 return out ; 24 } 25 friend istream& operator>>(istream& in, Complex<T>& c){ 26 in>>c.x>>c.y; 27 return in; 28 } 29 friend Complex<T> operator+(const Complex<T>& c1,const Complex<T>& c2){ 30 return Complex<T> (c1.x+c2.x,c1.y+c2.y); 31 } 32 bool operator==(const Complex<T>& c){ 33 return (this->x == c.x)&&(this->y == c.y ); 34 } 35 void operator+=(const Complex<T>& c){ 36 this->x +=c.x; 37 this->y +=c.y; 38 } 39 private: 40 T x,y; 41 };
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 }
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