实验任务一
源代码：
#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'; }
#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 <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(); }
其中由于我使用的编译器为devc++，task1.cpp中test2智能指针无法运行成功已注释掉。
运行结果：
问题：
Q1：
（1）决定publisher是抽象类的原因：它里面包含了“纯虚函数”，纯虚函数只有声明、没有定义，不能用来直接创建对象。
具体依据：virtual void publish() const = 0;virtual void use() const=0;
（2）不能编译通过。publisher是一个抽象类，它的存在是为了让别的类继承它就比如说book和film，所以单独使用它不能创建对象。
Q2：
（1）它们必须实现从 Publisher 类继承下来的两个纯虚函数：publish和use。
必须实现的具体函数声明：void publish() const override; void use() const override
（2）如果去掉了const，那么函数void publish()和基类要求的void publish() coonst被认为是两个不同的函数。故而在film类中就没有成功重写纯虚函数，导致编译失败。
Q3：
（1）ptr 的声明类型是 Publisher*，也就是“指向 Publisher 类对象的指针。
（2）第一次循环：指向一个 Book 类对象。第二次循环：指向一个 Film 类对象。第三次循环：指向一个 Music 类对象。
（3）这是为了确保当用基类Publisher的指针去删除一个派生类对象时，程序能够正确地调用到派生类自己的析构函数。
若删除virtual会出现的问题：当执行 delete ptr时，编译器只会调用基类 Publisher 的析构函数，而不会调用指针实际指向的那个派生类的析构函数。这会导致派生类对象中独有的部分可能得不到清理。
实验任务二
源代码：
#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>// 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 "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; }
#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 <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：
Q1：
（1）在代码中，<< 运算符被重载了 2 次：第一次重载是为了输出Book类的对象。第二次重载是为了输出BookSale类的对象。
（2）cout << record << '\n';
Q2：
（1）利用编写的compare_by_amount函数比较两本书的销量，如果第一本销量大于第二本，就返回true。然后调用sort函数，使其销量从高到低排序。
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(); }
#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：
task3_1.cpp
task3_2.cpp
实验任务四
源代码：
#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; // 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(); }
#include <string> class MachinePet { protected:std::string nickname; public:MachinePet(const std::string& name) : nickname(name) {}std::string get_nickname() const {return nickname;}virtual std::string talk() const = 0;virtual ~MachinePet() {} }; class PetCat : public MachinePet { public:PetCat(const std::string& name) : MachinePet(name) {}std::string talk() const override {return "meow";} }; class PetDog : public MachinePet { public:PetDog(const std::string& name) : MachinePet(name) {}std::string talk() const override {return "wang";} };
运行结果：
（智能指针无法运行已被注释）
实验任务五
源代码：
#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(); }
#include <iostream> #include <cmath>template<typename T> class Complex { private:T real;T imag;public:Complex(T r = 0, T i = 0);Complex(const Complex& other);T get_real() const;T get_imag() const;void set_real(T r);void set_imag(T i);Complex& operator+=(const Complex& other);Complex operator+(const Complex& other) const;bool operator==(const Complex& other) const;friend std::ostream& operator<<(std::ostream& out, const Complex& c) {out << c.real;if (c.imag >= 0) {out << " + " << c.imag << "i";} else {out << " - " << std::abs(c.imag) << "i";}return out;}friend std::istream& operator>>(std::istream& in, Complex& c) {in >> c.real >> c.imag;return in;} };template<typename T> Complex<T>::Complex(T r, T i) : real(r), imag(i) {}template<typename T> Complex<T>::Complex(const Complex& other) : real(other.real), imag(other.imag) {}template<typename T> T Complex<T>::get_real() const {return real; }template<typename T> T Complex<T>::get_imag() const {return imag; }template<typename T> void Complex<T>::set_real(T r) {real = r; }template<typename T> void Complex<T>::set_imag(T i) {imag = i; }template<typename T> Complex<T>& Complex<T>::operator+=(const Complex& other) {real += other.real;imag += other.imag;return *this; }template<typename T> Complex<T> Complex<T>::operator+(const Complex& other) const {return Complex<T>(real + other.real, imag + other.imag); }template<typename T> bool Complex<T>::operator==(const Complex& other) const {return (real == other.real) && (imag == other.imag); }
运行结果：
实验总结
在实验任务五中，按照学习通仿写类内声明类外定义发现很容易报错，需要多写很多声明模板参数，但如果在类内直接定义，可以避免链接出错、降低代码复杂性。故而经查阅总结面对模板类的友元函数，最好在类内定义和声明 ，它会自动与类模板的模板参数绑定。