实验5 多态
实验任务1
代码组织：
publisher.hpp 类publisher及其派生类book,film,music声明
publisher.cpp 类publisher及其派生类book,film,music实现
task1.cpp 测试模块+main
publisher.hpp
#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
};
publisher.cpp
#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';
}
task1.cpp
#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();
}
运行测试结果如下：
问题1（1）：publisher类将成员函数声明为了纯虚函数。代码依据：
virtual void publish() const = 0;
virtual void use() const = 0;
(2):不能通过编译，抽象类不支持声明对象，类的成员函数没有声明会导致链接错误，纯虚函数的声明允许这条声明没有对应的实现，将类变为抽象类，但尝试声明抽象类对象会直接导致编译错误。
问题2（1）：publisher的3个派生类必须实现：
void publish() const override;
void use() const override;
（2）：报错信息如下：
问题3（1）：ptr的类型是publisher抽象类的指针型变量
（2）：->Book->Film->Music
（3）：将基类析构函数声明为virtual,保证在析构时使用派生类对象自己的析构函数而非基类的析构函数，否则delete会使用ptr基类自己的析构函数来释放其指向的派生类对象的内存地址，几乎一定会导致内存泄漏
实验任务2
代码组织：
book.hpp 图书描述信息类Book声明
book.cpp 图书描述信息类Book实现
booksale.hpp 图书销售记录类BookSale声明
booksale.cpp 图书销售记录类BookSale实现
task2.cpp 测试模块 + main
book.hpp
#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
};
book.cpp
#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;
}
booksale.hpp
#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
};
booksale.cpp
#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;
}
task2.cpp
#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();
}
运行测试结果如下：
问题1（1）：运算符<<重载了2处，分别用于用输出流对象操作Book类和BookSale类对象的数据输出
（2）：使用<<重载输出对象的代码：
out << item.rb << '\n'...
...
cout << record << '\n';
...
问题2（1）：使用标准库的std::sort()函数，在第三个参数中传入自定义的比较函数compare_by_amount来重定义排序标准，以此实现降序的效果
（2）：在std::sort()第三个参数传入匿名函数[](const BookSale &x1, const BookSale &x2){return x1.get_amount() > x2.get_amount();}实现按类对象的售价排序
&#nbsp;
实验任务4
代码组织：
pet.hpp 机器宠物抽象类MachinePet、宠物猫类PetCat、宠物狗类PetDog定义
task4.cpp 测试模块 + main
pet.hpp
#pragma once
#include <string>
class MachinePet {
protected:
std::string nickname;
public:
MachinePet(const std::string& name): nickname(name) {}
const std::string& get_nickname() const {return nickname;}
virtual std::string talk() const = 0;
virtual ~MachinePet() = default;
};
class PetCat: public MachinePet {
public:
PetCat(const std::string& name): MachinePet(name) {}
std::string talk() const {return "miao wu~";}
};
class PetDog: public MachinePet {
public:
PetDog(const std::string& name): MachinePet(name) {}
std::string talk() const {return "wang wang~";}
};
task4.cpp
#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();
}
运行测试结果如下：
实验任务5
代码组织：
Complex.hpp 类模板 Complex定义
task5.cpp 测试模块 + main
Complex.hpp
#pragma once
#include <iostream>
#include <cmath>
template<class T>
class Complex {
private:
T real, imag;
public:
Complex<T>(T _real = 0, T _imag = 0): real(_real), imag(_imag) {}
Complex<T>(const Complex& other): real(other.real), imag(other.imag) {}
Complex<T>(Complex&& other) noexcept: real(other.real), imag(other.imag) {}
T get_real() const {return real;}
T get_imag() const {return imag;}
Complex<T>& operator+=(const Complex<T>& c) {this->real += c.real; this->imag += c.imag; return *this;}
Complex<T> operator+(const Complex<T>& c) const {Complex<T>temp(this->real + c.real, this->imag + c.imag); return temp;}
bool operator==(const Complex<T>& c) const {return this->real == c.real && this->imag == c.imag;}
friend std::istream& operator>>(std::istream& in, Complex<T>& c) {return in >> c.real >> c.imag;}
friend std::ostream& operator<<(std::ostream& out, const Complex<T>& c) {
if (c.real < 0) out << "- ";
out << abs(c.real);
if (!c.imag) {
return out;
} else {
if (c.imag < 0) out << " - ";
else out << " + ";
return out << abs(c.imag) << 'i';
}
}
};
task5.cpp
#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();
}
运行测试结果如下：
实验总结：
多态功能的实现由代码层面的模板化template<class T>和类的继承功能来完成，将类，函数的功能由编译时确定转为运行时确定。极大的增加了代码的灵活性和可复用性。需要注意的是，模板化的部分应该为代码不通用的类型重载特殊的具体化，确保功能的完整性，或者明确不会使用这种类型的实例化。继承也可以看作是抽象类的“具体化”，并且这种“具体化”比起模板更加自由，不止在类型层面（派生类与基类类名不同），同时也可以增加具体类自己的特殊成员，扩展数据和功能。
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