实验五 多态
Task1:
1.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();
}
2.运行截图:
3.问题回答:
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。
答：因为它包含纯虚函数
（2）如果在 main.cpp 里直接写 Publisher p; 能否编译通过？为什么？
答:不能，因为Publisher是抽象类，不能被实例化。
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。
答:必须实现
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？
答:
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？
答: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）
答: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？
答:是为了确保通过基类指针 delete 派生类对象时，能够正确地调用完整的析构链,如果删除virtual，执行delete ptr时，只会调用 Publisher 的析构函数，而不会调用 Book、Film、Music 的析构部分,从而导致资源泄漏。
Task2:
1.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();
}
2.运行截图:
3.问题回答:
问题1：重载运算符<<
（1）找出 << 被重载了几处？用于哪些类型？
答:两处，用于Book和BookSale
（2）找出使用重载 << 输出对象的代码，写在下面。
答:
for(auto &record: sales_records) {
cout << record << '\n';
cout << string(40, '-') << '\n';
}
}
问题2：图书销售统计
（1）"按销售数量降序排序"，描述降序排序实现方式。
答:通过 STL 的 sort() 函数配合自定义比较函数 compare_by_amount 实现,函数在 x1 销售数量大于 x2 时返回 true，从而使 sort 函数将销量大的对象排在前面
（2）拓展（选答*）：如果使用lambda表达式，如何实现？
答:
sort(sales_lst.begin(), sales_lst.end(),
[](const BookSale& x1, const BookSale& x2) {
return x1.get_amount() > x2.get_amount();
});
Task4:
1.源代码:
#pragma once
#include <string>
#include<iostream>
// 抽象类：机器宠物
class MachinePet {
public:
MachinePet(const std::string& nickname);
std::string get_nickname() const;
virtual std::string talk() const = 0; // 纯虚函数：返回叫声
virtual ~MachinePet() = default;
protected:
std::string nickname;
};
// 电子宠物猫类
class PetCat : public MachinePet {
public:
PetCat(const std::string& nickname);
std::string talk() const override;
};
// 电子宠物狗类
class PetDog : public MachinePet {
public:
PetDog(const std::string& nickname);
std::string talk() const override;
};
#include <string>
#include<iostream>
#include"pet.hpp"
//MachinePet实现
MachinePet::MachinePet(const std::string& nickname)
: nickname(nickname) {}
std::string MachinePet::get_nickname() const {
return nickname;
}
//PetCat实现
PetCat::PetCat(const std::string& nickname)
: MachinePet(nickname) {}
std::string PetCat::talk() const {
return "meow";
}
//PetDog实现
PetDog::PetDog(const std::string& nickname)
: MachinePet(nickname) {}
std::string PetDog::talk() const {
return "woof";
}
#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();
}
2.运行截图:
Task5:
1.源代码:
#pragma once
#include<iostream>
#include<algorithm>
//定义类模板
template<typename T>
class Complex{
public:
Complex() : real(0), imag(0) {}
Complex(const T& r, const T& i) : real(r), imag(i) {}
Complex(const Complex<T>& other) : real(other.real), imag(other.imag) {}
T get_real() const { return real; }
T get_imag() const { return imag; }
Complex& operator+=(const Complex& other){
real = real + other.real;
imag = imag + other.imag;
return *this;
}
// 重载 == 运算符
bool operator==(const Complex& other) const{
return (real==other.real&&imag==other.real);
}
// 重载全局运算符 +
friend Complex<T> operator+(const Complex<T>& a1,const Complex<T>& a2){
return Complex<T>(a1.real+a2.real,a1.imag+a2.imag);
}
// 重载全局运算符 <<
friend std::ostream& operator<<(std::ostream& out,const Complex<T>& complex){
if(complex.imag>0)
out << complex.real << " + " << abs(complex.imag) << "i";
else if(complex.imag<0)
out << complex.real << " - " << abs(complex.imag) << "i";
else
out << " 0 ";
return out;
}
// 重载全局运算符 >>
friend std::istream& operator>>(std::istream& in,Complex<T>& complex){
in >> complex.real >> complex.imag;
return in;
}
private:
T real,imag;
};
#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();
}
2.运行截图:
浙公网安备 33010602011771号