实验五
task1
publisher.hpp
#pragma once
#include<string>
class Publisher{
public:
Publisher(const std::string &name_="");
virtual ~Publisher()=default;
public:
virtual void publish() const=0;
virtual void use() const=0;
protected:
std::string name;
};
class Book:public Publisher{
public:
Book(const std::string &name_="",const std::string &author_="");
public:
void publish() const override;
void use() const override;
private:
std::string author;
};
class Film:public Publisher{
public:
Film(const std::string &name_="",const std::string &director_="");
public:
void publish() const override;
void use() const override;
private:
std::string director;
};
class Music:public Publisher{
public:
Music(const std::string &name_="",const std::string &artist_="");
public:
void publish() const override;
void use() const override;
private:
std::string artist;
};
publisher.cpp
#include<iostream>
#include<string>
#include "publisher.hpp"
Publisher::Publisher(const std::string &name_):name{name_}{}
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::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::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();
}
问题 1：
(1) 含有纯虚函数的类是抽象类，因为Publisher 类中声明了virtual void publish() const = 0;和virtual void use() const = 0两个纯虚函数。
(2) 不能。因为 Publisher 是抽象类无法实例化对象。
问题 2：
(1) void publish() const override;和void use() const override;
(2)
问题 3：运行时多态与虚析构
(1) ptr 的声明类型是Publisher*。
(2) Book、Film、Music。
(3) 基类析构函数声明为 virtual 是为了实现析构函数的多态，确保删除派生类对象时，先调用派生类析构函数，再调用基类析构函数，避免内存泄漏。若删除 virtual，执行delete ptr;时只会调用基类 Publisher 的析构函数，派生类的成员不会被释放，导致内存泄漏。
task2
book.hpp
#pragma once
#include<string>
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;
std::string author;
std::string translator;
std::string isbn;
double price;
};
book.cpp
#include <iomanip>
#include <iostream>
#include <string>
#include "book.hpp"
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_} {
}
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"
class BookSale{
public:
BookSale(const Book &rb_, double sales_price_, int sales_amount_);
int get_amount() const;
double get_revenue() const;
friend std::ostream& operator<<(std::ostream &out,const BookSale &item);
private:
Book rb;
double sales_price;
int sales_amount;
};
booksale.cpp
#include <iomanip>
#include <iostream>
#include <string>
#include "booksale.hpp"
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;
}
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 "booksale.hpp"
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
bool compare_by_amount(const BookSale &x1, const BookSale &x2) {
return x1.get_amount() > x2.get_amount();
}
void test(){
using namespace std;
vector<BookSale> sales_lst;
int books_number;
cout << "录入图书数量: ";
cin >> books_number;
cout << "录入图书销售记录" << endl;
for(int i = 0; i < books_number; ++i) {
string name, author, translator, isbn;
float price;
cout << string(20, '-') << "第" << i+1 << "本图书信息录入" << string(20, '-') << endl;
cout << "录入书名: "; cin >> name;
cout << "录入作者: "; cin >> author;
cout << "录入译者: "; cin >> translator;
cout << "录入isbn: "; cin >> isbn;
cout << "录入定价: "; cin >> price;
Book book(name, author, translator, isbn, price);
float 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_lst.push_back(record);
}
sort(sales_lst.begin(), sales_lst.end(), compare_by_amount);
cout << string(20, '=') << "图书销售统计" << string(20, '=') << endl;
for(auto &t: sales_lst) {
cout << t << endl;
cout << string(40, '-') << endl;
}
}
int main(){
test();
}
问题 1：
(1) 2 处，分别用于Book类型和BookSale类型。
(2) cout << item.rb << '\n';cout << t << endl;
问题 2：
(1) 降序排序实现，先定义比较函数compare_by_amount，该函数接收两个 BookSale 对象，返回第一个对象的销售数量是否大于第二个对象，再调用标准库sort函数，传入销售记录向量的首尾迭代器和比较函数，实现按销售数量降序排序。
(2) sort(sales_lst.begin(), sales_lst.end(), [](const BookSale &x1, const BookSale &x2) {
return x1.get_amount() > x2.get_amount();});
task4
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;
}
}
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() {
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();
}
Pet.hpp
#pragma once
#include <string>
class MachinePet {
public:
MachinePet(const std::string &nickname_) : nickname{nickname_} {}
virtual ~MachinePet() = default;
std::string get_nickname() const { return nickname; }
virtual std::string talk() const = 0;
protected:
std::string nickname;
};
class PetCat : public MachinePet {
public:
PetCat(const std::string &nickname_) : MachinePet{nickname_} {}
std::string talk() const override {
return "miao wu~";
}
};
class PetDog : public MachinePet {
public:
PetDog(const std::string &nickname_) : MachinePet{nickname_} {}
std::string talk() const override {
return "wang wang~";
}
};
task5
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();
}
complex.hpp
#pragma once
#include <iostream>
template<typename T>
class Complex {
public:
Complex() : real{0}, imag{0} {}
Complex(T r, T i) : real{r}, imag{i} {}
Complex(const Complex &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 += other.real;
imag += other.imag;
return *this;
}
bool operator==(const Complex &other) const {
return (real == other.real) && (imag == other.imag);
}
friend Complex operator+(const Complex &c1, const Complex &c2) {
return Complex(c1.real + c2.real, c1.imag + c2.imag);
}
friend std::ostream& operator<<(std::ostream &out, const Complex &c) {
out << c.real;
if (c.imag < 0) {
out << c.imag << "i";
} else {
out << "+" << c.imag << "i";
}
return out;
}
friend std::istream& operator>>(std::istream &in, Complex &c) {
in >> c.real >> c.imag;
return in;
}
private:
T real;
T imag;
};
实验总结
本次实验围绕 C++ 多态核心特性展开，涵盖了抽象类、虚函数、运算符重载、类模板等关键知识点。通过验证性实验，深入理解了运行时多态的实现原理、类模板的通用化设计思想以及运算符重载的实用场景；通过设计性实验，实践了从问题场景抽象到代码实现的完整流程。实验中发现，虚析构函数的正确声明是避免内存泄漏的关键，类模板的实例化类型必须支持模板内的所有操作，运算符重载需严格匹配参数类型与返回值要求。后续需进一步练习复杂场景下的多态应用，如多层继承中的虚函数重写、模板特化等高级用法，提升代码的灵活性与通用性。
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