析构函数 p157

析构函数

确保对象的各部分被正确的清除，及做一些用户指定的其他清理工作。

当对象超出它的作用域时，编译器将自动调用析构函数；手动用new在堆上分配的对象空间，需要调用'delete 对象地址'进行手动清除， delete 语句 先调用该对象的析构函数，然后释放内存

#include <iostream>
#include <string>

using namespace std;


class Publisher
{
    string name;
    string address;
    string telephone;

public:
    
    Publisher(string name, string address, string telephone) : name(name), address(address), telephone(telephone) 
    {
        cout << "Publisher(string name, string address, string telephone)" << endl;
    }

    ~Publisher()
    {
        cout << "~Publisher()" << endl;
    }

    friend ostream& operator<<(ostream& os, const Publisher& p)
    {
        return os << "PublisherName: " << p.name << ", PublisherAddress: " << p.address << ", Publishertelephone: " << p.telephone;
    }

};


class Book
{
    string name;
    string author;
    double price;
    Publisher* publisher;

public:

    Book(string name, string author, double price, Publisher* pub) : name(name), author(author), price(price), publisher(pub)
    {
        cout << "Book(string name, string author, double price, Publisher publisher)" << endl;
    }

    ~Book()
    {
        cout << "~Book()" << endl;
        if (publisher != 0)
        {
            delete publisher;
            publisher = 0;
            cout << "delete publisher" << endl;
        }    
    
    }

    friend ostream& operator<<(ostream& os, const Book& b)
    {
         os << "-------- print Book ---------------" << endl;
         os << "BookName: " << b.name << ", BookAuthor: " << b.author << ", BookPrice: " << b.price << endl;;
         os << *b.publisher << endl;;
         return os;
    }

};

int main()
{
    
    Publisher* pub = new Publisher("人民出版社", "北京市西城区", "021-2134343545");

    Book b1("算法精解", "Kyle Loudon", 56.2, pub);

    cout << b1 << endl;

};

运行结果：