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 != )
         {
             delete publisher;
             publisher = ;
             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：