boost相关函数

1、boost::scoped_ptr是一个比较简单的智能指针，它能保证在离开作用域之后它所管理对象能被自动释放

 #include <iostream>
 #include <boost/scoped_ptr.hpp>
 
 using namespace std;
 
 class Book
 {
 public:
     Book()
     {
         cout << "Creating book ..." << endl;
     }
 
     ~Book()
     {
         cout << "Destroying book ..." << endl;
     }
 };
 
 int main()
 {
     cout << "=====Main Begin=====" << endl;
     {
         boost::scoped_ptr<Book> myBook(new Book());
     }
     cout << "===== Main End =====" << endl;
 
     return ;
 }

2、 boost::shared_ptr是可以共享所有权的指针。如果有多个shared_ptr共同管理同一个对象时，只有这些shared_ptr全部与该对象脱离关系之后，被管理的对象才会被释放。通过下面这个例子先了解下shared_ptr的基本用法：。

 #include <iostream>
 #include <string>
 #include <boost/shared_ptr.hpp>
 
 using namespace std;
 
 class Book
 {
 private:
     string name_;
 
 public:
     Book(string name) : name_(name)
     {
         cout << "Creating book " << name_ << " ..." << endl;
     }
 
     ~Book()
     {
         cout << "Destroying book " << name_ << " ..." << endl;
     }
 };
 
 int main()
 {
     cout << "=====Main Begin=====" << endl;
     {
         boost::shared_ptr<Book> myBook(new Book("「1984」"));
         cout << "[From myBook] The ref count of book is " << myBook.use_count() << ".\n" << endl;
 
         boost::shared_ptr<Book> myBook1(myBook);
         cout << "[From myBook] The ref count of book is " << myBook.use_count() << "." << endl;
         cout << "[From myBook1] The ref count of book is " << myBook1.use_count() << ".\n" << endl;
 
         cout << "Reset for 1th time. Begin..." << endl;
         myBook.reset();
         cout << "[From myBook] The ref count of book is " << myBook.use_count() << "." << endl;
         cout << "[From myBook1] The ref count of book is " << myBook1.use_count() << "." << endl;
         cout << "Reset for 1th time. End ...\n" << endl;
 
         cout << "Reset for 2th time. Begin ..." << endl;
         myBook1.reset();
         cout << "Reset for 2th time. End ..." << endl;
     }
     cout << "===== Main End =====" << endl;
 
     return ;
 }

3、shared_from_this()

• 在一个类中需要传递类对象本身shared_ptr的地方使用shared_from_this函数来获得指向自身的shared_ptr，它是enable_shared_from_this的成员函数，返回shared_ptr。

• 这个函数仅在shared_ptr的构造函数被调用之后才能使用。原因是enable_shared_from_this::weak_ptr并不在enable_shared_from_this构造函数中设置，而是在shared_ptr的构造函数中设置。