使用enable_shared_from_this

说明

The header <boost/enable_shared_from_this.hpp> defines the class template enable_shared_from_this. It is used as a base class that allows a shared_ptr to the current object to be obtained from within a member function.

继承该类就可以进行基于当前子类进行安全的weap_ptr到shared_ptr的转换...

代码实例

以下代码中Y类继承enable_shared_from_this,, 从而我们可以直接在函数中调用shared_from_this获得该对象的shared_ptr

class Y: public enable_shared_from_this<Y>
 {
 public:

     shared_ptr<Y> f()
     {
         return shared_from_this();
     }
 }

 int main()
 {
     shared_ptr<Y> p(new Y);
 // 调用f获得shared_ptr

     shared_ptr<Y> q = p->f();
     assert(p == q);
     assert(!(p < q || q < p)); // p and q must share ownership

 }

该类的实现

template<class T> class enable_shared_from_this
 {
 protected:

     enable_shared_from_this()
     {
     }

     enable_shared_from_this(enable_shared_from_this const &)
     {
     }

     enable_shared_from_this & operator=(enable_shared_from_this const &)
     {
         return *this;
     }

     ~enable_shared_from_this()
     {
     }

 public:

     shared_ptr<T> shared_from_this()
     {
         shared_ptr<T> p(_internal_weak_this);
         BOOST_ASSERT(p.get()  == this);
         return p;
     }

     shared_ptr<T const> shared_from_this() const
     {
         shared_ptr<T const> p(_internal_weak_this);
         BOOST_ASSERT(p.get()  == this);
         return p;
     }

 // Note: No, you don't need to initialize _internal_weak_this

 //

 // Please read the documentation, not the code

 //

 // http://www.boost.org/libs/smart_ptr/enable_shared_from_this.html


     typedef T _internal_element_type; // for bcc 5.5.1

     mutable weak_ptr<_internal_element_type> _internal_weak_this;
 };

结论

这个实用类提供了简单的shared_ptr转换和安全的weak式验证... 这样通过继承就可以使用

shared_from_this进行安全当前类weak_ptr到shared_ptr的转换...