使用enable_shared_from_this
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_thisconst &)
{
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...