get weakptr point from this

和enable_shared_from_this刚好相反，http://www.cppblog.com/pizzx/archive/2014/07/02/207477.html
内部持有shared_ptr作为成员变量，生命周期和类相同，通过weak_ptr可以判断当前对象生命周期是否已经结束（可以在其他线程判断，线程安全）。

#include <iostream>

#include <boost/weak_ptr.hpp>

#include <boost/shared_ptr.hpp>

#include <vector>

using namespace std;

using namespace boost;

class null_deleter

{

public:

void operator()(void *)

{}

};

class X

{

private:

shared_ptr<X> this_;

int i_;

public:

explicit X(int i): this_(this, null_deleter()), i_(i)

{

}

// repeat in all constructors (including the copy constructor!)

X(X const & rhs): this_(this, null_deleter()), i_(rhs.i_)

{

}

// do not forget to not assign this_ in the copy assignment

X & operator=(X const & rhs)

{

i_ = rhs.i_;

}

weak_ptr<X> get_weak_ptr() const { return this_; }

};

int main()

{

vector<weak_ptr<X> > m_vcwptr;

{

X x(1);

}

{

shared_ptr<X> x(new X(1));

m_vcwptr.push_back(x->get_weak_ptr());

std::cout<<"x use count: "<<x.use_count()<<"\n";

weak_ptr<X> xinscope = m_vcwptr[0];

if(!xinscope.lock())

std::cout<<"xy is already expired"<<"\n";

else

std::cout<<"xy is exist "<<"\n";

}

weak_ptr<X> xy = m_vcwptr[0];

if(!xy.lock())

std::cout<<"xy is already expired"<<"\n";

}

posted on 2014-07-06 21:11 pizzx 阅读(325) 评论(0) 编辑收藏引用所属分类: c++/boost

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