c++ - how to convert a boost::weak_ptr to a boost::shared_ptr -

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i have shared_ptr , weak_ptr

typedef boost::weak_ptr<classname> classnameptr; typedef boost::shared_ptr<x> xptr;

how convert weak_ptr shared_ptr

shared_ptr = weak_ptr; xptr = classnameptr; ?????

as said 

boost::shared_ptr<type> ptr = weak_ptr.lock();

if not want exception or use cast constructor

boost::shared_ptr<type> ptr(weak_ptr);

this throw if weak pointer deleted.


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