[boost] weak_ptr, maybe empty

From: Andy Thomas-Cramer (Andy_Thomas-Cramer_at_[hidden])
Date: 2005-08-03 13:42:18

I have a weak_ptr that might be empty. If not empty, I'd like to make a
smart pointer from it. 
 
But the code below throws in the shared_ptr constructor, and I don't see
how to test whether a weak_ptr is empty.

    boost::weak_ptr<int> wp;
    boost::shared_ptr<int> sp(wp);
    if ( sp.get() ) {
        ...
    }

Suggestions?