To make an empty ("owns nothing") shared_ptr, you use shared_ptr's default ctor; shared_ptr<A>((A *)0) creates a non-empty shared_ptr which calls delete on the A pointer when all references expire (note that passing a null pointer to delete is valid in C++.) Emil Dotchevski Reverge Studios, Inc. http://www.revergestudios.com/reblog/index.php?n=ReCode On Wed, Jul 8, 2009 at 4:23 PM, Carl Hetherington<lists@carlh.net> wrote:

Hi,

In the following program...

#include <boost/shared_ptr.hpp> #include <boost/weak_ptr.hpp>

class A {};

int main () {        boost::shared_ptr<A> x; // A: bad_weak_ptr thrown //      boost::shared_ptr<A> x ((A *) 0); // B: works

       boost::weak_ptr<A> y (x);        boost::shared_ptr<A> z (y); }

... I observe that with line A included (but not line B), a bad_weak_ptr is thrown by the line which declares z.

With line B included (but not line A), all is well.

...

From looking at the boost source, it seems that line A results in a

shared_ptr to nothing (use_count() == 0), and line B results in a shared_ptr to 0 (use_count() == 1).

I can work around this, I'm sure.  Can anyone clarify my muddled thinking and explain why boost is behaving correctly in this situation (if indeed it is!)

Many thanks

Carl

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