Re: [Boost-Users] Why not "if (px != rpx) " ?

From: Peter Dimov (pdimov_at_[hidden])
Date: 2001-12-14 09:33:00

From: "Louis Lavery" <Louis_at_[hidden]>
> Hello,
> 
> The following is use by the boost shared_ptr assignment operators
> (see boost\smart_ptr.hpp)...
> 
>    void share(T* rpx, long* rpn) {
>       if (pn != rpn) { // Q: why not px != rpx? A: fails when both == 0
>          ++*rpn; // done before dispose() in case rpn transitively
>                  // dependent on *this (bug reported by Ken Johnson)
>          dispose();
>          px = rpx;
>          pn = rpn;
>       }
>    } // share
> 
> ...I curious to know what it means by "fails when both == 0".

It's possible that px == rpx == 0, yet pn != rpn.

--
Peter Dimov
Multi Media Ltd.