Re: [boost] [shared_ptr] Set pointer to null

Subject: Re: [boost] [shared_ptr] Set pointer to null
From: Sebastian Redl (sebastian.redl_at_[hidden])
Date: 2009-11-09 09:06:26

Mateusz Loskot wrote:
> Hi,
>
> I'd like to make a custom deleter resetting pointer to 0 or other value
> (e.g. for debugging purposes) after resource has been deallocated.
> Would anyone suggest better option to this presented below?
>
> struct DeleterT
> {
>     void operator()(::T* ptr)
>     {
>         ::DestroyT(ptr);
>
>         // uses Visual C++ specific integer type
>         *reinterpret_cast<__int64*>(&ptr) = 0;
>     }
> };
This doesn't actually do anything. The code is undefined (accessing 
casted pointer, aliasing violation), but even the most common 
interpretation simply does the same thing as "ptr = 0;". ptr is a by-val 
argument. You cannot know where the original member you want to reset 
is, so you can't reset it. All you are modifying here is your local 
function argument - and possibly the function return address, if you're 
on a 32-bit system ...

Sebastian