Re: out_ptr review is extended until Wednesday, July 10

From: Gavin Lambert (boost_at_[hidden])
Date: 2019-06-27 03:05:25

On 27/06/2019 13:52, Bagaskoro Kang wrote:
> the creator apis  have two out params:  Interface** pointer and  unsigned*
> size and the  destroyer functions must be called with pointer and the size.
> 
>      Interface** obj;
>      unsigned size;
>      int ret = Create(... ... ... &obj, &size);
> 
> and  then we need to call a Release(obj, size) if the ret is success.
> 
> I do not think I can use the out_ptr with these APIs ???

I assume that's a typo and should be "Interface* obj".

You wouldn't be able to use it out of the box with that interface, but 
if you define a custom smart pointer (which just wraps std::unique_ptr 
with a deleter that passes the size, for example) then you could 
probably get it to work.

Spreading the responsibilities over two parameters does make things more 
tricky, though.  If it's at all possible to remove the requirement to 
pass size around, you should do that instead.  (It's not normally needed 
for array allocation, for example.)

> also we call the Linux kernel C  API posix_memalign() and we assign to
> unique_ptr. is not possible to use out_ptr with ?
> 
>      std::unique_ptr<Numf, DoFree> upNumf;
>      void  * pNumf;
>      int ret = posix_memalign(&pNumf, 64, nNumf);
>      if (!ret)
>          upNumf.reset((Numf*)pNumf);

Why not use std::aligned_storage or put alignas on the class instead?