Re: C's sizeof

[Adam Beneschan <adam@irvine.com>]

On Thursday, April 12, 2012 11:42:46 AM UTC-7, Simon Wright wrote:
> Adam Beneschan writes:
> 
> > On Thursday, April 12, 2012 9:27:09 AM UTC-7, Simon Wright wrote:
> >> The (draft) ARM Annex B.3[1] says at para 73 - Note 7 -
> >> 
> >>     "To obtain the effect of C's sizeof(item_type), where Item_Type is
> >>     the corresponding Ada type, evaluate the expression:
> >>     size_t(Item_Type'Size/CHAR_BIT)."
> >> 
> >> Should that not be
> >> 
> >>     size_t((Item_Type'Size + CHAR_BIT - 1)/CHAR_BIT)
> >> 
> >> ?
> >> 
> >> [1] http://www.ada-auth.org/standards/12rm/html/RM-B-3.html
> >
> > Does C even support types whose sizes aren't a multiple of a byte?  If
> > it doesn't, then since B.3 is talking about the Ada type
> > "corresponding" to a C type, the question is probably moot.
> 
> Doesn't B.3 apply to types with Convention => C?
> 
> GNAT allows
> 
>    type N2 is range 0 .. Integer'Last - 1;
>    pragma Convention (C, N2);
> 
> and N2'Size is 31 ...

Yeah, you're right.  But then I don't think your formula would work either:

   type N3 is range 0 .. 2**22 - 1;
   pragma Convention (C, N3);

and N3'Size is 22.  But what would the sizeof() of the C type be?

                       -- Adam