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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: C's sizeof
Date: Thu, 12 Apr 2012 18:24:31 -0400
Organization: The World Public Access UNIX, Brookline, MA
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Date: 2012-04-12T18:24:31-04:00
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Simon Wright <simon@pushface.org> writes:

> 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)
>
> ?

I think it should be more like:

pragma Assert(Item_Type'Base'Size mod CHAR_BIT = 0);
pragma Assert(Item_Type'Size = Item_Type'Base'Size);
size_of_item: constant size_t := size_t(Item_Type'Size/CHAR_BIT);
pragma Assert(size_of_item*CHAR_BIT = Item_Type'Size);

See Jeff Carter's comment.

Maybe some of those asserts are overkill, but if you're interfacing to
C, you don't want to mess around with subranges that C doesn't
understand.

- Bob