Re: [boost] Endian library - request for comments

From: Beman Dawes (bdawes_at_[hidden])
Date: 2006-06-03 18:08:49

On 6/3/06, Sebastian Redl <sebastian.redl_at_[hidden]> wrote:
> Thorsten Ottosen wrote:
>
> >1. have I misunderstood aligmnet completely when I thought that a single
> >data member was not guaranteed to be aligned, but an array ways?
> >(your aligned types use a data member, your unaligned use a char array).
> >
> >
> Every variable is aligned according to its own alignment requirements.
> Typically, a variable needs to be aligned on a boundary of its own size,
> i.e. a byte type must be byte-aligned, a word type word-aligned and so on.
> An array is always aligned according to its underlying type.
> Thus, to get a simple aligned type, just use a member of that type. To
> get an unaligned type, you need to allocate storage that is
> byte-aligned, and the easiest way of doing this is using a char[sizeof(T)].
> I hope that answers the question as well.

Yes, that's correct. One minor note, though, is that the unaligned
storage is actually char[num_bytes].  That's because sizeof(T) ==
num_bytes if the cover type is the same size as the endian type, but
for, say, a 7 byte endian number the cover type is typically 8 bytes,
so char[sizeof(T)] would  be one byte too large.

--Beman