Re: Is this correct code for alignment?
Seungbeom Kim wrote:
kanze wrote:
A better solution in practice would probably involve taking
the address of the two members, converting them to char*, and
subtracting. Formally, however, this means having an
instance, which may not be practical (if, for example, T
doesn't have a default constructor).
I thought a better solution would be to use offsetof instead
of sizeof, and then soon it came to my mind that offsetof is
defined only for POD types. I don't know why taking an offset
is possible only for POD types; otherwise, offsetof would be
almost perfect for getting the alignment, wouldn't it?
If it worked, yes. I don't know the exact rationale behind the
current wording, but offsetof quite obviously cannot be used on
just any classe type---there are cases where the offset is not a
constante, e.g. where virtual inheritance is involved.
For this particular problem: the committee obviously didn't
consider it, or didn't consider it important enough to solve.
Had they done so, requiring offsetof to work in this case would
have solved the problem, but defining a new
macro/function/keyword to solve it explicitly would be even
cleaner and more straightforward.
--
James Kanze kanze.james@neuf.fr
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