Re: Zero length Objects

["Nick Roberts" <nick.roberts@acm.org>]

"Xenos" <dont.spam.me@spamhate.com> wrote in message
news:cc15on$nsc5@cui1.lmms.lmco.com...

> C++ has a similar rule that says an object cannot be zero bytes in
> size, but it does says that an empty (no data members) base class
> may be zero size within the inherited class.  Does Ada have a
> similar rule to this?

As far as I am aware, the Ada standard permits types, subtypes, and objects
of zero size. I think that X'Size must return 0 if it has been set to 0 (by
a representation clause) for any subtype or object X, but there is nothing
in the standard to prevent objects of zero size being allocated more than
zero bits when they are allocated in memory (and I gather this is what many
compilers actually do).

> Meaning if I create a null record and derive a another record from it,
> will the null record take up zero space within the derived record?

Again, I don't think the standard mandates exactly what the comnpiler does
by default. However, of course, you can always /tell/ the compiler where and
how big a member should be (in a record representation clause). Oddly, you
can specify something like:

      Empty_Member at 0 range 1..0;

in order to tell the compiler that Empty_Member is to take up no space in
the record.

> Sorry, if my terminology isn't exact for Ada, I a little new to the 95
> standard.

I have the same problem with C++ :-)

-- 
Nick Roberts