From: me22 <me22.ca@gmail.com>
To: ranjith kumar <ranjithproxy@gmail.com>
Cc: gcc-help@gcc.gnu.org
Subject: Re: sizeof empty class
Date: Fri, 09 Apr 2010 05:03:00 -0000 [thread overview]
Message-ID: <x2rfa28b9251004082203se7dec54ei53c5156c88a91e44@mail.gmail.com> (raw)
In-Reply-To: <t2u31cff80d1004080201gb7337940m34494bdebbf747b@mail.gmail.com>
On 8 April 2010 05:01, ranjith kumar <ranjithproxy@gmail.com> wrote:
>
> 1) What is the size of an an empty class? On my machine it is showing 1
>
Assuming you mean in C++...
struct Empty {};
Different objects of the same type must have different addresses, so
to allow for arrays, sizeof(Empty) must be > 0.
Empty a[2];
a != a+1 <=> (Empty*)((char*)a + sizeof(Empty))
There is, however, an "empty base class" optimization that the
compiler will try to perform.
struct D : Empty {};
You will probably find that sizeof(D) == sizeof(Empty), rather than
sizeof(D) == 2*sizeof(Empty).
But remember that, for a given type, different object <=> different
address applies to empty base classes too:
struct D2 : D, Empty {};
Because D2 contains 2 sub-objects of type Empty (one a base of D2, one
a base of D), sizeof(D2) >= 2*sizeof(Empty) >= 2.
~ Scott McMurray
prev parent reply other threads:[~2010-04-09 5:03 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-04-08 9:01 ranjith kumar
2010-04-08 11:20 ` John (Eljay) Love-Jensen
2010-04-09 3:38 ` leon zadorin
2010-04-09 5:03 ` me22 [this message]
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