From: William Lee Irwin III <wli@holomorphy.com>
To: Darren Williams <dsw@gelato.unsw.edu.au>
Cc: Linux Kern <linux-kernel@vger.kernel.org>
Subject: Re: VM code question
Date: Mon, 13 Oct 2003 18:44:27 -0700 [thread overview]
Message-ID: <20031014014427.GL16158@holomorphy.com> (raw)
In-Reply-To: <20031014013227.GA20406@cse.unsw.EDU.AU>
On Tue, Oct 14, 2003 at 11:32:27AM +1000, Darren Williams wrote:
> I have a small question wrt some VM code.
> source file is include/linux/kernel.h
> #define container_of(ptr, type, member) ({ \
> const typeof( ((type *)0)->member ) *__mptr = (ptr); \
> (type *)( (char *)__mptr - offsetof(type,member) );})
> what is the use of the 0 (zero) in the typeof? I am thinking
> that we are casting 0 to (type *) then referencing 'member' of
> 'type', however why do we require the 0 ?
> Just curious
It's an address calculation method. We subtract the address of the
start of the structure from the address of the member inside the
structure.
-- wli
next prev parent reply other threads:[~2003-10-14 1:41 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-10-14 1:32 VM code question Darren Williams
2003-10-14 1:44 ` William Lee Irwin III [this message]
2003-10-14 1:52 ` Nick Piggin
2003-10-14 2:03 ` William Lee Irwin III
2003-10-14 5:07 ` Matt Mackall
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