linux-kernel - Re: container-of Implementation

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Message-ID: <CAMuHMdVR_pviGjD4qUZtkSQR9Cst2cRQv53205E00CUxEGr33Q@mail.gmail.com>
Date:	Mon, 14 Jan 2013 13:23:21 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Schrober <franzschrober@...oo.de>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: container-of Implementation

On Mon, Jan 14, 2013 at 11:46 AM, Schrober <franzschrober@...oo.de> wrote:
> I wondered why the container_of implementation is so complicated.
>
> #define container_of(ptr, type, member) ({                      \
>         const typeof( ((type *)0)->member ) *__mptr = (ptr);    \
>         (type *)( (char *)__mptr - offsetof(type,member) );})
>
> isn't the __mptr not unnecessary? Why not following version?
>
> #define container_of(ptr, type, member) \
>     ((type *)((char *)(ptr) - offsetof(type, member)))

The __mptr construct will cause a compiler warning if ptr is of the
wrong type.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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