linux-kernel - Re: Question with "container

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Message-ID: <4E5D6EF3.3000908@gmail.com>
Date:	Wed, 31 Aug 2011 09:14:59 +1000
From:	Ryan Mallon <rmallon@...il.com>
To:	peter <lifulong2c2i2c@...il.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: Question with "container_of(ptr, type, member)"

On 30/08/11 20:44, peter wrote:
> I have a question about the macro " container_of(ptr, type, member) "
> I can write it as this,
>   #define container_of(ptr, type, member) ({ \
> 	(type *) ((char *) ptr - offset_of(type, member)); \
> 	})
> It can act the same as
> #define container_of(ptr, type, member) ({            \
> 	 const typeof( ((type *)0)->member ) *__mptr = (ptr);    \
> 	 (type *)( (char *)__mptr - offsetof(type,member) );})
> So why we don't use the first one ?
> Thanks for your answer.
> (I am a kernel newbie ,and sorry for my poor english~)

The version used by the Linux kernel does type checking.

~Ryan

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