* Question with "container_of(ptr, type, member)"
@ 2011-08-30 10:44 peter
2011-08-30 23:14 ` Ryan Mallon
0 siblings, 1 reply; 3+ messages in thread
From: peter @ 2011-08-30 10:44 UTC (permalink / raw)
To: linux-kernel
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~)
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: Question with "container_of(ptr, type, member)"
2011-08-30 10:44 Question with "container_of(ptr, type, member)" peter
@ 2011-08-30 23:14 ` Ryan Mallon
2011-08-31 0:52 ` peter
0 siblings, 1 reply; 3+ messages in thread
From: Ryan Mallon @ 2011-08-30 23:14 UTC (permalink / raw)
To: peter; +Cc: linux-kernel
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
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: Question with "container_of(ptr, type, member)"
2011-08-30 23:14 ` Ryan Mallon
@ 2011-08-31 0:52 ` peter
0 siblings, 0 replies; 3+ messages in thread
From: peter @ 2011-08-31 0:52 UTC (permalink / raw)
To: Ryan Mallon; +Cc: linux-kernel
I see now, It can gives an waring: "warning: initialization from
incompatible pointer type", when give it an wrong type.
thanks for your answer!
On Wed, 2011-08-31 at 09:14 +1000, Ryan Mallon wrote:
> 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
>
^ permalink raw reply [flat|nested] 3+ messages in thread
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2011-08-30 10:44 Question with "container_of(ptr, type, member)" peter
2011-08-30 23:14 ` Ryan Mallon
2011-08-31 0:52 ` peter
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