reason for code like this: "do { something } while (0)"

Hi,

I'm asking a pretty amateur question.

I've come accross code like this huge number of times in the kernel:

#define __set_task_state(tsk, state_value) \
do { (tsk)->state = (state_value); } while (0)

What is the reason to use do while loop if it is only meant to be
executed just once? Why not a simple:

#define __set_task_state(tsk, state_value) \
{ (tsk)->state = (state_value); }

TIA,

Rajat
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Re: reason for code like this: "do { something } while (0)"

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On 5/15/06, Rajat Jain wrote:
>
> Hi,
>
> I'm asking a pretty amateur question.
>
> I've come accross code like this huge number of times in the kernel:
>
> #define __set_task_state(tsk, state_value) \
> do { (tsk)->state =3D (state_value); } while (0)
>
> What is the reason to use do while loop if it is only meant to be
> executed just once? Why not a simple:
>
> #define __set_task_state(tsk, state_value) \
> { (tsk)->state =3D (state_value); }
>
> TIA,
>
> Rajat
>
> --
> Kernelnewbies: Help each other learn about the Linux kernel.
> Archive: http://mail.nl.linux.org/kernelnewbies/
> FAQ: http://kernelnewbies.org/faq/
>
>
See this
http://kernelnewbies.org/FAQ/DoWhile0

Rgds,
Adil

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Re: reason for code like this: "do { something } while (0)"

> What is the reason to use do while loop if it is only meant to be
> executed just once? Why not a simple:

look at kernelnewbies faq/google/search the archives for this list.

anupam

--
In the beginning was the lambda, and the lambda was with Emacs, and
Emacs was the lambda.
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Please read the FAQ at http://www.linux-learn.org/faqs

Re: reason for code like this: "do { something } while (0)"

On 15/05/06, Rajat Jain wrote:
> Hi,
>
> I'm asking a pretty amateur question.
>
> I've come accross code like this huge number of times in the kernel:
>
> #define __set_task_state(tsk, state_value) \
> do { (tsk)->state = (state_value); } while (0)
>
> What is the reason to use do while loop if it is only meant to be
> executed just once? Why not a simple:
>
> #define __set_task_state(tsk, state_value) \
> { (tsk)->state = (state_value); }
>

http://www.kernelnewbies.org/FAQ/DoWhile0

--
Jesper Juhl
Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html
Plain text mails only, please http://www.expita.com/nomime.html
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