linux-kernel - Re: do { } while (0) question

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Date:	Tue, 01 Aug 2006 11:45:53 +0159
From:	Jiri Slaby <jirislaby@...il.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Hua Zhong <hzhong@...il.com>,
	'Heiko Carstens' <heiko.carstens@...ibm.com>,
	'Andrew Morton' <akpm@...l.org>, linux-kernel@...r.kernel.org,
	'Martin Schwidefsky' <schwidefsky@...ibm.com>
Subject: Re: do { } while (0) question

Peter Zijlstra wrote:
> On Tue, 2006-08-01 at 02:03 -0700, Hua Zhong wrote:
>>> #if KILLER == 1
>>> #define MACRO
>>> #else
>>> #define MACRO do { } while (0)
>>> #endif
>>>
>>> {
>>> 	if (some_condition)
>>> 		MACRO
>>>
>>> 	if_this_is_not_called_you_loose_your_data();
>>> }
>>>
>>> How do you want to define KILLER, 0 or 1? I personally choose 0.
>> Really? Does it compile?
> 
> No, and that is the whole point.
> 
> The empty 'do {} while (0)' makes the missing semicolon a syntax error.

Bulls^WNope, it was a bad example (we don't want to break the compilation, just 
not want to emit a warn or an err).

I can't emit an error with the thing like that, only a warning, but we are not 
using -Werror to get err from a warn. Thing such this would emit empty-statement 
warn if define KILLER as 1:
#if KILLER == 1
#define MACRO
#else
#define MACRO do { } while (0)
#endif

{
  	if (some_condition)
  		MACRO;
	else
		do_something();
}

regards,
-- 
<a href="http://www.fi.muni.cz/~xslaby/">Jiri Slaby</a>
faculty of informatics, masaryk university, brno, cz
e-mail: jirislaby gmail com, gpg pubkey fingerprint:
B674 9967 0407 CE62 ACC8  22A0 32CC 55C3 39D4 7A7E
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