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

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Message-Id: <200608011449.k71En5VT015262@laptop13.inf.utfsm.cl>
Date:	Tue, 01 Aug 2006 10:49:05 -0400
From:	"Horst H. von Brand" <vonbrand@....utfsm.cl>
To:	Jiri Slaby <jirislaby@...il.com>
cc:	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 

Jiri Slaby <jirislaby@...il.com> wrote:
> Heiko Carstens wrote:
> > Hi Andrew,
> > your commit e2c2770096b686b4d2456173f53cb50e01aa635c does this:
> > ---
> > Always use do {} while (0).  Failing to do so can cause subtle compile
> > failures or bugs.
> > -#define hotcpu_notifier(fn, pri)
> > -#define register_hotcpu_notifier(nb)
> > -#define unregister_hotcpu_notifier(nb)
> > +#define hotcpu_notifier(fn, pri)	do { } while (0)
> > +#define register_hotcpu_notifier(nb)	do { } while (0)
> > +#define unregister_hotcpu_notifier(nb)	do { } while (0)
> 
> #if KILLER == 1
> #define MACRO
> #else
> #define MACRO do { } while (0)
> #endif
> 
> {
> 	if (some_condition)
> 		MACRO

                      ;  /* missing */
> 
> 	if_this_is_not_called_you_loose_your_data();
> }

> How do you want to define KILLER, 0 or 1? I personally choose 0.

Yep, at least in this case you'd get a compile failure.
-- 
Dr. Horst H. von Brand                   User #22616 counter.li.org
Departamento de Informatica                     Fono: +56 32 654431
Universidad Tecnica Federico Santa Maria              +56 32 654239
Casilla 110-V, Valparaiso, Chile                Fax:  +56 32 797513
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