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Date: Mon, 16 Aug 2010 13:32:31 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: Re: [Qemu-devel] Re: [PATCH 1/5] HACKING: add preprocessor rules
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To: Blue Swirl <blauwirbel@gmail.com>
Cc: Andreas Schwab <schwab@linux-m68k.org>, qemu-devel <qemu-devel@nongnu.org>

On 08/16/2010 01:05 PM, Blue Swirl wrote:
> On Sun, Aug 15, 2010 at 9:27 PM, Andreas Schwab<schwab@linux-m68k.org>  wrote:
>    
>> Blue Swirl<blauwirbel@gmail.com>  writes:
>>
>>      
>>> +For variadic macros, stick with C99 syntax:
>>> +
>>> +#define DPRINTF(fmt, ...)                                       \
>>> +    do { printf("IRQ: " fmt, ## __VA_ARGS__); } while (0)
>>>        
>> That's not C99 syntax, the combination with ## is a gcc extension.  In
>> C99 you cannot have an empty __VA_ARGS__.
>>      
> That's too bad, I picked the example from one of our current macros.
> Maybe just s/C99/this/ or perhaps we shouldn't specify any
> non-standard syntax.
>    

We definitely should discourage the GCC syntax [#define fn(arg...)] as 
it's deprecated by the new C99 syntax.  Very specifically, only the '##' 
is an extension and it's a widely adopted one.

Regards,

Anthony Liguori