linux-kernel - Re: macros: "do-while" versus "({ })" and a compile-time error

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Message-ID: <45A3CC15.1030005@zytor.com>
Date:	Tue, 09 Jan 2007 09:08:37 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"Robert P. J. Day" <rpjday@...dspring.com>
CC:	Linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: macros:  "do-while" versus "({ })" and a compile-time error

Robert P. J. Day wrote:
>   just to stir the pot a bit regarding the discussion of the two
> different ways to define macros, i've just noticed that the "({ })"
> notation is not universally acceptable.  i've seen examples where
> using that notation causes gcc to produce:
> 
>   error: braced-group within expression allowed only inside a function
> 
> i wasn't aware that there were limits on this notation.  can someone
> clarify this?  under what circumstances *can't* you use that notation?
> thanks.
> 

Well, you can apparently not use it as a part of a constant expression 
(which makes sense; do-while is illegal there too.)  That would be the 
only case in which an expression is permitted outside a function at all.

	-hpa

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