linux-kernel - Re: [PATCH] Documentation: Explain a second alternative for multi-line macros.

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Date:	Mon, 1 Jan 2007 14:20:20 +0000
From:	Christoph Hellwig <hch@...radead.org>
To:	"Robert P. J. Day" <rpjday@...dspring.com>
Cc:	Linux kernel mailing list <linux-kernel@...r.kernel.org>,
	Randy Dunlap <randy.dunlap@...cle.com>, trivial@...nel.org
Subject: Re: [PATCH] Documentation: Explain a second alternative for multi-line macros.

On Sun, Dec 31, 2006 at 02:32:25PM -0500, Robert P. J. Day wrote:
> + (a) Enclose those statements in a do - while block:
> +
> +	#define macrofun(a, b, c) 		\
> +		do {				\
> +			if (a == 5)		\
> +				do_this(b, c);	\
> +		} while (0)

nitpick, please don't add an indentaion level for the do {.  Do this
should look like:

	#define macrofun(a, b, c) 	\
	do {				\
		if (a == 5)		\
			do_this(b, c);	\
	} while (0)


> + (b) Use the gcc extension that a compound statement enclosed in
> +     parentheses represents an expression:
> +
> +	#define macrofun(a, b, c) ({		\
>  		if (a == 5)			\
>  			do_this(b, c);		\
> -	} while (0)
> +	})

I'd rather document to not use this - it makes the code far less
redable.  And it's a non-standard extension, something we only
use if it provides us a benefit which it doesn't here.

-
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