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

["Robert P. J. Day" <rpjday@mindspring.com>]

On Mon, 1 Jan 2007, Christoph Hellwig wrote:

> 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)

the former is the way it's presented in CodingStyle currently, it
wasn't my personal opinion on the subject.  i was just reproducing
what was already there.

> > + (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.

it might be a bit late to put a cork in *that* bottle:

  $ grep -r "#define.*({" *

rday