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

[Randy Dunlap]

Robert P. J. Day wrote:
> 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.*({" *

We aren't trying to prevent its past use.  We just aren't encouraging
the use of gcc extensions if there are reasonable & better ways to
do something.

--
~Randy
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