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From: frankw@hpcvra.CV.HP.COM (Frank Wales)
Newsgroups: comp.lang.c
Subject: Re: Multi-statement macros (again)
Message-ID: <17000001@hpcvra.CV.HP.COM>
Date: 9 Feb 90 22:01:47 GMT
References: <1990Feb8.235051.21779@aqdata.uucp>
Organization: Hewlett-Packard Co., Corvallis, OR, USA
Lines: 23

In some article, sullivan@aqdata.uucp (Michael T. Sullivan) wrote:
[an article about writing macros which do things that are forbidden
 in expressions, like using return, which concluded with...]

>I then changed BEGIN_ and END_BLOCK to:

>#define	BEGIN_BLOCK	do { if (1) {
>#define	END_BLOCK	} } while (0)

>This seems to make everything happy.  My question is, will this make other
>machines happy?  We are using a 3B2/400 SVR3 and it didn't even complain
>when just braces were used (resulting in "};").  Does this shut everything
>up on YOUR machine?

I have used the do { ... } while(0) trick on many occasions to write macros
which declare temporary variables.  This produces a warning of the form
"constant in conditional context" when compiled on an HP9000 PA machine
(s600 or s800), which I live with (a compiler directive to get rid of
it on a case-by-case basis would be useful, but I'm not that bothered;
I would definitely not want an option which just lost all these warnings).
--
Frank Wales, Guest of HP Corvallis, [frank@zen.co.uk||frankw@hpcvdq.cv.hp.com]
Zengrange Ltd., Greenfield Rd., LEEDS, England, LS9 8DB. (+44) 532 489048 x217