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From: gvr@cs.brown.edu (George V. Reilly)
Newsgroups: comp.lang.c
Subject: Re: Using Macros
Message-ID: <46860@brunix.UUCP>
Date: 8 Aug 90 23:29:30 GMT
References: <362.26be9dcc@astro.pc.ab.com> <21057@grebyn.com> <642@travis.csd.harris.com> <17298@haddock.ima.isc.com>
Sender: news@brunix.UUCP
Reply-To: gvr@cs.brown.edu (George V. Reilly)
Organization: Brown University Department of Computer Science
Lines: 24

In article <17298@haddock.ima.isc.com> karl@kelp.ima.isc.com (Karl Heuer) writes:
! %   In article <642@travis.csd.harris.com> brad@SSD.CSD.HARRIS.COM (Brad Appleton) writes:
! %    Glad to see a few people finally mentioned the comma operator! Another 
! %    alternative along those same lines (with similar limitations) is to make
! %    use of the logical operators || and &&. Using this, the following:
! %    
! %    	#define CHECK(cond)  { if (cond)  exit(-1);  }
! %    
! %    could be replaced by
! %    
! %    	#define CHECK(cond)  ((cond) || exit(-1))
! %    
! Won't work if exit() is properly declared as void.  Try one of
! 	#define CHECK(cond)  ((cond) ? exit(-1) : (void)0)
! 	#define CHECK(cond)  ((cond) || (exit(-1), 0))
! 

Ah, but Karl, you missed the more important bug that Brad should have
used &&, not ||.  In Brad's example, exit() will only be called if
cond == 0, which is exactly the inverse of what is desired.  The same is
true of your second offering.
________________
George V. Reilly			gvr@cs.brown.edu
uunet!brunix!gvr   gvr@browncs.bitnet	Box 1910, Brown U, Prov, RI 02912