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From: chris@umcp-cs.UUCP (Chris Torek)
Newsgroups: net.lang.c
Subject: Re: e1?(void_e2):(void_e3)
Message-ID: <2938@umcp-cs.UUCP>
Date: Wed, 13-Aug-86 23:01:01 EDT
Article-I.D.: umcp-cs.2938
Posted: Wed Aug 13 23:01:01 1986
Date-Received: Thu, 14-Aug-86 08:27:02 EDT
References: <155@cbnap.UUCP> <499@dg_rtp.UUCP> <518@hadron.UUCP> <243@desint.UUCP>
Reply-To: chris@umcp-cs.UUCP (Chris Torek)
Organization: University of Maryland, Dept. of Computer Sci.
Lines: 46

In article <243@desint.UUCP> geoff@desint.UUCP (Geoff Kuenning) writes:
>... let us not forget that there is *no* reason to ever write this
>particular expression.  Anywhere it's useful, you can just write
>
>	if (e1)
>	    void_e2;
>	else
>	    void_e3;

Not so!  The above is a statement, while `e1 ? void_e2 : void_e3' is an
expression; and expressions are useful in macros:

	#define strange()	((e1 ? void_e2 : void_e3), arbitrary_e4)

Using

	#define	strange()	if (e1) void_e2; else void_e3; arbitrary_e4

means that

	if (x) strange(); else ...

no longer works.

As a last resort, I now use the following for inline functions
returning void:

	#ifdef lint
	#define _false_ rand()
	#else
	#define _false_ 0
	#endif

	#define	strange() \
		do { \
			s1; \
			... \
			sn; \
		} while (_false_)

The funny `_false_' keeps lint from warning about constants in
conditional contexts.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 1516)
UUCP:	seismo!umcp-cs!chris
CSNet:	chris@umcp-cs		ARPA:	chris@mimsy.umd.edu