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Path: utzoo!watmath!clyde!burl!ulysses!allegra!mit-eddie!genrad!decvax!mulga!munnari!murdu!prl
From: prl@murdu.OZ (Peter Lamb)
Newsgroups: net.lang.c
Subject: Re: on1 construct
Message-ID: <159@murdu.OZ>
Date: Thu, 8-Nov-84 14:42:52 EST
Article-I.D.: murdu.159
Posted: Thu Nov  8 14:42:52 1984
Date-Received: Fri, 9-Nov-84 08:48:57 EST
References: <124@cadvax>, <4594@fortune.UUCP>
Organization: Melbourne Uni, Australia
Lines: 32

[]
A nice way to put on1 in is to avoid the text of the on1 being part
of the macro. This involves a pretty grotty-looking if (with side-effects)
so if you want to keep pure, read no further:

#define on1	static int _not1_ = 0; if(!_not1_ && (_not1_ = 1))

then on1 has EXACTLY the same behavior as the if, except that it must be
the first statement unless the whole lot is covered by {}'s.

eg:
	on1	do_this();
	else	do_that();

or:
	on1 {
		blah, blech; blah;
	}

If you don't want the on1 code as the first `executable' statement then

	{
		on1	do_this();
		else	do_that();
	}

will get you out of trouble, albeit inelegantly.

	Peter Lamb,	......!decvax!mulga!prl
	University of Melbourne
	Parkville 3052
	Australia