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From: brad@sdcrdcf.UUCP (Brad Spear)
Newsgroups: net.lang.c
Subject: Re: on1 construct
Message-ID: <1449@sdcrdcf.UUCP>
Date: Wed, 7-Nov-84 15:18:08 EST
Article-I.D.: sdcrdcf.1449
Posted: Wed Nov  7 15:18:08 1984
Date-Received: Fri, 9-Nov-84 08:58:48 EST
References: <124@cadvax> <1448@sdcrdcf.UUCP>
Reply-To: brad@sdcrdcf.UUCP (Brad Spear)
Organization: System Development Corp. R+D, Santa Monica
Lines: 28
Summary: 

Silly me. If I had thought about it for 10 more minutes, I would have had a
better version the first time.  In this case, the _f doesn't have to be
negated every time. I thought I had ruled this case out, but I made a mistake
somewhere originally, and it does work.  Note that it depends on the fact
that "_f" is evaluated before "!(_f=FALSE)", which is what C is supposed to
guarantee.

#define ON_FIRST_TIME   static char _f = TRUE; if (_f && !(_f=FALSE))

This expression can be used like:

{       declarations ...

	ON_FIRST_TIME
	  {
	  blah1, blah1, blah1 ...
	  }
	blah2, blah2, blah2 ...
}

It will cause "blah1, blah1, blah1 ..." to be executed the first time only.

It would be nice if someone could figure out how to make a non-function block
return a value, then the expression could go anywhere, and the _f could be
totally invisible.

Brad Spear
sdcrdcf!brad