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From: rpw3@amdcad.AMD.COM (Rob Warnock)
Newsgroups: comp.lang.c
Subject: Re: Perror complication
Message-ID: <18005@amdcad.AMD.COM>
Date: Fri, 21-Aug-87 22:27:55 EDT
Article-I.D.: amdcad.18005
Posted: Fri Aug 21 22:27:55 1987
Date-Received: Sun, 23-Aug-87 06:47:40 EDT
References: <8913@brl-adm.ARPA> <8048@mimsy.UUCP>
Reply-To: rpw3@amdcad.UUCP (Rob Warnock)
Organization: [Consultant] San Mateo, CA
Lines: 33

Sometimes when I get really frustrated by the fact that a successful
system call does *not* clear errno, I use the following macro:

	#define ERRED(x)   ((errno = 0), (x), errno != 0)

So you can say things like:

	while (ERRED(pid = fork())) {
		/* handle fork() failure */
		...decide how many times to sleep + loop, or
		   whether to exit() or longjmp() or what...
	}
	if (pid) {
		...parent...
	} else {
		...child...
	}

This bypasses problems with syscalls that can return "-1" as a valid successful
result, such as "nice()", and also avoids the "Not a typewriter" syndrome.

The problem is I don't use it consistently (nor does anyone else) and
therefore it can sometimes be a hindrance to maintenance rather than a help
(the old "Bourne Shell ALGOL" problem).  ;-}  ;-}


Rob Warnock
Systems Architecture Consultant

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