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From: chris@umcp-cs.UUCP
Newsgroups: net.unix,net.unix-wizards
Subject: Re: Not a typewriter
Message-ID: <2024@umcp-cs.UUCP>
Date: Sun, 15-Jun-86 17:23:05 EDT
Article-I.D.: umcp-cs.2024
Posted: Sun Jun 15 17:23:05 1986
Date-Received: Tue, 17-Jun-86 11:07:30 EDT
References: <1683@homxb.UUCP> <542@codas.ATT.UUCP>
Reply-To: chris@maryland.UUCP (Chris Torek)
Organization: University of Maryland, Dept. of Computer Sci.
Lines: 33
Xref: watmath net.unix:8173 net.unix-wizards:18421

In article <542@codas.ATT.UUCP> mikel@codas.ATT.UUCP (Mikel Manitius) writes:
>I think there may be one or two system calls that will alter
>errno to be 25, without returning a non-zero value, when in
>fact there was no error.

There are many library routines that may alter errno without in
fact failing; but there are no system calls that will do so.  This
is really the main distinction between manual sections 2 and 3,
as far as user code is concerned.

Incidentally, this points up a problem even with `good' error
handling routines.  I tend to write, e.g.,

	if ((fp = fopen(name, "w")) == NULL)
		error(1, errno, "cannot open %s for writing", name);

which usually results in a message like this:

	snerfle: cannot open breuglitz for writing: Permission denied

However, if the open failure were due to, say, running out of stdio
descriptors (but NOT file descriptors), it might say something wildly
inappropriate:

	snerfle: cannot open breuglitz for writing: Not a directory

My own opinion is that section 3 routines should set errno on errors
too.  (Actually, I think that `errno' itself should go away, but I
have no good replacement for it.)
-- 
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