From owner-freebsd-current  Thu Jun 18 01:09:13 1998
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Date: Thu, 18 Jun 1998 10:10:00 +0200 (CEST)
From: Wolfgang Helbig <helbig@Informatik.BA-Stuttgart.DE>
Message-Id: <199806180810.KAA05630@RVC1.Informatik.BA-Stuttgart.DE>
To: imp@village.org, richard@cogsci.ed.ac.uk, tlambert@primenet.com
Subject: Re: Bogus errno twiddling by lstat...
Cc: current@FreeBSD.ORG
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> > No.  When a system call returns success, the value of errno is
> > undefined.
>
> No!  A successful system call leaves it *unchanged*.  From intro(2):
>
>      Successful calls never set errno; once set, it remains
>      until another error occurs.

The wording in intro(2) is misleading. It should be:

	Successful calls never set errno to zero;

> I believe ANSI C has a similar requirement.
No, from the standard:

	The value of errno my be set to nonzero by a library function call
	whether or not there is an error ...

> You should only examine errno after an error, but you are allowed to have
> had intervening successful system calls.

This would be nice, but a program that depends on this behaviour is
not portable.

Wolfgang

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