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Date: Tue, 25 Nov 2003 18:21:13 -0800
From: Terry Lambert <tlambert2@mindspring.com>
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To: Stefan Farfeleder <stefan@fafoe.narf.at>
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cc: "boyd, rounin" <boyd@insultant.net>
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Subject: Re: [PATCH] libc_r bug: successful close(2) sets errno to ENOTTY
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Stefan Farfeleder wrote:
> On Mon, Nov 24, 2003 at 07:05:02PM +0100, boyd, rounin wrote:
> > From: "Jacques A. Vidrine" <nectar@FreeBSD.org>
> > > The application is broken.  You must only check errno if you get an
> > > error indication from the library call.
> >
> > errno is only meaningful after a syscall error.
> 
> Wrong, counter-example: strtol().

Wrong; the standard specifies that the errno shall only be
checked when the return value is -1.  The exception in the
strtol() case is only for presetting errno to 0 before you
make the call, and making a check only following a -1 return.

You cannot make assumptions about underlying implementations;
they may be either system calls or library routines, and your
application is not supposed to know or depend on which case
prevails.

-- Terry