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From: Artem Belevich <art@freebsd.org>
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Cc: "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org>
Subject: Re: Question about lseek/fseek
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On Sat, Jul 2, 2011 at 6:57 AM, Martin M=F6ller
<moeller.akt@googlemail.com> wrote:
> Hi Hackers,
>
> why does these function allow seeking beyond the EOF of a file in
> O_RDONLY/=B2rb=B2 mode ?

Perhaps because the standard explicitly says that it's allowed:
http://pubs.opengroup.org/onlinepubs/009695399/functions/lseek.html

> How does these function then signal the EOF correctly ?

It does not. It only sets offset for a given file descriptor. It's
read's job to signal EOF.

> Seeking beyond the EOF makes sense for me in write-mode but not in read-o=
nly
> mode !

Given that lseek does not change file size (I.e. it does not ever
modify the file), there's no reason to prohibit seek beyond end of
file even in read-only mode.

Now, if you would try to read after seeking beyond EOF, then the
read() should complain that there's no data.

--Artem

>
> With Regards,
> Martin
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