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Date: Fri, 1 Dec 2017 18:19:17 +0100
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: fseek(...,SEEK_CUR) calls _fflush_r(ptr, fp) in read only mode
Message-ID: <20171201171917.GB4325@calimero.vinschen.de>
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On Dec  1 17:02, Xiaofeng Liu via cygwin wrote:
> In ftello.c, it intentionally skipped fflush for read mode:
> https://github.com/openunix/cygwin/blob/master/newlib/libc/stdio/ftello.c=
#L121
>=20
> /* Find offset of underlying I/O object, then adjust for buffered=C2=A0 =
=C2=A0 =C2=A0bytes.=C2=A0 Flush a write stream, since the offset may be alt=
ered if=C2=A0 =C2=A0 =C2=A0the stream is appending.=C2=A0 Do not flush a re=
ad stream, since we=C2=A0 =C2=A0 =C2=A0must not lose the ungetc buffer.=C2=
=A0 */=C2=A0 if (fp->_flags & __SWR)=C2=A0 =C2=A0 _fflush_r (ptr, fp);
> But in fseeko.c, when fseek(..., SEEK_CUR) requires to get the current po=
sition first. But it calls _fflush_r(ptr, fp) in read mode, which screwed u=
p the current position after fflush.=C2=A0
> https://github.com/openunix/cygwin/blob/master/newlib/libc/stdio/fseeko.c=
#L174
>=20
>=20
> For my job, if I skip _fflush_r for read only mode in fseek(..., SEEK_CUR=
), the job runs OK.=C2=A0
> Considering fseek(..., SEEK_CUR) is a basic call, could my understanding =
be wrong?=C2=A0

Please provide a simple, self-contained testcase.  It might clear
up the problem.


Corinna

--=20
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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