fflush(NULL) clobbers input streams
Corinna Vinschen
corinna-cygwin@cygwin.com
Tue Jul 18 09:55:00 GMT 2017
On Jul 17 19:53, Achim Gratz wrote:
>
> Perl configure for 5.22.1 on Cygwin 2.4.0 said this:
>
> --8<---------------cut here---------------start------------->8---
> Checking how to flush all pending stdio output...
> Your fflush(NULL) works okay for output streams.
> Let's see if it clobbers input pipes...
> fflush(NULL) seems to behave okay with input streams.
> --8<---------------cut here---------------end--------------->8---
>
> I'm reasonably certain that the intervening Perl versions were also this
> way, but I didn't keep the log files around unfortunately.
>
> Now, using Cygwin 2.8.x to configure Perl 5.22.4 I got this instead:
>
> --8<---------------cut here---------------start------------->8---
> Checking how to flush all pending stdio output...
> Your fflush(NULL) works okay for output streams.
> Let's see if it clobbers input pipes...
> Ouch, fflush(NULL) clobbers input pipes! We will not use it.
> Good, at least fflush(stdin) seems to behave okay when stdin is a pipe.
> Sigh. Flushing explicitly all the stdio streams doesn't work.
> --8<---------------cut here---------------end--------------->8---
>
> It seems that fflush is only supposed to discard buffered input data on
> seekable files, but not pipes (per POSIX.1-2008), so this looks a
> regression to me.
Did you try to bisect the issue?
Corinna
--
Corinna Vinschen Please, send mails regarding Cygwin to
Cygwin Maintainer cygwin AT cygwin DOT com
Red Hat
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