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Date: Fri, 26 Jun 2020 07:14:00 +0200
From: Markus Wichmann <>
Subject: Re: errno not set to EBADF when reading from invalid

On Thu, Jun 25, 2020 at 11:38:04AM -0400, Rich Felker wrote:
> Note that there are lots of other reasons you can't safely use stdio
> read functions on a stream you don't know is suitable for it.
> Switching from writing to reading without a successful flush produces
> UB, and switching the other direction without a successful seek does,
> even if the FILE stream is open for both.
> Rich

So I can't actually use a FILE open for reading and writing that refers
to something non-seekable, like a serial line, to both read and write to
it? I mean, I suppose I could write something and then flush and stay in
read mode forever, but that is not really the nature of my application.
I suppose I'll just open the serial line twice.


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