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Date: Fri, 26 Jun 2020 15:39:51 +1000 (AEST)
From: Damian McGuckin <>
Subject: Re: errno not set to EBADF when reading from invalid

On Fri, 26 Jun 2020, Markus Wichmann wrote:

> 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?

Certainly STDIO allows this, but you need to be very careful. about doing 

Years ago, I would send a string down a serial line opened Read/Write, as 
an atomic write, and then immediately, sit on the line waiting for a reply 
on the same serial line. I was simply trying to retreive the Postscript 
handshake between the system and the printer which was a very small number 
of characters.

Doing it with 2 FILEs is much smarter for the general case.

Regards - Damian

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