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From: Kaz Kylheku <643-408-1753@kylheku.com>
Newsgroups: comp.lang.c
Subject: Re: C90 fpeek
Date: Sat, 25 Jan 2025 00:50:14 -0000 (UTC)
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On 2025-01-24, Scott Lurndal <scott@slp53.sl.home> wrote:
> Kaz Kylheku <643-408-1753@kylheku.com> writes:
>>It absolutely does; have you never done a poll() or select() on a tty
>>file descriptor?
>
> Hundreds of times over the last 35 years.  Never on a buffered stdio
> stream for which poll is basically useless.

It totally works, if done right.

> And always with O_NONBLOCK set
> on the file descriptor (from open, not fopen+fileno()), usually with
> the underlying tty or pty set to so-called 'raw' mode.

You can fdopen that that, fread or getchar until EOF + errno ==
EWOULDBLOCK, then poll the fileno. Clear the error state with
clearerr and off you go: you can read from the stream to refill
its buffer and get bytes.

It can be very useful!

In any case, if you ever find yourself building a little buffering layer
over a file descriptor, it's something to think about: could the
requirements just be satisfied with old stdio?

Just because the requirements for situations like timed out reads, or
multiplexing multiple buffered streams with one thread --- that does not
pull stdio off the table!

-- 
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