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Date: Mon, 25 Oct 2021 14:44:31 +0200
From: Quentin Rameau <>
Subject: Re: request: please detect reads from stdin with unflushed
 writes to stdout

> Hello,

Hi Lorenzo,

> there are a few programs around that do something like
> printf("question: ");
> fgets(ans, sizeof ans, stdin);
> without fflushing stdout and get away with it because it happens to work
> under glibc.
> (fyi the ones I stumbled onto are mkfs.xfs and, vipw/vigr from util-linux,
> then the developer noticed the same with chfn/chsh)
> Ideally that would be taken care of by either some compiler warning (but
> not even clang's -Weverything catches that) or by some static analysis
> tool, but I couldn't find any.
> ... with do_something() being either flushing stdout or printing some kind
> of warning to stderr (isatty?) or to syslog.
> Any suggestion, corrections etc are obviously very welcome.

Suggestion: fix those broken programs!

If one wants to make sure what you print is flushed at a certain point,
ones have to flush the stream.

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