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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c
Subject: Re: Question regarding fwrite() and fflush()
Date: Tue, 25 Jun 2024 13:55:47 -0700
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Lew Pitcher <lew.pitcher@digitalfreehold.ca> writes:

> In a recent reply here, I posted some code that used fwrite() to write
> binary data to a file.  One version of this code used mmap() to access
> this binary data in-situ, and I wonder if I should have called fflush()
> before calling mmap().
>
> I understand the where to use fflush() on standard text formatted output
> (where you use fprintf(), etc to externalize the output), but I don't see
> anything my copies of either the ISO C or POSIX standards that say that
> I /should/ use fflush(), but neither do I see anything that says I /need
> not/ use fflush().
>
> So, wiser and more experienced minds, should I use fflush() in this case
> or not?

Yes, do use fflush().

In the alternative, do a setbuf( file, 0 ) so that 'file' is
unbuffered.