Re: How to get buffer byte length (not number of characters)?

[Eli Zaretskii <eliz@gnu.org>]

> From: Joseph Turner <joseph@ushin.org>
> Cc: emacs-devel@gnu.org
> Date: Sun, 25 Aug 2024 23:49:52 -0700
> 
> Joseph Turner <joseph@ushin.org> writes:
> 
> > Eli Zaretskii <eliz@gnu.org> writes:
> >
> >> you need to consider the encoding process: Emacs always encodes the
> >> buffer text on output to the external world.  If this is what you
> >> want, then you need to use bufferpos-to-filepos, and make sure you
> >> pass the correct coding-system argument to it.
> >
> > Will the following code ever signal an error?
> >
> > (bufferpos-to-filepos
> >  (point-max) 'exact
> >  (select-safe-coding-system (point-min) (point-max)))
> >
> > The `bufferpos-to-filepos' docstring says, "It is an error to request
> > the ‘exact’ method when the buffer’s EOL format is not yet decided."
> >     
> > IOW, does `select-safe-coding-system' always return an encoding which
> > specifies EOL conversion?
> 
> Let me rephrase: I would like to get the size of a buffer's text encoded
> with the return value of select-safe-coding-system, which may return an
> encoding which does not specify EOL conversion.  Is there any way to
> calculate the `exact' buffer text size using bufferpos-to-filepos?
> 
> Or is `approximate' the only viable argument in this case?

Unless you must deal with exotic encodings (like iso-2022 and its
derivatives), I suggest to always use 'approximate'.