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Re: character encoding question

From: Stefan Monnier
Subject: Re: character encoding question
Date: Wed, 20 Feb 2013 09:42:49 -0500
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3.50 (gnu/linux)

> So the character 中 has a codepoint of #o47055 in octal notation.

Internally, in your Emacs, yes.  This value actually depends on the
internal representation chosen by Emacs, which happens to be Unicode
since Emacs-23 (and was something else before).

> Meanwhile:
> (string-as-unibyte "中") --> \344\270\255

This again shows the internal byte representation of this char inside
a buffer, which is utf-8 since Emacs-23 and was something else before.
Strong recommendation: stay far away from string-as-* because that will
mess you up.
You want instead to use encode-coding-string.  E.g.

   (encode-coding-string "中" 'utf-8)  ==>  "\344\270\255"

> What's the correspondence between these bytes and the multibyte
> character's octal codepoint?

#o47055 is not "multibyte".  It's just its "name" aka "codepoint".
"\344\270\255" is one if its multibyte encodings.

> Are there any functions that will get from one to the other?

   (encode-coding-string (string #o47055) 'utf-8)  ==>  "\344\270\255"

> Given a series of mystery bytes, can I test them against different
> charsets, and see what gibberish Emacs comes up with?

   (decode-coding-string "\344\270\255" 'utf-8)  ==>   "中"

-- Stefan

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