From: Stefan Monnier <monnier@iro.umontreal.ca>
To: Eli Zaretskii <eliz@gnu.org>
Cc: emacs-devel@gnu.org, Kenichi Handa <handa@m17n.org>
Subject: Re: Emacs 23 character code space
Date: Sat, 22 Nov 2008 23:16:49 -0500 [thread overview]
Message-ID: <jwvbpw7dr2w.fsf-monnier+emacs@gnu.org> (raw)
In-Reply-To: <uk5aviv36.fsf@gnu.org> (Eli Zaretskii's message of "Sat, 22 Nov 2008 18:28:13 +0200")
> What exactly is meant here by ``8-bit characters''? Do you mean
> eight-bit raw bytes, or do you mean Unicode characters whose
> codepoints are below 256?
It should be eight-bit raw bytes. In some cases it's difficult to tell
the difference, so Emacs may occasionally accept latin-1 chars as stand
ins for eight-bit raw bytes.
> Converting unibyte text to multibyte text leaves @acronym{ASCII}
> characters unchanged, and converts 8-bit characters (codes 128
> through 159) to the corresponding representation for
> multibyte text.
> Again, by ``8-bit characters'' you mean raw 8-bit bytes here, right?
Yes.
I think we should state somewhere that unibyte strings and buffers
contain bytes only. And that multibyte strings and buffers contain
chars. And that bytes are a subset of chars.
> @defun string-to-multibyte string
> This function returns a multibyte string containing the same sequence
> of characters as @var{string}. If @var{string} is a multibyte string,
> it is returned unchanged.
> @end defun
> I'm not sure I understand the effect of this function.
It returns a string containing the same bytes (in the sense of
ASCII+eight-bit, not in the sense of the underlying internal
representation, which we should as much as possible not mention
anywhere) but in a multibyte string instead. I.e. the output is
a multibyte string of the same length whose chars are bytes.
> @defun string-to-unibyte string
> This function returns a unibyte string containing the same sequence of
> characters as @var{string}. It signals an error if @var{string}
> contains a non-@acronym{ASCII} character. If @var{string} is a
> unibyte string, it is returned unchanged.
> @end defun
> Since this function handles any non-ASCII characters lossily, when
> would it be useful?
I think the "non-ASCII" part is incorrect. It probably should say
"non-byte char" instead. It's useful when you have a multibyte string
which you (think you) know only holds bytes.
In 99% (actually 99.99999% for the `as' case) of the cases you shouldn't
use string-{as/make/to}-{uni/multi}byte. Instead you should use
{en/de}code-coding-string.
> @defun multibyte-char-to-unibyte char
> This convert the multibyte character @var{char} to a unibyte
> character. If @var{char} is a non-@acronym{ASCII} character, the
> value is -1.
> @end defun
> @defun unibyte-char-to-multibyte char
> This convert the unibyte character @var{char} to a multibyte
> character.
> @end defun
> Again, when are these functions useful?
Rarely.
Stefan
next prev parent reply other threads:[~2008-11-23 4:16 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-11-01 14:20 Emacs 23 character code space Eli Zaretskii
2008-11-01 16:46 ` Eli Zaretskii
2008-11-03 1:34 ` Kenichi Handa
2008-11-03 12:45 ` Kenichi Handa
2008-11-03 20:13 ` Eli Zaretskii
2008-11-04 7:35 ` Kenichi Handa
2008-11-04 20:19 ` Eli Zaretskii
2008-11-05 12:27 ` Kenichi Handa
2008-11-05 18:23 ` Eli Zaretskii
2008-11-22 18:25 ` Eli Zaretskii
2008-11-26 1:41 ` Kenichi Handa
2008-11-26 4:13 ` Eli Zaretskii
2008-11-26 4:24 ` Kenichi Handa
2008-11-26 4:58 ` Kenichi Handa
2008-11-26 20:26 ` Eli Zaretskii
2008-11-26 22:52 ` Juanma Barranquero
2008-11-27 1:10 ` Stephen J. Turnbull
2008-11-27 1:35 ` Kenichi Handa
2008-11-26 20:18 ` Eli Zaretskii
2008-11-27 1:29 ` Kenichi Handa
2008-11-29 17:12 ` Eli Zaretskii
2008-12-02 5:40 ` Kenichi Handa
2008-11-28 13:19 ` Eli Zaretskii
2008-12-02 5:44 ` Kenichi Handa
2008-12-02 19:40 ` Eli Zaretskii
2008-11-29 12:01 ` Eli Zaretskii
2008-11-22 16:28 ` Eli Zaretskii
2008-11-23 4:16 ` Stefan Monnier [this message]
2008-11-23 11:22 ` Eli Zaretskii
2008-11-26 1:51 ` Kenichi Handa
2008-11-23 8:29 ` Ulrich Mueller
2008-11-23 11:11 ` Eli Zaretskii
2008-11-23 11:55 ` Ulrich Mueller
2008-11-24 3:06 ` Stefan Monnier
2008-11-26 1:31 ` Kenichi Handa
2008-11-22 17:03 ` New function: what-file-line, used when writing gdb script richardeng
2008-11-07 7:21 ` Emacs 23 character code space Kenichi Handa
2008-11-07 10:27 ` Eli Zaretskii
2008-11-07 11:52 ` Kenichi Handa
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