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Groups > comp.lang.c > #400745

Re: Default signedness of 'plain' char.

From cross@spitfire.i.gajendra.net (Dan Cross)
Newsgroups comp.lang.c
Subject Re: Default signedness of 'plain' char.
Date 2026-08-03 14:47 +0000
Organization PANIX Public Access Internet and UNIX, NYC
Message-ID <114q9lr$llq$1@reader1.panix.com> (permalink)
References <114nji9$li5u$1@news.xmission.com>

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In article <114nji9$li5u$1@news.xmission.com>,
Kenny McCormack <gazelle@shell.xmission.com> wrote:
>First off, I know the "standards" answer is "Either is correct; you have no
>right to complain about anything", but I am not interested in the
>"standards" answer.  If this is all you can do, then just click Next and go
>on.
>
>I'm interested in the "why" of why implementations might prefer one or the
>other.

The original ANSI C rationale touches on this; to quote two
excerpts:

From section 1.1, when discussing "Keep the spirit of C", they
mention, "Make it fast, even if it is not guaranteed to be
portable" and about this, say the following:

|The last proverb needs a little explanation. The potential for
|efficient code generation is one of the most important strengths
|of C. To help ensure that no code explosion occurs for what
|appears to be a very simple operation, many operations are
|defined to be _how the target machine’s hardware does it_ rather
|than by a general abstract rule. An example of this willingness
|to live with _what the machine does_ can be seen in the rules
|that govern the widening of `char` objects for use in
|expressions: whether the values of `char` objects widen to
|signed or unsigned quantities typically depends on which byte
|operation is more efficient on the target machine.

That is, whether `char` is treated as signed or unsigned depends
on the target.  The precedent for this seems to be taken from
history; later on, in the section on "Types" they write:

|Three types of char are specified: signed, plain, and unsigned.
|A plain char may be represented as either signed or unsigned,
|depending upon the implementation, as in prior practice.

So the motivation for chosing one way or the other seems to be,
"do what's fast" and the behavior originated in pre-standards C
compilers.

K&R1 chalks it up to machine differences, and says the following
when discussion type conversions:

|There is one subtle point about the conversion of characters to
|integers. The language does not specify whether variables of
|type `char` are signed or unsigned quantities. When a `char` is
|converted to an `int`, can it ever produce a _negative_
|integer? Unfortunately, this varies from machine to machine,
|reflecting differences in architecture. On some machines
|(PDP-ll, for instance), a `char` whose leftmost bit is 1 will
i|be converted to a negative integer ("sign extension"). On
|others, a `char` is promoted to an `int` by adding zeros at the
|left end, and thus is always positive.
|
|The definition of C guarantees that any character in the
|machine's standard character set will never be negative, so
|these characters may be used freely in expressions as positive
|quantities. But arbitrary bit patterns stored in to character
|variables may appear be negative on some machines, yet positive
|on others.
|
|The most common occurrence of this situation is when the value
|-1 is used for EOF. Consider the code
|
|   char c;
|
|   c = getchar();
|   if (c == EOF)
|       ...
|
|On a machine which does not do sign extension, `c` is always
|positive because it is a `char`, yet EOF is negative. As a
|result, the test always fails. To avoid this, we have been
|careful to use `int` instead of `char` for any variable which
|holds a value returned by `getchar`.

So the original motivation is differences between architectures
with respect to sign extension when converting a char-sized
quantity to something larger.

	- Dan C.

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Thread

Default signedness of 'plain' char. gazelle@shell.xmission.com (Kenny McCormack) - 2026-08-02 14:17 +0000
  Re: Default signedness of 'plain' char. Johann 'Myrkraverk' Oskarsson <johann@myrkraverk.invalid> - 2026-08-03 02:45 +0800
    Re: Default signedness of 'plain' char. gazelle@shell.xmission.com (Kenny McCormack) - 2026-08-03 01:47 +0000
      Re: Default signedness of 'plain' char. Johann 'Myrkraverk' Oskarsson <johann@myrkraverk.invalid> - 2026-08-03 23:14 +0800
        Re: Default signedness of 'plain' char. bart <bc@freeuk.com> - 2026-08-03 17:04 +0100
          The Spanish Inquisition (was: Re: Default signedness of 'plain' char.) Johann 'Myrkraverk' Oskarsson <johann@myrkraverk.invalid> - 2026-08-04 00:23 +0800
            Re: The Spanish Inquisition bart <bc@freeuk.com> - 2026-08-03 18:03 +0100
              Re: The Spanish Inquisition Johann 'Myrkraverk' Oskarsson <johann@myrkraverk.invalid> - 2026-08-04 01:26 +0800
        Re: Default signedness of 'plain' char. Theo <theom+news@chiark.greenend.org.uk> - 2026-08-04 13:13 +0100
          Re: Default signedness of 'plain' char. Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-08-05 07:30 +0000
            Re: Default signedness of 'plain' char. Johann 'Myrkraverk' Oskarsson <johann@myrkraverk.invalid> - 2026-08-05 18:18 +0800
              Re: Default signedness of 'plain' char. bart <bc@freeuk.com> - 2026-08-05 17:20 +0100
                Re: Default signedness of 'plain' char. Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-08-05 21:57 +0000
                Re: Default signedness of 'plain' char. Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-08-05 15:29 -0700
  Re: Default signedness of 'plain' char. David Brown <david.brown@hesbynett.no> - 2026-08-03 09:56 +0200
    Re: Default signedness of 'plain' char. BGB <cr88192@gmail.com> - 2026-08-03 13:56 -0500
  Re: Default signedness of 'plain' char. antispam@fricas.org (Waldek Hebisch) - 2026-08-03 13:48 +0000
  Re: Default signedness of 'plain' char. cross@spitfire.i.gajendra.net (Dan Cross) - 2026-08-03 14:47 +0000
  Re: Default signedness of 'plain' char. Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2026-08-03 14:47 +0000
    Re: Default signedness of 'plain' char. Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2026-08-03 15:04 +0000
      Re: Default signedness of 'plain' char. Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-08-03 16:58 -0700
        Re: Default signedness of 'plain' char. Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2026-08-04 15:10 +0000
          Re: Default signedness of 'plain' char. scott@slp53.sl.home (Scott Lurndal) - 2026-08-04 15:50 +0000
          Re: Default signedness of 'plain' char. Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-08-05 03:00 +0000
          Re: Default signedness of 'plain' char. David Brown <david.brown@hesbynett.no> - 2026-08-05 09:01 +0200
      Re: Default signedness of 'plain' char. antispam@fricas.org (Waldek Hebisch) - 2026-08-04 18:10 +0000
        Compilers targetting the C64 (was: Re: Default signedness of 'plain' char.) Johann 'Myrkraverk' Oskarsson <johann@myrkraverk.invalid> - 2026-08-05 03:17 +0800
        Re: Default signedness of 'plain' char. BGB <cr88192@gmail.com> - 2026-08-04 16:25 -0500
        Re: Default signedness of 'plain' char. Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-08-05 02:57 +0000
          Re: Default signedness of 'plain' char. Lynn McGuire <lynnmcguire5@gmail.com> - 2026-08-05 00:19 -0500
            Re: Default signedness of 'plain' char. Johann 'Myrkraverk' Oskarsson <johann@myrkraverk.invalid> - 2026-08-05 18:57 +0800
            Re: Default signedness of 'plain' char. scott@slp53.sl.home (Scott Lurndal) - 2026-08-05 14:33 +0000
            Re: Default signedness of 'plain' char. cross@spitfire.i.gajendra.net (Dan Cross) - 2026-08-05 22:38 +0000
        Re: Default signedness of 'plain' char. Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-08-04 21:36 -0700
          Re: Default signedness of 'plain' char. antispam@fricas.org (Waldek Hebisch) - 2026-08-06 00:21 +0000
  Re: Default signedness of 'plain' char. "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-03 13:20 -0700
    Re: Default signedness of 'plain' char. bart <bc@freeuk.com> - 2026-08-03 22:06 +0100
      Re: Default signedness of 'plain' char. "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-03 14:25 -0700
        Re: Default signedness of 'plain' char. BGB <cr88192@gmail.com> - 2026-08-03 18:38 -0500
          Re: Default signedness of 'plain' char. "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-03 19:34 -0700
            Re: Default signedness of 'plain' char. BGB <cr88192@gmail.com> - 2026-08-05 04:40 -0500
          Re: Default signedness of 'plain' char. Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-08-05 07:22 +0000
            Re: Default signedness of 'plain' char. BGB <cr88192@gmail.com> - 2026-08-05 04:02 -0500
              Re: Default signedness of 'plain' char. David Brown <david.brown@hesbynett.no> - 2026-08-05 12:35 +0200
              Re: Default signedness of 'plain' char. Johann 'Myrkraverk' Oskarsson <johann@myrkraverk.invalid> - 2026-08-05 18:49 +0800
                Re: Default signedness of 'plain' char. "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-05 12:39 -0700
                Dear Chris (was: Re: Default signedness of 'plain' char.) Johann 'Myrkraverk' Oskarsson <johann@myrkraverk.invalid> - 2026-08-06 20:15 +0800
                Re: Dear Chris bart <bc@freeuk.com> - 2026-08-06 15:05 +0100
                Re: Dear Chris Johann 'Myrkraverk' Oskarsson <johann@myrkraverk.invalid> - 2026-08-06 23:16 +0800
                Re: Dear Chris David Brown <david.brown@hesbynett.no> - 2026-08-06 20:10 +0200
              Re: Default signedness of 'plain' char. Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-08-05 21:54 +0000
                Re: Default signedness of 'plain' char. BGB <cr88192@gmail.com> - 2026-08-06 04:49 -0500
                Re: Default signedness of 'plain' char. Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-08-07 00:10 +0000
                Re: Default signedness of 'plain' char. David Brown <david.brown@hesbynett.no> - 2026-08-07 09:56 +0200
            Re: Default signedness of 'plain' char. James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-08-05 13:33 -0400
              Re: Default signedness of 'plain' char. Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-08-05 21:50 +0000
                Re: Default signedness of 'plain' char. David Brown <david.brown@hesbynett.no> - 2026-08-06 10:34 +0200
                Re: Default signedness of 'plain' char. BGB <cr88192@gmail.com> - 2026-08-09 15:19 -0500
                Re: Default signedness of 'plain' char. Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-08-09 20:33 +0000
                Re: Default signedness of 'plain' char. "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-09 18:04 -0700
                Re: Default signedness of 'plain' char. Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-08-10 02:45 +0000
                Re: Default signedness of 'plain' char. "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-10 02:24 -0700
                Re: Default signedness of 'plain' char. "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-09 18:03 -0700
                Re: Default signedness of 'plain' char. David Brown <david.brown@hesbynett.no> - 2026-08-10 08:58 +0200
                Re: Default signedness of 'plain' char. BGB <cr88192@gmail.com> - 2026-08-10 15:17 -0500
                Re: Default signedness of 'plain' char. Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-08-10 15:19 -0700
                Re: Default signedness of 'plain' char. BGB <cr88192@gmail.com> - 2026-08-10 17:31 -0500
                Re: Default signedness of 'plain' char. Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-08-10 23:48 +0000
                Re: Default signedness of 'plain' char. James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-08-10 20:03 -0400
                Re: Default signedness of 'plain' char. BGB <cr88192@gmail.com> - 2026-08-10 20:44 -0500
                Re: Default signedness of 'plain' char. James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-08-11 11:17 -0400
                Re: Default signedness of 'plain' char. BGB <cr88192@gmail.com> - 2026-08-11 14:54 -0500
                Re: Quaternions (was Re: Default signedness of 'plain' char.) Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-08-12 03:36 +0000
                Re: Quaternions (was Re: Default signedness of 'plain' char.) BGB <cr88192@gmail.com> - 2026-08-12 01:24 -0500
                Re: Quaternions (was Re: Default signedness of 'plain' char.) Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-08-12 07:47 +0000
                Re: Quaternions (was Re: Default signedness of 'plain' char.) "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-12 12:52 -0700
                Re: Quaternions (was Re: Default signedness of 'plain' char.) "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-12 12:56 -0700
                Re: Quaternions (was Re: Default signedness of 'plain' char.) Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-08-13 02:16 +0000
                Re: Quaternions (was Re: Default signedness of 'plain' char.) "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-12 21:04 -0700
                Re: Quaternions (was Re: Default signedness of 'plain' char.) BGB <cr88192@gmail.com> - 2026-08-12 23:07 -0500
                Re: Quaternions (was Re: Default signedness of 'plain' char.) Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-08-13 05:00 +0000
                Re: Quaternions (was Re: Default signedness of 'plain' char.) BGB <cr88192@gmail.com> - 2026-08-13 04:37 -0500
                Re: Quaternions (was Re: Default signedness of 'plain' char.) "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-13 14:36 -0700
                Re: Quaternions (was Re: Default signedness of 'plain' char.) BGB <cr88192@gmail.com> - 2026-08-13 23:07 -0500
                Re: Quaternions (was Re: Default signedness of 'plain' char.) Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-08-13 23:44 +0000
                Re: Quaternions (was Re: Default signedness of 'plain' char.) "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-13 18:50 -0700
                Re: Quaternions (was Re: Default signedness of 'plain' char.) Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-08-14 02:41 +0000
                Re: Quaternions (was Re: Default signedness of 'plain' char.) BGB <cr88192@gmail.com> - 2026-08-13 23:47 -0500
                Re: Quaternions (was Re: Default signedness of 'plain' char.) Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-08-14 04:59 +0000
                Re: Default signedness of 'plain' char. "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-11 13:47 -0700
                Re: Default signedness of 'plain' char. BGB <cr88192@gmail.com> - 2026-08-13 23:50 -0500
                Re: Default signedness of 'plain' char. Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-08-14 05:59 +0000
                Re: Default signedness of 'plain' char. BGB <cr88192@gmail.com> - 2026-08-14 03:16 -0500
                Re: Default signedness of 'plain' char. Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-08-14 08:32 +0000
                Re: Default signedness of 'plain' char. "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-14 12:36 -0700
                Re: Default signedness of 'plain' char. Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-08-15 03:16 +0000
                Re: Default signedness of 'plain' char. "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-14 22:38 -0700
                Re: Default signedness of 'plain' char. Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-08-16 00:08 +0000
                Re: Default signedness of 'plain' char. "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-14 12:17 -0700
                Re: Default signedness of 'plain' char. cross@spitfire.i.gajendra.net (Dan Cross) - 2026-08-11 13:46 +0000
                Re: Default signedness of 'plain' char. "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-11 13:49 -0700
                Re: Default signedness of 'plain' char. David Brown <david.brown@hesbynett.no> - 2026-08-11 08:58 +0200
                Re: Default signedness of 'plain' char. BGB <cr88192@gmail.com> - 2026-08-11 04:03 -0500
                Re: Default signedness of 'plain' char. steve g <Sgonedes1977@gmail.com> - 2026-08-10 20:29 -0400
                Re: Vectors! Quaternions! (was Re: Default signedness of 'plain' char.) Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-08-11 03:58 +0000
                Re: Default signedness of 'plain' char. David Brown <david.brown@hesbynett.no> - 2026-08-11 09:06 +0200
                Re: Default signedness of 'plain' char. Ross Finlayson <ross.a.finlayson@gmail.com> - 2026-08-10 21:15 -0700
                Re: Default signedness of 'plain' char. Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-08-11 04:52 +0000
                Re: Default signedness of 'plain' char. Ross Finlayson <ross.a.finlayson@gmail.com> - 2026-08-11 06:45 -0700
                Re: Default signedness of 'plain' char. "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-11 14:01 -0700
            Re: Default signedness of 'plain' char. "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-05 12:36 -0700
    Re: Default signedness of 'plain' char. Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-08-05 07:18 +0000
  Re: Default signedness of 'plain' char. Lynn McGuire <lynnmcguire5@gmail.com> - 2026-08-05 18:30 -0500
    Re: Default signedness of 'plain' char. Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-08-05 16:41 -0700
      Re: Default signedness of 'plain' char. bart <bc@freeuk.com> - 2026-08-06 01:24 +0100
        Re: Default signedness of 'plain' char. Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-08-05 17:46 -0700
        Re: Default signedness of 'plain' char. cross@spitfire.i.gajendra.net (Dan Cross) - 2026-08-06 22:59 +0000
          Re: Default signedness of 'plain' char. Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-08-06 19:54 -0700
            Re: Default signedness of 'plain' char. cross@spitfire.i.gajendra.net (Dan Cross) - 2026-08-07 11:02 +0000
              Re: Default signedness of 'plain' char. Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-08-07 10:35 -0700
                Re: Default signedness of 'plain' char. cross@spitfire.i.gajendra.net (Dan Cross) - 2026-08-07 18:32 +0000
                Re: Default signedness of 'plain' char. Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-08-07 20:55 +0200
              Use of isascii() back in early days (was Re: Default signedness of 'plain' char.) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-08-07 20:51 +0200
                Re: Use of isascii() back in early days (was Re: Default signedness of 'plain' char.) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-08-07 13:03 -0700
                Re: Use of isascii() back in early days (was Re: Default signedness of 'plain' char.) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-08-07 13:32 -0700
                Re: Use of isascii() back in early days (was Re: Default signedness of 'plain' char.) cross@spitfire.i.gajendra.net (Dan Cross) - 2026-08-07 21:44 +0000
                Re: Use of isascii() back in early days (was Re: Default signedness of 'plain' char.) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-08-07 23:47 +0200
                Re: Use of isascii() back in early days (was Re: Default signedness of 'plain' char.) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-08-07 15:26 -0700
      Re: Default signedness of 'plain' char. cross@spitfire.i.gajendra.net (Dan Cross) - 2026-08-06 22:57 +0000
        Re: Default signedness of 'plain' char. Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-08-06 18:23 -0700
          Re: Default signedness of 'plain' char. cross@spitfire.i.gajendra.net (Dan Cross) - 2026-08-07 11:47 +0000
    Re: Default signedness of 'plain' char. scott@slp53.sl.home (Scott Lurndal) - 2026-08-06 14:40 +0000
      Re: Default signedness of 'plain' char. Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-08-06 15:33 -0700

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