Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF''

From	Kaz Kylheku <480-992-1380@kylheku.com>
Newsgroups	comp.lang.c
Subject	Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF''
Date	2021-12-12 18:55 +0000
Organization	A noiseless patient Spider
Message-ID	<20211212091034.341@kylheku.com> (permalink)
References	<86pmqwkm7u.fsf@levado.to>

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On 2021-11-19, Meredith Montgomery <mmontgomery@levado.to> wrote:
> I did not get Brian Kernighan's concern with setting EOF to a char c.
> The context is
>
>   char c = getchar();
>
> And Kernighan says:
>
> --8<---------------cut here---------------start------------->8---
> We must declare c to be a type big enough to hold any value that getchar
> returns. We can't use char since c must be big enough to hold EOF in
> addition to any possible char . Therefore we use int.
> --8<---------------cut here---------------end--------------->8---

Not all of this is correct. The conclusion to use int is correct,
but it is incorrect to insinuate that:

- EOF is distinct from values of char (it isn't required to be,
  and quite often isn't: char is often signed, and EOF is often #defined
  as -1).

- getchar() returns values of char (it doesn't; if a datum is available
  from the stream, it returns it as a value from 0 to UCHAR_MAX).

Is the quote verbatim?

Also, the primary reason to capture the return value of getchar, getc
and fgetc using a value of type int is that this is the declared
return type of these functions.

If a function returns int, you capture that with int, or else (if
you have special reasons for it) an integer type whose range is a
superset of int. Your choice need not, and ideally should not, be
justified with the run-time semantics of the function; you know
from the type that you're capturing every value.

(To handle the value futher, you have to know something about its
semantics, like which subset of its range represents a datum and which
value(s) are in-band error signaling.)

> So I can't be sure a char would always be signed, for example.  I can't
> be sure EOF would fit in a char.

It is overwhelmingly common for EOF to have a value that is
representable in a char (informally, to "fit" into a char).

And that would be a problem if getchar returned char values,
and one not solved by the int return type.

-- 
TXR Programming Language: http://nongnu.org/txr
Cygnal: Cygwin Native Application Library: http://kylheku.com/cygnal

Thread

K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Meredith Montgomery <mmontgomery@levado.to> - 2021-11-19 15:57 -0300
  Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-11-19 12:21 -0800
    Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Meredith Montgomery <mmontgomery@levado.to> - 2021-11-19 18:14 -0300
      Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-11-19 14:10 -0800
        Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Meredith Montgomery <mmontgomery@levado.to> - 2021-11-20 17:30 -0300
        Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' scott@slp53.sl.home (Scott Lurndal) - 2021-11-21 16:01 +0000
    Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Philipp Klaus Krause <pkk@spth.de> - 2021-11-22 11:23 +0100
      Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-11-22 12:55 -0800
        Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Philipp Klaus Krause <pkk@spth.de> - 2021-11-23 17:04 +0100
          Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-11-23 09:43 -0800
            Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Philipp Klaus Krause <pkk@spth.de> - 2021-11-24 11:26 +0100
              Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-12-10 01:41 -0800
                Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' David Brown <david.brown@hesbynett.no> - 2021-12-10 14:40 +0100
  Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Barry Schwarz <schwarzb@delq.com> - 2021-11-19 12:22 -0800
    Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Meredith Montgomery <mmontgomery@levado.to> - 2021-11-19 18:10 -0300
    Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' David Brown <david.brown@hesbynett.no> - 2021-11-20 13:24 +0100
      Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Meredith Montgomery <mmontgomery@levado.to> - 2021-11-20 17:32 -0300
  Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Mark Bluemel <mark.bluemel@gmail.com> - 2021-11-22 00:27 -0800
  Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Mark Bluemel <mark.bluemel@gmail.com> - 2021-11-22 00:34 -0800
    Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-11-22 02:04 -0800
      Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Mark Bluemel <mark.bluemel@gmail.com> - 2021-11-22 02:46 -0800
      Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2021-11-22 21:22 -0800
        Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-11-22 22:03 -0800
          Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' scott@slp53.sl.home (Scott Lurndal) - 2021-11-23 14:52 +0000
  Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Dave Dunfield <dave.dunfield@gmail.com> - 2021-11-26 07:31 -0800
    Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Dave Dunfield <dave.dunfield@gmail.com> - 2021-12-08 07:26 -0800
      Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-12-08 12:16 -0800
        Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Dave Dunfield <dave.dunfield@gmail.com> - 2021-12-08 18:59 -0800
          Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-12-08 19:23 -0800
            Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Dave Dunfield <dave.dunfield@gmail.com> - 2021-12-09 06:30 -0800
              Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Manfred <noname@add.invalid> - 2021-12-09 16:10 +0100
              Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-12-09 16:05 +0000
                Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Bart <bc@freeuk.com> - 2021-12-09 17:41 +0000
                Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Dave Dunfield <dave.dunfield@gmail.com> - 2021-12-09 12:24 -0800
                Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-12-09 22:59 +0000
                Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-12-09 21:26 +0000
                Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Bart <bc@freeuk.com> - 2021-12-09 22:37 +0000
                Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-12-09 23:09 +0000
              Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-12-10 01:58 -0800
                Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-12-10 10:46 -0800
                Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-12-12 08:21 -0800
          Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Paul <nospam@needed.invalid> - 2021-12-09 10:31 -0500
            Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2021-12-09 13:32 -0800
          Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' luser droog <luser.droog@gmail.com> - 2021-12-09 17:08 -0800
            Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Dave Dunfield <dave.dunfield@gmail.com> - 2021-12-10 12:45 -0800
              Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Manfred <noname@add.invalid> - 2021-12-11 19:17 +0100
              Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Bart <bc@freeuk.com> - 2021-12-11 23:19 +0000
              Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-12-15 00:31 -0800
      Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Mark Bluemel <mark.bluemel@gmail.com> - 2021-12-09 02:26 -0800
        Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Bart <bc@freeuk.com> - 2021-12-09 11:20 +0000
          Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Dave Dunfield <dave.dunfield@gmail.com> - 2021-12-09 06:50 -0800
  Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Andrey Tarasevich <andreytarasevich@hotmail.com> - 2021-12-08 20:00 -0800
  Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' Kaz Kylheku <480-992-1380@kylheku.com> - 2021-12-12 18:55 +0000
    Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF'' James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-12-12 14:38 -0500

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