Re: Buffer contents well-defined after fgets() reaches EOF ?

From	Michael S <already5chosen@yahoo.com>
Newsgroups	comp.lang.c
Subject	Re: Buffer contents well-defined after fgets() reaches EOF ?
Date	2025-02-15 20:06 +0200
Organization	A noiseless patient Spider
Message-ID	<20250215200602.00004ac2@yahoo.com> (permalink)
References	(7 earlier) <86ldu9zxkb.fsf@linuxsc.com> <20250214165108.00002984@yahoo.com> <20250214085627.815@kylheku.com> <871pw073if.fsf@nosuchdomain.example.com> <20250214112225.480@kylheku.com>

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On Fri, 14 Feb 2025 19:34:59 -0000 (UTC)
Kaz Kylheku <643-408-1753@kylheku.com> wrote:

> On 2025-02-14, Keith Thompson <Keith.S.Thompson+u@gmail.com> wrote:
> > Kaz Kylheku <643-408-1753@kylheku.com> writes:
> > [...]  
> >> It would be good if fgets nuked the terminating newline.
> >>
> >> Many uses of fgets, after every operation, look for the newline
> >> and nuke it, before doing anything else.
> >>
> >> There is a nice idiom for that, by the way, which avoids an
> >> temporary variable and if test:
> >>
> >>    line[strcspn(line, "\n")] = 0;  
> > [...]
> >
> > Then how do you detect a partial line?  That can occur either if
> > the last line doesn't have a terminating newline (on systems that
> > permit it) or a line that's too long to fit in the array.  
> 
> I've seen many programs like this don't care. They have some
> 'char buf[4096]' and that's that.
> 

IMHO, even a program that is not designed to handle long lines should
give an informative error diagnostic when it encounters one.
Your trick described below is good for that, but one has to be rather
good programmer in order to invent such trick. I believe that if one
has to be good in order to use the API it's a clear indication that the
API is *not* good.

Similarly, IMHO, the programs not designed to handle presence of null
characters in the text should give an informative error diagnostic when
they are encountered. And in that fgets() is especially unhelpful.

> In a program not required or designed to handle arbitrarily
> long lines, you can do something very simple (prior to the
> above line[strcspn(line, "\n")] = 0 expression).
>
> - zero-initialize the buffer.
> 
> - after every call to fgets, inspect the value of the second-to-last
>   array element.  If the value is neither zero, nor '\n', then somehow
>   diagnose that a too-long line has been presented to the program,
>   contrary to its documented limitations.
> 
> This will yield a false positive on an unterminated last line.  That
> issue can be added as a documented limitation, or else the buffer can
> be sized one greater than what the documented line length limit
> requires, so that the program allows inner lines to be one character
> longer than the documented limit, but is strict with regard to an
> unterminated last line.
>

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Buffer contents well-defined after fgets() reaches EOF ? Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-09 06:59 +0100
  Re: Buffer contents well-defined after fgets() reaches EOF ? Kaz Kylheku <643-408-1753@kylheku.com> - 2025-02-09 06:23 +0000
  Re: Buffer contents well-defined after fgets() reaches EOF ? Andrey Tarasevich <noone@noone.net> - 2025-02-08 22:23 -0800
    Re: Buffer contents well-defined after fgets() reaches EOF ? Andrey Tarasevich <noone@noone.net> - 2025-02-08 23:12 -0800
      Re: Buffer contents well-defined after fgets() reaches EOF ? Lawrence D'Oliveiro <ldo@nz.invalid> - 2025-02-09 23:52 +0000
        Re: Buffer contents well-defined after fgets() reaches EOF ? Andrey Tarasevich <noone@noone.net> - 2025-02-09 17:06 -0800
          Re: Buffer contents well-defined after fgets() reaches EOF ? Andrey Tarasevich <noone@noone.net> - 2025-02-09 17:22 -0800
            Re: Buffer contents well-defined after fgets() reaches EOF ? Michael S <already5chosen@yahoo.com> - 2025-02-10 12:49 +0200
              Re: Buffer contents well-defined after fgets() reaches EOF ? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-02-13 07:14 -0800
                Re: Buffer contents well-defined after fgets() reaches EOF ? Michael S <already5chosen@yahoo.com> - 2025-02-14 16:51 +0200
                Re: Buffer contents well-defined after fgets() reaches EOF ? scott@slp53.sl.home (Scott Lurndal) - 2025-02-14 15:10 +0000
                Re: Buffer contents well-defined after fgets() reaches EOF ? Michael S <already5chosen@yahoo.com> - 2025-02-14 17:23 +0200
                Re: Buffer contents well-defined after fgets() reaches EOF ? scott@slp53.sl.home (Scott Lurndal) - 2025-02-14 16:46 +0000
                Re: Buffer contents well-defined after fgets() reaches EOF ? Kaz Kylheku <643-408-1753@kylheku.com> - 2025-02-14 17:28 +0000
                Re: Buffer contents well-defined after fgets() reaches EOF ? Kaz Kylheku <643-408-1753@kylheku.com> - 2025-02-14 17:22 +0000
                Re: Buffer contents well-defined after fgets() reaches EOF ? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-02-14 11:03 -0800
                Re: Buffer contents well-defined after fgets() reaches EOF ? Kaz Kylheku <643-408-1753@kylheku.com> - 2025-02-14 19:34 +0000
                Re: Buffer contents well-defined after fgets() reaches EOF ? Michael S <already5chosen@yahoo.com> - 2025-02-15 20:06 +0200
                Re: Buffer contents well-defined after fgets() reaches EOF ? scott@slp53.sl.home (Scott Lurndal) - 2025-02-14 20:01 +0000
                Re: Buffer contents well-defined after fgets() reaches EOF ? Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-14 20:51 +0100
                Re: Buffer contents well-defined after fgets() reaches EOF ? Michael S <already5chosen@yahoo.com> - 2025-02-15 19:02 +0200
                Re: Buffer contents well-defined after fgets() reaches EOF ? Michael S <already5chosen@yahoo.com> - 2025-02-15 19:29 +0200
                Re: Buffer contents well-defined after fgets() reaches EOF ? Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-16 04:29 +0100
                Re: Buffer contents well-defined after fgets() reaches EOF ? James Kuyper <jameskuyper@alumni.caltech.edu> - 2025-02-16 01:04 -0500
                Re: Buffer contents well-defined after fgets() reaches EOF ? Kaz Kylheku <643-408-1753@kylheku.com> - 2025-02-16 07:37 +0000
                Re: Buffer contents well-defined after fgets() reaches EOF ? Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-16 18:59 +0100
                Re: Buffer contents well-defined after fgets() reaches EOF ? Michael S <already5chosen@yahoo.com> - 2025-02-16 10:48 +0200
                Re: Buffer contents well-defined after fgets() reaches EOF ? Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-16 19:14 +0100
                Re: Buffer contents well-defined after fgets() reaches EOF ? Michael S <already5chosen@yahoo.com> - 2025-02-17 11:54 +0200
                Re: Buffer contents well-defined after fgets() reaches EOF ? Kaz Kylheku <643-408-1753@kylheku.com> - 2025-02-16 07:32 +0000
                Re: Buffer contents well-defined after fgets() reaches EOF ? Michael S <already5chosen@yahoo.com> - 2025-02-16 11:05 +0200
                Re: Buffer contents well-defined after fgets() reaches EOF ? Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-16 19:25 +0100
                Re: Buffer contents well-defined after fgets() reaches EOF ? Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-16 19:21 +0100
                Re: Buffer contents well-defined after fgets() reaches EOF ? scott@slp53.sl.home (Scott Lurndal) - 2025-02-16 20:26 +0000
                Re: Buffer contents well-defined after fgets() reaches EOF ? Michael S <already5chosen@yahoo.com> - 2025-02-15 19:41 +0200
                Re: Buffer contents well-defined after fgets() reaches EOF ? Michael S <already5chosen@yahoo.com> - 2025-02-15 20:29 +0200
                Re: Buffer contents well-defined after fgets() reaches EOF ? Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-16 04:33 +0100
                Re: Buffer contents well-defined after fgets() reaches EOF ? Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-14 20:23 +0100
                Re: Buffer contents well-defined after fgets() reaches EOF ? James Kuyper <jameskuyper@alumni.caltech.edu> - 2025-02-14 14:38 -0500
                Re: Buffer contents well-defined after fgets() reaches EOF ? Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-14 21:02 +0100
                Re: Buffer contents well-defined after fgets() reaches EOF ? Michael S <already5chosen@yahoo.com> - 2025-02-15 19:53 +0200
                Re: Buffer contents well-defined after fgets() reaches EOF ? Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-16 04:48 +0100
                Re: Buffer contents well-defined after fgets() reaches EOF ? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-02-15 08:37 -0800
                Re: Buffer contents well-defined after fgets() reaches EOF ? Michael S <already5chosen@yahoo.com> - 2025-02-15 20:08 +0200
                Re: Buffer contents well-defined after fgets() reaches EOF ? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-02-18 20:17 -0800
                Re: Buffer contents well-defined after fgets() reaches EOF ? Lawrence D'Oliveiro <ldo@nz.invalid> - 2025-02-21 05:58 +0000
            Re: Buffer contents well-defined after fgets() reaches EOF ? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-02-15 08:12 -0800
          Re: Buffer contents well-defined after fgets() reaches EOF ? Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-10 02:44 +0100
          Re: Buffer contents well-defined after fgets() reaches EOF ? Lawrence D'Oliveiro <ldo@nz.invalid> - 2025-02-10 03:28 +0000
            Re: Buffer contents well-defined after fgets() reaches EOF ? Andrey Tarasevich <noone@noone.net> - 2025-02-09 20:11 -0800
              Re: Buffer contents well-defined after fgets() reaches EOF ? Lawrence D'Oliveiro <ldo@nz.invalid> - 2025-02-10 07:21 +0000
                Re: Buffer contents well-defined after fgets() reaches EOF ? scott@slp53.sl.home (Scott Lurndal) - 2025-02-10 16:39 +0000
                Re: Buffer contents well-defined after fgets() reaches EOF ? James Kuyper <jameskuyper@alumni.caltech.edu> - 2025-02-10 13:58 -0500
                Re: Buffer contents well-defined after fgets() reaches EOF ? Lawrence D'Oliveiro <ldo@nz.invalid> - 2025-02-11 01:03 +0000
                Re: Buffer contents well-defined after fgets() reaches EOF ? James Kuyper <jameskuyper@alumni.caltech.edu> - 2025-02-10 22:33 -0500
                Re: Buffer contents well-defined after fgets() reaches EOF ? Kaz Kylheku <643-408-1753@kylheku.com> - 2025-02-11 03:42 +0000
                Re: Buffer contents well-defined after fgets() reaches EOF ? Lawrence D'Oliveiro <ldo@nz.invalid> - 2025-02-11 04:54 +0000
                Re: Buffer contents well-defined after fgets() reaches EOF ? James Kuyper <jameskuyper@alumni.caltech.edu> - 2025-02-11 13:07 -0500
                Re: Buffer contents well-defined after fgets() reaches EOF ? Lawrence D'Oliveiro <ldo@nz.invalid> - 2025-02-11 21:47 +0000
                Re: Buffer contents well-defined after fgets() reaches EOF ? James Kuyper <jameskuyper@alumni.caltech.edu> - 2025-02-11 17:44 -0500
                Re: Buffer contents well-defined after fgets() reaches EOF ? Lawrence D'Oliveiro <ldo@nz.invalid> - 2025-02-12 06:16 +0000
                Re: Buffer contents well-defined after fgets() reaches EOF ? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-02-11 13:59 -0800
                Re: Buffer contents well-defined after fgets() reaches EOF ? James Kuyper <jameskuyper@alumni.caltech.edu> - 2025-02-11 17:58 -0500
                Re: Buffer contents well-defined after fgets() reaches EOF ? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-02-11 15:40 -0800
                Re: Buffer contents well-defined after fgets() reaches EOF ? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-02-17 21:11 -0800
                Re: Buffer contents well-defined after fgets() reaches EOF ? Andrey Tarasevich <noone@noone.net> - 2025-02-10 22:32 -0800
                Re: Buffer contents well-defined after fgets() reaches EOF ? Andrey Tarasevich <noone@noone.net> - 2025-02-10 22:38 -0800
                Re: Buffer contents well-defined after fgets() reaches EOF ? Kaz Kylheku <643-408-1753@kylheku.com> - 2025-02-11 12:04 +0000
                Re: Buffer contents well-defined after fgets() reaches EOF ? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-02-13 07:29 -0800
    Re: Buffer contents well-defined after fgets() reaches EOF ? Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-09 08:13 +0100
      Re: Buffer contents well-defined after fgets() reaches EOF ? Michael S <already5chosen@yahoo.com> - 2025-02-09 12:50 +0200
        Re: Buffer contents well-defined after fgets() reaches EOF ? Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-09 18:29 +0100
          Re: Buffer contents well-defined after fgets() reaches EOF ? Mark Bourne <nntp.mbourne@spamgourmet.com> - 2025-02-10 21:57 +0000
      Re: Buffer contents well-defined after fgets() reaches EOF ? Andrey Tarasevich <noone@noone.net> - 2025-02-09 07:27 -0800
        Re: Buffer contents well-defined after fgets() reaches EOF ? Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-09 18:34 +0100
          Re: Buffer contents well-defined after fgets() reaches EOF ? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-02-09 16:57 -0800
            Re: Buffer contents well-defined after fgets() reaches EOF ? Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-10 02:35 +0100
              Re: Buffer contents well-defined after fgets() reaches EOF ? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-02-09 20:37 -0800
                Re: Buffer contents well-defined after fgets() reaches EOF ? Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-10 07:08 +0100
                Re: Buffer contents well-defined after fgets() reaches EOF ? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-02-09 22:41 -0800
                Re: Buffer contents well-defined after fgets() reaches EOF ? Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-10 07:54 +0100
                Re: Buffer contents well-defined after fgets() reaches EOF ? Mark Bourne <nntp.mbourne@spamgourmet.com> - 2025-02-10 23:22 +0000
                Re: Buffer contents well-defined after fgets() reaches EOF ? Kaz Kylheku <643-408-1753@kylheku.com> - 2025-02-11 00:59 +0000
                Re: Buffer contents well-defined after fgets() reaches EOF ? Lawrence D'Oliveiro <ldo@nz.invalid> - 2025-02-17 02:50 +0000
      Re: Buffer contents well-defined after fgets() reaches EOF ? Mark Bourne <nntp.mbourne@spamgourmet.com> - 2025-02-10 22:57 +0000
        Re: Buffer contents well-defined after fgets() reaches EOF ? Mark Bourne <nntp.mbourne@spamgourmet.com> - 2025-02-10 23:24 +0000
  Re: Buffer contents well-defined after fgets() reaches EOF ? Ben Bacarisse <ben@bsb.me.uk> - 2025-02-10 01:32 +0000
    Re: Buffer contents well-defined after fgets() reaches EOF ? Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-10 02:40 +0100

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