Re: sprintf and the trailing null

From	Bartc <bc@freeuk.com>
Newsgroups	comp.lang.c
Subject	Re: sprintf and the trailing null
Date	2015-07-10 12:09 +0100
Organization	A noiseless patient Spider
Message-ID	<mno92v$8il$1@dont-email.me> (permalink)
References	(6 earlier) <87k2ucucrk.fsf@bsb.me.uk> <87zj36d19c.fsf@bazspaz.fatphil.org> <e83cec81-7c17-4630-94ff-2f47bdbc971b@googlegroups.com> <mnjofu$2fs$1@dont-email.me> <87wpy8b8uj.fsf@bazspaz.fatphil.org>

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On 10/07/2015 11:33, Phil Carmody wrote:
> Bartc <bc@freeuk.com> writes:

>> But a % at the of a string should be an error.
>
> Says who? If you, on what authority? If the C standard, chapter
> and verse, please?

7.20.6.1p9 says the behaviour is undefined.

But whatever that says, under the current rules, a sole "%" at the end 
of format string produces no output and serves no purpose.

In your opinion however, you would be quite happy to see that in code, 
and would not question it? The possibility would never occur to you that 
perhaps it's a mistake, and that a format code is missing or it's just 
an extraneous character?

The problem is that under the new proposal, you can't distinguish such 
an erroneous use from a legitimate one.

>> If it now becomes an
>> acceptable format-specifier by itself, and /causes the trailing null
>> to be suppressed/, it can cause programs to crash if someone intended
>> "%d" but the "d" got missed out.
>
> Crashing was one of the available behaviours for such code anyway.
> And crashing is usualy far better than silently propagating inappropriate
> values around.

Under the new proposed behaviour, any string created by sprintf would 
not have terminating null if "%" was at the end of the format string.

This could give interesting results when subsequently processing by any 
code or functions that expect it to be zero-terminated. And a sole 
trailing "%" could occur inadvertently much more easily than with "%" 
followed by a mandatory code.

But this, in your opinion, is perfectly acceptable!

-- 
bartc

Thread

sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-06 06:16 -0700
  Re: sprintf and the trailing null John McCue <jmccue@jmcnet1.bstnma.east.verizon.net> - 2015-07-06 13:30 +0000
    Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-06 06:37 -0700
      Re: sprintf and the trailing null Reinhardt Behm <rbehm@hushmail.com> - 2015-07-06 21:58 +0800
        Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-06 07:12 -0700
          Re: sprintf and the trailing null Reinhardt Behm <rbehm@hushmail.com> - 2015-07-06 22:34 +0800
            Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-06 08:44 -0700
          Re: sprintf and the trailing null Bartc <bc@freeuk.com> - 2015-07-06 15:46 +0100
            Re: sprintf and the trailing null Keith Thompson <kst-u@mib.org> - 2015-07-06 08:06 -0700
              Re: sprintf and the trailing null Bartc <bc@freeuk.com> - 2015-07-06 17:42 +0100
                Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-06 09:48 -0700
                Re: sprintf and the trailing null Bartc <bc@freeuk.com> - 2015-07-06 18:07 +0100
                Re: sprintf and the trailing null Martin Shobe <martin.shobe@yahoo.com> - 2015-07-06 12:40 -0500
                Re: sprintf and the trailing null Keith Thompson <kst-u@mib.org> - 2015-07-06 10:46 -0700
                Re: sprintf and the trailing null Bartc <bc@freeuk.com> - 2015-07-06 18:58 +0100
          Re: sprintf and the trailing null Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-07-06 16:38 +0100
            Re: sprintf and the trailing null Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-07-06 23:44 +0100
              Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-06 15:48 -0700
              Re: sprintf and the trailing null Phil Carmody <pc+usenet@asdf.org> - 2015-07-08 20:09 +0300
                Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-08 10:11 -0700
                Re: sprintf and the trailing null Bartc <bc@freeuk.com> - 2015-07-08 19:01 +0100
                Re: sprintf and the trailing null David Kleinecke <dkleinecke@gmail.com> - 2015-07-09 09:02 -0700
                Re: sprintf and the trailing null Richard Heathfield <rjh@cpax.org.uk> - 2015-07-09 17:07 +0100
                Re: sprintf and the trailing null Phil Carmody <pc+usenet@asdf.org> - 2015-07-10 17:06 +0300
                Re: sprintf and the trailing null glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-07-09 17:42 +0000
                Re: sprintf and the trailing null Phil Carmody <pc+usenet@asdf.org> - 2015-07-10 13:33 +0300
                Re: sprintf and the trailing null Bartc <bc@freeuk.com> - 2015-07-10 12:09 +0100
                Re: sprintf and the trailing null Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-10 04:51 -0700
                Re: sprintf and the trailing null Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-07-10 17:24 +0100
                Re: sprintf and the trailing null Keith Thompson <kst-u@mib.org> - 2015-07-10 08:33 -0700
                Re: sprintf and the trailing null Tim Rentsch <txr@alumni.caltech.edu> - 2015-07-11 04:58 -0700
      Re: sprintf and the trailing null jt@toerring.de (Jens Thoms Toerring) - 2015-07-06 14:15 +0000
        Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-06 07:20 -0700
          Re: sprintf and the trailing null raltbos@xs4all.nl (Richard Bos) - 2015-07-06 19:54 +0000
            Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-06 13:31 -0700
              Re: sprintf and the trailing null Richard Heathfield <rjh@cpax.org.uk> - 2015-07-06 21:52 +0100
              Re: sprintf and the trailing null raltbos@xs4all.nl (Richard Bos) - 2015-07-06 22:52 +0000
                Re: sprintf and the trailing null Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-07-07 01:04 +0100
                Re: sprintf and the trailing null Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-06 19:13 -0700
                Re: sprintf and the trailing null Reinhardt Behm <rbehm@hushmail.com> - 2015-07-07 12:45 +0800
                Re: sprintf and the trailing null Rosario19 <Ros@invalid.invalid> - 2015-07-07 10:15 +0200
                Re: sprintf and the trailing null Bartc <bc@freeuk.com> - 2015-07-07 10:31 +0100
                Re: sprintf and the trailing null Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-07 02:51 -0700
                Re: sprintf and the trailing null Bartc <bc@freeuk.com> - 2015-07-07 12:10 +0100
                Re: sprintf and the trailing null Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-07 05:08 -0700
                Re: sprintf and the trailing null Bartc <bc@freeuk.com> - 2015-07-07 13:52 +0100
                Re: sprintf and the trailing null Phil Carmody <pc+usenet@asdf.org> - 2015-07-08 20:20 +0300
                Re: sprintf and the trailing null Bartc <bc@freeuk.com> - 2015-07-08 18:51 +0100
                Re: sprintf and the trailing null raltbos@xs4all.nl (Richard Bos) - 2015-07-09 10:27 +0000
                Re: sprintf and the trailing null Tim Rentsch <txr@alumni.caltech.edu> - 2015-07-10 19:03 -0700
              Re: sprintf and the trailing null gordonb.7tw58@burditt.org (Gordon Burditt) - 2015-07-07 15:40 -0500
                Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-07 15:14 -0700
        Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-06 07:27 -0700
          Re: sprintf and the trailing null jt@toerring.de (Jens Thoms Toerring) - 2015-07-06 16:46 +0000
        Re: sprintf and the trailing null Keith Thompson <kst-u@mib.org> - 2015-07-06 07:56 -0700
  Re: sprintf and the trailing null Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2015-07-06 09:32 -0600
  Re: sprintf and the trailing null Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-06 08:37 -0700
    Re: sprintf and the trailing null Keith Thompson <kst-u@mib.org> - 2015-07-06 08:54 -0700
  Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-06 08:53 -0700
    Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-06 09:00 -0700
    Re: sprintf and the trailing null Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-07-06 17:14 +0100
      Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-06 09:24 -0700
        Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-06 09:31 -0700
  Re: sprintf and the trailing null Sjouke Burry <burrynulnulfour@ppllaanneett.nnll> - 2015-07-07 01:43 +0200
    Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-06 17:09 -0700
      Re: sprintf and the trailing null Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2015-07-06 21:08 -0600
        Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-06 21:29 -0700
        Re: sprintf and the trailing null Phil Carmody <pc+usenet@asdf.org> - 2015-07-08 20:24 +0300
          Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-08 10:44 -0700
  Re: sprintf and the trailing null Les Cargill <lcargill99@comcast.com> - 2015-07-07 21:48 -0500

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