Re: sscanf error checking

From	Keith Thompson <kst-u@mib.org>
Newsgroups	comp.lang.c
Subject	Re: sscanf error checking
Date	2016-12-15 12:33 -0800
Organization	None to speak of
Message-ID	<lnlgvhkk4w.fsf@kst-u.example.com> (permalink)
References	<o2rp71$3e7$1@dont-email.me> <k2c35ctbq4lg3bnllpfbt15lc8l2qsfodm@4ax.com> <77a15075-1f22-405c-a896-061dda988473@googlegroups.com> <5852fa62.4681734@news.xs4all.nl>

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raltbos@xs4all.nl (Richard Bos) writes:
> supercat@casperkitty.com wrote:
>> On Wednesday, December 14, 2016 at 2:52:04 PM UTC-6, robert...@yahoo.com wrote:
>> > IMO, the *scanf() and ato*() functions are pretty much of no use
>> > outside of toy problems, the lack of meaningful error handling being
>> > the biggest issue.  YMMV.
>> 
>> Many programs are intended only for use upon validated input.
>
> There is no such thing as validated input; there is only _temporarily_
> validated input.
>
> A program using scanf()# and ato*() is only safe if:
> - it is used with a single set of input;
> - that input is validated _instantly_ before it is fed to the program;
> - the program is deleted or incapacitated immediately afterward.

scanf() can, with some care, be used safely for non-numeric input.
But the hassle of doing so can easily exceed the cost of using
an alternative.

> (A program using gets() is, of course, unsafe even then.)

In the circumstances you suggest, gets() *could* be used safely.  As
long as the input line doesn't exceed the size of the buffer, it has
well defined behavior.  Of course the conditions you suggest are
(deliberately) unrealistic, and it's not at all difficult to write code
that doesn't depend on them (if nothing else, fgets() followed by
deleting any trailing '\n').

> # sscanf() and fscanf() are _slightly_ better.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

Thread

sscanf error checking BartC <bc@freeuk.com> - 2016-12-14 15:42 +0000
  Re: sscanf error checking John Gordon <gordon@panix.com> - 2016-12-14 15:58 +0000
    Re: sscanf error checking Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2016-12-14 11:14 -0500
  Re: sscanf error checking gazelle@shell.xmission.com (Kenny McCormack) - 2016-12-14 16:11 +0000
    Re: sscanf error checking BartC <bc@freeuk.com> - 2016-12-14 17:51 +0000
      Re: sscanf error checking gazelle@shell.xmission.com (Kenny McCormack) - 2016-12-14 18:09 +0000
      Re: sscanf error checking Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-12-14 19:49 +0000
        Re: sscanf error checking BartC <bc@freeuk.com> - 2016-12-14 20:43 +0000
  Re: sscanf error checking Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-12-14 16:40 +0000
  Re: sscanf error checking Keith Thompson <kst-u@mib.org> - 2016-12-14 09:34 -0800
  Re: sscanf error checking Robert Wessel <robertwessel2@yahoo.com> - 2016-12-14 14:52 -0600
    Re: sscanf error checking supercat@casperkitty.com - 2016-12-15 07:24 -0800
      Re: sscanf error checking Keith Thompson <kst-u@mib.org> - 2016-12-15 11:26 -0800
        Re: sscanf error checking Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-12-15 15:35 -0800
          Re: sscanf error checking Keith Thompson <kst-u@mib.org> - 2016-12-15 16:28 -0800
            Re: sscanf error checking Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-12-15 16:37 -0800
              Re: sscanf error checking Robert Wessel <robertwessel2@yahoo.com> - 2016-12-26 17:25 -0600
        Re: sscanf error checking supercat@casperkitty.com - 2016-12-15 16:38 -0800
      Re: sscanf error checking raltbos@xs4all.nl (Richard Bos) - 2016-12-15 20:20 +0000
        Re: sscanf error checking Keith Thompson <kst-u@mib.org> - 2016-12-15 12:33 -0800
  sscanf error checking asetofsymbols@gmail.com - 2016-12-16 01:49 -0800
    sscanf error checking asetofsymbols@gmail.com - 2016-12-16 01:53 -0800

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