Re: on how to use the third argument of strncmp()

From	Vir Campestris <vir.campestris@invalid.invalid>
Newsgroups	comp.lang.c
Subject	Re: on how to use the third argument of strncmp()
Date	2022-02-02 22:01 +0000
Organization	A noiseless patient Spider
Message-ID	<steuvk$8bu$2@dont-email.me> (permalink)
References	<86czkbd4ey.fsf@levado.to> <st1idr$jc8$1@gioia.aioe.org> <86ee4rblvt.fsf@levado.to>

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On 28/01/2022 21:17, Meredith Montgomery wrote:
> Mateusz Viste <mateusz@xyz.invalid> writes:
> 
>> 2022-01-28 at 16:52 -0300, Meredith Montgomery wrote:
>>> What should choose for the n argument?  If I'm sure s1 and s2 are
>>> c-strings, then I have nothing to worry about, but if I have to
>>> specify the n argument, then I must choose a number.  To me the
>>> sensible thing is
>>>
>>>    min(strlen(s1), strlen(s2))
>>>
>>> So far so good.  What if I don't want to trust that s1 and s2 are
>>> c-strings?  In that case I can't use strlen() at all.  So I guess this
>>> procedure assumes c-strings.
>>
>> This function is intended to work with fixed-width (padded, not
>> necessarily terminated) string fields, like strncpy(). I don't think
>> this kind of fields is much in use nowadays.
>>
>> strncmp() also allows to compare prefix of strings (ie. "do s1 and s2
>> start with the exact same 7 characters?" situation).
>>
>> Since you wish to compare NULL-terminated strings in their entirety,
>> the usual strcmp() is the right tool for the job.
> 
> But what do I do when these strings come from a user?  I can't trust the
> user will close them properly.

If you can't trust the user to have put a null on for strcmp, then you 
can't trust it for strlen either.

Andy

Thread

on how to use the third argument of strncmp() Meredith Montgomery <mmontgomery@levado.to> - 2022-01-28 16:52 -0300
  Re: on how to use the third argument of strncmp() Mateusz Viste <mateusz@xyz.invalid> - 2022-01-28 21:07 +0100
    Re: on how to use the third argument of strncmp() Meredith Montgomery <mmontgomery@levado.to> - 2022-01-28 18:17 -0300
      Re: on how to use the third argument of strncmp() Mateusz Viste <mateusz@xyz.invalid> - 2022-01-28 22:35 +0100
      Re: on how to use the third argument of strncmp() Vir Campestris <vir.campestris@invalid.invalid> - 2022-02-02 22:01 +0000
    Re: on how to use the third argument of strncmp() Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-01-28 18:37 -0800
      Re: on how to use the third argument of strncmp() scott@slp53.sl.home (Scott Lurndal) - 2022-01-29 15:32 +0000
      Re: on how to use the third argument of strncmp() Bonita Montero <Bonita.Montero@gmail.com> - 2022-01-29 19:02 +0100
  Re: on how to use the third argument of strncmp() scott@slp53.sl.home (Scott Lurndal) - 2022-01-28 21:26 +0000
    Re: on how to use the third argument of strncmp() Mike Terry <news.dead.person.stones@darjeeling.plus.com> - 2022-01-28 22:03 +0000
      Re: on how to use the third argument of strncmp() scott@slp53.sl.home (Scott Lurndal) - 2022-01-29 15:31 +0000
  Re: on how to use the third argument of strncmp() Siri Cruise <chine.bleu@yahoo.com> - 2022-01-28 13:43 -0800
    Re: on how to use the third argument of strncmp() Bonita Montero <Bonita.Montero@gmail.com> - 2022-01-29 13:43 +0100
      Re: on how to use the third argument of strncmp() Bonita Montero <Bonita.Montero@gmail.com> - 2022-01-29 16:06 +0100
        Re: on how to use the third argument of strncmp() Bonita Montero <Bonita.Montero@gmail.com> - 2022-01-29 16:09 +0100
  Re: on how to use the third argument of strncmp() Kaz Kylheku <480-992-1380@kylheku.com> - 2022-01-28 21:54 +0000
    Re: on how to use the third argument of strncmp() Meredith Montgomery <mmontgomery@levado.to> - 2022-01-28 21:47 -0300
  Re: on how to use the third argument of strncmp() James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-01-28 19:40 -0500
    Re: on how to use the third argument of strncmp() Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-01-29 03:53 -0800
      Re: on how to use the third argument of strncmp() Bonita Montero <Bonita.Montero@gmail.com> - 2022-01-29 19:01 +0100
    Re: on how to use the third argument of strncmp() Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2022-01-29 10:54 -0700
      Re: on how to use the third argument of strncmp() James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-01-29 14:55 -0500
  Re: on how to use the third argument of strncmp() Manfred <noname@add.invalid> - 2022-01-30 04:03 +0100
    Re: on how to use the third argument of strncmp() Meredith Montgomery <mmontgomery@levado.to> - 2022-01-30 10:02 -0300
      Re: on how to use the third argument of strncmp() Dolores Filandro <dolfiland8@gmail.com> - 2022-02-03 18:48 -0800

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