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

From	Mike Terry <news.dead.person.stones@darjeeling.plus.com>
Newsgroups	comp.lang.c
Subject	Re: on how to use the third argument of strncmp()
Date	2022-01-28 22:03 +0000
Organization	Aioe.org NNTP Server
Message-ID	<st1p6r$1p07$1@gioia.aioe.org> (permalink)
References	<86czkbd4ey.fsf@levado.to> <ObZIJ.21451$V31.13472@fx47.iad>

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On 28/01/2022 21:26, Scott Lurndal wrote:
> Meredith Montgomery <mmontgomery@levado.to> writes:
>> I don't really get
>>
>> --8<---------------cut here---------------start------------->8---
>>   int strncmp(const char *s1, const char *s2, size_t n);
>>
>>   The strncmp() function shall compare not more than n bytes (bytes that
>>   follow a NUL character are not compared) from the array pointed to by
>>   s1 to the array pointed to by s2.
>> --8<---------------cut here---------------end--------------->8---
>>
>> --8<---------------cut here---------------start------------->8---
>> Definition.  A c-string is a 0-terminated array of characters.
>> --8<---------------cut here---------------end--------------->8---
>>
>> 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.
> 
>   The 'str' prefix on the library function names pretty much tells you
> they were designed to work with nul-terminated strings.   For non-strings one uses
> memcpy, memmove and memset.
> 
> Say you have input text of "cpu0", you can use
> strncmp(text, "cpu", sizeof("cpu")) to match on
> the prefix then parse the numeric suffix.

You mean strncmp(text, "cpu", sizeof("cpu") - 1).
Or strncmp(text, "cpu", strlen("cpu")).

Mike.

> 
> Or, say you have a command table, and you want to
> match the unique leading prefix of a command rather
> than the entire command.
>

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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