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

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Kaz Kylheku <480-992-1380@kylheku.com> writes:

> On 2022-01-28, Meredith Montgomery <mmontgomery@levado.to> 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 you don't actually have a real requirement that you're
> trying to implement; someone handed you a spcification which says "make
> me some kind of program that uses strncmp in some good way".
>
>> Is that the end of the story?  I feel there could be more to this.  Can
>> you share your experience?  Thank you.
>
> One use case is testing whether a given string s1 is the prefix of a
> string s2. Then we choose strlen(s1).
>
> For instance, suppose you have some simple command language, in which
> you'd like users to be able to use abbreviated commands. Say that if the
> user types at least two charcters, you'd like to do a prefix match.
> If the user types "li", you'd like to dispatch the "list" command.
> So then you're comparing the list of commands in your cmomand table like
> this:
>
>    size_t len  = strlen(user_input);
>
>    for (i = 0; len >= 2 && i < NCOMMANDS; i++)
>    {
>      if (0 == strncmp(user_input, command_table[i].command, len))
>      {
>         /* prefix match: e.g "lis" input matched "list".
>         break;
>      }
>    }
>
>    if (len < 2 || i == NCOMMANDS)
>    {
>       /* command not found */
>    }
>
> Under this scheme, if the user types "listing", then it will not match
> the "list" command, but "li" will.
>
> Alternatively, the command table could have short command in it like
> "li", whereby the user can use the longer "list", and it makes no
> diference.
>
>    const char *command_table[i].command;
>
>    if (0 == strncmp(user_input, command, strlen(command)))
>    {
>       /* the command, e.g. "li", is a prefix of the user's requested
>          command such as "listing", hence match */
>       break;
>    }

Pretty interesting illustration!

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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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