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

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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;
   }

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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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