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Re: C String terminator

Path csiph.com!eternal-september.org!feeder.eternal-september.org!reader01.eternal-september.org!.POSTED!not-for-mail
From Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups comp.lang.c
Subject Re: C String terminator
Date Tue, 21 Jan 2020 04:10:18 -0800
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Lew Pitcher <lew.pitcher@digitalfreehold.ca> writes:

> Two minor corrections
>
> Lew Pitcher wrote:
>
>> T wrote:
>>
>>> On 2020-01-17 12:48, T wrote:
>>>
>>>> On 2020-01-17 12:46, Ben Bacarisse wrote:
>>>>
>>>>> T <T@invalid.invalid> writes:
>>>>>
>>>>>> On 2020-01-16 15:45, Ben Bacarisse wrote:
>>>>>>
>>>>>>> T <T@invalid.invalid> writes:
>>>>>>>
>>>>>>>> On 2020-01-16 12:17, Ben Bacarisse wrote:
>>>>>
>>>>> <cut>
>>>>>
>>>>>>>>> $ gcc -o t t.c
>>>>>>>>> $ ./t
>>>>>
>>>>> <cut>
>>>>>
>>>>>>>> I am a total idiot when it comes to C.  How do
>>>>>>>> I run this?
>>>>>>>
>>>>>>> I don't know.  That depends on your compiler, OS and so on and that
>>>>>>> obviously different to mine sice whole process of compiling and
>>>>>>> running is shown above.
>>>>>>
>>>>>> I have Fedora Linux at my disposal, which has
>>>>>> a gcc c compiler.
>>>>>
>>>>> Then I am baffled.  I showed both the gcc command to compile the code,
>>>>> and the command to run it.  I've removed everything else so you can see
>>>>> them.
>>>>>
>>>>> <cut>
>>>>
>>>> Ben!  I am an idiot when it comes to C.  You
>>>> got to start out like I am a total noob!
>>>
>>> Okay, I looked at it from a bash standpoint instead
>>> of a mystery language I had no clue about.  And I
>>> feel dumb.  You were very precise!
>>>
>>> $ cd C
>>> $ vi t.c
>>> $ gcc -o t t.c
>>> $ t
>>> [FOOp@]
>>>
>>>
>>> Question:  why did I get
>>>      [FOOp@]
>>>
>>> and you got
>>>      [FOO]
>>> ?
>>
>> Because, as implied by Ben's source code comment, the program given
>>
>>>>>>>>> #include <stdio.h>
>>>>>>>>>
>>>>>>>>> void foo(const char *s)
>>>>>>>>> {
>>>>>>>>>     printf("[%s]\n", s);
>>>>>>>>> }
>>>>>>>>>
>>>>>>>>> int main(void)
>>>>>>>>> {
>>>>>>>>>      char str[3] = "FOO";
>>>>>>>>>      foo(str); // DANGER, WILL ROBINSON!
>>>>>>>>> }
>>
>> invokes undefined behaviour.
>>
>> It does this by passing an array of three characters (ultimately) to
>> printf(), which /expects/ a C "string" as it's first argument.  The array
>
> Correction #1: in this case, the critical point is that, here, printf()
> expects a C "string" as it's second argument (as well as the first argument,
> which is the given format string "[%s]\n").

Technically, that isn't right.  A %s conversion specifier requires
as its argument a pointer to the first element of an array of
character type, not a pointer to a string.  It is true in this
particular case that the array must have a null character in it to
avoid undefined behavior, but the argument description says "pointer
to array of character type", and does not mention "string".

(Also:  the possessive of "it" is "its", with no apostrophe.  The
word "it's", with an apostrophe, is a contraction of "it is".)

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Thread

C String terminator T <T@invalid.invalid> - 2020-01-14 09:22 -0800
  Re: C String terminator Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-01-14 09:32 -0800
    Re: C String terminator T <T@invalid.invalid> - 2020-01-14 09:43 -0800
      Re: C String terminator Bart <bc@freeuk.com> - 2020-01-14 17:53 +0000
        Re: C String terminator David Brown <david.brown@hesbynett.no> - 2020-01-14 20:17 +0100
          Re: C String terminator Bart <bc@freeuk.com> - 2020-01-14 20:01 +0000
      Re: C String terminator Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-01-14 09:57 -0800
        Re: C String terminator Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-01-14 11:37 -0800
          Re: C String terminator T <T@invalid.invalid> - 2020-01-15 09:02 -0800
            Re: C String terminator T <T@invalid.invalid> - 2020-01-15 09:38 -0800
              Re: C String terminator T <T@invalid.invalid> - 2020-01-15 09:53 -0800
        Re: C String terminator Manfred <noname@add.invalid> - 2020-01-14 20:48 +0100
    Re: C String terminator chad <cdalten@gmail.com> - 2020-01-15 05:43 -0800
      Re: C String terminator Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-01-15 07:12 -0800
      Re: C String terminator Jorgen Grahn <grahn+nntp@snipabacken.se> - 2020-01-15 15:35 +0000
        Re: C String terminator chad <cdalten@gmail.com> - 2020-01-19 06:20 -0800
    Re: C String terminator Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-01-15 10:52 -0800
      Re: C String terminator Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-01-15 12:52 -0800
        Re: C String terminator gazelle@shell.xmission.com (Kenny McCormack) - 2020-01-15 20:56 +0000
        Re: C String terminator Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-16 02:17 +0000
        Re: C String terminator Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-01-15 21:54 -0800
          Re: C String terminator fir <profesor.fir@gmail.com> - 2020-01-16 02:07 -0800
            Re: C String terminator Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-01-16 02:45 -0800
              Re: C String terminator Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2020-01-16 08:21 -0700
                Re: C String terminator Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-01-16 08:03 -0800
              Re: C String terminator John Bode <jfbode1029@gmail.com> - 2020-01-16 09:06 -0800
              Re: C String terminator James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-01-16 11:29 -0800
      Re: C String terminator Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-16 02:01 +0000
        Re: C String terminator James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-01-15 23:02 -0500
        Re: C String terminator David Brown <david.brown@hesbynett.no> - 2020-01-16 11:15 +0100
          Re: C String terminator Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-16 13:07 +0000
        Re: C String terminator Manfred <noname@add.invalid> - 2020-01-17 18:43 +0100
          Re: C String terminator Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-01-21 04:00 -0800
          Re: C String terminator James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-01-21 05:00 -0800
  Re: C String terminator Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2020-01-14 12:36 -0700
    Re: C String terminator Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-01-14 12:05 -0800
      Re: C String terminator Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2020-01-14 13:54 -0700
        Re: C String terminator James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-01-14 15:03 -0800
          Re: C String terminator Thiago Adams <thiago.adams@gmail.com> - 2020-01-15 04:55 -0800
            Re: C String terminator Guillaume <message@bottle.org> - 2020-01-15 20:49 +0100
              Re: C String terminator Thiago Adams <thiago.adams@gmail.com> - 2020-01-15 12:55 -0800
        Re: C String terminator Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-01-14 21:31 -0800
    Re: C String terminator T <T@invalid.invalid> - 2020-01-15 09:28 -0800
      Re: C String terminator T <T@invalid.invalid> - 2020-01-15 09:38 -0800
        Re: C String terminator Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2020-01-15 10:50 -0700
          Re: C String terminator T <T@invalid.invalid> - 2020-01-15 10:17 -0800
        Re: C String terminator T <T@invalid.invalid> - 2020-01-15 09:53 -0800
  Re: C String terminator Richard Damon <Richard@Damon-Family.org> - 2020-01-14 21:43 -0500
  Re: C String terminator "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2020-01-14 22:52 -0800
    Re: C String terminator "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2020-01-14 22:54 -0800
  Re: C String terminator Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-01-15 02:00 -0800
    Re: C String terminator gazelle@shell.xmission.com (Kenny McCormack) - 2020-01-15 10:47 +0000
      Re: C String terminator Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-01-15 03:02 -0800
    Re: C String terminator T <T@invalid.invalid> - 2020-01-15 10:19 -0800
      Re: C String terminator Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-01-15 11:33 -0800
        Re: C String terminator T <T@invalid.invalid> - 2020-01-15 12:03 -0800
          Re: C String terminator Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-16 01:30 +0000
            Re: C String terminator T <T@invalid.invalid> - 2020-01-15 18:17 -0800
              Re: C String terminator Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-16 03:44 +0000
                Re: C String terminator T <T@invalid.invalid> - 2020-01-15 20:33 -0800
          Re: C String terminator fir <profesor.fir@gmail.com> - 2020-01-16 02:26 -0800
  Re: C String terminator Jorgen Grahn <grahn+nntp@snipabacken.se> - 2020-01-15 15:11 +0000
    Re: C String terminator T <T@invalid.invalid> - 2020-01-15 09:32 -0800
      Re: C String terminator Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-01-15 10:47 -0800
        Re: C String terminator T <T@invalid.invalid> - 2020-01-15 10:58 -0800
          Re: C String terminator Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-16 01:39 +0000
            Re: C String terminator T <T@invalid.invalid> - 2020-01-15 18:27 -0800
              Re: C String terminator T <T@invalid.invalid> - 2020-01-15 19:03 -0800
              Re: C String terminator Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-16 03:28 +0000
                Re: C String terminator T <T@invalid.invalid> - 2020-01-15 19:33 -0800
                Re: C String terminator T <T@invalid.invalid> - 2020-01-15 19:38 -0800
                Re: C String terminator Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-16 13:31 +0000
                Re: C String terminator T <T@invalid.invalid> - 2020-01-16 09:09 -0800
                Re: C String terminator Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2020-01-16 10:27 -0700
                Re: C String terminator T <T@invalid.invalid> - 2020-01-16 10:54 -0800
                Re: C String terminator Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-16 20:59 +0000
                Re: C String terminator T <T@invalid.invalid> - 2020-01-16 14:11 -0800
                Re: C String terminator Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-16 20:17 +0000
                Re: C String terminator T <T@invalid.invalid> - 2020-01-16 14:14 -0800
                Re: C String terminator Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-16 23:45 +0000
                Yes, Ben makes house calls (Was: C String terminator) gazelle@shell.xmission.com (Kenny McCormack) - 2020-01-16 23:57 +0000
                Re: C String terminator T <T@invalid.invalid> - 2020-01-17 11:28 -0800
                Re: C String terminator Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-17 20:46 +0000
                Re: C String terminator T <T@invalid.invalid> - 2020-01-17 12:48 -0800
                Re: C String terminator T <T@invalid.invalid> - 2020-01-17 12:54 -0800
                Re: C String terminator Bart <bc@freeuk.com> - 2020-01-17 21:02 +0000
                Re: C String terminator Bart <bc@freeuk.com> - 2020-01-17 21:21 +0000
                Re: C String terminator T <T@invalid.invalid> - 2020-01-17 13:35 -0800
                Re: C String terminator T <T@invalid.invalid> - 2020-01-17 13:44 -0800
                Re: C String terminator fir <profesor.fir@gmail.com> - 2020-01-17 15:03 -0800
                Re: C String terminator fir <profesor.fir@gmail.com> - 2020-01-17 15:06 -0800
                Re: C String terminator Ike Naar <ike@sdf.lonestar.org> - 2020-01-18 07:30 +0000
                Re: C String terminator Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2020-01-17 16:06 -0500
                Re: C String terminator Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2020-01-17 16:23 -0500
                Re: C String terminator T <T@invalid.invalid> - 2020-01-17 13:37 -0800
                Re: C String terminator Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-01-21 04:10 -0800
                Re: C String terminator Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-01-21 10:41 -0800
                Re: C String terminator Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-01-17 01:55 -0800
                Re: C String terminator Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-01-17 09:52 -0800
                Re: C String terminator T <T@invalid.invalid> - 2020-01-17 11:29 -0800
                Re: C String terminator Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-16 18:21 +0000
                Re: C String terminator T <T@invalid.invalid> - 2020-01-16 10:50 -0800
                Re: C String terminator Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-16 20:50 +0000
                Re: C String terminator T <T@invalid.invalid> - 2020-01-16 14:17 -0800
  Re: C String terminator Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-01-15 09:59 -0800
  Re: C String terminator T <T@invalid.invalid> - 2020-01-15 10:15 -0800
  Re: C String terminator T <T@invalid.invalid> - 2020-01-18 21:42 -0800
    Re: C String terminator T <T@invalid.invalid> - 2020-01-19 22:13 -0800
  Re: C String terminator Bonita Montero <Bonita.Montero@gmail.com> - 2020-01-21 19:49 +0100
  Re: C String terminator John Bode <jfbode1029@gmail.com> - 2020-01-21 15:33 -0800
    Re: C String terminator Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-01-21 23:19 -0800
    Re: C String terminator Bonita Montero <Bonita.Montero@gmail.com> - 2020-01-22 08:39 +0100
      Re: C String terminator chad <cdalten@gmail.com> - 2020-01-22 06:59 -0800
        Re: C String terminator Bonita Montero <Bonita.Montero@gmail.com> - 2020-01-22 18:44 +0100

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