Re: Automatic strings without malloc

From	Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups	comp.lang.c
Subject	Re: Automatic strings without malloc
Date	2021-11-17 15:18 -0800
Organization	None to speak of
Message-ID	<87pmqype0g.fsf@nosuchdomain.example.com> (permalink)
References	(1 earlier) <ei9lJ.146291$I%1.54591@fx36.iad> <24d7df90-3564-407a-999f-a33e774897c5n@googlegroups.com> <sn38n4$l8i$1@dont-email.me> <87tugapoxu.fsf@nosuchdomain.example.com> <sn3lq4$qhj$4@dont-email.me>

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David Brown <david.brown@hesbynett.no> writes:
> On 17/11/2021 20:22, Keith Thompson wrote:
>> David Brown <david.brown@hesbynett.no> writes:
>>> On 17/11/2021 16:36, Malcolm McLean wrote:
>>>> On Wednesday, 17 November 2021 at 15:34:50 UTC, Scott Lurndal wrote:
>>>>> pozz <pozz...@gmail.com> writes: 
>>>>>> Many times I need to construct a string through a call to sprintf and 
>>>>>> pass it to an external function. 
>>>>>>
>>>>>> char s[32]; 
>>>>>> sprintf(s, "Hi %s, today is %d/%d/%d", yourname, day, month, year); 
>>>>>> lcd_write(s);
>>>>> One might consider using 'snprintf' instead of 'sprintf'; it is a bit safer. 
>>>>>
>>>> It depends whether wrong results are better or worse than no results.
>>>
>>> Generally, a truncated string on the output is better than a stack
>>> overflow with your embedded system crashing or going wild.  But your
>>> needs may vary.
>> 
>> Sure, truncation is probably better than undefined behavior, but
>> depending on the context it might not be *much* better.
>> 
>> For a small LCD display, truncation is probably the best fallback
>> (followed by thinking about how to make the message fit).  On the other
>> hand, truncating "rm -rf /home/user/temp_dir" to "rm -rf /home/user" is
>> likely to be far worse than crashing the program.
>
> Yes - "generally" does not mean "always" !  That's a good example of
> when truncation could be rather bad.

Depending on the context, "generally" can mean either "usually" or
"always".  I've found that people generally interpret it in the most
inconvenient way possible.

>> There's no general rule other than that you should always *think*
>> about what will/should happen if there's not enough room in the target
>> array.
>
> Alternatively, think about how to ensure that there /always/ will be
> enough room in the target array.  Either way, always /think/.

That's not always possible, especially if the "array" is a display
device.  But yes, "always think" is a good idea.  I think.

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
Working, but not speaking, for Philips
void Void(void) { Void(); } /* The recursive call of the void */

Thread

Automatic strings without malloc pozz <pozzugno@gmail.com> - 2021-11-17 11:36 +0100
  Re: Automatic strings without malloc pozz <pozzugno@gmail.com> - 2021-11-17 11:38 +0100
  Re: Automatic strings without malloc Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2021-11-17 03:00 -0800
  Re: Automatic strings without malloc David Brown <david.brown@hesbynett.no> - 2021-11-17 12:04 +0100
    Re: Automatic strings without malloc Manfred <noname@add.invalid> - 2021-11-17 18:19 +0100
      Re: Automatic strings without malloc David Brown <david.brown@hesbynett.no> - 2021-11-17 20:34 +0100
    Re: Automatic strings without malloc pozz <pozzugno@gmail.com> - 2021-11-18 10:07 +0100
  Re: Automatic strings without malloc Thiago Adams <thiago.adams@gmail.com> - 2021-11-17 05:11 -0800
    Re: Automatic strings without malloc Philipp Klaus Krause <pkk@spth.de> - 2021-11-18 15:29 +0100
  Re: Automatic strings without malloc Bart <bc@freeuk.com> - 2021-11-17 13:47 +0000
  Re: Automatic strings without malloc scott@slp53.sl.home (Scott Lurndal) - 2021-11-17 15:34 +0000
    Re: Automatic strings without malloc Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2021-11-17 07:36 -0800
      Re: Automatic strings without malloc David Brown <david.brown@hesbynett.no> - 2021-11-17 16:56 +0100
        Re: Automatic strings without malloc scott@slp53.sl.home (Scott Lurndal) - 2021-11-17 18:21 +0000
          Re: Automatic strings without malloc David Brown <david.brown@hesbynett.no> - 2021-11-17 20:37 +0100
            Re: Automatic strings without malloc scott@slp53.sl.home (Scott Lurndal) - 2021-11-17 21:35 +0000
              Re: Automatic strings without malloc Thiago Adams <thiago.adams@gmail.com> - 2021-11-19 05:38 -0800
                Re: Automatic strings without malloc Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2021-11-19 07:13 -0800
            Re: Automatic strings without malloc William Ahern <william@25thandClement.com> - 2021-11-17 20:46 -0800
              Re: Automatic strings without malloc David Brown <david.brown@hesbynett.no> - 2021-11-18 10:50 +0100
                Re: Automatic strings without malloc Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2021-11-18 03:56 -0800
                Re: Automatic strings without malloc Thiago Adams <thiago.adams@gmail.com> - 2021-11-18 05:54 -0800
                Re: Automatic strings without malloc Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-11-18 16:38 +0000
                Re: Automatic strings without malloc Thiago Adams <thiago.adams@gmail.com> - 2021-11-18 10:52 -0800
                Re: Automatic strings without malloc Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-11-18 11:27 -0800
                Re: Automatic strings without malloc Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-11-18 20:41 +0000
                Re: Automatic strings without malloc David Brown <david.brown@hesbynett.no> - 2021-11-18 16:05 +0100
        Re: Automatic strings without malloc Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-11-17 11:22 -0800
          Re: Automatic strings without malloc David Brown <david.brown@hesbynett.no> - 2021-11-17 20:39 +0100
            Re: Automatic strings without malloc Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-11-17 15:18 -0800
              [OT] Generally... [Was: Automatic strings without malloc] Jeremy Brubaker <jbrubake@orionarts.invalid> - 2021-11-18 17:46 +0000
                Re: [OT] Generally... [Was: Automatic strings without malloc] Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-11-18 11:21 -0800
  Re: Automatic strings without malloc Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-11-17 11:14 -0800
    Re: Automatic strings without malloc pozz <pozzugno@gmail.com> - 2021-11-18 10:08 +0100
  Re: Automatic strings without malloc Siri Cruise <chine.bleu@yahoo.com> - 2021-11-18 12:25 -0800
    Re: Automatic strings without malloc David Brown <david.brown@hesbynett.no> - 2021-11-18 23:19 +0100
      Re: Automatic strings without malloc Siri Cruise <chine.bleu@yahoo.com> - 2021-11-18 17:22 -0800
        Re: Automatic strings without malloc Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2021-11-19 01:46 -0800
          Re: Automatic strings without malloc David Brown <david.brown@hesbynett.no> - 2021-11-19 17:29 +0100
        Re: Automatic strings without malloc David Brown <david.brown@hesbynett.no> - 2021-11-19 17:26 +0100
          Re: Automatic strings without malloc Siri Cruise <chine.bleu@yahoo.com> - 2021-11-19 09:00 -0800
            Re: Automatic strings without malloc David Brown <david.brown@hesbynett.no> - 2021-11-19 18:25 +0100
              Re: Automatic strings without malloc "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2021-11-19 14:58 -0800
            Re: Automatic strings without malloc Guillaume <message@bottle.org> - 2021-11-19 19:37 +0100
          Re: Automatic strings without malloc "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2021-11-19 12:34 -0800
            Re: Automatic strings without malloc Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2021-11-19 13:44 -0800
              Re: Automatic strings without malloc David Brown <david.brown@hesbynett.no> - 2021-11-20 13:30 +0100
                Re: Automatic strings without malloc luser droog <luser.droog@gmail.com> - 2021-11-20 20:49 -0800

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