Automatic strings without malloc

From	pozz <pozzugno@gmail.com>
Newsgroups	comp.lang.c
Subject	Automatic strings without malloc
Date	2021-11-17 11:36 +0100
Organization	A noiseless patient Spider
Message-ID	<sn2lvp$sl7$1@dont-email.me> (permalink)

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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);

The size of s is fixed and calculated for the maximum length of 
yourname, that is 9.

Later in time, I need to change the message into:

   sprintf(s, "Hello %s, today is %d/%d/%d", yourname, day, month, year);

Of course, I need to re-calculate the worst-case length, that should be 
now 35. However this is error-prone and I could forget to change the 
size of array.

Is there a better way to manage this situation? I can't use malloc() 
because I'm on an embedded system where I can't use heap.

I'm thinking to use sprintf(NULL, ...), such as:

   const char fmt[] = "Hi %s, today is %d/%d/%d";
   size_t n = sprintf(NULL, fmt, yourname, day, month, year);
   char s[n + 1];
   sprintf(s, fmt, yourname, day, month, year);
   lcd_write(s);

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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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