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Groups > comp.arch.embedded > #28418

snprintf return value

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I usually have a static buffer and I don't want to use a dynamic buffer.

char buf[BUFLEN];

I have to construct a long string, and it is quite easy to call snprintf 
multiple times:

   int n = 0;
   n += snprintf(&buf[n], BUFLEN - n, ...);
   n += snprintf(&buf[n], BUFLEN - n, ...);
   n += snprintf(&buf[n], BUFLEN - n, ...);
   n += snprintf(&buf[n], BUFLEN - n, ...);

I was convinced the return value was the real number of characters 
written in buf, not counting final '\0'. In this case, the above code works.

I just noticed the return value of snprintf() is the number of 
characters of the generated string as if the buffer was long enough. So 
the above code doesn't work.

The return value of snprintf() is useful if you want to dynamically 
reallocate the buffer so it can store all the string. In my case I would 
prefer to truncate the string at the end of the static buffer. The above 
code should be redesigned as:

   int n = 0;
   n += snprintf(&buf[n], BUFLEN - n, ...);
   if (n >= BUFLEN - n) return;
   n += snprintf(&buf[n], BUFLEN - n, ...);
   if (n >= BUFLEN - n) return;
   n += snprintf(&buf[n], BUFLEN - n, ...);
   if (n >= BUFLEN - n) return;
   n += snprintf(&buf[n], BUFLEN - n, ...);
   if (n >= BUFLEN - n) return;

The code starts being not readable. I'm thinking to create a new 
snprintf2():

   int
   snprintf2(char *str, size_t size, const char *format, ...) {
       va_list args;

       va_start(args, format);
       int n = vsnprintf(str, size, format, args);
       va_end(args);
       return (n >= size) ? (size - 1) : n;
   }

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snprintf return value pozz <pozzugno@gmail.com> - 2018-12-10 11:20 +0100
  Re: snprintf return value Reinhardt Behm <rbehm@hushmail.com> - 2018-12-10 18:24 +0800
    Re: snprintf return value pozz <pozzugno@gmail.com> - 2018-12-10 11:32 +0100
      Re: snprintf return value Philipp Klaus Krause <pkk@spth.de> - 2019-01-01 12:59 +0100
  Re: snprintf return value David Brown <david.brown@hesbynett.no> - 2018-12-10 13:15 +0100
  Re: snprintf return value Clifford Heath <no.spam@please.net> - 2018-12-11 08:49 +1100
    Re: snprintf return value Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2018-12-11 11:41 -0500
      Re: snprintf return value Clifford Heath <no.spam@please.net> - 2018-12-12 10:34 +1100
        Re: snprintf return value David Brown <david.brown@hesbynett.no> - 2018-12-12 09:09 +0100
          Re: snprintf return value Clifford Heath <no.spam@please.net> - 2018-12-12 21:38 +1100
        Re: snprintf return value Les Cargill <lcargill99@comcast.com> - 2018-12-30 11:23 -0600
  Re: snprintf return value Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2018-12-11 00:47 +0100
    Re: snprintf return value Clifford Heath <no.spam@please.net> - 2018-12-11 13:31 +1100

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