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Re: snprintf return value

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AT Monday 10 December 2018 18:20, pozz wrote:

> 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;
>    }

Keep in mind that snprintf can even return negative values as error codes.

-- 
Reinhardt

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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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