ANSI C, integer to string without variadic functions

Question

I'm currently working with a PLC that supports ANSI C, but uses its own flavour of the GNU compiler, which doesn't compile any variadic functions and things like itoa. So using sprintf & co. isn't an option for converting integers to strings. Can anyone guide me to a site where a robust, sprintf- free implementation of itoa is listed or post a suitable algorithm here? Thanks in advance.

Well yes. This is indeed an ongoing discussion with the SPC providers marketing department ;) — Maxwin
– Maxwin, Commented Jan 26, 2010 at 11:53

Alok Singhal · Accepted Answer · 2010-01-26 08:35:28Z

6

This is from K&R:

void itoa(int n, char s[])
{
    int i, sign;

    if ((sign = n) < 0)  /* record sign */
        n = -n;          /* make n positive */
    i = 0;
    do {       /* generate digits in reverse order */
        s[i++] = n % 10 + '0';   /* get next digit */
    } while ((n /= 10) > 0);     /* delete it */
    if (sign < 0)
        s[i++] = '-';
    s[i] = '\0';
    reverse(s);
}

reverse() just reverses a string.

answered Jan 26, 2010 at 8:35

Alok Singhal

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4 Comments

R Samuel Klatchko Over a year ago

Use this version with care as it can overflow the buffer.

Alok Singhal Over a year ago

Yes, that's true. The caller has to know if the buffer has enough space or not. Just like sprintf().

R Samuel Klatchko Over a year ago

Which is why you should never use sprintf() and only use snprintf()

Alok Singhal Over a year ago

I agree with you, if you replace "never" with "almost never". In general, one should prefer snprintf(). But if one is sure that the target buffer has the required size, sprintf() is fine too. See stackoverflow.com/questions/1996374/… for example.

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