Optimal Base-10 only itoa() function? [closed]

Answer 1

Get rid of the auto char array and make them pass the size so you can check for overflow.

#define I32TOA( buff, val ) _i32toa( (buff), sizeof(buff), (val) )

char * _i32toa(char *const rtn, size_t size, int32_t i)    {
    if (NULL == rtn) return NULL;

    uint32_t  ut, ui;
    char minus_sign=0;
    char *p = rtn + size-1;
    *p-- = 0;    // nul-terminate buffer
    assert( p >= rtn );

    if (i < 0)    {
        minus_sign = '-';
        ui = (uint32_t)((int)-1 * (int)i);
    }    else    {
        ui = i;
    }

    while (ui > 9) {
        ut = ui;
        ui /= 10;
        *p-- = (ut - (ui * 10)) + 48;
        assert( p >= rtn );
    }
    *p = ui + 48;

    if ('-' == minus_sign) {
        *--p = minus_sign;
        assert( p >= rtn );
    }

    return p;
}