How to convert unsigned long long to string with NO STDLIB/STDIO functions

Question

I need to convert an unsigned long long to a string without using any stdlib or stdio functions.

Can anyone suggest a way to do this or provide an algorithm?

I attempted to use some bitwise math but my compiler tells me that the shift is too large. Thanks in advance!

Is there anything unusual about the architecture you're working on that would prevent you from using division and modulo by 10? — , Nov 08 '13 at 23:13
You could do it like this: `char const * to_string(unsigned long long n) { return "a long"; }` Produces a string when given an integer. — Kerrek SB, Nov 08 '13 at 23:13
http://stackoverflow.com/questions/19865471/get-number-into-a-string-c-without-stdio — Drakosha, Nov 08 '13 at 23:14
@Drakosha That post is about signed int. To get the full range of signed vs. unsigned, various subtle coding variations occur, though the overall algorithm is similar. — chux - Reinstate Monica, Nov 08 '13 at 23:19
the mod 10 thing would work, I'm not sure how to execute it so the most significant digit is the first char in the array — Neil Locketz, Nov 08 '13 at 23:26
@KerrekSB - _Funny_, well you _were_ truthful. It does return a string when given a long long. — ryyker, Nov 08 '13 at 23:38
@ryyker: And I was quite serious, too. Unless the OP can describe precisely why that solution doesn't suffice, there's no reason to do anything more complicated. And if he *can* describe why it doesn't suffice, then *that should be part of the question*. Either way, some thinking will have been done, which I count as a win. — Kerrek SB, Nov 09 '13 at 00:09

chux - Reinstate Monica · Accepted Answer · 2013-11-08T23:54:56.163

A recursive solution

static char *ullTostring_Helper(unsigned long long i, char *s) {
  if (i >= 10) {
    s = ullTostring_Helper(i/10, s);
  }
  *s++ = i%10 + '0' ;
  return s;
}

char *ullTostring( unsigned long long i, char *dest) {
  *ullTostring_Helper(i, dest) = '\0';
  return dest;
}

A non-recursive solution with no function calls

char *ullTostring2(unsigned long long i, char *dest) {
  char buf[(sizeof i)*3 + 3];
  char *p = &buf[sizeof(buf) - 1];
  *p = '\0';
  do {
    p--;
    *p = i%10 + '0';
    i /= 10;
  } while (i);
  char *dest2 = dest;
  do {
    *dest2++ = *p;
  } while (*p++);
  return dest;
}

How to convert unsigned long long to string with NO STDLIB/STDIO functions

1 Answers1