How to convert unsigned long to string

Question

In the C language  how do I convert unsigned long  value to a string  char    and keep my source code portable or just recompile it to work on other platform  without rewriting code   For example  if I have sprintf buffer  format  value   how do I determine the size of buffer with platform-independent manner

User · Answer

you can write a function which converts from unsigned long to str, similar to ltostr library function.

char *ultostr(unsigned long value, char *ptr, int base)
{
  unsigned long t = 0, res = 0;
  unsigned long tmp = value;
  int count = 0;

  if (NULL == ptr)
  {
    return NULL;
  }

  if (tmp == 0)
  {
    count++;
  }

  while(tmp > 0)
  {
    tmp = tmp/base;
    count++;
  }

  ptr += count;

  *ptr = '\0';

  do
  {
    res = value - base * (t = value / base);
    if (res < 10)
    {
      * -- ptr = '0' + res;
    }
    else if ((res >= 10) && (res < 16))
    {
        * --ptr = 'A' - 10 + res;
    }
  } while ((value = t) != 0);

  return(ptr);
}

you can refer to my blog here which explains implementation and usage with example.

User · Answer

Try using sprintf   unsigned long x 1000000  char buffer 21   sprintf buffer   lu   x     Edit   Notice that you have to allocate a buffer in advance  and have no idea how long the numbers will actually be when you do so  I m assuming 32bit longs  which can produce numbers as big as 10 digits    See Carl Smotricz s answer for a better explanation of the issues involved

User · Answer

char buffer  50    unsigned long a   5   int n sprintf  buffer    lu   a

User · Answer

For a long value you need to add the length info  l  and  u  for unsigned decimal integer   as a reference of available options see sprintf   include  lt stdio h gt       int main                unsigned long lval   123        char buffer  50         sprintf  buffer    lu    lval

User · Answer

The standard approach is to use sprintf buffer    lu   value   to write a string rep of value to buffer  However  overflow is a potential problem  as sprintf will happily  and unknowingly  write over the end of your buffer   This is actually a big weakness of sprintf  partially fixed in C   by using streams rather than buffers  The usual  answer  is to allocate a very generous buffer unlikely to overflow  let sprintf output to that  and then use strlen to determine the actual string length produced  calloc a buffer of  that size   1  and copy the string to that    This site discusses this and related problems at some length   Some libraries offer snprintf as an alternative which lets you specify a maximum buffer size

User · Answer

const int n   snprintf NULL  0    lu   ulong value   assert n  gt  0   char buf n 1   int c   snprintf buf  n 1    lu   ulong value   assert buf n       0    assert c    n

[c] How to convert unsigned long to string

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