padding with sprintf

Question

I have a dummy question. I would like to print an integer into a buffer padding with 0 but I cannot sort it out the sprintfformat. I am trying the following

Answer 1

It's %030d, with type-letter at the end.

Answer 2

A fairly effective version that doesn't need any slow library calls:

#include <stdio.h>

void uint_tostr (unsigned int n, size_t buf_size, char dst[buf_size])
{
  const size_t str_size = buf_size-1;

  for(size_t i=0; i<str_size; i++)
  {
    size_t index = str_size - i - 1;
    dst[index] = n%10 + '0';
    n/=10;
  }
  dst[str_size] = '\0';
}


int main (void)
{
  unsigned int n = 1234;
  char str[6+1];
  uint_tostr(n, 6+1, str);
  puts(str);
}

This can be optimized further, though it is still probably some hundred times faster than sprintf as is.

Answer 3

The padding and width come before the type specifier:

sprintf( buf, "%030d", my_val );

Answer 4

Your precision and width parameters need to go between the '%' and the conversion specifier 'd', not after. In fact all flags do. So if you want a preceeding '+' for positive numbers, use '%+d'.

Answer 5

"%030d" is the droid you are looking for

Answer 6

Try:

sprintf( buf, "%030d", my_val );