printf("%*d", width, num);

	printf("%2$*1$d", width, num);

	printf("%'.2f", 1234567.89);

#include <math.h>
#include <stdio.h>
fprintf(stdout, "pi = %.5f\n", 4 * atan(1.0));

#include <stdio.h>
fprintf(stdout, "%s, %s %d, %.2d:%.2d\n",
	weekday, month, day, hour, min);

#include <stdio.h>
fprintf(stdout, format,
	weekday, month, day, hour, min);

"%1$s, %3$d. %2$s, %4$d:%5$.2d\n"

#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
char *
make_message(const char *fmt, ...) {
   /* Guess we need no more than 100 bytes. */
   int n, size = 100;
   char *p;
   va_list ap;
   if ((p = malloc (size)) == NULL)
      return NULL;
   while (1) {
      /* Try to print in the allocated space. */
      va_start(ap, fmt);
      n = vsnprintf (p, size, fmt, ap);
      va_end(ap);
      /* If that worked, return the string. */
      if (n > -1 && n < size)
         return p;
      /* Else try again with more space. */
      if (n > -1)    /* glibc 2.1 */
         size = n+1; /* precisely what is needed */
      else           /* glibc 2.0 */
         size *= 2;  /* twice the old size */
      if ((p = realloc (p, size)) == NULL)
         return NULL;
   }
}