#include <stdio.h>
#include <string.h>
#include <ctype.h>

void hex_dump(void *data, int size)
{
  /* dumps size bytes of *data to stdout. Looks like:
   * [0000] 75 6E 6B 6E 6F 77 6E 20
   *                  30 FF 00 00 00 00 39 00 unknown 0.....9.
   * (in a single line of course)
   */

  unsigned char *p = data;
  unsigned char c;
  int n;
  char bytestr[20] = {0};
  char addrstr[10] = {0};
  char hexstr[ 16*3 + 5 + 20] = {0};
  char charstr[16*1 + 5] = {0};
  for (n=1;n<=size;n++)
  {
    if (n%8 == 1)
    {
      /* store address for this line */
      snprintf(addrstr, sizeof(addrstr), "%.4x",
          ((unsigned int)p-(unsigned int)data) );
    }

    c = *p;
    if (isalnum(c) == 0)
      c = '.';

    /* store hex str (for left side) */
    snprintf(bytestr, sizeof(bytestr), "0x%02x    ", *p);
    strncat(hexstr, bytestr, sizeof(hexstr)-strlen(hexstr)-1);

    /* store char str (for right side) */
    snprintf(bytestr, sizeof(bytestr), "%c", c);
    strncat(charstr, bytestr, sizeof(charstr)-strlen(charstr)-1);

    if (n%8 == 0)
    {
      /* line completed */
      fprintf(stderr, "[%4.4s]          %-65.65s  %s\n", addrstr, hexstr, charstr);
      hexstr[0] = 0;
      charstr[0] = 0;
    }
    else if (n%8 == 0)
    {
      /* half line: add whitespaces */
      strncat(hexstr, "  ", sizeof(hexstr)-strlen(hexstr)-1);
      strncat(charstr, " ", sizeof(charstr)-strlen(charstr)-1);
    }
    p++; /* next byte */
  }

  if (strlen(hexstr) > 0)
  {
    /* print rest of buffer if not empty */
    fprintf(stderr, "[%4.4s]          %-65.65s  %s\n", addrstr, hexstr, charstr);
  }
}