/*
 * Host name resolver
 * Copyright (c) Danny "Dr.T" <danny@any-mail.co.uk>
 *
 * Resolves IP address to hostname
 *
 * Test on Linux. Compile with gcc -o resolve resolve.c
 *
 */

#include <stdio.h>
#include <netdb.h>
#include <sys/socket.h>

int main ( int argc, char **argv )
{
  struct hostent *host;  /* hostent structure */
  struct in_addr addr;
  int i, ip[4];    /* i - counter, ip[4] - ip address */
  
  if ( argc != 2)
  {
    printf("%s <ip address>\n", argv[0]);
    return 0;
  }
  
  /* get ip address -> xxx.xxx.xxx.xxx */
  if ((i = sscanf(argv[1], "%d.%d.%d.%d", &ip[0], &ip[1], &ip[2], &ip[3])) < 4)
  {
    fprintf(stderr,"not a valid IP address\n");
    return 0;
  }

  /* check if it is a valid IP address */
  for (i = 0; i <4; i++)
  {
    if (ip[i] < 0 || ip[i] > 255)
      return 0;
    ((char *) &addr.s_addr)[i] = (char)ip[i];
  }
  
  if (!(host = gethostbyaddr((char *)&addr, sizeof(addr), AF_INET)))
  {
    fprintf(stderr, "unable to resolve host name\n");
    exit(0);
  }
  
  /* print hostname */
  printf("ip address -> hostname : %s\n", host->h_name);
}