/*
   gethostbyaddr.c: illustrate the use of gethostbyaddr function.

	compile: cc -c gethostbyaddr.c -lnsl
*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>

int main()
{
   unsigned long addr;
   char haddr[100];
   struct hostent *hp;		/* host pointer */
   char **p;			/* help... */
   int  help;

   printf("Enter host address in dotted decimal notation...\n");
   printf("  - Try cssun's numerical address (170.140.150.1)...\n");
   printf(">>> ");
   scanf("%s", haddr);

   addr = inet_addr(haddr);	/* Convert dotted notation to bits */
   if (addr == -1)
    { printf("IP-address must be of the form a.b.c.d\n");
      exit(1);
    }

   printf("\nDotted notation: %s, actual address: %u\n\n", haddr, addr);

   hp = gethostbyaddr((char*) &addr, sizeof(addr), AF_INET);

   if (hp == NULL)
    { printf("host information for %s not found\n", haddr);
      exit(1);
    }

   printf("official hostname h_name = `%s'\n", hp->h_name);

   printf("alias list:\n");
   for (p = hp->h_aliases; *p != 0; p++) 
    { printf("\t%s\n", *p);
    }

   printf("address type = %d (should be AF_INET = %d)\n",
		hp->h_addrtype, AF_INET);
   printf("address length = %d\n", hp->h_length);


   printf("list of Internet addresses for host:\n");
   for (p = hp->h_addr_list; *p != 0; p++) 
    { struct in_addr x;

      memcpy(&x.s_addr, *p, sizeof(x.s_addr));
      help = x.s_addr;
      printf("\tdotted: %s (unsigned decimal: %u)\n", 
			inet_ntoa(x), help);
    }
}