Very Computer

1. ip no ---> Internet name..

Date: Sun, 13 Jun 1993 01:55:36 GMT

:  Was wondering if anyone could help me out with this.....

:  If I have an ip no... say 128.164.136.204
:  and I want to figure out what the name is... how do I do it?

:  I know how to do a gethostbyname() to use the NAME to get a number.

:  Now how do I get a name from a number?

:  I tried playing with gethostbyaddr, but I can NOT get it to work
:  right.

:  Does anyone have a clue?

:  A 5-liner of C-code describing how to do this would be appreciated BIG-TIME.

Well, I can't do it in 5 lines, but this should work :-)
( compiled with gcc, run it by typing name a.b.c.d
  where 'name' is what you called the executable
       'a.. ' is an IP address )

/*
   Program to find a hostname by specifying an IP address
   to gethostbyaddr().

   Ian Couroulis.

*/

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

main(int argc, char **argv)
{
        struct hostent *hp;
        int x;
        int a,b,c,d;
        char caddr[BUFSIZ];
        int addr;

        for(x=1;x<argc;x++){
                sscanf(argv[x],"%d.%d.%d.%d",&a,&b,&c,&d);    
                addr = d+(c<<8)+(b<<16)+(a<<24);
                hp = gethostbyaddr(&addr, sizeof(addr), AF_INET);
                if(hp==NULL){
                        (void) fprintf(stderr,"Address not found\n");
                        exit(-1);
                }
                printf("%s\n",hp->h_name);
        }

Ian.
--
+------------------------------------------------------------------------+
|Ian Couroulis                  |      .         | " Errors, like straws |
|Dept. Comp. & Info Sciences    |  _--_|\        |   upon the surface    |
|UC of Northern Victoria        | /      \       |   flow; He who would  |
|Victoria, Australia.           | \_.--.*/<-here |   search for pearls   |

+------------------------------------------------------------------------+

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