Determining one's own IP address.

[Steve Dempsey]

> > I would like to be able to determine my local IP address without
> > involving a hosts file or yp lookup, i.e. from memory, from within a c
> > program.
> 
> Here's a little program that should do it for 4.3BSD systems...

[Larry's program deleted]

If you have a decent RPC implementation on your system, you can use
get_myaddress().  This works on Ultrix3.[01], HPUX 6.[25], SunOS4.0,
and 4.3BSD (at least):


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

main()
{
struct sockaddr_in me;

    get_myaddress(&me);

    fprintf(stderr,"local IP address = %u.%u.%u.%u\n",
        ((unsigned char*)  & me.sin_addr.s_addr)[0],
        ((unsigned char*)  & me.sin_addr.s_addr)[1],
        ((unsigned char*)  & me.sin_addr.s_addr)[2],
        ((unsigned char*)  & me.sin_addr.s_addr)[3]);
}

Of course you only get one interface address, usually the first one to be
configured via ifconfig(8).

> parmelee at cs.cornell.edu

        Steve Dempsey,  Center for Computer Assisted Engineering
  Colorado State University, Fort Collins, CO  80523    +1 303 491 0630
INET: steved at longs.LANCE.ColoState.Edu, dempsey at handel.CS.ColoState.Edu
UUCP: boulder!ccncsu!longs.LANCE.ColoState.Edu!steved, ...!ncar!handel!dempsey