Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!ames!ncar!boulder!ccncsu!longs.LANCE.ColoState.Edu!steved
From: steved@longs.LANCE.ColoState.Edu (Steve Dempsey)
Newsgroups: comp.unix.wizards
Subject: Re: Determining one's own IP address.
Message-ID: <3451@ccncsu.ColoState.EDU>
Date: 12 Dec 89 19:55:56 GMT
References: <35095@cornell.UUCP> <601@bmers58.UUCP> <4429@ur-cc.UUCP> <604@bmers58.UUCP>
Sender: news@ccncsu.ColoState.EDU
Reply-To: steved@longs.LANCE.ColoState.Edu (Steve Dempsey)
Organization: Colorado State University, College of Engineering
Lines: 43


 
> > 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@cs.cornell.edu

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