Well, I think it should be pointed out that machines do not have IP addresses. interfaces have IP addresses, and often more than one - and not necessarely unique. My home box for instance has 2 ethernet cards, but 4 interfaces, each with a different IP address (the interfaces are lo, eth0, eth1 and ppp0, with the IP addresses 127.0.0.1, 10.0.0.15, 192.168.0.1 and 213.84.146.74). Well, in fact there are 6 interfaces, but two of them don't have an IP address.

If you want something portable, your best chance is probably to just return 127.0.0.1.

Abigail