How to enumerate all IP addresses attached to a machine, in POSIX C?

Question

Background:

I\'m writing a daemon that makes outgoing TCP/IP connections. It will be running on machines with multiple (non-loopback) IP addresses.

Answer 1

You can get the interface info required a couple of ways including calling ioctl() with the SIOCGIFCONF option and looping through the returned structures to get the interface address info.

Given a list of all IP addresses, how would I filter out loopback addresses?

See ifreq struct in caskey's answer. You can determine the loopback (properly) with:

if (ifru_flags & IFF_LOOPBACK) 

Constants are in if.h