/share/examples/find_interface/README

1This is a simple program which demonstrates how to query the kernel
2routing mechanism using only a UDP socket.  Pass it a hostname on
3the command line (sorry, it doesn't parse dotted decimal) and it will
4print out an IP address which names the interface over which UDP
5packets intended for that destination would be sent.
6A more sophisticated program might use the list obtained from SIOCGIFCONF
7to match the address with an interface name, but applications programmers
8much more often need to know the address of the interface rather than
9the name.