On Fri, Nov 15, 2002 at 12:38:12PM -0500, Michael Richardson wrote:

1) Awhile ago there was a flame war about using SIOCGIFCONF/SIOCGLIFCONF
to get lists of interfaces. This was suggested as being a bad way.

2) bind 9.3snapshot is able to get a list of IPv4 addresses with SIOCGIFCONF,

3) it is not able to get IPv6 addresses with SIOCGLIFCONF.

Marc Andrews, sitting next to me, asked if I knew what the offical magic
was. Can someone point me that officially blessed way to do this?

Physical devices are read using /proc/net/dev

If you want IPv6 addresses you can read and parse /proc/net/if_inet6 

That is the old fashioned way.
 
The new fashioned one is to query them using rtnetlink. You use a RTM_GETADDR
NLM_F_REQUEST query with wildcard (NLM_F_ROOT) to get a full list.
See the netlink,rtnetlink, libnetlink manpages and iproute2 as an example. 
It is easier when you use libnetlink.

-Andi