How to get Fully qualified domain name in unix

Question

Is there any function(C or C++) which returns FQDN(Fully qualified domain name) in UNIX platforms?

Answer 1

Use getifaddrs() to get the interfaces for the box in question, then use the "resolver interface" (man resolver) to query the FQDNs for the ip-addresses return by the former call to getifaddrs().

Do not use gethostname() or the command line tool hostname in this context, as an IXish box's "hostname" does not necessarily correlate with the FQDN's returned by a query issued for the box's interface-addresses via the "resolver interface".