adns is a resolver library for C (and C++) programs. In contrast with
the existing interfaces, gethostbyname et al and libresolv, it has the
following features:

* It is reasonably easy to use for simple programs which just want
  to translate names to addresses, look up MX records, etc.
* It can be used in an asynchronous, non-blocking, manner. Many
  queries can be handled simultaneously.

Technical note: adns requires a real nameserver like BIND or
Dents running on the same system or a nearby one, which must be
willing to provide `recursive service'. I.e., adns is a `stub
resolver'.

WWW: http://www.chiark.greenend.org.uk/~ian/adns/