Programmatically obtain DNS servers of host

Question

Using C++, I would like to obtain the DNS servers being used by a host for three operating systems: OS X, FreeBSD, and Windows. I'd like confirmation that the approaches below are indeed best practice, and if not, a superior alternative.

• OS X: already answered; updated link at developer.apple.com
• Windows: GetNetworkParams
• FreeBSD: /etc/resolv.conf

Thanks in advance for your help!

Answer 1

On many unix systems (linux, bsd) you can use the resolver functions to obtain the list of DNS servers: man 3 resolver.

After calling res_init() the resolver structure is initialized. The resolver structure stores all the information you need. The list of DNS servers are stored in the struct entry nsaddr_list.

The exact specification of the resolver structure can most likely be found in resolv.h.

Using the resolver functions is the preferred way to obtain the list of DNS servers. res_init() will most likely fill the resolver structure with the information found in /etc/resolv.conf.

Also see Use of resolv.h