Do all DNS Nameserver functions have to be user-defined? Urgent...

Hi folks,
My last post here was quite helpful so I'm hoping it'll be even
better this time. I just wanted to know if the DNS Nameserver functions
( whose declarations are given in <arpa/nameser.h> ) have to be
user-defined.

I have some existing code which uses ns_initparse(), ns_sprintrr(),
ns_parserr() and some other Nameserver functions.... But the code works
fine for ns_parserr() without including the source file containing it's
body while functions like ns_initparse() do not work without the source
file containing their definition. I really need the answer urgently...
so can somebody please clarify this point?

Regards,

Timmy Jose.