I have tried to use the getpri function
(get priority) from the standard C library,
using the gcc compiler on AIX,
but the function does not seem to
reside in the library although it is declared in the
header. The gcc was installed the normal way

Any ideas ?

getpri() is part of the AIX libc.a
I don't believe it is present in GNU's libc.a
You do have getpriority() in GNU and you can find
source for getpri() at...
http://tivo.samba.org/download/mbm/src/