Use this type to learn about a vlen.
function nf90_inq_vlen(ncid, xtype, name, datum_size, base_nc_type)
integer, intent(in) :: ncid
integer, intent(in) :: xtype
character (len = *), intent(out) :: name
integer, intent(out) :: datum_size
integer, intent(out) :: base_nc_type
integer :: nf90_inq_vlen
NCIDXTYPENAMEDATUM_SIZEPBASE_NF90_TYPEPNF90_NOERRNF90_EBADTYPENF90_EBADIDNF90_EBADGRPID