isnull (2) --- see if a file is connected to the bit bucket  09/10/82


            _C_a_l_l_i_n_g _I_n_f_o_r_m_a_t_i_o_n

                 integer function isnull (fd)
                 file_des fd

                 Library:  vswtlb (standard Subsystem library)


            _F_u_n_c_t_i_o_n

                 'Isnull'  returns  YES  if  the  file referenced by the file
                 descriptor in 'fd' is connected to the null  device;  other-
                 wise  it  returns NO.  All file descriptors, including stan-
                 dard ports, can be tested.


            _I_m_p_l_e_m_e_n_t_a_t_i_o_n

                 'Isnull' simply looks in the Subsystem common  area  at  the
                 device  type  in  the  file descriptor and returns YES or NO
                 accordingly.


            _C_a_l_l_s

                 mapsu


            _S_e_e _A_l_s_o

                 isadsk (2), isatty (2)



























            isnull (2)                    - 1 -                    isnull (2)