Hi,
Try:
dc_in type DD40L-ROWTYPE value 'In',
dc_out type DD40L-ROWTYPE value 'Out',
TYPES: BEGIN OF t_alv,
field1 type zfield,
field2 type zfield,
field3 type zfield,
field4 type zfield,
dc_value type DD40L-ROWTYPE ,
END OF t_alv.
Regards.