PROGRAM A.

TYPE-POOLS: SLIS.
DATA: PRN LIKE SY-REPID,
      CT TYPE SLIS_T_FIELDCAT_ALV,
      CL LIKE LINE OF CT,
      BEGIN OF FNAMES OCCURS 0,
         FIELDNAME(30),
      END OF FNAMES,
      T_T001 TYPE TABLE OF T001.

START-OF-SELECTION.

  PRN = SY-REPID.
  CLEAR: CT, CT[], T_T001, T_T001[],
         FNAMES, FNAMES[].
         
  SELECT * FROM T001 INTO  TABLE T_T001.
  CALL FUNCTION 'REUSE_ALV_FIELDCATALOG_MERGE'
    EXPORTING
      I_PROGRAM_NAME     = PRN
      I_STRUCTURE_NAME   = 'T001'
    CHANGING
      CT_FIELDCAT        = CT.

  LOOP AT CT INTO CL.
    FNAMES-FIELDNAME = CL-FIELDNAME.
    APPEND FNAMES.
  ENDLOOP.

  CALL FUNCTION 'GUI_DOWNLOAD'
    EXPORTING
      FILENAME   = 'C:\T001.DBF'
      FILETYPE   = 'DBF'
    TABLES
      DATA_TAB   = T_T001[]
      FIELDNAMES = FNAMES
    EXCEPTIONS
      OTHERS     = 1.