compressed data records are indecipherable without the map. When compressed data records have been expanded to their original state and no further compression is desired, you should delete the map using the LIB$FREE_VM routine. DCX requires that you submit data records for analysis and then call the DCX$MAKE_MAP routine. Upon receiving the DCX$_AGAIN status code, you must again submit data records for analysis (in the same order) and call DCX$MAKE_MAP again; on the second iteration, DCX$MAKE_MAP returns the DCX$_NORMAL status code.

10.4  –  Condition Values Returned

    DCX$_AGAIN         Informational. The map has not been created
                       and the map_addr and map_size arguments have
                       not been written because further analysis is
                       required. The data records must be analyzed
                       (using DCX$ANALYZE_DATA) again, and DCX$MAKE_
                       MAP must be called again before DCX$MAKE_MAP
                       will create the map and return the DCX$_NORMAL
                       status code.
    DCX$_INVCTX        Error. The context variable is invalid, or the
                       context area is invalid or corrupted. This may
                       be caused by a failure to call the appropriate
                       routine to initialize the context variable or
                       by an application program error.
    DCX$_NORMAL        Normal successful completion.

    This routine also returns any condition values returned by
    LIB$GET_VM and LIB$FREE_VM.