The DDEUP structure is obsolete. Win32-based applications should use the DDEDATA and DDEPOKE structures.
typedef struct { // ddeup
unsigned short unused:12,
fAck:1,
fRelease:1,
fReserved:1,
fAckReq:1;
short cfFormat;
BYTE rgb[1];
} DDEUP;
Dynamic Data Exchange Overview, Dynamic Data Exchange Structures, WM_DDE_DATA, WM_DDE_POKE