The DDELN structure is obsolete. Win32-based applications should use the DDEADVISE structure.
typedef struct { // ddeln
unsigned short unused:13,
fRelease:1,
fDeferUpd:1,
fAckReq:1;
short cfFormat;
} DDELN;
Dynamic Data Exchange Overview, Dynamic Data Exchange Structures, DDEADVISE, WM_DDE_ADVISE, WM_DDE_UNADVISE