You can send a positive acknowledgment by posting a WM_DDE_ACK message with the DDE_FACK and DDE_FRESPONSE flags set in the status word of the shared-memory data structure. The following code fragment shows how to do so:
/* Specify the status flags, when allocating shared memory */
pDDEdata->fstatus = DDE_FACK | DDE_FRESPONSE;
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/* Post the message */
WinDdePostMsg(hwndDest, /* Handle of destination */
hwndSource, /* Handle of source */
WM_DDE_ACK, /* Message */
pDDEdata, /* Shared-memory pointer */
DDEPM_RETRY); /* Retry */