Transaction Classes

The DDEML has four classes of transactions. Each class is identified by a constant that begins with the XCLASS_ prefix. The classes are defined in the DDEML header file. The class value is combined with the transaction-type value and is passed to the DDE callback function of the receiving application.

A transaction's class determines the return value that a callback function is expected to return if it processes the transaction. The following return values and transaction types are associated with each of the four transaction classes.

Class	Return value	Transaction
XCLASS_BOOL	TRUE or FALSE	XTYP_ADVSTART XTYP_CONNECT
XCLASS_DATA	A data handle, the CBR_BLOCK return code, or NULL	XTYP_ADVREQ XTYP_REQUEST XTYP_WILDCONNECT
XCLASS_FLAGS	A transaction flag: DDE_FACK, DDE_FBUSY, or DDE_FNOTPROCESSED	XTYP_ADVDATA XTYP_EXECUTE XTYP_POKE
XCLASS_NOTIFICATION	None	XTYP_ADVSTOP XTYP_CONNECT_CONFIRM XTYP_DISCONNECT XTYP_ERROR XTYP_REGISTER XTYP_UNREGISTER XTYP_XACT_COMPLETE

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