DdeCallback

The DdeCallbackProc function is an application-defined callback function used with the Dynamic Data Exchange Management Library (DDEML) functions. It processes dynamic data exchange (DDE) transactions. The PFNCALLBACK type defines a pointer to this callback function. DdeCallback is a placeholder for the application-defined function name.

HDDEDATA CALLBACK DdeCallback(
  UINT uType,     // transaction type
  UINT uFmt,      // clipboard data format
  HCONV hconv,    // handle to the conversation
  HSZ hsz1,       // handle to a string
  HSZ hsz2,       // handle to a string
  HDDEDATA hdata, // handle to a global memory object
  DWORD dwData1,  // transaction-specific data
  DWORD dwData2   // transaction-specific data
);
 

Parameters

uType

Specifies the type of the current transaction. This parameter consists of a combination of transaction class flags and transaction type flags. The following table describes each of the transaction classes and provides a list of the transaction types in each class. For information about a specific transaction type, see the individual description of that type.

Class	Meaning
XCLASS_BOOL	A DDE callback function should return TRUE or FALSE when it finishes processing a transaction that belongs to this class. The XCLASS_BOOL transaction class consists of the following types:
	XTYP_ADVSTART XTYP_CONNECT
XCLASS_DATA	A DDE callback function should return a DDE handle, the CBR_BLOCK return code, or NULL when it finishes processing a transaction that belongs to this class. The XCLASS_DATA transaction class consists of the following types:
	XTYP_ADVREQ XTYP_REQUEST XTYP_WILDCONNECT
XCLASS_FLAGS	A DDE callback function should return DDE_FACK, DDE_FBUSY, or DDE_FNOTPROCESSED when it finishes processing a transaction that belongs to this class. The XCLASS_FLAGS transaction class consists of the following types:
	XTYP_ADVDATA XTYP_EXECUTE XTYP_POKE
XCLASS_NOTIFICATION	The transaction types that belong to this class are for notification purposes only. The return value from the callback function is ignored. The XCLASS_NOTIFICATION transaction class consists of the following types: XTYP_ADVSTOP XTYP_CONNECT_CONFIRM XTYP_DISCONNECT XTYP_ERROR XTYP_MONITOR XTYP_REGISTER XTYP_XACT_COMPLETE XTYP_UNREGISTER

uFmt

Specifies the format in which data is sent or received.

hconv

Handle to the conversation associated with the current transaction.

hsz1

Handle to a string. The meaning of this parameter depends on the type of the current transaction. For the meaning of this parameter, see the description of the transaction type.

hsz2

Handle to a string. The meaning of this parameter depends on the type of the current transaction. For the meaning of this parameter, see the description of the transaction type.

hdata

Handle to DDE data. The meaning of this parameter depends on the type of the current transaction. For the meaning of this parameter, see the description of the transaction type.

dwData1

Specifies transaction-specific data. For the meaning of this parameter, see the description of the transaction type.

dwData2

Specifies transaction-specific data. For the meaning of this parameter, see the description of the transaction type.

Return Values

The return value depends on the transaction class. For more information about the return values, see descriptions of the individual transaction types.

Remarks

The callback function is called asynchronously for transactions that do not involve the creation or termination of conversations. An application that does not frequently accept incoming messages will have reduced DDE performance because the DDEML uses messages to initiate transactions.

An application must register the callback function by specifying a pointer to the function in a call to the DdeInitialize function.

QuickInfo

  Windows NT: Requires version 3.1 or later.
  Windows: Requires Windows 95 or later.
  Windows CE: Unsupported.
  Header: Declared in ddeml.h.
  Import Library: User-defined.

See Also

Dynamic Data Exchange Management Library Overview, Dynamic Data Exchange Management Functions, DdeEnableCallback, DdeInitialize