WM_DDE_INITIATE

A DDE client application sends a WM_DDE_INITIATE message to initiate a conversation with a server application responding to the specified application and topic names. Upon receiving this message, all server applications with names that match the specified application and that support the specified topic are expected to acknowledge it. (For more information, see the WM_DDE_ACK message.)

WM_DDE_INITIATE 
wParam = (WPARAM) hwnd;             // handle of posting appl. 
lParam = MAKELPARAM(aApp, aTopic);  // appl. and topic atoms 
 

Parameters

hwnd

Value of wParam. Handle to the client window sending the message.

aApp

Value of the low-order word of lParam. Contains an atom that identifies the application with which a conversation is requested. The application name cannot contain slashes (/) or backslashes (\). These characters are reserved for network implementations. If aApp is NULL, a conversation with all applications is requested.

aTopic

Value of the high-order word of lParam. Contains an atom that identifies the topic for which a conversation is requested. If the topic is NULL, conversations for all available topics are requested.

Remarks

If aApp is NULL, any server application can respond. If aTopic is NULL, any topic is valid. Upon receiving a WM_DDE_INITIATE request with the aTopic parameter set to NULL, a server must send a WM_DDE_ACK message for each of the topics it supports.

Sending

The client application sends WM_DDE_INITIATE by calling the SendMessage function, not the PostMessage function. The client broadcasts the message to all top-level windows by setting the first parameter of SendMessage to –1.

If the client application has already obtained the window handle of the desired server, it can send WM_DDE_INITIATE directly to the server window by passing the server's window handle as the first parameter of SendMessage.

The client application allocates aApp and aTopic by calling GlobalAddAtom.

When SendMessage returns, the client application must delete the aApp and aTopic atoms.

Receiving

To complete the initiation of a conversation, the server application must respond with one or more WM_DDE_ACK messages, where each message is for a separate topic. When sending WM_DDE_ACK message, the server should create new aApp and aTopic atoms; it should not reuse the atoms sent with WM_DDE_INITIATE.

QuickInfo

  Windows NT: Requires version 3.1 or later.
  Windows: Requires Windows 95 or later.
  Windows CE: Unsupported.
  Header: Declared in dde.h.

See Also

Dynamic Data Exchange Overview, Dynamic Data Exchange Messages, GlobalAddAtom, GlobalAlloc, PostMessage, SendMessage, WM_DDE_ACK