SendMessageCallbackA function (winuser.h)
Sends the specified message to a window or windows. It calls the window procedure for the specified window and returns immediately if the window belongs to another thread. After the window procedure processes the message, the system calls the specified callback function, passing the result of the message processing and an application-defined value to the callback function.
Syntax
BOOL SendMessageCallbackA(
[in] HWND hWnd,
[in] UINT Msg,
[in] WPARAM wParam,
[in] LPARAM lParam,
[in] SENDASYNCPROC lpResultCallBack,
[in] ULONG_PTR dwData
);
Parameters
[in] hWnd
Type: HWND
A handle to the window whose window procedure will receive the message. If this parameter is HWND_BROADCAST ((HWND)0xffff), the message is sent to all top-level windows in the system, including disabled or invisible unowned windows, overlapped windows, and pop-up windows; but the message is not sent to child windows.
[in] Msg
Type: UINT
The message to be sent.
For lists of the system-provided messages, see System-Defined Messages.
[in] wParam
Type: WPARAM
Additional message-specific information.
[in] lParam
Type: LPARAM
Additional message-specific information.
[in] lpResultCallBack
Type: SENDASYNCPROC
A pointer to a callback function that the system calls after the window procedure processes the message. For more information, see SendAsyncProc.
If hWnd is HWND_BROADCAST ((HWND)0xffff), the system calls the SendAsyncProc callback function once for each top-level window.
[in] dwData
Type: ULONG_PTR
An application-defined value to be sent to the callback function pointed to by the lpCallBack parameter.
Return value
Type: BOOL
If the function succeeds, the return value is nonzero.
If the function fails, the return value is zero. To get extended error information, call GetLastError.
Remarks
If the target window belongs to the same thread as the caller, then the window procedure is called synchronously, and the callback function is called immediately after the window procedure returns. If the target window belongs to a different thread from the caller, then the callback function is called only when the thread that called SendMessageCallback also calls GetMessage, PeekMessage, or WaitMessage.
If you send a message in the range below WM_USER to the asynchronous message functions (PostMessage, SendNotifyMessage, and SendMessageCallback), its message parameters cannot include pointers. Otherwise, the operation will fail. The functions will return before the receiving thread has had a chance to process the message and the sender will free the memory before it is used.
Applications that need to communicate using HWND_BROADCAST should use the RegisterWindowMessage function to obtain a unique message for inter-application communication.
The system only does marshalling for system messages (those in the range 0 to (WM_USER-1)). To send other messages (those >= WM_USER) to another process, you must do custom marshalling.
Note
The winuser.h header defines SendMessageCallback as an alias that automatically selects the ANSI or Unicode version of this function based on the definition of the UNICODE preprocessor constant. Mixing usage of the encoding-neutral alias with code that is not encoding-neutral can lead to mismatches that result in compilation or runtime errors. For more information, see Conventions for Function Prototypes.
Requirements
| Requirement | Value |
|---|---|
| Minimum supported client | Windows 2000 Professional [desktop apps only] |
| Minimum supported server | Windows 2000 Server [desktop apps only] |
| Target Platform | Windows |
| Header | winuser.h (include Windows.h) |
| Library | User32.lib |
| DLL | User32.dll |
| API set | ext-ms-win-ntuser-message-l1-1-0 (introduced in Windows 8) |
See also
Conceptual
Reference