SendMessageTimeoutA function (winuser.h)
Sends the specified message to one or more windows.
Syntax
LRESULT SendMessageTimeoutA(
[in] HWND hWnd,
[in] UINT Msg,
[in] WPARAM wParam,
[in] LPARAM lParam,
[in] UINT fuFlags,
[in] UINT uTimeout,
[out, optional] PDWORD_PTR lpdwResult
);
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. The function does not return until each window has timed out. Therefore, the total wait time can be up to the value of uTimeout multiplied by the number of top-level 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
Any additional message-specific information.
[in] lParam
Type: LPARAM
Any additional message-specific information.
[in] fuFlags
Type: UINT
The behavior of this function. This parameter can be one or more of the following values.
[in] uTimeout
Type: UINT
The duration of the time-out period, in milliseconds. If the message is a broadcast message, each window can use the full time-out period. For example, if you specify a five second time-out period and there are three top-level windows that fail to process the message, you could have up to a 15 second delay.
[out, optional] lpdwResult
Type: PDWORD_PTR
The result of the message processing. The value of this parameter depends on the message that is specified.
Return value
Type: LRESULT
If the function succeeds, the return value is nonzero. SendMessageTimeout does not provide information about individual windows timing out if HWND_BROADCAST is used.
If the function fails or times out, the return value is 0. Note that the function does not always call SetLastError on failure. If the reason for failure is important to you, call SetLastError(ERROR_SUCCESS) before calling SendMessageTimeout. If the function returns 0, and GetLastError returns ERROR_SUCCESS, then treat it as a generic failure.
Remarks
The function calls the window procedure for the specified window and, if the specified window belongs to a different thread, does not return until the window procedure has processed the message or the specified time-out period has elapsed. If the window receiving the message belongs to the same queue as the current thread, the window procedure is called directly—the time-out value is ignored.
This function considers that a thread is not responding if it has not called GetMessage or a similar function within five seconds.
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 SendMessageTimeout 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