ShutdownBlockReasonCreate function (winuser.h)

Indicates that the system cannot be shut down and sets a reason string to be displayed to the user if system shutdown is initiated.


BOOL ShutdownBlockReasonCreate(
  [in] HWND    hWnd,
  [in] LPCWSTR pwszReason


[in] hWnd

A handle to the main window of the application.

[in] pwszReason

The reason the application must block system shutdown. This string will be truncated for display purposes after MAX_STR_BLOCKREASON characters.

Return value

If the call succeeds, the return value is nonzero.

If the call fails, the return value is zero. To get extended error information, call GetLastError.


This function can only be called from the thread that created the window specified by the hWnd parameter. Otherwise, the function fails and the last error code is ERROR_ACCESS_DENIED.

Applications should call this function as they begin an operation that cannot be interrupted, such as burning a CD or DVD. When the operation has completed, call the ShutdownBlockReasonDestroy function to indicate that the system can be shut down.

Because users are typically in a hurry when shutting down the system, they may spend only a few seconds looking at the shutdown reasons that are displayed by the system. Therefore, it is important that your reason strings are short and clear. For example "A CD burn is in progress." is better than "This application is blocking system shutdown because a CD burn is in progress. Do not shut down."


Requirement Value
Minimum supported client Windows Vista [desktop apps | UWP apps]
Minimum supported server Windows Server 2008 [desktop apps | UWP apps]
Target Platform Windows
Header winuser.h (include Windows.h)
Library User32.lib
DLL User32.dll
API set ext-ms-win-ntuser-misc-l1-1-0 (introduced in Windows 8)

See also


Shutting Down