IsWinEventHookInstalled function (winuser.h)

Article
02/22/2024

Determines whether there is an installed WinEvent hook that might be notified of a specified event.

Syntax

BOOL IsWinEventHookInstalled(
  [in] DWORD event
);

Parameters

[in] event

Type: DWORD

The event constant that hooks might be notified of. The function checks whether there is an installed hook for this event constant.

Return value

Type: BOOL

If there is a hook to be notified of the specified event, the return value is TRUE.

If there are no hooks to be notified of the specified event, the return value is FALSE.

Remarks

This method is guaranteed to never return a false negative. If this method returns FALSE, it means that no hooks in the system would be notified of the event. However, this method may return a false positive. In other words, it may return TRUE even though there are no hooks that would be notified. Thus, it is safe for components to circumvent some work if this method returns FALSE.

Event hooks can be installed at any time, so server developers should not cache the return value for long periods of time.

Requirements

Requirement	Value
Minimum supported client	Windows XP [desktop apps only]
Minimum supported server	Windows Server 2003 [desktop apps only]
Target Platform	Windows
Header	winuser.h
Library	User32.lib
DLL	User32.dll
Redistributable	Active Accessibility 2.0 RDK on Windows NT 4.0 with SP6 and later and Windows 98
API set	ext-ms-win-ntuser-server-l1-1-1 (introduced in Windows 10, version 10.0.14393)