WM_POWERBROADCAST

The WM_POWERBROADCAST message is broadcast to an application to notify it of power-management events.

A window receives this message through its WindowProc function.

LRESULT CALLBACK WindowProc(
  HWND hwnd,       // handle to window
  UINT uMsg,       // WM_POWERBROADCAST
  WPARAM wParam,   // power-management event
  LPARAM lParam    // function-specific data
);

Parameters

wParam

Specifies the power-management event. This parameter can be one of the following events.

Event	Meaning
PBT_APMBATTERYLOW	Battery power is low.
PBT_APMOEMEVENT	OEM-defined event occurred.
PBT_APMPOWERSTATUSCHANGE	Power status has changed.
PBT_APMQUERYSUSPEND	Request for permission to suspend.
PBT_APMQUERYSUSPENDFAILED	Suspension request denied.
PBT_APMRESUMEAUTOMATIC	Operation resuming automatically after event.
PBT_APMRESUMECRITICAL	Operation resuming after critical suspension.
PBT_APMRESUMESUSPEND	Operation resuming after suspension.
PBT_APMSUSPEND	System is suspending operation.

lParam

Function-specific data. For most events, this parameter is reserved and not used.

However, if wParam is one of the resume events (PBT_APMRESUME*), the lParam parameter can specify the PBTF_APMRESUMEFROMFAILURE flag. This flag indicates that a suspend operation failed after the PBT_APMSUSPEND event was broadcast.

Return Values

Return TRUE to grant a request.

Return BROADCAST_QUERY_DENY to deny a request.

Requirements

  Windows NT/2000: Requires Windows NT 4.0 or later.
  Windows 95/98: Requires Windows 95 or later.
  Header: Declared in Winuser.h; include Windows.h.

See Also

Power Management Overview, Power Management Messages