How To Determine Whether a Screen Saver Is Running on Windows NT

SUMMARY

On Windows 2000 and later versions, you can call the SystemParametersInfo function with the SPI_GETSCREENSAVERRUNNING flag to determine whether a screen saver is running on the system.

On Windows NT 4.0 and earlier versions, there is no direct method to determine whether a screen saver is running on the system. However, the indirect approach to determine whether a screen saver is running is to test for the existence of a desktop named "screen-saver". The "screen-saver" desktop is created by the Winlogon process for the screen saver to execute on. This desktop is created when the screen saver starts and is destroyed when the screen saver is stopped.

Sample Code

/*

   The following sample illustrates how to detect if a screen saver
   is running on Windows NT. This sample works by checking for the
   existence of a desktop named "screen-saver". This desktop is
   created dynamically by winlogon when a screen saver needs to be
   launched.

*/ 
#include <windows.h>
#include <stdio.h>

BOOL IsScreenSaverRunning( void );

int __cdecl main(void)
{
   if(IsScreenSaverRunning())
   {
      printf("Screen saver is running!\n");
   }
   else 
   {
      printf("Screen saver is NOT running!\n");
   }
   return 0;
}


/*

   IsScreenSaverRunning
      Returns TRUE if a screen saver is running; FALSE, otherwise.

*/ 
BOOL IsScreenSaverRunning(void)
{
   HDESK hDesktop;

   // 
   // Try to open the desktop that the screen saver runs on. This
   // desktop is created on the fly by Winlogon, so it only exists
   // when a screen saver is invoked.
   hDesktop = OpenDesktop(TEXT("screen-saver"), 
                          0,
                          FALSE,
                          MAXIMUM_ALLOWED);
   if(hDesktop == NULL) 
   {
      // 
      // If the call fails due to access denied, the screen saver
      // is running because the specified desktop exists -- you just
      // don't have any access.
      if(GetLastError() == ERROR_ACCESS_DENIED)
      {
         return TRUE;
      }

      // 
      // Otherwise, indicate the screen saver is not running.
      return FALSE;
   }

   // 
   // Successfully opened the desktop (the screen saver is running).
   CloseDesktop(hDesktop);
   return TRUE;
}