The framework calls this member function for all top-level windows when Windows detects that more than 12.5 percent of system time over a 30- to 60-second interval is being spent compacting memory.
This indicates that system memory is low.
When a CWnd object receives this call, it should free as much memory as possible, taking into account the current level of activity of the application and the total number of applications running in Windows. The application can call the Windows function to determine how many applications are running.
This member function is called by the framework to allow your application to handle a Windows message. The parameters passed to your function reflect the parameters received by the framework when the message was received. If you call the base-class implementation of this function, that implementation will use the parameters originally passed with the message and not the parameters you supply to the function.