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Important This document may not represent best practices for current development, links to downloads and other resources may no longer be valid. Current recommended version can be found here.


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.

afx_msg void OnCompacting( 
   UINT nCpuTime  


Specifies the ratio of CPU time currently spent by Windows compacting memory to CPU time spent performing other operations. For example, 8000h represents 50 percent of CPU time 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.

Header: afxwin.h

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