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Q174244: FIX: RESTORE SCREEN Causes Memory Leak in Visual FoxPro 5.0

Article: Q174244
Product(s): Microsoft FoxPro
Version(s): WINDOWS:5.0,5.0a
Operating System(s): 
Keyword(s): kberrmsg kbvfp kbVS97sp2fix
Last Modified: 12-AUG-1999

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The information in this article applies to:

- Microsoft Visual FoxPro for Windows, versions 5.0, 5.0a 
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SYMPTOMS
========

Repeatedly calling the SAVE SCREEN TO <memvar> and RESTORE SCREEN FROM
<memvar> commands causes the operating system to run low on memory.

In Windows NT 4.0, the following message appears in a window titled "System
Process-Out of Virtual Memory":

  Your system is running low on virtual memory. Please close some applications.
  You can then start the System option in the Control Panel and choose the
  Virtual Memory button to create as additional paging file or to increase the
  size of your current paging file.

After clicking OK, the following error message appears:

  Program Error There is not enough memory to complete this operation.

In Windows 95, the following error appears:

  Program Error There is not enough memory to complete this operation.

RESOLUTION
==========

As a workaround, place the following two commands before the RESTORE SCREEN FROM
command in the code example below:

     ACTIVATE SCREEN
     CLEAR

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. This bug has been fixed in Visual Studio 97 Service
Pack 3.

For more information, please see the following article in the Microsoft Knowledge
Base:

  Q170365 INFO: Visual Studio 97 Service Packs - What, Where, and Why

MORE INFORMATION
================

The amount of the memory leak with each iteration of the SAVE and RESTORE
combination is dependent on screen resolution, size of Visual FoxPro desktop,
and color depth. Memory leakage will be some multiple of the product of the
_SCREEN.Width and _SCREEN.Height. This can be on a magnitude of megabytes per
iteration.

Steps to Reproduce Behavior
---------------------------

WARNING: Running this code causes a low memory situation on the computer. This
condition may cause the operating system to become unstable. Close all running
applications and save your data before following this procedure. To close all
open applications, press CTRL+ALT+Delete to open the NT Task Manager or the
Windows 95 Close Program window, and then close all the other applications you
have running.

1. Create a program containing the following code:

        ON KEY LABEL f12 CANCEL
        SAVE SCREEN TO s_var
        Y=1
        DO WHILE .T.
        Y=Y+1
        @ 1,1 SAY Y
        RESTORE SCREEN FROM s_var
        ENDDO

2. Run the program.

The error message may take several minutes to appear depending on the amount of
physical memory and the hard drive space available for the swap file.

Additional query words: memory leak restore from

======================================================================
Keywords          : kberrmsg kbvfp kbVS97sp2fix 
Technology        : kbVFPsearch kbAudDeveloper kbVFP500 kbVFP500a
Version           : WINDOWS:5.0,5.0a
Issue type        : kbbug
Solution Type     : kbfix

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