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Q161053: FIX: CALCULATE SUM() on Currency Field Gives Illegal Operation

Article: Q161053
Product(s): Microsoft FoxPro
Version(s): 5.0
Operating System(s): 
Keyword(s): kbprogramming kbvfp kbvfp500aFIX kbvfp500bugkbbuglist kbfixlist
Last Modified: 25-AUG-1999

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The information in this article applies to:

- Microsoft Visual FoxPro for Windows, version 5.0 
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SYMPTOMS
========

Performing a comparison on a value created with the CALCULATE SUM() function
causes and illegal operation error. In Windows 95, the error message states the
following:

  This program performed an illegal operation and will be shut down.

After pressing the Details push button, the following message appears:

  VFP caused and invalid pagefault in module VFP .EXE at <register
  address>.

In Windows NT 4.0, the following error appears:

  An application error had occurred and an application error log is being
  generated.
  VFP.EXE
  Exception: access violation.

This behavior does not occur in Visual FoxPro 3.0a.

RESOLUTION
==========

The use of the STR() and VAL() functions may prevent this error. The modified
code example below shows the implementation of this resolution:

     SET TALK OFF
     CREATE TABLE junk (amt y)
     INSERT INTO junk (amt) VALUE(1.00)
     INSERT INTO junk (amt) VALUE(0.20)
     CALCULATE SUM(amt) TO mx
     mx=STR(mx)  && Converts the value from numeric to character type.
     mz = (VAL(mx) < 0)  && Converts mx back to numeric data type.
     ? mz

STATUS
======

Microsoft has confirmed this to be a problem in the Microsoft products listed at
the beginning of this article. This problem has been fixed in Visual FoxPro
5.0a.

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

The following code illustrates this behavior. The use of other aggregate
functions, such as AVG(), in the CALCULATE function produces similar results.

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

Enter the following code in a program and execute:

     SET TALK OFF
     CREATE TABLE junk (amt y)
     INSERT INTO junk (amt) VALUE(1.00)
     INSERT INTO junk (amt) VALUE(0.20)
     CALCULATE SUM(amt) TO mx
     mz = (mx < 0)
     ? mz

The error occurs during the comparison of the variable created with the CALCULATE
SUM() function and another value. In the example above, initially declaring the
variable mx numeric does not prevent the error.

Additional query words:

======================================================================
Keywords          : kbprogramming kbvfp kbvfp500aFIX kbvfp500bug kbbuglist kbfixlist
Technology        : kbVFPsearch kbAudDeveloper kbVFP500
Version           : 5.0
Issue type        : kbbug
Solution Type     : kbfix

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