DOCUMENT:Q130299  15-FEB-2002  [foxpro]
TITLE   :PRB: CURVAL() Returns Same Value as OLDVAL()
PRODUCT :Microsoft FoxPro
PROD/VER::3.0
OPER/SYS:
KEYWORDS:kbnetwork

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The information in this article applies to:

 - Microsoft Visual FoxPro for Windows, version 3.0 
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SYMPTOMS
========

Under certain circumstances, CURVAL() and OLDVAL() return the same value.

CAUSE
=====

This is by design. CURVAL() and OLDVAL() only return different values when the
following two conditions are both true:

 - Optimistic buffering is enabled.

 - Another user has modified the current record in a table while you were
   editing it.

In addition, CURVAL() and OLDVAL() return the same value if the all three of the
following conditions are met:

 - Two forms in the same Visual FoxPro session are using the same table.

 - The data on one instance of the form has been modified.

 - The data on another instance of the form has not been modified.

In this case, CURVAL() does not return a different value because the two
instances of the forms share a data session by default. Because the user has
locked the record in the first form, the data session in the second form
considers itself to have locked the record as well.

RESOLUTION
==========

Choose one of the following threee alternatives:

 - If you want to write code to determine if the current user has modified the
   current record, use the GETFLDSTATE() function. The GETFLDSTATE() function
   returns a numeric value indicating if one or more fields in the current
   record have changed, if a record was appended, or if the deletion status of
   the current record has changed. For more information on using GETFLDSTATE(),
   please see the Visual FoxPro Help file.

-or-

 - If you want to test code in a multiuser scenario, you must have two data
   sessions running. To do this:

    - Run two instances of Visual FoxPro simultaneously on the same or networked
      computers.

   -or-

    - Set the DataSession property of the form to 2 - Private Data Session, and
      run two instances of the form.


   -or-

 - If you are using pessimistic buffering, or no buffering, change to optimistic
   row or table buffering by using the CURSORSETPROP() function in the init
   method of the form. For example, enter the following command to set
   optimistic table buffering:

      =CURSORSETPROP("BUFFERING",5)

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

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

1. Create a new form, and add a table to the data environment.

2. Drag at least one field from the data environment onto the form.

3. Add a command button to the form. Set the caption of the button to "Display"
   (without the quotation marks). In the click event of the button, type the
   following code, substituting the field name from step 2 for
   <fieldname>. The field name should be enclosed in quotation marks:

      =MESSAGEBOX("Current value of field:  " + CURVAL(<'fieldname'>) + ;
                 CHR(13) + ;
                 "Old value of field:      " + OLDVAL(<'fieldname'>))

4. Add a second command button to the form. Set the caption of the button to
   "Update" (without the quotation marks). In the click event of the button,
   type the following code:

      =TABLEUPDATE()

5. In the init event of the form, add the following code:

      =CURSORSETPROP("BUFFERING",5)

6. Save the form as TESTFORM.

7. In the Command window, type DO FORM TESTFORM and press ENTER. Repeat this
   step.

8. Move the forms so that you can see each form on the screen.

9. Change the data in one copy of the form, and press ENTER. Click the Display
   button. The current value and old value should be the same. Click the Update
   button.

10. Click the second copy of the form. Click the Display button. The current and
   old value should be the same.

11. Close both instances of the form. Change the form.DataSession property to 2,
   and run both copies of the form again. The curval() and oldval() functions
   should display the same value on the copy of the form in which you changed
   the data. After clicking the Update button in this copy of the form, the
   unmodified copy of the form should display different values for the curval
   and oldval functions.

Additional query words: VFoxWin multi-user

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Keywords          : kbnetwork 
Technology        : kbVFPsearch kbAudDeveloper kbVFP300
Version           : :3.0

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