PRB: NULL and .NULL. Are Not Interchangeable in Properties (156925)


The information in this article applies to:

  • Microsoft Visual FoxPro for Windows 5.0
  • Microsoft Visual FoxPro for Windows 6.0
This article was previously published under Q156925

SYMPTOMS

In Visual FoxPro 5.0, when assigning a null value to a property in the Properties window, you need to use .NULL. instead of NULL. The values are not interchangeable when used in a property in the Properties window.

CAUSE

In the Properties window, you do not have to enter quotes to enter a string. The text NULL entered without the quotes is interpreted as the string 'NULL' instead of the actual .NULL. value.

WORKAROUND

You need to enter the string as .NULL. in the Properties window.

STATUS

This behavior is by design.

MORE INFORMATION

At times, you may wonder why you can enter the following in the Command window and get the expected result: 
   X=NULL
   ?ISNULL(X)   <-- .T. is return
However, ISNULL() evaluates as .F. instead of .T. when a NULL value, without the period on both ends, is assigned to a property in the Properties window.

Steps to Reproduce Behavior

  1. Create a new form.
  2. Create a new property named NullProperty.
  3. In the Properties window, assign NULL to NullProperty property (that is, without periods before and after NULL).
  4. Put the following in the form Init: 
          ?ISNULL(THIS.NullProperty)
  5. Run the form.
Visual FoxPro returns .F.
Modification Type:MajorLast Reviewed:10/15/2003
Keywords:KB156925
©2003 Microsoft Corporation. All rights reserved.