PRB: NULL and .NULL. Are Not Interchangeable in Properties

Last reviewed: October 29, 1996
Article ID: Q156925

The information in this article applies to:

Microsoft Visual FoxPro for Windows, version 5.0

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

Create a new form.
Create a new property named NullProperty.
In the Properties window, assign NULL to NullProperty property (that is, without periods before and after NULL).
Put the following in the form Init:
```
      ?ISNULL(THIS.NullProperty)
```
Run the form.

Visual FoxPro returns .F.

KBCategory: kbprg kbtool kbprb
KBSubcategory: FxprgGeneral
Additional reference words: 5.00 kbdse VFoxWin

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Last reviewed: October 29, 1996
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