Microsoft® Visual Basic® Scripting Edition IsNull Function | Language Reference Version 1

See Also

##### Description

> Returns a Boolean value that indicates whether an expression contains no valid data (Null).

##### Syntax

> IsNull(expression)

> The expression argument can be any expression.

##### Remarks

> IsNull returns True if expression is Null, that is, it contains no valid data; otherwise, IsNull returns False. If expression consists of more than one variable, Null in any constituent variable causes True to be returned for the entire expression.

> The Null value indicates that the variable contains no valid data. Null is not the same as Empty, which indicates that a variable has not yet been initialized. It is also not the same as a zero-length string (""), which is sometimes referred to as a null string.

> Important Use the IsNull function to determine whether an expression contains a Null value. Expressions that you might expect to evaluate to True under some circumstances, such as If Var = Null and If Var <> Null, are always False. This is because any expression containing a Null is itself Null, and therefore, False.

> The following example uses the IsNull function to determine whether a variable contains a Null:

> >     Dim MyVar, MyCheck
> >     MyCheck = IsNull(MyVar)      ' Returns False.

> >     MyVar = Null                 ' Assign Null.
> >     MyCheck = IsNull(MyVar)      ' Returns True.

> >     MyVar = Empty                ' Assign Empty.
> >     MyCheck = IsNull(MyVar)      ' Returns False.

© 1998 Microsoft Corporation. All rights reserved. Terms of Use.