[AccessD] vbNull = 1

Gustav,

There is a very short discussion of "When is Nothing something?" here:
http://www.vbdesign.net/expresso/archive/topic/3244.html

Mark

===================
When is Nothing something?

One of the most important elements of VBA, as a language, is its ability
to detect nothing! There are many different nothings, and some of them are
something, and as a rule they are not interchangeable. Lets take a look at
assigning and checking nothing...

*************
vbEmpty:

Determines if a variable has been initialized -

If varVariable = vbEmpty Then

You should not use vbEmpty to make your variable nothing, because it makes
it something! The value you are assigning is 0 (or if it is a string
variable, "0") and the IsEmpty test will fail!
************

vbNull

This one is great for testing for Null in a variable (database users take
note) using VarType:

If VarType (varVariable) = vbNull Then

again, don't use this constant to try to assign a Null value, because its
not nothing..
True value of vbNull is 1 (in a string variable "1")
************

vbNullChar

Test for, or assign, a NullChar

What is a Null char? The same thing as Chr(0). This one is great for
working with the API when you need to pass a string that ends with a Null
character, just add the constant onto the end of the string you are going
to pass..

strVariable = strVariable & vbNullChar
************

vbNullString

Test for, or assign, a null string

I use this one all of the time for the API. It is the same thing as this:

strVariable = ""

You can see it in much of the code when I am looking for the Hwnd of a
window using FindWindow

lngHwnd = FindWindow(vbNullstring, Me.Caption)
***********

Nothing

For objects only - determines if the variable has a valid object reference
or used to destroy the current object reference

If objVariable Is Not Nothing Then
objVariable = Nothing
End If
**********

Null

Saved this one for last because it can confuse your code. Null assigns a
Null value to your variant type variable, and you can use it to test for a
Null value using IsNull, but because Null = false, a test like this

varVariable = Null
If varVariable = Null Then
MsgBox "Its Null"
End If

will never show the message! Instead use this:

If IsNull(varVariable) Then
MsgBox "Its Null"
End If

and as a final not about nothing, don't try to use the Null keyword on
strongly typed variables, if you do you will get the error "Invalid use of
Null"






-----Original Message-----
From: Gustav Brock [mailto:gustav at cactus.dk] 
Sent: Wednesday, January 21, 2004 12:22 PM
To: Access Developers discussion and problem solving
Subject: [AccessD] vbNull = 1


Hi all

Why does the VB constant vbNull equal 1 and not 0 (zero)?

/gustav

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