Problem detecting Null

[corepaul]

I am using Acess 2000 and Windows 2000.

I have a form with a text box txLName. tStrGlobal As String is dimensioned
globally. The first time I enter the text box, the Enter event with the code

If txLName.Value = Null Then
tStrGlobal = ""
Else
tStrGlobal = txLName.Value ' error occurs in this line
End If

causes an "Invalid use of null" error in the assignment statement after the
Else statement. Why doesn't the If statement correctly detect the Null?

The following code works fine

If txLName.Value <> Null Then
tStrGlobal = txLName.Value
Else
tStrGlobal = ""
End If

I'm not stuck, so please reply at your convenience. I'm just trying to
better understand how Access works. I'm a relative newbie.

Paul Core
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[fredg]

On Thu, 13 Apr 2006 16:26:54 GMT, co******@aol.com wrote:

I am using Acess 2000 and Windows 2000.

I have a form with a text box txLName. tStrGlobal As String is dimensioned
globally. The first time I enter the text box, the Enter event with the code

If txLName.Value = Null Then
tStrGlobal = ""
Else
tStrGlobal = txLName.Value ' error occurs in this line
End If

causes an "Invalid use of null" error in the assignment statement after the
Else statement. Why doesn't the If statement correctly detect the Null?

The following code works fine

If txLName.Value <> Null Then
tStrGlobal = txLName.Value
Else
tStrGlobal = ""
End If

I'm not stuck, so please reply at your convenience. I'm just trying to
better understand how Access works. I'm a relative newbie.

Paul Core

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Use:

If IsNull(txLName) Then

--
Fred
Please respond only to this newsgroup.
I do not reply to personal e-mail

[corepaul]

On 13-Apr-2006, fredg <fg******@example.invalid> wrote:

I am using Acess 2000 and Windows 2000.

I have a form with a text box txLName. tStrGlobal As String is
dimensioned
globally. The first time I enter the text box, the Enter event with the
code

If txLName.Value = Null Then
tStrGlobal = ""
Else
tStrGlobal = txLName.Value ' error occurs in this line
End If

causes an "Invalid use of null" error in the assignment statement after
the Else statement. Why doesn't the If statement correctly detect the
Null?

Use:

If IsNull(txLName) Then

Thanks, this works as intended.

Paul
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[Bob Quintal]

co******@aol.com wrote in
news:11************@sp6iad.superfeed.net:

I have a form with a text box txLName. tStrGlobal As String is
dimensioned globally. The first time I enter the text box, the
Enter event with the code

If txLName.Value = Null Then

Nulls are strange beasts.
See http://allenbrowne.com/casu-02.html

Part of the null issue is that (x = null) will evaluate FALSE if x
contains any value and null if x is null. It will never evaluate to
true.

always test using isnull(x) in VBA or where x is null IN sql ,
--
Bob Quintal

PA is y I've altered my email address.

[Terry Kreft]

Null propagates so (x = Null) returns Null, no matter the value of x

e.g.
Dim x
x = Null
Debug.Print IsNull(x = Null)
x = 1
Debug.Print IsNull(x = Null)

Result
True
True

--

Terry Kreft
"Bob Quintal" <rq******@sympatico.ca> wrote in message
news:Xn**********************@207.35.177.135...

co******@aol.com wrote in
news:11************@sp6iad.superfeed.net:

I have a form with a text box txLName. tStrGlobal As String is
dimensioned globally. The first time I enter the text box, the
Enter event with the code

If txLName.Value = Null Then

Nulls are strange beasts.
See http://allenbrowne.com/casu-02.html

Part of the null issue is that (x = null) will evaluate FALSE if x
contains any value and null if x is null. It will never evaluate to
true.

always test using isnull(x) in VBA or where x is null IN sql ,
--
Bob Quintal

PA is y I've altered my email address.

[Bob Quintal]

"Terry Kreft" <te*********@mps.co.uk> wrote in
news:9L********************@karoo.co.uk:

Null propagates so (x = Null) returns Null, no matter the
value of x

That's what I think i meant to say..
e.g.
Dim x
x = Null
Debug.Print IsNull(x = Null)
x = 1
Debug.Print IsNull(x = Null)

Result
True
True

--
Bob Quintal

PA is y I've altered my email address.