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difference in if and iff handling a null value

 
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temp2

External


Since: Feb 16, 2005
Posts: 2



(Msg. 1) Posted: Wed Feb 16, 2005 6:03 pm
Post subject: difference in if and iff handling a null value
Archived from groups: comp>lang>basic>visual>database (more info?)

I'm having a problem with handling null values in a vb6(sp6) program.
For some reason a if.else.endif statement seems to work fine with
detecting a null value and assigning a default if necessary(1). I
would like to use the iif statement instead(2), but it always throws
the error "Invalid use of Null" for some reason.

Anybody have any ideas why this is occurring?

Thanks in advance.

strIndex = "lngAppliedTo" & CStr(i)

(1)
If IsNull(recReceipt.Fields(strIndex)) Then
lngAppliedTo(i) = 0
Else
lngAppliedTo(i) = CLng(recReceipt.Fields(strIndex))
End If

(2)
lngAppliedTo(i) = IIf(IsNull(recReceipt.Fields(strIndex)), 0,
CLng(recReceipt.Fields(strIndex)))

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Steve Gerrard1

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Since: Aug 04, 2004
Posts: 9



(Msg. 2) Posted: Wed Feb 16, 2005 6:51 pm
Post subject: Re: difference in if and iff handling a null value [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)

<temp2 RemoveThis @ienergygroup.com> wrote in message
news:1108602198.748918.27500@o13g2000cwo.googlegroups.com...
| I'm having a problem with handling null values in a vb6(sp6) program.
| For some reason a if.else.endif statement seems to work fine with
| detecting a null value and assigning a default if necessary(1). I
| would like to use the iif statement instead(2), but it always throws
| the error "Invalid use of Null" for some reason.
|
| Anybody have any ideas why this is occurring?
|
| Thanks in advance.
|

| lngAppliedTo(i) = IIf(IsNull(recReceipt.Fields(strIndex)), 0,
| CLng(recReceipt.Fields(strIndex)))
|

Unfortunately, this is a known characteristic of the IIf function. Here
is the MSDN on it:

<quote>

IIf(expr, truepart, falsepart)

IIf always evaluates both truepart and falsepart, even though it returns
only one of them. Because of this, you should watch for undesirable side
effects. For example, if evaluating falsepart results in a division by
zero error, an error occurs even if expr is True.

</quote>

In your case, it will try to evaluate CLng(recReceipt.Fields(strIndex))
even if it is Null, causing the error.

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temp2

External


Since: Feb 16, 2005
Posts: 2



(Msg. 3) Posted: Wed Feb 16, 2005 11:16 pm
Post subject: Re: difference in if and iff handling a null value [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)

Thanks! The surprising thing is that when I did a usenet search, a lot
of people were suggesting that they use the IIf function for the
purpose I was trying to use it for. Haha now I know.
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