[Bug] assign null to string

E

Eduard

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• Feb 5, 2013

• #1

B4X:

   Dim x As String
   x = Null
   If x = Null Then 
      Msgbox("x=null","")
   Else
      Msgbox("x<>null","")
   End If
   If x="" Then 
      Msgbox("weird","")
   End If
   If x="null" Then 
      Msgbox("o no!","")
   End If

The expected behavior would be that x = null would evaluate to true since this is the way in B4A to check for null values.

However. x = "null" evaluates to true! I believe this is a bug.

 

Vader

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• Feb 5, 2013

• #2

In a different language I would suggest that a string is not nullable.

IE, because you created a string, it cannot be null, rather it would be an empty string.

That's my guess.

 

M

melamoud

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• Feb 5, 2013

• #3

Its not a bug its how it works in b4a
String can not be null so it translate the null to "null"

If you want thus ability make the type object and translate / cast to string when you need it as string ...

 

francoisg

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• Aug 12, 2015

• #4

If you want a simple way to check for any kind of object (strings as well as other classes) you can use the following functions:

Sub isNull (o As Object) As Boolean

Return ((o = Null) Or (o = "null"))​

End Sub

Sub ifNull (o As Object, default As Object) As Object

If isNull(o) Then

Return default​

Else

Return o​

End If​

End Sub

 

Last edited: Aug 12, 2015

R

rboeck

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• Aug 12, 2015

• #5

francoisg said:

If you want a simple way to check for any kind of object (strings as well as other classes) you can use the following functions:

Sub isNull (o As Object) As Boolean

Return ((o = Null) Or (o = "null")) '<------------​

End Sub

Click to expand...

Hi, i was looking long time for this type of function; now i tried it, but i get an error in the second row: 'wrong input format' (translated from german); any idea, whats wrong?

 

francoisg

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• Aug 12, 2015

• #6

Hi,
I think the code is formatted wrong (remove all spaces in front of the lines, replace with tabs and try again). I had to play with formatting the code in order to display correctly on the web site.

 

R

rboeck

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• Aug 12, 2015

• #7

Hi,

that helped; i had to type it myself and the mistakes went away. Strange...
Thanks for your help!

 

francoisg

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• Aug 12, 2015

• #8

No problem - glad to be of some help!