Null Values

[WayneCusack]

How would I go about checking whether a function returns a NULL value?  I have been trying to find a reference in the documentation and the forums for something like "IsNull" or "IsNotNull", but I'm not finding it.

[water]

The latest AutoIt version (3.3.10.2) supports Null as a keyword.

Either directly check for Null or use function IsKeyword.

#include <MsgBoxConstants.au3>
If $Var = Null Then ...
If IsKeyword($Var) = $KEYWORD_NULL Then ...

[guinness]

How would I go about checking whether a function returns a NULL value?  I have been trying to find a reference in the documentation and the forums for something like "IsNull" or "IsNotNull", but I'm not finding it.

For the sake of ease, I have added IsNull() and IsDefault() as custom functions to the IsKeyword() example.

expandcollapse popup

#include <Constants.au3>
#include <MsgBoxConstants.au3>

Example()

Func Example()
    ; Check if a variable is the Default keyword.
    Local $vDefault = Default
    If IsDefault($vDefault) Then
        MsgBox($MB_SYSTEMMODAL, "", "The variable is the Default keyword")
    Else
        MsgBox($MB_SYSTEMMODAL, "", "The variable is not the Default keyword")
    EndIf

    ; Check if a variable is the Null keyword.
    Local $vNull = Null
    If IsNull($vNull) Then
        MsgBox($MB_SYSTEMMODAL, "", "The variable is the Null keyword")
    Else
        MsgBox($MB_SYSTEMMODAL, "", "The variable is not the Null keyword")
    EndIf

    ; Check if a variable is the Null keyword. This will be false as $sString is a string datatype.
    Local $sString = 'Default'
    If IsDefault($sString) Then
        MsgBox($MB_SYSTEMMODAL, "", "The variable is the Default keyword")
    Else
        MsgBox($MB_SYSTEMMODAL, "", "The variable is not the Default keyword")
    EndIf
EndFunc   ;==>Example

Func IsDefault($vKeyword)
    Return IsKeyword($vKeyword) = $KEYWORD_DEFAULT
EndFunc   ;==>IsDefault

Func IsNull($vKeyword)
    Return IsKeyword($vKeyword) = $KEYWORD_NULL
EndFunc   ;==>IsNull

[trancexx]

If  you want to check if your variable is set to Null then you do what water did first:

If $Var = Null Then ...

That's the most correct way. IsKeyword() is meant to be used for something else.
 

[guinness]

 

That's the most correct way. IsKeyword() is meant to be used for something else.

 

You know people are going to ask "..and what is that for?"

[jaberwacky]

IsKeyword() is meant to be used for something else.

..and what is that for?

[guinness]

Knew it!

[trancexx]

guinness don't let jaberwacky play with your head.

Default keyword wasn't implemented all that well. IsKeyword() is currently the only solution for situations when obvious doesn't work in obvious manner with that keyword. It provides an alibi for some past not so good decisions.

$x = "Default"

$y = ($x == Default)

ConsoleWrite($y & @CRLF)

That code is one of only few places where IsKeyword() could be useful.

Something like that happens when you have two developers with two different opinions and no one to say "WTF? Do it right or don't do it at all."

[guinness]

guinness don't let jaberwacky play with your head.

I am not born yesterday trancexx.

Edited January 13, 2014 by guinness

[WayneCusack]

Thanks for the feedback.  I had been running 3.3.08, which did not have the "null" keyword.  I had tried checking for null values but it didn't work.  I assume that 3.3.10.2 will solve the problem.

I would ordinarily use but now trancexx has made me curious - what is IsKeyword() intended to be used for?

[guinness]

Check their example again.