Testing for Null/empty variable

[scriptstopper]

How is everyone?

Stuck on detecting if a variable is blank.

If $Variablename has no value, has not been defined, then do ....

In the head it's:

If $Variable = Null Then

Ideas?

Thanks.

[BrewManNH]

To check if a variable has been declared use the If IsDeclared("variablename") function. If the variable you're looking for is called $variable, use "variable" in the function. To see if the variable contains nothing in it, use If $Variable = "".

[wakillon]

Do you want a detecting function like this ?

Global $_A = '', $_B = 0, $_C = ' ', $_D = 0.5

ConsoleWrite ( "Is $_A Null : " & _IsVarIsNull ( $_A ) & @Crlf )
ConsoleWrite ( "Is $_B Null : " & _IsVarIsNull ( $_B ) & @Crlf )
ConsoleWrite ( "Is $_C Null : " & _IsVarIsNull ( $_C ) & @Crlf )
ConsoleWrite ( "Is $_D Null : " & _IsVarIsNull ( $_D ) & @Crlf )
Exit

Func _IsVarIsNull ( $_Var )
    If Not $_Var Then 
        Return True 
    Else
        Return False
    EndIf
EndFunc

Edited September 26, 2010 by wakillon

[JohnOne]

I dont think it can be null in autoit, even if it does not hold a value it is seen as a string

Global $var

MsgBox(0,"Var Type",VarGetType($var))

[trancexx]

Do you want a detecting function like this ?

Global $_A = '', $_B = 0, $_C = ' ', $_D = 0.5

ConsoleWrite ( "Is $_A Null : " & _IsVarIsNull ( $_A ) & @Crlf )

ConsoleWrite ( "Is $_B Null : " & _IsVarIsNull ( $_B ) & @Crlf )

ConsoleWrite ( "Is $_C Null : " & _IsVarIsNull ( $_C ) & @Crlf )

ConsoleWrite ( "Is $_D Null : " & _IsVarIsNull ( $_D ) & @Crlf )

Exit

Func _IsVarIsNull ( $_Var )

If Not $_Var Then

Return True

Else

Return False

EndIf

EndFunc

In AutoIt much better solution than:

If Not somevar Then
    something
Else
    somethingelse
EndIf

is:

If somevar Then
    somethingelse
Else
    something
EndIf

@JohnOne, VarGetType is irrelevant. That function shows type (vt) of the variant holding the value of the variable.

[JohnOne]

But is it safe to say that all autoit variables start their life as a string type?

EDIT:

Sorry scriptstopper, we are all being terribly rude.

I'm fine, although I'm having a bit of trouble with my colon, nothing to worry about though, thanks for asking.

You?

Edited September 26, 2010 by JohnOne

[trancexx]

omg

[JohnOne]

We're allowed a little bit of a giggle I hope.

[trancexx]

We're allowed a little bit of a giggle I hope.

Maybe, maybe not.

To answer that question of yours from the above - probably not. It depends if the variable is initialized.

This is String type (VT_BSTR):

Local $Var

This is Int32 (VT_I4)

Local $Var = 4

If internally AutoIt would make VT_BSTR and then change its type to VT_I4 and then assign the value, it would make one step more than it should because it always starts with VT_EMPTY as that's the result of variant initialization.

So, logically it would be to start with VT_EMPTY (initialization) and then depending on the script code changing type to what's needed.

Edited September 26, 2010 by trancexx

[JohnOne]

What is confusing me, is what autoit classes the variable type as.

I know you said vargettype was irrelevant but i would have expected that function to to be the judge of that very question.

Local $var is seen as a string before it is initialzed, and then converted when assigned a value be that an object or a int.

I cant speak about autoits internal enviroment, but in the scripting enviroment, it must start its life as string since there is no null.

Im pretty crap at explaining myself, sorry.

[Nates]

Just found out where this might apply!

The _sql library that we use (from Chris Lambert) apparently brings in NULLS as "Default". I was trying to detect the NULL values using

If $varName = "" Then
...
EndIf

Which was not working, so now I do

If IsKeyword($varName) OR $varName = "" Then
...
EndIf

Which works as it should. 

 

Just thought I'd throw this note in here for anyone else using the _sql library and trying to detect empty (NULL) values.