How to check if a variable is undefined

[fabrizio_t 58]

I need to check if a certain variable is undefined (and assign to it a default value in that case).

Please give my your advice.

[sbsmac 0]

I think isNil may be what you want. Despite the text on Biki I think it tests for definedness rather than a null value (which is what isNull is for).

I'll do some checking when I can on my ArmA box...

[Scillion 0]

Things you can put in Init.sqs

score = "23" (this is a string global variable)

spore=12 (this is a numeric global variable)

"2" ObjStatus "HIDDEN"

"markername" SetMarkerType "Empty"

1 SetRadioMsg "NULL"

obj1=false

obj2=false

Hope this helps. If not good luck.

[whisper 0]

I didn't know about isNil

In OFP, it worked this way :

A non defined variable points to objNull

Therefore, you can use isNull. Do not use x==objNull, as explained ine the Biki.

What's the difference between isNull and isNil, if any?

[tj72 0]

Can you check if 0? If so then its undefined

variable = 0 in init.

Then when variable becomes defined its value is anything other than zero.

I guess it depends on the type of variable but you should be able to reserve a specific value as undefined at init, once its defined as something then switch the value and check for it at the start of a function. I know this creates a definition but its reserved as only one thing but maybe for some reason the avariable has to be completely empty.

[sbsmac 0]

Quote[/b] ]What's the difference between isNull and isNil, if any?

I just confirmed it.

Running this command

player sidechat format ["defined: %1 null: %2",not isNil ("_v"),isNull _v] ;

For _v =nil , results are "defined: FALSE null: BOOL"

For _v =grpNull , results are "defined: TRUE null: TRUE"

For _v =player , results are "defined: TRUE null: FALSE"

[fabrizio_t 58]

"isNil" works like a charm. Thanks.

[5133p39 16]

What's the difference between isNull and isNil, if any?

The difference is that isNil can tell you whether the variable has been even initialized - eg. whether it exists, while isNull cannot determine whether the variable exists and is null, or it doesn't exists at all.

Consider this:<table border="0" align="center" width="95%" cellpadding="0" cellspacing="0"><tr><td>Code Sample </td></tr><tr><td id="CODE">myVar1 = ObjNull

? isNil myVar1 : Hint "Variable 1 does not exists"

? isNull myVar1 : Hint "Variable 1 is null"

? isNil myVar2 : Hint "Variable 2 does not exists"

? isNull myVar2 : Hint "Variable 2 is null"

if you run the example above, you should get messages "Variable 1 is null", "Variable 2 does not exists", and "Variable 2 is null".

Because the variable myVar1 is initialized (it exists, and it has been assigned a value of ObjNull), the first condition will return false while the second will return true.

But both third and fourth conditions will return true because the variable myVar2 has not been initialized and doesn't exists.

I hope i didn't obscured things more, by this "explanation", than cleared them