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Apprentice Joined: 01 May 2002 Posts: 188 Location: USA

Excuse this question but I'm trying to get a better understanding on the %null. Can someone give a more layman example as to when I would use this.

I have read the manual about %null and even looked at scripts created that is posted here but I still don't understand it.

Thanks.

Apprentice Joined: 29 Jun 2001 Posts: 198 Location: USA

You can use %null to check to see if a variable has a value or is empty(aka: null). If you have an alias that can be set to use various parameters you can use %null to check them.
#ALIAS checknull {#SAY %if(%-1=%null,No parameters, %if(%2=%null, No second parameter))}

useage:
checknull test
result:
No second parameter
checknull
result:
No parameters

If a variable has a value of "0" it will not match %null. %null = ""
Say you have a variable @test with a value of 0
#VAR test {0}
#IF (@test) {#SAY true} {#SAY false}
This will return false since @test is 0
#IF (@test=%null) {#SAY true} {#SAY false}
This will return false since @test has a value and is not null.
#VAR test {}
#IF (@test) {#SAY true} {#SAY false}
This returns false since @test has no value to evaluate to true.
#IF (@test=%null) {#SAY true} {#SAY false}
This one returns true since @test has no value and is equal to null.

Apprentice Joined: 01 May 2002 Posts: 188 Location: USA

Thanks you for the response. I think I get it now.

Basically NULL is anything that has literally nothing in the "field".

Zero doesn't necessarily mean that it's null.

GURU Joined: 28 Sep 2000 Posts: 434 Location: USA

To further expand upon Vorax' explanation here are a couple more uses that immediately come to mind.

#VAR friends %null

#IF %null(@friends) {ECHO friends has no value} {#ECHO the value of friends is @friends}

It is my opinion that those examples are much cleaner looking than

#VAR friends ""

#IF (@friends=%null) {ECHO friends has no value} {#ECHO the value of friends is @friends}

But fortunately for us, zscript is very forgiving and does not impose one man's opinion or style on everyone.