Precondition string compare problem

[DrOnline82]

I can't believe I have to ask about this, but I am so confused why it doesn't work. It should be simple.

FileGlobal.ProductID = "07"

This is a string.

Why then, does this expression evaluate to True?

FileGlobals.ProductID == "01" || "02"

In order to debug, I made a Pass/fail step with it's Data Source expression set to:

(FileGlobals.ProductID == "01" || "02") ? (Step.Result.PassFail = True) : (Step.Result.PassFail = False)

This also evaluates to True.

I want it to be True for "01" or "02", but not for "03" etc...

[DrOnline82 · Accepted solution]

I found this in the expression builder for "logical or":

String operands are converted to True if the text [...] contains the representation of a non-zero number, False otherwise.

This seems like odd behavior to me, but I'll just have to work around it. I didn't know this.

I'm trying to use StrComp(), but I can't make heads or tails of the documentation here:

https://www.ni.com/docs/en-US/bundle/teststand-api-reference/page/tsfundamentals/strcomp-function.ht...

"A number less than 0 if the first string is less than the second. A number greater than 0 if the first string is greater than the second. 0 if the strings are equal."

What does it mean for a string to be great than another string? Mathematically?

StrComp("Buddy","Budgy") evaluates to -1

StrComp("Budgy","Buddy") evaluates to 1

I don't understand the logic here.

If anybody can shed some light on this for me, it would be appreciated! I've decided to solve it in LabVIEW instead. What I want is a TestStand expression like this: StringsMatch("01","01") evaluating to True (boolean)

[mateusz_owczarek · Accepted solution]

FileGlobals.ProductID == "01" || FileGlobals.ProductID == "02"

🙂 

The problem with "FileGlobals.ProductID == "01" || "02"" is that you're actually checking here if:

(FileGlobals.ProductID == "01" is TRUE) OR ("02" is TRUE)

While the first part is false (because FileGlobals.ProductID is actually "07"), the second part is true ("02" converts to boolean as TRUE) which results in TRUE as the "OR" result

[DrOnline82]

Holy cow I spent a lot of time on this. And it was that simple... Thanks Mateusz!!

[mateusz_owczarek]

Glad I could help 🙂 

[DrOnline82]

Yes, I see you added more to your answer. After you posted your answer I understood the same thing as you described it.