Bug in conditional for loop with an empty array

[TrevMrgn]

There appears to be a bug in the for loop with a conditional terminal.

If an empty array is wired to an auto-indexed array input tunnel, an output array tunnel has one element instead of zero.

 

The array constant on the left is empty.

Top loop without the conditional terminal produces an empty array.

The bottom loop with a never true conditional terminal produces an array with one element

Using LabVIEW version 8.5

Message Edited by TrevMrgn on 05-05-2009 02:01 PM

[Thoric]

Just for info - this doesn't occur in LV8.6. Both array indicators are empty.

[MikeS81]

Hi,

i also don't see this behaviour. Tested with LV8.5.

Mike

Message Edited by MikeS81 on 05-05-2009 04:14 PM

[Ben]

When constant folding was first introduced there was a bug that would show up only if either

Options >>> Block Diagram >>> Show Constant folding of wires

or

Options >>> Block Diagram >>> Show Constant folding of strutures

was turned on.

maybe that makes a difference?

Ben

[Thoric]

Nor in 8.5.1 in WinXP SP3.

[Thoric]

Ben,

I cannot replicate this behaviour in 8.5.1 with any of the constant folding options on and/or off.

Looking at the author's screenshot, constant folding of both wires and structures is on.

[MikeS81]

Hi Ben,

yes that's it.

Mike

Message Edited by MikeS81 on 05-05-2009 04:45 PM

[TrevMrgn]

I have done some more testing on this.

Creating the example from scratch, I do not see the error.

If I add one or more elements to the array (constant or control), then delete them all (using 'Delete Element') the bottom array has one element.

If I empty the array (using 'Empty Array') both are empty.

Also if I create an empty array using 'initialise array' with zero elements, I get one element.

'Show constant folding' does not appear to change the behaviour, but including a random operation in the loop does.

Trevor

[Ben]

Please post to demonstarte this condition along with a step by step instructions to reproduce it.

It we can follow your instructions and reproduce it we can log this as a bug.

Lacking the ability to reproduce.... there is very little any one can do.

Ben

[Thoric]

---

Creating the example from scratch, I do not see the error.

---

Neither do I.

---

If I add one or more elements to the array (constant or control), then delete them all (using 'Delete Element') the bottom array has one element.

---

Nup. Still empty.

---

If I empty the array (using 'Empty Array') both are empty.

---

Yep.

---

Also if I create an empty array using 'initialise array' with zero elements, I get one element.

---

Nup. Still empty.

---

'Show constant folding' does not appear to change the behaviour, but including a random operation in the loop does.

---

Agreed that constant folding doesn't cause any odd behaviour. Introducing a random operation (adding two constants) in the loop doesn't either.

I've tried all your methods here Trevor, but I can't replicate this behaviour in 8.5.1 under WinXP SP3. Sorry!

 Maybe somebody else will be able to help, or find a useable workaround.