Default values of cluster created from an empty Variant

[Munchuk]

Good Evening,

I am passing an empty Variant into the "Variant to Data" Function, and with a Type Deffed Cluster as the input to the type field, as shown below. The Type Deffed cluster has "Invalid" set as the default data for the type enum contained in the cluster, although not the 0 value in the enum.

When an empty Variant is passed into the function, the outputted cluster doesn't have "INVALID" as the type data. I was expecting INVALID to come out as it is the default option on the cluster. 

Whilst I can check for empty cluster before converting to data, am I experiencing known LabVIEW behaviour?

Regards

M

[altenbach]

You cannot use variant to data unless the variant data contains the matching data structure. Just use a small case structure wired to the error out and return either the converted cluster or your default cluster.

(the upper input specified the "type", not any default values)

[altenbach]

Easiest would be to ensure that the variant contain proper and expected data, so change the subVI before it.

[wiebe@CARYA]

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@Munchuk wrote:

I was expecting INVALID to come out as it is the default option on the cluster. 

That's the problem of course. It doesn't say anywhere that the "type" input is the default output. Not sure why it isn't the default, or if the output is defined when there is an error.

[Ben]

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wiebe@CARYA wrote:

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@Munchuk wrote:

I was expecting INVALID to come out as it is the default option on the cluster. 

That's the problem of course. It doesn't say anywhere that the "type" input is the default output. Not sure why it isn't the default, or if the output is defined when there is an error.

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I would be guessing it would be the "default-default".

That function checks that the variant passed to it is of the proper type and throws an error if not. If the data in the variant wire is the wrong type, the output would be empty since the operation is skipped completely. Sorta like the case of a VI set asn sub-routine and the instance marked as "skip if busy". The data returned when the sub-VI is called when it is busy is the "default default".

Ben

[altenbach]

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wiebe@CARYA wrote:

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That's the problem of course. It doesn't say anywhere that the "type" input is the default output. Not sure why it isn't the default, or if the output is defined when there is an error.

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Of course the "type" of the output is fully "defined" at compile time. (You get the same wire as whatever you wire to the type). No idea what the "value" would be. What are the default values of the typedef itself? Maybe that's what you should try.

(Yes, the value of the wired constant could probably be defined as the default output, but I guess it's not. Not sure if there would be side effects)

[Kyle97330]

I'm pretty sure the problem here is that you're under the impression that the default value of a type definition is what LabVIEW uses for a default value anywhere.

It *IS* the default value when you put a constant on the block diagram, or whatever.

It *IS NOT* the default value when LabVIEW has an error but needs to put something on the wire anyway.

When you have a type definition, the default value whenever there's an error is the "LabVIEW default"... empty arrays and strings, and zeroes for all numerics, including enums. 

If you want to have this pass out your "alternate" default, you need to do one of two things:

1. Manually look for error 91, and when it occurs, wire out your altered default cluster.

2. Change your type definition to a LVOOP class.  LVOOP classes actually do have their default values kept as part of their type definition.

[wiebe@CARYA]

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@Kyle97330 wrote:

If you want to have this pass out your "alternate" default, you need to do one of two things:

1. Manually look for error 91, and when it occurs, wire out your altered default cluster.

2. Change your type definition to a LVOOP class.  LVOOP classes actually do have their default values kept as part of their type definition.

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Or make the 'invalid' enum value the first value of the enum. That would return 'invalid' as default in case of error. Better put some text comment there though...

[Yamaeda]

As mentioned in other words, Variant to Data only cares about the data types of your connected Type, not the values. 

You'll have to create the 'default data' like Altenbach mentioned.

/Y

[wiebe@CARYA]

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@Yamaeda wrote:

As mentioned in other words, Variant to Data only cares about the data types of your connected Type, not the values. 

You'll have to create the 'default data' like Altenbach mentioned.

/Y

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Or make the 'invalid' enum value the first value of the enum. That would return 'invalid' as default in case of error.