Accessing a cluster like a hashtable

[reveazure]

Hi,

I have been trying to make a small scripiting language for a labview program that would allow the user to specify the value that he wants to assign to a value in a cluster. For example, say my cluster has a field named "q" and a field named "v". I want the user to be able to type q 10 and set the "q" field to 10. The problem is that I have not found any way to enter the cluster field name as a string, like I would be able to do in a hashtable in an ordinary programming language.

So then I tried making my own VI that converts the cluster to XML, does a search and replace to do what I want, then converts it back to a cluster. The problem is, it doesn't seem like there's any way to allow the VI to take in a generic cluster, only a cluster of a specific type. Then I tried creating a control from the cluster->XML  VI's "anything" terminal, but that didn't help either.

Does anyone have any ideas?

[Havarti]

If I understand what you need this may do what you want.  You could put it in a for loop to search for different field names.

Brian

[tst]

You can't access cluster elements by name, because clusters are always handled by their structure. There is no such thing as a "generic" cluster. Only an empty one.

What you can do is manage each element of the cluster seperately, but you have to know the structure of the cluster in advance.

[altenbach]

Clusters dont seem very suitable for this.

I would suggest to keep two arrays, one for the values (numeric) and one for the tags (array of strings).

Now just parse your line, find the index of the tag in the string array, then replace the numeric array element at the same index.

Attached is a simple example (LabVIEW 7.1).

[BenBabb]

In the properties of a cluster there is an array refnums ti the elements in it.  If you already know the name of the element you want to change you can search for that element's label name and make the changes there.  This will be slower than using the array method, but if you have existing code and are stuck with clusters this will work.

[mikeporter]

In addition to all the other advice you are getting, one other thing I would recommend is that you modify your proposed script "syntax" to utilize post-fix notation. It's much easier to parse and the resulting language is extensible with a very linear degree of effort--unlike normal in-fix notation that get exponentially more difficult to parse the more complex the notation gets.

If this interests you I can send you a command processor that I wrote to allow users to define custom math operations that they wanted to run against their data.

Mike...