topic Re: Creating sparse enums in CVI for LabVIEW in LabWindows/CVI

Creating sparse enums in CVI for LabVIEW

tst — Tue, 10 Jul 2007 18:17:20 GMT

LabVIEW, for some reason, does not support creating or editing sparse enums.

NI, however, describes a process to import sparse enums created in CVI.

I want to try to hack this and see if I can create an editor for these, but I don't have CVI, so I was hoping someone could create a couple of these sparse enums and upload them. I'm not sure if this matters, but I have access to LV 7.0 and 7.1, so I'd appreciate something in parallel versions.

Examples:

[value, label

1, one
4, four
6, six
2, two
]

[value, label

6, apple
24, orange
18, pear
27, peach
0, grape
]

Thank you.

Re: Creating sparse enums in CVI for LabVIEW

jr_2005 — Wed, 11 Jul 2007 08:44:16 GMT

Well, I followed steps 1 to 7 of the instructions in your link, using your sample data. I don't have LabView, so I couldn't go any further. Attached fp file was created with CVI 7.0 (the only version I have). (It is inside a zip file: the forum would not accept a file with the .fp extension...)

Good luck!

Re: Creating sparse enums in CVI for LabVIEW

tst — Wed, 11 Jul 2007 12:05:30 GMT

Thank you, but what I got there are rings, which can be sparse in LV.

Can you do the same with an enum?

Re: Creating sparse enums in CVI for LabVIEW

tst — Wed, 11 Jul 2007 12:10:49 GMT

Or did you already use an enum and this process simply converts it to a ring?

The article is from before LV 7.0 was released (which I believe was the first version which had sparse rings), so it's possible it never did produce sparse enums, but I saw people say that they did use this process to create sparse enums in LV. I suppose it is possible they did not remember correctly.

Re: Creating sparse enums in CVI for LabVIEW

jr_2005 — Wed, 11 Jul 2007 13:13:13 GMT

Looks like I misunderstood what you wanted...

In straight C, your 'sparse enum' could be simply written as follows:

enum fruit {

grape = 0,

apple = 6,

pear = 18,

orange = 24,

peach = 27

};

But I though you wanted something more complex - ie the Ring control in the link that you pointed to. Is this not so?

Re: Creating sparse enums in CVI for LabVIEW

tst — Wed, 11 Jul 2007 14:02:00 GMT

In LabVIEW, a ring is simply a numeric control which has a list of display strings. The strings and values in the control can be changed at any time since the control is a simple numeric.

An enum is a special numeric data type where the value includes both an integer and a string. The main advantage is when using case structures - wiring an enum to a case structure gives you the enum strings in the case structure, like this:

Changing the enum values after connecting it to the case structure will propogate accordingly. Wiring a ring control to a case structure is just like wiring any other numeric - you need to use numeric values.

The problem is that to set up enums you need to use the editing interface and that does not allow changing the values of the enum - they must be 0,1,2,3,4, etc. In my hacking I did manage to change the order of these, but not create a sparse one, and that's why I want the one from CVI. As I said, it is possible that this only applies to rings, but I was hoping it worked for enums as well. How do you place an enum into a control?

Re: Creating sparse enums in CVI for LabVIEW

jr_2005 — Wed, 11 Jul 2007 14:40:45 GMT

Well, we would probably use a Ring control or a List Box - both of these allow arbitrary Label/Value pairs, with a wide choice of data types (int, char, string, double etc.) so not restricted to just numbers. The fp editor (at least at CVI 7.0) does not support List Box controls so this looks like a dead end. Can LabView import CVI UIR files? This would give a larger field to experiment in.

Re: Creating sparse enums in CVI for LabVIEW

tst — Wed, 11 Jul 2007 18:32:14 GMT

LabVIEW has three basic types -

Ring - a numeric control with display strings. The value is the numeric value associated with the string you selected.
Combo box - a string control with a list of display strings.
Enum - a numeric type with fixed embedded strings.

I'm guessing the only way to import is using the process descibed there and explicitly refers to sparse enums, so I was hoping that would be simple, but I also see that the process says to use a ring control. I take it there is no other way to insert an enum into a control?

Re: Creating sparse enums in CVI for LabVIEW

jr_2005 — Thu, 12 Jul 2007 08:56:51 GMT

Looking at your description of a LabView enum it seems to have a correlation to a simple C string table, which can be defined like this:

    char *strings [] = {"Zero", "One", "Two", "Three", "Four", "Five"};

    n = 2;
    Print (strings [n]);    // Match the string to a numeric value

So this also gives a direct mapping of strings to sequential numeric values, where no gaps are allowed. With such a simple C primitive, CVI does not really need a specific GUI control to manipulate the resulting data.

Re: Creating sparse enums in CVI for LabVIEW

tst — Thu, 12 Jul 2007 11:53:38 GMT

If my C understanding is correct, you can go back at any point in your code and change the array to hold other strings, so that's just a string array. An enum has constant strings and values as part of its data type, just like you can't set an int variable to be 3.6.

The LV enum is not necessarily limited to an ordered list. In my hacking I did manage to create an out of order enum ("three, one, zero, two"; 3, 1, 0, 2), but not one which includes numbers which are not sequential from 0. I was hoping this process would help.

Re: Creating sparse enums in CVI for LabVIEW

GuenterMueller — Thu, 12 Jul 2007 14:38:42 GMT

Hi tst.

I also get rings instead of enums.
Confusing: The NI document introduces this method as a way to create sparse enums but in (14) it says: "On the front panel of this VI, the custom text ring control appears." This is what I get, too.

Then I checked the .fp and the rings had the data type "int". In LabVIEW, enums must be U8, U16 or U32 -> So I changed the data types in the .fp (see attachment) and again imported the .fp in LV7.1.1 -> no change, again I see the rings (but this time with unsigned data types).

Who knows, how to get the sparse enums in LabVIEW ???

Regards, Guenter

Re: Creating sparse enums in CVI for LabVIEW

tst — Thu, 12 Jul 2007 15:22:42 GMT

Yes, those are still rings.

The article definitely speaks about sparse enums and people also talked specifically about sparse enums, but I suppose it is possible that it refers only to sparse rings, which were unavailable before LV 7.0. I'm actually downloading CVI to see if I can play with it.

Re: Creating sparse enums in CVI for LabVIEW

jr_2005 — Thu, 12 Jul 2007 15:53:54 GMT

Careful! Once you start to use CVI you might just find that you like it!

Re: Creating sparse enums in CVI for LabVIEW

Ben M — Thu, 12 Jul 2007 21:15:39 GMT

Hello tst,

Unfortunately, you are correct. If I understand you correctly you are trying to create a way to pass a tuple (string,integer) the same way that the enum does. The enum is built on an array and just uses the array index as the integer when it passes the value. This is why you cannot create a sparse enum. I don't believe that there is currently a way to duplicate this behaviour using CVI widgets.

Re: Creating sparse enums in CVI for LabVIEW

tst — Fri, 13 Jul 2007 06:52:21 GMT

@Ben M wrote:

The enum is built on an array and just uses the array index as the integer when it passes the value.

At face value, I would agree, but I did manage to create an enum which is out of order fairly easily, without even using any supersecret scripting (see attached, LV 7.0), and that document and other people also clearly refered to sparse enums, which is why I'm still hoping this could work. Do you know this for a fact or are you just quoting some internal KB \ something you heard? (no offense, but not all of NI's AEs are created equal. I ran into more than one who were not always that helpful to the users in the forums).

BTW, the attached also demonstrates quite clearly that the value of the elements is not defined in the type descriptor, which means it must be somewhere else, but looking at the binary structure of that control didn't reveal anything conclusive either.

Re: Creating sparse enums in CVI for LabVIEW

tst — Fri, 13 Jul 2007 07:00:31 GMT

Actually, after trying it again just now, it seems that this reordering does not propogate and just stays in the control (makes sense, since it's not in the type descriptor). You can see this by probing the enum wire. The string displayed is the string which is found in index n of the string array, where n is the numeric value of the wire, so if you select "Three", the probe shows you 3 and "One", which is the fourth element in the string array.

Re: Creating sparse enums in CVI for LabVIEW

tst — Wed, 18 Jul 2007 10:03:45 GMT

@jr_2005 wrote:

Careful! Once you start to use CVI you might just find that you like it!

Not really.

I won't say I went through tutorials and really tried to learn it, but I wasn't that impressed. I think it looks (I'll be gentle) not very nice and I miss the ease of use of LV. For some reason, it does not seem to me to be very polished.

By the way, this has nothing to do with C vs. LV. I think Visual Studio and Eclipse, to name a couple of IDEs, look great. Why do people choose CVI over any other C compiler? Does it have any particular advantages?

Anyway, Rolf said that what he saw in the past was most likely sparse rings and not sparse enums, and that seems reasonable when you consider the way the enum datatype is represented in LV, so I think we can officially say that there is currently no way to have sparse enums in LV.