[RESOLVED] Problem when passing UDTs to subs

[krtxmrtz]

In a module I have the following declarations:

Public Type MyUDT
   X As Single
   Y() As Single
End Type
'
Public MyUDTInstance() As MyUDT

In a different module:

Sub MySub(DummyVarName)
'...
' Some operations are performed here
'with the quantities:
'DummyVarName(SomeIndex).X
'and
'DummyVarName(SomeIndex).Y(SomeOtherIndex)
'...
End Sub

Finally, in a form there's the calling statement:

Call MySub(MyUDTInstance)

Of course, MyUDTInstance and MyUDTInstance(SomeIndex).Y(SomeOtherIndex) have been previously ReDimensioned and given values.

Now, when the sub is called I get the error you can see in the attached picture which can be translated into English more or less as follows:

"Compiler error.

Only those user defined types from public obejct modules can be passed to functions linked at run time or forced to or from a variant"

Anyone knows the reason?

[robbedaya]

try

Sub MySub(DummyVarName as MyUDT) 
... 
End Sub

[krtxmrtz]

try

Sub MySub(DummyVarName as MyUDT) 
... 
End Sub

Now I get

"Compiler error.

The type of argument of ByRef does not coincide"

[opus]

I've doing something like that last night (..when trying first steps in VB2005).
Didn't get any errors there?
Since your UDT is Public, did you try to declare the Sub without the handing over the UDT like:

Sub MySub()
..
End Sub

[krtxmrtz]

I've doing something like that last night (..when trying first steps in VB2005).
Didn't get any errors there?
Since your UDT is Public, did you try to declare the Sub without the handing over the UDT like:

Sub MySub()
..
End Sub

OK, I've tried and it works. But I'd like to know what was wrong, I'd like my sub to be as general as possible.

[krtxmrtz]

All right, after trying out various possibilities I've found the correct syntax that won't fire any error. This is it:

Public Type MyUDT
   X As Single
   Y() As Single
End Type
'
Public MyUDTInstance() As MyUDT

In a different module:

Sub MySub(DummyVarName() As MyUDT)
'...
'
End Sub

The calling statement in a form:

Call MySub(MyUDTInstance())

I hope some guru sets his/her eyes on this thread and provides a clear explanation that makes sense.

[opus]

I hope some guru sets his/her eyes on this thread and provides a clear explanation that makes sense.

I always figured you as a guru, now I'm lost

[krtxmrtz]

I always figured you as a guru, now I'm lost

No kidding !!!???
Programming is just a hobby for me, I don't make a living out of it, I make programs for my own use and that of my workmates'.

[Al42]

All right, after trying out various possibilities I've found the correct syntax that won't fire any error. This is it:

Public Type MyUDT
   X As Single
   Y() As Single
End Type
'
Public MyUDTInstance() As MyUDT

In a different module:

Sub MySub(DummyVarName() As MyUDT)
'...
'
End Sub

The calling statement in a form:

Call MySub(MyUDTInstance())

I hope some guru sets his/her eyes on this thread and provides a clear explanation that makes sense.

MyUDT is not an array type. Your sub is using it as an array, so you have to declare it as an array in the sub

MyName() As MyType

the usual way of declaring an array. The caller has to pass the sub an array too.

[jcis]

About your last code, you don't need to send MyUDTInstance() as parameter, since its scope is the whole project, it can be used anywhere.

but if you want to send it as parameter, something like this would be better..

Module:

Public Type MyUDT
   X As Single
   Y() As Single
End Type

Public Sub MySub(DummyVarName() As MyUDT)
    'So something here
End Sub

Form:

    Dim lUdt() As MyUDT
    
    'Do something with lUdt
    Call MySub(lUdt())

[leinad31]

OK, I've tried and it works. But I'd like to know what was wrong, I'd like my sub to be as general as possible.

Then use classes/collections rather than UDTs, and receive it As Object.

[krtxmrtz]

About your last code, you don't need to send MyUDTInstance() as parameter, since its scope is the whole project, it can be used anywhere.
...

Actually MyUDT was declared initially in the form, but then I started fooling around with the code to test the various possibilities and it ended up in the same module as the type declaration.

But thanks for the clarification anyway. If anything at least it's a reminder for me to restore the previous situation.

[krtxmrtz]

MyUDT is not an array type....

Is there such a thing as an array type, like

Type Whatever()
'...
'...
End Type

???

[krtxmrtz]

Then use classes/collections rather than UDTs, and receive it As Object.

Believe it or not I have never used classes (of my own) just because I've never found the time to learn. All the VB I know I have learned either on my own or -to a large extent- in the forums. But I tend to learn new things only when I really need them and clearly see the benefit. And I don't see the benefit of using classes just because I'm hardly acquainted with them. Maybe I'd need a simple template to start with and learn gradually from that. Any hint, suggestion, tutorial, link in that direction will be most welcome.

[randem]

Actually the simplest class is a pure data class. You would define the elenments the same way you would in a module but you could reference them differently.

IE.

In a Class Module names clsData

Public sStr as String
Public lngOffset as Long

That's it!!!

In your program you would use it like this:

Dim myClass as clsData

   Set myClass = New clsData

   myClass.lngOffset = 5677
   myClass.sStr = "Test"

That's it. You can pass myClass as an object and place it into arrays and collections and create as may to hold the data as you need. In my opinion this is more flexible that using a UDT.

[krtxmrtz]

Actually the simplest class is a pure data class. You would define the elenments the same way you would in a module but you could reference them differently.

IE.

In a Class Module names clsData

Public sStr as String
Public lngOffset as Long

That's it!!!

In your program you would use it like this:

Dim myClass as clsData

   Set myClass = New clsData

   myClass.lngOffset = 5677
   myClass.sStr = "Test"

That's it. You can pass myClass as an object and place it into arrays and collections and create as may to hold the data as you need. In my opinion this is more flexible that using a UDT.

Thanks but I still don't see the advantage:
1. In which sense is it more flexible?
2. Can I make an array such as "Set myClass() = New clsData" and ReDim it at a later stage?
3. What do you exactly mean by passing it as an aobject? (To subs and functions?)
4. Do I have to destroy the class instance at program exit or at any other point in the program?

[randem]

1 - In every use

2 - No use dim myClass() as clsData, then redim it

3 - Since myClass is an object now, you can pass it like this.

Sub MySub(ArrayName() As Object)
'...
'
End Sub

This way you are passing an array of classes.

I believe you can even do this

Sub MySub(ArrayName() As clsData)
'...
'
End Sub

[randem]

You can also add it to a collection

   colData.Add myClass, myClass.sStr  ' or whatever key you would need

[krtxmrtz]

...

You sound very convincing...
How about my fourth?
"Do I have to destroy the class instance at program exit or at any other point in the program?"

[randem]

4 - Yes... Preferable when you are done with it.

Sorry.

[randem]

You can also code the class to enumerate thru the variables if you want. You can't do that with a UDT!

[krtxmrtz]

You can also code the class to enumerate thru the variables if you want. You can't do that with a UDT!

For example...? (Never done that!)

[randem]

You would then add a Emum function to your class that would return each data element name (type, length, etc...) from the class.

[krtxmrtz]

You would then add a Emum function to your class that would return each data element name (type, length, etc...) from the class.

I see. In your example above,

In a Class Module names clsData

Public sStr as String
Public lngOffset as Long

How would that work?

[krtxmrtz]

As far as I know Enum provides a useful way to remind you of constant names like intellisense. How can it be used to get the data information, as you say, like length, type, etc?

[krtxmrtz]

I have tried on my own and had to quit right after I'd started for it does not allow me to declare the variables below as public (produces an error)

In a Class Module names clsData

Public sStr as String
Public lngOffset as Long

[Al42]

Is there such a thing as an array type, like

Type Whatever()
'...
'...
End Type

???

Actually, no, it's an array of type.

Type Whatever
'...
'...
End Type

Dim myWhatever() as Whatever

But you declared your variable of your type as a single element, then used it as an array.

[randem]

In a Class Module names clsData

This is a statement not code...

Sure it works, I use Pure Data Classes extensively.

[krtxmrtz]

In a Class Module names clsData

This is a statement not code...

Sure it works, I use Pure Data Classes extensively.

All right, it works with simple data definitions, but not with UDTs:

Option Explicit

Public Start As Single
Public Finish As Single
Public Step As Single
Public Kounter As Long

Public Type Animal
    Size As Single
    CanFly As Boolean
    CanSwim As Boolean
    NumberOfLegs As Integer
End Type

It gives an error when run so, looks like it doesn't allow UDTs here. Shall I then dismiss using classes?

[leinad31]

The point of using classes is to drop the use of UDTs (eg. such is the case with Java)

[krtxmrtz]

The point of using classes is to drop the use of UDTs (eg. such is the case with Java)

Then is it possible to implement the following using classes?

Type Series
    nPts As Integer
    Nam As String
    X() As Single
    Y() As Single
End Type
Type DataChart
    ID As String
    nSeries As Integer
    S() As Series
End Type
Public DC() As DataChart
Public nDDCs As Integer

[leinad31]

Yes. You simply have to look around to see samples.

If I'm not mistaken you can retain the array of primitive data types (like the SubItems() property of listview listitem).

The array of UDT you will implement as a collection of objects (like the ListItems collection of listview). You can have a heirarchy (such as each ListItem in ListItems collection having ListSubItems collection).

[krtxmrtz]

Yes. You simply have to look around to see samples.

If I'm not mistaken you can retain the array of primitive data types (like the SubItems() property of listview listitem).

The array of UDT you will implement as a collection of objects (like the ListItems collection of listview). You can have a heirarchy (such as each ListItem in ListItems collection having ListSubItems collection).

Great, but I've never worked with collections of my own. Could you provide a couple of lines to show how you'd declare/define a suitable collection for the example I've presented in my previous post?

[leinad31]

If you have MSDN Library installed, look for "House of Straw"

[krtxmrtz]

If you have MSDN Library installed, look for "House of Straw"

I'll take a look at it. Thanks.