Need help passing array of UDT with string to C++ dll

[amrizal]

Hi. I'm trying to pass an array of UDT from Excel to a C++ dll but I have no idea how. My UDT looks like this

Private Type Student
    Age As Integer
    Name As String
    StudentID As String
End Type

And my dll function declaration..

Declare Function RegisterStudent Lib "SimpleDLL.dll" _
(arr() as Student) As String

.. which will return a unique Id in string

 

[RoryA]

I don't understand. Your function appears to take an array of Student types as an argument, so what is the string it returns?
My best guess would be something like:

   Dim arrStudents(1 To 3) As Student
   Dim n As Long
   Dim strID As String
   For n = 1 To 3
      With arrStudents(n)
         .Age = n
         .Name = "name " & n
         .StudentID = n * 4
      End With
   Next n
   strID = registerstudent(arrStudents)

 

[amrizal]

Yes. The dll function would do some processing and returns a unique processing id.

I can't find a way to pass an array of UDT with variable length string.

 

[RoryA]

Oh, I see - have you read this MSKB article?

 

[amrizal]

Thanks rorya.

 

[amrizal]

Thanks for the link. I'm a beginner with VBA much less with VB. How do I create the VBA function and type declaration for the dll?

I've tried..
Vba Code

Private Type TestUDT
    l As Long
    str As String
End Type
 
Declare Sub ModifyStruct Lib "UDTArray.dll" _
(arr() As TestUDT, l As Long)

But gave me a 'type mismatch : array or user-defined type expected' error when I ran the code.

Dim t(0 To 1) As TestUDT
Dim i as long
t(0).l = 1
t(0).str = "test1"
t(1).l = 2
t(1).str = "Test2"
i = UBound(t) - LBound(t) + 1
ModifyStruct t(0), i '<== type mismatch error here

... Any ideas?

 

[RoryA]

Try changing that last line to:

ModifyStruct t, i

so you are passing the array of UDTs, not a single UDT.

 

[amrizal]

Thanks rorya. I don't think I can do that since the c++ code in the dll requires me to pass a pointer of a single item.

void __stdcall ModifyStruct(struct tagTestUDT *t, long nTotalItem)

When I tried calling

ModifyStruct t, i

gave me "Run-time error 453: Can't find DLL entry point ModifyStruct ..."

I'm guessing it's my function declaration for the dll. I copied the rest of the code from here

 

[RoryA]

Have you tried setting a reference rather than using Declare? I don't know enough about C to help you, but you could try:

Declare Function RegisterStudent Lib "SimpleDLL.dll" _
(arr as Student) As String

and then pass the first member of the array t(0)

 

[amrizal]

Thanks Rory