Passing an Array of User Defined Types

[FiniteInfinity]

Ok, here's the problem first. I'd post the code, but it is quite hefty. Ill do so later if noone can help me with this.

I am writing some functions based around API calls such as GetLogicalDriveStrings and GetDriveType and so on.
I want to return more than one peice of information about each drive, whilst maintaining a nice coder friendly method to do it. My thought was this. A user type called DriveInformation that held 3 variables: Letter, VolumeName and DriveType. A function gets all the drives on a system, and the information about them, and put this into an array.
It then passes the array back to the function that called that called it. Boom, VB doesn't like this and the program falls over.

Anyone ever try something like this? Can you give me a hand.

REMEMBER, I HAVE NO PROBLEM WITH THE ARRYA OF UDT's, I HAVE PROBLEMS PASSING IT FROM ONE FUNCTION TO THE OTHER.

PS. Telling me to move to another language is not helpful

[Luthv]

You can pass the pointer to the variable containing the UDT, as long as you don't pass this variable to another computer you can use CopyMemory to return the pointer back to UDT structure

Note for array of UDT you have to Declare your own VarPtr function like so :

Private Declare Function VarPtrArray Lib "msvbvm60.dll" Alias "VarPtr" (Ptr() As Any) As Long
This function return the address of the first element of your array

Example:

Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (pDst As Any, pSrc As Any, ByVal ByteLen As Long)

SomeSub(UDTPtr as long)
'Copy it back to UDT
dim tUDT as YourUDT

copymemory tUDT, byval UDTPTR, len(tUDT)
'Do some calculation

'copy the result back
copymemory byval UDTptr,tUDT,len(tUDT)
end sub

in the calling sub use the same way to convert ptr back to UDT

Another way is to use a string variable to hold all the structure's data delimited with a unique character then in the calling sub just split the string back to its components

[Cimperiali]

'Legal: You can modify the values
'Legal: You can modify dimension
'Illegal: you cannot redim., redim preserve or erase if you passed
' a cell of the array in the function where you want to redim
'Illegal: you cannot redim, redim preserve or erase if you're inside
a With ...end with block and you've just accessed a single cell
value...

'Legal: within same module, you can pass arrays of Udt by ref.
Thus you do not need to have a "return value" of Udts: you will
modiofy same parameter passed.
'Illegal: you cannot pas same udt through modules: you will have
to declare it in a class of a Dll with instancing higher than public
not creatable. And you will have to use early binding in your
standard exe to be able to declare a variable of tipe of the one
you created in class

'ie:
Your class module: in a project of type dll called "pTheUdt"
Option Explicit

Public Type ThisUdt
Names As String
Numbers As Long
End Type
'---------------------------
'Your exe standard:
Dim myUdt() As pTheUdt.ThisUdt
'-----------


'Normal code inside a single form can do what you said:

Option Explicit
Private Type ThisUdt
   Names As String
   Numbers As Long
End Type
Dim myUdt() As ThisUdt
Private Sub Command1_Click()


ReDim myUdt(3)
Dim retvar As Boolean
retvar = theUdtFunction(myUdt)
MsgBox "Last:" & UBound(myUdt)
End Sub
Private Function theUdtFunction(ByRef AUdt() As ThisUdt) As Boolean
   MsgBox UBound(AUdt)
   ReDim Preserve AUdt(UBound(AUdt) + 1)
   theUdtFunction = the12nd_UdtFunction(AUdt)
End Function
Private Function the12nd_UdtFunction(ByRef AUdt() As ThisUdt) As Boolean
   MsgBox UBound(AUdt)
   ReDim Preserve AUdt(UBound(AUdt) + 1)
End Function

More detail on your crash?

[rxbagain]

You can return a UDT array from the function. Take a look at my code

Private Type myUDT
   x As Long
   y As Long
   z As Long
End Type

Private Function UDTProc() As myUDT()
   Dim arrUDT() As myUDT
   ReDim arrUDT(10) As myUDT
   arrUDT(0).x = 100
   arrUDT(10).x = 200
   UDTProc = arrUDT
End Function

Private Sub Form_Load()
   Dim retUDT() As myUDT
   retUDT = UDTProc
   MsgBox UBound(retUDT)
End Sub

I tested it and it worked well. I also placed the UDT and function in a module and it also worked well

Hope it will help you