what datatype to pass to DLL?

[Adri Gerritsen]

Hi!

I want to call a function in a DLL (written in C++). One of the arguments expected is of type "array of void pointers".

When passing the datatype "IntPrt" from VB.net, the 4 element size array from VB.net is truncated to a one element size array after the call.

What argument should be passed from VB.net to handle "arrays of void pointers"??

Thanks!!!

Adri Gerritsen

[Boumxyz2]

an array of void pointers would be a pointer of pointer to me.. so a pointer to the first address of your structure would be good.

[exterminator]

Here some code: C++ DLL code

//a C++ dll function taking an array
int _stdcall FillArr(int * inArr, int ArrSize) {
    int LoopArr; // Loop variable

    // Make sure they didn't pass anything silly
    if (ArrSize < 1) return 0;

    // Fill the array
    for (LoopArr = 0; LoopArr < ArrSize; LoopArr++) {
        inArr[LoopArr] = LoopArr;
    }

    // Return 1 if all went well
    return 1;
}

Here the VB code:

'VB code which calls the dll function.
Private Sub Form_Load()
    Dim MyArr() As Long
    Dim ArrSize As Long
    Dim LoopArr As Long
    Dim MakeString As String

    ' Create the array
    ArrSize = 10
    ReDim MyArr(ArrSize - 1) As Long

    ' Get the DLL to fill the array
    ' Note here that we pass the first entry of the array and not the
    ' array pointer itself, this is to make sure we fill the array
    ' data and not overwrite the array descriptor by mistake.
    Call MsgBox(FillArr(MyArr(0), ArrSize))

    ' Loop through the new array contents and make a string message
    For LoopArr = 0 To ArrSize - 1
        MakeString = MakeString & MyArr(LoopArr) & vbCrLf
    Next LoopArr

    ' Report array contents
    Call MsgBox(MakeString)
End Sub

The point to note here is that we pass the first entry of the array and not the array pointer itself, this is to make sure we fill the array data and not overwrite the array descriptor by mistake. This seems to be the issue with your code. Hope this helps.

If not then please paste some code so that we can have a look at what is happening.

Here are some links to some good articles upon this:
1. MSDN - How To Pass Arrays Between Visual Basic and C
2. FlipCode - Interfacing Visual Basic And C++
3. Passing Arrays to a DLL