Problem calling C++ API

[Cakkie]

I'm trying to call a C++ API function, which takes two parameters. The function will fill these 2 parameters. The first parameter will be a list of a specific structure, the second will be a number indicating how many elements the array contains.

The problem is that I don't know how te define and pass the 'list' to the function. I've tried a few things, but they all fail to work. The funtion call itself succeeds, since the count parameters is set properly

This is the exported function definition in C++

HRESULT WRAPIEnumerateDevices(
  WRAPI_NDIS_DEVICE** 	ppDeviceList
  long* 			plItems
);

In VB.Net, I've declared the function as follows: (note that the funny name in entrypoint is indeed correct)

<DllImport("wrapi.dll", EntryPoint:="?WRAPIEnumerateDevices@@YAJPAPAUWRAPI_NDIS_DEVICE@@PAJ@Z", SetLastError:=True, CharSet:=CharSet.Unicode, ExactSpelling:=True, CallingConvention:=CallingConvention.Cdecl)> _
Public Function WRAPIEnumerateDevices(ByRef ppDeviceList As WRAPI_NDIS_DEVICE, ByRef plItems As Int32) As Long
End Function

My guess is that I do not need to pass a WRAPI_NDIS_DEVICE structure, but somethign different. I just don't know what it should be. I've tried passing a WRAPI_NDIS_DEVICE element, the first element of an array of WRAPI_NDIS_DEVICE elements, but none of them worked.

If I look at a C++ example, it simply defines a WRAPI_NDIS_DEVICE element, and passes it to the function.

	WRAPI_NDIS_DEVICE    *pDeviceList = NULL;
	hRes = WRAPIEnumerateDevices(&pDeviceList, &lItems);

	for ( int i = 0; i < lItems; i++)
	{
		printf("%ws\n  - %ws\n", pDeviceList[i].pDeviceDescription, pDeviceList[i].pDeviceName);
	}

Anyone know what I should be passing here?

[wildfrog]

Ok, I've never worked with WRAPI (or VB.NET), but this might push you in some direction.

From searching the web the WRAPI_NDIS_DEVICE structure looks like this:

typedef struct
{
   WCHAR*    pDeviceName;
   WCHAR*    pDeviceDescription;
} WRAPI_NDIS_DEVICE;

So, wrapped in VB.NET, it should become something like this:

<StructLayout(LayoutKind.Sequential)> _
Public Structure WRAPI_NDIS_DEVICE
    <MarshalAs(UnmanagedType.LPTStr)> Public pDeviceName As String
    <MarshalAs(UnmanagedType.LPTStr)> Public pDeviceDescription As String
End Structure

Then, the import code (with a tiny modification):

    <DllImport( _
        "wrapi.dll", _
        EntryPoint:="?WRAPIEnumerateDevices@@YAJPAPAUWRAPI_NDIS_DEVICE@@PAJ@Z", _
        SetLastError:=True, CharSet:=CharSet.Unicode, ExactSpelling:=True, _
        CallingConvention:=CallingConvention.Cdecl)> _
        Public Function WRAPIEnumerateDevices(ByRef ppDeviceList As IntPtr, ByRef plItems As Int32) As Long
    End Function

Then there is the code calling the function:

Dim pInfo As IntPtr = IntPtr.Zero
Dim iItems As Int32
Dim lRes As Long 
Dim i As Int32

' call the method (add error checking)
lRes = WRAPIEnumerateDevices(pInfo, iItems)

Console.WriteLine("Number of devices :{0}", iItems)

' loop through all records
For i = 0 To iItems - 1

    ' marshal record
    Dim pDevice As WRAPI_NDIS_DEVICE = _
        CType(Marshal.PtrToStructure(pInfo, GetType(WRAPI_NDIS_DEVICE)), WRAPI_NDIS_DEVICE)

    ' use the record
    Console.WriteLine("{0} - {1}", pDevice.pDeviceName, pDevice.pDeviceDescription)

    ' get next record
    pInfo = New IntPtr(pInfo.ToInt32() + Marshal.SizeOf(pDevice))
Next

- petter

[Cakkie]

Perfect, works like a charm

Thanks!