Hello everyone,

I need to call the native function GetIfTable() and set up everything to
do so as follows:

----- START OF CODE -----
[DllImport("iphlpapi.dll", SetLastError = true)]
public static extern int GetIfTable(
    IntPtr pIfTable,
    ref uint pdwSize,
    bool bOrder
);

[StructLayout(LayoutKind.Sequential)]
public struct MIB_IFROW {
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst =
IpApi32.MAX_INTERFACE_NAME_LEN)]
    public string wszName;
    public uint dwIndex;
    public uint dwType;
    public uint dwMtu;
    public uint dwSpeed;
    public uint dwPhysAddrLen;
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = IpApi32.MAXLEN_PHYSADDR)]
    public byte[] bPhysAddr;
    public uint dwAdminStatus;
    public uint dwOperStatus;
    public uint dwLastChange;
    public uint dwInOctets;
    public uint dwInUcastPkts;
    public uint dwInNUcastPkts;
    public uint dwInDiscards;
    public uint dwInErrors;
    public uint dwInUnknownProtos;
    public uint dwOutOctets;
    public uint dwOutUcastPkts;
    public uint dwOutNUcastPkts;
    public uint dwOutDiscards;
    public uint dwOutErrors;
    public uint dwOutQLen;
    public uint dwDescrLen;
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = IpApi32.MAXLEN_IFDESCR)]
    public byte[] bDescr;
}

[StructLayout(LayoutKind.Sequential)]
public struct MIB_IFTABLE {
    public int         dwNumEntries;
    public MIB_IFROW[] table;
}
----- END OF CODE -----

The only problem I have is concerning the wszName member of MIB_IFROW.
Now comes the method that makes use of it and troubles me:

----- START OF CODE -----
public void GetIfTable() {
    uint size = 0;
    int result = 0;
    IntPtr pBuffer = IntPtr.Zero;

    result = IpApi32Wrapper.GetIfTable(IntPtr.Zero, ref size, false);
   
    if (result == ErrorCodes.ERROR_INSUFFICIENT_BUFFER) {
        pBuffer = Marshal.AllocHGlobal((int)size);
        result = IpApi32Wrapper.GetIfTable(pBuffer, ref size, false);
    } else {
        throw new System.ComponentModel.Win32Exception(result);
    }

    if (result != ErrorCodes.NO_ERROR) {
        throw new System.ComponentModel.Win32Exception(result);
    } else {
        int count = Marshal.ReadInt32(pBuffer);
        int ptr = pBuffer.ToInt32() + Marshal.SizeOf(typeof(int));
        MIB_IFROW ifRow;

        for (int i = 0; i < count; i++ ) {
            ifRow = (MIB_IFROW)Marshal.PtrToStructure(
                (IntPtr)ptr, typeof(MIB_IFROW));
            Console.WriteLine("ifRow.wszName: {0}", ifRow.wszName);
            ptr += Marshal.SizeOf(typeof(MIB_IFROW));
        }
    }

    Marshal.FreeHGlobal(pBuffer);
}
----- END OF CODE -----

The question is: why is the following output produced?

ifRow.wszName:
ifRow.wszName: Realtek RTL8139-Family-PCI-Fast Ethernet-NIC #2
ifRow.wszName:
ifRow.wszName:
ifRow.wszName:

There are 4 adapters installed (excl. Loopback), but only one entry is
displayed correctly.  I'v written a small C program that does almost the
same thing and it prints all entries as expected.

As you can see, the MIB_IFROW member wszName is a wide character string
and may need special treatment by using Charset.Unicode and the like,
but it seem have no effect, since I already tried.

What's wrong with my code?  Any ideas highly appreciated.  Thanks.

Catherine