Calling DhcpEnumServers from .Net

Question

I am attempting to call the routine DhcpEnumServers that exists in dhcpsapi.dll from a C# application. This call should return a status of 0 to indicate success however it is returning 87 which is not listed as a valid return code for this call. A status of 87 is the Windows error value for invalid argument so I'm assuming that I have a problem with the marshalling of arguments for the interop call. I've provided the smallest code sample that I can to reproduce the problem. Any help would be greatly appreciated.

using System;
using System.Runtime.InteropServices;

namespace QueryDhcp
{
    class Program
    {
        [DllImport("dhcpsapi.dll", SetLastError = true, CharSet = CharSet.Ansi)]
        public static extern uint DhcpEnumServers(
            uint flags,
            ref uint idInfo,
            out IntPtr servers,
            ref uint callbackFn,
            ref uint callbackData
            );

        static void Main(string[] args)
        {
            uint nr = 0;
            IntPtr svrs;
            uint dhcpResult = DhcpEnumServers(nr, ref nr, out svrs, ref nr, ref nr);
        }
    }
}

Answer 1

Try this definition:

[DllImport( "dhcpsapi.dll", SetLastError = true, CharSet = CharSet.Unicode )]
public static extern uint DhcpEnumServers(
         uint Flags,
         IntPtr IdInfo,
         out IntPtr Servers,
         IntPtr CallbackFn,
         IntPtr CallbackData
         );

. . . .

IntPtr svrs;
uint dhcpResult = DhcpEnumServers( 0, IntPtr.Zero, out svrs, IntPtr.Zero, IntPtr.Zero );

If now you receive other error codes, see http://msdn.microsoft.com/en-us/library/windows/desktop/aa363378(v=vs.85).aspx.

Answer 2

That worked.

Thanks for the help.