C# Signature:

        [DllImport("Netapi32.dll", SetLastError=true)]
        public extern static int NetUserGetGroups
            ([MarshalAs(UnmanagedType.LPWStr)] string servername,
             [MarshalAs(UnmanagedType.LPWStr)] string username,
             int level,
             out IntPtr bufptr,
             UInt32 prefmaxlen,
             out int entriesread,
             out int totalentries);

VB Signature:

        <DllImport("Netapi32.dll", SetLastError := True)> _
        Public Shared Function NetUserGetGroups(
            <MarshalAs(UnmanagedType.LPWStr)> ByVal servername As String, _
            <MarshalAs(UnmanagedType.LPWStr)> ByVal username As String, _
            ByVal level As Integer, ByRef bufptr As IntPtr, _
            ByVal prefmaxlen As Integer, ByRef entriesread As Integer, _
            ByRef totalentries As Integer) As Integer
        End Function

User-Defined Types:

    [StructLayout(LayoutKind.Sequential, CharSet=CharSet.Unicode)]
    internal struct LOCALGROUP_USERS_INFO_0
    {
        [MarshalAs(UnmanagedType.LPWStr)]internal string name;
    }

    [StructLayout(LayoutKind.Sequential)]
    internal struct LOCALGROUP_USERS_INFO_1
    {
        [MarshalAs(UnmanagedType.LPWStr)] public string name;
        [MarshalAs(UnmanagedType.LPWStr)] public string comment;
    }

Alternative Managed API:

Do you know one? Please contribute it!

Notes:

None.

Tips & Tricks:

When the data to receive is larger than the specified in 'prefmaxlen', an error code 234 is returned. You can pass 0xFFFFFFFF (which required the change from int to UInt32) in this parameter and then the needed amount of memory will be allocated.

Please add some!

Sample Code:

        //Example code to place in a class.

        #region  pInvoke Items

        [StructLayout(LayoutKind.Sequential, CharSet=CharSet.Unicode)]
        public struct LOCALGROUP_USERS_INFO_0
        {
            public string groupname;
        }

        [DllImport("Netapi32.dll", SetLastError=true)]
        public extern static int NetUserGetGroups
            ([MarshalAs(UnmanagedType.LPWStr)] string servername,
             [MarshalAs(UnmanagedType.LPWStr)] string username,
             int level,
             out IntPtr bufptr,
             UInt32 prefmaxlen,
             out int entriesread,
             out int totalentries);

        [DllImport("Netapi32.dll", SetLastError=true)]
        public static extern int NetApiBufferFree(IntPtr Buffer);

        #endregion

        private int ErrorCode;
        private string _ErrorMessage;

        public string ErrorMessage {
            get { return this._ErrorMessage; }
        }

        private ArrayList GetUserNetGroups(string ServerName,string Username, int Flags)
        {
            ArrayList myList = new ArrayList();
            int EntriesRead;
            int TotalEntries;
            IntPtr bufPtr;

            ErrorCode = NetUserGetGroups(ServerName,Username,Flags,out bufPtr,1024,out EntriesRead, out TotalEntries);
            if(ErrorCode==0)
            {
                _ErrorMessage="Successful";
            }
            else
            {
                _ErrorMessage="Username or computer not found";
            }
            if(Flags>1)
                _ErrorMessage="Flags can only be 0 or 1";
            if(EntriesRead> 0)
            {
                LOCALGROUP_USERS_INFO_0[] RetGroups = new LOCALGROUP_USERS_INFO_0[EntriesRead];
                IntPtr iter = bufPtr;
                for(int i=0; i < EntriesRead; i++)
                {
                    RetGroups[i] = (LOCALGROUP_USERS_INFO_0)Marshal.PtrToStructure(iter, typeof(LOCALGROUP_USERS_INFO_0));
                    iter = (IntPtr)((int)iter + Marshal.SizeOf(typeof(LOCALGROUP_USERS_INFO_0)));
                    myList.Add(RetGroups[i].groupname);
                }
                NetApiBufferFree(bufPtr);
            }
            return myList;
        }

        ////////////////////////////////////////////////////////////////////////////////////////////////////////

        //Example code for calling application
            ArrayList RetGroups = new ArrayList();
            RetGroups =DsDomain.GetUserNetGroups(null,"administrator",0);
            foreach(string str in RetGroups)
            {
                Console.WriteLine(str);
            }