[DllImport("Netapi32.dll ")]

extern static int NetUserEnum([MarshalAs(UnmanagedType.LPWStr)] string servername, int level, int filter, out IntPtr bufptr, int prefmaxlen, out int entriesread, out int totalentries, out int resume_handle);

[DllImport("Netapi32.dll ")]

extern static int NetApiBufferFree(IntPtr Buffer);

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]

public struct USER_INFO_0

{

    public string Username;

}

public static List<string> GetSysUserNames()

{

    List<string> users = new List<string>();

    NetUserEnum(null, , , out IntPtr bufPtr, -, out int entriesRead, out int totalEntries, out int resume);

    if (entriesRead > )

    {

        IntPtr iter = bufPtr;

        for (int i = ; i < entriesRead; i++)

        {

            var user = (USER_INFO_0)Marshal.PtrToStructure(iter, typeof(USER_INFO_0));

            iter = (IntPtr)((int)iter + Marshal.SizeOf(typeof(USER_INFO_0)));

            users.Add(user.Username);

        }

        NetApiBufferFree(bufPtr);

    }

    return users;

}