Re: GetIpNetTable

From: Nicholas Paldino [.NET/C# MVP] (mvp_at_spam.guard.caspershouse.com)
Date: 10/18/04


Date: Mon, 18 Oct 2004 09:58:24 -0400

James,

    Here is how I would do it:

using System;
using System.Runtime.InteropServices;
using System.ComponentModel;

namespace ConsoleApplication5
{
    class Program
    {
        // The max number of physical addresses.
        const int MAXLEN_PHYSADDR = 8;

        // Define the MIB_IPNETROW structure.
        [StructLayout(LayoutKind.Sequential)]
        struct MIB_IPNETROW
        {
            [MarshalAs(UnmanagedType.U4)]
            public int dwIndex;
            [MarshalAs(UnmanagedType.U4)]
            public int dwPhysAddrLen;
            [MarshalAs(UnmanagedType.ByValArray, SizeConst =
MAXLEN_PHYSADDR)]
            byte[] bPhysAddr;
            [MarshalAs(UnmanagedType.U4)]
            public int dwAddr;
            [MarshalAs(UnmanagedType.U4)]
            public int dwType;
        }

        // Declare the GetIpNetTable function.
        [DllImport("IpHlpApi.dll")]
        [return: MarshalAs(UnmanagedType.U4)]
        static extern int GetIpNetTable(
            IntPtr pIpNetTable,
            [MarshalAs(UnmanagedType.U4)]
            ref int pdwSize,
            bool bOrder);

        // The insufficient buffer error.
        const int ERROR_INSUFFICIENT_BUFFER = 122;

        static void Main(string[] args)
        {
            // The number of bytes needed.
            int bytesNeeded = 0;

            // The result from the API call.
            int result = GetIpNetTable(IntPtr.Zero, ref bytesNeeded, false);

            // Call the function, expecting an insufficient buffer.
            if (result != ERROR_INSUFFICIENT_BUFFER)
            {
                // Throw an exception.
                throw new Win32Exception(result);
            }

            // Allocate the memory, do it in a try/finally block, to ensure
            // that it is released.
            IntPtr buffer = IntPtr.Zero;

            // Try/finally.
            try
            {
                // Allocate the memory.
                buffer = Marshal.AllocCoTaskMem(bytesNeeded);

                // Make the call again. If it did not succeed, then
                // raise an error.
                result = GetIpNetTable(buffer, ref bytesNeeded, false);

                // If the result is not 0 (no error), then throw an
exception.
                if (result != 0)
                {
                    // Throw an exception.
                    throw new Win32Exception(result);
                }

                // Now we have the buffer, we have to marshal it. We can
read
                // the first 4 bytes to get the length of the buffer.
                int entries = Marshal.ReadInt32(buffer);

                // Increment the memory pointer by the size of the int.
                IntPtr currentBuffer = new IntPtr(buffer.ToInt64() +
sizeof(int));

                // Allocate an array of entries.
                MIB_IPNETROW[] table = new MIB_IPNETROW[entries];

                // Cycle through the entries.
                for (int index = 0; index < entries; index++)
                {
                    // Call PtrToStructure, getting the structure
information.
                    table[index] = (MIB_IPNETROW) Marshal.PtrToStructure(new
IntPtr(currentBuffer.ToInt64() + (index *
Marshal.SizeOf(typeof(MIB_IPNETROW)))), typeof(MIB_IPNETROW));
                }
            }
            finally
            {
                // Release the memory.
                Marshal.FreeCoTaskMem(buffer);
            }
        }
    }
}

    Hope this helps.

-- 
               - Nicholas Paldino [.NET/C# MVP]
               - mvp@spam.guard.caspershouse.com
"James Jenkins" <James@REMOVETHIS1STtamarsolutions.co.uk> wrote in message 
news:OWh%23A7ItEHA.3156@TK2MSFTNGP12.phx.gbl...
> does anyone know how to implement the following? - I am very new to using 
> Marshalling and could really do with some help - it's late and I am 
> tired - I have spent all day on this and the net comes up with very little 
> help - I have followed lots of tutorials and looked at many peoples 
> source - I am in need of enlightenment ;) - thanks
> [DllImport("iphlpapi.dll", EntryPoint="GetIpNetTable", SetLastError=true)]
>
> public static extern int GetIpNetTable(IntPtr buffer,ref int Size, bool 
> Order);
>
>
>
> I have got this far in the calling it- as below
>
>
>
> IntPtr lpBuffer = IntPtr.Zero;
>
> int size = 0;
>
> int result = IPHelperAPI.GetIpNetTable(lpBuffer,ref size,true);
>
> if(result != NO_ERROR)
>
> {
>
> Debug.WriteLine("NO ERROR");
>
> lpBuffer = Marshal.AllocHGlobal(size);
>
> result = IPHelperAPI.GetIpNetTable(lpBuffer,ref size,true);
>
> if(result != NO_ERROR)
>
> {
>
> Marshal.FreeHGlobal(lpBuffer);
>
> lpBuffer = IntPtr.Zero;
>
> Debug.WriteLine("RETURN ERROR");
>
> return;
>
> }
>
> Debug.WriteLine("I GOT THIS FAR");
>
> // But canot allocate the structures from here - I hope someone out there 
> can pointer me in the right direction -  good night all;;;
>
>
>
> JJ
>
>