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1181

answers:

3

I am trying to use a third party DLL that wants an int** as one of the parameters to the method. It describes the parameter as the address of the pointer that will point to the memory allocation.

Sorry for any confusion. The parameter is two-way I think. The DLL is for talking to an FPGA board and the method is setting up DMA transfer between the host PC and the PCI board.

+4  A: 

Use a by-ref System.IntPtr.

 [DllImport("thirdparty.dll")]
 static extern long ThirdPartyFunction(ref IntPtr arg);

 long f(int[] array)
  { long retval = 0;
    int  size   = Marshal.SizeOf(typeof(int));
    var  ptr    = IntPtr.Zero;

    try 
     { ptr = Marshal.AllocHGlobal(size * array.Length);

       for (int i= 0; i < array.Length; ++i) 
        { IntPtr tmpPtr = new IntPtr(ptr.ToInt64() + (i * size));
          Marshal.StructureToPtr(array, tmpPtr, false);
        }

       retval = ThirdPartyFunction(ref ptr);
     }
    finally 
     { if (ptr != IntPtr.Zero) Marshal.FreeHGlobal(ptr);
     }

    return retval;
  }
Mark Cidade
Since it's passing information out, out is preferable to ref
JaredPar
How do I convert an int[] to the IntPtr?
Robin Robinson
Using the ref IntPtr seems to be compiling and running. I have a little further to go until I know it is completely working.
Robin Robinson
+1  A: 

You will have to make use of the Marshal class or go unsafe in this case.

It could also just be a pointer to an array, so a ref int[] list might work.

leppie
This is something that I will keep in mind in case the other way doesn't work.
Robin Robinson
If you are passing data to the function, this might be the easiest.
leppie
A: 

An int** would be and array of IntPtr, from your description I think you might want to look into using C++/CLI to help you with the conversions e.g from an unmanaged int** to a managed array^>^

SpaceghostAli