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up vote 4 down vote favorite
1

Here is my code:

[StructLayout(LayoutKind.Sequential, Pack = 1)]
public struct Foo
{
  UInt32 StartAddr;
  UInt32 Type;
}


[DllImport(DllName, EntryPoint="_MyFunc", CallingConvention = CallingConvention.Cdecl)]
static extern unsafe IntPtr MyFunc([MarshalAs(UnmanagedType.LPArray)] Foo[] Foos);


List<Foo> Foos = new List<Foo>();
Foo1 = new Foo();
Foo1.StartAddr = 1;
Foo1.Type = 2;
Foos.Add(Foo1);
MyFunc(Foos.ToArray());

In the C-based DLL I print out the value of Foos[0].StartAddr and Foos[0].Type. This works great.

Now I want to add a parameterless constructor to the struct which means I have to switch to a class. By only changing the C# declaration from "struct" to "class" results in corrupted values being passed to the C-based DLL.

I believe this should work but I presume I am missing a step. How can I pass an array of C# classes as a array of structs to C code?

Thanks! Andy

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1  
Yes, won't work. The array will be marshaled as Foo** instead of Foo*. An array of pointers to Foo. No clean workaround either, manual marshaling is very ugly here. Don't do this if you can't change the C code. – Hans Passant Nov 7 '11 at 13:00

1 Answer 1

up vote 4 down vote accepted

If you need default item in your struct you can add static property to it

    [StructLayout(LayoutKind.Sequential, Pack = 1)]
    public struct Foo
    {
      UInt32 StartAddr;
      UInt32 Type;

      public static Foo Default
      {
          get 
          {
               Foo result = new Foo();
               result.StartAddr = 200;
               result.Type = 10;
               return result;
          }
      }
    }

And when you need to create new Foo struct just call Foo.Default

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