Marshall an array of structs

Question

I am calling a C++ function from C#. As arguments it receives a pointer to an array of structs.

struct A 
{
    int data;
}

int CFunction (A* pointerToFirstElementOfArray, int NumberOfArrayElements)

In C# I have created the same struct (as a class) and I marshall it correctly (the first element in the array is received correctly). Here is my C# definition of the C++ struct:

[StructLayout(LayoutKind.Sequential), Serializable]
class A
{
    int data;
}

The first element is read correctly so I know all the fields in the struct are marshalled correctly. The problem occurs when I try to send over an array of elements. How do I create an array of classes that will be in a single memory block (chunk), so the C++ function can increment the pointer to the array?

I guess I would need something similar to stackalloc, however I belive that only works for primitive types?

Thank you for your help.

Answer 1

check this post at msdn,

http://msdn.microsoft.com/en-us/library/z6cfh6e6.aspx

check this question too,

http://stackoverflow.com/questions/4033054/fixed-statement-with-jagged-array/4033266#4033266

Answer 2

This is not intended to be a definitive answer, but merely an example of you could accomplish this using stackalloc and unsafe code.

public unsafe class Example
{
  [DllImport("library.dll")]
  private static extern int CFunction(A* pointerToFirstElementOfArray, int NumberOfArrayElements); 

  public void DoSomething()
  {
    A* a = stackalloc A[LENGTH];
    CFunction(a, LENGTH);
  }
}

Also, pay attention to the packing of the struct that the API accepts. You may have to play around with the Pack property of the StructLayout attribute. I believe the default is 4, but some APIs expect 1.

Edit:

For this to work you will have to change the declaration of A from a class to a struct.

public struct A
{
  public int data;
}