Calling FORTRAN dll from C# and assigning values to array of structures

Question

I can pass a C# struct into FORTRAN just fine. I can even pass an array of a C# struct as an array of TYPE() in FOR

Answer 1

I have done this in the past using a pointer, not an array. I think that your structures are being copied for the P/Invoke call:

[DllImport("mathlib.dll")]
static extern void TEST_REF(ValueRef* t, int n);

You will need to pin your array before calling the method.

fixed (ValueRef* pointer = t)
{
  TEST_REF(pointer, n);
}

Edit: Based on the comments the solution is to declare the external as

[DllImport("mathlib.dll")]
static extern void TEST_REF([Out] ValueRef[] t, int n);

Here is a MSDN reference on Marshaling of arrays, and how they default to [In].