Pinning an updateble struct before passing to unmanaged code?

Question

I using some old API and need to pass the a pointer of a struct to unmanaged code that runs asynchronous.

In other words, after i passing the struct pointer to the unman

Answer 1

Struct example:

[StructLayout(LayoutKind.Sequential)]
public struct OVERLAPPED_STRUCT
{
   public IntPtr InternalLow;
   public IntPtr InternalHigh;
   public Int32 OffsetLow;
   public Int32 OffsetHigh;
   public IntPtr EventHandle;
}

How to pin it to the struct and use it:

OVERLAPPED_STRUCT over_lapped = new OVERLAPPED_STRUCT();
// edit struct in managed code
over_lapped.OffsetLow = 100;
IntPtr pinned_overlap_struct = Marshal.AllocHGlobal(Marshal.SizeOf(over_lapped));
Marshal.StructureToPtr(over_lapped, pinned_overlap_struct, true);

// Pass pinned_overlap_struct to your unmanaged code
// pinned_overlap_struct changes ...

// Get resulting new struct
OVERLAPPED_STRUCT nat_ov = (OVERLAPPED_STRUCT)Marshal.PtrToStructure(pinned_overlap_struct, typeof(OVERLAPPED_STRUCT));
// See what new value is
int offset_low = nat_ov.OffsetLow;
// Clean up
Marshal.FreeHGlobal(pinned_overlap_struct);