Hi Javier,
Ok, I understand :)
Another question, how should I get access to the nested structures?,
some unmanaged functions need access to the structures..
first declare a dummy field for the struct begining with
the first offset of the union:
[StructLayout (LayoutKind.Explicit)]
public struct event_struct {
[FieldOffset(0)] public IntPtr next;
[FieldOffset(4)] public int type;
[FieldOffset(8)] public int unionStart;
....
With Marshal.OffsetOf (typeof (event_struct), "unionStart")
you get the offset of the start of the union within the struct.
Next you have to change all p/invoke declarations to take
an IntPtr as an argument instead of the struct name:
from
static extern int foo (ev_levels input, ev_levels output);
to
static extern int foo (IntPtr input, IntPtr output);
Before you call such a p/invoke method you have to pin the
struct, because the default marshal cannot help you anymore:
int managed_foo (event_struct input , event_struct output)
{
GCHandle h1 = GCHandle.Alloc (input, GCHandleType.Pinned);
GCHandle h2 = GCHandle.Alloc (output, GCHandleType.Pinned);
try {
// this is actually a constant, you may factor the call out.
IntPtr offset = Marshal.OffsetOf (typeof (event_struct),
"unionStart");
return levels_callback (h1.AddrOfPinnedObject () + offset,
h2.AddrOfPinnedObject () + offset);
}
finally {
h1.Free ();
h2.Free ();
}
}
onother way (which I never used with Mono) using "unsafe" code
and pointers:
unsafe int managed_foo (event_struct input , event_struct output)
{
fixed (int* i = &input.ev.input)
fixed (int* o = &output.ev.output) {
return levels_callback (new IntPtr(i), new IntPtr(o));
}
}
> ---------------------------------------
>
> can I create something like this ?
>
> ---------------------------------------
> public struct new_event_struct : event_struct {
> public ev_levels levels {
> get { return ....; }
> }
> }
> ---------------------------------------
I don't know. You must use classes for inheritance. I don't know
how classes and inheritance cope with FieldOffset and StructLayout.
Rob
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