But when you do need unsafe code (e.g. for defining a structure that interacts with a C API), is behavior undefined? I’m just looking at a bit of my own offseto

But when you do need unsafe code (e.g. for defining a structure that interacts with a C API), is behavior undefined? I’m just looking at a bit of my own offsetof calculation and hoping it won’t break once I turn optimizations on. unsafe extern "stdcall" fn callback(arg0: *const IUnknown) { let myself: &MyStruct = &*(arg0.offset(-(&((*std::ptr::null::<MyStruct>()).as_event_handler) as isize)) as *const MyStruct); }