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// λeonid Onokhov, [19.07.18 00:08]
// А есть макрос offsetof для repr(C) структур?
 
// Антон, [19.07.18 00:24]
// [In reply to λeonid Onokhov]
// На, дарю:
macro_rules! offset_of {
    ($ty:ty, $field:ident) => {{
        let struct_: $ty = unsafe { ::std::mem::uninitialized() };
        let struct_offset: usize = &struct_ as * const _ as usize;
        let field_offset: usize = &struct_.$field as * const _ as usize;
        ::std::mem::forget(struct_);
        field_offset - struct_offset
    }}
}
 
#[repr(C)]
struct Foo {
    a: u32,
    b: char,
    c: u32,
}
 
fn main() {
    println!("{}", offset_of!(Foo, a));
    println!("{}", offset_of!(Foo, b));
    println!("{}", offset_of!(Foo, c));
}
 
// Vladimir, [19.07.18 00:50]
// [In reply to Антон]
// в сишном макросе юзается нулптр, если его заюзать, то будет без мемфоргета
 
macro_rules! offset_of {
    ($ty:ty, $field:ident) => {{
        unsafe{& (*(0 as * const $ty)).$field as *const _ as usize}
    }}
}