Precise memory layout control in Rust?

Question

As far as I know, the Rust compiler is allowed to pack, reorder, and add padding to each field of a struct. How can I specify the precise memory layout if I need it?

In

Answer 1

There's no longer to_uint. In Rust 1.0, the code can be:

#[repr(C, packed)]
struct Object {
    a: i8,
    b: i16,
    c: i32, // other members
}

fn main() {
    let obj = Object {
        a: 0x1a,
        b: 0x1bbb,
        c: 0x1ccccccc,
    };

    let base = &obj as *const _ as usize;
    let a_off = &obj.a as *const _ as usize - base;
    let b_off = &obj.b as *const _ as usize - base;
    let c_off = &obj.c as *const _ as usize - base;

    println!("a: {}", a_off);
    println!("b: {}", b_off);
    println!("c: {}", c_off);
}