rust/src/test/run-pass/packed-struct-layout.rs

// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.


use std::mem;

#[repr(packed)]
struct S4 {
    a: u8,
    b: [u8; 3],
}

#[repr(packed)]
struct S5 {
    a: u8,
    b: u32
}

pub fn main() {
    unsafe {
        let s4 = S4 { a: 1, b: [2,3,4] };
        let transd : [u8; 4] = mem::transmute(s4);
        assert!(transd == [1, 2, 3, 4]);

        let s5 = S5 { a: 1, b: 0xff_00_00_ff };
        let transd : [u8; 5] = mem::transmute(s5);
        // Don't worry about endianness, the u32 is palindromic.
        assert!(transd == [1, 0xff, 0, 0, 0xff]);
    }
}