20 releases

Uses old Rust 2015

0.9.1 Mar 26, 2024
0.9.0 May 19, 2023
0.8.0 Dec 15, 2022
0.7.1 Oct 17, 2022
0.1.0 Oct 17, 2017

#27 in Rust patterns

Download history 2491130/week @ 2024-12-09 2473405/week @ 2024-12-16 1052899/week @ 2024-12-23 1177228/week @ 2024-12-30 2244185/week @ 2025-01-06 2554321/week @ 2025-01-13 2365544/week @ 2025-01-20 2797828/week @ 2025-01-27 2865862/week @ 2025-02-03 3314771/week @ 2025-02-10 3122171/week @ 2025-02-17 3283227/week @ 2025-02-24 3498693/week @ 2025-03-03 3427814/week @ 2025-03-10 3618162/week @ 2025-03-17 3581131/week @ 2025-03-24

14,296,361 downloads per month
Used in 8,257 crates (209 directly)

MIT license

36KB
583 lines

memoffset

C-Like offset_of functionality for Rust structs.

Introduces the following macros:

  • offset_of! for obtaining the offset of a member of a struct.
  • offset_of_tuple! for obtaining the offset of a member of a tuple. (Requires Rust 1.20+)
  • offset_of_union! for obtaining the offset of a member of a union.
  • span_of! for obtaining the range that a field, or fields, span.

memoffset works under no_std environments.

If you're using a rustc version greater or equal to 1.77, this crate's offset_of!() macro simply forwards to core::mem::offset_of!().

Usage

Add the following dependency to your Cargo.toml:

[dependencies]
memoffset = "0.9"

These versions will compile fine with rustc versions greater or equal to 1.19.

Examples

use memoffset::{offset_of, span_of};

#[repr(C, packed)]
struct Foo {
    a: u32,
    b: u32,
    c: [u8; 5],
    d: u32,
}

fn main() {
    assert_eq!(offset_of!(Foo, b), 4);
    assert_eq!(offset_of!(Foo, d), 4+4+5);

    assert_eq!(span_of!(Foo, a),        0..4);
    assert_eq!(span_of!(Foo, a ..  c),  0..8);
    assert_eq!(span_of!(Foo, a ..= c),  0..13);
    assert_eq!(span_of!(Foo, ..= d),    0..17);
    assert_eq!(span_of!(Foo, b ..),     4..17);
}

Usage in constants

memoffset has support for compile-time offset_of! on rust>=1.65.

On versions below 1.77, this is an incomplete implementation with one caveat: Due to dependence on #![feature(const_refs_to_cell)], you cannot get the offset of a Cell field in a const-context.

No runtime deps