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

#31 in Rust patterns

Download history 2133122/week @ 2024-10-30 2257158/week @ 2024-11-06 2509493/week @ 2024-11-13 2473588/week @ 2024-11-20 1896560/week @ 2024-11-27 2513063/week @ 2024-12-04 2431918/week @ 2024-12-11 2048670/week @ 2024-12-18 985326/week @ 2024-12-25 1557647/week @ 2025-01-01 2418176/week @ 2025-01-08 2365278/week @ 2025-01-15 2612794/week @ 2025-01-22 2838860/week @ 2025-01-29 2883122/week @ 2025-02-05 2671937/week @ 2025-02-12

11,420,361 downloads per month
Used in 8,041 crates (208 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