https://github.com/Gilnaa/memoffset

offsetof for Rust
https://github.com/Gilnaa/memoffset

Last synced: 2 months ago
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offsetof for Rust

• Host: GitHub
• URL: https://github.com/Gilnaa/memoffset
• Owner: Gilnaa
• License: mit
• Created: 2017-10-16T20:08:21.000Z (over 7 years ago)
• Default Branch: master
• Last Pushed: 2024-03-26T19:58:49.000Z (10 months ago)
• Last Synced: 2024-11-01T16:04:13.170Z (3 months ago)
• Language: Rust
• Size: 156 KB
• Stars: 224
• Watchers: 8
• Forks: 29
• Open Issues: 3
• Metadata Files:
  • Readme: README.md
  • Changelog: CHANGELOG.md
  • License: LICENSE

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README

        
# memoffset #

[![](https://img.shields.io/crates/v/memoffset.svg)](https://crates.io/crates/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`:

```toml

[dependencies]

memoffset = "0.9"

```

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

## Examples ##

```rust

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)]`](https://github.com/rust-lang/rust/issues/80384), you cannot get the offset of a `Cell` field in a const-context.