| # memoffset # |
| |
| [](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. |
