1# memoffset # 2 3[](https://crates.io/crates/memoffset) 4 5C-Like `offset_of` functionality for Rust structs. 6 7Introduces the following macros: 8 * `offset_of!` for obtaining the offset of a member of a struct. 9 * `offset_of_tuple!` for obtaining the offset of a member of a tuple. (Requires Rust 1.20+) 10 * `span_of!` for obtaining the range that a field, or fields, span. 11 12`memoffset` works under `no_std` environments. 13 14## Usage ## 15Add the following dependency to your `Cargo.toml`: 16 17```toml 18[dependencies] 19memoffset = "0.7" 20``` 21 22These versions will compile fine with rustc versions greater or equal to 1.19. 23 24## Examples ## 25```rust 26use memoffset::{offset_of, span_of}; 27 28#[repr(C, packed)] 29struct Foo { 30 a: u32, 31 b: u32, 32 c: [u8; 5], 33 d: u32, 34} 35 36fn main() { 37 assert_eq!(offset_of!(Foo, b), 4); 38 assert_eq!(offset_of!(Foo, d), 4+4+5); 39 40 assert_eq!(span_of!(Foo, a), 0..4); 41 assert_eq!(span_of!(Foo, a .. c), 0..8); 42 assert_eq!(span_of!(Foo, a ..= c), 0..13); 43 assert_eq!(span_of!(Foo, ..= d), 0..17); 44 assert_eq!(span_of!(Foo, b ..), 4..17); 45} 46``` 47 48## Feature flags ## 49 50### Usage in constants ### 51`memoffset` has **experimental** support for compile-time `offset_of!` on a nightly compiler. 52 53In order to use it, you must enable the `unstable_const` crate feature and several compiler features. 54 55Cargo.toml: 56```toml 57[dependencies.memoffset] 58version = "0.7" 59features = ["unstable_const"] 60``` 61 62Your crate root: (`lib.rs`/`main.rs`) 63```rust,ignore 64#![feature(const_ptr_offset_from, const_refs_to_cell)] 65``` 66
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