README.md
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 = "0.6"
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 = "0.6"
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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