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+) * span_of! for obtaining the range that a field, or fields, span.

memoffset works under no_std environments.

Usage

Add the following dependency to your Cargo.toml:

toml [dependencies] memoffset = "0.6"

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

Add the following lines at the top of your main.rs or lib.rs files.

```rust,ignore

[macro_use]

extern crate memoffset; ```

Examples

```rust

[macro_use]

extern crate memoffset;

[repr(C, packed)]

struct Foo { a: u32, b: u32, c: [u8; 5], d: u32, }

fn main() { asserteq!(offsetof!(Foo, b), 4); asserteq!(offsetof!(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);

} ```

Feature flags

Usage in constants

memoffset has experimental support for compile-time offset_of! on a nightly compiler.

In order to use it, you must enable the unstable_const crate feature and several compiler features.

Cargo.toml: toml [dependencies.memoffset] version = "0.6" features = ["unstable_const"]

Your crate root: (lib.rs/main.rs) ```rust,ignore

![feature(ptroffsetfrom, constptroffsetfrom, constmaybeuninitasptr, constrawptrderef)]

```

If you intend to use offset_of! inside a const fn, also add the const_fn compiler feature.