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!().
Add the following dependency to your Cargo.toml:
[dependencies]
memoffset = "0.9"These versions will compile fine with rustc versions greater or equal to 1.19.
use memoffset::{offset_of, span_of};#[repr(C, packed)]structFoo{a:u32,b:u32,c:[u8;5],d:u32,}fnmain(){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);}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)], you cannot get the offset of a Cell field in a const-context.