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https://gitee.com/openharmony/third_party_rust_memoffset
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Since Rust 1.51.0, support for macro addr_of! has been stabilized[1], and this provides a way to get a raw pointer without potential UB in some cases. Memoffset alreadly uses the feature at the pre-stablilized stage (the macro was named as raw_const! then). Therefore, switch to use the stablilized version (and name) if Rust 1.51.0 and above is used, otherwise use the original fallback version, which works in a less technically correct way. [1]: https://github.com/rust-lang/rust/pull/72279 Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
1.8 KiB
1.8 KiB
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:
[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.
#[macro_use]
extern crate memoffset;
Examples
#[macro_use]
extern crate memoffset;
#[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);
}
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:
[dependencies.memoffset]
version = "0.6"
features = ["unstable_const"]
Your crate root: (lib.rs/main.rs)
#![feature(ptr_offset_from, const_ptr_offset_from, const_maybe_uninit_as_ptr, const_raw_ptr_deref)]
If you intend to use offset_of! inside a const fn, also add the const_fn compiler feature.