Crate memoffset

source ·
Expand description

A crate used for calculating offsets of struct members and their spans.

This functionality currently can not be used in compile time code such as const or const fn definitions.

Examples

use memoffset::{offset_of, span_of};

#[repr(C, packed)]
struct HelpMeIAmTrappedInAStructFactory {
    help_me_before_they_: [u8; 15],
    a: u32
}

fn main() {
    assert_eq!(offset_of!(HelpMeIAmTrappedInAStructFactory, a), 15);
    assert_eq!(span_of!(HelpMeIAmTrappedInAStructFactory, a), 15..19);
    assert_eq!(span_of!(HelpMeIAmTrappedInAStructFactory, help_me_before_they_ .. a), 0..15);
}

This functionality can be useful, for example, for checksum calculations:

#[repr(C, packed)]
struct Message {
    header: MessageHeader,
    fragment_index: u32,
    fragment_count: u32,
    payload: [u8; 1024],
    checksum: u16
}

let checksum_range = &raw[span_of!(Message, header..checksum)];
let checksum = crc16(checksum_range);

Macros

Calculates the offset of the specified field from the start of the named struct.
Calculates the offset of the specified union member from the start of the union.
Computes a const raw pointer to the given field of the given base pointer to the given parent type.
Computes a const raw pointer to the given field of the given base pointer to the given parent tuple typle.
Produces a range instance representing the sub-slice containing the specified member.