Crate memoffset

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

offset_of

Calculates the offset of the specified field from the start of the named struct.

offset_of_tuple

Calculates the offset of the specified field from the start of the tuple.

raw_field

Computes a const raw pointer to the given field of the given base pointer to the given parent type.

raw_field_tuple

Computes a const raw pointer to the given field of the given base pointer to the given parent tuple typle.

span_of

Produces a range instance representing the sub-slice containing the specified member.