[][src]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.


extern crate memoffset;

#[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:

This example is not tested
#[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);



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


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


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