Show u8 slice in hex representation

Rust 1.26.0 and up

The :x? “debug with hexadecimal integers” formatter can be used:

let data = b"hello";
// lower case
println!("{:x?}", data);
// upper case
println!("{:X?}", data);

let data = [0x0, 0x1, 0xe, 0xf, 0xff];
// print the leading zero
println!("{:02X?}", data);
// It can be combined with the pretty modifier as well
println!("{:#04X?}", data);


[68, 65, 6c, 6c, 6f]
[68, 65, 6C, 6C, 6F]
[00, 01, 0E, 0F, FF]

If you need more control or need to support older versions of Rust, keep reading.

Rust 1.0 and up

use std::fmt::Write;

fn main() {
    let mut s = String::new();
    for &byte in "Hello".as_bytes() {
        write!(&mut s, "{:X} ", byte).expect("Unable to write");

    println!("{}", s);

This can be fancied up by implementing one of the formatting traits (fmt::Debug, fmt::Display, fmt::LowerHex, fmt::UpperHex, etc.) on a wrapper struct and having a little constructor:

use std::fmt;

struct HexSlice<'a>(&'a [u8]);

impl<'a> HexSlice<'a> {
    fn new<T>(data: &'a T) -> HexSlice<'a>
        T: ?Sized + AsRef<[u8]> + 'a,

// You can choose to implement multiple traits, like Lower and UpperHex
impl fmt::Display for HexSlice<'_> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        for byte in self.0 {
            // Decide if you want to pad the value or have spaces inbetween, etc.
            write!(f, "{:X} ", byte)?;

fn main() {
    // To get a `String`
    let s = format!("{}", HexSlice::new("Hello"));

    // Or print it directly
    println!("{}", HexSlice::new("world"));

    // Works with
    HexSlice::new("Hello"); // string slices (&str)
    HexSlice::new(b"Hello"); // byte slices (&[u8])
    HexSlice::new(&"World".to_string()); // References to String
    HexSlice::new(&vec![0x00, 0x01]); // References to Vec<u8>

You can be even fancier and create an extension trait:

trait HexDisplayExt {
    fn hex_display(&self) -> HexSlice<'_>;

impl<T> HexDisplayExt for T
    T: ?Sized + AsRef<[u8]>,
    fn hex_display(&self) -> HexSlice<'_> {

fn main() {
    println!("{}", "world".hex_display());

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