Function core::str::converts::from_utf8

1.0.0 (const: 1.63.0) · source ·
pub const fn from_utf8(v: &[u8]) -> Result<&str, Utf8Error>
Expand description

Converts a slice of bytes to a string slice.

A string slice (&str) is made of bytes (u8), and a byte slice (&[u8]) is made of bytes, so this function converts between the two. Not all byte slices are valid string slices, however: &str requires that it is valid UTF-8. from_utf8() checks to ensure that the bytes are valid UTF-8, and then does the conversion.

If you are sure that the byte slice is valid UTF-8, and you don’t want to incur the overhead of the validity check, there is an unsafe version of this function, from_utf8_unchecked, which has the same behavior but skips the check.

If you need a String instead of a &str, consider String::from_utf8.

Because you can stack-allocate a [u8; N], and you can take a &[u8] of it, this function is one way to have a stack-allocated string. There is an example of this in the examples section below.


Returns Err if the slice is not UTF-8 with a description as to why the provided slice is not UTF-8.


Basic usage:

use std::str;

// some bytes, in a vector
let sparkle_heart = vec![240, 159, 146, 150];

// We know these bytes are valid, so just use `unwrap()`.
let sparkle_heart = str::from_utf8(&sparkle_heart).unwrap();

assert_eq!("💖", sparkle_heart);

Incorrect bytes:

use std::str;

// some invalid bytes, in a vector
let sparkle_heart = vec![0, 159, 146, 150];


See the docs for Utf8Error for more details on the kinds of errors that can be returned.

A “stack allocated string”:

use std::str;

// some bytes, in a stack-allocated array
let sparkle_heart = [240, 159, 146, 150];

// We know these bytes are valid, so just use `unwrap()`.
let sparkle_heart: &str = str::from_utf8(&sparkle_heart).unwrap();

assert_eq!("💖", sparkle_heart);