Strings and Slices

UTF-8 text with owned String and borrowed str slices. Results appear in the same fence: same-line // comments when short, multiline // blocks below the sample when not.

String vs str

String owns UTF-8 bytes; &str borrows them.

let owned = String::from("hi");
let borrowed: &str = &owned;
borrowed.len()  // 2

format Macro

Build owned strings without println.

format!("{}-{}", "a", 1)  // "a-1"

split collect

Split and collect parts.

let v: Vec<_> = "a,b,c".split(',').collect();
v  // ["a", "b", "c"]

chars count

Iterate Unicode scalar values, not bytes.

"é".chars().count()  // 1
"é".len()  // 2 bytes in UTF-8

to_string parse

Parse from strings; format into strings.

"42".parse::<i32>().unwrap()  // 42
42.to_string()  // "42"

push_str push

Grow a String in place.

let mut s = String::from("a");
s.push_str("b");
s.push('!');
s  // "ab!"

contains starts_with

Search helpers on str.

"hello".contains("ell")  // true
"hello".starts_with("he")  // true

trim lines

Whitespace and line iteration.

"  x\n".trim()  // "x"
"a\nb".lines().next()  // Some("a")

replace

Create a new string with replacements.

"a_b_a".replace('a', "x")  // "x_b_x"

Byte Index Danger

Indexing by byte can panic mid-char - prefer chars/get.

"hi".get(0..1)  // Some("h")

from_utf8

Validate bytes as UTF-8.

String::from_utf8(vec![104, 105]).unwrap()  // "hi"

Cow str

Clone-on-write borrowed or owned text.

use std::borrow::Cow;
let c: Cow<str> = "x".into();
c  // "x"

join path-like

Join string slices.

["a", "b"].join("/")  // "a/b"

match str Prefix

Match string prefixes with patterns.

match "https://x" {
    s if s.starts_with("https://") => "secure",
    _ => "other",
}  // "secure"

capacity reserve

Preallocate to reduce reallocs.

let mut s = String::with_capacity(8);
s.push_str("abcd");
s.capacity() >= 8  // true

Related

• Ownership and Borrowing - String moves and &str borrows
• Collections and Iterators - split iterators
• Syntax and Basics - format basics

External Related Links

• Standard Library (std) Docs - Complete API reference for the standard library.
• Rust By Example - Runnable examples covering language features and standard library.
• The Rust Programming Language (The Book) - Canonical beginner-to-intermediate guide (ownership, borrowing, traits, etc.).
• Rust in Action (Amazon) - Tim McNamara on Amazon.
• The Rust Programming Language, 3rd Edition (No Starch) - No Starch Press.

Stack versions: Rust 1.97.0 · edition 2024 · Tokio 1.x · serde 1.0

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