Rust Basics

Rust Strings: String vs &str

Rust has two string types. Learn when to use each, and how to grow, search and split text.

Beginner
2 min read
1 runnable example

What you'll learn

String and &str
push_str and push
contains, split, len

Run code →

Two string types

&str

a borrowed view
fixed size
"Hello"

String

owns its text
can grow
String::from("Hello")

An owned string and a borrowed view

Rust has two main string types. &str is a view of text stored somewhere else, such as a literal in your code. String owns its text and can grow.

String::from copies the literal into a String that the program owns, so push_str and push can add to it. len counts bytes, not characters. split returns the parts between the separator, one at a time.

Key points

&str borrows text stored somewhere else.
String owns its text and can grow.
len counts bytes, not characters.

Runnable Rust example

Rust

Run code →

main.rs

fn main() {
    let greeting = "Hello"; // &str: a borrowed string slice
    let mut message = String::from(greeting); // String: owned and growable
    message.push_str(", Rust");
    message.push('!');

    println!("{message}");
    println!("length: {}", message.len());
    println!("upper: {}", message.to_uppercase());
    println!("contains Rust: {}", message.contains("Rust"));

    for word in message.split(", ") {
        println!("{word}");
    }
}

Get a Run button for this example Result of running the code

Hello, Rust!
length: 12
upper: HELLO, RUST!
contains Rust: true
Hello
Rust!

Practice

Open the example in the online compiler, change a value or add a line, and predict the output before you run it. Then break the code on purpose and read the compiler's message.

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