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Answer: Rust strings use UTF-8 encoding. The common types are owned String and borrowed &str.

String and str

A String is stored as a vector of bytes guaranteed to be valid UTF-8. &str is a slice view onto valid UTF-8 bytes.

Indexing

Indexing a String with [] is discouraged: the return type of that operation is unclear. Use .chars() or .bytes() rather than ambiguous string indexing.

Claims

• id: C1 claim: Strings are UTF-8 encoded. source: S1 evidence: "strings are UTF-8 encoded, so we can include any properly encoded data in them, as"
• id: C2 claim: Indexing into a String is often a bad idea. source: S1 evidence: "indexing into a String is complicated by the differences between how people and computers interpret"
• id: C3 claim: The two most used string types are String and &str. source: S2 evidence: "The two most used string types in Rust are String and &str."
• id: C4 claim: A String is stored as a vector of bytes guaranteed UTF-8. source: S2 evidence: "A String is stored as a vector of bytes (Vec<u8>), but guaranteed to always be"

Sources

• [S1] Storing UTF-8 Encoded Text with Strings. The Rust Project (The Rust Programming Language book). https://doc.rust-lang.org/book/ch08-02-strings.html . License: MIT OR Apache-2.0. Accessed 2026-11-09.
• [S2] Strings - Rust By Example. Rust by Example (rust-lang/rust-by-example). https://doc.rust-lang.org/rust-by-example/std/str.html . License: MIT OR Apache-2.0. Accessed 2026-11-09.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted). Sources and notices: The Rust Programming Language book (rust-lang/book): Copyright (c) 2010 The Rust Project Developers; MIT OR Apache-2.0, used under MIT (https://github.com/rust-lang/book/blob/main/LICENSE-MIT). Rust by Example (rust-lang/rust-by-example): Copyright (c) 2014 Jorge Aparicio; MIT OR Apache-2.0, used under MIT (https://github.com/rust-lang/rust-by-example/blob/master/LICENSE-MIT). Text was condensed and changed from the originals.

@misc{iil_note_49vdhknr,
  author = {{iinventedlight}},
  title = {{Rust Strings and UTF-8 text}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-09},
  url = {https://iinventedlight.com/library/notes/rust-strings-utf8/},
  note = {Permanent ID iil:note:49vdhknr. License: CC-BY-4.0.},
}

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