Clippy lint · Correctness · checked with Clippy 0.1.99

clippy::out_of_bounds_indexing: index is out of bounds

What it meansChecks for out of bounds array indexing with a constant index. It is in the correctness group and denied by default (the build fails).

What you see

error: index is out of bounds
 --> main.rs:5:1
  |
5 | x[9];
  | ^^^^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#out_of_bounds_indexing
  = note: `#[deny(clippy::out_of_bounds_indexing)]` on by default

Real output of Clippy 0.1.99 (Rust 1.99) on the example below. Names and line numbers in yours will differ.

Does it matter?

This will always panic at runtime.

Code that is almost certainly wrong. Denied by default: the build fails until you fix it or allow it.

How to fix it

Clippy does not fix this one automatically. Change the code by hand:

Flagged

let x = [1, 2, 3, 4];

x[9];
&x[2..9];

Write this instead

// Index within bounds

x[0];
x[3];

Turn it off, or on

Allow it where it does not fit your code, as narrowly as you can:

On one item

#[allow(clippy::out_of_bounds_indexing)]
fn my_function() { /* ... */ }

Whole crate (Cargo.toml)

[lints.clippy]
out_of_bounds_indexing = "allow"

One run

cargo clippy -- -A clippy::out-of-bounds-indexing

The [lints] table needs Rust 1.74 or newer. In a workspace, put it under [workspace.lints.clippy] and add [lints] workspace = true to each member.

Correctnessgroup

denydefault level

nofixed by cargo clippy --fix

pre 1.29.0added in Rust

Clippy's own documentation

What it does

Checks for out of bounds array indexing with a constant index.

Why is this bad?

This will always panic at runtime.

Example

let x = [1, 2, 3, 4];

x[9];
&x[2..9];

Use instead:

// Index within bounds

x[0];
x[3];

From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.

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