Clippy lint · Pedantic · checked with Clippy 0.1.99

clippy::ptr_offset_by_literal: use of `offset` with a literal

What it meansChecks for usage of the offset pointer method with an integer literal. It is in the pedantic group and off by default.

What you see

warning: use of `offset` with a literal
 --> main.rs:7:5
  |
7 |     ptr.offset(-8);
  |     ^^^^^^^^^^^^^^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#ptr_offset_by_literal
  = note: `-W clippy::ptr-offset-by-literal` implied by `-W clippy::pedantic`
help: use `sub` instead
  |
7 -     ptr.offset(-8);
7 +     ptr.sub(8);
  |

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?

The add and sub methods more accurately express the intent.

Stricter lints with some false positives. Off by default; opt in with clippy::pedantic.

How to fix it

Clippy can fix this one for you: run cargo clippy --fix (add --allow-dirty if you have uncommitted changes). Review the diff before you commit.

Flagged

let vec = vec![b'a', b'b', b'c'];
let ptr = vec.as_ptr();

unsafe {
    ptr.offset(-8);
}

Write this instead

let vec = vec![b'a', b'b', b'c'];
let ptr = vec.as_ptr();

unsafe {
    ptr.sub(8);
}

Turn it off, or on

It is off by default. To use it, set it to warn or deny:

Whole crate (Cargo.toml)

[lints.clippy]
ptr_offset_by_literal = "warn"

In code

#![warn(clippy::ptr_offset_by_literal)]

One run

cargo clippy -- -W clippy::ptr-offset-by-literal

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.

Pedanticgroup

allowdefault level

yesfixed by cargo clippy --fix

1.94.0added in Rust

Clippy's own documentation

What it does

Checks for usage of the offset pointer method with an integer literal.

Why is this bad?

The add and sub methods more accurately express the intent.

Example

let vec = vec![b'a', b'b', b'c'];
let ptr = vec.as_ptr();

unsafe {
    ptr.offset(-8);
}

Could be written:

let vec = vec![b'a', b'b', b'c'];
let ptr = vec.as_ptr();

unsafe {
    ptr.sub(8);
}

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

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