Clippy lint · Style · checked with Clippy 0.1.99

clippy::manual_dangling_ptr: manual creation of a dangling pointer

What it meansChecks for casts of small constant literals or mem::align_of results to raw pointers. It is in the style group and warns by default.

What you see

warning: manual creation of a dangling pointer
 --> main.rs:3:11
  |
3 | let ptr = 4 as *const u32;
  |           ^^^^^^^^^^^^^^^ help: use: `std::ptr::dangling::<u32>()`
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#manual_dangling_ptr
  = note: `#[warn(clippy::manual_dangling_ptr)]` 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 creates a dangling pointer and is better expressed as {std, core}::ptr::{dangling, dangling_mut}.

Code that works but is not idiomatic Rust. Warns by default.

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 ptr = 4 as *const u32;
let aligned = std::mem::align_of::<u32>() as *const u32;
let mut_ptr: *mut i64 = 8 as *mut _;

Write this instead

let ptr = std::ptr::dangling::<u32>();
let aligned = std::ptr::dangling::<u32>();
let mut_ptr: *mut i64 = std::ptr::dangling_mut();

Turn it off, or on

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

On one item

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

Whole crate (Cargo.toml)

[lints.clippy]
manual_dangling_ptr = "allow"

One run

cargo clippy -- -A clippy::manual-dangling-ptr

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.

Stylegroup

warndefault level

yesfixed by cargo clippy --fix

1.88.0added in Rust

Clippy's own documentation

What it does

Checks for casts of small constant literals or mem::align_of results to raw pointers.

Why is this bad?

This creates a dangling pointer and is better expressed as {std, core}::ptr::{dangling, dangling_mut}.

Example

let ptr = 4 as *const u32;
let aligned = std::mem::align_of::<u32>() as *const u32;
let mut_ptr: *mut i64 = 8 as *mut _;

Use instead:

let ptr = std::ptr::dangling::<u32>();
let aligned = std::ptr::dangling::<u32>();
let mut_ptr: *mut i64 = std::ptr::dangling_mut();

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

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