Clippy lint · Complexity · checked with Clippy 0.1.99

clippy::zero_prefixed_literal: this is a decimal constant

What it meansWarns if an integral constant literal starts with 0. It is in the complexity group and warns by default.

What you see

warning: this is a decimal constant
 --> main.rs:2:13
  |
2 |     let a = 0123;
  |             ^^^^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#zero_prefixed_literal
  = note: `#[warn(clippy::zero_prefixed_literal)]` on by default
help: if you mean to use a decimal constant, remove the `0` to avoid confusion
  |
2 -     let a = 0123;
2 +     let a = 123;
  |
help: if you mean to use an octal constant, use `0o`
  |
2 |     let a = 0o123;
  |              +

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?

In some languages (including the infamous C language and most of its family), this marks an octal constant. In Rust however, this is a decimal constant. This could be confusing for both the writer and a reader of the constant.

Code that does something simple in a complicated way. Warns by default.

How to fix it

Clippy does not fix this one automatically (its suggestion may change behaviour, so it only shows it). Change the code by hand:

Flagged

fn main() {
    let a = 0123;
    println!("{}", a);
}

Turn it off, or on

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

On one item

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

Whole crate (Cargo.toml)

[lints.clippy]
zero_prefixed_literal = "allow"

One run

cargo clippy -- -A clippy::zero-prefixed-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.

Complexitygroup

warndefault level

nofixed by cargo clippy --fix

pre 1.29.0added in Rust

Clippy's own documentation

What it does

Warns if an integral constant literal starts with 0.

Why is this bad?

Example

In Rust:

fn main() {
    let a = 0123;
    println!("{}", a);
}

prints 123, while in C:

#include <stdio.h>

int main() {
    int a = 0123;
    printf("%d\n", a);
}

prints 83 (as 83 == 0o123 while 123 == 0o173).

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

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