Clippy lint · Complexity · checked with Clippy 0.1.99

clippy::strlen_on_c_strings: Checks for usage of libc::strlen on a CString or CStr value, and suggest calling count_bytes() instead

What it meansChecks for usage of libc::strlen on a CString or CStr value, and suggest calling count_bytes() instead. It is in the complexity group and warns by default.

Does it matter?

libc::strlen is an unsafe function, which we don’t need to call if all we want to know is the length of the c-string.

Code that does something simple in a complicated way. 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

use std::ffi::CString;
let cstring = CString::new("foo").expect("CString::new failed");
let len = unsafe { libc::strlen(cstring.as_ptr()) };

Write this instead

use std::ffi::CString;
let cstring = CString::new("foo").expect("CString::new failed");
let len = cstring.count_bytes();

Turn it off, or on

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

On one item

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

Whole crate (Cargo.toml)

[lints.clippy]
strlen_on_c_strings = "allow"

One run

cargo clippy -- -A clippy::strlen-on-c-strings

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

yesfixed by cargo clippy --fix

1.55.0added in Rust

Clippy's own documentation

What it does

Checks for usage of libc::strlen on a CString or CStr value, and suggest calling count_bytes() instead.

Why is this bad?

libc::strlen is an unsafe function, which we don’t need to call if all we want to know is the length of the c-string.

Example

use std::ffi::CString;
let cstring = CString::new("foo").expect("CString::new failed");
let len = unsafe { libc::strlen(cstring.as_ptr()) };

Use instead:

use std::ffi::CString;
let cstring = CString::new("foo").expect("CString::new failed");
let len = cstring.count_bytes();

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

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