Clippy lint · Complexity · checked with Clippy 0.1.99

clippy::manual_c_str_literals: Checks for the manual creation of C strings (a string with a NUL byte at the end), either through one of the CStr constructor functions, or more plainly by calling .as_ptr() on a (byte) string literal with a hardcoded \0 byte at the end

What it meansChecks for the manual creation of C strings (a string with a NUL byte at the end), either through one of the CStr constructor functions, or more plainly by calling .as_ptr() on a (byte) string literal with a hardcoded \0 byte at the end. It is in the complexity group and warns by default.

Does it matter?

This can be written more concisely using c"str" literals and is also less error-prone, because the compiler checks for interior NUL bytes and the terminating NUL byte is inserted automatically.

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

fn needs_cstr(_: &CStr) {}

needs_cstr(CStr::from_bytes_with_nul(b"Hello\0").unwrap());
unsafe { libc::puts("World\0".as_ptr().cast()) }

Write this instead

fn needs_cstr(_: &CStr) {}

needs_cstr(c"Hello");
unsafe { libc::puts(c"World".as_ptr()) }

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_c_str_literals)]
fn my_function() { /* ... */ }

Whole crate (Cargo.toml)

[lints.clippy]
manual_c_str_literals = "allow"

One run

cargo clippy -- -A clippy::manual-c-str-literals

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.

Settings in clippy.toml

msrv: The minimum rust version that the project supports. Defaults to the rust-version field in Cargo.toml

Complexitygroup

warndefault level

yesfixed by cargo clippy --fix

1.78.0added in Rust

Clippy's own documentation

What it does

Checks for the manual creation of C strings (a string with a NUL byte at the end), either through one of the CStr constructor functions, or more plainly by calling .as_ptr() on a (byte) string literal with a hardcoded \0 byte at the end.

Why is this bad?

This can be written more concisely using c"str" literals and is also less error-prone, because the compiler checks for interior NUL bytes and the terminating NUL byte is inserted automatically.

Example

fn needs_cstr(_: &CStr) {}

needs_cstr(CStr::from_bytes_with_nul(b"Hello\0").unwrap());
unsafe { libc::puts("World\0".as_ptr().cast()) }

Use instead:

fn needs_cstr(_: &CStr) {}

needs_cstr(c"Hello");
unsafe { libc::puts(c"World".as_ptr()) }

Configuration

msrv: The minimum rust version that the project supports. Defaults to the rust-version field in Cargo.toml

(default: current version)

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

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