Raw C string literalLiteral

Explanation

cr"..." (or cr#"..."#) combines the C-string and raw-string forms: a &CStr result with no escape processing, as in cr"C:\path\to\thing".

Useful for FFI constants that both need the C-compatible nul-terminated representation and contain literal backslashes.

Usage examples

Representing a firmware path for FFI

let path: &std::ffi::CStr = cr"C:\firmware\boot"; // <- `cr"..."`: raw (no escapes) C string (&CStr)

Restriction: the content still cannot contain an embedded NUL byte, and matching # delimiters (cr#"..."#) are required if the text itself contains a ".

Working with text

A path handed to a C API needs both nul-termination and, often, literal backslashes — cr"..." prepares that value without pretending to make the FFI call itself.

use std::ffi::CStr;

// A firmware image path for a C loader that expects a nul-terminated C string.
const FIRMWARE_PATH: &CStr = cr"C:\firmware\images\boot.bin"; // <- raw c-string literal: no escapes AND nul-terminated

fn firmware_path() -> &'static CStr {
    FIRMWARE_PATH // ready to pass across an FFI boundary -- the call itself is out of scope here
}

Combining raw and C-string semantics avoids the double burden of escaping every backslash and manually appending a nul terminator — see C string literal for the nul-termination behavior this form inherits unchanged. Like c"...", cr"..." requires Rust 1.77+ and edition 2021 or later.

Explanation

Embedded support: Full

cr"..." inherits both halves unchanged under #![no_std]: the core::ffi::CStr result from a C-string literal, and the raw, no-escape-processing text from a raw string. That combination is genuinely useful in embedded FFI work whenever the fixed, nul-terminated string handed to a vendor C HAL or SDK function itself contains backslashes — a Windows-style path baked into a host-side firmware-flashing tool that calls into a vendor's C flashing library, or a fixed pattern string passed to a C library's matching function — without needing to double every backslash on top of remembering the nul terminator.

Usage examples

Passing a firmware image path to a vendor C flashing SDK

use core::ffi::{c_char, CStr};

extern "C" {
    fn vendor_flash_load_image(path: *const c_char) -> i32;
}

const IMAGE_PATH: &CStr = cr"C:\firmware\images\app.bin"; // <- `cr"..."`: raw (no escapes) + nul-terminated, ready for FFI

fn flash_image() -> i32 {
    unsafe { vendor_flash_load_image(IMAGE_PATH.as_ptr()) }
}