Struct CStr

pub struct CStr { /* private fields */ }

Representation of a borrowed C string.

This type represents a borrowed reference to a nul-terminated array of bytes. It can be constructed safely from a &[u8] slice, or unsafely from a raw *const c_char. It can then be converted to a Rust &str by performing UTF-8 validation, or into an owned CString.

&CStr is to CString as &str is to String: the former in each pair are borrowed references; the latter are owned strings.

Note that this structure is not repr(C) and is not recommended to be placed in the signatures of FFI functions. Instead, safe wrappers of FFI functions may leverage the unsafe from_ptr constructor to provide a safe interface to other consumers.

Examples

Inspecting a foreign C string:

use cstr_core::CStr;
use cstr_core::c_char;

extern { fn my_string() -> *const c_char; }

unsafe {
    let slice = CStr::from_ptr(my_string());
    println!("string buffer size without nul terminator: {}", slice.to_bytes().len());
}

Passing a Rust-originating C string:

use cstr_core::{CString, CStr};
use cstr_core::c_char;

fn work(data: &CStr) {
    extern { fn work_with(data: *const c_char); }

    unsafe { work_with(data.as_ptr()) }
}

let s = CString::new("data data data data").expect("CString::new failed");
work(&s);

Converting a foreign C string into a Rust String:

use cstr_core::CStr;
use cstr_core::c_char;

extern { fn my_string() -> *const c_char; }

fn my_string_safe() -> String {
    unsafe {
        CStr::from_ptr(my_string()).to_string_lossy().into_owned()
    }
}

println!("string: {}", my_string_safe());

Implementations

impl CStr

pub unsafe fn from_ptr<'a>(ptr: *const c_char) -> &'a CStr

Wraps a raw C string with a safe C string wrapper.

This function will wrap the provided ptr with a CStr wrapper, which allows inspection and interoperation of non-owned C strings. The total size of the raw C string must be smaller than isize::MAX bytes in memory due to calling the slice::from_raw_parts function. This method is unsafe for a number of reasons:

• There is no guarantee to the validity of ptr.
• The returned lifetime is not guaranteed to be the actual lifetime of ptr.
• There is no guarantee that the memory pointed to by ptr contains a valid nul terminator byte at the end of the string.
• It is not guaranteed that the memory pointed by ptr won’t change before the CStr has been destroyed.

Note: This operation is intended to be a 0-cost cast but it is currently implemented with an up-front calculation of the length of the string. This is not guaranteed to always be the case.

Examples

use cstr_core::CStr;
use cstr_core::c_char;

extern {
    fn my_string() -> *const c_char;
}

unsafe {
    let slice = CStr::from_ptr(my_string());
    println!("string returned: {}", slice.to_str().unwrap());
}

pub fn from_bytes_with_nul(bytes: &[u8]) -> Result<&CStr, FromBytesWithNulError>

Creates a C string wrapper from a byte slice.

This function will cast the provided bytes to a CStr wrapper after ensuring that the byte slice is nul-terminated and does not contain any interior nul bytes.

Examples

use cstr_core::CStr;

let cstr = CStr::from_bytes_with_nul(b"hello\0");
assert!(cstr.is_ok());

Creating a CStr without a trailing nul terminator is an error:

use cstr_core::CStr;

let cstr = CStr::from_bytes_with_nul(b"hello");
assert!(cstr.is_err());

Creating a CStr with an interior nul byte is an error:

use cstr_core::CStr;

let cstr = CStr::from_bytes_with_nul(b"he\0llo\0");
assert!(cstr.is_err());

pub unsafe fn from_bytes_with_nul_unchecked(bytes: &[u8]) -> &CStr

Unsafely creates a C string wrapper from a byte slice.

This function will cast the provided bytes to a CStr wrapper without performing any sanity checks. The provided slice must be nul-terminated and not contain any interior nul bytes.

Examples

use cstr_core::{CStr, CString};

unsafe {
    let cstring = CString::new("hello").expect("CString::new failed");
    let cstr = CStr::from_bytes_with_nul_unchecked(cstring.to_bytes_with_nul());
    assert_eq!(cstr, &*cstring);
}

pub const fn as_ptr(&self) -> *const c_char

Returns the inner pointer to this C string.

The returned pointer will be valid for as long as self is, and points to a contiguous region of memory terminated with a 0 byte to represent the end of the string.

WARNING

The returned pointer is read-only; writing to it (including passing it to C code that writes to it) causes undefined behavior.

It is your responsibility to make sure that the underlying memory is not freed too early. For example, the following code will cause undefined behavior when ptr is used inside the unsafe block:

use cstr_core::CString;

let ptr = CString::new("Hello").expect("CString::new failed").as_ptr();
unsafe {
    // `ptr` is dangling
    *ptr;
}

This happens because the pointer returned by as_ptr does not carry any lifetime information and the CString is deallocated immediately after the CString::new("Hello").expect("CString::new failed").as_ptr() expression is evaluated. To fix the problem, bind the CString to a local variable:

use cstr_core::CString;

let hello = CString::new("Hello").expect("CString::new failed");
let ptr = hello.as_ptr();
unsafe {
    // `ptr` is valid because `hello` is in scope
    *ptr;
}

This way, the lifetime of the CString in hello encompasses the lifetime of ptr and the unsafe block.

pub fn to_bytes(&self) -> &[u8]

Converts this C string to a byte slice.

The returned slice will not contain the trailing nul terminator that this C string has.

Note: This method is currently implemented as a constant-time cast, but it is planned to alter its definition in the future to perform the length calculation whenever this method is called.

Examples

use cstr_core::CStr;

let cstr = CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed");
assert_eq!(cstr.to_bytes(), b"foo");

pub fn to_bytes_with_nul(&self) -> &[u8]

Converts this C string to a byte slice containing the trailing 0 byte.

This function is the equivalent of to_bytes except that it will retain the trailing nul terminator instead of chopping it off.

Note: This method is currently implemented as a 0-cost cast, but it is planned to alter its definition in the future to perform the length calculation whenever this method is called.

Examples

use cstr_core::CStr;

let cstr = CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed");
assert_eq!(cstr.to_bytes_with_nul(), b"foo\0");

pub fn to_str(&self) -> Result<&str, Utf8Error>

Yields a &str slice if the CStr contains valid UTF-8.

If the contents of the CStr are valid UTF-8 data, this function will return the corresponding &str slice. Otherwise, it will return an error with details of where UTF-8 validation failed.

Examples

use cstr_core::CStr;

let cstr = CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed");
assert_eq!(cstr.to_str(), Ok("foo"));

pub fn to_string_lossy(&self) -> Cow<'_, str>

Converts a CStr into a Cow<[str]>.

If the contents of the CStr are valid UTF-8 data, this function will return a Cow::Borrowed(&str) with the corresponding &str slice. Otherwise, it will replace any invalid UTF-8 sequences with U+FFFD REPLACEMENT CHARACTER and return a Cow::Owned(String) with the result.

Examples

Calling to_string_lossy on a CStr containing valid UTF-8:

use std::borrow::Cow;
use cstr_core::CStr;

let cstr = CStr::from_bytes_with_nul(b"Hello World\0")
                 .expect("CStr::from_bytes_with_nul failed");
assert_eq!(cstr.to_string_lossy(), Cow::Borrowed("Hello World"));

Calling to_string_lossy on a CStr containing invalid UTF-8:

use std::borrow::Cow;
use cstr_core::CStr;

let cstr = CStr::from_bytes_with_nul(b"Hello \xF0\x90\x80World\0")
                 .expect("CStr::from_bytes_with_nul failed");
assert_eq!(
    cstr.to_string_lossy(),
    Cow::Owned(String::from("Hello �World")) as Cow<'_, str>
);

pub fn into_c_string(self: Box<CStr>) -> CString

Converts a Box<CStr> into a CString without copying or allocating.

Examples

use cstr_core::CString;

let c_string = CString::new(b"foo".to_vec()).expect("CString::new failed");
let boxed = c_string.into_boxed_c_str();
assert_eq!(boxed.into_c_string(), CString::new("foo").expect("CString::new failed"));

Trait Implementations

impl AsRef<CStr> for CStr

fn as_ref(&self) -> &CStr

Converts this type into a shared reference of the (usually inferred) input type.

impl AsRef<CStr> for CString

fn as_ref(&self) -> &CStr

Converts this type into a shared reference of the (usually inferred) input type.

impl Borrow<CStr> for CString

fn borrow(&self) -> &CStr

Immutably borrows from an owned value.

impl Clone for Box<CStr>

fn clone(&self) -> Self

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for CStr

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<'a> Default for &'a CStr

fn default() -> &'a CStr

Returns the “default value” for a type.

impl Default for Box<CStr>

fn default() -> Box<CStr>

Returns the “default value” for a type.

impl From<&CStr> for Box<CStr>

fn from(s: &CStr) -> Box<CStr>

Converts to this type from the input type.

impl From<&CStr> for CString

fn from(s: &CStr) -> CString

Converts to this type from the input type.

impl<'a> From<&'a CStr> for Cow<'a, CStr>

fn from(s: &'a CStr) -> Cow<'a, CStr>

Converts to this type from the input type.

impl<'a> From<&'a CStr> for Rc<CStr>

fn from(s: &CStr) -> Rc<CStr>

Converts to this type from the input type.

impl From<CString> for Box<CStr>

fn from(s: CString) -> Box<CStr>

Converts a CString into a Box<CStr> without copying or allocating.

impl Hash for CStr

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

impl Ord for CStr

fn cmp(&self, other: &CStr) -> Ordering

This method returns an Ordering between self and other.

impl PartialEq for CStr

fn eq(&self, other: &CStr) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl PartialOrd for CStr

fn partial_cmp(&self, other: &CStr) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

fn lt(&self, other: &Rhs) -> bool

Tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, other: &Rhs) -> bool

Tests greater than (for self and other) and is used by the > operator.

fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for self and other) and is used by the >= operator.

impl ToOwned for CStr

type Owned = CString

The resulting type after obtaining ownership.

fn to_owned(&self) -> CString

Creates owned data from borrowed data, usually by cloning.

fn clone_into(&self, target: &mut Self::Owned)

Uses borrowed data to replace owned data, usually by cloning.

impl Eq for CStr