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//! [`CStr`] and its related types.
use crate::cmp::Ordering;
use crate::error::Error;
use crate::ffi::c_char;
use crate::iter::FusedIterator;
use crate::marker::PhantomData;
use crate::ptr::{addr_of, NonNull};
use crate::slice::memchr;
use crate::{fmt, intrinsics, ops, slice, str};
// FIXME: because this is doc(inline)d, we *have* to use intra-doc links because the actual link
// depends on where the item is being documented. however, since this is libcore, we can't
// actually reference libstd or liballoc in intra-doc links. so, the best we can do is remove the
// links to `CString` and `String` for now until a solution is developed
/// 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 <code>&[[u8]]</code>
/// slice, or unsafely from a raw `*const c_char`. It can be expressed as a
/// literal in the form `c"Hello world"`.
///
/// The `CStr` can then be converted to a Rust <code>&[str]</code> by performing
/// UTF-8 validation, or into an owned `CString`.
///
/// `&CStr` is to `CString` as <code>&[str]</code> is to `String`: the former
/// in each pair are borrowed references; the latter are owned
/// strings.
///
/// Note that this structure does **not** have a guaranteed layout (the `repr(transparent)`
/// notwithstanding) and should not be placed in the signatures of FFI functions.
/// Instead, safe wrappers of FFI functions may leverage [`CStr::as_ptr`] and the unsafe
/// [`CStr::from_ptr`] constructor to provide a safe interface to other consumers.
///
/// # Examples
///
/// Inspecting a foreign C string:
///
/// ```
/// use std::ffi::CStr;
/// use std::os::raw::c_char;
///
/// # /* Extern functions are awkward in doc comments - fake it instead
/// extern "C" { fn my_string() -> *const c_char; }
/// # */ unsafe extern "C" fn my_string() -> *const c_char { c"hello".as_ptr() }
///
/// 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 std::ffi::{CString, CStr};
/// use std::os::raw::c_char;
///
/// fn work(data: &CStr) {
/// # /* Extern functions are awkward in doc comments - fake it instead
/// extern "C" { fn work_with(data: *const c_char); }
/// # */ unsafe extern "C" fn work_with(s: *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 std::ffi::CStr;
/// use std::os::raw::c_char;
///
/// # /* Extern functions are awkward in doc comments - fake it instead
/// extern "C" { fn my_string() -> *const c_char; }
/// # */ unsafe extern "C" fn my_string() -> *const c_char { c"hello".as_ptr() }
///
/// fn my_string_safe() -> String {
/// let cstr = unsafe { CStr::from_ptr(my_string()) };
/// // Get copy-on-write Cow<'_, str>, then guarantee a freshly-owned String allocation
/// String::from_utf8_lossy(cstr.to_bytes()).to_string()
/// }
///
/// println!("string: {}", my_string_safe());
/// ```
///
/// [str]: prim@str "str"
#[derive(PartialEq, Eq, Hash)]
#[stable(feature = "core_c_str", since = "1.64.0")]
#[rustc_diagnostic_item = "cstr_type"]
#[rustc_has_incoherent_inherent_impls]
#[lang = "CStr"]
// `fn from` in `impl From<&CStr> for Box<CStr>` current implementation relies
// on `CStr` being layout-compatible with `[u8]`.
// However, `CStr` layout is considered an implementation detail and must not be relied upon. We
// want `repr(transparent)` but we don't want it to show up in rustdoc, so we hide it under
// `cfg(doc)`. This is an ad-hoc implementation of attribute privacy.
#[repr(transparent)]
pub struct CStr {
// FIXME: this should not be represented with a DST slice but rather with
// just a raw `c_char` along with some form of marker to make
// this an unsized type. Essentially `sizeof(&CStr)` should be the
// same as `sizeof(&c_char)` but `CStr` should be an unsized type.
inner: [c_char],
}
/// An error indicating that a nul byte was not in the expected position.
///
/// The slice used to create a [`CStr`] must have one and only one nul byte,
/// positioned at the end.
///
/// This error is created by the [`CStr::from_bytes_with_nul`] method.
/// See its documentation for more.
///
/// # Examples
///
/// ```
/// use std::ffi::{CStr, FromBytesWithNulError};
///
/// let _: FromBytesWithNulError = CStr::from_bytes_with_nul(b"f\0oo").unwrap_err();
/// ```
#[derive(Clone, PartialEq, Eq, Debug)]
#[stable(feature = "core_c_str", since = "1.64.0")]
pub struct FromBytesWithNulError {
kind: FromBytesWithNulErrorKind,
}
#[derive(Clone, PartialEq, Eq, Debug)]
enum FromBytesWithNulErrorKind {
InteriorNul(usize),
NotNulTerminated,
}
// FIXME: const stability attributes should not be required here, I think
impl FromBytesWithNulError {
#[rustc_const_stable(feature = "const_cstr_methods", since = "1.72.0")]
const fn interior_nul(pos: usize) -> FromBytesWithNulError {
FromBytesWithNulError { kind: FromBytesWithNulErrorKind::InteriorNul(pos) }
}
#[rustc_const_stable(feature = "const_cstr_methods", since = "1.72.0")]
const fn not_nul_terminated() -> FromBytesWithNulError {
FromBytesWithNulError { kind: FromBytesWithNulErrorKind::NotNulTerminated }
}
}
#[stable(feature = "frombyteswithnulerror_impls", since = "1.17.0")]
impl Error for FromBytesWithNulError {
#[allow(deprecated)]
fn description(&self) -> &str {
match self.kind {
FromBytesWithNulErrorKind::InteriorNul(..) => {
"data provided contains an interior nul byte"
}
FromBytesWithNulErrorKind::NotNulTerminated => "data provided is not nul terminated",
}
}
}
/// An error indicating that no nul byte was present.
///
/// A slice used to create a [`CStr`] must contain a nul byte somewhere
/// within the slice.
///
/// This error is created by the [`CStr::from_bytes_until_nul`] method.
///
#[derive(Clone, PartialEq, Eq, Debug)]
#[stable(feature = "cstr_from_bytes_until_nul", since = "1.69.0")]
pub struct FromBytesUntilNulError(());
#[stable(feature = "cstr_from_bytes_until_nul", since = "1.69.0")]
impl fmt::Display for FromBytesUntilNulError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "data provided does not contain a nul")
}
}
#[stable(feature = "cstr_debug", since = "1.3.0")]
impl fmt::Debug for CStr {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "\"{}\"", self.to_bytes().escape_ascii())
}
}
#[stable(feature = "cstr_default", since = "1.10.0")]
impl Default for &CStr {
#[inline]
fn default() -> Self {
const SLICE: &[c_char] = &[0];
// SAFETY: `SLICE` is indeed pointing to a valid nul-terminated string.
unsafe { CStr::from_ptr(SLICE.as_ptr()) }
}
}
#[stable(feature = "frombyteswithnulerror_impls", since = "1.17.0")]
impl fmt::Display for FromBytesWithNulError {
#[allow(deprecated, deprecated_in_future)]
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.write_str(self.description())?;
if let FromBytesWithNulErrorKind::InteriorNul(pos) = self.kind {
write!(f, " at byte pos {pos}")?;
}
Ok(())
}
}
impl 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 terminated buffer must be smaller than [`isize::MAX`] **bytes**
/// in memory (a restriction from [`slice::from_raw_parts`]).
///
/// # Safety
///
/// * The memory pointed to by `ptr` must contain a valid nul terminator at the
/// end of the string.
///
/// * `ptr` must be [valid] for reads of bytes up to and including the nul terminator.
/// This means in particular:
///
/// * The entire memory range of this `CStr` must be contained within a single allocated object!
/// * `ptr` must be non-null even for a zero-length cstr.
///
/// * The memory referenced by the returned `CStr` must not be mutated for
/// the duration of lifetime `'a`.
///
/// * The nul terminator must be within `isize::MAX` from `ptr`
///
/// > **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.
///
/// # Caveat
///
/// The lifetime for the returned slice is inferred from its usage. To prevent accidental misuse,
/// it's suggested to tie the lifetime to whichever source lifetime is safe in the context,
/// such as by providing a helper function taking the lifetime of a host value for the slice,
/// or by explicit annotation.
///
/// # Examples
///
/// ```
/// use std::ffi::{c_char, CStr};
///
/// fn my_string() -> *const c_char {
/// c"hello".as_ptr()
/// }
///
/// unsafe {
/// let slice = CStr::from_ptr(my_string());
/// assert_eq!(slice.to_str().unwrap(), "hello");
/// }
/// ```
///
/// ```
/// use std::ffi::{c_char, CStr};
///
/// const HELLO_PTR: *const c_char = {
/// const BYTES: &[u8] = b"Hello, world!\0";
/// BYTES.as_ptr().cast()
/// };
/// const HELLO: &CStr = unsafe { CStr::from_ptr(HELLO_PTR) };
///
/// assert_eq!(c"Hello, world!", HELLO);
/// ```
///
/// [valid]: core::ptr#safety
#[inline] // inline is necessary for codegen to see strlen.
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_cstr_from_ptr", since = "1.81.0")]
pub const unsafe fn from_ptr<'a>(ptr: *const c_char) -> &'a CStr {
// SAFETY: The caller has provided a pointer that points to a valid C
// string with a NUL terminator less than `isize::MAX` from `ptr`.
let len = unsafe { strlen(ptr) };
// SAFETY: The caller has provided a valid pointer with length less than
// `isize::MAX`, so `from_raw_parts` is safe. The content remains valid
// and doesn't change for the lifetime of the returned `CStr`. This
// means the call to `from_bytes_with_nul_unchecked` is correct.
//
// The cast from c_char to u8 is ok because a c_char is always one byte.
unsafe { Self::from_bytes_with_nul_unchecked(slice::from_raw_parts(ptr.cast(), len + 1)) }
}
/// Creates a C string wrapper from a byte slice with any number of nuls.
///
/// This method will create a `CStr` from any byte slice that contains at
/// least one nul byte. Unlike with [`CStr::from_bytes_with_nul`], the caller
/// does not need to know where the nul byte is located.
///
/// If the first byte is a nul character, this method will return an
/// empty `CStr`. If multiple nul characters are present, the `CStr` will
/// end at the first one.
///
/// If the slice only has a single nul byte at the end, this method is
/// equivalent to [`CStr::from_bytes_with_nul`].
///
/// # Examples
/// ```
/// use std::ffi::CStr;
///
/// let mut buffer = [0u8; 16];
/// unsafe {
/// // Here we might call an unsafe C function that writes a string
/// // into the buffer.
/// let buf_ptr = buffer.as_mut_ptr();
/// buf_ptr.write_bytes(b'A', 8);
/// }
/// // Attempt to extract a C nul-terminated string from the buffer.
/// let c_str = CStr::from_bytes_until_nul(&buffer[..]).unwrap();
/// assert_eq!(c_str.to_str().unwrap(), "AAAAAAAA");
/// ```
///
#[stable(feature = "cstr_from_bytes_until_nul", since = "1.69.0")]
#[rustc_const_stable(feature = "cstr_from_bytes_until_nul", since = "1.69.0")]
pub const fn from_bytes_until_nul(bytes: &[u8]) -> Result<&CStr, FromBytesUntilNulError> {
let nul_pos = memchr::memchr(0, bytes);
match nul_pos {
Some(nul_pos) => {
// FIXME(const-hack) replace with range index
// SAFETY: nul_pos + 1 <= bytes.len()
let subslice = unsafe { crate::slice::from_raw_parts(bytes.as_ptr(), nul_pos + 1) };
// SAFETY: We know there is a nul byte at nul_pos, so this slice
// (ending at the nul byte) is a well-formed C string.
Ok(unsafe { CStr::from_bytes_with_nul_unchecked(subslice) })
}
None => Err(FromBytesUntilNulError(())),
}
}
/// Creates a C string wrapper from a byte slice with exactly one nul
/// terminator.
///
/// 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.
///
/// If the nul byte may not be at the end,
/// [`CStr::from_bytes_until_nul`] can be used instead.
///
/// # Examples
///
/// ```
/// use std::ffi::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 std::ffi::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 std::ffi::CStr;
///
/// let cstr = CStr::from_bytes_with_nul(b"he\0llo\0");
/// assert!(cstr.is_err());
/// ```
#[stable(feature = "cstr_from_bytes", since = "1.10.0")]
#[rustc_const_stable(feature = "const_cstr_methods", since = "1.72.0")]
pub const fn from_bytes_with_nul(bytes: &[u8]) -> Result<&Self, FromBytesWithNulError> {
let nul_pos = memchr::memchr(0, bytes);
match nul_pos {
Some(nul_pos) if nul_pos + 1 == bytes.len() => {
// SAFETY: We know there is only one nul byte, at the end
// of the byte slice.
Ok(unsafe { Self::from_bytes_with_nul_unchecked(bytes) })
}
Some(nul_pos) => Err(FromBytesWithNulError::interior_nul(nul_pos)),
None => Err(FromBytesWithNulError::not_nul_terminated()),
}
}
/// 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.
///
/// # Safety
/// The provided slice **must** be nul-terminated and not contain any interior
/// nul bytes.
///
/// # Examples
///
/// ```
/// use std::ffi::{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);
/// }
/// ```
#[inline]
#[must_use]
#[stable(feature = "cstr_from_bytes", since = "1.10.0")]
#[rustc_const_stable(feature = "const_cstr_unchecked", since = "1.59.0")]
#[rustc_allow_const_fn_unstable(const_eval_select)]
pub const unsafe fn from_bytes_with_nul_unchecked(bytes: &[u8]) -> &CStr {
#[inline]
fn rt_impl(bytes: &[u8]) -> &CStr {
// Chance at catching some UB at runtime with debug builds.
debug_assert!(!bytes.is_empty() && bytes[bytes.len() - 1] == 0);
// SAFETY: Casting to CStr is safe because its internal representation
// is a [u8] too (safe only inside std).
// Dereferencing the obtained pointer is safe because it comes from a
// reference. Making a reference is then safe because its lifetime
// is bound by the lifetime of the given `bytes`.
unsafe { &*(bytes as *const [u8] as *const CStr) }
}
const fn const_impl(bytes: &[u8]) -> &CStr {
// Saturating so that an empty slice panics in the assert with a good
// message, not here due to underflow.
let mut i = bytes.len().saturating_sub(1);
assert!(!bytes.is_empty() && bytes[i] == 0, "input was not nul-terminated");
// Ending nul byte exists, skip to the rest.
while i != 0 {
i -= 1;
let byte = bytes[i];
assert!(byte != 0, "input contained interior nul");
}
// SAFETY: See `rt_impl` cast.
unsafe { &*(bytes as *const [u8] as *const CStr) }
}
intrinsics::const_eval_select((bytes,), const_impl, rt_impl)
}
/// 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.
///
/// The type of the returned pointer is
/// [`*const c_char`][crate::ffi::c_char], and whether it's
/// an alias for `*const i8` or `*const u8` is platform-specific.
///
/// **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:
///
/// ```no_run
/// # #![allow(unused_must_use)] #![allow(temporary_cstring_as_ptr)]
/// use std::ffi::CString;
///
/// // Do not do this:
/// 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:
///
/// ```no_run
/// # #![allow(unused_must_use)]
/// use std::ffi::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.
#[inline]
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_str_as_ptr", since = "1.32.0")]
#[rustc_never_returns_null_ptr]
pub const fn as_ptr(&self) -> *const c_char {
self.inner.as_ptr()
}
/// We could eventually expose this publicly, if we wanted.
#[inline]
#[must_use]
const fn as_non_null_ptr(&self) -> NonNull<c_char> {
// FIXME(effects) replace with `NonNull::from`
// SAFETY: a reference is never null
unsafe { NonNull::new_unchecked(&self.inner as *const [c_char] as *mut [c_char]) }
.as_non_null_ptr()
}
/// Returns the length of `self`. Like C's `strlen`, this does not include the nul terminator.
///
/// > **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 std::ffi::CStr;
///
/// let cstr = CStr::from_bytes_with_nul(b"foo\0").unwrap();
/// assert_eq!(cstr.count_bytes(), 3);
///
/// let cstr = CStr::from_bytes_with_nul(b"\0").unwrap();
/// assert_eq!(cstr.count_bytes(), 0);
/// ```
#[inline]
#[must_use]
#[doc(alias("len", "strlen"))]
#[stable(feature = "cstr_count_bytes", since = "1.79.0")]
#[rustc_const_stable(feature = "const_cstr_from_ptr", since = "1.81.0")]
pub const fn count_bytes(&self) -> usize {
self.inner.len() - 1
}
/// Returns `true` if `self.to_bytes()` has a length of 0.
///
/// # Examples
///
/// ```
/// use std::ffi::CStr;
/// # use std::ffi::FromBytesWithNulError;
///
/// # fn main() { test().unwrap(); }
/// # fn test() -> Result<(), FromBytesWithNulError> {
/// let cstr = CStr::from_bytes_with_nul(b"foo\0")?;
/// assert!(!cstr.is_empty());
///
/// let empty_cstr = CStr::from_bytes_with_nul(b"\0")?;
/// assert!(empty_cstr.is_empty());
/// assert!(c"".is_empty());
/// # Ok(())
/// # }
/// ```
#[inline]
#[stable(feature = "cstr_is_empty", since = "1.71.0")]
#[rustc_const_stable(feature = "cstr_is_empty", since = "1.71.0")]
pub const fn is_empty(&self) -> bool {
// SAFETY: We know there is at least one byte; for empty strings it
// is the NUL terminator.
// FIXME(const-hack): use get_unchecked
unsafe { *self.inner.as_ptr() == 0 }
}
/// 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 std::ffi::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");
/// ```
#[inline]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_cstr_methods", since = "1.72.0")]
pub const fn to_bytes(&self) -> &[u8] {
let bytes = self.to_bytes_with_nul();
// FIXME(const-hack) replace with range index
// SAFETY: to_bytes_with_nul returns slice with length at least 1
unsafe { slice::from_raw_parts(bytes.as_ptr(), bytes.len() - 1) }
}
/// Converts this C string to a byte slice containing the trailing 0 byte.
///
/// This function is the equivalent of [`CStr::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 std::ffi::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");
/// ```
#[inline]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_cstr_methods", since = "1.72.0")]
pub const fn to_bytes_with_nul(&self) -> &[u8] {
// SAFETY: Transmuting a slice of `c_char`s to a slice of `u8`s
// is safe on all supported targets.
unsafe { &*(addr_of!(self.inner) as *const [u8]) }
}
/// Iterates over the bytes in this C string.
///
/// The returned iterator will **not** contain the trailing nul terminator
/// that this C string has.
///
/// # Examples
///
/// ```
/// #![feature(cstr_bytes)]
/// use std::ffi::CStr;
///
/// let cstr = CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed");
/// assert!(cstr.bytes().eq(*b"foo"));
/// ```
#[inline]
#[unstable(feature = "cstr_bytes", issue = "112115")]
pub fn bytes(&self) -> Bytes<'_> {
Bytes::new(self)
}
/// Yields a <code>&[str]</code> 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 <code>&[str]</code> slice. Otherwise,
/// it will return an error with details of where UTF-8 validation failed.
///
/// [str]: prim@str "str"
///
/// # Examples
///
/// ```
/// use std::ffi::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"));
/// ```
#[stable(feature = "cstr_to_str", since = "1.4.0")]
#[rustc_const_stable(feature = "const_cstr_methods", since = "1.72.0")]
pub const fn to_str(&self) -> Result<&str, str::Utf8Error> {
// N.B., when `CStr` is changed to perform the length check in `.to_bytes()`
// instead of in `from_ptr()`, it may be worth considering if this should
// be rewritten to do the UTF-8 check inline with the length calculation
// instead of doing it afterwards.
str::from_utf8(self.to_bytes())
}
}
// `.to_bytes()` representations are compared instead of the inner `[c_char]`s,
// because `c_char` is `i8` (not `u8`) on some platforms.
// That is why this is implemented manually and not derived.
#[stable(feature = "rust1", since = "1.0.0")]
impl PartialOrd for CStr {
#[inline]
fn partial_cmp(&self, other: &CStr) -> Option<Ordering> {
self.to_bytes().partial_cmp(&other.to_bytes())
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl Ord for CStr {
#[inline]
fn cmp(&self, other: &CStr) -> Ordering {
self.to_bytes().cmp(&other.to_bytes())
}
}
#[stable(feature = "cstr_range_from", since = "1.47.0")]
impl ops::Index<ops::RangeFrom<usize>> for CStr {
type Output = CStr;
#[inline]
fn index(&self, index: ops::RangeFrom<usize>) -> &CStr {
let bytes = self.to_bytes_with_nul();
// we need to manually check the starting index to account for the null
// byte, since otherwise we could get an empty string that doesn't end
// in a null.
if index.start < bytes.len() {
// SAFETY: Non-empty tail of a valid `CStr` is still a valid `CStr`.
unsafe { CStr::from_bytes_with_nul_unchecked(&bytes[index.start..]) }
} else {
panic!(
"index out of bounds: the len is {} but the index is {}",
bytes.len(),
index.start
);
}
}
}
#[stable(feature = "cstring_asref", since = "1.7.0")]
impl AsRef<CStr> for CStr {
#[inline]
fn as_ref(&self) -> &CStr {
self
}
}
/// Calculate the length of a nul-terminated string. Defers to C's `strlen` when possible.
///
/// # Safety
///
/// The pointer must point to a valid buffer that contains a NUL terminator. The NUL must be
/// located within `isize::MAX` from `ptr`.
#[inline]
#[unstable(feature = "cstr_internals", issue = "none")]
#[rustc_const_stable(feature = "const_cstr_from_ptr", since = "1.81.0")]
#[rustc_allow_const_fn_unstable(const_eval_select)]
const unsafe fn strlen(ptr: *const c_char) -> usize {
const fn strlen_ct(s: *const c_char) -> usize {
let mut len = 0;
// SAFETY: Outer caller has provided a pointer to a valid C string.
while unsafe { *s.add(len) } != 0 {
len += 1;
}
len
}
#[inline]
fn strlen_rt(s: *const c_char) -> usize {
extern "C" {
/// Provided by libc or compiler_builtins.
fn strlen(s: *const c_char) -> usize;
}
// SAFETY: Outer caller has provided a pointer to a valid C string.
unsafe { strlen(s) }
}
intrinsics::const_eval_select((ptr,), strlen_ct, strlen_rt)
}
/// An iterator over the bytes of a [`CStr`], without the nul terminator.
///
/// This struct is created by the [`bytes`] method on [`CStr`].
/// See its documentation for more.
///
/// [`bytes`]: CStr::bytes
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[unstable(feature = "cstr_bytes", issue = "112115")]
#[derive(Clone, Debug)]
pub struct Bytes<'a> {
// since we know the string is nul-terminated, we only need one pointer
ptr: NonNull<u8>,
phantom: PhantomData<&'a [c_char]>,
}
#[unstable(feature = "cstr_bytes", issue = "112115")]
unsafe impl Send for Bytes<'_> {}
#[unstable(feature = "cstr_bytes", issue = "112115")]
unsafe impl Sync for Bytes<'_> {}
impl<'a> Bytes<'a> {
#[inline]
fn new(s: &'a CStr) -> Self {
Self { ptr: s.as_non_null_ptr().cast(), phantom: PhantomData }
}
#[inline]
fn is_empty(&self) -> bool {
// SAFETY: We uphold that the pointer is always valid to dereference
// by starting with a valid C string and then never incrementing beyond
// the nul terminator.
unsafe { self.ptr.read() == 0 }
}
}
#[unstable(feature = "cstr_bytes", issue = "112115")]
impl Iterator for Bytes<'_> {
type Item = u8;
#[inline]
fn next(&mut self) -> Option<u8> {
// SAFETY: We only choose a pointer from a valid C string, which must
// be non-null and contain at least one value. Since we always stop at
// the nul terminator, which is guaranteed to exist, we can assume that
// the pointer is non-null and valid. This lets us safely dereference
// it and assume that adding 1 will create a new, non-null, valid
// pointer.
unsafe {
let ret = self.ptr.read();
if ret == 0 {
None
} else {
self.ptr = self.ptr.add(1);
Some(ret)
}
}
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
if self.is_empty() { (0, Some(0)) } else { (1, None) }
}
#[inline]
fn count(self) -> usize {
// SAFETY: We always hold a valid pointer to a C string
unsafe { strlen(self.ptr.as_ptr().cast()) }
}
}
#[unstable(feature = "cstr_bytes", issue = "112115")]
impl FusedIterator for Bytes<'_> {}