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android / toolchain / rustc / 341341ca26dc7e8af58cc6f69b6348ca074511c9 / . / library / std / src / ffi / c_str.rs
blob: a68def1e83dbb42c7435f3360c261013b91ecf5f [file] [log] [blame]
#![deny(unsafe_op_in_unsafe_fn)]
#[cfg(test)]
mod tests;
use crate::ascii;
use crate::borrow::{Borrow, Cow};
use crate::cmp::Ordering;
use crate::error::Error;
use crate::fmt::{self, Write};
use crate::io;
use crate::mem;
use crate::num::NonZeroU8;
use crate::ops;
use crate::os::raw::c_char;
use crate::ptr;
use crate::rc::Rc;
use crate::slice;
use crate::str::{self, Utf8Error};
use crate::sync::Arc;
use crate::sys;
use crate::sys_common::memchr;
/// A type representing an owned, C-compatible, nul-terminated string with no nul bytes in the
/// middle.
///
/// This type serves the purpose of being able to safely generate a
/// C-compatible string from a Rust byte slice or vector. An instance of this
/// type is a static guarantee that the underlying bytes contain no interior 0
/// bytes ("nul characters") and that the final byte is 0 ("nul terminator").
///
/// `CString` is to <code>&[CStr]</code> as [`String`] is to <code>&[str]</code>: the former
/// in each pair are owned strings; the latter are borrowed
/// references.
///
/// # Creating a `CString`
///
/// A `CString` is created from either a byte slice or a byte vector,
/// or anything that implements <code>[Into]<[Vec]<[u8]>></code> (for
/// example, you can build a `CString` straight out of a [`String`] or
/// a <code>&[str]</code>, since both implement that trait).
///
/// The [`CString::new`] method will actually check that the provided <code>&[[u8]]</code>
/// does not have 0 bytes in the middle, and return an error if it
/// finds one.
///
/// # Extracting a raw pointer to the whole C string
///
/// `CString` implements an [`as_ptr`][`CStr::as_ptr`] method through the [`Deref`]
/// trait. This method will give you a `*const c_char` which you can
/// feed directly to extern functions that expect a nul-terminated
/// string, like C's `strdup()`. Notice that [`as_ptr`][`CStr::as_ptr`] returns a
/// read-only pointer; if the C code writes to it, that causes
/// undefined behavior.
///
/// # Extracting a slice of the whole C string
///
/// Alternatively, you can obtain a <code>&[[u8]]</code> slice from a
/// `CString` with the [`CString::as_bytes`] method. Slices produced in this
/// way do *not* contain the trailing nul terminator. This is useful
/// when you will be calling an extern function that takes a `*const
/// u8` argument which is not necessarily nul-terminated, plus another
/// argument with the length of the string — like C's `strndup()`.
/// You can of course get the slice's length with its
/// [`len`][slice::len] method.
///
/// If you need a <code>&[[u8]]</code> slice *with* the nul terminator, you
/// can use [`CString::as_bytes_with_nul`] instead.
///
/// Once you have the kind of slice you need (with or without a nul
/// terminator), you can call the slice's own
/// [`as_ptr`][slice::as_ptr] method to get a read-only raw pointer to pass to
/// extern functions. See the documentation for that function for a
/// discussion on ensuring the lifetime of the raw pointer.
///
/// [str]: prim@str "str"
/// [`Deref`]: ops::Deref
///
/// # Examples
///
/// ```ignore (extern-declaration)
/// # fn main() {
/// use std::ffi::CString;
/// use std::os::raw::c_char;
///
/// extern "C" {
/// fn my_printer(s: *const c_char);
/// }
///
/// // We are certain that our string doesn't have 0 bytes in the middle,
/// // so we can .expect()
/// let c_to_print = CString::new("Hello, world!").expect("CString::new failed");
/// unsafe {
/// my_printer(c_to_print.as_ptr());
/// }
/// # }
/// ```
///
/// # Safety
///
/// `CString` is intended for working with traditional C-style strings
/// (a sequence of non-nul bytes terminated by a single nul byte); the
/// primary use case for these kinds of strings is interoperating with C-like
/// code. Often you will need to transfer ownership to/from that external
/// code. It is strongly recommended that you thoroughly read through the
/// documentation of `CString` before use, as improper ownership management
/// of `CString` instances can lead to invalid memory accesses, memory leaks,
/// and other memory errors.
#[derive(PartialEq, PartialOrd, Eq, Ord, Hash, Clone)]
#[cfg_attr(not(test), rustc_diagnostic_item = "cstring_type")]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct CString {
// Invariant 1: the slice ends with a zero byte and has a length of at least one.
// Invariant 2: the slice contains only one zero byte.
// Improper usage of unsafe function can break Invariant 2, but not Invariant 1.
inner: Box<[u8]>,
}
/// 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 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 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 [`CStr::from_ptr`] constructor to provide
/// a safe interface to other consumers.
///
/// # Examples
///
/// Inspecting a foreign C string:
///
/// ```ignore (extern-declaration)
/// use std::ffi::CStr;
/// use std::os::raw::c_char;
///
/// extern "C" { 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:
///
/// ```ignore (extern-declaration)
/// use std::ffi::{CString, CStr};
/// use std::os::raw::c_char;
///
/// fn work(data: &CStr) {
/// extern "C" { 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`]:
///
/// ```ignore (extern-declaration)
/// use std::ffi::CStr;
/// use std::os::raw::c_char;
///
/// extern "C" { 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());
/// ```
///
/// [str]: prim@str "str"
#[derive(Hash)]
#[cfg_attr(not(test), rustc_diagnostic_item = "CStr")]
#[stable(feature = "rust1", since = "1.0.0")]
// FIXME:
// `fn from` in `impl From<&CStr> for Box<CStr>` current implementation relies
// on `CStr` being layout-compatible with `[u8]`.
// When attribute privacy is implemented, `CStr` should be annotated as `#[repr(transparent)]`.
// Anyway, `CStr` representation and layout are considered implementation detail, are
// not documented and must not be relied upon.
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 an interior nul byte was found.
///
/// While Rust strings may contain nul bytes in the middle, C strings
/// can't, as that byte would effectively truncate the string.
///
/// This error is created by the [`new`][`CString::new`] method on
/// [`CString`]. See its documentation for more.
///
/// # Examples
///
/// ```
/// use std::ffi::{CString, NulError};
///
/// let _: NulError = CString::new(b"f\0oo".to_vec()).unwrap_err();
/// ```
#[derive(Clone, PartialEq, Eq, Debug)]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct NulError(usize, Vec<u8>);
/// 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 = "cstr_from_bytes", since = "1.10.0")]
pub struct FromBytesWithNulError {
kind: FromBytesWithNulErrorKind,
}
/// An error indicating that a nul byte was not in the expected position.
///
/// The vector used to create a [`CString`] must have one and only one nul byte,
/// positioned at the end.
///
/// This error is created by the [`CString::from_vec_with_nul`] method.
/// See its documentation for more.
///
/// # Examples
///
/// ```
/// use std::ffi::{CString, FromVecWithNulError};
///
/// let _: FromVecWithNulError = CString::from_vec_with_nul(b"f\0oo".to_vec()).unwrap_err();
/// ```
#[derive(Clone, PartialEq, Eq, Debug)]
#[stable(feature = "cstring_from_vec_with_nul", since = "1.58.0")]
pub struct FromVecWithNulError {
error_kind: FromBytesWithNulErrorKind,
bytes: Vec<u8>,
}
#[derive(Clone, PartialEq, Eq, Debug)]
enum FromBytesWithNulErrorKind {
InteriorNul(usize),
NotNulTerminated,
}
impl FromBytesWithNulError {
fn interior_nul(pos: usize) -> FromBytesWithNulError {
FromBytesWithNulError { kind: FromBytesWithNulErrorKind::InteriorNul(pos) }
}
fn not_nul_terminated() -> FromBytesWithNulError {
FromBytesWithNulError { kind: FromBytesWithNulErrorKind::NotNulTerminated }
}
}
#[stable(feature = "cstring_from_vec_with_nul", since = "1.58.0")]
impl FromVecWithNulError {
/// Returns a slice of [`u8`]s bytes that were attempted to convert to a [`CString`].
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::ffi::CString;
///
/// // Some invalid bytes in a vector
/// let bytes = b"f\0oo".to_vec();
///
/// let value = CString::from_vec_with_nul(bytes.clone());
///
/// assert_eq!(&bytes[..], value.unwrap_err().as_bytes());
/// ```
#[must_use]
#[stable(feature = "cstring_from_vec_with_nul", since = "1.58.0")]
pub fn as_bytes(&self) -> &[u8] {
&self.bytes[..]
}
/// Returns the bytes that were attempted to convert to a [`CString`].
///
/// This method is carefully constructed to avoid allocation. It will
/// consume the error, moving out the bytes, so that a copy of the bytes
/// does not need to be made.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::ffi::CString;
///
/// // Some invalid bytes in a vector
/// let bytes = b"f\0oo".to_vec();
///
/// let value = CString::from_vec_with_nul(bytes.clone());
///
/// assert_eq!(bytes, value.unwrap_err().into_bytes());
/// ```
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "cstring_from_vec_with_nul", since = "1.58.0")]
pub fn into_bytes(self) -> Vec<u8> {
self.bytes
}
}
/// 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)]
#[unstable(feature = "cstr_from_bytes_until_nul", issue = "95027")]
pub struct FromBytesUntilNulError(());
#[unstable(feature = "cstr_from_bytes_until_nul", issue = "95027")]
impl Error for FromBytesUntilNulError {}
#[unstable(feature = "cstr_from_bytes_until_nul", issue = "95027")]
impl fmt::Display for FromBytesUntilNulError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "data provided does not contain a nul")
}
}
/// An error indicating invalid UTF-8 when converting a [`CString`] into a [`String`].
///
/// `CString` is just a wrapper over a buffer of bytes with a nul terminator;
/// [`CString::into_string`] performs UTF-8 validation on those bytes and may
/// return this error.
///
/// This `struct` is created by [`CString::into_string()`]. See
/// its documentation for more.
#[derive(Clone, PartialEq, Eq, Debug)]
#[stable(feature = "cstring_into", since = "1.7.0")]
pub struct IntoStringError {
inner: CString,
error: Utf8Error,
}
impl CString {
/// Creates a new C-compatible string from a container of bytes.
///
/// This function will consume the provided data and use the
/// underlying bytes to construct a new string, ensuring that
/// there is a trailing 0 byte. This trailing 0 byte will be
/// appended by this function; the provided data should *not*
/// contain any 0 bytes in it.
///
/// # Examples
///
/// ```ignore (extern-declaration)
/// use std::ffi::CString;
/// use std::os::raw::c_char;
///
/// extern "C" { fn puts(s: *const c_char); }
///
/// let to_print = CString::new("Hello!").expect("CString::new failed");
/// unsafe {
/// puts(to_print.as_ptr());
/// }
/// ```
///
/// # Errors
///
/// This function will return an error if the supplied bytes contain an
/// internal 0 byte. The [`NulError`] returned will contain the bytes as well as
/// the position of the nul byte.
#[stable(feature = "rust1", since = "1.0.0")]
pub fn new<T: Into<Vec<u8>>>(t: T) -> Result<CString, NulError> {
trait SpecNewImpl {
fn spec_new_impl(self) -> Result<CString, NulError>;
}
impl<T: Into<Vec<u8>>> SpecNewImpl for T {
default fn spec_new_impl(self) -> Result<CString, NulError> {
let bytes: Vec<u8> = self.into();
match memchr::memchr(0, &bytes) {
Some(i) => Err(NulError(i, bytes)),
None => Ok(unsafe { CString::_from_vec_unchecked(bytes) }),
}
}
}
// Specialization for avoiding reallocation
#[inline(always)] // Without that it is not inlined into specializations
fn spec_new_impl_bytes(bytes: &[u8]) -> Result<CString, NulError> {
// We cannot have such large slice that we would overflow here
// but using `checked_add` allows LLVM to assume that capacity never overflows
// and generate twice shorter code.
// `saturating_add` doesn't help for some reason.
let capacity = bytes.len().checked_add(1).unwrap();
// Allocate before validation to avoid duplication of allocation code.
// We still need to allocate and copy memory even if we get an error.
let mut buffer = Vec::with_capacity(capacity);
buffer.extend(bytes);
// Check memory of self instead of new buffer.
// This allows better optimizations if lto enabled.
match memchr::memchr(0, bytes) {
Some(i) => Err(NulError(i, buffer)),
None => Ok(unsafe { CString::_from_vec_unchecked(buffer) }),
}
}
impl SpecNewImpl for &'_ [u8] {
fn spec_new_impl(self) -> Result<CString, NulError> {
spec_new_impl_bytes(self)
}
}
impl SpecNewImpl for &'_ str {
fn spec_new_impl(self) -> Result<CString, NulError> {
spec_new_impl_bytes(self.as_bytes())
}
}
impl SpecNewImpl for &'_ mut [u8] {
fn spec_new_impl(self) -> Result<CString, NulError> {
spec_new_impl_bytes(self)
}
}
t.spec_new_impl()
}
/// Creates a C-compatible string by consuming a byte vector,
/// without checking for interior 0 bytes.
///
/// Trailing 0 byte will be appended by this function.
///
/// This method is equivalent to [`CString::new`] except that no runtime
/// assertion is made that `v` contains no 0 bytes, and it requires an
/// actual byte vector, not anything that can be converted to one with Into.
///
/// # Examples
///
/// ```
/// use std::ffi::CString;
///
/// let raw = b"foo".to_vec();
/// unsafe {
/// let c_string = CString::from_vec_unchecked(raw);
/// }
/// ```
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
pub unsafe fn from_vec_unchecked(v: Vec<u8>) -> Self {
debug_assert!(memchr::memchr(0, &v).is_none());
unsafe { Self::_from_vec_unchecked(v) }
}
unsafe fn _from_vec_unchecked(mut v: Vec<u8>) -> Self {
v.reserve_exact(1);
v.push(0);
Self { inner: v.into_boxed_slice() }
}
/// Retakes ownership of a `CString` that was transferred to C via
/// [`CString::into_raw`].
///
/// Additionally, the length of the string will be recalculated from the pointer.
///
/// # Safety
///
/// This should only ever be called with a pointer that was earlier
/// obtained by calling [`CString::into_raw`]. Other usage (e.g., trying to take
/// ownership of a string that was allocated by foreign code) is likely to lead
/// to undefined behavior or allocator corruption.
///
/// It should be noted that the length isn't just "recomputed," but that
/// the recomputed length must match the original length from the
/// [`CString::into_raw`] call. This means the [`CString::into_raw`]/`from_raw`
/// methods should not be used when passing the string to C functions that can
/// modify the string's length.
///
/// > **Note:** If you need to borrow a string that was allocated by
/// > foreign code, use [`CStr`]. If you need to take ownership of
/// > a string that was allocated by foreign code, you will need to
/// > make your own provisions for freeing it appropriately, likely
/// > with the foreign code's API to do that.
///
/// # Examples
///
/// Creates a `CString`, pass ownership to an `extern` function (via raw pointer), then retake
/// ownership with `from_raw`:
///
/// ```ignore (extern-declaration)
/// use std::ffi::CString;
/// use std::os::raw::c_char;
///
/// extern "C" {
/// fn some_extern_function(s: *mut c_char);
/// }
///
/// let c_string = CString::new("Hello!").expect("CString::new failed");
/// let raw = c_string.into_raw();
/// unsafe {
/// some_extern_function(raw);
/// let c_string = CString::from_raw(raw);
/// }
/// ```
#[must_use = "call `drop(from_raw(ptr))` if you intend to drop the `CString`"]
#[stable(feature = "cstr_memory", since = "1.4.0")]
pub unsafe fn from_raw(ptr: *mut c_char) -> CString {
// SAFETY: This is called with a pointer that was obtained from a call
// to `CString::into_raw` and the length has not been modified. As such,
// we know there is a NUL byte (and only one) at the end and that the
// information about the size of the allocation is correct on Rust's
// side.
unsafe {
let len = sys::strlen(ptr) + 1; // Including the NUL byte
let slice = slice::from_raw_parts_mut(ptr, len as usize);
CString { inner: Box::from_raw(slice as *mut [c_char] as *mut [u8]) }
}
}
/// Consumes the `CString` and transfers ownership of the string to a C caller.
///
/// The pointer which this function returns must be returned to Rust and reconstituted using
/// [`CString::from_raw`] to be properly deallocated. Specifically, one
/// should *not* use the standard C `free()` function to deallocate
/// this string.
///
/// Failure to call [`CString::from_raw`] will lead to a memory leak.
///
/// The C side must **not** modify the length of the string (by writing a
/// `null` somewhere inside the string or removing the final one) before
/// it makes it back into Rust using [`CString::from_raw`]. See the safety section
/// in [`CString::from_raw`].
///
/// # Examples
///
/// ```
/// use std::ffi::CString;
///
/// let c_string = CString::new("foo").expect("CString::new failed");
///
/// let ptr = c_string.into_raw();
///
/// unsafe {
/// assert_eq!(b'f', *ptr as u8);
/// assert_eq!(b'o', *ptr.offset(1) as u8);
/// assert_eq!(b'o', *ptr.offset(2) as u8);
/// assert_eq!(b'\0', *ptr.offset(3) as u8);
///
/// // retake pointer to free memory
/// let _ = CString::from_raw(ptr);
/// }
/// ```
#[inline]
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "cstr_memory", since = "1.4.0")]
pub fn into_raw(self) -> *mut c_char {
Box::into_raw(self.into_inner()) as *mut c_char
}
/// Converts the `CString` into a [`String`] if it contains valid UTF-8 data.
///
/// On failure, ownership of the original `CString` is returned.
///
/// # Examples
///
/// ```
/// use std::ffi::CString;
///
/// let valid_utf8 = vec![b'f', b'o', b'o'];
/// let cstring = CString::new(valid_utf8).expect("CString::new failed");
/// assert_eq!(cstring.into_string().expect("into_string() call failed"), "foo");
///
/// let invalid_utf8 = vec![b'f', 0xff, b'o', b'o'];
/// let cstring = CString::new(invalid_utf8).expect("CString::new failed");
/// let err = cstring.into_string().err().expect("into_string().err() failed");
/// assert_eq!(err.utf8_error().valid_up_to(), 1);
/// ```
#[stable(feature = "cstring_into", since = "1.7.0")]
pub fn into_string(self) -> Result<String, IntoStringError> {
String::from_utf8(self.into_bytes()).map_err(|e| IntoStringError {
error: e.utf8_error(),
inner: unsafe { Self::_from_vec_unchecked(e.into_bytes()) },
})
}
/// Consumes the `CString` and returns the underlying byte buffer.
///
/// The returned buffer does **not** contain the trailing nul
/// terminator, and it is guaranteed to not have any interior nul
/// bytes.
///
/// # Examples
///
/// ```
/// use std::ffi::CString;
///
/// let c_string = CString::new("foo").expect("CString::new failed");
/// let bytes = c_string.into_bytes();
/// assert_eq!(bytes, vec![b'f', b'o', b'o']);
/// ```
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "cstring_into", since = "1.7.0")]
pub fn into_bytes(self) -> Vec<u8> {
let mut vec = self.into_inner().into_vec();
let _nul = vec.pop();
debug_assert_eq!(_nul, Some(0u8));
vec
}
/// Equivalent to [`CString::into_bytes()`] except that the
/// returned vector includes the trailing nul terminator.
///
/// # Examples
///
/// ```
/// use std::ffi::CString;
///
/// let c_string = CString::new("foo").expect("CString::new failed");
/// let bytes = c_string.into_bytes_with_nul();
/// assert_eq!(bytes, vec![b'f', b'o', b'o', b'\0']);
/// ```
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "cstring_into", since = "1.7.0")]
pub fn into_bytes_with_nul(self) -> Vec<u8> {
self.into_inner().into_vec()
}
/// Returns the contents of this `CString` as a slice of bytes.
///
/// The returned slice does **not** contain the trailing nul
/// terminator, and it is guaranteed to not have any interior nul
/// bytes. If you need the nul terminator, use
/// [`CString::as_bytes_with_nul`] instead.
///
/// # Examples
///
/// ```
/// use std::ffi::CString;
///
/// let c_string = CString::new("foo").expect("CString::new failed");
/// let bytes = c_string.as_bytes();
/// assert_eq!(bytes, &[b'f', b'o', b'o']);
/// ```
#[inline]
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn as_bytes(&self) -> &[u8] {
// SAFETY: CString has a length at least 1
unsafe { self.inner.get_unchecked(..self.inner.len() - 1) }
}
/// Equivalent to [`CString::as_bytes()`] except that the
/// returned slice includes the trailing nul terminator.
///
/// # Examples
///
/// ```
/// use std::ffi::CString;
///
/// let c_string = CString::new("foo").expect("CString::new failed");
/// let bytes = c_string.as_bytes_with_nul();
/// assert_eq!(bytes, &[b'f', b'o', b'o', b'\0']);
/// ```
#[inline]
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn as_bytes_with_nul(&self) -> &[u8] {
&self.inner
}
/// Extracts a [`CStr`] slice containing the entire string.
///
/// # Examples
///
/// ```
/// use std::ffi::{CString, CStr};
///
/// let c_string = CString::new(b"foo".to_vec()).expect("CString::new failed");
/// let cstr = c_string.as_c_str();
/// assert_eq!(cstr,
/// CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed"));
/// ```
#[inline]
#[must_use]
#[stable(feature = "as_c_str", since = "1.20.0")]
pub fn as_c_str(&self) -> &CStr {
&*self
}
/// Converts this `CString` into a boxed [`CStr`].
///
/// # Examples
///
/// ```
/// use std::ffi::{CString, CStr};
///
/// let c_string = CString::new(b"foo".to_vec()).expect("CString::new failed");
/// let boxed = c_string.into_boxed_c_str();
/// assert_eq!(&*boxed,
/// CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed"));
/// ```
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "into_boxed_c_str", since = "1.20.0")]
pub fn into_boxed_c_str(self) -> Box<CStr> {
unsafe { Box::from_raw(Box::into_raw(self.into_inner()) as *mut CStr) }
}
/// Bypass "move out of struct which implements [`Drop`] trait" restriction.
#[inline]
fn into_inner(self) -> Box<[u8]> {
// Rationale: `mem::forget(self)` invalidates the previous call to `ptr::read(&self.inner)`
// so we use `ManuallyDrop` to ensure `self` is not dropped.
// Then we can return the box directly without invalidating it.
// See https://github.com/rust-lang/rust/issues/62553.
let this = mem::ManuallyDrop::new(self);
unsafe { ptr::read(&this.inner) }
}
/// Converts a <code>[Vec]<[u8]></code> to a [`CString`] without checking the
/// invariants on the given [`Vec`].
///
/// # Safety
///
/// The given [`Vec`] **must** have one nul byte as its last element.
/// This means it cannot be empty nor have any other nul byte anywhere else.
///
/// # Example
///
/// ```
/// use std::ffi::CString;
/// assert_eq!(
/// unsafe { CString::from_vec_with_nul_unchecked(b"abc\0".to_vec()) },
/// unsafe { CString::from_vec_unchecked(b"abc".to_vec()) }
/// );
/// ```
#[must_use]
#[stable(feature = "cstring_from_vec_with_nul", since = "1.58.0")]
pub unsafe fn from_vec_with_nul_unchecked(v: Vec<u8>) -> Self {
debug_assert!(memchr::memchr(0, &v).unwrap() + 1 == v.len());
unsafe { Self::_from_vec_with_nul_unchecked(v) }
}
unsafe fn _from_vec_with_nul_unchecked(v: Vec<u8>) -> Self {
Self { inner: v.into_boxed_slice() }
}
/// Attempts to converts a <code>[Vec]<[u8]></code> to a [`CString`].
///
/// Runtime checks are present to ensure there is only one nul byte in the
/// [`Vec`], its last element.
///
/// # Errors
///
/// If a nul byte is present and not the last element or no nul bytes
/// is present, an error will be returned.
///
/// # Examples
///
/// A successful conversion will produce the same result as [`CString::new`]
/// when called without the ending nul byte.
///
/// ```
/// use std::ffi::CString;
/// assert_eq!(
/// CString::from_vec_with_nul(b"abc\0".to_vec())
/// .expect("CString::from_vec_with_nul failed"),
/// CString::new(b"abc".to_vec()).expect("CString::new failed")
/// );
/// ```
///
/// An incorrectly formatted [`Vec`] will produce an error.
///
/// ```
/// use std::ffi::{CString, FromVecWithNulError};
/// // Interior nul byte
/// let _: FromVecWithNulError = CString::from_vec_with_nul(b"a\0bc".to_vec()).unwrap_err();
/// // No nul byte
/// let _: FromVecWithNulError = CString::from_vec_with_nul(b"abc".to_vec()).unwrap_err();
/// ```
#[stable(feature = "cstring_from_vec_with_nul", since = "1.58.0")]
pub fn from_vec_with_nul(v: Vec<u8>) -> Result<Self, FromVecWithNulError> {
let nul_pos = memchr::memchr(0, &v);
match nul_pos {
Some(nul_pos) if nul_pos + 1 == v.len() => {
// SAFETY: We know there is only one nul byte, at the end
// of the vec.
Ok(unsafe { Self::_from_vec_with_nul_unchecked(v) })
}
Some(nul_pos) => Err(FromVecWithNulError {
error_kind: FromBytesWithNulErrorKind::InteriorNul(nul_pos),
bytes: v,
}),
None => Err(FromVecWithNulError {
error_kind: FromBytesWithNulErrorKind::NotNulTerminated,
bytes: v,
}),
}
}
}
// Turns this `CString` into an empty string to prevent
// memory-unsafe code from working by accident. Inline
// to prevent LLVM from optimizing it away in debug builds.
#[stable(feature = "cstring_drop", since = "1.13.0")]
impl Drop for CString {
#[inline]
fn drop(&mut self) {
unsafe {
*self.inner.get_unchecked_mut(0) = 0;
}
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl ops::Deref for CString {
type Target = CStr;
#[inline]
fn deref(&self) -> &CStr {
unsafe { CStr::_from_bytes_with_nul_unchecked(self.as_bytes_with_nul()) }
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl fmt::Debug for CString {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Debug::fmt(&**self, f)
}
}
#[stable(feature = "cstring_into", since = "1.7.0")]
impl From<CString> for Vec<u8> {
/// Converts a [`CString`] into a <code>[Vec]<[u8]></code>.
///
/// The conversion consumes the [`CString`], and removes the terminating NUL byte.
#[inline]
fn from(s: CString) -> Vec<u8> {
s.into_bytes()
}
}
#[stable(feature = "cstr_debug", since = "1.3.0")]
impl fmt::Debug for CStr {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "\"")?;
for byte in self.to_bytes().iter().flat_map(|&b| ascii::escape_default(b)) {
f.write_char(byte as char)?;
}
write!(f, "\"")
}
}
#[stable(feature = "cstr_default", since = "1.10.0")]
impl Default for &CStr {
fn default() -> Self {
const SLICE: &[c_char] = &[0];
unsafe { CStr::from_ptr(SLICE.as_ptr()) }
}
}
#[stable(feature = "cstr_default", since = "1.10.0")]
impl Default for CString {
/// Creates an empty `CString`.
fn default() -> CString {
let a: &CStr = Default::default();
a.to_owned()
}
}
#[stable(feature = "cstr_borrow", since = "1.3.0")]
impl Borrow<CStr> for CString {
#[inline]
fn borrow(&self) -> &CStr {
self
}
}
#[stable(feature = "cstring_from_cow_cstr", since = "1.28.0")]
impl<'a> From<Cow<'a, CStr>> for CString {
/// Converts a `Cow<'a, CStr>` into a `CString`, by copying the contents if they are
/// borrowed.
#[inline]
fn from(s: Cow<'a, CStr>) -> Self {
s.into_owned()
}
}
#[stable(feature = "box_from_c_str", since = "1.17.0")]
impl From<&CStr> for Box<CStr> {
/// Converts a `&CStr` into a `Box<CStr>`,
/// by copying the contents into a newly allocated [`Box`].
fn from(s: &CStr) -> Box<CStr> {
let boxed: Box<[u8]> = Box::from(s.to_bytes_with_nul());
unsafe { Box::from_raw(Box::into_raw(boxed) as *mut CStr) }
}
}
#[stable(feature = "box_from_cow", since = "1.45.0")]
impl From<Cow<'_, CStr>> for Box<CStr> {
/// Converts a `Cow<'a, CStr>` into a `Box<CStr>`,
/// by copying the contents if they are borrowed.
#[inline]
fn from(cow: Cow<'_, CStr>) -> Box<CStr> {
match cow {
Cow::Borrowed(s) => Box::from(s),
Cow::Owned(s) => Box::from(s),
}
}
}
#[stable(feature = "c_string_from_box", since = "1.18.0")]
impl From<Box<CStr>> for CString {
/// Converts a <code>[Box]<[CStr]></code> into a [`CString`] without copying or allocating.
#[inline]
fn from(s: Box<CStr>) -> CString {
s.into_c_string()
}
}
#[stable(feature = "cstring_from_vec_of_nonzerou8", since = "1.43.0")]
impl From<Vec<NonZeroU8>> for CString {
/// Converts a <code>[Vec]<[NonZeroU8]></code> into a [`CString`] without
/// copying nor checking for inner null bytes.
#[inline]
fn from(v: Vec<NonZeroU8>) -> CString {
unsafe {
// Transmute `Vec<NonZeroU8>` to `Vec<u8>`.
let v: Vec<u8> = {
// SAFETY:
// - transmuting between `NonZeroU8` and `u8` is sound;
// - `alloc::Layout<NonZeroU8> == alloc::Layout<u8>`.
let (ptr, len, cap): (*mut NonZeroU8, _, _) = Vec::into_raw_parts(v);
Vec::from_raw_parts(ptr.cast::<u8>(), len, cap)
};
// SAFETY: `v` cannot contain null bytes, given the type-level
// invariant of `NonZeroU8`.
Self::_from_vec_unchecked(v)
}
}
}
#[stable(feature = "more_box_slice_clone", since = "1.29.0")]
impl Clone for Box<CStr> {
#[inline]
fn clone(&self) -> Self {
(**self).into()
}
}
#[stable(feature = "box_from_c_string", since = "1.20.0")]
impl From<CString> for Box<CStr> {
/// Converts a [`CString`] into a <code>[Box]<[CStr]></code> without copying or allocating.
#[inline]
fn from(s: CString) -> Box<CStr> {
s.into_boxed_c_str()
}
}
#[stable(feature = "cow_from_cstr", since = "1.28.0")]
impl<'a> From<CString> for Cow<'a, CStr> {
/// Converts a [`CString`] into an owned [`Cow`] without copying or allocating.
#[inline]
fn from(s: CString) -> Cow<'a, CStr> {
Cow::Owned(s)
}
}
#[stable(feature = "cow_from_cstr", since = "1.28.0")]
impl<'a> From<&'a CStr> for Cow<'a, CStr> {
/// Converts a [`CStr`] into a borrowed [`Cow`] without copying or allocating.
#[inline]
fn from(s: &'a CStr) -> Cow<'a, CStr> {
Cow::Borrowed(s)
}
}
#[stable(feature = "cow_from_cstr", since = "1.28.0")]
impl<'a> From<&'a CString> for Cow<'a, CStr> {
/// Converts a `&`[`CString`] into a borrowed [`Cow`] without copying or allocating.
#[inline]
fn from(s: &'a CString) -> Cow<'a, CStr> {
Cow::Borrowed(s.as_c_str())
}
}
#[stable(feature = "shared_from_slice2", since = "1.24.0")]
impl From<CString> for Arc<CStr> {
/// Converts a [`CString`] into an <code>[Arc]<[CStr]></code> by moving the [`CString`]
/// data into a new [`Arc`] buffer.
#[inline]
fn from(s: CString) -> Arc<CStr> {
let arc: Arc<[u8]> = Arc::from(s.into_inner());
unsafe { Arc::from_raw(Arc::into_raw(arc) as *const CStr) }
}
}
#[stable(feature = "shared_from_slice2", since = "1.24.0")]
impl From<&CStr> for Arc<CStr> {
/// Converts a `&CStr` into a `Arc<CStr>`,
/// by copying the contents into a newly allocated [`Arc`].
#[inline]
fn from(s: &CStr) -> Arc<CStr> {
let arc: Arc<[u8]> = Arc::from(s.to_bytes_with_nul());
unsafe { Arc::from_raw(Arc::into_raw(arc) as *const CStr) }
}
}
#[stable(feature = "shared_from_slice2", since = "1.24.0")]
impl From<CString> for Rc<CStr> {
/// Converts a [`CString`] into an <code>[Rc]<[CStr]></code> by moving the [`CString`]
/// data into a new [`Arc`] buffer.
#[inline]
fn from(s: CString) -> Rc<CStr> {
let rc: Rc<[u8]> = Rc::from(s.into_inner());
unsafe { Rc::from_raw(Rc::into_raw(rc) as *const CStr) }
}
}
#[stable(feature = "shared_from_slice2", since = "1.24.0")]
impl From<&CStr> for Rc<CStr> {
/// Converts a `&CStr` into a `Rc<CStr>`,
/// by copying the contents into a newly allocated [`Rc`].
#[inline]
fn from(s: &CStr) -> Rc<CStr> {
let rc: Rc<[u8]> = Rc::from(s.to_bytes_with_nul());
unsafe { Rc::from_raw(Rc::into_raw(rc) as *const CStr) }
}
}
#[stable(feature = "default_box_extra", since = "1.17.0")]
impl Default for Box<CStr> {
fn default() -> Box<CStr> {
let boxed: Box<[u8]> = Box::from([0]);
unsafe { Box::from_raw(Box::into_raw(boxed) as *mut CStr) }
}
}
impl NulError {
/// Returns the position of the nul byte in the slice that caused
/// [`CString::new`] to fail.
///
/// # Examples
///
/// ```
/// use std::ffi::CString;
///
/// let nul_error = CString::new("foo\0bar").unwrap_err();
/// assert_eq!(nul_error.nul_position(), 3);
///
/// let nul_error = CString::new("foo bar\0").unwrap_err();
/// assert_eq!(nul_error.nul_position(), 7);
/// ```
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn nul_position(&self) -> usize {
self.0
}
/// Consumes this error, returning the underlying vector of bytes which
/// generated the error in the first place.
///
/// # Examples
///
/// ```
/// use std::ffi::CString;
///
/// let nul_error = CString::new("foo\0bar").unwrap_err();
/// assert_eq!(nul_error.into_vec(), b"foo\0bar");
/// ```
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn into_vec(self) -> Vec<u8> {
self.1
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl Error for NulError {
#[allow(deprecated)]
fn description(&self) -> &str {
"nul byte found in data"
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl fmt::Display for NulError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "nul byte found in provided data at position: {}", self.0)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl From<NulError> for io::Error {
/// Converts a [`NulError`] into a [`io::Error`].
fn from(_: NulError) -> io::Error {
io::const_io_error!(io::ErrorKind::InvalidInput, "data provided contains a nul byte")
}
}
#[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",
}
}
}
#[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(())
}
}
#[stable(feature = "cstring_from_vec_with_nul", since = "1.58.0")]
impl Error for FromVecWithNulError {}
#[stable(feature = "cstring_from_vec_with_nul", since = "1.58.0")]
impl fmt::Display for FromVecWithNulError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self.error_kind {
FromBytesWithNulErrorKind::InteriorNul(pos) => {
write!(f, "data provided contains an interior nul byte at pos {pos}")
}
FromBytesWithNulErrorKind::NotNulTerminated => {
write!(f, "data provided is not nul terminated")
}
}
}
}
impl IntoStringError {
/// Consumes this error, returning original [`CString`] which generated the
/// error.
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "cstring_into", since = "1.7.0")]
pub fn into_cstring(self) -> CString {
self.inner
}
/// Access the underlying UTF-8 error that was the cause of this error.
#[must_use]
#[stable(feature = "cstring_into", since = "1.7.0")]
pub fn utf8_error(&self) -> Utf8Error {
self.error
}
}
#[stable(feature = "cstring_into", since = "1.7.0")]
impl Error for IntoStringError {
#[allow(deprecated)]
fn description(&self) -> &str {
"C string contained non-utf8 bytes"
}
fn source(&self) -> Option<&(dyn Error + 'static)> {
Some(&self.error)
}
}
#[stable(feature = "cstring_into", since = "1.7.0")]
impl fmt::Display for IntoStringError {
#[allow(deprecated, deprecated_in_future)]
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
self.description().fmt(f)
}
}
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 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
///
/// ```ignore (extern-declaration)
/// # fn main() {
/// use std::ffi::CStr;
/// use std::os::raw::c_char;
///
/// extern "C" {
/// fn my_string() -> *const c_char;
/// }
///
/// unsafe {
/// let slice = CStr::from_ptr(my_string());
/// println!("string returned: {}", slice.to_str().unwrap());
/// }
/// # }
/// ```
#[inline]
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
pub 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 of size less than `isize::MAX`, whose
// content remain valid and doesn't change for the lifetime of the
// returned `CStr`.
//
// Thus computing the length is fine (a NUL byte exists), the call to
// from_raw_parts is safe because we know the length is at most `isize::MAX`, meaning
// 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 {
let len = sys::strlen(ptr);
let ptr = ptr as *const u8;
Self::_from_bytes_with_nul_unchecked(slice::from_raw_parts(ptr, len as usize + 1))
}
}
/// Creates a C string wrapper from a byte slice.
///
/// This method will create a `CStr` from any byte slice that contains at
/// least one nul byte. The caller does not need to know or specify 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
/// ```
/// #![feature(cstr_from_bytes_until_nul)]
///
/// 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");
/// ```
///
#[unstable(feature = "cstr_from_bytes_until_nul", issue = "95027")]
pub fn from_bytes_until_nul(bytes: &[u8]) -> Result<&CStr, FromBytesUntilNulError> {
let nul_pos = memchr::memchr(0, bytes);
match nul_pos {
Some(nul_pos) => {
// 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.
let subslice = &bytes[..nul_pos + 1];
Ok(unsafe { CStr::from_bytes_with_nul_unchecked(subslice) })
}
None => Err(FromBytesUntilNulError(())),
}
}
/// 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.
///
/// 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")]
pub 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. 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")]
pub const unsafe fn from_bytes_with_nul_unchecked(bytes: &[u8]) -> &CStr {
// We're in a const fn, so this is the best we can do
debug_assert!(!bytes.is_empty() && bytes[bytes.len() - 1] == 0);
unsafe { Self::_from_bytes_with_nul_unchecked(bytes) }
}
#[inline]
const unsafe fn _from_bytes_with_nul_unchecked(bytes: &[u8]) -> &Self {
// 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 Self) }
}
/// 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:
///
/// ```no_run
/// # #![allow(unused_must_use)] #![allow(temporary_cstring_as_ptr)]
/// use std::ffi::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:
///
/// ```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")]
pub const fn as_ptr(&self) -> *const c_char {
self.inner.as_ptr()
}
/// 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")]
pub fn to_bytes(&self) -> &[u8] {
let bytes = self.to_bytes_with_nul();
// SAFETY: to_bytes_with_nul returns slice with length at least 1
unsafe { bytes.get_unchecked(..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")]
pub fn to_bytes_with_nul(&self) -> &[u8] {
unsafe { &*(&self.inner as *const [c_char] as *const [u8]) }
}
/// 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")]
pub 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())
}
/// Converts a `CStr` into a <code>[Cow]<[str]></code>.
///
/// If the contents of the `CStr` are valid UTF-8 data, this
/// function will return a <code>[Cow]::[Borrowed]\(&[str])</code>
/// with the corresponding <code>&[str]</code> slice. Otherwise, it will
/// replace any invalid UTF-8 sequences with
/// [`U+FFFD REPLACEMENT CHARACTER`][U+FFFD] and return a
/// <code>[Cow]::[Owned]\(&[str])</code> with the result.
///
/// [str]: prim@str "str"
/// [Borrowed]: Cow::Borrowed
/// [Owned]: Cow::Owned
/// [U+FFFD]: crate::char::REPLACEMENT_CHARACTER "std::char::REPLACEMENT_CHARACTER"
///
/// # Examples
///
/// Calling `to_string_lossy` on a `CStr` containing valid UTF-8:
///
/// ```
/// use std::borrow::Cow;
/// use std::ffi::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 std::ffi::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>
/// );
/// ```
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[stable(feature = "cstr_to_str", since = "1.4.0")]
pub fn to_string_lossy(&self) -> Cow<'_, str> {
String::from_utf8_lossy(self.to_bytes())
}
/// Converts a <code>[Box]<[CStr]></code> into a [`CString`] without copying or allocating.
///
/// # Examples
///
/// ```
/// use std::ffi::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"));
/// ```
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "into_boxed_c_str", since = "1.20.0")]
pub fn into_c_string(self: Box<CStr>) -> CString {
let raw = Box::into_raw(self) as *mut [u8];
CString { inner: unsafe { Box::from_raw(raw) } }
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl PartialEq for CStr {
fn eq(&self, other: &CStr) -> bool {
self.to_bytes().eq(other.to_bytes())
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl Eq for CStr {}
#[stable(feature = "rust1", since = "1.0.0")]
impl PartialOrd for CStr {
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 {
fn cmp(&self, other: &CStr) -> Ordering {
self.to_bytes().cmp(&other.to_bytes())
}
}
#[stable(feature = "cstr_borrow", since = "1.3.0")]
impl ToOwned for CStr {
type Owned = CString;
fn to_owned(&self) -> CString {
CString { inner: self.to_bytes_with_nul().into() }
}
fn clone_into(&self, target: &mut CString) {
let mut b = Vec::from(mem::take(&mut target.inner));
self.to_bytes_with_nul().clone_into(&mut b);
target.inner = b.into_boxed_slice();
}
}
#[stable(feature = "cstring_asref", since = "1.7.0")]
impl From<&CStr> for CString {
/// Copies the contents of the `&CStr` into a newly allocated `CString`.
fn from(s: &CStr) -> CString {
s.to_owned()
}
}
#[stable(feature = "cstring_asref", since = "1.7.0")]
impl ops::Index<ops::RangeFull> for CString {
type Output = CStr;
#[inline]
fn index(&self, _index: ops::RangeFull) -> &CStr {
self
}
}
#[stable(feature = "cstr_range_from", since = "1.47.0")]
impl ops::Index<ops::RangeFrom<usize>> for CStr {
type Output = CStr;
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() {
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
}
}
#[stable(feature = "cstring_asref", since = "1.7.0")]
impl AsRef<CStr> for CString {
#[inline]
fn as_ref(&self) -> &CStr {
self
}
}