571 lines
20 KiB
Rust
571 lines
20 KiB
Rust
use crate::ascii;
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use crate::cmp::Ordering;
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use crate::ffi::c_char;
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use crate::fmt::{self, Write};
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use crate::ops;
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use crate::slice;
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use crate::slice::memchr;
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use crate::str;
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/// Representation of a borrowed C string.
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///
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/// This type represents a borrowed reference to a nul-terminated
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/// array of bytes. It can be constructed safely from a <code>&[[u8]]</code>
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/// slice, or unsafely from a raw `*const c_char`. It can then be
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/// converted to a Rust <code>&[str]</code> by performing UTF-8 validation, or
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/// into an owned `CString`.
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///
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/// `&CStr` is to `CString` as <code>&[str]</code> is to `String`: the former
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/// in each pair are borrowed references; the latter are owned
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/// strings.
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///
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/// Note that this structure is **not** `repr(C)` and is not recommended to be
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/// placed in the signatures of FFI functions. Instead, safe wrappers of FFI
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/// functions may leverage the unsafe [`CStr::from_ptr`] constructor to provide
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/// a safe interface to other consumers.
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///
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/// # Examples
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///
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/// Inspecting a foreign C string:
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///
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/// ```ignore (extern-declaration)
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/// use std::ffi::CStr;
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/// use std::os::raw::c_char;
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///
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/// extern "C" { fn my_string() -> *const c_char; }
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///
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/// unsafe {
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/// let slice = CStr::from_ptr(my_string());
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/// println!("string buffer size without nul terminator: {}", slice.to_bytes().len());
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/// }
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/// ```
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///
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/// Passing a Rust-originating C string:
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///
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/// ```ignore (extern-declaration)
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/// use std::ffi::{CString, CStr};
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/// use std::os::raw::c_char;
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///
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/// fn work(data: &CStr) {
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/// extern "C" { fn work_with(data: *const c_char); }
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///
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/// unsafe { work_with(data.as_ptr()) }
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/// }
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///
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/// let s = CString::new("data data data data").expect("CString::new failed");
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/// work(&s);
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/// ```
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///
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/// Converting a foreign C string into a Rust `String`:
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///
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/// ```ignore (extern-declaration)
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/// use std::ffi::CStr;
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/// use std::os::raw::c_char;
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///
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/// extern "C" { fn my_string() -> *const c_char; }
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///
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/// fn my_string_safe() -> String {
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/// unsafe {
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/// CStr::from_ptr(my_string()).to_string_lossy().into_owned()
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/// }
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/// }
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///
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/// println!("string: {}", my_string_safe());
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/// ```
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///
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/// [str]: prim@str "str"
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#[derive(Hash)]
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#[cfg_attr(not(test), rustc_diagnostic_item = "CStr")]
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#[unstable(feature = "core_c_str", issue = "94079")]
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#[cfg_attr(not(bootstrap), rustc_has_incoherent_inherent_impls)]
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// FIXME:
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// `fn from` in `impl From<&CStr> for Box<CStr>` current implementation relies
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// on `CStr` being layout-compatible with `[u8]`.
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// When attribute privacy is implemented, `CStr` should be annotated as `#[repr(transparent)]`.
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// Anyway, `CStr` representation and layout are considered implementation detail, are
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// not documented and must not be relied upon.
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pub struct CStr {
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// FIXME: this should not be represented with a DST slice but rather with
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// just a raw `c_char` along with some form of marker to make
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// this an unsized type. Essentially `sizeof(&CStr)` should be the
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// same as `sizeof(&c_char)` but `CStr` should be an unsized type.
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inner: [c_char],
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}
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/// An error indicating that a nul byte was not in the expected position.
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///
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/// The slice used to create a [`CStr`] must have one and only one nul byte,
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/// positioned at the end.
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///
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/// This error is created by the [`CStr::from_bytes_with_nul`] method.
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/// See its documentation for more.
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///
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/// # Examples
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///
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/// ```
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/// use std::ffi::{CStr, FromBytesWithNulError};
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///
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/// let _: FromBytesWithNulError = CStr::from_bytes_with_nul(b"f\0oo").unwrap_err();
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/// ```
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#[derive(Clone, PartialEq, Eq, Debug)]
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#[unstable(feature = "core_c_str", issue = "94079")]
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pub struct FromBytesWithNulError {
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kind: FromBytesWithNulErrorKind,
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}
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#[derive(Clone, PartialEq, Eq, Debug)]
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enum FromBytesWithNulErrorKind {
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InteriorNul(usize),
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NotNulTerminated,
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}
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impl FromBytesWithNulError {
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fn interior_nul(pos: usize) -> FromBytesWithNulError {
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FromBytesWithNulError { kind: FromBytesWithNulErrorKind::InteriorNul(pos) }
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}
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fn not_nul_terminated() -> FromBytesWithNulError {
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FromBytesWithNulError { kind: FromBytesWithNulErrorKind::NotNulTerminated }
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}
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#[doc(hidden)]
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#[unstable(feature = "cstr_internals", issue = "none")]
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pub fn __description(&self) -> &str {
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match self.kind {
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FromBytesWithNulErrorKind::InteriorNul(..) => {
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"data provided contains an interior nul byte"
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}
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FromBytesWithNulErrorKind::NotNulTerminated => "data provided is not nul terminated",
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}
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}
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}
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/// An error indicating that no nul byte was present.
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///
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/// A slice used to create a [`CStr`] must contain a nul byte somewhere
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/// within the slice.
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///
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/// This error is created by the [`CStr::from_bytes_until_nul`] method.
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///
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#[derive(Clone, PartialEq, Eq, Debug)]
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#[unstable(feature = "cstr_from_bytes_until_nul", issue = "95027")]
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pub struct FromBytesUntilNulError(());
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#[unstable(feature = "cstr_from_bytes_until_nul", issue = "95027")]
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impl fmt::Display for FromBytesUntilNulError {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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write!(f, "data provided does not contain a nul")
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}
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}
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#[stable(feature = "cstr_debug", since = "1.3.0")]
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impl fmt::Debug for CStr {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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write!(f, "\"")?;
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for byte in self.to_bytes().iter().flat_map(|&b| ascii::escape_default(b)) {
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f.write_char(byte as char)?;
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}
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write!(f, "\"")
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}
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}
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#[stable(feature = "cstr_default", since = "1.10.0")]
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impl Default for &CStr {
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fn default() -> Self {
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const SLICE: &[c_char] = &[0];
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// SAFETY: `SLICE` is indeed pointing to a valid nul-terminated string.
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unsafe { CStr::from_ptr(SLICE.as_ptr()) }
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}
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}
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#[stable(feature = "frombyteswithnulerror_impls", since = "1.17.0")]
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impl fmt::Display for FromBytesWithNulError {
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#[allow(deprecated, deprecated_in_future)]
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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f.write_str(self.__description())?;
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if let FromBytesWithNulErrorKind::InteriorNul(pos) = self.kind {
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write!(f, " at byte pos {pos}")?;
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}
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Ok(())
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}
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}
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impl CStr {
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/// Wraps a raw C string with a safe C string wrapper.
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///
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/// This function will wrap the provided `ptr` with a `CStr` wrapper, which
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/// allows inspection and interoperation of non-owned C strings. The total
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/// size of the raw C string must be smaller than `isize::MAX` **bytes**
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/// in memory due to calling the `slice::from_raw_parts` function.
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/// This method is unsafe for a number of reasons:
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///
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/// * There is no guarantee to the validity of `ptr`.
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/// * The returned lifetime is not guaranteed to be the actual lifetime of
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/// `ptr`.
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/// * There is no guarantee that the memory pointed to by `ptr` contains a
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/// valid nul terminator byte at the end of the string.
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/// * It is not guaranteed that the memory pointed by `ptr` won't change
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/// before the `CStr` has been destroyed.
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///
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/// > **Note**: This operation is intended to be a 0-cost cast but it is
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/// > currently implemented with an up-front calculation of the length of
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/// > the string. This is not guaranteed to always be the case.
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///
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/// # Examples
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///
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/// ```ignore (extern-declaration)
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/// # fn main() {
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/// use std::ffi::CStr;
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/// use std::os::raw::c_char;
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///
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/// extern "C" {
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/// fn my_string() -> *const c_char;
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/// }
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///
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/// unsafe {
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/// let slice = CStr::from_ptr(my_string());
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/// println!("string returned: {}", slice.to_str().unwrap());
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/// }
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/// # }
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/// ```
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#[inline]
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#[must_use]
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#[stable(feature = "rust1", since = "1.0.0")]
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pub unsafe fn from_ptr<'a>(ptr: *const c_char) -> &'a CStr {
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// SAFETY: The caller has provided a pointer that points to a valid C
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// string with a NUL terminator of size less than `isize::MAX`, whose
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// content remain valid and doesn't change for the lifetime of the
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// returned `CStr`.
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//
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// Thus computing the length is fine (a NUL byte exists), the call to
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// from_raw_parts is safe because we know the length is at most `isize::MAX`, meaning
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// the call to `from_bytes_with_nul_unchecked` is correct.
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//
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// The cast from c_char to u8 is ok because a c_char is always one byte.
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unsafe {
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extern "C" {
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/// Provided by libc or compiler_builtins.
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fn strlen(s: *const c_char) -> usize;
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}
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let len = strlen(ptr);
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let ptr = ptr as *const u8;
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CStr::from_bytes_with_nul_unchecked(slice::from_raw_parts(ptr, len as usize + 1))
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}
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}
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/// Creates a C string wrapper from a byte slice.
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///
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/// This method will create a `CStr` from any byte slice that contains at
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/// least one nul byte. The caller does not need to know or specify where
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/// the nul byte is located.
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///
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/// If the first byte is a nul character, this method will return an
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/// empty `CStr`. If multiple nul characters are present, the `CStr` will
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/// end at the first one.
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///
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/// If the slice only has a single nul byte at the end, this method is
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/// equivalent to [`CStr::from_bytes_with_nul`].
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///
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/// # Examples
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/// ```
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/// #![feature(cstr_from_bytes_until_nul)]
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///
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/// use std::ffi::CStr;
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///
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/// let mut buffer = [0u8; 16];
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/// unsafe {
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/// // Here we might call an unsafe C function that writes a string
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/// // into the buffer.
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/// let buf_ptr = buffer.as_mut_ptr();
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/// buf_ptr.write_bytes(b'A', 8);
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/// }
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/// // Attempt to extract a C nul-terminated string from the buffer.
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/// let c_str = CStr::from_bytes_until_nul(&buffer[..]).unwrap();
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/// assert_eq!(c_str.to_str().unwrap(), "AAAAAAAA");
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/// ```
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///
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#[unstable(feature = "cstr_from_bytes_until_nul", issue = "95027")]
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pub fn from_bytes_until_nul(bytes: &[u8]) -> Result<&CStr, FromBytesUntilNulError> {
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let nul_pos = memchr::memchr(0, bytes);
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match nul_pos {
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Some(nul_pos) => {
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let subslice = &bytes[..nul_pos + 1];
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// SAFETY: We know there is a nul byte at nul_pos, so this slice
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// (ending at the nul byte) is a well-formed C string.
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Ok(unsafe { CStr::from_bytes_with_nul_unchecked(subslice) })
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}
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None => Err(FromBytesUntilNulError(())),
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}
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}
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/// Creates a C string wrapper from a byte slice.
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///
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/// This function will cast the provided `bytes` to a `CStr`
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/// wrapper after ensuring that the byte slice is nul-terminated
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/// and does not contain any interior nul bytes.
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///
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/// If the nul byte may not be at the end,
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/// [`CStr::from_bytes_until_nul`] can be used instead.
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///
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/// # Examples
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///
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/// ```
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/// use std::ffi::CStr;
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///
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/// let cstr = CStr::from_bytes_with_nul(b"hello\0");
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/// assert!(cstr.is_ok());
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/// ```
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///
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/// Creating a `CStr` without a trailing nul terminator is an error:
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///
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/// ```
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/// use std::ffi::CStr;
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///
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/// let cstr = CStr::from_bytes_with_nul(b"hello");
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/// assert!(cstr.is_err());
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/// ```
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///
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/// Creating a `CStr` with an interior nul byte is an error:
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///
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/// ```
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/// use std::ffi::CStr;
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///
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/// let cstr = CStr::from_bytes_with_nul(b"he\0llo\0");
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/// assert!(cstr.is_err());
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/// ```
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#[stable(feature = "cstr_from_bytes", since = "1.10.0")]
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pub fn from_bytes_with_nul(bytes: &[u8]) -> Result<&Self, FromBytesWithNulError> {
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let nul_pos = memchr::memchr(0, bytes);
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match nul_pos {
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Some(nul_pos) if nul_pos + 1 == bytes.len() => {
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// SAFETY: We know there is only one nul byte, at the end
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// of the byte slice.
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Ok(unsafe { Self::from_bytes_with_nul_unchecked(bytes) })
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}
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Some(nul_pos) => Err(FromBytesWithNulError::interior_nul(nul_pos)),
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None => Err(FromBytesWithNulError::not_nul_terminated()),
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}
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}
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/// Unsafely creates a C string wrapper from a byte slice.
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///
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/// This function will cast the provided `bytes` to a `CStr` wrapper without
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/// performing any sanity checks. The provided slice **must** be nul-terminated
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/// and not contain any interior nul bytes.
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///
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/// # Examples
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///
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/// ```
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/// use std::ffi::{CStr, CString};
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///
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/// unsafe {
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/// let cstring = CString::new("hello").expect("CString::new failed");
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/// let cstr = CStr::from_bytes_with_nul_unchecked(cstring.to_bytes_with_nul());
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/// assert_eq!(cstr, &*cstring);
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/// }
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/// ```
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#[inline]
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#[must_use]
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#[stable(feature = "cstr_from_bytes", since = "1.10.0")]
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#[rustc_const_stable(feature = "const_cstr_unchecked", since = "1.59.0")]
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pub const unsafe fn from_bytes_with_nul_unchecked(bytes: &[u8]) -> &CStr {
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// We're in a const fn, so this is the best we can do
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debug_assert!(!bytes.is_empty() && bytes[bytes.len() - 1] == 0);
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// SAFETY: Calling an inner function with the same prerequisites.
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unsafe { Self::_from_bytes_with_nul_unchecked(bytes) }
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}
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#[inline]
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const unsafe fn _from_bytes_with_nul_unchecked(bytes: &[u8]) -> &CStr {
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// SAFETY: Casting to CStr is safe because its internal representation
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// is a [u8] too (safe only inside std).
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// Dereferencing the obtained pointer is safe because it comes from a
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// reference. Making a reference is then safe because its lifetime
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// is bound by the lifetime of the given `bytes`.
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unsafe { &*(bytes as *const [u8] as *const CStr) }
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}
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/// Returns the inner pointer to this C string.
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///
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/// The returned pointer will be valid for as long as `self` is, and points
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/// to a contiguous region of memory terminated with a 0 byte to represent
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/// the end of the string.
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///
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/// **WARNING**
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///
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/// The returned pointer is read-only; writing to it (including passing it
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/// to C code that writes to it) causes undefined behavior.
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///
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/// It is your responsibility to make sure that the underlying memory is not
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/// freed too early. For example, the following code will cause undefined
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/// behavior when `ptr` is used inside the `unsafe` block:
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///
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/// ```no_run
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/// # #![allow(unused_must_use)] #![allow(temporary_cstring_as_ptr)]
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/// use std::ffi::CString;
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///
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/// let ptr = CString::new("Hello").expect("CString::new failed").as_ptr();
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/// unsafe {
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/// // `ptr` is dangling
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/// *ptr;
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/// }
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/// ```
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///
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/// This happens because the pointer returned by `as_ptr` does not carry any
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/// lifetime information and the `CString` is deallocated immediately after
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/// the `CString::new("Hello").expect("CString::new failed").as_ptr()`
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/// expression is evaluated.
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/// To fix the problem, bind the `CString` to a local variable:
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///
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/// ```no_run
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/// # #![allow(unused_must_use)]
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/// use std::ffi::CString;
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///
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/// let hello = CString::new("Hello").expect("CString::new failed");
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/// let ptr = hello.as_ptr();
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/// unsafe {
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/// // `ptr` is valid because `hello` is in scope
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/// *ptr;
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/// }
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/// ```
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///
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/// This way, the lifetime of the `CString` in `hello` encompasses
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/// the lifetime of `ptr` and the `unsafe` block.
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#[inline]
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#[must_use]
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#[stable(feature = "rust1", since = "1.0.0")]
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#[rustc_const_stable(feature = "const_str_as_ptr", since = "1.32.0")]
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pub const fn as_ptr(&self) -> *const c_char {
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self.inner.as_ptr()
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}
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/// Converts this C string to a byte slice.
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///
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/// The returned slice will **not** contain the trailing nul terminator that this C
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/// string has.
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///
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/// > **Note**: This method is currently implemented as a constant-time
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/// > cast, but it is planned to alter its definition in the future to
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/// > perform the length calculation whenever this method is called.
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///
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/// # Examples
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///
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/// ```
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/// use std::ffi::CStr;
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///
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/// let cstr = CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed");
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/// assert_eq!(cstr.to_bytes(), b"foo");
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/// ```
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#[inline]
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#[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] {
|
|
// SAFETY: Transmuting a slice of `c_char`s to a slice of `u8`s
|
|
// is safe on all supported targets.
|
|
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())
|
|
}
|
|
}
|
|
|
|
#[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_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() {
|
|
// 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
|
|
}
|
|
}
|