c_str.rs.html -- source
Description: Source to the Rust file `src\libstd\ffi\c_str.rs`.
Keywords: rust, rustlang, rust-lang

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    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::memchr;
    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;

    /// 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 [`&CStr`] as [`String`] is to [`&str`]: 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 [`Into`]`<`[`Vec`]`<`[`u8`]`>>` (for
    /// example, you can build a `CString` straight out of a [`String`] or
    /// a [`&str`], since both implement that trait).
    ///
    /// The [`new`] method will actually check that the provided `&[u8]`
    /// 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 a [`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`] 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 `&[`[`u8`]`]` slice from a
    /// `CString` with the [`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 `&[`[`u8`]`]` slice *with* the nul terminator, you
    /// can use [`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.
    ///
    /// [`Into`]: ../convert/trait.Into.html
    /// [`Vec`]: ../vec/struct.Vec.html
    /// [`String`]: ../string/struct.String.html
    /// [`&str`]: ../primitive.str.html
    /// [`u8`]: ../primitive.u8.html
    /// [`new`]: #method.new
    /// [`as_bytes`]: #method.as_bytes
    /// [`as_bytes_with_nul`]: #method.as_bytes_with_nul
    /// [`as_ptr`]: #method.as_ptr
    /// [slice.as_ptr]: ../primitive.slice.html#method.as_ptr
    /// [slice.len]: ../primitive.slice.html#method.len
    /// [`Deref`]: ../ops/trait.Deref.html
    /// [`CStr`]: struct.CStr.html
    /// [`&CStr`]: struct.CStr.html
    ///
    /// # Examples
    ///
    /// ```ignore (extern-declaration)
    /// # fn main() {
    /// use std::ffi::CString;
    /// use std::os::raw::c_char;
    ///
    /// extern {
    ///     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)]
    #[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 `&[`[`u8`]`]`
    /// slice, or unsafely from a raw `*const c_char`. It can then be
    /// converted to a Rust [`&str`] by performing UTF-8 validation, or
    /// into an owned [`CString`].
    ///
    /// `&CStr` is to [`CString`] as [`&str`] is to [`String`]: the former
    /// in each pair are borrowed references; the latter are owned
    /// strings.
    ///
    /// Note that this structure is **not** `repr(C)` and is not recommended to be
    /// placed in the signatures of FFI functions. Instead, safe wrappers of FFI
    /// functions may leverage the unsafe [`from_ptr`] constructor to provide a safe
    /// interface to other consumers.
    ///
    /// # Examples
    ///
    /// Inspecting a foreign C string:
    ///
    /// ```ignore (extern-declaration)
    /// use std::ffi::CStr;
    /// use std::os::raw::c_char;
    ///
    /// extern { fn my_string() -> *const c_char; }
    ///
    /// unsafe {
    ///     let slice = CStr::from_ptr(my_string());
    ///     println!("string buffer size without nul terminator: {}", slice.to_bytes().len());
    /// }
    /// ```
    ///
    /// Passing a Rust-originating C string:
    ///
    /// ```ignore (extern-declaration)
    /// use std::ffi::{CString, CStr};
    /// use std::os::raw::c_char;
    ///
    /// fn work(data: &CStr) {
    ///     extern { fn work_with(data: *const c_char); }
    ///
    ///     unsafe { work_with(data.as_ptr()) }
    /// }
    ///
    /// let s = CString::new("data data data data").expect("CString::new failed");
    /// work(&s);
    /// ```
    ///
    /// Converting a foreign C string into a Rust [`String`]:
    ///
    /// ```ignore (extern-declaration)
    /// use std::ffi::CStr;
    /// use std::os::raw::c_char;
    ///
    /// extern { fn my_string() -> *const c_char; }
    ///
    /// fn my_string_safe() -> String {
    ///     unsafe {
    ///         CStr::from_ptr(my_string()).to_string_lossy().into_owned()
    ///     }
    /// }
    ///
    /// println!("string: {}", my_string_safe());
    /// ```
    ///
    /// [`u8`]: ../primitive.u8.html
    /// [`&str`]: ../primitive.str.html
    /// [`String`]: ../string/struct.String.html
    /// [`CString`]: struct.CString.html
    /// [`from_ptr`]: #method.from_ptr
    #[derive(Hash)]
    #[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.
    ///
    /// [`CString`]: struct.CString.html
    /// [`CString::new`]: struct.CString.html#method.new
    ///
    /// # 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 [`from_bytes_with_nul`] method on [`CStr`].
    /// See its documentation for more.
    ///
    /// [`CStr`]: struct.CStr.html
    /// [`from_bytes_with_nul`]: struct.CStr.html#method.from_bytes_with_nul
    ///
    /// # 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 [`from_vec_with_nul`] method on [`CString`].
    /// See its documentation for more.
    ///
    /// [`CString`]: struct.CString.html
    /// [`from_vec_with_nul`]: struct.CString.html#method.from_vec_with_nul
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(cstring_from_vec_with_nul)]
    /// use std::ffi::{CString, FromVecWithNulError};
    ///
    /// let _: FromVecWithNulError = CString::from_vec_with_nul(b"f\0oo".to_vec()).unwrap_err();
    /// ```
    #[derive(Clone, PartialEq, Eq, Debug)]
    #[unstable(feature = "cstring_from_vec_with_nul", issue = "73179")]
    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 }
        }
    }

    #[unstable(feature = "cstring_from_vec_with_nul", issue = "73179")]
    impl FromVecWithNulError {
        /// Returns a slice of [`u8`]s bytes that were attempted to convert to a [`CString`].
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// #![feature(cstring_from_vec_with_nul)]
        /// 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());
        /// ```
        ///
        /// [`CString`]: struct.CString.html
        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:
        ///
        /// ```
        /// #![feature(cstring_from_vec_with_nul)]
        /// 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());
        /// ```
        ///
        /// [`CString`]: struct.CString.html
        pub fn into_bytes(self) -> Vec<u8> {
            self.bytes
        }
    }

    /// 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; [`into_string`][`CString::into_string`] performs UTF-8
    /// validation on those bytes and may return this error.
    ///
    /// This `struct` is created by the
    /// [`into_string`][`CString::into_string`] method on [`CString`]. See
    /// its documentation for more.
    ///
    /// [`String`]: ../string/struct.String.html
    /// [`CString`]: struct.CString.html
    /// [`CString::into_string`]: struct.CString.html#method.into_string
    #[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 { 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.
        ///
        /// [`NulError`]: struct.NulError.html
        #[stable(feature = "rust1", since = "1.0.0")]
        pub fn new<T: Into<Vec<u8>>>(t: T) -> Result<CString, NulError> {
            trait SpecIntoVec {
                fn into_vec(self) -> Vec<u8>;
            }
            impl<T: Into<Vec<u8>>> SpecIntoVec for T {
                default fn into_vec(self) -> Vec<u8> {
                    self.into()
                }
            }
            // Specialization for avoiding reallocation.
            impl SpecIntoVec for &'_ [u8] {
                fn into_vec(self) -> Vec<u8> {
                    let mut v = Vec::with_capacity(self.len() + 1);
                    v.extend(self);
                    v
                }
            }
            impl SpecIntoVec for &'_ str {
                fn into_vec(self) -> Vec<u8> {
                    let mut v = Vec::with_capacity(self.len() + 1);
                    v.extend(self.as_bytes());
                    v
                }
            }

            Self::_new(SpecIntoVec::into_vec(t))
        }

        fn _new(bytes: Vec<u8>) -> Result<CString, NulError> {
            match memchr::memchr(0, &bytes) {
                Some(i) => Err(NulError(i, bytes)),
                None => Ok(unsafe { CString::from_vec_unchecked(bytes) }),
            }
        }

        /// Creates a C-compatible string by consuming a byte vector,
        /// without checking for interior 0 bytes.
        ///
        /// This method is equivalent to [`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.
        ///
        /// [`new`]: #method.new
        ///
        /// # Examples
        ///
        /// ```
        /// use std::ffi::CString;
        ///
        /// let raw = b"foo".to_vec();
        /// unsafe {
        ///     let c_string = CString::from_vec_unchecked(raw);
        /// }
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        pub unsafe fn from_vec_unchecked(mut v: Vec<u8>) -> CString {
            v.reserve_exact(1);
            v.push(0);
            CString { inner: v.into_boxed_slice() }
        }

        /// Retakes ownership of a `CString` that was transferred to C via [`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 [`into_raw`] on a `CString`. 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
        /// [`into_raw`] call. This means the [`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.
        ///
        /// [`into_raw`]: #method.into_raw
        /// [`CStr`]: struct.CStr.html
        ///
        /// # 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 {
        ///     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);
        /// }
        /// ```
        #[stable(feature = "cstr_memory", since = "1.4.0")]
        pub unsafe fn from_raw(ptr: *mut c_char) -> CString {
            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
        /// [`from_raw`] to be properly deallocated. Specifically, one
        /// should *not* use the standard C `free()` function to deallocate
        /// this string.
        ///
        /// Failure to call [`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 [`from_raw`]. See the safety section
        /// in [`from_raw`].
        ///
        /// [`from_raw`]: #method.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]
        #[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.
        ///
        /// [`String`]: ../string/struct.String.html
        ///
        /// # 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 { CString::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']);
        /// ```
        #[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 the [`into_bytes`] function except that the returned vector
        /// includes the trailing nul terminator.
        ///
        /// [`into_bytes`]: #method.into_bytes
        ///
        /// # 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']);
        /// ```
        #[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
        /// [`as_bytes_with_nul`] instead.
        ///
        /// [`as_bytes_with_nul`]: #method.as_bytes_with_nul
        ///
        /// # 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]
        #[stable(feature = "rust1", since = "1.0.0")]
        pub fn as_bytes(&self) -> &[u8] {
            &self.inner[..self.inner.len() - 1]
        }

        /// Equivalent to the [`as_bytes`] function except that the returned slice
        /// includes the trailing nul terminator.
        ///
        /// [`as_bytes`]: #method.as_bytes
        ///
        /// # 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]
        #[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.
        ///
        /// [`CStr`]: struct.CStr.html
        ///
        /// # 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]
        #[stable(feature = "as_c_str", since = "1.20.0")]
        pub fn as_c_str(&self) -> &CStr {
            &*self
        }

        /// Converts this `CString` into a boxed [`CStr`].
        ///
        /// [`CStr`]: struct.CStr.html
        ///
        /// # 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"));
        /// ```
        #[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.
        ///
        /// [`Drop`]: ../ops/trait.Drop.html
        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 `Vec` of `u8` 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
        ///
        /// ```
        /// #![feature(cstring_from_vec_with_nul)]
        /// 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()) }
        /// );
        /// ```
        #[unstable(feature = "cstring_from_vec_with_nul", issue = "73179")]
        pub unsafe fn from_vec_with_nul_unchecked(v: Vec<u8>) -> Self {
            Self { inner: v.into_boxed_slice() }
        }

        /// Attempts to converts a `Vec` of `u8` 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 [`new`] when
        /// called without the ending nul byte.
        ///
        /// ```
        /// #![feature(cstring_from_vec_with_nul)]
        /// 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")
        /// );
        /// ```
        ///
        /// A incorrectly formatted vector will produce an error.
        ///
        /// ```
        /// #![feature(cstring_from_vec_with_nul)]
        /// 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();
        /// ```
        ///
        /// [`new`]: #method.new
        #[unstable(feature = "cstring_from_vec_with_nul", issue = "73179")]
        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 [`Vec`]`<u8>`.
        ///
        /// The conversion consumes the [`CString`], and removes the terminating NUL byte.
        ///
        /// [`Vec`]: ../vec/struct.Vec.html
        /// [`CString`]: ../ffi/struct.CString.html
        #[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 {
        #[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> {
        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> {
        #[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 [`Box`]`<CStr>` into a [`CString`] without copying or allocating.
        ///
        /// [`Box`]: ../boxed/struct.Box.html
        /// [`CString`]: ../ffi/struct.CString.html
        #[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 [`Vec`]`<`[`NonZeroU8`]`>` into a [`CString`] without
        /// copying nor checking for inner null bytes.
        ///
        /// [`CString`]: ../ffi/struct.CString.html
        /// [`NonZeroU8`]: ../num/struct.NonZeroU8.html
        /// [`Vec`]: ../vec/struct.Vec.html
        #[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`.
                CString::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 [`Box`]`<CStr>` without copying or allocating.
        ///
        /// [`CString`]: ../ffi/struct.CString.html
        /// [`Box`]: ../boxed/struct.Box.html
        #[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> {
        #[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> {
        #[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> {
        #[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 a [`Arc`]`<CStr>` without copying or allocating.
        ///
        /// [`CString`]: ../ffi/struct.CString.html
        /// [`Arc`]: ../sync/struct.Arc.html
        #[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> {
        #[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 a [`Rc`]`<CStr>` without copying or allocating.
        ///
        /// [`CString`]: ../ffi/struct.CString.html
        /// [`Rc`]: ../rc/struct.Rc.html
        #[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> {
        #[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.
        ///
        /// [`CString::new`]: struct.CString.html#method.new
        ///
        /// # 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);
        /// ```
        #[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");
        /// ```
        #[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`].
        ///
        /// [`NulError`]: ../ffi/struct.NulError.html
        /// [`io::Error`]: ../io/struct.Error.html
        fn from(_: NulError) -> io::Error {
            io::Error::new(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(())
        }
    }

    #[unstable(feature = "cstring_from_vec_with_nul", issue = "73179")]
    impl Error for FromVecWithNulError {}

    #[unstable(feature = "cstring_from_vec_with_nul", issue = "73179")]
    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.
        ///
        /// [`CString`]: struct.CString.html
        #[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.
        #[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 {
        ///     fn my_string() -> *const c_char;
        /// }
        ///
        /// unsafe {
        ///     let slice = CStr::from_ptr(my_string());
        ///     println!("string returned: {}", slice.to_str().unwrap());
        /// }
        /// # }
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        pub unsafe fn from_ptr<'a>(ptr: *const c_char) -> &'a CStr {
            let len = sys::strlen(ptr);
            let ptr = ptr as *const u8;
            CStr::from_bytes_with_nul_unchecked(slice::from_raw_parts(ptr, len as usize + 1))
        }

        /// Creates a C string wrapper from a byte slice.
        ///
        /// This function will cast the provided `bytes` to a `CStr`
        /// wrapper after ensuring that the byte slice is nul-terminated
        /// and does not contain any interior nul bytes.
        ///
        /// # Examples
        ///
        /// ```
        /// use 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<&CStr, FromBytesWithNulError> {
            let nul_pos = memchr::memchr(0, bytes);
            if let Some(nul_pos) = nul_pos {
                if nul_pos + 1 != bytes.len() {
                    return Err(FromBytesWithNulError::interior_nul(nul_pos));
                }
                Ok(unsafe { CStr::from_bytes_with_nul_unchecked(bytes) })
            } else {
                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]
        #[stable(feature = "cstr_from_bytes", since = "1.10.0")]
        #[rustc_const_unstable(feature = "const_cstr_unchecked", issue = "none")]
        pub const unsafe fn from_bytes_with_nul_unchecked(bytes: &[u8]) -> &CStr {
            &*(bytes as *const [u8] as *const CStr)
        }

        /// 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)]
        /// 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.
        ///
        /// [`CString`]: struct.CString.html
        #[inline]
        #[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]
        #[stable(feature = "rust1", since = "1.0.0")]
        pub fn to_bytes(&self) -> &[u8] {
            let bytes = self.to_bytes_with_nul();
            &bytes[..bytes.len() - 1]
        }

        /// Converts this C string to a byte slice containing the trailing 0 byte.
        ///
        /// This function is the equivalent of [`to_bytes`] except that it will retain
        /// the trailing nul terminator instead of chopping it off.
        ///
        /// > **Note**: This method is currently implemented as a 0-cost cast, but
        /// > it is planned to alter its definition in the future to perform the
        /// > length calculation whenever this method is called.
        ///
        /// [`to_bytes`]: #method.to_bytes
        ///
        /// # 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]
        #[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 [`&str`] slice if the `CStr` contains valid UTF-8.
        ///
        /// If the contents of the `CStr` are valid UTF-8 data, this
        /// function will return the corresponding [`&str`] slice. Otherwise,
        /// it will return an error with details of where UTF-8 validation failed.
        ///
        /// [`&str`]: ../primitive.str.html
        ///
        /// # 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 [`Cow`]`<`[`str`]`>`.
        ///
        /// If the contents of the `CStr` are valid UTF-8 data, this
        /// function will return a [`Cow`]`::`[`Borrowed`]`(`[`&str`]`)`
        /// with the corresponding [`&str`] slice. Otherwise, it will
        /// replace any invalid UTF-8 sequences with
        /// [`U+FFFD REPLACEMENT CHARACTER`][U+FFFD] and return a
        /// [`Cow`]`::`[`Owned`]`(`[`String`]`)` with the result.
        ///
        /// [`Cow`]: ../borrow/enum.Cow.html
        /// [`Borrowed`]: ../borrow/enum.Cow.html#variant.Borrowed
        /// [`Owned`]: ../borrow/enum.Cow.html#variant.Owned
        /// [`str`]: ../primitive.str.html
        /// [`String`]: ../string/struct.String.html
        /// [U+FFFD]: ../char/constant.REPLACEMENT_CHARACTER.html
        ///
        /// # 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>
        /// );
        /// ```
        #[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 [`Box`]`<CStr>` into a [`CString`] without copying or allocating.
        ///
        /// [`Box`]: ../boxed/struct.Box.html
        /// [`CString`]: struct.CString.html
        ///
        /// # 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"));
        /// ```
        #[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 {
        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 = "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
        }
    }

    #[cfg(test)]
    mod tests {
        use super::*;
        use crate::borrow::Cow::{Borrowed, Owned};
        use crate::collections::hash_map::DefaultHasher;
        use crate::hash::{Hash, Hasher};
        use crate::os::raw::c_char;
        use crate::rc::Rc;
        use crate::sync::Arc;

        #[test]
        fn c_to_rust() {
            let data = b"123\0";
            let ptr = data.as_ptr() as *const c_char;
            unsafe {
                assert_eq!(CStr::from_ptr(ptr).to_bytes(), b"123");
                assert_eq!(CStr::from_ptr(ptr).to_bytes_with_nul(), b"123\0");
            }
        }

        #[test]
        fn simple() {
            let s = CString::new("1234").unwrap();
            assert_eq!(s.as_bytes(), b"1234");
            assert_eq!(s.as_bytes_with_nul(), b"1234\0");
        }

        #[test]
        fn build_with_zero1() {
            assert!(CString::new(&b"\0"[..]).is_err());
        }
        #[test]
        fn build_with_zero2() {
            assert!(CString::new(vec![0]).is_err());
        }

        #[test]
        fn build_with_zero3() {
            unsafe {
                let s = CString::from_vec_unchecked(vec![0]);
                assert_eq!(s.as_bytes(), b"\0");
            }
        }

        #[test]
        fn formatted() {
            let s = CString::new(&b"abc\x01\x02\n\xE2\x80\xA6\xFF"[..]).unwrap();
            assert_eq!(format!("{:?}", s), r#""abc\x01\x02\n\xe2\x80\xa6\xff""#);
        }

        #[test]
        fn borrowed() {
            unsafe {
                let s = CStr::from_ptr(b"12\0".as_ptr() as *const _);
                assert_eq!(s.to_bytes(), b"12");
                assert_eq!(s.to_bytes_with_nul(), b"12\0");
            }
        }

        #[test]
        fn to_str() {
            let data = b"123\xE2\x80\xA6\0";
            let ptr = data.as_ptr() as *const c_char;
            unsafe {
                assert_eq!(CStr::from_ptr(ptr).to_str(), Ok("123…"));
                assert_eq!(CStr::from_ptr(ptr).to_string_lossy(), Borrowed("123…"));
            }
            let data = b"123\xE2\0";
            let ptr = data.as_ptr() as *const c_char;
            unsafe {
                assert!(CStr::from_ptr(ptr).to_str().is_err());
                assert_eq!(CStr::from_ptr(ptr).to_string_lossy(), Owned::<str>(format!("123\u{FFFD}")));
            }
        }

        #[test]
        fn to_owned() {
            let data = b"123\0";
            let ptr = data.as_ptr() as *const c_char;

            let owned = unsafe { CStr::from_ptr(ptr).to_owned() };
            assert_eq!(owned.as_bytes_with_nul(), data);
        }

        #[test]
        fn equal_hash() {
            let data = b"123\xE2\xFA\xA6\0";
            let ptr = data.as_ptr() as *const c_char;
            let cstr: &'static CStr = unsafe { CStr::from_ptr(ptr) };

            let mut s = DefaultHasher::new();
            cstr.hash(&mut s);
            let cstr_hash = s.finish();
            let mut s = DefaultHasher::new();
            CString::new(&data[..data.len() - 1]).unwrap().hash(&mut s);
            let cstring_hash = s.finish();

            assert_eq!(cstr_hash, cstring_hash);
        }

        #[test]
        fn from_bytes_with_nul() {
            let data = b"123\0";
            let cstr = CStr::from_bytes_with_nul(data);
            assert_eq!(cstr.map(CStr::to_bytes), Ok(&b"123"[..]));
            let cstr = CStr::from_bytes_with_nul(data);
            assert_eq!(cstr.map(CStr::to_bytes_with_nul), Ok(&b"123\0"[..]));

            unsafe {
                let cstr = CStr::from_bytes_with_nul(data);
                let cstr_unchecked = CStr::from_bytes_with_nul_unchecked(data);
                assert_eq!(cstr, Ok(cstr_unchecked));
            }
        }

        #[test]
        fn from_bytes_with_nul_unterminated() {
            let data = b"123";
            let cstr = CStr::from_bytes_with_nul(data);
            assert!(cstr.is_err());
        }

        #[test]
        fn from_bytes_with_nul_interior() {
            let data = b"1\023\0";
            let cstr = CStr::from_bytes_with_nul(data);
            assert!(cstr.is_err());
        }

        #[test]
        fn into_boxed() {
            let orig: &[u8] = b"Hello, world!\0";
            let cstr = CStr::from_bytes_with_nul(orig).unwrap();
            let boxed: Box<CStr> = Box::from(cstr);
            let cstring = cstr.to_owned().into_boxed_c_str().into_c_string();
            assert_eq!(cstr, &*boxed);
            assert_eq!(&*boxed, &*cstring);
            assert_eq!(&*cstring, cstr);
        }

        #[test]
        fn boxed_default() {
            let boxed = <Box<CStr>>::default();
            assert_eq!(boxed.to_bytes_with_nul(), &[0]);
        }

        #[test]
        fn test_c_str_clone_into() {
            let mut c_string = CString::new("lorem").unwrap();
            let c_ptr = c_string.as_ptr();
            let c_str = CStr::from_bytes_with_nul(b"ipsum\0").unwrap();
            c_str.clone_into(&mut c_string);
            assert_eq!(c_str, c_string.as_c_str());
            // The exact same size shouldn't have needed to move its allocation
            assert_eq!(c_ptr, c_string.as_ptr());
        }

        #[test]
        fn into_rc() {
            let orig: &[u8] = b"Hello, world!\0";
            let cstr = CStr::from_bytes_with_nul(orig).unwrap();
            let rc: Rc<CStr> = Rc::from(cstr);
            let arc: Arc<CStr> = Arc::from(cstr);

            assert_eq!(&*rc, cstr);
            assert_eq!(&*arc, cstr);

            let rc2: Rc<CStr> = Rc::from(cstr.to_owned());
            let arc2: Arc<CStr> = Arc::from(cstr.to_owned());

            assert_eq!(&*rc2, cstr);
            assert_eq!(&*arc2, cstr);
        }

        #[test]
        fn cstr_const_constructor() {
            const CSTR: &CStr = unsafe { CStr::from_bytes_with_nul_unchecked(b"Hello, world!\0") };

            assert_eq!(CSTR.to_str().unwrap(), "Hello, world!");
        }
    }