c_str.rs.html -- source
Description: Source to the Rust file `/usr/obj/ports/rust-1.20.0/rustc-1.20.0-src/src/libstd/ffi/c_str.rs`.
Keywords: rust, rustlang, rust-lang

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    // Copyright 2012 The Rust Project Developers. See the COPYRIGHT
    // file at the top-level directory of this distribution and at
    // http://rust-lang.org/COPYRIGHT.
    //
    // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
    // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
    // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
    // option. This file may not be copied, modified, or distributed
    // except according to those terms.

    use ascii;
    use borrow::{Cow, Borrow};
    use cmp::Ordering;
    use error::Error;
    use fmt::{self, Write};
    use io;
    use libc;
    use mem;
    use memchr;
    use ops;
    use os::raw::c_char;
    use ptr;
    use slice;
    use str::{self, Utf8Error};

    /// A type representing an owned C-compatible string.
    ///
    /// This type serves the primary 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 and the final byte is 0.
    ///
    /// A `CString` is created from either a byte slice or a byte vector. A [`u8`]
    /// slice can be obtained with the `as_bytes` method. Slices produced from a
    /// `CString` do *not* contain the trailing nul terminator unless otherwise
    /// specified.
    ///
    /// [`u8`]: ../primitive.u8.html
    ///
    /// # Examples
    ///
    /// ```no_run
    /// # fn main() {
    /// use std::ffi::CString;
    /// use std::os::raw::c_char;
    ///
    /// extern {
    ///     fn my_printer(s: *const c_char);
    /// }
    ///
    /// let c_to_print = CString::new("Hello, world!").unwrap();
    /// unsafe {
    ///     my_printer(c_to_print.as_ptr());
    /// }
    /// # }
    /// ```
    ///
    /// # Safety
    ///
    /// `CString` is intended for working with traditional C-style strings
    /// (a sequence of non-null bytes terminated by a single null 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 dynamically sized type is only safely constructed via a borrowed
    /// version of an instance of `CString`. This type can be constructed from a raw
    /// C string as well and represents a C string borrowed from another location.
    ///
    /// 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.
    ///
    /// [`from_ptr`]: #method.from_ptr
    ///
    /// # Examples
    ///
    /// Inspecting a foreign C string:
    ///
    /// ```no_run
    /// 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 length: {}", slice.to_bytes().len());
    /// }
    /// ```
    ///
    /// Passing a Rust-originating C string:
    ///
    /// ```no_run
    /// 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").unwrap();
    /// work(&s);
    /// ```
    ///
    /// Converting a foreign C string into a Rust [`String`]:
    ///
    /// [`String`]: ../string/struct.String.html
    ///
    /// ```no_run
    /// 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());
    /// ```
    #[derive(Hash)]
    #[stable(feature = "rust1", since = "1.0.0")]
    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 returned from [`CString::new`] to indicate that a nul byte was found
    /// in the vector provided.
    ///
    /// [`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 returned from [`CStr::from_bytes_with_nul`] to indicate that a nul
    /// byte was found too early in the slice provided or one wasn't found at all.
    ///
    /// [`CStr::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,
    }

    #[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,
            }
        }
    }

    /// An error returned from [`CString::into_string`] to indicate that a UTF-8 error
    /// was encountered during the conversion.
    ///
    /// [`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 method will consume the provided data and use the underlying bytes
        /// to construct a new string, ensuring that there is a trailing 0 byte.
        ///
        /// # Examples
        ///
        /// ```no_run
        /// use std::ffi::CString;
        /// use std::os::raw::c_char;
        ///
        /// extern { fn puts(s: *const c_char); }
        ///
        /// let to_print = CString::new("Hello!").unwrap();
        /// unsafe {
        ///     puts(to_print.as_ptr());
        /// }
        /// ```
        ///
        /// # Errors
        ///
        /// This function will return an error if the bytes yielded contain an
        /// internal 0 byte. The error returned will contain the bytes as well as
        /// the position of the nul byte.
        #[stable(feature = "rust1", since = "1.0.0")]
        pub fn new<T: Into<Vec<u8>>>(t: T) -> Result<CString, NulError> {
            Self::_new(t.into())
        }

        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 from 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.
        ///
        /// 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.
        ///
        /// [`into_raw`]: #method.into_raw
        ///
        /// # Examples
        ///
        /// Create a `CString`, pass ownership to an `extern` function (via raw pointer), then retake
        /// ownership with `from_raw`:
        ///
        /// ```no_run
        /// 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!").unwrap();
        /// 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 = libc::strlen(ptr) + 1; // Including the NUL byte
            let slice = slice::from_raw_parts(ptr, len as usize);
            CString { inner: mem::transmute(slice) }
        }

        /// Transfers ownership of the string to a C caller.
        ///
        /// The pointer 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.
        ///
        /// [`from_raw`]: #method.from_raw
        ///
        /// # Examples
        ///
        /// ```
        /// use std::ffi::CString;
        ///
        /// let c_string = CString::new("foo").unwrap();
        ///
        /// 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 Unicode data.
        ///
        /// On failure, ownership of the original `CString` is returned.
        ///
        /// [`String`]: ../string/struct.String.html
        #[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()) },
                })
        }

        /// Returns the underlying byte buffer.
        ///
        /// The returned buffer does **not** contain the trailing nul separator and
        /// it is guaranteed to not have any interior nul bytes.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::ffi::CString;
        ///
        /// let c_string = CString::new("foo").unwrap();
        /// 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 byte.
        ///
        /// [`into_bytes`]: #method.into_bytes
        ///
        /// # Examples
        ///
        /// ```
        /// use std::ffi::CString;
        ///
        /// let c_string = CString::new("foo").unwrap();
        /// 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 separator and
        /// it is guaranteed to not have any interior nul bytes.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::ffi::CString;
        ///
        /// let c_string = CString::new("foo").unwrap();
        /// 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 byte.
        ///
        /// [`as_bytes`]: #method.as_bytes
        ///
        /// # Examples
        ///
        /// ```
        /// use std::ffi::CString;
        ///
        /// let c_string = CString::new("foo").unwrap();
        /// 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()).unwrap();
        /// let c_str = c_string.as_c_str();
        /// assert_eq!(c_str, CStr::from_bytes_with_nul(b"foo\0").unwrap());
        /// ```
        #[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()).unwrap();
        /// let boxed = c_string.into_boxed_c_str();
        /// assert_eq!(&*boxed, CStr::from_bytes_with_nul(b"foo\0").unwrap());
        /// ```
        #[stable(feature = "into_boxed_c_str", since = "1.20.0")]
        pub fn into_boxed_c_str(self) -> Box<CStr> {
            unsafe { mem::transmute(self.into_inner()) }
        }

        // Bypass "move out of struct which implements [`Drop`] trait" restriction.
        ///
        /// [`Drop`]: ../ops/trait.Drop.html
        fn into_inner(self) -> Box<[u8]> {
            unsafe {
                let result = ptr::read(&self.inner);
                mem::forget(self);
                result
            }
        }
    }

    // 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> {
        #[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<'a> Default for &'a CStr {
        fn default() -> &'a CStr {
            static SLICE: &'static [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 = "box_from_c_str", since = "1.17.0")]
    impl<'a> From<&'a CStr> for Box<CStr> {
        fn from(s: &'a CStr) -> Box<CStr> {
            let boxed: Box<[u8]> = Box::from(s.to_bytes_with_nul());
            unsafe { mem::transmute(boxed) }
        }
    }

    #[stable(feature = "c_string_from_box", since = "1.18.0")]
    impl From<Box<CStr>> for CString {
        #[inline]
        fn from(s: Box<CStr>) -> CString {
            s.into_c_string()
        }
    }

    #[stable(feature = "box_from_c_string", since = "1.20.0")]
    impl From<CString> for Box<CStr> {
        #[inline]
        fn from(s: CString) -> Box<CStr> {
            s.into_boxed_c_str()
        }
    }

    #[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 { mem::transmute(boxed) }
        }
    }

    impl NulError {
        /// Returns the position of the nul byte in the slice that was provided to
        /// [`CString::new`].
        ///
        /// [`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 {
        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 {
        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 {
        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 {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            f.write_str(self.description())?;
            if let FromBytesWithNulErrorKind::InteriorNul(pos) = self.kind {
                write!(f, " at byte pos {}", pos)?;
            }
            Ok(())
        }
    }

    impl 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 {
        fn description(&self) -> &str {
            "C string contained non-utf8 bytes"
        }

        fn cause(&self) -> Option<&Error> {
            Some(&self.error)
        }
    }

    #[stable(feature = "cstring_into", since = "1.7.0")]
    impl fmt::Display for IntoStringError {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            self.description().fmt(f)
        }
    }

    impl CStr {
        /// Casts a raw C string to a safe C string wrapper.
        ///
        /// This function will cast the provided `ptr` to the `CStr` wrapper which
        /// allows inspection and interoperation of non-owned C strings. 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.
        ///
        /// > **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
        ///
        /// ```no_run
        /// # 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 = libc::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 it is null 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 byte is an error:
        ///
        /// ```
        /// use std::ffi::CStr;
        ///
        /// let c_str = CStr::from_bytes_with_nul(b"hello");
        /// assert!(c_str.is_err());
        /// ```
        ///
        /// Creating a `CStr` with an interior nul byte is an error:
        ///
        /// ```
        /// use std::ffi::CStr;
        ///
        /// let c_str = CStr::from_bytes_with_nul(b"he\0llo\0");
        /// assert!(c_str.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 null terminated
        /// and not contain any interior nul bytes.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::ffi::{CStr, CString};
        ///
        /// unsafe {
        ///     let cstring = CString::new("hello").unwrap();
        ///     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")]
        pub unsafe fn from_bytes_with_nul_unchecked(bytes: &[u8]) -> &CStr {
            mem::transmute(bytes)
        }

        /// 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**
        ///
        /// It is your responsibility to make sure that the underlying memory is not
        /// freed too early. For example, the following code will cause undefined
        /// behaviour when `ptr` is used inside the `unsafe` block:
        ///
        /// ```no_run
        /// use std::ffi::{CString};
        ///
        /// let ptr = CString::new("Hello").unwrap().as_ptr();
        /// unsafe {
        ///     // `ptr` is dangling
        ///     *ptr;
        /// }
        /// ```
        ///
        /// This happens because the pointer returned by `as_ptr` does not carry any
        /// lifetime information and the string is deallocated immediately after
        /// the `CString::new("Hello").unwrap().as_ptr()` expression is evaluated.
        /// To fix the problem, bind the string to a local variable:
        ///
        /// ```no_run
        /// use std::ffi::{CString};
        ///
        /// let hello = CString::new("Hello").unwrap();
        /// let ptr = hello.as_ptr();
        /// unsafe {
        ///     // `ptr` is valid because `hello` is in scope
        ///     *ptr;
        /// }
        /// ```
        #[inline]
        #[stable(feature = "rust1", since = "1.0.0")]
        pub fn as_ptr(&self) -> *const c_char {
            self.inner.as_ptr()
        }

        /// Converts this C string to a byte slice.
        ///
        /// This function will calculate the length of this string (which normally
        /// requires a linear amount of work to be done) and then return the
        /// resulting slice of `u8` elements.
        ///
        /// The returned slice will **not** contain the trailing nul that this C
        /// string has.
        ///
        /// > **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 c_str = CStr::from_bytes_with_nul(b"foo\0").unwrap();
        /// assert_eq!(c_str.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 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 c_str = CStr::from_bytes_with_nul(b"foo\0").unwrap();
        /// assert_eq!(c_str.to_bytes_with_nul(), b"foo\0");
        /// ```
        #[inline]
        #[stable(feature = "rust1", since = "1.0.0")]
        pub fn to_bytes_with_nul(&self) -> &[u8] {
            unsafe { mem::transmute(&self.inner) }
        }

        /// Yields a [`&str`] slice if the `CStr` contains valid UTF-8.
        ///
        /// This function will calculate the length of this string and check for
        /// UTF-8 validity, and then return the [`&str`] if it's valid.
        ///
        /// > **Note**: This method is currently implemented to check for validity
        /// > after a 0-cost cast, but it is planned to alter its definition in the
        /// > future to perform the length calculation in addition to the UTF-8
        /// > check whenever this method is called.
        ///
        /// [`&str`]: ../primitive.str.html
        ///
        /// # Examples
        ///
        /// ```
        /// use std::ffi::CStr;
        ///
        /// let c_str = CStr::from_bytes_with_nul(b"foo\0").unwrap();
        /// assert_eq!(c_str.to_str(), Ok("foo"));
        /// ```
        #[stable(feature = "cstr_to_str", since = "1.4.0")]
        pub fn to_str(&self) -> Result<&str, str::Utf8Error> {
            // NB: 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`]`>`.
        ///
        /// This function will calculate the length of this string (which normally
        /// requires a linear amount of work to be done) and then return the
        /// resulting slice as a [`Cow`]`<`[`str`]`>`, replacing any invalid UTF-8 sequences
        /// with `U+FFFD REPLACEMENT CHARACTER`.
        ///
        /// > **Note**: This method is currently implemented to check for validity
        /// > after a 0-cost cast, but it is planned to alter its definition in the
        /// > future to perform the length calculation in addition to the UTF-8
        /// > check whenever this method is called.
        ///
        /// [`Cow`]: ../borrow/enum.Cow.html
        /// [`str`]: ../primitive.str.html
        ///
        /// # Examples
        ///
        /// Calling `to_string_lossy` on a `CStr` containing valid UTF-8:
        ///
        /// ```
        /// use std::borrow::Cow;
        /// use std::ffi::CStr;
        ///
        /// let c_str = CStr::from_bytes_with_nul(b"Hello World\0").unwrap();
        /// assert_eq!(c_str.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 c_str = CStr::from_bytes_with_nul(b"Hello \xF0\x90\x80World\0").unwrap();
        /// assert_eq!(
        ///     c_str.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()).unwrap();
        /// let boxed = c_string.into_boxed_c_str();
        /// assert_eq!(boxed.into_c_string(), CString::new("foo").unwrap());
        /// ```
        #[stable(feature = "into_boxed_c_str", since = "1.20.0")]
        pub fn into_c_string(self: Box<CStr>) -> CString {
            unsafe { mem::transmute(self) }
        }
    }

    #[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() }
        }
    }

    #[stable(feature = "cstring_asref", since = "1.7.0")]
    impl<'a> From<&'a CStr> for CString {
        fn from(s: &'a 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 os::raw::c_char;
        use borrow::Cow::{Borrowed, Owned};
        use hash::{Hash, Hasher};
        use collections::hash_map::DefaultHasher;

        #[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]);
        }
    }

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