src/libstd/ffi/c_str.rs

   1 use crate::ascii;
   2 use crate::borrow::{Cow, Borrow};
   3 use crate::cmp::Ordering;
   4 use crate::error::Error;
   5 use crate::fmt::{self, Write};
   6 use crate::io;
   7 use crate::mem;
   8 use crate::memchr;
   9 use crate::ops;
  10 use crate::os::raw::c_char;
  11 use crate::ptr;
  12 use crate::rc::Rc;
  13 use crate::slice;
  14 use crate::str::{self, Utf8Error};
  15 use crate::sync::Arc;
  16 use crate::sys;
  17
  18 /// A type representing an owned, C-compatible, nul-terminated string with no nul bytes in the
  19 /// middle.
  20 ///
  21 /// This type serves the purpose of being able to safely generate a
  22 /// C-compatible string from a Rust byte slice or vector. An instance of this
  23 /// type is a static guarantee that the underlying bytes contain no interior 0
  24 /// bytes ("nul characters") and that the final byte is 0 ("nul terminator").
  25 ///
  26 /// `CString` is to [`&CStr`] as [`String`] is to [`&str`]: the former
  27 /// in each pair are owned strings; the latter are borrowed
  28 /// references.
  29 ///
  30 /// # Creating a `CString`
  31 ///
  32 /// A `CString` is created from either a byte slice or a byte vector,
  33 /// or anything that implements [`Into`]`<`[`Vec`]`<`[`u8`]`>>` (for
  34 /// example, you can build a `CString` straight out of a [`String`] or
  35 /// a [`&str`], since both implement that trait).
  36 ///
  37 /// The [`new`] method will actually check that the provided `&[u8]`
  38 /// does not have 0 bytes in the middle, and return an error if it
  39 /// finds one.
  40 ///
  41 /// # Extracting a raw pointer to the whole C string
  42 ///
  43 /// `CString` implements a [`as_ptr`] method through the [`Deref`]
  44 /// trait. This method will give you a `*const c_char` which you can
  45 /// feed directly to extern functions that expect a nul-terminated
  46 /// string, like C's `strdup()`. Notice that [`as_ptr`] returns a
  47 /// read-only pointer; if the C code writes to it, that causes
  48 /// undefined behavior.
  49 ///
  50 /// # Extracting a slice of the whole C string
  51 ///
  52 /// Alternatively, you can obtain a `&[`[`u8`]`]` slice from a
  53 /// `CString` with the [`as_bytes`] method. Slices produced in this
  54 /// way do *not* contain the trailing nul terminator. This is useful
  55 /// when you will be calling an extern function that takes a `*const
  56 /// u8` argument which is not necessarily nul-terminated, plus another
  57 /// argument with the length of the string — like C's `strndup()`.
  58 /// You can of course get the slice's length with its
  59 /// [`len`][slice.len] method.
  60 ///
  61 /// If you need a `&[`[`u8`]`]` slice *with* the nul terminator, you
  62 /// can use [`as_bytes_with_nul`] instead.
  63 ///
  64 /// Once you have the kind of slice you need (with or without a nul
  65 /// terminator), you can call the slice's own
  66 /// [`as_ptr`][slice.as_ptr] method to get a read-only raw pointer to pass to
  67 /// extern functions. See the documentation for that function for a
  68 /// discussion on ensuring the lifetime of the raw pointer.
  69 ///
  70 /// [`Into`]: ../convert/trait.Into.html
  71 /// [`Vec`]: ../vec/struct.Vec.html
  72 /// [`String`]: ../string/struct.String.html
  73 /// [`&str`]: ../primitive.str.html
  74 /// [`u8`]: ../primitive.u8.html
  75 /// [`new`]: #method.new
  76 /// [`as_bytes`]: #method.as_bytes
  77 /// [`as_bytes_with_nul`]: #method.as_bytes_with_nul
  78 /// [`as_ptr`]: #method.as_ptr
  79 /// [slice.as_ptr]: ../primitive.slice.html#method.as_ptr
  80 /// [slice.len]: ../primitive.slice.html#method.len
  81 /// [`Deref`]: ../ops/trait.Deref.html
  82 /// [`CStr`]: struct.CStr.html
  83 /// [`&CStr`]: struct.CStr.html
  84 ///
  85 /// # Examples
  86 ///
  87 /// ```ignore (extern-declaration)
  88 /// # fn main() {
  89 /// use std::ffi::CString;
  90 /// use std::os::raw::c_char;
  91 ///
  92 /// extern {
  93 ///     fn my_printer(s: *const c_char);
  94 /// }
  95 ///
  96 /// // We are certain that our string doesn't have 0 bytes in the middle,
  97 /// // so we can .expect()
  98 /// let c_to_print = CString::new("Hello, world!").expect("CString::new failed");
  99 /// unsafe {
 100 ///     my_printer(c_to_print.as_ptr());
 101 /// }
 102 /// # }
 103 /// ```
 104 ///
 105 /// # Safety
 106 ///
 107 /// `CString` is intended for working with traditional C-style strings
 108 /// (a sequence of non-nul bytes terminated by a single nul byte); the
 109 /// primary use case for these kinds of strings is interoperating with C-like
 110 /// code. Often you will need to transfer ownership to/from that external
 111 /// code. It is strongly recommended that you thoroughly read through the
 112 /// documentation of `CString` before use, as improper ownership management
 113 /// of `CString` instances can lead to invalid memory accesses, memory leaks,
 114 /// and other memory errors.
 115
 116 #[derive(PartialEq, PartialOrd, Eq, Ord, Hash, Clone)]
 117 #[stable(feature = "rust1", since = "1.0.0")]
 118 pub struct CString {
 119     // Invariant 1: the slice ends with a zero byte and has a length of at least one.
 120     // Invariant 2: the slice contains only one zero byte.
 121     // Improper usage of unsafe function can break Invariant 2, but not Invariant 1.
 122     inner: Box<[u8]>,
 123 }
 124
 125 /// Representation of a borrowed C string.
 126 ///
 127 /// This type represents a borrowed reference to a nul-terminated
 128 /// array of bytes. It can be constructed safely from a `&[`[`u8`]`]`
 129 /// slice, or unsafely from a raw `*const c_char`. It can then be
 130 /// converted to a Rust [`&str`] by performing UTF-8 validation, or
 131 /// into an owned [`CString`].
 132 ///
 133 /// `&CStr` is to [`CString`] as [`&str`] is to [`String`]: the former
 134 /// in each pair are borrowed references; the latter are owned
 135 /// strings.
 136 ///
 137 /// Note that this structure is **not** `repr(C)` and is not recommended to be
 138 /// placed in the signatures of FFI functions. Instead, safe wrappers of FFI
 139 /// functions may leverage the unsafe [`from_ptr`] constructor to provide a safe
 140 /// interface to other consumers.
 141 ///
 142 /// # Examples
 143 ///
 144 /// Inspecting a foreign C string:
 145 ///
 146 /// ```ignore (extern-declaration)
 147 /// use std::ffi::CStr;
 148 /// use std::os::raw::c_char;
 149 ///
 150 /// extern { fn my_string() -> *const c_char; }
 151 ///
 152 /// unsafe {
 153 ///     let slice = CStr::from_ptr(my_string());
 154 ///     println!("string buffer size without nul terminator: {}", slice.to_bytes().len());
 155 /// }
 156 /// ```
 157 ///
 158 /// Passing a Rust-originating C string:
 159 ///
 160 /// ```ignore (extern-declaration)
 161 /// use std::ffi::{CString, CStr};
 162 /// use std::os::raw::c_char;
 163 ///
 164 /// fn work(data: &CStr) {
 165 ///     extern { fn work_with(data: *const c_char); }
 166 ///
 167 ///     unsafe { work_with(data.as_ptr()) }
 168 /// }
 169 ///
 170 /// let s = CString::new("data data data data").expect("CString::new failed");
 171 /// work(&s);
 172 /// ```
 173 ///
 174 /// Converting a foreign C string into a Rust [`String`]:
 175 ///
 176 /// ```ignore (extern-declaration)
 177 /// use std::ffi::CStr;
 178 /// use std::os::raw::c_char;
 179 ///
 180 /// extern { fn my_string() -> *const c_char; }
 181 ///
 182 /// fn my_string_safe() -> String {
 183 ///     unsafe {
 184 ///         CStr::from_ptr(my_string()).to_string_lossy().into_owned()
 185 ///     }
 186 /// }
 187 ///
 188 /// println!("string: {}", my_string_safe());
 189 /// ```
 190 ///
 191 /// [`u8`]: ../primitive.u8.html
 192 /// [`&str`]: ../primitive.str.html
 193 /// [`String`]: ../string/struct.String.html
 194 /// [`CString`]: struct.CString.html
 195 /// [`from_ptr`]: #method.from_ptr
 196 #[derive(Hash)]
 197 #[stable(feature = "rust1", since = "1.0.0")]
 198 // FIXME:
 199 // `fn from` in `impl From<&CStr> for Box<CStr>` current implementation relies
 200 // on `CStr` being layout-compatible with `[u8]`.
 201 // When attribute privacy is implemented, `CStr` should be annotated as `#[repr(transparent)]`.
 202 // Anyway, `CStr` representation and layout are considered implementation detail, are
 203 // not documented and must not be relied upon.
 204 pub struct CStr {
 205     // FIXME: this should not be represented with a DST slice but rather with
 206     //        just a raw `c_char` along with some form of marker to make
 207     //        this an unsized type. Essentially `sizeof(&CStr)` should be the
 208     //        same as `sizeof(&c_char)` but `CStr` should be an unsized type.
 209     inner: [c_char]
 210 }
 211
 212 /// An error indicating that an interior nul byte was found.
 213 ///
 214 /// While Rust strings may contain nul bytes in the middle, C strings
 215 /// can't, as that byte would effectively truncate the string.
 216 ///
 217 /// This error is created by the [`new`][`CString::new`] method on
 218 /// [`CString`]. See its documentation for more.
 219 ///
 220 /// [`CString`]: struct.CString.html
 221 /// [`CString::new`]: struct.CString.html#method.new
 222 ///
 223 /// # Examples
 224 ///
 225 /// ```
 226 /// use std::ffi::{CString, NulError};
 227 ///
 228 /// let _: NulError = CString::new(b"f\0oo".to_vec()).unwrap_err();
 229 /// ```
 230 #[derive(Clone, PartialEq, Eq, Debug)]
 231 #[stable(feature = "rust1", since = "1.0.0")]
 232 pub struct NulError(usize, Vec<u8>);
 233
 234 /// An error indicating that a nul byte was not in the expected position.
 235 ///
 236 /// The slice used to create a [`CStr`] must have one and only one nul
 237 /// byte at the end of the slice.
 238 ///
 239 /// This error is created by the
 240 /// [`from_bytes_with_nul`][`CStr::from_bytes_with_nul`] method on
 241 /// [`CStr`]. See its documentation for more.
 242 ///
 243 /// [`CStr`]: struct.CStr.html
 244 /// [`CStr::from_bytes_with_nul`]: struct.CStr.html#method.from_bytes_with_nul
 245 ///
 246 /// # Examples
 247 ///
 248 /// ```
 249 /// use std::ffi::{CStr, FromBytesWithNulError};
 250 ///
 251 /// let _: FromBytesWithNulError = CStr::from_bytes_with_nul(b"f\0oo").unwrap_err();
 252 /// ```
 253 #[derive(Clone, PartialEq, Eq, Debug)]
 254 #[stable(feature = "cstr_from_bytes", since = "1.10.0")]
 255 pub struct FromBytesWithNulError {
 256     kind: FromBytesWithNulErrorKind,
 257 }
 258
 259 #[derive(Clone, PartialEq, Eq, Debug)]
 260 enum FromBytesWithNulErrorKind {
 261     InteriorNul(usize),
 262     NotNulTerminated,
 263 }
 264
 265 impl FromBytesWithNulError {
 266     fn interior_nul(pos: usize) -> FromBytesWithNulError {
 267         FromBytesWithNulError {
 268             kind: FromBytesWithNulErrorKind::InteriorNul(pos),
 269         }
 270     }
 271     fn not_nul_terminated() -> FromBytesWithNulError {
 272         FromBytesWithNulError {
 273             kind: FromBytesWithNulErrorKind::NotNulTerminated,
 274         }
 275     }
 276 }
 277
 278 /// An error indicating invalid UTF-8 when converting a [`CString`] into a [`String`].
 279 ///
 280 /// `CString` is just a wrapper over a buffer of bytes with a nul
 281 /// terminator; [`into_string`][`CString::into_string`] performs UTF-8
 282 /// validation on those bytes and may return this error.
 283 ///
 284 /// This `struct` is created by the
 285 /// [`into_string`][`CString::into_string`] method on [`CString`]. See
 286 /// its documentation for more.
 287 ///
 288 /// [`String`]: ../string/struct.String.html
 289 /// [`CString`]: struct.CString.html
 290 /// [`CString::into_string`]: struct.CString.html#method.into_string
 291 #[derive(Clone, PartialEq, Eq, Debug)]
 292 #[stable(feature = "cstring_into", since = "1.7.0")]
 293 pub struct IntoStringError {
 294     inner: CString,
 295     error: Utf8Error,
 296 }
 297
 298 impl CString {
 299     /// Creates a new C-compatible string from a container of bytes.
 300     ///
 301     /// This function will consume the provided data and use the
 302     /// underlying bytes to construct a new string, ensuring that
 303     /// there is a trailing 0 byte. This trailing 0 byte will be
 304     /// appended by this function; the provided data should *not*
 305     /// contain any 0 bytes in it.
 306     ///
 307     /// # Examples
 308     ///
 309     /// ```ignore (extern-declaration)
 310     /// use std::ffi::CString;
 311     /// use std::os::raw::c_char;
 312     ///
 313     /// extern { fn puts(s: *const c_char); }
 314     ///
 315     /// let to_print = CString::new("Hello!").expect("CString::new failed");
 316     /// unsafe {
 317     ///     puts(to_print.as_ptr());
 318     /// }
 319     /// ```
 320     ///
 321     /// # Errors
 322     ///
 323     /// This function will return an error if the supplied bytes contain an
 324     /// internal 0 byte. The [`NulError`] returned will contain the bytes as well as
 325     /// the position of the nul byte.
 326     ///
 327     /// [`NulError`]: struct.NulError.html
 328     #[stable(feature = "rust1", since = "1.0.0")]
 329     pub fn new<T: Into<Vec<u8>>>(t: T) -> Result<CString, NulError> {
 330         trait SpecIntoVec {
 331             fn into_vec(self) -> Vec<u8>;
 332         }
 333         impl<T: Into<Vec<u8>>> SpecIntoVec for T {
 334             default fn into_vec(self) -> Vec<u8> {
 335                 self.into()
 336             }
 337         }
 338         // Specialization for avoiding reallocation.
 339         impl SpecIntoVec for &'_ [u8] {
 340             fn into_vec(self) -> Vec<u8> {
 341                 let mut v = Vec::with_capacity(self.len() + 1);
 342                 v.extend(self);
 343                 v
 344             }
 345         }
 346         impl SpecIntoVec for &'_ str {
 347             fn into_vec(self) -> Vec<u8> {
 348                 let mut v = Vec::with_capacity(self.len() + 1);
 349                 v.extend(self.as_bytes());
 350                 v
 351             }
 352         }
 353
 354         Self::_new(SpecIntoVec::into_vec(t))
 355     }
 356
 357     fn _new(bytes: Vec<u8>) -> Result<CString, NulError> {
 358         match memchr::memchr(0, &bytes) {
 359             Some(i) => Err(NulError(i, bytes)),
 360             None => Ok(unsafe { CString::from_vec_unchecked(bytes) }),
 361         }
 362     }
 363
 364     /// Creates a C-compatible string by consuming a byte vector,
 365     /// without checking for interior 0 bytes.
 366     ///
 367     /// This method is equivalent to [`new`] except that no runtime assertion
 368     /// is made that `v` contains no 0 bytes, and it requires an actual
 369     /// byte vector, not anything that can be converted to one with Into.
 370     ///
 371     /// [`new`]: #method.new
 372     ///
 373     /// # Examples
 374     ///
 375     /// ```
 376     /// use std::ffi::CString;
 377     ///
 378     /// let raw = b"foo".to_vec();
 379     /// unsafe {
 380     ///     let c_string = CString::from_vec_unchecked(raw);
 381     /// }
 382     /// ```
 383     #[stable(feature = "rust1", since = "1.0.0")]
 384     pub unsafe fn from_vec_unchecked(mut v: Vec<u8>) -> CString {
 385         v.reserve_exact(1);
 386         v.push(0);
 387         CString { inner: v.into_boxed_slice() }
 388     }
 389
 390     /// Retakes ownership of a `CString` that was transferred to C via [`into_raw`].
 391     ///
 392     /// Additionally, the length of the string will be recalculated from the pointer.
 393     ///
 394     /// # Safety
 395     ///
 396     /// This should only ever be called with a pointer that was earlier
 397     /// obtained by calling [`into_raw`] on a `CString`. Other usage (e.g., trying to take
 398     /// ownership of a string that was allocated by foreign code) is likely to lead
 399     /// to undefined behavior or allocator corruption.
 400     ///
 401     /// > **Note:** If you need to borrow a string that was allocated by
 402     /// > foreign code, use [`CStr`]. If you need to take ownership of
 403     /// > a string that was allocated by foreign code, you will need to
 404     /// > make your own provisions for freeing it appropriately, likely
 405     /// > with the foreign code's API to do that.
 406     ///
 407     /// [`into_raw`]: #method.into_raw
 408     /// [`CStr`]: struct.CStr.html
 409     ///
 410     /// # Examples
 411     ///
 412     /// Creates a `CString`, pass ownership to an `extern` function (via raw pointer), then retake
 413     /// ownership with `from_raw`:
 414     ///
 415     /// ```ignore (extern-declaration)
 416     /// use std::ffi::CString;
 417     /// use std::os::raw::c_char;
 418     ///
 419     /// extern {
 420     ///     fn some_extern_function(s: *mut c_char);
 421     /// }
 422     ///
 423     /// let c_string = CString::new("Hello!").expect("CString::new failed");
 424     /// let raw = c_string.into_raw();
 425     /// unsafe {
 426     ///     some_extern_function(raw);
 427     ///     let c_string = CString::from_raw(raw);
 428     /// }
 429     /// ```
 430     #[stable(feature = "cstr_memory", since = "1.4.0")]
 431     pub unsafe fn from_raw(ptr: *mut c_char) -> CString {
 432         let len = sys::strlen(ptr) + 1; // Including the NUL byte
 433         let slice = slice::from_raw_parts_mut(ptr, len as usize);
 434         CString { inner: Box::from_raw(slice as *mut [c_char] as *mut [u8]) }
 435     }
 436
 437     /// Consumes the `CString` and transfers ownership of the string to a C caller.
 438     ///
 439     /// The pointer which this function returns must be returned to Rust and reconstituted using
 440     /// [`from_raw`] to be properly deallocated. Specifically, one
 441     /// should *not* use the standard C `free()` function to deallocate
 442     /// this string.
 443     ///
 444     /// Failure to call [`from_raw`] will lead to a memory leak.
 445     ///
 446     /// [`from_raw`]: #method.from_raw
 447     ///
 448     /// # Examples
 449     ///
 450     /// ```
 451     /// use std::ffi::CString;
 452     ///
 453     /// let c_string = CString::new("foo").expect("CString::new failed");
 454     ///
 455     /// let ptr = c_string.into_raw();
 456     ///
 457     /// unsafe {
 458     ///     assert_eq!(b'f', *ptr as u8);
 459     ///     assert_eq!(b'o', *ptr.offset(1) as u8);
 460     ///     assert_eq!(b'o', *ptr.offset(2) as u8);
 461     ///     assert_eq!(b'\0', *ptr.offset(3) as u8);
 462     ///
 463     ///     // retake pointer to free memory
 464     ///     let _ = CString::from_raw(ptr);
 465     /// }
 466     /// ```
 467     #[inline]
 468     #[stable(feature = "cstr_memory", since = "1.4.0")]
 469     pub fn into_raw(self) -> *mut c_char {
 470         Box::into_raw(self.into_inner()) as *mut c_char
 471     }
 472
 473     /// Converts the `CString` into a [`String`] if it contains valid UTF-8 data.
 474     ///
 475     /// On failure, ownership of the original `CString` is returned.
 476     ///
 477     /// [`String`]: ../string/struct.String.html
 478     ///
 479     /// # Examples
 480     ///
 481     /// ```
 482     /// use std::ffi::CString;
 483     ///
 484     /// let valid_utf8 = vec![b'f', b'o', b'o'];
 485     /// let cstring = CString::new(valid_utf8).expect("CString::new failed");
 486     /// assert_eq!(cstring.into_string().expect("into_string() call failed"), "foo");
 487     ///
 488     /// let invalid_utf8 = vec![b'f', 0xff, b'o', b'o'];
 489     /// let cstring = CString::new(invalid_utf8).expect("CString::new failed");
 490     /// let err = cstring.into_string().err().expect("into_string().err() failed");
 491     /// assert_eq!(err.utf8_error().valid_up_to(), 1);
 492     /// ```
 493
 494     #[stable(feature = "cstring_into", since = "1.7.0")]
 495     pub fn into_string(self) -> Result<String, IntoStringError> {
 496         String::from_utf8(self.into_bytes())
 497             .map_err(|e| IntoStringError {
 498                 error: e.utf8_error(),
 499                 inner: unsafe { CString::from_vec_unchecked(e.into_bytes()) },
 500             })
 501     }
 502
 503     /// Consumes the `CString` and returns the underlying byte buffer.
 504     ///
 505     /// The returned buffer does **not** contain the trailing nul
 506     /// terminator, and it is guaranteed to not have any interior nul
 507     /// bytes.
 508     ///
 509     /// # Examples
 510     ///
 511     /// ```
 512     /// use std::ffi::CString;
 513     ///
 514     /// let c_string = CString::new("foo").expect("CString::new failed");
 515     /// let bytes = c_string.into_bytes();
 516     /// assert_eq!(bytes, vec![b'f', b'o', b'o']);
 517     /// ```
 518     #[stable(feature = "cstring_into", since = "1.7.0")]
 519     pub fn into_bytes(self) -> Vec<u8> {
 520         let mut vec = self.into_inner().into_vec();
 521         let _nul = vec.pop();
 522         debug_assert_eq!(_nul, Some(0u8));
 523         vec
 524     }
 525
 526     /// Equivalent to the [`into_bytes`] function except that the returned vector
 527     /// includes the trailing nul terminator.
 528     ///
 529     /// [`into_bytes`]: #method.into_bytes
 530     ///
 531     /// # Examples
 532     ///
 533     /// ```
 534     /// use std::ffi::CString;
 535     ///
 536     /// let c_string = CString::new("foo").expect("CString::new failed");
 537     /// let bytes = c_string.into_bytes_with_nul();
 538     /// assert_eq!(bytes, vec![b'f', b'o', b'o', b'\0']);
 539     /// ```
 540     #[stable(feature = "cstring_into", since = "1.7.0")]
 541     pub fn into_bytes_with_nul(self) -> Vec<u8> {
 542         self.into_inner().into_vec()
 543     }
 544
 545     /// Returns the contents of this `CString` as a slice of bytes.
 546     ///
 547     /// The returned slice does **not** contain the trailing nul
 548     /// terminator, and it is guaranteed to not have any interior nul
 549     /// bytes. If you need the nul terminator, use
 550     /// [`as_bytes_with_nul`] instead.
 551     ///
 552     /// [`as_bytes_with_nul`]: #method.as_bytes_with_nul
 553     ///
 554     /// # Examples
 555     ///
 556     /// ```
 557     /// use std::ffi::CString;
 558     ///
 559     /// let c_string = CString::new("foo").expect("CString::new failed");
 560     /// let bytes = c_string.as_bytes();
 561     /// assert_eq!(bytes, &[b'f', b'o', b'o']);
 562     /// ```
 563     #[inline]
 564     #[stable(feature = "rust1", since = "1.0.0")]
 565     pub fn as_bytes(&self) -> &[u8] {
 566         &self.inner[..self.inner.len() - 1]
 567     }
 568
 569     /// Equivalent to the [`as_bytes`] function except that the returned slice
 570     /// includes the trailing nul terminator.
 571     ///
 572     /// [`as_bytes`]: #method.as_bytes
 573     ///
 574     /// # Examples
 575     ///
 576     /// ```
 577     /// use std::ffi::CString;
 578     ///
 579     /// let c_string = CString::new("foo").expect("CString::new failed");
 580     /// let bytes = c_string.as_bytes_with_nul();
 581     /// assert_eq!(bytes, &[b'f', b'o', b'o', b'\0']);
 582     /// ```
 583     #[inline]
 584     #[stable(feature = "rust1", since = "1.0.0")]
 585     pub fn as_bytes_with_nul(&self) -> &[u8] {
 586         &self.inner
 587     }
 588
 589     /// Extracts a [`CStr`] slice containing the entire string.
 590     ///
 591     /// [`CStr`]: struct.CStr.html
 592     ///
 593     /// # Examples
 594     ///
 595     /// ```
 596     /// use std::ffi::{CString, CStr};
 597     ///
 598     /// let c_string = CString::new(b"foo".to_vec()).expect("CString::new failed");
 599     /// let cstr = c_string.as_c_str();
 600     /// assert_eq!(cstr,
 601     ///            CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed"));
 602     /// ```
 603     #[inline]
 604     #[stable(feature = "as_c_str", since = "1.20.0")]
 605     pub fn as_c_str(&self) -> &CStr {
 606         &*self
 607     }
 608
 609     /// Converts this `CString` into a boxed [`CStr`].
 610     ///
 611     /// [`CStr`]: struct.CStr.html
 612     ///
 613     /// # Examples
 614     ///
 615     /// ```
 616     /// use std::ffi::{CString, CStr};
 617     ///
 618     /// let c_string = CString::new(b"foo".to_vec()).expect("CString::new failed");
 619     /// let boxed = c_string.into_boxed_c_str();
 620     /// assert_eq!(&*boxed,
 621     ///            CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed"));
 622     /// ```
 623     #[stable(feature = "into_boxed_c_str", since = "1.20.0")]
 624     pub fn into_boxed_c_str(self) -> Box<CStr> {
 625         unsafe { Box::from_raw(Box::into_raw(self.into_inner()) as *mut CStr) }
 626     }
 627
 628     /// Bypass "move out of struct which implements [`Drop`] trait" restriction.
 629     ///
 630     /// [`Drop`]: ../ops/trait.Drop.html
 631     fn into_inner(self) -> Box<[u8]> {
 632         // Rationale: `mem::forget(self)` invalidates the previous call to `ptr::read(&self.inner)`
 633         // so we use `ManuallyDrop` to ensure `self` is not dropped.
 634         // Then we can return the box directly without invalidating it.
 635         // See https://github.com/rust-lang/rust/issues/62553.
 636         let this = mem::ManuallyDrop::new(self);
 637         unsafe { ptr::read(&this.inner) }
 638     }
 639 }
 640
 641 // Turns this `CString` into an empty string to prevent
 642 // memory-unsafe code from working by accident. Inline
 643 // to prevent LLVM from optimizing it away in debug builds.
 644 #[stable(feature = "cstring_drop", since = "1.13.0")]
 645 impl Drop for CString {
 646     #[inline]
 647     fn drop(&mut self) {
 648         unsafe { *self.inner.get_unchecked_mut(0) = 0; }
 649     }
 650 }
 651
 652 #[stable(feature = "rust1", since = "1.0.0")]
 653 impl ops::Deref for CString {
 654     type Target = CStr;
 655
 656     #[inline]
 657     fn deref(&self) -> &CStr {
 658         unsafe { CStr::from_bytes_with_nul_unchecked(self.as_bytes_with_nul()) }
 659     }
 660 }
 661
 662 #[stable(feature = "rust1", since = "1.0.0")]
 663 impl fmt::Debug for CString {
 664     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 665         fmt::Debug::fmt(&**self, f)
 666     }
 667 }
 668
 669 #[stable(feature = "cstring_into", since = "1.7.0")]
 670 impl From<CString> for Vec<u8> {
 671     /// Converts a [`CString`] into a [`Vec`]`<u8>`.
 672     ///
 673     /// The conversion consumes the [`CString`], and removes the terminating NUL byte.
 674     ///
 675     /// [`Vec`]: ../vec/struct.Vec.html
 676     /// [`CString`]: ../ffi/struct.CString.html
 677     #[inline]
 678     fn from(s: CString) -> Vec<u8> {
 679         s.into_bytes()
 680     }
 681 }
 682
 683 #[stable(feature = "cstr_debug", since = "1.3.0")]
 684 impl fmt::Debug for CStr {
 685     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 686         write!(f, "\"")?;
 687         for byte in self.to_bytes().iter().flat_map(|&b| ascii::escape_default(b)) {
 688             f.write_char(byte as char)?;
 689         }
 690         write!(f, "\"")
 691     }
 692 }
 693
 694 #[stable(feature = "cstr_default", since = "1.10.0")]
 695 impl Default for &CStr {
 696     fn default() -> Self {
 697         const SLICE: &[c_char] = &[0];
 698         unsafe { CStr::from_ptr(SLICE.as_ptr()) }
 699     }
 700 }
 701
 702 #[stable(feature = "cstr_default", since = "1.10.0")]
 703 impl Default for CString {
 704     /// Creates an empty `CString`.
 705     fn default() -> CString {
 706         let a: &CStr = Default::default();
 707         a.to_owned()
 708     }
 709 }
 710
 711 #[stable(feature = "cstr_borrow", since = "1.3.0")]
 712 impl Borrow<CStr> for CString {
 713     #[inline]
 714     fn borrow(&self) -> &CStr { self }
 715 }
 716
 717 #[stable(feature = "cstring_from_cow_cstr", since = "1.28.0")]
 718 impl<'a> From<Cow<'a, CStr>> for CString {
 719     #[inline]
 720     fn from(s: Cow<'a, CStr>) -> Self {
 721         s.into_owned()
 722     }
 723 }
 724
 725 #[stable(feature = "box_from_c_str", since = "1.17.0")]
 726 impl From<&CStr> for Box<CStr> {
 727     fn from(s: &CStr) -> Box<CStr> {
 728         let boxed: Box<[u8]> = Box::from(s.to_bytes_with_nul());
 729         unsafe { Box::from_raw(Box::into_raw(boxed) as *mut CStr) }
 730     }
 731 }
 732
 733 #[stable(feature = "c_string_from_box", since = "1.18.0")]
 734 impl From<Box<CStr>> for CString {
 735     /// Converts a [`Box`]`<CStr>` into a [`CString`] without copying or allocating.
 736     ///
 737     /// [`Box`]: ../boxed/struct.Box.html
 738     /// [`CString`]: ../ffi/struct.CString.html
 739     #[inline]
 740     fn from(s: Box<CStr>) -> CString {
 741         s.into_c_string()
 742     }
 743 }
 744
 745 #[stable(feature = "more_box_slice_clone", since = "1.29.0")]
 746 impl Clone for Box<CStr> {
 747     #[inline]
 748     fn clone(&self) -> Self {
 749         (**self).into()
 750     }
 751 }
 752
 753 #[stable(feature = "box_from_c_string", since = "1.20.0")]
 754 impl From<CString> for Box<CStr> {
 755     /// Converts a [`CString`] into a [`Box`]`<CStr>` without copying or allocating.
 756     ///
 757     /// [`CString`]: ../ffi/struct.CString.html
 758     /// [`Box`]: ../boxed/struct.Box.html
 759     #[inline]
 760     fn from(s: CString) -> Box<CStr> {
 761         s.into_boxed_c_str()
 762     }
 763 }
 764
 765 #[stable(feature = "cow_from_cstr", since = "1.28.0")]
 766 impl<'a> From<CString> for Cow<'a, CStr> {
 767     #[inline]
 768     fn from(s: CString) -> Cow<'a, CStr> {
 769         Cow::Owned(s)
 770     }
 771 }
 772
 773 #[stable(feature = "cow_from_cstr", since = "1.28.0")]
 774 impl<'a> From<&'a CStr> for Cow<'a, CStr> {
 775     #[inline]
 776     fn from(s: &'a CStr) -> Cow<'a, CStr> {
 777         Cow::Borrowed(s)
 778     }
 779 }
 780
 781 #[stable(feature = "cow_from_cstr", since = "1.28.0")]
 782 impl<'a> From<&'a CString> for Cow<'a, CStr> {
 783     #[inline]
 784     fn from(s: &'a CString) -> Cow<'a, CStr> {
 785         Cow::Borrowed(s.as_c_str())
 786     }
 787 }
 788
 789 #[stable(feature = "shared_from_slice2", since = "1.24.0")]
 790 impl From<CString> for Arc<CStr> {
 791     /// Converts a [`CString`] into a [`Arc`]`<CStr>` without copying or allocating.
 792     ///
 793     /// [`CString`]: ../ffi/struct.CString.html
 794     /// [`Arc`]: ../sync/struct.Arc.html
 795     #[inline]
 796     fn from(s: CString) -> Arc<CStr> {
 797         let arc: Arc<[u8]> = Arc::from(s.into_inner());
 798         unsafe { Arc::from_raw(Arc::into_raw(arc) as *const CStr) }
 799     }
 800 }
 801
 802 #[stable(feature = "shared_from_slice2", since = "1.24.0")]
 803 impl From<&CStr> for Arc<CStr> {
 804     #[inline]
 805     fn from(s: &CStr) -> Arc<CStr> {
 806         let arc: Arc<[u8]> = Arc::from(s.to_bytes_with_nul());
 807         unsafe { Arc::from_raw(Arc::into_raw(arc) as *const CStr) }
 808     }
 809 }
 810
 811 #[stable(feature = "shared_from_slice2", since = "1.24.0")]
 812 impl From<CString> for Rc<CStr> {
 813     /// Converts a [`CString`] into a [`Rc`]`<CStr>` without copying or allocating.
 814     ///
 815     /// [`CString`]: ../ffi/struct.CString.html
 816     /// [`Rc`]: ../rc/struct.Rc.html
 817     #[inline]
 818     fn from(s: CString) -> Rc<CStr> {
 819         let rc: Rc<[u8]> = Rc::from(s.into_inner());
 820         unsafe { Rc::from_raw(Rc::into_raw(rc) as *const CStr) }
 821     }
 822 }
 823
 824 #[stable(feature = "shared_from_slice2", since = "1.24.0")]
 825 impl From<&CStr> for Rc<CStr> {
 826     #[inline]
 827     fn from(s: &CStr) -> Rc<CStr> {
 828         let rc: Rc<[u8]> = Rc::from(s.to_bytes_with_nul());
 829         unsafe { Rc::from_raw(Rc::into_raw(rc) as *const CStr) }
 830     }
 831 }
 832
 833 #[stable(feature = "default_box_extra", since = "1.17.0")]
 834 impl Default for Box<CStr> {
 835     fn default() -> Box<CStr> {
 836         let boxed: Box<[u8]> = Box::from([0]);
 837         unsafe { Box::from_raw(Box::into_raw(boxed) as *mut CStr) }
 838     }
 839 }
 840
 841 impl NulError {
 842     /// Returns the position of the nul byte in the slice that caused
 843     /// [`CString::new`] to fail.
 844     ///
 845     /// [`CString::new`]: struct.CString.html#method.new
 846     ///
 847     /// # Examples
 848     ///
 849     /// ```
 850     /// use std::ffi::CString;
 851     ///
 852     /// let nul_error = CString::new("foo\0bar").unwrap_err();
 853     /// assert_eq!(nul_error.nul_position(), 3);
 854     ///
 855     /// let nul_error = CString::new("foo bar\0").unwrap_err();
 856     /// assert_eq!(nul_error.nul_position(), 7);
 857     /// ```
 858     #[stable(feature = "rust1", since = "1.0.0")]
 859     pub fn nul_position(&self) -> usize { self.0 }
 860
 861     /// Consumes this error, returning the underlying vector of bytes which
 862     /// generated the error in the first place.
 863     ///
 864     /// # Examples
 865     ///
 866     /// ```
 867     /// use std::ffi::CString;
 868     ///
 869     /// let nul_error = CString::new("foo\0bar").unwrap_err();
 870     /// assert_eq!(nul_error.into_vec(), b"foo\0bar");
 871     /// ```
 872     #[stable(feature = "rust1", since = "1.0.0")]
 873     pub fn into_vec(self) -> Vec<u8> { self.1 }
 874 }
 875
 876 #[stable(feature = "rust1", since = "1.0.0")]
 877 impl Error for NulError {
 878     fn description(&self) -> &str { "nul byte found in data" }
 879 }
 880
 881 #[stable(feature = "rust1", since = "1.0.0")]
 882 impl fmt::Display for NulError {
 883     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 884         write!(f, "nul byte found in provided data at position: {}", self.0)
 885     }
 886 }
 887
 888 #[stable(feature = "rust1", since = "1.0.0")]
 889 impl From<NulError> for io::Error {
 890     /// Converts a [`NulError`] into a [`io::Error`].
 891     ///
 892     /// [`NulError`]: ../ffi/struct.NulError.html
 893     /// [`io::Error`]: ../io/struct.Error.html
 894     fn from(_: NulError) -> io::Error {
 895         io::Error::new(io::ErrorKind::InvalidInput,
 896                        "data provided contains a nul byte")
 897     }
 898 }
 899
 900 #[stable(feature = "frombyteswithnulerror_impls", since = "1.17.0")]
 901 impl Error for FromBytesWithNulError {
 902     fn description(&self) -> &str {
 903         match self.kind {
 904             FromBytesWithNulErrorKind::InteriorNul(..) =>
 905                 "data provided contains an interior nul byte",
 906             FromBytesWithNulErrorKind::NotNulTerminated =>
 907                 "data provided is not nul terminated",
 908         }
 909     }
 910 }
 911
 912 #[stable(feature = "frombyteswithnulerror_impls", since = "1.17.0")]
 913 impl fmt::Display for FromBytesWithNulError {
 914     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 915         f.write_str(self.description())?;
 916         if let FromBytesWithNulErrorKind::InteriorNul(pos) = self.kind {
 917             write!(f, " at byte pos {}", pos)?;
 918         }
 919         Ok(())
 920     }
 921 }
 922
 923 impl IntoStringError {
 924     /// Consumes this error, returning original [`CString`] which generated the
 925     /// error.
 926     ///
 927     /// [`CString`]: struct.CString.html
 928     #[stable(feature = "cstring_into", since = "1.7.0")]
 929     pub fn into_cstring(self) -> CString {
 930         self.inner
 931     }
 932
 933     /// Access the underlying UTF-8 error that was the cause of this error.
 934     #[stable(feature = "cstring_into", since = "1.7.0")]
 935     pub fn utf8_error(&self) -> Utf8Error {
 936         self.error
 937     }
 938 }
 939
 940 #[stable(feature = "cstring_into", since = "1.7.0")]
 941 impl Error for IntoStringError {
 942     fn description(&self) -> &str {
 943         "C string contained non-utf8 bytes"
 944     }
 945
 946     fn source(&self) -> Option<&(dyn Error + 'static)> {
 947         Some(&self.error)
 948     }
 949 }
 950
 951 #[stable(feature = "cstring_into", since = "1.7.0")]
 952 impl fmt::Display for IntoStringError {
 953     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 954         self.description().fmt(f)
 955     }
 956 }
 957
 958 impl CStr {
 959     /// Wraps a raw C string with a safe C string wrapper.
 960     ///
 961     /// This function will wrap the provided `ptr` with a `CStr` wrapper, which
 962     /// allows inspection and interoperation of non-owned C strings. The total
 963     /// size of the raw C string must be smaller than `isize::MAX` **bytes**
 964     /// in memory due to calling the `slice::from_raw_parts` function.
 965     /// This method is unsafe for a number of reasons:
 966     ///
 967     /// * There is no guarantee to the validity of `ptr`.
 968     /// * The returned lifetime is not guaranteed to be the actual lifetime of
 969     ///   `ptr`.
 970     /// * There is no guarantee that the memory pointed to by `ptr` contains a
 971     ///   valid nul terminator byte at the end of the string.
 972     /// * It is not guaranteed that the memory pointed by `ptr` won't change
 973     ///   before the `CStr` has been destroyed.
 974     ///
 975     /// > **Note**: This operation is intended to be a 0-cost cast but it is
 976     /// > currently implemented with an up-front calculation of the length of
 977     /// > the string. This is not guaranteed to always be the case.
 978     ///
 979     /// # Examples
 980     ///
 981     /// ```ignore (extern-declaration)
 982     /// # fn main() {
 983     /// use std::ffi::CStr;
 984     /// use std::os::raw::c_char;
 985     ///
 986     /// extern {
 987     ///     fn my_string() -> *const c_char;
 988     /// }
 989     ///
 990     /// unsafe {
 991     ///     let slice = CStr::from_ptr(my_string());
 992     ///     println!("string returned: {}", slice.to_str().unwrap());
 993     /// }
 994     /// # }
 995     /// ```
 996     #[stable(feature = "rust1", since = "1.0.0")]
 997     pub unsafe fn from_ptr<'a>(ptr: *const c_char) -> &'a CStr {
 998         let len = sys::strlen(ptr);
 999         let ptr = ptr as *const u8;
1000         CStr::from_bytes_with_nul_unchecked(slice::from_raw_parts(ptr, len as usize + 1))
1001     }
1002
1003     /// Creates a C string wrapper from a byte slice.
1004     ///
1005     /// This function will cast the provided `bytes` to a `CStr`
1006     /// wrapper after ensuring that the byte slice is nul-terminated
1007     /// and does not contain any interior nul bytes.
1008     ///
1009     /// # Examples
1010     ///
1011     /// ```
1012     /// use std::ffi::CStr;
1013     ///
1014     /// let cstr = CStr::from_bytes_with_nul(b"hello\0");
1015     /// assert!(cstr.is_ok());
1016     /// ```
1017     ///
1018     /// Creating a `CStr` without a trailing nul terminator is an error:
1019     ///
1020     /// ```
1021     /// use std::ffi::CStr;
1022     ///
1023     /// let cstr = CStr::from_bytes_with_nul(b"hello");
1024     /// assert!(cstr.is_err());
1025     /// ```
1026     ///
1027     /// Creating a `CStr` with an interior nul byte is an error:
1028     ///
1029     /// ```
1030     /// use std::ffi::CStr;
1031     ///
1032     /// let cstr = CStr::from_bytes_with_nul(b"he\0llo\0");
1033     /// assert!(cstr.is_err());
1034     /// ```
1035     #[stable(feature = "cstr_from_bytes", since = "1.10.0")]
1036     pub fn from_bytes_with_nul(bytes: &[u8])
1037                                -> Result<&CStr, FromBytesWithNulError> {
1038         let nul_pos = memchr::memchr(0, bytes);
1039         if let Some(nul_pos) = nul_pos {
1040             if nul_pos + 1 != bytes.len() {
1041                 return Err(FromBytesWithNulError::interior_nul(nul_pos));
1042             }
1043             Ok(unsafe { CStr::from_bytes_with_nul_unchecked(bytes) })
1044         } else {
1045             Err(FromBytesWithNulError::not_nul_terminated())
1046         }
1047     }
1048
1049     /// Unsafely creates a C string wrapper from a byte slice.
1050     ///
1051     /// This function will cast the provided `bytes` to a `CStr` wrapper without
1052     /// performing any sanity checks. The provided slice **must** be nul-terminated
1053     /// and not contain any interior nul bytes.
1054     ///
1055     /// # Examples
1056     ///
1057     /// ```
1058     /// use std::ffi::{CStr, CString};
1059     ///
1060     /// unsafe {
1061     ///     let cstring = CString::new("hello").expect("CString::new failed");
1062     ///     let cstr = CStr::from_bytes_with_nul_unchecked(cstring.to_bytes_with_nul());
1063     ///     assert_eq!(cstr, &*cstring);
1064     /// }
1065     /// ```
1066     #[inline]
1067     #[stable(feature = "cstr_from_bytes", since = "1.10.0")]
1068     #[cfg_attr(bootstrap, rustc_const_unstable(feature = "const_cstr_unchecked"))]
1069     #[cfg_attr(not(bootstrap), rustc_const_unstable(feature = "const_cstr_unchecked", issue = "0"))]
1070     pub const unsafe fn from_bytes_with_nul_unchecked(bytes: &[u8]) -> &CStr {
1071         &*(bytes as *const [u8] as *const CStr)
1072     }
1073
1074     /// Returns the inner pointer to this C string.
1075     ///
1076     /// The returned pointer will be valid for as long as `self` is, and points
1077     /// to a contiguous region of memory terminated with a 0 byte to represent
1078     /// the end of the string.
1079     ///
1080     /// **WARNING**
1081     ///
1082     /// The returned pointer is read-only; writing to it (including passing it
1083     /// to C code that writes to it) causes undefined behavior.
1084     ///
1085     /// It is your responsibility to make sure that the underlying memory is not
1086     /// freed too early. For example, the following code will cause undefined
1087     /// behavior when `ptr` is used inside the `unsafe` block:
1088     ///
1089     /// ```no_run
1090     /// # #![allow(unused_must_use)]
1091     /// use std::ffi::CString;
1092     ///
1093     /// let ptr = CString::new("Hello").expect("CString::new failed").as_ptr();
1094     /// unsafe {
1095     ///     // `ptr` is dangling
1096     ///     *ptr;
1097     /// }
1098     /// ```
1099     ///
1100     /// This happens because the pointer returned by `as_ptr` does not carry any
1101     /// lifetime information and the [`CString`] is deallocated immediately after
1102     /// the `CString::new("Hello").expect("CString::new failed").as_ptr()` expression is evaluated.
1103     /// To fix the problem, bind the `CString` to a local variable:
1104     ///
1105     /// ```no_run
1106     /// # #![allow(unused_must_use)]
1107     /// use std::ffi::CString;
1108     ///
1109     /// let hello = CString::new("Hello").expect("CString::new failed");
1110     /// let ptr = hello.as_ptr();
1111     /// unsafe {
1112     ///     // `ptr` is valid because `hello` is in scope
1113     ///     *ptr;
1114     /// }
1115     /// ```
1116     ///
1117     /// This way, the lifetime of the `CString` in `hello` encompasses
1118     /// the lifetime of `ptr` and the `unsafe` block.
1119     ///
1120     /// [`CString`]: struct.CString.html
1121     #[inline]
1122     #[stable(feature = "rust1", since = "1.0.0")]
1123     #[cfg_attr(not(bootstrap), rustc_const_stable(feature = "const_str_as_ptr", since = "1.32.0"))]
1124     pub const fn as_ptr(&self) -> *const c_char {
1125         self.inner.as_ptr()
1126     }
1127
1128     /// Converts this C string to a byte slice.
1129     ///
1130     /// The returned slice will **not** contain the trailing nul terminator that this C
1131     /// string has.
1132     ///
1133     /// > **Note**: This method is currently implemented as a constant-time
1134     /// > cast, but it is planned to alter its definition in the future to
1135     /// > perform the length calculation whenever this method is called.
1136     ///
1137     /// # Examples
1138     ///
1139     /// ```
1140     /// use std::ffi::CStr;
1141     ///
1142     /// let cstr = CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed");
1143     /// assert_eq!(cstr.to_bytes(), b"foo");
1144     /// ```
1145     #[inline]
1146     #[stable(feature = "rust1", since = "1.0.0")]
1147     pub fn to_bytes(&self) -> &[u8] {
1148         let bytes = self.to_bytes_with_nul();
1149         &bytes[..bytes.len() - 1]
1150     }
1151
1152     /// Converts this C string to a byte slice containing the trailing 0 byte.
1153     ///
1154     /// This function is the equivalent of [`to_bytes`] except that it will retain
1155     /// the trailing nul terminator instead of chopping it off.
1156     ///
1157     /// > **Note**: This method is currently implemented as a 0-cost cast, but
1158     /// > it is planned to alter its definition in the future to perform the
1159     /// > length calculation whenever this method is called.
1160     ///
1161     /// [`to_bytes`]: #method.to_bytes
1162     ///
1163     /// # Examples
1164     ///
1165     /// ```
1166     /// use std::ffi::CStr;
1167     ///
1168     /// let cstr = CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed");
1169     /// assert_eq!(cstr.to_bytes_with_nul(), b"foo\0");
1170     /// ```
1171     #[inline]
1172     #[stable(feature = "rust1", since = "1.0.0")]
1173     pub fn to_bytes_with_nul(&self) -> &[u8] {
1174         unsafe { &*(&self.inner as *const [c_char] as *const [u8]) }
1175     }
1176
1177     /// Yields a [`&str`] slice if the `CStr` contains valid UTF-8.
1178     ///
1179     /// If the contents of the `CStr` are valid UTF-8 data, this
1180     /// function will return the corresponding [`&str`] slice. Otherwise,
1181     /// it will return an error with details of where UTF-8 validation failed.
1182     ///
1183     /// > **Note**: This method is currently implemented to check for validity
1184     /// > after a constant-time cast, but it is planned to alter its definition
1185     /// > in the future to perform the length calculation in addition to the
1186     /// > UTF-8 check whenever this method is called.
1187     ///
1188     /// [`&str`]: ../primitive.str.html
1189     ///
1190     /// # Examples
1191     ///
1192     /// ```
1193     /// use std::ffi::CStr;
1194     ///
1195     /// let cstr = CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed");
1196     /// assert_eq!(cstr.to_str(), Ok("foo"));
1197     /// ```
1198     #[stable(feature = "cstr_to_str", since = "1.4.0")]
1199     pub fn to_str(&self) -> Result<&str, str::Utf8Error> {
1200         // N.B., when `CStr` is changed to perform the length check in `.to_bytes()`
1201         // instead of in `from_ptr()`, it may be worth considering if this should
1202         // be rewritten to do the UTF-8 check inline with the length calculation
1203         // instead of doing it afterwards.
1204         str::from_utf8(self.to_bytes())
1205     }
1206
1207     /// Converts a `CStr` into a [`Cow`]`<`[`str`]`>`.
1208     ///
1209     /// If the contents of the `CStr` are valid UTF-8 data, this
1210     /// function will return a [`Cow`]`::`[`Borrowed`]`(`[`&str`]`)`
1211     /// with the corresponding [`&str`] slice. Otherwise, it will
1212     /// replace any invalid UTF-8 sequences with
1213     /// [`U+FFFD REPLACEMENT CHARACTER`][U+FFFD] and return a
1214     /// [`Cow`]`::`[`Owned`]`(`[`String`]`)` with the result.
1215     ///
1216     /// > **Note**: This method is currently implemented to check for validity
1217     /// > after a constant-time cast, but it is planned to alter its definition
1218     /// > in the future to perform the length calculation in addition to the
1219     /// > UTF-8 check whenever this method is called.
1220     ///
1221     /// [`Cow`]: ../borrow/enum.Cow.html
1222     /// [`Borrowed`]: ../borrow/enum.Cow.html#variant.Borrowed
1223     /// [`Owned`]: ../borrow/enum.Cow.html#variant.Owned
1224     /// [`str`]: ../primitive.str.html
1225     /// [`String`]: ../string/struct.String.html
1226     /// [U+FFFD]: ../char/constant.REPLACEMENT_CHARACTER.html
1227     ///
1228     /// # Examples
1229     ///
1230     /// Calling `to_string_lossy` on a `CStr` containing valid UTF-8:
1231     ///
1232     /// ```
1233     /// use std::borrow::Cow;
1234     /// use std::ffi::CStr;
1235     ///
1236     /// let cstr = CStr::from_bytes_with_nul(b"Hello World\0")
1237     ///                  .expect("CStr::from_bytes_with_nul failed");
1238     /// assert_eq!(cstr.to_string_lossy(), Cow::Borrowed("Hello World"));
1239     /// ```
1240     ///
1241     /// Calling `to_string_lossy` on a `CStr` containing invalid UTF-8:
1242     ///
1243     /// ```
1244     /// use std::borrow::Cow;
1245     /// use std::ffi::CStr;
1246     ///
1247     /// let cstr = CStr::from_bytes_with_nul(b"Hello \xF0\x90\x80World\0")
1248     ///                  .expect("CStr::from_bytes_with_nul failed");
1249     /// assert_eq!(
1250     ///     cstr.to_string_lossy(),
1251     ///     Cow::Owned(String::from("Hello �World")) as Cow<'_, str>
1252     /// );
1253     /// ```
1254     #[stable(feature = "cstr_to_str", since = "1.4.0")]
1255     pub fn to_string_lossy(&self) -> Cow<'_, str> {
1256         String::from_utf8_lossy(self.to_bytes())
1257     }
1258
1259     /// Converts a [`Box`]`<CStr>` into a [`CString`] without copying or allocating.
1260     ///
1261     /// [`Box`]: ../boxed/struct.Box.html
1262     /// [`CString`]: struct.CString.html
1263     ///
1264     /// # Examples
1265     ///
1266     /// ```
1267     /// use std::ffi::CString;
1268     ///
1269     /// let c_string = CString::new(b"foo".to_vec()).expect("CString::new failed");
1270     /// let boxed = c_string.into_boxed_c_str();
1271     /// assert_eq!(boxed.into_c_string(), CString::new("foo").expect("CString::new failed"));
1272     /// ```
1273     #[stable(feature = "into_boxed_c_str", since = "1.20.0")]
1274     pub fn into_c_string(self: Box<CStr>) -> CString {
1275         let raw = Box::into_raw(self) as *mut [u8];
1276         CString { inner: unsafe { Box::from_raw(raw) } }
1277     }
1278 }
1279
1280 #[stable(feature = "rust1", since = "1.0.0")]
1281 impl PartialEq for CStr {
1282     fn eq(&self, other: &CStr) -> bool {
1283         self.to_bytes().eq(other.to_bytes())
1284     }
1285 }
1286 #[stable(feature = "rust1", since = "1.0.0")]
1287 impl Eq for CStr {}
1288 #[stable(feature = "rust1", since = "1.0.0")]
1289 impl PartialOrd for CStr {
1290     fn partial_cmp(&self, other: &CStr) -> Option<Ordering> {
1291         self.to_bytes().partial_cmp(&other.to_bytes())
1292     }
1293 }
1294 #[stable(feature = "rust1", since = "1.0.0")]
1295 impl Ord for CStr {
1296     fn cmp(&self, other: &CStr) -> Ordering {
1297         self.to_bytes().cmp(&other.to_bytes())
1298     }
1299 }
1300
1301 #[stable(feature = "cstr_borrow", since = "1.3.0")]
1302 impl ToOwned for CStr {
1303     type Owned = CString;
1304
1305     fn to_owned(&self) -> CString {
1306         CString { inner: self.to_bytes_with_nul().into() }
1307     }
1308 }
1309
1310 #[stable(feature = "cstring_asref", since = "1.7.0")]
1311 impl From<&CStr> for CString {
1312     fn from(s: &CStr) -> CString {
1313         s.to_owned()
1314     }
1315 }
1316
1317 #[stable(feature = "cstring_asref", since = "1.7.0")]
1318 impl ops::Index<ops::RangeFull> for CString {
1319     type Output = CStr;
1320
1321     #[inline]
1322     fn index(&self, _index: ops::RangeFull) -> &CStr {
1323         self
1324     }
1325 }
1326
1327 #[stable(feature = "cstring_asref", since = "1.7.0")]
1328 impl AsRef<CStr> for CStr {
1329     #[inline]
1330     fn as_ref(&self) -> &CStr {
1331         self
1332     }
1333 }
1334
1335 #[stable(feature = "cstring_asref", since = "1.7.0")]
1336 impl AsRef<CStr> for CString {
1337     #[inline]
1338     fn as_ref(&self) -> &CStr {
1339         self
1340     }
1341 }
1342
1343 #[cfg(test)]
1344 mod tests {
1345     use super::*;
1346     use crate::os::raw::c_char;
1347     use crate::borrow::Cow::{Borrowed, Owned};
1348     use crate::hash::{Hash, Hasher};
1349     use crate::collections::hash_map::DefaultHasher;
1350     use crate::rc::Rc;
1351     use crate::sync::Arc;
1352
1353     #[test]
1354     fn c_to_rust() {
1355         let data = b"123\0";
1356         let ptr = data.as_ptr() as *const c_char;
1357         unsafe {
1358             assert_eq!(CStr::from_ptr(ptr).to_bytes(), b"123");
1359             assert_eq!(CStr::from_ptr(ptr).to_bytes_with_nul(), b"123\0");
1360         }
1361     }
1362
1363     #[test]
1364     fn simple() {
1365         let s = CString::new("1234").unwrap();
1366         assert_eq!(s.as_bytes(), b"1234");
1367         assert_eq!(s.as_bytes_with_nul(), b"1234\0");
1368     }
1369
1370     #[test]
1371     fn build_with_zero1() {
1372         assert!(CString::new(&b"\0"[..]).is_err());
1373     }
1374     #[test]
1375     fn build_with_zero2() {
1376         assert!(CString::new(vec![0]).is_err());
1377     }
1378
1379     #[test]
1380     fn build_with_zero3() {
1381         unsafe {
1382             let s = CString::from_vec_unchecked(vec![0]);
1383             assert_eq!(s.as_bytes(), b"\0");
1384         }
1385     }
1386
1387     #[test]
1388     fn formatted() {
1389         let s = CString::new(&b"abc\x01\x02\n\xE2\x80\xA6\xFF"[..]).unwrap();
1390         assert_eq!(format!("{:?}", s), r#""abc\x01\x02\n\xe2\x80\xa6\xff""#);
1391     }
1392
1393     #[test]
1394     fn borrowed() {
1395         unsafe {
1396             let s = CStr::from_ptr(b"12\0".as_ptr() as *const _);
1397             assert_eq!(s.to_bytes(), b"12");
1398             assert_eq!(s.to_bytes_with_nul(), b"12\0");
1399         }
1400     }
1401
1402     #[test]
1403     fn to_str() {
1404         let data = b"123\xE2\x80\xA6\0";
1405         let ptr = data.as_ptr() as *const c_char;
1406         unsafe {
1407             assert_eq!(CStr::from_ptr(ptr).to_str(), Ok("123…"));
1408             assert_eq!(CStr::from_ptr(ptr).to_string_lossy(), Borrowed("123…"));
1409         }
1410         let data = b"123\xE2\0";
1411         let ptr = data.as_ptr() as *const c_char;
1412         unsafe {
1413             assert!(CStr::from_ptr(ptr).to_str().is_err());
1414             assert_eq!(CStr::from_ptr(ptr).to_string_lossy(), Owned::<str>(format!("123\u{FFFD}")));
1415         }
1416     }
1417
1418     #[test]
1419     fn to_owned() {
1420         let data = b"123\0";
1421         let ptr = data.as_ptr() as *const c_char;
1422
1423         let owned = unsafe { CStr::from_ptr(ptr).to_owned() };
1424         assert_eq!(owned.as_bytes_with_nul(), data);
1425     }
1426
1427     #[test]
1428     fn equal_hash() {
1429         let data = b"123\xE2\xFA\xA6\0";
1430         let ptr = data.as_ptr() as *const c_char;
1431         let cstr: &'static CStr = unsafe { CStr::from_ptr(ptr) };
1432
1433         let mut s = DefaultHasher::new();
1434         cstr.hash(&mut s);
1435         let cstr_hash = s.finish();
1436         let mut s = DefaultHasher::new();
1437         CString::new(&data[..data.len() - 1]).unwrap().hash(&mut s);
1438         let cstring_hash = s.finish();
1439
1440         assert_eq!(cstr_hash, cstring_hash);
1441     }
1442
1443     #[test]
1444     fn from_bytes_with_nul() {
1445         let data = b"123\0";
1446         let cstr = CStr::from_bytes_with_nul(data);
1447         assert_eq!(cstr.map(CStr::to_bytes), Ok(&b"123"[..]));
1448         let cstr = CStr::from_bytes_with_nul(data);
1449         assert_eq!(cstr.map(CStr::to_bytes_with_nul), Ok(&b"123\0"[..]));
1450
1451         unsafe {
1452             let cstr = CStr::from_bytes_with_nul(data);
1453             let cstr_unchecked = CStr::from_bytes_with_nul_unchecked(data);
1454             assert_eq!(cstr, Ok(cstr_unchecked));
1455         }
1456     }
1457
1458     #[test]
1459     fn from_bytes_with_nul_unterminated() {
1460         let data = b"123";
1461         let cstr = CStr::from_bytes_with_nul(data);
1462         assert!(cstr.is_err());
1463     }
1464
1465     #[test]
1466     fn from_bytes_with_nul_interior() {
1467         let data = b"1\023\0";
1468         let cstr = CStr::from_bytes_with_nul(data);
1469         assert!(cstr.is_err());
1470     }
1471
1472     #[test]
1473     fn into_boxed() {
1474         let orig: &[u8] = b"Hello, world!\0";
1475         let cstr = CStr::from_bytes_with_nul(orig).unwrap();
1476         let boxed: Box<CStr> = Box::from(cstr);
1477         let cstring = cstr.to_owned().into_boxed_c_str().into_c_string();
1478         assert_eq!(cstr, &*boxed);
1479         assert_eq!(&*boxed, &*cstring);
1480         assert_eq!(&*cstring, cstr);
1481     }
1482
1483     #[test]
1484     fn boxed_default() {
1485         let boxed = <Box<CStr>>::default();
1486         assert_eq!(boxed.to_bytes_with_nul(), &[0]);
1487     }
1488
1489     #[test]
1490     fn into_rc() {
1491         let orig: &[u8] = b"Hello, world!\0";
1492         let cstr = CStr::from_bytes_with_nul(orig).unwrap();
1493         let rc: Rc<CStr> = Rc::from(cstr);
1494         let arc: Arc<CStr> = Arc::from(cstr);
1495
1496         assert_eq!(&*rc, cstr);
1497         assert_eq!(&*arc, cstr);
1498
1499         let rc2: Rc<CStr> = Rc::from(cstr.to_owned());
1500         let arc2: Arc<CStr> = Arc::from(cstr.to_owned());
1501
1502         assert_eq!(&*rc2, cstr);
1503         assert_eq!(&*arc2, cstr);
1504     }
1505
1506     #[test]
1507     fn cstr_const_constructor() {
1508         const CSTR: &CStr = unsafe {
1509             CStr::from_bytes_with_nul_unchecked(b"Hello, world!\0")
1510         };
1511
1512         assert_eq!(CSTR.to_str().unwrap(), "Hello, world!");
1513     }
1514 }