1 // Copyright 2012 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
12 use borrow::{Cow, Borrow};
15 use fmt::{self, Write};
24 use str::{self, Utf8Error};
28 /// A type representing an owned, C-compatible, nul-terminated string with no nul bytes in the
31 /// This type serves the purpose of being able to safely generate a
32 /// C-compatible string from a Rust byte slice or vector. An instance of this
33 /// type is a static guarantee that the underlying bytes contain no interior 0
34 /// bytes ("nul characters") and that the final byte is 0 ("nul terminator").
36 /// `CString` is to [`CStr`] as [`String`] is to [`&str`]: the former
37 /// in each pair are owned strings; the latter are borrowed
40 /// # Creating a `CString`
42 /// A `CString` is created from either a byte slice or a byte vector,
43 /// or anything that implements [`Into`]`<`[`Vec`]`<`[`u8`]`>>` (for
44 /// example, you can build a `CString` straight out of a [`String`] or
45 /// a [`&str`], since both implement that trait).
47 /// The [`new`] method will actually check that the provided `&[u8]`
48 /// does not have 0 bytes in the middle, and return an error if it
51 /// # Extracting a raw pointer to the whole C string
53 /// `CString` implements a [`as_ptr`] method through the [`Deref`]
54 /// trait. This method will give you a `*const c_char` which you can
55 /// feed directly to extern functions that expect a nul-terminated
56 /// string, like C's `strdup()`.
58 /// # Extracting a slice of the whole C string
60 /// Alternatively, you can obtain a `&[`[`u8`]`]` slice from a
61 /// `CString` with the [`as_bytes`] method. Slices produced in this
62 /// way do *not* contain the trailing nul terminator. This is useful
63 /// when you will be calling an extern function that takes a `*const
64 /// u8` argument which is not necessarily nul-terminated, plus another
65 /// argument with the length of the string — like C's `strndup()`.
66 /// You can of course get the slice's length with its
67 /// [`len`][slice.len] method.
69 /// If you need a `&[`[`u8`]`]` slice *with* the nul terminator, you
70 /// can use [`as_bytes_with_nul`] instead.
72 /// Once you have the kind of slice you need (with or without a nul
73 /// terminator), you can call the slice's own
74 /// [`as_ptr`][slice.as_ptr] method to get a raw pointer to pass to
75 /// extern functions. See the documentation for that function for a
76 /// discussion on ensuring the lifetime of the raw pointer.
78 /// [`Into`]: ../convert/trait.Into.html
79 /// [`Vec`]: ../vec/struct.Vec.html
80 /// [`String`]: ../string/struct.String.html
81 /// [`&str`]: ../primitive.str.html
82 /// [`u8`]: ../primitive.u8.html
83 /// [`new`]: #method.new
84 /// [`as_bytes`]: #method.as_bytes
85 /// [`as_bytes_with_nul`]: #method.as_bytes_with_nul
86 /// [`as_ptr`]: #method.as_ptr
87 /// [slice.as_ptr]: ../primitive.slice.html#method.as_ptr
88 /// [slice.len]: ../primitive.slice.html#method.len
89 /// [`Deref`]: ../ops/trait.Deref.html
90 /// [`CStr`]: struct.CStr.html
96 /// use std::ffi::CString;
97 /// use std::os::raw::c_char;
100 /// fn my_printer(s: *const c_char);
103 /// // We are certain that our string doesn't have 0 bytes in the middle,
104 /// // so we can .unwrap()
105 /// let c_to_print = CString::new("Hello, world!").unwrap();
107 /// my_printer(c_to_print.as_ptr());
114 /// `CString` is intended for working with traditional C-style strings
115 /// (a sequence of non-nul bytes terminated by a single nul byte); the
116 /// primary use case for these kinds of strings is interoperating with C-like
117 /// code. Often you will need to transfer ownership to/from that external
118 /// code. It is strongly recommended that you thoroughly read through the
119 /// documentation of `CString` before use, as improper ownership management
120 /// of `CString` instances can lead to invalid memory accesses, memory leaks,
121 /// and other memory errors.
123 #[derive(PartialEq, PartialOrd, Eq, Ord, Hash, Clone)]
124 #[stable(feature = "rust1", since = "1.0.0")]
126 // Invariant 1: the slice ends with a zero byte and has a length of at least one.
127 // Invariant 2: the slice contains only one zero byte.
128 // Improper usage of unsafe function can break Invariant 2, but not Invariant 1.
132 /// Representation of a borrowed C string.
134 /// This type represents a borrowed reference to a nul-terminated
135 /// array of bytes. It can be constructed safely from a `&[`[`u8`]`]`
136 /// slice, or unsafely from a raw `*const c_char`. It can then be
137 /// converted to a Rust [`&str`] by performing UTF-8 validation, or
138 /// into an owned [`CString`].
140 /// `CStr` is to [`CString`] as [`&str`] is to [`String`]: the former
141 /// in each pair are borrowed references; the latter are owned
144 /// Note that this structure is **not** `repr(C)` and is not recommended to be
145 /// placed in the signatures of FFI functions. Instead, safe wrappers of FFI
146 /// functions may leverage the unsafe [`from_ptr`] constructor to provide a safe
147 /// interface to other consumers.
151 /// Inspecting a foreign C string:
154 /// use std::ffi::CStr;
155 /// use std::os::raw::c_char;
157 /// extern { fn my_string() -> *const c_char; }
160 /// let slice = CStr::from_ptr(my_string());
161 /// println!("string buffer size without nul terminator: {}", slice.to_bytes().len());
165 /// Passing a Rust-originating C string:
168 /// use std::ffi::{CString, CStr};
169 /// use std::os::raw::c_char;
171 /// fn work(data: &CStr) {
172 /// extern { fn work_with(data: *const c_char); }
174 /// unsafe { work_with(data.as_ptr()) }
177 /// let s = CString::new("data data data data").unwrap();
181 /// Converting a foreign C string into a Rust [`String`]:
184 /// use std::ffi::CStr;
185 /// use std::os::raw::c_char;
187 /// extern { fn my_string() -> *const c_char; }
189 /// fn my_string_safe() -> String {
191 /// CStr::from_ptr(my_string()).to_string_lossy().into_owned()
195 /// println!("string: {}", my_string_safe());
198 /// [`u8`]: ../primitive.u8.html
199 /// [`&str`]: ../primitive.str.html
200 /// [`String`]: ../string/struct.String.html
201 /// [`CString`]: struct.CString.html
202 /// [`from_ptr`]: #method.from_ptr
204 #[stable(feature = "rust1", since = "1.0.0")]
206 // FIXME: this should not be represented with a DST slice but rather with
207 // just a raw `c_char` along with some form of marker to make
208 // this an unsized type. Essentially `sizeof(&CStr)` should be the
209 // same as `sizeof(&c_char)` but `CStr` should be an unsized type.
213 /// An error indicating that an interior nul byte was found.
215 /// While Rust strings may contain nul bytes in the middle, C strings
216 /// can't, as that byte would effectively truncate the string.
218 /// This error is created by the [`new`][`CString::new`] method on
219 /// [`CString`]. See its documentation for more.
221 /// [`CString`]: struct.CString.html
222 /// [`CString::new`]: struct.CString.html#method.new
227 /// use std::ffi::{CString, NulError};
229 /// let _: NulError = CString::new(b"f\0oo".to_vec()).unwrap_err();
231 #[derive(Clone, PartialEq, Eq, Debug)]
232 #[stable(feature = "rust1", since = "1.0.0")]
233 pub struct NulError(usize, Vec<u8>);
235 /// An error indicating that a nul byte was not in the expected position.
237 /// The slice used to create a [`CStr`] must have one and only one nul
238 /// byte at the end of the slice.
240 /// This error is created by the
241 /// [`from_bytes_with_nul`][`CStr::from_bytes_with_nul`] method on
242 /// [`CStr`]. See its documentation for more.
244 /// [`CStr`]: struct.CStr.html
245 /// [`CStr::from_bytes_with_nul`]: struct.CStr.html#method.from_bytes_with_nul
250 /// use std::ffi::{CStr, FromBytesWithNulError};
252 /// let _: FromBytesWithNulError = CStr::from_bytes_with_nul(b"f\0oo").unwrap_err();
254 #[derive(Clone, PartialEq, Eq, Debug)]
255 #[stable(feature = "cstr_from_bytes", since = "1.10.0")]
256 pub struct FromBytesWithNulError {
257 kind: FromBytesWithNulErrorKind,
260 #[derive(Clone, PartialEq, Eq, Debug)]
261 enum FromBytesWithNulErrorKind {
266 impl FromBytesWithNulError {
267 fn interior_nul(pos: usize) -> FromBytesWithNulError {
268 FromBytesWithNulError {
269 kind: FromBytesWithNulErrorKind::InteriorNul(pos),
272 fn not_nul_terminated() -> FromBytesWithNulError {
273 FromBytesWithNulError {
274 kind: FromBytesWithNulErrorKind::NotNulTerminated,
279 /// An error indicating invalid UTF-8 when converting a [`CString`] into a [`String`].
281 /// `CString` is just a wrapper over a buffer of bytes with a nul
282 /// terminator; [`into_string`][`CString::into_string`] performs UTF-8
283 /// validation on those bytes and may return this error.
285 /// This `struct` is created by the
286 /// [`into_string`][`CString::into_string`] method on [`CString`]. See
287 /// its documentation for more.
289 /// [`String`]: ../string/struct.String.html
290 /// [`CString`]: struct.CString.html
291 /// [`CString::into_string`]: struct.CString.html#method.into_string
292 #[derive(Clone, PartialEq, Eq, Debug)]
293 #[stable(feature = "cstring_into", since = "1.7.0")]
294 pub struct IntoStringError {
300 /// Creates a new C-compatible string from a container of bytes.
302 /// This function will consume the provided data and use the
303 /// underlying bytes to construct a new string, ensuring that
304 /// there is a trailing 0 byte. This trailing 0 byte will be
305 /// appended by this function; the provided data should *not*
306 /// contain any 0 bytes in it.
311 /// use std::ffi::CString;
312 /// use std::os::raw::c_char;
314 /// extern { fn puts(s: *const c_char); }
316 /// let to_print = CString::new("Hello!").unwrap();
318 /// puts(to_print.as_ptr());
324 /// This function will return an error if the supplied bytes contain an
325 /// internal 0 byte. The [`NulError`] returned will contain the bytes as well as
326 /// the position of the nul byte.
328 /// [`NulError`]: struct.NulError.html
329 #[stable(feature = "rust1", since = "1.0.0")]
330 pub fn new<T: Into<Vec<u8>>>(t: T) -> Result<CString, NulError> {
334 fn _new(bytes: Vec<u8>) -> Result<CString, NulError> {
335 match memchr::memchr(0, &bytes) {
336 Some(i) => Err(NulError(i, bytes)),
337 None => Ok(unsafe { CString::from_vec_unchecked(bytes) }),
341 /// Creates a C-compatible string by consuming a byte vector,
342 /// without checking for interior 0 bytes.
344 /// This method is equivalent to [`new`] except that no runtime assertion
345 /// is made that `v` contains no 0 bytes, and it requires an actual
346 /// byte vector, not anything that can be converted to one with Into.
348 /// [`new`]: #method.new
353 /// use std::ffi::CString;
355 /// let raw = b"foo".to_vec();
357 /// let c_string = CString::from_vec_unchecked(raw);
360 #[stable(feature = "rust1", since = "1.0.0")]
361 pub unsafe fn from_vec_unchecked(mut v: Vec<u8>) -> CString {
364 CString { inner: v.into_boxed_slice() }
367 /// Retakes ownership of a `CString` that was transferred to C via [`into_raw`].
369 /// Additionally, the length of the string will be recalculated from the pointer.
373 /// This should only ever be called with a pointer that was earlier
374 /// obtained by calling [`into_raw`] on a `CString`. Other usage (e.g. trying to take
375 /// ownership of a string that was allocated by foreign code) is likely to lead
376 /// to undefined behavior or allocator corruption.
378 /// > **Note:** If you need to borrow a string that was allocated by
379 /// > foreign code, use [`CStr`]. If you need to take ownership of
380 /// > a string that was allocated by foreign code, you will need to
381 /// > make your own provisions for freeing it appropriately, likely
382 /// > with the foreign code's API to do that.
384 /// [`into_raw`]: #method.into_raw
385 /// [`CStr`]: struct.CStr.html
389 /// Create a `CString`, pass ownership to an `extern` function (via raw pointer), then retake
390 /// ownership with `from_raw`:
393 /// use std::ffi::CString;
394 /// use std::os::raw::c_char;
397 /// fn some_extern_function(s: *mut c_char);
400 /// let c_string = CString::new("Hello!").unwrap();
401 /// let raw = c_string.into_raw();
403 /// some_extern_function(raw);
404 /// let c_string = CString::from_raw(raw);
407 #[stable(feature = "cstr_memory", since = "1.4.0")]
408 pub unsafe fn from_raw(ptr: *mut c_char) -> CString {
409 let len = sys::strlen(ptr) + 1; // Including the NUL byte
410 let slice = slice::from_raw_parts_mut(ptr, len as usize);
411 CString { inner: Box::from_raw(slice as *mut [c_char] as *mut [u8]) }
414 /// Consumes the `CString` and transfers ownership of the string to a C caller.
416 /// The pointer which this function returns must be returned to Rust and reconstituted using
417 /// [`from_raw`] to be properly deallocated. Specifically, one
418 /// should *not* use the standard C `free()` function to deallocate
421 /// Failure to call [`from_raw`] will lead to a memory leak.
423 /// [`from_raw`]: #method.from_raw
428 /// use std::ffi::CString;
430 /// let c_string = CString::new("foo").unwrap();
432 /// let ptr = c_string.into_raw();
435 /// assert_eq!(b'f', *ptr as u8);
436 /// assert_eq!(b'o', *ptr.offset(1) as u8);
437 /// assert_eq!(b'o', *ptr.offset(2) as u8);
438 /// assert_eq!(b'\0', *ptr.offset(3) as u8);
440 /// // retake pointer to free memory
441 /// let _ = CString::from_raw(ptr);
445 #[stable(feature = "cstr_memory", since = "1.4.0")]
446 pub fn into_raw(self) -> *mut c_char {
447 Box::into_raw(self.into_inner()) as *mut c_char
450 /// Converts the `CString` into a [`String`] if it contains valid UTF-8 data.
452 /// On failure, ownership of the original `CString` is returned.
454 /// [`String`]: ../string/struct.String.html
459 /// use std::ffi::CString;
461 /// let valid_utf8 = vec![b'f', b'o', b'o'];
462 /// let cstring = CString::new(valid_utf8).unwrap();
463 /// assert_eq!(cstring.into_string().unwrap(), "foo");
465 /// let invalid_utf8 = vec![b'f', 0xff, b'o', b'o'];
466 /// let cstring = CString::new(invalid_utf8).unwrap();
467 /// let err = cstring.into_string().err().unwrap();
468 /// assert_eq!(err.utf8_error().valid_up_to(), 1);
471 #[stable(feature = "cstring_into", since = "1.7.0")]
472 pub fn into_string(self) -> Result<String, IntoStringError> {
473 String::from_utf8(self.into_bytes())
474 .map_err(|e| IntoStringError {
475 error: e.utf8_error(),
476 inner: unsafe { CString::from_vec_unchecked(e.into_bytes()) },
480 /// Consumes the `CString` and returns the underlying byte buffer.
482 /// The returned buffer does **not** contain the trailing nul
483 /// terminator, and it is guaranteed to not have any interior nul
489 /// use std::ffi::CString;
491 /// let c_string = CString::new("foo").unwrap();
492 /// let bytes = c_string.into_bytes();
493 /// assert_eq!(bytes, vec![b'f', b'o', b'o']);
495 #[stable(feature = "cstring_into", since = "1.7.0")]
496 pub fn into_bytes(self) -> Vec<u8> {
497 let mut vec = self.into_inner().into_vec();
498 let _nul = vec.pop();
499 debug_assert_eq!(_nul, Some(0u8));
503 /// Equivalent to the [`into_bytes`] function except that the returned vector
504 /// includes the trailing nul terminator.
506 /// [`into_bytes`]: #method.into_bytes
511 /// use std::ffi::CString;
513 /// let c_string = CString::new("foo").unwrap();
514 /// let bytes = c_string.into_bytes_with_nul();
515 /// assert_eq!(bytes, vec![b'f', b'o', b'o', b'\0']);
517 #[stable(feature = "cstring_into", since = "1.7.0")]
518 pub fn into_bytes_with_nul(self) -> Vec<u8> {
519 self.into_inner().into_vec()
522 /// Returns the contents of this `CString` as a slice of bytes.
524 /// The returned slice does **not** contain the trailing nul
525 /// terminator, and it is guaranteed to not have any interior nul
526 /// bytes. If you need the nul terminator, use
527 /// [`as_bytes_with_nul`] instead.
529 /// [`as_bytes_with_nul`]: #method.as_bytes_with_nul
534 /// use std::ffi::CString;
536 /// let c_string = CString::new("foo").unwrap();
537 /// let bytes = c_string.as_bytes();
538 /// assert_eq!(bytes, &[b'f', b'o', b'o']);
541 #[stable(feature = "rust1", since = "1.0.0")]
542 pub fn as_bytes(&self) -> &[u8] {
543 &self.inner[..self.inner.len() - 1]
546 /// Equivalent to the [`as_bytes`] function except that the returned slice
547 /// includes the trailing nul terminator.
549 /// [`as_bytes`]: #method.as_bytes
554 /// use std::ffi::CString;
556 /// let c_string = CString::new("foo").unwrap();
557 /// let bytes = c_string.as_bytes_with_nul();
558 /// assert_eq!(bytes, &[b'f', b'o', b'o', b'\0']);
561 #[stable(feature = "rust1", since = "1.0.0")]
562 pub fn as_bytes_with_nul(&self) -> &[u8] {
566 /// Extracts a [`CStr`] slice containing the entire string.
568 /// [`CStr`]: struct.CStr.html
573 /// use std::ffi::{CString, CStr};
575 /// let c_string = CString::new(b"foo".to_vec()).unwrap();
576 /// let c_str = c_string.as_c_str();
577 /// assert_eq!(c_str, CStr::from_bytes_with_nul(b"foo\0").unwrap());
580 #[stable(feature = "as_c_str", since = "1.20.0")]
581 pub fn as_c_str(&self) -> &CStr {
585 /// Converts this `CString` into a boxed [`CStr`].
587 /// [`CStr`]: struct.CStr.html
592 /// use std::ffi::{CString, CStr};
594 /// let c_string = CString::new(b"foo".to_vec()).unwrap();
595 /// let boxed = c_string.into_boxed_c_str();
596 /// assert_eq!(&*boxed, CStr::from_bytes_with_nul(b"foo\0").unwrap());
598 #[stable(feature = "into_boxed_c_str", since = "1.20.0")]
599 pub fn into_boxed_c_str(self) -> Box<CStr> {
600 unsafe { Box::from_raw(Box::into_raw(self.into_inner()) as *mut CStr) }
603 // Bypass "move out of struct which implements [`Drop`] trait" restriction.
605 /// [`Drop`]: ../ops/trait.Drop.html
606 fn into_inner(self) -> Box<[u8]> {
608 let result = ptr::read(&self.inner);
615 // Turns this `CString` into an empty string to prevent
616 // memory unsafe code from working by accident. Inline
617 // to prevent LLVM from optimizing it away in debug builds.
618 #[stable(feature = "cstring_drop", since = "1.13.0")]
619 impl Drop for CString {
622 unsafe { *self.inner.get_unchecked_mut(0) = 0; }
626 #[stable(feature = "rust1", since = "1.0.0")]
627 impl ops::Deref for CString {
631 fn deref(&self) -> &CStr {
632 unsafe { CStr::from_bytes_with_nul_unchecked(self.as_bytes_with_nul()) }
636 #[stable(feature = "rust1", since = "1.0.0")]
637 impl fmt::Debug for CString {
638 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
639 fmt::Debug::fmt(&**self, f)
643 #[stable(feature = "cstring_into", since = "1.7.0")]
644 impl From<CString> for Vec<u8> {
646 fn from(s: CString) -> Vec<u8> {
651 #[stable(feature = "cstr_debug", since = "1.3.0")]
652 impl fmt::Debug for CStr {
653 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
655 for byte in self.to_bytes().iter().flat_map(|&b| ascii::escape_default(b)) {
656 f.write_char(byte as char)?;
662 #[stable(feature = "cstr_default", since = "1.10.0")]
663 impl<'a> Default for &'a CStr {
664 fn default() -> &'a CStr {
665 const SLICE: &'static [c_char] = &[0];
666 unsafe { CStr::from_ptr(SLICE.as_ptr()) }
670 #[stable(feature = "cstr_default", since = "1.10.0")]
671 impl Default for CString {
672 /// Creates an empty `CString`.
673 fn default() -> CString {
674 let a: &CStr = Default::default();
679 #[stable(feature = "cstr_borrow", since = "1.3.0")]
680 impl Borrow<CStr> for CString {
682 fn borrow(&self) -> &CStr { self }
685 #[stable(feature = "box_from_c_str", since = "1.17.0")]
686 impl<'a> From<&'a CStr> for Box<CStr> {
687 fn from(s: &'a CStr) -> Box<CStr> {
688 let boxed: Box<[u8]> = Box::from(s.to_bytes_with_nul());
689 unsafe { Box::from_raw(Box::into_raw(boxed) as *mut CStr) }
693 #[stable(feature = "c_string_from_box", since = "1.18.0")]
694 impl From<Box<CStr>> for CString {
696 fn from(s: Box<CStr>) -> CString {
701 #[stable(feature = "box_from_c_string", since = "1.20.0")]
702 impl From<CString> for Box<CStr> {
704 fn from(s: CString) -> Box<CStr> {
709 #[stable(feature = "shared_from_slice2", since = "1.24.0")]
710 impl From<CString> for Arc<CStr> {
712 fn from(s: CString) -> Arc<CStr> {
713 let arc: Arc<[u8]> = Arc::from(s.into_inner());
714 unsafe { Arc::from_raw(Arc::into_raw(arc) as *const CStr) }
718 #[stable(feature = "shared_from_slice2", since = "1.24.0")]
719 impl<'a> From<&'a CStr> for Arc<CStr> {
721 fn from(s: &CStr) -> Arc<CStr> {
722 let arc: Arc<[u8]> = Arc::from(s.to_bytes_with_nul());
723 unsafe { Arc::from_raw(Arc::into_raw(arc) as *const CStr) }
727 #[stable(feature = "shared_from_slice2", since = "1.24.0")]
728 impl From<CString> for Rc<CStr> {
730 fn from(s: CString) -> Rc<CStr> {
731 let rc: Rc<[u8]> = Rc::from(s.into_inner());
732 unsafe { Rc::from_raw(Rc::into_raw(rc) as *const CStr) }
736 #[stable(feature = "shared_from_slice2", since = "1.24.0")]
737 impl<'a> From<&'a CStr> for Rc<CStr> {
739 fn from(s: &CStr) -> Rc<CStr> {
740 let rc: Rc<[u8]> = Rc::from(s.to_bytes_with_nul());
741 unsafe { Rc::from_raw(Rc::into_raw(rc) as *const CStr) }
745 #[stable(feature = "default_box_extra", since = "1.17.0")]
746 impl Default for Box<CStr> {
747 fn default() -> Box<CStr> {
748 let boxed: Box<[u8]> = Box::from([0]);
749 unsafe { Box::from_raw(Box::into_raw(boxed) as *mut CStr) }
754 /// Returns the position of the nul byte in the slice that caused
755 /// [`CString::new`] to fail.
757 /// [`CString::new`]: struct.CString.html#method.new
762 /// use std::ffi::CString;
764 /// let nul_error = CString::new("foo\0bar").unwrap_err();
765 /// assert_eq!(nul_error.nul_position(), 3);
767 /// let nul_error = CString::new("foo bar\0").unwrap_err();
768 /// assert_eq!(nul_error.nul_position(), 7);
770 #[stable(feature = "rust1", since = "1.0.0")]
771 pub fn nul_position(&self) -> usize { self.0 }
773 /// Consumes this error, returning the underlying vector of bytes which
774 /// generated the error in the first place.
779 /// use std::ffi::CString;
781 /// let nul_error = CString::new("foo\0bar").unwrap_err();
782 /// assert_eq!(nul_error.into_vec(), b"foo\0bar");
784 #[stable(feature = "rust1", since = "1.0.0")]
785 pub fn into_vec(self) -> Vec<u8> { self.1 }
788 #[stable(feature = "rust1", since = "1.0.0")]
789 impl Error for NulError {
790 fn description(&self) -> &str { "nul byte found in data" }
793 #[stable(feature = "rust1", since = "1.0.0")]
794 impl fmt::Display for NulError {
795 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
796 write!(f, "nul byte found in provided data at position: {}", self.0)
800 #[stable(feature = "rust1", since = "1.0.0")]
801 impl From<NulError> for io::Error {
802 fn from(_: NulError) -> io::Error {
803 io::Error::new(io::ErrorKind::InvalidInput,
804 "data provided contains a nul byte")
808 #[stable(feature = "frombyteswithnulerror_impls", since = "1.17.0")]
809 impl Error for FromBytesWithNulError {
810 fn description(&self) -> &str {
812 FromBytesWithNulErrorKind::InteriorNul(..) =>
813 "data provided contains an interior nul byte",
814 FromBytesWithNulErrorKind::NotNulTerminated =>
815 "data provided is not nul terminated",
820 #[stable(feature = "frombyteswithnulerror_impls", since = "1.17.0")]
821 impl fmt::Display for FromBytesWithNulError {
822 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
823 f.write_str(self.description())?;
824 if let FromBytesWithNulErrorKind::InteriorNul(pos) = self.kind {
825 write!(f, " at byte pos {}", pos)?;
831 impl IntoStringError {
832 /// Consumes this error, returning original [`CString`] which generated the
835 /// [`CString`]: struct.CString.html
836 #[stable(feature = "cstring_into", since = "1.7.0")]
837 pub fn into_cstring(self) -> CString {
841 /// Access the underlying UTF-8 error that was the cause of this error.
842 #[stable(feature = "cstring_into", since = "1.7.0")]
843 pub fn utf8_error(&self) -> Utf8Error {
848 #[stable(feature = "cstring_into", since = "1.7.0")]
849 impl Error for IntoStringError {
850 fn description(&self) -> &str {
851 "C string contained non-utf8 bytes"
854 fn cause(&self) -> Option<&Error> {
859 #[stable(feature = "cstring_into", since = "1.7.0")]
860 impl fmt::Display for IntoStringError {
861 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
862 self.description().fmt(f)
867 /// Wraps a raw C string with a safe C string wrapper.
869 /// This function will wrap the provided `ptr` with a `CStr` wrapper, which
870 /// allows inspection and interoperation of non-owned C strings. This method
871 /// is unsafe for a number of reasons:
873 /// * There is no guarantee to the validity of `ptr`.
874 /// * The returned lifetime is not guaranteed to be the actual lifetime of
876 /// * There is no guarantee that the memory pointed to by `ptr` contains a
877 /// valid nul terminator byte at the end of the string.
879 /// > **Note**: This operation is intended to be a 0-cost cast but it is
880 /// > currently implemented with an up-front calculation of the length of
881 /// > the string. This is not guaranteed to always be the case.
887 /// use std::ffi::CStr;
888 /// use std::os::raw::c_char;
891 /// fn my_string() -> *const c_char;
895 /// let slice = CStr::from_ptr(my_string());
896 /// println!("string returned: {}", slice.to_str().unwrap());
900 #[stable(feature = "rust1", since = "1.0.0")]
901 pub unsafe fn from_ptr<'a>(ptr: *const c_char) -> &'a CStr {
902 let len = sys::strlen(ptr);
903 let ptr = ptr as *const u8;
904 CStr::from_bytes_with_nul_unchecked(slice::from_raw_parts(ptr, len as usize + 1))
907 /// Creates a C string wrapper from a byte slice.
909 /// This function will cast the provided `bytes` to a `CStr`
910 /// wrapper after ensuring that the byte slice is nul-terminated
911 /// and does not contain any interior nul bytes.
916 /// use std::ffi::CStr;
918 /// let cstr = CStr::from_bytes_with_nul(b"hello\0");
919 /// assert!(cstr.is_ok());
922 /// Creating a `CStr` without a trailing nul terminator is an error:
925 /// use std::ffi::CStr;
927 /// let c_str = CStr::from_bytes_with_nul(b"hello");
928 /// assert!(c_str.is_err());
931 /// Creating a `CStr` with an interior nul byte is an error:
934 /// use std::ffi::CStr;
936 /// let c_str = CStr::from_bytes_with_nul(b"he\0llo\0");
937 /// assert!(c_str.is_err());
939 #[stable(feature = "cstr_from_bytes", since = "1.10.0")]
940 pub fn from_bytes_with_nul(bytes: &[u8])
941 -> Result<&CStr, FromBytesWithNulError> {
942 let nul_pos = memchr::memchr(0, bytes);
943 if let Some(nul_pos) = nul_pos {
944 if nul_pos + 1 != bytes.len() {
945 return Err(FromBytesWithNulError::interior_nul(nul_pos));
947 Ok(unsafe { CStr::from_bytes_with_nul_unchecked(bytes) })
949 Err(FromBytesWithNulError::not_nul_terminated())
953 /// Unsafely creates a C string wrapper from a byte slice.
955 /// This function will cast the provided `bytes` to a `CStr` wrapper without
956 /// performing any sanity checks. The provided slice **must** be nul-terminated
957 /// and not contain any interior nul bytes.
962 /// use std::ffi::{CStr, CString};
965 /// let cstring = CString::new("hello").unwrap();
966 /// let cstr = CStr::from_bytes_with_nul_unchecked(cstring.to_bytes_with_nul());
967 /// assert_eq!(cstr, &*cstring);
971 #[stable(feature = "cstr_from_bytes", since = "1.10.0")]
972 pub unsafe fn from_bytes_with_nul_unchecked(bytes: &[u8]) -> &CStr {
973 &*(bytes as *const [u8] as *const CStr)
976 /// Returns the inner pointer to this C string.
978 /// The returned pointer will be valid for as long as `self` is, and points
979 /// to a contiguous region of memory terminated with a 0 byte to represent
980 /// the end of the string.
984 /// It is your responsibility to make sure that the underlying memory is not
985 /// freed too early. For example, the following code will cause undefined
986 /// behavior when `ptr` is used inside the `unsafe` block:
989 /// use std::ffi::{CString};
991 /// let ptr = CString::new("Hello").unwrap().as_ptr();
993 /// // `ptr` is dangling
998 /// This happens because the pointer returned by `as_ptr` does not carry any
999 /// lifetime information and the [`CString`] is deallocated immediately after
1000 /// the `CString::new("Hello").unwrap().as_ptr()` expression is evaluated.
1001 /// To fix the problem, bind the `CString` to a local variable:
1004 /// use std::ffi::{CString};
1006 /// let hello = CString::new("Hello").unwrap();
1007 /// let ptr = hello.as_ptr();
1009 /// // `ptr` is valid because `hello` is in scope
1014 /// This way, the lifetime of the `CString` in `hello` encompasses
1015 /// the lifetime of `ptr` and the `unsafe` block.
1017 /// [`CString`]: struct.CString.html
1019 #[stable(feature = "rust1", since = "1.0.0")]
1020 pub fn as_ptr(&self) -> *const c_char {
1024 /// Converts this C string to a byte slice.
1026 /// The returned slice will **not** contain the trailing nul terminator that this C
1029 /// > **Note**: This method is currently implemented as a constant-time
1030 /// > cast, but it is planned to alter its definition in the future to
1031 /// > perform the length calculation whenever this method is called.
1036 /// use std::ffi::CStr;
1038 /// let c_str = CStr::from_bytes_with_nul(b"foo\0").unwrap();
1039 /// assert_eq!(c_str.to_bytes(), b"foo");
1042 #[stable(feature = "rust1", since = "1.0.0")]
1043 pub fn to_bytes(&self) -> &[u8] {
1044 let bytes = self.to_bytes_with_nul();
1045 &bytes[..bytes.len() - 1]
1048 /// Converts this C string to a byte slice containing the trailing 0 byte.
1050 /// This function is the equivalent of [`to_bytes`] except that it will retain
1051 /// the trailing nul terminator instead of chopping it off.
1053 /// > **Note**: This method is currently implemented as a 0-cost cast, but
1054 /// > it is planned to alter its definition in the future to perform the
1055 /// > length calculation whenever this method is called.
1057 /// [`to_bytes`]: #method.to_bytes
1062 /// use std::ffi::CStr;
1064 /// let c_str = CStr::from_bytes_with_nul(b"foo\0").unwrap();
1065 /// assert_eq!(c_str.to_bytes_with_nul(), b"foo\0");
1068 #[stable(feature = "rust1", since = "1.0.0")]
1069 pub fn to_bytes_with_nul(&self) -> &[u8] {
1070 unsafe { &*(&self.inner as *const [c_char] as *const [u8]) }
1073 /// Yields a [`&str`] slice if the `CStr` contains valid UTF-8.
1075 /// If the contents of the `CStr` are valid UTF-8 data, this
1076 /// function will return the corresponding [`&str`] slice. Otherwise,
1077 /// it will return an error with details of where UTF-8 validation failed.
1079 /// > **Note**: This method is currently implemented to check for validity
1080 /// > after a constant-time cast, but it is planned to alter its definition
1081 /// > in the future to perform the length calculation in addition to the
1082 /// > UTF-8 check whenever this method is called.
1084 /// [`&str`]: ../primitive.str.html
1089 /// use std::ffi::CStr;
1091 /// let c_str = CStr::from_bytes_with_nul(b"foo\0").unwrap();
1092 /// assert_eq!(c_str.to_str(), Ok("foo"));
1094 #[stable(feature = "cstr_to_str", since = "1.4.0")]
1095 pub fn to_str(&self) -> Result<&str, str::Utf8Error> {
1096 // NB: When CStr is changed to perform the length check in .to_bytes()
1097 // instead of in from_ptr(), it may be worth considering if this should
1098 // be rewritten to do the UTF-8 check inline with the length calculation
1099 // instead of doing it afterwards.
1100 str::from_utf8(self.to_bytes())
1103 /// Converts a `CStr` into a [`Cow`]`<`[`str`]`>`.
1105 /// If the contents of the `CStr` are valid UTF-8 data, this
1106 /// function will return a [`Cow`]`::`[`Borrowed`]`(`[`&str`]`)`
1107 /// with the the corresponding [`&str`] slice. Otherwise, it will
1108 /// replace any invalid UTF-8 sequences with `U+FFFD REPLACEMENT
1109 /// CHARACTER` and return a [`Cow`]`::`[`Owned`]`(`[`String`]`)`
1110 /// with the result.
1112 /// > **Note**: This method is currently implemented to check for validity
1113 /// > after a constant-time cast, but it is planned to alter its definition
1114 /// > in the future to perform the length calculation in addition to the
1115 /// > UTF-8 check whenever this method is called.
1117 /// [`Cow`]: ../borrow/enum.Cow.html
1118 /// [`Borrowed`]: ../borrow/enum.Cow.html#variant.Borrowed
1119 /// [`str`]: ../primitive.str.html
1120 /// [`String`]: ../string/struct.String.html
1124 /// Calling `to_string_lossy` on a `CStr` containing valid UTF-8:
1127 /// use std::borrow::Cow;
1128 /// use std::ffi::CStr;
1130 /// let c_str = CStr::from_bytes_with_nul(b"Hello World\0").unwrap();
1131 /// assert_eq!(c_str.to_string_lossy(), Cow::Borrowed("Hello World"));
1134 /// Calling `to_string_lossy` on a `CStr` containing invalid UTF-8:
1137 /// use std::borrow::Cow;
1138 /// use std::ffi::CStr;
1140 /// let c_str = CStr::from_bytes_with_nul(b"Hello \xF0\x90\x80World\0").unwrap();
1142 /// c_str.to_string_lossy(),
1143 /// Cow::Owned(String::from("Hello �World")) as Cow<str>
1146 #[stable(feature = "cstr_to_str", since = "1.4.0")]
1147 pub fn to_string_lossy(&self) -> Cow<str> {
1148 String::from_utf8_lossy(self.to_bytes())
1151 /// Converts a [`Box`]`<CStr>` into a [`CString`] without copying or allocating.
1153 /// [`Box`]: ../boxed/struct.Box.html
1154 /// [`CString`]: struct.CString.html
1159 /// use std::ffi::CString;
1161 /// let c_string = CString::new(b"foo".to_vec()).unwrap();
1162 /// let boxed = c_string.into_boxed_c_str();
1163 /// assert_eq!(boxed.into_c_string(), CString::new("foo").unwrap());
1165 #[stable(feature = "into_boxed_c_str", since = "1.20.0")]
1166 pub fn into_c_string(self: Box<CStr>) -> CString {
1167 let raw = Box::into_raw(self) as *mut [u8];
1168 CString { inner: unsafe { Box::from_raw(raw) } }
1172 #[stable(feature = "rust1", since = "1.0.0")]
1173 impl PartialEq for CStr {
1174 fn eq(&self, other: &CStr) -> bool {
1175 self.to_bytes().eq(other.to_bytes())
1178 #[stable(feature = "rust1", since = "1.0.0")]
1180 #[stable(feature = "rust1", since = "1.0.0")]
1181 impl PartialOrd for CStr {
1182 fn partial_cmp(&self, other: &CStr) -> Option<Ordering> {
1183 self.to_bytes().partial_cmp(&other.to_bytes())
1186 #[stable(feature = "rust1", since = "1.0.0")]
1188 fn cmp(&self, other: &CStr) -> Ordering {
1189 self.to_bytes().cmp(&other.to_bytes())
1193 #[stable(feature = "cstr_borrow", since = "1.3.0")]
1194 impl ToOwned for CStr {
1195 type Owned = CString;
1197 fn to_owned(&self) -> CString {
1198 CString { inner: self.to_bytes_with_nul().into() }
1202 #[stable(feature = "cstring_asref", since = "1.7.0")]
1203 impl<'a> From<&'a CStr> for CString {
1204 fn from(s: &'a CStr) -> CString {
1209 #[stable(feature = "cstring_asref", since = "1.7.0")]
1210 impl ops::Index<ops::RangeFull> for CString {
1214 fn index(&self, _index: ops::RangeFull) -> &CStr {
1219 #[stable(feature = "cstring_asref", since = "1.7.0")]
1220 impl AsRef<CStr> for CStr {
1222 fn as_ref(&self) -> &CStr {
1227 #[stable(feature = "cstring_asref", since = "1.7.0")]
1228 impl AsRef<CStr> for CString {
1230 fn as_ref(&self) -> &CStr {
1238 use os::raw::c_char;
1239 use borrow::Cow::{Borrowed, Owned};
1240 use hash::{Hash, Hasher};
1241 use collections::hash_map::DefaultHasher;
1247 let data = b"123\0";
1248 let ptr = data.as_ptr() as *const c_char;
1250 assert_eq!(CStr::from_ptr(ptr).to_bytes(), b"123");
1251 assert_eq!(CStr::from_ptr(ptr).to_bytes_with_nul(), b"123\0");
1257 let s = CString::new("1234").unwrap();
1258 assert_eq!(s.as_bytes(), b"1234");
1259 assert_eq!(s.as_bytes_with_nul(), b"1234\0");
1263 fn build_with_zero1() {
1264 assert!(CString::new(&b"\0"[..]).is_err());
1267 fn build_with_zero2() {
1268 assert!(CString::new(vec![0]).is_err());
1272 fn build_with_zero3() {
1274 let s = CString::from_vec_unchecked(vec![0]);
1275 assert_eq!(s.as_bytes(), b"\0");
1281 let s = CString::new(&b"abc\x01\x02\n\xE2\x80\xA6\xFF"[..]).unwrap();
1282 assert_eq!(format!("{:?}", s), r#""abc\x01\x02\n\xe2\x80\xa6\xff""#);
1288 let s = CStr::from_ptr(b"12\0".as_ptr() as *const _);
1289 assert_eq!(s.to_bytes(), b"12");
1290 assert_eq!(s.to_bytes_with_nul(), b"12\0");
1296 let data = b"123\xE2\x80\xA6\0";
1297 let ptr = data.as_ptr() as *const c_char;
1299 assert_eq!(CStr::from_ptr(ptr).to_str(), Ok("123…"));
1300 assert_eq!(CStr::from_ptr(ptr).to_string_lossy(), Borrowed("123…"));
1302 let data = b"123\xE2\0";
1303 let ptr = data.as_ptr() as *const c_char;
1305 assert!(CStr::from_ptr(ptr).to_str().is_err());
1306 assert_eq!(CStr::from_ptr(ptr).to_string_lossy(), Owned::<str>(format!("123\u{FFFD}")));
1312 let data = b"123\0";
1313 let ptr = data.as_ptr() as *const c_char;
1315 let owned = unsafe { CStr::from_ptr(ptr).to_owned() };
1316 assert_eq!(owned.as_bytes_with_nul(), data);
1321 let data = b"123\xE2\xFA\xA6\0";
1322 let ptr = data.as_ptr() as *const c_char;
1323 let cstr: &'static CStr = unsafe { CStr::from_ptr(ptr) };
1325 let mut s = DefaultHasher::new();
1327 let cstr_hash = s.finish();
1328 let mut s = DefaultHasher::new();
1329 CString::new(&data[..data.len() - 1]).unwrap().hash(&mut s);
1330 let cstring_hash = s.finish();
1332 assert_eq!(cstr_hash, cstring_hash);
1336 fn from_bytes_with_nul() {
1337 let data = b"123\0";
1338 let cstr = CStr::from_bytes_with_nul(data);
1339 assert_eq!(cstr.map(CStr::to_bytes), Ok(&b"123"[..]));
1340 let cstr = CStr::from_bytes_with_nul(data);
1341 assert_eq!(cstr.map(CStr::to_bytes_with_nul), Ok(&b"123\0"[..]));
1344 let cstr = CStr::from_bytes_with_nul(data);
1345 let cstr_unchecked = CStr::from_bytes_with_nul_unchecked(data);
1346 assert_eq!(cstr, Ok(cstr_unchecked));
1351 fn from_bytes_with_nul_unterminated() {
1353 let cstr = CStr::from_bytes_with_nul(data);
1354 assert!(cstr.is_err());
1358 fn from_bytes_with_nul_interior() {
1359 let data = b"1\023\0";
1360 let cstr = CStr::from_bytes_with_nul(data);
1361 assert!(cstr.is_err());
1366 let orig: &[u8] = b"Hello, world!\0";
1367 let cstr = CStr::from_bytes_with_nul(orig).unwrap();
1368 let boxed: Box<CStr> = Box::from(cstr);
1369 let cstring = cstr.to_owned().into_boxed_c_str().into_c_string();
1370 assert_eq!(cstr, &*boxed);
1371 assert_eq!(&*boxed, &*cstring);
1372 assert_eq!(&*cstring, cstr);
1376 fn boxed_default() {
1377 let boxed = <Box<CStr>>::default();
1378 assert_eq!(boxed.to_bytes_with_nul(), &[0]);
1383 let orig: &[u8] = b"Hello, world!\0";
1384 let cstr = CStr::from_bytes_with_nul(orig).unwrap();
1385 let rc: Rc<CStr> = Rc::from(cstr);
1386 let arc: Arc<CStr> = Arc::from(cstr);
1388 assert_eq!(&*rc, cstr);
1389 assert_eq!(&*arc, cstr);
1391 let rc2: Rc<CStr> = Rc::from(cstr.to_owned());
1392 let arc2: Arc<CStr> = Arc::from(cstr.to_owned());
1394 assert_eq!(&*rc2, cstr);
1395 assert_eq!(&*arc2, cstr);