2 use crate::borrow::{Cow, Borrow};
3 use crate::cmp::Ordering;
4 use crate::error::Error;
5 use crate::fmt::{self, Write};
10 use crate::os::raw::c_char;
14 use crate::str::{self, Utf8Error};
18 /// A type representing an owned, C-compatible, nul-terminated string with no nul bytes in the
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").
26 /// `CString` is to [`&CStr`] as [`String`] is to [`&str`]: the former
27 /// in each pair are owned strings; the latter are borrowed
30 /// # Creating a `CString`
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).
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
41 /// # Extracting a raw pointer to the whole C string
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.
50 /// # Extracting a slice of the whole C string
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.
61 /// If you need a `&[`[`u8`]`]` slice *with* the nul terminator, you
62 /// can use [`as_bytes_with_nul`] instead.
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.
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
87 /// ```ignore (extern-declaration)
89 /// use std::ffi::CString;
90 /// use std::os::raw::c_char;
93 /// fn my_printer(s: *const c_char);
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");
100 /// my_printer(c_to_print.as_ptr());
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.
116 #[derive(PartialEq, PartialOrd, Eq, Ord, Hash, Clone)]
117 #[stable(feature = "rust1", since = "1.0.0")]
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.
125 /// Representation of a borrowed C string.
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`].
133 /// `&CStr` is to [`CString`] as [`&str`] is to [`String`]: the former
134 /// in each pair are borrowed references; the latter are owned
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.
144 /// Inspecting a foreign C string:
146 /// ```ignore (extern-declaration)
147 /// use std::ffi::CStr;
148 /// use std::os::raw::c_char;
150 /// extern { fn my_string() -> *const c_char; }
153 /// let slice = CStr::from_ptr(my_string());
154 /// println!("string buffer size without nul terminator: {}", slice.to_bytes().len());
158 /// Passing a Rust-originating C string:
160 /// ```ignore (extern-declaration)
161 /// use std::ffi::{CString, CStr};
162 /// use std::os::raw::c_char;
164 /// fn work(data: &CStr) {
165 /// extern { fn work_with(data: *const c_char); }
167 /// unsafe { work_with(data.as_ptr()) }
170 /// let s = CString::new("data data data data").expect("CString::new failed");
174 /// Converting a foreign C string into a Rust [`String`]:
176 /// ```ignore (extern-declaration)
177 /// use std::ffi::CStr;
178 /// use std::os::raw::c_char;
180 /// extern { fn my_string() -> *const c_char; }
182 /// fn my_string_safe() -> String {
184 /// CStr::from_ptr(my_string()).to_string_lossy().into_owned()
188 /// println!("string: {}", my_string_safe());
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
197 #[stable(feature = "rust1", since = "1.0.0")]
199 // FIXME: this should not be represented with a DST slice but rather with
200 // just a raw `c_char` along with some form of marker to make
201 // this an unsized type. Essentially `sizeof(&CStr)` should be the
202 // same as `sizeof(&c_char)` but `CStr` should be an unsized type.
206 /// An error indicating that an interior nul byte was found.
208 /// While Rust strings may contain nul bytes in the middle, C strings
209 /// can't, as that byte would effectively truncate the string.
211 /// This error is created by the [`new`][`CString::new`] method on
212 /// [`CString`]. See its documentation for more.
214 /// [`CString`]: struct.CString.html
215 /// [`CString::new`]: struct.CString.html#method.new
220 /// use std::ffi::{CString, NulError};
222 /// let _: NulError = CString::new(b"f\0oo".to_vec()).unwrap_err();
224 #[derive(Clone, PartialEq, Eq, Debug)]
225 #[stable(feature = "rust1", since = "1.0.0")]
226 pub struct NulError(usize, Vec<u8>);
228 /// An error indicating that a nul byte was not in the expected position.
230 /// The slice used to create a [`CStr`] must have one and only one nul
231 /// byte at the end of the slice.
233 /// This error is created by the
234 /// [`from_bytes_with_nul`][`CStr::from_bytes_with_nul`] method on
235 /// [`CStr`]. See its documentation for more.
237 /// [`CStr`]: struct.CStr.html
238 /// [`CStr::from_bytes_with_nul`]: struct.CStr.html#method.from_bytes_with_nul
243 /// use std::ffi::{CStr, FromBytesWithNulError};
245 /// let _: FromBytesWithNulError = CStr::from_bytes_with_nul(b"f\0oo").unwrap_err();
247 #[derive(Clone, PartialEq, Eq, Debug)]
248 #[stable(feature = "cstr_from_bytes", since = "1.10.0")]
249 pub struct FromBytesWithNulError {
250 kind: FromBytesWithNulErrorKind,
253 #[derive(Clone, PartialEq, Eq, Debug)]
254 enum FromBytesWithNulErrorKind {
259 impl FromBytesWithNulError {
260 fn interior_nul(pos: usize) -> FromBytesWithNulError {
261 FromBytesWithNulError {
262 kind: FromBytesWithNulErrorKind::InteriorNul(pos),
265 fn not_nul_terminated() -> FromBytesWithNulError {
266 FromBytesWithNulError {
267 kind: FromBytesWithNulErrorKind::NotNulTerminated,
272 /// An error indicating invalid UTF-8 when converting a [`CString`] into a [`String`].
274 /// `CString` is just a wrapper over a buffer of bytes with a nul
275 /// terminator; [`into_string`][`CString::into_string`] performs UTF-8
276 /// validation on those bytes and may return this error.
278 /// This `struct` is created by the
279 /// [`into_string`][`CString::into_string`] method on [`CString`]. See
280 /// its documentation for more.
282 /// [`String`]: ../string/struct.String.html
283 /// [`CString`]: struct.CString.html
284 /// [`CString::into_string`]: struct.CString.html#method.into_string
285 #[derive(Clone, PartialEq, Eq, Debug)]
286 #[stable(feature = "cstring_into", since = "1.7.0")]
287 pub struct IntoStringError {
293 /// Creates a new C-compatible string from a container of bytes.
295 /// This function will consume the provided data and use the
296 /// underlying bytes to construct a new string, ensuring that
297 /// there is a trailing 0 byte. This trailing 0 byte will be
298 /// appended by this function; the provided data should *not*
299 /// contain any 0 bytes in it.
303 /// ```ignore (extern-declaration)
304 /// use std::ffi::CString;
305 /// use std::os::raw::c_char;
307 /// extern { fn puts(s: *const c_char); }
309 /// let to_print = CString::new("Hello!").expect("CString::new failed");
311 /// puts(to_print.as_ptr());
317 /// This function will return an error if the supplied bytes contain an
318 /// internal 0 byte. The [`NulError`] returned will contain the bytes as well as
319 /// the position of the nul byte.
321 /// [`NulError`]: struct.NulError.html
322 #[stable(feature = "rust1", since = "1.0.0")]
323 pub fn new<T: Into<Vec<u8>>>(t: T) -> Result<CString, NulError> {
327 fn _new(bytes: Vec<u8>) -> Result<CString, NulError> {
328 match memchr::memchr(0, &bytes) {
329 Some(i) => Err(NulError(i, bytes)),
330 None => Ok(unsafe { CString::from_vec_unchecked(bytes) }),
334 /// Creates a C-compatible string by consuming a byte vector,
335 /// without checking for interior 0 bytes.
337 /// This method is equivalent to [`new`] except that no runtime assertion
338 /// is made that `v` contains no 0 bytes, and it requires an actual
339 /// byte vector, not anything that can be converted to one with Into.
341 /// [`new`]: #method.new
346 /// use std::ffi::CString;
348 /// let raw = b"foo".to_vec();
350 /// let c_string = CString::from_vec_unchecked(raw);
353 #[stable(feature = "rust1", since = "1.0.0")]
354 pub unsafe fn from_vec_unchecked(mut v: Vec<u8>) -> CString {
357 CString { inner: v.into_boxed_slice() }
360 /// Retakes ownership of a `CString` that was transferred to C via [`into_raw`].
362 /// Additionally, the length of the string will be recalculated from the pointer.
366 /// This should only ever be called with a pointer that was earlier
367 /// obtained by calling [`into_raw`] on a `CString`. Other usage (e.g., trying to take
368 /// ownership of a string that was allocated by foreign code) is likely to lead
369 /// to undefined behavior or allocator corruption.
371 /// > **Note:** If you need to borrow a string that was allocated by
372 /// > foreign code, use [`CStr`]. If you need to take ownership of
373 /// > a string that was allocated by foreign code, you will need to
374 /// > make your own provisions for freeing it appropriately, likely
375 /// > with the foreign code's API to do that.
377 /// [`into_raw`]: #method.into_raw
378 /// [`CStr`]: struct.CStr.html
382 /// Creates a `CString`, pass ownership to an `extern` function (via raw pointer), then retake
383 /// ownership with `from_raw`:
385 /// ```ignore (extern-declaration)
386 /// use std::ffi::CString;
387 /// use std::os::raw::c_char;
390 /// fn some_extern_function(s: *mut c_char);
393 /// let c_string = CString::new("Hello!").expect("CString::new failed");
394 /// let raw = c_string.into_raw();
396 /// some_extern_function(raw);
397 /// let c_string = CString::from_raw(raw);
400 #[stable(feature = "cstr_memory", since = "1.4.0")]
401 pub unsafe fn from_raw(ptr: *mut c_char) -> CString {
402 let len = sys::strlen(ptr) + 1; // Including the NUL byte
403 let slice = slice::from_raw_parts_mut(ptr, len as usize);
404 CString { inner: Box::from_raw(slice as *mut [c_char] as *mut [u8]) }
407 /// Consumes the `CString` and transfers ownership of the string to a C caller.
409 /// The pointer which this function returns must be returned to Rust and reconstituted using
410 /// [`from_raw`] to be properly deallocated. Specifically, one
411 /// should *not* use the standard C `free()` function to deallocate
414 /// Failure to call [`from_raw`] will lead to a memory leak.
416 /// [`from_raw`]: #method.from_raw
421 /// use std::ffi::CString;
423 /// let c_string = CString::new("foo").expect("CString::new failed");
425 /// let ptr = c_string.into_raw();
428 /// assert_eq!(b'f', *ptr as u8);
429 /// assert_eq!(b'o', *ptr.offset(1) as u8);
430 /// assert_eq!(b'o', *ptr.offset(2) as u8);
431 /// assert_eq!(b'\0', *ptr.offset(3) as u8);
433 /// // retake pointer to free memory
434 /// let _ = CString::from_raw(ptr);
438 #[stable(feature = "cstr_memory", since = "1.4.0")]
439 pub fn into_raw(self) -> *mut c_char {
440 Box::into_raw(self.into_inner()) as *mut c_char
443 /// Converts the `CString` into a [`String`] if it contains valid UTF-8 data.
445 /// On failure, ownership of the original `CString` is returned.
447 /// [`String`]: ../string/struct.String.html
452 /// use std::ffi::CString;
454 /// let valid_utf8 = vec![b'f', b'o', b'o'];
455 /// let cstring = CString::new(valid_utf8).expect("CString::new failed");
456 /// assert_eq!(cstring.into_string().expect("into_string() call failed"), "foo");
458 /// let invalid_utf8 = vec![b'f', 0xff, b'o', b'o'];
459 /// let cstring = CString::new(invalid_utf8).expect("CString::new failed");
460 /// let err = cstring.into_string().err().expect("into_string().err() failed");
461 /// assert_eq!(err.utf8_error().valid_up_to(), 1);
464 #[stable(feature = "cstring_into", since = "1.7.0")]
465 pub fn into_string(self) -> Result<String, IntoStringError> {
466 String::from_utf8(self.into_bytes())
467 .map_err(|e| IntoStringError {
468 error: e.utf8_error(),
469 inner: unsafe { CString::from_vec_unchecked(e.into_bytes()) },
473 /// Consumes the `CString` and returns the underlying byte buffer.
475 /// The returned buffer does **not** contain the trailing nul
476 /// terminator, and it is guaranteed to not have any interior nul
482 /// use std::ffi::CString;
484 /// let c_string = CString::new("foo").expect("CString::new failed");
485 /// let bytes = c_string.into_bytes();
486 /// assert_eq!(bytes, vec![b'f', b'o', b'o']);
488 #[stable(feature = "cstring_into", since = "1.7.0")]
489 pub fn into_bytes(self) -> Vec<u8> {
490 let mut vec = self.into_inner().into_vec();
491 let _nul = vec.pop();
492 debug_assert_eq!(_nul, Some(0u8));
496 /// Equivalent to the [`into_bytes`] function except that the returned vector
497 /// includes the trailing nul terminator.
499 /// [`into_bytes`]: #method.into_bytes
504 /// use std::ffi::CString;
506 /// let c_string = CString::new("foo").expect("CString::new failed");
507 /// let bytes = c_string.into_bytes_with_nul();
508 /// assert_eq!(bytes, vec![b'f', b'o', b'o', b'\0']);
510 #[stable(feature = "cstring_into", since = "1.7.0")]
511 pub fn into_bytes_with_nul(self) -> Vec<u8> {
512 self.into_inner().into_vec()
515 /// Returns the contents of this `CString` as a slice of bytes.
517 /// The returned slice does **not** contain the trailing nul
518 /// terminator, and it is guaranteed to not have any interior nul
519 /// bytes. If you need the nul terminator, use
520 /// [`as_bytes_with_nul`] instead.
522 /// [`as_bytes_with_nul`]: #method.as_bytes_with_nul
527 /// use std::ffi::CString;
529 /// let c_string = CString::new("foo").expect("CString::new failed");
530 /// let bytes = c_string.as_bytes();
531 /// assert_eq!(bytes, &[b'f', b'o', b'o']);
534 #[stable(feature = "rust1", since = "1.0.0")]
535 pub fn as_bytes(&self) -> &[u8] {
536 &self.inner[..self.inner.len() - 1]
539 /// Equivalent to the [`as_bytes`] function except that the returned slice
540 /// includes the trailing nul terminator.
542 /// [`as_bytes`]: #method.as_bytes
547 /// use std::ffi::CString;
549 /// let c_string = CString::new("foo").expect("CString::new failed");
550 /// let bytes = c_string.as_bytes_with_nul();
551 /// assert_eq!(bytes, &[b'f', b'o', b'o', b'\0']);
554 #[stable(feature = "rust1", since = "1.0.0")]
555 pub fn as_bytes_with_nul(&self) -> &[u8] {
559 /// Extracts a [`CStr`] slice containing the entire string.
561 /// [`CStr`]: struct.CStr.html
566 /// use std::ffi::{CString, CStr};
568 /// let c_string = CString::new(b"foo".to_vec()).expect("CString::new failed");
569 /// let c_str = c_string.as_c_str();
570 /// assert_eq!(c_str,
571 /// CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed"));
574 #[stable(feature = "as_c_str", since = "1.20.0")]
575 pub fn as_c_str(&self) -> &CStr {
579 /// Converts this `CString` into a boxed [`CStr`].
581 /// [`CStr`]: struct.CStr.html
586 /// use std::ffi::{CString, CStr};
588 /// let c_string = CString::new(b"foo".to_vec()).expect("CString::new failed");
589 /// let boxed = c_string.into_boxed_c_str();
590 /// assert_eq!(&*boxed,
591 /// CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed"));
593 #[stable(feature = "into_boxed_c_str", since = "1.20.0")]
594 pub fn into_boxed_c_str(self) -> Box<CStr> {
595 unsafe { Box::from_raw(Box::into_raw(self.into_inner()) as *mut CStr) }
598 /// Bypass "move out of struct which implements [`Drop`] trait" restriction.
600 /// [`Drop`]: ../ops/trait.Drop.html
601 fn into_inner(self) -> Box<[u8]> {
603 let result = ptr::read(&self.inner);
610 // Turns this `CString` into an empty string to prevent
611 // memory unsafe code from working by accident. Inline
612 // to prevent LLVM from optimizing it away in debug builds.
613 #[stable(feature = "cstring_drop", since = "1.13.0")]
614 impl Drop for CString {
617 unsafe { *self.inner.get_unchecked_mut(0) = 0; }
621 #[stable(feature = "rust1", since = "1.0.0")]
622 impl ops::Deref for CString {
626 fn deref(&self) -> &CStr {
627 unsafe { CStr::from_bytes_with_nul_unchecked(self.as_bytes_with_nul()) }
631 #[stable(feature = "rust1", since = "1.0.0")]
632 impl fmt::Debug for CString {
633 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
634 fmt::Debug::fmt(&**self, f)
638 #[stable(feature = "cstring_into", since = "1.7.0")]
639 impl From<CString> for Vec<u8> {
640 /// Converts a [`CString`] into a [`Vec`]`<u8>`.
642 /// The conversion consumes the [`CString`], and removes the terminating NUL byte.
644 /// [`Vec`]: ../vec/struct.Vec.html
645 /// [`CString`]: ../ffi/struct.CString.html
647 fn from(s: CString) -> Vec<u8> {
652 #[stable(feature = "cstr_debug", since = "1.3.0")]
653 impl fmt::Debug for CStr {
654 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
656 for byte in self.to_bytes().iter().flat_map(|&b| ascii::escape_default(b)) {
657 f.write_char(byte as char)?;
663 #[stable(feature = "cstr_default", since = "1.10.0")]
664 impl Default for &CStr {
665 fn default() -> Self {
666 const SLICE: &[c_char] = &[0];
667 unsafe { CStr::from_ptr(SLICE.as_ptr()) }
671 #[stable(feature = "cstr_default", since = "1.10.0")]
672 impl Default for CString {
673 /// Creates an empty `CString`.
674 fn default() -> CString {
675 let a: &CStr = Default::default();
680 #[stable(feature = "cstr_borrow", since = "1.3.0")]
681 impl Borrow<CStr> for CString {
683 fn borrow(&self) -> &CStr { self }
686 #[stable(feature = "cstring_from_cow_cstr", since = "1.28.0")]
687 impl<'a> From<Cow<'a, CStr>> for CString {
689 fn from(s: Cow<'a, CStr>) -> Self {
694 #[stable(feature = "box_from_c_str", since = "1.17.0")]
695 impl From<&CStr> for Box<CStr> {
696 fn from(s: &CStr) -> Box<CStr> {
697 let boxed: Box<[u8]> = Box::from(s.to_bytes_with_nul());
698 unsafe { Box::from_raw(Box::into_raw(boxed) as *mut CStr) }
702 #[stable(feature = "c_string_from_box", since = "1.18.0")]
703 impl From<Box<CStr>> for CString {
704 /// Converts a [`Box`]`<CStr>` into a [`CString`] without copying or allocating.
706 /// [`Box`]: ../boxed/struct.Box.html
707 /// [`CString`]: ../ffi/struct.CString.html
709 fn from(s: Box<CStr>) -> CString {
714 #[stable(feature = "more_box_slice_clone", since = "1.29.0")]
715 impl Clone for Box<CStr> {
717 fn clone(&self) -> Self {
722 #[stable(feature = "box_from_c_string", since = "1.20.0")]
723 impl From<CString> for Box<CStr> {
724 /// Converts a [`CString`] into a [`Box`]`<CStr>` without copying or allocating.
726 /// [`CString`]: ../ffi/struct.CString.html
727 /// [`Box`]: ../boxed/struct.Box.html
729 fn from(s: CString) -> Box<CStr> {
734 #[stable(feature = "cow_from_cstr", since = "1.28.0")]
735 impl<'a> From<CString> for Cow<'a, CStr> {
737 fn from(s: CString) -> Cow<'a, CStr> {
742 #[stable(feature = "cow_from_cstr", since = "1.28.0")]
743 impl<'a> From<&'a CStr> for Cow<'a, CStr> {
745 fn from(s: &'a CStr) -> Cow<'a, CStr> {
750 #[stable(feature = "cow_from_cstr", since = "1.28.0")]
751 impl<'a> From<&'a CString> for Cow<'a, CStr> {
753 fn from(s: &'a CString) -> Cow<'a, CStr> {
754 Cow::Borrowed(s.as_c_str())
758 #[stable(feature = "shared_from_slice2", since = "1.24.0")]
759 impl From<CString> for Arc<CStr> {
760 /// Converts a [`CString`] into a [`Arc`]`<CStr>` without copying or allocating.
762 /// [`CString`]: ../ffi/struct.CString.html
763 /// [`Arc`]: ../sync/struct.Arc.html
765 fn from(s: CString) -> Arc<CStr> {
766 let arc: Arc<[u8]> = Arc::from(s.into_inner());
767 unsafe { Arc::from_raw(Arc::into_raw(arc) as *const CStr) }
771 #[stable(feature = "shared_from_slice2", since = "1.24.0")]
772 impl From<&CStr> for Arc<CStr> {
774 fn from(s: &CStr) -> Arc<CStr> {
775 let arc: Arc<[u8]> = Arc::from(s.to_bytes_with_nul());
776 unsafe { Arc::from_raw(Arc::into_raw(arc) as *const CStr) }
780 #[stable(feature = "shared_from_slice2", since = "1.24.0")]
781 impl From<CString> for Rc<CStr> {
782 /// Converts a [`CString`] into a [`Rc`]`<CStr>` without copying or allocating.
784 /// [`CString`]: ../ffi/struct.CString.html
785 /// [`Rc`]: ../rc/struct.Rc.html
787 fn from(s: CString) -> Rc<CStr> {
788 let rc: Rc<[u8]> = Rc::from(s.into_inner());
789 unsafe { Rc::from_raw(Rc::into_raw(rc) as *const CStr) }
793 #[stable(feature = "shared_from_slice2", since = "1.24.0")]
794 impl From<&CStr> for Rc<CStr> {
796 fn from(s: &CStr) -> Rc<CStr> {
797 let rc: Rc<[u8]> = Rc::from(s.to_bytes_with_nul());
798 unsafe { Rc::from_raw(Rc::into_raw(rc) as *const CStr) }
802 #[stable(feature = "default_box_extra", since = "1.17.0")]
803 impl Default for Box<CStr> {
804 fn default() -> Box<CStr> {
805 let boxed: Box<[u8]> = Box::from([0]);
806 unsafe { Box::from_raw(Box::into_raw(boxed) as *mut CStr) }
811 /// Returns the position of the nul byte in the slice that caused
812 /// [`CString::new`] to fail.
814 /// [`CString::new`]: struct.CString.html#method.new
819 /// use std::ffi::CString;
821 /// let nul_error = CString::new("foo\0bar").unwrap_err();
822 /// assert_eq!(nul_error.nul_position(), 3);
824 /// let nul_error = CString::new("foo bar\0").unwrap_err();
825 /// assert_eq!(nul_error.nul_position(), 7);
827 #[stable(feature = "rust1", since = "1.0.0")]
828 pub fn nul_position(&self) -> usize { self.0 }
830 /// Consumes this error, returning the underlying vector of bytes which
831 /// generated the error in the first place.
836 /// use std::ffi::CString;
838 /// let nul_error = CString::new("foo\0bar").unwrap_err();
839 /// assert_eq!(nul_error.into_vec(), b"foo\0bar");
841 #[stable(feature = "rust1", since = "1.0.0")]
842 pub fn into_vec(self) -> Vec<u8> { self.1 }
845 #[stable(feature = "rust1", since = "1.0.0")]
846 impl Error for NulError {
847 fn description(&self) -> &str { "nul byte found in data" }
850 #[stable(feature = "rust1", since = "1.0.0")]
851 impl fmt::Display for NulError {
852 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
853 write!(f, "nul byte found in provided data at position: {}", self.0)
857 #[stable(feature = "rust1", since = "1.0.0")]
858 impl From<NulError> for io::Error {
859 /// Converts a [`NulError`] into a [`io::Error`].
861 /// [`NulError`]: ../ffi/struct.NulError.html
862 /// [`io::Error`]: ../io/struct.Error.html
863 fn from(_: NulError) -> io::Error {
864 io::Error::new(io::ErrorKind::InvalidInput,
865 "data provided contains a nul byte")
869 #[stable(feature = "frombyteswithnulerror_impls", since = "1.17.0")]
870 impl Error for FromBytesWithNulError {
871 fn description(&self) -> &str {
873 FromBytesWithNulErrorKind::InteriorNul(..) =>
874 "data provided contains an interior nul byte",
875 FromBytesWithNulErrorKind::NotNulTerminated =>
876 "data provided is not nul terminated",
881 #[stable(feature = "frombyteswithnulerror_impls", since = "1.17.0")]
882 impl fmt::Display for FromBytesWithNulError {
883 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
884 f.write_str(self.description())?;
885 if let FromBytesWithNulErrorKind::InteriorNul(pos) = self.kind {
886 write!(f, " at byte pos {}", pos)?;
892 impl IntoStringError {
893 /// Consumes this error, returning original [`CString`] which generated the
896 /// [`CString`]: struct.CString.html
897 #[stable(feature = "cstring_into", since = "1.7.0")]
898 pub fn into_cstring(self) -> CString {
902 /// Access the underlying UTF-8 error that was the cause of this error.
903 #[stable(feature = "cstring_into", since = "1.7.0")]
904 pub fn utf8_error(&self) -> Utf8Error {
909 #[stable(feature = "cstring_into", since = "1.7.0")]
910 impl Error for IntoStringError {
911 fn description(&self) -> &str {
912 "C string contained non-utf8 bytes"
915 fn cause(&self) -> Option<&dyn Error> {
920 #[stable(feature = "cstring_into", since = "1.7.0")]
921 impl fmt::Display for IntoStringError {
922 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
923 self.description().fmt(f)
928 /// Wraps a raw C string with a safe C string wrapper.
930 /// This function will wrap the provided `ptr` with a `CStr` wrapper, which
931 /// allows inspection and interoperation of non-owned C strings. This method
932 /// is unsafe for a number of reasons:
934 /// * There is no guarantee to the validity of `ptr`.
935 /// * The returned lifetime is not guaranteed to be the actual lifetime of
937 /// * There is no guarantee that the memory pointed to by `ptr` contains a
938 /// valid nul terminator byte at the end of the string.
939 /// * It is not guaranteed that the memory pointed by `ptr` won't change
940 /// before the `CStr` has been destroyed.
942 /// > **Note**: This operation is intended to be a 0-cost cast but it is
943 /// > currently implemented with an up-front calculation of the length of
944 /// > the string. This is not guaranteed to always be the case.
948 /// ```ignore (extern-declaration)
950 /// use std::ffi::CStr;
951 /// use std::os::raw::c_char;
954 /// fn my_string() -> *const c_char;
958 /// let slice = CStr::from_ptr(my_string());
959 /// println!("string returned: {}", slice.to_str().unwrap());
963 #[stable(feature = "rust1", since = "1.0.0")]
964 pub unsafe fn from_ptr<'a>(ptr: *const c_char) -> &'a CStr {
965 let len = sys::strlen(ptr);
966 let ptr = ptr as *const u8;
967 CStr::from_bytes_with_nul_unchecked(slice::from_raw_parts(ptr, len as usize + 1))
970 /// Creates a C string wrapper from a byte slice.
972 /// This function will cast the provided `bytes` to a `CStr`
973 /// wrapper after ensuring that the byte slice is nul-terminated
974 /// and does not contain any interior nul bytes.
979 /// use std::ffi::CStr;
981 /// let cstr = CStr::from_bytes_with_nul(b"hello\0");
982 /// assert!(cstr.is_ok());
985 /// Creating a `CStr` without a trailing nul terminator is an error:
988 /// use std::ffi::CStr;
990 /// let c_str = CStr::from_bytes_with_nul(b"hello");
991 /// assert!(c_str.is_err());
994 /// Creating a `CStr` with an interior nul byte is an error:
997 /// use std::ffi::CStr;
999 /// let c_str = CStr::from_bytes_with_nul(b"he\0llo\0");
1000 /// assert!(c_str.is_err());
1002 #[stable(feature = "cstr_from_bytes", since = "1.10.0")]
1003 pub fn from_bytes_with_nul(bytes: &[u8])
1004 -> Result<&CStr, FromBytesWithNulError> {
1005 let nul_pos = memchr::memchr(0, bytes);
1006 if let Some(nul_pos) = nul_pos {
1007 if nul_pos + 1 != bytes.len() {
1008 return Err(FromBytesWithNulError::interior_nul(nul_pos));
1010 Ok(unsafe { CStr::from_bytes_with_nul_unchecked(bytes) })
1012 Err(FromBytesWithNulError::not_nul_terminated())
1016 /// Unsafely creates a C string wrapper from a byte slice.
1018 /// This function will cast the provided `bytes` to a `CStr` wrapper without
1019 /// performing any sanity checks. The provided slice **must** be nul-terminated
1020 /// and not contain any interior nul bytes.
1025 /// use std::ffi::{CStr, CString};
1028 /// let cstring = CString::new("hello").expect("CString::new failed");
1029 /// let cstr = CStr::from_bytes_with_nul_unchecked(cstring.to_bytes_with_nul());
1030 /// assert_eq!(cstr, &*cstring);
1034 #[stable(feature = "cstr_from_bytes", since = "1.10.0")]
1035 #[rustc_const_unstable(feature = "const_cstr_unchecked")]
1036 pub const unsafe fn from_bytes_with_nul_unchecked(bytes: &[u8]) -> &CStr {
1037 &*(bytes as *const [u8] as *const CStr)
1040 /// Returns the inner pointer to this C string.
1042 /// The returned pointer will be valid for as long as `self` is, and points
1043 /// to a contiguous region of memory terminated with a 0 byte to represent
1044 /// the end of the string.
1048 /// The returned pointer is read-only; writing to it (including passing it
1049 /// to C code that writes to it) causes undefined behavior.
1051 /// It is your responsibility to make sure that the underlying memory is not
1052 /// freed too early. For example, the following code will cause undefined
1053 /// behavior when `ptr` is used inside the `unsafe` block:
1056 /// # #![allow(unused_must_use)]
1057 /// use std::ffi::{CString};
1059 /// let ptr = CString::new("Hello").expect("CString::new failed").as_ptr();
1061 /// // `ptr` is dangling
1066 /// This happens because the pointer returned by `as_ptr` does not carry any
1067 /// lifetime information and the [`CString`] is deallocated immediately after
1068 /// the `CString::new("Hello").expect("CString::new failed").as_ptr()` expression is evaluated.
1069 /// To fix the problem, bind the `CString` to a local variable:
1072 /// # #![allow(unused_must_use)]
1073 /// use std::ffi::{CString};
1075 /// let hello = CString::new("Hello").expect("CString::new failed");
1076 /// let ptr = hello.as_ptr();
1078 /// // `ptr` is valid because `hello` is in scope
1083 /// This way, the lifetime of the `CString` in `hello` encompasses
1084 /// the lifetime of `ptr` and the `unsafe` block.
1086 /// [`CString`]: struct.CString.html
1088 #[stable(feature = "rust1", since = "1.0.0")]
1089 pub const fn as_ptr(&self) -> *const c_char {
1093 /// Converts this C string to a byte slice.
1095 /// The returned slice will **not** contain the trailing nul terminator that this C
1098 /// > **Note**: This method is currently implemented as a constant-time
1099 /// > cast, but it is planned to alter its definition in the future to
1100 /// > perform the length calculation whenever this method is called.
1105 /// use std::ffi::CStr;
1107 /// let c_str = CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed");
1108 /// assert_eq!(c_str.to_bytes(), b"foo");
1111 #[stable(feature = "rust1", since = "1.0.0")]
1112 pub fn to_bytes(&self) -> &[u8] {
1113 let bytes = self.to_bytes_with_nul();
1114 &bytes[..bytes.len() - 1]
1117 /// Converts this C string to a byte slice containing the trailing 0 byte.
1119 /// This function is the equivalent of [`to_bytes`] except that it will retain
1120 /// the trailing nul terminator instead of chopping it off.
1122 /// > **Note**: This method is currently implemented as a 0-cost cast, but
1123 /// > it is planned to alter its definition in the future to perform the
1124 /// > length calculation whenever this method is called.
1126 /// [`to_bytes`]: #method.to_bytes
1131 /// use std::ffi::CStr;
1133 /// let c_str = CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed");
1134 /// assert_eq!(c_str.to_bytes_with_nul(), b"foo\0");
1137 #[stable(feature = "rust1", since = "1.0.0")]
1138 pub fn to_bytes_with_nul(&self) -> &[u8] {
1139 unsafe { &*(&self.inner as *const [c_char] as *const [u8]) }
1142 /// Yields a [`&str`] slice if the `CStr` contains valid UTF-8.
1144 /// If the contents of the `CStr` are valid UTF-8 data, this
1145 /// function will return the corresponding [`&str`] slice. Otherwise,
1146 /// it will return an error with details of where UTF-8 validation failed.
1148 /// > **Note**: This method is currently implemented to check for validity
1149 /// > after a constant-time cast, but it is planned to alter its definition
1150 /// > in the future to perform the length calculation in addition to the
1151 /// > UTF-8 check whenever this method is called.
1153 /// [`&str`]: ../primitive.str.html
1158 /// use std::ffi::CStr;
1160 /// let c_str = CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed");
1161 /// assert_eq!(c_str.to_str(), Ok("foo"));
1163 #[stable(feature = "cstr_to_str", since = "1.4.0")]
1164 pub fn to_str(&self) -> Result<&str, str::Utf8Error> {
1165 // N.B., when `CStr` is changed to perform the length check in `.to_bytes()`
1166 // instead of in `from_ptr()`, it may be worth considering if this should
1167 // be rewritten to do the UTF-8 check inline with the length calculation
1168 // instead of doing it afterwards.
1169 str::from_utf8(self.to_bytes())
1172 /// Converts a `CStr` into a [`Cow`]`<`[`str`]`>`.
1174 /// If the contents of the `CStr` are valid UTF-8 data, this
1175 /// function will return a [`Cow`]`::`[`Borrowed`]`(`[`&str`]`)`
1176 /// with the corresponding [`&str`] slice. Otherwise, it will
1177 /// replace any invalid UTF-8 sequences with
1178 /// [`U+FFFD REPLACEMENT CHARACTER`][U+FFFD] and return a
1179 /// [`Cow`]`::`[`Owned`]`(`[`String`]`)` with the result.
1181 /// > **Note**: This method is currently implemented to check for validity
1182 /// > after a constant-time cast, but it is planned to alter its definition
1183 /// > in the future to perform the length calculation in addition to the
1184 /// > UTF-8 check whenever this method is called.
1186 /// [`Cow`]: ../borrow/enum.Cow.html
1187 /// [`Borrowed`]: ../borrow/enum.Cow.html#variant.Borrowed
1188 /// [`Owned`]: ../borrow/enum.Cow.html#variant.Owned
1189 /// [`str`]: ../primitive.str.html
1190 /// [`String`]: ../string/struct.String.html
1191 /// [U+FFFD]: ../char/constant.REPLACEMENT_CHARACTER.html
1195 /// Calling `to_string_lossy` on a `CStr` containing valid UTF-8:
1198 /// use std::borrow::Cow;
1199 /// use std::ffi::CStr;
1201 /// let c_str = CStr::from_bytes_with_nul(b"Hello World\0")
1202 /// .expect("CStr::from_bytes_with_nul failed");
1203 /// assert_eq!(c_str.to_string_lossy(), Cow::Borrowed("Hello World"));
1206 /// Calling `to_string_lossy` on a `CStr` containing invalid UTF-8:
1209 /// use std::borrow::Cow;
1210 /// use std::ffi::CStr;
1212 /// let c_str = CStr::from_bytes_with_nul(b"Hello \xF0\x90\x80World\0")
1213 /// .expect("CStr::from_bytes_with_nul failed");
1215 /// c_str.to_string_lossy(),
1216 /// Cow::Owned(String::from("Hello �World")) as Cow<'_, str>
1219 #[stable(feature = "cstr_to_str", since = "1.4.0")]
1220 pub fn to_string_lossy(&self) -> Cow<'_, str> {
1221 String::from_utf8_lossy(self.to_bytes())
1224 /// Converts a [`Box`]`<CStr>` into a [`CString`] without copying or allocating.
1226 /// [`Box`]: ../boxed/struct.Box.html
1227 /// [`CString`]: struct.CString.html
1232 /// use std::ffi::CString;
1234 /// let c_string = CString::new(b"foo".to_vec()).expect("CString::new failed");
1235 /// let boxed = c_string.into_boxed_c_str();
1236 /// assert_eq!(boxed.into_c_string(), CString::new("foo").expect("CString::new failed"));
1238 #[stable(feature = "into_boxed_c_str", since = "1.20.0")]
1239 pub fn into_c_string(self: Box<CStr>) -> CString {
1240 let raw = Box::into_raw(self) as *mut [u8];
1241 CString { inner: unsafe { Box::from_raw(raw) } }
1245 #[stable(feature = "rust1", since = "1.0.0")]
1246 impl PartialEq for CStr {
1247 fn eq(&self, other: &CStr) -> bool {
1248 self.to_bytes().eq(other.to_bytes())
1251 #[stable(feature = "rust1", since = "1.0.0")]
1253 #[stable(feature = "rust1", since = "1.0.0")]
1254 impl PartialOrd for CStr {
1255 fn partial_cmp(&self, other: &CStr) -> Option<Ordering> {
1256 self.to_bytes().partial_cmp(&other.to_bytes())
1259 #[stable(feature = "rust1", since = "1.0.0")]
1261 fn cmp(&self, other: &CStr) -> Ordering {
1262 self.to_bytes().cmp(&other.to_bytes())
1266 #[stable(feature = "cstr_borrow", since = "1.3.0")]
1267 impl ToOwned for CStr {
1268 type Owned = CString;
1270 fn to_owned(&self) -> CString {
1271 CString { inner: self.to_bytes_with_nul().into() }
1275 #[stable(feature = "cstring_asref", since = "1.7.0")]
1276 impl From<&CStr> for CString {
1277 fn from(s: &CStr) -> CString {
1282 #[stable(feature = "cstring_asref", since = "1.7.0")]
1283 impl ops::Index<ops::RangeFull> for CString {
1287 fn index(&self, _index: ops::RangeFull) -> &CStr {
1292 #[stable(feature = "cstring_asref", since = "1.7.0")]
1293 impl AsRef<CStr> for CStr {
1295 fn as_ref(&self) -> &CStr {
1300 #[stable(feature = "cstring_asref", since = "1.7.0")]
1301 impl AsRef<CStr> for CString {
1303 fn as_ref(&self) -> &CStr {
1311 use crate::os::raw::c_char;
1312 use crate::borrow::Cow::{Borrowed, Owned};
1313 use crate::hash::{Hash, Hasher};
1314 use crate::collections::hash_map::DefaultHasher;
1316 use crate::sync::Arc;
1320 let data = b"123\0";
1321 let ptr = data.as_ptr() as *const c_char;
1323 assert_eq!(CStr::from_ptr(ptr).to_bytes(), b"123");
1324 assert_eq!(CStr::from_ptr(ptr).to_bytes_with_nul(), b"123\0");
1330 let s = CString::new("1234").unwrap();
1331 assert_eq!(s.as_bytes(), b"1234");
1332 assert_eq!(s.as_bytes_with_nul(), b"1234\0");
1336 fn build_with_zero1() {
1337 assert!(CString::new(&b"\0"[..]).is_err());
1340 fn build_with_zero2() {
1341 assert!(CString::new(vec![0]).is_err());
1345 fn build_with_zero3() {
1347 let s = CString::from_vec_unchecked(vec![0]);
1348 assert_eq!(s.as_bytes(), b"\0");
1354 let s = CString::new(&b"abc\x01\x02\n\xE2\x80\xA6\xFF"[..]).unwrap();
1355 assert_eq!(format!("{:?}", s), r#""abc\x01\x02\n\xe2\x80\xa6\xff""#);
1361 let s = CStr::from_ptr(b"12\0".as_ptr() as *const _);
1362 assert_eq!(s.to_bytes(), b"12");
1363 assert_eq!(s.to_bytes_with_nul(), b"12\0");
1369 let data = b"123\xE2\x80\xA6\0";
1370 let ptr = data.as_ptr() as *const c_char;
1372 assert_eq!(CStr::from_ptr(ptr).to_str(), Ok("123…"));
1373 assert_eq!(CStr::from_ptr(ptr).to_string_lossy(), Borrowed("123…"));
1375 let data = b"123\xE2\0";
1376 let ptr = data.as_ptr() as *const c_char;
1378 assert!(CStr::from_ptr(ptr).to_str().is_err());
1379 assert_eq!(CStr::from_ptr(ptr).to_string_lossy(), Owned::<str>(format!("123\u{FFFD}")));
1385 let data = b"123\0";
1386 let ptr = data.as_ptr() as *const c_char;
1388 let owned = unsafe { CStr::from_ptr(ptr).to_owned() };
1389 assert_eq!(owned.as_bytes_with_nul(), data);
1394 let data = b"123\xE2\xFA\xA6\0";
1395 let ptr = data.as_ptr() as *const c_char;
1396 let cstr: &'static CStr = unsafe { CStr::from_ptr(ptr) };
1398 let mut s = DefaultHasher::new();
1400 let cstr_hash = s.finish();
1401 let mut s = DefaultHasher::new();
1402 CString::new(&data[..data.len() - 1]).unwrap().hash(&mut s);
1403 let cstring_hash = s.finish();
1405 assert_eq!(cstr_hash, cstring_hash);
1409 fn from_bytes_with_nul() {
1410 let data = b"123\0";
1411 let cstr = CStr::from_bytes_with_nul(data);
1412 assert_eq!(cstr.map(CStr::to_bytes), Ok(&b"123"[..]));
1413 let cstr = CStr::from_bytes_with_nul(data);
1414 assert_eq!(cstr.map(CStr::to_bytes_with_nul), Ok(&b"123\0"[..]));
1417 let cstr = CStr::from_bytes_with_nul(data);
1418 let cstr_unchecked = CStr::from_bytes_with_nul_unchecked(data);
1419 assert_eq!(cstr, Ok(cstr_unchecked));
1424 fn from_bytes_with_nul_unterminated() {
1426 let cstr = CStr::from_bytes_with_nul(data);
1427 assert!(cstr.is_err());
1431 fn from_bytes_with_nul_interior() {
1432 let data = b"1\023\0";
1433 let cstr = CStr::from_bytes_with_nul(data);
1434 assert!(cstr.is_err());
1439 let orig: &[u8] = b"Hello, world!\0";
1440 let cstr = CStr::from_bytes_with_nul(orig).unwrap();
1441 let boxed: Box<CStr> = Box::from(cstr);
1442 let cstring = cstr.to_owned().into_boxed_c_str().into_c_string();
1443 assert_eq!(cstr, &*boxed);
1444 assert_eq!(&*boxed, &*cstring);
1445 assert_eq!(&*cstring, cstr);
1449 fn boxed_default() {
1450 let boxed = <Box<CStr>>::default();
1451 assert_eq!(boxed.to_bytes_with_nul(), &[0]);
1456 let orig: &[u8] = b"Hello, world!\0";
1457 let cstr = CStr::from_bytes_with_nul(orig).unwrap();
1458 let rc: Rc<CStr> = Rc::from(cstr);
1459 let arc: Arc<CStr> = Arc::from(cstr);
1461 assert_eq!(&*rc, cstr);
1462 assert_eq!(&*arc, cstr);
1464 let rc2: Rc<CStr> = Rc::from(cstr.to_owned());
1465 let arc2: Arc<CStr> = Arc::from(cstr.to_owned());
1467 assert_eq!(&*rc2, cstr);
1468 assert_eq!(&*arc2, cstr);
1472 fn cstr_const_constructor() {
1473 const CSTR: &CStr = unsafe {
1474 CStr::from_bytes_with_nul_unchecked(b"Hello, world!\0")
1477 assert_eq!(CSTR.to_str().unwrap(), "Hello, world!");