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 // `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.
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.
212 /// An error indicating that an interior nul byte was found.
214 /// While Rust strings may contain nul bytes in the middle, C strings
215 /// can't, as that byte would effectively truncate the string.
217 /// This error is created by the [`new`][`CString::new`] method on
218 /// [`CString`]. See its documentation for more.
220 /// [`CString`]: struct.CString.html
221 /// [`CString::new`]: struct.CString.html#method.new
226 /// use std::ffi::{CString, NulError};
228 /// let _: NulError = CString::new(b"f\0oo".to_vec()).unwrap_err();
230 #[derive(Clone, PartialEq, Eq, Debug)]
231 #[stable(feature = "rust1", since = "1.0.0")]
232 pub struct NulError(usize, Vec<u8>);
234 /// An error indicating that a nul byte was not in the expected position.
236 /// The slice used to create a [`CStr`] must have one and only one nul
237 /// byte at the end of the slice.
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.
243 /// [`CStr`]: struct.CStr.html
244 /// [`CStr::from_bytes_with_nul`]: struct.CStr.html#method.from_bytes_with_nul
249 /// use std::ffi::{CStr, FromBytesWithNulError};
251 /// let _: FromBytesWithNulError = CStr::from_bytes_with_nul(b"f\0oo").unwrap_err();
253 #[derive(Clone, PartialEq, Eq, Debug)]
254 #[stable(feature = "cstr_from_bytes", since = "1.10.0")]
255 pub struct FromBytesWithNulError {
256 kind: FromBytesWithNulErrorKind,
259 #[derive(Clone, PartialEq, Eq, Debug)]
260 enum FromBytesWithNulErrorKind {
265 impl FromBytesWithNulError {
266 fn interior_nul(pos: usize) -> FromBytesWithNulError {
267 FromBytesWithNulError {
268 kind: FromBytesWithNulErrorKind::InteriorNul(pos),
271 fn not_nul_terminated() -> FromBytesWithNulError {
272 FromBytesWithNulError {
273 kind: FromBytesWithNulErrorKind::NotNulTerminated,
278 /// An error indicating invalid UTF-8 when converting a [`CString`] into a [`String`].
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.
284 /// This `struct` is created by the
285 /// [`into_string`][`CString::into_string`] method on [`CString`]. See
286 /// its documentation for more.
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 {
299 /// Creates a new C-compatible string from a container of bytes.
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.
309 /// ```ignore (extern-declaration)
310 /// use std::ffi::CString;
311 /// use std::os::raw::c_char;
313 /// extern { fn puts(s: *const c_char); }
315 /// let to_print = CString::new("Hello!").expect("CString::new failed");
317 /// puts(to_print.as_ptr());
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.
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> {
333 fn _new(bytes: Vec<u8>) -> Result<CString, NulError> {
334 match memchr::memchr(0, &bytes) {
335 Some(i) => Err(NulError(i, bytes)),
336 None => Ok(unsafe { CString::from_vec_unchecked(bytes) }),
340 /// Creates a C-compatible string by consuming a byte vector,
341 /// without checking for interior 0 bytes.
343 /// This method is equivalent to [`new`] except that no runtime assertion
344 /// is made that `v` contains no 0 bytes, and it requires an actual
345 /// byte vector, not anything that can be converted to one with Into.
347 /// [`new`]: #method.new
352 /// use std::ffi::CString;
354 /// let raw = b"foo".to_vec();
356 /// let c_string = CString::from_vec_unchecked(raw);
359 #[stable(feature = "rust1", since = "1.0.0")]
360 pub unsafe fn from_vec_unchecked(mut v: Vec<u8>) -> CString {
363 CString { inner: v.into_boxed_slice() }
366 /// Retakes ownership of a `CString` that was transferred to C via [`into_raw`].
368 /// Additionally, the length of the string will be recalculated from the pointer.
372 /// This should only ever be called with a pointer that was earlier
373 /// obtained by calling [`into_raw`] on a `CString`. Other usage (e.g., trying to take
374 /// ownership of a string that was allocated by foreign code) is likely to lead
375 /// to undefined behavior or allocator corruption.
377 /// > **Note:** If you need to borrow a string that was allocated by
378 /// > foreign code, use [`CStr`]. If you need to take ownership of
379 /// > a string that was allocated by foreign code, you will need to
380 /// > make your own provisions for freeing it appropriately, likely
381 /// > with the foreign code's API to do that.
383 /// [`into_raw`]: #method.into_raw
384 /// [`CStr`]: struct.CStr.html
388 /// Creates a `CString`, pass ownership to an `extern` function (via raw pointer), then retake
389 /// ownership with `from_raw`:
391 /// ```ignore (extern-declaration)
392 /// use std::ffi::CString;
393 /// use std::os::raw::c_char;
396 /// fn some_extern_function(s: *mut c_char);
399 /// let c_string = CString::new("Hello!").expect("CString::new failed");
400 /// let raw = c_string.into_raw();
402 /// some_extern_function(raw);
403 /// let c_string = CString::from_raw(raw);
406 #[stable(feature = "cstr_memory", since = "1.4.0")]
407 pub unsafe fn from_raw(ptr: *mut c_char) -> CString {
408 let len = sys::strlen(ptr) + 1; // Including the NUL byte
409 let slice = slice::from_raw_parts_mut(ptr, len as usize);
410 CString { inner: Box::from_raw(slice as *mut [c_char] as *mut [u8]) }
413 /// Consumes the `CString` and transfers ownership of the string to a C caller.
415 /// The pointer which this function returns must be returned to Rust and reconstituted using
416 /// [`from_raw`] to be properly deallocated. Specifically, one
417 /// should *not* use the standard C `free()` function to deallocate
420 /// Failure to call [`from_raw`] will lead to a memory leak.
422 /// [`from_raw`]: #method.from_raw
427 /// use std::ffi::CString;
429 /// let c_string = CString::new("foo").expect("CString::new failed");
431 /// let ptr = c_string.into_raw();
434 /// assert_eq!(b'f', *ptr as u8);
435 /// assert_eq!(b'o', *ptr.offset(1) as u8);
436 /// assert_eq!(b'o', *ptr.offset(2) as u8);
437 /// assert_eq!(b'\0', *ptr.offset(3) as u8);
439 /// // retake pointer to free memory
440 /// let _ = CString::from_raw(ptr);
444 #[stable(feature = "cstr_memory", since = "1.4.0")]
445 pub fn into_raw(self) -> *mut c_char {
446 Box::into_raw(self.into_inner()) as *mut c_char
449 /// Converts the `CString` into a [`String`] if it contains valid UTF-8 data.
451 /// On failure, ownership of the original `CString` is returned.
453 /// [`String`]: ../string/struct.String.html
458 /// use std::ffi::CString;
460 /// let valid_utf8 = vec![b'f', b'o', b'o'];
461 /// let cstring = CString::new(valid_utf8).expect("CString::new failed");
462 /// assert_eq!(cstring.into_string().expect("into_string() call failed"), "foo");
464 /// let invalid_utf8 = vec![b'f', 0xff, b'o', b'o'];
465 /// let cstring = CString::new(invalid_utf8).expect("CString::new failed");
466 /// let err = cstring.into_string().err().expect("into_string().err() failed");
467 /// assert_eq!(err.utf8_error().valid_up_to(), 1);
470 #[stable(feature = "cstring_into", since = "1.7.0")]
471 pub fn into_string(self) -> Result<String, IntoStringError> {
472 String::from_utf8(self.into_bytes())
473 .map_err(|e| IntoStringError {
474 error: e.utf8_error(),
475 inner: unsafe { CString::from_vec_unchecked(e.into_bytes()) },
479 /// Consumes the `CString` and returns the underlying byte buffer.
481 /// The returned buffer does **not** contain the trailing nul
482 /// terminator, and it is guaranteed to not have any interior nul
488 /// use std::ffi::CString;
490 /// let c_string = CString::new("foo").expect("CString::new failed");
491 /// let bytes = c_string.into_bytes();
492 /// assert_eq!(bytes, vec![b'f', b'o', b'o']);
494 #[stable(feature = "cstring_into", since = "1.7.0")]
495 pub fn into_bytes(self) -> Vec<u8> {
496 let mut vec = self.into_inner().into_vec();
497 let _nul = vec.pop();
498 debug_assert_eq!(_nul, Some(0u8));
502 /// Equivalent to the [`into_bytes`] function except that the returned vector
503 /// includes the trailing nul terminator.
505 /// [`into_bytes`]: #method.into_bytes
510 /// use std::ffi::CString;
512 /// let c_string = CString::new("foo").expect("CString::new failed");
513 /// let bytes = c_string.into_bytes_with_nul();
514 /// assert_eq!(bytes, vec![b'f', b'o', b'o', b'\0']);
516 #[stable(feature = "cstring_into", since = "1.7.0")]
517 pub fn into_bytes_with_nul(self) -> Vec<u8> {
518 self.into_inner().into_vec()
521 /// Returns the contents of this `CString` as a slice of bytes.
523 /// The returned slice does **not** contain the trailing nul
524 /// terminator, and it is guaranteed to not have any interior nul
525 /// bytes. If you need the nul terminator, use
526 /// [`as_bytes_with_nul`] instead.
528 /// [`as_bytes_with_nul`]: #method.as_bytes_with_nul
533 /// use std::ffi::CString;
535 /// let c_string = CString::new("foo").expect("CString::new failed");
536 /// let bytes = c_string.as_bytes();
537 /// assert_eq!(bytes, &[b'f', b'o', b'o']);
540 #[stable(feature = "rust1", since = "1.0.0")]
541 pub fn as_bytes(&self) -> &[u8] {
542 &self.inner[..self.inner.len() - 1]
545 /// Equivalent to the [`as_bytes`] function except that the returned slice
546 /// includes the trailing nul terminator.
548 /// [`as_bytes`]: #method.as_bytes
553 /// use std::ffi::CString;
555 /// let c_string = CString::new("foo").expect("CString::new failed");
556 /// let bytes = c_string.as_bytes_with_nul();
557 /// assert_eq!(bytes, &[b'f', b'o', b'o', b'\0']);
560 #[stable(feature = "rust1", since = "1.0.0")]
561 pub fn as_bytes_with_nul(&self) -> &[u8] {
565 /// Extracts a [`CStr`] slice containing the entire string.
567 /// [`CStr`]: struct.CStr.html
572 /// use std::ffi::{CString, CStr};
574 /// let c_string = CString::new(b"foo".to_vec()).expect("CString::new failed");
575 /// let cstr = c_string.as_c_str();
577 /// CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed"));
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()).expect("CString::new failed");
595 /// let boxed = c_string.into_boxed_c_str();
596 /// assert_eq!(&*boxed,
597 /// CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed"));
599 #[stable(feature = "into_boxed_c_str", since = "1.20.0")]
600 pub fn into_boxed_c_str(self) -> Box<CStr> {
601 unsafe { Box::from_raw(Box::into_raw(self.into_inner()) as *mut CStr) }
604 /// Bypass "move out of struct which implements [`Drop`] trait" restriction.
606 /// [`Drop`]: ../ops/trait.Drop.html
607 fn into_inner(self) -> Box<[u8]> {
608 // Rationale: `mem::forget(self)` invalidates the previous call to `ptr::read(&self.inner)`
609 // so we use `ManuallyDrop` to ensure `self` is not dropped.
610 // Then we can return the box directly without invalidating it.
611 // See https://github.com/rust-lang/rust/issues/62553.
612 let this = mem::ManuallyDrop::new(self);
613 unsafe { ptr::read(&this.inner) }
617 // Turns this `CString` into an empty string to prevent
618 // memory-unsafe code from working by accident. Inline
619 // to prevent LLVM from optimizing it away in debug builds.
620 #[stable(feature = "cstring_drop", since = "1.13.0")]
621 impl Drop for CString {
624 unsafe { *self.inner.get_unchecked_mut(0) = 0; }
628 #[stable(feature = "rust1", since = "1.0.0")]
629 impl ops::Deref for CString {
633 fn deref(&self) -> &CStr {
634 unsafe { CStr::from_bytes_with_nul_unchecked(self.as_bytes_with_nul()) }
638 #[stable(feature = "rust1", since = "1.0.0")]
639 impl fmt::Debug for CString {
640 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
641 fmt::Debug::fmt(&**self, f)
645 #[stable(feature = "cstring_into", since = "1.7.0")]
646 impl From<CString> for Vec<u8> {
647 /// Converts a [`CString`] into a [`Vec`]`<u8>`.
649 /// The conversion consumes the [`CString`], and removes the terminating NUL byte.
651 /// [`Vec`]: ../vec/struct.Vec.html
652 /// [`CString`]: ../ffi/struct.CString.html
654 fn from(s: CString) -> Vec<u8> {
659 #[stable(feature = "cstr_debug", since = "1.3.0")]
660 impl fmt::Debug for CStr {
661 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
663 for byte in self.to_bytes().iter().flat_map(|&b| ascii::escape_default(b)) {
664 f.write_char(byte as char)?;
670 #[stable(feature = "cstr_default", since = "1.10.0")]
671 impl Default for &CStr {
672 fn default() -> Self {
673 const SLICE: &[c_char] = &[0];
674 unsafe { CStr::from_ptr(SLICE.as_ptr()) }
678 #[stable(feature = "cstr_default", since = "1.10.0")]
679 impl Default for CString {
680 /// Creates an empty `CString`.
681 fn default() -> CString {
682 let a: &CStr = Default::default();
687 #[stable(feature = "cstr_borrow", since = "1.3.0")]
688 impl Borrow<CStr> for CString {
690 fn borrow(&self) -> &CStr { self }
693 #[stable(feature = "cstring_from_cow_cstr", since = "1.28.0")]
694 impl<'a> From<Cow<'a, CStr>> for CString {
696 fn from(s: Cow<'a, CStr>) -> Self {
701 #[stable(feature = "box_from_c_str", since = "1.17.0")]
702 impl From<&CStr> for Box<CStr> {
703 fn from(s: &CStr) -> Box<CStr> {
704 let boxed: Box<[u8]> = Box::from(s.to_bytes_with_nul());
705 unsafe { Box::from_raw(Box::into_raw(boxed) as *mut CStr) }
709 #[stable(feature = "c_string_from_box", since = "1.18.0")]
710 impl From<Box<CStr>> for CString {
711 /// Converts a [`Box`]`<CStr>` into a [`CString`] without copying or allocating.
713 /// [`Box`]: ../boxed/struct.Box.html
714 /// [`CString`]: ../ffi/struct.CString.html
716 fn from(s: Box<CStr>) -> CString {
721 #[stable(feature = "more_box_slice_clone", since = "1.29.0")]
722 impl Clone for Box<CStr> {
724 fn clone(&self) -> Self {
729 #[stable(feature = "box_from_c_string", since = "1.20.0")]
730 impl From<CString> for Box<CStr> {
731 /// Converts a [`CString`] into a [`Box`]`<CStr>` without copying or allocating.
733 /// [`CString`]: ../ffi/struct.CString.html
734 /// [`Box`]: ../boxed/struct.Box.html
736 fn from(s: CString) -> Box<CStr> {
741 #[stable(feature = "cow_from_cstr", since = "1.28.0")]
742 impl<'a> From<CString> for Cow<'a, CStr> {
744 fn from(s: CString) -> Cow<'a, CStr> {
749 #[stable(feature = "cow_from_cstr", since = "1.28.0")]
750 impl<'a> From<&'a CStr> for Cow<'a, CStr> {
752 fn from(s: &'a CStr) -> Cow<'a, CStr> {
757 #[stable(feature = "cow_from_cstr", since = "1.28.0")]
758 impl<'a> From<&'a CString> for Cow<'a, CStr> {
760 fn from(s: &'a CString) -> Cow<'a, CStr> {
761 Cow::Borrowed(s.as_c_str())
765 #[stable(feature = "shared_from_slice2", since = "1.24.0")]
766 impl From<CString> for Arc<CStr> {
767 /// Converts a [`CString`] into a [`Arc`]`<CStr>` without copying or allocating.
769 /// [`CString`]: ../ffi/struct.CString.html
770 /// [`Arc`]: ../sync/struct.Arc.html
772 fn from(s: CString) -> Arc<CStr> {
773 let arc: Arc<[u8]> = Arc::from(s.into_inner());
774 unsafe { Arc::from_raw(Arc::into_raw(arc) as *const CStr) }
778 #[stable(feature = "shared_from_slice2", since = "1.24.0")]
779 impl From<&CStr> for Arc<CStr> {
781 fn from(s: &CStr) -> Arc<CStr> {
782 let arc: Arc<[u8]> = Arc::from(s.to_bytes_with_nul());
783 unsafe { Arc::from_raw(Arc::into_raw(arc) as *const CStr) }
787 #[stable(feature = "shared_from_slice2", since = "1.24.0")]
788 impl From<CString> for Rc<CStr> {
789 /// Converts a [`CString`] into a [`Rc`]`<CStr>` without copying or allocating.
791 /// [`CString`]: ../ffi/struct.CString.html
792 /// [`Rc`]: ../rc/struct.Rc.html
794 fn from(s: CString) -> Rc<CStr> {
795 let rc: Rc<[u8]> = Rc::from(s.into_inner());
796 unsafe { Rc::from_raw(Rc::into_raw(rc) as *const CStr) }
800 #[stable(feature = "shared_from_slice2", since = "1.24.0")]
801 impl From<&CStr> for Rc<CStr> {
803 fn from(s: &CStr) -> Rc<CStr> {
804 let rc: Rc<[u8]> = Rc::from(s.to_bytes_with_nul());
805 unsafe { Rc::from_raw(Rc::into_raw(rc) as *const CStr) }
809 #[stable(feature = "default_box_extra", since = "1.17.0")]
810 impl Default for Box<CStr> {
811 fn default() -> Box<CStr> {
812 let boxed: Box<[u8]> = Box::from([0]);
813 unsafe { Box::from_raw(Box::into_raw(boxed) as *mut CStr) }
818 /// Returns the position of the nul byte in the slice that caused
819 /// [`CString::new`] to fail.
821 /// [`CString::new`]: struct.CString.html#method.new
826 /// use std::ffi::CString;
828 /// let nul_error = CString::new("foo\0bar").unwrap_err();
829 /// assert_eq!(nul_error.nul_position(), 3);
831 /// let nul_error = CString::new("foo bar\0").unwrap_err();
832 /// assert_eq!(nul_error.nul_position(), 7);
834 #[stable(feature = "rust1", since = "1.0.0")]
835 pub fn nul_position(&self) -> usize { self.0 }
837 /// Consumes this error, returning the underlying vector of bytes which
838 /// generated the error in the first place.
843 /// use std::ffi::CString;
845 /// let nul_error = CString::new("foo\0bar").unwrap_err();
846 /// assert_eq!(nul_error.into_vec(), b"foo\0bar");
848 #[stable(feature = "rust1", since = "1.0.0")]
849 pub fn into_vec(self) -> Vec<u8> { self.1 }
852 #[stable(feature = "rust1", since = "1.0.0")]
853 impl Error for NulError {
854 fn description(&self) -> &str { "nul byte found in data" }
857 #[stable(feature = "rust1", since = "1.0.0")]
858 impl fmt::Display for NulError {
859 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
860 write!(f, "nul byte found in provided data at position: {}", self.0)
864 #[stable(feature = "rust1", since = "1.0.0")]
865 impl From<NulError> for io::Error {
866 /// Converts a [`NulError`] into a [`io::Error`].
868 /// [`NulError`]: ../ffi/struct.NulError.html
869 /// [`io::Error`]: ../io/struct.Error.html
870 fn from(_: NulError) -> io::Error {
871 io::Error::new(io::ErrorKind::InvalidInput,
872 "data provided contains a nul byte")
876 #[stable(feature = "frombyteswithnulerror_impls", since = "1.17.0")]
877 impl Error for FromBytesWithNulError {
878 fn description(&self) -> &str {
880 FromBytesWithNulErrorKind::InteriorNul(..) =>
881 "data provided contains an interior nul byte",
882 FromBytesWithNulErrorKind::NotNulTerminated =>
883 "data provided is not nul terminated",
888 #[stable(feature = "frombyteswithnulerror_impls", since = "1.17.0")]
889 impl fmt::Display for FromBytesWithNulError {
890 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
891 f.write_str(self.description())?;
892 if let FromBytesWithNulErrorKind::InteriorNul(pos) = self.kind {
893 write!(f, " at byte pos {}", pos)?;
899 impl IntoStringError {
900 /// Consumes this error, returning original [`CString`] which generated the
903 /// [`CString`]: struct.CString.html
904 #[stable(feature = "cstring_into", since = "1.7.0")]
905 pub fn into_cstring(self) -> CString {
909 /// Access the underlying UTF-8 error that was the cause of this error.
910 #[stable(feature = "cstring_into", since = "1.7.0")]
911 pub fn utf8_error(&self) -> Utf8Error {
916 #[stable(feature = "cstring_into", since = "1.7.0")]
917 impl Error for IntoStringError {
918 fn description(&self) -> &str {
919 "C string contained non-utf8 bytes"
922 fn cause(&self) -> Option<&dyn Error> {
927 #[stable(feature = "cstring_into", since = "1.7.0")]
928 impl fmt::Display for IntoStringError {
929 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
930 self.description().fmt(f)
935 /// Wraps a raw C string with a safe C string wrapper.
937 /// This function will wrap the provided `ptr` with a `CStr` wrapper, which
938 /// allows inspection and interoperation of non-owned C strings. The total
939 /// size of the raw C string must be smaller than `isize::MAX` **bytes**
940 /// in memory due to calling the `slice::from_raw_parts` function.
941 /// This method is unsafe for a number of reasons:
943 /// * There is no guarantee to the validity of `ptr`.
944 /// * The returned lifetime is not guaranteed to be the actual lifetime of
946 /// * There is no guarantee that the memory pointed to by `ptr` contains a
947 /// valid nul terminator byte at the end of the string.
948 /// * It is not guaranteed that the memory pointed by `ptr` won't change
949 /// before the `CStr` has been destroyed.
951 /// > **Note**: This operation is intended to be a 0-cost cast but it is
952 /// > currently implemented with an up-front calculation of the length of
953 /// > the string. This is not guaranteed to always be the case.
957 /// ```ignore (extern-declaration)
959 /// use std::ffi::CStr;
960 /// use std::os::raw::c_char;
963 /// fn my_string() -> *const c_char;
967 /// let slice = CStr::from_ptr(my_string());
968 /// println!("string returned: {}", slice.to_str().unwrap());
972 #[stable(feature = "rust1", since = "1.0.0")]
973 pub unsafe fn from_ptr<'a>(ptr: *const c_char) -> &'a CStr {
974 let len = sys::strlen(ptr);
975 let ptr = ptr as *const u8;
976 CStr::from_bytes_with_nul_unchecked(slice::from_raw_parts(ptr, len as usize + 1))
979 /// Creates a C string wrapper from a byte slice.
981 /// This function will cast the provided `bytes` to a `CStr`
982 /// wrapper after ensuring that the byte slice is nul-terminated
983 /// and does not contain any interior nul bytes.
988 /// use std::ffi::CStr;
990 /// let cstr = CStr::from_bytes_with_nul(b"hello\0");
991 /// assert!(cstr.is_ok());
994 /// Creating a `CStr` without a trailing nul terminator is an error:
997 /// use std::ffi::CStr;
999 /// let cstr = CStr::from_bytes_with_nul(b"hello");
1000 /// assert!(cstr.is_err());
1003 /// Creating a `CStr` with an interior nul byte is an error:
1006 /// use std::ffi::CStr;
1008 /// let cstr = CStr::from_bytes_with_nul(b"he\0llo\0");
1009 /// assert!(cstr.is_err());
1011 #[stable(feature = "cstr_from_bytes", since = "1.10.0")]
1012 pub fn from_bytes_with_nul(bytes: &[u8])
1013 -> Result<&CStr, FromBytesWithNulError> {
1014 let nul_pos = memchr::memchr(0, bytes);
1015 if let Some(nul_pos) = nul_pos {
1016 if nul_pos + 1 != bytes.len() {
1017 return Err(FromBytesWithNulError::interior_nul(nul_pos));
1019 Ok(unsafe { CStr::from_bytes_with_nul_unchecked(bytes) })
1021 Err(FromBytesWithNulError::not_nul_terminated())
1025 /// Unsafely creates a C string wrapper from a byte slice.
1027 /// This function will cast the provided `bytes` to a `CStr` wrapper without
1028 /// performing any sanity checks. The provided slice **must** be nul-terminated
1029 /// and not contain any interior nul bytes.
1034 /// use std::ffi::{CStr, CString};
1037 /// let cstring = CString::new("hello").expect("CString::new failed");
1038 /// let cstr = CStr::from_bytes_with_nul_unchecked(cstring.to_bytes_with_nul());
1039 /// assert_eq!(cstr, &*cstring);
1043 #[stable(feature = "cstr_from_bytes", since = "1.10.0")]
1044 #[rustc_const_unstable(feature = "const_cstr_unchecked")]
1045 pub const unsafe fn from_bytes_with_nul_unchecked(bytes: &[u8]) -> &CStr {
1046 &*(bytes as *const [u8] as *const CStr)
1049 /// Returns the inner pointer to this C string.
1051 /// The returned pointer will be valid for as long as `self` is, and points
1052 /// to a contiguous region of memory terminated with a 0 byte to represent
1053 /// the end of the string.
1057 /// The returned pointer is read-only; writing to it (including passing it
1058 /// to C code that writes to it) causes undefined behavior.
1060 /// It is your responsibility to make sure that the underlying memory is not
1061 /// freed too early. For example, the following code will cause undefined
1062 /// behavior when `ptr` is used inside the `unsafe` block:
1065 /// # #![allow(unused_must_use)]
1066 /// use std::ffi::CString;
1068 /// let ptr = CString::new("Hello").expect("CString::new failed").as_ptr();
1070 /// // `ptr` is dangling
1075 /// This happens because the pointer returned by `as_ptr` does not carry any
1076 /// lifetime information and the [`CString`] is deallocated immediately after
1077 /// the `CString::new("Hello").expect("CString::new failed").as_ptr()` expression is evaluated.
1078 /// To fix the problem, bind the `CString` to a local variable:
1081 /// # #![allow(unused_must_use)]
1082 /// use std::ffi::CString;
1084 /// let hello = CString::new("Hello").expect("CString::new failed");
1085 /// let ptr = hello.as_ptr();
1087 /// // `ptr` is valid because `hello` is in scope
1092 /// This way, the lifetime of the `CString` in `hello` encompasses
1093 /// the lifetime of `ptr` and the `unsafe` block.
1095 /// [`CString`]: struct.CString.html
1097 #[stable(feature = "rust1", since = "1.0.0")]
1098 pub const fn as_ptr(&self) -> *const c_char {
1102 /// Converts this C string to a byte slice.
1104 /// The returned slice will **not** contain the trailing nul terminator that this C
1107 /// > **Note**: This method is currently implemented as a constant-time
1108 /// > cast, but it is planned to alter its definition in the future to
1109 /// > perform the length calculation whenever this method is called.
1114 /// use std::ffi::CStr;
1116 /// let cstr = CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed");
1117 /// assert_eq!(cstr.to_bytes(), b"foo");
1120 #[stable(feature = "rust1", since = "1.0.0")]
1121 pub fn to_bytes(&self) -> &[u8] {
1122 let bytes = self.to_bytes_with_nul();
1123 &bytes[..bytes.len() - 1]
1126 /// Converts this C string to a byte slice containing the trailing 0 byte.
1128 /// This function is the equivalent of [`to_bytes`] except that it will retain
1129 /// the trailing nul terminator instead of chopping it off.
1131 /// > **Note**: This method is currently implemented as a 0-cost cast, but
1132 /// > it is planned to alter its definition in the future to perform the
1133 /// > length calculation whenever this method is called.
1135 /// [`to_bytes`]: #method.to_bytes
1140 /// use std::ffi::CStr;
1142 /// let cstr = CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed");
1143 /// assert_eq!(cstr.to_bytes_with_nul(), b"foo\0");
1146 #[stable(feature = "rust1", since = "1.0.0")]
1147 pub fn to_bytes_with_nul(&self) -> &[u8] {
1148 unsafe { &*(&self.inner as *const [c_char] as *const [u8]) }
1151 /// Yields a [`&str`] slice if the `CStr` contains valid UTF-8.
1153 /// If the contents of the `CStr` are valid UTF-8 data, this
1154 /// function will return the corresponding [`&str`] slice. Otherwise,
1155 /// it will return an error with details of where UTF-8 validation failed.
1157 /// > **Note**: This method is currently implemented to check for validity
1158 /// > after a constant-time cast, but it is planned to alter its definition
1159 /// > in the future to perform the length calculation in addition to the
1160 /// > UTF-8 check whenever this method is called.
1162 /// [`&str`]: ../primitive.str.html
1167 /// use std::ffi::CStr;
1169 /// let cstr = CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed");
1170 /// assert_eq!(cstr.to_str(), Ok("foo"));
1172 #[stable(feature = "cstr_to_str", since = "1.4.0")]
1173 pub fn to_str(&self) -> Result<&str, str::Utf8Error> {
1174 // N.B., when `CStr` is changed to perform the length check in `.to_bytes()`
1175 // instead of in `from_ptr()`, it may be worth considering if this should
1176 // be rewritten to do the UTF-8 check inline with the length calculation
1177 // instead of doing it afterwards.
1178 str::from_utf8(self.to_bytes())
1181 /// Converts a `CStr` into a [`Cow`]`<`[`str`]`>`.
1183 /// If the contents of the `CStr` are valid UTF-8 data, this
1184 /// function will return a [`Cow`]`::`[`Borrowed`]`(`[`&str`]`)`
1185 /// with the corresponding [`&str`] slice. Otherwise, it will
1186 /// replace any invalid UTF-8 sequences with
1187 /// [`U+FFFD REPLACEMENT CHARACTER`][U+FFFD] and return a
1188 /// [`Cow`]`::`[`Owned`]`(`[`String`]`)` with the result.
1190 /// > **Note**: This method is currently implemented to check for validity
1191 /// > after a constant-time cast, but it is planned to alter its definition
1192 /// > in the future to perform the length calculation in addition to the
1193 /// > UTF-8 check whenever this method is called.
1195 /// [`Cow`]: ../borrow/enum.Cow.html
1196 /// [`Borrowed`]: ../borrow/enum.Cow.html#variant.Borrowed
1197 /// [`Owned`]: ../borrow/enum.Cow.html#variant.Owned
1198 /// [`str`]: ../primitive.str.html
1199 /// [`String`]: ../string/struct.String.html
1200 /// [U+FFFD]: ../char/constant.REPLACEMENT_CHARACTER.html
1204 /// Calling `to_string_lossy` on a `CStr` containing valid UTF-8:
1207 /// use std::borrow::Cow;
1208 /// use std::ffi::CStr;
1210 /// let cstr = CStr::from_bytes_with_nul(b"Hello World\0")
1211 /// .expect("CStr::from_bytes_with_nul failed");
1212 /// assert_eq!(cstr.to_string_lossy(), Cow::Borrowed("Hello World"));
1215 /// Calling `to_string_lossy` on a `CStr` containing invalid UTF-8:
1218 /// use std::borrow::Cow;
1219 /// use std::ffi::CStr;
1221 /// let cstr = CStr::from_bytes_with_nul(b"Hello \xF0\x90\x80World\0")
1222 /// .expect("CStr::from_bytes_with_nul failed");
1224 /// cstr.to_string_lossy(),
1225 /// Cow::Owned(String::from("Hello �World")) as Cow<'_, str>
1228 #[stable(feature = "cstr_to_str", since = "1.4.0")]
1229 pub fn to_string_lossy(&self) -> Cow<'_, str> {
1230 String::from_utf8_lossy(self.to_bytes())
1233 /// Converts a [`Box`]`<CStr>` into a [`CString`] without copying or allocating.
1235 /// [`Box`]: ../boxed/struct.Box.html
1236 /// [`CString`]: struct.CString.html
1241 /// use std::ffi::CString;
1243 /// let c_string = CString::new(b"foo".to_vec()).expect("CString::new failed");
1244 /// let boxed = c_string.into_boxed_c_str();
1245 /// assert_eq!(boxed.into_c_string(), CString::new("foo").expect("CString::new failed"));
1247 #[stable(feature = "into_boxed_c_str", since = "1.20.0")]
1248 pub fn into_c_string(self: Box<CStr>) -> CString {
1249 let raw = Box::into_raw(self) as *mut [u8];
1250 CString { inner: unsafe { Box::from_raw(raw) } }
1254 #[stable(feature = "rust1", since = "1.0.0")]
1255 impl PartialEq for CStr {
1256 fn eq(&self, other: &CStr) -> bool {
1257 self.to_bytes().eq(other.to_bytes())
1260 #[stable(feature = "rust1", since = "1.0.0")]
1262 #[stable(feature = "rust1", since = "1.0.0")]
1263 impl PartialOrd for CStr {
1264 fn partial_cmp(&self, other: &CStr) -> Option<Ordering> {
1265 self.to_bytes().partial_cmp(&other.to_bytes())
1268 #[stable(feature = "rust1", since = "1.0.0")]
1270 fn cmp(&self, other: &CStr) -> Ordering {
1271 self.to_bytes().cmp(&other.to_bytes())
1275 #[stable(feature = "cstr_borrow", since = "1.3.0")]
1276 impl ToOwned for CStr {
1277 type Owned = CString;
1279 fn to_owned(&self) -> CString {
1280 CString { inner: self.to_bytes_with_nul().into() }
1284 #[stable(feature = "cstring_asref", since = "1.7.0")]
1285 impl From<&CStr> for CString {
1286 fn from(s: &CStr) -> CString {
1291 #[stable(feature = "cstring_asref", since = "1.7.0")]
1292 impl ops::Index<ops::RangeFull> for CString {
1296 fn index(&self, _index: ops::RangeFull) -> &CStr {
1301 #[stable(feature = "cstring_asref", since = "1.7.0")]
1302 impl AsRef<CStr> for CStr {
1304 fn as_ref(&self) -> &CStr {
1309 #[stable(feature = "cstring_asref", since = "1.7.0")]
1310 impl AsRef<CStr> for CString {
1312 fn as_ref(&self) -> &CStr {
1320 use crate::os::raw::c_char;
1321 use crate::borrow::Cow::{Borrowed, Owned};
1322 use crate::hash::{Hash, Hasher};
1323 use crate::collections::hash_map::DefaultHasher;
1325 use crate::sync::Arc;
1329 let data = b"123\0";
1330 let ptr = data.as_ptr() as *const c_char;
1332 assert_eq!(CStr::from_ptr(ptr).to_bytes(), b"123");
1333 assert_eq!(CStr::from_ptr(ptr).to_bytes_with_nul(), b"123\0");
1339 let s = CString::new("1234").unwrap();
1340 assert_eq!(s.as_bytes(), b"1234");
1341 assert_eq!(s.as_bytes_with_nul(), b"1234\0");
1345 fn build_with_zero1() {
1346 assert!(CString::new(&b"\0"[..]).is_err());
1349 fn build_with_zero2() {
1350 assert!(CString::new(vec![0]).is_err());
1354 fn build_with_zero3() {
1356 let s = CString::from_vec_unchecked(vec![0]);
1357 assert_eq!(s.as_bytes(), b"\0");
1363 let s = CString::new(&b"abc\x01\x02\n\xE2\x80\xA6\xFF"[..]).unwrap();
1364 assert_eq!(format!("{:?}", s), r#""abc\x01\x02\n\xe2\x80\xa6\xff""#);
1370 let s = CStr::from_ptr(b"12\0".as_ptr() as *const _);
1371 assert_eq!(s.to_bytes(), b"12");
1372 assert_eq!(s.to_bytes_with_nul(), b"12\0");
1378 let data = b"123\xE2\x80\xA6\0";
1379 let ptr = data.as_ptr() as *const c_char;
1381 assert_eq!(CStr::from_ptr(ptr).to_str(), Ok("123…"));
1382 assert_eq!(CStr::from_ptr(ptr).to_string_lossy(), Borrowed("123…"));
1384 let data = b"123\xE2\0";
1385 let ptr = data.as_ptr() as *const c_char;
1387 assert!(CStr::from_ptr(ptr).to_str().is_err());
1388 assert_eq!(CStr::from_ptr(ptr).to_string_lossy(), Owned::<str>(format!("123\u{FFFD}")));
1394 let data = b"123\0";
1395 let ptr = data.as_ptr() as *const c_char;
1397 let owned = unsafe { CStr::from_ptr(ptr).to_owned() };
1398 assert_eq!(owned.as_bytes_with_nul(), data);
1403 let data = b"123\xE2\xFA\xA6\0";
1404 let ptr = data.as_ptr() as *const c_char;
1405 let cstr: &'static CStr = unsafe { CStr::from_ptr(ptr) };
1407 let mut s = DefaultHasher::new();
1409 let cstr_hash = s.finish();
1410 let mut s = DefaultHasher::new();
1411 CString::new(&data[..data.len() - 1]).unwrap().hash(&mut s);
1412 let cstring_hash = s.finish();
1414 assert_eq!(cstr_hash, cstring_hash);
1418 fn from_bytes_with_nul() {
1419 let data = b"123\0";
1420 let cstr = CStr::from_bytes_with_nul(data);
1421 assert_eq!(cstr.map(CStr::to_bytes), Ok(&b"123"[..]));
1422 let cstr = CStr::from_bytes_with_nul(data);
1423 assert_eq!(cstr.map(CStr::to_bytes_with_nul), Ok(&b"123\0"[..]));
1426 let cstr = CStr::from_bytes_with_nul(data);
1427 let cstr_unchecked = CStr::from_bytes_with_nul_unchecked(data);
1428 assert_eq!(cstr, Ok(cstr_unchecked));
1433 fn from_bytes_with_nul_unterminated() {
1435 let cstr = CStr::from_bytes_with_nul(data);
1436 assert!(cstr.is_err());
1440 fn from_bytes_with_nul_interior() {
1441 let data = b"1\023\0";
1442 let cstr = CStr::from_bytes_with_nul(data);
1443 assert!(cstr.is_err());
1448 let orig: &[u8] = b"Hello, world!\0";
1449 let cstr = CStr::from_bytes_with_nul(orig).unwrap();
1450 let boxed: Box<CStr> = Box::from(cstr);
1451 let cstring = cstr.to_owned().into_boxed_c_str().into_c_string();
1452 assert_eq!(cstr, &*boxed);
1453 assert_eq!(&*boxed, &*cstring);
1454 assert_eq!(&*cstring, cstr);
1458 fn boxed_default() {
1459 let boxed = <Box<CStr>>::default();
1460 assert_eq!(boxed.to_bytes_with_nul(), &[0]);
1465 let orig: &[u8] = b"Hello, world!\0";
1466 let cstr = CStr::from_bytes_with_nul(orig).unwrap();
1467 let rc: Rc<CStr> = Rc::from(cstr);
1468 let arc: Arc<CStr> = Arc::from(cstr);
1470 assert_eq!(&*rc, cstr);
1471 assert_eq!(&*arc, cstr);
1473 let rc2: Rc<CStr> = Rc::from(cstr.to_owned());
1474 let arc2: Arc<CStr> = Arc::from(cstr.to_owned());
1476 assert_eq!(&*rc2, cstr);
1477 assert_eq!(&*arc2, cstr);
1481 fn cstr_const_constructor() {
1482 const CSTR: &CStr = unsafe {
1483 CStr::from_bytes_with_nul_unchecked(b"Hello, world!\0")
1486 assert_eq!(CSTR.to_str().unwrap(), "Hello, world!");