1//! [`CStr`] and its related types.
2
3use crate::cmp::Ordering;
4use crate::error::Error;
5use crate::ffi::c_char;
6use crate::intrinsics::const_eval_select;
7use crate::iter::FusedIterator;
8use crate::marker::PhantomData;
9use crate::ptr::NonNull;
10use crate::slice::memchr;
11use crate::{fmt, ops, slice, str};
12
13// FIXME: because this is doc(inline)d, we *have* to use intra-doc links because the actual link
14// depends on where the item is being documented. however, since this is libcore, we can't
15// actually reference libstd or liballoc in intra-doc links. so, the best we can do is remove the
16// links to `CString` and `String` for now until a solution is developed
17
18/// Representation of a borrowed C string.
19///
20/// This type represents a borrowed reference to a nul-terminated
21/// array of bytes. It can be constructed safely from a <code>&[[u8]]</code>
22/// slice, or unsafely from a raw `*const c_char`. It can be expressed as a
23/// literal in the form `c"Hello world"`.
24///
25/// The `CStr` can then be converted to a Rust <code>&[str]</code> by performing
26/// UTF-8 validation, or into an owned `CString`.
27///
28/// `&CStr` is to `CString` as <code>&[str]</code> is to `String`: the former
29/// in each pair are borrowed references; the latter are owned
30/// strings.
31///
32/// Note that this structure does **not** have a guaranteed layout (the `repr(transparent)`
33/// notwithstanding) and should not be placed in the signatures of FFI functions.
34/// Instead, safe wrappers of FFI functions may leverage [`CStr::as_ptr`] and the unsafe
35/// [`CStr::from_ptr`] constructor to provide a safe interface to other consumers.
36///
37/// # Examples
38///
39/// Inspecting a foreign C string:
40///
41/// ```
42/// use std::ffi::CStr;
43/// use std::os::raw::c_char;
44///
45/// # /* Extern functions are awkward in doc comments - fake it instead
46/// extern "C" { fn my_string() -> *const c_char; }
47/// # */ unsafe extern "C" fn my_string() -> *const c_char { c"hello".as_ptr() }
48///
49/// unsafe {
50/// let slice = CStr::from_ptr(my_string());
51/// println!("string buffer size without nul terminator: {}", slice.to_bytes().len());
52/// }
53/// ```
54///
55/// Passing a Rust-originating C string:
56///
57/// ```
58/// use std::ffi::CStr;
59/// use std::os::raw::c_char;
60///
61/// fn work(data: &CStr) {
62/// unsafe extern "C" fn work_with(s: *const c_char) {}
63/// unsafe { work_with(data.as_ptr()) }
64/// }
65///
66/// let s = c"Hello world!";
67/// work(&s);
68/// ```
69///
70/// Converting a foreign C string into a Rust `String`:
71///
72/// ```
73/// use std::ffi::CStr;
74/// use std::os::raw::c_char;
75///
76/// # /* Extern functions are awkward in doc comments - fake it instead
77/// extern "C" { fn my_string() -> *const c_char; }
78/// # */ unsafe extern "C" fn my_string() -> *const c_char { c"hello".as_ptr() }
79///
80/// fn my_string_safe() -> String {
81/// let cstr = unsafe { CStr::from_ptr(my_string()) };
82/// // Get a copy-on-write Cow<'_, str>, then extract the
83/// // allocated String (or allocate a fresh one if needed).
84/// cstr.to_string_lossy().into_owned()
85/// }
86///
87/// println!("string: {}", my_string_safe());
88/// ```
89///
90/// [str]: prim@str "str"
91#[derive(PartialEq, Eq, Hash)]
92#[stable(feature = "core_c_str", since = "1.64.0")]
93#[rustc_diagnostic_item = "cstr_type"]
94#[rustc_has_incoherent_inherent_impls]
95#[lang = "CStr"]
96// `fn from` in `impl From<&CStr> for Box<CStr>` current implementation relies
97// on `CStr` being layout-compatible with `[u8]`.
98// However, `CStr` layout is considered an implementation detail and must not be relied upon. We
99// want `repr(transparent)` but we don't want it to show up in rustdoc, so we hide it under
100// `cfg(doc)`. This is an ad-hoc implementation of attribute privacy.
101#[repr(transparent)]
102pub struct CStr {
103 // FIXME: this should not be represented with a DST slice but rather with
104 // just a raw `c_char` along with some form of marker to make
105 // this an unsized type. Essentially `sizeof(&CStr)` should be the
106 // same as `sizeof(&c_char)` but `CStr` should be an unsized type.
107 inner: [c_char],
108}
109
110/// An error indicating that a nul byte was not in the expected position.
111///
112/// The slice used to create a [`CStr`] must have one and only one nul byte,
113/// positioned at the end.
114///
115/// This error is created by the [`CStr::from_bytes_with_nul`] method.
116/// See its documentation for more.
117///
118/// # Examples
119///
120/// ```
121/// use std::ffi::{CStr, FromBytesWithNulError};
122///
123/// let _: FromBytesWithNulError = CStr::from_bytes_with_nul(b"f\0oo").unwrap_err();
124/// ```
125#[derive(Clone, Copy, PartialEq, Eq, Debug)]
126#[stable(feature = "core_c_str", since = "1.64.0")]
127pub enum FromBytesWithNulError {
128 /// Data provided contains an interior nul byte at byte `position`.
129 InteriorNul {
130 /// The position of the interior nul byte.
131 position: usize,
132 },
133 /// Data provided is not nul terminated.
134 NotNulTerminated,
135}
136
137#[stable(feature = "frombyteswithnulerror_impls", since = "1.17.0")]
138impl Error for FromBytesWithNulError {
139 #[allow(deprecated)]
140 fn description(&self) -> &str {
141 match self {
142 Self::InteriorNul { .. } => "data provided contains an interior nul byte",
143 Self::NotNulTerminated => "data provided is not nul terminated",
144 }
145 }
146}
147
148/// An error indicating that no nul byte was present.
149///
150/// A slice used to create a [`CStr`] must contain a nul byte somewhere
151/// within the slice.
152///
153/// This error is created by the [`CStr::from_bytes_until_nul`] method.
154#[derive(Clone, PartialEq, Eq, Debug)]
155#[stable(feature = "cstr_from_bytes_until_nul", since = "1.69.0")]
156pub struct FromBytesUntilNulError(());
157
158#[stable(feature = "cstr_from_bytes_until_nul", since = "1.69.0")]
159impl fmt::Display for FromBytesUntilNulError {
160 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
161 write!(f, "data provided does not contain a nul")
162 }
163}
164
165#[stable(feature = "cstr_debug", since = "1.3.0")]
166impl fmt::Debug for CStr {
167 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
168 write!(f, "\"{}\"", self.to_bytes().escape_ascii())
169 }
170}
171
172#[stable(feature = "cstr_default", since = "1.10.0")]
173impl Default for &CStr {
174 #[inline]
175 fn default() -> Self {
176 const SLICE: &[c_char] = &[0];
177 // SAFETY: `SLICE` is indeed pointing to a valid nul-terminated string.
178 unsafe { CStr::from_ptr(SLICE.as_ptr()) }
179 }
180}
181
182#[stable(feature = "frombyteswithnulerror_impls", since = "1.17.0")]
183impl fmt::Display for FromBytesWithNulError {
184 #[allow(deprecated, deprecated_in_future)]
185 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
186 f.write_str(self.description())?;
187 if let Self::InteriorNul { position: &usize } = self {
188 write!(f, " at byte pos {position}")?;
189 }
190 Ok(())
191 }
192}
193
194impl CStr {
195 /// Wraps a raw C string with a safe C string wrapper.
196 ///
197 /// This function will wrap the provided `ptr` with a `CStr` wrapper, which
198 /// allows inspection and interoperation of non-owned C strings. The total
199 /// size of the terminated buffer must be smaller than [`isize::MAX`] **bytes**
200 /// in memory (a restriction from [`slice::from_raw_parts`]).
201 ///
202 /// # Safety
203 ///
204 /// * The memory pointed to by `ptr` must contain a valid nul terminator at the
205 /// end of the string.
206 ///
207 /// * `ptr` must be [valid] for reads of bytes up to and including the nul terminator.
208 /// This means in particular:
209 ///
210 /// * The entire memory range of this `CStr` must be contained within a single allocation!
211 /// * `ptr` must be non-null even for a zero-length cstr.
212 ///
213 /// * The memory referenced by the returned `CStr` must not be mutated for
214 /// the duration of lifetime `'a`.
215 ///
216 /// * The nul terminator must be within `isize::MAX` from `ptr`
217 ///
218 /// > **Note**: This operation is intended to be a 0-cost cast but it is
219 /// > currently implemented with an up-front calculation of the length of
220 /// > the string. This is not guaranteed to always be the case.
221 ///
222 /// # Caveat
223 ///
224 /// The lifetime for the returned slice is inferred from its usage. To prevent accidental misuse,
225 /// it's suggested to tie the lifetime to whichever source lifetime is safe in the context,
226 /// such as by providing a helper function taking the lifetime of a host value for the slice,
227 /// or by explicit annotation.
228 ///
229 /// # Examples
230 ///
231 /// ```
232 /// use std::ffi::{c_char, CStr};
233 ///
234 /// fn my_string() -> *const c_char {
235 /// c"hello".as_ptr()
236 /// }
237 ///
238 /// unsafe {
239 /// let slice = CStr::from_ptr(my_string());
240 /// assert_eq!(slice.to_str().unwrap(), "hello");
241 /// }
242 /// ```
243 ///
244 /// ```
245 /// use std::ffi::{c_char, CStr};
246 ///
247 /// const HELLO_PTR: *const c_char = {
248 /// const BYTES: &[u8] = b"Hello, world!\0";
249 /// BYTES.as_ptr().cast()
250 /// };
251 /// const HELLO: &CStr = unsafe { CStr::from_ptr(HELLO_PTR) };
252 ///
253 /// assert_eq!(c"Hello, world!", HELLO);
254 /// ```
255 ///
256 /// [valid]: core::ptr#safety
257 #[inline] // inline is necessary for codegen to see strlen.
258 #[must_use]
259 #[stable(feature = "rust1", since = "1.0.0")]
260 #[rustc_const_stable(feature = "const_cstr_from_ptr", since = "1.81.0")]
261 pub const unsafe fn from_ptr<'a>(ptr: *const c_char) -> &'a CStr {
262 // SAFETY: The caller has provided a pointer that points to a valid C
263 // string with a NUL terminator less than `isize::MAX` from `ptr`.
264 let len = unsafe { strlen(ptr) };
265
266 // SAFETY: The caller has provided a valid pointer with length less than
267 // `isize::MAX`, so `from_raw_parts` is safe. The content remains valid
268 // and doesn't change for the lifetime of the returned `CStr`. This
269 // means the call to `from_bytes_with_nul_unchecked` is correct.
270 //
271 // The cast from c_char to u8 is ok because a c_char is always one byte.
272 unsafe { Self::from_bytes_with_nul_unchecked(slice::from_raw_parts(ptr.cast(), len + 1)) }
273 }
274
275 /// Creates a C string wrapper from a byte slice with any number of nuls.
276 ///
277 /// This method will create a `CStr` from any byte slice that contains at
278 /// least one nul byte. Unlike with [`CStr::from_bytes_with_nul`], the caller
279 /// does not need to know where the nul byte is located.
280 ///
281 /// If the first byte is a nul character, this method will return an
282 /// empty `CStr`. If multiple nul characters are present, the `CStr` will
283 /// end at the first one.
284 ///
285 /// If the slice only has a single nul byte at the end, this method is
286 /// equivalent to [`CStr::from_bytes_with_nul`].
287 ///
288 /// # Examples
289 /// ```
290 /// use std::ffi::CStr;
291 ///
292 /// let mut buffer = [0u8; 16];
293 /// unsafe {
294 /// // Here we might call an unsafe C function that writes a string
295 /// // into the buffer.
296 /// let buf_ptr = buffer.as_mut_ptr();
297 /// buf_ptr.write_bytes(b'A', 8);
298 /// }
299 /// // Attempt to extract a C nul-terminated string from the buffer.
300 /// let c_str = CStr::from_bytes_until_nul(&buffer[..]).unwrap();
301 /// assert_eq!(c_str.to_str().unwrap(), "AAAAAAAA");
302 /// ```
303 ///
304 #[stable(feature = "cstr_from_bytes_until_nul", since = "1.69.0")]
305 #[rustc_const_stable(feature = "cstr_from_bytes_until_nul", since = "1.69.0")]
306 pub const fn from_bytes_until_nul(bytes: &[u8]) -> Result<&CStr, FromBytesUntilNulError> {
307 let nul_pos = memchr::memchr(0, bytes);
308 match nul_pos {
309 Some(nul_pos) => {
310 // FIXME(const-hack) replace with range index
311 // SAFETY: nul_pos + 1 <= bytes.len()
312 let subslice = unsafe { crate::slice::from_raw_parts(bytes.as_ptr(), nul_pos + 1) };
313 // SAFETY: We know there is a nul byte at nul_pos, so this slice
314 // (ending at the nul byte) is a well-formed C string.
315 Ok(unsafe { CStr::from_bytes_with_nul_unchecked(subslice) })
316 }
317 None => Err(FromBytesUntilNulError(())),
318 }
319 }
320
321 /// Creates a C string wrapper from a byte slice with exactly one nul
322 /// terminator.
323 ///
324 /// This function will cast the provided `bytes` to a `CStr`
325 /// wrapper after ensuring that the byte slice is nul-terminated
326 /// and does not contain any interior nul bytes.
327 ///
328 /// If the nul byte may not be at the end,
329 /// [`CStr::from_bytes_until_nul`] can be used instead.
330 ///
331 /// # Examples
332 ///
333 /// ```
334 /// use std::ffi::CStr;
335 ///
336 /// let cstr = CStr::from_bytes_with_nul(b"hello\0");
337 /// assert_eq!(cstr, Ok(c"hello"));
338 /// ```
339 ///
340 /// Creating a `CStr` without a trailing nul terminator is an error:
341 ///
342 /// ```
343 /// use std::ffi::{CStr, FromBytesWithNulError};
344 ///
345 /// let cstr = CStr::from_bytes_with_nul(b"hello");
346 /// assert_eq!(cstr, Err(FromBytesWithNulError::NotNulTerminated));
347 /// ```
348 ///
349 /// Creating a `CStr` with an interior nul byte is an error:
350 ///
351 /// ```
352 /// use std::ffi::{CStr, FromBytesWithNulError};
353 ///
354 /// let cstr = CStr::from_bytes_with_nul(b"he\0llo\0");
355 /// assert_eq!(cstr, Err(FromBytesWithNulError::InteriorNul { position: 2 }));
356 /// ```
357 #[stable(feature = "cstr_from_bytes", since = "1.10.0")]
358 #[rustc_const_stable(feature = "const_cstr_methods", since = "1.72.0")]
359 pub const fn from_bytes_with_nul(bytes: &[u8]) -> Result<&Self, FromBytesWithNulError> {
360 let nul_pos = memchr::memchr(0, bytes);
361 match nul_pos {
362 Some(nul_pos) if nul_pos + 1 == bytes.len() => {
363 // SAFETY: We know there is only one nul byte, at the end
364 // of the byte slice.
365 Ok(unsafe { Self::from_bytes_with_nul_unchecked(bytes) })
366 }
367 Some(position) => Err(FromBytesWithNulError::InteriorNul { position }),
368 None => Err(FromBytesWithNulError::NotNulTerminated),
369 }
370 }
371
372 /// Unsafely creates a C string wrapper from a byte slice.
373 ///
374 /// This function will cast the provided `bytes` to a `CStr` wrapper without
375 /// performing any sanity checks.
376 ///
377 /// # Safety
378 /// The provided slice **must** be nul-terminated and not contain any interior
379 /// nul bytes.
380 ///
381 /// # Examples
382 ///
383 /// ```
384 /// use std::ffi::CStr;
385 ///
386 /// let bytes = b"Hello world!\0";
387 ///
388 /// let cstr = unsafe { CStr::from_bytes_with_nul_unchecked(bytes) };
389 /// assert_eq!(cstr.to_bytes_with_nul(), bytes);
390 /// ```
391 #[inline]
392 #[must_use]
393 #[stable(feature = "cstr_from_bytes", since = "1.10.0")]
394 #[rustc_const_stable(feature = "const_cstr_unchecked", since = "1.59.0")]
395 #[rustc_allow_const_fn_unstable(const_eval_select)]
396 pub const unsafe fn from_bytes_with_nul_unchecked(bytes: &[u8]) -> &CStr {
397 const_eval_select!(
398 @capture { bytes: &[u8] } -> &CStr:
399 if const {
400 // Saturating so that an empty slice panics in the assert with a good
401 // message, not here due to underflow.
402 let mut i = bytes.len().saturating_sub(1);
403 assert!(!bytes.is_empty() && bytes[i] == 0, "input was not nul-terminated");
404
405 // Ending nul byte exists, skip to the rest.
406 while i != 0 {
407 i -= 1;
408 let byte = bytes[i];
409 assert!(byte != 0, "input contained interior nul");
410 }
411
412 // SAFETY: See runtime cast comment below.
413 unsafe { &*(bytes as *const [u8] as *const CStr) }
414 } else {
415 // Chance at catching some UB at runtime with debug builds.
416 debug_assert!(!bytes.is_empty() && bytes[bytes.len() - 1] == 0);
417
418 // SAFETY: Casting to CStr is safe because its internal representation
419 // is a [u8] too (safe only inside std).
420 // Dereferencing the obtained pointer is safe because it comes from a
421 // reference. Making a reference is then safe because its lifetime
422 // is bound by the lifetime of the given `bytes`.
423 unsafe { &*(bytes as *const [u8] as *const CStr) }
424 }
425 )
426 }
427
428 /// Returns the inner pointer to this C string.
429 ///
430 /// The returned pointer will be valid for as long as `self` is, and points
431 /// to a contiguous region of memory terminated with a 0 byte to represent
432 /// the end of the string.
433 ///
434 /// The type of the returned pointer is
435 /// [`*const c_char`][crate::ffi::c_char], and whether it's
436 /// an alias for `*const i8` or `*const u8` is platform-specific.
437 ///
438 /// **WARNING**
439 ///
440 /// The returned pointer is read-only; writing to it (including passing it
441 /// to C code that writes to it) causes undefined behavior.
442 ///
443 /// It is your responsibility to make sure that the underlying memory is not
444 /// freed too early. For example, the following code will cause undefined
445 /// behavior when `ptr` is used inside the `unsafe` block:
446 ///
447 /// ```no_run
448 /// # #![expect(dangling_pointers_from_temporaries)]
449 /// use std::ffi::{CStr, CString};
450 ///
451 /// // 💀 The meaning of this entire program is undefined,
452 /// // 💀 and nothing about its behavior is guaranteed,
453 /// // 💀 not even that its behavior resembles the code as written,
454 /// // 💀 just because it contains a single instance of undefined behavior!
455 ///
456 /// // 🚨 creates a dangling pointer to a temporary `CString`
457 /// // 🚨 that is deallocated at the end of the statement
458 /// let ptr = CString::new("Hi!".to_uppercase()).unwrap().as_ptr();
459 ///
460 /// // without undefined behavior, you would expect that `ptr` equals:
461 /// dbg!(CStr::from_bytes_with_nul(b"HI!\0").unwrap());
462 ///
463 /// // 🙏 Possibly the program behaved as expected so far,
464 /// // 🙏 and this just shows `ptr` is now garbage..., but
465 /// // 💀 this violates `CStr::from_ptr`'s safety contract
466 /// // 💀 leading to a dereference of a dangling pointer,
467 /// // 💀 which is immediate undefined behavior.
468 /// // 💀 *BOOM*, you're dead, you're entire program has no meaning.
469 /// dbg!(unsafe { CStr::from_ptr(ptr) });
470 /// ```
471 ///
472 /// This happens because, the pointer returned by `as_ptr` does not carry any
473 /// lifetime information, and the `CString` is deallocated immediately after
474 /// the expression that it is part of has been evaluated.
475 /// To fix the problem, bind the `CString` to a local variable:
476 ///
477 /// ```
478 /// use std::ffi::{CStr, CString};
479 ///
480 /// let c_str = CString::new("Hi!".to_uppercase()).unwrap();
481 /// let ptr = c_str.as_ptr();
482 ///
483 /// assert_eq!(unsafe { CStr::from_ptr(ptr) }, c"HI!");
484 /// ```
485 #[inline]
486 #[must_use]
487 #[stable(feature = "rust1", since = "1.0.0")]
488 #[rustc_const_stable(feature = "const_str_as_ptr", since = "1.32.0")]
489 #[rustc_as_ptr]
490 #[rustc_never_returns_null_ptr]
491 pub const fn as_ptr(&self) -> *const c_char {
492 self.inner.as_ptr()
493 }
494
495 /// We could eventually expose this publicly, if we wanted.
496 #[inline]
497 #[must_use]
498 const fn as_non_null_ptr(&self) -> NonNull<c_char> {
499 // FIXME(const_trait_impl) replace with `NonNull::from`
500 // SAFETY: a reference is never null
501 unsafe { NonNull::new_unchecked(&self.inner as *const [c_char] as *mut [c_char]) }
502 .as_non_null_ptr()
503 }
504
505 /// Returns the length of `self`. Like C's `strlen`, this does not include the nul terminator.
506 ///
507 /// > **Note**: This method is currently implemented as a constant-time
508 /// > cast, but it is planned to alter its definition in the future to
509 /// > perform the length calculation whenever this method is called.
510 ///
511 /// # Examples
512 ///
513 /// ```
514 /// assert_eq!(c"foo".count_bytes(), 3);
515 /// assert_eq!(c"".count_bytes(), 0);
516 /// ```
517 #[inline]
518 #[must_use]
519 #[doc(alias("len", "strlen"))]
520 #[stable(feature = "cstr_count_bytes", since = "1.79.0")]
521 #[rustc_const_stable(feature = "const_cstr_from_ptr", since = "1.81.0")]
522 pub const fn count_bytes(&self) -> usize {
523 self.inner.len() - 1
524 }
525
526 /// Returns `true` if `self.to_bytes()` has a length of 0.
527 ///
528 /// # Examples
529 ///
530 /// ```
531 /// assert!(!c"foo".is_empty());
532 /// assert!(c"".is_empty());
533 /// ```
534 #[inline]
535 #[stable(feature = "cstr_is_empty", since = "1.71.0")]
536 #[rustc_const_stable(feature = "cstr_is_empty", since = "1.71.0")]
537 pub const fn is_empty(&self) -> bool {
538 // SAFETY: We know there is at least one byte; for empty strings it
539 // is the NUL terminator.
540 // FIXME(const-hack): use get_unchecked
541 unsafe { *self.inner.as_ptr() == 0 }
542 }
543
544 /// Converts this C string to a byte slice.
545 ///
546 /// The returned slice will **not** contain the trailing nul terminator that this C
547 /// string has.
548 ///
549 /// > **Note**: This method is currently implemented as a constant-time
550 /// > cast, but it is planned to alter its definition in the future to
551 /// > perform the length calculation whenever this method is called.
552 ///
553 /// # Examples
554 ///
555 /// ```
556 /// assert_eq!(c"foo".to_bytes(), b"foo");
557 /// ```
558 #[inline]
559 #[must_use = "this returns the result of the operation, \
560 without modifying the original"]
561 #[stable(feature = "rust1", since = "1.0.0")]
562 #[rustc_const_stable(feature = "const_cstr_methods", since = "1.72.0")]
563 pub const fn to_bytes(&self) -> &[u8] {
564 let bytes = self.to_bytes_with_nul();
565 // FIXME(const-hack) replace with range index
566 // SAFETY: to_bytes_with_nul returns slice with length at least 1
567 unsafe { slice::from_raw_parts(bytes.as_ptr(), bytes.len() - 1) }
568 }
569
570 /// Converts this C string to a byte slice containing the trailing 0 byte.
571 ///
572 /// This function is the equivalent of [`CStr::to_bytes`] except that it
573 /// will retain the trailing nul terminator instead of chopping it off.
574 ///
575 /// > **Note**: This method is currently implemented as a 0-cost cast, but
576 /// > it is planned to alter its definition in the future to perform the
577 /// > length calculation whenever this method is called.
578 ///
579 /// # Examples
580 ///
581 /// ```
582 /// assert_eq!(c"foo".to_bytes_with_nul(), b"foo\0");
583 /// ```
584 #[inline]
585 #[must_use = "this returns the result of the operation, \
586 without modifying the original"]
587 #[stable(feature = "rust1", since = "1.0.0")]
588 #[rustc_const_stable(feature = "const_cstr_methods", since = "1.72.0")]
589 pub const fn to_bytes_with_nul(&self) -> &[u8] {
590 // SAFETY: Transmuting a slice of `c_char`s to a slice of `u8`s
591 // is safe on all supported targets.
592 unsafe { &*((&raw const self.inner) as *const [u8]) }
593 }
594
595 /// Iterates over the bytes in this C string.
596 ///
597 /// The returned iterator will **not** contain the trailing nul terminator
598 /// that this C string has.
599 ///
600 /// # Examples
601 ///
602 /// ```
603 /// #![feature(cstr_bytes)]
604 ///
605 /// assert!(c"foo".bytes().eq(*b"foo"));
606 /// ```
607 #[inline]
608 #[unstable(feature = "cstr_bytes", issue = "112115")]
609 pub fn bytes(&self) -> Bytes<'_> {
610 Bytes::new(self)
611 }
612
613 /// Yields a <code>&[str]</code> slice if the `CStr` contains valid UTF-8.
614 ///
615 /// If the contents of the `CStr` are valid UTF-8 data, this
616 /// function will return the corresponding <code>&[str]</code> slice. Otherwise,
617 /// it will return an error with details of where UTF-8 validation failed.
618 ///
619 /// [str]: prim@str "str"
620 ///
621 /// # Examples
622 ///
623 /// ```
624 /// assert_eq!(c"foo".to_str(), Ok("foo"));
625 /// ```
626 #[stable(feature = "cstr_to_str", since = "1.4.0")]
627 #[rustc_const_stable(feature = "const_cstr_methods", since = "1.72.0")]
628 pub const fn to_str(&self) -> Result<&str, str::Utf8Error> {
629 // N.B., when `CStr` is changed to perform the length check in `.to_bytes()`
630 // instead of in `from_ptr()`, it may be worth considering if this should
631 // be rewritten to do the UTF-8 check inline with the length calculation
632 // instead of doing it afterwards.
633 str::from_utf8(self.to_bytes())
634 }
635
636 /// Returns an object that implements [`Display`] for safely printing a [`CStr`] that may
637 /// contain non-Unicode data.
638 ///
639 /// Behaves as if `self` were first lossily converted to a `str`, with invalid UTF-8 presented
640 /// as the Unicode replacement character: �.
641 ///
642 /// [`Display`]: fmt::Display
643 ///
644 /// # Examples
645 ///
646 /// ```
647 /// #![feature(cstr_display)]
648 ///
649 /// let cstr = c"Hello, world!";
650 /// println!("{}", cstr.display());
651 /// ```
652 #[unstable(feature = "cstr_display", issue = "139984")]
653 #[must_use = "this does not display the `CStr`; \
654 it returns an object that can be displayed"]
655 #[inline]
656 pub fn display(&self) -> impl fmt::Display {
657 crate::bstr::ByteStr::from_bytes(self.to_bytes())
658 }
659}
660
661// `.to_bytes()` representations are compared instead of the inner `[c_char]`s,
662// because `c_char` is `i8` (not `u8`) on some platforms.
663// That is why this is implemented manually and not derived.
664#[stable(feature = "rust1", since = "1.0.0")]
665impl PartialOrd for CStr {
666 #[inline]
667 fn partial_cmp(&self, other: &CStr) -> Option<Ordering> {
668 self.to_bytes().partial_cmp(&other.to_bytes())
669 }
670}
671#[stable(feature = "rust1", since = "1.0.0")]
672impl Ord for CStr {
673 #[inline]
674 fn cmp(&self, other: &CStr) -> Ordering {
675 self.to_bytes().cmp(&other.to_bytes())
676 }
677}
678
679#[stable(feature = "cstr_range_from", since = "1.47.0")]
680impl ops::Index<ops::RangeFrom<usize>> for CStr {
681 type Output = CStr;
682
683 #[inline]
684 fn index(&self, index: ops::RangeFrom<usize>) -> &CStr {
685 let bytes: &[u8] = self.to_bytes_with_nul();
686 // we need to manually check the starting index to account for the null
687 // byte, since otherwise we could get an empty string that doesn't end
688 // in a null.
689 if index.start < bytes.len() {
690 // SAFETY: Non-empty tail of a valid `CStr` is still a valid `CStr`.
691 unsafe { CStr::from_bytes_with_nul_unchecked(&bytes[index.start..]) }
692 } else {
693 panic!(
694 "index out of bounds: the len is {} but the index is {}",
695 bytes.len(),
696 index.start
697 );
698 }
699 }
700}
701
702#[stable(feature = "cstring_asref", since = "1.7.0")]
703impl AsRef<CStr> for CStr {
704 #[inline]
705 fn as_ref(&self) -> &CStr {
706 self
707 }
708}
709
710/// Calculate the length of a nul-terminated string. Defers to C's `strlen` when possible.
711///
712/// # Safety
713///
714/// The pointer must point to a valid buffer that contains a NUL terminator. The NUL must be
715/// located within `isize::MAX` from `ptr`.
716#[inline]
717#[unstable(feature = "cstr_internals", issue = "none")]
718#[rustc_allow_const_fn_unstable(const_eval_select)]
719const unsafe fn strlen(ptr: *const c_char) -> usize {
720 const_eval_select!(
721 @capture { s: *const c_char = ptr } -> usize:
722 if const {
723 let mut len = 0;
724
725 // SAFETY: Outer caller has provided a pointer to a valid C string.
726 while unsafe { *s.add(len) } != 0 {
727 len += 1;
728 }
729
730 len
731 } else {
732 unsafe extern "C" {
733 /// Provided by libc or compiler_builtins.
734 fn strlen(s: *const c_char) -> usize;
735 }
736
737 // SAFETY: Outer caller has provided a pointer to a valid C string.
738 unsafe { strlen(s) }
739 }
740 )
741}
742
743/// An iterator over the bytes of a [`CStr`], without the nul terminator.
744///
745/// This struct is created by the [`bytes`] method on [`CStr`].
746/// See its documentation for more.
747///
748/// [`bytes`]: CStr::bytes
749#[must_use = "iterators are lazy and do nothing unless consumed"]
750#[unstable(feature = "cstr_bytes", issue = "112115")]
751#[derive(Clone, Debug)]
752pub struct Bytes<'a> {
753 // since we know the string is nul-terminated, we only need one pointer
754 ptr: NonNull<u8>,
755 phantom: PhantomData<&'a [c_char]>,
756}
757
758#[unstable(feature = "cstr_bytes", issue = "112115")]
759unsafe impl Send for Bytes<'_> {}
760
761#[unstable(feature = "cstr_bytes", issue = "112115")]
762unsafe impl Sync for Bytes<'_> {}
763
764impl<'a> Bytes<'a> {
765 #[inline]
766 fn new(s: &'a CStr) -> Self {
767 Self { ptr: s.as_non_null_ptr().cast(), phantom: PhantomData }
768 }
769
770 #[inline]
771 fn is_empty(&self) -> bool {
772 // SAFETY: We uphold that the pointer is always valid to dereference
773 // by starting with a valid C string and then never incrementing beyond
774 // the nul terminator.
775 unsafe { self.ptr.read() == 0 }
776 }
777}
778
779#[unstable(feature = "cstr_bytes", issue = "112115")]
780impl Iterator for Bytes<'_> {
781 type Item = u8;
782
783 #[inline]
784 fn next(&mut self) -> Option<u8> {
785 // SAFETY: We only choose a pointer from a valid C string, which must
786 // be non-null and contain at least one value. Since we always stop at
787 // the nul terminator, which is guaranteed to exist, we can assume that
788 // the pointer is non-null and valid. This lets us safely dereference
789 // it and assume that adding 1 will create a new, non-null, valid
790 // pointer.
791 unsafe {
792 let ret = self.ptr.read();
793 if ret == 0 {
794 None
795 } else {
796 self.ptr = self.ptr.add(1);
797 Some(ret)
798 }
799 }
800 }
801
802 #[inline]
803 fn size_hint(&self) -> (usize, Option<usize>) {
804 if self.is_empty() { (0, Some(0)) } else { (1, None) }
805 }
806
807 #[inline]
808 fn count(self) -> usize {
809 // SAFETY: We always hold a valid pointer to a C string
810 unsafe { strlen(self.ptr.as_ptr().cast()) }
811 }
812}
813
814#[unstable(feature = "cstr_bytes", issue = "112115")]
815impl FusedIterator for Bytes<'_> {}
816