core/ptr/mut_ptr.rs
1use super::*;
2use crate::cmp::Ordering::{Equal, Greater, Less};
3use crate::intrinsics::const_eval_select;
4use crate::mem::{self, SizedTypeProperties};
5use crate::slice::{self, SliceIndex};
6
7impl<T: ?Sized> *mut T {
8 /// Returns `true` if the pointer is null.
9 ///
10 /// Note that unsized types have many possible null pointers, as only the
11 /// raw data pointer is considered, not their length, vtable, etc.
12 /// Therefore, two pointers that are null may still not compare equal to
13 /// each other.
14 ///
15 /// # Panics during const evaluation
16 ///
17 /// If this method is used during const evaluation, and `self` is a pointer
18 /// that is offset beyond the bounds of the memory it initially pointed to,
19 /// then there might not be enough information to determine whether the
20 /// pointer is null. This is because the absolute address in memory is not
21 /// known at compile time. If the nullness of the pointer cannot be
22 /// determined, this method will panic.
23 ///
24 /// In-bounds pointers are never null, so the method will never panic for
25 /// such pointers.
26 ///
27 /// # Examples
28 ///
29 /// ```
30 /// let mut s = [1, 2, 3];
31 /// let ptr: *mut u32 = s.as_mut_ptr();
32 /// assert!(!ptr.is_null());
33 /// ```
34 #[stable(feature = "rust1", since = "1.0.0")]
35 #[rustc_const_stable(feature = "const_ptr_is_null", since = "1.84.0")]
36 #[rustc_diagnostic_item = "ptr_is_null"]
37 #[inline]
38 pub const fn is_null(self) -> bool {
39 self.cast_const().is_null()
40 }
41
42 /// Casts to a pointer of another type.
43 #[stable(feature = "ptr_cast", since = "1.38.0")]
44 #[rustc_const_stable(feature = "const_ptr_cast", since = "1.38.0")]
45 #[rustc_diagnostic_item = "ptr_cast"]
46 #[inline(always)]
47 pub const fn cast<U>(self) -> *mut U {
48 self as _
49 }
50
51 /// Try to cast to a pointer of another type by checking aligment.
52 ///
53 /// If the pointer is properly aligned to the target type, it will be
54 /// cast to the target type. Otherwise, `None` is returned.
55 ///
56 /// # Examples
57 ///
58 /// ```rust
59 /// #![feature(pointer_try_cast_aligned)]
60 ///
61 /// let aligned: *mut u8 = 0x1000 as _;
62 ///
63 /// // i32 has at most 4-byte alignment, so this will succeed
64 /// assert!(aligned.try_cast_aligned::<i32>().is_some());
65 ///
66 /// let unaligned: *mut u8 = 0x1001 as _;
67 ///
68 /// // i32 has at least 2-byte alignment, so this will fail
69 /// assert!(unaligned.try_cast_aligned::<i32>().is_none());
70 /// ```
71 #[unstable(feature = "pointer_try_cast_aligned", issue = "141221")]
72 #[must_use = "this returns the result of the operation, \
73 without modifying the original"]
74 #[inline]
75 pub fn try_cast_aligned<U>(self) -> Option<*mut U> {
76 if self.is_aligned_to(align_of::<U>()) { Some(self.cast()) } else { None }
77 }
78
79 /// Uses the address value in a new pointer of another type.
80 ///
81 /// This operation will ignore the address part of its `meta` operand and discard existing
82 /// metadata of `self`. For pointers to a sized types (thin pointers), this has the same effect
83 /// as a simple cast. For pointers to an unsized type (fat pointers) this recombines the address
84 /// with new metadata such as slice lengths or `dyn`-vtable.
85 ///
86 /// The resulting pointer will have provenance of `self`. This operation is semantically the
87 /// same as creating a new pointer with the data pointer value of `self` but the metadata of
88 /// `meta`, being fat or thin depending on the `meta` operand.
89 ///
90 /// # Examples
91 ///
92 /// This function is primarily useful for enabling pointer arithmetic on potentially fat
93 /// pointers. The pointer is cast to a sized pointee to utilize offset operations and then
94 /// recombined with its own original metadata.
95 ///
96 /// ```
97 /// #![feature(set_ptr_value)]
98 /// # use core::fmt::Debug;
99 /// let mut arr: [i32; 3] = [1, 2, 3];
100 /// let mut ptr = arr.as_mut_ptr() as *mut dyn Debug;
101 /// let thin = ptr as *mut u8;
102 /// unsafe {
103 /// ptr = thin.add(8).with_metadata_of(ptr);
104 /// # assert_eq!(*(ptr as *mut i32), 3);
105 /// println!("{:?}", &*ptr); // will print "3"
106 /// }
107 /// ```
108 ///
109 /// # *Incorrect* usage
110 ///
111 /// The provenance from pointers is *not* combined. The result must only be used to refer to the
112 /// address allowed by `self`.
113 ///
114 /// ```rust,no_run
115 /// #![feature(set_ptr_value)]
116 /// let mut x = 0u32;
117 /// let mut y = 1u32;
118 ///
119 /// let x = (&mut x) as *mut u32;
120 /// let y = (&mut y) as *mut u32;
121 ///
122 /// let offset = (x as usize - y as usize) / 4;
123 /// let bad = x.wrapping_add(offset).with_metadata_of(y);
124 ///
125 /// // This dereference is UB. The pointer only has provenance for `x` but points to `y`.
126 /// println!("{:?}", unsafe { &*bad });
127 #[unstable(feature = "set_ptr_value", issue = "75091")]
128 #[must_use = "returns a new pointer rather than modifying its argument"]
129 #[inline]
130 pub const fn with_metadata_of<U>(self, meta: *const U) -> *mut U
131 where
132 U: ?Sized,
133 {
134 from_raw_parts_mut::<U>(self as *mut (), metadata(meta))
135 }
136
137 /// Changes constness without changing the type.
138 ///
139 /// This is a bit safer than `as` because it wouldn't silently change the type if the code is
140 /// refactored.
141 ///
142 /// While not strictly required (`*mut T` coerces to `*const T`), this is provided for symmetry
143 /// with [`cast_mut`] on `*const T` and may have documentation value if used instead of implicit
144 /// coercion.
145 ///
146 /// [`cast_mut`]: pointer::cast_mut
147 #[stable(feature = "ptr_const_cast", since = "1.65.0")]
148 #[rustc_const_stable(feature = "ptr_const_cast", since = "1.65.0")]
149 #[rustc_diagnostic_item = "ptr_cast_const"]
150 #[inline(always)]
151 pub const fn cast_const(self) -> *const T {
152 self as _
153 }
154
155 /// Gets the "address" portion of the pointer.
156 ///
157 /// This is similar to `self as usize`, except that the [provenance][crate::ptr#provenance] of
158 /// the pointer is discarded and not [exposed][crate::ptr#exposed-provenance]. This means that
159 /// casting the returned address back to a pointer yields a [pointer without
160 /// provenance][without_provenance_mut], which is undefined behavior to dereference. To properly
161 /// restore the lost information and obtain a dereferenceable pointer, use
162 /// [`with_addr`][pointer::with_addr] or [`map_addr`][pointer::map_addr].
163 ///
164 /// If using those APIs is not possible because there is no way to preserve a pointer with the
165 /// required provenance, then Strict Provenance might not be for you. Use pointer-integer casts
166 /// or [`expose_provenance`][pointer::expose_provenance] and [`with_exposed_provenance`][with_exposed_provenance]
167 /// instead. However, note that this makes your code less portable and less amenable to tools
168 /// that check for compliance with the Rust memory model.
169 ///
170 /// On most platforms this will produce a value with the same bytes as the original
171 /// pointer, because all the bytes are dedicated to describing the address.
172 /// Platforms which need to store additional information in the pointer may
173 /// perform a change of representation to produce a value containing only the address
174 /// portion of the pointer. What that means is up to the platform to define.
175 ///
176 /// This is a [Strict Provenance][crate::ptr#strict-provenance] API.
177 #[must_use]
178 #[inline(always)]
179 #[stable(feature = "strict_provenance", since = "1.84.0")]
180 pub fn addr(self) -> usize {
181 // A pointer-to-integer transmute currently has exactly the right semantics: it returns the
182 // address without exposing the provenance. Note that this is *not* a stable guarantee about
183 // transmute semantics, it relies on sysroot crates having special status.
184 // SAFETY: Pointer-to-integer transmutes are valid (if you are okay with losing the
185 // provenance).
186 unsafe { mem::transmute(self.cast::<()>()) }
187 }
188
189 /// Exposes the ["provenance"][crate::ptr#provenance] part of the pointer for future use in
190 /// [`with_exposed_provenance_mut`] and returns the "address" portion.
191 ///
192 /// This is equivalent to `self as usize`, which semantically discards provenance information.
193 /// Furthermore, this (like the `as` cast) has the implicit side-effect of marking the
194 /// provenance as 'exposed', so on platforms that support it you can later call
195 /// [`with_exposed_provenance_mut`] to reconstitute the original pointer including its provenance.
196 ///
197 /// Due to its inherent ambiguity, [`with_exposed_provenance_mut`] may not be supported by tools
198 /// that help you to stay conformant with the Rust memory model. It is recommended to use
199 /// [Strict Provenance][crate::ptr#strict-provenance] APIs such as [`with_addr`][pointer::with_addr]
200 /// wherever possible, in which case [`addr`][pointer::addr] should be used instead of `expose_provenance`.
201 ///
202 /// On most platforms this will produce a value with the same bytes as the original pointer,
203 /// because all the bytes are dedicated to describing the address. Platforms which need to store
204 /// additional information in the pointer may not support this operation, since the 'expose'
205 /// side-effect which is required for [`with_exposed_provenance_mut`] to work is typically not
206 /// available.
207 ///
208 /// This is an [Exposed Provenance][crate::ptr#exposed-provenance] API.
209 ///
210 /// [`with_exposed_provenance_mut`]: with_exposed_provenance_mut
211 #[inline(always)]
212 #[stable(feature = "exposed_provenance", since = "1.84.0")]
213 pub fn expose_provenance(self) -> usize {
214 self.cast::<()>() as usize
215 }
216
217 /// Creates a new pointer with the given address and the [provenance][crate::ptr#provenance] of
218 /// `self`.
219 ///
220 /// This is similar to a `addr as *mut T` cast, but copies
221 /// the *provenance* of `self` to the new pointer.
222 /// This avoids the inherent ambiguity of the unary cast.
223 ///
224 /// This is equivalent to using [`wrapping_offset`][pointer::wrapping_offset] to offset
225 /// `self` to the given address, and therefore has all the same capabilities and restrictions.
226 ///
227 /// This is a [Strict Provenance][crate::ptr#strict-provenance] API.
228 #[must_use]
229 #[inline]
230 #[stable(feature = "strict_provenance", since = "1.84.0")]
231 pub fn with_addr(self, addr: usize) -> Self {
232 // This should probably be an intrinsic to avoid doing any sort of arithmetic, but
233 // meanwhile, we can implement it with `wrapping_offset`, which preserves the pointer's
234 // provenance.
235 let self_addr = self.addr() as isize;
236 let dest_addr = addr as isize;
237 let offset = dest_addr.wrapping_sub(self_addr);
238 self.wrapping_byte_offset(offset)
239 }
240
241 /// Creates a new pointer by mapping `self`'s address to a new one, preserving the original
242 /// pointer's [provenance][crate::ptr#provenance].
243 ///
244 /// This is a convenience for [`with_addr`][pointer::with_addr], see that method for details.
245 ///
246 /// This is a [Strict Provenance][crate::ptr#strict-provenance] API.
247 #[must_use]
248 #[inline]
249 #[stable(feature = "strict_provenance", since = "1.84.0")]
250 pub fn map_addr(self, f: impl FnOnce(usize) -> usize) -> Self {
251 self.with_addr(f(self.addr()))
252 }
253
254 /// Decompose a (possibly wide) pointer into its data pointer and metadata components.
255 ///
256 /// The pointer can be later reconstructed with [`from_raw_parts_mut`].
257 #[unstable(feature = "ptr_metadata", issue = "81513")]
258 #[inline]
259 pub const fn to_raw_parts(self) -> (*mut (), <T as super::Pointee>::Metadata) {
260 (self.cast(), super::metadata(self))
261 }
262
263 /// Returns `None` if the pointer is null, or else returns a shared reference to
264 /// the value wrapped in `Some`. If the value may be uninitialized, [`as_uninit_ref`]
265 /// must be used instead.
266 ///
267 /// For the mutable counterpart see [`as_mut`].
268 ///
269 /// [`as_uninit_ref`]: pointer#method.as_uninit_ref-1
270 /// [`as_mut`]: #method.as_mut
271 ///
272 /// # Safety
273 ///
274 /// When calling this method, you have to ensure that *either* the pointer is null *or*
275 /// the pointer is [convertible to a reference](crate::ptr#pointer-to-reference-conversion).
276 ///
277 /// # Panics during const evaluation
278 ///
279 /// This method will panic during const evaluation if the pointer cannot be
280 /// determined to be null or not. See [`is_null`] for more information.
281 ///
282 /// [`is_null`]: #method.is_null-1
283 ///
284 /// # Examples
285 ///
286 /// ```
287 /// let ptr: *mut u8 = &mut 10u8 as *mut u8;
288 ///
289 /// unsafe {
290 /// if let Some(val_back) = ptr.as_ref() {
291 /// println!("We got back the value: {val_back}!");
292 /// }
293 /// }
294 /// ```
295 ///
296 /// # Null-unchecked version
297 ///
298 /// If you are sure the pointer can never be null and are looking for some kind of
299 /// `as_ref_unchecked` that returns the `&T` instead of `Option<&T>`, know that you can
300 /// dereference the pointer directly.
301 ///
302 /// ```
303 /// let ptr: *mut u8 = &mut 10u8 as *mut u8;
304 ///
305 /// unsafe {
306 /// let val_back = &*ptr;
307 /// println!("We got back the value: {val_back}!");
308 /// }
309 /// ```
310 #[stable(feature = "ptr_as_ref", since = "1.9.0")]
311 #[rustc_const_stable(feature = "const_ptr_is_null", since = "1.84.0")]
312 #[inline]
313 pub const unsafe fn as_ref<'a>(self) -> Option<&'a T> {
314 // SAFETY: the caller must guarantee that `self` is valid for a
315 // reference if it isn't null.
316 if self.is_null() { None } else { unsafe { Some(&*self) } }
317 }
318
319 /// Returns a shared reference to the value behind the pointer.
320 /// If the pointer may be null or the value may be uninitialized, [`as_uninit_ref`] must be used instead.
321 /// If the pointer may be null, but the value is known to have been initialized, [`as_ref`] must be used instead.
322 ///
323 /// For the mutable counterpart see [`as_mut_unchecked`].
324 ///
325 /// [`as_ref`]: #method.as_ref
326 /// [`as_uninit_ref`]: #method.as_uninit_ref
327 /// [`as_mut_unchecked`]: #method.as_mut_unchecked
328 ///
329 /// # Safety
330 ///
331 /// When calling this method, you have to ensure that the pointer is [convertible to a reference](crate::ptr#pointer-to-reference-conversion).
332 ///
333 /// # Examples
334 ///
335 /// ```
336 /// #![feature(ptr_as_ref_unchecked)]
337 /// let ptr: *mut u8 = &mut 10u8 as *mut u8;
338 ///
339 /// unsafe {
340 /// println!("We got back the value: {}!", ptr.as_ref_unchecked());
341 /// }
342 /// ```
343 // FIXME: mention it in the docs for `as_ref` and `as_uninit_ref` once stabilized.
344 #[unstable(feature = "ptr_as_ref_unchecked", issue = "122034")]
345 #[inline]
346 #[must_use]
347 pub const unsafe fn as_ref_unchecked<'a>(self) -> &'a T {
348 // SAFETY: the caller must guarantee that `self` is valid for a reference
349 unsafe { &*self }
350 }
351
352 /// Returns `None` if the pointer is null, or else returns a shared reference to
353 /// the value wrapped in `Some`. In contrast to [`as_ref`], this does not require
354 /// that the value has to be initialized.
355 ///
356 /// For the mutable counterpart see [`as_uninit_mut`].
357 ///
358 /// [`as_ref`]: pointer#method.as_ref-1
359 /// [`as_uninit_mut`]: #method.as_uninit_mut
360 ///
361 /// # Safety
362 ///
363 /// When calling this method, you have to ensure that *either* the pointer is null *or*
364 /// the pointer is [convertible to a reference](crate::ptr#pointer-to-reference-conversion).
365 /// Note that because the created reference is to `MaybeUninit<T>`, the
366 /// source pointer can point to uninitialized memory.
367 ///
368 /// # Panics during const evaluation
369 ///
370 /// This method will panic during const evaluation if the pointer cannot be
371 /// determined to be null or not. See [`is_null`] for more information.
372 ///
373 /// [`is_null`]: #method.is_null-1
374 ///
375 /// # Examples
376 ///
377 /// ```
378 /// #![feature(ptr_as_uninit)]
379 ///
380 /// let ptr: *mut u8 = &mut 10u8 as *mut u8;
381 ///
382 /// unsafe {
383 /// if let Some(val_back) = ptr.as_uninit_ref() {
384 /// println!("We got back the value: {}!", val_back.assume_init());
385 /// }
386 /// }
387 /// ```
388 #[inline]
389 #[unstable(feature = "ptr_as_uninit", issue = "75402")]
390 pub const unsafe fn as_uninit_ref<'a>(self) -> Option<&'a MaybeUninit<T>>
391 where
392 T: Sized,
393 {
394 // SAFETY: the caller must guarantee that `self` meets all the
395 // requirements for a reference.
396 if self.is_null() { None } else { Some(unsafe { &*(self as *const MaybeUninit<T>) }) }
397 }
398
399 /// Adds a signed offset to a pointer.
400 ///
401 /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
402 /// offset of `3 * size_of::<T>()` bytes.
403 ///
404 /// # Safety
405 ///
406 /// If any of the following conditions are violated, the result is Undefined Behavior:
407 ///
408 /// * The offset in bytes, `count * size_of::<T>()`, computed on mathematical integers (without
409 /// "wrapping around"), must fit in an `isize`.
410 ///
411 /// * If the computed offset is non-zero, then `self` must be [derived from][crate::ptr#provenance] a pointer to some
412 /// [allocated object], and the entire memory range between `self` and the result must be in
413 /// bounds of that allocated object. In particular, this range must not "wrap around" the edge
414 /// of the address space.
415 ///
416 /// Allocated objects can never be larger than `isize::MAX` bytes, so if the computed offset
417 /// stays in bounds of the allocated object, it is guaranteed to satisfy the first requirement.
418 /// This implies, for instance, that `vec.as_ptr().add(vec.len())` (for `vec: Vec<T>`) is always
419 /// safe.
420 ///
421 /// Consider using [`wrapping_offset`] instead if these constraints are
422 /// difficult to satisfy. The only advantage of this method is that it
423 /// enables more aggressive compiler optimizations.
424 ///
425 /// [`wrapping_offset`]: #method.wrapping_offset
426 /// [allocated object]: crate::ptr#allocated-object
427 ///
428 /// # Examples
429 ///
430 /// ```
431 /// let mut s = [1, 2, 3];
432 /// let ptr: *mut u32 = s.as_mut_ptr();
433 ///
434 /// unsafe {
435 /// assert_eq!(2, *ptr.offset(1));
436 /// assert_eq!(3, *ptr.offset(2));
437 /// }
438 /// ```
439 #[stable(feature = "rust1", since = "1.0.0")]
440 #[must_use = "returns a new pointer rather than modifying its argument"]
441 #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
442 #[inline(always)]
443 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
444 pub const unsafe fn offset(self, count: isize) -> *mut T
445 where
446 T: Sized,
447 {
448 #[inline]
449 #[rustc_allow_const_fn_unstable(const_eval_select)]
450 const fn runtime_offset_nowrap(this: *const (), count: isize, size: usize) -> bool {
451 // We can use const_eval_select here because this is only for UB checks.
452 const_eval_select!(
453 @capture { this: *const (), count: isize, size: usize } -> bool:
454 if const {
455 true
456 } else {
457 // `size` is the size of a Rust type, so we know that
458 // `size <= isize::MAX` and thus `as` cast here is not lossy.
459 let Some(byte_offset) = count.checked_mul(size as isize) else {
460 return false;
461 };
462 let (_, overflow) = this.addr().overflowing_add_signed(byte_offset);
463 !overflow
464 }
465 )
466 }
467
468 ub_checks::assert_unsafe_precondition!(
469 check_language_ub,
470 "ptr::offset requires the address calculation to not overflow",
471 (
472 this: *const () = self as *const (),
473 count: isize = count,
474 size: usize = size_of::<T>(),
475 ) => runtime_offset_nowrap(this, count, size)
476 );
477
478 // SAFETY: the caller must uphold the safety contract for `offset`.
479 // The obtained pointer is valid for writes since the caller must
480 // guarantee that it points to the same allocated object as `self`.
481 unsafe { intrinsics::offset(self, count) }
482 }
483
484 /// Adds a signed offset in bytes to a pointer.
485 ///
486 /// `count` is in units of **bytes**.
487 ///
488 /// This is purely a convenience for casting to a `u8` pointer and
489 /// using [offset][pointer::offset] on it. See that method for documentation
490 /// and safety requirements.
491 ///
492 /// For non-`Sized` pointees this operation changes only the data pointer,
493 /// leaving the metadata untouched.
494 #[must_use]
495 #[inline(always)]
496 #[stable(feature = "pointer_byte_offsets", since = "1.75.0")]
497 #[rustc_const_stable(feature = "const_pointer_byte_offsets", since = "1.75.0")]
498 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
499 pub const unsafe fn byte_offset(self, count: isize) -> Self {
500 // SAFETY: the caller must uphold the safety contract for `offset`.
501 unsafe { self.cast::<u8>().offset(count).with_metadata_of(self) }
502 }
503
504 /// Adds a signed offset to a pointer using wrapping arithmetic.
505 ///
506 /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
507 /// offset of `3 * size_of::<T>()` bytes.
508 ///
509 /// # Safety
510 ///
511 /// This operation itself is always safe, but using the resulting pointer is not.
512 ///
513 /// The resulting pointer "remembers" the [allocated object] that `self` points to
514 /// (this is called "[Provenance](ptr/index.html#provenance)").
515 /// The pointer must not be used to read or write other allocated objects.
516 ///
517 /// In other words, `let z = x.wrapping_offset((y as isize) - (x as isize))` does *not* make `z`
518 /// the same as `y` even if we assume `T` has size `1` and there is no overflow: `z` is still
519 /// attached to the object `x` is attached to, and dereferencing it is Undefined Behavior unless
520 /// `x` and `y` point into the same allocated object.
521 ///
522 /// Compared to [`offset`], this method basically delays the requirement of staying within the
523 /// same allocated object: [`offset`] is immediate Undefined Behavior when crossing object
524 /// boundaries; `wrapping_offset` produces a pointer but still leads to Undefined Behavior if a
525 /// pointer is dereferenced when it is out-of-bounds of the object it is attached to. [`offset`]
526 /// can be optimized better and is thus preferable in performance-sensitive code.
527 ///
528 /// The delayed check only considers the value of the pointer that was dereferenced, not the
529 /// intermediate values used during the computation of the final result. For example,
530 /// `x.wrapping_offset(o).wrapping_offset(o.wrapping_neg())` is always the same as `x`. In other
531 /// words, leaving the allocated object and then re-entering it later is permitted.
532 ///
533 /// [`offset`]: #method.offset
534 /// [allocated object]: crate::ptr#allocated-object
535 ///
536 /// # Examples
537 ///
538 /// ```
539 /// // Iterate using a raw pointer in increments of two elements
540 /// let mut data = [1u8, 2, 3, 4, 5];
541 /// let mut ptr: *mut u8 = data.as_mut_ptr();
542 /// let step = 2;
543 /// let end_rounded_up = ptr.wrapping_offset(6);
544 ///
545 /// while ptr != end_rounded_up {
546 /// unsafe {
547 /// *ptr = 0;
548 /// }
549 /// ptr = ptr.wrapping_offset(step);
550 /// }
551 /// assert_eq!(&data, &[0, 2, 0, 4, 0]);
552 /// ```
553 #[stable(feature = "ptr_wrapping_offset", since = "1.16.0")]
554 #[must_use = "returns a new pointer rather than modifying its argument"]
555 #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
556 #[inline(always)]
557 pub const fn wrapping_offset(self, count: isize) -> *mut T
558 where
559 T: Sized,
560 {
561 // SAFETY: the `arith_offset` intrinsic has no prerequisites to be called.
562 unsafe { intrinsics::arith_offset(self, count) as *mut T }
563 }
564
565 /// Adds a signed offset in bytes to a pointer using wrapping arithmetic.
566 ///
567 /// `count` is in units of **bytes**.
568 ///
569 /// This is purely a convenience for casting to a `u8` pointer and
570 /// using [wrapping_offset][pointer::wrapping_offset] on it. See that method
571 /// for documentation.
572 ///
573 /// For non-`Sized` pointees this operation changes only the data pointer,
574 /// leaving the metadata untouched.
575 #[must_use]
576 #[inline(always)]
577 #[stable(feature = "pointer_byte_offsets", since = "1.75.0")]
578 #[rustc_const_stable(feature = "const_pointer_byte_offsets", since = "1.75.0")]
579 pub const fn wrapping_byte_offset(self, count: isize) -> Self {
580 self.cast::<u8>().wrapping_offset(count).with_metadata_of(self)
581 }
582
583 /// Masks out bits of the pointer according to a mask.
584 ///
585 /// This is convenience for `ptr.map_addr(|a| a & mask)`.
586 ///
587 /// For non-`Sized` pointees this operation changes only the data pointer,
588 /// leaving the metadata untouched.
589 ///
590 /// ## Examples
591 ///
592 /// ```
593 /// #![feature(ptr_mask)]
594 /// let mut v = 17_u32;
595 /// let ptr: *mut u32 = &mut v;
596 ///
597 /// // `u32` is 4 bytes aligned,
598 /// // which means that lower 2 bits are always 0.
599 /// let tag_mask = 0b11;
600 /// let ptr_mask = !tag_mask;
601 ///
602 /// // We can store something in these lower bits
603 /// let tagged_ptr = ptr.map_addr(|a| a | 0b10);
604 ///
605 /// // Get the "tag" back
606 /// let tag = tagged_ptr.addr() & tag_mask;
607 /// assert_eq!(tag, 0b10);
608 ///
609 /// // Note that `tagged_ptr` is unaligned, it's UB to read from/write to it.
610 /// // To get original pointer `mask` can be used:
611 /// let masked_ptr = tagged_ptr.mask(ptr_mask);
612 /// assert_eq!(unsafe { *masked_ptr }, 17);
613 ///
614 /// unsafe { *masked_ptr = 0 };
615 /// assert_eq!(v, 0);
616 /// ```
617 #[unstable(feature = "ptr_mask", issue = "98290")]
618 #[must_use = "returns a new pointer rather than modifying its argument"]
619 #[inline(always)]
620 pub fn mask(self, mask: usize) -> *mut T {
621 intrinsics::ptr_mask(self.cast::<()>(), mask).cast_mut().with_metadata_of(self)
622 }
623
624 /// Returns `None` if the pointer is null, or else returns a unique reference to
625 /// the value wrapped in `Some`. If the value may be uninitialized, [`as_uninit_mut`]
626 /// must be used instead.
627 ///
628 /// For the shared counterpart see [`as_ref`].
629 ///
630 /// [`as_uninit_mut`]: #method.as_uninit_mut
631 /// [`as_ref`]: pointer#method.as_ref-1
632 ///
633 /// # Safety
634 ///
635 /// When calling this method, you have to ensure that *either*
636 /// the pointer is null *or*
637 /// the pointer is [convertible to a reference](crate::ptr#pointer-to-reference-conversion).
638 ///
639 /// # Panics during const evaluation
640 ///
641 /// This method will panic during const evaluation if the pointer cannot be
642 /// determined to be null or not. See [`is_null`] for more information.
643 ///
644 /// [`is_null`]: #method.is_null-1
645 ///
646 /// # Examples
647 ///
648 /// ```
649 /// let mut s = [1, 2, 3];
650 /// let ptr: *mut u32 = s.as_mut_ptr();
651 /// let first_value = unsafe { ptr.as_mut().unwrap() };
652 /// *first_value = 4;
653 /// # assert_eq!(s, [4, 2, 3]);
654 /// println!("{s:?}"); // It'll print: "[4, 2, 3]".
655 /// ```
656 ///
657 /// # Null-unchecked version
658 ///
659 /// If you are sure the pointer can never be null and are looking for some kind of
660 /// `as_mut_unchecked` that returns the `&mut T` instead of `Option<&mut T>`, know that
661 /// you can dereference the pointer directly.
662 ///
663 /// ```
664 /// let mut s = [1, 2, 3];
665 /// let ptr: *mut u32 = s.as_mut_ptr();
666 /// let first_value = unsafe { &mut *ptr };
667 /// *first_value = 4;
668 /// # assert_eq!(s, [4, 2, 3]);
669 /// println!("{s:?}"); // It'll print: "[4, 2, 3]".
670 /// ```
671 #[stable(feature = "ptr_as_ref", since = "1.9.0")]
672 #[rustc_const_stable(feature = "const_ptr_is_null", since = "1.84.0")]
673 #[inline]
674 pub const unsafe fn as_mut<'a>(self) -> Option<&'a mut T> {
675 // SAFETY: the caller must guarantee that `self` is be valid for
676 // a mutable reference if it isn't null.
677 if self.is_null() { None } else { unsafe { Some(&mut *self) } }
678 }
679
680 /// Returns a unique reference to the value behind the pointer.
681 /// If the pointer may be null or the value may be uninitialized, [`as_uninit_mut`] must be used instead.
682 /// If the pointer may be null, but the value is known to have been initialized, [`as_mut`] must be used instead.
683 ///
684 /// For the shared counterpart see [`as_ref_unchecked`].
685 ///
686 /// [`as_mut`]: #method.as_mut
687 /// [`as_uninit_mut`]: #method.as_uninit_mut
688 /// [`as_ref_unchecked`]: #method.as_mut_unchecked
689 ///
690 /// # Safety
691 ///
692 /// When calling this method, you have to ensure that
693 /// the pointer is [convertible to a reference](crate::ptr#pointer-to-reference-conversion).
694 ///
695 /// # Examples
696 ///
697 /// ```
698 /// #![feature(ptr_as_ref_unchecked)]
699 /// let mut s = [1, 2, 3];
700 /// let ptr: *mut u32 = s.as_mut_ptr();
701 /// let first_value = unsafe { ptr.as_mut_unchecked() };
702 /// *first_value = 4;
703 /// # assert_eq!(s, [4, 2, 3]);
704 /// println!("{s:?}"); // It'll print: "[4, 2, 3]".
705 /// ```
706 // FIXME: mention it in the docs for `as_mut` and `as_uninit_mut` once stabilized.
707 #[unstable(feature = "ptr_as_ref_unchecked", issue = "122034")]
708 #[inline]
709 #[must_use]
710 pub const unsafe fn as_mut_unchecked<'a>(self) -> &'a mut T {
711 // SAFETY: the caller must guarantee that `self` is valid for a reference
712 unsafe { &mut *self }
713 }
714
715 /// Returns `None` if the pointer is null, or else returns a unique reference to
716 /// the value wrapped in `Some`. In contrast to [`as_mut`], this does not require
717 /// that the value has to be initialized.
718 ///
719 /// For the shared counterpart see [`as_uninit_ref`].
720 ///
721 /// [`as_mut`]: #method.as_mut
722 /// [`as_uninit_ref`]: pointer#method.as_uninit_ref-1
723 ///
724 /// # Safety
725 ///
726 /// When calling this method, you have to ensure that *either* the pointer is null *or*
727 /// the pointer is [convertible to a reference](crate::ptr#pointer-to-reference-conversion).
728 ///
729 /// # Panics during const evaluation
730 ///
731 /// This method will panic during const evaluation if the pointer cannot be
732 /// determined to be null or not. See [`is_null`] for more information.
733 ///
734 /// [`is_null`]: #method.is_null-1
735 #[inline]
736 #[unstable(feature = "ptr_as_uninit", issue = "75402")]
737 pub const unsafe fn as_uninit_mut<'a>(self) -> Option<&'a mut MaybeUninit<T>>
738 where
739 T: Sized,
740 {
741 // SAFETY: the caller must guarantee that `self` meets all the
742 // requirements for a reference.
743 if self.is_null() { None } else { Some(unsafe { &mut *(self as *mut MaybeUninit<T>) }) }
744 }
745
746 /// Returns whether two pointers are guaranteed to be equal.
747 ///
748 /// At runtime this function behaves like `Some(self == other)`.
749 /// However, in some contexts (e.g., compile-time evaluation),
750 /// it is not always possible to determine equality of two pointers, so this function may
751 /// spuriously return `None` for pointers that later actually turn out to have its equality known.
752 /// But when it returns `Some`, the pointers' equality is guaranteed to be known.
753 ///
754 /// The return value may change from `Some` to `None` and vice versa depending on the compiler
755 /// version and unsafe code must not
756 /// rely on the result of this function for soundness. It is suggested to only use this function
757 /// for performance optimizations where spurious `None` return values by this function do not
758 /// affect the outcome, but just the performance.
759 /// The consequences of using this method to make runtime and compile-time code behave
760 /// differently have not been explored. This method should not be used to introduce such
761 /// differences, and it should also not be stabilized before we have a better understanding
762 /// of this issue.
763 #[unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
764 #[rustc_const_unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
765 #[inline]
766 pub const fn guaranteed_eq(self, other: *mut T) -> Option<bool>
767 where
768 T: Sized,
769 {
770 (self as *const T).guaranteed_eq(other as _)
771 }
772
773 /// Returns whether two pointers are guaranteed to be inequal.
774 ///
775 /// At runtime this function behaves like `Some(self != other)`.
776 /// However, in some contexts (e.g., compile-time evaluation),
777 /// it is not always possible to determine inequality of two pointers, so this function may
778 /// spuriously return `None` for pointers that later actually turn out to have its inequality known.
779 /// But when it returns `Some`, the pointers' inequality is guaranteed to be known.
780 ///
781 /// The return value may change from `Some` to `None` and vice versa depending on the compiler
782 /// version and unsafe code must not
783 /// rely on the result of this function for soundness. It is suggested to only use this function
784 /// for performance optimizations where spurious `None` return values by this function do not
785 /// affect the outcome, but just the performance.
786 /// The consequences of using this method to make runtime and compile-time code behave
787 /// differently have not been explored. This method should not be used to introduce such
788 /// differences, and it should also not be stabilized before we have a better understanding
789 /// of this issue.
790 #[unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
791 #[rustc_const_unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
792 #[inline]
793 pub const fn guaranteed_ne(self, other: *mut T) -> Option<bool>
794 where
795 T: Sized,
796 {
797 (self as *const T).guaranteed_ne(other as _)
798 }
799
800 /// Calculates the distance between two pointers within the same allocation. The returned value is in
801 /// units of T: the distance in bytes divided by `size_of::<T>()`.
802 ///
803 /// This is equivalent to `(self as isize - origin as isize) / (size_of::<T>() as isize)`,
804 /// except that it has a lot more opportunities for UB, in exchange for the compiler
805 /// better understanding what you are doing.
806 ///
807 /// The primary motivation of this method is for computing the `len` of an array/slice
808 /// of `T` that you are currently representing as a "start" and "end" pointer
809 /// (and "end" is "one past the end" of the array).
810 /// In that case, `end.offset_from(start)` gets you the length of the array.
811 ///
812 /// All of the following safety requirements are trivially satisfied for this usecase.
813 ///
814 /// [`offset`]: pointer#method.offset-1
815 ///
816 /// # Safety
817 ///
818 /// If any of the following conditions are violated, the result is Undefined Behavior:
819 ///
820 /// * `self` and `origin` must either
821 ///
822 /// * point to the same address, or
823 /// * both be [derived from][crate::ptr#provenance] a pointer to the same [allocated object], and the memory range between
824 /// the two pointers must be in bounds of that object. (See below for an example.)
825 ///
826 /// * The distance between the pointers, in bytes, must be an exact multiple
827 /// of the size of `T`.
828 ///
829 /// As a consequence, the absolute distance between the pointers, in bytes, computed on
830 /// mathematical integers (without "wrapping around"), cannot overflow an `isize`. This is
831 /// implied by the in-bounds requirement, and the fact that no allocated object can be larger
832 /// than `isize::MAX` bytes.
833 ///
834 /// The requirement for pointers to be derived from the same allocated object is primarily
835 /// needed for `const`-compatibility: the distance between pointers into *different* allocated
836 /// objects is not known at compile-time. However, the requirement also exists at
837 /// runtime and may be exploited by optimizations. If you wish to compute the difference between
838 /// pointers that are not guaranteed to be from the same allocation, use `(self as isize -
839 /// origin as isize) / size_of::<T>()`.
840 // FIXME: recommend `addr()` instead of `as usize` once that is stable.
841 ///
842 /// [`add`]: #method.add
843 /// [allocated object]: crate::ptr#allocated-object
844 ///
845 /// # Panics
846 ///
847 /// This function panics if `T` is a Zero-Sized Type ("ZST").
848 ///
849 /// # Examples
850 ///
851 /// Basic usage:
852 ///
853 /// ```
854 /// let mut a = [0; 5];
855 /// let ptr1: *mut i32 = &mut a[1];
856 /// let ptr2: *mut i32 = &mut a[3];
857 /// unsafe {
858 /// assert_eq!(ptr2.offset_from(ptr1), 2);
859 /// assert_eq!(ptr1.offset_from(ptr2), -2);
860 /// assert_eq!(ptr1.offset(2), ptr2);
861 /// assert_eq!(ptr2.offset(-2), ptr1);
862 /// }
863 /// ```
864 ///
865 /// *Incorrect* usage:
866 ///
867 /// ```rust,no_run
868 /// let ptr1 = Box::into_raw(Box::new(0u8));
869 /// let ptr2 = Box::into_raw(Box::new(1u8));
870 /// let diff = (ptr2 as isize).wrapping_sub(ptr1 as isize);
871 /// // Make ptr2_other an "alias" of ptr2.add(1), but derived from ptr1.
872 /// let ptr2_other = (ptr1 as *mut u8).wrapping_offset(diff).wrapping_offset(1);
873 /// assert_eq!(ptr2 as usize, ptr2_other as usize);
874 /// // Since ptr2_other and ptr2 are derived from pointers to different objects,
875 /// // computing their offset is undefined behavior, even though
876 /// // they point to addresses that are in-bounds of the same object!
877 /// unsafe {
878 /// let one = ptr2_other.offset_from(ptr2); // Undefined Behavior! ⚠️
879 /// }
880 /// ```
881 #[stable(feature = "ptr_offset_from", since = "1.47.0")]
882 #[rustc_const_stable(feature = "const_ptr_offset_from", since = "1.65.0")]
883 #[inline(always)]
884 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
885 pub const unsafe fn offset_from(self, origin: *const T) -> isize
886 where
887 T: Sized,
888 {
889 // SAFETY: the caller must uphold the safety contract for `offset_from`.
890 unsafe { (self as *const T).offset_from(origin) }
891 }
892
893 /// Calculates the distance between two pointers within the same allocation. The returned value is in
894 /// units of **bytes**.
895 ///
896 /// This is purely a convenience for casting to a `u8` pointer and
897 /// using [`offset_from`][pointer::offset_from] on it. See that method for
898 /// documentation and safety requirements.
899 ///
900 /// For non-`Sized` pointees this operation considers only the data pointers,
901 /// ignoring the metadata.
902 #[inline(always)]
903 #[stable(feature = "pointer_byte_offsets", since = "1.75.0")]
904 #[rustc_const_stable(feature = "const_pointer_byte_offsets", since = "1.75.0")]
905 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
906 pub const unsafe fn byte_offset_from<U: ?Sized>(self, origin: *const U) -> isize {
907 // SAFETY: the caller must uphold the safety contract for `offset_from`.
908 unsafe { self.cast::<u8>().offset_from(origin.cast::<u8>()) }
909 }
910
911 /// Calculates the distance between two pointers within the same allocation, *where it's known that
912 /// `self` is equal to or greater than `origin`*. The returned value is in
913 /// units of T: the distance in bytes is divided by `size_of::<T>()`.
914 ///
915 /// This computes the same value that [`offset_from`](#method.offset_from)
916 /// would compute, but with the added precondition that the offset is
917 /// guaranteed to be non-negative. This method is equivalent to
918 /// `usize::try_from(self.offset_from(origin)).unwrap_unchecked()`,
919 /// but it provides slightly more information to the optimizer, which can
920 /// sometimes allow it to optimize slightly better with some backends.
921 ///
922 /// This method can be thought of as recovering the `count` that was passed
923 /// to [`add`](#method.add) (or, with the parameters in the other order,
924 /// to [`sub`](#method.sub)). The following are all equivalent, assuming
925 /// that their safety preconditions are met:
926 /// ```rust
927 /// # unsafe fn blah(ptr: *mut i32, origin: *mut i32, count: usize) -> bool { unsafe {
928 /// ptr.offset_from_unsigned(origin) == count
929 /// # &&
930 /// origin.add(count) == ptr
931 /// # &&
932 /// ptr.sub(count) == origin
933 /// # } }
934 /// ```
935 ///
936 /// # Safety
937 ///
938 /// - The distance between the pointers must be non-negative (`self >= origin`)
939 ///
940 /// - *All* the safety conditions of [`offset_from`](#method.offset_from)
941 /// apply to this method as well; see it for the full details.
942 ///
943 /// Importantly, despite the return type of this method being able to represent
944 /// a larger offset, it's still *not permitted* to pass pointers which differ
945 /// by more than `isize::MAX` *bytes*. As such, the result of this method will
946 /// always be less than or equal to `isize::MAX as usize`.
947 ///
948 /// # Panics
949 ///
950 /// This function panics if `T` is a Zero-Sized Type ("ZST").
951 ///
952 /// # Examples
953 ///
954 /// ```
955 /// let mut a = [0; 5];
956 /// let p: *mut i32 = a.as_mut_ptr();
957 /// unsafe {
958 /// let ptr1: *mut i32 = p.add(1);
959 /// let ptr2: *mut i32 = p.add(3);
960 ///
961 /// assert_eq!(ptr2.offset_from_unsigned(ptr1), 2);
962 /// assert_eq!(ptr1.add(2), ptr2);
963 /// assert_eq!(ptr2.sub(2), ptr1);
964 /// assert_eq!(ptr2.offset_from_unsigned(ptr2), 0);
965 /// }
966 ///
967 /// // This would be incorrect, as the pointers are not correctly ordered:
968 /// // ptr1.offset_from(ptr2)
969 /// ```
970 #[stable(feature = "ptr_sub_ptr", since = "1.87.0")]
971 #[rustc_const_stable(feature = "const_ptr_sub_ptr", since = "1.87.0")]
972 #[inline]
973 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
974 pub const unsafe fn offset_from_unsigned(self, origin: *const T) -> usize
975 where
976 T: Sized,
977 {
978 // SAFETY: the caller must uphold the safety contract for `offset_from_unsigned`.
979 unsafe { (self as *const T).offset_from_unsigned(origin) }
980 }
981
982 /// Calculates the distance between two pointers within the same allocation, *where it's known that
983 /// `self` is equal to or greater than `origin`*. The returned value is in
984 /// units of **bytes**.
985 ///
986 /// This is purely a convenience for casting to a `u8` pointer and
987 /// using [`offset_from_unsigned`][pointer::offset_from_unsigned] on it.
988 /// See that method for documentation and safety requirements.
989 ///
990 /// For non-`Sized` pointees this operation considers only the data pointers,
991 /// ignoring the metadata.
992 #[stable(feature = "ptr_sub_ptr", since = "1.87.0")]
993 #[rustc_const_stable(feature = "const_ptr_sub_ptr", since = "1.87.0")]
994 #[inline]
995 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
996 pub const unsafe fn byte_offset_from_unsigned<U: ?Sized>(self, origin: *mut U) -> usize {
997 // SAFETY: the caller must uphold the safety contract for `byte_offset_from_unsigned`.
998 unsafe { (self as *const T).byte_offset_from_unsigned(origin) }
999 }
1000
1001 /// Adds an unsigned offset to a pointer.
1002 ///
1003 /// This can only move the pointer forward (or not move it). If you need to move forward or
1004 /// backward depending on the value, then you might want [`offset`](#method.offset) instead
1005 /// which takes a signed offset.
1006 ///
1007 /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
1008 /// offset of `3 * size_of::<T>()` bytes.
1009 ///
1010 /// # Safety
1011 ///
1012 /// If any of the following conditions are violated, the result is Undefined Behavior:
1013 ///
1014 /// * The offset in bytes, `count * size_of::<T>()`, computed on mathematical integers (without
1015 /// "wrapping around"), must fit in an `isize`.
1016 ///
1017 /// * If the computed offset is non-zero, then `self` must be [derived from][crate::ptr#provenance] a pointer to some
1018 /// [allocated object], and the entire memory range between `self` and the result must be in
1019 /// bounds of that allocated object. In particular, this range must not "wrap around" the edge
1020 /// of the address space.
1021 ///
1022 /// Allocated objects can never be larger than `isize::MAX` bytes, so if the computed offset
1023 /// stays in bounds of the allocated object, it is guaranteed to satisfy the first requirement.
1024 /// This implies, for instance, that `vec.as_ptr().add(vec.len())` (for `vec: Vec<T>`) is always
1025 /// safe.
1026 ///
1027 /// Consider using [`wrapping_add`] instead if these constraints are
1028 /// difficult to satisfy. The only advantage of this method is that it
1029 /// enables more aggressive compiler optimizations.
1030 ///
1031 /// [`wrapping_add`]: #method.wrapping_add
1032 /// [allocated object]: crate::ptr#allocated-object
1033 ///
1034 /// # Examples
1035 ///
1036 /// ```
1037 /// let s: &str = "123";
1038 /// let ptr: *const u8 = s.as_ptr();
1039 ///
1040 /// unsafe {
1041 /// assert_eq!('2', *ptr.add(1) as char);
1042 /// assert_eq!('3', *ptr.add(2) as char);
1043 /// }
1044 /// ```
1045 #[stable(feature = "pointer_methods", since = "1.26.0")]
1046 #[must_use = "returns a new pointer rather than modifying its argument"]
1047 #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
1048 #[inline(always)]
1049 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
1050 pub const unsafe fn add(self, count: usize) -> Self
1051 where
1052 T: Sized,
1053 {
1054 #[cfg(debug_assertions)]
1055 #[inline]
1056 #[rustc_allow_const_fn_unstable(const_eval_select)]
1057 const fn runtime_add_nowrap(this: *const (), count: usize, size: usize) -> bool {
1058 const_eval_select!(
1059 @capture { this: *const (), count: usize, size: usize } -> bool:
1060 if const {
1061 true
1062 } else {
1063 let Some(byte_offset) = count.checked_mul(size) else {
1064 return false;
1065 };
1066 let (_, overflow) = this.addr().overflowing_add(byte_offset);
1067 byte_offset <= (isize::MAX as usize) && !overflow
1068 }
1069 )
1070 }
1071
1072 #[cfg(debug_assertions)] // Expensive, and doesn't catch much in the wild.
1073 ub_checks::assert_unsafe_precondition!(
1074 check_language_ub,
1075 "ptr::add requires that the address calculation does not overflow",
1076 (
1077 this: *const () = self as *const (),
1078 count: usize = count,
1079 size: usize = size_of::<T>(),
1080 ) => runtime_add_nowrap(this, count, size)
1081 );
1082
1083 // SAFETY: the caller must uphold the safety contract for `offset`.
1084 unsafe { intrinsics::offset(self, count) }
1085 }
1086
1087 /// Adds an unsigned offset in bytes to a pointer.
1088 ///
1089 /// `count` is in units of bytes.
1090 ///
1091 /// This is purely a convenience for casting to a `u8` pointer and
1092 /// using [add][pointer::add] on it. See that method for documentation
1093 /// and safety requirements.
1094 ///
1095 /// For non-`Sized` pointees this operation changes only the data pointer,
1096 /// leaving the metadata untouched.
1097 #[must_use]
1098 #[inline(always)]
1099 #[stable(feature = "pointer_byte_offsets", since = "1.75.0")]
1100 #[rustc_const_stable(feature = "const_pointer_byte_offsets", since = "1.75.0")]
1101 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
1102 pub const unsafe fn byte_add(self, count: usize) -> Self {
1103 // SAFETY: the caller must uphold the safety contract for `add`.
1104 unsafe { self.cast::<u8>().add(count).with_metadata_of(self) }
1105 }
1106
1107 /// Subtracts an unsigned offset from a pointer.
1108 ///
1109 /// This can only move the pointer backward (or not move it). If you need to move forward or
1110 /// backward depending on the value, then you might want [`offset`](#method.offset) instead
1111 /// which takes a signed offset.
1112 ///
1113 /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
1114 /// offset of `3 * size_of::<T>()` bytes.
1115 ///
1116 /// # Safety
1117 ///
1118 /// If any of the following conditions are violated, the result is Undefined Behavior:
1119 ///
1120 /// * The offset in bytes, `count * size_of::<T>()`, computed on mathematical integers (without
1121 /// "wrapping around"), must fit in an `isize`.
1122 ///
1123 /// * If the computed offset is non-zero, then `self` must be [derived from][crate::ptr#provenance] a pointer to some
1124 /// [allocated object], and the entire memory range between `self` and the result must be in
1125 /// bounds of that allocated object. In particular, this range must not "wrap around" the edge
1126 /// of the address space.
1127 ///
1128 /// Allocated objects can never be larger than `isize::MAX` bytes, so if the computed offset
1129 /// stays in bounds of the allocated object, it is guaranteed to satisfy the first requirement.
1130 /// This implies, for instance, that `vec.as_ptr().add(vec.len())` (for `vec: Vec<T>`) is always
1131 /// safe.
1132 ///
1133 /// Consider using [`wrapping_sub`] instead if these constraints are
1134 /// difficult to satisfy. The only advantage of this method is that it
1135 /// enables more aggressive compiler optimizations.
1136 ///
1137 /// [`wrapping_sub`]: #method.wrapping_sub
1138 /// [allocated object]: crate::ptr#allocated-object
1139 ///
1140 /// # Examples
1141 ///
1142 /// ```
1143 /// let s: &str = "123";
1144 ///
1145 /// unsafe {
1146 /// let end: *const u8 = s.as_ptr().add(3);
1147 /// assert_eq!('3', *end.sub(1) as char);
1148 /// assert_eq!('2', *end.sub(2) as char);
1149 /// }
1150 /// ```
1151 #[stable(feature = "pointer_methods", since = "1.26.0")]
1152 #[must_use = "returns a new pointer rather than modifying its argument"]
1153 #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
1154 #[inline(always)]
1155 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
1156 pub const unsafe fn sub(self, count: usize) -> Self
1157 where
1158 T: Sized,
1159 {
1160 #[cfg(debug_assertions)]
1161 #[inline]
1162 #[rustc_allow_const_fn_unstable(const_eval_select)]
1163 const fn runtime_sub_nowrap(this: *const (), count: usize, size: usize) -> bool {
1164 const_eval_select!(
1165 @capture { this: *const (), count: usize, size: usize } -> bool:
1166 if const {
1167 true
1168 } else {
1169 let Some(byte_offset) = count.checked_mul(size) else {
1170 return false;
1171 };
1172 byte_offset <= (isize::MAX as usize) && this.addr() >= byte_offset
1173 }
1174 )
1175 }
1176
1177 #[cfg(debug_assertions)] // Expensive, and doesn't catch much in the wild.
1178 ub_checks::assert_unsafe_precondition!(
1179 check_language_ub,
1180 "ptr::sub requires that the address calculation does not overflow",
1181 (
1182 this: *const () = self as *const (),
1183 count: usize = count,
1184 size: usize = size_of::<T>(),
1185 ) => runtime_sub_nowrap(this, count, size)
1186 );
1187
1188 if T::IS_ZST {
1189 // Pointer arithmetic does nothing when the pointee is a ZST.
1190 self
1191 } else {
1192 // SAFETY: the caller must uphold the safety contract for `offset`.
1193 // Because the pointee is *not* a ZST, that means that `count` is
1194 // at most `isize::MAX`, and thus the negation cannot overflow.
1195 unsafe { intrinsics::offset(self, intrinsics::unchecked_sub(0, count as isize)) }
1196 }
1197 }
1198
1199 /// Subtracts an unsigned offset in bytes from a pointer.
1200 ///
1201 /// `count` is in units of bytes.
1202 ///
1203 /// This is purely a convenience for casting to a `u8` pointer and
1204 /// using [sub][pointer::sub] on it. See that method for documentation
1205 /// and safety requirements.
1206 ///
1207 /// For non-`Sized` pointees this operation changes only the data pointer,
1208 /// leaving the metadata untouched.
1209 #[must_use]
1210 #[inline(always)]
1211 #[stable(feature = "pointer_byte_offsets", since = "1.75.0")]
1212 #[rustc_const_stable(feature = "const_pointer_byte_offsets", since = "1.75.0")]
1213 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
1214 pub const unsafe fn byte_sub(self, count: usize) -> Self {
1215 // SAFETY: the caller must uphold the safety contract for `sub`.
1216 unsafe { self.cast::<u8>().sub(count).with_metadata_of(self) }
1217 }
1218
1219 /// Adds an unsigned offset to a pointer using wrapping arithmetic.
1220 ///
1221 /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
1222 /// offset of `3 * size_of::<T>()` bytes.
1223 ///
1224 /// # Safety
1225 ///
1226 /// This operation itself is always safe, but using the resulting pointer is not.
1227 ///
1228 /// The resulting pointer "remembers" the [allocated object] that `self` points to; it must not
1229 /// be used to read or write other allocated objects.
1230 ///
1231 /// In other words, `let z = x.wrapping_add((y as usize) - (x as usize))` does *not* make `z`
1232 /// the same as `y` even if we assume `T` has size `1` and there is no overflow: `z` is still
1233 /// attached to the object `x` is attached to, and dereferencing it is Undefined Behavior unless
1234 /// `x` and `y` point into the same allocated object.
1235 ///
1236 /// Compared to [`add`], this method basically delays the requirement of staying within the
1237 /// same allocated object: [`add`] is immediate Undefined Behavior when crossing object
1238 /// boundaries; `wrapping_add` produces a pointer but still leads to Undefined Behavior if a
1239 /// pointer is dereferenced when it is out-of-bounds of the object it is attached to. [`add`]
1240 /// can be optimized better and is thus preferable in performance-sensitive code.
1241 ///
1242 /// The delayed check only considers the value of the pointer that was dereferenced, not the
1243 /// intermediate values used during the computation of the final result. For example,
1244 /// `x.wrapping_add(o).wrapping_sub(o)` is always the same as `x`. In other words, leaving the
1245 /// allocated object and then re-entering it later is permitted.
1246 ///
1247 /// [`add`]: #method.add
1248 /// [allocated object]: crate::ptr#allocated-object
1249 ///
1250 /// # Examples
1251 ///
1252 /// ```
1253 /// // Iterate using a raw pointer in increments of two elements
1254 /// let data = [1u8, 2, 3, 4, 5];
1255 /// let mut ptr: *const u8 = data.as_ptr();
1256 /// let step = 2;
1257 /// let end_rounded_up = ptr.wrapping_add(6);
1258 ///
1259 /// // This loop prints "1, 3, 5, "
1260 /// while ptr != end_rounded_up {
1261 /// unsafe {
1262 /// print!("{}, ", *ptr);
1263 /// }
1264 /// ptr = ptr.wrapping_add(step);
1265 /// }
1266 /// ```
1267 #[stable(feature = "pointer_methods", since = "1.26.0")]
1268 #[must_use = "returns a new pointer rather than modifying its argument"]
1269 #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
1270 #[inline(always)]
1271 pub const fn wrapping_add(self, count: usize) -> Self
1272 where
1273 T: Sized,
1274 {
1275 self.wrapping_offset(count as isize)
1276 }
1277
1278 /// Adds an unsigned offset in bytes to a pointer using wrapping arithmetic.
1279 ///
1280 /// `count` is in units of bytes.
1281 ///
1282 /// This is purely a convenience for casting to a `u8` pointer and
1283 /// using [wrapping_add][pointer::wrapping_add] on it. See that method for documentation.
1284 ///
1285 /// For non-`Sized` pointees this operation changes only the data pointer,
1286 /// leaving the metadata untouched.
1287 #[must_use]
1288 #[inline(always)]
1289 #[stable(feature = "pointer_byte_offsets", since = "1.75.0")]
1290 #[rustc_const_stable(feature = "const_pointer_byte_offsets", since = "1.75.0")]
1291 pub const fn wrapping_byte_add(self, count: usize) -> Self {
1292 self.cast::<u8>().wrapping_add(count).with_metadata_of(self)
1293 }
1294
1295 /// Subtracts an unsigned offset from a pointer using wrapping arithmetic.
1296 ///
1297 /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
1298 /// offset of `3 * size_of::<T>()` bytes.
1299 ///
1300 /// # Safety
1301 ///
1302 /// This operation itself is always safe, but using the resulting pointer is not.
1303 ///
1304 /// The resulting pointer "remembers" the [allocated object] that `self` points to; it must not
1305 /// be used to read or write other allocated objects.
1306 ///
1307 /// In other words, `let z = x.wrapping_sub((x as usize) - (y as usize))` does *not* make `z`
1308 /// the same as `y` even if we assume `T` has size `1` and there is no overflow: `z` is still
1309 /// attached to the object `x` is attached to, and dereferencing it is Undefined Behavior unless
1310 /// `x` and `y` point into the same allocated object.
1311 ///
1312 /// Compared to [`sub`], this method basically delays the requirement of staying within the
1313 /// same allocated object: [`sub`] is immediate Undefined Behavior when crossing object
1314 /// boundaries; `wrapping_sub` produces a pointer but still leads to Undefined Behavior if a
1315 /// pointer is dereferenced when it is out-of-bounds of the object it is attached to. [`sub`]
1316 /// can be optimized better and is thus preferable in performance-sensitive code.
1317 ///
1318 /// The delayed check only considers the value of the pointer that was dereferenced, not the
1319 /// intermediate values used during the computation of the final result. For example,
1320 /// `x.wrapping_add(o).wrapping_sub(o)` is always the same as `x`. In other words, leaving the
1321 /// allocated object and then re-entering it later is permitted.
1322 ///
1323 /// [`sub`]: #method.sub
1324 /// [allocated object]: crate::ptr#allocated-object
1325 ///
1326 /// # Examples
1327 ///
1328 /// ```
1329 /// // Iterate using a raw pointer in increments of two elements (backwards)
1330 /// let data = [1u8, 2, 3, 4, 5];
1331 /// let mut ptr: *const u8 = data.as_ptr();
1332 /// let start_rounded_down = ptr.wrapping_sub(2);
1333 /// ptr = ptr.wrapping_add(4);
1334 /// let step = 2;
1335 /// // This loop prints "5, 3, 1, "
1336 /// while ptr != start_rounded_down {
1337 /// unsafe {
1338 /// print!("{}, ", *ptr);
1339 /// }
1340 /// ptr = ptr.wrapping_sub(step);
1341 /// }
1342 /// ```
1343 #[stable(feature = "pointer_methods", since = "1.26.0")]
1344 #[must_use = "returns a new pointer rather than modifying its argument"]
1345 #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
1346 #[inline(always)]
1347 pub const fn wrapping_sub(self, count: usize) -> Self
1348 where
1349 T: Sized,
1350 {
1351 self.wrapping_offset((count as isize).wrapping_neg())
1352 }
1353
1354 /// Subtracts an unsigned offset in bytes from a pointer using wrapping arithmetic.
1355 ///
1356 /// `count` is in units of bytes.
1357 ///
1358 /// This is purely a convenience for casting to a `u8` pointer and
1359 /// using [wrapping_sub][pointer::wrapping_sub] on it. See that method for documentation.
1360 ///
1361 /// For non-`Sized` pointees this operation changes only the data pointer,
1362 /// leaving the metadata untouched.
1363 #[must_use]
1364 #[inline(always)]
1365 #[stable(feature = "pointer_byte_offsets", since = "1.75.0")]
1366 #[rustc_const_stable(feature = "const_pointer_byte_offsets", since = "1.75.0")]
1367 pub const fn wrapping_byte_sub(self, count: usize) -> Self {
1368 self.cast::<u8>().wrapping_sub(count).with_metadata_of(self)
1369 }
1370
1371 /// Reads the value from `self` without moving it. This leaves the
1372 /// memory in `self` unchanged.
1373 ///
1374 /// See [`ptr::read`] for safety concerns and examples.
1375 ///
1376 /// [`ptr::read`]: crate::ptr::read()
1377 #[stable(feature = "pointer_methods", since = "1.26.0")]
1378 #[rustc_const_stable(feature = "const_ptr_read", since = "1.71.0")]
1379 #[inline(always)]
1380 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
1381 pub const unsafe fn read(self) -> T
1382 where
1383 T: Sized,
1384 {
1385 // SAFETY: the caller must uphold the safety contract for ``.
1386 unsafe { read(self) }
1387 }
1388
1389 /// Performs a volatile read of the value from `self` without moving it. This
1390 /// leaves the memory in `self` unchanged.
1391 ///
1392 /// Volatile operations are intended to act on I/O memory, and are guaranteed
1393 /// to not be elided or reordered by the compiler across other volatile
1394 /// operations.
1395 ///
1396 /// See [`ptr::read_volatile`] for safety concerns and examples.
1397 ///
1398 /// [`ptr::read_volatile`]: crate::ptr::read_volatile()
1399 #[stable(feature = "pointer_methods", since = "1.26.0")]
1400 #[inline(always)]
1401 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
1402 pub unsafe fn read_volatile(self) -> T
1403 where
1404 T: Sized,
1405 {
1406 // SAFETY: the caller must uphold the safety contract for `read_volatile`.
1407 unsafe { read_volatile(self) }
1408 }
1409
1410 /// Reads the value from `self` without moving it. This leaves the
1411 /// memory in `self` unchanged.
1412 ///
1413 /// Unlike `read`, the pointer may be unaligned.
1414 ///
1415 /// See [`ptr::read_unaligned`] for safety concerns and examples.
1416 ///
1417 /// [`ptr::read_unaligned`]: crate::ptr::read_unaligned()
1418 #[stable(feature = "pointer_methods", since = "1.26.0")]
1419 #[rustc_const_stable(feature = "const_ptr_read", since = "1.71.0")]
1420 #[inline(always)]
1421 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
1422 pub const unsafe fn read_unaligned(self) -> T
1423 where
1424 T: Sized,
1425 {
1426 // SAFETY: the caller must uphold the safety contract for `read_unaligned`.
1427 unsafe { read_unaligned(self) }
1428 }
1429
1430 /// Copies `count * size_of::<T>()` bytes from `self` to `dest`. The source
1431 /// and destination may overlap.
1432 ///
1433 /// NOTE: this has the *same* argument order as [`ptr::copy`].
1434 ///
1435 /// See [`ptr::copy`] for safety concerns and examples.
1436 ///
1437 /// [`ptr::copy`]: crate::ptr::copy()
1438 #[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.83.0")]
1439 #[stable(feature = "pointer_methods", since = "1.26.0")]
1440 #[inline(always)]
1441 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
1442 pub const unsafe fn copy_to(self, dest: *mut T, count: usize)
1443 where
1444 T: Sized,
1445 {
1446 // SAFETY: the caller must uphold the safety contract for `copy`.
1447 unsafe { copy(self, dest, count) }
1448 }
1449
1450 /// Copies `count * size_of::<T>()` bytes from `self` to `dest`. The source
1451 /// and destination may *not* overlap.
1452 ///
1453 /// NOTE: this has the *same* argument order as [`ptr::copy_nonoverlapping`].
1454 ///
1455 /// See [`ptr::copy_nonoverlapping`] for safety concerns and examples.
1456 ///
1457 /// [`ptr::copy_nonoverlapping`]: crate::ptr::copy_nonoverlapping()
1458 #[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.83.0")]
1459 #[stable(feature = "pointer_methods", since = "1.26.0")]
1460 #[inline(always)]
1461 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
1462 pub const unsafe fn copy_to_nonoverlapping(self, dest: *mut T, count: usize)
1463 where
1464 T: Sized,
1465 {
1466 // SAFETY: the caller must uphold the safety contract for `copy_nonoverlapping`.
1467 unsafe { copy_nonoverlapping(self, dest, count) }
1468 }
1469
1470 /// Copies `count * size_of::<T>()` bytes from `src` to `self`. The source
1471 /// and destination may overlap.
1472 ///
1473 /// NOTE: this has the *opposite* argument order of [`ptr::copy`].
1474 ///
1475 /// See [`ptr::copy`] for safety concerns and examples.
1476 ///
1477 /// [`ptr::copy`]: crate::ptr::copy()
1478 #[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.83.0")]
1479 #[stable(feature = "pointer_methods", since = "1.26.0")]
1480 #[inline(always)]
1481 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
1482 pub const unsafe fn copy_from(self, src: *const T, count: usize)
1483 where
1484 T: Sized,
1485 {
1486 // SAFETY: the caller must uphold the safety contract for `copy`.
1487 unsafe { copy(src, self, count) }
1488 }
1489
1490 /// Copies `count * size_of::<T>()` bytes from `src` to `self`. The source
1491 /// and destination may *not* overlap.
1492 ///
1493 /// NOTE: this has the *opposite* argument order of [`ptr::copy_nonoverlapping`].
1494 ///
1495 /// See [`ptr::copy_nonoverlapping`] for safety concerns and examples.
1496 ///
1497 /// [`ptr::copy_nonoverlapping`]: crate::ptr::copy_nonoverlapping()
1498 #[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.83.0")]
1499 #[stable(feature = "pointer_methods", since = "1.26.0")]
1500 #[inline(always)]
1501 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
1502 pub const unsafe fn copy_from_nonoverlapping(self, src: *const T, count: usize)
1503 where
1504 T: Sized,
1505 {
1506 // SAFETY: the caller must uphold the safety contract for `copy_nonoverlapping`.
1507 unsafe { copy_nonoverlapping(src, self, count) }
1508 }
1509
1510 /// Executes the destructor (if any) of the pointed-to value.
1511 ///
1512 /// See [`ptr::drop_in_place`] for safety concerns and examples.
1513 ///
1514 /// [`ptr::drop_in_place`]: crate::ptr::drop_in_place()
1515 #[stable(feature = "pointer_methods", since = "1.26.0")]
1516 #[inline(always)]
1517 pub unsafe fn drop_in_place(self) {
1518 // SAFETY: the caller must uphold the safety contract for `drop_in_place`.
1519 unsafe { drop_in_place(self) }
1520 }
1521
1522 /// Overwrites a memory location with the given value without reading or
1523 /// dropping the old value.
1524 ///
1525 /// See [`ptr::write`] for safety concerns and examples.
1526 ///
1527 /// [`ptr::write`]: crate::ptr::write()
1528 #[stable(feature = "pointer_methods", since = "1.26.0")]
1529 #[rustc_const_stable(feature = "const_ptr_write", since = "1.83.0")]
1530 #[inline(always)]
1531 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
1532 pub const unsafe fn write(self, val: T)
1533 where
1534 T: Sized,
1535 {
1536 // SAFETY: the caller must uphold the safety contract for `write`.
1537 unsafe { write(self, val) }
1538 }
1539
1540 /// Invokes memset on the specified pointer, setting `count * size_of::<T>()`
1541 /// bytes of memory starting at `self` to `val`.
1542 ///
1543 /// See [`ptr::write_bytes`] for safety concerns and examples.
1544 ///
1545 /// [`ptr::write_bytes`]: crate::ptr::write_bytes()
1546 #[doc(alias = "memset")]
1547 #[stable(feature = "pointer_methods", since = "1.26.0")]
1548 #[rustc_const_stable(feature = "const_ptr_write", since = "1.83.0")]
1549 #[inline(always)]
1550 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
1551 pub const unsafe fn write_bytes(self, val: u8, count: usize)
1552 where
1553 T: Sized,
1554 {
1555 // SAFETY: the caller must uphold the safety contract for `write_bytes`.
1556 unsafe { write_bytes(self, val, count) }
1557 }
1558
1559 /// Performs a volatile write of a memory location with the given value without
1560 /// reading or dropping the old value.
1561 ///
1562 /// Volatile operations are intended to act on I/O memory, and are guaranteed
1563 /// to not be elided or reordered by the compiler across other volatile
1564 /// operations.
1565 ///
1566 /// See [`ptr::write_volatile`] for safety concerns and examples.
1567 ///
1568 /// [`ptr::write_volatile`]: crate::ptr::write_volatile()
1569 #[stable(feature = "pointer_methods", since = "1.26.0")]
1570 #[inline(always)]
1571 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
1572 pub unsafe fn write_volatile(self, val: T)
1573 where
1574 T: Sized,
1575 {
1576 // SAFETY: the caller must uphold the safety contract for `write_volatile`.
1577 unsafe { write_volatile(self, val) }
1578 }
1579
1580 /// Overwrites a memory location with the given value without reading or
1581 /// dropping the old value.
1582 ///
1583 /// Unlike `write`, the pointer may be unaligned.
1584 ///
1585 /// See [`ptr::write_unaligned`] for safety concerns and examples.
1586 ///
1587 /// [`ptr::write_unaligned`]: crate::ptr::write_unaligned()
1588 #[stable(feature = "pointer_methods", since = "1.26.0")]
1589 #[rustc_const_stable(feature = "const_ptr_write", since = "1.83.0")]
1590 #[inline(always)]
1591 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
1592 pub const unsafe fn write_unaligned(self, val: T)
1593 where
1594 T: Sized,
1595 {
1596 // SAFETY: the caller must uphold the safety contract for `write_unaligned`.
1597 unsafe { write_unaligned(self, val) }
1598 }
1599
1600 /// Replaces the value at `self` with `src`, returning the old
1601 /// value, without dropping either.
1602 ///
1603 /// See [`ptr::replace`] for safety concerns and examples.
1604 ///
1605 /// [`ptr::replace`]: crate::ptr::replace()
1606 #[stable(feature = "pointer_methods", since = "1.26.0")]
1607 #[rustc_const_stable(feature = "const_inherent_ptr_replace", since = "1.88.0")]
1608 #[inline(always)]
1609 pub const unsafe fn replace(self, src: T) -> T
1610 where
1611 T: Sized,
1612 {
1613 // SAFETY: the caller must uphold the safety contract for `replace`.
1614 unsafe { replace(self, src) }
1615 }
1616
1617 /// Swaps the values at two mutable locations of the same type, without
1618 /// deinitializing either. They may overlap, unlike `mem::swap` which is
1619 /// otherwise equivalent.
1620 ///
1621 /// See [`ptr::swap`] for safety concerns and examples.
1622 ///
1623 /// [`ptr::swap`]: crate::ptr::swap()
1624 #[stable(feature = "pointer_methods", since = "1.26.0")]
1625 #[rustc_const_stable(feature = "const_swap", since = "1.85.0")]
1626 #[inline(always)]
1627 pub const unsafe fn swap(self, with: *mut T)
1628 where
1629 T: Sized,
1630 {
1631 // SAFETY: the caller must uphold the safety contract for `swap`.
1632 unsafe { swap(self, with) }
1633 }
1634
1635 /// Computes the offset that needs to be applied to the pointer in order to make it aligned to
1636 /// `align`.
1637 ///
1638 /// If it is not possible to align the pointer, the implementation returns
1639 /// `usize::MAX`.
1640 ///
1641 /// The offset is expressed in number of `T` elements, and not bytes. The value returned can be
1642 /// used with the `wrapping_add` method.
1643 ///
1644 /// There are no guarantees whatsoever that offsetting the pointer will not overflow or go
1645 /// beyond the allocation that the pointer points into. It is up to the caller to ensure that
1646 /// the returned offset is correct in all terms other than alignment.
1647 ///
1648 /// # Panics
1649 ///
1650 /// The function panics if `align` is not a power-of-two.
1651 ///
1652 /// # Examples
1653 ///
1654 /// Accessing adjacent `u8` as `u16`
1655 ///
1656 /// ```
1657 /// # unsafe {
1658 /// let mut x = [5_u8, 6, 7, 8, 9];
1659 /// let ptr = x.as_mut_ptr();
1660 /// let offset = ptr.align_offset(align_of::<u16>());
1661 ///
1662 /// if offset < x.len() - 1 {
1663 /// let u16_ptr = ptr.add(offset).cast::<u16>();
1664 /// *u16_ptr = 0;
1665 ///
1666 /// assert!(x == [0, 0, 7, 8, 9] || x == [5, 0, 0, 8, 9]);
1667 /// } else {
1668 /// // while the pointer can be aligned via `offset`, it would point
1669 /// // outside the allocation
1670 /// }
1671 /// # }
1672 /// ```
1673 #[must_use]
1674 #[inline]
1675 #[stable(feature = "align_offset", since = "1.36.0")]
1676 pub fn align_offset(self, align: usize) -> usize
1677 where
1678 T: Sized,
1679 {
1680 if !align.is_power_of_two() {
1681 panic!("align_offset: align is not a power-of-two");
1682 }
1683
1684 // SAFETY: `align` has been checked to be a power of 2 above
1685 let ret = unsafe { align_offset(self, align) };
1686
1687 // Inform Miri that we want to consider the resulting pointer to be suitably aligned.
1688 #[cfg(miri)]
1689 if ret != usize::MAX {
1690 intrinsics::miri_promise_symbolic_alignment(
1691 self.wrapping_add(ret).cast_const().cast(),
1692 align,
1693 );
1694 }
1695
1696 ret
1697 }
1698
1699 /// Returns whether the pointer is properly aligned for `T`.
1700 ///
1701 /// # Examples
1702 ///
1703 /// ```
1704 /// // On some platforms, the alignment of i32 is less than 4.
1705 /// #[repr(align(4))]
1706 /// struct AlignedI32(i32);
1707 ///
1708 /// let mut data = AlignedI32(42);
1709 /// let ptr = &mut data as *mut AlignedI32;
1710 ///
1711 /// assert!(ptr.is_aligned());
1712 /// assert!(!ptr.wrapping_byte_add(1).is_aligned());
1713 /// ```
1714 #[must_use]
1715 #[inline]
1716 #[stable(feature = "pointer_is_aligned", since = "1.79.0")]
1717 pub fn is_aligned(self) -> bool
1718 where
1719 T: Sized,
1720 {
1721 self.is_aligned_to(align_of::<T>())
1722 }
1723
1724 /// Returns whether the pointer is aligned to `align`.
1725 ///
1726 /// For non-`Sized` pointees this operation considers only the data pointer,
1727 /// ignoring the metadata.
1728 ///
1729 /// # Panics
1730 ///
1731 /// The function panics if `align` is not a power-of-two (this includes 0).
1732 ///
1733 /// # Examples
1734 ///
1735 /// ```
1736 /// #![feature(pointer_is_aligned_to)]
1737 ///
1738 /// // On some platforms, the alignment of i32 is less than 4.
1739 /// #[repr(align(4))]
1740 /// struct AlignedI32(i32);
1741 ///
1742 /// let mut data = AlignedI32(42);
1743 /// let ptr = &mut data as *mut AlignedI32;
1744 ///
1745 /// assert!(ptr.is_aligned_to(1));
1746 /// assert!(ptr.is_aligned_to(2));
1747 /// assert!(ptr.is_aligned_to(4));
1748 ///
1749 /// assert!(ptr.wrapping_byte_add(2).is_aligned_to(2));
1750 /// assert!(!ptr.wrapping_byte_add(2).is_aligned_to(4));
1751 ///
1752 /// assert_ne!(ptr.is_aligned_to(8), ptr.wrapping_add(1).is_aligned_to(8));
1753 /// ```
1754 #[must_use]
1755 #[inline]
1756 #[unstable(feature = "pointer_is_aligned_to", issue = "96284")]
1757 pub fn is_aligned_to(self, align: usize) -> bool {
1758 if !align.is_power_of_two() {
1759 panic!("is_aligned_to: align is not a power-of-two");
1760 }
1761
1762 self.addr() & (align - 1) == 0
1763 }
1764}
1765
1766impl<T> *mut [T] {
1767 /// Returns the length of a raw slice.
1768 ///
1769 /// The returned value is the number of **elements**, not the number of bytes.
1770 ///
1771 /// This function is safe, even when the raw slice cannot be cast to a slice
1772 /// reference because the pointer is null or unaligned.
1773 ///
1774 /// # Examples
1775 ///
1776 /// ```rust
1777 /// use std::ptr;
1778 ///
1779 /// let slice: *mut [i8] = ptr::slice_from_raw_parts_mut(ptr::null_mut(), 3);
1780 /// assert_eq!(slice.len(), 3);
1781 /// ```
1782 #[inline(always)]
1783 #[stable(feature = "slice_ptr_len", since = "1.79.0")]
1784 #[rustc_const_stable(feature = "const_slice_ptr_len", since = "1.79.0")]
1785 pub const fn len(self) -> usize {
1786 metadata(self)
1787 }
1788
1789 /// Returns `true` if the raw slice has a length of 0.
1790 ///
1791 /// # Examples
1792 ///
1793 /// ```
1794 /// use std::ptr;
1795 ///
1796 /// let slice: *mut [i8] = ptr::slice_from_raw_parts_mut(ptr::null_mut(), 3);
1797 /// assert!(!slice.is_empty());
1798 /// ```
1799 #[inline(always)]
1800 #[stable(feature = "slice_ptr_len", since = "1.79.0")]
1801 #[rustc_const_stable(feature = "const_slice_ptr_len", since = "1.79.0")]
1802 pub const fn is_empty(self) -> bool {
1803 self.len() == 0
1804 }
1805
1806 /// Gets a raw, mutable pointer to the underlying array.
1807 ///
1808 /// If `N` is not exactly equal to the length of `self`, then this method returns `None`.
1809 #[unstable(feature = "slice_as_array", issue = "133508")]
1810 #[inline]
1811 #[must_use]
1812 pub const fn as_mut_array<const N: usize>(self) -> Option<*mut [T; N]> {
1813 if self.len() == N {
1814 let me = self.as_mut_ptr() as *mut [T; N];
1815 Some(me)
1816 } else {
1817 None
1818 }
1819 }
1820
1821 /// Divides one mutable raw slice into two at an index.
1822 ///
1823 /// The first will contain all indices from `[0, mid)` (excluding
1824 /// the index `mid` itself) and the second will contain all
1825 /// indices from `[mid, len)` (excluding the index `len` itself).
1826 ///
1827 /// # Panics
1828 ///
1829 /// Panics if `mid > len`.
1830 ///
1831 /// # Safety
1832 ///
1833 /// `mid` must be [in-bounds] of the underlying [allocated object].
1834 /// Which means `self` must be dereferenceable and span a single allocation
1835 /// that is at least `mid * size_of::<T>()` bytes long. Not upholding these
1836 /// requirements is *[undefined behavior]* even if the resulting pointers are not used.
1837 ///
1838 /// Since `len` being in-bounds it is not a safety invariant of `*mut [T]` the
1839 /// safety requirements of this method are the same as for [`split_at_mut_unchecked`].
1840 /// The explicit bounds check is only as useful as `len` is correct.
1841 ///
1842 /// [`split_at_mut_unchecked`]: #method.split_at_mut_unchecked
1843 /// [in-bounds]: #method.add
1844 /// [allocated object]: crate::ptr#allocated-object
1845 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1846 ///
1847 /// # Examples
1848 ///
1849 /// ```
1850 /// #![feature(raw_slice_split)]
1851 /// #![feature(slice_ptr_get)]
1852 ///
1853 /// let mut v = [1, 0, 3, 0, 5, 6];
1854 /// let ptr = &mut v as *mut [_];
1855 /// unsafe {
1856 /// let (left, right) = ptr.split_at_mut(2);
1857 /// assert_eq!(&*left, [1, 0]);
1858 /// assert_eq!(&*right, [3, 0, 5, 6]);
1859 /// }
1860 /// ```
1861 #[inline(always)]
1862 #[track_caller]
1863 #[unstable(feature = "raw_slice_split", issue = "95595")]
1864 pub unsafe fn split_at_mut(self, mid: usize) -> (*mut [T], *mut [T]) {
1865 assert!(mid <= self.len());
1866 // SAFETY: The assert above is only a safety-net as long as `self.len()` is correct
1867 // The actual safety requirements of this function are the same as for `split_at_mut_unchecked`
1868 unsafe { self.split_at_mut_unchecked(mid) }
1869 }
1870
1871 /// Divides one mutable raw slice into two at an index, without doing bounds checking.
1872 ///
1873 /// The first will contain all indices from `[0, mid)` (excluding
1874 /// the index `mid` itself) and the second will contain all
1875 /// indices from `[mid, len)` (excluding the index `len` itself).
1876 ///
1877 /// # Safety
1878 ///
1879 /// `mid` must be [in-bounds] of the underlying [allocated object].
1880 /// Which means `self` must be dereferenceable and span a single allocation
1881 /// that is at least `mid * size_of::<T>()` bytes long. Not upholding these
1882 /// requirements is *[undefined behavior]* even if the resulting pointers are not used.
1883 ///
1884 /// [in-bounds]: #method.add
1885 /// [out-of-bounds index]: #method.add
1886 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1887 ///
1888 /// # Examples
1889 ///
1890 /// ```
1891 /// #![feature(raw_slice_split)]
1892 ///
1893 /// let mut v = [1, 0, 3, 0, 5, 6];
1894 /// // scoped to restrict the lifetime of the borrows
1895 /// unsafe {
1896 /// let ptr = &mut v as *mut [_];
1897 /// let (left, right) = ptr.split_at_mut_unchecked(2);
1898 /// assert_eq!(&*left, [1, 0]);
1899 /// assert_eq!(&*right, [3, 0, 5, 6]);
1900 /// (&mut *left)[1] = 2;
1901 /// (&mut *right)[1] = 4;
1902 /// }
1903 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1904 /// ```
1905 #[inline(always)]
1906 #[unstable(feature = "raw_slice_split", issue = "95595")]
1907 pub unsafe fn split_at_mut_unchecked(self, mid: usize) -> (*mut [T], *mut [T]) {
1908 let len = self.len();
1909 let ptr = self.as_mut_ptr();
1910
1911 // SAFETY: Caller must pass a valid pointer and an index that is in-bounds.
1912 let tail = unsafe { ptr.add(mid) };
1913 (
1914 crate::ptr::slice_from_raw_parts_mut(ptr, mid),
1915 crate::ptr::slice_from_raw_parts_mut(tail, len - mid),
1916 )
1917 }
1918
1919 /// Returns a raw pointer to the slice's buffer.
1920 ///
1921 /// This is equivalent to casting `self` to `*mut T`, but more type-safe.
1922 ///
1923 /// # Examples
1924 ///
1925 /// ```rust
1926 /// #![feature(slice_ptr_get)]
1927 /// use std::ptr;
1928 ///
1929 /// let slice: *mut [i8] = ptr::slice_from_raw_parts_mut(ptr::null_mut(), 3);
1930 /// assert_eq!(slice.as_mut_ptr(), ptr::null_mut());
1931 /// ```
1932 #[inline(always)]
1933 #[unstable(feature = "slice_ptr_get", issue = "74265")]
1934 pub const fn as_mut_ptr(self) -> *mut T {
1935 self as *mut T
1936 }
1937
1938 /// Returns a raw pointer to an element or subslice, without doing bounds
1939 /// checking.
1940 ///
1941 /// Calling this method with an [out-of-bounds index] or when `self` is not dereferenceable
1942 /// is *[undefined behavior]* even if the resulting pointer is not used.
1943 ///
1944 /// [out-of-bounds index]: #method.add
1945 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1946 ///
1947 /// # Examples
1948 ///
1949 /// ```
1950 /// #![feature(slice_ptr_get)]
1951 ///
1952 /// let x = &mut [1, 2, 4] as *mut [i32];
1953 ///
1954 /// unsafe {
1955 /// assert_eq!(x.get_unchecked_mut(1), x.as_mut_ptr().add(1));
1956 /// }
1957 /// ```
1958 #[unstable(feature = "slice_ptr_get", issue = "74265")]
1959 #[inline(always)]
1960 pub unsafe fn get_unchecked_mut<I>(self, index: I) -> *mut I::Output
1961 where
1962 I: SliceIndex<[T]>,
1963 {
1964 // SAFETY: the caller ensures that `self` is dereferenceable and `index` in-bounds.
1965 unsafe { index.get_unchecked_mut(self) }
1966 }
1967
1968 /// Returns `None` if the pointer is null, or else returns a shared slice to
1969 /// the value wrapped in `Some`. In contrast to [`as_ref`], this does not require
1970 /// that the value has to be initialized.
1971 ///
1972 /// For the mutable counterpart see [`as_uninit_slice_mut`].
1973 ///
1974 /// [`as_ref`]: pointer#method.as_ref-1
1975 /// [`as_uninit_slice_mut`]: #method.as_uninit_slice_mut
1976 ///
1977 /// # Safety
1978 ///
1979 /// When calling this method, you have to ensure that *either* the pointer is null *or*
1980 /// all of the following is true:
1981 ///
1982 /// * The pointer must be [valid] for reads for `ptr.len() * size_of::<T>()` many bytes,
1983 /// and it must be properly aligned. This means in particular:
1984 ///
1985 /// * The entire memory range of this slice must be contained within a single [allocated object]!
1986 /// Slices can never span across multiple allocated objects.
1987 ///
1988 /// * The pointer must be aligned even for zero-length slices. One
1989 /// reason for this is that enum layout optimizations may rely on references
1990 /// (including slices of any length) being aligned and non-null to distinguish
1991 /// them from other data. You can obtain a pointer that is usable as `data`
1992 /// for zero-length slices using [`NonNull::dangling()`].
1993 ///
1994 /// * The total size `ptr.len() * size_of::<T>()` of the slice must be no larger than `isize::MAX`.
1995 /// See the safety documentation of [`pointer::offset`].
1996 ///
1997 /// * You must enforce Rust's aliasing rules, since the returned lifetime `'a` is
1998 /// arbitrarily chosen and does not necessarily reflect the actual lifetime of the data.
1999 /// In particular, while this reference exists, the memory the pointer points to must
2000 /// not get mutated (except inside `UnsafeCell`).
2001 ///
2002 /// This applies even if the result of this method is unused!
2003 ///
2004 /// See also [`slice::from_raw_parts`][].
2005 ///
2006 /// [valid]: crate::ptr#safety
2007 /// [allocated object]: crate::ptr#allocated-object
2008 ///
2009 /// # Panics during const evaluation
2010 ///
2011 /// This method will panic during const evaluation if the pointer cannot be
2012 /// determined to be null or not. See [`is_null`] for more information.
2013 ///
2014 /// [`is_null`]: #method.is_null-1
2015 #[inline]
2016 #[unstable(feature = "ptr_as_uninit", issue = "75402")]
2017 pub const unsafe fn as_uninit_slice<'a>(self) -> Option<&'a [MaybeUninit<T>]> {
2018 if self.is_null() {
2019 None
2020 } else {
2021 // SAFETY: the caller must uphold the safety contract for `as_uninit_slice`.
2022 Some(unsafe { slice::from_raw_parts(self as *const MaybeUninit<T>, self.len()) })
2023 }
2024 }
2025
2026 /// Returns `None` if the pointer is null, or else returns a unique slice to
2027 /// the value wrapped in `Some`. In contrast to [`as_mut`], this does not require
2028 /// that the value has to be initialized.
2029 ///
2030 /// For the shared counterpart see [`as_uninit_slice`].
2031 ///
2032 /// [`as_mut`]: #method.as_mut
2033 /// [`as_uninit_slice`]: #method.as_uninit_slice-1
2034 ///
2035 /// # Safety
2036 ///
2037 /// When calling this method, you have to ensure that *either* the pointer is null *or*
2038 /// all of the following is true:
2039 ///
2040 /// * The pointer must be [valid] for reads and writes for `ptr.len() * size_of::<T>()`
2041 /// many bytes, and it must be properly aligned. This means in particular:
2042 ///
2043 /// * The entire memory range of this slice must be contained within a single [allocated object]!
2044 /// Slices can never span across multiple allocated objects.
2045 ///
2046 /// * The pointer must be aligned even for zero-length slices. One
2047 /// reason for this is that enum layout optimizations may rely on references
2048 /// (including slices of any length) being aligned and non-null to distinguish
2049 /// them from other data. You can obtain a pointer that is usable as `data`
2050 /// for zero-length slices using [`NonNull::dangling()`].
2051 ///
2052 /// * The total size `ptr.len() * size_of::<T>()` of the slice must be no larger than `isize::MAX`.
2053 /// See the safety documentation of [`pointer::offset`].
2054 ///
2055 /// * You must enforce Rust's aliasing rules, since the returned lifetime `'a` is
2056 /// arbitrarily chosen and does not necessarily reflect the actual lifetime of the data.
2057 /// In particular, while this reference exists, the memory the pointer points to must
2058 /// not get accessed (read or written) through any other pointer.
2059 ///
2060 /// This applies even if the result of this method is unused!
2061 ///
2062 /// See also [`slice::from_raw_parts_mut`][].
2063 ///
2064 /// [valid]: crate::ptr#safety
2065 /// [allocated object]: crate::ptr#allocated-object
2066 ///
2067 /// # Panics during const evaluation
2068 ///
2069 /// This method will panic during const evaluation if the pointer cannot be
2070 /// determined to be null or not. See [`is_null`] for more information.
2071 ///
2072 /// [`is_null`]: #method.is_null-1
2073 #[inline]
2074 #[unstable(feature = "ptr_as_uninit", issue = "75402")]
2075 pub const unsafe fn as_uninit_slice_mut<'a>(self) -> Option<&'a mut [MaybeUninit<T>]> {
2076 if self.is_null() {
2077 None
2078 } else {
2079 // SAFETY: the caller must uphold the safety contract for `as_uninit_slice_mut`.
2080 Some(unsafe { slice::from_raw_parts_mut(self as *mut MaybeUninit<T>, self.len()) })
2081 }
2082 }
2083}
2084
2085impl<T, const N: usize> *mut [T; N] {
2086 /// Returns a raw pointer to the array's buffer.
2087 ///
2088 /// This is equivalent to casting `self` to `*mut T`, but more type-safe.
2089 ///
2090 /// # Examples
2091 ///
2092 /// ```rust
2093 /// #![feature(array_ptr_get)]
2094 /// use std::ptr;
2095 ///
2096 /// let arr: *mut [i8; 3] = ptr::null_mut();
2097 /// assert_eq!(arr.as_mut_ptr(), ptr::null_mut());
2098 /// ```
2099 #[inline]
2100 #[unstable(feature = "array_ptr_get", issue = "119834")]
2101 pub const fn as_mut_ptr(self) -> *mut T {
2102 self as *mut T
2103 }
2104
2105 /// Returns a raw pointer to a mutable slice containing the entire array.
2106 ///
2107 /// # Examples
2108 ///
2109 /// ```
2110 /// #![feature(array_ptr_get)]
2111 ///
2112 /// let mut arr = [1, 2, 5];
2113 /// let ptr: *mut [i32; 3] = &mut arr;
2114 /// unsafe {
2115 /// (&mut *ptr.as_mut_slice())[..2].copy_from_slice(&[3, 4]);
2116 /// }
2117 /// assert_eq!(arr, [3, 4, 5]);
2118 /// ```
2119 #[inline]
2120 #[unstable(feature = "array_ptr_get", issue = "119834")]
2121 pub const fn as_mut_slice(self) -> *mut [T] {
2122 self
2123 }
2124}
2125
2126/// Pointer equality is by address, as produced by the [`<*mut T>::addr`](pointer::addr) method.
2127#[stable(feature = "rust1", since = "1.0.0")]
2128impl<T: ?Sized> PartialEq for *mut T {
2129 #[inline(always)]
2130 #[allow(ambiguous_wide_pointer_comparisons)]
2131 fn eq(&self, other: &*mut T) -> bool {
2132 *self == *other
2133 }
2134}
2135
2136/// Pointer equality is an equivalence relation.
2137#[stable(feature = "rust1", since = "1.0.0")]
2138impl<T: ?Sized> Eq for *mut T {}
2139
2140/// Pointer comparison is by address, as produced by the [`<*mut T>::addr`](pointer::addr) method.
2141#[stable(feature = "rust1", since = "1.0.0")]
2142impl<T: ?Sized> Ord for *mut T {
2143 #[inline]
2144 #[allow(ambiguous_wide_pointer_comparisons)]
2145 fn cmp(&self, other: &*mut T) -> Ordering {
2146 if self < other {
2147 Less
2148 } else if self == other {
2149 Equal
2150 } else {
2151 Greater
2152 }
2153 }
2154}
2155
2156/// Pointer comparison is by address, as produced by the [`<*mut T>::addr`](pointer::addr) method.
2157#[stable(feature = "rust1", since = "1.0.0")]
2158impl<T: ?Sized> PartialOrd for *mut T {
2159 #[inline(always)]
2160 #[allow(ambiguous_wide_pointer_comparisons)]
2161 fn partial_cmp(&self, other: &*mut T) -> Option<Ordering> {
2162 Some(self.cmp(other))
2163 }
2164
2165 #[inline(always)]
2166 #[allow(ambiguous_wide_pointer_comparisons)]
2167 fn lt(&self, other: &*mut T) -> bool {
2168 *self < *other
2169 }
2170
2171 #[inline(always)]
2172 #[allow(ambiguous_wide_pointer_comparisons)]
2173 fn le(&self, other: &*mut T) -> bool {
2174 *self <= *other
2175 }
2176
2177 #[inline(always)]
2178 #[allow(ambiguous_wide_pointer_comparisons)]
2179 fn gt(&self, other: &*mut T) -> bool {
2180 *self > *other
2181 }
2182
2183 #[inline(always)]
2184 #[allow(ambiguous_wide_pointer_comparisons)]
2185 fn ge(&self, other: &*mut T) -> bool {
2186 *self >= *other
2187 }
2188}
2189
2190#[stable(feature = "raw_ptr_default", since = "1.88.0")]
2191impl<T: ?Sized + Thin> Default for *mut T {
2192 /// Returns the default value of [`null_mut()`][crate::ptr::null_mut].
2193 fn default() -> Self {
2194 crate::ptr::null_mut()
2195 }
2196}