2 use crate::cmp::Ordering::{self, Equal, Greater, Less};
4 use crate::slice::{self, SliceIndex};
7 impl<T: ?Sized> *mut T {
8 /// Returns `true` if the pointer is null.
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
15 /// ## Behavior during const evaluation
17 /// When this function is used during const evaluation, it may return `false` for pointers
18 /// that turn out to be null at runtime. Specifically, when a pointer to some memory
19 /// is offset beyond its bounds in such a way that the resulting pointer is null,
20 /// the function will still return `false`. There is no way for CTFE to know
21 /// the absolute position of that memory, so we cannot tell if the pointer is
29 /// let mut s = [1, 2, 3];
30 /// let ptr: *mut u32 = s.as_mut_ptr();
31 /// assert!(!ptr.is_null());
33 #[stable(feature = "rust1", since = "1.0.0")]
34 #[rustc_const_unstable(feature = "const_ptr_is_null", issue = "74939")]
36 pub const fn is_null(self) -> bool {
37 // Compare via a cast to a thin pointer, so fat pointers are only
38 // considering their "data" part for null-ness.
39 (self as *mut u8).guaranteed_eq(null_mut())
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")]
46 pub const fn cast<U>(self) -> *mut U {
50 /// Returns `None` if the pointer is null, or else returns a shared reference to
51 /// the value wrapped in `Some`. If the value may be uninitialized, [`as_uninit_ref`]
52 /// must be used instead.
54 /// For the mutable counterpart see [`as_mut`].
56 /// [`as_uninit_ref`]: #method.as_uninit_ref-1
57 /// [`as_mut`]: #method.as_mut
61 /// When calling this method, you have to ensure that *either* the pointer is NULL *or*
62 /// all of the following is true:
64 /// * The pointer must be properly aligned.
66 /// * It must be "dereferencable" in the sense defined in [the module documentation].
68 /// * The pointer must point to an initialized instance of `T`.
70 /// * You must enforce Rust's aliasing rules, since the returned lifetime `'a` is
71 /// arbitrarily chosen and does not necessarily reflect the actual lifetime of the data.
72 /// In particular, for the duration of this lifetime, the memory the pointer points to must
73 /// not get mutated (except inside `UnsafeCell`).
75 /// This applies even if the result of this method is unused!
76 /// (The part about being initialized is not yet fully decided, but until
77 /// it is, the only safe approach is to ensure that they are indeed initialized.)
79 /// [the module documentation]: crate::ptr#safety
86 /// let ptr: *mut u8 = &mut 10u8 as *mut u8;
89 /// if let Some(val_back) = ptr.as_ref() {
90 /// println!("We got back the value: {}!", val_back);
95 /// # Null-unchecked version
97 /// If you are sure the pointer can never be null and are looking for some kind of
98 /// `as_ref_unchecked` that returns the `&T` instead of `Option<&T>`, know that you can
99 /// dereference the pointer directly.
102 /// let ptr: *mut u8 = &mut 10u8 as *mut u8;
105 /// let val_back = &*ptr;
106 /// println!("We got back the value: {}!", val_back);
109 #[stable(feature = "ptr_as_ref", since = "1.9.0")]
111 pub unsafe fn as_ref<'a>(self) -> Option<&'a T> {
112 // SAFETY: the caller must guarantee that `self` is valid for a
113 // reference if it isn't null.
114 if self.is_null() { None } else { unsafe { Some(&*self) } }
117 /// Returns `None` if the pointer is null, or else returns a shared reference to
118 /// the value wrapped in `Some`. In contrast to [`as_ref`], this does not require
119 /// that the value has to be initialized.
121 /// For the mutable counterpart see [`as_uninit_mut`].
123 /// [`as_ref`]: #method.as_ref-1
124 /// [`as_uninit_mut`]: #method.as_uninit_mut
128 /// When calling this method, you have to ensure that *either* the pointer is NULL *or*
129 /// all of the following is true:
131 /// * The pointer must be properly aligned.
133 /// * It must be "dereferencable" in the sense defined in [the module documentation].
135 /// * You must enforce Rust's aliasing rules, since the returned lifetime `'a` is
136 /// arbitrarily chosen and does not necessarily reflect the actual lifetime of the data.
137 /// In particular, for the duration of this lifetime, the memory the pointer points to must
138 /// not get mutated (except inside `UnsafeCell`).
140 /// This applies even if the result of this method is unused!
142 /// [the module documentation]: crate::ptr#safety
149 /// #![feature(ptr_as_uninit)]
151 /// let ptr: *mut u8 = &mut 10u8 as *mut u8;
154 /// if let Some(val_back) = ptr.as_uninit_ref() {
155 /// println!("We got back the value: {}!", val_back.assume_init());
160 #[unstable(feature = "ptr_as_uninit", issue = "75402")]
161 pub unsafe fn as_uninit_ref<'a>(self) -> Option<&'a MaybeUninit<T>>
165 // SAFETY: the caller must guarantee that `self` meets all the
166 // requirements for a reference.
167 if self.is_null() { None } else { Some(unsafe { &*(self as *const MaybeUninit<T>) }) }
170 /// Calculates the offset from a pointer.
172 /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
173 /// offset of `3 * size_of::<T>()` bytes.
177 /// If any of the following conditions are violated, the result is Undefined
180 /// * Both the starting and resulting pointer must be either in bounds or one
181 /// byte past the end of the same allocated object. Note that in Rust,
182 /// every (stack-allocated) variable is considered a separate allocated object.
184 /// * The computed offset, **in bytes**, cannot overflow an `isize`.
186 /// * The offset being in bounds cannot rely on "wrapping around" the address
187 /// space. That is, the infinite-precision sum, **in bytes** must fit in a usize.
189 /// The compiler and standard library generally tries to ensure allocations
190 /// never reach a size where an offset is a concern. For instance, `Vec`
191 /// and `Box` ensure they never allocate more than `isize::MAX` bytes, so
192 /// `vec.as_ptr().add(vec.len())` is always safe.
194 /// Most platforms fundamentally can't even construct such an allocation.
195 /// For instance, no known 64-bit platform can ever serve a request
196 /// for 2<sup>63</sup> bytes due to page-table limitations or splitting the address space.
197 /// However, some 32-bit and 16-bit platforms may successfully serve a request for
198 /// more than `isize::MAX` bytes with things like Physical Address
199 /// Extension. As such, memory acquired directly from allocators or memory
200 /// mapped files *may* be too large to handle with this function.
202 /// Consider using [`wrapping_offset`] instead if these constraints are
203 /// difficult to satisfy. The only advantage of this method is that it
204 /// enables more aggressive compiler optimizations.
206 /// [`wrapping_offset`]: #method.wrapping_offset
213 /// let mut s = [1, 2, 3];
214 /// let ptr: *mut u32 = s.as_mut_ptr();
217 /// println!("{}", *ptr.offset(1));
218 /// println!("{}", *ptr.offset(2));
221 #[stable(feature = "rust1", since = "1.0.0")]
222 #[must_use = "returns a new pointer rather than modifying its argument"]
223 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
225 pub const unsafe fn offset(self, count: isize) -> *mut T
229 // SAFETY: the caller must uphold the safety contract for `offset`.
230 // The obtained pointer is valid for writes since the caller must
231 // guarantee that it points to the same allocated object as `self`.
232 unsafe { intrinsics::offset(self, count) as *mut T }
235 /// Calculates the offset from a pointer using wrapping arithmetic.
236 /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
237 /// offset of `3 * size_of::<T>()` bytes.
241 /// The resulting pointer does not need to be in bounds, but it is
242 /// potentially hazardous to dereference (which requires `unsafe`).
244 /// In particular, the resulting pointer remains attached to the same allocated
245 /// object that `self` points to. It may *not* be used to access a
246 /// different allocated object. Note that in Rust,
247 /// every (stack-allocated) variable is considered a separate allocated object.
249 /// In other words, `x.wrapping_offset(y.wrapping_offset_from(x))` is
250 /// *not* the same as `y`, and dereferencing it is undefined behavior
251 /// unless `x` and `y` point into the same allocated object.
253 /// Compared to [`offset`], this method basically delays the requirement of staying
254 /// within the same allocated object: [`offset`] is immediate Undefined Behavior when
255 /// crossing object boundaries; `wrapping_offset` produces a pointer but still leads
256 /// to Undefined Behavior if that pointer is dereferenced. [`offset`] can be optimized
257 /// better and is thus preferable in performance-sensitive code.
259 /// If you need to cross object boundaries, cast the pointer to an integer and
260 /// do the arithmetic there.
262 /// [`offset`]: #method.offset
269 /// // Iterate using a raw pointer in increments of two elements
270 /// let mut data = [1u8, 2, 3, 4, 5];
271 /// let mut ptr: *mut u8 = data.as_mut_ptr();
273 /// let end_rounded_up = ptr.wrapping_offset(6);
275 /// while ptr != end_rounded_up {
279 /// ptr = ptr.wrapping_offset(step);
281 /// assert_eq!(&data, &[0, 2, 0, 4, 0]);
283 #[stable(feature = "ptr_wrapping_offset", since = "1.16.0")]
284 #[must_use = "returns a new pointer rather than modifying its argument"]
285 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
287 pub const fn wrapping_offset(self, count: isize) -> *mut T
291 // SAFETY: the `arith_offset` intrinsic has no prerequisites to be called.
292 unsafe { intrinsics::arith_offset(self, count) as *mut T }
295 /// Returns `None` if the pointer is null, or else returns a unique reference to
296 /// the value wrapped in `Some`. If the value may be uninitialized, [`as_uninit_mut`]
297 /// must be used instead.
299 /// For the shared counterpart see [`as_ref`].
301 /// [`as_uninit_mut`]: #method.as_uninit_mut
302 /// [`as_ref`]: #method.as_ref-1
306 /// When calling this method, you have to ensure that *either* the pointer is NULL *or*
307 /// all of the following is true:
309 /// * The pointer must be properly aligned.
311 /// * It must be "dereferencable" in the sense defined in [the module documentation].
313 /// * The pointer must point to an initialized instance of `T`.
315 /// * You must enforce Rust's aliasing rules, since the returned lifetime `'a` is
316 /// arbitrarily chosen and does not necessarily reflect the actual lifetime of the data.
317 /// In particular, for the duration of this lifetime, the memory the pointer points to must
318 /// not get accessed (read or written) through any other pointer.
320 /// This applies even if the result of this method is unused!
321 /// (The part about being initialized is not yet fully decided, but until
322 /// it is, the only safe approach is to ensure that they are indeed initialized.)
324 /// [the module documentation]: crate::ptr#safety
331 /// let mut s = [1, 2, 3];
332 /// let ptr: *mut u32 = s.as_mut_ptr();
333 /// let first_value = unsafe { ptr.as_mut().unwrap() };
334 /// *first_value = 4;
335 /// # assert_eq!(s, [4, 2, 3]);
336 /// println!("{:?}", s); // It'll print: "[4, 2, 3]".
339 /// # Null-unchecked version
341 /// If you are sure the pointer can never be null and are looking for some kind of
342 /// `as_mut_unchecked` that returns the `&mut T` instead of `Option<&mut T>`, know that
343 /// you can dereference the pointer directly.
346 /// let mut s = [1, 2, 3];
347 /// let ptr: *mut u32 = s.as_mut_ptr();
348 /// let first_value = unsafe { &mut *ptr };
349 /// *first_value = 4;
350 /// # assert_eq!(s, [4, 2, 3]);
351 /// println!("{:?}", s); // It'll print: "[4, 2, 3]".
353 #[stable(feature = "ptr_as_ref", since = "1.9.0")]
355 pub unsafe fn as_mut<'a>(self) -> Option<&'a mut T> {
356 // SAFETY: the caller must guarantee that `self` is be valid for
357 // a mutable reference if it isn't null.
358 if self.is_null() { None } else { unsafe { Some(&mut *self) } }
361 /// Returns `None` if the pointer is null, or else returns a unique reference to
362 /// the value wrapped in `Some`. In contrast to [`as_mut`], this does not require
363 /// that the value has to be initialized.
365 /// For the shared counterpart see [`as_uninit_ref`].
367 /// [`as_mut`]: #method.as_mut
368 /// [`as_uninit_ref`]: #method.as_uninit_ref-1
372 /// When calling this method, you have to ensure that *either* the pointer is NULL *or*
373 /// all of the following is true:
375 /// * The pointer must be properly aligned.
377 /// * It must be "dereferencable" in the sense defined in [the module documentation].
379 /// * You must enforce Rust's aliasing rules, since the returned lifetime `'a` is
380 /// arbitrarily chosen and does not necessarily reflect the actual lifetime of the data.
381 /// In particular, for the duration of this lifetime, the memory the pointer points to must
382 /// not get accessed (read or written) through any other pointer.
384 /// This applies even if the result of this method is unused!
386 /// [the module documentation]: crate::ptr#safety
388 #[unstable(feature = "ptr_as_uninit", issue = "75402")]
389 pub unsafe fn as_uninit_mut<'a>(self) -> Option<&'a mut MaybeUninit<T>>
393 // SAFETY: the caller must guarantee that `self` meets all the
394 // requirements for a reference.
395 if self.is_null() { None } else { Some(unsafe { &mut *(self as *mut MaybeUninit<T>) }) }
398 /// Returns whether two pointers are guaranteed to be equal.
400 /// At runtime this function behaves like `self == other`.
401 /// However, in some contexts (e.g., compile-time evaluation),
402 /// it is not always possible to determine equality of two pointers, so this function may
403 /// spuriously return `false` for pointers that later actually turn out to be equal.
404 /// But when it returns `true`, the pointers are guaranteed to be equal.
406 /// This function is the mirror of [`guaranteed_ne`], but not its inverse. There are pointer
407 /// comparisons for which both functions return `false`.
409 /// [`guaranteed_ne`]: #method.guaranteed_ne
411 /// The return value may change depending on the compiler version and unsafe code may not
412 /// rely on the result of this function for soundness. It is suggested to only use this function
413 /// for performance optimizations where spurious `false` return values by this function do not
414 /// affect the outcome, but just the performance.
415 /// The consequences of using this method to make runtime and compile-time code behave
416 /// differently have not been explored. This method should not be used to introduce such
417 /// differences, and it should also not be stabilized before we have a better understanding
419 #[unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
420 #[rustc_const_unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
422 pub const fn guaranteed_eq(self, other: *mut T) -> bool
426 intrinsics::ptr_guaranteed_eq(self as *const _, other as *const _)
429 /// Returns whether two pointers are guaranteed to be unequal.
431 /// At runtime this function behaves like `self != other`.
432 /// However, in some contexts (e.g., compile-time evaluation),
433 /// it is not always possible to determine the inequality of two pointers, so this function may
434 /// spuriously return `false` for pointers that later actually turn out to be unequal.
435 /// But when it returns `true`, the pointers are guaranteed to be unequal.
437 /// This function is the mirror of [`guaranteed_eq`], but not its inverse. There are pointer
438 /// comparisons for which both functions return `false`.
440 /// [`guaranteed_eq`]: #method.guaranteed_eq
442 /// The return value may change depending on the compiler version and unsafe code may not
443 /// rely on the result of this function for soundness. It is suggested to only use this function
444 /// for performance optimizations where spurious `false` return values by this function do not
445 /// affect the outcome, but just the performance.
446 /// The consequences of using this method to make runtime and compile-time code behave
447 /// differently have not been explored. This method should not be used to introduce such
448 /// differences, and it should also not be stabilized before we have a better understanding
450 #[unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
451 #[rustc_const_unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
453 pub const unsafe fn guaranteed_ne(self, other: *mut T) -> bool
457 intrinsics::ptr_guaranteed_ne(self as *const _, other as *const _)
460 /// Calculates the distance between two pointers. The returned value is in
461 /// units of T: the distance in bytes is divided by `mem::size_of::<T>()`.
463 /// This function is the inverse of [`offset`].
465 /// [`offset`]: #method.offset-1
466 /// [`wrapping_offset_from`]: #method.wrapping_offset_from-1
470 /// If any of the following conditions are violated, the result is Undefined
473 /// * Both the starting and other pointer must be either in bounds or one
474 /// byte past the end of the same allocated object. Note that in Rust,
475 /// every (stack-allocated) variable is considered a separate allocated object.
477 /// * Both pointers must be *derived from* a pointer to the same object.
478 /// (See below for an example.)
480 /// * The distance between the pointers, **in bytes**, cannot overflow an `isize`.
482 /// * The distance between the pointers, in bytes, must be an exact multiple
483 /// of the size of `T`.
485 /// * The distance being in bounds cannot rely on "wrapping around" the address space.
487 /// The compiler and standard library generally try to ensure allocations
488 /// never reach a size where an offset is a concern. For instance, `Vec`
489 /// and `Box` ensure they never allocate more than `isize::MAX` bytes, so
490 /// `ptr_into_vec.offset_from(vec.as_ptr())` is always safe.
492 /// Most platforms fundamentally can't even construct such an allocation.
493 /// For instance, no known 64-bit platform can ever serve a request
494 /// for 2<sup>63</sup> bytes due to page-table limitations or splitting the address space.
495 /// However, some 32-bit and 16-bit platforms may successfully serve a request for
496 /// more than `isize::MAX` bytes with things like Physical Address
497 /// Extension. As such, memory acquired directly from allocators or memory
498 /// mapped files *may* be too large to handle with this function.
500 /// Consider using [`wrapping_offset_from`] instead if these constraints are
501 /// difficult to satisfy. The only advantage of this method is that it
502 /// enables more aggressive compiler optimizations.
506 /// This function panics if `T` is a Zero-Sized Type ("ZST").
513 /// #![feature(ptr_offset_from)]
515 /// let mut a = [0; 5];
516 /// let ptr1: *mut i32 = &mut a[1];
517 /// let ptr2: *mut i32 = &mut a[3];
519 /// assert_eq!(ptr2.offset_from(ptr1), 2);
520 /// assert_eq!(ptr1.offset_from(ptr2), -2);
521 /// assert_eq!(ptr1.offset(2), ptr2);
522 /// assert_eq!(ptr2.offset(-2), ptr1);
526 /// *Incorrect* usage:
529 /// #![feature(ptr_offset_from)]
531 /// let ptr1 = Box::into_raw(Box::new(0u8));
532 /// let ptr2 = Box::into_raw(Box::new(1u8));
533 /// let diff = (ptr2 as isize).wrapping_sub(ptr1 as isize);
534 /// // Make ptr2_other an "alias" of ptr2, but derived from ptr1.
535 /// let ptr2_other = (ptr1 as *mut u8).wrapping_offset(diff);
536 /// assert_eq!(ptr2 as usize, ptr2_other as usize);
537 /// // Since ptr2_other and ptr2 are derived from pointers to different objects,
538 /// // computing their offset is undefined behavior, even though
539 /// // they point to the same address!
541 /// let zero = ptr2_other.offset_from(ptr2); // Undefined Behavior
544 #[unstable(feature = "ptr_offset_from", issue = "41079")]
545 #[rustc_const_unstable(feature = "const_ptr_offset_from", issue = "41079")]
547 pub const unsafe fn offset_from(self, origin: *const T) -> isize
551 // SAFETY: the caller must uphold the safety contract for `offset_from`.
552 unsafe { (self as *const T).offset_from(origin) }
555 /// Calculates the distance between two pointers. The returned value is in
556 /// units of T: the distance in bytes is divided by `mem::size_of::<T>()`.
558 /// If the address different between the two pointers is not a multiple of
559 /// `mem::size_of::<T>()` then the result of the division is rounded towards
562 /// Though this method is safe for any two pointers, note that its result
563 /// will be mostly useless if the two pointers aren't into the same allocated
564 /// object, for example if they point to two different local variables.
568 /// This function panics if `T` is a zero-sized type.
575 /// #![feature(ptr_wrapping_offset_from)]
577 /// let mut a = [0; 5];
578 /// let ptr1: *mut i32 = &mut a[1];
579 /// let ptr2: *mut i32 = &mut a[3];
580 /// assert_eq!(ptr2.wrapping_offset_from(ptr1), 2);
581 /// assert_eq!(ptr1.wrapping_offset_from(ptr2), -2);
582 /// assert_eq!(ptr1.wrapping_offset(2), ptr2);
583 /// assert_eq!(ptr2.wrapping_offset(-2), ptr1);
585 /// let ptr1: *mut i32 = 3 as _;
586 /// let ptr2: *mut i32 = 13 as _;
587 /// assert_eq!(ptr2.wrapping_offset_from(ptr1), 2);
589 #[unstable(feature = "ptr_wrapping_offset_from", issue = "41079")]
592 reason = "Pointer distances across allocation \
593 boundaries are not typically meaningful. \
594 Use integer subtraction if you really need this."
597 pub fn wrapping_offset_from(self, origin: *const T) -> isize
601 #[allow(deprecated_in_future, deprecated)]
602 (self as *const T).wrapping_offset_from(origin)
605 /// Calculates the offset from a pointer (convenience for `.offset(count as isize)`).
607 /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
608 /// offset of `3 * size_of::<T>()` bytes.
612 /// If any of the following conditions are violated, the result is Undefined
615 /// * Both the starting and resulting pointer must be either in bounds or one
616 /// byte past the end of the same allocated object. Note that in Rust,
617 /// every (stack-allocated) variable is considered a separate allocated object.
619 /// * The computed offset, **in bytes**, cannot overflow an `isize`.
621 /// * The offset being in bounds cannot rely on "wrapping around" the address
622 /// space. That is, the infinite-precision sum must fit in a `usize`.
624 /// The compiler and standard library generally tries to ensure allocations
625 /// never reach a size where an offset is a concern. For instance, `Vec`
626 /// and `Box` ensure they never allocate more than `isize::MAX` bytes, so
627 /// `vec.as_ptr().add(vec.len())` is always safe.
629 /// Most platforms fundamentally can't even construct such an allocation.
630 /// For instance, no known 64-bit platform can ever serve a request
631 /// for 2<sup>63</sup> bytes due to page-table limitations or splitting the address space.
632 /// However, some 32-bit and 16-bit platforms may successfully serve a request for
633 /// more than `isize::MAX` bytes with things like Physical Address
634 /// Extension. As such, memory acquired directly from allocators or memory
635 /// mapped files *may* be too large to handle with this function.
637 /// Consider using [`wrapping_add`] instead if these constraints are
638 /// difficult to satisfy. The only advantage of this method is that it
639 /// enables more aggressive compiler optimizations.
641 /// [`wrapping_add`]: #method.wrapping_add
648 /// let s: &str = "123";
649 /// let ptr: *const u8 = s.as_ptr();
652 /// println!("{}", *ptr.add(1) as char);
653 /// println!("{}", *ptr.add(2) as char);
656 #[stable(feature = "pointer_methods", since = "1.26.0")]
657 #[must_use = "returns a new pointer rather than modifying its argument"]
658 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
660 pub const unsafe fn add(self, count: usize) -> Self
664 // SAFETY: the caller must uphold the safety contract for `offset`.
665 unsafe { self.offset(count as isize) }
668 /// Calculates the offset from a pointer (convenience for
669 /// `.offset((count as isize).wrapping_neg())`).
671 /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
672 /// offset of `3 * size_of::<T>()` bytes.
676 /// If any of the following conditions are violated, the result is Undefined
679 /// * Both the starting and resulting pointer must be either in bounds or one
680 /// byte past the end of the same allocated object. Note that in Rust,
681 /// every (stack-allocated) variable is considered a separate allocated object.
683 /// * The computed offset cannot exceed `isize::MAX` **bytes**.
685 /// * The offset being in bounds cannot rely on "wrapping around" the address
686 /// space. That is, the infinite-precision sum must fit in a usize.
688 /// The compiler and standard library generally tries to ensure allocations
689 /// never reach a size where an offset is a concern. For instance, `Vec`
690 /// and `Box` ensure they never allocate more than `isize::MAX` bytes, so
691 /// `vec.as_ptr().add(vec.len()).sub(vec.len())` is always safe.
693 /// Most platforms fundamentally can't even construct such an allocation.
694 /// For instance, no known 64-bit platform can ever serve a request
695 /// for 2<sup>63</sup> bytes due to page-table limitations or splitting the address space.
696 /// However, some 32-bit and 16-bit platforms may successfully serve a request for
697 /// more than `isize::MAX` bytes with things like Physical Address
698 /// Extension. As such, memory acquired directly from allocators or memory
699 /// mapped files *may* be too large to handle with this function.
701 /// Consider using [`wrapping_sub`] instead if these constraints are
702 /// difficult to satisfy. The only advantage of this method is that it
703 /// enables more aggressive compiler optimizations.
705 /// [`wrapping_sub`]: #method.wrapping_sub
712 /// let s: &str = "123";
715 /// let end: *const u8 = s.as_ptr().add(3);
716 /// println!("{}", *end.sub(1) as char);
717 /// println!("{}", *end.sub(2) as char);
720 #[stable(feature = "pointer_methods", since = "1.26.0")]
721 #[must_use = "returns a new pointer rather than modifying its argument"]
722 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
724 pub const unsafe fn sub(self, count: usize) -> Self
728 // SAFETY: the caller must uphold the safety contract for `offset`.
729 unsafe { self.offset((count as isize).wrapping_neg()) }
732 /// Calculates the offset from a pointer using wrapping arithmetic.
733 /// (convenience for `.wrapping_offset(count as isize)`)
735 /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
736 /// offset of `3 * size_of::<T>()` bytes.
740 /// The resulting pointer does not need to be in bounds, but it is
741 /// potentially hazardous to dereference (which requires `unsafe`).
743 /// In particular, the resulting pointer remains attached to the same allocated
744 /// object that `self` points to. It may *not* be used to access a
745 /// different allocated object. Note that in Rust,
746 /// every (stack-allocated) variable is considered a separate allocated object.
748 /// Compared to [`add`], this method basically delays the requirement of staying
749 /// within the same allocated object: [`add`] is immediate Undefined Behavior when
750 /// crossing object boundaries; `wrapping_add` produces a pointer but still leads
751 /// to Undefined Behavior if that pointer is dereferenced. [`add`] can be optimized
752 /// better and is thus preferable in performance-sensitive code.
754 /// If you need to cross object boundaries, cast the pointer to an integer and
755 /// do the arithmetic there.
757 /// [`add`]: #method.add
764 /// // Iterate using a raw pointer in increments of two elements
765 /// let data = [1u8, 2, 3, 4, 5];
766 /// let mut ptr: *const u8 = data.as_ptr();
768 /// let end_rounded_up = ptr.wrapping_add(6);
770 /// // This loop prints "1, 3, 5, "
771 /// while ptr != end_rounded_up {
773 /// print!("{}, ", *ptr);
775 /// ptr = ptr.wrapping_add(step);
778 #[stable(feature = "pointer_methods", since = "1.26.0")]
779 #[must_use = "returns a new pointer rather than modifying its argument"]
780 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
782 pub const fn wrapping_add(self, count: usize) -> Self
786 self.wrapping_offset(count as isize)
789 /// Calculates the offset from a pointer using wrapping arithmetic.
790 /// (convenience for `.wrapping_offset((count as isize).wrapping_sub())`)
792 /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
793 /// offset of `3 * size_of::<T>()` bytes.
797 /// The resulting pointer does not need to be in bounds, but it is
798 /// potentially hazardous to dereference (which requires `unsafe`).
800 /// In particular, the resulting pointer remains attached to the same allocated
801 /// object that `self` points to. It may *not* be used to access a
802 /// different allocated object. Note that in Rust,
803 /// every (stack-allocated) variable is considered a separate allocated object.
805 /// Compared to [`sub`], this method basically delays the requirement of staying
806 /// within the same allocated object: [`sub`] is immediate Undefined Behavior when
807 /// crossing object boundaries; `wrapping_sub` produces a pointer but still leads
808 /// to Undefined Behavior if that pointer is dereferenced. [`sub`] can be optimized
809 /// better and is thus preferable in performance-sensitive code.
811 /// If you need to cross object boundaries, cast the pointer to an integer and
812 /// do the arithmetic there.
814 /// [`sub`]: #method.sub
821 /// // Iterate using a raw pointer in increments of two elements (backwards)
822 /// let data = [1u8, 2, 3, 4, 5];
823 /// let mut ptr: *const u8 = data.as_ptr();
824 /// let start_rounded_down = ptr.wrapping_sub(2);
825 /// ptr = ptr.wrapping_add(4);
827 /// // This loop prints "5, 3, 1, "
828 /// while ptr != start_rounded_down {
830 /// print!("{}, ", *ptr);
832 /// ptr = ptr.wrapping_sub(step);
835 #[stable(feature = "pointer_methods", since = "1.26.0")]
836 #[must_use = "returns a new pointer rather than modifying its argument"]
837 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
839 pub const fn wrapping_sub(self, count: usize) -> Self
843 self.wrapping_offset((count as isize).wrapping_neg())
846 /// Sets the pointer value to `ptr`.
848 /// In case `self` is a (fat) pointer to an unsized type, this operation
849 /// will only affect the pointer part, whereas for (thin) pointers to
850 /// sized types, this has the same effect as a simple assignment.
852 /// The resulting pointer will have provenance of `val`, i.e., for a fat
853 /// pointer, this operation is semantically the same as creating a new
854 /// fat pointer with the data pointer value of `val` but the metadata of
859 /// This function is primarily useful for allowing byte-wise pointer
860 /// arithmetic on potentially fat pointers:
863 /// #![feature(set_ptr_value)]
864 /// # use core::fmt::Debug;
865 /// let mut arr: [i32; 3] = [1, 2, 3];
866 /// let mut ptr = &mut arr[0] as *mut dyn Debug;
867 /// let thin = ptr as *mut u8;
869 /// ptr = ptr.set_ptr_value(thin.add(8));
870 /// # assert_eq!(*(ptr as *mut i32), 3);
871 /// println!("{:?}", &*ptr); // will print "3"
874 #[unstable(feature = "set_ptr_value", issue = "75091")]
875 #[must_use = "returns a new pointer rather than modifying its argument"]
877 pub fn set_ptr_value(mut self, val: *mut u8) -> Self {
878 let thin = &mut self as *mut *mut T as *mut *mut u8;
879 // SAFETY: In case of a thin pointer, this operations is identical
880 // to a simple assignment. In case of a fat pointer, with the current
881 // fat pointer layout implementation, the first field of such a
882 // pointer is always the data pointer, which is likewise assigned.
883 unsafe { *thin = val };
887 /// Reads the value from `self` without moving it. This leaves the
888 /// memory in `self` unchanged.
890 /// See [`ptr::read`] for safety concerns and examples.
892 /// [`ptr::read`]: ./ptr/fn.read.html
893 #[stable(feature = "pointer_methods", since = "1.26.0")]
895 pub unsafe fn read(self) -> T
899 // SAFETY: the caller must uphold the safety contract for ``.
900 unsafe { read(self) }
903 /// Performs a volatile read of the value from `self` without moving it. This
904 /// leaves the memory in `self` unchanged.
906 /// Volatile operations are intended to act on I/O memory, and are guaranteed
907 /// to not be elided or reordered by the compiler across other volatile
910 /// See [`ptr::read_volatile`] for safety concerns and examples.
912 /// [`ptr::read_volatile`]: ./ptr/fn.read_volatile.html
913 #[stable(feature = "pointer_methods", since = "1.26.0")]
915 pub unsafe fn read_volatile(self) -> T
919 // SAFETY: the caller must uphold the safety contract for `read_volatile`.
920 unsafe { read_volatile(self) }
923 /// Reads the value from `self` without moving it. This leaves the
924 /// memory in `self` unchanged.
926 /// Unlike `read`, the pointer may be unaligned.
928 /// See [`ptr::read_unaligned`] for safety concerns and examples.
930 /// [`ptr::read_unaligned`]: ./ptr/fn.read_unaligned.html
931 #[stable(feature = "pointer_methods", since = "1.26.0")]
933 pub unsafe fn read_unaligned(self) -> T
937 // SAFETY: the caller must uphold the safety contract for `read_unaligned`.
938 unsafe { read_unaligned(self) }
941 /// Copies `count * size_of<T>` bytes from `self` to `dest`. The source
942 /// and destination may overlap.
944 /// NOTE: this has the *same* argument order as [`ptr::copy`].
946 /// See [`ptr::copy`] for safety concerns and examples.
948 /// [`ptr::copy`]: ./ptr/fn.copy.html
949 #[stable(feature = "pointer_methods", since = "1.26.0")]
951 pub unsafe fn copy_to(self, dest: *mut T, count: usize)
955 // SAFETY: the caller must uphold the safety contract for `copy`.
956 unsafe { copy(self, dest, count) }
959 /// Copies `count * size_of<T>` bytes from `self` to `dest`. The source
960 /// and destination may *not* overlap.
962 /// NOTE: this has the *same* argument order as [`ptr::copy_nonoverlapping`].
964 /// See [`ptr::copy_nonoverlapping`] for safety concerns and examples.
966 /// [`ptr::copy_nonoverlapping`]: ./ptr/fn.copy_nonoverlapping.html
967 #[stable(feature = "pointer_methods", since = "1.26.0")]
969 pub unsafe fn copy_to_nonoverlapping(self, dest: *mut T, count: usize)
973 // SAFETY: the caller must uphold the safety contract for `copy_nonoverlapping`.
974 unsafe { copy_nonoverlapping(self, dest, count) }
977 /// Copies `count * size_of<T>` bytes from `src` to `self`. The source
978 /// and destination may overlap.
980 /// NOTE: this has the *opposite* argument order of [`ptr::copy`].
982 /// See [`ptr::copy`] for safety concerns and examples.
984 /// [`ptr::copy`]: ./ptr/fn.copy.html
985 #[stable(feature = "pointer_methods", since = "1.26.0")]
987 pub unsafe fn copy_from(self, src: *const T, count: usize)
991 // SAFETY: the caller must uphold the safety contract for `copy`.
992 unsafe { copy(src, self, count) }
995 /// Copies `count * size_of<T>` bytes from `src` to `self`. The source
996 /// and destination may *not* overlap.
998 /// NOTE: this has the *opposite* argument order of [`ptr::copy_nonoverlapping`].
1000 /// See [`ptr::copy_nonoverlapping`] for safety concerns and examples.
1002 /// [`ptr::copy_nonoverlapping`]: ./ptr/fn.copy_nonoverlapping.html
1003 #[stable(feature = "pointer_methods", since = "1.26.0")]
1005 pub unsafe fn copy_from_nonoverlapping(self, src: *const T, count: usize)
1009 // SAFETY: the caller must uphold the safety contract for `copy_nonoverlapping`.
1010 unsafe { copy_nonoverlapping(src, self, count) }
1013 /// Executes the destructor (if any) of the pointed-to value.
1015 /// See [`ptr::drop_in_place`] for safety concerns and examples.
1017 /// [`ptr::drop_in_place`]: ./ptr/fn.drop_in_place.html
1018 #[stable(feature = "pointer_methods", since = "1.26.0")]
1020 pub unsafe fn drop_in_place(self) {
1021 // SAFETY: the caller must uphold the safety contract for `drop_in_place`.
1022 unsafe { drop_in_place(self) }
1025 /// Overwrites a memory location with the given value without reading or
1026 /// dropping the old value.
1028 /// See [`ptr::write`] for safety concerns and examples.
1030 /// [`ptr::write`]: ./ptr/fn.write.html
1031 #[stable(feature = "pointer_methods", since = "1.26.0")]
1033 pub unsafe fn write(self, val: T)
1037 // SAFETY: the caller must uphold the safety contract for `write`.
1038 unsafe { write(self, val) }
1041 /// Invokes memset on the specified pointer, setting `count * size_of::<T>()`
1042 /// bytes of memory starting at `self` to `val`.
1044 /// See [`ptr::write_bytes`] for safety concerns and examples.
1046 /// [`ptr::write_bytes`]: ./ptr/fn.write_bytes.html
1047 #[stable(feature = "pointer_methods", since = "1.26.0")]
1049 pub unsafe fn write_bytes(self, val: u8, count: usize)
1053 // SAFETY: the caller must uphold the safety contract for `write_bytes`.
1054 unsafe { write_bytes(self, val, count) }
1057 /// Performs a volatile write of a memory location with the given value without
1058 /// reading or dropping the old value.
1060 /// Volatile operations are intended to act on I/O memory, and are guaranteed
1061 /// to not be elided or reordered by the compiler across other volatile
1064 /// See [`ptr::write_volatile`] for safety concerns and examples.
1066 /// [`ptr::write_volatile`]: ./ptr/fn.write_volatile.html
1067 #[stable(feature = "pointer_methods", since = "1.26.0")]
1069 pub unsafe fn write_volatile(self, val: T)
1073 // SAFETY: the caller must uphold the safety contract for `write_volatile`.
1074 unsafe { write_volatile(self, val) }
1077 /// Overwrites a memory location with the given value without reading or
1078 /// dropping the old value.
1080 /// Unlike `write`, the pointer may be unaligned.
1082 /// See [`ptr::write_unaligned`] for safety concerns and examples.
1084 /// [`ptr::write_unaligned`]: ./ptr/fn.write_unaligned.html
1085 #[stable(feature = "pointer_methods", since = "1.26.0")]
1087 pub unsafe fn write_unaligned(self, val: T)
1091 // SAFETY: the caller must uphold the safety contract for `write_unaligned`.
1092 unsafe { write_unaligned(self, val) }
1095 /// Replaces the value at `self` with `src`, returning the old
1096 /// value, without dropping either.
1098 /// See [`ptr::replace`] for safety concerns and examples.
1100 /// [`ptr::replace`]: ./ptr/fn.replace.html
1101 #[stable(feature = "pointer_methods", since = "1.26.0")]
1103 pub unsafe fn replace(self, src: T) -> T
1107 // SAFETY: the caller must uphold the safety contract for `replace`.
1108 unsafe { replace(self, src) }
1111 /// Swaps the values at two mutable locations of the same type, without
1112 /// deinitializing either. They may overlap, unlike `mem::swap` which is
1113 /// otherwise equivalent.
1115 /// See [`ptr::swap`] for safety concerns and examples.
1117 /// [`ptr::swap`]: ./ptr/fn.swap.html
1118 #[stable(feature = "pointer_methods", since = "1.26.0")]
1120 pub unsafe fn swap(self, with: *mut T)
1124 // SAFETY: the caller must uphold the safety contract for `swap`.
1125 unsafe { swap(self, with) }
1128 /// Computes the offset that needs to be applied to the pointer in order to make it aligned to
1131 /// If it is not possible to align the pointer, the implementation returns
1132 /// `usize::MAX`. It is permissible for the implementation to *always*
1133 /// return `usize::MAX`. Only your algorithm's performance can depend
1134 /// on getting a usable offset here, not its correctness.
1136 /// The offset is expressed in number of `T` elements, and not bytes. The value returned can be
1137 /// used with the `wrapping_add` method.
1139 /// There are no guarantees whatsoever that offsetting the pointer will not overflow or go
1140 /// beyond the allocation that the pointer points into. It is up to the caller to ensure that
1141 /// the returned offset is correct in all terms other than alignment.
1145 /// The function panics if `align` is not a power-of-two.
1149 /// Accessing adjacent `u8` as `u16`
1152 /// # fn foo(n: usize) {
1153 /// # use std::mem::align_of;
1155 /// let x = [5u8, 6u8, 7u8, 8u8, 9u8];
1156 /// let ptr = &x[n] as *const u8;
1157 /// let offset = ptr.align_offset(align_of::<u16>());
1158 /// if offset < x.len() - n - 1 {
1159 /// let u16_ptr = ptr.add(offset) as *const u16;
1160 /// assert_ne!(*u16_ptr, 500);
1162 /// // while the pointer can be aligned via `offset`, it would point
1163 /// // outside the allocation
1167 #[stable(feature = "align_offset", since = "1.36.0")]
1168 pub fn align_offset(self, align: usize) -> usize
1172 if !align.is_power_of_two() {
1173 panic!("align_offset: align is not a power-of-two");
1175 // SAFETY: `align` has been checked to be a power of 2 above
1176 unsafe { align_offset(self, align) }
1180 #[lang = "mut_slice_ptr"]
1182 /// Returns the length of a raw slice.
1184 /// The returned value is the number of **elements**, not the number of bytes.
1186 /// This function is safe, even when the raw slice cannot be cast to a slice
1187 /// reference because the pointer is null or unaligned.
1192 /// #![feature(slice_ptr_len)]
1195 /// let slice: *mut [i8] = ptr::slice_from_raw_parts_mut(ptr::null_mut(), 3);
1196 /// assert_eq!(slice.len(), 3);
1199 #[unstable(feature = "slice_ptr_len", issue = "71146")]
1200 #[rustc_const_unstable(feature = "const_slice_ptr_len", issue = "71146")]
1201 pub const fn len(self) -> usize {
1202 // SAFETY: this is safe because `*const [T]` and `FatPtr<T>` have the same layout.
1203 // Only `std` can make this guarantee.
1204 unsafe { Repr { rust_mut: self }.raw }.len
1207 /// Returns a raw pointer to the slice's buffer.
1209 /// This is equivalent to casting `self` to `*mut T`, but more type-safe.
1214 /// #![feature(slice_ptr_get)]
1217 /// let slice: *mut [i8] = ptr::slice_from_raw_parts_mut(ptr::null_mut(), 3);
1218 /// assert_eq!(slice.as_mut_ptr(), 0 as *mut i8);
1221 #[unstable(feature = "slice_ptr_get", issue = "74265")]
1222 #[rustc_const_unstable(feature = "slice_ptr_get", issue = "74265")]
1223 pub const fn as_mut_ptr(self) -> *mut T {
1227 /// Returns a raw pointer to an element or subslice, without doing bounds
1230 /// Calling this method with an out-of-bounds index or when `self` is not dereferencable
1231 /// is *[undefined behavior]* even if the resulting pointer is not used.
1233 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1238 /// #![feature(slice_ptr_get)]
1240 /// let x = &mut [1, 2, 4] as *mut [i32];
1243 /// assert_eq!(x.get_unchecked_mut(1), x.as_mut_ptr().add(1));
1246 #[unstable(feature = "slice_ptr_get", issue = "74265")]
1248 pub unsafe fn get_unchecked_mut<I>(self, index: I) -> *mut I::Output
1252 // SAFETY: the caller ensures that `self` is dereferencable and `index` in-bounds.
1253 unsafe { index.get_unchecked_mut(self) }
1256 /// Returns `None` if the pointer is null, or else returns a shared slice to
1257 /// the value wrapped in `Some`. In contrast to [`as_ref`], this does not require
1258 /// that the value has to be initialized.
1260 /// For the mutable counterpart see [`as_uninit_slice_mut`].
1262 /// [`as_ref`]: #method.as_ref-1
1263 /// [`as_uninit_slice_mut`]: #method.as_uninit_slice_mut
1267 /// When calling this method, you have to ensure that *either* the pointer is NULL *or*
1268 /// all of the following is true:
1270 /// * The pointer must be [valid] for reads for `ptr.len() * mem::size_of::<T>()` many bytes,
1271 /// and it must be properly aligned. This means in particular:
1273 /// * The entire memory range of this slice must be contained within a single allocated object!
1274 /// Slices can never span across multiple allocated objects.
1276 /// * The pointer must be aligned even for zero-length slices. One
1277 /// reason for this is that enum layout optimizations may rely on references
1278 /// (including slices of any length) being aligned and non-null to distinguish
1279 /// them from other data. You can obtain a pointer that is usable as `data`
1280 /// for zero-length slices using [`NonNull::dangling()`].
1282 /// * The total size `ptr.len() * mem::size_of::<T>()` of the slice must be no larger than `isize::MAX`.
1283 /// See the safety documentation of [`pointer::offset`].
1285 /// * You must enforce Rust's aliasing rules, since the returned lifetime `'a` is
1286 /// arbitrarily chosen and does not necessarily reflect the actual lifetime of the data.
1287 /// In particular, for the duration of this lifetime, the memory the pointer points to must
1288 /// not get mutated (except inside `UnsafeCell`).
1290 /// This applies even if the result of this method is unused!
1292 /// See also [`slice::from_raw_parts`][].
1294 /// [valid]: crate::ptr#safety
1295 /// [`NonNull::dangling()`]: NonNull::dangling
1296 /// [`pointer::offset`]: ../std/primitive.pointer.html#method.offset
1298 #[unstable(feature = "ptr_as_uninit", issue = "75402")]
1299 pub unsafe fn as_uninit_slice<'a>(self) -> Option<&'a [MaybeUninit<T>]> {
1303 // SAFETY: the caller must uphold the safety contract for `as_uninit_slice`.
1304 Some(unsafe { slice::from_raw_parts(self as *const MaybeUninit<T>, self.len()) })
1308 /// Returns `None` if the pointer is null, or else returns a unique slice to
1309 /// the value wrapped in `Some`. In contrast to [`as_mut`], this does not require
1310 /// that the value has to be initialized.
1312 /// For the shared counterpart see [`as_uninit_slice`].
1314 /// [`as_mut`]: #method.as_mut
1315 /// [`as_uninit_slice`]: #method.as_uninit_slice-1
1319 /// When calling this method, you have to ensure that *either* the pointer is NULL *or*
1320 /// all of the following is true:
1322 /// * The pointer must be [valid] for reads and writes for `ptr.len() * mem::size_of::<T>()`
1323 /// many bytes, and it must be properly aligned. This means in particular:
1325 /// * The entire memory range of this slice must be contained within a single allocated object!
1326 /// Slices can never span across multiple allocated objects.
1328 /// * The pointer must be aligned even for zero-length slices. One
1329 /// reason for this is that enum layout optimizations may rely on references
1330 /// (including slices of any length) being aligned and non-null to distinguish
1331 /// them from other data. You can obtain a pointer that is usable as `data`
1332 /// for zero-length slices using [`NonNull::dangling()`].
1334 /// * The total size `ptr.len() * mem::size_of::<T>()` of the slice must be no larger than `isize::MAX`.
1335 /// See the safety documentation of [`pointer::offset`].
1337 /// * You must enforce Rust's aliasing rules, since the returned lifetime `'a` is
1338 /// arbitrarily chosen and does not necessarily reflect the actual lifetime of the data.
1339 /// In particular, for the duration of this lifetime, the memory the pointer points to must
1340 /// not get accessed (read or written) through any other pointer.
1342 /// This applies even if the result of this method is unused!
1344 /// See also [`slice::from_raw_parts_mut`][].
1346 /// [valid]: crate::ptr#safety
1347 /// [`NonNull::dangling()`]: NonNull::dangling
1348 /// [`pointer::offset`]: ../std/primitive.pointer.html#method.offset
1350 #[unstable(feature = "ptr_as_uninit", issue = "75402")]
1351 pub unsafe fn as_uninit_slice_mut<'a>(self) -> Option<&'a mut [MaybeUninit<T>]> {
1355 // SAFETY: the caller must uphold the safety contract for `as_uninit_slice_mut`.
1356 Some(unsafe { slice::from_raw_parts_mut(self as *mut MaybeUninit<T>, self.len()) })
1361 // Equality for pointers
1362 #[stable(feature = "rust1", since = "1.0.0")]
1363 impl<T: ?Sized> PartialEq for *mut T {
1365 fn eq(&self, other: &*mut T) -> bool {
1370 #[stable(feature = "rust1", since = "1.0.0")]
1371 impl<T: ?Sized> Eq for *mut T {}
1373 #[stable(feature = "rust1", since = "1.0.0")]
1374 impl<T: ?Sized> Ord for *mut T {
1376 fn cmp(&self, other: &*mut T) -> Ordering {
1379 } else if self == other {
1387 #[stable(feature = "rust1", since = "1.0.0")]
1388 impl<T: ?Sized> PartialOrd for *mut T {
1390 fn partial_cmp(&self, other: &*mut T) -> Option<Ordering> {
1391 Some(self.cmp(other))
1395 fn lt(&self, other: &*mut T) -> bool {
1400 fn le(&self, other: &*mut T) -> bool {
1405 fn gt(&self, other: &*mut T) -> bool {
1410 fn ge(&self, other: &*mut T) -> bool {