| use super::*; |
| use crate::cmp::Ordering::{Equal, Greater, Less}; |
| use crate::intrinsics::const_eval_select; |
| use crate::mem::{self, SizedTypeProperties}; |
| use crate::slice::{self, SliceIndex}; |
| |
| impl<T: PointeeSized> *const T { |
| #[doc = include_str!("docs/is_null.md")] |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let s: &str = "Follow the rabbit"; |
| /// let ptr: *const u8 = s.as_ptr(); |
| /// assert!(!ptr.is_null()); |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[rustc_const_stable(feature = "const_ptr_is_null", since = "1.84.0")] |
| #[rustc_diagnostic_item = "ptr_const_is_null"] |
| #[inline] |
| #[rustc_allow_const_fn_unstable(const_eval_select)] |
| pub const fn is_null(self) -> bool { |
| // Compare via a cast to a thin pointer, so fat pointers are only |
| // considering their "data" part for null-ness. |
| let ptr = self as *const u8; |
| const_eval_select!( |
| @capture { ptr: *const u8 } -> bool: |
| // This use of `const_raw_ptr_comparison` has been explicitly blessed by t-lang. |
| if const #[rustc_allow_const_fn_unstable(const_raw_ptr_comparison)] { |
| match (ptr).guaranteed_eq(null_mut()) { |
| Some(res) => res, |
| // To remain maximally conservative, we stop execution when we don't |
| // know whether the pointer is null or not. |
| // We can *not* return `false` here, that would be unsound in `NonNull::new`! |
| None => panic!("null-ness of this pointer cannot be determined in const context"), |
| } |
| } else { |
| ptr.addr() == 0 |
| } |
| ) |
| } |
| |
| /// Casts to a pointer of another type. |
| #[stable(feature = "ptr_cast", since = "1.38.0")] |
| #[rustc_const_stable(feature = "const_ptr_cast", since = "1.38.0")] |
| #[rustc_diagnostic_item = "const_ptr_cast"] |
| #[inline(always)] |
| pub const fn cast<U>(self) -> *const U { |
| self as _ |
| } |
| |
| /// Try to cast to a pointer of another type by checking alignment. |
| /// |
| /// If the pointer is properly aligned to the target type, it will be |
| /// cast to the target type. Otherwise, `None` is returned. |
| /// |
| /// # Examples |
| /// |
| /// ```rust |
| /// #![feature(pointer_try_cast_aligned)] |
| /// |
| /// let x = 0u64; |
| /// |
| /// let aligned: *const u64 = &x; |
| /// let unaligned = unsafe { aligned.byte_add(1) }; |
| /// |
| /// assert!(aligned.try_cast_aligned::<u32>().is_some()); |
| /// assert!(unaligned.try_cast_aligned::<u32>().is_none()); |
| /// ``` |
| #[unstable(feature = "pointer_try_cast_aligned", issue = "141221")] |
| #[must_use = "this returns the result of the operation, \ |
| without modifying the original"] |
| #[inline] |
| pub fn try_cast_aligned<U>(self) -> Option<*const U> { |
| if self.is_aligned_to(align_of::<U>()) { Some(self.cast()) } else { None } |
| } |
| |
| /// Uses the address value in a new pointer of another type. |
| /// |
| /// This operation will ignore the address part of its `meta` operand and discard existing |
| /// metadata of `self`. For pointers to a sized types (thin pointers), this has the same effect |
| /// as a simple cast. For pointers to an unsized type (fat pointers) this recombines the address |
| /// with new metadata such as slice lengths or `dyn`-vtable. |
| /// |
| /// The resulting pointer will have provenance of `self`. This operation is semantically the |
| /// same as creating a new pointer with the data pointer value of `self` but the metadata of |
| /// `meta`, being fat or thin depending on the `meta` operand. |
| /// |
| /// # Examples |
| /// |
| /// This function is primarily useful for enabling pointer arithmetic on potentially fat |
| /// pointers. The pointer is cast to a sized pointee to utilize offset operations and then |
| /// recombined with its own original metadata. |
| /// |
| /// ``` |
| /// #![feature(set_ptr_value)] |
| /// # use core::fmt::Debug; |
| /// let arr: [i32; 3] = [1, 2, 3]; |
| /// let mut ptr = arr.as_ptr() as *const dyn Debug; |
| /// let thin = ptr as *const u8; |
| /// unsafe { |
| /// ptr = thin.add(8).with_metadata_of(ptr); |
| /// # assert_eq!(*(ptr as *const i32), 3); |
| /// println!("{:?}", &*ptr); // will print "3" |
| /// } |
| /// ``` |
| /// |
| /// # *Incorrect* usage |
| /// |
| /// The provenance from pointers is *not* combined. The result must only be used to refer to the |
| /// address allowed by `self`. |
| /// |
| /// ```rust,no_run |
| /// #![feature(set_ptr_value)] |
| /// let x = 0u32; |
| /// let y = 1u32; |
| /// |
| /// let x = (&x) as *const u32; |
| /// let y = (&y) as *const u32; |
| /// |
| /// let offset = (x as usize - y as usize) / 4; |
| /// let bad = x.wrapping_add(offset).with_metadata_of(y); |
| /// |
| /// // This dereference is UB. The pointer only has provenance for `x` but points to `y`. |
| /// println!("{:?}", unsafe { &*bad }); |
| /// ``` |
| #[unstable(feature = "set_ptr_value", issue = "75091")] |
| #[must_use = "returns a new pointer rather than modifying its argument"] |
| #[inline] |
| pub const fn with_metadata_of<U>(self, meta: *const U) -> *const U |
| where |
| U: PointeeSized, |
| { |
| from_raw_parts::<U>(self as *const (), metadata(meta)) |
| } |
| |
| /// Changes constness without changing the type. |
| /// |
| /// This is a bit safer than `as` because it wouldn't silently change the type if the code is |
| /// refactored. |
| #[stable(feature = "ptr_const_cast", since = "1.65.0")] |
| #[rustc_const_stable(feature = "ptr_const_cast", since = "1.65.0")] |
| #[rustc_diagnostic_item = "ptr_cast_mut"] |
| #[inline(always)] |
| pub const fn cast_mut(self) -> *mut T { |
| self as _ |
| } |
| |
| #[doc = include_str!("./docs/addr.md")] |
| #[must_use] |
| #[inline(always)] |
| #[stable(feature = "strict_provenance", since = "1.84.0")] |
| pub fn addr(self) -> usize { |
| // A pointer-to-integer transmute currently has exactly the right semantics: it returns the |
| // address without exposing the provenance. Note that this is *not* a stable guarantee about |
| // transmute semantics, it relies on sysroot crates having special status. |
| // SAFETY: Pointer-to-integer transmutes are valid (if you are okay with losing the |
| // provenance). |
| unsafe { mem::transmute(self.cast::<()>()) } |
| } |
| |
| /// Exposes the ["provenance"][crate::ptr#provenance] part of the pointer for future use in |
| /// [`with_exposed_provenance`] and returns the "address" portion. |
| /// |
| /// This is equivalent to `self as usize`, which semantically discards provenance information. |
| /// Furthermore, this (like the `as` cast) has the implicit side-effect of marking the |
| /// provenance as 'exposed', so on platforms that support it you can later call |
| /// [`with_exposed_provenance`] to reconstitute the original pointer including its provenance. |
| /// |
| /// Due to its inherent ambiguity, [`with_exposed_provenance`] may not be supported by tools |
| /// that help you to stay conformant with the Rust memory model. It is recommended to use |
| /// [Strict Provenance][crate::ptr#strict-provenance] APIs such as [`with_addr`][pointer::with_addr] |
| /// wherever possible, in which case [`addr`][pointer::addr] should be used instead of `expose_provenance`. |
| /// |
| /// On most platforms this will produce a value with the same bytes as the original pointer, |
| /// because all the bytes are dedicated to describing the address. Platforms which need to store |
| /// additional information in the pointer may not support this operation, since the 'expose' |
| /// side-effect which is required for [`with_exposed_provenance`] to work is typically not |
| /// available. |
| /// |
| /// This is an [Exposed Provenance][crate::ptr#exposed-provenance] API. |
| /// |
| /// [`with_exposed_provenance`]: with_exposed_provenance |
| #[inline(always)] |
| #[stable(feature = "exposed_provenance", since = "1.84.0")] |
| pub fn expose_provenance(self) -> usize { |
| self.cast::<()>() as usize |
| } |
| |
| /// Creates a new pointer with the given address and the [provenance][crate::ptr#provenance] of |
| /// `self`. |
| /// |
| /// This is similar to a `addr as *const T` cast, but copies |
| /// the *provenance* of `self` to the new pointer. |
| /// This avoids the inherent ambiguity of the unary cast. |
| /// |
| /// This is equivalent to using [`wrapping_offset`][pointer::wrapping_offset] to offset |
| /// `self` to the given address, and therefore has all the same capabilities and restrictions. |
| /// |
| /// This is a [Strict Provenance][crate::ptr#strict-provenance] API. |
| #[must_use] |
| #[inline] |
| #[stable(feature = "strict_provenance", since = "1.84.0")] |
| pub fn with_addr(self, addr: usize) -> Self { |
| // This should probably be an intrinsic to avoid doing any sort of arithmetic, but |
| // meanwhile, we can implement it with `wrapping_offset`, which preserves the pointer's |
| // provenance. |
| let self_addr = self.addr() as isize; |
| let dest_addr = addr as isize; |
| let offset = dest_addr.wrapping_sub(self_addr); |
| self.wrapping_byte_offset(offset) |
| } |
| |
| /// Creates a new pointer by mapping `self`'s address to a new one, preserving the |
| /// [provenance][crate::ptr#provenance] of `self`. |
| /// |
| /// This is a convenience for [`with_addr`][pointer::with_addr], see that method for details. |
| /// |
| /// This is a [Strict Provenance][crate::ptr#strict-provenance] API. |
| #[must_use] |
| #[inline] |
| #[stable(feature = "strict_provenance", since = "1.84.0")] |
| pub fn map_addr(self, f: impl FnOnce(usize) -> usize) -> Self { |
| self.with_addr(f(self.addr())) |
| } |
| |
| /// Decompose a (possibly wide) pointer into its data pointer and metadata components. |
| /// |
| /// The pointer can be later reconstructed with [`from_raw_parts`]. |
| #[unstable(feature = "ptr_metadata", issue = "81513")] |
| #[inline] |
| pub const fn to_raw_parts(self) -> (*const (), <T as super::Pointee>::Metadata) { |
| (self.cast(), metadata(self)) |
| } |
| |
| #[doc = include_str!("./docs/as_ref.md")] |
| /// |
| /// ``` |
| /// let ptr: *const u8 = &10u8 as *const u8; |
| /// |
| /// unsafe { |
| /// let val_back = &*ptr; |
| /// assert_eq!(val_back, &10); |
| /// } |
| /// ``` |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let ptr: *const u8 = &10u8 as *const u8; |
| /// |
| /// unsafe { |
| /// if let Some(val_back) = ptr.as_ref() { |
| /// assert_eq!(val_back, &10); |
| /// } |
| /// } |
| /// ``` |
| /// |
| /// |
| /// [`is_null`]: #method.is_null |
| /// [`as_uninit_ref`]: #method.as_uninit_ref |
| #[stable(feature = "ptr_as_ref", since = "1.9.0")] |
| #[rustc_const_stable(feature = "const_ptr_is_null", since = "1.84.0")] |
| #[inline] |
| pub const unsafe fn as_ref<'a>(self) -> Option<&'a T> { |
| // SAFETY: the caller must guarantee that `self` is valid |
| // for a reference if it isn't null. |
| if self.is_null() { None } else { unsafe { Some(&*self) } } |
| } |
| |
| /// Returns a shared reference to the value behind the pointer. |
| /// If the pointer may be null or the value may be uninitialized, [`as_uninit_ref`] must be used instead. |
| /// If the pointer may be null, but the value is known to have been initialized, [`as_ref`] must be used instead. |
| /// |
| /// [`as_ref`]: #method.as_ref |
| /// [`as_uninit_ref`]: #method.as_uninit_ref |
| /// |
| /// # Safety |
| /// |
| /// When calling this method, you have to ensure that |
| /// the pointer is [convertible to a reference](crate::ptr#pointer-to-reference-conversion). |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(ptr_as_ref_unchecked)] |
| /// let ptr: *const u8 = &10u8 as *const u8; |
| /// |
| /// unsafe { |
| /// assert_eq!(ptr.as_ref_unchecked(), &10); |
| /// } |
| /// ``` |
| // FIXME: mention it in the docs for `as_ref` and `as_uninit_ref` once stabilized. |
| #[unstable(feature = "ptr_as_ref_unchecked", issue = "122034")] |
| #[inline] |
| #[must_use] |
| pub const unsafe fn as_ref_unchecked<'a>(self) -> &'a T { |
| // SAFETY: the caller must guarantee that `self` is valid for a reference |
| unsafe { &*self } |
| } |
| |
| #[doc = include_str!("./docs/as_uninit_ref.md")] |
| /// |
| /// [`is_null`]: #method.is_null |
| /// [`as_ref`]: #method.as_ref |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(ptr_as_uninit)] |
| /// |
| /// let ptr: *const u8 = &10u8 as *const u8; |
| /// |
| /// unsafe { |
| /// if let Some(val_back) = ptr.as_uninit_ref() { |
| /// assert_eq!(val_back.assume_init(), 10); |
| /// } |
| /// } |
| /// ``` |
| #[inline] |
| #[unstable(feature = "ptr_as_uninit", issue = "75402")] |
| pub const unsafe fn as_uninit_ref<'a>(self) -> Option<&'a MaybeUninit<T>> |
| where |
| T: Sized, |
| { |
| // SAFETY: the caller must guarantee that `self` meets all the |
| // requirements for a reference. |
| if self.is_null() { None } else { Some(unsafe { &*(self as *const MaybeUninit<T>) }) } |
| } |
| |
| #[doc = include_str!("./docs/offset.md")] |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let s: &str = "123"; |
| /// let ptr: *const u8 = s.as_ptr(); |
| /// |
| /// unsafe { |
| /// assert_eq!(*ptr.offset(1) as char, '2'); |
| /// assert_eq!(*ptr.offset(2) as char, '3'); |
| /// } |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[must_use = "returns a new pointer rather than modifying its argument"] |
| #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")] |
| #[inline(always)] |
| #[track_caller] |
| pub const unsafe fn offset(self, count: isize) -> *const T |
| where |
| T: Sized, |
| { |
| #[inline] |
| #[rustc_allow_const_fn_unstable(const_eval_select)] |
| const fn runtime_offset_nowrap(this: *const (), count: isize, size: usize) -> bool { |
| // We can use const_eval_select here because this is only for UB checks. |
| const_eval_select!( |
| @capture { this: *const (), count: isize, size: usize } -> bool: |
| if const { |
| true |
| } else { |
| // `size` is the size of a Rust type, so we know that |
| // `size <= isize::MAX` and thus `as` cast here is not lossy. |
| let Some(byte_offset) = count.checked_mul(size as isize) else { |
| return false; |
| }; |
| let (_, overflow) = this.addr().overflowing_add_signed(byte_offset); |
| !overflow |
| } |
| ) |
| } |
| |
| ub_checks::assert_unsafe_precondition!( |
| check_language_ub, |
| "ptr::offset requires the address calculation to not overflow", |
| ( |
| this: *const () = self as *const (), |
| count: isize = count, |
| size: usize = size_of::<T>(), |
| ) => runtime_offset_nowrap(this, count, size) |
| ); |
| |
| // SAFETY: the caller must uphold the safety contract for `offset`. |
| unsafe { intrinsics::offset(self, count) } |
| } |
| |
| /// Adds a signed offset in bytes to a pointer. |
| /// |
| /// `count` is in units of **bytes**. |
| /// |
| /// This is purely a convenience for casting to a `u8` pointer and |
| /// using [offset][pointer::offset] on it. See that method for documentation |
| /// and safety requirements. |
| /// |
| /// For non-`Sized` pointees this operation changes only the data pointer, |
| /// leaving the metadata untouched. |
| #[must_use] |
| #[inline(always)] |
| #[stable(feature = "pointer_byte_offsets", since = "1.75.0")] |
| #[rustc_const_stable(feature = "const_pointer_byte_offsets", since = "1.75.0")] |
| #[track_caller] |
| pub const unsafe fn byte_offset(self, count: isize) -> Self { |
| // SAFETY: the caller must uphold the safety contract for `offset`. |
| unsafe { self.cast::<u8>().offset(count).with_metadata_of(self) } |
| } |
| |
| /// Adds a signed offset to a pointer using wrapping arithmetic. |
| /// |
| /// `count` is in units of T; e.g., a `count` of 3 represents a pointer |
| /// offset of `3 * size_of::<T>()` bytes. |
| /// |
| /// # Safety |
| /// |
| /// This operation itself is always safe, but using the resulting pointer is not. |
| /// |
| /// The resulting pointer "remembers" the [allocation] that `self` points to |
| /// (this is called "[Provenance](ptr/index.html#provenance)"). |
| /// The pointer must not be used to read or write other allocations. |
| /// |
| /// In other words, `let z = x.wrapping_offset((y as isize) - (x as isize))` does *not* make `z` |
| /// the same as `y` even if we assume `T` has size `1` and there is no overflow: `z` is still |
| /// attached to the object `x` is attached to, and dereferencing it is Undefined Behavior unless |
| /// `x` and `y` point into the same allocation. |
| /// |
| /// Compared to [`offset`], this method basically delays the requirement of staying within the |
| /// same allocation: [`offset`] is immediate Undefined Behavior when crossing object |
| /// boundaries; `wrapping_offset` produces a pointer but still leads to Undefined Behavior if a |
| /// pointer is dereferenced when it is out-of-bounds of the object it is attached to. [`offset`] |
| /// can be optimized better and is thus preferable in performance-sensitive code. |
| /// |
| /// The delayed check only considers the value of the pointer that was dereferenced, not the |
| /// intermediate values used during the computation of the final result. For example, |
| /// `x.wrapping_offset(o).wrapping_offset(o.wrapping_neg())` is always the same as `x`. In other |
| /// words, leaving the allocation and then re-entering it later is permitted. |
| /// |
| /// [`offset`]: #method.offset |
| /// [allocation]: crate::ptr#allocation |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// # use std::fmt::Write; |
| /// // Iterate using a raw pointer in increments of two elements |
| /// let data = [1u8, 2, 3, 4, 5]; |
| /// let mut ptr: *const u8 = data.as_ptr(); |
| /// let step = 2; |
| /// let end_rounded_up = ptr.wrapping_offset(6); |
| /// |
| /// let mut out = String::new(); |
| /// while ptr != end_rounded_up { |
| /// unsafe { |
| /// write!(&mut out, "{}, ", *ptr)?; |
| /// } |
| /// ptr = ptr.wrapping_offset(step); |
| /// } |
| /// assert_eq!(out.as_str(), "1, 3, 5, "); |
| /// # std::fmt::Result::Ok(()) |
| /// ``` |
| #[stable(feature = "ptr_wrapping_offset", since = "1.16.0")] |
| #[must_use = "returns a new pointer rather than modifying its argument"] |
| #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")] |
| #[inline(always)] |
| pub const fn wrapping_offset(self, count: isize) -> *const T |
| where |
| T: Sized, |
| { |
| // SAFETY: the `arith_offset` intrinsic has no prerequisites to be called. |
| unsafe { intrinsics::arith_offset(self, count) } |
| } |
| |
| /// Adds a signed offset in bytes to a pointer using wrapping arithmetic. |
| /// |
| /// `count` is in units of **bytes**. |
| /// |
| /// This is purely a convenience for casting to a `u8` pointer and |
| /// using [wrapping_offset][pointer::wrapping_offset] on it. See that method |
| /// for documentation. |
| /// |
| /// For non-`Sized` pointees this operation changes only the data pointer, |
| /// leaving the metadata untouched. |
| #[must_use] |
| #[inline(always)] |
| #[stable(feature = "pointer_byte_offsets", since = "1.75.0")] |
| #[rustc_const_stable(feature = "const_pointer_byte_offsets", since = "1.75.0")] |
| pub const fn wrapping_byte_offset(self, count: isize) -> Self { |
| self.cast::<u8>().wrapping_offset(count).with_metadata_of(self) |
| } |
| |
| /// Masks out bits of the pointer according to a mask. |
| /// |
| /// This is convenience for `ptr.map_addr(|a| a & mask)`. |
| /// |
| /// For non-`Sized` pointees this operation changes only the data pointer, |
| /// leaving the metadata untouched. |
| /// |
| /// ## Examples |
| /// |
| /// ``` |
| /// #![feature(ptr_mask)] |
| /// let v = 17_u32; |
| /// let ptr: *const u32 = &v; |
| /// |
| /// // `u32` is 4 bytes aligned, |
| /// // which means that lower 2 bits are always 0. |
| /// let tag_mask = 0b11; |
| /// let ptr_mask = !tag_mask; |
| /// |
| /// // We can store something in these lower bits |
| /// let tagged_ptr = ptr.map_addr(|a| a | 0b10); |
| /// |
| /// // Get the "tag" back |
| /// let tag = tagged_ptr.addr() & tag_mask; |
| /// assert_eq!(tag, 0b10); |
| /// |
| /// // Note that `tagged_ptr` is unaligned, it's UB to read from it. |
| /// // To get original pointer `mask` can be used: |
| /// let masked_ptr = tagged_ptr.mask(ptr_mask); |
| /// assert_eq!(unsafe { *masked_ptr }, 17); |
| /// ``` |
| #[unstable(feature = "ptr_mask", issue = "98290")] |
| #[must_use = "returns a new pointer rather than modifying its argument"] |
| #[inline(always)] |
| pub fn mask(self, mask: usize) -> *const T { |
| intrinsics::ptr_mask(self.cast::<()>(), mask).with_metadata_of(self) |
| } |
| |
| /// Calculates the distance between two pointers within the same allocation. The returned value is in |
| /// units of T: the distance in bytes divided by `size_of::<T>()`. |
| /// |
| /// This is equivalent to `(self as isize - origin as isize) / (size_of::<T>() as isize)`, |
| /// except that it has a lot more opportunities for UB, in exchange for the compiler |
| /// better understanding what you are doing. |
| /// |
| /// The primary motivation of this method is for computing the `len` of an array/slice |
| /// of `T` that you are currently representing as a "start" and "end" pointer |
| /// (and "end" is "one past the end" of the array). |
| /// In that case, `end.offset_from(start)` gets you the length of the array. |
| /// |
| /// All of the following safety requirements are trivially satisfied for this usecase. |
| /// |
| /// [`offset`]: #method.offset |
| /// |
| /// # Safety |
| /// |
| /// If any of the following conditions are violated, the result is Undefined Behavior: |
| /// |
| /// * `self` and `origin` must either |
| /// |
| /// * point to the same address, or |
| /// * both be [derived from][crate::ptr#provenance] a pointer to the same [allocation], and the memory range between |
| /// the two pointers must be in bounds of that object. (See below for an example.) |
| /// |
| /// * The distance between the pointers, in bytes, must be an exact multiple |
| /// of the size of `T`. |
| /// |
| /// As a consequence, the absolute distance between the pointers, in bytes, computed on |
| /// mathematical integers (without "wrapping around"), cannot overflow an `isize`. This is |
| /// implied by the in-bounds requirement, and the fact that no allocation can be larger |
| /// than `isize::MAX` bytes. |
| /// |
| /// The requirement for pointers to be derived from the same allocation is primarily |
| /// needed for `const`-compatibility: the distance between pointers into *different* allocated |
| /// objects is not known at compile-time. However, the requirement also exists at |
| /// runtime and may be exploited by optimizations. If you wish to compute the difference between |
| /// pointers that are not guaranteed to be from the same allocation, use `(self as isize - |
| /// origin as isize) / size_of::<T>()`. |
| // FIXME: recommend `addr()` instead of `as usize` once that is stable. |
| /// |
| /// [`add`]: #method.add |
| /// [allocation]: crate::ptr#allocation |
| /// |
| /// # Panics |
| /// |
| /// This function panics if `T` is a Zero-Sized Type ("ZST"). |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = [0; 5]; |
| /// let ptr1: *const i32 = &a[1]; |
| /// let ptr2: *const i32 = &a[3]; |
| /// unsafe { |
| /// assert_eq!(ptr2.offset_from(ptr1), 2); |
| /// assert_eq!(ptr1.offset_from(ptr2), -2); |
| /// assert_eq!(ptr1.offset(2), ptr2); |
| /// assert_eq!(ptr2.offset(-2), ptr1); |
| /// } |
| /// ``` |
| /// |
| /// *Incorrect* usage: |
| /// |
| /// ```rust,no_run |
| /// let ptr1 = Box::into_raw(Box::new(0u8)) as *const u8; |
| /// let ptr2 = Box::into_raw(Box::new(1u8)) as *const u8; |
| /// let diff = (ptr2 as isize).wrapping_sub(ptr1 as isize); |
| /// // Make ptr2_other an "alias" of ptr2.add(1), but derived from ptr1. |
| /// let ptr2_other = (ptr1 as *const u8).wrapping_offset(diff).wrapping_offset(1); |
| /// assert_eq!(ptr2 as usize, ptr2_other as usize); |
| /// // Since ptr2_other and ptr2 are derived from pointers to different objects, |
| /// // computing their offset is undefined behavior, even though |
| /// // they point to addresses that are in-bounds of the same object! |
| /// unsafe { |
| /// let one = ptr2_other.offset_from(ptr2); // Undefined Behavior! ⚠️ |
| /// } |
| /// ``` |
| #[stable(feature = "ptr_offset_from", since = "1.47.0")] |
| #[rustc_const_stable(feature = "const_ptr_offset_from", since = "1.65.0")] |
| #[inline] |
| #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces |
| pub const unsafe fn offset_from(self, origin: *const T) -> isize |
| where |
| T: Sized, |
| { |
| let pointee_size = size_of::<T>(); |
| assert!(0 < pointee_size && pointee_size <= isize::MAX as usize); |
| // SAFETY: the caller must uphold the safety contract for `ptr_offset_from`. |
| unsafe { intrinsics::ptr_offset_from(self, origin) } |
| } |
| |
| /// Calculates the distance between two pointers within the same allocation. The returned value is in |
| /// units of **bytes**. |
| /// |
| /// This is purely a convenience for casting to a `u8` pointer and |
| /// using [`offset_from`][pointer::offset_from] on it. See that method for |
| /// documentation and safety requirements. |
| /// |
| /// For non-`Sized` pointees this operation considers only the data pointers, |
| /// ignoring the metadata. |
| #[inline(always)] |
| #[stable(feature = "pointer_byte_offsets", since = "1.75.0")] |
| #[rustc_const_stable(feature = "const_pointer_byte_offsets", since = "1.75.0")] |
| #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces |
| pub const unsafe fn byte_offset_from<U: ?Sized>(self, origin: *const U) -> isize { |
| // SAFETY: the caller must uphold the safety contract for `offset_from`. |
| unsafe { self.cast::<u8>().offset_from(origin.cast::<u8>()) } |
| } |
| |
| /// Calculates the distance between two pointers within the same allocation, *where it's known that |
| /// `self` is equal to or greater than `origin`*. The returned value is in |
| /// units of T: the distance in bytes is divided by `size_of::<T>()`. |
| /// |
| /// This computes the same value that [`offset_from`](#method.offset_from) |
| /// would compute, but with the added precondition that the offset is |
| /// guaranteed to be non-negative. This method is equivalent to |
| /// `usize::try_from(self.offset_from(origin)).unwrap_unchecked()`, |
| /// but it provides slightly more information to the optimizer, which can |
| /// sometimes allow it to optimize slightly better with some backends. |
| /// |
| /// This method can be thought of as recovering the `count` that was passed |
| /// to [`add`](#method.add) (or, with the parameters in the other order, |
| /// to [`sub`](#method.sub)). The following are all equivalent, assuming |
| /// that their safety preconditions are met: |
| /// ```rust |
| /// # unsafe fn blah(ptr: *const i32, origin: *const i32, count: usize) -> bool { unsafe { |
| /// ptr.offset_from_unsigned(origin) == count |
| /// # && |
| /// origin.add(count) == ptr |
| /// # && |
| /// ptr.sub(count) == origin |
| /// # } } |
| /// ``` |
| /// |
| /// # Safety |
| /// |
| /// - The distance between the pointers must be non-negative (`self >= origin`) |
| /// |
| /// - *All* the safety conditions of [`offset_from`](#method.offset_from) |
| /// apply to this method as well; see it for the full details. |
| /// |
| /// Importantly, despite the return type of this method being able to represent |
| /// a larger offset, it's still *not permitted* to pass pointers which differ |
| /// by more than `isize::MAX` *bytes*. As such, the result of this method will |
| /// always be less than or equal to `isize::MAX as usize`. |
| /// |
| /// # Panics |
| /// |
| /// This function panics if `T` is a Zero-Sized Type ("ZST"). |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let a = [0; 5]; |
| /// let ptr1: *const i32 = &a[1]; |
| /// let ptr2: *const i32 = &a[3]; |
| /// unsafe { |
| /// assert_eq!(ptr2.offset_from_unsigned(ptr1), 2); |
| /// assert_eq!(ptr1.add(2), ptr2); |
| /// assert_eq!(ptr2.sub(2), ptr1); |
| /// assert_eq!(ptr2.offset_from_unsigned(ptr2), 0); |
| /// } |
| /// |
| /// // This would be incorrect, as the pointers are not correctly ordered: |
| /// // ptr1.offset_from_unsigned(ptr2) |
| /// ``` |
| #[stable(feature = "ptr_sub_ptr", since = "1.87.0")] |
| #[rustc_const_stable(feature = "const_ptr_sub_ptr", since = "1.87.0")] |
| #[inline] |
| #[track_caller] |
| pub const unsafe fn offset_from_unsigned(self, origin: *const T) -> usize |
| where |
| T: Sized, |
| { |
| #[rustc_allow_const_fn_unstable(const_eval_select)] |
| const fn runtime_ptr_ge(this: *const (), origin: *const ()) -> bool { |
| const_eval_select!( |
| @capture { this: *const (), origin: *const () } -> bool: |
| if const { |
| true |
| } else { |
| this >= origin |
| } |
| ) |
| } |
| |
| ub_checks::assert_unsafe_precondition!( |
| check_language_ub, |
| "ptr::offset_from_unsigned requires `self >= origin`", |
| ( |
| this: *const () = self as *const (), |
| origin: *const () = origin as *const (), |
| ) => runtime_ptr_ge(this, origin) |
| ); |
| |
| let pointee_size = size_of::<T>(); |
| assert!(0 < pointee_size && pointee_size <= isize::MAX as usize); |
| // SAFETY: the caller must uphold the safety contract for `ptr_offset_from_unsigned`. |
| unsafe { intrinsics::ptr_offset_from_unsigned(self, origin) } |
| } |
| |
| /// Calculates the distance between two pointers within the same allocation, *where it's known that |
| /// `self` is equal to or greater than `origin`*. The returned value is in |
| /// units of **bytes**. |
| /// |
| /// This is purely a convenience for casting to a `u8` pointer and |
| /// using [`offset_from_unsigned`][pointer::offset_from_unsigned] on it. |
| /// See that method for documentation and safety requirements. |
| /// |
| /// For non-`Sized` pointees this operation considers only the data pointers, |
| /// ignoring the metadata. |
| #[stable(feature = "ptr_sub_ptr", since = "1.87.0")] |
| #[rustc_const_stable(feature = "const_ptr_sub_ptr", since = "1.87.0")] |
| #[inline] |
| #[track_caller] |
| pub const unsafe fn byte_offset_from_unsigned<U: ?Sized>(self, origin: *const U) -> usize { |
| // SAFETY: the caller must uphold the safety contract for `offset_from_unsigned`. |
| unsafe { self.cast::<u8>().offset_from_unsigned(origin.cast::<u8>()) } |
| } |
| |
| /// Returns whether two pointers are guaranteed to be equal. |
| /// |
| /// At runtime this function behaves like `Some(self == other)`. |
| /// However, in some contexts (e.g., compile-time evaluation), |
| /// it is not always possible to determine equality of two pointers, so this function may |
| /// spuriously return `None` for pointers that later actually turn out to have its equality known. |
| /// But when it returns `Some`, the pointers' equality is guaranteed to be known. |
| /// |
| /// The return value may change from `Some` to `None` and vice versa depending on the compiler |
| /// version and unsafe code must not |
| /// rely on the result of this function for soundness. It is suggested to only use this function |
| /// for performance optimizations where spurious `None` return values by this function do not |
| /// affect the outcome, but just the performance. |
| /// The consequences of using this method to make runtime and compile-time code behave |
| /// differently have not been explored. This method should not be used to introduce such |
| /// differences, and it should also not be stabilized before we have a better understanding |
| /// of this issue. |
| #[unstable(feature = "const_raw_ptr_comparison", issue = "53020")] |
| #[rustc_const_unstable(feature = "const_raw_ptr_comparison", issue = "53020")] |
| #[inline] |
| pub const fn guaranteed_eq(self, other: *const T) -> Option<bool> |
| where |
| T: Sized, |
| { |
| match intrinsics::ptr_guaranteed_cmp(self, other) { |
| 2 => None, |
| other => Some(other == 1), |
| } |
| } |
| |
| /// Returns whether two pointers are guaranteed to be inequal. |
| /// |
| /// At runtime this function behaves like `Some(self != other)`. |
| /// However, in some contexts (e.g., compile-time evaluation), |
| /// it is not always possible to determine inequality of two pointers, so this function may |
| /// spuriously return `None` for pointers that later actually turn out to have its inequality known. |
| /// But when it returns `Some`, the pointers' inequality is guaranteed to be known. |
| /// |
| /// The return value may change from `Some` to `None` and vice versa depending on the compiler |
| /// version and unsafe code must not |
| /// rely on the result of this function for soundness. It is suggested to only use this function |
| /// for performance optimizations where spurious `None` return values by this function do not |
| /// affect the outcome, but just the performance. |
| /// The consequences of using this method to make runtime and compile-time code behave |
| /// differently have not been explored. This method should not be used to introduce such |
| /// differences, and it should also not be stabilized before we have a better understanding |
| /// of this issue. |
| #[unstable(feature = "const_raw_ptr_comparison", issue = "53020")] |
| #[rustc_const_unstable(feature = "const_raw_ptr_comparison", issue = "53020")] |
| #[inline] |
| pub const fn guaranteed_ne(self, other: *const T) -> Option<bool> |
| where |
| T: Sized, |
| { |
| match self.guaranteed_eq(other) { |
| None => None, |
| Some(eq) => Some(!eq), |
| } |
| } |
| |
| #[doc = include_str!("./docs/add.md")] |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let s: &str = "123"; |
| /// let ptr: *const u8 = s.as_ptr(); |
| /// |
| /// unsafe { |
| /// assert_eq!(*ptr.add(1), b'2'); |
| /// assert_eq!(*ptr.add(2), b'3'); |
| /// } |
| /// ``` |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[must_use = "returns a new pointer rather than modifying its argument"] |
| #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")] |
| #[inline(always)] |
| #[track_caller] |
| pub const unsafe fn add(self, count: usize) -> Self |
| where |
| T: Sized, |
| { |
| #[cfg(debug_assertions)] |
| #[inline] |
| #[rustc_allow_const_fn_unstable(const_eval_select)] |
| const fn runtime_add_nowrap(this: *const (), count: usize, size: usize) -> bool { |
| const_eval_select!( |
| @capture { this: *const (), count: usize, size: usize } -> bool: |
| if const { |
| true |
| } else { |
| let Some(byte_offset) = count.checked_mul(size) else { |
| return false; |
| }; |
| let (_, overflow) = this.addr().overflowing_add(byte_offset); |
| byte_offset <= (isize::MAX as usize) && !overflow |
| } |
| ) |
| } |
| |
| #[cfg(debug_assertions)] // Expensive, and doesn't catch much in the wild. |
| ub_checks::assert_unsafe_precondition!( |
| check_language_ub, |
| "ptr::add requires that the address calculation does not overflow", |
| ( |
| this: *const () = self as *const (), |
| count: usize = count, |
| size: usize = size_of::<T>(), |
| ) => runtime_add_nowrap(this, count, size) |
| ); |
| |
| // SAFETY: the caller must uphold the safety contract for `offset`. |
| unsafe { intrinsics::offset(self, count) } |
| } |
| |
| /// Adds an unsigned offset in bytes to a pointer. |
| /// |
| /// `count` is in units of bytes. |
| /// |
| /// This is purely a convenience for casting to a `u8` pointer and |
| /// using [add][pointer::add] on it. See that method for documentation |
| /// and safety requirements. |
| /// |
| /// For non-`Sized` pointees this operation changes only the data pointer, |
| /// leaving the metadata untouched. |
| #[must_use] |
| #[inline(always)] |
| #[stable(feature = "pointer_byte_offsets", since = "1.75.0")] |
| #[rustc_const_stable(feature = "const_pointer_byte_offsets", since = "1.75.0")] |
| #[track_caller] |
| pub const unsafe fn byte_add(self, count: usize) -> Self { |
| // SAFETY: the caller must uphold the safety contract for `add`. |
| unsafe { self.cast::<u8>().add(count).with_metadata_of(self) } |
| } |
| |
| /// Subtracts an unsigned offset from a pointer. |
| /// |
| /// This can only move the pointer backward (or not move it). If you need to move forward or |
| /// backward depending on the value, then you might want [`offset`](#method.offset) instead |
| /// which takes a signed offset. |
| /// |
| /// `count` is in units of T; e.g., a `count` of 3 represents a pointer |
| /// offset of `3 * size_of::<T>()` bytes. |
| /// |
| /// # Safety |
| /// |
| /// If any of the following conditions are violated, the result is Undefined Behavior: |
| /// |
| /// * The offset in bytes, `count * size_of::<T>()`, computed on mathematical integers (without |
| /// "wrapping around"), must fit in an `isize`. |
| /// |
| /// * If the computed offset is non-zero, then `self` must be [derived from][crate::ptr#provenance] a pointer to some |
| /// [allocation], and the entire memory range between `self` and the result must be in |
| /// bounds of that allocation. In particular, this range must not "wrap around" the edge |
| /// of the address space. |
| /// |
| /// Allocations can never be larger than `isize::MAX` bytes, so if the computed offset |
| /// stays in bounds of the allocation, it is guaranteed to satisfy the first requirement. |
| /// This implies, for instance, that `vec.as_ptr().add(vec.len())` (for `vec: Vec<T>`) is always |
| /// safe. |
| /// |
| /// Consider using [`wrapping_sub`] instead if these constraints are |
| /// difficult to satisfy. The only advantage of this method is that it |
| /// enables more aggressive compiler optimizations. |
| /// |
| /// [`wrapping_sub`]: #method.wrapping_sub |
| /// [allocation]: crate::ptr#allocation |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let s: &str = "123"; |
| /// |
| /// unsafe { |
| /// let end: *const u8 = s.as_ptr().add(3); |
| /// assert_eq!(*end.sub(1), b'3'); |
| /// assert_eq!(*end.sub(2), b'2'); |
| /// } |
| /// ``` |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[must_use = "returns a new pointer rather than modifying its argument"] |
| #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")] |
| #[inline(always)] |
| #[track_caller] |
| pub const unsafe fn sub(self, count: usize) -> Self |
| where |
| T: Sized, |
| { |
| #[cfg(debug_assertions)] |
| #[inline] |
| #[rustc_allow_const_fn_unstable(const_eval_select)] |
| const fn runtime_sub_nowrap(this: *const (), count: usize, size: usize) -> bool { |
| const_eval_select!( |
| @capture { this: *const (), count: usize, size: usize } -> bool: |
| if const { |
| true |
| } else { |
| let Some(byte_offset) = count.checked_mul(size) else { |
| return false; |
| }; |
| byte_offset <= (isize::MAX as usize) && this.addr() >= byte_offset |
| } |
| ) |
| } |
| |
| #[cfg(debug_assertions)] // Expensive, and doesn't catch much in the wild. |
| ub_checks::assert_unsafe_precondition!( |
| check_language_ub, |
| "ptr::sub requires that the address calculation does not overflow", |
| ( |
| this: *const () = self as *const (), |
| count: usize = count, |
| size: usize = size_of::<T>(), |
| ) => runtime_sub_nowrap(this, count, size) |
| ); |
| |
| if T::IS_ZST { |
| // Pointer arithmetic does nothing when the pointee is a ZST. |
| self |
| } else { |
| // SAFETY: the caller must uphold the safety contract for `offset`. |
| // Because the pointee is *not* a ZST, that means that `count` is |
| // at most `isize::MAX`, and thus the negation cannot overflow. |
| unsafe { intrinsics::offset(self, intrinsics::unchecked_sub(0, count as isize)) } |
| } |
| } |
| |
| /// Subtracts an unsigned offset in bytes from a pointer. |
| /// |
| /// `count` is in units of bytes. |
| /// |
| /// This is purely a convenience for casting to a `u8` pointer and |
| /// using [sub][pointer::sub] on it. See that method for documentation |
| /// and safety requirements. |
| /// |
| /// For non-`Sized` pointees this operation changes only the data pointer, |
| /// leaving the metadata untouched. |
| #[must_use] |
| #[inline(always)] |
| #[stable(feature = "pointer_byte_offsets", since = "1.75.0")] |
| #[rustc_const_stable(feature = "const_pointer_byte_offsets", since = "1.75.0")] |
| #[track_caller] |
| pub const unsafe fn byte_sub(self, count: usize) -> Self { |
| // SAFETY: the caller must uphold the safety contract for `sub`. |
| unsafe { self.cast::<u8>().sub(count).with_metadata_of(self) } |
| } |
| |
| /// Adds an unsigned offset to a pointer using wrapping arithmetic. |
| /// |
| /// `count` is in units of T; e.g., a `count` of 3 represents a pointer |
| /// offset of `3 * size_of::<T>()` bytes. |
| /// |
| /// # Safety |
| /// |
| /// This operation itself is always safe, but using the resulting pointer is not. |
| /// |
| /// The resulting pointer "remembers" the [allocation] that `self` points to; it must not |
| /// be used to read or write other allocations. |
| /// |
| /// In other words, `let z = x.wrapping_add((y as usize) - (x as usize))` does *not* make `z` |
| /// the same as `y` even if we assume `T` has size `1` and there is no overflow: `z` is still |
| /// attached to the object `x` is attached to, and dereferencing it is Undefined Behavior unless |
| /// `x` and `y` point into the same allocation. |
| /// |
| /// Compared to [`add`], this method basically delays the requirement of staying within the |
| /// same allocation: [`add`] is immediate Undefined Behavior when crossing object |
| /// boundaries; `wrapping_add` produces a pointer but still leads to Undefined Behavior if a |
| /// pointer is dereferenced when it is out-of-bounds of the object it is attached to. [`add`] |
| /// can be optimized better and is thus preferable in performance-sensitive code. |
| /// |
| /// The delayed check only considers the value of the pointer that was dereferenced, not the |
| /// intermediate values used during the computation of the final result. For example, |
| /// `x.wrapping_add(o).wrapping_sub(o)` is always the same as `x`. In other words, leaving the |
| /// allocation and then re-entering it later is permitted. |
| /// |
| /// [`add`]: #method.add |
| /// [allocation]: crate::ptr#allocation |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// # use std::fmt::Write; |
| /// // Iterate using a raw pointer in increments of two elements |
| /// let data = [1u8, 2, 3, 4, 5]; |
| /// let mut ptr: *const u8 = data.as_ptr(); |
| /// let step = 2; |
| /// let end_rounded_up = ptr.wrapping_add(6); |
| /// |
| /// let mut out = String::new(); |
| /// while ptr != end_rounded_up { |
| /// unsafe { |
| /// write!(&mut out, "{}, ", *ptr)?; |
| /// } |
| /// ptr = ptr.wrapping_add(step); |
| /// } |
| /// assert_eq!(out, "1, 3, 5, "); |
| /// # std::fmt::Result::Ok(()) |
| /// ``` |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[must_use = "returns a new pointer rather than modifying its argument"] |
| #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")] |
| #[inline(always)] |
| pub const fn wrapping_add(self, count: usize) -> Self |
| where |
| T: Sized, |
| { |
| self.wrapping_offset(count as isize) |
| } |
| |
| /// Adds an unsigned offset in bytes to a pointer using wrapping arithmetic. |
| /// |
| /// `count` is in units of bytes. |
| /// |
| /// This is purely a convenience for casting to a `u8` pointer and |
| /// using [wrapping_add][pointer::wrapping_add] on it. See that method for documentation. |
| /// |
| /// For non-`Sized` pointees this operation changes only the data pointer, |
| /// leaving the metadata untouched. |
| #[must_use] |
| #[inline(always)] |
| #[stable(feature = "pointer_byte_offsets", since = "1.75.0")] |
| #[rustc_const_stable(feature = "const_pointer_byte_offsets", since = "1.75.0")] |
| pub const fn wrapping_byte_add(self, count: usize) -> Self { |
| self.cast::<u8>().wrapping_add(count).with_metadata_of(self) |
| } |
| |
| /// Subtracts an unsigned offset from a pointer using wrapping arithmetic. |
| /// |
| /// `count` is in units of T; e.g., a `count` of 3 represents a pointer |
| /// offset of `3 * size_of::<T>()` bytes. |
| /// |
| /// # Safety |
| /// |
| /// This operation itself is always safe, but using the resulting pointer is not. |
| /// |
| /// The resulting pointer "remembers" the [allocation] that `self` points to; it must not |
| /// be used to read or write other allocations. |
| /// |
| /// In other words, `let z = x.wrapping_sub((x as usize) - (y as usize))` does *not* make `z` |
| /// the same as `y` even if we assume `T` has size `1` and there is no overflow: `z` is still |
| /// attached to the object `x` is attached to, and dereferencing it is Undefined Behavior unless |
| /// `x` and `y` point into the same allocation. |
| /// |
| /// Compared to [`sub`], this method basically delays the requirement of staying within the |
| /// same allocation: [`sub`] is immediate Undefined Behavior when crossing object |
| /// boundaries; `wrapping_sub` produces a pointer but still leads to Undefined Behavior if a |
| /// pointer is dereferenced when it is out-of-bounds of the object it is attached to. [`sub`] |
| /// can be optimized better and is thus preferable in performance-sensitive code. |
| /// |
| /// The delayed check only considers the value of the pointer that was dereferenced, not the |
| /// intermediate values used during the computation of the final result. For example, |
| /// `x.wrapping_add(o).wrapping_sub(o)` is always the same as `x`. In other words, leaving the |
| /// allocation and then re-entering it later is permitted. |
| /// |
| /// [`sub`]: #method.sub |
| /// [allocation]: crate::ptr#allocation |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// # use std::fmt::Write; |
| /// // Iterate using a raw pointer in increments of two elements (backwards) |
| /// let data = [1u8, 2, 3, 4, 5]; |
| /// let mut ptr: *const u8 = data.as_ptr(); |
| /// let start_rounded_down = ptr.wrapping_sub(2); |
| /// ptr = ptr.wrapping_add(4); |
| /// let step = 2; |
| /// let mut out = String::new(); |
| /// while ptr != start_rounded_down { |
| /// unsafe { |
| /// write!(&mut out, "{}, ", *ptr)?; |
| /// } |
| /// ptr = ptr.wrapping_sub(step); |
| /// } |
| /// assert_eq!(out, "5, 3, 1, "); |
| /// # std::fmt::Result::Ok(()) |
| /// ``` |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[must_use = "returns a new pointer rather than modifying its argument"] |
| #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")] |
| #[inline(always)] |
| pub const fn wrapping_sub(self, count: usize) -> Self |
| where |
| T: Sized, |
| { |
| self.wrapping_offset((count as isize).wrapping_neg()) |
| } |
| |
| /// Subtracts an unsigned offset in bytes from a pointer using wrapping arithmetic. |
| /// |
| /// `count` is in units of bytes. |
| /// |
| /// This is purely a convenience for casting to a `u8` pointer and |
| /// using [wrapping_sub][pointer::wrapping_sub] on it. See that method for documentation. |
| /// |
| /// For non-`Sized` pointees this operation changes only the data pointer, |
| /// leaving the metadata untouched. |
| #[must_use] |
| #[inline(always)] |
| #[stable(feature = "pointer_byte_offsets", since = "1.75.0")] |
| #[rustc_const_stable(feature = "const_pointer_byte_offsets", since = "1.75.0")] |
| pub const fn wrapping_byte_sub(self, count: usize) -> Self { |
| self.cast::<u8>().wrapping_sub(count).with_metadata_of(self) |
| } |
| |
| /// Reads the value from `self` without moving it. This leaves the |
| /// memory in `self` unchanged. |
| /// |
| /// See [`ptr::read`] for safety concerns and examples. |
| /// |
| /// [`ptr::read`]: crate::ptr::read() |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[rustc_const_stable(feature = "const_ptr_read", since = "1.71.0")] |
| #[inline] |
| #[track_caller] |
| pub const unsafe fn read(self) -> T |
| where |
| T: Sized, |
| { |
| // SAFETY: the caller must uphold the safety contract for `read`. |
| unsafe { read(self) } |
| } |
| |
| /// Performs a volatile read of the value from `self` without moving it. This |
| /// leaves the memory in `self` unchanged. |
| /// |
| /// Volatile operations are intended to act on I/O memory, and are guaranteed |
| /// to not be elided or reordered by the compiler across other volatile |
| /// operations. |
| /// |
| /// See [`ptr::read_volatile`] for safety concerns and examples. |
| /// |
| /// [`ptr::read_volatile`]: crate::ptr::read_volatile() |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[inline] |
| #[track_caller] |
| pub unsafe fn read_volatile(self) -> T |
| where |
| T: Sized, |
| { |
| // SAFETY: the caller must uphold the safety contract for `read_volatile`. |
| unsafe { read_volatile(self) } |
| } |
| |
| /// Reads the value from `self` without moving it. This leaves the |
| /// memory in `self` unchanged. |
| /// |
| /// Unlike `read`, the pointer may be unaligned. |
| /// |
| /// See [`ptr::read_unaligned`] for safety concerns and examples. |
| /// |
| /// [`ptr::read_unaligned`]: crate::ptr::read_unaligned() |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[rustc_const_stable(feature = "const_ptr_read", since = "1.71.0")] |
| #[inline] |
| #[track_caller] |
| pub const unsafe fn read_unaligned(self) -> T |
| where |
| T: Sized, |
| { |
| // SAFETY: the caller must uphold the safety contract for `read_unaligned`. |
| unsafe { read_unaligned(self) } |
| } |
| |
| /// Copies `count * size_of::<T>()` bytes from `self` to `dest`. The source |
| /// and destination may overlap. |
| /// |
| /// NOTE: this has the *same* argument order as [`ptr::copy`]. |
| /// |
| /// See [`ptr::copy`] for safety concerns and examples. |
| /// |
| /// [`ptr::copy`]: crate::ptr::copy() |
| #[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.83.0")] |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[inline] |
| #[track_caller] |
| pub const unsafe fn copy_to(self, dest: *mut T, count: usize) |
| where |
| T: Sized, |
| { |
| // SAFETY: the caller must uphold the safety contract for `copy`. |
| unsafe { copy(self, dest, count) } |
| } |
| |
| /// Copies `count * size_of::<T>()` bytes from `self` to `dest`. The source |
| /// and destination may *not* overlap. |
| /// |
| /// NOTE: this has the *same* argument order as [`ptr::copy_nonoverlapping`]. |
| /// |
| /// See [`ptr::copy_nonoverlapping`] for safety concerns and examples. |
| /// |
| /// [`ptr::copy_nonoverlapping`]: crate::ptr::copy_nonoverlapping() |
| #[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.83.0")] |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[inline] |
| #[track_caller] |
| pub const unsafe fn copy_to_nonoverlapping(self, dest: *mut T, count: usize) |
| where |
| T: Sized, |
| { |
| // SAFETY: the caller must uphold the safety contract for `copy_nonoverlapping`. |
| unsafe { copy_nonoverlapping(self, dest, count) } |
| } |
| |
| /// Computes the offset that needs to be applied to the pointer in order to make it aligned to |
| /// `align`. |
| /// |
| /// If it is not possible to align the pointer, the implementation returns |
| /// `usize::MAX`. |
| /// |
| /// The offset is expressed in number of `T` elements, and not bytes. The value returned can be |
| /// used with the `wrapping_add` method. |
| /// |
| /// There are no guarantees whatsoever that offsetting the pointer will not overflow or go |
| /// beyond the allocation that the pointer points into. It is up to the caller to ensure that |
| /// the returned offset is correct in all terms other than alignment. |
| /// |
| /// # Panics |
| /// |
| /// The function panics if `align` is not a power-of-two. |
| /// |
| /// # Examples |
| /// |
| /// Accessing adjacent `u8` as `u16` |
| /// |
| /// ``` |
| /// # unsafe { |
| /// let x = [5_u8, 6, 7, 8, 9]; |
| /// let ptr = x.as_ptr(); |
| /// let offset = ptr.align_offset(align_of::<u16>()); |
| /// |
| /// if offset < x.len() - 1 { |
| /// let u16_ptr = ptr.add(offset).cast::<u16>(); |
| /// assert!(*u16_ptr == u16::from_ne_bytes([5, 6]) || *u16_ptr == u16::from_ne_bytes([6, 7])); |
| /// } else { |
| /// // while the pointer can be aligned via `offset`, it would point |
| /// // outside the allocation |
| /// } |
| /// # } |
| /// ``` |
| #[must_use] |
| #[inline] |
| #[stable(feature = "align_offset", since = "1.36.0")] |
| pub fn align_offset(self, align: usize) -> usize |
| where |
| T: Sized, |
| { |
| if !align.is_power_of_two() { |
| panic!("align_offset: align is not a power-of-two"); |
| } |
| |
| // SAFETY: `align` has been checked to be a power of 2 above |
| let ret = unsafe { align_offset(self, align) }; |
| |
| // Inform Miri that we want to consider the resulting pointer to be suitably aligned. |
| #[cfg(miri)] |
| if ret != usize::MAX { |
| intrinsics::miri_promise_symbolic_alignment(self.wrapping_add(ret).cast(), align); |
| } |
| |
| ret |
| } |
| |
| /// Returns whether the pointer is properly aligned for `T`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// // On some platforms, the alignment of i32 is less than 4. |
| /// #[repr(align(4))] |
| /// struct AlignedI32(i32); |
| /// |
| /// let data = AlignedI32(42); |
| /// let ptr = &data as *const AlignedI32; |
| /// |
| /// assert!(ptr.is_aligned()); |
| /// assert!(!ptr.wrapping_byte_add(1).is_aligned()); |
| /// ``` |
| #[must_use] |
| #[inline] |
| #[stable(feature = "pointer_is_aligned", since = "1.79.0")] |
| pub fn is_aligned(self) -> bool |
| where |
| T: Sized, |
| { |
| self.is_aligned_to(align_of::<T>()) |
| } |
| |
| /// Returns whether the pointer is aligned to `align`. |
| /// |
| /// For non-`Sized` pointees this operation considers only the data pointer, |
| /// ignoring the metadata. |
| /// |
| /// # Panics |
| /// |
| /// The function panics if `align` is not a power-of-two (this includes 0). |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(pointer_is_aligned_to)] |
| /// |
| /// // On some platforms, the alignment of i32 is less than 4. |
| /// #[repr(align(4))] |
| /// struct AlignedI32(i32); |
| /// |
| /// let data = AlignedI32(42); |
| /// let ptr = &data as *const AlignedI32; |
| /// |
| /// assert!(ptr.is_aligned_to(1)); |
| /// assert!(ptr.is_aligned_to(2)); |
| /// assert!(ptr.is_aligned_to(4)); |
| /// |
| /// assert!(ptr.wrapping_byte_add(2).is_aligned_to(2)); |
| /// assert!(!ptr.wrapping_byte_add(2).is_aligned_to(4)); |
| /// |
| /// assert_ne!(ptr.is_aligned_to(8), ptr.wrapping_add(1).is_aligned_to(8)); |
| /// ``` |
| #[must_use] |
| #[inline] |
| #[unstable(feature = "pointer_is_aligned_to", issue = "96284")] |
| pub fn is_aligned_to(self, align: usize) -> bool { |
| if !align.is_power_of_two() { |
| panic!("is_aligned_to: align is not a power-of-two"); |
| } |
| |
| self.addr() & (align - 1) == 0 |
| } |
| } |
| |
| impl<T> *const T { |
| /// Casts from a type to its maybe-uninitialized version. |
| #[must_use] |
| #[inline(always)] |
| #[unstable(feature = "cast_maybe_uninit", issue = "145036")] |
| pub const fn cast_uninit(self) -> *const MaybeUninit<T> { |
| self as _ |
| } |
| } |
| impl<T> *const MaybeUninit<T> { |
| /// Casts from a maybe-uninitialized type to its initialized version. |
| /// |
| /// This is always safe, since UB can only occur if the pointer is read |
| /// before being initialized. |
| #[must_use] |
| #[inline(always)] |
| #[unstable(feature = "cast_maybe_uninit", issue = "145036")] |
| pub const fn cast_init(self) -> *const T { |
| self as _ |
| } |
| } |
| |
| impl<T> *const [T] { |
| /// Returns the length of a raw slice. |
| /// |
| /// The returned value is the number of **elements**, not the number of bytes. |
| /// |
| /// This function is safe, even when the raw slice cannot be cast to a slice |
| /// reference because the pointer is null or unaligned. |
| /// |
| /// # Examples |
| /// |
| /// ```rust |
| /// use std::ptr; |
| /// |
| /// let slice: *const [i8] = ptr::slice_from_raw_parts(ptr::null(), 3); |
| /// assert_eq!(slice.len(), 3); |
| /// ``` |
| #[inline] |
| #[stable(feature = "slice_ptr_len", since = "1.79.0")] |
| #[rustc_const_stable(feature = "const_slice_ptr_len", since = "1.79.0")] |
| pub const fn len(self) -> usize { |
| metadata(self) |
| } |
| |
| /// Returns `true` if the raw slice has a length of 0. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::ptr; |
| /// |
| /// let slice: *const [i8] = ptr::slice_from_raw_parts(ptr::null(), 3); |
| /// assert!(!slice.is_empty()); |
| /// ``` |
| #[inline(always)] |
| #[stable(feature = "slice_ptr_len", since = "1.79.0")] |
| #[rustc_const_stable(feature = "const_slice_ptr_len", since = "1.79.0")] |
| pub const fn is_empty(self) -> bool { |
| self.len() == 0 |
| } |
| |
| /// Returns a raw pointer to the slice's buffer. |
| /// |
| /// This is equivalent to casting `self` to `*const T`, but more type-safe. |
| /// |
| /// # Examples |
| /// |
| /// ```rust |
| /// #![feature(slice_ptr_get)] |
| /// use std::ptr; |
| /// |
| /// let slice: *const [i8] = ptr::slice_from_raw_parts(ptr::null(), 3); |
| /// assert_eq!(slice.as_ptr(), ptr::null()); |
| /// ``` |
| #[inline] |
| #[unstable(feature = "slice_ptr_get", issue = "74265")] |
| pub const fn as_ptr(self) -> *const T { |
| self as *const T |
| } |
| |
| /// Gets a raw pointer to the underlying array. |
| /// |
| /// If `N` is not exactly equal to the length of `self`, then this method returns `None`. |
| #[unstable(feature = "slice_as_array", issue = "133508")] |
| #[inline] |
| #[must_use] |
| pub const fn as_array<const N: usize>(self) -> Option<*const [T; N]> { |
| if self.len() == N { |
| let me = self.as_ptr() as *const [T; N]; |
| Some(me) |
| } else { |
| None |
| } |
| } |
| |
| /// Returns a raw pointer to an element or subslice, without doing bounds |
| /// checking. |
| /// |
| /// Calling this method with an out-of-bounds index or when `self` is not dereferenceable |
| /// is *[undefined behavior]* even if the resulting pointer is not used. |
| /// |
| /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(slice_ptr_get)] |
| /// |
| /// let x = &[1, 2, 4] as *const [i32]; |
| /// |
| /// unsafe { |
| /// assert_eq!(x.get_unchecked(1), x.as_ptr().add(1)); |
| /// } |
| /// ``` |
| #[unstable(feature = "slice_ptr_get", issue = "74265")] |
| #[rustc_const_unstable(feature = "const_index", issue = "143775")] |
| #[inline] |
| pub const unsafe fn get_unchecked<I>(self, index: I) -> *const I::Output |
| where |
| I: [const] SliceIndex<[T]>, |
| { |
| // SAFETY: the caller ensures that `self` is dereferenceable and `index` in-bounds. |
| unsafe { index.get_unchecked(self) } |
| } |
| |
| #[doc = include_str!("docs/as_uninit_slice.md")] |
| #[inline] |
| #[unstable(feature = "ptr_as_uninit", issue = "75402")] |
| pub const unsafe fn as_uninit_slice<'a>(self) -> Option<&'a [MaybeUninit<T>]> { |
| if self.is_null() { |
| None |
| } else { |
| // SAFETY: the caller must uphold the safety contract for `as_uninit_slice`. |
| Some(unsafe { slice::from_raw_parts(self as *const MaybeUninit<T>, self.len()) }) |
| } |
| } |
| } |
| |
| impl<T> *const T { |
| /// Casts from a pointer-to-`T` to a pointer-to-`[T; N]`. |
| #[inline] |
| #[unstable(feature = "ptr_cast_array", issue = "144514")] |
| pub const fn cast_array<const N: usize>(self) -> *const [T; N] { |
| self.cast() |
| } |
| } |
| |
| impl<T, const N: usize> *const [T; N] { |
| /// Returns a raw pointer to the array's buffer. |
| /// |
| /// This is equivalent to casting `self` to `*const T`, but more type-safe. |
| /// |
| /// # Examples |
| /// |
| /// ```rust |
| /// #![feature(array_ptr_get)] |
| /// use std::ptr; |
| /// |
| /// let arr: *const [i8; 3] = ptr::null(); |
| /// assert_eq!(arr.as_ptr(), ptr::null()); |
| /// ``` |
| #[inline] |
| #[unstable(feature = "array_ptr_get", issue = "119834")] |
| pub const fn as_ptr(self) -> *const T { |
| self as *const T |
| } |
| |
| /// Returns a raw pointer to a slice containing the entire array. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(array_ptr_get)] |
| /// |
| /// let arr: *const [i32; 3] = &[1, 2, 4] as *const [i32; 3]; |
| /// let slice: *const [i32] = arr.as_slice(); |
| /// assert_eq!(slice.len(), 3); |
| /// ``` |
| #[inline] |
| #[unstable(feature = "array_ptr_get", issue = "119834")] |
| pub const fn as_slice(self) -> *const [T] { |
| self |
| } |
| } |
| |
| /// Pointer equality is by address, as produced by the [`<*const T>::addr`](pointer::addr) method. |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<T: PointeeSized> PartialEq for *const T { |
| #[inline] |
| #[allow(ambiguous_wide_pointer_comparisons)] |
| fn eq(&self, other: &*const T) -> bool { |
| *self == *other |
| } |
| } |
| |
| /// Pointer equality is an equivalence relation. |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<T: PointeeSized> Eq for *const T {} |
| |
| /// Pointer comparison is by address, as produced by the `[`<*const T>::addr`](pointer::addr)` method. |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<T: PointeeSized> Ord for *const T { |
| #[inline] |
| #[allow(ambiguous_wide_pointer_comparisons)] |
| fn cmp(&self, other: &*const T) -> Ordering { |
| if self < other { |
| Less |
| } else if self == other { |
| Equal |
| } else { |
| Greater |
| } |
| } |
| } |
| |
| /// Pointer comparison is by address, as produced by the `[`<*const T>::addr`](pointer::addr)` method. |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<T: PointeeSized> PartialOrd for *const T { |
| #[inline] |
| #[allow(ambiguous_wide_pointer_comparisons)] |
| fn partial_cmp(&self, other: &*const T) -> Option<Ordering> { |
| Some(self.cmp(other)) |
| } |
| |
| #[inline] |
| #[allow(ambiguous_wide_pointer_comparisons)] |
| fn lt(&self, other: &*const T) -> bool { |
| *self < *other |
| } |
| |
| #[inline] |
| #[allow(ambiguous_wide_pointer_comparisons)] |
| fn le(&self, other: &*const T) -> bool { |
| *self <= *other |
| } |
| |
| #[inline] |
| #[allow(ambiguous_wide_pointer_comparisons)] |
| fn gt(&self, other: &*const T) -> bool { |
| *self > *other |
| } |
| |
| #[inline] |
| #[allow(ambiguous_wide_pointer_comparisons)] |
| fn ge(&self, other: &*const T) -> bool { |
| *self >= *other |
| } |
| } |
| |
| #[stable(feature = "raw_ptr_default", since = "1.88.0")] |
| impl<T: ?Sized + Thin> Default for *const T { |
| /// Returns the default value of [`null()`][crate::ptr::null]. |
| fn default() -> Self { |
| crate::ptr::null() |
| } |
| } |
