use super::*; use crate::cmp::Ordering::{Equal, Greater, Less}; use crate::intrinsics::const_eval_select; use crate::marker::PointeeSized; use crate::mem::{self, SizedTypeProperties}; use crate::slice::{self, SliceIndex}; impl *mut T { #[doc = include_str!("docs/is_null.md")] /// /// # Examples /// /// ``` /// let mut s = [1, 2, 3]; /// let ptr: *mut u32 = s.as_mut_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_is_null"] #[inline] pub const fn is_null(self) -> bool { self.cast_const().is_null() } /// 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 = "ptr_cast"] #[inline(always)] pub const fn cast(self) -> *mut 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 mut x = 0u64; /// /// let aligned: *mut u64 = &mut x; /// let unaligned = unsafe { aligned.byte_add(1) }; /// /// assert!(aligned.try_cast_aligned::().is_some()); /// assert!(unaligned.try_cast_aligned::().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(self) -> Option<*mut U> { if self.is_aligned_to(align_of::()) { 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 mut arr: [i32; 3] = [1, 2, 3]; /// let mut ptr = arr.as_mut_ptr() as *mut dyn Debug; /// let thin = ptr as *mut u8; /// unsafe { /// ptr = thin.add(8).with_metadata_of(ptr); /// # assert_eq!(*(ptr as *mut 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 mut x = 0u32; /// let mut y = 1u32; /// /// let x = (&mut x) as *mut u32; /// let y = (&mut y) as *mut 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(self, meta: *const U) -> *mut U where U: PointeeSized, { from_raw_parts_mut::(self as *mut (), 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. /// /// While not strictly required (`*mut T` coerces to `*const T`), this is provided for symmetry /// with [`cast_mut`] on `*const T` and may have documentation value if used instead of implicit /// coercion. /// /// [`cast_mut`]: pointer::cast_mut #[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_const"] #[inline(always)] pub const fn cast_const(self) -> *const T { self as _ } #[doc = include_str!("./docs/addr.md")] /// /// [without_provenance]: without_provenance_mut #[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_mut`] 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_mut`] to reconstitute the original pointer including its provenance. /// /// Due to its inherent ambiguity, [`with_exposed_provenance_mut`] 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_mut`] to work is typically not /// available. /// /// This is an [Exposed Provenance][crate::ptr#exposed-provenance] API. /// /// [`with_exposed_provenance_mut`]: with_exposed_provenance_mut #[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 *mut 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 original /// pointer's [provenance][crate::ptr#provenance]. /// /// 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_mut`]. #[unstable(feature = "ptr_metadata", issue = "81513")] #[inline] pub const fn to_raw_parts(self) -> (*mut (), ::Metadata) { (self.cast(), super::metadata(self)) } #[doc = include_str!("./docs/as_ref.md")] /// /// ``` /// let ptr: *mut u8 = &mut 10u8 as *mut u8; /// /// unsafe { /// let val_back = &*ptr; /// println!("We got back the value: {val_back}!"); /// } /// ``` /// /// # Examples /// /// ``` /// let ptr: *mut u8 = &mut 10u8 as *mut u8; /// /// unsafe { /// if let Some(val_back) = ptr.as_ref() { /// println!("We got back the value: {val_back}!"); /// } /// } /// ``` /// /// # See Also /// /// For the mutable counterpart see [`as_mut`]. /// /// [`is_null`]: #method.is_null-1 /// [`as_uninit_ref`]: pointer#method.as_uninit_ref-1 /// [`as_mut`]: #method.as_mut #[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. /// /// For the mutable counterpart see [`as_mut_unchecked`]. /// /// [`as_ref`]: #method.as_ref /// [`as_uninit_ref`]: #method.as_uninit_ref /// [`as_mut_unchecked`]: #method.as_mut_unchecked /// /// # 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: *mut u8 = &mut 10u8 as *mut u8; /// /// unsafe { /// println!("We got back the value: {}!", ptr.as_ref_unchecked()); /// } /// ``` // 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-1 /// [`as_ref`]: pointer#method.as_ref-1 /// /// # See Also /// For the mutable counterpart see [`as_uninit_mut`]. /// /// [`as_uninit_mut`]: #method.as_uninit_mut /// /// # Examples /// /// ``` /// #![feature(ptr_as_uninit)] /// /// let ptr: *mut u8 = &mut 10u8 as *mut u8; /// /// unsafe { /// if let Some(val_back) = ptr.as_uninit_ref() { /// println!("We got back the value: {}!", val_back.assume_init()); /// } /// } /// ``` #[inline] #[unstable(feature = "ptr_as_uninit", issue = "75402")] pub const unsafe fn as_uninit_ref<'a>(self) -> Option<&'a MaybeUninit> 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) }) } } #[doc = include_str!("./docs/offset.md")] /// /// # Examples /// /// ``` /// let mut s = [1, 2, 3]; /// let ptr: *mut u32 = s.as_mut_ptr(); /// /// unsafe { /// assert_eq!(2, *ptr.offset(1)); /// assert_eq!(3, *ptr.offset(2)); /// } /// ``` #[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) -> *mut 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::(), ) => runtime_offset_nowrap(this, count, size) ); // SAFETY: the caller must uphold the safety contract for `offset`. // The obtained pointer is valid for writes since the caller must // guarantee that it points to the same allocation as `self`. 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::().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::()` 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 /// /// ``` /// // Iterate using a raw pointer in increments of two elements /// let mut data = [1u8, 2, 3, 4, 5]; /// let mut ptr: *mut u8 = data.as_mut_ptr(); /// let step = 2; /// let end_rounded_up = ptr.wrapping_offset(6); /// /// while ptr != end_rounded_up { /// unsafe { /// *ptr = 0; /// } /// ptr = ptr.wrapping_offset(step); /// } /// assert_eq!(&data, &[0, 2, 0, 4, 0]); /// ``` #[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) -> *mut T where T: Sized, { // SAFETY: the `arith_offset` intrinsic has no prerequisites to be called. unsafe { intrinsics::arith_offset(self, count) as *mut T } } /// 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::().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 mut v = 17_u32; /// let ptr: *mut u32 = &mut 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/write to it. /// // To get original pointer `mask` can be used: /// let masked_ptr = tagged_ptr.mask(ptr_mask); /// assert_eq!(unsafe { *masked_ptr }, 17); /// /// unsafe { *masked_ptr = 0 }; /// assert_eq!(v, 0); /// ``` #[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) -> *mut T { intrinsics::ptr_mask(self.cast::<()>(), mask).cast_mut().with_metadata_of(self) } /// Returns `None` if the pointer is null, or else returns a unique reference to /// the value wrapped in `Some`. If the value may be uninitialized, [`as_uninit_mut`] /// must be used instead. /// /// For the shared counterpart see [`as_ref`]. /// /// [`as_uninit_mut`]: #method.as_uninit_mut /// [`as_ref`]: pointer#method.as_ref-1 /// /// # Safety /// /// When calling this method, you have to ensure that *either* /// the pointer is null *or* /// the pointer is [convertible to a reference](crate::ptr#pointer-to-reference-conversion). /// /// # Panics during const evaluation /// /// This method will panic during const evaluation if the pointer cannot be /// determined to be null or not. See [`is_null`] for more information. /// /// [`is_null`]: #method.is_null-1 /// /// # Examples /// /// ``` /// let mut s = [1, 2, 3]; /// let ptr: *mut u32 = s.as_mut_ptr(); /// let first_value = unsafe { ptr.as_mut().unwrap() }; /// *first_value = 4; /// # assert_eq!(s, [4, 2, 3]); /// println!("{s:?}"); // It'll print: "[4, 2, 3]". /// ``` /// /// # Null-unchecked version /// /// If you are sure the pointer can never be null and are looking for some kind of /// `as_mut_unchecked` that returns the `&mut T` instead of `Option<&mut T>`, know that /// you can dereference the pointer directly. /// /// ``` /// let mut s = [1, 2, 3]; /// let ptr: *mut u32 = s.as_mut_ptr(); /// let first_value = unsafe { &mut *ptr }; /// *first_value = 4; /// # assert_eq!(s, [4, 2, 3]); /// println!("{s:?}"); // It'll print: "[4, 2, 3]". /// ``` #[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_mut<'a>(self) -> Option<&'a mut T> { // SAFETY: the caller must guarantee that `self` is be valid for // a mutable reference if it isn't null. if self.is_null() { None } else { unsafe { Some(&mut *self) } } } /// Returns a unique reference to the value behind the pointer. /// If the pointer may be null or the value may be uninitialized, [`as_uninit_mut`] must be used instead. /// If the pointer may be null, but the value is known to have been initialized, [`as_mut`] must be used instead. /// /// For the shared counterpart see [`as_ref_unchecked`]. /// /// [`as_mut`]: #method.as_mut /// [`as_uninit_mut`]: #method.as_uninit_mut /// [`as_ref_unchecked`]: #method.as_mut_unchecked /// /// # 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 mut s = [1, 2, 3]; /// let ptr: *mut u32 = s.as_mut_ptr(); /// let first_value = unsafe { ptr.as_mut_unchecked() }; /// *first_value = 4; /// # assert_eq!(s, [4, 2, 3]); /// println!("{s:?}"); // It'll print: "[4, 2, 3]". /// ``` // FIXME: mention it in the docs for `as_mut` and `as_uninit_mut` once stabilized. #[unstable(feature = "ptr_as_ref_unchecked", issue = "122034")] #[inline] #[must_use] pub const unsafe fn as_mut_unchecked<'a>(self) -> &'a mut T { // SAFETY: the caller must guarantee that `self` is valid for a reference unsafe { &mut *self } } /// Returns `None` if the pointer is null, or else returns a unique reference to /// the value wrapped in `Some`. In contrast to [`as_mut`], this does not require /// that the value has to be initialized. /// /// For the shared counterpart see [`as_uninit_ref`]. /// /// [`as_mut`]: #method.as_mut /// [`as_uninit_ref`]: pointer#method.as_uninit_ref-1 /// /// # Safety /// /// When calling this method, you have to ensure that *either* the pointer is null *or* /// the pointer is [convertible to a reference](crate::ptr#pointer-to-reference-conversion). /// /// # Panics during const evaluation /// /// This method will panic during const evaluation if the pointer cannot be /// determined to be null or not. See [`is_null`] for more information. /// /// [`is_null`]: #method.is_null-1 #[inline] #[unstable(feature = "ptr_as_uninit", issue = "75402")] pub const unsafe fn as_uninit_mut<'a>(self) -> Option<&'a mut MaybeUninit> 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 { &mut *(self as *mut MaybeUninit) }) } } /// 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: *mut T) -> Option where T: Sized, { (self as *const T).guaranteed_eq(other as _) } /// 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: *mut T) -> Option where T: Sized, { (self as *const T).guaranteed_ne(other as _) } /// 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::()`. /// /// This is equivalent to `(self as isize - origin as isize) / (size_of::() 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`]: pointer#method.offset-1 /// /// # 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::()`. // 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 mut a = [0; 5]; /// let ptr1: *mut i32 = &mut a[1]; /// let ptr2: *mut i32 = &mut 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)); /// let ptr2 = Box::into_raw(Box::new(1u8)); /// 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 *mut 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(always)] #[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, { // SAFETY: the caller must uphold the safety contract for `offset_from`. unsafe { (self as *const T).offset_from(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(self, origin: *const U) -> isize { // SAFETY: the caller must uphold the safety contract for `offset_from`. unsafe { self.cast::().offset_from(origin.cast::()) } } /// 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::()`. /// /// 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: *mut i32, origin: *mut 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 mut a = [0; 5]; /// let p: *mut i32 = a.as_mut_ptr(); /// unsafe { /// let ptr1: *mut i32 = p.add(1); /// let ptr2: *mut i32 = p.add(3); /// /// 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(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, { // SAFETY: the caller must uphold the safety contract for `offset_from_unsigned`. unsafe { (self as *const T).offset_from_unsigned(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(self, origin: *mut U) -> usize { // SAFETY: the caller must uphold the safety contract for `byte_offset_from_unsigned`. unsafe { (self as *const T).byte_offset_from_unsigned(origin) } } #[doc = include_str!("./docs/add.md")] /// /// # Examples /// /// ``` /// let mut s: String = "123".to_string(); /// let ptr: *mut u8 = s.as_mut_ptr(); /// /// unsafe { /// assert_eq!('2', *ptr.add(1) as char); /// assert_eq!('3', *ptr.add(2) as char); /// } /// ``` #[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::(), ) => 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::().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::()` bytes. /// /// # Safety /// /// If any of the following conditions are violated, the result is Undefined Behavior: /// /// * The offset in bytes, `count * size_of::()`, 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`) 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!('3', *end.sub(1) as char); /// assert_eq!('2', *end.sub(2) as char); /// } /// ``` #[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::(), ) => 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::().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::()` 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 /// /// ``` /// // 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); /// /// // This loop prints "1, 3, 5, " /// while ptr != end_rounded_up { /// unsafe { /// print!("{}, ", *ptr); /// } /// ptr = ptr.wrapping_add(step); /// } /// ``` #[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::().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::()` 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 /// /// ``` /// // 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; /// // This loop prints "5, 3, 1, " /// while ptr != start_rounded_down { /// unsafe { /// print!("{}, ", *ptr); /// } /// ptr = ptr.wrapping_sub(step); /// } /// ``` #[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::().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(always)] #[track_caller] pub const unsafe fn read(self) -> T where T: Sized, { // SAFETY: the caller must uphold the safety contract for ``. 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(always)] #[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(always)] #[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::()` 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(always)] #[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::()` 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(always)] #[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) } } /// Copies `count * size_of::()` bytes from `src` to `self`. The source /// and destination may overlap. /// /// NOTE: this has the *opposite* argument order of [`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(always)] #[track_caller] pub const unsafe fn copy_from(self, src: *const T, count: usize) where T: Sized, { // SAFETY: the caller must uphold the safety contract for `copy`. unsafe { copy(src, self, count) } } /// Copies `count * size_of::()` bytes from `src` to `self`. The source /// and destination may *not* overlap. /// /// NOTE: this has the *opposite* argument order of [`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(always)] #[track_caller] pub const unsafe fn copy_from_nonoverlapping(self, src: *const T, count: usize) where T: Sized, { // SAFETY: the caller must uphold the safety contract for `copy_nonoverlapping`. unsafe { copy_nonoverlapping(src, self, count) } } /// Executes the destructor (if any) of the pointed-to value. /// /// See [`ptr::drop_in_place`] for safety concerns and examples. /// /// [`ptr::drop_in_place`]: crate::ptr::drop_in_place() #[stable(feature = "pointer_methods", since = "1.26.0")] #[inline(always)] pub unsafe fn drop_in_place(self) { // SAFETY: the caller must uphold the safety contract for `drop_in_place`. unsafe { drop_in_place(self) } } /// Overwrites a memory location with the given value without reading or /// dropping the old value. /// /// See [`ptr::write`] for safety concerns and examples. /// /// [`ptr::write`]: crate::ptr::write() #[stable(feature = "pointer_methods", since = "1.26.0")] #[rustc_const_stable(feature = "const_ptr_write", since = "1.83.0")] #[inline(always)] #[track_caller] pub const unsafe fn write(self, val: T) where T: Sized, { // SAFETY: the caller must uphold the safety contract for `write`. unsafe { write(self, val) } } /// Invokes memset on the specified pointer, setting `count * size_of::()` /// bytes of memory starting at `self` to `val`. /// /// See [`ptr::write_bytes`] for safety concerns and examples. /// /// [`ptr::write_bytes`]: crate::ptr::write_bytes() #[doc(alias = "memset")] #[stable(feature = "pointer_methods", since = "1.26.0")] #[rustc_const_stable(feature = "const_ptr_write", since = "1.83.0")] #[inline(always)] #[track_caller] pub const unsafe fn write_bytes(self, val: u8, count: usize) where T: Sized, { // SAFETY: the caller must uphold the safety contract for `write_bytes`. unsafe { write_bytes(self, val, count) } } /// Performs a volatile write of a memory location with the given value without /// reading or dropping the old value. /// /// 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::write_volatile`] for safety concerns and examples. /// /// [`ptr::write_volatile`]: crate::ptr::write_volatile() #[stable(feature = "pointer_methods", since = "1.26.0")] #[inline(always)] #[track_caller] pub unsafe fn write_volatile(self, val: T) where T: Sized, { // SAFETY: the caller must uphold the safety contract for `write_volatile`. unsafe { write_volatile(self, val) } } /// Overwrites a memory location with the given value without reading or /// dropping the old value. /// /// Unlike `write`, the pointer may be unaligned. /// /// See [`ptr::write_unaligned`] for safety concerns and examples. /// /// [`ptr::write_unaligned`]: crate::ptr::write_unaligned() #[stable(feature = "pointer_methods", since = "1.26.0")] #[rustc_const_stable(feature = "const_ptr_write", since = "1.83.0")] #[inline(always)] #[track_caller] pub const unsafe fn write_unaligned(self, val: T) where T: Sized, { // SAFETY: the caller must uphold the safety contract for `write_unaligned`. unsafe { write_unaligned(self, val) } } /// Replaces the value at `self` with `src`, returning the old /// value, without dropping either. /// /// See [`ptr::replace`] for safety concerns and examples. /// /// [`ptr::replace`]: crate::ptr::replace() #[stable(feature = "pointer_methods", since = "1.26.0")] #[rustc_const_stable(feature = "const_inherent_ptr_replace", since = "1.88.0")] #[inline(always)] pub const unsafe fn replace(self, src: T) -> T where T: Sized, { // SAFETY: the caller must uphold the safety contract for `replace`. unsafe { replace(self, src) } } /// Swaps the values at two mutable locations of the same type, without /// deinitializing either. They may overlap, unlike `mem::swap` which is /// otherwise equivalent. /// /// See [`ptr::swap`] for safety concerns and examples. /// /// [`ptr::swap`]: crate::ptr::swap() #[stable(feature = "pointer_methods", since = "1.26.0")] #[rustc_const_stable(feature = "const_swap", since = "1.85.0")] #[inline(always)] pub const unsafe fn swap(self, with: *mut T) where T: Sized, { // SAFETY: the caller must uphold the safety contract for `swap`. unsafe { swap(self, with) } } /// 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 mut x = [5_u8, 6, 7, 8, 9]; /// let ptr = x.as_mut_ptr(); /// let offset = ptr.align_offset(align_of::()); /// /// if offset < x.len() - 1 { /// let u16_ptr = ptr.add(offset).cast::(); /// *u16_ptr = 0; /// /// assert!(x == [0, 0, 7, 8, 9] || x == [5, 0, 0, 8, 9]); /// } 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_const().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 mut data = AlignedI32(42); /// let ptr = &mut data as *mut 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::()) } /// 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 mut data = AlignedI32(42); /// let ptr = &mut data as *mut 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 *mut T { /// Casts from a type to its maybe-uninitialized 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_uninit(self) -> *mut MaybeUninit { self as _ } } impl *mut MaybeUninit { /// 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) -> *mut T { self as _ } } impl *mut [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: *mut [i8] = ptr::slice_from_raw_parts_mut(ptr::null_mut(), 3); /// assert_eq!(slice.len(), 3); /// ``` #[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 len(self) -> usize { metadata(self) } /// Returns `true` if the raw slice has a length of 0. /// /// # Examples /// /// ``` /// use std::ptr; /// /// let slice: *mut [i8] = ptr::slice_from_raw_parts_mut(ptr::null_mut(), 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 } /// Gets a raw, mutable 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_mut_array(self) -> Option<*mut [T; N]> { if self.len() == N { let me = self.as_mut_ptr() as *mut [T; N]; Some(me) } else { None } } /// Divides one mutable raw slice into two at an index. /// /// The first will contain all indices from `[0, mid)` (excluding /// the index `mid` itself) and the second will contain all /// indices from `[mid, len)` (excluding the index `len` itself). /// /// # Panics /// /// Panics if `mid > len`. /// /// # Safety /// /// `mid` must be [in-bounds] of the underlying [allocation]. /// Which means `self` must be dereferenceable and span a single allocation /// that is at least `mid * size_of::()` bytes long. Not upholding these /// requirements is *[undefined behavior]* even if the resulting pointers are not used. /// /// Since `len` being in-bounds it is not a safety invariant of `*mut [T]` the /// safety requirements of this method are the same as for [`split_at_mut_unchecked`]. /// The explicit bounds check is only as useful as `len` is correct. /// /// [`split_at_mut_unchecked`]: #method.split_at_mut_unchecked /// [in-bounds]: #method.add /// [allocation]: crate::ptr#allocation /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html /// /// # Examples /// /// ``` /// #![feature(raw_slice_split)] /// #![feature(slice_ptr_get)] /// /// let mut v = [1, 0, 3, 0, 5, 6]; /// let ptr = &mut v as *mut [_]; /// unsafe { /// let (left, right) = ptr.split_at_mut(2); /// assert_eq!(&*left, [1, 0]); /// assert_eq!(&*right, [3, 0, 5, 6]); /// } /// ``` #[inline(always)] #[track_caller] #[unstable(feature = "raw_slice_split", issue = "95595")] pub unsafe fn split_at_mut(self, mid: usize) -> (*mut [T], *mut [T]) { assert!(mid <= self.len()); // SAFETY: The assert above is only a safety-net as long as `self.len()` is correct // The actual safety requirements of this function are the same as for `split_at_mut_unchecked` unsafe { self.split_at_mut_unchecked(mid) } } /// Divides one mutable raw slice into two at an index, without doing bounds checking. /// /// The first will contain all indices from `[0, mid)` (excluding /// the index `mid` itself) and the second will contain all /// indices from `[mid, len)` (excluding the index `len` itself). /// /// # Safety /// /// `mid` must be [in-bounds] of the underlying [allocation]. /// Which means `self` must be dereferenceable and span a single allocation /// that is at least `mid * size_of::()` bytes long. Not upholding these /// requirements is *[undefined behavior]* even if the resulting pointers are not used. /// /// [in-bounds]: #method.add /// [out-of-bounds index]: #method.add /// [allocation]: crate::ptr#allocation /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html /// /// # Examples /// /// ``` /// #![feature(raw_slice_split)] /// /// let mut v = [1, 0, 3, 0, 5, 6]; /// // scoped to restrict the lifetime of the borrows /// unsafe { /// let ptr = &mut v as *mut [_]; /// let (left, right) = ptr.split_at_mut_unchecked(2); /// assert_eq!(&*left, [1, 0]); /// assert_eq!(&*right, [3, 0, 5, 6]); /// (&mut *left)[1] = 2; /// (&mut *right)[1] = 4; /// } /// assert_eq!(v, [1, 2, 3, 4, 5, 6]); /// ``` #[inline(always)] #[unstable(feature = "raw_slice_split", issue = "95595")] pub unsafe fn split_at_mut_unchecked(self, mid: usize) -> (*mut [T], *mut [T]) { let len = self.len(); let ptr = self.as_mut_ptr(); // SAFETY: Caller must pass a valid pointer and an index that is in-bounds. let tail = unsafe { ptr.add(mid) }; ( crate::ptr::slice_from_raw_parts_mut(ptr, mid), crate::ptr::slice_from_raw_parts_mut(tail, len - mid), ) } /// Returns a raw pointer to the slice's buffer. /// /// This is equivalent to casting `self` to `*mut T`, but more type-safe. /// /// # Examples /// /// ```rust /// #![feature(slice_ptr_get)] /// use std::ptr; /// /// let slice: *mut [i8] = ptr::slice_from_raw_parts_mut(ptr::null_mut(), 3); /// assert_eq!(slice.as_mut_ptr(), ptr::null_mut()); /// ``` #[inline(always)] #[unstable(feature = "slice_ptr_get", issue = "74265")] pub const fn as_mut_ptr(self) -> *mut T { self as *mut T } /// 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. /// /// [out-of-bounds index]: #method.add /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html /// /// # Examples /// /// ``` /// #![feature(slice_ptr_get)] /// /// let x = &mut [1, 2, 4] as *mut [i32]; /// /// unsafe { /// assert_eq!(x.get_unchecked_mut(1), x.as_mut_ptr().add(1)); /// } /// ``` #[unstable(feature = "slice_ptr_get", issue = "74265")] #[rustc_const_unstable(feature = "const_index", issue = "143775")] #[inline(always)] pub const unsafe fn get_unchecked_mut(self, index: I) -> *mut I::Output where I: [const] SliceIndex<[T]>, { // SAFETY: the caller ensures that `self` is dereferenceable and `index` in-bounds. unsafe { index.get_unchecked_mut(self) } } #[doc = include_str!("docs/as_uninit_slice.md")] /// /// # See Also /// For the mutable counterpart see [`as_uninit_slice_mut`](pointer::as_uninit_slice_mut). #[inline] #[unstable(feature = "ptr_as_uninit", issue = "75402")] pub const unsafe fn as_uninit_slice<'a>(self) -> Option<&'a [MaybeUninit]> { 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, self.len()) }) } } /// Returns `None` if the pointer is null, or else returns a unique slice to /// the value wrapped in `Some`. In contrast to [`as_mut`], this does not require /// that the value has to be initialized. /// /// For the shared counterpart see [`as_uninit_slice`]. /// /// [`as_mut`]: #method.as_mut /// [`as_uninit_slice`]: #method.as_uninit_slice-1 /// /// # Safety /// /// When calling this method, you have to ensure that *either* the pointer is null *or* /// all of the following is true: /// /// * The pointer must be [valid] for reads and writes for `ptr.len() * size_of::()` /// many bytes, and it must be properly aligned. This means in particular: /// /// * The entire memory range of this slice must be contained within a single [allocation]! /// Slices can never span across multiple allocations. /// /// * The pointer must be aligned even for zero-length slices. One /// reason for this is that enum layout optimizations may rely on references /// (including slices of any length) being aligned and non-null to distinguish /// them from other data. You can obtain a pointer that is usable as `data` /// for zero-length slices using [`NonNull::dangling()`]. /// /// * The total size `ptr.len() * size_of::()` of the slice must be no larger than `isize::MAX`. /// See the safety documentation of [`pointer::offset`]. /// /// * You must enforce Rust's aliasing rules, since the returned lifetime `'a` is /// arbitrarily chosen and does not necessarily reflect the actual lifetime of the data. /// In particular, while this reference exists, the memory the pointer points to must /// not get accessed (read or written) through any other pointer. /// /// This applies even if the result of this method is unused! /// /// See also [`slice::from_raw_parts_mut`][]. /// /// [valid]: crate::ptr#safety /// [allocation]: crate::ptr#allocation /// /// # Panics during const evaluation /// /// This method will panic during const evaluation if the pointer cannot be /// determined to be null or not. See [`is_null`] for more information. /// /// [`is_null`]: #method.is_null-1 #[inline] #[unstable(feature = "ptr_as_uninit", issue = "75402")] pub const unsafe fn as_uninit_slice_mut<'a>(self) -> Option<&'a mut [MaybeUninit]> { if self.is_null() { None } else { // SAFETY: the caller must uphold the safety contract for `as_uninit_slice_mut`. Some(unsafe { slice::from_raw_parts_mut(self as *mut MaybeUninit, self.len()) }) } } } impl *mut 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(self) -> *mut [T; N] { self.cast() } } impl *mut [T; N] { /// Returns a raw pointer to the array's buffer. /// /// This is equivalent to casting `self` to `*mut T`, but more type-safe. /// /// # Examples /// /// ```rust /// #![feature(array_ptr_get)] /// use std::ptr; /// /// let arr: *mut [i8; 3] = ptr::null_mut(); /// assert_eq!(arr.as_mut_ptr(), ptr::null_mut()); /// ``` #[inline] #[unstable(feature = "array_ptr_get", issue = "119834")] pub const fn as_mut_ptr(self) -> *mut T { self as *mut T } /// Returns a raw pointer to a mutable slice containing the entire array. /// /// # Examples /// /// ``` /// #![feature(array_ptr_get)] /// /// let mut arr = [1, 2, 5]; /// let ptr: *mut [i32; 3] = &mut arr; /// unsafe { /// (&mut *ptr.as_mut_slice())[..2].copy_from_slice(&[3, 4]); /// } /// assert_eq!(arr, [3, 4, 5]); /// ``` #[inline] #[unstable(feature = "array_ptr_get", issue = "119834")] pub const fn as_mut_slice(self) -> *mut [T] { self } } /// Pointer equality is by address, as produced by the [`<*mut T>::addr`](pointer::addr) method. #[stable(feature = "rust1", since = "1.0.0")] impl PartialEq for *mut T { #[inline(always)] #[allow(ambiguous_wide_pointer_comparisons)] fn eq(&self, other: &*mut T) -> bool { *self == *other } } /// Pointer equality is an equivalence relation. #[stable(feature = "rust1", since = "1.0.0")] impl Eq for *mut T {} /// Pointer comparison is by address, as produced by the [`<*mut T>::addr`](pointer::addr) method. #[stable(feature = "rust1", since = "1.0.0")] impl Ord for *mut T { #[inline] #[allow(ambiguous_wide_pointer_comparisons)] fn cmp(&self, other: &*mut T) -> Ordering { if self < other { Less } else if self == other { Equal } else { Greater } } } /// Pointer comparison is by address, as produced by the [`<*mut T>::addr`](pointer::addr) method. #[stable(feature = "rust1", since = "1.0.0")] impl PartialOrd for *mut T { #[inline(always)] #[allow(ambiguous_wide_pointer_comparisons)] fn partial_cmp(&self, other: &*mut T) -> Option { Some(self.cmp(other)) } #[inline(always)] #[allow(ambiguous_wide_pointer_comparisons)] fn lt(&self, other: &*mut T) -> bool { *self < *other } #[inline(always)] #[allow(ambiguous_wide_pointer_comparisons)] fn le(&self, other: &*mut T) -> bool { *self <= *other } #[inline(always)] #[allow(ambiguous_wide_pointer_comparisons)] fn gt(&self, other: &*mut T) -> bool { *self > *other } #[inline(always)] #[allow(ambiguous_wide_pointer_comparisons)] fn ge(&self, other: &*mut T) -> bool { *self >= *other } } #[stable(feature = "raw_ptr_default", since = "1.88.0")] impl Default for *mut T { /// Returns the default value of [`null_mut()`][crate::ptr::null_mut]. fn default() -> Self { crate::ptr::null_mut() } }