use super::*; use crate::cmp::Ordering::{self, Equal, Greater, Less}; use crate::intrinsics; use crate::mem; use crate::slice::{self, SliceIndex}; #[lang = "const_ptr"] impl *const T { /// Returns `true` if the pointer is null. /// /// Note that unsized types have many possible null pointers, as only the /// raw data pointer is considered, not their length, vtable, etc. /// Therefore, two pointers that are null may still not compare equal to /// each other. /// /// ## Behavior during const evaluation /// /// When this function is used during const evaluation, it may return `false` for pointers /// that turn out to be null at runtime. Specifically, when a pointer to some memory /// is offset beyond its bounds in such a way that the resulting pointer is null, /// the function will still return `false`. There is no way for CTFE to know /// the absolute position of that memory, so we cannot tell if the pointer is /// null or not. /// /// # Examples /// /// Basic usage: /// /// ``` /// 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_unstable(feature = "const_ptr_is_null", issue = "74939")] #[inline] 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. (self as *const u8).guaranteed_eq(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")] #[inline] pub const fn cast(self) -> *const U { self as _ } /// Returns `None` if the pointer is null, or else returns a shared reference to /// the value wrapped in `Some`. If the value may be uninitialized, [`as_uninit_ref`] /// must be used instead. /// /// [`as_uninit_ref`]: #method.as_uninit_ref /// /// # 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 properly aligned. /// /// * It must be "dereferencable" in the sense defined in [the module documentation]. /// /// * The pointer must point to an initialized instance of `T`. /// /// * 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, for the duration of this lifetime, the memory the pointer points to must /// not get mutated (except inside `UnsafeCell`). /// /// This applies even if the result of this method is unused! /// (The part about being initialized is not yet fully decided, but until /// it is, the only safe approach is to ensure that they are indeed initialized.) /// /// [the module documentation]: crate::ptr#safety /// /// # Examples /// /// Basic usage: /// /// ``` /// let ptr: *const u8 = &10u8 as *const u8; /// /// unsafe { /// if let Some(val_back) = ptr.as_ref() { /// println!("We got back the value: {}!", val_back); /// } /// } /// ``` /// /// # Null-unchecked version /// /// If you are sure the pointer can never be null and are looking for some kind of /// `as_ref_unchecked` that returns the `&T` instead of `Option<&T>`, know that you can /// dereference the pointer directly. /// /// ``` /// let ptr: *const u8 = &10u8 as *const u8; /// /// unsafe { /// let val_back = &*ptr; /// println!("We got back the value: {}!", val_back); /// } /// ``` #[stable(feature = "ptr_as_ref", since = "1.9.0")] #[inline] pub 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 `None` if the pointer is null, or else returns a shared reference to /// the value wrapped in `Some`. In contrast to [`as_ref`], this does not require /// that the value has to be initialized. /// /// [`as_ref`]: #method.as_ref /// /// # 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 properly aligned. /// /// * It must be "dereferencable" in the sense defined in [the module documentation]. /// /// * 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, for the duration of this lifetime, the memory the pointer points to must /// not get mutated (except inside `UnsafeCell`). /// /// This applies even if the result of this method is unused! /// /// [the module documentation]: crate::ptr#safety /// /// # Examples /// /// Basic usage: /// /// ``` /// #![feature(ptr_as_uninit)] /// /// let ptr: *const u8 = &10u8 as *const 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 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) }) } } /// Calculates the offset from a pointer. /// /// `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: /// /// * Both the starting and resulting pointer must be either in bounds or one /// byte past the end of the same allocated object. Note that in Rust, /// every (stack-allocated) variable is considered a separate allocated object. /// /// * The computed offset, **in bytes**, cannot overflow an `isize`. /// /// * The offset being in bounds cannot rely on "wrapping around" the address /// space. That is, the infinite-precision sum, **in bytes** must fit in a usize. /// /// The compiler and standard library generally tries to ensure allocations /// never reach a size where an offset is a concern. For instance, `Vec` /// and `Box` ensure they never allocate more than `isize::MAX` bytes, so /// `vec.as_ptr().add(vec.len())` is always safe. /// /// Most platforms fundamentally can't even construct such an allocation. /// For instance, no known 64-bit platform can ever serve a request /// for 263 bytes due to page-table limitations or splitting the address space. /// However, some 32-bit and 16-bit platforms may successfully serve a request for /// more than `isize::MAX` bytes with things like Physical Address /// Extension. As such, memory acquired directly from allocators or memory /// mapped files *may* be too large to handle with this function. /// /// Consider using [`wrapping_offset`] instead if these constraints are /// difficult to satisfy. The only advantage of this method is that it /// enables more aggressive compiler optimizations. /// /// [`wrapping_offset`]: #method.wrapping_offset /// /// # Examples /// /// Basic usage: /// /// ``` /// let s: &str = "123"; /// let ptr: *const u8 = s.as_ptr(); /// /// unsafe { /// println!("{}", *ptr.offset(1) as char); /// println!("{}", *ptr.offset(2) as char); /// } /// ``` #[stable(feature = "rust1", since = "1.0.0")] #[must_use = "returns a new pointer rather than modifying its argument"] #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")] #[inline] pub const unsafe fn offset(self, count: isize) -> *const T where T: Sized, { // SAFETY: the caller must uphold the safety contract for `offset`. unsafe { intrinsics::offset(self, count) } } /// Calculates the 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 /// /// The resulting pointer does not need to be in bounds, but it is /// potentially hazardous to dereference (which requires `unsafe`). /// /// In particular, the resulting pointer remains attached to the same allocated /// object that `self` points to. It may *not* be used to access a /// different allocated object. Note that in Rust, /// every (stack-allocated) variable is considered a separate allocated object. /// /// In other words, `x.wrapping_offset((y as usize).wrapping_sub(x as usize) / size_of::())` /// is *not* the same as `y`, and dereferencing it is undefined behavior /// unless `x` and `y` point into the same allocated object. /// /// Compared to [`offset`], this method basically delays the requirement of staying /// within the same allocated object: [`offset`] is immediate Undefined Behavior when /// crossing object boundaries; `wrapping_offset` produces a pointer but still leads /// to Undefined Behavior if that pointer is dereferenced. [`offset`] can be optimized /// better and is thus preferable in performance-sensitive code. /// /// If you need to cross object boundaries, cast the pointer to an integer and /// do the arithmetic there. /// /// [`offset`]: #method.offset /// /// # Examples /// /// Basic usage: /// /// ``` /// // 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); /// /// // This loop prints "1, 3, 5, " /// while ptr != end_rounded_up { /// unsafe { /// print!("{}, ", *ptr); /// } /// ptr = ptr.wrapping_offset(step); /// } /// ``` #[stable(feature = "ptr_wrapping_offset", since = "1.16.0")] #[must_use = "returns a new pointer rather than modifying its argument"] #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")] #[inline] 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) } } /// Calculates the distance between two pointers. The returned value is in /// units of T: the distance in bytes is divided by `mem::size_of::()`. /// /// This function is the inverse of [`offset`]. /// /// [`offset`]: #method.offset /// /// # Safety /// /// If any of the following conditions are violated, the result is Undefined /// Behavior: /// /// * Both the starting and other pointer must be either in bounds or one /// byte past the end of the same allocated object. Note that in Rust, /// every (stack-allocated) variable is considered a separate allocated object. /// /// * Both pointers must be *derived from* a pointer to the same object. /// (See below for an example.) /// /// * The distance between the pointers, **in bytes**, cannot overflow an `isize`. /// /// * The distance between the pointers, in bytes, must be an exact multiple /// of the size of `T`. /// /// * The distance being in bounds cannot rely on "wrapping around" the address space. /// /// The compiler and standard library generally try to ensure allocations /// never reach a size where an offset is a concern. For instance, `Vec` /// and `Box` ensure they never allocate more than `isize::MAX` bytes, so /// `ptr_into_vec.offset_from(vec.as_ptr())` is always safe. /// /// Most platforms fundamentally can't even construct such an allocation. /// For instance, no known 64-bit platform can ever serve a request /// for 263 bytes due to page-table limitations or splitting the address space. /// However, some 32-bit and 16-bit platforms may successfully serve a request for /// more than `isize::MAX` bytes with things like Physical Address /// Extension. As such, memory acquired directly from allocators or memory /// mapped files *may* be too large to handle with this function. /// /// # 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, but derived from ptr1. /// let ptr2_other = (ptr1 as *const u8).wrapping_offset(diff); /// 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 the same address! /// unsafe { /// let zero = ptr2_other.offset_from(ptr2); // Undefined Behavior /// } /// ``` #[stable(feature = "ptr_offset_from", since = "1.47.0")] #[rustc_const_unstable(feature = "const_ptr_offset_from", issue = "41079")] #[inline] pub const unsafe fn offset_from(self, origin: *const T) -> isize where T: Sized, { let pointee_size = mem::size_of::(); 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) } } /// Returns whether two pointers are guaranteed to be equal. /// /// At runtime this function behaves like `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 `false` for pointers that later actually turn out to be equal. /// But when it returns `true`, the pointers are guaranteed to be equal. /// /// This function is the mirror of [`guaranteed_ne`], but not its inverse. There are pointer /// comparisons for which both functions return `false`. /// /// [`guaranteed_ne`]: #method.guaranteed_ne /// /// The return value may change depending on the compiler version and unsafe code may not /// rely on the result of this function for soundness. It is suggested to only use this function /// for performance optimizations where spurious `false` 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) -> bool where T: Sized, { intrinsics::ptr_guaranteed_eq(self, other) } /// Returns whether two pointers are guaranteed to be unequal. /// /// At runtime this function behaves like `self != other`. /// However, in some contexts (e.g., compile-time evaluation), /// it is not always possible to determine the inequality of two pointers, so this function may /// spuriously return `false` for pointers that later actually turn out to be unequal. /// But when it returns `true`, the pointers are guaranteed to be unequal. /// /// This function is the mirror of [`guaranteed_eq`], but not its inverse. There are pointer /// comparisons for which both functions return `false`. /// /// [`guaranteed_eq`]: #method.guaranteed_eq /// /// The return value may change depending on the compiler version and unsafe code may not /// rely on the result of this function for soundness. It is suggested to only use this function /// for performance optimizations where spurious `false` 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) -> bool where T: Sized, { intrinsics::ptr_guaranteed_ne(self, other) } /// Calculates the offset from a pointer (convenience for `.offset(count as isize)`). /// /// `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: /// /// * Both the starting and resulting pointer must be either in bounds or one /// byte past the end of the same allocated object. Note that in Rust, /// every (stack-allocated) variable is considered a separate allocated object. /// /// * The computed offset, **in bytes**, cannot overflow an `isize`. /// /// * The offset being in bounds cannot rely on "wrapping around" the address /// space. That is, the infinite-precision sum must fit in a `usize`. /// /// The compiler and standard library generally tries to ensure allocations /// never reach a size where an offset is a concern. For instance, `Vec` /// and `Box` ensure they never allocate more than `isize::MAX` bytes, so /// `vec.as_ptr().add(vec.len())` is always safe. /// /// Most platforms fundamentally can't even construct such an allocation. /// For instance, no known 64-bit platform can ever serve a request /// for 263 bytes due to page-table limitations or splitting the address space. /// However, some 32-bit and 16-bit platforms may successfully serve a request for /// more than `isize::MAX` bytes with things like Physical Address /// Extension. As such, memory acquired directly from allocators or memory /// mapped files *may* be too large to handle with this function. /// /// Consider using [`wrapping_add`] instead if these constraints are /// difficult to satisfy. The only advantage of this method is that it /// enables more aggressive compiler optimizations. /// /// [`wrapping_add`]: #method.wrapping_add /// /// # Examples /// /// Basic usage: /// /// ``` /// let s: &str = "123"; /// let ptr: *const u8 = s.as_ptr(); /// /// unsafe { /// println!("{}", *ptr.add(1) as char); /// println!("{}", *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_unstable(feature = "const_ptr_offset", issue = "71499")] #[inline] pub const unsafe fn add(self, count: usize) -> Self where T: Sized, { // SAFETY: the caller must uphold the safety contract for `offset`. unsafe { self.offset(count as isize) } } /// Calculates the offset from a pointer (convenience for /// `.offset((count as isize).wrapping_neg())`). /// /// `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: /// /// * Both the starting and resulting pointer must be either in bounds or one /// byte past the end of the same allocated object. Note that in Rust, /// every (stack-allocated) variable is considered a separate allocated object. /// /// * The computed offset cannot exceed `isize::MAX` **bytes**. /// /// * The offset being in bounds cannot rely on "wrapping around" the address /// space. That is, the infinite-precision sum must fit in a usize. /// /// The compiler and standard library generally tries to ensure allocations /// never reach a size where an offset is a concern. For instance, `Vec` /// and `Box` ensure they never allocate more than `isize::MAX` bytes, so /// `vec.as_ptr().add(vec.len()).sub(vec.len())` is always safe. /// /// Most platforms fundamentally can't even construct such an allocation. /// For instance, no known 64-bit platform can ever serve a request /// for 263 bytes due to page-table limitations or splitting the address space. /// However, some 32-bit and 16-bit platforms may successfully serve a request for /// more than `isize::MAX` bytes with things like Physical Address /// Extension. As such, memory acquired directly from allocators or memory /// mapped files *may* be too large to handle with this function. /// /// 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 /// /// # Examples /// /// Basic usage: /// /// ``` /// let s: &str = "123"; /// /// unsafe { /// let end: *const u8 = s.as_ptr().add(3); /// println!("{}", *end.sub(1) as char); /// println!("{}", *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_unstable(feature = "const_ptr_offset", issue = "71499")] #[inline] pub const unsafe fn sub(self, count: usize) -> Self where T: Sized, { // SAFETY: the caller must uphold the safety contract for `offset`. unsafe { self.offset((count as isize).wrapping_neg()) } } /// Calculates the offset from a pointer using wrapping arithmetic. /// (convenience for `.wrapping_offset(count as isize)`) /// /// `count` is in units of T; e.g., a `count` of 3 represents a pointer /// offset of `3 * size_of::()` bytes. /// /// # Safety /// /// The resulting pointer does not need to be in bounds, but it is /// potentially hazardous to dereference (which requires `unsafe`). /// /// In particular, the resulting pointer remains attached to the same allocated /// object that `self` points to. It may *not* be used to access a /// different allocated object. Note that in Rust, /// every (stack-allocated) variable is considered a separate allocated object. /// /// Compared to [`add`], this method basically delays the requirement of staying /// within the same allocated object: [`add`] is immediate Undefined Behavior when /// crossing object boundaries; `wrapping_add` produces a pointer but still leads /// to Undefined Behavior if that pointer is dereferenced. [`add`] can be optimized /// better and is thus preferable in performance-sensitive code. /// /// If you need to cross object boundaries, cast the pointer to an integer and /// do the arithmetic there. /// /// [`add`]: #method.add /// /// # Examples /// /// Basic usage: /// /// ``` /// // 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_unstable(feature = "const_ptr_offset", issue = "71499")] #[inline] pub const fn wrapping_add(self, count: usize) -> Self where T: Sized, { self.wrapping_offset(count as isize) } /// Calculates the offset from a pointer using wrapping arithmetic. /// (convenience for `.wrapping_offset((count as isize).wrapping_sub())`) /// /// `count` is in units of T; e.g., a `count` of 3 represents a pointer /// offset of `3 * size_of::()` bytes. /// /// # Safety /// /// The resulting pointer does not need to be in bounds, but it is /// potentially hazardous to dereference (which requires `unsafe`). /// /// In particular, the resulting pointer remains attached to the same allocated /// object that `self` points to. It may *not* be used to access a /// different allocated object. Note that in Rust, /// every (stack-allocated) variable is considered a separate allocated object. /// /// Compared to [`sub`], this method basically delays the requirement of staying /// within the same allocated object: [`sub`] is immediate Undefined Behavior when /// crossing object boundaries; `wrapping_sub` produces a pointer but still leads /// to Undefined Behavior if that pointer is dereferenced. [`sub`] can be optimized /// better and is thus preferable in performance-sensitive code. /// /// If you need to cross object boundaries, cast the pointer to an integer and /// do the arithmetic there. /// /// [`sub`]: #method.sub /// /// # Examples /// /// Basic usage: /// /// ``` /// // 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_unstable(feature = "const_ptr_offset", issue = "71499")] #[inline] pub const fn wrapping_sub(self, count: usize) -> Self where T: Sized, { self.wrapping_offset((count as isize).wrapping_neg()) } /// Sets the pointer value to `ptr`. /// /// In case `self` is a (fat) pointer to an unsized type, this operation /// will only affect the pointer part, whereas for (thin) pointers to /// sized types, this has the same effect as a simple assignment. /// /// The resulting pointer will have provenance of `val`, i.e., for a fat /// pointer, this operation is semantically the same as creating a new /// fat pointer with the data pointer value of `val` but the metadata of /// `self`. /// /// # Examples /// /// This function is primarily useful for allowing byte-wise pointer /// arithmetic on potentially fat pointers: /// /// ``` /// #![feature(set_ptr_value)] /// # use core::fmt::Debug; /// let arr: [i32; 3] = [1, 2, 3]; /// let mut ptr = &arr[0] as *const dyn Debug; /// let thin = ptr as *const u8; /// unsafe { /// ptr = ptr.set_ptr_value(thin.add(8)); /// # assert_eq!(*(ptr as *const i32), 3); /// println!("{:?}", &*ptr); // will print "3" /// } /// ``` #[unstable(feature = "set_ptr_value", issue = "75091")] #[must_use = "returns a new pointer rather than modifying its argument"] #[inline] pub fn set_ptr_value(mut self, val: *const u8) -> Self { let thin = &mut self as *mut *const T as *mut *const u8; // SAFETY: In case of a thin pointer, this operations is identical // to a simple assignment. In case of a fat pointer, with the current // fat pointer layout implementation, the first field of such a // pointer is always the data pointer, which is likewise assigned. unsafe { *thin = val }; 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")] #[inline] pub 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] 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")] #[inline] pub 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() #[stable(feature = "pointer_methods", since = "1.26.0")] #[inline] pub 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() #[stable(feature = "pointer_methods", since = "1.26.0")] #[inline] pub 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`. It is permissible for the implementation to *always* /// return `usize::MAX`. Only your algorithm's performance can depend /// on getting a usable offset here, not its correctness. /// /// 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` /// /// ``` /// # fn foo(n: usize) { /// # use std::mem::align_of; /// # unsafe { /// let x = [5u8, 6u8, 7u8, 8u8, 9u8]; /// let ptr = x.as_ptr().add(n) as *const u8; /// let offset = ptr.align_offset(align_of::()); /// if offset < x.len() - n - 1 { /// let u16_ptr = ptr.add(offset) as *const u16; /// assert_ne!(*u16_ptr, 500); /// } else { /// // while the pointer can be aligned via `offset`, it would point /// // outside the allocation /// } /// # } } /// ``` #[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 unsafe { align_offset(self, align) } } } #[lang = "const_slice_ptr"] impl *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 /// #![feature(slice_ptr_len)] /// /// use std::ptr; /// /// let slice: *const [i8] = ptr::slice_from_raw_parts(ptr::null(), 3); /// assert_eq!(slice.len(), 3); /// ``` #[inline] #[unstable(feature = "slice_ptr_len", issue = "71146")] #[rustc_const_unstable(feature = "const_slice_ptr_len", issue = "71146")] pub const fn len(self) -> usize { // SAFETY: this is safe because `*const [T]` and `FatPtr` have the same layout. // Only `std` can make this guarantee. unsafe { Repr { rust: self }.raw }.len } /// 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(), 0 as *const i8); /// ``` #[inline] #[unstable(feature = "slice_ptr_get", issue = "74265")] #[rustc_const_unstable(feature = "slice_ptr_get", issue = "74265")] pub const fn as_ptr(self) -> *const T { self as *const 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 dereferencable /// 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")] #[inline] pub unsafe fn get_unchecked(self, index: I) -> *const I::Output where I: SliceIndex<[T]>, { // SAFETY: the caller ensures that `self` is dereferencable and `index` in-bounds. unsafe { index.get_unchecked(self) } } /// Returns `None` if the pointer is null, or else returns a shared slice to /// the value wrapped in `Some`. In contrast to [`as_ref`], this does not require /// that the value has to be initialized. /// /// [`as_ref`]: #method.as_ref /// /// # 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 for `ptr.len() * mem::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 allocated object! /// Slices can never span across multiple allocated objects. /// /// * 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() * mem::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, for the duration of this lifetime, the memory the pointer points to must /// not get mutated (except inside `UnsafeCell`). /// /// This applies even if the result of this method is unused! /// /// See also [`slice::from_raw_parts`][]. /// /// [valid]: crate::ptr#safety /// [`NonNull::dangling()`]: NonNull::dangling /// [`pointer::offset`]: ../std/primitive.pointer.html#method.offset #[inline] #[unstable(feature = "ptr_as_uninit", issue = "75402")] pub 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()) }) } } } // Equality for pointers #[stable(feature = "rust1", since = "1.0.0")] impl PartialEq for *const T { #[inline] fn eq(&self, other: &*const T) -> bool { *self == *other } } #[stable(feature = "rust1", since = "1.0.0")] impl Eq for *const T {} // Comparison for pointers #[stable(feature = "rust1", since = "1.0.0")] impl Ord for *const T { #[inline] fn cmp(&self, other: &*const T) -> Ordering { if self < other { Less } else if self == other { Equal } else { Greater } } } #[stable(feature = "rust1", since = "1.0.0")] impl PartialOrd for *const T { #[inline] fn partial_cmp(&self, other: &*const T) -> Option { Some(self.cmp(other)) } #[inline] fn lt(&self, other: &*const T) -> bool { *self < *other } #[inline] fn le(&self, other: &*const T) -> bool { *self <= *other } #[inline] fn gt(&self, other: &*const T) -> bool { *self > *other } #[inline] fn ge(&self, other: &*const T) -> bool { *self >= *other } }