pub struct NonNull<T>{ }
Expand description
*mut T
but non-zero and covariant.
This is often the correct thing to use when building data structures using raw pointers, but is ultimately more dangerous to use because of its additional properties. If youâre not sure if you should use NonNull<T>
, just use *mut T
!
Unlike *mut T
, the pointer must always be non-null, even if the pointer is never dereferenced. This is so that enums may use this forbidden value as a discriminant â Option<NonNull<T>>
has the same size as *mut T
. However the pointer may still dangle if it isnât dereferenced.
Unlike *mut T
, NonNull<T>
is covariant over T
. This is usually the correct choice for most data structures and safe abstractions, such as Box
, Rc
, Arc
, Vec
, and LinkedList
.
In rare cases, if your type exposes a way to mutate the value of T
through a NonNull<T>
, and you need to prevent unsoundness from variance (for example, if T
could be a reference with a shorter lifetime), you should add a field to make your type invariant, such as PhantomData<Cell<T>>
or PhantomData<&'a mut T>
.
Example of a type that must be invariant:
use std::cell::Cell;
use std::marker::PhantomData;
struct Invariant<T> {
ptr: std::ptr::NonNull<T>,
_invariant: PhantomData<Cell<T>>,
}
Notice that NonNull<T>
has a From
instance for &T
. However, this does not change the fact that mutating through a (pointer derived from a) shared reference is undefined behavior unless the mutation happens inside an UnsafeCell<T>
. The same goes for creating a mutable reference from a shared reference. When using this From
instance without an UnsafeCell<T>
, it is your responsibility to ensure that as_mut
is never called, and as_ptr
is never used for mutation.
Thanks to the null pointer optimization, NonNull<T>
and Option<NonNull<T>>
are guaranteed to have the same size and alignment:
use std::ptr::NonNull;
assert_eq!(size_of::<NonNull<i16>>(), size_of::<Option<NonNull<i16>>>());
assert_eq!(align_of::<NonNull<i16>>(), align_of::<Option<NonNull<i16>>>());
assert_eq!(size_of::<NonNull<str>>(), size_of::<Option<NonNull<str>>>());
assert_eq!(align_of::<NonNull<str>>(), align_of::<Option<NonNull<str>>>());
Source§ 1.89.0 (const: 1.89.0) · Source 1.25.0 (const: 1.36.0) · Source
Creates a new NonNull
that is dangling, but well-aligned.
This is useful for initializing types which lazily allocate, like Vec::new
does.
Note that the pointer value may potentially represent a valid pointer to a T
, which means this must not be used as a ânot yet initializedâ sentinel value. Types that lazily allocate must track initialization by some other means.
use std::ptr::NonNull;
let ptr = NonNull::<u32>::dangling();
1.89.0 · Source Source ð¬This is a nightly-only experimental API. (ptr_as_uninit
#75402)
Returns a shared references to the value. In contrast to as_ref
, this does not require that the value has to be initialized.
For the mutable counterpart see as_uninit_mut
.
When calling this method, you have to ensure that the pointer is convertible to a reference. Note that because the created reference is to MaybeUninit<T>
, the source pointer can point to uninitialized memory.
ptr_as_uninit
#75402)
Returns a unique references to the value. In contrast to as_mut
, this does not require that the value has to be initialized.
For the shared counterpart see as_uninit_ref
.
When calling this method, you have to ensure that the pointer is convertible to a reference. Note that because the created reference is to MaybeUninit<T>
, the source pointer can point to uninitialized memory.
Creates a new NonNull
.
ptr
must be non-null.
use std::ptr::NonNull;
let mut x = 0u32;
let ptr = unsafe { NonNull::new_unchecked(&mut x as *mut _) };
Incorrect usage of this function:
use std::ptr::NonNull;
let ptr = unsafe { NonNull::<u32>::new_unchecked(std::ptr::null_mut()) };
1.25.0 (const: 1.85.0) · Source
Creates a new NonNull
if ptr
is non-null.
This method will panic during const evaluation if the pointer cannot be determined to be null or not. See is_null
for more information.
use std::ptr::NonNull;
let mut x = 0u32;
let ptr = NonNull::<u32>::new(&mut x as *mut _).expect("ptr is null!");
if let Some(ptr) = NonNull::<u32>::new(std::ptr::null_mut()) {
unreachable!();
}
1.89.0 (const: 1.89.0) · Source
Converts a reference to a NonNull
pointer.
Converts a mutable reference to a NonNull
pointer.
ptr_metadata
#81513) Source ð¬This is a nightly-only experimental API. (ptr_metadata
#81513)
Decompose a (possibly wide) pointer into its data pointer and metadata components.
The pointer can be later reconstructed with NonNull::from_raw_parts
.
Gets the âaddressâ portion of the pointer.
For more details, see the equivalent method on a raw pointer, pointer::addr
.
This is a Strict Provenance API.
1.89.0 · Source 1.84.0 · Source 1.84.0 · Source 1.25.0 (const: 1.32.0) · SourceAcquires the underlying *mut
pointer.
use std::ptr::NonNull;
let mut x = 0u32;
let ptr = NonNull::new(&mut x).expect("ptr is null!");
let x_value = unsafe { *ptr.as_ptr() };
assert_eq!(x_value, 0);
unsafe { *ptr.as_ptr() += 2; }
let x_value = unsafe { *ptr.as_ptr() };
assert_eq!(x_value, 2);
1.25.0 (const: 1.73.0) · Source
Returns a shared reference to the value. If the value may be uninitialized, as_uninit_ref
must be used instead.
For the mutable counterpart see as_mut
.
When calling this method, you have to ensure that the pointer is convertible to a reference.
§Examplesuse std::ptr::NonNull;
let mut x = 0u32;
let ptr = NonNull::new(&mut x as *mut _).expect("ptr is null!");
let ref_x = unsafe { ptr.as_ref() };
println!("{ref_x}");
1.25.0 (const: 1.83.0) · Source
Returns a unique reference to the value. If the value may be uninitialized, as_uninit_mut
must be used instead.
For the shared counterpart see as_ref
.
When calling this method, you have to ensure that the pointer is convertible to a reference.
§Examplesuse std::ptr::NonNull;
let mut x = 0u32;
let mut ptr = NonNull::new(&mut x).expect("null pointer");
let x_ref = unsafe { ptr.as_mut() };
assert_eq!(*x_ref, 0);
*x_ref += 2;
assert_eq!(*x_ref, 2);
1.27.0 (const: 1.36.0) · Source
Casts to a pointer of another type.
§Examplesuse std::ptr::NonNull;
let mut x = 0u32;
let ptr = NonNull::new(&mut x as *mut _).expect("null pointer");
let casted_ptr = ptr.cast::<i8>();
let raw_ptr: *mut i8 = casted_ptr.as_ptr();
Source ð¬This is a nightly-only experimental API. (pointer_try_cast_aligned
#141221)
Try to cast to a pointer of another type by checking aligment.
If the pointer is properly aligned to the target type, it will be cast to the target type. Otherwise, None
is returned.
#![feature(pointer_try_cast_aligned)]
use std::ptr::NonNull;
let mut x = 0u64;
let aligned = NonNull::from_mut(&mut x);
let unaligned = unsafe { aligned.byte_add(1) };
assert!(aligned.try_cast_aligned::<u32>().is_some());
assert!(unaligned.try_cast_aligned::<u32>().is_none());
1.80.0 (const: 1.80.0) · Source
Adds an offset to a pointer.
count
is in units of T; e.g., a count
of 3 represents a pointer offset of 3 * size_of::<T>()
bytes.
If any of the following conditions are violated, the result is Undefined Behavior:
The computed offset, count * size_of::<T>()
bytes, must not overflow isize
.
If the computed offset is non-zero, then self
must be derived from 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 âwrap aroundâ the edge of the address space.
Allocations can never be larger than isize::MAX
bytes, so if the computed offset stays in bounds of the allocation, it is guaranteed to satisfy the first requirement. This implies, for instance, that vec.as_ptr().add(vec.len())
(for vec: Vec<T>
) is always safe.
use std::ptr::NonNull;
let mut s = [1, 2, 3];
let ptr: NonNull<u32> = NonNull::new(s.as_mut_ptr()).unwrap();
unsafe {
println!("{}", ptr.offset(1).read());
println!("{}", ptr.offset(2).read());
}
1.80.0 (const: 1.80.0) · Source
Calculates the offset from a pointer in bytes.
count
is in units of bytes.
This is purely a convenience for casting to a u8
pointer and using 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.
Adds an offset to 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::<T>()
bytes.
If any of the following conditions are violated, the result is Undefined Behavior:
The computed offset, count * size_of::<T>()
bytes, must not overflow isize
.
If the computed offset is non-zero, then self
must be derived from 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 âwrap aroundâ the edge of the address space.
Allocations can never be larger than isize::MAX
bytes, so if the computed offset stays in bounds of the allocation, it is guaranteed to satisfy the first requirement. This implies, for instance, that vec.as_ptr().add(vec.len())
(for vec: Vec<T>
) is always safe.
use std::ptr::NonNull;
let s: &str = "123";
let ptr: NonNull<u8> = NonNull::new(s.as_ptr().cast_mut()).unwrap();
unsafe {
println!("{}", ptr.add(1).read() as char);
println!("{}", ptr.add(2).read() as char);
}
1.80.0 (const: 1.80.0) · Source
Calculates the offset from a pointer in bytes (convenience for .byte_offset(count as isize)
).
count
is in units of bytes.
This is purely a convenience for casting to a u8
pointer and using 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.
Subtracts an 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::<T>()
bytes.
If any of the following conditions are violated, the result is Undefined Behavior:
The computed offset, count * size_of::<T>()
bytes, must not overflow isize
.
If the computed offset is non-zero, then self
must be derived from 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 âwrap aroundâ the edge of the address space.
Allocations can never be larger than isize::MAX
bytes, so if the computed offset stays in bounds of the allocation, it is guaranteed to satisfy the first requirement. This implies, for instance, that vec.as_ptr().add(vec.len())
(for vec: Vec<T>
) is always safe.
use std::ptr::NonNull;
let s: &str = "123";
unsafe {
let end: NonNull<u8> = NonNull::new(s.as_ptr().cast_mut()).unwrap().add(3);
println!("{}", end.sub(1).read() as char);
println!("{}", end.sub(2).read() as char);
}
1.80.0 (const: 1.80.0) · Source
Calculates the offset from a pointer in bytes (convenience for .byte_offset((count as isize).wrapping_neg())
).
count
is in units of bytes.
This is purely a convenience for casting to a u8
pointer and using 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.
Calculates the distance between two pointers within the same allocation. The returned value is in units of T: the distance in bytes divided by size_of::<T>()
.
This is equivalent to (self as isize - origin as isize) / (size_of::<T>() as isize)
, except that it has a lot more opportunities for UB, in exchange for the compiler better understanding what you are doing.
The primary motivation of this method is for computing the len
of an array/slice of T
that you are currently representing as a âstartâ and âendâ pointer (and âendâ is âone past the endâ 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.
§SafetyIf any of the following conditions are violated, the result is Undefined Behavior:
self
and origin
must either
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 âwrapping aroundâ), cannot overflow an isize
. This is implied by the in-bounds requirement, and the fact that no allocation can be larger than isize::MAX
bytes.
The requirement for pointers to be derived from the same allocation is primarily needed for const
-compatibility: the distance between pointers into different allocated objects is not known at compile-time. However, the requirement also exists at runtime and may be exploited by optimizations. If you wish to compute the difference between pointers that are not guaranteed to be from the same allocation, use (self as isize - origin as isize) / size_of::<T>()
.
This function panics if T
is a Zero-Sized Type (âZSTâ).
Basic usage:
use std::ptr::NonNull;
let a = [0; 5];
let ptr1: NonNull<u32> = NonNull::from(&a[1]);
let ptr2: NonNull<u32> = NonNull::from(&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:
use std::ptr::NonNull;
let ptr1 = NonNull::new(Box::into_raw(Box::new(0u8))).unwrap();
let ptr2 = NonNull::new(Box::into_raw(Box::new(1u8))).unwrap();
let diff = (ptr2.addr().get() as isize).wrapping_sub(ptr1.addr().get() as isize);
let diff_plus_1 = diff.wrapping_add(1);
let ptr2_other = NonNull::new(ptr1.as_ptr().wrapping_byte_offset(diff_plus_1)).unwrap();
assert_eq!(ptr2.addr(), ptr2_other.addr());
let one = unsafe { ptr2_other.offset_from(ptr2) };
1.80.0 (const: 1.80.0) · Source
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
on it. See that method for documentation and safety requirements.
For non-Sized
pointees this operation considers only the data pointers, ignoring the metadata.
Calculates the distance between two pointers within the same allocation, where itâs known that self
is equal to or greater than origin
. The returned value is in units of T: the distance in bytes is divided by size_of::<T>()
.
This computes the same value that offset_from
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 though of as recovering the count
that was passed to add
(or, with the parameters in the other order, to sub
). The following are all equivalent, assuming that their safety preconditions are met:
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
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, itâs 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
.
This function panics if T
is a Zero-Sized Type (âZSTâ).
use std::ptr::NonNull;
let a = [0; 5];
let ptr1: NonNull<u32> = NonNull::from(&a[1]);
let ptr2: NonNull<u32> = NonNull::from(&a[3]);
unsafe {
assert_eq!(ptr2.offset_from_unsigned(ptr1), 2);
assert_eq!(ptr1.add(2), ptr2);
assert_eq!(ptr2.sub(2), ptr1);
assert_eq!(ptr2.offset_from_unsigned(ptr2), 0);
}
1.87.0 (const: 1.87.0) · Source
Calculates the distance between two pointers within the same allocation, where itâs 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
on it. See that method for documentation and safety requirements.
For non-Sized
pointees this operation considers only the data pointers, ignoring the metadata.
Reads the value from self
without moving it. This leaves the memory in self
unchanged.
See ptr::read
for safety concerns and examples.
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.
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.
Copies count * size_of::<T>()
bytes from self
to dest
. The source and destination may overlap.
NOTE: this has the same argument order as ptr::copy
.
See ptr::copy
for safety concerns and examples.
Copies count * size_of::<T>()
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.
Executes the destructor (if any) of the pointed-to value.
See ptr::drop_in_place
for safety concerns and examples.
Overwrites a memory location with the given value without reading or dropping the old value.
See ptr::write
for safety concerns and examples.
Invokes memset on the specified pointer, setting count * size_of::<T>()
bytes of memory starting at self
to val
.
See ptr::write_bytes
for safety concerns and examples.
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.
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.
Replaces the value at self
with src
, returning the old value, without dropping either.
See ptr::replace
for safety concerns and examples.
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.
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.
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.
When this is called during compile-time evaluation (which is unstable), the implementation may return usize::MAX
in cases where that can never happen at runtime. This is because the actual alignment of pointers is not known yet during compile-time, so an offset with guaranteed alignment can sometimes not be computed. For example, a buffer declared as [u8; N]
might be allocated at an odd or an even address, but at compile-time this is not yet known, so the execution has to be correct for either choice. It is therefore impossible to find an offset that is guaranteed to be 2-aligned. (This behavior is subject to change, as usual for unstable APIs.)
The function panics if align
is not a power-of-two.
Accessing adjacent u8
as u16
use std::ptr::NonNull;
let x = [5_u8, 6, 7, 8, 9];
let ptr = NonNull::new(x.as_ptr() as *mut u8).unwrap();
let offset = ptr.align_offset(align_of::<u16>());
if offset < x.len() - 1 {
let u16_ptr = ptr.add(offset).cast::<u16>();
assert!(u16_ptr.read() == u16::from_ne_bytes([5, 6]) || u16_ptr.read() == u16::from_ne_bytes([6, 7]));
} else {
}
1.79.0 · Source
Returns whether the pointer is properly aligned for T
.
use std::ptr::NonNull;
#[repr(align(4))]
struct AlignedI32(i32);
let data = AlignedI32(42);
let ptr = NonNull::<AlignedI32>::from(&data);
assert!(ptr.is_aligned());
assert!(!NonNull::new(ptr.as_ptr().wrapping_byte_add(1)).unwrap().is_aligned());
Source ð¬This is a nightly-only experimental API. (pointer_is_aligned_to
#96284)
Returns whether the pointer is aligned to align
.
For non-Sized
pointees this operation considers only the data pointer, ignoring the metadata.
The function panics if align
is not a power-of-two (this includes 0).
#![feature(pointer_is_aligned_to)]
#[repr(align(4))]
struct AlignedI32(i32);
let data = AlignedI32(42);
let ptr = &data as *const AlignedI32;
assert!(ptr.is_aligned_to(1));
assert!(ptr.is_aligned_to(2));
assert!(ptr.is_aligned_to(4));
assert!(ptr.wrapping_byte_add(2).is_aligned_to(2));
assert!(!ptr.wrapping_byte_add(2).is_aligned_to(4));
assert_ne!(ptr.is_aligned_to(8), ptr.wrapping_add(1).is_aligned_to(8));
Source§ 1.70.0 (const: 1.83.0) · Source
Creates a non-null raw slice from a thin pointer and a length.
The len
argument is the number of elements, not the number of bytes.
This function is safe, but dereferencing the return value is unsafe. See the documentation of slice::from_raw_parts
for slice safety requirements.
use std::ptr::NonNull;
let mut x = [5, 6, 7];
let nonnull_pointer = NonNull::new(x.as_mut_ptr()).unwrap();
let slice = NonNull::slice_from_raw_parts(nonnull_pointer, 3);
assert_eq!(unsafe { slice.as_ref()[2] }, 7);
(Note that this example artificially demonstrates a use of this method, but let slice = NonNull::from(&x[..]);
would be a better way to write code like this.)
Returns the length of a non-null raw slice.
The returned value is the number of elements, not the number of bytes.
This function is safe, even when the non-null raw slice cannot be dereferenced to a slice because the pointer does not have a valid address.
§Examplesuse std::ptr::NonNull;
let slice: NonNull<[i8]> = NonNull::slice_from_raw_parts(NonNull::dangling(), 3);
assert_eq!(slice.len(), 3);
1.79.0 (const: 1.79.0) · Source
Returns true
if the non-null raw slice has a length of 0.
use std::ptr::NonNull;
let slice: NonNull<[i8]> = NonNull::slice_from_raw_parts(NonNull::dangling(), 3);
assert!(!slice.is_empty());
Source ð¬This is a nightly-only experimental API. (slice_ptr_get
#74265)
Returns a non-null pointer to the sliceâs buffer.
§Examples#![feature(slice_ptr_get)]
use std::ptr::NonNull;
let slice: NonNull<[i8]> = NonNull::slice_from_raw_parts(NonNull::dangling(), 3);
assert_eq!(slice.as_non_null_ptr(), NonNull::<i8>::dangling());
Source ð¬This is a nightly-only experimental API. (slice_ptr_get
#74265)
Returns a raw pointer to the sliceâs buffer.
§Examples#![feature(slice_ptr_get)]
use std::ptr::NonNull;
let slice: NonNull<[i8]> = NonNull::slice_from_raw_parts(NonNull::dangling(), 3);
assert_eq!(slice.as_mut_ptr(), NonNull::<i8>::dangling().as_ptr());
Source ð¬This is a nightly-only experimental API. (ptr_as_uninit
#75402)
Returns a shared reference to a slice of possibly uninitialized values. In contrast to as_ref
, this does not require that the value has to be initialized.
For the mutable counterpart see as_uninit_slice_mut
.
When calling this method, you have to ensure that all of the following is true:
The pointer must be valid for reads for ptr.len() * size_of::<T>()
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::<T>()
of the slice must be no larger than isize::MAX
. See the safety documentation of pointer::offset
.
You must enforce Rustâs 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 mutated (except inside UnsafeCell
).
This applies even if the result of this method is unused!
See also slice::from_raw_parts
.
ptr_as_uninit
#75402)
Returns a unique reference to a slice of possibly uninitialized values. In contrast to as_mut
, this does not require that the value has to be initialized.
For the shared counterpart see as_uninit_slice
.
When calling this method, you have to ensure that all of the following is true:
The pointer must be valid for reads and writes for ptr.len() * size_of::<T>()
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::<T>()
of the slice must be no larger than isize::MAX
. See the safety documentation of pointer::offset
.
You must enforce Rustâs 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
.
#![feature(allocator_api, ptr_as_uninit)]
use std::alloc::{Allocator, Layout, Global};
use std::mem::MaybeUninit;
use std::ptr::NonNull;
let memory: NonNull<[u8]> = Global.allocate(Layout::new::<[u8; 32]>())?;
let slice: &mut [MaybeUninit<u8>] = unsafe { memory.as_uninit_slice_mut() };
Source ð¬This is a nightly-only experimental API. (slice_ptr_get
#74265)
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.
#![feature(slice_ptr_get)]
use std::ptr::NonNull;
let x = &mut [1, 2, 4];
let x = NonNull::slice_from_raw_parts(NonNull::new(x.as_mut_ptr()).unwrap(), x.len());
unsafe {
assert_eq!(x.get_unchecked_mut(1).as_ptr(), x.as_non_null_ptr().as_ptr().add(1));
}
1.25.0 · Source§ 1.25.0 · Source§ 1.25.0 · Source§ Source§
Converts a &T
to a NonNull<T>
.
This conversion is safe and infallible since references cannot be null.
1.25.0 · Source§ Source§Converts a &mut T
to a NonNull<T>
.
This conversion is safe and infallible since references cannot be null.
1.25.0 · Source§ 1.25.0 · Source§ 1.25.0 · Source§ Source§Tests for self
and other
values to be equal, and is used by ==
.
Tests for !=
. The default implementation is almost always sufficient, and should not be overridden without very good reason.
This method returns an ordering between
self
and
other
values if one exists.
Read more 1.0.0 · Source§Tests less than (for
self
and
other
) and is used by the
<
operator.
Read more 1.0.0 · Source§Tests less than or equal to (for
self
and
other
) and is used by the
<=
operator.
Read more 1.0.0 · Source§Tests greater than (for
self
and
other
) and is used by the
>
operator.
Read more 1.0.0 · Source§Tests greater than or equal to (for
self
and
other
) and is used by the
>=
operator.
Read more 1.25.0 · Source§ Source§ 1.25.0 · Source§ Source§ 1.25.0 · Source§ 1.33.0 · Source§ Source§ 1.25.0 · Source§NonNull
pointers are not Send
because the data they reference may be aliased.
NonNull
pointers are not Sync
because the data they reference may be aliased.
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