pointer - Rust (original) (raw)

Primitive Type pointer

1.0.0

Expand description

Raw, unsafe pointers, *const T, and *mut T.

See also the std::ptr module.

Working with raw pointers in Rust is uncommon, typically limited to a few patterns. Raw pointers can be out-of-bounds, unaligned, or null. However, when loading from or storing to a raw pointer, it must be valid for the given access and aligned. When using a field expression, tuple index expression, or array/slice index expression on a raw pointer, it follows the rules of in-bounds pointer arithmetic.

Storing through a raw pointer using *ptr = data calls drop on the old value, sowrite must be used if the type has drop glue and memory is not already initialized - otherwise drop would be called on the uninitialized memory.

Use the null and null_mut functions to create null pointers, and theis_null method of the *const T and *mut T types to check for null. The *const T and *mut T types also define the offset method, for pointer math.

§Common ways to create raw pointers

§1. Coerce a reference (&T) or mutable reference (&mut T).

let my_num: i32 = 10;
let my_num_ptr: *const i32 = &my_num;
let mut my_speed: i32 = 88;
let my_speed_ptr: *mut i32 = &mut my_speed;

To get a pointer to a boxed value, dereference the box:

let my_num: Box<i32> = Box::new(10);
let my_num_ptr: *const i32 = &*my_num;
let mut my_speed: Box<i32> = Box::new(88);
let my_speed_ptr: *mut i32 = &mut *my_speed;

This does not take ownership of the original allocation and requires no resource management later, but you must not use the pointer after its lifetime.

§2. Consume a box (Box<T>).

The into_raw function consumes a box and returns the raw pointer. It doesn’t destroy T or deallocate any memory.

let my_speed: Box<i32> = Box::new(88);
let my_speed: *mut i32 = Box::into_raw(my_speed);

// By taking ownership of the original `Box<T>` though
// we are obligated to put it together later to be destroyed.
unsafe {
    drop(Box::from_raw(my_speed));
}

Note that here the call to drop is for clarity - it indicates that we are done with the given value and it should be destroyed.

§3. Create it using &raw

Instead of coercing a reference to a raw pointer, you can use the raw borrow operators &raw const (for *const T) and &raw mut (for *mut T). These operators allow you to create raw pointers to fields to which you cannot create a reference (without causing undefined behavior), such as an unaligned field. This might be necessary if packed structs or uninitialized memory is involved.

#[derive(Debug, Default, Copy, Clone)]
#[repr(C, packed)]
struct S {
    aligned: u8,
    unaligned: u32,
}
let s = S::default();
let p = &raw const s.unaligned; // not allowed with coercion

§4. Get it from C.

#[allow(unused_extern_crates)]
extern crate libc;

unsafe {
    let my_num: *mut i32 = libc::malloc(size_of::<i32>()) as *mut i32;
    if my_num.is_null() {
        panic!("failed to allocate memory");
    }
    libc::free(my_num as *mut core::ffi::c_void);
}

Usually you wouldn’t literally use malloc and free from Rust, but C APIs hand out a lot of pointers generally, so are a common source of raw pointers in Rust.

Source§

1.0.0 (const: 1.84.0) · Source

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.

§Panics during const evaluation

If this method is used during const evaluation, and self is a pointer that is offset beyond the bounds of the memory it initially pointed to, then there might not be enough information to determine whether the pointer is null. This is because the absolute address in memory is not known at compile time. If the nullness of the pointer cannot be determined, this method will panic.

In-bounds pointers are never null, so the method will never panic for such pointers.

§Examples

let s: &str = "Follow the rabbit";
let ptr: *const u8 = s.as_ptr();
assert!(!ptr.is_null());

1.38.0 (const: 1.38.0) · Source

Casts to a pointer of another type.

Source

🔬This is a nightly-only experimental API. (set_ptr_value #75091)

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 ofmeta, 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)]
let arr: [i32; 3] = [1, 2, 3];
let mut ptr = arr.as_ptr() as *const dyn Debug;
let thin = ptr as *const u8;
unsafe {
    ptr = thin.add(8).with_metadata_of(ptr);
    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.

#![feature(set_ptr_value)]
let x = 0u32;
let y = 1u32;

let x = (&x) as *const u32;
let y = (&y) as *const u32;

let offset = (x as usize - y as usize) / 4;
let bad = x.wrapping_add(offset).with_metadata_of(y);

// This dereference is UB. The pointer only has provenance for `x` but points to `y`.
println!("{:?}", unsafe { &*bad });

1.65.0 (const: 1.65.0) · Source

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.

1.84.0 · Source

Gets the “address” portion of the pointer.

This is similar to self as usize, except that the provenance of the pointer is discarded and not exposed. This means that casting the returned address back to a pointer yields a pointer without provenance, which is undefined behavior to dereference. To properly restore the lost information and obtain a dereferenceable pointer, usewith_addr or map_addr.

If using those APIs is not possible because there is no way to preserve a pointer with the required provenance, then Strict Provenance might not be for you. Use pointer-integer casts or expose_provenance and with_exposed_provenanceinstead. However, note that this makes your code less portable and less amenable to tools that check for compliance with the Rust memory model.

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 perform a change of representation to produce a value containing only the address portion of the pointer. What that means is up to the platform to define.

This is a Strict Provenance API.

1.84.0 · Source

Exposes the “provenance” part of the pointer for future use inwith_exposed_provenance and returns the “address” portion.

This is equivalent to self as usize, which semantically discards provenance information. Furthermore, this (like the as cast) has the implicit side-effect of marking the provenance as ‘exposed’, so on platforms that support it you can later callwith_exposed_provenance to reconstitute the original pointer including its provenance.

Due to its inherent ambiguity, with_exposed_provenance may not be supported by tools that help you to stay conformant with the Rust memory model. It is recommended to useStrict Provenance APIs such as with_addrwherever possible, in which case addr should be used instead of expose_provenance.

On most platforms this will produce a value with the same bytes as the original pointer, because all the bytes are dedicated to describing the address. Platforms which need to store additional information in the pointer may not support this operation, since the ‘expose’ side-effect which is required for with_exposed_provenance to work is typically not available.

This is an Exposed Provenance API.

1.84.0 · Source

Creates a new pointer with the given address and the provenance ofself.

This is similar to a addr as *const T cast, but copies the provenance of self to the new pointer. This avoids the inherent ambiguity of the unary cast.

This is equivalent to using wrapping_offset to offsetself to the given address, and therefore has all the same capabilities and restrictions.

This is a Strict Provenance API.

1.84.0 · Source

Creates a new pointer by mapping self’s address to a new one, preserving theprovenance of self.

This is a convenience for with_addr, see that method for details.

This is a Strict Provenance API.

Source

🔬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 from_raw_parts.

1.9.0 (const: 1.84.0) · Source

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_refmust be used instead.

§Safety

When calling this method, you have to ensure that either the pointer is null _or_the pointer is convertible to a reference.

§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.

§Examples

let ptr: *const u8 = &10u8 as *const u8;

unsafe {
    if let Some(val_back) = ptr.as_ref() {
        assert_eq!(val_back, &10);
    }
}

§Null-unchecked version

If you are sure the pointer can never be null and are looking for some kind ofas_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;
    assert_eq!(val_back, &10);
}

Source

🔬This is a nightly-only experimental API. (ptr_as_ref_unchecked #122034)

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.

§Safety

When calling this method, you have to ensure that the pointer is convertible to a reference.

§Examples

#![feature(ptr_as_ref_unchecked)]
let ptr: *const u8 = &10u8 as *const u8;

unsafe {
    assert_eq!(ptr.as_ref_unchecked(), &10);
}

Source

🔬This is a nightly-only experimental API. (ptr_as_uninit #75402)

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.

§Safety

When calling this method, you have to ensure that either the pointer is null _or_the pointer is convertible to a reference.

§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.

§Examples

#![feature(ptr_as_uninit)]

let ptr: *const u8 = &10u8 as *const u8;

unsafe {
    if let Some(val_back) = ptr.as_uninit_ref() {
        assert_eq!(val_back.assume_init(), 10);
    }
}

1.0.0 (const: 1.61.0) · Source

Adds a signed 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.

§Safety

If any of the following conditions are violated, the result is Undefined Behavior:

• The offset in bytes, count * size_of::<T>(), computed on mathematical integers (without “wrapping around”), must fit in an isize.
• If the computed offset is non-zero, then self must be derived from a pointer to someallocated object, and the entire memory range between self and the result must be in bounds of that allocated object. In particular, this range must not “wrap around” the edge of the address space. Note that “range” here refers to a half-open range as usual in Rust, i.e., self..result for non-negative offsets and result..self for negative offsets.

Allocated objects can never be larger than isize::MAX bytes, so if the computed offset stays in bounds of the allocated object, it is guaranteed to satisfy the first requirement. This implies, for instance, that vec.as_ptr().add(vec.len()) (for vec: Vec<T>) is always safe.

Consider using wrapping_offset instead if these constraints are difficult to satisfy. The only advantage of this method is that it enables more aggressive compiler optimizations.

§Examples

let s: &str = "123";
let ptr: *const u8 = s.as_ptr();

unsafe {
    assert_eq!(*ptr.offset(1) as char, '2');
    assert_eq!(*ptr.offset(2) as char, '3');
}

1.75.0 (const: 1.75.0) · Source

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 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.

1.16.0 (const: 1.61.0) · Source

Adds a signed offset to a pointer using wrapping arithmetic.

count is in units of T; e.g., a count of 3 represents a pointer offset of 3 * size_of::<T>() bytes.

§Safety

This operation itself is always safe, but using the resulting pointer is not.

The resulting pointer “remembers” the allocated object that self points to; it must not be used to read or write other allocated objects.

In other words, let z = x.wrapping_offset((y as isize) - (x as isize)) does not make zthe 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 unlessx 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 a pointer is dereferenced when it is out-of-bounds of the object it is attached to. offsetcan 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 allocated object and then re-entering it later is permitted.

§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_offset(6);

let mut out = String::new();
while ptr != end_rounded_up {
    unsafe {
        write!(&mut out, "{}, ", *ptr)?;
    }
    ptr = ptr.wrapping_offset(step);
}
assert_eq!(out.as_str(), "1, 3, 5, ");

1.75.0 (const: 1.75.0) · Source

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 on it. See that method for documentation.

For non-Sized pointees this operation changes only the data pointer, leaving the metadata untouched.

Source

🔬This is a nightly-only experimental API. (ptr_mask #98290)

Masks out bits of the pointer according to a mask.

This is convenience for ptr.map_addr(|a| a & mask).

For non-Sized pointees this operation changes only the data pointer, leaving the metadata untouched.

§Examples

#![feature(ptr_mask)]
let v = 17_u32;
let ptr: *const u32 = &v;

// `u32` is 4 bytes aligned,
// which means that lower 2 bits are always 0.
let tag_mask = 0b11;
let ptr_mask = !tag_mask;

// We can store something in these lower bits
let tagged_ptr = ptr.map_addr(|a| a | 0b10);

// Get the "tag" back
let tag = tagged_ptr.addr() & tag_mask;
assert_eq!(tag, 0b10);

// Note that `tagged_ptr` is unaligned, it's UB to read from it.
// To get original pointer `mask` can be used:
let masked_ptr = tagged_ptr.mask(ptr_mask);
assert_eq!(unsafe { *masked_ptr }, 17);

1.47.0 (const: 1.65.0) · Source

Calculates the distance between two pointers within the same allocation. The returned value is in units of T: the distance in bytes divided by size_of::<T>().

This is equivalent to (self as isize - origin as isize) / (size_of::<T>() as isize), except that it has a lot more opportunities for UB, in exchange for the compiler better understanding what you are doing.

The primary motivation of this method is for computing the len of an array/slice of T that you are currently representing as a “start” and “end” pointer (and “end” is “one past the end” of the array). In that case, end.offset_from(start) gets you the length of the array.

All of the following safety requirements are trivially satisfied for this usecase.

§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 a pointer to the same allocated object, 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 allocated object can be larger than isize::MAX bytes.

The requirement for pointers to be derived from the same allocated object 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>().

§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:

let ptr1 = Box::into_raw(Box::new(0u8)) as *const u8;
let ptr2 = Box::into_raw(Box::new(1u8)) as *const u8;
let diff = (ptr2 as isize).wrapping_sub(ptr1 as isize);
// Make ptr2_other an "alias" of ptr2.add(1), but derived from ptr1.
let ptr2_other = (ptr1 as *const u8).wrapping_offset(diff).wrapping_offset(1);
assert_eq!(ptr2 as usize, ptr2_other as usize);
// Since ptr2_other and ptr2 are derived from pointers to different objects,
// computing their offset is undefined behavior, even though
// they point to addresses that are in-bounds of the same object!
unsafe {
    let one = ptr2_other.offset_from(ptr2); // Undefined Behavior! ⚠️
}

1.75.0 (const: 1.75.0) · 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.

1.87.0 (const: 1.87.0) · Source

Calculates the distance between two pointers within the same allocation, where it’s known thatself 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_fromwould compute, but with the added precondition that the offset is guaranteed to be non-negative. This method is equivalent tousize::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 (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_fromapply to this method as well; see it for the full details.

Importantly, despite the return type of this method being able to represent a larger offset, it’s still not permitted to pass pointers which differ by more than isize::MAX bytes. As such, the result of this method will always be less than or equal to isize::MAX as usize.

§Panics

This function panics if T is a Zero-Sized Type (“ZST”).

§Examples

let a = [0; 5];
let ptr1: *const i32 = &a[1];
let ptr2: *const i32 = &a[3];
unsafe {
    assert_eq!(ptr2.offset_from_unsigned(ptr1), 2);
    assert_eq!(ptr1.add(2), ptr2);
    assert_eq!(ptr2.sub(2), ptr1);
    assert_eq!(ptr2.offset_from_unsigned(ptr2), 0);
}

// This would be incorrect, as the pointers are not correctly ordered:
// ptr1.offset_from_unsigned(ptr2)

1.87.0 (const: 1.87.0) · Source

Calculates the distance between two pointers within the same allocation, where it’s known thatself 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 sub_ptr on it. See that method for documentation and safety requirements.

For non-Sized pointees this operation considers only the data pointers, ignoring the metadata.

Source

🔬This is a nightly-only experimental API. (const_raw_ptr_comparison #53020)

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.

Source

🔬This is a nightly-only experimental API. (const_raw_ptr_comparison #53020)

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.

1.26.0 (const: 1.61.0) · Source

Adds an unsigned offset to a pointer.

This can only move the pointer forward (or not move it). If you need to move forward or backward depending on the value, then you might want offset instead which takes a signed offset.

count is in units of T; e.g., a count of 3 represents a pointer offset of 3 * size_of::<T>() bytes.

§Safety

If any of the following conditions are violated, the result is Undefined Behavior:

• The offset in bytes, count * size_of::<T>(), computed on mathematical integers (without “wrapping around”), must fit in an isize.
• If the computed offset is non-zero, then self must be derived from a pointer to someallocated object, and the entire memory range between self and the result must be in bounds of that allocated object. In particular, this range must not “wrap around” the edge of the address space.

Allocated objects can never be larger than isize::MAX bytes, so if the computed offset stays in bounds of the allocated object, it is guaranteed to satisfy the first requirement. This implies, for instance, that vec.as_ptr().add(vec.len()) (for vec: Vec<T>) is always safe.

Consider using wrapping_add instead if these constraints are difficult to satisfy. The only advantage of this method is that it enables more aggressive compiler optimizations.

§Examples

let s: &str = "123";
let ptr: *const u8 = s.as_ptr();

unsafe {
    assert_eq!(*ptr.add(1), b'2');
    assert_eq!(*ptr.add(2), b'3');
}

1.75.0 (const: 1.75.0) · Source

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 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.

1.26.0 (const: 1.61.0) · Source

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 instead which takes a signed offset.

count is in units of T; e.g., a count of 3 represents a pointer offset of 3 * size_of::<T>() bytes.

§Safety

If any of the following conditions are violated, the result is Undefined Behavior:

• The offset in bytes, count * size_of::<T>(), computed on mathematical integers (without “wrapping around”), must fit in an isize.
• If the computed offset is non-zero, then self must be derived from a pointer to someallocated object, and the entire memory range between self and the result must be in bounds of that allocated object. In particular, this range must not “wrap around” the edge of the address space.

Allocated objects can never be larger than isize::MAX bytes, so if the computed offset stays in bounds of the allocated object, it is guaranteed to satisfy the first requirement. This implies, for instance, that vec.as_ptr().add(vec.len()) (for vec: Vec<T>) is always safe.

Consider using wrapping_sub instead if these constraints are difficult to satisfy. The only advantage of this method is that it enables more aggressive compiler optimizations.

§Examples

let s: &str = "123";

unsafe {
    let end: *const u8 = s.as_ptr().add(3);
    assert_eq!(*end.sub(1), b'3');
    assert_eq!(*end.sub(2), b'2');
}

1.75.0 (const: 1.75.0) · Source

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 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.

1.26.0 (const: 1.61.0) · Source

Adds an unsigned offset to a pointer using wrapping arithmetic.

count is in units of T; e.g., a count of 3 represents a pointer offset of 3 * size_of::<T>() bytes.

§Safety

This operation itself is always safe, but using the resulting pointer is not.

The resulting pointer “remembers” the allocated object that self points to; it must not be used to read or write other allocated objects.

In other words, let z = x.wrapping_add((y as usize) - (x as usize)) does not make zthe 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 unlessx and y point into the same 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 a pointer is dereferenced when it is out-of-bounds of the object it is attached to. addcan 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 allocated object and then re-entering it later is permitted.

§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);

let mut out = String::new();
while ptr != end_rounded_up {
    unsafe {
        write!(&mut out, "{}, ", *ptr)?;
    }
    ptr = ptr.wrapping_add(step);
}
assert_eq!(out, "1, 3, 5, ");

1.75.0 (const: 1.75.0) · Source

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 on it. See that method for documentation.

For non-Sized pointees this operation changes only the data pointer, leaving the metadata untouched.

1.26.0 (const: 1.61.0) · Source

Subtracts an unsigned offset from a pointer using wrapping arithmetic.

count is in units of T; e.g., a count of 3 represents a pointer offset of 3 * size_of::<T>() bytes.

§Safety

This operation itself is always safe, but using the resulting pointer is not.

The resulting pointer “remembers” the allocated object that self points to; it must not be used to read or write other allocated objects.

In other words, let z = x.wrapping_sub((x as usize) - (y as usize)) does not make zthe 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 unlessx and y point into the same 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 a pointer is dereferenced when it is out-of-bounds of the object it is attached to. subcan 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 allocated object and then re-entering it later is permitted.

§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;
let mut out = String::new();
while ptr != start_rounded_down {
    unsafe {
        write!(&mut out, "{}, ", *ptr)?;
    }
    ptr = ptr.wrapping_sub(step);
}
assert_eq!(out, "5, 3, 1, ");

1.75.0 (const: 1.75.0) · Source

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 on it. See that method for documentation.

For non-Sized pointees this operation changes only the data pointer, leaving the metadata untouched.

1.26.0 (const: 1.71.0) · Source

Reads the value from self without moving it. This leaves the memory in self unchanged.

See ptr::read for safety concerns and examples.

1.26.0 · Source

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.

1.26.0 (const: 1.71.0) · Source

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.

1.26.0 (const: 1.83.0) · Source

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.

1.26.0 (const: 1.83.0) · Source

1.36.0 · Source

Computes the offset that needs to be applied to the pointer in order to make it aligned toalign.

If it is not possible to align the pointer, the implementation returnsusize::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

let x = [5_u8, 6, 7, 8, 9];
let ptr = x.as_ptr();
let offset = ptr.align_offset(align_of::<u16>());

if offset < x.len() - 1 {
    let u16_ptr = ptr.add(offset).cast::<u16>();
    assert!(*u16_ptr == u16::from_ne_bytes([5, 6]) || *u16_ptr == u16::from_ne_bytes([6, 7]));
} else {
    // while the pointer can be aligned via `offset`, it would point
    // outside the allocation
}

1.79.0 · Source

Returns whether the pointer is properly aligned for T.

§Examples

// On some platforms, the alignment of i32 is less than 4.
#[repr(align(4))]
struct AlignedI32(i32);

let data = AlignedI32(42);
let ptr = &data as *const AlignedI32;

assert!(ptr.is_aligned());
assert!(!ptr.wrapping_byte_add(1).is_aligned());

Source

🔬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.

§Panics

The function panics if align is not a power-of-two (this includes 0).

§Examples

#![feature(pointer_is_aligned_to)]

// On some platforms, the alignment of i32 is less than 4.
#[repr(align(4))]
struct AlignedI32(i32);

let data = AlignedI32(42);
let ptr = &data as *const AlignedI32;

assert!(ptr.is_aligned_to(1));
assert!(ptr.is_aligned_to(2));
assert!(ptr.is_aligned_to(4));

assert!(ptr.wrapping_byte_add(2).is_aligned_to(2));
assert!(!ptr.wrapping_byte_add(2).is_aligned_to(4));

assert_ne!(ptr.is_aligned_to(8), ptr.wrapping_add(1).is_aligned_to(8));

Source§

1.79.0 (const: 1.79.0) · Source

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

use std::ptr;

let slice: *const [i8] = ptr::slice_from_raw_parts(ptr::null(), 3);
assert_eq!(slice.len(), 3);

1.79.0 (const: 1.79.0) · Source

Returns true if the raw slice has a length of 0.

§Examples

use std::ptr;

let slice: *const [i8] = ptr::slice_from_raw_parts(ptr::null(), 3);
assert!(!slice.is_empty());

Source

🔬This is a nightly-only experimental API. (slice_ptr_get #74265)

Returns a raw pointer to the slice’s buffer.

This is equivalent to casting self to *const T, but more type-safe.

§Examples

#![feature(slice_ptr_get)]
use std::ptr;

let slice: *const [i8] = ptr::slice_from_raw_parts(ptr::null(), 3);
assert_eq!(slice.as_ptr(), ptr::null());

Source

🔬This is a nightly-only experimental API. (slice_as_array #133508)

Gets a raw pointer to the underlying array.

If N is not exactly equal to the length of self, then this method returns None.

Source

🔬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.

§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));
}

Source

🔬This is a nightly-only experimental API. (ptr_as_uninit #75402)

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.

§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() * 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 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 datafor 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 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 mutated (except inside UnsafeCell).

This applies even if the result of this method is unused!

See also slice::from_raw_parts.

§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.

Source§

Source

🔬This is a nightly-only experimental API. (array_ptr_get #119834)

Returns a raw pointer to the array’s buffer.

This is equivalent to casting self to *const T, but more type-safe.

§Examples

#![feature(array_ptr_get)]
use std::ptr;

let arr: *const [i8; 3] = ptr::null();
assert_eq!(arr.as_ptr(), ptr::null());

Source

🔬This is a nightly-only experimental API. (array_ptr_get #119834)

Returns a raw pointer to a slice containing the entire array.

§Examples

#![feature(array_ptr_get)]

let arr: *const [i32; 3] = &[1, 2, 4] as *const [i32; 3];
let slice: *const [i32] = arr.as_slice();
assert_eq!(slice.len(), 3);

Source§

1.0.0 (const: 1.84.0) · Source

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.

§Panics during const evaluation

If this method is used during const evaluation, and self is a pointer that is offset beyond the bounds of the memory it initially pointed to, then there might not be enough information to determine whether the pointer is null. This is because the absolute address in memory is not known at compile time. If the nullness of the pointer cannot be determined, this method will panic.

In-bounds pointers are never null, so the method will never panic for such pointers.

§Examples

let mut s = [1, 2, 3];
let ptr: *mut u32 = s.as_mut_ptr();
assert!(!ptr.is_null());

1.38.0 (const: 1.38.0) · Source

Casts to a pointer of another type.

Source

🔬This is a nightly-only experimental API. (set_ptr_value #75091)

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 ofmeta, 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)]
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);
    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.

#![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 });

1.65.0 (const: 1.65.0) · Source

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.

1.84.0 · Source

Gets the “address” portion of the pointer.

This is similar to self as usize, except that the provenance of the pointer is discarded and not exposed. This means that casting the returned address back to a pointer yields a pointer without provenance, which is undefined behavior to dereference. To properly restore the lost information and obtain a dereferenceable pointer, usewith_addr or map_addr.

If using those APIs is not possible because there is no way to preserve a pointer with the required provenance, then Strict Provenance might not be for you. Use pointer-integer casts or expose_provenance and with_exposed_provenanceinstead. However, note that this makes your code less portable and less amenable to tools that check for compliance with the Rust memory model.

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 perform a change of representation to produce a value containing only the address portion of the pointer. What that means is up to the platform to define.

This is a Strict Provenance API.

1.84.0 · Source

Exposes the “provenance” part of the pointer for future use inwith_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 callwith_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 useStrict Provenance APIs such as with_addrwherever possible, in which case 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 API.

1.84.0 · Source

Creates a new pointer with the given address and the provenance ofself.

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 to offsetself to the given address, and therefore has all the same capabilities and restrictions.

This is a Strict Provenance API.

1.84.0 · Source

Creates a new pointer by mapping self’s address to a new one, preserving the original pointer’s provenance.

This is a convenience for with_addr, see that method for details.

This is a Strict Provenance API.

Source

🔬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 from_raw_parts_mut.

1.9.0 (const: 1.84.0) · Source

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_refmust be used instead.

For the mutable counterpart see as_mut.

§Safety

When calling this method, you have to ensure that either the pointer is null _or_the pointer is convertible to a reference.

§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.

§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}!");
    }
}

§Null-unchecked version

If you are sure the pointer can never be null and are looking for some kind ofas_ref_unchecked that returns the &T instead of Option<&T>, know that you can dereference the pointer directly.

let ptr: *mut u8 = &mut 10u8 as *mut u8;

unsafe {
    let val_back = &*ptr;
    println!("We got back the value: {val_back}!");
}

Source

🔬This is a nightly-only experimental API. (ptr_as_ref_unchecked #122034)

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.

§Safety

When calling this method, you have to ensure that the pointer is convertible to a reference.

§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());
}

Source

🔬This is a nightly-only experimental API. (ptr_as_uninit #75402)

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.

For the mutable counterpart see as_uninit_mut.

§Safety

When calling this method, you have to ensure that either the pointer is null _or_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.

§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.

§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());
    }
}

1.0.0 (const: 1.61.0) · Source

Adds a signed 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.

§Safety

If any of the following conditions are violated, the result is Undefined Behavior:

• The offset in bytes, count * size_of::<T>(), computed on mathematical integers (without “wrapping around”), must fit in an isize.
• If the computed offset is non-zero, then self must be derived from a pointer to someallocated object, and the entire memory range between self and the result must be in bounds of that allocated object. In particular, this range must not “wrap around” the edge of the address space.

Allocated objects can never be larger than isize::MAX bytes, so if the computed offset stays in bounds of the allocated object, it is guaranteed to satisfy the first requirement. This implies, for instance, that vec.as_ptr().add(vec.len()) (for vec: Vec<T>) is always safe.

Consider using wrapping_offset instead if these constraints are difficult to satisfy. The only advantage of this method is that it enables more aggressive compiler optimizations.

§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));
}

1.75.0 (const: 1.75.0) · Source

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 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.

1.16.0 (const: 1.61.0) · Source

Adds a signed offset to a pointer using wrapping arithmetic.

count is in units of T; e.g., a count of 3 represents a pointer offset of 3 * size_of::<T>() bytes.

§Safety

This operation itself is always safe, but using the resulting pointer is not.

The resulting pointer “remembers” the allocated object that self points to; it must not be used to read or write other allocated objects.

In other words, let z = x.wrapping_offset((y as isize) - (x as isize)) does not make zthe 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 unlessx 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 a pointer is dereferenced when it is out-of-bounds of the object it is attached to. offsetcan 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 allocated object and then re-entering it later is permitted.

§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]);

1.75.0 (const: 1.75.0) · Source

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 on it. See that method for documentation.

For non-Sized pointees this operation changes only the data pointer, leaving the metadata untouched.

Source

🔬This is a nightly-only experimental API. (ptr_mask #98290)

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);

1.9.0 (const: 1.84.0) · Source

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_mutmust be used instead.

For the shared counterpart see as_ref.

§Safety

When calling this method, you have to ensure that _either_the pointer is null _or_the pointer is convertible to a reference.

§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.

§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;
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 ofas_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;
println!("{s:?}"); // It'll print: "[4, 2, 3]".

Source

🔬This is a nightly-only experimental API. (ptr_as_ref_unchecked #122034)

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.

§Safety

When calling this method, you have to ensure that the pointer is convertible to a reference.

§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;
println!("{s:?}"); // It'll print: "[4, 2, 3]".

Source

🔬This is a nightly-only experimental API. (ptr_as_uninit #75402)

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.

§Safety

When calling this method, you have to ensure that either the pointer is null _or_the pointer is convertible to a reference.

§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.

Source

🔬This is a nightly-only experimental API. (const_raw_ptr_comparison #53020)

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.

Source

🔬This is a nightly-only experimental API. (const_raw_ptr_comparison #53020)

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.

1.47.0 (const: 1.65.0) · Source

Calculates the distance between two pointers within the same allocation. The returned value is in units of T: the distance in bytes divided by size_of::<T>().

This is equivalent to (self as isize - origin as isize) / (size_of::<T>() as isize), except that it has a lot more opportunities for UB, in exchange for the compiler better understanding what you are doing.

The primary motivation of this method is for computing the len of an array/slice of T that you are currently representing as a “start” and “end” pointer (and “end” is “one past the end” of the array). In that case, end.offset_from(start) gets you the length of the array.

All of the following safety requirements are trivially satisfied for this usecase.

§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 a pointer to the same allocated object, 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 allocated object can be larger than isize::MAX bytes.

The requirement for pointers to be derived from the same allocated object 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>().

§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:

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! ⚠️
}

1.75.0 (const: 1.75.0) · 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.

1.87.0 (const: 1.87.0) · Source

Calculates the distance between two pointers within the same allocation, where it’s known thatself 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_fromwould compute, but with the added precondition that the offset is guaranteed to be non-negative. This method is equivalent tousize::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 (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_fromapply 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)

1.87.0 (const: 1.87.0) · Source

Calculates the distance between two pointers within the same allocation, where it’s known thatself 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 sub_ptr on it. See that method for documentation and safety requirements.

For non-Sized pointees this operation considers only the data pointers, ignoring the metadata.

1.26.0 (const: 1.61.0) · Source

Adds an unsigned offset to a pointer.

This can only move the pointer forward (or not move it). If you need to move forward or backward depending on the value, then you might want offset instead which takes a signed offset.

count is in units of T; e.g., a count of 3 represents a pointer offset of 3 * size_of::<T>() bytes.

§Safety

If any of the following conditions are violated, the result is Undefined Behavior:

• The offset in bytes, count * size_of::<T>(), computed on mathematical integers (without “wrapping around”), must fit in an isize.
• If the computed offset is non-zero, then self must be derived from a pointer to someallocated object, and the entire memory range between self and the result must be in bounds of that allocated object. In particular, this range must not “wrap around” the edge of the address space.

Allocated objects can never be larger than isize::MAX bytes, so if the computed offset stays in bounds of the allocated object, it is guaranteed to satisfy the first requirement. This implies, for instance, that vec.as_ptr().add(vec.len()) (for vec: Vec<T>) is always safe.

Consider using wrapping_add instead if these constraints are difficult to satisfy. The only advantage of this method is that it enables more aggressive compiler optimizations.

§Examples

let s: &str = "123";
let ptr: *const u8 = s.as_ptr();

unsafe {
    assert_eq!('2', *ptr.add(1) as char);
    assert_eq!('3', *ptr.add(2) as char);
}

1.75.0 (const: 1.75.0) · Source

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 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.

1.26.0 (const: 1.61.0) · Source

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 instead which takes a signed offset.

count is in units of T; e.g., a count of 3 represents a pointer offset of 3 * size_of::<T>() bytes.

§Safety

If any of the following conditions are violated, the result is Undefined Behavior:

• The offset in bytes, count * size_of::<T>(), computed on mathematical integers (without “wrapping around”), must fit in an isize.
• If the computed offset is non-zero, then self must be derived from a pointer to someallocated object, and the entire memory range between self and the result must be in bounds of that allocated object. In particular, this range must not “wrap around” the edge of the address space.

Allocated objects can never be larger than isize::MAX bytes, so if the computed offset stays in bounds of the allocated object, it is guaranteed to satisfy the first requirement. This implies, for instance, that vec.as_ptr().add(vec.len()) (for vec: Vec<T>) is always safe.

Consider using wrapping_sub instead if these constraints are difficult to satisfy. The only advantage of this method is that it enables more aggressive compiler optimizations.

§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);
}

1.75.0 (const: 1.75.0) · Source

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 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.

1.26.0 (const: 1.61.0) · Source

Adds an unsigned offset to a pointer using wrapping arithmetic.

count is in units of T; e.g., a count of 3 represents a pointer offset of 3 * size_of::<T>() bytes.

§Safety

This operation itself is always safe, but using the resulting pointer is not.

The resulting pointer “remembers” the allocated object that self points to; it must not be used to read or write other allocated objects.

In other words, let z = x.wrapping_add((y as usize) - (x as usize)) does not make zthe 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 unlessx and y point into the same 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 a pointer is dereferenced when it is out-of-bounds of the object it is attached to. addcan 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 allocated object and then re-entering it later is permitted.

§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);
}

1.75.0 (const: 1.75.0) · Source

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 on it. See that method for documentation.

For non-Sized pointees this operation changes only the data pointer, leaving the metadata untouched.

1.26.0 (const: 1.61.0) · Source

Subtracts an unsigned offset from a pointer using wrapping arithmetic.

count is in units of T; e.g., a count of 3 represents a pointer offset of 3 * size_of::<T>() bytes.

§Safety

This operation itself is always safe, but using the resulting pointer is not.

The resulting pointer “remembers” the allocated object that self points to; it must not be used to read or write other allocated objects.

In other words, let z = x.wrapping_sub((x as usize) - (y as usize)) does not make zthe 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 unlessx and y point into the same 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 a pointer is dereferenced when it is out-of-bounds of the object it is attached to. subcan 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 allocated object and then re-entering it later is permitted.

§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);
}

1.75.0 (const: 1.75.0) · Source

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 on it. See that method for documentation.

For non-Sized pointees this operation changes only the data pointer, leaving the metadata untouched.

1.26.0 (const: 1.71.0) · Source

Reads the value from self without moving it. This leaves the memory in self unchanged.

See ptr::read for safety concerns and examples.

1.26.0 · Source

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.

1.26.0 (const: 1.71.0) · Source

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.

1.26.0 (const: 1.83.0) · Source

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.

1.26.0 (const: 1.83.0) · Source

1.26.0 (const: 1.83.0) · Source

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.

1.26.0 (const: 1.83.0) · Source

1.26.0 · Source

Executes the destructor (if any) of the pointed-to value.

See ptr::drop_in_place for safety concerns and examples.

1.26.0 (const: 1.83.0) · Source

Overwrites a memory location with the given value without reading or dropping the old value.

See ptr::write for safety concerns and examples.

1.26.0 (const: 1.83.0) · Source

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.

1.26.0 · Source

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.

1.26.0 (const: 1.83.0) · Source

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.

1.26.0 · Source

Replaces the value at self with src, returning the old value, without dropping either.

See ptr::replace for safety concerns and examples.

1.26.0 (const: 1.85.0) · Source

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.

1.36.0 · Source

Computes the offset that needs to be applied to the pointer in order to make it aligned toalign.

If it is not possible to align the pointer, the implementation returnsusize::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

let mut x = [5_u8, 6, 7, 8, 9];
let ptr = x.as_mut_ptr();
let offset = ptr.align_offset(align_of::<u16>());

if offset < x.len() - 1 {
    let u16_ptr = ptr.add(offset).cast::<u16>();
    *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
}

1.79.0 · Source

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());

Source

🔬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.

§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));

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1.79.0 (const: 1.79.0) · Source

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

use std::ptr;

let slice: *mut [i8] = ptr::slice_from_raw_parts_mut(ptr::null_mut(), 3);
assert_eq!(slice.len(), 3);

1.79.0 (const: 1.79.0) · Source

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());

Source

🔬This is a nightly-only experimental API. (slice_as_array #133508)

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.

Source

🔬This is a nightly-only experimental API. (raw_slice_split #95595)

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 allocated object. Which means self must be dereferenceable and span a single allocation that is at least mid * size_of::<T>() 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.

§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]);
}

Source

🔬This is a nightly-only experimental API. (raw_slice_split #95595)

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 [allocated object]. Which means self must be dereferenceable and span a single allocation that is at least mid * size_of::<T>() bytes long. Not upholding these requirements is undefined behavior even if the resulting pointers are not used.

§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]);

Source

🔬This is a nightly-only experimental API. (slice_ptr_get #74265)

Returns a raw pointer to the slice’s buffer.

This is equivalent to casting self to *mut T, but more type-safe.

§Examples

#![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());

Source

🔬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.

§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));
}

Source

🔬This is a nightly-only experimental API. (ptr_as_uninit #75402)

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.

For the mutable counterpart see as_uninit_slice_mut.

§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() * 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 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 datafor 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 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 mutated (except inside UnsafeCell).

This applies even if the result of this method is unused!

See also slice::from_raw_parts.

§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.

Source

🔬This is a nightly-only experimental API. (ptr_as_uninit #75402)

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.

§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::<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 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 datafor 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 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.

§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.

Source§

Source

🔬This is a nightly-only experimental API. (array_ptr_get #119834)

Returns a raw pointer to the array’s buffer.

This is equivalent to casting self to *mut T, but more type-safe.

§Examples

#![feature(array_ptr_get)]
use std::ptr;

let arr: *mut [i8; 3] = ptr::null_mut();
assert_eq!(arr.as_mut_ptr(), ptr::null_mut());

Source

🔬This is a nightly-only experimental API. (array_ptr_get #119834)

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]);

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🔬This is a nightly-only experimental API. (core_intrinsics)

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🔬This is a nightly-only experimental API. (core_intrinsics)

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Converts a *mut T into an AtomicPtr<T>.

1.0.0 · Source§

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1.0.0 · Source§

Pointer comparison is by address, as produced by the [<*const T>::addr](pointer::addr) method.

1.0.0 · Source§

Pointer comparison is by address, as produced by the <*mut T>::addr method.

1.0.0 · Source§

Pointer equality is by address, as produced by the <*const T>::addr method.

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Tests for self and other values to be equal, and is used by ==.

1.0.0 · Source§

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

1.0.0 · Source§

Pointer equality is by address, as produced by the <*mut T>::addr method.

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Tests for self and other values to be equal, and is used by ==.

1.0.0 · Source§

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

1.0.0 · Source§

Pointer comparison is by address, as produced by the [<*const T>::addr](pointer::addr) method.

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This method returns an ordering between self and other values if one exists. Read more

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Tests less than (for self and other) and is used by the < operator. Read more

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Tests less than or equal to (for self and other) and is used by the<= operator. Read more

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Tests greater than (for self and other) and is used by the >operator. Read more

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Tests greater than or equal to (for self and other) and is used by the >= operator. Read more

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Pointer comparison is by address, as produced by the <*mut T>::addr method.

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This method returns an ordering between self and other values if one exists. Read more

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Tests less than (for self and other) and is used by the < operator. Read more

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Tests less than or equal to (for self and other) and is used by the<= operator. Read more

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Tests greater than (for self and other) and is used by the >operator. Read more

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Tests greater than or equal to (for self and other) and is used by the >= operator. Read more

1.0.0 · Source§

1.0.0 · Source§

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🔬This is a nightly-only experimental API. (portable_simd #86656)

The mask element type corresponding to this element type.

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🔬This is a nightly-only experimental API. (portable_simd #86656)

The mask element type corresponding to this element type.

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1.0.0 · Source§

1.0.0 · Source§

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Pointer equality is an equivalence relation.

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Pointer equality is an equivalence relation.

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1.33.0 · Source§

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1.0.0 · Source§

1.0.0 · Source§

1.0.0 · Source§

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1.38.0 · Source§

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1.9.0 · Source§

1.9.0 · Source§