std::ptr::Unique

Creates a new Unique.

Safety

ptr must be non-null.

Dereferences the content.

Mutably dereferences the content.

Returns true if the pointer is null.

Examples

Basic usage:

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

Returns None if the pointer is null, or else returns a reference to the value wrapped in Some.

Safety

While this method and its mutable counterpart are useful for null-safety, it is important to note that this is still an unsafe operation because the returned value could be pointing to invalid memory.

Additionally, the lifetime 'a returned is arbitrarily chosen and does not necessarily reflect the actual lifetime of the data.

Examples

Basic usage:

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

unsafe {
    if let Some(val_back) = val.as_ref() {
        println!("We got back the value: {}!", val_back);
    }
}

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

Safety

Both the starting and resulting pointer must be either in bounds or one byte past the end of an allocated object. If either pointer is out of bounds or arithmetic overflow occurs then any further use of the returned value will result in undefined behavior.

Examples

Basic usage:

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

unsafe {
    println!("{}", *ptr.offset(1) as char);
    println!("{}", *ptr.offset(2) as char);
}

Calculates the offset from a pointer using wrapping arithmetic. count is in units of T; e.g. a count of 3 represents a pointer offset of 3 * size_of::<T>() bytes.

Safety

The resulting pointer does not need to be in bounds, but it is potentially hazardous to dereference (which requires unsafe).

Always use .offset(count) instead when possible, because offset allows the compiler to optimize better.

Examples

Basic usage:

// Iterate using a raw pointer in increments of two elements
let data = [1u8, 2, 3, 4, 5];
let mut ptr: *const u8 = data.as_ptr();
let step = 2;
let end_rounded_up = ptr.wrapping_offset(6);

// This loop prints "1, 3, 5, "
while ptr != end_rounded_up {
    unsafe {
        print!("{}, ", *ptr);
    }
    ptr = ptr.wrapping_offset(step);
}

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

If the address different between the two pointers ia not a multiple of mem::size_of::<T>() then the result of the division is rounded towards zero.

This function returns None if T is a zero-sized typed.

Examples

Basic usage:

#![feature(offset_to)]

fn main() {
    let a = [0; 5];
    let ptr1: *const i32 = &a[1];
    let ptr2: *const i32 = &a[3];
    assert_eq!(ptr1.offset_to(ptr2), Some(2));
    assert_eq!(ptr2.offset_to(ptr1), Some(-2));
    assert_eq!(unsafe { ptr1.offset(2) }, ptr2);
    assert_eq!(unsafe { ptr2.offset(-2) }, ptr1);
}

Returns true if the pointer is null.

Examples

Basic usage:

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

Returns None if the pointer is null, or else returns a reference to the value wrapped in Some.

Safety

While this method and its mutable counterpart are useful for null-safety, it is important to note that this is still an unsafe operation because the returned value could be pointing to invalid memory.

Additionally, the lifetime 'a returned is arbitrarily chosen and does not necessarily reflect the actual lifetime of the data.

Examples

Basic usage:

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

unsafe {
    if let Some(val_back) = val.as_ref() {
        println!("We got back the value: {}!", val_back);
    }
}

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

Safety

The offset must be in-bounds of the object, or one-byte-past-the-end. Otherwise offset invokes Undefined Behavior, regardless of whether the pointer is used.

Examples

Basic usage:

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

unsafe {
    println!("{}", *ptr.offset(1));
    println!("{}", *ptr.offset(2));
}

Calculates the offset from a pointer using wrapping arithmetic. count is in units of T; e.g. a count of 3 represents a pointer offset of 3 * size_of::<T>() bytes.

Safety

The resulting pointer does not need to be in bounds, but it is potentially hazardous to dereference (which requires unsafe).

Always use .offset(count) instead when possible, because offset allows the compiler to optimize better.

Examples

Basic usage:

// 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]);

Returns None if the pointer is null, or else returns a mutable reference to the value wrapped in Some.

Safety

As with as_ref, this is unsafe because it cannot verify the validity of the returned pointer, nor can it ensure that the lifetime 'a returned is indeed a valid lifetime for the contained data.

Examples

Basic usage:

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]".

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

If the address different between the two pointers ia not a multiple of mem::size_of::<T>() then the result of the division is rounded towards zero.

This function returns None if T is a zero-sized typed.

Examples

Basic usage:

#![feature(offset_to)]

fn main() {
    let mut a = [0; 5];
    let ptr1: *mut i32 = &mut a[1];
    let ptr2: *mut i32 = &mut a[3];
    assert_eq!(ptr1.offset_to(ptr2), Some(2));
    assert_eq!(ptr2.offset_to(ptr1), Some(-2));
    assert_eq!(unsafe { ptr1.offset(2) }, ptr2);
    assert_eq!(unsafe { ptr2.offset(-2) }, ptr1);
}

Formats the value using the given formatter.

The resulting type after dereferencing

The method called to dereference a value