zeroed in std::mem - Rust (original) (raw)

Function zeroed

1.0.0 (const: 1.75.0) · Source

pub const unsafe fn zeroed<T>() -> T

Expand description

Returns the value of type T represented by the all-zero byte-pattern.

This means that, for example, the padding byte in (u8, u16) is not necessarily zeroed.

There is no guarantee that an all-zero byte-pattern represents a valid value of some type T. For example, the all-zero byte-pattern is not a valid value for reference types (&T, &mut T) and function pointers. Using zeroedon such types causes immediate undefined behavior because the Rust compiler assumes that there always is a valid value in a variable it considers initialized.

This has the same effect as MaybeUninit::zeroed().assume_init(). It is useful for FFI sometimes, but should generally be avoided.

§Examples

Correct usage of this function: initializing an integer with zero.

use std::mem;

let x: i32 = unsafe { mem::zeroed() };
assert_eq!(0, x);

Incorrect usage of this function: initializing a reference with zero.

use std::mem;

let _x: &i32 = unsafe { mem::zeroed() }; // Undefined behavior!
let _y: fn() = unsafe { mem::zeroed() }; // And again!