# Function std::mem::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 functions pointers. Using `zeroed` on 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);

Run

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!

Run