Function std::ptr::copy_nonoverlapping 1.0.0 (const: unstable)[−][src]
pub unsafe fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize)Expand description
Copies count * size_of::<T>() bytes from src to dst. The source
and destination must not overlap.
For regions of memory which might overlap, use copy instead.
copy_nonoverlapping is semantically equivalent to C’s memcpy, but
with the argument order swapped.
Safety
Behavior is undefined if any of the following conditions are violated:
-
srcmust be valid for reads ofcount * size_of::<T>()bytes. -
dstmust be valid for writes ofcount * size_of::<T>()bytes. -
Both
srcanddstmust be properly aligned. -
The region of memory beginning at
srcwith a size ofcount * size_of::<T>()bytes must not overlap with the region of memory beginning atdstwith the same size.
Like read, copy_nonoverlapping creates a bitwise copy of T, regardless of
whether T is Copy. If T is not Copy, using both the values
in the region beginning at *src and the region beginning at *dst can
violate memory safety.
Note that even if the effectively copied size (count * size_of::<T>()) is
0, the pointers must be non-null and properly aligned.
Examples
Manually implement Vec::append:
use std::ptr;
/// Moves all the elements of `src` into `dst`, leaving `src` empty.
fn append<T>(dst: &mut Vec<T>, src: &mut Vec<T>) {
let src_len = src.len();
let dst_len = dst.len();
// Ensure that `dst` has enough capacity to hold all of `src`.
dst.reserve(src_len);
unsafe {
// The call to offset is always safe because `Vec` will never
// allocate more than `isize::MAX` bytes.
let dst_ptr = dst.as_mut_ptr().offset(dst_len as isize);
let src_ptr = src.as_ptr();
// Truncate `src` without dropping its contents. We do this first,
// to avoid problems in case something further down panics.
src.set_len(0);
// The two regions cannot overlap because mutable references do
// not alias, and two different vectors cannot own the same
// memory.
ptr::copy_nonoverlapping(src_ptr, dst_ptr, src_len);
// Notify `dst` that it now holds the contents of `src`.
dst.set_len(dst_len + src_len);
}
}
let mut a = vec!['r'];
let mut b = vec!['u', 's', 't'];
append(&mut a, &mut b);
assert_eq!(a, &['r', 'u', 's', 't']);
assert!(b.is_empty());Run