1.0.0[−][src]Function std::intrinsics::copy_nonoverlapping
pub unsafe fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize)
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:
-
src
must be valid for reads ofcount * size_of::<T>()
bytes. -
dst
must be valid for writes ofcount * size_of::<T>()
bytes. -
Both
src
anddst
must be properly aligned. -
The region of memory beginning at
src
with a size ofcount * size_of::<T>()
bytes must not overlap with the region of memory beginning atdst
with 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