1.0.0[−][src]Function std::ptr::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:
-
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