/// value is not necessarily valid to be used to actually access memory.
pub fn arith_offset<T>(dst: *const T, offset: isize) -> *const T;
- /// Copies `count * size_of::<T>()` bytes from `src` to `dst`. The source
- /// and destination must *not* overlap.
+ /// Copies `count * size_of<T>` bytes from `src` to `dst`. The source
+ /// and destination may *not* overlap.
///
- /// For regions of memory which might overlap, use [`copy`] instead.
- ///
- /// `copy_nonoverlapping` is semantically equivalent to C's [`memcpy`].
- ///
- /// [`copy`]: ./fn.copy.html
- /// [`memcpy`]: https://www.gnu.org/software/libc/manual/html_node/Copying-Strings-and-Arrays.html#index-memcpy
+ /// `copy_nonoverlapping` is semantically equivalent to C's `memcpy`.
///
/// # Safety
///
- /// Behavior is undefined if any of the following conditions are violated:
- ///
- /// * The region of memory which begins at `src` and has a length of
- /// `count * size_of::<T>()` bytes must be *both* valid and initialized.
- ///
- /// * The region of memory which begins at `dst` and has a length of
- /// `count * size_of::<T>()` bytes must be valid (but may or may not be
- /// initialized).
- ///
- /// * The two regions of memory must *not* overlap.
- ///
- /// * `src` must be properly aligned.
- ///
- /// * `dst` must be properly aligned.
- ///
- /// Additionally, if `T` is not [`Copy`], only the region at `src` *or* the
- /// region at `dst` can be used or dropped after calling
- /// `copy_nonoverlapping`. `copy_nonoverlapping` creates bitwise copies of
- /// `T`, regardless of whether `T: Copy`, which can result in undefined
- /// behavior if both copies are used.
- ///
- /// [`Copy`]: ../marker/trait.Copy.html
+ /// Beyond requiring that the program must be allowed to access both regions
+ /// of memory, it is Undefined Behavior for source and destination to
+ /// overlap. Care must also be taken with the ownership of `src` and
+ /// `dst`. This method semantically moves the values of `src` into `dst`.
+ /// However it does not drop the contents of `dst`, or prevent the contents
+ /// of `src` from being dropped or used.
///
/// # Examples
///
- /// Manually implement [`Vec::append`]:
+ /// A safe swap function:
///
/// ```
+ /// use std::mem;
/// 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);
- ///
+ /// # #[allow(dead_code)]
+ /// fn swap<T>(x: &mut T, y: &mut T) {
/// unsafe {
- /// // The call to offset is always safe because `Vec` will never
- /// // allocate more than `isize::MAX` bytes.
- /// let dst = dst.as_mut_ptr().offset(dst_len as isize);
- /// let src = src.as_ptr();
- ///
- /// // The two regions cannot overlap becuase mutable references do
- /// // not alias, and two different vectors cannot own the same
- /// // memory.
- /// ptr::copy_nonoverlapping(src, dst, src_len);
- /// }
+ /// // Give ourselves some scratch space to work with
+ /// let mut t: T = mem::uninitialized();
///
- /// unsafe {
- /// // Truncate `src` without dropping its contents.
- /// src.set_len(0);
+ /// // Perform the swap, `&mut` pointers never alias
+ /// ptr::copy_nonoverlapping(x, &mut t, 1);
+ /// ptr::copy_nonoverlapping(y, x, 1);
+ /// ptr::copy_nonoverlapping(&t, y, 1);
///
- /// // Notify `dst` that it now holds the contents of `src`.
- /// dst.set_len(dst_len + src_len);
+ /// // y and t now point to the same thing, but we need to completely forget `t`
+ /// // because it's no longer relevant.
+ /// mem::forget(t);
/// }
/// }
- ///
- /// 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());
/// ```
- ///
- /// [`Vec::append`]: ../../std/vec/struct.Vec.html#method.append
#[stable(feature = "rust1", since = "1.0.0")]
pub fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize);
- /// Copies `count * size_of::<T>()` bytes from `src` to `dst`. The source
+ /// Copies `count * size_of<T>` bytes from `src` to `dst`. The source
/// and destination may overlap.
///
- /// If the source and destination will *never* overlap,
- /// [`copy_nonoverlapping`] can be used instead.
- ///
- /// `copy` is semantically equivalent to C's [`memmove`].
- ///
- /// [`copy_nonoverlapping`]: ./fn.copy_nonoverlapping.html
- /// [`memmove`]: https://www.gnu.org/software/libc/manual/html_node/Copying-Strings-and-Arrays.html#index-memmove
+ /// `copy` is semantically equivalent to C's `memmove`.
///
/// # Safety
///
- /// Behavior is undefined if any of the following conditions are violated:
- ///
- /// * The region of memory which begins at `src` and has a length of
- /// `count * size_of::<T>()` bytes must be *both* valid and initialized.
- ///
- /// * The region of memory which begins at `dst` and has a length of
- /// `count * size_of::<T>()` bytes must be valid (but may or may not be
- /// initialized).
- ///
- /// * `src` must be properly aligned.
- ///
- /// * `dst` must be properly aligned.
- ///
- /// Additionally, if `T` is not [`Copy`], only the region at `src` *or* the
- /// region at `dst` can be used or dropped after calling `copy`. `copy`
- /// creates bitwise copies of `T`, regardless of whether `T: Copy`, which
- /// can result in undefined behavior if both copies are used.
- ///
- /// [`Copy`]: ../marker/trait.Copy.html
+ /// Care must be taken with the ownership of `src` and `dst`.
+ /// This method semantically moves the values of `src` into `dst`.
+ /// However it does not drop the contents of `dst`, or prevent the contents of `src`
+ /// from being dropped or used.
///
/// # Examples
///
/// dst
/// }
/// ```
+ ///
#[stable(feature = "rust1", since = "1.0.0")]
pub fn copy<T>(src: *const T, dst: *mut T, count: usize);
- /// Sets `count * size_of::<T>()` bytes of memory starting at `dst` to
- /// `val`.
- ///
- /// `write_bytes` is semantically equivalent to C's [`memset`].
- ///
- /// [`memset`]: https://www.gnu.org/software/libc/manual/html_node/Copying-Strings-and-Arrays.html#index-memset
- ///
- /// # Safety
- ///
- /// Behavior is undefined if any of the following conditions are violated:
- ///
- /// * The region of memory which begins at `dst` and has a length of
- /// `count` bytes must be valid.
- ///
- /// * `dst` must be properly aligned.
- ///
- /// Additionally, the caller must ensure that writing `count` bytes to the
- /// given region of memory results in a valid value of `T`. Creating an
- /// invalid value of `T` can result in undefined behavior. An example is
- /// provided below.
+ /// Invokes memset on the specified pointer, setting `count * size_of::<T>()`
+ /// bytes of memory starting at `dst` to `val`.
///
/// # Examples
///
- /// Basic usage:
- ///
/// ```
/// use std::ptr;
///
/// }
/// assert_eq!(vec, [b'a', b'a', 0, 0]);
/// ```
- ///
- /// Creating an invalid value:
- ///
- /// ```no_run
- /// use std::{mem, ptr};
- ///
- /// let mut v = Box::new(0i32);
- ///
- /// unsafe {
- /// // Leaks the previously held value by overwriting the `Box<T>` with
- /// // a null pointer.
- /// ptr::write_bytes(&mut v, 0, mem::size_of::<Box<i32>>());
- /// }
- ///
- /// // At this point, using or dropping `v` results in undefined behavior.
- /// // v = Box::new(0i32); // ERROR
- /// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn write_bytes<T>(dst: *mut T, val: u8, count: usize);
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