OpenE2K/rust
2
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

std: Add more docs for ptr mod

Browse Source
This commit is contained in:
Brian Anderson 2014-04-07 14:00:19 -07:00 committed by Alex Crichton
parent c3ea3e439f
commit ef37cfdecc
1 changed files with 182 additions and 53 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

235
src/libstd/ptr.rs
View File

@ -8,7 +8,87 @@
// option. This file may not be copied, modified, or distributed
// except according to those terms.
//! Unsafe pointer utility functions
//! Conveniences for working with unsafe pointers, the `*T`, and `*mut T` types.
//!
//! Working with unsafe pointers in Rust is fairly uncommon,
//! and often limited to some narrow use cases: holding
//! an unsafe pointer when safe pointers are unsuitable;
//! checking for null; and converting back to safe pointers.
//! As a result, there is not yet an abundance of library code
//! for working with unsafe poniters, and in particular,
//! since pointer math is fairly uncommon in Rust, it is not
//! all that convenient.
//!
//! Use the [`null` function](fn.null.html) to create null pointers,
//! the [`is_null`](trait.RawPtr.html#tymethod.is_null)
//! and [`is_not_null`](trait.RawPtr.html#method.is_not_null)
//! methods of the [`RawPtr` trait](trait.RawPtr.html) to check for null.
//! The `RawPtr` trait is imported by the prelude, so `is_null` etc.
//! work everywhere.
//!
//! # Common ways to create unsafe pointers
//!
//! ## 1. Coerce a reference (`&T`) or mutable reference (`&mut T`).
//!
//! ```
//! let my_num: int = 10;
//! let my_num_ptr: *int = &my_num;
//! let mut my_speed: int = 88;
//! let my_speed_ptr: *mut int = &mut my_speed;
//! ```
//!
//! This does not take ownership of the original allocation
//! and requires no resource management later,
//! but you must not use the pointer after its lifetime.
//!
//! ## 2. Transmute an owned box (`~T`).
//!
//! The `transmute` function takes, by value, whatever it's given
//! and returns it as whatever type is requested, as long as the
//! types are the same size. Because `~T` and `*T` have the same
//! representation they can be trivially,
//! though unsafely, transformed from one type to the other.
//!
//! ```
//! use std::cast;
//!
//! unsafe {
//! let my_num: ~int = ~10;
//! let my_num: *int = cast::transmute(my_num);
//! let my_speed: ~int = ~88;
//! let my_speed: *mut int = cast::transmute(my_speed);
//!
//! // By taking ownership of the original `~T` though
//! // we are obligated to transmute it back later to be destroyed.
//! drop(cast::transmute::<_, ~int>(my_speed));
//! drop(cast::transmute::<_, ~int>(my_num));
//! }
//! ```
//!
//! Note that here the call to `drop` is for clarity - it indicates
//! that we are done with the given value and it should be destroyed.
//!
//! ## 3. Get it from C.
//!
//! ```
//! extern crate libc;
//!
//! use std::mem;
//!
//! fn main() {
//! unsafe {
//! let my_num: *mut int = libc::malloc(mem::size_of::<int>() as libc::size_t) as *mut int;
//! if my_num.is_null() {
//! fail!("failed to allocate memory");
//! }
//! libc::free(my_num as *mut libc::c_void);
//! }
//! }
//! ```
//!
//! Usually you wouldn't literally use `malloc` and `free` from Rust,
//! but C APIs hand out a lot of pointers generally, so are a common source
//! of unsafe pointers in Rust.
use cast;
use clone::Clone;
@ -51,31 +131,97 @@ pub unsafe fn position<T>(buf: *T, f: |&T| -> bool) -> uint {
}
}
/// Create an unsafe null pointer
/// Create an null pointer.
///
/// # Example
///
/// ```
/// use std::ptr;
///
/// let p: *int = ptr::null();
/// assert!(p.is_null());
/// ```
#[inline]
pub fn null<T>() -> *T { 0 as *T }
/// Create an unsafe mutable null pointer
/// Create an unsafe mutable null pointer.
///
/// # Example
///
/// ```
/// use std::ptr;
///
/// let p: *mut int = ptr::mut_null();
/// assert!(p.is_null());
/// ```
#[inline]
pub fn mut_null<T>() -> *mut T { 0 as *mut T }
/**
* Copies data from one location to another.
*
* Copies `count` elements (not bytes) from `src` to `dst`. The source
* and destination may overlap.
*/
/// Copies data from one location to another.
///
/// Copies `count` elements (not bytes) from `src` to `dst`. The source
/// and destination may overlap.
///
/// `copy_memory` is semantically equivalent to C's `memmove`.
///
/// # Example
///
/// Efficiently create a Rust vector from an unsafe buffer:
///
/// ```
/// use std::ptr;
/// use std::slice;
///
/// unsafe fn from_buf_raw<T>(ptr: *T, elts: uint) -> ~[T] {
/// let mut dst = slice::with_capacity(elts);
/// dst.set_len(elts);
/// ptr::copy_memory(dst.as_mut_ptr(), ptr, elts);
/// dst
/// }
/// ```
///
#[inline]
pub unsafe fn copy_memory<T>(dst: *mut T, src: *T, count: uint) {
intrinsics::copy_memory(dst, src, count)
}
/**
* Copies data from one location to another.
*
* Copies `count` elements (not bytes) from `src` to `dst`. The source
* and destination may *not* overlap.
*/
/// Copies data from one location to another.
///
/// Copies `count` elements (not bytes) from `src` to `dst`. The source
/// and destination may *not* overlap.
///
/// `copy_nonoverlapping_memory` is semantically equivalent to C's `memcpy`.
///
/// # Example
///
/// A safe swap function:
///
/// ```
/// use std::cast;
/// use std::mem;
/// use std::ptr;
///
/// fn swap<T>(x: &mut T, y: &mut T) {
/// unsafe {
/// // Give ourselves some scratch space to work with
/// let mut t: T = mem::uninit();
///
/// // Perform the swap, `&mut` pointers never alias
/// ptr::copy_nonoverlapping_memory(&mut t, &*x, 1);
/// ptr::copy_nonoverlapping_memory(x, &*y, 1);
/// ptr::copy_nonoverlapping_memory(y, &t, 1);
///
/// // y and t now point to the same thing, but we need to completely forget `tmp`
/// // because it's no longer relevant.
/// cast::forget(t);
/// }
/// }
/// ```
///
/// # Safety Note
///
/// If the source and destination overlap then the behavior of this
/// function is undefined.
#[inline]
pub unsafe fn copy_nonoverlapping_memory<T>(dst: *mut T,
src: *T,
@ -83,27 +229,21 @@ pub unsafe fn copy_nonoverlapping_memory<T>(dst: *mut T,
intrinsics::copy_nonoverlapping_memory(dst, src, count)
}
/**
* Invokes memset on the specified pointer, setting `count * size_of::<T>()`
* bytes of memory starting at `dst` to `c`.
*/
/// Invokes memset on the specified pointer, setting `count * size_of::<T>()`
/// bytes of memory starting at `dst` to `c`.
#[inline]
pub unsafe fn set_memory<T>(dst: *mut T, c: u8, count: uint) {
intrinsics::set_memory(dst, c, count)
}
/**
* Zeroes out `count * size_of::<T>` bytes of memory at `dst`
*/
/// Zeroes out `count * size_of::<T>` bytes of memory at `dst`
#[inline]
pub unsafe fn zero_memory<T>(dst: *mut T, count: uint) {
set_memory(dst, 0, count);
}
/**
* Swap the values at two mutable locations of the same type, without
* deinitialising either. They may overlap.
*/
/// Swap the values at two mutable locations of the same type, without
/// deinitialising either. They may overlap.
#[inline]
pub unsafe fn swap<T>(x: *mut T, y: *mut T) {
// Give ourselves some scratch space to work with
@ -120,19 +260,15 @@ pub unsafe fn swap<T>(x: *mut T, y: *mut T) {
cast::forget(tmp);
}
/**
* Replace the value at a mutable location with a new one, returning the old
* value, without deinitialising either.
*/
/// Replace the value at a mutable location with a new one, returning the old
/// value, without deinitialising either.
#[inline]
pub unsafe fn replace<T>(dest: *mut T, mut src: T) -> T {
mem::swap(cast::transmute(dest), &mut src); // cannot overlap
src
}
/**
* Reads the value from `*src` and returns it.
*/
/// Reads the value from `*src` and returns it.
#[inline(always)]
pub unsafe fn read<T>(src: *T) -> T {
let mut tmp: T = mem::uninit();
@ -140,10 +276,8 @@ pub unsafe fn read<T>(src: *T) -> T {
tmp
}
/**
* Reads the value from `*src` and nulls it out.
* This currently prevents destructors from executing.
*/
/// Reads the value from `*src` and nulls it out.
/// This currently prevents destructors from executing.
#[inline(always)]
pub unsafe fn read_and_zero<T>(dest: *mut T) -> T {
// Copy the data out from `dest`:
@ -155,13 +289,9 @@ pub unsafe fn read_and_zero<T>(dest: *mut T) -> T {
tmp
}
/**
Given a **T (pointer to an array of pointers),
iterate through each *T, up to the provided `len`,
passing to the provided callback function
SAFETY NOTE: Pointer-arithmetic. Dragons be here.
*/
/// Given a **T (pointer to an array of pointers),
/// iterate through each *T, up to the provided `len`,
/// passing to the provided callback function
pub unsafe fn array_each_with_len<T>(arr: **T, len: uint, cb: |*T|) {
if arr.is_null() {
fail!("ptr::array_each_with_len failure: arr input is null pointer");
@ -173,15 +303,14 @@ pub unsafe fn array_each_with_len<T>(arr: **T, len: uint, cb: |*T|) {
}
}
/**
Given a null-pointer-terminated **T (pointer to
an array of pointers), iterate through each *T,
passing to the provided callback function
SAFETY NOTE: This will only work with a null-terminated
pointer array. Barely less-dodgy Pointer Arithmetic.
Dragons be here.
*/
/// Given a null-pointer-terminated **T (pointer to
/// an array of pointers), iterate through each *T,
/// passing to the provided callback function
///
/// # Safety Note
///
/// This will only work with a null-terminated
/// pointer array.
pub unsafe fn array_each<T>(arr: **T, cb: |*T|) {
if arr.is_null() {
fail!("ptr::array_each_with_len failure: arr input is null pointer");