1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 // FIXME: talk about offset, copy_memory, copy_nonoverlapping_memory
13 //! Operations on unsafe pointers, `*const T`, and `*mut T`.
15 //! Working with unsafe pointers in Rust is uncommon,
16 //! typically limited to a few patterns.
18 //! Use the [`null` function](fn.null.html) to create null pointers,
19 //! the [`is_null`](trait.PtrExt.html#tymethod.is_null)
20 //! methods of the [`PtrExt` trait](trait.PtrExt.html) to check for null.
21 //! The `PtrExt` trait is imported by the prelude, so `is_null` etc.
22 //! work everywhere. The `PtrExt` also defines the `offset` method,
25 //! # Common ways to create unsafe pointers
27 //! ## 1. Coerce a reference (`&T`) or mutable reference (`&mut T`).
30 //! let my_num: int = 10;
31 //! let my_num_ptr: *const int = &my_num;
32 //! let mut my_speed: int = 88;
33 //! let my_speed_ptr: *mut int = &mut my_speed;
36 //! This does not take ownership of the original allocation
37 //! and requires no resource management later,
38 //! but you must not use the pointer after its lifetime.
40 //! ## 2. Transmute an owned box (`Box<T>`).
42 //! The `transmute` function takes, by value, whatever it's given
43 //! and returns it as whatever type is requested, as long as the
44 //! types are the same size. Because `Box<T>` and `*mut T` have the same
45 //! representation they can be trivially,
46 //! though unsafely, transformed from one type to the other.
49 //! # use std::boxed::Box;
53 //! let my_num: Box<int> = Box::new(10);
54 //! let my_num: *const int = mem::transmute(my_num);
55 //! let my_speed: Box<int> = Box::new(88);
56 //! let my_speed: *mut int = mem::transmute(my_speed);
58 //! // By taking ownership of the original `Box<T>` though
59 //! // we are obligated to transmute it back later to be destroyed.
60 //! drop(mem::transmute::<_, Box<int>>(my_speed));
61 //! drop(mem::transmute::<_, Box<int>>(my_num));
65 //! Note that here the call to `drop` is for clarity - it indicates
66 //! that we are done with the given value and it should be destroyed.
68 //! ## 3. Get it from C.
71 //! extern crate libc;
77 //! let my_num: *mut int = libc::malloc(mem::size_of::<int>() as libc::size_t) as *mut int;
78 //! if my_num.is_null() {
79 //! panic!("failed to allocate memory");
81 //! libc::free(my_num as *mut libc::c_void);
86 //! Usually you wouldn't literally use `malloc` and `free` from Rust,
87 //! but C APIs hand out a lot of pointers generally, so are a common source
88 //! of unsafe pointers in Rust.
95 use option::Option::{self, Some, None};
96 use marker::{Send, Sized, Sync};
98 use cmp::{PartialEq, Eq, Ord, PartialOrd};
99 use cmp::Ordering::{self, Less, Equal, Greater};
101 // FIXME #19649: intrinsic docs don't render, so these have no docs :(
104 pub use intrinsics::copy_nonoverlapping_memory;
107 pub use intrinsics::copy_memory;
109 #[unstable = "uncertain about naming and semantics"]
110 pub use intrinsics::set_memory;
113 /// Creates a null raw pointer.
120 /// let p: *const int = ptr::null();
121 /// assert!(p.is_null());
125 pub fn null<T>() -> *const T { 0 as *const T }
127 /// Creates a null mutable raw pointer.
134 /// let p: *mut int = ptr::null_mut();
135 /// assert!(p.is_null());
139 pub fn null_mut<T>() -> *mut T { 0 as *mut T }
141 /// Zeroes out `count * size_of::<T>` bytes of memory at `dst`. `count` may be
146 /// Beyond accepting a raw pointer, this is unsafe because it will not drop the
147 /// contents of `dst`, and may be used to create invalid instances of `T`.
149 #[unstable = "may play a larger role in std::ptr future extensions"]
150 pub unsafe fn zero_memory<T>(dst: *mut T, count: uint) {
151 set_memory(dst, 0, count);
154 /// Swaps the values at two mutable locations of the same type, without
155 /// deinitialising either. They may overlap, unlike `mem::swap` which is
156 /// otherwise equivalent.
160 /// This is only unsafe because it accepts a raw pointer.
163 pub unsafe fn swap<T>(x: *mut T, y: *mut T) {
164 // Give ourselves some scratch space to work with
165 let mut tmp: T = mem::uninitialized();
166 let t: *mut T = &mut tmp;
169 copy_nonoverlapping_memory(t, &*x, 1);
170 copy_memory(x, &*y, 1); // `x` and `y` may overlap
171 copy_nonoverlapping_memory(y, &*t, 1);
173 // y and t now point to the same thing, but we need to completely forget `tmp`
174 // because it's no longer relevant.
178 /// Replaces the value at `dest` with `src`, returning the old
179 /// value, without dropping either.
183 /// This is only unsafe because it accepts a raw pointer.
184 /// Otherwise, this operation is identical to `mem::replace`.
187 pub unsafe fn replace<T>(dest: *mut T, mut src: T) -> T {
188 mem::swap(mem::transmute(dest), &mut src); // cannot overlap
192 /// Reads the value from `src` without dropping it. This leaves the
193 /// memory in `src` unchanged.
197 /// Beyond accepting a raw pointer, this is unsafe because it semantically
198 /// moves the value out of `src` without preventing further usage of `src`.
199 /// If `T` is not `Copy`, then care must be taken to ensure that the value at
200 /// `src` is not used before the data is overwritten again (e.g. with `write`,
201 /// `zero_memory`, or `copy_memory`). Note that `*src = foo` counts as a use
202 /// because it will attempt to drop the value previously at `*src`.
205 pub unsafe fn read<T>(src: *const T) -> T {
206 let mut tmp: T = mem::uninitialized();
207 copy_nonoverlapping_memory(&mut tmp, src, 1);
211 /// Reads the value from `src` and nulls it out without dropping it.
215 /// This is unsafe for the same reasons that `read` is unsafe.
217 #[unstable = "may play a larger role in std::ptr future extensions"]
218 pub unsafe fn read_and_zero<T>(dest: *mut T) -> T {
219 // Copy the data out from `dest`:
220 let tmp = read(&*dest);
222 // Now zero out `dest`:
223 zero_memory(dest, 1);
228 /// Overwrites a memory location with the given value without reading or
229 /// dropping the old value.
233 /// Beyond accepting a raw pointer, this operation is unsafe because it does
234 /// not drop the contents of `dst`. This could leak allocations or resources,
235 /// so care must be taken not to overwrite an object that should be dropped.
237 /// This is appropriate for initializing uninitialized memory, or overwriting
238 /// memory that has previously been `read` from.
241 pub unsafe fn write<T>(dst: *mut T, src: T) {
242 intrinsics::move_val_init(&mut *dst, src)
245 /// Methods on raw pointers
247 pub trait PtrExt: Sized {
250 /// Returns true if the pointer is null.
252 fn is_null(self) -> bool;
254 /// Returns `None` if the pointer is null, or else returns a reference to
255 /// the value wrapped in `Some`.
259 /// While this method and its mutable counterpart are useful for
260 /// null-safety, it is important to note that this is still an unsafe
261 /// operation because the returned value could be pointing to invalid
263 #[unstable = "Option is not clearly the right return type, and we may want \
264 to tie the return lifetime to a borrow of the raw pointer"]
265 unsafe fn as_ref<'a>(&self) -> Option<&'a Self::Target>;
267 /// Calculates the offset from a pointer. `count` is in units of T; e.g. a
268 /// `count` of 3 represents a pointer offset of `3 * sizeof::<T>()` bytes.
272 /// The offset must be in-bounds of the object, or one-byte-past-the-end.
273 /// Otherwise `offset` invokes Undefined Behaviour, regardless of whether
274 /// the pointer is used.
276 unsafe fn offset(self, count: int) -> Self;
279 /// Methods on mutable raw pointers
281 pub trait MutPtrExt {
284 /// Returns `None` if the pointer is null, or else returns a mutable
285 /// reference to the value wrapped in `Some`.
289 /// As with `as_ref`, this is unsafe because it cannot verify the validity
290 /// of the returned pointer.
291 #[unstable = "Option is not clearly the right return type, and we may want \
292 to tie the return lifetime to a borrow of the raw pointer"]
293 unsafe fn as_mut<'a>(&self) -> Option<&'a mut Self::Target>;
297 impl<T> PtrExt for *const T {
302 fn is_null(self) -> bool { self as uint == 0 }
306 unsafe fn offset(self, count: int) -> *const T {
307 intrinsics::offset(self, count)
311 #[unstable = "return value does not necessarily convey all possible \
313 unsafe fn as_ref<'a>(&self) -> Option<&'a T> {
323 impl<T> PtrExt for *mut T {
328 fn is_null(self) -> bool { self as uint == 0 }
332 unsafe fn offset(self, count: int) -> *mut T {
333 intrinsics::offset(self as *const T, count) as *mut T
337 #[unstable = "return value does not necessarily convey all possible \
339 unsafe fn as_ref<'a>(&self) -> Option<&'a T> {
349 impl<T> MutPtrExt for *mut T {
353 #[unstable = "return value does not necessarily convey all possible \
355 unsafe fn as_mut<'a>(&self) -> Option<&'a mut T> {
364 // Equality for pointers
366 impl<T> PartialEq for *const T {
368 fn eq(&self, other: &*const T) -> bool {
372 fn ne(&self, other: &*const T) -> bool { !self.eq(other) }
376 impl<T> Eq for *const T {}
379 impl<T> PartialEq for *mut T {
381 fn eq(&self, other: &*mut T) -> bool {
385 fn ne(&self, other: &*mut T) -> bool { !self.eq(other) }
389 impl<T> Eq for *mut T {}
392 impl<T> Clone for *const T {
394 fn clone(&self) -> *const T {
400 impl<T> Clone for *mut T {
402 fn clone(&self) -> *mut T {
407 // Equality for extern "C" fn pointers
408 mod externfnpointers {
413 impl<_R> PartialEq for extern "C" fn() -> _R {
415 fn eq(&self, other: &extern "C" fn() -> _R) -> bool {
416 let self_: *const () = unsafe { mem::transmute(*self) };
417 let other_: *const () = unsafe { mem::transmute(*other) };
421 macro_rules! fnptreq {
424 impl<_R,$($p),*> PartialEq for extern "C" fn($($p),*) -> _R {
426 fn eq(&self, other: &extern "C" fn($($p),*) -> _R) -> bool {
427 let self_: *const () = unsafe { mem::transmute(*self) };
429 let other_: *const () = unsafe { mem::transmute(*other) };
439 fnptreq! { A,B,C,D,E }
442 // Comparison for pointers
444 impl<T> Ord for *const T {
446 fn cmp(&self, other: &*const T) -> Ordering {
449 } else if self == other {
458 impl<T> PartialOrd for *const T {
460 fn partial_cmp(&self, other: &*const T) -> Option<Ordering> {
461 Some(self.cmp(other))
465 fn lt(&self, other: &*const T) -> bool { *self < *other }
468 fn le(&self, other: &*const T) -> bool { *self <= *other }
471 fn gt(&self, other: &*const T) -> bool { *self > *other }
474 fn ge(&self, other: &*const T) -> bool { *self >= *other }
478 impl<T> Ord for *mut T {
480 fn cmp(&self, other: &*mut T) -> Ordering {
483 } else if self == other {
492 impl<T> PartialOrd for *mut T {
494 fn partial_cmp(&self, other: &*mut T) -> Option<Ordering> {
495 Some(self.cmp(other))
499 fn lt(&self, other: &*mut T) -> bool { *self < *other }
502 fn le(&self, other: &*mut T) -> bool { *self <= *other }
505 fn gt(&self, other: &*mut T) -> bool { *self > *other }
508 fn ge(&self, other: &*mut T) -> bool { *self >= *other }
511 /// A wrapper around a raw `*mut T` that indicates that the possessor
512 /// of this wrapper owns the referent. This in turn implies that the
513 /// `Unique<T>` is `Send`/`Sync` if `T` is `Send`/`Sync`, unlike a
514 /// raw `*mut T` (which conveys no particular ownership semantics).
515 /// Useful for building abstractions like `Vec<T>` or `Box<T>`, which
516 /// internally use raw pointers to manage the memory that they own.
517 #[unstable = "recently added to this module"]
518 pub struct Unique<T>(pub *mut T);
520 /// `Unique` pointers are `Send` if `T` is `Send` because the data they
521 /// reference is unaliased. Note that this aliasing invariant is
522 /// unenforced by the type system; the abstraction using the
523 /// `Unique` must enforce it.
524 #[unstable = "recently added to this module"]
525 unsafe impl<T:Send> Send for Unique<T> { }
527 /// `Unique` pointers are `Sync` if `T` is `Sync` because the data they
528 /// reference is unaliased. Note that this aliasing invariant is
529 /// unenforced by the type system; the abstraction using the
530 /// `Unique` must enforce it.
531 #[unstable = "recently added to this module"]
532 unsafe impl<T:Sync> Sync for Unique<T> { }
535 /// Returns a null Unique.
536 #[unstable = "recently added to this module"]
537 pub fn null() -> Unique<T> {
541 /// Return an (unsafe) pointer into the memory owned by `self`.
542 #[unstable = "recently added to this module"]
543 pub unsafe fn offset(self, offset: int) -> *mut T {
544 self.0.offset(offset)