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, and
19 //! the `is_null` method of the `*const T` type to check for null.
20 //! The `*const T` type also defines the `offset` method, for pointer math.
22 //! # Common ways to create unsafe pointers
24 //! ## 1. Coerce a reference (`&T`) or mutable reference (`&mut T`).
27 //! let my_num: i32 = 10;
28 //! let my_num_ptr: *const i32 = &my_num;
29 //! let mut my_speed: i32 = 88;
30 //! let my_speed_ptr: *mut i32 = &mut my_speed;
33 //! To get a pointer to a boxed value, dereference the box:
36 //! let my_num: Box<i32> = Box::new(10);
37 //! let my_num_ptr: *const i32 = &*my_num;
38 //! let mut my_speed: Box<i32> = Box::new(88);
39 //! let my_speed_ptr: *mut i32 = &mut *my_speed;
42 //! This does not take ownership of the original allocation
43 //! and requires no resource management later,
44 //! but you must not use the pointer after its lifetime.
46 //! ## 2. Consume a box (`Box<T>`).
48 //! The `into_raw` function consumes a box and returns
49 //! the raw pointer. It doesn't destroy `T` or deallocate any memory.
52 //! # #![feature(alloc)]
56 //! let my_speed: Box<i32> = Box::new(88);
57 //! let my_speed: *mut i32 = boxed::into_raw(my_speed);
59 //! // By taking ownership of the original `Box<T>` though
60 //! // we are obligated to put it together later to be destroyed.
61 //! drop(Box::from_raw(my_speed));
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 //! # #![feature(libc)]
72 //! extern crate libc;
78 //! let my_num: *mut i32 = libc::malloc(mem::size_of::<i32>() as libc::size_t) as *mut i32;
79 //! if my_num.is_null() {
80 //! panic!("failed to allocate memory");
82 //! libc::free(my_num as *mut libc::c_void);
87 //! Usually you wouldn't literally use `malloc` and `free` from Rust,
88 //! but C APIs hand out a lot of pointers generally, so are a common source
89 //! of unsafe pointers in Rust.
91 #![stable(feature = "rust1", since = "1.0.0")]
92 #![doc(primitive = "pointer")]
99 use option::Option::{self, Some, None};
100 use marker::{PhantomData, Send, Sized, Sync};
101 use nonzero::NonZero;
103 use cmp::{PartialEq, Eq, Ord, PartialOrd};
104 use cmp::Ordering::{self, Less, Equal, Greater};
106 // FIXME #19649: intrinsic docs don't render, so these have no docs :(
108 #[stable(feature = "rust1", since = "1.0.0")]
110 pub use intrinsics::copy_nonoverlapping;
114 #[stable(feature = "rust1", since = "1.0.0")]
115 pub unsafe fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize) {
116 intrinsics::copy_nonoverlapping(dst, src, count)
119 #[stable(feature = "rust1", since = "1.0.0")]
121 pub use intrinsics::copy;
125 #[stable(feature = "rust1", since = "1.0.0")]
126 pub unsafe fn copy<T>(src: *const T, dst: *mut T, count: usize) {
127 intrinsics::copy(dst, src, count)
131 #[stable(feature = "rust1", since = "1.0.0")]
132 pub use intrinsics::write_bytes;
134 /// Creates a null raw pointer.
141 /// let p: *const i32 = ptr::null();
142 /// assert!(p.is_null());
145 #[stable(feature = "rust1", since = "1.0.0")]
146 pub fn null<T>() -> *const T { 0 as *const T }
148 /// Creates a null mutable raw pointer.
155 /// let p: *mut i32 = ptr::null_mut();
156 /// assert!(p.is_null());
159 #[stable(feature = "rust1", since = "1.0.0")]
160 pub fn null_mut<T>() -> *mut T { 0 as *mut T }
162 /// Swaps the values at two mutable locations of the same type, without
163 /// deinitialising either. They may overlap, unlike `mem::swap` which is
164 /// otherwise equivalent.
168 /// This is only unsafe because it accepts a raw pointer.
170 #[stable(feature = "rust1", since = "1.0.0")]
171 pub unsafe fn swap<T>(x: *mut T, y: *mut T) {
172 // Give ourselves some scratch space to work with
173 let mut tmp: T = mem::uninitialized();
176 copy_nonoverlapping(x, &mut tmp, 1);
177 copy(y, x, 1); // `x` and `y` may overlap
178 copy_nonoverlapping(&tmp, y, 1);
180 // y and t now point to the same thing, but we need to completely forget `tmp`
181 // because it's no longer relevant.
185 /// Replaces the value at `dest` with `src`, returning the old
186 /// value, without dropping either.
190 /// This is only unsafe because it accepts a raw pointer.
191 /// Otherwise, this operation is identical to `mem::replace`.
193 #[stable(feature = "rust1", since = "1.0.0")]
194 pub unsafe fn replace<T>(dest: *mut T, mut src: T) -> T {
195 mem::swap(mem::transmute(dest), &mut src); // cannot overlap
199 /// Reads the value from `src` without moving it. This leaves the
200 /// memory in `src` unchanged.
204 /// Beyond accepting a raw pointer, this is unsafe because it semantically
205 /// moves the value out of `src` without preventing further usage of `src`.
206 /// If `T` is not `Copy`, then care must be taken to ensure that the value at
207 /// `src` is not used before the data is overwritten again (e.g. with `write`,
208 /// `zero_memory`, or `copy_memory`). Note that `*src = foo` counts as a use
209 /// because it will attempt to drop the value previously at `*src`.
211 #[stable(feature = "rust1", since = "1.0.0")]
212 pub unsafe fn read<T>(src: *const T) -> T {
213 let mut tmp: T = mem::uninitialized();
214 copy_nonoverlapping(src, &mut tmp, 1);
218 /// Reads the value from `src` and nulls it out without dropping it.
222 /// This is unsafe for the same reasons that `read` is unsafe.
224 #[unstable(feature = "core",
225 reason = "may play a larger role in std::ptr future extensions")]
226 pub unsafe fn read_and_zero<T>(dest: *mut T) -> T {
227 // Copy the data out from `dest`:
228 let tmp = read(&*dest);
230 // Now zero out `dest`:
231 write_bytes(dest, 0, 1);
236 /// Variant of read_and_zero that writes the specific drop-flag byte
237 /// (which may be more appropriate than zero).
239 #[unstable(feature = "core",
240 reason = "may play a larger role in std::ptr future extensions")]
241 pub unsafe fn read_and_drop<T>(dest: *mut T) -> T {
242 // Copy the data out from `dest`:
243 let tmp = read(&*dest);
245 // Now mark `dest` as dropped:
246 write_bytes(dest, mem::POST_DROP_U8, 1);
251 /// Overwrites a memory location with the given value without reading or
252 /// dropping the old value.
256 /// Beyond accepting a raw pointer, this operation is unsafe because it does
257 /// not drop the contents of `dst`. This could leak allocations or resources,
258 /// so care must be taken not to overwrite an object that should be dropped.
260 /// This is appropriate for initializing uninitialized memory, or overwriting
261 /// memory that has previously been `read` from.
263 #[stable(feature = "rust1", since = "1.0.0")]
264 pub unsafe fn write<T>(dst: *mut T, src: T) {
265 intrinsics::move_val_init(&mut *dst, src)
268 #[stable(feature = "rust1", since = "1.0.0")]
269 #[lang = "const_ptr"]
270 impl<T: ?Sized> *const T {
271 /// Returns true if the pointer is null.
272 #[stable(feature = "rust1", since = "1.0.0")]
274 pub fn is_null(self) -> bool where T: Sized {
275 self == 0 as *const T
278 /// Returns `None` if the pointer is null, or else returns a reference to
279 /// the value wrapped in `Some`.
283 /// While this method and its mutable counterpart are useful for
284 /// null-safety, it is important to note that this is still an unsafe
285 /// operation because the returned value could be pointing to invalid
287 #[unstable(feature = "core",
288 reason = "Option is not clearly the right return type, and we may want \
289 to tie the return lifetime to a borrow of the raw pointer")]
291 pub unsafe fn as_ref<'a>(&self) -> Option<&'a T> where T: Sized {
299 /// Calculates the offset from a pointer. `count` is in units of T; e.g. a
300 /// `count` of 3 represents a pointer offset of `3 * sizeof::<T>()` bytes.
304 /// The offset must be in-bounds of the object, or one-byte-past-the-end.
305 /// Otherwise `offset` invokes Undefined Behaviour, regardless of whether
306 /// the pointer is used.
307 #[stable(feature = "rust1", since = "1.0.0")]
309 pub unsafe fn offset(self, count: isize) -> *const T where T: Sized {
310 intrinsics::offset(self, count)
314 #[stable(feature = "rust1", since = "1.0.0")]
316 impl<T: ?Sized> *mut T {
317 /// Returns true if the pointer is null.
318 #[stable(feature = "rust1", since = "1.0.0")]
320 pub fn is_null(self) -> bool where T: Sized {
324 /// Returns `None` if the pointer is null, or else returns a reference to
325 /// the value wrapped in `Some`.
329 /// While this method and its mutable counterpart are useful for
330 /// null-safety, it is important to note that this is still an unsafe
331 /// operation because the returned value could be pointing to invalid
333 #[unstable(feature = "core",
334 reason = "Option is not clearly the right return type, and we may want \
335 to tie the return lifetime to a borrow of the raw pointer")]
337 pub unsafe fn as_ref<'a>(&self) -> Option<&'a T> where T: Sized {
345 /// Calculates the offset from a pointer. `count` is in units of T; e.g. a
346 /// `count` of 3 represents a pointer offset of `3 * sizeof::<T>()` bytes.
350 /// The offset must be in-bounds of the object, or one-byte-past-the-end.
351 /// Otherwise `offset` invokes Undefined Behaviour, regardless of whether
352 /// the pointer is used.
353 #[stable(feature = "rust1", since = "1.0.0")]
355 pub unsafe fn offset(self, count: isize) -> *mut T where T: Sized {
356 intrinsics::offset(self, count) as *mut T
359 /// Returns `None` if the pointer is null, or else returns a mutable
360 /// reference to the value wrapped in `Some`.
364 /// As with `as_ref`, this is unsafe because it cannot verify the validity
365 /// of the returned pointer.
366 #[unstable(feature = "core",
367 reason = "return value does not necessarily convey all possible \
370 pub unsafe fn as_mut<'a>(&self) -> Option<&'a mut T> where T: Sized {
379 // Equality for pointers
380 #[stable(feature = "rust1", since = "1.0.0")]
381 impl<T: ?Sized> PartialEq for *const T {
383 fn eq(&self, other: &*const T) -> bool { *self == *other }
386 #[stable(feature = "rust1", since = "1.0.0")]
387 impl<T: ?Sized> Eq for *const T {}
389 #[stable(feature = "rust1", since = "1.0.0")]
390 impl<T: ?Sized> PartialEq for *mut T {
392 fn eq(&self, other: &*mut T) -> bool { *self == *other }
395 #[stable(feature = "rust1", since = "1.0.0")]
396 impl<T: ?Sized> Eq for *mut T {}
398 #[stable(feature = "rust1", since = "1.0.0")]
399 impl<T: ?Sized> Clone for *const T {
401 fn clone(&self) -> *const T {
406 #[stable(feature = "rust1", since = "1.0.0")]
407 impl<T: ?Sized> Clone for *mut T {
409 fn clone(&self) -> *mut T {
414 // Equality for extern "C" fn pointers
415 mod externfnpointers {
419 #[stable(feature = "rust1", since = "1.0.0")]
420 impl<_R> PartialEq for extern "C" fn() -> _R {
422 fn eq(&self, other: &extern "C" fn() -> _R) -> bool {
423 let self_: *const () = unsafe { mem::transmute(*self) };
424 let other_: *const () = unsafe { mem::transmute(*other) };
428 macro_rules! fnptreq {
430 #[stable(feature = "rust1", since = "1.0.0")]
431 impl<_R,$($p),*> PartialEq for extern "C" fn($($p),*) -> _R {
433 fn eq(&self, other: &extern "C" fn($($p),*) -> _R) -> bool {
434 let self_: *const () = unsafe { mem::transmute(*self) };
436 let other_: *const () = unsafe { mem::transmute(*other) };
446 fnptreq! { A,B,C,D,E }
449 // Comparison for pointers
450 #[stable(feature = "rust1", since = "1.0.0")]
451 impl<T: ?Sized> Ord for *const T {
453 fn cmp(&self, other: &*const T) -> Ordering {
456 } else if self == other {
464 #[stable(feature = "rust1", since = "1.0.0")]
465 impl<T: ?Sized> PartialOrd for *const T {
467 fn partial_cmp(&self, other: &*const T) -> Option<Ordering> {
468 Some(self.cmp(other))
472 fn lt(&self, other: &*const T) -> bool { *self < *other }
475 fn le(&self, other: &*const T) -> bool { *self <= *other }
478 fn gt(&self, other: &*const T) -> bool { *self > *other }
481 fn ge(&self, other: &*const T) -> bool { *self >= *other }
484 #[stable(feature = "rust1", since = "1.0.0")]
485 impl<T: ?Sized> Ord for *mut T {
487 fn cmp(&self, other: &*mut T) -> Ordering {
490 } else if self == other {
498 #[stable(feature = "rust1", since = "1.0.0")]
499 impl<T: ?Sized> PartialOrd for *mut T {
501 fn partial_cmp(&self, other: &*mut T) -> Option<Ordering> {
502 Some(self.cmp(other))
506 fn lt(&self, other: &*mut T) -> bool { *self < *other }
509 fn le(&self, other: &*mut T) -> bool { *self <= *other }
512 fn gt(&self, other: &*mut T) -> bool { *self > *other }
515 fn ge(&self, other: &*mut T) -> bool { *self >= *other }
518 /// A wrapper around a raw `*mut T` that indicates that the possessor
519 /// of this wrapper owns the referent. This in turn implies that the
520 /// `Unique<T>` is `Send`/`Sync` if `T` is `Send`/`Sync`, unlike a raw
521 /// `*mut T` (which conveys no particular ownership semantics). It
522 /// also implies that the referent of the pointer should not be
523 /// modified without a unique path to the `Unique` reference. Useful
524 /// for building abstractions like `Vec<T>` or `Box<T>`, which
525 /// internally use raw pointers to manage the memory that they own.
526 #[unstable(feature = "unique")]
527 pub struct Unique<T: ?Sized> {
528 pointer: NonZero<*const T>,
529 _marker: PhantomData<T>,
532 /// `Unique` pointers are `Send` if `T` is `Send` because the data they
533 /// reference is unaliased. Note that this aliasing invariant is
534 /// unenforced by the type system; the abstraction using the
535 /// `Unique` must enforce it.
536 #[unstable(feature = "unique")]
537 unsafe impl<T: Send + ?Sized> Send for Unique<T> { }
539 /// `Unique` pointers are `Sync` if `T` is `Sync` because the data they
540 /// reference is unaliased. Note that this aliasing invariant is
541 /// unenforced by the type system; the abstraction using the
542 /// `Unique` must enforce it.
543 #[unstable(feature = "unique")]
544 unsafe impl<T: Sync + ?Sized> Sync for Unique<T> { }
546 impl<T: ?Sized> Unique<T> {
547 /// Create a new `Unique`.
548 #[unstable(feature = "unique")]
549 pub unsafe fn new(ptr: *mut T) -> Unique<T> {
550 Unique { pointer: NonZero::new(ptr), _marker: PhantomData }
553 /// Dereference the content.
554 #[unstable(feature = "unique")]
555 pub unsafe fn get(&self) -> &T {
559 /// Mutably dereference the content.
560 #[unstable(feature = "unique")]
561 pub unsafe fn get_mut(&mut self) -> &mut T {
566 #[unstable(feature = "unique")]
567 impl<T:?Sized> Deref for Unique<T> {
568 type Target = *mut T;
571 fn deref<'a>(&'a self) -> &'a *mut T {
572 unsafe { mem::transmute(&*self.pointer) }
576 #[stable(feature = "rust1", since = "1.0.0")]
577 impl<T> fmt::Pointer for Unique<T> {
578 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
579 fmt::Pointer::fmt(&*self.pointer, f)