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 raw pointers, `*const T`, and `*mut T`.
15 //! Working with raw pointers in Rust is uncommon,
16 //! typically limited to a few patterns.
18 //! Use the `null` function to create null pointers, and the `is_null` method
19 //! of the `*const T` type to check for null. The `*const T` type also defines
20 //! the `offset` method, for pointer math.
22 //! # Common ways to create raw 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 raw 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")]
109 pub use intrinsics::copy_nonoverlapping;
111 #[stable(feature = "rust1", since = "1.0.0")]
112 pub use intrinsics::copy;
114 #[stable(feature = "rust1", since = "1.0.0")]
115 pub use intrinsics::write_bytes;
117 /// Creates a null raw pointer.
124 /// let p: *const i32 = ptr::null();
125 /// assert!(p.is_null());
128 #[stable(feature = "rust1", since = "1.0.0")]
129 pub fn null<T>() -> *const T { 0 as *const T }
131 /// Creates a null mutable raw pointer.
138 /// let p: *mut i32 = ptr::null_mut();
139 /// assert!(p.is_null());
142 #[stable(feature = "rust1", since = "1.0.0")]
143 pub fn null_mut<T>() -> *mut T { 0 as *mut T }
145 /// Swaps the values at two mutable locations of the same type, without
146 /// deinitialising either. They may overlap, unlike `mem::swap` which is
147 /// otherwise equivalent.
151 /// This is only unsafe because it accepts a raw pointer.
153 #[stable(feature = "rust1", since = "1.0.0")]
154 pub unsafe fn swap<T>(x: *mut T, y: *mut T) {
155 // Give ourselves some scratch space to work with
156 let mut tmp: T = mem::uninitialized();
159 copy_nonoverlapping(x, &mut tmp, 1);
160 copy(y, x, 1); // `x` and `y` may overlap
161 copy_nonoverlapping(&tmp, y, 1);
163 // y and t now point to the same thing, but we need to completely forget `tmp`
164 // because it's no longer relevant.
168 /// Replaces the value at `dest` with `src`, returning the old
169 /// value, without dropping either.
173 /// This is only unsafe because it accepts a raw pointer.
174 /// Otherwise, this operation is identical to `mem::replace`.
176 #[stable(feature = "rust1", since = "1.0.0")]
177 pub unsafe fn replace<T>(dest: *mut T, mut src: T) -> T {
178 mem::swap(mem::transmute(dest), &mut src); // cannot overlap
182 /// Reads the value from `src` without moving it. This leaves the
183 /// memory in `src` unchanged.
187 /// Beyond accepting a raw pointer, this is unsafe because it semantically
188 /// moves the value out of `src` without preventing further usage of `src`.
189 /// If `T` is not `Copy`, then care must be taken to ensure that the value at
190 /// `src` is not used before the data is overwritten again (e.g. with `write`,
191 /// `zero_memory`, or `copy_memory`). Note that `*src = foo` counts as a use
192 /// because it will attempt to drop the value previously at `*src`.
194 #[stable(feature = "rust1", since = "1.0.0")]
195 pub unsafe fn read<T>(src: *const T) -> T {
196 let mut tmp: T = mem::uninitialized();
197 copy_nonoverlapping(src, &mut tmp, 1);
201 /// Reads the value from `src` and nulls it out without dropping it.
205 /// This is unsafe for the same reasons that `read` is unsafe.
207 #[unstable(feature = "read_and_zero",
208 reason = "may play a larger role in std::ptr future extensions")]
209 pub unsafe fn read_and_zero<T>(dest: *mut T) -> T {
210 // Copy the data out from `dest`:
211 let tmp = read(&*dest);
213 // Now zero out `dest`:
214 write_bytes(dest, 0, 1);
219 /// Variant of read_and_zero that writes the specific drop-flag byte
220 /// (which may be more appropriate than zero).
222 #[unstable(feature = "filling_drop",
223 reason = "may play a larger role in std::ptr future extensions")]
224 pub unsafe fn read_and_drop<T>(dest: *mut T) -> T {
225 // Copy the data out from `dest`:
226 let tmp = read(&*dest);
228 // Now mark `dest` as dropped:
229 write_bytes(dest, mem::POST_DROP_U8, 1);
234 /// Overwrites a memory location with the given value without reading or
235 /// dropping the old value.
239 /// Beyond accepting a raw pointer, this operation is unsafe because it does
240 /// not drop the contents of `dst`. This could leak allocations or resources,
241 /// so care must be taken not to overwrite an object that should be dropped.
243 /// This is appropriate for initializing uninitialized memory, or overwriting
244 /// memory that has previously been `read` from.
246 #[stable(feature = "rust1", since = "1.0.0")]
247 pub unsafe fn write<T>(dst: *mut T, src: T) {
248 intrinsics::move_val_init(&mut *dst, src)
251 #[stable(feature = "rust1", since = "1.0.0")]
252 #[lang = "const_ptr"]
253 impl<T: ?Sized> *const T {
254 /// Returns true if the pointer is null.
255 #[stable(feature = "rust1", since = "1.0.0")]
257 pub fn is_null(self) -> bool where T: Sized {
258 self == 0 as *const T
261 /// Returns `None` if the pointer is null, or else returns a reference to
262 /// the value wrapped in `Some`.
266 /// While this method and its mutable counterpart are useful for
267 /// null-safety, it is important to note that this is still an unsafe
268 /// operation because the returned value could be pointing to invalid
270 #[unstable(feature = "ptr_as_ref",
271 reason = "Option is not clearly the right return type, and we \
272 may want to tie the return lifetime to a borrow of \
275 pub unsafe fn as_ref<'a>(&self) -> Option<&'a T> where T: Sized {
283 /// Calculates the offset from a pointer. `count` is in units of T; e.g. a
284 /// `count` of 3 represents a pointer offset of `3 * sizeof::<T>()` bytes.
288 /// Both the starting and resulting pointer must be either in bounds or one
289 /// byte past the end of an allocated object. If either pointer is out of
290 /// bounds or arithmetic overflow occurs then
291 /// any further use of the returned value will result in undefined behavior.
292 #[stable(feature = "rust1", since = "1.0.0")]
294 pub unsafe fn offset(self, count: isize) -> *const T where T: Sized {
295 intrinsics::offset(self, count)
299 #[stable(feature = "rust1", since = "1.0.0")]
301 impl<T: ?Sized> *mut T {
302 /// Returns true if the pointer is null.
303 #[stable(feature = "rust1", since = "1.0.0")]
305 pub fn is_null(self) -> bool where T: Sized {
309 /// Returns `None` if the pointer is null, or else returns a reference to
310 /// the value wrapped in `Some`.
314 /// While this method and its mutable counterpart are useful for
315 /// null-safety, it is important to note that this is still an unsafe
316 /// operation because the returned value could be pointing to invalid
318 #[unstable(feature = "ptr_as_ref",
319 reason = "Option is not clearly the right return type, and we \
320 may want to tie the return lifetime to a borrow of \
323 pub unsafe fn as_ref<'a>(&self) -> Option<&'a T> where T: Sized {
331 /// Calculates the offset from a pointer. `count` is in units of T; e.g. a
332 /// `count` of 3 represents a pointer offset of `3 * sizeof::<T>()` bytes.
336 /// The offset must be in-bounds of the object, or one-byte-past-the-end.
337 /// Otherwise `offset` invokes Undefined Behaviour, regardless of whether
338 /// the pointer is used.
339 #[stable(feature = "rust1", since = "1.0.0")]
341 pub unsafe fn offset(self, count: isize) -> *mut T where T: Sized {
342 intrinsics::offset(self, count) as *mut T
345 /// Returns `None` if the pointer is null, or else returns a mutable
346 /// reference to the value wrapped in `Some`.
350 /// As with `as_ref`, this is unsafe because it cannot verify the validity
351 /// of the returned pointer.
352 #[unstable(feature = "ptr_as_ref",
353 reason = "return value does not necessarily convey all possible \
356 pub unsafe fn as_mut<'a>(&self) -> Option<&'a mut T> where T: Sized {
365 // Equality for pointers
366 #[stable(feature = "rust1", since = "1.0.0")]
367 impl<T: ?Sized> PartialEq for *const T {
369 fn eq(&self, other: &*const T) -> bool { *self == *other }
372 #[stable(feature = "rust1", since = "1.0.0")]
373 impl<T: ?Sized> Eq for *const T {}
375 #[stable(feature = "rust1", since = "1.0.0")]
376 impl<T: ?Sized> PartialEq for *mut T {
378 fn eq(&self, other: &*mut T) -> bool { *self == *other }
381 #[stable(feature = "rust1", since = "1.0.0")]
382 impl<T: ?Sized> Eq for *mut T {}
384 #[stable(feature = "rust1", since = "1.0.0")]
385 impl<T: ?Sized> Clone for *const T {
387 fn clone(&self) -> *const T {
392 #[stable(feature = "rust1", since = "1.0.0")]
393 impl<T: ?Sized> Clone for *mut T {
395 fn clone(&self) -> *mut T {
400 // Equality for extern "C" fn pointers
401 mod externfnpointers {
405 #[stable(feature = "rust1", since = "1.0.0")]
406 impl<_R> PartialEq for extern "C" fn() -> _R {
408 fn eq(&self, other: &extern "C" fn() -> _R) -> bool {
409 let self_: *const () = unsafe { mem::transmute(*self) };
410 let other_: *const () = unsafe { mem::transmute(*other) };
414 macro_rules! fnptreq {
416 #[stable(feature = "rust1", since = "1.0.0")]
417 impl<_R,$($p),*> PartialEq for extern "C" fn($($p),*) -> _R {
419 fn eq(&self, other: &extern "C" fn($($p),*) -> _R) -> bool {
420 let self_: *const () = unsafe { mem::transmute(*self) };
422 let other_: *const () = unsafe { mem::transmute(*other) };
432 fnptreq! { A,B,C,D,E }
435 // Comparison for pointers
436 #[stable(feature = "rust1", since = "1.0.0")]
437 impl<T: ?Sized> Ord for *const T {
439 fn cmp(&self, other: &*const T) -> Ordering {
442 } else if self == other {
450 #[stable(feature = "rust1", since = "1.0.0")]
451 impl<T: ?Sized> PartialOrd for *const T {
453 fn partial_cmp(&self, other: &*const T) -> Option<Ordering> {
454 Some(self.cmp(other))
458 fn lt(&self, other: &*const T) -> bool { *self < *other }
461 fn le(&self, other: &*const T) -> bool { *self <= *other }
464 fn gt(&self, other: &*const T) -> bool { *self > *other }
467 fn ge(&self, other: &*const T) -> bool { *self >= *other }
470 #[stable(feature = "rust1", since = "1.0.0")]
471 impl<T: ?Sized> Ord for *mut T {
473 fn cmp(&self, other: &*mut T) -> Ordering {
476 } else if self == other {
484 #[stable(feature = "rust1", since = "1.0.0")]
485 impl<T: ?Sized> PartialOrd for *mut T {
487 fn partial_cmp(&self, other: &*mut T) -> Option<Ordering> {
488 Some(self.cmp(other))
492 fn lt(&self, other: &*mut T) -> bool { *self < *other }
495 fn le(&self, other: &*mut T) -> bool { *self <= *other }
498 fn gt(&self, other: &*mut T) -> bool { *self > *other }
501 fn ge(&self, other: &*mut T) -> bool { *self >= *other }
504 /// A wrapper around a raw `*mut T` that indicates that the possessor
505 /// of this wrapper owns the referent. This in turn implies that the
506 /// `Unique<T>` is `Send`/`Sync` if `T` is `Send`/`Sync`, unlike a raw
507 /// `*mut T` (which conveys no particular ownership semantics). It
508 /// also implies that the referent of the pointer should not be
509 /// modified without a unique path to the `Unique` reference. Useful
510 /// for building abstractions like `Vec<T>` or `Box<T>`, which
511 /// internally use raw pointers to manage the memory that they own.
512 #[unstable(feature = "unique", reason = "needs an RFC to flesh out design")]
513 pub struct Unique<T: ?Sized> {
514 pointer: NonZero<*const T>,
515 _marker: PhantomData<T>,
518 /// `Unique` pointers are `Send` if `T` is `Send` because the data they
519 /// reference is unaliased. Note that this aliasing invariant is
520 /// unenforced by the type system; the abstraction using the
521 /// `Unique` must enforce it.
522 #[unstable(feature = "unique")]
523 unsafe impl<T: Send + ?Sized> Send for Unique<T> { }
525 /// `Unique` pointers are `Sync` if `T` is `Sync` because the data they
526 /// reference is unaliased. Note that this aliasing invariant is
527 /// unenforced by the type system; the abstraction using the
528 /// `Unique` must enforce it.
529 #[unstable(feature = "unique")]
530 unsafe impl<T: Sync + ?Sized> Sync for Unique<T> { }
532 #[unstable(feature = "unique")]
533 impl<T: ?Sized> Unique<T> {
534 /// Creates a new `Unique`.
535 pub unsafe fn new(ptr: *mut T) -> Unique<T> {
536 Unique { pointer: NonZero::new(ptr), _marker: PhantomData }
539 /// Dereferences the content.
540 pub unsafe fn get(&self) -> &T {
544 /// Mutably dereferences the content.
545 pub unsafe fn get_mut(&mut self) -> &mut T {
550 #[unstable(feature = "unique")]
551 impl<T:?Sized> Deref for Unique<T> {
552 type Target = *mut T;
555 fn deref<'a>(&'a self) -> &'a *mut T {
556 unsafe { mem::transmute(&*self.pointer) }
560 #[stable(feature = "rust1", since = "1.0.0")]
561 impl<T> fmt::Pointer for Unique<T> {
562 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
563 fmt::Pointer::fmt(&*self.pointer, f)