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: i32 = 10;
31 //! let my_num_ptr: *const i32 = &my_num;
32 //! let mut my_speed: i32 = 88;
33 //! let my_speed_ptr: *mut i32 = &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.
52 //! let my_num: Box<i32> = Box::new(10);
53 //! let my_num: *const i32 = mem::transmute(my_num);
54 //! let my_speed: Box<i32> = Box::new(88);
55 //! let my_speed: *mut i32 = mem::transmute(my_speed);
57 //! // By taking ownership of the original `Box<T>` though
58 //! // we are obligated to transmute it back later to be destroyed.
59 //! drop(mem::transmute::<_, Box<i32>>(my_speed));
60 //! drop(mem::transmute::<_, Box<i32>>(my_num));
64 //! Note that here the call to `drop` is for clarity - it indicates
65 //! that we are done with the given value and it should be destroyed.
67 //! ## 3. Get it from C.
70 //! extern crate libc;
76 //! let my_num: *mut i32 = libc::malloc(mem::size_of::<i32>() as libc::size_t) as *mut i32;
77 //! if my_num.is_null() {
78 //! panic!("failed to allocate memory");
80 //! libc::free(my_num as *mut libc::c_void);
85 //! Usually you wouldn't literally use `malloc` and `free` from Rust,
86 //! but C APIs hand out a lot of pointers generally, so are a common source
87 //! of unsafe pointers in Rust.
89 #![stable(feature = "rust1", since = "1.0.0")]
94 use option::Option::{self, Some, None};
95 use marker::{self, Send, Sized, Sync};
97 use cmp::{PartialEq, Eq, Ord, PartialOrd};
98 use cmp::Ordering::{self, Less, Equal, Greater};
100 // FIXME #19649: intrinsic docs don't render, so these have no docs :(
102 #[unstable(feature = "core")]
103 pub use intrinsics::copy_nonoverlapping_memory;
105 #[unstable(feature = "core")]
106 pub use intrinsics::copy_memory;
108 #[unstable(feature = "core",
109 reason = "uncertain about naming and semantics")]
110 pub use intrinsics::set_memory;
113 /// Creates a null raw pointer.
120 /// let p: *const i32 = ptr::null();
121 /// assert!(p.is_null());
124 #[stable(feature = "rust1", since = "1.0.0")]
125 pub fn null<T>() -> *const T { 0 as *const T }
127 /// Creates a null mutable raw pointer.
134 /// let p: *mut i32 = ptr::null_mut();
135 /// assert!(p.is_null());
138 #[stable(feature = "rust1", since = "1.0.0")]
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(feature = "core",
150 reason = "may play a larger role in std::ptr future extensions")]
151 pub unsafe fn zero_memory<T>(dst: *mut T, count: usize) {
152 set_memory(dst, 0, count);
155 /// Swaps the values at two mutable locations of the same type, without
156 /// deinitialising either. They may overlap, unlike `mem::swap` which is
157 /// otherwise equivalent.
161 /// This is only unsafe because it accepts a raw pointer.
163 #[stable(feature = "rust1", since = "1.0.0")]
164 pub unsafe fn swap<T>(x: *mut T, y: *mut T) {
165 // Give ourselves some scratch space to work with
166 let mut tmp: T = mem::uninitialized();
167 let t: *mut T = &mut tmp;
170 copy_nonoverlapping_memory(t, &*x, 1);
171 copy_memory(x, &*y, 1); // `x` and `y` may overlap
172 copy_nonoverlapping_memory(y, &*t, 1);
174 // y and t now point to the same thing, but we need to completely forget `tmp`
175 // because it's no longer relevant.
179 /// Replaces the value at `dest` with `src`, returning the old
180 /// value, without dropping either.
184 /// This is only unsafe because it accepts a raw pointer.
185 /// Otherwise, this operation is identical to `mem::replace`.
187 #[stable(feature = "rust1", since = "1.0.0")]
188 pub unsafe fn replace<T>(dest: *mut T, mut src: T) -> T {
189 mem::swap(mem::transmute(dest), &mut src); // cannot overlap
193 /// Reads the value from `src` without moving it. This leaves the
194 /// memory in `src` unchanged.
198 /// Beyond accepting a raw pointer, this is unsafe because it semantically
199 /// moves the value out of `src` without preventing further usage of `src`.
200 /// If `T` is not `Copy`, then care must be taken to ensure that the value at
201 /// `src` is not used before the data is overwritten again (e.g. with `write`,
202 /// `zero_memory`, or `copy_memory`). Note that `*src = foo` counts as a use
203 /// because it will attempt to drop the value previously at `*src`.
205 #[stable(feature = "rust1", since = "1.0.0")]
206 pub unsafe fn read<T>(src: *const T) -> T {
207 let mut tmp: T = mem::uninitialized();
208 copy_nonoverlapping_memory(&mut tmp, src, 1);
212 /// Reads the value from `src` and nulls it out without dropping it.
216 /// This is unsafe for the same reasons that `read` is unsafe.
218 #[unstable(feature = "core",
219 reason = "may play a larger role in std::ptr future extensions")]
220 pub unsafe fn read_and_zero<T>(dest: *mut T) -> T {
221 // Copy the data out from `dest`:
222 let tmp = read(&*dest);
224 // Now zero out `dest`:
225 zero_memory(dest, 1);
230 /// Overwrites a memory location with the given value without reading or
231 /// dropping the old value.
235 /// Beyond accepting a raw pointer, this operation is unsafe because it does
236 /// not drop the contents of `dst`. This could leak allocations or resources,
237 /// so care must be taken not to overwrite an object that should be dropped.
239 /// This is appropriate for initializing uninitialized memory, or overwriting
240 /// memory that has previously been `read` from.
242 #[stable(feature = "rust1", since = "1.0.0")]
243 pub unsafe fn write<T>(dst: *mut T, src: T) {
244 intrinsics::move_val_init(&mut *dst, src)
247 /// Methods on raw pointers
248 #[stable(feature = "rust1", since = "1.0.0")]
249 pub trait PtrExt: Sized {
252 /// Returns true if the pointer is null.
253 #[stable(feature = "rust1", since = "1.0.0")]
254 fn is_null(self) -> bool;
256 /// Returns `None` if the pointer is null, or else returns a reference to
257 /// the value wrapped in `Some`.
261 /// While this method and its mutable counterpart are useful for
262 /// null-safety, it is important to note that this is still an unsafe
263 /// operation because the returned value could be pointing to invalid
265 #[unstable(feature = "core",
266 reason = "Option is not clearly the right return type, and we may want \
267 to tie the return lifetime to a borrow of the raw pointer")]
268 unsafe fn as_ref<'a>(&self) -> Option<&'a Self::Target>;
270 /// Calculates the offset from a pointer. `count` is in units of T; e.g. a
271 /// `count` of 3 represents a pointer offset of `3 * sizeof::<T>()` bytes.
275 /// The offset must be in-bounds of the object, or one-byte-past-the-end.
276 /// Otherwise `offset` invokes Undefined Behaviour, regardless of whether
277 /// the pointer is used.
278 #[stable(feature = "rust1", since = "1.0.0")]
279 unsafe fn offset(self, count: isize) -> Self;
282 /// Methods on mutable raw pointers
283 #[stable(feature = "rust1", since = "1.0.0")]
284 pub trait MutPtrExt {
287 /// Returns `None` if the pointer is null, or else returns a mutable
288 /// reference to the value wrapped in `Some`.
292 /// As with `as_ref`, this is unsafe because it cannot verify the validity
293 /// of the returned pointer.
294 #[unstable(feature = "core",
295 reason = "Option is not clearly the right return type, and we may want \
296 to tie the return lifetime to a borrow of the raw pointer")]
297 unsafe fn as_mut<'a>(&self) -> Option<&'a mut Self::Target>;
300 #[stable(feature = "rust1", since = "1.0.0")]
301 impl<T> PtrExt for *const T {
305 #[stable(feature = "rust1", since = "1.0.0")]
306 fn is_null(self) -> bool { self as usize == 0 }
309 #[stable(feature = "rust1", since = "1.0.0")]
310 unsafe fn offset(self, count: isize) -> *const T {
311 intrinsics::offset(self, count)
315 #[unstable(feature = "core",
316 reason = "return value does not necessarily convey all possible \
318 unsafe fn as_ref<'a>(&self) -> Option<&'a T> {
327 #[stable(feature = "rust1", since = "1.0.0")]
328 impl<T> PtrExt for *mut T {
332 #[stable(feature = "rust1", since = "1.0.0")]
333 fn is_null(self) -> bool { self as usize == 0 }
336 #[stable(feature = "rust1", since = "1.0.0")]
337 unsafe fn offset(self, count: isize) -> *mut T {
338 intrinsics::offset(self, count) as *mut T
342 #[unstable(feature = "core",
343 reason = "return value does not necessarily convey all possible \
345 unsafe fn as_ref<'a>(&self) -> Option<&'a T> {
354 #[stable(feature = "rust1", since = "1.0.0")]
355 impl<T> MutPtrExt for *mut T {
359 #[unstable(feature = "core",
360 reason = "return value does not necessarily convey all possible \
362 unsafe fn as_mut<'a>(&self) -> Option<&'a mut T> {
371 // Equality for pointers
372 #[stable(feature = "rust1", since = "1.0.0")]
373 impl<T> PartialEq for *const T {
375 fn eq(&self, other: &*const T) -> bool {
379 fn ne(&self, other: &*const T) -> bool { !self.eq(other) }
382 #[stable(feature = "rust1", since = "1.0.0")]
383 impl<T> Eq for *const T {}
385 #[stable(feature = "rust1", since = "1.0.0")]
386 impl<T> PartialEq for *mut T {
388 fn eq(&self, other: &*mut T) -> bool {
392 fn ne(&self, other: &*mut T) -> bool { !self.eq(other) }
395 #[stable(feature = "rust1", since = "1.0.0")]
396 impl<T> Eq for *mut T {}
398 #[stable(feature = "rust1", since = "1.0.0")]
399 impl<T> Clone for *const T {
401 fn clone(&self) -> *const T {
406 #[stable(feature = "rust1", since = "1.0.0")]
407 impl<T> 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> 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> 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> 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> 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
521 /// raw `*mut T` (which conveys no particular ownership semantics).
522 /// Useful for building abstractions like `Vec<T>` or `Box<T>`, which
523 /// internally use raw pointers to manage the memory that they own.
524 #[unstable(feature = "core", reason = "recently added to this module")]
525 pub struct Unique<T: ?Sized> {
526 /// The wrapped `*mut T`.
528 _own: marker::PhantomData<T>,
531 /// `Unique` pointers are `Send` if `T` is `Send` because the data they
532 /// reference is unaliased. Note that this aliasing invariant is
533 /// unenforced by the type system; the abstraction using the
534 /// `Unique` must enforce it.
535 #[unstable(feature = "core", reason = "recently added to this module")]
536 unsafe impl<T: Send + ?Sized> Send for Unique<T> { }
538 /// `Unique` pointers are `Sync` if `T` is `Sync` because the data they
539 /// reference is unaliased. Note that this aliasing invariant is
540 /// unenforced by the type system; the abstraction using the
541 /// `Unique` must enforce it.
542 #[unstable(feature = "core", reason = "recently added to this module")]
543 unsafe impl<T: Sync + ?Sized> Sync for Unique<T> { }
546 /// Returns a null Unique.
547 #[unstable(feature = "core",
548 reason = "recently added to this module")]
549 pub fn null() -> Unique<T> {
553 /// Return an (unsafe) pointer into the memory owned by `self`.
554 #[unstable(feature = "core",
555 reason = "recently added to this module")]
556 pub unsafe fn offset(self, offset: isize) -> *mut T {
557 self.ptr.offset(offset)
561 /// Creates a `Unique` wrapped around `ptr`, taking ownership of the
562 /// data referenced by `ptr`.
563 #[allow(non_snake_case)]
564 pub fn Unique<T: ?Sized>(ptr: *mut T) -> Unique<T> {
565 Unique { ptr: ptr, _own: marker::PhantomData }