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.
52 //! let my_num: Box<int> = box 10;
53 //! let my_num: *const int = mem::transmute(my_num);
54 //! let my_speed: Box<int> = box 88;
55 //! let my_speed: *mut int = 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<int>>(my_speed));
60 //! drop(mem::transmute::<_, Box<int>>(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 int = libc::malloc(mem::size_of::<int>() as libc::size_t) as *mut int;
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.
94 use option::Option::{mod, Some, None};
95 use kinds::{Send, Sized, Sync};
97 use cmp::{PartialEq, Eq, Ord, PartialOrd, Equiv};
98 use cmp::Ordering::{mod, Less, Equal, Greater};
100 // FIXME #19649: instrinsic docs don't render, so these have no docs :(
103 pub use intrinsics::copy_nonoverlapping_memory;
106 pub use intrinsics::copy_memory;
108 #[experimental = "uncertain about naming and semantics"]
109 pub use intrinsics::set_memory;
112 /// Creates a null raw pointer.
119 /// let p: *const int = ptr::null();
120 /// assert!(p.is_null());
124 pub fn null<T>() -> *const T { 0 as *const T }
126 /// Creates a null mutable raw pointer.
133 /// let p: *mut int = ptr::null_mut();
134 /// assert!(p.is_null());
138 pub fn null_mut<T>() -> *mut T { 0 as *mut T }
140 /// Zeroes out `count * size_of::<T>` bytes of memory at `dst`. `count` may be
145 /// Beyond accepting a raw pointer, this is unsafe because it will not drop the
146 /// contents of `dst`, and may be used to create invalid instances of `T`.
148 #[unstable = "may play a larger role in std::ptr future extensions"]
149 pub unsafe fn zero_memory<T>(dst: *mut T, count: uint) {
150 set_memory(dst, 0, count);
153 /// Swaps the values at two mutable locations of the same type, without
154 /// deinitialising either. They may overlap, unlike `mem::swap` which is
155 /// otherwise equivalent.
159 /// This is only unsafe because it accepts a raw pointer.
162 pub unsafe fn swap<T>(x: *mut T, y: *mut T) {
163 // Give ourselves some scratch space to work with
164 let mut tmp: T = mem::uninitialized();
165 let t: *mut T = &mut tmp;
168 copy_nonoverlapping_memory(t, &*x, 1);
169 copy_memory(x, &*y, 1); // `x` and `y` may overlap
170 copy_nonoverlapping_memory(y, &*t, 1);
172 // y and t now point to the same thing, but we need to completely forget `tmp`
173 // because it's no longer relevant.
177 /// Replaces the value at `dest` with `src`, returning the old
178 /// value, without dropping either.
182 /// This is only unsafe because it accepts a raw pointer.
183 /// Otherwise, this operation is identical to `mem::replace`.
186 pub unsafe fn replace<T>(dest: *mut T, mut src: T) -> T {
187 mem::swap(mem::transmute(dest), &mut src); // cannot overlap
191 /// Reads the value from `src` without dropping it. This leaves the
192 /// memory in `src` unchanged.
196 /// Beyond accepting a raw pointer, this is unsafe because it semantically
197 /// moves the value out of `src` without preventing further usage of `src`.
198 /// If `T` is not `Copy`, then care must be taken to ensure that the value at
199 /// `src` is not used before the data is overwritten again (e.g. with `write`,
200 /// `zero_memory`, or `copy_memory`). Note that `*src = foo` counts as a use
201 /// because it will attempt to drop the value previously at `*src`.
204 pub unsafe fn read<T>(src: *const T) -> T {
205 let mut tmp: T = mem::uninitialized();
206 copy_nonoverlapping_memory(&mut tmp, src, 1);
210 /// Reads the value from `src` and nulls it out without dropping it.
214 /// This is unsafe for the same reasons that `read` is unsafe.
216 #[unstable = "may play a larger role in std::ptr future extensions"]
217 pub unsafe fn read_and_zero<T>(dest: *mut T) -> T {
218 // Copy the data out from `dest`:
219 let tmp = read(&*dest);
221 // Now zero out `dest`:
222 zero_memory(dest, 1);
227 /// Overwrites a memory location with the given value without reading or
228 /// dropping the old value.
232 /// Beyond accepting a raw pointer, this operation is unsafe because it does
233 /// not drop the contents of `dst`. This could leak allocations or resources,
234 /// so care must be taken not to overwrite an object that should be dropped.
236 /// This is appropriate for initializing uninitialized memory, or overwritting
237 /// memory that has previously been `read` from.
240 pub unsafe fn write<T>(dst: *mut T, src: T) {
241 intrinsics::move_val_init(&mut *dst, src)
244 /// Methods on raw pointers
246 pub trait PtrExt: Sized {
249 /// Returns the null pointer.
250 #[deprecated = "call ptr::null instead"]
253 /// Returns true if the pointer is null.
255 fn is_null(self) -> bool;
257 /// Returns true if the pointer is not equal to the null pointer.
258 #[deprecated = "use !p.is_null() instead"]
259 fn is_not_null(self) -> bool { !self.is_null() }
261 /// Returns true if the pointer is not null.
262 #[deprecated = "use `as uint` instead"]
263 fn to_uint(self) -> uint;
265 /// Returns `None` if the pointer is null, or else returns a reference to
266 /// the value wrapped in `Some`.
270 /// While this method and its mutable counterpart are useful for
271 /// null-safety, it is important to note that this is still an unsafe
272 /// operation because the returned value could be pointing to invalid
274 #[unstable = "Option is not clearly the right return type, and we may want \
275 to tie the return lifetime to a borrow of the raw pointer"]
276 unsafe fn as_ref<'a>(&self) -> Option<&'a Self::Target>;
278 /// Calculates the offset from a pointer. `count` is in units of T; e.g. a
279 /// `count` of 3 represents a pointer offset of `3 * sizeof::<T>()` bytes.
283 /// The offset must be in-bounds of the object, or one-byte-past-the-end.
284 /// Otherwise `offset` invokes Undefined Behaviour, regardless of whether
285 /// the pointer is used.
287 unsafe fn offset(self, count: int) -> Self;
290 /// Methods on mutable raw pointers
292 pub trait MutPtrExt {
295 /// Returns `None` if the pointer is null, or else returns a mutable
296 /// reference to the value wrapped in `Some`.
300 /// As with `as_ref`, this is unsafe because it cannot verify the validity
301 /// of the returned pointer.
302 #[unstable = "Option is not clearly the right return type, and we may want \
303 to tie the return lifetime to a borrow of the raw pointer"]
304 unsafe fn as_mut<'a>(&self) -> Option<&'a mut Self::Target>;
308 impl<T> PtrExt for *const T {
312 #[deprecated = "call ptr::null instead"]
313 fn null() -> *const T { null() }
317 fn is_null(self) -> bool { self as uint == 0 }
320 #[deprecated = "use `as uint` instead"]
321 fn to_uint(self) -> uint { self as uint }
325 unsafe fn offset(self, count: int) -> *const T {
326 intrinsics::offset(self, count)
330 #[unstable = "return value does not necessarily convey all possible \
332 unsafe fn as_ref<'a>(&self) -> Option<&'a T> {
342 impl<T> PtrExt for *mut T {
346 #[deprecated = "call ptr::null instead"]
347 fn null() -> *mut T { null_mut() }
351 fn is_null(self) -> bool { self as uint == 0 }
354 #[deprecated = "use `as uint` instead"]
355 fn to_uint(self) -> uint { self as uint }
359 unsafe fn offset(self, count: int) -> *mut T {
360 intrinsics::offset(self as *const T, count) as *mut T
364 #[unstable = "return value does not necessarily convey all possible \
366 unsafe fn as_ref<'a>(&self) -> Option<&'a T> {
376 impl<T> MutPtrExt for *mut T {
380 #[unstable = "return value does not necessarily convey all possible \
382 unsafe fn as_mut<'a>(&self) -> Option<&'a mut T> {
391 // Equality for pointers
393 impl<T> PartialEq for *const T {
395 fn eq(&self, other: &*const T) -> bool {
399 fn ne(&self, other: &*const T) -> bool { !self.eq(other) }
403 impl<T> Eq for *const T {}
406 impl<T> PartialEq for *mut T {
408 fn eq(&self, other: &*mut T) -> bool {
412 fn ne(&self, other: &*mut T) -> bool { !self.eq(other) }
416 impl<T> Eq for *mut T {}
418 // Equivalence for pointers
420 #[deprecated = "Use overloaded `core::cmp::PartialEq`"]
421 impl<T> Equiv<*mut T> for *const T {
422 fn equiv(&self, other: &*mut T) -> bool {
423 self.to_uint() == other.to_uint()
428 #[deprecated = "Use overloaded `core::cmp::PartialEq`"]
429 impl<T> Equiv<*const T> for *mut T {
430 fn equiv(&self, other: &*const T) -> bool {
431 self.to_uint() == other.to_uint()
436 impl<T> Clone for *const T {
438 fn clone(&self) -> *const T {
444 impl<T> Clone for *mut T {
446 fn clone(&self) -> *mut T {
451 // Equality for extern "C" fn pointers
452 mod externfnpointers {
457 impl<_R> PartialEq for extern "C" fn() -> _R {
459 fn eq(&self, other: &extern "C" fn() -> _R) -> bool {
460 let self_: *const () = unsafe { mem::transmute(*self) };
461 let other_: *const () = unsafe { mem::transmute(*other) };
465 macro_rules! fnptreq {
468 impl<_R,$($p),*> PartialEq for extern "C" fn($($p),*) -> _R {
470 fn eq(&self, other: &extern "C" fn($($p),*) -> _R) -> bool {
471 let self_: *const () = unsafe { mem::transmute(*self) };
473 let other_: *const () = unsafe { mem::transmute(*other) };
483 fnptreq! { A,B,C,D,E }
486 // Comparison for pointers
488 impl<T> Ord for *const T {
490 fn cmp(&self, other: &*const T) -> Ordering {
493 } else if self == other {
502 impl<T> PartialOrd for *const T {
504 fn partial_cmp(&self, other: &*const T) -> Option<Ordering> {
505 Some(self.cmp(other))
509 fn lt(&self, other: &*const T) -> bool { *self < *other }
512 fn le(&self, other: &*const T) -> bool { *self <= *other }
515 fn gt(&self, other: &*const T) -> bool { *self > *other }
518 fn ge(&self, other: &*const T) -> bool { *self >= *other }
522 impl<T> Ord for *mut T {
524 fn cmp(&self, other: &*mut T) -> Ordering {
527 } else if self == other {
536 impl<T> PartialOrd for *mut T {
538 fn partial_cmp(&self, other: &*mut T) -> Option<Ordering> {
539 Some(self.cmp(other))
543 fn lt(&self, other: &*mut T) -> bool { *self < *other }
546 fn le(&self, other: &*mut T) -> bool { *self <= *other }
549 fn gt(&self, other: &*mut T) -> bool { *self > *other }
552 fn ge(&self, other: &*mut T) -> bool { *self >= *other }
555 /// A wrapper around a raw `*mut T` that indicates that the possessor
556 /// of this wrapper owns the referent. This in turn implies that the
557 /// `Unique<T>` is `Send`/`Sync` if `T` is `Send`/`Sync`, unlike a
558 /// raw `*mut T` (which conveys no particular ownership semantics).
559 /// Useful for building abstractions like `Vec<T>` or `Box<T>`, which
560 /// internally use raw pointers to manage the memory that they own.
561 #[unstable = "recently added to this module"]
562 pub struct Unique<T>(pub *mut T);
564 /// `Unique` pointers are `Send` if `T` is `Send` because the data they
565 /// reference is unaliased. Note that this aliasing invariant is
566 /// unenforced by the type system; the abstraction using the
567 /// `Unique` must enforce it.
568 #[unstable = "recently added to this module"]
569 unsafe impl<T:Send> Send for Unique<T> { }
571 /// `Unique` pointers are `Sync` if `T` is `Sync` because the data they
572 /// reference is unaliased. Note that this aliasing invariant is
573 /// unenforced by the type system; the abstraction using the
574 /// `Unique` must enforce it.
575 #[unstable = "recently added to this module"]
576 unsafe impl<T:Sync> Sync for Unique<T> { }
579 /// Returns a null Unique.
580 #[unstable = "recently added to this module"]
581 pub fn null() -> Unique<T> {
585 /// Return an (unsafe) pointer into the memory owned by `self`.
586 #[unstable = "recently added to this module"]
587 pub unsafe fn offset(self, offset: int) -> *mut T {
588 self.0.offset(offset)