rust/src/libcore/ptr.rs
Alex Crichton 748bc3ca49 std: Rename {Eq,Ord} to Partial{Eq,Ord}
This is part of the ongoing renaming of the equality traits. See #12517 for more
details. All code using Eq/Ord will temporarily need to move to Partial{Eq,Ord}
or the Total{Eq,Ord} traits. The Total traits will soon be renamed to {Eq,Ord}.

cc #12517

[breaking-change]
2014-05-30 15:52:24 -07:00

727 lines
20 KiB
Rust

// Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
// FIXME: talk about offset, copy_memory, copy_nonoverlapping_memory
//! Operations on unsafe pointers, `*T`, and `*mut T`.
//!
//! Working with unsafe pointers in Rust is uncommon,
//! typically limited to a few patterns.
//!
//! Use the [`null` function](fn.null.html) to create null pointers,
//! the [`is_null`](trait.RawPtr.html#tymethod.is_null)
//! and [`is_not_null`](trait.RawPtr.html#method.is_not_null)
//! methods of the [`RawPtr` trait](trait.RawPtr.html) to check for null.
//! The `RawPtr` trait is imported by the prelude, so `is_null` etc.
//! work everywhere. The `RawPtr` also defines the `offset` method,
//! for pointer math.
//!
//! # Common ways to create unsafe pointers
//!
//! ## 1. Coerce a reference (`&T`) or mutable reference (`&mut T`).
//!
//! ```
//! let my_num: int = 10;
//! let my_num_ptr: *int = &my_num;
//! let mut my_speed: int = 88;
//! let my_speed_ptr: *mut int = &mut my_speed;
//! ```
//!
//! This does not take ownership of the original allocation
//! and requires no resource management later,
//! but you must not use the pointer after its lifetime.
//!
//! ## 2. Transmute an owned box (`Box<T>`).
//!
//! The `transmute` function takes, by value, whatever it's given
//! and returns it as whatever type is requested, as long as the
//! types are the same size. Because `Box<T>` and `*T` have the same
//! representation they can be trivially,
//! though unsafely, transformed from one type to the other.
//!
//! ```
//! use std::mem;
//!
//! unsafe {
//! let my_num: Box<int> = box 10;
//! let my_num: *int = mem::transmute(my_num);
//! let my_speed: Box<int> = box 88;
//! let my_speed: *mut int = mem::transmute(my_speed);
//!
//! // By taking ownership of the original `Box<T>` though
//! // we are obligated to transmute it back later to be destroyed.
//! drop(mem::transmute::<_, Box<int>>(my_speed));
//! drop(mem::transmute::<_, Box<int>>(my_num));
//! }
//! ```
//!
//! Note that here the call to `drop` is for clarity - it indicates
//! that we are done with the given value and it should be destroyed.
//!
//! ## 3. Get it from C.
//!
//! ```
//! extern crate libc;
//!
//! use std::mem;
//!
//! fn main() {
//! unsafe {
//! let my_num: *mut int = libc::malloc(mem::size_of::<int>() as libc::size_t) as *mut int;
//! if my_num.is_null() {
//! fail!("failed to allocate memory");
//! }
//! libc::free(my_num as *mut libc::c_void);
//! }
//! }
//! ```
//!
//! Usually you wouldn't literally use `malloc` and `free` from Rust,
//! but C APIs hand out a lot of pointers generally, so are a common source
//! of unsafe pointers in Rust.
use mem;
use clone::Clone;
use intrinsics;
use iter::{range, Iterator};
use option::{Some, None, Option};
#[cfg(not(test))] use cmp::{PartialEq, TotalEq, PartialOrd, Equiv};
/// Return the offset of the first null pointer in `buf`.
#[inline]
pub unsafe fn buf_len<T>(buf: **T) -> uint {
position(buf, |i| *i == null())
}
impl<T> Clone for *T {
#[inline]
fn clone(&self) -> *T {
*self
}
}
impl<T> Clone for *mut T {
#[inline]
fn clone(&self) -> *mut T {
*self
}
}
/// Return the first offset `i` such that `f(buf[i]) == true`.
#[inline]
pub unsafe fn position<T>(buf: *T, f: |&T| -> bool) -> uint {
let mut i = 0;
loop {
if f(&(*buf.offset(i as int))) { return i; }
else { i += 1; }
}
}
/// Create a null pointer.
///
/// # Example
///
/// ```
/// use std::ptr;
///
/// let p: *int = ptr::null();
/// assert!(p.is_null());
/// ```
#[inline]
pub fn null<T>() -> *T { 0 as *T }
/// Create an unsafe mutable null pointer.
///
/// # Example
///
/// ```
/// use std::ptr;
///
/// let p: *mut int = ptr::mut_null();
/// assert!(p.is_null());
/// ```
#[inline]
pub fn mut_null<T>() -> *mut T { 0 as *mut T }
/// Copies data from one location to another.
///
/// Copies `count` elements (not bytes) from `src` to `dst`. The source
/// and destination may overlap.
///
/// `copy_memory` is semantically equivalent to C's `memmove`.
///
/// # Example
///
/// Efficiently create a Rust vector from an unsafe buffer:
///
/// ```
/// use std::ptr;
///
/// unsafe fn from_buf_raw<T>(ptr: *T, elts: uint) -> Vec<T> {
/// let mut dst = Vec::with_capacity(elts);
/// dst.set_len(elts);
/// ptr::copy_memory(dst.as_mut_ptr(), ptr, elts);
/// dst
/// }
/// ```
///
#[inline]
pub unsafe fn copy_memory<T>(dst: *mut T, src: *T, count: uint) {
intrinsics::copy_memory(dst, src, count)
}
/// Copies data from one location to another.
///
/// Copies `count` elements (not bytes) from `src` to `dst`. The source
/// and destination may *not* overlap.
///
/// `copy_nonoverlapping_memory` is semantically equivalent to C's `memcpy`.
///
/// # Example
///
/// A safe swap function:
///
/// ```
/// use std::mem;
/// use std::ptr;
///
/// fn swap<T>(x: &mut T, y: &mut T) {
/// unsafe {
/// // Give ourselves some scratch space to work with
/// let mut t: T = mem::uninitialized();
///
/// // Perform the swap, `&mut` pointers never alias
/// ptr::copy_nonoverlapping_memory(&mut t, &*x, 1);
/// ptr::copy_nonoverlapping_memory(x, &*y, 1);
/// ptr::copy_nonoverlapping_memory(y, &t, 1);
///
/// // y and t now point to the same thing, but we need to completely forget `tmp`
/// // because it's no longer relevant.
/// mem::forget(t);
/// }
/// }
/// ```
///
/// # Safety Note
///
/// If the source and destination overlap then the behavior of this
/// function is undefined.
#[inline]
pub unsafe fn copy_nonoverlapping_memory<T>(dst: *mut T,
src: *T,
count: uint) {
intrinsics::copy_nonoverlapping_memory(dst, src, count)
}
/// Invokes memset on the specified pointer, setting `count * size_of::<T>()`
/// bytes of memory starting at `dst` to `c`.
#[inline]
pub unsafe fn set_memory<T>(dst: *mut T, c: u8, count: uint) {
intrinsics::set_memory(dst, c, count)
}
/// Zeroes out `count * size_of::<T>` bytes of memory at `dst`
#[inline]
pub unsafe fn zero_memory<T>(dst: *mut T, count: uint) {
set_memory(dst, 0, count);
}
/// Swap the values at two mutable locations of the same type, without
/// deinitialising either. They may overlap.
#[inline]
pub unsafe fn swap<T>(x: *mut T, y: *mut T) {
// Give ourselves some scratch space to work with
let mut tmp: T = mem::uninitialized();
let t: *mut T = &mut tmp;
// Perform the swap
copy_nonoverlapping_memory(t, &*x, 1);
copy_memory(x, &*y, 1); // `x` and `y` may overlap
copy_nonoverlapping_memory(y, &*t, 1);
// y and t now point to the same thing, but we need to completely forget `tmp`
// because it's no longer relevant.
mem::forget(tmp);
}
/// Replace the value at a mutable location with a new one, returning the old
/// value, without deinitialising either.
#[inline]
pub unsafe fn replace<T>(dest: *mut T, mut src: T) -> T {
mem::swap(mem::transmute(dest), &mut src); // cannot overlap
src
}
/// Reads the value from `*src` and returns it.
#[inline(always)]
pub unsafe fn read<T>(src: *T) -> T {
let mut tmp: T = mem::uninitialized();
copy_nonoverlapping_memory(&mut tmp, src, 1);
tmp
}
/// Reads the value from `*src` and nulls it out.
/// This currently prevents destructors from executing.
#[inline(always)]
pub unsafe fn read_and_zero<T>(dest: *mut T) -> T {
// Copy the data out from `dest`:
let tmp = read(&*dest);
// Now zero out `dest`:
zero_memory(dest, 1);
tmp
}
/// Given a **T (pointer to an array of pointers),
/// iterate through each *T, up to the provided `len`,
/// passing to the provided callback function
pub unsafe fn array_each_with_len<T>(arr: **T, len: uint, cb: |*T|) {
if arr.is_null() {
fail!("ptr::array_each_with_len failure: arr input is null pointer");
}
//let start_ptr = *arr;
for e in range(0, len) {
let n = arr.offset(e as int);
cb(*n);
}
}
/// Given a null-pointer-terminated **T (pointer to
/// an array of pointers), iterate through each *T,
/// passing to the provided callback function
///
/// # Safety Note
///
/// This will only work with a null-terminated
/// pointer array.
pub unsafe fn array_each<T>(arr: **T, cb: |*T|) {
if arr.is_null() {
fail!("ptr::array_each_with_len failure: arr input is null pointer");
}
let len = buf_len(arr);
array_each_with_len(arr, len, cb);
}
/// Methods on raw pointers
pub trait RawPtr<T> {
/// Returns the null pointer.
fn null() -> Self;
/// Returns true if the pointer is equal to the null pointer.
fn is_null(&self) -> bool;
/// Returns true if the pointer is not equal to the null pointer.
fn is_not_null(&self) -> bool { !self.is_null() }
/// Returns the value of this pointer (ie, the address it points to)
fn to_uint(&self) -> uint;
/// Returns `None` if the pointer is null, or else returns the value wrapped
/// in `Some`.
///
/// # Safety Notes
///
/// While this method is useful for null-safety, it is important to note
/// that this is still an unsafe operation because the returned value could
/// be pointing to invalid memory.
unsafe fn to_option(&self) -> Option<&T>;
/// Calculates the offset from a pointer. The offset *must* be in-bounds of
/// the object, or one-byte-past-the-end. `count` is in units of T; e.g. a
/// `count` of 3 represents a pointer offset of `3 * sizeof::<T>()` bytes.
unsafe fn offset(self, count: int) -> Self;
}
impl<T> RawPtr<T> for *T {
#[inline]
fn null() -> *T { null() }
#[inline]
fn is_null(&self) -> bool { *self == RawPtr::null() }
#[inline]
fn to_uint(&self) -> uint { *self as uint }
#[inline]
unsafe fn offset(self, count: int) -> *T { intrinsics::offset(self, count) }
#[inline]
unsafe fn to_option(&self) -> Option<&T> {
if self.is_null() {
None
} else {
Some(&**self)
}
}
}
impl<T> RawPtr<T> for *mut T {
#[inline]
fn null() -> *mut T { mut_null() }
#[inline]
fn is_null(&self) -> bool { *self == RawPtr::null() }
#[inline]
fn to_uint(&self) -> uint { *self as uint }
#[inline]
unsafe fn offset(self, count: int) -> *mut T {
intrinsics::offset(self as *T, count) as *mut T
}
#[inline]
unsafe fn to_option(&self) -> Option<&T> {
if self.is_null() {
None
} else {
Some(&**self)
}
}
}
// Equality for pointers
#[cfg(not(test))]
impl<T> PartialEq for *T {
#[inline]
fn eq(&self, other: &*T) -> bool {
*self == *other
}
#[inline]
fn ne(&self, other: &*T) -> bool { !self.eq(other) }
}
#[cfg(not(test))]
impl<T> TotalEq for *T {}
#[cfg(not(test))]
impl<T> PartialEq for *mut T {
#[inline]
fn eq(&self, other: &*mut T) -> bool {
*self == *other
}
#[inline]
fn ne(&self, other: &*mut T) -> bool { !self.eq(other) }
}
#[cfg(not(test))]
impl<T> TotalEq for *mut T {}
// Equivalence for pointers
#[cfg(not(test))]
impl<T> Equiv<*mut T> for *T {
fn equiv(&self, other: &*mut T) -> bool {
self.to_uint() == other.to_uint()
}
}
#[cfg(not(test))]
impl<T> Equiv<*T> for *mut T {
fn equiv(&self, other: &*T) -> bool {
self.to_uint() == other.to_uint()
}
}
// Equality for extern "C" fn pointers
#[cfg(not(test))]
mod externfnpointers {
use mem;
use cmp::PartialEq;
impl<_R> PartialEq for extern "C" fn() -> _R {
#[inline]
fn eq(&self, other: &extern "C" fn() -> _R) -> bool {
let self_: *() = unsafe { mem::transmute(*self) };
let other_: *() = unsafe { mem::transmute(*other) };
self_ == other_
}
}
macro_rules! fnptreq(
($($p:ident),*) => {
impl<_R,$($p),*> PartialEq for extern "C" fn($($p),*) -> _R {
#[inline]
fn eq(&self, other: &extern "C" fn($($p),*) -> _R) -> bool {
let self_: *() = unsafe { mem::transmute(*self) };
let other_: *() = unsafe { mem::transmute(*other) };
self_ == other_
}
}
}
)
fnptreq!(A)
fnptreq!(A,B)
fnptreq!(A,B,C)
fnptreq!(A,B,C,D)
fnptreq!(A,B,C,D,E)
}
// Comparison for pointers
#[cfg(not(test))]
impl<T> PartialOrd for *T {
#[inline]
fn lt(&self, other: &*T) -> bool { *self < *other }
}
#[cfg(not(test))]
impl<T> PartialOrd for *mut T {
#[inline]
fn lt(&self, other: &*mut T) -> bool { *self < *other }
}
#[cfg(test)]
pub mod ptr_tests {
use super::*;
use prelude::*;
use realstd::c_str::ToCStr;
use mem;
use libc;
use realstd::str;
use realstd::str::Str;
use slice::{ImmutableVector, MutableVector};
#[test]
fn test() {
unsafe {
struct Pair {
fst: int,
snd: int
};
let mut p = Pair {fst: 10, snd: 20};
let pptr: *mut Pair = &mut p;
let iptr: *mut int = mem::transmute(pptr);
assert_eq!(*iptr, 10);
*iptr = 30;
assert_eq!(*iptr, 30);
assert_eq!(p.fst, 30);
*pptr = Pair {fst: 50, snd: 60};
assert_eq!(*iptr, 50);
assert_eq!(p.fst, 50);
assert_eq!(p.snd, 60);
let v0 = box [32000u16, 32001u16, 32002u16];
let mut v1 = box [0u16, 0u16, 0u16];
copy_memory(v1.as_mut_ptr().offset(1),
v0.as_ptr().offset(1), 1);
assert!((v1[0] == 0u16 && v1[1] == 32001u16 && v1[2] == 0u16));
copy_memory(v1.as_mut_ptr(),
v0.as_ptr().offset(2), 1);
assert!((v1[0] == 32002u16 && v1[1] == 32001u16 &&
v1[2] == 0u16));
copy_memory(v1.as_mut_ptr().offset(2),
v0.as_ptr(), 1u);
assert!((v1[0] == 32002u16 && v1[1] == 32001u16 &&
v1[2] == 32000u16));
}
}
#[test]
fn test_position() {
use libc::c_char;
"hello".with_c_str(|p| {
unsafe {
assert!(2u == position(p, |c| *c == 'l' as c_char));
assert!(4u == position(p, |c| *c == 'o' as c_char));
assert!(5u == position(p, |c| *c == 0 as c_char));
}
})
}
#[test]
fn test_buf_len() {
"hello".with_c_str(|p0| {
"there".with_c_str(|p1| {
"thing".with_c_str(|p2| {
let v = box [p0, p1, p2, null()];
unsafe {
assert_eq!(buf_len(v.as_ptr()), 3u);
}
})
})
})
}
#[test]
fn test_is_null() {
let p: *int = null();
assert!(p.is_null());
assert!(!p.is_not_null());
let q = unsafe { p.offset(1) };
assert!(!q.is_null());
assert!(q.is_not_null());
let mp: *mut int = mut_null();
assert!(mp.is_null());
assert!(!mp.is_not_null());
let mq = unsafe { mp.offset(1) };
assert!(!mq.is_null());
assert!(mq.is_not_null());
}
#[test]
fn test_to_option() {
unsafe {
let p: *int = null();
assert_eq!(p.to_option(), None);
let q: *int = &2;
assert_eq!(q.to_option().unwrap(), &2);
let p: *mut int = mut_null();
assert_eq!(p.to_option(), None);
let q: *mut int = &mut 2;
assert_eq!(q.to_option().unwrap(), &2);
}
}
#[test]
fn test_ptr_addition() {
unsafe {
let xs = box [5, ..16];
let mut ptr = xs.as_ptr();
let end = ptr.offset(16);
while ptr < end {
assert_eq!(*ptr, 5);
ptr = ptr.offset(1);
}
let mut xs_mut = xs.clone();
let mut m_ptr = xs_mut.as_mut_ptr();
let m_end = m_ptr.offset(16);
while m_ptr < m_end {
*m_ptr += 5;
m_ptr = m_ptr.offset(1);
}
assert_eq!(xs_mut, box [10, ..16]);
}
}
#[test]
fn test_ptr_subtraction() {
unsafe {
let xs = box [0,1,2,3,4,5,6,7,8,9];
let mut idx = 9i8;
let ptr = xs.as_ptr();
while idx >= 0i8 {
assert_eq!(*(ptr.offset(idx as int)), idx as int);
idx = idx - 1i8;
}
let mut xs_mut = xs.clone();
let m_start = xs_mut.as_mut_ptr();
let mut m_ptr = m_start.offset(9);
while m_ptr >= m_start {
*m_ptr += *m_ptr;
m_ptr = m_ptr.offset(-1);
}
assert_eq!(xs_mut, box [0,2,4,6,8,10,12,14,16,18]);
}
}
#[test]
fn test_ptr_array_each_with_len() {
unsafe {
let one = "oneOne".to_c_str();
let two = "twoTwo".to_c_str();
let three = "threeThree".to_c_str();
let arr = box [
one.with_ref(|buf| buf),
two.with_ref(|buf| buf),
three.with_ref(|buf| buf),
];
let expected_arr = [
one, two, three
];
let mut ctr = 0;
let mut iteration_count = 0;
array_each_with_len(arr.as_ptr(), arr.len(), |e| {
let actual = str::raw::from_c_str(e);
let expected = expected_arr[ctr].with_ref(|buf| {
str::raw::from_c_str(buf)
});
assert_eq!(actual.as_slice(), expected.as_slice());
ctr += 1;
iteration_count += 1;
});
assert_eq!(iteration_count, 3u);
}
}
#[test]
fn test_ptr_array_each() {
unsafe {
let one = "oneOne".to_c_str();
let two = "twoTwo".to_c_str();
let three = "threeThree".to_c_str();
let arr = box [
one.with_ref(|buf| buf),
two.with_ref(|buf| buf),
three.with_ref(|buf| buf),
// fake a null terminator
null(),
];
let expected_arr = [
one, two, three
];
let arr_ptr = arr.as_ptr();
let mut ctr = 0;
let mut iteration_count = 0;
array_each(arr_ptr, |e| {
let actual = str::raw::from_c_str(e);
let expected = expected_arr[ctr].with_ref(|buf| {
str::raw::from_c_str(buf)
});
assert_eq!(actual.as_slice(), expected.as_slice());
ctr += 1;
iteration_count += 1;
});
assert_eq!(iteration_count, 3);
}
}
#[test]
#[should_fail]
fn test_ptr_array_each_with_len_null_ptr() {
unsafe {
array_each_with_len(0 as **libc::c_char, 1, |e| {
str::raw::from_c_str(e);
});
}
}
#[test]
#[should_fail]
fn test_ptr_array_each_null_ptr() {
unsafe {
array_each(0 as **libc::c_char, |e| {
str::raw::from_c_str(e);
});
}
}
#[test]
fn test_set_memory() {
let mut xs = [0u8, ..20];
let ptr = xs.as_mut_ptr();
unsafe { set_memory(ptr, 5u8, xs.len()); }
assert!(xs == [5u8, ..20]);
}
}