1.0.0[−][src]Module std::ptr
Manually manage memory through raw pointers.
See also the pointer primitive types.
Safety
Many functions in this module take raw pointers as arguments and read from
or write to them. For this to be safe, these pointers must be valid.
Whether a pointer is valid depends on the operation it is used for
(read or write), and the extent of the memory that is accessed (i.e.,
how many bytes are read/written). Most functions use *mut T
and *const T
to access only a single value, in which case the documentation omits the size
and implicitly assumes it to be size_of::<T>()
bytes.
The precise rules for validity are not determined yet. The guarantees that are provided at this point are very minimal:
- A null pointer is never valid, not even for accesses of size zero.
- All pointers (except for the null pointer) are valid for all operations of size zero.
- All accesses performed by functions in this module are non-atomic in the sense
of atomic operations used to synchronize between threads. This means it is
undefined behavior to perform two concurrent accesses to the same location from different
threads unless both accesses only read from memory. Notice that this explicitly
includes
read_volatile
andwrite_volatile
: Volatile accesses cannot be used for inter-thread synchronization. - The result of casting a reference to a pointer is valid for as long as the underlying object is live and no reference (just raw pointers) is used to access the same memory.
These axioms, along with careful use of offset
for pointer arithmetic,
are enough to correctly implement many useful things in unsafe code. Stronger guarantees
will be provided eventually, as the aliasing rules are being determined. For more
information, see the book as well as the section in the reference devoted
to undefined behavior.
Alignment
Valid raw pointers as defined above are not necessarily properly aligned (where
"proper" alignment is defined by the pointee type, i.e., *const T
must be
aligned to mem::align_of::<T>()
). However, most functions require their
arguments to be properly aligned, and will explicitly state
this requirement in their documentation. Notable exceptions to this are
read_unaligned
and write_unaligned
.
When a function requires proper alignment, it does so even if the access
has size 0, i.e., even if memory is not actually touched. Consider using
NonNull::dangling
in such cases.
Structs
NonNull |
|
Functions
copy⚠ | Copies |
copy_nonoverlapping⚠ | Copies |
drop_in_place⚠ | Executes the destructor (if any) of the pointed-to value. |
eq | Compares raw pointers for equality. |
hash | Hash a raw pointer. |
null | Creates a null raw pointer. |
null_mut | Creates a null mutable raw pointer. |
read⚠ | Reads the value from |
read_unaligned⚠ | Reads the value from |
read_volatile⚠ | Performs a volatile read of the value from |
replace⚠ | Moves |
swap⚠ | Swaps the values at two mutable locations of the same type, without deinitializing either. |
swap_nonoverlapping⚠ | Swaps |
write⚠ | Overwrites a memory location with the given value without reading or dropping the old value. |
write_bytes⚠ | Sets |
write_unaligned⚠ | Overwrites a memory location with the given value without reading or dropping the old value. |
write_volatile⚠ | Performs a volatile write of a memory location with the given value without reading or dropping the old value. |