aligned_alloc
Defined in header
<stdlib.h>
|
||
(since C11) | ||
Allocate size
bytes of uninitialized storage whose alignment is specified by alignment
. The size
parameter must be an integral multiple of alignment
.
aligned_alloc
is thread-safe: it behaves as though only accessing the memory locations visible through its argument, and not any static storage.
A previous call to free or realloc that deallocates a region of memory synchronizes-with a call to aligned_alloc that allocates the same or a part of the same region of memory. This synchronization occurs after any access to the memory by the deallocating function and before any access to the memory by aligned_alloc
. There is a single total order of all allocation and deallocation functions operating on each particular region of memory.
Contents |
[edit] Parameters
alignment | - | specifies the alignment. Must be a valid alignment supported by the implementation. |
size | - | number of bytes to allocate. An integral multiple of alignment
|
[edit] Return value
On success, returns the pointer to the beginning of newly allocated memory. The returned pointer must be deallocated with free() or realloc()
.
On failure, returns a null pointer.
[edit] Notes
Passing a size
which is not an integral multiple of alignment
or a alignment
which is not valid or not supported by the implementation causes the function to fail and return a null pointer (C11, as published, specified undefined behavior in this case, this was corrected by DR 460).
As an example of the "supported by the implementation" requriement, POSIX function posix_memalign accepts any alignment
that is a power of two and a multiple of sizeof(void *)
, and POSIX-based implementations of aligned_alloc
inherit this requirements.
Regular malloc aligns memory suitable for any object type (which, in practice, means that it is aligned to alignof(max_align_t)). This function is useful for over-aligned allocations, such as to SSE, cache line, or VM page boundary.
[edit] Example
Possible output:
default-aligned addr: 0x17d6010 1024-byte aligned addr: 0x17d6400
[edit] References
- C11 standard (ISO/IEC 9899:2011):
-
- 7.22.3.1 The aligned_alloc function (p: 347-348)
[edit] See also
C++ documentation for aligned storage
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