_aligned_malloc
Allocates memory on a specified alignment boundary.
Syntax
void * _aligned_malloc(
size_t size,
size_t alignment
);
Parameters
size
Size of the requested memory allocation.
alignment
The alignment value, which must be an integer power of 2.
Return value
A pointer to the memory block that was allocated or NULL
if the operation failed. The pointer is a multiple of alignment
.
Remarks
_aligned_malloc
is based on malloc
.
_aligned_malloc
is marked __declspec(noalias)
and __declspec(restrict)
, meaning that the function is guaranteed not to modify global variables and that the pointer returned isn't aliased. For more information, see noalias
and restrict
.
This function sets errno
to ENOMEM
if the memory allocation failed or if the requested size was greater than _HEAP_MAXREQ
. For more information about errno
, see errno
, _doserrno
, _sys_errlist
, and _sys_nerr
. Also, _aligned_malloc
validates its parameters. If alignment
isn't a power of 2 or size
is zero, this function invokes the invalid parameter handler, as described in Parameter validation. If execution is allowed to continue, this function returns NULL
and sets errno
to EINVAL
.
Use _aligned_free
to deallocate memory obtained by both _aligned_malloc
and _aligned_offset_malloc
. Don't use free
, which doesn't reclaim the aligned memory correctly and can lead to hard-to-diagnose bugs.
By default, this function's global state is scoped to the application. To change this behavior, see Global state in the CRT.
Requirements
Routine | Required C header | C++ header |
---|---|---|
_aligned_malloc |
<malloc.h> |
<cstdlib> |
Example
// crt_aligned_malloc.c
#include <malloc.h>
#include <stdio.h>
int main() {
void *ptr;
size_t alignment,
off_set;
// Note alignment should be 2^N where N is any positive int.
alignment = 16;
off_set = 5;
// Using _aligned_malloc
ptr = _aligned_malloc(100, alignment);
if (ptr == NULL)
{
printf_s( "Error allocation aligned memory.");
return -1;
}
if (((unsigned long long)ptr % alignment ) == 0)
printf_s( "This pointer, %p, is aligned on %zu\n",
ptr, alignment);
else
printf_s( "This pointer, %p, is not aligned on %zu\n",
ptr, alignment);
// Using _aligned_realloc
ptr = _aligned_realloc(ptr, 200, alignment);
if ( ((unsigned long long)ptr % alignment ) == 0)
printf_s( "This pointer, %p, is aligned on %zu\n",
ptr, alignment);
else
printf_s( "This pointer, %p, is not aligned on %zu\n",
ptr, alignment);
_aligned_free(ptr);
// Using _aligned_offset_malloc
ptr = _aligned_offset_malloc(200, alignment, off_set);
if (ptr == NULL)
{
printf_s( "Error allocation aligned offset memory.");
return -1;
}
if ( ( (((unsigned long long)ptr) + off_set) % alignment ) == 0)
printf_s( "This pointer, %p, is offset by %zu on alignment of %zu\n",
ptr, off_set, alignment);
else
printf_s( "This pointer, %p, does not satisfy offset %zu "
"and alignment %zu\n",ptr, off_set, alignment);
// Using _aligned_offset_realloc
ptr = _aligned_offset_realloc(ptr, 200, alignment, off_set);
if (ptr == NULL)
{
printf_s( "Error reallocation aligned offset memory.");
return -1;
}
if ( ( (((unsigned long long)ptr) + off_set) % alignment ) == 0)
printf_s( "This pointer, %p, is offset by %zu on alignment of %zu\n",
ptr, off_set, alignment);
else
printf_s( "This pointer, %p, does not satisfy offset %zu and "
"alignment %zu\n", ptr, off_set, alignment);
// Note that _aligned_free works for both _aligned_malloc
// and _aligned_offset_malloc. Using free is illegal.
_aligned_free(ptr);
}
This pointer, 3280880, is aligned on 16
This pointer, 3280880, is aligned on 16
This pointer, 3280891, is offset by 5 on alignment of 16
This pointer, 3280891, is offset by 5 on alignment of 16
See also
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