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_aligned_malloc

Visual Studio .NET 2003

Allocates memory on a specified alignment boundary.

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.

Remarks

_aligned_malloc is based on malloc; see malloc for more information on using _aligned_malloc.

Requirements

Routine	Required header	Compatibility
_aligned_malloc	<malloc.h>	Win 98, Win Me, Win NT, Win 2000, Win XP

For additional compatibility information, see Compatibility in the Introduction.

Libraries

All versions of the C run-time libraries.

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;

ptr = _aligned_malloc(100, alignment);
   if ( ((int)ptr % alignment ) == 0 && ptr != NULL)
      printf("This pointer, %d is aligned on %d\n", ptr, alignment);
   else
      printf("This pointer, %d is not aligned on %d\n",ptr, alignment);

   ptr = _aligned_realloc(ptr, 200, alignment);
   if ( ((int)ptr % alignment ) == 0)
       printf("This pointer, %d is aligned on %d\n", ptr, alignment);
   else
      printf("This pointer, %d is not aligned on %d\n",ptr, alignment);
   _aligned_free(ptr);

ptr = _aligned_offset_malloc(200, alignment, off_set);
   if ( ( (((int)ptr) + off_set) % alignment ) == 0 && ptr != NULL)
      printf("This pointer, %d is offset by %d on alignment of %d\n", ptr,
   off_set, alignment);
   else
      printf("This pointer, %d is does not satisfy of offset %d and alignment %d\n",ptr, off_set, alignment);
 
ptr = _aligned_offset_realloc(ptr, 200, alignment, off_set);
   if ( ( (((int)ptr) + off_set) % alignment ) == 0 && ptr != NULL)
      printf("This pointer, %d is offset by %d on alignment of %d\n", ptr, off_set, alignment);
   else
      printf("This pointer, %d is does not satisfy of offset %d and alignment %d\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);
}

Sample Output

This pointer, 3082224 is aligned on 16
This pointer, 3082224 is aligned on 16
This pointer, 3082219 is offset by 5 on alignment of 16
This pointer, 3082219 is offset by 5 on alignment of 16