|POSIX_MEMALIGN(3)||Linux Programmer's Manual||POSIX_MEMALIGN(3)|
NAME¶posix_memalign, aligned_alloc, memalign, valloc, pvalloc - allocate aligned memory
#include <stdlib.h>int posix_memalign(void **memptr, size_t alignment, size_t size); void *aligned_alloc(size_t alignment, size_t size); void *valloc(size_t size);#include <malloc.h>void *memalign(size_t alignment, size_t size); void *pvalloc(size_t size);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
- Since glibc 2.12:
_BSD_SOURCE || (_XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED) && !(_POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600)
- Before glibc 2.12:
- _BSD_SOURCE || _XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
DESCRIPTION¶The function posix_memalign() allocates size bytes and places the address of the allocated memory in *memptr. The address of the allocated memory will be a multiple of alignment, which must be a power of two and a multiple of sizeof(void *). If size is 0, then posix_memalign() returns either NULL, or a unique pointer value that can later be successfully passed to free(3).
RETURN VALUE¶aligned_alloc(), memalign(), valloc(), and pvalloc() return a pointer to the allocated memory, or NULL if the request fails.
- The alignment argument was not a power of two, or was not a multiple of sizeof(void *).
- There was insufficient memory to fulfill the allocation request.
VERSIONS¶The functions memalign(), valloc(), and pvalloc() have been available in all Linux libc libraries.
CONFORMING TO¶The function valloc() appeared in 3.0BSD. It is documented as being obsolete in 4.3BSD, and as legacy in SUSv2. It does not appear in POSIX.1-2001.
Headers¶Everybody agrees that posix_memalign() is declared in <stdlib.h>.
NOTES¶On many systems there are alignment restrictions, for example, on buffers used for direct block device I/O. POSIX specifies the pathconf(path,_PC_REC_XFER_ALIGN) call that tells what alignment is needed. Now one can use posix_memalign() to satisfy this requirement.
SEE ALSO¶brk(2), getpagesize(2), free(3), malloc(3)
COLOPHON¶This page is part of release 3.44 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.