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POSIX_MEMALIGN(3)	   Linux Programmer's Manual	     POSIX_MEMALIGN(3)

       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)):

       posix_memalign(): _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600

       aligned_alloc(): _ISOC11_SOURCE

	   Since glibc 2.12:
	       _BSD_SOURCE ||
		   (_XOPEN_SOURCE >= 500 ||
		   !(_POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600)
	   Before glibc 2.12:
	       _BSD_SOURCE || _XOPEN_SOURCE >= 500 ||
	       (The (nonstandard) header file <malloc.h> also exposes the dec‐
	       laration of valloc(); no feature test macros are required.)

       The function posix_memalign()  allocates	 size  bytes  and  places  the
       address	of  the allocated memory in *memptr.  The address of the allo‐
       cated 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_mema‐
       lign() returns either NULL, or a unique pointer value that can later be
       successfully passed to free(3).

       The  obsolete  function	memalign()  allocates size bytes and returns a
       pointer to the allocated memory.	 The memory address will be a multiple
       of alignment, which must be a power of two.

       The  function aligned_alloc() is the same as memalign(), except for the
       added restriction that size should be a multiple of alignment.

       The obsolete function valloc()  allocates  size	bytes  and  returns  a
       pointer to the allocated memory.	 The memory address will be a multiple
       of the page  size.   It	is  equivalent	to  memalign(sysconf(_SC_PAGE‐

       The  obsolete function pvalloc() is similar to valloc(), but rounds the
       size of the allocation up to the next multiple of the system page size.

       For all of these functions, the memory is not zeroed.

       aligned_alloc(), memalign(), valloc(), and pvalloc() return  a  pointer
       to the allocated memory, or NULL if the request fails.

       posix_memalign()	 returns  zero	on success, or one of the error values
       listed in the next section on failure.  Note that errno is not set.

       EINVAL The alignment argument was not a power of two, or was not a mul‐
	      tiple of sizeof(void *).

       ENOMEM There was insufficient memory to fulfill the allocation request.

       The  functions  memalign(), valloc(), and pvalloc() have been available
       in all Linux libc libraries.

       The function aligned_alloc() was added to glibc in version 2.16.

       The function posix_memalign() is available since glibc 2.1.91.

       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

       The function pvalloc() is a GNU extension.

       The function memalign() appears in SunOS 4.1.3 but not in 4.4BSD.

       The function posix_memalign() comes from POSIX.1d.

       The function aligned_alloc() is specified in the C11 standard.

       Everybody agrees that posix_memalign() is declared in <stdlib.h>.

       On some systems memalign() is declared in <stdlib.h> instead  of	 <mal‐

       According  to  SUSv2,  valloc() is declared in <stdlib.h>.  Libc4,5 and
       glibc declare it in <malloc.h>, and also in <stdlib.h> if suitable fea‐
       ture test macros are defined (see above).

       On  many systems there are alignment restrictions, for example, on buf‐
       fers used for direct block  device  I/O.	  POSIX	 specifies  the	 path‐
       conf(path,_PC_REC_XFER_ALIGN) call that tells what alignment is needed.
       Now one can use posix_memalign() to satisfy this requirement.

       posix_memalign()	 verifies  that	 alignment  matches  the  requirements
       detailed	 above.	  memalign() may not check that the alignment argument
       is correct.

       POSIX requires that memory obtained from posix_memalign() can be	 freed
       using free(3).  Some systems provide no way to reclaim memory allocated
       with memalign() or valloc() (because one can pass  to  free(3)  only  a
       pointer	obtained  from malloc(3), while, for example, memalign() would
       call malloc(3) and then align the obtained value).  The glibc implemen‐
       tation  allows  memory  obtained	 from  any  of	these  functions to be
       reclaimed with free(3).

       The glibc malloc(3) always returns 8-byte aligned memory addresses,  so
       these functions are needed only if you require larger alignment values.

       brk(2), getpagesize(2), free(3), malloc(3)

       This  page  is  part of release 3.53 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at

GNU				  2012-03-23		     POSIX_MEMALIGN(3)

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