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

NAME
       posix_memalign,	aligned_alloc,	memalign,  valloc,  pvalloc - allocate
       aligned memory

SYNOPSIS
       #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

       valloc():
	   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
	       (The (nonstandard) header file <malloc.h> also exposes the dec‐
	       laration of valloc(); no feature test macros are required.)

DESCRIPTION
       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 the value
       placed in *memptr is 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‐
       SIZE),size).

       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.

RETURN VALUE
       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.  The value of errno is  indeter‐
       minate after a call to posix_memalign().

ERRORS
       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.

VERSIONS
       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.

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.

       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.

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

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

       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).

NOTES
       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.

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

COLOPHON
       This page is part of release 3.63 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/.

GNU				  2013-09-02		     POSIX_MEMALIGN(3)
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