Provided by: manpages-dev_5.10-1ubuntu1_all bug


       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

       aligned_alloc(): _ISOC11_SOURCE

           Since glibc 2.12:
               (_XOPEN_SOURCE >= 500) && !(_POSIX_C_SOURCE >= 200112L)
                   || /* Glibc since 2.19: */ _DEFAULT_SOURCE
                   || /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
           Before glibc 2.12:
               _BSD_SOURCE || _XOPEN_SOURCE >= 500
               (The  (nonstandard)  header  file  <malloc.h>  also  exposes  the  declaration  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 allocated memory will be a multiple of alignment,
       which must be a power of two and a multiple of sizeof(void *).  This address can later  be
       successfully  passed to free(3).  If size is 0, then the value placed in *memptr is either
       NULL or a unique pointer value.

       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

       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  on success.  On error, NULL is returned, and errno is set to indicate the cause of
       the error.

       posix_memalign() returns zero on success, or one of the error values listed  in  the  next
       section  on  failure.   The  value  of  errno  is  not set.  On Linux (and other systems),
       posix_memalign() does not modify memptr on  failure.   A  requirement  standardizing  this
       behavior was added in POSIX.1-2008 TC2.


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

       ENOMEM There was insufficient memory to fulfill the allocation request.


       The functions memalign(), valloc(), and pvalloc() have been available since at least glibc

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

       The function posix_memalign() is available since glibc 2.1.91.


       For an explanation of the terms used in this section, see attributes(7).

       │InterfaceAttributeValue          │
       │aligned_alloc(), │ Thread safety │ MT-Safe        │
       │memalign(),      │               │                │
       │posix_memalign() │               │                │
       │valloc(),        │ Thread safety │ MT-Unsafe init │
       │pvalloc()        │               │                │


       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.

       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 and is  specified  in  POSIX.1-2001  and

       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 <malloc.h>.

       According  to SUSv2, valloc() is declared in <stdlib.h>.  Glibc declares it in <malloc.h>,
       and also in <stdlib.h> if suitable feature test macros are defined (see above).


       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.

       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
       implementation  allows  memory  obtained  from any of these functions to be reclaimed with

       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 5.10 of the Linux man-pages project.  A description of the
       project, information about reporting bugs, and the latest version of  this  page,  can  be
       found at