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       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 ||
                       _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED) &&
                   !(_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
               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 *).  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

       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.   The  value  of  errno  is
       indeterminate after a call to posix_memalign().


       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
       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.


       For   an   explanation   of   the  terms  used  in  this  section,  see

       │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

       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 POSIX.1-2008.

       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

       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
       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 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)


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