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

NAME
       posixmemalign,  alignedalloc,  memalign,  valloc,  pvalloc - allocate
       aligned memory

SYNOPSIS
       #include 

       int posixmemalign(void **memptr, sizet alignment, sizet size);
       void *alignedalloc(sizet alignment, sizet size);
       void *valloc(sizet size);

       #include 

       void *memalign(sizet alignment, sizet size);
       void *pvalloc(sizet size);

   Feature Test Macro Requirements for glibc (see featuretestmacros(7)):

       posixmemalign(): POSIXCSOURCE >= 200112L || XOPENSOURCE >= 600

       alignedalloc(): ISOC11SOURCE

       valloc():
           Since glibc 2.12:
               BSDSOURCE ||
                   (XOPENSOURCE >= 500 ||
                       XOPENSOURCE && XOPENSOURCEEXTENDED) &&
                   !(POSIXCSOURCE >= 200112L || XOPENSOURCE >= 600)
           Before glibc 2.12:
               BSDSOURCE || XOPENSOURCE >= 500 ||
               XOPENSOURCE && XOPENSOURCEEXTENDED
               (The (nonstandard) header file  also exposes the dec‐
               laration of valloc(); no feature test macros are required.)

DESCRIPTION
       The function posixmemalign()  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 posixmema‐
       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 alignedalloc() 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(SCPAGE‐
       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
       alignedalloc(), memalign(), valloc(), and pvalloc() return  a  pointer
       to the allocated memory, or NULL if the request fails.

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

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 alignedalloc() was added to glibc in version 2.16.

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

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

   Headers
       Everybody agrees that posixmemalign() is declared in .

       On some systems memalign() is declared in  instead  of  .

       According  to  SUSv2,  valloc() is declared in .  Libc4,5 and
       glibc declare it in , and also in  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,PCRECXFERALIGN) call that tells what alignment is needed.
       Now one can use posixmemalign() to satisfy this requirement.

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

       POSIX requires that memory obtained from posixmemalign() 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 3.53 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                               2012-03-23                 POSIXMEMALIGN(3)