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



NAME
       posix_memalign, memalign, valloc - Allocate aligned memory

SYNOPSIS
       #include <stdlib.h>

       int posix_memalign(void **memptr, size_t alignment, size_t size);
       void *memalign(size_t boundary, size_t size);
       void *valloc(size_t size);

DESCRIPTION
       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 *).

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

       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 equiv-
       alent to memalign(sysconf(_SC_PAGESIZE),size).

       For all three routines, the memory is not zeroed.


RETURN VALUE
       memalign() and valloc() return the pointer  to  the  allo-
       cated 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.


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

       ENOMEM There was insufficient memory to fulfill the  allo-
              cation request.


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

       POSIX  requires that memory obtained from posix_memalign()
       can be freed using free().  Some systems provide no way to
       reclaim  memory  allocated  with  memalign()  or  valloc()
       (because one can only pass to free() a pointer gotten from
       malloc(),  while  e.g.  memalign() would call malloc() and
       then align the obtained value).  GNU  libc  allows  memory
       obtained  from any of these three routines to be reclaimed
       with free().

       GNU libc malloc() always  returns  8-byte  aligned  memory
       addresses,  so  these  routines  are  only  needed  if you
       require larger alignment values.


AVAILABILITY
       The functions memalign() and valloc() have been  available
       in  all  Linux  libc  libraries.  The function posix_mema-
       lign() is available since glibc 2.1.91.


CONFORMING TO
       The function valloc() appeared in 3.0  BSD.  It  is  docu-
       mented  as  being  obsolete  in  BSD 4.3, and as legacy in
       SUSv2. It no longer occurs in SUSv3.  The  function  mema-
       lign()  appears  in  SunOS  4.1.3 but not in BSD 4.4.  The
       function posix_memalign() comes from POSIX 1003.1d.

SEE ALSO
       malloc(c), free(e), getpagesize(e), brk(k)



GNU                         2001-10-11          POSIX_MEMALIGN(N)