memalign

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



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  allo-
       cated  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  equivalent  to  memalign(sysconf(_SC_PAGE-
       SIZE),size).

       For all three routines, the memory is not zeroed.


RETURN VALUE
       memalign()  and valloc() return the 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. 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 allocation 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  mal-
       loc()  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_memalign() is available since glibc
       2.1.91.


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

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



GNU                               2001-10-11                 POSIX_MEMALIGN(3)