#define _XOPEN_SOURCE 600 #include <stdlib.h> int posix_memalign(void **memptr, size_t alignment, size_t size); #include <malloc.h> void *valloc(size_t size); void *memalign(size_t boundary, size_t size);
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_PAGESIZE),size).
For all three routines, the memory is not zeroed.
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.
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.
On some systems memalign() is declared in <stdlib.h> instead of <malloc.h>.
According to SUSv2, valloc() is declared in <stdlib.h>. Libc4,5 and glibc declare it in <malloc.h> and perhaps also in <stdlib.h> (namely, if _GNU_SOURCE is defined, or _BSD_SOURCE is defined, or, for glibc, if _XOPEN_SOURCE_EXTENDED is defined, or, equivalently, _XOPEN_SOURCE is defined to a value not less than 500).