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NAME

posix_memalign, memalign, valloc - Allocate aligned memory
 

SYNOPSIS

#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);

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

posix_memalign(): _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600  

DESCRIPTION

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.  

RETURN VALUE

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 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.

VERSIONS

CONFORMING TO

Headers

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).  

NOTES

posix_memalign() verifies that alignment matches the requirements detailed above. memalign() may not check that the boundary 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 only pass to free(3) a pointer gotten 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 three routines to be reclaimed with free(3).

The glibc malloc(3) always returns 8-byte aligned memory addresses, so these routines are only needed if you require larger alignment values.  

SEE ALSO

COLOPHON

Index

NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

ERRORS

VERSIONS

CONFORMING TO

Headers

NOTES

SEE ALSO

COLOPHON

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