NAME

posix_memalign - aligned memory allocation (ADVANCED REALTIME)

SYNOPSIS

[ADV] #include <stdlib.h>

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

DESCRIPTION

The posix_memalign() function shall allocate size bytes aligned on a boundary specified by alignment, and shall return a pointer to the allocated memory in memptr. The value of alignment shall be a power of two multiple of sizeof(void *).

Upon successful completion, the value pointed to by memptr shall be a multiple of alignment.

If the size of the space requested is 0, the behavior is implementation-defined: either a null pointer shall be returned in memptr, or the behavior shall be as if the size were some non-zero value, except that the behavior is undefined if the the value returned in memptr is used to access an object.

^[CX] The free() function shall deallocate memory that has previously been allocated by posix_memalign().

RETURN VALUE

Upon successful completion, posix_memalign() shall return zero; otherwise, an error number shall be returned to indicate the error and the contents of memptr shall either be left unmodified or be set to a null pointer.

If size is 0, either:

• posix_memalign() shall not attempt to allocate any space, in which case either an implementation-defined error number shall be returned, or zero shall be returned with a null pointer returned in memptr, or

• posix_memalign() shall attempt to allocate some space and, if the allocation succeeds, zero shall be returned and a pointer to the allocated space shall be returned in memptr. The application shall ensure that the pointer is not used to access an object.

ERRORS

The posix_memalign() function shall fail if:

[EINVAL]

The value of the alignment parameter is not a power of two multiple of sizeof(void *).

[ENOMEM]

There is insufficient memory available with the requested alignment.

EXAMPLES

The following example shows how applications can obtain consistent behavior on error by setting * memptr to be a null pointer before calling posix_memalign().

void *ptr = NULL;
...
//do some work, which might goto error
if (posix_memalign(&ptr, align, size))
    goto error;


//do some more work, which might goto error
...
error:
    free(ptr);
    //more cleanup;

APPLICATION USAGE

The posix_memalign() function is part of the Advisory Information option and need not be provided on all implementations.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

free, malloc

XBD <stdlib.h>

CHANGE HISTORY

First released in Issue 6. Derived from IEEE Std 1003.1d-1999.

In the SYNOPSIS, the inclusion of <sys/types.h> is no longer required.

Issue 7

Austin Group Interpretation 1003.1-2001 #058 is applied, clarifying the value of the alignment argument in the DESCRIPTION.

Austin Group Interpretation 1003.1-2001 #152 is applied, clarifying the behavior when the size of the space requested is 0.

POSIX.1-2008, Technical Corrigendum 2, XSH/TC2-2008/0251 [526] and XSH/TC2-2008/0252 [520,526] are applied.