posix_memalign - Man Page

aligned memory allocation (ADVANCED REALTIME)


This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.


#include <stdlib.h>

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


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.

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.


The posix_memalign() function shall fail if:


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


There is insufficient memory available with the requested alignment.

The following sections are informative.


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
    //more cleanup;

Application Usage

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



Future Directions


See Also

free(), malloc()

The Base Definitions volume of POSIX.1-2017, <stdlib.h>

Referenced By

free(3p), malloc(3p), stdlib.h(0p).

2017 IEEE/The Open Group POSIX Programmer's Manual