posix_memalign(3)          Library Functions Manual          posix_memalign(3)

NAME
       posix_memalign - allocate aligned memory

LIBRARY
       Standard C library (libc, -lc)

SYNOPSIS
       #include <stdlib.h>

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

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

       posix_memalign():
           _POSIX_C_SOURCE >= 200112L

DESCRIPTION
       posix_memalign() allocates size bytes and places the address of the
       allocated memory in *memptr.  The address of the allocated memory will
       be a multiple of alignment, which must be a power of two and a multiple
       of sizeof(void *).  This address can later be successfully passed to
       free(3).  If size is 0, then the value placed in *memptr is either NULL
       or a unique pointer value.

       The memory is not zeroed.

       aligned_alloc(3) is a standard function that provides the same
       functionality, and has a more ergonomic prototype.  Use that instead.

RETURN VALUE
       posix_memalign() returns zero on success, or one of the error values
       listed in the next section on failure.  The value of errno is not set.

ERRORS
       EINVAL The alignment argument was not a power of two, or was not a
              multiple of sizeof(void *).

       ENOMEM Out of memory.

ATTRIBUTES
       For an explanation of the terms used in this section, see
       attributes(7).

       +--------------------------------------------+---------------+---------+
       |Interface                                   | Attribute     | Value   |
       +--------------------------------------------+---------------+---------+
       |posix_memalign ()                           | Thread safety | MT-Safe |
       +--------------------------------------------+---------------+---------+
STANDARDS
       POSIX.1-2024.

HISTORY
       glibc 2.1.91.  POSIX.1d, POSIX.1-2001.

CAVEATS
       On Linux (and other systems), posix_memalign() does not modify memptr
       on failure.  A requirement standardizing this behavior was added in
       POSIX.1-2008 TC2.

SEE ALSO
       aligned_alloc(3)

Linux man-pages 6.17              2026-02-08                 posix_memalign(3)