'\" t
.\" Copyright 2001, John Levon <moz@compsoc.man.ac.uk>
.\" Copyright, the authors of the Linux man-pages project
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH posix_memalign 3 2026-02-08 "Linux man-pages 6.18"
.SH NAME
posix_memalign
\-
allocate aligned memory
.SH LIBRARY
Standard C library
.RI ( libc ,\~ \-lc )
.SH SYNOPSIS
.nf
.B #include <stdlib.h>
.P
.BI "int posix_memalign(void **" memptr ", size_t " alignment ", size_t " size );
.fi
.P
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.P
.BR posix_memalign ():
.nf
    _POSIX_C_SOURCE >= 200112L
.fi
.SH DESCRIPTION
.BR posix_memalign ()
allocates
.I size
bytes and places the address of the allocated memory in
.IR "*memptr" .
The address of the allocated memory will be a multiple of
.IR "alignment" ,
which must be a power of two and a multiple of
.IR "sizeof(void\ *)" .
This address can later be successfully passed to
.BR free (3).
If
.I size
is 0, then
the value placed in
.I *memptr
is either NULL
.\" glibc does this:
or a unique pointer value.
.P
The memory is not zeroed.
.P
.BR aligned_alloc (3)
is a standard function that provides the same functionality,
and has a more ergonomic prototype.
Use that instead.
.SH RETURN VALUE
.BR posix_memalign ()
returns zero on success, or one of the error values listed in the
next section on failure.
The value of
.I errno
is not set.
.SH ERRORS
.TP
.B EINVAL
The
.I alignment
argument was not a power of two, or was not a multiple of
.IR "sizeof(void\ *)" .
.TP
.B ENOMEM
Out of memory.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.na
.nh
.BR posix_memalign ()
T}	Thread safety	MT-Safe
.TE
.SH STANDARDS
POSIX.1-2024.
.SH HISTORY
glibc 2.1.91.
POSIX.1d, POSIX.1-2001.
.SH CAVEATS
On Linux (and other systems),
.BR posix_memalign ()
does not modify
.I memptr
on failure.
A requirement standardizing this behavior was added in POSIX.1-2008 TC2.
.\" http://austingroupbugs.net/view.php?id=520
.SH SEE ALSO
.BR aligned_alloc (3)