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.\" FreeBSD: src/lib/libc/stdlib/posix_memalign.3,v 1.3 2007/03/28 04:32:51 jasone Exp
.\"
.Dd July 27, 2018
.Dt POSIX_MEMALIGN 3
.Os
.Sh NAME
.Nm posix_memalign , aligned_alloc
.Nd aligned memory allocation
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdlib.h
.Ft int
.Fn posix_memalign "void **ptr" "size_t alignment" "size_t size"
.Ft void *
.Fn aligned_alloc "size_t alignment" "size_t size"
.Sh DESCRIPTION
The
.Fn posix_memalign
function allocates
.Fa size
bytes of memory such that the allocation's base address is an even multiple of
.Fa alignment ,
and returns the allocation in the value pointed to by
.Fa ptr .
The requested
.Fa alignment
must be a power of 2 at least as large as
.Fn sizeof "void *" .
.Pp
The
.Fn aligned_alloc
function allocates
.Fa size
bytes of memory such that the allocation's base address is an even multiple of
.Fa alignment .
The requested
.Fa alignment
must be a power of 2.
.Pp
Memory that is allocated via
.Fn posix_memalign
or
.Fn aligned_alloc
can be used as an argument in subsequent calls to
.Xr realloc 3
and
.Xr free 3 .
.Sh RETURN VALUES
The
.Fn posix_memalign
function returns the value 0 if successful; otherwise it returns an error value.
.Pp
The
.Fn aligned_alloc
function returns a pointer to the allocated memory if successful; on failure it
returns
.Dv NULL
and sets
.Fa errno
to indicate the error.
.Sh ERRORS
The
.Fn posix_memalign
and
.Fn aligned_alloc
functions will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The
.Fa alignment
parameter is not a power of 2.
.It Bq Er ENOMEM
Memory allocation error.
.El
.Pp
The
.Fn posix_memalign
function will also fail if
.Bl -tag -width Er
.It Bq Er EINVAL
The
.Fa alignment
parameter is not at least as large as
.Fn sizeof "void *" .
.El
.Pp
The
.Fn aligned_alloc
function will also fail if
.Bl -tag -width Er
.It Bq Er EINVAL
The
.Fa size
parameter is not an integer multiple of
.Fa alignment .
.El
.Sh SEE ALSO
.Xr free 3 ,
.Xr malloc 3 ,
.Xr realloc 3 ,
.Xr valloc 3
.Sh STANDARDS
The
.Fn posix_memalign
function conforms to
.St -p1003.1-2001 .
The
.Fn aligned_alloc
function conforms to
.St -isoC-2018 .
.Sh HISTORY
.St -isoC-2011
required size to be an integer multiple of alignment.
This requirement was removed in later standards.