.\" Copyright (c) 1990, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" Chris Torek and the American National Standards Committee X3,
.\" on Information Processing Systems.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"     from: @(#)memset.3	8.1 (Berkeley) 6/4/93
.\"	$NetBSD: memset.3,v 1.13 2016/08/04 16:36:45 sevan Exp $
.\"
.Dd June 23, 2013
.Dt MEMSET 3
.Os
.Sh NAME
.Nm memset
.Nd write a byte to byte string
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In string.h
.Ft void *
.Fn memset "void *b" "int c" "size_t len"
.Sh DESCRIPTION
The
.Fn memset
function
writes
.Fa len
bytes of value
.Fa c
(converted to an unsigned char) to the string
.Fa b .
.Sh RETURN VALUES
The
.Fn memset
function
returns the original value of
.Fa b .
.Pp
Note that the compiler may optimize away a call to
.Fn memset
if it can prove that the string will not be used by the program again,
for example if it is allocated on the stack and about to go out of scope.
If you want to guarantee that zeros are written to memory, for example
to sanitize a buffer holding a cryptographic secret, use
.Xr explicit_memset 3 .
.Sh SEE ALSO
.Xr bzero 3 ,
.Xr explicit_memset 3 ,
.Xr swab 3
.Sh STANDARDS
The
.Fn memset
function
conforms to
.St -ansiC .