1.\" Copyright (c) 1990, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" This code is derived from software contributed to Berkeley by 5.\" Chris Torek. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. Neither the name of the University nor the names of its contributors 16.\" may be used to endorse or promote products derived from this software 17.\" without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.\" @(#)bzero.3 8.1 (Berkeley) 6/4/93 32.\" $FreeBSD$ 33.\" 34.Dd October 6, 2014 35.Dt BZERO 3 36.Os 37.Sh NAME 38.Nm bzero , 39.Nm explicit_bzero 40.Nd write zeroes to a byte string 41.Sh LIBRARY 42.Lb libc 43.Sh SYNOPSIS 44.In strings.h 45.Ft void 46.Fn bzero "void *b" "size_t len" 47.Ft void 48.Fn explicit_bzero "void *b" "size_t len" 49.Sh DESCRIPTION 50The 51.Fn bzero 52function 53writes 54.Fa len 55zero bytes to the string 56.Fa b . 57If 58.Fa len 59is zero, 60.Fn bzero 61does nothing. 62.Pp 63The 64.Fn explicit_bzero 65variant behaves the same, but will not be removed by a compiler's dead store 66optimization pass, making it useful for clearing sensitive memory such as a 67password. 68.Sh SEE ALSO 69.Xr memset 3 , 70.Xr swab 3 71.Sh HISTORY 72A 73.Fn bzero 74function 75appeared in 76.Bx 4.3 . 77Its prototype existed previously in 78.In string.h 79before it was moved to 80.In strings.h 81for 82.St -p1003.1-2001 83compliance. 84.Pp 85The 86.Fn explicit_bzero 87function first appeared in 88.Ox 5.5 89and 90.Fx 11.0 . 91