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.Dd August 24, 2015 32.Dt BZERO 3 33.Os 34.Sh NAME 35.Nm bzero , 36.Nm explicit_bzero 37.Nd write zeroes to a byte string 38.Sh LIBRARY 39.Lb libc 40.Sh SYNOPSIS 41.In strings.h 42.Ft void 43.Fn bzero "void *b" "size_t len" 44.Ft void 45.Fn explicit_bzero "void *b" "size_t len" 46.Sh DESCRIPTION 47The 48.Fn bzero 49function 50writes 51.Fa len 52zero bytes to the string 53.Fa b . 54If 55.Fa len 56is zero, 57.Fn bzero 58does nothing. 59.Pp 60The 61.Fn explicit_bzero 62variant behaves the same, but will not be removed by a compiler's dead store 63optimization pass, making it useful for clearing sensitive memory such as a 64password. 65.Sh SEE ALSO 66.Xr memset 3 , 67.Xr swab 3 68.Sh HISTORY 69A 70.Fn bzero 71function 72appeared in 73.Bx 4.3 . 74Its prototype existed previously in 75.In string.h 76before it was moved to 77.In strings.h 78for 79.St -p1003.1-2001 80compliance. 81.Pp 82The 83.Fn explicit_bzero 84function first appeared in 85.Ox 5.5 86and 87.Fx 11.0 . 88.Pp 89.St -p1003.1-2008 90removes the specification of 91.Fn bzero 92and it is marked as LEGACY in 93.St -p1003.1-2004 . 94For portability with other systems new programs should use 95.Xr memset 3 . 96