1.\" $OpenBSD: memcmp.3,v 1.9 2014/06/13 02:12:17 matthew Exp $ 2.\" 3.\" Copyright (c) 1990, 1991 The Regents of the University of California. 4.\" All rights reserved. 5.\" 6.\" This code is derived from software contributed to Berkeley by 7.\" Chris Torek and the American National Standards Committee X3, 8.\" on Information Processing Systems. 9.\" 10.\" Redistribution and use in source and binary forms, with or without 11.\" modification, are permitted provided that the following conditions 12.\" are met: 13.\" 1. Redistributions of source code must retain the above copyright 14.\" notice, this list of conditions and the following disclaimer. 15.\" 2. Redistributions in binary form must reproduce the above copyright 16.\" notice, this list of conditions and the following disclaimer in the 17.\" documentation and/or other materials provided with the distribution. 18.\" 3. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.Dd $Mdocdate: June 13 2014 $ 35.Dt MEMCMP 3 36.Os 37.Sh NAME 38.Nm memcmp 39.Nd compare byte string 40.Sh SYNOPSIS 41.In string.h 42.Ft int 43.Fn memcmp "const void *b1" "const void *b2" "size_t len" 44.Sh DESCRIPTION 45The 46.Fn memcmp 47function compares byte string 48.Fa b1 49against byte string 50.Fa b2 . 51Both strings are assumed to be 52.Fa len 53bytes long. 54.Sh RETURN VALUES 55The 56.Fn memcmp 57function returns zero if the two strings are identical, 58otherwise returns the difference between the first two differing bytes 59(treated as 60.Li unsigned char 61values, so that 62.Sq Li \e200 63is greater than 64.Sq Li \&\e0 , 65for example). 66Zero-length strings are always identical. 67.Sh SEE ALSO 68.Xr bcmp 3 , 69.Xr strcasecmp 3 , 70.Xr strcmp 3 , 71.Xr strcoll 3 , 72.Xr strxfrm 3 , 73.Xr timingsafe_memcmp 3 , 74.Xr wmemcmp 3 75.Sh STANDARDS 76The 77.Fn memcmp 78function conforms to 79.St -ansiC . 80.Sh HISTORY 81The 82.Fn memcmp 83function first appeared in 84.At V 85and was reimplemented for 86.Bx 4.3 Tahoe . 87