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 and the American National Standards Committee X3, 6.\" on Information Processing Systems. 7.\" 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 2. Redistributions in binary form must reproduce the above copyright 14.\" notice, this list of conditions and the following disclaimer in the 15.\" documentation and/or other materials provided with the distribution. 16.\" 3. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.Dd November 20, 2024 33.Dt MEMCMP 3 34.Os 35.Sh NAME 36.Nm memcmp 37.Nd compare bytes in memory 38.Sh LIBRARY 39.Lb libc 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 48compares byte object 49.Fa b1 50against byte object 51.Fa b2 . 52Both objects are assumed to be 53.Fa len 54bytes long. 55.Sh RETURN VALUES 56The 57.Fn memcmp 58function returns zero if the two objects are identical. 59Zero-length objects are considered identical. 60The 61.Fn memcmp 62function returns a negative value if the first differing byte has a lower 63value in 64.Fa b1 65and a positive value if the first differing byte has a higher value in 66.Fa b1 . 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 79conforms to 80.St -isoC . 81.Sh CAVEATS 82If the objects differ, the C library 83.Fn memcmp 84implementation returns the difference between the first two differing bytes 85.Po treated as 86.Vt "unsigned char" 87values 88.Pc . 89This behavior is not specified by 90.St -isoC , 91is not portable, and may not occur in light of compiler optimizations. 92