memcmp — compare memory areas
#include <string.h>
int
memcmp( |
const void *s1, |
| const void *s2, | |
size_t n); |
The memcmp() function
compares the first n
bytes (each interpreted as unsigned
char) of the memory areas s1 and s2.
The memcmp() function
returns an integer less than, equal to, or greater than zero
if the first n bytes
of s1 is found,
respectively, to be less than, to match, or be greater than
the first n bytes of
s2.
For a nonzero return value, the sign is determined by the
sign of the difference between the first pair of bytes
(interpreted as unsigned char) that
differ in s1 and
s2.
If n is zero, the
return value is zero.
For an explanation of the terms used in this section, see attributes(7).
| Interface | Attribute | Value |
memcmp() |
Thread safety | MT-Safe |
Do not use memcmp() to
compare security critical data, such as cryptographic
secrets, because the required CPU time depends on the number
of equal bytes. Instead, a function that performs comparisons
in constant time is required. Some operating systems provide
such a function (e.g., NetBSD's consttime_memequal()), but no such function
is specified in POSIX. On Linux, it may be necessary to
implement such a function oneself.
bcmp(3), bstring(3), strcasecmp(3), strcmp(3), strcoll(3), strncasecmp(3), strncmp(3), wmemcmp(3)
This page is part of release 5.11 of the Linux man-pages project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man−pages/.
|
Copyright 1993 David Metcalfe (davidprism.demon.co.uk) %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. %%%LICENSE_END References consulted: Linux libc source code Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991) 386BSD man pages Modified Sat Jul 24 18:55:27 1993 by Rik Faith (faithcs.unc.edu) |