MEMCMP
Section: Linux Programmer's Manual (3)
Updated: 2017-09-15
Page Index
NAME
memcmp - compare memory areas
SYNOPSIS
#include <string.h>
int memcmp(const void *s1, const void *s2, size_t n);
DESCRIPTION
The
memcmp()
function compares the first
n bytes (each interpreted as
unsigned char)
of the memory areas
s1 and
s2.
RETURN VALUE
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.
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
| Interface | Attribute | Value
|
|
memcmp()
| Thread safety | MT-Safe
|
CONFORMING TO
POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
NOTES
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.
SEE ALSO
bcmp(3),
bstring(3),
strcasecmp(3),
strcmp(3),
strcoll(3),
strncasecmp(3),
strncmp(3),
wmemcmp(3)
COLOPHON
This page is part of release 5.10 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/.