x SuSE Linux 13.1-RELEASE x
x SuSE Linux 13.1-RELEASEx
memcmp(3) Library Functions Manual memcmp(3)
NAME
memcmp - compare memory areas
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#include <string.h>
int memcmp(const void s1[.n], const void s2[.n], 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 at-
tributes(7).
+--------------------------------------------+---------------+---------+
|Interface | Attribute | Value |
+--------------------------------------------+---------------+---------+
|memcmp() | Thread safety | MT-Safe |
+--------------------------------------------+---------------+---------+
STANDARDS
C11, POSIX.1-2008.
HISTORY
POSIX.1-2001, C89, SVr4, 4.3BSD.
CAVEATS
Do not use memcmp() to compare security critical data, such as crypto-
graphic 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 speci-
fied in POSIX. On Linux, you may need to implement such a function
yourself.
SEE ALSO
bstring(3), strcasecmp(3), strcmp(3), strcoll(3), strncasecmp(3),
strncmp(3), wmemcmp(3)
Linux man-pages 6.04 2023-03-30 memcmp(3)
Want to link to this manual page? Use this URL:
<https://star2.abcm.com/cgi-bin/bsdi-man?query=memcmp&sektion=3&manpath=>