plan9 man page for memcmp

MEMCMP(3)						     Linux Programmer's Manual							 MEMCMP(3)

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  func-
       tion  (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 4.15 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/.

								    2017-09-15								 MEMCMP(3)