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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
MEMCMP(3) Linux Programmer's Manual MEMCMP(3)
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 │
└──────────┴───────────────┴─────────┘
POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
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 4.12 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/.
2017-03-13 MEMCMP(3)
Pages that refer to this page: bcmp(3), bstring(3), strcasecmp(3), strcmp(3), strcoll(3), strxfrm(3), wmemcmp(3), signal-safety(7)