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.  In‐
       stead, 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)

                                                                               2021-03-22                                                                      MEMCMP(3)