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 attributes(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 confidential data, such as cryptographic secrets,  because  the  CPU  time
       required  for  the comparison depends on the contents of the addresses compared, this function is subject
       to  timing-based  side-channel  attacks.   In  such  cases,  a  function  that  performs  comparisons  in
       deterministic  time,  depending  only  on n (the quantity of bytes compared) 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, 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)