MEMCMP(3)

NAME
memcmp - compare byte string

LIBRARY
libc

SYNOPSIS
#include <string.h>
int
memcmp(const void *b1, const void *b2, size_t len);

DESCRIPTION
The memcmp() function compares byte string b1 against byte string b2. Both strings are assumed to be len bytes long.

RETURN VALUES
The memcmp() function returns zero if the two strings are identical, otherwise returns the difference between the first two differing bytes (treated as unsigned char values, so that ‘\200’ is greater than ‘\0’, for example). Zero-length strings are always identical.

Do not use memcmp() to compare cryptographic secrets, because the time it takes varies depending on how many bytes are the same, and thus leaks information about the two strings by a timing side channel. To compare secrets, hashes, message authentication codes, etc., use consttime_memequal(3) instead.

SEE ALSO
bcmp(3), consttime_memequal(3), strcasecmp(3), strcmp(3), strcoll(3), strxfrm(3)

STANDARDS
The memcmp() function conforms to ansiC.