memcmp(3) - NetBSD Manual Pages

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MEMCMP(3)               NetBSD Library Functions Manual              MEMCMP(3)


NAME

     memcmp -- compare byte string


LIBRARY

     Standard C Library (libc, -lc)


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, oth-
     erwise 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 ANSI X3.159-1989 (``ANSI C89'').

NetBSD 9.3                       June 23, 2013                      NetBSD 9.3