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.  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.

SEE ALSO

   bcmp(3),    strcasecmp(3),   strcmp(3),   strcoll(3),   strncasecmp(3),
   strncmp(3), wmemcmp(3)

COLOPHON

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   https://www.kernel.org/doc/man-pages/.

                              2015-08-08                         MEMCMP(3)

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