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man:memcmp

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 crypto-
     graphic 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 speci-
     fied in POSIX.  On Linux, it may be necessary to implement such a func-
     tion oneself.

SEE ALSO

     bcmp(3),   bstring(3),   strcasecmp(3),  strcmp(3),  strcoll(3),  strn-
     casecmp(3), strncmp(3), wmemcmp(3)

COLOPHON

     This page is part of release 4.16 of the Linux  man-pages  project.   A
     description  of  the project, information about reporting bugs, and the
     latest    version    of    this    page,    can     be     found     at
     https://www.kernel.org/doc/man-pages/.
                                2017-09-15                         MEMCMP(3)
/data/webs/external/dokuwiki/data/pages/man/memcmp.txt · Last modified: 2019/05/17 09:47 by 127.0.0.1

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