147 lines
3.8 KiB
HTML
147 lines
3.8 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of MEMCMP</TITLE>
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</HEAD><BODY>
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<H1>MEMCMP</H1>
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Section: Linux Programmer's Manual (3)<BR>Updated: 2017-09-15<BR><A HREF="#index">Index</A>
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<A HREF="/cgi-bin/man/man2html">Return to Main Contents</A><HR>
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<A NAME="lbAB"> </A>
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<H2>NAME</H2>
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memcmp - compare memory areas
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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<PRE>
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<B>#include <<A HREF="file:///usr/include/string.h">string.h</A>></B>
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<B>int memcmp(const void *</B><I>s1</I><B>, const void *</B><I>s2</I><B>, size_t </B><I>n</I><B>);</B>
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</PRE>
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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The
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<B>memcmp</B>()
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function compares the first <I>n</I> bytes (each interpreted as
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<I>unsigned char</I>)
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of the memory areas <I>s1</I> and <I>s2</I>.
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<A NAME="lbAE"> </A>
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<H2>RETURN VALUE</H2>
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The
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<B>memcmp</B>()
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function returns an integer less than, equal to, or
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greater than zero if the first <I>n</I> bytes of <I>s1</I> is found,
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respectively, to be less than, to match, or be greater than the first
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<I>n</I> bytes of <I>s2</I>.
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<P>
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For a nonzero return value, the sign is determined by the sign of
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the difference between the first pair of bytes (interpreted as
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<I>unsigned char</I>)
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that differ in
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<I>s1</I>
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and
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<I>s2</I>.
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<P>
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If
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<I>n</I>
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is zero, the return value is zero.
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<A NAME="lbAF"> </A>
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<H2>ATTRIBUTES</H2>
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For an explanation of the terms used in this section, see
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<B><A HREF="/cgi-bin/man/man2html?7+attributes">attributes</A></B>(7).
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<TABLE BORDER>
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<TR VALIGN=top><TD><B>Interface</B></TD><TD><B>Attribute</B></TD><TD><B>Value</B><BR></TD></TR>
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<TR VALIGN=top><TD>
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<B>memcmp</B>()
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</TD><TD>Thread safety</TD><TD>MT-Safe<BR></TD></TR>
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</TABLE>
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<A NAME="lbAG"> </A>
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<H2>CONFORMING TO</H2>
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POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
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<A NAME="lbAH"> </A>
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<H2>NOTES</H2>
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<P>
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Do not use
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<B>memcmp</B>()
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to compare security critical data, such as cryptographic secrets,
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because the required CPU time depends on the number of equal bytes.
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Instead, a function that performs comparisons in constant time is required.
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Some operating systems provide such a function (e.g., NetBSD's
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<B>consttime_memequal</B>()),
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but no such function is specified in POSIX.
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On Linux, it may be necessary to implement such a function oneself.
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<A NAME="lbAI"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?3+bcmp">bcmp</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+bstring">bstring</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+strcasecmp">strcasecmp</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+strcmp">strcmp</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+strcoll">strcoll</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+strncasecmp">strncasecmp</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+strncmp">strncmp</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+wmemcmp">wmemcmp</A></B>(3)
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<A NAME="lbAJ"> </A>
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<H2>COLOPHON</H2>
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This page is part of release 5.05 of the Linux
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<I>man-pages</I>
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project.
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A description of the project,
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information about reporting bugs,
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and the latest version of this page,
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can be found at
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<A HREF="https://www.kernel.org/doc/man-pages/.">https://www.kernel.org/doc/man-pages/.</A>
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<P>
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<HR>
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<A NAME="index"> </A><H2>Index</H2>
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<DL>
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<DT id="1"><A HREF="#lbAB">NAME</A><DD>
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<DT id="2"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="3"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="4"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DT id="5"><A HREF="#lbAF">ATTRIBUTES</A><DD>
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<DT id="6"><A HREF="#lbAG">CONFORMING TO</A><DD>
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<DT id="7"><A HREF="#lbAH">NOTES</A><DD>
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<DT id="8"><A HREF="#lbAI">SEE ALSO</A><DD>
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<DT id="9"><A HREF="#lbAJ">COLOPHON</A><DD>
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</DL>
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<HR>
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This document was created by
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<A HREF="/cgi-bin/man/man2html">man2html</A>,
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using the manual pages.<BR>
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Time: 00:05:48 GMT, March 31, 2021
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</BODY>
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</HTML>
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