Free Knowledge Resources


Linux Manual Pages


Free Software * Books

Source Code

Free Media

Linux

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

   This page is part of release 4.09 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/.

                              2015-08-08                         MEMCMP(3)



Opportunity


Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.

Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.



Free Software


Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.

Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.



Free Books


The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.

Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.



Education


Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.

Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.


birds banner