visus
/
toolchain-gcc-arm-embedded

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<!-- Created by GNU Texinfo 6.5, http://www.gnu.org/software/texinfo/ -->
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>random (The Red Hat newlib C Library)</title>

<meta name="description" content="random (The Red Hat newlib C Library)">
<meta name="keywords" content="random (The Red Hat newlib C Library)">
<meta name="resource-type" content="document">
<meta name="distribution" content="global">
<meta name="Generator" content="makeinfo">
<link href="index.html#Top" rel="start" title="Top">
<link href="Document-Index.html#Document-Index" rel="index" title="Document Index">
<link href="Document-Index.html#SEC_Contents" rel="contents" title="Table of Contents">
<link href="Stdlib.html#Stdlib" rel="up" title="Stdlib">
<link href="rand48.html#rand48" rel="next" title="rand48">
<link href="rand.html#rand" rel="prev" title="rand">
<style type="text/css">
<!--
a.summary-letter {text-decoration: none}
blockquote.indentedblock {margin-right: 0em}
blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
blockquote.smallquotation {font-size: smaller}
div.display {margin-left: 3.2em}
div.example {margin-left: 3.2em}
div.lisp {margin-left: 3.2em}
div.smalldisplay {margin-left: 3.2em}
div.smallexample {margin-left: 3.2em}
div.smalllisp {margin-left: 3.2em}
kbd {font-style: oblique}
pre.display {font-family: inherit}
pre.format {font-family: inherit}
pre.menu-comment {font-family: serif}
pre.menu-preformatted {font-family: serif}
pre.smalldisplay {font-family: inherit; font-size: smaller}
pre.smallexample {font-size: smaller}
pre.smallformat {font-family: inherit; font-size: smaller}
pre.smalllisp {font-size: smaller}
span.nolinebreak {white-space: nowrap}
span.roman {font-family: initial; font-weight: normal}
span.sansserif {font-family: sans-serif; font-weight: normal}
ul.no-bullet {list-style: none}
-->
</style>


</head>

<body lang="en">
<a name="random"></a>
<div class="header">
<p>
Next: <a href="rand48.html#rand48" accesskey="n" rel="next">rand48</a>, Previous: <a href="rand.html#rand" accesskey="p" rel="prev">rand</a>, Up: <a href="Stdlib.html#Stdlib" accesskey="u" rel="up">Stdlib</a> &nbsp; [<a href="Document-Index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Document-Index.html#Document-Index" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="random_002c-srandom_002d_002d_002dpseudo_002drandom-numbers"></a>
<h3 class="section">2.34 <code>random</code>, <code>srandom</code>&mdash;pseudo-random numbers</h3>
<a name="index-random"></a>
<a name="index-srandom"></a>
<p><strong>Synopsis</strong>
</p><div class="example">
<pre class="example">#define _XOPEN_SOURCE 500
#include &lt;stdlib.h&gt;
long int random(void);
void srandom(unsigned int <var>seed</var>);

</pre></div>
<p><strong>Description</strong><br>
<code>random</code> returns a different integer each time it is called; each
integer is chosen by an algorithm designed to be unpredictable, so
that you can use <code>random</code> when you require a random number.
The algorithm depends on a static variable called the &ldquo;random seed&rdquo;;
starting with a given value of the random seed always produces the
same sequence of numbers in successive calls to <code>random</code>.
</p>
<p>You can set the random seed using <code>srandom</code>; it does nothing beyond
storing its argument in the static variable used by <code>rand</code>.  You can
exploit this to make the pseudo-random sequence less predictable, if
you wish, by using some other unpredictable value (often the least
significant parts of a time-varying value) as the random seed before
beginning a sequence of calls to <code>rand</code>; or, if you wish to ensure
(for example, while debugging) that successive runs of your program
use the same &ldquo;random&rdquo; numbers, you can use <code>srandom</code> to set the same
random seed at the outset.
</p>
<br>
<p><strong>Returns</strong><br>
<code>random</code> returns the next pseudo-random integer in sequence; it is a
number between <code>0</code> and <code>RAND_MAX</code> (inclusive).
</p>
<p><code>srandom</code> does not return a result.
</p>
<br>
<p><strong>Notes</strong><br>
<code>random</code> and <code>srandom</code> are unsafe for multi-threaded applications.
</p>
<p>_XOPEN_SOURCE may be any value &gt;= 500.
</p>
<br>
<p><strong>Portability</strong><br>
<code>random</code> is required by XSI. This implementation uses the same
algorithm as <code>rand</code>.
</p>
<p><code>random</code> requires no supporting OS subroutines.
</p>
<br>


</body>
</html>