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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><meta name="generator" content="HTML Tidy, see www.w3.org"><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 --><!-- Copyright (c) 2001-2003 The Open Group, All Rights Reserved --><title>initstate</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="initstate"></a> <a name="tag_03_280"></a><!-- initstate --> <!--header start--><center><font size="2">The Open Group Base Specifications Issue 6<br>IEEE Std 1003.1, 2003 Edition<br>Copyright © 2001-2003 The IEEE and The Open Group, All Rights reserved.</font></center><!--header end--><hr size="2" noshade><h4><a name="tag_03_280_01"></a>NAME</h4><blockquote>initstate, random, setstate, srandom - pseudo-random number functions</blockquote><h4><a name="tag_03_280_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><div class="box"><code><tt><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> #include <<a href="../basedefs/stdlib.h.html">stdlib.h</a>><br><br> char *initstate(unsigned</tt> <i>seed</i><tt>, char *</tt><i>state</i><tt>, size_t</tt> <i>size</i><tt>);<br> long random(void);<br> char *setstate(const char *</tt><i>state</i><tt>);<br> void srandom(unsigned</tt> <i>seed</i><tt>); <img src="../images/opt-end.gif" alt="[Option End]" border="0"></tt></code></div><tt><br></tt></blockquote><h4><a name="tag_03_280_03"></a>DESCRIPTION</h4><blockquote><p>The <i>random</i>() function shall use a non-linear additive feedback random-number generator employing a default state arraysize of 31 <b>long</b> integers to return successive pseudo-random numbers in the range from 0 to 2<sup><small>31</small></sup>-1.The period of this random-number generator is approximately 16 x (2<small><sup>31</sup></small>-1). The size of the state arraydetermines the period of the random-number generator. Increasing the state array size shall increase the period.</p><p>With 256 bytes of state information, the period of the random-number generator shall be greater than2<small><sup>69</sup></small>.</p><p>Like <a href="../functions/rand.html"><i>rand</i>()</a>, <i>random</i>() shall produce by default a sequence of numbers that canbe duplicated by calling <i>srandom</i>() with 1 as the seed.</p><p>The <i>srandom</i>() function shall initialize the current state array using the value of <i>seed</i>.</p><p>The <i>initstate</i>() and <i>setstate</i>() functions handle restarting and changing random-number generators. The<i>initstate</i>() function allows a state array, pointed to by the <i>state</i> argument, to be initialized for future use. The<i>size</i> argument, which specifies the size in bytes of the state array, shall be used by <i>initstate</i>() to decide what typeof random-number generator to use; the larger the state array, the more random the numbers. Values for the amount of stateinformation are 8, 32, 64, 128, and 256 bytes. Other values greater than 8 bytes are rounded down to the nearest one of thesevalues. If <i>initstate</i>() is called with 8<=<i>size</i><32, then <i>random</i>() shall use a simple linear congruentialrandom number generator. The <i>seed</i> argument specifies a starting point for the random-number sequence and provides forrestarting at the same point. The <i>initstate</i>() function shall return a pointer to the previous state information array.</p><p>If <i>initstate</i>() has not been called, then <i>random</i>() shall behave as though <i>initstate</i>() had been called with<i>seed</i>=1 and <i>size</i>=128.</p><p>Once a state has been initialized, <i>setstate</i>() allows switching between state arrays. The array defined by the<i>state</i> argument shall be used for further random-number generation until <i>initstate</i>() is called or <i>setstate</i>() iscalled again. The <i>setstate</i>() function shall return a pointer to the previous state array.</p></blockquote><h4><a name="tag_03_280_04"></a>RETURN VALUE</h4><blockquote><p>If <i>initstate</i>() is called with <i>size</i> less than 8, it shall return NULL.</p><p>The <i>random</i>() function shall return the generated pseudo-random number.</p><p>The <i>srandom</i>() function shall not return a value.</p><p>Upon successful completion, <i>initstate</i>() and <i>setstate</i>() shall return a pointer to the previous state array;otherwise, a null pointer shall be returned.</p></blockquote><h4><a name="tag_03_280_05"></a>ERRORS</h4><blockquote><p>No errors are defined.</p></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_03_280_06"></a>EXAMPLES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_280_07"></a>APPLICATION USAGE</h4><blockquote><p>After initialization, a state array can be restarted at a different point in one of two ways:</p><ol><li><p>The <i>initstate</i>() function can be used, with the desired seed, state array, and size of the array.</p></li><li><p>The <i>setstate</i>() function, with the desired state, can be used, followed by <i>srandom</i>() with the desired seed. Theadvantage of using both of these functions is that the size of the state array does not have to be saved once it isinitialized.</p></li></ol><p>Although some implementations of <i>random</i>() have written messages to standard error, such implementations do not conform toIEEE Std 1003.1-2001.</p><p>Issue 5 restored the historical behavior of this function.</p><p>Threaded applications should use <a href="../functions/erand48.html"><i>erand48</i>()</a>, <a href="../functions/nrand48.html"><i>nrand48</i>()</a>, or <a href="../functions/jrand48.html"><i>jrand48</i>()</a> instead of<i>random</i>() when an independent random number sequence in multiple threads is required.</p></blockquote><h4><a name="tag_03_280_08"></a>RATIONALE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_280_09"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_280_10"></a>SEE ALSO</h4><blockquote><p><a href="drand48.html"><i>drand48</i>()</a> , <a href="rand.html"><i>rand</i>()</a> , the Base Definitions volume ofIEEE Std 1003.1-2001, <a href="../basedefs/stdlib.h.html"><i><stdlib.h></i></a></p></blockquote><h4><a name="tag_03_280_11"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 4, Version 2.</p></blockquote><h4><a name="tag_03_280_12"></a>Issue 5</h4><blockquote><p>Moved from X/OPEN UNIX extension to BASE.</p><p>In the DESCRIPTION, the phrase "values smaller than 8" is replaced with "values greater than or equal to 8, or less than32", "<i>size</i><8" is replaced with "8<=<i>size</i> <32", and a new first paragraph is added to the RETURN VALUEsection. A note is added to the APPLICATION USAGE indicating that these changes restore the historical behavior of thefunction.</p></blockquote><h4><a name="tag_03_280_13"></a>Issue 6</h4><blockquote><p>In the DESCRIPTION, duplicate text "For values greater than or equal to 8 ..." is removed.</p><p>IEEE Std 1003.1-2001/Cor 1-2002, item XSH/TC1/D6/30 is applied, removing <a href="../functions/rand_r.html"><i>rand_r</i>()</a> from the list of suggested functions in the APPLICATION USAGE section.</p></blockquote><div class="box"><em>End of informative text.</em></div><hr><hr size="2" noshade><center><font size="2"><!--footer start-->UNIX ® is a registered Trademark of The Open Group.<br>POSIX ® is a registered Trademark of The IEEE.<br>[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href="../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>]</font></center><!--footer end--><hr size="2" noshade></body></html>⌨️ 快捷键说明
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