📄 initstate.html
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><html><head><!-- Copyright 1997 The Open Group, All Rights Reserved --><title>initstate</title></head><body bgcolor=white><center><font size=2>The Single UNIX ® Specification, Version 2<br>Copyright © 1997 The Open Group</font></center><hr size=2 noshade><h4><a name = "tag_000_005_968"> </a>NAME</h4><blockquote>initstate, random, setstate, srandom - pseudorandom number functions</blockquote><h4><a name = "tag_000_005_969"> </a>SYNOPSIS</h4><blockquote><pre><code>#include <<a href="stdlib.h.html">stdlib.h</a>>char *initstate(unsigned int <i>seed</i>, char <i>*state</i>, size_t <i>size</i>);long random(void);char *setstate(const char *<i>state</i>);void srandom(unsigned int <i>seed</i>);</code></pre></blockquote><h4><a name = "tag_000_005_970"> </a>DESCRIPTION</h4><blockquote>The<i><a href="random.html">random()</a></i>function uses a non-linear additive feedbackrandom-number generator employing a default state array size of 31long integers to return successive pseudo-random numbers in the rangefrom 0 to 2<sup><small>31</small></sup>-1. The period of this random-number generatoris approximately 16 x (2<small><sup>31</sup></small>-1).The size of the state array determines the period of the random-numbergenerator. Increasing the state array size increases the period.<p>With 256 bytes of state information, the period of therandom-number generator is greater than 2<small><sup>69</small></sup>.<p>Like<i><a href="rand.html">rand()</a></i>,<i><a href="random.html">random()</a></i>produces by default a sequence of numbers that can be duplicated by calling<i><a href="srandom.html">srandom()</a></i>with 1 as the seed.<p>The<i><a href="srandom.html">srandom()</a></i>function initialises the current state array using the value of <i>seed</i>.<p>The<i>initstate()</i>and<i><a href="setstate.html">setstate()</a></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 beinitialised for future use.The <i>size</i> argument, which specifies the sizein bytes of the state array, is used by<i>initstate()</i>to decide what type of random-number generator to use;the larger the state array, the more random the numbers. Valuesfor the amount of state information are 8, 32, 64, 128, and 256bytes. Other values greater than 8 bytes are rounded down to the nearest oneof these values. For values greater than or equal to 8, or less than 32<i><a href="random.html">random()</a></i>uses a simple linear congruential random number generator. The <i>seed</i>argument specifies a starting point for the random-number sequence andprovides for restarting at the same point. The<i>initstate()</i>function returns a pointer to the previous state information array.<p>If<i>initstate()</i>has not been called, then<i><a href="random.html">random()</a></i>behaves as though<i>initstate()</i>had been called with <i>seed</i>=1 and <i>size</i>=128.<p>If<i>initstate()</i>is called with 8 <= <i>size</i> <32, then<i><a href="random.html">random()</a></i>uses a simple linear congruential random number generator.<p>Once a state has been initialised,<i><a href="setstate.html">setstate()</a></i>allows switching between state arrays. The array defined by the <i>state</i>argument is used for further random-number generation until<i>initstate()</i>is called or<i><a href="setstate.html">setstate()</a></i>is called again. The<i><a href="setstate.html">setstate()</a></i>function returns a pointer to the previous state array.</blockquote><h4><a name = "tag_000_005_971"> </a>RETURN VALUE</h4><blockquote>If <i>initstate()</i>is called with <i>size</i> less than 8, it returns NULL.<p>The<i><a href="random.html">random()</a></i>function returns the generated pseudo-random number.<p>The<i><a href="srandom.html">srandom()</a></i>function returns no value.<p>Upon successful completion,<i>initstate()</i>and<i><a href="setstate.html">setstate()</a></i>return a pointer to the previous state array. Otherwise, a null pointer isreturned.</blockquote><h4><a name = "tag_000_005_972"> </a>ERRORS</h4><blockquote>No errors are defined.</blockquote><h4><a name = "tag_000_005_973"> </a>EXAMPLES</h4><blockquote>None.</blockquote><h4><a name = "tag_000_005_974"> </a>APPLICATION USAGE</h4><blockquote>After initialisation, a state array can be restarted at a differentpoint in one of two ways:<ul><p><li>The<i>initstate()</i>function can be used, with the desired seed, state array, and size of thearray.<p><li>The<i><a href="setstate.html">setstate()</a></i>function, with the desired state, can be used, followed by<i><a href="srandom.html">srandom()</a></i>with the desired seed. The advantage of using both of these functions is thatthe size of the state array does not have to be saved once it is initialised.<p></ul><p>Although some implementations of<i><a href="random.html">random()</a></i>have written messages to standard error, such implementations do not conformto this specification.<p>Issue 5 restores the historical behaviour of this function.<p>Threaded applications should use<i><a href="rand.html">rand_r()</a></i>,<i><a href="erand48.html">erand48()</a></i>,<i><a href="nrand48.html">nrand48()</a></i>or<i><a href="jrand48.html">jrand48()</a></i>instead of<i><a href="random.html">random()</a></i>when an independent random number sequence in multiple threads isrequired.</blockquote><h4><a name = "tag_000_005_975"> </a>FUTURE DIRECTIONS</h4><blockquote>None.</blockquote><h4><a name = "tag_000_005_976"> </a>SEE ALSO</h4><blockquote><i><a href="drand48.html">drand48()</a></i>,<i><a href="rand.html">rand()</a></i>,<i><a href="stdlib.h.html"><stdlib.h></a></i>.</blockquote><hr size=2 noshade><center><font size=2>UNIX ® is a registered Trademark of The Open Group.<br>Copyright © 1997 The Open Group<br> [ <a href="../index.html">Main Index</a> | <a href="../xshix.html">XSH</a> | <a href="../xcuix.html">XCU</a> | <a href="../xbdix.html">XBD</a> | <a href="../cursesix.html">XCURSES</a> | <a href="../xnsix.html">XNS</a> ]</font></center><hr size=2 noshade></body></html>⌨️ 快捷键说明
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