function.srand.html
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html> <head> <title>Seed the random number generator</title> <meta http-equiv="content-type" content="text/html; charset=UTF-8"> </head> <body><div style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="function.sqrt.html">sqrt</a></div> <div class="next" style="text-align: right; float: right;"><a href="function.tan.html">tan</a></div> <div class="up"><a href="ref.math.html">Math Functions</a></div> <div class="home"><a href="index.html">PHP Manual</a></div></div><hr /><div id="function.srand" class="refentry"> <div class="refnamediv"> <h1 class="refname">srand</h1> <p class="verinfo">(PHP 4, PHP 5)</p><p class="refpurpose"><span class="refname">srand</span> — <span class="dc-title">Seed the random number generator</span></p> </div> <div class="refsect1 description"> <h3 class="title">Description</h3> <div class="methodsynopsis dc-description"> <span class="type"><span class="type void">void</span></span> <span class="methodname"><b><b>srand</b></b></span> ([ <span class="methodparam"><span class="type">int</span> <tt class="parameter">$seed</tt></span> ] )</div> <p class="para rdfs-comment"> Seeds the random number generator with <i><tt class="parameter">seed</tt></i> or with a random value if no <i><tt class="parameter">seed</tt></i> is given. </p> <blockquote><p><b class="note">Note</b>: <span class="simpara">As of PHP 4.2.0, there is no need to seed the random number generator with <b>srand()</b> or <a href="function.mt-srand.html" class="function">mt_srand()</a> as this is now done automatically.</span></p></blockquote> </div> <div class="refsect1 parameters"> <h3 class="title">Parameters</h3> <p class="para"> <dl> <dt> <span class="term"><i><tt class="parameter">seed</tt></i></span> <dd> <p class="para"> Optional seed value </p> </dd> </dt> </dl> </p> </div> <div class="refsect1 changelog"> <h3 class="title">ChangeLog</h3> <p class="para"> <table class="informaltable"> <colgroup> <thead valign="middle"> <tr valign="middle"> <th colspan="1">Version</th> <th colspan="1">Description</th> </tr> </thead> <tbody valign="middle" class="tbody"> <tr valign="middle"> <td colspan="1" rowspan="1" align="left">Since 4.2.0</td> <td colspan="1" rowspan="1" align="left"> The <i><tt class="parameter">seed</tt></i> becomes optional and defaults to a random value if omitted. </td> </tr> </tbody> </colgroup> </table> </p> </div> <div class="refsect1 examples"> <h3 class="title">Examples</h3> <p class="para"> <div class="example"> <p><b>Example #1 <b>srand()</b> example</b></p> <div class="example-contents"><div class="phpcode"><code><span style="color: #000000"><span style="color: #0000BB"><?php<br /></span><span style="color: #FF8000">// seed with microseconds<br /></span><span style="color: #007700">function </span><span style="color: #0000BB">make_seed</span><span style="color: #007700">()<br />{<br /> list(</span><span style="color: #0000BB">$usec</span><span style="color: #007700">, </span><span style="color: #0000BB">$sec</span><span style="color: #007700">) = </span><span style="color: #0000BB">explode</span><span style="color: #007700">(</span><span style="color: #DD0000">' '</span><span style="color: #007700">, </span><span style="color: #0000BB">microtime</span><span style="color: #007700">());<br /> return (float) </span><span style="color: #0000BB">$sec </span><span style="color: #007700">+ ((float) </span><span style="color: #0000BB">$usec </span><span style="color: #007700">* </span><span style="color: #0000BB">100000</span><span style="color: #007700">);<br />}<br /></span><span style="color: #0000BB">srand</span><span style="color: #007700">(</span><span style="color: #0000BB">make_seed</span><span style="color: #007700">());<br /></span><span style="color: #0000BB">$randval </span><span style="color: #007700">= </span><span style="color: #0000BB">rand</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">?></span></span></code></div> </div> </div> </p> </div> <div class="refsect1 seealso"> <h3 class="title">See Also</h3> <p class="para"> <ul class="simplelist"> <li class="member"><a href="function.rand.html" class="function" rel="rdfs-seeAlso">rand()</a></li> <li class="member"><a href="function.getrandmax.html" class="function" rel="rdfs-seeAlso">getrandmax()</a></li> <li class="member"><a href="function.mt-srand.html" class="function" rel="rdfs-seeAlso">mt_srand()</a></li> </ul> </p> </div></div><hr /><div style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="function.sqrt.html">sqrt</a></div> <div class="next" style="text-align: right; float: right;"><a href="function.tan.html">tan</a></div> <div class="up"><a href="ref.math.html">Math Functions</a></div> <div class="home"><a href="index.html">PHP Manual</a></div></div></body></html>⌨️ 快捷键说明
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