<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >srand</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK REL="HOME" TITLE="PHP 手册" HREF="index.html"><LINK REL="UP" TITLE="Math 数学函数" HREF="ref.math.html"><LINK REL="PREVIOUS" TITLE="sqrt" HREF="function.sqrt.html"><LINK REL="NEXT" TITLE="tan" HREF="function.tan.html"><META HTTP-EQUIV="Content-type" CONTENT="text/html; charset=UTF-8"></HEAD ><BODY CLASS="refentry" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >PHP 手册</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="function.sqrt.html" ACCESSKEY="P" >上一页</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="function.tan.html" ACCESSKEY="N" >下一页</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><H1 ><A NAME="function.srand" ></A >srand</H1 ><DIV CLASS="refnamediv" ><A NAME="AEN109162" ></A ><P > (PHP 3, PHP 4, PHP 5)</P >srand -- 播下随机数发生器种子</DIV ><DIV CLASS="refsect1" ><A NAME="AEN109165" ></A ><H2 >说明</H2 >void <B CLASS="methodname" >srand</B > ( [int seed] )<BR ></BR ><P > 用 <CODE CLASS="parameter" >seed</CODE > 播下随机数发生器种子。从 PHP 4.2.0 版开始,<CODE CLASS="parameter" >seed</CODE > 参数变为可选项,当该项为空时,会被设为随时数。 </P ><P > <TABLE WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" CLASS="EXAMPLE" ><TR ><TD ><DIV CLASS="example" ><A NAME="AEN109177" ></A ><P ><B >例 1. <B CLASS="function" >srand()</B > 范例</B ></P ><TABLE BORDER="0" BGCOLOR="#E0E0E0" CELLPADDING="5" ><TR ><TD ><code><font color="#000000"> <font color="#0000BB"><?php<br /></font><font color="#FF8000">// seed with microseconds<br /></font><font color="#007700">function </font><font color="#0000BB">make_seed</font><font color="#007700">()<br />{<br /> list(</font><font color="#0000BB">$usec</font><font color="#007700">, </font><font color="#0000BB">$sec</font><font color="#007700">) = </font><font color="#0000BB">explode</font><font color="#007700">(</font><font color="#DD0000">' '</font><font color="#007700">, </font><font color="#0000BB">microtime</font><font color="#007700">());<br /> return (float) </font><font color="#0000BB">$sec </font><font color="#007700">+ ((float) </font><font color="#0000BB">$usec </font><font color="#007700">* </font><font color="#0000BB">100000</font><font color="#007700">);<br />}<br /></font><font color="#0000BB">srand</font><font color="#007700">(</font><font color="#0000BB">make_seed</font><font color="#007700">());<br /></font><font color="#0000BB">$randval </font><font color="#007700">= </font><font color="#0000BB">rand</font><font color="#007700">();<br /></font><font color="#0000BB">?></font> </font> </code></TD ></TR ></TABLE ></DIV ></TD ></TR ></TABLE > </P ><DIV CLASS="note" ><BLOCKQUOTE CLASS="note" ><P ><B >注意: </B >自 PHP 4.2.0 起,不再需要用 <B CLASS="function" >srand()</B > 或 <A HREF="function.mt-srand.html" ><B CLASS="function" >mt_srand()</B ></A > 函数给随机数发生器播种,现已自动完成。</P ></BLOCKQUOTE ></DIV ><P > 参见 <A HREF="function.rand.html" ><B CLASS="function" >rand()</B ></A >,<A HREF="function.getrandmax.html" ><B CLASS="function" >getrandmax()</B ></A > 和 <A HREF="function.mt-srand.html" ><B CLASS="function" >mt_srand()</B ></A >。 </P ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="function.sqrt.html" ACCESSKEY="P" >上一页</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >起始页</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="function.tan.html" ACCESSKEY="N" >下一页</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >sqrt</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="ref.math.html" ACCESSKEY="U" >上一级</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >tan</TD ></TR ></TABLE ></DIV ></BODY ></HTML >