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<h1 class="refname">mt_srand</h1>
<p class="verinfo">(PHP 4, PHP 5)</p><p class="refpurpose"><span class="refname">mt_srand</span> — <span class="dc-title">Seed the better random number generator</span></p>
</div>
<div class="refsect1 description" id="refsect1-function.mt-srand-description">
<h3 class="title">Description</h3>
<div class="methodsynopsis dc-description">
<span class="type"><span class="type void">void</span></span> <span class="methodname"><strong>mt_srand</strong></span>
([ <span class="methodparam"><span class="type">int</span> <code class="parameter">$seed</code></span>
] )</div>
<p class="para rdfs-comment">
Seeds the random number generator with
<em><code class="parameter">seed</code></em> or with a random value
if no <em><code class="parameter">seed</code></em> is given.
</p>
<blockquote class="note"><p><strong class="note">Note</strong>: <span class="simpara">As of PHP 4.2.0, there is no need
to seed the random number generator with <span class="function"><a href="function.srand.html" class="function">srand()</a></span> or
<span class="function"><strong>mt_srand()</strong></span> as this is now done automatically.
</span></p></blockquote>
</div>
<div class="refsect1 parameters" id="refsect1-function.mt-srand-parameters">
<h3 class="title">Parameters</h3>
<p class="para">
<dl>
<dt>
<span class="term"><em><code class="parameter">seed</code></em></span>
<dd>
<p class="para">
An optional seed value
</p>
</dd>
</dt>
</dl>
</p>
</div>
<div class="refsect1 returnvalues" id="refsect1-function.mt-srand-returnvalues">
<h3 class="title">Return Values</h3>
<p class="para">
No value is returned.
</p>
</div>
<div class="refsect1 changelog" id="refsect1-function.mt-srand-changelog">
<h3 class="title">Changelog</h3>
<p class="para">
<table class="doctable informaltable">
<thead>
<tr>
<th>Version</th>
<th>Description</th>
</tr>
</thead>
<tbody class="tbody">
<tr>
<td>4.2.0</td>
<td>
The <em><code class="parameter">seed</code></em> becomes optional
and defaults to a random value if omitted.
</td>
</tr>
<tr>
<td>5.2.1</td>
<td>
The Mersenne Twister implementation in PHP now uses a new seeding
algorithm by Richard Wagner. Identical seeds no longer produce the same
sequence of values they did in previous versions. This behavior is not
expected to change again, but it is considered unsafe to rely upon it
nonetheless.
</td>
</tr>
</tbody>
</table>
</p>
</div>
<div class="refsect1 examples" id="refsect1-function.mt-srand-examples">
<h3 class="title">Examples</h3>
<p class="para">
<div class="example" id="example-3468">
<p><strong>Example #1 <span class="function"><strong>mt_srand()</strong></span> example</strong></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">$usec </span><span style="color: #007700">* </span><span style="color: #0000BB">100000</span><span style="color: #007700">);<br />}<br /></span><span style="color: #0000BB">mt_srand</span><span style="color: #007700">(</span><span style="color: #0000BB">make_seed</span><span style="color: #007700">());<br /></span><span style="color: #0000BB">$randval </span><span style="color: #007700">= </span><span style="color: #0000BB">mt_rand</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
</div>
<div class="refsect1 seealso" id="refsect1-function.mt-srand-seealso">
<h3 class="title">See Also</h3>
<p class="para">
<ul class="simplelist">
<li class="member"> <span class="function"><a href="function.mt-rand.html" class="function" rel="rdfs-seeAlso">mt_rand()</a> - Generate a better random value</span></li>
<li class="member"> <span class="function"><a href="function.mt-getrandmax.html" class="function" rel="rdfs-seeAlso">mt_getrandmax()</a> - Show largest possible random value</span></li>
<li class="member"> <span class="function"><a href="function.srand.html" class="function" rel="rdfs-seeAlso">srand()</a> - Seed the random number generator</span></li>
</ul>
</p>
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