PHP生成uuid

uuid.php

<?php
function uuid($prefix = '')
{
    $chars = md5(uniqid(mt_rand(), true));
    $uuid  = substr($chars,0,8) . '-';
    $uuid .= substr($chars,8,4) . '-';
    $uuid .= substr($chars,12,4) . '-';
    $uuid .= substr($chars,16,4) . '-';
    $uuid .= substr($chars,20,12);
    return $prefix . $uuid;
}
echo uuid();
echo '<br/>'.session_create_id();