/**
     * 方法一：获取随机字符串
     * @param number $length 长度
     * @param string $type 类型
     * @param number $convert 转换大小写
     * @return string 随机字符串
     */
    function random($length = 6, $type = 'string', $convert = 0)
    {
        $config = array(
            'number' => '1234567890',
            'letter' => 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ',
            'string' => 'abcdefghjkmnpqrstuvwxyzABCDEFGHJKMNPQRSTUVWXYZ23456789',
            'all' => 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890'
        );
 
        if (!isset($config[$type]))
            $type = 'string';
        $string = $config[$type];
 
        $code = '';
        $strlen = strlen($string) - 1;
        for ($i = 0; $i < $length; $i++) {
            $code .= $string{mt_rand(0, $strlen)};
        }
        if (!empty($convert)) {
            $code = ($convert > 0) ? strtoupper($code) : strtolower($code);
        }
        return $code;
    }
 
    /**
     * 方法二：获取随机字符串
     * @param int $randLength 长度
     * @param int $addtime 是否加入当前时间戳
     * @param int $includenumber 是否包含数字
     * @return string
     */
    function rand_str($randLength = 6, $addtime = 1, $includenumber = 0)
    {
        if ($includenumber) {
            $chars = 'abcdefghijklmnopqrstuvwxyzABCDEFGHJKLMNPQEST123456789';
        } else {
            $chars = 'abcdefghijklmnopqrstuvwxyz';
        }
        $len = strlen($chars);
        $randStr = '';
        for ($i = 0; $i < $randLength; $i++) {
            $randStr .= $chars[mt_rand(0, $len - 1)];
        }
        $tokenvalue = $randStr;
        if ($addtime) {
            $tokenvalue = $randStr . time();
        }
        return $tokenvalue;
    }