php生成制定长度随机字符串

/**
 * 产生随机字符串
 *
 * 产生一个指定长度的随机字符串,并返回给用户
 *
 * @access public
 * @param int $length 产生字符串的位数
 * @return string
 */

function genRandomString($length = 10)
{
    $characters = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
    $string = "";

    for ($p = 0; $p < $length; $p++) {
        $string .= $characters[mt_rand(0, strlen($characters) - 1)];
    }

    return $string;
}