/**
 * 生成一个随机的字符串
 * 
 * @param int $length
 * @param boolean $special_chars
 * @return string
 * @author 编程之家 jb51.cc jb51.cc
 */
function getRandStr($length = 12,$special_chars = true) {
 $chars = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';
 if ($special_chars) {
  $chars .= '!@#$%^&*()';
 }
 $randStr = '';
 for ($i = 0; $i < $length; $i++) {
  $randStr .= substr($chars,mt_rand(0,strlen($chars) - 1),1);
 }
 return $randStr;
}