//配合JavaScript的ajaxObject函数, 对字串进行转码.
function ajax_encode($str){
    $patern = array("/%/","/=/","/&/");// % 必须是第一个项, 替换是按项的顺序进行的.
    $rp = array("%25","%26","%3D");
    return preg_replace($patern,$rp,$str);
}
//逆函数
function ajax_decode($str){
    $patern = array("/%25/","/%26/","/%3D/");
    $rp = array("%","=","&");
    return preg_replace($patern,$rp,$str);
}