function setCookie(name, value)        //cookies设置
{
    var argv = setCookie.arguments;
    var argc = setCookie.arguments.length;
    var expires = (argc > 2) ? argv[2] : null;
    if(expires!=null&&expires!="")
    {
        var LargeExpDate = new Date ();
        LargeExpDate.setTime(LargeExpDate.getTime() + (expires*1000*3600*24));
    }
    document.cookie = name + "=" + escape (value)+((expires == null) ? "" : ("; expires=" +LargeExpDate.toGMTString()));
}

function getCookie(name)            //cookies读取
{
    //if(document.cookie=="")alert("由于您没有开启cookie，所以无法使用该功能！请使用前先开启cookie");
    var search = name + "="
    if(document.cookie.length > 0) 
    {
        offset = document.cookie.indexOf(search)
        if(offset != -1) 
        {
            offset += search.length
            end = document.cookie.indexOf(";", offset)
            if(end == -1) end = document.cookie.length
            return unescape(document.cookie.substring(offset, end))
         }
        else return ""
    }
}

------解决方案--------------------

把path的值设为"/"，这样表示对整个网站都有效

------解决方案--------------------
7楼不是已经给出答案了吗……