//写入cookie
//@param name 表示cookie的名称
//@param value 表示cookie的值
//@param hours 表示cookie的有效期
function writeCookie(name, value, hours)
{
   var expire = "";
   if(hours != null)
   {
       expire = new Date((new Date()).getTime() + hours * 3600000);
       expire = "; expires=" + expire.toGMTString();
   }
   document.cookie = name + "=" + escape(value) + expire;
}

//读取cooike
function readCookie(name)
{
   var cookieValue = "";
   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;
           cookieValue = unescape(document.cookie.substring(offset, end))
       }
   }
   return  cookieValue;
}