[DllImport("wininet.dll", CharSet = CharSet.Auto, SetLastError = true)]

        static extern bool InternetGetCookieEx(string pchURL, string pchCookieName, StringBuilder pchCookieData, ref System.UInt32 pcchCookieData, int dwFlags, IntPtr lpReserved);

        [DllImport("wininet.dll", CharSet = CharSet.Auto, SetLastError = true)]

        static extern int InternetSetCookieEx(string lpszURL, string lpszCookieName, string lpszCookieData, int dwFlags, IntPtr dwReserved);

  WebBrowser browser = (WebBrowser)sender;

            HtmlDocument doc = browser.Document;

            this.Text = doc.Title;

            string url = doc.Url.AbsoluteUri;

            //string cookies2 = GetCookies(url);

            //保留cookie

           // cookieString = doc.Cookie;

            cookieString = GetCookies(url);

       private static string GetCookies(string url)

        {

            uint datasize = ;

            StringBuilder cookieData = new StringBuilder((int)datasize);

            if (!InternetGetCookieEx(url, null, cookieData, ref datasize, 0x2000, IntPtr.Zero))

            {

                if (datasize < )

                    return null;

                cookieData = new StringBuilder((int)datasize);

                if (!InternetGetCookieEx(url, null, cookieData, ref datasize, 0x00002000, IntPtr.Zero))

                    return null;

            }

            return cookieData.ToString();

        }