如果向某网址Post信息，并得到CookieContainer以便以后直接通过验证

using  System;
using  System.Net;
using  System.IO;
using  System.Text;

        [STAThread]
         static   void  Main( string [] args)
         {
            //
            // TODO: 在此处添加代码以启动应用程序
            //
            string url="http://localhost/csdn2/1.asp";
//            <%
//            if request("aa")="zhuye" then session("ok")="ok"
//            if session("ok")="ok" then
//            response.write("登录")
//            else
//            response.write("没有登录")
//            end if
//            %>
            string indata="aa=zhuye";
            string outdata="";
            CookieContainer myCookieContainer=new CookieContainer();
            //新建一个CookieContainer来存放Cookie集合
            HttpWebRequest myHttpWebRequest=(HttpWebRequest)WebRequest.Create(url);
            //新建一个HttpWebRequest
            myHttpWebRequest.ContentType="application/x-www-form-urlencoded";
            myHttpWebRequest.ContentLength=indata.Length;
            myHttpWebRequest.Method="POST";
            myHttpWebRequest.CookieContainer=myCookieContainer;
            //设置HttpWebRequest的CookieContainer为刚才建立的那个myCookieContainer
            Stream myRequestStream=myHttpWebRequest.GetRequestStream();
            StreamWriter myStreamWriter=new StreamWriter(myRequestStream,Encoding.GetEncoding("gb2312"));                
            myStreamWriter.Write(indata);
            //把数据写入HttpWebRequest的Request流
            myStreamWriter.Close();
            myRequestStream.Close();
            //关闭打开对象
            HttpWebResponse myHttpWebResponse=(HttpWebResponse)myHttpWebRequest.GetResponse();
            //新建一个HttpWebResponse
            myHttpWebResponse.Cookies=myCookieContainer.GetCookies(myHttpWebRequest.RequestUri);
            //获取一个包含url的Cookie集合的CookieCollection
            Stream myResponseStream=myHttpWebResponse.GetResponseStream();
            StreamReader myStreamReader=new StreamReader(myResponseStream,Encoding.GetEncoding("gb2312"));
            outdata=myStreamReader.ReadToEnd();
            //把数据从HttpWebResponse的Response流中读出
            myStreamReader.Close();
            myResponseStream.Close();
            Console.WriteLine(outdata);
            //显示"登录"

            //拿到了Cookie，再进行请求就能直接读取到登录后的内容了
            myHttpWebRequest=(HttpWebRequest)WebRequest.Create(url);
            myHttpWebRequest.CookieContainer=myCookieContainer;//*
            //刚才那个CookieContainer已经存有了Cookie,把它附加到HttpWebRequest中则能直接通过验证
            myHttpWebResponse=(HttpWebResponse)myHttpWebRequest.GetResponse();
            myHttpWebResponse.Cookies=myCookieContainer.GetCookies(myHttpWebRequest.RequestUri);            
            myResponseStream=myHttpWebResponse.GetResponseStream();
            myStreamReader=new StreamReader(myResponseStream,Encoding.GetEncoding("gb2312"));
            outdata=myStreamReader.ReadToEnd();
            myStreamReader.Close();
            myResponseStream.Close();
            Console.WriteLine(outdata);    
            //再次显示"登录"
            //如果把*行注释调，就显示"没有登录"
        }

注释写得很明确了，不多罗嗦了。
补充：如果是以get方式登录的话，直接修改url就可以了，indate可以不写任何东西。（不要去修改myHttpWebRequest.Method为GET），比如把asp文件修改为if request.querystring("aa")="zhuye" then session("ok")="ok"，只要修改url为string url="http://localhost/csdn2/1.asp?aa=zhuye";即可。

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using System;
using System.IO;
using System.Net;
using System.Text;


/// <summary>
/// Fetches a Web Page
/// </summary>
class WebFetch
{
static void Main(string[] args)
{
// used to build entire input
StringBuilder sb = new StringBuilder();

// used on each read operation
byte[] buf = new byte[8192];

// prepare the web page we will be asking for
HttpWebRequest request = (HttpWebRequest)
WebRequest.Create("http://www.mayosoftware.com");

// execute the request
HttpWebResponse response = (HttpWebResponse)
request.GetResponse();

// we will read data via the response stream
Stream resStream = response.GetResponseStream();

string tempString = null;
int count = 0;

do
{
// fill the buffer with data
count = resStream.Read(buf, 0, buf.Length);

// make sure we read some data
if (count != 0)
{
// translate from bytes to ASCII text
tempString = Encoding.ASCII.GetString(buf, 0, count);

// continue building the string
sb.Append(tempString);
}
}
while (count > 0); // any more data to read?

// print out page source
Console.WriteLine(sb.ToString());
}
}