通过IP查询城市天气预报（抓取sina网天气预报）

public string GetWeather(string city)
{
string weacherhtml = string.Empty;
//转换输入参数的编码类型
string mycity = System.Web.HttpUtility.UrlEncode(city, System.Text.UnicodeEncoding.GetEncoding("GB2312"));
//初始化新的 WebRequest
HttpWebRequest webrt = (HttpWebRequest)WebRequest.Create("http://php.weather.sina.com.cn/search.php?city=" + mycity);
HttpWebResponse webrs = (HttpWebResponse)webrt.GetResponse();
//从Internet资源返回数据流
Stream stream = webrs.GetResponseStream();
//读取数据流
StreamReader srm = new StreamReader(stream, System.Text.Encoding.Default);
//读取数据
weacherhtml = srm.ReadToEnd();
srm.Close();
stream.Close();
webrs.Close();
//针对不同的网站，请查看HTML源文件
int start = weacherhtml.IndexOf("<!-- box begin-->"); //取的字符位置
int end = weacherhtml.IndexOf("<!-- box end-->");
return weacherhtml.Substring(start + 17, end - start);
}