asp.net 得到图片

public string getImgUrls(string HTMLStr)    {        string str = "";

        Regex reg = new Regex(@"<img/s+[^>]*/s*src/s*=/s*([']?)(?<url>/S+)'?[^>]*>", RegexOptions.IgnoreCase);        MatchCollection mc = reg.Matches(HTMLStr);        if (mc == null)        { }        foreach (Match match in mc)        {            str += str == "" ? match.Groups["url"].Value.ToString() : "|" + match.Groups["url"].Value.ToString();        }        return str;    }