c#截取两个指定字符串中间的字符串

public static string MidStrEx_New(string sourse, string startstr, string endstr)
        {
            Regex rg = new Regex("(?<=(" + startstr + "))[.\s\S]*?(?=(" + endstr + "))", RegexOptions.Multiline | RegexOptions.Singleline);
            return rg.Match(sourse).Value;
        }

public static string MidStrEx(string sourse, string startstr, string endstr)
        {
            string result = string.Empty;
            int startindex, endindex;
            try
            {
                startindex = sourse.IndexOf(startstr);
                if (startindex == -1)
                    return result;
                string tmpstr = sourse.Substring(startindex + startstr.Length);
                endindex = tmpstr.IndexOf(endstr);           
                if (endindex == -1)
                    return result;
                result = tmpstr.Remove(endindex);
            }
            catch (Exception ex)
            {
                Log.WriteLog("MidStrEx Err:" + ex.Message);
            }
            return result;
        }