新手求助！关于指定字符串截取的问题

Question

如何在一大字符串中截取以下这两段字符串？第二段字符串中间有换行，听说一般都用正则来截取，如何实现？谢谢！
filename="=?GBK?Q?=B0=D7=D6=A4.dwg?="filename="=?GBK?Q?11-25=D5=C5=C1=C1=D7=AA90=D7=F8?=
 =?GBK?Q?=B1=EA=B4=F808=C4=EA=B8=DF=B3=CC.txt?="

Answer 1

String strToSearch = "";
if(str.ToSearch.IndexOf(fileName) != -1)
{
  DoSth();
}有换行就用\n吧，没试过

Answer 2

我举个例子，比如在如下的2个文本里截取
Content-Type: application/octet-stream; name="=?GBK?Q?=B0=D7=D6=A4.dwg?="
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="=?GBK?Q?=B0=D7=D6=A4.dwg?="在这文本里我想截取 filename="=?GBK?Q?=B0=D7=D6=A4.dwg?="Content-Type: text/plain; name="=?GBK?Q?11-25=D5=C5=C1=C1=D7=AA90=D7=F8?=
 =?GBK?Q?=B1=EA=B4=F808=C4=EA=B8=DF=B3=CC.txt?="
Content-Transfer-Encoding: base64
Content-Disposition: attachment;
 filename="=?GBK?Q?11-25=D5=C5=C1=C1=D7=AA90=D7=F8?=
 =?GBK?Q?=B1=EA=B4=F808=C4=EA=B8=DF=B3=CC.txt?="在这文本里我想截取filename="=?GBK?Q?11-25=D5=C5=C1=C1=D7=AA90=D7=F8?=
 =?GBK?Q?=B1=EA=B4=F808=C4=EA=B8=DF=B3=CC.txt?="

Answer 3

 string str22="Content-Type: application/octet-stream; name=\"=?GBK?Q?=B0=D7=D6=A4.dwg?=\"Content-Transfer-Encoding: base64Content-Disposition: attachment; filename=\"=?GBK?Q?=B0=D7=D6=A4.dwg?=\"";
  foreach (Match match in new Regex("filename=\"[^\"]*\"").Matches(str22)) 
  {
      Console.WriteLine(match);
  }

Answer 4

       我自己写的方法哈
public static string GetStartEndStr(string source, string start, string end)
        {
            string str = "";
            int len1 = source.IndexOf(start);
            if (len1 > -1)
            {
                string cutstr = source.Substring(len1 + (start).Length);
                int len2 = cutstr.IndexOf(end);
                str = cutstr.Substring(0, len2);
            }
            return str;
        }调用
GetStartEndStr(str,"filename=\"","\"");得到的结果是 
=?GBK?Q?11-25=D5=C5=C1=C1=D7=AA90=D7=F8?=
  =?GBK?Q?=B1=EA=B4=F808=C4=EA=B8=DF=B3=CC.txt?=