c# 用正则表达式获取开始和结束字符串中间的值

/// <summary>
/// 获得字符串中开始和结束字符串中间得值
/// </summary>
/// <param name="str">字符串</param>
/// <param name="s">开始</param>
/// <param name="e">结束</param>
/// <returns></returns> 
public static string GetValue(string str, string s, string e)
{
Regex rg = new Regex("(?<=(" + s + "))[.\s\S]*?(?=(" + e + "))", RegexOptions.Multiline | RegexOptions.Singleline);
return rg.Match(str).Value;
}