<param name="origStr">原始字符串</param>
<param name="endIndex">提取前endIdex个字节</param>
<returns></returns>

public static string GetSubString(string origStr, int endIndex)
{
  if (origStr == null || origStr.Length == 0 || endIndex < 0)
    return "";
  int bytesCount = System.Text.Encoding.GetEncoding("gb2312").GetByteCount(origStr);
  if (bytesCount > endIndex)
  {
    int readyLength = 0;
    int byteLength;
    for (int i = 0; i < origStr.Length; i++)
    {
      byteLength = System.Text.Encoding.GetEncoding("gb2312").GetByteCount(new char[] { origStr[i] });
      readyLength += byteLength;
      if (readyLength == endIndex)
      {
        origStr = origStr.Substring(0, i + 1) + "...";
        break;
      }
      else if (readyLength > endIndex)
      {
        origStr = origStr.Substring(0, i) + "...";
        break;
      }
    }
  }
  return origStr;
}

/// 按字节数截取字符串(不带省略号)
/// </summary>
/// <param name="origStr">原始字符串</param>
/// <param name="endIndex">提取前endIdex个字节</param>
/// <returns></returns>
public static string GetSub1String(string origStr, int endIndex)
{
  if (origStr == null || origStr.Length == 0 || endIndex < 0)
    return "";
  int bytesCount = System.Text.Encoding.GetEncoding("gb2312").GetByteCount(origStr);
  if (bytesCount > endIndex)
  {
    int readyLength = 0;
    int byteLength;
    for (int i = 0; i < origStr.Length; i++)
    {
      byteLength = System.Text.Encoding.GetEncoding("gb2312").GetByteCount(new char[] { origStr[i] });
      readyLength += byteLength;
      if (readyLength == endIndex)
      {
        origStr = origStr.Substring(0, i + 1);
        break;
      }
      else if (readyLength > endIndex)
      {
        origStr = origStr.Substring(0, i);
        break;
      }
    }
  }
  return origStr;
}