/// <summary>
/// 截取中英文混合字符串
/// </summary>
/// <param name="text">字符文本</param>
/// <param name="length">截取长度</param>
/// <param name="replacetxt">replacetxt替换的多余字符</param>
/// <returns></returns>
public string GetString(string text, int length, string replacetxt)
{
 int strLength = 0;
 StringBuilder strb = new StringBuilder();
 char[] Temp = text.ToCharArray();
 for (int i = 0; i != Temp.Length; i++)
 {
  if (strLength >= length) //
  {
   strb.Append(replacetxt);
   break;
  }
  else
  {
   if (((int)Temp[i]) < 255) //大于255的都是汉字或者特殊字符
   {
    strLength++;
   }
   else
   {
    strLength = strLength + 2;
   }
   strb.Append(Temp[i]);
  }
 }
 return strb.ToString();
}