c#中自定義字符截取函數：Left、Right 、Mid

c#中沒有字符截取函數Left 、Right、Mid，所以只能自定義：

        /// <summary>
       /// 截取左邊字符
       /// </summary>
       /// <param name="sSource"></param>
       /// <param name="iLength"></param>
       /// <returns></returns>
       public static string Left(string sSource, int iLength)
       {
           return sSource.Substring(0, iLength > sSource.Length ? sSource.Length : iLength);
       }

       /// <summary>
       /// 截取右邊字符
       /// </summary>
       /// <param name="sSource"></param>
       /// <param name="iLength"></param>
       /// <returns></returns>
       public static string Right(string sSource, int iLength)
       {
           return sSource.Substring(iLength > sSource.Length ? 0 : sSource.Length - iLength);
       }

       /// <summary>
       /// 截取中間字符
       /// </summary>
       /// <param name="sSource"></param>
       /// <param name="iStart"></param>
       /// <param name="iLength"></param>
       /// <returns></returns>
       public static string Mid(string sSource, int iStart, int iLength)
       {
           int iStartPoint = iStart > sSource.Length ? sSource.Length : iStart;
           return sSource.Substring(iStartPoint, iStartPoint + iLength > sSource.Length ? sSource.Length - iStartPoint : iLength);
       }