c#中自定义字符截取函数：Left、Right 、Mid

c#中没有字符截取函数Left 、Right、Mid，所以只能自定义：

        /// <summary>
       /// 截取左边字符
       /// </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>
       /// 截取右边字符
       /// </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>
       /// 截取中间字符
       /// </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);
       }