字符串指定长度

   ///   <summary>   
   ///   将指定字符串按指定长度进行剪切，   
   ///   </summary>   
   ///   <param   name= "oldStr "> 需要截断的字符串 </param>   
   ///   <param   name= "maxLength "> 字符串的最大长度 </param>   
   ///   <param   name= "endWith "> 超过长度的后缀 </param>   
   ///   <returns> 如果超过长度，返回截断后的新字符串加上后缀，否则，返回原字符串 </returns>   
   public static string StringTruncat(string oldStr, int maxLength, string endWith)  
   {  
       if (string.IsNullOrEmpty(oldStr))  
           //   throw   new   NullReferenceException( "原字符串不能为空 ");   
           return oldStr + endWith;  
       if (maxLength < 1)  
           throw new Exception("返回的字符串长度必须大于[0] ");  
       if (oldStr.Length > maxLength)  
       {  
           string strTmp = oldStr.Substring(0, maxLength);  
           if (string.IsNullOrEmpty(endWith))  
               return strTmp;  
           else  
               return strTmp + endWith;  
       }  
       return oldStr;  
   }