String扩展 让你在PadLeft和PadRight时不再受单双字节问题困扰

 /// <summary>  
        /// 按单字节字符串向左填充长度  
        /// </summary>  
        /// <param name="input"></param>  
        /// <param name="length"></param>  
        /// <param name="paddingChar"></param>  
        /// <returns></returns>  
        public static string PadLeft2(this string input, int length, char paddingChar = '')
        {
            return Pad(input, length, paddingChar, true);
        }
        /// <summary>  
        /// 按单字节字符串向右填充长度  
        /// </summary>  
        /// <param name="input">输入字符串</param>  
        /// <param name="length">单字节长度</param>  
        /// <param name="paddingChar">补位字符</param>  
        /// <returns></returns>   
        public static string PadRight2(this string input, int length, char paddingChar = '')
        {
            return Pad( input,  length, paddingChar, false);
        }

        private static string Pad(string input, int length, char paddingChar,bool isLeft)
        {
            var isDoubleChar = Regex.IsMatch(paddingChar.ToString(), @"[^x00-xff]");
            var singleLength = Regex.Replace(input, @"[^x00-xff]", "aa").Length;
            var num = (length - singleLength) *1.0/(isDoubleChar?2:1);
            var newStr=new string(paddingChar,(int)num);
            if (isLeft)
            {
                input = newStr + input;
            }
            else
            {
                 input = input + newStr;
            }
            return input;
        }