在C#中截取指定长度的中文字符串

private static string SubString(string stringToSub, int length) {
            Regex regex = new Regex("[\u4e00-\u9fa5]+", RegexOptions.Compiled);
            char[] stringChar = stringToSub.ToCharArray();
            StringBuilder sb = new StringBuilder();
            int nLength = 0;

            for(int i = 0; i < stringChar.Length; i++) {
                if (regex.IsMatch((stringChar[i]).ToString())) {
                    sb.Append(stringChar[i]);
                    nLength += 2;
                }
                else {
                    sb.Append(stringChar[i]);
                    nLength = nLength + 1;
                }

                if (nLength > length)
                    break;
            }

            return sb.ToString();
        }