根据字节长度截取字符串

public string SubStrByByteLength(string str, int bytesLength)
        {
            if (Encoding.Default.GetByteCount(str) <= bytesLength)
            {
                return str;
            }
            else
            {
                string _tempStr = string.Empty;

                int _tempLength = 0;

                char[] chrs = str.ToCharArray();

                foreach (char chr in chrs)
                {
                    _tempLength += Encoding.Default.GetByteCount(chr.ToString());

                    if (_tempLength > bytesLength)
                    {
                        break;
                    }

                    _tempStr += chr;
                }

                return _tempStr;
            }
        }