Question

I have written a function to take in the data from a Sirit IDentity MaX AVI reader and parse out the facility code and keycard number. How I am currently doing it works, but is there a better way? Seems little hackish… buff & buf are size 264

buf and buff are char

Data received from reader:

2009/12/30 14:56:18 epc0 LN:001
C80507A0008A19FA 0000232F Xlat’d

char TAccessReader::HexCharToInt(char n)
{
    if (n >= '0' && n <= '9')
        return (n-'0');
    else

    if (n >= 'A' && n <= 'F')
        return (n-'A'+10);
    else
        return 0;
}

bool TAccessReader::CheckSirit(char *buf, long *key_num, unsigned char *fac) {

   unsigned short i, j, k;

   *key_num = 0; // Default is zero
   memset(buff, 0, sizeof(buff));

   i = sscanf(buf, "%s %s %s %s %s %s %s", &buff[0], &buff[20], &buff[40],
              &buff[60], &buff[80], &buff[140], &buff[160]);
   if (i == 7 && buff[147] && !buff[148]) {
       // UUGGNNNN UU=spare, GG=Facility Code, NNNN=Keycard Number (all HEX)

       // get facility code

       *fac = HexCharToInt(buff[142]) * 16 + HexCharToInt(buff[143]);
       *key_num = (unsigned short)HexCharToInt(buff[144]) * 4096 +
                  (unsigned short)HexCharToInt(buff[145]) * 256 +
                  (unsigned short)HexCharToInt(buff[146]) * 16 +
                  HexCharToInt(buff[147]);
   }
   // do some basic checks.. return true or false
}

Answer 1

Here’s an easy way to get at the data you want. I do work in the access control business so this was something that interested me…

template<typename TRet, typename Iterator>
TRet ConvertHex(Iterator begin) {
    unsigned long result;

    Iterator end = begin + (sizeof(TRet) * 2);
    std::stringstream ss(std::string(begin, end));
    ss >> std::hex >> result;

    return result;
}

bool TAccessReader::CheckSirit(char *buf, long *key_num, unsigned char *fac) {
   *key_num = 0; // Default is zero

   std::istringstream sbuf(std::string(buf, buf+264));

   // Stuff all of the string elements into a vector
   std::vector<std::string> elements;
   std::copy (std::istream_iterator<std::string>(sbuf), std::istream_iterator<std::string>(), std::back_inserter (elements));

   // We're interested in the 6th element
   std::string read = elements[5];

   if (read.length() == 8) {
       // UUGGNNNN UU=spare, GG=Facility Code, NNNN=Keycard Number (all HEX)

       // get facility and card code
       std::string::const_iterator iter = read.begin();
       *fac = ConvertHex<unsigned char>(iter + 2);
       *key_num = ConvertHex<unsigned short>(iter + 4);
   }
   // do some basic checks.. return true or false
}