10 char string to int on Arduino

Question

On my current project, I have RFID badges which sends a 10 chars ID to my Arduino UNO (ex: 2700BBA0E8). The doc says "Printable ASCII", but I don't know if it's always [0-9A-F].

On Arduino, the memory is limited:

• char is 1 byte
• int is 2 bytes
• long is 4 bytes

an int or a long would be shorter than a char[10] and simpler to compare (strcmp() vs ==), so I wonder how I can transform the 10 chars received one by one (on serial) to an int or a long?

Thanks for your help

Answer 1

As already mention, you want put 5 bytes inside a long which can store only 4 bytes. Also, you have to use structure:

struct RFIDTagId
{
    unsigned long low;
    unsigned long high; // can also be unsigned char
};

And use something like that:

unsigned int hex2int(char c)
{
    if (c >= 'A' && c <= 'F')
        return (c - 'A' + 0x0A);
    if (c >= '0' && c <= '9')
        return c - '0';
    return 0;
}

void char2Id(char *src, RFIDTagId *dest)
{
    int i = 0;

    dest->low = 0;
    for(i = 0; i < 8; ++i)
    {
        dest->low |= hex2int(src[i]) << (i*4);
    }

    dest->high = 0;
    for(i = 8; i < 10; ++i)
    {
        dest->high |= hex2int(src[i]) << ((i-8)*4);
    }
}

And to compare 2 ids:

int isRFIDTagIdIsEqual(RFIDTagId * lhs, RFIDTagId * rhs)
{
    return lhs->low == rhs->low && lhs->high == lhs->high;
}

or if you really have c++:

bool operator==(RFIDTagId const & lhs, RFIDTagId const & rhs)
{
    return lhs.low == rhs.low && lhs.high == lhs.high;
}