You say these are IDs?

Will you be performing any math on these? Is there a requirement for your numbers ever to be output as base-10?

If your answer is "no" to both, your solution is alot simpler. Just use a 3-element array of unsigned int. If you need to store things in ASCII, use hexidecimal formatting.

If the answer is "yes" to either, use Nuzzle's solution. You are pretty much stuck to using assembly too, as you will have to use carry-in/carry-out bits which aren't directly supported in C++.