cweinhofer:
I think the thing that threw me off was was that the function was named "mac2String". But if I understand your example right, that initial code I doesn't have anything specifically to do with the MAC address. It's just code to use a byte array to convert a 64-bit integer (which could be any 64-bit integer) to a string.
The code expects a pointer to a place in memory where you have 6 bytes to be converted in Hexadecimal, separated by ':'. So it's not really a 64 bit integer, could be an array of 6 bytes for example