The quoted string makes a 17-byte array of characters somewhere in memory that contains each of the 16 possible hex digits, followed by a single byte of all zeros that terminates the string. The syntax given then simply returns the element of that array that's indexed by 'HexValue'. The net effect is a mini lookup table, much as if you'd defined the table explicitly, like this:

char hexDigits[] = "0123456789ABCDEF";

return hexDigits[HexValue]; 

This trick is standard C stuff, and works just fine, as you have demonstrated. Whether or not it is actually a good trick is debatable, for at least a couple of reasons:

• Some would say that it's little bit cryptic, and that's almost never a good thing.


• On a microcontroller, you need to be aware of where the compiler puts the array. You probably want it in the code space, which is usually more plentiful than RAM and which is not subject to corruption by buggy code. I suppose various compilers would support various options and/or language extensions that would let you control this sort of thing. You wouldn't want to leave it to chance.

-- Russ