c++ [] operator with multiple parameters

comma operator.

values[2,1] == values[(2,1)] == values[1]

It's not operator[], but operator,, which is used here in a manner which is equivalent to:

int temp = (2,1);values[temp]

Where a,b, in C and C++, first evaluates a, and then evaluates and is equal to the value of b. In your case, since a is 2 and thus has no side-effect, your code is in fact accessing values[1].

The comma (,) is an operator by itself (which you can overload as well). The default operation of the comma operator is to return its second argument. So the access to the array by array[2,1] will most likely be equivalent to array[1].
AFAIK the [] operator can only take one argument, but I may be wrong with this.

Edit: Damn it! Two were faster than me

Me stupid! I always repeat to myself to never stay away from c++ for more than a couple month :-)
Yep, and most probably this is not even the only thing I forgot (templates syntax being another one :-(

Thank you!