Question

I am new to C++ and wanted to know what’d this declaration mean:

typedef pair<double,double> pairD;
pair<pairD, long> unknown;

what’d unknown be?

And more specifically, what’d these operators do:

unknown.FF.FF;
unknown.FF.SS;

Can you provide an example on what data one could initialize or fill in in such unknown data structure?

Thanks!

Answer 1

unknown is a pair<pair<double, double>, long>.

Impossible to guess what FF and SS mean with any certainty though. The obvious interpretation would be something about FirstFirst and SecondSecond — but those don’t fit with how they’re being used (and while FirstFirst sort of makes sense, SecondSecond really doesn’t, since unknown.second is a long, not a pair).

Having ruled that out, about all that’s left is that they just stand for first and second, so unknown.FF.SS is equivalent to unknown.first.second and unknown.FF.FF is equivalent to unknown.first.first.

As to how to put data into an unknown like this, one possibility would be something like:

unknown x = std::make_pair(std::make_pair(1.0, 2.0), 3L);