What does the C??? operator do?

C++17 will deprecate trigraphs, but interestingly they still are a thing in mainframe space. Here are two (PDF) documents from IBM about it:

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n421...

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n291...

I've never seen them around. Even my dad who was a programmer during the 90's says so.

For those that are wondering, its a trigraph sequence! No one uses them anymore.