Question

I want to use container like unordered map, but i have two special requirements…

• I know from the start all the keys can be, so i want to first enter all the keys without the values.
• After the keys entered, and the program continue, i want to know which value was filled already, but not with const value like ‘0’ etc., and not with pointers.

thank you, and sorry about my poor English

Answer 1

std::unordered_map<key_type,boost::optional<value_type>>

http://www.boost.org/doc/libs/1_49_0/libs/optional/doc/html/index.html