Preventing sorting in std::map

The std::map always orders the entries in some order, which you can specify/change by supplying its comparison object.

However, is std::unordered_map what you are after then?

If you are putting your own class or struct in the map, you can overload the < operator to always return false. Or you can pass a comparator in the constructor that always returns false. This will make the map think all the elements are equal and it will not sort. Of course, if you prevent sorting, map lookups will be much less efficient. If you want efficiency without sorting, try some kind of hash table.