last key in a std::map

I am looking for the highest key value (a defined by the comparison operator) of a std::map.

Is this guaranteed to be

map.rbegin()->first

?

(I am a bit shaky on reverse iterators, and how much freedom there is in the implementation of std::map)

If not, please advise. I cannot change the data structure.

From stackoverflow

• Yes. Map is a sorted container, the reverse iterator must return the elements in reverse (i.e. decreasing) order of their keys.

  [Edit: as Charles Bailey points out in his answer, your code gives the greatest key if it exists - i.e. if the map is non-empty]

• Yes, but remember to check that map.rbegin() != map.rend().

  peterchen : map.size()>0 should do it, too, right?

  dalle : !map.empty() is even clearer.

  Charles Bailey : They are all equivalent checks.

  Andreas Magnusson : map::size() *could* be O(N)...

  Thomas : ... while .empty() is guaranteed to be O(1). (just to clarify what Andreas said)