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.
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]
Map store the key value pairs in sorted order so we can access the last element by :-
auto it=m.end();
it--;
int element=it->first;