Last key in a std::map

c++ iterator stdmap
peterchen picture peterchen · Nov 14, 2008 · Viewed 51.4k times · Source

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.

Answer

Steve Jessop picture Steve Jessop · Nov 14, 2008

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]

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