Returning the greatest key strictly less than the given key in a C++ Map

Question

Is there a way the C++ STL Maps support this, since lower_bound and upper_bound on maps strictly return the value greater than the passed value.

Lower key

U

Answer 1

Your method will work, but you need to check to make sure you don't back over the beginning of the map. Plus you need lower_bound, not upper_bound.

iterator = map.lower_bound(2.3)
if (iterator != map.begin())
    --iterator;