I had exactly the same need. I couldn’t find any suitable (simple, modern, portable) implementations, so I used a python implementation by Brent Pedersen as a guide and wrote a barebones C++ version. The IntervalTree behaves like a standard STL container, with some caveats due to its simplicity (no iterators, for instance). You use it like this (“T” is an arbitrary type):
vector<Interval<T> > intervals;
// ... make intervals!
IntervalTree<T> tree(intervals);
And you query it like this:
vector<Interval<T> > results;
tree.findContained(start, stop, results);
// results now contains Intervals which are fully contained in the query interval
results.clear();
tree.findOverlapping(start, stop, results);
// results now contains Intervals which overlap the query interval