Example of using a custom sorting predicate function in C++

custom_sort.cpp

struct Interval {
  int start;
  int end;
  Interval() : start(0), end(0) {}
  Interval(int s, int e) : start(s), end(e) {}
};

// Must return true if the first argument (a) should appear before the second argument (b).
bool interval_by_start(const Interval& a, const Interval& b) {
  return a.start < b.start;
}

void merge(vector<Interval>& intervals) {
  // Sort the intervals by their starting value, using a custom comparison function.
  std::sort(intervals.begin(), intervals.end(), interval_by_start);
}