advanced patterns with std::map and custom comparator in C++17 leading to incorrect order
I've been struggling with this for a few days now and could really use some help. I'm relatively new to this, so bear with me. I'm experiencing an scenario with `std::map` when using a custom comparator. I've implemented a simple comparator for a class `Point`, which compares two points based on their distance from the origin. However, I noticed that the ordering of the elements in the `std::map` is not what I expected. Here’s the relevant code snippet: ```cpp #include <iostream> #include <map> #include <cmath> class Point { public: int x, y; Point(int x, int y) : x(x), y(y) {} }; struct PointComparator { bool operator()(const Point& p1, const Point& p2) const { return (std::sqrt(p1.x * p1.x + p1.y * p1.y) < std::sqrt(p2.x * p2.x + p2.y * p2.y)); } }; int main() { std::map<Point, std::string, PointComparator> pointMap; pointMap.emplace(Point(1, 2), "A"); pointMap.emplace(Point(3, 4), "B"); pointMap.emplace(Point(0, 5), "C"); for (const auto& entry : pointMap) { std::cout << entry.second << " at distance " << std::sqrt(entry.first.x * entry.first.x + entry.first.y * entry.first.y) << '\n'; } } ``` When I run this code, I expect the points to be ordered by their distances from the origin, but the output does not reflect that. Instead, it seems to be unordered. I have tried adding debug print statements inside the comparator to track the comparisons, and it seems to be called with the expected values, but the map does not maintain the expected order when iterating over it. I’ve also checked that the comparator is consistent and does not produce equal comparisons for different points, yet the behavior continues. Is there something I’m missing regarding how `std::map` utilizes the comparator or its entry ordering? Any insights would be appreciated! This is part of a larger API I'm building. I'd really appreciate any guidance on this.