Unexpected behavior when using std::map with custom comparator in C++20
I'm reviewing some code and I've looked through the documentation and I'm still confused about I'm not sure how to approach I've been struggling with this for a few days now and could really use some help... I'm encountering unexpected behavior when using `std::map` with a custom comparator in C++20. My custom comparator is intended to sort keys in a case-insensitive manner. However, when I try to insert a key that differs only in case from an existing key, the map does not behave as expected. Below is the relevant code: ```cpp #include <iostream> #include <map> #include <string> #include <algorithm> #include <cctype> struct CaseInsensitiveCompare { bool operator()(const std::string& lhs, const std::string& rhs) const { return std::lexicographical_compare(lhs.begin(), lhs.end(), rhs.begin(), rhs.end(), [](char a, char b) { return std::tolower(a) < std::tolower(b); }); } }; int main() { std::map<std::string, int, CaseInsensitiveCompare> caseInsensitiveMap; caseInsensitiveMap["Hello"] = 1; caseInsensitiveMap["hello"] = 2; // Should overwrite the previous entry for (const auto& pair : caseInsensitiveMap) { std::cout << pair.first << " : " << pair.second << '\n'; } return 0; } ``` When I run this program, I expect that the second insertion will overwrite the first, but instead, it creates a new entry in the map. The output I receive is: ``` Hello : 1 hello : 2 ``` I have verified that the comparator works correctly in terms of case insensitivity, yet it seems that the `std::map` is treating the two keys as distinct. I have tried explicitly checking the comparator's return value during insertions, and it seems to return `false` when comparing "Hello" and "hello". To troubleshoot, I also printed the iterator results for the comparisons directly in the comparator. It appears that the issue lies within the insertion logic rather than with the comparator itself. Is there a known limitation or behavior of `std::map` regarding custom comparators that I might be overlooking? Any suggestions for resolving this issue would be greatly appreciated. For reference, this is a production service. Any ideas what could be causing this? The stack includes Cpp and several other technologies. Thanks for your help in advance!