在std::set上查找不区分大小写

#include <iostream>
#include <set>
#include <algorithm>
#include <cctype>

struct CaseInsensitiveCompare {
    bool operator()(const std::string& str1, const std::string& str2) const {
        std::string str1Lower = str1;
        std::string str2Lower = str2;
        std::transform(str1Lower.begin(), str1Lower.end(), str1Lower.begin(), ::tolower);
        std::transform(str2Lower.begin(), str2Lower.end(), str2Lower.begin(), ::tolower);
        return str1Lower < str2Lower;
    }
};

int main() {
    std::set<std::string, CaseInsensitiveCompare> mySet;
    mySet.insert("apple");
    mySet.insert("Banana");
    mySet.insert("CHERRY");

    std::string searchKey = "banana";
    auto it = mySet.find(searchKey);
    if (it != mySet.end()) {
        std::cout << "Element found: " << *it << std::endl;
    } else {
        std::cout << "Element not found." << std::endl;
    }

    return 0;
}