C++获取map所有键的方法

#include <iostream>
#include <map>
#include <vector>
#include <string>

int main() {
    std::map<std::string, int> myMap = {
        {"apple", 1},
        {"banana", 2},
        {"cherry", 3}
    };

    std::vector<std::string> keys;
    for (const auto& pair : myMap) {
        keys.push_back(pair.first);
    }

    // 输出所有键
    for (const auto& key : keys) {
        std::cout << key << " ";
    }
    return 0;
}

std::vector<std::string> keys;
for (auto it = myMap.begin(); it != myMap.end(); ++it) {
    keys.push_back(it->first);
}

#include <algorithm>
std::vector<std::string> keys(myMap.size());
std::transform(myMap.begin(), myMap.end(), keys.begin(),
    [](const std::pair<const std::string, int>& pair) {
        return pair.first;
    });

keys.reserve(myMap.size());