[Solved] How to use map container?

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

std::ostream& operator<<(std::ostream &os, std::pair<std::string, int> const &s)
{
    os << s.first << " served " << s.second;
    return os;
}

int main()
{
    std::map<std::string, int> servers;
    servers["foo"]++;
    servers["foo"]++;
    servers["foo"]++;
    servers["foo"]++;
    servers["bar"]++;
    servers["bar"]++;

    for (auto s : servers)
        std::cout << s << '\n';
}

solved How to use map container?