Unordered_map to binary file

Question

Why I can't write unordered_map structure to a file ?

std::ostream& operator<<(std::ostream& stream, PassLibrary const& data){
    stream << data.local_login << " " //std::string
           << data.local_pass << " "  //std::string
           << data.libs;              //std::unordered_map - error
    return stream;
}

Best regards.

Answer 1

The compiler doesn't know how to print a unordered_map to a file. It's up to you doing it. As @Barry said you can define the function operator<<(std::ostream&, std::unordered_map<K, T, H, KE, A> const&) in order to tell the compiler how to do it. And maybe you also want to intruct him it on how to load it back from file.