unordered_map对值c ++

Question

I am trying to use the unordered_map in C++, such that, for the key I have an int , while for the value there is a pair of floats. But, I am not sure how to access the pair of values. I am just trying to make sense of this data structure. I know to access the elements we need an iterator of the same type as this unordered map declaration. I tried using iterator->second.first and iterator->second.second . Is this the correct way to do access elements?

typedef std::pair<float, float> Wkij;
tr1::unordered_map<int, Wkij> sWeight;
tr1::unordered_map<int, Wkij>:: iterator it;
it->second.first     //  access the first element of the pair
it->second.second    //  access the second element of the pair

Thanks for your help and time.

Answer 1

Yes, this is correct, but don't use tr1 , write std , since unordered_map is already part of STL.

Use iterators like you said

for(auto it = sWeight.begin(); it != sWeight.end(); ++it) {
    std::cout << it->first << ": "
              << it->second.first << ", "
              << it->second.second << std::endl;
}

Also in C++11 you can use range-based for loop

for(auto& e : sWeight) {
    std::cout << e.first << ": "
              << e.second.first << ", "
              << e.second.second << std::endl;
}

And if you need it you can work with std::pair like this

for(auto it = sWeight.begin(); it != sWeight.end(); ++it) {
    auto& p = it->second;
    std::cout << it->first << ": "
              << p.first << ", "
              << p.second << std::endl;
}