How can i sort a map by its second parameter

Question

How can I output all the int values that are sorted if I have a stl map from string to int?

Answer 1

The implementation of the map prevents you from sorting a map by its values.

If you wish to emit the items in the map in this sorted order, you must first dump the contents of the map into a vector (say) and sort  that vector:

template <typename T1, typename T2>
struct less_second {
    typedef pair<T1, T2> type;
    bool operator ()(type const& a, type const& b) const {
        return a.second < b.second;
    }
};

map<string, int> mymap;
// …

vector<pair<string, int> > mapcopy(mymap.begin(), mymap.end());
sort(mapcopy.begin(), mapcopy.end(), less_second<string, int>());

Alternatively, you can just copy the values from the map while leaving the keys alone and sort the resultant vector directly.