Inserting into a std::Multimap of std::Map (C++)

Question

If I have a std::multimap<int, std::map<int, MyClass>> myMultimap how to I insert a class object MyClassA into the map with value 1 at multimap value 2 ?

It looks like I can do myMultimap.at(2).insert(std::pair<1,MyClassA>); in c++11 but I am using c++98 due to a library regression/incomparability out of my control.

I've also tried

myMultimap[2].insert(
            std::make_pair(
                myMultimap[2].end(),
                myClassA
            )
        );

which gives: error: no match for 'operator[]' (operand types are 'std::multimap<int, std::map<int, ns_namespace::MyClassType> >' and 'int')| for both of the [ ... ] 's.

I don't want to do something like myMultimap.insert(std::make_pair(2,std::make_pair(1,MyClassA))) because if I understand correctly, this would make a new map in the multimap rather than assigning the class object to the existing map within the multimap.

Answer 1

It is a two stage process:

1. Locate the position in the outer map where you want to do something to the inber map. If necessary, insert a new element.
2. Update the inner map withthe appropriatevalue.

I don't know why the outer map us a multimap (they are rarely useful) so the exampke just uses the first entry:

auto it = mymultimap.lower_bound(2);
if (it == mymultimap.end() || it->first != 2) {
    it = mymultimap.insert(
        std::make_pair(2, std::map<int, MyClass>())).first;
}
(*it)[1] = MyClassA;

(typed on a mobile device: there are probably typos but the overall approach should work).