Getting the Iterator for an inner STL Container? - stl

Question

I am having trouble trying to get iterators for inner sub-containers.
Basically imagine this simplified code:
typedef map<string, map<string, map> > double_map;
double_map dm;
.. //some code here
for(double_map::iterator it = dm.begin(); it != dm.end(); it++){
//some code here
it->first // string
it->second // <---- this is the 2nd map, how do i get its iterator so I can wrap it
//in a for loop like above?
}
I need to be able to do this without using typedefs for every single inner container, is there a way to get an iterator for the inner container? I have structure that has 4 inner containers and I need to iterate through them all.

Answer 1

(Beware, nothing compiled in the following snippets.)
for(double_map::iterator it = dm.begin(); it != dm.end(); it++){
//some code here
it->first; // string
it->second.begin();
it->second.end();
}
Edit: I fI understand your comment correctly, you want to get at the type of the iterators of the inner map. If that is so, here's one way:
double_map::mapped_type::iterator inner_iter = it->second.begin();
Off the top of my head, this should work, too:
double_map::value_type::second_type::iterator inner_iter = it->second.begin();

Answer 2

Simple:
typedef map<string, map> inner_map; //Typedef for readability
typedef map<string, inner_map > double_map;
double_map dm;
.. //some code here
for(double_map::iterator it = dm.begin(); it != dm.end(); it++){
//some code here
it->first // string
inner_map &innerMap(it->second); //Reference to the inner map for readability
for(inner_map::iterator it2 = innerMap.begin(); it2 != innerMap.end(); ++it2) {
//Do whatever you like
}
}