How can I iterate over an STL map inside an STL map?

Question

I have an STL map definition as follows:

map<string, map<int, string> > info;

I iterate that map using the following code:

for( map<string, map<int, string> >::iterator ii=info.begin(); ii!=info.end(); ++ii){
    for(map<int, string>::iterator j=ii->second.begin(); j!=ii->second.end();++j){
        cout << (*ii).first << " : " << (*j).first << " : "<< (*j).second << endl;
    }
}

Is this the correct way to iterate or is there a better way to do so? The above code works for me, but I'm looking for a more elegant solution.

Answer 1

This is correct, it just lacks a few typedef and readability improvements :

typedef std::map<int, std::string> inner_map;
typedef std::map<std::string, inner_map> outer_map;

for (outer_map::iterator i = outerMap.begin(), iend = outerMap.end(); i != iend; ++i)
{
    inner_map &innerMap = i->second;
    for (inner_map::iterator j = innerMap.begin(), jend = innerMap.end(); j != jend; ++j)
    {
        /* ... */
    }
}

Answer 2

If C++11 is available you may use range for loop:

for(auto &i: info) {
    for(auto &j: i.second) {
        /* */
    }
}

If only C++11 auto is available:

for( auto i=info.begin(); i!=info.end(); ++i) {
   for( auto j=i->second.begin(); j!=i->second.end(); ++j) {
       /* */
   }
}

If you may use BOOST there is BOOST_FOREACH:

typedef std::map<int, std::string> inner_map;
typedef std::map<std::string, inner_map> outer_map;

outer_map outer;

BOOST_FOREACH(outer_map::value_type &outer_value, outer){
    BOOST_FOREACH(inner_map::value_type &inner_value, outer_value->second){
        /* use outer_value and inner_value as std::pair */
    }
}