initializing map<string, vector<string> >

Question

I am initializing map<string, vector<string> > as follows:

map <string, vector<string> > dict;

dict["USA"].push_back("NYC");
dict["USA"].push_back("LA");
dict["USA"].push_back("Chicago");
dict["USA"].push_back("Dallas");

dict["India"].push_back("Delhi");
dict["India"].push_back("Bombay");

dict["Australia"].push_back("Melbourne");
dict["Australia"].push_back("Sydney");
dict["Australia"].push_back("Adelaide");

I find this cumbersome. The same thing can be done in tcl as follows which is cleaner:

array set dict {
USA {NYC LA Chicago Dallas}
India {Delhi Bombay}
Australia {Melbourne Sydney Adelaide}
}

Is there a more cleaner way to initialize in C++? My compiler is gcc 3.4.6

Answer 1

Initialization had many limitations in the old C++. Your code is in fact not initializing anything at all; it's just calling a lot of member functions on an already initialized object.

In the current C++ (C++11) you can initialize your map properly:

std::map<std::string, std::vector<std::string>> const dict {
   { "USA", { "NYC", "LA", "Chicago" } },
   { "India", { "Delhi", "Bombay" }    }
};

Answer 2

If you're not opposed to using the Boost.Assign library and you are using C++ older than C++11, you can do it like this:

#include <boost/assign/list_of.hpp>
#include <boost/assign/std/vector.hpp>
#include <map>
#include <string>
#include <vector>

std::map<std::string, vector<std::string> > dict = boost::assign::map_list_of<std::string, std::vector<std::string> >
    ("USA",   boost::assign::list_of<std::string>("NYC")("LA")("Chicago")("Dallas"))
    ("India", boost::assign::list_of<std::string>("Delhi")("Bombay"))
;