sorting in std::map where key is a std::string

I have a std::map mymap

Now, if I insert values in the map like:

std::map <string, string> mymap;
mymap["first"] = "hi";
mymap["third"] = "how r you";
mymap["second"] = "hello";

Now I want to iterate over the map and print the value in sorted(keys) manner:

map<string, string>::iterator itr;
for(itr = mymap.begin(); itr != mymap.end(); itr++)
{
   string newline = itr->second;
   cout << newline << endl;
}

Output should be:

hi 
hello 
how r you 

I thought that by default map stores in sorted keys manner but I'm getting the same order in output as I'm giving in input. Do I need to provide my sort function for this or need to do something extra before iterating over the map?