C++ – sorting in std::map where key is a std::string

cstl

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?

Best Answer

The elements in std::map are ordered (by default) by operator< applied to the key.

The code you posted, with minor edits, worked for me as you expected:

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

for (std::map<string, string>::iterator i = mymap.begin(); i != mymap.end(); i++)
{
    cout << i->second << "\n";
}

Prints:

hi
hello
how r you
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