std::map

  std::map<char,int> mymap;
  std::map<char, set<string> > mmap;

  mmap['a'].insert("hello");
  mmap['a'].insert("hello1");

  map<char, set<string> >::iterator iter = mmap.begin();
  for(;iter!=mmap.end();++iter){
   cout << iter->first << endl;
   set<string>::iterator itt = iter->second.begin();

   for (;itt != iter->second.end(); ++itt){
      cout << *itt << endl;
   }
  }

  // first insert function version (single parameter):
  mymap.insert ( std::pair<char,int>('a',100) );
  mymap.insert ( std::pair<char,int>('z',200) );

  std::pair<std::map<char,int>::iterator,bool> ret;
  ret = mymap.insert ( std::pair<char,int>('z',500) );
  if (ret.second==false) {
    std::cout << "element 'z' already existed";
    std::cout << " with a value of " << ret.first->second << '\n';
  }