12. std::map

• A map is a container that holds unique pairs of keys and values.

• The elements in std::map are always sorted by its keys.

• Each element of the map is formed by the combination of the key value and a mapped value.

• Map iterators access both the key and the mapped value at the same time.

  
      #include <cassert>
      #include <iostream>
      #include <string>
      #include <map>
      using namespace std;
      int main (int argc, char* argv[])
      {
          map< string, string > phone_book;
          phone_book[ "411" ] = "Directory";
          phone_book[ "911" ] = "Emergency";
          phone_book[ "508-678-2811" ] = "BCC";
          if ( phone_book.find( "411" ) != phone_book.end() ) {
              phone_book.insert(
                  make_pair(
                      string( "411" ),
                      string( "Directory" )
                  )
              );
          }
          assert( phone_book.size() == 3 );
          map< string, string >::iterator it;
          for ( it = phone_book.begin(); it != phone_book.end(); ++it ) {
              cout
                  << " " << it->first
                  << " " << it->second
                  << endl
                  ;
          }
          return 0;
      }
      /* Output:
       411 Directory
       508-678-2811 BCC
       911 Emergency
      */