cppreference.com > C++ Maps > Map Constructors & Destructors Map Constructors & Destructors Syntax:
      #include <map>
      map();
      map( const map& m );
      map( iterator start, iterator end );
      map( iterator start, iterator end, const key_compare& cmp );
      map( const key_compare& cmp );
      ~map();
The default constructor takes no arguments, creates a new instance of that map, and runs in constant time. The default copy constructor runs in linear time and can be used to create a new map that is a copy of the given map m. You can also create a map that will contain a copy of the elements between start and end, or specify a comparison function cmp. The default destructor is called when the map should be destroyed. For example, the following code creates a map that associates a string with an integer:
      map<const char*, int> ages;
      ages["Homer"] = 38;
      ages["Marge"] = 37;
      ages["Lisa"] = 8;
      ages["Maggie"] = 1;
      ages["Bart"] = 11;

      cout << "Bart is " << ages["Bart"] << " years old" << endl;
Related topics: Map Operators