Defining Map Classes

Every file in every program that uses a map class must include <Map.h>. This header file defines three template classes: Map, Map_pair, and Mapiter. Each of these templates takes two type names as arguments representing the key and value types for a particular map class. Thus we use Map<int,double> as the class name of a map with int keys and double values, Map<String,String> as the class name of a map with String keys and String values, and so on.