Essential C++

3.7. Using a Map

A map is defined as a pair of values: a key, typically a string that serves as an index and a value associated with that key. A dictionary is one example of a map. A program analyzing the occurrence count of words in a text keeps a map with a string key and an integer value representing an occurrence count:

#include <map> 
#include <string> 
map<string,int> words; 

The simplest way to enter a key/value pair is

words[ "vermeer" ] = 1; 

For our word occurrence program, we can write the following:

string tword; 
while ( cin >> tword ) 
        words[tword]++; 

The expression

words[tword] 

retrieves the value associated with the string tword contains. If tword is not present in the map, it is entered into the map with a default value of ...