C++ Primer, Fifth Edition

Using a map

A classic example that relies on associative arrays is a word-counting program:

// count the number of times each word occurs in the inputmap<string, size_t> word_count; // empty map from string to size_tstring word;while (cin >> word)        ++word_count[word];   // fetch and increment the counter for wordfor (const auto &w : word_count) // for each element in the map    // print the results    cout <<  w.first << " occurs " << w.second         << ((w.second > 1) ? " times" : " time") << endl;

This program reads its input and reports how often each word appears.

Like the sequential containers, the associative containers are templates (§ 3.3, p. 96). To define a map, we must specify both the key and value types. In this program, the ...