C++ Primer, Fifth Edition

11.2.3. The pair Type

Before we look at the operations on associative containers, we need to know about the library type named pair , which is defined in the utility header.

A pair holds two data members. Like the containers, pair is a template from which we generate specific types. We must supply two type names when we create a pair. The data members of the pair have the corresponding types. There is no requirement that the two types be the same:

pair<string, string> anon;       // holds two stringspair<string, size_t> word_count; // holds a string and an size_tpair<string, vector<int>> line;  // holds string and vector<int>

The default pair constructor value initializes (§ 3.3.1, p. 98) the data members. Thus, anon is a pair of two empty