std::pair

With std::pair, we can build pairs of arbitrary types. The class template std::pair needs the header <utility>. std::pair has a default, copy, and move constructor. Pair objects can be swapped: std::swap(pair1, pair2).

Pairs are used in the C++ library. For example, the function std::minmax returns its result as a pair and the associative containers std::map, std::unordered_map, std::multimap, and std::unordered_multimap manage their key/value association in pairs.

To get the elements of a pair p, we can either access them directly or via an index. So, with p.first or std::get<0>(p) we get the first element of the pair, and with p.second or std::get<1>(p), we get the second element of the pair.

Pairs support the comparison operators ==, !=, <, >, <=, and >=. If we want to know if two pairs are identical, first the members pair1.first and pair2.first will be compared, followed by pair1.second and pair2.second. The same strategy holds true for the other comparison operators.

std::make_pair #

C++ has the practical help function std::make_pair to generate pairs, without specifying their types, since the function will automatically deduce their types.

Let’s take a look at an example: