11.1. Using an Associative Container

Although most programmers are familiar with data structures such as vectors and lists, many have never used an associative data structure. Before we look at the details of how the library supports these types, it will be helpful to start with examples of how we can use these containers.

A map is a collection of key–value pairs. For example, each pair might contain a person’s name as a key and a phone number as its value. We speak of such a data structure as “mapping names to phone numbers.” The map type is often referred to as an associative array. An associative array is like a “normal” array except that its subscripts don’t have to be integers. Values in a map are found by a key rather than by their position. Given a map of names to phone numbers, we’d use a person’s name as a subscript to fetch that person’s phone number.

In contrast, a set is simply a collection of keys. A set is most useful when we simply want to know whether a value is present. For example, a business might define a set named bad_checks to hold the names of individuals who have written bad checks. Before accepting a check, that business would query bad_checks to see whether the customer’s name was present.