C++ Primer, Fifth Edition

Declaring a Nested Class

The TextQuery class from § 12.3.2 (p. 487) defined a companion class named QueryResult. The QueryResult class is tightly coupled to our TextQuery class. It would make little sense to use QueryResult for any other purpose than to represent the results of a query operation on a TextQuery object. To reflect this tight coupling, we’ll make QueryResult a member of TextQuery.

class TextQuery {public:    class QueryResult; // nested class to be defined later    // other members as in § 12.3.2 (p. 487)};

We need to make only one change to our original TextQuery class—we declare our intention to define QueryResult as a nested class. Because QueryResult is a type member (§ 7.4.1, p. 284), we must declare QueryResult before we use ...