What is aggregation in C plus plus?

Answer 1

Aggregation and composition are two sides of the same coin. Both an aggregate and a composite object encapsulate one or more sub-objects. But while a composite object owns its sub-objects, an aggregate object does not. That is, when a composite object is destroyed, its sub-objects are also destroyed. But with an aggregate object, the sub-objects are not destroyed.

Aggregate objects typically use references or pointers to refer to their sub-objects, whereas composite objects typically use member variables or pointers to refer to their objects. In essence, a composite object instantiates its own sub-objects, whereas an aggregate object's sub-objects must be passed to it, typically via the constructor.

In complex models you will often find a combination of composition, aggregation and inheritance, even within the same object.