Chapter 07 Composition and Aggregation

In the previous chapter, we talked about encapsulation and information hiding. In this chapter, we continue with object orientation in C and we'll discuss the various relationships that can exist between two classes. Eventually, this will allow us to expand our object model and express the relations between objects as part of the upcoming chapters.

As part of this chapter, we discuss:

• Types of relations that can exist between two objects and their corresponding classes: We will talk about to-have and to-be relationships, but our focus will be on to-have relations in this chapter.
• Composition as our first to-have relation: An example will be given to demonstrate a real composition relationship between two classes. Using the given example, we explore the memory structure which we usually have in case of composition.
• Aggregation as the second to-have relation: It is similar to composition since both of them address a to-have relationship. But they are different. We will give a separate complete example to cover an aggregation case. The difference among aggregation and composition will shine over the memory layout associated with these relationships.

This is the second of the four chapters covering OOP in C. The to-be relationship, which is also called inheritance, will be covered in the next chapter.