Practical C Programming, 3rd Edition

Chapter 17. Advanced Pointers

A race that binds

Its body in chains and calls them Liberty,

And calls each fresh link progress.

—Robert Buchanan

One of the more useful and complex features of C is its use of pointers. With pointers, you can create complex data structures like linked lists and trees. Figure 17-1 illustrates some of these data structures.

Figure 17-1. How pointers may be used

Up to now, all of our data structures have been allocated by the compiler as either permanent or temporary variables. With pointers, we can create and allocate dynamic data structures that can grow or shrink as needed. In this chapter, you will learn how to use some of the more common dynamic data structures.

Pointers and Structures

Structures can contain pointers, even a pointer to another instance of the same structure. In the following example:

struct node { 
    struct node *next_ptr;    /* Pointer to the next node */
    int value;                /* Data for this node */
}

the structure node is illustrated in Figure 17-2. This structure contains two fields, one named value, shown here as the section containing the number 2. The other is a pointer to another structure. The field next_ptr is shown as an arrow.

Figure 17-2. Node

The question is: how do we create nodes? We could declare them explicitly:

struct node *node_1; struct node ...