Programming in C

244 Chapter 11 Pointers

printf ("i1 = %i, *pointers.p1 = %i\n", i1, *pointers.p1);

printf ("i2 = %i, *pointers.p2 = %i\n", i2, *pointers.p2);

return 0;

}

Program 11.5 Output

i1 = 100, *pointers.p1 = 100

i2 = -97, *pointers.p2 = -97

After the variables have been defined, the assignment statement

pointers.p1 = &i1;

sets the p1member of pointerspointing to the integer variable i1, whereas the next

statement

pointers.p2 = &i2;

sets the p2member pointing to i2. Next,–97is assigned to the variable that is pointed

to by pointers.p2. Because you just set this to point to i2,–97is stored in i2.No

parentheses are needed in this assignment statement because, as mentioned previously, the

structure member operator .has higher precedence than the indirection operator.

Therefore, the pointer is correctly referenced from the structure beforethe indirection

operator is applied. Of course, parentheses could have been used just to play it safe, as at

times it can be difficult to try to remember which of two operators has higher prece-

dence.

The two printfcalls that follow each other in the preceding program verify that the

correct assignments were made.

Figure 11.3 has been provided to help you understand the relationship between the

variables i1,i2,and pointersafter the assignment statements from Program 11.5 have

been executed. As you can see in Figure 11.3, the p1member points to the variable i1,

which contains the value 100 , whereas the p2member points to the variable i2, which

contains the value –97.

Linked Lists

The concepts of pointers to structures and structures containing pointers are very pow-

erful ones in C, for they enable you to create sophisticated data structures, such as linked

lists,doubly linked lists,and trees.

Suppose you define a structure as follows:

struct entry

{

int value;

struct entry *next;

};

Program 11.5 Continued