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© 2016 Pearson Education, Ltd. All rights reserved. Chapter 7 C Pointers C How to Program, 8/e, GE © 2016 Pearson Education, Ltd. All rights reserved.

© 2016 Pearson Education, Ltd. All rights reserved. 7.1 Introduction In this chapter, we discuss one of the most powerful features of the C programming language, the pointer. Pointers enable programs to simulate pass-by-reference, to pass functions between functions, and to create and manipulate dynamic data structures, i.e., data structures that can grow and shrink at execution time, such as linked lists, queues, stacks and trees. © 2016 Pearson Education, Ltd. All rights reserved.

7.2 Pointer Variable Definitions and Initialization Pointers are variables whose values are memory addresses. Normally, a variable directly contains a specific value. A pointer, on the other hand, contains an address of a variable that contains a specific value. In this sense, a variable name directly references a value, and a pointer indirectly references a value (Fig. 7.1). Referencing a value through a pointer is called indirection. © 2016 Pearson Education, Ltd. All rights reserved.

© 2016 Pearson Education, Ltd. All rights reserved.

7.2 Pointer Variable Definitions and Initialization (cont.) Declaring Pointers Pointers, like all variables, must be defined before they can be used. The definition int *countPtr; specifies that variable countPtr is of type int * (i.e., a pointer to an integer) and is read (right to left), “countPtr is a pointer to int” or “countPtr points to an object of type int.” © 2016 Pearson Education, Ltd. All rights reserved.

7.2 Pointer Variable Definitions and Initialization (cont.) The * applies only to countPtr in the definition. When * is used in this manner in a definition, it indicates that the variable being defined is a pointer. Pointers can be defined to point to objects of any type. © 2016 Pearson Education, Ltd. All rights reserved.

© 2016 Pearson Education, Ltd. All rights reserved. 7.3 Pointer Operators The &, or address operator, is a unary operator that returns the address of its operand. For example, assuming the definitions int y = 5; int *yPtr; the statement yPtr = &y; assigns the address of the variable y to pointer variable yPtr. Variable yPtr is then said to “point to” y. Figure 7.2 shows a schematic representation of memory after the preceding assignment is executed. © 2016 Pearson Education, Ltd. All rights reserved.

7.3 Pointer Operators (Cont.) The Indirection (*) Operator The * operator, commonly referred to as the indirection operator or dereferencing operator, returns the value of the object to which its operand (i.e., a pointer) points. For example, the statement printf("%d", *yPtr); prints the value of variable y, namely 5. Using * in this manner is called dereferencing a pointer. © 2016 Pearson Education, Ltd. All rights reserved.

7.3 Pointer Operators (Cont.) Demonstrating the & and * Operators Figure 7.4 demonstrates the pointer operators & and *. The printf conversion specifier %p outputs the memory location as a hexadecimal integer on most platforms. © 2016 Pearson Education, Ltd. All rights reserved.

© 2016 Pearson Education, Ltd. All rights reserved.

© 2016 Pearson Education, Ltd. All rights reserved.

© 2016 Pearson Education, Ltd. All rights reserved. Null Pointers It is always a good practice to assign a NULL value to a pointer variable in case you do not have an exact address to be assigned. This is done at the time of variable declaration. A pointer that is assigned NULL is called a null pointer. © 2016 Pearson Education, Ltd. All rights reserved.

© 2016 Pearson Education, Ltd. All rights reserved. Null Pointer example © 2016 Pearson Education, Ltd. All rights reserved.