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Understanding Pointers 227

8

Pointers, Addresses, and Variables ................................................................

It is important to distinguish between a pointer, the address that the pointer holds, and

the value at the address held by the pointer. This is the source of much of the confusion

about pointers.

Consider the following code fragment:

int theVariable = 5;

int * pPointer = &theVariable ;

theVariableis declared to be an integer variable initialized with the value 5. pPointer

is declared to be a pointer to an integer; it is initialized with the address of theVariable.

pPointeris the pointer. The address that pPointerholds is the address of theVariable.

The value at the address that pPointerholds is 5. Figure 8.2 shows a schematic repre-

sentation of theVariableand pPointer.

// make a pointer to an unsigned short

unsigned short * pAge = 0;

When the pointer is dereferenced, the dereference (or indirection) operator indicates

that the value at the memory location stored in the pointer is to be accessed, rather than

the address itself.

// assign 5 to the value at pAge

*pAge = 5;

Also note that this same character (*) is used as the multiplication operator. The compiler

knows which operator to call based on how you are using it (context).

FIGURE8.2
A schematic
representation
of memory.

5

0000

100 101 102 103 104 105 106 107 108 109

000000000101 00000000000000000000000001100101

101

Address location

theVariable pPointer

In Figure 8.2, the value 5 is stored at address location 101. This is shown in the binary

number

0000 0000 0000 0101