Sams Teach Yourself C++ in 21 Days

What Is a Pointer?................................................................................................

A pointer is a variable that holds a memory address. That’s it. If you understand this sim-

ple sentence, then you know the core of what there is to know about pointers.

A Bit About Memory......................................................................................

To understand pointers, you must know a little about computer memory. Computer mem-

ory is divided into sequentially numbered memory locations. Each variable is located at a

unique location in memory, known as its address. Figure 8.1 shows a schematic represen-

tation of the storage of an unsigned longinteger variable named theAge.

222 Day 8

The ability to use pointers and manipulate memory at a low level is one of

the factors that makes C++ the language of choice for embedded and real-

time applications.

NOTE

FIGURE8.1

A schematic

representation

of theAge.

theAge

100 101 102 103 104 105 106 107 108 109 110

each location = 1 byte

unsigned long int theAge = 4 bytes = 32 bits

variable name theAge points to 1st byte

the address of theAge is 102

1011

0101

0111

0110

1111

0110

1110

1110

Memory

Getting a Variable’s Memory Address............................................................

Different computers number this memory using different complex schemes. Usually, as a

programmer, you don’t need to know the particular address of any given variable because

the compiler handles the details. If you want this information, though, you can use the

address-of operator (&), which returns the address of an object in memory. Listing 8.1 is

used to illustrate the use of this operator.